Organic electroluminescent element, display device, and illumination device

Abstract

The present invention addresses the problem of providing an organic electroluminescent element (1) which can emit light at a low applied voltage while using an excitation complex formed between a donor material and an acceptor material, and which has excellent driving stability. The present invention is provided with a positive electrode (3), a hole transport layer (5), a light-emitting layer (6), and a negative electrode (8) in this order, the hole transport layer (5) containing a first organic compound which is a donor material having a small ionization potential, and the light-emitting layer (6) containing a second organic compound which is an acceptor material having a large electron affinity. An excitation complex is formed between the first organic compound and the second organic compound, and the first organic compound is a thermally activated delayed fluorescent material.

Description

Technical Field

[0001] This invention relates to organic electroluminescent (hereinafter, electroluminescent (field luminescence) is sometimes referred to as "EL") elements, display devices, and lighting devices. Background Technology

[0002] In recent years, efforts have been actively made to enable organic electroluminescent elements to emit light at low applied voltages. For example, reports have included using rubrene, a tetraphenylbenzene derivative, as a donor and fullerene, a fullerene with high electron affinity, as an acceptor, to extract the energy of the exciplex formed at its interface through triplet-triplet annihilation in the organic electroluminescent element as the emission of light in the singlet excited state of rubrene (see, for example, Non-Patent Literature 1 and 2).

[0003] In addition, as compounds capable of utilizing triplet-triplet annihilation, anthracene derivatives, tetraphenyl derivatives, and other compounds have excellent electronic properties and exhibit high luminescence quantum yields, and are therefore used as luminescent materials for organic electroluminescent elements that emit light at low driving voltages (see, for example, Non-Patent Literature 1-5).

[0004] In this low-voltage organic electroluminescent element, the charge recombination region and the luminescent region are concentrated at the interface between the donor material and the acceptor material. Generally, it has been reported that if the charge recombination region and the luminescent region are concentrated at the interface, the lifetime of the organic electroluminescent element is shortened. Although luminescence at low voltage can be obtained by utilizing the excitation complex formed at the interface between the donor material and the acceptor material, the prospect of long lifetime for practical application has not been achieved (see, for example, Non-Patent Literature 6).

[0005] Existing technical documents

[0006] Non-patent literature

[0007] Non-patent literature 1: Sebastian Engmann, et al., 5, "Nature Communications", Vol. 10, 2019, p. 227, doi.org / 10.1038 / s41467-018-08075-z

[0008] Non-patent literature 2: Seiichiro Izawa, et al., DOI: 10.26434 / chemrxiv.14685417.v1

[0009] Non-Patent Literature 3: Xiangyang Tang, Qing Bai, Tong Shan, Jinyu Li, Yu Gao, Futong Liu, Hui Liu, Qiming Peng, Bing Yang, Feng Li, and Ping Lu, Advanced Functional Materials, 28: 1705813, DOI: 10.1002 / adfm.201705813

[0010] Non-patent literature 4: Futong Liu, et al., 8, "Journal of Materials Chemistry C", Vol. 7, 2019, p14881, DOI: 10.1039 / c9tc05040j

[0011] Non-patent literature 5: Youn Jue Bae, et al., 9, "Journal of the American Chemicals Society", 2018, Vol. 140, p. 15140, DOI: 10.1021 / jacs.8b07498

[0012] Non-patent literature 6: Yifan Zhang, et al., "Nature Communications", Vol. 5, 2014, p. 5008, doi.org / 10.1038 / ncomms6008 Summary of the Invention

[0013] As described above, in Non-Patent Documents 1 and 2, fluorene, as a tetraphenylene derivative, was used as a donor material, resulting in luminescence at a low applied voltage. However, the charge recombination region and luminescence region are concentrated at the interface, thus leaving room for improvement in device lifetime. To extend the lifetime of the device, a thorough re-evaluation of the material composition used in the donor and acceptor is required.

[0014] The present invention was made in view of the above circumstances, and its object is to provide an organic electroluminescent element that can emit light at a low applied voltage and has excellent driving stability while utilizing an excitation complex formed between a donor material and an acceptor material.

[0015] Furthermore, a further objective of the present invention is to provide a display device and a lighting device having the above-described organic electroluminescent element, low driving voltage, and excellent driving stability.

[0016] The inventors conducted various studies on combinations of donor and acceptor materials, and as a result, they realized that by using a material exhibiting thermally activated delayed fluorescence as a donor material, the above-mentioned problems could be solved excellently, thus realizing the present invention.

[0017] That is, the main structure of the organic electroluminescent element, display device, and lighting device of the present invention, which solves the above-mentioned problems, is as follows.

[0018] [1] An organic electroluminescent element, characterized in that it comprises, in sequence, an anode, a hole transport layer, a light-emitting layer, and a cathode.

[0019] The aforementioned hole transport layer contains a donor material with a low ionization potential, namely the first organic compound.

[0020] The aforementioned light-emitting layer contains an acceptor material with high electron affinity, namely a second organic compound.

[0021] An excited complex is formed between the first organic compound and the second organic compound.

[0022] The first organic compound mentioned above is a thermally activated delayed fluorescence material.

[0023] [2] According to the organic electroluminescent element of [1], wherein the calculated value of the ionization potential (IP) of the first organic compound is 4.8 eV or less, or the measured value of the ionization potential (IP) obtained by ultraviolet photoelectron spectroscopy is 5.5 eV or less.

[0024] [3] The organic electroluminescent element according to [1] or [2], wherein the calculated value of the electron affinity (EA) of the second organic compound is 2.1 eV or more, calculated by density functional method, or the measured value of the electron affinity (EA) obtained by low-energy back-photoelectron spectroscopy is 2.8 eV or more.

[0025] [4] An organic electroluminescent element according to any one of [1] to [3], wherein the first organic compound has a dimethylacridine skeleton represented by the following formula (1-1) and a phenanthrene skeleton represented by the following formula (1-2). The aziridine skeleton or the carbazole skeleton represented by the following formulas (1-3).

[0026]

[0027] [In equations (1-1), (1-2), and (1-3), X represents the bonding site with other atoms.]

[0028] [5] An organic electroluminescent element according to any one of [1] to [4], wherein the light-emitting layer further comprises a phosphorescent material.

[0029] [6] An organic electroluminescent element according to any one of [1] to [4], wherein the light-emitting layer further comprises a fluorescent light-emitting material.

[0030] [7] An organic electroluminescent element according to any one of [1] to [4], wherein the light-emitting layer further comprises a thermally activated delayed fluorescence material.

[0031] [8] A display device, characterized in that it comprises an organic electroluminescent element as described in any one of [1] to [7].

[0032] [9] A lighting device, characterized in that it comprises an organic electroluminescent element as described in any one of [1] to [7].

[0033] According to the present invention, an organic electroluminescent element that can emit light at a low applied voltage and has excellent driving stability can be provided while utilizing an excitation complex formed between a donor material and an acceptor material.

[0034] In addition, according to the present invention, a display device and a lighting device with low driving voltage and excellent driving stability can be provided. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating an example of the structure of the organic EL element of the present invention.

[0036] Figure 2 This is a schematic diagram showing the energy levels within an example of the organic EL element of the present invention.

[0037] Figure 3 This is a schematic diagram illustrating, as an example, the luminescence mechanism of an organic EL element utilizing an excitation complex, the efficient utilization of energy transfer from the excitation complex and the singlet excited state of the material from the luminescent layer through triplet-triplet annihilation.

[0038] Figure 4 This is a schematic diagram illustrating an example of the light emission mechanism of the organic EL element of the present invention, showing the efficient use of energy transfer from a triplet excited state to a singlet excited state caused by anti-intersystem crossing in a thermally activated delayed fluorescent material, energy transfer from the singlet excited state of the thermally activated delayed fluorescent material to the material of the emitting layer, energy transfer from the excitation complex, and light emission from the singlet excited state of the material of the emitting layer after triplet-triple annihilation.

