Engineering Halide Perovskite Crystals through Precursor Chemistry

The composition, crystallinity, morphology, and trap‐state density of halide perovskite thin films critically depend on the nature of the precursor solution. A fundamental understanding of the liquid‐to‐solid transformation mechanism is thus essential to the fabrication of high‐quality thin films of halide perovskite crystals for applications such as high‐performance photovoltaics and is the topic of this Review. The roles of additives on the evolution of coordination complex species in the precursor solutions and the resulting effect on perovskite crystallization are presented. The influence of colloid characteristics, DMF/DMSO‐free solutions and the degradation of precursor solutions on the formation of perovskite crystals are also discussed. Finally, the general formation mechanism of perovskite thin films from precursor solutions is summarized and some questions for further research are provided. The nature of precursor solutions not only impacts the nucleation rate and crystallization kinetics of perovskite crystals, but also influences the physical properties of perovskite thin films. This Review presents the comprehensive understanding on the nature of perovskite precursor solutions and the formation mechanism of perovskite thin films from these precursor solutions.