JP6262935B2 - Organic electroluminescence device - Google Patents

Description

  The present invention relates to an organic electroluminescent device.

An organic electroluminescent element (organic EL element) is expected as a new light emitting element applicable to a display device or illumination.

An organic EL element has a structure in which one or a plurality of organic compounds containing a light-emitting organic compound is sandwiched between an anode and a cathode, and holes injected from the anode and electrons injected from the cathode are recombined. The light-emitting organic compound is excited using the energy of time to obtain light emission. The organic EL element is a current-driven element, and the light emission intensity is proportional to the injected current. In order to utilize the flowing current more efficiently, various element structures have been improved.

The most basic and extensively studied structure of the organic EL element is that of a three-layer structure proposed by Adachi et al. (Non-patent Document 1), in which a hole transport layer and a light emitting layer are provided between an anode and a cathode. The structure is such that the electron transport layer is sandwiched in this order. Since this proposal, the organic EL element has been based on a three-layer structure, and many studies have been made with the aim of improving performance such as efficiency and lifetime.

By the way, organic EL elements are generally easily deteriorated by oxygen and water, and strict sealing is indispensable in order to prevent these intrusions. The cause of the deterioration is that the materials that can be used as the cathode are limited to those with a small work function, such as alkali metals and alkali metal compounds, due to the ease of electron injection into the organic compounds, and the organic compounds used The main reason for this is that it itself easily reacts with oxygen and water. Strict sealing impairs the features such as low cost and flexibility that organic EL elements were considered to have superiority to other light emitting elements in the early stages of development.

Morii et al. Of the present inventors have proposed a light-emitting element that can be used without sealing (Patent Document 1). In this element, by changing the hole transport layer and the electron transport layer to inorganic oxides, it became possible to use FTO or ITO, which are conductive oxide electrodes, as the cathode, and gold as the anode. Since it is not necessary to use a metal having a small work function such as an alkali metal or an alkali metal compound, it is possible to emit light without strict sealing. That is, the organic-inorganic hybrid type electroluminescent device (HOILED device) is completely different from the conventional organic EL device.
As described in Patent Document 1, the basic structure of the HOILED element is a hole injecting metal oxide layer and an electron injecting metal between the anode and the organic compound layer and between the cathode and the organic compound layer, respectively. It consists of an oxide layer. Preferably, the hole injecting metal oxide layer is made of vanadium oxide or molybdenum oxide, and the electron injecting oxide layer is made of titanium oxide.

Among these, various studies have been made on the electron injecting metal oxide layer, and light emission has been confirmed even in an element using zinc oxide, zirconium oxide, magnesium oxide, hafnium oxide, and the like (Non-Patent Documents 2, 3, and 4). .

In addition, providing a hole blocking metal compound layer between the electron injecting metal oxide layer and the organic compound layer has been studied. Patent Document 2 reports that the efficiency is improved by a method of forming a cesium compound layer as a hole blocking metal compound layer on a titanium oxide layer which is an electron injecting metal oxide layer. In addition, the cesium compound layer described in Patent Document 2 is formed by depositing cesium carbonate by vacuum deposition and then exposed to the atmosphere. The chemical state is unknown, and any of cesium carbonate, cesium hydroxide, cesium oxide, or these It is supposed to be a mixture of Cesium carbonate deliquesces to produce cesium hydroxide, while cesium hydroxide reacts with carbon dioxide to produce cesium carbonate. On the other hand, cesium oxide reacts very violently with water to produce cesium hydroxide. From these facts, it can be inferred that the cesium compound layer described in Patent Document 2 will be mainly composed of a mixture of cesium carbonate and cesium hydroxide. A HOILED element using a cesium compound layer is known to have a problem in that it has excellent initial characteristics but a short driving life.

As the organic compound layer, poly (9,9-dioctylfluorene-alt-benzothiadiazole) that emits green light has been mainly studied. As an example of examining other emission colors, Non-Patent Document 3 describes the emission characteristics of blue, red, and green polymers in an element using zirconium oxide as an electron injecting metal oxide layer. Only the light emission starting voltage is high and the efficiency is low. As described above, the reported HOILED elements (particularly blue light emitting elements) have high driving voltage and low efficiency, and are not practically sufficient.

