Organic electroluminescent element

Abstract

The present invention addresses of the problem of providing an organic EL element that has high efficiency, low drive voltage, and a long lifespan by combining various materials for an organic EL element, which have excellent hole injection / transport performance, such that the properties of each material can be effectively demonstrated.　Given that using, in combination, materials for a hole transport layer which have specific mobility leads to efficient transportation of holes that are injected from a positive electrode-side and to high electron blocking ability, the present invention was completed by using a specific amine compound for a hole transport layer to produce an organic EL element having high efficiency, low drive voltage, and a long lifespan.

Description

organic electroluminescence element

[0001] The present invention relates to an organic electroluminescent element, which is a self-luminous element suitable for various display devices, and more particularly to an organic electroluminescent element (hereinafter abbreviated as organic EL element) using a compound having a specific mobility.

[0002] Organic EL elements are self-luminous elements, and therefore are brighter than liquid crystal elements, have excellent visibility, 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 are assigned to each material. They layered a phosphor capable of transporting electrons and an organic material capable of transporting holes, and emitted light by injecting both charges into the phosphor layer, achieving 1000 cd / m at a voltage of 10 V or less. ２ Such high brightness is achieved (see, for example, Patent Documents 1 and 2).

[0004] To date, many improvements have been made to put organic EL elements into practical use, and the various roles of the laminated structure have been further subdivided. In 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, high efficiency and durability have been achieved by light-emitting elements with a bottom emission structure that emits light from the bottom (see, for example, Non-Patent Document 1).

[0005] In recent years, light-emitting elements with a top-emission structure, which uses a metal with a high work function as the anode and emits light from the top, have come into use. In a bottom-emission structure, where light is extracted from the bottom where the pixel circuit is located, the area of ​​the light-emitting section is limited, but in a light-emitting element with a top-emission structure, light is extracted from the top, so it is not blocked by the pixel circuit, and so the light-emitting section can be made larger.

[0006] In organic EL devices, charges injected from both electrodes are recombined in the light-emitting layer to emit light, but it is important to efficiently transfer both charges, holes and electrons, to the light-emitting layer, and it is therefore necessary to create a device with excellent carrier balance. To improve light-emitting efficiency, the hole injection property and the electron blocking property that blocks electrons injected from the cathode are enhanced to increase the probability of recombination of holes and electrons, and further, high light-emitting efficiency can be achieved by confining excitons generated in the light-emitting layer.

[0007] N,N'-diphenyl-N,N'-di(α-naphthyl)benzidine (NPD) and various aromatic amine derivatives have been known to be hole transport materials used in organic EL devices up to now (see, for example, Patent Document 1 and Patent Document 2). NPD has good hole transport ability, but its glass transition point (Tg), which is an index of heat resistance, is as low as 96°C, and crystallization occurs under high temperature conditions, resulting in a deterioration of device characteristics (see, for example, Non-Patent Document 3). In addition, among the aromatic amine derivatives described in the above patent documents, there are those with a hole mobility of 10 －３ cm ２ Although compounds having excellent mobility of .gtoreq..times ...

[0008] Arylamine compounds having a substituted carbazole structure have been proposed as compounds with improved properties such as heat resistance and hole injection properties (see, for example, Patent Documents 3 and 4). However, in devices using these compounds in the hole injection layer or hole transport layer, although improvements have been achieved in heat resistance and luminous efficiency, these improvements are still insufficient, and further reductions in driving voltage and further improvements in luminous efficiency are desired.

[0009] To improve the device characteristics of organic EL devices and increase the device production yield, there is a demand for devices that can recombine holes and electrons with high efficiency, have high luminous efficiency, low driving voltage, and have a long life, by combining materials that have excellent hole and electron injection and transport properties, and have excellent thin film stability and durability.

[0010] Furthermore, in order to improve the device characteristics of organic EL devices, there is a demand for devices with a good carrier balance, high efficiency, low driving voltage, and long life, which can be achieved by combining materials that have excellent hole and electron injection and transport properties, as well as thin film stability and durability.

[0011] US5792557US5639914US8021764 B2US8394510 B2International Publication No. 2014 / 009310US2019 / 0006596 A1US2016 / 0118591 A1US2017 / 0179398 A1

[0012] Proceedings of the 9th Seminar of the Society of Applied Physics, pp. 55-61 (2001); Appl. Phys. Lett., 98, 083302 (2011); Proceedings of the 3rd Regular Meeting of the Organic EL Discussion Society, pp. 13-14 (2006)

[0013] An object of the present invention is to provide an organic EL element that is highly efficient, has a low driving voltage, and has a long life, by combining various materials for organic EL elements that have excellent hole injection and transport properties so that the properties of each material can be effectively exhibited.

