JP2006128636A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element having proper driving durability and luminescent characteristics. <P>SOLUTION: A light emitting element has an organic compound layer containing at least one layer of luminescent layer between a pair of electrodes. The luminescent layer contains at least one kind of luminescent dopant and a plurality of host compounds. Expressing the ionization potential of the dopant as Ip(D) and the minimum value of the ionization potential of a plurality of host compounds as Ip(H)min, ΔIp defined by ΔIp=Ip(D)-Ip(H)min satisfies the relation ΔIp>0eV. Expressing the electron affinity of the dopant as Ea(D) and the maximum value of the electron affinity of a plurality of host compounds as Ea(H)max, ΔEa defined by ΔEa=Ea(H)max-Ea(D) satisfies the relation ΔEa>0eV. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescent element (hereinafter also referred to as “organic EL element”, “light emitting element”, or “EL element”) that can emit light by converting electric energy into light.

Today, research and development on various display elements are active. Among them, organic electroluminescence (EL) elements are attracting attention as promising display elements because they can emit light with high luminance at a low voltage. It is disclosed that a plurality of compounds are used as the host material of the light emitting layer, and each of them is used as an electron transporting host and a hole transporting host to reduce power consumption and improve driving durability (for example, (See Patent Documents 1 and 2). These conventional techniques show that the carriers injected into the light emitting layer are trapped by the light emitting dopant and recombined to emit light, thereby obtaining high light emission efficiency.
However, in this method, since the luminescent dopant traps carriers, deterioration of the luminescent dopant due to carriers is unavoidable, and it is difficult to obtain sufficient driving durability.
JP 2002-313583 A JP 2002-324673 A

  An object of the present invention is to provide an organic electroluminescence device having good driving durability and light emission characteristics.

As a result of the study, the inventors made a specific range of energy levels such as the electron affinity and ionization potential of the host material and the luminescent dopant in the luminescent layer, so that the luminescent dopant does not trap carriers, The mechanism by which the luminescent dopant emits light by energy transfer from the host was discovered.
As a result, it is possible to obtain an organic electroluminescence device that can suppress deterioration due to the carrier of the dopant and is excellent in driving durability.
That is, the present invention is achieved by the following means.

<1> An organic electroluminescence device having an organic compound layer including at least one light emitting layer between a pair of electrodes, wherein the light emitting layer contains at least one luminescent dopant and a plurality of host compounds. Defined as ΔIp = Ip (D) −Ip (H) min, where Ip (D) is the ionization potential of the dopant and Ip (H) min is the minimum of the ionization potentials of the plurality of host compounds. ΔIp satisfies the relationship of ΔIp> 0 eV, the electron affinity of the dopant is Ea (D), and the maximum of the electron affinity of the plurality of host compounds is Ea (H) max. = ΔEa defined by Ea (H) max−Ea (D) satisfies the relationship of ΔEa> 0 eV.

<2> The organic electric field according to <1>, wherein ΔIp satisfies 1.2 eV> ΔIp> 0.2 eV and / or ΔEa satisfies a relationship of 1.2 eV> ΔEa> 0.2 eV. Light emitting element.

<3> The above-mentioned <1>, wherein the fluorescence phosphorescence spectrum measured with a single layer film formed only of the plurality of host compounds is emission attributed to the single emission spectrum of each of the plurality of host compounds. > Or <2>.

<4> The organic electroluminescent element as described in <1> or <2> above, wherein the organic compound layer has a carrier transport layer adjacent to the light emitting layer.

<5> The carrier transport layer is an electron transport layer, and the electron affinity Ea (ETL) of the electron transport layer is larger than the electron affinity Ea (D) of the dopant contained in the light emitting layer. The organic electroluminescent element as described in <4>.

<6> The carrier transport layer is a hole transport layer, and the ionization potential Ip (HTL) of the hole transport layer is smaller than the ionization potential Ip (D) of the dopant contained in the light emitting layer. The organic electroluminescent element according to <4> above.

<7> Among the lowest excited triplet energies of a plurality of host compounds, when T1 (H) min is the minimum, T1 (H) between the lowest triplet excited energy T1 (D) of the dopant The organic electroluminescence device according to any one of <1> to <6>, wherein the relationship of min> T1 (D) is satisfied.

<8> Any one of the above <1> to <7>, wherein the content of the plurality of host compounds is 15% by mass or more and 85% by mass or less with respect to the total compound mass forming the light emitting layer. The organic electroluminescent element according to one item.

  ADVANTAGE OF THE INVENTION According to this invention, an organic electroluminescent element with favorable drive durability and a light emission characteristic can be provided.

