Unlocking the full potential of organic light-emitting diodes on flexible plastic

Abstract

Typical high-efficiency organic light-emitting diodes (OLEDs) require exotic high-refractive-index (n ≥ 1.8) substrates to enhance the outcoupling of trapped light in the device. One of the exciting possibilities of OLEDs is the use of lightweight flexible plastic substrates, which unfortunately have a low refractive index (n ≤ 1.6). To unlock the full potential of OLEDs on flexible plastic, we report high-efficiency phosphorescent OLEDs using a thin-film outcoupling enhancement method that does not depend on high-index substrates. In these devices, multifunctional anode stacks, consisting of a high-index Ta2O5 optical coupling layer, electrically conductive gold layer and hole-injection MoO3 layer, are collectively optimized to achieve high efficiency. The maximum external quantum efficiency reaches 63% for green, which remains as high as 60% at >10,000 cd m–2.

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Figure 1: Device structure of the flexible OLED.
Figure 2: Calculation of optical enhancement ratio.
Figure 3: Comparison of calculated and measured luminance and electroluminescence spectra.
Figure 4: Device performance of optimized OLEDs.

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Acknowledgements

The authors acknowledge funding for this research from the Natural Sciences and Engineering Research Council (NSERC) of Canada. Z.H.L. is a Government of Canada Research Chair in Organic Optoelectronics, Tier I. The authors are grateful to W.Q. Shi and G.C. Walker (University of Toronto) for atomic force microscopy measurements.

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Contributions

Z.B.W. and M.G.H. designed the device concept, performed the optical simulations, fabricated and characterized the devices and wrote the manuscript. J.Q., D.P.P., M.T.G., Z.M.H., S.W., Z.W.L. and Z.H.L. assisted in characterization and data analysis. Z.H.L. motivated this work and co-wrote the manuscript.

Corresponding authors

Correspondence to Z. B. Wang or M. G. Helander or Z. H. Lu.

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The authors declare no competing financial interests.

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Wang, Z., Helander, M., Qiu, J. et al. Unlocking the full potential of organic light-emitting diodes on flexible plastic. Nature Photon 5, 753–757 (2011). https://doi.org/10.1038/nphoton.2011.259

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