JPH0541281A - Electroluminescence device - Google Patents

Abstract

PURPOSE:To improve a defect lowering the life of an organic thin film electroluminescent element which is quickly and acceleratedly deteriorated because of moisture and the like produced by heating caused when the element is driven. CONSTITUTION:An organic thin film electroluminescent element provided with an electroluminescent material layer including at least, one kind of an organic compound, is held in an inert liquid compound composed of carbon fluoride including dehydrating agent while being interposed between an anode and a cathode, at least, either on of which is transparent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic thin film electroluminescent device which is an element having an electroluminescent organic layer provided between electrodes and which is used for a flat light source or a display device.

[0002]

2. Description of the Related Art Conventionally, an electroluminescent device (EL device) made of an electroluminescent material of an organic compound has been attracting attention as an inexpensive full-color display device having a large area. For example, an organic thin film element in which a condensed polycyclic aromatic system such as anthracene or perylene is used as a raw material as an organic compound by a LB film method or a vacuum deposition method has been developed, and its light emitting characteristics have been studied. However, conventional organic thin film EL
The device had a high driving voltage, and the efficiency of its emission luminance was lower than that of the inorganic thin film EL device. In addition, the organic thin film E
The L element was not at a practical level because the deterioration during light emission was remarkable. However, recently, a new type of organic thin film EL device in which the organic thin film has a two-layer structure has been reported, and has attracted strong interest (Abride, Physics, Letters,
51, 913, 1987). According to the report, a driving voltage of 6 to 7 V gives a luminance of several hundred cd / m2.

[0003]

However, since this organic thin film EL element is of the current drive type, a high current must be passed between the electrodes. As a result, the EL element accelerates deterioration of the element due to heat generated by Joule heat, and in a remarkable case, the element is destroyed. Further, the present inventors have found that water is one of the major causes of deterioration of the EL element. The present invention has been made in view of the circumstances of a conventional organic thin film EL element that is significantly deteriorated due to the causes described above, and is deteriorated by holding the organic thin film EL element in a specific liquid capable of being highly dehydrated. An object of the present invention is to provide an organic thin film electroluminescent device in which the Joule heat generated when an electric current is passed between electrodes is removed as much as possible to remove the water that causes the above, and the durability of the organic thin film EL element is improved.

[0004]

That is, according to the present invention, an organic thin film electroluminescent device having an electroluminescent material layer containing at least one organic compound between an anode and a cathode, at least one of which is transparent, is dehydrated. The electroluminescent device is characterized in that it is held in an inert liquid compound made of fluorinated carbon containing an agent.

The organic thin film EL element used in the present invention has a basic structure of an organic electroluminescent material layer composed of an anode and an organic compound, or an electroluminescent material composed of an anode, an inorganic semiconductor and an organic compound, and a cathode. And the anode is, for example, gold,
A metal thin film of platinum, palladium or the like or an oxide film of tin, indium-tin or the like is used, and it is more preferable that it is transparent. The cathode may be a single metal or a co-deposited metal as long as it is a solid metal that can be vacuum deposited.

The organic electroluminescent substance made of an organic compound provided between the electrodes is, for example, a hole transporting agent and an electron transporting light emitting agent, or a hole transporting agent, a light emitting agent and an electron transporting agent, and a combination of the above. It is a mixture of substances that show a graded structure portion in which the components continuously change between substances or a substance and a layer made of the combination, and a substance that makes the combination.

Specific examples of the hole transfer agent include aromatic amine derivatives, polyindene derivatives, polyaniline derivatives,
Phthalocyanines, polyvinyl phthalocyanines, oxadiazole derivatives, other compounds having a hole-transporting ability, and mixtures thereof or high-concentration mixtures with other polymers are organic compounds exhibiting p-type semiconductivity.

Next, as a specific example of the electron transfer agent, 2- (4-t
ert-Butylphenyl) -1,2,3-oxadiazole and 5,10,15,20-t
It is a compound showing n-type semiconductor properties such as x = 2-pyridyl group, 3-pyridyl group, 4-pyridyl group, 4-quinidyl group, 6-quinodyl group and quinoxalyl group in etra (x) porphyrin.

Further, specific examples of the electron transport luminescent agent include:
There are luminescent organic compounds in which oxine and a metal complex, tetraphenylcyclopentadiene, pentaphenylcyclopentadiene, and an electron transfer agent are mixed. In addition, as the light-emitting organic compound, many compounds that emit fluorescence by being irradiated with ultraviolet rays are included.

