JP3265395B2 - Organic electroluminescence device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device which is used as a light-emitting body of various display devices whose manufacturing method is simple and inexpensive. And a method of manufacturing the same.

[Conventional technology]

Electroluminescent elements using organic fluorescent materials (hereinafter referred to as EL elements) have the characteristics of lower driving voltage, higher luminance, and easier emission of any color than inorganic EL elements. Many attempts have been reported. However, the luminance was low because carriers were hardly injected from the electrode into the organic light emitting layer. To solve this problem, Tang and colleagues fabricated a two-layer structure in which an organic hole transporting material, which was used as a photoreceptor, was laminated on an organic light emitting layer, and realized a high-efficiency, high-brightness EL device. Kaisho 59
-194393). Further, thereafter, a three-layered device having an organic light emitting layer sandwiched between an organic electron transporting material and an organic hole transporting material [Japan Journal of Applied Physics (Jpn. J. Appl. Phys.) 27, L269] (198
8)], and EL light-emitting devices of various colors have been produced by doping the light-emitting layer with various dyes [Journal of Applied Physics (J. Appl. Phys.)
65, 3610 (1989)].

[Problems to be solved by the invention]

The organic EL devices reported so far have been manufactured by evaporating a light emitting layer and a charge transport layer in a vacuum. However, vacuum evaporation is not suitable for mass production,
In addition, there is a limit in manufacturing a large-area element. Also, EL
When the element is used as a non-light-emitting backlight for an LCD or the like, a large area is required, and mass production is also required.

In this regard, spin-coating of a polymer semiconductor represented by polyvinyl carbazole with a fluorescent substance such as perylene or triphenylbutadiene dispersed in it.
Attempts have been made to use the light emitting layer of an EL element (Polymer., 24, 748 (1
983)), however, there is a problem in obtaining a film strength and a uniform light emitting surface.

[Means for solving the problem]

The present inventors have conducted intensive studies on the application of conductive polymers.As a result, those having a sufficiently long conjugated chain have high carrier mobility and can be easily formed into a thin film by a spin coating method or a casting method. They have found that they can be used as transport materials and arrived at the present invention.

That is, the present invention provides an organic electroluminescent device having a light emitting layer and a charge transport layer between a pair of electrodes, at least one of which is transparent or translucent, as a charge transport layer represented by the general formula (I) -Ar-B- (I Ar) an aromatic hydrocarbon group having 6 or more carbon atoms, or 4 carbon atoms
Using a conductive polymer having a repeating unit represented by the above heterocyclic aromatic hydrocarbon group, B: -CH = CH- group or -NH- group,
Another object of the present invention is to provide an organic electroluminescent device, wherein the charge transport layer has a thickness of 100 to 1 μm.

 Hereinafter, the EL device according to the present invention will be described in detail.

The conductive polymer represented by the general formula (I) used in the present invention includes:
A polymer in which aromatic rings and bonding groups are bonded alternately. However,
When used as a charge transport material, those having a relatively long conjugate chain length are preferred.

The method for synthesizing the conductive polymer is not particularly limited,
For example, several methods described below can be used.

In the method for decomposing a sulfonium salt described in JP-A-1-254734, a compound represented by the general formula (II) (Ar is an aromatic hydrocarbon group having 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms, and R ¹ and R ² are those having 1 carbon atom.
8 carbon hydrogen group, X ^- represents a counter ion. A) a polymer intermediate having a sulfonium salt in a side chain obtained by reacting a monomer represented by the formula with an alkali in an aqueous solution at around 0 ° C., or an alkoxy group obtained by reacting the same with an alcohol solvent. The conductive polymer represented by the general formula (I) can be obtained by heat-treating the polymer intermediate in the chain.

In the dehalogenation method described in JP-A-59-199746, the general formula (III) X ₁ -CH ₂ -Ar-CH ₂ -X ₁ (III) (Ar represents the same as above, X ₁ Represents a halogen.) In a solution with an alkali such as potassium t-butoxide,
A conductive polymer can be obtained.

