JPH10231476A - Organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an org. EL element which has a high luminance, durability, and a specified peak wavelength by using a diamine compd. as the luminescent substance of an org. luminescent layer and an Eu complex having an alkoxy, fluorene, or heterocyclic group as the dopant for the luminescent layer. SOLUTION: This EL element at least comprises an anode, an org. luminescent layer, a hole blocking layer, an org. electron transport layer, and a cathode. The luminescent substance of the luminescent layer is N,N'-diphenyl-N,N'-di(3- methylphenyl)-1,1'-biphenyl-4,4'-diamine represented by formula I or N,N'- diphenyl-N,N'-dinaphthyl-1,1'-biphenyl-4,4'-diamine represented by formula III, and the dopant for the luminescent layer mainly comprises an Eu complex represented by formula II [wherein R1 is (substd.) 1-20C alkyl, cycloalkyl, or aryl; and R2 is H, OH, (substd.) 1-20C alkyl, etc.]. This element has a peak wavelength of 600nm or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting device utilizing electroluminescence (hereinafter, referred to as an organic EL device), and more particularly, to a device having an EL emission peak wavelength of 600 nm.
The present invention relates to the above-described organic EL device which has high luminance and is less deteriorated even when used for a long time.

[0002]

2. Description of the Related Art Since a so-called electroluminescence phenomenon, which emits light when a DC electric field is applied to an anthracene crystal, was observed in 1963, an organic EL device material showing the EL phenomenon from various viewpoints and an organic material using the same have been observed. Research on EL elements has been carried out. W. Tang and S.M. A. VanSlyke realizes high-luminance light emission by low-voltage direct-current driving by a structure in which a thin film of a fluorescent metal chelate complex molecule and a hole transporting diamine-based molecule is laminated.

Here, the structure of the conventional organic EL device is described in “Organic EL Device Development Strategy” (edited next-generation display device workshop, published by Science Forum Co., Ltd. in 1992). In general, an anode in which an organic light emitting layer also serves as an organic electron transport layer, an anode, an organic hole transport layer, a two-layer structure composed of an organic light emitting layer and a cathode, or an anode in which the organic light emitting layer also serves as an organic hole transport layer -Layer structure composed of an organic light emitting layer, an organic electron transporting layer and a cathode -B
A mold, or an organic hole transport layer and an organic electron transport layer each provided independently of the organic light emitting layer, an anode,
It is a three-layer structure type comprising an organic hole transport layer, an organic light emitting layer, an organic electron transport layer, and a cathode, and a hole blocking layer or an electron blocking layer is appropriately provided in accordance with these structures to further enhance luminous efficiency. It is what is being done.

More specifically, for example, in the two-layer structure-A type, a transparent electrode such as indium tin oxide (ITO) formed on a glass substrate by a sputtering method or the like is used as an anode, and an organic hole is used. In the transport layer, copper phthalocyanine, 1,1′-bis- (4-
N, N'-ditolylaminophenyl) cyclohexane,
N, N'-diphenyl-N, N'- represented by the formula (1)
(3-methylphenyl) -1,1′-biphenyl-4,
Diamine compounds such as 4'-diamine (hereinafter, TPD) and derivatives thereof are generally used, and tris (8-quinolinol) represented by the formula (9) is further provided in the organic light emitting layer.
Aluminum (hereinafter, Alq) and the like were used, and metals such as magnesium, magnesium-silver alloy, and aluminum were used for the cathode.

[0005] In order to enhance the luminous efficiency in the organic light emitting layer, an Eu complex having a heterocyclic ring represented by the formula (6) or a 4-dicyanomethylene-methylene compound represented by the formula (10) is appropriately used as a dopant. 2-Methyl-6-p-dimethylaminostyryl-4H-pyran, coumarin, or the like has been used in the organic light emitting layer in an amount of about 0.1 to 3 mol%.

[0006]

Embedded image

[0007] Improvements and developments of various organic EL device materials have been made, and particularly, hole transport materials have been actively studied, and Japanese Patent Publication Nos. 34-10966 and 58-65 are disclosed.
440 or US Pat. No. 5,061,569 discloses various hole transporting materials including TPD.

Further, as a part of the material for the organic EL device, a study on a dopant has been made. In particular, an Eu complex having a heterocyclic ring represented by the formula (6) is described in "Jpn.J. Ap.
pl. Phys. ", Vol. 34 (1995), p
p. As described in Nos. 1883 to 1887, the organic light-emitting layer of an A-type organic EL device having a two-layer structure composed of an anode, an organic hole transport layer, an organic light-emitting layer, and a cathode mainly has a light-emitting material such as Alq. Has been studied as an easy-to-deposit dopant.

