JPH10231479A - Red-luminescent organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an org. EL element which emits light in brilliant red with high color purity and luminance by using an Eu complex as the main component of a dopant for a luminescent substance in an org. luminescent layer and by incorporating a red-luminescent substance comprising an imidazole compd. into an org. electron transport layer. SOLUTION: This EL element at least comprises an anode, an org. luminescent layer, an org. electron transport layer, and a cathode and uses an Eu complex represented by formula I [wherein R1 is (substd.) 1-20C alkyl, cycloalkyl, alkoxy, aryl, etc.; and R2 is H, OH, (substd.) 1-20C alkyl, etc.] as the main component of a dopant for a luminescent substance in the luminescent layer. A hole blocking layer is formed between the luminescent layer and the electron transport layer, and a red-luminescent substance having an electron transport capability and a peak wavelength of 600nm or higher, pref. at least either an imidazole compd. represented by formula II or its deriv., is incorporated into the electron transport layer.

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 "organic EL device"), and more particularly, to an organic EL device having high color purity of EL light emission, high luminance and bright red light emission. Related to the element.

[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 (3) are used. A diamine compound such as (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (hereinafter, TPD) and a derivative thereof are generally used, and an organic light emitting layer is represented by the formula (9). Tris (8-quinolinol) aluminum (hereinafter, Alq) or the like is used.
Metals such as magnesium-silver alloy and aluminum have been used.

[0005] In order to enhance the luminous efficiency of the organic light emitting layer, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran or coumarin may be used as a dopant. The layer was used in a range of about 0.1 to 3 mol%.

[0006]

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[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, researches on dopants have been made. In particular, an Eu complex having a heterocyclic ring represented by the formula (7) 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, the material of the organic electron transporting layer in the conventional red light emitting organic EL device is excellent in the electron transporting property and requires a certain heat resistance. Although Alq represented by 9) has been mainly used, the Alq emits green light with a wavelength of about 500 nm due to holes transmitted through the organic light emitting layer, and the color purity of red light emission in the original organic light emitting layer. And it is difficult to emit bright red light.

[0010] Of course, as described above, the hole blocking layer is provided between the organic light emitting layer and the organic electron transport layer to reduce the amount of holes transmitted through the organic light emitting layer, thereby reducing light emission other than red light emission. Attempts have been made to do so.

However, even if a hole blocking layer is provided, it is difficult to completely block the holes, and thus it is difficult to prevent light emission other than red light emission in the organic electron transport layer.

Further, a conventional organic EL device emitting red light is
In general, there has been a problem that (1) light emission luminance is poor, and (2) a light emitting substance is easily deteriorated due to heat generation or the like accompanying driving of the organic EL element.

Therefore, improvement of various organic EL element materials,
Although development is underway, particularly research on hole transport materials is underway, but the focus of the research is on the organic hole transport layer, as described in the “Organic EL Device Development Strategy”. Attempts have not been made to use a material having a high hole transporting performance as a light emitting substance of an organic light emitting layer.

Also, in research on dopants added to a light emitting substance in a predetermined amount, almost no attempt has been made to use the dopant in combination with a substance having a high hole transporting property and to use the dopant as a light emitting substance in an organic light emitting layer. .

That is, a red light emitting organic EL element having high color purity and capable of emitting vivid red light,
In addition, a high-luminance and durable red light-emitting organic EL device has been desired.

[0016]

According to the present invention, there is provided an organic EL device comprising at least an anode, an organic light emitting layer, an organic electron transport layer, and a cathode as components of formula (1)
Is used as a main component of a dopant of a light emitting substance in the organic light emitting layer, and the organic electron transporting layer has an electron transporting property and a peak wavelength of 6
It is characterized by containing a red light-emitting substance of at least 00 nm.

[0017]

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(R ₁ is a substituted or unsubstituted C ₁ -C 1
20 alkyl groups, cycloalkyl groups, alkoxy groups,
R ₂ represents a cycloalkoxy group or an aryl group,
Represents a hydrogen or hydroxy group, or a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group or an aryl group. That is, in the present invention, the E represented by the formula (1)
By using the u complex as the main component of the dopant of the light emitting substance in the organic light emitting layer, the peak wavelength 600
nm or more, because high luminance, and red light emission with a narrow half width is obtained, furthermore, by including a red light emitting material having an electron transporting property, having a peak wavelength of 600 nm or more, having an electron transporting property. This is because clear red light with high purity, which is free from mixture of green light emission and blue light emission of less than 600 nm, is obtained.

