Two-Dimensional Copolymers Based on an Alkylthionaphthyl-Substituted Benzo[1,2-b:4,5-b′]dithiophene for High-Efficiency Polymer Solar Cells

Two new D–A donor polymers of PBDTNS-DTBO and PBDTNS-DTBT are designed and synthesized with a two-dimensional alkylthionaphthyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTNS) unit. The influence of the BDTNS unit and another modified acceptor unit of benzo-oxadiazole (BO) (or benzo-thiadiazole (BT)) on optical, electrochemical, and photovoltaic properties is primarily studied. A stronger photoresponse with a higher external quantum efficiency is observed in the PBDTNS-DTBO film. As a result, PBDTNS-DTBO with a dialkoxy-substituted BO unit exhibits better photovoltaic properties than PBDTNS-DTBT with a difluorine-substituted BT unit in their solution-processing bulk heterojunction polymer solar cells (PSCs) using [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor. The maximum power conversion efficiency of 8.02% with a short-circuit current density of 13.05 mA/cm2 and a high fill factor of 71.5% is obtained in the PBDTNS-DTBO based devices. Our study indicates that PBDTNS-DTBO is a promising narrow-band photovoltaic polymer for the construction of high-performance PSCs.