Australian Centre for Advanced Photovoltaics Annual Report 2019

Stanford University Acknowledgements

Written and compiled by

Australian Centre for Advanced Photovoltaics

Photos, figures and graphs Courtesy of Centre staff, students and others

Copyright © ACAP May 2020 Please note that the views expressed herein are not necessarily the views of the Australian Government, and the Australian Government does not accept responsibility for any information or advice contained within this report

CRICOS Provider Code: 00098G TABLE OF CONTENTS

01 DIRECTOR'S REPORT 2

02 HIGHLIGHTS 4

03 ORGANISATIONAL STRUCTURE AND RESEARCH OVERVIEW 14

04 AFFILIATED STAFF AND STUDENTS 16

05 RESEARCH REPORTS

Program Package 1 Silicon Solar Cells 22 Program Package 2 Thin-Film, Third Generation and Hybrid Devices 40 Program Package 3 Optics and Characterisation 74 Program Package 4 Manufacturing Issues 91 Program Package 5 Education, Training and Outreach 102

06 COLLABORATIVE ACTIVITIES

Collaboration Grants 107 Fellowships 120

07 FINANCIAL SUMMARY 123

08 PUBLICATIONS 125 01

ACAP DIRECTOR'S REPORT

Solar photovoltaics involves the generation of electricity directly from sunlight when this light shines upon solar cells packaged into a solar module. Silicon is the most common material used to make these photovoltaic cells, similarly to its predominant role in microelectronics, although several other photovoltaic materials are being actively investigated.

The year 2019 was another important one for photovoltaics both in Australia and internationally. Rooftop solar installations in Australia (<100 kW) increased by over 2.1 gigawatts during the year, a 35% increase over 2018, the previous record year, with a similar increase in large commercial systems. Solar’s contribution to electricity generation in the Australian National Electricity Market increased to 7.6% averaged over 2019, likely to exceed 10% average in 2020. Even more importantly, this strong solar contribution has significantly improved the power network’s ability to meet peaks in electricity demand during summer heatwaves, where solar is proving much more reliable than conventional coal generators, whether new or aging.

The other big news from an Australian perspective is that the Australian invented and developed PERC (passivated emitter and rear cell) in 2019 became the cell manufactured in the highest volume internationally.

Also, on this international front, annual global photovoltaic installations increased to a new record of 124 gigawatts installed in 2019, according to market analysts. Photovoltaics also reinforced its position as one of the lowest cost options for electricity production yet developed, with wholesale module selling prices dropping 20% from 2018 averaged over the year. The lowest bid for the long-term supply of solar via a power purchase agreement decreased to US$16.54/MWh in July 2019. Bids in Australia dropped to more closely match this international benchmark with the Clean Energy Regulator reporting that bids of AUD$45/MWh were now not uncommon. By combining with the company’s pumped hydro storage assets, Snowy Hydro claimed it was now able to offer “firm” solar- and wind-generated power on demand at AUD$70/MWh, well below the price from “baseload” coal plant.

Australia has played a major role in achieving these very low costs and is expected to play a key role in future cost reductions through the ongoing activities of the Australian Centre for Advanced Photovoltaics (ACAP), documented in this 2019 Annual Report.

This is the seventh annual ACAP report, with ACAP activities supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). ACAP aims to significantly accelerate photovoltaic development by leveraging development of “over the horizon” photovoltaic technology, providing a pipeline of improved technology for increased performance and ongoing cost reduction. A second aim is to provide high quality training opportunities for the next generation of photovoltaic researchers, with one targeted outcome being to consolidate Australia’s position as the photovoltaic research and educational hub of the Asia-Pacific manufacturing region. In achieving these aims, ACAP works with a wide range of both local and international partners.

ACAP came into being on 1 February 2013 after the signing of a Head Agreement between the University of New South Wales (UNSW) and ARENA. During 2013, related Collaboration Agreements were signed between UNSW and the other ACAP nodes, Australian National University (ANU), University of Melbourne (UoM), Monash University, University of Queensland (UQ) and CSIRO (Materials Science and Engineering, Melbourne) and, additionally, with the ACAP industrial partners, Suntech Research and Development, Australia (SRDA) (partnership now transferred to Wuxi Suntech Power Co., Ltd.), Trina Solar Ltd, BlueScope Steel and BT Imaging, and subsequently with PV Lighthouse, Greatcell Pty Ltd and RayGen Resources Pty Ltd. Our major international partners include the NSF-DOE Engineering Research Center for Quantum Energy and Sustainable Solar Technologies (QESST), based at Arizona State University, and the US National Renewable Energy Laboratory (NREL), as well as the Molecular Foundry, Berkeley, Stanford University, Georgia Institute of Technology, the University of California, Santa Barbara and the the Korean Green Energy Institute.

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This report covers the period from 1 January to 31 December 2019. Over the past seven years, ACAP has moved effectively to establish a high profile within the international research community. This is evidenced by the string of independently confirmed world records for energy conversion efficiency in efforts led by different nodes and for several different technologies since ACAP’s commencement. These include records for rear-junction silicon cells (ANU: 24.4%, 2013), overall sunlight to electricity conversion (UNSW, 40.4%,

2014; 40.6%, 2016), one-sun mini-module (UNSW: 34.5%, 2016), small-area “thin-film” CZTS (Cu2ZnSnS4) cells (UNSW: 9.5%, 2016; 11.0%, 2017), for >1 cm2 CZTS cells (UNSW: 10.0%, 2017), perovskite mini- modules (UNSW: 11.5%, 2016) and for >1 cm2 perovskite cells (UNSW: 18.0%, 2016; 19.6%, 2017; ANU: 21.6%, 2019).

This tradition was continued into 2019 with key developments during the year summarised in the highlight pages immediately following this report. Particularly significant was the continued high level of recognition of ACAP’s impact through major local and international awards. In 2019, the Australian Academy of Technology and Engineering (ATSE) selected Professor Thorsten Trupke and Associate Professor Robert Bardos from the UNSW node for the prestigious Clunies Ross Award. The pair developed and commercialised photoluminescence imaging of silicon cells, ingots and wafers at UNSW, with development of this work supported over recent years by ACAP. This technology has been a gamechanger for the photovoltaics research community and the solar cell and module manufacturing industry, both locally and internationally. This and more detailed results described in the body of this 2019 Annual Report contributed to making 2019, once again, an extremely successful year for ACAP.

I would like to thank ARENA for its ongoing financial support and also for the very effective involvement of ARENA personnel in supporting the ACAP program, both informally and via the ACAP National Steering Committee and the International Advisory Committee. I would additionally like to thank, in particular, all researchers affiliated with ACAP for their contributions to the broad range of progress reported in the following pages.

Finally, I am pleased to be able to report that ACAP has taken another major step towards attaining its significant long-term objectives by achieving its key seventh-year milestones, on time and within budget. We look forward to similar progress in 2020 and in subsequent years.

SCIENTIA PROFESSOR MARTIN GREEN Director, ACAP

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2 019 HIGHLIGHTS

OUTSTANDING CELL EFFICIENCY RESULTS Another outstanding result was obtained on solar-grade silicon, representing a low-cost and low-embodied energy alternative to A team at ANU, led by Professor Andrew Blakers, and comprising the standard silicon feedstock used to make silicon wafers and of Dr Matthew Stocks, Dr Osorio Mayon, Dr Katherine Booker and solar cells. These solar-grade silicon wafers often contain additional Christopher Jones, in collaboration with NREL, has fabricated a defects and impurities that can reduce device efficiency. A team at four-terminal tandem GaAs/silicon solar cell with a measured tandem ANU aims to demonstrate that, with specially developed processing efficiency of 29.8% at AM1.5G. This tandem solar cell with a silicon conditions, such solar-grade wafers can achieve cell efficiencies cell as the bottom cell and a GaAs top cell has demonstrated as high as standard silicon wafers and in 2019 reported the first efficiency above the theoretical limit of a single silicon cell. The solar-grade silicon solar cell with an efficiency of above 22%. The measured GaAs cell efficiency was 24.9% while the measured silicon wafers were n-type Czochralski-grown wafers made with silicon cell efficiency in tandem was 4.9%. The silicon cell is an upgraded metallurgical-grade (UMG) silicon feedstock, provided interdigitated back contact (IBC) device that was fabricated at ANU. by our partner Apollon Solar. The wafers were then fabricated into The GaAs cell was fabricated from epitaxial III-V layers grown at the solar cells at ANU using a specially developed low thermal budget National Renewable Energy Laboratories (NREL) on GaAs wafers. process, featuring a phosphorus-doped poly-silicon full-area rear These GaAs wafers with the grown III-V epitaxial layers were then side contact and the best device had an efficiency of 22.6%, as processed at ANU into thin, semi-transparent GaAs solar cells with a certified by ISFH CalTeC. metal grid on the front and back so that sub-bandgap light can pass through to the bottom silicon cell.

Figure 2.2(a): Certified I-V curve for the record 22.6% efficient solar- grade silicon cell.

Figure 2.1: (a) Schematic of the GaAs/silicon tandem solar cell. (b) Measured current-voltage curves of the GaAs cell and silicon IBC cell in tandem and standalone. Figure 2.2(b): Solar-grade UMG silicon wafer with 2 × 2 cm solar cells fabricated at ANU. The red square indicates the record device.

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Figure 2.3(a): ANU researchers Dr Jun Peng and Associate Professor Tom White with the record perovskite solar cells.

Perovskite solar cells continue to increase in efficiency, but many of the reported breakthroughs are on very small cells of a few millimetres in size. Achieving high efficiencies on larger areas remains a challenge due to the requirement for high film uniformity and low charge transport resistance. Dr Jun Peng and colleagues from the ANU perovskite PV group, working with Sun Yat-sen University in China, have achieved a certified efficiency record of 21.6% on a 1.02 cm2 cell – the highest reported performance from a cell of this size. The record result was achieved with a novel nanopatterned electron transport layer that provides highly effective charge collection and extraction while maintaining excellent passivation, resulting in a remarkable fill factor of 83.4% and an open-circuit voltage of 1.19 V. Furthermore, the use of a dopant- free organic hole transport layer significantly improved the stability of the cells. Encapsulated cells retained more than 90% of their initial efficiency after 1000 hr of damp heat exposure at 85ºC/85% humidity.

Inverted, or p-i-n, perovskite solar cells do not require the high temperature processing associated with standard n-i-p perovskite devices that contain metal oxide extraction layers and often suffer less issues relating to hysteresis. However, in common with standard devices, inverted 3D-perovskite solar cells can suffer from poor stability. The University of Queensland node has fabricated inverted perovskite devices with a hero cell efficiency of 21.1%, an open-circuit voltage (VOC) of 1.12 V, a fill factor of 84% and a -2 short-circuit current (JSC) of 22.4 mAcm . The cells containing a methylammonium lead iodide (MAPI) layer incorporating an additive were essentially hysteresis-free and showed improved stability to humidity relative to the MAPI 3D-perovskite-based devices. Figure 2.3(b): Certification of champion cell.

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Figure 2.4: Current-voltage characteristics (a) and stability (b) to a relative humidity of 80 ± 10% at room temperature of the inverted MAPI devices with and without the additive.

Figure 2.5: (a) The energy level diagram of a PbSe solar cell fabricated by PTLE method with SnO2/PCBM as the electron transport layer and (b) current-voltage charateristics.

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CSIRO achieved efficiency for perovskite cells of 16% and 9.3% for the record 20.1% result for a monolithic tandem GaAsP/Si cell in small area cells (0.1 cm2). These are the highest for air-processed conjunction with Ohio State University and SolAero Technologies drop-cast 2D perovskite solar cells and roll-to-roll (R2R) slot-die Corp., as well as the UNSW 34.5% result for a one-sun minimodule processed cells, respectively. The CSIRO node also achieved involving Si plus GaInP/GaInAs/Ge tandem cells, a concentrator a record for organic solar cells in 2019 – the highest efficiency submodule of 40.6% efficiency, using similar technology, and a reported in the literature from R2R slot-die coated ternary organic PV UNSW 21.7% large-area Si concentrator cell. The recent ANU record cells, 9.75% for an area of 0.1 cm2. result of 21.6% efficiency for a reasonably sized perovskite solar cell mentioned above will appear in this documentation in 2020. PbSe colloidal quantum dots (CQD) are a promising next generation PV material due to their efficient multiple exciton generation (MEG), Two other papers with lead author Andrew Blakers from the ANU strong quantum confinement and excellent bandgap tunability. node titled “Development of the PERC Solar Cell” and “Pathway to However, surface defects arising from oxidation of the QDs have 100% Renewable Electricity” have appeared in the IEEE Journal been the major limitation for their development. The quantum dot of Photovoltaics list of Popular Documents, the most frequently team led by Dr Shujuan Huang at the UNSW node, in collaboration accessed documents for this publication, each month since their with Professor Tom Wu at the UNSW School of Materials Science and publication in May and November 2019, respectively. Engineering, have strategically tackled surface and interface defects Another group of papers was selected as sufficiently timely and and optimised the charge transport layer for PbSe CQD solar cells. interesting to provide the cover illustration for some of the field’s The champion PbSe CQD cell demonstrated an efficiency of 10.4%, most prestigious journals. One paper with lead authors Boyi Chen which was the highest reported efficiency of PbSe CQDs solar cell. and Hieu Nguyen of the ANU node titled “Imaging spatial variations The work has been published in Nano Energy. of optical bandgaps in perovskite solar cells” was selected as the February issue back cover of Advanced Energy Materials (Figure 2.6(a)). Another paper with lead authors Mike Tebyetekerwa and HIGH IMPACT PAPERS Hieu Nguyen again from the ANU node titled “Quantifying quasi- Fermi level splitting and mapping its heterogeneity in atomically Papers published under the ACAP program since ACAP’s formation thin transition metal dichalcogenides” was selected as the June in 2013 have already been recognised as making a large impact at issue frontispiece of Advanced Materials (Figure 2.6(b)). A third the international level. A total of 56 of these have been classified paper by lead author Dongchen Lan of the UNSW node titled as “Highly Cited Papers”, based on their ranking within the top 1% “The potential and design principle for next-generation spectrum- in their field. Nearly half of these, 27 in total, earned the additional splitting photovoltaics: targeting 50% efficiency through built-in distinction of being identified as “Hot Papers”, within the top 0.1% filters and generalization of concept” was ranked as one of the in their field. This is a disproportionately high number relative to the best in its category submitted to the 35th European Photovoltaic total number of ACAP publications and reflects the impact and high Solar Energy Conference, prompting an invitation to publish in the international standing of ACAP research. journal, Progress in Photovoltaics. The paper received the additional Three additional papers were recognised as “Highly Cited Papers” distinction of featuring on the cover of the November issue in which in 2019 with all three additionally being identified as “Hot Papers”, it appeared (Figure 2.6(c)). A fourth paper with lead author Jianghui within the top 0.1% in the field. The first of these was based on Zheng also from the UNSW node, titled “Large-Area 23%-Efficient results generated in ACAP program strand PP2: “Thin-Film, Third Monolithic Perovskite/Homojunction-Silicon Tandem Solar Cell with Generation and Hybrid Devices”. With lead author Chang Yan Enhanced UV Stability Using Down-Shifting Material” was also affiliated with the UNSW node, this Nature Energy paper describes selected to provide the cover illustration for the November issue of the achievement of a landmark efficiency above 10% for a solar cell ACS Energy Letters (Figure 2.6(d)). A fifth piece of work achieving based on the abundant and relatively benign elements Cu, Zn, Sn cover status (Figure 2.6(e)), led by Boer Tan from the Monash node, and S, forming the compound semiconductor Cu2ZnSnS4 (CZTS). was entitled “P-Dopant: LiTFSI-Free Spiro-OMeTADBased Perovskite The other two “Highly Cited” and “Hot Papers” arose from Solar Cells with Power Conversion Efficiencies Exceeding 19%”. The collaboration between ACAP partners, UNSW and Colorado-based team employed the oxidized form of spiro-OMeTAD as a dopant NREL, documenting recent efficiency improvements in photovoltaics to improve the efficiency of the spiro-OMeTAD-based lithium-free across a range of technologies. Included in these two papers are perovskite solar cells from 10% to 19.3% while simultaneously the UNSW record 10% and 11% CZTS cell results, the record 25% enhancing the device stability. UNSW PERC (passivated emitter and rear cell) silicon cell result,

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Figure 2.6: Journal covers where ACAP work was featured in 2019: (a) Advanced Energy Materials (14 February). (b) Advanced Materials. (c) Progress in Photovoltaics. (d) ACS Energy Letters. (e) Advanced Energy Materials (28 August).

The Monash solar cell group invented two processing techniques AWARDS AND PRIZES for making pinhole free perovskite films and high efficiency solar cells in the early stages of perovskite development: the antisolvent The Australian Academy of Technology and Engineering (ATSE) method, reported by M. Xiao et al. with the title, “A fast deposition- selected UNSW’s Professor Thorsten Trupke and Associate Professor crystallization procedure for highly efficient lead iodide perovskite Robert Bardos for their prestigious Clunies Ross Awards in 2019. thin film solar cells” inAngew. Chem. Int. Ed. 53, 9898–9903 The pair developed and commercialised photoluminescence (2014), and a gas blowing method, published as “Gas-assisted imaging of silicon cells, ingots and wafers at UNSW, a game-changer preparation of lead iodide perovskite films consisting of a monolayer milestone for the photovoltaics research community and the solar of single crystalline grains for high efficiency planar solar cells” cell/module manufacturing industry, both in Australia and globally. in Nano Energy 10, 10–18 (2014). Both were highlighted in a Photoluminescence imaging technology from the company founded 2018 commentary article published in Joule (Babayigit et al. “Gas by the pair, BT imaging Pty Ltd, has been adopted by all Tier 1 Quenching for Perovskite Thin Film Deposition”, Joule (2018), https:// manufacturers (and virtually all leading manufacturers of solar panels) doi.org/10.1016/ j.joule.2018.06.009), specifically highlighting the globally, including the world’s five largest module manufacturers. It significance of the group’s gas blowing technique, while mentioning lifts the quality of product, lowers cost and makes proliferation of the team’s antisolvent method as well. renewable energy easier.

ARENA BOARD’S VISIT TO THE SOLAR INDUSTRIAL RESEARCH FACILITY

ARENA Board visited the Solar Industrial Research Facility in September, hearing more about the strong industry links and support for advanced technologies and the earlier stage research occurring in parallel in this world-class facility.

Figure 2.8: The Minister for Industry, Science and Technology, Karen Andrews, congratulated Thorsten Trupke (left) and Robert Bardos, winners of the 2019 Clunies Ross Innovation Award, presented by Professor Mark Hoffman (right).

Xiaojing Hao, a Scientia Fellow in the UNSW node, has been recognised by Engineers Australia for her research in the field of kesterite photovoltaics as one of Australia’s most innovative engineers. Figure 2.7: UNSW’s Angus Keenan, Operations Manager, Australia’s Most Innovative Engineers is an annual program run by explains the Solar Industrial Research Facility to ARENA create magazine, the publication of Engineers Australia. It seeks Board members in September. to recognise engineering innovation and raise the profile of the

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profession by showcasing the important role engineers play in solving Marco Ernst (ANU) led the team (with I. Haedrich, Y. Li, P.-C. Hsiao, some of the world’s biggest challenges. Hao and her team have been A. Lennon) awarded a Best Paper Award at the closing ceremony building solar cells made of kesterite materials, which are cheaper of the 29th International Photovoltaic Science and Engineering and more environmentally friendly than other thin-film photovoltaic Conference (PVSEC29) in Xi’An, China for their work on, “Impact of market competitors and provide renewable energy solutions without (Multi) Busbar Design in Full and Halved Cell Modules on the Cell-to- posing environmental concerns. Between 2016 and 2018, she and her Module-Yield under Realistic Conditions”. team set four new world records for kesterite solar cell efficiency. In March 2017, the team increased that efficiency to 11% , the first time that the 10% efficiency threshold was broken for this type of solar cell. These breakthroughs represent a major advance in the development of solar cells that are flexible, low-cost and non-toxic. She hopes to improve the efficiency of kesterite photovoltaic cells to 20% in the next five years.

Figure 2.11: Marco Ernst (ANU) with his Best Paper Award plaque from PVSEC29. The research of UNSW PhD student, Rong Deng (with co-authors M. Monteiro Lunardi, Y.-C. Chang, J. Jiang, S. Wang, J. Ji, Figure 2.9: Xiaojing Hao shows the award-winning kesterite cells. C.M. Chong), was recognised for the best Visual Presentation in her theme at the conference’s closing session for the 36th A UNSW and BT Imaging team comprising Oliver Kunz, Zi Ouyang European PVSEC 2019, in Marseille, France on 13 September and Thorsten Trupke are taking their outdoor photoluminescence 2019 for “A Simple Method for Rapid Recycling of Silver from (PL) project, Outdoor Photoluminescence Imaging for Residential Decommissioned Silicon Photovoltaics”. and Commercial Applications, to the next stage with the help of ARENA and CSIRO’s ON Prime program. ON Prime is a national program open to researchers from Australian universities and public research organisations. ON Prime’s hands-on learning program teaches skills to take projects and careers forward and to attract the resources they need to create impact. Their outdoor PL technique can identify all the invisible defects, arising from production, transport, installation or degradation that are relevant for power production, without having to touch any electrical wiring, closing the feedback loop from manufacturing to deployment. They hope to find users among solar farm developers and investors that want to de- risk their installations and in research institutes who want to perform long-term studies of solar PV installations.

Figure 2.12: Florence Lambert, Director of CEA Liten, France, presented the award to UNSW’s Rong Deng. Researchers from ANU and UNSW were each lead authors on awarded Best Posters in Areas 5 and 4, respectively, at the 46th IEEE Photovoltaics Specialists Conference, held in Chicago in June 2019. Qian Jiadong presented “Unravelling Optical and Electrical Degradation of Perovskite Solar Cells and Impact on Perovskite/ Silicon Tandem Modules” on behalf of an ANU team including Marco Ernst, Nandi Wu and Andrew Blakers. Their work generated an economic and experimental analysis of perovskite degradation and its impacts on tandem 2T and 4T perovskite-silicon tandems.

Figure 2.10: Oliver Kunz accepts the ON Prime award on behalf of the UNSW team that also includes Zi Ouyang and Thorsten Trupke 9 02

Michelle Vaqueiro-Contreras (UNSW) was lead author, with Vladimir GLOBAL PHOTOVOLTAIC CONFERENCE 2019 Markevich, José Coutinho, Paulo Santos, Iain Crowe, Matthew Two Best Oral Presentation Awards were given to UNSW presenters Halsall, Ian Hawkins, Stanislau Lastovskii, Leonid Murin and Anthony at the Global Photovoltaic Conference 2019, held at the Kimdaejung Peaker, on “Direct Observation of the Boron-Oxygen Complex Convention Center, Gwangju, South Korea in March. Moonyong Kim Precursor Responsible for Light Induced Degradation in Silicon with a team comprising Shaoyang Liu, Daniel Chen, Malcolm Abbott Photovoltaic Cells”. As stated in the official Conference Highlights and Brett Hallam, were recognised for their paper, “Application to regarding this work: “Using low temperature spectroscopy, a level In-Situ Accelerated Light Induced Degradation Testing on Crystalline with an apparent activation energy of 42 meV has been found Silicon”. that was previously impossible to detect using DLTS. This level is suggested to be responsible for the light induced degradation Rong Deng was the recipient of another award at this conference, promoting trap assisted Auger recombination.” for her presentation on behalf of the team with Nathan Chang, Zi Ouyang and Chee Mun Chong, about their work on, “Comparative Economic Assessment of Silicon Photovoltaic Module Recycling”.

Figure 2.13: Jiadong Qian from ANU (a) and Michelle Vaqueiro- Figure 2.14: Moonyong Kim (a) and Rong Deng (b) received Best Oral Contreras (b) from UNSW won Best Poster Awards at the 46th IEEE Presentation Awards at the Global Photovoltaic Conference 2019, in Photovoltaics Specialists Conference, Chicago, June 2019. Gwangju, South Korea.

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Figure 2.15: Régine Chantler (a) and Boer Tan (b) show their Best Poster Awards at conclusion of the 2019 ACAP Conference.

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Figure 2.17: Michelle Vaqueiro-Contreras accepts her award from Figure 2.16: Boer Tan and Dr Sonia Ruiz Raga accepting their poster Professor Dame Nancy Rothwell. prizes.

UNSW SIGNS MOU WITH CENTER NATIONAL DE LA NSW NATURE CONSERVATION COUNCIL’S RECHERCHE SCIENTIFIQUE (CNRS) DUNPHY AWARD France’s President Emmanuel Macron and Australia’s Prime Minister Oliver Kunz, a photovoltaics researcher in the UNSW node, is Malcolm Turnbull, witnessed the signing in Sydney in May 2018 by also a co-founder of the UNSW Climate Change Network. He was Vice-Chancellor and President Ian Jacobs and Dr Patrick Patrick recently awarded the NSW Nature Conservation Council’s Dunphy Nédellec, Director of the European Research and International Award, which is “given to an individual who has demonstrated Cooperation Office of the Center National de la Recherche outstanding commitment to the conservation of the NSW Scientifique (CNRS), of a Memorandum of Understanding with Environment, and courageously challenged Government and non- France’s largest government research organisation to progress joint Government decision-makers”. research in sustainable energy.

Boer Tan (Monash node), for her work on “LiTFSI-Free Spiro- OMeTAD-Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19%”, and Sonia Ruiz Raga for her work on “Origin of reversible performance increase in Perovskite Solar cells” were awarded the student and postdoctoral poster prizes in the Excitonic Systems for Solar Energy Conversion section at the 2019 ACEx meeting at the Melbourne Arts Centre in December.

Michelle Vaqueiro-Contreras, now at the UNSW node, received the distinguished achievement medal, one of the University of Manchester’s Postgraduate Research Excellence awards from the Vice-Chancellor Professor Dame Nancy Rothwell on 1 July 2019 (Figure 2.17). This award recognises an outstanding research student who has excelled in some significant manner and is awarded each year to a single student of each of the three university faculties.

At ANU, the ACAP node’s Hieu Nguyen received in 2019 the College of Engineering and Computer Science Dean’s Award for Excellence in Supervision and was also nominated for the Vice-Chancellor’s Award for Excellence in Supervision.

Figure 2.18: Oliver Kunz took out the NSW Nature Conservation Council’s Dunphy Award.

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Figure 2.19: Finalists for the UNSW Faculty of Engineering heat, won by Utkarshaa Varshney, fourth from left in the middle row.

LINE HONOURS FOR SUNSWIFT NEW PARTNERSHIPS FOR ACAP UNSW Sydney’s solar car team Sunswift took the line honours and Tindo Solar, Australia’s only one-sun PV module manufacturer, joined second place in the Cruiser Class of the 2019 Bridgestone World ACAP as a new collaborating industry participant in 2019. Solar Challenge (BWSC) in Adelaide in October. Sunswift’s car, Green Energy Institute (GEI), specialising in research on new Violet, crossed the finish line first in the 3,000 km race down the and renewable energy, is based in South Jeolla Province, at the centre of Australia. Eleven from 14 starters in the Cruiser Class did southwestern tip of the Korean Peninsula. This area has good not finish the race. resources of sunlight, wind, water and soil required for renewable energy production. GEI, which undertakes R&D on photovoltaic, wind, tidal and geothermal power generation as well as materials for electric cars, has joined ACAP as a new collaborating international research institution in 2019.

Figure 2.20: The UNSW Sunswift student team for the 2019 World Solar Challenge.

Fig 2.21: ACAP welcomed the Green Energy Institute as a new collaborating international research institution.

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ORGANISATIONAL STRUCTURE AND RESEARCH OVERVIEW

The Australian Centre for Advanced Photovoltaics (ACAP) was established to As well as these collaborative activities, the major develop the next generations of photovoltaic technology and to provide a pipeline of partners, ACAP, QESST and NREL, conduct their own opportunities for performance increase and cost reduction. The Australian partners largely independent research programs meeting in ACAP are the University of New South Wales (UNSW), the Australian National the specific research and training objectives of their University (ANU), the University of Melbourne (UoM), Monash University, the University major supporters and sponsors. In the case of ACAP, of Queensland (UQ) and CSIRO, plus our industrial partners Wuxi Suntech Power research is milestone driven with annual milestone Co. Ltd, Trina Solar Ltd, BlueScope Steel, BT Imaging, PV Lighthouse, Greatcell Solar targets established through each year’s Action Plan, and RayGen Resources Pty Ltd. ACAP links with international partners, specifically in accordance with the Funding Agreement with the National Science Foundation and Department of Energy–supported Engineering ARENA. Research Center for Quantum Energy and Sustainable Solar Technologies (QESST), ACAP’s National Steering Committee comprises a based at Arizona State University, the National Renewable Energy Laboratory (NREL), representative of ARENA, industrial and academic Lawrence Berkeley National Laboratory (LBNL), Stanford University, Georgia Institute representatives and the node directors, of Technology and the University of California, Santa Barbara. ACAP began its life as the Australian side of an Australia–US partnership but formal collaboration began to ACAP is managed by a Management Committee, expand globally in 2019 and beyond, with the addition of the Green Energy Institute which consists of the node leaders or delegates from (GEI), based in South Korea, to the set of research partners. These national and each of the nodes. The Management Committee international research collaborations provide a pathway for highly visible, structured takes advice from the National Steering Committee, photovoltaic research collaboration between Australian and international researchers, with an independent Charter, but with membership research institutes and agencies, with significant joint programs based on the including representatives from each node and the clear synergies between the participating bodies. Sandia National Laboratories and Director and manager of ACAP. University of California, Santa Barbara finished their partnerships in 2019.

ACAP is driving significant acceleration of photovoltaic development beyond that achievable by institutes acting individually, with significant leveraging of past and current funding. This program is supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). The Australian Government, through ARENA, is supporting Australian research and development in solar photovoltaic and solar thermal technologies to help solar power become cost competitive with other energy sources. (The views expressed herein are not necessarily the views of the Australian Government, and the Australian Government does not accept responsibility for any information or advice contained within this report.)

The organisational chart is shown in Figure 3.1. The international activities are coordinated by an International Advisory Committee with membership drawn from ARENA, researcher representatives from several countries, a representative nominated by major industry partners, and the Director of ACAP. The International Advisory Committee is also charged with identifying, developing and monitoring progress in areas where synergies exist between Australian and international nodes that can be exploited and to monitor joint collaborative

projects with existing and new partners. Some examples of current international activities, many arising from competitive ACAP Collaboration Grants, are reported in Section 6 of this report.

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Australia-USAustr alianInstitute Centr fore Adv foranced Photovoltaics (AUSIAPV) Advanced Photovoltaics (ACAP)

International Advisory Committee QESST NREL Georgia Tech Stanford

GEI LBNL National Steering Management Committee Committee UCSB

PP2: Organic and Earth- Abundant Inorganic Thin-Film Cells PP4: Manufacturing Issues

UNSW Monash CSIRO UNSW CSIRO

Melb UQ

PP1: Silicon Cells PP3: Optics/Characterisation PP5: Education, Training and Outreach

UNSW ANU UQ UNSW ANU UNSW Melb UQ

ANU Monash CSIRO

Figure 3.1: Organisational chart. Collaborating industry participants are involved in collaborative research as well as in the Advisory and Steering Committees.

As indicated in Figure 3.1, the ACAP program is organised under five Program PP4, ”Manufacturing Issues”, aims at delivery Packages (PP1–PP5), each supported by multiple nodes. PP1 deals with silicon of a substantiated methodology for assessing wafer–based cells, by far the dominant photovoltaic technology commercially, and manufacturing costs of the different technologies likely to remain so for at least the next 10 years. Here the challenge is to continue under investigation by ACAP. The overall cost target to reduce manufacturing costs and degradation, while maintaining or preferably, is to undercut the US Government’s SunShot targets, improving, energy conversion efficiency. PP1 focuses on three main areas: cells for one or more of the technologies, in at least one made from solar-grade silicon, rear contact cells and silicon-based tandem cells, both major SunShot targeted application, as deduced by a monolithic and mechanically stacked. substantiated costing methodology. Environmental costs are also considered by ACAP, through PP2 involves collaborative research into a range of organic, organic-inorganic hybrid application of the rigorous life cycle assessment cells and “Earth-abundant” thin-film materials, including Si and Cu ZnSnS (CZTS), 2 4 regime and end-of-life options. as well as more futuristic “third generation” approaches. Recently, the relatively new photovoltaic material, the organic-inorganic perovskites, has been included within the Additional targets for PP1–PP4 may be established scope of this program package and additional funding has been provided from 2016 through the Action Plan for each year. to expand and intensify the research on these materials and devices. The program PP5 involves education, training and outreach. ACAP now has the overall goal of demonstrating high efficiencies for these new thin-film monitors the number of researchers in different cells of above 1 cm2 area and of demonstrating the feasibility of costs below the US categories benefiting from the support it provides, as Department of Energy SunShot targets for cost reductions. well as outreach activities, including public lectures PP3, ”Optics and Characterisation”, targets experimental demonstration that on material relevant to ACAP activities, newspaper theoretical conversion limits can be increased by the use of structures that have a and magazine articles, responses to governmental high local density of optical states, with particular emphasis on thin-film organic and calls for submissions, visits by policy developers and inorganic solar cells. their advisors, information papers and presentations to both policy developers and their advisors.

15 04

AFFILIATED STAFF AND STUDENTS

Chan, Catherine Song, Ning UNIVERSITY OF NEW SOUTH WALES Chang, Nathan Sugianto, Adeline

Green, Martin (Centre Director) Chung, Daniel Sun, Kaiwen

Corkish, Richard (Centre Chief Operating Chen, Ran Telford, Andrew Officer) Ciesla, Alison Teymouri, Arastoo

Academic Staff and Senior Researchers Cui, Hongtao Wang, Li

Egan, Renate (Node Leader) Cui, Xin Western, Ned

Abbott, Malcolm Dias, Pablo Ribeiro Wright, Matthew

Bilbao, Jose Evans, Rhett Yan, Chang

Bremner, Stephen Hallam, Brett Yang, Yang

Chong, Chee Mun Hamer, Phillip Yun, Jae Sung

Conibeer, Gavin Hsiao, Pei-Chieh Zhang, Meng

Edwards, Matthew Huang, Jialiang PhD Students Ekins-Daukes, Nicholas Jiang, Yajie Abdullah, Taufiq Mohammad Hameiri, Ziv Juhl, Matthias Baldacchino, Alexander James Hao, Xiaojing Kampwerth, Henner (from June 2019)

Ho-Baillie, Anita Lan, Dongchen Bhoopathy, Raghavi

Hoex, Bram Lau, Cho Fai Jonathan Bing, Jueming

Huang, Shujuan Lui, Xu Yalun, Cai

Keevers, Mark Liu, Ziheng Chan, Kai-Yuen Kevin

Lennon, Alison Ma, Fajun Chen, Daniel

Mehrvarz, Hamid Mahboubi Soufiani, Arman Chen, Zihan (until March 2019)

Perez-Wurfl, Ivan Monteiro Lunardi, Marina Khoo, Kean Thong (from February 2019) Rougieux, Fiacre Cui, Xin Mai, Ly Shrestha, Santosh Dehghani Madvar, Mohammad Paduthol, Appu (from September 2019) Trupke, Thorsten Patterson, Robert Deng, Rong Uddin, Ashraf Payne, David (Adjunct) Deng, Shuo (until March 2019) Young, Trevor Pillai, Supriya Duan, Leiping ECR and Postdoctoral Fellows Pollard, Michael

16 ACAP ANNUAL REPORT 2019

Dumbrell, Robert (until May 2019) Poduval, Geedhika Kallidil Zhang, Xueyun

Fung, Tsun Hang Radhwi, Haytham Zhang, Yian

Gao, Yijun Samadi, Aref Zhang, Yu

Granados Caro, Laura Sang, Borong Zhang, Yuanfang

Hall, Charles Aram Mandela Sen, Chandany Zhang, Yuchao (from June 2019)

Hanif, Muhammad (from June 2019) Shen, Xiaowei Zhao, Jing

Haque, Faiazul Sharma, Abhinav Sanjay Zhao, Xin (from September 2019) He, Mingrui Zhou, Fangzhou Sun, Heng Hu, Yicong (until May 2019) Zhu, Yan Sun, Zhenyu Jafari, Saman Masters Students Tabari-Saadi, Yasaman Jiang, Yu (until March 2019) Abidin, Chairil Tang, Shi Kaleem, Akasha (from June 2019) Askarisereshgi, Samaneh Thapa, Bharat Kim, Moonyong Bei, Wan (since September 2019) Vargas Castrillon, Carlos (until May 2019) Kim, Taehyun Lambert, Daniel Bolin, Zheng (since September 2019) Varshney, Utkarshaa Lambert, Daniel (until March 2019) Chen, Long Vicari Stefani, Bruno Lau, Derwin Deng, Shuo (from June 2019) Wang, Zhimeng Le, Anh Huy Tuan Dong, Yaocheng Xu, Cheng (until January 2019) Lehmann, Alex Geoffrey Han, Jingweir Ye, Qilin Li, Yong He, Yuxuan Yi, Chuqi Mengdi, Liu Kaushik, Muthusamy (since September 2019) Yi, Haimang Liu, Shaoyang Kim, Kyung Hun Yuan, Xiaojie (from June 2019) Lunardi, Marina Monteiro (until January 2019) Kumar, Suraj Sudeep Qian, Chen Madumelu, Chukwuka Uzochukwu Lei, Zhao (since September 2019) (from June 2019) Teh, Zhi Li Liao, Anqi (from June 2019) Mungra, Mreedula Wang, Shaozhou Liao, Chwen Haw Mussakhanuly, Nursultan Zhou, Zhuangyi (from September 2019) Li-Chun, Cheng (since September 2019) Zafirovska, Iskra Nie, Shuai Lingyun, Xu (since September 2019) Zhang, Meng Fei (from September 2019) Phua, Benjamin Ming, Sheng (since September 2019) Zhang, Tian (until May 2019)

17 04

Sandhu, Udaibir Singh Podgorski, Adam Marcus (until August 2019) Shen, Heping

Shi, Ruoxuan (since September 2019) Shamali, Ramsey Sieu Phang, Pheng

Song, Yupeng Sun,Wenxin (from September 2019) Sio, Hang Cheong

Wang, Yanlin (since September 2019) Tan, Vincent Stuckelberger, Josua

Wang, Yihao Thompson, Dion Sun, Chang

Waranya, Thummachart Xiang, Zeyang (from June 2019) Tong, Jingnan (since September 2019) Yang, Yilin Walter, Daniel Wu, Xinyuan Zhao, Zihao Wang, Haiqian Wu, Yutong Zhou, Yize Yan, Di Xian, Jiexin Yang, Wenjie Zhai, Weixin AUSTRALIAN NATIONAL UNIVERSITY PhD Students Zhang, Mengqi Basnet, Robin Zhou, Xuan Academic Staff and Senior Researchers Cheng, Cheng Zhu, Peisong Blakers, Andrew (Node Leader) Ding, Zetao Catchpole, Kylie Honours Students Dolati Ilkhechi, Noushin Chern Fong, Kean Alkiyumi, Lamees Fu, Xiao Macdonald, Daniel Chan, Lawrence Goodarzi, Mohsen Stocks, Matthew Chen, Guo Haedrich, Ingrid Wan, Yimao Collins, Miles Kang, Di Weber, Klaus Fei, Fan (until August 2019) Lu, Bin White, Tom Fowler, Christopher (from June 2019) Peng, Jun Fu, Jiawen ECR and Postdoctoral Fellows Qian, Harry Fu, Jiawen (from September 2019) Black, Lachlan Truong, Thien Gao, Ziqin (from September 2019) Booker, Katherine Tebyeteker, Mike Gu, Alexander Ga-Hing (until August 2019) Duong, The Wu, Huiting He, Wenhui Ernst, Marco Wu, Nandi Hourani, An Liz He Jian Wu, Yiliang Hu, Heng (from June 2019) Jacobs, Daniel

Huang, Chris (from September 2019) Karuturi, Siva CSIRO MANUFACTURING

Huang, Libin Liu, Anyao Academic Staff and Senior Researchers Legras, Peter (from September 2019) Lu, Bin Scholes, Fiona (Node Leader) Lim, Jihoo Mayon, Yahuitl Osorio Wilson, Gerry (Node Leader) Liu, Chen (from September 2019) Mahmud, Md Arafat Chantler, Régine Liu, Xiaozhou Mulmudi, Hemant Kumar Chesman, Anthony Nathapakti, Dhammasorn (from September Narangari, Parvathala Dunn, Christopher 2019) Nguyen, Hieu Faulks, Andrew Pan, Yida (from September 2019) Peng, Jun Gao, Mei

18 ACAP ANNUAL REPORT 2019

Ramamurthy, Jyothi Saxena, Sonam UNIVERSITY OF QUEENSLAND Scully, Andrew Zhang, Bolong Academic Staff and Senior Researchers Vak, Doojin Masters Students Burn, Paul (Node Leader) ECR and Postdoctoral Fellows Lin, Jianchao Shaw, Paul (Node Leader) Weerasinghe, Hasitha Nalenan, Marissa ECR and Postdoctoral Fellows Zuo, Chuantian Ruoxuan Shi Hutchinson, Kinitra (from 5 August 2019 Yanlin Wang PhD Students to 24 December 2019)

Ellis, Ryan Jiang, Wei MONASH UNIVERSITY Hu, Yinghong (Hongi) Jin, Hui Academic Staff and Senior Researchers Jang, Hyungsu Lee, Thomas (from 1 January 2019 Bach, Udo (Node Leader) to 21 December 2019) Kim, Juengeun (visiting) Simonov, Alexandr Rakstys, Kasparas (until 30 August 2019) Mathiazhagan, Gayathri Raynor, Aaron Peng, Xiaojin ECR and Postdoctoral Fellows Stephen, Meera (until 20 December 2019) Tan, Boer (co-supervised with Monash) Fürer, Sebastian Wang, Xiao (from June 2019) Huang, Wenchao UNIVERSITY OF MELBOURNE Kashif, Kalim PhD Students

Academic Staff and Senior Researchers Liu, Chang McGregor, Sarah (PhD awarded July, 2019)

Ghiggino, Ken (Node Leader) Lu, Jian Feng Zhang, Shanshan (PhD awarded March, 2020)

Goerigk, Lars McMeekin, David Li, Hui (from October 2019)

Holmes, Andrew Ruiz Raga, Sonia QESST Jones, David PhD Students Augusto, André Smith, Trevor Bacal, Dorota Bertoni, Mariana Wong, Wallace Deng, Siqi Bowden, Stuart ECR and Postdoctoral Fellows Eskandarian, Masoomeh Holman, Zachary Mitchell, Valerie Guo, Qianying Honsberg, Christiana Subbiah, Jegadesian Mao, Wenxin

Taheri, Abuzar (from 20 October 2018) Milhuisen, Rebecca NATIONAL RENEWABLE ENERGY LABORATORY Zhao, Pengjun (from 1 March 2018) ) Pai, Narendra Al-Jassim, Mowafak Tan, Boer (co-supervised with CSIRO) PhD Students Emery, Keith Zhao, Boya Ahluwalia, Gagandeep Heath, Garvin Gao, Can Johnston, Steve Hong, Quentin Levi, Dean Lee, Calvin Moriarty, Tom Masoomi‐Godarzi, Saghar Ottoson, Larry Novakovic, Sacha Reid, Obadiah Saker-Neto, Nicolau

19 04

Rumbles, Garry BLUESCOPE STEEL Stradins, Paul Zappacosta, Dion Wilson, Gregory

Woodhouse, Michael PV LIGHTHOUSE

Abbott, Malcolm MOLECULAR FOUNDRY, McIntosh, Keith LAWRENCE BERKELEY NATIONAL LABORATORIES Sudbury, Ben

Javey, Ali

Neaton, Jeffrey RAYGEN

Lasich, John STANFORD UNIVERSITY Thomas, Ian Dauskardt, Reinhold Modra, Danny Rolston, Nick GREEN ENERGY INSTITUTE GEORGIA TECHNOLOGY Park, Jongsung INSTITUTE

Marder, Seth TINDO SOLAR Graham, Samuel Sporne, Robert

WUXI SUNTECH POWER CO. LTD

Chen, Liping

Chen, Rulong

Zhou, Min

TRINA SOLAR

Feng, Zhiqiang

Verlinden, Pierre

Yang, Yang

Zhang, Xueling

BT IMAGING

Bardos, Robert

Trupke, Thorsten

20 ACAP ANNUAL REPORT 2019

21 05 – PP1

PP1 SILICON SOLAR CELLS

OVERVIEW PP1.1 SOLAR-GRADE SILICON

Crystalline silicon is the most widely used semiconductor material in Solar-grade silicon offers a low-cost and low-embodied energy photovoltaics (PV), making up 95% of commercially available products alternative to the standard electronic-grade silicon feedstocks used in the solar PV market. This share is predicted to continue into the next in the PV industry today. Research into fabricating high efficiency decade due to silicon’s abundance, moderate cost, low toxicity, high solar cells on low-cost upgraded metallurgical-grade (UMG) silicon and stable cell efficiency, robustness, bankability, highly advanced and wafers is being carried out through a collaboration between ANU (cell widespread understanding of silicon and extensive and sophisticated fabrication), UNSW (defect hydrogenation) and Apollon Solar (solar- supply chains. grade silicon supplier). The aim is to demonstrate that the use of less pure solar-grade silicon does not reduce cell efficiency. A key outcome The ongoing goal for the industry is to continue to reduce the cost per in 2019 was a world-first demonstration of solar cell efficiencies above watt of power produced from silicon solar cells, through lowering the 22.5% for devices made with UMG wafers. A low thermal budget cost of silicon solar cells, improving the power conversion efficiency of fabrication sequence designed to maintain wafer quality has been the cells or both. Program Package 1 (PP1) supports the fundamental developed at ANU, which is capable of efficiencies above 24% on investigation and demonstration of novel technology leading towards electronic-grade wafers. Using this process, combined with UNSW’s improved cost-effectiveness of silicon-based solar cells. Specifically, expertise on defect hydrogenation, we aim to demonstrate efficiencies research activities are carried out in the areas of low-cost solar-grade above 23% on UMG wafers in the near term. silicon, rear contact high efficiency solar cells, passivated contacts and silicon-tandem structures. The UNSW-led hydrogenation projects include the ongoing development of defect engineering and advanced hydrogenation processes for high efficiency silicon solar cell technologies made from low-cost Si materials. Complementary to the work being conducted on compensated n-type UMG silicon at ANU, a record VOC of >690 mV was demonstrated on a silicon heterojunction (SHJ) cell made from p-type UMG silicon from the edge of a silicon cast. In addition, it was demonstrated for the first time that SHJ cells can be susceptible to light and elevated temperature induced degradation (LeTID) if they undergo a bulk hydrogenation process. Understanding and eliminating LeTID in silicon has been an ongoing focus of the work at UNSW. In 2019, work continued studying the kinetic behaviour of the LeTID defect under a variety of conditions: in n-type silicon, in p-type silicon, under illumination and in the dark. A key finding was that the LeTID defect kinetics could be explained by the migration of and interactions between charged hydrogen species and dopant atoms within the diffused layers and the silicon bulk. This understanding of hydrogen’s involvement in LeTID helps with the development of LeTID suppression and mitigation strategies which continue to be explored.

22 ACAP ANNUAL REPORT 2019

PP1.2A REAR CONTACT SILICON CELLS PP1.3 SILICON TANDEM CELLS

Rear contact solar cells are the epitome of single junction silicon solar One approach to convert more of the sun’s spectrum into electricity cell design. Formation of metal contacts of both polarities on the rear is to use multiple solar cells which absorb different wavelengths of eliminates the trade-off between front optics to electrical requirements light. PP1.3 aims to successfully mate the commercially dominant and allows maximum photon collection from the absence of front optical PV technology based on silicon solar cells with other promising PV obstructions. The key highlight in this component so far is achieving materials, including the III-V semiconductors, the chalcogenides 25.0% independently confirmed IBC cell efficiency. Further investigation and perovskite technologies. Work continued in 2019 to develop into the effect of metal contact formation on the fill-factor is reported. monolithic silicon and mechanically stacked tandem cells. In the monolithic approach, a wide bandgap top cell (or cells) is grown onto a silicon cell with the two (or more) cells operating in series. PP1.2B PASSIVATED CONTACTS In the mechanically stacked approach, a high bandgap top cell is independently operated in conjunction with a standard silicon bottom One of the primary loss mechanisms in modern industrial silicon cell. Several different approaches to forming these structures are solar cells is recombination at the metal/silicon contact interface. being explored and are explained in section PP1.3. Highlights in To reduce this loss, “passivated contacts” which suppress 2019 included the development of a mechanically stacked III-V/Si interface recombination while selectively transporting electrons tandem cell with an efficiency >30%, the optimisation of anti-reflection or holes towards the cell’s terminals are being developed. We are coating layers for III-V/Si tandem cells, and demonstration of 5.4% developing several types of such contacts, from the synthesis and and >10% efficient cells suitable for top cells using Sb S and ultrathin characterisation of the component layers to the fabrication of proof-of- 2 3 Sb (S,Se) respectively. In addition, a corrected estimate for the concept devices. In the high temperature approach, we are developing 2 3 improved bandgap prediction of new photovoltaic materials for top low-cost methods to create localised polysilicon/tunnelling oxide cells was established and evaluated, showing much closer agreement contacts for application under the front fingers of silicon solar cells. to experimental data. This technique has subsequently been used Device modelling shows that efficiencies above 24% are within reach to assess bandgaps in promising candidate absorber materials. In with this approach. In the low-temperature approach, we continue the perovskite/Si tandem area, efficiencies of 27.7% and 23.0% were to develop a range of new materials for high carrier selectivity, in demonstrated for a four-terminal and two-terminal perovskite/Si combination with ultrathin inter-layers for improved passivation. monolithic tandem cell respectively. Finally, efficiencies of 29.8% and These carrier-selective contact stacks are being applied both locally, 32.3% were measured on GaAs/Si mechanically stacked tandem cells for example in an interdigitated back-contact device, and across the at one-sun and seven-sun illumination respectively. full device surface for reduced processing complexity.

23 05 – PP1

PP1.1A SOLAR-GRADE SILICON We have also applied the Tabula Rasa process, in addition to other pre- ANU Team treatment steps including phosphorus impurity gettering and defect Prof. Dan Macdonald, Dr Chang Sun, Dr Pheng Phang hydrogenation, to n-type UMG wafers which were then processed into silicon heterojunction solar cells by our partners at ASU. This resulted ANU Student in a peak efficiency of 21.2% (in-house measurement) for the pre- Rabin Basnet treated UMG wafers, more than 3% absolute higher than the untreated UNSW Team UMG wafers. This further demonstrates the importance of effective Dr Fiacre Rougieux, Dr Brett Hallam pre-treatments for achieving high efficiencies with solar-grade silicon wafers. Due to the introduction of atomic hydrogen into the wafers UNSW Student during the heterojunction process, the cells were found to be stable Daniel Chen after illuminated annealing, a process which deactivates the boron- Partners oxygen defects. These defects can otherwise cause light-induced Arizona State University (ASU) degradation in the compensated n-type UMG wafers. Apollon Solar (France)

Funding Support ACAP, ARENA, ARC, ANU

Aims

The use of low-cost solar-grade silicon materials has the potential to contribute to further cost reductions for photovoltaic modules. However, to enable the widespread industrial application of such solar- grade materials, it is necessary to demonstrate that the cell efficiency and stability is the same as those obtained when using standard electronic-grade silicon wafers. To help achieve this, the aims for the previous reporting period were to: fabricate solar-grade silicon solar cells with efficiencies above 22% at ANU using specially optimised processes for solar-grade silicon wafers; and to demonstrate that Figure PP1.1a.1: Certified I-V curve from ISFH CalTec. these devices are stable under illumination, after the deactivation of the boron-oxygen defect via illuminated annealing.

Progress

Based on our previous results in this ACAP work package, we have successfully developed a modified high efficiency solar cell process that is very well suited to temperature-sensitive silicon wafers made from low-cost solar-grade silicon feedstock. The cell design includes a pre-treatment step known as a Tabula-Rasa (or "clean slate") that dissolves oxygen precipitate nuclei formed during ingot growth, which can otherwise cause detrimental ring defects during high temperature cell processing. We have previously found that solar-grade silicon wafers are particularly prone to such ring defects. The rear side of the cell features a full-area thin tunnelling oxide with an overlying phosphorus-doped polysilicon layer, to form a high quality passivated contact. This structure is simpler to fabricate than our previous PERL (passivated emitter and rear locally diffused) cell process, has a lower thermal budget, and provides outstanding impurity gettering for low-cost wafers. As a result, we have recently achieved Figure PP1.1a.2: PL image of the champion cells embedded on the a world record efficiency of 22.6% (certified) on a 2 cm × 2 cm cell host wafer. fabricated at ANU on an n-type Cz-grown upgraded metallurgical-grade (UMG) solar-grade wafer supplied by our partners Apollon Solar. A photoluminescence image of the UMG wafer with seven cells prior to metallisation is shown in Figure PP1.1a.1, and the certified I-V curve from ISFH CalTec for the champion cell is shown in Figure PP1.1a.2.

