Organic thin films, organic electroluminescent elements, display devices, lighting devices, organic thin-film solar cells, and organic thin-film transistors.

Abstract

The problem to be solved by the present invention is to provide an organic thin film that uses an organic material with a high electron affinity as a hole injection material, and that can improve the drive stability of organic devices. The solution is this hole-injectable organic thin film that includes at least two organic acceptor materials that differ in the electron affinity. The organic thin film is characterized: by comprising a first layer that includes an organic acceptor material with a relatively low electron affinity and a second layer that is layered onto the first layer and includes an organic acceptor material with a relatively high electron affinity; and in that the organic acceptor material with the relatively low electron affinity has an electron affinity lower than that of the organic acceptor material with the relatively high electron affinity and is used by disposing the first layer on a positive electrode side.

Description

[Technical Field]

[0001] The present invention relates to organic thin films, organic electroluminescent elements, display devices, lighting devices, organic thin-film solar cells, and organic thin-film transistors. [Background technology]

[0002] In organic devices such as organic electroluminescent elements (hereinafter, electroluminescence (electric field emission) may be written as "EL"), organic thin-film solar cells, and organic thin-film transistors, charge exchange is necessary between the electrode and the organic thin film, and hole injection materials and electron injection materials used between the electrode and the organic thin film are being actively researched. To inject electrons into an organic thin film, an electron injection material is needed that can make the cathode's work function equivalent to the electron affinity (EA) of the organic thin film. Traditionally, alkali metals have been widely used, but the development of organic materials is also progressing (Non-Patent Literature 1).

[0003] On the other hand, both inorganic and organic hole injection materials have been developed (Non-Patent Literature 1). As for inorganic materials, materials with high work functions, such as molybdenum oxide and nickel oxide, have been reported to be suitable for hole injection. As for organic materials, materials with high electron affinity, such as 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), have been reported to be suitable for hole injection. Due to their high electron affinity, organic materials can extract electrons from their highest occupied molecular orbital (HOMO), thereby generating holes.

[0004] The aforementioned HAT-CN is widely used as a hole injection material for organic electroluminescent devices (OLEDs). Other materials with high electron affinity have been reported, such as tetracyanonaphthoquinodimethane (TNAP), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ). These have higher electron affinity than HAT-CN and are considered suitable as hole injection materials. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Karsten Walzer,Chemical Reviews,107,2007,p1233-1271 [Non-Patent Document 2] Satoshi Seo, JJ Appl. Phys., 53, 2014, p042102 [Non-Patent Document 3] Jeong-Hwan Lee,ACS Applied Materials & Interfaces,9,2017,p3277 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, no highly stable organic devices using materials other than HAT-CN that have high electron affinity (such as TNAP, F4TCNQ, F6TCNNQ, etc.) have been reported. If materials with high electron affinity can be used, it will be possible to extract electrons from various organic materials with high ionization potential (IP), which can lead to lower voltages in organic EL devices, improved power generation efficiency in organic thin-film solar cells, and improved mobility in p-type organic thin-film transistors.

[0007] Therefore, the object of the present invention is to provide an organic thin film that can improve the driving stability of an organic device by using an organic material with high electron affinity as a hole injection material. Furthermore, a further objective of the present invention is to provide an organic electroluminescent element, a display device, a lighting device, an organic thin-film solar cell, and an organic thin-film transistor that use such an organic thin film and have excellent driving stability. [Means for solving the problem]

[0008] The inventors have found that by using two or more organic acceptor materials with different electron affinities in a hole injection layer, placing the organic acceptor material with a relatively low electron affinity on the anode side, and laminating the material with a relatively high electron affinity on top of the organic acceptor material with a relatively low electron affinity, it is possible to realize a hole injection layer with high hole injection performance and excellent driving stability, thereby solving the above-mentioned problems. In other words, the essential configuration of the organic thin film, organic electroluminescent element, display device, lighting device, organic thin-film solar cell, and organic thin-film transistor of the present invention, which solve the above problems, is as follows.

[0009] [1] A hole-injection organic thin film comprising two or more organic acceptor materials with different electron affinities, A first layer containing an organic acceptor material with relatively low electron affinity, The present invention comprises a second layer laminated on the first layer, which contains an organic acceptor material having a relatively high electron affinity, The aforementioned organic acceptor material with relatively low electron affinity has a lower electron affinity than the aforementioned organic acceptor material with relatively high electron affinity. An organic thin film characterized in that the first layer is positioned on the anode side.

[0010] [2] The organic acceptor material having a relatively low electron affinity has an electron affinity less than 4.5 eV, The organic acceptor material with a relatively large electron affinity is the organic thin film described in [1], having an electron affinity of 4.5 eV or more.

[0011] [3] The organic thin film according to [1] or [2], wherein the second layer is a film obtained by mixing the organic acceptor material with a relatively large electron affinity with another organic material.

[0012] [4] The organic thin film according to any one of [1] to [3], wherein the organic acceptor material is a cyano-containing compound or a fluorine-containing compound.

[0013] [5] The organic thin film according to any one of [1] to [4], wherein the organic acceptor material is a compound containing a 2-methylenepropanedinitrile group.

[0014] [6] The organic thin film according to any one of [1] to [3], wherein the organic acceptor material with a relatively small electron affinity is any one of a fluorine-containing compound, an aromatic hydrocarbon, a phosphonic acid, and a material constituting a self-assembled monolayer.

[0015] [7] The organic thin film according to any one of [1] to [3], wherein the organic acceptor material with a relatively small electron affinity has an electron affinity of 0.35 eV or more and less than 4.5 eV.

[0016] [8] An organic electroluminescence device comprising a cathode, a light-emitting layer, and an anode in this order, wherein an organic thin film according to any one of [1] to [7] is provided between the anode and the light-emitting layer, and the first layer of the organic thin film is disposed on the anode side. An organic electroluminescence device characterized by this.

[0017] [9] The organic electroluminescence device according to [8], wherein the average thickness of the organic thin film is 2 to 100 nm.

[0018] A display device characterized by comprising an organic electroluminescent element as described in

[10] [8] or [9].

[0019] A lighting device characterized by comprising an organic electroluminescent element as described in

[11] [8] or [9].

[0020]

[12] An organic thin-film solar cell characterized by containing an organic thin film described in any one of [1] to [7].

[0021]

[13] An organic thin-film transistor characterized by containing an organic thin film described in any one of [1] to [7]. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide an organic thin film that can improve the driving stability of organic devices. Furthermore, according to the present invention, it is possible to provide an organic electroluminescent element, a display device, a lighting device, an organic thin-film solar cell, and an organic thin-film transistor that have excellent driving stability using such an organic thin film. [Brief explanation of the drawing]

[0023] [Figure 1] This is a schematic diagram showing an example of the structure of the organic EL element of the present invention. [Figure 2] This is a schematic diagram showing two examples of hole injection layer configurations for the organic EL element of the present invention. [Figure 3] This is an explanatory diagram showing the energy levels within the organic EL elements of the examples and comparative examples. [Figure 4] These are the inverse photoelectron spectra of each organic acceptor material used in the examples and comparative examples. [Figure 5] This is an explanatory diagram showing an example of the configuration of a hole injection layer and its relationship to electron affinity. [Figure 6] This graph shows the relationship between the applied voltage and current density of the organic EL elements in Examples 1 to 4. [Figure 7]This graph shows the relationship between applied voltage and current density for the organic EL elements of Comparative Examples 1 to 7. [Figure 8] This graph shows the relationship between the applied voltage and current density of the organic EL elements in Examples 5-8 and Comparative Examples 8-9. [Figure 9] This graph shows the correlation between measured and calculated electron affinity values ​​for several organic materials. [Modes for carrying out the invention]

[0024] The organic thin film, organic electroluminescent element, display device, lighting device, organic thin-film solar cell, and organic thin-film transistor of the present invention will be described in detail below based on their embodiments.