[0014] The physical properties that the organic EL element to be provided by the present invention should have are (1) high luminous efficiency and power efficiency, (2) low practical driving voltage, and (3) long life.

[0015] In order to achieve the above object, the present inventors have discovered that by using a combination of materials for the hole transport layer having specific mobilities, holes injected from the anode side can be efficiently transported and electron blocking properties can be enhanced, resulting in an organic EL device with high efficiency, low driving voltage, and long life. As a result, the present invention has been completed.

[0016] That is, the present invention provides the following organic EL element.

[0017] 1) An organic electroluminescence device having at least an anode, a first hole transport layer, a second hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in this order, wherein the second hole transport layer contains an amine compound represented by the following general formula (1) or (2), and the mobility μ1 of the first hole transport layer and the mobility μ2 of the second hole transport layer simultaneously satisfy the following formulas (A) and (B): μ2>1.0×10 －３ cm ２ / Vs (A) μ2 / μ1>1.5 (B)

[0018] In formula (1), A and B may be the same or different and represent a monovalent group represented by the following general formula (1-1): Ar １ represents a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted condensed polycyclic aromatic group.

[0019] In formula (1-1), the dashed line represents a binding site, and R １ and R ２ may be the same or different, and represent a hydrogen atom, a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group of 1 to 6 carbon atoms which may have a substituent, a cycloalkyl group of 5 to 10 carbon atoms which may have a substituent, a linear or branched alkenyl group of 2 to 6 carbon atoms which may have a substituent, a linear or branched alkyloxy group of 1 to 6 carbon atoms which may have a substituent, a cycloalkyloxy group of 5 to 10 carbon atoms which may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted condensed polycyclic aromatic group, or a substituted or unsubstituted aryloxy group. １ and R ２ 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.

[0020] In formula (2), Ar ２ , Ar ３ , Ar ４ and Ar ５may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted condensed polycyclic aromatic group, R ３ When a plurality of groups are present, they may be the same or different and represent a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted condensed polycyclic aromatic group; and n represents an integer of 1 to 5.

[0021] 2) In the monovalent group represented by the general formula (1-1), R １ and R ２ may be the same or different and are a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted fused polycyclic aromatic group having 6 to 30 carbon atoms.

[0022] 3) In the amine compounds represented by the general formula (1) and the general formula (2), Ar １ , Ar ２ , Ar ３ , Ar ４ and Ar ５ may be the same or different and are a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms or a substituted or unsubstituted fused polycyclic aromatic group having 6 to 30 carbon atoms.

[0023] 4) The mobility μ1 of the first hole transport layer is 1.5×10 －３ cm ２ 4) The organic electroluminescence device according to any one of 1) to 3), wherein the Vref is 0.1 V or less.

[0024] 5) The mobility μ2 of the second hole transport layer is 2.0×10 －３ cm ２ 5) The organic electroluminescence device according to any one of 1) to 4), wherein the Vref is 0.1 V or more.

[0025] 6) The organic electroluminescence device according to any one of 1) to 5), wherein the first hole transport layer has a thickness of more than 30 nm and less than 200 nm, and the second hole transport layer has a thickness of more than 3 nm and less than 20 nm.

[0026] Ar in general formula (1)１ Specifically, the "aromatic hydrocarbon group" or "fused polycyclic aromatic group" in the "substituted or unsubstituted aromatic hydrocarbon group" or "substituted or unsubstituted fused polycyclic aromatic group" represented by the formula (I) can be selected from aryl groups having 6 to 30 carbon atoms, as well as phenyl groups, biphenylyl groups, terphenylyl groups, naphthyl groups, anthracenyl groups, phenanthrenyl groups, fluorenyl groups, spirobifluorenyl groups, indenyl groups, pyrenyl groups, perylenyl groups, fluoranthenyl groups, triphenylenyl groups, etc., and preferred are phenyl groups, biphenylyl groups, terphenylyl groups, naphthyl groups, anthracenyl groups, phenanthrenyl groups, fluorenyl groups, and spirobifluorenyl groups. 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, a substituted or unsubstituted amine group, an oxygen atom, or a sulfur atom to form a ring.

[0027] Ar in general formula (1) １Specific examples of the "substituent" in the "substituted or unsubstituted aromatic hydrocarbon group" or "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; and aromatic hydrocarbon groups or condensed polycyclic aromatic groups such as a pyridyl group, a biphenylyl group, a terphenylyl 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, a substituted or unsubstituted amine group, an oxygen atom, or a sulfur atom to form a ring.

