Novel copolymers incorporating dithieno[3,2-b:2′,3′-d]thiophene moieties for air-stable and high performance organic field-effect transistors

A series of semiconducting copolymers incorporating dithieno[3,2-b:2′,3′-d]thiophene moieties in the polythiophene backbone were synthesized. The resulting four copolymers are found to have large band gap (∼ 2.5 eV) and large ionization potential (−5.1 eV). Organic field-effect transistors were fabricated by spin-coating polymer solutions onto OTS-modified SiO2/Si substrates with top-contact configuration. The best resulting hole mobility afforded was 0.028 cm2V−1 s−1 with an on/off ratio of 2 × 104 and a threshold voltage of about −18.9 V in the saturation regime. Furthermore, all the devices exhibited high environmental stability against oxygen doping and relatively high ambient humidity (∼30%).