Role of organic cations on hybrid halide perovskite CH3NH3PbI3 surfaces

Organic-inorganic hybrid halide perovskite CH3NH3PbI3 (MAPbI(3)) has received rapid progress in power conversion efficiency as promising photovoltaic materials, yet the surface structures and the role of MA cations are not well understood. In this work, we investigated the structural stability and electronic properties of (001) surface of cubic, (001) and (110) surfaces of tetragonal and orthorhombic phases of MAPbI(3) with considering the orientation of MA cations, by density functional theory calculations. We demonstrate that the orientation of MA cations has profound consequences on the structural stability and the electronic properties of the surfaces, in contrast to the bulk phases. Compared with the MA-I terminated surfaces, the Pb-I-2 terminated ones generally have smaller band gaps and the advantage to enable the photo-excited holes to transfer to the hole transport materials in both tetragonal and orthorhombic phases. Overall, we suggest that the films with Pb-I-2 terminated surfaces would prevail in high performance solar energy absorbers.