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In order to improve light extraction efficiency from organic light emitting diodes (OLED), we report a novel structure of topemission OLED by integrating a scattering reflector with microbumps into the substrate. The mechanism of light extraction has been investigated by evaluating the dependency of flux on the shape of the micro-bumps. It was confirmed that the scattering effect of the micro-bumps improves the light extraction of OLED. Moreover, the scattering reflector has been applied on a 20.8-inch WXGA full color AMOLED display. This is the world's first report that actually proves a light extraction technology, integrating scattering reflector, applied on AMOLED display. IntroductionOrganic light emitting diode (OLED) displays are one of the most promising next generation flat panel displays on account of their several advantages such as high contrast ratio, extremely fast response, very wide viewing angle, and simple structure. Recently, active-matrix OLED (AMOLED) displays, using thin film transistor (TFT) backplane, have been developed for pursuing higher resolution and lower power consumption [1][2][3][4][5]. However, the problems on power consumption and lifetime, especially for large-scale TV applications, have not been solved. A breakthrough is needed to improve light extraction efficiency. Although several novel structures have been reported in order to effectively extract the light from the OLED emission layer, there are few reports that have been applied to actual display [6][7][8][9][10][11][12], due to the complexity of the structure, procedures, and the limitation of the fabrication area. It is also because of a double-image attributed to the parallax effect in bottom-emission OLED displays.In this paper, we propose a novel light extraction structure of OLED, which can be easily applied to an actual AM-OLED to improve the light extraction. The mechanisms of the scattering reflector are discussed. Moreover, AMOLED display integrating the scattering reflector is demonstrated. PrinciplesThe schematic diagram of AMOLED incorporating a scattering reflector with micro-bumps is presented in Fig. 1. The device structure is based on top-emission type. The scattering reflector consists of micro-bumps layer, reflection layer, and planar layer.Since the refractive index of the planar layer (n=1.51), is smaller than the emission layer (n=1.81), part of the waveguided light in OLED reaches the scattering reflector. Then, the scattered light within the critical angle between the air and the emission layer can be extracted into the air. Figure 1 Cross-section view of AMOLED Figure 2 Cross-section views of experimental devices. Fig. 2 shows the devices with no TFT circuits which were experimentally employed in order to evaluate the effect of the scattering reflector. One is the integrated-type device which is similar to an actual device structure shown in Fig. 1. The other is the attached-type device in which the scattering reflector is optically attached at the bottom, emits light to both sides, with refractiv...

An efficient emissive site has been investigated by inserting a monolayer size porphine layer (TPP) as a marker in an organic electroluminescent (EL) device consisting of 8-hydroxyquinoline aluminium as an emissive layer and diamine derivative (TPD) as the hole transporting layer. Emissions from and TPP have been observed from the device and the emission intensity from the TPP has been noted to change depending on the distance between the hetero-interface and the inserted site. Emission from the marker layer shows its highest intensity at a position 7 nm from the interface of and TPD. The result also shows that the hetero-interface is not the highest emissive site, but a site several nanometres inside the emissive layer shows the highest emission intensity. The mechanism of emissive recombination has been investigated in an EL device with an emissive layer and a carrier transporting layer.

In order to improve light extraction from an organic light emitting diode (OLED), a novel structure of a top emission OLED was proposed by applying the diffraction layer. We have achieved 1.65 times higher light extraction efficiency in case of electroluminescence (EL), and 2.37 times in case of photoluminescence (PL).

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