Fine‐Tuning Active Layer Morphology via Modification of Both Side Chains and Terminal Groups toward High‐Performance Organic Solar Cells

Both the structures and the phase properties of electron acceptors with nonfused aromatic cores (NCAs) have received intensive investigation in very recent years, nevertheless, there remains a large space for manipulating their phase properties through synergistically tuning the side chains and end groups of the NCAs. Herein, four unfused acceptors based on quinoxaline‐core, namely QOD‐4H, QOD‐2Cl, QOS‐4H, and QOS‐2Cl, are designed and synthesized by simple steps, and multiple characterizations are conducted to further explore their blend morphology properties and stacking orientations. Particularly, the alkyl side chains in QOS‐4H and QOS‐2Cl with lower steric hindrance slightly decrease the crystallinity, optical absorption, and tendency toward the face‐on orientation but distinctly cause shorter π–π stacking distance. Meanwhile, two chlorine atoms introduced to the end caps of QOD‐2Cl and QOS‐2Cl produce weaker crystallinity, but with more compact molecular packing, stronger face‐on orientation, and distinctly larger extinction coefficients. As a combinative result, the better nanofibrillar networks and closer molecular stacking are detected in QOD‐2Cl‐ and QOS‐2Cl‐based blends, which lead to a higher efficiency of 10.67% and 12.19%, respectively, of the related devices than those from acceptors QOD‐4H (6.94%) and QOS‐4H (8.01%).