[Organic electroluminescence device]
The organic electroluminescent device of the present invention is an organic electroluminescent device having an organic compound layer including at least one luminescent layer between a pair of electrodes, wherein the luminescent layer includes at least one luminescent dopant and a plurality of hosts. When the ionization potential of the dopant is Ip (D) and the ionization potential of the plurality of host compounds is Ip (H) min, ΔIp = Ip (D) −Ip (H) ΔIp defined by min satisfies the relationship of ΔIp> 0 eV, the electron affinity of the dopant is Ea (D), and the maximum of the electron affinity of the plurality of host compounds is Ea (H) max In this case, ΔEa defined by ΔEa = Ea (H) max−Ea (D) satisfies the relationship of ΔEa> 0 eV.
The organic electroluminescent element of the present invention exhibits excellent light emission characteristics and driving durability by adopting the above-described configuration.

Furthermore, the organic electroluminescent device of the present invention is driven such that ΔIp satisfies 1.2 eV>ΔIp> 0.2 eV and / or ΔEa satisfies any one relationship of 1.2 eV>ΔEa> 0.2 eV. From the viewpoint of durability, it is preferable that ΔIp satisfies 1.2 eV>ΔIp> 0.4 eV and / or ΔEa satisfies any one of the following relationships: 1.2 eV>ΔEa> 0.4 eV.
When ΔIp satisfies 1.2 eV>ΔIp> 0.2 eV and / or ΔEa satisfies any one of the following relationships: 1.2 eV>ΔEa> 0.2 eV, holes and / or electrons are hardly trapped by the dopant. From the viewpoint of driving durability, it is preferable.

Furthermore, in the organic electroluminescent device of the present invention, the Ip (H) min is 5.1 eV or more and / or the Ea (H) max is 3.0 eV or less. It is preferable from the viewpoint. More preferable ranges are Ip (H) min of 5.4 eV or more and Ea (H) max of 2.8 eV or less.
This leads to suppression of interaction between a plurality of host compounds in the light emitting layer. When a charge transfer complex or exciplex having a lower excitation energy state is formed as a result of the interaction between a plurality of host compounds, the excited state that should originally be possible for any host compound is changed to the charge transfer complex or exciplex. Formed on a plex. As a result, energy transfer to the dopant becomes insufficient, and predetermined light emission may not be obtained. Moreover, it is because there exists a concern about a drive durability fall by decomposition | disassembly from an excited state on a charge transfer complex and an exciplex.
Whether or not there is an interaction between a plurality of host compounds in the light emitting layer is determined by producing a single layer film of only the plurality of host compounds contained in the light emitting layer in the same manner as the formation conditions of the light emitting layer. It can be judged by measuring the film and measuring the fluorescence phosphorescence spectrum and comparing it with the emission spectrum of each individual host compound.
That is, when a long-wave emission spectrum component that cannot be attributed to each emission spectrum contained in a plurality of host compounds is observed in the fluorescent phosphorescence spectrum, an interaction is considered to have occurred. The fluorescence phosphorescence spectrum measured in the state of a single-layer film in which only a plurality of host compounds are formed is preferably luminescence attributed to each single emission spectrum of the plurality of host compounds. It is preferable that an emission spectrum component is not observed on the longer wave side of 15 nm or more than any of the main peaks of the emission spectrum alone.
For the measurement of the fluorescence phosphorescence spectrum, for example, RF-5300PC manufactured by Shimadzu Corporation can be used, and as the excitation light, light having a wavelength that each contained host compound has absorption alone is used.

Here, the ionization potential (Ip), the electron affinity (Ea), and the triplet state level (T ₁ ) described later in the present invention will be described.
The ionization potential (Ip), the electron affinity (Ea), and the triplet state level (T ₁ ) described later are obtained by measuring a single layer film obtained by depositing each material on quartz by a vacuum deposition method. Value.

  The ionization potential (Ip) is defined by a value measured at room temperature and in the atmosphere with an ultraviolet photoelectron analyzer AC-1 (manufactured by Riken Keiki Co., Ltd.). The measurement principle of AC-1 is described in Chiba Adachi et al., “Collection of Organic Thin Film Work Function Data”, issued by CMC Publishing Co., Ltd. 2004.

  The electron affinity (Ea) is defined by a value obtained by calculating the band gap from the long wave end of the absorption spectrum of the single layer film and calculating the electron affinity (Ea) from the value of the ionization potential.

The lowest triplet excitation energy (triplet state level T ₁ ) is defined by a value calculated from the short wave end of a phosphorescence emission spectrum measured at room temperature. The measurement can also be performed at a nitrogen cooling temperature.

