JP2998187B2 - Organic electroluminescence device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device, and more particularly, to an organic electroluminescence device having improved luminous efficiency, luminous brightness, and uniformity of luminescence. It is.

[Conventional technology]

Electroluminescent devices using organic fluorescent materials (hereinafter referred to as EL devices) have the features of lower driving voltage, higher luminance, and easier emission of various colors than inorganic EL devices. Attempts have been reported. However, the brightness was low because it was difficult to inject charges from the electrode into the organic light emitting layer. To solve this
Tang et al. Produced a two-layer structure in which an organic light emitting layer and an organic hole transporting material used for an electrophotographic photoreceptor were laminated, thereby realizing a high-efficiency, high-brightness EL device. Showa 59
-194393). Further, thereafter, a three-layered device in which an organic light emitting layer is sandwiched between an organic electron transporting material and an organic hole transporting material [Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.) 27, L269]
(1988)] and have various luminescent colors by doping various dyes into the luminescent layer.
EL devices have been manufactured [Journal of Applied Physics (J. Appl. Phys.) 65, 3610 (19
89)).

[Problems to be solved by the invention]

However, although the organic EL devices that have been reported so far have high luminance, they have a problem that the luminance and the luminous efficiency per power are lower than those of other light emitting devices. In order to solve this problem, it is necessary to improve the efficiency of injecting charges from the electrodes and realize high luminance with a low driving voltage. Further, the display element must emit light uniformly over a large area. However, the thickness of the organic thin film layer constituting the organic EL element is very thin, about 1000 mm, and there is a problem that unevenness of light emission, which is considered to be caused by unevenness of the substrate, non-uniformity of the electrodes, and the like, is likely to occur.

[Means for solving the problem]

The present inventors have found that thin films can be easily formed by a spin coating method, a casting method, or the like. Organic composed of transport layer
The inventors have found that luminous efficiency and luminance are significantly improved by providing a conductive polymer layer between a charge transport layer and an electrode of an EL element, and have reached the present invention.

That is, the present invention provides 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, wherein a general formula (1) -Ar —B— (1) (Ar represents an aromatic hydrocarbon group having 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms, and B represents a —CH ＝ CH— group or a —NH— group. It is an object of the present invention to provide an organic electroluminescence device comprising a conductive polymer layer having a repeating unit represented by the following formula:

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

The conductive polymer represented by the general formula (1) used in the present invention is:
A polymer in which an aromatic ring and a bonding group are bonded to each other.

The method for synthesizing the conductive polymer is not particularly limited,
In the case of a polyarylenevinylene-based polymer in which B is a vinylene group in the conductive polymer of the general formula (1), a polymer having a relatively long conjugate chain length is required to ensure sufficient performance. Japanese Unexamined Patent Publication (Kokai) No. 1-24734, JP-A-1-92221, JP-A-63-159429, JP-A-1-257473, JP-A-64-79
No. 217, etc., via a polymer intermediate (hereinafter collectively referred to as polymer sulfonium salt decomposition method);
It is preferable to use the dehalogenation method described in JP-A-59-199746.

In the polymer sulfonium salt decomposition method, a polymer intermediate having a sulfonium salt in a side chain or a polymer intermediate having an alkoxy group in a side chain obtained by reacting the polymer intermediate with an alcohol solvent is subjected to heat treatment to obtain a compound represented by the general formula (1). ) Can be obtained.

In the dehalogenation method, a dihalogen represented by the general formula (2) X ₁ —CH ₂ —Ar—CH ₂ —X ₁ (2) (Ar means the same as above, and X ₁ represents halogen.) A conductive polymer can be obtained by condensing the compound with an alkali such as potassium t-butoxy in a solution.

