CN101300692A - Organic Electroluminescent Devices - Google Patents

Abstract

Disclosed is an organic electroluminescent device (organic EL device) utilizing phosphorescent emission, wherein the luminous efficiency is improved and driving stability is sufficiently secured. Specifically disclosed is an organic EL device wherein an anode (2), a hole transporting layer (4), an organic layer containing a light-emitting layer (5) and an electron transporting layer (6), and a cathode (7) are arranged in layers on a substrate (1). The hole transporting layer is arranged between the light-emitting layer and the anode, while the electron transporting layer is arranged between the light-emitting layer and the cathode. The light-emitting layer contains an organic Al complex represented by the general formula (I) below as a host material, and an organic Ir complex represented by the general formula (II) below as a guest material. In the formulae below, L represents ArO-, ArCOO-, Ar3SiO-, Ar3GeO- or Ar2AlO-.

Description

Organic Electroluminescent Devices

technical field

The present invention relates to an organic electroluminescence device (hereinafter referred to as an organic EL device), and more particularly, to a thin-film type device that emits light by applying an electric field to a light-emitting layer containing an organic compound.

technical background

In the development of electroluminescent devices using organic materials, by optimizing the type of electrodes for the purpose of increasing the charge injection efficiency from the electrodes, a hole transport layer containing aromatic diamine is provided as a thin film between the electrodes The development of a device including a light-emitting layer of 8-hydroxyquinoline aluminum complex (hereinafter referred to as Alq3) has greatly improved the luminous efficiency compared with the existing device using a single crystal such as anthracene. Progress has been made towards the practical use of high-performance flat panels featuring self-illumination and high-speed response.

In order to further improve the efficiency of such organic EL devices, based on the structure of the above-mentioned anode/hole transport layer/luminescent layer/cathode, a device in which a hole injection layer, an electron injection layer or an electron transport layer is appropriately arranged, such as Anode/hole injection layer/hole transport layer/light emitting layer/cathode, anode/hole injection layer/light emitting layer/electron transport layer/cathode, anode/hole injection layer/light emitting layer/electron transport layer/electron injection layer /cathode, anode/hole injection layer/hole transport layer/light emitting layer/hole blocking layer/electron transport layer/cathode and other structures are known. The hole transport layer has a function of transporting holes injected from the hole injection layer to the light emitting layer, and the electron transport layer has a function of transporting electrons injected from the cathode to the light emitting layer. In addition, the hole injection layer is sometimes called an anode buffer layer, and the electron injection layer is sometimes called a cathode buffer layer.

In addition, it is known that by inserting the hole transport layer between the light emitting layer and the hole injection layer, a large amount of holes can be injected into the light emitting layer under a lower electric field, and since electrons are extremely difficult to flow through the hole transport layer, thus from Electrons injected into the light-emitting layer from the cathode or the electron transport layer are accumulated in the light-emitting layer, and the luminous efficiency increases.

Likewise, it is known that by inserting an electron transport layer between the light emitting layer and the electron injection layer, a large amount of electrons can be injected into the light emitting layer at a lower electric field, and since it is extremely difficult for holes to flow through the electron transport layer, the electrons from the anode or hole The holes injected into the light-emitting layer by the hole-transporting layer are accumulated in the light-emitting layer, and the luminous efficiency increases. According to the functions of such structural layers, various organic materials have been developed so far.

On the other hand, most devices represented by devices provided with a hole-transporting layer containing aromatic diamine and a light-emitting layer containing Alq3 use fluorescence emission, and if phosphorescence emission is used, that is, if the triplet excited state is used to generate Compared with conventional devices using fluorescence (singlet state), an efficiency improvement of about 3 times can be expected. In order to achieve this purpose, studies have been made on using coumarin derivatives or benzophenone derivatives as light-emitting layers, but only extremely low luminance can be obtained. Then, as an attempt to utilize the triplet state, the use of europium complexes was studied, but high-efficiency light emission was also not achieved.

In recent years, it has been reported that red phosphorescence can be efficiently emitted by using a platinum complex (PtOEP). Afterwards, by doping an iridium complex (Ir(ppy)3) in the light-emitting layer, a high-efficiency green light-emitting device utilizing the same phosphorescent light emission was fabricated.

