Organic electroluminescent element

Abstract

Provided is an organic compound that has excellent characteristics including excellent hole injection / transport performance, electron blocking ability, high stability in a thin film state, and high luminous efficiency, the organic compound serving as a material for an organic EL element that exhibits phosphorescent light emission at low voltage and with high durability. Further provided is an organic EL element that exhibits phosphorescent light emission at low driving voltage and with high durability, the organic EL element being obtained by combining the organic compound with various materials for the organic EL element, which have excellent hole and electron injection / transport performance, electron blocking ability, stability in a thin film state, and durability, in a manner that effectively brings out the characteristics of the respective materials.

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 compound comprising a specific indenocarbazole ring.

[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 practical by developing a layered structure element in which various roles were assigned to each material. They developed a phosphor that can transport electrons, tris(8-hydroxyquinoline)aluminum (hereinafter referred to as "Alq"), ３ ") and an aromatic amine compound capable of transporting holes are laminated together, and both charges are injected into the phosphor layer to emit light, achieving 1000 cd / m at a voltage of 10 V or less. ２ The above 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, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode are sequentially provided on a substrate.

[0005] Furthermore, in order to further improve the 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 light-emitting material.

[0006] In Patent Documents 4 and 5, a host compound having a nitrogen-containing heteroaromatic ring structure and electron transporting ability and a host compound having a carbazole structure and hole transporting ability are used in combination in the light-emitting layer, thereby increasing the electron and hole transporting properties and improving the luminous efficiency compared to when these compounds are used alone.

[0007] 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.

[0008]

[0009] Japanese Patent Application Publication No. 2017 / 0104163 Japanese Patent No. 6715781 International Publication No. 2014 / 009310 Japanese Patent No. 5936229

[0010] Nature Photonics 16, 212-218 Eungdo Kim et al., Science Advances. Vol8, Issue 41 (2022)

[0011] Although SiCzCz has a high triplet excitation energy (hereinafter abbreviated as "T1 level"), there is a problem in that the molecular design that increases the T1 level limits pi-conjugation, resulting in 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, and there is a concern that an excess of electrons may occur in the emitting layer.

[0012] Furthermore, in devices using SiCzCz for the second hole transport layer, the device driving voltage increases, and the device life is not sufficient due to the influence of an excess of electrons in the light-emitting layer. Therefore, a second hole transport material having high hole mobility and excellent durability against electrons is desired.

[0013] An object of the present invention is to provide an organic compound that has excellent hole injection / transport properties, electron blocking ability, high stability in a thin film state, and long life properties as a material for an organic EL device that exhibits phosphorescence at a low voltage and with high durability. Another object of the present invention is to provide an organic EL device that exhibits phosphorescence at a low driving voltage and with high durability by combining this compound with various materials for organic EL devices that have excellent hole and electron injection / transport properties, electron blocking ability, stability in a thin film state, and durability so that the properties of each material can be effectively exhibited.

[0014] The physical properties that the organic compound according to 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. The physical properties that the organic EL device according to the present invention should have include (1) a low light emission starting voltage, (2) a low practical driving voltage, and (3) a long life.

[0015] In order to achieve the above object, the present inventors focused on the fact that compounds having an indenocarbazole ring with a specific structure have excellent hole injection / transport capabilities, thin film stability, and durability. They selected various compounds having an indenocarbazole ring, fabricated organic EL devices, and thoroughly evaluated the device characteristics. As a result, the present inventors discovered that selecting a compound having an indenocarbazole ring with a specific structure as a material for the hole transport layer can efficiently transport holes injected from the anode side. Furthermore, they fabricated various organic EL devices by combining light-emitting materials and the like having specific structures, and thoroughly evaluated the device characteristics. As a result, the present invention was completed.

[0016] That is, according to the present invention, the following compounds and organic EL devices are provided: 1) A compound represented by the following formula (2-1):

[0017] 2) A compound represented by the following formula (2-2):

[0018] 3) A compound represented by the following formula (2-3):

[0019] 4) 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, wherein the hole transport layer contains a compound having an indenocarbazole ring represented by the following general formula (1), and the emitting layer contains at least one phosphorescent emitting dopant:

[0020]

[0021] [wherein Ar represents a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenylyl group, a substituted or unsubstituted terphenyl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthrenyl group, a substituted or unsubstituted dibenzofuranyl group, or a substituted or unsubstituted dibenzothienyl group; R １ ~R １６ represents a hydrogen atom, a deuterium atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group; R １７ represents a methyl group, an unsubstituted phenyl group, or a deuterium-substituted phenyl group; X represents an oxygen atom or a sulfur atom; R １８ represents the same group as Ar shown above.

[0022] 5) The organic electroluminescence device according to 4), wherein the hole transport layer is represented by a compound having an indenocarbazole ring of the following general formula (2):

[0023]

[0024] (where Ar, X and R １ ~R １７ is defined as in general formula (1).

[0025] 6) The organic electroluminescence element according to 4) or 5), 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 a compound having an indenocarbazole ring represented by general formula (1).

[0026] 7) The organic electroluminescence device according to any one of 4) to 6), 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.

[0027] 8) The organic electroluminescence device according to 4), wherein a platinum complex is used as the phosphorescent material.

[0028] 9) The organic electroluminescence device according to 8), wherein the platinum complex comprises 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 comprises a carbene bond.

