PHYSICAL MODELS FOR PREDICTING THE PERFORMANCE OF SI SI, ALGAAS/GAAS,AND SI/SIGE SOLAR-CELLS/

Analytical and physical models for homojunction and heterojunction sol ar cells are developed, and the performances of solar cells made by th e Si/Si homojunction and made by the increasingly important and popula r AlGaAs/GaAs and Si/SiGe heterojunctions compared. The models develop ed, which include relevant device physics such as the effective surfac e recombination velocity at the high-low junction and band discontinui ties associated with heterojunctions, correctly explain the solar cell characteristics experimentally observed. Our calculations suggest tha t the highest efficiencies attainable for AlGaAs/GaAs, Si/Si, and Si/S iGe cells, with optimized doping concentrations but without surface pa ssivation and geometry optimization, are 21.25%, 17.8% and 13.5%, resp ectively, under 1 AM1.5 sun condition. For concentrator cell applicati ons, the efficiencies improve to about 24.5%, 22.2%, and 22.0% for AlG aAs/GaAs, Si/Si, and Si/SiGe cells, respectively, under 100 AM1.5 suns . While the AlGaAs/GaAs cell possesses the highest efficiency among th e three cells, the Si/Si and Si/SiGe cells can achieve a satisfactory conversion efficiency at high sun concentration (22% at 100 suns), mak ing them attractive for concentrator cell applications because their p rocessing is the same as or is compatible with existing silicon techno logy. Model predictions for two Si/Si and one AlGaAs/GaAs cells compar e favorably with data reported in the literature.