Organic electroluminescent element

Abstract

An organic EL element which is high in efficiency, low in driving voltage, and high in durability, and which emits phosphorescent light is provided by combining an organic compound having excellent properties, which is excellent in hole injection and transport properties, has electron blocking ability, is high in stability in a thin film state, and is high in emission efficiency, with various materials for an organic EL element, which are excellent in hole and electron injection and transport properties, electron blocking ability, stability in a thin film state, and durability, in a manner such that the respective materials can effectively exhibit the properties possessed thereby. The organic electroluminescent element successively has an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode, the hole transport layer contains an arylamine compound represented by general formula (1), the light-emitting layer contains a host and a dopant, and the dopant includes a phosphorescent light-emitting material. In the formula, A1 represents a divalent group of an aromatic hydrocarbon or the like, and Ar1 to Ar3 represent an aromatic hydrocarbon group or the like.

Description

Technical Field

[0001] This invention relates to an organic electroluminescent element (hereinafter also referred to as "organic EL element") suitable for various display devices, and more specifically, to an organic EL element using a specific arylamine compound. Background Technology

[0002] Organic EL elements are self-emissive, and therefore brighter and more visible than liquid crystal elements, enabling clear displays. As a result, they have been the subject of much research.

[0003] In 1987, Eastman Kodak's CWTang et al. developed a layered structure element in which various materials perform different functions, thus making organic EL elements using organic materials practical. They layered tris(8-hydroxyquinoline)aluminum (hereinafter referred to as "Alq3"), which is a phosphor capable of transporting electrons, with an aromatic amine compound capable of transporting holes, and injected the charges of both into the phosphor layer to make it emit light, thereby achieving 1000 cd / m² at voltages below 10V. 2 The above high brightness (for example, see Patent Document 1 and Patent Document 2).

[0004] To date, numerous improvements have been made to facilitate the practical application of organic EL devices, further refining various functions. High efficiency and durability have been achieved by sequentially arranging an anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode on a substrate. Furthermore, with the aim of further improving luminous efficiency, research has been conducted utilizing phosphorescence accompanying the transition from the triplet excited state to the ground state. Patent Document 3 proposes a blue phosphorescent organic EL device using a platinum complex as the phosphorescent luminescent material.

[0005] In Patent Documents 4 and 5, by combining a host compound containing a nitrogen-containing heteroaromatic ring structure with electron transport capability and a host compound containing a carbazole structure with hole transport capability in the luminescent layer, the electron and hole transport capabilities are improved, and the luminous efficiency is improved compared to using them alone.

[0006] Non-Patent Document 1 discloses a blue phosphorescent organic EL element, which, in addition to a host material with electron transport capability and a host material with hole transport capability, also incorporates a platinum complex with a specific structure to form a light-emitting layer. Carbazole derivatives (e.g., SiCzCz hereinafter referred to as the host material) used in Non-Patent Document 1 have recently been proposed as hole transport materials and host materials with hole transport capability in phosphorescent organic EL elements.

[0007] [Chemical Formula 1]

[0008] Patent Document 1: Japanese Patent Application Publication No. 8-048656 Patent Document 2: Japanese Patent No. 3194657 Patent Document 3: International Publication No. 2012 / 116231 Patent Document 4: Japanese Patent Publication No. 2016-532307 Patent Document 5: U.S. Patent Application Publication No. 2017 / 0104163 Patent Document 6: Japanese Patent No. 6715781 Patent Document 7: International Publication No. 2021 / 079856 Patent Document 8: International Publication No. 2014 / 009310 Non-patent literature 1: Nature Photonics, 2022, Vol.16, pp.212-218 Non-patent literature 2: Eungdo Kim et al., Science Advances, 2022, Vol. 8, Issue 41 Summary of the Invention SiCzCz possesses a high triplet excitation energy (hereinafter referred to as the "T1 level"), but the molecular design for increasing the T1 level restricts π-conjugation, leading to a decrease in hole mobility. Therefore, when SiCzCz is combined with an emissive layer that enhances electron transport capabilities, the supply of holes to the emissive layer may become a rate-limiting factor, resulting in an excess of electrons within the emissive layer and causing deviation. Furthermore, in devices using SiCzCz as the second hole transport layer, the driving voltage increases, and the excess electrons within the emissive layer result in insufficient device lifetime. Therefore, a second hole transport material with high hole mobility and excellent electron transport durability is required. The purpose of this invention is to achieve the goal of injecting holes. Organic compounds with excellent properties such as high transmission performance, electron blocking ability, high stability in the thin film state, and high luminous efficiency are combined with various materials for organic EL elements with excellent hole and electron injection / transmission performance, electron blocking ability, stability in the thin film state, and durability in a way that can effectively utilize the characteristics of each material, thereby providing a high-efficiency, low-driving-voltage, and high-durability organic EL element for displaying phosphorescent light emission.

[0009] The physical characteristics that the organic compounds used in the organic EL element involved in this invention should possess include (1) good hole injection characteristics, (2) high hole mobility, (3) excellent electron blocking ability, (4) stable thin film state, and (5) excellent heat resistance. In addition, the physical characteristics that the organic EL element involved in this invention should possess include (1) low light emission initiation voltage, (2) low practical driving voltage, and (3) long lifetime.

[0010] In order to achieve the above-mentioned objective, the inventors considered the injection of holes in arylamine compounds having a specific structure. Organic EL devices were prepared by selecting various arylamine compounds, demonstrating excellent transport capability, thin film stability, and durability, and the characteristics of these devices were thoroughly evaluated. As a result, the inventors obtained the following insight: if an arylamine compound with a specific structure is selected as the material for the hole transport layer, holes injected from the anode side can be transported efficiently. Furthermore, various organic EL devices were fabricated by combining this arylamine compound with a luminescent material having a specific structure, and the characteristics of these devices were evaluated. As a result, the present invention was completed.

[0011] That is, according to the present invention, the following organic electroluminescent element is provided.

[0012] 1) An organic electroluminescent element, comprising at least an anode, a hole transport layer, an emissive layer, an electron transport layer, and a cathode in sequence, wherein the hole transport layer contains an arylamine compound represented by the following general formula (1), and the emissive layer contains a host and a dopant, the dopant comprising a phosphorescent material. [Chemical Formula 2]

[0013] In the formula, A1 represents a single bond, a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted heterocycle, or a divalent group of a substituted or unsubstituted fused polycyclic hydrocarbon. Ar1 to Ar3 are selectively the same or different from each other and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group.

[0014] 2) The organic electroluminescent element according to 1), wherein, In the general formula (1), A1 is a single bond or a substituted or unsubstituted phenylene.

[0015] 3) The organic electroluminescent element according to 1) or 2), wherein, In the general formula (1), Ar1 and Ar2 are substituted or unsubstituted phenyl or substituted or unsubstituted biphenyl, which are selectively the same or different from each other.

[0016] 4) The organic electroluminescent element according to any one of 1) to 3), wherein, In the general formula (1), Ar3 is a substituted or unsubstituted phenyl, a substituted or unsubstituted biphenyl, or a substituted or unsubstituted terphenyl.

