Enhanced photovoltaic performance of quinoxaline-based donor-acceptor type polymers with monocyano substituent

Abstract

A series of quinoxaline-based polymers with CN group are synthesized to elucidate the effect of strong electron-withdrawing CN groups on the photovoltaic properties of the polymers and to clarify the influence of CN group on the photovoltaic properties of conjugated polymers for manufacturing high-performance polymer solar cells. The reference polymer (PAB-Qx) without CN is prepared by the polymerization between electron-donating benzodithiophene (BDT) and electron-accepting 2,3-diphenylquinoxaline (DPQ) monomer. Subsequently, a CN group is substituted at the 6-position of the DPQ unit of the reference polymer to yield PAB-CNQx. An additional target polymer (PTB-CNQx) is prepared by replacing two 2-ethylhexyloxy groups on the BDT unit in PAB-QxCN with 2-ethylhexyl thiophene side chains. The photovoltaic properties of the polymers are examined by constructing a nonfullerene inverted-type PSCs. Owing to the positive contributions of the strong electron-withdrawing CN group and alkylthienyl side chains, the power conversion efficiencies of the devices are significantly improved in the following order: PAB-Qx (4.35%), PAB-CNQx (8.66%), and PTB-CNQx (13.3%). Therefore, this study confirms the great potential of electron-withdrawing CN groups for developing high-performance quinoxaline-based polymers for photovoltaic applications.