JPH10233284A - Organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blue-light emitting organic EL element having high brightness and durability, and specifically an organic EL element having a peak wavelength of 400 to 520nm. SOLUTION: In an organic EL element including as components, at least, a positive electrode, an organic luminous layer, an organic electron carrying layer, and a negative electrode, the organic EL element is constituted so that a hole blocking layer is provided between the said organic luminous layer and the negative electrode while that a diamine compound having a naphtyl radical expressed by the formula is used, as a major constituent, in the organic luminous layer, and that a wavelength peak of light generated by the organic EL element ranges from 400 to 520nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic element utilizing electroluminescence (hereinafter referred to as "organic EL element").
In particular, the present invention relates to an organic EL element which can obtain high-luminance EL light emission even when a low voltage is applied, and is less deteriorated with time, and is most suitable as an organic element which emits blue light having a wavelength peak of 400 to 520 nm.

[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, a two-layer structure composed of an anode, an organic hole transporting layer, an organic light emitting layer and a cathode, in which the light emitting layer also serves as an electron transporting layer, or an anode and an organic light emitting layer in which the light emitting layer also serves as a hole transporting layer A two-layer structure-B type comprising an organic electron transport layer and a cathode, or an anode, an organic hole transport layer, an organic light emitting layer, in which a hole transport layer and an electron transport layer are each provided independently of the light emitting layer,
It is a three-layer structure type including an organic electron transport layer and a cathode, and a hole block layer or an electron block layer is provided in accordance with these structures, as needed, to further enhance luminous efficiency.

More specifically, for example, as a 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 for the anode, and an organic material is used. In the hole transport layer, copper phthalocyanine, 1,1′-bis- (4-
N, N'-ditolylaminophenyl) cyclohexane,
N, N'-diphenyl-N, N'- represented by the formula (4)
(3-methylphenyl) -1,1′-biphenyl-4,
Diamine compounds such as 4′-diamine (hereinafter, TPD) are generally used, and tris (8-quinolinol) aluminum (hereinafter, Alq) represented by the formula (5) is used for the organic light emitting layer. For the cathode, magnesium,
A magnesium-silver alloy, aluminum, or the like is used. In order to appropriately increase the luminous efficiency in the organic light emitting layer, an E having a hetero ring represented by the formula (6) is used as a dopant.
u complex or 4-dicyanomethylene- represented by the formula (7)
2-methyl-6-p-dimethylaminostyryl-4H-
Pyran, coumarin, or the like is added to the organic light emitting layer in an amount of about 0.1 to 3.
It was added and used in the range of 0 mol%.

[0005]

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[0006]

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[0007] Among organic EL device materials, hole transport materials have been studied particularly, and Japanese Patent Publication No.
0966, JP-B-34-5466, JP-B-58-323
72, JP-A-58-65440, JP-A-64-1306
1, various publications such as US Pat. No. 5,061,569 disclose various hole transporting materials. Among them, TPD has excellent hole transporting performance (hole mobility: 1.2 × 10 ⁻⁵ cm ^2).
/ V · s, ionization potential: 5.4 eV).

[0008]

However, conventional hole transport materials include TPD and other organic EL device development strategies (edited next-generation display device workshop, 199).
2 years, pp. As described in 99), it has little luminous performance, or has too good hole transporting performance, and easily passes holes, making it difficult to use as an organic luminescent layer. There was a problem.

On the other hand, in the case of an organic EL device emitting blue light having a peak wavelength of light emission of less than 520 nm, various types of organic EL devices have been used in order to color display panels using the organic EL device.
Although studies and studies have been made, (1) the luminance is low from the initial stage, and (2) the blue light-emitting substance is easily deteriorated due to heat generation of the organic EL element and the durability is poor.
PD is poor in heat resistance and easily deteriorates due to heat generated by driving the element. (3) To increase the brightness,
A high voltage needs to be applied, and in the conventional organic EL device emitting blue light, there is a problem that deterioration due to heat generation of the organic EL device is easily promoted.

Therefore, conventionally, a high-luminance and durable blue light-emitting organic EL device, specifically, a peak wavelength of 520 n
An organic EL device having a diameter of less than m has been desired.

[0011] However, in the present invention,
Due to the high glass transition point and easy crystallization,
Formula (1) has not been studied as a luminescent material.
N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (NPD) represented by By focusing attention, it has been found that by controlling the mobility of the holes of the NPD, a function as an excellent light emitting substance is exhibited, and the invention has been completed.

