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Enhanced Light Extraction from Buckling-structured OLED
(Published in Nature Photonics, Takezoe-Ishikawa Lab.)
"Light extraction from organic light emitting diodes enhanced by spontaneously formed buckles"
Won Hoe Koo, Soon Moon Jeong, Fumito Araoka, Ken Ishikawa, Suzushi Nishimura, Takehiro Toyooka, Hideo Takezoe,
Nature Photonics, Advance online publication, DOI: 10.1038/NPHOTON.2010.7.
Most of the light in the conventional organic light-emitting diodes is confined to high refractive index layers such as those of organic medium and indium tin oxide, and glass substrate, resulting in a low light extraction efficiency of ~20%. So far, many studies have utilized wavelength-scale periodic gratings to improve external efficiency of organic light-emitting diodes. However, efficiency is only enhanced at particular wavelengths satisfying the Bragg condition.
Here, we demonstrated that a quasi-periodic buckling structure with a broad distribution and directional randomness (Fig. 1) 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 2 across the entire visible wavelength regime (Fig 2 and 3). These buckling patterns are formed spontaneously on elastic materials with a thin metallic film. The emitting image of the buckled organic light-emitting diode device are shown in Fig. 4 (Right). The buckling structure is practical and attractive for use in fabricating full colour and white organic light-emitting diodes.