Organic electroluminescent element

Abstract

The present invention provides a thermally activated delayed fluorescence emitting organic electric field light emitting element (organic EL element) with high luminous efficiency and long life under low driving voltage. The delayed fluorescence emitting organic EL element comprises one or more light emitting layers between an anode and a cathode facing each other, and at least one light emitting layer comprises a host material of a biphenylcarbazole compound type represented by the general formula (1) and a thermally activated delayed fluorescence emitting material of an indolecarbazole compound type containing an indolecarbazole ring in the molecule.

Description

Technical Field

[0001] The present invention relates to a delayed fluorescence emitting organic electric field light emitting element (also called organic electroluminescence (EL) element). Background Art

[0002] By applying voltage to the organic EL element, holes are injected into the light-emitting layer from the anode, and electrons are injected into the light-emitting layer from the cathode. Moreover, in the light-emitting layer, the injected holes recombine with electrons to generate excitons. At this time, according to the statistical law of electron spin, singlet excitons and triplet excitons are generated in a ratio of 1:3. It can be said that the limit of the internal quantum efficiency of the fluorescent organic EL element using the light emission of singlet excitons is 25%. On the other hand, it is known that the internal quantum efficiency of the phosphorescent organic EL element using the light emission of triplet excitons is increased to 100% when the intersystem crossing is efficiently performed from the singlet excitons.

[0003] In recent years, the technology of extending the life of phosphorescent organic EL elements has been developed and applied to displays of mobile phones, etc. However, as for blue organic EL elements, practical phosphorescent organic EL elements have not yet been developed, and there is a demand for the development of a blue organic EL element with high efficiency and long life.

[0004] Furthermore, a delayed fluorescence emitting organic EL element with high efficiency using delayed fluorescence is being developed recently. For example, Patent Document 1 discloses an organic EL element using a triplet-triplet fusion (TTF) mechanism as one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes the phenomenon of generating singlet excitons by the collision of two triplet excitons, and it is believed that the internal quantum efficiency can be increased to 40% in theory. However, compared with the phosphorescent organic EL element, the efficiency is lower, so further improvement of efficiency is required.

[0005] On the other hand, a delayed fluorescence emitting organic EL element using a thermally activated delayed fluorescence (TADF) mechanism is disclosed in non-patent document 1. The TADF mechanism is a mechanism that utilizes the following phenomenon: in a material with a small energy difference between a singlet energy level and a triplet energy level, an inverse intersystem crossing from a triplet exciton to a singlet exciton occurs, and it is believed that the internal quantum efficiency can be increased to 100% in theory. However, as with phosphorescent emitting elements, further improvement in life characteristics is required.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent document 1: WO2011 / 070963

[0009] Patent Document 2: US2014 / 0197386 A1

[0010] Patent Document 3: WO2016 / 017760

[0011] Patent Document 4: WO2015 / 022987

[0012] Patent Document 5: US2017 / 0352816 A1

[0013] Non-patent literature

[0014] Non-patent document 1: "Phys. Rev. Lett." 2013, 110, 247401

[0015] Patent Document 1 and Non-Patent Document 1 disclose the use of an indolocarbazole compound as a TADF material.

[0016] Patent Document 2 discloses a phosphorescent organic EL device using an indolocarbazole compound and a carbazole compound as a host, but does not disclose the use of the indolocarbazole compound as a delayed fluorescence emitting type light emitting layer material.

[0017] Patent Document 3 discloses a delayed fluorescence emitting organic EL device using the following compound as a host and an indoloindole compound as a light emitting material.

[0018] [Chemistry 1]

[0019]

[0020] Patent Document 4 discloses a delayed fluorescence emitting organic EL device using a compound to which 9-([1,1′-biphenyl]-4-yl)-9H-carbazole is linked as a host and a cyanobenzene compound as a light emitting material.

[0021] Patent Document 5 discloses a delayed fluorescence emitting organic EL device using the following compound as a host and a cyano group-containing indolocarbazole compound as a light-emitting material.

[0022] [Chemistry 2]

[0023]

[0024] However, none of the above can be said to be sufficient, and further improvement in characteristics is required. Summary of the invention

[0025] In order to apply organic EL elements to display elements such as flat panel displays or light sources, it is necessary to improve the luminous efficiency of the elements while fully ensuring the stability during driving. In view of the above situation, the present invention aims to provide an organic EL element that has high efficiency and high driving stability despite low driving voltage.

[0026] The present invention is an organic electroluminescent element, which is an organic EL element comprising one or more light-emitting layers between an anode and a cathode facing each other, wherein at least one light-emitting layer of the organic electroluminescent element comprises at least one host material and at least one thermally activated delayed fluorescence luminescent material, wherein at least one of the host materials is represented by the general formula (1), and at least one of the thermally activated delayed fluorescence luminescent materials is represented by the following general formula (2).

