Unraveling Cross‐Scale Fluorination Mechanisms in Non‐Fullerene Acceptors for High‐Efficiency Organic Photovoltaics

Abstract While fluorination strategy has advanced non‐fullerene acceptor (NFA) development, current structure–property correlations remain largely empirical, lacking mechanistic bridges across molecular, mesoscopic, and device scales. Through multiscale analysis of Y‐series molecules with and without fluorine atoms, a comprehensive understanding of fluorine‐induced optoelectronic enhancement spanning quantum, morphology, and device scales is established for the first time. Take Y5 and Y6 for instance, first‐principles calculations demonstrate that Y6's fluorination‐induced π‐conjugation compaction simultaneously suppresses vibrational relaxation, amplifying exciton dissociation driving forces. Molecular dynamics simulations reveal the enhanced coplanarity of Y6 lowers reorganization energy while boosting intermolecular transfer integrals, synergistically enabling superior charge transport. Crucially, in situ analysis uncovers PM6/Y6 systems undergo crystallization‐induced phase separation kinetics with accelerated nucleation rates and prolonged crystal growth, ultimately forming 3D percolation networks with optimal domain sizes and improved crystalline matching degree. These advantages culminate in balanced charge transport and efficient exciton dissociation, achieving dramatic PCE enhancement from 8.23% to 18.12%. Critically, the fluorination strategy demonstrates universal applicability, validated by 4.3‐fold efficiency gains in PM6/Y18 (fluorinated, 18.51%) versus PM6/Y16 (non‐fluorinated, 4.31%), and consistent high‐performance across PM6/Y6‐BO (18.05%), PM6/N3 (18.24%), and PM6/L8‐BO (19.20%) fluorinated systems. This work provides a hierarchical design framework for rational molecular engineering of high‐performance OPVs.