Homogenized Phosphonate‐Functionalized Fullerenes for Enhanced Electron Extraction in Perovskite Solar Cells

Abstract Pristine fullerene C 60 has been widely applied as an electron extractor in state‐of‐the‐art perovskite solar cells (PSCs); however, its poor solubility, arising from its strong tendency to aggregate in solution, limits its applicability. In parallel, the weak perovskite–C 60 interaction may induce interfacial energy losses, thereby degrading device performance. To address these limitations, two novel phosphonate‐functionalized fullerene electron derivatives are designed and synthesized and incorporated them into PSCs through the anti‐solvent process. Phosphonate groups offer the C 60 cage a higher solubility and enhance the perovskite–C 60 interaction. By tuning the terminal alkyl chains, a homogenized fullerene‐based electron extracting layer (EEL) on the perovskite surface is successfully fabricated, achieving a power conversion efficiency (PCE) of 25.62% and substantially enhanced operational stability (maintaining 91.7% of its initial PCE after continuous light soaking for 1000 h). Moreover, the structure–property–performance relationships of the fullerenes are comprehensively analyzed, highlighting the pivotal role of a homogenized EEL in concurrently enhancing both the PCE and stability of the PSCs.