Ferrocene‐Terminated Perylene Diimide‐Based Small Molecular Electrolyte as Electron‐Transport Layer for Efficient Organic Solar Cells

The electron‐transport layer (ETL) is essential for achieving high performance and stability of organic solar cells (OSCs). However, most organic ETLs suffer from low conductivity, low electron mobility, and difficult modification, resulting in mitigation of charge collection and transport. Metal–organic complex, such as ferrocene, is a promising candidate to improve organic ETL due to their excellent film‐forming property, easy preparation, and high electrical properties. Herein, a small molecule, PDIN‐Fc, based on PDIN modified by ferrocene is designed, which can be synthesized by environmentally friendly esterification and quaternization reactions. PDIN‐Fc displays outstanding alcohol solubility and tunable work function. Interestingly, introducing the ferrocene group can lead to increased self‐doping of PDIN‐Fc. As a result, PDIN‐Fc shows significantly improved charge transport performance and conductivity compared to PDIN. When using PM6:L8‐BO as the photoactive layer, the OSCs with PDIN‐Fc as ETL achieve a remarkable power conversion efficiency of 18.45% and exhibit notable high light stability. This study demonstrates an effective strategy to design efficient ETLs by incorporating metal complexes, which enable thickness insensitivity, good stability, and high‐performance photovoltaic devices.