Extrinsic Interstitial Ions in Metal Halide Perovskites: A Review

Perovskite solar cells have rapidly developed as a promising technology for the next generation of low-cost photovoltaics, receiving enormous attention from researchers and industries. Compared to traditional semiconducting materials, metal halide perovskite exhibits outstanding tolerance to extrinsic ions. At a certain range of doping concentration, the interstitial occupancy of extrinsic ions provides appealing benefits to the perovskite films, contributing to higher performance and stability of the devices. This review summarizes the research progress of interstitial ions for metal halide perovskite, providing insights into the mechanism and identification of interstitial doping of extrinsic ions, covering the benefits of interstitial ions in regulating crystal growth, inhibiting ion migration, and reducing defect density. Finally, based on the latest progress and findings, further topics and directions of research on interstitial ions in metal halide perovskite are proposed to advance the understanding of interstitial ions in perovskite and promote the development of perovskite photovoltaic technology.