용액 공정 기반 TiO2 나노 입자 층 삽입으로의 마이크로캐비티 효과를 통한 유기발광소자의 효율 향상

Abstract

In the display industry, liquid crystal display (LCD) dominate the display market. But in these days new candidate for the dominator of the display market comes up and that is organic light emitting diodes (OLED). The clear reappearance of the color, low power consumption, high contrast ratio and fast response are the reason for the candidate of the dominator in the display market. In contrast with LCD, OLED can be fabricated on the numerous substrate such as polyethylene terephthalate (PET) and fabric. The OLEDs display can be flexible and stretchable with these substrates. Also OLED can be transparent display. In spite of numerous advantage it still has some problems to solve. Among the problems, low external quantum efficiency is the main theme in this study. Previous studies have suggested many methods to extract the light confined inside the OLED due to total reflection and surface plasmon. We suggest a microcavity effect using embedded nanoparticle layer for the enhancement of the efficiency of the OLED. Generally, microcavity effects are used within two metal layer inside the OLED, but we used TiO2 nanoparticle layer which has high refractive index and there were 25% improvement of current efficiency, 15% improved EQE and 23% improved power efficiency at 1000cd/m2. By the experimental results, we found the possibility of the nanoparticle layer as the candidates of reflector for the microcavity effect in OLED. The method for the fabricating embedded nanoparticle layer inside the OLED is spin coating and it is very simple method compare with the fabrication of the metal layer in the OLED. Also, TiO2 nanoparticle and its solution, Xylene, are very cheap, and that means it is competitiveness method in the industry. The roughness and quasi-periodic surface of the nanoparticle layer can reinforce the side effect of the microcavity. When there is a microcavity effect in the OLED color coordinates are shifted, but the rough surface on the nanoparticle layer surface have decline the movement of the color coordinates of the OLED.