Asymmetric Fluorination of the π‐Bridge in Wide‐Bandgap Small Molecule Acceptors for High‐Voltage Organic Solar Cells

Comprehensive Summary Achieving an open‐circuit voltage ( V OC ) exceeding 1.2 V in organic solar cells (OSCs) often comes at the cost of limited short‐circuit current density ( J SC ) and power conversion efficiency (PCE). Modulating intermolecular interactions to optimize active layer morphology is an effective strategy to balance exciton dissociation and carrier recombination. In this work, we adopt an asymmetric fluorination strategy on A 2 ‐A 1 ‐D‐A 1 ‐A 2 type nonfullerene acceptors (NFAs) by introducing one fluorine atom on the π‐bridge, aiming to tune molecular dipole moments and stacking behavior. The resulting asymmetric acceptor (HF‐BTA3) shows a larger dipole moment than the symmetric BTA3, promoting tighter π‐π stacking and favorable donor‐acceptor interactions. Using classic D18 or PTQ10 as donors, all devices yield V OC above 1.2 V. Notably, HF‐BTA3‐based devices achieve significantly higher PCE (10.18% for D18:HF‐BTA3, V OC = 1.240 V; 10.05% for PTQ10:HF‐BTA3, V OC = 1.271 V) compared to BTA3‐based ones (8.03% and 6.61%, respectively). Our findings demonstrate that asymmetric fluorination is an effective molecular engineering approach for A 2 ‐A 1 ‐D‐A 1 ‐A 2 type NFAs to modulate intermolecular interactions, enabling high V OC (>1.2 V) and PCE over 10%.