JPH07109451A - Electroluminescent device - Google Patents

Abstract

PURPOSE:To improve the durability of an electroluminescent device by forming at least one of layers sandwiched between an anode and a cathode from an org. compd. represented by a specific formula. CONSTITUTION:This electroluminescent device is obtd. by forming the following layers on a transparent glass plate successively in that order: an anode comprising a transparent conductive film of SnO2, etc.; a hole transport layer comprising a thin film of an arom. tert. amine of formula I, etc.; a luminescent layer comprising a thin film of an oxadiazole compd. of formula II (wherein Ar1 and Ar2 are each an arom. hydrocarbon group or an arom. heterocycle; and X is a naphthalene residue); an electron transport layer comprising a thin film of an oxadiazole compd. of formula III, etc.; and a cathode comprising an Mg-Ag alloy, etc. The hole transport, luminescent, and electron transport layers are formed, e.g. by vacuum deposition, under such conditions that the thickness of each of these layers is about 10-100nm and the total thickness is about 0.15mum or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a light emitting layer made of a light emitting material, and can directly convert electric energy into light energy by applying an electric field, and can be used as a conventional incandescent lamp, fluorescent lamp or light emitting diode. In contrast, the present invention relates to an electroluminescent device that enables realization of a low power consumption light emitter, a micro volume light emitter, a light weight light emitter, or a large-area planar light emitter.

[0002]

2. Description of the Related Art In recent years, with the diversification and space saving of information equipment, there is an increasing need for a flat display device which consumes less power and occupies less space than a CRT. Liquid crystal, plasma displays, etc. are available as such flat display elements. Recently, in particular, self-emission type displays have a clear display.
In addition, there are increasing expectations for organic electroluminescent devices that can be driven with a constant DC voltage. A device structure of an organic electroluminescent device has so far been a two-layer structure (a structure in which a hole transport layer and a light emitting layer are formed between a hole injection electrode and an electron injection electrode (SH
-A structure) (JP-A-59-194393, Appl.
Phys. Lett. 51, 913 (1987), or a structure in which a light emitting layer and an electron transport layer are formed between a hole injecting electrode and an electron injecting electrode (SH-B structure) (USP).
No. 5,085947, JP-A-2-25092, A
ppl. Phys. Lett. 55, 1489 (198
9)) or a three-layer structure (a structure in which a hole transport layer, a light emitting layer, and an electron transport layer are formed between a hole injection electrode and an electron injection electrode (DH structure) (Appl.Phys.Le).
tt. 57, 531 (1990)) has been reported.

As the hole injecting electrode, Au or IT is used.
An electrode material having a large work function such as O (indium tin oxide) is used, and Ca, Mg, A is used as the electron injection electrode.
Electrode materials having a low work function such as 1 and the like and alloys thereof are used. Until now, the hole transport layer, the light emitting layer,
Various organic compounds have been reported as materials that can be used for the electron transport layer. Examples of organic materials used for these are aromatic tertiary amines for the hole transport layer, and aluminum trisoxine for the light emitting layer material (JP-A-59-194393, JP-A-63-29569).
5), styrylamine derivatives, styrylbenzene derivatives and the like (JP-A-2-209988), and as the electron transport layer, oxadiazole derivatives and the like (Journal of the Chemical Society of Japan N
o. 11, p1540 (1991) has been reported.
Up to now, by using various element structures and organic materials, an element with high-luminance light emission of 1000 cd / m ² or more and a driving voltage of about 10 V has been obtained initially. In the organic material, a decrease in light output and an increase in driving voltage are observed in a few hours, and there is a big problem in the long-term durability of the EL element. Particularly in blue light emitting devices, the search for materials has not been sufficiently conducted, and many problems such as improvement in light emission efficiency remain. Carrier injection type electroluminescent devices using organic compounds as light emitters, including these examples, have a short history of research and development, and it cannot be said that the material research and device research have been sufficiently conducted. The reality is that there are many problems such as further improvement of brightness, control of emission wavelength, and improvement of durability.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art, and an object thereof is to have sufficient brightness and light emitting performance, which is excellent in durability for a long time. It is to provide an organic electroluminescence device (organic EL device).