[0028] In the general formula (1), Ar １ is preferably a phenyl group or a biphenylyl group.

[0029] R in general formula (1-1) １ , R ２Specific examples of the "straight-chain or branched alkyl group having 1 to 6 carbon atoms," "cycloalkyl group having 5 to 10 carbon atoms," or "straight-chain or branched alkenyl group having 2 to 6 carbon atoms" in the "straight-chain or branched alkyl group having 1 to 6 carbon atoms which may have a substituent," "cycloalkyl group having 5 to 10 carbon atoms which may have a substituent," or "straight-chain or branched alkenyl group having 2 to 6 carbon atoms which may have a substituent" represented by the above formula include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an ethyl ... Examples of the substituent include an aryl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, a cyclopentyl group, a cyclohexyl group, a 1-adamantyl group, a 2-adamantyl group, a vinyl group, an allyl group, an isopropenyl group, and a 2-butenyl group. 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, a substituted or unsubstituted amine group, an oxygen atom, or a sulfur atom to form a ring.

[0030] R in general formula (1-1) １ , R ２ Specific examples of the "straight-chain or branched alkyloxy group having 1 to 6 carbon atoms" or "cycloalkyloxy group having 5 to 10 carbon atoms" in the "straight-chain or branched alkyloxy group having 1 to 6 carbon atoms which may have a substituent" or "cycloalkyloxy group having 5 to 10 carbon atoms which may have a substituent" represented by the formula (I) include a methyloxy group, an ethyloxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, a tert-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, a cyclopentyloxy group, a cyclohexyloxy group, a cycloheptyloxy group, a cyclooctyloxy group, a 1-adamantyloxy group, a 2-adamantyloxy group, and the like. 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, a substituted or unsubstituted amine group, an oxygen atom, or a sulfur atom to form a ring.

[0031] R in general formula (1-1) １ , R ２ Specific examples of the "aryloxy group" in the "substituted or unsubstituted aryloxy group" represented by the formula (I) include a phenyloxy group, a biphenylyloxy group, a terphenylyloxy group, a naphthyloxy group, an anthracenyloxy group, a phenanthrenyloxy group, a fluorenyloxy group, an indenyloxy group, a pyrenyloxy group, and a perylenyloxy group.

[0032] R in general formula (1-1) １ , R ２ The "substituted or unsubstituted aromatic hydrocarbon group" or the "substituted or unsubstituted fused polycyclic aromatic group" represented by the following general formula (1) is Ar １ This is the same as the "substituted or unsubstituted aromatic hydrocarbon group" or "substituted or unsubstituted condensed polycyclic aromatic group" represented by the following formula:

[0033] In general formula (1-1), R １ and R ２ may be the same or different, and are preferably a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted condensed polycyclic aromatic group, more preferably a substituted or unsubstituted aromatic hydrocarbon group, and even more preferably a phenyl group. １ and R ２ It is also preferred that one of the groups is a methyl group which may have a substituent and the other is a phenyl group, and that they are bonded to each other via a single bond to form a five-membered ring.

[0034] Ar in general formula (2) ２ , Ar ３ , Ar ４ and Ar ５ The "substituted or unsubstituted aromatic hydrocarbon group" or the "substituted or unsubstituted fused polycyclic aromatic group" represented by the following general formula (1) is Ar １ This is the same as the "substituted or unsubstituted aromatic hydrocarbon group" or "substituted or unsubstituted condensed polycyclic aromatic group" represented by the following formula:

[0035] R in general formula (2)３ The "substituted or unsubstituted aromatic hydrocarbon group" or the "substituted or unsubstituted fused polycyclic aromatic group" represented by the following general formula (1) is Ar １ This is the same as the "substituted or unsubstituted aromatic hydrocarbon group" or "substituted or unsubstituted condensed polycyclic aromatic group" represented by the following formula:

[0036] In the general formula (2), Ar ２ , Ar ３ , Ar ４ and Ar ５ may be the same or different and are preferably substituted or unsubstituted aromatic hydrocarbon groups, more preferably phenyl groups or biphenylyl groups.

[0037] In general formula (2), R ３ When there are a plurality of groups, they may be the same or different and are preferably a hydrogen atom or a substituted or unsubstituted aromatic hydrocarbon group, more preferably a hydrogen atom or a phenyl group.

[0038] In formula (2), n represents an integer of 1 to 5, preferably 2, 3, 4 or 5, and particularly preferably 3.

