Physical models for predicting the performance of Si/Si, AlGaAs/GaAs, and Si/SiGe solar cells

Abstract

Abstract Analytical and physical models for homojunction and heterojunction solar cells are developed, and the performances of solar cells made by the Si/Si homojunction and made by the increasingly important and popular AlGaAs/GaAs and Si/SiGe heterojunctions compared. The models developed, which include relevant device physics such as the effective surface recombination velocity at the high-low junction and band discontinuities associated with heterojunctions, correctly explain the solar cell characteristics experimentally observed. Our calculations suggest that the highest efficiencies attainable for AlGaAs/GaAs, Si/Si, and Si/SiGe cells, with optimized doping concentrations but without surface passivation and geometry optimization, are 21.25%, 17.8% and 13.5%, respectively, under 1 AM1.5 sun condition. For concentrator cell applications, the efficiencies improve to about 24.5%, 22.2%, and 22.0% for AlGaAs/GaAs, Si/Si, and Si/SiGe cells, respectively, under 100 AM1.5 suns. While the AlGaAs/GaAs cell possesses the highest efficiency among the three cells, the Si/Si and Si/SiGe cells can achieve a satisfactory conversion efficiency at high sun concentration (22% at 100 suns), making them attractive for concentrator cell applications because their processing is the same as or is compatible with existing silicon technology. Model predictions for two Si/Si and one AlGaAs/GaAs cells compare favorably with data reported in the literature.