In-plane compressive strain stabilized formamidinium-based perovskite

Compressive strain is often considered as a key factor in stabilizing formamidinium (FA)-based perovskites. However, the compression along which direction stabilizes perovskite remains unclear due to the presence of non-uniform strain within the material. Here, we introduce a metal encapsulation method to apply compressive strain along the in-plane or out-of-plane direction of perovskite film. According to the grazing-incidence wide-angle X-ray scattering (GIWAXS) results, in-plane compression enhances the stability of perovskites, whereas out-of-plane compression has a detrimental effect. Specifically, out-of-plane compression can lead to the formation of an inactive δ-phase, which compromises the stability of the perovskite. Finally, we develop a general process to integrate in-plane compression into perovskite solar cell (PSC) devices, thereby improving their stability. Our study clarifies the mechanism by which compressive strain affects perovskite stability, offering valuable guidance for strain engineering to optimize perovskite performance.