With this iridium complex, it was found that light in a wide wavelength range from cyan to red can be emitted by changing the chemical structure of its ligand. However, it has been clarified that the triligand complex, which is considered to be the most stable and useful complex, can only be prepared with a limited number of ligands. A hybrid of linked intermediates (Proceeding of SPIE, Vol. 4105, p. 119).

The existing documents related to the present invention are the following documents.

Patent Document 1: JP-A-2002-299061

Patent Document 2: JP-A-2001-313178

Patent Document 3: JP-A-2002-352957

Patent Document 4: Special Publication No. 2003-515897

Non-Patent Document 1: Appl. Phys. Lett., Vol. 77, p. 904

In the development of phosphorescent organic EL devices, 4,4'-bis(9-carbazolyl)biphenyl (hereinafter referred to as CBP) described in Patent Document 2 is used as a host material. If CBP is used as the host material of the tris(2-phenylpyridine) iridium complex (hereinafter referred to as Ir(ppy)3) of the green phosphorescent luminescent material, then CBP has the advantages of easy hole flow and difficult electron flow. In addition to the excessive characteristics, it also breaks the charge injection balance, causing excess holes to flow to the electron transport side, resulting in a decrease in the luminous efficiency from Ir(ppy)3.

As a solution to the above, there is a method of providing a hole blocking layer between the light emitting layer and the electron transport layer. By efficiently accumulating holes in the light-emitting layer using the hole-blocking layer, the probability of recombination with electrons in the light-emitting layer can be increased, and high-efficiency light emission can be realized. As hole-blocking materials commonly used at present, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (hereinafter referred to as BCP) and p-phenylphenol-bis( 2-methyl-8-quinolinephenolo-N1,08)aluminum (hereinafter referred to as BAlq). This can prevent the recombination of electrons and holes in the electron transport layer, but BCP is also easy to crystallize at room temperature and lacks reliability as a material, so the device life is extremely short. In addition, relatively good device lifetime results were reported for BAlq, but the hole-blocking ability was insufficient and the luminous efficiency from Ir(ppy)3 decreased. In addition, since the layer structure is increased by one layer, the device structure becomes complicated, and there is a problem that the cost increases.

In Patent Document 3, 3,5-diphenyl-4-(1-naphthyl)-1,2,4-triazole (hereinafter referred to as TAZ) is proposed as a host material for a phosphorescent organic EL device, but except In addition to the characteristics of easy flow of electrons and difficulty of flow of holes, the light emitting region is shifted to the side of the hole transport layer. Therefore, due to the compatibility problem with Ir(ppy)3 due to the difference in the material of the hole transport layer, the luminous efficiency from Ir(ppy)3 decreases. For example, 4,4'-bis(N-(1-naphthyl)-N-phenylamino)biphenyl (hereinafter The poor compatibility between α-NPD) and Ir(ppy)3 caused the energy transfer from TAZ to α-NPD, and the efficiency of energy transfer from Ir(ppy)3 to Ir(ppy)3 decreased, resulting in the existence of There is a problem of reduced luminous efficiency.

As a solution to the above, there is the use of 4,4'-bis(N,N'-(3-toluoyl)amino)-3,3'-dimethylbiphenyl (hereinafter referred to as HMTPD) which does not cause Approach of materials with energy transfer from Ir(ppy)3 as hole transport layer. In Non-Patent Document 1, it is reported that by using TAZ, 1,3-bis(N,N-tert-butyl-phenyl)-1,3,4-oxazole or BCP in the host material of the light-emitting layer, in the guest Ir(ppy)3 is used in the material, Alq3 is used in the electron transport layer, and HMTPD is used in the hole transport layer. In phosphorescent light-emitting devices, high-efficiency light emission can be obtained through a three-layer structure, especially the system using TAZ is excellent. . However, since HMTPD has a glass transition temperature (Tg) of about 50° C., it is easy to crystallize and lacks reliability as a material. Therefore, the lifetime of the device is extremely short, commercial application is difficult, and there is also a problem of high driving voltage.

Patent Document 1 discloses an organic EL device comprising a light-emitting layer having a host agent and a dopant emitting phosphorescence. As an example of the dopant, Ir(ppy)3, a phenyl-substituted benzothiazole The ligand of the structure is coordinated with a three-ligand complex of Ir.

