JP2000030869A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance luminous efficiency and to stably keep it for a long time by installing an electron transport layer containing β-diketone complex between a luminescent layer and a cathode. SOLUTION: A compound represented by formula I is contained in an electron transport layer of an organic electroluminescence device. For example, 0.1 mol.% or more of lithium complex of β-diketone in formula II is preferably contained. A transparent electrode acting as an anode is formed on a substrate of the device, a luminescent layer containing an organic luminescent material, the electron transport layer, and a cathode are formed in order on the anode. By using the electron transport layer containing β-diketone complex, driving voltage of the device is lowered, high brightness can be obtained, and efficiency by rebonding of a hole and an electron in a fluorescent organic material within the luminescent layer is enhanced. In formula I, R1 and R2 is each hydrogen, halogen element, alkyl group, alkoxy group, aryl group, acyl group, cyano group, aromatic hydrocarbon group, or aromatic hetrocyclic group; M is boron, alkali metal, aluminum, or zinc; and m is 1-4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence (organic EL) device used for a flat display or a flat light source, and more particularly, to an organic EL device having improved light emission characteristics and excellent life characteristics. It is about.

[0002]

2. Description of the Related Art With the rapid progress of technological development in the field of information communication in recent years, great expectations have been placed on flat displays instead of CRTs. Among them, EL elements have been actively studied since they are excellent in high-speed response, visibility, luminance, and the like.

At present, a practically used ZnS / Mn-based inorganic EL device has a problem that the driving voltage is as high as about 100 V and sufficient luminance cannot be obtained. On the other hand, the electroluminescence of organic fluorescent substances has been known for a long time, and many studies using an anthracene single crystal have been conducted.However, since the driving voltage is high and the emission luminance is low, it has not been possible to develop a practical device. Did not.

[0004] However, in 1987, Kodak T
The organic EL device disclosed by Ang et al. can be driven at a low DC voltage of 10 V or less, has a high luminance of 1000 cd / m ^2, and has an excellent luminous efficiency of 1.5 lm / W (Appl. Phys. Lett., 51, 913 (1987)). The announcement showed the advantages of low-voltage driving and multi-coloring by designing organic molecules compared to inorganic EL devices.
Many organic EL devices such as new organic materials and new cathode materials have been studied.

[0005]

As a conventionally known electron transporting layer, 8-electron represented by tris (8-quinolinolato) aluminum (hereinafter abbreviated as "Alq").
Examples include a metal complex of a hydroxyquinoline derivative and an oxazole derivative. Since these organic materials have both an electron transporting property and a fluorescent property, they can function as an electron transporting layer simultaneously with the light emitting layer. The holes injected from the anode move in the hole transport layer, the electrons injected from the cathode move in the electron transport layer, and the holes and electrons recombine in the light emitting layer to emit light.

In an organic EL, electrons are injected from a cathode into the lowest unoccupied orbit (LUMO) of a substance used for an electron transport layer. For this reason, alloys such as magnesium and alkali metals (see JP-A-5-198380) having a small work function are used for the cathode. In addition, the lower the electron injection barrier from the cathode, the easier the electron injection of the substance used for the electron transporting layer, so that the driving voltage can be reduced.

Conventionally, although there have been many reports on cathodes having a low work function, a metal complex of an 8-hydroxyquinoline derivative such as Alq or an oxazole derivative has been used for the electron transporting layer. It has been unsatisfactory, and the development of an organic EL device having higher luminous efficiency and longer life has been desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL device capable of improving luminous efficiency and maintaining stable luminescent characteristics for a long period of time. It is in.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the present invention relates to an organic EL device having at least an anode, a light-emitting layer containing an organic light-emitting substance, and a cathode. An organic EL device comprising an electron transporting layer containing a β-diketone complex represented by the following general formula (1) provided between the cathode and the cathode.

[0010]

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(Wherein R ¹ and R ² each independently represent hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic group, A group hydrocarbon group, a phenylethynyl group, or an aromatic heterocyclic group, M represents a boron or metal atom, and m represents an integer of 1 to 4.)

