JP7538664B2 - Organic thin film and method for producing organic thin film, organic electroluminescence element, display device, lighting device, organic thin film solar cell, photoelectric conversion element, thin film transistor, coating composition, and material for organic electroluminescence element - Google Patents

Description

The present invention relates to an organic thin film and a method for producing an organic thin film, an organic electroluminescence (hereinafter, electroluminescence (field emission) may be abbreviated as "EL") element, a display device, a lighting device, an organic thin film solar cell, a photoelectric conversion element, a thin film transistor, a coating composition, and a material for an organic electroluminescence element.

Organic EL elements are thin, soft, and flexible. Furthermore, displays using organic EL elements are capable of displaying images with higher brightness and higher resolution than the currently mainstream liquid crystal display devices and plasma display devices. Furthermore, displays using organic EL elements have a wider viewing angle than liquid crystal display devices. For this reason, it is expected that displays using organic EL elements will be used more widely in the future as displays for televisions, mobile phones, and the like.
Organic EL elements are also expected to be used as lighting devices.

An organic EL element is a laminate of a cathode, a light-emitting layer, and an anode. In an organic EL element, the energy difference between the work function of the anode and the highest occupied molecular orbital (HOMO) of the light-emitting layer is smaller than the energy difference between the work function of the cathode and the lowest unoccupied molecular orbital (LUMO) of the light-emitting layer. Therefore, it is more difficult to inject electrons from the cathode into the light-emitting layer than to inject holes from the anode. For this reason, in conventional organic EL elements, an electron injection layer is disposed between the cathode and the light-emitting layer to promote the injection of electrons from the cathode into the light-emitting layer. The electron injection layer most widely used in the electron injection layer is a complex containing an alkali metal such as lithium fluoride (LiF) or an alkali metal such as lithium quinoline (Liq) (see, for example, Non-Patent Document 1 and Non-Patent Document 2).
It is also widely practiced to provide an electron transport layer between the light-emitting layer and the electron injection layer, and as a material for the electron transport layer, a compound having a nitrogen-containing heterocycle such as pyridine has been used as a material that easily transports electrons (see, for example, Non-Patent Document 3). It has been reported that the interaction between the nitrogen in the heterocycle contained in these materials that easily transport electrons and Li lowers the barrier for electron injection from the cathode (see Non-Patent Document 2). It has also been reported that if there is a steric hindrance at a site that can coordinate with Li in the material that easily transports electrons, electron injection becomes difficult (see Non-Patent Document 4).

In recent years, several electron injection methods have been proposed that do not use unstable alkali metals such as lithium, in addition to the electron injection method that utilizes the interaction between nitrogen in a heterocycle and Li. One of these is an electron injection method that utilizes hydrogen bonds between a base material and an organic compound (see, for example, Non-Patent Document 5).

L. S. Hung, C. W. Tang, and M. G. Mason, Appl. Phys. Lett. 70, 152 (1997) Sato, S. et al. Air-Stable and High-Performance Solution-Processed Organic Light-Emitting Devices Based on Hydrophobic Polymeric Ionic Li Quid Carrier-Injection Layers. Adv Mater 30, e1705915, (2014) Lixin Xiao, Zhijian Chen, Bo Qu, Jiaxiu Luo, Sheng Kong, Qihuang Gong, and Junji Kido, Adv Mater 23, 926-952 (20 11) Yong-Jin Pu, Makoto Yoshizaki, Takahiro Akiniwa, Junji Kido, Organic Electronics, 10, 877-882 (2009) Hirohiko Fukagawa and 8 others, "Advanced Materials", Vol. 31, 2019, p. 1904201

As mentioned above, in organic EL elements, the materials used between the light-emitting layer and the cathode (electron transport layer) are limited to compounds with nitrogen-containing heterocycles such as pyridine as materials that easily transport electrons, and the degree of freedom in the materials that can be used is low. If it is not necessary to have nitrogen-containing heterocycles such as pyridine, the degree of freedom in material design will increase, and it is expected that the operating stability of the device will improve, the operating voltage will decrease, and the luminous efficiency will improve.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an organic thin film that can broaden the options for materials used between an emitting layer and a cathode in an organic EL element, a method for producing the organic thin film, a coating composition that can be suitably used for producing the organic thin film, and a material for an organic EL element that serves as a raw material for the organic thin film and the coating composition.
Another object of the present invention is to provide an organic EL element using the organic thin film, a display device and a lighting device including the organic EL element, and an organic thin film solar cell, a photoelectric conversion element, and an organic thin film transistor including the organic thin film.

The present inventors have focused on the materials and electron injection mechanisms used in the electron injection layer and electron transport layer of conventional organic EL devices. As the electron injection layer for lowering the barrier for electron injection from the cathode has mainly been made of alkali metal salts such as LiF, the inventors have considered that the electron transport layer is limited to compounds having a nitrogen-containing heterocycle such as pyridine that can effectively interact with Li. As a result of intensive research, the present inventors have found that by using an electron injection method utilizing hydrogen bonding between a specific base material and an organic compound, it is no longer necessary to use a compound having a nitrogen-containing heterocycle such as pyridine in the electron transport layer, and the options for materials that can be used in the electron transport layer are greatly expanded.
That is, as long as the barrier for electron injection from the cathode to the organic layer is lowered by utilizing hydrogen bonds between a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and an organic compound, the material usable for the electron transport layer is not limited to conventional compounds having a nitrogen-containing heterocycle such as pyridine, and for example, aromatic hydrocarbon compounds, compounds having a nitrogen-boron bond, π-electron-rich heteroaromatic compounds, compounds having a silole ring, and the like can also be used for the electron transport layer in an organic EL device.
The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [1] An organic thin film, characterized in that it is a single film containing a first material which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a second material which is a compound having no structure coordinated to an alkali metal in its molecule, or a laminated film of a film containing the first material and a film containing the second material.

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

[2] The organic thin film according to [1], wherein the second material is a compound having an aromatic heterocycle that does not have a carbon-nitrogen double bond in its structure.

[3] The organic thin film according to [1], wherein the second material is a compound that does not have a π-electron-deficient aromatic heterocycle in the molecule.

（一般式（２）中、Ｙは、置換基を有していてもよい、芳香族炭化水素環、π電子過剰芳香族複素環、ケイ素及び／又はホウ素を構成元素として含むπ共役系環状構造を表す。Ｗは、連結基又は直接結合を表す。Ｚは、構造中に炭素－窒素二重結合を含まないアリール基を表す。ｒは１～６の整数である。ｓは１～６の整数である。） [4] The organic thin film according to any one of [1] to [3], wherein the second material is a compound represented by the following general formula (2):

(In general formula (2), Y represents an aromatic hydrocarbon ring, a π-electron-rich aromatic heterocycle, or a π-conjugated cyclic structure containing silicon and/or boron as a constituent element, which may have a substituent. W represents a linking group or a direct bond. Z represents an aryl group not containing a carbon-nitrogen double bond in the structure. r represents an integer of 1 to 6. s represents an integer of 1 to 6.)

[5] The organic thin film according to any one of [1] to [4], wherein the first material is a hexahydropyrimidopyrimidine compound in which n in general formula (1) is 2 or 3.

[6] The organic thin film according to any one of [1] to [5], wherein the second material is any one or more of an aromatic hydrocarbon compound, a compound having a nitrogen-boron bond, a π-electron-rich heteroaromatic compound, and a compound containing a silole ring.

[7] A laminated film comprising an oxide layer and a layer of an organic thin film according to any one of [1] to [6] formed on the oxide layer.

[8] An organic electroluminescence element having a light-emitting layer between a cathode and an anode,
An organic electroluminescence element, comprising the organic thin film according to any one of [1] to [6] or the laminated film according to [7] between the cathode and the light-emitting layer.

[9] The organic electroluminescence element according to [8], having an oxide layer between the cathode and the organic thin film.

[10] The organic electroluminescence element according to [8] or [9], having a laminated film of a film containing the first material and the second material and a film containing the second material between the cathode and the light-emitting layer.

[11] The organic electroluminescence element described in [10], having a film containing the second material between the light-emitting layer and the film containing the first material and the second material.

[12] The organic electroluminescence element described in [10], having a film containing the second material between the cathode and the film containing the first material and the second material.

[13] The organic electroluminescence element according to any one of [8] to [12], having a layer containing the second material between the anode and the light-emitting layer.

[14] The organic electroluminescence element according to any one of [8] to [13], wherein the light-emitting layer contains the second material.

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [15] A material for an organic electroluminescence device, comprising a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a compound having no structure coordinated to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [16] An organic electroluminescence element having a light-emitting layer between a cathode and an anode,
An organic electroluminescence element, comprising a material layer between the cathode and the anode, the material layer containing a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and/or a compound not having a structure coordinated to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

[17] The organic electroluminescence element according to [16], having the material layer between the cathode and the light-emitting layer.

[18] The organic electroluminescence element according to [16] or [17], having an oxide layer between the cathode and the material layer.

[19] A display device comprising an organic electroluminescence element according to any one of [8] to [14] and [16] to [18].

[20] A lighting device comprising an organic electroluminescence element according to any one of [8] to [14] and [16] to [18].

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [21] A material for an organic thin-film solar cell, comprising: a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a compound not having a structure coordinated to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

[22] An organic thin-film solar cell comprising either the organic thin-film described in any one of [1] to [6], the laminated film described in [7], or a layer containing the material for organic thin-film solar cells described in [21].

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [23] A material for a photoelectric conversion element, comprising a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a compound not having a structure coordinated to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

[24] A photoelectric conversion element comprising any one of the organic thin film described in any one of [1] to [6], the laminated film described in [7], or a layer containing the material for photoelectric conversion elements described in [23].

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [25] A material for an organic transistor, comprising: a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a compound not having a structure coordinated to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

[26] A thin-film transistor comprising either the organic thin film described in any one of [1] to [6], the laminated film described in [7], or a layer containing the organic transistor material described in [25].

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [27] A coating composition comprising: a first material which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a second material which is a compound having no structure for coordinating to an alkali metal in the molecule:

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [28] A process of forming a single film containing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1), and a second material, which is a compound having no structure coordinated to an alkali metal in the molecule, on a surface to be formed, or
forming a film containing the first material and a film containing the second material in that order on a surface on which the organic thin film is to be formed.

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。） [29] A method for producing an organic thin film, comprising the step of forming a film containing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1), on a formation surface containing a second material.

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

The organic thin film of the present invention includes a first material consisting of a hexahydropyrimidopyrimidine compound of a specific structure, and a second material which is a compound that does not have a structure in the molecule that coordinates to an alkali metal. Therefore, when the organic thin film of the present invention is used, for example, in the electron injection layer of an organic EL device, the material options are greatly expanded compared to conventional electron transport layers that are based on the assumption of electron injection from alkali metals. This allows for excellent electron injection and electron transport properties.

In addition, since the organic EL element of the present invention has the organic thin film of the present invention between the cathode and the light-emitting layer, the organic thin film provides excellent electron injection and electron transport properties.

The organic thin film of the present invention, which includes a first material consisting of a hexahydropyrimidopyrimidine compound of a specific structure and a second material that is a compound that does not have a structure in its molecule that coordinates to an alkali metal, can be formed by either coating or vapor deposition, so there are fewer process constraints when manufacturing an organic EL element that includes the organic thin film of the present invention, and it is easy to use as a material for a layer that constitutes an organic EL element. The method for manufacturing an organic thin film of the present invention is a method for manufacturing such an organic thin film of the present invention.

