Thickness‐Dependent Microstructural Evolution of CsPbBr3 Nanobricks Induced by Electron Beam Irradiation

All‐inorganic halide perovskites exhibit exceptional optical properties and are promising photoactive materials for optoelectronics. However, their stability remains a key challenge, exacerbated by a limited understanding of degradation mechanisms. Herein, in situ transmission electron microscopy (TEM) is used to investigate the effect of thickness on the structural stability of CsPbBr 3 nanobricks under electron beam irradiation. CsPbBr 3 nanobricks with different thicknesses have been prepared using a traditional hot‐injection method, giving rise to a distinctive cubic structure. A modulated structure, caused by bromine vacancy ordering, has been observed in the thin nanobricks. The degradation behaviors of nanobricks are related to thickness‐dependent bromine vacancy formation in the CsPbBr 3 lattice. More bromine vacancies exist in thin nanobricks than thick ones, resulting in a greater number of undercoordinated Pb atoms which accelerate irradiation‐induced degradation. Decomposition products include Pb nanoparticles, which also demonstrate thickness‐dependent characteristics. TEM images of Pb nanoparticles formed from thin nanobricks show evidence of irradiation‐induced amorphization. In thicker nanobricks, Pb nanoparticle size increases with the duration of electron beam irradiation, while the remaining Cs atoms bond with Br atoms to form relatively stable CsBr nanoparticles. These results contribute to understanding of degradation mechanisms in cesium lead halide perovskites under electron beam irradiation.