WO2012176674A1

WO2012176674A1 - Light-emitting element

Info

Publication number: WO2012176674A1
Application number: PCT/JP2012/065170
Authority: WO
Inventors: 田中　大作; 富永　剛
Original assignee: 東レ株式会社
Priority date: 2011-06-23
Filing date: 2012-06-13
Publication date: 2012-12-27
Also published as: JP2014167946A; TW201304232A

Abstract

Provided is an organic thin-film light-emitting element having improved light-emission efficiency, drive voltage, and durability life. The light-emitting element comprises at least a hole transport layer and an electron transport layer between an anode and a cathode, and emits light by electric energy. The light-emitting element is characterized by: the hole transport layer including a compound having a triphenylene skeleton; and the electron transport layer including a compound having a phenanthroline skeleton.

Description

Light emitting element

The present invention relates to a light emitting element capable of converting electric energy into light. More specifically, the present invention relates to a light emitting element that can be used in fields such as a display element, a flat panel display, a backlight, illumination, interior, a sign, a signboard, an electrophotographic machine, and an optical signal generator.

In recent years, research on organic thin-film light emitting devices that emit light when electrons injected from a cathode and holes injected from an anode are recombined in an organic phosphor sandwiched between both electrodes has been actively conducted. This light emitting element is characterized by thin light emission with high luminance under a low driving voltage and multicolor light emission by selecting a fluorescent material. This study was conducted by C.D. W. Since Tang et al. Showed that organic thin film devices emit light with high brightness, they have been studied by many research institutions.

After that, as a result of many practical studies, organic thin-film light-emitting elements have been steadily put into practical use, such as being used in the main display of mobile phones. However, there are still many technical issues. Above all, it is one of the big issues to achieve both low voltage driving and long life of the device.

The driving voltage of the element greatly depends on a carrier transport material that transports carriers such as holes and electrons to the light emitting layer. Among these, a technique using a material having a triphenylene skeleton as a hole transport material is disclosed (for example, see Patent Documents 1 to 3).
In addition, as one of techniques for driving a device at a low voltage from the viewpoint of electron transport, a technique using a material having a phenanthroline skeleton as an electron transport material is disclosed (see, for example, Patent Documents 4 to 7).

JP-A-11-251063 JP 2005-259472 A JP 2009-292760 A JP-A-5-331459 JP 2001-267080 A JP 2004-55258 A JP 2004-281390 A

However, in the prior art, a light emitting device that is driven at a low voltage, has high luminous efficiency, and has excellent durability life has not been found. For example, even though conventionally known hole transport materials and electron transport materials are excellent in hole transport properties and electron transport properties themselves, performance as a light emitting device is not necessarily improved when used in combination. Absent.

Among them, a compound containing a phenanthroline skeleton as known in Patent Documents 4 to 7 may cause a decrease in luminous efficiency and a decrease in durability life, although the effect of lowering the driving voltage is seen. This was found by the study by the present inventor. The inventor presumed the reason as follows. A compound containing a phenanthroline skeleton has a large electron affinity, and when this is used for an electron transport layer, the electron injecting property from the cathode is improved. A compound containing a phenanthroline skeleton is also excellent in electron transport properties. However, due to its high performance, the inside of the light-emitting layer becomes excessive in electrons depending on the types of hole transport materials used in combination, and as a result, the above-described problems may occur.

An object of the present invention is to provide an organic thin-film light-emitting element that solves the problems of the prior art and has improved luminous efficiency, driving voltage, and durability life.

The present invention was made in consideration of the balance of mobility of electrons and holes in a light emitting device, and found an optimal combination as a material contained in a hole transport layer and an electron transport layer. is there.

That is, the present invention is a light-emitting element that includes at least a hole transport layer and an electron transport layer between an anode and a cathode and emits light by electric energy, and the hole transport layer is represented by the following general formula (1). The light-emitting element is characterized by containing the compound represented, wherein the electron transport layer contains a compound having a phenanthroline skeleton.

In the general formula (1), R ¹ to R ¹² may be the same or different, and are hydrogen, alkyl group, cycloalkyl group, amino group, aryl group, heterocyclic group, alkenyl group, cycloalkenyl group, alkynyl. Selected from the group consisting of a group, an alkoxy group, an alkylthio group, an aryl ether group, an aryl thioether group, a halogen, a cyano group, —P (═O) R ¹³ R ¹⁴ and a silyl group. R ¹³ and R ¹⁴ may be the same or different, and are an aryl group or a heteroaryl group. These substituents may be further substituted, and adjacent substituents may further form a ring. However, n of R ¹ to R ¹² is an amino group represented by —NR ¹⁵ R ¹⁶ . R ¹⁵ and R ¹⁶ may be the same or different and are selected from the group consisting of an alkyl group, a cycloalkyl group, an aryl group, and a heteroaryl group. The alkyl group, cycloalkyl group, aryl group, or heteroaryl group may have a substituent. n represents an integer of 1 to 6.

The light emitting device according to the present invention has an effect of being able to be driven at a low voltage and improving luminous efficiency and durability.

The light-emitting element of the present invention is characterized in that a compound having a specific structure is used for each of the hole transport layer and the electron transport layer.
First, the compound represented by the general formula (1) will be described in detail. The hole transport layer of the light emitting device of the present invention contains a compound represented by the general formula (1).

Of these substituents, hydrogen may be deuterium. The alkyl group represents, for example, a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, or a tert-butyl group, which is a substituent. It may or may not have. There is no restriction | limiting in particular in the additional substituent in the case of being substituted, For example, an alkyl group, an aryl group, etc. can be mentioned, This point is common also in the following description. The number of carbon atoms of the alkyl group is not particularly limited, but is usually in the range of 1 to 20 and more preferably 1 to 8 from the viewpoint of easy availability of raw materials and cost. Furthermore, since there exists a possibility that hole transport property may be inhibited when the carbon number of an alkyl group is large, a methyl group and an ethyl group are more preferable.

The cycloalkyl group represents, for example, a saturated alicyclic hydrocarbon group such as a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group, an adamantyl group, etc., which may or may not have a substituent. Also good. Although carbon number of an alkyl group part is not specifically limited, Usually, it is the range of 3-20. When the number of carbon atoms is large, the hole transport property may be hindered. Therefore, a cyclopropyl, cyclopentyl, or cyclohexyl group is more preferable.

The amino group may or may not have a substituent, and examples of the substituent include an alkyl group, a cycloalkyl group, an aryl group, and a heteroaryl group, and these substituents are further substituted. It may be.

The aryl group represents an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, a biphenyl group, a phenanthryl group, a fluorenyl group, an anthracenyl group, a pyrenyl group, or a terphenyl group. The aryl group may or may not further have a substituent. There is no restriction | limiting in particular in the additional substituent in the case of being substituted, For example, an alkyl group, a cycloalkyl group, heteroaryl group, an alkoxy group, an amino group etc. can be mentioned. The number of carbon atoms of the aryl group is not particularly limited, but is usually in the range of 6 to 40.

The heterocyclic group is, for example, a cycloaliphatic group having atoms other than carbon, such as a pyranyl group, a piperidinyl group, and a cyclic amide group, and a furanyl group, a thiophenyl group, a pyridyl group, a quinolinyl group, a pyrazinyl group, Cyclic aromatic groups (heteroaryl groups) having one or more atoms other than carbon such as naphthyridyl group, benzofuranyl group, benzothiophenyl group, indolyl group, dibenzofuranyl group, dibenzothiophenyl group, carbazolyl group in the ring Which may be unsubstituted or substituted. Of the heterocyclic groups, a heteroaryl group is preferred. There is no restriction | limiting in particular in the additional substituent in the case of being substituted, For example, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, an amino group etc. can be mentioned. The number of carbon atoms of the heterocyclic group is not particularly limited, but is usually in the range of 2-30.

