Multi-Fluorination of Quinoxaline-Fused-Core-Based Non-Fullerene Acceptors with Modulated Molecular Stacking for...

The quinoxaline (Qx)-fused-core-based small molecular acceptors (SMAs) have garnered significant attention owing to their extremely low energy loss in organic solar cells (OSCs). However, excessive molecular stacking and poor processability limit up-scaling and operational stability. Herein, two novel SMAs, Qx2-D7F and Qx2-D10F, were synthesized by introducing multiple fluorine atoms into the Qx2 core. Theoretical and experimental results demonstrate that fluorine incorporation significantly alters local dipole moments and electrostatic potentials, thereby tuning energy levels and stacking modes. Compared with D18:Qx2 and D18:Qx2-D10F, D18:Qx2-D7F blends exhibit optimal phase separation and balanced charge mobility due to extended film-forming time and moderate donor-acceptor interactions. As a result, D18:Qx2-D7F devices reach a high PCE of 18.12%, with a V_OC of 0.945 V and a low non-radiative loss of 0.197 eV. Ternary D18:L8-BO:Qx2-D7F devices yield 20.25% PCE. Fluorine substitution enhances SMAs processability, achieving 14.61% PCE in 1 cm² large-area slot-die-coated PM6:Qx2-D7F devices, higher than PM6:Qx2 (10.45%). D18:Qx2-D7F devices also exhibit excellent thermal and photostability, with T₈₀ lifetimes over 3500 and 2000 h. These results highlight that precise regulation of donor-acceptor intermolecular interactions with the multi-fluorination strategy enables significant improvements in the morphology and stability of OSCs.