Low‐Cost Pentacyclic Nonfullerene Acceptors to Exceed 13% Efficiency by Thermal Annealing‐Free Treatment

Nonfullerene electron acceptors (NFAs) improve the photoelectrical conversion efficiency of organic solar cells (OSCs), but they suffer from high synthetic cost and time‐consuming thermal annealing treatment. Nevertheless, low‐cost NFAs and simple device fabrication are still crucial issues to boosting the commercial application of OSCs. Herein, one kind of low‐cost pentacyclic NFAs based on benzothiadiazole and thiophene derivatives named L1‐EH and L1‐BO with different substitutions is successfully synthesized and characterized. The optimized OSCs based on PM6:L1‐BO (2‐butyloctyl side chain) display an outstanding power conversion efficiency of 13.15%. Moreover, OSC devices based on these acceptors operate in thermal annealing‐free conditions. Further studies manifest that the proper side chains in NFAs can induce more favorable face‐on molecule orientation, enhance carrier mobility, balance charge transport, and reduce recombination losses. This research demonstrates that these types of low‐cost NFAs are promising active layer candidates of high‐efficiency organic solar cells featuring simple device manufacture.