[0029] 10) The organic electroluminescence device according to 8) or 9), wherein the platinum complex is represented by the following general formula (3):

[0030]

[0031] [In the formula, L １ and L ２ may be the same or different, and may represent a single bond, NR ２２ , 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 １８ ~R ２２ 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, or a substituted or unsubstituted aromatic heterocyclic group; L １ and L ２ At least one of the following is NR ２２ If R ２２ and R １９ , R ２２ and R ２０ and R ２２ and R ２１ may be bonded to each other to form a ring.

[0032] 11) The organic electroluminescence device according to any one of 8) to 10), wherein the dopant comprises a platinum complex as a phosphorescent light-emitting material and an organoboron compound as a thermally activated delayed fluorescence (TADF) material.

[0033] The compounds of the present invention represented by the formulas (2-1) to (2-3) have the following properties: good hole injection characteristics, large hole mobility, excellent electron blocking ability, stable thin film state, and excellent heat resistance.

[0034] The organic EL device of the present invention uses a compound having an indenocarbazole ring represented by general formula (1) or formulas (2-1) to (2-3), which has a higher hole mobility than conventional hole transport materials, an excellent electron blocking ability, and an excellent amorphous property, and is stable in a thin film state. Therefore, it is possible to realize an organic EL device that exhibits phosphorescent emission with high power efficiency, a low driving voltage, and a long life.

[0035] FIG. 1 is a diagram showing the organic EL device configurations of Examples 4, 5, 6, 7, 12, 13, 14, 15, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 6. FIG. 2 is a diagram showing the organic EL device configurations of Examples 8, 9, 10, 11, 12, Comparative Example 3, and Comparative Example 4, Comparative Example 5, Comparative Example 7, Comparative Example 8, and Comparative Example 9. FIG. 3 is a diagram showing the structures of compounds (2-1) to (2-12) as examples of compounds represented by general formula (1). FIG. 4 is a diagram showing the structures of compounds (2-13) to (2-24) as examples of compounds represented by general formula (1). FIG. 5 is a diagram showing the structures of compounds (2-25) to (2-36) as examples of compounds represented by general formula (1). FIG. 6 is a diagram showing the structures of compounds (2-37) to (2-47) as examples of compounds represented by general formula (1). FIG. 7 is a diagram showing the structures of compounds (2-48) to (2-56) as examples of compounds represented by general formula (1). FIG. 1 shows the structures of compounds (2-57) to (1-62) as examples of compounds represented by general formula (1).

[0036] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments or specific examples of the present invention, but the present invention is not limited to such embodiments or specific examples. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0037] The present invention relates to compounds represented by formulas (2-1) to (2-3). The present invention also relates to an organic EL device having at least an anode, a hole transport layer, an emitting layer, an electron transport layer, and a cathode in this order, wherein the hole transport layer contains a compound having an indenocarbazole ring represented by the following general formula (1), and the emitting layer uses at least one phosphorescent dopant. The compound represented by general formula (1) used in the present invention is described below.

[0038] <Compound represented by general formula (1)>

[0039] [wherein Ar represents a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted terphenyl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthrenyl group, a substituted or unsubstituted dibenzofuranyl group, or a substituted or unsubstituted dibenzothienyl group; R １ ~R １６ represents a hydrogen atom, a deuterium atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group; R １７ represents a methyl group, an unsubstituted phenyl group, or a deuterium-substituted phenyl group, and X represents an oxygen atom or a sulfur atom.

[0040] R in general formula (1) １ ~R １６The aromatic ring constituting the "aromatic hydrocarbon group" (aryl group) in the substituted or unsubstituted aromatic hydrocarbon group represented by the formula (I) may be a monocyclic ring, a fused ring in which two or more rings are fused (fused polycyclic aromatic group), a linked ring in which two or more rings are linked by a single bond, a linked ring in which two or more rings are linked by a single bond, or a spiro ring in which two or more rings are linked by a spiro bond. The number of carbon atoms in the aromatic ring is selected, for example, from the range of 6 to 30. Specific examples of the "aromatic hydrocarbon group" include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, a triphenylenyl group, a fluorenyl group, and a spirobifluorenyl group.

[0041] R in general formula (1) １ ~R １６ The "aromatic heterocyclic group" (heteroaryl group) in the substituted or unsubstituted aromatic heterocyclic group represented by the following formula may be a single ring or a fused ring in which two or more rings are fused together. The number of carbon atoms in the aromatic heterocyclic ring is selected from the range of 2 to 40, for example, and may also be selected from the range of 2 to 20. Specific examples of the "aromatic heterocyclic group" include a pyridyl group, a pyrimidinyl group, a triazinyl group, a furyl group, a pyrrolyl group, a thienyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, an azafluorenyl group, a diazafluorenyl group, an azaspirobifluorenyl group, a diazaspirobifluorenyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, a naphthyridinyl group, a phenanthrolinyl group, an acridinyl group, and a carbolinyl group.

