Continuous Side‐Chain Heteroatom Engineering of Quinoxaline‐Based Acceptors for Efficient Binary Organic Solar Cells

Comprehensive Summary This work presents a continuous side‐chain engineering strategy to precisely regulate molecular packing and interfacial compatibility in quinoxaline‐based small‐molecule acceptors (SMAs). By stepwise evolution of the side chain from methyl (D1) to methoxy (D2) and ultimately to trifluoromethoxy (D3), the electronic character and polarity of the substituent are systematically tuned while maintaining the integrity of the conjugated backbone. In particular, the trifluoromethoxy group simultaneously integrates the electron‐donating effect of oxygen and the strong electronegativity of fluorine, enabling the formation of multiple non‐covalent interactions, which collectively direct molecular packing and aggregation behavior. As a result, the D18:D3 blend exhibits optimized donor–acceptor miscibility, efficient exciton dissociation, enhanced charge transport, and suppressed recombination, as evidenced by pronounced photoluminescence quenching, reduced trap‐state density, prolonged carrier lifetime, and improved molecular ordering. Benefiting from these synergistic effects, the D18:D3 device achieves a high power conversion efficiency of 19.31%, accompanied by a high fill factor of 78.8%. This study demonstrates that integrating oxygen‐ and fluorine‐containing functionalities within a single side‐chain substituent offers an effective pathway to simultaneously optimize morphology, charge dynamics, and device performance, providing a versatile design paradigm for high‐efficiency acceptors.