GCEP Distinguished Lecture October 2008 Third Generation Photovoltaics Gavin Conibeer Deputy Director ARC Photovoltaics Centre of Excellence School of Photovoltaics and Renewable energy Engineering University of New South Wales Photovoltaics Centre of Excellence supported by the Australian Research Council, the Global Climate and Energy Project and Toyota CRDL School of Photovoltaics & RE Eng. ARCCorodination Photovoltaics of previously Centre separately of fundedExcellence strands Stuart Wenham, Martin Green + Management Committee PV and Renewable Energy Laboratories Laboratory Development U/G degrees Mark Silver 1st Generation: 3rd Generation: PV Wafers High eff and thin film 2nd Generation: Silicon Photonics Thin Films Si light emission School of Photovoltaics & RE Eng. History • PV research, UNSW Electrical Eng. 1974 – 1998 • Buried contact solar cell – Martin Green, Stuart Wenham 1986 • Crystalline Si on glass spin off company 1995 • Separate Centre 1999 – 2005 • First UG program - Photovoltaics 2000 • PG coursework program 2001 • Second UG program – Renewable Energy 2003 • New School formally declared 2006 UNSW International Collaborations •DARPA & U. Delaware (50% efficient solar cell) •Global Climate & Energy Project, Stanford (1) •Global Climate & Energy Project, Stanford (2) •Toyota Central R&D Labs. •Suntech, Wuxi (NYSE) •Nanjing PV Tech, Nanjing (NASDAQ) •JA Solar, Ningjin (NASDAQ) •E-Ton Solar, Taiwan •Asia-Pacific Partnership (Australia, China, India, Japan, Korea, India, USA) UNSW Photovoltaics R&D Commercialisation • First Generation Photovoltaics – Buried contact cell (UNSW, BP Solar) – Inkjet printing (UNSW, Suntech, E-Ton) – Semiconductor Fingers (UNSW, Suntech, E-Ton) – Laser doping (UNSW, Suntech) • Second Generation Photovoltaics – Crystalline Silicon on Glass (UNSW, CSG Solar) • Characterisation Equipment – Photoluminescence characterisation (UNSW, BT Imaging) Undergraduate Education Two 4-year Engineering programs (189 students): • Photovoltaics and Solar Energy (2000) (101 students) • Renewable Energy (2003) (88 students) UAI Distribution 2000-2005 70 60 3656 50 3655 40 3657 30 3642 # Students # 20 10 0 Below 80 80-84.99 85-89.99 90-94.99 95-100 University Admission Index Postgraduate Education • Master of Engineering Science in Photovoltaics and Solar Energy (14 students) – 1.5 year addition to UG; – PV devices; PV systems; RE technologies; • Research degrees – PhD (47 students) – MPhil (10 students) UNSW Centre for Energy and Environmental Markets • Interdisciplinary research in energy and environmental markets, policy • Faculties of Engineering and Commerce & Economics • Environmental sustainability: – eg. PV load & pricing at Olympic Village • Economic tools & climate change: – e.g. Market design (Aust. Stock Exchange, CSIRO) • Sustainable technology: – e.g. Stochastic renewable energy (wind). • Aust. Greenhouse Office Third Generation Photovoltaics Outline • The importance of Photovoltaics • Three generations of Photovoltaics • The main losses in photovoltaic cells • Third Generation approaches • Silicon nanostructure tandem cells • Band gap engineering – quantum confinement • Fabrication of materials / devices • Hot Carrier cells • Contacts – energy filtering • Hot Carrier cooling – energy loss to phonons • Modification of the solar spectrum • Up- and Down-conversion • Potentialities and Viabilities • Summary Meeting the IPCC target of 60% reduction in GHG emission by 2050 Transforming the global energy mix: appointedThe for aexemplary term of four years pathby the federal until cabinet 2050/ (Bundeskabinett) 2100 Booming Photovoltaics Market growth at 35%/yr for last 10 years, 60%+ in 2007 Approx 1 million jobs in PV by 2020 Approx 1 million jobs in RE by 2010 5000 USA Global PV market 4000 Europe US$6.5 billion in 2006 → $16.4 billion in 2012 3000 Japan Rest of World MWp 2000 Driven by rebates/tariffs: Total Japan, Germany 1000 Now other Euro. Countries and S Australia 0 USA: Power purchase agreements 1988 1991 1994 1997 2000 2003 Japan: market is stable 2006 with reducing rebates Learning curves 1981 1981 20000 20000 1st Generation Photovoltaics Photovoltaics 10000 10000 Wind turbines 5000 5000 2002 Thin-film PV 2002 2002 W 1982 (~20%) W (~20%) k /k bulk-Si / 2nd Generation bulk-Si $ 2000 (~10%) S$ 2000 (~10%) US 1993 3 1987 1000 03 U 1000 00 Gas turbines (USA) 1963 2001 3rd Generation 2 20 500 500 1980 200 200 0.01 0.1 1.0 10.0 100.0 0.01 0.1 1.0 10.0 100.0 Cumulative GW installed Cumulative GW installed . more potential for learning . lower cost at smaller volumes Photovoltaics: Three Generations US$0.10/W US$0.20/W US$0.50/W 100 Thermodynamic 80 limit % 60 US$1.00/W III concentration 40 III-V Present limit tandem Efficiency, a-Si c-Si 20 tandem mc-Si I US$3.50/W II * 0 100 200 300 400 500 thin film Cost, US$/m2 Efficiency Loss Mechanisms Energy 1. Sub bandgap losses 2 3 2. Lattice thermalisation 4 Two major losses – 50% 5 qV Also: 3. Junction loss 5 1 4 4. Contact loss 2 5. Recombination Limiting efficiencies 1 sun Single p-n junction: 31% Multiple threshold: 68.2% Third generation options JVC - CB Jh e E2,e E h - - Eg e e Erela Ef E0,e x El VB intermediate Multiple level One photon - J electrons l E 100% h+ 0,h E2,h h+ circulators 74% tandem (n ) 68% hot carrier 65% tandem (n = 6) 58% thermal, thermoPV, thermionics 54% 49% tandem (n = 3) 44% impurity PV & band, up-converters impact ionisation 39% tandem (n = 2) 31% down-converters single cell 0% Silicon based Tandem Cell Martin Green, Gavin Conibeer, Dirk König, Eunchel Cho, Tom Puzzer, Yidan Huang, Shujuan Huang, Dengyuan Song, Angus Gentle, Ivan Perez-Wufl, Chris Flynn, Jeana Hao, Sangwook Park, Yong So, Bo Zhang Free choice or Si cell 50.5% 47.5% 42.5% 45% 40 33% 30 29% Sunlight 20 Decreasing band gap 10 AM1.5G Efficiency 0 Free choice 0 Si bottom cell 12 3 Number of cells Intrinsic radiative and Auger losses included Silicon based Tandem Cell Decreasing band gap Anneal 1100°C – Si precipitation Solar Cell 1 1 Cell Cell Solar Solar 2 2 Cell Cell Solar Solar 3 3 Cell Cell Solar Solar Si, Ge or Sn rich layer Dielectric layer 2nm QD, E =1.7eV Thin film Si cell g Substrate Eg = 1.1eV Substrate Zacharias, 2000 Engineer wider band gap defect or Si SiO2 QDs barriers tunnel Si QDs junction Si QD characterisation XRD Si QDs in oxide dQD 4.5nm Diameter of Si QDs [nm] 2.03.0 3.5 4.7 5.5 Integrated