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

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 similar to 20% (refs 1,2). Many studies have used wavelength-scale periodic gratings to increase the external efficiency of organic light-emitting diodes(3-9). 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.