Illustrated in copending U.S. Ser. No. 10/205,632, the disclosure of which is totally incorporated herein by reference, filed concurrently herewith, is an electroluminescent device comprised of an anode, a cathode, and situated between the anode and the cathode a carbazole layer of the formula 
wherein R1, R2, R3, and R4 are independently selected from the group consisting of a hydrocarbyl, and wherein Ar is an aryl.
Illustrated in copending applications U.S. Ser. No. 09/935,031 on xe2x80x9cOleds Having Light Absorbing Electrodexe2x80x9d, filed on Aug. 22, 2001; U.S. Ser. No. 10/005,930 on xe2x80x9cOrganic Devicesxe2x80x9d, filed on Nov. 8, 2001; U.S. Ser. No. 10/005,404 on xe2x80x9cRed Organic Light Emitting Devicesxe2x80x9d, filed Nov. 8, 2001; U.S. Ser. No. 10/005,970 on xe2x80x9cOrganic Light Emitting Devicesxe2x80x9d, filed Nov. 8, 2001; U.S. Ser. No. 10/005,993 on xe2x80x9cOrganic Light Emitting Devices, filed Nov. 8, 2001; and U.S. Ser. No. 10/005,518 on xe2x80x9cGreen Organic Light Emitting Devicesxe2x80x9d, filed Nov. 8, 2001, the disclosures of each application being totally incorporated herein by reference, are a number of electroluminescent devices. The appropriate components and process of these copending applications may be selected for the devices of the present invention in embodiments thereof.
This invention is related to organic electroluminescent (EL) devices, and more specifically, to organic EL devices with excellent performance characteristics, and which devices contain novel carbazole compounds. Organic EL devices are desired that are capable of providing uniform luminescence, saturated color in blue, green and red, and low driving voltages. The organic EL devices of the present invention enable in embodiments the aforementioned characteristics, and which devices contain charge transport/luminescent materials comprised of a new class of carbazole compounds, and wherein these devices can be selected for use in flat-panel emissive display technologies, including TV screens, computer screens, and the like.
An 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. Several prior art organic EL devices have been constructed 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. However, these devices usually require excitation voltages on the order of 100 volts or greater.
Organic EL devices with a multilayer structure can be formed as a dual layer structure comprising one organic layer adjacent to the anode supporting hole transport, and another organic layer adjacent to the cathode supporting electron transport and acting as the organic luminescent zone of the device. Another alternate device configuration is comprised of three separate layers, a hole transport layer, a luminescent layer, and an electron transport layer, which layers are laminated in sequence and are sandwiched between an anode and a cathode. Optionally, a fluorescent dopant material can be added to the emission zone or layer whereby the recombination of charges results in the excitation of the fluorescent dopant material.
In U.S. Pat. No. 4,539,507, the disclosure of which is totally incorporated herein by reference, 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 4,4xe2x80x2-bis(5,7-di-tert-pentyl-2-benzoxyzolyl)stilben, and an indium cathode. In U.S. Pat. No. 6,229,012, the disclosure of which is totally incorporated herein by reference, there are illustrated devices with certain carbazoles.
U.S. Pat. No. 4,720,432, the disclosure of which is totally incorporated herein by reference, 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, the disclosure of which is totally incorporated herein by reference, 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. One host material disclosed in the ""292 patent is an aluminum complex of 8-hydroxyquinoline, and more specifically, tris(8-hydroxyquinolinate)aluminum.
U.S. Pat. No. 5,409,783, the disclosure of which is totally incorporated herein by reference, discloses a red-emitting organic EL device containing a dopant of a tris(8-hydroxyquinolinate)aluminum with a red fluorescent dye. Further, blue-emitting organic EL devices are illustrated in, for example, U.S. Pat. Nos. 5,151,629 and 5,516,577, the disclosures of which are totally incorporated herein by reference.