[0039] The organic EL device of the present invention exhibits the following characteristics by virtue of the mobilities of the first hole transport layer and the second hole transport layer simultaneously satisfying the above formulas (A) and (B): (1) good hole injection characteristics, (2) high luminous efficiency, and (3) long life. The combination of the first hole transport layer and the second hole transport layer of the present invention is suitable for organic EL devices.

[0040] In the present invention, by using a compound in which the ratio of the mobility of the second hole transport layer to the mobility of the first hole transport layer is greater than 1.5, carrier transport into the light-emitting layer is enhanced, and quenching of carriers and excitons due to accumulation of carriers at the interface between the second hole transport layer and the light-emitting layer is reduced, thereby achieving high light-emitting efficiency.Furthermore, deterioration and quenching due to decomposition of the compound due to accumulation of carriers and excitons at the interface between the second hole transport layer and the light-emitting layer are prevented, thereby providing a device with a long life.

[0041] In the present invention, the hole transport layer has a two-layer structure of a first hole transport layer and a second hole transport layer, and the second hole transport layer located adjacent to the light-emitting layer contains an arylamine compound represented by general formula (1) or (2). This makes it possible to make the most of the electron blocking ability of the compound, thereby realizing an organic EL element with higher efficiency and longer life.

[0042] Furthermore, in the present invention, by using a compound that simultaneously satisfies the above formula (A) and formula (B) and has a large difference in mobility as a constituent material of the hole transport layer of a two-layer structure, excellent hole injection properties and hole transport properties are exhibited, thereby making it possible to realize an organic EL device with a low driving voltage.

[0043] 1 is a diagram showing the structural formulas of compounds (1-1) to (1-12) as examples of arylamine compounds represented by general formula (1). 2 is a diagram showing the structural formulas of compounds (2-1) to (2-12) as examples of arylamine compounds represented by general formula (2). 3 is a diagram showing an example of the configuration of an organic EL element of the present invention.

[0044] Of the arylamine compounds represented by the general formula (1) that are suitably used in the organic EL device of the present invention, specific examples of preferred compounds are shown in FIG. 1, and of the arylamine compounds represented by the general formula (2), specific examples of preferred compounds are shown in FIG. 2, but the present invention is not limited to these compounds.

[0045] The arylamine compounds represented by general formula (1) and general formula (2) can be purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization or crystallization using a solvent, sublimation purification, etc. The compounds can be identified by NMR analysis. It is preferable to measure mobility as a physical property value. Mobility is an index of hole transportability and hole blocking ability. It is preferable to use compounds used in the organic EL device of the present invention that have been purified by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization or crystallization using a solvent, sublimation purification, etc., and then finally purified by sublimation purification (see, for example, Patent Documents 6, 7, and 8).

[0046] The mobility can be measured by the time of flight method using a highly sensitive carrier mobility measurement device (TOF-401, manufactured by Sumitomo Heavy Industries, Ltd.). The time of flight method is a method in which an electric field is applied to an element in which a thin film of an organic semiconductor material of several micrometers is sandwiched between a transparent anode such as ITO and a cathode such as Al, carriers are generated in a sheet form near the transparent electrode with a pulsed laser, and the mobility is calculated from the time it takes for the carriers to reach the cathode due to the applied voltage. The mobility is expressed by the following formula (C): μ = L / (tE) (C), where μ is the mobility (cm ２ / Vs), where L is the film thickness (cm), t is the time it takes to reach the cathode (s), and E is the electric field (V / cm). The mobility in the present invention is a value at an electric field strength of 250,000 (V / cm).

[0047] The organic EL device of the present invention has, in order on at least a substrate, an anode, a first hole transport layer, a second hole transport layer, an emitting layer, an electron transport layer, and a cathode. The organic EL device of the present invention may have a hole injection layer between the anode and the first hole transport layer, a hole blocking layer between the emitting layer and the electron transport layer, or an electron injection layer between the electron transport layer and the cathode. For example, the organic EL device may have a layer that serves both as a hole injection layer and a first hole transport layer, or a layer that serves both as an electron injection layer and an electron transport layer. Furthermore, the organic EL device may have a two-layer first hole transport layer, a two-layer second hole transport layer, a two-layer emitting layer, or a two-layer electron transport layer. In the organic EL device of the present invention, it is preferable that the second hole transport layer is adjacent to the emitting layer and functions as an electron blocking layer.

