First-Principles Investigation of the Structural, Electronic and Optical Properties of Inorganic Cs2SnI6 Double Perovskite

Ab initio study using density functional theory (DFT) is carried out to explore the structural, electronic and optical properties of Cs2SnGeI6 compound. The structural properties of this compound are determined by using the approximation (GGA-PBE) asimplemented in WIEN2k code. The calculated lattice parameters of the Cs2SnGeI6 compound are found to be a = 12, 17 Å. The calculated electronic band structure and density of states indicate that the Cs2SnGeI6 compound has a semiconducting bahaviorwith narrow direct band gap of 0.43 eV and 0.35 eV with PBE and TB-mBJ exchange-correlation potentials. The different contributions of the electronic orbitals are discussed using the total and partial DOS with PBE and TB-mBJ approximations, which shows significant contributions from the I atom especially with p orbital. The optical properties such as dielectric function, refractive index, absorption coefficient and extinction coefficient are calculated and discussed. The findings in this study open new possibilities for developing optoelectronic and thermoelectric devices based on Cs2SnGeI6 halide double perovskites.