JPH07286170A - Light emitting element - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a high brightness light emitting device. [Structure] In an element that has a positive electrode, a negative electrode, and a substance that controls light emission, and emits light by electric energy,
A light-emitting device comprising a carbazole compound represented by the following general formula and / or an oxidized polymer thereof dispersed in a polymer compound. [Chemical 1] (However, in the above formula, R ^{1 to} R ⁵ represent hydrogen or an alkyl group having 1 to 18 carbon atoms, X is the above-mentioned xylylene or alkylene, and n represents a natural number.)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device capable of converting electric energy into light, and is used as a display device, a flat panel display, a backlight, a lighting, an interior, a sign, a signboard, a planar light-emitting device such as an electrophotographic machine. It can be suitably used.

[0002]

2. Description of the Related Art In recent years, active research has been conducted on organic laminated thin-film light emitting devices in which electrons injected from a cathode and holes injected from an anode emit light when recombined in an organic phosphor sandwiched between both electrodes. It's starting to happen. This element is thin,
It has attracted attention because it is characterized by high-luminance light emission under low drive voltage and multicolor light emission by selecting fluorescent material.

This work was carried out by Kodak Corp. W. Tan
Since g. et al. showed that an organic laminated thin film device emits light with high brightness (Appl. Phys. Lett. 51 (12)
21, p. 913, 1987), many research institutes are investigating. A typical structure of an organic laminated thin film light emitting device presented by a research group of Kodak Company is a hole transporting diamine compound and a light emitting layer on an ITO glass substrate.
Hydroxyquinoline aluminum and M as cathode
g: Ag was sequentially provided, and a green emission of 1000 cd / m ² was possible with a driving voltage of about 10V. Current organic laminated thin-film light-emitting devices have some configurations such as those provided with an electron transport layer in addition to the above-mentioned device components, but basically follow the configuration of Kodak. The device characteristics largely depend on the material, and various substances have been studied for that reason. Among them, the hole transport material is an important material that greatly affects the characteristics of the device, and many studies have been made. For example, in the "Organic EL device development strategy" edited by the Next Generation Display Device Study Group (Science Forum, published in 1992), the hole transport material for organic laminated thin film light-emitting devices is highly carrier-transported to improve the luminous efficiency against power. Materials are effective, and it is important to select an appropriate electron level material for confining excitons in the light emitting layer and improving carrier injection efficiency. Furthermore, light emission is required to efficiently convert electric energy into light. It has been shown that it is important not to form exciplexes at the interface with the layers. Further, the film thickness and film forming ability are also important requirements in actual device fabrication. Representative N, N'-diphenyl-N, N 'as a specific hole transport material
-Bis (3-phenyl) -1,1'-biphenyl-4,
In addition to 4′-diamine (TPD), hydrazone compounds, stilbene compounds, triphenylamine compounds, heterocyclic compounds represented by oxadiazole derivatives and phthalocyanine derivatives, in polymer systems, the above monomers are used as side chains. Polycarbonates, styrene derivatives, polyvinylcarbazole, polysilane, and the like are shown.

[0004]

However, the prior art has not been put into practical use as an element because of its low luminous efficiency and short lifetime. For example, as a monomer compound, a compound that exhibits relatively high performance such as TPD is known, but it has been pointed out that the performance of the device is deteriorated due to insufficient heat resistance and crystallinity. As a material having excellent durability, polyvinyl carbazole (hereinafter abbreviated as PVCz) which is a polymer compound is a typical example, but it does not have high characteristics as high as a monomer compound. Therefore, a method for improving the performance of PVCz while maintaining its durability is desired. PV as this method
It is known that an electron-accepting property such as trinitrofluorenone is added to Cz to form a charge transfer (hereinafter abbreviated as CT) complex in the ground state, and a carrier can be efficiently generated by exciting the CT complex. Since nitrofluorenone is an electron-accepting compound, the electron-transporting ability is improved as the amount of nitrofluorenone is increased, so that it cannot be effectively applied to this device.

An object of the present invention is to solve the above-mentioned conventional problems, and an object thereof is to provide a light emitting element having high brightness and low power consumption.

[0006]

To achieve the above object, the present invention has the following constitution.

