19.7% efficiency binary organic solar cells achieved by selective core fluorination of nonfullerene electron acceptors

The development of high-performance binary organic solar cells (OSCs) with a simplified working mechanism and fabrication process is highly desirable to promote the commercial applications of OSCs. Although terminal fluorination has been widely applied to obtain efficient nonfullerene acceptors (NFAs), core fluorination has rarely been explored. Herein, we adopted the structural expandability of quinoxaline and synthesized a series of NFAs, AQx-nF (n = 0–4, representing the number of fluorine atoms on the core) with tunable photoelectric and aggregation properties. AQx-2F not only provides a proper energy offset and crystallinity to balance charge generation and recombination but also exhibits improved dipole moment and 3D network packing for a fibrous morphology with favorable exciton/charge carrier dynamics. These features yield a superior power conversion efficiency (PCE) of 19.7%, which is the highest value for binary OSCs ever reported. Our work highlights the significance of core fluorination, providing insight into the design of more efficient NFAs for higher-performance OSCs.