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.