[0042] A substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted terphenyl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthrenyl group, a substituted or unsubstituted dibenzofuranyl group, a substituted or unsubstituted dibenzothienyl group, and R１ ~R １６ Specific examples of the "substituent" in the substituted or unsubstituted aromatic hydrocarbon group, substituted or unsubstituted aromatic heterocyclic group, and substituted or unsubstituted fused polycyclic aromatic group represented by the formula (I) include a deuterium atom, a cyano group, a nitro group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a silyl group such as a trimethylsilyl group or a triphenylsilyl group; a linear or branched alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, or a propyl group; a linear or branched alkyloxy group having 1 to 6 carbon atoms such as a methyloxy group, an ethyloxy group, or a propyloxy group; an alkenyl group such as a vinyl group or an allyl group; an aryloxy group such as a phenyloxy group or a tolyloxy group; an arylalkyloxy group such as a benzyloxy group or a phenethyloxy group. aromatic hydrocarbon groups or condensed polycyclic aromatic groups such as a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a fluorenyl group, a spirobifluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, or a triphenylenyl group; and aromatic heterocyclic groups such as a pyridyl group, a thienyl group, a furyl group, a pyrrolyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, or a carbolinyl group, and these substituents may be further substituted with the substituents exemplified above. In addition, benzene rings substituted with these substituents, or multiple substituents substituted on the same benzene ring, may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring.

[0043] In the present invention, Ar in general formula (1) is preferably a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted terphenyl group, or a substituted or unsubstituted fluorenyl group, and more preferably a substituted or unsubstituted phenyl group.

[0044] In the present invention, R in general formula (1)１ ~R １６ is preferably a hydrogen atom or a deuterium atom.

[0045] In the present invention, X in general formula (1) is preferably an oxygen atom.

[0046] In the present invention, the general formula (1) is preferably represented by the general formula (2). Ar, X, and R in the general formula (2) １ ~R １７ is defined as in general formula (1).

[0047] Among the compounds having a structure represented by the above general formula (1) of the present invention, specific examples of preferred compounds are shown in Figures 3 to 10, but the present invention is not limited to these compounds.

[0048] The specific compounds can be synthesized according to known methods (see, for example, Patent Document 8).

[0049] The compound having the structure represented by general formula (1) of the present invention can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization or crystallization using a solvent, etc. The compound can be identified by NMR analysis. It is preferable to measure the glass transition temperature (Tg), HOMO level, and hole mobility as physical property values.

[0050] The glass transition temperature (Tg) is an index of the stability of a thin film. The glass transition temperature (Tg) can be determined using a powder with a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS). From the viewpoints of application to a manufacturing process having a heating step and improving storage stability, the glass transition temperature (Tg) is preferably 100°C or higher, more preferably 110°C or higher.

[0051] The HOMO level is an index for smoothly exchanging holes between the adjacent first hole transport layer and light-emitting layer. The HOMO level can be determined by forming a 100 nm organic film on an ITO substrate by vacuum deposition and using an ionization potential measurement device (PYS-202, manufactured by Sumitomo Heavy Industries, Ltd.). From the viewpoint of the energy difference between the HOMO levels of the adjacent light-emitting layer and first hole transport layer, the absolute value of the HOMO level is preferably in the range of 5.0 eV to 7.0 eV, more preferably in the range of 5.2 to 6.0 eV.

[0052] The hole mobility is an index of hole transport ability. The hole mobility can be determined by forming an organic film of 3 to 4 μm on an ITO substrate by vacuum deposition and using a time-of-flight measurement device (TOF-401, manufactured by Optel). 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 set to 1.0 × 10 －６ (cm ２ / Vs) or more, and －５ (cm ２ / Vs) or more is more preferable.

[0053] 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.

[0054] 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 sequentially stacked 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 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.

[0055] <Substrate> The substrate is not particularly limited, and a glass substrate, a plastic substrate, or the like can be used. The substrate may be transparent or opaque. Examples of the substrate 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, polyetherimide, 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, silicon substrates, and polyimide substrates, which have excellent heat resistance, are preferred from the viewpoint of forming transistors.

[0056] <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 alloy, magnesium-indium alloy, and aluminum-magnesium alloy, organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, and laminates of these with ITO. Among these, from the viewpoint of work function, ITO or IGZO is preferred as the anode, and aluminum or magnesium-silver alloy is preferred as the cathode.

[0057] <Hole Injection Layer> For the hole injection layer, known compounds such as porphyrin compounds typified by copper phthalocyanine, starburst triphenylamine derivatives, and 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, can be used. Furthermore, acceptor heterocyclic compounds such as hexacyanoazatriphenylene and coating-type polymer materials such as poly(3,4-ethylenedioxythiophene) (hereinafter abbreviated as "PEDOT") / poly(styrenesulfonate) (hereinafter abbreviated as "PSS") can also be used.

[0058] 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 and materials 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 as a partial structure, such as N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (hereinafter abbreviated as "TPD").

[0059] These compounds and materials can be used to form films by known methods such as vapor deposition, spin coating, and ink jet printing.

[0060] <Hole Transport Layer> In addition to the compound having an indenocarbazole ring represented by the general formula (1) of the present invention, known compounds having hole transport properties can be used for the hole transport layer in the organic EL device of the present invention. Examples of known compounds having hole transport properties include benzidine derivatives such as TPD, NPD, N,N,N',N'-tetrabiphenylylbenzidine, 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (hereinafter abbreviated as "TAPC"), and arylamine compounds having two or more triphenylamine structures or carbazolyl structures in the molecule, each of which is linked by a single bond or a divalent group not containing a heteroatom. Coating-type polymer materials such as the above-mentioned PEDOT and PSS can also be used. These compounds may be formed into a film alone or in a mixture of two or more types, and 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 thin films by known methods such as vapor deposition, spin coating, ink jetting, etc.