The coating composition of the present invention contains a first material consisting of a hexahydropyrimidopyrimidine compound of a specific structure, and a second material which is a compound having no structure in the molecule that coordinates to an alkali metal. Therefore, by applying the coating composition of the present invention to the surface on which the organic thin film is to be formed, an organic thin film suitable for the electron injection layer of an organic EL element can be obtained.

The material for organic EL devices of the present invention is a useful material for use in the organic thin film and coating composition of the present invention used in the production of organic EL devices, etc. This material is also useful in that it can be used alone as an electron injection layer or electron transport layer.

The display device and lighting device of the present invention have a low driving voltage and excellent characteristics since they include the organic EL element of the present invention.
Moreover, the organic thin-film solar cell, the photoelectric conversion element and the organic thin-film transistor of the present invention have excellent properties since they contain the organic thin film of the present invention.

FIG. 1 is a schematic cross-sectional view illustrating an example of an organic EL element of the present invention. FIG. 2 is a schematic cross-sectional view illustrating another example of the organic EL element of the present invention. FIG. 1 is a schematic cross-sectional view showing an example of a laminate structure of an organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminated structure of the organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminated structure of the organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminated structure of the organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminated structure of the organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminated structure of the organic thin film of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminate structure of the organic EL element of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the laminate structure of the organic EL element of the present invention. FIG. 2 is a schematic cross-sectional view showing a laminated structure of an organic thin film used in the examples and comparative examples. 1 is a graph showing the relationship between the applied voltage and the luminance of the organic EL elements produced in Example 1 and Comparative Example 1. 13 is a graph showing the relationship between the applied voltage and the luminance of the organic EL element produced in Example 8. 1 is a graph showing the relationship between the applied voltage and the luminance of the organic EL elements produced in Example 10 and Comparative Example 3. 1 is a graph showing the relationship between the applied voltage and the luminance of the organic EL elements produced in Examples 11 to 14 and Comparative Example 4. 1 is a graph showing the relationship between the applied voltage and the luminance of the organic EL elements produced in Example 15 and Comparative Example 5.

The organic thin film and the method for producing the organic thin film, the organic electroluminescence element, the display device, the lighting device, the organic thin film solar cell, the thin film transistor, the coating composition, and the material for the organic electroluminescence element of the present invention will be described in detail below with reference to the embodiments.

<Organic thin films, materials for organic EL elements>
The organic thin film of the present invention comprises a first material which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1), and a second material which is a compound having no structure in its molecule that coordinates to an alkali metal. The organic thin film of the present invention may be a single-layer film containing the first material and the second material, or may be a film in which a layer containing the first material and a layer containing the second material are laminated. It may be a laminated film.

（一般式（１）中、Ｒ¹は、置換基を有していてもよい芳香族炭化水素基、芳香族複素環基、アリールアルキレン基、２価若しくは３価の鎖状または環状炭化水素基、又は、これらの基を２つ以上組み合わせてできる基、これらの基の１つ若しくは２つ以上と窒素原子とを組み合わせてできる基を表す。ｎは、１～３の整数である。）

(In general formula (1), R ¹ represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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. n is an integer from 1 to 3.)

The first material constituting the organic thin film of the present invention is a hexahydropyrimidopyrimidine compound having a specific structure, and therefore has the ability to form hydrogen bonds with the second material and generate a negative charge on the second material side.
The first material preferably has a pKa of 1 or more, more preferably 5 or more, and even more preferably 11 or more. The higher the pKa of the first material, the higher the ability of the first material to generate negative charges on the second material side. As a result, when the organic thin film is used as, for example, an electron injection layer of an organic EL device, excellent electron injection and electron transport properties are obtained.
It has also been confirmed that the hexahydropyrimidopyrimidine compound of formula (1) is suitably coordinated to the vacant sites of the inorganic compound, and therefore has the effect of preventing reactions at the interface with oxygen or water entering from the outside, thereby enhancing the atmospheric stability of the element. Furthermore, the hexahydropyrimidopyrimidine compound of formula (1) can reduce the work function of the inorganic compound by interacting with the inorganic compound, thereby improving the electron injection property of the metal oxide layer.
Therefore, the organic thin film of the present invention can be used not only in elements composed of only organic compounds, but also in elements composed of organic and inorganic compounds, and can exhibit the effect of enhancing electron injection properties and atmospheric stability.

One of the features of the organic thin film of the present invention is that it contains a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1) as a first material, and when the organic thin film of the present invention is used in an electron injection layer, excellent electron injection and electron transport properties are obtained. A material for an organic EL device containing a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1), which exhibits such excellent effects, is also one aspect of the present invention, and excellent electron injection and electron transport properties can be obtained even by using this material alone in an electron injection layer or electron transport layer.

In the present invention, "pKa" usually means "acid dissociation constant in water", but if it cannot be measured in water, it means "acid dissociation constant in dimethyl sulfoxide (DMSO)", and if it cannot be measured even in DMSO, it means "acid dissociation constant in acetonitrile". Preferably, it means "acid dissociation constant in water".

^R1 in the above general formula (1) represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene group, a divalent or trivalent 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 have 4 to 24 carbon atoms, and even more preferably have 5 to 20 carbon atoms.
Examples of the aromatic hydrocarbon group include a compound consisting of only one aromatic ring, such as benzene; a compound in which a plurality of aromatic rings, such as biphenyl and diphenylbenzene, are directly bonded to each other via one carbon atom; and a group obtained by removing one to three hydrogen atoms from any of the aromatic rings of a condensed ring aromatic hydrocarbon compound, 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 one to three hydrogen atoms from any of the aromatic heterocycles of condensed ring heteroaromatic hydrocarbon compounds, such as quinoline, quinoxaline, benzothiophene, benzothiazole, benzimidazole, benzoxazole, indole, carbazole, dibenzofuran, dibenzothiophene, acridine, and phenanthroline.
The arylalkylene group includes a group formed by combining the above aromatic hydrocarbon group with an alkylene group having 1 to 3 carbon atoms.
The divalent or trivalent chain or cyclic hydrocarbon group preferably has 1 to 12 carbon atoms, more preferably has 1 to 6 carbon atoms, and even more preferably has 1 to 4 carbon atoms. The chain hydrocarbon group may be a straight chain or a branched chain.
Furthermore, R ¹ 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 or trivalent chain hydrocarbon groups.
Furthermore, R ¹ may be a group formed by combining one or more of the above aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, and divalent or trivalent chain hydrocarbon groups with a nitrogen atom. Examples of such groups include groups formed by removing 1 to 3 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 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; linear or branched alkoxy groups having 1 to 20 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, and an octyloxy group; a nitro group; a cyano group; alkylamino groups having an alkyl group having 1 to 10 carbon atoms such as a methylamino group, an ethylamino group, a dimethylamino group, and a diethylamino group; cyclic amino groups such as a pyrrolidino group, a piperidino group, and a morpholino group; group, diarylamino groups such as a carbazolyl group; acyl groups such as an acetyl group, a propionyl group, a butyryl group; alkenyl groups having 2 to 30 carbon atoms such as a styryl group; aryl groups having 5 to 20 carbon atoms which may be substituted with a halogen atom such as a fluorine atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, an amino group, or the like (specific examples of the aryl group are the same as those of the aromatic hydrocarbon group described above); heterocyclic groups containing one or more of a nitrogen atom, a sulfur atom, and an oxygen atom having 4 to 20 carbon atoms which may be substituted with a halogen atom such as a fluorine atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, an amino group, or the like (heterocyclic groups may be composed of only one ring, or may be compounds in which a plurality of compounds consisting of only one aromatic heterocyclic ring are directly bonded to each other at one carbon atom, or may be condensed heterocyclic groups. Specific examples of heterocyclic groups include the specific examples of the aromatic heterocyclic groups described above); ester groups, thioether groups, and the like. These groups may be substituted with a halogen atom, a hetero element, an alkyl group, an aromatic ring, or the like.

In the above general formula (1), n is an integer from 1 to 3, preferably 2 or 3.

Specific examples of the hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1) include compounds represented by the following structural formulas (1-1) to (1-30).

The compound represented by the above general formula (1) can be synthesized by Ullmann coupling reaction, Buchwald-Hartwig amination reaction, nucleophilic substitution reaction, or the like using a halogen compound having iodine, bromine, chlorine, or fluorine and hexahydropyrimidopyrimidine as raw materials, as shown in the following reaction formula.

（一般式（２）中、Ｙは、置換基を有していてもよい、芳香族炭化水素環、π電子過剰芳香族複素環、ケイ素及び／又はホウ素を構成元素として含むπ共役系環状構造を表す。Ｗは、連結基又は直接結合を表す。Ｚは、構造中に炭素－窒素二重結合を含まないアリール基を表す。ｒは１～６の整数である。ｓは１～６の整数である。） The second material constituting the organic thin film of the present invention is a compound that does not have a structure that coordinates to an alkali metal in the molecule. Here, the second material is preferably a compound having an aromatic heterocycle that does not have a carbon-nitrogen double bond in the structure, or a compound that does not have a π-electron deficient aromatic heterocycle in the molecule. In addition, the second material is preferably a compound represented by the following general formula (2):

(In general formula (2), Y represents an aromatic hydrocarbon ring, a π-electron-rich aromatic heterocycle, or a π-conjugated cyclic structure containing silicon and/or boron as a constituent element, which may have a substituent. W represents a linking group or a direct bond. Z represents an aryl group not containing a carbon-nitrogen double bond in the structure. r represents an integer of 1 to 6. s represents an integer of 1 to 6.)

In formula (2), Y represents an aromatic hydrocarbon ring, a π-electron rich aromatic heterocycle, or a π-conjugated cyclic structure containing silicon and/or boron as a constituent element, which may have a substituent.
Examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, an anthracene ring, a biphenyl ring, a triphenylene ring, a fluoranthene ring, a fluorene ring, a chrysene ring, and a dibenzochrysene ring.
Examples of the π-electron-rich aromatic heterocycle include a thiophene ring, a furan ring, a pyrrole ring, a dibenzothiophene ring, a dibenzofuran ring, and a carbazole ring.
Examples of the π-conjugated cyclic structure containing silicon and/or boron as a constituent element include a silole ring, a cyclic structure in which a portion of a dibenzo[g,p]chrysene ring is substituted with nitrogen-boron, and a cyclic structure in which a portion of a spiro-bifluorene ring is substituted with nitrogen-boron.
The aromatic hydrocarbon ring, the π-electron-rich aromatic heterocycle, and the π-conjugated cyclic structure containing silicon and/or boron as a constituent element may have a substituent, and examples of the substituent include the same groups as the monovalent substituent of R ¹ in the above-mentioned general formula (1).

In formula (2), W represents a linking group or a direct bond. When W represents a linking group, W is a linking group having a valency of (r+1).
Here, examples of the linking group include an arylene group, a heteroarylene group, an ethenylene group, an ethynylene group, a nitrogen atom, an oxygen atom, a sulfur atom, a silicon atom, a boron atom, etc. These linking groups may have a substituent, and examples of the substituent include the same groups as the monovalent substituent of R ¹ in the above-mentioned general formula (1).

In formula (2), Z represents an aryl group that does not contain a carbon-nitrogen double bond in the structure.
Here, examples of the aryl group that does not contain a carbon-nitrogen double bond in the structure include a phenyl group, a tolyl group, a naphthyl group, a triphenylenyl group, a fluoranthenyl group, a dibenzothiophenyl group, a dibenzofuranyl group, and a carbazolyl group.
The aryl group may have a substituent as long as it does not contain a carbon-nitrogen double bond in the structure. Examples of the substituent include the same groups as the monovalent substituent of R ¹ in the above general formula (1).

