JPH08236273A - Organic el element and its manufacture - Google Patents

Abstract

PURPOSE: To provide an organic EL element which has high luminance and a long luminescent life by heating an organic layer composed of an organic mixture containing an organic material having an electroluminescent function at the temperature of not less than the melting point of the organic mixture, while holding it between electrode substrates. CONSTITUTION: This organic EL element has such a constitution that an organic layer 4 composed of an organic mixture containing an organic material having an electroluminescent function is heated at the temperature of not less than the melting point of the organic mixture in high vacuum and at the same time held between a transparent electrode substrate 5 and an electrode substrate 6 while a pressure is applied thereto. The transparent electrode substrate 5 is formed by the vacuum evaporation of an ITO film 2 on a glass substrate 1, and the electrode substrate 6 is formed by the co-evaporation of an alloy film 3 of silver and magnesium on the glass substrate 1. Therefore, it can be used for the back light of a liquid crystal display, a luminaire, an interior luminaire and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL element which can be used as a light source for backlights for liquid crystal flat panel displays, lighting equipment and the like, and more specifically to an organic EL element having high brightness and long life and a method for producing the same. Regarding

[0002]

2. Description of the Related Art A prototype of an organic electroluminescence device (hereinafter referred to as an organic EL device) is a light emitting diode (LED) which is practically used as a semiconductor light emitting device. Therefore, the organic EL element is sometimes called an organic light emitting diode or an injection type EL element. In particular, it has ideal characteristics as a display because high-luminance three-primary-color light emission is obtained by direct current low voltage and surface emission is performed. Organic EL element is an inorganic LED
It has characteristics comparable to or exceeding existing light emitting elements such as and inorganic EL elements.

In 1966, Helfrich et al. Succeeded in injecting carriers into the anthracene single crystal, and observed electroluminescence (hereinafter referred to as EL) that matches the fluorescence spectrum from the anthracene single crystal. In 1986, Saito et al.
An EL element was observed by covering the gold surface with a poly (3-methylthiophene) thin film by an electric field polymerization method, and forming a perylene vapor deposition film and an aluminum electrode on the film, and observing the EL visually observed in a room in the daytime. In 1987, Eastman Kodak Company, known as an organic semiconductor known as an organic semiconductor having a hole transporting ability between a light emitting layer and an ITO electrode on the hole injecting side by forming a light emitting layer with a quinolinium A1 complex vapor deposition film. Insert a vapor-deposited film of phenylamine derivative, 1000 cd
A high-brightness EL element reaching up to / m ² was obtained (CWTang, SAV
anSlyke: Appl.Phys.Lett., 51, 913 (1987)). The drive voltage of this element is about 10V. With these research results as a starting point, material development for higher efficiency was carried out, especially blue-
The possibility of a flexible organic EL device using a plastic substrate with high brightness and low voltage driving in the green region was examined.

As described above, researches on organic EL devices using organic low molecular weight materials have been actively conducted. For example, Wakimoto et al. Describe organic compounds using starburst amine as a hole transport material and a quinacridone derivative as a light emitting material. Fabricate EL element,
Maximum 104,000 cd / m ² , luminous efficiency 10.8 lm
/ W (300 cd / m ² o'clock) with high brightness and high efficiency, green light emission is obtained (1993 Spring Society of Applied Physics Proceedings, 30a-SZK-14). This is because the quinacridone molecule has a very high fluorescence quantum yield as an isolated molecule and has a lower excitation energy than that of aluminum quinoline, and it is effectively excited also by the exciton of the aluminum quinolinol complex host molecule. This is an attempt to take away energy and create a second emission center.

EL of EL element to which quinacridone is added
It was confirmed that the spectrum was in agreement with the fluorescence spectrum of the quinacridone solution, and it was confirmed that the emission of the EL device was from the quinacridone excitons. This organic EL
In the device, it is more improved than the green phosphor used in the CRT. The starburst amine material is a material developed by Shirota et al. Of Osaka University and can form a stable amorphous film. In addition, Matsuura et al. Synthesized a distilarylene derivative material for the purpose of obtaining high-intensity blue light emission, and measured 7,000 cd / m ² (DC of 16 V or less).
Driving (N ₂ gas atmosphere) is obtained (1993 Spring Applied Physics Society Proceedings, 30a-SZK-13).

