JP2003272870A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element that is capable of securing appropriate luminescence, while suppressing short circuit between electrodes by making the organic layers thick. <P>SOLUTION: This is an organic EL element S1 in which, as a layer made of hole transporting material, a hole injection layer 30, a hole transporting mixing layer 40, and a hole transporting layer 50 are interposed between a positive electrode 20 and a luminous layer 60 made of organic EL material, and an electron transporting layer 70 made of electron transporting material is interposed between the luminous layer 60 and a negative electrode 80. The hole transporting mixing layer 40 is made by mixing at least two kinds or more of hole transporting materials, and one material out of the two kinds or more of the hole transporting materials in the mixing layer 40 has higher hole transporting capability than the other hole transporting materials. The hole transporting mixing layer 40 is thickest out of the layers 30-50 made of hole transporting material. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic EL (electroluminescence) device.

[0002]

2. Description of the Related Art In an organic EL device, a layer made of a hole transporting material is sandwiched between an anode and a light emitting layer made of an organic EL material, and an electron transporting material is made between a light emitting layer and a cathode. It is composed of sandwiched layers. Here, the layer between the anode and the cathode is an organic layer made of an organic compound.

Then, by applying an electric field between the electrodes, that is, between the anode and the cathode, holes are injected from the anode into the light emitting layer through the layer made of the hole transporting material, and electrons are emitted from the cathode. Electrons are injected into the light emitting layer through the layer made of the electron transporting material. Then, holes and electrons are recombined in the light emitting layer, and the energy generated at that time causes the light emitting layer to emit light.

Since such an organic EL element emits light by itself, it is excellent in visibility and can be driven at a low voltage of several V to several tens of V, so that the weight including the drive circuit can be reduced. Therefore, the organic EL element is expected to be used as a thin film type display, lighting, and backlight.

The organic EL element is also characterized by abundant color variations. Another feature is that various colors can be emitted by mixing a plurality of colors.

Although the organic EL element has the above-mentioned advantages, it has a problem that since the thickness of the organic layer is thin, minute foreign matters and short circuits between the electrodes due to changes in the morphology of the organic film and the electrodes over time easily occur. .

On the other hand, for example, it is generally possible to adopt a method of thickening a material having a high conductivity and a hole transporting property which is not easily deteriorated even if it is thickened, out of two or more layers of the hole transporting material. . A porphyrin-based material represented by copper phthalocyanine, a starburst amine-based material, or the like is used as a material having high conductivity and having a high hole-transport property even if it is thick.

[0008]

However, according to the study by the present inventors, a hole injection layer in which these porphyrin-based materials and starburst amine-based materials are in contact with the anode among layers made of the hole-transporting material is used. It has been found that the following problems occur when used as.

First, since the porphyrin-based material has high crystallinity, if it is made too thick (for example, 30 nm or more), concavity and convexity are increased, and a short circuit between electrodes (between the anode and the cathode) is likely to occur. It was also found that the dark spots increased because the anode could not be covered.

On the other hand, a starburst amine-based material or the like can be thickened at room temperature level, but since the morphological change is large originally, the thicker it is, the larger the morphological change at high temperature becomes. Then, the adhesion with the anode as the base is deteriorated, and the hole injection characteristic is deteriorated even if a short circuit is not caused due to peeling or the like, resulting in a decrease in brightness.

Further, even when a material having a high conductivity and having a high hole transport property even if it is thick is used as the hole transport layer in contact with the light emitting layer, if the hole transport layer is made thicker, the positive hole transport layer becomes positive. The movement distance of the hole becomes long, and the electric field strength per unit length decreases. Therefore, there arises a problem that the luminous efficiency is reduced.

Therefore, in view of the above problems, it is an object of the present invention to provide an organic EL element capable of ensuring proper light emission while suppressing the short circuit between electrodes by thickening the organic layer.

[0013]

In order to achieve the above object, in the invention described in claim 1, the anode (20) and the organic E are used.
A layer (30, 40, 50) made of a hole transporting material is sandwiched between the light emitting layer (60) made of an L material, and an electron transporting material is made between the light emitting layer and the cathode (80). In the organic EL device in which the layer (70) formed by sandwiching the layer (70) is sandwiched, the layer formed by the hole transport material includes the mixed layer (40) formed by mixing at least two kinds of hole transport materials. One of the two or more kinds of hole transporting materials in the mixed layer is a material having a higher hole transporting capacity than the other hole transporting materials.

According to this, since the above-mentioned mixed layer is a mixed layer, the degree of crystallinity and morphological change when the mixed layer is thickened can be reduced, so that even if the mixed layer is thickened, increase in unevenness or the like is less likely to occur. Further, by using one hole-transporting material forming the mixed layer as a material having a higher hole-transporting ability than the other material, the hole-transporting function can be ensured even if the mixed layer is thickened.

Therefore, according to the present invention, it is possible to thicken the layer made of the hole transporting material without degrading the hole transporting function. As a result, it is possible to provide an organic EL element capable of ensuring proper light emission while suppressing the short circuit between the electrodes by thickening the organic layer.

According to the second aspect of the present invention, the material having a high hole transporting ability has a layer (20) on the anode side whose valence band highest level is in contact with the mixed layer (40) containing the material. Three
It is characterized in that it is within ± 0.2 eV with respect to the highest level of the valence band of 0).

