Ion migration mechanism in all-inorganic Ruddlesden–Popper lead halide perovskites by first-principles calculations

Ion migration under light illumination or electric field could cause several complex phenomena, such as hysteresis, phase segregation, and interface passivation, in optoelectronic devices based on hybrid organic-inorganic perovskites. The high ionic conductivity of metal halide perovskites can be ascribed to the lower migration barrier of halide anions, which has been demonstrated to be inhibited by the large organic layer of two-dimensional perovskite structures. However, in all-inorganic two-dimensional perovskites, the diffusion mechanism of halide anions has not been comprehensively studied. Herein, we investigate the diffusion mechanism of halide anions in all-inorganic Ruddlesden-Popper (RP) halide perovskites by first-principles calculations. In these all-inorganic perovskites, the inorganic CsI layer can also prevent halide diffusion between the adjacent octahedral slabs via the vacancy-hopping mechanism. However, intercalation provides an additional diffusion channel for halide interstitials, which promote in-plane diffusion in RP perovskites. These results reveal the migration properties of halide vacancies and interstitials in all-inorganic RP perovskites, which would be beneficial for exploring their novel optoelectronic applications.