Fluorinated Fullerene Derivatives for Thermally Stable Perovskite Solar Cells

ABSTRACT PCBM (phenyl‐C 61 ‐butyric acid methyl ester) is one of the most used electron transport layers (ETLs) in perovskite solar cells (PSCs). However, PCBM tends to self‐aggregate during the thermal aging process, disrupting film continuity and limiting device lifetime. To address this issue, we synthesized new fluorinated phenyl fullerene derivatives, FPCPB and 5FPCPB, forming a composite fullerene ETL by blending with PCBM. We found that fullerene self‐aggregation was suppressed through the synergistic effects of weak interactions, such as π–π conjugation between phenyl and fluorophenyl groups and C─H···F van der Waals interactions, and the constrained molecular conformation induced by intermolecular steric hindrance, thereby markedly improving film uniformity and thermal stability, reducing defect‐state density, and suppressing ion migration. In addition, the energy level alignment between perovskite and ETL is optimized, enhancing electron transport. Ultimately, 5FPCPB, having more compatible energy levels and stronger conjugation effects than FPCPB, achieved a 26.42% power conversion efficiency (PCE), with improved operational and thermal stability (T 90 under light = 1200 h; T 95 under 85°C > 700 h). The fullerene co‐doping strategy opens a new pathway for achieving high‐performance and thermally stable perovskite devices.