Fluorine-functionalization of an isoindoline-1,3-dione-based conjugated polymer for organic solar cells

We report the first synthesis of a difluorinated 4,7-dibromo-2-(2-butyloctyl)-5,6-difluoroisoindoline-1,3-dione (dibromoffIDD) unit flanked with 3-octylthieno[3,2-b]thiophene pi-bridges to form the novel acceptor unit dibromoTTffIDD, which was then polymerized with a donor unit based on benzo[1,2-b: 4,5-b']dithiophene (BDT) to yield the polymer PBDT-TTffIDD for applications in organic solar cells (OSCs). To determine the effects in this system of fluorination on photovoltaic performance, we designed two electron donor-and-acceptor copolymers, difluorinated PBDT-TTffIDD and unfluorinated PBDT-TTIDD, and studied their properties systematically. The maximum power-conversion efficiencies of OSCs based on PBDT-TTffIDD: PC71BM and PBDT-TTIDD:PC71BM were found to be 4.1% and 3.8% respectively.