Patent Application
20240224800
The present invention relates to an organic electroluminescent device (also referred to as an organic EL device) that can transform electric energy into light, and a material for an organic electroluminescent device used therein.
When a voltage is applied to an organic EL device, holes and electrons are injected from the anode and the cathode, respectively, into the light emitting layer. Then, the injected holes and electrons are recombined in the light emitting layer to thereby generate excitons. At this time, according to the electron spin statistics theory, singlet excitons and triplet excitons are generated at a ratio of 1:3. In the fluorescent organic EL device that uses emission caused by singlet excitons, the limit of the internal quantum efficiency is said to be 25%. On the other hand, it has been known that, in the phosphorescent organic EL device that uses emission caused by triplet excitons, the internal quantum efficiency can be enhanced up to 100% when intersystem crossing efficiently occurs from singlet excitons.
A technology for extending the lifetime of a phosphorescent organic EL device has advanced in recent years, and the device is being applied to a display of a mobile phone and others. Regarding a blue organic EL device, however, a practical phosphorescent organic EL device has not been developed, and thus the development of a blue organic EL device having high efficiency and a long lifetime is desired.
Further, a highly efficient delayed fluorescence organic EL device utilizing delayed fluorescence has been developed, in recent years. For example, Patent Literature 1 discloses an organic EL device utilizing the Triplet-Triplet Fusion (TTF) mechanism, which is one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes a phenomenon in which a singlet exciton is generated by the collision of two triplet excitons, and it is believed that the internal quantum efficiency can be enhanced up to 40%, in theory. However, its efficiency is low as compared with the efficiency of the phosphorescent organic EL device, and thus further improvement in efficiency is desired.
On the other hand, Patent Literature 2 discloses an organic EL device utilizing the Thermally Activated Delayed Fluorescence (TADF) mechanism. The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing occurs from the triplet exciton to the singlet exciton in a material having a small energy difference between the singlet level and the triplet level, and it is believed that the internal quantum efficiency can be enhanced up to 100%, in theory.
The driving voltage, emission efficiency, and lifetime characteristics of the organic EL device largely depend on electron transporting materials that transport charges such as holes and electrons to the light emitting layer and host materials in the light emitting layer. Among them, materials having a carbazole backbone are known as the material for transporting holes (hole transport material) (e.g., see Patent Literatures 3 to 5). The above materials having a carbazole backbone are also known as the host material of the light emitting layer (e.g., see Patent Literatures 4 to 7 and Non Patent Literature 1).
In view of applying an organic EL device to a display device such as a flat panel display and a light source, it is necessary to improve the emission efficiency of the device and sufficiently ensure the stability of the device at the time of driving, at the same time. The present invention has been made under such circumstances, and an object thereof is to provide a material for an organic electroluminescent device that has high emission efficiency and high driving stability and allows a practically useful organic EL device to be obtained, and an organic EL device including the material for an organic electroluminescent device.
The present invention is a material for an organic electroluminescent device represented by the following general formula (1).
In the formula, Ar1 is a group represented by any of the following general formulas (2) to (11), and “*” represents a bonding site. Some or all hydrogen atoms in the compounds represented by the general formula (1) and the following general formulas (2) to (11) are optionally replaced by deuterium atoms.
In the formula, Ar2 represents an unsubstituted phenyl group or an unsubstituted biphenyl group. X1 represents oxygen or sulfur. X2 represents unsubstituted N-phenyl, unsubstituted N-biphenyl, unsubstituted N-terphenyl, oxygen, or sulfur.
In the formula, n represents an integer of 0 to 1, and preferably 0.
The general formula (1) is preferably represented by the following general formula (12).
In the formula, Ar1 is the same as those defined in the general formula (1). A hydrogen atom in the compound represented by the general formula (12) is optionally replaced by a deuterium atom.
In the general formulas (1) and (12), Ar1 is preferably represented by the general formula (2) or (3)
The general formulas (1) and (12) are preferably represented by the following general formula (13).
In the formula, Ar2 is the same as those defined in the general formula (3). A hydrogen atom in the compound represented by the general formula (13) is optionally replaced by a deuterium atom.
The present invention is an organic electroluminescent device including one or more organic layers between an anode and a cathode opposite to each other, wherein at least one of the organic layers contains the above material for an organic electroluminescent device.
In the organic electroluminescent device of the present invention, it is preferred that at least one organic layer of the organic layers be a light emitting layer and the organic electroluminescent device additionally contain a thermally activated delayed fluorescence material in the light emitting layer.
