Random Copolymer Acceptors for Efficient Small-Molecule Donor/Polymer Acceptor Organic Solar Cells

Abstract

Small-molecule donor/polymer acceptor (SD/PA) organic solar cells (OSCs) are attractive for their morphological stability, yet their efficiencies still lag behind those of mainstream systems. One key difficulty is that the acceptor must aggregate strongly enough to form ordered electron-transport domains while remaining miscible enough with the crystalline donor to avoid oversized phase separation. Here, we address this issue by randomly copolymerizing two Y-series acceptor units bearing alkoxy and alkyl side chains, which affords four PAs, namely PY-O, PY-22, PY-13, and PY-C. Varying the copolymer composition tunes optoelectronic properties, aggregation strength, and miscibility with the SD BTR-Cl. Among the four acceptors, PY-13 combines relatively strong and ordered molecular packing with the best compatibility with BTR-Cl, leading to finer nanoscale phase separation and reduced charge recombination. The BTR-Cl:PY-13 device delivers a power conversion efficiency of 10.39% with an open-circuit voltage of 0.99 V. These results indicate that random copolymerization is an effective approach to balancing PA aggregation with donor–acceptor compatibility in SD/PA OSCs.