Bis‐Fullerene With Conjugated Bridge as Hybrid Electron Transport Layers for Efficient and Stable Inverted Perovskite Solar Cells

ABSTRACT Enhancing electron extraction and suppressing interfacial recombination are essential for achieving high‐performance inverted perovskite solar cells. However, the commonly used [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM) electron transport layer (ETL) suffers from self‐aggregation during operation and possesses insufficient functional groups for perovskite passivation, which deteriorate charge collection and long‐term stability. Here, two C 60 ‐terminated bis‐fullerene derivatives, namely C 60 ‐IT‐C 60 and C 60 ‐L8BO‐C 60 , are employed to modify the PCBM ETL. These additives preserve high compatibility with PCBM and feature π‐conjugated bridge‐linkers that can regulate the intermolecular interactions with PCBM as well as the interfacial defect passivation toward perovskite. Compared with the IT‐bridged molecule, C 60 ‐L8BO‐C 60 , featuring a more rigid and extended dithienothiophen[3,2‐b]‐pyrrolobenzothiadiazole (TPBT) bridge, enables more extensive π‐conjugated contacts with surrounding PCBM molecules and more effective interfacial passivation, leading to enhanced electron mobility, reduced trap density, and accelerated interfacial electron extraction. As a result, the unencapsulated C 60 ‐L8BO‐C 60 ‐based inverted device achieves a power conversion efficiency of 25.40%, and retains 80% of its initial efficiency after more than 1400 h of continuous thermal aging at 85°C in a N 2 atmosphere in the dark.