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High-Efficiency Amorphous Silicon and Nanocrystalline Silicon- DE-AC36-99-GO10337 Based Solar Cells and Modules: Final Technical Progress Report, 5B 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 High-Efficiency Amorphous Subcontract Report NREL/SR-520-43191 Silicon and Nanocrystalline May 2008 Silicon-Based Solar Cells and Modules Final Technical Progress Report 30 January 2006 – 29 January 2008 S. Guha and J. Yang United Solar Ovonic LLC Troy, Michigan NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 High-Efficiency Amorphous Subcontract Report NREL/SR-520-43191 Silicon and Nanocrystalline May 2008 Silicon-Based Solar Cells and Modules Final Technical Progress Report 30 January 2006 – 29 January 2008 S. Guha and J. Yang United Solar Ovonic LLC Troy, Michigan NREL Technical Monitor: Bolko von Roedern Prepared under Subcontract No. ZXL-6-44205-14 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. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste Table of Contents Preface.......................................................................................................................v Executive Summary ............................................................................................... vi Objectives.....................................................................................................................vi Approaches...................................................................................................................vi Status/Accomplishments .............................................................................................vii Publications...............................................................................................................x 1. Fundamental research on mixed-phase silicon solar cells and nc-Si:H solar cells...................................................................................................................1 1.1. Introduction....................................................................................................... 1 1.2. Experimental details.......................................................................................... 2 1.3. Results and discussion ...................................................................................... 2 1.3.1. Microscopic local current flow in mixed-phase Si:H solar cells.......................................................2 1.3.2. Light-induced change of local current flow in mixed-phase Si:H solar cells....................................8 1.3.3. Doping effect on the material structure in mixed-phase Si:H solar cells ..........................................9 2. Correlation of hydrogen dilution profiling with material structure and solar cell performance .......................................................................................... 16 2. 1. Introduction..................................................................................................... 16 2. 2. Experimental details........................................................................................ 17 2. 3. Results and discussion .................................................................................... 17 2.3.1. Material structures...........................................................................................................................17 2.3.2. Solar cell performance ....................................................................................................................20 2. 4. Summary ......................................................................................................... 21 3. Optimization of Ag/ZnO back reflector..................................................... 26 3. 1. Introduction..................................................................................................... 26 3. 2. Experimental details........................................................................................ 27 3. 3. Results and discussion .................................................................................... 27 3.3.1. Structural analysis...........................................................................................................................27 3.3.2. a-SiGe:H solar cells on improved Ag/ZnO back reflectors.............................................................32 3.3.3. Calculation of optical enhancement in a-SiGe:H cells on Ag/ZnO back reflector..........................37 3. 4. Summary ......................................................................................................... 39 4. High efficiency a-Si:H/a-SiGe:H/nc-Si:H and a-Si:H/nc-Si:H/nc-Si:H triple-junction solar cells...................................................................................... 42 4. 1. Introduction..................................................................................................... 42 4. 2. Experimental details........................................................................................ 42 4. 3. Results and discussion .................................................................................... 42 4.3.1. a-Si:H top cell .................................................................................................................................42 4.3.2. a-SiGe:H middle cell.......................................................................................................................44 4.3.3. nc-Si:H bottom cell .........................................................................................................................45 4.3.4. Optimization of a-Si:H/a-SiGe:H/nc-Si:H Triple-junction design..................................................56 4.3.5. High efficiency triple-junction cells................................................................................................58 4. 4. Summary ......................................................................................................... 59 5. High rate deposition of a-Si:H and a-SiGe:H solar cells using modified very high frequency glow discharge.................................................................... 62 iii 5. 1. Introduction..................................................................................................... 62 5. 2. a-Si:H and a-SiGe:H single-junction solar cells made with MVHF at high deposition rates............................................................................................................ 62 5. 3. a-Si:H/a-SiGe:H double-junction solar cells made with MVHF at high rates69 5. 4. Summary ......................................................................................................... 69 6. Large-area a-Si:H/a-SiGe:H/a-SiGe:H triple-junction and a-Si:H/nc-Si:H double-junction solar cells.................................................................................... 71 6. 1. Introduction..................................................................................................... 71 6. 2. Experimental details........................................................................................ 71 6. 3. a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cells under manufacturing constraints.................................................................................................................... 72 6. 4. Large-area a-Si:H/nc-Si:H double-junction modules ..................................... 75 6. 5. Summary ......................................................................................................... 77 References:............................................................................................................. 77 iv Preface This
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