Crystallization dynamics and stabilization of FAPbI₃ single-phase perovskite

The fundamental ABX₃ structure of metal-halide perovskites is crucial for maintaining the crystal lattice stability and also enables exceptional optoelectronic properties. One main goal of the research community is to produce phase-stable (“black phase”) FAPbI₃. Here, we used the LaMer model and an in situ optical microscope to investigate the perovskite crystallization process. We aim to develop a stable (black) single-phase FAPbI₃ perovskite by investigating the [PbX₆]⁴⁻ template and associated A-cations. Specifically, the addition of MACl is shown to facilitate the crystallization of FAPbI₃ without changing the [PbI₆]⁴⁻ skeleton. On the other hand, MABr acts as a passivation agent for the film, resulting in stable FAPbI₃ films with a pure black phase when exposed to air with a humidity of 45%.