Revealing the impact of ammonium ions from different low-dimensional perovskite structures on the film formation and degradation mechanism of FAPbI3 via sequential deposition

In recent years, the organic–inorganic hybrid perovskite community has been widely employed as the photo-active layer in optical-electronic devices. The black α-phase formamidinium lead iodide (FAPbI3) is the most popular perovskite for realizing high-efficiency solar cells due to its suitable bandgap. However, the issue of stability is also a concern in the research on FAPbI3 solar cells. In this study, different ammonium ions, such as butylamine (BA), guanidine (GA), and butylene diamine (BDA), which are commonly used to construct two-dimensional perovskites, including Ruddlesden–Popper, Dion–Jacobson, and alternating cations in the interlayer space, respectively, were introduced in the fabrication of FAPbI3 using a sequential deposition method. Several structures of PbI2 precursor films were formed by introducing the aforementioned ions, which exhibited different arrangements and connection modes in lead iodides. BA-PbI2 precursor films exhibited higher specific surface areas, which were beneficial to the diffusion, ion exchange, and sequential reaction of FA+. The BDA-PbI2 precursor film slowed down the sequential reaction of FAPbI3 because of reduced van der Waals bonds. The nucleation dynamics and degradation processes of perovskites were deeply investigated in this study. Solar cells based on BA-PbI2, GA-PbI2, and BDA-PbI2 were also fabricated.