[0027] [Chemistry 3]

[0028]

[0029] Here, R 1 Each independently represents hydrogen, an aliphatic hydrocarbon group having 1 to 8 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group consisting of two to six aromatic rings of aromatic groups selected from the above aromatic hydrocarbon groups and the above aromatic heterocyclic groups, and may be condensed with a carbazole ring to form a condensed ring. 1 It is not a carbazole group.

[0030] [Chemistry 4]

[0031]

[0032] Here, Z is represented by formula (2a), wherein ring A is an aromatic hydrocarbon ring represented by formula (2b), ring B is a heterocyclic ring represented by formula (2c), and ring A and ring B are condensed with the adjacent ring at any position. 2 , an oxygen atom, and a sulfur atom.

[0033] Ar 1 with Ar 2 Each of them is independently a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group consisting of two to six linked aromatic rings of aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. 1 ,Ar 2In the case of linked aromatic groups, the linked aromatic rings may be the same or different. 2 Each of them is independently an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, and may be condensed with an adjacent ring to form a condensed ring. a represents an integer of 1 to 3, c and d independently represent an integer of 0 to 4, and j represents an integer of 0 to 2.

[0034] Preferred embodiments of the present invention are shown below.

[0035] 1) In the general formula (1), R 1 At least one of the groups is a substituted or unsubstituted phenyl group, a substituted or unsubstituted dibenzofuranyl group, a substituted or unsubstituted dibenzophenylthio group, a substituted or unsubstituted triazolyl group, a substituted or unsubstituted benzimidazolyl group, a substituted or unsubstituted fluorenyl group, or a linked aromatic group composed of two to four of these groups linked together.

[0036] 2) In the general formula (1), R 1 At least two of the groups are independently substituted or unsubstituted phenyl, substituted or unsubstituted dibenzofuranyl, substituted or unsubstituted dibenzophenylthio, substituted or unsubstituted triazolyl, substituted or unsubstituted benzimidazolyl, substituted or unsubstituted fluorenyl, or a linked aromatic group formed by linking two to four of these groups.

[0037] 3) The host material is a mixed host material containing at least one compound represented by the general formula (1).

[0038] 4) The host material is a mixed host material containing at least two compounds represented by the general formula (1).

[0039] 5) The difference between the excited singlet energy (S1) and the excited triplet energy (T1) of the thermally activated delayed fluorescence luminescent material is less than 0.2 eV, and the excited triplet energy (T1) of the main material represented by the general formula (1) is greater than the excited singlet energy (S1) and the excited triplet energy (T1) of the thermally activated delayed fluorescence luminescent material.

[0040] 6) In the general formula (2), X is N-Ar 2 Indicated.

[0041] 7) In the general formula (2), a=1, Ar 1 It is expressed by formula (3).

[0042] [Chemistry 5]

[0043]

[0044] Here, Y is a nitrogen atom or CR 3 , at least one Y is a nitrogen atom. 3 L is a hydrogen atom or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms. 2 is a single bond, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or an aromatic heterocyclic group having 3 to 17 carbon atoms, Ar 3 Each of them is independently a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a group formed by linking two to four aromatic rings of aromatic groups selected from the above aromatic hydrocarbon groups and the above aromatic heterocyclic groups.

[0045] The organic EL device of the present invention contains a specific host material and a specific thermally activated delayed fluorescence emitting material in the emitting layer, and thus can be an organic EL device with high luminous efficiency and long life at a low driving voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic cross-sectional view showing an example of an organic EL element.

[0047] Explanation of symbols

[0048] 1: Substrate

[0049] 2: Anode

[0050] 3: Hole injection layer

[0051] 4: Hole transport layer

[0052] 5: Luminous layer

[0053] 6: Electron transport layer

[0054] 7: Cathode DETAILED DESCRIPTION

[0055] The organic EL element of the present invention has one or more light-emitting layers between the opposing anode and cathode, and at least one of the light-emitting layers contains a host material represented by the general formula (1) and a thermally activated delayed fluorescence material (called TADF material) represented by the general formula (2).

[0056] The general formula (1) is described.

[0057] The compound represented by the general formula (1) has a skeleton in which biphenyl and a carbazole ring are linked at the para position, and is therefore also called a p-biphenylcarbazole compound.

[0058] R 1Each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 8 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group consisting of two to six aromatic rings of aromatic groups selected from the above aromatic hydrocarbon groups and the above aromatic heterocyclic groups. Preferably, it represents a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 16 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 15 carbon atoms, or a linked aromatic group consisting of two to four aromatic rings of aromatic groups selected from the above aromatic hydrocarbon groups and the above aromatic heterocyclic groups. Wherein, R 1 is not a substituted or unsubstituted carbazole group. 1 When the compound has a ring, the ring may be condensed with the carbazole ring.

[0059] Specific examples of the aliphatic hydrocarbon group having 1 to 8 carbon atoms include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, methylcyclohexyl, heptyl, and octyl.

