Organic electroluminescent element

Abstract

Provided is an organic EL element in which high efficiency, low drive voltage, and highly durable phosphorescent emission are achieved by combining an organic compound having excellent hole injection / transport performance and electron blocking capability, high stability in a thin film state, and high emission efficiency, with various materials for an organic EL element having excellent hole and electron injection / transport performance, electron blocking capability, stability in a thin film state, and durability so that the characteristics of the respective materials can be effectively exhibited. This organic electroluminescent element comprises an anode, a hole transport layer, an emission layer, an electron transport layer, and a cathode in this order, wherein the hole transport layer contains an aryl amine compound represented by general formula (1). The emission layer contains a host and a dopant, the dopant containing a phosphorescent emission material.　In the formula, A1 represents a divalent group, for example, of an aromatic hydrocarbon, and Ar1 to Ar3 represent an aromatic hydrocarbon group, for example.

Description

organic electroluminescence element

[0001] The present invention relates to an organic electroluminescence element (hereinafter also abbreviated as "organic EL element") suitable for various display devices, and more particularly to an organic EL element using a specific arylamine compound.

[0002] Organic EL elements are self-luminous elements, and therefore are brighter and more visible than liquid crystal elements, and are capable of producing clearer displays, and therefore have been the subject of vigorous research.

[0003] In 1987, C. W. Tang et al. of Eastman Kodak Company made organic EL devices using organic materials practical by developing a layered structure element in which various roles are assigned to each material. They layered tris(8-hydroxyquinoline)aluminum (hereinafter abbreviated as "Alq3"), a phosphor capable of transporting electrons, and an aromatic amine compound capable of transporting holes, and injected both charges into the phosphor layer to emit light, achieving 1000 cd / m at a voltage of 10 V or less. ２ Such high brightness was obtained (see, for example, Patent Documents 1 and 2).

[0004] To date, many improvements have been made to the practical application of organic EL elements, and various functions have been further subdivided to achieve high efficiency and durability by electroluminescent elements in which an anode, a hole injection layer, a hole transport layer, an emitting layer, an electron transport layer, an electron injection layer, and a cathode are sequentially provided on a substrate. Furthermore, in order to further improve luminous efficiency, studies have been conducted on utilizing phosphorescence accompanying transition from a triplet excited state to a ground state, and Patent Document 3 proposes a blue phosphorescent organic EL element using a platinum complex as a phosphorescent emitting material.

[0005] In Patent Documents 4 and 5, a host compound having a nitrogen-containing heteroaromatic ring structure and an electron transporting ability is used in combination with a host compound having a carbazole structure and a hole transporting ability in an emitting layer, thereby improving the electron and hole transporting properties and the luminous efficiency compared to when these compounds are used alone.

[0006] Non-Patent Document 1 discloses a blue phosphorescent organic EL device in which an emitting layer is formed by combining a platinum complex having a specific structure with a host material having electron transport ability and a host material having hole transport ability. The carbazole derivative (e.g., SiCzCz shown below) used as the host material in Non-Patent Document 1 has recently been proposed as a hole transport material or a host material having hole transport ability in phosphorescent organic EL devices.

[0007]

[0008] Japanese Patent Publication No. 8-048656, Japanese Patent No. 3194657, International Publication No. 2012 / 116231, Japanese Patent Publication No. 2016-532307, U.S. Patent Application Publication No. 2017 / 0104163, Japanese Patent No. 6715781, International Publication No. 2021 / 079856, International Publication No. 2014 / 009310

[0009] Nature Photonics, 2022, Vol. 16, p. 212-218 Eungdo Kim et al., Science Advances, 2022, Vol. 8, Issue 41

[0010] Although SiCzCz has a high triplet excitation energy (hereinafter referred to as "T1 level"), molecular design that increases the T1 level limits pi conjugation, resulting in a problem of low hole mobility. Therefore, when SiCzCz is combined with an emitting layer with improved electron transport ability, the supply of holes to the emitting layer becomes rate-limiting, raising concerns about the occurrence of an electron excess bias in the emitting layer. Furthermore, in devices using SiCzCz as a second hole transport layer, the device driving voltage increases, and the electron excess bias in the emitting layer results in insufficient device life. Therefore, there is a demand for a second hole transport material that has high hole mobility and excellent durability against electrons.

[0011] An object of the present invention is to provide an organic EL device that exhibits phosphorescent emission with high efficiency, low driving voltage, and high durability by combining an organic compound having excellent properties, such as excellent hole injection / transport performance, electron blocking ability, high stability in a thin film state, and high luminous efficiency, with various materials for organic EL devices that have excellent hole and electron injection / transport performance, electron blocking ability, stability in a thin film state, and durability, in a manner that allows the properties of each material to be effectively exhibited.

[0012] The physical properties that the organic compound used in the organic EL device of the present invention should have include (1) good hole injection properties, (2) high hole mobility, (3) excellent electron blocking ability, (4) a stable thin film state, and (5) excellent heat resistance. Furthermore, the physical properties that the organic EL device of the present invention should have include (1) a low light emission initiation voltage, (2) a low practical driving voltage, and (3) a long life.

[0013] In order to achieve the above object, the present inventors focused on the fact that arylamine compounds having a specific structure have excellent hole injection / transport capabilities, thin film stability, and durability, and selected various arylamine compounds to prepare organic EL devices and thoroughly evaluated the device characteristics. As a result, the present inventors discovered that selecting an arylamine compound having a specific structure as a material for the hole transport layer can efficiently transport holes injected from the anode side. Furthermore, they prepared various organic EL devices by combining the arylamine compound with a light-emitting material having a specific structure, and thoroughly evaluated the device characteristics. As a result, they have completed the present invention.

[0014] That is, according to the present invention, the following organic electroluminescence device is provided.

[0015] 1) An organic electroluminescence device having at least an anode, a hole transport layer, an emitting layer, an electron transport layer, and a cathode in this order, characterized in that the hole transport layer contains an arylamine compound represented by the following general formula (1), the emitting layer contains a host and a dopant, and the dopant contains a phosphorescent material:

[0016]

[0017] 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 heterocyclic ring, or a divalent group of a substituted or unsubstituted condensed polycyclic hydrocarbon; Ar １ ~Ar ３ may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group.

[0018] 2) The organic electroluminescence device according to 1), wherein in the general formula (1), A1 is a single bond or a substituted or unsubstituted phenylene group.

[0019] 3) In the general formula (1), Ar １ and Ar ２ and may be the same or different and are a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenylyl group.

