Origin of Microstrain in FAPbI3 Perovskite and Its Effect on the Stability

Lattice strain is often regarded as an important factor affecting the stability of organic–inorganic hybrid perovskite solar cells, but the current understanding on the origin of the strain is still unclear. Herein, the microstructure of formamidinium perovskite is analyzed by the Rietveld refinement method to reveal the origin of its microstrain. It is found that there is a lattice mismatch between the α‐phase perovskite and the δ‐phase impurity during the fabrication process, which generates strong microstrain in perovskite film. Moreover, the strain also exacerbates the aging process of formamidinium perovskite. By introducing Cs ions, the lattice mismatch of α‐phase and δ‐phase perovskites is reduced, thereby reducing the microstrain of perovskites and improving the device performance.