WO2013027735A1

WO2013027735A1 - Organic electroluminescent element

Info

Publication number: WO2013027735A1
Application number: PCT/JP2012/071098
Authority: WO
Inventors: 洋一有元; 森井　克行; 威夫赤塚; 宗弘長谷川; 剛呉屋; 隼郷田
Original assignee: 株式会社日本触媒
Priority date: 2011-08-24
Filing date: 2012-08-21
Publication date: 2013-02-28

Abstract

Provided is an organic-inorganic hybrid organic electroluminescent element which has excellent brightness, luminous efficiency, and drive life. The organic electroluminescent element comprises a structure in which a plurality of layers are stacked between a positive pole and negative pole, characterized in that the organic electroluminescent element has one or a plurality of organic compound layers between the positive pole and negative pole and also has a layer including a plurality of metal species between the positive pole and the organic compound layer(s) and/or between the negative pole and the organic compound layer(s), and at least one of the plurality of metal species is a metal oxide.

Description

Organic electroluminescence device

The present invention relates to an organic electroluminescent device. More specifically, the present invention relates to an organic electroluminescent element that can be used as a display device such as a display unit of an electronic device, a lighting device, or the like.

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. An organic EL element is a current-driven element, and various element structures have been improved in order to more efficiently utilize a flowing current.

The structure of the organic EL element most fundamentally studied is a three-layer structure proposed by Adachi et al. (See Non-Patent Document 1), a hole transport layer between the anode and the cathode, The light emitting layer and the electron transport layer are sandwiched in this order. Since this proposal, organic EL elements have been based on a three-layer structure, and many studies have been conducted with the aim of improving performance such as efficiency and lifetime by sharing more roles. This basic idea stems from the fact that the injected electrons have a high energy at that time (in the electrode).
Therefore, the organic EL element is generally easily deteriorated by oxygen or 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 It is easy to react with oxygen and water. By applying strict sealing, the organic EL element is superior to other light emitting elements, but at the same time, the features such as low cost and flexibility are impaired.

In view of the above situation, Morii et al. Included in the present inventor have studied and proposed a light-emitting element that can be used without being sealed in principle, assuming an upcoming film element (Patent Document) 2). 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. As a result, it is not necessary to use a metal having a small work function such as an alkali metal or an alkali metal compound, and it is possible to emit light without strict sealing. That is, an organic-inorganic hybrid electroluminescent element (HOILED element) that is completely different from the conventional organic EL element is obtained.

As described in Patent Document 1, the basic structure of a HOILED element is a hole-injecting metal oxide layer and an electron-injecting metal made between an anode and an organic compound layer and between a cathode and an 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 elements using zinc oxide, zirconium oxide, magnesium oxide, hafnium oxide, and the like (see

Non-Patent Documents

2, 3, and 4). .) However, none of them has sufficient electron injection ability, and as a result, efficiency and lifetime are practically insufficient.

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. This fact can also be said to be evidence that the electron injection performance is insufficient. As a result, as expected, a HOILED element using a cesium compound layer is known to have a short driving life although it has excellent initial characteristics. From the above, in order to realize a highly efficient and long-lived HOILED element, it is necessary to improve the electron injection property so as not to impair the atmospheric stability.

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

As described above, various studies have been made on organic EL devices, and various studies have been conducted on the HOILED devices that can be used without sealing, as well as the constitution of the devices and the materials constituting each layer. However, the HOILED element is still not sufficient in terms of characteristics such as luminance, light emission efficiency, and driving life as compared with the conventional organic EL element. Originally, the organic electroluminescent element is thin, and when used as a display device, it is possible to display with high brightness and high definition compared with the liquid crystal and plasma display devices which are currently mainstream, compared with the liquid crystal display device. In addition, it has excellent features such as a wide viewing angle, so it is expected that it will be used as a display for TVs and mobile phones in the future. Improvement in the characteristics of HOILED elements that can dramatically reduce the structure has been rapidly demanded.

The present invention has been made in view of the above-described present situation, and an object thereof is to provide an organic-inorganic hybrid organic electroluminescent element that is excellent in luminance, luminous efficiency, and driving life.

The present inventor has made various studies on the configuration and materials used for the organic electroluminescent device. As a result, in the organic electroluminescent device having a structure in which a plurality of layers are laminated between the anode and the cathode, the organic electroluminescent device is provided between the anode and the cathode. It has one or more organic compound layers, and further includes a layer containing a plurality of metal species between the anode and the organic compound layer and / or between the cathode and the organic compound layer, and the plurality of metal species It has been found that an organic electroluminescent device having high luminance, high luminous efficiency, and long driving life can be obtained by having at least one of the metal oxides as a structure, and the present invention has been achieved. .

That is, the present invention is an organic electroluminescent device having a structure in which a plurality of layers are laminated between an anode and a cathode, and the organic electroluminescent device has one or more layers between the anode and the cathode. An organic compound layer, and a layer containing a plurality of metal species between the anode and the organic compound layer and / or between the cathode and the organic compound layer, wherein at least one of the plurality of metal species is An organic electroluminescent element characterized by being a metal oxide.
The present invention is described in detail below.
A combination of two or more preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

The organic electroluminescent element of the present invention includes an anode, a cathode, one or more organic compound layers, and a plurality of metal species, and at least one of the plurality of metal species is a metal oxide (hereinafter, Also referred to as a multiple metal species-containing layer).
The organic electroluminescent device of the present invention includes a plurality of metal species, and a layer in which at least one of the plurality of metal species is a metal oxide is provided between the anode and the organic compound layer and / or between the cathode and the organic compound layer. By having it in between, the movement of electrons and holes from the cathode and anode necessary for light emission can be promoted smoothly, so that excellent light emission efficiency can be shown, and as a result, the driving life is also long. is there.
The organic electroluminescent element of the present invention includes an anode, a cathode, one or more organic compound layers, and a plurality of metal species, and at least one of the plurality of metal species is a metal oxide. Other layers may be provided between these layers.

The multiple metal species-containing layer is preferably any of a mixed metal oxide layer, a laminated metal oxide layer, or a layer including a structure having a metal species on the metal oxide layer. When the multiple metal species-containing layer is any one of these, the organic electroluminescent element of the present invention is more excellent in luminous efficiency and driving life of the element.
Hereinafter, a mixed metal oxide layer, a stacked metal oxide layer, and a layer including a structure having a metal species on the metal oxide layer will be described in order.

<Mixed metal oxide layer>
The mixed metal oxide layer used in the present invention is a semiconductor or insulator thin film in which two or more kinds of metal elements are mixed with each other from the atomic level to the submicron level to form an oxide film. The mixed metal oxide included in the mixed metal oxide layer is (1) one in which two or more kinds of metal elements each form an oxide, and these two or more kinds of oxides are mixed, (2) described later. Any of one metal oxide having two or more kinds of metal elements as constituent elements, such as barium titanate, or a mixture of these may be used.

The metal elements forming the mixed metal oxide layer include magnesium, calcium, strontium, barium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper, It is preferably selected from the group consisting of zinc, cadmium, aluminum and silicon.
That is, the mixed metal oxide contained in the mixed metal oxide thin film layer preferably contains an oxide of at least two kinds of metal elements selected from these metal elements. When two kinds of metal elements are included, the combination is not particularly limited, but the first metal element selected from magnesium, calcium, strontium, barium, zirconium, hafnium, niobium, tantalum, chromium, manganese, nickel, aluminum, silicon And a combination of a second metal element selected from titanium, vanadium, molybdenum, tungsten, iron, cobalt, copper, zinc, and cadmium.

As an example of the mixed metal oxide thin film (layer), Applied Physics Letters, 83, 2010 (2003). Describes an oxide thin film in which zinc and magnesium are mixed at an atomic level. Journal of Physics D: Applied Physics, 42 (2009) 065421. Describes an oxide thin film in which cadmium and zinc are mixed at an atomic level. Further, a thin film of barium titanate, strontium titanate or the like also corresponds to the mixed metal oxide thin film layer of the present invention. As described above, the mixed metal oxide layer of the present invention desirably contains magnesium element.

