Solvent engineering for the formation of high-quality perovskite films: a review

Organic-inorganic hybrid perovskite solar cells have made tremendous breakthroughs in device photovoltaic performance, but the solution chemistry features are poorly understood. Herein, the fundamental processes of perovskite crystal crystallization and several templates for crystal growth are described. Then the solvent systems for preparing perovskite thin films are introduced, including pure, binary, and ternary solvents. The interaction of precursor ligand molecules in solution, which is related to the nature of the intermediate phase, is dependent on distinct ligand molecules, including dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), acetonitrile (ACN), urea, etc. The polarity of the solvent determines the degree of binding to Pb2+ and the stability of the complex, which affects the quality of the perovskite films. In solvent engineering research field, strong polar solvents will interact with Pb2+, which leads to the extensive study of perovskite intermediate phases. In this review, several typical intermediate phases are summarized as solvent-induced intermediates, HI intermediates, MA intermediates and MAAc intermediates. The intermediate phases are annealed or antisolvent treated to further form perovskite films, resulting in perovskite films with low defects, high-quality and few pinholes. On this basis, we propose the use of green solvents instead of toxic solvents for the preparation of perovskite thin films by multi-solvent systems, which provides some feasible ideas for further realization of high-performance perovskite solar cells with long-term device stability. Overall, this review seeks to provide a comprehensive and detailed analysis of the most recent advancements in solvent engineering for perovskite film formation, emphasizing its potential to improve the performance and stability of PSCs. In addition, it offers insights into the mechanisms underlying solvent engineering and its influence on film morphology and crystallization.