In the organic electroluminescent device of the present invention, it is preferred that at least one organic layer of the organic layers be a light emitting layer and the organic electroluminescent device additionally contain a phosphorescence material in the light emitting layer.
In the organic electroluminescent device of the present invention, it is preferred that at least one organic layer of the organic layers be a light emitting layer, the light emitting layer contain one or more host materials, and at least one host material be the above material for an organic electroluminescent device.
In the organic electroluminescent device of the present invention, it is preferred that at least one organic layer of the organic layers be a light emitting layer, the light emitting layer contain two or more host materials, the above material for an organic electroluminescent device be used as the first host, and a compound represented by any of the following general formulas (14) to (20) be used as the second host.
In the formula, Ar3 to Ar20 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon group and the aromatic heterocyclic group. Ar21 and Ar22 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 17 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group and the aromatic heterocyclic group. A hydrogen atom in the compounds represented by the general formulas (14) to (20) is optionally replaced by a deuterium atom.
In the organic electroluminescent device of the present invention, at least one organic layer of the organic layers is an electron blocking layer or a hole transport layer, and the organic electroluminescent device can contain the above material for an organic electroluminescent device in the electron blocking layer or the hole transport layer.
According to the present invention, a practically useful organic EL device having high emission efficiency as well as high driving stability and long lifetime characteristics can be obtained.
The compound represented by the general formula (1) in the present invention will be described in detail.
Ar1 is a group represented by any of the general formulas (2) to (11), preferably a group represented by any of the general formula (2) or (3), and more preferably a group represented by the general formula (3), and “*” represents a bonding site.
Ar2 represents an unsubstituted phenyl group or an unsubstituted biphenyl group, and preferably an unsubstituted phenyl group.
X1 represents oxygen or sulfur, and preferably represents oxygen.
X2 represents unsubstituted N-phenyl, unsubstituted N-biphenyl, unsubstituted N-terphenyl, oxygen, or sulfur, and preferably N-phenyl. When X2 represents unsubstituted N-terphenyl, the terphenyl may be linear or branched.
The “*” in the general formulas (2) to (11) represents a bonding site, and Ar1 can be bonded at any position of the carbazole ring in the general formula (1), and preferably bonded at the 3-position of the carbazole ring in the general formula (1).
Some or all hydrogen atoms in the compounds represented by the general formula (1) and the general formulas (2) to (11) can be replaced by deuterium atoms.
The t-Bu group in the compound represented by the general formula (1) can be substituted at the ortho, meta, or para position, and is preferably substituted at the meta or para position.
The t-Bu group in the compound represented by the general formula (1) refers to a tert-butyl group substituted at a specific phenyl group in the general formula (1).
Conventional compounds having a carbazole backbone do not necessarily have sufficient performance as the light emitting device material. For example, it is known that lifetime characteristics are improved by using 9-[1,1′-biphenyl]-4-yl-9′-phenyl-3,3′-bi-9H-carbazole having a backbone in which two carbazoles are linked as a hole-transporting host of a phosphorescence device. However, driving voltage increases, and the heat resistance of the organic EL device decreases due to a relatively low glass transition temperature. In this regard, the present inventors have considered that introducing a t-Bu group into a conventional carbazole compound improves hole injection properties, allows driving voltage to be reduced when the compound is used as an electron blocking layer or a hole-transporting host, increases the glass transition temperature, and improves the heat resistance of the organic EL device. In addition, the present inventors have considered that, when a t-Bu group is introduced into the carbazole compound, lifetime characteristics may vary depending on the introduction position or the number of introductions, and thus the invention of the compound represented by the general formula (1) have achieved.
Specific examples of the material for an organic electroluminescent device represented by the general formula (1) are shown below, but the materials are not limited to these exemplified compounds.
A practically excellent organic EL device having high emission efficiency and high driving stability can be provided by containing the material for an organic electroluminescent device represented by the general formula (1) in the organic layer.
The organic EL device is preferably an organic EL device in which at least one of the organic layers is a light emitting layer, and which contains a thermally activated delayed fluorescence material or a phosphorescence material in the light emitting layer, and more preferably an organic EL device containing a thermally activated delayed fluorescence material in the light emitting layer.
A superior organic EL device can be provided by the light emitting layer containing, as needed, at least one host material with a thermally activated delayed fluorescence material or phosphorescence material, and the at least one host material is preferably the material for an organic electroluminescent device represented by the general formula (1).
Next, the structure of the organic EL device of the present invention will be described with reference to the drawing, but the structure of the organic EL device of the present invention is not limited thereto.