When B is a vinylene group in the conductive polymer of the general formula (I) used in the present invention, it is an aromatic hydrocarbon having 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon having 4 or more carbon atoms. Yes, specifically, those in which Ar is unsubstituted are p-phenylene, 2,5-dialkyl-p-phenylene, 2,5-dialkoxy-p-phenylene, 2,5-thienylene, 2,6-naphthalenediyl , 5,10-anthracenediyl, and is preferably p-phenylene. As the nucleus-substituted aromatic hydrocarbon group, one obtained by substituting one or two nuclei of a hydrocarbon group having 1 to 22 carbon atoms or an alkoxy group having 1 to 22 carbon atoms is preferably used. Examples of the substituent, a hydrocarbon group having 1 to 22 carbon atoms, include a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, lauryl, octadecyl group and the like. In addition, carbon number 1
Examples of the alkoxy group to -22 include a methoxy, ethoxy, propyloxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, lauryloxy, octadecyloxy group and the like. For the nucleus-substituted aromatic group, more specifically, monomethyl-p-phenylene, monomethoxy-p-phenylene, 2,5-dimethyl-p-phenylene, 2,5-dimethoxy-p-phenylene, monoethyl-p-phenylene 2,5-diethoxy-p-phenylene, 2,5-diethyl-p-phenylene, monobutyl-p
-Phenylene, monobutoxy-p-phenylene, monobutyl-p-phenylene, 2,5-dibutoxy-p-phenylene, 2,5-diheptyl-p-phenylene, 2,5-diheptoxy-p-phenylene, 2,5-dioctyl -P-phenylene, 2,5-dioctoxy-p-phenylene, 2,5-dilauryl-p-phenylene, 2,5-dilauryloxy-
Examples thereof include p-phenylene, 2,5-distearyl-p-phenylene, and 2,5-distearyloxy-p-phenylene.

Further, as the heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms, a 5-membered heterocyclic ring is preferable, and 2,5-thienylene, 2,5-furandiyl, 2,5-pyrrolediyl,
And / or 4-position substituents. More preferably, 2,5-thienylene, 3- _C1-22 alkyl-
2,5-thienylene.

Most preferably, Ar is p-phenylene, 2,5-diC
_1-2 alkyl-p-phenylene, 2,5-diC _1-2 alkoxy-p-phenylene, and 2,5-thienylene.

Among the conductive polymers used in the present invention, when B is -NH-, polyaniline and its derivatives obtained by subjecting aniline or an aniline derivative to electrolytic oxidation polymerization or chemical oxidation polymerization by a known method are preferable. . In order to dissolve polyaniline and its derivatives in a solvent, it is preferable to treat with an alkaline solution after polymerization. As the alkali, sodium hydroxide, potassium hydroxide, aqueous ammonia, hydrazine and the like can be used.

As a method for thinning the above-mentioned polymer intermediate or conductive polymer, a sufficiently high molecular weight is required for obtaining a uniform thin film by a method such as spin coating or casting. The degree of polymerization is 5 or more, more preferably 10 to 50,000. Specifically, in molecular weight measurement by gel permeation chromatography, a molecular weight of 28
Those having a high molecular weight eluted before the solvent elution position corresponding to the standard polystyrene of 00 are effective.

When a polymer intermediate obtained by a sulfonium salt decomposition method is used, a side chain elimination treatment is performed to convert the polymer intermediate into a conjugated polymer. As the desorption treatment, a method of giving light energy and heat is generally used, but a heat treatment is preferable. When forming the conjugate chain length by the thermal desorption treatment of the side chain, the conjugate chain length can be defined by the heat treatment temperature. That is, at a certain temperature or lower, the conjugate chain length becomes longer as the heat treatment temperature becomes higher. Therefore, as the heat treatment temperature, a high-temperature heat treatment is performed in the case of using a charge transport material. Specifically, 200 ℃
It is preferred to perform the heat treatment at ~ 400 ° C.