[0039] Figure 5 This is a schematic diagram illustrating another example of the structure of the organic EL element of the present invention.

[0040] Figure 6This is a graph showing the decay process of luminescence from 2-SF-PHX under nitrogen atmosphere and atmospheric atmosphere, respectively.

[0041] Figure 7 This is a graph showing the decay process of luminescence from 2Cz-DMAC under nitrogen atmosphere and atmospheric atmosphere, respectively.

[0042] Figure 8 This is a schematic diagram illustrating another example of the light-emitting mechanism of the organic EL element of the present invention, showing the energy transfer from the triplet excited state to the singlet excited state caused by anti-intersystem crossing in the thermally activated delayed fluorescent material, the energy transfer from the singlet excited state of the thermally activated delayed fluorescent material to the material of the light-emitting layer, the energy transfer from the excitation complex, triplet-triplet annihilation, and the energy transfer from the singlet excited state of the light-emitting layer material to the light-emitting dopant, as well as the light emission from the singlet excited state of the light-emitting dopant.

[0043] Figure 9 The graphs represent the results obtained from measuring (a) current density-voltage characteristics, (b) luminance-voltage characteristics, and (c) EL spectra of various organic EL elements manufactured in Examples 1, 2, and 1.

[0044] Figure 10 This indicates that the organic EL elements manufactured in Example 1, Example 2, and Comparative Example 1 were compared from an initial brightness of 100 cd / m². 2 A graph showing the brightness changes during continuous driving.

[0045] Figure 11 The graphs represent the results obtained from measuring (a) current density-voltage characteristics, (b) luminance-voltage characteristics, and (c) EL spectra of various organic EL elements manufactured in Examples 3, 4, and Comparative Example 2.

[0046] Figure 12 This indicates that the organic EL elements manufactured in Examples 3, 4, and Comparative Example 2 were compared from an initial brightness of 100 cd / m². 2 A graph showing the brightness changes during continuous driving. Detailed Implementation

[0047] Hereinafter, the organic electroluminescent element, display device and lighting device of the present invention will be described in detail based on their embodiments.

[0048] It should be noted that combining two or more of the preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0049] Organic electroluminescent devices

[0050] The organic electroluminescent element of the present invention comprises, sequentially, an anode, a hole transport layer, an emissive layer, and a cathode. The hole transport layer contains a donor material with a low ionization potential, namely a first organic compound, and the emissive layer contains an acceptor material with a high electron affinity, namely a second organic compound. Furthermore, the organic electroluminescent element of the present invention is characterized in that an excitation complex is formed between the first organic compound and the second organic compound, wherein the first organic compound is a thermally activated delayed fluorescence material.

[0051] The aforementioned thermally activated delayed fluorescence material is a material that emits thermally activated delayed fluorescence (TADF). This thermally activated delayed fluorescence refers to the fluorescence observed from the singlet excited state, which is generated by thermal excitation from the triplet excited state to the singlet excited state, causing antisystem crossover and delay.

[0052] In addition, the aforementioned donor materials are materials that can donate electrons to neighboring molecules and atoms. The smaller the ionization potential (IP), the easier it is to donate electrons.

[0053] In addition, the aforementioned acceptor materials are materials that can attract electrons from neighboring molecules and atoms. The greater the electron affinity (EA), the easier it is to attract electrons.

[0054] Furthermore, the low ionization potential of the donor material and the high electron affinity of the acceptor material refer to the degree to which an excited complex is formed between the donor material (first organic compound) and the acceptor material (second organic compound), the high electron affinity, and the low energy difference between them.

[0055] In the organic electroluminescent element of the present invention, the energy difference between the ionization potential (IP) of the donor material, i.e., the first organic compound, and the electron affinity (EA) of the acceptor material, i.e., the second organic compound, is small. Therefore, by using the donor material, i.e., the first organic compound, in the hole transport layer and the acceptor material, i.e., the second organic compound, in the light-emitting layer, and placing them adjacent to each other in such a way that an excitation complex is formed between the donor material, i.e., the first organic compound, and the acceptor material, i.e., the second organic compound, luminescence can be obtained at a low applied voltage.

[0056] Furthermore, in the organic electroluminescent element of the present invention, the donor material, namely the first organic compound, is a thermally activated delayed fluorescence material, which has a small energy difference between its singlet excited state and triplet excited state, thus shortening the existence lifetime of the unstable excited state and extending its lifetime.

[0057] Next, one embodiment of the organic electroluminescent element of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is a schematic diagram illustrating an example of the structure of the organic EL element of the present invention. Figure 1The organic EL element 1 shown has a stacked structure on a substrate 2 in which an anode 3, a hole injection layer 4, a hole transport layer 5, a light-emitting layer 6, an electron injection layer 7, and a cathode 8 are formed sequentially.

[0058] In addition, Figure 1 The energy levels within the organic electroluminescent element 1 shown are illustrated in the diagram. Figure 2 In the organic EL element 1, electrons injected into the light-emitting layer 6, which contains a second organic compound and an acceptor material with high electron affinity, form an excitation complex with holes injected into the hole transport layer 5, which contains a first organic compound and a donor material with low ionization potential. This causes current to flow and light to be emitted. The voltage required for light emission is determined by the energy difference between the electron affinity (EA) of the material used in the light-emitting layer 6 and the ionization potential (IP) of the material used in the hole transport layer 5. When the electron affinity of the material used in the light-emitting layer 6 is high and the ionization potential of the material used in the hole transport layer 5 is low, this energy difference decreases, and the externally applied voltage required for light emission is reduced.

[0059] Next, in Figure 3 The diagram illustrates the energy transfer process from the formation of the excited complex to luminescence. Additionally, in... Figure 4 The diagram illustrates the energy transfer process when a thermally activated delayed fluorescent material is used in hole transport layer 5.

[0060] like Figure 3 As shown, a low external voltage required for the formation of the excitation complex means that the energy of the light emitted by the resulting excitation complex is not high. However, if the triplet energy of the material used in the luminescent layer 6 (e.g., anthracene derivatives) associated with the formation of the excitation complex is lower than the energy of the excited state of the excitation complex, the energy of the excitation complex is transferred to the triplet excited state of the material used in the luminescent layer 6. It is well known that anthracene derivatives generate singlet excited states by utilizing triplet-triplet annihilation; therefore, by utilizing this property, it is possible to generate singlet excited states and obtain light emission from these singlet excited states. Here, the light emission from the singlet excited state has a higher energy than the light emitted by the excitation complex.

[0061] However, as Figure 3 As shown, when a general donor material is used in the hole transport layer 5, it is expected that excited states (singlet excited states and triplet excited states) of the hole transport layer 5 material or the light-emitting layer 6 material will be formed as the applied voltage to the device increases. At this time, the triplet excited state of the light-emitting layer 6 material can be obtained in the form of light emission by utilizing triplet-triplet annihilation. Although the triplet excited state of the hole transport layer 5 material is unstable, it still exists as is, becoming a factor in the reduction of luminous efficiency and the degradation of the organic EL element 1.

[0062] In contrast, such as Figure 4As shown, when a thermally activated delayed fluorescence (TEF) material is used in the hole transport layer 5, the energy difference between the singlet and triplet excited states of this TEF material is small. Therefore, the energy of the triplet excited state is transferred to the singlet excited state through antisystem crossing. Furthermore, the singlet excited state transfers energy to the material of the light-emitting layer 6, and light emission is obtained from the light-emitting layer 6. By enabling such an energy transfer process, the lifetime of the triplet excited state of the hole transport layer 5 material generated when a voltage is applied can be shortened, thus achieving a longer lifetime for the organic EL element 1.

[0063] It should be explained that, for example Figure 5 As shown, the organic EL element 1 in this embodiment can also be an organic EL element having a reverse structure of cathode 8 on substrate 2. Figure 5 The organic EL element 1 shown has a stacked structure on a substrate 2 in which a cathode 8, an electron injection layer 7, a light-emitting layer 6, a hole transport layer 5, a hole injection layer 4, and an anode 3 are sequentially formed.