Here, the layer on the anode side in contact with the mixed layer (40) may be the anode (20) or the layer (30) made of a hole transporting material between the anode and the mixed layer. good.

If the difference between the highest valence band level of the material having a high hole transport ability in the mixed layer and the highest valence band level of the layer adjacent to the mixed layer on the anode side is too large, the energy barrier becomes large. It becomes difficult for holes to be injected from the adjacent layers on the anode side into the mixed layer. Therefore, the difference between the highest valence band levels is preferably within ± 0.2 eV.

Further, in order to increase the thickness of the layer (30, 40, 50) made of the hole transporting material without degrading the hole transporting function, the mixed layer (4
It is preferable to adopt a material having a hole mobility of 1 × 10 ⁻³ cm ² / V · sec or more as the material having a high hole transporting ability in 0).

Specifically, as the material having a high hole transporting ability in the mixed layer (40), any one of the porphyrin-based material, the starburst amine-based material and the pentacene-based material can be used as in the invention of claim 4. One can be adopted.

Further, as in the fifth aspect of the invention, in the mixed layer (40), as the hole transporting material mixed with the material having a high hole transporting ability, a tertiary amine type material is adopted. be able to.

In particular, when a porphyrin-based material or a pentacene-based material is used as a material having a high hole-transporting ability, these materials are often colored due to their high crystallinity. In such a case, if a tertiary amine-based material is mixed, the crystallinity of the mixed layer can be lowered, so that the degree of coloring can be reduced and unevenness can be reduced.

Further, in the invention according to claim 6, the layer (30, 40, 50) made of the hole transporting material is composed of a plurality of layers, and the mixed layer (40) is the thickest layer among these layers. It is characterized by being.

As described above, since the hole transporting function can be ensured even if the mixed layer is thickened, when the layer made of the hole transporting material is composed of a plurality of layers, the mixed layer among the plurality of layers is selected. It can be the thickest layer.

Further, in the invention as set forth in claim 7, the layer (40, 50) made of the hole transporting material is more than the hole injection layer (40) in contact with the anode (20) and the hole injection layer. The mixed layer (40) comprises a hole transport layer (50) located on the light emitting layer (60) side, and is configured as a hole injection layer.

Further, in the invention described in claim 8, the layer (30, 40, 50) made of the hole transporting material is the anode (2
0) in contact with the hole injection layer (30) and the hole transport layer (40, 5) located closer to the light emitting layer (60) than the hole injection layer.
0) and the mixed layer (40) is configured as a hole transport layer.

Thus, the mixed layer (40) can be used as a hole injection layer or a hole transport layer.

In particular, when the mixed layer (40) is used as the hole transport layer as in the organic EL device according to claim 8, the hole injection layer as in the invention according to claim 9 is obtained. (3
It is preferable to adopt a porphyrin-based material having high crystallinity as 0). This is because the hole injection layer made of the porphyrin-based material and the anode can have high adhesion.

Further, the invention according to claim 10 is characterized in that the thickness of the entire layer (30, 40, 50) made of the hole transporting material is not less than the thickness of the anode (20). .

Since the anode is usually patterned, a step is formed on the end face of the anode in the portion where the anode is not formed. Although the organic layer is formed on the anode and also on the step portion, the thickness of the organic layer is likely to be thin at the step portion, and a short circuit between electrodes is likely to occur at the thin portion.

Therefore, as in the present invention, the thickness of the organic layer in the step portion can be secured by increasing the thickness of the entire layer made of the hole transporting material to the thickness of the anode or more. Therefore, it is preferable.

Furthermore, it is preferable to make the layer made of the hole transporting material thicker than the layer made of the electron transporting material. This is because the electron transporting material generally has hole mobility, and a current flows in the reverse bias, whereas the hole transporting material has a property that almost no current flows in the reverse bias. Therefore, if the layer made of the hole transporting material is made thicker, the current leakage due to the reverse bias can be appropriately prevented.

According to the invention described in claim 11,
The layer (30, 40, 50) made of the hole transporting material can be made of three or more layers.

Further, in each of the above means, the layer made of the hole transporting material is made thick without degrading the hole transporting function, so that the organic layer is made thicker and the short circuit between the electrodes is suppressed, and at the same time, it is suitable. It was possible to secure luminescence.

As a result of further study, the same effect can be obtained even if the electron transporting function is not deteriorated while the layer made of the electron transporting material is thickened in order to prevent a short circuit between the upper and lower electrodes. I found that there is. The inventions of claims 12 to 17 were created based on this finding.

That is, according to the invention of claim 12,
A layer (30, 50) made of a hole transporting material is sandwiched between an anode (20) and a light emitting layer (60) made of an organic EL material, and an electron is provided between the light emitting layer and the cathode (80). In an organic EL device in which a layer (72) made of a transport material is sandwiched, the layer made of an electron transport material is a mixed layer (72) formed by mixing at least two kinds of electron transport materials.
One of the two or more types of electron transporting materials in the mixed layer is a material having a higher electron transporting capacity than the other electron transporting materials.

According to this, since the above-mentioned mixed layer is a mixed layer, the degree of crystallinity and morphological change can be reduced when the mixed layer is thickened, so that even if the mixed layer is thickened, increase in unevenness or the like is less likely to occur. Further, by using one electron-transporting material forming the mixed layer as a material having a higher electron-transporting ability than the other, the electron-transporting function can be ensured even if the mixed layer is thickened.