[0020] 4) In the general formula (1), Ar ３ is a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenylyl group, or a substituted or unsubstituted terphenylyl group.

[0021] 5) The organic electroluminescence device according to any one of 1) to 4), wherein the hole transport layer has a two or more layer structure including a first hole transport layer and a second hole transport layer, and the second hole transport layer contains the arylamine compound represented by general formula (1).

[0022] 6) The organic electroluminescence device according to any one of 1) to 5), wherein the host contains a first host compound having an electron transporting ability and a second host compound having a hole transporting ability, and the second host compound includes a compound having a carbazole structure.

[0023] 7) The organic electroluminescence device according to any one of 1) to 6), wherein a platinum complex is used as the phosphorescent material.

[0024] 8) The organic electroluminescence device according to 7), wherein the platinum complex contains one or more polydentate ligands that form a five-membered chelate ring with platinum, at least one of the polydentate ligands being a tetradentate ligand, and the five-membered chelate ring contains a carbene bond.

[0025] 9) The organic electroluminescence device according to 8), wherein the platinum complex is represented by the following general formula (2):

[0026]

[0027] In the ceremony, L １ and L ２ may be the same or different, and may represent a single bond, NR ５ , an oxygen atom, or a sulfur atom; １ represents 0 or 1, n ２ represents 0 or 1, Z １ and Z ２ may be the same or different and represent a nitrogen atom or a carbon atom; R １ ~R ５ may be the same or different and represent a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group; L １ and L ２ At least one of the following is NR ５ If R ５ and R ２ , R ５ and R ３ , and R ５ and R ４may be bonded to each other to form a ring.

[0028] 10) The organic electroluminescence device according to any one of 7) to 9), wherein the dopant comprises a platinum complex as a phosphorescent light-emitting material and a thermally activated delayed fluorescence (TADF) material.

[0029] 11) The arylamine compound represented by the general formula (1) has a hole mobility of 1.0×10 at an electric field strength of 0.25 MV / cm. -５ cm ２ 11. The organic electroluminescence device according to any one of 1) to 10), wherein the Vref is 0.1 V or more.

[0030] The arylamine compound of the present invention represented by the general formula (1) has the following properties: (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 of the general formula (1) which has higher hole mobility than conventional hole transport materials, excellent electron blocking ability, excellent amorphousness, and stable thin film state, it is possible to realize an organic EL device that exhibits phosphorescent emission, has high power efficiency, a low driving voltage, and a long life.

[0031] FIG. 1 is a diagram showing an example of an organic EL element configuration having a hole transport layer with a two-layer structure. FIG. 2 is a diagram showing an example of an organic EL element configuration having a hole transport layer with a three-layer structure. FIG. 3 is a diagram showing structures of compounds (1-1) to (1-15) as examples of compounds represented by general formula (1). FIG. 4 is a diagram showing structures of compounds (1-16) to (1-27) as examples of compounds represented by general formula (1). FIG. 5 is a diagram showing structures of compounds (1-28) to (1-39) as examples of compounds represented by general formula (1). FIG. 6 is a diagram showing structures of compounds (1-40) to (1-48) as examples of compounds represented by general formula (1).

[0032] The organic EL device of the present invention has at least an anode, a hole transport layer, an emissive layer, an electron transport layer, and a cathode, in this order. In addition, in the present invention, the hole transport layer contains an arylamine compound represented by the general formula (1), the emissive layer contains a host and a dopant, and the dopant contains a phosphorescent material.

[0033] As shown in FIG. 1 , an organic EL device according to one embodiment of the present invention has a structure in which an anode 2, a hole transport layer 4, an emitting layer 5, an electron transport layer 7, and a cathode 9 are stacked in this order on a substrate 1. The organic EL device of the present invention may have a hole injection layer 3 between the anode and the hole transport layer, a hole blocking layer 6 between the emitting layer and the electron transport layer, or an electron injection layer 8 between the electron transport layer and the cathode. In these multilayer structures, some organic layers may be omitted or may serve as both layers. For example, a layer may serve as both a hole injection layer and a hole transport layer, or a layer may serve as both an electron injection layer and an electron transport layer. Two or more organic layers having the same function may also be stacked. FIG. 1 shows an example of a structure in which two hole transport layers are stacked, including a first hole transport layer 4a and a second hole transport layer 4b. As shown in FIG. 2 , a third hole transport layer 4c may be stacked on the second hole transport layer 4b, resulting in a three-layer hole transport layer structure. However, the organic EL element of the present invention is not limited to the embodiments shown in Figures 1 and 2. As long as the organic EL element of the present invention has at least an anode, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in this order, it does not exclude embodiments in which other layers are present between the layers.

[0034] <Substrate> The substrate is not particularly limited, and may be a glass substrate, a plastic substrate, etc. The substrate may be transparent or opaque. Examples of substrates include plastic substrates such as polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate phthalate, cellulose nitrate, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide, polyether sulfone, polyphenylene sulfide, polysulfones, polyether imide, polyether ketone imide, polyamide, fluororesin, nylon, polymethyl methacrylate, acrylic or polyarylate, and organic-inorganic hybrid resins; inorganic substrates such as glass, quartz, aluminum oxide, silicon, silicon oxide, tantalum dioxide, tantalum pentoxide, and indium tin oxide; and metal substrates such as gold, copper, chromium, titanium, and aluminum. Among these, glass substrates and polyimide substrates, which have excellent heat resistance, are preferred from the viewpoint of transistor formation.

[0035] <Electrodes (Anode and Cathode)> The anode and cathode are not particularly limited as long as they are conductive materials that are generally used as electrodes, and metals, metal oxides, metal nitrides, metal borides, organic conductive compounds, and mixtures thereof can be used. 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); mixtures or laminates of these metals and 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; and laminates of these organic conductive compounds and ITO. Among these, from the viewpoint of work function, ITO or IGZO is preferred as the anode, and aluminum or magnesium-silver alloys is preferred as the cathode.

[0036] <Hole Injection Layer> The hole injection layer can be formed using an arylamine compound represented by the general formula (1). Other known compounds that can be used include porphyrin compounds such as copper phthalocyanine, starburst triphenylamine derivatives, and arylamine compounds having two or more structures selected from triphenylamine structures and carbazolyl structures in the molecule, each structure linked by a single bond or a divalent group not containing a heteroatom. Acceptor heterocyclic compounds such as hexacyanoazatriphenylene and coating-type polymeric materials such as poly(3,4-ethylenedioxythiophene) (hereinafter abbreviated as "PEDOT") / poly(styrene sulfonate) (hereinafter abbreviated as "PSS") can also be used.

