Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-01-26
2002-11-12
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C428S704000, C257S040000, C257S103000, C313S504000, C313S506000, C252S301160, C252S301350
Reexamination Certificate
active
06479172
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to organic electroluminescent (EL) devices, and more specifically, to organic EL devices with a number of excellent performance characteristics inclusive of the enablement of blue emitting EL devices, which devices contain luminescent components or a luminescent component with excellent high thermal stability, film forming characteristics and intense blue fluorescence. Organic EL devices are desired that are capable of providing uniform luminescence, saturated color especially in the blue regions of the visible spectrum, and low driving voltages. The organic EL devices of the present invention enable in embodiments the above characteristics and which devices contain organic luminescent materials or light emitting components comprised of fluorescent hydrocarbon compounds, and which devices can be selected for use in flat-panel emissive display technologies, including TV screens, computer screens, and the like.
PRIOR ART
A simple organic EL device can be comprised of a layer of an organic luminescent material conductively sandwiched between an anode, typically comprised of a transparent conductor, such as indium tin oxide, and a cathode, typically a low work function metal such as magnesium, calcium, aluminum, or the alloys thereof with other metals. The EL device functions on the principle that under an electric field, positive charges (holes) and negative charges (electrons) are respectively injected from the anode and cathode into the luminescent layer and undergo recombination to form excitonic states which subsequently emit light. A number of prior art organic EL devices have been prepared from a laminate of an organic luminescent material and electrodes of opposite polarity, which devices include a single crystal material, such as single crystal anthracene, as the luminescent substance as described, for example, in U.S. Pat. No. 3,530,325. However, these devices usually require excitation voltages on the order of 100 volts or greater.
In U.S. Pat. No. 4,539,507 there is disclosed an EL device formed of a conductive glass transparent anode, a hole transporting layer of 1,1-bis(4-p-tolylaminophenyl)cyclohexane, an electron transporting layer of 4,4′-bis(5,7-di-tert-pentyl-2-benzoxzolyl)stilben, and an indium cathode.
U.S. Pat. No. 4,720,432 discloses an organic EL device comprising a dual-layer hole injecting and transporting zone, one layer being comprised of porphyrinic compounds supporting hole injection and the other layer being comprised of aromatic tertiary amine compounds supporting hole transport.
U.S. Pat. No. 4,769,292 discloses an EL device employing a luminescent zone comprised of an organic host material capable of sustaining hole-electron recombination and a fluorescent dye material capable of emitting light in response to energy released by hole-electron recombination. A preferred host material is an aluminum complex of 8-hydroxyquinoline, namely tris(8-hydroxyquinolinate)aluminum.
While recent progress in organic EL research has elevated the potential of organic EL devices for widespread applications, the performance levels of a number of current available devices, especially with respect to blue emission, may still be below expectations. Further, for visual display applications, organic luminescent materials should provide a satisfactory color in the visible spectrum, normally with emission maxima at about 460, 550 and 630 nanometers for blue, green and red. These organic EL devices may comprise a light-emitting layer which is comprised of a host material doped with a guest fluorescent material that is responsible for color emission. For efficient down-shifting of EL emission wavelength in the host-guest emitting layer, it may be desirable that the host material should fluorescence in the blue or shorter wavelength region. In many conventional organic EL devices, the luminescent zone or layer is formed of a green-emitting luminophor of tris(8-hydroxyquinolinate)aluminum with certain fluorescent materials. U.S. Pat. No. 5,409,783 discloses a red-emitting organic EL device by doping the tris(8-hydroxyquinolinate)aluminum layer with a red fluorescent dye. However, up-shifting of the tris(8-hydroxyquinolinate)aluminum emission to blue region is believed to be highly inefficient. Although there have been several disclosures describing blue-emitting organic EL devices, for example in U.S. Pat. Nos. 5,151,629 and 5,516,577, the disclosures of which are totally incorporated herein by reference, their performance characteristics still possess many disadvantages such as poor emission hue, high operation voltages, low luminance, and poor operation stability. Thus, there continues to be a need for improved luminescent compositions for organic EL devices, which may vacuum evaporable and form thin films with excellent thermal stability. There is also a need for luminescent compositions which are capable of providing uniform and satisfactory emission in the blue region of the light spectrum. In particular, there is a need for efficient blue luminescent materials for organic EL devices, which may optionally be doped with a fluorescent dye. Further, there is also a need for luminescent compositions which can enhance charge transporting characteristics, thus lowering device driving voltages. Therefore, a primary feature of the present invention is to provide luminescent materials comprised of certain fluorescent hydrocarbon compounds, which in comparison to certain EL devices comprised of the metal chelates of oxadiazole compounds can provide improved and excellent emission characteristics particularly in the blue region, such as a saturated blue color and a narrow emission spectrum.
SUMMARY OF THE INVENTION
It is a feature of the present invention to provide luminescent compositions for organic EL devices.
It is another feature of the present invention to provide organic EL devices with many advantages, such as low operation voltages, uniform light emission with spectrum spreading from blue to longer wavelengths, thermal stability, electrochemical stability, and charge transport capability.
In an another feature of the present invention there are provided organic EL devices with a light emitting layer containing a luminescent material comprised of novel fluorescent hydrocarbon compounds.
In yet another feature of the present invention there are provided organic EL devices with a light-emitting layer comprised of a luminescent hydrocarbon compound.
Further, in a feature of the present invention there are provided organic EL devices comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer, a vacuum deposited organic hole transporting layer comprised of, for example, 4,4′-bis-(9-carbazolyl)-1,1-biphenyl, a vacuum deposited light emitting layer comprised of a luminescent hydrocarbon compound, an optional vacuum deposited electron transporting layer, and in contact therewith a low work function metal, such as magnesium, lithium, and their alloys as a cathode.
Yet in another feature of the present invention there is provided an organic EL device comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer, a vacuum deposited organic hole transporting layer comprised of tertiary aromatic amines, for example, N,N′-1-naphthyl-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine, a vacuum deposited light emitting layer, an optional vacuum deposited electron transporting layer, and in contact therewith a low work function metal, such as magnesium and its alloys as a cathode, wherein the light emitting layer is comprised of a mixture of a novel hydrocarbon compound as a host component and an optional fluorescent material.
These and the other features of the present invention are accomplished by the provision of luminescent or light emitting components comprised of the hydrocarbon compounds illustrated by the Formula (I)
wherein R
1
and R
2
are substituents, which may be selected from the group consisting of hydrogen, an alkyl group wi
Aziz Hany
Hu Nan-Xing
Jain Poonam
Popovic Zoran D.
Jones Deborah
Palazzo E. O.
Xerox Corporation
Xu Ling
LandOfFree
Electroluminescent (EL) devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electroluminescent (EL) devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electroluminescent (EL) devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2975084