Regarding an organic EL device using an organic polymer, a research group at the University of Cambridge, UK, plays a central role, and has an organic thin film prepared by a wet method such as a spin coating method and has a hole transporting property and blue fluorescence. Research on a stacked EL device in which polyvinylcarbazole (PVK) and an electron transport layer are combined has been conducted. High brightness blue light emission exceeding 700 cd / m ² was obtained from the PVK layer. Furthermore, by dispersing three types of dyes of blue, green, and red in a polymer resin, high-luminance white light emission equivalent to that of a fluorescent lamp has been obtained (J.kido et al, Appl.Phys.Lett., 64 ( 19
94) 815.). In addition, a flexible organic E that uses polyphenylene vinylene (PPV) and continues to emit light even when bent
An L element has also been prototyped (G. Gustafsson, Nature, 356, 47
(1992).). In this organic EL device, polyethylene terephthalate is used for the substrate, polyaniline is used for the anode, and all the materials except the cathode are made of polymer.

[0007]

The above-mentioned proposal of the laminated EL device expands the selection range of the light emitting layer material, and makes the development of a full color flat panel display a reality.
Although almost satisfactory emission colors, emission luminances, and driving voltages have been obtained, there is a problem that they cannot withstand long-term use, that is, the emission life is short. The present invention has been made to solve the above problems, and an object of the present invention is to provide an organic EL device having high brightness and a long emission life, and a method for manufacturing the same.

[0008]

The inventors of the present invention have pointed out that the cause of the short emission life of the conventional organic EL element is the deterioration of the interface between the electrode and the organic thin film due to residual oxygen or water and the crystallization of the organic layer. Based on this finding, the present invention has been completed.

That is, according to the present invention, an organic layer made of an organic mixture containing an organic material having an electroluminescence function is heated to a temperature at which the organic mixture is melted under a high vacuum degree and a pressure is applied, The present invention relates to an organic EL device, wherein at least one is sandwiched between two transparent or semitransparent electrode substrates.

Further, according to the present invention, an organic mixture containing an organic material having an electroluminescence function is heated under a high vacuum at a temperature at which the organic mixture is melted or higher, and at least one of the molten organic mixture is heated. The present invention relates to a method for manufacturing an organic EL element, which comprises forming an organic layer by sandwiching two transparent or semitransparent electrode substrates while applying pressure.

Generally, an organic EL element is an organic EL element in which an organic layer made of an organic mixture containing a hole transport material, an electron transport material and an electroluminescent material is sandwiched between an electron injection electrode and a hole injection electrode, An organic EL element in which an organic layer made of an organic mixture containing a hole transport material and an electron transport material without using an electroluminescent substance is sandwiched between an electron injection electrode and a hole injection electrode is classified. That is, in the latter case, the hole-transporting material or the electron-transporting material exhibits strong fluorescence and serves also as an electroluminescent material.

In the organic EL device of the present invention, an organic layer made of an organic mixture containing an organic material having an electroluminescent function is sandwiched between two electrode substrates under a high degree of vacuum. Therefore, it is possible to remove the residual gas such as oxygen and water contained in the organic mixture that causes the element deterioration, so the higher the degree of vacuum is, the better. However, considering the manufacturing cost, etc., the degree of vacuum is 10 ^−7. It is 10 ^{-10 -10} Torr, preferably 10 ^{-9 -10 -10} Torr. Further, although the above organic layer is compressed and pressed by two electrode substrates, the pressure is preferably in the range of 3 to 10 kg / cm ² from a practical viewpoint.

Further, in the organic EL device of the present invention, the periphery of the organic layer sandwiched between the two electrode substrates is sealed with a sealant. This encapsulation protects the organic layer from the effects of atmospheric oxygen and improves the emission lifetime. Examples of the sealing agent include ultraviolet curable resin, polyethylene, polypropylene, polystyrene, epoxy resin, silicone resin, epoxy silicon resin, fluororesin and the like.

In the present invention, the transparent or semi-transparent electrode substrate is provided with a dielectric multilayer mirror between the substrate and the electrode film. Thereby, a Fabry-Perot type optical resonator structure is formed, and electroluminescence is confined by the mirror, and as a result, an emission spectrum having an extremely narrow half width is obtained.

[0015]

According to the present invention, since an organic mixture containing an organic material having an electroluminescent function is heated and melted under a high vacuum degree, residual oxygen and water contained in the organic mixture are removed. To be done. Further, the organic mixture melted in a high vacuum is compressed and pressed by the electrode substrate, and the periphery of the obtained organic layer is sealed with a sealant, so that the contact with the outside air is blocked.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of an organic EL element according to the present invention. As shown in FIG. 1, an organic layer 4 made of an organic mixture containing an organic material having an electroluminescence function is a transparent electrode substrate 5 formed by vacuum-depositing an ITO film 2 on a transparent glass substrate 1. It is sandwiched by an electrode substrate 6 formed by co-evaporating a silver-magnesium alloy film 3 on a transparent glass substrate 1. If a polymer resin substrate made of polycarbonate, polyimide, polymethylmethacrylate or the like is used instead of the glass substrate, the weight of the organic EL element can be reduced.