Here, as the red light-emitting substance having an electron-transporting property and having a peak wavelength of 600 nm or more contained in the organic electron-transporting layer, various substances can be used. 3,4,9,10 represented by 2)
-Use of both or one of perylenetetracarboxylic acid bisbenzimidazole (hereinafter, PTCIz) and a derivative thereof.

[0020]

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This is because the PTCI expressed by the equation (2)
z and its derivatives have peak wavelengths around 620 nm, and even if some holes pass through the organic light emitting layer without recombination with electrons, and even if EL is emitted in the organic electron transport layer, , Emits red light, so organic E
This is because clear red light emission with high purity can be obtained for the entire L element. PTCIz and its derivatives are shown in FIG.
As shown in FIG.
In the red region from 00 to 670 nm;
Emits light, but as a result, the organic EL
This is because the element is considered to emit only red light emission to the outside.

Further, PTCIz and its derivatives are
It has an excellent electron transporting property and also has an advantage of good heat resistance and oxidation resistance, and is most suitable as a red light emitting substance used in the organic electron transporting layer of the present invention.

The PTCIz can be prepared by various known methods. For example, an anhydride of perylenetetracarboxylic acid and o-phenylenediamine are prepared by
It is preferable to prepare by dehydration condensation by a solid phase reaction at about 190 ° C.

On the other hand, as the Eu complex represented by the formula (1), for example, an Eu complex represented by the formula (10) having a benzene ring at both terminals of a diketone is also preferable because of its high heat resistance. In particular, among Eu complexes having an alkoxy group represented by the formula (5), Eu complexes having a fluorene group represented by the formula (6), and Eu complexes having a hetero ring represented by the formula (7) , At least one type.

[0025]

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[0026]

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(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. )

[0028]

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(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. )

[0030]

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(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 (5)
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 _4, 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 (5) 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 (6) 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 _{5 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.

Further, the Eu complex having a heterocyclic ring represented by the formula (7) is not as electron-donating as alkoxynaphthyl or fluorene, but is superior to the substituents of other Eu complexes. This is because it has an electron-donating heterocyclic ring, has been deeply studied, and has an advantage of being easily available.

In the present invention, the substituent R ₂ of the Eu complex represented by the formula (1), the substituent R _{4 of} the Eu complex having an alkoxy group represented by the formula (5), the formula (6)
The substituent R of the Eu complex having a fluorene group represented by
₅ or Eu having a heterocyclic ring represented by the formula (7)
As the substituent R _{6 of the} complex, those having a high electron-withdrawing property are preferable.

Specific examples of the substituent include a hydrogen or hydroxy group, an alkyl group having 1 to 20 carbon atoms such as a substituted or unsubstituted methyl group and ethyl group, cyclopentane,
A cycloalkyl group such as cyclohexane or an aryl group such as a benzyl group or a naphthyl group can be suitably used. This is because it is considered that electrons can be effectively attracted by the substituent and strongly extruded by a substituent having a high electron-donating property via Eu, which is a direct light emitting site.

Accordingly, among the substituents having a high electron-donating property, alkyl halides are preferable for the present invention in that they exhibit higher electron-donating properties. Further, among the halogenated alkyls, CF ₃ , C ₂ F ₅ and C ₃ F ₇ have higher electron-withdrawing properties, are less bulky, have no steric hindrance,
It is most suitable for the present invention because it can be easily introduced into a molecule using a general material.

The Eu complex represented by the formula (1) 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 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 (1) may be used alone. The use of the Eu complex derivative alone or the Eu complex represented by the formula (1) and the Eu complex
A mixed use with a derivative of the complex is also preferably possible.

Next, preferable physical properties of the Eu complex represented by the formula (1) 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 (1) used in the present invention is, the more preferable it is.
In a wavelength range of 650 nm, the fluorescence intensity of the Eu complex having a heterocyclic ring represented by the formula (7) is at least equivalent, more preferably 5% or more, and most preferably 10 to 10%.
That is 100% higher.

As a method for 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 (1) 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 device becomes good, while the Eu complex is less likely to be easily crystallized, Further, vacuum deposition can be easily performed using the Eu complex.

Therefore, from the viewpoint of better balance, the Eu represented by the formula (1) used in the present invention is used.
The melting point of the complex is more preferably in the range of 200 to 450 ° C.