Therefore, according to the present invention, the layer made of the electron transporting material can be thickened without deteriorating the electron transporting function. As a result, it is possible to provide an organic EL element capable of ensuring proper light emission while suppressing the short circuit between the electrodes by thickening the organic layer.

Further, in the invention according to claim 13, the material having a high electron transporting capacity has a conduction band lowest level which is in contact with the mixed layer (72) containing the material and is on the side of the cathode (80).
It is characterized in that it is within ± 0.2 eV with respect to the lowest level of the conduction band.

Here, the layer on the cathode side in contact with the mixed layer (72) may be the cathode (80) or a layer made of an electron transporting material between the cathode and the mixed layer.

If the difference between the conduction band lowest level of the material having a high electron transporting ability in the mixed layer and the conduction band lowest level of the layer on the cathode side which is in contact with the mixed layer is too large, the energy barrier becomes large, and the contact band becomes large. It becomes difficult for electrons to be injected from the cathode side layer into the mixed layer. Therefore, the difference between the conduction band lowest levels is ±
It is preferably within 0.2 eV.

In order to increase the thickness of the layer (72) made of an electron-transporting material without deteriorating the electron-transporting function, the electron-transporting ability of the mixed layer (72) may be increased as in the invention of claim 14. As a high material, electron mobility is 1x
It is preferable to use a material of 10 ⁻⁵ cm ² / V · sec or more.

Specifically, as the material having a high electron transporting ability in the mixed layer (72), a pyrene compound, a diphenylanthracene, a distyrylbenzene derivative, a spiro compound and an oxadiazole may be used as in the invention of claim 15. Any one of the materials having a skeleton can be adopted.

According to the sixteenth aspect of the present invention,
In the mixed layer (72), an aluminum chelate-based material can be used as the electron transporting material mixed with the material having a high electron transporting ability.

This aluminum chelate-based material has a lower conduction band minimum level than the above-mentioned materials having a pyrene compound, diphenylanthracene, distyrylbenzene derivative, spiro compound, or oxadiazole skeleton. Therefore, by using the mixed layer, the energy barrier between the layer on the cathode side and the mixed layer is reduced, and the injection property of electrons from the cathode side to the mixed layer is improved.

Further, the invention according to claim 17 is characterized in that the layer made of the electron transporting material is composed of a plurality of layers, and the mixed layer is the thickest layer among the plurality of layers.

As described above, since the electron transporting function can be ensured even if the mixed layer is thickened, when the layer made of the electron transporting material is composed of a plurality of layers, the mixed layer is the thickest among the plurality of layers. Can be layered.

The reference numerals in parentheses for each means described above are examples showing the correspondence with specific means described in the embodiments described later.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention shown in the drawings will be described. The same parts in each of the following embodiments are given the same reference numerals in the drawings.

(First Embodiment) FIG. 1 is a diagram showing a schematic sectional structure of an organic EL element S1 according to a first embodiment of the present invention. The substrate 10 is a substrate that is transparent to visible light, such as glass. On one surface of the substrate 10, an anode 20, layers 30, 40 and 50 made of a hole transporting material, a light emitting layer 60, a layer 70 made of an electron transporting material, and a cathode 80 are sequentially laminated.

The anode 20 is formed as a transparent electrode, is made of ITO (indium-tin oxide) or indium-zinc oxide, which is a transparent conductive film, and is formed by a sputtering method or the like. The film thickness of the anode 20 is 100 nm to 1
It can be about μm. In this example, the anode 20 is made of ITO and its thickness is about 100 nm.

The layers 30 to 50 made of the hole transporting material are
It is composed of a hole injection layer 30, a hole transporting mixed layer 40, and a hole transport layer 50 which are sequentially formed from the anode 20 side.
The hole injection layer 30 in contact with the anode 20 is made of a porphyrin-based material or the like. In this example, it is a film of copper phthalocyanine that is a 10-nm-thick porphyrin-based material formed by vacuum deposition.

The hole-transporting mixed layer 40, together with the hole-transporting layer 50 thereon, constitutes a hole-transporting layer located closer to the light-emitting layer 60 than the hole-injecting layer 30. In particular, in this example, ,
The hole transporting mixed layer 40 is configured as a hole transporting layer in contact with the hole injection layer 30.

The hole transporting mixed layer 40 is a mixed layer in which at least two kinds of hole transporting materials are mixed, and two or more kinds of hole transporting materials in the hole transporting mixed layer 40. One of the materials has a higher hole transporting ability than the other hole transporting materials.

In the present example, the hole transporting mixed layer 40 is formed by vacuuming copper phthalocyanine, which is a material having a relatively high hole transporting ability, and triphenylamine tetramer, which is a material having a relatively low hole transporting ability. It is a film having a thickness of 60 nm formed by co-evaporation using an evaporation method.

The mixing ratio of the material having a high hole transporting ability and the material having a low hole transporting ability in the mixed layer 40 is not limited, but it is possible to select 1:10 to 10: 1. Depending on the nature of the material having a high hole-transporting ability, it is preferable to increase the ratio of the material having a high hole-transporting ability in order to improve the light emission efficiency. However, when the crystallinity of the material having a high hole-transporting ability is high, if the ratio is increased, the unevenness tends to be large and the electrode short circuit tends to occur when the mixed layer 40 is thick. It costs.