The heat treatment time is not particularly limited as long as the side chain elimination reaction occurs, and is generally about 10 minutes to 20 hours, preferably about 30 minutes to 8 hours. The atmosphere for the heat treatment is not particularly limited as long as the polymer film does not deteriorate, especially if the oxidation reaction by oxygen and air does not occur. Generally, the atmosphere such as N ₂ , Ar, and He is not affected. It is an active gas atmosphere, and may be a vacuum or an inert medium.

For, Cl ^{- -} counterion X polymer intermediate sulfonium salt, Br ^- halogen ions such by further replacing the halogen ion, BF ₄ ^-, and p- toluenesulfonic acid ion compound such as ion You can also.
Very different nature of the polymer intermediate sulfonium salt according to the type of counter ions, taking the halide ion Examples Cl ^-
When Br ^- is a counter ion, the thermal elimination reaction is more likely to occur. Counterion BF ₄ ^- N in the case of, N- become organic solvent soluble such as dimethylformamide, in the case of a p- toluenesulfonic acid ion can be alkoxy functionalizing the polymeric sulfonium salt intermediate side chain is there.

FIG. 1 shows the structure of the EL device of the present invention. As a transparent thin film electrode used in the process of manufacturing an EL element, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, indium-tin-oxide (ITO), tin oxide (NESA), Au, Pt, Ag, Cu, or the like is used as the material of the electrode, and the film thickness is about 50 to 1 μm, and preferably about 100 μm.
About 500Å, and as a manufacturing method, a vacuum evaporation method,
A sputtering method, a plating method, or the like is used.

When preparing a charge transporting layer of a conductive polymer, a solution of a conductive polymer represented by the general formula (I) or a polymer intermediate thereof is spin-coated on an electrode, a casting method, a dipping method, a bar coating method. , Using a roll coating method or the like. The film thickness is 100 ° -1 μm in order to increase the current density and increase the luminous efficiency.

In the case where the polymer intermediate is thinned, heat treatment is performed thereafter to convert the polymer intermediate into a conductive polymer.

Further, a material used as a charge transport material in conventional electrophotography may be mixed with a conductive polymer. Examples of these charge transport materials include triphenylamine-based materials.

The light-emitting layer used in the present invention is not particularly limited, and known layers such as those described in JP-A-57-51781 and JP-A-59-194393 can be used.

In the present invention, each of the light emitting layer and the charge transport layer is used alone, but may be used in combination with a known charge transport material or light emitting material. That is, it can be combined with the charge transport layer of the conductive polymer of the present invention or a known charge transporter (for example, a triphenyldiamine derivative, a perylene derivative, or the like). The layer can also be combined with a known luminescent material (tris (8-hydroxyquinoline) aluminum condensed polycyclic compound and its derivative, etc.).

The charge transport layer and the light emitting layer are (light emitting layer / charge transport layer)
Or, in addition to the combination of two layers (charge transport layer / light-emitting layer), 3 (charge transport layer / light-emitting layer / charge transport layer)
A structure of a combination of layers can be adopted. In the case of three layers, the two charge transport layers may be different materials.

More specifically, as an example of the structure of the organic EL device of the present invention (charge transport layer / light emitting layer / charge transport layer), as shown in FIG. 1, a transparent electrode 2 is provided on a transparent substrate 1, and It has a structure in which a charge transport layer 3, a light emitting layer 4, a charge transport layer 3, and an electrode 5 are provided thereon.

As the electron injection cathode material used in the manufacturing process of the EL device of the present invention, a metal having a small ionization energy such as Al, In, Mg, an Mg-Ag alloy, an In-Ag alloy, and a graphite thin film is used. The film thickness is preferably from 500 to 1000 in order to make the device of 50 to 1 μm as thin as possible, and a vacuum deposition method, a sputtering method, or the like is used as a manufacturing method.

〔The invention's effect〕

The material of the charge transport layer in the EL device of the present invention is thermally stable, and the conductive polymer or an intermediate thereof is soluble in an organic solvent and has good shaping properties, so that the device can be easily manufactured.

According to the EL device of the present invention, it is suitably used as a device such as a planar light source as a backlight and a flat panel display.