Ar in the general formula (1) is an aromatic hydrocarbon having 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon having 4 or more carbon atoms. Specifically, when Ar is an aromatic hydrocarbon group, it is an unsubstituted aromatic hydrocarbon group having 6 or more carbon atoms or a nucleus-substituted aromatic hydrocarbon group. In unsubstituted aromatic hydrocarbon groups, p-phenylene, o-phenylene, 2,6-naphthalenediyl, 5,10-
Anthracenediyl is exemplified, preferably p-phenylene. The nucleus-substituted aromatic hydrocarbon group has 1 carbon atom.
Those obtained by substituting one or two nuclei of a hydrocarbon group of 1 to 22 or an alkoxy group of 1 to 22 carbon atoms are preferably used. As a hydrocarbon group having 1 to 22 carbon atoms as a substituent, methyl, ethyl, propyl, butyl, pentyl, hexyl,
Examples include heptyl, octyl, lauryl, and octadecyl groups, and examples of the alkoxy group having 1 to 22 carbon atoms include methoxy, ethoxy, propyloxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, lauryloxy, and octadecyloxy groups. Etc. are exemplified. 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-diheptyloxy-p-phenylene, 2,5-dioctyl-p-phenylene, 2,5-dioctoxy-p-phenylene, 2,5-dilauryl-p-phenylene, 2,5-diene Lauryloxy-p-phenylene, 2,5-
Distearyl-p-phenylene, 2,5-distearyloxy-p-phenylene and the like are exemplified. Preferably, 2,
5-dimethoxy-p-phenylene, 2,5-diethoxy-p
-Phenylene, 2,5-diheptyloxy-p-phenylene.

Further, as the heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms and its nuclear substituent, 2,5-thienylene, 2,5-furandiyl, 2,5-pyrrolediyl and their 3-position and / or
Alternatively, a substituent at the 4-position is exemplified. Preferably, 2,
5-thienylene and 3-alkyl-2,5 having 1 to 22 carbon atoms
-Thienylene, or 3-alkoxy having 1 to 22 carbon atoms-
2,5-thienylene. Specifically, 3-methyl-2,5-
Thienylene, 3-ethoxy-2,5-thienylene, 3-acetyl-2,5-thienylene, 3,4-dimethyl-2,5-thienylene, 3,4-diethoxy-2,5-thienylene and the like are exemplified. . Preferably, it is 2,5-thienylene.

To uniformly thin the above polymer intermediate or conductive polymer by a method such as spin coating or casting,
Its molecular weight must be high enough. The degree of polymerization is 5 or more, more preferably 10 to 50,000.
Specifically, those having a high molecular weight that elutes before the solvent elution position corresponding to the standard polystyrene having a molecular weight of 2800 in the molecular weight measurement by gel permeation chromatography are effective.

In the case of a polymer intermediate, a method in which a solution of the polymer intermediate is thinned by a thinning method described below, and then a side chain is eliminated by a known method to convert it into a conductive polymer having a conjugated system is preferable. .

In the conductive polymer used in the present invention, B is-
In the case of an NH- group, 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.

The polymerization degree of the polyaniline and its derivative used is preferably 0.1 dl / g or more (N-methyl-2-pyrrolidone, 30 ° C.) in intrinsic viscosity [η].

It is known that the conductivity of these conductive polymers is increased by doping impurities such as sulfuric acid, iodine, and ferrous chloride. It has been known that the absorption coefficient of the compound also increases, the optical transmittance remarkably decreases, and transparency is lost. Therefore, when taking out light emission from the conductive polymer side, it is desirable not to dope. Since the absorption spectrum and the electric conductivity are correlated, the electric conductivity is preferably 0.1 S / cm or less.

This will be described more specifically using an example of the structure of the EL device of the present invention shown in FIG. A transparent electrode 2 is formed on a transparent substrate 1 such as glass or transparent plastic. As a material of the electrode, 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 and the like are used. As a manufacturing method, a vacuum evaporation method, a sputtering method, a plating method, or the like is used.

Next, the conductive polymer layer 3 is formed thereon. When the conductive polymer is the former polyarylenevinylene-based polymer, a solution of the polymer intermediate or a solution of a soluble polyarylenevinylene-based polymer is used, and when the latter is a polyaniline-based polymer, the solution is used as an electrode. A thin film is formed thereon using a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, or the like. In the case of a conductive polymer, a thin film can be formed by an evaporation method.