The hole-transporting layer 50 formed on the hole-transporting mixed layer 40 is made of a tertiary amine-based material or the like,
In this example, a film of triphenylamine tetramer, which is a tertiary amine-based material and has a thickness of 20 nm, is formed by vacuum evaporation.

Here, the material having a high hole-transporting ability in the hole-transporting mixed layer 40 has the highest valence band level of the valence electrons of the layer on the side of the anode 20 in contact with the mixed layer 40 containing the material. It is preferably within ± 0.2 eV with respect to the highest band level. In this example, the layer on the anode 20 side that is in contact with the mixed layer 40 is the hole injection layer 30 made of copper phthalocyanine.

It is preferable that the valence band highest level has such a relationship that the valence band highest level of the material having a high hole transporting ability in the hole transporting mixed layer 40 is in contact with the mixed layer 40. The difference from the highest level of the valence band of the layer 30 on the anode 20 side is ±
When it is larger than 0.2 eV, the energy barrier is large and it becomes difficult to inject holes from the layer 30 on the anode 20 side to the mixed layer 40.

In this example, the highest valence band level (HOMO level) of the ITO film forming the anode 20 is 5.0 eV. Regarding copper phthalocyanine, the valence band highest level is 5.2 eV, the conduction band lowest level (LUMO level) is 3.5 eV, and the energy gap is 1.7 eV. The triphenylamine tetramer has a valence band highest level of 5.4 eV, a conduction band lowest level of 2.4 eV, and an energy gap of 3.0 eV.

In this example, the material having a high hole-transporting ability and the layer 30 (hole-injecting layer) 30 on the side of the anode 20 which is in contact with the mixed layer 40 are both copper phthalocyanine, and therefore the value of both of them is high. The difference in the highest level of the electron band is 0 eV.

The material having a high hole transporting ability in the hole transporting mixed layer 40 is for ensuring the hole transporting function in the hole transporting mixed layer 40 and has a high hole mobility. Is preferred. Specifically, the hole mobility is 1 × 1.
It is preferable that the material is 0 ⁻³ cm ² / V · sec or more. By the way, the hole mobility of a tertiary amine material represented by a triphenylamine tetramer is 1 × 10 ⁻³ cm ² /
It is smaller than Vsec.

Such 1 × 10 ⁻³ cm ² / V · sec
As a hole transporting material having the above hole mobility,
Porphyrin-based material typified by the above-mentioned copper phthalocyanine, m-MTBATA (valence band highest level: 5.0e
V, conduction band lowest level: 1.9 eV, energy gap: 3.1 eV), starburst amine-based material, pentacene (valence band highest level: 5.2 eV), pentacene-based material, etc. Can be used.

That is, as the material having a high hole transporting ability in the hole transporting mixed layer 40, a material selected from these porphyrin-based materials, starburst amine-based materials, pentacene-based materials and the like can be adopted.

In the hole transporting mixed layer 40, as the hole transporting material mixed with the material having a high hole transporting ability, a tertiary amine material represented by triphenylamine tetramer or the like is used. Can be adopted.

In particular, when a porphyrin-based material or a pentacene-based material is used as a material having a high hole-transporting ability, these materials are often colored due to their high crystallinity. In such a case, if a tertiary amine-based material is mixed, the crystallinity of the mixed layer can be lowered, so that the degree of coloring can be reduced and unevenness can be reduced.

For example, in the case of copper phthalocyanine, which is a porphyrin-based material, itself has blue and red absorption characteristics. Therefore, when copper phthalocyanine is used as a hole transport layer, for example, an organic EL device having a red light emitting layer is obtained.
The device has a problem of reducing luminous efficiency.

On the other hand, in the mixed layer 40 in which copper phthalocyanine and a tertiary amine-based material are mixed, the crystallinity can be lowered as compared with a single layer of copper phthalocyanine, so that the red absorption characteristic can be suppressed. . Further, the unevenness of the film can be reduced, and the short circuit between the electrodes 20 and 80 can be effectively suppressed.

In the present embodiment, the porphyrin-based material, starburst amine-based material, pentacene-based material and the like described above can also be used in the hole injection layer 30. When the hole transporting mixed layer 40 is used as the hole transporting layer as in this embodiment, the hole injecting layer 3 is used as in this example.
It is preferable to use a porphyrin-based material having high crystallinity as 0 because the hole injection layer 30 made of this porphyrin-based material can have high adhesion to the anode 20.

Then, as shown in FIG. 1, a light emitting layer 60 made of an organic EL material is formed on the layers 30 to 50 made of the hole transporting material thus constituted. In this example, the light emitting layer 60 is a film having a thickness of 40 nm formed by vacuum deposition of trisaluminoquinolinol (Alq3) containing 1 wt% of dimethylquinacridone as a fluorescent dye.

Further, the electron transport layer 70 on the light emitting layer 60.
Is a layer made of an electron transporting material, and in this example, it is an Alq3 film having a thickness of 20 nm formed by a vacuum evaporation method. Alq3 has a valence band highest level of 5.8 eV, a conduction band lowest level of 3.0 eV, and an energy gap of 2.8 eV.

Cathode 80 formed on the electron transport layer 70
Is an electrode for injecting electrons into the electron transport layer 70, and is obtained by depositing a metal or the like by a vacuum deposition method or the like. In this example, as the cathode 80, a LiF film having a thickness of 0.5 nm is formed from the side of the electron transport layer 70, and a film having a thickness of 100 is formed thereon.
It has a two-layer structure in which a film made of Al of nm is formed.

