Interface-Enriched Fluorinated Covalent Organic Framework Enables Stable, High-Performance n-i-p Perovskite Solar Cells.

Buried interfacial integrity remains a major bottleneck limiting both the efficiency and long-term stability of perovskite solar cells (PSCs). Existing surface-modification strategies often introduce additional interfacial discontinuities, thereby exacerbating rather than alleviating buried-interface vulnerabilities. Here, we report an in situ buried-interface modification strategy that reinforces the SnO₂/perovskite interface using a fully conjugated covalent organic framework (COF) grafted with polyfluoroalkyl side chains. During perovskite crystallization, strong dipolar interactions between the polyfluoroalkyl chains and the SnO₂ drive the COF toward the buried SnO₂/perovskite interface. The COF anchors at the SnO₂/perovskite interface and forms a robust and functionally active interlayer. This dynamic interfacial assembly simultaneously 1) establishes a continuous, graded energy landscape that enhances electronic coupling and accelerates charge extraction; 2) induces facet-selective SnO₂-COF-perovskite interactions that guide the oriented growth of perovskite grains; and 3) suppresses interfacial defects and halide migration, thereby stabilizing carrier transport. Consequently, n-i-p PSCs achieve a power conversion efficiency of 26.24% with a fill factor of 85.4%, and retain 86% of their initial efficiency after 2000 h of continuous operation. By transforming spontaneous molecular self-assembly into a processing advantage, this work establishes a new materials paradigm for achieving high-efficiency, stable, and scalable perovskite photovoltaics.