[0061] In addition to compounds and materials that are commonly used, the hole transport layer may further include trisbromophenylaminehexachloroantimony, P-doped radialene derivatives (see, for example, Patent Document 7), and polymer compounds having a benzidine derivative structure such as TPD in their partial structure.

[0062] Furthermore, in the present invention, the hole transport layer may have a two-layer structure of at least one layer, including a first hole transport layer and a second hole transport layer. In the case of a two-layer structure, it is preferable that a compound having an indenocarbazole ring represented by the general formula (1) is located on the light-emitting layer side and serves as the second hole transport layer. By forming the second hole transport layer located on the light-emitting layer side using a compound having an indenocarbazole ring represented by the general formula (1), the electron blocking ability of the compound having an indenocarbazole ring can be fully utilized, thereby realizing an organic EL device that exhibits phosphorescence emission with a lower driving voltage and a longer life. Furthermore, in the present invention, 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 a compound having an indenocarbazole ring represented by the general formula (1) is used as an intermediate layer in the second hole transport layer.

[0063] <Light-emitting layer (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 second host compounds may be used. The mass ratio of the first host compound to the second host compound may be, for example, 1:10 to 10:1.

[0064] 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).

[0065] The light-emitting layer may further contain one or more host compounds in addition to the first host compound and the second host compound.

[0066] (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 In, 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.

[0067] The platinum complex preferably 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 is formed by a carbene bond, and is more preferably represented by the general formula (3). 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.

[0068] R represented by general formula (3) １８ ~R ２２ Specific examples of the "substituted or unsubstituted alkyl group" and "substituted or unsubstituted alkenyl group" in the above include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an s-butyl group, a t-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, an isooctyl group, a nonyl group, a decyl group, a vinyl group, a 1-propenyl group, an allyl group, a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 1-hexenyl group, an isopropenyl group, an isobutenyl group, and the like.

[0069] R represented by general formula (3) １８ ~R ２２ The "substituted or unsubstituted aromatic hydrocarbon group" or "substituted or unsubstituted aromatic heterocyclic group" includes R １ ~R １６Examples of the substituted or unsubstituted aromatic hydrocarbon group include the same as the "substituted or unsubstituted aromatic heterocyclic group" represented by the following formula:

[0070] R represented by general formula (3) １８ ~R ２２ Examples of the "substituent" of the "substituted or unsubstituted alkyl group," "substituted or unsubstituted alkenyl group," "substituted or unsubstituted aromatic hydrocarbon group," or "substituted or unsubstituted aromatic heterocyclic group" in the general formula (1) include the same as the "substituent" in the substituted or unsubstituted phenyl group, substituted or unsubstituted naphthyl group, substituted or unsubstituted dibenzofuranyl group, substituted or unsubstituted dibenzothienyl group, substituted or unsubstituted phenanthrenyl group, or substituted or unsubstituted biphenyl group represented by Ar in the general formula (1).

[0071] In the present invention, L represented by the general formula (3) １ and L ２ may be the same or different, and may be a single bond, NR ２３ , an oxygen atom, and a sulfur atom; L １ is preferably an oxygen atom or a sulfur atom, and L ２ is NR ２２ It is preferable that:

[0072] In the present invention, L １ and L ２ At least one of the following is NR ２２ If R ２２ and R １９ , R ２２ and R ２０ and R ２２ and R ２１ may be bonded to each other via a single bond, an oxygen atom, a sulfur atom, or a nitrogen atom to form a ring.

[0073] 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.

[0074] Furthermore, a thermally activated delayed fluorescent (TADF) material may be used as a dopant together with the phosphorescent material. Examples of the thermally activated delayed fluorescent material include triazine derivatives such as PIC-TRZ and CC2TA, phenoxazine derivatives such as PXZ-TRZ, carbazolyldicyanobenzene derivatives (CDCB derivatives) such as 4CzIPN, and organic boron compounds such as DABNA (see, for example, Non-Patent Document 2).

[0075] In the present invention, it is preferable to use an organoboron compound that utilizes the multiple resonance effect, and the organoboron compound is preferably a triarylboron compound.

[0076]

[0077] The organic boron compound is preferably a triaryl boron compound, and specific examples thereof include compounds represented by the following general formula (4).

[0078]

[0079] [In the formula, 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.] 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 ａ３ The 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 Examples of the aromatic hydrocarbon group, heterocyclic group, and fused polycyclic hydrocarbon group represented by the formula (I) include the same groups as those exemplified for Ar in the general formula (1). Examples of the substituent that these groups may have include the same groups as those exemplified as the "substituent" for Ar in the general formula (1).

[0080] 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.

[0081] Examples of the compound represented by general formula (4) 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.

[0082]

[0083] The thermally activated delayed fluorescent light-emitting material is preferably doped into the host in a concentration of 0.1 to 10% by mass based on the total mass of the emitting layer to avoid concentration quenching, and is preferably doped by co-evaporation. These materials can be formed into a film by known methods such as vapor deposition, spin coating, and ink-jet printing.

