Synergistic Buried Interface Engineering via Bisphosphonate-Anchored Co-Self-Assembled Monolayers for High-Performance Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) have emerged as promising materials for interface engineering in invert perovskite solar cells (PSCs). Nevertheless, conventional SAM architectures struggle to simultaneously achieve uniform molecular anchoring and effective defect passivation. To overcome this limitation, we developed a coself-assembled monolayers (Co-SAMs) strategy employing two bisphosphonate-anchored molecules: (indolo[2,3- a ]carbazole-11,12-diylbis(propane-3,1-diyl))bis(phosphonic acid) (3-BPIC) and its fluorine-substituted analogue, ((3,8-difluoroindolo[2,3- a ]carbazole-11,12-diyl)bis(propane-3,1-diyl))bis(phosphonic acid) (3-BPIC-F). This synergistic interfacial architecture overcomes the intrinsic limitations of conventional single-component SAMs by simultaneously integrating effective defect passivation with robust anchoring capability within a unified molecular framework. The bisphosphonate anchoring groups ensure robust interfacial stability through enhanced multidentate anchoring, thereby establishing a highly ordered and uniform buried interface with improved energy level alignment with the perovskite. Specifically, this collaborative arrangement enables the fluorine-substituted groups to stabilize organic cations and passivate halide vacancies, which is beneficial to the high-quality perovskite growth. As a result, the Co-SAMs-based PSCs achieve a power conversion efficiency (PCE) of 26.09%, and unencapsulated devices retain over 95% of their initial performance after 1000 h of long-term stability testing under a nitrogen atmosphere. This work demonstrates a promising Co-SAMs design strategy for developing high-efficiency and durable next-generation photovoltaics.