[0060] The aromatic hydrocarbon group, aromatic heterocyclic group, or linked aromatic group may have a substituent. Specific examples of the substituent include an aliphatic hydrocarbon group having 1 to 12 carbon atoms and an alkoxy group having 1 to 12 carbon atoms, preferably an aliphatic hydrocarbon group having 1 to 8 carbon atoms and an alkoxy group having 1 to 8 carbon atoms. Specific examples of the aliphatic hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, methylcyclohexyl, heptyl, and octyl. Specific examples of the alkoxy group include methoxy, ethoxy, propoxy, and butoxy.

[0061] Specific examples of the aromatic hydrocarbon group having 6 to 18 carbon atoms, the aromatic heterocyclic group having 3 to 17 carbon atoms, or the linked aromatic group consisting of two to six aromatic rings of aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group include benzene, naphthalene, azulene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, ethanenaphthalene, coronene, indene, fluorene, fluoranthene, tetracene, pentacene, furan, dibenzofuran, thiophene, dibenzothiophene, oxazole, pyrrole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, benzimidazole, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carboline, diazacarbazole, or a group formed by removing one hydrogen atom from a linked aromatic compound in which two to six of these are linked. Preferred examples include benzene, naphthalene, phenanthrene, triphenylene, dibenzofuran, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, quinazoline, quinoline, diazacarbazole, benzimidazole, fluorene, or a group formed by removing one hydrogen from a linked aromatic compound composed of two to four of these. Further more preferred examples include benzene, dibenzofuran, dibenzothiophene, triazine, benzimidazole, fluorene, or a group formed by removing one hydrogen from a linked aromatic compound composed of two to four of these. As linked aromatic compounds, biphenyl, terphenyl, etc. can be mentioned.

[0062] In addition, in R 1 In the case of a ring, the ring may be condensed with a carbazole ring. For example, in the case of a benzene ring, a naphthalene ring, a furan ring, a thiophene ring, an indole ring, etc., these rings may be condensed with a carbazole ring to form a condensed ring of four or more rings. In the above case, the condensed ring is preferably four to six rings, and more preferably four or five rings.

[0063] Furthermore, in this specification, a linked aromatic group is a group in which two or more aromatic rings are directly bonded and linked, and the linked aromatic rings may be the same or different, may be an aromatic hydrocarbon ring, may be an aromatic heterocycle, may be straight-chained, or may be branched. In addition, it may also have a substituent. The carbon number of the linked aromatic group is the sum of the carbon numbers of the aromatic groups formed.

[0064] More preferably, R 1 At least one of them is an aromatic group selected from the group consisting of phenyl, dibenzofuranyl, dibenzophenylthio, triazolyl, benzimidazolyl, fluorenyl, and linked aromatic groups formed by linking two to four of these, or a substituted aromatic group having a substituent bonded to these. More preferably, R 1 At least two of the above-mentioned aromatic groups or substituted aromatic groups are said aromatic groups.

[0065] The substituent in this case is the same as described above, and is preferably an alkyl group having 1 to 8 carbon atoms or an alkoxy group having 1 to 8 carbon atoms.

[0066] In this specification, in the case of an aromatic hydrocarbon group, an aromatic heterocyclic group, etc. having a specific carbon number, when these have a substituent, the carbon number of the substituent is not counted when calculating the carbon number of these aromatic hydrocarbon groups, aromatic heterocyclic groups, etc. However, it is preferred that the total carbon number including the substituent is within the specific range.

[0067] Specific examples of the compound represented by the general formula (1) are shown below.

[0068] [Chemistry 6]

[0069]

[0070] [Chemistry 7]

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[0072] [Chemistry 8]

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[0074] [Chemistry 9]

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[0080] [Chemistry 12]

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[0100] [Chemistry 22]

[0101]

[0102] [Chemistry 23]

[0103]

[0104] [Chemistry 24]

[0105]

[0106] Next, the thermally activated delayed fluorescence material (TADF material) will be described.

[0107] The TADF material is a compound represented by the general formula (2) or a material containing the same.

[0108] In the general formula (2), Z is a group represented by the formula (2a), in the formula (2a), ring A is an aromatic hydrocarbon ring represented by the formula (2b), ring B is a heterocyclic ring represented by the formula (2c), and ring A and ring B are condensed with the adjacent ring at any position. X is selected from N-Ar 2 , oxygen atom, or sulfur atom. Preferably, X is N-Ar 2 .

[0109] a represents an integer of 1 to 3, preferably an integer of 1 to 2, and more preferably an integer of 1. c and d independently represent an integer of 0 to 4, and j represents an integer of 0 to 2. Preferably, c+d+j is an integer of 0 to 4, and more preferably 0, 1 or 2.

[0110] 1 For a valence group, Ar 2 It is a monovalent group. 1 with Ar 2Each independently represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, or a linked aromatic group consisting of two to six aromatic rings of aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. Preferably, it is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 16 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 15 carbon atoms, or a linked aromatic group consisting of two to four aromatic rings of aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. More preferably, it is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 12 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a linked aromatic group consisting of two to four aromatic rings of aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. For the description of the linked aromatic group, reference may be made to the description of the above-mentioned linked aromatic group.