An alkenyl group refers to an unsaturated aliphatic hydrocarbon group containing a double bond such as a vinyl group, an allyl group, or a butadienyl group, which may or may not have a substituent. The number of carbon atoms of the alkenyl group is not particularly limited, but is usually in the range of 2-20.

The cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond such as a cyclopentenyl group, a cyclopentadienyl group, or a cyclohexenyl group, which may have a substituent. You don't have to.

The alkynyl group indicates, for example, an unsaturated aliphatic hydrocarbon group containing a triple bond such as an ethynyl group, which may or may not have a substituent. The number of carbon atoms of the alkynyl group is not particularly limited, but is usually in the range of 2-20.

The alkoxy group refers to, for example, a functional group having an aliphatic hydrocarbon group bonded through an ether bond such as a methoxy group, an ethoxy group, or a propoxy group, and the aliphatic hydrocarbon group may have a substituent. It may not have. Although carbon number of an alkoxy group is not specifically limited, Usually, it is the range of 1-20. Furthermore, since there exists a possibility that hole transport property may be inhibited when the carbon number of an alkoxy group is large, it is more preferably a methoxy group or an ethoxy group.

The alkylthio group is a group in which an oxygen atom of an ether bond of an alkoxy group is substituted with a sulfur atom. The hydrocarbon group of the alkylthio group may or may not have a substituent. Although carbon number of an alkylthio group is not specifically limited, Usually, it is the range of 1-20.

An aryl ether group refers to a functional group to which an aromatic hydrocarbon group is bonded via an ether bond, such as a phenoxy group, and the aromatic hydrocarbon group may or may not have a substituent. Good. Although carbon number of an aryl ether group is not specifically limited, Usually, it is the range of 6-40.

The aryl thioether group is a group in which an oxygen atom of an ether bond of an aryl ether group is substituted with a sulfur atom. The aromatic hydrocarbon group in the aryl ether group may or may not have a substituent. Although carbon number of an aryl ether group is not specifically limited, Usually, it is the range of 6-40.

Halogen means fluorine, chlorine, bromine and iodine.

In the substituent —P (═O) R ¹³ R ¹⁴ , R ¹³ and R ¹⁴ are an aryl group or a heteroaryl group, and in the substituent —P (═O) R ¹³ R ¹⁴ , an aryl group or a heteroaryl group Has the same meaning as above.

The silyl group refers to, for example, a functional group having a bond to a silicon atom such as a trimethylsilyl group, which may or may not have a substituent. The carbon number of the silyl group is not particularly limited, but is usually in the range of 3-20. The number of silicon is usually 1-6.

Adjacent substituents form a ring when any adjacent two substituents (for example, R ¹ and R ^{2 in} formula (1)) are bonded to each other to form a conjugated or non-conjugated condensed ring. It means that As a constituent element of the condensed ring, in addition to carbon, nitrogen, oxygen, sulfur, phosphorus and silicon atoms may be contained, or further condensed with another ring.

Preferred examples of R ¹ to R ¹² include hydrogen, an alkyl group, an amino group, an alkoxy group, an aryl group, or a hetero group in consideration of deposition stability (thermal stability) of the material, synthesis cost, and availability of raw materials. An aryl group. More preferred are hydrogen, amino group, aryl group or heteroaryl group. In the case of an aryl group or heteroaryl group, an aryl group or heteroaryl group having 6 to 18 carbon atoms is preferable in consideration of vapor deposition stability (thermal stability) of the material. Specifically, a phenyl group, a naphthyl group, or biphenylyl. Group, fluorenyl group, anthracenyl group, phenanthryl group, pyrenyl group, dibenzofuranyl group, dibenzothiophenyl group, carbazolyl group. These groups may further have a substituent.

In the general formula (1), n of R ¹ to R ¹² is an amino group represented by —NR ¹⁵ R ¹⁶ , and R ¹⁵ and R ¹⁶ are alkyl groups in view of synthesis cost and availability of raw materials. A group, an aryl group or a heteroaryl group is preferred. Among them, an aryl group or a heteroaryl group is preferable in consideration of vapor deposition stability (thermal stability), amorphous thin film stability (having a high glass transition temperature), and good hole transport properties. Specifically, an aryl group or heteroaryl group having 6 to 20 carbon atoms is preferable, and phenyl group, naphthyl group, biphenylyl group, terphenyl group, fluorenyl group, anthracenyl group, phenanthryl group, pyrenyl group, triphenylenyl group, dibenzofuran group. Preferred examples include nyl group, dibenzothiophenyl group, carbazolyl group and the like. These groups may further have a substituent. Among them, excellent amorphous thin film stability (high glass transition temperature) can be obtained, and the lifetime of the device can be extended, and if the energy gap (HOMO-LUMO energy difference) is narrowed, the light emitting layer is excited. A phenyl group, a naphthyl group, a biphenylyl group, a terphenyl group, a fluorenyl group, a phenanthryl group, and a triphenylenyl group are more preferable because they are less likely to deactivate the child energy.

In the general formula (1), n, which is the number of substituents —NR ¹⁵ R ¹⁶ , represents an integer of 1 to 6. In consideration of vapor deposition stability (thermal stability), n is preferably 1 to 3, more preferably 2 or 3 from the viewpoint of having an appropriate ionization potential and facilitating injection of holes. When n = 1, it is preferable that R ¹ is —NR ¹⁵ R ¹⁶ in view of ease of synthesis. In the case of n = 2, considering the ease of synthesis, it is preferable that R ¹ and R ⁶ , R ² and R ⁵ , or R ³ and R ¹² are —NR ¹⁵ R ¹⁶ , and further suitable ionization potential From the viewpoint of having R ¹ , R ¹ and R ⁶ are more preferably —NR ¹⁵ R ¹⁶ . In the case of n = 3, considering the ease of synthesis, R ¹ , R ⁵ and R ⁹ or R ¹ , R ⁶ and R ⁹ are preferably —NR ¹⁵ R ¹⁶ , and an appropriate ionization potential is obtained. From the viewpoint of having R ¹ , R ^6, and R ⁹ are more preferably —NR ¹⁵ R ¹⁶ . In the case of n = 4, R ¹ , R ² , R ⁵ and R ⁶ , or R ¹ , R ⁶ , R ⁸ and R ¹¹ , or R ² , R ⁵ , R ⁸ and R are considered in consideration of the ease of synthesis. ¹¹ is preferably —NR ¹⁵ R ¹⁶ , and more preferably R ¹ , R ⁶ , R ⁸ and R ¹¹ are —NR ¹⁵ R ¹⁶ from the viewpoint of having an appropriate ionization potential.

The compound represented by the general formula (1) is not particularly limited, but specific examples include the following compounds.

The compound represented by the general formula (1) can be synthesized by combining known methods. A synthesis example of diamino type with n = 2 is shown below.

Also, as a monoamino type synthesis method of n = 1, for example, it can be easily synthesized by a coupling reaction using commercially available bromotriphenylene and a desired diarylamine using a palladium catalyst. Note that the synthesis method is not limited to these.

Next, the compound having a phenanthroline skeleton will be described. The electron transport layer of the light emitting device of the present invention contains a compound containing a phenanthroline skeleton. Combining the electron transport layer containing the compound containing the phenanthroline skeleton and the hole transport layer containing the compound represented by the general formula (1) has the effect of improving the light emission efficiency and the durability life while driving at a low voltage. Was found to be obtained. This is because the hole transport material represented by the general formula (1) has higher hole mobility and better hole injection characteristics than, for example, a well-known arylamine-based hole transport material. Therefore, it is considered that when combined with an electron transport material containing a phenanthroline skeleton, excess of electrons in the light emitting layer is eliminated, and injection of electrons into the hole transport layer can be prevented.

