Decreasing the Molecular Polarity of Naphthalimide by a π-Bridge Strategy as Cathode Interlayers to Enable High-Efficient Electron Transfer in Organic Solar Cells

Naphthalimide-based molecules bridged by selenophene, namely, NSeN, have been reported as cathode interfacial layers (CILs) to establish high-quality interfaces in organic solar cells (OSCs). Various characterizations were carried out to assess the relationship between the molecular polarity, quality of the interlayer, and performance of charge transfer. A continuous and homogeneous film of NSeN achieved a balance between the crystallization and film-forming property and broke through the limitation of high molecular polarity in our previous work. NSeN achieved a relatively low molecular polarity, an aligned work function, and a high electron mobility, thus enhancing the filling factor and short-circuit current density of OSCs. As a result, PM6:Y6-based OSCs with NSeN as the CIL-engineered Al cathode afforded a maximum power conversion efficiency of 15.41%, which is higher than that of control devices based on N-dimethylaminopropyl-4-bromo-1,8-naphthalimide (NA) and perylenediimide functionalized with amino oxide (PDINO). The enhancement is attributed to the outstanding conductivity and suitable molecular polarity of NSeN. This study highlights a π-bridge strategy of molecular design to improve the charge-transfer performance for OSCs.