It is also possible to have a structure that is the reverse of the structure shown in
The organic EL device of the present invention is preferably supported on a substrate. The substrate is not particularly limited and may be a substrate conventionally used for organic EL devices, and for example, a substrate made of glass, transparent plastic, or quartz can be used.
As the anode material in the organic EL device, a material made of a metal, alloy, or conductive compound having a high work function (4 eV or more), or a mixture thereof is preferably used. Specific examples of such an electrode material include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO2, and ZnO. An amorphous material capable of producing a transparent conductive film such as IDIXO (In2O3—ZnO) may also be used. As the anode, these electrode materials may be formed into a thin film by a method such as vapor deposition or sputtering, and then a pattern of a desired form may be formed by photolithography. Alternatively, when a highly precise pattern is not required (about 100 μm or more), a pattern may be formed through a mask of a desired form at the time of vapor deposition or sputtering of the above electrode materials. Alternatively, when a coatable material such as an organic conductive compound is used, a wet film forming method such as a printing method and a coating method can also be used. When light is extracted from the anode, the transmittance is desirably more than 10%, and the sheet resistance as the anode is preferably several hundred Ω/square or less. The film thickness is selected within a range of usually 10 to 1,000 nm, and preferably 10 to 200 nm, although it depends on the material.
On the other hand, a material made of a metal (referred to as an electron injection metal), alloy, or conductive compound having a low work function (4 eV or less) or a mixture thereof is used as the cathode material. Specific examples of such an electrode material include sodium, a sodium-potassium alloy, magnesium, lithium, a magnesium/copper mixture, a magnesium/silver mixture, a magnesium/aluminum mixture, a magnesium/indium mixture, an aluminum/aluminum oxide (Al2O3) mixture, indium, a lithium/aluminum mixture, and a rare earth metal. Among them, in terms of electron injection properties and durability against oxidation and the like, a mixture of an electron injection metal with a second metal that has a higher work function value than the electron injection metal and is stable, for example, a magnesium/silver mixture, a magnesium/aluminum mixture, a magnesium/indium mixture, an aluminum/aluminum oxide (Al2O3) mixture, a lithium/aluminum mixture, or aluminum is suitable. The cathode can be produced by forming a thin film from these cathode materials by a method such as vapor deposition and sputtering. The sheet resistance as the cathode is preferably several hundred Ω/square or less, and the film thickness is selected within a range of usually 10 nm to 5 μm, and preferably 50 to 200 nm. To transmit the light emitted, either one of the anode and the cathode of the organic EL device is favorably transparent or translucent because light emission brightness is improved.
The above metal is formed on the cathode to have a film thickness of 1 to 20 nm, and then a conductive transparent material mentioned in the description of the anode is formed on the metal, so that a transparent or translucent cathode can be produced. By applying this process, a device in which both anode and cathode have transmittance can be produced.
The light emitting layer is a layer that emits light after holes and electrons respectively injected from the anode and the cathode are recombined to form exciton. The light emitting layer may be either a single layer or a plurality of layers, and each layer contains an organic light emitting dopant material and a host material.
Only one organic light emitting dopant or two or more organic light emitting dopants may be contained in the light emitting layer. The content of the organic light emitting dopant is preferably 0.1 to 50 wt %, and more preferably 0.1 to 40 wt % based on the host material.
When a phosphorescence dopant (also referred to as a phosphorescence material) is used as the organic light emitting dopant material, a phosphorescence dopant containing an organic metal complex including at least one metal selected from the group consisting of ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold is preferred. Specifically, iridium complexes described in J. Am. Chem. Soc. 2001, 123, 4304 and JP2013-530515 A are suitably used, but are not limited thereto.
The phosphorescence dopant material is not particularly limited, but specific examples thereof include the following.
When a fluorescence dopant is used as the light emitting dopant material, examples of the fluorescence dopant include, but are not particularly limited to, fused polycyclic aromatic derivatives, styrylamine derivatives, fused ring amine derivatives, boron-containing compounds, pyrrole derivatives, indole derivatives, carbazole derivatives, and indolocarbazole derivatives. Among them, fused ring amine derivatives, boron-containing compounds, carbazole derivatives, and indolocarbazole derivatives are preferred. Examples of the fused ring amine derivatives include diaminepyrene derivatives, diaminochrysene derivatives, diaminoanthracene derivatives, diaminofluorenone derivatives, and diaminofluorene derivatives fused with one or more benzofuro backbones. Examples of the boron-containing compounds include pyrromethene derivatives and triphenylborane derivatives.