Further, as described above, silver
Although a vapor deposited film of a magnesium alloy is used, a vapor deposited film of a metal having a low work function may be used. For example, a vapor deposited film of silver, gold, calcium, magnesium, indium / silver alloy, lithium / silver alloy, or the like is used as an electrode. You can use it. In particular, it is better to use a metal electrode having a low work function. In the present invention, an unstable metal work film having a small work function is formed in a chamber, and an organic layer is sandwiched between two electrode substrates in another chamber while the vacuum is not turned off. The membrane can always be isolated from oxygen.

FIG. 2 is a constitutional view showing a second embodiment of the organic EL element according to the present invention. Organic EL shown in FIG.
The element is different from the organic EL element of FIG. 1 in that the periphery of the organic layer 4 sandwiched by the electrode substrates 5 and 6 is sealed with a sealant 7 such as an ultraviolet curable resin. The film surface of the fluorescent dye or the organic semiconductor adsorbs oxygen immediately when it comes into contact with the atmosphere, and its electronic state changes. However, the structure as shown in FIG. 2 can remove the influence from the outside.

FIG. 3 is a constitutional view showing a third embodiment of the organic EL element according to the present invention. Organic EL shown in FIG.
In the element, an organic layer 4 is sandwiched by an electrode substrate 9 formed by forming a dielectric multilayer film mirror 8 on a glass substrate 1 and further forming an ITO film 2 thereon, and the electrode substrate 6. This is different from the organic EL device of FIG.

Various organic EL devices will be produced below, and the organic EL device of the present invention will be described more specifically. Example 1 The following structural formula (I) is used as a hole transport material.

Embedded image Polyvinylcarbazole (PVK, molecular weight 1
0000) 3 g, the following structural formula (II) as an electron transport material

Embedded image Phenyloxadiazole (OXD-7) 5 represented by
00 mg and the following structural formula (III) as a luminescent substance

Embedded image 20 mg of the quinacridone derivative (Qd) shown in (3) was put together in an agate mortar, pulverized, and ground until sufficiently homogenized in a solid state.

Next, one opening of the glass tube is sealed with a gas burner, the above-mentioned mixed powder is put into the other opening of the glass tube, and the glass tube is wrapped around the glass tube while being evacuated by a turbo molecular pump from the other opening. The gas contained in the powder was sufficiently degassed by heating with the heater ribbon.

FIG. 4 is a constitutional view showing a vacuum melting apparatus used for producing the organic EL element of the present invention. The apparatus shown in FIG. 4 is a chamber 31 which is a sealed room for covering the entire apparatus, copper holders 34 and 36 for fixing the electrode substrate, an elevating mechanism 32 for moving the copper holder 36 up and down, a heater 39, A copper block 40, a turbo molecular pump 37, and a rotary pump 38 are provided.

First, as shown in FIG. 5, a sufficiently cleaned transparent glass substrate with an ITO film (hereinafter referred to as an ITO electrode substrate) 33 (manufactured by Furuuchi Chemical Co., Ltd., resistivity 10 Ω /
□, size 20 mm × 20 mm, thickness 1.0 mm) was fixed to the lower holder 34, and the prepared mixed powder 30 was placed on the ITO electrode substrate 33. Then, a glass substrate with an Ag / Mg film (hereinafter referred to as an Ag / Mg electrode substrate) is obtained by co-evaporating silver (Ag) and magnesium (Mg) in a volume ratio of 1:20 on a glass substrate to a thickness of 100 nm. ) 35
Was fixed to the upper holder 36.

Turbo molecular pump 37 and rotary pump 38
By evacuation of the chamber 31 after baking, the degree of vacuum reached 5.0 × 10 ⁻⁸ Torr. Upper and lower copper holders 34, 36 and electrode substrate 3
PVKs 3 and 35 were heated to 150 ° C. by the heater 39 through the copper block 40 to sufficiently melt PVK. Next, as shown in FIG. 6, nitrogen gas is introduced into the bellows attached to the elevating mechanism 32, and the upper holder 36 is gradually pushed down by using the pressure difference, so that the two electrode substrates 33,
The 35 pieces were pressed against each other with a pressure of 3 kg / cm ² . In this way, a single-layer organic EL device was obtained. The distance between the two substrates 33 and 35 changes depending on the polymer concentration and viscosity and the pressure applied to the electrode substrate.
When the film thickness of the organic film of the device obtained in this example was measured by a film thickness meter, it was about 2 μm.

