JPH03273087A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain a thin organic electroluminescent element readily by spin coating or casting, by employing as a charge transfer material a specific conductive polymer in which aromatic rings and bonding groups are alternately combined. CONSTITUTION:In an organic electroluminescent element in which a luminescent layer and a charge transfer layer are provided between a pair of electrodes, at least one of which being transparent or translucent, a conductive polymer having a repeating unit represented by Ar-B (Ar: an aromatic hydrocarbon group with 6 or more carbon atoms or a heterocyclic aromatic hydrocarbon group with 4 or more carbon atoms; B: CH=CH or NH) is employed for the charge transfer layer. Examples of such conductive polymer include poly-p- phenylenevinylene, poly-2,5-dialkyl-p-phenylenevinylene, poly-2,5-dialkoxy-p- phenylenevinylene, poly-2,5-thienylenevinylene and polyaniline.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device that is used as a light emitting body of various types of display devices that are simple and inexpensive. and its manufacturing method.

[Conventional technology]

Electroluminescent device using organic fluorescent material (
Compared to inorganic EL elements, EL elements (hereinafter referred to as EL elements) have the characteristics of low driving voltage, high brightness, and the ability to easily emit light of any color, and many attempts have been reported. However, the luminance was low because it was difficult to inject carriers from the electrode to the organic light emitting layer. To solve this problem, Tang et al. We created a two-layer structure with high efficiency and high brightness (
JP-A-59-194393). Furthermore, since then, a device with a three-layer structure in which an organic light emitting layer is sandwiched between an organic electron transport material and an organic hole transport material [Japan Journal of Applied Physics (Jpn, J, A
ppl, Phys, )27. L269 (l988))
In addition, EL light-emitting elements of various colors have been fabricated by doping the light-emitting layer with various dyes [Journal.
of Applied Physics (J, App 1.
Phys, ) Volume 65, Page 3610 (1989)
].

[Problem to be solved by the invention]

Organic EL devices that have been reported so far have been fabricated by depositing a light-emitting layer and a charge transport layer in a vacuum. However, the vacuum evaporation method is not suitable for mass production, and there are limits to the production of large-area devices. Also, EL
When the device is used as a non-luminous backlight for an LCD or the like, there is a strong demand for a large area, and mass production is also required.

Regarding this, we have developed a method for spin-coating polymer semiconductors such as polyvinylcarbazole with fluorescent substances such as perylene and triphenylbutadiene dispersed therein.
There are attempts to use it as a light-emitting layer for L elements (Polymer,
, 24.748 (1983)), there are problems in obtaining film strength and a uniform light emitting surface.

[Means for Solving the Problems] As a result of intensive studies on the application of conductive polymers, the present inventors have found that those with sufficiently long conjugated chains have high carrier mobility, and have been found to be suitable for spin coating, casting, etc. The present invention was achieved based on the discovery that it can be used as a charge transport material that can be easily made into a thin film.

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, in which the charge transport layer is composed of the general formula (I)-Ar-B-(I ) Ar: aromatic hydrocarbon group having 6 or more carbon atoms, or heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms, B: -CI (conductive unit having a repeating unit represented by =CH- group or -NH- group) An object of the present invention is to provide an organic electroluminescent device characterized by using a synthetic polymer.

The EL element according to the present invention will be explained in detail below.

The conductive polymer represented by the general formula (I) used in the present invention is a polymer in which aromatic rings and bonding groups are alternately bonded. However, when used as a charge transporting material, one with a relatively long conjugated chain length is preferred.

Although the method for synthesizing the conductive polymer is not particularly limited, for example, several methods such as those described below can be used.

In the sulfonium salt decomposition method described in JP-A-1-254734, 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, R1 , R2 is a hydrocarbon group having 1 to 8 carbon atoms, and X- represents a counter ion), which has a sulfonium salt in its side chain and is obtained by reacting a monomer represented by the following with an alkali in an aqueous solution at around 0°C. A conductive polymer represented by general formula (I) can be obtained by heat-treating a polymer intermediate or a polymer intermediate having an alkoxy group in its side chain obtained by reacting it with an alcohol solvent. .

