Nature of the band gap of halide perovskites ABX₃ (A= CH₃NH₃, Cs; B= Sn, Pb; X= Cl, Br, I): First-principles calculations

The electronic structures of cubic structure of ABX₃ (A= CH₃NH₃,Cs; B= Sn, Pb; X= Cl, Br, I) are analyzed by density functional theory using the Perdew-Burke-Ernzerhof exchange-correlation functional and using the Heyd-Scuseria-Ernzerhof hybrid functional. The valence band maximum (VBM) is found to be made up by an antibonding hybridization of B s and X p states, whereas bands made up by the π antibonding of B p and X p states dominates the conduction band minimum (CBM). The changes of VBM, CBM, and band gap with ion B and X are then systematically summarized. The natural band offsets of ABX₃ are partly given. We also found for all the ABX₃ perovskite materials in this study, the bandgap increases with an increasing lattice parameter. This phenomenon has good consistency with the experimental results.