First-principles study on the electronic and optical properties of cubic ABX3 halide perovskites

The electronic properties of ABX3 (A = Cs, CH3NH3, NH2CHNH2; B = Sn, Pb; X = Cl, Br, I) type compounds in the cubic phase are systematically studied using the first-principles calculations. We find that these compounds have direct band gaps at R point where the valance band maximum is an anti-bonding state of B s-X p coupling, while the conduction band minimum is a non-bonding state with B p characters. The chemical trend of their properties as A or B or X varies is fully investigated, which is of great importance to understand and optimize this kind of solar cell materials. We find that: (i) as the size of A increases, the band gap of ABX3 will increase; (ii) as B varies from Sn to Pb, the band gap of ABX3 will increase; and (iii) as X ranges from Cl to Br to I, the band gap will decrease. We explained these trends by analyzing their band structures. Furthermore, optical properties of the ABX3 compounds are investigated. Our calculations show that taking into account the spin-orbit coupling effect is crucial for predicting the accurate band gap of these halide perovskites. We predict that CH3NH3SnBr3 is a promising material for solar cells absorber with a perfect band gap and good optical absorption.