In recent years, the ternary strategy has been proven to be an effective way to improve the performance of organic solar cells (OSCs). Herein, an asymmetric medium-band gap non-fullerene acceptor (AFIC) is synthesized and added as the third component into the PM6:BTP-eC9 binary blend for a highly efficient ternary OSC. AFIC exhibits a well-complementary absorption spectrum with the host binary blend, which benefits light harvesting of the active layer. Furthermore, AFIC shows a large dipole moment and good miscibility with BTP-eC9, which facilitates the formation of a stable well-mixed phase and enhances molecular packing in the blend, leading to improved charge transport and suppressed charge recombination in ternary devices. As a result, the ternary OSC based on PM6:BTP-eC9:AFIC demonstrates a significantly improved power conversion efficiency (PCE) of 18.7% while the binary OSC based on PM6:BTP-eC9 shows a PCE of 17.5%, which is attributed to the synergistic enhancement of the open-circuit voltage (V_oc), short-circuit current density (J_sc), and fill factor (FF).