RECENT TRENDS IN PHOTOVOLTAICS TECHNOLOGY: CRYSTALLINE WAFERS VERSUS FLEXIBLE THIN FILMS. Saleem H. Zaidi, Gratings, Inc., Nov.

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1 RECENT TRENDS IN PHOTOVOLTAICS TECHNOLOGY: CRYSTALLINE WAFERS VERSUS FLEXIBLE THIN FILMS OUTLINE Saleem H. Zaidi, Gratings, Inc., Nov. 6, 2008 Motivation Silicon PV Technology Growth and Trends Conventional Manufacturing (a) Automated Manufacturing (b) Thin Film Manufacturing Cottage Industry Approach (a) Application to 110 W Panel Manufacturing Silicon Solar Research Directions (a) Water-free Manufacturing (b) Crystalline Thin-Films

2 ACKNOWLEDGEMENTS Sam McCormack, Richard Marquardt, Matt Channon, Robert Ellis, Karen DeZetter, Laure Koltunski, David Modisette, Rich Winder, Rajiv Prinja, Abdul Latif, Gary Begay, Bernard Stuart, Dr. J. Tringe, and Prof. K. Sopian Prof. S. Brueck, Dr. James Lyke, James Gee, Dr. D. Ruby, John Wohlgemuth, and Steve Rockholm NSF, DoD, Sandia National Labs, UKM, and AFRL BP Solar, Adventsolar, LMCO

3 INTRODUCTION TO GRATINGS Turn-key solar cell and module manufacturing systems Multi-vapor etching systems Pulsed laser annealing systems Solar cells and Modules Nanostructures

4 INTRODUCTION TO GRATINGS Si nanostructure Au nanospheres Laser-etched Thru Features 6-inch diameter Solar Cell 110 W Panel

5 GLOBAL ELECTRICITY GENERATION Green Land Russia USA China Africa Australia United States 3816 billion KWh Annually Pakistan 66 billion KWh Annually Tanzania 1 billion KWh Annually

6 ELECTRICITY GENERATION VS GDP Higher energy usage leads to higher income Most of the world at much lower income Quality-of-life linked to energy usage

7 ELECTRICITY GENERATION IN ASIA India and China will generate most electricity Coal usage will lead to environment degradation Climate is globally linked

8 PARADIGM SHIFT IN ELECTRICITY GENERATION FUNDAMENTAL ASSUMPTIONS Access to electricity is fundamental human right and responsibility Energy generation must be at the point of use Transition from macro grids (hundreds of miles) to nano grids (~ mile) Power plants from ~ 100s MW capacity to ~ 1 MW capacity Renewable PV technology to by-pass carbon-based fuels

9 COTTAGE INDUSTRY APPROACH TO PHOTOVOLTAICS FUNDAMENTAL ASSUMPTIONS A solar cell is just a large area diode Manufacturing model based on IC model is not needed Energy conversion costs ($/W) is the key parameter PV technology is adaptable to a society s technological level Investment in PV technology infrastructure (education, economy) PV technology creates jobs

10 PV RESIDENTIAL APPLICATIONS BIPV ~ 2-5 kw

11 PV INDUSTRIAL APPLICATIONS Agriculture ~ kw Power Plant ~ 1 M W Industrial ~ M W

12 PV INDUSTRY OVERVIEW PV Power in MW PV Power in MW Cumulative PV Power From PV Power From Sustained Growth over Last 15 Years Grid-integrated PV is dominant Off-grid is economically profitable today!

13 PV GENERATION SECTORS IN USA 2005 installations ~ 100 MW Grid-connected ~ 90 % of the Total Significant residential and commercial sectors Off-grid growth is ~ 10 % of total

14 IMPACT OF SUBSIDIES ON PV GENERATION Residential Programs in Japan PV Growth is dependent on subsidies Costs in Grid-connected regions still too high Off-grid regions, PV is the most economical

15 PV GENERATION BY TECHNOLOGY SECTORS Multicrystalline Si is Dominant Monocrystalline Si share has increased Thin-film technologies have reduced

16 PROJECTED PV GROWTH IN NEXT FEW YEARS 3.25 GW Generation 4 GW Generation Germany and Japan will lead growth China will compete strongly ROW and US may lag behind

17 PV INDUSTRY OUTLOOK --- Wall Street Analysis Grid-Parity ~ 2015 Huge financial growth in 2003 to 2008 with competing technologies Period of consolidation 2009 through 2012 Financial activity will rebound, partly from merger and acquisition

18 PRINCIPAL PV TECHNOLOGY SECTORS Raw material to purified Si Mono/poly silicon wafers from feedstock Wafer processing into solar cells Solar cell packaging into modules Module arrays for system integration

19 PV TECHNOLOGY SECTOR: SILICON PURIFICATION Raw SiO 2 produced by Mining Purified Silicon Feedstock Si is the 2 nd most abundant element on earth; Si is ~ 25.7 % of Earth s mass Si is capable of supplying all our Energy

20 MAJOR PRODUCERS OF PURIFIED SILICON SUMMARY 2005 Hemlock 7,700 Wacker Polysilicon 5,600 REC 5,550 Tokuyama 5,200 MEMC 3,800 Mitsubishi Materials 1,600 Mitsubishi Polysilicon 1,260 Sumitomo Titanium 700 Other 220 TOTAL 31,630 Very expensive to produce purified Si Dominated by few companies Production of feedstock in tonnes annually

21 PV TECHNOLOGY SECTOR: MONOCRYSTALLINE AND POLYCRYSTALLINE SILICON MANUFACTURING Critical Technology Wafer manufacturing: key to success Mono-Si superior to and more expensive than Poly-Si Gratings focus on mono-si CZ-Growth Mono-Si Cast Growth Poly-Si

22 BRIEF INTRO TO SILICON SOLAR CELL Solar Spectrum on Earth Basic Cell Configuration Converts sunlight into electricity Silicon Wafer is processed into solar cell Current Extraction uses Screen Printing and Electroplating Optical Absorption in thinner wafers using 3D Structures Cell Efficiencies ~ % range

23 PRINCIPAL SOLAR CELL MANUFACTURING STEPS Damage Removal NOTES: Technology Trend: Thinner Wafers and Dry Processing Need for Low-Thermal Budget Processes Replacement of Screen-Printing by Electroplating High throughput using Automated Equipment

24 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Acid Etch System Following IC manufacturing model High throughput to meet profitability

25 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Diffusion System Several approaches are used POCl 3 produces best results

26 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Edge Isolation System Several process approaches Proprietary and commercial systems PECVD nitride is often the most expensive machine Automated Nitride System

27 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Contact Firing System Screen Printing System Low-cost screen printing options available Contact firing system is unique to screen printing

28 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Solar Cell Tester High Throughput Robotics for Cell Transfer and Sorting

29 SOLAR CELL MANUFACTURING CHALLENGES High wafer cost relative to conventional fuels Wafer supplies for smaller companies High wafer costs High startup costs in extensive automation Harmful Chemicals Extensive water usage Lack of Innovation due to cost considerations

30 THIN-FILM CIGS MANUFACTURING PROCESS Large area vacuum equipment High power lasers

31 TYPICAL CIGS PRODUCTION LINE Startup costs ~ US $ 30 million Annual production ~ 10 MW/year

32 RETURN ON INVESTMENT PROJECTIONS High profitability High initial investment

33 LOW COST MANUFACTURING PROCESS Modular approach Step-wise process characterization Efficiency ~ % range

34 SURFACE TEXTURING FOR PERFORMANCE ENHANCEMENT RIE Texture Wet-Chemical Texture Spectral Reflectance Cell Description Eff. (%) Open Circuit Voltage (V) Short Circuit Current (A) Fill Factor Planar RIE chemical

35 LOW VOLUME, LOW COST MANUFACTURING APPROACH PRINCIPAL PROCESSES and EQUIPMENT Gratings Edge Isolation System LabVIEW Interface Coin stack Wafer Arrangement Etching Gas from Sidewalls 6 -diameter wafer capability

