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Correlating structure with fluorescence emission in phase-separated conjugated-polymer blends

Nature Materials volume 2, pages 616–621 (2003)Cite this article

Abstract

Blends of conjugated polymers are frequently used as the active semiconducting layer in light-emitting diodes and photovoltaic devices. Here we report the use of scanning near-field optical microscopy, scanning force microscopy and nuclear-reaction analysis to study the structure of a thin film of a phase-separated blend of two conjugated polymers prepared by spin-casting. We show that in addition to the well-known micrometre-scale phase-separated morphology of the blend, one of the polymers preferentially wets the surface and forms a 10-nm-thick, partially crystallized wetting layer. Using near-field microscopy we identify unexpected changes in the fluorescence emission from the blend that occurs in a 300-nm-wide band located at the interface between the different phase-separated domains. Our measurements provide an insight into the complex structure of phase-separated conjugated-polymer thin films. Characterizing and controlling the properties of the interfaces in such films will be critical in the further development of efficient optoelectronic devices.

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Figure 1: The absorption and fluorescence of PFO, F8BT and a (1:1) blend of PFO and F8BT.
Figure 2: Scanning near-field optical micrographs of the transmission and fluorescence from a PFO/F8BT blend.
Figure 3: Fluorescence and topography cross-sections across an interface in a PFO/F8BT polymer blend.
Figure 4: The d-PFO volume fraction (φPFO) depth profile of a 70-nm-thick film of a 1:1 d-PFO/F8BT blend as determined by nuclear-reaction analysis.
Figure 5: The structure of a PFO-rich domain as measured using a scanning force microscope.

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Acknowledgements

We thank the UK Engineering and Physical Sciences Research Council for support of this research through grants GR/R26658/01 and GR/R10479/01 and for the provision of funding for D.G.L. and J.C. We also thank Franco Cacialli and Simon Martin for useful comments and discussions.

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Authors and Affiliations

  1. Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK

    John Chappell, David G. Lidzey, Paul C. Jukes, Anthony M. Higgins, Mark Geoghegan & Richard A. L. Jones

  2. Department of Chemistry, University of Durham, South Road, Durham, DH1 3LE, UK

    Richard L. Thompson

  3. Cambridge Display Technology Ltd, Greenwich House, Madingley Rise, Madingley Road, Cambridge, CB3 0HJ, UK

    Stephen O'Connor & Ilaria Grizzi

  4. The Dow Chemical Company Ltd, Building 1702, Midland, 48674, Michigan, USA

    Robert Fletcher & Jim O'Brien

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Correspondence to David G. Lidzey.

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Chappell, J., Lidzey, D., Jukes, P. et al. Correlating structure with fluorescence emission in phase-separated conjugated-polymer blends. Nature Mater 2, 616–621 (2003). https://doi.org/10.1038/nmat959

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