In the general formula (2), r is an integer of 1 to 6, and s is an integer of 1 to 6.
Here, when r is an integer of 2 to 6, a plurality of Z's may be the same or different.
Furthermore, when s is an integer of 2 to 6, a plurality of Ws may be the same or different, and a plurality of Zs may be the same or different.

In the present invention, the first material forms a hydrogen bond with the second material, which allows smooth exchange of electrons between the cathode and the organic layer. Therefore, the second material in the present invention does not need to be a material capable of injecting electrons through interaction with an alkali metal, which has been used between the cathode and the light-emitting layer or photoelectric conversion film in organic EL elements and organic thin-film solar cells.
So far, examples of the second material 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, phenanthroline derivatives such as bathophenanthroline (BPhen), 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT), tris-1,3,5 triazine derivatives such as 1-(3'-(pyridin-3"-yl)phenyl)triazine (TmPhPyTz), triazole derivatives such as 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), oxazole derivatives, oxadiazole derivatives such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) (PBD), imidazole derivatives such as 2,2',2"-(1,3,5-pentriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), and various metal complexes represented by tris(8-hydroxyquinolinato)aluminum ( _Alq3 ), etc. have been widely used.

Therefore, materials that can be used as the second material in the present invention are significantly different from the above-mentioned materials, and the options are greatly expanded, such as aromatic hydrocarbon compounds, compounds having a nitrogen-boron bond, π-electron-rich heteroaromatic compounds, compounds containing a silole ring, etc.
The π-electron rich aromatic heterocycle and the π-electron deficient aromatic heterocycle are heteroaromatic rings classified as described in "New Edition Heterocyclic Compounds Basic Edition" edited by Kodansha Scientific, pp. 1 to 5.
A π-electron-rich heteroaromatic ring (π-rich heteroaromatic ring) is a heteroaromatic ring having a higher π-electron density on each carbon compared to benzene. For example, pyrrole ring, furan ring, thiophene ring, etc. correspond to π-electron-rich heteroaromatic rings, and the heteroaromatic ring has six π-electrons because the heteroatom constituting the ring has a lone electron pair, and the six π-electrons are distributed on five atoms, making it π-electron-rich. The above-mentioned "π-electron-rich heteroaromatic compound" is a compound having such a π-electron-rich heteroaromatic ring.
On the other hand, a π-electron-deficient aromatic heterocycle (π-deficient heteroaromatic ring) is a heteroaromatic ring having a lower π-electron density on each carbon compared to benzene. For example, a pyridine ring corresponds to a π-electron-deficient aromatic heterocycle, and the heteroaromatic ring has six π-electrons even without using the lone electron pair of the nitrogen in the ring, while the nitrogen in the ring has an electron-withdrawing effect, which is exerted on each carbon, resulting in a π-electron deficiency. The above-mentioned "compound having no π-electron-deficient aromatic heterocycle in the molecule" is a compound having no such π-electron-deficient aromatic heterocycle.

The aromatic hydrocarbon compound is not particularly limited, and various hydrocarbon compounds having an aromatic ring can be used.

Examples of the compound having a nitrogen-boron bond include the following compound (structural formula (3-1)) in which a portion of dibenzo[g,p]chrysene is substituted with nitrogen-boron, the following compound (structural formula (3-2)) in which a portion of spiro-bifluorene is substituted with nitrogen-boron, and further, compounds containing these heterocyclic structures in the molecule.

Examples of the π-electron-rich heteroaromatic compound include dibenzothiophene, a compound represented by the following structural formula (3-3), dibenzofuran (structural formula (3-4)), benzo[b]benzo[4,5]thieno[2,3-d]thiophene (structural formula (3-5)), and further, compounds containing these heterocyclic structures in the molecule.

Examples of compounds containing a silole ring include 1,1,2,3,4,5-hexaphenylsilole.

The ratio of the first material to the second material contained in the organic thin film of the present invention is not particularly limited and can be appropriately determined depending on the type of compound used for each of the first and second materials. The ratio of the first material to the second material is preferably 0.1:99.9 to 20:1 in mass ratio (first material:second material). More preferably, it is 0.5:99.5 to 10:1. When the ratio is as above, the effect of improving the electron transport property and electron injection property due to the inclusion of the first material and the second material in the organic thin film becomes significant.

The organic thin film in the present invention may be a single film containing the first material and the second material, or may be a laminated film of a film containing at least the first material and a film containing at least the second material. In the case of a laminated film, it may be a laminated film of a film containing only the first material and a film containing only the second material, or a laminated film of a film containing the first material and the second material and a film containing only one of the first material and the second material. In the case of a laminated film of a film containing the first material and the second material and a film containing only one of the first material and the second material, the film containing only one of the first material and the second material may contain either the first material or the second material, but it is preferable that it contains the second material.
Furthermore, when such an organic thin film is used as a layer constituting an organic electroluminescence element, either the film containing the first material and the second material or the film containing only one of the first material and the second material may be on the cathode side, but it is preferable that the film containing only one of the first material and the second material is on the cathode side.

When the organic thin film in the present invention is a laminated film of a film containing a first material and a second material and a film containing only the first material, the first material is contained in both of the two laminated films, and the first materials contained in the two films may be the same or different.
Similarly, when the organic thin film in the present invention is a laminated film of a film containing a first material and a second material and a film containing only the second material, the second material is contained in both of the two laminated films, and the second materials contained in the two films may be the same or different.

<Method of manufacturing organic thin film>
Next, the method for producing an organic thin film of the present invention will be described with reference to examples.
The organic thin film of the present invention includes a first material made of a hexahydropyrimidopyrimidine compound having a structure represented by the above general formula (1), and a second material which is a compound having no structure coordinated to an alkali metal in the molecule. Because both the first material and the second material have relatively large molecular weights, the organic thin film of the present invention can be formed not only by coating but also by vapor deposition. Therefore, there are few process restrictions when manufacturing an organic EL device including the organic thin film of the present invention, and it is easy to use it as a material for a layer constituting an organic EL device.
When the organic thin film is produced by deposition, it can be produced by the same method as when other layers constituting the organic EL element are produced by deposition, and the first material and the second material may be simultaneously deposited or sequentially deposited. When sequentially deposited, either the first material or the second material may be deposited first. In addition, either one may be deposited first and then both may be co-deposited, or both may be co-deposited and then either one may be deposited. Such a method for producing an organic thin film including a step of simultaneously depositing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the above general formula (1), and a second material, which is a compound having no structure coordinated to an alkali metal in the molecule, on a surface on which the organic thin film is to be formed is one of the preferred embodiments of the method for producing an organic thin film of the present invention.
In addition, a method for producing an organic thin film comprising a step of first depositing either a first material or a second material onto a surface on which an organic thin film is to be formed, and then depositing the other material or both of the materials, or a method for producing an organic thin film comprising a step of simultaneously depositing a first material and a second material onto a surface on which an organic thin film is to be formed, and then depositing either the first material or the second material onto the surface on which an organic thin film is to be formed, is also one of the preferred embodiments of the method for producing an organic thin film of the present invention.

The organic thin film of the present invention can also be produced by coating. In this case, a coating composition containing a first material and a second material, which is a compound that does not have a structure coordinated to an alkali metal in the molecule, is prepared and the coating composition is applied, or a coating composition containing a first material and a coating composition containing a second material are prepared and applied in order to produce an organic thin film. When coating in order, either the coating composition containing the first material or the coating composition containing the second material may be applied first. Also, after applying a coating composition containing only one of the materials, a coating composition containing both of these materials may be applied, or after applying a coating composition containing both of these materials, a coating composition containing only one of the materials may be applied. Such a method for producing an organic thin film, which includes a step of coating a coating composition containing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the above general formula (1), and a second material, which is a compound that does not have a structure coordinated to an alkali metal in the molecule, on a surface on which the organic thin film is to be formed, is one of the preferred embodiments of the method for producing an organic thin film of the present invention.
Furthermore, a method for producing an organic thin film comprising a step of first applying either a coating composition containing only the first material or a coating composition containing only the second material onto a surface on which an organic thin film is to be formed, and a step of applying a coating composition containing the other or both of the materials onto the coating film formed by the step, or a method for producing an organic thin film comprising a step of applying a coating composition containing both the first material and the second material, and a step of applying a coating composition containing only either the first material or the second material onto the coating film formed by the step, is also one of the preferred embodiments of the method for producing an organic thin film of the present invention.
In the following, a method for producing an organic thin film by preparing a coating composition containing a first material consisting of a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and a second material which is a compound having no structure coordinated to an alkali metal within the molecule, and applying the coating composition will be described.

The coating composition can be obtained, for example, by supplying a predetermined amount of each of the first material and the second material into a solvent contained in a container, or by supplying a solvent to the first material and the second material contained in a container and stirring them to dissolve them.
The solvent used to dissolve the first material and the second material may be, for example, an inorganic solvent, an organic solvent, or a mixed solvent containing these.
Examples of inorganic solvents include nitric acid, sulfuric acid, ammonia, hydrogen peroxide, water, phosphoric acid, and hydrochloric acid.

Organic solvents include ketone-based solvents such as methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), diisobutyl ketone, 3,5,5-trimethylcyclohexanone, diacetone alcohol, cyclopentanone, and cyclohexanone; alcohol-based solvents such as methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol (DEG), and glycerin; diethyl ether, diisopropyl ether, and 1,2-dimethoxyethane. Ether solvents such as dimethyl ether (DME), 1,4-dioxane, tetrahydrofuran (THF), tetrahydropyran (THP), anisole, diethylene glycol dimethyl ether (diglyme), and diethylene glycol ethyl ether (carbitol); cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and phenyl cellosolve; aliphatic hydrocarbon solvents such as hexane, pentane, heptane, and cyclohexane; aromatic hydrocarbon solvents such as toluene, xylene, and benzene; pyridine, pyrazine, furan, pyrrole, and thiophene; Aromatic heterocyclic compound solvents such as 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, formic acid, acetic acid, trichloroacetic acid, and trifluoroacetic acid, etc. Examples of organic solvents include organic acids, organic amines such as triethylamine and pyridine, and carbonate solvents such as diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate. Among these, ketone solvents such as methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), diisobutyl ketone, 3,5,5-trimethylcyclohexanone, diacetone alcohol, and cyclopentanone are preferred.

As a method for applying the coating composition containing the first material and the second material, various application methods can be used, such as spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, and inkjet printing.

After applying the coating composition in this manner, it is preferable to carry out an annealing treatment. The annealing treatment is preferably carried out at 70 to 200°C for 0.1 to 5 hours in a nitrogen atmosphere or in the air. By carrying out such an annealing treatment, the solvent can be evaporated to form an organic thin film.

<Organic EL element>
The present invention also relates to an organic electroluminescence (EL) element having a light-emitting layer between a cathode and an anode, and further comprising any one of a layer of the organic thin film of the present invention, a layer of a laminate film of the organic thin film layer and a metal oxide layer, or a layer of a material containing a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and/or a compound not having a structure coordinated to an alkali metal in the molecule.
In the organic EL element of the present invention, the organic thin film layer, the laminated film layer of the organic thin film layer and a metal oxide layer, and the material layer containing a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and/or a compound not having a structure coordinated to an alkali metal in its molecule may all be located between the cathode and the light-emitting layer, or between the anode and the light-emitting layer, but are preferably located between the cathode and the light-emitting layer.
In addition, the material layer containing a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and/or a compound not having a structure in the molecule that coordinates to an alkali metal may contain other components as long as it contains a hexahydropyrimidopyrimidine compound having a structure represented by the above-mentioned general formula (1) and/or a compound not having a structure in the molecule that coordinates to an alkali metal, but it is preferable that the layer is composed only of a hexahydropyrimidopyrimidine compound and/or a compound not having a structure in the molecule that coordinates to an alkali metal.