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies on the constituent elements of an organic EL device for solving the above problems, and as a result, have formed an anode and a cathode and one or more layers sandwiched between them. In the electroluminescent layer element constituted by the organic compound layer of 1, the at least one of the organic compound layers is a layer containing a specific oxadiazole-based compound as a constituent component, so that the electroluminescence effective against the above problems is achieved. We have found that we can provide elements.

Further, an electroluminescent device containing one or more light emitting layers and one or more electron transport layers as constituent elements between the anode and the cathode, or one or more hole transport layers and one layer between the anode and the cathode. In the electroluminescent device containing the above-mentioned light-emitting layer and one or more electron-transporting layers as constituent elements, at least one of the electron-transporting layers is further formed into a layer containing a specific oxadiazole-based compound as a constituent component. It has been found that an effective electroluminescent device can be provided.

That is, according to the present invention, in an electroluminescent device composed of an anode and a cathode and one or a plurality of layers of an organic compound sandwiched therebetween, at least one of the organic compound layers is Provided is an electroluminescent device comprising a layer containing an organic compound represented by the general formula (I) (Chemical Formula 1) as a constituent component.

[Chemical 1] (In the formula, Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group, which may be the same or different.
Represents a naphthalene residue. ) Also, according to the invention,
An electroluminescent device containing one or more light emitting layers and one or more electron transport layers as constituent elements between an anode and a cathode, or one or more hole transport layers and one or more light emitting layers between an anode and a cathode. And an electroluminescent device containing one or more electron-transporting layers as constituents, at least one of the electron-transporting layers is a layer containing an organic compound represented by the general formula (I) (Formula 1) as a constituent. An electroluminescent device is provided.

In the present invention, as described above, at least one of the organic compound layers contains a specific oxadiazole-based compound.
The compound represented by will be described below with reference to specific examples. However, the present invention is not limited to these.

The aromatic hydrocarbon group or aromatic heterocyclic group applied to Ar ₁ and Ar ₂ in the general formula (I) 1 is styryl, phenyl, biphenyl, terphenyl, naphthyl, anthryl, acenaphthenyl, fluorenyl, Phenanthryl, indenyl, pyrenyl, pyridyl, pyrimidyl, furanyl, pyronyl, thiophenyl,
Examples thereof include quinolyl, benzofuranyl, benzothiophenyl, indolyl, carbazolyl, benzoxazolyl, quinoxalyl, benzimidazolyl, pyrazolyl, dibenzofuranyl, dibenzothiophenyl, oxazolyl and oxadiazolyl groups. These aromatic hydrocarbon groups or aromatic heterocyclic groups further include one or more halogen atom, hydroxyl group, cyano group, nitro group, amino group, trifluoromethyl group, carbon number 1-12, preferably 1-6 alkyl. Groups, alkoxy groups, aryloxy groups, phenyl groups, styryl groups, naphthyl groups, thiophenyl groups, aralkyl groups, biphenyl groups, bithiophenyl groups, furanyl groups, bifuranyl groups, pyronyl groups, bipyronyl groups, etc. Is also good.

X represents a divalent naphthalene residue,
For example, the following groups are specifically mentioned.

[Table 1]

Next, specific examples of the oxadiazole compound represented by the general formula (I) used in the present invention are shown below.

[Table 2- (1)]

[Table 2- (2)]

The electroluminescent device according to the present invention is obtained by subjecting the above-described organic compound to a vacuum deposition method, a solution coating method, or the like.
The organic compound layer as a whole has a thickness of less than 0.5 μm, and more preferably, each organic compound layer is thinned to a thickness of 10 nm to 100 nm to form an organic compound layer, and the organic compound layer is directly or indirectly sandwiched by an anode and a cathode. It is composed of In addition, when the constituent organic compound is extremely rich in thin film forming ability, it is possible to form a layer with a film thickness of 10 nm or less. Further, it is also effective to dope into another organic compound layer or the polymer semiconductor layer as an additive. On the contrary, it is also possible to add a plurality of other substances as additives to each organic compound layer described in the present invention.

