Light-induced annihilation of Frenkel defects in organo-lead halide perovskites

In spite of the unprecedented advances of organohalide lead perovskites in optoelectronic devices, many of the characteristics of this class of materials remain poorly understood. Several experimental hints point to defect migration as a plausible mechanism underlying such anomalous properties. Here we present an experimental and theoretical investigation combining measurements of PL rise dynamics at varying temperatures with first principles computational modeling of defect migration under light irradiation. We propose a model in which light irradiation promotes the annihilation of VI+/Ii− Frenkel pairs, which we show to be relatively abundant in polycrystalline MAPbI3. This partly restores a non-defective crystalline environment and eliminates the trapping centers associated with such defect pairs. The PL rise time dynamics at varying temperature provide an activation energy consistent with that calculated for migration of iodine defects, supporting the proposed model. We further illustrate a synergistic effect of ion/defect migration and lattice dynamics, with local reorientation of the methylammonium cations assisting the migration of charged defects. Our results provide the interpretative basis for further investigating the unusual light-induced modifications characterizing organohalide perovskites.