When a compound containing a phenanthroline skeleton contains a plurality of phenanthroline skeletons, the electron injecting and transporting properties tend to increase. Since the hole transport material represented by the general formula (1) has high hole injecting and transporting properties, in order to obtain the above-described effect more remarkably, a compound containing a plurality of phenanthroline skeletons is used. It is preferably used for the electron transport layer. Further, the compound containing a plurality of phenanthroline skeletons is preferably a compound represented by the following general formula (2) because it exhibits particularly high electron injection and transport properties and is driven at a lower voltage.

In the general formula (2), R ¹⁷ to R ²⁴ may be the same as or different from each other, and hydrogen, alkyl group, cycloalkyl group, amino group, aryl group, heterocyclic group, alkenyl group, cycloalkenyl group, alkynyl Selected from the group consisting of a group, an alkoxy group, an alkylthio group, an aryl ether group, an aryl thioether group, a halogen, a cyano group, —P (═O) R ²⁵ R ²⁶ , a silyl group, and A. R ²⁵ and R ²⁶ may be the same or different and each is an aryl group or a heteroaryl group. These substituents may be further substituted, and adjacent substituents may further form a ring. A represents a single bond directly connecting m phenanthroline skeletons, or a linking unit linking m phenanthroline skeletons, wherein the linking unit is a double bond, triple bond, substituted or unsubstituted aromatic hydrocarbon residue. , A substituted or unsubstituted aromatic heterocyclic residue, or a combination thereof. However, one of R ¹⁷ to R ²⁴ is A, and m represents an integer of 2 or more.

The explanation of R ¹⁷ to R ²⁴ and the substituents of R ²⁵ and R ²⁶ is the same as in the case of the general formula (1). Preferable examples of the substituent represented by R ¹⁷ to R ²⁴ include hydrogen, an alkyl group, an aryl group, and a heteroaryl group. Further, hydrogen, an aryl group, or a heteroaryl group is more preferable because good amorphous thin film stability can be obtained. In particular, hydrogen bonded to carbon adjacent to the nitrogen atom has high activity and may cause some chemical reaction in the radical anion state, and therefore, at least one of R ^{17 and} R ²⁴ is preferably an aryl group.

In A, a double bond is a divalent to tetravalent group represented by a C═C structure. The triple bond is a divalent group represented by a C≡C structure.

Of A, a substituted or unsubstituted aromatic hydrocarbon residue is a remaining portion obtained by removing m hydrogen atoms from an aromatic hydrocarbon such as benzene, naphthalene, anthracene, pyrene, fluorene, and spirofluorene, These may or may not have a substituent. The number of nuclear carbon atoms of the aromatic hydrocarbon residue is preferably in the range of 6 to 40, more preferably 6 to 25, and still more preferably 6 to 18. The number of carbon atoms in the nucleus does not include substituent carbon. Examples of the substituent when substituted are the same as the above-described substituents. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

Of A, a substituted or unsubstituted aromatic heterocyclic residue is, for example, pyridine, pyrimidine, pyrazine, triazine, quinoline, quinoxaline, phenanthroline, phenazine, furan, thiophene, bithiophene, N-phenylcarbazole, bipyridine, biquinoline, The remaining part of the aromatic compound having atoms other than carbon in the ring, such as benzofuran, benzothiophene, dibenzofuran, dibenzothiophene, silole (silacyclopentadiene), silafluorene, spirosilafluorene, etc., by removing m hydrogen atoms It is. These may or may not have a substituent. The number of nuclear carbon atoms of the aromatic heterocyclic residue is preferably in the range of 5 to 40, more preferably 5 to 25, still more preferably 5 to 18. The number of carbon atoms in the nucleus does not include substituent carbon. Examples of the substituent when substituted are the same as the above-described substituents. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups.

Of A, the combination of a double bond, a triple bond, an aromatic hydrocarbon residue, and an aromatic heterocyclic residue includes, for example, biphenyl, terphenyl, diphenylfluorene, diphenylanthracene, 2,6-diphenylpyridine, Remove m hydrogen atoms from mixed structure of double bond, triple bond, aromatic hydrocarbon and aromatic heterocycle such as 2,5-diphenylthiophene, 2,4,6-triphenyltriazine, stilbene Is the rest. In these rings, each ring may or may not have a substituent. Examples of the substituent when substituted are the same as the above-described substituents. Among these, preferred substituents from the viewpoint of thermal stability include aryl groups and heteroaryl groups. Among these, the number of nuclear carbons of the linking unit in which aromatic hydrocarbon residues are combined is preferably in the range of 6 to 40, more preferably in the range of 6 to 25, and still more preferably in the range of 6 to 18. The number of carbon atoms in the nucleus does not include substituent carbon.

例 Examples of A are not particularly limited, but specific examples include the following.

In the compound represented by the general formula (2), hydrogen bonded to the carbon adjacent to the nitrogen atom has high activity and may cause some chemical reaction in a radical anion state. Therefore, R ¹⁷ or R ²⁴ is A is preferred.

In the present invention, m, which is the number of phenanthroline skeletons contained in the compound represented by the general formula (2), is 2 or more. However, if it is 3 or more, there is a concern of thermal decomposition during deposition. Is preferably 2. Further, the m phenanthroline skeletons connected by A may be the same or different.

Preferred examples of the compound containing a phenanthroline skeleton include the following compounds, but are not limited thereto.

Next, an embodiment of the light emitting device in the present invention will be described in detail with an example. The light-emitting element of the present invention includes an anode, a cathode, and at least a hole transport layer and an electron transport layer between the anode and the cathode.

In such a light emitting device, the layer structure between the anode and the cathode includes a hole transport layer / a light emitting layer / an electron transport layer, a hole injection layer / a hole transport layer / a light emitting layer / an electron transport layer. , Hole transport layer / light emitting layer / electron transport layer / electron injection layer, hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer, and the like. Each of the layers may be a single layer or a plurality of layers.

The compound represented by the general formula (1) is contained in the hole transport layer in the light emitting device. The hole transport layer is a layer that transports holes injected from the anode to the light emitting layer. The hole transport layer may be a single layer or may be configured by laminating a plurality of layers. When the hole transport layer is composed of a plurality of layers, the compound represented by the general formula (1) may be contained in any layer, but the compound represented by the general formula (1) is good. Since it has an electron blocking property, the hole transport layer containing the compound represented by the general formula (1) is in direct contact with the light emitting layer from the viewpoint of preventing the penetration of electrons into the hole transport layer. Is preferred.

The hole transport layer may be composed of only the compound represented by the general formula (1), or may be mixed with other materials as long as the effects of the present invention are not impaired. In this case, as other materials used, for example, 4,4′-bis (N- (3-methylphenyl) -N-phenylamino) biphenyl (TPD), 4,4′-bis (N- (1 -Naphthyl) -N-phenylamino) biphenyl (NPD), 4,4'-bis (N, N-bis (4-biphenylyl) amino) biphenyl (TBDB), bis (N, N'-diphenyl-4-amino) Benzidine derivatives such as phenyl) -N, N-diphenyl-4,4′-diamino-1,1′-biphenyl (TPD232), 4,4 ′, 4 ″ -tris (3-methylphenyl (phenyl) amino) triphenyl Starburst aryl such as amine (m-MTDATA), 4,4 ′, 4 ″ -tris (1-naphthyl (phenyl) amino) triphenylamine (1-TNATA) Biscarbazole derivatives such as bis (N-arylcarbazole) or bis (N-alkylcarbazole), carbazole trimers, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxaphene derivatives Heterocyclic compounds such as diazole derivatives, phthalocyanine derivatives, porphyrin derivatives, and polymer systems include polycarbonates and styrene derivatives, polythiophene, polyaniline, polyfluorene, polyvinylcarbazole and polysilane having the above-mentioned monomers in the side chain.