Further, the formula (1) 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 Eu represented by the formula (1) used in the present invention is used.
As a thermal decomposition temperature of the complex, a range of 300 to 450 ° C. is more preferable.

Next, the amount of the Eu complex represented by the formula (1) used in the present invention will be described. That is, it is preferable that the addition amount of the Eu complex be determined in consideration of the luminance of the organic EL element and the like. As a specific addition amount, for example, it is preferable that the organic light-emitting layer is contained in a range of 0.01 to 20 mol%. The reason is,
This is because a sufficient effect of addition as a dopant is 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 transporting ability.

From the viewpoint of better balance, the addition amount of the Eu complex represented by the formula (1) 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 (1) in the organic light emitting layer can be easily adjusted by controlling the ratio of the evaporation rate of the Eu complex to the light emitting substance. .

Next, a synthesis example of the Eu complex represented by the formula (1) 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 (1) 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, by obtaining and using a β-diketone having a fluorene group or a β-diketone having a heterocycle in advance, the β-diketone, a phenanthroline and a europium salt are simply mixed and reacted. This is suitable in that a desired Eu complex can be synthesized.

Further, in a preferred embodiment of the present invention,
A hole blocking layer is provided between the organic light emitting layer and the organic electron transport layer.

The reason is that by providing the hole blocking layer, the number of holes passing through the organic light emitting layer can be reduced as much as possible, and the red light emission of the original organic light emitting layer can be effectively used. This is also to fill the energy gap and to facilitate the movement of electrons injected from the cathode.

As the material for the hole blocking layer, any material having a high ionization potential and a low hole mobility can be suitably used. In particular, the triazole compound represented by the formula (8) and its derivative It is preferable to use both or either of them as a main component.

[0057]

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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 blocking effect can be obtained, and the compound can be easily prepared by a vacuum evaporation method or the like. This is because a thin film can be formed and the usability as an organic EL device material is good.

Further, the triazole compound and its derivative have an ultraviolet absorption wavelength of 300 to 4
Because it is within the range of 00 nm (3.1 to 4.1 eV), there is little possibility that the mobility of electrons is adversely affected in terms of energy level.

Here, the thickness of the hole blocking layer of the present invention is preferably determined in consideration of the hole blocking effect, the mechanical strength, and the increase in the internal resistance of the organic EL element. Specifically, for example, 0.1 to 1
It can be in the range of 000 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, most preferably , A high luminance of 100 cd / m ² or more can be more easily obtained by applying a low voltage of less than 15 V.

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.

As a further preferred embodiment of the present invention, as described above, a hole blocking layer is provided between the organic light emitting layer and the organic electron transporting layer to emit the Eu complex represented by the formula (1). Used as a main component of the dopant of the substance, and used as a light-emitting substance of the organic light-emitting layer by the formula (3)
N, N'-diphenyl-N, N '-(3-
Methylphenyl) -1,1′-biphenyl-4,4′-
Diamine (hereinafter, TPD) or N, N′-diphenyl-N, N′-dinaphthyl- represented by formula (4)
1,1'-biphenyl--4,4'-diamine (hereinafter, referred to as
NPD).

[0064]

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That is, at least the anode, the organic light emitting layer,
In an organic EL device including a hole blocking layer, an organic electron transport layer, and a cathode as constituent elements, TPD or NPD is used as a light emitting substance of the organic light emitting layer, and an Eu complex represented by the formula (1) is used as a dopant. And the organic electron transporting layer further has a wavelength of 6
That is, a red light emitting material having a thickness of 00 nm or more is used.

Because such TPD and NPD
(1) having a small ionization potential and high hole transportability; (2) on the other hand, by providing a hole blocking layer, the mobility of holes can be controlled relatively easily, and (3) a specific Eu complex By using as a dopant, high-luminance red light emission having a peak wavelength of 600 nm or more can be achieved, and (4) the organic EL of the present invention has a high glass transition point and excellent heat resistance.
This is because it is most suitable as a light emitting substance of an element.

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, the terms TPD and NPD refer not only to the individual use but also to the respective derivatives. 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.

Here, preferable physical properties of TPD and NPD used in the present invention will be described. First, T
The glass transition point of PD is basically determined from the structure, but can be adjusted by the molecular weight distribution, the content of additives and impurities, and is preferably in the range of 60 to 200 ° C. It is. The reason is that if the glass transition point of TPD is in such a range, not only the heat resistance is good, but also a thin film of TPD can be easily formed by a vacuum evaporation method or the like.

