A comparative study of bithiophene and thienothiophene based polymers for organic field-effect transistor applications

2,2′-Bithiophene and thieno[3,2-b]thiophene were polymerized separately with bis(2,3-dialkylthienyl)benzo[1,2-b:4,5-b’]dithiophene by Stille coupling reactions to afford new conjugated polymer PBDTT-2T and PBDTT-TT. The polymers showed band gaps about 1.90 eV and the highest occupied molecular orbital (HOMO) energy levels below −5.20 eV. The PBDTT-2T and PBDTT-TT achieved hole mobilities of 0.035 and 0.008 cm2 V−1 s−1 in top-contact/bottom-gate organic field-effect transistor devices. The investigation of thin-film microstructures and morphologies showed that PBDTT-2T thin films had more uniform surface and better crystalline quality than PBDTT-TT did.