Enhancing power conversion efficiency in organic solar cells via rational end-group engineering of non-fullerene acceptors

End-group engineering plays a critical role in tuning the electronic properties of non-fullerene small-molecule acceptors for organic solar cells (OSCs). In this work, two acceptors (BTP-BO and BTP-BS) were designed using oxygen- and sulfur-substituted barbituric acid derivatives to investigate the effects of end-group modification. Compared to BTP-BO, BTP-BS exhibited stronger intramolecular charge transfer, broader absorption, deeper HOMO/LUMO levels, and a higher dipole moment. As a result, the power conversion efficiency of the BTP-BS-based OSC is improved to 4.90%, compared to 4.07% for BTP-BO. These findings highlight that rational end-group modification can significantly improve charge transport and device performance, offering guidance for developing efficient non-fullerene acceptors.