Unveiling the Intrinsic Structure and Intragrain Defects of Organic-Inorganic Hybrid Perovskites by Ultralow Dose Transmission Electron Microscopy.

Transmission electron microscopy (TEM) is a powerful tool for unveiling the structural, compositional, and electronic properties of organic-inorganic hybrid perovskites (OIHPs) at the atomic to micrometer length scales. However, the structural and compositional instability of OIHPs under electron beam radiation results in misunderstandings of the microscopic structure-property-performance relationship in OIHP devices. Here, ultralow dose TEM is utilized to identify the mechanism of the electron-beam-induced changes in OHIPs and clarify the cumulative electron dose thresholds (critical dose) of different commercially interesting state-of-the-art OIHPs, including methylammonium lead iodide (MAPbI 3 ), formamidinium lead iodide (FAPbI 3 ), FA 0.83 Cs 0.17 PbI 3 , FA 0.15 Cs 0.85 PbI 3 , and MAPb 0.5 Sn 0.5 I 3 . The critical dose is related to the composition of the OIHPs, with FA 0.15 Cs 0.85 PbI 3 having the highest critical dose of ≈84 e Å -2 and FA 0.83 Cs 0.17 PbI 3 having the lowest critical dose of ≈4.2 e Å -2 . The electron beam irradiation results in the formation of a superstructure with ordered I and FA vacancies along <110> c , as identified from the three major crystal axes in cubic FAPbI 3 , <100> c , <110> c , and <111> c . The intragrain planar defects in FAPbI 3 are stable, while an obvious modification is observed in FA 0.83 Cs 0.17 PbI 3 under continuous electron beam exposure. This information can serve as a guide for ensuring a reliable understanding of the microstructure of OIHP optoelectronic devices by TEM.