24 ACAP ANNUAL REPORT 2019

Funding Support References ACAP, ARENA, IET AF Harvey Engineering Prize, ARC DECRA BASNET, R., PHANG, S. P., SAMUNDSETT, C., YAN, D., LIANG, W. S., SUN, C., ARMAND, S., EINHAUS, R., DEGOULANGE, J. & MACDONALD, Aims D. 2019. 22.6% Efficient Solar Cells with Polysilicon Passivating The aims of the various hydrogenation projects in 2019 included the Contacts on n-type Solar-Grade Wafers. Solar RRL, 3. https://doi. development of advanced hydrogenation processes for high efficiency org/10.1002/solr.201900297 silicon solar cell technologies, as well as improving the understanding BASNET, R., SUN, C., WU, H. T., NGUYEN, H. T., ROUGIEUX, F. E. & of and eliminating degradation mechanisms in silicon solar cells. MACDONALD, D. 2018. Ring defects in n-type Czochralski-grown Some of the progress highlights from 2019 are included below. silicon: A high spatial resolution study using Fourier-transform infrared spectroscopy, micro-photoluminescence, and micro-Raman. Journal of Progress Applied Physics, 124. Improvements in p-type silicon quality through defect BASNET, R., WEIGAND, W., YU, Z. J., SUN, C., PHANG, S. P., SIO, H. C., engineering and hydrogenation ROUGIEUX, F. E., HOLMAN, Z. C. & MACDONALD, D. 2020. Impact of pre-fabrication treatments on n-type UMG wafers for 21% efficient Following on from work done in 2018 on commercial-grade p-type silicon heterojunction solar cells. Solar Energy Materials and Solar monocrystalline and multicrystalline silicon (mc-Si) wafers (Chen et Cells, 205, 110287. https://doi.org/10.1016/j.solmat.2019.110287 al. 2018) the potential of low-cost p-type upgraded metallurgical-grade (UMG) multicrystalline silicon was demonstrated, with a record open- SUN, C., CHEN, D., WEIGAND, W., BASNET, R., PHANG, S. P., HALLAM, circuit voltage of 690 mV being achieved on silicon heterojunction B., HOLMAN, Z. C. & MACDONALD, D. 2018. Complete regeneration of (SHJ) solar cells made from low-quality UMG wafers from the edge BO-related defects in n-type upgraded metallurgical-grade Czochralski- of a silicon cast (Stefani et al. 2019). A multi-stage defect engineering grown silicon heterojunction solar cells. Applied Physics Letters, 113. approach incorporating gettering and hydrogenation was able to significantly improve the wafer bulk lifetime from 15 µs to 130 µs. It PP1.1B HYDROGENATION was shown that the gettering process was able to remove significant concentrations of metallic impurities from the wafers, including iron. The wafers were fabricated into SHJ cells at partner site Arizona Lead Partner State University and were further improved using the UNSW advanced UNSW hydrogenation process (AHP) to achieve the record open-circuit UNSW Team voltage for p-type UMG silicon. The efficiencies of the cells (18.7% Prof. Chee Mun Chong, A/Prof. Brett Hallam, Dr Malcolm Abbott, for the champion cell) were limited by the short-circuit current and fill Dr Catherine Chan, Dr Alison Ciesla, Dr Ran Chen, Dr David Payne, factor, due to the non-optimised texturing and the parasitic absorption Dr Sisi Wang, Dr Phillip Hamer, Dr Michael Pollard, Dr Michelle Vaqueiro losses in the ITO and a-Si:H layers, and the poor conductivity of low Contreras, Dr Anastasia Soeriyadi, Dr Arman Mahboubi Soufiani, temperature pastes used for contact formation. However, the high Dr Li Wang, Dr Brendan Wright, Dr Matthew Wright, A/Prof. Bram Hoex, voltages achieved suggest that this approach, which eliminates the A/Prof. Ziv Hameiri, Dr Fiacre Rougieux, A/Prof. Jingjia Ji. need for expensive n-type Cz wafers for SHJ fabrication, may be viable in the future, whereby efficiencies exceeding 20% for low-cost p-type UNSW Students UMG mc-Si SHJ solar cells may be possible. It was also demonstrated Daniel Chen, Rong Deng, Tsun-Hang Fung, Muhammad Umair Khan, for the first time that hydrogenated mc-Si SHJ cells can suffer from Moonyong Kim, Shaoyang Liu, Aref Samadi Chandany Sen, light and elevated temperature induced degradation (LeTID), and this Carlos Vargas, Utkarshaa Varshney, Yu Zhang, Bruno Vicari Stefani, can be induced during the fabrication process (Chen et al. 2019). The Chukwuka Madumelu mitigation or suppression of this defect in such structures is an area that requires further investigation, particularly when using low‐quality Partners substrates that require bulk hydrogenation. Apollon Solar Canadian Solar China Sunergy Chint Sunport Jinko Solar Linuo Group LONGi Solar Meyer Burger Phono Solar SAS Sunrise Suntech Power Tongwei Solar

25 05 – PP1

Light and elevated temperature induced degradation (LeTID) and involvement of hydrogen

LeTID remained an important area of research in 2019, to both understand the root cause of the defect and how to mitigate it. Varshney et al. studied the extent of LeTID in p-type mc-Si wafers passivated with different configurations of hydrogenated silicon nitride

(SiNx:H) and aluminium oxide (AlOx:H) (Varshney et al. 2020). It was demonstrated that the configuration of passivation layers significantly

affected the degradation extent. When ALD AlOx:H was deposited

onto the silicon wafer and then capped with SiNx:H, less LeTID was

observed compared to the case with only SiNx:H; and when a SiNx:H

passivation layer was capped with ALD AlOx:H the LeTID extent was

larger. It was hypothesised that the ALD AlOx:H layer may impede the diffusion of hydrogen. This would either reduce or increase the

Figure PP1.1b.1: Calibrated iVOC (left) and ΔiVOC (right) maps of amount of hydrogen that can diffuse into the underlying silicon, the SiNx:H-passivated UMG wafers: (a) without any pre-treatment; depending on whether the ALD AlO :H layer is underneath or above (b) with hydrogenation; (c) gettering; and (d) both gettering and x the SiNx:H layer. Notably, when the experiments were performed with hydrogenation. The ΔiVOC maps on the right represent the absolute difference between (e) hydrogenation and control; (f) gettering and PECVD AlOx:H, a greater degradation extent was observed for both control; (g) gettering + hydrogenation and gettering only; and (h) configurations, possibly implying that PECVD AlOx:H did not act as gettering + hydrogenation and control. The results demonstrate the a hydrogen diffusion barrier, but rather an extra hydrogen source. In benefit of including gettering and hydrogenation in the solar cell summary, the work demonstrated that LeTID is strongly dependent on fabrication sequence. the composition and configuration of the surface passivation scheme and has a direct impact on the manufacturing of industrial PERC cells

which utilise an AlOx:H/SiNx:H rear passivation stack.

Figure PP1.1b.2: Current-voltage curves of the champion pre- fabrication gettered and hydrogenated UMG SHJ cell before and after advanced hydrogenation processing, resulting in a VOC of >690 mV. Figure PP1.1b.3: Evolution of normalised defect densities as a function of cumulative laser exposure time under accelerated Cast-monocrystalline silicon is another promising low-cost material, degradation conditions of 38 kW/m² at 130 °C. The results suggest which makes use of cheaper casting methods while maintaining that the composition and configuration of the passivation stack has mono-like quality. However, due to dislocation clusters that form a significant impact on LeTID extent and imply that ALD AlOx:H might during the casting process, there Is spatial uniformity variation in an act as a barrier to the diffusion of H. ingot. A method of dark annealing to improve the carrier lifetime of To gain further insight into the mechanism of LeTID, the degradation cast-mono wafers was investigated (Samadi et al. 2019). It was found and regeneration of n- and p-type silicon wafers with different surface that while a conventional hydrogenation process carried out in a firing diffused layers under dark and illuminated annealing was compared, furnace increased the effective lifetime by 40%, a post-fire annealing in highlighting previously unobserved similarities in defect formation the dark at 400°C was able to further increase the effective lifetime of and recovery kinetics (Chen et al. 2019). It was found that surface the wafers by 70% compared to the lifetime after firing. It was shown diffused layers can modulate LeTID degradation and recovery kinetics. that the improvement with dark annealing at 400°C was only achieved A particularly surprising observation was that on n-type samples if the wafer had been fired first, implying the improvement is likely due with a phosphorus diffused surface, LeTID reaction rates were to hydrogen passivation of the dislocations.

26 ACAP ANNUAL REPORT 2019

slowed with the addition of illumination instead of accelerated as Mitigation of LeTID would be expected for a carrier-induced defect. Through modelling One of the main approaches to mitigate LeTID is through post-firing of the hydrogen charge state fractions, it was demonstrated that thermal processes, that Is annealing of the finished solar cell. A new the behaviour of LeTID both in the dark and under illumination may approach to mitigate LeTID was proposed whereby the annealing be explained by the migration of and interactions between charged process is performed prior to the metal contact firing step (Sen et al. hydrogen species and dopant atoms within the diffused layers and the 2019). This approach is potentially more favourable, as post-firing silicon bulk. It was postulated that hydrogen is accelerated towards a thermal processes can lead to large losses in fill factor caused by high-low junction and repelled from a p-n junction. Through evaluating hydrogen migrating to the metal/Si interface, causing increased the differences in electric fields brought about by phosphorus and contact resistance. It was shown that an annealing process performed boron diffusions, it was also concluded that the influence of such in a rapid thermal processing (RTP) furnace prior to the firing step fields on hydrogen flux towards the surface can be used to explain the could substantially suppress LeTID on p-type mc-Si lifetime test recently observed surface-related degradation that occurs in the latter structures. It was hypothesised that the pre-fire annealing step acts stages of a LeTID cycle. to reduce the final concentration of hydrogen within the bulk that would otherwise lead to LeTID. It was found that higher annealing temperatures and longer annealing times were more effective at suppressing LeTID, however lead to lower starting lifetimes that did not recover, therefore the annealing temperature and duration must be carefully optimised.

Figure PP1.1b.5: Evolution of (a) normalised defect density of a control sample and samples which underwent pre-fire annealing for 6 s; and (b) effective minority carrier lifetime pre-fire annealing for 1 min of a control sample and the samples pre-fire annealing for 1 min with ranges of temperature from 550°C to 750°C. The effective lifetime was extracted at Δn = 8.5 × 1014 cm-3. The stability testing condition was 130°C with an illumination intensity of 1000 W/m². The results show that applying an annealing step prior to firing can significantly reduce LeTID (with higher annealing temperatures being more effective at suppressing degradation), however there is an optimum condition, as higher temperature annealing can lead to lower overall lifetimes. Rapid detection of LID/LeTID on full area solar cells.

Highlights

• Record open-circuit voltage of 690 mV being achieved on silicon heterojunction (SHJ) solar cells made from low quality UMG wafers.

• 70% improvement in effective lifetime of cast-monocrystalline silicon after the post-fire annealing process.

• LeTID extent is highly dependent on surface passivation layer

composition and configuration; ALD AlOX:H likely acts as a barrier to hydrogen diffusion.

Figure PP1.1b.4: Comparison of LeTID degradation and recovery • The behaviour of LeTID both in the dark and under illumination can in boron and phosphorus diffused n-type Cz-Si and phosphorus be explained by the migration of and interactions between charged diffused p-type mc-Si silicon showing: (a) effective lifetime hydrogen species and dopant atoms within the diffused layers and normalised to the lifetime after firing; (b) apparent defect concentration (N ); and (c) normalised apparent J . Measurements the silicon bulk. app* 0S were taken in situ at a temperature of approximately 160 ± 4°C. 27 05 – PP1

• A new LeTID mitigation process was proposed whereby solar Aims cells are annealed prior to the contact-formation or ‘firing’ step (demonstrated on a wafer level). The objectives of PP1.2a are twofold: to develop very high efficiency laboratory-based silicon solar cells; and, in parallel, to develop cell References fabrication techniques and processes compatible with industrially feasible low-cost implementation of interdigitated back contact CHEN, D., KIM, M., SHI, J., VICARI STEFANI, B., YU, Z., LIU, S., EINHAUS, (IBC) solar cells. IBC cells, by their very nature, are both inherently R., WENHAM, S., HOLMAN, Z. & HALLAM, B. Defect engineering of capable of very high efficiencies owing to superior optics compared p-type silicon heterojunction solar cells fabricated using commercial- to conventional cell architectures and owing to an improved ability grade low-lifetime silicon wafers. 2019. Progress in Photovoltaics: to tailor fabrication processes to meet specific goals of cell features. Research and Applications, 1– 15. https://doi.org/10.1002/pip.3230. However, such cells are also characterised by more complex and CHEN, D., KIM, M., SHI, J. W., YU, Z. S., LEILAEIOUN, A. M., LIU, S. Y., expensive fabrication processes. The target for the end of the program STEFANI, B., WENHAM, S., EINHAUS, R., HOLMAN, Z. & HALLAM, B. is to fabricate cells using any techniques with efficiencies of 26% or > 700 mV Open-Circuit Voltages on Defect-Engineered P-type Silicon above, and in parallel to produce cells using industrially applicable Heterojunction Solar Cells on Czochralski and Multicrystalline Wafers. techniques, and by doing so meeting an informal or internal efficiency 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion. target of 24% or above.

SAMADI, A., SEN, C., LIU, S., VARSHNEY, U., CHEN, D., KIM, M., Progress SOUFIANI, A. M., CONTRERAS, M. V., CHONG, C. M., CIESLA, A., ABBOTT, M. & CHAN, C. 2019. Hydrogenation of dislocations in p-type The current highest efficiency attained in this project is 25.0%, cast-mono silicon. AIP Conference Proceedings, 2147, 140007. independently measured at CSIRO. Detailed analysis indicates non- https://aip.scitation.org/doi/abs/10.1063/1.5123894. ideal recombination attributed to the metal contact formation process as the key loss mechanism. In this report, we present investigation SEN, C., CHAN, C., HAMER, P., WRIGHT, M., VARSHNEY, U., LIU, S. Y., results using a wide range of viable metallisation stacks combining CHEN, D., SAMADI, A., CIESLA, A., CHONG, C., HALLAM, B. & ABBOTT, Al, Cr, Pd and Ag. Results obtained via boron diffused test samples M. 2019. Annealing prior to contact firing: A potential new approach to with Transfer Length Method (TLM) structures as presented in Figure suppress LeTID. Solar Energy Materials and Solar Cells, 200. PP1.21.1, indicate a wide range of metal contact schemes provides https://doi.org/10.1016/j.solmat.2019.109938 improved contact resistivity over pure Al evaporation. STEFANI, B. V., WEIGAND, W., WRIGHT, M., SOERIYADI, A., YU, Z. S., The two most promising stacks as selected based on contact KIM, M., CHEN, D., HOLMAN, Z. & HALLAM, B. 2019. P-type Upgraded resistivity, adhesion and compatibility to the IBC fabrication process Metallurgical-Grade Multicrystalline Silicon Heterojunction Solar were AlPd-Al and CrPdAg-Al, which were then implemented in a batch Cells with Open-Circuit Voltages over 690 mV. Physica Status Solidi of IBC solar cells with baseline Al contact as the control. Excellent a-Applications and Materials Science, 216. efficiencies above 24% were achieved on all three batches of cells, https://doi.org/10.1002/pssa.201900319 however, contrary to contact resistance measurement on TLM VARSHNEY, U., HALLAM, B., HAMER, P., CIESLA, A., CHEN, D., LIU, structures, both trialled metallisation stacks exhibit lower fill factors S., SEN, C., SAMADI, A., ABBOTT, M., CHAN, C. & HOEX, B. 2020. when compared to the Al contact cells, due to high series resistance. Controlling Light- and Elevated-Temperature-Induced Degradation With Furthermore, a much wider spread in the measured s eries resistance Thin Film Barrier Layers. IEEE Journal of Photovoltaics, 10, 19-27. was observed in the metal stacks, particularly the AlPd-Al stack. The metallisation stack of AlPd-Al and CrPdAg-Al cells measured series resistance ranged at 0.60–2.3 Ω.cm2 and 0.34–0.60 Ω.cm2 PP1.2A REAR CONTACT SILICON CELLS respectively.

There are a few plausible reasons for high series resistances on the ANU Team IBC cells with metal stacks. The measured metallised stacks on a Prof. Andrew Blakers, Dr Matthew Stocks, Dr Kean Fong, Dr WenSheng TLM structure were performed with a single run without breaking the Liang, Dr Marco Ernst, Dr Daniel Walter chamber vacuum. However, the metal stack performed on IBC solar ANU Student cells required a total of two metal depositions, exposing the metal to Teng Choon Kho air and wet chemicals before evaporating the final Al layer. Moreover, wet chemical processing which involves spinning and stripping Partner photoresist may leave residue on the metal dots (AlPd and CrPdAg) PV Lighthouse: Dr Keith McIntosh during the lift-off process, which could contribute to increased contact Funding Support resistance. ACAP, ARENA, ANU Despite the high series resistance, subsequent analysis indicates that both AlPd-Al and CrPdAg-Al contact stacks provide a significant boost to the pseudo-fill factor (FF) and pseudo-efficiency, indicating significantly reduced non-ideal recombination in these cells. Improvement over the pre-existing fabrication sequence, via in situ evaporation of multiple metal layers, or reducing exposure to ambient 28 ACAP ANNUAL REPORT 2019

conditions between metal evaporation stacks Is likely to achieve PP1.2B PASSIVATED CONTACTS further improvement in the absolute cell efficiency.

ANU Team Prof. Dan Macdonald, Dr Di Yan, Dr Pheng Phang, Dr Josua Stuckelberger, Dr Lachlan Black

ANU Students Mr Zetao Ding, Mr Wenhao Chen, Mr Wenjie Wang, Mr Mohamed Ismael, Mr Gabriel Carvalho

Academic Partners EPFL/CSEM Switzerland, University of Melbourne

Funding Support ARENA, ANU Figure PP1.2a.1: (a) The measured contact resistivity for various metal stacks on light boron diffusion. The metallisation (filled sym- bols) were performed with lift-off except for the Al performed by Aims Franklin et al. 2014. (b) The TLM measurement for the Al, AlPdAl and CrPdAg structures. Today’s most advanced silicon solar cells use “passivated contacts” to selectively transport electrons and holes towards the cell terminals. This project aims to help bring such passivated contacts to the broader PV industry, by developing low-cost and simple approaches to creating such contacting schemes. We are following a two- pronged approach to develop novel silicon solar cells that incorporate passivated contacts. Part of our work is based on the proven high temperature approach of depositing a silicon film onto an ultrathin dielectric layer, enabling tunnelling to take place. We also pursue low temperature approaches, based on depositing materials that have either a very high or a very low work function, which makes them selective to the transport of holes or electrons, respectively.

Progress

Building on our previous success in developing full-area polysilicon passivated contacts, recent work has focused on developing low-cost processes for localised polysilicon passivating contacts underneath Figure PP1.2a.2: Three batches of ONO IBC solar cells were the metal fingers of silicon solar cells. The first implementation of created that are identical except for the rear metallisation on the such localised n+ polysilicon contacts would be under the fingers on diffusion region. The cells have metallisation stacks of AlPd-Al, the front side of standard p-type PERC cells. This will enable reduced

Al and CrPdAg-Al. The (a) series resistance, (b) VOC, (c) FF and recombination losses at the front contacts without causing unwanted pFF, and (d) Eff and pEff were measured at 25 ± ˚C. The box absorption in the polysilicon layer between the fingers. A further step represents the range of data between 25 and 75% with the line would be to apply localised p+ polysilicon layers to the rear side to showing the mean, and the whiskers represent the maximum and create a highly bifacial cell with passivated contacts on both sides. A minimum values obtained. schematic diagram of such a device is shown in Figure PP1.2b.1. To this end, we have developed a simple process for forming patterned Reference polysilicon regions that only requires a single dopant diffusion process, creating both the heavily doped polysilicon regions and the lightly- FRANKLIN, E., FONG, K., MCINTOSH, K., FELL, A., BLAKERS, A., KHO, doped regions between the fingers in a single high temperature step. T., WALTER, D., WANG, D., ZIN, N., STOCKS, M., WANG, E. C., GRANT, We aim to demonstrate cell efficiencies above 24% with this approach N., WAN, Y. M., YANG, Y., ZHANG, X. L., FENG, Z. Q. & VERLINDEN, P. in the near future. with the University of Oxford, progress was made J. 2016. Design, fabrication and characterisation of a 24.4% efficient in investigating the cause of an increase in contact resistance interdigitated back contact solar cell. Progress in Photovoltaics, 24, that is often observed after post-firing thermal treatments to solar 411-427. cells (Hamer et al. 2018). It was shown that the increased contact resistance of p-type mc-Si PERCs with post-firing thermal processes is highly dependent on the application of currents and voltages to the solar cell contacts during annealing, which can act to either accelerate

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or suppress the effect. It was also demonstrated that the increase in contact resistance is highly reversible with applied voltage and can be relatively quickly recovered with the appropriate treatment. An excellent agreement was shown between the experimentally observed behaviour and the presence of hydrogen near the metal-silicon interface, as obtained from modelling of hydrogen transport in these structures (Hamer et al. 2018). This modelling is able to explain the observed effects upon annealing under an applied bias, as well as the high degree of reversibility in the results. This not only provides an important insight into the problem of increased contact resistance, it is potentially a very useful tool for investigating the behaviour of hydrogen in silicon at temperatures between 300°C and 700°C. In particular, it may be possible to determine the kinetics of hydrogen release from complexes within the bulk, which in turn may provide better understanding of degradation mechanisms in mc-Si related to hydrogen. The redistribution of hydrogen from the bulk of the device to the emitter is also of particular interest given several recent reports linking hydrogen to LeTID.

Figure PP1.2b.2: Cross-sectional TEM image of the TiOx/LiF/Al full-area rear-side contact.

References

BASNET, R., PHANG, S. P., SAMUNDSETT, C., YAN, D., LIANG, W. S., SUN, C., ARMAND, S., EINHAUS, R., DEGOULANGE, J. & MACDONALD, D. 2019. 22.6% Efficient Solar Cells with Polysilicon Passivating Contacts on n-type Solar-Grade Wafers. Rapid Research Letters 3: 1900297.

WANG, W., HE, J., YAN, D., SAMUNDSETT, C., PHANG, S. P., HUANG, Z., SHEN, W., BULLOCK, J. & WAN, Y. 2019. 21.3%-efficient n-type silicon solar cell with a full area rear TiOx/LiF/Al electron-selective Figure PP1.2b.1: Schematic diagram of a bifacial n-type Si cell with localised polysilicon contacts under the front and rear contact. Accepted for publication in Solar Energy Materials and Solar fingers. Cells: https://doi.org/10.1016/j.solmat.2019.110291 We have also recently applied our previously developed full-area polysilicon passivated contacts to low-cost silicon wafers, namely YAN, D., PHANG, S. P., WAN, Y. M., SAMUNDSETT, C., MACDONALD, n-type cast-mono wafers and solar-grade silicon wafers. The D. & CUEVAS, A. 2019. High efficiency n-type silicon solar cells polysilicon process is very well suited to such wafers as it allows with passivating contacts based on PECVD silicon films doped by excellent gettering of metallic impurities to the wafer bulk, while phosphorus diffusion. Solar Energy Materials and Solar Cells, 193, retaining outstanding surface passivation and contact properties. This 80-84. has enabled us to achieve a world record efficiency of 22.6% (certified measurement) for solar-grade silicon wafers, and 22.5% (in-house measurement) for cast mono-like wafers. We have a clear pathway PP1.3 SILICON TANDEM CELLS to achieve efficiencies above 23% with polysilicon contacts on these III-V materials and Chalcogenides for Silicon-based Tandem Cells wafers in the near term. UNSW Team For the low temperature dopant-free passivating contact approach, A/Prof. Xiaojing Hao, Prof. Martin Green, A/Prof. Nicholas Ekins- we have commenced the development of interdigitated back contact Daukes, Dr Ziheng Liu, Dr Jialiang Huang, Dr Chang Yan, Dr Kaiwen (IBC) solar cells featuring all dopant-free contacts, using MoOx and LiF Sun, Dr Xu Liu, Dr Fajun Ma, Dr Pengfei Zhang, Dr Mahesh Suryawanshi carrier selective contacts. Initial results are promising with open-circuit voltages above 700 mV on finished devices. We have also recently UNSW Students fabricated 21.3% efficient n-type solar cells with a TiOX/LiF/Al full-area Caixia Li, Yuanfang Zhang, Yiyu Zeng, Yasaman Tabari-Saadi, Chen rear contact, demonstrating a low temperature dopant-free contacting Qian, Xiaojie Yuan scheme that does not require any patterning, and which is capable of high efficiency. Figure PP1.2b.2 shows a high-resolution TEM cross- section of this passivating contact structure.

30 ACAP ANNUAL REPORT 2019

Academic Partners III-V sub-cells to improve the photon recycling effect and therefore University of Sydney boost the overall tandem efficiency. A III-V/Si triple-junction cell with University of Science and Technology of China (UTSC) an energy conversion efficiency of 30.9% has been achieved. The J-V Huazhong University of Science and Technology characteristics and EQE spectra of the III-V/Si tandem cell are shown Nanyang Technology University in Figure PP1.3.1.

Industry Partners IBM LONGi Solar Jinko Solar Tianjin Institute of Power Sources

Funding Support ACAP, ARENA

Aims Figure PP1.3.1: (a) J-V characteristics. (b) EQE spectra of the stacking III-V/Si tandem cell. The dominant Si solar cells have achieved record efficiency close to Optical optimisation has been conducted to improve the tandem cell their theoretical limit. One promising approach to boost the efficiency efficiency. For high quality single junction GaAs cells, the radiative limit beyond the limit is integrating high bandgap top cells with Si cells has higher external radiative efficiency which allows it to benefit more to fabricate tandem solar cells. The aim of this project is to work from the photon recycling effect. A low refractive index intermediate with collaboration partners, which have world-leading expertise on layer acting as an angle selective reflector provides a narrow escape tandem solar cells and complementary characterisations, to exploit cone, most of the anisotropic photons from radiative recombination the synergies for the development of a new generation of Si wafer cell could be reflected back. However, within the escape cone, emitted technology by stacking top cells based on inorganic materials, with photons can pass through the intermediate layer to be absorbed by the performance of the Si cell substantially improved by the deposition bottom cell with a lower bandgap. This results in the efficiency of GaAs of thin layers of high performance top cells on its surface to produce cell in the III-V/Si tandem structure being ~2% lower compared with tandem devices. the record of a single junction GaAs cell with a metal back layer. III-V is one of the promising top cell candidates. The III-V/Si tandem This work focuses on maximising the utilisation of photons emitted cells can be realised through direct growth, wafer bonding and from radiative recombination through optical optimisation. Simulation mechanical stacking. Due to the differences in lattice constants and of the intermediate layer with epoxy and various nanostructures as thermal expansion coefficients, the efficiency of direct grown III-V/Si is angle and wavelength selective reflectors has been conducted. GaAs limited to ~20% owing to the poor material quality. The wafer bonding and Si are applied as the top and bottom cells, respectively. Periodic method has a high requirement on surface roughness which involves metal nanostructures, silicon pillar/holes and TiO2 holes with different the high-cost and low throughput processes and encounters the geometrical parameters are studied and compared as shown in Figure current mismatch issue. In contrast, the mechanical stacking method PP1.3.2. allows the fabrication of four-terminal III-V/Si tandem cells with the advantage of no restriction on lattice or current matching between the top and bottom cells. Our work in 2019 was aimed at the development of III-V/Si high efficiency tandem solar cells through the stacking approach.

As an alternative to III-V materials, chalcogenide semiconductors are another group of promising photovoltaic materials due to their direct and tunable bandgaps, high absorption coefficient (>104 cm-1), high energy conversion efficiency, low-cost potential, and stable device performance. In addition to the pure sulfide kesterite and chalcopyrite which have been developed before, we extended our exploration Figure PP1.3.2: Schematic diagram of different intermediate structures. to other Earth-abundant and environmentally friendly adamantine materials, RoHS-compliant Earth-abundant V2VI3 (Sb2(S,Se)3). Calculation results are illustrated in Figure PP1.3.3. The electric current density of the top and bottom cells is calculated by integrating their Progress optical absorption with solar irradiance (AM 1.5), the enhancement factor indicates the current improvement of the cell compared with the Good progress has been made on fabrication of four-terminal III-V/ reference cell with epoxy as an intermediate layer. Si tandem solar cells. We have developed a method employing layer transfer and stacking that gets rid of the lattice mismatch and Simulation results shown in Figure PP1.3.4 indicate that metal current limiting issues. The III-V sub-cells are transferred onto a nanostructures show a promising effect in wavelength manipulation transparent substrate and then stacked on top of the Si bottom cell. by metal localised surface plasmonics resonance. For the structure of A specially designed optical layer has been inserted at the back of

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PP1.3.3: Simulation results of different intermediate layers.

No. 9, with the silver nanostructure, photons at a wavelength of 890 as shown in Figure PP1.3.3. This is consistent with the typical design nm are strongly reflected back to the top cell which brings idea of the anti-reflection layer. ~1.2 mAcm-2 improvement in current density for the top cell with an Referring to the silicon nano pillar, the simulation result suggests their ignorable influence on the bottom cell. Moreover, the wavelength of transmission relates to the height of the nanostructure. Mie scattering the photons' interaction with resonator sensitively depends on the dominates the interaction between the structure and incident photons geometrical parameter of the nanostructure, which means by carefully when the nano pillar has a smaller length-diameter ratio. In this changing the size of the metal nanostructure, this intermediate layer situation, wavelength selective reflector is achieved. With increasing can be applied to top cells with different bandgaps. the height of the pillar, nano pillar shows a better result in transmission accompanied with more absorption which should be considered carefully for the intermediate layer design. According to these results, metal nanostructure and silicon pillar with small length-diameter ratio are the most promising candidates to enhance the photon recycling effect of the top cell and therefore improve the tandem cell efficiency.

Optimisation of the anti-reflection coating is also conducted for tandem cell efficiency improvement. Comparing with conventional III-V solar cells, the III-V/Si tandem cell captures a different range of the solar spectrum. Therefore, optimisation on the design of an anti- reflection coating layer is required to efficiently absorb the targeted

range of photons. The ZnS/MgF2 bilayer anti-reflection coating Figure PP1.3.4: Spectra of metal nanostructure intermediate layer. structures on top of the tandem cell with different thicknesses are simulated. Their performance at the range between 300 nm and 1200 Metal nanostructures show relatively good results. However, they nm is estimated by integrating the solar irradiance of AM1.5 with the will absorb light converting photon energy into heat and introducing energy reflected. JR represents the reflection loss with anti-reflection current loss. Dielectric scatter such as silicon disk showing a narrow coating in this design. As shown in Figure PP1.3.5, the blue area scatter wavelength with ignorable absorption is the promising indicates good performance of the anti-reflection coating, which is candidate. Periodic TiO2 and SiO2 holes array as the intermediate layer 50~70 nm for ZnS and 110~130 nm for MgF2. show relatively strong enhancement in long wavelength transmission

32 ACAP ANNUAL REPORT 2019

−2 increases the JSC from 13.6 to 15.8 mAcm . The optimised full-

inorganic epitaxial Sb2S3 device obtained an efficiency of 5.4% with −2 a VOC of 0.69 V, a JSC of 15.3 mAcm , and an FF of 51.2% as shown in Figure PP1.3.7. The device indicated good environmental stability retaining more than 95% of its initial efficiency after 250 days in high humidity air. The present facile epitaxial strategy opens the door to support a high quality heterointerface, which is expected to accelerate the progress of such new non-cubic absorber solar cells.

Figure PP1.3.5: Schematic sketch of a bilayer anti-reflection coa- ting design and reflection losses.

Antimony selenosulfide offers another kind of stable and cost-effective light harvesting material for the top cell candidate. Highlighted progress in this area includes (1) the demonstration of a 5.4% efficiency Sb2S3 top cell (published in Advanced Functional Materials) and (2) the demonstration of first >10% efficiency ultrathin Sb2(S,Se)3 solar cells by collaborating with UTSC (relevant work has been submitted to Nature Energy and is currently under review).

For Sb2S3, we developed a facile strategy to achieve quasi-epitaxy growth of Sb2S3. Engineering the CdS/ or TiO2 exposure facets which support the overlying lattice-matched surface and bonding sites, facilitates the quasi-epitaxial growth of vertical orientation Sb2S3. The local epitaxial can efficiently suppress the interface and bulk recombination. Figure PP1.3.7: (a, b) JSC and PCE distribution evolved with average grain sizes. (c, d) The optimised J-V and EQE curves of The mechanism of vertical preferential orientation was investigated Sb2S3 solar cells. in comparison with horizontal orientations-dominated Sb2S3 films. As found in Figure PP1.3.6, the VTD (vapour transport deposition) The VTD deposited vertical preferential orientation was achieved synthesised Sb2S3 film is [hk1] dominant and the grains are vertically for both CdS/ Sb2S3 and TiO2/ Sb2S3 heterojunction structures. The aligned on the CdS buffer layer through the entire film. By adjusting the effect of the buffer layer has been investigated and it is found that

Sb2S3 grain orientation, the overall performance of the Sb2S3 solar cell the film deposited on a TiO2 buffer layer presents better overall can be improved considerably. performance under the same processing conditions. The TiO2/ Sb2S3

device presents much lower open circuit voltage (VOC) but higher short

circuit current (JSC) and fill factor (FF), and consequently achieves a higher efficiency as shown in Figure PP1.3.8. Therefore, under the premise of the vertical orientation, the decisive factor that contributed

to better performance of the TiO2/ Sb2S3 is not so straightforward as other determining factors are multiple, such as bulk defects and lattice match in the interface and band alignment, etc. We therefore conducted the insight physics study of both devices to better understand the limitation and prospects of each heterojunction. To investigate the interface defects for both heterojunctions, high resolution transmission electron microscopy together with capacitance-voltage measurements and drive level capacitance profiles were carried out. In addition, the deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) analyses Figure PP1.3.6: Top-view SEM images of (a) H- Sb S , (b) sulfu- 2 3 were used to examine the defects in the Sb2S3 thin film solar cells rized H- Sb S , (c) R- Sb S , (d) sulfurized R- Sb S ; STEM images 2 3 2 3 2 3 and found the defect level in CdS/ Sb S is shallower compared with of the cross-section of (e) H- Sb S , (f) sulfurized H- Sb S , (g) 2 3 2 3 2 3 TiO / Sb S . To figure out the heterojunction energy band diagram, the R- Sb S , (h) sulfurized R- Sb S ; and AFM surface topography 2 2 3 2 3 2 3 X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron images of (i) H- Sb2S3, (j) sulfurized H- Sb2S3, (k) R- Sb2S3 and (i) spectroscopy (UPS) measurements were processed. The diagram is sulfurized R- Sb2S3. shown in Figure PP1.3.9, the smaller band offset for the CdS/ Sb S The RTE (rapid thermal evaporation) grown quasi-epitaxy films are 2 3 heterojunction indicates a better band alignment exists in the CdS/ used to fabricate fully inorganic Sb S solar cells. The “epitaxial" 2 3 Sb S heterojunction. This comparative study would direct a way for devices can efficiently suppress the interface and bulk recombination 2 3 how to optimise every Sb2S3 heterojunction solar cell within the device enhancing the VOC from 0.49 to 0.65 V. The rough Sb2S3 surface from epitaxial growth introduced a light trapping effect, which further

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physics limits. CdS buffer has more potential in the future to push the

PCE of Sb2S3 at the following aspects: (a) better epitaxy quality, (b) better band alignment with Sb2S3, and (c) shallower defect level.

Figure PP1.3.10: Schematic and energy band diagram of a Sb2(S,Se)3 solar cell.

Figure PP1.3.8: Boxplots of performance parameters of Sb2S3 /TiO2 and Sb2S3 /CdS solar cells. Boxes, horizontal bars and point symbols indicate 25/75 percentile, min/max and mean values, respectively.

Figure PP1.3.11: I-V curve of the champion Sb2(S,Se)3 device.

Figure PP1.3.9: Energy band diagram of planar Sb2S3 /TiO2 and Sb2S3 /CdS.

The bandgap of Sb2S3 and Sb2Se3 are ~1.7 eV and ~1.1 eV, respectively. Considering S and Se belong to the same group, the bandgap varies with different ratios between S and Se, making a solid solution a promising material to serve as the top cell in Si-based tandem solar cells. The hydrothermal method deposited Sb2(S,Se)3 film is used to fabricate cells with the configuration of FTO/CdS/Sb2(S,Se)3/ Figure PP1.3.12: EQE curve of the champion Sb (S,Se) device. Spiro-OMeTAD/Au with a good band alignment as shown in Figure 2 3 PP1.3.10. With further incorporation of additives in the precursor The EQE result in Figure PP1.3.12 indicates the good absorption of solution, the efficiency of Sb2(S,Se)3 solar cells was increased to photons and efficient collection of photo generated carriers. The major -2 10.14% with VOC of 647 mV, JSC of 24.29 mAcm and FF of 64.5, which EQE loss at the short wavelength region (around 490 nm) arises from is the highest for this kind of solar cell (see Figure PP1.3.11). It is the absorption of light by the CdS layer. With the use of a thinner CdS -2 notable that the JSC of 24.29 mAcm is achieved from an ultrathin or a higher bandgap buffer, the JSC can be further improved. To solve

(about 300 nm thick) Sb2(S,Se)3 absorber. The demonstrated >10% the Spiro-OMeTAD induced instability, thermal evaporated MnS is efficiency, low synthesis temperature of Sb2(S,Se)3, high stability and used as a hole transport layer replacing the Spiro-OMeTAD. With the high absorption coefficient make it a promising top cell candidate for structure of FTO/CdS/Sb2(S,Se)3/MnS/Au, >9% efficiency full inorganic

Si-based tandem solar cells. Sb2(S,Se)3 solar cells are demonstrated.

While exploring new PV absorber materials, accurate knowledge of the bandgap of a material is the first quantity required when considering a material as a candidate in a top cell for a silicon tandem solar cell. A well-known problem with mainstream ab initio/DFT methods is that they typically, and in some cases substantially, underestimate semiconductor bandgaps. This is a significant problem when 34 ACAP ANNUAL REPORT 2019

designing new materials for top cells in tandems computationally, where tolerances on optimal bandgap are relatively tight (1.6–1.9 eV optimal). Using conventional DFT methods (PBE/GGA) underestimates are typically at least 0.3 eV and can be greater than 1 eV, leaving substantial uncertainty as to whether a material of interest is a good candidate regarding this first, most fundamental design criteria. More sophisticated techniques to assess the bandgap are therefore required to successfully assess candidate materials.

Conventional bandgap estimates were initially provided by DFT+U techniques, which contain an arbitrary parameter U that can be set by the user. This allows for improved estimates but comes with user bias. Hybrid functional (HSE06) methods and the GW approximation, typically require significantly more computation time and power than conventional techniques. Hybrid functional calculations also suffer from the same arbitrariness due to a free parameter choice. To provide increased accuracy with minimal additional computational overheads, the GLLB-SC approximation, equivalent to a first order G0W0 approximation but much less computationally intensive, has been implemented. Previously, the accuracy of this technique was unclear. In this work, we have effectively calibrated the technique for the first time and these calibration curves are shown in Figure PP1.3.13. From this we show for the first time that for adamantine compounds the trend for the GLLB-SC is almost identical to the experimental bandgap on average. The statistical spread around the experimental bandgap can be quantified in terms of the standard deviation of the deviation from the experimental bandgap. The above technique has subsequently been used to assess bandgaps in promising candidate novel oxidation state adamantine compounds. Several promising candidates have been identified computationally.

Figure PP1.3.13: (a) The PBE/LDA results for bandgaps, showing that the trend for this data deviates from the trend for experimental data. (b) Shows a corrected GLLB-SC estimate that shows a much closer agreement to experiment, particularly in the critical region for silicon top cells around 1.6–1.9 eV. Finally, (c) shows a summary of all of the results for known materials.

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Highlights LIU, Z., HAO, X., HUANG, J., & GREEN, M.A. 2019. Effects of layer • Development of III-V/Si tandem cell with efficiency above 30%. thicknesses on laser-induced aluminium-assisted crystallization of Ge- rich SiGe epitaxy on Si. 46th IEEE PVSC, June 2019, Chicago, USA. • Optimisation of anti-reflection coating layers for III-V/Si tandem cell. PATTERSON, R., XU, W., WEI, S.-H., GREEN, M. A. & HAO, X. Ab-initio • Design of nano-patterned intermediate layers for III-V/Si tandem assessment of new sulfo-iodide compounds as candidate top-cell cell for efficiency improvement. materials for silicon-based multi-junction tandem solar cells. IEEE PVSC 46, 2019, Chicago, USA. • Demonstrated 5.4% efficiency 2Sb S3 (1.7 eV bandgap) solar cells.

• Demonstrated >10% efficiency 1-D Sb2(S,Se)3 thin film solar cells ZHANG, Y., HUANG, J., GREEN, M. & HAO, X. High open-circuit voltage

by collaborating with UTSC CuSbS3 solar cells achieved through the formation of epitaxial growth of CdS/CuSbS hetero-interface by post-annealing treatment. EU- • Established and evaluated the corrected GLLB-SC estimate for the 3 PVSEC, 2019, Marseille, France. improved bandgap prediction of new photovoltaic materials, that shows a much closer agreement to experiment. This technique ZENG, Y., SUN, K., HUANG, J., NIELSEN, M., LIU, F., GREEN, M. & has subsequently been used to assess bandgaps in promising HAO, X. Fabrication of Sb S Planar Thin-Film Solar Cell with Vapor candidate absorber materials. 2 3 Transport Deposition (VTD) Method. MRS Fall Meeting, 2019, Boston, Massachusetts, USA. Future Work Future work in 2020 will be focused on: TABARISAADI, Y., SUN, K., YOUNG, T., LIU, F., GREEN, M. & HAO, X.

• Exploration of new PV absorber materials; Chemical processed AgBiS2 deposition as an absorber layer for high performance solar cell application, Asia Pacific Solar Research • Understanding the performance loss and further improving Conference, 2018, Sydney, Australia. the efficiency of III-V/Si tandem cells; and

• Understanding the performance loss and further improving

the efficiency of Sb2(S,Se)3 solar cells.

References NON-EPITAXIAL TANDEM CELLS ON SILICON – DENG, H., ZENG, Y. Y., ISHAQ, M., YUAN, S. J., ZHANG, H., YANG, X. PEROVSKITES ON SILICON K., HOU, M. M., FAROOQ, U., HUANG, J. L., SUN, K. W., WEBSTER, R., WU, H., CHEN, Z. H., YI, F., SONG, H. S., HAO, X. J. & TANG, J. UNSW Team 2019. Quasiepitaxy Strategy for Efficient Full-Inorganic Sb S Solar 2 3 A/Prof. Anita Ho-Baillie, Dr Shujuan Huang, Dr Jae S. Yun, Dr Meng Cells. Advanced Functional Materials, 29. https://doi.org/10.1002/ Zhang, Dr Trevor Young, Dr Jincheol Kim, Dr Nathan Chang, Prof. adfm.201901720 Martin Green

TANG, R., WANG, X., LIAN, W., HUANG, J., WEI, Q., YIN, Y., JIANG, UNSW Students C., YANG, S., XING, G., ZHU, C., HAO, X.J., GREEN, M.A. & CHEN, T. Adrian Shi, Cho Fai Jonathan Lau, Jianghui Zheng, Daseul Lee, 10% efficient antimony selenosulfide solar cells enabled by defect Yongyoon Cho, Jueming Bing engineering. Nature Energy (under review). Monash Team Prof. Udo Bach, Prof. Yi-Bing Cheng, Dr Wei Li, Dr Tian Zhang ZENG, Y., SUN, K., HUANG, J., NIELSEN, P. M., JI, F., SHA, C., YUAN, S., ZHANG, X., YAN, C., LIU, X., DENG, H., LAI, Y., SEIDEL, J., EKINS- Monash Students DAUKES, N.J., LIU, F., SONG, H., GREEN, M. A. & HAO, X.J., Vertical Liangcong Jiang, Qicheng Hou, Jinbao Zhang, Jianfeng Lu oriented antimony sulphide full inorganic thin film solar cells achieved ANU Team by vapour transport deposition. Journal of Materials Chemistry A, Dr The Duong, Dr Daniel Jacobs, Dr Mulmudi Hemant Kumar, Dr Jun (under review). Peng, Dr Heping Shen, Dr Tom White, Prof. Klaus Weber, Prof. Kylie Catchpole LI, C., LIU, Z., HAO, X., & GREEN, M.A. 2019. Optical optimization for III-V/Si multijunction solar cells. PVSEC-29, November 2019, Xi’An, ANU Students China. Yiliang Wu, Xiao Fu

Academic Partners LI, C., LIU, Z., ZHANG, P., HAO, X., & GREEN, M.A. 2019. Optimization Monash University of Ag/PMMA particles in transparent conductive adhesive layer for Australian National University multijunction solar cells. 36th EUPVSEC, September 2019, Marseille, France.

36 ACAP ANNUAL REPORT 2019

Korea Research Institute of Chemical Technology (KRICT) achieved on 4 cm2 by improvement in optical management. This was Ulsan National Institute of Science and Technology (UNIST) done by applying textured polydimethylsiloxane (PDMS) films that 2+ School of Materials Science and Engineering, UNSW School of incorporate a down-shifting material (Ba,Sr)2SiO4:Eu micron phosphor Physics, UNSW on the front of monolithic perovskite/silicon tandem cells. This film Institute of Materials for Electronics and Energy Technology (I-MEET) serves multiple purposes: anti-reflective control for the top cell, light at Department of Materials Science and Engineering, Friedrich- trapping in the Si cell, as well as absorbing UV and re-emitting green Alexander University Erlangen-Nuremberg, Germany light with high quantum yield. A high fill factor (FF) of 81% has also Some of these tasks are conducted under the ARENA RND075 been achieved by the champion device which was the highest at the program in collaboration with Monash University, Australian National time of reporting (Zheng et al. 2019). University, Arizona State University, Suntech Power Co. Ltd and Trina Solar Energy Co. Ltd. Preliminary cost analysis highlights the need to minimise the additional cost of fabrication of the top cell stack as a cost increase of Funding Support $1/cell requires an absolute efficiency improvement of 5% absolute. ACAP, ARENA Other cost items are spiro-OMeTAD, PCBM and mp-TiO2. Also, spin- coating is a high cost process due to low material usage and should Aim not be used for mass production. It is also evident that the lifetime Investigate material systems where epitaxial growth on a crystalline of the perovskite top cell must match that of the Si bottom cell to template is not required for good cell performance. One such material maintain the same levelised cost of energy. system is organic metal halide perovskite. Highlights Progress Significant progress has been made towards high efficiency tandem • Demonstrated 1 cm2 27.7% four-terminal perovskite/Si solar cells. In terms of four-terminal devices, efficiencies have improved monolithic tandem device. from 23% (split spectrum [Sheng et al. 2015 and Duong et al. 2016]) • Demonstrated 4 cm2 23.0% two-terminal perovskite/Si solar to 24.5% (Peng et al. 2016) in 2016, to 26.4% (Duong et al. 2017) monolithic tandem device. and 26.7% (Quiroz et al. 2018) in 2017, and to 27.7% in late 2019, early 2020 (Duong et al. 2019). The most recent result was achieved • Preliminary costing analysis highlighting high cost items and by the formation of a Ruddlesden–Popper “quasi‐2D” perovskite processes and criteria to achieve cost-effectiveness. phase formed on the surface of a 3D perovskite that passivates the surface defects and significantly improves the performance of the Future Work semitransparent perovskite top cell. • Exploration of alternative carrier transport materials to eliminate optical losses. In terms of monolithic integration for a two-terminal tandem, 22.5% efficiency was reported in 2017 on 1 cm2 (Wu et al. 2017). In 2018, • Stability study and encapsulation strategies for perovskite/Si efficiency was improved to 22.9% and 24.1% (steady state) on 1 cm2 tandem technology, extending to large areas. for perovskite on homojunction Si cells and perovskite on passivating • Complete techno-economic analysis. contact heterojunction Si cells, respectively (Shen et al. 2018). The latter has a cell structure of compact TiO (c-TiO )/mesoporous TiO 2 2 2 References (mp-TiO ) /perovskite/hole transport layer/MoO /IZO/Au fabricated on 2 X DUONG, T., GRANT, D., RAHMAN, S., BLAKERS, A., WEBER, K. J., an n-type PERL cell with front p+ emitter passivated by a SiOx(1.4nm)/ CATCHPOLE, K. R. & WHITE, T. P. 2016. Filterless Spectral Splitting p+ poly-Si(50nm) stack where p-Si is recrystallised a-Si deposited Perovskite-Silicon Tandem System With >23% Calculated Efficiency. by PECVD and doped with boron at 850°C for 30 min. The common IEEE Journal of Photovoltaics, 6, 1432-1439. theme of an interfacial-ITO-free concept (eliminating both optical losses and processing steps) is found in this work and in the other DUONG, T., PHAM, H., KHO, T. C., PHANG, P., FONG, K. C., YAN, D., work for large-area perovskite/Si tandems. YIN, Y., PENG, J., MAHMUD, M. A., GHARIBZADEH, S., NEJAND, B. A., HOSSAIN, I. M., KHAN, M. R., MOZAFFARI, N., WU, Y., SHEN, H., ZHENG, For the large-area demonstration, a perovskite cell with the structure J., MAI, H., LIANG, W., SAMUNDSETT, C., STOCKS, M., MCINTOSH, K., of SnO /perovskite/hole transport layer/MoO /ITO/Ag is fabricated on 2 x ANDERSSON, G. G., LEMMER, U., RICHARDS, B. S., PAETZOLD, U. W., an n-type PERL cell with front p+ emitter. The advantages of SnO are 2 HO-BALLIE, A., LIU, Y., MACDONALD, D., BLAKERS, A., WONG-LEUNG, low processing temperature, and dual function serving as an electron J., WHITE, T., WEBER, K. & CATCHPOLE, K. 2020. High Efficiency transport layer for the perovskite cell and recombination contact with Perovskite-Silicon Tandem Solar Cells: Effect of Surface Coating silicon supported by device modelling (Zheng et al. 2018). The lack of versus Bulk Incorporation of 2D Perovskite. Advanced Energy Materials, lateral conductance thereby localising undesirable shunt effects also 1903553. doi:10.1002/ aenm.201903553. makes it easy to scale up to large areas. After metal grid optimisation and implementing anti-reflection control, an efficiency of 21.8% is achieved on large-area 16 cm2 devices. In 2019, 23.0% has been

37 05 – PP1

DUONG, T., WU, Y., SHEN, H., PENG, J., FU, X., JACOBS, D., WANG, MECHANICALLY STACKED GAAS/SI TANDEM E.-C., KHO, T. C., FONG, K. C., STOCKS, M., FRANKLIN, E., BLAKERS, A., CELLS ZIN, N., MCINTOSH, K., LI, W., CHENG, Y.-B., WHITE, T. P., WEBER, K. & CATCHPOLE, K. 2017. Rubidium Multication Perovskite with Optimized Bandgap for Perovskite-Silicon Tandem with over 26% Efficiency. ANU Team Advanced Energy Materials, 7, 1700228. Prof. Andrew Blakers, Dr Matthew Stocks, Dr Katherine Brook, Dr Osorio Mayon, Mr Chris Jones PENG, J., DUONG, T., ZHOU, X. Z., SHEN, H. P., WU, Y. L., MULMUDI, Academic Partner H. K., WAN, Y. M., ZHONG, D. Y., LI, J. T., TSUZUKI, T., WEBER, K. J., NREL CATCHPOLE, K. R. & WHITE, T. P. 2017. Efficient Indium-Doped TiOx Electron Transport Layers for High-Performance Perovskite Solar Funding Support Cells and Perovskite-Silicon Tandems. Advanced Energy Materials, 7,. ACAP, ARENA 1601768 Aim RAMÍREZ QUIROZ, C. O., SHEN, Y., SALVADOR, M., FORBERICH, K., The ultimate aim of this project is to deliver a mechanically stacked SCHRENKER, N., SPYROPOULOS, G. D., HEUMÜLLER, T., WILKINSON, tandem cell with 32% efficiency. This is being pursued with gallium B., KIRCHARTZ, T., SPIECKER, E., VERLINDEN, P. J., ZHANG, X., GREEN, arsenide (GaAs) top cells with the precursors grown by NREL, with M. A., HO-BAILLIE, A. & BRABEC, C. J. 2018. Balancing electrical GaAs and silicon bottom cells processed at ANU. and optical losses for efficient 4-terminal Si–perovskite solar cells with solution processed percolation electrodes. Journal of Materials Progress Chemistry A, 6, 3583-3592. DOI:10.1039/C7TA10945H. Measured 29.8% efficiency for a mechanically stacked GaAs/Si tandem solar cell at one sun SHENG, R., HO-BAILLIE, A. W. Y., HUANG, S. J., KEEVERS, M., HAO, X. J., JIANG, L. C., CHENG, Y. B. & GREEN, M. A. 2015. Four-Terminal Tandem solar cells with a silicon cell as the bottom cell have been

Tandem Solar Cells Using CH33NH33PbBr33 by Spectrum Splitting. demonstrated to achieve efficiencies above the theoretical limit of Journal of Physical Chemistry Letters, 6, 3931-3934. single silicon cells. However, achieving high efficiencies requires precise optical and electrical control in the complex fabrication WU, Y. L., YAN, D., PENG, J., DUONG, T., WAN, Y. M., PHANG, S. P., procedures and a combination of excellent individual solar cells. GaAs SHEN, H. P., WU, N. D., BARUGKIN, C., FU, X., SURVE, S., GRANT, D., is an excellent top cell for silicon with high and stable efficiencies and WALTER, D., WHITE, T. P., CATCHPOLE, K. R. & WEBER, K. J. 2017. a bandgap sufficiently close to the optimal 1.7 eV for high tandem Monolithic perovskite/silicon-homojunction tandem solar cell with over efficiencies. Figure PP1.3.14 is a schematic of the GaAs top cell and 22% efficiency.Energy & Environmental Science, 10, 2472-2479. interdigitated back contact (IBC) Si tandem stack.

ZHENG, J. H., LAU, C. F. J., MEHRVARZ, H., MA, F. J., JIANG, Y. J., DENG, X. F., SOERIYADI, A., KIM, J., ZHANG, M., HU, L., CUI, X., LEE, D. S., BING, J. M., CHO, Y., CHEN, C., GREEN, M. A., HUANG, S. J. & HO-BAILLIE, A. W. Y. 2018. Large area efficient interface layer free monolithic perovskite/homo-junction-silicon tandem solar cell with over 20% efficiency.Energy & Environmental Science, 11, 2432-2443.

ZHENG, J. H., MEHRVARZ, H., LIAO, C., BING, J. M., CUI, X., LI, Y., GONCALES, V. R., LAU, C. F. J., LEE, D. S., LI, Y., ZHANG, M., KIM, J. C., CHO, Y., CARO, L. G., TANG, S., CHEN, C., HUANG, S. J. & HO-BAILLIE, A. W. Y. 2019. Large-Area 23%-Efficient Monolithic Perovskite/ Homojunction-Silicon Tandem Solar Cell with Enhanced UV Stability Using Down-Shifting Material. ACS Energy Letters, 4, 2623-2631.

ZHENG, J., MEHRVARZ, H., MA, F.-J., LAU, C. F. J., GREEN, M. A., HUANG, S. & HO-BAILLIE, A. W. Y. 2018. 21.8% Efficient Monolithic Perovskite/Homo-Junction-Silicon Tandem Solar Cell on 16 cm². ACS Energy Letters, 3, 2299-2300. PP1.3.14: Schematic of GaAs/Si mechanically stacked tandem.

The measured GaAs cell efficiency was 24.9%, with an open circuit

voltage (VOC) of 1061 mV, fill factor of 85% and short circuit current -2 (JSC) of 27.6 mAcm . The measured silicon cell efficiency in tandem

38 ACAP ANNUAL REPORT 2019

was 4.9% with a V of 660 mV, fill factor of 72% and J of 10.4 OC SC Highlights mAcm-2. This measurement of the performance of both cells in tandem at the ANU laboratories using an LED class "A" solar simulator • Fully measured 29.8% GaAs/Si mechanically stacked tandem at is near the previously reported partially measured and simulated one sun. GaAs/silicon tandem efficiency. The silicon cell is an IBC device that • Fully measured 32.3% GaAs/Si mechanically stacked tandem at was fabricated at ANU by another team led by Professor Andrew seven suns. Blakers, Teng Kho (PhD), Dr Kean Chern Fong, Dr Matthew Stocks and Dr Wensheng Liang in collaboration with Dr Keith McIntosh of PV Future Work Lighthouse. The standalone IBC silicon cell has an efficiency of 25% -2 with a VOC of 717 mV, fill factor of 81% and JSC of 43 mAcm (Franklin • Reduce rear surface reflection from GaAs top cell with optical et al. 2016). The GaAs cell was fabricated from epitaxial III-V layers coatings. grown at the National Renewable Energy Laboratories (NREL) on • Integration of a GaAs/Si tandem micro concentrator with a module GaAs wafers. These GaAs wafers with the grown III-V epitaxial layers efficiency ≥30%. were then processed at ANU into thin, semitransparent GaAs solar cells with a metal grid on the front and back so that sub-bandgap light References can pass through to the bottom silicon cell. This processing included FRANKLIN, E., FONG, K., MCINTOSH, K., FELL, A., BLAKERS, A., removal of the GaAs wafer, singulation of the GaAs cells and addition KHO, T., WALTER, D., WANG, D., ZIN, N., STOCKS, M., WANG, E.-C., of the front and back metal grid and busbars plus a double front anti- GRANT, N., WAN, Y., YANG, Y., ZHANG, X., FENG, Z. & VERLINDEN, P. reflection coating. J. 2016. Design, fabrication and characterisation of a 24.4% efficient Table PP1.3.1: GaAs, silicon and tandem cell parameters at interdigitated back contact solar cell. Progress in Photovoltaics: one sun. Research and Applications, 24, 411-427. https://doi.org/10.1002/ pip.2556. V (V) J (mAcm-2) FF Efficiency GaAs/Si tandem OC SC (%) efficiency (%)

GaAs 1061 27.6 0.85 24.9 KEOGH, W. M., BLAKERS, A. W. & CUEVAS, A. 2004. Constant voltage Si cell 30.0% I–V curve flash tester for solar cells. Solar Energy Materials and Solar Standalone 703 42.0 0.83 24.4 Cells, 81, 183-196. DOI: 10.1016/j.solmat.2003.11.001. In tandem 660 10.4 0.72 4.9

If the top cell is left at open circuit it will emit light with a wavelength equivalent to its bandgap that the bottom cell can absorb. Therefore, care should be taken to bias the top cell at maximum power point or short-circuit while measuring the performance of the bottom cell, otherwise the efficiency of the bottom cell in tandem will be overestimated.

Measured 32.3% efficiency for a mechanically stacked GaAs/Si tandem solar cell at seven suns

The efficiency of the mechanically stacked GaAs/Si tandem solar cell at seven suns was measured using a Flash Tester (Keogh et al. 2004). At seven suns the measured GaAs cell efficiency was 26.3%, with an open circuit voltage (VOC) of 1.115 V, fill factor of 86% and short circuit -2 current (JSC) of 192.6 mAcm . At seven suns the measured silicon cell efficiency in tandem was 6.0% with aOC V of 717 mV, fill factor of -2 81% and JSC of 72.7 mAcm . These results clearly demonstrate the potential of the GaAs/Si tandem for delivering high efficiencies with concentrated light. Table PP1.3.2: GaAs, silicon and tandem cell parameters at seven suns.

