Enhancing photovoltaic performance through fluorine- and chlorine-substituted quinoxaline polymers in ternary organic solar cells

Ternary blend organic solar cells (TB-OSCs) have emerged as a promising strategy to overcome the intrinsic limitations of binary OSCs by incorporating a third component into the active layer. This approach enables complementary light absorption, improved charge separation, and favorable cascade-like energy-level alignments, which together contribute to enhanced device performance. In this study, two novel halogen-modified quinoxaline-based polymers were synthesized by coupling fluorine- (P1) or chlorine-substituted (P2) quinoxaline acceptors with chlorine-containing thiophene-derived BDT donor units via Stille cross-coupling using a selenophene π-bridge. P1 and P2 exhibited optical bandgaps of 1.76 and 1.90 eV, with HOMO/LUMO levels of −5.67/−3.63 and −5.84/−3.76 eV, respectively. The device exhibiting the highest power conversion efficiency (PCE) was P1:P2:Y6 (1:0.25:1.5) with a VOC of 0.83 V, JSC of 19.14 mA/cm2, FF of 45.02%, PCE of 7.11%. In contrast, the best-performing binary devices, P1:Y6 (1:1.2) and P2:Y6 (1:1.2), delivered PCEs of 5.94% and 1.62%, respectively. Notably, the ternary device achieved a significant improvement in both PCE and JSC compared to its binary counterparts, with PCE increasing from 5.94% to 7.11% and JSC from 16.96 mA/cm2 to 19.14 mA/cm2. These enhancements can be attributed to optimized morphology, more efficient charge transport, and the cascade energy alignment facilitated by the halogen-induced differences between P1 and P2. Overall, this work demonstrates that integrating halogen-substituted quinoxaline-based polymers into ternary blends is an effective approach to fine-tuning energy levels, improving morphology, and boosting photovoltaic performance in OSCs.