Application of n-type microcrystalline silicon oxide as back reflector of crystalline silicon heterojunction solar cells

Abstract

We investigated the application of n-type hydrogenated microcrystalline silicon oxide (n-µc-Si1−xOx:H) as an alternative back reflector material for n-type heterojunction solar cells. The effect of the CO2 and PH3 flow rates on the refractive index, oxygen content, conductivity, and crystalline fraction (Xc) of n-µc-Si1−xOx:H films was evaluated. By controlling the film oxygen content, the refractive index could be widely changed, while the absorption coefficient at wavelengths exceeding 800 nm was practically zero. We found that the insertion of an n-µc-Si1−xOx:H layer between the back surface field and the rear electrode improves the reflectance at long wavelengths. The improvement in reflectance resulted in higher internal quantum efficiency in the IR range, suggesting that the application of n-µc-Si1−xOx:H as a back reflector is promising for reducing long-wavelength losses in heterojunction solar cells.