While progress in organic EL research has elevated the potential of organic EL devices for widespread applications, the performance levels of a number of devices are still below expectations in several instances. 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. Moreover, although the use of aromatic tertiary amines as hole transport materials in organic EL devices is known, the amine compounds selected, such as N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidines, have a tendency to form complexes with the EL electron transport materials in contact therewith, thus resulting in, for example, emission with a broad spectra. This complexation for blue emitting devices results in the electron transport materials retaining a larger band gap than those used in devices with green or red emission. Thus, there continues to be a need for hole transport compositions for organic EL devices, and which materials are suitable for selection in blue emitting devices. Also, there is a need for EL hole transports which are vacuum evaporable and form films with excellent thermal stability. There is also a need for luminescent compositions which are capable of providing uniform and satisfactory emission in the visible spectrum from blue to red colors. In particular, there is a need for efficient blue luminescent materials for organic EL devices, which can be doped with a fluorescent dye to provide different colors by a downhill energy transfer process. Further there is also a need for luminescent compositions which can enhance the EL charge transporting characteristics thus lowing device driving voltages. Therefore, one feature disclosed herein is to provide charge transport/luminescent materials comprised of a new class of carbazole compounds and wherein there is avoided or there is minimized poor film forming properties, thermal instability, and weaker fluorescent properties.
It is a feature of the present invention to provide new charge transport compositions for organic EL devices.
In another feature of the present invention there is provided organic EL devices with a light emitting layer containing a luminescent material comprised of novel carbazole compounds.
It is another feature of the present invention to provide organic EL devices with several advantages, such as low operation voltages, and uniform light emission with spectrum spreading from blue to longer wavelengths.
Yet in a further 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 of, for example, copper phthalocyanine, a hole transporting layer comprised of a carbazole illustrated herein, an electron transporting layer comprised of, for example, a triazine compound, and in contact therewith a low work function metal, such as a cathode, wherein light emission may originate from the carbazole layer, the electron transport layer, or both layers thereof.
Moreover, 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 of, for example, copper phthalocyanine, a hole injection-assistant layer comprised of, for example, a N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidine compound, a carbazole hole transporting layer, an electron transporting layer comprised of, for example, a triazine compound, and in contact therewith a low work function metal, such as a cathode, and wherein light emission may originate from the carbazole layer, the electron transport layer, or both layers thereof.
Disclosed herein are devices comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer of, for example, copper phthalocyanine, a hole injection-assistant layer comprised of, for example, a N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidine compound, a hole transporting layer comprised of a novel carbazole compound, an electron transporting layer comprised of, for example, a triazine compound, an organic electron injecting-assistant layer comprised of, for example, tris(8-hydroxyquinolinato)aluminum, and in contact therewith a low work function metal cathode, wherein light emission may originate from the carbazole layer, the electron transport layer, or both layers thereof; and organic EL devices comprised of a supporting substrate of, for example, glass, an anode, a buffer layer of, for example, copper phthalocyanine, a hole injection-assistant layer comprised of, for example, a N,N,Nxe2x80x2,Nxe2x80x2-tetraarylbenzidine compound, a hole transporting layer comprised of a carbazole compound illustrated herein of the formulas recited herein, an organic light emitting layer comprised of, for example, a fluorescent anthracene compound, an electron transporting layer comprised of, for example, tris(8-hydroxyquinolinato)aluminum, and in contact therewith a cathode.
Illustrated herein is a class of charge transport/luminescent materials comprised of carbazole compounds of the formula 
wherein R1, R2, R3, and R4 are each a non-hydrogen substituent, which may be individually selected from the group consisting of an alkyl with, for example, (for the number ranges recited herein there is envisioned that other numbers outside the ranges indicated may be acceptable) 1 to about 10 carbon atoms, an alkoxyl group containing from 1 to about 6 carbon atoms, a hydrocarbon aryl group containing, for example, from about 6 to about 60 carbon atoms and, more specifically, from about 6 to about 30 carbon atoms, or a heteroaromatic group, wherein the alkyl or alkoxyl group may be selected from the group consisting of a methyl, a butyl, a cyclohexyl, a methoxy, and the like; wherein the hydrocarbon aryl group can be independently selected, for example, from the group consisting of a phenyl, a stilbenyl, a biphenylyl, a naphthyl, an anthryl and the like; wherein the hydrocarbon aryl group may further possess a substituent of, for example, an alkyl with from 1 to about 6 carbon atoms, a alkoxy group containing from 1 to about 6 carbons, and the like; the heteroaromatic group may contain from about 2 to about 30 carbon atoms, and which group may be independently selected from the group consisting of a thienyl, a carbozolyl, a quinolyl, and the like; wherein Ar is a bivalent aromatic group of, for example, an arylene with from about 6 to about 30 carbon atoms, or a heteroaromatic divalent group.