Further, the present invention provides an organic EL device characterized in that M of the compound of the general formula (1) is any one of boron, an alkali metal, an alkaline earth metal, aluminum and zinc.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an electron transporting layer containing a compound represented by the formula (1) is provided between a light emitting layer and a cathode of an organic EL device. As a result, an organic EL device having excellent luminous efficiency and capable of emitting light stably for a long period of time is obtained.

FIG. 1 is a side view of the basic structure of the organic EL device of the present invention, and FIG. 2 is a side view of a more preferred example. In FIG. 1, reference numeral 1 denotes a substrate, 2 denotes an anode, 3 denotes a light emitting layer containing an organic light emitting substance, 4 denotes an electron transport layer, and 5 denotes a cathode. FIG. 2 shows that a hole transport layer 6 and an interface layer 7 are provided between the anode 2 and the light emitting layer 3, and an interface layer 8 is provided between the cathode 5 and the electron transport layer 4.

The substrate 1 in the present invention is a support for an organic EL device, and a transparent substrate such as glass or plastic is generally used. In the case of plastic, polycarbonate, polymethacrylate, polysulfone, or the like can be used.

On the substrate 1, a transparent electrode as an anode is provided. As the transparent electrode, an indium tin oxide (ITO) thin film or a tin oxide film can be usually used. Further, it may be made of a metal having a large work function, such as aluminum or gold, an inorganic conductive substance such as copper iodide, or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or polyaniline.

The method of producing the anode is generally performed by a vacuum deposition method, a sputtering method, or the like. In the case of a conductive polymer, a solution with an appropriate binder is applied to the substrate. Alternatively, a thin film can be formed directly on a substrate by electrolytic polymerization. The thickness of the anode depends on the required transparency, but the visible light transmittance is 60% or more, preferably 80% or more.
It is 5 to 1000 nm, preferably 10 to 500 nm.

A light emitting layer 3 is provided on the anode 2. As the organic light emitting substance used in the light emitting layer, a compound having a high fluorescence quantum yield, a high electron injection efficiency from the cathode 4, and a high electron mobility is effective. In particular, a chelate complex of a quinoline derivative which is excellent in stability and heat resistance in an amorphous thin film can be preferably used.

The metal element forming such a chelate complex includes lithium, silver, beryllium, magnesium, calcium, strontium, zinc, cadmium,
Examples include aluminum, gallium, indium, thallium, yttrium, scandium, lanthanum, zirconium, manganese, and lutetium. Among them, chelate complexes of beryllium, magnesium, aluminum, calcium, zinc, scandium and the like having high fluorescence quantum yield are particularly preferable.

The thickness of the light emitting layer 3 is usually 10 to
It is 200 nm, preferably 40 to 100 nm.

In the present invention, as a method for further improving the luminous efficiency of the device and enabling a full-color display,
The organic light emitting layer may be doped with another fluorescent organic material.

As such a doped dye material, known organic substances can be used, for example, stilbene dyes, oxazole dyes, cyanine dyes, xanthene dyes, oxazine dyes, coumarin dyes, acridine dyes Dyes and quinacridone derivatives (JP-A-5-70)
773), perylene derivatives (JP-A-3-791), 4-dicyanomethylene-2-methyl-6-p-
Dimethylaminostyryl-4H-pyran (DCM1) derivative, europium (III) complex (Chem. Lett., 1991, 126)
7), zinc porphyrin derivatives, rhodamine dyes (JP-A-8-286033), biolanthrone derivatives (JP-A-7-90259), neil red derivatives (Science, 1995, 1332), bis (2-styryl-8) -Quinolinolato) zinc (II) complex (Chem. Lett., 1997, 633)
It can be used widely. The concentration of such a doped organic material is 0.01 to 3 in the light emitting layer.
It is preferably 0 mol%.

In the present invention, an electron containing a β-diketone complex represented by the formula (1) is provided between the light emitting layer and the cathode in order to improve the luminous efficiency of the device and maintain a high luminous efficiency for a long period of time. A transport layer 4 is provided.

[0024]

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(Wherein R ¹ and R ² each independently represent hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic group, A group hydrocarbon group, a phenylethynyl group, or an aromatic heterocyclic group, M represents a boron or metal atom, and m represents an integer of 1 to 4.)