[0017] 5) The organic electroluminescent element according to any one of 1) to 4), wherein, The hole transport layer has a structure of two or more layers including a first hole transport layer and a second hole transport layer, wherein the second hole transport layer contains an arylamine compound represented by the general formula (1).

[0018] 6) The organic electroluminescent element according to any one of 1) to 5), wherein, The host compound contains a first host compound with electron transport capability and a second host compound with hole transport capability, the second host compound comprising a compound having a carbazole structure.

[0019] 7) An organic electroluminescent element according to any one of 1) to 6), wherein, Platinum complexes are used as the phosphorescent luminescent material.

[0020] 8) The organic electroluminescent element according to 7), wherein, The platinum complex comprises one or more polydentate ligands that form a 5-membered chelate ring with platinum, at least one of which is a tetradentate ligand, and the 5-membered chelate ring comprises a carbene bond.

[0021] 9) The organic electroluminescent element according to 8), wherein, The platinum complex is represented by the following general formula (2), [Chemical Formula 3]

[0022] In the formula, L 1 and L 2 They are selectively the same or different from each other, and represent single bonds, NR 5 oxygen or sulfur atoms n1 represents 0 or 1, n2 represents 0 or 1. Z 1 and Z 2 They may be selectively the same or different from each other, and represent either nitrogen atoms or carbon atoms. R 1 ~R 5 They may be selectively the same or different from each other, and represent hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, or substituted or unsubstituted fused polycyclic hydrocarbon groups. When L 1 and L 2 At least one of them is NR 5 At that time, selected from R 5 With R 2 R 5 With R 3 and R 5 With R 4 One or more of them selectively bond to each other to form a ring.

[0023] 10) The organic electroluminescent element according to any one of 7) to 9), wherein, The dopants include platinum complexes used as phosphorescent materials and thermally activated delayed fluorescence (TADF) materials.

[0024] 11) An organic electroluminescent element according to any one of 1) to 10), wherein, The arylamine compound represented by the general formula (1) has a hole mobility of 1.0 × 10⁻⁶ at an electric field strength of 0.25 MV / cm. -5 cm 2 / Vs and above.

[0025] The arylamine compound represented by the general formula (1) of the present invention has the following characteristics: (1) good hole injection characteristics, (2) high hole mobility, (3) excellent electron blocking ability, (4) stable thin film state, and (5) excellent heat resistance. Furthermore, according to the present invention, by using the arylamine compound represented by the general formula (1), which has a high hole mobility, excellent electron blocking ability, excellent amorphous properties, and stable thin film state compared to conventional hole transport materials, it is possible to realize an organic EL device with high power efficiency, low driving voltage, and long lifetime that displays phosphorescent light emission. Attached Figure Description

[0026] Figure 1 This diagram illustrates an example of an organic EL element with a hole transport layer having a two-layer structure.

[0027] Figure 2 This diagram illustrates an example of an organic EL element with a three-layer hole transport layer.

[0028] Figure 3 This is a diagram showing the structures of compounds (1-1) to (1-15) as examples of compounds represented by general formula (1).

[0029] Figure 4 The diagram shows the structures of compounds (1-16) to (1-27) as examples of compounds represented by general formula (1).

[0030] Figure 5 The diagram shows the structures of compounds (1-28) to (1-39) as examples of compounds represented by general formula (1).

[0031] Figure 6 The diagram shows the structures of compounds (1-40) to (1-48) as examples of compounds represented by general formula (1). Detailed Implementation

[0032] <Organic EL Components> The organic EL element of the present invention comprises at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in sequence. Furthermore, in the present invention, the hole transport layer contains an arylamine compound represented by the above general formula (1), and the light-emitting layer contains a host and a dopant, the dopant comprising a phosphorescent material.

[0033] like Figure 1 As shown, an organic EL element according to one embodiment of the present invention has a structure in which an anode 2, a hole transport layer 4, a light-emitting layer 5, an electron transport layer 7, and a cathode 9 are sequentially stacked on a substrate 1. The organic EL element of the present invention may be an element having a hole injection layer 3 between the anode and the hole transport layer, an element having a hole blocking layer 6 between the light-emitting layer and the electron transport layer, and an element having an electron injection layer 8 between the electron transport layer and the cathode. In these multilayer structures, some organic layers may be omitted or several organic layers may be included; for example, it can be formed with both a hole injection layer and a hole transport layer, or with both an electron injection layer and an electron transport layer. Furthermore, it is also possible to form a structure in which two or more organic layers with the same function are stacked. Figure 1 This is an example of a structure consisting of two stacked hole transport layers, with a first hole transport layer 4a and a second hole transport layer 4b. For example... Figure 2 As shown, a third hole transport layer 4c can be further stacked on the second hole transport layer 4b, making the hole transport layer a three-layer structure. The organic EL element of this invention is not limited to... Figure 1 as well as Figure 2 The organic EL element of the present invention, provided that it has at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in sequence, does not exclude the possibility of having other layers between these layers.

[0034] <Substrate> The substrate is not particularly limited and can include glass substrates, plastic substrates, etc. The substrate can be transparent or opaque. Examples of substrates include: polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, celluloid, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate phthalate, cellulose nitrocellulose, polyvinylidene chloride, polyvinyl alcohol, polyvinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyetherketone, polyimide, polyethersulfone, polyphenylene sulfide, polysulfones, polyetherimide, polyetherketoneimide, polyamide, fluoropolymers, nylon, polymethyl methacrylate, acrylic or polyarylates, organic-inorganic hybrid resins, etc.; inorganic substrates such as glass, quartz, alumina, silicon, silica, tantalum dioxide, tantalum pentoxide, indium tin oxide, etc.; metal substrates such as gold, copper, chromium, titanium, aluminum, etc.; and so on. From the viewpoint of forming transistors, glass substrates and polyimide substrates with excellent heat resistance are preferred.

[0035] Electrode (Anode) (cathode) There are no particular restrictions on the use of conductive materials that are commonly used as electrodes, such as metals, metal oxides, metal nitrides, metal borides, organic conductive compounds, and mixtures thereof, as well as the use of anodes and cathodes. Specific examples of electrodes include: conductive metal oxides such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), indium tungsten oxide (IWO), molybdenum oxide (MoO), and titanium oxide; metal nitrides such as titanium oxynitride (TiNxOx) and titanium nitride (TiN); metals such as gold (Au), platinum (Pt), silver (Ag), chromium (Cr), nickel (Ni), and aluminum (Al), as well as mixtures or laminates of these metals with conductive metal oxides; alloys such as magnesium-silver alloys, magnesium-indium alloys, and aluminum-magnesium alloys; organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, as well as laminates of these organic conductive compounds with ITO; and so on. From the perspective of work function, ITO or IGZO is preferred as the anode, and aluminum or magnesium-silver alloy is preferred as the cathode.