[0025] <Organic thin film> The organic thin film of this embodiment is a hole-injection organic thin film containing two or more organic acceptor materials with different electron affinities. The organic thin film of this embodiment comprises a first layer containing an organic acceptor material with a relatively low electron affinity, and a second layer laminated on the first layer containing an organic acceptor material with a relatively high electron affinity, wherein the organic acceptor material with a relatively low electron affinity has a lower electron affinity than the organic acceptor material with a relatively high electron affinity, and the first layer is used positioned on the anode side. There are two methods for measuring electron affinity: low-energy inverse photoemission spectroscopy (LEIPS) and a method that involves measuring the ionization energy and optical gap and then subtracting the result. However, the value measured using the optical gap is approximately 0.5 eV larger than the value measured using LEIPS, indicating that electron affinity depends on the measurement method. Therefore, in this specification, the electron affinity (EA) of organic acceptor materials is a calculated value, obtained using molecular orbital calculations [density functional theory, B3LYP, basis set: 6-31G(d)].

[0026] Organic acceptor materials can attract electrons from adjacent molecules and atoms, and the greater their electron affinity (EA), the easier it is for them to attract electrons. When an organic acceptor material with high electron affinity is deposited on the anode, the amount of electron transfer from the anode to the organic acceptor material increases, causing the film made of the organic acceptor material to become strongly negatively charged. This strongly negatively charged state is not stable, so depositing an organic acceptor material with high electron affinity on the anode of an organic device reduces the driving stability of the organic device. In contrast, the organic thin film of this embodiment has a first layer placed on the anode side that contains an organic acceptor material with relatively low electron affinity, and a second layer laminated on the first layer that contains an organic acceptor material with relatively high electron affinity. By providing a first layer containing an organic acceptor material with relatively low electron affinity on the anode side, the amount of electron transfer from the anode side is reduced, suppressing the first layer from becoming negatively charged and bringing it closer to neutrality, thereby improving the stability of the first layer and improving the driving stability of the organic device to which the organic thin film is applied. Furthermore, by providing a second layer containing an organic acceptor material with relatively high electron affinity on top of the first layer (on the cathode side of the first layer), the second layer extracts electrons from the cathode side (for example, the hole transport layer in an organic EL device), which enables lower voltage in organic EL devices, improved power generation efficiency in organic thin-film solar cells, and improved mobility in p-type organic thin-film transistors.

[0027] The organic thin film of this embodiment is a hole-injection organic thin film containing two or more organic acceptor materials with different electron affinities, and the number of types of organic acceptor materials contained may be two or three or more. The organic thin film of this embodiment has hole-injection properties, that is, it has the property of injecting holes sent from the anode side into the layer adjacent to the cathode side.

[0028] The organic thin film of this embodiment comprises a first layer containing an organic acceptor material with relatively low electron affinity, and a second layer laminated on the first layer containing an organic acceptor material with relatively high electron affinity. It may also have other layers besides the first and second layers. Here, the organic acceptor material with relatively low electron affinity used in the first layer has a lower electron affinity than the organic acceptor material with relatively high electron affinity used in the second layer. Furthermore, as described above, by providing a first layer containing an organic acceptor material with relatively low electron affinity on the anode side, the amount of electron transfer from the anode side is reduced, and the first layer is suppressed from becoming negatively charged. Therefore, the organic thin film of this embodiment is characterized in that the first layer of the organic thin film is positioned on the anode side.

[0029] The organic acceptor material with relatively low electron affinity preferably has an electron affinity of less than 4.5 eV. If the electron affinity of the organic acceptor material with relatively low electron affinity used in the first layer is less than 4.5 eV, the amount of electron transfer from the anode side is further reduced, the negative charging of the first layer is further suppressed, and it is brought closer to neutrality, thereby further improving the stability of the first layer and further improving the driving stability of the organic device to which the organic thin film is applied. The lower limit of the electron affinity of the organic acceptor material with relatively low electron affinity is not particularly limited, but in one embodiment it is 0.35 eV or more, and in other embodiments it is 1.0 eV or more. Furthermore, the organic acceptor material with relatively low electron affinity preferably has an electron affinity of 0.35 eV or more and less than 4.5 eV.

[0030] Furthermore, the organic acceptor material with relatively high electron affinity preferably has an electron affinity of 4.5 eV or more, more preferably 4.8 eV or more, and preferably 7.0 eV or less. When the electron affinity of the organic acceptor material with relatively high electron affinity used in the second layer is 4.5 eV or more, the second layer can more easily extract electrons from the cathode side (for example, the hole transport layer in an organic EL device), which enables further voltage reduction in organic EL devices, further improvement in power generation efficiency in organic thin-film solar cells, and further improvement in mobility in p-type organic thin-film transistors.

[0031] The second layer may be a film made of an organic acceptor material with relatively high electron affinity, but it is also preferable that the organic acceptor material with relatively high electron affinity be mixed with another organic material. Here, the other material may be a donor material, and as the donor material, the material used for the hole transport layer of the organic EL element described later can be applied. Furthermore, if the second layer is a film obtained by mixing an organic acceptor material having a relatively high electron affinity with another organic material, the ratio of the organic acceptor material to the other organic material is preferably 5.0:95.0 to 50.0:50.0 by mass ratio (organic acceptor material:other organic material).

[0032] Various hole-injection-performing organic materials can be used as the organic acceptor material, but in one embodiment, cyano-containing compounds and fluorine-containing compounds are preferred, and compounds containing a 2-methylenepropanedinitrile group are more preferred. When the organic acceptor material is a cyano-containing compound or a fluorine-containing compound, the hole injection properties of the organic thin film are improved. Furthermore, when the organic acceptor material is a compound containing a 2-methylenepropanedinitrile group, the hole injection properties of the organic thin film are further improved. Here, the 2-methylenepropanedinitrile group is a group [=C(CN)2] in which two cyano groups are bonded to one of the carbon atoms constituting a carbon-carbon double bond, and is also called a dicyanomethylene group.

[0033] Examples of the aforementioned cyano compounds include 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), tetracyanonaphthoquinodimethane (TNAP), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ), and hexacyano-trimethylene-cyclopropane (CN6-CP).

[0034] Examples of the aforementioned fluorine-containing compounds include 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ), and 1,2,3,4,5,6,7,8-octafluoro-9,10-bis[4-(trifluoromethyl)phenyl]anthracene.

[0035] Furthermore, examples of compounds containing the 2-methylenepropanedinitrile group include tetracyanonaphthoquinodimethane (TNAP), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ), and hexacyano-trimethylene-cyclopropane (CN6-CP).

[0036] The organic acceptor material used in the second layer, which has a relatively high electron affinity, is preferably a compound containing a 2-methylenepropanedinitrile group. Compounds containing a 2-methylenepropanedinitrile group have a particularly high electron affinity (EA), making it easier for the second layer to extract electrons from the cathode side (for example, the hole transport layer in an organic EL device), which enables further lower voltages in organic EL devices, further improvements in power generation efficiency in organic thin-film solar cells, and further improvements in mobility in p-type organic thin-film transistors.

[0037] Furthermore, in one embodiment, the organic acceptor material with relatively low electron affinity used in the first layer is preferably one of a fluorine-containing compound, an aromatic hydrocarbon, a phosphonic acid, or a material constituting a self-assembled monolayer. These materials further reduce the amount of electron transfer from the anode side, further suppress the negative charging of the first layer, and bring it closer to neutrality, thereby further improving the stability of the first layer and further improving the driving stability of the organic device to which the organic thin film is applied. Examples of fluorine-containing compounds include 1,2,3,4,5,6,7,8-octafluoro-9,10-bis[4-(trifluoromethyl)phenyl]anthracene (BCF3Ph-F8-Ant), examples of aromatic hydrocarbons include 2-(9,9'-spirobifluorene-2-yl)-9,9'-spirobifluorene (BSBF), examples of phosphonic acids include 4-fluorobenzylphosphonic acid (FP-ly-POA), and examples of materials constituting self-assembled monolayers include 4-fluorobenzylphosphonic acid (FP-ly-POA).

[0038] <Organic electroluminescent element> The organic electroluminescent element of this embodiment comprises a cathode, a light-emitting layer, and an anode in that order, with the above-mentioned organic thin film between the anode and the light-emitting layer. Furthermore, the organic EL electroluminescent element of this embodiment is characterized in that the first layer of the above-mentioned organic thin film is arranged on the anode side.

[0039] In the organic EL element of this embodiment, since the first layer of the organic thin film is located on the anode side, the amount of electron transfer from the anode side is reduced, suppressing the first layer from becoming negatively charged and bringing it closer to neutrality. This improves the stability of the first layer and thus improves the driving stability of the organic EL element. Furthermore, in the organic EL element of this embodiment, since the second layer of the organic thin film is arranged on top of the first layer (on the cathode side of the first layer), the second layer extracts electrons from the cathode side (for example, a hole transport layer, an emissive layer, etc.), thereby enabling a lower voltage.