[0009]

However, in a conventional organic EL element, particularly, an organic EL element which emits EL light of a long wavelength of 600 nm or more, (1) the light emission luminance is poor, and (2) the driving of the organic EL element. However, there is a problem that the light emitting substance is liable to be deteriorated due to heat and the like accompanying the heat generation.

Of course, as described above, various organic ELs
Improvements and developments of device materials are being carried out. In particular, although research is progressing on hole transport materials, the center of that research is
As described in “Organic EL Device Development Strategy”,
Almost no attempt has been made to use a material having a high hole-transporting property as a hole-transporting material in an organic hole-transporting layer as a light-emitting substance in an organic light-emitting layer.

Also, in research on dopants, almost no attempt has been made to use the dopant in combination with a specific substance having a high hole-transporting property for use in an organic light-emitting layer.

That is, conventionally, a high-luminance and durable red light-emitting organic EL device, more specifically, 100 cd / m ² due to a low-voltage load of less than 15 V having a peak wavelength of 600 nm or more. There has been a demand for an organic EL device having an organic light-emitting layer having the above-mentioned luminance and capable of emitting EL light and having heat resistance and oxidation resistance.

[0013]

According to the present invention, in an organic EL device including at least an anode, an organic light emitting layer, a hole blocking, an organic electron transporting layer, and a cathode as constituents, the organic light emitting layer has a light emitting material. , N, N'-diphenyl-N, N'- represented by formula (1)
(3-methylphenyl) -1,1′-biphenyl-4,
4'-Diamine (hereinafter, TPD) is used, and an Eu complex represented by the formula (2) is used as a main component of a dopant.

[0014]

Embedded image

(R ₁ is a substituted or unsubstituted C ₁ -C 1
20 represents an alkyl group, a cycloalkyl group or an aryl group, and R ₂ represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group, cycloalkyl group or aryl group having 1 to 20 carbon atoms. According to another aspect of the present invention, at least an anode,
An organic light emitting layer, a hole blocking layer, an organic electron transporting layer, and an organic EL element including a cathode as a constituent element.
As a light emitting substance of the organic light emitting layer, N, N′-diphenyl-N, N′-dinaphthyl- represented by the formula (3) is used.
1,1′-biphenyl-4,4′-diamine (hereinafter referred to as N
PD) and the Eu complex represented by the formula (2) is used as a main component of the dopant.

[0016]

Embedded image

Therefore, first, the organic light emitting layer which is a feature of the present invention will be described. That is, the organic light emitting layer is a layer in which holes injected from the anode and electrons injected from the cathode are recombined, and the energy of the recombination excites the organic light emitting material in the organic light emitting layer to generate EL light. I do.

In the present invention, it is essential to use TPD represented by the formula (1) or NPD represented by the formula (3) for the organic light emitting layer. This is because TPD and NPD have (1) a low ionization potential and a high hole transport property, and (2) on the other hand, by providing a hole blocking layer, the mobility of holes can be controlled relatively easily. (3) By using a specific Eu complex as a dopant, heat resistance and oxidation resistance are dramatically improved, and as a result, a peak wavelength of 6
This is because high luminance can be maintained for a long time in red light emission of 00 nm or more.

It should be noted that TPD and NPD used in the present invention have a broad meaning including their respective derivatives. Therefore, in this specification, when TPD and NPD are used, not only each of them alone but also each derivative thereof is used. Or a mixture of TPD or NPD with the respective derivatives.

The derivatives of TPD and NPD are
More specifically, at least one hydrogen present on the benzene ring or naphthalene ring contained in the molecule is an alkyl group such as a hydroxy group, methyl, ethyl, or methyl halide, or a cycloalkyl group such as cyclopentane or cyclohexane. Alternatively, it refers to one substituted by an aryl group such as a benzene ring or a naphthalene ring, and various derivatives are suitable for use in the present invention.

Next, various physical properties of TPD and NPD used in the present invention will be described.

First, regarding the glass transition point of TPD,
It is preferable that the temperature be in the range of 60 to 200 ° C. The reason is that if the glass transition point of TPD is in such a range,
This is because not only the heat resistance and oxidation resistance are good, but also a thin film of TPD can be easily formed by a vacuum deposition method or the like.

The ionization potential of TPD is preferably in the range of 5.0 to 5.8 eV. The reason is that if the ionization potential of TPD is in such a range, excellent hole injection efficiency can be obtained through the anode.

Similarly, the glass transition point of NPD is preferably in the range of 90 to 200 ° C. The reason is that if the glass transition point of NPD is in such a range, not only good heat resistance and oxidation resistance can be obtained, if not as much as TPD, provided that a specific Eu complex is combined as a dopant. This is because an NPD thin film can be easily formed by a vacuum deposition method or the like.

Further, the ionization potential of NPD is preferably in the range of 5.0 to 5.8 eV. The reason is that if the ionization potential of NPD is in such a range, excellent hole injection efficiency can be obtained via the anode, similarly to TPD.