[0048] The anode of the organic EL element of the present invention uses an electrode material with a large work function, such as ITO or gold. The hole injection layer of the organic EL element of the present invention can use materials such as starburst triphenylamine derivatives and various triphenylamine tetramers; porphyrin compounds typified by copper phthalocyanine; acceptor heterocyclic compounds such as hexacyanoazatriphenylene; and coating-type polymer materials. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0049] The hole-transporting material that can be used for the first hole-transporting layer of the organic EL device of the present invention may be any material that satisfies the above formula (A), and examples thereof include benzidine derivatives such as N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (hereinafter abbreviated as TPD), N,N'-diphenyl-N,N'-di(α-naphthyl)benzidine (hereinafter abbreviated as NPD), and N,N,N',N'-tetrabiphenylylbenzidine; 1,1-bis[4-(di-4-tolylamino)phenyl]cyclohexane (hereinafter abbreviated as TAPC); and in particular, arylamine compounds having a structure in which two triphenylamine structures are linked in the molecule by a single bond or a divalent group not containing a heteroatom, such as N,N,N',N'-tetrabiphenylylbenzidine. Further, arylamine compounds having a structure in which three or more triphenylamine structures are linked by a single bond or a divalent group not containing a heteroatom in the molecule, such as various triphenylamine trimers and tetramers, can be mentioned. These may be formed into a film alone, or may be mixed with other materials to form a single layer. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0050] Furthermore, it is also possible to use materials that are typically used for the hole injection layer or the first hole transport layer, such as those doped with P-trisbromophenylaminehexachloroantimony or radialene derivatives (see, for example, Patent Document 5), or polymer compounds having a structure of a benzidine derivative such as TPD in their partial structure.

[0051] The arylamine compound represented by the general formula (1) or (2) is used as a material for the second hole transport layer of the organic EL device of the present invention. Examples of hole transport materials that can be mixed with or used simultaneously with the arylamine compound represented by the general formula (1) or (2) include carbazole derivatives such as 4,4',4''-tri(N-carbazolyl)triphenylamine (TCTA), 9,9-bis[4-(carbazol-9-yl)phenyl]fluorene, 1,3-bis(carbazol-9-yl)benzene (mCP), and 2,2-bis(4-carbazol-9-ylphenyl)adamantane (Ad-Cz), and compounds having a triphenylsilyl group and a triarylamine structure, such as 9-[4-(carbazol-9-yl)phenyl]-9-[4-(triphenylsilyl)phenyl]-9H-fluorene. These compounds may be used alone or as a single layer formed by mixing with other materials. These materials can be used to form thin films by known methods such as vapor deposition, spin coating, and ink jet printing.

[0052] The mobility μ1 of the compound listed as a constituent material of the first hole transport layer is 1.5×10 －３ cm ２ / Vs or less, and preferably 1.0×10 －３ cm ２ It is more preferable that the voltage is equal to or less than / Vs.

[0053] The mobility μ2 of the compound listed as a constituent material of the second hole transport layer is 1.0×10 －３ cm ２ / Vs, and preferably more than 2.0 × 10 －３ cm ２ It is more preferable that the voltage is equal to or higher than / Vs.

[0054] The ratio (μ2 / μ1) of the mobility μ1 of the second hole transport layer μ2 to the mobility μ1 of the first hole transport layer in the present invention is preferably greater than 1.5, more preferably greater than 2.0, and even more preferably greater than 3.0.

[0055] The light-emitting layer of the organic EL element of the present invention is ３In addition to metal complexes of quinolinol derivatives such as those mentioned above, various metal complexes, anthracene derivatives, bisstyrylbenzene derivatives, pyrene derivatives, oxazole derivatives, polyparaphenylenevinylene derivatives, etc. can be used. The light-emitting layer may be composed of a host material and a dopant material. Anthracene derivatives are preferably used as the host material. In addition to the light-emitting materials, heterocyclic compounds having an indole ring as a partial structure of a fused ring, heterocyclic compounds having a carbazole ring as a partial structure of a fused ring, carbazole derivatives, thiazole derivatives, benzimidazole derivatives, polydialkylfluorene derivatives, etc. can also be used. Pyrene derivatives are preferably used as the dopant material. Other examples include quinacridone, coumarin, rubrene, perylene, and derivatives thereof, benzopyran derivatives, indenophenanthrene derivatives, rhodamine derivatives, and aminostyryl derivatives. These may be formed alone, or may be mixed with other materials to form a single layer, or may be stacked with other layers formed alone, other layers formed as a mixture, or a layer formed alone and a layer formed as a mixture.