The electroluminescent substance provided between the electrodes is, for example, (1) a p-type inorganic semiconductor thin film and an organic electron transporting luminescent agent, (2) a p-type inorganic semiconductor thin film, an organic luminescent agent and an organic electron transporting agent, ( 3) p-type inorganic semiconductor thin film and organic hole transporting agent and organic electron transporting luminescent agent, (4) p-type inorganic semiconductor thin film, organic hole transporting agent, organic luminescent agent and organic electron transporting agent,
Further, (5) is a mixed thin film of the p-type inorganic semiconductor thin film and the organic substance. Specific examples of the p-type inorganic semiconductor thin film include P-type amorphous silicon and P-type amorphous silicon carbide.
The above compounds are typical compounds having respective properties, and the present invention is not limited to them.

As the dehydrating agent used in the present invention, any solid having a strong dehydrating ability can be used.
There are many materials such as synthetic zeolite, silica gel, anhydrous calcium chloride, anhydrous potassium sulfate, and zeolite. In particular, synthetic zeolite is a preferable dehydrating agent because it has a constant composition and is pure and the shape can be selected.
The above compounds are typical as dehydrating agents, and the present invention is not limited thereto.

As the inactive liquid compound composed of fluorinated carbon used in the present invention, liquid fluorinated carbon compounds having various boiling points can be used. However, in practice, liquids having a low boiling point require a special technique for sealing, and the sealing material also needs a material and a structure that are resistant to vapor pressure. A liquid fluorinated carbon compound having a boiling point of 50 ° C. or higher is preferable.
And specific examples are the product names Fluorinert FC-72 (boiling point 56 ° C.), Fluorinert FC-84 (boiling point 80 ° C.), Fluorinert F, which are commercially available from Sumitomo 3M Limited.
C-77 (boiling point 97 ° C), Fluorinert FC-75 (boiling point 102 ° C) Fluorinert FC-40 (boiling point 155)
C.), Fluorinert FC-43 (boiling point 174 ° C.) and Fluorinert FC-70 (boiling point 215 ° C.).

The method of immersing the electroluminescent device in the liquid fluorinated carbon compound containing a dehydrating agent is, for example, (1) a desiccant is put in a transparent container, for example, in a container having a small hole, and is held in one corner. Then, a liquid fluorinated carbon compound is put in, and then an electroluminescent device having an electrode terminal is put in, the electrode is pulled out, and the lid is sealed. (2) For example, a soft pipe having a small hole filled with a desiccant. Is placed around an electroluminescent device with electrode terminals, at least one side is covered with a transparent plastic sheet, both sides are sealed in a bag shape so that the electrode terminals go out of the plastic, and a liquid fluorinated carbon compound is injected. Then, a method of sealing the injection port, (3) arranging a soft pipe having a small hole filled with a desiccant around the electroluminescent element with the electrode terminal, and the non-emission side, one side with the injection port Open And the box body is an electrode terminal joined in an arrangement such as exits, after injection of a liquid fluorinated carbon compound from the injection port, a method of sealing the injection port can be used. And it is more preferable if a heat exchanging component such as a fin is attached to the immersion container. If the liquid fluorinated carbon compound is subjected to deoxygenation treatment by blowing a dry inert gas before immersing the electroluminescent element, the influence of oxygen can be suppressed.

Next, the packaging method of the liquid fluorinated carbon compound in which the electroluminescent device is immersed is preferably designed so that at least the light emitting surface side of the electroluminescent device is a transparent container. It is also a preferable method to apply the liquid fluorinated carbon compound so that the liquid fluorinated carbon compound is soaked only on the side of the electroluminescent device from which light is not extracted, in order to apply it only to the necessary portion.

As the packaging material of the liquid fluorinated carbon compound in which the electroluminescent device is immersed, since the liquid fluorinated carbon compound is chemically very stable, many substances can be used. Further, as for the bonding material and the adhesive, many materials can be used like the package material.

As described above, although the present invention has many practically important features, the most important point is that heat generation that accelerates deterioration of an electroluminescent device can be effectively removed, and By immersing in a liquid fluorinated carbon compound containing a strong dehydrating agent, water, which is one of the causes of deterioration of the electroluminescent device during handling during assembly or brought in from the electroluminescent device and electrode terminals, is removed. And in addition,
An organic thin film electroluminescence device characterized in that deterioration of an electroluminescence device is improved by the fact that a fluorinated carbon compound is a chemically extremely stable liquid.