[0111] As Ar 1 ,Ar 2 Specific examples include benzene, naphthalene, azulene, anthracene, phenanthrene, pyrene, Naphthacene, triphenylene, naphthalene, coronene, indene, fluorene, fluoranthene, tetracene, pentacene, furan, dibenzofuran, thiophene, dibenzothiophene, oxazole, pyrrole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carbazole, carboline, diazacarbazole, or a group formed by linking two to six of these to form a linked aromatic compound. Preferred are benzene, naphthalene, anthracene, phenanthrene, fluorene, furan, dibenzofuran, thiophene, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carbazole, carboline, diazacarbazole, or a group formed by linking an aromatic compound composed of two to four of these. More preferred are benzene, naphthalene, dibenzofuran, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, quinoline, isoquinoline, carbazole, or a group formed by linking an aromatic compound composed of two to four of these.

[0112] In addition, when a=1 in formula (2), Ar 1 Preferred examples include groups represented by the above formula (3).

[0113] In formula (3), L 2is a single bond or a divalent group. The divalent group is an aromatic hydrocarbon group having 6 to 18 carbon atoms or an aromatic heterocyclic group having 3 to 17 carbon atoms. An aromatic hydrocarbon group having 6 to 16 carbon atoms is preferred, and an aromatic hydrocarbon group having 6 carbon atoms is more preferred. Here, the aromatic hydrocarbon group having 6 carbon atoms is a phenylene group.

[0114] As L 2 Specific examples other than single bonds include benzene, naphthalene, azulene, anthracene, phenanthrene, pyrene, The group is a group generated from naphthacene, triphenylene, ethanenaphthalene, coronene, indene, fluorene, fluoranthene, tetracene, pentacene, furan, dibenzofuran, thiophene, dibenzothiophene, oxazole, pyrrole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carbazole, carboline, diazacarbazole, etc. Preferably, the group is a group generated from benzene, naphthalene, anthracene, phenanthrene, triphenylene, fluorene, etc. More preferably, it is a phenylene group.

[0115] In formula (3), Y is a nitrogen atom or CR 3 , at least one Y is a nitrogen atom. Ar 3 Each of them is independently a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms.

[0116] Specific examples of these aromatic hydrocarbon groups or aromatic heterocyclic groups include groups generated by removing one hydrogen from benzene, fluorene, dibenzofuran, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, carbazole, carboline, diazacarbazole, etc.

[0117] In Ar 1 ,Ar 2 ,Ar 3 , L 2 When it is an aromatic hydrocarbon group, an aromatic heterocyclic group, or a linked aromatic group, it may have a substituent. When it has a substituent, the substituent has the same meaning as R in the general formula (1). 1 The substituents of are the same as those described above.

[0118] R 2 is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 17 carbon atoms, and R 2 When the ring is present, it may be condensed with a substituted ring to form a condensed ring. In this case, the condensed ring is preferably six to ten rings.

[0119] Specific examples of the aliphatic hydrocarbon group having 1 to 10 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group.

[0120] Specific examples of the aromatic hydrocarbon group having 6 to 18 carbon atoms or the aromatic heterocyclic group having 3 to 17 carbon atoms include groups formed by removing one hydrogen atom from benzene, naphthalene, azulene, anthracene, phenanthrene, fluorene, dibenzofuran, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carbazole, carboline, diazacarbazole and the like. Preferred are groups formed by removing one hydrogen from benzene, naphthalene, dibenzofuran, thiophene, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, oxadiazole, triazole, imidazole, pyrazole, thiazole, indole, indazole, benzimidazole, benzothiazole, benzoxazole, quinoxaline, quinazoline, cinnoline, quinoline, isoquinoline, phthalazine, naphthyridine, carbazole, carboline, diazacarbazole, etc. More preferred are groups formed by removing one hydrogen from benzene, naphthalene, dibenzofuran, dibenzothiophene, pyridine, pyridazine, pyrimidine, pyrazine, triazine, diphenyltriazine, quinoline, isoquinoline, carbazole, etc.

[0121] In R 2 In the case of an aromatic hydrocarbon group or an aromatic heterocyclic group, it may have a substituent. 2 When having a substituent, the substituent is preferably an aliphatic hydrocarbon group having 1 to 8 carbon atoms or an alkoxy group having 1 to 8 carbon atoms.

[0122] Specific examples of the aliphatic hydrocarbon group having 1 to 8 carbon atoms and the alkoxy group having 1 to 8 carbon atoms are as follows: 1 The specific examples of the substituents are the same as those of .

[0123] Specific examples of the compound represented by general formula (2) are shown below.

[0124] [Chemistry 25]

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[0250] The compound represented by the general formula (1) is a host material, and the compound represented by the general formula (2) is a TADF material. By incorporating these compounds in the form of a host material or a TADF material in the light-emitting layer, a delayed fluorescence emitting organic EL device having excellent characteristics can be provided.

