Electron Density and Optoelectronic Properties of Copper Antimony Sulphur Ternary Compounds for Photovoltaic Applications

Design of efficient solar energy-conversion materials has attracted much interest in the last few decades. Among these materials, copper-based semiconducting chalcogenides have been employed as alternatives for copper indium gallium selenide thin-film solar cells due to their low toxicity and earth-abundant absorber components. In the present manuscript, structural, electronic, quantum theory of atoms in molecules (QTAIM) topological, and optical properties of ternary chalcogenide CuSbS, CuSbS, and CuSbS have been investigated using the full potential linear augmented plane wave method. An indirect band gap is observed for CuSbS with E = 1.18 eV and a direct band gap is found for CuSbS, and CuSbS with E = 1.28 and 1.0 eV, respectively. The valence band maximum of CuSbS, CuSbS, and CuSbS are mainly predominated by a strong Cu-3d and S-3p orbitals hybridization. The conduction band of CuSbS and CuSbS are mainly characterized by Sb-5p orbital and S-3p orbital mixing. However, conduction band of CuSbS is dominated by the mixing of Sb-5s and S-3p orbitals. It is found that the Cu-S and Sb-S bonds lie in the transit closed-shell zone, between the typical ionic and covalent bonds, the Cu-S bonds being more ionic in nature and the Sb-S bonds being more covalent. The optical properties of CuSbS, CuSbS, and CuSbS in terms of absorption coefficient, extinction coefficient, refractive index, and reflectivity have been investigated. It is found that CuSbS is probably less suitable for optical application than CuSbS and CuSbS as the chemical bonds in CuSbS are seemingly less polarizable, as assumed from the QTAIM analysis, which seems to be correlated with a lower absorption coefficient.