In the dehalogenation method described in JP-A-59-199746, general formula (III) X+-CH2-Am-C)I2-Xl (I[[)
(Ar represents the same thing as above, Xl represents halogen. By condensing the dihalogen compound represented by
A conductive polymer can be obtained.

In addition, in the conductive polymer of general formula (I) used in the present invention, when B is a vinylene group, it is an aromatic hydrocarbon having 6 or more carbon atoms, or a heterocyclic aromatic hydrocarbon having 4 or more carbon atoms. Specifically, unsubstituted A is p-phenylene, 2,5-dialkyl p-phenylene, 2,5-dialkoxy-p-phenylene, 2,5-chenylene, 2,6
Examples include -naphthalenediyl and 5,10-anthracenediyl, with p-phenylene being preferred. In addition, as the nuclear-substituted aromatic hydrocarbon group, 1 to 2 hydrocarbon groups having 1 to 22 carbon atoms or alkoxy groups having 1 to 22 carbon atoms can be used.
Those in which individual nuclei have been replaced are preferably used. Examples of the hydrocarbon substituents having 1 to 22 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, lauryl, and octadecyl groups. Examples of the alkoxy group having 1 to 22 carbon atoms include methoxy, ethoxy, propyloxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, lauryloxy, and octadecyloxy groups. Regarding nuclear substituted aromatic groups, more specifically monomethyl-p
-phenylene, monomethoxy-p-phenylene, 2,5
-dimethyl-p-phenylene, 2,5-dimethoxy-p
-phenylene, monoethyl-p-phenylene, 2,5-
Jetoxy-p-phenylene, 2,5-dinityl-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-p-phenylene, 2,5-distearyl-p-phenylene, 2
．． Examples include 5-distearyloxy-p-phenylene.

Furthermore, the heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms is preferably a 5-membered heterocyclic ring, such as 2.5-thennylene, 2,5
Examples thereof include -furandiyl, 2,5-pyrrolediyl, and substituted products thereof at the 3- and/or 4-positions.

More preferably 2,5-thennylene, 3-C, ~22
Alkyl-2,5-chenylene.

Most preferably Ar is p-phenylene, 2,5-diC1
~2alkyl-p-phenylene, 2,5-diC1-2alkoxy p-phenylene, and 2,5-chenylene.

Among the conductive polymers used in the present invention, in the case of B or -NH-, polyaniline and its derivatives obtained by electrolytic oxidative polymerization or chemical oxidative polymerization of aniline or aniline derivatives 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, etc. can be used.

In order to obtain a uniform thin film using a method such as a spin cord method or a casting method to form a thin film from the above-mentioned polymer intermediate or conductive polymer, the molecular weight must be sufficiently high. The degree of polymerization is 5 or more, more preferably 10 to 50,000.

Specifically, in molecular weight measurement by gel verminion chromatography, it is effective to have a high molecular weight that elutes before the solvent elution position corresponding to standard polystyrene having a molecular weight of 2800.

When using a polymer intermediate obtained by the sulfonium salt decomposition method, a side chain elimination process is performed to convert it into a conjugated polymer. As a desorption treatment, a method of applying light energy or heat is generally used, but a heat treatment is preferable. When forming a conjugated chain length by thermal elimination treatment of side chains, the conjugated chain length can be defined by the heat treatment temperature. That is, the higher the heat treatment temperature is below a certain temperature, the longer the conjugated chain length becomes. Therefore, the heat treatment temperature is high when used as a charge transport material. Specifically 200°
It is preferable to carry out the heat treatment at a temperature of C to 400C.

There is no particular restriction on the heat treatment time as long as the side chain elimination reaction occurs, and it is generally 10 minutes to 20 hours.
Preferably it is about 30 minutes to 8 hours.

The atmosphere during heat treatment is not particularly limited as long as it does not cause deterioration of the polymer film, especially an atmosphere that does not cause oxidation reactions due to oxygen or air, and is generally an inert gas atmosphere such as N7 or Ar5He. It may also be under vacuum or in an inert medium.

The counter ion X- of the polymer intermediate sulfonium salt can be a halogen ion such as Cl-1Br-, and by further substituting the halogen ion, it can be a compound ion such as BF or -1p-toluenesulfonate ion. can. The properties of the polymeric intermediate sulfonium salt vary greatly depending on the type of counter ion; taking a halogen ion as an example, thermal elimination reactions are more likely to occur when Br- is the counter ion than C1-. When the counterion is BF4-, N, N
- Becomes soluble in organic solvents such as dimethylformamide, p-
In the case of toluenesulfonate ion, it is possible to convert the side chain of the polymeric sulfonium salt intermediate into an alkoxy group.