[0251] The difference (ΔE) between the excited singlet energy (S1) and the excited triplet energy (T1) of the TADF material is preferably 0.2 eV or less, more preferably 0 eV to 0.15 eV. By satisfying the above, it becomes an excellent TADF material, but if ΔE becomes larger than 0.3 eV, it is difficult to function as a TADF material.

[0252] In addition, if the triplet excited state energy (T1) of the host material is set to be larger than the singlet excited state energy (S1) and the triplet excited state energy (T1) of the TADF material, the function as a host is improved.

[0253] The TADF material and the main material may also include one compound or a mixture of multiple compounds.

[0254] When two or more compounds are used as TADF materials, it is sufficient that the compounds occupying more than 50 wt% satisfy the above characteristics, and it is preferred that all the compounds satisfy the above characteristics. Similarly, when two or more compounds are used as main materials, it is sufficient that the compounds occupying more than 50 wt% satisfy the above characteristics, and it is preferred that all the compounds satisfy the above characteristics.

[0255] In addition, by containing two or more compounds as host materials, the characteristics of the organic EL element can also be improved. If a compound with a large singlet energy (S1) is set as the first host, and a compound with a small singlet energy (S1) is set as the second host, it is preferred that the first host is a compound represented by the general formula (1). The second host may be a compound represented by the general formula (1) or a compound other than this, but is preferably a compound represented by the general formula (1).

[0256] Here, S1 and T1 were measured as follows.

[0257] On a quartz substrate, vacuum evaporation was performed at a vacuum degree of 10-4 The sample compound is evaporated under the condition of less than 100 Pa to form an evaporation film with a thickness of 100 nm. The luminescence spectrum of the evaporation film is measured, a tangent line is drawn to the starting point on the short wavelength side of the luminescence spectrum, and the wavelength value λedge[nm] of the intersection of the tangent line and the horizontal axis is substituted into the following formula (i) to calculate S1.

[0258] S1[eV]=1239.85 / λedge (i)

[0259] T1 is the phosphorescence spectrum of the vapor-deposited film, but in the case of a thin film of a single compound, the phosphorescence spectrum may not be obtained. In this case, a mixed thin film with an appropriate material having a T1 higher than that of the sample compound is prepared, and the phosphorescence spectrum is measured. A tangent is drawn to the starting point on the short wavelength side of the phosphorescence spectrum, and the wavelength value λedge [nm] of the intersection of the tangent and the horizontal axis is substituted into formula (ii) to calculate T1.

[0260] T1[eV]=1239.85 / λedge (ii)

[0261] Next, the structure of the organic EL element of the present invention will be described with reference to the drawings, but the structure of the organic EL element of the present invention is not limited thereto.

[0262] Figure 1 It is a cross-sectional view showing a structural example of a general organic EL element used in the present invention, wherein 1 represents a substrate, 2 represents an anode, 3 represents a hole injection layer, 4 represents a hole transport layer, 5 represents a light-emitting layer, 6 represents an electron transport layer, and 7 represents a cathode. The organic EL element of the present invention may also have an exciton blocking layer adjacent to the light-emitting layer, and may also have an electron blocking layer between the light-emitting layer and the hole injection layer. The exciton blocking layer may also be inserted into either the cathode side or the anode side of the light-emitting layer, or may be inserted into both sides at the same time. In the organic EL element of the present invention, an anode, a light-emitting layer, and a cathode are required layers, but in addition to the required layers, a hole injection transport layer and an electron injection transport layer may also be provided, and further, a hole blocking layer may also be provided between the light-emitting layer and the electron injection transport layer. Furthermore, a hole injection transport layer refers to either or both of a hole injection layer and a hole transport layer, and an electron injection transport layer refers to either or both of an electron injection layer and an electron transport layer.

[0263] Can also be Figure 1 In the opposite structure, that is, the cathode 7, the electron transport layer 6, the light emitting layer 5, the hole transport layer 4, and the anode 2 are sequentially stacked on the substrate 1, in which case, layers may be added or omitted as needed.

[0264] -Substrate-

[0265] The organic EL element of the present invention is preferably supported on a substrate. The substrate is not particularly limited as long as it is a substrate conventionally used in organic EL elements, and for example, a substrate made of glass, transparent plastic, quartz, etc. can be used.

[0266] -anode-

[0267] As the anode material in the organic EL element, a material containing a metal, alloy, conductive compound or a mixture of these with a large work function (4 eV or more) can be preferably used. As specific examples of such electrode materials, conductive transparent materials such as Au, CuI, indium tin oxide (ITO), SnO2, and ZnO can be listed. In addition, amorphous materials such as IDIXO (In2O3-ZnO) that can be made into transparent conductive films can also be used. The anode can be formed into a thin film by methods such as evaporation or sputtering, and a pattern of the desired shape can be formed by photolithography, or when the pattern accuracy is not very required (about 100 μm or more), a mask of the desired shape can be used during the evaporation or sputtering of the electrode material to form a pattern. Or when using a coatable substance such as an organic conductive compound, a wet film forming method such as printing or coating can also be used. In the case of extracting luminescence from the anode, it is ideal to make the transmittance greater than 10%. In addition, the sheet resistance of the anode is preferably less than hundreds of Ω / Y. The film thickness also depends on the material, but is usually selected within the range of 10 nm to 1000 nm, preferably 10 nm to 200 nm.