Contents of the invention

In order to apply an organic EL device to a display device such as a flat panel display, it is necessary to sufficiently ensure stability during driving while improving the luminous efficiency of the device. An object of the present invention is to provide a practically useful organic EL device having high efficiency, long life and enabling a simplified device structure.

The present invention relates to an organic electroluminescent device formed by laminating an anode, an organic layer including a hole transport layer, a light emitting layer, and an electron transport layer, and a cathode on a substrate, with an The hole transport layer has an electron transport layer between the light-emitting layer and the cathode, and is characterized in that: the light-emitting layer contains an organometallic complex represented by the following general formula (I) as a host material, and contains the general formula The organometallic complex shown in (II) was used as the guest material.

In the formula, R ₁ to R ₆ each independently represent a hydrogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an alkoxy group, an aromatic hydrocarbon group that may have a substituent, or an aromatic heterohydrocarbon group that may have a substituent. Ring base. L represents a monovalent group represented by the following general formula (1), (2), (3) or (4):

-O-Ar ₁ (1)

Ar ₁ to Ar ₅ each independently represent an optionally substituted aromatic hydrocarbon ring group or an optionally substituted aromatic heterocyclic group, Z represents silicon or germanium, and R ₁ to R ₆ have the same formula (I) meaning.

In the formula, R ₇ to R ₁₄ each independently represent a hydrogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an alkoxy group, an optionally substituted aromatic hydrocarbon group or an optionally substituted aromatic hetero Ring base.

The organic EL device of the present invention relates to an organic metal complex compound (also called an Al complex) compound represented by the above general formula (I) and an organic metal complex compound represented by the above general formula (II) in the light-emitting layer. (also referred to as Ir complex) so-called organic EL devices utilizing phosphorescence. An Al complex represented by general formula (I) is used as a host material, and an Ir complex represented by general formula (II) is used as a phosphorescent guest material.

Here, the host material refers to a component that accounts for more than 50% by weight of the material forming the layer, and the so-called guest material refers to a component that accounts for less than 50% by weight of the material forming the layer. In the organic EL device of the present invention, the excited triplet energy level of the Al complex contained in the light-emitting layer has an energy state higher than the excited triplet energy level of the phosphorescent Ir complex contained in the layer is substantially necessary.

In addition, compounds that can provide stable thin film shapes, have high Tg, and transport holes and/or electrons efficiently are desired. In addition, it is also required to be electrochemically and chemically stable, and it is difficult to generate a compound that forms a trap or eliminates an impurity that emits light during production or use. In order to make the light emission of the phosphorescent organic complex less affected by the excited triplet level of the hole transport layer, it is also important to have a hole injection capability that ensures an appropriate distance between the light emitting region and the interface of the hole transport layer.

As a material for forming a light-emitting layer satisfying these conditions, the Al complex represented by the above general formula (I) is used as a host material in the present invention. In the general formula (I), R ₁ to R ₆ each independently represent a hydrogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an alkoxy group, an aromatic hydrocarbon group that may have a substituent, or an optional substituent aromatic heterocyclic group. As an alkyl group, preferably an alkyl group having 1 to 6 carbon atoms (hereinafter referred to as a lower alkyl group), as an aralkyl group, preferably a benzyl group or a phenethyl group, as an alkenyl group, preferably an example having a carbon number of As for the lower alkenyl group of 1 to 6, the lower alkyl group is preferably exemplified as the alkyl portion of the alkoxy group.

In addition, as an aromatic hydrocarbon group, preferable examples include aromatic hydrocarbon groups such as phenyl, naphthyl, acenaphthyl, and anthracenyl groups, and as an aromatic heterocyclic group, preferable examples include pyridyl, quinolinyl, thienyl, carbazolyl, and indole. Aromatic heterocyclic groups such as radicals and furyls. When they are aromatic hydrocarbon groups or aromatic heterocyclic groups having substituents, examples of substituents include lower alkyl, lower alkoxy, phenoxy, benzyloxy, phenyl, naphthyl and the like.

As for the compound represented by the general formula (I), it is more preferable to select a compound in which R ₁ to R ₆ is a hydrogen atom, a lower alkyl group or a lower alkoxy group.