[Example] An example of the present invention will be shown below, and will be described in more detail. However, the present invention is not limited at all by the following examples.

Example 1 Molecular Crystals and Liquid Crystals (Mol.Cryst.Liq.Cryst.) Part E, 119,173
Pp. 180 (1985), aniline was chemically oxidized and polymerized using ammonium persulfate as an oxidizing agent to obtain polyaniline (hereinafter PAn). Then, it was treated with an aqueous sodium hydroxide solution, washed, dried, and dissolved in N, N-dimethylformamide (DMF). A DMF solution of PAn was applied to a glass substrate having a thickness of 200 mm by sputtering using a spun coating method at a rotation speed of 2000 rpm to a thickness of 200 mm. Then, it dried at 200 degreeC for 2 hours. Next, perylene was formed thereon by a vapor deposition method. The degree of vacuum at the time of vapor deposition is 5 × 10 ^-6 Torr and the thickness of perylene is 18001.
Met. And then deposit an aluminum electrode on it
The EL device was completed. When a voltage of 45 V was applied to this device, a current having a current density of 42 mA / cm ² flowed and a luminance of 0.11 cd / m ²
Of the sample was observed. Brightness was proportional to current density.

Example 2 According to the method described in JP-A-1-92221, 2,5-thienylenedisulfonium bromide was polymerized with an alkali,
Reaction with methanol yielded poly-2,5-thienylene-methoxyethylene, an intermediate of poly-2,5-thienylenevinylene (PTV). A DMF solution of the obtained PTV intermediate was applied to a glass substrate having a thickness of 700 mm by spin coating at 2,000 rpm on a glass substrate on which an ITO thin film was formed by a thickness of 200 mm by sputtering. Thereafter, 200 ° C. in N _2, 2
Heat treated for hours. The thickness of the PTV intermediate was reduced to 400mm by the heat treatment. Here, when the infrared absorption spectrum was measured, the absorption peak peculiar to the intermediate at 1100 cm ^-1 was not present. Therefore, the PTV structure was confirmed, and the resultant was used as a charge transport material.

Then, 2,5-diheptyloxy-p-xylylene bromide was polycondensed with potassium t-butoxy according to the method described in JP-A-1-79217 to obtain poly-2,5-diheptyloxy-p- Phenylene vinylene (HO-PPV) was obtained. This chloroform solution was applied on the PTV thin film applied on the ITO by a spin coating method at a rotation speed of 2000 rpm to a thickness of 1000 ° to obtain a light emitting material. Further, an Al electrode was formed thereon to a thickness of 1000 mm by vapor deposition. ITO electrode, Al
Terminals were formed on the electrodes with silver paste and fixed with epoxy resin.

When a voltage of 35 V was applied to the manufactured two-layer stacked element, yellow-orange light emission with a luminance of 0.12 cd / m ² was observed at a current density of 7 mA / cm ² . Peak wavelength of emission spectrum is 580nm
And was consistent with the fluorescence spectrum of the HO-PPV spin-coated thin film. Also, the emission intensity increased in proportion to the current density.

Example 3 According to the description in JP-A-59-199746, p-xylylene-bis (diethylsulfonium bromide) was polymerized by dropping an aqueous solution of sodium hydroxide in an aqueous solution.
An aqueous solution of poly-p-phenylenevinylene-bis (diethylsulfonium bromide) ethylene (hereinafter, PPV intermediate), which is an intermediate of p-phenylenevinylene (hereinafter, PPV), was obtained. A film was formed using the obtained PPV intermediate in place of the PTV intermediate in Example 2. The film forming conditions were as follows: the PPV intermediate aqueous solution was spin-coated at 2000 rpm.
It was applied with a thickness of 00 °. Thereafter, the PPV intermediate spin-coated film was heat-treated at 370 ° C. for 2 hours to obtain a PPV thin film. The film thickness after the heat treatment was 300 °. The change to the PPV structure was confirmed by the change in the infrared absorption spectrum. This was used as a charge transport layer. Further, HO-PPV was spin-coated thereon in the same manner as in Example 2, and an Al electrode was deposited to complete an EL device.