The structure of the EL element of the present invention is shown in FIG. As transparent thin film electrodes used in the manufacturing process of EL elements, conductive metal oxide films, translucent metal thin films, etc. are used. Specifically, the materials for this electrode include indium tin oxide (ITo), tin oxide (NESA), Au, Pt,
Ag, Cu, etc. are used, and the film thickness is 50 to 1μ.
The number of people required is approximately 100 to 500, and the manufacturing method includes a vacuum evaporation method, a sputtering method, a plating method, and the like.

When preparing a charge transport layer of a conductive polymer, -maximum (I)
A solution of a conductive polymer or its polymer intermediate represented by is formed into a thin film on an electrode using a spin coating method, a casting method, a dipping method, a barcoding method, a roll coating method, or the like.

The film thickness is preferably 50 μm to 10 μm, and preferably 100 μm to 171 μm in order to increase current density and luminous efficiency.

In addition, when the polymer intermediate is made into a thin film, heat treatment is performed after that to convert it into a conductive polymer.

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

The light-emitting layer used in the present invention is not particularly limited,
For example, JP-A-57-51781, JP-A-59-1.9439
Known materials such as those described in Publication No. 3 can be used.

In the present invention, the light emitting layer and the charge transport layer each use a compound alone, but may also be used in combination with a known charge transport material or light emitting material.

That is, the charge transport layer of the conductive polymer in the present invention can be combined with a known charge transporter (for example, a triphenyldiamine derivative, a perylene derivative, etc.), and the charge transport layer of the conductive polymer in the present invention The layer can also be combined with known light emitters, such as tris(8-hydroxyquinoline)aluminum fused polycyclic compounds and derivatives thereof.

In addition, the charge transport layer and the light-emitting layer are not only a combination of two layers (light-emitting layer/charge transport layer) or (charge transport layer/light-emitting layer), but also a three-layer combination (charge transport layer/light-emitting layer/charge transport layer). In the case of three layers, the two charge transport layers may be made of different materials.

That is, to specifically show an example of the structure of the organic EL element 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.

Electron injection cathode materials used in the manufacturing process of the EL device of the present invention include AI, In, Mg, Mg-Ag alloy,
Metals with low ionization energy, such as In--Ag alloys and graphite thin films, are used. The film thickness is preferably 500 to 1,000 in order to make the device as thin as possible, with a thickness of 50 to 1 μm, and a vacuum evaporation method, a sputtering method, etc. are used as the manufacturing method.

〔Effect of the invention〕

The material for the charge transport layer in the EL device of the present invention is thermally stable, the conductive polymer or its intermediate is soluble in organic solvents, and has excellent shapeability, making the device easy to manufacture.

The EL element according to the present invention can be suitably used as a planar light source as a backlight, a device such as a flat panel display, etc.

〔Example〕

Examples of the present invention will be shown below and explained in more detail.

However, the present invention is not limited in any way by the following examples.

Example 1 Molecular Crystals and Liquid Crystals (Mat, Cryst, Liq, Cry
Polyaniline (hereinafter referred to as PAn) was obtained by chemical oxidative polymerization of aniline using ammonium persulfate as an oxidizing agent according to the method described in Part E, 119.1.73-180 (1985). Thereafter, it was treated with an aqueous sodium hydroxide solution, washed, dried, and dissolved in N,N-dimethylformamide (DMF). PAn was deposited on a glass substrate on which an ITO thin film was attached by sputtering to a thickness of 200 mm.
The DMF solution was applied to a thickness of 200 mm by spin coating at a rotation speed of 2000 rpm. After that, 20
It was dried at 0°C for 2 hours. Next, perylene was formed thereon by vapor deposition. The degree of vacuum during vapor deposition is 5X 1O
At -6 Torr, the perylene film thickness was 1800 mm.

Furthermore, an aluminum electrode was deposited on top of it to complete the EL device. When a voltage of 45V was applied to this element,
A current with a current density of 42 mA/cm' flows, the brightness is 0, l
Purple EL emission of 1 cd/m2 was observed. The brightness was proportional to the current density.