Next, the organic EL element of the present invention will be described in detail with reference to examples.
Fig. 1 is a schematic cross-sectional view for explaining one example of an organic EL element of the present invention. An organic EL element 1 of the present embodiment shown in Fig. 1 has an emitting layer 6 between an anode 3 and a cathode 9. The organic EL element 1 shown in Fig. 1 has an electron injection layer 8 between the cathode 9 and the emitting layer 6, the electron injection layer 8 being made of the organic thin film of the present invention, or a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and/or a compound not having a structure coordinated to an alkali metal in the molecule.
The organic EL element 1 of the present embodiment has a laminated structure in which an anode 3, a hole injection layer 4, a hole transport layer 5, a light emitting layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 are formed in this order on a substrate 2.

The organic EL element 1 shown in FIG. 1 is a typical organic EL element having an anode 3 on the substrate 2 side. However, as shown in FIG. 2, an organic EL element 1 having an inverted structure in which a cathode 9 is disposed between the substrate 2 and the light-emitting layer 6 is also one of the preferred embodiments of the organic EL element of the present invention.
In addition, an embodiment in which an inorganic oxide layer 10 is provided between a cathode 9 and an electron injection layer 8 made of the organic thin film of the present invention or a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) and/or a compound not having a structure coordinated to an alkali metal in the molecule is also one of the preferred embodiments of the organic EL element of the present invention.

The organic EL element 1 shown in Figures 1 and 2 may be a top-emission type that extracts light on the side opposite the substrate 2, or a bottom-emission type that extracts light on the substrate 2 side.

"substrate"
Examples of materials for the substrate 2 include resin materials and glass materials.
Examples of the resin material used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, etc. When a resin material is used as the material for the substrate 2, it is preferable because an organic EL element 1 having excellent flexibility can be obtained.
Examples of the glass material used for the substrate 2 include quartz glass and soda glass.

When the organic EL element 1 is of a bottom emission type, the substrate 2 is made of a transparent material.
When the organic EL element 1 is of a top emission type, not only a transparent substrate but also an opaque substrate may be used as the material of the substrate 2. Examples of opaque substrates include a substrate made of a ceramic material such as alumina, a substrate in which an oxide film (insulating film) is formed on the surface of a metal plate such as stainless steel, and a substrate made of a resin material.

The average thickness of the substrate 2 can be determined depending on the material of the substrate 2, and is preferably 0.1 to 30 mm, and more preferably 0.1 to 10 mm. The average thickness of the substrate 2 can be measured using a digital multimeter and a vernier caliper.

"anode"
The anode 3 shown in FIG. 1 is formed on and in direct contact with the substrate 2. However, in the case of an organic EL element having an inverted structure as shown in FIG. 2, the anode 3 does not have to be formed on and in direct contact with the substrate 2.
Examples of materials for the anode 3 include 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. Of these, it is preferable to use ITO, IZO, or FTO as the material for the anode 3.
The average thickness of the anode 3 is not particularly limited, but is preferably 10 to 500 nm, and more preferably 100 to 200 nm.
The average thickness of the anode 3 can be measured by a stylus step gauge or spectroscopic ellipsometry.

"Hole injection layer"
The hole injection layer 4 may be made of an inorganic material or an organic material.
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.
Examples of 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), and poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS).

The average thickness of the hole injection layer 4 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 4 can be measured by, for example, a stylus step gauge or spectroscopic ellipsometry.

"Hole transport layer"
As the hole transporting organic material used in the hole transport layer 5, various p-type polymeric materials (organic polymers) and various p-type low molecular weight materials can be used alone or in combination.
Specifically, examples of the material for the hole transport layer 5 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, or derivatives thereof. These materials for the hole transport layer 5 can also be used as a mixture with other compounds. An example of a mixture containing polythiophene used as a material for the hole transport layer 5 is poly(3,4-ethylenedioxythiophene/styrenesulfonic acid) (PEDOT/PSS).

The average thickness of the hole transport layer 5 is not particularly limited, but is preferably from 10 to 150 nm, and more preferably from 20 to 100 nm.
The average thickness of the hole transport layer 5 can be measured by, for example, a stylus step gauge or spectroscopic ellipsometry.

"Light-emitting layer"
The material for forming the light-emitting layer 6 may be any material that can be typically used as the material for the light-emitting layer 6, or a mixture of these materials may be used. Specifically, for example, the light-emitting layer 6 may contain bis[2-(2-benzothiazolyl)phenolato]zinc(II) (Zn(BTZ) ₂ ) and tris[1-phenylisoquinoline]iridium(III) (Ir(piq) ₃ ).
The material forming the light-emitting layer 6 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.

Examples of polymeric materials for forming the light-emitting layer 6 include polyacetylene compounds such as trans-polyacetylene, cis-polyacetylene, poly(diphenylacetylene) (PDPA), and poly(alkylphenylacetylene) (PAPA); poly(para-phenylenevinylene) (PPV), poly(2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly(para-phenylenevinylene) (CN-PPV), and poly(2-diphenylacetylene). polyparaphenylenevinylene-based compounds such as poly(methyloctylsilyl-para-phenylenevinylene) (DMOS-PPV) and poly(2-methoxy,5-(2'-ethylhexoxy)-para-phenylenevinylene) (MEH-PPV); polythiophene-based compounds such as poly(3-alkylthiophene) (PAT) and poly(oxypropylene)triol (POPT); poly(9,9-dialkylfluorene) (PDAF) and poly(dioctylfluorene-a polyfluorene-based compounds such as α,ω-bis[N,N'-di(methylphenyl)aminophenyl]-poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6am4) and poly(9,9-dioctyl-2,7-divinylenefluorenyl-ortho-co(anthracene-9,10-diyl)); poly(para-phenylene) (PPP), poly(1,5-dialkoxy-para-phenylene); ) (RO-PPP); polycarbazole compounds such as poly(N-vinylcarbazole) (PVK); polysilane compounds such as poly(methylphenylsilane) (PMPS), poly(naphthylphenylsilane) (PNPS), and poly(biphenylylphenylsilane) (PBPS); and boron compound-based polymer materials described in JP-A-2011-184430 and JP-A-2012-151148.

Examples of low molecular weight materials for forming the light emitting layer 6 include a three-coordinate iridium complex having 2,2'-bipyridine-4,4'-dicarboxylic acid as a 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 ), (1,10-phenanthroline)-tris-(4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dionate)europium(III) (Eu(TTA) ₃ ), and the like. (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 xazolethiophene; 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; phthalocyanine (H ₂ Pc), metallic or non-metallic phthalocyanine compounds such as copper phthalocyanine; and further, boron compound materials described in JP-A-2009-155325, JP-A-2011-184430, and JP-A-2012-151149.

The average thickness of the light-emitting layer 6 is not particularly limited, but is preferably from 10 to 150 nm, and more preferably from 20 to 100 nm.
The average thickness of the light-emitting layer 6 may be measured by a stylus type step gauge, or may be measured by a quartz crystal thickness gauge during the deposition of the light-emitting layer 6 .

"Electron transport layer"
For the electron transport layer 7, a material different from the material that is used as the second material for the electron injection layer 8 and that can inject electrons from the cathode when an alkali metal is added thereto, which has been generally used as the material for the electron transport layer so far, can be used.
Specifically, the second material may be an aromatic hydrocarbon compound, a compound having a nitrogen-boron bond, a π-electron-rich heteroaromatic compound, a compound containing a silole ring, or the like, and one or more of these may be used.
On the other hand, although the number of materials required for producing the organic EL element increases, for example, a compound capable of injecting electrons from an alkali metal, which has been generally used as a material for the electron transport layer, may be used as a hole blocking layer between the light emitting layer 6 and the electron transport layer 7.
The average thickness of the electron transport layer 7 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 7 can be measured by a stylus step gauge or spectroscopic ellipsometry.
On the other hand, as described later, when the organic thin film of the present invention in which the first material and the second material are mixed is used as the electron injection layer 8 and the electron transport layer 7, the electron transport layer may be omitted.

"Electron injection layer"
The electron injection layer 8 improves the speed of injection of electrons from the cathode 9 to the light emitting layer 6 and improves the electron transport properties. The electron injection layer 8 is made of the above-mentioned organic thin film.
The average thickness of the electron injection layer 8 is preferably 0.5 to 100 nm, and more preferably 1 to 50 nm. The electron injection layer 8 has a smooth surface, and is formed by applying a coating composition containing the first material and the second material, or by sequentially applying a coating composition containing the first material and a coating composition containing the second material. Alternatively, the electron injection layer 8 made of the first material and the second material is obtained by co-deposition using a vacuum deposition method. In addition, when the average thickness of the electron injection layer 8 is 100 nm or less, an increase in the driving voltage of the organic EL element 1 due to the provision of the electron injection layer 8 can be sufficiently suppressed.

In addition, when forming a film containing the first material and the second material, the structure between the cathode 9 and the light-emitting layer 6 may be any of the structures shown in Figures 3 to 8. For example, a mixed film of the first material and the second material may be the electron injection layer 8, and a film made of the second material may be the electron transport layer 7 (Figure 3), a film made only of the first material may be the electron injection layer 8, and a film made only of the second material may be the electron transport layer 7 (Figure 4), a laminated film of the second material and the first material may be the electron injection layer 8, and a film made only of the second material may be the electron transport layer 7 (Figure 5), a film made of the second material may be provided on the cathode 9 side, a laminated film of this and a mixed film of the first material and the second material may be the electron injection layer 8, and a film made only of the second material may be the electron transport layer 7 (Figure 6), and as described above, a mixed film of the first material and the second material may be the electron injection layer 8 and electron transport layer 7 (Figures 7 and 8). In addition, when two adjacent films both contain a second material, as in Figure 3, Figure 6, or Figure 8, the second materials contained in these two films may be the same or different.
The average thickness of the electron injection layer 8 can be measured by, for example, a stylus step gauge or spectroscopic ellipsometry.

As described above, the first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the general formula (1), is a material that has the ability to form hydrogen bonds with other materials and generate negative charges in the other materials. Therefore, in order to sufficiently promote electron injection from the cathode 9, it is preferable that the first material is present in greater amounts on the cathode 9 side. However, since this negative charge can contribute to the promotion of electron injection even if it is not in direct contact with the cathode 9, the effect of electron injection due to the presence of the first material can be obtained even in the laminated structure shown in Figures 5, 6, and 8. When an organic EL element includes a cathode and a layer of the organic thin film of the present invention formed under the cathode in the laminated structure, the organic EL element can be said to be configured to include the laminated film of the present invention. An organic EL element configured to include such a laminated film of the present invention is also one of the present inventions.

"cathode"
Examples of materials used for the cathode 9 include ITO, IZO, Au, Pt, Ag, Cu, Al, Mg, and alloys containing these. Among these, it is preferable to use ITO, IZO, Au, Ag, or Al as the material for the cathode 9.
The average thickness of the cathode 9 is not particularly limited, but is preferably 10 to 1000 nm, and more preferably 30 to 150 nm. Even when an opaque material is used as the material of the cathode 9, by setting the average thickness to, for example, about 10 to 30 nm, it can be used as a transparent cathode in a top-emission organic EL element.
The average thickness of the cathode 9 can be measured by a quartz crystal film thickness meter during the deposition of the cathode 9 .

