A national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy National Renewable Energy Laboratory Innovation for Our Energy Future Subcontract Report High-Efficiency Amorphous NREL/SR-520-38728 Silicon Alloy Based Solar October 2005 Cells and Modules Final Technical Progress Report 30 May 2002 – 31 May 2005 S. Guha and J. Yang United Solar Ovonic Corporation Troy, Michigan NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 High-Efficiency Amorphous Subcontract Report NREL/SR-520-38728 Silicon Alloy Based Solar October 2005 Cells and Modules Final Technical Progress Report 30 May 2002 – 31 May 2005 S. Guha and J. Yang United Solar Ovonic Corporation Troy, Michigan NREL Technical Monitor: B. von Roedern Prepared under Subcontract No. ZDJ-2-30630-19 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 This publication was reproduced from the best available copy submitted by the subcontractor and received no editorial review at NREL. NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. 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Introduction ...................................................................................................................... 3 2.2. Experimental .................................................................................................................... 4 2.3. Layer thickness uniformity............................................................................................... 4 2.4. Design of Experiments (DOE) ......................................................................................... 6 2.5. Uniformity of component cell performance..................................................................... 6 2.6. Summary .......................................................................................................................... 8 Section 3: Fundamental Study of nc-Si:H and Optimization of High Efficiency nc-Si:H Solar Cells .............................................................................................................................................. 10 3.1. Introduction .................................................................................................................... 10 3.2. Experimental .................................................................................................................. 10 3.3. Thickness dependence of nc-Si:H solar cells................................................................. 11 3.4. Microstructure changes with thickness in nc-Si:H solar cells........................................ 16 3.5. Hydrogen dilution profiling in nc-Si:H solar cell deposition......................................... 23 3.6. Control of interfaces....................................................................................................... 29 3.7. Dark J-V measurements for nc-Si:H solar cells............................................................. 29 3.8. Summary ........................................................................................................................ 32 Section 4: Optimization of Ag/ZnO Back Reflector..................................................................... 35 4.1. Introduction .................................................................................................................... 35 4.2. Experimental .................................................................................................................. 35 4.4. a-SiGe:H bottom cells on various BR substrates ........................................................... 37 4.5. nc-Si:H solar cells on various BR substrates ................................................................. 43 4.6. Summary ........................................................................................................................ 43 Section 5: High Efficiency Multi-junction Cell with nc-Si:H Bottom Cell.................................. 45 5.1. Optimization of a-Si:H/nc-Si:H double-junction solar cell............................................ 45 5.2. Optimization of a-Si:H/a-SiGe:H/nc-Si:H triple-junction solar cell.............................. 47 Section 6: High Rate Deposition of nc-Si:H Single-junction and Multi-junction Solar Cells Using Modified VHF Glow Discharge.................................................................................................... 49 6.1. Introduction .................................................................................................................... 49 6.2. Experimental .................................................................................................................. 49 6.3. MVHF high rate nc-Si:H single-junction solar cell ....................................................... 51 6.4. a-Si:H/nc-Si:H double-junction cells made with MVHF at high rates .......................... 53 6.5. a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells made with MVHF at high rates............. 54 6.6. Summary ........................................................................................................................ 54 iii Section 7: High Rate Deposition of nc-Si:H Solar Cells Using RF Glow Discharge in the High Pressure Regime............................................................................................................................ 58 7.1. Introduction .................................................................................................................... 58 7.2. Experimental .................................................................................................................. 58 7.3. RF high rate nc-Si:H single-junction cell....................................................................... 58 7.4. a-Si:H/nc-Si:H double-junction solar cells with RF glow discharge under high pressure and high power....................................................................................................................... 60 7.5. Summary ........................................................................................................................ 60 Section 8: Large-area a-Si:H/nc-Si:H Double-junction Solar Cells ............................................. 62 8.1. Introduction .................................................................................................................... 62 8.2. Experimental .................................................................................................................. 62 8.3. Uniformity of thickness and cell performance..............................................................