JP7811856B2 - Thin-film light-emitting element, string-shaped light source using the same, and light source system using the same - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Nippon Shokubai Co., Ltd. News Release April 19, 2021 https://www.shokubai.co.jp/ja/news/news0462.html Exhibition "Ambient Weaving - Environment and Textiles" to be held from April 17, 2021 to July 18, 2021

The present invention relates to a thin-film light-emitting element, a string-shaped light source using the same, and a light source system using the same.

Light irradiation is used for a variety of purposes, including lighting to obtain brightness, chemical reactions, sterilization, and disinfection. Light sources used for light irradiation vary in shape depending on the application. For example, a lighting device for visual inspection using a curved, hemispherical, or spherical light source, used in visual inspection methods to observe the surface condition of metal objects, has been disclosed (see Patent Document 1). In recent years, attempts have also been made to utilize light irradiation for cosmetic purposes and the treatment of injuries and diseases. Examples include portable devices that emit light using organic light-emitting semiconductors and are adapted to conform to the surface of the area to be treated with light, light treatment patches that conform to non-planar parts of the patient's body, and sealed biocompatible light irradiation devices that include a flexible substrate and a light-emitting element containing an organic semiconductor or quantum dots, enclosed in a protective bag (see Patent Documents 2 to 4). Furthermore, a method has been proposed in which a sheet containing organic electroluminescent elements is applied to the skin and irradiated with light to activate the skin, thereby achieving cosmetic or therapeutic effects (see Patent Document 5 and Non-Patent Documents 1 and 2).

Japanese Patent Application Publication No. 04-178541 Patent No. 4651281 International Publication No. 00/015296 International Publication No. WO 17/038655 JP 2015-142717 A

Yongmin Jeon and seven others, "Advanced Materials Technologies," 2018, 1700391 Tomoyuki Yokota and 9 others, "Science Advances", 2016, No. 2, e1501856

As mentioned above, light sources are used in shapes suited to their applications, and in the fields of beauty and medical treatment, the use of flexible light sources has been proposed, which allow light to be emitted in a way that conforms to the shape of the area to be affected. Flexible light sources are expected to be used in a variety of applications, not limited to the beauty and medical treatment fields, including curved surface illumination and decoration of curved structural surfaces. However, because they are, in principle, two-dimensional light sources, it is physically impossible for them to conform to free-form surfaces, except on stretchable substrates. Meanwhile, while there have been research reports on fabricating light-emitting devices on stretchable substrates, several breakthroughs are currently required for practical use due to issues such as manufacturing and device reliability. From this perspective, there is a demand for thin-film light-emitting devices that are practical, highly flexible, and have the ability to conform to free-form surfaces.

The present invention was made in consideration of the above-mentioned current situation, and aims to provide a thin-film light-emitting device with excellent flexibility.

The inventors investigated thin-film light-emitting devices with excellent flexibility and discovered that by adjusting a thin-film light-emitting device with a Young's modulus within a specified range to a specified thickness and shape, it becomes a thin-film light-emitting device with excellent flexibility, leading to the present invention.

In other words, the present invention is a thin-film light-emitting device characterized by having a Young's modulus of 10,000 MPa or less, an average thickness of 0.2 mm or less, and a ratio of the longitudinal length of the element to the longest length perpendicular to the longitudinal direction of 10 or more.

It is preferable that the above-mentioned thin-film light-emitting element has electrode lead-out portions at both longitudinal ends of the element.

The above-mentioned thin-film light-emitting element is preferably an organic electroluminescent element having a structure in which multiple layers are stacked between an anode and a cathode, with one or more organic compound layers between the anode and the cathode, and with the cathode located on the substrate side.

In the above organic electroluminescent device, it is preferable that the average thickness of the upper electrode be 20 nm or more.

The present invention also relates to a strip-shaped light source characterized by using the thin-film light-emitting element of the present invention.

The present invention is also a light source system that achieves the effect of a surface light source by using multiple strip light sources of the present invention.

The thin-film light-emitting device of the present invention is highly flexible and has excellent conformability to free-form surfaces, making it suitable for applications requiring high flexibility, such as lighting curved surfaces and decorating the surfaces of curved structures.

FIG. 10 is a diagram showing the results of a nonlinear stress analysis performed when a PET substrate having a Young's modulus of 3000 MPa is bent. FIG. 10 is a diagram showing the results of a nonlinear stress analysis performed when a PET substrate having a Young's modulus of 2000 MPa is bent. 10 is a diagram showing the results of a nonlinear stress analysis of a string-shaped film having a film thickness of 200 μm and an aspect ratio of 10, in which the film is subjected to forced rotation about an axis. 10 is a diagram showing the results of a nonlinear stress analysis of a string-shaped film having a film thickness of 200 μm and an aspect ratio of 15, in which the film is subjected to forced rotation about its axis. 10 is a diagram showing the results of a nonlinear stress analysis of a string-shaped film having a film thickness of 100 μm and an aspect ratio of 10, in which the film is subjected to forced rotation about an axis. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a schematic diagram showing an example of a laminate structure when the thin-film light-emitting element of the present invention is an organic electroluminescent element. 1 is a photograph showing the thin-film light-emitting element produced in Example 1 wound around a glass rod having an outer diameter of 3 mm and emitting light.

The present invention will be described in detail below.
It should be noted that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