The method for synthesizing TPD and NPD and their derivatives is not particularly limited. For example, the Ullmann (Ullmann) reaction converts an aryl halide and an arylamine into a diarylamine. It is possible to make TPD and NPD. Further, whether or not the compound of TPD or NPD represented by Formula (1) or Formula (3) has been synthesized can be easily confirmed using an infrared spectrophotometer or NMR. is there.

Next, the Eu complex used in the present invention will be described. That is, TPD or NPD
It is necessary to add a dopant mainly composed of the Eu complex represented by the formula (2). Because TPD
Alternatively, NPD alone has insufficient heat resistance and oxidation resistance, and has a high luminance red-based E having a wavelength of 600 nm or more.
This is because it is difficult to cause L light emission.

Here, the Eu complex represented by the formula (2) will be described in more detail. As the substituent R ₁ , those having a high electron donating property are preferable.
20 substituted or unsubstituted alkyl, cycloalkyl or aryl groups are preferred.

The reason is that by using a substituent having such a number of carbon atoms, it is possible to exhibit a stronger electron-donating property, and the electrons attracted from the substituent R ₂ can be transferred via the Eu metal which is a light-emitting site. This is because electrons can be efficiently pushed out to the outside, and high emission luminance can be obtained.

Further, with a substituent having such a carbon number, the resistance and oxidation resistance of the Eu complex itself are improved, or the reactivity of β-diketone is reduced due to steric hindrance of the substituent and the like. This is because there is little possibility that it becomes difficult to synthesize the Eu complex.

Here, among the Eu complexes represented by the formula (2), those having an alkoxy group represented by the formula (4)
u complex, Eu having a fluorene group represented by the formula (5)
A complex or E having a heterocyclic ring represented by the formula (6):
The u complex is suitable for the present invention as an Eu complex having a substituent R ₁ having a high electron donating property.

[0032]

Embedded image

(R ₃ is a substituted or unsubstituted C 1 -C 1
It represents an alkyl group or a cycloalkyl group of 20, R ₄
Represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group. )

[0034]

Embedded image

(R ₅ is hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms;
Represents a cycloalkyl group or an aryl group. )

[0036]

Embedded image

(R ₆ is hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms;
Represents a cycloalkyl group or an aryl group. Eu having an alkoxynaphthyl group represented by the formula (4)
Complex, by further electron donating highly alkoxy group contained in the alkoxy naphthyl group terminal is located in the para position of the carbon atoms of β- diketone, the electrons attracted by the substituents R _2, the direct emission region Can be strongly extruded to the outside through Eu, which is preferable for the present invention in that a stronger electron donating property can be exhibited, and a high fluorescence intensity can be obtained as a result.

Preferred examples of the alkoxynaphthyl group of the Eu complex represented by the formula (4) include a substituted or unsubstituted methoxynaphthyl group, an ethoxynaphthyl group, a propoxynaphthyl group, a butoxynaphthyl group and a cyclopropoxynaphthyl group. , Cyclobutoxynaphthyl group, tertiary butoxynaphthyl group, etc., in particular, methoxynaphthyl group is chemically stable and also not very bulky, so that it is not easily hindered during synthesis. It has advantages and is best suited for this invention.

In the present invention, it is preferable to use an Eu complex having a fluorene group represented by the formula (5) because the Eu complex has a fluorene group having a high electron-donating property and β- It is located at the terminal of the diketone and has a substituent R _{2 in the same} manner as the aforementioned alkoxynaphthyl group.
This is because it can be considered that the electrons attracted in step (1) can be pushed out to the outside through Eu, which is a direct light emitting part.

Furthermore, the Eu complex having a heterocyclic ring represented by the formula (6) is not as highly electron-donating as the alkoxynaphthyl group or the fluorene group, but is superior to the substituents of other Eu complexes. This is because it has a heterocyclic ring having an electron donating property, has been extensively studied in the past, and has an advantage of being easily available.

On the other hand, the substituent R ₂ in the Eu complex represented by the formula (2) is preferably different from the substituent R ₁ and has a high electron-withdrawing property. A substituted or unsubstituted methyl group having 1 to 20 carbon atoms, an alkyl group such as an ethyl group, a cycloalkyl group such as cyclopentane and cyclohexane, or a benzyl group;
An aryl group such as a naphthyl group can be suitably used.

In particular, alkyl halides are suitable for the present invention in that they have higher electron withdrawing properties. More specifically, they are CF ₃ , C ₂ F ₅ and C ₃ F ₇ , and Is higher and less bulky, using common materials,
It is most suitable for the present invention because it can be easily introduced into a molecule.

Here, the number of carbon atoms of the substituent R ₂ in the formula (2) is preferably in the range of 1 to 20. The reason is that by using a substituent having such a number of carbon atoms,
It becomes easier to show a strong electron-withdrawing property, and on the other hand, heat resistance decreases or reactivity decreases,
This is because there is little possibility that it becomes difficult to synthesize the Eu complex.

