Molecular Peripheral Electronegativity Modulates Crystallization Kinetics for Efficient Organic Solar Cells

Peripheral electronegativity of non-fullerene acceptors, despite its significant potential in modulating intermolecular interactions, remains largely unexplored. Herein, we develop three Y-series acceptors, namely Y-2FPh, Y-Ph, and Y-2OMePh, featuring a gradual transition from electron-deficient to electron-rich periphery. We reveal that the Y-2FPh exhibits accelerated crystallization, compact but relatively limited long-range π-π stacking. Conversely, the Y-2OMePh, functionalized with electron-rich dimethoxyphenyl groups, displays delayed crystallization, promoting long-range molecular ordering and superior charge transport. However, the improved crystallinity of Y-2OMePh exacerbates the aggregation-induced quenching effect, reducing luminescence property and slightly increasing non-radiative energy loss (∆E_nr). As a result, devices employing Y-2FPh, Y-Ph, and Y-2OMePh as acceptors achieve photovoltaic efficiencies of 18.28%, 19.00%, and 18.84%, respectively. Notably, when incorporated as guest components, all three acceptors markedly enhance the performance of the D18:L8-BO reference, with the Y-2OMePh-based ternary device delivering an impressive efficiency of 20.01%. This work establishes peripheral electronegativity as a pivotal handle for finely tuning aggregation and exciton/charge properties toward high-performance solar cells.