[0040] In the organic EL element of this embodiment, the average thickness of the organic thin film is preferably 2 to 100 nm, and more preferably 5 to 100 nm. When the average thickness of the organic thin film is 2 to 100 nm, it becomes possible to further reduce the driving voltage while further improving the driving stability of the organic EL element. Here, the average thickness of the organic thin film can be measured using a stylus-type step meter or spectroscopic ellipsometry.

[0041] Next, the organic EL element of this embodiment will be described in detail with reference to an example. Figure 1 is a schematic cross-sectional view illustrating an example of an organic EL element of this embodiment. The organic EL element 1 shown in Figure 1 has an emissive layer 6 between an anode 3 and a cathode 9, and further has the organic thin film of this embodiment as a hole injection layer 4 between the anode 3 and the emissive layer 6. More specifically, the organic EL element 1 shown in Figure 1 has a laminated structure on a substrate 2 in the following order: an anode 3, a hole injection layer (organic thin film) 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. Here, the hole injection layer (organic thin film) 4 has a first layer 4-1 on the anode 3 side and a second layer 4-2 on the hole transport layer 5 side.

[0042] In the organic EL element 1 shown in Figure 1, holes are injected from the anode 3 and electrons from the cathode 9. These charges travel through the transport layers 5 and 7 to the light-emitting layer 6, where they recombine to generate light. The organic EL element 1 shown in Figure 1 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.

[0043] (substrate) Examples of materials for substrate 2 include resin materials and glass materials. Substrate 2 may use only one type of material, or it may use a combination of two or more types. Examples of resin materials used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. Using a resin material for the substrate 2 is preferable because it allows for the production of an organic EL element 1 with excellent flexibility. On the other hand, examples of glass materials used for substrate 2 include quartz glass and soda glass.

[0044] If the organic EL element 1 is a bottom-emission type, a transparent substrate is used as the material for the substrate 2. On the other hand, if the organic EL element 1 is of the top-emission type, the substrate 2 may be made of an opaque substrate as well as a transparent substrate. Examples of opaque substrates include substrates made of ceramic materials such as alumina, substrates with an oxide film (insulating film) formed on the surface of a metal plate such as stainless steel, and substrates made of resin materials.

[0045] The average thickness of the substrate 2 can be determined according to 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 or calipers.

[0046] (electrode) In the organic EL element 1 of this embodiment, known conductive materials can be used as the anode 3 and cathode 9 as appropriate, but it is preferable that at least one of them be transparent in order to extract light. Examples of known transparent conductive materials include ITO (tin-doped indium oxide), ATO (antimond-doped indium oxide), IZO (indium-doped zinc oxide), AZO (aluminum-doped zinc oxide), FTO (fluorine-doped indium oxide), and the like. On the other hand, examples of opaque conductive materials include calcium, magnesium, aluminum, barium, tin, indium, copper, silver, ytterbium, and alloys thereof. Among these, ITO, IZO, and FTO are preferred as anode 3. On the other hand, among these, Al and AgMg alloys are preferred as the cathode 9.

[0047] The average thickness of the anode 3 is not particularly limited, but is preferably 10 to 500 nm, and more preferably 70 to 200 nm. The average thickness of the anode 3 can be measured by a stylus step meter or spectroscopic ellipsometry.

[0048] 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. Furthermore, even when using an opaque material, by setting the average thickness to approximately 10 to 30 nm, it can be used as a top-emission type or transparent type cathode 9. The average thickness of the cathode 9 can be measured during film formation using a quartz crystal film thickness gauge.

[0049] (Hole injection layer) The hole injection layer 4 can have the same configuration as the organic thin film described above, namely, a first layer 4-1 containing an organic acceptor material with relatively low electron affinity, and a second layer 4-2 containing an organic acceptor material with relatively high electron affinity, which is laminated on the first layer 4-1, with the first layer 4-1 positioned on the anode 3 side. This configuration makes it possible to form a hole injection layer 4 with improved hole injection performance and stability.

[0050] In the organic EL element 1 of this embodiment, it is preferable to form a hole injection layer 4 by stacking two types of organic acceptor materials, but the hole injection layer 4 can have various configurations. For example, as shown in Figure 2A, a first layer 4-1 containing an organic acceptor material with relatively low electron affinity (organic acceptor material 1) and a second layer 4-2 containing an organic acceptor material with relatively high electron affinity (organic acceptor material 2) can be stacked and used as the hole injection layer 4. Alternatively, as shown in Figure 2B, a layer (second layer 4-2) made by mixing an organic acceptor material with relatively high electron affinity (organic acceptor material 2) and a donor material can be stacked on a single film (first layer 4-1) of an organic acceptor material with relatively low electron affinity (organic acceptor material 1) and used as the hole injection layer 4. Here, the donor material to be mixed with the organic acceptor material can be the material of the hole transport layer 5 described later. Furthermore, if the second layer 4-2 contains both the organic acceptor material and the donor material, the ratio of the organic acceptor material to the donor material is preferably 5.0:95.0 to 50.0:50.0 by mass ratio (organic acceptor material:donor material). Furthermore, the configuration of the hole injection layer in the organic EL element of the present invention is not limited to these, and other configurations can also be adopted.

[0051] The average thickness of the hole injection layer 4 is not particularly limited, but is preferably 1 to 1000 nm, more preferably 2 to 100 nm, even more preferably 5 to 100 nm, and particularly preferably 5 to 50 nm. In addition, the average film thickness of the first layer 4-1 and the second layer 4-2 are each preferably in the range of 1 to 50 nm. The average thickness of the hole injection layer 4 (first layer 4-1 and second layer 4-2) can be measured, for example, by a stylus step meter or spectroscopic ellipsometry.

[0052] (Hole transport layer) Any compound (donor material) that can be commonly used as a material for a hole transport layer can be used for the hole transport layer 5, and various p-type polymer materials and various p-type low-molecular-weight materials can be used alone or in combination.

[0053] Examples of the aforementioned p-type polymer material (organic polymer) include polyarylamine, fluorene-arylamine copolymer, fluorene-bithiophene copolymer, poly(N-vinylcarbazole), polyvinylpyrene, polyvinylanthracene, polythiophene, polyalkylthiophene, polyhexylthiophene, poly(p-phenylenevinylene), polyphenylenevinylene, pyreneformaldehyde resin, ethylcarbazoleformaldehyde resin, or derivatives thereof. These polymer materials can also be used as mixtures with other compounds. As an example, a mixture containing polythiophene includes poly(3,4-ethylenedioxythiophene / styrenesulfonic acid) (PEDOT / PSS).

[0054] Examples of the aforementioned p-type low molecular weight materials include arylcycloalkane compounds such as 1,1-bis(4-di-p-triaminophenyl)cyclohexane and 1,1'-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane, 4,4',4”-trimethyltriphenylamine, N,N,N',N'-tetraphenyl-1,1'-biphenyl-4,4'-diamine, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD1), and N,N'-diphenyl- N,N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD2), N,N,N',N'-tetrakis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD3), N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD), 4,4'-bis[N-phenyl-N-[4'-diphenylamino-1,1'-biphenyl-4-yl]amino]-1,1'-biphenyl (TPTE), tris(4-carbazolyl) Arylamine compounds such as -9-ylphenyl)amine (TcTa), phenylenediamine compounds such as N,N,N',N'-tetraphenyl-para-phenylenediamine, N,N,N',N'-tetra(para-tolyl)-para-phenylenediamine, and N,N,N',N'-tetra(meth-tolyl)-meth-phenylenediamine (PDA), carbazole compounds such as carbazole, N-isopropylcarbazole, and N-phenylcarbazole, and stilbene compounds such as stilbene and 4-di-para-tolylaminostilbene. , oxazole compounds such as OxZ, triphenylmethane, triphenylmethane compounds such as 4,4',4”-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA), pyrazoline compounds such as 1-phenyl-3-(para-dimethylaminophenyl)pyrazoline, benzine (cyclohexadiene) compounds, triazole compounds such as triazole, imidazole compounds such as imidazole, 1,3,4-oxadiazole, 2,5-di(4-dimethylaminophenyl)-1,3,Oxadiazole compounds such as 4-oxadiazole, anthracene compounds such as anthracene and 9-(4-diethylaminostyryl)anthracene, fluorenone compounds such as fluorenone, 2,4,7-trinitro-9-fluorenone, and 2,7-bis(2-hydroxy-3-(2-chlorophenylcarbamoyl)-1-naphthylazo)fluorenone, aniline compounds such as polyaniline, silane compounds, pyrrole compounds such as 1,4-dithioketo-3,6-diphenyl-pyrrolo-(3,4-c)pyrrolopyrrole, fluorene compounds such as fluorene, porphyrin, and metal tetraphenyl Examples include porphyrin compounds such as porphyrin, quinacridone compounds such as quinacridone, metallic or metal-free phthalocyanine compounds such as phthalocyanine, copper phthalocyanine, tetra(t-butyl)copper phthalocyanine, and iron phthalocyanine, metallic or metal-free naphthalocyanine compounds such as copper naphthalocyanine, vanadyl naphthalocyanine, and monochlorogallium naphthalocyanine, and benzidine compounds such as N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine and N,N,N',N'-tetraphenylbenzidine. One or more of these can be used. Among these, arylamine compounds such as TcTa, α-NPD, and TPTE are particularly preferred.