[0084] <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.

[0085] <Electron Transport Layer> A known compound having electron transport properties can be used in the electron transport layer. Known compounds having electron transport properties include Alq ３Examples of suitable compounds include metal complexes of quinolinol derivatives such as 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 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 the above compounds alone and a layer formed from a mixture of the above compounds. These materials can be used to form films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0086] <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.

[0087] The electron injection layer and the electron transport layer may be made of materials that are n-type doped with a metal such as cesium, in addition to materials that are normally used for these layers.

[0088] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0089] <Synthesis of Intermediate 1> 29.5 g of 2-bromo-5,7-dihydro-5,7,7-triphenyl-indeno[2,1-b]carbazole, 14.6 g of bispinacolatodiboron, 7.7 g of potassium acetate, 0.4 g of the dichloromethane adduct of {1,1'-bis(diphenylphosphino)ferrocene}palladium(II) dichloride, and 150 ml of 1,4-dioxane were added to a nitrogen-purged reaction vessel and stirred under reflux for 4 hours. After confirming the completion of the reaction, the mixture was allowed to cool to room temperature, methanol was added, and the mixture was filtered to obtain a crude product. The obtained crude product was dissolved in chloroform, subjected to adsorption treatment with silica gel, and purified by crystallization using toluene / methanol to obtain 25.4 g of Intermediate 1 (yield: 79.4%).

[0090]

[0091] Synthesis Example 1 Synthesis of Compound (2-1) 5.0 g of 2-bromo-5,7-dihydro-5,7,7-triphenyl-indeno[2,1-b]carbazole, 2.0 g of 4-dibenzofuranboronic acid, 1.6 g of potassium carbonate, 0.2 g of tetrakistriphenylphosphine palladium(0), 48 ml of toluene, 12 ml of ethanol, and 5 ml of water were added to a nitrogen-purged reaction vessel and stirred under reflux for 5 hours. After confirming the completion of the reaction, the mixture was allowed to cool to room temperature, and then water and toluene were added. The organic layer was separated and collected. The organic layer was dehydrated with anhydrous sodium sulfate and concentrated under reduced pressure to obtain a crude product. The crude product was recrystallized from toluene to obtain 5.0 g of Compound (2-1) (yield: 86.5%).

[0092] The structure of the resulting compound (2-1) was identified using NMR.

[0093] １ H-NMR (CDCl ３ ) the following 31 hydrogen signals were detected:

[0094] ​δ (ppm) = 8.72 (1H), 8.58 (1H), 8.02-8.03 (1H), 7.95-7.96 (2H), 7.91-7.92 (1H), 7.74-7.75 (1H), 7.64-7.66 (1H), 7.37-7.58 (12H), 7.20-7.25 (11H)

[0095]

[0096] Synthesis Example 2 Synthesis of Compound (2-2) 2.2 g of 2-bromodibenzofuran, 5.2 g of Intermediate 1, 1.6 g of potassium carbonate, 0.2 g of tetrakistriphenylphosphine palladium(0), 40 ml of toluene, 10 ml of ethanol, and 5 ml of water were added to a nitrogen-purged reaction vessel and stirred under reflux for 10 hours. After confirming the completion of the reaction, the mixture was allowed to cool to room temperature, and then water and toluene were added. The organic layer was separated and collected. The organic layer was dehydrated with anhydrous sodium sulfate and concentrated under reduced pressure to obtain a crude product. The crude product was purified by column chromatography (toluene / n-hexane) to obtain 3.6 g of Compound (2-2) (yield: 63.0%).

[0097] The structure of the resulting compound (2-2) was identified using NMR.

[0098] １ H-NMR (CDCl ３ ) the following 31 hydrogen signals were detected:

[0099] δ (ppm) = 8.57 (1H), 8.48 (1H), 8.27 (1H), 8.05-8.07 (1H), 7.90-7.92 (1 H), 7.81-7.84 (1H), 7.66-7.71 (2H), 7.37-7.62 (12H), 7.19-7.25 (11H)

[0100]

[0101] ​Synthesis Example 3 Synthesis of Compound (2-3) 2.0 g of 3-bromodibenzofuran, 4.7 g of Intermediate 1, 1.5 g of potassium carbonate, 0.2 g of tetrakistriphenylphosphine palladium(0), 40 ml of toluene, 10 ml of ethanol, and 5 ml of water were added to a nitrogen-purged reaction vessel and stirred under reflux for 9 hours. After confirming the completion of the reaction, the mixture was allowed to cool to room temperature and then filtered to obtain a crude product. The obtained crude product was dissolved in toluene, subjected to an adsorption treatment with silica gel, and recrystallized from toluene to obtain 1.4 g of Compound (2-3) (yield: 26.6%).

[0102] The structure of the resulting compound (2-3) was identified using NMR.

[0103] １ H-NMR (CDCl ３ ) the following 31 hydrogen signals were detected:

[0104] δ (ppm) = 8.57 (1H), 8.51 (1H), 8.03-8.06 (1H), 7.99-8.01 (1H), 7.91-7.9 3 (2H), 7.71-7.76 (2H), 7.55-7.62 (3H), 7.36-7.52 (9H), 7.19-7.25 (11H)

[0105]

[0106] [Example 1: Measurement of glass transition temperature] The glass transition temperatures of the compounds (2-1), (2-2), and (2-3) of the present invention, SiCzCz having the following structure disclosed in Non-Patent Document 1 as a comparative compound, and Compound A having the following structure were measured using a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS). The results of the measured glass transition temperatures are summarized in Table 1.

