White organic light-emitting diodes with fluorescent tube efficiency

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.

References

  1. 1

    Kido, J., Kimura, M. & Nagai, K. Multilayer white light-emitting organic electroluminescent device. Science 267, 1332–1334 (1995)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Sun, Y. et al. Management of singlet and triplet excitons for efficient white organic light-emitting devices. Nature 440, 908–912 (2006)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Williams, E. L., Haavisto, K., Li, J. & Jabbour, G. E. Excimer-based white phosphorescent organic light emitting diodes with nearly 100% internal quantum efficiency. Adv. Mater. 19, 197–202 (2007)

    CAS  Article  Google Scholar 

  4. 4

    Sun, Y. & Forrest, S. R. High-efficiency white organic light emitting devices with three separate phosphorescent emission layers. Appl. Phys. Lett. 91, 263503 (2007)

    ADS  Article  Google Scholar 

  5. 5

    Nakayama, T., Hiyama, K., Furukawa, K. & Ohtani, H. Development of phosphorescent white OLED with extremely high power efficiency and long lifetime. SID07 Dig. 1018–1021 (2006)

  6. 6

    D’Andrade, B. W. et al. Realizing white phosphorescent 100 lm/W OLED efficacy. Proc. SPIE 7051, 70510Q (2008)

    Article  Google Scholar 

  7. 7

    Su, S.-J., Gonmori, E., Sasabe, H. & Kido, J. Highly efficient organic blue-and white-light-emitting devices having a carrier- and exciton-confining structure for reduced efficiency roll-off. Adv. Mater. 20, 4189–4195 (2008)

    CAS  Google Scholar 

  8. 8

    Nakamura, T., Tsutsumi, N., Juni, N. & Fujii, H. Thin-film waveguiding mode light extraction in organic electroluminescent device using high refractive index substrate. Appl. Phys. Lett. 97, 054505 (2005)

    Google Scholar 

  9. 9

    Gärtner, G. & Greiner, H. Light extraction from OLEDs with (high) index matched glass substrates. Proc. SPIE 6999, 69992T (2008)

    ADS  Article  Google Scholar 

  10. 10

    Baldo, M. A. et al. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 395, 151–154 (1998)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Goushi, K., Kwong, R., Brown, J. J., Sasabe, H. & Adachi, C. Triplet exciton confinement and unconfinement by adjacent hole-transport layers. J. Appl. Phys. 95, 7798–7802 (2004)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Schwartz, G., Fehse, K., Pfeiffer, M., Walzer, K. & Leo, K. Highly efficient white organic light emitting diodes comprising an interlayer to separate fluorescent and phosphorescent regions. Appl. Phys. Lett. 89, 083509 (2006)

    ADS  Article  Google Scholar 

  13. 13

    Qin, D. & Tao, Y. White organic light-emitting diode comprising of blue fluorescence and red phosphorescence. Appl. Phys. Lett. 86, 113507 (2005)

    ADS  Article  Google Scholar 

  14. 14

    Schwartz, G., Pfeiffer, M., Reineke, S., Walzer, K. & Leo, K. Harvesting triplet excitons from fluorescent blue emitters in white organic light-emitting diodes. Adv. Mater. 19, 3672–3676 (2007)

    CAS  Article  Google Scholar 

  15. 15

    Greenham, N. C., Friend, R. H. & Bradley, D. D. C. Angular-dependence of the emission from a conjugated polymer light-emitting diode - implications for efficiency calculations. Adv. Mater. 6, 491–494 (1994)

    CAS  Article  Google Scholar 

  16. 16

    He, G. et al. High-efficiency and low-voltage p-i-n electrophosphorescent organic light-emitting diodes with double-emission layers. Appl. Phys. Lett. 85, 3911–3913 (2004)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Kawamura, Y., Brooks, J., Brown, J. J., Sasabe, H. & Adachi, C. Intermolecular interaction and a concentration-quenching mechanism of phosphorescent Ir(III) complexes in a solid film. Phys. Rev. Lett. 96, 017404 (2006)

    ADS  Article  Google Scholar 

  18. 18

    Reineke, S., Schwartz, G., Walzer, K. & Leo, K. Reduced efficiency roll-off in phosphorescent organic light emitting diodes by suppression of triplet-triplet annihilation. Appl. Phys. Lett. 91, 123508 (2007)

    ADS  Article  Google Scholar 

  19. 19

    Kawamura, Y. et al. 100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films. Appl. Phys. Lett. 86, 071104 (2005)

    ADS  Article  Google Scholar 

  20. 20

    Greenham, N. C. et al. Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers. Chem. Phys. Lett. 241, 89–96 (1995)

    ADS  CAS  Article  Google Scholar 

  21. 21

    Huang, Q., Reineke, S., Walzer, K., Pfeiffer, M. & Leo, K. Quantum efficiency enhancement in top-emitting organic light-emitting diodes as a result of enhanced intrinsic quantum yield. Appl. Phys. Lett. 89, 263512 (2006)

    ADS  Article  Google Scholar 

  22. 22

    D’Andrade, B. W., Holmes, R.-J. & Forrest, S. R. Efficient organic electrophosphorescent white-light-emitting device with a triple doped emissive layer. Adv. Mater. 16, 624–628 (2004)

    Article  Google Scholar 

  23. 23

    Madigan, C. F., Lu, M.-H. & Sturm, J. C. Improvement of output coupling efficiency of organic light-emitting diodes by backside substrate modification. Appl. Phys. Lett. 76, 081114 (2006)

    Google Scholar 

  24. 24

    Möller, S. & Forrest, S. R. Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays. J. Appl. Phys. 91, 3324–3327 (2002)

    ADS  Article  Google Scholar 

  25. 25

    Lin, C.-H., Cho, T.-Y., Chang, C.-H. & Wu, C.-C. Enhancing light outcoupling of organic light-emitting devices by locating emitters around the second antinode of the reflective metal electrode. Appl. Phys. Lett. 88, 081114 (2006)

    ADS  Article  Google Scholar 

  26. 26

    Baldo, M. A., Adachi, C. & Forrest, S. R. Transient analysis of organic electrophosphorescence: II. Transient analysis of triplet-triplet annihilation. Phys. Rev. B 62, 10967 (2000)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Meerheim, R. et al. Influence of charge balance and exciton distribution on efficiency and lifetime of phosphorescent organic light-emitting devices. Appl. Phys. Lett. 104, 014510 (2008)

    Google Scholar 

  28. 28

    Adamovich, V. et al. New charge-carrier blocking materials for high efficiency OLEDs. Org. Electron. 4, 77–87 (2003)

    CAS  Article  Google Scholar 

  29. 29

    Reineke, S. et al. Measuring carrier mobility in conventional multilayer organic light emitting devices by delayed exciton generation. Phys. Status Solidi B 245, 804–809 (2008)

    ADS  CAS  Article  Google Scholar 

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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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Correspondence to Karl Leo.

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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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