[0055] The average thickness of the hole transport layer 5 is not particularly limited, but is preferably 5 to 150 nm, and more preferably 10 to 100 nm. The average thickness of the hole transport layer 5 can be measured, for example, by a stylus step meter or spectroscopic ellipsometry.

[0056] (Emitting layer) In the organic EL element 1 of this embodiment, the material forming the light-emitting layer 6 may be a low-molecular-weight compound or a high-molecular-weight compound, or a mixture thereof may be used. In this invention, a 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. Furthermore, the light-emitting layer 6 can also be used in combination with materials generally known as light-emitting materials, as well as donor materials and electron transport materials. Examples of donor materials include the materials used in the hole transport layer 5 described above, and examples of electron transport materials include the materials used in the electron transport layer 7, which will be described later.

[0057] Examples of polymer materials that form the light-emitting layer 6 include polyacetylene compounds such as trans-type polyacetylene, cis-type polyacetylene, poly(di-phenylacetylene) (PDPA), and poly(alkyl,phenylacetylene) (PAPA); poly(para-phenylene vinylene) (PPV), poly(2,5-dialkoxy-para-phenylene vinylene) (RO-PPV), cyano-substituted-poly(para-phenylene vinylene) (CN-PPV), and poly( Poly(2-dimethyloctylsilyl-p-phenylenevinylene) (DMOS-PPV), poly(2-methoxy,5-(2'-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV), and other poly(p-phenylenevinylene) compounds; poly(3-alkylthiophene) (PAT), poly(oxypropylene)triol (POPT), and other polythiophene compounds; poly(9,9-dialkylfluorene) (PDAF), poly(dioctylfluorene) Polyfluorene compounds such as (9,9-(9,9-(9,9-(9,9-(2-ethylhexyl))fluorene-2,7-dyl)(PF2 / 6am4), (9,9-( Examples include poly(p-phenylene) compounds such as (nilen)(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 polymer materials described in Japanese Patent Publication No. 2011-184430 and Japanese Patent Publication No. 2012-151148.

[0058] Examples of low molecular weight materials that form the light-emitting layer 6 include three-coordinate iridium complexes having 2,2'-bipyridine-4,4'-dicarboxylic acid as a ligand, such as funci(2-phenylpyridine)iridium (Ir(ppy)3), fac-tris(3-methyl-2-phenylpyridinate-N,C2'-)iridium(III) (Ir(mppy)3), 8-hydroxyquinoline aluminum (Alq3), and tris(4-methyl-8-) Various metal complexes such as (norinolate)aluminum(III)(Almq3), 8-hydroxyquinoline zinc(Znq2), (1,10-phenanthroline)-tris-(4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dionete)europium(III)(Eu(TTA)3(phen)), and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II);Benzene compounds such as distyrylbenzene (DSB) and diaminodistyrylbenzene (DADSB), naphthalene compounds such as naphthalene and Nile Red, phenanthrene compounds such as phenanthrene, chrysene compounds such as chrysene and 6-nitrochrysene, perylene compounds such as perylene and N,N'-bis(2,5-di-t-butylphenyl)-3,4,9,10-perylene-di-carboxyimide (BPPC), coronene compounds such as coronene, anthracene, and bisstyrylanthracene Anthracene compounds such as pyrene, pyrene compounds such as pyrene, pyran compounds such as 4-(di-cyanomethylene)-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran (DCM), acridine compounds such as acridine, stilbene compounds such as stilbene, carbazole compounds such as 4,4'-bis[9-dicarbazolyl]-2,2'-biphenyl (CBP) and 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi), 2,5-dibenzo 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 xadiazole, 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; triazine compounds such as 2,4-diphenyl-6-bis(12-phenylindoro[2,3-a]carbazole-11-yl)-1,3,5-triazine (DIC-TRZ);Examples include spiro compounds such as 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene, metallic or metal-free phthalocyanine compounds such as phthalocyanine (H2Pc) and copper phthalocyanine, and boron compound materials described in Japanese Patent Publication No. 2009-155325 and Japanese Patent No. 5660371. One or more of these can be used. Quantum dots and perovskite materials can also be used as the light-emitting layer.

[0059] The average thickness of the light-emitting layer 6 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm. The average thickness of the light-emitting layer 6 may be measured using a stylus-type step meter, or it may be measured using a quartz crystal thickness gauge during the deposition of the light-emitting layer 6.

[0060] (electron transport layer) As the material for the electron transport layer 7, a wide range of known materials capable of transporting electrons (electron transport materials) can be used, specifically, phosphine oxide derivatives such as phenyl-dipyrenylphosphine oxide (POPy2), pyridine derivatives such as tris-1,3,5-(3'-(pyridine-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), pyr Zin derivatives, phenanthroline derivatives such as vasophenanthroline (BPhen), triazine derivatives such as 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT), 2,4,6-tris(m-pyridine-3-ylphenyl)triazine (TmPPyTz), 2,4-diphenyl-6-bis(12-phenylindoro[2,3-a]carbazole-11-yl)-1,3,5-triazine (DIC-TRZ), 3-phenyl-4-(1'-naphthyl)-5-phenyl-1, Triazole derivatives such as 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-bentriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring tetracarboxylic anhydrides such as naphthalene and perylene, bis[2-(2-hydroxyphenyl)benzothiazolat]zinc (Zn(BTZ)2), tris(8-hydro Examples include various metal complexes represented by xikinolinato)aluminum (Alq3), organosilane derivatives represented by silole derivatives such as 2,5-bis(6'-(2',2"-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy), and boron-containing compounds described in Japanese Patent Publication No. 2013-239691, International Publication No. 2014 / 133141, Japanese Patent Publication No. 2016-172728, Japanese Patent Publication No. 2016-199507, and Japanese Patent Publication No. 2016-199508, and one or more of these can be used.

[0061] 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 using a stylus-type step meter and spectroscopic ellipsometry.

[0062] (electron injection layer) The material used for the electron injection layer 8 is selected from the viewpoint of the work function of the cathode 9 and the LUMO level of the electron transport layer 7. If the electron transport layer 7 is not provided, the material used for the light-emitting layer 6 is selected considering its LUMO level. The material for the electron injection layer 8 may be an organic compound or an inorganic compound. If the electron injection layer 8 is made of an inorganic compound, for example, alkali metals, alkaline earth metals, lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, cesium carbonate, etc. can be used. If the electron injection layer 8 is made of an organic compound, for example, 8-quinolinolatritium (Liq), hexahydropyrimidopyrimidine compounds having the structure represented by the following general formula (1), or compounds having the structure represented by the following general formula (2) can be used.

[0063] [ka] (In general formula (1), R 1 n represents an aromatic hydrocarbon group which may have substituents, an aromatic heterocyclic group, an arylalkylene group, a 2- to 4-valent linear or cyclic hydrocarbon group, or 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. 1 (This is an integer between 1 and 4.)