[0268] -cathode-

[0269] On the other hand, as a cathode material, a material containing a metal (called an electron injecting metal) with a small work function (less than 4 eV), an alloy, a conductive compound or a mixture of these can be used. As specific examples of such electrode materials, sodium, sodium-potassium alloys, magnesium, lithium, magnesium / copper mixtures, magnesium / silver mixtures, magnesium / aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al2O3) mixtures, indium, lithium / aluminum mixtures, rare earth metals, etc. Among these, in terms of electron injectability and durability relative to oxidation, etc., a mixture of an electron injecting metal and a second metal as a metal having a work function greater than that and being stable is suitable, such as a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al2O3) mixture, a lithium / aluminum mixture, aluminum, etc. The cathode can be made by forming a thin film of these cathode materials using methods such as evaporation or sputtering. In addition, as a cathode, the sheet resistance is preferably less than hundreds of Ω / Υ, and the film thickness is usually selected in the range of 10nm to 5μm, preferably 50nm to 200nm. Furthermore, in order to allow the emitted light to pass through, if either the anode or cathode of the organic EL element is transparent or semi-transparent, then the emission brightness is improved, which is advantageous.

[0270] In addition, after the metal is formed in the cathode with a film thickness of 1nm to 20nm, the conductive transparent material listed in the description of the anode is formed thereon, thereby making a transparent or translucent cathode. By applying the method, an element in which both the anode and the cathode are transparent can be made.

[0271] -Luminous layer-

[0272] The light-emitting layer is a layer that emits light after the holes and electrons injected from the anode and cathode are recombined to generate excitons. The TADF material represented by the general formula (2) and the host material represented by the general formula (1) are used simultaneously in the light-emitting layer. In addition, by containing two or more host materials as described above, the characteristics can also be improved. Furthermore, the TADF material can be used as a dopant material.

[0273] The dopant material may be contained in the light emitting layer in the form of one or more dopant materials. The content of the organic light emitting dopant material including the TADF material is preferably 0.1 wt% to 50 wt%, more preferably 1 wt% to 30 wt%, relative to the host material.

[0274] The organic EL element of the present invention is an organic EL element utilizing TADF, and therefore no phosphorescent dopant material is used.

[0275] The host material is preferably a compound having hole transporting ability, electron transporting ability and a high glass transition temperature.

[0276] When a plurality of host materials are used, each host can be deposited from different deposition sources, or they can be pre-mixed before deposition to form a premix, thereby allowing a plurality of hosts to be simultaneously deposited from one deposition source.

[0277] -Injection layer-

[0278] The so-called injection layer is a layer disposed between the electrode and the organic layer in order to reduce the driving voltage or increase the luminous brightness, including a hole injection layer and an electron injection layer, and may exist between the anode and the light-emitting layer or the hole transport layer, and between the cathode and the light-emitting layer or the electron transport layer. The injection layer may be disposed as required.

[0279] -Hole blocking layer-

[0280] The hole blocking layer, in a broad sense, has the function of an electron transport layer and includes a hole blocking material that has the function of transporting electrons but has a significantly lower ability to transport holes. It can increase the probability of recombination between electrons and holes in the light-emitting layer by transporting electrons and blocking holes.

[0281] Existing hole blocking layer materials can also be used in the hole blocking layer.

[0282] -Electron blocking layer-

[0283] The electron blocking layer, in a broad sense, has the function of a hole transporting layer, and can increase the probability of recombination between electrons and holes in the light-emitting layer by transporting holes and blocking electrons.

[0284] As the material of the electron blocking layer, existing electron blocking layer materials can be used, and in addition, the material of the hole transport layer described below can be used as needed. The film thickness of the electron blocking layer is preferably 3nm to 100nm, more preferably 5nm to 30nm. In addition, a compound represented by general formula (1) can also be used.

[0285] - Exciton blocking layer -

[0286] The so-called exciton blocking layer is a layer used to block the excitons generated by the recombination of holes and electrons in the light-emitting layer from diffusing to the charge transport layer. By inserting this layer, the excitons can be efficiently sealed in the light-emitting layer, which can improve the luminous efficiency of the element. The exciton blocking layer can be inserted between two adjacent light-emitting layers in an element with two or more adjacent light-emitting layers.

[0287] As the material of the exciton-blocking layer, a conventional exciton-blocking layer material can be used, for example, 1,3-dicarbazolylbenzene (mCP) or bis(2-methyl-8-hydroxyquinoline)-4-phenylphenol aluminum (III) (BAlq) can be mentioned.

[0288] -Hole transport layer-

[0289] The hole transport layer contains a hole transport material having a function of transporting holes, and the hole transport layer may be provided as a single layer or a plurality of layers.