[0036] <Hollow Injection Layer> Aromatic amine compounds represented by the above general formula (1) can be used in the hole injection layer. In addition, known compounds can be used, such as porphyrin compounds represented by copper phthalocyanine, starburst-type triphenylamine derivatives, and aryl amine compounds having two or more structures selected from triphenylamine and carbazole structures, each linked by a single bond or a divalent group without heteroatoms. Furthermore, electron-accepting heterocyclic compounds such as hexacyanoazabenzophenanthrene and coating-type polymers such as poly(3,4-ethylenedioxythiophene) (hereinafter referred to as "PEDOT") / poly(styrene sulfonate) (hereinafter referred to as "PSS") can also be used.

[0037] These compounds and materials can be used individually or in combination for film formation. When used in combination for film formation, one example can be a substance doped with tribromophenylamine hexachloroantimony or an axylene derivative (e.g., see Patent Document 6), or a polymeric compound having a benzidine derivative such as N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (hereinafter referred to as "TPD") as a partial structure. These compounds and materials can be formed into films using known methods such as spin coating and inkjet printing, in addition to vapor deposition.

[0038] Hole transport layer In the organic EL element of the present invention, the hole transport layer contains an arylamine compound represented by the general formula (1). In general formula (1), A1 represents a single bond, a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted heterocyclic ring, or a divalent group of a substituted or unsubstituted fused polycyclic hydrocarbon. In addition, Ar1 to Ar3 are selectively the same or different from each other, and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group.

[0039] As "aromatic hydrocarbon", "heterocyclic" or "fused polycyclic hydrocarbon" in "a divalent group of a substituted or unsubstituted aromatic hydrocarbon", "a divalent group of a substituted or unsubstituted heterocyclic hydrocarbon", or "a divalent group of a substituted or unsubstituted fused polycyclic hydrocarbon", specifically, benzene, biphenyl, terphenyl, tetraphenyl, styrene, naphthalene, anthracene, acenaphthene, fluorene, phenanthrene, indene, pyrene, benzo[a]phenanthrene, pyridine, pyrimidine, triazine, pyrrole, furan, thiophene, quinoline, isoquinoline, benzo[a]furan, benzo[a]thiophene, indoline, carbazole, carboline, benzo[a]oxazole, benzo[a]thiazole, quinoxaline, benz[a]imidazolium, pyrazole, dibenzo[a]furan, dibenzo[a]thiophene, naphthidine, phenanthrene, and acridine, etc.

[0040] As for the "divalent group of an aromatic hydrocarbon", "divalent group of a heterocycle" or "divalent group of a fused polycyclic hydrocarbon" represented by A1 in general formula (1), examples can be found of divalent groups obtained by removing two hydrogen atoms from the "aromatic hydrocarbon", "heterocycle" or "fused polycyclic hydrocarbon" exemplified above. These divalent groups may optionally have substituents. Specifically, examples of substituents include: deuterium, cyano, nitro; halogen atoms such as fluorine, chlorine, bromine, and iodine; straight-chain or branched alkoxy groups with 1 to 6 carbon atoms such as methoxy, ethoxy, and propoxy; alkenyl groups such as vinyl and allyl; aryloxy groups such as phenoxy and tolyloxy; arylalkoxy groups such as benzyloxy and phenethoxy; aromatic hydrocarbon groups or fused polycyclic hydrocarbon groups such as phenyl, biphenyl, terphenyl, naphthyl, anthracene, phenanthryl, fluorenyl, indene, pyrene, perylene, fluoranyl, and benzophenanthryl; pyridyl, pyrimidine... Heterocyclic groups such as triazinyl, thiopheneyl, furanyl, pyrroleyl, quinolinyl, isoquinolinyl, benzofuranyl, benzothiopheneyl, indolyl, carbazoyl, benzoxazolyl, benzothiazoyl, quinoxalinyl, benzimidazolyl, pyrazolyl, dibenzofuranyl, dibenzothiopheneyl, and carbazoyl; disubstituted amino groups such as diphenylamino and dinaphthylamino substituted with aromatic hydrocarbon groups or fused polycyclic hydrocarbon groups; disubstituted amino groups such as dipyridylamino and dithiopheneylamino substituted with heterocyclic groups; and disubstituted amino groups substituted with substituents selected from aromatic hydrocarbon groups, fused polycyclic hydrocarbon groups, and heterocyclic groups; etc. These "substituents" may further have the substituents exemplified above.

[0041] Specifically, the "aromatic hydrocarbon group", "heterocyclic group" or "fused polycyclic hydrocarbon group" represented by Ar1 to Ar3 in general formula (1) can be exemplified by: phenyl, biphenyl, terphenyl, naphthyl, anthracene, phenanthrene, fluorenyl, indene, pyrene, perylene, fluoranyl, benzophenanthrene, pyridyl, pyrimidinyl, triazine, furanyl, pyrrolithyl, thiophene, quinolinyl, isoquinolinyl, benzofuranyl, benzothiophene, indoleyl, carbazoyl, benzooxazolyl, benzothiazoyl, quinoxalinyl, benzimidazolyl, pyrazolyl, dibenzofuranyl, dibenzothiophene, naphthidyl, phenanthrene, acridineyl, and carbazoyl, etc. These groups may have substituents, and as “substituents”, the same groups as those exemplified as “substituents” in A1 of the above general formula (1) can be listed.

[0042] In general formula (1), A1 is preferably a single bond or a substituted or unsubstituted divalent group that can be obtained by removing two hydrogen atoms from benzene, biphenyl or naphthalene, more preferably a single bond or a substituted or unsubstituted divalent group (phenylene) that can be obtained by removing two hydrogen atoms from benzene.

[0043] In general formula (1), Ar1 and Ar2 are preferably "substituted or unsubstituted aromatic hydrocarbon groups" or "substituted or unsubstituted fused polycyclic hydrocarbon groups" that are selectively the same or different from each other, and more preferably substituted or unsubstituted phenyl or substituted or unsubstituted biphenyl. Specifically, Ar1 is preferably substituted or unsubstituted phenyl, biphenyl, terphenyl, naphthyl, phenanthryl, anthracene, fluorenyl, carbazolyl, indolyl, dibenzofuranyl or dibenzothiophene, and more preferably substituted or unsubstituted biphenyl. In addition, Ar2 is preferably substituted or unsubstituted phenyl, biphenyl, terphenyl, naphthyl, phenanthryl, anthracene or fluorenyl, and more preferably substituted or unsubstituted phenyl.

[0044] In general formula (1), Ar3 is preferably substituted or unsubstituted phenyl, biphenyl, terphenyl, naphthyl, phenanthryl, fluorenyl or benzophenanthryl, more preferably substituted or unsubstituted phenyl, biphenyl or terphenyl, and especially preferably substituted or unsubstituted biphenyl.

[0045] exist Figures 3-6 Specific examples of preferred compounds among the arylamine compounds represented by the above general formula (1) are shown, but the present invention is not limited to these compounds. Furthermore, the arylamine compounds represented by the above general formula (1) can be synthesized by known methods (see, for example, Patent Document 6 and Patent Document 7).

