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Optics Letters

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  • Vol. 22, Iss. 6 — Mar. 15, 1997
  • pp: 396–398

High-external-quantum-efficiency organic light-emitting devices

G. Gu, D. Z. Garbuzov, P. E. Burrows, S. Venkatesh, S. R. Forrest, and M. E. Thompson  »View Author Affiliations


Optics Letters, Vol. 22, Issue 6, pp. 396-398 (1997)
http://dx.doi.org/10.1364/OL.22.000396


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Abstract

We study the internal and external quantum efficiencies of vacuum-deposited organic light-emitting devices (OLED’s). The internal quantum efficiency of OLED’s based on tris-(8-hydroxyquinoline) aluminum is calculated to be 5.7 times the observed external quantum efficiency ƞe, consistent with measurements. We demonstrate a shaped substrate that increases ƞe by a factor of 1.9±0.2 over similar OLED’s fabricated upon flat glass substrates and leads to a 100%-emissive aperture, i.e., the emitting area completely occupies the display area even in the presence of metal interconnects. We also discuss a substrate structure that increases ƞe by an additional factor of 2. The high device efficiencies are promising for developing OLED-based displays with extremely low power consumption and increased operational lifetime.

© 1997 Optical Society of America

Citation
G. Gu, D. Z. Garbuzov, P. E. Burrows, S. Venkatesh, S. R. Forrest, and M. E. Thompson, "High-external-quantum-efficiency organic light-emitting devices," Opt. Lett. 22, 396-398 (1997)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-22-6-396


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References

  1. D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
  2. D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
  3. I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
  4. P. E. Burrows, Z. Shen, V. Bulovic, D. M. McCarty, S. R. Forrest, J. A. Cronin, and M. E. Thompson, J. Appl. Phys. 79, 7991 (1996).
  5. N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
  6. Assuming isotropic emission, and that the reflectance of the OLED top contact is 1, the angular energy distribution in the emitting layer is F1(q1)=1/(2p). Energy conservation, F1(q1)sin q1d q1=F(q)sin qdq, along with Snell’s law, gives F(q) =nglass F1(q)cos qnAlq cos q1 = nglass2cos q2pnAlq2[1-( nglass nAlq sin θ)2]1/2 This equation is valid only in the absence of microcavity effects, where the radiation is isotropic. This is the case for low-finesse optical cavities formed by the OLED layers with significant damping of the emission at the transparent anode.
  7. N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).

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