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

Abstract

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.

Dynamic Observations on Formation of Coffee-Ring Structures from the Degradation of Cesium Lead Halide Perovskite Nanocrystals

“…has limited the large-scale applications. − For example, films of organic–inorganic hybrid halide perovskites suffered from both lateral and vertical migration of various ion species driven by light exposure; perovskite solar cells involving a methylammonium lead iodide (MAPbI 3 ) layer experienced severe structural and chemical changes that directly affected their performance . In particular, the rapid structural degradation of halide perovskites under electron beam irradiation has severely impeded the exploration of their structure–property relationships with a range of characterization techniques as well as the practical applications of their devices. − …”

Effect of Air Exposure on Electron-Beam-Induced Degradation of Perovskite Films

“…In addition to the total dose, the decomposition of perovskites is also considered to be sensitive to the dose rate. ,, The same experiments were repeated at a dose rate of 0.82 eÅ –2 s –1 to investigate the impact of low dose rate on the structural changes in MAPbI 3 . Figure S3 shows the time evolution of the rotationally averaged SAED intensity for the two samples, i.e., MAPbI 3 exposed to air for 3 min and not exposed to air.…”

Colloidal synthesis of size-confined CsAgCl2 nanocrystals: implications for electroluminescence applications

“…13,19 Similar results were observed when Pb perovskites were exposed to electronbeam irradiation in TEM measurement, which usually produces metallic Pb atoms. [20][21][22] To gain more accurate information about the element distribution in the NCs, scanning electron microscopy (SEM)-EDS which typically uses lower energy beams was performed. As expected, Cs, Ag, and Cl elements are now shown to be homogeneously distributed along the crystals (Fig.…”