[0012]

According to the present invention, in an organic EL device including at least an anode, an organic light emitting layer, an organic electron transport layer, and a cathode as components, hole blocking is provided between the organic light emitting layer and the cathode. A layer is provided, and a diamine compound having a naphthyl group represented by the formula (1) (N, N′-diphenyl-N, N ′-(3-methylphenyl) -1,1′-) is provided on the organic light emitting layer. Biphenyl-4,4'-diamine (hereinafter referred to as NPD) as a main component, and the wavelength peak of the organic EL element is 4%.
It is characterized in that the thickness is from 00 to 520 nm.

[0013]

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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 a light emitting material in the organic light emitting layer to emit EL light. .

In the present invention, it is essential that a diamine compound having a naphthyl group represented by the formula (1) is used in the organic light emitting layer.

Because NPD is a diamine compound having a naphthyl group in the molecule, (1) has a smaller ionization potential than TPD or the like which has been conventionally known as a similar compound. Holes are easily injected, (2) and although the hole transportability is high, by separately providing a hole blocking layer,
The mobility of the hall can be controlled relatively easily,
(3) Because of the naphthyl group in the molecule, it has an appropriate glass transition point and is excellent in heat resistance, and easily forms a thin film by vacuum deposition or the like within the range of the glass transition point. And (4) a peak wavelength of 400
This is because high luminance can be obtained in blue EL light emission of up to 520 nm and a function as an excellent light-emitting substance which has not been found conventionally.

The NPD used in the present invention has a broad meaning including various NPD derivatives. Therefore, in this specification, NPD means not only NPD alone but also NPD derivatives. Used alone or N
It also means a mixed use with derivatives of PD and NPD.

More specifically, the derivative of NPD means that at least one hydrogen present in a benzene ring or a naphtan ring contained in the molecule is a compound such as a hydroxy group, a methyl group, an ethyl group, a methyl halide or the like. A compound substituted by an alkyl group, a cycloalkyl group such as cyclopentane, cyclohexane or the like, or an aryl group such as benzyl group or naphthyl group, etc., and various derivatives can be used in the present invention.

Next, various physical properties of NPD will be described. First, regarding the glass transition point of NPD, 90 to 2
Preferably it is in the range of 00 ° C. The reason is,
If the glass transition point of NPD is within such a temperature range,
This is because not only the heat resistance and the oxidation resistance are good, but also the NPD thin film can be easily formed by a vacuum evaporation method or the like.

Therefore, from the viewpoint that such balance is more preferable, the glass transition point of NPD is 100 to 200.
C. is more preferable.

The glass transition point is basically NP
Although it is determined by the structural formula of D, it can be adjusted by the molecular weight, molecular weight distribution, purity, type or amount of the substituent of NPD, and addition of an additive.

Also, the ionization potential of NPD is
Preferably, it is in the range of 4.7 to 5.5 eV.
The reason is that if the ionization potential of the NPD is within such a range, the efficiency of hole injection through the anode is excellent.

Therefore, from the viewpoint that such a balance is more preferable, the ionization potential of NPD is more preferably in the range of 5.0 to 5.3 eV.

The ionization potential is basically determined by the structural formula of NPD. However, the molecular weight, molecular weight distribution, purity, water absorption or the type and amount of the substituent of NPD, and the additive It can be adjusted by adding.

The method of synthesizing NPD and its derivatives used in the present invention is not particularly limited. For example, UPD (Ullmann) reaction is used to convert NPD from diarylamine to arylamine from aryl halide and arylamine. Can be synthesized.
Whether or not the synthesized compound has the structure represented by the formula (1) can be easily confirmed using an infrared spectrophotometer, NMR, or the like.

In the organic light emitting layer according to the present invention,
In addition to NPD, a conventional light-emitting substance or dopant can be added in a predetermined amount without departing from the purpose of the present invention. Specific preferred luminescent materials include Al oxine complex, perylene compound, naphthalene compound, coumarin compound, oxadiazole compound, aldazine compound, bisbenzoxazoline compound, bisstyryl compound, pyrazine compound. , CPD compounds, I
Examples include an n-oxin complex, a Zn complex, a Fe-oxin complex, a Ga-imine complex, and an Eu complex.

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 showing high light emission luminance. On the other hand, in order to obtain a highly durable organic EL element, the thickness of the organic light emitting layer is required. It is necessary to consider the increase in the internal resistance of the device, 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 1 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. And from a viewpoint that such a balance is more preferable, the thickness of the organic light emitting layer is more preferably 20 to 100.
nm.

