Cyclopenta[c]thiophene-4,6-dione-Based Copolymers as Organic Photovoltaic Donor Materials

A class of "push-pull" conjugated copolymers based on cyclopenta[c]thiophene-4,6-dione (CTD) and benzodithiophene (BDT) is synthesized for application as an electron donor in organic photovoltaics (OPV). Given the diverse electronic and structural tunability of the CTD unit, specific CTD-containing copolymers are chosen with the aid of theoretical calculations from a broad array of potential candidate materials. Evaluation of the chosen materials as OPV absorbers includes characterization of the optical, electronic, and structural properties of the polymer films using UV-vis absorbance, photoluminescence, cyclic voltammetry, and X-ray diffraction techniques. In addition, the contactless time-resolved microwave conductivity (TRMC) technique is used to measure the photoconductance of polymer/fullerene blends. Excellent correlation between measured photoconductance and OPV device efficiency is demonstrated with these materials and TRMC is discussed as a tool for screening potential active layer materials for OPV devices.