WO2015001691A1

WO2015001691A1 - Organic electroluminescent element

Info

Publication number: WO2015001691A1
Application number: PCT/JP2014/001808
Authority: WO
Inventors: 松本　敏男
Original assignee: エイソンテクノロジー株式会社
Priority date: 2013-07-05
Filing date: 2014-03-27
Publication date: 2015-01-08
Also published as: JPWO2015001691A1

Abstract

With the aim of making possible efficient production at low cost of a laminate having a multitude of units, there is provided an organic electroluminescent element into which are introduced intermediate layers (charge generating layers) of novel structure composed of organic material only, without the use of the metal aluminum (Al), which has a vapor deposition temperature in excess of 1,200°C. The present invention pertains to an organic electroluminescent element of stack type (multi-photon type), characterized by having an anode, a cathode, a plurality of light-emitting units situated between the anode and the cathode, and including a light-emitting layer, and intermediate layers situated between the plurality of light-emitting units, the intermediate layers being constituted by mixed layers of a fullerene compound, and an electron-donating organic material having the function of donating electrons to the fullerene compound.

Description

Organic electroluminescent device

The present invention relates to an organic electroluminescent element (hereinafter sometimes abbreviated as “organic EL element”) used for a planar light source and a display element.

In recent years, an organic EL element having a light emitting layer made of an organic compound between an anode and a cathode, which are opposed to each other, has attracted attention as a means for realizing a large-area display element driven at a low voltage. Tang et al. Of Eastman Kodak Company has adopted a structure in which organic compounds having different carrier transport properties are stacked, and holes and electrons are injected in a balanced manner from the anode and the cathode, respectively, in order to increase the efficiency of the device. By making the thickness of the organic layer sandwiched between the anodes 200 nm or less, we succeeded in obtaining high luminance and high efficiency sufficient for practical application of 1000 cd / m ² and an external quantum efficiency of 1% at an applied voltage of 10 V or less. did.

For example, according to Patent Documents 1 to 6, it is said that a device capable of emitting light with a lower applied voltage can be provided by setting the film thickness of the entire organic layer sandwiched between the cathode and the anode to 1 μm or less. If the film thickness is in the range of 100 to 500 nm, an electric field (E = Vcm ⁻¹ ) useful for obtaining light emission with an applied voltage of 25 V or less is obtained.

The structure of the organic EL element has been developed on the basis of the structure shown by Tang et al. As described above. Recently, for example, as shown in Patent Document 7 and Patent Document 8, a structure sandwiched between electrodes. An organic EL element having a structure in which a plurality of light emitting units are stacked so that can be connected in series has been developed. This technology has been attracting attention as a technology that enables the organic EL device to dramatically extend its life, achieve high brightness required for light sources and illumination, and emit light uniformly over a large area. This is because the structure of the organic EL element of Tang et al. Which requires a large current despite the low voltage cannot satisfy these requirements.

In contrast, the inventor of the present application has devised and realized an organic EL element having a series type (tandem type) structure, and ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) is provided in the connection layer portion of each unit. A plurality of light emitting units can be connected in series by using a charge generation layer with low conductivity instead of the transparent electrode material as described above (Patent Document 8). In this organic EL element, only the region where the cathode and the anode intersect as in the conventional organic EL element emits light, and the sputtering process, which is essential for forming the transparent electrode, is no longer necessary. It is recognized as the most useful among the structures of organic EL elements, and has been widely known as a multiphoton organic EL element. The reason for being referred to as multiphoton is that if the number of light emitting units is set to a predetermined number or more, the number of photons exceeding the number of electrons passing through the organic EL element can be generated (Non-Patent Document 1).

However, this multi-photon organic EL element has a problem that it requires several times the manufacturing process time as compared with the conventional organic EL element.

As described above, the series organic EL element is suitable for emitting light over a large area with uniform intensity. This is because, compared with a conventional organic EL element, the voltage V required to obtain the same brightness can be increased by multiplying by the number of units, while the current I is decreased by dividing by the number of units. As a result, the element resistance (ratio of voltage to current: VI ^-1 ) increases by approximately the square of the number of units, the voltage drop due to the surface resistance of the external electrode can be reduced, and a substantially uniform potential in the surface can be obtained. This is because it can be realized.

Needless to say, this potential uniformity (in other words, luminance uniformity) increases as the number of units increases. According to the present inventor's previous knowledge, when a luminance of 5000 cdm ⁻² or more necessary for illumination is required, for example, when the emission area is 15 inches or more diagonal, at least about 15 units are considered necessary. It is almost impossible to produce such a large number of unit laminates efficiently and at low cost.