JP 2007-53286 A JP 2009-70954 A

Japan Journal of Applied Physics, 27 (1988) L269. Applied Physics Letters 91, 223501 (2007). Advanced Materials, 2009, 21, 3475. Journal of Materials Chemistry, 2010, 20, 4047.

  An object of the present invention is to provide an organic electroluminescent device exhibiting high efficiency and having a long driving life.

As a result of intensive studies, the present inventors have found that the above-described problems can be solved by arranging a layer containing a laminated oxide thin film as an electron injection layer of an organic electroluminescence device, and the present invention has been completed.
That is, the present invention provides [1] an anode and a cathode, one or more organic compound layers sandwiched between the anode and the cathode, and between the anode and the organic compound layer and / or the cathode. It is an organic electroluminescent element characterized by having a laminated metal oxide thin film layer between the organic compound layers. [2] Moreover, the organic electroluminescent element of the present invention comprises an anode and a cathode, one or more organic compound layers sandwiched between the anode and the cathode, and between the cathode and the organic compound layer. Furthermore, it is preferable to have a laminated metal oxide thin film layer. [3] Furthermore, in the organic electroluminescent element of the present invention, at least one of the layers constituting the laminated metal oxide layer is made of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, or zinc oxide. It is desirable to include a metal oxide selected from the group consisting of [4] Further, in the organic electroluminescent element of the present invention, among the layers constituting the laminated metal oxide layer, the layer in contact with the organic compound layer is magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, It is desirable to include a metal oxide selected from the group consisting of titanium oxide and zinc oxide. [5] Furthermore, the present invention is an illumination device, [6] and a display device, each including the above-described organic electroluminescent element.

According to the present invention, it is possible to provide an organic thin film light emitting element with high efficiency and a long driving life, and an illumination device and a display device including the organic thin film light emitting device.

1 is a cross-sectional view of an embodiment of an organic electroluminescent device according to the present invention having a HOILED structure. It is a graph which shows the voltage-luminance characteristic of the organic electroluminescent element created in Example 1 and Comparative Examples 1-2. It is a graph which shows the current density-current efficiency characteristic of the organic electroluminescent element created in Example 1 and Comparative Examples 1-2. It is a graph which shows the lifetime characteristic of the organic electroluminescent element created in Example 2 and Comparative Example 3.

Hereinafter, the organic electroluminescence device of the present invention will be described in detail.

The organic electroluminescent device of the present invention includes an anode and a cathode, one or more organic compound layers sandwiched between the anode and the cathode, and between the anode and the organic compound layer and / or the cathode. And a laminated metal oxide thin film layer between the organic compound layer and the organic compound layer.

The laminated metal oxide thin film layer used in the present invention is a semiconductor or insulator laminated thin film in which two or more kinds of metal oxide films are laminated. Metal elements constituting the metal oxide include magnesium, calcium, strontium, barium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, zinc, cadmium , Aluminum and silicon. Among these, at least one of the layers constituting the laminated metal oxide layer contains a metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide. Preferably, among the layers constituting the laminated metal oxide layer, the layer in contact with the organic compound layer is selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide. It is desirable to include a metal oxide.

Examples of the laminated metal oxide thin film layer include titanium oxide / zinc oxide, titanium oxide / magnesium oxide, titanium oxide / zirconium oxide, titanium oxide / aluminum oxide, titanium oxide / hafnium oxide, titanium oxide / silicon oxide, and zinc oxide. / Magnesium oxide, zinc oxide / zirconium oxide, zinc oxide / hafnium oxide, zinc oxide / silicon oxide, etc., or titanium oxide / zinc oxide / magnesium oxide, titanium oxide / zinc oxide / zirconium oxide, titanium oxide Examples include a three-layer structure such as / zinc oxide / aluminum oxide, titanium oxide / zinc oxide / hafnium oxide, and titanium oxide / zinc oxide / silicon oxide.

