Summary: Organic solar cells (OSCs) have developed rapidly in recent years. However, the energy loss (Eloss) remains a major obstacle to further improving the photovoltaic performance. To address this issue, a ternary strategy has been employed to precisely tune the Eloss and boost the efficiency of OSCs. The B‒N-based polymer donor has been proved to process high E(T1) and small ΔEST characters, which can inhibition of CT state recombination. Herin, B‒N-based polymer donor PBNT-BDD was incorporated into the state-of-the-art PM6:L8-BO binary to construct ternary OSCs. Together with the optimal morphology, the ternary device affords an impressive power conversion efficiency of 18.95% with an improved open-circuit voltage (Voc), short-circuit density (Jsc), and reduced Eloss in comparison to the binary ones, which is the highest PCE for B‒N materials-based ternary device. This work broadens the selection of guest materials toward realizing the high performance of OSCs.