In the general formula (I), L represents a group represented by the above general formula (1), (2), (3) or (4), Ar ₁ to Ar ₅ each independently represent an aromatic hydrocarbon group which may have a substituent Or an aromatic heterocyclic group which may have a substituent, and Z represents silicon or germanium. Preferable examples of Ar ₁ to Ar ₂ include phenyl, naphthyl, and aromatic hydrocarbon groups substituted with alkyl or aryl. The alkyl group is preferably a lower alkyl group such as a methyl group, and the aryl group is preferably a phenyl group, a naphthyl group, or a group substituted by a lower alkyl group. Preferable examples of Ar ₃ to Ar ₅ include phenyl or lower alkyl-substituted phenyl. R ₁ to R ₆ in the above general formula (4) have the same meanings as R ₁ to R ₆ described in the above general formula (I).

The Al complex compound shown in general formula (I) is by for example corresponding metal salt and the compound shown in formula (III) and the compound shown in formula (1'), (2') or (3') in 2 ratios A molar ratio of 1 was synthesized by complex formation reaction. It should be noted that in formula (III), R ₁ to R ₆ correspond to R ₁ to R ₆ in general formula (I), and in formulas (1') to (3'), Ar ₁ to Ar ₅ correspond to Z Ar ₁ to Ar ₅ and Z of L in the general formula (I).

HO-Ar ₁

(1')

The Al complex compound represented by the general formula (I) in which L is a group represented by the general formula (4), is synthesized by a complex forming reaction between the corresponding metal salt and the compound represented by the formula (III). The synthesis reaction is carried out, for example, according to the method shown by Y. Kushi et al. (J. Amer. Chem. Soc., Vol. 92, p. 91, 1970).

Al complexes represented by the general formula (I) are exemplified below, but are not limited to the following compounds. In addition, compound 1 is abbreviated as BmqAl, and compound 11 is abbreviated as BAlq.

(化合物1)

(Compound 1)

(化合物2)

(compound 2)

(化合物3)

(compound 3)

(Compound 4)

(化合物5)

(Compound 5)

(化合物11)

(Compound 11)

(化合物12)

(Compound 12)

(化合物13)

(compound 13)

(化合物14)

(Compound 14)

(化合物15)

(compound 15)

(compound 16)

(化合物17)

(compound 17)

(化合物18)

(compound 18)

(化合物19)

(compound 19)

(化合物20)

(compound 20)

(化合物21)

(Compound 21)

(化合物22)

(compound 22)

As the guest material in the light-emitting layer, an Ir complex represented by the above general formula (II) is used.

In the general formula (II), R ₇ to R ₁₄ each independently represent a hydrogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an alkoxy group, an aromatic hydrocarbon group that may have a substituent, or an optional substituent aromatic heterocyclic group. In addition, adjacent R ₇ and R ₈ , R ₈ and R ₉ , R ₉ and R ₁₀ , R ₁₁ and R ₁₂ , R ₁₂ and R ₁₃ , R ₁₃ and R ₁₄ may form a ring, and these rings may be aromatic rings.

As an alkyl group, preferably an alkyl group having 1 to 6 carbon atoms (hereinafter referred to as a lower alkyl group), as an aralkyl group, preferably a benzyl group or a phenethyl group, as an alkenyl group, preferably an example having a carbon number of As for the lower alkenyl group of 1 to 6, the lower alkyl group is preferably exemplified as the alkyl portion of the alkoxy group.

In addition, as the aromatic hydrocarbon group, preferably, phenyl, naphthyl, acenaphthyl, anthracenyl, etc. are exemplified, and as the aromatic heterocyclic group, preferably, pyridyl, quinolinyl, thienyl, carbazolyl, indolyl, furanyl, etc. are exemplified. Base etc. When they are aromatic hydrocarbon groups or aromatic heterocyclic groups having substituents, examples of substituents include lower alkyl, lower alkoxy, phenoxy, benzyloxy, phenyl, naphthyl and the like.

Irbt3 etc. are mentioned as a more preferable Ir complex. Specific examples of the organometallic complex represented by the general formula (II) are shown below, but are not limited to the following compounds. In addition, compound 31 is abbreviated as Irbt3.