[0017]

Although the organic thin film electroluminescent device has been improved, the conversion efficiency into light is insignificant, and most of the electric current is emitted as heat. Compared to inorganic compounds, organic compounds are weak against heat and may be crystallized or decomposed depending on substances. Since it is considered that generated heat accelerates the deterioration reaction like a general reaction, it is presumed that by effectively removing the heat generated from the element, the deterioration of the element is dramatically improved. Based on such an idea, as a result of earnest research for solving a heat problem, the present invention found that the heat problem can be solved by immersing the electroluminescent device in a liquid fluorinated carbon compound. Further, the liquid fluorinated carbon compound effectively prevents the alteration of the electrode formed by metal vapor deposition, and does not change the organic thin film layer such as the hole transport material or the electron transport luminescent material made of the organic compound at all. It has been found that it has properties and that the deterioration is dramatically improved. However, in assembling an actual electroluminescent device, water mixed in from the atmosphere and water mixed in from elements, electrode terminals, wirings, etc., drastically reduce the original effect. Therefore, the inventors of the present invention have conducted intensive studies to remove even a very small amount of water which causes deterioration of the device, and found that it is effective to add a strong dehydrating agent to the liquid fluorinated carbon compound. Came to.

Since the inert liquid compound comprising fluorinated carbon used in the present invention has a completely fluorinated structure, it is a colorless, transparent and odorless inert liquid having a low viscosity and a large dielectric strength. And has a thermal conductivity of silicone oil 2
It has a capacity of 5 times that of forced air cooling. Further, it has a property that neither water nor oil is dissolved, and it does not dissolve the organic thin film layer formed of the organic compound provided between the electrodes. Further, by adding a dehydrating agent to the liquid fluorinated carbon compound as in the present invention, in addition to the characteristics that the deterioration of the electroluminescent element is less likely to proceed, it is possible to remove the water that is brought in at the time of assembly that causes the deterioration. It is possible to obtain an organic thin film electroluminescent device having practically excellent characteristics.

[0019]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 A glass substrate with a transparent electrode (manufactured by Matsuzaki Vacuum Co., Ltd.) in which a 1000-liter ITO (indium oxide-tin oxide film) film was formed on a substrate glass was ultrasonically cleaned in acetone and then boiled in ethanol. Further, plasma treatment with air composition was performed. This surface-treated glass substrate with a transparent electrode is set in a vacuum device, and N, N'- is applied at a vacuum degree of 5 × 10 -6 torr.
Diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (hereinafter referred to as TPD) was vapor-deposited at 200Å, and subsequently, aluminum complex of TPD and 8-oxyquinoline (hereinafter referred to as Alq (Referred to as ³ ) and 100 Å of a portion (gradient structure part) having a concentration gradient in which the components of ( ³ ) are continuously changed were formed, and subsequently 200 Å of Alq ³ was vapor deposited. Further, magnesium (Mg) and silver (Ag) are added at an atomic ratio of 10: 1 to 20
An organic thin film electroluminescent device was prepared by co-deposition with 00Å. The manufactured device was prepared by using a liquid fluorinated carbon compound (Sumitomo 3M: trade name “Fluorinert FC-43”, boiling point 174
As a result of immersing in a solution of 1 g of synthetic zeolite (manufactured by Tosoh Corporation: trade name "Zeorum") in 100 ml of 100 ° C and pour point of -50 ° C and driving with direct current, the maximum brightness was 7200.
A green emission of cd / m ² was observed. Also, the current density 1
Under the conditions of 0.2 mA / cm ² and emission luminance of 80 cd / m ² , the luminance did not decrease even after 140 hours.

Comparative Example 1 The organic thin film electroluminescent device prepared in Example 1 was replaced with 8 × 10 −5.
Approximately 500 cd in a torr glass bell jar type vacuum container
When it was driven at a speed of / m ² , element destruction accompanied by breakage of the glass substrate occurred. After opening, when checking the state of the element,
The element was very hot.

Comparative Example 2 When the organic thin film electroluminescent device prepared in Example 1 was driven by direct current in the atmosphere, a maximum brightness of 250 at a driving voltage of 19v was obtained.
The brightness was reduced to a peak of 0 cd / m ² and the product was destroyed at 23 v. Further, as a result of driving under the condition of light emission luminance of 80 cd / m ² , after 20 hours, the cathode metal was denatured and a large non-light emitting portion was formed.

[0022]

As described above, according to the present invention, there is provided an organic thin film electroluminescent device having significantly improved reliability. As described above, according to the present invention, the organic thin film electroluminescent device can be raised to a practical level, and its industrial value is high.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Kato 3-5-1, Asahimachi, Machida-shi, Tokyo Inside Denka Kagaku Kogyo Co., Ltd. (72) Inventor Shinichiro Asai 3-chome, Asahimachi, Machida-shi, Tokyo No. 5-1 Denka Kagaku Kogyo Co., Ltd.

Claims (2)

[Claims] 1. An organic thin film electroluminescent device comprising an electroluminescent material layer containing at least one kind of organic compound between an anode and a cathode, at least one of which is transparent, comprising a fluorinated carbon containing a dehydrating agent. An electroluminescent device characterized by being held in an inert liquid compound. 2. The electroluminescent device according to claim 1, wherein the dehydrating agent is synthetic zeolite.