New insight into solvent engineering technology from evolution of intermediates via one-step spin-coating approach

The anti-polar solvent technique is an effective way to improve the film quality in a perovskite solar cell. In this work, we reveal the reason why chlorobenzene (CBZ) plays an important role in controlling the crystallization process. By investigating the formation of intermediate phases in the precursor solution, we observed that the CH₃NH₃I (MAI)-PbI₂-dimethylformamide (DMF) or MAI-PbI₂-dimethylsulphoxide (DMSO) adducts have not yet formed until washed with non-polar solvent. The accelerated formation of intermediate phase yields high crystalline perovskite layers. Rapid solvent evaporation and retarded perovskite crystallization in one-step method are efficient to obtain high-quality perovskite films. Consequently, MAI-PbI₂-DMSO intermediate shows neat rod-like structure with high crystallinity, which eventually transforms extremely dense and uniform perovskite films.