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 ηe, consistent with measurements. We demonstrate a shaped substrate that increases ηe 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 ηe 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

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  1. D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
    [CrossRef]
  2. D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
    [CrossRef]
  3. I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
    [CrossRef]
  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).
    [CrossRef]
  5. N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
    [CrossRef]
  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(θ1)=1/(2π). Energy conservation, F1(θ1)sin θ1dθ1=F(θ)sin θdθ, along with Snell's law, gives F(θ) = nglassF1(θ)cosθnAlqcosθ1=nglass2cosθ2πnAlq21-nglassnAlqsinθ21/2. This equation is valid only in the absence of micro-cavity effects,7 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).
    [CrossRef]

1996 (3)

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

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).
[CrossRef]

1994 (1)

N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[CrossRef]

1993 (2)

N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).
[CrossRef]

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Bradley, D. D. C.

N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[CrossRef]

Bulovic, V.

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).
[CrossRef]

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

Burn, P. L.

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Burrows, P. E.

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).
[CrossRef]

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

Cronin, J. A.

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).
[CrossRef]

Crystall, B.

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Forrest, S. R.

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

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).
[CrossRef]

Friend, R. H.

N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[CrossRef]

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Garbuzov, D. Z.

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

Greenham, N. C.

N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[CrossRef]

Holmes, A. B.

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

McCarty, D. M.

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).
[CrossRef]

Rumbles, G.

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Saito, S.

N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).
[CrossRef]

Samuel, I. D. W.

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Shen, Z.

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).
[CrossRef]

Takada, N.

N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).
[CrossRef]

Thompson, M. E.

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).
[CrossRef]

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

Tsekoun, A. G.

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

Tsutsui, T.

N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).
[CrossRef]

Adv. Mater. (1)

N. C. Greenham, R. H. Friend, and D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[CrossRef]

Appl. Phys. Lett. (1)

N. Takada, T. Tsutsui, and S. Saito, Appl. Phys. Lett. 63, 2032 (1993).
[CrossRef]

Chem. Phys. Lett. (1)

D. Z. Garbuzov, V. Bulovic, P. E. Burrows, and S. R. Forrest, Chem. Phys. Lett. 249, 433 (1996).
[CrossRef]

J. Appl. Phys. (2)

D. Z. Garbuzov, S. R. Forrest, A. G. Tsekoun, V. Bulovic, and M. E. Thompson, J. Appl. Phys. 80, 4644 (1996).
[CrossRef]

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).
[CrossRef]

Synth. Metals (1)

I. D. W. Samuel, B. Crystall, G. Rumbles, P. L. Burn, A. B. Holmes, and R. H. Friend, Synth. Metals 54, 281 (1993).
[CrossRef]

Other (1)

Assuming isotropic emission, and that the reflectance of the OLED top contact is 1, the angular energy distribution in the emitting layer is F1(θ1)=1/(2π). Energy conservation, F1(θ1)sin θ1dθ1=F(θ)sin θdθ, along with Snell's law, gives F(θ) = nglassF1(θ)cosθnAlqcosθ1=nglass2cosθ2πnAlq21-nglassnAlqsinθ21/2. This equation is valid only in the absence of micro-cavity effects,7 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.

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Figures (4)

Fig. 1
Fig. 1

Typical Alq3-based OLED on a flat glass substrate. The rays waveguided by the device layers, by the glass substrate, and coupled out from the substrate surface are shown along with the refractive indices of each layer.

Fig. 2
Fig. 2

External efficiency improvement S and the top to bottom mesa area ratio K as functions of mesa sidewall angle β and parameter q=Rt/h. Inset: schematic of the circular mesa, defining various rays, angles, and dimensions.

Fig. 3
Fig. 3

Light output power versus drive current characteristics of an OLED measured with and without index-matching fluid filling the OLED-photodetector gap. Inset:external quantum efficiency versus drive current of the same device.

Fig. 4
Fig. 4

Light output power versus drive current characteristics of an OLED on a shaped substrate with and without index-matching fluid used to eliminate reflection at the mesa walls. Inset: proposed improved shaped substrate structure.

Equations (2)

Equations on this page are rendered with MathJax. Learn more.

p(r)=p1+p2(r)=02πdφ0θcF(θ)sinθdθ+02πdφθ1θ2F(θ)sinθdθ.
F(θ)=nglassF1(θ)cosθnAlqcosθ1=nglass2cosθ2πnAlq21-nglassnAlqsinθ21/2.

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