[0107]

[0108] (Compound A)

[0109]

[0110] ​As can be seen from Table 1, the compounds (2-1), (2-2), and (2-3) of the present invention have high glass transition temperatures of 110° C. or higher, indicating that they are stable in a thin film state. Therefore, by using the compounds (2-1), (2-2), and (2-3) in an organic EL device, it is possible to prepare a device with excellent thermal stability.

[0111] [Example 2: Measurement of HOMO level] Using compound (2-1), compound (2-2), compound (2-3), comparative compounds (SiCzCz and compound A) of the present invention, 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 obtained 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.

[0112]

[0113]

[0114] It can be seen from Table 2 that compounds (2-1), (2-2), and (2-3) of the present invention have higher absolute values ​​of HOMO levels than BCFN, a common hole-transport material. Furthermore, when BCFN is used in the first hole-transport layer and the compound represented by general formula (1) of the present invention, comparative compound (SiCzCz), and compound A are used in the second hole-transport layer, it can be seen that the energy difference in the HOMO level between the compound represented by general formula (1) of the present invention and BCFN is smaller than that of the comparative compound (SiCzCz), indicating that the compound has a HOMO level appropriate from the viewpoint of hole transport.

[0115] However, when BCFN is used in the first hole transport layer and Compound A is used in the second hole transport layer, the energy difference between the HOMO levels of Compound A and the light-emitting layer becomes large, and it has been shown that hole transport from the second hole transport layer to the light-emitting layer may be inhibited.

[0116] [Example 3: Measurement of hole mobility] Using Compound (2-1), Compound (2-2), Compound (2-3) of the present invention, and a comparative compound (SiCzCz), a film of the organic compound to be measured was formed on a glass substrate with ITO by vacuum deposition to a thickness of 3 to 4 μm. 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.

[0117] The hole mobility of the device was measured using a transient photocurrent measurement device under the following conditions. The results are shown in Table 3.

[0118] (Measurement conditions) Apparatus: Time-of-flight measurement apparatus TOF-401 (trade name, manufactured by Optel Corporation) 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

[0119]

[0120] As shown in Table 3, the hole mobility of the compounds (2-1), (2-2), and (2-3) of the present invention was observed to be higher than that of the comparative compound (SiCzCz). By using the compounds (2-1), (2-2), and (2-3) of the present invention 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.

[0121] Example 4 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.

[0122] 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 placed 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 compound (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. On the hole injection layer 3, a compound (BCFN) having the above structure was vapor-deposited to a thickness of 55 nm as a first hole transport layer 4a. On the first hole-transporting layer 4a, a compound (2-1) of the present invention was deposited to a thickness of 10 nm as a second hole-transporting layer 4b. On the second hole-transporting layer 4b, a hole-transporting host (SiCzCz), an electron-transporting host (SiTrzCz2) having the following structure, and a blue phosphorescent-emitting dopant (PtON-TBBI) having the following structural formula were ternary deposited at a deposition rate ratio of SiCzCz:SiTrzCz2:PtON-TBBI=60:27:13, to form an emitting layer 5 having a thickness of 30 nm. On the emitting layer 5, a compound (mSiTrz) having the following structure was deposited to a thickness of 5 nm as a hole-blocking layer 6. On the hole-blocking layer 6, a compound (ETM-1) and a compound (ETM-2) having the following structures were binary-deposited at a deposition rate ratio of compound (ETM-1):compound (ETM-2) = 50:50 to form an electron-transporting layer 7 having a thickness of 30 nm. On the electron-transporting layer 7, ETM-2 was vapor-deposited to a thickness of 1 nm as an electron-injecting layer 8. Finally, aluminum was vapor-deposited to a thickness of 100 nm to form a cathode 9, thereby producing an organic EL device.

[0123]

[0124]

[0125]

[0126] Example 5 An organic EL device was produced under the same conditions as in Example 4, except that the compound (2-2) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0127] Example 6 An organic EL device was produced under the same conditions as in Example 4, except that the compound (2-3) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0128] Comparative Example 1 An organic EL device was fabricated under the same conditions as in Example 4, except that the compound (2-1) was replaced with the comparative compound SiCzCz as the material for the second hole transport layer 4b.

[0129] Comparative Example 2 An organic EL device was fabricated under the same conditions as in Example 4, except that BCFN was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0130] Comparative Example 3 An organic EL device was fabricated under the same conditions as in Example 4, except that compound A was used instead of compound (2-1) as the material for the second hole transport layer 4b.

[0131] The organic EL devices prepared in Examples 4 to 6 and Comparative Examples 1 to 3 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 4.

[0132]

[0133] As shown in Table 4, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.25 V for the organic EL element of Comparative Example 1 and 4.34 V for the organic EL element of Comparative Example 3, while the driving voltage was 4.17 to 4.22 V for the organic EL elements of Examples 4 to 6, which was a low driving voltage. Furthermore, the power efficiency was also high, at 16.1 to 16.7 lm / W, while the power efficiency was 13.5 to 15.3 lm / W for the organic EL elements of Comparative Examples 1 to 3. Furthermore, it can be seen that the element lifetime was 23 to 50 hours for the organic EL elements of Comparative Examples 1 to 3, while the organic EL elements of Examples 4 to 6 had a longer lifetime of 55 to 60 hours.

