Correlations between Electrochemical Ion Migration and Anomalous Device Behaviors in Perovskite Solar Cells

Ion migration is a solid-state electrochemical phenomenon widely observed in the family of halide perovskite materials, which is attributed to their intrinsically soft ionic crystal structures and mixed electronic–ionic conduction properties. Numerous studies in the literature have indicated that ion migration is the major cause of various anomalous device behaviors, including light-soaking effect, photocurrent–voltage hysteresis, and slow open-circuit voltage decay, which are commonly observed in perovskite solar cells. Herein we present a comprehensive review on these studies. We also provide a mechanistic understanding, featuring the built-in electrical field as a key factor for the elucidation of ion migration and associated device behaviors in a consistent manner. Finally, we discuss future research directions toward a better understanding of these phenomena.