[0064] Alternatively, the organic EL element 1 in this embodiment may also be an organic-inorganic hybrid organic field-emitting light-emitting element (HOILED element) in which an inorganic compound is used to form part of the layer constituting the organic EL element.

[0065] "Substrate"

[0066] Materials used as substrate 2 include resin materials, glass materials, etc.

[0067] Examples of resin materials used in substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polypropylene, cyclic olefin polymers, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, and polyarylate. Using a resin material as the substrate 2 results in an organic EL element 1 with excellent flexibility, and is therefore preferred.

[0068] Examples of glass materials used in substrate 2 include quartz glass and soda glass.

[0069] When the organic EL element 1 is a bottom-emitting element, a transparent substrate is used as the material for the substrate 2.

[0070] When the organic EL element 1 is a top-emitting element, the substrate 2 can be made of either a transparent substrate or an opaque 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.

[0071] The average thickness of the substrate 2 can be determined based on the material of the substrate 2, and is preferably 0.1 to 30 mm, more preferably 0.1 to 10 mm. The average thickness of the substrate 2 can be measured using a digital multimeter or vernier calipers.

[0072] "anode"

[0073] Figure 1 The anode 3 shown is formed directly on the substrate 2, but as... Figure 5 In the case of the organic EL element with the reverse structure shown, it can also be formed on the substrate 2 without direct contact.

[0074] Examples of conductive materials that can be used as the anode 3 include oxides such as ITO (indium tin oxide), IZO (indium zinc oxide), FTO (tin fluoride oxide), In2O3, SnO2, Sb-containing SnO2, and Al-containing ZnO. Among these, ITO, IZO, and FTO are preferred as the anode 3.

[0075] 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.

[0076] The average thickness of anode 3 can be determined using a stylus step meter or a spectrophotometer.

[0077] "hole injection layer"

[0078] The hole injection layer 4 can be made of either inorganic or organic materials. Inorganic materials are more stable than organic materials, and therefore, compared to using organic materials, it is easier to obtain high resistance to oxygen and water.

[0079] As an inorganic material, there are no particular restrictions; for example, one or more metal oxides such as vanadium oxide (V2O5), molybdenum oxide (MoO3), and ruthenium oxide (RuO2) can be used.

[0080] As organic materials, dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarboxynitrile (HAT-CN) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinone dimethyl ether (F4-TCNQ) can be used. Alternatively, polymeric materials such as poly(3,4-ethylenedioxythiophene) (PEDOT) can also be used.

[0081] 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.

[0082] The average thickness of the hole injection layer 4 can be measured during film formation using a crystal oscillator film thickness gauge.

[0083] Hole transport layer

[0084] As described above, the hole transport layer 5 contains a donor material with a low ionization potential, namely a first organic compound, which is a thermally activated delayed fluorescence material. That is, the hole transport layer 5 contains an organic compound with a low ionization potential and exhibits thermally activated delayed fluorescence. It should be noted that the hole transport layer 5 may consist solely of the first organic compound, or it may contain other components.

[0085] As the first organic compound used in hole transport layer 5, it preferably comprises a triarylamine skeleton, a carbazole skeleton, or a phenanthrene skeleton. Materials with highly donor molecular structures such as aziridine skeleton, phenazine skeleton, acridine skeleton, aziridine skeleton, and dicyclohexane skeleton.

[0086] Furthermore, the aforementioned first organic compound preferably has a dimethylacridine skeleton represented by the following formula (1-1) and a phenanthrene skeleton represented by the following formula (1-2). The aziridine skeleton or the carbazole skeleton represented by the following formulas (1-3).

[0087]

[0088] In formulas (1-1), (1-2), and (1-3) above, X represents a bonding site with other atoms, and various substituents can be bonded to the front end of the bonding site. Furthermore, in the dimethylacridine skeleton of formula (1-1) and the phenanthrene skeleton of formula (1-2)... Various substituents can be bonded to the carbazole skeleton of the aziridine skeletal formula (1-3) to replace the hydrogen atoms in these skeletons. Examples of substituents include alkyl groups with 1 to 10 carbon atoms, alkoxy groups with 1 to 10 carbon atoms, alkylthio groups with 1 to 10 carbon atoms, alkylamino groups with 1 to 10 carbon atoms, acyl groups with 2 to 10 carbon atoms, aralkyl groups with 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups with 6 to 40 carbon atoms, and substituted or unsubstituted aromatic six-membered heterocyclic groups with 3 to 40 carbon atoms.

[0089] More specifically, the first organic compound mentioned above is preferably 2-SF-PHX, 2Cz-DMAC, etc.

[0090]

[0091] It should be noted that whether the donor material exhibits thermally activated delayed fluorescence can be determined by observing the decay process of the luminescence under nitrogen and atmospheric atmospheres, respectively.

[0092] As an example, the method for confirming whether the above-mentioned 2-SF-PHX and 2Cz-DMAC exhibit thermally activated delayed fluorescence and the results are shown.

[0093] First, a 100 nm film of 2-SF-PHX and 2Cz-DMAC was deposited on a quartz substrate by vacuum evaporation. The decay process of luminescence was observed using a streak camera from Hamamatsu Photonics KK. The results are presented below. Figure 6 and Figure 7 .

[0094] For any given material, delayed fluorescence was observed in measurements taken under a nitrogen atmosphere, while the delayed fluorescence was significantly weaker in measurements taken under an atmospheric atmosphere. This indicates that the delayed fluorescence disappears due to oxygen in the atmosphere. Based on these results, it can be confirmed that 2-SF-PHX and 2Cz-DMAC exhibit thermally activated delayed fluorescence.

[0095] The first organic compound contained in the hole transport layer 5 preferably has an ionization potential (IP) of 4.8 eV or less calculated using density functional theory [B3LPY / 6-31G (d,p)], or a measured ionization potential (IP) of 5.5 eV or less obtained by ultraviolet photoelectron spectroscopy (UPS). More preferably, the calculated ionization potential (IP) of 4.72 eV or less calculated using density functional theory, or a measured ionization potential (IP) of 5.4 eV or less obtained by ultraviolet photoelectron spectroscopy. If the ionization potential (IP) of the first organic compound contained in the hole transport layer 5 is 4.8 eV or less calculated using density functional theory, or 5.5 eV or less obtained by ultraviolet photoelectron spectroscopy, the energy difference with the electron affinity (EA) of the acceptor material, i.e., the second organic compound, described later, becomes even smaller, thus enabling luminescence at even lower applied voltages.

[0096] Table 1 shows the calculated and measured values ​​of the ionization potential (IP) of 2-SF-PHX and 2Cz-DMAC using density functional theory and ultraviolet photoelectron spectroscopy (UPS). Additionally, for reference, the calculated and measured values ​​of the ionization potential (also known as "ionization energy") of α-NPD and TPDI are also shown.

[0097]

[0098] [Table 1]

[0099]

[0100] 2-SF-PHX and 2Cz-DMAC exhibit thermally activated delayed fluorescence while having a low ionization potential similar to that of N,N'-di-1-naphthyl-N,N'-diphenylbenzidine (α-NPD), which is a general hole transport material. Therefore, long-term stable luminescence at low applied voltages can be expected.

[0101] The average thickness of the hole transport layer 5 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm.

[0102] The average thickness of the hole transport layer 5 can be determined, for example, by a stylus step meter or a spectrophotometer.

[0103] "Emitting layer"

[0104] As described above, the luminescent layer 6 contains a second organic compound, which is an acceptor material with high electron affinity and is capable of forming an excited complex with the first organic compound. It should be noted that the luminescent layer 6 may consist solely of the second organic compound or may contain other components (e.g., dopants). The luminescent layer 6 is primarily formed of a material capable of generating a singlet excited state through triplet-triplet annihilation, preferably containing tetraphenylbenzene derivatives such as fluorene derivatives or anthracene derivatives. In other words, tetraphenylbenzene derivatives such as fluorene derivatives or anthracene derivatives are preferred as the second organic compound.

