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Enhanced light out-coupling of organic light-emitting devices using embedded low-index grids

Nature Photonics volume 2, pages 483–487 (2008)Cite this article

Abstract

The application of organic light-emitting devices to reduce the energy consumption of interior lighting, which now costs more than $230 billion annually1, is attracting interest due to the high efficiency of these devices. Indeed, electrophosphorescent organic light-emitting devices with an internal quantum efficiency ηIQE of 100% (refs 2,3) already approach the efficiency of fluorescent lamps4,5,6. However, because of the high refractive index of organic materials and the optical confinement and internal reflection that results, the light out-coupling efficiency ηout for conventional organic light-emitting devices is limited to ∼20% (refs 2,7). Here we demonstrate that embedding a low-index grid in the organic layers can enhance the out-coupling of the waveguided light without spectral distortion. When combined with microlenses that out-couple the glass modes, the external quantum efficiency ηEQE and power efficiency of a white organic light-emitting device are improved to 34 ± 2% and 68 ± 4 lm W–1. The resulting ηout is 2.3 ± 0.2 times that of a conventional organic light-emitting device used as a comparison, and simulations indicate that the enhancement can be further increased to 3.4 ± 0.2.

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Figure 1: Schematic diagram of the OLED with the embedded low-index grid (LIG) in the organic layers.
Figure 2: Simulations of enhancement in out-coupling efficiency.
Figure 3: Scanning electron microscope (SEM) images of the OLED with a low-index grid (LIG) and of the microlens array.
Figure 4: Performance characteristics of devices 1 to 4.

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Acknowledgements

The authors thank the US Department of Energy for support through a subcontract from the University of Southern California and Universal Display Corporation for partial financial support of this work.

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Authors and Affiliations

  1. Department of Electrical Engineering, Princeton University, New Jersey, Princeton, 08544, USA

    Yiru Sun

  2. Departments of Electrical Engineering and Computer Science, Physics, and Materials Science and Engineering, University of Michigan, Ann Arbor, 48109, Michigan, USA

    Yiru Sun & Stephen R. Forrest

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  1. Yiru Sun
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Correspondence to Stephen R. Forrest.

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Sun, Y., Forrest, S. Enhanced light out-coupling of organic light-emitting devices using embedded low-index grids. Nature Photon 2, 483–487 (2008). https://doi.org/10.1038/nphoton.2008.132

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