Dual Side Chain Functionalization of Small Molecule Acceptors Affords High‐Performance Organic Solar Cells With Refined Blend Morphology

Abstract Regulating blend morphology in photoactive films is essential for enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs). However, achieving precise control over blend morphology remains a significant challenge due to the difficulty of simultaneously controlling the thermodynamic and kinetic parameters that govern morphology formation. In this study, a series of new small‐molecule acceptors (SMAs) employing a dual side chain functionalization strategy is designed that incorporates trifluoromethyl (CF₃) and phenyl (Ph) groups: SMA‐CH₃, SMA‐CF₃ (with CF₃ group), and SMA‐Ph‐CF₃ (with both CF₃ and phenyl groups). This approach successfully enables delicate tuning of the blend morphology and the development of high‐performance OSCs (PCE = 18.5%). CF₃ functionalization enhances the thermodynamic compatibility of SMAs with the hydrophobic D18 polymer donor, promoting the formation of intermixed donor/acceptor domains and efficient charge generation. Meanwhile, phenyl functionalization improves SMA aggregation and crystallinity, facilitating strong interconnected SMA assembly and efficient charge transport. As a result, binary OSCs based on D18:SMA‐Ph‐CF₃ achieve a significantly higher PCE of 18.5%, compared to 14.3% for D18:SMA‐CH₃ and 16.5% for D18:SMA‐CF₃ OSCs. These results highlight the importance of dual side chain functionalization in optimizing blend morphology and PCE of OSCs.