Measuring the light emission profile in organic light-emitting diodes with nanometre spatial resolution

Abstract

Determining the precise shape of the emission profile across the thickness of the active layer in organic light-emitting diodes is of importance for device optimization and assessing the validity of advanced device models. We present a comprehensive method for accurately measuring the shape of the emission profile, the intrinsic spectrum of emitting dipoles and the emitting dipole orientation. The method uses a microcavity light outcoupling model, which includes self-absorption and optical anisotropy, and is based on the full wavelength, angle and polarization resolved emission intensity. Application to blue (polyfluorene-based) and orange-red (NRS-PPV) polymer organic light-emitting diodes reveals a peaked shape of the emission profile. A significant voltage and layer thickness dependence of the peak positions is observed, with a demonstrated resolution better than 5 nm.

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Figure 1: Schematic illustrating the measurement of the shape of the emission profile in an OLED.
Figure 2: Angular dependence of the electroluminescence spectra for PF-TAA based OLEDs.
Figure 3: Comparison of measured and modelled spectra.
Figure 4: Position-dependent emission intensities.
Figure 5: Voltage and layer thickness dependence of the emission profile.
Figure 6: Consistency and resolution.

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Acknowledgements

The authors wish to thank L.W.G. Stofmeel for assistance with the measurements on the Autronic system, A.J.M. van den Biggelaar for device preparation, A.P.M. de Win for carrying out the refractive index measurements, M. Kaiser for carrying out the TEM measurements, and Sumation Co., Ltd for the supply of LumationTM Blue Series polymers. This research has received funding from NanoNed, a national nanotechnology programme coordinated by the Dutch Ministry of Economic Affairs (contribution S.L.M.v.M.), from the Dutch Polymer Institute (project no. 518, contribution M.C.), from the European Commission's Marie Curie Fellowship program (IST-2004-27580 SPRINT project, contribution M.B.), and from the European Community's Seventh Framework programme under grant agreement no. 213708 (AEVIOM, contribution R.C.).

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S.L.M.v.M. and M.C. contributed equally to this work. They designed and carried out the experiment, carried out the analysis, and contributed to the writing of the paper. M.M. contributed to the development of the analysis method. D.W. contributed to the experiments and analysis of NRS-PPV OLEDs. M.B. contributed to the experiments on PF-TAA OLEDs. H.G. developed the Lightex program. R.A.J.J. contributed by useful discussions. R.C. supervised the work and contributed to the development of the analysis method and to the writing of the paper.

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Correspondence to M. Carvelli or R. Coehoorn.

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van Mensfoort, S., Carvelli, M., Megens, M. et al. Measuring the light emission profile in organic light-emitting diodes with nanometre spatial resolution. Nature Photon 4, 329–335 (2010). https://doi.org/10.1038/nphoton.2010.32

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