Strain‐Modulated Phase Stability in Inorganic Perovskites: Origins, Impacts, and Regulation Strategies

Perovskite solar cells (PSCs) have drawn wide attention for their high power conversion efficiency, facile deposition process, and low cost. Organic‐inorganic hybrid PSCs have reached an astounding power conversion efficiency of >26%, but unfortunately exhibit poor long‐term stability, which severely impeded their commercialization. Inorganic perovskite exhibits excellent thermal stability compared to hybrid perovskite. Among inorganic perovskite, cesium lead triiodide (CsPbI3) is an ideal material for constructing tandem solar cells. However, the spontaneous transition of the black phase to a non‐perovskite phase hinders their reliable application. These phase transitions are largely correlated with the unexpected strain introduced during fabrication and operation. Strain engineering is an ideal method to address this issue, which directly acts on the crystal lattice and has a straight impact on phase stability. In this review, we outline the characterization and impacts of strain in inorganic perovskite and recent breakthroughs in strain engineering. In addition, we point out the challenges and perspectives for future strain engineering.