[0290] As a hole transport material, it is a material having any of the injection or transport of holes and the barrier property of electrons, and can be any of organic and inorganic substances. In the hole transport layer, any compound can be selected from existing existing compounds and used. As the hole transport material, for example, porphyrin derivatives, arylamine derivatives, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styryl anthracene derivatives, fluorenone derivatives, hydrazone derivatives, distyrene derivatives, silazane derivatives, aniline copolymers, or conductive polymer oligomers, especially thiophene oligomers, etc., preferably using porphyrin derivatives, arylamine derivatives and styrylamine derivatives, more preferably using arylamine derivatives.

[0291] -Electron transport layer-

[0292] The electron transport layer contains a material having a function of transporting electrons, and the electron transport layer may be provided as a single layer or multiple layers.

[0293] As an electron transport material (also serving as a hole blocking material), it is sufficient to have the function of transmitting the electrons injected from the cathode to the light-emitting layer. In the electron transport layer, any compound can be selected from existing existing compounds for use, for example, polycyclic aromatic derivatives such as naphthalene, anthracene, and phenanthroline, tris (8-hydroxyquinoline) aluminum (III) derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, dioxide thiopyran derivatives, carbodiimide, fluorenyl methane derivatives, anthraquinone dimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, oxadiazole derivatives, benzimidazole derivatives, benzothiazole derivatives, indole and carbazole derivatives, etc. Furthermore, it is also possible to use polymer materials that introduce these materials into polymer chains or use these materials as the main chain of polymers.

[0294] The film-forming method of each layer when producing the organic EL device of the present invention is not particularly limited, and the device can be produced by any of a dry process and a wet process.

[0295] Example

[0296] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0297] The compounds used in the Examples are shown below. Table 1 shows S1, T1, and S1-T1 (ΔE) of the compounds used in the Examples and Comparative Examples.

[0298] [Chemistry 88]

[0299]

[0300] [Table 1]

[0301] Compound S1(eV) T1(eV) ΔE(eV) H-1 3.8 2.9 0.9 1-1 3.7 2.9 0.8 1-2 3.2 2.8 0.4 1-3 3.6 2.8 0.8 2-50 2.9 2.9 0.0 2-91 2.8 2.7 0.1 2-120 2.9 2.7 0.2 2-178 2.7 2.7 0.0 D-1 2.4 2.4 0.0 mCP 3.6 3.1 0.5

[0302] Experimental Example 1

[0303] The fluorescence lifetime of compound 2-120 was measured. On a quartz substrate, the vacuum was evaporated at a vacuum degree of 10 -4 Compound 2-120 and compound 1-1 were evaporated from different evaporation sources under conditions below 100 nm, and a co-evaporated film with a concentration of 15 wt% of compound 2-120 was formed with a thickness of 100 nm. The luminescence spectrum of the film was measured, and luminescence with a peak at 483 nm was confirmed. In addition, under a nitrogen environment, the luminescence lifetime was measured by a small fluorescence lifetime measurement device (Quantaurus-tau manufactured by Hamamatsu Photonics). Fluorescence with an excitation lifetime of 12 ns and delayed fluorescence of 13 μs were observed, and it was confirmed that compound 2-120 was a compound that exhibited delayed fluorescence.

[0304] The fluorescence lifetimes of Compound 2-50, Compound 2-91, and Compound 2-178 were measured in the same manner as described above, and delayed fluorescence was observed, confirming that they were materials that exhibited delayed fluorescence.

[0305] Example 1

[0306] On a glass substrate on which an anode made of ITO with a film thickness of 70 nm was formed, a vacuum deposition method was used at a vacuum degree of 4.0×10 -5 Pa is used to stack each thin film. First, on ITO, HAT-CN is formed to a thickness of 10nm as a hole injection layer, and then, compound HT-1 is formed to a thickness of 25nm as a hole transport layer. Then, compound HT-2 is formed to a thickness of 5nm as an electron blocking layer. Moreover, compound 1-1 as the main body and compound 2-50 as a dopant are co-deposited from different evaporation sources to form a light-emitting layer with a thickness of 30nm. At this time, co-evaporation is performed under evaporation conditions in which the concentration of compound 2-50 becomes 30wt%. Then, compound ET-2 is formed to a thickness of 5nm as a hole blocking layer. Then, compound ET-1 is formed to a thickness of 40nm as an electron transport layer. Furthermore, on the electron transport layer, lithium fluoride (LiF) is formed to a thickness of 1nm as an electron injection layer. Finally, on the electron injection layer, aluminum (Al) is formed to a thickness of 70nm as a cathode to produce an organic EL element.

[0307] Examples 1 to 10, Comparative Examples 1 to 5

[0308] In Example 1, an organic EL element was produced in the same manner as in Example 1 except that the host and the dopant were the compounds shown in Table 2. Here, when the second host was used as the host, co-evaporation was performed under the evaporation conditions where the weight ratio of the first host to the second host was 50:50, thereby producing the light-emitting layer.

