New Thienothiadiazole-Based Conjugated Copolymers for Electronics and Optoelectronics

Abstract

Four new donor–acceptor conjugated copolymers incorporating thieno[3,4-c][1,2,5]thiadiazole as the acceptor moiety and various electron donor moieties were synthesized and their electronic structures and properties were investigated. The new thienothiadiazole copolymers obtained by Stille coupling polymerizations had weight-average molecular weights of 10–46 kDa. Their broad absorption bands and optical band gaps of 0.9–1.2 eV demonstrate strong intramolecular charge transfer and potential for extending light harvesting deep into the near-infrared. The HOMO/LUMO energy levels were 4.9–5.1/3.4–3.6 eV (below vacuum). As p-channel semiconductors in field-effect transistors, the thienothiadiazole copolymers had a carrier mobility of up to 4.6 × 10–3 cm2/(Vs). Bulk heterojunction solar cells made from blends of the thienothiadiazole copolymers with fullerenes gave a photovoltaic efficiency of 0.4%.