The fluorescence dopant material is not particularly limited, but specific examples thereof include the following.
When a thermally activated delayed fluorescence dopant (also referred to as a thermally activated delayed fluorescence material) is used as the light emitting dopant material, examples of the thermally activated delayed fluorescence dopant include, but are not particularly limited to, metal complexes such as tin complexes and copper complexes, the indolocarbazole derivative described in WO2011/070963, the cyanobenzene derivative and carbazole derivative described in Nature 2012, 492, 234, the fenadine derivative, oxadiazole derivative, triazole derivative, sulfone derivative, phenoxazine derivative, acridine derivative described in Nature Photonics 2014, 8, 326, and the arylborane derivative described in Adv. Mater. 2016, 28, 2777.
The thermally activated delayed fluorescence dopant material is not particularly limited, but specific examples thereof include the following.
The compound represented by the general formula (1) is preferably used as the host material in the light emitting layer. The glass transition temperature of the compound represented by the general formula (1) is preferably 120° C. or more. When the compound represented by the general formula (1) is used in any of the organic layers other than the light emitting layer, a known host material used for a phosphorescence device or a fluorescence device can be used other than the compound represented by the general formula (1). A usable known host material is a compound having the ability to transport hole, the ability to transport electron, and a high glass transition temperature, and preferably has a higher triplet excited energy (T1) than the triplet excited energy (T1) of the light emitting dopant material. A TADF-active compound may also be used as the host material, and the TADF-active compound preferably has a difference (ΔEST=S1−T1) between the singlet excited energy (S1) and the triplet excited energy (T1), of 0.20 eV or less. In addition, the compound represented by the general formula (1) and a further known host material may be used in combination. Further, a plurality of known host materials may be used in combination.
Here, S1 and T1 are measured as follows.
A sample compound (thermally activated delayed fluorescence material) is deposited on a quartz substrate by a vacuum deposition method under conditions of a degree of vacuum of 10−4 Pa or less to form a deposition film having a thickness of 100 nm. For S1, the emission spectrum of this deposition film is measured, a tangent is drawn to the rise of the emission spectrum on the short-wavelength side, and the wavelength value λedge [nm] of the point of intersection of the tangent and the horizontal axis is substituted into the following equation (i) to calculate S1.
S1 [eV]=1239.85/λedge (i)
For T1, on the other hand, the phosphorescence spectrum of the above deposition film is measured, a tangent is drawn to the rise of the phosphorescence spectrum on the short-wavelength side, and the wavelength value λedge [nm] of the point of intersection of the tangent and the horizontal axis is substituted into the following equation (ii) to calculate T1.
T1 [eV]=1239.85/λedge (ii)
The known host materials are known in a large number of Patent Literatures and the like, and hence may be selected from them. Specific examples of the host material include, but are not particularly limited to, various metal complexes typified by metal complexes of indole compounds, carbazole compounds, indolocarbazole compounds, pyridine compounds, pyrimidine compounds, triazine compounds, triazole compounds, oxazole compounds, oxadiazole compounds, imidazole compounds, phenylenediamine compounds, arylamine compounds, anthracene compounds, fluorenone compounds, stilbene compounds, triphenylene compounds, carborane compounds, porphyrin compounds, phthalocyanine compounds, and 8-quinolinol compounds, and metal phthalocyanine, and metal complexes of benzoxazole and benzothiazole compounds; and polymer compounds such as poly(N-vinyl carbazole) compounds, aniline-based copolymer compounds, thiophene oligomers, polythiophene compounds, polyphenylene compounds, polyphenylene vinylene compounds, and polyfluorene compounds. Preferred examples thereof include carbazole compounds, indolocarbazole compounds, pyridine compounds, pyrimidine compounds, triazine compounds, anthracene compounds, triphenylene compounds, carborane compounds, and porphyrin compounds.
A preferred host is not particularly limited, but specific examples thereof include the following.
When the compound represented by the general formula (1) and a further known host material are used in combination, the compound represented by the general formula (1) has good hole injection/transport properties, and thus it is preferred to use the compound represented by the general formula (1) as the first host in combination with an electron-transporting compound as the second host. The electron-transporting compound is not particularly limited, but a triazine compound is preferred. Such a preferred triazine compound as the second host will be described below.
When a plurality of hosts is used, each host is deposited from different deposition sources, or a plurality of hosts is premixed before vapor deposition to form a premix, whereby a plurality of hosts can be simultaneously deposited from one deposition source.