The film thickness is preferably from 5 to 10 μm, and preferably from 10 to 1 μm in order to increase the current density and increase the luminous efficiency. More preferably, it is in the range of 20 to 2000 °.

When the polymer intermediate is thinned, heat treatment or the like is performed thereafter to convert the polymer intermediate into a conductive polymer.

Next, the charge transport layer 4 is formed on the conductive polymer layer 3, and the light emitting layer 5 is formed thereon.

The material for the light emitting layer and the charge transport layer is not particularly limited, and known materials such as those described in JP-A-57-51781 and JP-A-59-194393 can be used. For example, as the light emitting layer, naphthalene derivatives, anthracene derivatives, perylene derivatives, polymethine-based, xanthene-based, coumarin-based, cyanine-based dyes, metal complexes of 8-hydroxyquinoline and its derivatives, aromatic amines, tetraphenylcyclopentadiene Derivatives, tetraphenylbutadiene derivatives and the like.

In the structure shown in the figure, it is necessary to use a material having a hole transporting property for the charge transporting layer. As a material for the hole transport layer, And aromatic amine-based materials.

The structure of the organic EL element has an electron transport layer between the light emitting layer and the cathode, in addition to the structure shown in the figure (anode / conductive polymer layer / charge transport layer / light emitting layer / cathode). A so-called sandwich structure may be used. In this case, as a material of the electron transport layer, And the like.

The charge transport layer 4 and the light emitting layer 5 may be formed by a vacuum deposition method, a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, or the like. From the viewpoint of forming a uniform thin film over a wide area, the vapor deposition method is preferable because it has excellent controllability.

The thickness of the charge transport layer 4 and the light emitting layer 5 needs to be at least such that pinholes do not occur. On the other hand, if the thickness is too large, the resistance of the element increases, and a high drive voltage is required. Absent. Therefore, the thickness of the charge transport layer and the light emitting layer is 5Å to 10 μm,
Preferably from 10 to 1 μm, more preferably from 50 to 2000 °
It is.

Next, an electrode 6 is provided on the light emitting layer 5, and this electrode becomes an electron injection cathode. The materials are Al, In, Mg,
Materials having a small ionization energy such as an Mg-Ag alloy, an In-Ag alloy, a Mg-In alloy, and a graphite thin film are used.
As a method for manufacturing the cathode, a vacuum evaporation method, a sputtering method, or the like is used.

Thus, the organic EL device of the present invention can be manufactured.

〔The invention's effect〕

By providing a conductive polymer layer in the EL device of the present invention, the luminous efficiency and the maximum luminance are improved and the luminescence can be made more uniform as compared with the conventional device.

Although the mechanism of action of using the conductive polymer layer and another charge transport layer together is unknown, the potential barrier for holes between the conductive polymer layer and the light emitting layer in the charge transfer from the electrode to the light emitting layer is unknown. It is presumed that there is a function of lowering this.

The EL device according to the present invention is suitably used as a device such as a planar light source as a backlight and a flat panel display.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited at all by the following examples.

Example 1 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 commercially available ITO / glass substrate having been ultrasonically cleaned in acetone to a thickness of 500 ° by a spin coating method at a rotation speed of 2000 rpm. Thereafter, heat treatment was performed at 200 ° C. for 2 hours in a vacuum. The heat treatment reduced the thickness of the PTV intermediate to 300. Here, when the infrared absorption spectrum was measured, it was confirmed that the absorption peak peculiar to the intermediate at 1100 cm ^-1 had disappeared, and thus the PTV structure was confirmed.