Therefore, since such a balance is better, the number of carbon atoms of the alkyl group or cycloalkyl group as the substituent R ₂ is more preferably in the range of 1 to 10.

The Eu complex represented by the formula (2) needs to have a phenanthroline ring. By introducing the phenanthroline ring into the Eu complex, the evaporability can be improved, and a thin film can be easily formed in the light emitting layer of the organic EL element by a vacuum evaporation method or the like.

Here, the phenanthroline ring is a heterocyclic aromatic ring group in which the rings at both ends of the three formed rings have at least one nitrogen, and the three rings forming the phenanthroline ring are: Hydroxy group, methyl group, alkyl group such as ethyl group, cyclopentane, cycloalkyl group such as cyclohexane, or benzyl group,
It may be a derivative having a substituent such as an aryl group such as a naphthyl group.

In this specification, the term “Eu complex” has a broad meaning including a derivative of the Eu complex. In the present invention, the Eu complex represented by the formula (2) may be used alone. In addition, it is also possible to suitably use the Eu complex derivative alone or a mixture of the Eu complex represented by the formula (2) and the Eu complex derivative.

Next, various physical properties of the Eu complex represented by the formula (2) used in the present invention will be described. First, the fluorescence intensity of the Eu complex will be described. In general, the emission luminance of an organic EL element varies greatly depending on the materials of constituent elements, such as a light-emitting substance and a dopant. It is said that the higher the luminance, the higher the emission luminance can be obtained when an organic EL element is manufactured using the material.

Therefore, the higher the fluorescence intensity of the Eu complex represented by the formula (2) used in the present invention is, the more preferable it is.
In the wavelength range of 650 nm, the fluorescence intensity of the Eu complex having a heterocyclic ring represented by the formula (6) is at least equivalent, more preferably 5% or more, and most preferably 10 to 10%.
That is 100% higher.

As a method of measuring the fluorescence intensity, for example, using a fluorescence spectrophotometer, tetrahydrofuran (T
It is preferable to measure by dissolving the target Eu complex in a solvent such as HF) so as to have a concentration of 1 × 10 ⁻⁴ mol / l.

The melting point of the Eu complex represented by the formula (2) used in the present invention can be measured from the position of the melting peak using a differential scanning calorimeter (DSC) or the like. Although it is possible, for example, the range of 100 to 500 ° C. is preferable. The reason is that if the Eu complex has a melting point in such a temperature range, the heat resistance of the light emitting layer in the organic EL element becomes good, while the Eu complex is less likely to be crystallized, and This is also because vacuum deposition can be easily performed using the Eu complex. Therefore, from the viewpoint of better balance, the melting point of the Eu complex represented by the formula (2) used in the present invention is more preferably in the range of 200 to 450 ° C.

Further, the formula (2) used in the present invention
The thermal decomposition temperature of the Eu complex represented by can be determined from a measurement chart as a temperature at which the mass is reduced by half using a thermobalance (TGA) or the like.
A range of 500 ° C. is preferred. The reason is that if the Eu complex has a thermal decomposition temperature in such a range, the heat resistance of the light emitting layer in the organic EL device becomes good,
This is because vacuum deposition can be easily performed using the u complex. Therefore, from the viewpoint of better balance, the thermal decomposition temperature of the Eu complex represented by the formula (2) used in the present invention is more preferably in the range of 300 to 450 ° C.

Next, the amount of the Eu complex represented by the formula (2) used in the present invention will be described. That is, the addition amount of the Eu complex is preferably determined in consideration of the luminance of the organic EL element and the like.
For example, it is preferable that the organic light-emitting layer be contained in the range of 0.01 to 20 mol%. The reason is that a sufficient effect of addition as a dopant can be obtained, and on the other hand, there is little possibility that the luminance and the life of the organic EL element are reduced due to a decrease in the carrier transport ability.

From the viewpoint of better balance, the addition amount of the Eu complex represented by the formula (2) is as follows.
It is good to be in the range of 0.1 to 10.0 mol%, optimally 0.2 to 3.0 mol%.

The amount of the Eu complex represented by the formula (2) in the organic light emitting layer can be easily adjusted by controlling the evaporation rate ratio of the Eu complex and the light emitting substance. .

Next, a synthesis example of the Eu complex represented by the formula (2) used in the present invention will be described.
However, in the Eu complex, various known synthesis methods can be employed without being limited to the synthesis method.