[0134] Therefore, due to the appropriate HOMO level and high hole mobility of the compound having a structure represented by general formula (1) of the present invention, an organic EL device using the compound of the present invention in the second hole transport layer can improve the driving voltage compared to devices using conventional compounds, and becomes a device with high power efficiency and long life.

[0135] Example 7 Evaluation of Organic EL Device As shown in FIG. 2 , an ITO electrode was previously formed on a glass substrate 1 as a transparent anode 2, 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, thereby producing an organic EL device having a three-layer hole transport layer structure.

[0136] 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 compound (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. On this hole injection layer 3, a compound (BCFN) having the structural formula described above was deposited to a thickness of 55 nm as a first hole transport layer 4a. On the first hole transport layer 4a, a compound (2-1) of the present invention was deposited to a thickness of 5 nm as a second hole transport layer 4b. On the second hole-transporting layer 4b, SiCzCz was vapor-deposited to form a third hole-transporting layer 4c to a thickness of 5 nm. On the third hole-transporting layer 4c, a hole-transporting host (SiCzCz), an electron-transporting host (SiTrzCz2), and a blue phosphorescent-emitting dopant (PtON-TBBI) were ternary vapor-deposited at a vapor deposition rate ratio of SiCzCz:SiTrzCz2:PtON-TBBI=60:27:13, thereby forming an emitting layer 5 to a thickness of 30 nm. On the emitting layer 5, a compound (mSiTrz) was vapor-deposited to form a hole-blocking layer 6 to a thickness of 5 nm. On the hole-blocking layer 6, compound (ETM-1) and compound (ETM-2) were binary-deposited at a deposition rate ratio of compound (ETM-1):compound (ETM-2) = 50:50, thereby forming an electron-transporting layer 7 having a thickness of 30 nm. On the electron-transporting layer 7, ETM-2 was vapor-deposited to a thickness of 1 nm as an electron-injecting layer 8. Finally, aluminum was vapor-deposited to a thickness of 100 nm to form a cathode 9, thereby producing an organic EL device.

[0137] Example 8 An organic EL device was produced under the same conditions as in Example 7, except that the compound (2-2) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0138] Example 9 An organic EL device was produced under the same conditions as in Example 7, except that the compound (2-3) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0139] Comparative Example 4 An organic EL device was fabricated under the same conditions as in Example 7, except that SiCzCz was used instead of compound (2-1) as the material for the second hole transport layer 4b.

[0140] Comparative Example 5 An organic EL device was fabricated under the same conditions as in Example 7, except that BCFN was used instead of the compound (2-1) as the material for the second hole transport layer 4b.

[0141] Comparative Example 6 An organic EL device was fabricated under the same conditions as in Example 7, except that compound A was used instead of compound (2-1) as the material for the second hole transport layer 4b.

[0142] The organic EL devices fabricated in Examples 7 to 9 and Comparative Examples 4 to 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 5.

[0143] [Rule 26 Amendment 13.05.2025]

[0144] As shown in Table 5, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.30 V for the organic EL element of Comparative Example 6, while the driving voltage at 1000 kJ / s was 4.09 to 4.13 V for the organic EL elements of Examples 7 to 9, which was a low driving voltage. In addition, the power efficiency was also high, at 17.3 to 17.8 lm / W, while the power efficiency was 15.3 to 16.0 lm / W for the organic EL elements of Comparative Examples 4 to 6. Furthermore, it can be seen that the element lifetime was 55 to 61 hours for the organic EL elements of Examples 7 to 9, which was longer than the element lifetime of 25 to 50 hours for the organic EL elements of Comparative Examples 4 to 6.

[0145] Therefore, even when the compound having a structure represented by general formula (1) of the present invention is used in the intermediate layer (second hole transport layer) of a three-layer hole transport layer, the organic EL device of the present invention can improve the driving voltage compared to devices using conventional compounds due to the appropriate HOMO level and high hole mobility, and becomes a device with high power efficiency and long life.

[0146] Example 10 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.

[0147] 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, the electron acceptor (Acceptor-1) and the compound (BCFN) were deposited by binary deposition at a deposition rate ratio of Acceptor-1:BCFN = 3:97 so as to cover the transparent anode 2, thereby forming a 10 nm-thick hole injection layer 3. A compound (BCFN) having the above structural formula was deposited on the hole injection layer 3 to form a first hole transport layer 4a, with a thickness of 55 nm. A compound (2-1) of the present invention was deposited on the first hole transport layer 4a to form a second hole transport layer 4b, with a thickness of 10 nm. On the second hole-transporting layer 4b, a hole-transporting host (SiCzCz), an electron-transporting host (SiTrzCz2), a blue phosphorescent dopant (PtON-TBBI), and a TADF dopant (TBE02) having the following structure disclosed in Non-Patent Document 2 were deposited by quaternary vapor deposition at a deposition rate ratio of SiCzCz:SiTrzCz2:PtON-TBBI=60:27:12:1 to form an emitting layer 5 having a thickness of 30 nm. On the emitting layer 5, a compound (mSiTrz) was deposited to a thickness of 5 nm as a hole-blocking layer 6. On the hole-blocking layer 6, compound (ETM-1) and compound (ETM-2) were binary-deposited at a deposition rate ratio of compound (ETM-1):compound (ETM-2) = 50:50, thereby forming an electron-transporting layer 7 having a thickness of 30 nm. On the electron-transporting layer 7, ETM-2 was vapor-deposited to a thickness of 1 nm as an electron-injecting layer 8. Finally, aluminum was vapor-deposited to a thickness of 100 nm to form a cathode 9, thereby producing an organic EL device.