The fact that the light emitting device of the present invention is remarkably excellent in driving durability and light emission characteristics (external light emission efficiency) is presumed to function by the following light emission mechanism.
That is, most of the holes injected from the anode are injected into the hole transporting host in the light emitting layer via the hole injection layer and the hole transport layer. On the other hand, most of the electrons injected from the cathode are injected into the electron transporting host in the light emitting layer via the electron injection layer and the electron transport layer. Holes are injected from the hole transporting host in the light emitting layer into the HOMO of the electron transporting host, and excitons are generated on the electron transporting host. Alternatively, electrons are injected from the electron transporting host into the LUMO of the hole transporting host, and excitons are generated on the hole transporting host. The excited state energy of this host moves to the dopant and emits light from the singlet and / or triplet state of the dopant.
Here, when holes and electrons are injected into the light emitting layer, holes are injected into the hole transporting host and electrons are injected into the electron transporting host. As a result, the hole transporting host can be released from the anionic state and the electron transporting host from the cationic state, and as a result, driving durability can be improved. In addition, when holes and electrons are injected into the light emitting layer, the dopants HOMO and LUMO are on the outside, so that almost no carriers are injected into the dopant, and it is durable against dopants that have low resistance to cation or anion states. Can be improved.

Next, the structure in the organic electroluminescent element of this invention is demonstrated.
The organic electroluminescent element of the present invention preferably has an organic compound layer including at least a light emitting layer between a pair of electrodes, and further has a carrier transport layer adjacent to the light emitting layer. More preferably, the carrier transport layer is an electron transport layer and / or a hole transport layer.
From the property of the light emitting element, it is preferable that at least one of the pair of electrodes is transparent with respect to the emission wavelength of the dopant.

  In the present invention, the organic compound layer is preferably laminated in the order of the hole transport layer, the light emitting layer, and the electron transport layer from the anode side. Further, an electron blocking layer or the like may be provided between the hole transport layer and the light emitting layer, or a hole blocking layer or the like may be provided between the light emitting layer and the electron transport layer. Further, a hole injection layer may be provided between the anode and the hole transport layer, and similarly, an electron injection layer may be provided between the cathode and the electron transport layer.

  A preferred embodiment of the organic compound layer in the organic electroluminescence device of the present invention is, in order from the anode side, at least a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer. It is the aspect which has.

When a hole blocking layer is provided between the light emitting layer and the electron transporting layer, the organic compound layer adjacent to the light emitting layer is the hole transporting layer on the anode side and the hole blocking layer on the cathode side. .
Each layer may be divided into a plurality of secondary layers.

  Next, elements constituting the light emitting device of the present invention will be described in detail.

<Organic compound layer>
The organic compound layer in the present invention will be described.
The organic electroluminescent element of the present invention has an organic compound layer including at least one light emitting layer, and as the organic compound layer other than the light emitting layer, as described above, a carrier transport layer ( Hole transport layer or electron transport layer), hole block layer, hole injection layer, electron injection layer and the like.

The organic compound layer preferably has a thickness of 50 nm or less, more preferably 5 to 50 nm, and particularly preferably 10 to 40 nm from the viewpoint of lowering the driving voltage.
The layer adjacent to the light emitting layer on the anode side may be a hole injection layer, and the layer adjacent to the light emitting layer on the cathode side may be an electron injection layer or a charge blocking layer. Details of these layers will be described later.

(Formation of organic compound layer)
In the organic electroluminescent element of the present invention, each layer constituting the organic compound layer can be suitably formed by any of a dry film forming method such as a vapor deposition method and a sputtering method, a transfer method, and a printing method.

(Light emitting layer)
The light-emitting layer receives holes from the anode, the hole injection layer, or the hole transport layer when an electric field is applied, receives electrons from the cathode, the electron injection layer, or the electron transport layer, and recombines holes and electrons. It is a layer which has the function to provide and to emit light.
The light emitting layer in the present invention contains at least one light emitting dopant and a plurality of host compounds.
Further, the light emitting layer may be a single layer or two or more layers, and each layer may emit light in different emission colors. Even when there are a plurality of light-emitting layers, it is preferable that each layer of the light-emitting layer contains at least one light-emitting dopant and a plurality of host compounds.

As the light-emitting dopant and the plurality of host compounds contained in the light-emitting layer in the present invention, (1) ΔIp (= Ip (D) −Ip (H) min)> 0 eV and ΔEa (= Ea (H ) Max-Ea (D))> 0 eV can be used without particular limitation as long as the relationship is satisfied.
That is, a phosphorescent dopant and a plurality of phosphorescent dopants capable of emitting light (phosphorescence) from triplet excitons even in a combination of a plurality of host compounds with a fluorescence emitting dopant capable of emitting light (fluorescence) from singlet excitons. In combination with the host compound, a combination of a phosphorescent dopant and a plurality of host compounds is preferable from the viewpoint of luminous efficiency.
The light emitting layer in the present invention can contain two or more kinds of luminescent dopants in order to improve the color purity of the luminescent dopant.