(化合物31)

(化合物32)

(compound 31)

(compound 32)

(化合物33)

(化合物34)

(compound 33)

(compound 34)

(化合物35)

(化合物36)

(compound 35)

(Compound 36)

(化合物37)(化合物38)

(compound 37) (compound 38)

The host material used for the light-emitting layer in the present invention allows electrons and holes to flow approximately equally, and thus can cause light to be emitted in the center of the light-emitting layer. Therefore, it will not emit light on the hole transport side like TAZ to generate energy transfer to the hole transport layer, resulting in a decrease in efficiency, nor will it emit light on the electron transport layer side like CPB, so that energy will migrate to the electron transport layer to make Efficiency decreases, and highly reliable materials such as α-NPD as a hole transport layer and Alq3 as an electron transport layer can be used.

Description of drawings

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescence device.

Explanation of reference signs

1: substrate, 2: anode, 3: hole injection layer, 4: hole transport layer, 5: light emitting layer, 6: electron transport layer, 7: cathode

Detailed ways

Hereinafter, the organic EL device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a structural example of a general organic EL device used in the present invention. In the organic EL device of the present invention, there are substrate 1, anode 2, hole transport layer 4, light emitting layer 5, electron transport layer 6 and cathode 7 as essential layers, and layers other than the essential layers, such as hole injection layer 3, can be omitted. , and other layers can be set if necessary. However, in the organic EL device of the present invention, the hole blocking layer is unnecessary. Since no hole blocking layer is provided, the layer structure is simplified, which brings advantages in manufacture and performance.

The substrate 1 serves as a support for the organic electroluminescence device, and a quartz or glass plate, a metal plate or metal foil, a plastic film or sheet, or the like can be used. Particularly preferred are glass plates, and plates of transparent synthetic resins such as polyester, polymethacrylate, polycarbonate, and polysulfone. When using a synthetic resin substrate, attention must be paid to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescence device will be degraded due to external air passing through the substrate, which is not preferable. Therefore, a method of ensuring gas barrier properties by providing a dense silicon oxide film or the like on at least one surface of a synthetic resin substrate is also one of preferable methods.

An anode 2 is provided on the substrate 1, and the anode plays a role of injecting holes into the hole transport layer. The anode is usually made of metals such as aluminum, gold, silver, nickel, palladium, platinum, metal oxides such as indium and/or tin oxides, metal halides such as copper iodide, carbon black, or poly(3-methylthiophene) , polypyrrole, polyaniline and other conductive polymers. The formation of the anode is generally performed by a sputtering method, a vacuum evaporation method, or the like. In addition, in the case of metal particles such as silver, particles such as copper iodide, carbon black, conductive metal oxide particles, conductive polymer fine powder, etc., it can also be dispersed in a suitable binder resin solution, coated on the substrate 1 to form the anode 2 . In addition, in the case of a conductive polymer, a thin film may be directly formed on a substrate by electrolytic polymerization, or an anode may be formed by coating a conductive polymer on a substrate. The anode can also be formed by laminating different substances. The thickness of the anode varies depending on the desired transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more, and in this case, the thickness is usually 5 to 1000 nm, preferably about 10 to 500 nm. The anode 2 can be the same as the substrate 1 when it can be opaque. In addition, a different conductive material may be further laminated on the above-mentioned anode.

A hole transport layer 4 is arranged on the anode 2 . A hole injection layer 3 may also be provided between them. The conditions required for the material of the hole transport layer must be a material that has high hole injection efficiency from the anode and can efficiently transport the injected holes. Therefore, it is required to have a low ionization potential, high transparency to visible light, high hole mobility, excellent stability, and difficulty in generating trap-forming impurities during manufacture or use. In addition, since it is in contact with the light-emitting layer 5, it is required not to eliminate light emitted from the light-emitting layer, or not to form an exciplex with the light-emitting layer, thereby reducing efficiency. In addition to the general requirements described above, heat resistance is also required for devices when considering the application of in-vehicle displays. Therefore, a material having a Tg of 85° C. or higher is preferable.

In the organic EL device of the present invention, known triarylamine dimers such as α-NPD can be used as the hole transport material.

It should be noted that, if necessary, a known compound may be used in combination with the triarylamine dimer as another hole transport material. Examples include aromatic diamines containing two or more tertiary amines and two or more fused aromatic rings substituted on nitrogen atoms, 4,4',4"-tris(1-naphthylphenylamino)triphenylamine Aromatic amine compounds with a star structure, aromatic amine compounds composed of tetramers of triphenylamine, 2,2',7,7'-tetra-(diphenylamino)-9,9'-spirobi Spiral compounds such as fluorene, etc. These compounds may be used alone or in combination as necessary.