[0037] These compounds and materials may be used alone for film formation, or a mixture of two or more types may be used for film formation. When a mixture of two or more types is used for film formation, one of the compounds may be a P-doped compound such as trisbromophenylaminehexachloroantimony or a radialene derivative (see, for example, Patent Document 6), or a polymer compound having a benzidine derivative such as N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (hereinafter abbreviated as "TPD") as a partial structure. These compounds and materials can be used for film formation by known methods such as vapor deposition, spin coating, and inkjet printing.

[0038] <Hole transport layer> In the organic EL device of the present invention, the hole transport layer contains an arylamine compound represented by the general formula (1). In the 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 condensed polycyclic hydrocarbon. １ ~Ar ３ may be the same or different 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] Specific examples of the "aromatic hydrocarbon," "heterocyclic ring," or "fused polycyclic hydrocarbon" in the "divalent substituted or unsubstituted aromatic hydrocarbon group," "divalent substituted or unsubstituted heterocyclic ring group," or "divalent substituted or unsubstituted fused polycyclic hydrocarbon group" represented by A1 in general formula (1) include benzene, biphenyl, terphenyl, tetrakisphenyl, styrene, naphthalene, anthracene, acenaphthalene, fluorene, phenanthrene, indane, pyrene, triphenylene, pyridine, pyrimidine, triazine, pyrrole, furan, thiophene, quinoline, isoquinoline, benzofuran, benzothiophene, indoline, carbazole, carboline, benzoxazole, benzothiazole, quinoxaline, benzimidazole, pyrazole, dibenzofuran, dibenzothiophene, naphthyridine, phenanthroline, and acridine.

[0040] Examples of the "divalent aromatic hydrocarbon group," "divalent heterocyclic group," or "divalent fused polycyclic hydrocarbon group" in the "divalent substituted or unsubstituted aromatic hydrocarbon group," "divalent substituted or unsubstituted heterocyclic group," or "divalent substituted or unsubstituted fused polycyclic hydrocarbon group" represented by A1 in general formula (1) include divalent groups obtained by removing two hydrogen atoms from the above-mentioned "aromatic hydrocarbon," "heterocyclic ring," or "fused polycyclic hydrocarbon." These divalent groups may have a substituent, and specific examples of the "substituent" include a deuterium atom, a cyano group, a nitro group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom; a linear or branched alkyloxy group having 1 to 6 carbon atoms such as a methyloxy group, an ethyloxy group, and a propyloxy group; an alkenyl group such as a vinyl group and an allyl group; an aryloxy group such as a phenyloxy group and a tolyloxy group; an arylalkyloxy group such as a benzyloxy group and a phenethyloxy group; an aromatic hydrocarbon group or a condensed polycyclic group such as a phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl group, an anthryl group, a phenanthryl group, a fluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, and a triphenylenyl group. heterocyclic groups such as pyridyl, pyrimidinyl, triazinyl, thienyl, furyl, pyrrolyl, quinolyl, isoquinolyl, benzofuranyl, benzothienyl, indolyl, carbazolyl, benzoxazolyl, benzothiazolyl, quinoxalinyl, benzimidazolyl, pyrazolyl, dibenzofuranyl, dibenzothienyl, and carbolinyl; di-substituted amino groups substituted with aromatic hydrocarbon groups or condensed polycyclic hydrocarbon groups such as diphenylamino and dinaphthylamino; di-substituted amino groups substituted with heterocyclic groups such as dipyridylamino and dithienylamino; and di-substituted amino groups substituted with a substituent selected from aromatic hydrocarbon groups, condensed polycyclic hydrocarbon groups, and heterocyclic groups. These substituents may further have the substituents exemplified above.

[0041] Ar in general formula (1)１ ~Ar ３ Specific examples of the "aromatic hydrocarbon group", "heterocyclic group" or "condensed polycyclic hydrocarbon group" in the "substituted or unsubstituted aromatic hydrocarbon group", "substituted or unsubstituted heterocyclic group" or "substituted or unsubstituted condensed polycyclic hydrocarbon group" represented by the above formula (1) include a phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl group, an anthryl group, a phenanthryl group, a fluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group and a triphenylenyl group. , pyridyl group, pyrimidinyl group, triazinyl group, furyl group, pyrrolyl group, thienyl group, quinolyl group, isoquinolyl group, benzofuranyl group, benzothienyl group, indolyl group, carbazolyl group, benzoxazolyl group, benzothiazolyl group, quinoxalinyl group, benzimidazolyl group, pyrazolyl group, dibenzofuranyl group, dibenzothienyl group, naphthyridinyl group, phenanthrolinyl group, acridinyl group, and carbolinyl group. These groups may have a substituent, and examples of the "substituent" include the same as those exemplified as the "substituent" for A1 in general formula (1) above.

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

[0043] In the general formula (1), Ar １ and Ar ２ are preferably a "substituted or unsubstituted aromatic hydrocarbon group" or a "substituted or unsubstituted condensed polycyclic hydrocarbon group", which may be the same or different, and more preferably a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenylyl group. １is preferably a substituted or unsubstituted phenyl group, biphenylyl group, terphenylyl group, naphthyl group, phenanthryl group, anthryl group, fluorenyl group, carbazolyl group, indolyl group, dibenzofuranyl group, or dibenzothienyl group, and more preferably a substituted or unsubstituted biphenylyl group. ２ As the alkyl group, a substituted or unsubstituted phenyl group, biphenylyl group, terphenylyl group, naphthyl group, phenanthryl group, anthryl group, or fluorenyl group is preferred, and a substituted or unsubstituted phenyl group is more preferred.

[0044] In the general formula (1), Ar ３ As the group, a substituted or unsubstituted phenyl group, biphenylyl group, terphenylyl group, naphthyl group, phenanthryl group, fluorenyl group, or triphenylene group is preferable, a substituted or unsubstituted phenyl group, biphenylyl group, or terphenylyl group is more preferable, and a substituted or unsubstituted biphenylyl group is particularly preferable.

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

[0046] The arylamine compound represented by the general formula (1) can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, or the like, or by solvent recrystallization or crystallization. The compound can be identified by NMR analysis. It is preferable to measure the glass transition temperature (Tg), HOMO level, and hole mobility (μh) as physical property values ​​of the compound. The glass transition temperature is an indicator of the stability of the thin film state. When the compound is used in a second hole transport layer, the HOMO level is an indicator of smooth hole exchange between the adjacent first hole transport layer and the light-emitting layer. Furthermore, the hole mobility is an indicator of hole transport ability.