[0309] [Table 2]

[0310] Dopant main body Second subject Example 1 2-50 1-1 - Example 2 2-50 1-3 - Example 3 2-120 1-1 - Example 4 2-120 1-3 - Example 5 2-91 1-1 - Example 6 2-91 1-3 - Example 7 2-178 1-1 - Example 8 2-178 1-3 - Example 9 2-120 1-1 1-2 Example 10 2-120 1-1 ET-2 Comparative Example 1 2-50 mCP - Comparative Example 2 2-120 mCP - Comparative Example 3 2-50 H-1 - Comparative Example 4 2-120 H-1 - Comparative Example 5 D-1 1-1 -

[0311] The maximum wavelength of the emission spectrum, external quantum efficiency (EQE), voltage, and device life of the prepared organic EL device are shown in the following table. Maximum wavelength, EQE, and voltage are when the driving current density is 2.5 mA / cm 2 The lifetime is set at 2.5 mA / cm 2 The time it takes for the brightness to decay to 95% of the initial brightness at a constant current density.

[0312] [Table 3]

[0313]

[0314] According to the table, it is known that Examples 1 to 10 using a host represented by the general formula (1) and a dopant represented by the general formula (2) in the light-emitting layer have high luminous efficiency and excellent life characteristics compared with Comparative Examples 1 to 2 using mCP generally used as a host. In addition, it is known that Examples 1 to 8 using a host represented by the general formula (1) and a dopant represented by the general formula (2) in the light-emitting layer have excellent life characteristics compared with Comparative Example 5 using an indole indole compound as a dopant. In addition, it is known that Examples 1 to 8 using a biphenylcarbazole compound have high luminous efficiency and excellent life characteristics compared with Comparative Examples 3 and 4 using a phenylcarbazole compound. In addition, it is known that Examples 9 and 10 using a second host have high luminous efficiency and excellent life characteristics compared with Example 3 using a single host.

Claims

1. An organic electric field light-emitting element, comprising one or more light-emitting layers between an anode and a cathode facing each other, wherein at least one light-emitting layer comprises at least one host material and at least one thermally activated delayed fluorescent light-emitting material, at least one of the host materials is represented by the following general formula (1), and at least one of the thermally activated delayed fluorescent light-emitting materials is represented by the following general formula (2), Here, R 1 Each independently represents hydrogen, an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or an aromatic heterocyclic group having 3 to 17 carbon atoms; wherein, R 1 It is not a carbazole group; R 1 At least one of the groups is an aromatic group selected from the group consisting of a dibenzofuranyl group, a dibenzothiophenyl group, and a fluorenyl group; Here, Z is represented by formula (2a), wherein ring A is an aromatic hydrocarbon ring represented by formula (2b), ring B is a heterocyclic ring represented by formula (2c), and ring A and ring B are condensed with the adjacent ring at any position; X is N-Ar 2 ; Ar 1 is a group represented by the following formula (3), Ar 2 is phenyl; a represents 1, c, d, and j represent 0; Here, Y is a nitrogen atom or CR 3 , at least one Y is a N atom; L 2 is a single bond or a phenylene group, R 3 is a hydrogen atom or an aromatic hydrocarbon group having 6 to 18 carbon atoms; Ar 3 are each independently phenyl.

2. The organic electroluminescent element according to claim 1, characterized in that: R 1 At least two of the above mentioned aromatic groups are aromatic groups.

3. The organic electroluminescent element according to claim 1 or 2, characterized in that: The host material is a mixed host material containing two or more compounds.

4. The organic electroluminescent element according to claim 3, characterized in that: The host material is a mixed host material containing at least two host compounds represented by the general formula (1).

5. The organic electroluminescent element according to claim 1, characterized in that: The difference between the excited singlet energy (S1) and the excited triplet energy (T1) of the thermally activated delayed fluorescence luminescent material represented by the general formula (2) is less than 0.2 eV, and the excited triplet energy (T1) of the main material represented by the general formula (1) is greater than the excited singlet energy (S1) and the excited triplet energy (T1) of the thermally activated delayed fluorescence luminescent material.

6. An organic electric field light-emitting element comprising one or more light-emitting layers between an anode and a cathode facing each other, wherein at least one light-emitting layer comprises at least one host material and at least one thermally activated delayed fluorescence light-emitting material, at least one of the host materials is represented by the following compound 1-2, and at least one of the thermally activated delayed fluorescence light-emitting materials is represented by the following general formula (2): Here, Z is represented by formula (2a), wherein ring A is an aromatic hydrocarbon ring represented by formula (2b), ring B is a heterocyclic ring represented by formula (2c), and ring A and ring B are condensed with the adjacent ring at any position; X is N-Ar 2 ; Ar 1 is a group represented by the following formula (3), Ar 2 is phenyl; a represents 1, c, d, and j represent 0; Here, Y is a nitrogen atom or CR 3 , at least one Y is a N atom; L 2 is a single bond or a phenylene group, R 3 is a hydrogen atom or an aromatic hydrocarbon group having 6 to 18 carbon atoms; Ar 3 are each independently phenyl.

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