PLintensity 1.8 30000 PL 1.7 25000 optical 1.6 20000 energy 1.5 15000 levels 1.4 10000 PL energy [eV] 1.3 5000 (au) 1.2 0 100 150 200 250 300 350 Deposition time [sec] Range of QD materials Si QDs in oxide/nitride Greater σ for Si N 3.5 3 4 Y. Kanemitsu et al Alternative matrices but also lowerH. Takagi Eact et al 3.0 S. Takeoka et al 1.0E+01 SiO2 T. Y. Kim et al T.SiQDs W. Kim in et alSi 3N4 Eσ =0.30eV Oxide (UNSW) Si3N4 1.0E-01 2.5 3.2 eV SiC NitrideEσ =0.36eV (UNSW) 1.9 eV 0.5 eV 1.0E-03 2.0 1.0E-05 c-Si 1.1 eV c-Si 1.1 eV c-Si 1.1 eV [eV] PL energy Eσ = 0.63eV SiQDs in SiO2 0.9 eV 1.0E-07 1.5 2.3 eV 4.7 eV Conductivity (S/cm) Eσ = 0.76eV 1.0E-09 1.0 2.00 2.50 3.00 3.50 01234567 Dot1000/T diameter (1/K) [nm] DFT model -ling Various material combinations Quantum Dot / Matrix combinations and current status of investigations Increasing conductivity Decreasing processing temperature SiO2 Si3N4 SiC Si SPOED SPOED SPOD Ge SP - - Sn SPO PO - S = Simulation (ab-initio modelling - DFT) P = Physical (electron microscopy, X-ray difraction) O = Optical (photoluminescence, absorptance) E = Electronic (conductivity, conductivity with Temp.) D = Devices (Diodes, Cells) Hot Carrier solar cell Started September 2008 University of New South Wales, Sydney: Gavin Conibeer, Martin Green, Dirk König, Shujuan Huang, Santosh Shrestha, Chris Flynn, Lara Treiber, Pasquale Aliberti, Andy Hsieh, Rob Patterson, Binesh Puthen Veettil, Martin Kirkengen Institute Energie Solar, Universitas Polytechnic Madrid: A. Luque, A. Marti, E. Cánovas, A. Martí, P.G. Linares, E. Antolín, D. Fuertes Marrón, C. Tablero Inst. Research Development Energie Photovoltaic / CNRS, Paris: Jean Francois Guillemoles, Lunmei Huang University of Sydney: Timothy Schmidt, Raphael Clady, Murad Tayebjee Hot Carrier cell Extract hot carriers before they can thermalise: Ross & Nozik, JAP, 53 (1982) 3813 Würfel, SOLMAT, 46 (1997) 43 1995 • Need to slow carrier cooling Green, 3rd Gen PV (S-Verlag) 2003 • Collect carriers over narrow range of energies Würfel, PIP, 13 (2005) 277 • Renormalisation of electron (hole) energies Conibeer, TSF, 516(2008) 6948 Takeda et al, SOLMAT, 08 δE E e- energy s selective contact Ef(n) Ef ΔµA = qV small Eg h+ energy selective contact Ef(p) Es Hot carrier TA TH TA distribution Resonant Tunneling Transport Si QD Energy Selective Contact Energy Resonant Transport Filter 0.04 0.03 Two different sites Dielectric on the wafer 0.02 Ig(A) matrix 0.01 I 0 00.511.5 Gate voltage (V) Ef EC E V NDR at 300K - Repeatable f Hot Carrier cooling Energy Optical phonons Electrons carry most energy emitted Cool predominantly via small wave vector optical phonon emission - timescale of ps inelastic – energy relaxation Hot Optical phonon population “phonon bottleneck effect” Decay of Optical phonons to Acoustic is critical Slows further carrier cooling Optical phonon decay Optical phonon decay O → LA + LA (Anharmonicity or Klemens mechanism) Allowed phonon energies Element Compound – e.g. Si – e.g. InN meV Optical phonons 60 (standing waves) 30 E Phonon energies (density of states) Acoustic phonons (heat in the lattice) Nō 0 Some evidence for slowed carrier cooling in InN: Chen & Cartwright, APL,