Example 2 According to the method described in JP-A-1-9221, 2°5
-Thienylene disulfonium bromide was polymerized with an alkali and reacted with methanol to obtain poly-2,5-thienylene-methoxyethylene, which is an intermediate of poly-2,5-thienylene vinylene (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 a rotation speed of 2000 rpm onto a glass substrate on which an ITO thin film had been applied by sputtering to a thickness of 200 mm. After that, 200 in N2
It was heat-treated at ℃ for 2 hours. The film thickness of the PTV intermediate was reduced to 400 by heat treatment. Here, when the infrared absorption spectrum was measured, there was no absorption peak specific to the intermediate at 1100 cm-', so it was found that PTV
The structure was confirmed and it was used as a charge transport material.

Next, according to the method described in JP-A-1-79217, t-
Condensation polymerization with butoxypotassium produces poly-2゜5-diheptyloxy-p-phenylenevinylene (HO-PPV)
I got it. This chloroform solution was applied to a thickness of 1,000 coats on the PTV thin film coated on the TTO by spin coating at a rotation speed of 2,000 rpm to obtain a luminescent material. Furthermore, on top of that, 100
It was made with a thickness of 0.

The terminals of the ITO electrode and the AI main electrode were made with silver paste and fixed with epoxy resin.

When a voltage of 35 V was applied to the fabricated two-layer stacked element, the brightness was 0.12 cd/m at a current density of 7 mA/cm2.
2 yellow-orange luminescence was observed. The peak wavelength of the emission spectrum was 580 nm, which matched the fluorescence spectrum of the HO-PPV spin cord thin film. Furthermore, the luminescence 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 sodium hydroxide solution into an aqueous solution to obtain poly-p-phenylene vinylene (hereinafter referred to as PPV). ), an aqueous solution of poly-roof vinylene bis(diethylsulfonium bromide) ethylene (hereinafter referred to as PPV intermediate) was obtained. In Example 2, the obtained PPV intermediate was used instead of the PTV intermediate to form a film. The film was formed by applying a PPV intermediate aqueous solution to a thickness of 600 mm by spin coating at a rotation speed of 2000 rpm. Thereafter, the PPV intermediate spin cord film was heat-treated at 370° C. for 2 hours to form a PPV thin film. The film thickness after heat treatment was 300 mm. Changes to the PPV structure were confirmed by changes in the infrared absorption spectrum. This was used as a charge transport layer. Furthermore, HO-PPV was spin-coated thereon in the same manner as in Example 2, and an AI main electrode was deposited to complete the EL device.

When a voltage of 30 V was applied to the fabricated two-layer stacked element, the brightness was 0°09 cd/c at a current density of 17 mA/c.
Yellow-orange light emission of m2 was confirmed. The emission spectrum was similar to Example 2.

Example 4 A PAn film was formed in the same manner as in Example 1 to form a charge transport layer. Furthermore, HO-PP was added thereon in the same manner as in Example 2.
The device was completed by spin coating V and depositing the A1 electrode.

When a voltage of 50 V was applied to the fabricated two-layer stacked element, the luminance was 0.04 cd/cm at a current density of 2 mA/Cm2.
m! Yellow-orange luminescence was confirmed. The emission spectrum was similar to Example 2.

[Brief explanation of drawings]

FIG. 1 shows a conceptual cross-sectional structure of an embodiment of an organic electroluminescent device according to the present invention.

Claims (1)

[Claims] (l) 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, wherein the charge transport layer has the general formula (I) -Ar-B -(I) Ar: an aromatic hydrocarbon group having 6 or more carbon atoms, or a heterocyclic aromatic hydrocarbon group having 4 or more carbon atoms; B: a repeating unit represented by a -CH=CH- group or -NH- group; (2) An organic electroluminescent device characterized by using a conductive polymer having the following characteristics: (2) The conductive polymer is poly-p-phenylenevinylene,
poly-2,5-dialkyl-p-phenylene vinylene,
The organic electroluminescent device according to claim 1, which is poly-2,5-dialkoxy-p-phenylene vinylene, poly-2,5-thienylene vinylene, or polyaniline.