In such an organic EL element S1,
By applying an electric field between the anode 20 and the cathode 80, the layers 30 to 5 made of the hole-transporting material are emitted from the anode 20.
Holes are injected into the light emitting layer 60 through 0, electrons are injected into the light emitting layer 60 from the cathode 80 through the electron transport layer 70, and the holes and electrons are recombined in the light emitting layer 60. The light emitting layer 60 emits light due to the energy generated at that time. In this example, green light emission due to dimethylquinacridone in the light emitting layer 60 is obtained.

By the way, in this embodiment, the layers 30 to 50 made of the hole transporting material are assumed to include the hole transporting mixed layer 40 in which at least two kinds of hole transporting materials are mixed. A unique structure is adopted in which one material of the two or more kinds of hole transporting materials in the mixed layer 40 is a material having a higher hole transporting capacity than the other hole transporting materials.

According to this, since the hole transporting mixed layer 40 is a mixed layer in which two or more kinds of materials are mixed, the crystallinity and the morphological change when the mixed layer 40 is thickened should be reduced. You can Therefore, the mixed layer 40
Even if the thickness is increased, it is possible to make it difficult for the unevenness of the film surface to be increased or to be peeled from the anode 20.

Further, by making one hole-transporting material forming the hole-transporting mixed layer 40 a material having a higher hole-transporting ability than the other, even if the mixed layer 40 is thickened, the hole-transporting material can be transported. The function can be secured.

Therefore, in the above-described present example, in the plurality of layers 30 to 50 made of the hole transporting material, the hole injecting layer 30 is 10 nm, the hole transporting mixed layer 40 is 60 nm, and the hole transporting layer 50 is. The hole transporting mixed layer 40 is the thickest layer such as 20 nm.

As described above, according to this embodiment, the layer 3 made of the hole-transporting material can be used without lowering the hole-transporting function.
0 to 50 can be thickened. As a result, the organic layer 3
It is possible to provide the organic EL element S1 capable of ensuring proper light emission while suppressing the short circuit between the electrodes 20 and 80 by increasing the overall thickness of 0, 40, 50, 60 and 70.

An example in which the effect of this embodiment is specifically verified will be shown. Organic EL element S of this embodiment
As 1 was used one having each material and each film thickness shown in the above example. Here, the mixture ratio of the copper phthalocyanine (CuPc) and the triphenylamine tetramer (TPTE) in the hole transporting mixed layer 40 is CuPc: TPTE.
= 2: 1.

As a comparative example, an organic EL device as shown in FIG. 2 was produced. This is the organic EL shown in FIG.
This is a device in which the hole transporting mixed layer 40 is eliminated in the element S1. That is, the layer made of the hole transport material is composed of the hole injection layer 30 made of copper phthalocyanine and having a thickness of 10 nm and the hole transport layer 50 made of triphenylamine tetramer.

In the organic EL device shown in FIG. 2, the case where the thickness of the hole transport layer 50 is relatively thin as 40 nm is Comparative Example 1, and the case where the thickness of the hole transport layer 50 is relatively thick as 80 nm. Is referred to as Comparative Example 2. That is, in Comparative Example 1, the mixed layer 40 was simply removed from the organic EL element S1 of the present embodiment, and in Comparative Example 2, the hole transport layer 50 was added so as to compensate for the loss of the mixed layer 40. Is thickened.

FIG. 3 shows the initial current and luminance characteristics of these embodiments and Comparative Examples 1 and 2, and shows the luminance deterioration characteristics when a high temperature operation test is performed in an 85 ° C. environment. Is shown in FIG.

As shown in FIGS. 3 and 4, as compared with Comparative Example 1, the structure of the present embodiment has a thicker organic layer, so that the light emission efficiency is somewhat lower, but a short circuit between the electrodes 20 and 80 occurs. It can be seen that the effect of prevention is great. As shown in FIG. 4, in Comparative Example 1 in which the organic layers 30 to 70 were thin, a short circuit occurred in about 1200 hours and no light was emitted.

Further, as compared with Comparative Example 2 in which the hole transport layer 50 is simply thickened, it is understood that the structure of this embodiment has a higher luminous efficiency with respect to current and a longer life. This is because, in the present embodiment, the hole transporting mixed layer 40 can thicken the organic layers 30 to 70 without reducing the hole transporting function and suppressing the unevenness and peeling of the film.

Next, a modification of the first embodiment will be described. In the above example, the hole injection layer 30 is 10 nm, the hole transporting mixed layer 40 is 60 nm, and the hole transport layer 50 is 20 nm.
As a whole, the total thickness of the layers 30 to 50 made of the hole transporting material is 90 nm. In addition, the anode 20 made of ITO
Has a thickness of 100 nm.

Here, as a first modification, the hole transporting mixed layer 40 may be further thickened so that the total thickness of the layers 30 to 50 made of the hole transporting material is not less than the thickness of the anode 20. good. For example, the hole transporting mixed layer 40 has a thickness of 80.
In the case of nm, the layer 30 to 50 made of a hole transporting material
The total thickness is 110 nm, which is more than the thickness of the anode 20. This has the following advantages.