When the laminated metal oxide thin film layer is formed between a cathode and an organic compound layer, the layer closest to the cathode among the plurality of laminated metal oxide thin film layers is titanium, vanadium, molybdenum, tungsten , Iron, cobalt, copper, zinc, cadmium oxide layer, the layer closest to the organic compound layer is magnesium, calcium, strontium, barium, zirconium, hafnium, niobium, tantalum, chromium, A layer of any of manganese, nickel, aluminum, and silicon is preferable. With such a layer structure, electron injection from the cathode to the organic compound and blocking of holes flowing from the organic compound are compatible, and high luminance and efficiency can be realized.

In the present invention, an object having a sheet resistance lower than 100Ω / □ is classified as a conductor, and an object having a sheet resistance higher than 100Ω / □ is classified as a semiconductor or an insulator. Therefore, ITO (tin-doped indium oxide), ATO (antimony-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), FTO (fluorine-doped indium oxide), etc., known as transparent electrodes The thin film does not correspond to one layer constituting the laminated metal oxide thin film layer of the present invention because it has high conductivity and is not included in the category of a semiconductor or an insulator.

The thickness of each thin film constituting the laminated metal oxide thin film layer is acceptable from about 1 nanometer to several micrometers, but in order to obtain an organic electroluminescent device that can be driven at a low voltage, it is 1 nanometer to 100 nanometer. The degree is preferred.

A method for producing each thin film layer constituting the laminated metal oxide thin film layer is not particularly limited, and a known method can be used as appropriate, but a sputtering method, a vacuum deposition method, a sol-gel method, a spray pyrolysis (SPD) method can be used. Examples include an atomic layer deposition (ALD) method and a chemical vapor deposition (CVD) method. These methods are preferably selected according to the characteristics of the material of each thin film layer, and the production method may be different for each layer.

As the anode and cathode used in the present invention, known conductive materials can be used as appropriate, but at least one of them is preferably transparent for light extraction. Examples of known transparent conductive materials include ITO (tin-doped indium oxide), ATO (antimony-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), and FTO (fluorine-doped indium oxide). Is raised. Examples of the opaque conductive material include calcium, magnesium, aluminum, tin, indium, copper, silver, gold, and alloys thereof.

As the organic compound layer used in the present invention, known organic low molecular weight materials, organometallic complexes, polymer materials and the like can be used as appropriate, and they can be used in combination as necessary. At least one of the organic compounds is selected from light emitting materials.

Examples of the polymer light-emitting material include polyacetylene compounds such as trans-type polyacetylene, cis-type polyacetylene, poly (di-phenylacetylene) (PDPA), poly (alkyl, phenylacetylene) (PAPA), and poly (para-para-). Fenvinylene) (PPV), poly (2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly (para-phenvinylene) (CN-PPV), poly (2-dimethyloctyl) Polyparaphenylene vinylene compounds such as silyl-para-phenylene vinylene (DMOS-PPV), poly (2-methoxy, 5- (2′-ethylhexoxy) -para-phenylene vinylene) (MEH-PPV), poly ( 3-alkylthiophene) (PAT), poly (oxypropylene) Polythiophene compounds such as riol (POPT), poly (9,9-dialkylfluorene) (PDAF), poly (dioctylfluorene-alt-benzothiadiazole) (F8BT), α, ω-bis [N, N′-di (Methylphenyl) aminophenyl] -poly [9,9-bis (2-ethylhexyl) fluorene-2,7-zyl] (PF2 / 6am4), poly (9,9-dioctyl-2,7-divinylenefluore Polyfluorene compounds such as nyl-ortho-co (anthracene-9,10-diyl)), poly (para-phenylene) (PPP), poly (1,5-dialkoxy-para-phenylene) (RO-PPP) ) Polyparaphenylene compounds such as poly (N-vinylcarbazole) (PVK) Polysilane compounds such as poly (methylphenylsilane) (PMPS), poly (naphthylphenylsilane) (PNPS), poly (biphenylylphenylsilane) (PBPS), and Japanese Patent Application Nos. 2010-230995 and 2011-2011 Examples thereof include boron compound polymer materials described in No. 6457.

