Cu(Sb,Bi)(S,Se)2 as Indium-free Absorber Material with High Optical Efficiency

Abstract

Ternary Cu(Sb,Bi)(S,Se)2 compounds such as CuSbS2, CuSbSe2, CuBiS2, and CuBiSe2, are potential photovoltaic materials that contain earth abundant and low-cost elements. Employing an atomistic first-principles modeling within the density function theory we calculate the electronic and optical properties of Cu(Sb,Bi)(S,Se)2 compounds. We find that these four materials have indirect fundamental band gaps in the range of 1.1–1.7eV. The indirect gap nature is different to the previous experimental measurements (direct gap). Calculations reveal that these materials have strong optical absorption compared to chalcopyrite CuIn(S,Se)2 and kesterite Cu2ZnSn(S,Se)4. The strong absorption of these compounds is explained by the localized p-states of cation Sb/Bi in the lower region of conduction band. Thereby, ternary Cu(Sb,Bi)(S,Se)2 compounds have the potential to be used as absorber material in thin-film PV technologies.