Ion Migration in Metal Halide Perovskites: Characterization Protocols and Physicochemical Mechanisms.

Metal halide perovskites (MHPs) have demonstrated considerable promise for a range of photoelectronic applications owing to their prominent photophysical properties. However, MHPs suffer from remarkable ion migration under illumination and bias voltage, which generally poses operational instability of MHP-based devices and restricts their practicality. While numerous chemical strategies have been proposed for manipulating ion migration dynamics, the relevant mechanistic research relatively lags behind, which is nevertheless imperative for guiding ion migration engineering. In this perspective, we first review the well-established experimental techniques for characterizing ion migration in MHP films and photovoltaic devices. For the sake of gaining insights into the underlying mechanism, we also present a series of physical models that elucidate the dynamics of ion migration and the coupling interaction between ions and charge carriers in MHP photovoltaics. Finally, we identify several crucial areas for future investigation, with the aim of advancing both the fundamental and applied research on high-efficiency and high-stability MHP materials and devices.