[0046] The arylamine compounds represented by the above general formula (1) can be purified by column chromatography, adsorption purification based on silica gel, activated carbon, activated clay, etc., solvent-based recrystallization, crystallization, etc. The compounds can be identified by NMR analysis. As the physical properties of the above compounds, the glass transition temperature (Tg), HOMO level, and hole mobility (μh) are preferably measured. The glass transition temperature is an indicator of the stability of the thin film state. The HOMO level is an indicator of the smooth hole exchange between the above compounds and the adjacent first hole transport layer and the emitting layer when the above compounds are used as the second hole transport layer. In addition, the hole mobility is an indicator of the hole transport capability.

[0047] The glass transition temperature can be determined using a high-sensitivity differential scanning calorimeter (e.g., Bruker AXS, trade name: DSC3100SA) for powders. From the viewpoint of application in manufacturing processes involving heating steps and improving shelf life, a glass transition temperature of 100°C or higher is preferred, and more preferably 110°C or higher.

[0048] For a 100 nm organic film fabricated on an ITO substrate by vacuum evaporation, the HOMO energy level can be measured using an ionization potential measuring device (e.g., Sumitomo Heavy Industries, Ltd., trade name: PYS-202). From the viewpoint of the energy difference between the HOMO energy levels of adjacent light-emitting layers and the first hole transport layer, the absolute value of the HOMO energy level is preferably in the range of 5.0 eV to 7.0 eV, more preferably in the range of 5.2 eV to 5.8 eV.

[0049] Hole mobility can be measured using a time-of-flight measuring device (e.g., OPTEL, trade name: TOF-401) on an ITO substrate, for organic films of 3 μm to 4 μm thickness deposited by vacuum evaporation. From the viewpoint of efficiently transporting holes generated in the photoelectric conversion layer to the anode, a hole mobility of 1.0 × 10⁻⁶ at an electric field strength of 0.25 MV / cm is preferred. -6 (cm) 2 ( / Vs) or higher, more preferably 1.0×10 -5 (cm) 2 ( / Vs) or higher, further preferred is 1.0×10 -4 (cm) 2 / Vs) and above.

[0050] In addition to the arylamine compounds represented by the general formula (1) above, the hole transport layer may also contain other known compounds with hole transport properties. Examples of known compounds with hole transport properties include benzidine derivatives such as TPD, NPD, and N,N,N',N'-tetraphenylbenzidine; arylamine compounds having two or more structures selected from triphenylamine and carbazole structures, each linked by a single bond or a divalent group without heteroatoms; and carbazole derivatives with hole transport properties such as SiCzCz. Furthermore, coating-type polymers such as PEDOT and PSS can also be used. These materials can be formed into films individually or in combination, and each can be used as a monolayer. It can also be a stacked structure of layers formed by individual compounds or materials, a stacked structure of layers formed by mixing multiple compounds or materials, or a stacked structure of layers formed by individual compounds or materials and layers formed by mixing multiple compounds or materials. In addition to vapor deposition, these compounds and materials can also be formed into films by known methods such as spin coating and inkjet printing.

[0051] In addition to the known compounds and materials mentioned above, P-doped compounds of tribromoaniline antimony hexachloride or axialene derivatives (e.g., see Patent Document 6) and polymeric compounds having benzidine derivatives such as TPD as part of the structure can also be used in the hole transport layer.

[0052] Furthermore, in this invention, the hole transport layer can be configured as a structure comprising two or more layers, including a first hole transport layer and a second hole transport layer. When the hole transport layer is a two-layer structure, it is preferable to have an arylamine compound represented by the above general formula (1) located on the light-emitting layer side. That is, the second hole transport layer preferably contains the above arylamine compound. By using the above arylamine compound to form the second hole transport layer located on the light-emitting layer side, the electron blocking properties of the arylamine compound can be utilized to the maximum extent. As a result, an organic EL element displaying phosphorescent light emission with a lower driving voltage and a longer lifetime can be realized. In addition, when the hole transport layer is configured as a three-layer structure comprising a first hole transport layer, a second hole transport layer, and a third hole transport layer, it is preferable to use the above arylamine compound as the second hole transport layer as the intermediate layer.

[0053] Between the hole transport layer and the light-emitting layer, an electron blocking layer (not shown) can be provided to suppress the diffusion of electrons present in the light-emitting layer to the outside of the light-emitting layer (hole transport layer side). Alternatively, a material with such a function can also be used in the hole transport layer. In this case, in a hole transport layer with a 2-layer or 3-layer structure, it is preferable to use a material with this function in the hole transport layer (second hole transport layer or third hole transport layer) located on the light-emitting layer side.

[0054] <Emitting Layer> The light-emitting layer consists of a host and dopants.

[0055] (main body) In this invention, the light-emitting layer comprises one or more substrates, preferably two or more substrates. Specifically, the light-emitting layer preferably comprises at least a first substrate compound with electron transport capability and a second substrate compound with hole transport capability. One or more of the first and second substrate compounds can be used. The mass ratio of the first substrate compound to the second substrate compound can be, for example, 1:10 to 10:1.

[0056] As the first host compound, a compound having a nitrogen-containing heteroaromatic ring structure is preferred (e.g., see Patent Documents 4 and 5). As the second host compound, a compound having a carbazole structure is preferred (e.g., see Non-Patent Document 1). It should be noted that, in addition to the first host compound and the second host compound, the luminescent layer may also contain more than one host compound.

[0057] (Dopant) The light-emitting layer contains one or more dopants, at least one of which is a phosphorescent material (hereinafter also referred to as a "phosphorescent dopant"). That is, in this invention, the dopant comprises a phosphorescent material. Platinum complexes are preferred as phosphorescent materials; in addition, organometallic compounds containing Pt, Os, Ti, Zr, Hf, Eu, Tb, Tm, Fe, Co, Ni, Ru, Rh, Pd, or combinations thereof can be used. The dopant can be a blue, green, or red phosphorescent dopant, and by using them, high-performance organic EL devices can be fabricated.

[0058] As a platinum complex, it is preferably a platinum complex containing one or more polydentate ligands that form a 5-membered chelate ring with platinum, at least one of the polydentate ligands being a tetradentate ligand, and the aforementioned 5-membered chelate ring containing a carbene bond, and more preferably a platinum complex represented by the aforementioned general formula (2). Here, the aforementioned carbene bond is the bond between the 5-membered chelate ring carbene and the platinum atom, and can also be described as the structure of the 5-membered chelate ring carbene located at the platinum atom.

[0059] In general formula (2), L 1 and L 2 They are selectively the same or different from each other, and represent single bonds, NR 5 Oxygen or sulfur atoms. L 1 Preferably, oxygen or sulfur atoms, L 2 NR is preferred 5 Furthermore, in general formula (2), n1 represents 0 or 1, and n2 represents 0 or 1. 1 and Z 2 They may be selectively the same or different from each other, and represent either nitrogen or carbon atoms. R 1 ~R 5 They may be selectively the same or different from each other, and represent hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, or substituted or unsubstituted fused polycyclic hydrocarbon groups. When L 1 and L 2 At least one of them is NR 5 At that time, selected from R 5 With R 2 R 5 With R 3 and R 5 With R 4 One or more of them can bond together to form a ring through the use of single bonds, oxygen atoms, sulfur atoms, and nitrogen atoms.