In addition to the above-mentioned compounds, polymer materials such as polyvinylcarbazole, polyvinyltriphenylamine, polyarylene ether sulfone containing tetraphenylbenzidine, and the like are exemplified as materials for the hole transport layer.

In the case of forming the hole transport layer by the coating method, add one or more hole transport materials, and if necessary, additives such as a binder resin that does not form hole traps, a coatability improver, etc., and prepare by dissolving The coating solution is applied on the anode 2 by a method such as a spin coating method, and dried to form the hole transport layer 4 . Examples of the binder resin include polycarbonate, polyarylate, polyester and the like. If the added amount of the binder resin is large, the hole mobility will be lowered, so the added amount is desirably small, usually preferably 50% by weight or less.

In the case of forming by the vacuum evaporation method, the hole transport material is placed in a crucible placed in a vacuum container, and the inside of the vacuum container is evacuated to about 10 ^-4 Pa with an appropriate vacuum pump, and then the crucible is heated to make the air The hole transport material is evaporated, and the hole transport layer 4 is formed on the substrate on which the anode is formed facing the crucible. The film thickness of the hole transport layer is usually 5 to 300 nm, preferably 10 to 100 nm. In order to uniformly form such a thin film, a vacuum evaporation method is generally used.

A light emitting layer 5 is provided on the hole transport layer 4 . The light-emitting layer contains the Al complex represented by the general formula (I) and the Ir complex represented by the general formula (II). Excited by recombination with electrons injected from the cathode and moving through the electron transport layer 6, strong luminescence is exhibited. It should be noted that, within the range that does not impair the performance of the present invention, the light-emitting layer 5 may contain other host materials (playing the same role as the complex of general formula (I)) or other components such as fluorescent dyes.

The content of the Ir complex represented by the general formula (II) in the light-emitting layer is preferably in the range of 0.1 to 30% by weight. When it is 0.1% by weight or less, it does not contribute to the improvement of the luminous efficiency of the device, and when it exceeds 30% by weight, dimers and the like are formed between Ir complexes to cause concentration extinction, resulting in a decrease in luminous efficiency. In conventional devices using fluorescence (singlet state), it tends to be preferable to have a slightly larger amount of the fluorescent dye (dopant) than that contained in the light emitting layer. The Ir complex may be partially contained in the light-emitting layer with respect to the film thickness direction, or may be non-uniformly distributed. The film thickness of the light emitting layer 5 is usually 10 to 200 nm, preferably 20 to 100 nm. A thin film was formed by the same method as the hole transport layer.

In order to further improve the luminous efficiency of the device, an electron transport layer 6 is provided between the luminescent layer 5 and the cathode 7 . The electron transport layer is formed of a compound capable of efficiently transporting electrons injected from the cathode toward the light emitting layer between electrodes to which an electric field is applied. The electron-transporting compound used in the electron-transporting layer 6 must be a compound that has high electron injection efficiency from the cathode 7 and has high electron mobility so that the injected electrons can be efficiently transported.

Examples of electron transport materials satisfying such conditions include metal complexes such as Alq3, metal complexes of 10-hydroxybenzo[h]quinoline, oxadiazole derivatives, and distyrylbiphenyl derivatives. , silole derivatives, 3- or 5-hydroxyflavone metal complexes, benzoxazole metal complexes, benzothiazole metal complexes, tribenzimidazolylbenzene, quinoxaline compounds, phenanthroline derivatives substances, 2-tert-butyl-9,10-N,N'-dicyanoanthraquinone diimide, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, etc. The film thickness of the electron transport layer 6 is usually 5 to 200 nm, preferably 10 to 100 nm. Like the hole transport layer, the electron transport layer is formed by being laminated on the light emitting layer by a coating method or a vacuum deposition method. Usually a vacuum evaporation method is used.