The thin-film light-emitting element of the present invention is characterized in that the Young's modulus of the element is 10,000 MPa or less, the average thickness is 0.2 mm or less, and the ratio of the length in the longitudinal direction of the element to the longest length direction perpendicular to the longitudinal direction (aspect ratio) is 10 or more.
The present invention aims to achieve this by studying the conditions under which a thin-film light-emitting element can have excellent conformability to a free-form surface and realizing an element that can be twisted.
The inventors calculated the conditions for an element that can be twisted by performing a bending test using a film light source with an element thickness of 0.1 mm and a mechanical simulation.
(1) First, using the 0.1 mm thick organic electroluminescent element (element size 3.5 cm × 3.5 cm) produced in Example 1 of Japanese Patent Application No. 2021-071277, a bending test was performed 100,000 times at a bending radius of 2 mm using a bending tester manufactured by Yuasa System Co., Ltd. It was confirmed that there was no change in the visual unevenness of light emission before and after the test, and furthermore, there was no change in the voltage-luminance characteristics at multiple light-emitting positions. This confirmed that the characteristics of the thin-film light-emitting element were not affected by the stress applied under these conditions.
(2) Next, the stress to which the element is subjected under the conditions of this bending test was calculated by a mechanical simulation under the following conditions, and the generated stress was estimated to be about 100 MPa.
These results indicate that the thin film light emitting device under the above conditions is not affected by a stress of at least about 100 MPa.
<Mechanical simulation of stress in bending tests>
The analysis method is as follows.
A nonlinear stress analysis was performed using a continuum simulation. It was confirmed that the final state could be reproduced by multi-stage bending.
The usage model is as follows:
- Homogeneous linear elastic body (plasticity not considered)
Young's modulus: variable Poisson's ratio: 0.4 (bulk physical property value of PET)
・Shell primary accuracy (thickness 0.1 mm)
・Mesh pitch 1mm
Since the Young's modulus of PET, the base material of the organic electroluminescent device subjected to the bending test, was 2000 to 3000 MPa, stress analysis was performed when the device was bent at a Young's modulus of 3000 MPa and 2000 MPa. The analysis results are shown in Figures 1 and 2, respectively. As a result of the stress analysis, when the Young's modulus was 3000 MPa, an equivalent stress of about 95 MPa was generated at the bent portion, and when the Young's modulus was 2000 MPa, an equivalent stress of about 63 MPa was generated at the bent portion. From these results, it was estimated that the maximum stress generated under the bending test conditions in (1) above was about 100 MPa.
(3) Furthermore, using these results, we performed a simulation under the following conditions to calculate what conditions an element would have to have in order to generate a stress of less than 100 MPa in response to the torsion stress that is the target of the present invention.
<Mechanical simulation of stress in twisting>
The analysis method is as follows.
A nonlinear stress analysis was performed using a continuum simulation to calculate the stress caused by forced rotation around the axis.
The usage model is as follows:
- Homogeneous linear elastic body (plasticity not considered)
Young's modulus: 10,000 MPa
Poisson's ratio: 0.4 (bulk physical property value of PET)
・Shell primary accuracy (thickness 0.2 mm)
・Mesh pitch 0.5mm
The results of analysis of a string-like shape with a film thickness of 200 μm and an aspect ratio of 10, a string-like shape with a film thickness of 200 μm and an aspect ratio of 15, and a string-like shape with a film thickness of 100 μm and an aspect ratio of 10 are shown in Figures 3 to 5, respectively. As a result of the analysis, the maximum stress when twisted was approximately 110 MPa for the string-like shape with a film thickness of 200 μm and an aspect ratio of 10. Furthermore, the maximum stress when twisted was 70 MPa for the film thickness of 200 μm and an aspect ratio of 15 and 40 MPa for the film thickness of 100 μm and an aspect ratio of 10.
These simulation results showed that the criteria for a stress equivalent to 100 MPa on the element were a Young's modulus of 10,000 MPa, a film thickness of 0.2 mm, and an aspect ratio of 10. It is clear that a good element can be obtained in a direction where the stress is smaller than this, and therefore, from the viewpoint of materials engineering, it was found that an element having physical properties of a Young's modulus of 10,000 MPa or less, a film thickness of 0.2 mm or less, and an aspect ratio of 10 or more will be subjected to a stress of 100 MPa or less and will be unaffected by twisting.
The present invention has discovered that by forming an element having a Young's modulus of 10,000 MPa or less into a shape having an average thickness of 0.2 mm or less and an aspect ratio of 10 or more, it becomes a highly flexible light-emitting element that can also be twisted.

The Young's modulus of the thin-film light-emitting device of the present invention may be 10,000 MPa or less, preferably 5,000 MPa or less, and more preferably 3,000 MPa or less.
The Young's modulus of the thin-film light-emitting device can be measured using a tensile tester.

The thin-film light-emitting device of the present invention may have an average thickness of 0.2 mm or less and an aspect ratio (ratio) of the longitudinal length of the device to the longest direction perpendicular to the longitudinal length of 10 or more, but the average thickness is preferably 0.12 mm or less. More preferably, it is 0.10 mm or less, and even more preferably, it is 0.07 mm or less. Furthermore, from the viewpoint of device handleability, the average thickness is preferably 0.07 μm or more. More preferably, it is 0.10 μm or more.
The thin-film light-emitting element of the present invention may have an elongated shape with an aspect ratio of 10 or more, but the aspect ratio is preferably 15 or more, and more preferably 30 or more. From the viewpoint of handling, the actual length of the shorter side that constitutes the length ratio is preferably 1 mm or more, and more preferably 3 mm or more.

The thin-film light-emitting element of the present invention preferably has electrode lead-out portions at both longitudinal ends of the element. Because the thin-film light-emitting element of the present invention is a thin film, the resistance of the wiring cannot be ignored, causing a drop in voltage and resulting in uneven light emission brightness. One method of preventing this can be to position the lead-out portions of both electrodes, which are normally placed close to each other for convenience in wiring placement, at the farthest positions. In this case, the upper electrode may be led out not only on one side but also on both sides. Similarly, the lower electrode may be led out not only on one side but also on both sides. This makes it possible to realize a film light source that can be twisted to follow free-form surfaces and has more uniform light emission.

A string-shaped light source made of the light-emitting element of the present invention is, by itself, merely a linear light source, and is not sufficient for, for example, cosmetic or medical applications that use light to produce effects. Therefore, by arranging multiple string-shaped light sources of the present invention on a free-form surface, it is possible to create a pseudo-planar light source. This makes it possible to provide a light source system with a pseudo-planar light source that can follow the free-form surface.

Described below is the configuration of an organic electroluminescent device that can be used as a thin-film light-emitting device, with a Young's modulus of 10,000 MPa, an average thickness of 0.2 mm or less, and an aspect ratio of 10 or more, as discovered from the bending test results and simulations of the actual device described above. Realizing a practical organic electroluminescent device with this thickness and length (the short axis side does not have enough physical distance to prevent water and oxygen penetration) places limitations on the sealing configuration of barrier films, etc., and therefore organic electroluminescent devices that are resistant to water and oxygen and do not rely too heavily on barrier function are suitable for the organic electroluminescent device of the present invention. The details are as follows:

The organic electroluminescent element used as the thin-film light-emitting element of the present invention preferably has a structure in which a plurality of layers are stacked between an anode and a cathode, has one or more organic compound layers between the anode and the cathode, and further has the cathode present on the substrate side.
Among organic electroluminescent devices, the thin-film light-emitting device is an organic electroluminescent device with a so-called inverted structure in which a cathode is formed on a substrate, making the organic electroluminescent device resistant to water and oxygen and less dependent on a barrier film, resulting in a more flexible thin-film light-emitting device that is practical and has excellent flexibility against twisting, etc.

The organic electroluminescent device is preferably an element having an electron injection layer and/or an electron transport layer, a light-emitting layer, and a hole transport layer and/or a hole injection layer, in this order, between a cathode and an anode formed on a substrate. The organic electroluminescent device may have layers other than these layers, such as a hole blocking layer, which will be described later.
The organic electroluminescent device is preferably an element having an electron injection layer and/or electron transport layer, a light-emitting layer, a hole transport layer and/or hole injection layer, which are adjacent to each other in this order between a cathode and an anode formed on a substrate, or more preferably an element having an electron injection layer and/or electron transport layer, a hole blocking layer, a light-emitting layer, a hole transport layer and/or hole injection layer, which are adjacent to each other in this order between a cathode and an anode formed on a substrate.
Each layer constituting these organic electroluminescent devices may consist of one layer or two or more layers.

Preferred embodiments of the organic electroluminescent device include: (1) an organic electroluminescent device having an organic layer including a light-emitting layer between a cathode and an anode, and comprising a laminated layer in which a metal electron injection layer that is a metal thin film adjacent to the cathode and an organic electron injection layer that contains an organic material that undergoes a coordination reaction with a metal element in the metal layer are stacked; and (2) an organic electroluminescent device having an organic layer including a light-emitting layer between a cathode and an anode, and comprising a cathode that is a layer that contains magnesium, silver, and/or aluminum, where the volume ratio of magnesium is 2% or more and 30% or less, has an average thickness of 40 nm or less, and an organic electron injection layer adjacent to the cathode that contains an organic material that can form a coordinate bond to a metal atom.
Hereinafter, the organic electroluminescent device of (1) above will be referred to as an organic electroluminescent device of a first preferred embodiment, the organic electroluminescent device of (2) above will be referred to as an organic electroluminescent device of a second preferred embodiment, and the combination of both will be referred to as an organic electroluminescent device of a preferred embodiment of the present invention.
When configured as in the organic electroluminescent device of the second preferred embodiment, excellent electron injection properties are achieved through the coordination bond between magnesium and an organic material capable of forming a coordination bond with a metal atom. Furthermore, by incorporating a small amount of magnesium into the cathode together with silver and/or aluminum to form a layer with an average thickness of 40 nm or less, it is possible to obtain a device with excellent atmospheric stability while using magnesium, which has a low work function. Furthermore, devices with such a configuration have a longer life than devices with a metal oxide layer on the cathode described above. The mechanism behind this is thought to be that magnesium has denser coordination bonds than an oxide layer, thereby firmly and uniformly reducing the injection barrier and reducing the intrusion of oxygen and water from the outside.

Next, the organic electroluminescent device of the present invention will be described in detail with reference to examples.
Figure 6 is a schematic cross-sectional view illustrating an example of the layered structure of the organic electroluminescent device of the first preferred embodiment. Here, an inverted structure is shown. The organic electroluminescent device 1 of this embodiment shown in Figure 6 has an emitting layer 8 between a cathode 3 and an anode 11. In the organic electroluminescent device 1 shown in Figure 6, a metal electron injection layer 5 and an organic electron injection layer 6, which are components of the present invention, are adjacently present between the cathode 3 and the emitting layer 8. Furthermore, an electron transport layer 7 and a hole blocking layer 12 are also present as necessary. A hole transport layer 9 and a hole injection layer 10 are present between the emitting layer 8 and the anode 11.
Other examples of the configuration of the organic electroluminescent device according to the first preferred embodiment of the present invention include the configurations shown in FIGS.

Figures 12 and 13 are schematic cross-sectional views illustrating an example of the layered structure of an organic electroluminescent device according to a second preferred embodiment. An inverted structure is shown here. The organic electroluminescent device 1 of this embodiment shown in Figures 12 and 13 has an emitting layer 8 between a cathode 3 and an anode 11. In the organic electroluminescent device 1 shown in Figures 12 and 13, an organic electron injection layer 6 is present adjacent to the cathode 3 between the cathode 3 and the emitting layer 8. An electron transport layer 7 and a hole blocking layer 12 are also present as necessary. A hole transport layer 9 and a hole injection layer 10 are present between the emitting layer 8 and the anode 11. A metal oxide layer 4 may be used as a base for the cathode 3 to enhance the stability of the cathode (Figures 15 and 16). Another example of the configuration of the organic electroluminescent device according to the second preferred embodiment is the configuration shown in Figure 14.

In this embodiment, an organic electroluminescent device 1 having an inverted structure will be described as an example, but the organic electroluminescent device of the present invention may also have a forward structure in which an anode is disposed between a substrate and a light-emitting layer. Furthermore, the organic electroluminescent device may be a bottom emission device in which light is extracted from the substrate side, or a top emission device in which light is extracted from above the substrate.
When the organic electroluminescent device of the first preferred embodiment of the present invention has a forward structure, it has a laminated structure in which the organic electron injection layer and the metal electron injection layer are in contact with each other between the cathode and the light-emitting layer, as in the case of the inverted structure.
When the organic electroluminescent device of the second preferred embodiment has a forward structure, it also has an organic electron injection layer adjacent to the cathode between the cathode and the light-emitting layer, as in the case of the inverted structure.
The materials, thicknesses, and sealing of each layer constituting the organic electroluminescent element described below are the same for the organic electroluminescent element of the first preferred embodiment as for the organic electroluminescent element of the forward structure, except for the materials of the cathode and anode described later. Only for the top emission element of the inverted structure, there is no limitation on the film thickness of the metal electron injection layer described later, and any thickness is acceptable.
Regarding the organic electroluminescent device of the second preferred embodiment, the materials, thicknesses and sealing of each layer constituting the organic electroluminescent device are the same as those of the organic electroluminescent device of the forward structure, except for the material of the anode, which will be described later.
The materials for each layer of the organic electroluminescent device will be described below.

"substrate"
Examples of materials for the substrate include resin materials.
Examples of resin materials used for the substrate include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, etc. When a resin material is used as the substrate material, an organic electroluminescent device having excellent flexibility can be obtained, which is preferable.

When the organic electroluminescent device is a bottom emission type, a transparent substrate is used as the substrate material.
When the organic electroluminescent element is a top-emission type, the substrate may be an opaque substrate as well as a transparent substrate. Examples of the opaque substrate include a substrate in which an oxide film (insulating film) is formed on the surface of an ultrathin metal plate such as stainless steel, and a substrate made of a resin material.

The average thickness of the substrate can be determined depending on the material of the substrate, etc., and is preferably 0.01 to 0.2 mm, more preferably 0.02 to 0.1 mm.
The average thickness of the substrate can be measured using a digital multimeter and a vernier caliper.

"cathode"
The cathode is formed on and in direct contact with the substrate.
The cathode can be made of a transparent conductive material such as ITO (tin-doped indium oxide), ATO (antimony-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), or FTO (fluorine-doped indium oxide), or an opaque conductive material such as calcium, magnesium, aluminum, tin, indium, copper, silver, gold, platinum, or an alloy of these.

In the organic electroluminescent device according to the first preferred embodiment of the present invention, the cathode material is preferably a material having a work function of 4.0 eV or more, such as conductive oxide materials such as ITO (indium tin oxide), IZO (indium zinc oxide), _{FTO (fluorine tin oxide), In3O3 , SnO2} , Sb-containing _SnO2 , and Al-containing ZnO, as well as silver or a silver alloy. Among these, ITO, IZO, FTO, and silver are preferably used as the cathode material.
In the organic electroluminescent device according to a second preferred embodiment of the present invention, the cathode is a layer formed containing magnesium, which is an elemental metal, and silver and/or aluminum. The cathode may contain either silver or aluminum, or both. The volume ratio of magnesium in the layer containing magnesium and silver and/or aluminum is 30% or less. With such a ratio, the device exhibits excellent electron injection properties and also excellent atmospheric stability. The volume ratio of magnesium is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. Furthermore, in order to exhibit better electron injection properties, the volume ratio of magnesium is 2% or more, preferably 3% or more, and more preferably 4% or more.
These materials can be used as the anode material when the organic electroluminescent device of the present invention has a forward structure in which the anode is disposed between the substrate and the light-emitting layer. In this case, the average thickness of the anode is preferably the same as that of the cathode.
The work function was based on the value described in Journal of Applied Physics, Vol. 48, 1977, p. 4729.

The average thickness of the cathode is preferably 7 nm or more. With such a thickness, the electrical resistance of the electrode can be reduced, the thin-film light-emitting device of the present invention can have better light-emitting properties, and manufacturing variations can be suppressed. The average thickness of the cathode is more preferably 5 nm or more, and even more preferably 10 nm or more. Furthermore, the average thickness of the cathode is preferably 40 nm or less. With such a thickness, the device has excellent atmospheric stability. The average thickness of the cathode is preferably 35 nm or less, and more preferably 25 nm or less.
The average thickness of the cathode can be measured by a stylus step gauge or spectroscopic ellipsometry.
In the case of an inverted structure, the cathode is the lower electrode and an auxiliary electrode can be disposed, so the thickness is not very important.

"Electron injection layer"
The electron injection layer may be made of an organic material or an inorganic material.
When the electron injection layer is made of an inorganic material, examples of the electron injection layer include a layer made of a single metal oxide film, or a semiconductor or insulator laminated thin film layer in which a single metal oxide or two or more types of metal oxides are laminated and/or mixed, and examples of the metal element constituting the metal oxide include a metal element selected from the group consisting of magnesium, calcium, strontium, barium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, indium, gallium, iron, cobalt, nickel, copper, zinc, cadmium, aluminum, and silicon.
When the electron injection layer is made of an organic material, examples of the material include nitrogen-containing compounds, such as pyrrolidones such as polyvinylpyrrolidone, pyrroles such as polypyrrole, anilines such as polyaniline, pyridines such as polyvinylpyridine, as well as compounds having a nitrogen-containing heterocycle such as pyrrolidines, imidazoles, piperidines, pyrimidines, and triazines, and amine compounds.

"Metal electron injection layer"
When the organic electroluminescent device is the device of the first preferred embodiment of the present invention, the metal electron injection layer in the device is a layer composed of a metal species that is positioned as the central metal of a metal complex when the material contained in the organic electron injection layer is used as a ligand, so that it may be a thin film functionally, and in the case of bottom emission, transparency is required, so that the thickness is preferably 0.1 to 5 nm, more preferably 0.5 to 2 nm. In the case of top emission, transparency is not required, and there is no limit to the thickness.
The average thickness of the metal electron injection layer can be measured by a stylus profilometer or spectroscopic ellipsometry.

The material contained in the metal electron injection layer may be a simple substance of a metal species having coordination ability, but in view of stability in the atmosphere, it is preferable that the material has a work function of 4.0 eV or more.
The metal electron injection layer may be a metal layer of a single metal, a layer in which a layer of a mixture of two or more metals and a layer of a single metal are laminated, or a layer in which two or more metals are mixed. The metal electron injection layer may also serve as a cathode.
Examples of metal elements that form the metal electron injection layer include copper, nickel, palladium, platinum, gold, cobalt, zinc, aluminum, chromium, manganese, iron, tin, indium, titanium, zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, indium, gallium, and cadmium.
The work function was determined based on the value described in Journal of Applied Physics, Vol. 48, 1977, p. 4729.
When the metal electron injection layer includes a layer containing a mixture of two or more metal elements, it is preferable that at least one of the metal elements constituting the metal layer is aluminum, zinc, or copper.
When the metal electron injection layer is a layer made of one kind of metal, it is preferably a layer made of a metal selected from the group consisting of aluminum, zinc, and copper.

"Organic electron injection layer"
In the organic electroluminescent device of the first preferred embodiment, the organic electron injection layer improves electron injection by forming a complex with the metal electron injection layer.
In the organic electroluminescent device of the second preferred embodiment, the organic electron injection layer improves electron injection by forming a complex with magnesium contained in the cathode.
In this case, the organic material forming the organic electron injection layer may be any organic material having coordination ability. Among them, compounds having a nitrogen atom-containing substituent are preferred, and compounds having a nitrogen atom-containing heterocyclic condensed ring structure are more preferred. For example, the organic material contained in the organic electron injection layer of the present invention may be a compound having a structure represented by the following general formula (1):

(In general formula (1), X ¹ and X ² are the same or different and represent a nitrogen atom, oxygen atom, sulfur atom, or divalent linking group which may have a substituent. L represents a direct bond or a p-valent linking group. ^{n 1} is the number 0 or 1, p is the number of 1 to 4. q is the number 0 or 1, and when p is 1, q is 0. ^{R 1} to R ³ are the same or different and represent a monovalent substituent. m ¹ to m ³ are the same or different and represent the numbers 0 to 3. ^{R 1} to R ³ may be bonded to X ¹ and X ² to form a ring structure. When there are multiple R ^1s , multiple R ^1s may be bonded to form a ring structure. The same applies to ^{R 2} and R ^3. )

In the general formula (1), X ¹ and X ² are the same or different and represent a nitrogen atom, an oxygen atom, a sulfur atom or a divalent linking group which may have a substituent.
Examples of the divalent linking group include divalent hydrocarbon groups and groups in which some of the carbon atoms of a hydrocarbon group have been substituted with a heteroatom such as a nitrogen atom, an oxygen atom, or a sulfur atom.
The hydrocarbon group preferably has 1 to 6 carbon atoms, and more preferably has 1, 2 or 6 carbon atoms.
The hydrocarbon group may be linear, branched, cyclic, or a combination thereof.
The divalent hydrocarbon group may be an alkylene group, which is a saturated hydrocarbon group, or an unsaturated hydrocarbon group such as an alkenylene group or an alkynylene group.
Specific examples of divalent hydrocarbon groups are those represented by the following formulas (2-1) to (2-4). R in the following formulas (2-1) to (2-4) represents a substituent. Specific examples of the substituents in X ¹ and X ² , including R in (2-1) to (2-4), include the same groups as the monovalent substituents of R ¹ to R ³ described below.

In the general formula (1), L represents a direct bond or a p-valent linking group. L is a direct bond only when p is 2.
Examples of the p-valent linking group include a nitrogen atom, an oxygen atom, a sulfur atom, and a carbon atom, as well as a group obtained by removing p hydrogen atoms from a hydrocarbon group or a group in which some of the carbon atoms of a hydrocarbon group have been substituted with a hetero atom such as a nitrogen atom, an oxygen atom, or a sulfur atom.
When the p-valent linking group has carbon atoms, it preferably has 1 to 30 carbon atoms, and more preferably has 1 to 20 carbon atoms.
The hydrocarbon group may be linear, branched, cyclic, or a combination thereof.
The hydrocarbon group may be any of a saturated hydrocarbon group, an unsaturated hydrocarbon group, and an aromatic hydrocarbon group.
Examples of aromatic hydrocarbon groups include groups formed by removing a hydrogen atom from an aromatic compound such as a benzene ring, a naphthalene ring, an anthracene ring, a tetracene ring, a pentacene ring, a triphenylene ring, a pyrene ring, a fluorene ring, or an indene ring.

In the above general formula (1), R ¹ to R ³ are the same or different and represent monovalent substituents.
Examples of the monovalent substituent include a fluorine atom; haloalkyl groups such as a fluoromethyl group, a difluoromethyl group, and a trifluoromethyl group; linear or branched alkyl groups having 1 to 20 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group; cyclic alkyl groups having 5 to 7 carbon atoms such as a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group; methoxy groups, ethoxy groups, propoxy groups, isopropoxy groups, butoxy groups, isobutoxy groups, tert-butoxy groups, pentyloxy groups, hexyloxy groups, heptyloxy groups, and oxy groups. linear or branched alkoxy groups having 1 to 20 carbon atoms, such as a ctyloxy group; a nitro group; a cyano group; an alkylamino group having an alkyl group having 1 to 10 carbon atoms, such as a methylamino group, an ethylamino group, a dimethylamino group, or a diethylamino group; a cyclic amino group, such as a pyrrolidino group, a piperidino group, or a morpholino group; a diarylamino group, such as a diphenylamino group or a carbazolyl group; an acyl group, such as an acetyl group, a propionyl group, or a butyryl group; an alkenyl group having 2 to 30 carbon atoms, such as a styryl group; a halogen atom, such as a fluorine atom, or an alkyl group, alkoxy group, or amino group having 1 to 20 carbon atoms, an aryl group having 5 to 20 carbon atoms which may be substituted with (specific examples of the aryl group are the same as those of the aromatic hydrocarbon group described above); a heterocyclic group having 4 to 40 carbon atoms which contains one or more of a nitrogen atom, a sulfur atom, and an oxygen atom which may be substituted with a halogen atom such as a fluorine atom, an alkyl group, an alkoxy group, an amino group, or the like having 1 to 20 carbon atoms (the heterocyclic group may consist of only one ring, or may be a compound in which a plurality of compounds consisting of only one aromatic heterocyclic ring are directly bonded together at one carbon atom, or may be a fused heterocyclic group. Specific examples of the heterocyclic group include a thiophene ring, a furan ring, a phenyl ... Specific examples of aromatic heterocyclic groups include a ring, a pyrrole ring, a benzothiophene ring, a benzofuran ring, an indole ring, a dibenzothiophene ring, a dibenzofuran ring, a carbazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an imidazole ring, a benzimidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzothiadiazole ring, and a phenanthridine ring.); an ester group, a thioether group, etc., and groups formed by combining these. These groups may be substituted with a halogen atom, a hetero element, an alkyl group, an aromatic ring, etc.

The compounds represented by the above general formula (1) include compounds having a structure represented by the following general formula (3), which has only one phenanthroline skeleton, and these compounds are also suitable as materials for the organic electron injection layer in the present invention.

(In general formula (3), R ⁴ and R ⁵ are the same or different and represent a dialkylamino group or an alkoxy group. ^{m 4} and m ⁵ are the same or different and represent the number 1 or 2. When there are multiple R ^4s , the multiple R ^4s may be bonded to form a ring structure. The same applies to R ^5. )

R ⁴ and R ⁵ in the above general formula (3) may be the same or different and represent a dialkylamino group or an alkoxy group.
The dialkylamino group preferably has an alkyl group having 1 to 20 carbon atoms, such as a methyl group or an ethyl group. More preferably, it has an alkyl group having 1 to 10 carbon atoms. The two alkyl groups in the dialkylamino group may have the same or different carbon atoms. Also preferred are amino groups in which two alkyl groups are linked together, such as cyclic amino groups such as piperidino, pyrrolidino, and morpholino groups.
Examples of the alkoxy group include the same as those in the case where R ¹ to R ³ in the general formula (1) are alkoxy groups.

In addition to compounds with only one phenanthroline skeleton, compounds with multiple phenanthroline skeletons, such as those shown in formulas (4-1) to (4-4) below, are also thought to be effective in generating negative charges.

Furthermore, p in the above general formula (1) represents a number from 1 to 4, but is preferably a number from 1 to 3. Specific examples of compounds in which p in general formula (1) is 1 include compounds represented by the following formulas (5-1) to (5-9).

In the general formula (1), ⁿ¹ represents the number 0 or 1, and in one preferred embodiment of the present invention, the compound represented by the general formula (1) is a compound in which ⁿ¹ is 0. Specific examples of the compound in the general formula (1) in which ⁿ¹ is 0 include the compounds represented by the formulae (5-1) to (5-6).

Also suitable are compounds represented by the following formulas (5-10) to (5-65), which are included in the above general formula (1) and have a structure similar to the above.

Furthermore, various compounds having a structure represented by the following formulae (5-66) to (5-68) as a skeletal structure, which has a coordinating nitrogen atom, can also be used as a material for the organic electron injection layer. These compounds include compounds having the structures represented by the following formulae (5-66) to (5-68), as well as compounds having a substituent in the structure represented by the following formulae (5-66) to (5-68). Examples of the substituent include the same as those for R ¹ to R ³ in the above-mentioned general formula (1), and the number of substituents may be one or more. When there are more than one substituent, the substituents may be bonded to each other to form a ring structure.

Furthermore, a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (6) can also be used as a material for the organic electron injection layer.

(In general formula (6), ^R6 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent to tetravalent linear or cyclic hydrocarbon group which may have a substituent, a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom. ⁿ² is an integer of 1 to 4.)

Hexahydropyrimidopyrimidine compounds having the structure represented by the above general formula (6) can coordinate with the magnesium contained in the cathode when the cathode contains magnesium, preventing reactions at the interface with oxygen or water entering from the outside and improving the atmospheric stability of the device. Furthermore, the dipole generated by interacting with the magnesium contained in the cathode can result in improved electron injection from the cathode.

