Remote Modification-Induced Butterfly Effect on Nonfullerene Acceptor Aggregation for Efficient Organic Solar Cells

Organic solar cells (OSCs) possess unique advantages for next-generation photovoltaic applications, yet their power conversion efficiencies (PCE) are still constrained by substantial voltage losses. Simultaneously achieving high luminescence and charge transport properties of nonfullerene acceptors (NFAs) remains a major challenge due to the complex, nonlinear relationship between molecular structure and solid-state packing. In this study, we demonstrate a molecular design concept based on the "butterfly effect" that enables precise control over intermolecular packing in A-DA'D-A-type NFAs through subtle substituent modifications on the remote phenyl ring. Systematic modulation with methoxy, methyl, hydrogen, and fluorine groups reveals distinct packing configurations: methoxy-substituted AQxPO enhances photoluminescence quantum yield (PLQY to 9.96%) via depressed end-bridge (E-B) stacking but disrupts vital charge transport pathways, while fluorine-substituted AQxPF promotes E-B/end-end (E-E) stacking, enhancing carrier transport at the cost of reduced PLQY (4.78%). Notably, the hydrogen-substituted AQxPH optimally suppressing detrimental E-B stacking while maintaining efficient E-E interactions, yielding both high PLQY and superior charge transport. Consequently, the D18:AQxPH-based binary OSC achieves a remarkable PCE of 20.9% with a high V_OC of 0.925 V at an ultralow non-radiative energy loss of 0.176 eV. This work provides a design principle to overcome OSC efficiency bottlenecks through precise stacking control.