[0105] Here, rubrene derivatives refer to rubrene and compounds in which hydrogen atoms in their molecular structure are replaced by substituents. Additionally, tetraphenyl derivatives refer to compounds having a tetraphenyl skeleton (tetraphenyl ring), including tetraphenyl and compounds in which hydrogen atoms in their molecular structure are replaced by substituents. Furthermore, anthracene derivatives refer to compounds having an anthracene skeleton (anthracene ring), including anthracene and compounds in which hydrogen atoms in their molecular structure are replaced by substituents. Examples of substituents include cyano, alkyl with 1 to 10 carbon atoms, alkoxy with 1 to 10 carbon atoms, alkylthio with 1 to 10 carbon atoms, alkylamino with 1 to 10 carbon atoms, acyl with 2 to 10 carbon atoms, aralkyl with 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups with 6 to 30 carbon atoms, and substituted or unsubstituted aromatic six-membered heterocyclic groups with 3 to 30 carbon atoms.

[0106] The second organic compound preferably has an electron affinity (EA) of 2.1 eV or higher calculated using density functional theory [B3LPY / 6-31G (d,p)], or an electron affinity (EA) of 2.8 eV or higher measured using low-energy inverse photoemission spectroscopy (LEIPS). If the electron affinity (EA) of the second organic compound contained in the luminescent layer 6 is 2.1 eV or higher calculated using density functional theory, or 2.8 eV or higher measured using low-energy inverse photoemission spectroscopy, the energy difference between the ionization potential of the second organic compound and the donor material, i.e., the first organic compound, is further reduced, thus enabling luminescence at a further low applied voltage.

[0107] In the light-emitting layer 6, such as Figure 4 As shown, it is also possible to extract luminescence from singlet excited states generated through triplet-triplet annihilation. On the other hand, as... Figure 8 As shown, the second organic compound (excitation complex) can also be used as the main body of the luminescent layer 6 to extract the luminescence of other luminescent dopants. In this case, phosphorescent materials such as iridium complexes or platinum complexes, fluorescent materials, and thermally activated delayed fluorescence materials can be mixed into the luminescent layer 6 as dopants. The mixing ratio of the dopant relative to the second organic compound (excitation complex) is preferably 20% by mass or less, more preferably 10% by mass or less.

[0108] In one embodiment, the light-emitting layer 6 further comprises a phosphorescent material in addition to the second organic compound described above. As this phosphorescent material, metal complexes containing metals such as Ir and Pt can be used. Examples of iridium complexes include tris(2-phenylpyridine)iridium (Ir(ppy)3), tris(3-methyl-2-phenylpyridine-N,C2'-)iridium(III) (Ir(mppy)3), and tris[1-phenylisoquinoline]iridium(III) (Ir(piq)3). Examples of platinum complexes include 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II).

[0109] In another embodiment, the light-emitting layer 6 further comprises a fluorescent luminescent material in addition to the aforementioned second organic compound. Examples of such fluorescent luminescent materials include various metal complexes such as aluminum 8-hydroxyquinoline (Alq3), tris(4-methyl-8-hydroxyquinoline)aluminum(III) (Almq3), and zinc 8-hydroxyquinoline (Znq2); benzene compounds such as stilbene (DSB) and diaminostilbene (DADSB); naphthalene compounds such as naphthalene and nitrored; phenanthrene compounds such as phenanthrene; β- and 6-nitroβ- compounds; perylene, N,N'- Perylene compounds such as bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (BPPC); benzene compounds such as benzoxene; anthracene compounds such as anthracene and bis(styryl)anthracene; pyrene compounds such as pyrene and BD-1; pyran compounds such as 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM); acridine compounds such as acridine; piracene compounds such as piracene; 2,5-dibenzo[a]benzene Thiophene compounds such as azolethiophene; benzo[a] benzo[a]azole and other benzo[a]azole Azolium compounds; benzimidazole and other benzimidazole compounds; 2,2'-(p-phenylenevinylene)-bisbenzothiazole and other benzothiazole compounds; bis-styryl(1,4-diphenyl-1,3-butadiene), tetraphenylbutadiene and other butadiene compounds; naphthalenedicarboximide and other naphthalenedicarboximide compounds; coumarin and other coumarin compounds; perylene ketone and other perylene ketone compounds; diazole, etc. Diazole compounds; aldehyde-azo 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 thiadiazopyridine; spiro compounds such as 2,2',7,7'-tetraphenyl-9,9'-spirodifluorene, etc.

[0110] In another embodiment, the luminescent layer 6 further comprises a thermally activated delayed fluorescence material in addition to the aforementioned second organic compound. Examples of thermally activated delayed fluorescence materials include 2,4,5,6-tetra(9-carbazole)-isophthalonitrile (4CzIPN), 4,5-di(9-carbazole)-o-phthalonitrile (2CzPN), 3,4,5,6-tetra(9-carbazole)-o-phthalonitrile (4CzPN), 2,3,5,6-tetra(9-carbazole)-terephthalonitrile (4CzTPN), 2,3,5,6-tetra(3,6-dimethyl-9-carbazole)-terephthalonitrile (4CzTPN-Me), and 2,3,5,6-tetra(3,6-diphenyl-9-carbazole)-terephthalonitrile (4CzTPN-Ph). Furthermore, compounds described in Japanese Patent Application Publication No. 2012-193352 and International Patent Publication No. 2011 / 070963 are also examples.

[0111] 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.

[0112] The average thickness of the light-emitting layer 6 can be measured by a stylus-type step difference meter or by a crystal oscillator film thickness gauge during the film formation of the light-emitting layer 6.

[0113] "Electron injection layer"

[0114] The electron injection layer 7 can be made of materials with small work functions such as alkali metals, alkaline earth metals, lithium quinoline, lithium fluoride, cesium carbonate, calcium carbonate, etc., containing metals with small work functions, hexahydropyrimidine compounds with the structure represented by the following general formula (2), or compounds with the structure represented by the following general formula (3).

[0115]

[0116] (In general formula (2), R) 1 This indicates an aromatic hydrocarbon group, aromatic heterocyclic group, arylalkylene group, divalent to tetravalent chain or cyclic hydrocarbon group that 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. 1 (Integers from 1 to 4.)

[0117]

[0118] (In general formula (3), X) 1 X 2 The same or different symbols represent nitrogen, oxygen, sulfur atoms, or divalent linkages that can have substituents. L represents a direct bond or a p-valent linkage. n 2Let p represent a number from 1 to 4. Let Q represent a number from 0 to 1, where p is 1 and q is 0. 2 ~R 4 The same or different indicates a monovalent substituent. m 1 ~m 3 Represent numbers from 0 to 3 in the same or different ways. R 2 ~R 4 Can be with X 1 X 2 They bond together to form a ring structure. Multiple Rs exist. 2 At that time, multiple R 2 They can bond together to form a ring structure. Additionally, there are multiple R... 3 At that time, multiple R 3 They can bond together to form a ring structure. Additionally, there are multiple R... 4 At that time, multiple R 4 They can bond together to form a ring structure.

[0119] R in the above general formula (2) 1 This refers to an aromatic hydrocarbon group, aromatic heterocyclic group, arylalkylene group, divalent to tetravalent chain or cyclic hydrocarbon group that 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.

[0120] As aromatic hydrocarbon groups or aromatic heterocyclic groups, groups with 3 to 30 carbon atoms are preferred, groups with 4 to 24 carbon atoms are more preferred, and groups with 5 to 20 carbon atoms are even more preferred.

