Atomic structure and electronic properties of lead and tin based hybrid halide perovskite surface for photovoltaic applications

Organic-inorganic hybrid halide perovskites are emerging as one of the potential materials in the photovoltaic community due to its attractive power conversion efficiency and cost-effective device fabrication. The photovoltaic performance of hybrid halide perovskite is linked to its atomic and electronic structure at the surface. Here we have used electronic structure calculations to determine the structural and electronic properties at the surface of MABX3 (MA = CH3NH3; B = Sn or Pb; X= I, Br, or Cl) perovskites. Next, we compared calculated electronic properties of the surface with the corresponding bulk values. Our results reveal that the structural properties like B-X distances, B-X-B angles, and orientation of MA are different between bulk to perovskite surface. Such changes in structural features at the perovskite surface lead to change in the band gap between surface and bulk perovskite. Both structural features and the band gap at the surface are found to be dependent on the crystal symmetry and chemistry of the perovskite. Further, for all perovskite compositions investigated, no midgap surface electronic states were observed.