Strategic Structural Modification of Quinoxaline-Based D-A-Type Polymers via Tuning Electron-Withdrawing Substituents for Photovoltaic Applications.

The development of high-performance polymer donors is crucial to advancing polymer solar cell technology. In this study, a set of quinoxaline (Qx)-based D-A-type polymer donors was systematically developed by introducing various electron-withdrawing substituents to tailor their photovoltaic properties. First, a reference polymer, PDBT-QxF, was rationally designed by linking an electron-donating dithienobenzodithiophene (DTBDT) unit and a monofluorinated Qx via a thiophene linker. Subsequently, chlorinated PDBTCl-QxF was synthesized by introducing additional Cl atoms on the thienyl side groups of the DTBDT donor in PDBT-QxF. Next, the F atoms on the Qx units of PDBT-QxF and PDBTCl-QxF were replaced with the stronger electron-withdrawing cyano (CN) group to yield two cyanated polymers, PDBT-QxCN and PDBTCl-QxCN, respectively. Structural modifications via the introduction of Cl atoms and CN moieties into the DTBDT donor and Qx acceptor positively altered the electronic structures of the polymers and enhanced their charge-carrier mobilities, while suppressing charge recombination. Therefore, attributing to the synergistic effects of the Cl and CN substituents, PDBTCl-QxCN exhibited the highest power conversion efficiency of 15.17% among the studied polymers: PDBT-QxF (9.29%), PDBTCl-QxF (12.09%), and PDBT-QxCN (12.66%).