The electroluminescent device of the present invention is one in which a bias is electrically applied to the light emitting layer to cause it to emit light. However, since a short circuit may occur due to a slight pinhole and the device may not function as an element, an organic compound layer of the organic compound layer is formed. For formation, it is desirable to use a compound having excellent film forming properties together. Further, it is possible to form an organic compound layer by combining a compound having such excellent film-forming property with a polymer binder. Examples of the polymer binder that can be used in this case include polystyrene, polyvinyltoluene, poly-N-vinylcarbazole, polymethylmethacrylate, polymethylacrylate, polyester, polycarbonate and polyamide.

As the anode material, nickel, gold, platinum,
Palladium, alloys of these, or tin oxide (Sn
O ₂ )), tin oxide-indium (ITO), copper iodide and other metals having a large work function, alloys and compounds thereof,
Further, a polyalkylthiophene such as poly (3-methylthiophene) or a conductive polymer such as polypyrrole or polyarylene vinylene can be used. It may be a laminate of a metal and a conductive polymer. On the other hand, as the cathode material, silver, tin, lead, calcium, magnesium, manganese, indium, aluminum, or an alloy thereof having a small work function is used. At least one of the materials used as the anode and the cathode is preferably sufficiently transparent in the emission wavelength region of the device. Specifically 8
It is desirable to have a light transmittance of 0% or more. But,
In the case of an edge emitting device, it is preferable that both electrodes have high light reflectance.

The electroluminescent device of the present invention is constructed as a device by sequentially laminating the above layers on a transparent substrate such as glass or a plastic film. However, the stability of the device is improved, especially the moisture content in the atmosphere. In order to protect against oxygen, a separate protective layer is provided, or the entire device is placed in the cell,
Silicon oil, a desiccant, or the like may be enclosed, or may be enclosed in a vacuum cell.

The present invention will be described in more detail below with reference to the drawings. 1 to 7, 1 is a substrate, 2 and 4 are electrodes, 3a is a light emitting layer, 3b is an electron transport layer, and 3c is a hole transport layer. FIG. 1 shows a structure in which an electrode 2 is provided on a substrate, a light emitting layer 3a is independently provided on the electrode 2, and an electrode is provided thereon. 2 shows an electrode 2 and a light emitting layer 3a in FIG.
The hole transport layer 3c is provided between the two. FIG. 3 shows an electron transport layer 3b provided between the light emitting layer 3a and the electrode 4 in FIG. In FIG. 4, the hole transport layer 3c is provided between the electrode 2 and the light emitting layer 3a in FIG. Although typical configuration examples have been illustrated above, these are the most basic configuration examples, and layers for improving charge transportability may be inserted in various places. For example, in FIG.
2 is a case where the hole transport layer 3c is composed of at least two layers or more in FIG. 2, and FIG. 6 is a case where the electron transport layer 3b is composed of at least two or more layers in FIG. Further, FIG. 7 shows a case where either or both of the hole transport layer and the electron transport layer in FIG. 4 are composed of at least two layers. These plural organic compound layers may be called by different names depending on their roles. For example,
The hole transport layer may be a hole injection layer, an electron barrier layer, or an exciton barrier layer. In the present invention, the hole transport layer means all organic compound layers between the light emitting layer and the anode electrode, and the electron transport layer means all organic compound layers between the light emitting layer and the cathode electrode. It is also applied to the case where a tandem type laminated structure having a plurality of light emitting layers is adopted. Further, in the present invention, it is desirable that the transparent anode is formed on the transparent substrate to have the structure as shown in FIGS. 1 to 7, but the reverse structure may be adopted depending on the case.

As the various materials used in combination in the present invention, any one can be used as long as it has a function of hole transporting property, electron transporting property, light emitting property and the like.
For example, the following conventionally known ones can be used.