[0121] As aromatic hydrocarbon groups, examples include groups formed by removing one to four hydrogen atoms from any aromatic ring of the following compounds: compounds consisting of only one aromatic ring, such as benzene; compounds consisting of multiple aromatic rings directly bonded together by a single carbon atom, such as biphenyl and diphenylbenzene; and fused-ring aromatic hydrocarbon compounds such as naphthalene, anthracene, phenanthrene, and pyrene.

[0122] As aromatic heterocyclic groups, examples include groups formed by removing one to four hydrogen atoms from any aromatic heterocycle of the following compounds: thiophene, furan, pyrrole, etc. azole, Compounds consisting of only one aromatic heterocycle, such as diazoles, thiazoles, thiadiazoles, imidazoles, pyridines, pyrimidines, pyrazines, and triazines; compounds consisting of only one aromatic heterocycle that are formed by direct bonding of multiple of these compounds through a single carbon atom (e.g., bipyridine); quinoline, quinoxaline, benzothiophene, benzothiazole, benzimidazole, benzo[i] Fused-ring heteroaromatic hydrocarbons such as azoles, indoles, carbazoles, dibenzofurans, dibenzothiophenes, acridine, and phenanthrene-rhein.

[0123] Examples of aryl alkylene groups include those formed by combining the above-mentioned aromatic hydrocarbon groups with alkylene groups having 1 to 3 carbon atoms.

[0124] As a divalent to tetravalent chain or cyclic hydrocarbon group, it is preferred to have a group with 1 to 12 carbon atoms, more preferably a group with 1 to 6 carbon atoms, and even more preferably a group with 1 to 4 carbon atoms. The chain hydrocarbon group can be straight-chain or branched.

[0125] Additionally, R 1 It can be a group formed by combining two or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, and divalent to tetravalent chain hydrocarbon groups.

[0126] Furthermore, R 1 It can be a group formed by combining one or more of the above-mentioned aromatic hydrocarbon groups, aromatic heterocyclic groups, arylalkylene groups, and divalent to tetravalent chain hydrocarbon groups with a nitrogen atom. Examples of such groups include those formed by removing one to four hydrogen atoms from trialkylamines such as trimethylamine and triphenylamine.

[0127] The aforementioned aromatic hydrocarbon group, aromatic heterocyclic group, or arylalkylene group may have one or more monovalent substituents.

[0128] Examples of monovalent substituents include: fluorine atoms; halogenated alkyl groups such as fluoromethyl, difluoromethyl, and trifluoromethyl; straight-chain or branched alkyl groups with 1 to 20 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl; cyclic alkyl groups with 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, and cycloheptyl; straight-chain or branched alkoxy groups with 1 to 20 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentoxy, hexoxy, heptoxy, and octoxy; nitro groups; cyano groups; alkylamino groups with 1 to 10 carbon atoms such as methylamino, ethylamino, dimethylamino, and diethylamino; cyclic amino groups such as pyrrolidinyl, piperidinyl, and morpholinyl; diarylamino groups such as diphenylamino and carbazole; acyl groups such as acetyl, propionyl, and butyryl; and styryl groups. Alkenyl groups with 2 to 30 carbon atoms; aryl groups with 5 to 20 carbon atoms that can be substituted by halogen atoms such as fluorine atoms or alkyl, alkoxy, amino, etc., having 1 to 20 carbon atoms (specific examples of aryl groups are the same as those of the aromatic hydrocarbon groups mentioned above); heterocyclic groups with 4 to 40 carbon atoms containing one or more of nitrogen, sulfur, and oxygen atoms that can be substituted by halogen atoms such as fluorine atoms or alkyl, alkoxy, amino, etc., having 1 to 20 carbon atoms (heterocyclic groups can consist of only one ring, or can be compounds consisting of only one aromatic heterocycle formed by direct bonding of multiple rings through one carbon atom, or can be fused heterocyclic groups. Specific examples of heterocyclic groups include thiophene rings, furan rings, pyrrole rings, benzothiophene rings, benzofuran rings, indole rings, dibenzothiophene rings, dibenzofuran rings, carbazole rings, thiazole rings, benzothiazole rings, etc. azole ring, benzo[a] Specific examples of aromatic heterocyclic groups such as azole 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; ester groups, thioether groups, etc. It should be noted that these groups can be substituted by halogen atoms or heteroelements, alkyl groups, aromatic rings, etc.

[0129] In the above general formula (2), n 1 It is an integer from 1 to 4, preferably 2 or 3.

[0130] In the above general formula (3), X 1 X 2 The same or different can refer to nitrogen atoms, oxygen atoms, sulfur atoms or divalent linkages that may have substituents.

[0131] As divalent linking groups, examples include divalent hydrocarbon groups and groups formed by replacing a portion of the carbon atom of a hydrocarbon group with any heteroatom among nitrogen, oxygen, and sulfur atoms.

[0132] As a hydrocarbon group, a group having 1 to 6 carbon atoms is preferred, and a group having 1, 2 or 6 carbon atoms is more preferred.

[0133] The hydrocarbon group can be any of the following: straight-chain, branched, cyclic, or a combination thereof.

[0134] Divalent hydrocarbon groups can be alkylene groups that are saturated hydrocarbon groups, or unsaturated hydrocarbon groups such as alkenylene groups and alkyne groups.

[0135] In the above general formula (3), L represents a direct bond or a p-valent linker. It should be noted that L is a direct bond only when p is 2.

[0136] As a p-valent linking group, in addition to nitrogen, oxygen, sulfur, and carbon atoms, it can also be a group formed by removing p hydrogen atoms from a group formed by replacing a portion of the carbon atom of a hydrocarbon group with any heteroatom among nitrogen, oxygen, and sulfur atoms.

[0137] When the p-valent linking group has carbon atoms, it is preferable to have a linking group with 1 to 30 carbon atoms. More preferably, it is a linking group with 1 to 20 carbon atoms.

[0138] The hydrocarbon group can be any of the following: straight-chain, branched, cyclic, or a combination thereof.

[0139] As a hydrocarbon group, it can be any of the following: saturated hydrocarbon group, unsaturated hydrocarbon group, or aromatic hydrocarbon group.

[0140] As aromatic hydrocarbon groups, examples include groups formed by removing hydrogen atoms from aromatic compounds such as benzene rings, naphthalene rings, anthracene rings, tetraphenyl rings, pentaphenyl rings, triphenylene rings, pyrene rings, fluorene rings, and indene rings.

[0141] R in the above general formula (3) 2 ~R 4 The same or different can represent monovalent substituents. Additionally, m 1 ~m 3 Numbers representing 0 to 3, either in the same or different ways.

[0142] Examples of monovalent substituents include: fluorine atoms; halogenated alkyl groups such as fluoromethyl, difluoromethyl, and trifluoromethyl; straight-chain or branched alkyl groups with 1 to 20 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl; cyclic alkyl groups with 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, and cycloheptyl; straight-chain or branched alkoxy groups with 1 to 20 carbon atoms such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentoxy, hexoxy, heptoxy, and octoxy; nitro groups; cyano groups; alkylamino groups with 1 to 10 carbon atoms such as methylamino, ethylamino, dimethylamino, and diethylamino; cyclic amino groups such as pyrrolidinyl, piperidinyl, and morpholinyl; diarylamino groups such as diphenylamino and carbazole; acyl groups such as acetyl, propionyl, and butyryl; and styryl groups. Alkenyl groups with 2 to 30 carbon atoms; aryl groups with 5 to 20 carbon atoms that can be substituted by halogen atoms such as fluorine atoms or alkyl, alkoxy, amino, etc., having 1 to 20 carbon atoms (specific examples of aryl groups are the same as those of the aromatic hydrocarbon groups mentioned above); heterocyclic groups with 4 to 40 carbon atoms containing one or more of nitrogen, sulfur, and oxygen atoms that can be substituted by halogen atoms such as fluorine atoms or alkyl, alkoxy, amino, etc., having 1 to 20 carbon atoms (heterocyclic groups can consist of only one ring, or can be compounds consisting of only one aromatic heterocycle formed by direct bonding of multiple rings through one carbon atom, or can be fused heterocyclic groups. Specific examples of heterocyclic groups include thiophene rings, furan rings, pyrrole rings, benzothiophene rings, benzofuran rings, indole rings, dibenzothiophene rings, dibenzofuran rings, carbazole rings, thiazole rings, benzothiazole rings, etc. azole ring, benzo[a] Specific examples of aromatic heterocyclic groups such as azole 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; ester groups, thioether groups, etc. It should be noted that these groups can be substituted by halogen atoms or heteroelements, alkyl groups, aromatic rings, etc.

