Real‐Time In Situ Observation of Microstructural Change in Organometal Halide Perovskite Induced by Thermal Degradation

Abstract Organometal halide perovskites have demonstrated remarkable achievements in solar cell applications and have attracted tremendous attention as next‐generation photovoltaic materials. Regardless of the unprecedented success, the degradation of the perovskite has caused the performance of the perovskite solar cells to be unreliable and prevented their commercialization. However, the detailed degradation mechanism of the perovskite has yet to be elucidated. In this study, the entire procedure of the thermally induced degradation of methylammonium lead iodide (MAPbI 3 ) is reported using real‐time in situ transmission electron microscopy. The in situ investigation directly illustrates the detailed process of precipitating trigonal PbI 2 grains during thermal degradation and confirms that trigonal PbI 2 is precipitated from the amorphized MAPbI 3 layer via intermediate states. The intermediate states and their stackings enable the generation of 3D linear‐empty spaces that can be utilized as passages by elements during the decomposition and intercalation of the perovskite. This report will provide critical clues for the commercialization of the perovskite‐based solar cells and for further investigation of the synthesis of the perovskite, which is not fully understood.