[0047] The glass transition temperature can be determined using a powder with a high-sensitivity differential scanning calorimeter (e.g., DSC3100SA, manufactured by Bruker AXS). From the viewpoints of application to a production process having a heating step and improving storage stability, the glass transition temperature is preferably 100°C or higher, and more preferably 110°C or higher.

[0048] The HOMO level can be measured for a 100 nm organic film formed on an ITO substrate by vacuum deposition using an ionization potential measurement device (for example, product name: PYS-202, manufactured by Sumitomo Heavy Industries, Ltd.) The absolute value of the HOMO level is preferably in the range of 5.0 to 7.0 eV, more preferably in the range of 5.2 to 5.8 eV, from the viewpoint of the energy difference between the HOMO levels of the adjacent light-emitting layer and first hole transport layer.

[0049] The hole mobility can be measured using a time-of-flight measurement device (for example, TOF-401, manufactured by Optel Co., Ltd.) for a 3-4 μm organic film formed on an ITO substrate by vacuum deposition. From the viewpoint of efficiently transporting holes generated in the photoelectric conversion layer to the anode, the hole mobility at an electric field strength of 0.25 MV / cm is 1.0×10 －６ (cm ２ / Vs) or more, and －５ (cm ２ / Vs) or more, and more preferably 1.0 × 10 －４ (cm ２ / Vs) or more is more preferable.

[0050] In addition to the arylamine compound represented by the general formula (1), the hole transport layer may contain other known compounds having hole transport properties. Examples of known compounds having hole transport properties include benzidine derivatives such as TPD, NPD, and N,N,N',N'-tetrabiphenylylbenzidine; 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC); arylamine compounds having two or more structures selected from triphenylamine structures and carbazolyl structures in the molecule, each of which is linked by a single bond or a divalent group not containing a heteroatom; and carbazole derivatives having hole transport properties, such as the above-mentioned SiCzCz. Coating-type polymer materials such as the above-mentioned PEDOT and PSS can also be used. These compounds may be used alone or in combination, or each may be used as a single layer. The compound or material may be a laminated structure of layers formed solely from the compound or material, a laminated structure of layers formed from a mixture of a plurality of types, or a laminated structure of a layer formed solely from the compound or material and a layer formed from a mixture of a plurality of types. These compounds and materials can be formed into films by known methods such as vapor deposition, spin coating, ink jetting, etc.

[0051] In addition to the above-mentioned known compounds and materials, the hole transport layer may further include trisbromophenylaminehexachloroantimony or a P-doped radialene derivative (see, for example, Patent Document 6), or a polymer compound having a benzidine derivative such as TPD as a partial structure.

[0052] Furthermore, in the present invention, the hole transport layer can have a two-layer or more structure including a first hole transport layer and a second hole transport layer. When the hole transport layer has a two-layer structure, it is preferable that the arylamine compound represented by the general formula (1) is located on the light-emitting layer side. That is, it is preferable that the second hole transport layer contains the arylamine compound. By forming the second hole transport layer located on the light-emitting layer side using the arylamine compound, the electron blocking ability of the arylamine compound can be fully utilized. As a result, an organic EL device exhibiting phosphorescent emission with a lower driving voltage and a longer life can be realized. Furthermore, when the hole transport layer has a three-layer structure including a first hole transport layer, a second hole transport layer, and a third hole transport layer, it is preferable that the arylamine compound be used in the second hole transport layer as an intermediate layer.

[0053] An electron blocking layer (not shown) having the function of suppressing the diffusion of electrons present in the light-emitting layer to the outside of the light-emitting layer (toward the hole transport layer) may be provided between the hole transport layer and the light-emitting layer. Alternatively, a material having such a function may be used in the hole transport layer. In this case, in a two-layer or three-layer hole transport layer, it is preferable to use a material having such a function in the hole transport layer (second hole transport layer or third hole transport layer) located on the light-emitting layer side.

[0054] <Light-emitting layer> The light-emitting layer contains a host and a dopant.

[0055] (Host) In the present invention, the light-emitting layer contains one or more hosts, preferably two or more hosts. Specifically, the light-emitting layer preferably contains at least a first host compound having electron transport capability and a second host compound having hole transport capability. One or more types of the first host compound and the second host compound may be used. The mass ratio of the first host compound to the second host compound can be, for example, 1:10 to 10:1.

[0056] The first host compound is preferably a compound having a nitrogen-containing heteroaromatic ring structure (see, for example, Patent Document 4 and Patent Document 5). The second host compound is preferably a compound having a carbazole structure (see, for example, Non-Patent Document 1). The light-emitting layer may further contain one or more host compounds in addition to the first host compound and the second host compound.

[0057] (Dopant) The light-emitting layer contains one or more dopants, and at least one of the dopants is a phosphorescent light-emitting material (hereinafter also referred to as a "phosphorescent light-emitting dopant"). That is, in the present invention, the dopant includes a phosphorescent light-emitting material. As the phosphorescent light-emitting material, a platinum complex is preferable, and other organometallic compounds containing Pt, Os, Ti, Zr, Hf, Eu, Tb, Tm, Fe, Co, Ni, Ru, Rh, Pd, or a combination thereof can also be used. The dopant may be a blue, green, or red phosphorescent light-emitting dopant, and by using such a dopant, a high-performance organic EL device can be produced.

[0058] The platinum complex is preferably a platinum complex containing one or more polydentate ligands that form a five-membered chelate ring with platinum, at least one of the polydentate ligands being a tetradentate ligand, and the five-membered chelate ring containing a carbene bond, and more preferably a platinum complex represented by the general formula (2). Here, the carbene bond is a bond between a five-membered chelate ring carbene and a platinum atom, and can also be said to have a structure in which a five-membered chelate ring carbene is coordinated to a platinum atom.

[0059] In general formula (2), L １ and L ２ may be the same or different, and may represent a single bond, NR ５ , an oxygen atom, or a sulfur atom. １ is preferably an oxygen atom or a sulfur atom, and L ２ is NR ５ In addition, in the general formula (2), n １ represents 0 or 1, n ２ represents 0 or 1. Z １ and Z ２may be the same or different and represent a nitrogen atom or a carbon atom. １ ~R ５ may be the same or different and represent a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted fused polycyclic hydrocarbon group. １ and L ２ At least one of the following is NR ５ If R ５ and R ２ , R ５ and R ３ , and R ５ and R ４ may be bonded to each other via a single bond, an oxygen atom, a sulfur atom, or a nitrogen atom to form a ring.