[0056] It is also possible to use a phosphorescent emitter as the light-emitting material. As the phosphorescent emitter, a phosphorescent emitter of a metal complex such as iridium or platinum can be used. For example, Ir(ppy) ３ green phosphorescent emitters such as FIrpic and FIr6; blue phosphorescent emitters such as Btp ２ Examples of suitable host materials include red phosphorescent emitters such as Ir(acac), and examples of suitable host materials include hole-injecting / transporting host materials such as 4,4'-di(N-carbazolyl)biphenyl (CBP), carbazole derivatives such as TCTA, and mCP. Examples of suitable host materials include p-bis(triphenylsilyl)benzene (UGH2) and 2,2',2''-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) (TPBI), allowing the fabrication of high-performance organic EL devices.

[0057] The phosphorescent light-emitting material is preferably doped into the host material by co-evaporation in a range of 1 to 30 weight percent based on the total weight of the light-emitting layer in order to avoid concentration quenching.

[0058] Furthermore, materials that emit delayed fluorescence, such as CDCB derivatives such as PIC-TRZ, CC2TA, PXZ-TRZ, and 4CzIPN, can also be used as light-emitting materials (see, for example, Non-Patent Document 2).

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

[0060] For the hole-blocking layer of the organic EL device of the present invention, compounds having hole-blocking properties can be used, such as metal complexes of phenanthroline derivatives such as bathocuproine (BCP) and quinolinol derivatives such as aluminum(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (hereinafter abbreviated as BAlq), as well as various rare earth complexes, triazole derivatives, triazine derivatives, and oxadiazole derivatives. These materials may also serve as materials for the electron-transporting layer. These materials may be formed alone or mixed with other materials to form a single layer, or may form a laminate structure of layers formed alone, layers formed in a mixture, or layers formed in a mixture with layers formed alone. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0061] The electron transport layer of the organic EL element of the present invention is ３Examples of materials that can be used include metal complexes of quinolinol derivatives such as BAlq, various metal complexes, triazole derivatives, triazine derivatives, oxadiazole derivatives, pyridine derivatives, pyrimidine derivatives, benzimidazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silole derivatives. These materials may be formed into films alone, or may be mixed with other materials to form a single layer, or may be laminated with other layers formed alone, other layers formed as a mixture, or layers formed as a mixture with other layers formed alone. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0062] For the electron injection layer of the organic EL element of the present invention, 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), and cesium (Cs) can be used, but this can be omitted in the preferred selection of the electron transport layer and the cathode.

[0063] Furthermore, materials normally used for the electron injection layer or electron transport layer may be doped with N-type metal such as cesium.

[0064] The cathode of the organic EL device of the present invention is made of an electrode material having a low work function such as aluminum, or an alloy having an even lower work function such as a magnesium-silver alloy, a magnesium-indium alloy, or an aluminum-magnesium alloy.

[0065] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0066] [Mobility Measurement] The mobility of the compounds used in the Examples and Comparative Examples was measured as follows. On a bottom substrate on which a 50 nm thick ITO film had been formed, the following compounds (1-10), (2-3), and (2-10), which were used as constituent materials for the second hole transport layer, were each vapor-deposited to a thickness of 4 μm, and aluminum was formed thereon as a cathode to a thickness of 100 nm to prepare a device, and the mobility was measured using a highly sensitive carrier mobility measurement device (TOF-401, manufactured by Sumitomo Heavy Industries, Ltd.). The following compounds (HTM-1) and (HTM-2), which were used as constituent materials for the first hole transport layer, were also measured. Furthermore, for comparison, the following compound (HTM-3) was also measured, and the results are summarized below.

[0067]

[0068]

[0069] Mobility of each compound (cm ２ / Vs) were as follows: Compound (1-10): 2.63 × 10 －３ Compound (2-3): 5.61×10 －３ Compound (2-10): 3.70×10 －３ Compound (HTM-1): 8.41×10 －４ Compound (HTM-2): 5.75×10 －４ Compound (HTM-3): 8.06×10 －４

[0070] [Example 1] An organic EL device was fabricated using the compound, and its characteristics were evaluated. As shown in Figure 3, the organic EL device was fabricated by vapor-depositing a hole injection layer 3, a first hole transport layer 4, a second hole transport layer 5, a light-emitting layer 6, an electron transport layer 7, an electron injection layer 8, a cathode 9, and a capping layer 10 in this order on a glass substrate 1 on which a reflective ITO electrode was previously formed as a transparent anode 2.