V (mV) J (mAcm-2) FF Efficiency GaAs/Si tandem OC SC (%) efficiency (%)

GaAs 1115 192.6 0.86 26.3 32.4% Silicon in tandem 717 73.5 0.81 6.1

39 05 – PP2

PP2 THIN-FILM, THIRD GENERATION AND HYBRID DEVICES

OVERVIEW PP2.2 CZTS SOLAR CELLS

Program Package 2 (PP2) encompasses research into a range of next Thin films of the compound semiconductor Cu2ZnSnS4 (CZTS) are generation cell technologies with the overall goals of demonstrating the focus of PP2.2. In 2019, the team at UNSW set another two world efficiency above 16% for cells of greater than 1 cm2 area and of record efficiencies in CZTS solar cells: a 12.5% efficiency pure selenide demonstrating the feasibility of significantly reduced costs. The CZTSe cell and a Cd-free 10% efficiency CZTS cell. current program is divided into tasks to address the key materials groups: organic photovoltaics (OPV), organic-inorganic hybrid cells, “Earth-abundant” inorganic thin-film materials and the hot topic of PP2.5 PEROVSKITES organic-inorganic perovskites. Good progress has again been made in A new work program was started in 2016, to advance the organohalide 2019 in all target areas. perovskite technologies, addressing scale and durability. Advances in 2019 include demonstrating that cell efficiencies exceeding 22% PP2.1 ORGANIC PHOTOVOLTAIC DEVICES (measured in house) can be routinely achieved on small-area devices; a certified efficiency of 21.6% was achieved on a 1.01 cm2 cell; a new The thin-film organic photovoltaics task (PP2.1) aims to identify and cell design, using a honeycomb-shaped back contact (HBC) electrode address roadblocks in organic photovoltaics to enable cost-effective, was developed for dipole-field-assisted back contact cells at Monash; mass manufacture of modules using this technology. The research and a spin-coating-free method for fabricating quasi-2D perovskite targets lower cost materials and/or processes compared to those films in air, yielding perovskite solar cells with PCEs of up to 16%. of conventional cells or, alternatively, applications such as flexible or partly transparent cells for which conventional cells are not well suited. In 2019, the materials development program led to improved high dielectric constant organic semiconductors, a new design for singlet fission (SF) materials for “third generation” solar cells, and development of active surfactants to stabilise organic semiconductor nanoparticles in industry-relevant solvents. Studies of characterisation and device architectures led to a high performance flexible OPV free of indium tin oxide, ternary blend OPV devices with power conversion efficiencies (PCEs) exceeding 16%, efficient semitransparent OPV devices with good colour rendering index, and matched dye pairs for the world’s best large-area luminescent solar concentrators. The printing and scale-up work generated highlights including the best demonstrated efficiency (13.5% for 0.1 cm2 area) for ternary single- junction slot-die coated cells; the highest efficiency (9.75% for 0.1 cm2 area) in the literature for roll-to-roll slot-die coated cells; and 8.6% for 30 cm2 slot-die coated mini-modules.

40 ACAP ANNUAL REPORT 2019

PP2 THIN-FILM, THIRD GENERATION Our research strengths across the consortium are in the areas of development of process technology for the fabrication of high AND HYBRID DEVICES efficiency devices, electrical and optical characterisations of materials and devices, mathematical modelling and design of new organic photovoltaic (OPV) devices for commercial applications.

ACAP Team We are working on fundamental issues involved in the morphology University of Queensland: Prof. Paul Burn, Dr Hui Jin, Dr Aaron Raynor, control of donor/acceptor and high dielectric constant light absorbing Dr Ravi Nagiri organic films for OPV devices, which includes control of electronic University of Melbourne: Dr David Jones, Prof. Ken Ghiggino, Prof. structure at film interfaces, exciton dissociation and carrier transport Trevor Smith, Dr Jegadesan Subbiah, Dr Calvin Lee, Dr Wallace Wong, properties for efficient photovoltaic operation. We have also employed Dr Valerie Mitchell ab initio (density functional theory – DFT) methods which are valuable University of New South Wales: A/Prof. Ashraf Uddin, Prof. Gavin tools to obtain insight into the charge separation (exciton dissociation) Conibeer, Dr Naveen Kumar Elumalai, Dr Matthew Wright, Dr Vinicius and transport process as well as the photochemical stability of organic R. Goncales molecules – a major challenge for organic PV. This method helps CSIRO: Dr Fiona Scholes, Dr Gerry Wilson, Dr Mei Gao, Régine Chantler, us to find robust and electronically suitable molecules, which has Dr Doojin Vak, Dr Hasitha Weerasinghe, Dr Andrew Scully, Dr Anthony implications for the morphology of the active layer in OPV devices. Chesman, Mr Andrew Faulks The key issues of materials design include engineering the optical gap

Students and energy levels to achieve high JSC and VOC, enhancing planarity to University of Queensland: Xiao Wang, Beta Zenia Poliquit attain high carrier mobility, and materials processability and stability, University of Melbourne: Saghar Masoomi-Godarzi, Nicolau Saker- all of which are interrelated. Neto, Sonam Saxena, Gagandeep Ahluwalia, Jianchao Lin, Marissa Nalenan MATERIALS University of New South Wales: Mushfika Baishakhi Upama, Cheng Xu, Arafat Mahmud, Dian Wang, Faiazul Haque, Haimang Yi and Leiping Aims Duan To this end the materials development program has had the following CSIRO: Na Gyeong An, Gayathri Mathiazhagan, Hyungsu Jang aims: Academic Partners • Creation and understanding the properties of organic University of Electronic Science and Technology of China: Prof. semiconductor materials with a high dielectric constant. Junsheng Yu Central South University, China: Prof. Yingping Zou • New transparent conducting electrodes for flexible substrates. National Centre for Nanoscience and Technology, Beijing, China: Prof. • New singlet fission materials for third generation solar cells. Liming Ding Princeton University, USA: Prof. Gregory Scholes, Dr Kyra Schwarz, • Active interface modifiers to stabilise organic semiconductor Mr Bryan Kudisch, Department of Chemistry, Prof. Barry P. Rand, Mr blend nanoparticles to allow deposition from industrially relevant Saeed-Uz-Zaman Kahn solvents. Karlsruhe Institute of Technology, Germany: Dr Alexander Colsmann, • Controlling morphology development through materials design. Mr Philip Marlow, Mr Lorenz Graf von Reventlow Swansea University, UK: Dr Ardalan Armin, Oskar J. Sandberg, Nasim • Understanding materials performance. Zarrabi Chonbuk National University, Korea: Prof. Seok-In Na Progress Fraunhofer Institute for Solar Energy Systems, Germany: Prof. Andreas High dielectric materials Hinsch Organic semiconductor materials generally have dielectric constants UIsan National Institute of Science and Technology (UNIST), Korea: lower than their inorganic and hybrid counterparts. Consequently, Prof. Jin Young Kim, bound excitons are formed when the organic semiconductor is Macquarie University photoexcited. To generate free charge carriers it is necessary to blend Funding Support one or more donor and acceptor materials with suitable electron ACAP, ARENA, UQ, UoM, UNSW, CSIRO affinities and ionisation potentials to provide sufficient energy to overcome the exciton binding energy. High dielectric constant organic We investigate the use of Earth-abundant materials in next generation semiconductor materials could potentially remove the need for the photovoltaic technologies. We use multidisciplinary knowledge donor/acceptor blend, thus simplifying device fabrication. However, from physics, chemistry and materials science to engineer high the design rules for achieving high dielectric constant organic performance thin-film solar cells with Earth-abundant materials semiconducting materials that are suitable for homojunction organic and characterise their performance. In particular, we fabricate and photovoltaic devices are not yet fully known. UQ has developed a characterise solution-processed organic and perovskite solar cells, both of which have shown great potential for commercial application.

41 05 – PP2

series of donor/acceptor chromophores that vary primarily in the number of dithienothiophene units (one [monomer], two [dimer] and three [trimer]) that are terminated with dicyanovinyl-substituted benzothiadiazole units (Figure PP2.1.1). It has been previously reported that the length of chromophore between the benzothiadiazole units affected the magnitude of the optical frequency dielectric constant (Table PP2.1.1). The aim of the program this year has been to shed more light on the losses that occur when using these materials in homojunction photovoltaic devices.

Monomer Dimer Trimer Figure PP2.1.1: The chemical structures of the glycolated monomer, dimer and trimer.

Table PP2.1.1: Dielectric constants at low and high frequency and Figure PP2.1.2: Normalised film absorption spectrum (UV-Vis), mobilities for the materials shown in Figure PP2.1.1. External Quantum Efficiency (EQE), IQE and IPC of the monomer, dimer and trimer glycolated materials. 2 2 lf* hf# e cm /Vs h cm /Vs To explore the importance of the benzothiadiazole unit a new material Monomer 9.5 3.4 3.0 x 10-6 N/A without the benzothiadiazole moieties (Di-CN-V, Figure PP2.1.3) was 훆 훆 µ µ prepared. For films of comparable thickness (20 nm) to the dimer Dimer 5.0 4.6 3.5 x 10-6 6.0 x 10-10 containing the benzothiadiazole units it was found that the optical Trimer 6.5 4.3 6.5 x 10-6 1.5 x 10-5 frequency dielectric constant was around 25% less, indicating that * At a frequency of 5 MHz. the size of the internal dipole moment and/or polarisation of the 14 # At a frequency of 2 x 10 Hz with a film thickness of around 50 nm. chromophore was important. We also explored the effect of thermal A first step in the analysis was to measure the charge mobilities and solvent annealing on the optical frequency dielectric constant of the materials. It was found that the monomer was essentially Di-CN-V and observed no strong effects. unipolar, transporting essentially only electrons. The dimer still had a considerable imbalance in hole and electron mobilities (≈ four orders of magnitude), with the electron mobility being the larger. However, addition of the third dithienothiophene into the chromophore led to the trimer having almost balanced hole and electron transport. One of the key features of the dimer and trimer is that the shape of the external quantum efficiencies mirrors its absorption spectra (Figure PP2.1.2). The fact that a photocurrent is generated near the optical gap means that excess energy is not required for exciton separation and this has been ascribed to the higher optical frequency dielectric constant of these materials. An interesting feature of the optical frequency dielectric constant is that it was film thickness dependent. Figure PP2.1.3: The dimer Di-CN-V that does not have the benzothiadiazole units. For example, the dimer was found to have an optical frequency dielectric constant of 5.8 for a 20 nm thick film, with it dropping to New singlet fission materials for “third generation” solar cells around 4.6 for a film that was 100 nm thick. However, the external UoM has been developing new singlet fission (SF) materials for quantum efficiency was found to be still lower than what is achievable “third generation” solar cells. Theoretical studies have suggested in a bulk heterojunction device and using a variety of measurements that incorporation of SF materials into solar cells could increase the (internal quantum efficiency [IQE] and light intensity dependence theoretical maximum power conversion efficiency (PCE) to 45%, of photocurrent [IPC]) we have been able to identify some of the significantly reducing the cost per watt of delivered power. More sources of losses (optical and recombination) (Figure PP2.1.2). We recent studies have suggested coupling efficient SF materials to the currently believe that recombination is not the major reason for the low best silicon solar cells could improve their PCE to around 38%. UoM photoconversion efficiencies of the homojunction devices, but rather has designed a new class of solid state singlet fission materials charge generation losses account for more than 90% of the losses. using self-association to preorganise the organic semiconductors Further work therefore needs to be undertaken to determine the to enhance singlet fission and have reached up to a 170% SF yield in structural features that govern the magnitude of the optical frequency the initial proof-of-principle studies. In these studies, a strongly self- dielectric constant. organising hexabenzocoronene core in FHBC has been used to drive self-assembly, see Figure PP2.1.4. UoM is currently designing energy matched SF materials to couple with silicon solar cells.

42 ACAP ANNUAL REPORT 2019

Figure PP2.1.4: UoM has been leading the development of solid state singlet fission materials for inclusion in “third generation” solar cells. Use of strong self-association through p-p stacking of hexabenzocoronene (FHBC) cores leads to ideal packing to enhance singlet fission.

In a second study a series of substituted perylenediimides (Figure PP2.1.5) have been examined for their ability to promote SF. Single crystal structures of these materials have been obtained allowing a detailed structure-property analysis to be completed using the crystal structures to map SF yield against molecular interactions. In summary, the closer the interaction between molecules and the greater the asymmetry of the orbital interactions the greater the SF yield. This will allow design of better SF materials.

Figure PP2.1.5: A series of four perylene diimides have been synthesised and single crystal structures have been determined. The imide R group has been modified, leading to PDI1-PDI4 with single crystal structures a-d respectively. PDI1-PDI4 then have different molecular interactions, however the core chromophore energies are not changed. A simplified graphic demonstrating the singlet fission process is shown in A and B, while the UV-Vis absorption and emission spectra are shown in the inset.

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Active interface modifiers to stabilise organic semiconductor blend UoM has designed a series of active surfactants where manipulation nanoparticles to allow deposition from industrially relevant solvents of the electric double layer is possible in solution, allowing for formation of stable nanoparticle dispersions, however the chemistry One of the issues raised in the development of organic solar cells is can be reversed under mild heating effectively removing the surfactant the use of toxic chlorinated solvents for processing the active layers from the deposited thin film. By exploiting the chemistry of the reaction under laboratory conditions. UoM has run an extended program of pyridine with weak acids, like acetic acid, we can from a pyridinium looking at the translation of OPV device assembly using industrially acetate, which acts like a surfactant in solution generating a stable relevant solvent systems. One approach is to form nanoparticles of electric double layer around nanoparticle dispersions. However, under the organic semiconductor blends in solvents such as water, alcohols mild heating to around 120°C the reaction is reversed and the acetic or ketones that are currently used in printing industries. However, acid can be removed from the film removing the surfactant (Figure inclusion of surfactants to stabilise the nanoparticles normally leads PP2.1.6). By attaching a pyridine to the end of a donor polymer, to a significant drop in solar cell performance, as the surfactant P3HT in this case as proof of principle, we can enhance the impact remains in the active layer hindering charge generation, transport and of the surfactant and effectively stabilise organic semiconductor collection. On the other hand, although nanoparticles formed in the nanoparticles with as little as 0.025 wt% inclusion of pyridine with no absence of surfactants can give excellent device performance, the impact on the final device performance, even though the solar cell nanoparticle suspensions are often not stable for extended periods active layers were deposited from methanol. Analysis has shown that leading to difficulties in reproducibility over time. there is no residual acid present in the active thin films to the limits of detection of UV-Vis absorption measurements.

Figure PP2.1.6: A series of active surfactants were synthesised to manipulate the electric double layer around organic semiconductor nanoparticles in solution to stabilise the nanoparticle dispersions. The three precursor polymers were end-capped with either, (a) benzoic acid (P3HT-COOH) to form a negatively charged nanoparticle, (b) pyridine (P3HT-Py) to form a positively charged nanoparticle, or (c) an ethylene glycol side-chain (P3HT-TEG) to form a neutral nanoparticle for comparison. Compounds P3HT-COOH and P3HT-Py form pyridinium acetates in methanol solution on reaction with pyridine or acetic acid, respectively, allowing reversible stabilisation of the nanoparticles through electric double layer formation.

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Controlling morphology development through materials design and is able to maintain device performance even with thick active layers films (for OPV up to 500 nm). In conjunction with collaborators UoM has completed work in collaboration with Georgia Institute of at Princeton University and the University of Swansea a detailed Technology examining the impact of side-chain engineering in p-type understanding of the device under illumination has been developed. organic semiconductors on morphology development in spin-cast Surprisingly, after solvent vapour annealing of the active layer OPV OPV active layers. In this work it has been shown that subtle variations device performance is enhanced from around 4.5% PCE to around in alkyl chain substitution modifies the material solubility thereby 10% PCE, a performance that is maintained even in films of up to impacting the relative point of crystallite nucleation, nucleation density 320 nm thickness (Figure PP2.1.7). Extensive spectroscopic studies and crystal growth. High solubility is required to delay crystallisation using ultrafast laser spectroscopy has indicated a charge build-up in and maximise phase separation. the crystalline domains in the thin film. These charges lead to a very Understanding materials performance intense internal electric field which shifts the absorption and emission spectra allowing analysis. This charge build-up is unexpected as To improve materials design a detailed understanding of materials there is no obvious dielectric holding the charges apart or shielding performance is often required. UoM has previously reported the the charges. However, this process leads to a suppression of charge excellent performance of OPV devices containing a class of p-type recombination in these thin films, and the suppression of charge organic semiconductors designated as the benzodithiophene-X- recombination is the largest recorded for materials of this class. It is thiophene-rhodanine (BXR) materials, of which benzodithiophene- expected that this understanding will lead to new materials designs for quaterthiophene-rhodanine (BQR) demonstrates the best performance, greater enhancement in performance.

Figure PP2.1.7: Spectroscopic studies of charge recombination in BQR:PC71BM thin films. The J-V curves for as-cast and solvent vapour annealed (SVA) OPV devices are shown in (a) and (c), a schematic of the developed morphology in the thin films is shown in (b) and (d) along with a schematic indicating suppression of charge regeneration, as indicated by the lack of formation of triplet excitons. The proposed mechanism of charge pooling is indicated in (e) with a demonstration of the change in electro-absorption (EA) recorded as a function of time.

This leads to an extensive capacitive charge build-up in BQR:PC71BM thin films.

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Highlights WANG, X., JIN, H., NAGIRI, R. C. R., POLIQUIT, B. Z. L., SUBBIAH, J., JONES, D. J., KOPIDAKIS, N., BURN, P. L. & YU, J. 2019. Flexible ITO‐ • High dielectric constant organic semiconductors demonstrate Free Organic Photovoltaics on Ultra‐Thin Flexible Glass Substrates reduced energy required for exciton harvesting. with High Efficiency and Improved Stability.Solar RRL, 3, 1800286. • A new design for singlet fission (SF) materials for “third WANG, X., ZHANG, D., JIN, H., POLIQUIT, B. Z., PHILIPPA, B., NAGIRI, generation” solar cells has been described based on self- R. C. R., SUBBIAH, J., JONES, D. J., REN, W., DU, J., BURN, P. L. & YU, J. association to order chromophores leading to high SF efficiency. 2019. Graphene-Based Transparent Conducting Electrodes for High • SF studies on a series of perylenediimides has allowed structure- Efficiency Flexible Organic Photovoltaics: Elucidating the Source of the property relationships to be extracted, which should feed into Power Losses. Solar RRL, 3, 1900042. improved SF materials design. ZHANG, D., DU, J., HONG, Y. L., ZHANG, W., WANG, X., JIN, H., BURN, • Active surfactants have been developed to stabilise organic P. L., YU, J., CHEN, M., SUN, D. M., LI, M., LIU, L., MA, L. P., CHENG, H. semiconductor nanoparticles in industry-relevant solvents. M. & REN, W. 2019. A Double Support Layer for Facile Clean Transfer of Two-Dimensional Materials for High-Performance Electronic and Future Work Optoelectronic Devices. ACS Nano, 13, 5513-5522. • Design new classes of high dielectric constant materials to ZHANG, S., HOSSEINI, S. M., GUNDER, R., PETSIUK, A., CAPRIOGLIO, overcome the limitations of charge generation. P., WOLFF, C. M., SHOAEE, S., MEREDITH, P., SCHORR, S., UNOLD, T., • Use design criteria developed for improved SF materials to BURN, P. L., NEHER, D. & STOLTERFOHT, M. 2019. The Role of Bulk energy match SF materials to silicon solar cells. and Interface Recombination in High-Efficiency Low-Dimensional Perovskite Solar Cells. Advanced Materials, 31, 1901090. a • Use our understanding of reversible surfactant formation to develop generic stabilisers for high performance organic CHARACTERISATION AND DEVICE ARCHITECTURES semiconductor blends. Aims

References • Creation of ITO-free organic solar cells (including large area).

CHANDRASEKHARAN, A., JIN, H., STOLTERFOHT, M., GANN, • OPV deposition from industrially relevant solvents. E., MCNEILL, C. R., HAMBSCH, M. & BURN, P. L. 2019. • Ternary blend device architectures. 9,9′-Bifluorenylidene-diketopyrrolopyrrole donors for non-polymeric solution processed solar cells. Synthetic Metals, 250, 79-87. • Use of non-fullerene acceptors.

LEE, C. J., JRADI, F. M., MITCHELL, V. D., WHITE, J., MCNEILL, C. R., • Semitransparent OPV devices for window applications. SUBBIAH, J., MARDER, S. & JONES, D. J. 2020. A structural study of • Organic-organic and organic-perovskite tandem solar cells for p-type A–D–A oligothiophenes: effects of regioregular alkyl sidechains high efficiency devices for commercial application. on annealing processes and photovoltaic performances. Journal of Materials Chemistry C, 8, 567-580. • Encapsulation of OPV devices.

LEE, C., MITCHELL, V. D., WHITE, J., JIAO, X., MCNEILL, C. R., SUBBIAH, • Luminescent solar concentrators (LSCs) – developing high J. & JONES, D. J. 2019. Solubilizing core modifications on high- efficiency dye pairs. performing benzodithiophene-based molecular semiconductors and ITO free flexible solar cells their influences on film nanostructure and photovoltaic performance. Journal of Materials Chemistry A, 7, 6312-6326. The ability for organic solar cells to have a conformable shape makes them useful for a broad range of applications, including building MASOOMI‐GODARZI, S., LIU, M., TACHIBANA, Y., MITCHELL, V. D., integration. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) GOERIGK, L., GHIGGINO, K. P., SMITH, T. A. & JONES, D. J. 2019. Liquid (PEDOT:PSS) and indium tin oxide (ITO) have been used on plastic Crystallinity as a Self‐Assembly Motif for High‐Efficiency, Solution‐ substrates such as poly(ethylene terephthalate) and poly(ethylene Processed, Solid‐State Singlet Fission Materials. Advanced Energy napthalate) (PET/PEN) as transparent conductive electrodes (TCEs) Materials, 9, 1901069. for flexible devices. The acidity of PEDOT:PSS can corrode the ester- SAJJAD, M. T., ZHANG, Y., GERAGHTY, P. B., MITCHELL, V. D., based plastic substrates and cause device degradation, whereas ITO RUSECKAS, A., BLASZCZYK, O., JONES, D. J. & SAMUEL, I. D. W. 2019. is brittle and when used on flexible substrates is prone to cracking. UQ Tailoring exciton diffusion and domain size in photovoltaic small has explored the use of high conductivity PEDOT:PSS [PEDOT:PSS = molecules by annealing. Journal of Materials Chemistry C, 7, 7922-7928. poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] on 100 µm- thick flexible Corning® Willow® Glass (supplied by Corning Research SCHWARZ, K. N., GERAGHTY, P. B., MITCHELL, V. D., KHAN, S. U., & Development Corporation) substrates as the anode for organic SANDBERG, O. J., ZARRABI, N., KUDISCH, B., SUBBIAH, J., SMITH, T. A., solar cells. The PEDOT:PSS TCE was built up by sequential deposition RAND, B. P., ARMIN, A., SCHOLES, G. D., JONES, D. J. & GHIGGINO, K. of the polymer solution followed by solvent and thermal annealing. P. 2020. Reduced Recombination and Capacitor-like Charge Buildup in We found that there was a clear trade-off between transmission an Organic Heterojunction. Journal of the American Chemical Society, and sheet resistance with the values changing depending on the ASAP DOI: 10.1021/jacs.9b12526.

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number of PEDOT:PSS depositions. The best PEDOT:PSS TCE Use of non-fullerene acceptors anode on flexible glass had a sheet resistance of ~30 Ω/sq and a One of the driving forces in the improvement of organic solar cells transmission of ~77% at 550 nm with a broad transmission window has been the introduction of high performance n-type organic between 300 nm and 800 nm. The addition of a molybdenum oxide semiconductors to replace the ubiquitous functionalised fullerenes (MoO ) interlayer between the PEDOT:PSS and light-absorbing layer x like PC BM, an area in which UQ was one of the pioneers. Non- was found to control the work function and surface energy. The 71 fullerene acceptors like Y6 (Figure PP2.1.8) have shown remarkable best PEDOT:PSS on flexible glass-based organic solar cells with an efficiencies when used as the acceptor in bulk heterojunction OPV architecture of glass/PEDOT:PSS/MoO /BQR:PC BM/Ca/Al [BQR = x 71 devices. As UoM has developed some of the best small molecule (5Z,5'Z)‐5,5'‐[(5''',5'''''''‐{4,8‐bis[5‐(2‐ethylhexyl)‐4‐n-hexylthiophen‐2‐yl] donors, for example see Figure PP2.1.8, it may be expected that benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl}bis{3',3'',3'''‐tri-n-hexyl‐ improved performance could be seen when paired with new non- [2,2':5',2'':5'',2'''‐quaterthiophene]‐5''',5‐diyl})bis(methanylylidene)]bis[3‐n- fullerene acceptors. Ternary blend devices, combining UoM small hexyl‐2‐thioxothiazolidin‐4‐one] and PC71BM = [6,6]-phenyl-C -butyric 71 molecule donors BTR, BTR-TE and BTR-TIPS with Y6, have been tested acid methyl ester] had a power conversion efficiency (PCE) of 8.0%, and a summary of the results is listed in Table PP2.1.2. The use of Y6 which was higher than devices comprising ITO or PEDOT:PSS TCEs on significantly enhanced the performance of BTR and BTR analogue PEN, which had PCEs of 6.4% and 5.8%, respectively. The efficiency of containing devices. However, the fill factor (FF) remained relatively the best device was also competitive of equivalent devices comprised low at around 67% indicating charge collection was an issue, which of commercial ITO that had PCEs of 9.0±0.2%. We also show that the was addressed in ternary blend devices described in the next section ultra-thin glass devices can be scaled, with the 1.6 cm2 flexible cells (manuscript under preparation). having an efficiency of 5.2%. A preliminary stability study indicated that the methanol-treated PEDOT:PSS on flexible glass had the best shelf- life pointing a way forward for the development of commercially viable organic solar cells that avoid ITO as the TCE.

Figure PP2.1.8: OPV devices containing UoM developed small molecule p-type organic semiconductors (donors), chemical structures of BTR, BTR- TE and BTR-TIPS, device architecture, chemical structure of non-fullerene acceptor Y6, and typical J-V curves for blend devices.

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Table PP2.1.2: Summary of typical device performance combining (D1:D2:A) or donor:acceptor:acceptor (D:A1:A2) combinations, can give the non-fullerene acceptor Y6 with BTR analogues. a higher device performance than its binary blend counterpart. A small amount of the third component (D or A ) is added into a binary blend Normal Jsc Voc FF PCE 2 2 and can have various roles in the TOSCs. Polymer acceptors, small Geometry (mAcm-2) (V) (%) (%) molecular non-fullerene and fullerene acceptor materials are widely BTR-TIPS:Y6 (1:0.6) 18.5 0.83 54 8.3 (8.1) used as the third component in the ternary strategy. BTR:Y6 (1:0.6) 22.1 0.83 61 11.1 (10.8) UNSW has designed and developed a new ternary blend inverted BTR-TE:Y6 (1:0.6 ) 23.4 0.84 67 13.1 (12.9) OPV device to address the challenge of improving the device stability Ternary blend device architectures and efficiency by interface engineering buffer layers. In line with this approach, we achieved PTB7-Th:COi8DFIC:PC BM-based OPV The ternary organic solar cell is a promising approach towards high 71 devices with a high PCE of ~14% complemented with good device power conversion efficiency OPV devices. Ternary OSCs (TOSCs) lifetime of several months without any encapsulation in ambient is an approach to extend the absorption spectrum of organic conditions. A schematic diagram of the device structure, energy level semiconductors into the near IR region and enhance the light diagram, and chemical structures of PTB7-Th, COi8DFIC and PC BM harvesting properties as well as improve the PCE. Ternary blends, 71 and J-V curves of cells are shown in Figure PP2.1.9. which contain three organic materials; either donor:donor:acceptor

Figure PP2.1.9: (a) Schematic diagram of the ternary blend device structure. (b) Chemical structures of the donor material PTB7-Th and

acceptor materials COi8DFIC and PC71BM. (c) The normalised absorbance spectra of donor material PTB7-Th and acceptor materials COi8DFIC and PC71BM. (d) Energy levels of the donor material PTB7-Th and acceptor materials COi8DFIC and PC71BM (Leiping Duan, et al., DOI: 10.1039/c9qm00130a).

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Investigation of photo-degradation

A challenge for OPV devices is the initial photo-degradation of the cells known as “burn-in” that can sometimes be observed. In some cases up to 25% of the OPV efficiency degrades during the first few hours of device operation under illumination. To address this issue, UNSW has studied photo-degradation of inverted OPV devices with ZnO and Al doped ZO (AZO) as an electron transport layer (ETL) over a time period of 5 hours during which the degradation is most severe for the materials investigated. COi8DFIC is a newly developed efficient non-fullerene acceptor material that exhibits strong near infrared range (NIR) light absorption. Here, we present the first systematic research on the burn-in photo-degradation of a COi8DFIC-based ternary organic solar cell with the active layer consisting of a PTB7-

Th:COi8DFIC:PC71BM blend and compared it with its corresponding binary organic solar cells. The as-fabricated device was characterised immediately after the last fabrication step and labelled as a “fresh device”. The fresh device was then exposed to continuous one-sun illumination with the test period of 5 hours. Measurements with a regular interval of 1 hour were conducted for those devices. Devices after burn-in photo-degradation of 5 hours are called “Photo-degraded devices” in the following discussion. The current density to voltage (J-V) curves of all devices measured under one-sun test conditions (AM 1.5 G, 100 mW cm-2), at room temperature, are shown in Figure PP2.1.10 and the data tabulated in Table PP2.1.3. As a result, PTB7- Th:COi8DFIC-based binary and ternary organic solar cells exhibit a similar degradation mechanism, which is very different from the burn- in photo-degradation mechanism in PTB7-Th:PC71BM-based binary organic solar cells. The burn-in photo-degradation in PTB7-Th:PC71BM binary organic solar cells is found to be dominated by an induced non-radiative carrier recombination, poor energy transfer and low exciton dissociation. However, the burn-in photo-degradation in PTB7- Th:COi8DFIC-based binary and ternary organic solar cells is found to be more related to the degradation-induced high shunt resistance.

Figure PP2.1.10: (a) Current-voltage characteristics of the fabricated binary and ternary, and fresh and photo-degraded devices at room temperature under one-sun test conditions (AM1.5 G illumination at 100 mW cm-2) for 5 hours. (b) External quantum efficiency (EQE) spectra for binary and ternary, fresh and photo-degraded devices. (c) Absorption spectra of binary and ternary, fresh and photo-degraded devices.

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Table PP2.1.3: Photovoltaic parameters including VOC, JSC, FF and PCE of binary and ternary, fresh and photo-degraded devices measured at room temperature under one-sun test conditions (AM1.5 G illumination at 100 mW cm-2) obtained from at least 5 devices.

-1 Device VOC (V) JSC (mAcm ) FF Ave PCE (%)

Fresh PTB7-Th:PC71BM 0.819 ± 0.001 15.26 ± 0.26 0.62 ± 0.01 7.74 ± 0.26 Photo-degraded PTB7-Th:PC71BM 0.775 ± 0.006 13.08 ± 0.69 0.52 ± 0.03 5.28 ± 0.39 Fresh PTB7-Th:COi8DFIC 0.701 ± 0.002 22.32 ± 1.04 0.60 ± 0.01 9.39 ± 0.47 Photo-degraded PTB7-Th:COi8DFIC 0.606 ± 0.022 16.99 ± 1.17 0.41 ± 0.04 4.24 ± 0.75 Fresh PTB7-Th:COi8DFIC: PC71BM 0.711 ± 0.002 25.13 ± 0.61 0.68 ± 0.01 12.06 ± 0.29 Photo-degraded PTB7-Th:COi8DFIC:PC71BM 0.686 ± 0.013 21.51 ± 0.80 0.52 ± 0.03 7.73 ± 0.46

UoM has also been looking at ternary blend devices using in-house developed BTR and BTR analogues BTR-TE and BTR-TIPS (see Figure PP2.1.8 for structures). It has been postulated in the literature that inclusion of small amounts of a third component can significantly modify the thin-film morphology improving charge extraction. A summary of device data collected after inclusion of BTR analogues in ternary blend films is given in Table PP2.1.4, while the device architecture, structure of the non-fullerene acceptor Y6, and typical J-V curves are shown in Figure PP2.1.11. The PCE improves to 16% on addition of BTR small molecules with an enhancement of JSC, FF and

VOC (manuscript under preparation).

Figure PP2.1.11: Ternary blend devices containing UoM developed small molecule p-type organic semiconductors (donors, see Figure PP2.1.8). Device architecture, chemical structure of non-fullerene, acceptor Y6, and typical J-V curves for ternary blend devices.

Table PP2.1.4: Summary of data collected for typical ternary blend devices containing the non-fullerene acceptor Y6 with BTR analogues. Jsc Voc FF PCE Normal Geometry (mA cm-2) (V) (%) (%) PM6:Y6 (1:1.2) 24.2 0.83 75 15.1 PM6:Y6 (0.9:0.1:1.2) (BTR 10%) 24.6 0.84 76 15.7 PM6:Y6 (0.9:0.1:1.2) (BTR-TE 10%) 24.5 0.84 78 16.0

PM6:Y6 (0.9:0.1:1.2) (BTR-TIPS 10%) 24.1 0.82 71 14.0

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Semitransparent organic solar cells

UNSW has been examining semitransparent organic solar cells (STOSCs) with neutral colour perception based on a PffBT4T-

2OD:PC71BM thick active layer for the first time. The active layer thickness of the devices has been optimised from 300 nm to 120 nm to obtain the best performance. As a result, semitransparent devices showed a decreasing PCE and an increasing average visible transmittance (AVT) with the reduction of the active layer thickness. All semitransparent devices showed an excellent colour rendering index (CRI) above 90. The semitransparent device with an active layer thickness of 250 nm exhibits the best performance among all devices which corresponds to a considerable PCE of 6.6%, AVT of

16.3% and CRI of 90.7. This reveals that the PffBT4T-2OD:PC71BM- based semitransparent devices with a thick active layer are suitable for application in building windows in terms of colour perception and large-scale fabrication. The PffBT4T-2OD:PC71BM-based STOSCs Figure PP2.1.12: (a) The schematic diagram of the inverted device structure of ITO/ZnO/PffBT4T-2OD:PC BM/MoO /Ag used in this were fabricated with an inverted device structure of ITO/ZnO/active 71 3 study. (b) Chemical structures of the conjugated polymer donor layer/MoO /Ag as shown in Figure PP2.1.12(a). 3 PffBT4T-2OD and fullerene acceptor PC71BM. (c) Energy levels for the conjugated polymer donor PffBT4T-2OD and fullerene acceptor The J-V curves of the optimised opaque device compared with all PC71BM. semitransparent devices are shown in figure PP2.1.13(a). Figure PP2.1.13(b) depicts the relationship between the PCE and AVT versus the active layer thickness. It is obvious to see that all devices possess a similar Voc value of around 0.76 V, which indicates that the use of the transparent electrode and the reduction of active layer thickness have less effect on the voltage performance of the device.

Figure PP2.1.13: (a) Current density-voltage (J-V) curves for the opaque device and semitransparent devices with different active layer thicknesses from 300 nm to 120 nm. (b) The relationship between the power conversion efficiency (PCE) and average visible transmittance (AVT) versus the active layer thickness.

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The colour coordinates of all semitransparent (STOSC) devices with different active layer thicknesses are plotted in the CIE colour map, as shown in Figure PP2.1.14. It is obvious to see that all STOSCs fabricated in this study are located within the white region and close to the achromatic point [(xD65, yD65) ¼ (0.3127, 0.3290)] on the CIE chromaticity diagram which demonstrated that these devices can transmit high quality visible light with a near-white sensation to the human eye. The Colour Rendering Index (CRI) is an objective indicator of the colour rendering properties of a semitransparent device. It is expressed as a percentage, indicating the ability of a device to accurately present an image compared to a perfect light source such as daylight. A CRI close to 100 is desirable for semitransparent devices as it can correctly distinguish the colour of an object and hence satisfy the natural lighting purposes. To calculate the CRI, according to the CIE 13.3 1995 protocol, the (x, y) coordinates from the CIE 1931 colour space can be converted to (u, v) coordinated in the CIE 1960 colour space, and then modified according to the eight test colour samples. Each test sample should provide a special CRI.

Figure PP2.1.14: Representation of the colour coordinates (x, y) of all semitransparent devices with different active layer thicknesses from 300 nm to 120 nm.

Luminescent solar concentrators (LSCs) – developing high efficiency dye pairs

Luminescent solar concentrators (LSCs) use light-absorbing dyes to collect and channel light to solar cells positioned at the edges of the collector, that is, a window or cladding. The window acts as a collector and waveguide, concentrating the light at the window’s edge to potentially improve the efficiency of the solar cells, and reducing the area of solar cells required. UoM has led the way in developing tailored dye pairs to significantly reduce losses in the concentrator. Using matched pairs of perylene diimide dyes, coupled to printed perovskite solar cells UoM has demonstrated the best LSC efficiency gains for large-area concentrators (400 cm2 area, flux gain 7.4, EQE 14.8%, PCE 2.9% under one-sun illumination) (Figure PP2.1.15). This is a major step forward in this field. Further work where the emitter is selectively aligned to increase the percentage of light that is guided to Figure PP2.1.15: A high performance large-area luminescence the attached solar cell indicates a viable route to further enhance the solar concentrator (LSC) incorporating a donor-emitter fluorophore system. The donor-emitter pair reduce reabsorption losses. The dye efficiency of LSCs. pairs can be printed on a substrate (Perspex shown) that acts as a waveguide channelling the light to the substrate edge. Solar cells can then be affixed to the edge to collect concentrated light (not shown).

52 ACAP ANNUAL REPORT 2019

Highlights UPAMA, M. B., ELUMALAI, N. K., MAHMUD, M. A., WANG, D., HAQUE, F., GONÇALES, V. R., GOODING, J. J., WRIGHT, M., XU, C. & UDDIN, A. • Developed a high performance ITO-free flexible OPV. 2017. Role of fullerene electron transport layer on the morphology and • Developed high performance all small molecule OPV devices optoelectronic properties of perovskite solar cells. Organic Electronics, combining BTR-TE with Y6 to give over 13% PCE. 50, 279-289.

• Morphology control of donor and acceptor systems for different UPAMA, M. B., ELUMALAI, N. K., MAHMUD, M. A., WRIGHT, M., WANG, donor/acceptor-based OPV devices. D., XU, C., HAQUE, F., CHAN, K. H. & UDDIN, A. 2017. Interfacial engineering of electron transport layer using Caesium Iodide for • Developed ternary blend OPV devices with PCEs of >16% using efficient and stable organic solar cells. Applied Surface Science, 416, in-house materials. 834-844. • Understand the mechanism of initial photo-degradation of OPV UPAMA, M. B., MAHMUD, M. A., CONIBEER, G. & UDDIN, A. 2019. devices. Trendsetters in High‐Efficiency Organic Solar Cells: Toward 20% Power • Improve the OPV device efficiency and stability by interface Conversion Efficiency.Solar RRL, 4. 1900342. engineering of buffer layers. UPAMA, M. B., MAHMUD, M. A., YI, H., ELUMALAI, N. K., CONIBEER, • Developed highly efficient semitransparent OPV devices with good G., WANG, D., XU, C. & UDDIN, A. 2019. Low-temperature processed colour rendering index and transparency. efficient and colourful semitransparent perovskite solar cells for building integration and tandem applications. Organic Electronics, 65, • Developed matched dye pairs for the world’s best large-area 401-411. luminescent solar concentrators. UPAMA, M. B., WRIGHT, M., ELUMALAI, N. K., MAHMUD, M. A., WANG, D., XU, C. & UDDIN, A. 2017. High-Efficiency Semitransparent Organic Future Work Solar Cells with Non-Fullerene Acceptor for Window Application. ACS • Continued investigation into morphology control of donor/ Photonics, 4, 2327-2334. acceptor materials in bulk heterojunction solar cells. UPAMA, M. B., WRIGHT, M., MAHMUD, M. A., ELUMALAI, N. K., • Extended lifetimes study and degradation mechanism in OPV MAHBOUBI SOUFIANI, A., WANG, D., XU, C. & UDDIN, A. 2017. Photo- devices. degradation of high efficiency fullerene-free polymer solar cells. Nanoscale, 9, 18788-18797 • Develop high efficiency ternary blend OPV devices. UPAMA, M. B., WRIGHT, M., PUTHEN-VEETTIL, B., ELUMALAI, N. K., • Develop highly efficient semitransparent OPV devices with high MAHMUD, M. A., WANG, D., CHAN, K. H., XU, C., HAQUE, F. & UDDIN, A. AVT for window application. 2016. Analysis of burn-in photo degradation in low bandgap polymer • Develop high efficiency organic-organic and organic-perovskite PTB7 using photothermal deflection spectroscopy. RSC Advances, 6, tandem solar cells. 103899-103904.

• Enhance LSC efficiency through dye design and dye alignment. ZHANG, B., GAO, C., SOLEIMANINEJAD, H., WHITE, J. M., SMITH, T. A., JONES, D. J., GHIGGINO, K. P. & WONG, W. W. H. 2019. Highly Efficient References Luminescent Solar Concentrators by Selective Alignment of Donor– Emitter Fluorophores. Chemistry of Materials, 31, 3001-3008. DUAN, L., MENG, X., ZHANG, Y., YI, H., JIN, K., HAQUE, F., XU, C., XIAO, Z., DING, L. & UDDIN, A. 2019. Comparative analysis of burn-in photo- ZHANG, B., ZHAO, P., WILSON, L. J., SUBBIAH, J., YANG, H., degradation in non-fullerene COi8DFIC acceptor based high-efficiency MULVANEY, P., JONES, D. J., GHIGGINO, K. P. & WONG, W. W. H. 2019. ternary organic solar cells. Materials Chemistry Frontiers, 3, 1085-1096. High-Performance Large-Area Luminescence Solar Concentrator Incorporating a Donor–Emitter Fluorophore System. ACS Energy DUAN, L., XU, C., YI, H., UPAMA, M. B., MAHMUD, M. A., WANG, D., Letters, 4, 1839-1844. HAQUE, F. & UDDIN, A. 2019. Non-Fullerene-Derivative-Dependent Dielectric Properties in High-Performance Ternary Organic Solar Cells. PRINTING AND SCALE-UP IEEE Journal of Photovoltaics, 9, 1031-1039.

DUAN, L., YI, H., ZHANG, Y., HAQUE, F., XU, C. & UDDIN, A. 2019. Aims Comparative study of light- and thermal-induced degradation for both Recently, TOSCs containing three absorption-complementary materials fullerene and non-fullerene-based organic solar cells. Sustainable (one donor/two acceptors or two donors/one acceptor) have attracted Energy & Fuels, 3, 723-735. considerable attention for achieving improved power conversion DUAN, L., ZHANG, Y., YI, H., HAQUE, F., DENG, R., GUAN, H., ZOU, Y. & efficiencies (PCEs). Ternary solar cells are capable of harvesting UDDIN, A. 2019. Trade‐Off between Exciton Dissociation and Carrier a greater portion of the solar spectrum, and have demonstrated Recombination and Dielectric Properties in Y6‐Sensitized Nonfullerene better performance than binary OSCs. To demonstrate that these Ternary Organic Solar Cells. Energy Technology, 8, 1900924. outstanding efficiencies are not limited to laboratory-scale devices,

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significant efforts were made to apply scalable slot-die and roll-to- roll (R2R) continuous processes developed at CSIRO to address the challenges associated with the scale-up of these printed solar films.

These activities include:

• Optimising slot-die coating using higher performance, commercially available materials.

• Screening commercially available acceptors for ternary blends.

• Machine learning–assisted optimisation of OPVs from in situ blending during R2R slot-die coating. Progress Figure PP2.1.17: Comparisons of PCEs of slot-die coated TOSCs

Optimising slot-die coating using higher performance, commercially based at (a) different concentrations of PTB7-Th:PC71BM:COi8DFIC, available materials (b) DIO volume, and (c) thermal annealing temperatures. (d) Representative J-V curve of slot-die coated TOSCs that are pristine, A novel narrow optical gap non-fullerene acceptor, COi8DFIC, which use DIO, and use DIO/annealing and (e,f) their corresponding EQE has strong NIR absorption, has previously been incorporated into a and IQE measurements, respectively. ternary OSC containing the one donor/two acceptor system of PTB7- To demonstrate the scalability of this method, similar conditions Th, PC BM, and COi DFIC, and was reported to have a PCE of 14%, a 71 8 were used to fabricate series connected mini-modules, resulting higher performance than PTB7-Th:COi8DFIC (1:1) binary OSCs (12%) in an impressive PCE of 8.6% on an ITO/glass substrate (30 cm2) (Xiao et al. 2017a,b). In order to demonstrate the lab-to-fab translation (Figure PP2.1.18(a)). More importantly, the slot-die deposition of this ternary blend from size-limited spin-coating in a glove box to a conditions developed by the batch process were fully translated to scalable slot-die coating process under ambient conditions, a bench- R2R processing equipment, resulting in R2R-processed flexible OSCs top slot-die coater was employed. This work was performed as part of with a PCE of 9.6% (0.1 cm2), which is one of the highest PCEs to a collaboration with Chonbuk National University, South Korea. date (Figure PP2.1.18(b)). This outcome proves that the parameters The molecular structures and device configuration are shown developed using a bench-top slot-die coater can be fully translated in Figure PP2.1.16. An optimised ternary blend ratio of PTB7- into a continuous R2R process. The work discussed above has been

Th:PC71BM:COi8DFIC (1:0.45:1.05, w:w:w) was utilised as reported (Li published in the Journal of Advanced Energy Materials (Lee at al. 2019). et al. 2018). All active layers were slot-die coated with a 3D-printer- Fabrication of large-area flexible modules with improved performance based slot-die coater. To determine the optimum slot-die processing will be performed next year. conditions and directly evaluate the effect of the slot-die coated PTB7-

Th:PC71BM:COi8DFIC layer on photovoltaic characteristics, various conditions, such as concentration, additive concentration and heat-treatment were varied. All OSCs were prepared on an ITO/ Figure PP2.1.18: glass substrate. The optimised conditions used a blend solution (a) J-V curves of a fully slot-die coated concentration of 13.5 mg mL-1, incorporated 0.5% DIO as an additive, single cell and a and employed a post-thermal treatment annealing at 80°C to generate mini-module with -2 a champion cell of Jsc of 27.12 mAcm , FF of 69.8%, VOC of 0.71 V and an active area of a PCE of 13.5% in a single-junction OSC (0.1 cm2). This exceeds the 30 cm2. The inset highest PCE reported in the literature for the fully printed OSCs (except shows a photograph of a slot-die coated for metal top electrode). The device external quantum efficiency (EQE) OSC mini-module. and internal quantum efficiency (IQE) were also studied, as shown in (b) J-V curves of the Figure PP2.1.17. slot-die coated TOSC fabricated by a batch process on a glass substrate and by a roll-to-roll process on a flexible substrate. The inset shows the flexible OSC and experimental setup.

Figure PP2.1.16: (a) Chemical structure of PTB7-Th, PC71BM and COi8DFIC. (b) Schematic of TOSC architecture used in this study. (c) Schematic of the slot-die coating process.

54 ACAP ANNUAL REPORT 2019

Screening commercial acceptors for ternary blends using slot-die Table PP2.1.5: Photovoltaic performance of ternary devices under coating AM 1.5 G, 100 mWcm-2 illumination.

The use of non-fullerene acceptors has become essential for the Head Coating T Bed T Speed J production of high performance OSCs. The current focus at CSIRO SC VOC PCE Active Layer (mms-1) (mAcm-2) (V) FF (%) is one donor/two acceptor ternary systems, the same as the PM6:Y6:ITIC-4F (oC)90 (oC)130 5 21.8 0.80 0.67 11.6 aforementioned PTB7-Th:PC71BM:COi8DFIC blend. In addition to the COi8DFIC acceptor, there are several other non-fullerene acceptors PM6:Y6:FEH-IDT 90 130 5 22.2 0.78 0.61 10.6 now available, thus one of the tasks this year was to evaluate selected PM6(New):Y6:i-IEICO-4F 90 130 5 18.8 0.82 0.60 9.2 donor and acceptor combinations and investigate their performance Structure = Glass/ITO/ZnO NPs/PM6(New):Y6:Acceptor/MoO /Ag. using an R2R adaptable slot-die coating process. Figure PP2.1.19 3 lists some donors and acceptors used in this work. The acceptor Machine learning–assisted optimisation of OPVs from in situ blending FEH-IDT-PRH was synthesised at CSIRO in the previous Victorian during R2R slot-die coating Organicic Solar Cell Consortium (VICOSC) project and all others were The advantage of R2R continuous printing processes is that they commercial products. enable the preparation of numerous devices with variable deposition conditions within the same run. However, a problem arises when analysing said devices in large numbers, as it is a very time-consuming task, particularly when trying to compare different datasets at similar/ different conditions. In this regard, machine learning through AI provides the potential to produce reliable, repeatable, precise results to mimic human behaviour and eventually free manpower for other activities. Machine learning algorithms are used in a wide variety of applications at present. With this in mind, the development of software to allow machines to process data using data platforms (Data Sheet) is highly preferred for our current research, particularly in longer large-area flexible solar cells/modules. Under this initiative, in-house developed software with fast, statistic-analysing tools, as well as a filtering function, was developed using conventional machine learning protocols, as shown in Figure PP2.1.20. Using this self-developed tool, a series of experiments were carried out.

Figure PP2.1.19: Chemical structures of the selected donors and acceptors used in the slot-die evaluation process.

The fabrication conditions, including the donor/acceptor weight ratios, blend film thickness, and thermal annealing temperature of the active layer, were carefully optimised. Since the fabricated devices with PM6 show better performance than a PCE of 11%, the data shown here focus on PM6 only. The key device parameters and all detailed photovoltaic data are summarised in Table PP2.1.5. Slot-die coated devices based on a PM6:Y6:ITIC-4F blend achieved a PCE of 11. 6% on -2 ITO/glass with Voc of 0.86 V, Jsc of 24.3 mAcm , and an FF of 73% for a 0.1 cm2 device, outperforming other acceptors. Further optimisation of the donor/acceptor ratio is underway.

Figure PP2.1.20: Conventional machine learning protocol.

Herein, R2R-printed TOSCs were fabricated as a machine learning– assisted (ML-assisted) case study. The ternary blend system was based on donor:acceptor 1:acceptor 2. Compositions of each material were varied and the film thickness was controlled by altering the rate of feed-in. Figure PP2.1.21 presents the experimental data 55 05 – PP2

collected from the R2R-printed devices and each legend corresponds to the different batch conditions (that is, donor:acceptor ratio and thickness etc). As shown in Figure PP2.1.21(b), PCEs were calculated by machine learning–based regression under the various conditions. Dark red circles represent the predicted PCEs, which possess higher values than other regions. This ML-assisted study suggests the deposition conditions have been optimised, although direct human intervention was not required in the process. This is a preliminary design and test, and the on-going development of an advanced deep learning system will be explored in the following year.

Figure PP2.1.21: (a) Experimental data set of R2R-printed OPVs. (b) Machine learning–assisted data set from given experimental data.

Highlights

• 13.5% PCE at @ 0.1 cm2 – highest for ternary single-junction slot-die coated cells.

• 9.75% PCE at @ 0.1 cm2 – highest from R2R slot-die coated cells in the literature.

• 8.6% PCE at @ 30 cm2 – competitive for slot-die coated mini-modules.

References

LEE, J., SEO, Y. H., KWON, S. N., KIM, D. H., JANG, S., JUNG, H., LEE, Y., WEERASINGHE, H., KIM, T., KIM, J. Y., VAK, D. & NA, S. I. 2019. Slot‐ Die and Roll‐to‐Roll Processed Single Junction Organic Photovoltaic Cells with the Highest Efficiency.Advanced Energy Materials, 9(36), 1901805.

LI, H., XIAO, Z., DING, L. & WANG, J. 2018. Thermostable single-junction organic solar cells with a power conversion efficiency of 14.62%. Science Bulletin, 63, 340-342.

XIAO, Z., JIA, X. & DING, L. 2017a. Ternary organic solar cells offer 14% power conversion efficiency.Science Bulletin, 62, 1562-1564.

XIAO, Z., JIA, X., LI, D., WANG, S., GENG, X., LIU, F., CHEN, J., YANG, S., RUSSELL, T. P. & DING, L. 2017b. 26 mA cm−2 Jsc from organic solar cells with a low-bandgap nonfullerene acceptor. Science Bulletin, 62, 1494-1496.

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PP2.2 CZTS SOLAR CELLS

Lead Partner UNSW

UNSW Team A/Prof. Xiaojing Hao, Prof. Martin Green, A/Prof. Nicholas (Ned) Ekins- Daukes, A/Prof. Yansong Shen, Dr Jialiang Huang, Dr Chang Yan, Dr Chaowei Xue, Dr Kaiwen Sun, Dr Xu Liu, Dr Jianjun Li

UNSW Students Jongsung Park, Aobo Pu, Heng Sun, Xin Cui, Mingrui He, Xiaojie Yuan

Industry Partner Baosteel Figure PP2.2.1: The schematic of “Synthetic Si” showing how the Other Partners CZTS is derived. Catalonia Institute for Energy Research (IREC), LONGi Solar, IBM, NTU, NREL, Corning Research & Development Corp., University of Sydney, ACAP’s work in the CZTS area takes the sputtering fabrication Tsinghua University direction, a low-cost, high-throughput and up-scalable manufacturing process which has been used in the commercialised high performance Funding Support CIGS solar cells. In this regard, CZTS offers a realistic potential ARENA, ACAP, ARC, Baosteel to achieve the efficiency levels required for transferring lab-scale processes to commercialisation in the short time as being fully Aims compatible with current CIGS production lines. Using kesterite All successfully commercialised non-concentrating photovoltaic materials less than two micron thick, cells can be light and flexible technologies to date are based on silicon or chalcogenides if grown on flexible substrate, which has the wide applications in (semiconductors containing Group VI elements, specifically Te, Se areas such as building integrated photovoltaics (BIPV), transport and S). The successful chalcogenide semiconductor materials, CdTe vehicles, unmanned aerial vehicles (UAVs), and Internet of Things (IoT), and Cu(In,Ga)Se2 (CIGS), can be regarded as “synthetic silicon” where harvesting light and reducing greenhouse gas emissions. the balance between atoms in these materials provides the same Work in this strand includes the development of high efficiency CZTS average number of valence band electrons as in silicon, resulting in solar cells on soda lime glass and flexible stainless steel. the same tetrahedral coordination (Figure PP2.2.1) (Walsh et al. 2012). Cd and Se are toxic while Te and In are among the 12 most scarce Progress elements in Earth’s crust. These factors would seem to clearly limit the long-term potential of the established chalcogenide technologies. 12.5% efficiency CZTSe solar cells by control intrinsic defects By delving more deeply into the Periodic Table, an alternative option can be uncovered with the same number of valence band electrons on Obtaining high quality CZTSSe absorber with suppressed detrimental average but involving only Earth-abundant, non-toxic elements. intrinsic defects is one of the key challenges in this kesterite CZTSSe area. To control the intrinsic defects, we explored the intrinsic defect Kesterite Cu ZnSnS (CZTS) compound semiconductor has emerged, 2 4 formation mechanism based on first-principle calculation with based on such reasoning, as a promising candidate for thin-film solar collaborators and developed a robust growth process based on our cells. Analogous to the chalcopyrite structure of CIGS, CZTS shares previous baseline. We unveiled that the defect formation mechanism similar optical and electrical properties. CZTS has a bandgap of is mainly governed by the local chemical environment during the around 1.5 eV, a large absorption coefficient of over 104 cm-1. Notable synthesis of CZTSSe phase (Figure PP2.2.2). The modified CZTSe is that the bandgap of the CZTS family can be tuned to span a wide growth process improved the previous baseline (up to 10% efficiency range beyond 2.25 eV, even above the accessible range of the highest CZTSe solar cells) to a much higher level (>12% efficiency). An efficiency III-V cells. This makes the material suitable for tandem cells. independently confirmed total area (0.2397 cm2) efficiency of 12.5% For thin-film solar cells, energy conversion efficiency up to 12.6% and is achieved (Figure PP2.2.3), which is the new record of pure-selenide 11% have been achieved so far for CZTSSe and CZTS solar cells by CZTSe solar cell (previous record is 11.6% achieved by IBM (Lee et al. IBM/DGIST and UNSW, respectively. 2015)) and very close to IBM’s 12.6% record efficiency in the whole area of CZTSSe solar cells (Wang et al. 2014). Our CZTSe device

significantly reduced the OCV loss and we firstly demonstrated a high

VOC which is comparable to the record counterpart CuInSe2 solar cell. With our developed defect-control strategy, the modified CZTSe absorber demonstrates very encouraging characteristics comparable to high performance CIGS solar cells, including long minority carrier lifetime (>10 ns), highly effective minority carrier collection, activated shallow acceptor VCU and consequently greatly improved hole

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mobility. These greatly improved properties indicate an over 14% >11% efficiency CZTSSe solar cells by alkali-PDT treatment efficiency CZTSSe device can be obtained if better window layer with In CIGS solar cells, alkali elements have proven beneficial for the higher conductivity and higher transmittance is employed. We also improvement of V and J . Due to the similarity between CIGS and employed similar growth process to the sulfuro-selenide process for OC SC CZTSSe, it is expected that alkali may play a similar role in CZTSSe, sulfur-containing CZTSSe solar cells and demonstrated 12.1% total which might be able to address its key problem of V deficit (Cabas- area efficiency. OC Vidani et al. 2018; Haass et al. 2018). During the SPREE lab shutdown period, we collaborated with Professor Kim at Chonnam National University by accessing their facility for the device fabrication of CZTSSe solar cells. We designed an alkali chloride solution-based post deposition treatment (PDT) to introduce extra alkali into the CZTSSe absorber. For example, the CZTSSe absorber was soaked in the prepared LiCl solution for a few seconds. After soaking, the absorbers were immersed for 1 s in DI water and dried by Ar gas in order to clean the surface from contaminations. Compared with a reference device without LiCl PDT, the LiCl treated CZTSSe device shows the increased carrier concentration of absorber and modified interface of CdS/

CZTSSe, resulting in boosted VOC and FF by up to 10% by optimising the LiCl PDT process. The bandgap of CZTSSe has been slightly changed by the treatment, indicating Li alloying with the host lattice. Finally, A highest performance of 10.7% was achieved for CZTSSe when the LiCl soaking duration was optimised at 30 s, compared to 9.3% for the reference device (Figure PP2.2.4).