Since the anode is usually patterned to form a plurality of pixels, a step is formed between the end face of the anode and the substrate in the portion where the anode is not formed. Although the organic layer is formed on the anode and also on the step portion, the thickness of the organic layer is likely to be thin at the step portion, and a short circuit between electrodes is likely to occur at the thin portion.

In that respect, the layer 30 made of the hole transporting material is used.
It is preferable to make the thickness of the entire layer 50 as thick as the thickness of the anode 20 or more because the thickness of the organic layers 30 to 70 in the step portion can be secured.

Furthermore, it is preferable to make the layers 30 to 50 made of the hole transporting material thicker than the layer 70 made of the electron transporting material. This is because the electron transporting material generally has hole mobility, and a current flows in the reverse bias, whereas the hole transporting material has a property that almost no current flows in the reverse bias. Therefore, if the layers 30 to 50 made of the hole transporting material are made thicker, the current leakage due to the reverse bias can be appropriately prevented.

FIG. 5 is a diagram showing a schematic sectional structure of an organic EL element S11 as a second modification. This modification is different from the organic EL element S1 shown in FIG. 1 in that the hole injection layer 30 is eliminated.

That is, in the case where the layer composed of the hole transporting material is composed of the hole injecting layer in contact with the anode 20 and the hole transporting layer located closer to the light emitting layer 60 than the hole injecting layer, the layer shown in FIG. In contrast, while the hole transporting mixed layer 40 is used as a hole transporting layer, in FIG. 5, the hole transporting mixed layer 40 is used as a hole injecting layer.

The hole transporting mixed layer 40 may be used as a hole injecting layer. In that case, the mixing ratio of the copper phthalocyanine which is a crystalline compound in the mixed layer 40 is increased to form the anode 20. It is preferable to increase the adhesion to ITO.

Also in FIG. 5, the material having a high hole transporting ability in the hole transporting mixed layer 40 has the highest valence band level in contact with the mixed layer 40 containing the material on the side of the anode 20. ± 0.2 eV with respect to the highest level of the valence band of the layer
Although it is preferably within the range, the layer on the side of the anode 20 that is in contact with the mixed layer 40 is the anode 20 itself.

Further, in the first embodiment, the number of layers made of the hole transporting material is more than three layers, and may be, for example, four layers or more. Further, the layer made of the hole transporting material does not have to be a plurality of layers, and may be only one layer of the hole transporting mixed layer 40.

As described above, in the first embodiment, the layers 30 to 50 made of the hole transporting material include the mixed layer 40 in which at least two kinds of hole transporting materials are mixed. By using one material of the two or more kinds of hole transporting materials in the mixed layer 40 as a material having a higher hole transporting capacity than the other hole transporting materials, the organic layer 30
Up to 70 is thickened to suppress a short circuit between the electrodes 20 and 80, while ensuring proper light emission.
1 can be provided.

Incidentally, an organic EL device having a hole blocking layer provided between a light emitting layer and a cathode for the purpose of improving the luminous efficiency is described in JP-A-2001-237079. This prior art publication further describes a configuration in which one or more mixed layers made of a plurality of materials having a hole transporting ability are provided between the light emitting layer and the anode, but the purpose of this mixed layer is clarified. Not listed.

By analogy with the main purpose described in this prior art publication, that is, holes and electrons also increase the recombination probability, the mixed layer has a function of transporting holes and a function of blocking electrons. Considered to be

Therefore, as in the present embodiment, in the hole transporting mixed layer 40, a material having a high hole transporting ability is included to secure the hole transporting function, and the degree of crystallinity and morphological change are reduced. It is different from the one that made it possible to thicken. Furthermore, in the case where there are a plurality of layers 30 to 50 made of a hole transporting material, there is no description or suggestion in the conventional publication that the hole transporting mixed layer 40 is the thickest layer among them. The present embodiment is different from the present embodiment.

(Second Embodiment) In the first embodiment,
By thickening the layers 30 to 50 made of the hole transporting material without degrading the hole transporting function, as a result, the organic layer 3 is obtained.
The thickness of 0 to 70 was made thicker, and it was possible to secure appropriate light emission while suppressing a short circuit between the electrodes 20 and 80.

In the second embodiment of the present invention, the upper and lower electrodes 20,
In order to prevent a short circuit between 80, the layer made of an electron transporting material is made thick and the electron transporting function is not deteriorated. FIG. 6 is an organic EL according to the second embodiment.
It is a figure which shows the schematic sectional structure of element S2. Hereinafter, differences from the first embodiment will be mainly described.

In the organic EL element S2 shown in FIG. 6, the hole transporting mixed layer 40 is eliminated from the organic EL element S1 shown in FIG. 1, and the electron transporting layer 70 is replaced by the electron transporting mixed layer 72. It is the configuration used.

That is, the hole injecting layer 30 and the hole transporting layer 50 are sandwiched between the anode 20 and the light emitting layer 60 as layers made of the hole transporting material, and the hole injecting layer 30 and the hole transporting layer 50 are sandwiched between the light emitting layer 60 and the cathode 80. The electron-transporting mixed layer 72 is sandwiched between the two as layers made of the electron-transporting material.

The electron-transporting mixed layer 72 is a mixed layer in which at least two or more kinds of electron-transporting materials are mixed, and one of the two or more kinds of electron-transporting materials in the electron-transporting mixed layer 72 is a material. Is a material having a higher electron transporting capacity than other electron transporting materials.

