Polymer donor with halogenated-aromatic side chain enables efficient ternary organic solar cells

Ternary strategy has demonstrated great potential in promoting the power conversion efficiency (PCE) of bulk-heterojunction organic solar cells (BHJ OSCs). Two new polymer donors, TPQ-2F-2Cl and TPQ-2F-4F, were synthesized with chlorinated and fluorinated aromatic side chains, respectively, which contributed to distinct noncovalent interactions. Compared with the PM6: L8-BO host system, the TPQ-2F-2Cl based ternary OSCs obtained enhanced exciton dissociation and more balanced carrier mobility. Moreover, benefiting from the favorable miscibility of the PM6: L8-BO: TPQ-2F-2Cl blend, the ternary blending film featured a well-defined fibrillar morphology and improved molecular ordering. Consequently, the optimal PM6: L8-BO:TPQ-2F-2Cl device achieved a more outstanding PCE of 18.2%, a higher open circuit voltage (V_oc), and a better fill factor (FF) in comparison with the binary device (PCE=17.7%). In contrast, the addition of TPQ-2F-4F would generate excessive aggregation of blend, thereby reducing the PCE of ternary OSCs (16.0%). This work shows a promising idea for designing efficient third component donor polymers.