Terminal Phenylation Suppresses Slow‐Drying‐Induced Over‐Aggregation for Efficient Green‐Solvent Printed Organic Solar Modules

ABSTRACT Scalable organic solar modules processed from green, halogen‐free solvents are fundamentally constrained by slow‐drying‐induced over‐aggregation, which disrupts the phase‐separated morphology of the bulk‐heterojunction (BHJ) and amplifies performance losses upon scaling. Here we show that terminal phenylation of the acceptor side chain offers an effective molecular lever to control solubility, crystallization, and assembly under slot‐die coating with high‐boiling‐point solvents (e.g. o ‐XY). Guided by Hansen solubility analysis, we develop the non‐fullerene acceptor (NFA) S7, in which a bulky terminal phenyl group improves solvent/blend compatibility while suppressing excessive aggregation during printing. The resulting PM6:S7 films exhibit a more favorable fibrillar network and improved module performance. Introducing a small amount of Y6‐BO further reinforces π–π interactions and densifies the interconnected morphology, leading to enhanced face‐on organization, longer coherence length, more balanced charge transport, and reduced non‐radiative loss. As a result, ambient slot‐die printed organic solar modules achieve power conversion efficiencies (PCE) of 17.2% at 17.6 cm ² and 15.1% at 268.8 cm ² . This work demonstrates that terminal phenylation is an effective handle for improving printability and morphology control in o ‐XY‐processed OSC modules.