When a voltage of 30 V was applied to the manufactured two-layer stacked device, yellow-orange light emission with a luminance of 0.09 cd / m ² was confirmed at a current density of 17 mA / cm ² . The emission spectrum was the same as in Example 2.

Example 4 In the same manner as in Example 1, PAn was formed into a film to form a charge transport layer. Further, HO-PPV was spin-coated thereon in the same manner as in Example 2, and an Al electrode was deposited to complete the device.

When a voltage of 50 V was applied to the manufactured two-layer stacked element, yellow-orange light emission with a luminance of 0.04 cd / m ² was confirmed at a current density of ² mA / cm ² . The emission spectrum was the same as in Example 2.

[Brief description of the drawings]

FIG. 1 shows a conceptual cross-sectional structure of an embodiment of the organic electroluminescence device according to the present invention. 1 ... Transparent substrate, 2 ... Transparent electrode, 3, ... Charge transport layer,
4 ... light emitting layer, 5 ... electrode

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kiminobu Noguchi 6 Kitahara, Tsukuba, Ibaraki Pref. Within Sumitomo Chemical Co., Ltd. (72) Inventor Toshihiro Onishi 6 Kitahara, Tsukuba, Ibaraki Pref. References JP-A-63-309961 (JP, A) JP-A-1-142556 (JP, A) JP-A-61-148231 (JP, A) JP-A-1-193868 (JP, A) JP-A-63 —198213 (JP, A) JP-A-63-250482 (JP, A) JP-A-63-264692 (JP, A) “Application of organic dye / conductive polymer double-layer thin film to optoelectronics” Convertec, 1989, Vol. 17, No. 9, PP. 6-10 (58) Field surveyed (Int. Cl. ⁷ , DB name) C09K 11/06 C08G 61/02 C08G 61 / 12,73 / 00 H05B 33/14

Claims (7)

(57) [Claims] 1. An organic electroluminescence device having a light emitting layer and a charge transport layer between a pair of electrodes, at least one of which is transparent or translucent, has a general formula (I) -Ar-B- (I) as a charge transport layer. Ar: an aromatic hydrocarbon group having 6 or more carbon atoms, or 4 carbon atoms
Using a conductive polymer having a repeating unit represented by the above heterocyclic aromatic hydrocarbon group, B: -CH = CH- group or -NH- group,
An organic electroluminescent device, wherein the charge transport layer has a thickness of 100 to 1 μm. 2. The organic electroluminescent device according to claim 1, wherein a conductive polymer in which B is a —CH ＝ CH— group is used. 3. The conductive polymer is poly-p-phenylenevinylene, poly-2,5-dialkyl-p-phenylenevinylene, poly-2,5-dialkoxy-p-phenylenevinylene, poly-2,5. -Thienylenevinylene or poly-2,6-
3. The organic electroluminescence device according to claim 2, wherein the organic electroluminescence device is naphthalenediylvinylene. 4. The organic electroluminescence device according to claim 1, wherein a conductive polymer in which B is an —NH— group is used. 5. The organic electroluminescence device according to claim 4, wherein the conductive polymer is polyaniline or a polyaniline derivative. 6. The organic electroluminescent device according to claim 2, wherein Ar is p-phenylene, 2,5-dialkyl-p-phenylene, 2,5-dialkoxy-p-phenylene, 2,5-thienylene, , 6-Naphthalenediyl, p-phenylene mono- or di-substituted with an alkyl group having 1 to 22 carbon atoms, p-phenylene mono- or di-substituted with an alkoxy group having 1 to 22 carbon atoms, alkyl group having 1 to 22 carbon atoms But
2,5-disubstituted p-phenylene, or carbon number 1-2
An organic electroluminescent device, wherein the alkoxy group 2 is p-phenylene disubstituted at the 2,5-position. 7. The organic electroluminescent device according to claim 5, wherein the conductive polymer is polyaniline or a polyaniline derivative obtained by subjecting aniline or an aniline derivative to electrolytic oxidation polymerization or chemical oxidation polymerization. Organic electroluminescent element.