Asymmetric non-fused ring acceptor with low energy loss for efficient organic solar cells

Non-fused ring acceptors (NFRA) show high structural diversity with low synthesis complexities and high costeffectiveness, which holds the potential to boost the performance of organic solar cells (OSCs). For OSCs, it is crucial to broaden the absorption range while minimizing energy loss. One strategy involves creating acceptors with asymmetric structures. However, to date, there have been relatively few reports on NFRA with asymmetric backbones. Here, we designed a new NFRA molecule UF-ATT-2F with asymmetric pi-bridges (thieno [3,2-b] thiophene and thiophene) and studied its performance in OSC. Compared with two symmetric reference molecules UF-T-2F and UF-TT-2F, the device based on the asymmetric acceptor UF-ATT-2F exhibits much lower energy loss, more appropriate phase separation scale and broader absorption range, consequently achieving a higher open-circuit voltage ( V oc ) exceeding 0.9 V and a decent PCE of 13.26 %. This work demonstrates that incorporating asymmetric pi-bridge is an effective strategy for the design low-energy loss and high-performance organic photovoltaic acceptor.