Biaxially extended thiophene–isoindigo donor–acceptor conjugated polymers for high-performance flexible field-effect transistors

Biaxially extended thiophene–isoindigo donor–acceptor polymers, PIITT4T, PIITT4TSi, PII2T4T, PII2T4TSi, PII2T8T, and PII2T8TSi, were synthesized with different biaxially extended thiophene architectures and isoindigo alkyl chain groups. The electronic characteristics of the studied polymers could be manipulated by the polymer conformations and charge transfer interaction. Thin film morphologies and molecular organizations were explored through atomic force microscopy and grazing incidence X-ray diffraction, demonstrating that the conformational distortion would effectively affect the self-organization ability and packing structures between polymer chains. The averaged charge carrier mobilities of the studied polymer-based field-effect transistors were in the range of 0.001–0.5 cm2 V−1 s−1 with on/off ratios up to 105, relating to the architecture of the polymer skeleton and biaxially extended side chains. More attractive, flexible transistor devices fabricated on the poly(ethylene naphthalate) substrate were integrated using PII2T4TSi as the charge transporting material. Reproducible and reliable electrical characteristics (with a mobility ∼1 cm2 V−1 s−1) of the fabricated flexible device were achieved with the bending curvature of 5 mm, and stable transistor properties were maintained under 1000 bending cycles under ambient atmosphere. The experimental results suggested that the newly designed thiophene–isoindigo polymers could have potential applications in flexible electronic devices.