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.