In the mixed metal oxide thin film layer, the degree of mixing is preferably mixed at an atomic level, but the effect of the present invention can be obtained even when a segregation portion at a submicron level is formed.

As the mixing ratio of the metal elements contained in the mixed metal oxide layer, the number of metal atoms is 1 atomic% with respect to the total number of metal atoms contained in the mixed metal oxide layer even if the ratio of each metal element is the lowest. Preferably, it is preferably 10 atomic% or more.
More preferably, it is 20 atomic% or more.

The mixed metal oxide layer can have a thickness of about 1 nm to several μm, but is preferably about 1 nm to 100 nm for an organic electroluminescent device that can be driven at a low voltage.
The film thickness of the mixed metal oxide layer can be measured by a stylus profilometer or spectroscopic ellipsometry.

The mixed metal oxide layer may be formed by applying a metal oxide solution or dispersion and drying, or applying a solution or dispersion of a metal compound that is not an oxide, and applying the solution or dispersion. The metal compound in the solution may be oxidized to form a metal oxide, and the coating solution may be dried. In this case, the operation of oxidizing the metal compound and the operation of drying the coating solution may be performed separately or simultaneously.
A method for forming the mixed metal oxide layer is not particularly limited, and a known method can be used as appropriate, but a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, chemical vapor deposition ( CVD) method.

<Laminated metal oxide layer>
The laminated metal oxide 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.
As a metal element which comprises a metal oxide, the 1 type (s) or 2 or more types of the same element as the metal element which forms the mixed metal oxide layer mentioned above can be used. Among these metal element oxides, at least one of the layers constituting the laminated metal oxide layer is selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide. Among the layers constituting the laminated metal oxide layer, the layer in contact with the organic compound layer is preferably magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, zinc oxide. It is desirable to include a metal oxide selected from the group consisting of

Examples of laminated metal oxide layers 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 / oxide. In the case of a two-layer structure such as magnesium, zinc oxide / zirconium oxide, zinc oxide / hafnium oxide, zinc oxide / silicon oxide, titanium oxide / zinc oxide / magnesium oxide, titanium oxide / zinc oxide / zirconium oxide, titanium oxide / oxidation Examples include a three-layer structure of zinc / aluminum oxide, titanium oxide / zinc oxide / hafnium oxide, titanium oxide / zinc oxide / silicon oxide, and the like.

When the laminated metal oxide layer is formed between the cathode and the organic compound layer, the layer closest to the cathode among the plurality of laminated metal oxide 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, manganese, A layer of an oxide of nickel, aluminum, or 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.

The thickness of each thin film constituting the laminated metal oxide layer can be allowed to be about 1 nm to several μm, but is preferably about 1 nm to 100 nm in order to obtain an organic electroluminescent device that can be driven at a low voltage.
The film thickness of each thin film constituting the laminated metal oxide layer can be measured by a stylus type step meter or spectroscopic ellipsometry.

<Layer including structure having metal species on metal oxide layer>
In a layer including a structure having a metal species on the metal oxide layer, the structure having a metal species on the metal oxide layer is sufficient if the metal species exists on the metal oxide layer. The metal oxide layer may be entirely covered by the metal seed layer, or a part of the metal oxide layer may not be covered by the metal seed layer, and the metal seed may be formed on the metal oxide layer. It may be scattered. Moreover, as long as the structure which has a metal seed | species on a metal oxide layer is included, another layer may be further included and the thing of the structure where the metal seed | species was pinched | interposed into two metal oxide layers may be sufficient. .
The metal species may be a simple substance or a metal compound.

In the present invention, the layer including a structure having a metal species on the metal oxide layer is a layer having a magnesium compound layer between the metal oxide layer and the organic compound layer, or has a work function of 4.0 eV. It is preferable that the following metal simple substance or its oxide is a layer having a structure sandwiched between two layers of metal oxide. These layers will be described in order below.

<Layer having a magnesium compound layer between a metal oxide layer and an organic compound layer>
When the layer containing a structure having a metal species on the metal oxide layer is a layer having a magnesium compound layer between the metal oxide layer and the organic compound layer, the metal element that forms the metal oxide layer is One or more of the same elements as the metal elements forming the mixed metal oxide layer described above can be used. The metal oxide layer may be a single layer or a plurality of layers.
The magnesium compound layer is a layer containing at least one magnesium compound. Examples of the magnesium compound include magnesium oxide, magnesium carbonate, magnesium acetate, magnesium hydroxide, magnesium sulfate, magnesium nitrate, magnesium fluoride, magnesium chloride, odor Magnesium iodide, magnesium iodide, magnesium acetylacetonate, etc. are mentioned. The magnesium compound layer may be a simple substance, a mixture thereof, or a compound other than these. Note that in the case where there are a plurality of metal oxide layers, a magnesium compound layer may be provided between at least one of the metal oxide layers and the organic compound layer.

<A metal having a work function of 4.0 eV or less or a layer having a structure in which an oxide thereof is sandwiched between two layers of metal oxide>
In the following, a single metal having a work function of 4.0 eV or less, or an oxide thereof is also referred to as a metal species having a work function of 4.0 eV or less, or a single metal having a work function of 4.0 eV or less, or A layer having a structure in which an oxide is sandwiched between two layers of metal oxide is also referred to as a laminated metal compound layer.

The laminated metal compound layer has a structure in which a metal species having a work function of 4.0 eV or less is sandwiched between two layers of metal oxide. Here, the layer is sandwiched between two layers of metal oxide. In this structure, there is a layer formed by a metal species having a work function of 4.0 eV or less between two layers of metal oxide, and the two layers of metal oxide are separated by the layer. A structure in which two layers of oxide are not in direct contact may be formed, and a sea island structure in which a metal species having a work function of 4.0 eV or less is scattered on one layer of metal oxide is formed. As in the case of the metal oxide, there are a portion covered with a metal species having a work function of 4.0 eV or less and a portion not covered on one layer of the metal oxide. A structure in which one layer is covered with another metal oxide layer, i.e. There may be a structure such as a portion not covered with the following metal species 4.0eV are in contact two layers of metal oxides. Therefore, as long as a metal species having a work function of 4.0 eV or less exists between the two layers of the metal oxide, this corresponds to a structure sandwiched between the two layers of the metal oxide. What is important is that the metal compound having a work function of 4.0 eV or less is not in direct contact with the organic compound layer side, and is difficult to be deteriorated at the interface, while changing to an oxide in the metal oxide. The new electronic level that occurs is to act as an interpolated level of the surrounding metal oxide.
Thus, the presence of a metal species having a work function of 4.0 eV or less between the two layers of metal oxide makes the organic electroluminescent device have high luminance. Moreover, an organic electroluminescent element becomes the thing excellent in the drive life by having the laminated metal compound layer by which the metal seed | species whose work function is 4.0 eV or less was pinched | interposed between two layers of metal oxide.

As described above, the metal species having a work function of 4.0 eV or less may form a layer covering the entire metal oxide layer or may have a sea-island structure. It is preferable that 50% or more of the area is covered with a metal species having a work function of 4.0 eV or less. With such a ratio, the organic electroluminescent element is excellent in luminance. More preferably, 80% or more of the area of the metal oxide layer is covered with a metal species having a work function of 4.0 eV or less.
Further, in a portion covered with a metal species having a work function of 4.0 eV or less, the thickness of the metal species layer having a work function of 4.0 eV or less is preferably 5 nm or less. More preferably, it is 1 nm or less.
The thickness of the metal seed layer having a work function of 4.0 eV or less can be determined by measuring at the time of film formation with a crystal thickness meter using a value estimated from the measurement with a stylus type step gauge of the thick film.

As the metal element forming the metal oxide or sulfide layer, one or more of the same elements as the metal element forming the mixed metal oxide layer described above can be used.
The metal elements forming the two layers of metal oxide may be the same element or different.

At least one of the two metal oxide layers sandwiching a metal species having a work function of 4.0 eV or less is any of metal elements selected from the group consisting of magnesium, aluminum, zirconium, hafnium, silicon, titanium, and zinc. It is preferable to contain such an oxide. More preferably, it contains any metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide.
In the organic electroluminescence device, electrons supplied from the cathode enter LUMO of the light emitting layer, and when the LUMO electrons move to HOMO (recombine with holes), the energy difference between LUMO and HOMO is emitted as light. Emits light. For this light emission, it is necessary to smoothly move the electrons from the cathode to the light emitting layer. Therefore, when a metal compound layer (laminated metal compound layer) exists between the cathode and the light emitting layer, the metal compound layer It is necessary that the energy level of the conduction band is close to the LUMO energy level of the organic layer. Here, the range of selection of the organic compound forming the organic layer can be widened by using a metal compound layer having a conduction band energy level as high as possible. Since oxides of the above metal elements have high energy levels in the conduction band, when a metal compound layer formed using these metal elements is used as the electron transport layer, electrons from the cathode to the light emitting layer are used. The organic electroluminescence device can be made excellent in luminous efficiency, and the range of selection of the organic compound forming the organic layer can be expanded.
This is the same in the case of the mixed metal oxide layer, the laminated metal oxide layer, and the layer having a magnesium compound layer between the metal oxide layer and the organic compound layer. In the case of containing an oxide of a metal element having a high energy level in the conduction band as described above, the same effect as described above can be obtained by using these layers as an electron transport layer.

Of the two layers of metal oxide sandwiching a metal species having a work function of 4.0 eV or less, the layer on the side having the organic compound layer preferably contains any of the above-mentioned preferred elements. It is more preferable that a product is included. With such a structure, electrons can be more smoothly transferred from the metal compound layer to the organic layer.
Further, it is more preferable that both of the two layers of metal oxide sandwiching a metal species having a work function of 4.0 eV or less include an oxide of any of the above metal elements, and both of the two layers of metal oxide are It is particularly preferable that any one of the above metal oxides is included.

The metal oxide layer may consist of only one layer or a plurality of layers. That is, each of the metal oxide layers sandwiching a metal species having a work function of 4.0 eV or less may be composed of one metal oxide layer or a plurality of metal oxide layers.
Examples of combinations of metal oxide layers sandwiching a metal species having a work function of 4.0 eV or less in the laminated metal compound layer included in the organic electroluminescent element of the present invention 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, zinc oxide / magnesium oxide, zinc oxide / zirconium oxide, zinc oxide / hafnium oxide, zinc oxide / silicon oxide, etc. Such as two layers, titanium oxide / zinc oxide / magnesium oxide, titanium oxide / zinc oxide / zirconium oxide, titanium oxide / zinc oxide / aluminum oxide, titanium oxide / zinc oxide / hafnium oxide, titanium oxide / zinc oxide / The thing of three layers like a silicon oxide etc. is mentioned.
When the combination of the metal oxide layers is the above two layers, a metal species having a work function of 4.0 eV or less is sandwiched between the two layers to form the laminated metal compound layer of the present invention. When the combination of the metal oxide layers is the above three layers, a metal species having a work function of 4.0 eV or less is sandwiched between any two of the three layers, so that the laminated metal compound layer of the present invention It is formed.
Among the metal elements forming the metal oxide layer described above, it is preferable to use these elements because the energy level of the conduction band of the laminated metal compound layer can be made higher.

The metal oxide layer can have a thickness of 1 nm to 10 μm, but is preferably 1 nm to 100 nm for an organic electroluminescent device that can be driven at a low voltage. More preferably, it is 1 nm to 10 nm.
The thicknesses of the metal oxide layer and the laminated metal oxide layer can be measured by a stylus profilometer or spectroscopic ellipsometry.

The metal having a work function of 4.0 eV or less is preferably an alkali metal and / or an alkaline earth metal. Examples of the alkali metal include Li, Na, K, Rb, and Cs. Examples of the alkaline earth metal include Mg, Ca, Sr, and Ba, and one or more of these can be used.
Among these, it is one of the preferred embodiments of the present invention that the metal having a work function of 4.0 eV or less is at least one selected from metals having a work function of 3.0 eV or more. Among these, Mg is more preferable.
As described above, the presence of a metal species having a work function of 4.0 eV or less between two layers of an oxide of a metal element can increase the luminance of light emission of the organic electroluminescent element. In addition, in the case of using a metal element oxide having a high energy level in the above-described conduction band, a single metal having a work function of 4.0 eV or less or the oxide is sandwiched between oxide layers of these metal elements. The energy level of the conduction band of the entire laminated metal compound layer is also high, and it can be suitably used as an electron transport layer disposed between the cathode and the light emitting layer. Furthermore, the present invention has a multilayer metal compound layer having a structure in which an alkali metal and / or alkaline earth metal is sandwiched between an oxide or sulfide layer of a metal element having a high energy level in the conduction band described above. This organic electroluminescent element is superior in driving life.

The organic electroluminescent element of the present invention contains a simple substance of a metal having a work function of 4.0 eV or less, or at least one of its oxides may be either a simple substance or an oxide, Two or three types may be used. In the case of an oxide, an oxide may be deposited on the metal oxide layer in advance, and in the process of depositing a metal species having a work function of 4.0 eV or less, it becomes an oxide. Also good.

As a method for depositing (or forming a layer of) a metal species having a work function of 4.0 eV or less on the metal oxide layer, a method similar to the method for forming the metal oxide layer described later is used. Can do.
As another method, after a solution obtained by dissolving a metal organic compound salt having a work function of 4.0 eV or less in a solvent is applied on a metal oxide or sulfide layer, a coating film is formed. In addition, a method of removing a solvent by heating and converting a metal organic compound salt having a work function of 4.0 eV or less into a metal oxide having a work function of 4.0 eV or less can be used. In this case, as a solvent, a solvent capable of dissolving a metal organic compound salt having a work function of 4.0 eV or less is appropriately selected from solvents that can be used when an organic compound layer described later is formed by coating. Can be used. In addition, as a method for applying a solution of a metal organic compound salt having a work function of 4.0 eV or less, a method similar to that for forming an organic compound layer described later by application can be used.
After applying a solution of a metal organic compound salt with a work function of 4.0 eV or less, the heating temperature is as long as the solvent is volatilized and the metal organic compound salt with a work function of 4.0 eV or less becomes an oxide. Although it can be set appropriately, it is preferably 200 to 450 ° C.

As described above, the multiple metal species-containing layer of the present invention includes (1) a mixed metal oxide layer, (2) a laminated metal oxide layer, and (3) a magnesium compound between the metal oxide layer and the organic compound layer. There are four preferred forms: a layer having a layer, (4) a simple substance of a metal having a work function of 4.0 eV or less, or a layer having a structure in which an oxide is sandwiched between two layers of metal oxide However, these four are not clearly distinguished, for example, when the multiple metal species-containing layer falls under both (2) and (3) or when falls under both (3) and (4) There is also. Naturally, the organic electroluminescent element including the multiple metal species-containing layer corresponding to two or more of the above four forms is also included in the present invention.

The metal oxide contained in the multiple metal species-containing layer of the present invention may be a single oxide containing one kind of metal element or a complex oxide containing two or more kinds. The metal oxide layer may be composed of one kind of metal oxide or may contain two or more kinds of metal oxides. The metal oxide layer is preferably composed of a single oxide containing one kind of metal element.

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 Since the thin film has high conductivity and is not included in the category of a semiconductor or an insulator, the thin film does not correspond to one layer constituting the multiple metal species-containing layer in the present invention.

The method for producing the metal oxide contained in the multiple metal species-containing layer is not particularly limited, and a normal method for forming each layer constituting the organic electroluminescent element can be appropriately used. Examples include vapor deposition, sol-gel, spray pyrolysis (SPD), atomic layer deposition (ALD), and chemical vapor deposition (CVD). These methods are preferably selected according to the characteristics of the material of the metal oxide layer, and the manufacturing method may be different for each layer.

In the organic electroluminescent device of the present invention, a plurality of metal species-containing layers may be provided between the anode and the organic compound layer, between the cathode and the organic compound layer, or both. It is preferable to have a multiple metal species-containing layer between the compound layer. In this case, the multiple metal species-containing layer functions as an electron transport layer. Since the multiple metal species-containing layer can efficiently perform such electron transfer, an organic electroluminescent device having these layers between the cathode and the organic compound layer is superior in luminous efficiency. Become.

When the multiple metal species-containing layer functions as an electron transport layer, the electron transport layer may consist of only the multiple metal species-containing layer, and uses the multiple metal species-containing layer and the organic electron transport layer at the same time. Also good. When the multiple metal species-containing layer and the organic electron transport layer are used simultaneously, the order of stacking the multiple metal species-containing layer and the organic electron transport layer is not particularly limited, and the multiple metal species-containing layer and the organic electron Each transport layer may be a single layer or two or more layers.
Specific examples of the organic compound forming the organic electron transport layer will be described later.

Below, it describes about the other layer and electrode which comprise an organic electroluminescent element.

The organic compound layer of the organic electroluminescent device of the present invention is a layer formed of an organic compound or a plurality of layers formed of an organic compound, and one of the layers is a light emitting layer. It is what is. That is, the organic compound layer is either a light-emitting layer formed of an organic compound or a layer in which a light-emitting layer formed of an organic compound and another layer formed of an organic compound are stacked. The other layer formed of the organic compound may be one layer or two or more layers. Further, the order in which the light emitting layer and other layers are laminated is not particularly limited. However, in the case where the multiple metal species-containing layer is provided between the cathode and the organic compound layer, the multiple metal species-containing layer and the organic compound layer It is preferable that the light emitting layer is in contact.

The other layer formed of the organic compound is preferably a hole transport layer or an electron transport layer. That is, when the organic compound layer is composed of a plurality of layers, it is preferable to have a hole transport layer and / or an electron transport layer as other layers other than the light emitting layer. Thus, it is one of the preferred embodiments of the organic electroluminescent device of the present invention that the organic electroluminescent device has a hole transport layer and / or an electron transport layer as an independent layer different from the light emitting layer. is there.
When the organic electroluminescent element of the present invention has a hole transport layer as an independent layer, it has a hole transport layer between the light emitting layer and the anode.
In the organic electroluminescent device of the present invention, the mixed metal oxide layer, the laminated metal oxide layer, or the layer containing a structure having a metal species on the metal oxide layer is between the cathode and the organic compound layer. When it does not have any of these, it is preferable to have a layer which functions as an electron carrying layer in an organic compound layer. In this case, a layer functioning as an electron transport layer is provided between the cathode and the light emitting layer.
When the organic electroluminescent device of the present invention does not have a hole transport layer or an electron transport layer as an independent layer, any of the layers possessed as an essential component of the organic electroluminescent device of the present invention functions as these layers. It will also serve as.

As the organic compound forming the organic compound layer, an organic low molecular weight material, an organometallic complex, a high molecular weight material, or the like can be used as appropriate, and these can be used in combination as necessary. At least one of the compounds is selected from luminescent materials.
In the present invention, the organic low molecular weight material means a material that is not a polymer material (polymer), and does not necessarily mean an organic compound having a low molecular weight.

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); -Phenvinylene) (PPV), poly (2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly (para-phenvinylene) (CN-PPV), poly (2-dimethyl) Polyparaphenylene vinylene compounds such as octylsilyl-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 triol (POP); 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-divinylenefull Polyfluorene compounds such as oleenyl-ortho-co (anthracene-9,10-diyl)); poly (para-phenylene) (PPP), poly (1,5-dialkoxy-para-phenylene) (RO— Polyparaphenylene compounds such as PPP); polycarbazole compounds such as poly (N-vinylcarbazole) (PVK) Polysilane compounds such as poly (methylphenylsilane) (PMPS), poly (naphthylphenylsilane) (PNPS), poly (biphenylylphenylsilane) (PBPS); and Japanese Patent Application No. 2010-230995 Examples thereof include boron compound polymer materials described in 2011-6457.

Examples of the low-molecular light-emitting material include a tricoordinate iridium complex having 2,2′-bipyridine-4,4′-dicarboxylic acid as a ligand, and 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 , 7 , 8, 12, 13, 17, 18-octaethyl-21H, 23H-porphine Various metal complexes such as platinum (II); distyrylbenzene (D B), benzene compounds such as diaminodistyrylbenzene (DADSB); naphthalene compounds such as naphthalene and nile red; phenanthrene compounds such as phenanthrene; chrysene compounds such as chrysene and 6-nitrochrysene; Perylene compounds such as N, N′-bis (2,5-di-t-butylphenyl) -3,4,9,10-perylene-di-carboximide (BPPC); coronene compounds such as coronene Anthracene compounds such as anthracene and bisstyrylanthracene; pyrene compounds 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 rubene; thiophene compounds such as 2,5-dibenzoxazole thiophene; benzoxazole compounds such as benzoxazole; benzimidazole compounds such as benzimidazole; 2,2 ′-(para- Benzodiazole compounds such as phenylenedivinylene) -bisbenzothiazole; butadiene compounds such as bistyryl (1,4-diphenyl-1,3-butadiene) and tetraphenylbutadiene; naphthalimide compounds such as naphthalimide A coumarin compound such as coumarin; a perinone compound such as perinone; an oxadiazole compound such as oxadiazole; an aldazine compound; 1,2,3,4,5-pentaphenyl-1,3- Cyclopentadiene (PPCP Cyclopentadiene compounds such as quinacridone, quinacridone compounds such as 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 and Japanese Patent Application No. 2010-230995 Examples include boron compound materials described in 2011-6458.

When the organic compound layer has a hole transport layer in addition to the light emitting layer, the hole transport organic material used as the hole transport layer includes various p-type polymer materials and various p-type low molecular materials. They can be used alone or in combination.
Examples of the p-type polymer material (organic polymer) include polyarylamine, fluorene-arylamine copolymer, fluorene-bithiophene copolymer, poly (N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, polythiophene, Examples thereof include polyalkylthiophene, polyhexylthiophene, poly (p-phenylene vinylene), polytinylene vinylene, pyrene formaldehyde resin, ethylcarbazole formaldehyde resin, and derivatives thereof.
These compounds can also be used as a mixture with other compounds. As an example, examples of the mixture containing polythiophene include poly (3,4-ethylenedioxythiophene / styrene sulfonic acid) (PEDOT / PSS).

Examples of the p-type low molecular weight material include 1,1-bis (4-di-para-triaminophenyl) cyclohexane, 1,1′-bis (4-di-para-tolylaminophenyl)- Arylcycloalkane compounds such as 4-phenyl-cyclohexane; 4,4 ′, 4 ″ -trimethyltriphenylamine, N, N, N ′, N′-tetraphenyl-1,1′-biphenyl-4, 4′-diamine, N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (TPD1), N, N′-diphenyl-N , N′-bis (4-methoxyphenyl) -1,1′-biphenyl-4,4′-diamine (TPD2), N, N, N ′, N′-tetrakis (4-methoxyphenyl) -1,1 '-Biphenyl-4,4'-diamine (TPD3), N N′-di (1-naphthyl) -N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD), arylamine compounds such as TPTE; N, N, N ', N'-tetraphenyl-para-phenylenediamine, N, N, N', N'-tetra (para-tolyl) -para-phenylenediamine, N, N, N ', N'-tetra (meta-tolyl) ) -Phenylenediamine compounds such as meta-phenylenediamine (PDA); Carbazole compounds such as carbazole, N-isopropylcarbazole and N-phenylcarbazole; Stilbenes such as stilbene and 4-di-para-tolylaminostilbene system compound; oxazole-based compounds such as _{O x} Z; triphenylmethane, triphenylmethane compounds such as m-MTDATA; 1-full Pyrazoline compounds such as nyl-3- (para-dimethylaminophenyl) pyrazoline; benzine (cyclohexadiene) compounds, triazole compounds such as triazole; imidazole compounds such as imidazole, 1,3,4-oxa Oxadiazole compounds such as diazole, 2,5-di (4-dimethylaminophenyl) -1,3,4, -oxadiazole; anthracene, anthracene such as 9- (4-diethylaminostyryl) anthracene Fluorenone compounds such as fluorenone, 2,4,7, -trinitro-9-fluorenone, 2,7-bis (2-hydroxy-3- (2-chlorophenylcarbamoyl) -1-naphthylazo) fluorenone; polyaniline Aniline compounds such as silane Compound: 1,4-dithioketo-3,6-diphenyl-pyrrolo- (3,4-c) pyrrolopyrrole compound such as pyrrolopyrrole; fluorene compound such as fluorene; porphyrin, metal tetraphenylporphyrin and the like Porphyrin compounds; quinacridone compounds such as quinacridone; metal or metal-free phthalocyanine compounds such as phthalocyanine, copper phthalocyanine, tetra (t-butyl) copper phthalocyanine, iron phthalocyanine; copper naphthalocyanine, vanadyl naphthalocyanine, monochlorogallium Metallic or metal-free naphthalocyanine compounds such as naphthalocyanine; N, N′-di (naphthalen-1-yl) -N, N′-diphenyl-benzidine, N, N, N ′, N′-tetraphenyl Benzidine like benzidine Thing, and the like.

In the organic electroluminescent element of the present invention, it is preferable to use the multiple metal species-containing layer as an electron transport layer, but when the electron transport layer is formed of an organic compound, the material is usually used as a material for the electron transport layer. Any low molecular weight compound that can be used can be used, and these may be used in combination. These low molecular weight compounds can also be used to form a layer formed of an organic compound when the layer formed of an organic compound and the laminated metal compound layer described above are simultaneously used as an electron transport layer.
Examples of low molecular weight compounds that can be used as a material for the electron transport layer include pyridine derivatives such as tris-1,3,5- (3 ′-(pyridin-3 ″ -yl) phenyl) benzene (TmPyPhB). , Quinoline derivatives such as (2- (3- (9-carbazolyl) phenyl) quinoline (mCQ)), pyrimidines such as 2-phenyl-4,6-bis (3,5-dipyridylphenyl) pyrimidine (BPyPPM) Derivatives, pyrazine derivatives, phenanthroline derivatives such as bathophenanthroline (BPhen), 2,4-bis (4-biphenyl) -6- (4 ′-(2-pyridinyl) -4-biphenyl)-[1,3,5 Triazine derivatives such as triazine (MPT), 3-phenyl-4- (1′-naphthyl) -5-phenyl-1,2,4-triazol Triazole derivatives such as (TAZ), oxazole derivatives, oxadiazole derivatives such as 2- (4-biphenylyl) -5- (4-tert-butylphenyl-1,3,4-oxadiazole) (PBD) , 2,2 ′, 2 ″-(1,3,5-bentriyl) -tris (1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring tetras such as naphthalene and perylene Various metal complexes represented by carboxylic anhydride, bis [2- (2-hydroxyphenyl) benzothiazolate] zinc (Zn (BTZ) ₂ ), tris (8-hydroxyquinolinato) aluminum (Alq ₃ ), 5-bis (6 ′-(2 ′, 2 ″ -bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy), etc. Organic silane derivatives, and the like typified by silole derivatives, can be used alone or in combination of two or more thereof.
Among these, a metal complex such as Alq ₃ and a pyridine derivative such as TmPyPhB are preferable.

Among the organic compound layers, the average thickness of the light emitting layer is not particularly limited, but is preferably 10 to 150 nm. More preferably, it is 20 to 100 nm.
When the organic compound layer has a hole transport layer or an electron transport layer, the average thickness of these layers is not particularly limited, but is preferably 10 to 150 nm. More preferably, it is 20 to 100 nm.
The average thicknesses of the light emitting layer, the hole transport layer, and the electron transport layer can be measured at the time of film formation using a crystal oscillator thickness meter.

The method for forming the organic compound layer is not particularly limited, and various methods can be used as appropriate in accordance with the characteristics of the material. However, when it can be applied as a solution, a spin coating method, a casting method, a micro gravure coating method, Film formation using various coating methods such as gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, and inkjet printing can do. Among these, the spin coat method and the slit coat method are preferable because the film thickness can be more easily controlled. When it is 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.

When the organic compound layer is formed by applying an organic compound solution, examples of the solvent used for dissolving the organic compound include nitric acid, sulfuric acid, ammonia, hydrogen peroxide, water, carbon disulfide, and carbon tetrachloride. , Inorganic solvents such as ethylene carbonate, ketone solvents such as methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), cyclohexanone, methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol (DEG), alcohol solvents such as glycerin, diethyl ether, diisopropyl ether, 1,2-dimethoxyethane (DME), 1,4-dioxane, tetrahydrofuran (THF), tetrahydropyran (THP), aniso , Ether solvents such as diethylene glycol dimethyl ether (diglyme), diethylene glycol ethyl ether (carbitol), cellosolve solvents such as methyl cellosolve, ethyl cellosolve, phenyl cellosolve, aliphatic hydrocarbon solvents such as hexane, pentane, heptane, cyclohexane Aromatic hydrocarbon solvents such as toluene, xylene and benzene, aromatic heterocyclic solvents such as pyridine, pyrazine, furan, pyrrole, thiophene and methylpyrrolidone, N, N-dimethylformamide (DMF), N, N An amide solvent such as dimethylacetamide (DMA), a halogen compound solvent such as chlorobenzene, dichloromethane, chloroform, 1,2-dichloroethane, an ester solvent such as ethyl acetate, methyl acetate, ethyl formate, Various organic solvents such as methyl sulfoxide (DMSO), sulfur compound solvents such as sulfolane, nitrile solvents such as acetonitrile, propionitrile, acrylonitrile, organic acid solvents such as formic acid, acetic acid, trichloroacetic acid, trifluoroacetic acid, Or the mixed solvent containing these etc. are mentioned.
Among these, as the solvent, a nonpolar solvent is suitable, for example, an aromatic hydrocarbon solvent such as xylene, toluene, cyclohexylbenzene, dihydrobenzofuran, trimethylbenzene, tetramethylbenzene, pyridine, pyrazine, furan, Examples include aromatic heterocyclic compound solvents such as pyrrole, thiophene, and methylpyrrolidone, and aliphatic hydrocarbon solvents such as hexane, pentane, heptane, and cyclohexane. These can be used alone or in combination.

As the anode and cathode of the organic electroluminescent device of the present invention, ordinary conductive materials used as the anode and cathode of the organic electroluminescent device can be used as appropriate, but at least one of them can be used for light extraction. Is preferably transparent. Examples of normal transparent conductive materials include 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. Is raised. Examples of the opaque conductive material include calcium, magnesium, aluminum, tin, indium, copper, silver, gold, and alloys thereof. These may be used alone or in combination of two or more.

The average thickness of the anode is not particularly limited, but is preferably 10 to 500 nm. More preferably, it is 100 to 200 nm. The average thickness of the anode can be measured by a stylus profilometer or spectroscopic ellipsometry.
The average thickness of the cathode is not particularly limited, but is preferably 10 to 1000 nm. More preferably, it is 30 to 150 nm.
The average thickness of the cathode can be measured at the time of film formation with a crystal oscillator thickness meter.

Since the organic electroluminescent element of the present invention is a HOILED element, it is preferable to have a hole injection layer between the organic compound (light emitting layer or hole transport layer) 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 thickness of the hole injection layer is preferably 1 nm to 20 nm. More preferably, it is 5 nm to 10 nm.
The thickness of the hole injection layer can be measured at the time of film formation with a crystal oscillator thickness meter.

The cathode, anode, and hole injection layer are formed by sputtering, vacuum deposition, sol-gel, spray pyrolysis (SPD), atomic layer deposition (ALD), vapor deposition, liquid deposition, etc. Can be formed. Metal foil bonding can also be used to form the anode and cathode.
Among these, the hole injection layer is preferably formed using a vacuum vapor deposition method which is a vapor deposition method. According to the vapor deposition method, the hole injection layer can be formed cleanly and in good contact with the anode without damaging the surface of the organic compound layer. As a result, the effect of the organic electroluminescence device of the present invention is further improved. It will be remarkable.

For the purpose of further improving the characteristics of the organic electroluminescence device of the present invention, for example, an electron injection layer, a hole blocking layer, an electron device layer and the like may be included as necessary. As a material for forming these layers, materials usually used for forming these layers can be used, and the layers can be formed by a method usually used for forming these layers.