That is, as an example of a method for synthesizing the Eu complex represented by the formula (2) used in the present invention, for example, a 2-alkoxynaphthalene is reacted with an acetyl halide using a Friedel-Crafts reaction. After letting
By adding a halogenated alkyl carboxylic acid ester using a Claisen condensation reaction, a specific β
It can be synthesized by obtaining a diketone and reacting it with phenanthroline and a europium salt. Further, β- having a fluorene group in advance
If a diketone or a β-diketone having a heterocycle is obtained and used, it can be synthesized by mixing and reacting phenanthroline and a europium salt.

Next, the structure of the organic light emitting layer in the present invention will be described. As described above, the organic light emitting layer has a function of exciting a light emitting substance to emit light by energy generated by recombination of holes injected from the anode and electrons injected from the cathode. Therefore, it is preferable to determine the thickness of the organic light-emitting layer from the viewpoint of high emission luminance or not, but on the other hand, in order to obtain a highly durable organic EL element, It is necessary to consider the increase in resistance and the mechanical durability of the organic light emitting layer.

The more specific thickness of the organic light emitting layer is, for example, preferably in the range of 10 to 1000 nm.
The reason is that within this range, the rate at which the recombination energy of holes and electrons is absorbed by the electrode decreases, and the internal resistance of the organic EL element also increases with an increase in the thickness of the organic light emitting layer. This is because there is not much problem, and furthermore, a certain mechanical durability of the organic light emitting layer can be obtained. Therefore, from the viewpoint that such balance is more preferable, the thickness of the organic light emitting layer is more preferably 15 to 500.
nm, optimally in the range of 20-100 nm.

When the material used for the organic light emitting layer also has a hole transporting property, it is generally not necessary to separately provide an organic hole transporting layer in the organic EL device. As described above, NPD and TPD used in the present invention have an excellent hole transporting property in addition to the function as a light emitting substance. Is not always an essential requirement, and conversely, the present invention omits the organic hole transport layer or makes it as thin as possible to facilitate manufacture or reduce the internal resistance of the organic EL element. It has the advantage that it can be reduced.

However, when it is desired to more efficiently introduce holes from the anode into the organic light emitting layer, or when a light emitting substance having no hole transporting property or poor hole transporting property is mixed with NPD in the organic light emitting layer. When used as shown in FIG. 2, between the anode and the organic light emitting layer,
It is also preferable to provide an organic hole transport layer having a thickness of 1 to 1000 nm, more preferably 5 to 100 nm, for adjusting the hole transport property.

Next, the hole blocking layer in the organic EL device of the present invention will be described. That is, the hole blocking layer effectively shields holes that easily pass through the organic light emitting layer due to the excellent hole transporting property of NPD and TPD, and makes the NPD and TPD function as a light emitting substance. It is provided between the layer and the organic electron transport layer.

As the material of the hole blocking layer, any material having a high ionization potential and a small hole mobility can be suitably used. In particular, the triazole compound represented by the formula (7) It is preferable that both or any one of the derivatives is used as a main component.

[0064]

Embedded image

This is because the triazole compound and its derivative have an ionization potential as high as 6.0 eV or more, and an excellent hole shielding effect can be obtained. The compound can be easily formed into a thin film by a vacuum evaporation method or the like. This is also because it can be formed and is easy to use as an organic EL device material. Further, the fact that the triazole compound and its derivative are suitable for the present invention means that the triazole compound and its derivative generally have an ultraviolet absorption wavelength of 300 to 400 nm (3.1 to 4.1 nm).
eV), because a compound having a wavelength within such a range in terms of energy level does not significantly affect electron mobility.

Here, the thickness of the hole blocking layer depends on the hole blocking effect and mechanical strength, and furthermore,
It is preferable that the value be determined in consideration of an increase in the internal resistance of the organic EL element, and specifically, for example, 0.1 to 1000
It can be in the range of nm. The reason is that with such a thickness, a certain mechanical strength and a certain hole blocking effect can be obtained, and the increase in the internal resistance of the organic EL element caused by the hole blocking layer does not cause much problem. . Therefore, since the balance is better and the thickness of the hole blocking layer is easily controlled, the thickness of the hole blocking layer is more preferably 1 to 100 nm, and most preferably 15 to 100 nm.
When a low voltage of less than V is applied, a high luminance of 100 cd / m ² or more can be more easily obtained.
m.

The thickness of the hole blocking layer can be easily adjusted by controlling the deposition time, the deposition rate, and the like in the vacuum deposition method.

Next, the organic electron transport layer of the organic EL device according to the present invention will be described. That is, the organic electron transport layer has a function of transmitting electrons injected from the cathode to the organic light emitting layer. As a material of the organic electron transport layer, a metal chelate compound, a polycyclic fused hydrocarbon,
Benzoxazole, benzothiazole, perylene compounds and the like can be suitably used.

Of the metal chelate compounds, aluminum chelate compounds are particularly suitable for the present invention because of their high electron transport properties. Among them, Alq represented by the formula (9) is excellent in electron transport properties. It is suitable as a material for the organic electron transporting layer in the present invention because of its high heat resistance and its proven track record.

