HIGH EFFICIENCY ORGANIC LIGHT EMITTING DEVICES DEVELOPED BY FRESNAL'S THEORY

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We investigated on optical properties in organic light emitting devices on the basis of the wave optics by Fresnel's theory, and developed very high efficiency deep-blue and white emission. Research results are summarized as follows.1.A high-efficiency deep-blue OLED has been developed in the device consisting of dye-doped polymer layer and light-emitting α-NPD layer. The optimized device showed very high external-quantum-efficiency of 6.0% with keeping deep-blue color of CIE color coordinates (0.15,0.07).2.A high efficiency white-OLED has been developed based on a Side-Coupling-Color-Conversion-Method (SC3M), in which the blue emission from an organic layer is laterally transferred to an adjacent orange color-conversion material. A white-OLED with SC3M structure showed an external quantum efficiency of 8.9%.3.Optical behavior of multi-stacked thin film devices has been evaluated by using a newly developed optical simulator for OLEDs. It was found that the outcoupling efficiency(ηo) strongly depends on the width of the emission zone near the interface between organic layers. According to our new theoretical analysis based on the Fresnel's analysis and characteristic matrix, a maximum efficiency approaches approximately 35% when the light-emitting layer is carefully designed with keeping confined emission zone.In conclusion, the emission efficiencies of blue and white OLEDs was significantly improved by optical design based on Fresnel's analysis. These results will be utilized for the development of very high efficiency organic light source in the next research stage.