[0060] R １ ~R ５ Examples of the substituted or unsubstituted alkyl group represented by the formula (I) include substituted or unsubstituted linear or branched alkyl groups having 1 to 20 carbon atoms. Specific examples of the linear or branched alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, n-hexyl, 2-ethylhexyl, heptyl, octyl, isooctyl, nonyl, and decyl groups. Among these, linear or branched alkyl groups having 1 to 10 carbon atoms are preferred. R １ ~R ５ Examples of the substituted or unsubstituted alkenyl group represented by the formula (I) include substituted or unsubstituted linear or branched alkenyl groups having 2 to 20 carbon atoms. Specific examples of the linear or branched alkenyl group include vinyl, 1-propenyl, allyl, 1-butenyl, 2-butenyl, 1-pentenyl, 1-hexenyl, isopropenyl, and isobutenyl. Examples of the substituent that these groups may have include the same groups as those exemplified as the "substituent" for A1 in general formula (1).

[0061] R １ ~R ５ The aromatic hydrocarbon group, heterocyclic group, and condensed polycyclic hydrocarbon group represented by the formula (1) include Ar １ Examples of the substituent that these groups may have include the same as those exemplified as the "substituent" in A1 in the general formula (1).

[0062] In general formula (2), R １ is preferably a substituted or unsubstituted alkyl group, alkenyl group, aromatic hydrocarbon group, heterocyclic group, or fused polycyclic hydrocarbon group, and more preferably a substituted or unsubstituted aromatic hydrocarbon group, heterocyclic group, or fused polycyclic hydrocarbon group. ２ ~R ４ may be the same or different, and are preferably a hydrogen atom, a substituted or unsubstituted alkyl group, an aromatic hydrocarbon group, a heterocyclic group, or a condensed polycyclic hydrocarbon group, and more preferably a hydrogen atom or a substituted or unsubstituted alkyl group (preferably having 1 to 10 carbon atoms). ５ is preferably a substituted or unsubstituted alkyl group, aromatic hydrocarbon group, heterocyclic group, or fused polycyclic hydrocarbon group, and more preferably a substituted or unsubstituted aromatic hydrocarbon group, heterocyclic group, or fused polycyclic hydrocarbon group.

[0063] The phosphorescent dopant is preferably doped into the host in a range of 1 to 30% by mass based on the entire light-emitting layer to avoid concentration quenching, and is preferably doped by co-evaporation.

[0064] Furthermore, a thermally activated delayed fluorescent (TADF) material may be used as the dopant together with the phosphorescent material. That is, in the present invention, the dopant preferably includes a phosphorescent material and a TADF material. Examples of TADF materials include triazine derivatives such as PIC-TRZ, CC2TA, and PBICT (described below), phenoxazine derivatives such as PXZ-TRZ (described below), carbazolyldicyanobenzene derivatives (CDCB derivatives) such as 4CzIPN and 4CzTPN-Me (described below), and organoboron compounds utilizing the multiple resonance effect. Among these, organoboron compounds are preferred as the TADF material.

[0065]

[0066]

[0067] The organic boron compound is preferably a triaryl boron compound, and specific examples thereof include compounds represented by the following general formula (3).

[0068]

[0069] In general formula (3), R ａ１ ~R ａ３ may be the same or different and represent 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 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aromatic hydrocarbon group.

[0070] R ａ１ ~R ａ３ The alkyl group and alkenyl group represented by the formula (2) are １ The same applies to the substituents that these groups may have. ａ１ ~R ａ３The substituted or unsubstituted amino group represented by the formula (I) is an unsubstituted amino group (—NH ２ ), mono-substituted amino groups having a substituent with 2 to 20 carbon atoms (e.g., ethylamino, acetylamino, phenylamino, and pyridylamino), and di-substituted amino groups (e.g., diethylamino, diphenylamino, acetylphenylamino, phenylpyridylamino, and carbazolyl). ａ１ ~R ａ３ The aromatic hydrocarbon group, heterocyclic group, and condensed polycyclic hydrocarbon group represented by the formula (1) include Ar １ Examples of the substituent that these groups may have include the same as those exemplified as the "substituent" in A1 in the general formula (1).

[0071] R ａ１ ~R ａ３ is preferably 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 condensed polycyclic hydrocarbon group, and more preferably a hydrogen atom, a substituted or unsubstituted amino group, or a substituted or unsubstituted aromatic hydrocarbon group. ｂ is preferably a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic hydrocarbon group, and more preferably a substituted or unsubstituted aromatic hydrocarbon group.

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

[0073]

[0074] The doping of the TADF material into the host is preferably in the range of 0.1 to 10 mass % based on the entire light-emitting layer to avoid concentration quenching, and is preferably done by co-evaporation. These materials can be formed into films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0075] <Hole Blocking Layer> A hole blocking layer can be provided between the light-emitting layer and the electron transport layer. Known compounds having hole blocking properties can be used for the hole blocking layer. Examples of known compounds having hole blocking properties include phenanthroline derivatives such as bathocuproine, metal complexes of quinolinol derivatives such as aluminum(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (hereinafter abbreviated as "BAlq"), various rare earth complexes, oxazole derivatives, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, and benzoazole derivatives. These compounds may also serve as materials for the electron transport layer. These compounds may be used alone or in combination to form a film, and each may be used as a single layer. The hole-blocking layer may have a laminated structure of layers formed from the above compounds alone, a laminated structure of layers formed from a mixture of the above compounds, or a laminated structure of a layer formed from a layer formed from the above compounds alone and a layer formed from a mixture of the above compounds. These materials can be formed into films by known methods such as vapor deposition, spin coating, and ink-jet printing.

[0076] <Electron Transport Layer> Known compounds having electron transport properties can be used for the electron transport layer. Examples of known compounds having electron transport properties include metal complexes of quinolinol derivatives, such as Alq3 and BAlq, various metal complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, pyridine derivatives, benzimidazole derivatives, benzoazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silole derivatives. These compounds may be used alone or in combination, and each may be used as a single layer. The electron transport layer may have a laminate structure of layers formed using the above compounds alone, a laminate structure of layers formed using a mixture of the above compounds, or a laminate structure of a layer formed using a layer formed using the above compounds alone and a layer formed using a mixture of the above compounds. These materials can be used to form films using known methods, such as vapor deposition, spin coating, or inkjet printing.

[0077] <Electron injection layer> The electron injection layer can be made of alkali metal salts such as lithium fluoride and cesium fluoride, alkaline earth metal salts such as magnesium fluoride, metal complexes of quinolinol derivatives such as lithium quinolinol, metal oxides such as aluminum oxide, or metals such as ytterbium (Yb), samarium (Sm), calcium (Ca), strontium (Sr), cesium (Cs), etc. Note that the electron injection layer can be omitted by selecting a preferred combination of the electron transport layer and the cathode.

