Amorphous silicon based tandem solar cells entirely fabricated by hot-wire CVD

Abstract

For the first time, we report on a-Si:H/a-Si:H tandem solar cells, entirely fabricated by hot-wire CVD. Until now, our effort to develop a-Si:H/a-Si:H tandem cells has resulted in a 7.0% initial efficiency. Two types of tunnel junction, n/sup +/-/spl mu/c-Si:H/p/sup +/-a-SiC:H and n/sup +/-/spl mu/c-Si:H/p/sup +/-/spl mu/cSi:H, have been developed which yield low series resistance (<25 /spl Omega/cm/sup 2/). Systematic variation of top i-layer thickness was carried out to optimize the current matching, which otherwise appeared to be difficult since band gap tailoring of top and bottom junction could not yet be accomplished in our hot wire CVD process. For a-Si:H//spl mu/c-Si:H tandem structure, an intrinsic microcrystalline Si material with high photosensitivity (/spl ap/10/sup 3/) has been developed with a growth rate, 10 /spl Aring//s by controlling its microstructure. The problems encountered in incorporating this material into a-Si:H//spl mu/c-Si:H tandem solar cells are discussed.