Then TPD as a sequential charge transport material thereon, by tris (8-quinolinol) aluminum (hereinafter referred to as Alq ₃₎ and indium deposition method as an electrode as a luminescent material was deposited 1140Å, 1040Å, the thickness of 6400Å, respectively. The deposition of each of these layers was performed continuously without breaking vacuum. The degree of vacuum during evaporation is 3 × 10 ^-6 To
rr or less. When a voltage of 28 V was applied to this device, a current having a current density of 208 mA / cm ² flowed and green EL light emission with a luminance of 3992 cd / m ² was observed. Brightness was proportional to current density. Observation with a stereoscopic microscope at a magnification of × 8 revealed that light emission was uniform over the entire device. Table 1 shows the results of measuring the characteristics and the like of this device.

Example 2 According to the method described in JP-A-59-199746, poly-
An intermediate of p-phenylenevinylene (PPV) was obtained. An organic EL device was produced in the same manner as in Example 1 except that this was used. When a voltage of 35 V was applied to this device, a current having a current density of 190 mA / cm ² flowed and green EL light emission of 3395 cd / m ² was observed. Table 1 shows the results of observing the light emitting state and the results of measuring the characteristics and the like of this device as in Example 1.

Example 3 The PPV intermediate produced in Example 2 was mixed with the PTV intermediate in Example 1 at 23% by weight, and the ITO / glass substrate was prepared in the same manner as in the method for producing a conductive polymer film in Example 1. A mixed film of PTV and PPV was formed thereon. Next, TPD, Alq ₃ , and indium were vapor-deposited on the thus-formed conductive polymer film in the same manner as in Example 1 to produce an EL device.

When a voltage of 25 V was applied to the fabricated device, 208 mA / cm ²
At a current density of, light emission with a luminance of 4606 cd / m ² was observed. Table 1 shows the results of observing the light emitting state in the same manner as in Example 1, and the results of measuring the characteristics and the like of this device.

Example 4 Chemical oxidation polymerization of aniline using ammonium persulfate as an oxidizing agent according to the method described in Molecular Crystals Liquid Crystals (Mol. Cryst. Liq. Cryst.) Part E, pages 119, 173 to 180 (1985). Then, polyaniline (hereinafter referred to as PAn) was obtained. Then, it was treated with an aqueous solution of sodium hydroxide, washed, dried, and dissolved in DMF. A DMF solution of PAn was applied to a thickness of 130 ° on an ITO / glass substrate by a spin coating method at a rotation speed of 2000 rpm. Then, it dried at 60 degreeC in vacuum for 2 hours. Further, TPD, Alq ₃ , and indium were laminated thereon by vacuum evaporation in the same manner as in Example 1 to produce an EL device.

When a voltage of 35 V was applied to the fabricated device, 200 mA / c
at a current density of m ^2, green light emission luminance 4818cd / m ² was observed. Table 1 shows the results of observing the light emitting state in the same manner as in Example 1, and the results of measuring the characteristics and the like of this device.

Comparative Example 1 An EL element was prepared in the same manner as in Example 1 except that the conductive polymer layer was not provided. When a voltage of 27 V was applied to the manufactured device, green light emission with a luminance of 3022 cd / m ² was confirmed at a current density of 185 mA / cm ² . Table 1 shows the results of observing the light emitting state in the same manner as in Example 1, and the results of measuring the characteristics and the like of this device.

[Brief description of the drawings]

The figure shows a conceptual cross-sectional structure of one embodiment of the organic EL device according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... Transparent electrode, 3 ... Conducting polymer layer, 4 ... Charge transport layer, 5 ... Emitting layer, 6 ... Electrode

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Toshihiro Onishi 6 Kitahara, Tsukuba, Ibaraki Prefecture Within Sumitomo Chemical Co., Ltd. (56) References JP-A-63-264692 (JP, A) JP-A-3-273087 ( JP, A) Tokuhyo Hei 4-500582 (JP, A) Convertech, Vol. 17, No. 9, (1989) p6-10 (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33 / 00-33/28 JICST file (JOIS)

Claims (1)

(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, comprises a compound represented by the general formula (1) -Ar- B- (1) (Ar represents an aromatic hydrocarbon group having 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms, and B represents a -CH = CH- group or a -NH- group.) An organic electroluminescence device comprising a conductive polymer layer having a repeating unit represented by the formula: