Ab initio design of CsSn(XxY 1−x)3 (X and Y = Cl, Br, and I) perovskites for photovoltaics

Ab initio calculations on CsSnX3 perovskites and mixed halides CsSn(XxY 1−x)3, X and Y = I, Cl, and Br, show that all of them have a direct band gap of ∼1 eV which can be tuned by varying the compositions of X and Y. The optimized supercells are tetragonal, orthorhombic or monoclinic. The top of the valence band arises from hybridization of Sn 4s and halogen p valence orbitals while the bottom of the conduction band has predominantly Sn p character. Similar to organo-metallic lead halides this is expected to facilitate p-p optical transitions that are highly favourable for photoabsorption. Our results suggest that these inorganic perovskites have the desired features to achieve high efficiency of photo-response with appropriate combination of halogens