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

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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° 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.

©2005 Optical Society of America

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Figures (7)

Fig. 1.
Fig. 1. Device structures of the conventional transflective LCD using vertically aligned LC.
Fig. 2.
Fig. 2. (a) Cross section of the tandem device cell, and (b) the equivalent circuit of the display.
Fig. 3.
Fig. 3. Simulated iso-contrast contours of (a) T-mode of the conventional VA transflective LCD, (b) R-mode of the conventional VA transflective LCD, and (c) RLCD of the tandem device.
Fig. 4.
Fig. 4. Simulated viewing angle dependent OLED intensity at different bumpy-transmitter area-ratios.
Fig. 5.
Fig. 5. The tandem device structure used for experimental measurements.
Fig. 6.
Fig. 6. Measured (symbols) and fitted (lines) ambient-contrast-ratio under different ambient intensities.
Fig. 7.
Fig. 7. Photographs showing the operation of the tandem device: (a) low ambient, RLCD-off, OLED-off; (b) low ambient, RLCD-on, OLED-off; (c) low ambient, RLCD-off, OLED-on; (d) high ambient, RLCD-off, OLED-off; (e) high ambient, RLCD-on, OLED-off; and (f) high ambient, RLCD-off, OLED-on.

Equations (1)

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A CR = Device luminance ( On ) + Reflected ambient light Device luminance ( Off ) + Reflected ambient light
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