"Oxide layer for electron injection"
When the organic thin film of the present invention is applied to an inverted organic EL element shown in FIG. 2, it is preferable to have an inorganic oxide layer 10 on the cathode 9. This oxide layer 10 functions as an electron injection layer 8. The electron injection layer 8 used between the light emitting layer 6 and the cathode 9 shown in FIGS. 3 to 8 can also be applied to an inverted structure organic EL element. This results in an oxide layer 10 being inserted between the organic layer and the oxide layer 9.
The oxide layer 10 is a semiconductor or insulator laminated thin film layer. Specifically, the oxide layer 10 may be a layer made of a single metal oxide, a layer made of a mixture of two or more metal oxides, or a layer made of a single metal oxide. The metal oxide layer may be a layer in which one or both of the above metal oxide layers are laminated, or a layer in which two or more metal oxides are mixed.

Metal elements constituting the metal oxide that forms the oxide layer 10 include 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 oxide layer 10 includes a layer containing a mixture of two or more types of metal oxides, it is preferable that at least one of the metal elements constituting the metal oxide is a layer containing magnesium, aluminum, calcium, zirconium, hafnium, silicon, titanium, or zinc.
When the oxide layer 10 is a layer made of a simple metal oxide, it is preferable that the oxide layer 10 is a layer made of a metal oxide selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide.

When the oxide layer 10 is a layer in which either or both of a layer in which two or more kinds of metal oxides are mixed and a layer made of a single metal oxide are laminated, or a layer in which two or more kinds of metal oxides are mixed, examples of the layer include a laminate and/or mixture of a combination of two kinds of metal oxides selected from 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, and calcium oxide/aluminum oxide, a laminate and/or mixture of a combination of three kinds of metal oxides selected from 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/silicon oxide, and indium oxide/gallium oxide/zinc oxide.

The oxide layer 10 may contain IGZO (indium gallium zinc oxide), which is an oxide semiconductor that exhibits favorable characteristics as a special composition, and/or 12CaO.7Al ₂ O ₃ , which is an electride.
The average thickness of the oxide layer 10 is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 2 to 100 nm.
The average thickness of the oxide layer 10 can be measured by a stylus step gauge or spectroscopic ellipsometry.

"Sealing"
The organic EL element 1 shown in FIG. 1 and FIG. 2 may be sealed, if necessary.
1 and 2 may be sealed by a sealing container (not shown) having a concave space for accommodating the organic EL element 1, and an adhesive for bonding the edge of the sealing container to the substrate 2. Alternatively, the organic EL element 1 may be accommodated in a sealing container and sealed by filling it with a sealant made of an ultraviolet (UV) curable resin or the like.
In addition, for example, the organic EL element 1 shown in FIG. 1 may be sealed using a sealing member consisting of a plate member (not shown) arranged on the cathode 9 and a frame member (not shown) arranged along the edge of the plate member on the side facing the cathode 9, and an adhesive that bonds between the plate member and the frame member and between the frame member and the substrate 2.
In addition, the organic EL element 1 shown in FIG. 2 may be sealed using a sealing member consisting of a plate member (not shown) arranged on the anode 3 and a frame member (not shown) arranged along the edge of the plate member on the side facing the anode 3, and an adhesive that bonds between the plate member and the frame member and between the frame member and the substrate 2.

When the organic EL element 1 is sealed using a sealing container or a sealing member, a desiccant that absorbs moisture may be placed inside the sealing container or inside the sealing member. A material that absorbs moisture may also be used as the sealing container or the sealing member. A space may also be formed inside the sealed sealing container or inside the sealing member.

The material of the sealing container or sealing member used to seal the organic EL element 1 shown in Figures 1 and 2 can be a resin material, a glass material, or the like. The resin material and glass material used for the sealing container or sealing member can be the same as the material used for the substrate 2.

In the organic EL element 1 of this embodiment, when the electron injection layer 8 is formed using an organic thin film consisting of a first material that is a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1) and a second material that is a compound that does not have a structure coordinated to an alkali metal in the molecule, excellent durability can be obtained compared to, for example, a case in which an alkali metal, which is a material that is unstable in the atmosphere, is used as the electron injection layer 8. Therefore, if the water vapor transmission rate of the sealing container or sealing member is about 10 ^-3 to 10 ^-4 g/m ² /day, deterioration of the organic EL element 1 can be sufficiently suppressed. Therefore, it is possible to use a resin material having a water vapor transmission rate of more than about 10 ^-4 g/m ² /day as the material of the sealing container or sealing member, and an organic EL element 1 with excellent flexibility can be realized.

"Method of manufacturing organic EL element"
Next, as an example of a method for manufacturing an organic EL element of the present invention, a method for manufacturing an organic EL element 1 shown in FIG. 1 will be described.
To manufacture the organic EL element 1 shown in FIG. 1, first, the anode 3 is formed on the substrate 2 .
The anode 3 can be formed by a sputtering method, a vacuum deposition method, a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, a vapor phase deposition method, a liquid phase deposition method, etc. The anode 3 may be formed by bonding a metal foil.

Next, the hole injection layer 4 is formed on the anode 3 .
The hole injection layer 4 can be formed by the above-mentioned method for producing an organic thin film.

Next, on the hole injection layer 4, a hole transport layer 5, a light emitting layer 6, an electron transport layer 7, and an electron injection layer 8 are formed in this order.
The methods for forming the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 are not particularly limited, and various conventionally known formation methods can be appropriately used in accordance with the properties of the materials used for each of the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8.

Specifically, methods for forming the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 include a coating method in which an organic compound solution containing an organic compound that will become the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 is applied, a vacuum deposition method, and an ESDUS (Evaporative Spray Deposition from Ultra-dilute Solution) method.

When forming the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 using a coating method, the organic compounds that will become the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 are dissolved in a solvent to form an organic compound solution that contains the organic compounds that will become the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8.

Preferred solvents for dissolving the organic compounds that form the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 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, and these can be used alone or in combination.

As a method for applying an organic compound solution containing an organic compound that will become the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8, various application methods such as spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, and inkjet printing can be used. Among these application methods, it is preferable to use spin coating or slit coating because it is easier to control the film thickness.

Next, the cathode 9 is formed.
The cathode 9 can be formed, for example, in the same manner as the anode 3 .
Through the above steps, the organic EL element 1 shown in FIG. 1 is obtained.

"Sealing method"
When sealing the organic EL element 1 shown in FIG. 1, it can be sealed by using a method normally used for sealing an organic EL element.

The organic EL element 1 of the present embodiment has an electron injection layer 8 made of an organic thin film containing a first material, which is a hexahydropyrimidopyrimidine compound having the structure represented by the above-mentioned general formula (1), and a second material, so that the first material forms a hydrogen bond with the second material to generate a negative charge, thereby obtaining excellent electron injection properties. Therefore, the organic EL element 1 has a high speed of electron injection and electron transport from the cathode 9 to the light-emitting layer 6, and has a low driving voltage.
As described above, an organic EL element 1 in which an organic thin film containing a first material, which is a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1), and a second material, which is a compound having no structure coordinated to an alkali metal in the molecule, is a laminated film, and the layer formed by the second material is a layer different from the electron injection layer formed by the first material, is also another embodiment of the organic EL element of the present invention. In the organic EL element of such an embodiment, the speed of electron injection and electron transport from the cathode 9 to the light-emitting layer 6 is high, and the organic EL element 1 has a low driving voltage.

"Other examples"
The organic EL element of the present invention is not limited to the organic EL element described in the above-mentioned embodiment.
Specifically, in the above-mentioned embodiment, the organic thin film functions as an electron injection layer, but the organic EL element of the present invention may have an organic thin film between the cathode and the light-emitting layer. Therefore, the organic thin film is not limited to the electron injection layer, and may be provided as a layer that functions both as the electron injection layer and the electron transport layer, or may be provided as the electron transport layer.

In the organic EL element 1 shown in FIG. 1, the electron transport layer 7, the hole transport layer 5, and the hole injection layer 4 may be formed as necessary, and may not be provided.
In addition, each of the anode 3, the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, the electron injection layer 8, and the cathode 9 may be formed as a single layer or may be formed as two or more layers.

The organic EL element 1 shown in FIG. 1 may have other layers between the layers shown in FIG. 1. Specifically, the organic EL element may have a hole blocking layer, etc., as necessary, for reasons such as further improving the characteristics of the organic EL element.

Figures 9 and 10 show schematic cross-sectional views illustrating other examples of the layered structure of the organic EL element of the present invention.

As described above, the first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the above general formula (1), has extremely excellent electron injection properties, so when the first material is used in the electron injection layer 8, it is possible to directly inject electrons into the material used in the light-emitting layer 6. Therefore, even if the material used in the light-emitting layer 6 is used in the electron transport layer 7, it is possible to operate at a low driving voltage. Therefore, as shown in FIG. 9, even an organic EL element 1 having a simple structure in which the material used in the light-emitting layer 6 is used in the electron transport layer 7 can operate at a low driving voltage. In this case, it is possible to reduce the number of materials used by one compared to a typical organic EL element.

Therefore, when a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the above general formula (1), is used in the electron injection layer 8 and a second material is used in the electron transport layer 7, the second material can also be used in the light-emitting layer 6. In other words, an embodiment in which the light-emitting layer 6 contains the second material is also a suitable embodiment of the organic EL element of the present invention.

Furthermore, since holes can be relatively easily injected from the hole injection layer 4 into the material used for the light emitting layer 6, when the first material, which is a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1), is used for the electron injection layer 8, it is possible to operate at a low driving voltage even if the material used for the light emitting layer 6 is used for the hole transport layer 5. Therefore, as shown in FIG. 10, even an organic EL element 1 having a simple structure in which the material used for the light emitting layer 6 is used for the electron transport layer 7 and hole transport layer 5 can operate at a low driving voltage. In this case, it is possible to reduce the number of materials used by two compared to a typical organic EL element.

Therefore, when the first material, which is a hexahydropyrimidopyrimidine compound having the structure represented by the above general formula (1), is used in the electron injection layer 8 and the second material is used in the electron transport layer 7, the second material can also be used in the light-emitting layer 6 and the hole transport layer 5. In other words, an embodiment in which the light-emitting layer 6 contains the second material is also a preferred embodiment of the organic EL element of the present invention. In addition, an embodiment in which a layer containing the second material (e.g., the hole transport layer 5) is provided between the anode 3 and the light-emitting layer 6 is also a preferred embodiment of the organic EL element of the present invention.

In the above-described embodiment, an organic EL element having a normal structure in which the anode 3, the light-emitting layer 6, and the cathode 9 are arranged in this order on the substrate 2 has been described as an example. However, the organic EL element may have an inverted structure in which the cathode 9 is arranged between the substrate 2 and the light-emitting layer 6 (see, for example, FIG. 2).
In the organic EL element shown in FIG. 2, the inorganic oxide layer 10, the electron transport layer 7, the hole transport layer 5, and the hole injection layer 4 may be formed as necessary, and may not be provided.

<Display device, lighting device>
The organic EL element of the present invention can change the emission color by appropriately selecting the materials for the light-emitting layer, etc., and can also obtain a desired emission color by using a color filter, etc. in combination. The light emitting portion and the lighting device can be suitably used.

The display device of the present invention has an organic thin film between the cathode and the light-emitting layer, and is equipped with the organic EL element of the present invention, which has excellent productivity and a low driving voltage. For this reason, it is preferable as a display device.

The lighting device of the present invention is also equipped with the organic EL element of the present invention, which has excellent productivity and a low driving voltage. For this reason, it is preferable as a lighting device.

<Organic thin-film solar cells, photoelectric conversion elements, thin-film transistors>
The present invention is not limited to the above-described embodiment, and the organic thin film of the present invention can be used in devices such as organic thin film solar cells, photoelectric conversion elements, and thin film transistors.