The reason why it is impossible to produce such a multi-unit laminate efficiently and at low cost is that the present inventors have described the hole charge and the hole charge as described in Example 6 of Patent Document 8. The point that metal aluminum (Al) whose vapor deposition temperature exceeds 1200 degreeC was essential for preparation of the charge generation layer provided in order to produce | generate an electronic charge is mentioned.

In Example 1 of Patent Document 8, there is an example in which a mixed layer of an electron transport material, bathocuproine and metal cesium (Cs), and a laminated structure of V ₂ O ₅ (vanadium pentoxide) is used as a charge generation layer. In the case of this structure, metal aluminum (Al) is not used, but it is clear from comparison of the characteristic graphs (FIGS. 21 to 32 and FIGS. 42 to 44) that the metal aluminum is used. Compared with the charge generation layer device using (Al), there was an undesired increase in driving voltage.

The film formation of metal aluminum (Al) needs to be installed in a place separated from the manufacturing chamber for forming a layer made of an organic substance such as a light emitting layer and a hole transport layer in an actual manufacturing process. Therefore, when it is necessary to repeatedly manufacture substantially the same process many times, such as a multi-photon organic EL element having a plurality of light emitting units, a plurality of vapor deposition chambers are installed and what is between them. There is a need to go back and forth, and the process of forming the charge generation layer and the layer in contact therewith becomes complicated, raising the problem of increasing the product price.

JP 59-194393 A JP-A 63-264692 Japanese Patent Laid-Open No. 02-15595 US Pat. No. 4,539,507 U.S. Pat. No. 4,769,292 US Pat. No. 4,885,211 Japanese Patent Laid-Open No. 11-329748 Japanese Patent No. 3933591

In view of the problems of the prior art as described above, the present invention aims to make it possible to produce a laminate of a large number of units efficiently and at a low cost by using metal aluminum (Al) having a deposition temperature exceeding 1200 ° C. The present invention provides an organic electroluminescent device in which an intermediate layer (charge generation layer) having a new structure and made only of an organic material is used without being used. According to the present invention, by introducing the intermediate layer (charge generation layer) of this new structure, it is possible to efficiently produce a laminate of a large number of units at low cost while avoiding an undesirable increase in driving voltage.

As described above, the present inventor does not use metal aluminum (Al), but is C60 of the organic fullerene compound, and an electron donating organic substance having an electron donating function for C60.

By successfully introducing an intermediate layer (charge generation layer) including a mixed layer of AOB (acidine orange) base indicated by the following, an undesired increase in driving voltage was successfully achieved and the present invention was completed. It came to do.

That is, the present invention
The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units;
Have
The intermediate layer is composed of a mixed layer of a fullerene compound and an electron-donating organic substance having a function of donating electrons to the fullerene compound;
A stack type (multi-photon type) organic electroluminescent element characterized by the above is provided.

In the organic electroluminescent device of the present invention having the above-described configuration, in particular, the fullerene compound is preferably C60, and the electron-donating organic substance is AOB (acidine orange base). Although preferable, it is not limited to these.

In the organic electroluminescent element of the present invention having the above-described configuration,
The intermediate layer has a two-layer structure adjacent to each other,
The anode side of the two-layer structure is composed of a mixed layer of C60 and AOB (acidine orange base),
The cathode side of the two-layer structure has the general formula:

(In the formula, Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent) are preferably used. .

That is, the present invention more preferably,
The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units;
Have
The intermediate layer is composed of a mixed layer of a fullerene compound and an electron-donating organic substance having a function of donating electrons to the fullerene compound;
Adjacent to the cathode side of the mixed layer, the following general formula:

(Wherein Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent), a layer formed of an arylamine compound represented by Having
A stack type (multi-photon type) organic electroluminescent device characterized by the above is provided.

Here, the role of the intermediate layer is to inject the same amount of electrons into adjacent light-emitting units into the anode side unit from the intermediate layer and holes into the cathode side unit. is there. By maintaining the balance of the injection, each light emitting unit is equivalently connected in series, and an operation expected as a stack type element can be obtained.

Further, due to the series connection by the intermediate layer, the light emission efficiency is lowered when there is a substantial voltage rise. Therefore, the above-described electron and hole injection are required to have no energy barrier with potential consumption.

