Substrate effect on ultra-thin hydrogenated amorphous silicon solar cells

We report a comprehensive study of ultra-thin a-Si:H solar cells on various transparent conductive oxide (TCO) coated glass substrates. We find that the highly textured boron doped zinc oxide (BZO) with multi-scale features made with metal organic chemical vapor deposition (MOCVD) outperforms the flat aluminum doped zinc oxide (AZO) deposited by sputtering and the highly textured AZO with only large features after the chemical etching with diluted HCl. We believe that the much larger features than the cell thickness provide only an enhancement of the effective area for increasing the light absorption, while the variable sizes of features similar to and smaller than cell thickness provide- a highly effective light trapping for thin film solar cells. In addition, the ultra-thin a-Si:H solar cell on the BZO has a better p/i interface than the cell on the AZO substrates, which leads to a high cell performance. A high efficiency of 8.15% was obtained using an a-Si:H p-i-n structure on the BZO with the intrinsic layer of 70 nm.