[0071] Specifically, a glass substrate 1 on which a 50 nm thick ITO film, a 100 nm thick silver alloy reflective film, and a 5 nm thick ITO film were sequentially formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes and then dried for 10 minutes on a hot plate heated to 250°C. This was then subjected to UV ozone treatment for 15 minutes, 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, a hole injection layer 3 was formed covering the transparent anode 2 by binary deposition of an electron acceptor (Acceptor-1) and a compound (HTM-1) of the following structural formula at a deposition rate ratio of Acceptor-1:compound (HTM-1) = 3:97, resulting in a thickness of 10 nm. On this hole injection layer 3, a first hole transport layer 4 was formed of a compound (HTM-1) to a thickness of 140 nm. On this first hole transport layer 4, the compound (1-10) was formed as a second hole transport layer 5 to a thickness of 5 nm. On this second hole transport layer 5, a compound (EMD-1) having the following structure and a compound (EMH-1) having the following structural formula were binary-evaporated at a vapor deposition rate ratio of compound (EMD-1):(EMH-1) = 5:95 to form a light-emitting layer 6 to a thickness of 20 nm. On this light-emitting layer 6, a compound (ETM-1) having the following structural formula and a compound (ETM-2) having the following structural formula were binary-evaporated at a vapor deposition rate ratio of compound (ETM-1):(ETM-2) = 50:50 to form a layer to a thickness of 30 nm. On this electron transport layer 7, lithium fluoride was formed as an electron injection layer 8 to a thickness of 1 nm. On this electron injection layer 8, a magnesium-silver alloy was formed as a cathode 9 to a thickness of 12 nm. Finally, a compound (CPL-1) having the following structural formula was formed as a capping layer 10 to a thickness of 60 nm. For the fabricated organic EL devices, the mobility (μ2) of the second hole transport layer and the mobility (μ1) of the first hole transport layer, based on the values ​​in the "mobility measurement" above, as well as the ratio of the mobility of the second hole transport layer to the mobility of the first hole transport layer (μ2 / μ1), were calculated. The results are summarized in Table 1. Furthermore, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0072]

[0073]

[0074]

[0075]

[0076] [Example 2] Organic EL devices were fabricated under the same conditions as in Example 1, except that compound (2-3) was used instead of compound (1-10) as the material for the second hole transport layer 5. For the fabricated organic EL devices, the mobility ratios (μ2 / μ1) of compound (2-3) in the second hole transport layer and compound (HTM-1) in the first hole transport layer are summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0077] Example 3 Organic EL devices were fabricated under the same conditions as in Example 1, except that compound (2-10) was used instead of compound (1-10) as the material for the second hole transport layer 5. For the fabricated organic EL devices, the mobility ratios (μ2 / μ1) of compound (2-10) in the second hole transport layer and compound (HTM-1) in the first hole transport layer are summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0078] Example 4 Organic EL devices were fabricated under the same conditions as in Example 1, except that compound (HTM-2) was used instead of compound (HTM-1) as the material for hole injection layer 3 and first hole transport layer 4. For the fabricated organic EL devices, the mobility ratios (μ2 / μ1) of compound (1-10) in the second hole transport layer and compound (HTM-2) in the first hole transport layer are summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0079] Example 5 Organic EL devices were fabricated under the same conditions as in Example 2, except that compound (HTM-2) was used instead of compound (HTM-1) as the material for hole injection layer 3 and first hole transport layer 4. For the fabricated organic EL devices, the mobility ratios (μ2 / μ1) of compound (2-3) in the second hole transport layer and compound (HTM-2) in the first hole transport layer are summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0080] Example 6 Organic EL devices were fabricated under the same conditions as in Example 3, except that compound (HTM-2) was used instead of compound (HTM-1) as the material for hole injection layer 3 and first hole transport layer 4. For the fabricated organic EL devices, the mobility ratios (μ2 / μ1) of compound (2-10) in the second hole transport layer and compound (HTM-2) in the first hole transport layer are summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0081] [Comparative Example 1] For comparison, an organic EL device was fabricated under the same conditions as in Example 1, except that compound (HTM-3) was used instead of compound (1-10) as the material for second hole transport layer 5. For the fabricated organic EL device, the mobility ratio (μ2 / μ1) of compound (HTM-3) in the second hole transport layer to compound (HTM-1) in the first hole transport layer is summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0082] [Comparative Example 2] For comparison, an organic EL device was fabricated under the same conditions as in Example 4, except that compound (HTM-3) was used instead of compound (1-10) as the material for second hole transport layer 5. For the fabricated organic EL device, the mobility ratio (μ2 / μ1) of compound (HTM-3) in the second hole transport layer to compound (HTM-2) in the first hole transport layer is summarized in Table 1. In addition, the results of measuring the luminescence characteristics when a DC voltage was applied in the atmosphere at room temperature are summarized in Table 2.

