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Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles

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Abstract

Most of the light in conventional organic light-emitting diodes is confined to high-refractive-index layers (such as an organic medium, indium tin oxide and glass substrate) resulting in a low light extraction efficiency of 20% (refs 1,2). Many studies have used wavelength-scale periodic gratings to increase the external efficiency of organic light-emitting diodes3,4,5,6,7,8,9. However, the efficiency is only enhanced at particular wavelengths satisfying the Bragg condition. Here, we demonstrate that a quasi-periodic buckling structure with broad distribution and directional randomness can enhance the light extraction efficiency without introducing spectral changes and directionality. Organic light-emitting diodes corrugated by buckles showed improved current and power efficiencies and an electroluminescence spectrum enhanced by at least a factor of two across the entire visible wavelength regime. These buckling patterns are formed spontaneously on elastic materials with a thin metallic film. The buckled organic light-emitting diode devices are practical and attractive for use in fabricating full colour and white organic light-emitting diodes.

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Figure 1: AFM analysis of buckling patterns.
Figure 2: Characterization of waveguide modes by the transfer matrix method.
Figure 3: Device performance.
Figure 4: Electroluminescence spectral characteristics.

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Contributions

W.H.K. performed most experiments, including fabrication of the OLED devices (with and without buckling) and characterization, with assistance from S.M.J., F.A. and K.I. Suggestions on the characterization of data were made by S.N. and T.T. H.T. and W.H.K. wrote the manuscript.

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Correspondence to Hideo Takezoe.

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The authors declare no competing financial interests.

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Koo, W., Jeong, S., Araoka, F. et al. Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles. Nature Photon 4, 222–226 (2010). https://doi.org/10.1038/nphoton.2010.7

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