The luminescent dopant and the plurality of host compounds that satisfy the relationship (1) in the present invention will be described below.
When one luminescent dopant is used and a plurality of host compounds are used, Ip (D) of the luminescent dopant is larger than one ionization potential Ip (H) min of the host compound, that is, Ip (D)> Ip (H ) Min, it is necessary to make the dopant such that Ea (D) is smaller than the electron affinity Ea (H) max of the other host compound, that is, Ea (H) max> Ea (D).
The host compound used as Ip (H) min at this time includes a hole transporting host, and the host compound used as Ea (H) max includes an electron transporting host.
When a plurality of light-emitting dopants are used, Ip (D) means the dopant having the smallest Ip, and Ea (D) means the dopant having the largest Ea.

-Luminescent dopant-
As a luminescent dopant in this invention, if the relationship of said (1) is satisfy | filled between the luminescent dopant of said (1) and several host compounds, a phosphorescent luminescent material, a fluorescent luminescent material, etc. Either can be used as a dopant.
The luminescent dopant in the present invention is a dopant satisfying the relationship of (2) 1.2 eV>ΔIp> 0.2 eV and / or 1.2 eV>ΔEa> 0.2 eV with the host compound. Is preferable from the viewpoint of driving durability.

= Phosphorescent dopant =
In general, examples of the phosphorescent light-emitting dopant include complexes containing a transition metal atom or a lanthanoid atom.
For example, the transition metal atom is not particularly limited, but preferably includes ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum, and more preferably rhenium, iridium, and platinum.
Examples of lanthanoid atoms include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these lanthanoid atoms, neodymium, europium, and gadolinium are preferable.

Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H.C. Examples include ligands described in Yersin's "Photochemistry and Photophysics of Coordination Compounds" published by Springer-Verlag 1987, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications-" .
Specific ligands are preferably halogen ligands (preferably chlorine ligands), nitrogen-containing heterocyclic ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, phenanthroline, etc.), diketones Ligand (for example, acetylacetone), carboxylic acid ligand (for example, acetic acid ligand), carbon monoxide ligand, isonitrile ligand, cyano ligand, more preferably nitrogen-containing Heterocyclic ligand.
The complex may have one transition metal atom in the compound, or may be a so-called binuclear complex having two or more. Different metal atoms may be contained at the same time.

  Among these, specific examples of the luminescent dopant satisfying the relationship (1) above include, for example, US 6303238 B1, US 6097147, WO 00/57676, WO 00/70655, WO 01/08230, WO 01/39234 A2, WO 01/41512 A1, WO 02/02714 A2, WO 02/15645 A1, WO 02/44189 A1, JP 2001-247659, Japanese Patent Application 2000-33561, JP 2002-117978, Japanese Patent Application 2001-248165, JP 2002-235076, Japanese Patent Application No. 2001-239281, JP 2002-170684, EP 12112257, JP 2002-226495, JP 2002-234894, JP 2001-247659, JP 2001-29847 , JP-A-2002-173684, JP-A-2002-203678, JP-A-2002-203679, and Japanese Patent Application No. 2003-157066, and the like. Examples of the luminescent dopant to be satisfied include Ir complex, Pt complex, Cu complex, Re complex, W complex, Rh complex, Ru complex, Pd complex, Os complex, Eu complex, Tb complex, Gd complex, Dy complex, and Ce complex. It is done. Particularly preferable are an Ir complex, a Pt complex, and a Re complex. Among them, an Ir complex including at least one coordination mode of a metal-carbon bond, a metal-nitrogen bond, a metal-oxygen bond, and a metal-sulfur bond, a Pt complex, Re complexes are preferred.

= Fluorescent dopant =
As the fluorescent light-emitting dopant, generally, benzoxazole, benzimidazole, benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin, pyran, perinone, oxadiazole, aldazine, Pyraridin, cyclopentadiene, bisstyrylanthracene, quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene, styrylamine, aromatic dimethylidin compounds, condensed polycyclic aromatic compounds (anthracene, phenanthroline, pyrene, perylene, rubrene, pentacene, etc.) , 8-quinolinol metal complexes, various metal complexes represented by pyromethene complexes and rare earth complexes, polythiophene, polyphenylene, polyphenylene vinyle Polymeric compounds such as organosilanes, and the like, and their derivatives.

  Among these, the following compounds are mentioned as a specific example of the luminescent dopant which satisfy | fills the relationship of said (1), for example.

  Among the above, the luminescent dopant satisfying the more preferable relationship (2) is D-2, D-3, D-4, D-5, D-6, D-7, D-8, D-9. , D-10, D-11, D-12, D-13, and D-14.

  The light-emitting dopant in the light-emitting layer is contained in an amount of 0.1 to 20% by mass based on the total mass of the compound generally forming the light-emitting layer in the light-emitting layer. It is preferable to contain 15 mass%, and it is more preferable to contain 2-12 mass%.

  The thickness of the light emitting layer is not particularly limited, but is usually preferably 1 nm to 500 nm, and more preferably 5 nm to 200 nm from the viewpoint of light emission efficiency, among which 10 nm to 100 nm. Is more preferable.

