Piperazine‐Functionalized Arylene Diimides as Electron Transport Layers for High‐Efficiency and Stable Organic Solar Cells

Abstract In organic solar cells (OSCs), electron transport layer (ETL) materials are typically designed with highly polar groups to lower the work function (WF) of the cathode and ensure solvent orthogonality. However, the increased surface energy associated with these polar groups results in significant hygroscopicity and poor interfacial contact with the active layer, posing a challenge for interlayer engineering that must balance device efficiency and stability. Herein, two novel arylene diimides (PDI‐P and NDI‐P) are developed with side chains that are end‐capped with piperazine groups, as opposed to the commonly used amine groups. As ETLs, these materials not only exhibit excellent electron conductivity but also effectively lower the WF of the silver cathode. Compared to the amine‐functionalized perylene diimide (PDI‐N), the piperazine‐functionalized perylene diimide (PDI‐P) exhibits reduced surface energy and hygroscopicity, resulting in improved wettability with the active layer and decreased moisture sensitivity. These characteristics contribute to enhanced interfacial contact and device stability. The PDI‐P ETL is compatible with various high‐performance electron acceptor materials, achieving high efficiencies across a wide thickness range of ≈7 to 30 nm, with a maximum efficiency of 19.8%. These findings highlight the great potential of PDI‐P as an ETL for high‐efficiency and stable OSCs.