[0060] As a result of R 1 ~R 5 The substituted or unsubstituted alkyl group can be exemplified by straight-chain or branched alkyl groups having 1 to 20 carbon atoms. Specifically, examples of straight-chain or branched alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, 2-ethylhexyl, heptyl, octyl, isooctyl, nonyl, and decyl. Preferably, straight-chain or branched alkyl groups having 1 to 10 carbon atoms are used. As for R... 1 ~R 5 Examples of substituted or unsubstituted alkenyl groups include straight-chain or branched alkenyl groups with 2 to 20 carbon atoms. Specifically, examples of straight-chain or branched alkenyl groups include vinyl, 1-propenyl, allyl, 1-butenyl, 2-butenyl, 1-pentenyl, 1-hexenyl, isopropenyl, and isobutenyl. Furthermore, examples of substituents that can be present in these groups include groups that are the same as those exemplified as "substituents" in A1 of the above general formula (1).

[0061] As a result of R 1 ~R 5The aromatic hydrocarbon groups, heterocyclic groups, and fused polycyclic hydrocarbon groups represented can be the same groups as those exemplified for Ar1 in the above general formula (1). In addition, as substituents that these groups may have, the same groups as those exemplified as "substituents" in A1 in the above general formula (1) can be included.

[0062] In general formula (2), R 1 Preferably, the substituted or unsubstituted alkyl, alkenyl, aromatic hydrocarbon, heterocyclic, or fused polycyclic hydrocarbon groups are used; more preferably, the substituted or unsubstituted aromatic hydrocarbon, heterocyclic, or fused polycyclic hydrocarbon groups are used. 2 ~R 4 They may be selectively the same or different from each other, and preferably are hydrogen atoms, substituted or unsubstituted alkyl groups, aromatic hydrocarbon groups, heterocyclic groups or fused polycyclic hydrocarbon groups, more preferably hydrogen atoms or substituted or unsubstituted alkyl groups (preferably having 1 to 10 carbon atoms). R 5 Preferably, the substituted or unsubstituted alkyl, aromatic hydrocarbon, heterocyclic or fused polycyclic hydrocarbon groups are used; more preferably, the substituted or unsubstituted aromatic hydrocarbon, heterocyclic or fused polycyclic hydrocarbon groups are used.

[0063] To avoid concentration quenching, the phosphorescent dopant is preferably applied to the host in the range of 1% to 30% by mass relative to the overall luminescent layer, and preferably by co-evaporation.

[0064] Furthermore, thermally activated delayed fluorescence (TADF) materials can also be used as dopants in conjunction with the aforementioned phosphorescent materials. That is, in this invention, the dopant preferably comprises both a phosphorescent material and a TADF material. Examples of TADF materials include triazine derivatives such as PIC-TRZ, CC2TA, and PBICT; phenoxazine derivatives such as PXZ-TRZ; carbazolium dicyanobenzene derivatives (CDCB derivatives) such as 4CzIPN and 4CzTPN-Me; and organoboron compounds utilizing multiple resonance effects. Among these, organoboron compounds are preferred as TADF materials.

[0065] [Chemical Formula 4]

[0066] [Chemical Formula 5]

[0067] As organoboron compounds, triarylboron compounds are preferred, and specifically, compounds represented by the following general formula (3) can be cited.

[0068] [Chemical Formula 6]

[0069] In general formula (3), R a1 ~R a3 Selectively identical or different from each other, and representing a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group, R b It indicates a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aromatic hydrocarbon group.

[0070] As a result of R a1 ~R a3 The alkyl and alkenyl groups represented can be exemplified by those corresponding to R in the above general formula (2). 1 The same groups as those illustrated. Furthermore, the substituents these groups can have are also the same. As for R... a1 ~R a3 The substituent or unsubstituted amino group can be represented by unsubstituted amino groups (-NH2), monosubstituted amino groups with 2 to 20 carbon atoms (ethylamino, acetylamino, phenylamino, pyridylamino, etc.), and disubstituted amino groups (diethylamino, diphenylamino, acetylphenylamino, phenylpyridylamino, carbazole, etc.). As a group composed of R... a1 ~R a3 The aromatic hydrocarbon groups, heterocyclic groups, and fused polycyclic hydrocarbon groups represented can be the same groups as those exemplified in Ar1 of the above general formula (1). In addition, as substituents that these groups may have, groups can be the same groups as those exemplified as "substituents" in A1 of the above general formula (1).

[0071] R a1 ~R a3 Preferably, it comprises a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted fused polycyclic hydrocarbon group; more preferably, it comprises a hydrogen atom, a substituted or unsubstituted amino group, or a substituted or unsubstituted aromatic hydrocarbon group. b Preferably, it is a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic hydrocarbon group, more preferably a substituted or unsubstituted aromatic hydrocarbon group.

[0072] Examples of compounds represented by general formula (3) include DABNA and TBE02 (see, for example, Non-Patent Document 2). Additionally, boron compounds such as ν-DABNA can also be used.

[0073] [Chemical Formula 7]

[0074] To avoid concentration quenching, the doping of TADF material into the substrate is preferably in the range of 0.1% to 10% by mass relative to the overall light-emitting layer, and doping is preferably performed by co-evaporation. In addition to evaporation, these materials can also be deposited using known methods such as spin coating and inkjet printing.

[0075] <Cavity barrier> A hole-blocking layer can be disposed between the light-emitting layer and the electron transport layer. Known compounds with hole-blocking properties can be used for the hole-blocking layer. Examples of known compounds with hole-blocking properties include phenanthrene derivatives such as copper hydroxide, metal complexes of hydroxyquinoline derivatives such as bis(2-methyl-8-hydroxyquinoline)-4-phenylphenol aluminum(III) (hereinafter referred to as "BAlq"), various rare earth complexes, oxazole derivatives, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, and benzo[a]azole derivatives. These compounds can also serve as materials for the electron transport layer. They can be formed into films individually or in mixtures, each functioning as a monolayer. The hole-blocking layer can be a stacked structure of layers formed by individually using the above-mentioned compounds, a stacked structure of layers formed by mixing the above-mentioned compounds, or a stacked structure of layers formed by individually using the above-mentioned compounds and layers formed by mixing the above-mentioned compounds. These materials can be formed into films using known methods such as spin coating and inkjet printing, in addition to vapor deposition.

[0076] <Electron transport layer> The electron transport layer can utilize known compounds with electron transport properties. Examples of known compounds with electron transport properties include metal complexes of hydroxyquinoline derivatives (represented by Alq3 and BAlq), various metal complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, pyridine derivatives, benzimidazole derivatives, benzoxazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and thiophene derivatives. These materials can be formed into films individually or in mixtures, each functioning as a monolayer. The electron transport layer can be a stacked structure of layers formed by individually using the aforementioned compounds, a stacked structure of layers formed by mixing the aforementioned compounds, or a stacked structure of layers formed by individually using the aforementioned compounds and layers formed by mixing the aforementioned compounds. These materials can be formed into films using known methods such as spin coating and inkjet printing, in addition to vapor deposition.

