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.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Horowitz, G. Organic thin film transistors: From theory to real devices. J. Mater. Res. 19, 1946–1962 (2004).
Chabinyc, M. L. & Salleo, A. Materials requirements and fabrication of active matrix arrays of organic thin-film transistors for displays. Chem. Mater. 16, 4509–4521 (2004).
Katz, H. & Bao, Z. The physical chemistry of organic field-effect transistors. J. Phys. Chem. B 104, 671–678 (2000).
Dimitrakopoulos, C. & Malenfant, P. Organic thin film transistors for large area electronics. Adv. Mater. 14, 99–117 (2002).
Sirringhaus, H. et al. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature 401, 685–688 (1999).
Chang, J. F. et al. Enhanced mobility of poly(3-hexylthiophene) transistors by spin-coating from high-boiling-point solvents. Chem. Mater. 16, 4772–4776 (2004).
Kline, R. J. et al. Dependence of regioregular poly(3-hexylthiophene) film morphology and field-effect mobility on molecular weight. Macromolecules 38, 3312–3319 (2005).
Sirringhaus, H. et al. Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase. Appl. Phys. Lett. 77, 406–408 (2000).
Tanase, C., Blom, P. W. M., De Leeuw, D. M. & Meijer, E. J. Charge carrier density dependence of the hole mobility in poly(p-phenylene vinylene). Phys. Status Solidi A 201, 1236–1245 (2004).
Sirringhaus, H., Tessler, N. & Friend, R. H. Integrated optoelectronic devices based on conjugated polymers. Science 280, 1741–1744 (1998).
Salleo, A., Chabinyc, M., Yang, M. & Street, R. Polymer thin-film transistors with chemically modified dielectric interfaces. Appl. Phys. Lett. 81, 4383–4385 (2002).
Salleo, A. et al. Intrinsic hole mobility and trapping in a regioregular poly(thiophene). Phys. Rev. B 70, 115311 (2004).
Veres, J., Ogier, S., Lloyd, G. & De Leeuw, D. Gate insulators in organic field-effect transistors. Chem. Mater. 16, 4543–4555 (2004).
Wu, Y. et al. Controlled orientation of liquid-crystalline polythiophene semiconductors for high-performance organic thin-film transistors. Appl. Phys. Lett. 86, 1–3 (2005).
Kim, D. H. et al. Enhancement of field-effect mobility due to surface-mediated molecular ordering in regioregular polythiophene thin film transistors. Adv. Mater. 15, 77–82 (2005).
Chabinyc, M. L. et al. Lamination method for the study of interfaces in polymeric thin film transistors. J. Am. Chem. Soc. 126, 13928–13929 (2004).
Chua, L. L. et al. General observation of n-type field-effect behaviour in organic semiconductors. Nature 434, 194–199 (2005).
Rost, H., Ficker, J., Alonso, J. S., Leenders, L. & Mcculloch, L. Air-stable all-polymer field-effect transistors with organic electrodes. Synth. Met. 145, 83–85 (2004).
Park, S. K., Kim, Y. H., Han, J. I., Moon, D. G. & Kim, W. K. High-performance polymer TFTs printed on a plastic substrate. IEEE Trans. Electron Dev. 49, 2008–2015 (2002).
Park, J., Park, S. Y., Shim, S. O., Kang, H. & Lee, H. H. A polymer gate dielectric for high-mobility polymer thin-film transistors and solvent effects. Appl. Phys. Lett. 85, 3283–3285 (2004).
Nickel, B. et al. Dislocation arrangements in pentacene thin films. Phys. Rev. B 70, 125401 (2004).
Kline, R. J., Mcgehee, M. D., Kadnikova, E. N., Liu, J. & Frechet, J. M. J. Controlling the field-effect mobility of regioregular polythiophene by changing the molecular weight. Adv. Mater. 15, 1519–1522 (2003).
Knaapila, M. et al. The influence of the molecular weight on the thermotropic alignment and self-organized structure formation of branched side chain hairy-rod polyfluorene in thin films. Macromolecules 38, 2744–2753 (2005).
Aasmundtveit, K. E. et al. Structural anisotropy of poly(alkylthiophene) films. Macromolecules 33, 3120–3127 (2000).
Winokur, M. J. & Chunwachirasiri, W. Nanoscale structure-property relationships in conjugated polymers: implications for present and future device applications. J. Polym. Sci. B 41, 2630–2648 (2003).
Yang, H. et al. Effect of mesoscale crystalline structure on the field-effect mobility of regioregular poly(3-hexyl thiophene) in thin-film transistors. Adv. Funct. Mater. 15, 671–676 (2005).
Zen, A. et al. Effect of molecular weight and annealing of poly(3-hexylthiophene)s on the performance of organic field-effect transistors. Adv. Funct. Mater. 14, 757–764 (2004).
Lang, P. Surface induced ordering effects in soft condensed matter systems. J. Phys. Condens. Matter 16, R699–R720 (2004).
Brown, G. & Chakrabarti, A. Surface-induced ordering in block copolymer melts. J. Chem. Phys. 101, 3310–3317 (1994).
Gutman, L. & Chakraborty, A. K. Surface-induced ordering for confined random block copolymers. J. Chem. Phys. 101, 10074–10091 (1994).
Factor, B. J., Russell, T. P. & Toney, M. F. Surface-induced ordering of an aromatic polyimide. Phys. Rev. Lett. 66, 1181–1184 (1991).
Munkholm, A., Brennan, S. & Carr, E. C. A comparison of surface roughness as measured by atomic force microscopy and X-ray scattering. J. Appl. Phys. 82, 2944–2953 (1997).
Nefedov, A., Abromeit, A., Morawe, C. & Stierle, A. High-resolution X-ray scattering study of platinum thin films on sapphire. J. Phys. Condens. Matter 10, 717–730 (1998).
Wolfing, B., Theis-Brohl, K., Sutter, C. & Zabel, H. AFM and X-ray studies on the growth and quality of Nb(110) on alpha-Al{sub 2}O{sub 3}(1120) . J. Phys. Condens. Matter 11, 2669–2678 (1999).
Liu, J. S., Sheina, E., Kowalewski, T. & Mccullough, R. D. Tuning the electrical conductivity and self-assembly of regioregular polythiophene by block copolymerization: Nanowire morphologies in new di- and triblock copolymers. Angew. Chem. Int. Edn 41, 329–332 (2002).
Toney, M. F. & Wiesler, D. G. Instrumental effects on measurements of surface X-ray diffraction rods: resolution function and active sample area. Acta Crystallogr. A 49, 624–642 (1993).
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.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Supplementary information
Supplementary figures S1 and S2
Supplementary figures S1 and S2 (PDF 485 kb)
Rights and permissions
About this article
Cite this article
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
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nmat1590
This article is cited by
-
Autopolymerization of 2-bromo-3-methoxythiophene, analysis of reaction products and estimation of polymer structure
Polymer Journal (2021)
-
Supramolecular cocrystals built through redox-triggered ion intercalation in π-conjugated polymers
Communications Materials (2021)
-
Influence of different aligning surfaces on the morphology of dichroic squaraine films
Polymer Bulletin (2021)
-
Evolution in morphology and structure of poly(3-hexylthiophene) blending with liquid crystals under magnetic field treatment
Journal of Polymer Research (2021)
-
Charge carrier transport in thin conjugated polymer films: influence of morphology and polymer/substrate interactions
Colloid and Polymer Science (2021)