"In a device that has a positive electrode, a negative electrode, and a substance that controls light emission and emits light by electric energy, the device is a carbazole compound represented by the following general formula dispersed in a polymer compound and / or its oxidation. A light-emitting device comprising a polymer.

[0008]

[Chemical 3] (However, in the above formula, R ^{1 to} R ⁵ represent hydrogen or an alkyl group having 1 to 18 carbon atoms, X is the above-mentioned xylylene or alkylene, and n represents a natural number.) If transparent for extracting light, conductive metal oxides such as tin oxide, indium oxide, indium tin oxide (ITO), metals such as gold, silver and chromium, inorganic conductive substances such as copper iodide and copper sulfide. The conductive material such as a conductive substance, polythiophene, polypyrrole, polyaniline and the like is not particularly limited, but it is particularly preferable to use ITO glass or Nesa glass in terms of high transmittance of emitted light. The resistance of the transparent electrode is not limited as long as it can supply a sufficient current for light emission of the device, but is preferably low resistance from the viewpoint of power consumption of the device. For example, an ITO substrate having a resistance of 300 Ω / □ or less functions as an element electrode, but since it is now possible to supply a substrate having a resistance of about 10 Ω / □, it is particularly desirable to use a low resistance product. The thickness of the positive electrode can be arbitrarily selected according to the resistance value, but it is usually preferably used in the range of 1000 to 3000 angstrom. Further, as the glass substrate, soda lime glass, non-alkali glass or the like is used, and the thickness is not limited as long as it has a thickness sufficient to maintain mechanical strength, but is not limited to 0.7 m.
It is sufficient to have m or more. As for the material of the glass, non-alkali glass is preferable because it is preferable that less ions are eluted from the glass, but it is also preferable to use soda lime glass having a barrier coat such as SiO ₂ . The ITO film forming method is not particularly limited, such as an electron beam method, a sputtering method and a chemical reaction method.

Since the negative electrode must efficiently supply electrons to a substance that controls light emission or a substance adjacent to the substance that controls light emission (for example, an electron transport layer), the adhesiveness and energy between the electrode and the substance adjacent to the electrode are high. It is preferable to appropriately adjust the level. In addition, it is desirable to use a material that is relatively stable in the air in order to maintain stable performance for long-term use, but this is not the case when a protective film or the like is used. Specifically, indium, gold,
Although it is possible to use metals such as silver, aluminum, lead, magnesium, lanthanum, europium, and ytterbium, simple earth elements, alkali metals, or alloys thereof, low work functions such as magnesium and lithium are taken into consideration when considering device characteristics. It is desirable to use a metal.
However, since these metals are very active and unstable, alloys with silver or aluminum can be used. A resistance heating method, an electron beam method, a sputtering method, a coating method, or the like is used to manufacture the electrodes, and the metal can be vapor-deposited alone or two or more components can be vapor-deposited simultaneously. Particularly, for forming an alloy, it is possible to easily form an alloy electrode by simultaneously vapor-depositing a plurality of metals.

The substances that control light emission are 1) hole transporting layer / light emitting layer, 2) hole transporting layer / light emitting layer / electron transporting layer, 3) light emitting layer / electron transporting layer, and 4) the above groups. It may be in a form in which the combined substances are mixed in one layer. That is, as the device structure, in addition to the multilayer laminated structure of the above 1) to 3), only one layer containing a light emitting material and a hole transport material and / or an electron transport material may be provided as in 4).

The carbazole compound and / or its oxidized polymer in the present invention is used by being dispersed in a polymer compound, but is preferably used by being contained in a hole transport layer, a light emitting layer and an electron transport layer. In particular, it is preferably contained in the hole transport layer.