The ionization potential of TPD is basically determined from the structure.
It is preferable to be within 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 via the anode.

Similarly, the glass transition point of NPD is basically determined from the structure.
It can be adjusted by the molecular weight distribution, the content of additives and impurities, and the like, and 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 can be obtained, but also a thin film of NPD can be easily obtained by a vacuum deposition method or the like, provided that a specific Eu complex is used as a dopant. This is because formation is possible.

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, like TPD, via the anode,
This is because excellent hole injection efficiency can be obtained.

The method for synthesizing the TPD and NPD used in the present invention and the derivatives thereof are not particularly limited. For example, an aryl halide and an aryl may be synthesized by using the Ullmann reaction. It can be easily prepared from amines. Whether or not the TPD and NPD represented by the formulas (3) and (4) have been synthesized can be easily confirmed using an infrared spectrophotometer or NMR.

Next, the organic EL device of the present invention
Other components will be briefly described. First, the organic light-emitting layer is formed by the energy generated by the recombination of holes injected from the anode and electrons injected from the cathode.
It has a function of exciting a light emitting substance to emit light. Therefore, it is preferable to determine the thickness of the organic light emitting layer from the viewpoint of showing high light emission luminance,
On the other hand, in order to obtain a highly durable organic EL element, it is necessary to consider the increase in internal resistance of the organic EL element, the mechanical durability of the organic light emitting layer, and the like.

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 20 to 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 suitably used in the present invention have an excellent hole transporting property in addition to the function as a light emitting substance. The provision of the transport layer is not always an essential requirement. Conversely, the present invention omits the organic hole transport layer or makes it as thin as possible, thereby facilitating the production, or the inside of the organic EL device. This has the advantage that the resistance 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 organic electron transport layer of the organic EL device according to the present invention will be described. That is, the organic electron transporting layer has a function of transmitting electrons injected from the cathode to the organic light emitting layer. As described above, in the present invention, the organic electron transporting layer has an electron transporting property and has a peak wavelength of 600.
It is required to use a red light emitting substance having a wavelength of nm or more. However, within a range not departing from the object of the present invention, a predetermined amount of a metal chelate compound, a polycyclic fused hydrocarbon, benzoxazole, benzothiazole, a perylene-based compound, etc.
It is also preferable to use a mixture with a red light emitting substance having a peak wavelength of 600 nm or more.

The thickness of the organic electron transport layer is preferably determined in consideration of red light emission intensity, electron transportability, increase in internal resistance of the organic EL element, mechanical strength, and the like. For example, the 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, the deposition rate, and the like 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 electrically conductive material having a large work function (generally, 4.0 eV or more) can be used. Specifically, a transparent oxide 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 toward 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 40 to improve the transmission of EL light.
It is desirable to use a translucent thin film in the range of nm.

On the other hand, the cathode is preferably made of a metal or an 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 has excellent electron injection efficiency, is inexpensive, and chemically stable.
It is most suitable as the cathode material of the present invention.

[0085]

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, on which an organic material comprising TPD or NPD and an Eu complex represented by the formula (1) is formed. Emitting layer 14, hole blocking layer 16, having electron transporting property, peak wavelength of 600 nm
The organic electron transport layer 18 and the cathode 20 made of the above red light emitting material are sequentially laminated 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 supply 22, so that 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 and is mostly shielded by organic light emitting layer 14
Will stay within.

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

The electrons are shielded by the hole blocking layer 16 in the organic light emitting layer 14 and recombine with the holes remaining in the organic light emitting layer 14, and the energy of the recombination causes TPD or TPD which is a luminescent substance to be emitted. N
When the PD is excited, the excited energy of the TPD or NPD is transferred to the Eu complex represented by the formula (1), and the organic EL element 100 has a peak wavelength of 600 n.
m or more, and emits a red-based high-luminance EL light emission.

Furthermore, even if some of the holes do not recombine with electrons in the organic light emitting layer 14 and further pass through the hole blocking layer 16 and reach the organic electron transporting layer 18, the holes are still there. By recombining with the electrons injected from the cathode, the red light emitting material of the organic electron transporting layer 18 can be excited to emit red light having a wavelength of 600 nm or more.