The electroluminescent element of the present invention may be sealed if necessary. As the sealing step, a normal 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 organic electroluminescent element of the present invention may be one in which each layer constituting the organic electroluminescent element is laminated on a substrate. When each layer is laminated on the substrate, it is preferable that each layer is formed on the electrode formed on the substrate. In this case, the organic electroluminescent element of the present invention may be a top emission type that extracts light to the side opposite to the side where the substrate is present, or a bottom emission type that extracts light to the side where the substrate is present. May be.

As the material of the substrate, resin materials such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, quartz glass, soda glass, etc. A glass material etc. are mentioned, These 1 type (s) or 2 or more types can be used.
In the case of the top emission type, an opaque substrate can be used. For example, an oxide film (insulating film) is formed on the surface of a ceramic substrate such as alumina or a metal substrate such as stainless steel. A substrate made of a resin material or the like can also be used.

The average thickness of the substrate is preferably 0.1 to 30 mm. More preferably, it is 0.1 to 10 mm.
The average thickness of the substrate can be measured with a digital multimeter or a caliper.

The electroluminescent element of the present invention can change the luminescent color by appropriately selecting the material of the organic compound layer, and can also obtain a desired luminescent color by using a color filter or the like in combination. Therefore, it can be suitably used as a light emitting part of a display device or a lighting device.
Such a display device including the organic electroluminescent element of the present invention and an illumination device including the organic electroluminescent element of the present invention are also one aspect of the present invention.

The organic electroluminescent device of the present invention is a HOILED device having the above-described configuration and usable without sealing, and is a useful organic electroluminescent device that exhibits high luminous efficiency and has a long driving life. It can be suitably used as a display device or a lighting device.

1 is a cross-sectional view of an embodiment of an organic electroluminescent device according to the present invention having a HOILED structure. 3 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Examples 1 to 3 and Comparative Examples 1 and 2. 3 is a graph showing current density-power efficiency characteristics of organic electroluminescent elements prepared in Examples 1 to 3 and Comparative Examples 1 and 2. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 4 and Comparative Examples 3 to 4. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 5 and Comparative Example 5. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 6 and Comparative Example 6. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 7 and Comparative Examples 7 to 8. 6 is a graph showing current density-current efficiency characteristics of organic electroluminescent elements prepared in Example 7 and Comparative Example 8. It is a graph which shows the lifetime characteristic of the organic electroluminescent element created in Example 8 and Comparative Example 9. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 9, Comparative Example 10 and Comparative Example 12. 4 is a graph showing current density-power efficiency characteristics of organic electroluminescent elements prepared in Example 9, Comparative Example 10 and Comparative Example 12. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements prepared in Example 10, Comparative Example 11 and Comparative Example 12. 6 is a graph showing current density-power efficiency characteristics of organic electroluminescent elements prepared in Example 10, Comparative Example 11 and Comparative Example 12. It is a graph which shows the lifetime characteristic of the organic electroluminescent element created in Example 9 and Comparative Example 13. 6 is a graph showing voltage-luminance characteristics of organic electroluminescent elements fabricated in Example 11 and Comparative Examples 14 to 15. 6 is a graph showing voltage-current efficiency characteristics of organic electroluminescence elements fabricated in Example 11 and Comparative Examples 14 to 15. 6 is a graph showing lifetime characteristics of organic electroluminescent elements produced in Example 11 and Comparative Examples 14 to 15.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by weight” and “%” means “mass%”.

In the following examples, the thicknesses of the multiple metal species-containing layer, the organic compound layer, the hole injecting metal oxide layer, and the anode were all measured at the time of film formation with a crystal resonator thickness meter.

(Synthesis of luminescent 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 stirred at −78 ° C. for 1 hour. A solution of zinc chloride in diethyl ether (1M, 24.3 ml, 24.3 mmol) was added dropwise thereto with stirring. After completion of dropping, the mixture was stirred at room temperature for 1 hour. Thereto was added a toluene solution (200 mL) containing 5-bromo-2- (4-bromo-2-dibromoborylphenyl) pyridine (5.6 g, 11.6 mmol), and the mixture was heated and stirred 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 (3) represented by these was obtained. The weight average molecular weight in terms of polystyrene as determined by gel permeation chromatography (tetrahydrofuran solvent) was 71,000.

Examples of the organic electroluminescence device of the present invention and comparative examples will be described below. In the following, for convenience, 1. 1. an organic electroluminescent device having a mixed metal oxide layer; 2. an organic electroluminescent device having a laminated metal oxide layer; 3. an organic electroluminescent device having a layer having a magnesium compound layer between the metal oxide layer and the organic compound layer; Although the work function is 4.0 eV or less, a single metal or an organic electroluminescent element having a structure in which an oxide is sandwiched between two layers of metal oxide is described. This does not mean that the embodiment described below corresponds to only one of these four.

<1. Example of organic electroluminescent device having mixed metal oxide layer, comparative example>
(Creation of organic electroluminescence device)
(Comparative 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. The substrate was taken out from isopropanol, dried by nitrogen blowing, and UV ozone cleaning was performed for 20 minutes.
[2] This substrate was placed on a hot plate, and heated to 400 ° C. with the electrode extraction part covered with another glass plate. A 0.1 mol / L ethanol solution of magnesium acetate tetrahydrate was sprayed onto a heated substrate using a reagent spray. This process was repeated 10 times at 30 second intervals. After spraying, after heating for 10 minutes at that temperature, the hot plate was turned off and naturally radiated to room temperature to obtain a substrate with a single metal oxide thin film layer.
[3] 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.
[4] 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 pressure was reduced to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, gold was vapor-deposited so as to have a film thickness of 20 nm, and an organic electroluminescent element (Mg: Zn = 4: 0 (atomic ratio)) was created. 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 2, Examples 1 to 3)
In the same manner as in Step [2] of Comparative Example 1, except that a substrate with an oxide thin film layer was prepared using the solution shown in Table 1 instead of the 0.1 mol / L ethanol solution of magnesium acetate tetrahydrate. Organic electroluminescent elements were respectively prepared.

(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. The organic electroluminescence devices prepared in Examples 1 to 3 and Comparative Examples 1 to 2 have voltage-luminance characteristics and current density-power efficiency characteristics when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. It shows in FIG. 2, FIG. 3, respectively. Note that the reading of BM-7 was about 20 cd / m ² when the device was not emitting light due to external light or the like.
From FIG. 2, the organic electroluminescent elements of Examples 1 to 3 using the mixed oxide thin film according to the present invention have a lower voltage than the organic electroluminescent elements of Comparative Examples 1 to 2 using the single composition oxide thin film. It is clear that light is emitted.
Further, from FIG. 3, the organic electroluminescent elements of Examples 1 to 3 using the mixed metal oxide thin film of the present invention have higher power than the organic electroluminescent elements of Comparative Examples 1 to 2 using the single metal oxide thin film. It is clear that it shows efficiency.

(Example 4)
[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 placed on a hot plate, and heated to 400 ° C. with the electrode extraction part covered with another glass plate. A mixed ethanol solution of 0.0125 mol / L of bis (2,4-pentanedionato) zinc and 0.0375 mol / L of tetrakis (2,4-pentandionato) zirconium is sprayed onto a heated substrate using a reagent spray. did. This process was repeated 10 times at 30 second intervals. After spraying, after heating for 10 minutes at that temperature, the hot plate was turned off and naturally dissipated to room temperature to obtain a substrate with a mixed metal oxide thin film layer.
[3] 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 a mixed metal 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.
[4] 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 pressure was reduced to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, gold was vapor-deposited so as to have a film thickness of 20 nm, and an organic electroluminescent element (Zn: Zr = 1: 3 (atomic ratio)) was produced. 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)
In step [2] of Example 4, bis (2,4-pentanedionato) zinc 0.0125 mol / L, tetrakis (2,4-pentandionato) zirconium 0.0375 mol / L mixed ethanol solution instead of bis An organic electroluminescent device (Zn: Zr = 4: 0) was prepared in the same manner except that a substrate with a single metal oxide thin film layer was prepared using an ethanol solution of (2,4-pentanedionato) zinc 0.050 mol / L. (Atom ratio)).

