Effect of surface composition on electronic properties of methylammonium lead iodide perovskite

Methylammonium lead iodide perovskite, CH₃NH₃PbI₃, is one of the most promising photovoltaic materials for low-cost and clean source of energy. In this work, the first-principles calculations were carried out to investigate the different composition of CH₃NH₃PbI₃ (001), including both methylammonium iodide terminated (MAI-T) and PbI₂ terminated (PBI₂-T) surfaces. The calculated surface energies show that the MAI-T is thermodynamical more stable than the PBI₂-T one under the equilibrium growth condition. The electronic properties of the two types of surfaces are also different. The band gap of PBI₂-T is obviously smaller than that of MAI-T due to the surface Pb states. Band gaps of MAI-T decrease with increasing thickness, while band gaps of PBI₂-T are insensitive to the slab thickness. The calculated optical absorption coefficients suggest that both terminations are effective solar energy absorbers in the visible light spectrum.