Abstract
This report describes the research program intended to expand, enhance, and accelerate knowledge and capabilities for developing high-performance, two-terminal multijunction amorphous silicon (a-Si) alloy cells, and modules with low manufacturing cost and high reliability. United Solar uses a spectrum-splitting, triple-junction cell structure. The top cell uses an amorphous silicon alloy of~1.8-eV bandgap to absorb blue photons. The middle cell uses an amorphous silicon germanium alloy (~20% germanium) of~1.6-eV bandgap to capture green photons. The bottom cell has~40% germanium to reduce the bandgap to~1.4-eV to capture red photons. The cells are deposited on a stainless-steel substrate with a predeposited silver/zinc oxide back reflector to facilitate light-trapping. A thinlayer of antireflection coating is applied to the top of the cell to reduce reflection loss. The major research activities conducted under this program were: 1) Fundamental studies to improve our understanding of materials and devices; the work included developing and analyzing a-Si alloy and a-SiGe alloy materials prepared near the threshold of amorphous-to-microcrystalline transition andstudying solar cells fabricated using these materials. 2) Deposition of small-area cells using a radio-frequency technique to obtain higher deposition rates. 3) Deposition of small-area cells using a modified very high frequency technique to obtain higher deposition rates. 4) Large-area cell research to obtain the highest module efficiency. 5) Optimization of solar cells and modules fabricatedusing production parameters in a large-area reactor.
Original language | American English |
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Publisher | National Renewable Energy Laboratory (NREL) |
Number of pages | 93 |
State | Published - 2001 |
Bibliographical note
Work performed by United Solar Systems Corp., Troy, MichiganNREL Publication Number
- NREL/SR-520-31290
Keywords
- amorphous silicon (a-si) alloy cells
- manufacturing
- modified very-high-frequency technique
- PV
- radio frequency technique
- spectrum-splitting
- triple-junction cell structure
- two-terminal multijunction