According to the present invention, the stack type can be formed without causing an undesirable voltage rise without using metal aluminum (Al) having a deposition temperature exceeding 1200 ° C., which is essential for the structure of a conventional stack type organic EL device. Since the organic EL element can be produced, the product cost can be reduced while maintaining the performance.

It is a schematic sectional drawing which shows the typical structure of the organic EL element of this invention. It is a schematic sectional drawing which shows the typical structure of the light emission unit part of the organic EL element of this invention. It is a schematic sectional drawing which shows the laminated structure of the organic EL element produced by the reference example (reference example) 1. FIG. 3 is a schematic cross-sectional view showing a laminated structure of an organic EL element produced in Example 1. FIG. 3 is a schematic cross-sectional view showing a laminated structure of an organic EL element produced in Example 2. FIG. 6 is a schematic cross-sectional view showing a laminated structure of an organic EL element produced in Comparative Example 1. FIG. 3 is a graph plotting voltage (V) -luminance (cd / m ² ) characteristics of an organic EL element implemented in the present invention.

Hereinafter, representative embodiments of the organic EL device of the present invention will be described in detail, but the present invention is not limited to these. In the following description, overlapping description may be omitted.

The organic EL element of the present embodiment includes an anode, a cathode, a plurality of light emitting units including a light emitting layer, which are positioned between the anode and the cathode, and an intermediate layer positioned between the plurality of light emitting units. The intermediate layer has a two-layer structure adjacent to each other, and the two-layer structure is composed of a mixed layer of C60 and AOB (acidine orange base) from the anode side, and the cathode side has the following general formula:

(Wherein, Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent). The structural formula of AOB (acidine orange base) is the following formula:

It is represented by

As shown in FIG. 1, the organic EL element 1 of the present embodiment includes n light emitting units (n is an integer of 2 or more), for example, an anode 2 formed in order on a glass substrate 1 and The first light emitting unit 3-1, the first intermediate layer 4-1, the second light emitting unit 3-2, the second intermediate layer 4-2, and the (n-1) th intermediate layer It has a structure including 4- (n−1), an nth light emitting unit 3-n, and a cathode 14.

Further, in some cases, a layered structure of an nth intermediate layer 4-n and a hole injection layer, which will be described later, may be added as a layer in contact with the cathode to function as a buffer layer that reduces damage during cathode film formation. Good.

Each light emitting unit can adopt various structures as in the case of conventionally known organic EL elements. For example, the configuration of the light emitting unit is not limited to this, but in the structure shown in FIG. 2 (that is, in a portion sandwiched between the anode 2 and the cathode 5 of a normal organic EL element), hole injection is performed. A typical example is a light-emitting unit comprising a layer 6, a hole transport layer 7, a light-emitting layer 8, and an electron transport (injection) layer 9.

The hole transporting compound used for the hole injection layer and the hole transport layer of the light emitting unit has the following general formula:

(In the formula, Ar ₁ , Ar ₂ and Ar ₃ each independently represents an aromatic hydrocarbon group which may have a substituent) are preferable.