On the other hand, as a low-molecular light-emitting material, for example, a tricoordinate iridium complex having 2,2′-bipyridine-4,4′-dicarboxylic acid as a ligand, factory (2-phenylpyridine) iridium ( Ir (ppy) ₃ ), 8-hydroxyquinoline aluminum (Alq ₃ ), tris (4-methyl-8 quinolinolate) aluminum (III) (Almq ₃ ), 8-hydroxyquinoline zinc (Znq ₂ ), (1,10- Phenanthroline) -tris- (4,4,4-trifluoro-1- (2-thienyl) -butane-1,3-dionate) europium (III) (Eu (TTA) ₃ (phen)), 2, 3, Various metal complexes such as 7,8,12,13,17,18-octaethyl-21H, 23H-porphine platinum (II), distyrylbenzene ( SB), benzene compounds such as diamino distyrylbenzene (DADSB), naphthalene compounds such as naphthalene and nile red, phenanthrene compounds such as phenanthrene, chrysene, chrysene compounds such as 6-nitrochrysene, perylene N, N′-bis (2,5-di-t-butylphenyl) -3,4,9,10-perylene-di-carboximide (BPPC), coronene such as coronene Compound, anthracene, anthracene compound such as bisstyrylanthracene, pyrene compound such as pyrene, 4- (di-cyanomethylene) -2-methyl-6- (para-dimethylaminostyryl) -4H-pyran (DCM) ) Pyran compounds such as acridine, acridine compounds such as acridine, Stilbene compounds such as tilbene, thiophene compounds such as 2,5-dibenzoxazolethiophene, benzoxazole compounds such as benzoxazole, benzimidazole compounds such as benzimidazole, 2,2 ′-(para- Benzothiazole compounds such as phenylenedivinylene) -bisbenzothiazole, butadiene compounds such as bistyryl (1,4-diphenyl-1,3-butadiene), tetraphenylbutadiene, naphthalimide compounds such as naphthalimide , Coumarin compounds such as coumarin, perinone compounds such as perinone, oxadiazole compounds such as oxadiazole, aldazine compounds, 1,2,3,4,5-pentaphenyl-1,3- Cyclopentadiene (PPC ), Cycloquinadiene compounds such as quinacridone and quinacridone red, pyridine compounds such as pyrrolopyridine and thiadiazolopyridine, 2,2 ′, 7,7′-tetraphenyl-9,9 Spiro compounds such as' -spirobifluorene, metal or metal-free phthalocyanine compounds such as phthalocyanine (H ₂ Pc) and copper phthalocyanine, and Japanese Patent Application Laid-Open No. 2009-155325, Japanese Patent Application No. 2010-230995 and Japanese Patent Application Examples include boron compound materials described in 2011-6458.

The method for forming the organic compound layer is not particularly limited, and a known method can be appropriately used according to the characteristics of the material. However, when it can be applied as a solution, a spin coat method, a slit coat method, a dip coat method, a spray Examples include a coating method and a casting method. Among these, the spin coat method and the slit coat method are preferable because the film thickness can be more easily controlled. When not applied or when the solvent solubility is low, a vacuum deposition method, an ESDUS (Evaporative Spray Deposition Ultra-dilute Solution) method, or the like can be cited as a suitable example.

For reasons such as further improving the characteristics of the organic electroluminescent element, there may be layers other than the above-described layers as necessary. Examples of such a layer include an electron injection layer, a hole blocking layer, a hole injection layer, and an electronic element layer, and known materials can be appropriately used.

When the organic electroluminescent element to which the present invention is applied is a HOILED element, it is desirable to provide a hole injection layer between the organic compound layer and the anode. Examples of the material used for the hole injection layer include molybdenum oxide, tungsten oxide, vanadium oxide, and rhenium oxide, with molybdenum oxide being most preferred.

The electroluminescent element of the present invention may be sealed if necessary. As the sealing step, a known method can be used as appropriate. For example, a method of adhering a sealing container in an inert gas, a method of forming a sealing film directly on the organic EL element, or the like can be given. In addition to these, a method of enclosing a moisture absorbing material may be used in combination.

The electroluminescent element of the present invention can emit light by applying a voltage (usually 15 volts or less) between the anode and the cathode. Normally, a DC voltage is applied, but an AC component may be included.

