Theoretical investigation of Cu-containing materials with different valence structure types: BaCu2S2, Li2CuSb, and LiCuS

•DFT employed to study the electronic band structure of β-BaCu2S2, Li2CuSb and LiCuS.•E-V proved to be accurate than GGA for compounds with localized valence electrons.•Li2CuSb is the most thermoelectric stable one between the studied compounds.•Calculated parameters seem likely to be in agreement with the experimental values.

Optoelectronics research requires cheap materials with a broad spectrum of optical, electronic, and structural properties. The class of Heusler compounds and ternary structures provide many possibilities for finding alternative group IV and III–V semiconductor compounds. This study introduces wider band gap materials for use in solar cells as an alternative to cadmium sulfide buffer layers. The buffer layer is inserted between the absorber layer (p-type) and the transparent window layer (n-type) to enhance the maximum amount of light transmission. Reasonable calculations are reported for the band gaps of copper-containing materials: LiCuS, BaCu2S2, and Li2CuSb. Previous optical analysis measurements of these films determined that the band gaps were 1.8 and 1.9 eV for BaCu2S2 and LiCuS, respectively. In general, semiconductor compounds have been studied theoretically, but there are major differences between the experimental and theoretically calculated band gaps. A suitable calculation method for semiconductor compounds is described in this study. For the first time, calculations based on the Engel and Vosko method are introduced for these semiconductor compounds. This method yields band gaps that are comparable to the experimental values, which facilitate the development of microscopic analyses of these compounds. Direct band gaps of 1.15 and 1.7 eV were obtained for BaCu2S2 and LiCuS, respectively, whereas the indirect band gap was 0.7 eV for Li2CuSb.