The organic thin-film solar cell and photoelectric conversion element of the present invention include an organic thin-film. For example, when the organic thin-film is used in the electron injection layer of an organic thin-film solar cell or photoelectric conversion element, negative charges are generated by forming hydrogen bonds between the first and second materials of the organic thin-film, resulting in a fast electron transport rate and high power generation efficiency. Therefore, it is preferable as an organic thin-film solar cell or photoelectric conversion element.

The thin film transistor of the present invention includes an organic thin film. For example, when the channel layer of the thin film transistor is formed of an organic thin film, a channel layer with high electron mobility can be obtained.
Furthermore, when the organic thin film is formed on an electrode, a reduction in contact resistance can be expected.

Thus, the organic thin film of the present invention is suitable as a material for organic thin film solar cells, photoelectric conversion elements, and thin film transistors, and therefore the compound having the structure represented by the above general formula (1) constituting the organic thin film and the compound not having a structure in the molecule that coordinates to an alkali metal are also suitable as these materials. Such materials for organic thin film solar cells, materials for photoelectric conversion elements, and materials for thin film transistors that contain a compound having the structure represented by the above general formula (1) and a compound not having a structure in the molecule that coordinates to an alkali metal are also part of the present invention.

The present invention will be described 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 mass" and "%" means "mol %."

(Synthesis Example 1)
In a 200 mL three-neck flask, rac-BINAP (747 mg) and toluene (67 mL) were placed and dissolved by heating to 90° C. under a nitrogen atmosphere. After cooling to room temperature, palladium acetate (180 mg) was added and stirred at room temperature for 1 hour. 2,6-dibromopyridine (4.74 g), 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (6.13 g), and KOtBu (6.28 g) were added thereto and heated and stirred at 90° C. overnight. After cooling to room temperature, diethyl ether was added, the precipitated solid was filtered off, and the filtrate was concentrated. Acetone was added to the resulting residue, and the precipitated solid was filtered off to obtain the compound of the following structural formula (1-2) (3.7 g, 52.5%).

(Synthesis Example 2)
In a 500 mL eggplant flask, rac-BINAP (1.21 g, 1.95 mmol) and dehydrated toluene (350 mL) were placed and dissolved by heating at 90 ° C. This was cooled to room temperature, palladium acetate (0.345, 1.54 mmol) was added, and the inside of the reaction vessel was replaced with argon. After 55 minutes, 9,10-dibromoanthracene (5.01 g, 14.9 mmol), 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (4.45 g, 32.0 mmol), and potassium tert-butoxide (4.26 g, 37.9 mmol) were added, and the inside of the reaction vessel was again placed under an argon atmosphere, and then the mixture was heated and stirred in an oil bath at 90 ° C. After 140 minutes, the mixture was cooled to room temperature, diethyl ether (1 L) was added, and the mixture was stirred for a while, and the precipitated solid was suction filtered and washed with diethyl ether. The diethyl ether in the filtrate was distilled off under reduced pressure, the toluene layer was back-extracted with water (150 mL), and the aqueous layer was distilled off under reduced pressure to obtain 3.77 g of an orange solid.
This was suspended in acetone (50 mL) and stirred overnight at room temperature, after which the solid was suction filtered and washed with acetone to obtain 1.0 g of a yellow solid.
Furthermore, this yellow solid was dissolved in chloroform (41 mL) at 60° C., and then hexane (48 mL) was gradually added. After confirming the precipitation of a solid, the mixture was cooled overnight in a freezer, and the solid was suction filtered and washed with hexane to obtain 0.657 g (1.45 mmol, yield 10%) of a compound represented by the following structural formula (1-30) as a yellow solid.

(Examples 1 to 9 and Comparative Examples 1 to 2)
An organic EL element 1 shown in FIG. 1 was produced by the method described below and evaluated.
[Step 1]
As the substrate 2, a commercially available transparent glass substrate having an average thickness of 0.7 mm and having an electrode (anode 3) patterned to a width of 3 mm and made of ITO with a thickness of 100 nm was prepared.
The substrate 2 having the anode 3 was ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and boiled in isopropanol for 5 minutes. Thereafter, the substrate 2 having the anode 3 was taken out of the isopropanol, dried by nitrogen blowing, and subjected to UV ozone cleaning for 20 minutes.

[Step 2]
The substrate 2 on which the anode 3 cleaned in [Step 1] was formed was set on a spin coater, and a hole injection material "Clevios HIL1.3N" manufactured by Heraeus was formed into a film having a thickness of 10 nm as the hole injection layer 4. Then, the film was heated on a hot plate heated to 180° C. for 1 hour.

[Step 3]
Next, the substrate 2 on which the hole injection layer 4 had been formed was fixed to a substrate holder of a vacuum deposition apparatus.
In addition, 2,4-diphenyl-6-bis(12-phenylindolo)[2,3-a]carbazol-11-yl)-1,3,5-triazine (DIC-TRZ) represented by the following structural formula (4),
fac-tris(3-methyl-2-phenylpyridinato-N,C2′-)iridium(III) (Ir(mppy) ₃ ) represented by the following structural formula (5),
N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD) represented by the following structural formula (6),
N3,N3'''-bis(dibenzo[b,d]thiophen-4-yl)-N3,N3'''-diphenyl-[1,1':2',1'':2'',1'''-quaterphenyl]-3,3'''-diamine (4DBTP3Q) represented by the following structural formula (7),
A compound represented by structural formula (1-2) and a compound represented by structural formula (1-30) as a first material,
Various materials that are the second material;
Al were placed in an alumina crucible and set as deposition sources.

As for the second material, as an example of an aromatic hydrocarbon compound, a compound represented by the following structural formula (8), (9), (10) or (11) is used:
As an example of a compound having a nitrogen-boron bond, a compound represented by the following structural formula (12) or (13) is
As an example of the π-electron-rich heteroaromatic compound, a compound represented by the following structural formula (14) or (15) is
As an example of a compound containing a silole ring, a compound represented by the following structural formula (16):
As an example of a compound capable of injecting electrons from an alkali metal, which is a conventional material, a compound represented by the following structural formula (17) or (18) was used.

The pressure in the chamber of the vacuum deposition apparatus was then reduced to 1×10 ⁻⁵ Pa, and a hole transport layer 5 , a light emitting layer 6 , an electron transport layer 7 , an electron injection layer 8 and a cathode 9 were successively formed by vacuum deposition using resistance heating.

Specifically, first, a hole transport layer 5 having a thickness of 30 nm and made of α-NPD of 20 nm and 4DBTP3Q of 10 nm was formed.
Subsequently, DIC-TRZ was used as a host and Ir(mppy) ₃ was used as a dopant to be co-evaporated to a thickness of 25 nm to form the light-emitting layer 6. At this time, the doping concentration of Ir(mppy) ₃ was set to 3 mass % relative to the entire light-emitting layer 6.
Next, the electron transport layer 7 and the electron injection layer 8 having the structures A to F shown in FIG. 11 were formed on the substrate 2 on which the light emitting layer 6 had been formed.
Next, a cathode 9 made of aluminum and having a thickness of 100 nm was formed by vacuum deposition on the substrate 2 on which the electron injection layer 8 had been formed. The cathode 9 was formed using a stainless steel deposition mask so that the deposition surface would be in the shape of a strip having a width of 3 mm, and the light-emitting area of the fabricated organic EL element was ⁹ mm2.

Details of configurations A to F are as follows.
Configuration A: After the material to be the second material was formed to a thickness of 40 nm, lithium fluoride (LiF), which is a typical electron injection material, was deposited to a thickness of 0.8 nm, and then the cathode 9 was formed.
Configuration B: After forming a film of the material to be the second material to a thickness of 40 nm, 8-quinolinolatolithium (Liq), which is a typical electron injection material, was evaporated to a thickness of 1 nm, and then the cathode 9 was formed.
Configuration C: After depositing the material to be the second material to a thickness of 40 nm, the compound of structural formula (1-2) as the first material was deposited to a thickness of 1 nm, and then the cathode 9 was formed.
Configuration C-2: After forming a film of the material to be the second material to a thickness of 40 nm, the compound of the structural formula (1-30) as the first material was deposited to a thickness of 1 nm, and then the cathode 9 was formed.
Configuration D: After forming a film of the material to be the second material to a thickness of 40 nm, a mixed film of the first material (the compound represented by structural formula (1-2)) and the second material in a mass ratio of 6:4 (first material:second material) was co-evaporated to a thickness of 5 nm, and then a cathode 9 was formed.
Configuration D-2: After forming a film of the material to be the second material to a thickness of 40 nm, a mixed film of the first material (a compound represented by structural formula (1-30)) and the second material in a mass ratio of 6:4 (first material:second material) was co-evaporated to a thickness of 5 nm, and then a cathode 9 was formed.
Configuration E: After depositing a 40 nm thick film of the material to be the second material, the compound of structural formula (1-2) was evaporated as the first material to a thickness of 1 nm, and then the material to be the second material was deposited to a thickness of 1 nm to form the cathode 9.
Configuration F: After forming a film of the material to be the second material to a thickness of 40 nm, the cathode 9 was formed without forming an electron injection layer.

In each of the examples and comparative examples, the compounds used as the second material are as follows.
Example 1: An organic EL element was produced using the compound of structural formula (8) as the second material.
Example 2: An organic EL element was produced using the compound of structural formula (9) as the second material.
Example 3: An organic EL element was produced using the compound of structural formula (10) as the second material.
Example 4: An organic EL element was produced using the compound of structural formula (11) as the second material.
Example 5: An organic EL element was produced using the compound of structural formula (12) as the second material.
Example 6: An organic EL element was produced using the compound of structural formula (13) as the second material.
Example 7: An organic EL element was produced using the compound of structural formula (14) as the second material.
Example 8: An organic EL element was produced using the compound of structural formula (15) as the second material.
Example 9: An organic EL element was produced using the compound of structural formula (16) as the second material.
Comparative Example 1: An organic EL element was produced using the compound of structural formula (17) as the second material.
Comparative Example 2: An organic EL element was produced using the compound of structural formula (18) as the second material.

[Step 4]
Next, the substrate 2 on which each layer up to the cathode 9 was formed was placed in a glass cap (sealing container) having a concave space, and sealed by filling a sealant made of an ultraviolet (UV) curable resin, thereby obtaining each organic EL element.

A voltage was applied to each of the prepared organic EL elements using a Keithley 2400-type source meter, and the luminance was measured using a Konica Minolta LS-100 to examine the relationship between the applied voltage and the luminance. The results are shown in Table 1. However, the results of Example 8 are not shown in Table 1, but are shown in FIG. 13.
In configurations A to E, many elements achieved a luminance of 10,000 nits or more, so the applied voltage at 10,000 nits is shown, but in configuration F, many elements had a high driving voltage, so the applied voltage at 1 nit is shown in Table 1. In addition, as representative data, the luminance-applied voltage characteristics of Example 1 and Comparative Example 1 are shown in FIG.

