High ambient-contrast-ratio display using tandem reflective liquid crystal display and organic light-emitting device

Abstract

A high ambient-contrast-ratio (A-CR) and large aperture-ratio display is conceptually demonstrated and experimentally validated by stacking a normally black reflective liquid crystal display (NB-RLCD) and an organic light-emitting device (OLED). Such a tandem device can be switched between the NB-RLCD mode and the OLED mode under bright and dark ambient light, respectively. The normally black characteristic of the RLCD also helps to boost the A-CR under OLED-mode operation. To obtain a better image quality in the RLCD mode, a bumpy and transmissive structure is used to eliminate the specular reflection and to increase the viewing angle performance that results in CR>2:1 over 55 degrees viewing cone. Besides, such a structure can also increase the external quantum efficiency of the OLED by 49.4%. In our experiments, regardless of the ambient intensity the A-CR is kept higher than 100:1.

Emission Characteristics of Organic Light-Emitting Diodes and Organic Thin-Films with Planar and Corrugated Structures

“…In a real OLED display, a circular polarizer film is attached to the glass substrate for reducing the electrode reflection and hence improving the contrast ratio [94]. However, with the introduction of microstructures, it is not possible to attach such a film.…”

Transflective device with a transparent organic light‐emitting diode and a reflective liquid‐crystal device

“…Although the definition of the light source and measuring unit were different from the original cases, the results were still meaningful. 8 3 On the other hand, the A-CR of the RLCD held stable at 105:1 and was insensitive to the ambient light intensities for both device configurations. When the RLCD and transparent OLED were both turned on, the overall A-CR was even higher than that for the individual devices.…”

“…In this configuration, the thin-film transistors (TFTs) used for driving the OLED need to be fabricated on the top glass, instead of underneath the reflector of the RLCD, causing the aperture ratio to decrease. 8 There are two possible solutions to overcome this drawback. The first approach makes use of the dual-plate OLED display structure by depositing the TFTs and OLED on a separate glass substrate and then connecting them electrically via a contact spacer, was demonstrated on a 15-in.…”

“…On the other hand, vertical integration of the OLED and reflective LCD (RLCD) holds promise for a transflective device with the advantages of high A-CR and large aperture ratio for both T-and R-modes. [7][8][9][10] In this paper, we demonstrate a hybrid device by using a vertical alignment (VA) or phasechanged guest-host (PCGH) RLCD stacking with an OLED to achieve high A-CR. Notably, the integrated device with the R-mode of the PCGH RLCD exhibits a higher transmittance and allows for simpler fabrication processes compared to the VA case due to its polarizer-free characteristics.…”

Comparative study of organic light emitting diode efficiency enhancement by the use of optical films

“…Such a display would be high-contrast under a wide range of lighting conditions and well suited for mobile applications. Although this concept has been already reported, 17 its optical design requires further considerations. Transparent structures, which refract, scatter, or diffract light, should be positioned in the right place to prevent specular reflection and to improve light utilization.…”