Research and product development at DuPont Photovoltaic Solutions Daniel Inns, PhD UNSW Public Research Seminar 10-March-2016 Outline • DuPont Introduction • DuPont Photovoltaics • Solamet® PV Metallization Pastes • Metal Induced recombination • Holistic Reliablitiy program • Advanced module encapsulation Copyright © DuPont 2015. All rights reserved. 2 Let me introduce myself • UNSW: • Undergrad (PV) • Worked at Pacific Solar on student project • Worked for thin-film group as lab assistant • PhD – thin-film c-Si solar cells • IBM: Postdoc • Silexos: Device team leader • Innovalight: Process Engineering • DuPont: Current Copyright © DuPont 2015. All rights reserved. 3 Understanding Materials, Cells, Modules – Under One Roof DuPont Silicon Valley Technology Center Copyright © DuPont 2015. All rights reserved. 4 Our Purpose DuPont is a Science Company We work collaboratively to find sustainable, innovative, market-driven solutions to solve some of the world’s biggest challenges, making lives better, safer, and healthier for people everywhere. Copyright © DuPont 2015. All rights reserved. 5 DuPont Has Evolved Over Two Centuries INTEGRATED CHEMICALS SCIENCE EXPLOSIVES 1999 – ACQUIRES 1966 – TYVEK® PIONEER HI-BRED 1967 – NOMEX® 1972 – ELECTRONICS 1949 – ENGINEERING EXPANSION 2003 – SOLAE JOINT POLYMERS 1935 – NYLON® VENTURE 1936 – LUCITE® 1800 1850 1900 1950 2000 2050 1986 – CORIAN® 2011 – ACQUIRES DANISCO 1802 – 1923 – CELLOPHANE® 2012 – ACQUIRES 100% OF E.I. DUPONT 1924 – RAYON® ® SOLAE 1924 – FILMS 1961 – TEDLAR 2000 – 1880 – ® 2013 – COMPLETES SALE OF 1805 – CORE VALUES FIRST BUSINESS BEGINS 1962 – LYCRA® SORONA BIO BASED PERFORMANCE COATINGS DYNAMITE ® 1804 – FIRST 1928 – CHEMICAL 1965 – KEVLAR POLYMER BUSINESS AND ANNOUNCES POWDER MILL EXPANSION PLANS TO SEPARATE PERFORMANCE CHEMICALS 1903 – EXPERIMENTAL STATION 1952 – MYLAR® 1915 – PLASTICS 1917 – MAKING DYES Copyright © DuPont 2015. All rights reserved. 6 Our Strategic Priorities Our strategy is to be a premier market-driven science company and generate superior shareholder returns. AGRICULTURE BIOBASED ADVANCED & NUTRITION INDUSTRIALS MATERIALS Copyright © DuPont 2015. All rights reserved. 7 Copyright © DuPont 2015. All rights reserved. 8 DuPont: The Leading Specialty Material Supplier in PV Rynite® PET Solamet® Tedlar® Elvax® and Zytel® Nylon metallization backsheet Ionomer composite pastes films encapsulants materials Driving higher Protecting PV Delivering Reducing energy conversion modules long-term system costs efficiency protection of cells and speed up installation Copyright © DuPont 2015. All rights reserved. 9 Three Areas Driving The Growth in PVs Efficiency Cost Lifetime Reduce panel and Improve efficiency with installation cost with Safe power generation innovative materials and improvements in for > 25 years cells architectures materials and processes All Three Drivers are Inseparable Copyright © DuPont 2015. All rights reserved. 10 Solamet® Metallization Paste – Delivering Higher Electrical Power Copyright © DuPont 2015. All rights reserved. 11 DuPont™ Solamet® Driving Cell Performance Evolution Higher efficiency New PV19x Looking to the future: Fine line aspect ratio will be High efficiency key focus in metallization improved fine line, PV18x High efficiency development to improve enhanced LDE, PV18x p-type cell efficiency High efficiency LDE, PV17x Standard p-type PV16x First to introduce LDE with New Gen. Solamet® PV19x Solamet® PV17x achieving a enabling extreme LDE with step change in efficiency excellent fine line capability Copyright © DuPont 2015. All rights reserved. 12 DuPont™ Solamet® PV19x Industry Collaboration: Superior Performance and Yield Demonstrated on mc-Si Cell Efficiency Distribution 18.14 18.29 9 Ref-2 8 • >0.15% efficiency gain on PV19x multi proven in pilot run 7 6 • Robust processing latitude ] % allowing tighter cell distribution to [ 5 t n reduce low efficiency binning e c r 4 <17.8% e P 3 • Production yield increased 2 from 93% to 98.5% for >260W 1 power output 0 17.44 17.60 17.76 17.92 18.08 18.24 18.40 18.56 Customer A Efficiency N=2500pc Copyright © DuPont 2015. All rights reserved. 13 DuPont™ Solamet® PV76x Front Side Silver Paste Series Designed for PERC • Excellent contact performance at lower peak firing temperatures • Lower firing temperature reduces voids and passivation damage • >0.15% cell efficiency gain vs. conventional front side pastes Copyright © DuPont 2015. All rights reserved. 14 Proven Performance on Industry Leading Mono PERC • DuPont collaborated with TSEC to develop front and rear side silver PV36x pastes optimized to maximize Si PERC cell performance Si • With the new PERC pastes TSEC gained 0.15% cell efficiency to reach over 21% • The power output of TSEC’s newest “V-Series” panels is more than 300Wp and 360Wp in 60-cell and 72-cell configuration respectively Image courtesy of TSEC Read more at: http://www.dupont.com/products-and-services/solar-photovoltaic-materials/media/press-releases/20150224-dupont-tsec-high-efficiency-solar-panels.html Copyright © DuPont 2015. All rights reserved. 