Organic semiconductors that can be fabricated by simple processing techniques and possess excellent electrical performance, are key requirements in the progress of organic electronics. Both high semiconductor charge-carrier mobility, optimized through understanding and control of the semiconductor microstructure, and stability of the semiconductor to ambient electrochemical oxidative processes are required. We report on new semiconducting liquid-crystalline thieno[3,2-b ]thiophene polymers, the enhancement in charge-carrier mobility achieved through highly organized morphology from processing in the mesophase, and the effects of exposure to both ambient and low-humidity air on the performance of transistor devices. Relatively large crystalline domain sizes on the length scale of lithographically accessible channel lengths ( approximately 200 nm) were exhibited in thin films, thus offering the potential for fabrication of single-crystal polymer transistors. Good transistor stability under static storage and operation in a low-humidity air environment was demonstrated, with charge-carrier field-effect mobilities of 0.2-0.6 cm(2) V(-1) s(-1) achieved under nitrogen.

The synthesis of regioregular poly(3-hexyl)selenophene is reported, and its optical and electrical properties are compared to those of regioregular poly(3-hexyl)thiophene.

This work describes a new design methodology that allows the preparation of air stable, semiconducting thiophene polymers with high charge carrier mobilities. The incorporation of thieno[2,3-b]thiophene into a polythiophene backbone introduces cross-conjugated double bonds that disfavor full delocalization, leading to high ionization potential in comparison to a fully conjugated polythiophene, with no reduction in charge carrier mobility. The resulting solution processable polymers exhibit charge carrier mobilities up to 0.15 cm2/V s and on/off ratios greater than 105 when measured in air. Transistors exhibit lifetimes of several months in air with no encapsulation necessary.

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A series of thiophene oligomers bearing core phenylene and fluorinated phenylene units has been synthesized as potential semiconductor materials for organic field-effect transistors (OFETs). Polymerization of these compounds has been achieved using Stille and oxidative coupling methods. Functionalization of the phenylene unit with fluorine atoms has a marked effect on the self-assembly and electronic properties of the parent materials:  the optical band gaps and highest occupied molecular orbital levels are affected with the introduction of fluorine atoms as a result of a combination of inductive effects and rigidification of the main chain. The design of these materials has focused on the self-assembly and solution processability of the materials. All the polymers are readily soluble in common organic solvents. Self-assembly and planarization of the fluorinated materials in the solid state are identified by a combination of X-ray diffraction studies, absorption spectroscopy, and cyclic voltammetry. The organizational behavior of the films is in contrast to the conformational freedom observed in solution (absorption spectroscopy) and in the gas phase (computational studies). Thin-film OFETs have been fabricated for the entire polymer series. Hole mobilities have been measured up to 10-3 cm2/(V·s), with high current modulation (on/off ratios up to 105) and low turn-on voltages (down to 2 V). For the Stille coupled polymers, replacement of the bridging thiophene unit with selenophene generally increases the hole mobility of the polymers.