Asymmetric acceptors with fluorinated and chlorinated end-groups enable organic solar cells with almost 19% efficiency and high thickness tolerance

Abstract

Asymmetric non-fullerene acceptors (NFAs) play crucial roles in improving the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, monophenyl derivative-substituted quinoxaline served as the central core to construct asymmetric acceptors named L36 and L37, which were differentiated from the F-/Cl-substituted terminal. Compared with chlorinated L37, fluorinated L36 exhibited broader absorption, upshifted energy levels, closer intermolecular π–π stacking, and favorable fibrous phase-separation morphology beneficial to exciton generation and charge transport. Consequently, L36-based binary devices exhibited a high PCE of 17.74%, which could be further improved to 18.94% via ternary devices optimization. Moreover, benefiting from the improved charge transport and collection, the ternary OSC with a thickness of 500 nm exhibited an impressive PCE of 15.67%, which was one of the highest values exhibited by high-efficiency thick-film OSCs. This work illustrates the importance of synergetic design principles of central symmetry-breaking and end group manipulation for boosting the photovoltaic performance of OSCs.