[0064] [ka] (In general formula (2), X 1 , X 2represents a nitrogen atom, an oxygen atom, a sulfur atom or a divalent linking group which may have substituents, either the same or different. L represents a direct bond or a p-valent linking group. n 2 represents a number of 0 or 1, p represents a number of 1 to 4. q represents a number of 0 or 1, and when p is 1, q is 0. R 2 ~R 4 represents, either the same or different, a monovalent substituent. m 1 ~m 3 represents, either the same or different, a number of 0 to 3. R 2 ~R 4 is X 1 、X 2 and may combine with to form a ring structure. When there are a plurality of R 2 s, a plurality of R 2 [ s may combine to form a ring structure. Also, when there are a plurality of R 3 s, a plurality of R 3 s may combine to form a ring structure. Also, when there are a plurality of R 4 s, a plurality of R 4 s may combine to form a ring structure.)

[0065] <able> R in the above general formula (1) 1 represents an aromatic hydrocarbon group, an aromatic heterocyclic group, an arylalkylene group, a chain or cyclic hydrocarbon group with a valence of 2 to 4, which may have substituents, or 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. As the aromatic hydrocarbon group and the aromatic heterocyclic group, those having 3 to 30 carbon atoms are preferred, those having 4 to 24 carbon atoms are more preferred, and those having 5 to 20 carbon atoms are even more preferred. 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 through one carbon atom; and a group formed by removing 1 to 4 hydrogen atoms from any aromatic ring of a condensed polycyclic aromatic hydrocarbon compound such as naphthalene, anthracene, phenanthrene, and pyrene. Aromatic heterocyclic groups include compounds consisting of only one aromatic heterocyclic ring, such as thiophene, furan, pyrrole, oxazole, oxadiazole, thiazole, thiadiazole, imidazole, pyridine, pyrimidine, pyrazine, and triazine; compounds in which multiple of these compounds consisting of only one aromatic heterocyclic ring are directly bonded to each other by a single carbon atom (such as bipyridine); and groups formed by removing 1 to 4 hydrogen atoms from any aromatic heterocyclic ring of fused cyclic heteroaromatic hydrocarbon compounds such as quinoline, quinoxaline, benzothiophene, benzothiazole, benzimidazole, benzoxazole, indole, carbazole, dibenzofuran, dibenzothiophene, acridine, and phenanthroline. Examples of arylalkylene groups include groups that combine the above-mentioned aromatic hydrocarbon group with an alkylene group having 1 to 3 carbon atoms. The 2-4 valent linear or cyclic hydrocarbon group is preferably one with 1 to 12 carbon atoms, more preferably one with 1 to 6 carbon atoms, and even more preferably one with 1 to 4 carbon atoms. The linear hydrocarbon group may be linear or branched. Also, R 1 This may also be a group formed by combining two or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, or divalent to tetravalent chain hydrocarbon groups. Furthermore, R 1 The group may be formed by combining one or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, or 2- to 4-valent linear hydrocarbon groups with a nitrogen atom. Examples of such groups include trialkylamines such as trimethylamine and groups formed by removing 1 to 4 hydrogen atoms from triphenylamine.

[0066] The above-mentioned aromatic hydrocarbon group, aromatic heterocyclic group, or arylalkylene group may have one or more monovalent substituents. Monovalent substituents include fluorine atoms; haloalkyl groups such as fluoromethyl, difluoromethyl, and trifluoromethyl groups; linear or branched alkyl groups with 1 to 20 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl groups; cyclic alkyl groups with 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, and cycloheptyl groups; methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, and heptyloxy groups. Linear or branched alkoxy groups with 1 to 20 carbon atoms, such as oxy groups and octyloxy groups; nitro groups; cyano groups; alkylamino groups with alkyl groups with 1 to 10 carbon atoms, such as methylamino groups, ethylamino groups, dimethylamino groups, and diethylamino groups; cyclic amino groups such as pyrrolidino groups, piperidino groups, and morpholino groups; diarylamino groups such as diphenylamino groups and carbazolyl groups; acyl groups such as acetyl groups, propionyl groups, and butyryl groups; alkenyl groups with 2 to 30 carbon atoms, such as styryl groups; halogen atoms such as fluorine atoms, and alkyl groups with 1 to 20 carbon atoms, alkoxy groups A C5-C20 aryl group (specific examples of aryl groups are the same as those for aromatic hydrocarbon groups above) which may be substituted with a C1 group, an amino group, etc.; a C4-C40 heterocyclic group containing one or more C1-C4 nitrogen, sulfur, or oxygen atoms which may be substituted with a halogen atom such as a fluorine atom, or a C1-C20 alkyl group, an alkoxy group, an amino group, etc. (The heterocyclic group may consist of only one ring, or may be a compound in which multiple compounds consisting of only one aromatic heterocyclic ring are directly bonded to each other by a single carbon atom, or may be a fused heterocyclic group. Specific examples of heterocyclic groups are as follows: This includes specific examples of aromatic heterocyclic groups such as thiophene rings, furan rings, pyrrole rings, benzothiophene rings, benzofuran rings, indole rings, dibenzothiophene rings, dibenzofuran rings, carbazole rings, thiazole rings, benzothiazole rings, oxazole rings, benzoxazole rings, imidazole rings, benzimidazole rings, pyridine rings, pyrimidine rings, pyrazine rings, pyridazine rings, triazine rings, quinoline rings, isoquinoline rings, quinoxaline rings, benzothiadiazole rings, and phenanthridine rings. Examples include ester groups and thioether groups.These groups may also be substituted with halogen atoms, heteroatoms, alkyl groups, aromatic rings, etc.

[0067] n in the general formula (1) above 1 This is an integer from 1 to 4, but is preferably 2 or 3.

[0068] The compound represented by the above general formula (1) can be synthesized using a halogen compound containing iodine, bromine, chlorine, and fluorine, and hexahydropyrimidopyrimidine as starting materials, by a Ullmann coupling reaction, a Buchwald-Hartwig amination reaction, or a nucleophilic substitution reaction, etc.

[0069] X in the above general formula (2) 1 , X 2 This represents a nitrogen atom, oxygen atom, sulfur atom, or divalent linking group, which may have substituents, and are identical or different. Examples of divalent linking groups include divalent hydrocarbon groups and groups in which some of the carbon atoms of a hydrocarbon group are replaced by heteroatoms of nitrogen, oxygen, or sulfur. The hydrocarbon group is preferably one having 1 to 6 carbon atoms, and more preferably one having 1, 2, or 6 carbon atoms. The hydrocarbon group may be linear, branched, cyclic, or a combination of these. The divalent hydrocarbon group may be an alkylene group, which is a saturated hydrocarbon group, or an unsaturated hydrocarbon group such as an alkenylene group or an alkylylene group.

[0070] In the general formula (2) above, L represents either a direct bond or a p-valent linking group. Note that L is a direct bond only when p is 2. Examples of p-valent linking groups include nitrogen atoms, oxygen atoms, sulfur atoms, and carbon atoms, as well as groups formed by removing p hydrogen atoms from hydrocarbon groups or groups in which some of the carbon atoms of a hydrocarbon group are replaced by heteroatoms of nitrogen, oxygen, or sulfur atoms. When the p-valent linking group has a carbon atom, it is preferable that it has 1 to 30 carbon atoms. More preferably, it has 1 to 20 carbon atoms. The hydrocarbon group may be linear, branched, cyclic, or a combination of these. The hydrocarbon group may be a saturated hydrocarbon group, an unsaturated hydrocarbon group, or an aromatic hydrocarbon group. Aromatic hydrocarbon groups include those formed by removing hydrogen atoms from aromatic compounds such as benzene rings, naphthalene rings, anthracene rings, tetracene rings, pentacene rings, triphenylene rings, pyrene rings, fluorene rings, and indene rings.