Similar to the first embodiment, the anode 20, the hole injection layer 30, the hole transport layer 50, and the light emitting layer 60 are formed on the substrate 10, and then the electron transport mixed layer 72 is formed. . In this example, a film is formed by co-evaporating a pyrene compound (for example, an adamantane derivative), which is a material having a relatively high electron transporting ability, and Alq3, which is a material having a relatively low electron transporting ability, using a vacuum deposition method. The film has a thickness of 40 nm.

The mixing ratio of the materials in the mixing layer 72 of this example is not limited, but is 1:10 to 10: 1.
It is possible to choose. On the electron transporting mixed layer 72, the cathode 80 is formed similarly to the above. The cathode 80 of this example also has a two-layer structure in which a LiF film having a thickness of 0.5 nm and an Al film having a thickness of 100 nm are sequentially formed from the electron transporting mixed layer 72 side.

Here, the material having a high electron-transporting ability in the electron-transporting mixed layer 72 has the lowest conduction band level in the lowest conduction band of the layer on the cathode 80 side in contact with the mixed layer 72 containing the material. It is preferably within ± 0.2 eV with respect to the position. In this example, the layer on the side of the cathode 80 that is in contact with the mixed layer 72 is the LiF film in the cathode 80.

It is preferable that the relationship between the conduction band lowest levels is such that the conduction band lowest level of the material having a high electron transporting ability in the electron transporting mixed layer 72 and the cathode 80 side adjacent to the mixed layer 72. When the difference from the lowest level of the conduction band of the layer is larger than ± 0.2 eV, the energy barrier is large and it becomes difficult to inject electrons from the layer on the cathode 80 side into the mixed layer 72.

In this example, the lowest conduction band levels of LiF and Al constituting the cathode 80 are 2.9, respectively.
eV and 3.7 eV. In addition, regarding the adamantane derivative that is a pyrene compound, the highest level of the valence band is 5.
7 eV, the lowest conduction band level is 2.7 eV, and the energy gap is 3.0 eV.

In this example, the material having a high electron transporting ability is an adamantane derivative, and the layer adjacent to the cathode 80, which is in contact with the mixed layer 72, is LiF. Is 0.2 eV.

The material having a high electron transporting ability in the electron transporting mixed layer 72 is for ensuring the electron transporting function in the electron transporting mixed layer 72, and it is preferable that the electron mobility is high. Specifically, the electron mobility is 1 × 1.
It is preferable that the material is 0 ⁻⁵ cm ² / V · sec or more.

Such a 1 × 10 ⁻⁵ cm ² / V · se
As the electron transporting material having an electron mobility of c or more, a pyrene compound represented by the above-mentioned adamantane derivative, diphenylanthracene (highest valence band level:
6.0 eV, conduction band lowest level: 3.1 eV, energy gap: 2.9 eV), distyrylbenzene derivatives, other spiro compounds, materials having an oxadiazole skeleton, and the like can be used.

That is, as the material having a high electron transporting ability in the electron transporting mixed layer 72, a material selected from a pyrene compound, diphenylanthracene, a distyrylbenzene derivative, a spiro compound, a material having an oxadiazole skeleton, etc. is adopted. can do.

In the electron transporting mixed layer 72, as the electron transporting material mixed with the material having a high electron transporting ability, an aluminum chelate material represented by Alq3 can be adopted.

This aluminum chelate-based material has a lower conduction band minimum level than the above-mentioned materials having a pyrene compound, a diphenylanthracene, a distyrylbenzene derivative, a spiro compound and an oxadiazole skeleton. Therefore, by forming the mixed layer 72 mixed with these, the energy barrier between the layer on the cathode 80 side and the mixed layer 72 is reduced, and the electron injection property from the cathode 80 side to the mixed layer 72 is improved.

As described above, in the second embodiment, the layer made of the electron transporting material is composed of the electron transporting mixed layer 72 in which at least two kinds of electron transporting materials are mixed, and the mixed layer is formed. A unique structure is adopted in which one of the two or more types of electron transporting materials in 72 has a higher electron transporting capacity than the other electron transporting materials.

According to this, since the electron transporting mixed layer 72 is a mixed layer in which two or more kinds of materials are mixed, it is possible to reduce the crystallinity and the morphological change when the mixed layer 72 is thickened. it can. Therefore, the mixed layer 72
Even if the thickness is increased, it is possible to prevent an increase in irregularities on the film surface.

Further, by making one electron-transporting material forming the electron-transporting mixed layer 72 a material having a higher electron-transporting ability than the other, the electron-transporting function is ensured even if the mixed layer 72 is thickened. be able to.

Therefore, according to the second embodiment, the layer 72 made of the electron-transporting material can be made thick without degrading the electron-transporting function. As a result, the organic layers 30, 50,
It is possible to provide the organic EL element S2 capable of ensuring appropriate light emission while suppressing the short circuit between the electrodes 20 and 80 by thickening the electrodes 60 and 72.

In FIG. 6, only one electron transporting mixed layer 72 is formed of the electron transporting material.
The layer made of an electron transporting material may be a plurality of layers having an electron transporting layer other than the electron transporting mixed layer 72.

In this case, as described above, since the electron transporting function can be ensured even if the mixed layer 72 is made thick, the mixed layer 72 among the layers made of a plurality of electron transporting materials.
Can be the thickest layer.

