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

Nature Materials volume 5, pages 222–228 (2006)Cite this article

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.

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Figure 1: Effect of surface treatment on the charge transport of polymer films with various molecular weights.
Figure 2: Effect of substrate and annealing on in-plane packing.
Figure 3: Specular diffraction of the 〈100〉 peak.
Figure 4: Rocking-curve measurements on the (100) peaks and resulting crystal orientations.
Figure 5: Specular diffraction and rocking curve of the 〈100〉 peak for various film thicknesses with low molecular weight.
Figure 6: Schematic of possible packing arrangements of crystals at the buried interface of films with low molecular weight.

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Acknowledgements

We acknowledge M. Chabinyc for assistance in OTS deposition, J. Fréchet for providing the polymers and B. Clemens for discussion on the rocking curves. Financial support was provided by National Science Foundation MRSEC Program (award number DMR-0213618), the Department of Energy and Xerox Corporation. Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences.

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Authors and Affiliations

  1. Department of Materials Science and Engineering, Stanford University, Stanford, California, 94305, USA

    R. Joseph Kline & Michael D. McGehee

  2. Stanford Synchrotron Radiation Laboratory, Menlo Park, California, 94025, USA

    Michael F. Toney

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  1. R. Joseph Kline
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Correspondence to Michael D. McGehee.

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Joseph Kline, R., McGehee, M. & Toney, M. Highly oriented crystals at the buried interface in polythiophene thin-film transistors. Nature Mater 5, 222–228 (2006). https://doi.org/10.1038/nmat1590

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