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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References

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Appl. Phys. Lett. (3)

C. W. Tang and S. A. Vanslyke, �??Organic electroluminescent diodes,�?? Appl. Phys. Lett. 51, 913-915 (1987).
[CrossRef]

S. H. Li, H. Liem, C. W. Chen, E. H. Wu, Z. Xu, and Y. Yang, �??Stacked metal cathode for high-contrast-ratio polymeric light-emitting devices,�?? Appl. Phys. Lett. 86, 143514-143516 (2005).
[CrossRef]

H. Aziz, Y. F. Liew, H. M. Grandin, and Z. D. Popovic, �??Reduced reflectance cathode for organic light-emitting devices using metalorganic mixtures,�?? Appl. Phys. Lett. 83, 186-188 (2003).
[CrossRef]

IEEE J. Select. Top. Quantum Electron. (1)

J. S. Lewis, and M. S. Weaver, �??Thin-film permeation-barrier technology for flexible organic light-emitting devices,�?? IEEE J. Select. Top. Quantum Electron. 10, 45-57 (2004).
[CrossRef]

J. Appl. Phys. (4)

S. Möller and S. R. Forrest, �??Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays,�?? J. Appl. Phys. 91, 3324-3327 (2002).
[CrossRef]

H. J. Peng, Y. L. Ho, X. J. Yu, and H. S. Kwok, �??Enhanced coupling of light from organic light emitting diodes using nanoporous films,�?? J. Appl. Phys. 96, 1649-1654 (2004).
[CrossRef]

G. Gu, G. Parthasarathy, P. E. Burrows, P. Tian, I. G. Hill, A. Kahn, and S. R. Forrest, �??Transparent stacked organic light emitting devices. I. Design principles and transparent compound electrodes,�?? J. Appl. Phys. 86, 4067-4075 (1999).
[CrossRef]

H. Riel, S. Karg, T. Beierlein, W. Rieâ, and K. Neyts, �??Tuning the emission characteristics of top-emitting organic light-emitting devices by means of a dielectric capping layer: An experimental and theoretical study,�?? J. Appl. Phys. 94, 5290-5296 (2003).
[CrossRef]

J. Display Technology (1)

S. Ishihara, "How far has the molecular alignment of liquid crysals been elucidated?" J. Display Technology, 1, 30-40 (2005).
[CrossRef]

J. Display Technology. (1)

X. Zhu, Z. Ge, T. X. Wu, and S. T. Wu, �??Transflective liquid crystal displays�??, J. Display Technology. 1, 15-29 (2005).
[CrossRef]

J. Opt. Soc. Am. A (1)

Z. Ge, T. X. Wu, X. Zhu, and S. T. Wu, �??Reflective liquid-crystal displays with asymmetric incident and exit angles,�?? J. Opt. Soc. Am. A 93, 966-977 (2005), <a href="http://josaa.osa.org/abstract.cfm?id=83591">http://josaa.osa.org/abstract.cfm?id=83591</a>
[CrossRef]

Opt. Express (1)

US patent application (1)

I. Fujieda, �??Display device and driving method thereof,�?? US patent application, 20030201960 (2003).

Other (1)

S. T. Wu and D. K. Yang, Reflective Liquid Crystal Displays, (Wiley, New York, 2001).

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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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