Dual-Interface Modification with BMIMPF₆ for High-Efficiency and Stable Carbon-Based CsPbI₂Br Perovskite Solar Cells

The interface closely related to carrier transport plays a vital role in high-performance perovskite solar cells (PSCs). In this work, an ionic liquid (IL) 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF6) has been introduced to simultaneously modify the TiO2 and perovskite films, which improves the energy level matching and contact of the TiO2/CsPbI2Br interface as well as provides perovskite films with larger grain size, leading to more faster charge transfer and lower energy loss. Furthermore, the BMIMPF6 modifier passivates the perovskite film defects and reduces defect-induced charge trapping and recombination in CsPbI2Br PSCs. Under dual-interface modification, the open-circuit voltage of the modified device increased to 1.22 V, and the power conversion efficiency (PCE) increased from 10.65 to 13.19%. Moreover, the unencapsulated modified devices exhibit an enhanced stability and maintain 91% of their initial PCE after 60 days of storage. This work has provided a strategy for efficient and stable PSCs by exploiting an IL to optimize the dual-interface at the same time.