(Comparative Example 4)
In Step [2] of Example 4, tetrakis (2,4-pentanedionato) zinc 0.0125 mol / L, tetrakis (2,4-pentanedionato) zirconium 0.0375 mol / L in place of the mixed ethanol solution An organic electroluminescent device (Zn: Zr = 0: 4) was prepared in the same manner except that a substrate with a single metal oxide thin film layer was prepared using an ethanol solution of (2,4-pentanedionato) zirconium 0.050 mol / L. (Atom ratio)).

(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. 4 shows voltage-luminance characteristics when a DC voltage of −4 V to 15 V is applied to the organic electroluminescent elements prepared in Example 4 and Comparative Examples 3 to 4 in an argon atmosphere. Note that the reading of BM-7 was about 20 cd / m ² when the device was not emitting light due to external light or the like.
From FIG. 4, the organic electroluminescent device of Example 4 using the mixed metal oxide thin film of the present invention emits light from a voltage lower than that of the organic electroluminescent devices of Comparative Examples 3 and 4 using a single metal oxide thin film. It is clear to do.

(Example 5)
[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 placed on a hot plate, and heated to 400 ° C. with the electrode extraction part covered with another glass plate. A mixed ethanol solution of titanium tetraisopropoxide 0.0375 mol / L and magnesium acetate 0.0125 mol / L was sprayed onto a heated substrate using a reagent spray. This process was repeated 10 times at 30 second intervals. After spraying, after heating for 10 minutes at that temperature, the hot plate was turned off and naturally dissipated to room temperature to obtain a substrate with a mixed metal oxide thin film layer.
[3] 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 a mixed metal 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.
[4] 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 pressure was reduced to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, gold was vapor-deposited to a film thickness of 20 nm to prepare an organic electroluminescent element (Ti: Mg = 3: 1 (atomic ratio)). 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 5)
In the step [2] of Example 5, a titanium tetraisopropoxide 0.050 mol / L ethanol solution was used instead of a titanium tetraisopropoxide 0.0375 mol / L, magnesium acetate 0.0125 mol / L mixed ethanol solution. An organic electroluminescent element (Ti: Mg = 4: 0 (atomic ratio)) was prepared in the same manner except that a substrate with a single metal oxide thin film layer was prepared.

(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. 5 shows the voltage-luminance characteristics of the organic electroluminescent devices prepared in Example 5 and Comparative Example 5 when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. Note that the reading of BM-7 was about 20 cd / m ² when the device was not emitting light due to external light or the like.
From FIG. 5, the organic electroluminescent device of Example 5 using the mixed metal oxide thin film of the present invention emits light from a voltage lower than that of the organic electroluminescent device of Comparative Example 5 using a single metal oxide thin film. Is clear.

(Example 6)
[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 placed on a hot plate, and heated to 400 ° C. with the electrode extraction part covered with another glass plate. A mixed ethanol solution of tris (2,4-pentanedionato) aluminum 0.0375 mol / L and magnesium acetate 0.0125 mol / L was sprayed onto a heated substrate using a reagent spray. This process was repeated 10 times at 30 second intervals. After spraying, after heating for 10 minutes at that temperature, the hot plate was turned off and naturally dissipated to room temperature to obtain a substrate with a mixed metal oxide thin film layer.
[3] 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 a mixed metal 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.
[4] 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 pressure was reduced to about 1 × 10 ⁻⁴ Pa, and molybdenum trioxide was deposited to a thickness of 10 nm. Next, gold was vapor-deposited so as to have a film thickness of 20 nm to prepare an organic electroluminescent element (Al: Mg = 3: 1 (atomic ratio)). 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 6)
In step [2] of Example 6, tris (2,4-pentanedionato) aluminum 0.0375 mol / L, magnesium acetate 0.0125 mol / L mixed ethanol solution instead of tris (2,4-pentanedionato) An organic electroluminescent device (Al: Mg = 4: 0 (atomic ratio)) was prepared in the same manner except that a substrate with a single metal oxide thin film layer was prepared using an aluminum 0.050 mol / L ethanol solution. .

(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. 6 shows voltage-luminance characteristics of the organic electroluminescent devices prepared in Example 6 and Comparative Example 6 when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. Note that the reading of BM-7 was about 20 cd / m ² when the device was not emitting light due to external light or the like.
From FIG. 6, the organic electroluminescent device of Example 6 using the mixed metal oxide thin film of the present invention emits light from a voltage lower than that of the organic electroluminescent device of Comparative Example 6 using a single metal oxide thin film. Is clear.

<2. Example of organic electroluminescent device having laminated metal oxide layer, comparative example>
(Creation of organic electroluminescence device)
(Example 7)
[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, gold was vapor-deposited so as to have a film thickness of 20 nm, and an organic electroluminescent element (Mg: Zn = 4: 0 (atomic ratio)) was created. 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 7)
An organic electroluminescent device having a titanium oxide single layer as an oxide thin film layer was produced in the same manner except that Step [3] in Example 7 was omitted.

(Comparative Example 8)
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 7 was omitted and the thickness of zinc oxide was changed to 2 nm in step [3]. Created.

(Example 8)
[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, gold was vapor-deposited so as to have a film thickness of 20 nm, and an organic electroluminescent element (Mg: Zn = 4: 0 (atomic ratio)) was created. 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 9)
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 8.
[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 deposition apparatus was depressurized to about 1 × 10 ⁻⁴ Pa, and cesium carbonate was deposited to a 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 7 and 8 and Comparative Examples 7 to 9 are summarized 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. 7 shows the voltage-luminance characteristics and current density-current efficiency characteristics of the organic electroluminescent devices prepared in Example 7 and Comparative Examples 7-8 when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. Each is shown in FIG.
From FIG. 7, the organic electroluminescent device of Example 7 using the laminated oxide thin film of the present invention emits light from a lower voltage than the organic electroluminescent devices of Comparative Examples 7 to 8 using a single layer oxide thin film. It is clear.
Further, from FIG. 8, the organic electroluminescent device of Example 7 using the laminated oxide thin film of the present invention shows higher current efficiency than the organic electroluminescent device of Comparative Example 8 using a single layer oxide thin film. Is clear. However, as is clear from FIG. 7, the organic electroluminescence device of Comparative Example 7 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. 9 shows the lifetime characteristics of the organic electroluminescent elements prepared in Example 8 and Comparative Example 9.
From FIG. 9, the organic electroluminescent element of Example 8 using the laminated oxide thin film of the present invention has a longer lifetime than the organic electroluminescent element of Comparative Example 9 having a single-layer oxide thin film and a cesium compound layer. I understand.

<3. Examples of organic electroluminescent elements having a layer having a magnesium compound layer between a metal oxide layer and an organic compound layer, comparative examples>
(Creation of organic electroluminescence device)
Example 9
[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 (volume ratio 1: 3 (atomic ratio)) 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, gold was vapor-deposited so as to have a film thickness of 20 nm, and an organic electroluminescent element (Mg: Zn = 4: 0 (atomic ratio)) was created. 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 .

(Example 10)
An organic electroluminescent element having a magnesium compound layer on a titanium oxide thin film layer was prepared in the same manner except that a titanium metal target was used instead of the zinc metal target in the step [2] of Example 9.

(Comparative Example 10)
An organic electroluminescent element having a zinc oxide single layer as an oxide thin film layer was produced in the same manner except that the step [3] in Example 9 was omitted.

(Comparative Example 11)
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 10 was omitted.

(Comparative Example 12)
An organic electroluminescent element having a magnesium oxide single layer as an oxide thin film layer was produced in the same manner except that Step [2] in Example 9 was omitted.

