Direct Observation of the Inhibition of Phase Segregation by Quaternary Ammonium in Mixed-Halide Perovskite

Due to their tunable bandgaps, mixed-halide perovskites (MHPs), such as CsPbBrxI3–x (0 < x < 1), have excellent prospects for tandem solar cells and wavelength-tunable light-emitting diodes (LEDs). Yet MHPs experience light-induced halide phase segregation (LIHPS) when exposed to light or an electric field, and the origin of this is still under debate. In this work, it was discovered that local electric fields caused by vacancy defects stimulated ion migration under the synergistic influence of strain. These findings were based on the observation that tetrabutylammonium bromide (TBAB) considerably suppresses LIHPS. The significance of minimizing surface defects by ligand passivation was emphasized so as to suppress LIHPS. In years to come, it is anticipated to attain stable mixed-halide perovskites with bandgap tunability under electrical bias or light-induced conditions, which is essential for applications including tandem solar cells and wavelength-tunable LEDs.