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

We carried out first-principles calculations to investigate the methylammonium iodide terminated (MAI-T) and PbI2 terminated (PBI2-T) of CH3NH3PbI3 (001) surface. Highlight its the calculated surface energies show that the MAI-T is thermodynamically more stable than the PBI2-T one under the equilibrium growth condition. 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.