Subsequently, an ultraviolet curable resin (manufactured by ThreeBond Co., Ltd.) was applied to the side surfaces of the bonded electrode substrates, and the joint portion was irradiated with ultraviolet rays using a spot cure irradiation device (manufactured by Ushio Inc.). The ultraviolet curing resin was cured by the irradiation time of 30 seconds, and the two electrode substrates 33 and 35 were firmly fixed. When a lead wire was attached to the electrodes with a silver paste and a DC voltage of 12 V was applied between the electrodes, high-luminance light emission exceeding 1000 cd / m ² was obtained. The electroluminescence intensity was measured, and the operation was stable even after 3000 hours or more with the voltage applied at 8V. Although OXD-7 was used as the electron transport material in this example, the following structural formula (IV)

[Chemical 4] It is considered that similar results can be obtained by using an oxadiazole derivative such as phenyloxadiazole (OXD-1) represented by

Although PVK is used as the hole transport material in this embodiment, poly (3-alkylthiophene),
Polymer materials such as poly (naphthalene vinylene), poly (p-phenylene vinylene), poly (2-methoxy-5- (2′-ethylhexoxy) -phenylene vinylene), and poly (9-alkylfluorene) may be used. . In addition, although Qd is used as the light emitting material in this embodiment,
-Quinolinol / Al complex, 9,10 diphenylanthracene, perylene, tetraphenylbutadiene, perylenetetracarboxylic acid, etc. may be used.

Further, although the mixed powder is used in this embodiment, the mixed powder is dissolved in an organic solvent to form an organic film on the ITO substrate by a wet method such as a spin coating method, a dipping method, an LB method, or ITO. The electrode substrate may be attached after forming the organic vapor deposition film or the organic molecular beam vapor deposition film on the substrate.

Example 2 1 g of polymethylmethacrylate (PMMA, molecular weight 2000) as an electrically inactive binder polymer and the following structural formula (V) as a hole transport material.

Embedded image 100 mg of arylamine derivative (PDA) represented by
And the following structural formula (VI) as an electron transport material

[Chemical 6] A mixed powder of 200 mg of an aluminum quinolinol complex (Alq3, manufactured by Dojindo Kagaku Co., Ltd.) shown in 1 was prepared by the same operation as in Example 1 and placed on an ITO electrode substrate.

Next, the Ag / Mg electrode substrate and the ITO electrode substrate are fixed at a fixed interval and fixed, and the degree of vacuum is 8.0 × 10.
^A vacuum was applied until the pressure reached ^-8 Torr. Further, in the same manner as in Example 1, the upper and lower holders and the electrode substrate were heated to 130 ° C. through the copper block by the heater. When the PMMA was in a molten state, the two electrodes were laminated in the same manner as in Example 1. The distance between the electrode substrates was adjusted to 1 μm with a metal spacer. In this way, a single-layer type organic EL device using no luminescent substance was produced. For the organic EL device manufactured by the above manufacturing method,
When a DC voltage of 10 V is applied in the same manner as in Example 1,
Green emission from Alq3 of about 800 cd / m ² was obtained. In addition, the emission life when an applied voltage of 8 V is 25
It was over 00 hours. It is considered that white light can be obtained by sandwiching an organic layer prepared by mixing red, blue, and green dyes such as coumarin dye, quinadrine, and squarylium with the above mixed powder between electrode substrates. Although PDA was used as the hole transport material in this example, a triphenylamine derivative may be used.

Example 3 PV represented by the above structural formula (I) as a hole transport material
A mixed powder was prepared in the same manner as in Example 1, except that K 3 g, 500 mg of Alq3 represented by the above structural formula (VI) as an electron transport material, and 10 mg of Qd represented by the above structural formula (III) as a light emitting substance were processed. Then, the mixed powder was sandwiched between electrode substrates under the same conditions as in Example 1, and a single-layer organic EL device was produced by a vacuum melting method. When a DC voltage of 15 V was applied to the obtained organic EL device in the same manner as in Example 1, light emission of 500 cd / m ² was obtained. In addition, the light emission lifetime when an applied voltage of 10 V was 2500 hours or more.