Examples of such arylamine compounds are not particularly limited, but include JP-A-6-25659, JP-A-6-203963, JP-A-6-215874, JP-A-7-145116, Japanese Unexamined Patent Publication No. 7-2224012, Japanese Unexamined Patent Publication No. 157473, Japanese Unexamined Patent Publication No. 8-48656, Japanese Unexamined Patent Publication No. 7-126226, Japanese Unexamined Patent Publication No. 7-188130, Japanese Unexamined Patent Publication No. 8-40995, Japanese Unexamined Patent Publication No. 8- The arylamine compounds disclosed in Japanese Patent No. 40996, Japanese Patent Application Laid-Open No. 8-40997, Japanese Patent Application Laid-Open No. 7-126225, Japanese Patent Application Laid-Open No. 7-101911, and Japanese Patent Application Laid-Open No. 7-97355 are preferable. , N, N ′, N′-tetraphenyl-4,4′-diaminophenyl, N, N ′ ′-diphenyl-N, N ′ ′-di (3-methyl Ruphenyl) -4,4′-diaminobiphenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane N, N, N ′, N′-tetra-p-tolyl-4,4′- diamino Biphenyl, bis (4-di-p-tolylaminophenyl) phenylmethane, N, N′-diphenyl-N, N ′ ′-di (4-methoxyphenyl) -4,4′-diaminobiphenyl, N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether, 4,4'-bis (diphenylamino) quadriphenyl, 4-N, N-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy -4'-N, N-diphenylaminostilbenzene N-phenylcarbazole, 1,1-bis (4-di-p-triaminophenyl) -cyclohexane 1,1- (4-di-p-triaminophenyl) -4-phenylcyclohexane, bis (4-dimethylamino-2-methylphenyl) -phenylmethane, N, N, N-tri (p-tolyl) amine, 4- (Di-p-tolylamino) -4 ′-[4 (di-p-tolylamino) styryl] stilbene, N, N, N ′, N′-tetraphenyl-4,4′-diamino-biphenyl N-phenylcarbazole, 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl, 4,4 ″ -bis [N- (1-nafur) -N-phenyl-amino] p-terphenyl, 4,4′-bis [N- (3-acenaphthenyl) -N-phenyl-amino] biphenyl, 1,5-bis [N- (1-naphthyl) -N-phenyl-amino] naphthalene, 4,4′- Screw [N- (9-anthryl) -N-phenyl-amino] biphenyl, 4,4 ″ -bis [N-(1-anthryl) -N-phenyl-amino] p-terphenyl, 4,4′-bis [N— (2-phenanthryl) -N-phenyl-amino] biphenyl, 4,4′-bis [N- (8-fluoranthenyl) -N-phenyl-amino] biphenyl, 4,4′-bis [N- (2 -Pyrenyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (2-perylenyl) -N-phenyl-amino] biphenyl, 4,4'-bis [N- (1-colonenyl)- N-phenyl-amino] biphenyl, 2,6-bis (di-p-tolylamino) naphthalene, 2,6-bis [di- (1-naphthyl) amino] naphthalene, 2,6-bis [N- (1- Naphthyl) -N- (2- Phthyl) amino] naphthalene, 4,4 '' -bis [N, N-di (2-naphthyl) amino] terphenyl, 4.4 '-bis {N-phenyl-N- [4- (1-naphthyl)] Phenyl] amino} biphenyl, 4,4 '-bis [N-phenyl-N- (2-pyrenyl) -amino] biphenyl, 2,6-bis [N, N-di (2-naphthyl) amino] fluorene, 4 , 4 ″ -bis (N, N-di-p-tolylamino) terphenyl, bis (N-1-naphthyl) (N-2-naphthyl) amine, and the like.

In the hole injection layer, the arylamine compound and the electron-accepting compound (Lewis acid compound) are preferably used as a mixture, and the electron-accepting compound (Lewis acid compound) is not particularly limited. Ferric bromide, ferric bromide, ferric iodide, aluminum chloride, aluminum bromide, aluminum iodide, gallium chloride, gallium bromide, gallium iodide, indium chloride, indium bromide, indium iodide, 5 Inorganic compounds such as antimony chloride, arsenic chloride, boron trifluoride, vanadium oxide, molybdenum oxide, rhenium oxide, tungsten oxide, DDQ (dicyano-dichloroquinone), TNF (trinitrofluorenone), TCNQ (tetracyano) Organic such as (quinodimethane), (tetrafluoro-tetracyanoquinodimethane) Compounds can be used.

The molar ratio of the Lewis acid compound is preferably 0.01 or more with respect to the arylamine compound. With the hole injection layer having such a configuration, holes generated in the intermediate layer are injected into each light emitting unit without an energy barrier.

The “light emitting layer” may be a conventional light emitting layer used in a conventional organic EL device, and the light emitting material constituting the light emitting layer is not particularly limited, and various known fluorescent materials or phosphorescent materials are known. Any can be used. For example, the following formula:

And tris (8-quinolinolato) aluminum complex (Alq3) and the like.

The “electron transport (injection) layer” may be formed using an electron transport material constituting the electron transport layer of the conventional organic EL device, and is not particularly limited. For example, KLET02 manufactured by Chemipro Kasei Co., Ltd. Etc. The physical properties of the electron transporting organic compound manufactured by Chemipro Kasei Co., Ltd. are as follows (from Chemipro Kasei Co., Ltd. HP. Http://www.chemipro.co.jp/Yuki#EL/Products) .html).

In the “electron transport (injection) layer”, an electron donating compound (Lewis base compound) is often used by mixing with the electron transporting substance. As the electron donating compound (Lewis base compound), As disclosed in Kaihei 10-270171 and JP-A-2001-102175, it is preferably made of one or more metals selected from alkali metals, alkaline earth metals, and rare earth metals.
The molar ratio of the electron donating compound in the electron injection layer is preferably 0.1 to 10 with respect to the organic compound. With the electron injection layer having such a configuration, electrons generated in the intermediate layer are injected into each light emitting unit without an energy barrier.