The material for the light emitting layer is preferably a substance which has strong fluorescence in a solid state and forms a dense film in a thin film of 50 nm or less. All the conventionally known materials that have been used for the light emitting layer of the organic EL device so far are the organic EL of the present invention.
It can be applied to devices. For example, a metal chelated oxinoid compound (8-hydroxyquinoline metal complex) (JP-A-49-194393, JP-A-63-295).
695), butadiene derivatives such as 1,4 diphenylbutadiene and tetraphenylbutadiene, coumarin derivatives, benzoxazole derivatives, oxadiazole derivatives, oxazole derivatives, thiadiazole derivatives,
Styrylamine derivatives, bisstyrylbenzene derivatives (JP-A-2-247277), trisstyrylbenzene derivatives (JP-A-3-296595), bisstyrylanthracene derivatives (JP-A-3-163186), perinone derivatives, aminopyrene derivatives and the like have excellent light emission. It is a layer material. Specific examples of the light emitting layer material useful in the present invention are shown below.

[0019]

[Table 3- (1)]

[0020]

[Table 3- (2)]

[0021]

[Table 3- (3)]

As the hole transport layer material, all the materials which have been used as the hole transport layer material so far can be used, but at least two aromatic tertiary amines are contained and the aromatic tertiary amine is contained. Compounds in which is a monoarylamine, diarylamine, triarylamine are preferred. USP as a typical useful aromatic tertiary amine
No. 4,175,960, USP No. 4,53
The compounds disclosed in 9,507, 63-264692 can be utilized. Also, USP N
o. Porphyrin derivatives (phthalocyanines) disclosed in 4,720,432 are also useful compounds. Specific examples of useful hole transport layer materials are shown below.

[0023]

[Table 4- (1)]

[0024]

[Table 4- (2)]

As the electron transport layer material, all known materials which have been used as the electron transport layer material can be used. One preferable electron transporting material is a compound containing at least one oxadiazole ring which is an expression unit having an electron transporting ability. Representative useful oxadiazole compounds are described in Appl. Phys. Let
t55, 1489 (1989) and the Chemical Society of Japan 15
40 (1991). Further, preferred organic materials for use in the electron transport layer of the laminated electroluminescent device of the present invention are metal chelated oxinoid compounds including chelates of 8-hydroxyquinoline. further,
Other preferred electron transport layer materials include butadiene derivatives such as 1,4-diphenylbutadiene and tetraphenylbutadiene, coumarin derivatives, bisstyrylbenzene derivatives, bisstyrylanthracene derivatives, benzoxazole derivatives, oxadiazole derivatives, oxazole derivatives. , Thiadiazole derivative, naphthalimide derivative, perylenetetracarboxylic acid diimide derivative,
Examples thereof include quinacridone derivatives. Specific examples of these are shown below.

[0026]

[Table 5]

[0027]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 On a glass substrate having an ITO anode having a surface resistance of 20Ω / □, a hole-transporting layer having a thickness of 400 Å and comprising the triphenylamine derivative represented by the compound (C-10), the compound (B-8). ) Having a thickness of 150 Å and a compound having the formula (I) (No. 10) having a thickness of 200
An electron transport layer of Å, an electron injection layer of the compound (D-5) of 250 Å, and a cathode of 2000 Å of MgAg alloy having an atomic ratio of 10: 1 are sequentially laminated by a vacuum deposition method to obtain the structure shown in FIG. An EL device as shown was produced. The substrate temperature at the time of device fabrication is room temperature, and the degree of vacuum is 0.7 × 10 ⁻⁶ to
It was rr. The light emitting surface of the EL element has a size of 2 × 2 mm. When a direct current voltage was applied to the EL device thus obtained to drive it, 5.6 cd / m ² at a drive voltage of 14.0 V and a current density of 107.5 mA / cm ² .
The luminescence brightness of The EL emission peak wavelength at this time was 499 nm. When this device was stored in dry air for 1 month at room temperature and then driven again, clear light emission was observed.