Next, the electron transport layer in the present invention will be described. The electron transport layer is a layer that transports electrons injected from the cathode to the light emitting layer.

The electron transport layer may be composed of only a layer made of a compound containing a phenanthroline skeleton, or a plurality of layers may be laminated. When multiple layers are stacked, the layer containing the compound containing the phenanthroline skeleton may be used anywhere, but the electron injection due to the large electron affinity, which is one of the characteristics of the compound containing the phenanthroline skeleton, In order to make the most of it, it is preferably used for the layer closest to the cathode. Examples of the compound used in the layer not containing the compound containing the phenanthroline skeleton are not particularly limited, but include compounds having a condensed polycyclic aromatic skeleton such as naphthalene, anthracene, pyrene, and derivatives thereof, 4,4′- Styryl aromatic ring derivatives represented by bis (diphenylethenyl) biphenyl, perylene derivatives, perinone derivatives, coumarin derivatives, naphthalimide derivatives, quinone derivatives such as anthraquinone and diphenoquinone, phosphate derivatives, carbazole derivatives and indole derivatives, tris ( Quinolinol complexes such as 8-quinolinolato) aluminum (III), hydroxyazole complexes such as hydroxyphenyloxazole complexes, azomethine complexes, tropolone metal complexes and flavonol metal complexes. Since the driving voltage can be reduced, the electron transport material is composed of an element selected from carbon, hydrogen, nitrogen, oxygen, silicon and phosphorus, and a compound having a heteroaryl ring structure containing electron-accepting nitrogen is used. preferable.

The electron-accepting nitrogen represents a nitrogen atom that forms a multiple bond with an adjacent atom. Since the nitrogen atom has a high electronegativity, the multiple bond has an electron-accepting property, has an excellent electron transporting ability, and can be used for an electron transporting layer to reduce the driving voltage of the light emitting element. Therefore, heteroaryl rings containing electron-accepting nitrogen have a high electron affinity. Examples of the heteroaryl ring containing an electron-accepting nitrogen include, for example, a pyridine ring, pyrazine ring, pyrimidine ring, quinoline ring, quinoxaline ring, naphthyridine ring, pyrimidopyrimidine ring, benzoquinoline ring, phenanthroline ring, imidazole ring, oxazole ring, Examples thereof include an oxadiazole ring, a triazole ring, a thiazole ring, a thiadiazole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, and a phenanthrimidazole ring.

Examples of these compounds having a heteroaryl ring structure include benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, pyridine derivatives, pyrazine derivatives, phenanthroline derivatives, quinoxaline derivatives, quinoline. Preferred examples include derivatives, benzoquinoline derivatives, oligopyridine derivatives such as bipyridine and terpyridine, quinoxaline derivatives and naphthyridine derivatives, and phenanthroline derivatives. Among these derivatives, considering electrochemical stability, benzimidazole derivatives, pyridine derivatives, quinoline derivatives, quinoxaline derivatives, and phenanthroline derivatives are more preferable. Further, it is more preferable that these derivatives have a condensed polycyclic aromatic skeleton because the glass transition temperature is improved, the electron mobility is increased, and the effect of lowering the voltage of the light emitting element is great. Furthermore, considering that the device durability life is improved, the synthesis is easy, and the availability of raw materials is easy, the condensed polycyclic aromatic skeleton is particularly preferably an anthracene skeleton or a pyrene skeleton. The electron transport material may be used alone, but two or more of the electron transport materials may be mixed and used, or one or more of the other electron transport materials may be mixed with the electron transport material. Further, a mixture containing a compound containing a phenanthroline skeleton may be used.

The hole injection layer is a layer inserted between the anode and the hole transport layer. The hole injection layer may be either a single layer or a plurality of layers stacked. If a hole injection layer is present between the positive hole transport layer containing the compound represented by the general formula (1) and the anode, it not only operates at a lower voltage and the durability life is improved, but also the carrier balance of the device. Is improved, and the luminous efficiency is also improved.

The material used for the hole injection layer is not particularly limited as long as the material represented by the general formula (1) is used as it is. For example, 4,4′-bis (N- (3-methylphenyl) -N— Phenylamino) biphenyl (TPD), 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl (NPD), 4,4′-bis (N, N-bis (4-biphenylyl)) Benzidine derivatives such as amino) biphenyl (TBDB), bis (N, N′-diphenyl-4-aminophenyl) -N, N-diphenyl-4,4′-diamino-1,1′-biphenyl (TPD232), 4, 4 ′, 4 ″ -tris (3-methylphenyl (phenyl) amino) triphenylamine (m-MTDATA), 4,4 ′, 4 ″ -tris (1-naphthyl (phenyl) amino) to A group of materials called starburst arylamines such as phenylamine (1-TNATA), biscarbazole derivatives such as bis (N-arylcarbazole) or bis (N-alkylcarbazole), pyrazoline derivatives, stilbene compounds, hydrazone compounds, Heterocyclic compounds such as benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, porphyrin derivatives, polycarbonates and styrene derivatives having the above monomers in the side chain in the polymer system, polythiophene, polyaniline, polyfluorene, polyvinylcarbazole and polysilane Etc. are used. Among them, there are more benzidine derivatives and starburst arylamine group materials from the viewpoint of having a shallower HOMO level than the compound represented by the general formula (1) and smoothly injecting and transporting holes from the anode to the hole transport layer. Preferably used.

These materials may be used alone or as a mixture of two or more materials. A plurality of materials may be stacked to form a hole injection layer. Further, it is more preferable that the hole injection layer is composed of an acceptor compound alone or that the hole injection material is doped with an acceptor compound so that the above-described effects can be obtained more remarkably. . An acceptor compound is a material that forms a charge transfer complex with a material that forms a hole-injecting layer in contact with a hole-transporting layer when used as a single-layer film and a material that forms a hole-injecting layer when used as a doped layer. When such a material is used, the conductivity of the hole injection layer is improved, which contributes to lowering of the driving voltage of the device, and the effects of improving the light emission efficiency and improving the durability life can be obtained.

Examples of acceptor compounds include metal chlorides such as iron (III) chloride, aluminum chloride, gallium chloride, indium chloride, antimony chloride, metal oxides such as molybdenum oxide, vanadium oxide, tungsten oxide, ruthenium oxide, A charge transfer complex such as tris (4-bromophenyl) aminium hexachloroantimonate (TBPAH). In addition, organic compounds having a nitro group, cyano group, halogen or trifluoromethyl group in the molecule, quinone compounds, acid anhydride compounds, fullerenes, and the like are also preferably used. Specific examples of these compounds include hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane (TCNQ), tetrafluorotetracyanoquinodimethane (F4-TCNQ), 2, 3, 6, 7 , 10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN6), p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone 2,5-dichlorobenzoquinone, tetramethylbenzoquinone, 1,2,4,5-tetracyanobenzene, o-dicyanobenzene, p-dicyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5 , 6-Dicyanobenzoquinone, p-dinitrobenzene, m-dini Lobenzene, o-dinitrobenzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1-nitronaphthalene, 2-nitronaphthalene, 1,3-dinitro Naphthalene, 1,5-dinitronaphthalene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, 2,4,7-trinitro-9-fluorenone, 2 , 3,5,6-tetracyanopyridine, maleic anhydride, phthalic anhydride, C60, and C70.

Among these, metal oxides and cyano group-containing compounds are preferable because they are easy to handle and can be easily deposited, so that the above-described effects can be easily obtained. Examples of preferred metal oxides include molybdenum oxide, vanadium oxide, or ruthenium oxide. Among the cyano group-containing compounds, (a) a compound having at least one electron-accepting nitrogen other than the nitrogen atom of the cyano group in the molecule and further having a cyano group, (b) a halogen and a cyano group in the molecule (C) a compound having both a carbonyl group and a cyano group in the molecule, or (d) an electron-accepting nitrogen other than the nitrogen atom of the cyano group, a halogen and a cyano group. A compound having all is more preferable because it becomes a strong electron acceptor. Specific examples of such a compound include the following compounds.