In the present invention, the organic hole transporting layer and the organic electron transporting layer are directly laminated, and especially when the organic hole transporting layer is not provided as the organic light emitting layer, the organic hole transporting layer and the organic electron transporting layer may be provided at the interface. Substantial light emitting sites when emitting light are also included in the organic light emitting layer.

In addition, when 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. The diamine compound having a naphthyl group represented by the formula (1) used in the present invention has an excellent hole transporting property as described above. Providing layers is not always a requirement,
The present invention has an advantage that the internal resistance of the organic EL element can be reduced by omitting the organic hole transport layer.

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,
Providing an organic hole transporting layer having a thickness of 10 to 1000 nm is also suitable for adjusting the hole transporting property.

Next, the hole blocking layer in the organic EL device of the present invention will be described. In other words, the hole blocking layer effectively shields holes that easily pass through the organic light emitting layer due to the excellent hole transport property of the NPD, and makes the NPD function as a light emitting substance. It is provided between the 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 (2) It is preferable that both or any one of the derivatives is used as a main component.

[0035]

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The reason is that the triazole compound and its derivative have an ionization potential as high as 6.0 eV or more and have an excellent hole blocking effect, and the compound can be easily formed into a thin film by a vacuum deposition 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 triazole compounds and derivatives thereof are suitable for the present invention is as follows.
The ultraviolet absorption wavelength of the triazole compound and its derivative is generally 300 to 400 nm (3.1 to 4.1 e).
V), 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, mechanical strength, and the like.
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 can be easily controlled, the thickness of the hole blocking layer is more preferably 1 to 100 nm, and most preferably, It is preferable that the thickness be in the range of 5 to 30 nm.

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 transporting layer 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 for the organic electron transporting layer, a metal chelate compound, a polycyclic fused hydrocarbon, benzoxazole, benzothiazole, a perylene compound, or the like can be preferably 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 (5) is suitable for electron transport properties and heat resistance. It is most suitable as a material for the organic electron transporting layer of the present invention because of its excellent properties 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 element, 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, the balance is better, and the thickness of the organic electron transporting layer is easily controlled, so that 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 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 an organic EL device, since light is emitted toward the anode, a transparent oxide conductive material is preferably used as the material of the anode because of its excellent light transmittance in the visible light region. .

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. As the cathode material, more specifically, a metal such as magnesium, indium, or aluminum, or an alloy such as magnesium and aluminum, magnesium and indium, or aluminum and lithium is most suitable for use. In particular, magnesium is most suitable for use as the cathode of the present invention because it has excellent electron injection efficiency, is inexpensive, and is chemically stable.

[0049]

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. On a glass substrate 10, indium tin oxide (ITO) or the like is laminated by sputtering or the like to form an anode 12, and an organic light emitting layer 14, a hole blocking layer 16,
The organic electron transport layer 18 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 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, 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 NP used in the present invention.
D tries to pass through the organic light emitting layer 14 due to the excellent hole transporting property, but is effectively shielded by the hole blocking layer 16 and 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 are the light emitting material in the present invention by the energy of the recombination. NPD is excited, and as a result, the organic EL device 100 is excited.
Emits blue-based high-brightness EL light with a peak wavelength of 400 to 520 nm. Further, since the organic EL element 100 uses NPD having excellent heat resistance and oxidation resistance as a luminescent material, the high-luminance EL emission is maintained.

FIG. 2 shows an example of a three-layer structure type organic EL device according to the present invention. On the glass substrate 10, indium tin oxide (ITO) or the like is laminated 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, Organic electron transport layer 18 and cathode 20
Are sequentially laminated by vapor deposition or the like. And the anode 1
2 and the cathode 20 are connected to the power supply 22 to
00 is configured.

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 are moved to the organic light emitting layer 14 faster and more efficiently through the organic hole transport layer 24.

Further, due to the excellent hole transporting property of the NPD used in the present invention, the holes are further increased in the organic light emitting layer 1.
4 are effectively shielded by the hole blocking layer 16 and remain in the organic light emitting layer 14.

On the other hand, similarly to the organic EL device 100 of FIG. 1, electrons are injected into the cathode 20 from the power supply 22. Then, the injected electrons move to the organic light emitting layer 14 via the organic electron transport layer 18 and the hole blocking layer 16. Further, the electrons are further applied to the organic light emitting layer 1.
4, the holes recombine with the holes staying in the organic light-emitting layer 14, and the energy of the recombination excites the NPD, which is a light-emitting substance in the present invention. As a result, the organic EL element 200 emits high-luminance EL light. And high-luminance EL emission is maintained.