Example 4 In this example, a dielectric multilayer film mirror and an I
An organic film containing an organic material having an electroluminescent function was sandwiched between an electrode substrate provided with a TO electrode and a metal electrode substrate, and heated under vacuum to melt the polymer layer, thereby producing an element. Specifically, a disk-shaped glass substrate (diameter 30
(mm, thickness 3 mm), 19 layers of TiO ₂ and SiO ₂ were alternately laminated on one surface, and an AR-coated dielectric multilayer mirror (manufactured by Shonan Optical Film Laboratory) was used on the opposite substrate surface. The reflectance of this mirror is 3 to 5% in the wavelength region of 200 nm to 450 nm, and 9 in the wavelength region of 500 nm to 600 nm.
9%. Then, an ITO film was formed as a transparent electrode on the surface of the dielectric multilayer film mirror by a sputtering method.

PVK 3g represented by the above structural formula (I) as a hole transport material, Alq3 500 mg represented by the above structural formula (VI) as an electron transport material, and Qd 10 mg represented by the above structural formula (III) as a luminescent substance. A mixed powder was prepared in the same manner as in Example 1. continue,
The ITO electrode substrate provided with the dielectric multilayer mirror and the Al electrode substrate were attached to the upper and lower metal holders, and the first embodiment was prepared.
Similarly, the above mixed powder is placed on an ITO electrode substrate,
Under a vacuum degree of 8.0 × 10 ⁻⁸ Torr, the Al electrode substrate was pressed against the ITO electrode substrate by heating to 150 ° C. with a heater to fabricate a single-layer organic EL device. When a DC voltage of 15 V was applied to the obtained organic EL device in the same manner as in Example 1, the optical confinement effect between the dielectric mirror and the metal mirror resulted in a narrow emission spectrum width of 500 cd / m ² having a peak at 500 nm. The green emission of was observed.

[0033]

According to the present invention, microcrystallization can be suppressed by using a polymer material that forms a stable amorphous film or by dispersing an electroluminescent material in the polymer material. Since an organic mixture containing an organic material having an electroluminescent function is heated and melted under a high degree of vacuum, residual oxygen, water and the like contained in the organic mixture are removed. As a result, oxygen in the atmosphere is not adsorbed on the fluorescent dye or the organic semiconductor, and it is possible to prevent the electronic states of these from changing. The organic mixture melted in a high vacuum is compressed and pressed by the electrode substrate, and the periphery of the obtained organic layer is sealed with a sealant, so that contact with the outside air is blocked and the light emission life can be extended. . Further, as compared with the organic vapor deposition method, red, blue, and green fluorescent dyes such as coumarin dye, quinadrine, and squarylium can be easily doped into the light emitting layer, and white light can be easily obtained. Therefore, the organic EL element of the present invention is a backlight of a liquid crystal display,
It can be used for lighting equipment, interior lighting equipment and the like.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an organic EL element according to the present invention.

FIG. 2 is a constitutional view showing a second embodiment of the organic EL element according to the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the organic EL element according to the present invention.

FIG. 4 is a configuration diagram showing a manufacturing apparatus used for manufacturing an organic EL element according to the present invention.

FIG. 5 is a diagram showing a state in which an organic mixed powder is placed on an electrode substrate.

FIG. 6 is a diagram showing a state in which a molten organic mixed powder is compressed and pressed and sandwiched between electrode substrates.

[Explanation of symbols]

 1 glass substrate 2 ITO film 3 silver-magnesium alloy film 4 organic layer 5 transparent electrode substrate 6 electrode substrate

Claims (6)

[Claims] 1. An organic layer made of an organic mixture containing an organic material having an electroluminescent function is heated to a temperature at which the organic mixture is melted under a high degree of vacuum and a pressure is applied, and at least one of them is transparent. Alternatively, an organic EL element characterized by being sandwiched between two semitransparent electrode substrates. 2. The degree of vacuum is 10 ⁻⁷ to 10 ⁻¹⁰ Torr.
The organic EL device according to claim 1, wherein 3. The organic EL device according to claim 1, wherein the pressure is 3 to 10 kg / cm ² . 4. The organic EL element according to claim 1, wherein a periphery of the organic layer sandwiched between the two electrode substrates is sealed with a sealant. 5. The organic EL device according to claim 1, wherein the transparent or semitransparent electrode substrate has a dielectric multilayer mirror between the substrate and the electrode. 6. An organic mixture containing an organic material having an electroluminescence function is heated under a high degree of vacuum at a temperature at which the organic mixture melts or higher, and at least one of the molten organic mixtures is transparent or translucent. A method for manufacturing an organic EL element, characterized in that an organic layer is formed by sandwiching the two electrode substrates while applying pressure.