Dual Modification Strategy of Ionic Liquid for Durable Perovskite Photovoltaics

The inverted perovskite solar cell (PSC), featuring self-assembled monolayers (SAMs) as the hole transport layer, has achieved a power conversion efficiency (PCE) exceeding 27%. However, the non-uniformity of SAMs and intrinsic defects within the perovskite film continue to constrain further enhancements in device performance. Herein, we developed a strategy for the synchronous modification of SAMs and perovskite by incorporating an ionic liquid of 1-butyl-3-methylimidazole-hexafluorophosphate (BM) to enhance the uniformity of SAMs and passivate defects in perovskite. Specifically, BM was incorporated into the perovskite precursor solution to effectively occupy halide vacancies and passivate the uncoordinated Pb²⁺. Meanwhile, owing to its ionic properties and the interaction between its functional groups and SAM, BM can effectively regulate the colloidal properties and reduce surface roughness, achieving a more uniform SAM layer. By employing this dual modification strategy, BM significantly modulates the crystallization kinetics, thereby facilitating the formation of highly crystalline perovskite films characterized by substantially enlarged grain sizes and a markedly reduced defect density. Consequently, the device incorporating dual modification of BM achieved a champion PCE of 26.59%, demonstrating exceptional operational stability with no observable PCE degradation after continuous power output at maximum power point (MPP) for 1000 h.