^R6 in the general formula (6) above represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent to tetravalent linear or cyclic hydrocarbon group which may have a substituent, a group formed by combining two or more of these groups, or a group formed by combining one or more of these groups with a nitrogen atom.
The aromatic hydrocarbon group and aromatic heterocyclic group preferably have 3 to 30 carbon atoms, more preferably 4 to 24 carbon atoms, and even more preferably 5 to 20 carbon atoms.
Examples of aromatic hydrocarbon groups include compounds consisting of only one aromatic ring, such as benzene; compounds in which multiple aromatic rings are directly bonded to each other via one carbon atom, such as biphenyl and diphenylbenzene; and groups obtained by removing 1 to 4 hydrogen atoms from any of the aromatic rings of fused-ring aromatic hydrocarbon compounds, such as naphthalene, anthracene, phenanthrene, and pyrene.
Examples of the aromatic heterocyclic group include compounds consisting of only one aromatic heterocycle, such as thiophene, furan, pyrrole, oxazole, oxadiazole, thiazole, thiadiazole, imidazole, pyridine, pyrimidine, pyrazine, and triazine; compounds in which a plurality of such compounds consisting of only one aromatic heterocycle are directly bonded to each other via one carbon atom (e.g., bipyridine); and groups obtained by removing 1 to 4 hydrogen atoms from any aromatic heterocycle of fused-ring heteroaromatic hydrocarbon compounds, such as quinoline, quinoxaline, benzothiophene, benzothiazole, benzimidazole, benzoxazole, indole, carbazole, dibenzofuran, dibenzothiophene, acridine, and phenanthroline.
The aryl alkylene group includes a group formed by combining the above aromatic hydrocarbon group with an alkylene group having 1 to 3 carbon atoms.
The divalent to tetravalent chain or cyclic hydrocarbon group preferably has 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. The chain hydrocarbon group may be linear or branched.
Furthermore, ^R6 may be a group formed by combining two or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, aryl alkylene groups, and divalent to tetravalent chain hydrocarbon groups.
Furthermore, ^R6 may be a group formed by combining one or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, and divalent to tetravalent chain hydrocarbon groups with a nitrogen atom. Examples of such groups include groups formed by removing 1 to 4 hydrogen atoms from trialkylamines such as trimethylamine or triphenylamine.

The aromatic hydrocarbon group, aromatic heterocyclic group, or arylalkylene group may have one or more monovalent substituents.
Examples of the monovalent substituent include the same as the specific examples of the monovalent substituents of R ¹ to R ³ in the general formula (1) described above.

In the above general formula (6), ⁿ² is an integer of 1 to 4, preferably 2 or 3.
Specific examples of the hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (6) include compounds represented by the following formulas (7-1) to (7-34).

The compound represented by the above general formula (6) can be synthesized using a halogen compound containing iodine, bromine, chlorine, or fluorine and hexahydropyrimidopyrimidine as raw materials via Ullmann coupling reaction, Buchwald-Hartwig amination reaction, nucleophilic substitution reaction, or the like, as shown in the following formula (8).

In addition to these, other compounds that can be used as ligands can also be used, such as compounds in which the nitrogen atoms of the above-mentioned nitrogen-containing compounds are replaced with oxygen atoms. Examples of such compounds include acetylacetonato derivatives.

The average thickness of the organic electron injection layer is preferably 0.5 to 10 nm, more preferably 1 to 5 nm, and even more preferably 1 to 5 nm.
The average thickness of the organic electron injection layer can be measured, for example, by a stylus profilometer or spectroscopic ellipsometry.
Alternatively, the organic electron injection layer may be blended with a subsequent electron transport layer.

"Electron transport material"
For the electron transport layer, any material that can be normally used as a material for an electron transport layer may be used, and can be used as needed.
Specifically, materials for the electron transport layer include phosphine oxide derivatives such as phenyl-dipyrenylphosphine oxide (POPy ₂ ), pyridine derivatives such as tris-1,3,5-(3'-(pyridin-3''-yl)phenyl)benzene (TmPhPyB), quinoline derivatives such as (2-(3-(9-carbazolyl)phenyl)quinoline (mCQ)), pyrimidine derivatives such as 2-phenyl-4,6-bis(3,5-dipyridylphenyl)pyrimidine (BPyPPM), pyrazine derivatives, and bathophenanthroline (BPhen). phenanthroline derivatives such as 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT), triazine derivatives such as 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT), triazole derivatives such as 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), oxazole derivatives such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) ( oxadiazole derivatives such as 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), imidazole derivatives such as 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring carboxylic acid anhydrides such as naphthalene-1,4,5,8-tetracarboxylic dianhydride and 3,4,9,10-perylenetetracarboxylic dianhydride, aromatic ring carboxylic acid anhydrides such as N,N'-dimethyl-3,4,9,10-perylenetetracarboxylic diimide, Cyclic imide compounds, isoindigo derivatives and 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione derivatives (diketopyrrolopyrroles), compounds with a carbonyl group such as truxenone, 1,2,5-thiadiazole derivatives such as naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole and benzo[c][1,2,5]thiadiazole, bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (Zn(BTZ)), ₂ ), various metal complexes represented by tris(8-hydroxyquinolinato)aluminum (Alq ₃ ), and the like; organosilane derivatives represented by silole derivatives such as 2,5-bis(6'-(2',2''-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy); tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB); and boron-containing compounds described in Japanese Patent Application Nos. 2012-228460, 2015-503053, 2015-053872, 2015-081108, and 2015-081109, and these may be used alone or in combination.
In addition to the above materials, aromatic hydrocarbon compounds, which are various hydrocarbon compounds having an aromatic ring, compounds having a nitrogen-boron bond, π-electron-rich heteroaromatic compounds containing an aromatic ring such as a pyrrole ring, a furan ring, or a thiophene ring, and compounds containing a silole ring can also be used.
Among these materials for the electron transport layer, it is particularly preferable to use a phosphine oxide derivative such as _POPy2 , a metal complex such as _Alq3 , or a pyridine derivative such as TmPhPyB.

When the material of the electron injection layer of the organic electroluminescent device is mixed with the electron transport material, the electron transport layer may not be necessary. Furthermore, a portion of these materials may be used as a hole blocking material to form a hole blocking layer. Separately, any material that can be normally used may be used as the material for the hole blocking layer, and can be used as needed.

The average thickness of the electron transport layer is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm.
The average thickness of the electron transport layer can be measured by a stylus profilometer or spectroscopic ellipsometry.

"Emitting layer"
The light-emitting layer may be formed from any of the materials typically used for light-emitting layers, or may be a mixture of these materials. For example, the light-emitting layer may contain bis[2-(2-benzothiazolyl)phenolato]zinc(II) (Zn(BTZ) ₂ ) and tris[1-phenylisoquinoline]iridium(III) (Ir(piq) ₃ ).
For example, three-coordinate iridium complexes with 2,2'-bipyridine-4,4'-dicarboxylic acid as the ligand, such as factotris(2-phenylpyridine)iridium (Ir(ppy) ₃ ), 8-hydroxyquinoline aluminum (Alq ₃ ), tris(4-methyl-8-quinolinolato)aluminum(III) (Almq ₃ ), 8-hydroxyquinoline zinc (Znq ₂ ), and (1,10-phenanthroline)-tris-(4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dionate)europium(III) (Eu(TTA) _{3 ).} (phen)), various metal complexes such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II); benzene-based compounds such as distyrylbenzene (DSB) and diaminodistyrylbenzene (DADSB); naphthalene-based compounds such as naphthalene and Nile Red; phenanthrene-based compounds such as phenanthrene; chrysene-based compounds such as chrysene and 6-nitrochrysene; perylene, N,N'-bis(2,5-di-t-butylphenyl perylene compounds such as 4-(di-cyanomethylene)-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran (DCM); acridine compounds such as acridine; stilbene compounds such as stilbene; 2,5-dibenzothiophene; Thiophene compounds such as thiazolidinone, benzoxazole compounds such as benzoxazole, benzimidazole compounds such as benzimidazole, benzothiazole compounds such as 2,2'-(para-phenylenedivinylene)-bisbenzothiazole, butadiene compounds such as bistyryl(1,4-diphenyl-1,3-butadiene) and tetraphenylbutadiene, naphthalimide compounds such as naphthalimide, coumarin compounds such as coumarin, perinone compounds such as perinone, oxadiazole compounds such as oxadiazole, aldazine compounds, cyclopentadiene compounds such as 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), quinacridone compounds such as quinacridone and quinacridone red, pyridine compounds such as pyrrolopyridine and thiadiazolopyridine, spiro compounds such as 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene, phthalocyanines (H _2Pc ), metal or metal-free phthalocyanine compounds such as copper phthalocyanine; and further, boron compound materials described in JP-A Nos. 2009-155325, 2011-184430, and 2011-6458.
The material forming the light-emitting layer may be a low-molecular-weight compound or a high-molecular-weight compound. In the present invention, the low-molecular-weight material means a material that is not a high-molecular-weight material (polymer), and does not necessarily mean an organic compound with a low molecular weight.

The average thickness of the light-emitting layer is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm.
The average thickness of the light-emitting layer may be measured by a stylus-type step gauge, or may be measured by a quartz crystal film thickness gauge during the formation of the light-emitting layer.

"Hole transport layer"
As the hole transporting organic material used in the hole transport layer, various p-type high molecular weight materials (organic polymers) and various p-type low molecular weight materials can be used alone or in combination.
Specific examples of materials for the hole transport layer include N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD), N4,N4'-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (DBTPB), polyarylamine, fluorene-arylamine copolymer, fluorene-bithiophene copolymer, poly(N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, polythiophene, polyalkylthiophene, polyhexylthiophene, poly(p-phenylenevinylene), polythienylenevinylene, pyrene formaldehyde resin, ethylcarbazole formaldehyde resin, and derivatives thereof. These materials for the hole transport layer 8 can also be used as mixtures with other compounds. An example of a mixture containing polythiophene that can be used as a material for the hole transport layer 8 is poly(3,4-ethylenedioxythiophene/styrenesulfonic acid) (PEDOT/PSS).

The average thickness of the hole transport layer is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm.
The average thickness of the hole transport layer can be measured, for example, by a stylus profilometer or spectroscopic ellipsometry.

"Hole injection layer"
The hole injection layer may be made of an inorganic material or an organic material. Inorganic materials are more stable than organic materials, and therefore tend to have higher resistance to oxygen and water than organic materials.

The inorganic material is not particularly limited, but for example, one or more metal oxides such as vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ), and ruthenium oxide (RuO ₂ ) can be used.

Organic materials that can be used include low molecular weight materials such as dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ), as well as poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS).

The average thickness of the hole injection layer is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 5 to 50 nm.
The average thickness of the hole injection layer can be measured during film formation using a quartz crystal film thickness gauge, a stylus step gauge, or spectroscopic ellipsometry.

"anode"
Examples of materials used for the anode include ITO, IZO, Au, Pt, Cu, Ag, Al, and alloys containing these. Among these, ITO, IZO, Au, and Al are preferably used as the material for the anode 10.

In an organic electroluminescent device with an inverted structure, the anode is the upper electrode, and since it is difficult to provide a conductive layer to support conduction, the anode itself must be responsible for conduction. Therefore, the average thickness of the anode is preferably 200 nm or more. With such a thickness, the electrical resistance of the electrode can be reduced, the thin-film light-emitting device of the present invention can have better light-emitting characteristics, and manufacturing variations can be reduced. The average thickness of the anode is more preferably 300 nm or more, and even more preferably 400 nm or more. Furthermore, from the viewpoint of reducing thermal damage to the device, the average thickness of the anode is preferably 300 nm or less.
The average thickness of the anode can be measured during the deposition of the anode using a quartz crystal film thickness meter.

"Sealing"
The organic electroluminescent device of the present invention may be sealed, if necessary.
For example, the organic electroluminescent element may be sealed with a sealed container having a recessed space for accommodating the organic electroluminescent element and an adhesive for bonding the edge of the sealed container to the substrate. Alternatively, the organic electroluminescent element may be housed in a sealed container and sealed by filling it with a sealant made of an ultraviolet (UV) curable resin or the like. Alternatively, the organic electroluminescent element may be sealed with a sealing member made of a plate member disposed on the anode and a frame member disposed along the edge of the plate member facing the anode, and an adhesive for bonding between the plate member and the frame member and between the frame member and the substrate.

When the organic electroluminescent element of the present invention is sealed, the distance from the edge of the sealing container or sealing member to the organic electroluminescent element is preferably 0.1 to 10 mm. If the distance from the edge of the sealing container or sealing member to the organic electroluminescent element is within this range, sealing can be sufficiently maintained even when the element is bent or twisted. The distance is more preferably 0.1 to 5 mm, and even more preferably 0.1 to 2 mm.
The distance from the end of the sealing container or sealing member to the organic electroluminescent element referred to here can also be rephrased as the width of the portion where the sealing containers or sealing members above and below the organic electroluminescent element are in direct contact with each other via an adhesive, ultraviolet curable resin, or the like.

When sealing an organic electroluminescent element using a sealing container or sealing member, a moisture-absorbing desiccant may be placed inside the sealing container or the sealing member. Also, a moisture-absorbing material may be used for the sealing container or the sealing member. Furthermore, a space may be formed inside the sealed sealing container or the sealing member.

Resin materials can be used as the material for the sealing container or sealing member used to seal the organic electroluminescent element. Examples of resin materials used for the sealing container or sealing member include materials similar to those used for the substrate.

In the organic electroluminescent device according to the first preferred embodiment of the present invention, when ITO is used as the cathode, the metal thin film having a work function of 4.0 eV or more is used as the metal electron injection layer, and the organic material having the coordinating ability represented by the general formula (1) is used as the organic electron injection layer, superior durability can be obtained compared to, for example, a case in which an alkali metal, which is an unstable material in the atmosphere, is used as the electron injection layer.
Furthermore, in the organic electroluminescent device according to the second preferred embodiment of the present invention, when the electron injection layer is formed using an organic material having a coordinating ability represented by the general formula (1), superior durability can be obtained compared to, for example, a device in which the electron injection layer is formed only with an alkali metal, which is a material that is unstable in the atmosphere. Therefore, if the water vapor transmission rate of the sealing container or sealing member is on the order of 10 ^-4 to 10 ^-3 (g/m ² /day), deterioration of the organic electroluminescent device can be sufficiently suppressed. Therefore, it is possible to use a resin material having a water vapor transmission rate of on the order of 10 ^-3 (g/m ² /day) or less as the material for the sealing container or sealing member, and an organic electroluminescent device with excellent flexibility can be realized.

