Low Band Gap Polymers Incorporating a Dicarboxylic Imide-Derived Acceptor Moiety for Efficient Polymer Solar Cells

Abstract

Two novel copolymers incorporating <i>N</i>-alkyl-4,7-di­(thien-2-yl)-2,1,3-benzothiadiazole-5,6-dicarboxylic imide (DI) and benzo­[1,2-b:4,5-b′]­dithiophene (BDT) units have been designed, synthesized, and characterized. By the incorporation of the DI unit, both polymers show a bathochromically shifted absorption with a deep lying highest occupied molecular orbital (HOMO) energy level. The polymer based on thienyl group substituted BDT exhibits an intense absorption in the longer-wavelength region, a deeper lying HOMO energy level, and a higher carrier mobility, all of which contribute to the resulting polymer solar cells with a higher power conversion efficiency (PCE) of 5.19% and an increased <i>V</i>_oc of 0.91 V