High-Efficiency, Thin-Film GaAs Solar Cells

The present research is directed toward demonstrating the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratio by organo-metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. Antireflection-coated, metal-oxide-semiconductor (AMOS), GaAs solar cells grown on bulk polycrystalline Ge substrates were initially studied, with the best efficiency achieved being about 9 percent AM1 (7 percent AM0). Subsequently, a new direct deposition method for fabricating ultra-thin top layer, epitaxial n⁺ /p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed by means of which large area (1 cm²) cells were produced with about 19 percent AM1 (15 percent AM0) conversion efficiency. An AM1 conversion efficiency of about 18 percent (14 percent AM0), or about 17 percent (13 percent AM0) with 5 percent grid coverage, was achieved for a single-crystal, GaAs, n⁺ /p cell grown by OM-CVD on a Ge wafer. These achievements led to the fabrication, for the first time, of thin GaAs epi-layers OM-CVD grown with good crystallographic quality, using a (100) Si-substrate on which a thin Ge epi-interlayer was first deposited by CVD from GeH₄ and processed for improved surface morphology.