[0143] In the above general formula (3), p represents a number from 1 to 4, preferably a number from 1 to 3.

[0144] In addition, n in the above general formula (3) 2 A number representing 0 or 1, preferably 0.

[0145] The average thickness of the electron injection layer 7 is preferably 0.5 to 100 nm, more preferably 1 to 10 nm. The electron injection layer 7 can be formed by coating a coating composition or by co-deposition using a vacuum evaporation method.

[0146] The average thickness of the electron injection layer 7 can be determined, for example, by a stylus step meter or a spectrophotometer.

[0147] "cathode"

[0148] Examples of materials used in the cathode 8 include ITO, IZO, Au, Pt, Ag, Cu, Al, or alloys containing them. Among these, ITO, IZO, Au, Ag, and Al are preferred as materials for the cathode 8.

[0149] The average thickness of the cathode 8 is not particularly limited, but is preferably 10 to 1000 nm, and more preferably 30 to 150 nm. In addition, even when using an opaque material as the cathode 8, it is possible to use it as a transparent cathode in a top-emitting organic EL element by making the average thickness about 10 to 30 nm.

[0150] The average thickness of cathode 8 can be measured during the film formation of cathode 8 using a crystal oscillator film thickness gauge.

[0151] Especially Figure 5 In the organic EL element with the reverse structure shown, the portion on the cathode 8 where a layer composed of inorganic oxides is formed is also treated as part of the cathode.

[0152] The oxide used here is a layer of semiconductor or insulating laminated thin film. Specifically, it can be a layer composed of elemental metal oxides, a layer formed by laminating any one or both of the following: a layer containing two or more metal oxides and a layer composed of elemental metal oxides.

[0153] Examples of metallic elements that constitute metal oxides that form inorganic oxides 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.

[0154] When the layer composed of inorganic oxides includes a layer containing two or more metal oxides, it is preferable that at least one of the metal elements constituting the metal oxides is composed of magnesium, aluminum, calcium, zirconium, hafnium, silicon, titanium, or zinc.

[0155] When the layer composed of inorganic oxides is a layer composed of elemental metal oxides, it is preferable to have a layer composed of metal oxides selected from magnesium oxide, aluminum oxide, zirconium oxide, hafnium oxide, silicon oxide, titanium oxide, and zinc oxide.

[0156] When the layer composed of inorganic oxides is a layer formed by stacking any one or both of a layer containing two or more metal oxides and a layer composed of elemental metal oxides, or a layer containing two or more metal oxides, examples include layers formed by stacking and / or mixing two metal oxides selected from titanium oxide / zinc oxide, titanium oxide / magnesium oxide, titanium oxide / zirconia, titanium oxide / aluminum oxide, titanium oxide / hafnium oxide, titanium oxide / silicon oxide, zinc oxide / magnesium oxide, zinc oxide / zirconia, zinc oxide / hafnium oxide, zinc oxide / silicon oxide, and calcium oxide / aluminum oxide; and layers formed by stacking and / or mixing three metal oxides selected from titanium oxide / zinc oxide / magnesium oxide, titanium oxide / zinc oxide / zirconia, 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.

[0157] Inorganic oxides may include oxide semiconductors exhibiting good properties as a special component, namely IGZO (indium gallium zinc oxide) and / or 12CaO·7Al2O3 as an electron compound.

[0158] The average thickness of the inorganic oxide film is not particularly limited, but is preferably 1 to 1000 nm, more preferably 2 to 100 nm.

[0159] The average thickness of the layer composed of inorganic oxides can be determined by a stylus step meter or a spectrophotometer.

[0160] "seal"

[0161] Organic EL element 1 can be sealed as needed.

[0162] For example, the organic EL element 1 can be sealed using a sealed container (not shown) having a concave space for housing the organic EL element 1 and an adhesive for bonding the edge of the sealed container to the substrate 2. Alternatively, it can be sealed by housing the organic EL element 1 in a sealed container and filling it with a sealing material made of ultraviolet (UV) curable resin or the like.

[0163] When sealing the organic EL element 1 using a sealed container or sealing component, a moisture-absorbing drying material can be placed inside the sealed container or inside the sealing component. Alternatively, a moisture-absorbing material can be used as the sealed container or sealing component. Furthermore, a space can be formed inside the sealed container or inside the sealing component.

[0164] The material used as the sealing container or sealing component for sealing the organic EL element 1 can be resin material, glass material, etc. Examples of resin and glass materials used as the sealing container or sealing component are the same materials used in the substrate 2.

[0165] Manufacturing methods for organic EL devices

[0166] Next, as an example of the manufacturing method of the organic EL element of the present invention, the manufacturing method of the organic EL element 1 will be described.

[0167] In manufacturing organic EL element 1, firstly, an anode 3 is formed on substrate 2.

[0168] The anode 3 can be formed by sputtering, vacuum evaporation, sol-gel deposition, spray thermal decomposition (SPD), atomic layer deposition (ALD), vapor phase deposition, liquid phase deposition, etc. The anode 3 can also be formed using a bonding metal foil method.

[0169] Next, hole injection layer 4, hole transport layer 5, light emission layer 6, and electron injection layer 7 are sequentially formed on anode 3.

[0170] There are no particular limitations on the formation methods of hole injection layer 4, hole transport layer 5, light emission layer 6, and electron injection layer 7. Various previously known formation methods can be appropriately used according to the characteristics of the materials used in hole injection layer 4, hole transport layer 5, light emission layer 6, and electron injection layer 7.

[0171] Specifically, methods for forming the hole injection layer 4, hole transport layer 5, light emission layer 6, and electron injection layer 7 include coating methods, vacuum evaporation methods, and ESDUS (Evaporative Spray Deposition from Ultra-dilute Solution) methods, etc.

[0172] Next, a cathode 8 is formed on the electron injection layer 7. The cathode 8 can be formed, for example, in the same manner as the anode 3.

[0173] In production Figure 5 In the case of the reversed structure of organic EL elements shown, the order is reversed. It should be noted that in... Figure 5 In the organic EL element with the reverse structure shown, when a layer composed of inorganic oxides is formed on the cathode 8, the oxides are formed by methods such as spray pyrolysis, sol-gel method, sputtering method, and vacuum evaporation method.

[0174] Through the above processes, organic EL element 1 can be obtained.

[0175] "Sealing method"

[0176] In the case of sealing organic EL element 1, the usual sealing methods used in sealing organic EL elements can be used.

[0177] Display devices, lighting devices

[0178] The organic EL element 1 of this embodiment emits light by forming an excitation complex between a first organic compound, a donor material with a low ionization potential and exhibiting thermally activated delayed fluorescence, and a second organic compound, an acceptor material, which can form a singlet excited state through triplet-triplet annihilation. Therefore, charge recombination can occur with low energy. Consequently, this results in an organic EL element 1 with a low driving voltage, a shorter lifetime of unstable excited states, and excellent driving stability.

[0179] The organic EL element of the present invention can change the emission color by appropriately selecting the material of the light-emitting layer, etc., and can also obtain the desired emission color by using a color filter, etc. Therefore, the organic EL element of the present invention can be used as the light-emitting part of a display device or an illumination device.

[0180] The display device of the present invention includes the organic EL element of the present invention, which has excellent productivity and low driving voltage due to its simple element structure. Therefore, it is preferred as a display device. The display device of the present invention emits light stably over a long period of time under low applied voltage.

