Crystallization dynamics and stabilization of FAPbI3 single-phase perovskite

The fundamental ABX(3) 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") FAPbI(3). 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 FAPbI(3) perovskite by investigating the [PbX6](4-) template and associated A-cations. Specifically, the addition of MACl is shown to facilitate the crystallization of FAPbI(3) without changing the [PbI6](4-) skeleton. On the other hand, MABr acts as a passivation agent for the film, resulting in stable FAPbI(3) films with a pure black phase when exposed to air with a humidity of 45%.