Therefore, the organic EL device 100 of the present invention
Is a device that emits bright red light by combining the high-brightness EL light emission of the organic light-emitting layer 14 and the red light emission of the red light-emitting material of the organic electron transport layer 18. Since the organic EL element 100 of the present invention uses TPD or NPD doped with the Eu complex represented by the formula (1) for the organic light emitting layer 14, it has excellent heat resistance, high brightness, Bright red EL emission is maintained.

FIG. 2 shows an example of a three-layer structure type organic EL device provided with an organic hole transport layer 24. 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 an organic hole transport layer 24, an organic light emitting layer 14, a hole blocking layer 16, an organic Electron transport layer 1
8 and the cathode 20 are sequentially laminated by vapor deposition or the like. Then, the anode 12 and the cathode 20 are connected to the power supply 22 to constitute 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 are injected into the anode 12. Then, the injected holes move faster and more efficiently to the organic light emitting layer 14 through the organic hole transport layer 24. Further, due to the excellent hole transporting property of the TPD or NPD used for the organic light emitting layer 14, the holes are more likely to pass through the organic light emitting layer 14, but are effectively blocked by the hole blocking layer 16, and most of the organic light emitting layer Will stay in layer 14.

On the other hand, electrons are injected into the cathode 20 from the power supply 22, and the electrons are then transmitted through the organic electron transport layer 18 and the hole blocking layer 16 to the organic light emitting layer 1.
Move to 4. Then, the electrons are applied to the organic light emitting layer 14.
In the above, the holes recombine with the holes staying in the organic light emitting layer 14, and the energy of the recombination excites TPD or NPD which is a luminescent material, and the energy of the excited TPD or NPD is expressed by the formula (1). The light shifts to the Eu complex represented, and emits red-based high-brightness EL light having a peak wavelength of 600 nm or more.

Then, even if some of the holes do not recombine with the electrons in the organic light emitting layer 14 and further pass through the hole blocking layer 16 and reach the organic electron transporting layer 18, there are some holes there. By recombining with the electrons injected from the cathode, the red light emitting material of the organic electron transporting layer 18 can be excited to emit red light having a wavelength of 600 nm or more.

Therefore, the organic EL device 200 of the present invention
The device emits bright red light by combining the high-brightness EL light emission of the organic light-emitting layer 14 and the red light emission of the red light-emitting material of the organic electron transport layer 18.

The organic EL device 200 of the present invention
Since TPD or NPD doped with the Eu complex represented by the formula (1) is used for the organic light emitting layer 14, the organic light emitting layer 14 has excellent heat resistance, and maintains high brightness and bright red EL light emission. .

[0098]

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

Example 1 200 nm thick anode
Indium tin oxide (ITO) was sputtered on a glass substrate, and the glass substrate was washed sequentially with acetone and 2-propanol. About 5: 1
Then, TPD and an Eu complex represented by the formula (10) were stacked to a thickness of 50 nm (addition amount of the Eu complex: about 10 mol%) as an organic light emitting layer.

Then, a triazole compound represented by the formula (8) was further added thereon as a hole blocking layer.
The layers are laminated to a thickness of 5 nm, and are sequentially formed as organic electron transporting layers having a thickness of 30 nm and having a thickness of 3, 4 represented by Formula (2).
Bisbenzimidazole 9,10-perylenetetracarboxylate (PTCIz) and 150 nm-thick magnesium as a cathode are each laminated using a vacuum deposition method,
A two-layer structure-B type organic EL device shown in FIG. 1 was obtained.

When a voltage of 15 V was applied to the organic EL element using a power supply, it was confirmed that the organic EL element emitted bright red light with high luminance. Further, when the voltage application of 15 V was continued, no remarkable decrease in luminance was observed even after 10 hours or more.

On the other hand, the emission spectrum of the organic EL device when a voltage of 15 V was applied was examined using a fluorescence spectrophotometer. The result is shown in FIG. Note that the measurement data is shown with the wavelength (nm) on the horizontal axis and the emission intensity (arbitrary unit) on the vertical axis.

As is apparent from the experimental results, the emission spectrum of the organic EL device has a wavelength peak of 615.
Even when a slit having a resolution of 10 nm was used and the half-value width was near 20 nm, a value as narrow as 20 nm or less was obtained. It was also separately confirmed that when a slit having a resolution of 1.5 nm was used, the half width was 3 nm or less.

In addition, the fluorescence intensity of PTCiz itself used in Example 1 was separately measured. The result is shown in FIG. Note that the measurement data is shown with the wavelength (nm) on the horizontal axis and the emission intensity (arbitrary unit) on the vertical axis. As is apparent from the experimental results, the emission spectrum has a wavelength peak of 620 although the half width is weakly wide.
It was confirmed that the compound had a peak in the vicinity of nm.