[0077] <Electron Injection Layer> In the electron injection layer, alkali metal salts such as lithium fluoride and cesium fluoride, alkaline earth metal salts such as magnesium fluoride, metal complexes of hydroxyquinoline derivatives such as lithium hydroxyquinoline, metal oxides such as alumina, and metals such as ytterbium (Yb), samarium (Sm), calcium (Ca), strontium (Sr), and cesium (Cs) can be used. It should be noted that by selecting an optimal combination of the electron transport layer and the cathode, the electron injection layer can be omitted.

[0078] In the electron injection layer and electron transport layer, materials that are n-type doped with metals such as cesium can be used. Furthermore, the thickness of each of the aforementioned layers constituting the organic EL device is not limited and can be appropriately selected.

[0079] The embodiments of the present invention will be specifically described below using examples, but the present invention is not limited to the following examples.

[0080] Example [Synthetic Example 1: Synthesis of Compound (1-21)] As compounds represented by the general formula (1), compounds (1-21) having the following structures were synthesized.

[0081] In a reaction vessel, 14.5 g of biphenyl-4-yl-[1,2';1',1'';4'',1''']-tetraphenyl-4'-yl-amine, 9.3 g of 9-(4-bromo-phenyl)-phenanthrene, 3.2 g of sodium tert-butoxide, and 93 mL of toluene were added, and nitrogen gas was introduced while the mixture was irradiated with ultrasound for 30 minutes. Next, 0.1 g of palladium(II) acetate and 0.2 g of tris(tert-butyl)phosphine were added, and the mixture was refluxed and stirred for 3 hours. After natural cooling, water was added to the system, and the precipitated solid was filtered to obtain a crude product. The crude product was purified by crystallization using a monochlorobenzene / acetone mixed solvent, yielding 14.0 g (69% yield) of a white powder of compound (1-21). The structure of the obtained white powder was identified using NMR. 1 H-NMR (CDCl3) detected the signals of the following 39 hydrogen atoms.

[0082] δ (ppm) = 8.84 (1H), 8.77 (1H), 8.14 (1H), 7.90 (1H), 7.80 (1H), 7.78-7.60 (10H), 7.60-7.33 (17H), 7.33-7.20 (7H).

[0083] [Chemical Formula 8]

[0084] [Example 1: Determination of glass transition temperature] The glass transition temperatures of the above compounds (1-21) and the SiCzCz compound disclosed in Non-Patent Document 1, which has the following structure, were determined using a high-sensitivity differential scanning calorimeter (Bruker AXS, trade name: DSC3100SA). The results are summarized in Table 1.

[0085] [Chemical Formula 9]

[0086] [Table 1]

[0087] As shown in Table 1, the compound (1-21) of Example 1 has a high glass transition temperature of over 110°C, and the thin film is stable. In addition, it can be seen that the glass transition temperature of compound (1-21) is equal to or higher than that of SiCzCz. By using compound (1-21) in organic EL devices, devices with excellent thermal stability can be fabricated.

[0088] [Example 2: Determination of HOMO energy levels] Using the compounds (1-21) of the present invention, the comparative compound (SiCzCz), and BCFN with the following structure commonly used as a first hole transport material (see, for example, Non-Patent Document 1), vapor-deposited films with a thickness of 100 nm were fabricated on ITO substrates. The work function (equivalent to the absolute value of the HOMO energy level) of the obtained vapor-deposited films was measured using an ionization potential measuring device (Sumitomo Heavy Industries, Ltd., trade name: PYS-202). The results are summarized in Table 2.

[0089] [Chemical Formula 10]

[0090] [Table 2]

[0091] As shown in Table 2, compared with the comparative compound (SiCzCz), compound (1-21) has a smaller energy difference with the HOMO level of BCFN, and from the perspective of hole transport, it has an appropriate HOMO level.

[0092] [Example 3: Determination of the T1 energy level] Prepare 2-methyltetrahydrofuran solutions (10g) of compounds (1-21) of the present invention, comparative compound (SiCzCz), and BCFN with the structure described above, which are commonly used as first hole transport materials. -5The phosphorescence spectrum was measured at 77 K using a spectrophotometer (manufactured by Nippon Spectrophotometer Co., Ltd., trade name: FP-8500). The T1 energy levels calculated from the starting edge of the phosphorescence spectrum are summarized in Table 3.

[0093] [Table 3]

[0094] As shown in Table 3, the T1 energy level of compounds (1-21) is lower than that of SiCzCz and BCFN. However, by using carbazole compounds as hole transport hosts in the luminescent layer, the recombination region can be moved away from the interface between the hole transport layer and the luminescent layer, thus suppressing the efficiency reduction caused by the low T1 energy level.

[0095] [Example 4: Determination of hole mobility] Using the compounds (1-21) of this invention and the comparative compound (SiCzCz), an organic compound of the test object was deposited on a glass substrate with ITO by vacuum evaporation to a film thickness of 3 μm to 4 μm. Then, aluminum was deposited to a film thickness of approximately 100 nm, thereby fabricating an element for hole mobility measurement. To prevent degradation caused by the adsorption of moisture and oxygen, the element was sealed in a nitrogen atmosphere with a glass cover fitted with a moisture-removing sheet for organic electroluminescence. The hole mobility of the element was measured using a transient photocurrent measuring device under the following conditions. The results are shown in Table 4.

[0096] (Measurement conditions) Device: Time of Flight (TOF-401) (trade name, manufactured by OPTEL) Excitation source: Nitrogen laser (337.1nm) Optical pulse width: less than 1 nsec Measured area: 0.04 cm² 2 Sample temperature: 25℃ Load resistance: 50Ω Electric field strength: 0.25 MV / cm [Table 4]

[0097] As shown in Table 4, the hole mobility of compound (1-21) is more than 20 times that of the comparative compound (SiCzCz). By using compound (1-21) in the second hole transport layer of an organic EL device, holes supplied from the first hole transport layer can be efficiently transported to the light-emitting layer, thereby improving the driving voltage.

[0098] [Example 5: Evaluation of Organic EL Components] like Figure 1 As shown, an ITO electrode is pre-formed on a glass substrate 1 as a transparent anode 2, and a hole injection layer 3, a first hole transport layer 4a, a second hole transport layer 4b, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 are sequentially deposited on it, thereby fabricating an organic EL device with a hole transport layer structure of 2 layers.

