New roles of fused-ring electron acceptors in organic solar cells

Abstract

Recently, we developed fused-ring electron acceptors (FREAs) as a class of high-performance nonfullerene acceptors, which have been widely used in organic solar cells (OSCs). Here, we explore new functions of FREAs in addition to being an acceptor in a photoactive layer, and use them as an interfacial layer, which significantly improves the performance of OSCs. Compared with the conventional cathode modifying layers (CMLs) of ZnO and ZnO/polyethylenimine ethoxylated (PEIE), a novel CML of ZnO/FREA/PEIE enhances the optical mode and absorption of the device and suppresses geminate recombination via charge separation, both of which increase the short-circuit current density. In addition, FREAs passivate the surface defects of ZnO and then facilitate electron transport. The OSCs based on ZnO/FREA/PEIE exhibit a power conversion efficiency of 13.04%, higher than those based on ZnO and ZnO/PEIE (12.15% and 12.12%).