Figure PP2.2.2: Defect formation mechanism analysis. The schematic atomic coordination of (a) half-selenised and (b) fully-selenised S-Ref, and (c) half-selenised and (d) fully-selenised S-Mod. The Sn2+ and Cu2+ in the square frames indicate the mis-occupation of Zn-sites, and the ion cluster in the triangle frame indicates the [SnZn+2CuZn] defect cluster. The h+ represents the ionised Cu vacancy.

Figure PP2.2.4: J-V curve, EQE spectra and bandgap of champion CZTSSe cells of the reference and LiCl treated device.

In order to further enhance device performance, we investigated the impact of potassium chloride treatment on a CZTSSe solar cell. It is shown that potassium concentration and deposition duration significantly influence final device performance (Figure PP2.2.5). Potassium is also found to accumulate at the surface of CZTSSe, facilitating a Cu depleted surface confirmed by XPS depth profile. Therefore, KCl PDT suppresses the interfacial recombination and Figure PP2.2.3: Photovoltaic performance. (a) Statistical box and histogram plots of device performance parameters of S-Mod and S-Ref. improves heterojunction quality. By applying a thinner CdS buffer layer The sample size is 124 cells for S-Mod and 73 cells for S-Ref. All the (around 20 nm, standard CdS thickness 25 nm), we realised beyond photovoltaic performance parameters are measured based on total-area an 11% K-treated CZTSSe solar cell. The thinner buffer layer further devices. (b) Certified J-V data. (c) EQE data of the champion CZTSe solar improves the short wavelength EQE response and thus enhances cell from S-Mod. JSC. Through the facile control of K doping concentration, deposition duration and thinner buffer layer, solar cell performance has been increased from 8.8% to 11.1%.

58 ACAP ANNUAL REPORT 2019

Figure PP2.2.6: The performance of CZTSSe devices with and without Ag, Ge and Cd alloying.

The results obtained for single cation substitution (Ag, Cd and Ge) suggest that the partial substitution of the cations may provide a viable strategy to modify the characteristics of the detrimental defects. Figure PP2.2.5: The device parameters of reference and K-doped Double cation substitution, therefore, could be a feasible strategy to CZTSSe solar cells as a function of KCl concentration, duration and mitigate the negative effects of different types of defects. CdS deposition time. With the controlled Cd content, we introduce additional Ge by sputtering a thin Ge layer (3 nm) between the Cu-Zn-Sn precursor Cation substitution enabling 12.6% efficiency CZTSSe solar cells and CdS layer. Figure PP2.2.7 demonstrates the performance of the Using Ag (1.14 A) as a substitute for Cu (0.74 A), Cd (0.92 A) for Zn champion cell from reference and controlled samples. Compared to (0.74 A), and Ge (0.53 A) for Sn (0.69 A) might reduce/suppress the the device without alloying, the double cation substitution (Cd and formation of cationic anti-site defects in the lattice (Qi et al. 2017; Ge) improves the efficiency up to 12.30%, which is very close to the Yan et al. 2017; Kim et al. 2016; Hadke et al. 2018). We incorporated current world record kesterite efficiency (12.62%). The comprehensive these cation substitution elements in CZTSSe by depositing a metal characterisations are in preparation to reveal the underlying or compound layer on CZTSSe precursors. For example, Ag-alloyed mechanism. CZTSSe was realised by thermal-evaporating an ultrathin 8 nm Ag layer on a Cu-Zn-Sn precursor, followed by the pre-alloying process and then a sulfo-selenisation process. In case of Ge-alloyed CZTSSe, we sputter a 3 nm Ge layer on a pre-alloyed Cu-Zn-Sn precursor before the annealing process. Different from the physical vapour deposition of Ag and Ge, we used the chemical bath deposited CdS as the Cd source on top of the pre-alloyed Cu-Zn-Sn precursor for Cd-alloyed CZTSSe.

Both Ag- and Ge-alloyed CZTSSe result in a remarkable improvement in VOC (Figure PP2.2.6), whereas the Cd-alloyed CZTSSe only slightly influences OCV . By contrast, all of these alloyed devices (Ag-, G-e and Figure PP2.2.7: The performance of devices with and without double cation substitution and their champion cell efficiency. Cd-alloyed devices) show enhanced JSC and FF. The improvement for each parameter has been compared as follows, V : Ag > Ge ?> Cd, OC Another double cation substitution (Cd and Ag) also showed improved J : Ag > Cd > Ge, FF: Ge > Cd > Ag. Substituting Ag for Cu, and Ge for SC device performance. For the single Ag cation substitution, we found Sn in kesterite can enlarge the bandgap of alloyed CZTSSe, whereas that the bulk defect can be addressed which reduces V deficit, substituting Cd for Zn reduces the bandgap, which would contribute OC and the improved junction quality was confirmed. For double Cd to the higher V enhancement by alloying Ag and Ge rather than Cd. OC and Ag cation substitution, we deposited Cd on an Ag-Cu-Zn-Sn Additionally, the improved crystallisation and grain growth by alloying alloyed precursor. The Cd alloying has a similar pronounced effect new elements facilitates the charge collection of the cells in the long on bulk, reducing recombination significantly. With the double cation wavelength range, contributing to JSC. As shown in Figure PP2.2.6, a substitutions strategy, we realised a 12.6% CZTSSe solar cell (Figure 10.80% efficiency Ag-CZTSSe, a 10.65% efficiency Ge-CZTSSe and an PP2.2.8), which shows similar efficiency with current highest reported 11.35% efficiency Cd-CZTSSe have been demonstrated. kesterite solar cells.

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concentration of Na and O, forming a homogeneous passivation layer across the CZTS surface. This nanolayer reduces the local potential fluctuation of band edges and leads to the widened electrical bandgap,

hence the improvement in VOC and device performance. By introducing

the ALD Al2O3 passivation layer, we realised beyond 10% Cd-free buffer-based CZTS solar cells, which is the highest reported for Cd-free pure sulfide CZTS solar cells with relevant work published in Energy & Environment Science (Figure PP2.2.10) (Cui et al. 2019). Figure PP2.2.8: EQE spectra and J-V curve of Ag-CZTSSe and Ag+Cd-CZTSSe device.

Cd-free CZTS solar cells with efficiency over 10%

Expecting the scale-up potential of the kesterite single-junction as well as the Si-based tandem multi-junction solar cells, the Cd-free process is an inevitable trend. New buffer materials with lower (ZnCdS) or no Cd usage (ZnSnO) have been explored and a Cd-free CZTS solar cell baseline has been set up at UNSW. In addition to their green image, these two new buffer materials can also alleviate the interface recombination in Cu2ZnSnS4 solar cells and address its VOC deficit issue because they can form more favourable conduction band alignment with the absorber layer. Figure PP2.2.10: (a) SEM cross-sectional image of Cd-free CZTS solar cell with an Al O passivation layer inserted between CZTS and For ZnCdS buffer, a modified process was applied to deposit the 2 3 ZnSnO. (b) Current density–voltage (J–V) characteristics and (c) buffer material, which is able to improve the chemistry environment external quantum efficiency (EQE) of CZTS/ZnSnO record devices at the interface. Introducing ammonium hydroxide during the with an Al2O3 interlayer. (d) Mechanism illustration of the CZTS

ZnCdS deposition process can effectively reduce the Zn(OH)2 and absorber surface modification when exposed to ALD-Al2O3 treatment. ZnO impurities formed during the deposition process. This will help facilitate the epitaxial growth, enhance the interface microstructure >10% efficiency standard sized CZTSSe solar cells (>1 cm2) and reduce the interface defects (Figure PP2.2.9). Thanks to the Uniformity of the performance of kesterite solar cells has been greatly improved interface structure, the interface recombination is effectively improved by reducing the secondary phases and voids at the back supressed and the V and FF of the device is accordingly enhanced. OC contact area. 10% efficiency CZTS solar cells are demonstrated by A champion cell with efficiency over 10% using this low-toxic buffer is modifying the kesterite/Mo reaction (Figure PP2.2.11). An Alumina finally demonstrated (Sun et al. 2019). nanolayer is introduced between CZTS and Mo, which modifies the Mo into MoS(e)x before being exposed to CZTS(e). The removal of direct reaction between CZTS(e) and Mo solves the detrimental effects from secondary phases and voids at the back contact area.

Figure PP2.2.9: High-resolution transmission electron microscopy (HRTEM) images of the interface regions showing the microstructure of CZTS covered by ZnCdS buffer deposited with (a) low and (b) high ammonia concentration in the cation solution.

For ZnSnO buffer, the favourable band alignment at the heterojunction has already been approved. An ALD-Al2O3 passivation layer was introduced to further alleviate the interface recombination. The independent effects from the trimethylaluminum (TMA) precursor, Figure PP2.2.11: Statistics of the performance of standard-sized CZTS solar cells. H2O and heating effects involved in the ALD process reveals that the devices with TMA treatment only show a similar improvement with respect to Al2O3 treatment. A detailed chemical and electronic analysis at the surface demonstrates that the ALD Al2O3 facilitates the formation of a thicker Cu-deficient nanolayer with a higher

60 ACAP ANNUAL REPORT 2019

The uniformity of large-area CZTSe solar cells has also been References greatly improved. Figure PP2.2.12 shows the distribution of device performance on a 16 cm2 (4 cm × 4 cm) soda-lime-glass substrate. CABAS-VIDANI, A., HAASS, S. G., ANDRES, C., CABALLERO, R., Within 39 solar cells produced in this area, an average efficiency FIGI, R., SCHREINER, C., MÁRQUEZ, J. A., HAGES, C., UNOLD, T., of 10.11% has been demonstrated with the average deviation of BLEINER, D., TIWARI, A. N. & ROMANYUK, Y. E. 2018. High-Efficiency efficiency only 0.52% in absolute. Though no anti-reflection coating (LixCu1−x)2ZnSn(S,Se)4 Kesterite Solar Cells with Lithium Alloying. is employed, there are 27 cells that demonstrate over 10% efficiency. Advanced Energy Materials, 8, 1801191. After ARC coating, the efficiency of the 10.8% champion cell is boosted to 12.5% (independently confirmed), and most of the other cells reach CUI, X., SUN, K., HUANG, J., YUN, J. S., LEE, C.-Y., YAN, C., SUN, H., an efficiency greater than 11%. This is achieved by mainly engineering ZHANG, Y., XUE, C., EDER, K., YANG, L., CAIRNEY, J. M., SEIDEL, J., the precursor treatment where the metal Cu/Zn/Sn precursor is EKINS-DAUKES, N. J., GREEN, M., HOEX, B. & HAO, X. 2019. Cd-Free annealed in an Se atmosphere at a relatively lower temperature Cu2ZnSnS4 solar cell with an efficiency greater than 10% enabled by compared to the second stage selenisation. Al2O3 passivation layers. Energy & Environmental Science, 12, 2751- 2764.

HAASS, S. G., ANDRES, C., FIGI, R., SCHREINER, C., BÜRKI, M., TIWARI, A. N. & ROMANYUK, Y. E. 2018. Effects of potassium on kesterite solar cells: Similarities, differences and synergies with sodium. AIP Advances, 8, 015133.

HADKE, S. H., LEVCENKO, S., LIE, S., HAGES, C. J., MÁRQUEZ, J. A., UNOLD, T. & WONG, L. H. 2018. Synergistic Effects of Double Cation Substitution in Solution-Processed CZTS Solar Cells with over 10% Efficiency.Advanced Energy Materials 8, 1802540.

KIM, S., KIM, K. M., TAMPO, H., SHIBATA, H. & NIKI, S. 2016. Figure PP2.2.12: Larger area uniformity and device performance of Improvement of voltage deficit of Ge-incorporated kesterite solar cell CZTSe solar cells. with 12.3% conversion efficiency.Applied Physics Express, 9, 102301.

LEE, Y. S., GERSHON, T., GUNAWAN, O., TODOROV, T. K., GOKMEN, T., Highlights VIRGUS, Y. & GUHA, S. 2015. Cu2ZnSnSe4 Thin-Film Solar Cells by UNSW has set another two world record efficiencies in CZTS solar Thermal Co-evaporation with 11.6% Efficiency and Improved Minority cells, holding its leadership in the CZTS kesterite solar cell community. Carrier Diffusion Length. Advanced Energy Materials, 5, 1401372. . The 12.5% efficiency pure selenide CZTSe solar cell demonstrates successful transfer to the Se-containing kesterite area with the QI, Y.-F., KOU, D.-X., ZHOU, W.-H., ZHOU, Z.-J., TIAN, Q.-W., MENG, established technology and knowledge. The Cd-free 10% efficiency Y.-N., LIU, X.-S., DU, Z.-L. & WU, S.-X. 2017. Engineering of interface CZTS solar cell shows the promising green image of this thin-film PV band bending and defects elimination via a Ag graded active layer for technology. New approaches of improving the performance of a CZTS efficient (Cu,Ag)2ZnSn(S,Se)4 solar cells. Energy & Environmental device such as alkali treatment and cation substitution are tested and Science, 10, 2401-2410. identified. The larger area uniformity and device performance have also been enhanced based on the process modification. SUN, K., YAN, C., HUANG, J., LIU, F., LI, J., SUN, H., ZHANG, Y., CUI, X., WANG, A., FANG, Z., CONG, J., LAI, Y., GREEN, M. A. & HAO, X. 2019. Future Work Beyond 10% efficiency Cu2ZnSnS4 solar cells enabled by modifying Future work in 2020 will be focused on the integration of our recently the heterojunction interface chemistry. Journal of Materials Chemistry developed effective strategies, such as defect control, alkali PDT and A, 7, 27289-27296. cation substitution and is expected to further improve the device performance. In addition, the interface defect engineering like type WANG, W., WINKLER, M. T., GUNAWAN, O., GOKMEN, T., TODOROV, T. inversion and back surface field are also proposed to improve device K., ZHU, Y. & MITZI, D. B. 2014. Device Characteristics of CZTSSe Thin- performance. Film Solar Cells with 12.6% Efficiency. Advanced Energy Materials, 4.

YAN, C., SUN, K., HUANG, J., JOHNSTON, S., LIU, F., VEETTIL, B. P., SUN, K., PU, A., ZHOU, F., STRIDE, J. A., GREEN, M. A. & HAO, X. 2017. Beyond 11% Efficient Sulfide Kesterite Cu2ZnxCd1– xSnS4 Solar Cell: Effects of Cadmium Alloying. ACS Energy Letters, 2, 930-936.

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Publications PP2.5 PEROVSKITES

CUI, X., SUN, K., HUANG, J., YUN, J. S., LEE, C.-Y., YAN, C., SUN, H., UNSW Team ZHANG, Y., XUE, C., EDER, K., YANG, L., CAIRNEY, J. M., SEIDEL, J., A/Prof. Anita Ho-Baillie, Dr Shujuan Huang, Dr Trevor Young, Dr EKINS-DAUKES, N. J., GREEN, M., HOEX, B. & HAO, X. 2019. Cd-Free Jae Yun, Dr Meng Zhang, Dr Arman Mahboubi Soufiani, Dr Fa-jun Cu2ZnSnS4 solar cell with an efficiency greater than 10% enabled by Ma, Adrian Shi, Jincheol Kim, Xiaofan Deng, Cho Fai Jonathan Lau, Al2O3 passivation layers. Energy & Environmental Science, 12, 2751- Benjamin Wilkinson, Jianghui Zheng, Nathan Chang, Prof. Martin 2764. Green

UoM Team HE, M., KIM, J., HAO, X., et al. KCl assisted Cu2ZnSn(S,Se)4 solar cell Prof. Ken Ghiggino, Dr David Jones, Dr Jegadesan Subbiah, with an efficiency greater than 11%, (In preparation). Dr Pengjun Zhao

HE, M., KIM, J., HAO, X., et al. Beyond 12% efficient kesterite solar cell Monash University Team enabled by Ag and Ge co-alloying method, (In preparation). Prof. Udo Bach, Dr Jianfeng Lu, Dr Sebastian Fürer, Dr Muhammad Kashif HE, M., KIM, J., HAO, X., et al. Synergistic effects of double cation ANU Team substitution: role of Cd and Ge, (In preparation). Prof. Kylie Catchpole, Prof. Klaus Weber, Dr Thomas White, Dr Daniel Walter, Dr Heping Shen, Dr The Duong, Dr Jun Peng, Dr Yiliang Wu HE, M., YAN, C., HUANG, J., KIM, J., HAO, X. Beyond 10% efficiency kesterite solar cell by modifying the heterojunction quality by LiCl post UQ Team deposition treatment, (In preparation). Prof. Paul Burn, Dr Paul Shaw, Dr Hui Jin, Dr Kasparas Rakstys, Dr Meera Stephen, Dr Xiao Wang LI, J., HUANG, J., HUANG, Y., YAN, C., SUN, K., SUN, Y., XUE, C., MAI, Commonwealth Scientific and Industrial Research Organisation Y., GREEN, M. & HAO, X., Interface states predominated open-circuit- Manufacturing Flagship (CSIRO) Team voltage limitation of current state-of-the-art Cu2ZnSnS4 thin-film solar Dr Gerry Wilson, Dr Fiona Scholes, Dr Mei Gao, Dr Doojin Vak, Ms cells, (In preparation). Jyothi Ramamurthy, Dr Hasitha Weerasinghe, Dr Andrew Scully, Dr Anthony Chesman, Regine Chantler, Andrew Faulks, Dr Chuantian Zuo LI, J., HUANG, Y., HUANG, J., LIANG, G., ZHANG, Y., REY, G., GUO, F., SU, Z., YOU, X., ZHU, H., CAI, L., SUN, K., SUN, Y., CHEN, S., HAO, X., MAI, Y. Academic Partners & GREEN, M. Defect control for 12% efficiency Cu2ZnSnSe4 kesterite Korea Research Institute of Chemical Technology (KRICT), Ulsan thin-film solar cells by engineering of local chemical environment, National Institute of Science and Technology (UNIST), Korea: Prof. (Submitted). Sang II Seok Friedrich–Alexander University Erlangen–Nürnberg: Prof. Christoph SUN, K., YAN, C., HUANG, J., LIU, F., LI, J., SUN, H., ZHANG, Y., CUI, X., Brabec WANG, A., FANG, Z., CONG, J., LAI, Y., GREEN, M. A. & HAO, X. 2019. Swinburne University of Technology: Dr Xiaoming Wen Beyond 10% efficiency Cu2ZnSnS4 solar cells enabled by modifying Nanyang Technological University (NTU), Singapore: Prof. Nripan the heterojunction interface chemistry. Journal of Materials Chemistry Mathews A, 7, 27289-27296. Los Alamos National Laboratory (LANL): Dr Ghanshyam Pilania Washington University: Prof. Rohan Mishra Potsdam University, Germany: Prof. Dieter Neher, Dr Martin Stolterfoht Stanford University: Prof. Reinhold H. Dauskardt Monash University: A/Prof. Jacek Jasieniak, Prof. Christopher R. McNeill King Abdullah University of Science and Technology (KAUST): Prof. Stefaan De Wolf Sun Yat-sen University: Prof. Juntao Li Flinders University: Prof. Gunther Andersson Georgia Institute of Technology: Prof. Samuel Graham Wuhan University of Technology Nanjing Tech University Gwangju Institute of Science and Technology (GIST), South Korea Ludwig-Maximilians-Universität-München Purdue University, USA Central South University, China Ecole Normal Supérieure, France Fraunhofer Institute, Germany

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UNSW Students The research is divided into the following main areas Da Seul Lee, Yongyoon Cho, Jueming Bing, Shi Tang, Laura Granados, 1. Thorough understanding of basic material and device properties Chwenhaw Liao, Nursultan Mussakhanuly by taking full advantage of the expertise, facilities and experience Monash Students within the partner organisations. The project will undertake Liancong Jiang, Dorota Bacal, Boer Tan research in a diverse range of applications of perovskite materials and devices to develop a path to cost-effective, stable perovskite ANU Students solar cells. Nandi Wu, Naeimeh Mozaffari 2. Investigation of prospects for Pb-free perovskite materials. CSIRO Students Hengyue Li, Na Gyeong An, Hyungsu Jang, Adrien Smith, Gayathri 3. Understanding the stability of these materials and on both material Mathiazhagan, Hongyan Huang, Caria Evans synthesis and on encapsulation approaches to addressing present stability and durability issues. UoM Students Jianchao Lin 4. Development of tandem thin-film cells both within the perovskite material system and in combination with inorganic thin-films (Si UQ Students wafer tandems specifically excluded since they are covered by Hui Li (UQ), Shanshan Zhang another ARENA project). Aims 5. Scaling to commercially relevant devices including improving the Since the establishment of ACAP in 2012, mixed organic-inorganic performance of reasonably large devices (>1 cm2 in area) rather halide perovskites have emerged as a new class of solar cell with than on the tiny devices (<0.1 cm2 in area) where the majority potential as a material for the development of efficient, lower cost of international attention is focused. This task also includes the photovoltaic (PV) cells. evaluation of manufacturing costs for the most promising of the fabrication approaches identified and scaling issues. The potential of perovskites for PV cells as an absorber material lies in its ability to achieve good cell efficiencies, while being relatively cheap to produce and simple to manufacture (i.e., competitive cell efficiency Progress at a lower cost).

A significant effort has been initiated internationally on this materials Materials and device properties class, and ACAP has several unique advantages that place the At UNSW, the relation between the external radiative efficiency (ERE) proposed activities at the forefront of these international efforts. and efficiency limits of perovskite solar cells and other thin-film PV Foremost among these advantages are the different relevant technology is explained and updated. One result of general interest is perspectives that ACAP is able to offer given the expertise within that the optimal cell bandgap is not something static but decreases the different groups constituting ACAP in the dye-sensitised, organic as each technology evolves, with this evolution documented by the photovoltaics (OPV), inorganic thin-film and silicon cell and module cell’s radiative efficiency (Figure PP2.5.1). Another key finding is that areas, as well as the strong contacts to the commercial sector, and control of the ideality factor will be the key to ongoing improvements the co-ordination of this expertise and research effort made possible as perovskite solar cell and other emerging PV technologies push to through the ACAP organisational structure. the Shockley−Queisser ideal (Green et al. 2019). To capture these research efforts within ACAP, a new program In terms of light-induced effect on material properties, scanning probe package for Perovskite Solar Cells under PP2 Thin-Film, Third microscopy techniques have been used to investigate perovskite grain Generation and Hybrid Devices with additional funding was established structural variations at UNSW (Kim et al. 2019) while at Monash, in to carry out focused and highly collaborative Australian research and situ laser excited photoluminescence spectroscopy has been used to industry effort in perovskite photovoltaics. The aim is to establish an show light-induced degradation of the I-rich domain after initial phase internationally leading activity in this exciting new materials group, and segregation (Ruan et al. 2019) (Figure PP2.5.2(d)). In the Monash consistent with the original intent of ACAP, the team will undertake study, it is found that the oxygen sensitivity of the I-rich domain is highly innovative and competitive research with a strategic focus on identified as a key factor to inducing this irreversible decomposition as PV technologies that targets breakthroughs in the cost of solar energy. supported by in situ Raman spectroscopy (Figure PP2.5.2(a–c)). This With a focus on issues that need to be resolved to enable low-cost, work provides insight into the degradation of mixed-halide perovskites full-scale production, the work would enhance the commercial viability under high light intensities and direction for the development and of perovskites. processing of compositionally and environmentally stable perovskite materials. In the UNSW study, it has been shown that periodically striped ferroelastic domains, spacing between 40 and 350 nm, exist within grains and can be modulated significantly under illumination as well as by electric bias. A Williamson-Hall analysis of X-ray diffraction results shows that strain disorder is induced by these applied external

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Figure PP2.5.1: Theoretical and experimental cell efficiencies and optimal absorption thresholds reported by UNSW. (a) Shockley–Queisser (SQ) efficiency limits (solid and dashed lines) for different external radiative efficiencies (ERE). Also shown are best experimental results for a range of materials, including recent efficiency improvement trajectories for CIGS and perovskite cells. (b) SQ limits as a function of ERE and corresponding optimal energy absorption thresholds.

Figure PP2.5.2: The evolution of Raman spectra of (a) MAPbI3, (b) MAPbBr3, and (c) MAPbI1Br2 single crystals under 20 mW 407 nm laser after 600 s at Monash. (d) Illustration of initial perovskite followed by phase segregation and phase decomposition.

stimuli. The structural emergence of domains can provide transfer device model (in which mobile ionic species are neither created nor pathways for holes to a hole transport layer with positive bias. These destroyed) displays a constant set of properties (such as mobility) findings point to potential origins of I–V hysteresis in halide perovskite as cell operating conditions are changed. The model can accurately solar cells. reproduce a wide range of phenomena observed in the different measurements. Moreover, the model can be used to make predictions To model the effect of ion migration on perovskite solar cell (PSC) about phenomena that were later confirmed experimentally. The hysteresis at ANU, building on a numerical ionic drift-diffusion IDD model is thus a powerful tool to understand the behaviour of (IDD) model, a second computational model has been developed to PSCs that allows us to identify the key mechanisms responsible for model the properties of the transport layers, and a range of transient limiting device performance, as well as pathways for mitigation of the phenomena was reported in the literature, arising from a wide range deleterious effects. As an example, Figure PP2.5.3 shows Kelvin force of different measurements. It is shown that the relatively simple probe microscopy (KPFM) experimental and simulated differential

64 ACAP ANNUAL REPORT 2019

Figure PP2.5.3: Experimental and simulated, time- resolved KPFM data for a perovskite solar cell at ANU.

Figure PP2.5.4: ANU’s (a.1, b.1) EL intensity images of two PSCs in the same batch. (a.2, b.2) Extracted optical bandgap images from the EL intensity images. (a.3, b.3) Optical bandgap maps extracted from µ‐PLS scans, confirming the results from the EL‐imaging method. (c) Optical bandgap images of PSCs from various batches, from the top to the bottom: ≈1.63 eV (760 nm), ≈1.61 eV (770 nm), ≈1.60 eV (775 nm), and ≈1.58 eV (785 nm).

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contact potential difference (CPD) measurement scans across a cross- n-butylammonium iodide salt with n = 4 exhibited power conversion section of perovskite solar cells, with excellent qualitative agreement. efficiencies (PCEs) >14% (Zhang et al. 2019) (Figure PP2.5.5). UQ has also synthesised a range of bespoke cations to be used in RPP ANU also developed a fast, non-destructive, camera‐based method inverted solar cells in conjunction with MAPI. Preliminary work on to capture optical bandgap images of perovskite solar cells with these materials has led to laboratory-scale cells with a PCE of >21%, micrometre‐scale spatial resolution (Chen et al. 2019). This imaging which is among the best in the world at this time. A feature of the best technique utilises the well‐defined and relatively symmetrical band‐ combination is its enhanced stability against heat and humidity with to‐band luminescence spectra emitted from perovskite materials, un-encapsulated devices having T s of >1500 h (T= 85 °C) and >500 h whose spectral peak locations coincide with absorption thresholds and 50 (RH = 80±10%), respectively. thus represent their optical bandgaps. The technique was employed to capture relative variations in optical bandgaps across various At UNSW, it has been found that how phenethylammonium‐based PSCs, and to resolve optical bandgap inhomogeneity within the same mixed perovskite precursors are prepared for the fabrication device due to material degradation and impurities (Figure PP2.5.4). PEA2(FA 0.85MA0.15)Pbn (I0.85Br0.15)3n+1 will have different impacts on film Degradation and impurities are found to cause optical bandgap shifts quality and the corresponding photovoltaic device performance and inside the materials. The development of this new technique continues stability. Two methods have been studied (Lee et al. 2020) (Figure to strengthen the high value of luminescence imaging for the research PP2.5.6). One is called the different phase (DP) method whereby and development of this photovoltaic technology. perovskite precursors with different phases – 2D PEA2Pb(I0.85Br0.15)4 and 3D (FAPbI ) (MAPbBr ) – are prepared separately before At UQ (collaborating with Potsdam University), absolute 3 0.85 3 0.15 being mixed for the fabrication of the film. The other method is called photoluminescence (PL) and temperature-dependent PL studies the same phase (SP) method whereby two perovskite precursors have been carried out on solution-processed MAPbI (MAPI) and 3 with the same phases – quasi‐2D PEA FA Pb I and quasi‐2D (CsPbI ) [(FAPbI ) (MAPbBr ) ] (triple cation) perovskite solar 2 n−1 n 3n+1 3 0.05 3 0.83 3 0.17 0.95 PEA MA Pb Br – are prepared and then mixed. Although the films cells. It has been found that the observed high density of sub-states 2 n−1 n 3n+1 prepared differently have the same compositions, their properties are in MAPbI3 led to a narrower quasi-fermi-level splitting and larger non- very different revealed by X-ray diffraction measurement (XRD), PL, radiative recombination losses than in the triple cation perovskite films. ultra-violet visible (UV–vis) optical measurement, and KPFM. There is In terms of device engineering, surface passivation and the use evidence of an additional lower‐dimensional perovskites phase in the of bulky cation for the formation of quasi-2D (two-dimensional) DP film. This has an impact on film properties such as the presence perovskites for various purposes are the common themes of research. of the additional lower‐dimensional perovskites phase near the TiO2 The former includes (i) amine-induced anchored crystallisation for interface reducing short wavelength optical absorption. However, the efficient interface passivation at UoM; (ii) the use of n-butylammonium lower‐dimensional perovskites phase possibly of higher bandgap also iodide (BAI) as a seed layer for the subsequent 3D perovskite layer as induces higher photo-voltage. With a sufficiently small amount of PEA well as interface passivation at UoM; (iii) a post-treatment using tert- at 1.67 mol%, film device stability against moisture and light can be butylammonium cations (tBA) to passivate perovskite surfaces and to dramatically improved without sacrificing device performance where reduce grain boundary defects at Monash (Bu et al. 2019) achieving 19% efficient cells can be achieved by all methods. As SP film is more improved device performance of over 20% with negligible hysteresis of a quasi‐2D film, the most stable cell fabricated by this method and enhanced stability (Figure PP2.5.6); and (iv) the development maintained 86% of its initial performance after exposure to RH 80 ± 5% of insoluble glycol derivatised poly(1,4-phenylenevinylene) (PPV) for 1000 h and over 80% of its initial PCE after continuous one-sun interlayers for inverted perovskite solar cells at UQ. illumination (including UV) at RH 70%. This is the best stability results for highly efficient PEA un-encapsulated cells. This work demonstrates At ANU, n-BAI is used to provide double-sided passivation for three- the importance of the precursor preparation process as a powerful dimensional (3D) perovskite films for devices with a remarkable tool for fabricating quasi‐2D perovskite films for efficient and stable open-circuit voltage of 1.2 V for a bulk perovskite film having an optical photovoltaic devices. bandgap of ~1.6 eV, with a conversion efficiency of 22.8%. Researchers at CSIRO have improved the orientation of the layered Researchers at UQ in collaboration with Potsdam University have structure of quasi-2D Ruddlesden–Popper perovskites by carefully studied 2D Ruddlesden–Popper perovskite (RPP) inverted solar cells selecting proper cation materials. Figure PP2.5.7 shows an illustration based on (CH (CH ) NH ) (CH NH ) Pb I with different numbers 3 2 3 3 2 3 3 n−1 n 3n+1 of the natural-drying and N blow-drying processes used to prepare of [PbI ]4- sheets (n = 2­4). Using photoluminescence quantum yield 2 6 drop-cast quasi-2D perovskite films. Visual inspection of the drop-cast (PLQY) measurements they found that the non-radiative open-circuit 2D films revealed significant differences in the appearance caused voltage (V ) losses outweighed radiative V losses in materials with OC OC by the various drying techniques (Figure PP2.5.8). The N blow-dried n > 2, while the opposite was the case for the n = 2 system due to its 2 films (Figure PP2.5.8(c, d) appear smoother and more uniform than excitonic nature. The quasi-Fermi level splitting was found to match their naturally dried counterparts, which appear grey and have several the device V within 20 meV, which indicated minimal recombination OC fringes on the surface (Figure PP2.5.8(a, b)). This is supported by a losses at the metal contacts. In addition, poor charge transport, surface morphology study via SEM (Figure PP2.5.8(e–h)). Several especially in the n = 2 compound, rather than field-dependent exciton cations were explored using this method, namely n-butyl ammonium, dissociation was found to be the primary reason for the substantial iso-butyl ammonium, phenylethyl ammonium, pentyl ammonium and reduction in fill factor of the devices. Optimised solar cells utilising the

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Figure PP2.5.5: Charge transport in 2D perovskite at UQ. (a) The fill factor (FF) versus power conversion efficiency highlights the impact of the FF on the photovoltaic performance of the BA-based 2D perovskite and MAPI cells. (b) The normalised external quantum efficiency at 445 nm and short-circuit conditions as a function of the device photocurrent (light minus dark current), which was increased using the applied laser power. The photocurrent at which the EQE starts to decrease is proportional to the mobility of the slowest charges in the device, which highlights the large decrease in the extraction efficiency with decreasing number of [PbI6]4− layers (MAPI > BA4 > BA3 > BA2). The arrows mark the one-sun short-circuit current density, which highlights the substantial bimolecular recombination losses in BA2. (c) Integral time of flight transients measured on BA3 and BA2 cells at a bias of 0 V, a load resistance of 1 MΩ after an ns laser excitation. The large resistance– capacitance (RC) time of the external circuit allows visualisation of the displacement of photogenerated charges within the active layer and consequently the saturation of the photovoltage signal marks the transit time of all photogenerated charges through the device (30 ns and ≈10 μs for BA3 and BA2, respectively). (d) Field dependence of the external charge generation efficiency (EGE) of the BA perovskites as measured using time-delayed collection field experiments. The results suggest field-independent charge generation in the layered perovskite film devices.

Figure PP2.5.6: UNSW’s schematic illustration of the fabrication of

PEA2(FA 0.85MA0.15)n-1Pbn(I0.85Br0.15)3n+1 perovskite by the (a) different phase (DP) method by mixing

[(FAPbI3)0.85(MAPbBr3)0.15](1-X) with

[PEA2Pb(I0.85Br0.15)4]X, and (b) the same phase (SP) method by mixing

PEA2FA n-1PbnI3n+1 with PEA2MAn-

1PbnBr3n+1.

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Figure PP2.5.7: Illustration of the natural-drying and N2 blow-drying processes used to prepare drop-cast quasi-2D perovskite films at CSIRO. (a) The 2D perovskite precursor solution is drop-cast onto a heated substrate; (b) the solution spreads spontaneously on the substrate and dries naturally; the supersaturation and number of crystal nuclei are low due to the slow drying; (c) the crystal

nuclei grow into large crystal grains during drying. (d) The film spreads on the substrate and then an N2 stream is used to dry the film rapidly; the supersaturation and number of crystal nuclei is higher owing to the fast drying; (e) the crystal nuclei grow into a compact quasi-2D perovskite film.

Figure PP2.5.8: CSIRO’s (a)–(d) Photographic images of PEA-2D and iso-BA-2D perovskite films prepared by natural drying (a) and (b), and N2 blow drying (c) and (d); (e)–(h) SEM images of PEA-2D and iso-BA-2D perovskite films prepared by natural drying (e) and (f), and blow drying (g) and (h).

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Figure PP2.5.9: CSIRO’s (a) device structure of the quasi-2D perovskite solar cells; (b) J-V curves for the PEA-2D and iso-BA-2D perovskite solar cells prepared by natural drying, and N2 blow-drying with and without MACl additive; and (c) J-V curves for the “champion” cell under reverse and forward scan.

Figure PP2.5.10: CSIRO’s GIWAX patterns for drop-cast PEA-2D and iso- BA-2D perovskite films. (a) Naturally-

dried PEA-2D film. (b) N2 blow-dried

PEA-2D film. (c) N2 blow-dried PEA-2D film with MACl additive. (d) Naturally-

dried iso-BA-2D film. (e) N2 blow-dried

iso-BA-2D film. (f) N2 blow-dried iso-BA- 2D film with MACl additive.

Figure PP2.5.11: Monash’s statistic photovoltaic properties of back contact perovskite solar cells using honeycomb-shaped electrodes (HBC-PSC) with small, medium and large feature sizes. (a) Distribution of device open-circuit voltage (Voc), (b) short-circuit current density (Jsc), (c) fill factor (FF) and (d) power conversion efficiency (PCE). Statistics were taken from at least seven devices for each condition. (e, h) Photocurrent (PC) mapping of HBC-PSC with small feature size and the corresponding normalised cross-section profile. (f, i) PC mapping of HBC-PSC with medium feature size and the corresponding normalised cross-section profile. (g, j) PC mapping of HBC-PSC with large feature size and the corresponding normalised cross-section profile.

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propyl ammonium. The device with iso-butyl ammonium (iso-BA-2D) for improving efficiencies allowing cells with thick absorbers to be outperforms the others with a PCE near 16% (Figure PP2.5.9). To our fabricated achieving efficiencies above 80% of their theoretical limits knowledge, this is the highest PCE recorded to date for a quasi-2D/3D (Ho-Baillie et al. 2019) (Figure PP2.5.12). PSC with a non-spin-cast perovskite layer prepared under ambient laboratory conditions. The near-perfect vertical orientation of the 2D Lead-free perovskites perovskite crystals in the iso-BA-2D films with respect to the substrate The team at Monash University is making progress building as confirmed by GIWAX (Figure PP2.5.10) is beneficial for charge on previous work of demonstrating silver bismuth sulfoiodides carrier transport and may help to explain the enhanced PCE compared Ag Bi I S (Pai et al. 2019) and expanding material choice to to PEA-2D films. a b a+3b−2x x Cs2AgBiSxBr6-2x. With regards to cell design, a novel highly defect-tolerant honeycomb- shaped back contact (HBC) electrode has been developed for Device durability dipole-field-assisted back contact PSCs at Monash (Lee et al. 2020) Stabilising hole transport layers or using alternative hole transport (Figure PP2.5.11). The device performance is found to be inversely materials has been a common theme among the nodes in terms of proportional to the honeycomb electrode feature sizes. Suppressed research on device stability. recombination and more homogeneous photocurrent generation Researchers at ANU investigated the properties of an inexpensive hole Tandem transporting material (HTM), copper phthalocyanine (CuPc), deposited by a solution-processing method in perovskite solar cells (PSCs). One advantage of perovskites is that their bandgap can be tuned by They found that cracks are abundant on the as-deposited CuPc films, varying the composition. Higher bandgap perovskites can be used which lead to serious shunts and interface recombination. Surprisingly, as a “top” sub-cell for multi-junction thin-film tandems. CsPbI has 3 shunts and interface recombination are significantly reduced, and cell an optical bandgap of 1.72 eV, which is suitable for tandem devices performance is greatly improved after heat treatment at 85°C (Duong combining with either silicon or low bandgap perovskite solar cells. et al. 2018). The latter is attractive for inorganic halide perovskites which have a higher temperature tolerance and can be fabricated first as the high To date, most efficient PSCs employ an n–i–p device architecture bandgap cell on the superstrate followed by the fabrication of the that uses spiro‐OMeTAD as the HTM. Common additives such as lower bandgap lower-temperature-tolerant cell. 4-tert-butylpyridine (tBP) and lithium bis(trifluoromethane)sulfonimide (LiTFSI) as the oxidising agents require air exposure for p-type doping, At UNSW, a simple cation exchange growth (CEG) method has been however they cause instability. reported for fabricating inorganic high quality CsPbI3 by adding MAI additive in the precursor (Lau et al. 2019). X-ray diffraction At UNSW, one effective way of eliminating tBP is by engineering the results reveal a multi-stage film formation process whereby (i) solvent mixture (a combination of chlorobenzene (CB) and acetone

MAPbI3 perovskite first formed acting as a perovskite template for nitrile (ACN)) for spiro-OMeTAD (Cho et al. 2019). It is found that using

(ii) subsequent ion exchange whereby the MA+ ions in the MAPbI3 a CB:ACN of 85%:15% for the tBP-free spiro-OMeTAD produces the are replaced by Cs+ (as temperature ramps up) (iii) to form ϒ-phase best device in terms of performance and thermal stability. perovskite CsPbI . Interestingly, the CEG method requires a sufficient 3 At Monash, a dicationic salt spiro‐OMeTAD(TFSI) , is employed as an amount of MAI additive to achieve full conversion to the desired 2 effective p‐dopant to replace LiTFSI. Power conversion efficiencies ϒ- CsPbI with negligible PbI and δ- CsPbI . Optical, microscopy, 3 2 3 of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm2) with excellent photoluminescence and electrical characterisations reveal a very high reproducibility can be achieved (Tan et al. 2019). As far as it is known, quality film, by the CEG process, with better broadband absorption, these are the highest performing n–i–p PSCs without LiTFSI or more uniform and dense film with a better perovskite/TiO interface, 2 air exposure. Comprehensive analysis demonstrates that precise lower defects and better stability. Using the CEG approach, the PCE control of the proportion of [spiro‐OMeTAD]+ directly provides high of the best CsPbI solar cell was significantly increased from 8.9% 3 conductivity in HTM films with low series resistance, fast hole for the control device to 14.1% for the device fabricated using 1.0 M extraction and lower interfacial charge recombination. Moreover, MAI additive. The outcome is beneficial for further improvement on the spiro‐OMeTAD(TFSI) ‐doped devices show improved stability, inorganic perovskite solar cells and their application in perovskite/ 2 benefiting from well‐retained HTM morphology without forming silicon tandem devices. aggregates or voids when tested under an ambient atmosphere. A

In a review conducted by UNSW, it was found that CsPbIXBr3-X cells facile approach is presented to fabricate highly efficient PSCs by were performing well optically with some reaching 90% of their replacing LiTFSI with spiro‐OMeTAD(TFSI)2. Furthermore, this study theoretical current output limits. However, low carrier lifetime and provides an insight into the relationship between device performance high surface recombination are limiting the voltages and fill factors of and the HTM doping level. these cells limiting their performance to only 60% of their theoretical efficiency limits. Appropriate transport layer designs (producing positive band-offsets); reducing surface recombination velocities (to 103 cm s-1); improving lifetimes (10 μs) are effective strategies

70 ACAP ANNUAL REPORT 2019

Figure PP2.5.12: Review of inorganic perovskite solar cells by UNSW. Demonstrated cell efficiencies since first reported. Roadmap of improving inorganic perovskite solar cells compared to “baselines”.

Figure PP2.5.13: CSIRO’s (left) schematic drawing of a dual-feed approach; (right) component ratio changing along the coating direction (X position).

Figure PP2.5.14: CSIRO’s SEM images of R2R-coated perovskite films via a dual- feeding method.

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Commercial prospects, up-scaling and manufacturing costs Highlights The use of phenyl-C61-butyric acid methyl ester (PCBM) as an • A better understanding of the light soaking effect on perovskite electron transport layer creates tremendous challenges for upscaling grain structural variations and degradation of the I-rich domain PSCs using industry-relevant methods such as those developed at after initial phase segregation is achieved via investigation CSIRO due to its aggregation behaviour, which undermines the power by scanning probe microscopy and in situ laser excited conversion efficiency and stability. In recent years, ITIC (3,9-bis(2- photoluminescence spectroscopy. methylene-(3-(1,1-dicyanomethylene)-indanone))-,5,11,11-tetrakis(4- hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′] dithiophene), • A more refined model has been developed to the effect of ion a non-fullerene acceptor material, was found to be an excellent migration on perovskite solar cell hysteresis, building on the acceptor material in bulk heterojunction solar cells, showing similar numerical ionic drift-diffusion model reported in the 2018 Annual electronic properties as fullerene, but also enabling light harvesting Report. The model can be used to reproduce a wide range of in the visible and near-infrared regions. The energy levels of ITIC phenomena observed in the different measurements and can are comparable to that of PCBM. It has been observed that silver be used to make predictions about phenomena that were later electrodes in PCBM-based devices lose their lustre, even when stored confirmed experimentally. in a glovebox, whereas they remain reflective and unchanged in ITIC • Bulky cations and 2D perovskites continue to be widely used devices after months of storage in a glovebox. This suggests that ITIC across different nodes to form layered perovskite for passivation, provides a barrier between the perovskite layer and the electrodes, for improving cell performance and for improving moisture preventing the halide ions from migrating to the silver electrode. stability. A deeper understanding has been developed including At CSIRO, it is found that slot-die-processed ITIC film on perovskite (i) the mechanism of voltage losses in 2D Ruddlesden–Popper forms a uniform film with full coverage on perovskite films, yet perovskites based on (CH3(CH2)3NH3)2(CH3NH3)n−1PbnI3n+1 for PCBM coalesces into segregated domains (Angmo 2018). This inverted solar cells and (ii) how the precursor preparation method could be related to the poor adhesion of PCBM to the perovskites. for phenethylammonium‐based PEA2(FA 0.85MA0.15)Pbn (I0.85Br0.15)3n+1 The mechanical integrity of ITIC was characterised using a double will affect film properties such as the presence of an additional cantilever beam (DCB) test, a standard technique for measuring lower‐dimensional perovskites phase that affects voltage output the fracture energy (Gc) of thin films. This work was performed in and device stability. collaboration with Stanford University. The higher G , the better the c • Cell efficiencies exceeding 22% (measured in house) can be interlayer adhesion. As a result, the mechanical analysis of the p−i−n routinely achieved on small-area devices by various nodes. PSC structures revealed the PCBM layer to be the most brittle layer, and therefore highly susceptible to fracture. The fracture path for the • Great progress has been made in the demonstration of a ITIC-perovskite samples occurred in the perovskite layer, indicating >1 cm2 device. In particular, certified efficiency of 21.6% has been that ITIC is not the weakest layer in the solar cell, which is the case for achieved on a 1.01 cm2 cell. PCBM. • A better understanding of loss mechanisms of higher bandgap Optimisation of the ratios and concentration of each component in the (e.g., inorganic) perovskite cells and a report of roadmap perovskite precursor solution, particularly in complex mixed cation and outlining strategies for improving their performance for tandem halide formulations, is a prerequisite for achieving high performance applications. devices processed by roll-to-roll (R2R). Other factors, including • Continued progress being made on discovery of new lead-free web speed, coating temperature, solution injection rate, drying perovskite solar cells. and annealing temperature/time, also play a critical role in device performance. Optimisation of all of these parameters is required to • Stabilising hole transport layers or using alternative hole transport obtain the desired film thickness and large crystal grains. To effectively materials has been a common theme among the nodes reporting carry out this optimisation, a dual-feed approach was devised, and progress on improving device stability. tool-fitting was made in house at CSIRO (Figure PP2.5.13). Using this • A new cell design, using a honeycomb-shaped back contact (HBC) dual-feed method, the ratio of the two components across a gradient electrode was developed for dipole-field-assisted back contact during the continuous coating process can be adjusted in situ to PSCs at Monash. optimise deposition conditions within a single run. The advantage of using this method is that it dramatically reduces the optimisation • In terms of scale-up, there has been continued progress on using time and effort, and this process can be applied universally to other a spin-coating-free method for fabricating quasi-2D perovskite formulations. The SEM images obtained for different coating distances films in air, yielding perovskite solar cells with power conversion (X) corresponding to the optimised ratios can be found in Figure efficiencies (PCEs) of up to 16%. Slot-die processed electron PP2.5.14. Further work on this is anticipated in 2020. transport layer ITIC is a better alternative to PCBM due to higher mechanical robustness. Dual feeding has been demonstrated as an effective tool to optimise the ratios of each component of perovskite precursor for R2R printing.

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Future Work

We will link theoretical models to the design of new perovskite materials, predicting the behaviours of material modification, then verification by synthesis of the new materials (including mixed cation, mixed halide and 2D/3D hybrid perovskites; new interlayer materials; new cell architectures) for better performance and stability.

We will develop better understanding on the mechanism of passivation and doping techniques in altering material and electrical properties of individual layers in the cells for minimising hysteresis, improving stabilities and efficiencies in various types of perovskite solar cells.

We will continue to develop advanced characterisation compatible with perovskite test structures and full devices such as luminescence spectroscopy including photoluminescence and cathodoluminescence; EDX mapping under SEM; Kelvin probe force microscopy (KPFM); advanced TEM; and electron backscatter diffraction analysis (EBSD) to investigate micro-structure, device level properties and defects as well as changes under external stimuli such as light and biased conditions.

We will continue to improve lab-to-fab translation tools for optimising printing processes. We will continue to improve characterisation approaches as required for large-area and flexible devices.

We will conduct study to identify degradation mechanisms, degradation pathways and degradation products when perovskite solar cells degrade to better understand causes of degradations.

We will conduct study to elucidate film formation mechanism under different fabrication conditions and using different fabrication methods.

We will continue to develop a low-cost, lithography-free approach for fabricating honeycomb-shaped back contact (HBC) electrodes for back contact PSCs.

We will continue the work of precursor engineering to better understand film formation and effect on device performance.

We will continue developing low-cost encapsulation strategies for perovskite solar cells. is observed for devices with smaller feature sizes. Improved light absorption and less variation in the photocurrent generation across the solar cell are found with respect to inter-digitated solar cells.

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PP3 OPTICS AND CHARACTERISATION

OVERVIEW

Program Package 3 (PP3), “Optics and Characterisation”, aims to the PDS tool will enable substantial advances in the field of thin-film utilise and manipulate the fundamental interactions between light and PV device design and fabrication. Finally, the UNSW team report their matter to develop high efficiency, low-cost photovoltaic (PV) devices. progress on the development of photoreflectance spectroscopy, an This includes particular thin-film organic and Earth-abundant solar easy-to-use optical characterisation method for determining cells. These devices rely on special optical properties – imparted the bandgap and higher order band edges of new materials. either by their constituent materials or by structural modifications – to enhance energy conversion efficiency well beyond what would be expected for a conventional PV device of comparable thickness. PP3.1 METHODS TO CHARACTERISE THE However, the characterisation of such devices can be much more OPTICAL AND ELECTRICAL PROPERTIES challenging than for standard devices, requiring the development of a range of new characterisation techniques. OF ORGANIC AND OTHER THIN-FILM

Previous reports for this Program Package have outlined our EARTH-ABUNDANT SOLAR CELLS achievements in these areas; in this report we present our recent progress and suggest promising new directions for the work. In PP3.1 the UQ team describe their advances in the development PP3.1A COMPUTATIONAL METHODS of computational methods for simulating the structural, optical TO CHARACTERISE THE STRUCTURAL, and electrical properties of organic thin films for solar cells. These innovative methods provide a new perspective for probing the OPTICAL AND ELECTRICAL PROPERTIES relationship between film morphology and device performance and OF ORGANIC THIN FILMS FOR SOLAR are expected to deliver significant insights. Included in PP3.1 is an overview of the ultrafast spectroscopic techniques developed at the CELLS University of Melbourne for probing the photo-physical processes relating to charge generation in novel materials for organic solar cells. Lead Partner Under PP3.3 ANU presents a number of critical advances in the UQ development of methods for characterising perovskite and perovskite/ silicon tandem solar cells, which help understand the charge transport UQ Team and degradation in these materials. ANU has developed a rapid, Thomas Lee, Alan Mark, Paul Burn non-destructive technique based on spatially resolved absorptivity for Industry Partner identifying and monitoring degradation in perovskite solar cells. The Heliatek ANU team also describe their advances in the use of luminescence as a tool for the characterisation of defects and impurities in silicon Funding Support materials. The team from UNSW describes how they have developed ACAP, UQ scanning probe microscopy as a tool for probing local charge carrier generation and separation in a range of solar cell materials. Aim

Also included in PP3, are activities in the development of The performance of organic solar cells is critically dependent on the spectroscopic instruments (PP3.4). UNSW and Open Instruments orientation of molecules in the semiconductor film. For example, the report on their effort to commercialise a high performance orientation of the chromophores has a substantial impact on the photothermal deflection spectroscopy (PDS) tool. The tool efficiency of light absorption and is maximised when the transition demonstrates excellent sensitivity and robustness compared to dipole moment is oriented perpendicular to the incoming light. standard benchtop optical characterisation techniques such as R&T Similarly, the mobility of the generated charge carriers is strongly and ellipsometry and also provides a means of quantifying non- dependent on the relative orientation of chromophores. Probing radiative recombination within a sample. The commercial rollout of the molecular orientation within organic semiconductor layers

74 ACAP ANNUAL REPORT 2019

experimentally is challenging and the analysis of the data can be suggest that a substantial population of the molecules in thin films complex, especially for birefringent materials. Optical techniques, of DCV4T-Et2 have a horizontally oriented transition dipole moment. such as variable angle spectroscopic ellipsometry (VASE), can provide Over 29% of the molecules deposited on a smooth substrate had a the average molecular orientation in the film. However, this may not tilt of less than 6° to the horizontal, compared to the average angle of be particularly useful as organic photovoltaic materials are generally 21°. The difference in orientation within films deposited on smooth composed of a combination of amorphous and polycrystalline and rough substrates would correspond to a difference in absorption domains and the distribution of orientations is potentially broad. In on the order of 6% for films of comparable thickness. This suggests order to obtain the detailed atomic-level insight into the mechanism that surface roughness must be considered in the design of model of growth and orientation of molecules in photovoltaic thin films, systems in order to maintain relevance to devices. The simulations and the subsequent device performance, we have developed also indicate a preference for a horizontal orientation of the thiophene computational approaches based on molecular dynamics. These allow rings, which would be beneficial to charge transport through stacked the distribution of the components in an active layer, their orientation π-systems. Results were also consistent with existing grazing- and their effect on the device performance to be calculated. These incidence wide-angle X-ray scattering (GIWAXS) and ellipsometry data, methods represent a powerful new approach for understanding the indicating the power of this approach and its robustness. relationship between material and device performance in organic More recently, molecular dynamics simulations have been applied solar cells. towards understanding film formation as a result of solution deposition. Previously reported simulations did not specifically Progress consider the interface between the solution and the atmosphere, In early work, atomistic simulations of vacuum deposition were instead removing the solvent randomly from the solution. used to study the orientation of an ethyl-substituted dicyanovinyl This approach led to spinodal decomposition and unrealistic quaterthiophene, DCV4T-Et2 (Figure PP3.1.1) in neat films deposited film morphology. The team at UQ developed a new simulation onto C60 layers (Lee et al. 2019). Similar systems have been methodology that took into account the removal of solvent from the investigated in the context of relatively efficient planar heterojunction surface of the solution and also the effect of the substrate (Figure devices, in which donor and acceptor species are deposited as PP3.1.2). This methodology does not lead to spinodal decomposition separate layers with thicknesses less than 10 nm. The reason for and yields a realistic film morphology. such thin films is that the exciton diffusion length is less than 10 nm These studies demonstrate the broad scope for the use of atomically and so the orientation of the absorber is of particular importance detailed morphologies accessible via molecular simulation in in planar heterojunctions. Dicyanovinyl oligothiophenes have been facilitating a more precise interpretation of experimental results and demonstrated to have high extinction coefficients and good charge providing important design criteria for organic semiconductor devices. transport properties and, hence, were good material systems for the characterisation of the film structure and properties with molecular dynamics simulations.

