High Mobility Thiazole-Diketopyrrolopyrrole Copolymer Semiconductors for High Performance Field-Effect Transistors and Photovoltaic Devices

New donor-acceptor copolymers incorporating both a strong electron accepting diketopyrrolopyrrole unit and a weak electron deficient thiazolothiazole or benzobisthiazole moiety were synthesized, characterized, and found to exhibit very high charge carrier mobility. Stille coupling copolymerization gave copolymers having moderate number-average molecular weights of 17.0-18.5 kDa with polydispersities of 3.3-4.0 and optical band gaps of 1.22-1.38 eV. High performance p-channel field-effect transistors were obtained using the thizolothiazole-linked copolymers, PDPTT and PDPTTOx, giving hole mobilities of 0.5 and 1.2 cm(2)/(V s), respectively, with on/off current ratios of 10(5) to 10(6). In contrast, the benzobisthiazole-linked copolymer PDPBT had a substantially lower field-effect mobility of holes (0.005 cm(2)/(V s)) due to its amorphous solid state morphology. Bulk heterojunction solar cells fabricated by using one of the thiazolothiazole-linked copolymer, PDPTT, as electron donor and PC71BM acceptor show a power conversion efficiency of 3.4% under 100 mW/cm(2) AM1.5 irradiation in air.