From the luminance-applied voltage characteristics of Example 1 and Comparative Example 1 shown in FIG. 12, it can be seen that the characteristics of the compound of structural formula (8) and the compound of structural formula (17), which have almost similar structures, are completely different depending on the presence or absence of a pyridine group. Compared to Comparative Example 1 using the compound of structural formula (17), Example 1 using the compound of structural formula (8) has a significantly higher applied voltage at luminance 1 nit in configuration F. Furthermore, in Comparative Example 1 using the compound of structural formula (17), 10,000 nits are obtained at a low voltage in configurations A and B using LiF and Liq, whereas in Example 1 using the compound of structural formula (8), which is an aromatic hydrocarbon compound without pyridine, electrons are not introduced in configurations A and B using LiF and Liq, and the voltage required to obtain 10,000 nits is significantly higher. A similar tendency was observed for Example 5 and Comparative Example 2 regarding the effect of the pyridine group on the characteristics. Furthermore, in the other examples, the driving voltage is high in configurations A and B. Therefore, compounds that have been widely used as electron transport layers in organic EL devices up to now, such as pyridine group-containing compounds, can be said to be compounds that can easily inject electrons from the cathode if an alkali metal is added. As mentioned above, this is due to the interaction between pyridine and alkali metals such as Li.

On the other hand, in Examples 1 to 9, since the drive voltage is high in Structures A and B, it can be said that the aromatic hydrocarbon compounds (Examples 1 to 4), compounds having a nitrogen-boron bond (Examples 5 and 6), π-electron-rich heteroaromatic compounds (Examples 7 and 8), and compounds containing a silole ring (Example 9) are compounds that do not have a structure that coordinates to an alkali metal within the molecule.

In contrast, in the structures C and D of Example 1, the compound of structural formula (1-2) is used, so that electrons can be smoothly injected and 10,000 nits can be obtained at a significantly lower driving voltage. This is believed to be due to the strong hydrogen bond between the compound of structural formula (1-2) and the aromatic hydrocarbon compound, resulting in high electron injection properties.
Similar results were obtained in Examples 2, 3, and 4, and it was found that the use of the compound of the structural formula (1-2) enabled electron injection from the aromatic hydrocarbon to the organic layer.

In addition, in the configurations C-2 and D-2 of Example 2, in which the compound of structural formula (1-30) was used as the first material, 10,000 nits could be obtained at a significantly lower drive voltage. This shows that a hexahydropyrimidopyrimidine compound having a structure represented by general formula (1) induces strong hydrogen bonds with the second material, resulting in high electron injection properties. In addition, the slight difference in drive voltage between configurations C and C-2, and between configurations D and D-2 of Example 2 is thought to be due to the strength of the hydrogen bonds resulting from factors such as the size of the pKa, and those with a large pKa and strong hydrogen bonds are preferable.

Next, attention will be paid to the results of Example 5 and Comparative Example 2, which used the compound of structural formula (12) and the compound of structural formula (18) having a nitrogen-boron bond. As described above, in Comparative Example 2, which used the compound of structural formula (18) having bipyridine, 10,000 nits were obtained at a low voltage in the element using LiF or Liq, whereas in Example 5, which used the compound of structural formula (12), which is a compound having a nitrogen-boron bond without bipyridine, electrons were not introduced in the configurations A and B using LiF and Liq, and the voltage required to obtain 10,000 nits was significantly higher.
Therefore, it is clear that the injection of electrons from an alkali metal such as Li requires interaction between the alkali metal and bipyridine or the like, and that the combination of a compound having a nitrogen-boron bond and an alkali metal makes it difficult to inject electrons into an element.
In contrast, in the structures C and E of Example 5, the compound of structural formula (1-2) is used, which allows smooth injection of electrons and allows 10,000 nits to be obtained at a significantly lower driving voltage. This is believed to be due to the strong hydrogen bond between the compound of structural formula (1-2) and the compound having a nitrogen-boron bond, resulting in high electron injection properties. In this way, the use of the compound of structural formula (1-2) allows electron injection from the compound having a nitrogen-boron bond into the organic layer.
Similar results were obtained in Example 6, and it was found that the use of the compound of structural formula (1-2) enabled electron injection from a compound having a nitrogen-boron bond into an organic layer.

Next, as an example of a π-electron-rich heteroaromatic compound, attention is focused on Example 7 using the compound of structural formula (14). It is extremely difficult to inject electrons into the compound of structural formula (14), and the applied voltage at 1 nit in structure F is significantly higher than in other examples and comparative examples. In structure A using LiF, 10,000 nits can be obtained at a high voltage of about 17 V, and in structure B using Liq, the maximum luminance obtained is about 2,000 nits.
In contrast, by using the compound of structural formula (1-2) in the configuration E, a significant reduction in voltage was observed, and although the voltage was higher than in the other examples, a brightness of 10,000 nits was obtained. Thus, the present invention is also effective for organic EL elements using a π-electron-rich heteroaromatic compound, into which electrons are very difficult to inject, in the electron transport layer.

As another example, attention will be paid to Example 8 using the compound of structural formula (15). Since Example 8 has a lower luminance than the other Examples, the results are not shown in Table 1, but are shown in Figure 13. Here again, since there is no substituent such as pyridine that can interact with Li, in the structure A using LiF, electrons do not enter, and the maximum luminance is less than 60 nits.
In contrast, in the structure D of Example 8, the compound of structural formula (1-2) is used, which allows smooth injection of electrons, enables driving at a significantly lower voltage, and allows a maximum brightness exceeding 10,000 nits to be obtained. Thus, it is found that the use of the compound of structural formula (1-2) also enables injection of electrons from a π-electron-rich heteroaromatic compound into an organic layer.

Next, as an example of a compound containing a silole ring, attention is focused on Example 9, which uses a compound of structural formula (16). Since it does not have a substituent that can interact with Li, such as pyridine, in structures A and B using LiF and Liq, electrons do not enter, and the voltage required to obtain 10,000 nits is significantly high.
In contrast, in the structures C and E of Example 9, the compound of structural formula (1-2) is used, which allows smooth injection of electrons and allows 10,000 nits to be obtained at a significantly lower driving voltage. This is believed to be due to the strong hydrogen bond between the compound of structural formula (1-2) and the compound containing a silole ring, resulting in high electron injection properties. In this way, the use of the compound of structural formula (1-2) allows electron injection from the compound containing a silole ring into the organic layer.

(Example 10 and Comparative Example 3)
In order to demonstrate that the present invention can be applied to an organic EL element having an inverted structure as shown in FIG. 2, an organic EL element having an inverted structure was fabricated using a compound represented by structural formula (1-2), which is a hexahydropyrimidopyrimidine compound having the structure represented by general formula (1) above, and a compound represented by structural formula (8), which is an aromatic hydrocarbon, in the electron injection layer.

[Step 1]
In the same manner as in Examples 1 to 9 and Comparative Examples 1 and 2, [Step 1] was carried out to prepare a substrate 2 on which a patterned cathode 9 having a width of 3 mm and made of cleaned ITO having a thickness of 150 nm was formed.

[Step 2]
The substrate 2 on which the cathode 9 cleaned in [Step 1] was formed was fixed to a substrate holder of a Miratron sputtering device having a zinc metal target. After the pressure inside the chamber of the sputtering device was reduced to about 1×10 ⁻⁴ Pa, sputtering was performed with argon and oxygen introduced, and a zinc oxide layer (oxide layer 10) with a thickness of about 3 nm was formed on the cathode 9 of the substrate 2. Note that when forming the zinc oxide layer, care was taken to prevent the formation of a zinc oxide film on a portion of the ITO electrode (cathode 9) in order to allow for electrode extraction. The substrate 2 on which the oxide layer 10 was formed was annealed at 400° C. for 1 hour in the atmosphere.

[Step 3]
Next, an organic thin film containing a first material and a second material was formed as the electron injection layer 8 on the oxide layer 10 by the method described below (Example 10).
First, the compound of structural formula (8) and the compound of structural formula (1-2) were dissolved in cyclopentanone in a mass ratio of 1:0.1 (compound of structural formula (8): compound of structural formula (1-2)) (concentration: 1 mass%) to obtain a coating composition.
Next, the cathode 9 prepared in [Step 2] and the substrate 2 on which the oxide layer 10 was formed were placed on a spin coater. Then, while dropping the coating composition onto the oxide layer 10, the substrate 2 was rotated at 3000 rpm for 30 seconds to form a coating film. Thereafter, an annealing treatment was performed at 150° C. for 1 hour in a nitrogen atmosphere using a hot plate to form an electron injection layer 8. The average thickness of the obtained electron injection layer 8 was 20 nm.

As a comparative example, a mixed solvent not containing the compound of structural formula (1-2) was prepared, and the other steps were carried out in the same manner to form an electron injection layer 8 (Comparative Example 3).

Next, the substrate 2 on which each of the layers up to the electron injection layer 8 had been formed was fixed to a substrate holder of a vacuum deposition apparatus.
Also, bis[2-(2-benzothiazolyl)phenolato]zinc(II) (Zn(BTZ) ₂ ) represented by the following structural formula (21),
Tris[1-phenylisoquinoline]iridium(III) (Ir(piq) ₃ ) represented by the following structural formula (20),
N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD) represented by the above structural formula (6),
N4,N4'-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (DBTPB) represented by the following structural formula (19),
1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) represented by the following structural formula (22),
Al and were placed in alumina crucibles and set as deposition sources.

The pressure in the chamber of the vacuum deposition apparatus was then reduced to 1×10 ⁻⁵ Pa, and the electron transport layer 7 , light emitting layer 6 , hole transport layer 5 , hole injection layer 4 and anode 3 were successively formed by vacuum deposition using resistance heating.

First, an electron transport layer 7 made of Zn(BTZ) ₂ and having a thickness of 10 nm was formed.
Subsequently, Zn(BTZ) ₂ as a host and Ir(piq) ₃ as a dopant were co-evaporated to a thickness of 20 nm to form the light-emitting layer 6. At this time, the doping concentration of Ir(piq) ₃ was set to 6 mass % with respect to the entire light-emitting layer 6.
Next, on the substrate 2 on which the light-emitting layer 6 had been formed, DBTPB and α-NPD were deposited to a thickness of 10 nm and 40 nm, respectively, to form a hole-transporting layer 5 .
Furthermore, a film of HAT-CN was formed to a thickness of 10 nm to form a hole injection layer 4 .
Next, on the substrate 2 on which the hole injection layer 4 had been formed, an anode 3 made of aluminum and having a thickness of 100 nm was formed by vacuum deposition.
These were sealed with a glass cap to obtain organic EL elements of Example 10 and Comparative Example 3.

The results of evaluating the luminance-voltage characteristics of the organic EL elements of Example 10 and Comparative Example 3 are shown in FIG.
14, the organic EL element of Example 10, in which the compound of structural formula (1-2), which is a hexahydropyrimidopyrimidine compound having the structure represented by the general formula (1) described above, is doped into the electron injection layer, achieves high luminance at a significantly lower applied voltage than the organic EL element of Comparative Example 3. While it is difficult to directly inject electrons from zinc oxide into the compound of structural formula (8), which is an aromatic hydrocarbon, by utilizing the strong hydrogen bond between the compound of structural formula (1-2) and the aromatic hydrocarbon compound, electrons can be efficiently injected, thereby realizing an organic EL element with an inverted structure that can be driven at a low voltage even when aromatic hydrocarbon is used as part of the electron injection layer.

(Examples 11 to 14 and Comparative Example 4)
The organic EL element 1 shown in FIGS. 9 and 10 was manufactured by the method described below and evaluated.

[Step 1]
As the substrate 2, a commercially available transparent glass substrate having an average thickness of 0.7 mm and having an electrode (anode 3) patterned to a width of 3 mm and made of ITO with a thickness of 70 nm was prepared.
The substrate 2 having the anode 3 was ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and boiled in isopropanol for 5 minutes. Thereafter, the substrate 2 having the anode 3 was taken out of the isopropanol, dried by nitrogen blowing, and subjected to UV ozone cleaning for 20 minutes.

