Effect of cyano substituent on photovoltaic properties of quinoxaline-based polymers

Abstract

Three donor-acceptor type quinoxaline-based conjugated polymers, in which electron-donating indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) were connected to the electron-accepting 2,3-diphenylquinoxaline (DPQ) derivatives, were synthesized using the Stille coupling reaction. To investigate the effects of the strong electron-withdrawing cyano (CN) substituent on the photovoltaic properties of polymers, it was selectively introduced in the DPQ unit on the polymer backbone. The combination of IDT and the standard DPQ produced the reference polymer IDT-Qx, while the coupling of IDT and IDTT with mono-CN substituted DPQ provided the target polymers IDT-QxCN and IDTT-QxCN, respectively. Owing to the significant contributions of the CN substituent, IDT-QxCN and IDTT-QxCN exhibited better photovoltaic performances than IDT-Qx reference. Furthermore, the presence of more planar two thieno[3,2-b] thiophenes in IDTT than the two thiophenes in IDT allowed IDTT-QxCN to display the highest power conversion efficiency (5.47%) with an open circuit voltage of 0.95V, short-circuit current density of 15.30mAcm−2, and fill factor of 56.95%.