Engineering CsPbI₂Br Perovskite Thin Film Morphology with Ionic Liquid Additives for Enhanced Performance Solar Cells

Ionic liquids (ILs) have emerged as a promising class of additive for modulating perovskite crystallization behavior and thin film morphology. However, the influence of incorporating ILs directly within the cesium lead iodide bromide (CsPbI₂Br) perovskite precursor system is less explored. This work aims to investigate the impact of using various IL additives in the bulk of the CsPbI₂Br perovskite material and how it affects thin film formation. We study the morphology of CsPbI₂Br when incorporated with five different ILs based on the common 1-ethyl-3-methylimidazolium [EMIM]⁺cation, but varying the anion: bis(pentafluoroethylsulfonyl)imide ([EMIM]⁺[PFSI]^-), bis(trifluoromethylsulfonyl)imide ([EMIM]⁺[TFSI]^-), diethyl phosphate ([EMIM]⁺[DEP]^-), dimethyl phosphate ([EMIM]⁺[DMP]^-), and hexafluorophosphate ([EMIM]⁺[PF6]^-). Through characterization of the perovskite films, we found that the morphology of CsPbI₂Br is largely different depending on the choice of IL used. These morphological changes provide insights into how different IL-perovskite interactions affect crystallization and thus thin film quality. The experimental results help in understanding of IL-mediated crystallization, facilitating the development of additive engineering for high-performance perovskite solar cells (PSCs).