표면 고정 에너지 제어를 통한 유기 디스플레이 소자 광효율 향상에 관한 연구

Abstract

High performance liquid crystal displays (LCDs) with wide viewing angle and fast response time characteristics are widely used in both large and small size LCD application. For securing the high display performance, many kinds of researches have been done with internal/external modification of LCDs. In internal modification, uniform alignment of LC molecules is essential known as well till now. Various approaches have been taken including rubbing of polymer films which is most popular and conventional process. In external modification, optical efficiency enhancement of the incident light using unidirectional alignment of emitting material becomes important owing to high resolution and power consumption. Therefore, control of surface ordering of anisotropic molecules and theoretical analysis should be investigated for obtaining a high performance LCD device and scientific researches. In this dissertation, scientific and technological researches related to surface alignment of liquid crystalline molecules and optical phenomenon for optical applications are presented. Especially, by controlling the surface anchoring energy, order parameters and associated optical characteristics could be enhanced. It is classified into two departments, as LC modes and polarized light source. In the LC mode part, we introduce a new LC mode with high transmittance and wide viewing angle. By physical modelling of an anchoring energy variation and director configuration in stacked alignment system, inverse twisted nematic (ITN) mode could be achieved. For enhancing a viewing angle characteristic, multi-domain structure is adopted. Finally, a new LC mode, inverse four-domain twisted nematic (IFDTN) mode which represent high optical performance such as high transmittance and wide viewing angle, is achieved through enhancement of azimuthal anchoring energy without chiral agents. In the polarized light source part, we present polarized organic light emitting diodes (OLEDs) with controlled surface anchoring strength using rubbing and nano-lithography method. Order parameters of organic molecule from electroluminescence (EL) and photoluminescence (PL) are analyzed by a physical model based on second harmonic generation (SHG) effect and optical measurement. And also, surface morphologies according to the anchoring energy variation are presented. Finally, optimized OLEDs are combined to IFDTN mode to complete a LCD device with high optical efficiency. In conclusion, throughout the thesis, surface anchoring energy control for LC alignment has been intensively explored. Especially, LC mode and polarized emission are dealt with for high performance LC devices. The theoretical analysis and optical device application for organic display device could be expected to adopt in future display.