[0078] The electron injection layer and the electron transport layer may be made of materials that are typically used for these layers and are doped with a metal such as cesium as an n-type dopant. The thickness of each of the layers constituting the organic EL element is not limited and may be appropriately selected.

[0079] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0080] Synthesis Example 1 Synthesis of Compound (1-21) Compound (1-21) having the following structure was synthesized as a compound represented by general formula (1). 14.5 g of biphenyl-4-yl-[1,2';1',1";4",1"']-quaterphenyl-4'-yl-amine, 9.3 g of 9-(4-bromo-phenyl)-phenanthrene, 3.2 g of sodium t-butoxide, and 93 mL of toluene were placed in a reaction vessel, and nitrogen gas was bubbled through the mixture while irradiating with ultrasound for 30 minutes. Subsequently, 0.1 g of palladium(II) acetate and 0.2 g of tri(t-butyl)phosphine were added, and the mixture was refluxed and stirred for 3 hours. After allowing the mixture to cool, 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 of compound (1-21) as a white powder (yield 69%). The structure of the resulting white powder was identified using NMR. １ H-NMR (CDCl ３ ) the following 39 hydrogen signals were detected: 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).

[0081]

[0082] [Example 1: Measurement of glass transition temperature] The glass transition temperatures of the above compound (1-21) and SiCzCz having the following structure, which is disclosed as a comparative compound in Non-Patent Document 1, were measured using a high-sensitivity differential scanning calorimeter (manufactured by Bruker AXS, product name: DSC3100SA). The results are summarized in Table 1.

[0083]

[0084]

[0085] It can be seen from Table 1 that compound (1-21) of Example 1 has a high glass transition temperature of 110° C. or higher and is stable in a thin film state. Furthermore, the glass transition temperature of compound (1-21) is equal to or higher than that of SiCzCz, and it can be seen that by using compound (1-21) in an organic EL device, a device with excellent thermal stability can be produced.

[0086] [Example 2: Measurement of HOMO level] Using compound (1-21) of the present invention, a comparative compound (SiCzCz), and BCFN having the following structure, which is 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 each produced on an ITO substrate. The work function (corresponding to the absolute value of the HOMO level) of the resulting vapor-deposited films was measured using an ionization potential measurement device (manufactured by Sumitomo Heavy Industries, Ltd., product name: PYS-202). The results are summarized in Table 2.

[0087]

[0088]

[0089] From Table 2, it can be seen that compound (1-21) has a smaller energy difference in the HOMO level with BCFN than the comparative compound (SiCzCz), and has an appropriate HOMO level from the viewpoint of hole transport.

[0090] [Example 3: Measurement of T1 level] A 2-methyltetrahydrofuran solution (100 ml) containing the compound (1-21) of the present invention, a comparative compound (SiCzCz), and BCFN having the above structure, which is generally used as a first hole transport material, was prepared. －５ M) was prepared and its phosphorescence spectrum was measured using a spectrofluorometer (manufactured by JASCO Corporation, trade name: FP-8500) under the condition of 77 K. The T1 levels calculated from the rise of the phosphorescence spectrum are summarized in Table 3.

[0091]

[0092] As shown in Table 3, the T1 level of compound (1-21) was smaller than those of SiCzCz and BCFN. However, by using a carbazole compound as a hole-transporting host in the light-emitting layer, the recombination region can be located away from the interface between the hole-transporting layer and the light-emitting layer, and a decrease in efficiency due to a low T1 level can be suppressed.

[0093] Example 4: Measurement of hole mobility Using the compound (1-21) of the present invention and the comparative compound (SiCzCz), a film of the organic compound to be measured was formed to a thickness of 3 to 4 μm on a glass substrate with ITO by vacuum deposition. Subsequently, an aluminum film was formed to a thickness of approximately 100 nm to prepare a device for measuring hole mobility. This device was sealed in a nitrogen atmosphere with a glass cap to which a moisture getter sheet for organic EL was attached to prevent deterioration due to adsorption of moisture or oxygen. The hole mobility of the device was measured under the following conditions using a transient photocurrent measurement device. The results are shown in Table 4. (Measurement conditions) Device: Time-of-flight measurement device TOF-401 (trade name, manufactured by Optel) Excitation light source: Nitrogen laser (337.1 nm) Light pulse width: 1 nsec or less Measurement area: 0.04 cm ２ Sample temperature: 25°C Load resistance: 50Ω Electric field strength: 0.25MV / cm

[0094]

[0095] As shown in Table 4, the hole mobility of compound (1-21) was 20 times or more 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 effectively transported to the light-emitting layer, and the driving voltage can be improved.

[0096] Example 5 Evaluation of Organic EL Device As shown in FIG. 1 , an ITO electrode was previously formed as a transparent anode 2 on a glass substrate 1, and a hole injection layer 3, a first hole transport layer 4 a, a second hole transport layer 4 b, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 were sequentially deposited thereon by vapor deposition to prepare an organic EL device having a two-layer hole transport layer structure.

[0097] Specifically, a glass substrate 1 on which a 150 nm-thick ITO film had been formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes and then dried for 10 minutes on a hot plate heated to 200°C. This was followed by 15 minutes of UV ozone treatment, after which the ITO-coated glass substrate was mounted in a vacuum deposition machine and the pressure was reduced to 0.001 Pa or less. Subsequently, an electron acceptor (Acceptor-1) having the following structure and the BCFN were binary-deposited at a deposition rate ratio of Acceptor-1:BCFN = 3:97, covering the transparent anode 2, to form a 10 nm-thick hole injection layer 3. The BCFN was vapor-deposited on the hole injection layer 3 to a thickness of 55 nm as a first hole transport layer 4a. Compound (1-21) of the present invention was vapor-deposited on the first hole transport layer 4a to a thickness of 10 nm as a second hole transport layer 4b. On the second hole transport layer 4b, a hole transporting host (SiCzCz) and an electron transporting host (SiTrzCz) having the following structure are formed. ２ ) and a blue phosphorescent dopant (PtON-TBBI) having the following structure were vapor-deposited at a deposition rate ratio of SiCzCz:SiTrzCz ２ Ternary evaporation was performed at a deposition rate of 1:100:100 PtON-TBBI = 60:27:13 to form a light-emitting layer 5 having a thickness of 30 nm. On the light-emitting layer 5, mSiTrz having the following structure was evaporated to a thickness of 5 nm as a hole-blocking layer 6. On the hole-blocking layer 6, ETM-1 and ETM-2 having the following structure were evaporated to a thickness of 50:50 to form a 30 nm-thick electron-transporting layer 7. On the electron-transporting layer 7, ETM-2 was evaporated to a thickness of 1 nm as an electron-injecting layer 8. Finally, aluminum was evaporated to a thickness of 100 nm to form a cathode 9, thereby producing an organic EL device.

[0098]

[0099] Comparative Example 1 For comparison, an organic EL device was fabricated under the same conditions as in Example 5, except that SiCzCz was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0100] Comparative Example 2 For comparison, an organic EL device was fabricated under the same conditions as in Example 5, except that BCFN was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0101] The organic EL elements prepared in Example 5 and Comparative Examples 1 and 2 were driven by a direct current in the atmosphere at room temperature to emit light, and the luminance was 1000 cd / m ２ The driving voltage, power efficiency, and the lifetime until the luminance decreases to 95% (100% at the start of light emission) were measured. The measurement results are summarized in Table 5.

[0102]

[0103] As shown in Table 5, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.10 to 4.25 V for the organic EL elements of Comparative Examples 1 and 2, while the driving voltage for the organic EL element of Example 5 was 3.80 V, which was a low driving voltage. Furthermore, the power efficiency was also high, at 16.5 lm / W, while the power efficiency for the organic EL elements of Comparative Examples 1 and 2 was 13.5 to 15.3 lm / W. Furthermore, the device lifetime was 60 hours, longer than the device lifetime of 39 to 50 hours for the organic EL elements of Comparative Examples 1 and 2. These results demonstrate that the appropriate HOMO level and high hole mobility of the arylamine compound represented by general formula (1) can significantly improve the driving voltage of an organic EL element.

[0104] Example 6 Evaluation of Organic EL Device As shown in FIG. 2 , an ITO electrode was previously formed as a transparent anode 2 on a glass substrate 1, and a hole injection layer 3, a first hole transport layer 4 a, a second hole transport layer 4 b, a third hole transport layer 4 c, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 were sequentially deposited thereon by vapor deposition to prepare an organic EL device having a three-layer hole transport layer structure.

[0105] Specifically, a glass substrate 1 on which a 150 nm-thick ITO film had been formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes and then dried on a hot plate heated to 200°C for 10 minutes. This was followed by 15 minutes of UV ozone treatment, after which the ITO-coated glass substrate was placed in a vacuum deposition machine and the pressure was reduced to 0.001 Pa or less. Subsequently, the electron acceptor (Acceptor-1) and the BCFN were binary-evaporated at a deposition rate ratio of Acceptor-1:BCFN = 3:97, covering the transparent anode 2, to form a 10 nm-thick hole injection layer 3. On the hole injection layer 3, the BCFN was vapor-deposited to a thickness of 55 nm as a first hole transport layer 4a. On the first hole transport layer 4a, the compound (1-21) of the present invention was vapor-deposited to a thickness of 5 nm as a second hole transport layer 4b. On the second hole transport layer 4b, SiCzCz was vapor-deposited to form a third hole transport layer 4c to a thickness of 5 nm. On the third hole transport layer 4c, a hole transporting host (SiCzCz) and an electron transporting host (SiTrzCz ２ ) and a blue phosphorescent dopant (PtON-TBBI) were deposited at a deposition rate ratio of SiCzCz:SiTrzCz ２ A 30-nm-thick light-emitting layer 5 was formed by ternary vapor deposition at a vapor deposition rate of 1:100:13 (PtON-TBBI:PtON-TBBI). A 5-nm-thick hole-blocking layer 6 was formed on the light-emitting layer 5 by vapor deposition of the mSiTrz. A 30-nm-thick electron-transporting layer 7 was formed on the hole-blocking layer 6 by binary vapor deposition of ETM-1 and ETM-2 at a vapor deposition rate ratio of ETM-1:ETM-2=50:50. A 1-nm-thick electron-injecting layer 8 was formed on the electron-transporting layer 7 by vapor deposition of ETM-2. Finally, a 100-nm-thick cathode 9 was formed by vapor deposition of aluminum, thereby completing the production of an organic EL device.

[0106] Comparative Example 3 For comparison, an organic EL device was fabricated under the same conditions as in Example 6, except that SiCzCz was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0107] Comparative Example 4 For comparison, an organic EL device was fabricated under the same conditions as in Example 6, except that BCFN was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0108] The organic EL devices prepared in Example 6 and Comparative Examples 3 and 4 were driven by a direct current in the atmosphere at room temperature to emit light, and the luminance was 1000 cd / m ２ The driving voltage, power efficiency, and lifetime until the luminance decreases to 95% were measured. The measurement results are summarized in Table 6.

[0109]

[0110] As shown in Table 6, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.00 V, which was a low driving voltage, compared to 4.11 to 4.25 V for the organic EL elements of Comparative Examples 3 and 4. Furthermore, the power efficiency was 17.0 lm / W, which was a high power efficiency, compared to 15.3 to 16.0 lm / W for the organic EL elements of Comparative Examples 3 and 4. Furthermore, it can be seen that the device lifetime was 65 hours for the organic EL element of Example 6, which was longer than 49 to 50 hours for the organic EL elements of Comparative Examples 3 and 4. These results demonstrate that even when an arylamine compound represented by general formula (1) is used in the intermediate layer (second hole transport layer) of a three-layer hole transport layer, the driving voltage of the organic EL element can be significantly improved due to the appropriate HOMO level and high hole mobility of the compound.

[0111] Example 7 Evaluation of Organic EL Device As shown in FIG. 1 , an ITO electrode was previously formed as a transparent anode 2 on a glass substrate 1, and a hole injection layer 3, a first hole transport layer 4 a, a second hole transport layer 4 b, an emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and a cathode 9 were sequentially deposited thereon by vapor deposition to prepare an organic EL device combining a phosphorescent light-emitting material and a TADF material.

