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Comprehensive Summary: Fine‐tuning of the electron‐deficient unit in A‐DA1D‐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‐DA1D‐A SMAs. [ABSTRACT FROM AUTHOR]

Utilizing intermolecular hydrogen‐bonding interactions stands for an effective approach in advancing the efficiency and stability of small‐molecule acceptors (SMAs) for polymer solar cells. Herein, we synthesized three SMAs (Qo1, Qo2, and Qo3) using indeno[1,2‐b]quinoxalin‐11‐one (Qox) as the electron‐deficient group, with the incorporation of a methylation strategy. Through crystallographic analysis, it is observed that two Qox‐based methylated acceptors (Qo2 and Qo3) exhibit multiple hydrogen bond‐assisted 3D network transport structures, in contrast to the 2D transport structure observed in gem‐dichlorinated counterpart (Qo4). Notably, Qo2 exhibits multiple and stronger hydrogen‐bonding interactions compared with Qo3. Consequently, PM6 : Qo2 device realizes the highest power conversion efficiency (PCE) of 18.4 %, surpassing the efficiencies of devices based on Qo1 (15.8 %), Qo3 (16.7 %), and Qo4 (2.4 %). This remarkable PCE in PM6 : Qo2 device can be primarily ascribed to the enhanced donor‐acceptor miscibility, more favorable medium structure, and more efficient charge transfer and collection behavior. Moreover, the PM6 : Qo2 device demonstrates exceptional thermal stability, retaining 82.8 % of its initial PCE after undergoing annealing at 65 °C for 250 hours. Our research showcases that precise methylation, particularly targeting the formation of intermolecular hydrogen‐bonding interactions to tune crystal packing patterns, represents a promising strategy in the molecular design of efficient and stable SMAs. [ABSTRACT FROM AUTHOR]

Utilizing intermolecular hydrogen‐bonding interactions stands for an effective approach in advancing the efficiency and stability of small‐molecule acceptors (SMAs) for polymer solar cells. Herein, we synthesized three SMAs (Qo1, Qo2, and Qo3) using indeno[1,2‐b]quinoxalin‐11‐one (Qox) as the electron‐deficient group, with the incorporation of a methylation strategy. Through crystallographic analysis, it is observed that two Qox‐based methylated acceptors (Qo2 and Qo3) exhibit multiple hydrogen bond‐assisted 3D network transport structures, in contrast to the 2D transport structure observed in gem‐dichlorinated counterpart (Qo4). Notably, Qo2 exhibits multiple and stronger hydrogen‐bonding interactions compared with Qo3. Consequently, PM6 : Qo2 device realizes the highest power conversion efficiency (PCE) of 18.4 %, surpassing the efficiencies of devices based on Qo1 (15.8 %), Qo3 (16.7 %), and Qo4 (2.4 %). This remarkable PCE in PM6 : Qo2 device can be primarily ascribed to the enhanced donor‐acceptor miscibility, more favorable medium structure, and more efficient charge transfer and collection behavior. Moreover, the PM6 : Qo2 device demonstrates exceptional thermal stability, retaining 82.8 % of its initial PCE after undergoing annealing at 65 °C for 250 hours. Our research showcases that precise methylation, particularly targeting the formation of intermolecular hydrogen‐bonding interactions to tune crystal packing patterns, represents a promising strategy in the molecular design of efficient and stable SMAs. [ABSTRACT FROM AUTHOR]