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

Abstract

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.