[0099] Specifically, a glass substrate 1 with an ITO film thickness of 150 nm was ultrasonically cleaned in isopropanol for 20 minutes, and then dried on a hot plate heated to 200°C for 10 minutes. After a 15-minute UV ozone treatment, the ITO-coated glass substrate was placed in a vacuum evaporation machine and the pressure was reduced to below 0.001 Pa. Next, with a transparent anode 2 covered, a binary evaporation was performed on the electron acceptor (Acceptor-1) and the BCFN with a evaporation rate ratio of Acceptor-1:BCFN = 3:97, thereby forming a hole injection layer 3 with a thickness of 10 nm. The BCFN was then deposited on the hole injection layer 3 with a thickness of 55 nm as a first hole transport layer 4a. The compounds of the present invention (1-21) were then deposited on the first hole transport layer 4a with a thickness of 10 nm as a second hole transport layer 4b. On the second hole transport layer 4b, a ternary deposition process was performed on a hole transport host (SiCzCz), an electron transport host (SiTrzCz2) with the following structure, and a blue phosphorescent dopant (PtON-TBBI) with the following structure, at a deposition rate ratio of SiCzCz:SiTrzCz2:PtON-TBBI = 60:27:13, forming a light-emitting layer 5 with a film thickness of 30 nm. On the light-emitting layer 5, an mSiTrz structure with the following structure was deposited with a film thickness of 5 nm as a hole blocking layer 6. On the hole blocking layer 6, an electron transport layer 7 with a film thickness of 30 nm was formed by binary deposition of ETM-1 and ETM-2 with the following structure at a deposition rate ratio of ETM-1:ETM-2 = 50:50. On the electron transport layer 7, an ETM-2 structure with a film thickness of 1 nm was deposited with an electron injection layer 8. Finally, 100nm of aluminum was vapor-deposited to form the cathode 9, thus fabricating an organic EL element.

[0100] [Chemical Formula 11]

[0101] [Comparative Example 1] For comparison, instead of compounds (1-21), SiCzCz was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 5.

[0102] [Comparative Example 2] For comparison, instead of compounds (1-21), BCFN was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 5.

[0103] The organic EL elements prepared in Example 5 and Comparative Examples 1 and 2 were driven by direct current to emit light in the atmosphere at room temperature, and the luminance was measured to be 1000 cd / m². 2 The driving voltage, power efficiency, and lifetime with brightness reduced to 95% (setting the starting emission level to 100%) were measured. The measurement results are summarized in Table 5.

[0104] [Table 5]

[0105] As shown in Table 5, for a brightness of 1000 cd / m² 2 Regarding the driving voltage, the organic EL element of Example 5 has a low driving voltage of 3.80V, compared to 4.10V to 4.25V for the organic EL elements of Comparative Examples 1 and 2. Furthermore, in terms of power efficiency, the organic EL element of Example 5 has a high power efficiency of 16.5lm / W, compared to 13.5m / W to 15.3lm / W for the organic EL elements of Comparative Examples 1 and 2. Moreover, in terms of device lifetime, the organic EL element of Example 5 has a long lifetime of 60 hours, compared to 39 hours to 50 hours for the organic EL elements of Comparative Examples 1 and 2. These results demonstrate that the driving voltage of organic EL elements can be significantly improved through the appropriate HOMO energy level and high hole mobility of the arylamine compound represented by general formula (1).

[0106] [Example 6: Evaluation of Organic EL Components] like Figure 2 As shown, an ITO electrode is pre-formed on a glass substrate 1 as a transparent anode 2, and a hole injection layer 3, a first hole transport layer 4a, a second hole transport layer 4b, a third hole transport layer 4c, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 are sequentially deposited on it, thereby fabricating an organic EL device with a three-layer hole transport layer structure.

[0107] Specifically, a glass substrate 1 with an ITO film thickness of 150 nm was ultrasonically cleaned in isopropanol for 20 minutes, and then dried on a hot plate heated to 200°C for 10 minutes. After a 15-minute UV ozone treatment, the ITO-coated glass substrate was placed in a vacuum evaporation machine, and the pressure was reduced to below 0.001 Pa. Next, with a transparent anode 2 covered, a binary evaporation of the electron acceptor (Acceptor-1) and the BCFN was performed at a evaporation rate of Acceptor-1:BCFN = 3:97, thereby forming a hole injection layer 3 with a thickness of 10 nm. On the hole injection layer 3, the BCFN was deposited with a thickness of 55 nm as a first hole transport layer 4a. On the first hole transport layer 4a, the compounds of the present invention (1-21) were deposited with a thickness of 5 nm as a second hole transport layer 4b. SiCzCz was deposited on the second hole transport layer 4b with a thickness of 5 nm to form the third hole transport layer 4c. On the third hole transport layer 4c, a ternary deposition process was performed on the hole transport host (SiCzCz), the electron transport host (SiTrzCz2), and the blue phosphorescent dopant (PtON-TBBI) at a deposition rate ratio of SiCzCz:SiTrzCz2:PtON-TBBI = 60:27:13, thereby forming a 30 nm thick light-emitting layer 5. On the light-emitting layer 5, the mSiTrz was deposited with a thickness of 5 nm to form the hole blocking layer 6. On the hole blocking layer 6, ETM-1 and ETM-2 were binary deposited at a deposition rate ratio of ETM-1:ETM-2 = 50:50, thereby forming a 30 nm thick electron transport layer 7. ETM-2 was deposited on electron transport layer 7 with a thickness of 1 nm as electron injection layer 8. Finally, 100 nm of aluminum was deposited to form cathode 9, thus fabricating an organic EL device.

[0108] [Comparative Example 3] For comparison, instead of compounds (1-21), SiCzCz was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 6.

[0109] [Comparative Example 4] For comparison, instead of compounds (1-21), BCFN was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 6.

[0110] The organic EL elements prepared in Example 6, Comparative Examples 3 and 4 were driven by direct current to emit light in the atmosphere at room temperature, and the luminance was measured to be 1000 cd / m². 2The driving voltage, power efficiency, and brightness are reduced to 95% of the lifetime. The measurement results are summarized in Table 6.

[0111] [Table 6]

[0112] As shown in Table 6, for a brightness of 1000 cd / m² 2 Regarding the driving voltage, the organic EL element of Example 6 has a low driving voltage of 4.00V, compared to 4.11V to 4.25V for the organic EL elements of Comparative Examples 3 and 4. Furthermore, in terms of power efficiency, the organic EL element of Example 6 has a high power efficiency of 17.0lm / W, compared to 15.3 to 16.0lm / W for the organic EL elements of Comparative Examples 3 and 4. Moreover, in terms of device lifetime, the organic EL element of Example 6 has a long lifetime of 65 hours, compared to 49 to 50 hours for the organic EL elements of Comparative Examples 3 and 4. This result indicates that when an arylamine compound represented by general formula (1) is used in the middle layer (second hole transport layer) of a hole transport layer with a three-layer structure, the driving voltage of the organic EL element can be significantly improved through the appropriate HOMO energy level and high hole mobility of this compound.

[0113] [Example 7: Evaluation of Organic EL Components] like Figure 1 As shown, an ITO electrode is pre-formed on a glass substrate 1 as a transparent anode 2, and a hole injection layer 3, a first hole transport layer 4a, a second hole transport layer 4b, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 are sequentially deposited on it, thereby fabricating an organic EL element that combines phosphorescent light-emitting material and TADF material.