[0071] In the above general formula (2), R 2 ~R 4 represents a monovalent substituent that is identical or different. Also, m 1 ~m 3 These represent numbers from 0 to 3, which are either the same or different. Monovalent substituents include fluorine atoms; haloalkyl groups such as fluoromethyl, difluoromethyl, and trifluoromethyl groups; linear or branched alkyl groups with 1 to 20 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl groups; cyclic alkyl groups with 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, and cycloheptyl groups; methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, and heptyloxy groups. Linear or branched alkoxy groups with 1 to 20 carbon atoms, such as oxy groups and octyloxy groups; nitro groups; cyano groups; alkylamino groups with alkyl groups with 1 to 10 carbon atoms, such as methylamino groups, ethylamino groups, dimethylamino groups, and diethylamino groups; cyclic amino groups such as pyrrolidino groups, piperidino groups, and morpholino groups; diarylamino groups such as diphenylamino groups and carbazolyl groups; acyl groups such as acetyl groups, propionyl groups, and butyryl groups; alkenyl groups with 2 to 30 carbon atoms, such as styryl groups; halogen atoms such as fluorine atoms, and alkyl groups with 1 to 20 carbon atoms, alkoxy groups A C5-C20 aryl group (specific examples of aryl groups are the same as those for aromatic hydrocarbon groups above) which may be substituted with a C1 group, an amino group, etc.; a C4-C40 heterocyclic group containing one or more C1-C4 nitrogen, sulfur, or oxygen atoms which may be substituted with a halogen atom such as a fluorine atom, or a C1-C20 alkyl group, an alkoxy group, an amino group, etc. (The heterocyclic group may consist of only one ring, or may be a compound in which multiple compounds consisting of only one aromatic heterocyclic ring are directly bonded to each other by a single carbon atom, or may be a fused heterocyclic group. Specific examples of heterocyclic groups are as follows: This includes specific examples of aromatic heterocyclic groups such as thiophene rings, furan rings, pyrrole rings, benzothiophene rings, benzofuran rings, indole rings, dibenzothiophene rings, dibenzofuran rings, carbazole rings, thiazole rings, benzothiazole rings, oxazole rings, benzoxazole rings, imidazole rings, benzimidazole rings, pyridine rings, pyrimidine rings, pyrazine rings, pyridazine rings, triazine rings, quinoline rings, isoquinoline rings, quinoxaline rings, benzothiadiazole rings, and phenanthridine rings. Examples include ester groups and thioether groups.These groups may also be substituted with halogen atoms, heteroatoms, alkyl groups, aromatic rings, etc.

[0072] In the general formula (2) above, p represents a number from 1 to 4, but it is preferable that it be a number from 1 to 3. Furthermore, n in the general formula (2) above 2 This represents a number that is either 0 or 1, but it is preferably 0.

[0073] The average thickness of the electron injection layer 8 can range from 1 nm to several μm, but is preferably 1 to 1000 nm, and more preferably 2 to 100 nm, in order to create an organic EL element that can be driven at a low voltage. The average thickness of the electron injection layer 8 can be measured by a stylus step meter or spectroscopic ellipsometry.

[0074] (Formation method) The organic EL element 1 shown in Figure 1 can be manufactured by forming an anode 3, a hole injection layer 4, a hole transport layer 5, an emissive layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 on a substrate 2 in this order. The method for forming each layer, anode 3, hole injection layer 4, hole transport layer 5, emissive layer 6, electron transport layer 7, electron injection layer 8, and cathode 9, is not particularly limited, and various conventionally known formation methods can be used as appropriate according to the characteristics of the material used for each layer. Methods for forming each layer include chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, and laser CVD, which are vapor phase deposition methods; dry plating methods such as vacuum deposition, sputtering, and ion plating; thermal spraying; and wet plating methods such as electrolytic plating, immersion plating, and electroless plating, which are liquid phase deposition methods; and printing technologies such as sol-gel method, MOD method, spray pyrolysis method, doctor blade method using fine particle dispersion, spin coating method, inkjet method, and screen printing method. These methods should preferably be selected according to the characteristics of the material of each layer, and the manufacturing method may differ for each layer.

[0075] The organic EL element 1 of this embodiment can change the emission color by appropriately selecting the material of the light-emitting layer 6, and a desired emission color can also be obtained by using a color filter or the like in combination. For this reason, the organic EL element of the present invention can be suitably used in display devices and lighting devices.

[0076] (Other examples) The organic EL element of the present invention is not limited to the organic EL element described in the above-described embodiment. Specifically, in the embodiments described above, an organic EL element 1 with a forward structure in which an anode 3 is placed between the substrate 2 and the light-emitting layer 6 was used as an example. However, the organic EL element of the present invention may also have an inverse structure in which a cathode is placed between the substrate and the light-emitting layer.

[0077] Furthermore, in the organic EL element of the present invention, the hole transport layer, electron transport layer, and electron injection layer may be formed as needed, or they may not be provided. Furthermore, each of the layers—anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode—may be formed as a single layer or as two or more layers. Furthermore, the organic EL element of the present invention may have other layers between the anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode. Specifically, an electron blocking layer or the like may be included as needed to further improve the characteristics of the organic EL element.

[0078] <Display device> The display device of the present invention is characterized by comprising the above-described organic electroluminescent element. Because the display device of the present invention comprises the above-described organic EL element with low driving voltage and excellent driving stability, it has a low driving voltage and excellent driving stability. In addition to the above-described organic electroluminescent element, the display device of the present invention may also comprise other components commonly used in display devices.

[0079] <Lighting equipment> The lighting device of the present invention is characterized by comprising the above-described organic electroluminescent element. Because the lighting device of the present invention comprises the above-described organic EL element with low driving voltage and excellent driving stability, it has a low driving voltage and excellent driving stability. In addition to the above-described organic electroluminescent element, the lighting device of the present invention may also comprise other components commonly used in lighting devices.

[0080] <Organic thin-film solar cells, organic thin-film transistors> The present invention is not limited to the embodiments described above, and the organic thin film of the present invention can be used in devices such as organic thin-film solar cells and organic thin-film transistors.

[0081] The organic thin-film solar cell of the present invention includes an organic thin film. For example, when an organic thin film is used as the hole injection layer of an organic thin-film solar cell, holes are easily injected, resulting in a faster hole transport rate and high power generation efficiency. Therefore, it is preferable as an organic thin-film solar cell or photoelectric conversion element.

[0082] Furthermore, the organic thin-film transistor of the present invention includes an organic thin film. For example, by providing the above-mentioned organic thin film on an electrode, it is possible to improve mobility. [Examples]

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0084] To demonstrate the effectiveness of the present invention, an organic EL element was selected as the organic device. By driving multiple organic EL elements, each dependent on a hole injection layer, with a constant current and measuring the change in brightness, it is possible to evaluate the stability of the hole injection layer. The examples and comparative examples shown here relate to organic EL elements, but the organic thin film of the present invention can also be used in organic thin-film solar cells and organic thin-film transistors using organic materials.

[0085] The layer configuration of the fabricated organic EL element 1 is as shown in Figure 1, and consists of 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. The characteristics of the organic EL element dependent on the hole injection layer 4 were evaluated.

[0086] <Materials used in hole transport layer 5, light-emitting layer 6, electron transport layer 7, and electron injection layer 8> In this embodiment, an excitation complex consisting of a donor material and another material is used as the host for the light-emitting layer 6. Furthermore, this donor material is used for the hole transport layer 5, and the other material is used for the electron transport layer 7. Specifically, Ir(mppy)3 was used as the luminescent material, DIC-TRZ was used as the other material for excitation complex formation (electron transport layer 7), and Py-hpp2 was used as the electron injection layer 8.

[0087] Here, the transfer of electrons from the donor material (the material used in the hole transport layer 5) to the hole injection layer 4 significantly affects the hole injection characteristics. Therefore, the selection of the donor material is important when discussing the hole injection layer 4. It has been previously reported that efficient hole injection is possible between N,N'-diphenyl-N,N'-bis(1-naphthalenyl)-1,1'-biphenyl-4,4'-diamine (α-NPD), a common donor material with an ionization potential (IP) of about 5.4 eV, and HAT-CN, a widely used hole injection layer material (Yong-Ki Kim, Applied. Physics. Letters. 94, 2009, p063305). In this embodiment, in order to discuss the device application of materials with high electron affinity (EA), tris(4-carbazolyl-9-ylphenyl)amine (TcTa), which has an ionization potential (IP) of approximately 5.7 eV, was selected as a donor material that cannot efficiently inject holes from HAT-CN. As shown in Figure 3, since there is no energy barrier within the organic EL element 1 of this embodiment, the influence of the hole injection layer 4 on the characteristics of the organic EL element 1 can be accurately investigated.