In the compound represented by the general formula (1), M represents an atom of boron or a metal. Examples of the metal atom include alkali metals, alkaline earth metals, aluminum, bismuth, cadmium, chromium, and cobalt. , Copper, gallium, indium, iron, lead, manganese, nickel, niobium, platinum, ruthenium, rare earth elements, etc. can be widely used.

When m is 2, R 1 of the first group is
¹ and R ^2, the two first of R ¹ and R ² groups may be the same or different. When m is 3 or more, all of them may be the same, all may be different, or some may be partially different.

The compound of the general formula (1) of the present invention includes
In order to facilitate electron injection from the cathode and reduce the driving voltage of the device, a compound having a high electron affinity is preferable. As such a compound, it is particularly preferable that M is any one of boron, an alkali metal, an alkaline earth metal, aluminum and zinc.

The compound represented by the general formula (1) can be used alone or as a mixture with a conventionally known electron-transporting substance.
Examples of such conventionally known electron transporting substances include cyclopentadiene derivatives (JP-A-2-28967).
No. 5), oxadiazole derivatives (JP-A-2-21)
No. 6791), bisstyrylbenzene derivatives (Japanese Patent Application Laid-Open No. 1-245087), p-phenylene compounds (Japanese Patent Application Laid-Open No. 3-33183), phenanthroline derivatives (Japanese Patent Application Laid-Open No. 5-331559), and triazole derivatives (Japanese Patent Application Laid-open No. Hei 5-331559). 7-90260).

In these electron transporting layers, the compound of the general formula (1) is effective even in a small amount, and it is particularly preferable that the compound is contained in an amount of 0.1 mol% or more. If the amount is less than 0.1 mol%, the efficiency of electron injection from the cathode may decrease. The thickness of the electron transport layer of the present invention is preferably in the range of 0.5 to 60 nm. If the thickness is 0.5 nm or less, the affinity and adhesion between the cathode and the light emitting layer cannot be obtained. If the thickness is 60 nm or more, the driving voltage of the device may increase.

In the present invention, a hole transport layer 6 can be provided between the anode 2 and the light emitting layer 3 if necessary. By providing the hole transport layer, electrons that are injected from the cathode and move in the light emitting layer are efficiently blocked,
The probability of recombination of holes and electrons in the light emitting layer increases, and high luminous efficiency can be achieved.

As the hole transport material, a material having a low injection barrier from the anode 2 and a high hole mobility can be used. As such a hole transport material, a known hole transport material can be used. For example, N, N'-diphenyl-
N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (hereinafter referred to as TPD) and 1,1'-bis (4-di-p-tolylaminophenyl)
Aromatic diamine compounds such as cyclohexane;
The hydrazone compound shown in JP-A-311591 can be used.

Further, polymer materials such as poly-N-vinylcarbazole and polysilane can be preferably used (Appl. Phys. Lett., 59, 2760 (1991)).

As a method for producing a thin film of the organic hole transporting material, a vacuum evaporation method, a dipping method, a spin coating method, an L
Various methods such as the method B can be applied. In order to produce a uniform thin film of submicron order without defects such as pinholes, a vacuum evaporation method and a spin coating method are particularly preferable.

In the case of spin coating, a binder resin which does not trap holes can be used by dissolving it in a coating solution. Examples of such a binder resin include polyether sulfone, polycarbonate, and polyester. The content of the binder resin is preferably from 10 to 50% by weight which does not decrease the hole mobility.

The material of the hole transport layer is not limited to the above-mentioned organic substances, but also includes p-metals such as metal chalcogenides, metal halides, metal carbides, nickel oxides, lead oxides, copper iodides, and lead sulfides. A type compound semiconductor, p-type hydrogenated amorphous silicon, p-type hydrogenated amorphous silicon carbide, or the like can also be used.

The hole transport layer of such an inorganic substance can be formed by a known method such as a vacuum evaporation method, a sputtering method, and a CVD method. Regardless of whether an organic substance or an inorganic substance is used, the thickness of the hole transport layer is usually
10 to 200 nm, preferably 20 to 80 nm
It is.

