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

• Published in: Nature photonics Vol. 4; no. 4; pp. 222 - 226
• Main Authors: Takezoe, Hideo, Koo, Won Hoe, Jeong, Soon Moon, Araoka, Fumito, Ishikawa, Ken, Nishimura, Suzushi, Toyooka, Takehiro
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2010; Nature Publishing Group
• Subjects: 639/624/1020/1091; Applied and Technical Physics; Applied sciences; Buckling; Devices; Electronics; Exact sciences and technology; Extraction; Fasteners; Fourier transforms; Glass substrates; Gratings (spectra); Indium tin oxide; Indium tin oxides; letter; Light emitting diodes; Optoelectronic devices; Photonics; Physics; Physics and Astronomy; Quantum Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Wavelengths; Japan; White light; Refraction index; Visible radiation; Organic light emitting diodes; Tin; Electroluminescence; Indium oxide; Periodic structure; Thin film
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/nphoton.2010.7

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 diodes 3 , 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. Organic light-emitting diodes featuring layers with a spontaneously formed buckled geometry are demonstrated to offer at least a twofold improvement in light extraction efficiency across the entire visible spectrum.