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White organic light-emitting diodes with fluorescent tube efficiency

Nature volume 459, pages 234–238 (2009)Cite this article

Abstract

The development of white organic light-emitting diodes1 (OLEDs) holds great promise for the production of highly efficient large-area light sources. High internal quantum efficiencies for the conversion of electrical energy to light have been realized2,3,4. Nevertheless, the overall device power efficiencies are still considerably below the 60–70 lumens per watt of fluorescent tubes, which is the current benchmark for novel light sources. Although some reports about highly power-efficient white OLEDs exist5,6, details about structure and the measurement conditions of these structures have not been fully disclosed: the highest power efficiency reported in the scientific literature is 44 lm W-1 (ref. 7). Here we report an improved OLED structure which reaches fluorescent tube efficiency. By combining a carefully chosen emitter layer with high-refractive-index substrates8,9, and using a periodic outcoupling structure, we achieve a device power efficiency of 90 lm W-1 at 1,000 candelas per square metre. This efficiency has the potential to be raised to 124 lm W-1 if the light outcoupling can be further improved. Besides approaching internal quantum efficiency values of one, we have also focused on reducing energetic and ohmic losses that occur during electron–photon conversion. We anticipate that our results will be a starting point for further research, leading to white OLEDs having efficiencies beyond 100 lm W-1. This could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future.

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Figure 1: Energy level diagram and light modes in an OLED.
Figure 2: Spectrum- and time-resolved electroluminescence transients.
Figure 3: Current density and luminance as a function of driving voltage and electroluminescence spectra of all devices.
Figure 4: Power efficiency of the white OLEDs.

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Acknowledgements

We thank the European Commission within the sixth framework IST programme under contract IST-2002-004607 (project OLLA), for funding. We received further support via the Leibniz Prize of the Deutsche Forschungsgemeinschaft. We also thank Novaled AG, Dresden, for providing the hole-transport layer dopant NDP-2 as well as J. Förster and T. Günther for technical assistance throughout sample preparation.

Author Contributions S.R. designed the emission concept, performed the transient electroluminescence measurements, wrote the manuscript, analysed most of the data and, together with F.L., optimized and characterized the devices and designed the outcoupling structure. G.S. was involved in the development of the second maximum devices. N.S. performed the photoluminescence quantum yield measurements. K.W. and B.L. coordinated the high efficiency white OLED project. K.L. motivated this work and co-wrote the manuscript.

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Authors and Affiliations

  1. Institut für Angewandte Photophysik, George-Bähr-Strasse 1, D-01062 Dresden, Germany ,

    Sebastian Reineke, Frank Lindner, Gregor Schwartz, Nico Seidler, Karsten Walzer, Björn Lüssem & Karl Leo

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  1. Sebastian Reineke
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Corresponding author

Correspondence to Karl Leo.

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Supplementary Information

This file contains Supplementary Figures 1-5 with Legends, Supplementary Data and Supplementary References. Missing lines from the Supplementary Figure 1 Legend were corrected on 21 May 2009. (PDF 1000 kb)

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Reineke, S., Lindner, F., Schwartz, G. et al. White organic light-emitting diodes with fluorescent tube efficiency. Nature 459, 234–238 (2009). https://doi.org/10.1038/nature08003

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