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 ), formamidinium lead iodide (FAPbI ), FA Cs PbI , FA Cs PbI , and MAPb Sn I . The critical dose is related to the composition of the OIHPs, with FA Cs PbI having the highest critical dose of ≈84 e Å and FA Cs PbI having the lowest critical dose of ≈4.2 e Å . The electron beam irradiation results in the formation of a superstructure with ordered I and FA vacancies along <110> , as identified from the three major crystal axes in cubic FAPbI , <100> , <110> , and <111> . The intragrain planar defects in FAPbI are stable, while an obvious modification is observed in FA Cs PbI 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.