Effect of the length of a symmetric branched side chain on charge transport in thienoisoindigo-based polymer field-effect transistors

摘要： Compounds consisting of the electron-accepting thienoisoindigo (TIIG) moiety with branched alkyl side chains of various lengths were each copolymerized with thiophenylene vinylene thiophene (TVT) and selenophenylene vinylene selenophene (SVS) donor moieties, to investigate how the length of the side chain between the branch point and backbone affects the microstructure and charge transport of thin films made of these TIIGTVT and TIIGSVS copolymers. All of the organic field-effect devices based on these copolymers exhibited p-type behaviors, and these devices displayed hole mobility values as high as 1.15 cm2/V/s. Interestingly, the longer side chains in both series of TIIGTVT and TIIGSVS copolymers, the more improved was the molecular ordering of the thin films. But the relationship between charge mobility and side chain length differed for these two series of copolymers, a result attributed to differences between the microstructures of their films. The TIIGTVT series showed localized aggregation, with the greater length of the side chain between the branch point and backbone enhancing the charge transport by increasing the quantity and average size of the aggregates. In contrast, the TIIGSVS series showed long-range order, and aggregates that were too large and prevented charge transport.