[0083]

[0084] As shown in Table 1, in the hole transport layers of the devices of Examples 1 to 6, the mobility of the compound in the second hole transport layer was 2.0×10 －３ cm ２ / Vs or more, satisfying general formula (A), and the ratio (μ2 / μ1) of the mobility of the second hole transport layer to the mobility of the first hole transport layer is greater than 3.0, satisfying general formula (B). On the other hand, in the hole transport layers of the elements of Comparative Examples 1 and 2, the mobility of the compound in the second hole transport layer is 1.0×10 －３ cm ２ / Vs or less, and the ratio (μ2 / μ1) of the mobility of the second hole transport layer to the mobility of the first hole transport layer is less than 1.5, which indicates that general formula (A) and general formula (B) are not satisfied.

[0085] The voltage, brightness, luminous efficiency, and power efficiency shown in Table 2 are measured in air at room temperature and at a current density of 10 mA / cm ２ The value is the value when a current of 1000 cd / m is applied. ２ When the device is driven at a constant current, the luminance is 1900 cd / m ２ (corresponding to 95% of the initial brightness: 95% decay)

[0086]

[0087] As shown in Table 2, the current density was 10 mA / cm ２ The voltage when a current of 10 mA / cm was passed was 3.59 to 3.67 V for the elements of Comparative Examples 1 and 2, while it was 3.41 to 3.51 V for the elements of Examples 1 to 6, which was clearly a lower voltage. ２ The luminous efficiency when a current of 100 kJ / s was passed through the devices of Examples 1 to 6 was 8.20 to 8.67 cd / A, which was clearly higher than that of the devices of Comparative Examples 1 and 2, which was 7.66 to 7.94 cd / A. The power efficiency was also clearly higher, at 7.48 to 7.90 lm / W, which was higher than that of the devices of Comparative Examples 1 and 2, which was 6.56 to 6.94 lm / W. Furthermore, the device lifetime (95% decay) was 371 to 453 hours, which was significantly longer than that of the devices of Comparative Examples 1 and 2, which was 263 to 279 hours.

[0088] As is clear from the above results, the organic EL element of the present invention, which uses an arylamine compound having a specific structure represented by general formula (1) or general formula (2) in the second hole transport layer and further satisfies general formulas (A) and (B), is an organic EL element that has a lower driving voltage, higher luminous efficiency, and a longer lifetime than the conventional organic EL element of the comparative example that does not satisfy general formulas (A) and (B).

[0089] The organic EL device of the present invention has a two-layer hole transport layer, and an arylamine compound having a specific structure is used in the second hole transport layer, and satisfies general formula (A) and general formula (B). As a result, the organic EL device has improved luminous efficiency and durability compared to conventional organic EL devices, and can be used in applications such as home appliances and lighting.

[0090] REFERENCE SIGNS LIST 1 glass substrate 2 transparent anode 3 hole injection layer 4 first hole transport layer 5 second hole transport layer 6 light emitting layer 7 electron transport layer 8 electron injection layer 9 cathode 10 capping layer

Claims

1. An organic electroluminescent device having at least an anode, a first hole transport layer, a second hole transport layer, a light-emitting layer, an electron transport layer, and a cathode in this order, the second hole transport layer contains an amine compound represented by general formula (2), An organic electroluminescence device, wherein the mobility μ1 of the first hole transport layer and the mobility μ2 of the second hole transport layer simultaneously satisfy the following formulas (A) and (B): μ2>1.0×10 －３ cm ２ / Vs (A) μ2 / μ1>1.5 (B) 【Chemical 1】 In formula (2), Ar ２ , Ar ３ , Ar ４ and Ar ５ may be the same or different and represent a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted condensed polycyclic aromatic group, R ３ When a plurality of groups are present, they may be the same or different and each represents a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group, or a substituted or unsubstituted condensed polycyclic aromatic group, n represents an integer from 1 to 5;

2. In the amine compound represented by the general formula (2), Ar 2, Ar ３ , Ar ４ and Ar ５ may be the same or different and are a substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms or a substituted or unsubstituted fused polycyclic aromatic group having 6 to 30 carbon atoms.

3. The mobility μ1 of the first hole transport layer is 1.5×10 －３ cm ２ 2. The organic electroluminescence device according to claim 1, wherein the voltage V s is 0.1 V or less.

4. The mobility μ2 of the second hole transport layer is 2.0×10 －３ cm ２ 2. The organic electroluminescence device according to claim 1, wherein the Vref is 0.1 V or more.

5. 5. The organic electroluminescence device according to claim 1, wherein the first hole transport layer has a thickness of more than 30 nm and less than 200 nm, and the second hole transport layer has a thickness of more than 3 nm and less than 20 nm.

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