Effects of solvent coordination on perovskite crystallization

Abstract

Halide perovskites are ionic semiconductors with outstanding features, such as high defect tolerance, long carrier diffusion length, strong photoluminescence, narrow emission line width, solution processability, and low cost of fabrication. These advantages render them promising candidates for photovoltaics, lasers, displays, and photodetectors. Theoretical and experimental studies have demonstrated that the optical properties of perovskite materials can be strongly affected by their crystal size and dimension. Owing to their ionic nature and low formation energy, perovskites can be synthesized via precipitation. This process typically involves in situ transformation of the precursors with solvent evaporation and/or solvent mixing. It is well known that the physical/chemical properties of solvents play a vital role in determining the size and dimension of the resultant products. Therefore, elucidating the effects of the solvent on perovskite crystallization is crucial for improving the performance of perovskite-based devices. Moreover, the coordination effects between perovskite precursors and solvents are a dominant parameter that influence the crystallization process because the dissolution of perovskite precursors is strongly correlated with the coordination between the perovskite precursors and solvents. Herein, this minireview summarizes recent research advances in comprehending the perovskite precursor-solvent interactions with a focus on the coordination effects. In particular, we have endeavored to discuss the influence of coordination effects on the formation of polycrystalline thin films, quantum dots, and single crystals. It was found that the formation of perovskite-solvent intermediates in coordinated solvents retard the nucleation and growth of perovskite crystals; this proves beneficial for the fabrication of high-quality micrometer-sized perovskite polycrystalline films. Meanwhile, the preformed intermediates contribute to undesired impurities and defects in single crystals and quantum dots. These insights are exceedingly helpful for the crystallization control of perovskites, thus enabling better device performance and enhanced stability. Finally, the minireview discusses the challenges facing perovskite crystallization, along with a short perspective for future studies.