In the carbazole compound used in the present invention, R ^{1 to} R ⁵ are hydrogen or ^{1 to 5} carbon atoms.
It is an alkyl group of 18 and it is possible to change the device characteristics and the thin film forming ability by introducing one or more substituents. Such an alkyl group is a substituted or unsubstituted alkyl group, and in the case of the substituted alkyl group, a triphenylamino group that facilitates hole transfer is particularly preferably used as the substituent. Further, the unsubstituted alkyl is C _1-
Although it may be any of C ₃₆ , C _{1 to} C ₁₈ are particularly preferable in view of thin film forming ability. However, these R ^{1 to} R ⁵
The substituent is not particularly limited to an alkyl group, an alkoxy group,
An electron-donating substituent such as a cycloalkyl group or a dialkylamino group, or an aromatic substituent through a methylene chain can be used for improving the durability and film-forming property of the material.
In addition, the role of X in the formula is also important because the ionization potential greatly changes depending on the N-substituted skeleton. X is
Xylylene or alkylene is shown, but in the case of alkylene, the chain length is not particularly limited, but it is preferably selected from C _{1 to} C ₃₆ . Particularly, if the carbazoles are too close to each other, the performance is likely to be deteriorated by the interaction, and if they are too far apart, the functional skeleton is diluted and the performance is also likely to be deteriorated. Therefore, the alkylene chain length is selected from C _{6 to} C _9. Is particularly preferred. In the case of a xylylene skeleton, para-substitution results in a rigid structure, which reduces solubility in hydrocarbons, halogenated hydrocarbons, thin-film coating solvents such as tetrahydrofuran, and the ortho or meta positions are preferred, but the solubility is Para-substitution may be used when a high solvent such as sulfuric acid, trifluoroethanol or aprotic polar solvent can be used. Para-substitution may be preferable in terms of device durability. When used as an oxidation polymer, iron (III) chloride, aluminum chloride / copper (II) chloride, aluminum chloride / vanadium pentoxide, etc. are preferably used as the catalyst. The degree of polymerization is not particularly limited as long as it is 2 or more.

In the present invention, the polymer compound in which the carbazole compound and / or its oxidative polymer is dispersed is not particularly limited, but PVCz is preferred. In addition, since the carbazole compound and / or its oxidative polymer has a high hole-transporting property, it is possible to use, for example, conductive polymers such as polysilane, polypyrrole, polythiol, and polyaniline, and transparent polymers such as polymethylmethacrylate, polycarbonate, and polysulfone. It is also preferable to disperse it in a resin. The weight mixing ratio of the present carbazole compound and / or its oxidized polymer and the polymer compound is 5/95 in consideration of the characteristics of the device.
60/40 is preferable, and 5/9 from the viewpoint of thin film forming ability.
5 to 30/70 is particularly preferable, but it is not particularly limited.

As a method for forming a thin film, a solvent of a mixture of a carbazole compound and / or its oxidative polymer and a polymer compound is prepared, foreign substances are removed, and then a transparent conductive film is coated (spin coating, dip coating, etc.). . Further, the mixed solvent at that time, for example,
Triphenylamines such as N, N'-diphenyl-N, N'-di (3-methylphenyl) -4,4'-diamine, tertiary amines such as N-isopropylcarbazole, pyrazoline derivatives, stilbene compounds , Hydrazone compounds, heterocyclic compounds typified by oxadiazole derivatives and phthalocyanine derivatives, and polycarbonates and styrene derivatives having the above-mentioned monomer in the side chain are preferably used in polymer systems.

As the material for the light emitting layer, in addition to anthracene and pyrene, which have been known as light emitters for a long time, and the above-mentioned 8-hydroxyquinoline aluminum, for example, a bisstyrylanthracene derivative, a tetraphenylbutadiene derivative, and coumarin. Derivative, oxadiazole derivative, distyrylbenzene derivative, pyrrolopyridine derivative, perinone derivative, cyclopentadiene derivative, oxadiazole derivative, thiadiazolopyridine derivative,
In the polymer system, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polythiophene derivatives and the like can be used. As the dopant added to the light emitting layer, the above-mentioned rubrene, quinacridone derivative, phenoxazone 660, DCM1, perinone, perylene, coumarin 540 and the like can be used as they are. The method for forming the light-emitting layer is not particularly limited, such as resistance heating vapor deposition, electron beam vapor deposition, sputtering, molecular lamination method and coating method, but resistance heating vapor deposition and electron beam vapor deposition are usually preferable in terms of characteristics. The thickness of the layer cannot be limited because it depends on the resistance value of the substance that controls light emission, but it is empirically selected from the range of 100 to 10000 angstrom. For example, when polyvinylcarbazole is used for the hole transport layer and 8-hydroxyquinoline aluminum is used for the light emitting layer, the thickness of each layer is preferably 100 to 700 angstroms, with the thickness of polyvinylcarbazole being 2
More preferably, it is from 00 to 500 angstroms, and the film thickness of 8-hydroxyquinoline aluminum is 200.
~ 2000 angstroms are preferred, 500-12
00 angstrom is more preferable.