Figure PP3.1.1: Molecular dynamics simulation of an evaporated film of DCV4T-Et2 (Heliatek material) on a C60 substrate, exploring the effect of surface roughness on absorber orientation.

The molecules of DCV4T-Et2 were randomly deposited onto either a smooth or rough layer of C60 supported on a 17.0 nm by 16.7 nm graphene sheet as illustrated in Figure PP3.1.1. During the deposition Figure PP3.1.2: Snapshot from a molecular dynamics simulation of thin-film formation from solution deposition. process, new molecules were inserted 2 nm from the top of the film every 20 ps with a random orientation and an initial velocity towards the surface to ensure they reached the growing film. The simulations

75 05 – PP3

film solar cells these intermediates include excitons, charge transfer Highlights states and various radical ion species. These transient species • Molecular dynamics simulations applied towards understanding form and decay over a wide time-range from femtoseconds (10-15 the morphology of both evaporated and solution-processed secs) to milliseconds (10-3 secs). An ultrafast transient absorption organic thin films for organic solar cells. spectrometer has been developed at the University of Melbourne that is able to undertake transient absorption investigations over • Simulations confirm the importance of surface roughness when time scales to several microseconds (see Figure PP3.1.3 for a evaluating the performance of devices based on evaporated thin schematic diagram). The instrument is based on a femtosecond films. regenerative amplifier as the pump source and a super-continuum • The inclusion of the atmosphere/solution and solution/ laser that produces white light pulses of <1 ns duration synchronised substrate interfaces is found to be critical for preventing spinodal to the pump pulse. The inherent timing jitter between the triggering decomposition in simulations of solution-processed thin films. of the super-continuum laser and when it emits a pulse provides a distribution of probe times relative to the pump pulse. A transverse • Powerful innovative method for correlating film structure with acoustic (TA) phonon spectrum is collected for every pump-probe device performance. event and each spectrum is tagged with the actual time that the probe pulse was emitted after the pump pulse. These spectra are then sorted Future Work according to their pump-probe delay time and normalised to produce • Simulations on greater time and length scales may in the future TA spectral sets of long-lived transient states. lead to a more complete reproduction of X-ray diffraction patterns of these films. (2) Femtosecond transient absorption microscope (UoM)

Organic and hybrid thin-film solar cell materials are often blends of PP3.1B DEVELOPMENT OF ADVANCED electron donor and acceptor compounds that have heterogeneous composition on micron and sub-micron spatial scales. Characterising SPECTROSCOPIC TECHNIQUES the behaviour of light-induced transient species in these materials requires both high time and spatial resolution to fully map the Lead Partner distribution of behaviours that take place. A transient absorption UoM microscope is under development at the University of Melbourne to allow such measurements to be undertaken. A block diagram of the UoM Team apparatus is provided below. The system is based on the output of a Trevor Smith, Ken Ghiggino mode-locked titanium:sapphire laser, producing pulses of ~25 fs at 80 UoM Students MHz. This is split to provide both a pump beam at 400 nm (through Can Gao, Saghar Masoomi-Godarzi, Yang Xu frequency doubling) and a white light continuum (using a photonic crystal fibre, FemtoWhite) as the probe beam. The probe pulses are Funding Support delayed relative to the pump pulses with a translation stage, and ACAP, ARENA, UoM colinearly introduced into an inverted microscope. The intensity of the transmitted probe beam is monitored as a function of the sample Aim position, and as a function of the pump-probe delay to build a map of The aim of this program is to develop advanced spectroscopic the transient absorption signal over micrometre-sized sample regions. techniques to provide insights into the structure-property relationships This microscope is designed to be flexible to enable simultaneous in thin-film organic and Earth-abundant solar cell materials – collection of absorption, emission and other detection modes (e.g. structural, optical and electrical. In doing so the program contributes photocurrent mapping). to programs in PP2 and provides a valuable resource for the ACAP program more broadly.

Progress Substantial progress in instrumentation development has occurred during 2019 that allows investigations of the mechanisms of charge generation in thin-film solar cells and light-induced processes in other light harvesting materials (such as singlet fission and energy up- conversion materials). Highlights are provided below.

(1) Long time-range transient absorption spectrometer (UoM)

An important requirement in developing and evaluating new materials for solar cells is to measure the evolution and fate of the intermediate species involved in converting absorbed light energy into separated Figure PP3.1.3: Schematic diagram of the femtosecond transient charges and ultimately electrical power. In organic and hybrid thin- absorption spectrometer.

76 ACAP ANNUAL REPORT 2019

Highlights Progress

• Transient absorption microscope developed for spatial imaging of The team at ANU, led by Dr Hieu Nguyen, has developed a new transient kinetics in PV materials. contactless, non-destructive approach to study degradation across perovskite and perovskite/silicon tandem solar cells. The • Extended the time capabilities of transient spectroscopy technique employs spectrally and spatially resolved absorptivity at measurements to cover the range from femtoseconds to sub-bandgap wavelengths of perovskite materials, extracted from milliseconds. their photoluminescence (PL) spectra. Parasitic absorption in other • Completed transient spectroscopy measurements of energy up- layers, carrier diffusion, and photon smearing phenomena are all conversion kinetics and efficiencies for light harvesting porphyrin demonstrated to have negligible effects on the extracted absorptivity. polymers and organic singlet fission materials. The absorptivity is demonstrated to reflect real degradation in the perovskite film and is much more robust and sensitive than its Future Work luminescence spectral peak position, representing its optical bandgap, and intensity. The transient microscopy instrumentation will be developed further to allow simultaneous photocurrent mapping, emission and absorption In Figure PP3.3.1, the sub-bandgap absorptivity map (row 4) clearly measurements to provide detailed information on the mechanisms of shows that the air slowly invades the solar cell through the edge photocurrent generation in PV materials. The spectroscopy techniques of the gold contact when the cell is exposed in the atmosphere. developed will be applied to undertake studies of new singlet fission Various pinholes through the gold contact can also be observed, and energy up-conversion materials with the potential to provide as indicated by the white circles (row 4, absorptivity @ 800 nm). improved solar energy conversion efficiencies for PV devices (under The technique is also applied to study other common factors which PP2.1). induce and accelerate degradation in perovskite solar cells including heat exposure and light soaking. Finally, it is employed to extract the individual absorptivity component from the perovskite layer in PP3.3 TRANSPORT AND DEGRADATION a monolithic perovskite/silicon tandem structure (Figure PP3.3.2). MECHANISMS IN PEROVSKITE The results demonstrate the value of this approach for monitoring degradation mechanisms in perovskite and perovskite/silicon tandem MATERIALS cells at early stages of degradation and various fabrication stages. This work has been published in Advanced Energy Materials (Nguyen et al. 2020). PP3.3A NEW APPROACH FOR DEGRADATION STUDY OF PEROVSKITE AND PEROVSKITE/SILICON TANDEM SOLAR CELLS

Lead Partner ANU

ANU Team Hieu Nguyen, Arafat Mahmud, Yiliang Wu, Jun Peng, The Duong, Klaus Weber, Thomas White, Kylie Catchpole, Daniel Macdonald

ANU Students Sven Gerritsen, Ziyuan Cai

Funding Support ACAP, ARENA, ANU

Aim Figure PP3.3.1: PL intensity, spectral peak location, and extracted absorptivity maps of a perovskite solar cell versus exposure time in a Instability of perovskite solar cells is the main challenge for the room atmospheric environment. commercialisation of this solar technology and for their integration in tandem configurations. The groups involved in this work aim to deepen the understanding of the complex degradation mechanisms observed in perovskite materials, with the objective of bringing this very promising technology to a high technology readiness level. Rapid, non-destructive, reliable methods for characterising these materials and devices will be critical for their commercial deployment.

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Funding Support ACAP, ARENA, ANU

Aim

Understanding material properties, carrier dynamics, defects and impurities in starting silicon (Si) materials and during device fabrication helps identify potential problems for final devices and their root causes in early stages. Also, advances in characterisation metrologies have been critical for historical development of more efficient Si solar cells. Therefore, the groups involved in this work aim to continue advancing the understanding of microscopic structural and optoelectronic properties of various components across different Si solar cell technologies, as well as to develop fast and reliable techniques to monitor these properties.

Figure PP3.3.2: Various absorptivity components from a monolithic Progress perovskite/silicon tandem solar cell. (1) Optoelectronic properties of doped poly-Si films Highlights Passivating contact Si solar cells featuring an ultrathin SiOx layer • Spectrally and spatially resolved absorptivity for perovskite solar capped with a doped polycrystalline Si (poly-Si) film have achieved cells. efficiencies of >25%. However, the community has focused mainly

• Degradation studies (heat, air, light) of perovskite solar cells using on aggregate performances of the poly-Si/SiOx contacts via sub-bandgap absorptivity. their passivation qualities. Little is known about structures and optoelectronic properties of the poly-Si films themselves and how • Sub-bandgap absorptivity is more sensitive to early stages of these properties relate to the contacts’ performances. The ANU team, degradation than luminescence intensity. led by Dr Hieu Nguyen and Professor Daniel Macdonald, has provided • Separation of absorptivity in perovskite layers from other layers in new insights into some important properties of the poly-Si films, and monolithic perovskite/silicon tandem cells. developed a luminescence-based method to quickly track hydrogen content inside the films. • Powerful way to study degradation in top perovskite cells in tandem configurations. The team's poly-Si films are fabricated from plasma enhanced chemical vapour deposition (PECVD) amorphous Si films followed Future Work by thermal diffusion processes at high temperatures. However, the poly-Si films still contain both amorphous (a-) and crystalline (c-) Si The team will continue to refine their technique to support the phases, as shown by the transmission electron microscope (TEM) drive to near-term commercial viability of perovskite solar cells. image in Figure PP3.3.3(a). These different Si phases yield very Particularly, the technique will be thoroughly quantified and its use distinct photoluminescence (PL) peaks at low temperatures (Figure for characterisation of single-junction and tandem cells under various PP3.3.3(b)), compared to the c-Si substrate. After high temperature conditions will be explored. diffusion processes to form the doped poly-Si films, most of the hydrogen content has effused out of the films, leaving the film un- PP3.3B ADVANCED CHARACTERISATION hydrogenated. Un-hydrogenated amorphous Si (a-Si) contains a very high density of non-radiative defects, yielding no PL signal. Once OF SILICON hydrogenated, the a-Si:H phase will emit a strong PL peak in which the intensity is proportional to the hydrogen content inside the films. Lead Partner Tracking the a-Si:H PL emission, the team can study the effectiveness ANU and mechanisms of various hydrogenation techniques on different poly-Si films. Their findings and the various applications of their ANU Team method have been reported in a series of four journal papers (Nguyen Hieu Nguyen, Di Yan, Chang Sun, Anyao Liu, Andres Cuevas, Daniel et al. 2018; Truong at al. 2019a, b, c). Macdonald

ANU Students Thien Truong, Rabin Basnet, Zhuofeng Li, Huiting Wu

UNSW Team Fiacre Rougieux

ACAP Partner NREL

78 ACAP ANNUAL REPORT 2019

Figure PP3.3.3: (a) Doped poly-Si films contain both amorphous (a-Si) and crystalline phases (c-Si). (b) Photoluminescence from the a-Si phase in poly-Si films indicates the effectiveness of various hydrogen treatments.

(2) Determination of dopant profiles of localised heavily doped regions

In this project, the ANU team, led by Dr Hieu Nguyen, has developed a PL-based technique to determine dopant profiles of localised boron-diffused regions in c-Si wafers and solar cell precursors. It is fast, contactless and non-destructive. The measurements can be performed at room temperature with micron-scale spatial resolution. They have applied the technique to reconstruct dopant profiles of a large-area boron-diffused sample and heavily doped regions (30 μm in diameter) of passivated emitter rear locally-diffused (PERL) solar cell precursors. The reconstructed profiles are confirmed with the well- established electrochemical capacitance voltage (ECV) technique. The developed technique helps quickly determine boron dopant profiles in small doped features employed in c-Si solar cells.

During a thermal boron diffusion process, if the boron-rich layer is removed before the final thermal drive-in step (that is, the dopant source is finite), the resultant dopant profile can be fitted with a Gaussian function (Figure PP3.3.4): Figure PP3.3.4: ECV dopant profiles of some boron-diffused samples and their corresponding Gaussian fits using Eq. PP3.1. where Np is the peak dopant concentration, zp is the depth at which the peak locates, and zf is a depth factor. Therefore, it is possible to At low temperatures ~80 K, a diffused c-Si sample emits two distinct reconstruct the dopant profiles using Eq. PP3.1 given that PL spectra PL peaks associated with the substrate and the diffused layer (Figure from boron-diffused regions can be converted into the parameters PP3.3.5(a)). At room temperature, although the two PL peaks are

{Np, zf, zp}. indistinguishable due to thermal broadening effects, the effect of the diffused layer is still noticeable at the long wavelength side of the normalised PL spectrum (Figure PP3.3.5(b)). Moreover, by varying excitation wavelengths, the long wavelength side varies significantly due to the different penetration depths of the light in the sample (Figure PP3.3.5(c)). These two characteristics, the relative intensity at the long wavelength side and its change versus the excitation wavelength, are unique for a certain diffusion dopant profile. From 15 boron-diffused samples with known dopant profiles, the team

established calibration curves to extract {Np, zf, zp} based on the two spectral characteristics.

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The technique is then demonstrated to re-establish dopant profiles of a localised p+ region of a PERL solar cell precursor (Figure PP3.3.6). Micro-PL spectroscopy (micro-PLS) mapping is performed around a localised p+ region using the 500 nm and 600 nm excitation wavelengths. The map provides an entire spectrum for every pixel in the X-Y map, allowing an extraction of the PL intensity at various wavelengths with micron-scale spatial resolution. Based on the two spectral characteristics, the relative intensity at the long wavelength side and its change with 500 nm and 600 nm excitation light, of every

single pixel, Np, zf, and zp maps can be extracted (Figure PP3.3.6(a) and PP3.3.6(b)) using the calibration curves. The reconstructed dopant profile at the centre of the p+ region reasonably matches the measured dopant profile on a test location (1 cm × 1 cm diffused region on the PERL precursor) (Figure 3.3.6(c)). The sheet resistances calculated from the reconstructed and measured dopant profiles are 67 and 60 Ω/ , respectively. This work has been published in Scientific Reports (Nguyen et al. 2019).

Figure PP3.3.5: Comparison of normalised PL spectra from c-Si samples with and without a diffused layer at (a) 80 K and (b) 296 K, captured with the 500 nm excitation wavelength. (c) PL spectra from the diffused wafer with various excitation wavelengths at 296 K.

Figure PP3.3.6: (a) zf and (b) Np maps of a localised p+ region in the PERL solar cell precursor, determined by the µ-PLS method at room temperature. (c) Comparison between the ECV measured and reconstructed dopant profiles. Note: zp and zf are inherently correlated.

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(3) High spatial resolution study of ring defects in Cz silicon wafers

A study by the ANU team, led by Mr Rabin Basnet and Professor Daniel Macdonald, has investigated ring defects induced by a two-step anneal in n-type Czochralski-grown (Cz) Si wafers using a combination of high spatial resolution Fourier transform infrared spectroscopy (FTIR), micro-PL mapping, and micro-Raman mapping. Through FTIR measurements, they show the inhomogeneous loss in interstitial oxygen with a positive correlation with the inverse lifetime. Furthermore, combining PL imaging (Figure PP3.3.7) and Figure PP3.3.7: PL-based carrier lifetime images of the (a) as- high-resolution micro-PL mapping (Figure PP3.3.8), they are able to grown sample and the Group II (650°C - 5 hrs; 1000°C - 15 hrs) distinguish individual recombination-active oxygen precipitates within sample captured with (b) standard lens (pixel size of 162 μm) and the rings with a decreasing density from the centre to the edge of the (c) magnifying lens (pixel size of 23 μm). The PL images were captured at an average injection level of Δp = 5×1013 cm-3. The red sample. The radial inhomogeneity of the oxygen precipitates is likely points indicate the locations (not the size) of the micro-PL maps in to be related to variations in the distribution of grown-in defects. They this work. The black box in (b) indicates the area of the PL image also demonstrate that micro-Raman mapping reveals the oxygen captured with the magnifying lens shown in (c). The bright circle precipitates without the smearing effects of carrier diffusion that are in the images is an artefact due to the conductance coil in the PL present in micro-PL mapping. This work has been published in Journal imaging tool. The straight lines in (b) and (c) are laser marks for locating specific regions. of Applied Physics (Basnet et al. 2018).

Figure PP3.3.8: Micro-PL maps of 300 μm × 300 μm areas on (a) the as-grown sample, (b), (c), and (d) on the Group II sample (650°C-5 hrs; 1000°C-15 hrs). The locations of the micro-PL maps are indicated in the PL images in Figure PP3.3.8. (e) Inverse lifetime extracted from the PL image as a function of apparent oxygen precipitate areal density obtained from micro-PL maps on the Group II sample.

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Highlights Progress

• Poly-Si films contain both amorphous and crystalline phases, each One of the most fundamental parameters of any photovoltaic material of which yields distinct luminescence peaks at low temperatures. is its quasi-Fermi level splitting under illumination. This quantity represents the maximum open circuit voltage (V ) that a solar cell • Luminescence from the amorphous Si phase in poly-Si films can OC fabricated from that material can achieve. However, no study of be used to track the hydrogen content inside the films. TMDs materials has focused on quantifying this limitation either • Dopant profiles of localised boron-diffused regions can be experimentally or theoretically, although thousands of works on other determined using room temperature photoluminescence with two aspects of TMDs have been published. By quantifying light absorbed different excitation wavelengths. and emitted from the TMDs, the ANU team, led by Dr Hieu Nguyen, has developed a method to predict the possible open circuit voltages that • High resolution micro-PL maps successfully resolve the could be achieved from TMD-based solar cells, at the material stage. recombination-active individual particles and their distribution

within the ring defects in Cz Si wafers. The team applies the technique to quantify the upper limits of VOC that can possibly be achieved from monolayer WS , MoS , WSe and • Ring defects or lifetime striations are due to the cumulative effect 2 2 2 MoSe -based solar cells, and compares them with other thin-film of individual oxygen precipitates. 2 technologies. Their results show that Voc values of ~1.4, ~1.12, ~1.06 and ~0.93 V could be potentially achieved from solar cells fabricated Future Work from WS2, MoS2, WSe2 and MoSe2 monolayers at one-sun illumination, The team will refine their techniques and apply their findings to respectively, as shown in Figure PP3.3.9. The results suggest that support high efficiency silicon solar cell teams at ANU and UNSW. In the requirements of high-voltage, flexibility, ultralight, transparency addition, the team will continue exploring structural and optoelectronic and stability for future solar cells are possible with 2D TMDs. More properties of various components across different silicon solar cell significantly, the established limits could be a reference for numerous technologies. future works on fabricating TMD-based photovoltaic devices.

The team also observed that the predicted VOC values are PP3.3C UNLOCKING THE POTENTIAL OF inhomogeneous across different regions of these monolayers. Therefore, they attempt to engineer the observed VOC heterogeneity EMERGING 2D MATERIALS by electrically gating the TMD monolayers in a metal-oxide- semiconductor (MOS) structure which effectively changes the Lead Partners doping level of the monolayers electrostatically and improves their ANU VOC heterogeneity (Figure PP3.3.10). These preliminary results demonstrate that indeed both the predicted V and its homogeneity ANU Team OC can be manipulated by the doping levels inside monolayer TMDs. Hieu Nguyen, Yuerui Lu, Zongyou Yin, Daniel Macdonald This work has been published in Advanced Materials (Tebyetekerwa ANU Student et al. 2019) Mike Tebyetekerwa

Funding Support ACAP, ARENA, ANU

Aims

STwo-dimensional (2D) transition metal dichalcogenides (TMDs) are currently receiving enormous attention for photovoltaic applications due to their very strong light-matter interaction, atomic thickness and naturally occurring surface passivation. Also, there has been a rapid improvement in their large-scale material processing capability and quality. This signals that in the next few years, large-area (millimetres to centimetres) solar cells based on TMDs could be fabricated. Therefore, this work aims to understand and quantify the potential of these future solar cells using experimental and/or theoretical means in Figure PP3.3.9: 2D TMD-based solar cells could potentially yield high early days. voltages, very competitive to other thin-film technologies.

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Highlights

• 2D TMDs could yield very high implied open circuit voltages of more than 1 V.

• 2D TMDs can be engineered by doping to improve their uniformity and implied open circuit voltages.

• The requirements of high-voltage, flexibility, ultralight, transparency and stability for future solar cells are possible with 2D TMDs.

Future Work

The team will continue to explore various surface treatment and doping techniques to improve the quality of the 2D TMDs. The team will also move to the next steps to demonstrate proof-of-concept solar cells, aiming to achieve a 2D TMD-based cell with VOC values of more than 1 V.

Figure PP3.3.10: Effects of electrical

gating on predicted VOC of the

monolayer WS2. (a) Schematic assembly of the monolayer-based MOS structure with electrical connections. (b) Optical microscope image of the analysed monolayer on the MOS setup (scale bar 50 µm). (c) Photoluminescence spectra

obtained from the monolayer WS2 with back gate voltages of -10, 0 and +10 V. (d) The corresponding mapping of

predicted VOC across the monolayer WS2 (scale bar 10 µm).

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Figure PP3.3.11: Illustration of the scanning probe microscope measurements with various techniques on different types of solar cells. A new AFM (Park System NX10) with KPFM, C-AFM, STM and SCM has been recently purchased and commissioned in SPREE (Support from ACAP and UNSW).

PP3.3D NANOSCALE FUNCTIONAL an external light source can be illuminated onto the sample surface IMAGING USING SCANNING PROBE which provides morphology dependent photovoltaic parameters such as open-circuit potential, photocurrent, resistance and pn junction MICROSCOPE (SPM) profile.

Lead Partner Progress UNSW In a recent publication with collaborators in Korea (Ann et al. 2019), UNSW Team UNSW researchers presented an intriguing role of grain boundaries Jae Sung Yun, Martin Green, Ziv Hameiri, Xiaojing Hao, Yajie Jiang, of organic-inorganic halide perovskite (OIHP) solar cells under Stephen Bremner, Shujuan Huang, N. J. Ekins-Daukes low-illumination light. Our primary interest was to characterise PV performance at an indoor light or low-illumination condition as OIHP Academic Partner solar cells have a suitable bandgap for absorbing visible lights, thus, School of Materials Science and Engineering at UNSW: Jan Seidel have a great potential for indoor applications such as self-powered Oak Ridge National Laboratory and The University of Tennessee: Dr internet of things (IoT) devices. Although a higher performance was

Dohyung Kim obtained from the OIHP based on mesoporous-TiO2 (m-TiO2) under one-sun illumination, compared to the compact-TiO (c-TiO ) sample, Funding Support 2 2 the c-TiO sample generated higher power than m-TiO perovskite ACAP, UNSW, ARC 2 2 solar cells under low-illumination (200–1600 lux; ~5.0×10−2 mW cm-2) condition as shown in Figure PP3.3.12 (c) and (d). We performed Aim KPFM measurement on both types of OIHP solar cells under different We aim to understand the local charge carrier generation and light intensities. Figure PP3.3.12 shows contact potential difference separation properties of various types of solar cells using a scanning (CPD) images measured under dark and low-illumination LED light probe microscope (SPM), an instrument for functional imaging (400 and 1600 lux) for perovskite layers on c- (b) and m-TiO2 (e). From surfaces of samples using a nanoscale tip at the nanoscale to atomic the result of perovskite on c-TiO2, it is evident that some regions of the level. A schematic illustration of a scanning probe microscope setup grain boundaries (GBs) exhibit a higher CPD compared to the grain is shown in Figure PP3.3.11. Powerful techniques include Kelvin interiors (GIs) at 400 lux under the illumination. This increase in the probe force microscopy (KPFM), conductive atomic force microscopy CPD is attributed to the effective charge separation (holes in this case) (C-AFM), scanning tunnelling microscopy (STM) and scanning that accumulate on the top surface, which implies efficient charge capacitance microscopy (SCM). These techniques allow imaging of separation at GBs. morphology dependent electrical properties. During the measurement,

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As the light intensity increases, those higher CPD GBs become more distinctive and more GBs have a higher CPD compared to GIs. In sharp contrast, such CPD variation was not detected in the GBs of perovskite on the m-TiO2 sample. Line profiles are shown to clearly demonstrate a clear contrast between GIs and GBs in Figure PP3.3.12 (c) and (f) for the OIHP on c- and m-TiO2, respectively. Our results indicate that the charge carriers are effectively separated at GBs for only c-TiO2-based OIHP at a low-illumination condition. This could be one of the reasons for outperformance of the OIHP solar cells with c-TiO2 compared to m-TiO2 at low-illumination.

Highlights

KPFM measurement was successfully performed on OIHP solar cells for elucidating performance at a low-illumination condition. We observed that charge separation at GBs in OIHP solar cells is higher when c-TiO2 is employed as an electron transport layer compared to that of m-TiO2. Our results highlight that our KPFM technique can be effectively employed for elucidating charge transport properties of nanoscale defects under different light intensities.

Future Work

• We plan to set up a time-resolved KPFM measurement which will allow us to image nanoscale charge-carrier dynamics using light modulation or bias modulation.

• UNSW team and ORNL researchers will collaborate on nanoscale elemental mapping of halide perovskites using a nano-IR technique.

• In order to investigate pn junction properties, we will develop procedures for imaging a cross-section of solar cells

Figure 3.3.12: Device structures of halide perovskite solar cells based on (a) compact- and (d) mesoporous-TiO2 layers employed in this study. CPD images (16 μm2) measured under dark, 400 lux and 1600 lux LED light for perovskites on (b) compact- and (e) mesoporous-TiO2 layers. CPD line profiles of white dotted lines in (b) and (e) at different light intensities 400 (low), 800 (med) and 1600 (high) lux.

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PP3.4A PHOTOTHERMAL DEFLECTION One of the most important parameters to measure is the optical absorption spectrum. Unfortunately, this can be problematic. Currently SPECTROSCOPY (PDS) available instruments are typically insufficiently sensitive to extract an accurate absorption spectrum from thin-film materials. This is Lead Partner particularly true for measurements in the so-called ‘sub-bandgap’ UNSW region; this region contains vital information on defects and Urbach tails, which are key determinants of material quality. Without detailed UNSW Team feedback on their material characteristics, researchers have to work Xiaojing Hao, Gavin Conibeer, Michael Pollard, Henner Kampwerth, blindly via trial and error. Ivan Perez-Würfl Initially, the aim was to establish a new photo-absorption spectrometer UNSW Student at UNSW with sufficient sensitivity to fulfil all of our researchers’ needs. Xueyun Zhang This aim went so well and the popularity of the spectrometer was so Macquarie University Team great, that the aim was extended to include the commercialisation Binesh Puthen Veettil of this instrument. This way, it is possible to make it available to the greater PV community. Tokyo University Team Prof. Masakazu Sugiyama, Prof. Yoshitaka Okada Background Industry Partner The optical setup that was chosen is based on a photothermal Open Instruments deflection spectrometer (PDS). The PDS setup measures the heat Funding Support signature of a material sample, or thin film, that is created by absorbed AUSIAPV, UNSW, Tokyo University light. As shown in Figure PP3.4.1, monochromatic light illuminates a thin-film sample immersed in a viscous, optically transparent solution Aims (in this case Fluorinert FC72). The film heats up depending on the amount of light absorbed; this in turn heats the liquid, changing locally Second and third generation photovoltaic devices employ increasingly its refractive index. thin films of photoactive materials. Important examples are those based on CZTS and perovskites, which are promising for commercial The amount of heat dissipated by the liquid is then measured deployment. The electrical and optical properties of these materials by passing a laser beam through the heated zone of the liquid. can be tuned over a wide wavelength range by altering their The refractive index gradient within the liquid forms a “lens” that constituent elements and growth methods. As with all optimisation deflects the laser beam slightly. This is also called a mirage effect. procedures, accurately measuring the effect of material changes is The deflection of the laser beam is measured at a distance with a critical. position-sensitive detector. To increase the sensitivity, the heating monochromatic light is optically chopped, allowing operation in lock-in mode.

Figure PP3.4.1: The heart of the PDS system is the “mirage effect” that makes the very small amount of absorbed light measurable. It is doing so by suspending the material sample in a liquid (e.g. carbon tetrachloride, carbon disulfide) that changes its optical refractive index strongly with temperature. Light that is absorbed by the sample creates a tiny amount of heat, which then causes a refractive gradient (mirage) around that area in the liquid. This gradient is effectively forming a lens that can deflect a probing laser beam. The beam deflection can then be measured by a position detector. The distance to that detector acts as an optical cantilever, making the entire system extremely sensitive.

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The three principal advantages of this technique are that: Progress

• It is exceptionally sensitive to photo-absorption (100 to 1000 times From 2013 to 2015, ARENA funded the basic development of a more sensitive compared to the commonly used reflection and photothermal deflection spectrometer (PDS) at SPREE, UNSW transmission technique). (Figure PP3.4.2). With ultra-high sensitivity, this instrument was able to accurately measure absorption spectra and it exceeded the • It is particularly sensitive to near-surface photo-absorption, thus performance of commercially available absorption spectrometers by significantly reducing the influence of substrate absorption. 3 orders of magnitude (1000x). Since commissioning, it has become • It has no wavelength limitations. The actual detection mechanism popular among researchers in several research groups. (temperature  refractive index laser deflection) is wavelength- independent. Unlike techniques that rely on photodetectors, PDS is insensitive to strong dark noise in the IR range.

Figure PP3.4.2: The first version of a working PDS system at UNSW was built in 2013.

The first step to commercialisation was to overcome the very time- advanced vibration isolation. It was showcased to great interest at the consuming mechanical alignment procedure that has to be performed annual Asia-Pacific Solar Research Conference (APSRC) at UNSW in for each sample, which can cost even experienced users more than December 2018. an hour. This important hurdle was surmounted in 2017 through an The third step towards sustained commercialisation was to work ACAP-funded project (Puthen-Veettil 2016) that included a highly on continued research in advanced measurement modes. ARENA/ effective collaboration between UNSW and Open Instruments Pty. Ltd., AUSIAPV funding allowed for a strategic collaboration between which was founded by Dr Kampwerth. The successful co-development UNSW, Tokyo University and Open Instruments (Hao, X. 2018). The between both project partners resulted in two reliable working collaboration is set to explore a new PDS measurement technique, prototypes that met the goals. A sample can be loaded and unloaded attempting to measure the “dark” portion of carrier recombination in less than four minutes and positioning repeatability of better than via combinations of optical and electrical biasing during the PDS 5 μm has been achieved. measurement. Direct measurement of the “dark” carrier recombination The second step towards commercialisation was marked by would be a world first and would open up new insight into materials. the increased efforts of the primary industrial collaborator, Open This new project has already provided fruitful discussions with Instruments. Dr Kampwerth and Dr Pollard (both Open Instruments) Professor Sugiyama and Professor Okada from Tokyo University. The and Dr Veettil (UNSW) took the next steps towards commercialisation. project is ongoing. First Dr Veettil’s first version, shown in Figure PP3.4.2, had a footprint The fourth step is to build a demonstrator unit, develop a prototype of 240 cm x 90 cm and required an air-suspended vibration isolation that is manufacturable in reasonable quantities and launch the table, a quiet room and literally no air movement. The work by Open product. With this in mind, Dr Kampwerth and Dr Pollard attended an Instruments first began on making the system more compact while ARENA / CSIRO ON Prime program and subsequently secured the retaining the instrument’s functionality. After multiple iterations and associated competitive ARENA “Commercialisation of R&D Funding testing of OEM parts, a fully integrated system was built, as shown Initiative” (Kampwerth, 2019). The majority of this exciting work will in Figure PP3.4.3. Its size was further reduced to 35% of that of the occur in 2020. first laboratory version and includes all electronics, the computer and

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Aims

Recent advances in photovoltaic research, particularly in novel material synthesis, require the use of an optoelectronic characterisation technique to complement standard photoluminescence measurements in support of developing new photovoltaic technologies. With the development of novel photovoltaic materials, driven by the push to find the ideal tandem-on-silicon material, the determination of critical points in the material band structure (such as the bandgap) can be directly linked back to theoretical calculations to Figure PP3.4.3: The first commercial beta version of a PDS unit was assist in the development of synthesis/fabrication parameters. presented at the APSRC at UNSW in December 2018. In modulation spectroscopic techniques an external periodic Highlights perturbation to a material yields information on the optical spectra of a material in the form of sharp differential features around • The world’s first alignment-free sample stage for an ultra-sensitive optical transitions. In photoreflectance (PR), an external optical bias PDS system was successfully built and tested. The time for (normally a laser) provides the perturbation to the optical spectra via sample loading was reduced from 30–60 minutes to less than the diffusion of optically generated charge carriers. These create a 4 minutes. perturbation of the dielectric function of the material around critical • The first pre-commercial (beta version) unit of a PDS instrument points (such as band edges), observed optically as a change in was presented at APSRC at UNSW in December 2018. the reflection or transmission of a sample. Photoreflectance thus measures tiny changes in the reflection. This can be done even for • International collaboration with Tokyo University commenced defected materials which may not produce any photoluminescence, to further enhance the capabilities of PDS to new measurement providing an early characterisation step. Moreover, the PR signal modes. position is not influenced by the presence of defects, providing a • Funding for a commercial launch have been found and work has more accurate measurement of the bandgap than photoluminescence begone. can provide.

Future Work

The UNSW/Open Instruments team intends to include further research groups and companies into the exciting co-development of the PDS system. Early commercial units will be made available to partners beginning 2021. The aim is to make the instrument as robust, reliable and user-friendly as possible. A public release is planned for the second half of 2021.

Figure PP3.4.4: Image and schematic of the double demodulation photoreflectance setup. PP3.4B PHOTOREFLECTANCE (PR) In addition to identifying critical points in the band structure of a SPECTROSCOPY material, PR yields information relating to electric fields at interfaces and surfaces according to the Franz–Keldysh effect. As such, PR is Lead Partner useful for comparing surface field-effect passivation layers on new UNSW materials without requiring full device fabrication. Moreover, it provides a method to measure the built-in electric field (or voltage) of a finished UNSW Team device. Nicholas J. Ekins-Daukes, Michael P. Nielsen, Xiaojing Hao, Martin Green, Henner Kampwerth Where PR is similar to photoluminescence as an optical characterisation technique relying on a pump laser, there is also UNSW Student an electrical analogue similar to electroluminescence called Xueyun Zhang electroreflectance. This requires contacted devices but has a much Funding Support stronger signal than PR. For fully contacted devices, this technique ARENA, UNSW also limits the resultant signal to the junction area of the device.

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Progress PP3.4.6 depicts two representative examples, a single-junction GaAs cell (Figure PP3.4.6A-C) and a GaInP/GaAs tandem cell (Figure As seen in the schematic of the experimental setup shown in PP3.4.6D-F). Figure PP3.4.4, the PR technique here is implemented in a double demodulation scheme for improved signal detection. A probe beam Highlights from a xenon/halogen lamp and monochromator is chopped at ω1 and focused on the sample. The reflected beam is then focused • An easy-to-use non-contact optical characterisation method for and detected on a biased Si or InGaAs detector, depending on the determining the bandgap and higher order band edges of new wavelength regime of interest, and the resultant signal is boosted by materials. a current pre-amplifier before being fed into a multi-channel lock-in. • Can also measure the intensity of the electric field related to built- To generate the perturbation, a 532 nm pump laser chopped at ω is 2 in potentials at interfaces and surfaces, associated with what is aligned to the probe spot on the sample. The PR signal ∆R⁄R is the known as Franz–Keldysh Oscillations (FKOs). signal detected at ω1+ ω2 divided by the baseline reflectance detected at ω1. • Adaptable to an electrically driven characterisation technique known as electroreflectance for fully contacted samples and Antimony sulfide (Sb S ) is a representative example of a photovoltaic 2 3 devices. absorber material attracting interest for its Earth-abundant and non-toxic composite materials. Figure PP3.4.5 compared the PR Future Work and photoluminescence spectra from an Sb2S3 solar cell. While the photoluminescence measurements show a broad peak centred The UNSW team would like to apply the technique to a further range roughly around 1.62 eV, the PR measurement gives a more accurate of photovoltaic materials such as quantum dot solar cells and estimation of the bandgap of the Sb2S3 absorber layer of 1.64 eV, and quantum well solar cells to demonstrate the capacity of the system also provides a determination of the bandgap of the CdS electron to distinguish signatures related to quantum confinement from those transport layer (ETL) of 2.3 eV. from delocalised band states. Other goals include the application to materials with strong exciton binding energies, such as perovskites, The other main application of photoreflectance is the analysis and extending the study on field-effect passivation layers to standard of Franz–Keldysh oscillations (FKOs) which can occur at higher photovoltaic materials such as silicon. energies than the critical point in the PR spectra and are associated with the built-in electric fields at interfaces and surfaces. Not shown References here, but the measurement of the electric field at a surface can be ANN, M. H., KIM, J., KIM, M., ALOSAIMI, G., KIM, D., HA, N. Y., SEIDEL, directly related to the effect of the surface passivation layer, as one J., PARK, N., YUN, J. S. & KIM, J. H. 2020. Device design rules and of the main purposes of a passivation layer is to create a surface operation principles of high-power perovskite solar cells for indoor electric field to screen carriers from surface recombination sites. applications. Nano Energy, 68, 104321. Thus, photoreflectance can provide a contactless measurement for passivation layer development of new and old photovoltaic materials. BASNET, R., SUN, C., WU, H. T., NGUYEN, H. T., ROUGIEUX, F. E. & MACDONALD, D. 2018. Ring defects in n-type Czochralski-grown In addition, the analysis of FKOs can be extended to measuring silicon: A high spatial resolution study using Fourier-transform infrared the built-in electric fields of the junction region of a finished spectroscopy, micro-photoluminescence, and micro-Raman. Journal of photovoltaic cell, providing a value for the PR technique throughout Applied Physics, 124. DOI: 10.1063/1.5057724 the development life cycle of a new photovoltaic material. Figure

Figure PP3.4.5: Photoreflectance characterisation of an Sb2S3 solar cell compared to standard photoluminescence measurements. (A)

Schematic representation of the Sb2S3 solar cell. (B) Photoluminescence measurements indicating an absorber bandgap of 1.62 eV. (C) Photoreflectance measurements depicting a more accurate bandgap estimate of 1.64 eV along with an estimate of the CdS electron transport layer (ETL) bandgap of 2.3 eV.

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Figure PP3.4.6: Determination of built-in electric fields via analysis of Franz–Keldysh oscillations (FKOs) of both single and tandem devices. (A) Single-junction GaAs photovoltaic stack along with (B) photoreflectance spectra to determine the bandgap of the absorber, and (C) Franz–Keldysh oscillation analysis of the built-in electric field. (D) Tandem GaAs/GaInP photovoltaic stack along with (E) photoreflectance spectra to determine the bandgap of the absorbers, and (F) Franz–Keldysh oscillation analysis of the built-in electric field of the GaAs using an alternative analysis to (C).

HAO, X. 2018. Advancing the PDS technique for all photovoltaic thin- Understanding Passivating-Contact Solar Cells. ACS Applied Energy films. ARENA / ASI-USASEC Strategic Research Initiative, Collaboration Materials, 1, 6619-6625. Grants, Round 4. PUTHEN-VEETTIL, B. 2016. Alignment-free PDS tool: From university KAMPWERTH, H. 2019. Launch of a Photothermal Absorption to industry. ARENA / ACAP Collaboration Grant, Round 3. Spectrometer for Cost Reduction in PV Materials. ARENA TEBYETEKERWA, M., ZHANG, J., LIANG, K., DUONG, T., NEUPANE, G. P., Commercialisation of R&D Funding Initiative. ZHANG, L. L., LIU, B. Q., TRUONG, T. N., BASNET, R., QIAO, X. J., YIN, Z. LEE, T., BURN, P. L. & MARK, A. E. 2019. Effect of Surface Roughness Y., LU, Y. R., MACDONALD, D. & NGUYEN, H. T. 2019. Quantifying Quasi- on Light-Absorber Orientation in an Organic Photovoltaic Film. Fermi Level Splitting and Mapping its Heterogeneity in Atomically Thin Chemistry of Materials, 31, 6918-6924. Transition Metal Dichalcogenides. Advanced Materials, 31, 1900522.

NGUYEN, H. T., GERRITSEN, S., MAHMUD, M. A., WU, Y. L., CAI, Z. Y., TRUONG, T. N., YAN, D., CHEN, W. H., TEBYETEKERWA, M., YOUNG, M., TRUONG, T., TEBYETEKERWA, M., DUONG, T., PENG, J., WEBER, K., AL-JASSIM, M., CUEVAS, A., MACDONALD, D. & NGUYEN, H. T. 2019b. WHITE, T. P., CATCHPOLE, K. & MACDONALD, D. 2020. Spatially and Hydrogenation Mechanisms of Poly-Si/SiOx Passivating Contacts by Spectrally Resolved Absorptivity: New Approach for Degradation Different Capping Layers. Solar RRL. DOI: 10.1002/solr.201900476 Studies in Perovskite and Perovskite/Silicon Tandem Solar Cells. TRUONG, T. N., YAN, D., SAMUNDSETT, C., BASNET, R., Advanced Energy Materials, 10. DOI: 10.1002/aenm.201902901 TEBYETEKERWA, M., LI, L., KRERNER, F., CUEVAS, A., MACDONALD, NGUYEN, H. T., LI, Z. F., HAN, Y. J., BASNET, R., TEBYETEKERWA, D. & NGUYEN, H. T. 2019a. Hydrogenation of Phosphorus-Doped M., TRUONG, T. N., WU, H. T., YAN, D. & MACDONALD, D. 2019. Polycrystalline Silicon Films for Passivating Contact Solar Cells. ACS Contactless, nondestructive determination of dopant profiles of Applied Materials & Interfaces, 11, 5554-5560. localized boron-diffused regions in silicon wafers at room temperature. TRUONG, T. N., YAN, D., SAMUNDSETT, C., LIU, A. Y., HARVEY, S. P., Scientific Reports, 9. YOUNG, M., DING, Z. T., TEBYETEKERWA, M., KREMER, F., AL-JASSIM, NGUYEN, H. T., LIU, A., YAN, D., GUTHREY, H., TRUONG, T. N., M., CUEVAS, A., MACDONALD, D. & NGUYEN, H. T. 2019c. Hydrogen- TEBYETEKERWA, M., LI, Z., LI, Z., AL-JASSIM, M. M., CUEVAS, A. & Assisted Defect-Engineering of Doped Poly-Si Films for Passivating MACDONALD, D. 2018. Sub-Bandgap Luminescence from Doped Contact Solar Cells. ACS Applied Energy Materials, 2, 8783-8791. DOI: Polycrystalline and Amorphous Silicon Films and Its Appliication to 10.1021/acsaem.9b01771

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PP4 MANUFACTURING ISSUES

OVERVIEW

PP4, entitled “Manufacturing Issues” concentrates on costs, both financial (PP4.1) and environmental (PP4.2). The methods in each have a great deal of similarity, since both rely heavily on inventories of estimates and measurements of inputs and outputs of manufacturing processes.

Work under PP4.1 has produced a methodology for assessing manufacturing costs for the different technologies under investigation under the ACAP program. This is a resource for assessing the cost of different processes with a view to informing research efforts on the key cost drivers and opportunities and to understand how the technology fits in roadmaps for photovoltaics. In 2019, the cost methodology was again applied to a wide variety of PV technologies building on the library of results of earlier modelling. The methods are tolerant of uncertainty in the data and, so, permit rapid assessment of emerging technologies. The new analyses included additional silicon/ perovskite tandems, colloidal quantum dot solar cells, III-V on silicon tandems, uncertainties in future c-Si PV manufacturing costs and production of hydrogen using PV driven electrolysis.

Similarly, in PP4.2, the initial focus was on using the life cycle assessment (LCA) methodology to assess the life cycle environmental costs, to inform research directions and policymakers by documenting the costs for a set of key environmental impacts of different ways of manufacturing cells and modules. Interest in extending the boundaries of these studies has now led to an inclusion of end-of-life (EoL), to “close the loop”. EoL of products has traditionally been excluded from manufacturing costs estimates but some jurisdictions globally are already requiring “stewardship” or other responsibility measures for certain types of products, including photovoltaic modules, so it is becoming necessary to incorporate it into costs models. In this context, LCA studies have been extended to include EoL and to apply LCA to alternative EoL pathways, along with exploring new technology pathways for recycling.

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PP4.1 COST ANALYSES

Lead Partner UNSW

UNSW Team Dr Nathan Chang, A/Prof Renate Egan, Dr Anita Ho-Baillie, Prof Martin Green

Partner Organisations CSIRO, ANU, Monash, UoM, UQ

Academic Partner NREL

Aims Figure PP4.1.1: Sunshot 2030 goals. Driven by a need to provide a framework for costing of new technologies, the aim of Program Package 4 (PP4) is to deliver a Progress methodology for assessing manufacturing costs for the different technologies under investigation under the ACAP program. Modelling A key outcome of the efforts under PP4.1 is to provide a resource for of the cost and competitiveness quantifies the potential of new assessing the cost of different processes with a view to informing technologies and informs decision making around priority areas for research efforts on the key cost drivers and opportunities and to research, giving consideration to potential benefit, risk, scale and understand how the technology fits on the costs and marketing capital cost. roadmaps for photovoltaics.

The SunShot targets are used as benchmarks for comparison of the Over 2019, the cost methodology has been applied again to a wide outcomes of the cost calculations. The aims for ACAP are to develop variety of PV technologies, in particular: (i) recent improvements in technologies that contribute to meeting and exceeding the SunShot silicon/perovskite tandems, (ii) colloidal quantum dot cells and (iii) targets, which will help to provide the stimulus needed to encourage III-V/Silicon tandems. In addition, it has expanded in its application increasing investment in these technology developments. – to (iv) consider uncertainty in future (5-year time frame) costs of c-Si PV, as well as (v) the levelised cost of hydrogen produced using Targets standalone PV driven electrolysis.

The US SunShot Initiative has LCOE (levelised cost of energy) A. Costing methodology targets for photovoltaics (PV), and the US Department of Energy has developed models to project how these might be met. The current The costing methodology developed by ACAP is summarised in SunShot 2030 goal and pathways to meeting it are summarised Figure PP4.1.2. This methodology has been described in publications in Figure PP4.1.1. The ACAP research program aims to contribute (Chang 2017; Chang 2018) and has been applied this year to the to meeting these cost targets through new materials and device various technologies described in section B below. More detail on the developments that improve the sustainable module price measured in motivation for such cost analysis, and the Monte Carlo uncertainty $/W (through both efficiency improvements and cost improvements) methodology developed by ACAP are described in Fellowship and improve lifetime by reducing degradation mechanisms. These Report F1. ACAP efforts are described in detail in PP1, PP2 and PP3. The Manufacturing Issues program provides the framework for comparing the manufacturability and competitiveness of the innovative technologies under investigation within the ACAP group.

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These two new tandem cell results were achieved using different process sequences and were analysed and compared to the old results. Analysis of the cost of these four structures resulted in the cost distribution shown in Figure PP4.1.4. For the UNSW structures, there was a small increase in cost, as a more complex perovskite mixture was used, as well as modifications to the silicon cell – this partially offset the benefit gained with the higher efficiency. For the ANU structure, the improved efficiency was achieved while simplifying the processing sequence, thus saving in projected manufacturing costs ($/cell) as well as improving efficiency. A publication that combines the analysis of all four sequences is under preparation (Chang, in preparation (a)).

Figure PP4.1.2: Cost model overview.

B. Perovskite/silicon tandem cells (UNSW, ANU)

In the 2018 ACAP report, it was already reported that two perovskite/ silicon tandem structures (Zheng, 2018 and Wu, 2017) were analysed using the ACAP cost analysis methodology. Since that time, two improved efficiency tandem cells have been achieved (Zheng, 2019 and Shen, 2018). All four structures are shown in Figure PP4.1.3.

Figure PP4.1.4: Cost model overview.

C. Colloidal quantum dots (UNSW)

Colloidal quantum dot (CQD) photovoltaics is an emerging technology with the potential for high efficiency and stability, combined with the potential for low temperature and low-cost fabrication techniques. However, at this early stage of development, the process sequences are not optimised for cost, and the efficiency of the cells is much lower than other technologies.

As a first step, it was assumed that the lab-based processes currently used to make CQD solar cells were used to produce large volumes of cells and modules. The resulting baseline cost distribution is shown as sequence A in Figure PP4.1.5. This cost of manufacture is very high – which is not surprising given the early stage of development. Closer examination of the cost components (Figure PP4.1.6) revealed that the labour-intensive fabrication methods assumed for making the CQDs, combined with high wastage of the fabricated CQDs and the use of gold in the top metal layer dominated the cost. A pathway to improve cost was identified – scaling up CQD fabrication to larger batch sizes, using a less wasteful dip-coating process rather than spin coating to deposit the CQD, and replacing the gold with silver. The cost modelling showed that if successful, these changes would reduce the Figure PP4.1.3: Cost model overview. manufacturing cost by nearly a factor of 10, shown as sequence B in Figure PP4.1.5. This provided direction and motivation to implement these process improvements.

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E. Future cost projections for c-Si PV (UNSW, TNO)

The projected future cost of the industry standard c-Si PV modules is commonly estimated from historical learning rates and expected growth in the industry. In this collaboration with TNO, Netherlands, a more fine-grained analysis was completed, where an estimate of future (5-year) costs is completed using a bottom-up cost-of- ownership calculator. The uncertainty range of over 100 input variables are estimated based on historical trends and combined using the ACAP Monte Carlo uncertainty model. Figure PP4.1.8 shows an example of the impact of key uncertainty variables on the expected 5-year timeframe cost reduction. This work is under preparation for publication (Chang, in preparation (b)).

Figure PP4.1.5: Cost uncertainty distributions for the baseline and improved sequences.

Figure PP4.1.8: The impact of three dominant uncertainties on the Figure PP4.1.6: Cost breakdown of the baseline sequence by process 5-year cost reduction projections. step. F. Hydrogen production using PV-driven electrolysis (UNSW) D. III-V/silicon tandems (UNSW, SKKU) As discussed in Fellowship Report F1, the cost methodology has New developments in III-V on silicon tandem cells have been achieved been expanded to an area new to ACAP. In collaboration with UNSW’s in a partnership between UNSW and Sungkyunkwan University. As part Chemical Engineering school, the use of a PV system combined with of this project, ACAP assisted in conducting some cost analysis of the electrolysis in a standalone configuration (that is not grid connected) III-V on silicon structure developed during the project, and compared was analysed to calculate the levelised cost of hydrogen (LCOH). it to an alternative direct deposition structure. Using data from cost A cost that is compatible with targets for green hydrogen were reports in literature allowed an overview comparison of the two obtained, with sensitivities to system size, electrolyser efficiency and structures. PV/electrolyser capex explored. This work is described in a paper Results as shown in Figure PP4.1.7 identified the key cost drivers as under review (Yates, in review). An example of an exploration of the the III-V layers, with high uncertainty as to their potential for lower cost parameter space is shown in Figure PP4.1.9. deposition, as well as the high cost epitaxial lift-off (ELO) process.

Figure PP4.1.9: Sensitivity of the levelised cost of hydrogen to Figure PP4.1.7: Cost compenents of the alternate tandem the capital costs of the PV system, electrolyser system and the sequences. efficiency of the electrolyser. 94 ACAP ANNUAL REPORT 2019

Summary SHEN, H. P., OMELCHENKO, S. T., JACOBS, D. A., YALAMANCHILI, The Manufacturing Issues program continues to develop methods for S., WAN, Y. M., YAN, D., PHANG, P., DUONG, T., WU, Y. L., YIN, Y. T., assessing the manufacturing costing of new technologies. The cost SAMUNDSETT, C., PENG, J., WU, N. D., WHITE, T. P., ANDERSSON, and uncertainty methods developed allow uncertainties in individual G. G., LEWIS, N. S. & CATCHPOLE, K. R. 2018. In situ recombination process costs, performance and market value to be assessed. These junction between p-Si and TiO enables high-efficiency monolithic uncertainties are combined using a Monte Carlo simulation. 2 perovskite/Si tandem cells. Science Advances, 4. The methods used do not require precise information on every data WU, Y. L., YAN, D., PENG, J., DUONG, T., WAN, Y. M., PHANG, S. P., parameter and so allow for rapid analysis of emerging technologies. SHEN, H. P., WU, N. D., BARUGKIN, C., FU, X., SURVE, S., GRANT, D., In doing so, the analysis reveals the key drivers, technology risks and WALTER, D., WHITE, T. P., CATCHPOLE, K. R. & WEBER, K. J. 2017. critical uncertainties to guide research directions. Monolithic perovskite/silicon-homojunction tandem solar cell with The costing analyses in 2019 included an expansion of the previous over 22% efficiency.Energy & Environmental Science, 10, 2472-2479. silicon/perovskite tandem results, colloidal quantum dot solar YATES, J., DAIYAN, R., PATTERSON, R., EGAN, R. J., AMAL, R., HO- cells and III-V on silicon tandems. The method was also applied to BAILLIE, A. & CHANG, N. L. (Under review). Techno-economic analysis uncertainties in future c-Si PV manufacturing costs and to the cost of of hydrogen electrolysis from off-grid stand-alone photovoltaics producing hydrogen using PV-driven electrolysis. incorporating uncertainty analysis.

Highlights ZHENG, J. H., LAU, C. F. J., MEHRVARZ, H., MA, F. J., JIANG, Y. J., DENG, X. F., SOERIYADI, A., KIM, J., ZHANG, M., HU, L., CUI, X., LEE, • Techno-economic analysis of a wide variety of PV technologies at D. S., BING, J. M., CHO, Y., CHEN, C., GREEN, M. A., HUANG, S. J. & different technology readiness levels (TRLs). HO-BAILLIE, A. W. Y. 2018. Large area efficient interface layer free • Collaboration with a variety of institutions in Australia and monolithic perovskite/homo-junction-silicon tandem solar cell with internationally. over 20% efficiency.Energy & Environmental Science, 11, 2432-2443.

• Application to future cost projections of c-Si PV. ZHENG, J. H., MEHRVARZ, H., LIAO, C., BING, J. M., CUI, X., LI, Y., GONCALES, V. R., LAU, C. F. J., LEE, D. S., LI, Y., ZHANG, M., KIM, J. C., • Application to the generation of hydrogen using PV-driven CHO, Y., CARO, L. G., TANG, S., CHEN, C., HUANG, S. J. & HO-BAILLIE, electrolysis. A. W. Y. 2019. Large-Area 23%-Efficient Monolithic Perovskite/ Homojunction-Silicon Tandem Solar Cell with Enhanced UV Stability Future Work Using Down-Shifting Material. ACS Energy Letters, 4, 2623-2631. • Analysis of additional PV technologies and processes.

• Development of the methodology as required for new analyses.

• Continuing dissemination of the methods via collaboration and the creating of tools to enable effective collaboration.

References

CHANG, N. L., HO-BAILLIE, A. W. Y., BASORE, P. A., YOUNG, T. L., EVANS, R. & EGAN, R. J. 2017. A manufacturing cost estimation method with uncertainty analysis and its application to perovskite on glass photovoltaic modules. Progress in Photovoltaics, 25, 390-405.

CHANG, N. L., HO-BAILLIE, A., WENHAM, S., WOODHOUSE, M., EVANS, R., TJAHJONO, B., QI, F., CHONG, C. M. & EGAN, R. J. 2018. A techno- economic analysis method for guiding research and investment directions for c-Si photovoltaics and its application to Al-BSF, PERC, LDSE and advanced hydrogenation. Sustainable Energy & Fuels, 2, 1007-1019.