[0181] Furthermore, the lighting device of the present invention incorporates the organic EL element of the present invention, which boasts excellent productivity and low driving voltage due to its simple element structure. Therefore, it is preferred as a lighting device. The lighting device of the present invention emits light stably over a long period of time under low applied voltage.

[0182] Example

[0183] The present invention will be described in more detail below with examples, but the present invention is not limited to any of the examples described below.

[0184] Example 1

[0185] (Fabrication of organic EL components)

[0186] Manufacturing using the methods shown below Figure 1 The organic EL element 1 with the structure shown is evaluated.

[0187] [Process 1]

[0188] As substrate 2, a commercially available transparent glass substrate with an average thickness of 0.7 mm is prepared, having an electrode (anode 3) patterned with a width of 3 mm made of ITO.

[0189] Then, the substrate 2 with anode 3 is ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and boiled in isopropanol for 5 minutes. Then, the substrate 2 with anode 3 is removed from the isopropanol, dried by nitrogen blowing, and subjected to UV ozone cleaning for 20 minutes.

[0190] [Process 2]

[0191] The substrate 2 with the anode 3 formed in [Step 1] is placed in a spin coater and spin-coated with Heraeus Company hole injection material "Clevios HIL1.3N" as hole injection layer 4. The substrate is then heated in the atmosphere to form a 10nm hole injection layer 4.

[0192] [Process 3]

[0193] Next, the substrate 2, on which the layers up to the hole injection layer 4 are formed, is fixed to the substrate holder of the vacuum evaporation apparatus. The pressure inside the vacuum evaporation apparatus is reduced to 1×10⁻⁶. －5 Pa of pressure.

[0194] On hole injection layer 4, 2-SF-PHX (represented by the following structural formula) and Novaled's NDP-9 as a p-type dopant are first deposited at a mass ratio of 9:1 for 30 nm, and then 2-SF-PHX is deposited for 10 nm as hole transport layer 5.

[0195]

[0196] Furthermore, a film formed by vapor deposition of anthracene derivative represented by the following structural formula (4-1) for 30 nm is formed as the light-emitting layer 6.

[0197]

[0198] Here, the electron affinity (EA) of the anthracene derivative of the above-mentioned structural formula (4-1) used in the luminescent layer 6 is estimated to be 2.1 eV using density functional theory, and 2.8 eV using low-energy inverse photoemission spectroscopy (LEIPS).

[0199] It should be noted that the anthracene derivative of structural formula (4-1) is synthesized as follows.

[0200] First, using 5-bromoisophthalic acid as the starting material, its carboxyl group is chlorinated with oxalyl chloride to obtain a carboxylic acid chloride (acyl chloride). The carboxylic acid chloride is amidated with tert-butylamine to obtain an amide compound. The amide compound is nitrified with thionyl chloride to obtain a benzene derivative having a bromine group and two cyano groups. This benzene derivative having a bromine group and two cyano groups is then reacted with bis(pinacol)diboron to introduce a pinacolboron group, resulting in an organoboron compound having two cyano groups.

[0201] On the other hand, using 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine as a starting material, it was Suzuki coupled with 9-anthraboronic acid to obtain an anthracene derivative having a triphenyltriazine site. This anthracene derivative having a triphenyltriazine site was then brominated with N-bromosuccinimide (NBS) to obtain an anthracene derivative having a triphenyltriazine site and a bromine group.

[0202] An anthracene derivative of structural formula (4-1) was synthesized by Suzuki coupling of an organoboron compound with two cyano groups obtained as described above with an anthracene derivative having a triphenyltriazine site and a bromine group.

[0203] After forming the light-emitting layer 6, the compound represented by the following structural formula (2-1) is vapor-deposited for 3 nm as the electron injection layer 7.

[0204]

[0205] It should be noted that the compound represented by the above structural formula (2-1) 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.

[0206] Next, on the substrate 2 to which the electron injection layer 7 is formed, a cathode 8 with a film thickness of 100 nm made of aluminum is formed by vacuum evaporation.

[0207] It should be noted that cathode 8 uses a stainless steel vapor deposition mask to form a strip with a 3mm wide deposition surface, resulting in an organic EL element with a light-emitting area of ​​9mm². 2 .

[0208] [Process 4]

[0209] Next, the substrate 2, on which the layers up to the cathode 8 are formed, is placed in a glass cover (sealed container) with a concave space, and a sealing material made of ultraviolet (UV) curable resin is filled in to seal it, thereby obtaining the organic EL element of Example 1.

[0210] Example 2

[0211] The material used in the hole transport layer 5 is 2Cz-DMAC, represented by the following structural formula. Otherwise, the organic EL element of Example 2 is fabricated in the same manner as in Example 1.

[0212]

[0213] It should be noted that 2Cz-DMAC is synthesized according to the following reaction scheme.

[0214]

[0215] First, 3,6-dibromo-9-phenylcarbazole was used as the starting material and reacted with 9-phenylcarbazole-3-boric acid in the presence of Pd(PPh3)4 and K2CO3 to obtain the compound represented by formula (5).

[0216] Next, the compound represented by formula (5) was reacted with 9,9-dimethyl-9,10-dihydroacridine in the presence of Pd2(dba)3, t-BuONa, and [(t-Bu)3PH]BF4 to synthesize 2Cz-DMAC.

[0217] Comparative Example 1

[0218] The material used in the hole transport layer 5 is TPDI, which is represented by the following structural formula. Otherwise, the organic EL element of Comparative Example 1 is fabricated in the same manner as in Example 1.

[0219]

[0220] It should be noted that TPDI is a material with the same ionization potential as 2-SF-PHX, but it does not exhibit thermally activated delayed fluorescence.

[0221] Example 3

[0222] (Fabrication of organic EL components)

[0223] Organic EL elements are manufactured and evaluated using the methods shown below.

[0224] [Process 1]

[0225] As substrate 2, a commercially available transparent glass substrate with an average thickness of 0.7 mm is prepared, having an electrode (anode 3) patterned with a width of 3 mm made of ITO.

[0226] Then, the substrate 2 with anode 3 is ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and boiled in isopropanol for 5 minutes. Then, the substrate 2 with anode 3 is removed from the isopropanol, dried by nitrogen blowing, and subjected to UV ozone cleaning for 20 minutes.

[0227] [Process 2]

[0228] The substrate 2 with the anode 3 formed in [Step 1] is placed in a spin coater and spin-coated with Heraeus Company hole injection material "Clevios HIL1.3N" as hole injection layer 4. The substrate is then heated in the atmosphere to form a 10nm hole injection layer 4.

[0229] [Process 3]

[0230] Next, the substrate 2, on which the layers up to the hole injection layer 4 are formed, is fixed to the substrate holder of the vacuum evaporation apparatus. The pressure inside the vacuum evaporation apparatus is reduced to 1×10⁻⁶. －5 Pa of pressure.

[0231] On the hole injection layer 4, 2-SF-PHX represented by the above structural formula and NDP-9 from Novaled, which is a p-type dopant, are first deposited at a mass ratio of 9:1 for 30 nm. Then, 2-SF-PHX is deposited for 10 nm as the hole transport layer 5.

[0232] Furthermore, a film formed by evaporating anthracene derivative represented by the following structural formula (4-2) for 30 nm is formed as the light-emitting layer 6.

[0233]

[0234] Here, the electron affinity (EA) of the anthracene derivative of the above-mentioned structural formula (4-2) used in the luminescent layer 6 is estimated to be 2.73 eV using density functional theory, and 3.0 eV using low-energy inverse photoemission spectroscopy (LEIPS).

[0235] It should be noted that the anthracene derivatives of structural formula (4-2) are synthesized as follows.

