Crystal and electronic structures of substituted halide perovskites based on density functional calculation and molecular dynamics

Durability of organo-lead halide perovskite are important issue for its practical application in a solar cells. In this study, using density functional theory (DFT) and molecular dynamics, we theoretically investigated a crystal structure, electronic structure, and ionic diffusivity of the partially substituted cubic MA_0.5X_0.5PbI₃ (MA = CH₃NH₃⁺, X = NH₄⁺ or (NH₂)₂CH⁺ or Cs⁺). Our calculation results indicate that a partial substitution of MA induces a lattice distortion, resulting in preventing MA or X from the diffusion between A sites in the perovskite. DFT calculations show that electronic structures of the investigated partially substituted perovskites were similar with that of MAPbI₃, while their bandgaps slightly decrease compared to that of MAPbI_3. Our results mean that partial substitution in halide perovskite is effective technique to suppress diffusion of intrinsic ions and tune the band gap.