CHANG, N. L., NEWMAN, B. & EGAN, R. J. (in preparation b). A future cost model of c-Si PV modules incorporating uncertainty.

CHANG, N. L., ZHENG, J. H., WU, Y., SHEN, H., CATCHPOLE, K. R., HO-BAILLIE, A. & EGAN, R. J. (in preparation a). A techno-economic analysis of silicon perovskite tandem cell.

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PP4.2 LIFE CYCLE ASSESSMENTS

Lead Partner UNSW

UNSW Team Dr Marina Monteiro Lunardi, Dr Jose Bilbao, Dr Richard Corkish

UNSW Students Rong Deng, Xinyi Zhang

Academic Partners Federal University of Rio Grande do Sul (UFRGS), Brazil

Aims

Motivated by a necessity to look at possible end-of-life (EoL) solutions for c-Si solar modules, the PP4.2 program aims to deliver a comprehensive study of waste management approaches for PV modules using the life Figure PP4.2.1: Outlook of global installations today and in the future (in TW ). Adapted from (ITRPV, 2018). cycle assessment (LCA) methodology for assessing their environmental p impacts and those of various EoL options. Modelling the ecological costs modules management (de Wild-Scholten et al., 2005), and regulations of different methods quantifies the potential of new technologies under can encourage cost-effective and environmentally friendly recycling investigation in the ACAP program and informs decision making around technologies (Kang et al., 2012, Bombach et al., 2006, Tao and Yu, priority areas for research, considering potential environmental benefit 2015). and risks or recycling processes. It is well known that today most of the PV modules go to landfill At UNSW, EoL processes were evaluated for c-Si solar modules, and and the reason for that is mainly because the regulation in most comparative LCA studies were conducted aiming to guide research of countries is not yet established, as already mentioned, and also efforts towards recycling processes with minimum environmental because the recycling processes are not yet economically favourable. impacts. The LCA studies conducted considered different impact It has been shown that, for the current PV recycling technologies, categories such as global warming potential (GWP), human toxicity Si-based modules do not have sufficient valuable materials to make potential, cancer and non-cancer effects (HTP-CE and HTP-nCE, recycling financially viable. Consequently, the amount of PV waste respectively), freshwater eutrophication potential (FEuP), freshwater being taken to recycling facilities is currently insignificant compared ecotoxicity potential (FEcP) and abiotic depletion potential (ADP) impacts. to the amount of other electronic waste. There are different PV waste approaches, which are landfill, incineration, reuse and recycling, and Progress each one of them has particular characteristics and can offer various environmental benefits or disadvantages on the PV modules’ overall Predictions for the growth of the solar photovoltaic (PV) market impacts (Lunardi et al., 2018). are optimistic (Figure PP4.2.1). According to a new report issued by research firm IHS Markit (Nhede, 2019), in 2019 PV systems Aiming to reduce the environmental impacts and to recover some of should reach more than 120 GW of solar installations globally, which the valuable materials from PV waste, methods for recycling solar represents a considerable growth compared to 2017 (compound modules are being developed worldwide. There is still a lot of room annual rate: 93.9-GWp), and even more significant if compared to 1997 for improvement in these processes, as current recycling methods are (yearly compound rate: 114.1-MWp) (Mints, 2018). Crystalline silicon mostly based on downcycling processes, recovering only a portion of (c-Si) technologies continue to lead this market (approximately 95%) the materials and value. (ITRPV, 2018). Current indications show that China remains the world’s Recycling processes for thin-film PV technologies are under largest PV market, after reaching around 44 GW in 2018 (Bahar, 2019). development in countries including Italy, Japan and South Korea. The substantial progress in solar energy usage is critical in the search Even with up to 90% recovery of materials from CdTe solar modules for a more sustainable economy. However, this global increase in their value is still not sufficient compared to the production costs, PV installations will also produce a considerable amount of waste, so these processes are not yet competitive (AssiaBiomassOffice, which may account for up to 8.0 million tonnes annually by 2030 2017). It has been shown that more complex procedures can achieve (Weckend et al., 2016). The global rise of PV waste requires specific recovery rates up to 95% and high commercial value materials can regulations and proper treatment/recycling processes to deal with be recovered but, currently, these processes are still being tested at this type of discarded material. The European Union has included PV laboratory scale (Kadro et al., 2016). waste into their Waste of Electrical and Electronic Equipment (WEEE) Commercially available in Europe and created by PV Cycle, the most directive since 2012 (Shin et al., 2017) but policies addressing the recent recycling process for Si-based modules can recover 96% of EoL management of PV waste are less developed in other countries. materials from the EoL modules using a new method that combines The progress of PV technology and its maintenance as a sustainable mechanical and thermal treatments (Kenning, 2016). technology depends on the continuous development of the EoL

96 ACAP ANNUAL REPORT 2019

Generally, the first step to recycle c-Si PV modules is to separate the aluminium frame and the junction box mechanically. After that, the challenge is to delaminate or remove the encapsulant material, which is usually ethylene-vinyl-acetate (EVA) for Si-based solar modules. Several techniques can be used in this phase, including thermal, and chemical (organic and inorganic) and mechanical recycling processes.

The existing PV recycling processes involve significant quantities of electricity (which may come from non-renewable sources) and/ or chemicals, which creates some concerns about the potential environmental impacts associated with these methods. Hence, the LCA method should be conducted together with the development of new recycling technologies.

A. LCA of experimental recycling processes for c-Si solar modules (UNSW, UFRGS) Figure PP4.2.2: ReCiPe results (Human Health, Ecosystem and Resources) for Experiments 1 (E1) and Experiment 2 (E2). Based on experiments conducted at UNSW (Australia) and UFRGS (Brazil) and available data from the literature, we estimated the environmental impacts of different EoL scenarios for Si-based PV A simple method for rapid recycling of silver from modules (Lunardi, M. M. et al., 2018), excluding transportation. A decommissioned silicon PV (UNSW) summary of all results is calculated using the ReCiPe method, which Another critical study was conducted at UNSW focusing on the harmonises the environmental impacts calculated. An LCA analysis importance of recovering precious metals, such as silver (Ag), from was implemented by collecting and analysing information from the solar cells. Methods of recovering Ag have been studied and they whole product/process life cycle, considering inputs and outputs such usually consist of two main steps: leaching Ag in an acidic solution, as energy, materials, wastes and emissions, and the results can be then extracting the metal by hydrometallurgical processes. Different used to inform the public sector, stakeholders, manufacturers and in leaching solutions have been tested, such as NaOH and H SO , but the design and implementation of new policies. The details and results 2 4 high leaching yield (>90%) is usually obtained by using concentrated are presented in Section 6.36, in the Appendix to this report. Here, we nitric acid (HNO ) or aqua regia (Lee et al., 2013). After dissolving in the briefly describe our experimental processes (Table PP4.2.1) and show 3 chemical solution, Ag can be extracted by different methods, such as the results in Figure PP4.2.2. See Section 6.36 for more information. precipitation, electrowinning and metal replacement. The limitations The results are presented using the ReCiPe method, which is usually of this process are that it takes hours to achieve high recovery rate, beneficial to aid the understanding of the different environmental it requires a large amount of concentrated acid solutions, and this impacts if the target audience is not expert in this field because chemical generates health and environmental concerns (e.g. emission they are represented in terms of three main effects: Human Health of nitric oxides). effects, Ecosystems impacts and Resources depletion. The results for At UNSW, we introduced a novel method and setup to recover front Experiments 1 and 2 are shown in Figure PP4.2.2. side Ag metallisation from decommissioned Si solar cells (R. Deng et al., 2019). The simple process can recycle more than 75% Ag (> 99% purity) within 10 minutes, and it starts with an HNO3 etching, in which all surface Ag residues can be removed to recover the high-purity Table PP4.2.1: Brief description of Experiments 1 and 2. Si wafer. The LCA study of this process was conducted showing its

Experiment 1 Experiment 2

Preparation – Frameless module Preparation – Mechanical separation

(without junction box) (junction box and frame are removed manually)*

Step 1 – Thermal separation Step 1 – Chemical separation (toluene + heating plate)

Step 2 – Chemical separation (nitric acid + ultrasonic bath) Step 2 – Manual separation

*Not considering the impacts of this process step, since there was no electricity/chemical usage involved (manually separated).

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potential environmental impacts and identified directions to lower the negative effects further.

Six-inch commercial multicrystalline Si solar cells (output efficiency of 17.5–19.0%) were used in the experiment. The solar cell aluminium rear contact was attached to the graphite pad, and an Ag mesh was chosen as the cathode and it was placed on the bottom of the recycling bath. Diluted Helios Silver Plating Solution was used as the electrolyte, HNO3 was added to the solution to adjust the pH to 1.2–1.8 with a final Ag content of approximately 1 g/L. A constant current of 0.4 A was applied between the solar cell and the recycling object. In order to recover high-purity Si wafer, a following HNO3 (15%) etching was performed for 10 minutes to remove the residue on the silicon surface. The process setup is shown in Figure PP4.2.3.

Figure PP4.2.3: Schematic of silver recycling setups for local contact (on the left) and full-area contact (on the right).

Chemical and electricity consumption was recorded and averaged when recycling eight commercial solar cells. It was then normalised to 100 g (LCA functional unit) input material in order to compare the results to other published Ag recycling processes, including leaching followed by electrowinning, and leaching followed by precipitation. The inventory data was calculated based on published results for all experiments. The summary of inventory data is presented in Table PP4.2.2.

Electricity Method Chemical Usage Output (kWh)

HNO 7.8 g 3 0.90 a Ag

This work AgNO3 0.78 g 0.04 0.0065 g

NO Water 10 L X

HNO 39 g Table PP4.2.2: LCA Inventory 3 0.89 g Ag Leaching + electrowinning 0.00035 Data for three different silver 0.21 g NO recycling methods. Water 10 L X

HNO3 39 g

1.1 g Ag Leaching + precipitation AgNO3 10 g 0.27

0.37 g NOX Water 10 L

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To investigate the extent of Ag removal from an Si surface, scanning This new method and setup overcome two conventional challenges in electron microscope and energy-dispersive X-ray (SEM-EDX) studies recycling Ag from old solar cells. Firstly, Ag dissolving and deposition were carried out using an SEM-Hitachi S3400 to do imaging and X-ray happened in one redox reaction so that the removal and recovery microanalysis in the Electron Microscope Unit at UNSW. SEM images can be completed simultaneously. This significantly reduces the and EDX spectrums of the solar cell front surface were recorded over processing time and complexity while achieving comparable recycling time. As shown in Figures PP4.2.4 and PP4.2.5, Ag metallisation was yield with other approaches. Secondly, this method can recover Ag removed from the Si surface and the Ag peak decreased orders of even though the metal concentration in the electrolyte is very low. magnitude in the EDX spectrum after applying the current. This single- inductively coupled plasma analysis of the recycling solution confirms step recycling process can successfully remove more than 98% Ag the Ag content was maintained at 0.9 g–1.0 g/L during recycling. Even within 10 minutes. A follow-up HNO3 dip removes remaining residue though the recycling yield is currently low, compared to other similar Ag particles and etches Ag+ that still adhere on the surface to prevent experiments, it can be improved by optimising the current density unwanted Si etching by metal-catalysed chemical etching (Hsu et al., to avoid dendritic deposition of Ag. The simplicity of the setup and 2014) the capability of recycling a small amount of Ag make it considered suitable for large-scale practice.

Figure PP4.2.6 shows the environmental impacts of the accelerated process developed in this paper (Method 1), compared with acid leaching followed by electrowinning (Method 2) and acid leaching followed by precipitation (Method 3). The results are calculated using the ReCiPe indicator. The environmental outcomes are considering the impacts of the recycling processes, assuming that the product from these processes is Ag. We are not considering the impacts of solar cell production.

Figure PP4.2.4: SEM image of the Si wafer after applying the current for (a) 0 min, (b) 1 min, (c) 3 min, (d) 4 min, (e) 6 min and (d) 9 min.

Figure PP4.2.5: EDX spectrums of the silicon wafer surface, the measurement was taken on the busbar region. Figure (b) is the zoom-in image of the black-line area in (a). Figure PP4.2.6: ReCiPe results comparing three silver recycling methods. Constant current flowed into the electrolytic cell system smoothly, driving the rapid dissolution of Ag from the solar cell surface and Most environmental impacts come from the use of chemicals simultaneous deposition on the recycling object. The electrolytic cell and electricity, mostly because the energy assumed in this LCA is was in an equilibrium. When almost all Ag was dissolved into the considered to be from a non-renewable source (coal). Methods 1 bath, only a thin layer of sparsely distributed Ag particles remained and 2 have similar impacts because the processes use comparable on the Si surface. The analysed process implies that it is important to quantities of chemicals and electricity. Comparing the three recycling implement the full-area contact to achieve shorter recycling time and processes analysed, Method 3 uses much more electricity during higher recovery yield, because Ag can deplete faster in the region that precipitation purification, causing higher environmental impacts. is close to the local contact before the current is conducted across Considering Method 1 (this work), the use of silver nitrate has some the entire solar cell. Non-uniformity and local depletion of Ag force impacts in all ReCiPe categories, even though the quantity is very the electrolytic cell into open-circuit condition, which suppresses the low, mainly because of the extraction of Ag to produce this chemical. continuous rapid reaction happening in other regions of the cell (Yao Lower impacts would be achieved if part of the resultant Ag from this et al., 2013). This will ultimately decelerate the reaction and affect the overall recycling yield.

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recycling process could be recirculated, which, in theory, is possible process can recycle silver and silicon with more than 99% purity. as the dissolution of Ag will replenish the Ag+ loss in the electrolyte Recycled silicon wafers underwent electrical characterisation. The in the recycling solution. In addition, the follow-up HNO3 dip results result shows that these recycled silicon wafers have a minority carrier in a solution containing Ag+, H+ and NO-, identical to the electrolytic lifetime of 20–30 µs, which is similar to commercial wafers from the recycling solution. This leachate may be reused as additive or market, indicating they are suitable to go back in the supply chain and replenishment into the first bath after a while to maintain the pH and made into second-life solar cells. Ag content within the optimal operating condition of the electrolyte. These lab-scale processes show promising results to close the loop. LCA suggests the circular use of the electrolytic recycling solution will We will use life cycle assessment to suggest essential changes to the further improve overall AG recovery rate and reduce the environmental process and try to further reduce the environmental impacts related to impacts but further analysis should be conducted to verify this these processes. We are thinking of changes such as recirculating the outcome. solution and alternative etching processes to replace the current wild This work has demonstrated a simple method for rapid recovery of acidic etching. Ag from decommissioned Ag solar cells. Preliminarily, this single-step process with full-area contact can recycle up to 75% Ag with >99% References purity within 10 minutes. LCA shows that this process has relatively ASIA BIOMASS OFFICE. 2017. Start of Examinations for Recycling low environmental impacts because the chemical and electricity usage Solar Panels [Online]. Available: https://www.asiabiomass.jp/english/ is low. The impacts can be reduced by recirculating the electrolyte and topics/1510_01.html [Accessed 09/01/2018]. optimising electricity usage. This simple, fast and environmentally friendly process can potentially solve the difficulty in recycling high- BAHAR, H. 2019. Solar PV: Tracking Clean Energy Progress. purity Ag from EoL Si PV modules. International Energy Agency The International Energy Agency

BOMBACH, E., RÖVER, I., MÜLLER, A., SCHLENKER, S., WAMBACH, Summary K., KOPECEK, R. & WEFRINGHAUS, E. Technical experience during • The LCA reinforced the importance of recovering materials from thermal and chemical recycling of a 23 year old PV generator formerly solar cells, showing negative impacts for all categories analysed, installed on Pellworm island. 21st European Photovoltaic Solar Energy which means that their recovery is environmentally beneficial. Conference, 2006. 4-8.

• Ag has the greatest environmental benefits among all materials DE WILD-SCHOLTEN, M., WAMBACH, K., ALSEMA, E. & JÄGER- from solar cells, based on our analysis. WALDAU, A. Implications of European environmental legislation for photovoltaic systems. 20th European Photovoltaic Solar Energy • We have demonstrated a simple method for rapid recovery of Ag Conference, Barcelona, 2005. from decommissioned Ag solar cells. DENG, R., LUNARDI, M. M., CHANG, Y.-C., JIANG, J., WANG, S., CHONG, Highlights J. JI & C. M. 2019. A Simple Method for Rapid Recycling of Silver from Decommissioned Silicon Photovoltaics. EU PVSEC France, Marseille • LCA studies are important to show the importance of recovering Chanot Convention and Exhibition Centre. materials from solar cells. HSU, C.-H., WU, J.-R., LU, Y.-T., FLOOD, D. J., BARRON, A. R. & CHEN, • The recovery of Ag from solar cells has important environmental L.-C. 2014. Fabrication and characteristics of black silicon for solar benefits considering. cell applications: An overview. Materials science in semiconductor • The presented simple, fast and environmentally friendly process processing, 25, 2-17. can potentially solve the difficulty in recycling high-purity Ag from ITRPV 2018. International Technology Roadmap for Photovoltaic Si PV modules. Results 2017.

Future Work KADRO, J. M., PELLET, N., GIORDANO, F., ULIANOV, A., MÜNTENER, O., MAIER, J., GRÄTZEL, M. & HAGFELDT, A. 2016. Proof-of-concept for Closed-loop recycling aims at reusing the high-quality recycled facile perovskite solar cell recycling. Energy & Environmental Science, parts again in the photovoltaic supply chain therefore avoiding high 9, 3172-3179. energy and material demand relating to photovoltaic manufacturing processes. The key elements to be recycled are silver and silicon KANG, S., YOO, S., LEE, J., BOO, B. & RYU, H. 2012. Experimental wafers, because of their price and high energy demand during primary investigations for recycling of silicon and glass from waste production. photovoltaic modules. Renewable Energy, 47, 152-159.

UNSW has developed a process flow to target silver and silicon KENNING, T. 2016. PV Cycle achieves record 96% recycle rate for wafer recovery from decommissioned solar cells. The process uses silicon-based PV modules. [Online]. Available: https://www.pv-tech.org/ commercial monocrystalline silicon wafers as the starting material, news/pv-cycle-achieves-record-96-recycle-rate-for-silicon-based-pv- and it integrates electrochemical recycling, alkaline etching and acidic modules [Accessed 17/05/2018 2018]. etching to recover silver and silicon. Preliminarily, this integrated

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LEE, C.-H., HUNG, C.-E., TSAI, S.-L., POPURI, S. R. & LIAO, C.-H. 2013. Resource recovery of scrap silicon solar battery cell. Waste management & research, 31, 518-524.

LUNARDI, M. M., ALVAREZ-GAITAN, J. P., BILBAO, J. & CORKISH, R. 2018. A Review of Recycling Processes for Photovoltaic Modules. In: ZAIDI, B. (ed.) Solar Panels and Photovoltaic Materials. IntechOpen.

MINTS, P. 2018. The solar flare, Issue 4. SPV Market Research.

NHEDE, N. 2019. Eight trends shaping 2019 global solar pv market. Smart Energy International. www.smart-energy.com.

SHIN, J., PARK, J. & PARK, N. 2017. A method to recycle silicon wafer from end-of-life photovoltaic module and solar panels by using recycled silicon wafers. Solar Energy Materials and Solar Cells, 162, 1-6.

TAO, J. & YU, S. 2015. Review on feasible recycling pathways and technologies of solar photovoltaic modules. Solar Energy Materials and Solar Cells, 141, 108-124.

WECKEND, S., WADE, A. & HEATH, G. 2016. End-of-Life Management: Solar Photovoltaic Panels. NREL (National Renewable Energy Laboratory (NREL), Golden, CO (United States)).

YAO, Y., RODRIGUEZ, J., CUI, J., LENNON, A. & WENHAM, S. 2013. Uniform plating of thin nickel layers for silicon solar cells. Energy Procedia, 38, 807-815.

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PP5 EDUCATION, TRAINING AND OUTREACH

Nodes Involved Aim All nodes involved The work described here is about promoting knowledge of the Academic Partners opportunities and successes of Australian photovoltaics research, Swinburne University adding to the global body of knowledge, engaging the next generation of researchers and sharing knowledge with the broader community Industry Partners including industry, government and the general public. Australian Photovoltaic Institute (APVI)

Funding Support Progress All nodes, ACAP AACAP holds an annual research conference near the end of each year in order to keep ARENA and its National Steering Committee Overview informed, and to exchange research results, enhance collaboration Within the PP5 Education, Training and Outreach package, ACAP has and reinforce face-to-face contacts between students and staff from specific targets for high quality publications and for the number of the different nodes. The program typically includes an oral summary researchers in different categories who benefit from the infrastructural of progress and plans for each Program Package as well as oral and support it provides, as well as for the number and length of researcher poster presentations of technical progress from staff and student exchanges. A significant number of outreach events are also targeted researchers, and a situation summary presentation by ARENA. for each year. As well as major events such as those reported in the The 7th ACAP annual conference in 2019 ran over two days, with Day PP5 section of this annual report, other outreach activities in 2019 One as a stream on the final day of the 6th Asia-Pacific Solar Research included public lectures on material relevant to ACAP’s activities, Conference (APSRC), organised by the Australian PV Institute, followed newspaper and magazine articles, and visits, information papers and by a workshop for ACAP participants on Day Two. Day One was held at presentations for policy developers and their advisors. The Canberra Rex Hotel and Day Two was hosted by the ANU node at Again in 2019, there was very strong international interest in the their main campus in Canberra. articles by ACAP researchers in leading journals. A remarkably high The ACAP proceedings began with three inspiring keynote number of these were “Hot Papers” and “Highly Cited Papers”, as presentations from invited guest speakers: identified by Clarivate Analytics Web of Science. See Chapter 2 of this report for further information. In general, interest in and citations of • Alexander Colsmann, Head of Organic Photovoltaics Group, AUSIAPV/ACAP’s work continue to grow. Spokesperson of the KIT Energy Center, Karlsruhe Institute of Technology, Germany – "The perfect solar cell: How ferroelectricity The ACAP nodes continue to educate future investors, industry improves power harvesting in perovskite solar cells". partners, practitioners, researchers and educators to support the necessary rapid expansion of the national and global photovoltaics • Andreas Zourellis, Technical Lead, Aalborg CSP, Denmark – (PV) industry and to develop more effective educational tools. This "Integrated Concentrated Solar Energy Systems – A combined was advanced considerably in 2019 through the uptake of thirteen heat and power solution for the industrial sector". ACAP Fellowships and additional Collaboration Grants.. • Lachlan Blackhall, Entrepreneurial Fellow and Head, Battery Storage and Grid Integration Program, ANU, Australia – "The decarbonised, decentralised and democratised".

A joint ACAP/APSRC poster session followed, and a series of speakers from all the ACAP nodes rounded out the day by presenting their research work in the dedicated ACAP oral sessions.

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Dr Giovanni DeLuca and Prof. Udo Bach organized a photovoltaic workshop at Monash University with international experts in the field of renewable energy from the Georgia Institute of Technology, Monash University, CSIRO, NREL and many more. The workshop brought together expertise from around the world through high quality presentations and a fruitful exchange of ideas. Furthermore, the workshop enabled ACAP funded research to be showcased to an international audience and offered an excellent opportunity to intensify and kickstart further national and international collaborations.

Professional bodies

In addition to involvement in the APSRC, ACAP has continuing strong engagement with the APVI, one of the more effective vehicles for Australian policy development through its focus on data, analysis and Figure PP5.1: The ACAP poster session generated considerable collaborative research. ACAP was a founding “Large Organisation” interest and interaction. member of the APVI and ACAP partners were active members of APVI throughout 2019. ACAP collaborators contributed to and participated OOn Day Two the director’s welcome was followed by an ARENA in Australian representation on the Executive Committee for the presentation and summary presentations of progress in each of the International Energy Agency, Photovoltaic Power Systems. Program Packages. The 13th ACAP National Steering Committee meeting and the 25th Management Committee meeting were held on Education and training the afternoon of the second day of the conference. All the nodes are involved in undergraduate and/or postgraduate The APVI’s APSRC, mentioned above, aims to provide a forum for education as capacity building for the next generation of photovoltaics development and discussion of content specific to Australia and its researchers. Of particular note in 2019, ACAP nodes were involved in: region, and an opportunity to foster collaboration between institutes, and to promote engagement between industry and academics. ACAP partners with the APVI to support the development of the conference program through financial sponsorship, participation in its organisation and through scheduling ACAP presentations as a stream of the conference.

The 6th APSRC was held on 3–5 December 2019 at The Canberra Rex Hotel (APVI 2019). The host ACAP node was ANU and the Chairs were Dr Anna Bruce and Associate Professor Xiaojing Hao. Representatives from the UNSW and ACAP nodes served on the organising committee. Staff and students from all the nodes participated in academic review committees and contributed papers and posters to the conference. The conference drew approximately 260 participants from academia, government and industry, and ran parallel streams including photovoltaic devices, deployment and integration, solar heating and Figure PP5.2: UNSW second year undergraduate students testing cooling, low carbon living, concentrating solar power, solar fuels and their low-cost PV battery chargers on the playing field. chemistry, and solar energy solutions for emerging economies. The • Delivery of PV-focused courses, including an Organic Electronics list of invited plenary speakers included ACAP Director, Prof Martin Masters course at the University of Melbourne and a solar battery Green, speaking on “The Future of Photovoltaics”, Ms Melissa Pang, charger design, build and test course and competition at UNSW. Director of Project Solutions, ARENA, on "ARENA's role in accelerating Australia's uptake of solar energy" and Prof Kylie Catchpole, Research • Customer-focused learning through participation of teams from School of Engineering, ANU on "High efficiency photovoltaics for ACAP (Monash, UNSW) in CSIRO’s ON Prime Program. electricity and hydrogen". • Product-focused learning through CSIRO’s partnership with ACAP supported the Australasian Community for Advanced Organic Swinburne University’s undergraduate industrial design project to Semiconductors (AUCAOS) held in Katoomba, Blue Mountains, design and develop a printed solar window furnishing prototype. NSW, from 2 to 4 December 2019. The symposium had more than • A new two-year full time Master of Engineering in Renewable 80 registered attendees with over 50% of the presentations relating Energy has been established at UNSW in 2019 and Engineers to photovoltaic technologies. The keynote speaker, Dr Alexander Australia accreditation is being sought. Colsmann spoke on “Eco-friendly solution processing of organic solar cells” before attending the APSRC 2019 conference in Canberra as the ACAP keynote speaker.

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• UNSW reviewed course learning outcomes and assessments of • Jianghui Zheng (UNSW) “Industry relevant high-performance all relevant courses and the (Undergraduate) Renewable Energy monolithic perovskite/silicon homojunction tandem solar cells”. Engineering program and updated them where necessary. • Wenxin Mao (Monash) “Towards single-crystalline perovskite solar • A Renewables Makerspace has been established at UNSW. cells”.

Overall, to date, ACAP has supported at least 122 early career • Jun Peng (ANU) “Development of thermal stable hole transport researchers, at least 211 Honours and 99 Masters students, and over layers for highly efficient and stable perovskite solar cells”. 310 PhD students and graduated more than 163 PhD graduates. • Xin Cui (UNSW) “Interface engineering by atomic layer deposition for high performance earth abundant solar cells”.

• Li Wang (UNSW) “Hydrogen passivation of Si1-xGex for Si1-xGex/ Si tandem solar cells”.

• Appu Paduthol (UNSW) “Applications for magnetic field imaging for characterisation of photovoltaic cells and modules”.

• Chang Sun (ANU) “Insights into hydrogenation of defects in silicon solar cells”.

• Peng Jun Chen (UQ) “The development of high efficiency quantum dot-organic tandem solar cells for new generation wearable and lightweight photovoltaics”.

• Cho Fai Jonathan Lau (UNSW) “Efficient thermochromic switchable inorganic perovskite solar cells for smart window Figure PP5.3: UNSW staff Zi Ouyang, Oliver Kunz, Ziv Hameiri and application”. Thorsten Trupke pitching “Outdoor Photoluminescence Imaging for Residential and Commercial Applications” at CSIRO’s ON Prime • Pablo Ribeiro (UNSW) “Recycling end-of-life silicon photovoltaic Program. modules using low cost and low emission processes”.

One Round 1 Fellow, Valerie Mitchell, relinquished her Fellowship at the end of 2019.

Researcher exchanges

An additional educational and training aspect supported by ACAP is researcher exchange. Exchange activity is supported by core ACAP activities as well as the collaboration grants reported in Chapter 6. Researcher exchanges provide a broader experience to ACAP researchers and strengthen collaborations, through secondments to international laboratories (e.g. National Renewable Energy Laboratory (NREL), Fraunhofer ISE, Jülich Research Center) or through hosting Figure PP5.4: Printed solar vertical blind designed and developed international researchers at node institutions (e.g. from Georgia by CSIRO in partnership with Swinburne University undergraduate Institute of Technology, Eindhoven University of Technology, INSA industrial design students. France, Ulsan National Institute of Science and Technology (UNIST) ACAP Postdoctoral Fellowships Korea, CSU, Karlsruhe Institute of Technology, Jülich Research Center, Federal University of Rio Grande do Sul, Brazil). Through 2019, thirteen ARENA-funded Round 2 ACAP Postdoctoral Fellowships were taken up by outstanding young researchers in Outreach and external engagement cutting-edge projects across the nodes. ACAP was again very active in the areas of outreach and external The recipients (host node) and projects are: engagement in 2019. • Bin Lu (ANU) “The role of solar photovoltaics in a 100% renewable CSIRO put their printed solar technology to the test through their energy future”. collaboration with STELR (Science and Technology Education • David McMeekin (Monash) “Solution-processed multi-junction Leveraging Relevance, with additional support from an ACAP architectures for high-throughput, flexible and printable solar cells”. collaboration grant, see Chapter 6), with students who engaged in hands-on experiments with printed solar modules. Thanks to STELR’s • James Bullock (University of Melbourne) “Printed reflective- contacts for high efficiency silicon solar cells”.

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network of over 700 schools in Australia and in the Asia-Pacific region, UNSW’s Sunswift student team and their car “Violet” secured a 100 schools were selected and so far over 25,000 students have been second-place finish in the cruiser class in the 2019 World Solar exposed to this new generation of solar technology. Challenge, which saw solar-powered vehicles crossing the continent from Darwin to Adelaide.

Figure PP5.7: The UNSW Sunswift student team for the 2019 World Solar Challenge. Figure PP5.5: Children at Thalgarrah Environmental Education Centre, Armidale, NSW, learn about solar energy with CSIRO’s printed uACAP researchers were involved in a range of technical, industry solar technology. and public presentations throughout 2019. In addition to many presentations at leading photovoltaics devices conferences across the UNSW’s Women in Renewable Energy (WIRE) is a society that aims to world (see above and Chapter 8), highlights in the industry and public create a platform to support and network the women who are striving space included: to become engineers in the field of renewable energy. In 2019, WIRE was supported in part by ACAP to organise both social and networking • Martin Green (UNSW) participated in a UNSW Alumni Association events including: Panel Discussion addressing the question “Is it too soon to end fossil fuels?”. • A picnic celebrating International Women’s Day. • Fiona Scholes (CSIRO) presented at the Australian Institute of • Several barbecues in partnership with the Renewable Energy Physics Industry Day on “Powering the future with printed solar Society (RESOC) and Project Everest Ventures. films” together with other researchers and industry representatives • An industry panel night in partnership with Solgen Energy Group, who addressed the theme “Solving Global Challenges”. featuring Renate Egan from the UNSW ACAP node together with industry representatives from Downer and Solgen.

• Humanitarian engineering Q&A panel, featuring representatives from Aurecon, Pollinate, Engineering Without Borders and Project Everest.

Figure PP5.8: ACAP Director Martin Green highlighted the benefits of renewable energy at a session of UNSW Engineering's thought leadership series “Engineering the Future”, entitled, “Is it too soon to Figure PP5.6: WIRE Humanitarian engineering Q&A panel was held in end fossil fuels?”, held in the Sydney CBD. Term 2, 2019.

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ACAP nodes hosted many visitors to their laboratories, providing Future Work opportunities to discuss their research outcomes and activities with industry and government parties, including: The next ACAP Conference will be held in coordination with the 7th Asia-Pacific Solar Research Conference in Melbourne in December • The CSIRO Flexible Electronics Laboratory in Melbourne, which 2020. This event will also be held in conjunction with the International saw industry visitors from Singapore, Brazil, Papua New Guinea, Solar Energy Society’s 50 Year Event (2–4 December), resulting in even the Netherlands, Japan, China, India and Korea. broader international exposure for ACAP. • The Monash Energy Institute, which hosted many industry visitors ACAP, with CSIRO, is sponsoring the International Electrotechnical including the entire Shell Australia leadership team. Commission (IEC) Technical Committee 82 (the international PV • UNSW’s Tyree Energy Technologies Building and Solar Industry standards committee) plenary meeting for 2020, in Newcastle. Also in Research Facility, which hosted a visit from the ARENA Board. Newcastle, ACAP and CSIRO will support a Cutting Edge Symposium at the Newcastle Energy Centre in 2020 on “R&D and Commercial ACAP nodes were also visited by many leading international Application of Emerging PV Technologies”. researchers who delivered seminars to ACAP research teams and their collaborators. These included CNRS (France), Institut National APSRC 2021 (14–16 December 2021) will be held in Sydney in de l’Energie Solaire (France), Eurac Research (Italy); Arizona State collaboration with Asia PVSEC 31 (12–17 December 2021). University (USA), Eindhoven University of Technology (Netherlands), Ongoing representation on the Executive Committee for the Federal University of Rio Grande do Sul (Brazil), University of Milano- International Energy Agency, Photovoltaic Power Systems, and Bicocca (Italy), University of Southampton (UK), Autonic Energy growing participation in several tasks, will also continue. Systems (India), Soochow University (China), University of Exeter (UK), Aalto University (Finland), Ben-Gurion University (Israel), Jülich References Research Center (Germany), SERIS (Singapore), Beijing Computational Science Research Center (China), University of Wisconsin-Platteville APVI (2019). Solar Research Conference, http://apvi.org.au/solar- (USA), Wuhan University of Technology (China) and Reuniwatt research-conference/ [accessed 6 November 2019]. (Germany). BLAKERS, A. 2019. The Conversation. “Curious Kids: how do solar ACAP researchers were again prominent in media channels. panels work?”, https://theconversation.com/curious-kids-how-do-solar- For example: panels-work-123515 [accessed 6 November 2019].

• Andrew Blakers (ANU) made several contributions to “The Master of Engineering in Renewable Energy Engineering, https://www. Conversation” including a response in their “Curious Kids” stream handbook.unsw.edu.au/postgraduate/specialisations/2020/SOLAGS. to the question “How do solar panels work?”. NGUYEN, H. & TRUONG, T. PV Magazine (2019). “Australian scientists • Hieu Nguyen and Thien Truong (ANU) were featured in PV use hydrogen atoms to boost solar cell efficiency”, https://www. Magazine for their work on understanding how hydrogen pv-magazine.com/2019/02/22/australian-scientists-use-hydrogen- atoms may improve the performance of phosphorus-doped atoms-to-boost-solar-cell-efficiency/ [accessed 16 January 2020]. multicrystalline silicon films for passivating contact solar cells. Renewables Makerspace, https://www.making.unsw.edu.au/tyree- • Martin Green (UNSW) addressed the 2019 Times Higher Education makerspace/. Research Excellence Summit: Asia-Pacific and the Smart Energy STELR (2019). “Flexible solar: Providing solar for everyone, Summit in Sydney and was interviewed on ABC Radio National. everywhere”, https://stelr.org.au/2019/07/23/flexible-solar-providing- • Regine Chantler’s (CSIRO) outreach project with STELR was solar-for-everyone-everywhere/ [accessed 6 November 2019]. featured as headline news on Indonesian television. UNSW Alumni, Engineering the Future, UNSW Engineering Thought Leadership Series, 25 July 2019, https://bit.ly/2Zi2SvH. Highlights

• Thirteen new ACAP Fellows started on their postdoctoral research projects.

• The 6th Asia-Pacific Solar Research Conference was held, in conjunction with ACAP annual meetings, bringing the Australian PV research community together with many prominent international guests.

• ACAP was actively involved in education, outreach and external engagement activities with students, industry and the general public.

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COLLABORATIVE ACTIVITIES

OVERVIEW

The Australian Centre for Advanced Photovoltaics’ international Additional Fellows were appointed in 2019 and their reports will be collaborations are directed at the highest level through an International included in the appendix to the 2020 Annual Report. Advisory Committee, with representatives from the key partners in Finally, the education, training and outreach activities reported in Australia and around the world’s strongest PV R&D nations, with PP5 include a wide range of international interactions, the ACAP engagement fostered through the development of collaborative Conference, regular and special public lectures, and partnership research programs, the annual ACAP conference and the major global arrangements in teaching and on-line learning, such as the research conferences. development and delivery of courses between institutes in Australia Specific project activities that leverage the benefits of the international and around the world. relationships include the following key projects:

• Section 6.1 describes the simplification of the overall design for the one-sun high efficiency spectrum splitting modules by inclusion of the band-pass filter into the cell fabrication sequence;

• Section 6.2 outlines the development of dye-sensitised solar cells;

• The collaboration described in Section 6.4 is a long-standing one that records the status of a whole range of photovoltaic technologies in the maintenance and publication of Solar Cell Efficiency Tables; and

• The work on PV Factory, reported in Section 6.5, a project with collaborating organisation, PV Lighthouse, has grown into a leading tool for teaching photovoltaics manufacturing globally.

Since late 2015 and through 2019 the organisation has had five rounds of small collaboration grants to researchers based at ACAP nodes. Many of the hot topics of the advancing silicon cell technology are being addressed by the collaboration grants. The progress reports for those still active in 2019 are presented online at www.acap.net.au/ annual-reports and their titles and participants are listed here.

In addition to the specific activities captured in this section, many of the reports already presented as detailed research reports also involve collaborations with international partners. Many of the twenty ACAP Fellowships awarded in 2018 involved collaborations and there is a report for each included at www.acap.net.au/annual-reports.

107 06

and encapsulated under glass by ENEA, Italy, followed by MgF AR 6.1 IMPROVED SUNLIGHT TO ELECTRICITY 2 coating at UNSW. This 3J + Si combination, or 3 + 1 = 4J receiver, CONVERSION EFFICIENCY: ABOVE 40% FOR gave a record 40.4% efficiency in testing at NREL in late 2014, the first DIRECT SUNLIGHT AND ABOVE 30% FOR GLOBAL demonstrated conversion of sunlight to electricity with efficiency over Lead Partner 40% (Green et al. 2015). UNSW In 2015, the enhanced-silver parabolic mirror was replaced by an all- UNSW Team dielectric mirror custom-designed and fabricated by Omega Optical Dr Mark Keevers, Prof. Martin Green, A/Prof. Ned Ekins-Daukes, Inc., with shorter focal length (800 mm versus 1000 mm). Independent Dr Jessica Yajie Jiang measurements of the dielectric mirror by the US National Institute of Standards and Technology (NIST) confirmed R = 99.7% ± 0.2% NREL Team over the 400–1800 nm range (Figure 6.1.3), likely setting a record Keith Emery, Larry Ottoson, Tom Moriarty, Gregory Wilson, Dean Levi, for high reflectance over solar wavelengths (Fredel et al. 2017). An Mowafak Al-Jassim improved version of the prototype using this new parabolic mirror Industry Partners was independently tested at NREL’s outdoor test facility in Colorado in RayGen Resources Pty Ltd: Ian Thomas, Danny Modra, Dr John Lasich 2016, again in a four-terminal configuration, with efficiency of 40.6% at Spectrolab: Prof. Richard King (now ASU) AM1.5 certified, a new world record for a system of this size. Presently, Trina Solar: Dr Pierre Verlinden, Yang Yang, Xueling Zhang we are reoptimising the CPV receiver targeting 42%.

Funding Support In March 2019, NREL launched its “Champion Module Efficiencies” ASI/ARENA, AUSIAPV, NREL, Spectrolab, RayGen Resources Pty Ltd, chart, to complement its “Best Research-Cell Efficiency” chart. Our Trina Solar, UNSW 40.6% efficiency result tops the Champion Module Efficiencies chart (Figure 6.1.4). Aim One-sun module The original aim of the project was to design, fabricate and test a proof-of-concept, prototype spectrum splitting concentrating The project was extended in 2015 to investigate how the spectrum photovoltaic (CPV) module demonstrating an independently confirmed splitting approach could be applied to standard non- concentrating efficiency above 40%. The combination of such a spectrum splitting or terrestrial solar modules that have to respond to sunlight from a “Power Cube” receiver and a CPV power tower system (Figure 6.1.1) wide range of incident angles. The approach adopted was based on has the potential to reduce the cost of utility-scale photovoltaics. With an earlier UNSW discovery (Mills and Guitronich 1978) of the near- the targeted record performance level achieved in 2014, the project ideal angular response properties of triangular glass prisms. In our was extended in 2015 to target 42% CPV module efficiency and over application of this “prismatic encapsulation” concept, light reflected 30% efficiency for a non-concentrating, flat-plate implementation of from the first cell along the prism hypotenuse is channelled to the the spectrum splitting approach. second cell (Figure 6.1.5). We envisage that a PV module could be comprised of an array of these cell-sized prisms, without increasing Progress module thickness.

For our mini-module, we used a 4 x 8 cm 3J III-V cell designed for one- CPV prototype sun applications (Bett et al. 2009) acquired from AZUR SPACE and a The CPV prototype is based on a 287 cm2 aperture area parabolic 4 x 4 cm high performance interdigitated back contact Si cell specially enhanced (that is, dielectric-coated) silver mirror, a custom band-pass fabricated by Trina Solar for the project with anti-reflection coating (spectrum splitting) dielectric filter, and two 1 cm2 high efficiency optimised for the narrow-band (900–1050 nm) illumination involved. commercial CPV cells – one a triple-junction (3J) III-V cell and the The spectrum splitting band-reflect filter (inverse of the band-pass other a Si cell – each mounted on a concentrator cell assembly filter used for the CPV prototype) was deposited on the hypotenuse and a water-cooled heatsink (Figure 6.1.2). The mechanical design face of the triangular prism prior to encapsulation of the 3J III-V cell uses optomechanical components to give a lightweight, robust and on that face. fully adjustable structure, enabling optimisation about all critical An efficiency of 34.5% in a four-terminal configuration was linear and rotation axes. The high performance band-pass filter was independently confirmed in April 2016 by NREL for the 28 cm2 mini- supplied by Omega Optical Inc. The 3J III-V cell was a commercial module, the highest ever one-sun measurement for a solar module Spectrolab concentrator cell (C3MJ + cell, nominally 39.2% efficient of this size, far above the previous record of 24.1% (albeit for an at 500-suns concentration, mounted on a ceramic substrate), while appreciably larger area module). This result received considerable the Si cell was a SunPower back contact cell of circa 1998 vintage media attention and there are now mini-modules on display at the (nominally 26% efficient at 200 suns), mounted on a ceramic substrate Sydney Powerhouse Museum and at the London Science Museum in

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Figure 6.1.1: CPV power tower: (left) RayGen’s PV Ultra technology uses a field of heliostats to concentrate sunlight onto a 1 m2 high efficiency PV receiver (inset shows a close-up of the receiver); and (right) possible design of an advanced spectrum splitting receiver implementing the demonstrated improvements at scale (in this example, the band-pass “BP” filter cover glass on the Si array transmits 900–1050 nm sunlight to the Si array and reflects the remainder of the solar spectrum to the triple-junction “TJ” array).

Figure 6.1.2: CPV prototype: (top) ray trace diagram, including enlarged view of the filter and cell layout; and (bottom) during outdoor testing at NREL with Mark Keevers on 5 April 2016 where a four-terminal efficiency of 40.6% at AM1.5 was measured on that day.

Figure 6.1.3: Measured reflectance of the concentrating mirrors, showing the remarkable performance of the dielectric mirror (measured by NIST).

Figure 6.1.5: One-sun spectrum splitting mini-module: (left) concept (courtesy Channel 7 News); and (right) a fabricated mini-module. A four-terminal efficiency of 34.5% was certified at NREL in April 2016. 109 06

Figure 6.1.4: UNSW holds the top entry on NREL’s international Champion Module Efficiencies chart (https://www.nrel.gov/pv/module- efficiency.html). The Sun exhibition. Presently, the approach is being used to fabricate a • The Power Cube project was officially closed on 1 June 2019. much larger 800 cm2 device, using 30 such mini-modules, with similar • Progress towards a higher efficiency CPV prototype and a one-sun high efficiency targeted. much larger 800 cm2 device, using 30 such module comprised of 30 mini-modules. mini-modules, with similar high efficiency targeted. • Realisation that a Bragg reflector incorporated into the 3J III-V cell, Bragg reflectors for spectrum splitting rather than use of a dielectric filter, has advantages for spectrum splitting [Symbol] spin-off project. During this project we realised that (band-reflect) spectrum splitting could be achieved using a Bragg reflector incorporated into the 3J • Identification of a practical path to a landmark 50% efficiency, III-V cell during fabrication, instead of using a separate dielectric filter. using a 3 + 3 = 6J spectrum splitting receiver [Symbol] spin-off A Bragg reflector is already used in some commercial 3J III-V space project. cells, and a modified Bragg design to broaden its reflectance range could be used for spectrum splitting applications, giving lower cost Project Completion and Future Work and reduced angle-of-incidence dependence compared to dielectric filters (Jiang et al. 2019). This approach is now the subject of a more The Power Cube project (1 January 2012–1 June 2019) is now detailed study (see sections 6.43 and F7). officially closed.

Due to unanticipated delays with a number of critical supplies and Practical path to landmark 50% efficiency services, the final milestones are now being pursued after the official During this project we identified a practical path to achieving a project closure: (1) Further refinement of the concentrator prototype landmark 50% PV efficiency, utilising spectrum splitting between design is expected to allow an efficiency of 42% to be demonstrated, two triple-junction (3J) solar cells grown on separate GaAs and InP increasing the margin over the alternative CPV and solar thermal substrates, to form a 3 + 3 = 6J receiver. Benefits include simpler approaches; (2) Applying a similar spectrum splitting approach to a solar cell structures (three instead of six monolithic sub-cells), better standard non-concentrating, flat-plate module is expected to result optimised AR coatings (smaller wavelength ranges) and avoidance of in confirmation of a record efficiency well over 30% for an 800 cm2 costly solar cell bonding (used by other groups). Future projects are module. planned to pursue this path to 50% efficiency, including to optimise/ fabricate the required 3J solar cells, longpass filter and overall receiver, References and develop a commercialisation roadmap for application to RayGen’s BETT, A. W., DIMROTH, F., GUTER, W., HOHEISEL, R., OLIVA, E., CPV technology. Seed funding has enabled us to begin this work (see PHILIPPS, S. P., SCHÖNE, J., SIEFER, G., STEINER, M., WEKKELI, section 6.44). A., WELSER, E., MEUSEL, M., KÖSTLER, W. & STROBL, G. 2009. Highest efficiency multi-junction solar cell for terrestrial and space Highlights applications. Proceedings 24th EU PVSEC, Hamburg, Germany. • Highest efficiency (40.6%) entry on NREL’s newly introduced “Champion Module Efficiencies” chart.

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FREDELL, M., WINCHESTER, K., JARVIS, G., LOCKNAR, S., JOHNSON, crystals grown in the presence of the various Lewis bases reveal R. & KEEVERS, M. J. 2017. Ultra-wide broadband dielectric mirrors for a deep understanding of the chemical interactions that occur. For 2+ solar collector applications. Proceedings of SPIE 10105, Oxide-based [Cu(dmp)2] , it was shown that tBP and NMBI can coordinate to the Materials and Devices VIII, 101051L. fifth coordination site of the Cu(II) centre to form a pentacoordinated complex, while for [Cu(dpp) ]2+, complete ligand exchange occurs. GREEN, M. A., KEEVERS, M. J., THOMAS, I., LASICH, J. B., EMERY, K. 2 TFMP, on the other hand, did not coordinate to the Cu(II) centre & KING, R. R. 2015. 40% efficient sunlight to electricity conversion. of either complex. Based on our observations, we propose a Progress in Photovoltaics: Research and Applications, 23: 685-691. mechanism of Lewis base coordination to Cu(II) complexes depending JIANG, Y., KEEVERS, M. J., PEARCE, P., EKINS-DAUKES, N. & GREEN, M. on the nature of the phenanthroline ligand. A. 2019. Design of an intermediate Bragg reflector within triple-junction Currently we are testing a wide range of combinations of additives and solar cells for spectrum splitting applications. Solar Energy Materials alternative organic dyes that have the potential to replace the TBP and and Solar Cells, 193: 259-269. Y123 in order to achieve highly efficient and stable dye-sensitised solar MILLS, D. & GIUTRONICH, J. 1978. Ideal prism solar concentrators. cells. Solar Energy, 21: 423. The team has also looked into other transition metal complexes like Co and Fe. For the very first time, a carbene-based cobalt (II/III) metal 6.2. DYE-SENSITISED SOLAR CELLS complex has been used for liquid and solid state dye-sensitised solar cells, having exceptional stability and efficiency. Lead Partner Monash he resultant coordination has been found to have significant implications on the performance of these compounds as redox Monash Team mediators in DSCs. Impedance spectroscopy of full devices showed Prof. Udo Bach the recombination resistance to be at least an order of magnitude Monash Student larger for devices containing tBP and NMBI with respect to the Rebecca Milhuisen TFMP-containing and base-free electrolytes, thereby boosting solar efficiencies by at least four times. This higher recombination Academic Partner resistance has been attributed to the ligand exchange/dissociation of RMIT Lewis base and/or the overpotential required for the electron transfer Funding Support process to occur as observed from cyclic voltammetry measurements. ACAP, ARENA, ARC, Monash However, the same mechanism that slows down recombination, also slows down the regeneration at the counter electrode – more Aim significantly so if the coordination involves a ligand exchange, as is the case for [Cu(dpp) ]+/2+, resulting with hugely current-limited devices Copper(I/II) bisdiimide complexes have been shown to be highly 2 (see Figure 6.2.2). These studies show the importance of fine-tuning efficient redox couples for liquid and solid state dye-sensitised solar the Cu(II) complex – Lewis base interaction and the counter electrode cells (DSCs) due to their exceptionally low reorganisation energy in order to have an efficient electrolyte regeneration for high efficiency (Cao et al. 2017; Freitag et al. 2015). The addition of Lewis base solar cells. additives such a 4-tert-butylpyridine (tBP) to these Copper(I/II)- based electrolytes have helped achieve high solar cell performances, however, emerging evidence suggests tBP interacts with the Cu(II) centre that limit the performance of these electrolytes (Wang [year?].; Hamann 2018). In this project, we aim to gain a deeper understanding of the interaction between Copper(I/II) bisdiimide complexes and Lewis base additives, their mechanism of charge transfer and overall consequence to their performance as redox mediators in DSCs.

Progress

The team at Monash has reported thorough insights into the influence of three common Lewis base additives, TFMP (4-(trifluoromethyl) pyridine), tBP and NMBI (1-methyl-benzimidazole), on the performance +/2+ +/2+ of two copper electrolytes, [Cu(dmp)2] and [Cu(dpp)2] (with dmp = 2,9-dimethyl-1,10-phenanthroline and dpp = 2,9-diphenyl-1,10- phenanthroline).

UV/Vis absorption spectroscopy and NMR studies of Cu(II) complex solutions together with X-ray diffraction studies of Cu(II) single

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Figure 6.2.1: Postulated Lewis base interaction for the Cu(II)-complexes 2+ [Cu(dmp)2] and N Ph N 2+ N [Cu(dpp)2] . While the N Cu2+ N Cu2+ N dmp ligand allows for N N N Ph additional coordination

2+ 2+ [Cu(dmp)2tBP] [Cu(dpp)x(tBP)y] of a Lewis base leading to pentacoordinated tBP tBP complexes, the presence Ph Ph of Lewis base leads to a N N N N Cu2+ Cu2+ ligand exchange for the N N N N Ph Ph well shielded dpp ligand.

NMBI 2+ 2+ NMBI [Cu(dmp)2] [Cu(dpp)2]

N N N N N N N Cu2+ N Cu2+ N N N N N N

2+ [Cu(dmp)2NMBI]

2+ [Cu(NMBI)4]

Future Work

+/2+ +/2+ Currently we are testing [Cu(dmp)2] and [Cu(dpp)2] complexes as additive-free hole-transporting materials (HTMs) for perovskite solar cells (PSCs) as cheaper and more stable alternatives to existing HTMs, with initial results yielding solar efficiencies as high as 10%.

References

CAO, Y. M., SAYGILI, Y., UMMADISINGU, A., TEUSCHER, J., LUO, J. S., PELLET, N., GIORDANO, F., ZAKEERUDDIN, S. M., MOSER, J. E., FREITAG, M., HAGFELDT, A. & GRATZEL, M. 2017. 11% efficiency solid-state dye-sensitized solar cells with copper (II/I) hole transport materials. Nature Communications, 8. DOI: 10.1038/ncomms15390

FREITAG, M., DANIEL, Q., PAZOKI, M., SVEINBJORNSSON, K., ZHANG, J. B., SUN, L. C., HAGFELDT, A. & BOSCHLOO, G. 2015. High-efficiency dye-sensitized solar cells with molecular copper phenanthroline as solid hole conductor. Energy & Environmental Science, 8, 2634-2637.

WANG, Y. J. & HAMANN, T. W. 2018. Improved performance induced by in situ ligand exchange reactions of copper bipyridyl redox couples in dye- sensitized solar cells. Chemical Communications, 54, 12361- 12364.

6.4 SOLAR CELL PERFORMANCE DOCUMENTATION

Lead Partner UNSW

UNSW Team +/2+ Figure 6.2.2: J–V curves for DSCs employing (a) [Cu(dmp)2] Prof. Martin Green, A/Prof. Anita Ho-Baillie, A/Prof. Xiaojing Hao +/2+ and (b) [Cu(dpp)2] -based electrolytes in conjunction with Y123- NREL Team sensitised TiO2 photoanodes and PEDOT counter electrodes, measured under dark conditions (dotted lines) and simulated Dr Dean Levi, Dr Nikos Kopidakis standard AM 1.5G irradiation at 100 mW cm-2 (solid lines). All electrolytes comprised of 0.2 M Cu(I) complex, 0.04 M Cu(II) complex and 0.1 M LiTFSI in CH3CN with no additive (black), or 0.6 M of additive; tBP (red), NMBI (blue) or TFMP (yellow).

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Academic Partners The Tables are widely used and referenced by the photovoltaic CSIRO Newcastle research community. According to the ISI Web of Knowledge, the Fraunhofer Institute for Solar Energy Systems fourteen versions prepared since 2013 under the ACAP banner have JRC Ispra, Italy all been among the most cited papers published since then in the AIST Japan engineering discipline worldwide. ISFH Germany JET Japan

Funding Support ACAP, UNSW, NREL

Aim

To improve accuracy and quality of photovoltaic device measurement and reporting.

Progress

A long-standing research collaboration between UNSW and NREL, Figure 6.4.1: Cell area definitions: (a) total area; (b) aperture area; now being conducted as an ACAP international collaborative project, and (c) designated illumination area. involves the reliable documentation of the status of the whole range Highlight of photovoltaic technologies worldwide. This is by the biannual publication of the “Solar Cell Efficiency Tables” in the Wiley journal, • Value and widespread use of Tables validated by exceptionally Progress in Photovoltaics. high citation rates.