When the first host and the second host are premixed and then used, the difference in 50% weight reduction temperature (T50) is desirably small to produce an organic EL device having good characteristics with good reproducibility. The 50% weight reduction temperature refers to a temperature at which the weight is reduced by 50%, when the temperature is raised from room temperature at a rate of 10° C. per minute until 550° C. in TG-DTA measurement under reduced nitrogen gas pressure (1 Pa). The vaporization due to evaporation or sublimation is considered to be most frequently generated around this temperature.
The difference in the 50% weight reduction temperature between the first host and the second host in the premix is preferably within 20° C. By vaporizing and depositing the premix from a single deposition source, a uniform deposition film can be obtained. In this case, the light emitting dopant material that is necessary to form the light emitting layer or a further host used as needed may be mixed into the premix, but when there is a large difference in the temperatures at which they reach a desired vapor pressure, the light emitting dopant material and the further host are preferably deposited from other deposition sources.
As for the mixing ratio (weight ratio) of the first host to the second host, the proportion of the first host is 40 to 80%, and preferably 40 to 70% based on the total amount of the first host and the second host.
As the method of premixing, a method by which hosts can be mixed as uniformly as possible is desirable, and examples thereof include, but are not limited to, milling, a method of heating and melting hosts under reduced pressure or under an inert gas atmosphere such as nitrogen, and sublimation.
The host and a premix thereof may be in the form of powder, sticks, or granules.
Here, when the light emitting layer contains two or more host materials and the compound represented by the general formula (1) is used as the first host, a compound represented by any of the following general formulas (14) to (20) can be used as the second host, and the compounds represented by the following general formulas (14) to (20) are preferably electron-transporting compounds.
In the formula, Ar3 to Ar20 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group and the aromatic heterocyclic group. Ar3 to Ar20 preferably each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 15 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 15 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group and the aromatic heterocyclic group. Ar3 to Ar20 more preferably each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 15 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group.
Specific examples of the unsubstituted Ar3 to Ar20 include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, chrysene, pyrene, phenanthrene, triphenylene, fluorene, benzo[a]anthracene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, quinoline, isoquinoline, quinoxaline, quinazoline, thiadiazole, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole, and a linked aromatic group formed by linking 2 to 3 of these aromatic groups. Preferred examples thereof include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, phenanthrene, fluorene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, quinoline, isoquinoline, quinoxaline, quinazoline, thiadiazole, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzoisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole, and a linked aromatic group formed by linking 2 to 3 of these aromatic groups. More preferred examples thereof include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, phenanthrene, fluorene, and a linked aromatic group formed by linking 2 to 3 of these aromatic groups.
Ar21 and Ar22 each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 17 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group and the aromatic heterocyclic group. Ar21 and Ar22 preferably each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 15 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 2 to 15 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group and the aromatic heterocyclic group. Ar21 and Ar22 more preferably each independently represent a substituted or unsubstituted aromatic hydrocarbon group having 6 to 15 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the group consisting of the aromatic hydrocarbon group.
Specific examples of the unsubstituted Ar21 and Ar22 are the same as those described for the above unsubstituted Ar3 to Ar20, except that the aromatic heterocyclic group has 2 to 17 carbon atoms. Preferred examples thereof include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, phenanthrene, fluorene, pyridine, pyrimidine, triazine, thiophene, isothiazole, thiazole, pyridazine, pyrrole, pyrazole, imidazole, triazole, thiadiazole, pyrazine, furan, isoxazole, quinoline, isoquinoline, quinoxaline, quinazoline, thiadiazole, phthalazine, tetrazole, indole, benzofuran, benzothiophene, benzoxazole, benzothiazole, indazole, benzimidazole, benzotriazole, benzisothiazole, benzothiadiazole, purine, pyranone, coumarin, isocoumarin, chromone, dibenzofuran, dibenzothiophene, dibenzoselenophene, carbazole, and a linked aromatic group formed by linking 2 to 3 these aromatic groups. More preferred examples thereof include benzene, naphthalene, acenaphthene, acenaphthylene, azulene, anthracene, phenanthrene, fluorene, and a linked aromatic group formed by linking 2 to 3 of these aromatic groups.
Each of the above unsubstituted aromatic hydrocarbon group, aromatic heterocyclic group, or linked aromatic group may have a substituent. In the case where the above groups have a substituent, the substituent is preferably a deuterium, a halogen, a cyano group, an alkyl group having 1 to 10 carbon atoms, a triarylsilyl group having 9 to 30 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, or a diarylamino group having 12 to 44 carbon atoms.