[0236] First, using 5-bromoisophthalic acid as the starting material, its carboxyl group is chlorinated with oxalyl chloride to obtain a carboxylic acid chloride (acyl chloride). The carboxylic acid chloride is amidated with tert-butylamine to obtain an amide compound. The amide compound is nitrified with thionyl chloride to obtain a benzene derivative having a bromine group and two cyano groups. This benzene derivative having a bromine group and two cyano groups is then reacted with bis(pinacol)diboron to introduce a pinacolboron group, resulting in an organoboron compound having two cyano groups.

[0237] On the other hand, using 4-iodobenzonitrile as a starting material, a Grignard reagent with cyanophenyl groups is obtained through a metal-halogen exchange reaction with iPrMgCl. This Grignard reagent with cyanophenyl groups is then reacted with cyanuric chloride to obtain a triazine compound with two cyanophenyl groups and one chloro group. This triazine compound with two cyanophenyl groups and one chloro group is then Suzuki coupled with 4-chlorophenylboronic acid to obtain a triazine compound with two cyanophenyl groups and one chlorophenyl group. This triazine compound with two cyanophenyl groups and one chlorophenyl group is then Suzuki coupled with 9-anthrabenzic acid to obtain an anthracene derivative with a triazine site containing two cyanophenyl groups and one phenyl group. This anthracene derivative with a triazine site containing two cyanophenyl groups and one phenyl group is then brominated with N-bromosuccinimide (NBS) to obtain an anthracene derivative with a triazine site containing two cyanophenyl groups and one phenyl group and a bromo group.

[0238] An anthracene derivative of structural formula (4-2) was synthesized by Suzuki coupling of an organoboron compound with two cyano groups obtained as described above with an anthracene derivative having a triazine site containing two cyanophenyl groups and a phenyl group and a bromo group.

[0239] After forming the light-emitting layer 6, the compound represented by the above structural formula (2-1) is vapor-deposited for 3 nm as the electron injection layer 7.

[0240] Next, on the substrate 2 to which the electron injection layer 7 is formed, a cathode 8 with a film thickness of 100 nm made of aluminum is formed by vacuum evaporation.

[0241] It should be noted that cathode 8 uses a stainless steel vapor deposition mask to form a strip with a 3mm wide deposition surface, resulting in an organic EL element with a light-emitting area of ​​9mm². 2 .

[0242] [Process 4]

[0243] Next, the substrate 2, on which the layers up to the cathode 8 are formed, is placed in a glass cover (sealed container) with a concave space, and a sealing material made of ultraviolet (UV) curable resin is filled in to seal it, thereby obtaining the organic EL element of Example 3.

[0244] Example 4

[0245] The material used in the hole transport layer 5 is 2Cz-DMAC as represented by the above structural formula. Otherwise, the organic EL element of Example 4 is fabricated in the same manner as in Example 3.

[0246] Comparative Example 2

[0247] The material used in the hole transport layer 5 is TPDI as represented by the above structural formula. Otherwise, the organic EL element of Comparative Example 2 is fabricated in the same manner as in Example 3.

[0248] (Characteristic evaluation of organic EL devices)

[0249] For the components of the obtained embodiments and comparative examples, a voltage was applied using a Keithley "Type 2400 Source Meter," and the brightness was measured using a Konica Minolta "LS-100" meter. The relationship between the applied voltage and the brightness was investigated. Additionally, the relationship between the applied voltage and the current density, as well as the emission spectrum, were investigated. These results are presented below. Figure 9 and Figure 11 .

[0250] Figure 9 (a) shows the applied voltage-current density characteristics of Examples 1, 2 and Comparative Example 1. It can be confirmed that in the use of TPDI or 2-SF-PHX with small ionization potential, the current rises at low voltage, albeit weakly.

[0251] in addition, Figure 9 (b) and (c) show the applied voltage-luminosity characteristics and EL spectra of Examples 1, 2, and Comparative Example 1. According to... Figure 9 (b) and (c) confirm that blue light emission can be obtained at low driving voltages. For example... Figure 2 , 3 As shown in Figure 4, it is believed that an excited complex is formed under a low applied voltage, and the energy of the excited complex can be extracted in the form of blue light through triplet-triplet annihilation.

[0252] Figure 10 The diagram shows the elements of Example 1, Example 2, and Comparative Example 1 starting from an initial brightness of 100 cd / m². 2 Brightness variation during continuous driving. Compared to the element in Comparative Example 1, the elements in Examples 1 and 2 exhibit a significantly longer lifespan. This is believed to be due to, as... Figure 3 , 4 As shown, when thermally activated delayed fluorescence materials are used as donors, the lifetime of the triplet excited state of the donor becomes shorter, resulting in a longer lifetime.

[0253] in addition, Figure 11(a) shows the applied voltage-current density characteristics of Examples 3, 4 and Comparative Example 2. It can be confirmed that in the use of TPDI or 2-SF-PHX with small ionization potential, the current rises at low voltage, albeit weakly.

[0254] in addition, Figure 11 (b) and (c) show the applied voltage-luminosity characteristics and EL spectra of Examples 3, 4, and Comparative Example 2. According to... Figure 11 (b) and (c) confirm that green light emission can be obtained at a low driving voltage below 2V. For example... Figure 2 , 3 As shown in Figure 4, it is believed that an excited complex is formed under a low applied voltage, and the energy of the excited complex can be extracted in the form of green light through triplet-triplet annihilation.

[0255] Figure 12 The diagram shows the elements of Example 3, Example 4, and Comparative Example 2 starting from an initial brightness of 100 cd / m². 2 Brightness variation during continuous driving. Compared to the element in Comparative Example 2, the elements in Examples 3 and 4 exhibit a significantly longer lifespan. This is believed to be due to, as... Figure 3 , 4 As shown, when thermally activated delayed fluorescence materials are used as donors, the lifetime of the triplet excited state of the donor becomes shorter, resulting in a longer lifetime.

[0256] Symbol Explanation

[0257] 1: Organic EL element; 2: Substrate; 3: Anode; 4: Hole injection layer; 5: Hole transport layer; 6: Light-emitting layer; 7: Electron injection layer; 8: Cathode

Claims

1. An organic electroluminescent element, characterized in that, It consists of an anode, a hole transport layer, a light-emitting layer, and a cathode, in sequence. The hole transport layer contains a donor material with a low ionization potential, namely a first organic compound. The light-emitting layer contains an acceptor material with high electron affinity, namely a second organic compound. An excited complex is formed between the first organic compound and the second organic compound. The first organic compound is a thermally activated delayed fluorescence material.

2. The organic electroluminescent element according to claim 1, wherein, The calculated ionization potential (IP) of the first organic compound using density functional theory is below 4.8 eV, or the measured ionization potential (IP) obtained by ultraviolet photoelectron spectroscopy is below 5.5 eV.

3. The organic electroluminescent element according to claim 1, wherein, The calculated value of the electron affinity (EA) of the second organic compound obtained by density functional theory is 2.1 eV or higher, or the measured value of the electron affinity (EA) obtained by low-energy back-photoelectron spectroscopy is 2.8 eV or higher.

4. The organic electroluminescent element according to claim 1, wherein, The first organic compound has a dimethylacridine skeleton represented by formula (1-1) and a phenanthrene skeleton represented by formula (1-2). A azine skeleton or a carbazole skeleton represented by the following formulas (1-3), ， In equations (1-1), (1-2), and (1-3), X represents the bonding site that bonds with other atoms.

5. The organic electroluminescent element according to claim 1, wherein, The light-emitting layer further comprises a phosphorescent material.

6. The organic electroluminescent element according to claim 1, wherein, The light-emitting layer further comprises a fluorescent light-emitting material.

7. The organic electroluminescent element according to claim 1, wherein, The luminescent layer further comprises a thermally activated delayed fluorescence material.

8. A display device, characterized in that, An organic electroluminescent element comprising any one of claims 1 to 7.

9. A lighting device, characterized in that, An organic electroluminescent element comprising any one of claims 1 to 7.

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