16.8%-Efficient n+/p GaAs Solar Cells on Si With High Short-Circuit Current Density

Abstract

The highest efficiency heteroepitaxial GaAs solar cells on Si have historically been grown in the p + /n polarity, which was preferred due to the decreased sensitivity of open-circuit voltage in such cells to threading dislocations. The n± /p polarity also has potential advantages due to the higher mobility of electrons than holes in GaAs, and most multi-junction solar cells in the literature are grown in this polarity. Here, we demonstrate n + /p GaAs solar cells on Si with a certified AM1.5G efficiency of 16.8%, approaching the best certified efficiency of 18.1% for p + /n cells in the literature. The high efficiency of our n + /p cells is primarily due to the short-circuit current density of 26.5 mA/cm 2 , which is significantly higher than prior p + /n record cells. The strong carrier collection results from the use of a highly transparent AlInP window layer, thin n + emitter, and a relatively high minority electron diffusion length in the p-type base. The high quantum efficiency of these n + /p cells at wavelengths of 700-880 nm makes them promising for future triple-junction devices on Si, where the GaAs will serve as a middle sub-cell.