The electroluminescent element of the present invention can be used as a light emitting site of illumination or a display device. The light emission color can be changed by appropriately selecting the material of the organic compound layer, and a desired light emission color can be obtained by using a color filter or the like together.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, the scope of the present invention is not limited only to these Examples.

(Synthesis of blue light-emitting polymer)
(Synthesis Example 1)
Under a nitrogen atmosphere, 200 ml of diethyl ether was added to 1-bromo-3,5-bis (trifluoromethyl) benzene (14.8 g, 50.3 mmol), cooled to −78 ° C., and then a normal butyl lithium hexane solution (1 .65M, 30.9 ml, 50.9 mmol) was added dropwise, and the mixture was stirred at -78 ° C for 1 hour. Further, a solution of zinc chloride in diethyl ether (1M, 24.3 ml, 24.3 mmol) was added dropwise with stirring. After completion of dropping, the mixture was stirred at room temperature for 1 hour. Toluene solution (200 mL) containing 5-bromo-2- (4-bromo-2-dibromoborylphenyl) pyridine (5.6 g, 11.6 mmol) was added thereto, and the mixture was stirred with heating at 85 ° C. for 15 hours. After cooling to room temperature, the reaction solution was added to ice water and extracted with chloroform. The organic phase was washed with saturated brine, dried over sodium sulfate and filtered. The filtrate was concentrated with a rotary evaporator and then purified by silica gel chromatography (hexane: dichloromethane = 1: 2) to obtain the following formula (1);

Was obtained in a yield of 69%.
The obtained boron-containing compound (1) (187.2 mg, 0.25 mmol), a fluorene compound represented by the following formula (2) (140.2 mg, 0.251 mmol), tetrakistriphenylphosphine palladium (2.9 mg, 0.0025 mmol) was dissolved in 3 ml of toluene and stirred at room temperature for 10 minutes under a nitrogen flow.

To this was added an aqueous solution prepared by dissolving ammonium carbonate (240.4 mg, 0.8 mmol) in 0.75 ml of distilled water, and the mixture was further stirred at room temperature for 20 minutes under a nitrogen flow to complete devolatilization. This was heated and stirred at 115 ° C. for 17 hours under reflux, and bromobenzene (39.3 mg, 0.25 mmol) was added for end-capping, followed by stirring for 1 hour, and phenylboronic acid (30.5 mg, 0.25 mmol) was further added. added. The solution was allowed to cool to room temperature, and the toluene solution was separated and washed once with hydrochloric acid and twice with pure water, and the organic layer was concentrated to about several ml. The concentrated solution was dropped into 300 ml of methanol and stirred for 10 minutes as it was, and the resulting precipitate was collected by filtration. By repeating the same purification process three times in total and drying the solid under reduced pressure, the following formula (3);

The blue light emitting polymer represented by this was obtained. The weight average molecular weight in terms of polystyrene by gel permeation chromatography (tetrahydrofuran solvent) was 71,000.

