Full Paper

Surface-Directed Phase Separation of Conjugated Polymer Blends for Efficient Light-Emitting Diodes†

  1. Keng-Hoong Yim3,
  2. Zijian Zheng1,2,
  3. Richard H. Friend3,
  4. Wilhelm T. S. Huck1,2,*,
  5. Ji-Seon Kim3,4,*

Article first published online: 9 SEP 2008

DOI: 10.1002/adfm.200800287

Issue

Advanced Functional Materials

Advanced Functional Materials

Volume 18, Issue 19, pages 2897–2904, October 9, 2008

Additional Information

How to Cite

Yim, K.-H., Zheng, Z., Friend, R. H., Huck, W. T. S. and Kim, J.-S. (2008), Surface-Directed Phase Separation of Conjugated Polymer Blends for Efficient Light-Emitting Diodes. Advanced Functional Materials, 18: 2897–2904. doi: 10.1002/adfm.200800287

Author Information

  1. 1

    Melville Laboratory for Polymer Synthesis, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (UK)

  2. 2

    The Nanoscience Centre, University of Cambridge J. J. Thomson Avenue, Cambridge CB3 0FF (UK)

  3. 3

    Cavendish Laboratory, University of Cambridge J. J. Thomson Avenue, Cambridge CB3 0HE (UK)

  4. 4

    Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK

*Melville Laboratory for Polymer Synthesis, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (UK).

  1. †

    The authors thank Cambridge Display Technology (CDT) Ltd. for the F8BT and TFB materials and financial support (K.-H. Y., Z. Z.), EPSRC for fund, Dorothy Hodgkin Postgraduate Studentship (Z. Z.) and Advanced Research Fellowship (J.-S. K.).

Publication History

  1. Issue published online: 6 OCT 2008
  2. Article first published online: 9 SEP 2008
  3. Manuscript Revised: 25 APR 2008
  4. Manuscript Received: 28 FEB 2008

Funded by

  • (K.-H. Y., Z. Z.)
  • EPSRC

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Keywords:

  • conjugated polymers;
  • light-emitting diodes;
  • microcontact printing;
  • polymer blends

Graphical Abstract

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A surface-directed phase separation in conjugated-polymer blend thin films is used to fabricate efficient light-emitting diodes and detailed structure analysis of phase-separated blend thin films is performed to explain the improved device performance.

Abstract

The ability to control organic-organic interfaces in conjugated polymer blends is critical for further device improvement. Here, we control the phase separation in blends of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-di-n-octylfluorene-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene) (TFB) via chemical modification of the substrate by microcontact printing of octenyltrichlorosilane molecules. The lateral phase-separated structures in the blend film closely replicate the underlying micrometer-scale chemical pattern. We found nanometer-scale vertical segregation of the polymers within both lateral domains, with regions closer to the substrate being substantially pure phases of either polymer. Such phase separation has important implications for the performance of light-emitting diodes fabricated using these patterned blend films. In the absence of a continuous TFB wetting layer at the substrate interface, as typically formed in spin-coated blend films, charge carrier injection is confined in the well-defined TFB-rich domains. This confinement leads to high electroluminescence efficiency, whereas the overall reduction in the roughness of the patterned blend film results in slower decay of device efficiency at high voltages. In addition, the amount of surface out-coupling of light in the forward direction observed in these blend devices is found to be strongly correlated to the distribution of periodicity of the phase-separated structures in the active layer.

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