In any case where the hole injection layer is composed of an acceptor compound alone or when the hole injection layer is doped with an acceptor compound, the hole injection layer may be a single layer, A plurality of layers may be laminated. Further, the acceptor compound according to the present invention may be composed of the acceptor compound alone, or the hole injection layer containing the acceptor compound may be used as a charge generation layer in a tandem structure type element connecting a plurality of light emitting elements. .

The anode is not particularly limited as long as it can efficiently inject holes into the organic layer, but it is preferable to use a material having a relatively large work function. Examples of the material for the anode include conductive metal oxides such as tin oxide, indium oxide, indium zinc oxide, and indium tin oxide (ITO), metals such as gold, silver, and chromium, copper iodide, and copper sulfide. Examples include inorganic conductive materials, conductive polymers such as polythiophene, polypyrrole, and polyaniline. These electrode materials may be used alone, or a plurality of materials may be laminated or mixed.

The resistance of the anode is not limited as long as a current sufficient for light emission of the light emitting element can be supplied, but it is desirable that the resistance is low in terms of power consumption of the light emitting element. For example, if the resistance is 300Ω / □ or less, it functions as an electrode. However, since it is now possible to supply an ITO substrate of about 10Ω / □, it is possible to use a low resistance product of 100Ω / □ or less. Particularly desirable. The thickness of the anode can be arbitrarily selected according to the resistance value, but is usually used in a range of 100 to 300 nm.

In order to maintain the mechanical strength of the light emitting element, it is preferable to form the anode on the substrate. As the substrate, a glass substrate such as soda glass or non-alkali glass is preferably used. As the thickness of the glass substrate, it is sufficient that the thickness is sufficient to maintain the mechanical strength. The glass material is preferably alkali-free glass because it is better to have less ions eluted from the glass, but soda lime glass with a barrier coat such as SiO ₂ is also available on the market. it can. Furthermore, if the anode functions stably, the substrate does not have to be glass. For example, the anode may be formed on a plastic substrate. The method for forming the anode is not particularly limited, and for example, an electron beam method, a sputtering method, a chemical reaction method, or the like can be used.

The material used for the cathode is not particularly limited as long as it can efficiently inject electrons into the organic layer, but platinum, gold, silver, copper, iron, tin, zinc, aluminum, indium, chromium, lithium, sodium, potassium , Cesium, calcium and magnesium, and alloys thereof. Lithium, sodium, potassium, cesium, calcium, magnesium, or alloys containing these low work function metals are effective for increasing the electron injection efficiency and improving device characteristics. However, since these low work function metals are generally unstable in the atmosphere, the organic layer is doped with a small amount of lithium or magnesium (1 nm or less in the thickness gauge display of vacuum deposition) to stabilize the organic layer. A preferred example is a method for obtaining a high electrode. Also, an inorganic salt such as lithium fluoride can be used. Furthermore, for electrode protection, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, or alloys using these metals, inorganic substances such as silica, titania and silicon nitride, polyvinyl alcohol, polyvinyl chloride Lamination of organic polymer compounds such as hydrocarbon polymer compounds is a preferred example. The method for forming the cathode is not particularly limited, and for example, resistance heating, electron beam, sputtering, ion plating and coating can be used.

The light emitting layer may be either a single layer or a plurality of layers, each formed by a light emitting material (host material, dopant material), which may be a mixture of a host material and a dopant material or a host material alone, Either is acceptable. That is, in the light emitting element of the present invention, only the host material or the dopant material may emit light in each light emitting layer, or both the host material and the dopant material may emit light. From the viewpoint of efficiently using electric energy and obtaining light emission with high color purity, the light emitting layer is preferably composed of a mixture of a host material and a dopant material. Further, the host material and the dopant material may be either one kind or a plurality of combinations, respectively. The dopant material may be included in the entire host material or may be partially included. The dopant material may be laminated or dispersed. The dopant material can control the emission color. When the amount of the dopant material is too large, a concentration quenching phenomenon occurs, so that it is preferably used in an amount of 20% by mass or less, more preferably 10% by mass or less based on the host material. The doping method can be formed by a co-evaporation method with a host material, but may be simultaneously deposited after being previously mixed with the host material.

Specifically, the light-emitting material includes condensed ring derivatives such as anthracene and pyrene, which have been known as light emitters, metal chelated oxinoid compounds such as tris (8-quinolinolato) aluminum, bisstyrylanthracene derivatives and diesters. Bisstyryl derivatives such as styrylbenzene derivatives, tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, oxadiazole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole In derivatives, indolocarbazole derivatives, and polymer systems, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polythiophene derivatives, etc. can be used, but are not particularly limited. Not shall.

The host material contained in the light emitting material is not particularly limited, but is a compound having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, naphthacene, triphenylene, perylene, fluoranthene, fluorene, indene, and derivatives thereof, N, Aromatic amine derivatives such as N′-dinaphthyl-N, N′-diphenyl-4,4′-diphenyl-1,1′-diamine, metal chelating oxinoids including tris (8-quinolinato) aluminum (III) Compounds, bisstyryl derivatives such as distyrylbenzene derivatives, tetraphenylbutadiene derivatives, indene derivatives, coumarin derivatives, oxadiazole derivatives, pyrrolopyridine derivatives, perinone derivatives, cyclopentadiene derivatives, pyrrolopyrrole derivatives For thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, polymer systems, polyphenylene vinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinyl carbazole derivatives, polythiophene derivatives, etc. can be used, but in particular limited Is not to be done. The dopant material is not particularly limited, but is a compound having a condensed aryl ring such as naphthalene, anthracene, phenanthrene, pyrene, chrysene, triphenylene, perylene, fluoranthene, fluorene, indene or a derivative thereof (for example, 2- (benzothiazole-2) -Yl) -9,10-diphenylanthracene, 5,6,11,12-tetraphenylnaphthacene), furan, pyrrole, thiophene, silole, 9-silafluorene, 9,9'-spirobisilafluorene, benzo Compounds having heteroaryl rings such as thiophene, benzofuran, indole, dibenzothiophene, dibenzofuran, imidazopyridine, phenanthroline, pyridine, pyrazine, naphthyridine, quinoxaline, pyrrolopyridine, thioxanthene Derivatives thereof, borane derivatives, distyrylbenzene derivatives, 4,4′-bis (2- (4-diphenylaminophenyl) ethenyl) biphenyl, 4,4′-bis (N- (stilben-4-yl) -N— Aminostyryl derivatives such as phenylamino) stilbene, aromatic acetylene derivatives, tetraphenylbutadiene derivatives, stilbene derivatives, aldazine derivatives, pyromethene derivatives, diketopyrrolo [3,4-c] pyrrole derivatives, 2,3,5,6-1H, Coumarin derivatives such as 4H-tetrahydro-9- (2′-benzothiazolyl) quinolidino [9,9a, 1-gh] coumarin, azole derivatives such as imidazole, thiazole, thiadiazole, carbazole, oxazole, oxadiazole and triazole and their metals Complex and N, '- diphenyl -N, etc. N'- di (3-methylphenyl) -4,4'-aromatic amine derivative typified by diphenyl-1,1'-diamine can be used.