[0088] Furthermore, in this embodiment, organic EL elements were fabricated in two forms: one in which organic acceptor materials are stacked and used as the hole injection layer 4, as shown in Figure 2A, and another in which a layer of a mixture of organic acceptor material and donor material is stacked on a single film of organic acceptor material and used as the hole injection layer 4, as shown in Figure 2B.

[0089] <Regarding the organic acceptor material used in hole injection layer 4> In this embodiment, three types of cyano-containing compounds, HAT-CN, TNAP, and F6TCNNQ, were mainly used as organic acceptor materials for the hole injection layer 4. In addition, F16CuPc was used as an organic acceptor material other than cyano compounds. The structure of the material used in hole injection layer 4 is shown below. [ka]

[0090] The magnitude of the electron affinity (EA) of organic acceptor materials is highly dependent on the charge state of the organic acceptor material, and it has recently been reported that the electron affinity decreases when the material is negatively charged (David Kiefer, Nature Materials, 18, 2019, pp. 149-155). Therefore, we investigated the correlation of the electron affinity (EA) of three materials, HAT-CN, TNAP, and F6TCNNQ, using molecular orbital calculations [density functional theory, B3LYP, basis set: 6-31G(d)]. The results are shown in Table 1.

[0091] [Table 1]

[0092] As shown in Table 1, the electron affinity (EA) differs depending on the material. Among these three materials, HAT-CN had the lowest electron affinity (EA), while F6TCNNQ had the highest.

[0093] Furthermore, Figure 4 shows the results of measuring the electron affinity of each material using low-energy inverse photoemission spectroscopy (LEIPS).

[0094] Figure 4A shows that when HAT-CN is deposited on ITO at a thickness of 1 nm, the electron affinity (EA) is approximately 3.8 eV, but by increasing the thickness of HAT-CN to 5 nm, the electron affinity (EA) increases to 4.3 eV. Furthermore, Figure 4B shows that for TNAP, the electron affinity (EA) is 3.8 eV when a 1 nm thick film is deposited on ITO, and 4.7 eV when the thickness is 5 nm. It also shows that the electron affinity (EA) is 4.7 eV when a 5 nm thick HAT-CN film is deposited on ITO, and then a 1 nm thick TNAP film is deposited on top of it. Furthermore, Figure 4C shows that for F6TCNNQ, when a 1nm film is deposited on ITO, the electron affinity (EA) is 4.2eV, and when a 5nm HAT-CN film is deposited on ITO and then a 1nm F6TCNNQ film is deposited on top of it, the electron affinity (EA) is 5.0eV.

[0095] The results described above are schematically shown in Figure 5. When an ultrathin film is formed on a substrate in this way, the organic acceptor material becomes negatively charged due to charge transfer from the substrate, resulting in a small electron affinity (EA), while the electron affinity (EA) of the organic acceptor material located away from the substrate is large. Furthermore, it was found that there is a strong correlation between the measured electron affinity (EA) of the neutral state measured by LEIPS and the electron affinity (EA) estimated by molecular orbital calculations.Therefore, although organic EL elements were fabricated using four types of materials in this embodiment, materials with large electron affinity (EA) determined by molecular orbital calculations, such as CN6-CP (EA calculated value: 5.4eV, Jing Li, Material Horizons, 6, 2019, p107-114) and TECTFCNBN (EA calculated value: 5.3eV, Zhenhua Ci, Organic Electronics 95, 2021, p106197), are also considered suitable for the present invention. [ka]

[0096] <Examples 1-8 and Comparative Examples 1-9> A commercially available transparent glass substrate (anode 3) made of ITO with a thickness of 100 nm was prepared as substrate 2. On the anode 3 of substrate 2, a hole injection layer 4 (first layer 4-1, second layer 4-2), a hole transport layer 5, an emissive layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 were sequentially laminated.

[0097] The configuration of the hole injection layer 4 (first layer 4-1, second layer 4-2) and the hole transport layer 5 is as shown in Table 2.

[0098] Also, as a common layer, On the hole transport layer 5, Ir(mppy)3, TcTa, and DIC-TRZ are co-deposited as an emissive layer 6 [Ir(mppy)3:TcTa:DIC-TRZ (mass ratio) = 0.05:0.475:0.475, thickness 30 nm]. As the electron transport layer 7, DIC-TRZ was deposited (thickness 40 nm), As the electron injection layer 8, Py-hpp2 and DIC-TRZ were co-deposited [Py-hpp2:DIC-TRZ (mass ratio) = 0.4:0.6, thickness 5 nm]. For cathode 9, Al (100 nm thick) was layered and sealed using glass and UV-curing resin.

[0099] The structures of the materials used in the hole transport layer 5, light-emitting layer 6, electron transport layer 7, and electron injection layer 8 are shown below. [ka]

[0100] The above Py-hpp2 was synthesized according to the method described in T. Sasaki, M. Hasegawa, K. Inagaki, H. Ito, K. Suzuki, T. Oono, K. Morii, T. Shimizu and H. Fukagawa, Nature Communications, 12, pp. 2706.1, DOI: 10.1038 / s41467-021-23067-2.

[0101] For the organic EL elements of Examples 1-8 and Comparative Examples 1-9 obtained in this manner, a voltage was applied using a Keithley "2400 type source meter," and the brightness was measured using a Konica Minolta "LS-100." The relationship between applied voltage and brightness, as well as the relationship between applied voltage and current density, were investigated. Figures 6-8 show the current density-voltage characteristics of multiple organic EL elements that depend on the hole injection layer. Table 2 shows the configurations of the hole injection layer 4 and hole transport layer 5 in Examples 1-8 and Comparative Examples 1-9, as well as the characteristics of the organic EL element 1 fabricated using them. From the results shown in the figures and tables, it can be seen that the way the current flows depends greatly on the hole injection layer 4.

[0102] [Table 2]

[0103] Focusing on the results of Comparative Examples 1, 2, and 3, it can be seen that even with hole injection layers of the same thickness, the hole injection performance in organic EL devices largely depends on the electron affinity (EA) of the material. When compared at the same applied voltage, the current density values ​​increased in the order of HAT-CN, TNAP, and F6TCNNQ, indicating that the greater the electron affinity (EA) of the organic acceptor material used in the hole injection layer, the easier it is to extract electrons from the donor material TcTa.

[0104] Next, we focus on the driving stability of Comparative Examples 1, 2, and 3. The driving stability of the organic EL element using Ir(mppy)3 as the light-emitting material is as follows: Initial brightness 10,000 cd / m² 2 It has been reported that a brightness half-life of approximately 300 hours can be obtained when continuously driven (Tsubasa Sasaki, Nature Communications, 12, 2021, p2706). However, the brightness half-life of the organic EL elements in Comparative Examples 1, 2, and 3 was less than 100 hours, indicating poor driving stability.

[0105] Next, we focus on the results of Example 1, in which a hole injection layer was formed by stacking HAT-CN 5nm and F6TCNNQ 1nm. Compared to Comparative Example 3, which also used F6TCNNQ 1nm, the insertion of HAT-CN 5nm resulted in a higher current density, confirming improved hole injection performance. Furthermore, a brightness half-life, an indicator of driving stability, was achieved at 550 hours, demonstrating a dramatic increase of more than five times in lifespan due to the insertion of HAT-CN 5nm.

[0106] Furthermore, in Example 3, where a hole injection layer was formed by stacking HAT-CN 5nm and TNAP 1nm, the same results as in Example 1 were obtained. Compared to Comparative Example 2, which also used TNAP 1nm, the insertion of HAT-CN 5nm resulted in a higher current density, confirming improved hole injection performance. Moreover, the brightness half-life, an indicator of driving stability, was dramatically extended by approximately 10 times with the insertion of HAT-CN 5nm.

[0107] Thus, it was found that by forming a hole injection layer on HAT-CN, an organic acceptor material with a relatively low electron affinity (EA), by depositing an organic acceptor material with a high electron affinity (EA), a hole injection layer with excellent hole injection performance and driving stability can be formed.

[0108] This paper explains why a hole injection layer using multiple organic acceptor materials like this leads to the formation of a hole injection layer with excellent hole injection performance and driving stability. Organic acceptor materials can pull electrons from adjacent molecules and atoms, and the greater the electron affinity (EA), the easier it is to pull electrons. Therefore, among the three materials used in this study, F6TCNNQ and TNAP were more likely to pull electrons than HAT-CN. When these organic acceptor materials were deposited on a substrate, the amount of electron transfer from the substrate to the organic acceptor material was greater for F6TCNNQ and TNAP than for HAT-CN, suggesting that F6TCNNQ and TNAP are more negatively charged than HAT-CN. Furthermore, this strongly negatively charged state is not a stable state, and in the organic EL devices of Comparative Examples 2 and 3, even if holes were injected relatively well, the driving stability may be poor.

