Showing papers by "R. Joseph Kline published in 2006"

Liquid-crystalline semiconducting polymers with high charge-carrier mobility.

Abstract: 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 (∼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 cm2 V−1 s−1 achieved under nitrogen.

Highly oriented crystals at the buried interface in polythiophene thin-film transistors

Abstract: Thin films of polymer semiconductors are being intensively investigated for large-area electronics applications such as light-emitting diodes, photovoltaic cells and thin-film transistors. Understanding the relationship between film morphology and charge transport is key to improving the performance of thin-film transistors. Here we use X-ray diffraction rocking curves to provide direct evidence for highly oriented crystals at the critical buried interface between the polymer and the dielectric where the current flows in thin-film transistors. Treating the substrate surface with self-assembled monolayers significantly varies the concentration of these crystals. We show that the polymer morphology at the buried interface can be different from that in the bulk of the thin films, and provide insight into the processes that limit charge transport in polythiophene films. These results are used to build a more complete model of the relationship between chain packing in polymer thin-films and charge transport.

The influence of molecular weight on the microstructure and thin film transistor characteristics of pBTTT polymers.

Abstract: A common strategy to improve the electrical performance of organic field effect transistors is to optimize the charge carrier mobility of the semiconducting thin film. Polymer semiconductor transport properties have shown a dependence on the chain length, due principally to the strong influence of molecular weight on the thin film microstructure. In this work, we report on a study of the influence of increasing molecular weight of poly(2,5-bis(3-docecylthiophen-2-yl)thieno[3,2-b]thiophenes) (pBTTT-C12) on the polymer bulk thermal properties, thin film microstructure and the electrical performance of thin film field effect transistor devices. Clear differences can be observed within a number average molecular weight range of 8,000 - 18,000 Dalton. A Liquid crystalline phase was only observed at the highest molecular weight, different thin film morphology was observed within the molecular weight range, and the field effect mobility was shown to increase with increasing molecular weight.