Further, a phosphorescent material may be included in the light emitting layer. A phosphorescent material is a material that exhibits phosphorescence even at room temperature. As a dopant, it is basically necessary to obtain phosphorescence even at room temperature, but it is not particularly limited, and iridium (Ir), ruthenium (Ru), rhodium (Rh), palladium (Pd), platinum ( An organometallic complex compound containing at least one metal selected from the group consisting of Pt), osmium (Os), and rhenium (Re) is preferable. Among these, from the viewpoint of having a high phosphorescence emission yield even at room temperature, an organometallic complex having iridium or platinum is more preferable. Hosts of phosphorescent materials include indole derivatives, carbazole derivatives, indolocarbazole derivatives, pyridine, pyrimidine, nitrogen-containing aromatic compound derivatives having a triazine skeleton, polyarylbenzene derivatives, spirofluorene derivatives, truxene derivatives, triphenylene derivatives, etc. A compound containing a chalcogen element such as an aromatic hydrocarbon compound derivative, a dibenzofuran derivative or a dibenzothiophene derivative, or an organometallic complex such as a beryllium quinolinol complex is preferably used. As long as holes are smoothly injected and transported from the respective transport layers, the present invention is not limited thereto. Two or more triplet light-emitting dopants may be contained, or two or more host materials may be contained. Further, one or more triplet light emitting dopants and one or more fluorescent light emitting dopants may be contained.

Preferred phosphorescent dopants are not particularly limited, but specific examples include the following.

In addition, the preferred host of the phosphorescent light emitting layer is not particularly limited, but specific examples include the following.

The compound represented by the general formula (1) has a high triplet level in addition to good hole injection and transport properties and high electron blocking performance. Therefore, when the phosphorescence layer and the hole transport layer containing the compound represented by the general formula (1) are combined, triplet energy transfer from the phosphorescence layer to the hole transport layer is suppressed, Thermal deactivation of phosphorescence energy in the transport layer can be prevented. For this reason, it is possible to prevent a decrease in light emission efficiency and to obtain a light emitting element with low voltage drive and long life, which is preferable.

In the present invention, an electron injection layer may be provided between the cathode and the electron transport layer. In general, the electron injection layer is inserted for the purpose of assisting injection of electrons from the cathode to the electron transport layer, but in the case of insertion, the compound having a heteroaryl ring structure containing the electron accepting nitrogen described above is used as it is. Also good. An insulator or a semiconductor inorganic substance can also be used for the electron injection layer. Use of these materials is preferable because a short circuit of the light emitting element can be effectively prevented and the electron injection property can be improved. As such an insulator, it is preferable to use at least one metal compound selected from the group consisting of alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides and alkaline earth metal halides. If the electron injection layer is composed of these alkali metal chalcogenides or the like, it is more preferable because the electron injection property can be further improved. Specifically, preferred alkali metal chalcogenides include, for example, Li ₂ O, Na ₂ S, and Na ₂ Se, and preferred alkaline earth metal chalcogenides include, for example, CaO, BaO, SrO, BeO, BaS, and CaSe. Is mentioned. Further, preferable alkali metal halides include, for example, LiF, NaF, KF, LiCl, KCl, and NaCl. Examples of preferable alkaline earth metal halides include fluorides such as CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ and BeF ₂ , and halides other than fluorides. Furthermore, a complex of an organic substance and a metal is also preferably used. When an insulator or a semiconductor inorganic material is used for the electron injection layer, if the film thickness is too large, there may be a problem that the light emitting element is insulated or the driving voltage becomes high. That is, there is a possibility that the yield of the light-emitting element is reduced due to the film thickness margin of the electron injection layer, but it is more preferable to use a complex of an organic substance and a metal for the electron injection layer because the film thickness can be easily adjusted. Examples of such organometallic complexes include quinolinol, benzoquinolinol, pyridylphenol, flavonol, hydroxyimidazopyridine, hydroxybenzazole, hydroxytriazole and the like as preferred examples of the organic substance in a complex with an organic substance. Among these, a complex of an alkali metal and an organic substance is preferable, a complex of lithium and an organic substance is more preferable, and lithium quinolinol is particularly preferable.

The light emitting element of the present invention has a function of converting electrical energy into light. Here, a direct current is mainly used as the electric energy, but a pulse current or an alternating current can also be used. The current value and voltage value are not particularly limited, but should be selected so that the maximum luminance can be obtained with as low energy as possible in consideration of the power consumption and lifetime of the device.

The light-emitting element of the present invention is suitably used as a display for displaying in a matrix and / or segment system, for example.

In the matrix method, pixels for display are arranged two-dimensionally such as a lattice shape or a mosaic shape, and characters and images are displayed by a set of pixels. The shape and size of the pixel are determined by the application. For example, a square pixel with a side of 300 μm or less is usually used for displaying images and characters on a personal computer, monitor, TV, and a pixel with a side of mm order for a large display such as a display panel. become. In monochrome display, pixels of the same color may be arranged. However, in color display, red, green, and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. The matrix driving method may be either a line sequential driving method or an active matrix. Although the structure of the line sequential drive is simple, the active matrix may be superior in consideration of the operation characteristics, and it is necessary to use it depending on the application.

The segment system in the present invention is a system in which a pattern is formed so as to display predetermined information and a region determined by the arrangement of the pattern is caused to emit light. For example, the time and temperature display in a digital clock or a thermometer, the operation state display of an audio device or an electromagnetic cooker, the panel display of an automobile, etc. The matrix display and the segment display may coexist in the same panel.

The light-emitting element of the present invention is also preferably used as a backlight for various devices. The backlight is used mainly for the purpose of improving the visibility of a display device that does not emit light, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display panel, a sign, and the like. In particular, the light-emitting element of the present invention is preferably used for a backlight for a liquid crystal display device, particularly a personal computer for which a reduction in thickness is being considered, and a backlight that is thinner and lighter than conventional ones can be provided.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) on which ITO transparent conductive film was deposited at 165 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. As a hole transport layer, HT-1 was deposited to 60 nm by a resistance heating method. Next, as a light emitting layer, the compound H-1 was used as the host material, the compound D-1 was used as the dopant material, and the dopant material was deposited to a thickness of 40 nm so that the doping concentration was 5 mass%. Next, Compound E-1 was laminated to a thickness of 20 nm as an electron transport layer.
Next, Liq (lithium quinolinol) was deposited as an electron injection layer to a thickness of 0.5 nm, and then magnesium and silver were deposited at a thickness of 1000 nm so as to have a mass ratio of 1: 1, thereby forming a 5 × 5 mm square device. The film thickness here is a display value of a crystal oscillation type film thickness monitor. The characteristics of this light emitting element at 1000 cd / m ² were a driving voltage of 5.4 V and an external quantum efficiency of 4.1%. When this element was set to an initial luminance of 1000 cd / m ² and the endurance life was measured, the time of 20% reduction from the initial luminance was 115 hours. Compounds HT-1, H-1, D-1, E-1, and Liq are the compounds shown below.

(Examples 2 to 28)
Using the materials described in Table 1 as the hole transport layer, the light emitting layer host material, the light emitting layer dopant material, and the electron transport layer, a light emitting device was produced and evaluated in the same manner as in Example 1. The results of each example are shown in Table 1. HT-2, HT-3, HT-4, HT-5, HT-6, HT-7, E-2, E-3 and E-4 are the compounds shown below.

(Comparative Examples 1-34)
Using the materials described in Table 2 as a hole transport layer, a light emitting layer host material, a light emitting layer dopant material, and an electron transport layer, a light emitting device was produced and evaluated in the same manner as in Example 1. The results of each comparative example are shown in Table 2. HT-8, HT-9, HT-10, HT-11, HT-12, E-5, E-6 are the compounds shown below.

From Tables 1 and 2, Examples 1 to 7 and Comparative Examples 1 to 5, Examples 8 to 14 and Comparative Examples 6 to 10, Examples 15 to 21 and Comparative Examples 11 to 15, Examples 22 to 28 and Comparative Examples By comparing 16 to 20, when a compound having a phenanthroline skeleton is used in the electron transport layer, the compound represented by the general formula (1) is used in the hole transport layer, so that low voltage driving and light emission efficiency are achieved. It can be seen that there are effects such as improvement of durability and improvement of durability life.