The number of substituents is 0 to 5, and preferably 0 to 2. When the aromatic hydrocarbon group, the aromatic heterocyclic group, or the linked aromatic group has a substituent, the number of carbon atoms of the substituent is not included in the calculation of the number of carbon atoms. However, it is preferred that the total number of carbon atoms including the number of carbon atoms of the substituent satisfy the above range.
Specific examples of the above substituent include deuterium, cyano, bromo, fluorine, methyl, ethyl, propyl, i-propyl, butyl, t-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, triphenylsilyl, vinyl, propenyl, butenyl, pentenyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, diphenylamino, naphthylphenylamino, dinaphthylamino, dianthranilamino, diphenanthrenylamino, and dipyrenylamino. Preferred examples thereof include deuterium, cyano, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, vinyl, propenyl, butenyl, pentenyl, methoxy, ethoxy, propoxy, butoxy, and pentoxy.
As used herein, the linked aromatic group refers to an aromatic group linked by bonding carbon atoms of the aromatic rings of two or more aromatic groups by a single bond. These linked aromatic groups may be linear or branched. The linking position when benzene rings are linked to each other may be any of ortho, meta, and para, but the para linkage or the meta linkage is preferred. The aromatic group may be an aromatic hydrocarbon group or an aromatic heterocyclic group, and a plurality of aromatic groups may be the same or different from each other.
In the host material of the present invention and the known host material that can be used in combination, hydrogen in the compound to be used may be deuterium. That is, some or all hydrogen on the aromatic rings in the compounds represented by the general formulas (1) to (20), hydrogen in the t-Bu group, hydrogen on the aromatic rings of Ar1 to Ar22, and further, hydrogen on the aromatic ring of the known host material that can be used in combination, or hydrogen in a substituent may be deuterium.
The injection layer refers to a layer provided between the electrode and the organic layer to reduce the driving voltage and improve the light emission brightness, and includes the hole injection layer and the electron injection layer. The injection layer may be present between the anode and the light emitting layer or the hole transport layer, as well as between the cathode and the light emitting layer or the electron transport layer. The injection layer may be provided as necessary.
The hole blocking layer has the function of the electron transport layer in a broad sense, is made of a hole blocking material having a very small ability to transport holes while having the function of transporting electrons, and can improve the recombination probability between the electrons and the holes in the light emitting layer by blocking the holes while transporting the electrons. For the hole blocking layer, a known hole blocking material can be used. A plurality of hole blocking materials may be used in combination.
The electron blocking layer has the function of the hole transport layer in a broad sense, and can improve the recombination probability between the electrons and the holes in the light emitting layer by blocking the electrons while transporting the holes. As the material for the electron blocking layer, the compound represented by the general formula (1) is preferably used, and a known electron blocking layer material can be used. When the compound represented by the general formula (1) is used for the electron blocking layer, the compound represented by the general formula (1), a known host material described above, and a host material obtained by combining a plurality of the host materials may be used as the host material.
The layer adjacent to the light emitting layer includes the hole blocking layer, and the electron blocking layer, and when these layers are not provided, the adjacent layer is the hole transport layer, the electron transport layer, and the like.
The hole transport layer is made of a hole transport material having the function of transporting holes, and the hole transport layer may be provided as a single layer or a plurality of layers.
The hole transport material has any of hole injection properties, hole transport properties, or electron barrier properties, and may be either an organic material or an inorganic material. As the material for the hole transport layer, the compound represented by the general formula (1) is preferably used, and any of conventionally known compounds may be selected and used. Examples of such a hole transport material include porphyrin derivatives, arylamine derivatives, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, and conductive polymer oligomers, particularly, thiophene oligomers. When the compound represented by the general formula (1) is used for the hole transport layer, the compound represented by the general formula (1), a known host material described above, and a host material obtained by combining a plurality of the host materials may be used as the host material.
The electron transport layer is made of a material having the function of transporting electrons, and the electron transport layer may be provided as a single layer or a plurality of layers.
The electron transport material (may also serve as the hole blocking material) has the function of transmitting electrons injected from the cathode to the light emitting layer. As the electron transport layer, any of conventionally known compounds may be selected and used, and examples thereof include polycyclic aromatic derivatives such as naphthalene, anthracene, and phenanthroline, tris(8-quinolinolato)aluminum (III) derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidene methane derivatives, anthraquinodimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, oxadiazole derivatives, benzimidazole derivatives, benzothiazole derivatives, and indolocarbazole derivatives. Further, polymer materials in which these materials are introduced in the polymer chain or these materials constitute the main chain of the polymer can also be used.
