Hybrid-Type Transparent Organic Light Emitting Diode Display with High Contrast Using liquid crystal Mode CHOI SEONG WOOK Dept. of Electronic Engineering Graduate School, Dong-A University Busan, Korea Transparent organic light emitting diode (OLED) displays are one of the most promising next-generation information display devices. However, conventional transparent OLED displays suffer from two intrinsic problems. One is a low light efficiency due to light emission from the environment, and the other is a low contrast ratio due to visual disturbances caused by light emission from the background. To solve this problem of transparent OLED display, we propose a hybrid-type transparent OLED display by replacing the transparent window part of the empty space with a liquid crystal (LC) cell. We considered switching the liquid crystal in accordance with voltage by designing a patterned electrode structure and improved the electro-optical characteristics by optimizing the mixing ratio of the dyes and liquid crystal. In this study, an actively operational transparent window part, which is an electrically controlled birefringence (ECB) mode liquid crystal (one-polarized mode) and cholesteric liquid crystal (Ch-LC) mode cell using dichroic dyes (non-polarized mode), was applied to an empty space to block light from the back of the display, improving forward light efficiency and contrast. Therefore, a dark state transmittance of up to 1.3 % could be expected for transparent OLED with the proposed liquid crystal mode of the transparent window compared to the dark state transmittance of high transmittance in a conventional empty space. In addition, high-performance transparent OLEDs were verified through a comparative analysis of one-polarized and non-polarized modes using dichroic dyes.