-Host compound-
The host compound used in the light-emitting layer needs to use at least a plurality of host compounds. However, (1) ΔIp (= Ip (D) −Ip (H) min)> 0 eV and ΔEa ( = Ea (H) max-Ea (D))> 0 eV can be used without particular limitation.
Among the above ranges, it is more preferable that the host compound satisfy the relationship of (2) 1.2 eV>ΔIp> 0.2 eV and / or 1.2 eV>ΔEa> 0.2 eV.
As the plurality of host compounds, a hole transporting host compound (hole transporting host) excellent in hole transporting property and an electron transporting host compound (electron transporting host) excellent in electron transporting property can be used.

= Hole-transporting host =
The hole transporting host in the light emitting layer used in the present invention is a known hole transporting material (1) ΔIp (= Ip (D) −Ip (H) min)> 0 eV, and Although what is necessary is just to satisfy | fill the relationship of (DELTA) Ea (= Ea (H) max-Ea (D))> 0eV, although depending on the relationship with the said luminescent dopant, especially from a viewpoint of durability and color purity, The ionization potential is preferably in the range of 4.6 to 7.5 eV, more preferably 5.1 to 7.1 eV, and particularly preferably 5.4 to 7.1 eV.
Specific examples of such a hole transporting host include the following materials.
Pyrrole, carbazole, triazole, oxazole, oxadiazole, imidazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary amine compound , Styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N-vinylcarbazole), aniline copolymers, thiophene oligomers, conductive polymer oligomers such as polythiophene, organic silanes, carbon films And derivatives thereof.
Among them, the hole transporting host satisfying (2) is preferably a carbazole derivative, an aromatic tertiary amine compound, or a thiophene derivative, and particularly has a plurality of carbazole skeleton and / or aromatic tertiary amine skeleton in the molecule. Those are preferred.
Specific examples of such a hole transporting host include the following compounds.

= Electron transporting host =
The electron transporting host in the light emitting layer used in the present invention may be any known electron transporting material that satisfies the above-mentioned relationship (1). Among these, from the viewpoint of durability and color purity, electron affinity Ea is preferably in the range of 1.2 to 4.0 eV, more preferably 1.2 to 3.4 eV, still more preferably 1.2 to 3.0 eV, and particularly preferably 1.2 to 2.8 eV. .
Specifically, the following materials can be mentioned, for example. Pyridine, pyrimidine, triazine, imidazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine substitution Aromatic compounds, anhydrides of aromatic ring tetracarboxylic acids such as naphthalene and perylene, and imides, anhydrides of aromatic ring dicarboxylic acids such as benzene and naphthalene, and imides, phthalocyanines, and their derivatives (form condensed rings with other rings) Or metal complexes of 8-quinolinol derivatives, metal phthalocyanines, various metal complexes typified by metal complexes having benzoxazole or benzothiazole as a ligand, and the like.

  The electron transporting host is preferably a metal complex, an azole derivative (benzimidazole derivative, imidazopyridine derivative, etc.), or an azine derivative (pyridine derivative, pyrimidine derivative, triazine derivative). The metal complex compound is preferably a metal complex having a ligand having at least one nitrogen atom or oxygen atom or sulfur atom coordinated to the metal, and the metal ion in the metal complex is not particularly limited, but preferably a beryllium ion, Magnesium ions, aluminum ions, gallium ions, zinc ions, indium ions, and tin ions, more preferably beryllium ions, aluminum ions, gallium ions, and zinc ions, and still more preferably aluminum ions and zinc ions.

  There are various known ligands contained in the metal complex. For example, “Photochemistry and Photophysics of Coordination Compounds” Springer-Verlag H. Examples include the ligands described in Yersin's 1987 issue, “Organometallic Chemistry-Fundamentals and Applications”, Akebono Yamamoto, Akio Yamamoto, 1982 issue, etc.

  The ligand is preferably a nitrogen-containing heterocyclic ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 3 to 15 carbon atoms, and a monodentate ligand. Or a bidentate or higher ligand, preferably a bidentate ligand such as a pyridine ligand, a bipyridyl ligand, a quinolinol ligand, a hydroxyphenylazole ligand (hydroxyphenyl) Benzimidazole, hydroxyphenylbenzoxazole ligand, hydroxyphenylimidazole ligand)), alkoxy ligand (preferably 1-30 carbon atoms, more preferably 1-20 carbon atoms, particularly preferably carbon 1-10, for example, methoxy, ethoxy, butoxy, 2-ethylhexyloxy, etc.), aryloxy ligands Preferably it has 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenyloxy, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl Oxy, 4-biphenyloxy, etc.),

Heteroaryloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, and examples thereof include pyridyloxy, pyrazyloxy, pyrimidyloxy, quinolyloxy, etc.) An alkylthio ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methylthio and ethylthio), arylthio ligand ( Preferably, it has 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, and examples thereof include phenylthio, etc., a heteroarylthio ligand (preferably 1 to 1 carbon atoms). 30, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as pyridylthio, 2 Benzimidazolylthio, 2-benzoxazolylthio, 2-benzthiazolylthio, etc.), siloxy ligands (preferably having 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms, particularly preferably carbon atoms). 6 to 20, for example, a triphenylsiloxy group, a triethoxysiloxy group, a triisopropylsiloxy group, etc.), more preferably a nitrogen-containing heterocyclic ligand, an aryloxy ligand, a heteroaryl. An oxy group and a siloxy ligand are preferable, and a nitrogen-containing heterocyclic ligand, an aryloxy ligand, and a siloxy ligand are more preferable.