By enforcing guidelines for the inclusion of solar cell efficiency results Future Work into these Tables, these not only provide an authoritative summary of the current state of the art but also ensure measurements are reported • Publish two updated versions of the Tables during 2020 and seek on a consistent basis. One criterion that has been important to enforce accreditation of an additional designated test centre based in has been that results be independently certified at one of a limited but China to reflect the level of manufacturing and research being increasing number of “designated test centres”, generally of a national conducted in that country. facility status, with a certified measurement capability and additionally involving international “round robin” testing. 6.5 PV MANUFACTURING EDUCATION This rigour has been important particularly as new device technologies Lead Partner come to the fore and groups relatively inexperienced with cell testing UNSW suddenly are thrust into the limelight. The other important role has been in developing measurement standards when international UNSW Team standards are not available. Figure 6.4.1 shows standards in Prof. Bram Hoex this category developed for defining the area used for efficiency UNSW Student determination for experimental laboratory cells. Zubair Abdullah-Vetter Several results from the ACAP program have set new world standards PV Lighthouse and are featured in these Tables. In 2019, these included the retention Ben Sudbury, Malcolm Abbott, Keith McIntosh of two UNSW record efficiencies for CZTS cell performance, with 10.0% confirmed for a 1 cm2 device and 11.0% for a smaller device, a QESST Team UNSW 25.0% record for an Si PERC (Passivated Emitter and Rear Cell), Prof. Stuart Bowden, Dr Andre Augusto a 20.1% record for a GaAsP/Si monolithic tandem solar cell (UNSW Funding Support with Ohio State University and SolAero), a 34.5% UNSW record for a ACAP, UNSW GaInP/GaInAs/Ge plus Si spectral split mini-module, a UNSW 40.6% result for a concentrator submodule using a similar cell combination Aims and 21.7% for a large-area UNSW Si concentrator cell. One new result for 2019 was a record 21.6% efficiency for a 1 cm2 perovskite cell UNSW has a strong track record in the development of (online) fabricated by ANU with the efficiency confirmed by CSIRO (Newcastle), educational resources in the field of PV manufacturing. In 2014, the first test centre in the southern hemisphere accepted as a PV Factory (a cloud-based simulation platform (UNSW and PV designated test centre. Lighthouse, 2015)) was developed through an ACAP-supported collaboration involving PV Lighthouse, UNSW and Arizona State University as a teaching application that engages PV and Solar Energy Engineering students as they learned about how solar cells are made.

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PV Factory was released to the public in January 2015 and can be accessed at https://factory.pvlighthouse.com.au. It has attracted more than 9,000 unique users since its inception and is currently used by at least five universities in their teaching programs (including UNSW and ASU). More recently, the PV-Manfacturing.org platform was released in January 2018 (Hoex, 2018). This platform was developed in an ACAP- funded project in a collaboration between UNSW and Arizona State University and combines text with videos and tailored animations to teach students and engineers about solar cell manufacturing. The site has received over 10,000 unique visitors to date from all over the world and is complemented by a playlist on YouTube (Hoex, 2017).

The manufacturing process of solar cells is very well covered by the combination of the practical PV Factory and PV-Manufacturing platform. On the other hand, the PV module part of the value chain is Figure 6.5.1: Screenshot of the dedicated SunSolve server for not extensively covered on existing platforms such as PV-Education teaching education. The screenshot shows the template for a bifacial and PV-Manufacturing.org, nor is there an equivalent of PV Factory PERC module which was developed as part of this project. available for modules. We felt that it was time to significantly enhance WP2: Development of the online educational modules (Lead: the educational resources in the area of PV module manufacturing UNSW) and optimisation, incorporating current industry trends such as black silicon, heterojunction solar cells, multi-busbars and bifacial solar We developed online education modules targeting key manufacturing cells so that they can be fully appreciated at the PV module level. We steps and trends in PV manufacturing. Each module consists felt that the SunSolve platform (PV Lighthouse) from PV Lighthouse of a tailored exercise in the SunSolve server developed in WP1 was the ideal vehicle to address these important trends. The usage complemented with a section on PV-Manufacturing.org which of an existing and highly successful platform such as SunSolve has contains the training material. The topics which were released in 2019 additional benefits as it significantly reduces the cost of the project on PV-Manufacturing.org are (Abdullah-Vetter and Hoex, 2019b): while also training the students and engineers in software that is 1. optimisation of anti-reflection coatings actively used in the PV industry. . 2. optimisation of surface texturing Progress 3. optimisation of front and rear surface metallisation from an The following work packages were completed during the reporting electrical and optical point of view period. 4. optimisation of bill of materials (for example backsheets, WP1: Development of a dedicated SunSolve version that can be encapsulants) for PV module manufacturing used for educational purposes (Lead: PVL) 5. bifacial vs monofacial solar cells. SunSolve is actively used by the PV industry and research institutes to optimise their PV modules. SunSolve is a high performance ray tracer that is coupled with an electrical solar cell and circuit solver allowing the simulation of the full optical and electrical performance of PV modules. The standard version is “out of the box” and not suitable for use in tertiary education or for the training of engineers. We implemented significant changes in terms of administrative management, user management, cloud capacity allocation, and undergraduate-level self-run tutorials on how to use the software, and expanded the availability of features. The updated version of SunSolve went live in April 2019 (PV Lighthouse, 2019).

Figure 6.5.2: Screenshot of the training resource section of PV- Manufacturing.org. It currently contains five SunSolve tutorials and more tutorials will be released in the near future.

WP3: Beta-testing of the online educational resources

The tutorials developed in WP2 were used during the SOLA3020 course at UNSW in 2019. The students were really happy using them and it definitely improved their learning. The students also stress-

114 ACAP ANNUAL REPORT 2019

tested the SunSolve server and provided valuable feedback on the tutorials which have already been implemented in the online versions.

WP4: Expansion of the PV module section of PV-Manufacturing.org

Due to the very significant reduction in the costs of solar cells many innovations in terms of PV module design were enabled such as paving, shingling and half cells. These innovations are now described in quite some detail in the new “Recent advances in PV Modules” section of PV-Manufacturing.org (Abdullah-Vetter and Hoex, 2019a) .

Highlights

• A new version of SunSolve was developed tailored for education and was released in 2019.

• Five tutorials were developed to teach students and engineers various aspects of PV module optimisation. The tutorials are available free of charge on PV-Manufacturing.org.

• The PV module section of PV-Manufacturig.org was significantly expanded.

Future Work

We will continue to work on developing more tutorials using SunSolve and articles about recent development and publishing them on PV-Manufacturing.org.

References

ABDULLAH-VETTER, Z. & HOEX, B. 2019a. Recent advances in PV modules [Online]. Available: https://pv-manufacturing.org/solar-cell- manufacturing/recent-advances-in-pv-modules/ [Accessed 20 January 2020].

ABDULLAH-VETTER, Z. & HOEX, B. 2019b. Sunsolve Tutorials [Online]. Available: https://pv-manufacturing.org/teaching-resources/sunsolve- tutorials/ [Accessed 20 January 2020].

HOEX, B. 2017. UNSW E-Learning playlist on PV Manufacturing. [Online]. Available: https://www.youtube.com/ playlist?list=PLHSIfioizVW0zKzDhCwU3MhwCqKz0ORrk [Accessed 20 January 2020].

HOEX, B. 2018. PV-Manufacturing.org [Online]. Available: https://pv- manufacturing.org/ [Accessed 20 January 2020].

PV LIGHTHOUSE. SunSolve [Online]. Available: https://www. pvlighthouse.com.au/sunsolve [Accessed 20 January 2020].

PV LIGHTHOUSE. 2019. Sunsolve Teaching Server [Online]. Available: https://training.pvlighthouse.com.au/sunsolve [Accessed 20 January 2020].

UNSW & PV LIGHTHOUSE. 2015. PV Factory [Online]. Available: https:// factory.pvlighthouse.com.au/ [Accessed 20 January 2020].

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COLLABORATION GRANTS 6.38 NANOSCALE LOCALISATION OF DEFECTS IN SILICON AND CZTS VIA CATHODOLUMINESCENCE ACAP’s competitively selected Collaboration Grants, whose titles are AND PHOTOLUMINESCENCE SPECTROSCOPY shown below, are reported online at http://www.acap.net.au/annual- reports. Lead Partner UNSW 6.35 A CASE STUDY OF THE DEGRADATION OF UNSW Team FLEXIBLE PHOTOVOLTAIC MODULES A/Prof. Ziv Hameiri Lead Partner A/Prof. Xiaojing Hao CSIRO Dr Michael Pollard Mr Robert Lee Chin CSIRO Team Dr Hasitha Weerasinghe, Régine Chantler, Dr Doojin Vak, Jyothi Academic Partner Ramamurthy, Andrew Faulks, Karl Weber, Fiona Glenn, AMOLF: Prof. Albert Polman Dr Andrew Scully Funding Support Interns: Rahul Banakar, Oscar Elsasser ACAP Collaboration Grant, UNSW, UNSW RIS, AMOLF Academic Partner Australian Academy of Technology and Engineering (ATSE): Peter 6.39 OPTIMISATION OF SILICON SOLAR CELL Pentland, Executive Manager ATSE Schools Program FABRICATION PROCESSES USING MACHINE LEARNING ALGORITHM Stanford University: Prof. Reinhold Dauskardt, Dept of Materials Lead Partner Science and Engineering UNSW Funding Support UNSW Team ACAP, CSIRO A/Prof. Ziv Hameiri, Dr Rhett Evans, Mr Yoann Buratti, Mr Caspre Eijkens (exchange student; Delft University of Technology) 6.36 LIFE CYCLE ASSESSMENT OF RECYCLING PROCESSES OF SILICON SOLAR MODULES Academic Partner SERIS: Dr Shubham Duttagupta Lead Partner UNSW Funding Support ACAP Collaboration Grant, UNSW, SERIS UNSW Team Dr Marina Monteiro Lunardi, Dr Jose Bilbao, Dr Richard Corkish 6.40 ADVANCING THE PDS TECHNIQUE FOR ALL Academic Partner PHOTOVOLTAIC THINFILMS Federal University of Rio Grande do Sul (UFRGS) – Brazil: Dr Hugo Lead Partner Marcelo Veit, Dr Pablo Ribeiro Dias UNSW

6.37 IMPROVING UV STABILITY AND EFFICIENCY UNSW Team OF FOUR-TERMINAL PEROVSKITE-SILICON Xiaojing Hao, Gavin Conibeer TANDEM SYSTEM WITH LUMINESCENT UNSW Student DOWNSHIFTING INCORPORATED ENCAPSULANT Xueyun Zhang Lead Partner Academic Partners ANU Tokyo University: Prof. Masakazu Sugiyama, Prof. Yoshitaka Okada ANU Team Macquarie University: Dr Binesh Puthen Veettil Dr The Duong, Prof. Kylie Catchpole, A/Prof. Thomas White Industry Partner Academic Partners Open Instruments: Henner Kampwerth, Michael Pollard Karlsruhe Institute of Technology (KIT): Prof. Bryce Richard, Dr Ulrich Funding Support Paetzold AUSIAPV, UNSW, Tokyo University CSIRO Newcastle: Dr Benjamin Duck

Funding Support ACAP

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Academic Partners 6.42 OUTDOOR STABILITY/DURABILITY Macquarie University (Sydney): Dr Supriya Pillai, Dr Noushin Nasiri ASSESSMENT OF TWO-TERMINAL PEROVSKITE- National Institute for Material Science (Japan): Dr Esmaeil SILICON TANDEM CELLS Adabifiroozjaei Lead Partner Funding Support UNSW ACAP UNSW Team A/Prof. Anita Ho-Baillie, Dr Jianghui Zheng, Mr Lei (Adrian) Shi 6.46 MANIPULATING THE PROPERTIES OF OXYGEN-RELATED DEFECTS FOR RECORD Academic Partner EFFICIENCY CELLS CSIRO, Energy, Newcastle Lead Partner Funding Support UNSW ACAP UNSW Team 6.43 HIGH EFFICIENCY SPECTRUM SPLITTING CPV Dr Fiacre Rougieux RECEIVER USING A TRIPLE-JUNCTION SOLAR Academic Partners CELL WITH INTERNAL BRAGG REFLECTOR Fraunhofer Institute for Solar Energy Systems ISE: Prof. Martin Lead Partner Schubert UNSW University of Freiburg: Dr Wolfram Kwapil Australian National University: Prof. Daniel Macdonald, Manjula UNSW Team Siriwardhana Dr Yajie Jiang, Dr Mark Keevers, Scientia Prof. Martin Green Funding Support Industry Partners ACAP AZUR SPACE Solar Power RayGen Resources Pty Ltd 6.48 ITO-FREE PVS PRINTED DIRECTLY ONTO Funding Support FLEXIBLE BARRIER FILMS ACAP Lead Partner CSIRO 6.44 LANDMARK 50% EFFICIENT PV RECEIVER CSIRO Team Lead Partner Dr Doojin Vak, Mrs Fiona Glenn UNSW Academic Partners UNSW Team Chonbuk National University (CBNU): A/Prof. Seok-In Na Dr Mark Keevers, Dr Yajie Jiang, Dr Anastasia Soeriyadi, A/Prof. Ned KoreaTech: A/Prof. Yoon Chae Nah Ekins-Daukes, Prof. Martin Green Industry Partner Industry Partners Norwood Industries: Mr Graham Dancey Tianjin Institute of Power Sources and 18th Research Institute of China Electronics Technology Group (CETC-18), Tianjin, China: Prof. Funding Support Qiang Sun, He Wang ACAP RayGen Resources Pty Ltd: Dr John Lasich IQE (informal collaboration): Andrew Johnson 6.50 DEVELOPMENT AND IMPLEMENTATION OF INORGANIC TRANSPORT LAYERS IN THE Funding Support PEROVSKITE CELLS OF PEROVSKITE/SILICON ACAP TANDEM STRUCTURES

6.45 THIN SILVER NANOWIRE-BASED PROMISING Lead Partner TRANSPARENT CONDUCTIVE LAYER FOR SOLAR ANU CELLS ANU Team Lead Partner A/Prof. Klaus Weber, Mr Yiliang Wu, Ms Nandi Wu UNSW Academic Partner UNSW Team Peking University (PKU): A/Prof. Huanping Zhou Dr Arastoo Teymouri, Dr Supriya Pillai, A/Prof. Xiaojing Hao, A/Prof. Beijing Institute of Technology Ashraf Uddin, Mushfika Upama, Prof. Martin A. Green Funding Support ACAP, ANU, PKU

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Funding Support 6.51 HIGH EFFICIENCY SEMI-PLANAR ARENA, UNSW PEROVSKITE CELLS COMBINING NANO- TEXTURED ELECTRON TRANSPORT LAYERS AND 6.55 COMPUTATIONAL MATERIALS DISCOVERY: INORGANIC HOLE TRANSPORT MATERIALS AB INITIO MODELLING OF NEW, HIGH Lead Partner PERFORMANCE SEMICONDUCTORS FOR TOP ANU CELLS IN MULTI-JUNCTION TANDEMS ON SILICON SOLAR CELLS ANU Team A/Prof. Thomas White, Dr Jun Peng Lead Partner UNSW Academic Partner Sun Yat-sen University (SYSU), Guangzhou, China UNSW Team Dr Rob Patterson, Dr Judy Hart, A/Prof. Xiaojing Hao, Prof. Martin Funding Support Green ACAP Academic Partners 6.52 MICROSTRUCTURE CHARACTERISATION OF University of Bristol, United Kingdom: Neil Allen THERMALLY EVAPORATED PEROVSKITE SOLAR Beijing Computational Science Research Center: Su-huai Wei CELLS FOR THE APPLICATION OF MONOLITHIC Funding Support PEROVSKITE/SILICON TANDEM SOLAR CELLS ARENA, ACAP Lead Partner Monash University 6.56 TOWARDS A MULTIPLE EXCITON- GENERATING SILICON SOLAR CELL Monash Team Prof. Udo Bach Lead Partner UNSW Academic Partner Wuhan University of Technology (WHUT), China: Dr Wei Li, Prof. Yi-Bing UNSW Team Cheng Dr Murad Tayebjee, Prof. Dane McCamey

Funding Support Academic Partners ARENA, Monash, WHUT Harvard University, USA: Dr Daniel Congreve Columbia University, USA: A/Prof. Luis Campos 6.53 MAGNETIC FIELD IMAGING FOR Funding Support PHOTOVOLTAIC CELLS AND MODULES ARENA, UNSW Lead Partner UNSW 6.57 PV EDUCATION EXPANSION: LEARN HOW TO OPTIMISE PV MODULE PERFORMANCE UNSW Team Dr Oliver Kunz, Prof. Thorsten Trupke, Dr Appu Paduthol Lead Partner UNSW Industry Partner DENKweit GmbH, Halle (Saale) Germany UNSW Team Prof. Bram Hoex Funding Support ACAP UNSW Student Zubair Abdullah-Vetter 6.54 INVESTIGATION OF PERFORMANCE PV Lighthouse DEGRADATION PATHWAYS IN SILICON Ben Sudbury, Malcolm Abbott, Keith McIntosh PHOTOVOLTAIC MODULES ARISING FROM COPPER-PLATED METALLISATION QESST Team Prof. Stuart Bowden, Dr Andre Augusto Lead Partner UNSW Funding Support ACAP, UNSW UNSW Team Prof. Alison Lennon

Academic Partner Arizona State University (ASU), USA: Dr André Filipe Rodrigues Augusto, Prof. Stuart Bowden

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Industry Partner 6.58 MICROWAVE PROCESSING: FOR SILICON Bert Thin Films, USA: Dr Thad Druffel, Dr Ruvini Dharmadasa SOLAR CELLS AND BEYOND Funding Support Lead Partner ARENA, UNSW, BTF UNSW

UNSW Team 6.62 DEVELOPMENT OF QUANTUM DOTS SOLAR A/Prof. B. Hallam, A/Prof. S. Huang INKS FOR ECONOMICAL MASSIVE-SCALE PRODUCTION OF THIN-FILM PHOTOVOLTAIC UNSW Student CELLS Yuchao Zhang Lead Partner Academic Partner UNSW Macquarie University UNSW Team Macquarie University Team Dr Shujuan Huang, Prof. Gavin Conibeer, Dr Robert Patterson Dr B. Puthen Veettil, Dr D. Payne UNSW Students Funding Support Mr Zhi Li Teh, Mr Yijun Gao ARENA, ACAP 6.59 COLLATING AND SHARING INFORMATION ON Academic Partner DEFECTS IN SILICON AMOLF

Lead Partner AMOLF Team UNSW Prof. Albert Polman, Mr Stefan Tabernig

UNSW Team 6.63 ENGINEERING INTERFACES FOR HIGH Dr Mattias Juhl, Dr Fiacre Rougieux PERFORMANCE SILICON TANDEM CELL Academic Partners STRUCTURES Australian National University: Prof. Daniel MacDonald Lead Partner ECN Solar Energy: Dr Stuart Bowden CSIRO, Energy, Newcastle Fraunhofer ISE: Dr Martin Schubert CSIRO Team Industry Partner Dr Gregory Wilson, Dr Timothy Jones, Dr Jacob Wang, Dr Terry Yang, PV Lighthouse: Keith Macintosh Dr Chris Fell, Dr Benjamin Duck Funding Support Academic Partner ACAP Fellowship UNSW: A/Prof. Anita Ho-Baillie

6.60 SILICON SOLAR CELLS WITH SILICON Funding Support CARBIDE PASSIVATED CONTACTS ACAP

Lead Partner 6.65 ADVANCED LUMINESCENCE UNSW CHARACTERISATION FOR DOPED-POLY AND UNSW Team PASSIVATION FILMS IN SILICON PHOTOVOLTAICS Dr Ning Song, Dr Udo Römer, Prof. Alison Lennon Lead Partner Industry Partners ANU Trina Solar Ltd, China. ANU Team Funding Support Dr Hieu Nguyen (lead), Thien Truong, Mike Tebyetekerwa, Prof. Daniel ACAP Macdonald

Academic Partner 6.61 ALL-SCREEN-PRINTED NANOPARTICLE Fraunhofer ISE (Fh-ISE), Germany: Dr Martin Schubert CONTACTS Funding Support Lead Partner ARENA, ACAP, ANU, Fh-ISE UNSW

UNSW Team Dr Malcolm Abbott

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6.66 SILICON DEVICES FOR III-V TANDEMS FELLOWSHIPS

Lead Partner ACAP’s competitively selected Fellowships, whose titles are shown ANU below, are reported online at http://www.acap.net.au/annual-reports.

ANU Team Matthew Stocks, Teng Kho F1 TECHNO-ECONOMIC ANALYSIS OF Academic Partner PHOTOVOLTAIC CELL AND MODULE FABRICATION SERIS TECHNOLOGIES

SERIS Team Lead Partner Armin Aberle UNSW

Funding Support UNSW Team ARENA Dr Nathan L. Chang, Prof. Renate Egan

Funding Support ACAP Fellowship 6.67 SINGLET FISSION ENHANCED SOLAR CELLS

UoM Team F2 DEVELOPMENT OF PRACTICAL HIGH Dr David Jones, Dr Jegadesan Subbiah EFFICIENCY PEROVSKITE/SILICON TANDEM MODULES Academic Partner KIT (Germany): Dr Alexander Colsmann, Mr Lorenz Graf von Reventlow Lead Partner ANU Funding Support AUSIAPV, UoM, KIT ANU Team The Duong

Academic Partner 6.68 ORGANIC ELECTRON TRANSPORT LAYER Peking University: Assistant Prof. Huanping Zhou TOWARDS UPSCALING OF HIGH EFFICIENCY UNSW: A/Prof. Anita Wing Yi Ho-Baillie PEROVSKITE SOLAR CELLS Funding Support Lead Partner ACAP CSIRO

CSIRO Team F3 TRANSPARENT DOPED LPCVD POLYSILICON Dr Dechan Angmo, Dr Doojin Vak, Dr Andrew Scully Fellowship Holder Academic Partner Dr Kean Chern Fong Chinese Academy of Sciences (CAS), Beijing: Prof. Jinhui Hou Supervisor University of Cambridge, UK: Dr Samuel Stranks Prof. Andrew Blakers Funding Support Funding Support ARENA, CSIRO, University of Cambridge, Chinese Academy of Science. ACAP

F4 HYDROGEN DRIFT AND DIFFUSION IN SILICON SOLAR ARCHITECTURES AT INTERMEDIATE TEMPERATURES

Lead Partner UNSW

UNSW Team Dr Phillip Hamer, Dr Catherine Chan, Chandany Sen, Daniel Chen, Dr Michael Pollard, Prof. Renate Egan

Academic Partner The University of Oxford, Department of Materials: Dr Sebastian Bonilla, Prof. Peter Wilshaw

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F5 CHARACTERISATION OF MICROSTRUCTURE F8 DETERMINATION OF DEFECT ENERGY LEVELS FORMATION IN SOLUTION-PROCESSED FROM INJECTION-DEPENDENT TRAPPING PHOTOVOLTAIC PEROVSKITE THIN FILMS WITH Lead Partner SYNCHROTRON-BASED X-RAY SCATTERING UNSW TECHNIQUES UNSW Team Lead Partner Dr Mattias Juhl, Prof. Thorsten Trupke Monash University Academic Partners Monash Team Australian National University: Prof.Daniel Macdonald Dr Wenchao Huang, Prof. Christopher R. McNeill, Prof. Udo Bach Arizona State University: Prof. Stuart Bowden Academic Partner Fraunhofer ISE: Dr Martin Schubert Wuhan University of Technology: Prof. Fuzhi Huang, Prof. Yi-Bing Funding Support Cheng ACAP Funding Support ACAP F10 TOWARDS A 50% EFFICIENT MULTIJUNCTION PV SYSTEM F6 HIGH DIELECTRIC CONSTANT Lead Partner SEMICONDUCTORS FOR HOMOJUNCTION UNSW ORGANIC SOLAR CELLS UNSW Team Lead Partner Dr Dongchen Lan UQ Funding Support UQ Team ACAP Dr Hui Jin, Mr Mohammad Babazadeh, Prof. Paul Burn

Funding Support F11 NEW IMPURITY REMOVAL TECHNOLOGIES ACAP, ARC Laureate Fellowship (PB), National Computing FOR LOW-COST, HIGH EFFICIENCY SILICON Infrastructure SOLAR CELLS

ACAP Fellow F7 PRACTICAL 50% EFFICIENT SPECTRUM Dr AnYao Liu, ANU SPLITTING CPV RECEIVERS USING INTERMEDIATE BRAGG REFLECTORS Academic Partners UNSW: A/Prof. Ziv Hameiri Lead Partner Aalto University (Finland): Toni Pasanen, A/Prof. Hele Savin UNSW Funding Support UNSW Team ACAP Dr Yajie Jiang, Dr Mark Keevers, Scientia Prof. Martin Green

Industry Partners F12 BLOCK COPOLYMERS FOR HIGH AZUR SPACE Solar Power PERFORMANCE, THERMALLY ROBUST ORGANIC RayGen Resources Pty Ltd PHOTOVOLTAIC DEVICES VIA AN INDUSTRIALLY RELEVANT PRINTING PROCESS Funding Support ACAP Lead Partner University of Melbourne (UoM)

UoM Team Dr Valerie Mitchell, Dr David Jones, Gagandeep Ahluwalia

Academic Partners Melbourne Energy Institute: Prof. Mukundan Thelakkat (University of Bayreuth), A/Prof. Chris McNeill (Monash University), Dr Mei Gao (CSIRO Manufacturing Flagship, Victoria)

Funding Support ACAP, MEI

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F13 MULTISCALE AND DEPTH-RESOLVED F18 TOWARDS 20% EFFICIENCY CU2ZNSNS4 THIN- SPECTRAL PHOTOLUMINESCENCE FOR FILM SOLAR CELL BY DEFECT ENGINEERING CHARACTERISING SOLAR CELLS AND BAND GRADING ENGINEERING

Lead Partner Lead Partner ANU UNSW

ANU Team UNSW Team Dr Hieu Nguyen Dr Chang Yan, Prof. Martin Green, A/Prof. Xiaojing Hao, A/Prof. Nicholas (Ned) Ekins-Daukes, Dr Jialiang Huang, Dr Kaiwen Sun Academic Partners National Renewable Energy Laboratory (NREL), UNSW Academic Partner National Renewable Energy Laboratory (NREL): Dr Steven Johnston Funding Support ACAP Funding Support ACAP F14 OVERCOMING THE MATERIAL LIMITATIONS OF CAST-GROWN MULTICRYSTALLINE AND F19 ADVANCED NANOSCALE CHARACTERISATION MONO-LIKE SILICON FOR HIGH EFFICIENCY OF LOCAL STRUCTURES AND DEFECTS FOR SOLAR CELLS LARGE BANDGAP MATERIALS FOR TANDEM SOLAR CELLS Fellowship Holder Dr Hang Cheong Sio Lead Partner UNSW Supervisor Prof. Daniel Macdonald UNSW Team Dr Jae Sung Yun, Prof. Martin Green, Dr Jincheol Kim, Funding Support Dr Xin Cui, A/Prof. Jeana Hao ACAP Fellowship Academic Partners Academic and Industrial Partners School of Materials Science and Engineering at UNSW: Jinko Solar Prof. Jan Seidel, Dr Dohyung Kim Fraunhofer Institute for Solar Energy Systems University of Queensland: Dr Jungho Yun AF Simulations Funding Support F15 DEVICE ARCHITECTURE DESIGN FOR ACAP COMMERCIAL KESTERITE SINGLE-JUNCTION AND MULTI-JUNCTION SOLAR CELLS F20 SEMITRANSPARENT FLEXIBLE PEROVSKITE SOLAR CELLS FOR LAMINATED TANDEM CELL Lead Partner UNSW Lead Partner CSIRO UNSW Team Dr Kaiwen Sun, Prof. Martin Green, A/Prof. Xiaojing Hao, Dr Jialiang CSIRO Team Huang, Dr Chang Yan, Xin Cui, Heng Sun, Ao Wang Dr Chuantian Zuo, Dr Mei Gao, Dr Doojin Vak

Academic Partner Academic Partners Nanyang Technological University (NTU): A/Prof. Lydia Helena Wong Monash University University of Melbourne Funding Support ACAP Funding Support ACAP F16 COMPREHENDING CHARGE TRANSPORT IN PEROVSKITE/SILICON TANDEM SOLAR CELLS

Fellowship Holder Daniel Walter

Supervisor A/Prof. Klaus Weber

Funding Support ACAP

122 ACAP ANNUAL REPORT 2019

FINANCIAL SUMMARY

In December 2012, a grant of $33.1 million from the Australian The 20 Fellowships were all taken up during 2018. The fourth round Government through ARENA was announced to support an of Small Grants were selected in Q2 of 2018, offering a total of 17 initial eight-year program of the Australian Centre for Advanced projects sharing $821,800. A further, fifth, round was offered late in Photovoltaics (ACAP). This support leveraged an additional $55.4 2018 (for projects to start in 2019). Again, 17 projects were successful million cash and in-kind commitment from ACAP participants taking and shared $856,305. Greatcell Solar Pty Ltd, ceased to trade during the total value of the project to $88.5 million. Q4 of 2018 and is no longer a collaborating industry participant in ACAP. ACAP commenced on 1 February 2013 after the signing of the Head Agreement between ARENA and UNSW, and with the receipt of Variation #7 was executed on 4 April 2019. This provided additional letters of confirmation of participation under the terms of the Head funding of $10.6 million in the overall budget to extend the life of Agreement by the other project participants. Collaboration Agreements ACAP for an extra two years (its ninth and tenth) until the end of 2022 with the Australian participants in the ACAP were completed on and $8.4 million for an additional two rounds each of 15 Fellowships, 1 July 2013. Round 2 in 2019 and Round 3 in 2020. $13.9 million was awarded for research infrastructure and will be distributed in 2020. An extension to the program, to undertake an Australian Solar PV Cell and Module Research lnfrastructure Plan and Feasibility Study was The Collaboration Agreement, between UNSW and the other signed in October 2014, generating an additional milestone, 4A. This Collaborating Australian Research Institutions was renegotiated during project was completed and Milestone 4A was paid in October 2015. 2019 and is expected to be executed in early 2020. A further extension was formalised through Variation #4, executed Three of the 2018 Fellows resigned during 2019, freeing $542,813 in February 2016. It extended perovskites research in ACAP and of the Round 1 funds, which the Management Committee chose generated two new Milestones (4B and 5B) for 2016 and others in to use to offer extra opportunities in Round 3, which was opened subsequent years. Both the new 2016 milestones were met and paid. for applications in Q2 of 2019. Partnerships with Sandia National The Milestone 5 and 6 payments from ARENA to UNSW were also Laboratories and the University of California Santa Barbara were paid, in 2016 and 2017, respectively. Disbursements were made to formally brought to an end through Variation #7. each node following confirmation of institutional cash contributions. All technical milestones for 2019 were achieved, apart from one that Variation #5 in June 2016 added a new partner, Dyesol Pty Ltd (now was delayed in 2017 and 2018, with ARENA approval, by damage to known as Greatcell Solar Pty Ltd) and pooled the cash and in-kind one of the ACAP laboratories. contributions of most of the collaborating international research institutions and of the collaborating industry participants. The breakdown by institution of the $16 million total cash and in-kind budget for 2019 is shown in Figure 7.1(a). The actual total 2019 cash Variation #6 in October 2017 and #6A in December 2017 implemented and in-kind expenditure was $19.8 million and its breakdown is shown many of the changes proposed by the Mid-Term Review Panel in 2016, in Figure 7.1(b). including the provision of additional funding for Capacity Building (Fellowships) and Small Grants, and made several minor updates The Green Energy Institute became ACAP’s first Korea-based and corrections. These variations brought the total funds granted Collaborating International Research Institution and Tindo Solar, the to $46 million. A robust and transparent process to distribute Small South Australian manufacturer of silicon PV modules, joined as a new Grants was developed in 2015 and implemented in a small first Collaborating Industry Participant, both in Q4 of 2019. funding round in that year. Two larger rounds were undertaken during 2016 and a fourth round was offered in Q1 of 2018. In addition, 20 Fellowships were offered in Q4 of 2017. RayGen Resources Pty Ltd joined as a new collaborating industry participant during 2017.

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(a) Figure 7.1: (a) Total AUSIAPV/ACAP cash and in-kind expenditure budget ($m) for 2019 broken down by institution. (b) Total cash and in-kind actuals ($m) breakdown by institution for 2019.

(b)

124 ACAP ANNUAL REPORT 2019

PUBLICATIONS

8.2 BOOK CHAPTERS GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 Apparatus for cooling a photovoltaic module, PCT PCT/ SHRESTHA, S., CONIBEER, G. & HUANG, S. 2019. Solar Cells Based AU2019/050170 on Hot Carriers and Quantum Dots. In: GAO, F. (ed.) Advanced GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 Nanomaterials for Solar Cells and Light Emitting Diodes. Elsevier. Apparatus for cooling a photovoltaic module, National Phase (Non- PCT) Taiwan 108106840

8.2 PATENTS AND PATENT APPLICATIONS HALLAM, B., CHEN, D., KIM, M., WRIGHT, M. 2019 A method for improving the performance of a heterojunction solar cell, PCT PCT/ CHONG, C.M., OUYANG, Z., DENG, R. 2019 Method of correcting AU2019/051168 degradation in a photovoltaic module, Provisional Australia 2019901859 HALLAM, B., CHEN, D., KIM, M., WRIGHT, M. 2019 A method for improving the performance of a heterojunction solar cell, National CUI, H., GALLARDO, O., HUANG, Z., MUQAIBAL, A. 2019 Building Phase (Non-PCT) Taiwan 108138436 integrated photovoltaic window, Provisional Australia 2019901402 HOEX, B., SANG, B. 2019 Edge passivation of shingled solar cells, GREEN, M., HAO, X., CHEN, S., PATTERSON, R. 2019 Adamantine Provisional Australia 2019901449 semiconductor and uses thereof, PCT PCT/AU2019/050121 LENNON, A., HSIAO, P.-H. 2019 Thermomechanical stress in solar cells, GREEN, M., HAO, X., CHEN, S., PATTERSON, R. 2019 Adamantine Provisional Australia 2019900521 semiconductor and uses thereof, National Phase (Non-PCT) Taiwan 108105164 LENNON, A., HSIAO, P.-H., OUYANG, Z., HALL, C., SONG, N., ROEMER, C., WANG, Z., LI, Y. 2019 A method of forming a device structure. GREEN, M., HAO, X., LIU, F., YAN, C., HUANG, J., SUN, K. 2019 A copper- Provisional Australia 2019901501 based chalcogenide photovoltaic device and a method of forming the same, National Phase Europe 17814327.7 LENNON, A., HSIAO, P.-H., OUYANG, Z., SONG, N., ROEMER, C., LI, Y., MUNGRA, M. 2019 A structured connector for interconnecting device GREEN, M., HAO, X., LIU, F., YAN, C., HUANG, J., SUN, K. 2019 A copper- components, Provisional Australia 2019901505 based chalcogenide photovoltaic device and a method of forming the same, National Phase India 201947002392 SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method for improving wafer performance for photovoltaic devices, National GREEN, M., JIANG, Y., KEEVERS, M. 2019 A photovoltaic cell structure, Phase Australia 2017363825 PCT PCT/AU2019/050611 SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method GREEN, M., JIANG, Y., KEEVERS, M. 2019 A photovoltaic cell structure, for improving wafer performance for photovoltaic devices, National National Phase (Non-PCT) Taiwan 108120561 Phase China 201780071912.X GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method A photovoltaic module, PCT PCT/AU2019/050164 for improving wafer performance for photovoltaic devices, National GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 Phase Europe 17874819 A photovoltaic module, National Phase (Non-PCT) Taiwan 108106837 SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 for improving wafer performance for photovoltaic devices, National A photovoltaic module, PCT PCT/AU2019/050168 Phase India 201927021460

GREEN, M., JIANG, Y., KEEVERS, M., EKINS-DAUKES, N., ZHOU, Z. 2019 SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method A photovoltaic module, National Phase (Non-PCT) Taiwan 108106839 for improving wafer performance for photovoltaic devices, National Phase Japan 2019-527401

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SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method WENHAM, S., HALLAM, B., EINHAUS, R. 2019 A method for for improving wafer performance for photovoltaic devices, National manufacturing a photovoltaic device, National Phase China Phase South Korea 10-2019-7016969 201780043607.X

SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method WENHAM, S., HALLAM, B., EINHAUS, R. 2019 A method for for improving wafer performance for photovoltaic devices, National manufacturing a photovoltaic device, National Phase Europe Phase Singapore 11201903426Y 17826685.4

SHI, Z., WENHAM, S., CIESLA, A., CHAN, C., CHEN, R. 2019 A method WENHAM, S., HALLAM, B., EINHAUS, R. 2019 A method for for improving wafer performance for photovoltaic devices, National manufacturing a photovoltaic device, National Phase India Phase United States 16/461864 201947004626

TRUPKE, T., PADUTHOL, A.R., KUNZ, O. 2019 Apparatus and methods WENHAM, S., HALLAM, B., EINHAUS, R. 2019 A method for for investigating contacting structures on semiconductor materials manufacturing a photovoltaic device, National Phase South using magnetic field measurements, Provisional Australia 2019902087 Korea10-2019-7004061

WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 WENHAM, S., HALLAM, B., EINHAUS, R. 2019 A method for Advanced hydrogen passivation that mitigates hydrogen-induced manufacturing a photovoltaic device, National Phase United States recombination (HIR) and surface passivation deterioration in PV 16/316691 devices, National Phase Australia 2017363826 WENHAM, S., HALLAM, B., HAMER, P., ABBOTT, M. 2019 Method for WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 processing silicon material, Divisional Singapore 10201908439W Advanced hydrogen passivation that mitigates hydrogen-induced recombination (HIR) and surface passivation deterioration in PV devices, National Phase China 201780072249.5 8.3 PAPERS IN REFEREED SCIENTIFIC

WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 AND TECHNICAL JOURNALS Advanced hydrogen passivation that mitigates hydrogen-induced AALONSO-ÁLVAREZ, D., AUGUSTO, A., PEARCE, P., LLIN, L. F., MELLOR, recombination (HIR) and surface passivation deterioration in PV A., BOWDEN, S., PAUL, D. J. & EKINS-DAUKES, N. 2019. Thermal devices, National Phase Europe 17874676.4 emissivity of silicon heterojunction solar cells. Solar Energy Materials WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 and Solar Cells, 201. DOI: 10.1016/j.solmat.2019.110051. Advanced hydrogen passivation that mitigates hydrogen-induced ALONSO-ÁLVAREZ, D., WEISS, C., FERNANDEZ, J., JANZ, S. & EKINS- recombination (HIR) and surface passivation deterioration in PV DAUKES, N. 2019. Assessing the operating temperature of multi- devices National Phase, India 201947024411 junction solar cells with novel rear side layer stack and local electrical WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 contacts. Solar Energy Materials and Solar Cells, 200. https://dx.doi. Advanced hydrogen passivation that mitigates hydrogen-induced org/10.1016/j.solmat.2019.110025. recombination (HIR) and surface passivation deterioration in PV ANGMO, D., PENG, X. J., SEEBER, A., ZUO, C. T., GAO, M., HOU, Q. C., devices, National Phase South Korea 10-2019-7018247 YUAN, J., ZHANG, Q., CHENG, Y. B. & VAK, D. Controlling Homogenous WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 Spherulitic Crystallization for High-Efficiency Planar Perovskite Solar Advanced hydrogen passivation that mitigates hydrogen-induced Cells Fabricated under Ambient High-Humidity Conditions. Small, 15, recombination (HIR) and surface passivation deterioration in PV 1904422. devices, National Phase United States 16/461852 ANN, M. H., KIM, J., KIM, M., ALOSAIMI, G., KIM, D., HA, N. Y., SEIDEL, WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019 J., PARK, N., YUN, J. S. & KIM, J. H. 2019. Device design rules and Advanced hydrogen passivation that mitigates hydrogen-induced operation principles of high-power perovskite solar cells for indoor recombination (HIR) and surface passivation deterioration in PV applications. Nano Energy. 68, 104321-104321, http://dx.doi. devices, National Phase Japan 2019-527396 org/10.1016/j.nanoen.2019.104321.

WENHAM, S., CIESLA, A., BAGNALL, D., ABBOTT, M., CHEN, R. 2019, BASNET, R., WEIGAND, W., YU, Z. J., SUN, C., PHANG, S. P., SIO, H. C., Advanced hydrogen passivation that mitigates hydrogen-induced ROUGIEUX, F. E., HOLMAN, Z. C. & MACDONALD, D. 2020. Impact of recombination (HIR) and surface passivation deterioration in PV pre-fabrication treatments on n-type UMG wafers for 21% efficient devices, National Phase Singapore 11201903183Q silicon heterojunction solar cells. Solar Energy Materials and Solar Cells, 205. DOI:10.1016/j.solmat.2019.110287. WENHAM, S., CIESLA, A., HALLAM, B., CHAN, C., CHONG, C.M., ABBOTT, M., PAYNE, D., CHEN, R. 2019 A method for processing silicon BERTHOD, C., KRISTENSEN, S. T., STRANDBERG, R., ODDEN, J. O., material, National PhaseSouth Korea 10-2019-7000342 NIE, S., HAMEIRI, Z. & SATRE, T. O. 2019. Temperature sensitivity of multicrystalline silicon solar cells. IEEE Journal of Photovoltaics, 9(4), WENHAM, S., CIESLA, A., HALLAM, B., CHAN, C., CHONG, C.M., 957-964. DOI: 10.1109/JPHOTOV.2019.2911871. ABBOTT, M., PAYNE, D., CHEN, R. 2019 A method for processing silicon material, National Phase India 201927000347

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BING, J., HUANG, S. & HO-BAILLIE, A. W. Y. 2019. A Review on Halide CHEN, B. Y., PENG, J., SHEN, H. P., DUONG, T., WALTER, D., JOHNSTON, Perovskite Film Formation by Sequential Solution Processing for Solar S., AL-JASSIM, M. M., WEBER, K. J., WHITE, T. P., CATCHPOLE, K. R., Cell Applications. Energy Technology. DOI: 10.1002/ente.201901114. MACDONALD, D. & NGUYEN, H. T. 2019. Imaging Spatial Variations of Optical Bandgaps in Perovskite Solar Cells. Advanced Energy Materials, BING, J., KIM, J., ZHANG, M., ZHENG, J., LEE, D. S., CHO, Y., DENG, 9, 18027909. X., LAU, C. F. J., LI, Y., GREEN, M. A., HUANG, S. & HO-BAILLIE, A. W. Y. 2019. The Impact of a Dynamic Two-Step Solution Process on CHEN, D., HAMER, P., KIM, M., MULLINS, J., SEN, C., KHAN, M.,

Film Formation of Cs0.15 (MA0.7 FA 0.3)0.85 PbI3 Perovskite and Solar Cell OSHIMA, T., ABE, H., LIU, S., CIESLA, A., CHAN, C., CHEN, R., Performance. Small, 15. https://doi.org/10.1002/smll.201804858. ROUGIEUX, F., ZHOU, Z., WRIGHT, B., VARSHNEY, U., VICARI STEFANI, B., SOERIYADI, A., VARGAS CASTRILLON, C., SAMADI, A., HAMEIRI, BING, J., LEE, D. S., ZHENG, J., ZHANG, M., LI, Y., KIM, J., LAU, C. F. Z., ZHANG, X., JIN, H., QI, W., ABBOTT, M., CHONG, C., PEAKER, A. & J., CHO, Y., GREEN, M. A., HUANG, S. & HO-BAILLIE, A. W. Y. 2019. HALLAM, B. Will LeTID remain a commercial problem? Evaluating the Deconstruction-assisted perovskite formation for sequential solution solutions and a possible root cause. (LeTID仍是一个商业难题吗？ processing of Cs (MA FA ) PbI solar cells. Solar Energy Materials 0.15 0.7 0.3 0.85 3 根源分析和问题解决). 18th Issue PV WE CLASS-Crystalline Silicon and Solar Cells, 203. 10.1016/j.solmat.2019.110200. Advanced Technology and Materials Forum. Wuxi, China. BLAKERS, A., STOCKS, M., LU, B. & CHENG, C. 2019. Renewable Energy CHEN, D., KIM, M., SHI, J., VICARI STEFANI, B., YU, Z., LIU, S., Update. Energy News, 37, 6–8. EINHAUS, R., WENHAM, S., HOLMAN, Z. & HALLAM, B. 2019. Defect BLAKERS, A., STOCKS, M., LU, B., CHENG, C. & STOCKS, R. 2019. engineering of p-type silicon heterojunction solar cells fabricated Hydroelectricity in Australia. Energy News, 37, 11–13. using commercial-grade low-lifetime silicon wafers. Progress in Photovoltaics: Research and Applications. DOI: 10.1002/pip.3230. BLAKERS, A., STOCKS, M., LU, B., CHENG, C. & STOCKS, R. 2019. Pathway to 100% Renewable Electricity. IEEE Journal of Photovoltaics, CHEN, H., ZHANG, M., FU, X., FUSCO, Z., BO, R., XING, B., NGUYEN, H. 9, 1828-1833. T., BARUGKIN, C., ZHENG, J., LAU, C. F. J., HUANG, S., HO-BAILLIE, A. W. Y., CATCHPOLE, K. R. & TRICOLI, A. 2019. Light-activated inorganic BOURQUE, A. J., ENGMANN, S., FUSTER, A., SNYDER, C. R., RICHTER, CsPbBr2I perovskite for room-temperature self-powered chemical L. J., GERAGHTY, P. B. & JONES, D. J. 2019. Morphology of a thermally sensing. Physical Chemistry Chemical Physics, 21, 24187-24193. stable small molecule OPV blend comprising a liquid crystalline donor and fullerene acceptor. Journal of Materials Chemistry A, 7, 16458- CHEN, J., GE, K., CHEN, B., GUO, J., YANG, L., WU, Y., COLETTI, G., LIU, 16471. H., LI, F., LIU, D., WANG, Z., XU, Y. & MAI, Y. 2019. Establishment of a novel functional group passivation system for the surface engineering BU, T., LI, J., HUANG, W., MAO, W., ZHENG, F., BI, P., HAO, X., ZHONG, of c-Si solar cells. Solar Energy Materials and Solar Cells, 195, 99-105. J., CHENG, Y.B., HUANG, F., 2019. Surface modification via self- assembling large cations for improved performance and modulated CHEN, W. M., LI, W., GAN, Z., CHENG, Y. B., JIA, B. & WEN, X. 2019. hysteresis of perovskite solar cells, Journal of Materials Chemistry A, 7, Long-Distance Ionic Diffusion in Cesium Lead Mixed Halide Perovskite 6793-6800. Induced by Focused Illumination. Chemistry of Materials, 31, 9049- 9056. BU, T., LIU, X., LI, J., LI, W., HUANG, W., KU, Z., PENG, Y., HUANG, F., CHENG, Y.B., ZHONG, J., 2019. Sub-sized monovalent alkaline cations CHEN, W., MAO, W., BACH, U., JIA, B. & WEN, X. 2019. Tracking enhanced electrical stability for over 17% hysteresis-free planar Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals perovskite solar mini-module, Electrochimica Acta, 306, 635-642. under Two‐Photon Scanning Laser Illumination. Small Methods, 1900273-1900273. BU., T., LIU, X., LI, J., HUANG, W., WU, Z., HUANG, F., CHENG, Y.B., ZHONG, J., 2019. Dynamic Antisolvent Engineering for Spin Coating CHENG, C., BLAKERS, A., STOCKS, M. & LU, B. 2019. Pumped hydro of 10 × 10 cm2 Perovskite Solar Module Approaching 18%, Solar RRL, energy storage and 100% renewable electricity for East Asia. Global DOI:10.1002/solr.201900263 Energy Interconnection, 2, 387-393.

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Repurposing commercial anaerobic digester TAPPING, P., KEE, T. W., JIA, B. & WEN, X. 2019. Perovskites: Triggering wastewater to improve cyanobacteria cultivation and digestibility for the Passivation Effect of Potassium Doping in Mixed‐Cation Mixed‐ bioenergy systems. Sustainable Energy and Fuels, 3, 841-849. Halide Perovskite by Light Illumination. Advanced Energy Materials, 9, YI, H., WANG, D., DUAN, L., HAQUE, F., XU, C., ZHANG, Y., CONIBEER, G. 1970093-1970093. & UDDIN, A. 2019. Solution-processed WO3 and water-free PEDOT:PSS ZHENG, J., MEHRVARZ, H., LIAO, C., BING, J., CUI, X., LI, Y., GONCĄLES, composite for hole transport layer in conventional perovskite solar cell. V. R., LAU, C. F. J., LEE, D. S., LI, Y., ZHANG, M., KIM, J., CHO, Y., CARO, L. Electrochimica Acta, 319, 349-358. G., TANG, S., CHEN, C., HUANG, S. & HO-BAILLIE, A. W. Y. 2019. Large- ZAFIROVSKA, I., JUHL, M. K., CIESLA, A., EVANS, R. & TRUPKE, T. 2019. area 23%-efficient monolithic perovskite/homojunction-silicon tandem Low temperature sensitivity of implied voltages from luminescence solar cell with enhanced uv stability using down-shifting material. ACS measured on crystalline silicon solar cells. Solar Energy Materials and Energy Letters, 4, 2623-2631. Solar Cells, 199, 50-58.

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ZHOU, C., CAO, G., GAN, Z., OU, Q., CHEN, W., BAO, Q., JIA, B. & WEN, BLAKERS, A., STOCKS, M., STOCKS, R., LU, B. & CHENG, C. 2019. A X. 2019. Spatially Modulating the Fluorescence Color of Mixed-Halide Global Atlas Of 616,000 Pumped Hydro Energy Storage Sites, Solar Perovskite Nanoplatelets through Direct Femtosecond Laser Writing. World Conference. November 2019, Santiago, Chile. ACS Applied Materials and Interfaces, 11, 26017-26023. BURATTI, Y., DICK, J., GIA, Q. L. & HAMEIRI, Z. A Machine Learning ZHU, H., DONG, Z., NIU, X., LI, J., SHEN, K., MAI, Y. & WAN, M. 2019. DC Approach to Defect Parameters Extraction: Using Random Forests to and RF sputtered molybdenum electrodes for Cu(In,Ga)Se2 thin film Inverse the Shockley-Read-Hall Equation. 2019 IEEE 46th Photovoltaic solar cells. Applied Surface Science, 465, 48-55. Specialists Conference (PVSC), 16-21 June 2019. 3070-3073.

ZHU, H., DONG, Z., PAN, L., HAN, Q., NIU, X., LI, J., SHEN, K., MAI, Y., BURATTI, Y., DICK, J., LE GIA, Q., ZHU, Y. & HAMEIRI, Z. Inversion of the LI, Y. & WAN, M. 2019. Investigation of Mo:Na and Mo related back Shockley-Read-Hall equation using random forests.6th Asia Pacific contacts for the application in Cu(In,Ga)Se2 thin film solar cells. Solid- Solar Research Conference, 3-5 Dec. 2019, Canberra. State Electronics, 157, 48-54. BURATTI, Y., SOWMYA, A., EVANS, R., TRUPKE, T. & HAMEIRI, Z. Deep ZHU, Y., JUHL, M. K., COLETTI, G. & HAMEIRI, Z. 2019. Reassessments learning on electroluminescence imaging for end-of-line cell binning. of minority carrier traps in silicon with photoconductance decay 29th International Photovoltaic Science and Engineering Conference measurements. IEEE Journal of Photovoltaics, 9, 652-652. (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

BURN, P. L., JIN, H., RAYNOR, A., STOLTZFUS, D., GAO, M, GENTLE, 8.4 CONFERENCE PAPERS AND I. & SHAW, P. The development of high dielectric constant organic materials. SPIE Optics and Photonics 2019, 11-15 Aug.2019 San PRESENTATIONS Diego, California.

ABBOTT, M., MCINTOSH, K., SUDBURY, B., MEYDBRAY, J., FUNG, T. H., BURN, P. L., JIN, H., RAYNOR, A., STOLTZFUS, D., GAO, M., GENTLE, KHAN, M. U., ZHANG, Y., ZOU, S., WANG, X., XING, G., SCARDERA, G. & I. & SHAW, P. The development of high dielectric constant organic PAYNE, D. Annual energy yield analysis of solar cell technology. 2019 materials. 2-4 Jun. 2019 Berlin, Germany. IEEE 46th Photovoltaic Specialists Conference (PVSC), 16-21 June BURN, P. L., STEPHEN, M., RAKSTYS, K., SAGHAEI, J., JIN, H., GAO, 2019. 3046-3050. M., ZHANG, G., HUTCHINSON, K., GENTLE, I. & SHAW, P. Device AN, N-G., Morphological Characterization and Photovoltaic engineering for inverted perovskite solar cells. Photovoltaics Applications for Indoloindole-based Small Molecule, 7th ACAP Workshop, Monash University, 12-13 Dec. 2019 Melbourne, Victoria. Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. BURN, P. L., WANG, X., JIN, H., POLIQUIT, B. Z., NAGIRI, R., SUBBIAH, J., 2019, Australian National University JONES, D., HONG DU, J., ZHANG, D. & REN, W. Flexible ITO-free organic ANGMO, D. Towards Scalable, Stable, and Reproducible Roll-to-roll solar cells. International Conference of Flexible Electronics, 13-14 Jul. Processed Perovskite Solar Cells. 7th ACAP Conference and 6th Asia 2019 Hangzhou, China. Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. BURN, P. L., WANG, X., JIN, H., POLIQUIT, B. Z., NAGIRI, R., SUBBIAH, J., BASNET, R. Onset of Ring Defects in n-Type Czochralski Silicon. 7th JONES, D., HONG DU, J., ZHANG, D. & REN, W. Flexible ITO-free organic ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 solar cells. Optoelectronics Meeting, Wuhan University, 17-18 Jul. 2019 Dec. 2019, Canberra. Wuhan, China.

Onset of Ring Defects in n-type Czochralski Silicon. 29th International BURN, P. L., WANG, X., JIN, H., POLIQUIT, B. Z., NAGIRI, R., SUBBIAH, Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, J., JONES, D., HONG DU, J., ZHANG, D. & REN, W. Graphene-based China, 4-8 Nov 2019. transparent conducting electrodes for high efficiency flexible organic photovoltaics: study in interfacial layer and power losses. 10th BHOOPATHY, R., KUNZ, O., DUMBRELL, R., TRUPKE, T. & HAMEIRI, Z. International Conference on Materials for Advanced Technologies, Application of suns-photoluminescence to extract implied I-V curves ICMAT 2019, 23-28 Jun. 2019 Marina Bay Sands, Singapore. of individual cells in modules installed in the field. 36th European Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, CHANG, N. Techno-Economic Analysis-What is it, Why is it Important, France 9-13 September 2019. and How to do it?, 7th ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra BHOOPATHY, R., KUNZ, O., DUMBRELL, R., TRUPKE, T. & HAMEIRI, Z. Outdoor non-contact measurement of pseudo I-V curves of solar cells CHANTLER, R., A Case Study of the Dedradation of Flexible Soalr in a module. 6th Asia Pacific Solar Research Conference, 3-5 Dec. Modules with High Schools’ Outreach. 7th ACAP Conference and 6th 2019, Canberra. Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra.

BHOOPATHY, R., KUNZ, O., JUHL, M., TRUPKE, T. & HAMEIRI, Z. CHEN, C., HSIAO, P.-H. OUYANG, Z., SHEN, C., ZHU, C., LV, J. & A simplified contactless method for outdoor photoluminescence LENNON, A. Modeling Study of Thermomechanical Stress in Silicon imaging. 46th IEEE Photovoltaic Specialists Conference, 16-21 June Solar Cells Interconnection. 29th International Photovoltaic Science 2019 Chicago, USA. and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

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CHEN, D., WEIGAND, W., WRIGHT, M., KIM, M., SHI, J., YU, Z. J., DENG, R., MONTEIRO LUNARDI, M. CHANG, Y.-C, JIANG, J., WANG, STEFANI, B. V., SOERIYADI, A., HOLMAN, Z. & HALLAM, B. Evaluating S., JI, J., & CHONG, C.M. A Simple Method for Rapid Recycling of the Impact of and Solutions to Light-induced Degradation in Silicon Silver from Decommissioned Silicon Photovoltaics. 36th European Heterojunction Solar Cells. 2019 IEEE 46th Photovoltaic Specialists Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, Conference (PVSC), 16-21 June 2019. 1099-1103. France 9-13 September 2019.

CHEN, W. Influence of PECVD Deposition Temperature on Phosphorus Deposition Annealing. 29th International Photovoltaic Science and Diffused Polysilicon Passivating Contacts. 7th ACAP Conference and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. DIAS, P.R., SHMIDT, L., SPIER, G., MONTEIRO LUNARDI, M., BILBAO, CHENG, C., BLAKERS, A., STOCKS, M. & LU, B. 2019. Pumped hydro J., CORKISH, R. & VEIT, H.M. Recycling waste solar modules using storage and 100% renewable electricity. Special Interest Group organic solvents, 7th International Conference on Sustainable Solid Meeting: Precision Engineering for Sustainable Energy Systems. 09-10 Waste Management, 26-29 June 2019, Heraklion, Crete, Greece. October 2019, Glasgow, UK. DING, Z., YAN, D., CHEN, W., PHANG, S.P., SAMUNDSETT, C. & CHENG, C., NADOLNY, A., LU, B., BLAKERS, A. & STOCKS, M. 2019. WANG, Z. P. Doped poly-Si/Oxide Passivating Contact via Spin-on Electrified Land Transport and Low Temperature Heating in Australia. Doping. 29th International Photovoltaic Science and Engineering 2019 Asia-Pacific Solar Research Conference. 3-5 December 2019, Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Canberra, Australia. DUAN, L., ZHANG, Y., YI, H., XU, C., HAQUE, F. & UDDIN, A. Degradation CHENG, C., NADOLNY, A., LU, B., BLAKERS, A. & STOCKS, M. 2019. Mechanism Identified for the Fullerene and Non-fullerene based Electrified Land Transport and Low Temperature Heating in Australia. Organic Solar Cells under Ambient Condition. 2019 IEEE 46th 3rd E-Mobility Power System Integration Symposium. 14 October Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 0461- 2019, Dublin, Ireland. 0464.

