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 thiazolothiazole-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 PC 71 BM acceptor show a power conversion efficiency of 3.4% under 100 mW/cm 2 AM1.5 irradiation in air.