Fusion Strategy Toward Highly Crystalline Non‐Fullerene Acceptor Enables Simultaneously Enhanced Current and Voltage in Organic Solar Cells

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Organic solar cells (OSCs) offer unique advantages, yet their photovoltaic performance is limited by the challenge of optimizing molecular packing in photoactive materials. While A-D-A'-D-A-type acceptors have improved efficiency by forming favorable 3D network packing, strategies to further enhance crystallinity without causing detrimental over-aggregation are scarce. Herein, we report a distinctive non-fullerene acceptor (NFA) congener, BrTh-2Cl, via a molecular fusion strategy. This design ingeniously integrates a highly crystalline brominated-thiophene unit with a chlorinated phenyl group onto the central core, engineering a highly effective terminal functionality that can effectively modulate molecular packing without over-aggregation. In addition, the blue-shifted absorption of BrTh-2Cl caused by weak electron-withdrawing of thiophene terminal group without malononitrile achieves complementary advantages with light harvest of L8-BO. The incorporation of BrTh-2Cl into a D18-Cl: L8-BO host blend enhances film ordering and electron mobility for higher current, while simultaneously suppressing non-radiative energy loss. Consequently, the adjusted OSC achieves a remarkable power-conversion efficiency (PCE) of 20.82% (certified 20.34%), a significant increase from the 19.03% of the binary device, accompanied by concurrent improvements in both short-circuit current density and open-circuit voltage. This work provides an effective molecular fusion strategy by terminal groups to refine molecular packing and propel the photovoltaic performance of OSCs.

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