High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer

To obtain the maximum luminous efficiency from an organic material, it is necessary to harness both the spin-symmetric and anti-symmetric molecular excitations (bound electron–hole pairs, or excitons) that result from electrical pumping. This is possible if the material is phosphorescent, and high efficiencies have been observed in phosphorescent organic light-emitting devices. However, phosphorescence in organic molecules is rare at room temperature. The alternative radiative process of fluorescence is more common, but it is approximately 75% less efficient, due to the requirement of spin-symmetry conservation. Here, we demonstrate that this deficiency can be overcome by using a phosphorescent sensitizer to excite a fluorescent dye. The mechanism for energetic coupling between phosphorescent and fluorescent molecular species is a long-range, non-radiative energy transfer: the internal efficiency of fluorescence can be as high as 100%. As an example, we use this approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device.

[1]  Martin Klessinger,et al.  Excited states and photochemistry of organic molecules , 1995 .

[2]  C. H. Chen,et al.  Improved red dopants for organic electroluminescent devices , 1997 .

[3]  T. Főrster,et al.  10th Spiers Memorial Lecture. Transfer mechanisms of electronic excitation , 1959 .

[4]  Stephen R. Forrest,et al.  EXCITONIC SINGLET-TRIPLET RATIO IN A SEMICONDUCTING ORGANIC THIN FILM , 1999 .

[5]  S. Forrest,et al.  VERY HIGH-EFFICIENCY GREEN ORGANIC LIGHT-EMITTING DEVICES BASED ON ELECTROPHOSPHORESCENCE , 1999 .

[6]  J. R. Schrieffer,et al.  Spectral properties of quasiparticle excitations induced by magnetic moments in superconductors , 1996, cond-mat/9610198.

[7]  Local electronic structure of defects in superconductors , 1996, cond-mat/9612213.

[8]  S. Forrest,et al.  Highly efficient phosphorescent emission from organic electroluminescent devices , 1998, Nature.

[9]  R. Wiesendanger,et al.  Scattering States of Ionized Dopants Probed by Low Temperature Scanning Tunneling Spectroscopy , 1998 .

[10]  A. Dodabalapur,et al.  Light amplification in organic thin films using cascade energy transfer , 1997, Nature.

[11]  U. Brackmann.  Lambdachrome laser dyes , 1986 .

[12]  Stephen R. Forrest,et al.  Bright, saturated, red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts , 1998 .

[13]  Richard H. Friend,et al.  Harvesting Singlet and Triplet Energy in Polymer LEDs , 1999 .

[14]  Ching Wan Tang,et al.  Recent developments in molecular organic electroluminescent materials , 1997 .

[15]  Stephen R. Forrest,et al.  Improved energy transfer in electrophosphorescent devices , 1999 .

[16]  Stephen R. Forrest,et al.  Photoluminescence efficiency and absorption of aluminum-tris-quinolate (Alq3) thin films , 1996 .

[17]  C.W. Tang,et al.  Organic Electroluminescent Devices , 1995, IEEE/LEOS 1995 Digest of the LEOS Summer Topical Meetings. Flat Panel Display Technology.

[18]  Th. Förster,et al.  Transfer Mechanisms of Electronic Excitation Energy , 1960 .

[19]  C. H. Chen,et al.  Electroluminescence of doped organic thin films , 1989 .

[20]  Stephen R. Forrest,et al.  Tuning the color emission of thin film molecular organic light emitting devices by the solid state solvation effect , 1999 .