Atomic-Scale Insights into Surface Instability in Halide Perovskites

The pathway of surface structure evolution plays a vital role in determining the stability of the halide perovskites. Understanding the mechanism of surface instability and how external stimuli interact with the surface is essential for developing strategies to mitigate the degradation of halide perovskites. Here, we directly observed structural evolutions on the surface of CsPbBr₃ via an integrated differential phase contrast scanning transmission electron microscope. We find that surface degradation, different from bulk decomposition, follows a layer-by-layer pathway in the CsPbBr₃ perovskite. This layer-by-layer decomposition method further facilitated a coating strategy to mitigate the degradation via preserving the integrity of the surface layer, as verified through in situ methods. Thus, we have achieved the improved stability of perovskites and as-fabricated light-emitting diodes. These findings advance the fundamental understanding on the mechanism of surface instability and effectiveness of coating, thus providing guidance for future study of surface protection toward stable optoelectronic devices.