[0148]

[0149] Example 11 An organic EL device was produced under the same conditions as in Example 10, except that the compound (2-2) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 5 .

[0150] Example 12 An organic EL device was produced under the same conditions as in Example 10, except that the compound (2-3) of the present invention was used instead of the compound (2-1) as the material for the second hole transport layer 5 .

[0151] Comparative Example 7 An organic EL device was fabricated under the same conditions as in Example 10, except that SiCzCz was used as the material for the second hole transport layer 5 instead of the compound (2-1).

[0152] Comparative Example 8 An organic EL device was fabricated under the same conditions as in Example 10, except that BCFN was used as the material for the second hole transport layer 5 instead of the compound (2-1).

[0153] Comparative Example 9 An organic EL device was produced under the same conditions as in Example 10, except that compound A was used instead of compound (2-1) as the material for the second hole transport layer 5 .

[0154] The organic EL devices prepared in Examples 10 to 12 and Comparative Examples 7 to 9 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.

[0155] [Rule 26 Amendment 13.05.2025]

[0156] As shown in Table 6, at a brightness of 1000 cd / m ２ The driving voltage at 1000 kJ / s was 4.44 V for the organic EL element of Comparative Example 9, while the driving voltage at 1000 kJ / s was 4.27 to 4.28 V for the organic EL elements of Examples 10 to 12, which was a low driving voltage. In addition, the power efficiency was also high, at 15.4 to 15.8 lm / W, while the power efficiency was 13.6 to 14.6 lm / W for the organic EL elements of Comparative Examples 7 to 9. Furthermore, it can be seen that the element lifetime was 51 to 56 hours for the organic EL elements of Examples 10 to 12, which was longer than the element lifetime of 22 to 49 hours for the organic EL elements of Comparative Examples 7 to 9.

[0157] Therefore, even in an organic EL device having a second hole transport layer containing the compound represented by general formula (1) of the present invention and an emitting layer containing a phosphorescent emitting dopant and a TADF dopant, the organic EL device of the present invention can improve the driving voltage and become a device with high power efficiency and long life compared to devices using conventional compounds due to the appropriate HOMO level and high hole mobility.

[0158] 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.

[0159] The organic EL device of the present invention, which uses a compound having an indenocarbazole ring with a specific structure, has improved durability in addition to a reduced driving voltage, and can be applied to, for example, home appliances, lighting, and the like.

[0160] 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 10 third hole transport layer

Claims

1. A compound represented by the following formula (2-1):

2. A compound represented by the following formula (2-2):

3. A compound represented by the following formula (2-3):

4. 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, wherein the hole transport layer contains a compound having an indenocarbazole ring represented by the following general formula (1), and the emitting layer contains at least one phosphorescent emitting dopant: [wherein Ar represents a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenylyl group, a substituted or unsubstituted terphenyl group, a substituted or unsubstituted fluorenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthrenyl group, a substituted or unsubstituted dibenzofuranyl group, or a substituted or unsubstituted dibenzothienyl group; R １ ~R １６ represents a hydrogen atom, a deuterium atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted aromatic heterocyclic group; R １７ represents a methyl group, an unsubstituted phenyl group, or a deuterium-substituted phenyl group, and X represents an oxygen atom or a sulfur atom.

5. The organic electroluminescence device according to claim 4, wherein the hole transport layer is represented by a compound having an indenocarbazole ring of the following general formula (2): [wherein Ar, X and R １ ~R １７ is defined as in general formula (1).

6. The organic electroluminescence device according to claim 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 a compound having an indenocarbazole ring represented by general formula (1).

7. The organic electroluminescence device according to claim 4, wherein the host contains a first host compound having electron transporting ability and a second host compound having hole transporting ability, and the second host compound includes a compound having a carbazole structure.

8. The organic electroluminescence device according to claim 4, wherein a platinum complex is used as the phosphorescent material.

9. The organic electroluminescent device of claim 8, wherein the platinum complex comprises 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 comprises a carbene bond.

10. The organic electroluminescence device according to claim 9, wherein the platinum complex is represented by the following general formula (3): [In the formula, L １ and L ２ may be the same or different, and may represent a single bond, NR ２２ , 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 １８ ~R ２２ 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, or a substituted or unsubstituted aromatic heterocyclic group; L １ and L ２ At least one of the following is NR ２３ If R ２３ and R ２０ , R ２３ and R ２１ and R ２２ and R ２２ may be bonded to each other to form a ring.

11. The organic electroluminescence device according to claim 8, wherein the dopant comprises a platinum complex as a phosphorescent light-emitting material and an organoboron compound as a thermally activated delayed fluorescence (TADF) material.

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