  Specific examples of such an electron transporting host include the following materials.

  Among them, E-1 to E-6 are preferable as the electron transporting host satisfying (2), and E-3 is particularly preferable.

  In the light emitting layer of the present invention, when a phosphorescent dopant is used as the luminescent dopant, the lowest triplet excitation energy T1 (D) of the phosphorescent dopant and the lowest excited triplet energy of the plurality of host compounds. Among these, the minimum T1 (H) min preferably satisfies the relationship of T1 (H) min> T1 (D) in terms of color purity and light emission efficiency. More preferably, T1 (H) min-T1 (D)> 0.1 eV, and still more preferably T1 (H) min-T1 (D)> 0.2 eV.

Further, the content of the plurality of host compounds of the present invention is not particularly limited, but from the viewpoint of driving durability, it is 15% by mass or more and 85% by mass with respect to the total compound mass forming the light emitting layer, respectively. The following is preferable. A more preferable range is 20% by mass or more and 80% by mass or less, and a further preferable range is 25% by mass or more and 75% by mass or less.
Although content of the host compound of this invention is not specifically limited, It is preferable that they are 5 mass% or more and 95 mass% or less, respectively with respect to the total host compound mass contained in a light emitting layer. More preferable content is 10% by mass or more and 90% by mass or less, respectively, and further preferable content is 15% by mass or more and 85% by mass or less.
As a preferable combination of the host compound and the luminescent dopant, a hole transporting host selected from H-1 to H-16, an electron transporting host selected from E-1 to E-12, and D-1 And a combination of a luminescent dopant selected from D-3 and a combination of a hole-transporting host H-10, an electron-transporting host E-12, and a luminescent dopant D-10. Among these combinations, a hole transporting host selected from H-1, H-3, H-4, H-7, and H-8, and an electron transport selected from E-1 and E-11. And a combination of a light-emitting host, a light-emitting dopant selected from D-1 and D-3, and a hole-transporting host H-10, an electron-transporting host E-12, and a light-emitting dopant D-10. A combination is more preferred.

Further, the carrier mobility in the light emitting layer is generally 10 ⁻⁷ cm ² / V / s or more and 10 ⁻¹ cm ² / V / s or less, and from the viewpoint of light emission efficiency, 10 ⁻⁵ cm ² / V − s or more and 10 ⁻¹ cm ² / V / s or less is preferable, 10 ⁻⁴ cm ² / V / s or more and 10 ⁻¹ cm ² / V / s or less is more preferable, and 10 ⁻³ cm ² / V / s or less. It is particularly preferably 10 ⁻¹ cm ² / V / s or less.
The carrier mobility of the light emitting layer is preferably smaller than the carrier mobility of the carrier transport layer described later from the viewpoint of driving durability.
The carrier mobility was measured by the TOF method (time of flight method), and the obtained value was defined as the carrier mobility. For details on the TOF method, see Kazuyuki Horie's “Handbook of Optical and Electronic Functional Organic Materials” published by Asakura Shoten (1995) 287.

(Hole injection layer, hole transport layer)
The hole injection layer and the hole transport layer are layers having a function of receiving holes from the anode or the anode side and transporting them to the cathode side.
Specifically, the hole injection layer and the hole transport layer are carbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, arylamines. Derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, organosilane derivatives, carbon , Etc. are preferable.

The thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but are usually preferably in the range of 1 nm to 5 μm, more preferably 5 nm to 1 μm, and still more preferably 10 nm to 500 nm. is there.
The hole injection layer and the hole transport layer may have a single-layer structure composed of one or more of the materials described above, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions. .

When the carrier transport layer adjacent to the light emitting layer is a hole transport layer, the driving durability is such that the Ip (HTL) of the hole transport layer is smaller than the Ip (D) of the dopant contained in the light emitting layer. This is preferable. More preferably, Ip (D) -Ip (HTL)> 0.1 eV, and still more preferably Ip (D) -Ip (HTL)> 0.2 eV.
The Ip (HTL) in the hole transport layer can be measured by the Ip measurement method.