In the organic electroluminescent device of the present invention, the method for forming the layer made of the organic compound is not particularly limited, and various methods can be used as appropriate depending on the characteristics of the material. However, if the material can be applied in solution, various coating methods such as spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, slit coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, and inkjet printing can be used to form the film. Of these, spin coating and slit coating are preferred because they allow easier control of the film thickness. In cases where no coating is required or where the solvent solubility is low, suitable examples include vacuum deposition and ESDUS (Evaporative Spray Deposition from Ultra-dilute Solution) methods.

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

Among the layers of the organic electroluminescent device, those made of inorganic materials can be formed by sputtering, vacuum deposition, sol-gel, spray pyrolysis (SPD), atomic layer deposition (ALD), vapor-phase deposition, liquid-phase deposition, and other methods. Metal foil bonding can also be used to form the anode and cathode. These methods are preferably selected based on the characteristics of the material used for each layer, and different fabrication methods may be used for each layer. When the hole injection layer is made of an inorganic material, it is more preferable to form it using a vapor-phase deposition method. Vapor-phase deposition allows the hole injection layer to be formed cleanly and in good contact with the anode without damaging the surface of the organic compound layer, resulting in a more pronounced effect of having a hole injection layer.

The thin-film light-emitting element of the present invention has an average thickness of 0.2 mm or less, and has a long, slender shape in which the ratio of the longitudinal length of the element to the longest length perpendicular to the longitudinal direction is 10 or more. Because the element is highly flexible, it can be used as a string-shaped light source. A string-shaped light source using such a thin-film light-emitting element of the present invention also constitutes one aspect of the present invention.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass."

(Synthesis Example 1)
The compound represented by the following formula (9) was synthesized by the method shown below.

In a 100 mL round-bottom flask, a mixture of 4,7-dichloro-1,10-phenanthroline (3.00 g) and pyrrolidine (19.5 mL) was heated to reflux in an oil bath at 100°C for 1 hour. The mixture was returned to room temperature and concentrated under reduced pressure. Water was added and the mixture was sonicated. The precipitated solid was collected by filtration. The resulting solid was dried under reduced pressure and then dissolved in methanol (100 mL). Activated carbon was added to the mixture and stirred at room temperature for 1 hour, after which the insoluble matter was filtered off. The filtrate was concentrated under reduced pressure, and the resulting solid was recrystallized from methanol (9 mL). The resulting solid was washed with a small amount of methanol and dried under reduced pressure to obtain the compound represented by formula (9) above (1.69 g, 44%) as a white solid.

Example 1
[Step 1] A resist material was applied onto a barrier film manufactured by Oike Kogyo Co., Ltd. (PT7/25GT3, thickness: 25 μm, WVTR: 4×10 ⁻³ g/m ² /day, Young's modulus: 5 GPa) to form a film, and zinc oxide was deposited to a thickness of 24 nm using a sputtering device to form a metal oxide layer 4.
[Step 2] Next, to form a layer containing silver and zinc in a volume ratio of 10:1 and having a total thickness of 14.85 nm as the cathode 3 and metal electron injection layer 5, the substrate treated in [Step 1] was placed in a vacuum chamber, the pressure was reduced to 5 × 10 ^-5 Pa or less, and a film was formed by vacuum deposition.
[Step 3] Next, the material of the above formula (9), which is a material for organic electron injection layers, was laminated by vacuum deposition to form an organic electron injection layer 6 with a thickness of 3 nm, KHLHEI-02 manufactured by Chemipro Chemical Co., Ltd., which is an electron transport material, with a thickness of 15 nm, KHLHS-04 manufactured by Chemipro Chemical Co., Ltd., with a thickness of 15 nm, KHLHS-03, KHLHS-04, and KHLDG-01 manufactured by Chemipro Chemical Co., Ltd., with a thickness of 35 nm, and KHLHS-03, manufactured by Chemipro Chemical Co., Ltd., with a thickness of 25 nm, as a hole-blocking layer 12.
[Step 4] Next, the hole injection layer 10 was formed on the hole transport layer 9. Here, molybdenum oxide was formed to a thickness of 10 nm by vacuum deposition, which is a vapor phase film formation method.
[Step 5] Next, as the final step, an anode 11 was formed on the hole injection layer 10. Here, an aluminum film was formed by vacuum deposition to a thickness of 400 nm. Further, a barrier film (thickness: 25 μm, WVTR: 4×10 ⁻³ g/m ² /day) manufactured by Oike Kogyo Co., Ltd. was applied on top of the anode 11 for sealing.
By the above steps [Step 1] to [Step 5], a film organic electroluminescent device with the configuration shown in Figure 11 was produced. By adjusting the shape of the electrodes, etc., a film element with a length of 150 mm, a width of 5.5 mm, and a thickness of approximately 98 μm was created. The Young's modulus follows the rule of composition, and since most of the volume fraction is made up of the film substrate, it can be approximated and considered to be equivalent to the Young's modulus of the barrier film.
The light-emitting state is shown in Figure 17. The element was successfully wrapped around a glass rod with an outer diameter of 3 mm. The pitch was 1 cm, and it was confirmed that the deterioration behavior in this state was equivalent to that of a normal-shaped element with the same configuration.

1, 21: Organic electroluminescent element, 2: Substrate, 3: Cathode, 4: Metal oxide layer, 5: Metal electron injection layer, 6: Organic electron injection layer, 7: Electron transport layer, 8: Light-emitting layer, 9: Hole transport layer, 10: Hole injection layer, 11: Anode, 12: Hole blocking layer

Claims (6)

a thin-film light-emitting element comprising a film substrate, a structure in which a plurality of layers are laminated between an anode and a cathode, one or more organic compound layers are disposed between the anode and the cathode, the entire laminate structure including the organic compound layers being formed directly on the film substrate, the surface of the laminate structure opposite to the film substrate being sealed with a film, the element having a Young's modulus of 10,000 MPa or less, an average thickness of 0.2 mm or less, and a ratio of the length of the element in the longitudinal direction to the longest length direction perpendicular to the longitudinal direction of 10 or more. The thin-film light-emitting element described in claim 1, characterized in that the thin-film light-emitting element has electrode lead-out portions at both longitudinal ends of the element. The thin-film light-emitting element described in claim 1 or 2 is an organic electroluminescent element having a structure in which multiple layers are stacked between an anode and a cathode, one or more organic compound layers are between the anode and the cathode, and the cathode is further present on the substrate side. The thin-film light-emitting device described in claim 3, characterized in that the average thickness of the upper electrode of the organic electroluminescent device is 20 nm or more. A string-shaped light source characterized by using the thin-film light-emitting element described in any one of claims 1 to 4. A light source system that achieves the effect of a surface light source by using multiple strip light sources as described in claim 5.