Structural properties and quasiparticle band structures of Cu-based quaternary semiconductors for photovoltaic applications

Cu-based quaternary chalcogenide semiconductors (Cu₂-II-IV-VI₄) are a large group of materials that hold great promises for a variety of applications, especially as thin-film solar cell absorbers. However, despite intensive research activities, a systematic understanding of the evolution of the electronic and structural properties with chemical compositions of these materials is still lacking. In this paper, we present first-principles calculations of the structural and electronic properties of eight such semiconductors (Cu₂-II-IV-VI₄, with II = Zn and Cd; IV = Ge and Sn; VI = S and Se). The variation of the structural parameters with chemical compositions, investigated using the HSE06 hybrid functional, follows a few interesting trends. The quasiparticle bandgap, calculated using the state-of-the-art GW approximation, also varies systematically with chemical compositions. Effects of cation disordering on the band gaps are also investigated. This systematic understanding of the structural parameters and quasiparticle band gaps would be useful for future structural characterization and material design.