In the present invention, the anode 2 and the hole transport layer 6
Between them, an interface layer 7 may be provided for the purpose of preventing a leak current, reducing a hole injection barrier, improving adhesion, and the like.
Such an interface layer material is disclosed in JP-A-4-30868.
No. 8,4,4 ′, 4 ″ -tris {N- (3-methylphenyl) -N-phenylamino} triphenylamine (hereinafter referred to as MTDATA) and , 4 ', 4 "-Tris {N, N diphenylamino} triphenylamine (hereinafter referred to as TDATA), copper phthalocyanine and the like can be preferably used. The film thickness when providing this interface layer is 5 to 10
0 nm can be preferably used.

In the present invention, the electron transport layer 4 and the cathode 5
Between them, an interface layer 8 can be provided as needed. By providing this interface layer, a reduction in driving voltage, an improvement in luminous efficiency, and a longer life can be achieved. This interface layer has the effect of facilitating electron injection from the cathode and the effect of increasing the adhesion to the cathode.

Examples of such an interfacial layer material include alkali metal fluorides represented by lithium fluoride (Appl. Phys. Lett., 70, 152 (1997)), alkaline earth metal fluorides, magnesium oxide, and oxides. There are oxides such as strontium, aluminum oxide, and barium oxide. Since such an interface layer material is itself an insulator, the film thickness used is usually a thin film of 5 nm or less, and preferably 2 nm or less.
It is considered that tunnel injection from the cathode becomes possible by setting the thickness to nm or less.

The cathode 5 is provided on the electron transport layer 4. As the cathode, various kinds of cathodes including known organic EL cathodes can be used. For example, there are a magnesium-aluminum alloy, a magnesium-silver alloy, a magnesium-indium alloy, an aluminum-lithium alloy, and aluminum.

In the organic EL device of the present invention, in order to secure storage stability and drive stability in the atmosphere, even if it is shielded from oxygen and moisture in the atmosphere by coating a polymer film or sealing with glass. Good.

The organic EL device of the present invention is used as a full-surface light emitter, used as a backlight or a wall illumination device of a liquid crystal display device, or formed by patterning pixels.
It can be used as a display.

[0044]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not necessarily limited to these.

Example 1 (Example) An anode 2 (sheet resistance 7 Ω / □) was formed on a glass substrate by depositing ITO with a thickness of 200 nm. On this anode 2, TPD (Formula 2) was deposited to a film thickness of 60 nm by a vacuum deposition method to form a hole transport layer 6. Next, a distyryl arylene compound (formula 3) was deposited to a thickness of 55 nm to form a light-emitting layer 3.

Further, a β-diketone compound represented by the formula (4) (M = Li, R ¹ = R ² = methyl group, m = 1)
Was deposited by 5 nm to form an electron transport layer 4. Finally,
Mg and Ag are co-evaporated to form a 200 nm-thick MgAg (1
0: 1) A cathode alloy was formed to produce an organic EL device.

[0047]

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[0048]

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[0049]

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Example 2 (Comparative Example) Instead of the β-diketone compound represented by the formula (4) in Example 1, Al which is an aluminum complex of 8-oxyquinoline was used.
An organic EL device was produced in the same manner as above except that 5 nm was vapor-deposited to form an electron transport layer.

Example 3 (Example) On the anode 2 used in Example 1, 1 part by weight of polyvinylcarbazole and 1 part by weight of TPD (formula 2) were added with 500 parts of dichloromethane.
Using the solution dissolved in parts by weight, the number of rotations was 5000 rpm.
The substrate was spin-coated with a film thickness of 60 nm to form a hole transport layer. Next, Alq was deposited to a thickness of 55 nm to form a light-emitting layer 3.

Further, a β-diketone compound represented by the formula (5) (M = Li, R ¹ = R ² = tert-butyl group, m =
1) was evaporated to a thickness of 5 nm to form an electron transport layer. Finally,
Mg and Ag are co-evaporated to form a 200 nm-thick MgAg (1
0: 1) A cathode alloy was formed to produce an organic EL device.

[0053]

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Example 4 (Comparative Example) The thickness of the light emitting layer 3 made of Alq in Example 3 was set to 60 nm.
An organic EL device was produced in the same manner except that the electron transport layer 4 was used also as a light emitting layer.