Further, the carrier mobility in the hole transport layer is generally 10 ⁻⁷ cm ² / V / s or more and 10 ⁻¹ cm ² / V / s or less, and from the viewpoint of luminous efficiency, 10 ⁻⁵ cm. ^It is preferably ² / V / s or more and 10 ^-1 cm ² / V / s or less, more preferably 10 ^-4 cm ² / V / s or more and 10 ^-1 cm ² / V / s or less, and more preferably 10 ^-3 cm ² / V. / S to 10 ⁻¹ cm ² / V / s is particularly preferable.
As the carrier mobility, a value measured by a method similar to the method for measuring the carrier mobility of the light emitting layer is adopted.
The carrier mobility of the hole transport layer is preferably greater than the carrier mobility of the light emitting layer from the viewpoint of driving durability.

(Electron injection layer, electron transport layer)
The electron injection layer and the electron transport layer are layers having any one of a function of injecting electrons from the cathode, a function of transporting electrons, and a function of blocking holes that can be injected from the anode.
Specific examples of the material for the electron injection layer and the electron transport layer include pyridine, pyrimidine, triazine, imidazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiol. Pyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine-substituted aromatic compounds, anhydrides of aromatic ring tetracarboxylic acids such as naphthalene and perylene and anhydrides of aromatic ring dicarboxylic acids such as imide, benzene and naphthalene and Imido, phthalocyanine, and derivatives thereof (which may form a condensed ring with other rings), metal complexes of 8-quinolinol derivatives, metal phthalocyanines, metals having benzoxazole or benzothiazol as a ligand Examples of various metal complexes represented by complexes It is possible.

The thicknesses of the electron injection layer and the electron transport layer are not particularly limited, but from the viewpoint of lowering the driving voltage, those in the range of usually 1 nm to 5 μm are preferable, more preferably 5 nm to 1 μm. Preferably it is 10 nm-500 nm.
The electron injection layer and the electron transport layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.
When the carrier transport layer adjacent to the light emitting layer is an electron transport layer, the Ea (ETL) of the electron transport layer is greater than the dopant Ea (D) contained in the light emitting layer. More preferably, Ea (ETL) -Ea (D)> 0.1 eV, and more preferably Ea (ETL) -Ea (D)> 0.2 eV.
The Ea (ETL) uses a value measured by the same method as the Ea measuring method.

Further, the carrier mobility in the electron transport layer is generally 10 ⁻⁷ cm ² / V / s or more and 10 ⁻¹ cm ² / V / s or less, and from the viewpoint of luminous efficiency, 10 ⁻⁵ cm ^2. / V / s to 10 ⁻¹ cm ² / V / s, preferably 10 ⁻⁴ cm ² / V / s to 10 ⁻¹ cm ² / V / s, more preferably 10 ⁻³ cm ² / V / s. s to 10 ⁻¹ cm ² / V / s is particularly preferable.
The carrier mobility of the electron transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoint of driving durability. The carrier mobility was measured in the same manner as the hole transport layer measurement method.
In the carrier mobility of the light-emitting element in the present invention, the carrier mobility in the hole transport layer, electron transport layer, and light-emitting layer is (electron transport layer ≧ hole transport layer)> light-emitting layer. From the viewpoint of sex.

(Hole blocking layer)
The hole blocking layer is a layer having a function of preventing holes transported from the anode side to the light emitting layer from passing through to the cathode side. In the present invention, a hole blocking layer can be provided as an organic compound layer adjacent to the light emitting layer on the cathode side.
Although the hole blocking layer is not particularly limited, specifically, an aluminum complex such as BAlq ₂ , a triazole derivative, a pyraza ball derivative, or the like can be contained.
Further, the thickness of the hole blocking layer is generally preferably 50 nm or less, preferably 1 to 50 nm, and more preferably 5 to 40 nm in order to lower the driving voltage.

(anode)
The anode usually has a function as an electrode for supplying holes to the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element. , Can be appropriately selected from known electrode materials. As described above, the anode is usually provided as a transparent anode.

  As a material of the anode, for example, a metal, an alloy, a metal oxide, a conductive compound, or a mixture thereof can be suitably cited, and a material having a work function of 4.0 eV or more is preferable. Specific examples of the anode material include conductive metals such as tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Metals such as oxides, gold, silver, chromium, nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, polyaniline, polythiophene, polypyrrole, etc. Organic conductive materials, and a laminate of these and ITO. Among these, conductive metal oxides are preferable, and ITO is particularly preferable from the viewpoints of productivity, high conductivity, transparency, and the like.

  The anode is composed of, for example, a wet method such as a printing method and a coating method, a physical method such as a vacuum deposition method, a sputtering method, and an ion plating method, and a chemical method such as a CVD and a plasma CVD method. It can be formed on the substrate according to a method appropriately selected in consideration of suitability with the material to be processed. For example, when ITO is selected as the anode material, the anode can be formed according to a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like.

