In Situ Characterization for Understanding the Degradation in Perovskite Solar Cells

In the past decade, organic–inorganic hybrid perovskite solar cells (PSCs) have made unprecedented progress and recently achieved high efficiency of over 25%, comparable with commercial silicon solar cells. However, PSCs still face poor long‐term stability hindering their commercial application. Because PSCs undergo severe degradation under environmental stress factors, such as moisture, heat, light, and electrical bias. Thus, exploring and evaluating the degradation pathways of perovskites and the degradation mechanisms of PSCs is quite essential. In situ diagnostic techniques can track the real‐time changes of structure, morphology, and optoelectronic properties of the materials in the device during the degradation process. Herein, the progress on in situ characterization for understanding the degradation in PSCs is reviewed, including advanced characterization techniques in the aspects of electron microscopy, X‐Ray, and optoelectronic spectroscopy. Besides, in situ characterization tracking the degradation process of perovskite material films from typical methylamine (MA) perovskite to formamidinium (FA)–cesium (Cs) mixed‐cation perovskite and PSCs dependent on external factors is also discussed. This overview can provide a further understanding of the stability of PSCs and solve the problems on their road to commercialization. Finally, the future perspectives of in situ characterization for understanding the degradation of PSCs are provided at the end of this review.