When the organic EL device of the present invention is produced, the film formation method of each layer is not particularly limited, and the layers may be produced by either a dry process or a wet process.
Hereinafter, the present invention will be described in further detail with reference to Examples, but the present invention is not limited to these Examples.
As shown in the above reaction scheme, 5.0 g of a raw material (A), 5.0 g of a raw material (B), 5.0 g of copper, 18.6 g of potassium carbonate, and 100 ml of DMI (1,3-dimethyl-2-imidazolidinone) were put in a three-necked flask under a nitrogen atmosphere and stirred at 200° C. for 66 hours. After the reaction solution was cooled to room temperature, the reaction solution was put in a flask containing 800 ml of water, and stirred for 1 hour. The precipitated solid was collected by filtering, and then dissolved in dichloromethane, washed with water, and then concentrated. The concentrate was purified by silica gel column chromatography and recrystallization, and thereafter the resulting solid was dried to yield 6.5 g of a compound (1) (yield: 86%).
APCI-TOFMS m/z 617 [M+1]
As shown in the above reaction scheme, 5.0 g of the raw material (A), 13.2 g of a raw material (C), 5.0 g of copper, 18.6 g of potassium carbonate, and 200 ml of DMI were put in a three-necked flask under a nitrogen atmosphere and stirred at 200° C. for 39 hours. After the reaction solution was cooled to room temperature, the reaction solution was put in a flask containing 800 ml of water, and stirred for 1 hour. The precipitated solid was collected by filtering, and then dissolved in dichloromethane, washed with water, and then concentrated. The concentrate was purified by silica gel column chromatography and recrystallization, and thereafter the resulting solid was dried to yield 2.4 g of a compound (47) (yield: 32%).
APCI-TOFMS m/z 617 [M+1]
The glass transition temperatures of the above compounds and the following compounds are shown in Table 1.
Each thin film shown below was laminated on the glass substrate on which an anode made of ITO having a film thickness of 70 nm was formed by a vacuum deposition method at a degree of vacuum of 4.0×10−5 Pa. First, the previously presented HAT-CN was formed on ITO to a thickness of 10 nm as a hole injection layer, and then HT-1 was formed to a thickness of 25 nm as a hole transport layer. Then, HT-2 was formed to a thickness of 5 nm as an electron blocking layer. Then, the compound (1) as the host and BD-1 as the thermally activated delayed fluorescence dopant were co-deposited from different deposition sources to form a light emitting layer having a thickness of 30 nm. At this time, they were co-deposited under deposition conditions such that the concentration of BD-1 was 2 wt %. Then, ET-2 was formed to a thickness of 5 nm as a hole blocking layer. Then, ET-1 was formed to a thickness of 40 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer to a thickness of 1 nm as an electron injection layer. Finally, aluminum (Al) was formed on the electron injection layer to a thickness of 70 nm as a cathode, whereby an organic EL device according to Example 1 was produced.
Each organic EL device was produced in the same manner as in Example 1, except that BH-1 was used as the host.
Each thin film shown below was laminated on the glass substrate on which an anode made of ITO having a film thickness of 70 nm was formed by a vacuum deposition method at a degree of vacuum of 4.0×10−5 Pa. First, the previously presented HAT-CN was formed on ITO to a thickness of 10 nm as a hole injection layer, and then HT-1 was formed to a thickness of 25 nm as a hole transport layer. Then, HT-2 was formed to a thickness of 5 nm as an electron blocking layer. Then, the compound (1) as the first host, BH-6 as a second host, and BD-1 as the thermally activated delayed fluorescence dopant were co-deposited from different deposition sources to form a light emitting layer having a thickness of 30 nm. At this time, they were co-deposited under deposition conditions such that the concentration of BD-1 was 2 wt % and the weight ratio of the first host to the second host was 70:30. Then, ET-2 was formed to a thickness of 5 nm as a hole blocking layer. Then, ET-1 was formed to a thickness of 40 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer to a thickness of 1 nm as an electron injection layer. Finally, aluminum (Al) was formed on the electron injection layer to a thickness of 70 nm as a cathode, whereby an organic EL device according to Example 1 was produced.
Each organic EL device was produced in the same manner as in Example 2, except that the electron blocking layer material, the first host, and the second host were changed to the compounds shown in Table 2.