[0114] Specifically, a glass substrate 1 with an ITO film thickness of 150 nm was ultrasonically cleaned in isopropanol for 20 minutes and then dried on a hot plate heated to 200°C for 10 minutes. After a 15-minute UV ozone treatment, the ITO-coated glass substrate was placed in a vacuum evaporation machine and the pressure was reduced to below 0.001 Pa. Next, with a transparent anode 2 covered, binary evaporation was performed on the electron acceptor (Acceptor-1) and the BCFN at a evaporation rate ratio of Acceptor-1:BCFN = 3:97, thereby forming a hole injection layer 3 with a thickness of 10 nm. On the hole injection layer 3, the BCFN was deposited with a thickness of 55 nm as a first hole transport layer 4a. On the first hole transport layer 4a, the compounds of the present invention (1-21) were deposited with a thickness of 10 nm as a second hole transport layer 4b. On the second hole transport layer 4b, a quaternary deposition process is performed on the hole transport host (SiCzCz), the electron transport host (SiTrzCz2), the blue phosphorescent dopant (PtON-TBBI), and the TADF dopant (TBE02) with the structure disclosed in Non-Patent Document 2, at a deposition rate of SiCzCz:SiTrzCz2:PtON-TBBI:TBE02 = 60:27:12:1, thereby forming a light-emitting layer 5 with a film thickness of 30 nm. On the light-emitting layer 5, the aforementioned mSiTrz is deposited with a film thickness of 5 nm as a hole blocking layer 6. On the hole blocking layer 6, ETM-1 and ETM-2 are binary deposited at a deposition rate of ETM-1:ETM-2 = 50:50, thereby forming an electron transport layer 7 with a film thickness of 30 nm. ETM-2 was deposited on electron transport layer 7 with a thickness of 1 nm as electron injection layer 8. Finally, 100 nm of aluminum was deposited to form cathode 9, thus fabricating an organic EL device.

[0115] [Chemical Formula 12]

[0116] [Comparative Example 5] For comparison, instead of compounds (1-21), SiCzCz was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 7.

[0117] [Comparative Example 6] For comparison, instead of compounds (1-21), BCFN was used as the material for the second hole transport layer 4b, and an organic EL element was fabricated under the same conditions as in Example 7.

[0118] The organic EL elements prepared in Example 7, Comparative Examples 5 and 6 were driven by direct current to emit light in the atmosphere at room temperature, and the luminance was measured to be 1000 cd / m². 2 The driving voltage, power efficiency, and brightness are reduced to 95% of the lifetime. The measurement results are summarized in Table 7.

[0119] [Table 7]

[0120] As shown in Table 7, for a brightness of 1000 cd / m² 2 Regarding the driving voltage, the organic EL device of Example 7 has a low driving voltage of 3.93V, compared to 4.10V to 4.35V for the organic EL devices of Comparative Examples 5 and 6. Furthermore, in terms of power efficiency, the organic EL device of Example 7 has a high power efficiency of 15.8lm / W, compared to 13.6m / W to 14.6lm / W for the organic EL devices of Comparative Examples 5 and 6. Moreover, in terms of device lifetime, the organic EL device of Example 7 has a long lifetime of 55 hours, compared to 29 hours to 49 hours for the organic EL devices of Comparative Examples 5 and 6. These results demonstrate that in organic EL devices having a second hole transport layer comprising a compound represented by general formula (1) and a light-emitting layer comprising a phosphorescent dopant and a TADF dopant, the driving voltage of the organic EL device can be significantly improved through appropriate HOMO energy levels and high hole mobility.

[0121] As described above, the organic EL element of the present invention, which uses a compound represented by general formula (1) in the second hole transport layer, has a HOMO energy level suitable for hole movement from the first hole transport layer, high heat resistance, and high hole mobility, and is an organic EL element with low driving voltage and long lifetime. It is known that by adopting the structure represented by general formula (1) in the hole transport layer, compared with organic EL elements using conventional materials, it is possible to achieve an organic EL element that exhibits phosphorescent emission with excellent characteristics of reduced driving voltage, improved power efficiency, and long lifetime.

[0122] The organic EL element of the present invention, which uses an arylamine compound with a specific structure, not only reduces the driving voltage but also improves durability, and can be used for applications such as home appliances and lighting.

[0123] (Explanation of reference numerals in the attached image) 1: Substrate 2: Anode 3: Hole injection layer 4: Hole transport layer 4a: First hole transport layer 4b: Second Hole Transport Layer 4c: Third hole transport layer 5: Emissive layer 6: Cavity blocking layer 7: Electron transport layer 8: Electron injection layer 9: Cathode

Claims

1. An organic electroluminescent element, comprising at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in sequence, characterized in that, The hole transport layer contains an arylamine compound represented by the following general formula (1), and the light-emitting layer contains a host and a dopant, the dopant comprising a phosphorescent material. [Chemical Formula 1] In the formula, A1 represents a single bond, a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted heterocycle, or a divalent group of a substituted or unsubstituted fused polycyclic hydrocarbon. Ar1 to Ar3 are selectively the same or different from each other and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group.

2. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), A1 is a single bond or a substituted or unsubstituted phenylene.

3. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), Ar1 and Ar2 are substituted or unsubstituted phenyl or substituted or unsubstituted biphenyl, which are selectively the same or different from each other.

4. The organic electroluminescent element according to claim 1, wherein, In the general formula (1), Ar3 is a substituted or unsubstituted phenyl, a substituted or unsubstituted biphenyl, or a substituted or unsubstituted terphenyl.

5. The organic electroluminescent element according to any one of claims 1 to 4, wherein, The hole transport layer has a structure of two or more layers including a first hole transport layer and a second hole transport layer, wherein the second hole transport layer contains an arylamine compound represented by the general formula (1).

6. The organic electroluminescent element according to claim 1, wherein, The host compound contains a first host compound with electron transport capability and a second host compound with hole transport capability, the second host compound comprising a compound having a carbazole structure.

7. The organic electroluminescent element according to claim 1, wherein, Platinum complexes are used as the phosphorescent luminescent material.

8. The organic electroluminescent element according to claim 7, wherein, The platinum complex comprises one or more polydentate ligands that form a 5-membered chelate ring with platinum, at least one of which is a tetradentate ligand, and the 5-membered chelate ring comprises a carbene bond.

9. The organic electroluminescent element according to claim 8, wherein, The platinum complex is represented by the following general formula (2), [Chemical Formula 2] In the formula, L 1 and L 2 They are selectively the same or different from each other, and represent single bonds, NR 5 oxygen or sulfur atoms n1 represents 0 or 1, n2 represents 0 or 1. Z 1 and Z 2 They may be selectively the same or different from each other, and represent either nitrogen atoms or carbon atoms. R 1 ~R 5 They may be selectively the same or different from each other, and represent hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted aromatic hydrocarbon groups, substituted or unsubstituted heterocyclic groups, or substituted or unsubstituted fused polycyclic hydrocarbon groups. When L 1 and L 2 At least one of them is NR 5 At that time, selected from R 5 With R 2 R 5 With R 3 and R 5 With R 4 One or more of them selectively bond with each other to form a ring.

10. The organic electroluminescent element according to any one of claims 7 to 9, wherein, The dopants include platinum complexes used as phosphorescent materials and thermally activated delayed fluorescence (TADF) materials.

11. The organic electroluminescent element according to claim 1, wherein, The arylamine compound represented by the general formula (1) has a hole mobility of 1.0 × 10⁻⁶ at an electric field strength of 0.25 MV / cm. -5 cm 2 / Vs and above.

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