The thickness of the organic electron transporting layer is preferably determined in consideration of the electron transporting property, the increase in the internal resistance of the organic EL device, the mechanical strength, and the like.
For example, a range of 10 to 1000 nm is preferable. The reason is that with the thickness, a certain electron transporting property and the mechanical strength of the thin film can be obtained, and the increase in the internal resistance of the organic EL element due to the organic electron transporting layer does not cause much problem. .

Therefore, since the balance is better and the thickness of the organic electron transporting layer is easily controlled, it is more preferably 15 to 500 nm, and most preferably 20 to 500 nm.
It is better to be within the range of 100 nm.

The thickness of the organic electron transporting layer can be easily adjusted by controlling the deposition time and the degree of vacuum in the vacuum deposition method.

Next, in the organic EL device of the present invention,
The electrodes (anode and cathode) will be described. That is, the anode has a function of injecting holes by applying a voltage from the outside. Therefore, as the anode material, a metal or an electric conductive material having a large work function (generally, 4.0 eV or more) can be used. Specifically, a transparent oxide conductive material such as indium tin oxide (ITO), SnO ₂ , ZnO, or a metal such as gold is suitable.

In general, in order to emit light on the anode side in an organic EL device, it is preferable to use a transparent oxide conductive material as a material for the anode because of its excellent light transmittance in the visible light region. . However, when a metal such as gold is used, the film thickness should be 10 to 4 to improve the transmission of EL light.
It is desirable to use a translucent thin film in the range of 0 nm.

On the other hand, the cathode is preferably made of a metal or alloy having a small work function (generally 4.0 eV or less) because of its excellent electron injection efficiency into the organic light emitting layer and the organic hole transport layer. More specifically, as the cathode material, a metal such as magnesium, indium, or aluminum, or an alloy such as magnesium and aluminum, magnesium and indium, or aluminum and lithium is suitable for use. In particular, magnesium is excellent in electron injection efficiency, inexpensive and chemically stable,
It is most suitable as the cathode material of the present invention.

[0076]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below more specifically with reference to FIGS.

FIG. 1 shows a two-layer structure-B according to the present invention.
It is an example of a type organic EL element. Indium tin oxide (ITO) or the like is laminated on a glass substrate 10 by sputtering or the like to form an anode 12.
An organic light emitting layer 14, a hole blocking layer 16, an organic electron transporting layer 18, and a cathode 20, each of which is made of TPD or NPD and an Eu complex represented by the formula (2), are sequentially stacked thereon by vapor deposition or the like. Then, the anode 12 and the cathode 20 are connected to the power supply 22 to configure the organic EL element 100.

According to the configuration of the organic EL element 100, first, a predetermined voltage is applied to the electrode by the power source 22, whereby holes are injected into the anode 12, and the injected holes are quickly removed. It moves to the organic light emitting layer 14. At this time, the hole is the TP used in the present invention.
Due to the excellent hole transporting property of D or NPD, the organic compound tries to transmit through the organic light emitting layer 14, but the hole blocking layer 1
6 effectively stays in the organic light emitting layer 14.

On the other hand, electrons are injected from the power supply 22 into the cathode 20, and the injected electrons are moved to the organic light emitting layer 14 via the organic electron transport layer 18 and the hole blocking layer 16.

The electrons are recombined in the organic light emitting layer 14 with the holes that are blocked by the hole blocking layer 16 and remain in the organic light emitting layer 14, and the energy of the recombination causes the electrons to emit light in the light emitting material of the present invention. A certain TPD or NPD is excited, and the energy of the excited TPD or NPD is transferred to the Eu complex. As a result, the organic EL device 100 has a peak wavelength of 600 nm.
It emits high-luminance red light with a wavelength of not less than nm. Further, the organic EL element 100 is provided with TPD or N
By using a material having excellent heat resistance, which is composed of an Eu complex represented by the formula (6) and combined with PD, as the light-emitting substance, the high-luminance EL light emission is maintained.

FIG. 2 shows an example of an organic EL device having a three-layer structure in which the organic hole transport layer is made as thin as possible. Indium tin oxide (ITO) or the like is laminated on a glass substrate 10 by sputtering or the like to form an anode 12, and a thin organic hole transport layer 24, an organic light emitting layer 14, and a hole blocking layer 16 are formed thereon. The organic electron transport layer 18 and the cathode 20 are sequentially laminated by vapor deposition or the like. And the anode 12 and the cathode 2
0 is connected to the power supply 22 to configure the organic EL element 200.

According to the configuration of the organic EL element 200, first, a predetermined voltage is applied to the electrodes by the power supply 22, whereby holes separated from electrons are injected into the anode 12. Then, the injected holes are moved to the organic light emitting layer 14 faster and more efficiently through the thin organic hole transport layer 24.

