Degradation mechanism and stability improvement of formamidine-based perovskite solar cells under high humidity conditions

Formamidine (FA)-based perovskite solar cells (PSCs) are promising candidates for photoelectric conversion devices due to their excellent optoelectronic properties. However, the instability of perovskites, especially moisture instability, remains one of the biggest obstacles to the commercialization of perovskite devices. Therefore, it is very important to explore and target the effect of moisture on FA-based perovskites to prevent this effect and improve device stability. Herein, we studied the degradation process of commonly used FA-based perovskite films by X-ray diffraction and scanning electron microscopy characterization and analyzed the reasons for their humidity-induced degradation. Subsequently, we further adopted a strategy by adding methylammonium bromine powder into a PbI2 precursor solution to prepare a seed solution in a two-step preparation process to enhance the performance and stability of FA-based PSCs. Finally, the degradation rate of the obtained perovskite film was significantly slowed down under high humidity compared to that of perovskite films prepared by a two-step method without applying a seed solution. The corresponding device achieved a remarkable power conversion efficiency of 23.22%, and the efficiency of this device showed no attenuation after 900 h of exposure to air.