When a plurality of layers made of an electron transporting material are used, a layer made of another electron transporting material may be interposed between the electron transporting mixed layer 72 and the cathode 80.
In this case, the layer on the cathode 80 side in contact with the mixed layer 72 is
It is a layer made of an electron transporting material located between the cathode 80 and the mixed layer 72.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an organic EL element according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of an organic EL element as a comparative example.

FIG. 3 is a diagram showing initial current and luminance characteristics of the organic EL element of the first embodiment and the organic EL element of the comparative example.

FIG. 4 is a diagram showing luminance deterioration characteristics of the organic EL element of the first embodiment and an organic EL element of a comparative example.

FIG. 5 is a schematic cross-sectional view of an organic EL element as a second modification example of the first embodiment.

FIG. 6 is a schematic sectional view of an organic EL element according to a second embodiment of the present invention.

[Explanation of symbols]

20 ... Anode, 30 ... Hole injection layer, 40 ... Hole transporting mixed layer, 50 ... Hole transporting layer, 60 ... Light emitting layer, 70 ... Electron transporting layer, 72 ... Electron transporting mixed layer, 80 ... Cathode.

Claims (17)

[Claims] 1. A layer (3) made of a hole transporting material between the anode (20) and a light emitting layer (60) made of an organic EL material.
0, 40, 50) are sandwiched, and a layer (70) made of an electron transporting material is sandwiched between the light emitting layer and a cathode (80). The layer consisting of includes a mixed layer (40) in which at least two kinds of hole transporting materials are mixed, and one material of the two or more kinds of hole transporting materials in the mixed layer is An organic EL element, which is a material having a higher hole transporting capacity than other hole transporting materials. 2. A valence electron of the layer (20, 30) on the anode side in which the highest valence band level of the material having a high hole transporting capacity is in contact with the mixed layer (40) containing the material. The organic EL element according to claim 1, wherein the organic EL element is within ± 0.2 eV with respect to the highest band level. 3. The material having a high hole-transporting ability is a material having a hole mobility of 1 × 10 ⁻³ cm ² / V · sec or more, according to claim 1 or 2. Organic EL
element. 4. The material having a high hole transporting ability is any one of a porphyrin-based material, a starburst amine-based material, and a pentacene-based material. The organic EL device described in 1. 5. The hole transporting material mixed with the material having a high hole transporting ability in the mixed layer (40) is a tertiary amine-based material.
2. The organic EL device according to any one of 1. 6. A layer (30, comprising the hole transporting material.
40, 50) is composed of a plurality of layers, and the mixed layer (40) is the thickest layer among the plurality of layers, The organic EL device according to any one of claims 1 to 5. 7. A layer (40, consisting of the hole transporting material.
50) is a hole injection layer (4) in contact with the anode (20).
0) and a hole transport layer (50) located closer to the light emitting layer (60) than the hole injection layer, and the mixed layer (40) is configured as the hole injection layer. 7. The organic EL device according to claim 1, which is characterized in that. 8. A layer (30, composed of the hole-transporting material)
40, 50) comprises a hole injection layer (30) in contact with the anode (20) and a hole transport layer (40, 50) located closer to the light emitting layer (60) than the hole injection layer. The organic EL device according to any one of claims 1 to 6, wherein the mixed layer (40) is configured as the hole transport layer. 9. The organic EL device according to claim 8, wherein the hole injection layer (30) is made of a porphyrin-based material. 10. A layer (3 comprising the hole-transporting material.
The organic EL device according to any one of claims 1 to 9, characterized in that the total thickness of (0, 40, 50) is equal to or larger than the thickness of the anode (20). 11. A layer (3) made of the hole-transporting material.
0, 40, 50) is composed of three or more layers, and the organic E according to any one of claims 1 to 10.
L element. 12. A layer (3) made of a hole transporting material between the anode (20) and a light emitting layer (60) made of an organic EL material.
0, 50) are sandwiched between the light emitting layer and the cathode (80).
An organic EL device having a layer (72) made of an electron transporting material sandwiched between and, the layer made of the electron transporting material is a mixed layer in which at least two kinds of electron transporting materials are mixed. (72) is included, wherein one material of the two or more kinds of electron transporting materials in the mixed layer is a material having a higher electron transporting ability than other electron transporting materials. Organic EL device. 13. The mixed layer (72) wherein the material having a high electron-transporting ability has a conduction band lowest level thereof containing the material.
13. The organic EL device according to claim 12, wherein the conduction band lowest level of the layer (80) on the cathode side in contact with is within ± 0.2 eV. 14. The material having a high electron-transporting ability is an electron.
Mobility is 1 × 10 ^-Fivecm²/ V ・ sec or higher material
The present invention according to claim 12 or 13, characterized in that
Machine EL element. 15. The material having a high electron-transporting ability is any one of a pyrene compound, a diphenylanthracene, a distyrylbenzene derivative, a spiro compound, and a material having an oxadiazole skeleton.
15. The organic EL device according to any one of 2 to 14. 16. The electron transporting material mixed with the material having a high electron transporting ability in the mixed layer (72) is an aluminum chelate-based material.
16. The organic EL device according to any one of 1 to 15. 17. The layer made of the electron transporting material is made up of a plurality of layers, and the mixed layer is the thickest layer among the plurality of layers. Organic EL device.