(Creation of organic electroluminescence device)
Example 1
[1] A commercially available transparent glass substrate with an ITO electrode layer having an average thickness of 0.7 mm was prepared. At this time, an ITO electrode patterned to have a width of 2 mm was used. This substrate was subjected to ultrasonic cleaning in acetone and isopropanol for 10 minutes, and then boiled in isopropanol for 5 minutes. This substrate was taken out from isopropanol, dried by nitrogen blowing, and UV ozone cleaning was performed for 20 minutes.
[2] This substrate was fixed to a substrate holder of a Miratron sputtering apparatus having a titanium metal target. After reducing the pressure to about 1 × 10 ⁻⁴ Pa, sputtering was performed in a state where argon and oxygen were introduced to form a titanium oxide layer having a thickness of about 10 nm. At this time, a metal mask was used together so that titanium oxide was not formed on a part of the ITO electrode for electrode extraction.
[3] This substrate was fixed to a substrate holder of a Miratron sputtering apparatus having a zinc metal target. After reducing the pressure to about 1 × 10 ⁻⁴ Pa, sputtering was performed in a state where argon and oxygen were introduced to form a zinc oxide layer having a thickness of about 1 nm. At this time, a metal mask was used in combination so that a portion of the ITO electrode was not deposited with zinc oxide for electrode extraction.
[4] Next, 1 mL of a 1.2 wt% tetrahydrofuran solution of the blue light-emitting polymer (3) prepared in Synthesis Example 1 was prepared. The prepared substrate with an oxide thin film layer was set on a spin coater. A blue light emitting polymer solution was dropped on the substrate and rotated at 1600 rpm for 30 seconds to form an organic compound layer having a thickness of about 100 nm. This was moved into a glove box in an argon atmosphere, and heated at 200 ° C. for 1 hour using a hot plate to remove the residual solvent in the organic compound layer.
[5] The substrate formed up to the organic compound layer was fixed to a substrate holder of a vacuum deposition apparatus. Molybdenum trioxide was placed in an alumina crucible and set in the first vapor deposition source. At the same time, gold was put in an alumina crucible and set in the second vapor deposition source. The inside of the vacuum deposition apparatus was depressurized to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, deposition to a gold thickness of 20 nm, was prepared an organic electroluminescent element. At this time, a vapor deposition surface was formed into a strip shape having a width of 2 mm using a stainless steel vapor deposition mask. That is, the light emitting area of the produced organic electroluminescent element was 4 mm ² .

(Comparative Example 1)
An organic electroluminescence device having a titanium oxide single layer as an oxide thin film layer was produced in the same manner except that the step [3] in Example 1 was omitted.

(Comparative Example 2)
An organic electroluminescent device having a zinc oxide single layer as an oxide thin film layer was obtained in the same manner except that step [2] in Example 1 was omitted and the thickness of zinc oxide was changed to 2 nm in step [3]. Created.

(Example 2)
[1] A commercially available transparent glass substrate with an ITO electrode layer having an average thickness of 0.7 mm was prepared. At this time, an ITO electrode patterned to have a width of 2 mm was used. This substrate was subjected to ultrasonic cleaning in acetone and isopropanol for 10 minutes, and then boiled in isopropanol for 5 minutes. This substrate was taken out from isopropanol, dried by nitrogen blowing, and UV ozone cleaning was performed for 20 minutes.
[2] This substrate was fixed to a substrate holder of a Miratron sputtering apparatus having a zinc metal target. After reducing the pressure to about 1 × 10 ⁻⁴ Pa, sputtering was performed in a state where argon and oxygen were introduced to form a zinc oxide layer having a thickness of about 2 nm. At this time, a metal mask was used in combination so that a portion of the ITO electrode was not deposited with zinc oxide for electrode extraction.
[3] A mixed solution of magnesium acetate in 1% water-ethanol (1: 3 by volume) was prepared. The substrate prepared in step [2] was washed again in the same manner as in step [1]. The cleaned substrate with a zinc oxide thin film was set on a spin coater. A magnesium acetate solution was dropped on the substrate and rotated at 1300 rpm for 60 seconds. The magnesium oxide layer was formed by baking this for 2 hours with the hotplate set to 400 degreeC in air | atmosphere.
[4] Next, 1 mL of a 1.2 wt% tetrahydrofuran solution of the blue light-emitting polymer (3) prepared in Synthesis Example 1 was prepared. The prepared substrate with an oxide thin film layer was set on a spin coater. A blue light emitting polymer solution was dropped on the substrate and rotated at 1600 rpm for 30 seconds to form an organic compound layer having a thickness of about 100 nm. This was moved into a glove box in an argon atmosphere, and heated at 200 ° C. for 1 hour using a hot plate to remove the residual solvent in the organic compound layer.
[5] The substrate formed up to the organic compound layer was fixed to a substrate holder of a vacuum deposition apparatus. Molybdenum trioxide was placed in an alumina crucible and set in the first vapor deposition source. At the same time, gold was put in an alumina crucible and set in the second vapor deposition source. The inside of the vacuum deposition apparatus was depressurized to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, deposition to a gold thickness of 20 nm, was prepared an organic electroluminescent element. At this time, a vapor deposition surface was formed into a strip shape having a width of 2 mm using a stainless steel vapor deposition mask. That is, the light emitting area of the produced organic electroluminescent element was 4 mm ² .

