Abstract

Microlens arrays are introduced on glass substrates to improve the out-coupling efficiency of organic light-emitting devices (OLEDs). The microlenses suppress waveguiding loss in the substrate. A theoretical model, based on electromagnetic wave propagation and geometric ray tracing, is developed to simulate the enhancement effects and optimize the structure parameters of the lens pattern. A simple soft-lithography approach is employed to fabricate the microlens array on glass substrates. With the use of an optimized lens pattern, an increase of over 85% in the coupling efficiency of the OLED is expected theoretically. An increase of 70% in the coupling efficiency is achieved experimentally, without detrimental effect to the electrical performance of the OLED.

© 2005 IEEE

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Other (20)

C. Adachi, M. A. Baldo, M. E. Thompson and S. R. Forrest, "Nearly 100% internal phosphorescence efficiency in an organic light-emitting device", J. Appl. Phys., vol. 90, no. 10, pp. 5048-5051, Nov. 2001.

M. Ikai, S. Tokito, Y. Sakamoto, T. Suzuki and Y. Taga, "Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer", Appl. Phys. Lett. , vol. 79, no. 2, pp. 156-158, Jul. 2001.

N. C. Greenham, R. H. Friend and D. D. C. Bradley, "Angular dependence of the emission from a conjugated polymer light-emitting diode: implications for efficiency calculations", Adv. Mater., vol. 6, no. 6, pp. 491 -494, Jun. 1994.

B. J. Matterson, J. M. Lupton, A. F. Safonov, M. G. Salt, W. L. Barnes and I. D. W. Samuel, "Increased efficiency and controlled light output from a microstructured light-emitting diode", Adv. Mater , vol. 13, no. 2, pp. 123-127, Jan. 2001.

P. A. Hobson, S. Wedge, J. A. E. Wasey, I. Sage and W. L. Barnes, "Surface plasmon mediated emission from organic light-emitting diodes", Adv. Mater, vol. 14, no. 19, pp. 1393-1396, Oct. 2002.

T. Yamasaki, K. Sumioka and T. Tsutsui, "Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium", Appl. Phys. Lett., vol. 76, no. 10, pp. 1243-1245, Mar. 2000.

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., vol. 22, no. 6, pp. 396-398, Mar. 1997.

S. Mller and S. R. Forrest, "Improved light out-coupling in organic light emitting diodes employing ordered microlens arrays", J. Appl. Phys., vol. 91, no. 5, pp. 3324-3327, Mar. 2002.

M. K. Wei and I. L. Su, "Method to evaluate the enhancement of luminance efficiency in planar OLED light emitting devices for microlens array", Optics Exp., vol. 12, no. 23, pp. 5777-5782, Nov. 2004.

C. F. Madigan, M. H. Lu and J. C. Strum, "Improvement of output coupling efficiency of organic light-emitting diodes by backside substrate modification", Appl. Phys. Lett., vol. 76, no. 13, pp. 1650-1652, Mar. 2000.

J. J. Shiang, J. J. Faircloth and A. R. Duggal, "Experimental demonstration of increased organic light emitting device output via volumetric light scattering", J. Appl. Phys., vol. 95, no. 5, pp. 2889-2895, Mar. 2004.

T. Tsutsui, M. Yahiro, H. Yokogawa, K. Kawano and M. Yokoyama, "Doubling coupling-out efficiency in organic light-emitting devices using a thin silica aerogel layer", Adv. Mater. , vol. 13, no. 15, pp. 1149-1152, Aug. 2001.

A. Dodablapur, L. J. Tothberg, R. H. Jordan, T. M. Miller, R. E. Slusher and J. M. Philips, "Physics and applications of organic microcavity light emitting diodes", J. Appl. Phys., vol. 80, no. 12, pp. 6954-6964, Dec. 1996.

H. W. Choi, C. Liu, E. Gu, G. McConnell, J. M. Girkin, I. M. Watson and M. D. Dawson, "GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses", Appl. Phys. Lett. , vol. 84, no. 13, pp. 2253-2255, Mar. 2004.

V. Bulovic, V. B. Khalfin, G. Gu, P. E. Burrows, D. Z. Garbuzov and S. R. Forrest, "Weak microcavity effects in organic light-emitting devices", Phys. Rev. B., vol. 58, no. 7, pp. 3730 -3740, Aug. 1998.

M. Born and E. Wolf, Principles of Optics, 7th ed. Cambridge: U.K.: Cambridge Unv. Press, 1999.

Optical Research Associates, "Code V Release Notes", 2003.

W. Lukosz, "Light emission by multipole sources in thin layers. I. Radiation patterns of electric and magnetic dipoles", J. Opt. Soc. Amer., vol. 71, no. 6, pp. 744-754, Jun. 1981.

H. Benisty, R. Stanley and M. Mayer, "Method of source terms for dipole emission modification in modes of arbitrary planar structures", J. Opt. Soc. Amer. A, vol. 15, no. 5, pp. 1192-1201, May 1998.

S. Sinzinger and J. Jahns, Microoptics, 2nd ed. Weinheim: Germany: WILEY-VCH/C. KGaA,

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