Strategy for Crystallization Management of Perovskite: Incorporation of FAI in a PbI₂ Precursor for a Two-Step Spin-Coating Process

FAMACs triple-cation perovskite is an excellent organic–inorganic perovskite material widely used in solar cells, light-emitting diodes (LEDs), and other optoelectronic devices. This work proposes a crystallization management strategy by adding formamidinium iodide (FAI) to PbI2 precursor in a two-step spin-coating process for FAMACs perovskite solar cells and obtains the best PCE of 22.88%. Nonstoichiometric FAI interacts with PbI2 to form FAI-PbI2 low-dimensional perovskites, which is demonstrated using X-ray diffraction (XRD), UV–vis, and X-ray photoelectron spectroscopy (XPS) measurements. The efficiency and stability of the cells are improved due to the improvement in the perovskite crystal quality and reduced crystal defects.