As the electron transporting material, it is necessary to efficiently transport the electrons from the cathode between the electrodes to which an electric field is applied, and the electron injection efficiency is high, and it is desirable that the injected electrons are efficiently transported. . For that purpose, it is required that the substance has a high electron affinity, a high electron mobility, an excellent stability, and an impurity that becomes a trap is hard to be generated during production and use. Oxadiazole derivatives and 8-
There is hydroxyquinoline aluminum and the like, but it is not particularly limited.

[0017]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 A glass substrate (15 Ω / □) on which an ITO transparent conductive film was deposited in a thickness of 1500 Å was cut into a predetermined size, etched and washed. Compound 3 / PVCz = 20
The ITO transparent conductive film was immersed in a 0.85 wt% dichloroethane solution of 80/80 (weight ratio) and then pulled up by dip coating at a speed of 50 mm / min. This was installed in a vacuum evaporation system and the vacuum degree in the system was 5 × 10 ^-6.
It was evacuated to below Torr. 8-Hydroxyquinoline Aluminum Aluminum 1000 Å, Lithium 30 Å, Silver 1500
An element of 5 × 5 mm square was prepared by vapor deposition to a thickness of angstrom. This light-emitting element emits light at 4.0 V, and the maximum luminance is 17280 cd / m ² (16 V, 14 V
4 mA).

[0019]

[Chemical 4] Example 2 A device was prepared in the same manner as in Example 1 except that compound 4 was used instead of compound 3,
Light emission is recognized from 4.0 V, and the maximum brightness is 19680.
It was cd / m ² (18 V, 141 mA).

[0020]

[Chemical 5] Example 3 A device was prepared in the same manner as in Example 1 except that compound 5 was used instead of compound 3,
Light emission was recognized from 4.0 V, and the maximum brightness was 10530.
Although it was cd / m ² , it emitted light at a low power of 16 V and 84 mA.

[0021]

[Chemical 6] Comparative Example 1 A glass substrate (15 Ω / □) on which an ITO transparent conductive film was deposited in a thickness of 1500 Å was cut into a predetermined size, etched and washed. The ITO transparent conductive film was dipped in a 0.85 wt% dichloroethane solution of polyvinylcarbazole, and then pulled up for dip coating at a speed of 50 mm / min. This was placed in a vacuum vapor deposition apparatus and evacuated until the degree of vacuum inside the apparatus became 5 × 10 ⁻⁶ Torr or less. 8-Hydroxyquinoline aluminum Aluminum 1000 Å, lithium 3
A device of 5 × 5 mm square was prepared by vapor-depositing 0 angstrom and silver to a thickness of 1500 angstrom. This light emitting device emits light from 4.0 V, and the maximum brightness is
It was 12130 cd / m ² (19 V, 140 mA).

[0022]

INDUSTRIAL APPLICABILITY The present invention can provide a high brightness light emitting device, and can contribute to lower power consumption and longer life of the device.

Claims (4)

[Claims] 1. A device that has a positive electrode, a negative electrode, and a substance that controls light emission, and emits light by electric energy, wherein the device is a carbazole compound represented by the following general formula dispersed in a polymer compound and / or the same. A light emitting device comprising an oxidative polymer. [Chemical 1] (However, in the above formula, R ^{1 to} R ⁵ represent hydrogen or an alkyl group having 1 to 18 carbon atoms, X is the above-mentioned xylylene or alkylene, and n represents a natural number.) 2. The light emitting device according to claim 1, wherein the carbazole compound is a compound represented by the following general formula. [Chemical 2] 3. The light emitting device according to claim 1, wherein the carbazole compound and / or its oxidized polymer is dispersed in polyvinylcarbazole. 4. The light emitting device according to claim 1, wherein the carbazole compound and / or its oxidized polymer is used as a hole transport layer.