[0058]

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

(Example 1) As an anode, a thickness of 200 nm
Indium tin oxide (ITO) was sputtered on a glass substrate, and the glass substrate was washed sequentially with acetone and 2-propanol, and then the organic light emitting layer was formed using a vacuum evaporation method. As NP
D was laminated to a thickness of 50 nm. The NPD used
Has a glass transition point of 92.0 ° C. and an ionization potential of 5.2 eV.

Then, as a hole blocking layer, a triazole compound represented by the formula (2)
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 of up to 17 V was applied to the organic EL device using a power supply, and the 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 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 under} a voltage load of 10 V.
With the voltage load of 14V, about 400 cd /
It showed a maximum luminance of m ² .

When a voltage load of 14 V was continued,
No significant decrease in luminance was observed even after 100 hours.

On the other hand, when the wavelength of the organic EL device at a voltage load of 14 V was examined using a fluorescence spectrophotometer,
A peak wavelength of about 450 nm was obtained, and it was confirmed that blue light was emitted.

(Examples 2 and 3) The thickness of the hole blocking layer was changed from 15 nm in Example 1 to Example 2
Then, an organic EL device similar to that of Example 1 was manufactured except that the thickness was changed to 1 nm in Example 3 and 100 nm in Example 3, and the luminance and the peak wavelength were similarly measured.

As a result, the peak wavelengths of the organic EL elements were the same, but the luminance was reduced by the application of a voltage of 14 V, and became less than about 100 cd / m ² . It is considered that the reason for this is that in Example 2, the thickness of the hole blocking layer was small, so that the ratio of holes remaining in the organic light emitting layer was small. On the other hand, in Example 3, the thickness of the hole blocking layer was small. It is considered that the internal resistance was increased due to the large thickness, and the coupling ratio between holes and electrons was reduced.

Comparative Example 1 An organic EL device similar to that of Example 1 was prepared except that TPD was used instead of NPD in Example 1, 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
Which was about 1/20 that of Example 1. Further, when the voltage application was continued, the organic EL element was deteriorated, and a remarkable decrease in luminance was observed within one hour, and EL light emission hardly occurred.

Comparative Example 2 An organic EL device was prepared in the same manner as in Example 1 except that the hole blocking layer was not provided, and the luminance and the peak wavelength were measured in the same manner.

As a result, in the organic EL device,
Alq of the organic electron transport layer only emits green light,
The layer composed of NPD only functioned as an organic hole transport layer.

[0071]

As described above, the organic light emitting layer is made of NPD, which has a high hole transporting property and has a low ionization potential, so that holes are easily injected from the anode, and a hole blocking layer is provided in the organic light emitting layer. The organic EL device of the present invention, whose properties have been adjusted, has the following advantages.
At the following low voltages, the luminance of high EL emission, specifically, at a wavelength of blue emission of 400 to 520 nm, 1
It exhibited a high luminance of 00 cd / m ² or more, more preferably 200 cd / m ² or more.

(2) Also, the heat generated by the organic EL element causes
The light-emitting luminance did not significantly decrease over time without easily deteriorating the light-emitting substance NPD.

(3) Further, since the NPD used for the organic light emitting layer of the present invention has a high hole transporting property, the organic light emitting layer can also serve as the organic hole transport layer, and it is necessary to separately provide an organic hole transport layer. There is also the advantage that it can be omitted.

[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 diagram showing voltage-luminance characteristics of the organic EL device shown in FIG.

FIG. 4 is a view showing an EL emission spectrum of the organic EL device shown in FIG.

[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 (7)

[Claims] 1. An organic EL device comprising at least an anode, an organic light emitting layer, an organic electron transporting layer and a cathode as constituent elements, wherein a hole blocking layer is provided between the organic light emitting layer and the cathode. , Equation (1)
Wherein a diamine compound having a naphthyl group represented by formula (1) is used as a main component of a light-emitting substance, and a wavelength peak of light emission of the organic EL element is 400 to 520 nm. Embedded image 2. The organic EL device according to claim 1, wherein the diamine compound having a naphthyl group has a glass transition point of 90 to 200 ° C. 3. The organic EL according to claim 1, wherein the ionization potential of the diamine compound having a naphthyl group is 5.0 to 5.5 eV.
element. 4. The method according to claim 1, wherein the hole blocking layer has the formula (2)
The organic EL device according to any one of claims 1 to 3, wherein a triazole compound represented by the following formula is used as a main component. Embedded image 5. The thickness of the hole blocking layer,
The organic EL device according to claim 1, wherein the thickness is 0.1 to 1000 nm. 6. An organic electron transporting layer wherein an aluminum chelate compound is used as a main component.
The organic EL device according to claim 1. 7. 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. .