[Step 2]
The substrate 2 on which the anode 3 cleaned in [Step 1] was formed was set on a spin coater, and a hole injection material "Clevios HIL1.3N" manufactured by Heraeus was deposited to a thickness of 10 nm as part of the hole injection layer 4. This was then heated for one hour on a hot plate heated to 180°C. Furthermore, a 5 nm film of HAT-CN (1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile represented by the above structural formula (22)) was deposited to form a hole injection layer 4 having a total thickness of 15 nm.

[Step 3]
Next, the substrate 2 on which the hole injection layer 4 had been formed was fixed to a substrate holder of a vacuum deposition apparatus.
In addition, a compound represented by the following structural formula (23) [host material of the light-emitting layer, 9-(naphthalene-1-yl)-10-(naphthalene-2-yl)anthracene],
A compound (blue light-emitting material) represented by the following structural formula (24),
Merck's hole transport material "HTM-081"
A compound represented by the above structural formula (1-2),
Lithium quinoline,
Al were placed in an alumina crucible and set as deposition sources.

The pressure in the chamber of the vacuum deposition apparatus was then reduced to 1×10 ⁻⁵ Pa, and a 30 nm hole transport layer 5, a 25 nm light emitting layer 6, a 25 nm electron transport layer 7, a 1 nm electron injection layer 8, and a cathode 9 were successively formed by vacuum deposition using resistance heating.
The compound represented by structural formula (23) was used as a host and the compound represented by structural formula (24) was used as a dopant to be co-evaporated to a thickness of 25 nm to form an emitting layer 6. At this time, the doping concentration of the compound represented by structural formula (24) was set to 3 mass% with respect to the entire emitting layer 6.
The materials used in each layer in Examples 11 to 14 and Comparative Example 4 are summarized in Table 2.

In Example 11, the compound represented by the structural formula (23) which is a host for the light-emitting layer is used in the portion corresponding to the electron transport layer 7 .
In Example 12, the same layer as the light-emitting layer, in which the compound represented by structural formula (24) is doped into the compound represented by structural formula (23) as a host, is used for the portion corresponding to the electron transport layer 7, and the layers are formed by vapor deposition in a continuous manner from the light-emitting layer.
Examples 11 and 12 have a structure corresponding to that shown in FIG.

On the other hand, in Example 13, the compound represented by the structural formula (23) which is a host for the light-emitting layer is used in the portions corresponding to the hole transport layer 5 and the electron transport layer 7 .
Furthermore, in Example 14, the same layer as the light-emitting layer, in which the compound represented by Structural Formula (24) is doped into the compound represented by Structural Formula (23) as a host, is also used for the hole-transporting layer 5 and the electron-transporting layer 7, and all are formed by continuous vapor deposition.
Examples 13 and 14 have a structure corresponding to that shown in FIG.

Only in Comparative Example 4, the electron injection layer 8 was composed of lithium quinoline, and in Examples 11 to 14, the electron injection layer 8 was composed of a compound represented by structural formula (1-2). After the electron injection layer 8 was vapor-deposited, the cathode 9 was formed by vapor deposition.

The results of measuring the luminance-voltage characteristics of the organic EL elements of Examples 11 to 14 and Comparative Example 4 using the same method as for the other Examples and Comparative Examples are shown in Figure 15.

In Comparative Example 4, it is difficult to inject electrons from lithium quinoline to the compound represented by structural formula (23), which is an aromatic hydrocarbon, and therefore the driving voltage is high. On the other hand, in Examples 11 to 14, electrons can be efficiently injected, and operation can be achieved at a low driving voltage.
Furthermore, it can be seen that, in Examples 13 and 14 in which the hole transport layer 5 has the same structure as the light emitting layer host or the light emitting layer, operation is achieved at a significantly lower driving voltage than in Comparative Example 4.
In this way, by using a material with excellent electron injection properties, it is possible to simplify the structure of the organic EL element and reduce the number of necessary materials.

(Example 15 and Comparative Example 5)
In Example 14, the emitting layer was composed of two types of materials, namely, a host and a dopant. In order to demonstrate that the simple structure shown in FIG. 10 can be realized even in an organic EL element having an emitting layer composed of a single type of material, the organic EL elements of Example 15 and Comparative Example 5 were produced.

[Step 1]
As the substrate 2, a commercially available transparent glass substrate having an average thickness of 0.7 mm and having an electrode (anode 3) patterned to a width of 3 mm and made of ITO with a thickness of 70 nm was prepared.
The substrate 2 having the anode 3 was ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and boiled in isopropanol for 5 minutes. Thereafter, the substrate 2 having the anode 3 was taken out of the isopropanol, dried by nitrogen blowing, and subjected to UV ozone cleaning for 20 minutes.

[Step 2]
The substrate 2 on which the anode 3 cleaned in [Step 1] was formed was set on a spin coater, and a hole injection material "Clevios HIL1.3N" manufactured by Heraeus was deposited to a thickness of 10 nm as part of the hole injection layer 4. This was then heated for one hour on a hot plate heated to 180°C. Furthermore, a 5 nm film of HAT-CN (1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile represented by the above structural formula (22)) was deposited to form a hole injection layer 4 having a total thickness of 15 nm.

[Step 3]
Next, the substrate 2 on which the hole injection layer 4 had been formed was fixed to a substrate holder of a vacuum deposition apparatus.
In addition, a compound represented by the following structural formula (25) [light-emitting material, 9-(9-phenylcarbazol-3-yl)-10-(naphthalen-1-yl)anthracene (PCAN)],
A compound represented by the above structural formula (1-2),
Lithium quinoline,
Al were placed in an alumina crucible and set as deposition sources.

The pressure in the chamber of the vacuum deposition apparatus was then reduced to 1× ¹⁰ Pa, and each layer was deposited by a vacuum deposition method using resistance heating. Only the compound represented by structural formula (25) was deposited to a thickness of 80 nm as the hole transport layer 5, the light emitting layer 6, and the electron transport layer 7, and then the electron injection layer 8 and the cathode 9 were successively formed to a thickness of 1 nm.

In Example 15, the compound represented by structural formula (1-2) was used for the electron injection layer 8, and in Comparative Example 5, lithium quinoline, a common electron injection material, was used for the electron injection layer 8.

The luminance-voltage characteristics of the organic EL elements of Example 15 and Comparative Example 5 were measured using the same method as in the other Examples and Comparative Examples, and the results are shown in Figure 16.

In Comparative Example 5, it is difficult to inject electrons from lithium quinoline to the compound represented by structural formula (25), which does not interact with alkali metals, and therefore the driving voltage is high. On the other hand, in Example 15, electrons are efficiently injected, and operation can be achieved at a low driving voltage.
In this way, by using a material with excellent electron injection properties, it is possible to simplify the structure of the organic EL element and reduce the number of necessary materials.

The organic thin film of the present invention can be used in organic electroluminescence elements, display devices, lighting devices, organic thin film solar cells, photoelectric conversion elements, thin film transistors, etc.

1: Organic EL element 2: Substrate 3: Anode 4: Hole injection layer 5: Hole transport layer 6: Light-emitting layer 7: Electron transport layer 8: Electron injection layer 9: Cathode 10: Oxide layer

Claims (28)

An organic thin film, characterized in that it is a single film containing a first material which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a second material which is a compound having no structure in its molecule that coordinates to an alkali metal, or a laminated film containing a film containing the first material and a film containing the second material.
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) The organic thin film according to claim 1, wherein the second material is a compound having an aromatic heterocycle that does not have a carbon-nitrogen double bond in its structure. The organic thin film according to claim 1, wherein the second material is a compound that does not have a π-electron deficient aromatic heterocycle in the molecule. The organic thin film according to any one of claims 1 to 3, wherein the second material is a compound represented by the following general formula (2):
(In general formula (2), Y represents an aromatic hydrocarbon ring, a π-electron-rich aromatic heterocycle, or a π-conjugated cyclic structure containing silicon and/or boron as a constituent element, which may have a substituent. W represents a linking group or a direct bond. Z represents an aryl group not containing a carbon-nitrogen double bond in the structure. r represents an integer of 1 to 6. s represents an integer of 1 to 6.) The organic thin film according to any one of claims 1 to 4, wherein the second material is any one or more of an aromatic hydrocarbon compound, a compound having a nitrogen-boron bond, a π-electron-rich heteroaromatic compound, and a compound containing a silole ring. A laminate film comprising an oxide layer and a layer of the organic thin film according to any one of claims 1 to 5 formed on the oxide layer. An organic electroluminescence element having a light-emitting layer between a cathode and an anode,
10. An organic electroluminescence element comprising the organic thin film according to claim 1 or the laminated film according to claim 6 between the cathode and the light-emitting layer. The organic electroluminescence element according to claim 7, having an oxide layer between the cathode and the organic thin film. The organic electroluminescence element according to claim 7 or 8, comprising a laminated film of a film containing the first material and the second material and a film containing the second material between the cathode and the light-emitting layer. The organic electroluminescence element according to claim 9, further comprising a film containing the second material between the light-emitting layer and the film containing the first material and the second material. The organic electroluminescence element according to claim 9, further comprising a film containing the second material between the cathode and the film containing the first material and the second material. The organic electroluminescence element according to any one of claims 7 to 11, comprising a layer containing the second material between the anode and the light-emitting layer. The organic electroluminescence element according to any one of claims 7 to 12, wherein the light-emitting layer contains the second material. A material for an organic electroluminescence device, comprising a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a compound not having a structure coordinated to an alkali metal in the molecule:
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) An organic electroluminescence element having a light-emitting layer between a cathode and an anode,
An organic electroluminescence element, comprising a material layer between the cathode and the anode, the material layer including a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1) and a compound not having a structure coordinated to an alkali metal in its molecule:
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) The organic electroluminescence element according to claim 15, comprising the material layer between the cathode and the light-emitting layer. The organic electroluminescence element according to claim 15 or 16, comprising an oxide layer between the cathode and the material layer. A display device comprising an organic electroluminescence element according to any one of claims 7 to 13 and 15 to 17. A lighting device comprising an organic electroluminescence element according to any one of claims 7 to 13 and 15 to 17. A material for an organic thin-film solar cell, comprising: a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a compound not having a structure coordinated to an alkali metal within the molecule:
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) An organic thin-film solar cell comprising the organic thin-film according to any one of claims 1 to 5, the laminated film according to claim 6, or a layer containing the material for organic thin-film solar cells according to claim 20. A material for a photoelectric conversion element, comprising: a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a compound not having a structure coordinated to an alkali metal in the molecule:
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) A photoelectric conversion element comprising the organic thin film according to any one of claims 1 to 5, the laminated film according to claim 6, or a layer containing the material for photoelectric conversion elements according to claim 22. A material for an organic transistor, comprising: a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a compound having no structure coordinated to an alkali metal within the molecule:
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) A thin film transistor comprising the organic thin film according to any one of claims 1 to 5, the laminated film according to claim 6, or a layer containing the organic transistor material according to claim 24. A coating composition comprising: a first material which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1); and a second material which is a compound having no structure in its molecule that coordinates to an alkali metal.
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) A step of forming a single film containing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1), and a second material, which is a compound having no structure coordinated to an alkali metal in the molecule, on a surface to be formed; or
forming a film containing the first material and a film containing the second material in that order on a surface on which the organic thin film is to be formed.
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.) A method for producing an organic thin film, comprising the steps of: forming a film containing a first material, which is a hexahydropyrimidopyrimidine compound having a structure represented by the following general formula (1), on a surface to be formed, the film containing a second material, which is a compound not having a structure in its molecule that coordinates to an alkali metal :
(In general formula (1), ^R1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an aryl alkylene 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. n is 2 or 3.)

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