[0109] In contrast, in Examples 1 and 3, in which HAT-CN was inserted, F6TCNNQ and TNAP were less susceptible to electron transfer from the substrate and could exist in a neutral state without becoming negatively charged. Therefore, they were able to come into contact with the donor material with a high electron affinity (EA), and thus could be driven at a low voltage. Furthermore, a negatively charged state on ITO is considered unstable, and it is thought that by existing neutrally on HAT-CN, organic EL elements with excellent driving stability were realized.

[0110] Furthermore, since the characteristics and lifespan of the organic EL element in Comparative Example 7 are significantly worse than those of Example 1, it is clear that the order in which the organic acceptor material with low electron affinity is stacked on the anode and the material with high electron affinity is stacked on top of the organic acceptor material with low electron affinity is important.

[0111] Furthermore, although the driving voltage of the organic EL element in Example 4, in which F16CuPc was inserted between ITO and F6TCNNQ, was higher than that of Comparative Example 3, the organic EL element in Example 4 exhibited superior driving stability, yielding results that support this assumption regarding driving stability.

[0112] Next, we will discuss the characteristics of an organic EL element having a hole injection layer 4 as shown in Figure 2B, which is another embodiment of the present invention. Compared to the organic EL element of Comparative Example 8, which has a hole injection layer 4 doped with F6TCNNQ in TcTa, the organic EL element of Example 5, which has HAT-CN inserted between the hole injection layer 4 and the anode 3, showed better performance in both drive voltage and lifespan. Furthermore, compared to the organic EL element of Comparative Example 9, which has a hole injection layer 4 doped with TANP in TcTa, the organic EL element of Example 7, which has HAT-CN inserted between the hole injection layer 4 and the anode 3, showed better performance in both drive voltage and lifespan. Therefore, even when using a hole injection layer 4 in which an organic acceptor material is doped into a donor material, it was found that stacking an organic acceptor material with low electron affinity on the anode 3 and a layer containing a material with high electron affinity on top of the organic acceptor material with low electron affinity is effective in reducing the drive voltage and extending the lifespan. In this case, forming a system in which an organic acceptor material with low electron affinity (HAT-CN) is doped into another organic material on the anode 3 can also be said to be one embodiment of the present invention.

[0113] <Investigation of organic acceptor materials with relatively low electron affinity for use in the first layer> Various organic acceptor materials with relatively low electron affinity to be used in the first layer were investigated (BCF3Ph-F8-Ant, BSBF, FP-ly-POA). The structures of BCF3Ph-F8-Ant (1,2,3,4,5,6,7,8-octafluoro-9,10-bis[4-(trifluoromethyl)phenyl]anthracene), BSBF (2-(9,9'-spirobifluorene-2-yl)-9,9'-spirobifluorene), and FP-ly-POA (4-fluorobenzylphosphonic acid) are shown below. [ka]

[0114] Figure 9 shows the correlation between measured and calculated electron affinity values ​​for several organic materials (a1-a7, b1-b4). From the data shown in Figure 9, the following equation can be derived: Measured electron affinity = 0.92 × Calculated electron affinity + 0.52 The following relationship can be obtained. Based on this formula, the electron affinity was estimated from the calculated electron affinity values ​​for BCF3Ph-F8-Ant, BSBF, and FP-ly-POA. Table 3 shows the electron affinity of each material.

[0115] [Table 3]

[0116] <Examples 9-11> Organic EL devices of Examples 9 to 11 were fabricated in the same manner as in Examples 1 to 8, using BCF3Ph-F8-Ant and BSBF as the first layer.

[0117] Furthermore, for 4-fluorobenzylphosphonic acid (FP-ly-POA), a material constituting the self-assembled monolayer, a 0.012% by mass ethanol solution was prepared. This ethanol solution was dispensed onto a substrate and spin-coated at 3500 rpm for 45 seconds, followed by heating at 105°C for 30 minutes under a nitrogen atmosphere. Subsequently, the substrate was washed with ethanol and then re-dried at 80°C for 30 minutes under a nitrogen atmosphere to produce a self-assembled monolayer of FP-ly-POA. An organic EL device was then fabricated in the same manner as in Examples 1 to 8, except that F6TCNNQ was deposited on top of the monolayer to form a hole injection layer.

[0118] For the organic EL elements obtained in Examples 9 to 11 in this manner, the relationship between applied voltage and brightness, and furthermore, the relationship between applied voltage and current density, were investigated in the same manner as in Examples 1 to 8. The obtained characteristics are summarized in Table 4. For comparison, the results of Comparative Example 3 are also included in Table 4.

[0119] [Table 4]

[0120] As shown in Table 4, by inserting the material used in the first layer between ITO and F6TCNNQ, the organic EL elements of Examples 9-11 were able to be driven at a lower voltage compared to Comparative Example 3. Furthermore, higher driving stability was confirmed for almost all organic EL elements compared to Comparative Example 3.

[0121] Since BCF3Ph-F8-Ant is a fluorine-containing compound, BSBF is an aromatic hydrocarbon, and FP-ly-POA is a phosphonic acid and a material that constitutes a self-assembled monolayer, we were able to demonstrate that these materials are suitable for the first layer. [Industrial applicability]

[0122] The organic thin film of the present invention can be used in organic EL elements, display devices, lighting devices, organic thin-film solar cells, and organic thin-film transistors, etc. [Explanation of Symbols]

[0123] 1: Organic EL element 2: Circuit board 3:Anode 4: Hole injection layer (organic thin film) 4-1: The first layer 4-2: The second layer 5: Hole transport layer 6: Emitting layer 7:Electron transport layer 8:Electron injection layer 9: Cathode

Claims

1. An organic electroluminescent element comprising a cathode, a light-emitting layer, and an anode in this order, Between the anode and the light-emitting layer, there is an organic thin film, the organic thin film being a hole-injection organic thin film containing two or more organic acceptor materials with different electron affinities, The aforementioned organic thin film is A first layer containing an organic acceptor material with relatively low electron affinity, The present invention comprises a second layer, which is laminated adjacent to the first layer and contains an organic acceptor material having a relatively high electron affinity, The organic acceptor material with relatively low electron affinity has an electron affinity of 2.52 eV or more and less than 4.5 eV, and the organic acceptor material with relatively high electron affinity has an electron affinity of 4.5 eV or more and 5.4 eV or less. The first layer of the organic thin film is disposed adjacent to the anode, An organic electroluminescent element characterized by comprising the anode, the first layer of the organic thin film, and the second layer of the organic thin film in this order.

2. The organic electroluminescent element according to claim 1, wherein the second layer of the organic thin film is a film obtained by mixing an organic acceptor material having a relatively high electron affinity with another organic material.

3. The organic electroluminescent element according to claim 1, wherein the organic acceptor material is a cyano compound or a fluorine compound.

4. The organic electroluminescent element according to claim 1, wherein the organic acceptor material is a compound containing a 2-methylenepropanedinitrile group.

5. The organic electroluminescent element according to claim 1, wherein the organic acceptor material with relatively low electron affinity is one of a fluorine-containing compound, an aromatic hydrocarbon, a phosphonic acid, or a material constituting a self-assembled monolayer.

6. The organic electroluminescent element according to claim 1, wherein the organic acceptor material is selected from the group consisting of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), tetracyanonaphthoquinodimethane (TNAP), and hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ).

7. The organic acceptor material with relatively low electron affinity contained in the first layer is 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), The organic electroluminescent element according to claim 1, wherein the organic acceptor material with relatively high electron affinity contained in the second layer is selected from the group consisting of tetracyanonaphthoquinodimethane (TNAP) and hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ).

8. The organic electroluminescent element according to claim 1, wherein the average thickness of the organic thin film is 2 to 100 nm.

9. A display device comprising an organic electroluminescent element according to any one of claims 1 to 8.

10. A lighting device characterized by comprising an organic electroluminescent element according to any one of claims 1 to 8.

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