[0112] Specifically, a glass substrate 1 on which a 150 nm-thick ITO film had been formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes and then dried on a hot plate heated to 200°C for 10 minutes. This was followed by 15 minutes of UV ozone treatment, after which the ITO-coated glass substrate was placed in a vacuum deposition machine and the pressure was reduced to 0.001 Pa or less. Subsequently, the electron acceptor (Acceptor-1) and the BCFN were deposited by binary deposition at a deposition rate ratio of Acceptor-1:BCFN = 3:97, covering the transparent anode 2, to form a 10 nm-thick hole injection layer 3. The BCFN was deposited on the hole injection layer 3 to a thickness of 55 nm as a first hole transport layer 4a. Compound (1-21) of the present invention was deposited on the first hole transport layer 4a to a thickness of 10 nm as a second hole transport layer 4b. On the second hole transport layer 4b, a hole transporting host (SiCzCz) and an electron transporting host (SiTrzCz ２ ), a blue phosphorescent dopant (PtON-TBBI), and a TADF dopant (TBE02) having the following structure disclosed in Non-Patent Document 2 were evaporated at a deposition rate ratio of SiCzCz:SiTrzCz ２ A 30-nm-thick light-emitting layer 5 was formed by quaternary evaporation at a deposition rate of 1:100:PtON-TBBI:TBE02=60:27:12:1. On the light-emitting layer 5, the above-described mSiTrz was evaporated to a thickness of 5 nm as a hole-blocking layer 6. On the hole-blocking layer 6, a 30-nm-thick electron-transporting layer 7 was formed by binary evaporation of ETM-1 and ETM-2 at a deposition rate ratio of ETM-1:ETM-2=50:50. On the electron-transporting layer 7, ETM-2 was evaporated to a thickness of 1 nm as an electron-injecting layer 8. Finally, 100-nm-thick aluminum was evaporated to form a cathode 9, thereby completing the production of an organic EL device.

[0113]

[0114] Comparative Example 5 For comparison, an organic EL device was fabricated under the same conditions as in Example 7, except that SiCzCz was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0115] Comparative Example 6 For comparison, an organic EL device was produced under the same conditions as in Example 7, except that BCFN was used instead of compound (1-21) as the material for the second hole transport layer 4b.

[0116] The organic EL devices prepared in Example 7 and Comparative Examples 5 and 6 were driven by a direct current in the atmosphere at room temperature to emit light, and the luminance was 1000 cd / m ２ The driving voltage, power efficiency, and lifetime until the luminance decreases to 95% were measured. The measurement results are summarized in Table 7.

[0117]

[0118] As shown in Table 7, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.10 to 4.35 V for the organic EL elements of Comparative Examples 5 and 6, while the driving voltage at 1000 kJ / s was 3.93 V for the organic EL element of Example 7. Furthermore, the power efficiency was also high, at 15.8 lm / W, compared with 13.6 to 14.6 lm / W for the organic EL elements of Comparative Examples 5 and 6. Furthermore, the device lifetime was 55 hours for the organic EL element of Example 7, compared with 29 to 49 hours for the organic EL elements of Comparative Examples 5 and 6. These results demonstrate that the driving voltage of an organic EL element can be significantly improved by an appropriate HOMO level and high hole mobility, even in an organic EL element having a second hole-transporting layer containing a compound represented by general formula (1) and an emitting layer containing a phosphorescent emitting dopant and a TADF dopant.

[0119] As described above, the organic EL device of the present invention, which uses a compound represented by general formula (1) in the second hole-transporting layer, has a HOMO level suitable for hole transfer from the first hole-transporting layer, high heat resistance, and high hole mobility, and is an organic EL device with low driving voltage and long lifetime. It has been found that by adopting the structure represented by general formula (1) in the hole-transporting layer, it is possible to realize an organic EL device that exhibits phosphorescent emission and is excellent in all three properties, namely, reduced driving voltage, improved power efficiency, and long lifetime, compared to organic EL devices using conventional materials.

[0120] The organic EL device of the present invention, which uses an arylamine compound having a specific structure, has improved durability in addition to a reduced driving voltage, and can be applied to, for example, home electrical appliances and lighting.

[0121] REFERENCE SIGNS LIST 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 light-emitting layer 6 hole blocking layer 7 electron transport layer 8 electron injection layer 9 cathode

Claims

1. An organic electroluminescence device having at least an anode, a hole transport layer, a light emitting layer, an electron transport layer and a cathode in this order, characterized in that the hole transport layer contains an arylamine compound represented by the following general formula (1), the light emitting layer contains a host and a dopant, and the dopant contains a phosphorescent light emitting material: 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 heterocyclic ring, or a divalent group of a substituted or unsubstituted condensed polycyclic hydrocarbon; Ar １ ~Ar ３ may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted condensed polycyclic hydrocarbon group.

2. The organic electroluminescence device according to claim 1, wherein in said general formula (1), A1 is a single bond, or a substituted or unsubstituted phenylene group.

3. In the general formula (1), Ar １ and Ar ２ 2. The organic electroluminescence device according to claim 1, wherein each of the groups may be the same or different and is a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenylyl group.

4. In the general formula (1), Ar ３ 2. The organic electroluminescence device according to claim 1, wherein is a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenylyl group, or a substituted or unsubstituted terphenylyl group.

5. The organic electroluminescence device 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, and the second hole transport layer contains the arylamine compound represented by general formula (1).

6. The organic electroluminescence device according to claim 1, wherein the host contains a first host compound having an electron transporting ability and a second host compound having a hole transporting ability, and the second host compound includes a compound having a carbazole structure.

7. The organic electroluminescence device according to claim 1, wherein the phosphorescent light-emitting material is a platinum complex.

8. The organic electroluminescence device according to claim 7, wherein the platinum complex comprises one or more polydentate ligands forming a five-membered chelate ring with platinum, at least one of the polydentate ligands being a tetradentate ligand, and the five-membered chelate ring comprises a carbene bond.

9. The organic electroluminescence device according to claim 8, wherein the platinum complex is represented by the following general formula (2): In the ceremony, L １ and L ２ may be the same or different, a single bond, NR ５ , an oxygen atom, or a sulfur atom; １ represents 0 or 1, n ２ represents 0 or 1; Z １ and Z ２ may be the same or different and represent a nitrogen atom or a carbon atom; R １ ~R ５ may be the same or different and each represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted heterocyclic group, or a substituted or unsubstituted condensed polycyclic hydrocarbon group; L １ and L ２ At least one of the following is NR ５ If R ５ and R ２ , R ５ and R ３ , and R ５ and R ４ may be bonded to each other to form a ring.

10. The organic electroluminescence device according to any one of claims 7 to 9, wherein the dopant comprises a platinum complex as a phosphorescent emitting material and a thermally activated delayed fluorescent (TADF) material.

11. The arylamine compound represented by the general formula (1) has a hole mobility of 1.0×10 at an electric field strength of 0.25 MV / cm. -５ cm ２ 2. The organic electroluminescence device according to claim 1, wherein the Vref is 1. / Vs or more.

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