Si-based thin-film solar cells: process and device performance analysis

This paper briefly introduces silicon based thin film solar cells: amorphous (a-Si:H), microcrystalline (μc-Si:H) single junction and a-Si:H/μc-Si:H tandem solar cells. The major difference of a-Si:H and μc-Si:H cells comes from electro-optical properties of intrinsic Si-films (active layer) that absorb incident photon and generate electron-hole pairs. The a-Si:H film has energy band-gap (Eg) of 1.7-1.8 eV and solar cells incorporating this wide Eg a-Si:H material as active layer commonly give high voltage and low current, when illuminated, compared to μc-Si:H solar cells that employ low Eg (1.1 eV) material. This Eg difference of two materials make possible tandem configuration in order to effectively use incident photon energy. The a-Si:H/μc-Si:H tandem solar cells, therefore, have a great potential for low cost photovoltaic device by its various advantages such as low material cost by thin-film structure on low cost substrate instead of expensive c-Si wafer and high conversion efficiency by tandem structure. In this paper, the structure, process and operation properties of Si-based thin-film solar cells will be discussed.