Medium‐Bandgap Acceptors for Efficient Ternary Organic Solar Cells Achieved by End‐Group Engineering

The ternary strategy has been evidenced as one of the most crucial methods to improve the photovoltaic performance of organic solar cells. However, the selection and design of the third components are decisive factors facilitating the progress of ternary organic solar cells (TOSCs). In this study, focuses are concentrated on the D18‐Cl:N3 binary host device by developing a weakly electron‐withdrawing end group and synthesizing a guest acceptor, BTP‐CM, which holds a similar backbone to N3. The structure resemblance ensures good compatibility of the molecule with N3, which improves charge transport and reduces charge recombination. Thereby, the D18‐Cl:N3:BTP‐CM‐based TOSC exhibits an improved power conversion efficiency to 18.32%, compared to 17.13% of the binary device. This work provides an effective strategy for the design of guest acceptors, which aims to introduce new weakly electron‐withdrawing end groups to obtain molecules with complementary absorptions and matched energy levels while preserving the molecular backbone of the host acceptor.