Further, by comparing Examples 1 to 28 and Comparative Examples 21 to 34, when the compound represented by the general formula (1) is used for the hole transport layer, a compound having a phenanthroline skeleton is used for the electron transport layer. Thus, it can be seen that effects such as low voltage driving, improvement in light emission efficiency, and improvement in durability life can be seen, and in particular, the contribution to low voltage driving and improvement in light emission efficiency is large.

(Example 29)
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) on which ITO transparent conductive film was deposited at 165 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. By the resistance heating method, first, HAT-CN6, which is an acceptor compound, was deposited as a hole injection layer by 10 nm, and then HT-1 was deposited as a hole transport layer by 50 nm. Next, as a light emitting layer, the compound H-1 was used as the host material, the compound D-1 was used as the dopant material, and the dopant material was deposited to a thickness of 40 nm so that the doping concentration was 5 mass%. Next, as an electron transport layer, Compound E-1 was laminated to a thickness of 20 nm on the electron transport material.
Next, Liq was deposited as an electron injection layer to a thickness of 0.5 nm, and then magnesium and silver were deposited at a thickness of 1000 nm so as to have a mass ratio of 1: 1 to form a cathode, thereby producing a 5 × 5 mm square device. The film thickness here is a display value of a crystal oscillation type film thickness monitor. The characteristics at 1000 cd / m ² of this light emitting device were a driving voltage of 3.7 V and an external quantum efficiency (light emission efficiency) of 5.0%. When this element was set to an initial luminance of 1000 cd / m ² and the endurance life was measured, the time of 20% reduction from the initial luminance was 263 hours. HAT-CN6 is a compound shown below.

(Examples 30 and 31)
A light emitting device was prepared and evaluated in the same manner as in Example 29 except that the compounds listed in Table 3 were used for the hole transport layer. The results of each example are shown in Table 3.

(Example 32)
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) on which ITO transparent conductive film was deposited at 165 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. First, HT-1 was used as a hole injection material as a hole injection layer and F4-TCNQ was used as an acceptor compound by a resistance heating method, and 30 nm was deposited so that the acceptor compound had a doping concentration of 5 mass%. Next, 30 nm of HT-1 was deposited as a hole transport layer. Next, as a light emitting layer, the compound H-1 was used as the host material, the compound D-1 was used as the dopant material, and the dopant material was deposited to a thickness of 40 nm so that the doping concentration was 5 mass%. Next, as an electron transport layer, Compound E-1 was laminated to a thickness of 20 nm on the electron transport material.
Next, Liq was deposited as an electron injection layer to a thickness of 0.5 nm, and then magnesium and silver were deposited at a thickness of 1000 nm so as to have a mass ratio of 1: 1 to form a cathode, thereby producing a 5 × 5 mm square device. The film thickness here is a display value of a crystal oscillation type film thickness monitor. The characteristics of this light emitting element at 1000 cd / m ² were a driving voltage of 3.7 V and an external quantum efficiency of 5.1%. When this element was set to an initial luminance of 1000 cd / m ² and the endurance life was measured, the time of 20% reduction from the initial luminance was 265 hours. F4-TCNQ is a compound shown below.

(Examples 33 and 34)
A light emitting device was produced and evaluated in the same manner as in Example 32 except that the compounds described in Table 3 were used for the hole injection layer and the hole transport layer. The results of each example are shown in Table 3.

(Examples 35 to 37)
A light emitting device was fabricated and evaluated in the same manner as in Example 29 except that the compounds listed in Table 3 were used for the hole transport layer and E-2 was used for the electron transport layer. The results of each example are shown in Table 3.

(Examples 38 to 40)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds shown in Table 3 were used for the hole injection layer and the hole transport layer, and E-2 was used for the electron transport layer. The results of each example are shown in Table 3.

(Examples 41 to 49)
A light emitting device was fabricated and evaluated in the same manner as in Example 29 except that the compounds listed in Table 3 were used for the hole transport layer and E-3 was used for the electron transport layer. The results of each example are shown in Table 3. HT-13 and HT-14 are the following compounds.

(Examples 50 to 58)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds shown in Table 3 were used for the hole injection layer and the hole transport layer, and E-3 was used for the electron transport layer. The results of each example are shown in Table 3.

(Example 59)
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) on which ITO transparent conductive film was deposited at 165 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. By resistance heating, molybdenum oxide (MoO ₃ ) was first deposited as a hole injection layer by 1 nm, and then HT-1 was deposited as a hole transport layer by 59 nm. Next, as a light emitting layer, the compound H-1 was used as the host material, the compound D-1 was used as the dopant material, and the dopant material was deposited to a thickness of 40 nm so that the doping concentration was 5 mass%. Next, as an electron transport layer, Compound E-3 was laminated to a thickness of 20 nm on the electron transport material.
Next, Liq was deposited as an electron injection layer to a thickness of 0.5 nm, and then magnesium and silver were deposited at a thickness of 1000 nm so as to have a mass ratio of 1: 1 to form a cathode, thereby producing a 5 × 5 mm square device. The film thickness here is a display value of a crystal oscillation type film thickness monitor. The characteristics of this light emitting element at 1000 cd / m ² were a driving voltage of 3.5 V and an external quantum efficiency of 5.5%. When this element was set to an initial luminance of 1000 cd / m ² and the endurance life was measured, the time to decrease 20% from the initial luminance was 379 hours.

(Examples 60 to 67)
Using the compounds listed in Table 3 for the hole injection layer and the hole transport layer, a light emitting device was produced and evaluated in the same manner as in Example 59. The results of each example are shown in Table 3.

(Example 68)
A glass substrate (manufactured by Geomat Co., Ltd., 11Ω / □, sputtered product) on which ITO transparent conductive film was deposited at 165 nm was cut into 38 × 46 mm and etched. The obtained substrate was ultrasonically cleaned with “Semico Clean 56” (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes and then with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the device, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁴ Pa or less. First, HT-1 was used as a hole injection material as a hole injection layer and PD-1 was used as an acceptor compound by a resistance heating method, and vapor deposition was performed at 30 nm so that the acceptor compound had a doping concentration of 3 mass%. Next, 30 nm of HT-1 was deposited as a hole transport layer. Next, as a light emitting layer, the compound H-1 was used as the host material, the compound D-1 was used as the dopant material, and the dopant material was deposited to a thickness of 40 nm so that the doping concentration was 5 mass%. Next, as an electron transport layer, Compound E-3 was laminated to a thickness of 20 nm on the electron transport material.
Next, Liq was deposited as an electron injection layer to a thickness of 0.5 nm, and then magnesium and silver were deposited at a thickness of 1000 nm so as to have a mass ratio of 1: 1 to form a cathode, thereby producing a 5 × 5 mm square device. The film thickness here is a display value of a crystal oscillation type film thickness monitor. The characteristics of this light-emitting element at 1000 cd / m ² were a driving voltage of 3.4 V and an external quantum efficiency of 5.5%. When this element was set to an initial luminance of 1000 cd / m ² and the endurance life was measured, the time for a 20% decrease from the initial luminance was 402 hours. PD-1 is a compound shown below.

(Examples 69 to 76)
Using the compounds listed in Table 3 for the hole injection layer and the hole transport layer, a light emitting device was produced and evaluated in the same manner as in Example 68. The results of each example are shown in Table 3.

(Examples 77 to 85)
A light emitting device was prepared and evaluated in the same manner as in Example 29 except that the compounds shown in Table 4 were used for the hole injection layer and the hole transport layer, and E-4 was used for the electron transport layer. The results of each example are shown in Table 4.