(Comparative Example 3)
An organic electroluminescence device having a cesium compound layer on a zinc oxide thin film layer was prepared in the same manner except that the next step [3 ′] was performed instead of the step [3] in Example 2.
[3 ′] The substrate formed up to the oxide thin film layer was fixed to a substrate holder of a vacuum deposition apparatus. Cesium carbonate was placed in an alumina crucible and set in a vapor deposition source. The inside of the vacuum evaporation apparatus was depressurized to about 1 × 10 ⁻⁴ Pa, and cesium carbonate was evaporated to a film thickness of 3 nm. This substrate was left in the atmosphere for 12 hours to form a cesium compound layer.

(Created organic electroluminescence device)
The configurations of the organic electroluminescent elements prepared in Examples 1 and 2 and Comparative Examples 1 to 3 are summarized as shown in the following table.

(Measurement of light emission characteristics of organic electroluminescence device)
Voltage application to the device and current measurement were performed using a “2400 type source meter” manufactured by Keithley. Luminance was measured with “BM-7” manufactured by Topcon Corporation. FIG. 2 shows voltage-luminance characteristics and current density-current efficiency characteristics when the organic electroluminescent elements prepared in Example 1 and Comparative Examples 1-2 were applied with a DC voltage of −4 V to 15 V in an argon atmosphere. Each is shown in FIG.
From FIG. 2, the organic electroluminescent element of Example 1 using the laminated oxide thin film of the present invention emits light from a voltage lower than that of the organic electroluminescent elements of Comparative Examples 1 and 2 using a single layer oxide thin film. It is clear.
Furthermore, from FIG. 3, the organic electroluminescent element of Example 1 using the laminated oxide thin film of the present invention has higher current efficiency than the organic electroluminescent elements of Comparative Examples 1 and 2 using a single layer oxide thin film. It is clear to show. However, as is clear from FIG. 2, the organic electroluminescence device of Comparative Example 1 did not emit light at all in the measured voltage range, so that the current efficiency was not measurable, and is omitted from the plot of FIG.

(Measurement of lifetime characteristics of organic electroluminescent devices)
Application of voltage to the element and measurement of relative luminance were performed using an “organic EL lifetime measuring device” manufactured by System Giken. This device can measure relative luminance by a photodiode while automatically adjusting the voltage so that a constant current flows through the element. The current value was set for each element so that the luminance at the start of measurement was 100 cd / m ² . FIG. 4 shows the lifetime characteristics of the organic electroluminescent elements prepared in Example 2 and Comparative Example 3.
From FIG. 4, the organic electroluminescent element of Example 2 using the laminated oxide thin film of the present invention has a longer lifetime than the organic electroluminescent element of Comparative Example 3 having a single-layer oxide thin film and a cesium compound layer. I understand.

The electroluminescent device of the present invention is a light-emitting device having a high efficiency and a long driving life, and the luminescent color can be changed by appropriately selecting the material of the organic compound layer. A luminescent color can also be obtained, and it can be suitably used as a light emitting part of illumination or a display device.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Cathode 3 ... Laminated metal oxide thin film layer 4 ... Organic compound layer 5 ... Hole injection metal oxide layer 6 ... Anode

Claims (5)

Two types are provided between an anode and a cathode, one or more organic compound layers sandwiched between the anode and the cathode, and an organic compound layer closest to the cathode among the cathode and the organic compound layer. It possesses more metal oxide film laminated metal oxide thin layer formed by laminating (except those containing molybdenum oxide on any layer),
Of the plurality of stacked metal oxide thin film layers, the layer closest to the cathode is an oxide layer of any of titanium, vanadium, tungsten, iron, cobalt, copper, zinc, and cadmium. Organic electroluminescent element characterized. At least one of the layers constituting the laminated metal oxide thin film layer includes a metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide. The organic electroluminescent element according to claim 1. The metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide and zinc oxide is a layer in contact with the organic compound layer among the layers constituting the laminated metal oxide thin film layer The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device comprises an object.   An illuminating device comprising the organic electroluminescent element according to claim 1.   A display device comprising the organic electroluminescent element according to claim 1.

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