In order to further increase the efficiency of hole injection and improve the adhesion of the entire organic layer to the anode, a hole injection layer 3 may also be inserted between the hole transport layer 4 and the anode 2 . Insertion of the hole injection layer 3 has the effect of suppressing the voltage rise when the device is continuously driven with a constant current while reducing the initial device driving voltage. As the conditions required for the material used in the hole injection layer, it is required to have good adhesion with the anode, be able to form a uniform film, and be thermally stable, that is, the melting point and glass transition temperature are high, the melting point is above 300 ° C, and the Tg is 100. ℃ or more. Further examples include low ionization potential, easy injection of holes from the anode, and high hole mobility.

For this purpose, phthalocyanine compounds such as copper phthalocyanine, organic compounds such as polyaniline and polythiophene, sputtered carbon films, and metal oxides such as vanadium oxide, ruthenium oxide, and molybdenum oxide have been reported so far. The hole injection layer can also be formed into a thin film in the same manner as the hole transport layer, but in the case of an inorganic substance, sputtering, electron beam evaporation, or plasma CVD can also be used. The film thickness of the anode buffer layer 3 formed as described above is usually 3 to 100 nm, preferably 5 to 50 nm.

It is preferable that the electron transport layer 6 is laminated on the light emitting layer 5 without a hole blocking layer in between.

The cathode 7 functions to inject electrons into the light emitting layer 5 . As the material for the cathode, the material used in the anode 2 can be used. In order to efficiently perform electron injection, a metal with a low work function is preferred, and appropriate metals such as tin, magnesium, indium, calcium, aluminum, silver, or their alloys can be used. . As specific examples, low work function alloy electrodes such as magnesium-silver alloys, magnesium-indium alloys, and aluminum-lithium alloys may be mentioned. The film thickness of the cathode is usually the same as that of the anode. In order to protect the cathode formed of a metal with a low work function, the stability of the device is increased by further stacking a metal layer having a high work function and being stable to the atmosphere on it. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum, etc. are used.

Furthermore, inserting an extremely thin insulating film (0.1-5nm) such as LiF, MgF ₂ , Li ₂ O, etc. as an electron injection layer between the cathode 7 and the electron transport layer 6 is also an effective method for improving device efficiency.

It should be noted that the structure opposite to that of FIG. 1, that is, the cathode 7, the electron transport layer 6, the light emitting layer 5, the hole transport layer 4, and the anode 2 are stacked in the order of the substrate 1. The organic EL device of the present invention is provided between two substrates at least one of which is highly transparent. In this case, layers may be added or omitted as necessary.

The organic EL device of the present invention can be applied to any of a single device, a device composed of a structure arranged in an array, and a structure in which an anode and a cathode are arranged in an X-Y matrix. According to the organic EL device of the present invention, by making the light-emitting layer contain a compound having a specific skeleton and a phosphorescent metal complex, it is possible to obtain higher luminous efficiency than conventional devices using light emission from a singlet state, and drive stability is also improved. Greatly improved device, capable of excellent performance in full-color or multi-color flat panel applications

Example

Hereinafter, the present invention will be described in more detail using synthesis examples and examples, but the present invention is not limited to the description of the following examples unless the gist is exceeded.

Example 1

/秒在ITO上形成作为空穴注入层的CuPC，其厚度为25nm。其次以

/秒的蒸镀速度在空穴注入层上形成作为空穴传输层的α-NPD，其厚度为55nm。Copper phthalocyanine (CuPC) was used for the hole injection layer, α-NPD was used for the hole transport layer, and Alq3 was used for the electron transport layer. On a glass substrate on which an anode made of ITO with a film thickness of 110 nm was formed, each thin film was laminated at a vacuum degree of 5.0×10 ^-4 Pa by a vacuum evaporation method. first with

/sec CuPC as a hole injection layer is formed on ITO with a thickness of 25nm. followed by

α-NPD as a hole transport layer was formed on the hole injection layer at a vapor deposition rate of 55 nm at a vapor deposition rate of 55 nm.

Next, BmqAl (compound 1) and Irbt ₃ (compound 31) were co-evaporated on the hole transport layer from different deposition sources to form a light emitting layer with a thickness of 47.5 nm. At this time, the concentration of Irbt ₃ was 7.0%.