As the material constituting the “cathode”, generally a metal having a small work function, an alloy containing them, a metal oxide, or the like is used. Specifically, simple metals such as alkaline metals such as Li and Cs, alkaline earth metals such as Mg and Ca, rare earth metals such as Eu, or alloys of these metals with Al, Ag, In, etc. Is mentioned.

In addition, when the layer in contact with the cathode has a laminated structure of the intermediate layer and the hole injection layer of the present invention as in the following examples, the value of the work function or the like is limited if the cathode is a conductive material. In addition, an electrode material having a high work function, such as an ITO (indium tin oxide) transparent electrode, can be used as the cathode.

The material constituting the “anode” is not particularly limited, and for example, a transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide) can be used.

Therefore, it is possible to make a transparent light emitting element by making both the cathode and the anode transparent (because both the organic film and the intermediate layer are also transparent). In contrast to the case of a general organic EL element, the anode is An organic EL element having a structure in which light is extracted not from the substrate side but from the film formation surface side can be formed by using a metal and forming the cathode as a transparent electrode. In addition, regarding the order of forming each layer, it is not always necessary to start from the formation (film formation) of the anode, and the formation may be started from the cathode.

As mentioned above, although the embodiment of the typical laminated structure of the organic EL element of the present invention has been described, the present invention can be modified in various ways within the scope of the technical idea of the present invention, and these design modified inventions Of course, this is also included in the present invention. Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[Manufacturing equipment and conditions]
For the formation of the organic compound layer, the metal layer, and the intermediate layer, a vacuum deposition machine manufactured by Eiko Co., Ltd. was used. The thickness of each layer is measured using a stylus type surface shape measuring device (DEKTAK3030), and for the characteristic evaluation of the obtained organic EL element, source meter 2400 manufactured by Keithley Instruments Co., Ltd. and Topcon Co., Ltd. Luminometer BM-7. Further, a direct current voltage is applied in a stepwise manner at a rate of 0.1 V / 2 seconds or 0.5 V / 2 seconds between the anode electrode on the substrate and the cathode electrode on the organic film, so that the luminance and The current value was measured.

≪Reference Example 1≫
As the organic EL element of Reference Example 1, a light emitting element having a layer structure corresponding to the light emitting unit shown in FIG. 2 was produced on a glass substrate (see FIG. 3). The details of each layer were as follows.
1) Anode ITO (Indium Tin Oxide), 110 nm
2)

Hole injection layer

4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (hereinafter abbreviated as NPB), which is an arylamine compound, and molybdenum trioxide, which is a Lewis acid compound ( MoO ₃ ) co-deposited layer (hereinafter referred to as NPB: MoO ₃ ), 10 nm (the mixing ratio is 1: 1 by weight)
3) Hole transport layer NPB, 50nm
4) Light-emitting layer Tris (8-quinolinolato) aluminum complex (hereinafter abbreviated as Alq3), 30 nm
5) Electron injection layer Co-deposited layer of cesium (hereinafter referred to as Cs) as a Lewis base compound and KLET02 as an electron transport material (hereinafter referred to as Cs: KLET02), 40 nm
6) Cathode Aluminum (hereinafter referred to as Al), 80 nm

Example 1
As the organic EL element of Example 1, the light emitting element having the layer structure shown in FIG. 4 was produced on a glass substrate. The details of each layer were as follows.
1) Anode ITO (Indium Tin Oxide), 110 nm
2) Hole injection layer NPB: MoO, 10 nm (equivalent to Reference Example 1)
3) Hole transport layer NPB, 50 nm (equivalent to Reference Example 1)
4) Light emitting layer Alq3, 30 nm (equivalent to Reference Example 1)
5) Electron injection layer Cs: KLET02, 20 nm
6) Intermediate layer 1
A mixed layer of C60, which is a fullerene compound, and AOB (acidic orange base) having an electron donating property to C60 (hereinafter referred to as C60: AOB), 2 nm (Note that the mixing ratio of AOB is 5 with respect to C60. Weight percent)
7) Intermediate layer 2
An arylamine compound, the following formula:

4,4 ', 4 "-Tris (3-methyl-phenylphenylamino) tri-phenylamine (hereinafter referred to as MTDATA), 2 nm
8) Hole injection layer NPB: MoO, 20 nm
9) Cathode Al, 80nm

If it is demonstrated that the organic EL element of Example 1 has no voltage loss (voltage increase) in the intermediate layer portion and exhibits the same characteristics as those of Reference Example 1, the following structure is obtained. By repeating the light emitting unit structure of the organic EL element using the intermediate layer of the present invention, an organic EL element having properties equivalent to those of the multiphoton organic EL element can be obtained.
a) Anode b) Light emitting unit Hole injection layer Hole transport layer Light emitting layer Electron injection layer c) Intermediate layer Intermediate layer 1
Middle layer 2
d) Light emitting unit Hole injection layer Hole transport layer Light emitting layer Electron injection layer e) Repeat b) to d) above f) Cathode

Therefore, in this example, an organic EL element having the same hole injection layer configuration in the layers adjacent to the anode and the cathode was produced.