Example 2 On a glass substrate having an ITO anode having a surface resistance of 20 Ω / □, a hole-transporting layer having a thickness of 400 Å and comprising the triphenylamine derivative represented by the compound (C-10), the compound (B-8). ) And a light emitting layer having a thickness of 150 Å, and a thickness of 200 including the compound of formula (I) (No. 14).
An electron transport layer of Å, an electron injection layer of the compound (D-5) of 250 Å, and a cathode of 2000 Å of MgAg alloy having an atomic ratio of 10: 1 are sequentially laminated by a vacuum deposition method to obtain the structure shown in FIG. An EL device as shown was produced. The substrate temperature at the time of device fabrication is room temperature, and the degree of vacuum is 0.7 × 10 ⁻⁶ to
It was rr. The light emitting surface of the EL element has a size of 2 × 2 mm. When a direct current voltage was applied to the EL device thus obtained and the device was driven, an emission luminance of 15 cd / m ² was exhibited at a driving voltage of 16.4 V and a current density of 135 mA / cm ² . The EL emission peak wavelength at this time was 475 nm. This device was placed in dry air at 1
After storage at room temperature for a month, driving again, clear emission was observed.

Comparative Example 1 An EL device was prepared in the same manner as in Example 1 except that the following compound (Formula 2) was used in the electron transport layer. When a DC voltage was applied to this device, clear blue-green light emission was observed. However, no EL emission was observed after storage at room temperature for 1 month.

[Chemical 2] Comparative Example 2 An EL device was produced in the same manner as in Example 1 except that the following compound (Chemical Formula 3) was used in the electron transport layer. When a DC voltage was applied to this device, a light emission luminance of 40 cd / m ² was observed even at a current density of 30 mA / cm ² . The drive voltage at this time was 10.7V. However, this element had extremely poor durability, and EL emission stopped within a few minutes.

[Chemical 3]

[0031]

In the electroluminescent device of the present invention, the compound represented by the general formula (I) (Chemical formula 1) is used as a constituent material of the organic compound. It has excellent properties.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electroluminescent device in which a light emitting layer is sandwiched between two electrodes.

FIG. 2 is a schematic cross-sectional view of an electroluminescent device having a light emitting layer and a hole transport layer sandwiched between two electrodes.

FIG. 3 is a schematic cross-sectional view of an electroluminescent device having a light emitting layer and an electron transport layer sandwiched between two electrodes.

FIG. 4 is a schematic cross-sectional view of an electroluminescent device in which a hole transport layer, a light emitting layer, and an electron transport layer are sandwiched between two electrodes in that order.

FIG. 5 is a schematic cross-sectional view of an electroluminescence device having two or more hole transport layers in FIG.

FIG. 6 is a schematic cross-sectional view of an electroluminescent device having two or more electron transport layers in FIG.

FIG. 7 is a schematic cross-sectional view of an electroluminescent device in which one or both of a hole transport layer and an electron transport layer in FIG. 4 is composed of at least two layers.

[Explanation of symbols]

1 ... Substrate, 2, 4 ... Electrode, 3a ... Light emitting layer, 3b ...
... electron transport layer, 3c ... hole transport layer.

Front page continued (72) Inventor Nozomi Tamoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (2)

[Claims] 1. An electroluminescent device comprising an anode and a cathode and one or a plurality of layers of an organic compound sandwiched therebetween, wherein at least one of the organic compound layers has the following general formula (I) ( An electroluminescent device comprising a layer containing an organic compound represented by Chemical formula 1) as a constituent component. [Chemical 1] (In the formula, Ar ₁ and Ar ₂ each independently represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group. Ar ₁ and Ar ₂ may be the same or different. Good. X represents a naphthalene residue.) 2. An electroluminescent device containing one or more light emitting layers and one or more electron transport layers as constituent elements between an anode and a cathode, or one or more hole transport layers and one layer between an anode and a cathode. In the electroluminescent device containing the above light emitting layer and one or more electron transport layers as constituent elements, at least one of the electron transport layers comprises the organic compound represented by the general formula (I) according to claim 1. An electroluminescent device comprising a layer as a constituent component.