The emission color, voltage, power efficiency, and lifetime of each organic EL device produced in Examples and Comparative Examples are shown in Table 3. The emission color, voltage, and emission efficiency are values at a current density of 2.5 mA/cm2 and were initial characteristics. The time taken for the luminance to reduce to 50% of the initial luminance when the current density was 2.5 mA/cm2 was measured as the lifetime.
It is found from Examples and Comparative Examples of Table 2 that organic EL devices using the material for an organic electroluminescent device of the present invention as the electron blocking layer or the host of the organic EL device containing a thermally activated delayed fluorescence material in the light emitting layer exhibit blue light emission and have low voltage, high efficiency, and long lifetime characteristics.
Each thin film was laminated on the glass substrate on which an anode made of ITO having a film thickness of 110 nm was formed by a vacuum deposition method at a degree of vacuum of 4.0×10−5 Pa. First, HAT-CN was formed on ITO to a thickness of 25 nm as a hole injection layer, and then HT-3 was formed to a thickness of 30 nm as a hole transport layer. Then, BH-1 was formed to a thickness of 10 nm as an electron blocking layer. Then, the compound (1) as the first host, BH-5 as the second host, and GD-1 as the phosphorescence dopant were co-deposited from different deposition sources to form a light emitting layer having a thickness of 40 nm. At this time, they were co-deposited under deposition conditions such that the concentration of GD-1 was 5 wt % and the weight ratio of the first host to the second host was 50:50. Then, ET-1 was formed to a thickness of 20 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer to a thickness of 1 nm as an electron injection layer. Finally, aluminum (Al) was formed on the electron injection layer to a thickness of 70 nm as a cathode, whereby an organic EL device was produced.
Examples 14 to 18 and Comparative Examples 6 to 9 Each organic EL device was produced in the same manner as in Example 13, except that the electron blocking layer material, the first host, and the second host were changed to the compounds shown in Table 4.
The emission color, voltage, power efficiency, and lifetime of each organic EL device produced in Examples and Comparative Examples are shown in Table 5. The emission color, voltage, and emission efficiency are values at a current density of 20 mA/cm2 and were initial characteristics. The time taken for the luminance to reduce to 95% of the initial luminance when the current density was 20 mA/cm2 was measured as the lifetime.
It is found from Examples and Comparative Examples of Table 4 that organic EL devices using the material for an organic electroluminescent device of the present invention as the electron blocking layer or the host of the organic EL device containing a phosphorescence material in the light emitting layer exhibit green light emission and have low voltage, high efficiency, and long lifetime characteristics.
Each thin film was laminated on the glass substrate on which an anode made of ITO having a film thickness of 110 nm was formed by a vacuum deposition method at a degree of vacuum of 4.0×10−5 Pa. First, HAT-CN was formed on ITO to a thickness of 25 nm as a hole injection layer, and then HT-3 was formed to a thickness of 45 nm as a hole transport layer. Then, BH-1 was formed to a thickness of 10 nm as an electron blocking layer. Then, the compound (1) as the first host, BH-5 as the second host, and RD-1 as the phosphorescence dopant were co-deposited from different deposition sources to form a light emitting layer having a thickness of 40 nm. At this time, they were co-deposited under deposition conditions such that the concentration of RD-1 was 3 wt % and the weight ratio of the first host to the second host was 50:50. Then, ET-1 was formed to a thickness of 40 nm as an electron transport layer. Further, lithium fluoride (LiF) was formed on the electron transport layer to a thickness of 1 nm as an electron injection layer. Finally, aluminum (Al) was formed on the electron injection layer to a thickness of 70 nm as a cathode, whereby an organic EL device was produced.
Each organic EL device was produced in the same manner as in Example 19, except that the electron blocking layer material, the first host, and the second host were changed to the compounds shown in Table 6.
The emission color, voltage, power efficiency, and lifetime of each organic EL device produced in Examples and Comparative Examples are shown in Table 7. The emission color, voltage, and emission efficiency are values at a current density of 20 mA/cm2 and were initial characteristics. The time taken for the luminance to reduce to 95% of the initial luminance when the current density was 40 mA/cm2 was measured as the lifetime.
It is found from Examples and Comparative Examples of Table 7 that organic EL devices using the material for an organic electroluminescent device of the present invention as the electron blocking layer or the host of the organic EL device containing a phosphorescence material in the light emitting layer exhibit red light emission and have low voltage, high efficiency, and long lifetime characteristics.
According to the present invention, a practically useful organic EL device having high emission efficiency as well as high driving stability and long lifetime characteristics can be obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-101586 | Jun 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/016139 | 3/30/2022 | WO |