(Example 2) In Example 1, 20 nm
An organic hole transporting layer made of NPD having a thickness of 5 nm is provided between the anode and the organic light emitting layer, and NPD and the Eu complex represented by the formula (7) are deposited on the organic light emitting layer by a deposition rate ratio of about 5: 1
Vacuum deposited at a thickness of 30 nm (addition amount of Eu complex is about 10
(Mol%), and an organic EL device was prepared and evaluated in the same manner as in Example 1, except that the organic light-emitting layer was used.

As a result, it was confirmed that the organic EL device emitted a bright, bright red light having a wavelength peak near 615 nm. Further, when the voltage application of 15 V was continued, no remarkable decrease in luminance was observed even after 100 hours or more, and it was confirmed that the durability was higher than that of Example 1. This is considered to be mainly because NPD used for the organic light emitting layer has a higher glass transition point and better heat resistance and oxidation resistance than the TPD used in Example 1.

(Comparative Example 1) In Example 1, the PTCI
Example 1 was repeated except that Alq was used instead of z.
An organic EL device similar to that described above was prepared and evaluated.

As a result, as shown in FIG.
The L element showed EL light emission in which red and green light were mixed.

This is presumably because holes that could not be completely shielded by the hole block layer were recombined in Alq and emitted light.

(Comparative Example 2) In Example 1, the formula (7)
An organic EL device similar to that of Example 1 was prepared and evaluated except that the Eu complex represented by is not used as a dopant of a light emitting substance of an organic light emitting layer.

As a result, the organic EL device did not emit red EL light at all.

[0112]

According to the present invention, Eu represented by the formula (1) is added to the organic light emitting layer.
A light emitting substance doped with a complex is used, and the organic electron transporting layer further has an electron transporting property and has a peak wavelength of 600.
using a red light-emitting substance of nm or more, for example, PTCIz,
The organic EL device of the present invention was able to (1) exhibit high color purity, vivid red light emission with high luminance.

(2) When TPD or NPD was used as the luminescent substance, the luminance did not significantly decrease with time without deterioration due to heat generation of the organic EL element.

[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 is a view showing an EL emission spectrum of the organic EL device shown in Example 1.

FIG. 4 is a diagram showing an emission (fluorescence) spectrum when measuring the fluorescence intensity of PTCIz.

FIG. 5 is a view showing an EL emission spectrum of the organic EL device shown in Comparative Example 1.

[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 (6)

[Claims] 1. An organic EL device comprising at least an anode, an organic light emitting layer, an organic electron transport layer, and a cathode as constituents, wherein an Eu complex represented by the formula (1) is used as a dopant of a light emitting substance in the organic light emitting layer. A red light-emitting organic EL device, wherein the organic electron-transporting layer contains a red light-emitting substance having a peak wavelength of 600 nm or more and having an electron-transporting property. Embedded image (R ₁ represents a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, an alkoxy group, a cycloalkoxy group or an aryl group; R ₂ represents hydrogen or a hydroxy group, or a substituted or unsubstituted group; Carbon number 1-2
0 represents an alkyl group, a cycloalkyl group or an aryl group. ) 2. A red light emitting substance having an electron transporting property and having a peak wavelength of 600 nm or more, which is contained in the organic electron transporting layer, is an imidazole compound represented by the formula (2). 2. The red light-emitting organic EL device according to 1. Embedded image A hole blocking layer is provided between the organic light emitting layer and the organic electron transporting layer, and a light emitting substance of the organic light emitting layer is represented by the formula (3):
N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine or N, N'-diphenyl- represented by the formula (4) N,
N'-dinaphthyl-1,1'-biphenyl-4,4'-
The red light emitting organic EL device according to claim 1, wherein a diamine is used. Embedded image 4. An Eu complex having an alkoxy group represented by the formula (5), an Eu complex having a fluorene group represented by the formula (6), or a hetero complex represented by the formula (7). The red light-emitting organic EL device according to any one of claims 1 to 3, wherein at least one of the Eu complexes having a ring is used. 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.) 5. The method according to claim 1, wherein the hole blocking layer has the formula (8)
The red light-emitting 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. A hole transport layer is further provided between the anode and the organic light emitting layer.
The red light-emitting organic EL device according to any one of the above items.