Reversible Light-Induced Enhancement of Photoluminescence Lifetime and Intensity in Perovskite-Phase CsPbI₃ Nanocrystals

Light-induced changes in photophysical and electronic properties in metal halide perovskites can affect their performance in photovoltaic devices, light-emitting diodes, and other applications. Here we reveal that light induces a slow, reversible enhancement in photoluminescence (PL) lifetime and intensity in films of perovskite-phase CsPbI3 nanocrystals. When films of CsPbI3 nanocrystals stored in air are photoexcited, their PL lifetime and intensity increase by as much as a factor of 5 over the course of 20-30 min. Several hours later, without additional light excitation, the initial PL lifetime and intensity return. Placing the films under vacuum or nitrogen for several minutes was also found to increase the PL lifetime and intensity. We propose a model of slow, humidity-and lightsensitive surface states in perovskite-phase CsPbI3 nanocrystals.