The hole tends to further pass through the organic light emitting layer 14 due to the excellent hole transporting property of the TPD or NPD used in the present invention. 14 will remain.

On the other hand, similarly to the organic EL element 100 of FIG. 1, electrons separated from holes are injected into the cathode 20 from the power supply 22. Then, the injected electrons pass through the organic electron transport layer 18 and the hole blocking layer 16,
It moves to the organic light emitting layer 14. Further, the electrons are recombined with the holes staying in the organic light emitting layer 14 in the organic light emitting layer 14, and the energy of the recombination excites TPD or NPD which is the light emitting material in the present invention, Then, the energy of the excited TPD or the like is transferred to the Eu complex, and as a result, the organic EL element 20
0 performs high-luminance EL emission, and high-luminance EL emission continues.

[0085]

The present invention will be described in further detail with reference to examples.

Example 1 A 200 nm thick anode was used.
In this case, a glass substrate was sputtered with indium tin oxide (ITO), and the glass substrate was sequentially washed with acetone and 2-propanol. Then, using a vacuum deposition method, as an organic light emitting layer, TPD as a light emitting substance, and as a dopant,
The Eu complex represented by the formula (6) is added at a deposition rate ratio of about 5: 1.
(Eu complex: about 10 mol%), and laminated to a thickness of 50 nm. The glass transition point of the TPD used was 63 ° C., and the ionization potential was 5.4.
eV.

Then, as a hole blocking layer, a triazole compound represented by the formula (2) was
m, and sequentially, as an organic electron transport layer, Alq having a thickness of 30 nm, and a cathode having a thickness of 150 n.
m of magnesium were laminated using a vacuum evaporation method, to obtain a two-layer structure-B type organic EL device.

Then, a voltage up to 16 V was applied to the organic EL device using a power supply, and the light emission luminance was measured using a luminance meter. FIG. 3 shows the measurement results. In the measurement data, the horizontal axis represents voltage (V), and the vertical axis represents luminance (c).
d / m ² ).

As is apparent from the measurement results, the organic EL device of the present invention starts EL emission from a voltage exceeding 5 V, and has a luminance of 100 cd / m 2 with a voltage load of 12 V.
² or more, and about 150 cd with a voltage load of 15 V
/ M ² . Further, when the voltage application of 15 V was continued, no remarkable decrease in luminance was observed even after 100 hours.

On the other hand, the wavelength of the organic EL element when a voltage of 15 V was applied was examined using a fluorescence spectrophotometer. FIG. 4 shows the measurement results. The measurement data is shown with the horizontal axis representing wavelength (nm) and the vertical axis representing emission intensity (arbitrary unit). As is clear from the measurement results, 615n
m was obtained, and the organic EL device of the present invention
Red light emission was confirmed. Also, resolution 1
The half width measured using a 0 nm slit is also 20 nm.
Was as narrow as the following.

(Example 2) An experiment was conducted in the same manner as in Example 1, except that NPD was used instead of TPD. The glass transition point of the used NPD was 92 ° C.
And the ionization potential was 5.2 eV. FIG. 5 shows the measurement results. The measurement data is
The horizontal axis represents voltage (V), and the vertical axis represents luminance (cd / m ² ).

As is clear from the measurement results, the organic EL device of the present invention starts EL emission from a voltage exceeding 5 V, and has a luminance of 100 cd / m ² or more when a voltage of 12 V is applied, and a voltage of 15 V is applied. Approximately 210 cd
/ M ² .

On the other hand, the wavelength of the organic EL device when a voltage of 15 V was applied was examined using a fluorescence spectrophotometer. FIG. 6 shows the measurement results. The measurement data is shown with the horizontal axis representing wavelength (nm) and the vertical axis representing emission intensity (arbitrary unit). As is clear from the measurement results, 615n
m was obtained, and the organic EL device of the present invention
Red light emission was confirmed. Also, resolution 1
The half width measured using a 0 nm slit is also 20 nm.
It was also confirmed that the value was as narrow as below.

(Examples 3 and 4) An organic EL device similar to that of Example 1 was manufactured except that the thickness of the hole blocking layer was changed from 15 nm to 1 nm in Example 3 and 300 nm in Example 4. , Luminance and peak wavelength were similarly measured.

As a result, the values of the peak wavelengths of the organic EL elements were equal to each other, but the luminance was less than 100 cd / m ² by applying a voltage of 14 V, which was lower than that of Example 1.

Comparative Example 1 An organic EL device was produced in the same manner as in Example 1 except that the hole blocking layer was not provided and the Eu complex represented by the formula (6) was not used as a dopant. Then, the luminance and the peak wavelength were measured in the same manner.

As a result, in the organic EL device, slight green light emission from Alq as the organic electron transporting layer was obtained. That is, the organic light emitting layer made of TPD only functioned as a hole transport layer.

