Abstract
Transparent display is one of the most promising concepts among the next generation information display devices. Nevertheless, conventional transparent displays have two inherent problems: low forward light efficiency due to the light being emitted also in a backward direction; and low legibility due to the visual interruption caused by the light coming from the background. In this work, a cholesteric liquid crystal (Ch-LC) based, actively operational blind panel is combined with transparent organic light-emitting diodes (TR-OLEDs) to recycle the light wasted by backward propagation in transparent displays while blocking the light from behind the display, pursuing both improved forward light efficiency and enhanced image legibility. By tuning the reflectance spectrum of the Ch-LC panel to match the emission spectrum of TR-OLEDs, we achieved luminous efficiency increase by as large as 21% (85%) when the top metal cathode side (the bottom ITO side) of the OLEDs fa'transparent OLED' ces the blind panel. Maximum transmittance of the proposed device reached a high value of 60%, successfully demonstrating a new window-like transparent display concept.
Highlights
Transparent display is among the highly promising next-generation displays and refers to a display device that is optically clear when it is not under operation but can show images or texts when turned on
We try to resolve these issues through a novel concept named “actively transparent displays (ATD)” in which transparent OLED (TR-OLED) are combined with an electric blind panel based on cholesteric liquid crystals (Ch-LCs) that can be switched electrically between reflection (‘R’) and transmission (‘T’) states
To verify the luminance enhancement of the TR-OLED assisted by the reflection from the Ch-LC blind panel, we have measured the forward luminance of the transparent display while varying the current density within the TR-OLED
Summary
Transparent display is among the highly promising next-generation displays and refers to a display device that is optically clear when it is not under operation but can show images or texts when turned on. Various approaches to transparent displays have been reported including transparent inorganic electroluminescent device [1, 2], transparent plasma display panels [3,4,5], microelectromechanical/ electrowetting based transmissive displays [6, 7], and transparent organic light emitting diodes (TR-OLEDs) [8,9,10,11] Among such transparent displays, those based on OLEDs are considered as most promising because active layers comprising OLEDs are mostly based on very thin layers of wide-gap materials that are highly transparent. With the proposed blind panel in the reflection state, the light emitted backwards in the associated TR-OLEDs is recycled so that the brightness of the display can be enhanced, and, at the same time, the background light from behind the display is blocked so that the legibility of the displayed images and texts can be significantly improved
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