Illustrative examples of the divalent aromatic group follow 
wherein R1, R2 and R3 are independently a substituent group, which can be selected from the group consisting of hydrogen, halogen, a cyan; a hydrocarbyl of from 1 to about 20 carbons, a hydrocarbyl of from about 5 to about 15 carbons, a hydrocarbyl of from 1 to about 20 carbons further containing one or more heteroatoms of oxygen, sulfur, silicon and like; specifically R1, R2 and R3 can be selected from the group consisting of hydrogen, a halogen, such as fluorine, cyan, methyl, methoxy, ethoxy, propoxy, butoxy, and the like; m is an integer of from 1 to about 6; G is a hydrocarbyl of from 1 to about 20 carbons, or a hydrocarbyl of from 6 to about 18 carbons, a hydrocarbyl of from 1 to about 20 carbons further containing one or more heteroatoms of oxygen, sulfur, silicon and like; G is an alkyl with from about 1 to about 20 carbons, a phenyl; an alkylphenyl, an alkoxyphenyl and the like; also together the 9-carbon in fluorene G may form a ring structure with from 5 to about 18 members; X may be selected from the group consisting of an oxygen atom, a sulfur atom, an imine group substituted with a radical of R being selected from, for example, the group consisting of an alkyl with from 1 to about 6 carbon atoms, a phenyl, a naphthyl, and the like; and wherein A is an aryl group containing from about 6 to about 36 carbon atoms, which aryl may be, for example, independently selected from the group consisting of a phenyl, a tolyl, a naphthyl, and the like. Preferably, Ar is selected from the group consisting of a phenylene, a biphenyl-4,4xe2x80x2-diyl, a naphthalene, a stilben-4,4xe2x80x2-diyl, and the like.
A specific class of the carbazole compounds are illustrated by the following formula: 
wherein Ar1, Ar2, Ar3, and Ar4 are each an aryl group with, for example, from about 6 to about 18 carbons, or a heteroaromatic group containing a heteroatom of, for example, oxygen, sulfur, nitrogen or silicon; wherein the aryl or heteoaromatic groups may further contain a substituent comprised of fluorine, cyan, an alkyl of from 1 to about 15 carbons, an alkoxyl containing from 1 to about 15 carbons, and the like. More specifically, Ar1, Ar2, Ar3, and Ar4 are selected from the group consisting of phenyl, a tolyl, a xylyl, a methyoxyphenyl, a fluorophenyl, a stilbenyl, a biphenylyl, a naphthyl, an anthyl group and the like.
Illustrated herein are EL devices that are comprised in the following sequence of a supporting substrate of, for example, glass, an anode, an optional buffer layer, an organic hole transporting layer, an organic light emitting layer, and an optional electron transporting layer, and in contact therewith a low work function metal wherein the hole transport layer contains at least one carbazole compound illustrated by Formulas I and II; layered EL devices with a light emitting layer comprised of a luminescent composition comprised of a carbazole compound illustrated by Formulas I and II; layered EL devices with a light emitting layer comprised of a luminescent composition comprised of a carbazole compound illustrated by formulas I and/or II as a host component capable of sustaining hole-electron recombination and a guest fluorescent or phosphorescent material capable of emitting light in response to energy released by the hole-electron recombination. The light emitting layer may be formed by vacuum deposition from the simultaneous evaporation of the host material and the fluorescent/phosphorescent material. The presence of the fluorescent/phosphorescent material permits, for example, a wide latitude of wavelengths of light emission and may enable the enhancement of electroluminescent efficiency and excellent device operation stability.
The charge transport/luminescent carbazole materials illustrated herein possess in embodiments several advantages. For example, the carbazole compounds possess excellent charge transport properties; exhibit strong fluorescence in the solid state in the region of, for example, from about 400 nanometers to longer wavelengths of, for example, about 600 nanometers, and in particular in the blue region of about 400 nanometers to about 490 nanometers; possess the ability of forming films with excellent thermal stability by vacuum evaporation; and can also be blended with numerous fluorescent materials to form a common phase.
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