(Comparative Example 13)
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 9.
[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 deposition apparatus was depressurized to about 1 × 10 ⁻⁴ Pa, and cesium carbonate was deposited to a 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 devices prepared in Examples 9 to 10 and Comparative Examples 10 to 13 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. The organic electroluminescence devices prepared in Example 9, Comparative Example 10 and Comparative Example 12 are shown with voltage-luminance characteristics and current density-power efficiency characteristics when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. 10 and FIG. 11 respectively.
From FIG. 10, the organic electroluminescent element of Example 9 using the laminated structure of the oxide film and magnesium compound film of the present invention is the organic electroluminescent element of Comparative Example 10 and Comparative Example 12 using a single layer oxide thin film. It is clear that light is emitted from a voltage lower than that of.
Further, from FIG. 11, the organic electroluminescence device of Example 9 using the laminated structure of the oxide film and the magnesium compound film of the present invention is the organic electroluminescence of Comparative Example 10 and Comparative Example 12 using a single layer oxide thin film. It is clear that the power efficiency is higher than that of the device.
Next, the organic electroluminescence devices prepared in Example 10, Comparative Example 11 and Comparative Example 12 were subjected to voltage-luminance characteristics, current density-power efficiency when a DC voltage of −4 V to 15 V was applied in an argon atmosphere. The characteristics are shown in FIGS. 12 and 13, respectively.
From FIG. 12, the organic electroluminescent element of Example 10 using the laminated structure of the oxide film and magnesium compound film of the present invention is the organic electroluminescent element of Comparative Example 11 and Comparative Example 12 using a single layer oxide thin film. It is clear that light is emitted from a voltage lower than that of.
Further, from FIG. 13, the organic electroluminescence device of Example 10 using the laminated structure of the oxide film and the magnesium compound film of the present invention is the organic electroluminescence of Comparative Example 11 and Comparative Example 12 using a single layer oxide thin film. It is clear that the power efficiency is higher than that of the device.

(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. 14 shows the lifetime characteristics of the organic electroluminescent elements prepared in Example 9 and Comparative Example 13.
From FIG. 14, the organic electroluminescent element of Example 9 using the laminated structure of the oxide film and the magnesium compound film of the present invention is an organic electroluminescent element of Comparative Example 13 having a single-layer oxide thin film and a cesium compound layer. It can be seen that the lifetime is longer.

<4. Examples of organic electroluminescent elements having a structure in which a metal having a work function of 4.0 eV or less, or an oxide thereof is sandwiched between two layers of metal oxide, and comparative examples>
(Production of organic electroluminescence device)
(Example 11)
[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. The ITO electrode is used as the cathode 2. 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 again to the substrate holder of the 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 part of the ITO electrode was not formed with zinc oxide for electrode extraction.
[3] This substrate was fixed to a substrate holder of a vapor deposition apparatus having a resistance heating vapor deposition source. After reducing the pressure to about 1 × 10 ⁻⁴ Pa, a magnesium layer having a thickness of about 0.5 nm was produced. At this time, a metal mask was used in combination, and in the same way as [2], a part of the ITO electrode was made not to be formed of magnesium metal for electrode extraction.
[4] This substrate was fixed again to the substrate holder of the Miratron sputtering apparatus having a zinc metal target. After reducing the pressure to about 1 × 10 ⁻⁴ Pa, sputtering was performed with argon and oxygen introduced, and a zinc oxide layer having a thickness of about 2 nm was produced. At this time, a metal mask was used in combination, and as in [2], a part of the ITO electrode was not formed with zinc oxide for electrode extraction. The series of film forming steps [2] to [4] were consistently produced under vacuum without exposure to the atmosphere. The thin film formed in [2] to [4] was used as the laminated metal compound layer 3.
[5] Next, poly (dioctylfluorene-alt-benzothiadiazole) (F8BT), which is a light-emitting polymer material, was formed as the organic compound layer 4 by the following method.
It is also possible to mix a hole transporting material in this, and it is also possible to form a layer in which a light emitting polymer material is first formed and a hole transporting material is formed thereon. An organic compound layer was formed by layer deposition. Lamination can be achieved by repeating this.
First, F8BT was dissolved in xylene to prepare a liquid material (1.0% solution). Next, this liquid material was spin-coated at 1000 rpm for 100 seconds to supply it onto the laminated metal oxide layer 3 to form a liquid film. The liquid film was dried by heating to 100 ° C. on a hot plate to volatilize xylene as a solvent to form an organic compound layer. The formed film thickness was 45 nm.
[6] Next, a molybdenum oxide layer was formed as a hole-injecting metal oxide layer 5 on the organic compound layer 4 by a vacuum deposition method. The thickness of the hole injecting metal oxide layer 5 was 10 nm.
[7] Finally, as a final step, a gold layer was formed on the hole-injecting metal oxide layer 5 as the anode 6 by vacuum deposition. The thickness of the anode 6 was 40 nm.

(Comparative Example 14)
An organic electroluminescent element having a zinc oxide single layer as a laminated oxide thin film layer was produced in the same manner except that Step [3] in Example 11 was omitted.

(Comparative Example 15)
An organic electroluminescent device having zinc oxide / magnesium as a laminated oxide thin film layer was prepared in the same manner except that the thickness of the zinc oxide layer in step [2] of Example 11 was 4 nm and step [4] was omitted. did.

(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. 15 shows the voltage-luminance characteristics and voltage-current efficiency characteristics of the organic electroluminescent elements prepared in Example 11 and Comparative Examples 14 to 15 when a DC voltage of −4 V to 15 V is applied in an argon atmosphere. 16 respectively.
As is clear from FIG. 15, the organic electroluminescent device of Example 11 using the laminated metal compound thin film of the present invention has a lower voltage than the organic electroluminescent device of Comparative Example 14 using a single layer oxide thin film. It was confirmed that light was emitted. Although the threshold voltage was the same as that of Comparative Example 15, it was revealed that the organic electroluminescent element of Example 11 was superior in terms of luminance.
Further, as apparent from FIG. 16, the organic electroluminescent device of Example 11 using the laminated metal compound thin film of the present invention is compared with the organic electroluminescent devices of Comparative Examples 14 to 15 using a single layer oxide thin film. It was confirmed that high current efficiency was exhibited.

(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. 17 shows the lifetime characteristics of the organic electroluminescent elements prepared in Example 11 and Comparative Examples 14 and 15.
As can be seen from FIG. 17, the organic electroluminescent device of Example 11 using the laminated metal compound thin film of the present invention is the organic of Comparative Example 15 in which a metal having a work function of 4.0 eV or less is in direct contact with the organic compound layer. It was confirmed that the lifetime was significantly longer than that of the electroluminescent device. Moreover, compared with the organic electroluminescent element which has the single layer oxide thin film of the comparative example 14, it is thought that a brightness | luminance raise is small and it has shown that the carrier balance is favorable, as guessed from the past result. For this reason, higher durability can be expected in driving for a longer time.
From the above, it has been proved that the structure in which the low work function metal, which is the basis of the present invention, is sandwiched between metal oxides and the like has good results in device characteristics.

1: Substrate 2: Cathode 3: Laminated metal compound layer 4: Organic compound layer 5: Hole-injecting metal oxide layer 6: Anode

Claims

An organic electroluminescent device having a structure in which a plurality of layers are laminated between an anode and a cathode,
The organic electroluminescent element has one or more organic compound layers between the anode and the cathode, and further includes a plurality of layers between the anode and the organic compound layer and / or between the cathode and the organic compound layer. An organic electroluminescent device comprising a layer containing a metal species, wherein at least one of the plurality of metal species is a metal oxide.
The layer containing a plurality of metal species is any one of a mixed metal oxide layer, a laminated metal oxide layer, or a layer containing a structure having a metal species on the metal oxide layer. 2. The organic electroluminescent element according to 1.
The organic layer according to claim 2, wherein the layer including a structure having a metal species on the metal oxide layer is a layer having a magnesium compound layer between the metal oxide layer and the organic compound layer. Electroluminescent device.
The layer including a structure having a metal species on the metal oxide layer has a structure in which a single metal having a work function of 4.0 eV or less or an oxide thereof is sandwiched between two layers of metal oxide. The organic electroluminescent element according to claim 2, wherein the organic electroluminescent element is a layer.
A display device comprising the organic electroluminescent element according to any one of claims 1 to 4.
An illumination device comprising the organic electroluminescent element according to any one of claims 1 to 4.