Crystal chemistry investigations on photovoltaic chalcogenides

Chalcogenides have strong potential applications for thin-film photovoltaics due to their high light absorption coefficient and because their band gap can be easily tuned as desired via appropriate chemical substitutions. The thin-film fabrication processes lead unavoidably to local slight variations of the compositions. The ability of photovoltaic materials to accommodate such disparities in composition of the absorber is a critical point to achieve high photovoltaic conversion efficiency. This chapter sums up the results of fundamental chemical crystallographic investigations on compounds derived from Cu2ZnSnS4 (CZTS) and from CuInS2 (CIGS). From this study, the pseudo-ternary diagrams (Cu2(S,Se)-Zn(S,Se)-Sn(S,Se)2, and Cu2S-In2S3-Ga2S3) can be proposed and could serve as support to better understand the lower photovoltaic performances of sulphides compared to selenides in both systems.