High Mobility Thiazole–Diketopyrrolopyrrole
Copolymer Semiconductors for High Performance Field-Effect Transistors
and Photovoltaic Devices
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Abstract
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<sup>2</sup>/(V s), respectively, with on/off current ratios of
10<sup>5</sup> to 10<sup>6</sup>. In contrast, the benzobisthiazole-linked
copolymer PDPBT had a substantially lower field-effect mobility of
holes (0.005 cm<sup>2</sup>/(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<sub>71</sub>BM acceptor show a power conversion efficiency
of 3.4% under 100 mW/cm<sup>2</sup> AM1.5 irradiation in air