Metal Halide Perovskites as Mixed Electronic–Ionic Conductors: Challenges and Opportunities—From Hysteresis to Memristivity

Metal halide perovskites are promising candidates for many classes of different optoelectronic devices. Apart from being a semiconductor, they additionally show ionic conductivity. It expresses itself in slow response times, reversible degradation, and hysteresis in the current-voltage characteristics of solar cells. This Perspective gives a condensed overview about experiments and theory on ion migration in metal halide perovskites focusing on its effects in solar cells. Apart from being a potential stability concern for photovoltaics, ion migration paired with the excellent optoelectronic properties of this material offers opportunities for novel devices such as optically controlled memristors and switchable diodes.