Probing the Electron Beam-Induced Structural Evolution of Halide Perovskite Thin Films by Scanning Transmission Electron Microscopy

A deep understanding of the fine structure at the atomic scale of halide perovskite materials has been limited by their sensitivity to the electron beam that is widely used for structural characterization. The sensitivity of a γ-CsPbIBr 2 perovskite thin film under electron beam irradiation is revealed by scanning transmission electron microscopy (STEM) through a universal large-range electron dose measurement, which is based on discrete single-electron events in the STEM mode. Our research indicates that the γ-CsPbIBr 2 thin film undergoes structural changes with increasing electron overall dose (e – ·Å –2 ) rather than dose rate (e – ·Å –2 ·s –1 ), which suggests that overall dose is the key operative parameter. The electron beam-induced structural evolution of γ-CsPbIBr 2 is monitored by fine control of the electron beam dose, together with the analysis of high-resolution (S)TEM, diffraction, and energy-dispersive X-ray spectroscopy. Our results show that the γ-CsPbIBr 2 phase first forms an intermediate phase [e.g., CsPb (1– x ) (IBr) (3– y ) ] with a superstructure of ordered vacancies in the pristine unit cell, while a fraction of Pb 2+ is reduced to Pb 0 . As the electron dose increases, Pb nanoparticles precipitate, while the remaining framework forms the Cs 2 IBr phase, accompanied by some amorphization. This work provides guidelines to minimize electron beam irradiation artifacts for atomic-resolution imaging on CsPbIBr 2 thin films.