Strategic structural evolution for enhancing the photovoltaic performance of quinoxaline-based polymers

Abstract

In this study, strategic structural modifications of quinoxaline-based polymers were performed to improve their photovoltaic properties. First, an indacenodithiophene (IDT) unit was connected to methoxy-substituted quinoxaline via a thiophene linker to produce the reference polymer, PIDT-QxTM. The electron-accepting quinoxaline unit was surrounded by the electron-donating IDT and methoxy group in its horizontal and vertical directions, respectively, creating a beneficial two-dimensional configuration. Subsequently, two promising attempts to position the electron-pulling fluorine atom on the quinoxaline acceptor and replace IDT with a more extended indacenodithieno[3,2-b]thiophene unit were sequentially performed to afford the objective polymers PIDT-FQxTM and PIDTT-FQxTM, respectively. Because of the positive and synergistic effects, the photovoltaic characteristics of the polymers in an inverted-type non-fullerene polymer solar cell gradually enhanced in the order of PIDT-QxTM, PIDT-FQxTM, and PIDTT-FQxTM, with power conversion efficiencies of 6.50%, 7.82%, and 8.51%, respectively. The best performance from the device with PIDTT-FQxTM is primarily ascribed to the superior short-circuit current density to that of the others.