(Examples 86 to 94)
A light emitting device was fabricated and evaluated in the same manner as in Example 32 except that the compounds shown in Table 4 were used for the hole injection layer and the hole transport layer, and E-4 was used for the electron transport layer. The results of each example are shown in Table 4.

(Examples 95 to 103)
A light emitting device was fabricated and evaluated in the same manner as in Example 59 except that the compounds shown in Table 4 were used for the hole transport layer and E-4 was used for the electron transport layer. The results of each example are shown in Table 4.

(Examples 104 to 112)
A light emitting device was prepared and evaluated in the same manner as in Example 68 except that the compounds shown in Table 4 were used for the hole injection layer and the hole transport layer, and E-4 was used for the electron transport layer. The results of each example are shown in Table 4.

Examples 1 to 3, Examples 29 to 34, Examples 8 to 10 and Examples 35 to 40, Examples 15 to 17, Examples 41 to 43, 50 to 52, 59 to 61, 68 to 70, Examples 22 to 24 and Examples 77 to 79, 86 to 88, 95 to 97, 104 to 106 are respectively compared to provide a hole injection layer, and the hole injection layer is composed of an acceptor compound alone, Alternatively, it can be seen that the inclusion of an acceptor compound further enhances the effects of low voltage driving, improved luminous efficiency, and improved durability life.

(Comparative Examples 35 to 37)
A light emitting device was produced and evaluated in the same manner as in Example 29 except that the compounds listed in Table 5 were used for the hole transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 38 to 40)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds described in Table 5 were used for the hole injection layer and the hole transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 41 to 43)
A light emitting device was prepared and evaluated in the same manner as in Example 29 except that the compounds shown in Table 5 were used for the hole transport layer and E-2 was used for the electron transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 44 to 46)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds shown in Table 5 were used for the hole injection layer and the hole transport layer, and E-2 was used for the electron transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 47-53)
A light emitting device was prepared and evaluated in the same manner as in Example 29 except that the compounds shown in Table 5 were used for the hole transport layer and E-3 was used for the electron transport layer. The results of each comparative example are shown in Table 5. HT-15 and HT-16 are the compounds shown below.

(Comparative Examples 54-60)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds shown in Table 5 were used for the hole injection layer and the hole transport layer, and E-3 was used for the electron transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 61-67)
A light emitting device was fabricated and evaluated in the same manner as in Example 59 using the compounds listed in Table 5 for the hole transport layer. The results of each comparative example are shown in Table 5.

(Comparative Examples 68-74)
Using the compounds listed in Table 5 for the hole injection layer and the hole transport layer, a light emitting device was produced and evaluated in the same manner as in Example 68. The results of each comparative example are shown in Table 5.

(Comparative Examples 75-81)
A light emitting device was prepared and evaluated in the same manner as in Example 29 except that the compounds shown in Table 6 were used for the hole transport layer and E-4 was used for the electron transport layer. The results of each comparative example are shown in Table 6.

(Comparative Examples 82-88)
A light emitting device was prepared and evaluated in the same manner as in Example 32 except that the compounds shown in Table 6 were used for the hole injection layer and the hole transport layer, and E-4 was used for the electron transport layer. The results of each comparative example are shown in Table 6.

(Comparative Examples 89-95)
A light emitting device was prepared and evaluated in the same manner as in Example 59 except that the compounds shown in Table 6 were used for the hole transport layer and E-4 was used for the electron transport layer. The results of each comparative example are shown in Table 6.

(Comparative Examples 96 to 102)
A light emitting device was fabricated and evaluated in the same manner as in Example 68 except that the compounds shown in Table 6 were used for the hole injection layer and the hole transport layer, and E-4 was used for the electron transport layer. The results of each comparative example are shown in Table 6.

Examples 29 to 31 and Comparative Examples 35 to 37, Examples 32 to 34 and Comparative Examples 38 to 40, Examples 35 to 37 and Comparative Examples 41 to 43, Examples 38 to 40 and Comparative Examples 44 to 46, Examples 41-49 and Comparative Examples 47-53, Examples 50-58 and Comparative Examples 54-60, Examples 59-67, Comparative Examples 61-67, Examples 68-76, Comparative Examples 68-74, and Examples 77- By comparing 85 and Comparative Examples 75 to 81, Examples 86 to 94 and Comparative Examples 82 to 88, Examples 95 to 103 and Comparative Examples 89 to 95, Examples 104 to 112 and Comparative Examples 96 to 102, respectively. When a hole injection layer is provided in a light-emitting element and the hole injection layer is composed of an acceptor compound alone or contains an acceptor compound, a compound having a phenanthroline skeleton is used in the electron transport layer. In transport layer By using a compound represented by the general formula (1), low-voltage driving, the improvement of luminous efficiency, it can be seen that the effect is seen at improvement of durability.

The light-emitting element according to the present invention is useful in fields that are driven at a low voltage and require high luminous efficiency and durability, and is a display element, flat panel display, backlight, illumination, interior, sign, signboard, and electrophotography. It can be used for a machine and an optical signal generator.

Claims

A light emitting device comprising at least a hole transport layer and an electron transport layer between an anode and a cathode, and emitting light by electric energy,
The hole transport layer contains a compound represented by the following general formula (1),
The light-emitting element, wherein the electron transport layer contains a compound having a phenanthroline skeleton.

(In the general formula (1), R 1 to R 12 may be the same or different from each other, and hydrogen, alkyl group, cycloalkyl group, amino group, aryl group, heterocyclic group, alkenyl group, cycloalkenyl group, An alkynyl group, an alkoxy group, an alkylthio group, an aryl ether group, an aryl thioether group, a halogen, a cyano group, —P (═O) R 13 R 14 and a silyl group, each selected from R 13 and R 14 These substituents may be the same or different and are an aryl group or a heteroaryl group, and these substituents may be further substituted, and adjacent substituents may further form a ring, provided that R N of 1 to R 12 is an amino group represented by —NR 15 R 16. R 15 and R 16 may be the same or different. The alkyl group, the cycloalkyl group, the aryl group, or the heteroaryl group may be selected from the group consisting of an alkyl group, a cycloalkyl group, an aryl group, and a heteroaryl group. (N represents an integer of 1 to 6)
The light-emitting element according to claim 1, wherein the compound having a phenanthroline skeleton is a compound having a plurality of phenanthroline skeletons.
The light emitting device according to claim 2, wherein the compound having a plurality of phenanthroline skeletons is a compound represented by the following general formula (2).

(In the general formula (2), R 17 to R 24 may be the same as or different from each other, and hydrogen, alkyl group, cycloalkyl group, amino group, aryl group, heterocyclic group, alkenyl group, cycloalkenyl group, Alkynyl group, alkoxy group, alkylthio group, aryl ether group, aryl thioether group, halogen, cyano group, —P (═O) R 25 R 26 , silyl group and A are selected from the group consisting of R 25 and R 26. These substituents may be the same or different and each is an aryl group or a heteroaryl group, and these substituents may be further substituted, and adjacent substituents may further form a ring. Represents a single bond directly connecting m phenanthroline skeletons or a linking unit linking m phenanthroline skeletons. Tsu doo is a double bond, a triple bond, a substituted or unsubstituted aromatic hydrocarbon residue, a substituted or unsubstituted aromatic heterocyclic residue, or a combination thereof. However, the R 17 ~ R 24 One of them is A, and m represents an integer of 2 or more.)
A hole injection layer is provided between the hole transport layer and the anode, and the hole injection layer is composed of an acceptor compound alone or contains an acceptor compound. The light emitting device according to any one of 1 to 3.
The light-emitting element according to claim 4, wherein the acceptor compound is a metal oxide or a cyano group-containing compound.