/秒的蒸镀速度形成作为电子传输层的Alq3，其厚度为30nm。再以

/秒的蒸镀速度在电子传输层上形成作为电子注入层的氧化锂(Li₂O)，其厚度为1nm。最后，以

/秒的蒸镀速度在电子注入层上形成作为电极的铝(Al)，其厚度为100nm，从而制成有机EL器件。Secondly, with

/sec evaporation speed forms Alq3 as an electron transport layer with a thickness of 30nm. Then with

Lithium oxide (Li ₂ O) as an electron injection layer was formed on the electron transport layer at a vapor deposition rate of 1/sec to a thickness of 1 nm. Finally, with

Aluminum (Al) as an electrode was formed on the electron injection layer at a vapor deposition rate of 100 nm in thickness to form an organic EL device.

Example 2

An organic EL device was produced in the same manner as in Example 1, except that BAlq (compound 11) and Irbt ₃ (compound 31) were co-deposited from different deposition sources to form a light emitting layer with a thickness of 47.5 nm. It should be noted that the concentration of Irbt ₃ was 7.0%.

Comparative example 1

An organic EL device was produced in the same manner as in Example 1 except that bt ₂ Ir(acac) was used as the guest material of the light-emitting layer. It should be noted that bt ₂ Ir(acac) has a structure in which one bt of Irbt ₃ is replaced by acac (acetylacetonate).

Comparative example 2

An organic EL device was fabricated in the same manner as in Example 2 except that bt ₂ Ir(acac) was used as the guest material of the light-emitting layer.

Comparative example 3

An organic EL device was fabricated in the same manner as in Example 1 except that BCP was used as the host material of the light-emitting layer.

Comparative example 4

An organic EL device was produced in the same manner as in Example 1, except that BCP was used as the host material of the light-emitting layer and bt ₂ Ir(acac) was used as the guest material.

Table 1 shows the emission peak wavelength, maximum luminous efficiency, and luminance half-life (initial luminance: 500 cd/m ² ) of each organic EL device obtained in Examples and Comparative Examples.

[Table 1]

Luminescence peak wavelength (nm) Maximum luminous efficiency (cd/A) Brightness half-life time (hr) Example 1 554 11.0 1000 Example 2 554 11.4 1000 Comparative Example 1 554 10.5 800 Comparative example 2 554 10.5 800 Comparative example 3 555 9.2 300 Comparative example 4 554 8.5 200

According to the present invention, it is possible to obtain an organic EL device having a long driving life while maintaining good light emission characteristics. Therefore, the organic EL device of the present invention can be applied to flat panel displays (such as OA computer use or wall-mounted TVs), vehicle-mounted display devices, mobile phone displays, and light sources that utilize the characteristics of surface luminous bodies (such as photocopier light sources, liquid crystal displays, and instruments). Class backlight source), display panel, identification light, its technical value is great.

Claims (4)

1. organic electroluminescence device, this organic electroluminescence device is by stacked anode on substrate, comprise hole transmission layer, the organic layer of luminescent layer and electron transfer layer and negative electrode and form, between luminescent layer and anode, has hole transmission layer, between luminescent layer and negative electrode, has electron transfer layer, it is characterized in that: in luminescent layer, contain the metal-organic complex shown in the following general formula (I) as material of main part, and contain the metal-organic complex shown in the general formula (II) as guest materials

In the formula, R ₁～R ₆Represent hydrogen atom, alkyl, aralkyl, alkenyl, cyano group, alkoxyl independently of one another, can have substituent aromatic hydrocarbyl and maybe can have substituent aromatic heterocycle, L represents 1 valency group shown in following general formula (1), (2), (3) or (4)

-O-Ar ₁ (1)

Ar ₁～Ar ₅Expression independently of one another can have substituent aromatic hydrocarbyl and maybe can have substituent aromatic heterocycle, and Z represents silicon or germanium, R ₁～R ₆Have and the identical implication of general formula (I),

In the formula, R ₇～R ₁₄Represent hydrogen atom, alkyl, aralkyl, alkenyl, cyano group, alkoxyl independently of one another, can have substituent aromatic hydrocarbyl and maybe can have substituent aromatic heterocycle.

2. organic electroluminescence device as claimed in claim 1 wherein disposes hole injection layer at anode and hole transport interlayer.

3. organic electroluminescence device as claimed in claim 1 wherein disposes electron injecting layer at negative electrode and electric transmission interlayer.

4. organic electroluminescence device as claimed in claim 2 wherein disposes electron injecting layer at negative electrode and electric transmission interlayer.

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