Abstract

A high-contrast organic light-emitting diode (OLED) structure is presented. Because of poor contrast of conventional OLED resulting from high reflective metal cathode, the hybrid cathode structure was developed for low reflectivity. It consists the semitransparent cathode layers, passivation layers and a thick light-absorbing film. By optical reflectivity measurement and OLED electrical characterization tests for both OLED with the hybrid cathode and conventional OLED, it was found that the spectrum reflectance of OLED with hybrid cathode is among 8%–12%, about eight times lower than the conventional one when the two types of devices have similar turn-on voltages and current-voltage characteristics. The hybrid cathode for the high-contrast OLED is easily fabricated and its optical reflectance is slightly dependent on wavelength.

© 2005 Optical Society of America

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References

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Adv. Mater.

L.S. Hung and J. Madathil, �??Reduction of Ambient light reflection in organic light-emitting diodes,�?? Adv. Mater. 23, 1787-1790 (2001)
[CrossRef]

Appl. Opt.

Appl. Phys. Lett.

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

Z.Y. Xie and L.S. Hung, �??High-contrast organic light-emitting diodes,�?? Appl. Phys. Lett. 84, 1207-1209 (2004)
[CrossRef]

X.D. Feng, RE. Khangura, and Z.H. Lu, �??Metal-organic-metal cathode for high-contrast organic light-emitting diodes,�?? Appl. Phys. Lett. 85, 497-499 (2004)
[CrossRef]

G. Gu, V. Bulovic, P.E. Burrows, and S.R. Forrest M.E. Thompson, �??Transparent organic light emitting diodes,�?? Appl. Phys. Lett. 68, 2606-2608(1996)
[CrossRef]

L.S. Hung, C.W. Tang, M.G. Mason, P. Raychaudhuri and J. Madathil �??Application of an ultrathin LiF/Al bilayer in organic surface-emitting diodes,�?? Appl. Phys. Lett. 78, 544-546(2001)
[CrossRef]

A.N. Krasnov, �??High-contrast organic light-emitting diodes on flexible subtrate,�?? Appl. Phys. Lett. 80, 3853 (2002)
[CrossRef]

Chem. Phys. Lett.

S.L. Lai, M.Y. Chan, M.K. Fung, C.S. Lee, L.S. Hung and S.T. Lee, �??Applications of Ytterbium in organic light-emitting devices as high performance and transparent electrodes,�?? Chem. Phys. Lett. 366, 128-133 (2002)
[CrossRef]

Y.Q. Li, J.X. Tang and L.S. Hung, �??Interfacial chemistry of Sm with Alq3 and its implication to organic light-emitting devices,�?? Chem. Phys. Lett. 376, 90-95 (2003)
[CrossRef]

Nature

J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackey, R. H. Friend, P. L. Burns, A. B. Holmes, �??Light-emitting diodes based on conjugated polymers,�?? Nature 1990, 347, 539.
[CrossRef]

Synthetic Metals

J.H. Lee, C.C. Liao, P.J. Hu, Y. Chang, �??High contrast ratio organic light-emitting devices based on CuPc as electron transport material,�?? Synthetic Metals, 144, 279-283, (2004)
[CrossRef]

Thin Solid Film

F.L. Wong M.K. Fung, X. Jiang, C.S. Lee, S.T. Lee, �??Non-reflective black cathode in organic light-emitting diode,�?? Thin Solid Film, 446, 143-146, (2004)
[CrossRef]

Other

P.G. Hofstra and A.N. Krasnov, US Patent IPN No. WO 01/08240

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Figures (5)

Fig. 1.
Fig. 1.

Schematic diagram of the OLED with conventional metallic cathode (Device 1) and hybrid cathode (Device 2)

Fig. 2.
Fig. 2.

I-V and L-V characteristics of Device 1 and Device 2

Fig. 3.
Fig. 3.

The measured spectrum reflectance of Device 1 and Device 2

Fig. 4.
Fig. 4.

Contrast-ratio of Device 1 and Device 2

Fig. 5.
Fig. 5.

Photographs of Device 1 and Device2 at 3, 4 and 5 operational voltages.

Equations (2)

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R L = λ 1 λ 2 V ( λ ) S ( λ ) R ( λ ) d λ λ 1 λ 2 V ( λ ) S ( λ ) d λ
CR = L max + L ambient L min + L ambient

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