CLEVELAND, E. R., KOTULAK, N., TOMASULO, S., JENKINS, P. P., DUONG, T., WALTER, D., WEBER, K., WHITE, T. & CATCHPOLE, K. MELLOR, A., PEARCE, P., EKINS-DAUKES, N. J. & YAKES, M. K. Perovskite Solar Cells Employing Copper Phthalocyanine Hole- Interstitial Light Trapping and Optical Confinement in Multijunction Transport Material with an Efficiency over 20% and Excellent Thermal Solar Cells. 2019 IEEE 46th Photovoltaic Specialists Conference Stability. 10th International Conference on Materials for Advanced (PVSC), 16-21 June 2019. 2826-2828. Technologies, ICMAT 2019, 2019 Singapore, Singapore.

CONIBEER, G., DUBAJIC, M., SHRESTHA, S., BREMNER, S., DUONG, T., YIN, Y., JACOBS, D., WEBER, K., WHITE, T., ANDDERSSON, PATTERSON, R. & THAPA, B. Investigation of materials for hot G. & CATCHPOLE, K. Instability of Molybdenum Oxide and Implications carrier solar cell absorbers. 2019 IEEE 46th Photovoltaic Specialists on the Ambient Stability of Perovskite Solar Cells. 5th International Conference (PVSC), 16-21 June 2019. 2997-3000. Conference on Perovskite Solar Cells and Optoelectronics, PSCO 2019, 2019 Lausanne, Switzerland. CUI, X., SUN, K., HUANG, J., LEE, C., YAN, C., SUN, H., ZHANG, Y., GREEN, M., HOEX, B. & HAO, X. High-efficient Cd-free CZTS solar cells EIJKENS, C., BURATTI, Y. & HAMEIRI, Z. Optimization of industrial achieved by nanoscale atomic layer deposited aluminium oxide. 2019 manufacturing of solar cells with machine learning. 29th International IEEE 46th Photovoltaic Specialists Conference (PVSC), 16-21 June Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, 2019. 2482-2484. China, 4-8 Nov 2019.

CONIBEER, G., SHRESTHA, S., BREMNER, S., ZHANG, Y., TAYEBJEE, M. EIJKENS, C., BURATTI, Y. & HAMEIRI, Z. Optimization of industrial & DUBAJIC, M. 2019. Slowed hot carrier cooling in Multiple Quantum manufacturing of solar cells with machine learning. 6th Asia Pacific Wells for application to Hot Carrier Solar Cells. In: FREUNDLICH, A., Solar Research Conference, 3-5 Dec. 2019, Canberra. LOMBEZ, L. & SUGIYAMA, M. (eds.) Physics, Simulation, and Photonic EIJKENS, C.A. BURATTI, Y. & HAMEIRI, Z. Optimization of Industrial Engineering of Photovoltaic Devices VIII. Proceedings of SPIE 10913 Solar Cell Manufacturing Using Machine Learning. 29th International Article UNSP 109130G Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, CUI, X., SUN, K., HUANG, J., LEE, C.-Y., YAN, C., SUN, H., ZHANG, China, 4-8 Nov 2019. Y., MARTIN GREEN, M. & HAO, X., Heterojunction Passivation for EKINS-DAUKES, N. Navigating the 1eV Junction Challenge Beyond 10% Efficiency Cd-free CZTS Solar Cells by Nanoscale ALD- with Lattice-Matched GaAs Based Multi-Junction (Invited). 29th Alumina. 29th International Photovoltaic Science and Engineering International Photovoltaic Science and Engineering Conference Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. (PVSEC-29), Xi'an, China, 4-8 Nov 2019. DENG, R., MONTEIRO LUNARDI , M., JI, J. & CHONG C.M. ERNST, M, HAEDRICH, I, LI, Y & LENNON, A 2019, Impact of (Multi-) Demonstration of A Potential Closed-Loop Approach to Recycle End- Busbar Design on the PERC Cell-to-Module Yield under Realistic Of-Life Silicon Photovoltaic Modules. 29th International Photovoltaic Conditions, 6th Asia Pacific Solar Research Conference 2019 Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov (APSRC-2019), Canberra, Australia, 3-5 December 2019. 2019.

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ERNST, M, HAEDRICH, I, LI, Y, HSIAO, P-C & LENNON, A 2019, Impact GAO, M., Development of Roll-to-Roll Compatible Process for Highly of (Multi) Busbar Design in Full and Halved Cell Modules on the Efficient Thin Film Solar Cells. keynote speaker at International Cell-to-Module-Yield under Realistic Conditions. 29th International Conference on Flexible & Printed Optoelectronic Materials and Devices, Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, 20-22 Sep. 2019, China China, 4-8 Nov 2019. GAO, M., Reliability Improvement of Perovskite Solar Cells Through a ERNST, M, QIAN, J, WU, N & BLAKERS, A 2019, Impact of Perovskite Roll-to-Roll (R2R) Continuous Process. 7th ACAP Conference and 6th Solar Cell Degradation on Long-Term Performance of Perovskite/ Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. Silicon Tandem Modules, State-of-Energy-Research Conference 2019, GAO, M., Roll to Roll Compatible Process for Highly Efficient Perovskite Canberra, Australia, https://www.erica.org.au/speaker-presentations. Solar Cell. Monash University – Georgia Tech Photovoltaic Exchange ERNST, M, QIAN, J, WU, N & BLAKERS, A. 2019, Unravelling Program, 13-14 Jun. 2019, Atlanta, GA, USA Degradation of Perovskite Solar Cells and Long-Term Impact on GHIGGINO, K. 2019. High performance luminescent solar Perovskite/Silicon Tandem Modules, 36th European Photovoltaic concentrating devices. Interdisciplinary Workshop on Thin Films, Solar Energy Conference (EU PVSEC 2019). Marseille, France 9-13 Photonics & Organic Electronics, TF-POE2019, 21 November 2019, September 2019. Jinan, China. EVANS, R. & SHI, Z. Durability Benchmarking of a Light-weight GHIGGINO, K. P., ZHANG, B. & WONG, W. W. H. 2019. Developing high Polymer-based PV Module. 29th International Photovoltaic Science performance large area luminescent solar concentrator devices. 29th and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. International Conference on Photochemistry, ICP2019, 21-26 July EVANS, R. & WONG, J. Automated, Real-Time Analysis of PV 2019, Boulder, Colorado, Boulder, Colorado, USA. Manufacturing Data Using a “loss component” Approach. 2019 IEEE GHIGGINO, K., 2019. Luminescent materials for solar concentration. 46th Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 8th International Summer Course on ‘Nano Material Discovery’, 24-26 0372-0376. June 2019, Hsinchu, Taiwan. FIACRE, R., ZHANG, M., MOUETTE, G., XINGRU TAN, X. & JUHL, M. GLEN, F., Replacing ITO with Slot-die Coated Silver Nanowire/ End-End Multi-Scale Modelling of the Evolution of Oxygen Impurities PEDOT:PSS Composites as the Transparent Electrodes for Flexible Along the Silicon Solar Cells Value Chain. 7th ACAP Conference and Solar Films. 7th ACAP Conference and 6th Asia Pacific Solar Research 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. Conference, 3-6 Dec. 2019, Canberra. FONG, K.C. Loss Analysis of 25% IBC and IBC Tandem Solar Cells. 7th GRASSMAN, T. J., LEPKOWSKI, D. L., BOYER, J. T., CHMIELEWSKI, D. ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 J., YI, C., WESTERN, N., MEHRVARZ, H., HO-BAILLIE, A., KERESTES, Dec. 2019, Canberra. C., DERKACS, D., WHIPPLE, S. G., STAVRIDES, A. P., BREMNER, S. P. FONG, K.C., MAYON, O., DUONG, T., LIANG, W., KHO, T., SURVE, & RINGEL, S. A. Toward >25% Efficient Monolithic Epitaxial GaAsP/ S., MCINTOSH, K., STOCKS, M. & BLAKERS, A. Detailed Analysis Si Tandem Solar Cells. 2019 IEEE 46th Photovoltaic Specialists of 25% Silicon IBC, and IBC-Tandem Solar Cells 29th International Conference (PVSC), 16-21 June 2019. 0734-0737. Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, GREEN, M. A. What Comes after PERC? 29th International China, 4-8 Nov 2019. Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, FÜRER, S.O., MILHUISEN, R., KASHIF, K., RUIZ RAGA, S., FORSYTH, China, 4-8 Nov 2019. (Keynote). C. & BACH, U. The Effect of Additives on the Performance of Copper HALILOV, S., HOSSAIN, M.A., ZHANG, T., HOEX, B., ABDALLAH, Bisphenanthroline Electrolytes. poster presentation, Photovoltaic A. & RASHKEEV, S. NixAlyO Alloy as a Charge Transport Material: Workshop, Monash University, 12 Dec. 2019, Melbourne. Photoemission Study. 29th International Photovoltaic Science and FÜRER, S.O., MILHUISEN, R., KASHIF, K., RUIZ RAGA, S., FORSYTH, Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. C. & BACH, U. The Effect of Additives on the Performance of Copper HAMEIRI, Z., NIE, S., KRISTENSEN, S.T., GU, A. CHIN, R.L. & TRUPKE, T. Bisphenanthroline Electrolytes. poster presentation, Exciton Science & Photoluminescence-Based Temperature Coefficient Maps of Silicon Annual Workshop 2019. 12 Dec. 2019, Melbourne. Wafers and Solar Cells, 7th ACAP Conference and 6th Asia Pacific FÜRER, S.O., MILHUISEN, R., KASHIF, K., RUIZ RAGA, S., FORSYTH, Solar Research Conference, 3-6 Dec3-6 Dec. 2019, Canberra C. & BACH, U. The Effect of Additives on the Performance of Copper HAO, X., Beyond 10% Efficiency Cd-Free Earth-Abundant and Bisphenanthroline Electrolytes. 7th ACAP Conference and 6th Asia Environmentally-Friendly CZTS Solar Cells. 29th International Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, FÜRER, S.O., MILHUISEN, R., KASHIF, K., RUIZ RAGA, S., FORSYTH, C. & China, 4-8 Nov 2019. (Invited) BACH, U. How Electrolyte Additives Define the Performance of Copper HAQUE, F., YI, H., LIM, J. DUAN, L., HONG DUC PHAM, H.D., SONAR, Bisphenanthroline Electrolytes. 2019 Monash Energy Conference, 19 P., WRIGHT, M., CONIBEER, G. & UDDIN, A. Incorporation of a Sep. 2019, Melbourne. Novel Interfacial Layer for Improved Efficiency in Inverted Structure Perovskite Solar Cells. 29th International Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

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HE, M., KIM, J. & HAO, X. 10.7% Efficient Kesterite Solar Cells: Interconnection Methods, . 29th International Photovoltaic Science and Modification of Absorber Surface by LiCl Post Deposition Treatment. Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. DOI: 29th International Photovoltaic Science and Engineering Conference 10.1109/PVSC40753.2019.8981176 (PVSEC-29), Xi'an, China, 4-8 Nov 2019. JAFARI, S., ZHU, Y., ROUGIEUX, F. & HAMEIRI, Z. Trapping in Multi- HO BAILLIE, A. Perovskite Solar Cells: Challenges and Progress, 7th Crystalline Silicon Wafers: Impact of Laser Treatment and Firing. 36th ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 European Photovoltaic Solar Energy Conference (EU PVSEC 2019). Dec. 2019, Canberra Marseille, France 9-13 September 2019.

HOEX, B. Nanoscale Thin Films for Contact and Surface Passivation JAFARI, S., ZHU, Y., ROUGIEUX, F. & HAMEIRI, Z. Trapping in multi- of Silicon Solar Cells. 29th International Photovoltaic Science and crystalline silicon wafers: Impact of laser treatment and firing. 6th Asia Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Pacific Solar Research Conference, 3-5 Dec. 2019, Canberra. (Invited) JIADONG QIAN, MARCO ERNST, YILIANG WU, ANDREW BLAKERS. HOEX, B., ADBULLAH-VETTER, Z., SUDBURY, B., ABBOTT, M., & Unravelling Optical and Electrical Degradation of Perovskite Solar MCINTOSH, K. Adapting SunSolve for Enhanced Photovoltaic Cells and Impact on Perovskite/Silicon Tandem Modules. 46th IEEE Manufacturing and Education, 7th ACAP Conference and 6th Asia Photovoltaic Specialists Conference, Chicago, 16-21 June 2019. Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra JIANG, W. Development of high dielectric constant materials for HSIAO, P., WANG, Z., SONG, N., LI, Y., OUYANG, Z., HALL, C., ZHU, homojunction organic solar cells. Wuhan University Workshop, 17-18 C., LV, J., SHEN, C., CHEN, C., CHEN, G., ZHANG, X. & LENNON, A. July 2019 Wuhan, China. Comparative Models of Induced Thermomechanical Stress in Silicon JIANG, W., JIN, H., GAO, M., & BURN, P. L. High dielectric constant Solar Cells Interconnected with Conventional Tabbing and Wire-Based materials for homojunction organic photovoltaics. 10th International Interconnection Methods. 2019 IEEE 46th Photovoltaic Specialists Conference on Materials for Advanced Technologies, ICMAT 2019, Conference (PVSC), 16-21 June 2019. 0122-0125. 3-28 Jun 2019 Singapore. HSIAO, P.-C., WANG, Z., SONG, N., LI, Y., OUYANG, Z., ZHU, C., JIANG, W., JIN, H., GAO, M., & BURN, P. L. High dielectric constant LV, J., SHEN, C., CHEN, C., CHEN, G., ZHANG, X. & LENNON, A. materials for homojunction organic photovoltaics. 2nd International Thermomechanical Stress in Glass-Glass Modules of Half Silicon Conference on Flexible Electronics, ICFE 2019, 13-14 Jul. 2019 Solar Cells, 7th ACAP Conference and 6th Asia Pacific Solar Research Hangzhou, China. Conference, 3-6 Dec. 2019, Canberra. JIANG, W., JIN, H., GAO, M., & BURN, P. L. High dielectric constant HSIAO, P.-C., WANG, Z., SONG, N., LI, Y., OUYANG, Z., ZHU, C., LV, J., materials for homojunction organic photovoltaics. Australasian SHEN, C., CHEN, C., CHEN, G. & ZHANG, X. Balanced Contact Method Community for Advanced Organic Semiconductors (AUCAOS) to Reduce Thermomechanical Stress in Silicon Solar Cells Induced Symposium, 2 Dec 2019, Katoomba, Australia. by Interconnection. 29th International Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. JIANG, W., JIN, H., GAO, M., & BURN, P. L. High dielectric constant materials for homojunction organic photovoltaics. 7th ACAP HUANG, J., SUN, K., CUI, X. & HAO, X. Investigation of Nanostructure Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. at the Heterojunction Interface of High-Efficiency CZTS. Solar Cell 2019, Canberra. Using High-resolution Scanning Transmission Electron Microscopy. 29th International Photovoltaic Science and Engineering Conference JIANG, Y., KEEVERS, M.J., PEARCE, P., EKINS-DAUKES, N. & GREEN, (PVSEC-29), Xi'an, China, 4-8 Nov 2019. M.A. Bragg Reflector within Triple-Junction Solar Cells for Spectrum Splitting Application. 36th European Photovoltaic Solar Energy HUANG, W., High Mobility Indium Oxide Electron Transport Layer for Conference (EU PVSEC 2019). Marseille, France 9-13 September 2019. Organic Photovoltaics, Australasian Community for Advanced Organic Semiconductors (AUCAOS) Symposium, 2 Dec 2019, Katoomba, JIN H., JIANG W., STOLTERFOHT M., CHEN T. & BURN P. L. Low donor Australia. content solar cells. Australasian Community for Advanced Organic Semiconductors (AUCAOS) Symposium, 2 Dec 2019, Katoomba, HUANG, W., Mechanically Robust and High Efficiency Ultraflexible Australia. Organic Solar Cells, 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. JIN H., JIANG W., STOLTERFOHT M., CHEN T. & BURN P. L. Low donor content solar cells. 7th ACAP Conference and 6th Asia Pacific Solar HUANG, W., Morphological Control in Organic Solar Cells, Georgia Research Conference, 3-6 Dec. 2019, Canberra. Tech-Monash Photovoltaic Workshop, 14 Jun. 2019, Atlanta, USA. JIN, H., RAYNOR, A., JIANG, W., BURN, P., GENTLE, I. & SHAW, P. HSIAO, P.-C., CHEN, C., CHEN G., ZHANG, X., LENNON, A., WANG, High dielectric constant materials for organic solar cells. 7th ACAP X, SONG, N., LI, Y., OUYANG, Z., HALL, C., ZHU, C., LV, J. & SHEN, C., Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. Comparative Models of Induced Thermomechanical Stress in Silicon 2019, Canberra. Solar Cells Interconnected with Conventional Tabbing and Wire-Based

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JONES, D. J., Liquid Crystallinity as a pre-organisation motif for high ANDRES, C. & HAMEIRI, Z. On the impact of the metal work function efficiency, solid-state singlet fission NanoGe-Advances in Organic and on the recombination in passivating contacts using quasi-steady-state Hybrid Electronic Materials, 17-22 March 2019, Dubrovnik, Croatia. photoluminescence. 46th IEEE photovoltaic specialists conference, 16-21 June 2019 Chicago, USA. JONES, D. J., Liquid crystallinity as a self-assembly motif for solid state singlet fission materials, removing local order constraints, International LEE, T., SANZOGNI, A. BURN, P. L. & MARK, A. E. Evolution and Conference on Organic Electronics ICOE2019, 24-28 June 2019 morphology of organic semiconductor films formed by solvent Hasselt, Belgium. evaporation. Australasian Community for Advanced Organic Semiconductors (AUCAOS) Symposium, 2 Dec 2019, Katoomba, JONES, D. J., Side-Chain Engineering in Morphology Control in Organic Australia. Solar Cells, Materials Research Society- Spring Meeting, 21-26 April 2019, Phoenix, Arizona, USA. LEHMANN, A. G., EKINS-DAUKES, N. & KEEVERS, M. Numerical flowline concentrator design in 3D. Proceedings of SPIE 11120, JONES, D. J., Using Liquid Crystallinity to Pre-Organise Chromophores Nonimaging Optics: Efficient Design for Illumination and in High Efficiency, Solid-State Singlet Fission Materials, Materials Solar Concentration XVI, 111200A (9 September 2019); doi: Research Society-Spring Meeting, 21-26 April 2019, Phoenix, Arizona, 10.1117/12.2526849. USA. LI, C. Optical Optimization for III-V/Si Multijunction Solar Cells. 29th JUHL, M.K., HEINZ, F.D., COLETTI, G., ROUGIEUX, F.E., SUN, C., International Photovoltaic Science and Engineering Conference NIEWELT, T., KRICH, J.J., MACDONALD, D. & SCHUBERT, M.C. INSIGHts (PVSEC-29), Xi'an, China, 4-8 Nov 2019. on the Electronic Parameterisation of Defects in Silicon Obtained from the Formation of the Defect Repository. 36th European Photovoltaic LI, H., High Performance of Perovskite Solar Cells Fabricated by Two- Solar Energy Conference (EU PVSEC 2019). Marseille, France 9-13 step Slot-die Coating in Ambient Condition. 7th ACAP Conference and September 2019. 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra.

KANG, D., SIO, H.C., ZHANG, X., WANG, Q., JIN, H. & MACDONALD, LI, J., DENG, B., ZHU, H., MAI, Y. Rear Interface Modification for D. LETID in p-Type and n-Type Mono-Like and Float-Zone Silicon, Efficient Cu(In, Ga)Se2 Solar Cells. 29th International Photovoltaic and Their Dependence on SiNx Film Properties. 36th European Science and Engineering Conference (PVSEC-29), Xi'an, China, Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, 4-8 Nov 2019. France 9-13 September 2019. LI, Y., SONG, N., HSIAO, P.-C., MUNGRA, M., OUYANG, Z., HAEDRICH, KEMPWORTH, H., POLLARD, M., SUGIYAMA, M. & HAO, X. Ultra- I., ERNST, M., NEWMAN, B., JANSEN, M., ZHU, C., LV, J. & LENNON, A. Sensitive Defect Measurements of Thin-films. 7th ACAP Conference Comparison of Ribbon Light Management Designs for Photovoltaic and 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Modules. 46th IEEE Photovoltaic Specialists Conference, Chicago, Canberra. 16-21 June 2019.

KRISTENSEN, S. T., NIE, S., BERTHOD, C., STRANDBERG, R., ODDEN, J. LIANG, W. & TONG, J. Design and Optimization of IBC Solar Cells using O. & HAMEIRI, Z. How gettering affects the temperature sensitivity of Metal Oxide Passivated Contacts. 6th Asia Pacific Solar Research the implied open circuit voltage of multicrystalline silicon wafers. 46th Conference, 3-6 Dec. 2019, Canberra. IEEE photovoltaic specialists conference, 16-21 June 2019 Chicago, LIU, A. Y. & MACDONALD, D. An overview of impurity gettering to USA. deposited thin films in silicon solar cells. 6th Asia-Pacific Solar KRISTENSEN, S. T., NIE, S., WIIG, M. S., HAUG, H., BERTHOD, C., Research Conference, APSRC 2019, 3-5 December 2019, Canberra, STRANDBERG, R. & HAMEIRI, Z. A high-accuracy calibration method Australia. for temperature dependent photoluminescence imaging. 9th LIU, A. Y. & MACDONALD, D. Impurity gettering to dielectric thin films International Conference on Crystalline Silicon Photovoltaics, 8-10 April in silicon photovoltaic materials. 18th Conference on Gettering and 2019 Leuven, Belgium. Defect Engineering in Semiconductor Technology, GADEST 2019, 22- KUNZ, O., PADUTHOL, A., SLADE, A., EDWARDS, M., KAUFMANN, 27 September 2019, Zeuthen, Germany. K., PATZOLD, M., LAUSCH, D. & TRUPKE, T. Investigating metal- LU, B. 2019. Large-scale energy storage, the energy mix & the future semiconductor contacts in solar cells using magnetic field NEM. 2nd Annual Snowy Region Construction and Development measurements. 2019 IEEE 46th Photovoltaic Specialists Conference Conference. 18 November 2019, Cooma, Australia. (PVSC), 16-21 June 2019. 2764-2768. LU, B. 2019. The road towards 100% renewable energy. Virtual Power LE, A. H. T., P. SEIF, J., G. ALLEN, T., DUMBRELL, R., SAMUNDSETT, C., Plants, New Energy Storage and Renewable Energy Innovations Global CUEVAS, A. & HAMEIRI, Z. Effect of the metal work function on the Summit 2019. 13-15 November 2019, Melbourne, Australia. recombination in passivating contacts using QSSPL. 6th Asia Pacific Solar Research Conference, 3-5 Dec. 2019, Canberra. LU, B., BLAKERS, A., STOCKS, M., CHENG, C. & NADOLNY, A. 2019. Deep decarbonisation of energy sector in Australia. State-of-Energy- LE, A.H.T., SEIF, J. P., ALLEN, T. G., DUMBRELL, R., CHRISTIAN, S., Research Conference. 3-4 July 2019, Canberra, Australia.

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LU, B., BLAKERS, A., STOCKS, M., CHENG, C. & NADOLNY, A. 2019. MONTEIRO LUNARDI, M., ALVAREZ-GAITAN, J.P., BILBAO, J.I. & Large-scale solar energy integration in Australia and Asia-Pacific. 29 CORKISH, R. Life Cycle Assessment of Solar Photovoltaics and International Photovoltaic Science and Engineering Conference. 4-8 their End-of-Life, Third International Conference Series on Life Cycle November 2019, Xian, China. Assessment, Jakarta, 24-25 October 2018.

LU, B., BLAKERS, A., STOCKS, M., CHENG, C. & NADOLNY, A. 2019. MONTEIRO LUNARDI, M., DIAS, P.R., VEIT, H.M., BILBAO, J.& Modelling of 100% renewable energy in Australia. 9 International CORKISH, R., Life Cycle Assessment of Experimental Recycling Workshop on Integration of Solar Power and Storage into Power Processes of Silicon Solar Modules, Solar World Congress, 4-8 Systems. 15-16 October 2019, Dublin, Ireland. November 2019, Santiago, Chile.

LU, B., BLAKERS, A., STOCKS, M., CHENG, C. & NADOLNY, A. 2019. NADOLNY, A., BLAKERS, A. & STOCKS, M. 2019. Sustainable carbon Storage and super grid: the key to 100% renewable energy. 2019 Asia- sources for industrial applications. Asia-Pacific Solar Research Pacific Solar Research Conference. 3-5 December 2019, Canberra, Conference. 3-5 December 2019, Canberra, Australia. Australia. NGUYEN, H. & MACDONALD, D. Luminescence: Science and LU, B., BLAKERS, A., STOCKS, M., CHENG, C. & NADOLNY, A. Applications in Silicon Photovoltaics. 29th International Photovoltaic Large-scale Solar Energy Integration in Australia and the Asia-Pacific. Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 29th International Photovoltaic Science and Engineering Conference 2019. (PVSEC-29), Xi'an, China, 4-8 Nov 2019. NGUYEN, H. T. et al., Imaging spatial variations of optical bandgaps in LU, J., The Stability pf Perovskite Solar Cells. 20th International Union perovskite solar cells, 46th IEEE Photovoltaic Specialists Conference, of Materials Research Societies International Conference in Asia, 22-26 Chicago, 16-21 June 2019. Sep. 2019, Perth. NGUYEN, H. T. et al., Imaging spatial variations of optical bandgaps MA, D., LAN, G., HASSAN, M., HU, W., UPAMA, M., UDDIN, A. & in perovskite solar cells. 29th International Photovoltaic Science and YOUSSEF, M. SolarGest: Ubiquitous and Batt ery-free Gesture Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Recognition using Solar Cells. 25th Annual International Conference NGUYEN, H. T. et al., Luminescence from poly-Si films and its on Mobile Computing and Networking (MobiCom ’19), 21-25 October applications in Si PV, 46th IEEE Photovoltaic Specialists Conference, 2019/01/21/ Los Cabos, Mexico. Association for Computing Chicago, 16-21 June 2019. Machinery (ACM). NGUYEN, H. T. et al., Luminescence from poly-Si films and its MA, J.& LENNON, A. Optimization of Silicon PV Modules for Power/ applications in Si PV, The 6th Asia-Pacific Solar Research Conference, Yield and Durability Using Light Redirecting Films. 29th International Canberra, December 2019. Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. NGUYEN, H. T., Luminescence from poly-Si films and its applications in Si PV. 29th International Photovoltaic Science and Engineering MAO, W., Towards Single-Crystalline Perovskite Device. Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. 5th International Conference on Perovskite Solar Cells and Optoelectronics, PSCO 2019, 30 Sep. 2019-2 Oct. 2019, Lausanne. NGUYEN, H., CHEN, B., MACDONALD, D. Imaging Spatial Variations of Optical Bandgaps in Perovskite Solar Cells. 29th International MASOOMI‐GODARZI, S., LIU, M., TACHIBANA, Y., MITCHELL, V. D., Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, GOERIGK, L., GHIGGINO, K. P., SMITH, T. A. & JONES, D. J., Non- China, 4-8 Nov 2019. traditional singlet fission materials, 29th International Conference on Photochemistry, ICP2019, 21-26 July, 2019, Boulder, Colorado, Boulder, NGUYEN, H., TRUONG, T., YAN, D., SAMUNDSETT, C., BASNET, R., Colorado, USA. TEBYETEKERWA, M., GUTHREY, H., AL-JASSIM, M., ZIYUAN LI, LILY, KREMER, F., CUEVAS, A. & MACDONALD, D. Luminescence from Poly- MASOOMI‐GODARZI, S., LIU, M., TACHIBANA, Y., MITCHELL, V. D., Si Films and Its Application to Study Passivating-Contact Solar Cells. GOERIGK, L., GHIGGINO, K. P., SMITH, T. A. & JONES, D. J., Non- 46th IEEE Photovoltaic Specialists Conference, Chicago, 16-21 June traditional singlet fission materials, Fall NanoGe, 3-8 November 2019, 2019. Berlin, Germany. NIE, S., KRISTENSEN, S. T., GU, A., TRUPKE, T. & HAMEIRI, Z. A Novel MASOOMI‐GODARZI, S., LIU, M., TACHIBANA, Y., MITCHELL, V. D., Method for Characterizing Temperature Sensitivity of Silicon Wafers GOERIGK, L., GHIGGINO, K. P., SMITH, T. A. & JONES, D. J., Liquid and Cells. 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), crystallinity as a self-assembly motif for solid state singlet fission 16-21 June 2019. Chicago, USA 0813-0816. materials, Fp14, 2-7 June 2019, Berlin, Germany. PADUTHOL, A., KUNZ, O., KAUFMANN, K., PATZOLD, M., LAUSCH, D. MASOOMI‐GODARZI, S., SMITH, T. A. & JONES, D. J., Liquid crystallinity & TRUPKE, T. Magnetic Field Imaging: Strengths and limitations in as a self-assembly motif for singlet fission materials, 2nd International characterising solar cells. 2019 IEEE 46th Photovoltaic Specialists Conference on “Interface Properties in Organic and Hybrid Electronics” Conference (PVSC), 16-21 June 2019. 0822-0824. IPOE 2019, 8-11 July 2019, Cergy-Pontoise, France.

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PARASKEVA, V., HADJIPANAYI, M., ZHENG, J., THEOCHARIDES, REINDERS, A., EKINS-DAUKES, N., SCHMIDT, T., YANG, H., MICHALSKA, S., EKINS-DAUKES, N.J., HO-BAILLIE, A.W.Y. & GEORGHIOU, G.E. M., PELOSI, R., NITTI, M., GILLAN, L., MCCAMEY, D., GHOLIZADEH, Time Response Analysis of Perovskite/Si Tandem Solar Cells. 36th E. M., HOSSEINABADI, P., WELSH, B. & KABLE, S. Designing with European Photovoltaic Solar Energy Conference (EU PVSEC 2019). Luminescent Solar Concentrator Photovoltaics. 2019 IEEE 46th Marseille, France 9-13 September 2019. Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 0221- 0226. PEARCE, P. & EKINS-DAUKES, N. Open-source integrated optical modelling with RayFlare. 2019 IEEE 46th Photovoltaic Specialists SAMADI, A., SEN, C., LIU, S., VARSHNEY, U., CHEN, D., KIM, M., Conference (PVSC), 16-21 June 2019. 2627-2633. SOUFIANI, A. M., CONTRERAS, M. V., CHONG, C. M., CIESLA, A., ABBOTT, M. & CHAN, C. 2019. Hydrogenation of dislocations in p-type PHUA, B., HSIAO, P.-C., RÖMER, C., AUGUSTO, A. F. R., BOWDEN, cast-mono silicon. 2019/08/27/. AIP Conference Proceedings 2147, S. & LENNON, A. Performance Degradation Pathways in Silicon 140007; https://doi.org/10.1063/1.5123894. Photovoltaic Modules Arising from Copper-Plated Metallisation. 7th ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 SCHOLES, F. H, Powering the future with printed solar films, Australian Dec. 2019, Canberra. Institute of Physics Industry Day, 7 Nov. 2019, Sydney

PILLAI, S. & GREEN, M., Low Temperature Silver Nanowires as SEIF, J., ALLEN, T. G., ZHANG, M. F. & HAMEIRI, Z. Temperature- Transparent Conducting Layer for Solar Cells. 29th International dependent Suns-Voc and Suns-iVoc methods for advanced Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, characterization of solar cells. 29th International Photovoltaic Science China, 4-8 Nov 2019. and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

PILLAI, S., KOPIDAKIS, N., WANG, C., ANDERSON, M. & MCNEILL, SEIF, J., ALLEN, T., BASNET, R., LE, A. H. T., ZHANG, S. & HAMEIRI, Z. C. Time-Resolved Microwave Conductivity Measurements for Organic Temperature-dependent Suns-Voc and Suns-PL method for advanced Solar Cell Materials. 29th International Photovoltaic Science and characterization of solar cells. 6th Asia Pacific Solar Research Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Conference, 3-5 Dec. 2019, Canberra.

PUSCH, A. & EKINS-DAUKES, N. J. The Role of Etendue and Ratchets SEIF, J., LE, A. H. T., ALLEN, T., DUMBRELL, R., SAMUNDSETT, C. in Spectral Conversion and Multi-color Emission. OSA Advanced & HAMEIRI, Z. Advanced suns-photoluminescence technique for Photonics Congress (AP) 2019 (IPR, Networks, NOMA, SPPCom, the optimization of crystalline silicon solar cells. 36th European PVLED), 29 July 2019. Burlingame, California. Optical Society of Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, America, PM2C.4. France 9-13 September 2019.

PUSCH, A. & EKINS-DAUKES, N. J. Thinking Beyond Limiting SHEN, X., HSIAO, P.-H., COLWELL, J., PHUA, B., WANG, Z., STOKES, A. Efficiencies Of Advanced Concepts: Design Rules And Material & LENNON, A. Durability of Encapsulated Ni/Cu Plated Si Solar Cells: Requirements For Realistic Devices. 2019 IEEE 46th Photovoltaic Influence of Partially-Ablated SiNx. 29th International Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 0008-0011. Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. QIAN, J, ERNST, M, THOMSON, A & BLAKERS, A 2019, Hotspots in Half Cell Modules Undetected by Current Test Standards, PV Reliability SHRESTHA, S., LIAO, Y., CAO, W. & CONIBEER, G. Experimental Workshop 2019, Lakewood, CO, 26-28 February 2019. investigation of double barrier structures for energy selective contacts for hot carrier solar cells. 2019 IEEE 46th Photovoltaic Specialists QIAN, J, ERNST, M, WU, Y & BLAKERS, A. 2019, Unravelling Optical Conference (PVSC), 16-21 June 2019. 1780-1782. and Electrical Degradation of Perovskite Solar Cells and Impact on Perovskite/Silicon Tandem Modules, in 46th IEEE Photovoltaic SIERRA, A., T. DE SANTANA, MACGILL, I.F., EKINS-DAUKES, N.J. & Specialists Conference 2019. REINDERS, A.H.M.E. A Feasibility Study of Solar PV Powered Electric Cars Using an Interdisciplinary Modelling Approach for the Electricity R. BASNET, R., PHANG, S.P., SAMUNDSETT, C., YAN, D., SUN, C., Balance, CO2 Emissions and Economic Aspects: The Cases of the NGUYEN, H.T., ROUGIEUX, F.E. & MACDONALD, D. Elucidating the Role Netherlands, Norway, Brazil and Australia. 36th European Photovoltaic of the Thermal Budget on the Bulk Degradation of n-Type Czochralski- Solar Energy Conference (EU PVSEC 2019). Marseille, France 9-13 Grown Upgraded Metallurgical-Grade Silicon Wafers During the September 2019. Processing of Phosphorus-Doped Polysilicon Cells. 36th European Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, SIO, H.C., MACDONALD, D. & KANG, D. Stability Study on the France 9-13 September 2019. Passivation Quality of Polysilicon-based Passivating Contacts for Silicon Solar Cells RAYNOR, A., JIN H., STOLTZFUS, D., GAO, M., SHAW, P., GENTLE, I. & BURN P. L. 2019 The Development of High Dielectric Constant Organic SIU, V., NIE, S., ZHU, Y. & HAMEIRI, Z. An incomplete ionization model Materials for Homojunction Solar Cells. Australasian Community for for indium in silicon. 6th Asia Pacific Solar Research Conference, 3-5 Advanced Organic Semiconductors (AUCAOS) Symposium, 2 Dec Dec. 2019, Canberra. 2019, Katoomba, Australia. SKINNER, I., BROWN, S. & EVANS, R. Unplugged Game-Play Motivates the Study of Engineering Ethics. TALE2019 Yogyakarta, Indonesia, 10- 13 December 2019 DOI:10.1109/tale.2018.8615259

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SOERIYADI, A., WEIGAND, W., WRIGHT, B., STEFANI, B. V., WRIGHT, M., Grain Boundaries for High Efficiency Kesterite Cu2ZnSnS4 Solar Cells SEN, C., CHEN, D., KIM, M., HOLMAN, Z. & HALLAM, B. Elevating Low- Chalcogenide Thin Film Solar Cells. 46th IEEE Photovoltaic Specialists Quality Silicon Wafers For High-Efficiency Silicon Heterojunction Solar Conference, Chicago, 16-21 June 2019. Cell Applications. 2019 IEEE 46th Photovoltaic Specialists Conference SUN, K., HUANG, J., YAN, C., WANG, A., CUI, X., SUN, H. & GREEN, (PVSC), 16-21 June 2019. 0807-0812. M. Xiaojing Hao Efficiency Improvement of Kesterite Cu2ZnSnS4 STOCKS M. How Snowy 2.0 and Battery of the Nation will help Solar Cell Achieved by Controlling the Donor Concentration in N-type stabilise the grid. Maintaining Grid Stability Forum 2-3 December 2019 Buffer Layer. 29th International Photovoltaic Science and Engineering Melbourne, Australia. Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

STOCKS M., BLAKERS, A., NAEFF H. & CURRIE J. Development of TAN, B., LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with a Global Atlas of Off-River Pumped Hydro Storage. 23-25 July 2019, Power Conversion Efficiencies Exceeding 19%, 7th ACAP Conference Portland, USA. and 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. STOCKS M., LU, B. & BLAKERS A. Balancing variable renewables in Australia: The role for transmission. State-of-Energy-Research TAYEBJEE, M., BALDACCHINO, A. & MCCAMEY, D. Spectroscopy Conference. 3-4 July 2019, Canberra, Australia. of Intramolecular Singlet Fission Photovoltaic Devices. 7th ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. STOCKS M., LU, B. & BLAKERS A. The Battery of Europe: Norway’s 2019, Canberra. opportunity to help decarbonize Europe’s electricity. Australia Norway Energy Transition symposium. 12 November 2019, Canberra, Australia. TEBYETEKERWA, M. et al., Maximum Possible Open-Circuit Voltages in Atomic-Thin Layered Semiconductors, The 6th Asia-Pacific Solar STOCKS M., LU, B. & BLAKERS A.; Transmission and Interconnection- Research Conference, Canberra, December 2019. supporters or obstacles for change. Tasmania Energy Development Conference. 19-20 June 2019, Devonport, Australia. TEBYETEKERWA, M. et al., Predicting Open-Circuit Voltages in Atomically-Thin Monolayer Transition Metal Dichalcogenides-Based STOCKS M., LU, B. CHENG C. & BLAKERS A. Towards 100% renewable Solar Cells, 46th IEEE Photovoltaic Specialists Conference, Chicago, electricity for Indonesia: the role for solar and pumped hydro storage. 16-21 June 2019. International Conference on Technology and Policy in energy and electric power. 21-23 October Yogyakarta, Indonesia. THAPA, B., PATTERSON, R., DUBAJIC, M., CONIBEER, G. & SHRESTHA, S. Investigation of Structural and Optical Properties of Atomic Layer STOCKS M., LU, B., STOCKS R., CHENG C., & BLAKERS A. Development Deposited Hafnium Nitride Films. 2019 IEEE 46th Photovoltaic of a Global Atlas of Off-River Pumped Hydro Storage. Asia-Pacific Solar Specialists Conference (PVSC), 16-21 June 2019. 1797-1801. Research Conference. 3-5 December 2019, Canberra, Australia. THE, Z.L., PATTERSON, R.J., GAO, Y., CONIBEER, G. & HUANG, S. STOCKS, M. Renewable energy’s role in a sustainable campus. Enhanced Power Conversion Efficiency Via Hybrid Ligand Exchange University Planning, Design & Construction Conference. 20-21 June Treatment of p-Type PbS Quantum Dot. 29th International Photovoltaic 2019, Melbourne, Australia. Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov STOCKS, M., STOCKS, R., LU, B., CHENG, C. & BLAKERS, A. 2019. 2019. Development of a global atlas of off-river pumped hydro storage. 29 TONG, J., FONG, K.C., LIANG, W., ERNST, M., WALTER, D., International Photovoltaic Science and Engineering Conference. 4-8 NARANGARI, P., ARMAND, S., SURVE, S., KHO, T., MCINTOSH, K., November 2019, Xian, China. STOCKS, M. & BLAKERS, A. Investigation of Carrier Selectivity and STOCKS, M., STOCKS, R., LU, B., CHENG, C. & BLAKERS, A. 2019. Thermal Stability of Transition Metal Oxides with Pre-grown Thin Development of a Global Atlas of Off-River Pumped Hydro Energy SiOx for Si Solar Cells. 29th International Photovoltaic Science and Storage. 18th Wind Integration Workshop. 16-18 October 2019, Dublin, Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Ireland. TRUONG, T. N. et al., Effects of hydrogenation on poly-Si/SiOx SUN ,H., HUANG, J., YAN, C., SUN, K., YUN, J., YOUNG, T., GREEN, passivating contacts for silicon solar cells, The 6th Asia-Pacific Solar M. & HAO, X. High Efficiency Cu2ZnSnS4 Solar Cells Through a Novel Research Conference, Canberra, December 2019. Moisture-Assisted Post- TRUONG, T. N. et al., Hydrogenation of polycrystalline silicon films for SUN, C., WEIGAND, W., CHEN, D., SHI, J., BASNET, R., YU, Z., PHANG, passivating contacts solar cells, 46th IEEE Photovoltaic Specialists S.P., HOLMAN, Z.C., BRETT HALLAM, B., MACDONALD, D. Origins Conference, Chicago, 16-21 June 2019. of Hydrogen for Bulk Defect Passivation in Silicon Heterojunction VAK, D. Finding Printable Materials vis High-Throughput Devices Solar Cells. 29th International Photovoltaic Science and Engineering Fabrication and Testing. 7th ACAP Conference and 6th Asia Pacific Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. Solar Research Conference, 3-6 Dec. 2019, Canberra. SUN, H., HUANG, J., YUN, J., SUN, K., YAN, C., LIU, F., PARK, J., PU, A., VAK, D. Toward Fully Roll-to-Roll Printed Large-Area Perovskite Solar SEIDEL, J., STRIDE, J., GREEN, M.A. & HAO, X. Solution-processed Cells. State of Energy Research Conference, 2-3 July 2019, Canberra Ultrathin SnO2 Passivation of Absorber/Buffer Heterointerface and

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VAK, D., 20th International Union of Materials Research Societies YAN, D., CUEVAS, A., PHANG, S.P., WAN, Y., YANG, W. & MACDONALD, International Conference in Asia, Sep. 2019, Perth. D., Passivating Contacts for Silicon Solar Cells Based on Physical Vapour Deposition of Doped Silicon Films. 29th International VAQUEIRO-CONTRERAS, M., WALTON, A. S., BARTLAM, C., BYRNE, C., Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, BONILLA, R. S., MARKEVICH, V. P., HALSALL, M. P., VIJAYARAGHAVAN, China, 4-8 Nov 2019. A. & PEAKER, A. R. The surface passivation mechanism of graphene oxide for crystalline silicon. 2019 IEEE 46th Photovoltaic Specialists YAN. C., HUANG, J., SUN, K., HE, M., XIAOJING HAO, X., GREEN, M.A. Conference (PVSC), 16-21 June 2019. 1931-1934. High Efficiency CZTS Solar Cell. 7th ACAP Conference and 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. WALTER, D. Perovskite Solar Cells as Ion-Conducting Semiconductor Devices: Explaining a Wide Range of Hysteretic Phenomena. 6th Asia YANG, X., LIU, W., DEBASTIANI, M., KANG, J., XU, H., AYDIN, E., Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. ALLEN, T., XU, L., ALHABSHI, E., ALSAGGAF, A., GEREIGE, I., YIMAO WAN, Y., SAMUNDSETT, C., CUEVAS, A. & DEWOLF, S. High- WANG, S, LIM ,K.N., CHONG, C.M., TAN, M. Field Performance of the Conductive, Hole-Blocking Layer for Silicon Solar Cells. 46th IEEE Industrial Si Mono-Crystalline PERC Solar Module Arrayswith the Use Photovoltaic Specialists Conference, Chicago, 16-21 June 2019. of Advanced Hydrogenation Technologies. 36th European Photovoltaic Solar Energy Conference (EU PVSEC 2019). Marseille, France 9-13 YI, C., WESTERN, N., MA, F., HO-BAILLIE, A. & BREMNER, S. On September 2019 the Origin of Silicon Lifetime Degradation During Anneal in III-V Material Growth Chambers. 2019 IEEE 46th Photovoltaic Specialists WANG, W., HE, J., YAN, D., SAMUNDSETT, C., SHEN, W., BULLOCK, J. & Conference (PVSC), 16-21 June 2019. 1074-1077. WAN, Y. 21.3%-Efficient n-Type Silicon Solar Cell with a Full Area Rear TiO2/LiF/Al Electron-selective Contact. 29th International Photovoltaic YI, H., DUAN, L., HAQUE, F., CONIBEER, G. & UDDIN, A. Thiocyanate Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov Assisted Nucleation for Perovskite Solar Cell by Gas-Quenched 2019. Deposition. 29th International Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. WANG, X., RAKSTYS, K., ZHANG, G., SAGHAEI, J., STEPHEN, M., BURN, P. & SHAW, P. 2D Hybrid perovskite solar cells. 7th ACAP Conference YI, H., DUAN, L., HAQUE, F., XU, C., CONIBEER, G. & UDDIN, A. Surface and 6th Asia Pacific Solar Research Conference, 3-6 Dec. 2019, Passivation on PEDOT:PSS in conventional perovskite solar cells. 2019 Canberra. IEEE 46th Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 1200-1202. WEERASINGHE, H. Towards Highly Efficient Roll-to-Roll Printed Perovskite Modules. 7th ACAP Conference and 6th Asia Pacific Solar YUAN, X., ZHANG, J., PENG, F., GREEN, M. & HAO, X. Enhanced Research Conference, 3-6 Dec. 2019, Canberra. Performance of Solution-processed CZTSSe Thin Film Solar Cells by Selenium Addition in Non-hydrazine Precursor Solution. 29th WONG W. W. H., Aggregation-induced Emitters in Light Harvesting, 4th International Photovoltaic Science and Engineering Conference International Conference on Aggregation Induced Emission, 21 Jan (PVSEC-29), Xi'an, China, 4-8 Nov 2019. 2019, Flinders University, Adelaide, Australia. ZHANG, M.F., BHOOPATHY, R., GENTLE, A. & HAMEIRI, Z. Investigation WONG, W. W. H., Light Harvesting with Highly Fluorescent Organic of the Temperature Dependence of the Optical Properties of Silicon Fluorophores, 18th International Symposium on Novel Aromatics, 23 Nitride Anti-Reflection Coating on Silicon Photovoltaic Modules. 36th Jul 2019, University of Hokkaido, Sapporo, Japan. European Photovoltaic Solar Energy Conference (EU PVSEC 2019). WRIGHT, M., CHEN, D., SOERIYADI, A., STEFANI, B.V., KIM, M. & Marseille, France 9-13 September 2019. HALLAM, B. Defect Engineering for Silicon Heterojunction Solar Cells. ZHANG, S., BHOOPATHY, R., GENTLE, A. & HAMEIRI, Z. Investigation of 29th International Photovoltaic Science and Engineering Conference the temperature dependence of the optical properties of silicon nitride (PVSEC-29), Xi'an, China, 4-8 Nov 2019. anti-reflection coatings. 6th Asia Pacific Solar Research Conference, WRIGHT, M., KIM, M., DEXIANG, P., XIN, X., WENBIN, Z., WRIGHT, B. & 3-5 Dec. 2019, Canberra. HALLAM, B. Multifunctional process to improve surface passivation ZHANG, T., HOSSAIN, M. A., KHOO, K. T., LEE, C., ZAKARIA, Y., and carrier transport in industrial N-type silicon heterojunction solar ABDALLAH, A. A. & HOEX, B. Atomic Layer Deposited AlxNiyO as Hole cells by 0.7% absolute. AIP Conference Proceedings 2147, 110006 Selective Contact for Silicon Solar Cells. 2019 IEEE 46th Photovoltaic (2019). https://doi.org/10.1063/1.5123882 Specialists Conference (PVSC), 16-21 June 2019. 2338-2341. WU, H., NGUYEN, H.T., KANG, D., GAGRANI, N., YANG, W. & ZHANG, X., TABARI-SAADI, Y., NIELSEN, M., KAMPWERTH, H. & MACDONALD, D. A Study on Amorphous Silicon Lifetime, Hydrogen HAO, X. Optical Characterization Methods of Photovoltaics New Effusion and Passivation Quality. 29th International Photovoltaic Materials. 29th International Photovoltaic Science and Engineering Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. 2019.

YAN, C., HUANG, J., SUN, K., HAO, X., & GREEN, M.A. Effect of Cadmium Alloying on Sulfide Kesterite thin Film Solar Cell. 29th International Photovoltaic Science and Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019.

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ZHANG, Y., KONG, C., KHAN, M. U., FUNG, T. H., DAVIDSEN, R. S., HONG, Q. 2019. Discotic compounds and columnar materials within HANSEN, O., SCARDERA, G., ABBOTT, M. D., HOEX, B. & PAYNE, D. N. R. organic photovoltaic material blends: synthesis and characterisation. Advanced Characterisation of Black Silicon Surface Topography with PhD University of Melbourne. 3D PFIB-SEM. 2019 IEEE 46th Photovoltaic Specialists Conference HU, Y. 2019. Surface Engineering of CuInS2 Colloidal Quantum Dots (PVSC), 16-21 June 2019. 0825-0828. for Advanced Photovoltaics. PhD UNSW. ZHENG, B., FLETCHER, J. E., LENNON, A., JIANG, Y. & BURR, P. A. JIANG, L. 2019. The investigation on the stability of perovskite solar Photovoltaic Power Generation with Module-Based Capacitive Energy cells. PhD Monash University Storage. 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 0900-0905. KIM, K. H. Industrial PECVD AlOx films with very low surface recombination for silicon solar cells. PhD UNSW. ZHENG, J., LAU, J., MEHRVARZ, H., MA, F.-J., YAJIE JIANG, Y., DENG, X., SOERIYADI, A., KIM, J., ZHANG, M., HU, L., CUI, X., LEE, D.S., BING,J., LAMBERT, D.S. 2019. Ab initio modelling of the defect chemistry of CHO, Y., LIAO, C., LI, Y., LI, Y., CHEN, C., GREEN, M., HUANG, S. & HO- MoO3 and Si: Applications for carrier selective contacts of solar cells. BAILLIE, A. Large A rea Efficient Monolithic Perovskite/Homo-Junction- PhD UNSW. Silicon Tandem Solar Cell. 29th International Photovoltaic Science and LAU, C.F.J. 2019. Inorganic cesium perovskite solar cells. PhD UNSW. Engineering Conference (PVSEC-29), Xi'an, China, 4-8 Nov 2019. LEE, C. 2019. Morphological Advancements through Sidechain ZHU, Y., COLETTI, G. & HAMEIRI, Z. Injection Dependent Lifetime Engineering for Organic Photovoltaic Applications. PhD University Spectroscopy for Two-Level Defects in Silicon. 2019 IEEE 46th of Melbourne. Photovoltaic Specialists Conference (PVSC), 16-21 June 2019. 0829- 0832. LEE, C.Y. 2019. Metal oxide thin films for silicon solar cells. PhD UNSW.

ZHU, Y., ROUGIEUX, F., GRANT, N., MULLINS, J., ANN DE GUZMAN, LIN, X. 2019. Dipole-Field-Tuning of Back-Contact Perovskite Solar Cells. J., MURPHY, J., MARKEVICH, V., COLETTI, G., PEAKER, A. & HAMEIRI, PhD Monash University. Z. New insights into the thermally activated defects in n-type float- LU, B. 2019. Short-term off-river pumped hydro energy storage. zone silicon. 9th International Conference on Crystalline Silicon PhD, Australian National University. Photovoltaics, 8-10 April 2019 Leuven, Belgium. MAHMUD, M.A. 2019. Low -temperature processed perovskite solar ZHUOFENG, L. et al., Contactless and Non-destructive Determination cells. PhD UNSW. of Dopant Profiles of Localized Boron-Diffused Regions in Silicon Wafers at Room Temperature, The 6th Asia-Pacific Solar Research MAO, W., Study of Lead Halide Perovskite Single Crystals. Conference, Canberra, December 2019. PHD Monash University.

ZUO, C. Crystallization Control of Drop-Cast Quasi-2D Perovskite MCGREGOR, S. 2019. Development of a library of compounds for use Layers for Efficient Solar Cells. 7th ACAP Conference and 6th Asia in organic solar cells. PhD, University of Queensland. Pacific Solar Research Conference, 3-6 Dec. 2019, Canberra. MILHUISEN, R., Investigation of New Redox Active Materials for Thin ZUO, C. Self-Assembled Two-Dimensional Perovskites Layers for Film Solar Cells. PhD Monash University. Efficient Printable Solar Cells, 11th International Conference on Hybrid MONTEIRO LUNARDI, M. 2019. Life cycle assessment of silicon based and Organic Photovoltaics, 12-15 May 2019. Rome, Italy, tandem and advanced silicon solar modules. PhD UNSW.

NOH, S., 2019. Silicon-on-insulator for compliant substrates. PhD 8.5 THESES UNSW.

CHEN, Z. 2019. Interfacial optimisation in colloidal quantum dot solar PAI, N. 2019. Low-temperature solution-processed bismuth-based cells. PhD UNSW thin-film solar cells. PhD Monash University.

CHUNG, D. 2019. Applications of photoluminescence imaging of silicon PU, A. 2019. Device simulation and modelling of Cu2ZnSnS4 thin film bricks. PhD UNSW. solar cells. PhD UNSW.

COLWELL J.K. 2019. Copper and Silicon: Implications for the long-term SAKER-NETO, N. 2019. Exponential Iterative Coupling for Low Dispersity stability of plated contacts for silicon solar cells. PhD UNSW. Conjugated Polymers. PhD University of Melbourne.

DUMBRELL, R.W. 2019. Applications of dynamic photoluminescence SHI, L. 2019. Low Cost Encapsulations for perovskite solar cells. measurements to metallised silicon solar cells. PhD UNSW. PhD UNSW.

GAO, C. 2019. Organic Chromophore Aggregates for Solid-State Photon TEYMOURI, A. 2019. Low temperature solution based silver nanowires Upconversion. PhD University of Melbourne. for transparent conductive layers in solar cells. PhD UNSW.

GUPTA, N. 2019. Study of germanium carbide and zirconium nitride UPAMA M.B.2019. Interface engineering of high performance organic as an absorber material for hot carrier solar cells. PhD UNSW. and perovskite solar cell. PhD UNSW.

144 ACAP ANNUAL REPORT 2019

VARGAS CASTRILLON, C.A. 2019. Effects of Dark and Illuminated Anneals on Multi-crystalline Silicon Wafers and on Mono-crystalline Silicon Wafers Passivate with Carrier-Selective Contacts. PhD UNSW

WANG, X. 2019. Elucidating the role of donor and acceptor in photocurrent generation. PhD, University of Queensland.

WANG, P. 2019. An investigation into titanium hydride as a hot carrier solar cell absorber. PhD UNSW.

XU, C. 2019. Interfacial and compositional engineering of thick film PffBT4T-2OD organic solar cells. PhD UNSW.

YI, C. 2019. Silicon Bottom Cell for III-V/Si Multi-junction Solar Cells. PhD UNSW.

ZHANG, B. 2019. Donor-Emitter Fluorophore Pairs in Luminescent Solar Concentrators: from Material Synthesis to Device Fabrication. PhD University of Melbourne.

ZHANG, T., 2019. PECVD fabrication, electrical characterization and laser dopant activation of silicon nanocrystals. PhD UNSW.

ZHANG, T. P. 2019. Transition metal oxides and their application xas hole-selective contacts for silicon solar cells. PhD UNSW.

ZHU, Y. P. 2020. Advanced Characterization of Defects in Silicon Wafers and Solar Cells. PhD UNSW.

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