Crystalline engineering of FAPbI₃ via pyrrolidinium ionic liquid for stable perovskite solar cells with 21.72%...

Improving the crystallinity of formamidinium triiodide (FAPbI₃) perovskite layer is one of the most effective approaches to increase the photovoltaic performance and stability of FAPbI₃-based solar cells (FSCs). In the current study, FAPbI₃ layers were fabricated through a sequential deposition method. The morphology and crystalline properties of the FAPbI₃ layers were modified by controlling the lead iodide (PbI₂) precursor by adding pyrrolidinium (Pyr) material into the PbI₂ layer and modulating the FAPbI₃ crystallization. The Pyr contributed to obtain (001)-preferred FAPbI₃ orientation with no yellow photo-inactive phase. Subsequently, it reduced the unreacted PbI₂ phase in the perovskite layer and suppressed the defect density, resulting in extended carrier lifetimes and improved ambient air and illumination stabilities. The Pyr-mediated FSCs recorded a champion efficiency of 21.72%, which is higher than that of control FSCs with a maximum efficiency of 19.08%. The developed Pyr-mediated method offers a practical and effective approach to fabricate stable and efficient FSCs.