15 Fine Line Evolution by Solamet® Paste 90 PV16x PV17x PV18x PV19x 80 70 60 50 40 Screen Opening (µm) Opening Screen 30 ? 20 2010 2011 2012 2013 2014 2015 2016 2017 Year 35µm finger lines are now possible with PV19X Copyright © DuPont 2015. All rights reserved. 16 DuPont™ Solamet® Driving Cell Performance Evolution 30µm Screen Reference Technology DuPont™ Solamet® for Fine Line Process + Paste Pattern Solamet® PV19A Advance fine line innovations achieved by synergy from screen technology, paste and pattern design Copyright © DuPont 2015. All rights reserved. 17 Metal induced recombination: Jo.m Solar cell Jo is the sum of all component, including Jo.m 2 Line width / shading / JL Voc Jo.m = 1015 fA/cm Intercept = 608 +/- 15 Slope = 945 +/- 80 R2=0.86 Copyright © DuPont 2015. All rights reserved. 18 Metal induced recombination study: Shallow emitters Non idealities stem from many places: Shunts, Schottky contacts, edges Lighter and shallower emitters = high risk Use the two diode model for non-idealities -Suns-Voc tester + fit Image: PV Lighthouse https://www2.pvlighthouse.com.au/calculators/EC%20calculator/EC%20calculator.aspx Copyright © DuPont 2015. All rights reserved. 19 non-idealities Jo1.m increases for shallower / higher Rsheet emitters n=2 recombination is quantified for very shallow emitter n=1 n=2 Rsheet (Ω/sq) Jo1.m (fA/cm2) Jo2.m (nA/cm2) 90 1420 +/- 200 -12 +/- 6 110 1820 +/- 260 -20 +/- 20 130 2390 +/- 290 510 +/- 80 Copyright © DuPont 2015. All rights reserved. 20 Metal recombination: emitter etch model EDNA emitter recombination model After M. Abbott et al, IEEE PVSC Denver 2014 EDNA model indicates 20-40nm silicon etch by metal would deliver the Jo.m we measure Effective profile (a) for 100nm etch (b) measured Jo.m range Fundamental limit? Copyright © DuPont 2015. All rights reserved. 21 Holistic Cell and Module Durability Program • Evaluate durability for PV materials and their interactions and synergies in module • Provide science-based understanding of materials-related lifetime performance • Develop products with highest durability to deliver more power output Copyright © DuPont 2015. All rights reserved. 22 Proven Track Record of Paste Reliability in Various Industries Automotive • More than 40 years thick film composition Photovoltaic Military experiences in high reliable requirement industries e.g., Microcircuit automotive, telecom, Materials military… Component Telecom • Over 30 years engagement in solar applications Biomedical Copyright © DuPont 2015. All rights reserved. 23 Field Studies Reveal Quality Issues Encapsulant, 4% Backsheet, 9% Cell, 24% DuPont Field Module Program • Inspected >60 global installations (>200 MW & 1.5 million modules) in NA, EU, & AP ranging from 0-30 years installed Others, 1% • Data includes c-Si modules from Defect Not > 45 module manufacturers Glass, 2% Detected, 59% Mismatch, 1% IEEE PVSC (New Orleans, 2015, A. Bradley et al) Subcomponent degradation mode pareto based on visual inspection 41% of inspected modules exhibited some visual defect Findings consistent with BP and SunPower data Copyright © DuPont 2015. All rights reserved. 24 Advanced Encapsulants Modules with Ionomer encapsulant provide superior reliability Modules with Ionomer encapsulant are free of snail trails Modules with Ionomer encapsulant are PID free Copyright © DuPont 2015. All rights reserved. 25 EVA as encapsulant Ionomer as encapsulant Modules with Standard types of EVA show snail trails, while Ionomers Prevent the Failure Mode Copyright © DuPont 2015. All rights reserved. 26 Snail Trails • Mysterious dark lines criss-crossing PV modules • First occurrence in Spain in March 2007 • Rapid increase in occurrence over past few years • Location is at the interface of cell and EVA • Always form on top of micro-cracks • Have affected a large number of module makers Copyright © DuPont 2015. All rights reserved. 27 Root Cause of Snail Trail Ag finger Si cell EVA Backsheet OM SEM Ag finger Microscopy analysis showed EVA nano-particles of different Si cell sizes and densities exist on the EVA OM SEM surface of Ag finger, caused by Backsheet OM SEM an interaction between Ag finger and chemistry in EVA. Combined experiments (XPS, Raman and ionic chromatography) revealed that the dark nanoparticle in the snail trail region is silver compound. Root cause of snail trail is interaction between Ag finger and chemistry in EVA Copyright © DuPont 2015. All rights reserved. 28 Acetic Acid in EVA Accelerates