(Comparative Example 2) In Example 1, the formula (6)
An organic EL device was prepared in the same manner as in Example 1 except that the Eu complex represented by was not used as a dopant, and the luminance and the peak wavelength were measured in the same manner.

As a result, the maximum luminance is about 20 cd / m ²
Blue light emission, which was about 1/20 of that in Example 1. Further, when the voltage application was continued, the organic EL element was significantly deteriorated, and a remarkable decrease in luminance was observed within one hour.

[0100]

According to the present invention, TPD and NPD having a high hole transporting property are used as a light emitting substance in the organic light emitting layer, and a specific Eu complex is used as a dopant, and a hole blocking layer is provided. By controlling the following, the organic EL device of the present invention exhibited (1) high-luminance EL light emission at a peak wavelength of red light emission of 600 nm or more. Further, by further adjusting the thickness of the hole blocking layer,
When a low voltage of V or lower was applied, EL light emission with a high luminance of 100 cd / m ² or more was exhibited.

(2) In addition, TPD or NPD, which is a light emitting substance, did not easily deteriorate due to heat generation of the organic EL element or the like, and light emission luminance did not significantly decrease with time.

(3) Further, since TPD and NPD used in the organic light emitting layer of the present invention have a high hole transporting property, the organic light emitting layer can also serve as the organic hole transporting layer, and the organic hole transporting layer is omitted. The advantage is that it can be made as thin as possible.

[Brief description of the drawings]

FIG. 1 is a structural example of an organic EL device of the present invention (two-layer structure—
FIG.

FIG. 2 is a diagram showing a configuration example (three-layer structure type) of the organic EL element of the present invention.

FIG. 3 shows the organic EL device shown in FIG.
FIG. 4 is a diagram illustrating voltage-luminance characteristics when a PD is used.

FIG. 4 shows the organic EL device shown in FIG.
FIG. 4 is a diagram showing an EL emission spectrum when a PD is used.

FIG. 5 shows the organic EL device shown in FIG.
FIG. 4 is a diagram illustrating voltage-luminance characteristics when a PD is used.

FIG. 6 shows that the organic EL device shown in FIG.
FIG. 4 is a diagram showing an EL emission spectrum when a PD is used.

[Explanation of symbols]

 10: Glass substrate 12: Anode 14: Organic light emitting layer 16: Hole blocking layer 18: Organic electron transport layer 20: Cathode 22: Power supply 24: Organic hole transport layer 100, 200: Organic EL device

Claims (8)

[Claims] 1. An organic EL device comprising at least an anode, an organic light emitting layer, a hole blocking layer, an organic electron transport layer, and a cathode as constituent elements, wherein the light emitting substance of the organic light emitting layer is represented by the formula (1). , N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-
An organic EL device using biphenyl-4,4'-diamine and using an Eu complex represented by the formula (2) as a main component of a dopant. Embedded image (R ₁ represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group, R ₂
Represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group. ) 2. An organic EL device comprising at least an anode, an organic light emitting layer, a hole blocking, an organic electron transporting layer, and a cathode as constituent elements, wherein a light emitting substance of the organic light emitting layer is represented by the formula (3): N, N'-diphenyl-N, N'-dinaphthyl-1,1'-biphenyl-
An organic EL device using 4,4′-diamine and using an Eu complex represented by the formula (2) as a main component of a dopant. Embedded image (R ₁ represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group, R ₂
Represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group. ) 3. An Eu complex having an alkoxy group represented by the formula (4), an Eu complex having a fluorene group represented by the formula (5), or a hetero complex represented by the formula (6). The organic E according to claim 1, wherein the organic E is at least one kind among Eu complexes having a ring.
L element. Embedded image (R ₃ represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms or a cycloalkyl group; R ₄ represents a hydrogen or a hydroxy group, or a substituted or unsubstituted 1
Represents an alkyl group, a cycloalkyl group or an aryl group of from 20 to 20; ) (R ₅ represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group.) (R ₆ represents hydrogen or a hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group.) Wherein R ₄ in Formula (4), R ₆ in the formulas R ₅ and the formula in (5) (6), characterized in that a halogenated alkyl group, organic claim 3 EL element. 5. The method according to claim 1, wherein the hole blocking layer has the formula (7)
The organic EL device according to any one of claims 1 to 4, wherein a triazole compound represented by the following formula is used as a main component. Embedded image 6. The organic light-emitting layer according to claim 1, wherein the Eu complex is added as a main component of a dopant to the organic light-emitting layer in an amount of 0.01 to 10 mol%. Organic EL element. 7. A peak wavelength of the organic EL device is 60
The organic EL device according to claim 1, wherein the thickness is 0 nm or more. 8. The organic EL device according to claim 1, wherein the organic EL device has a luminance of 100 cd / m ² or more when a low voltage of 15 V or less is applied. element.