Lead halide perovskites show exceptional defect tolerance; however, their microscopic origin remains debated, with various models including high dielectric screening and shallow defect states. To clarify the origin of defect tolerance in this type of material, we investigate the phase-dependent electronic band structure, which is sensitive to the scattering with defects of prototypical CH3NH3PbBr3 with the combination of angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Minimal change of defect density and few defect states are found in both phases; however, the measured hole effective mass (mh) of cubic and tetragonal CH3NH3PbBr3 varies from 0.235 m0 (m0 is the mass of a free electron) to 0.378 m0. DFT calculations that account for the effects of lattice distortion and organic cation reorientation reproduce the measured mh of cubic CH3NH3PbBr3; however, they underestimate this value by 33.6% in the tetragonal phase. Including Br vacancies, the predicted mh increases by 11.5% and 66.9% for the cubic and tetragonal CH3NH3PbBr3, respectively, close to the measured ones. The much more significant effect of defects on the electronic structure of the tetragonal than cubic CH3NH3PbBr3 suggests much more efficient defect screening from the lattice distortions and organic–cation rotation of the latter. Given the similarities in the geometric and electronic structures, these findings in CH3NH3PbBr3 may be applicable to other lead-halide perovskites.
Dong et al. (Tue,) studied this question.