Example 5 (Example) Instead of the β-diketone compound represented by the formula (5) in Example 3, a β-diketone compound represented by the formula (6) (M = B, 3
An organic EL device was produced in the same manner as in Example 3, except that all of the groups (R ¹ = R ² = methyl group, m = 3) were used.

[0056]

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Example 6 (Example) Instead of the β-diketone compound represented by the formula (5) in Example 3, a β-diketone compound represented by the formula (7) (M = Al,
An organic EL device was produced in the same manner as in Example 3, except that all three groups, R ¹ = R ² = methyl group, m = 3) were used.

[0058]

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Example 7 (Example) On the anode 2 used in Example 1, copper phthalocyanine (formula 8) was deposited to a thickness of 20 nm to form an interface layer 7. Then
TPD (formula 2) is deposited to a thickness of 30 nm to form a hole transport layer 6
Was formed. Next, Alq and quinacridone (Formula 9) were co-evaporated using different boats to form a light-emitting layer by co-evaporation to a thickness of 55 nm. At this time, the concentration of quinacridone was 0.8 mol% (Alq was 99.2 mol%).

[0060]

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[0061]

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Further, a β-diketone compound represented by the formula (10) (M = Mg, all R ¹ = R ² = methyl groups of ^two groups, m = 2) is deposited to a thickness of 5 nm to form an electron transport layer 4. Was formed. Next, lithium fluoride was deposited to a thickness of 0.5 nm to form an interface layer 8. Finally, an AlLi alloy (Li content: 0.07% by weight) was vapor-deposited to a thickness of 200 nm using an alumina-coated crucible to form a cathode 5 to form an organic E layer.
An L element was produced.

[0063]

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Example 8 (Comparative Example) The same procedure as in Example 7 was carried out except that the thickness of the light emitting layer composed of Alq and quinacridone (formula 9) was 55 nm, and then the electron transport layer formed only of Alq was 5 nm. Thus, an organic EL device was manufactured.

The luminous efficiency characteristics (luminance (c) when 10 V was applied) of the organic EL elements manufactured in the above-described examples (Examples and Comparative Examples)
d / m ² ) and luminous efficiency (lm / W) are shown in Table 1.
The symbol in the column of the electron transport layer indicates an abbreviation of the substance, and the number indicates the formula number of the β-diketone compound used.

The driving stability (10 mA / c in nitrogen)
initial luminance when driven at a constant current of m ² is the time required for a drop to half of the original half-life time (hours))
Table 2 shows the measurement results of the luminous efficiency (lm / W) after the luminance was reduced by half.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

As described above, according to the present invention,
By using the electron transporting layer containing the specific β-diketone complex represented by the general formula (1), the driving voltage of the device can be reduced and high luminance can be obtained. Further, the efficiency of the fluorescent organic material in the light emitting layer due to hole and electron recombination is improved, and an organic EL device having high light emitting efficiency and excellent life can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a basic example of an organic EL device of the present invention.

FIG. 2 is a side view of a preferred example of the organic EL device of the present invention.

[Explanation of symbols]

 1: substrate 2: anode 3: light-emitting layer 4: electron transport layer 5: cathode 6: hole transport layer 7: interface layer 8: interface layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Irisawa 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term within Asahi Glass Co., Ltd. 2H068 AA20 AA35 BA01 BA11 3K007 AB02 AB03 AB06 AB11 DA01 DB03 EB00 FA01

Claims (2)

[Claims] 1. An organic electroluminescent device having at least an anode, a light emitting layer containing an organic light emitting substance, and a cathode, a β-diketone complex represented by the following general formula (1) between the light emitting layer and the cathode: An organic electroluminescence device comprising an electron transport layer comprising: Embedded image (In the above formula, R ¹ and R ² each independently represent hydrogen, a halogen element, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an acyl group, an aralkyl group, a cycloalkyl group, a cyano group, an aromatic hydrocarbon. Group, phenylethynyl group, or aromatic heterocyclic group, M represents a boron or metal atom, and m represents an integer of 1 to 4.) 2. The organic electroluminescent device according to claim 1, wherein M of the compound of the general formula (1) is any of boron, an alkali metal, an alkaline earth metal, aluminum and zinc.