36 LOW VOLUME, LOW COST MANUFACTURING APPROACH PRINCIPAL PROCESSES and EQUIPMENT Manual Solar Cell Tester LabVIEW Interface Cells and Modules Programmable Power Supply

37 SCREEN-PRINTED, TEXTURED 6 -DIAMETER SOLAR CELLS Cell Description Wetchemical Eff. (%) Open Circuit Voltage (V) Short Circuit Current (A) Fill Factor

38 PRINCIPAL SOLAR MODULE MANUFACTURING STEPS NOTES: Technology Trend: High throughput using Automated Equipment Combine Cell and Module Manufacturing Operations Opportunities for low-cost, Manual Manufacturing

39 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Solar Cell Tester and Sorter High Throughput Robotic for Cell Transfer and Sorting

40 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Solar Cell Tabbing and Soldering

41 LARGE VOLUME, HIGH COST MANUFACTURING APPROACH USING TURNKEY SYSTEMS Automated Lamination Module Tester High Throughput at High Cost Robotic for Cell Transfer and Sorting

42 LOW COST MANUFACTURING APPROACH PRINCIPAL PROCESSES and EQUIPMENT Manual Cell Tabbing Manual Cell Stringing Low cost and effective Employment oriented Simple throughput extension

43 LOW COST MANUFACTURING APPROACH PRINCIPAL PROCESSES and EQUIPMENT Manual Operation Light tables for defect detection Yields comparable to automated equipment

44 LOW COST MANUFACTURING APPROACH MODULE LAMINATION AND FRAMING Manual Laminator Manual operation Manual loading of laminator Manual Framing

45 LOW COST MANUFACTURING APPROACH SOLAR MODULE LIV CHARACTERIZATION Module LIV Tester Manual operation Manual loading of modules

46 LOW VOLUME, LOW COST MANUFACTURING APPROACH BASIC FACTORY LAYOUT Reduced startup cost and employment oriented

47 COST AND BENEFIT ANALYSIS Cross-over point ~ 2 MW/year in US Cross-over point ~ 0.5 MW/year in developing country

48 SILICON SOLAR RESEARCH DIRECTIONS NEEDS FOR WATER-FREE MANUFACTURING 1 MW production requires ~ 10 million Gal DI water Harmful chemicals such as HF, HCl, NaOH Reduced yields for Thinner wafers Al BSF process incompatibility on Thinner wafers PLASMA PROCESSES IN SOLAR CELL MANUFACTURING Plasma texturing Plasma implantation Reduced thermal budget No wet-chemical processing

49 PLASMA PROCESSES IN SOLAR CELL MANUFACTURING IQE PLANAR Ref--PLANAR Ref--PLANAR I QE--TEXTURED IQE and Reflectance Random RIE Texture Wavelength ( nm) Reflection and IQE Plasma implantation System Implant Profile

50 SILICON SOLAR RESEARCH DIRECTIONS NEED FOR CRYSTALLINE SILICON THIN-FILMS Reduce energy conversion costs Flexible substrates Higher Efficiencies THIN-FILM SOLAR CELL MANUFACTURING Epitaxial growth Porous Si etching and de-lamination Reduced optical absorption Expensive and low throughput

51 OPTICAL ABSORPTION IN THIN FILMS Surface and Sidewall Texture Surface Texture Short-circuit Enhancement Short-circuit Enhancement

52 OPTICAL ABSORPTION IN THIN FILMS Short-circuit Enhancement Short-circuit Enhancement

53 CONCLUDING THOUGHTS ON PV TECHNOLOGY On-Grid PV Off-Grid Village-No Electricity PV Technology is Special Needed Most by Poorest of the Poor PV Technology is Expensive PV Technology Must Become Indigenous PV technology Must evolve Into Cottage/ Community Industry PV Technology Combines Silicon, Oxygen, And Sun---abundant and free

54 SUMMARY: PV ENERGY IS THE ULTIMATE SOLUTION A Shift in Energy Generation from Fossil Fuels to Renewables: a Paradigm Shift as Fundamental as That from Coal to Oil in 20 th Century Paradigm Shifts We are Familiar With Cell Phones versus land-based line phones Satellite TV Systems