<< Example 2 >>
As the organic EL element of Example 2, a light emitting element having the layer structure shown in FIG. 5 was produced on a glass substrate. The details of each layer were as follows.
1) Anode ITO (Indium Tin Oxide), 110 nm
2) Hole injection layer NPB: MoO, 10 nm (equivalent to Reference Example 1)
3) Hole transport layer NPB, 50 nm (equivalent to Reference Example 1)
4) Light emitting layer Alq3, 30 nm (equivalent to Reference Example 1)
5) Electron injection layer Cs: KLET02, 20 nm (equivalent to Reference Example 1)
6) Intermediate layer (equivalent to Example 1)
C60: AOB, 2 nm (The mixing ratio of AOB is 5% by weight with respect to C60)
7) Hole injection layer (equivalent to Example 1)
NPB: MoO, 20nm
8) Cathode Al, 80 nm

≪Comparative example 1≫
As the organic EL element of Comparative Example 1, a light emitting element having the layer structure shown in FIG. 6 was produced on a glass substrate. The details of each layer were as follows.
1) Anode ITO (Indium Tin Oxide), 110 nm
2) Hole injection layer NPB: MoO, 10 nm (equivalent to Reference Example 1)
3) Hole transport layer NPB, 50 nm (equivalent to Reference Example 1)
4) Light emitting layer Alq3, 30 nm (equivalent to Reference Example 1)
5) Electron injection layer Cs: KLET02, 20 nm (equivalent to Reference Example 1)
6) Hole injection layer (equivalent to Example 1)
NPB: MoO, 20nm
7) Cathode Al, 80 nm

[Evaluation]
FIG. 7 is a graph in which voltage (V) −luminance L (cd / m ² ) of each light-emitting element manufactured in Reference Example 1, Example 1, Example 2, and Comparative Example 1 is plotted. As shown in FIG. 7, the light emitting devices of Examples 1 and 2 have a lower driving voltage than the light emitting device of the comparative example without the intermediate layer of the present invention, and are substantially the same as the light emitting device of the reference example. It was found to have properties. Further, comparing the characteristics of the light emitting devices of Example 1 and Example 2, the light emitting device of Example 1 having a two-layer structure having an arylamine layer in the intermediate layer can be driven at a lower voltage. It was shown that.

The organic EL device of the present invention as described above can be used in a wide range of product fields that require light generation, such as various light sources and image display devices that are required to have low energy consumption.

1 ... substrate
2 ... Anode,
3 ... light emitting unit,
4 ... intermediate layer,
5 ... cathode,
6 ... hole injection layer,
7 ... Hole transport layer,
8 ... light emitting layer,
9: Electron transport (injection) layer,
60, 61 ... hole injection layer,
70, 71 ... hole transport layer,
80, 81 ... light emitting layer,
90, 91 ... electron transport (injection) layer,
101: Intermediate layer 1,
102: Intermediate layer 2

Claims

The anode,
A cathode,
A plurality of light emitting units including a light emitting layer located between the anode and the cathode;
An intermediate layer located between the plurality of light emitting units;
Have
The intermediate layer is composed of a mixed layer of a fullerene compound and an electron-donating organic substance having a function of donating electrons to the fullerene compound;
An organic electroluminescent device characterized by the above.
The organic electroluminescent device according to claim 1, wherein the fullerene compound is C60.
2. The organic electroluminescent device according to claim 1, wherein the electron-donating organic substance is AOB (acidine orange base).
The intermediate layer has a two-layer structure adjacent to each other,
The anode side of the two-layer structure is composed of a mixed layer of C60 and AOB (acidine orange base),
The cathode side of the two-layer structure has the general formula:

(Wherein, Ar 1 , Ar 2 and Ar 3 each independently represents an aromatic hydrocarbon group which may have a substituent),
The organic electroluminescent element according to claim 1.