Regulating the Electron-Deficient Component in A-DA₁D-A Typed Small-Molecule Acceptors for High-Performance Organic Solar Cells

Fine-tuning of the electron-deficient unit in A-DA(1)D-A typed small-molecule acceptors (SMAs) plays a crucial role in developing efficient SMAs for organic solar cells (OSCs). Here, we developed a SMA based on benzo[4,5]thieno[2,3-b]quinoxaline, designated as QW1, as well as three SMAs based on 1-methylindoline-2,3-dione, identified as QW2, QW3, and QW4. Compared with QW2, QW1 displays slightly blue-shifted absorption spectra and a lower LUMO energy level due to the stronger electron-withdrawing capability of BTQx in contrast to MDO. On the other hand, the introduction of a bromine atom in QW3 and QW4 causes a blue shift in absorption and a reduction in the LUMO energy level compared to QW2. Density functional theory analysis reveals that QW1 exhibits the best molecular planarity, which endows QW1 with larger electron mobility and tighter molecular stacking. Consequently, PM6:QW1 device affords a better efficiency of 15.63% than those of the devices based on QW2 (14.25%), QW3 (13.21%) and QW4 (15.03%). Moreover, the QW4-based device yields the highest open-circuit voltage of 0.933 V, and the PM6:L8-BO:QW4 ternary device realizes a PCE of 19.03%. Overall, our work demonstrates that regulation of electron-deficient central units is an effective strategy to improve the photovoltaic performance of the resulting A-DA(1)D-A SMAs.