  In the organic electroluminescent element of the present invention, the formation position of the anode is not particularly limited and can be appropriately selected according to the use and purpose of the light emitting element. The anode may be formed on the entire one surface of the substrate, or may be formed on a part thereof.

  The patterning for forming the anode may be performed by chemical etching such as photolithography, or may be performed by physical etching such as laser, or vacuum deposition or sputtering with a mask overlapped. It may be performed by a lift-off method or a printing method.

  The thickness of the anode can be appropriately selected depending on the material constituting the anode and cannot be generally defined, but is usually about 10 nm to 50 μm, and preferably 50 nm to 20 μm.

The resistance value of the anode is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less. When the anode is transparent, it may be colorless and transparent or colored and transparent. In order to take out light emission from the transparent anode side, the transmittance is preferably 60% or more, and more preferably 70% or more.

  The transparent anode is detailed in Yutaka Sawada's “New Development of Transparent Conductive Film” published by CMC (1999), and the matters described here can be applied to the present invention. In the case of using a plastic substrate having low heat resistance, a transparent anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

(cathode)
The cathode usually has a function as an electrode for injecting electrons into the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element, It can select suitably from well-known electrode materials.

  Examples of the material constituting the cathode include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof, and those having a work function of 4.5 eV or less are preferable. Specific examples include alkali metals (eg, Li, Na, K, Cs, etc.), alkaline earth metals (eg, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys, magnesium. -Rare earth metals such as silver alloys, indium, ytterbium, and the like. These may be used alone, but two or more can be suitably used in combination from the viewpoint of achieving both stability and electron injection.

Among these, as a material constituting the cathode, an alkali metal or an alkaline earth metal is preferable from the viewpoint of electron injecting property, and a material mainly composed of aluminum is preferable from the viewpoint of excellent storage stability.
The material mainly composed of aluminum is aluminum alone, an alloy of aluminum and 0.01 to 10% by mass of alkali metal or alkaline earth metal, or a mixture thereof (for example, lithium-aluminum alloy, magnesium-aluminum alloy, etc.) Say.

  The materials for the cathode are described in detail in JP-A-2-15595 and JP-A-5-121172, and the materials described in these public relations can also be applied in the present invention.

  There is no restriction | limiting in particular about the formation method of a cathode, According to a well-known method, it can carry out. For example, the cathode described above is configured from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as CVD or plasma CVD method. It can be formed according to a method appropriately selected in consideration of suitability with the material. For example, when a metal or the like is selected as the cathode material, one or more of them can be simultaneously or sequentially performed according to a sputtering method or the like.

  Patterning when forming the cathode may be performed by chemical etching such as photolithography, physical etching by laser, or the like, or by vacuum deposition or sputtering with the mask overlaid. It may be performed by a lift-off method or a printing method.

In the present invention, the cathode formation position is not particularly limited, and may be formed on the entire organic compound layer or a part thereof.
Further, a dielectric layer made of an alkali metal or alkaline earth metal fluoride or oxide may be inserted between the cathode and the organic compound layer with a thickness of 0.1 to 5 nm. This dielectric layer can also be regarded as a kind of electron injection layer. The dielectric layer can be formed by, for example, a vacuum deposition method, a sputtering method, an ion plating method, or the like.

The thickness of the cathode can be appropriately selected depending on the material constituting the cathode and cannot be generally defined, but is usually about 10 nm to 5 μm, and preferably 50 nm to 1 μm.
Further, the cathode may be transparent or opaque. The transparent cathode can be formed by depositing a thin cathode material to a thickness of 1 to 10 nm and further laminating a transparent conductive material such as ITO or IZO.

(substrate)
In the present invention, a substrate can be used. The substrate used is preferably a substrate that does not scatter or attenuate light emitted from the organic compound layer. Specific examples thereof include zirconia stabilized yttrium (YSZ), inorganic materials such as glass, polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, and polycycloolefin. , Organic materials such as norbornene resin and poly (chlorotrifluoroethylene).
For example, when glass is used as the substrate, alkali-free glass is preferably used as the material in order to reduce ions eluted from the glass. Moreover, when using soda-lime glass, it is preferable to use what gave barrier coatings, such as a silica. In the case of an organic material, it is preferable that it is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability.

  There is no restriction | limiting in particular about the shape of a board | substrate, a structure, a magnitude | size, It can select suitably according to the use, purpose, etc. of a light emitting element. In general, the shape of the substrate is preferably a plate shape. The structure of the substrate may be a single layer structure, a laminated structure, may be formed of a single member, or may be formed of two or more members.

  The substrate may be colorless and transparent or colored and transparent, but is preferably colorless and transparent in that it does not scatter or attenuate light emitted from the organic light emitting layer.

The substrate can be provided with a moisture permeation preventing layer (gas barrier layer) on the front surface or the back surface.
As a material for the moisture permeation preventive layer (gas barrier layer), inorganic materials such as silicon nitride and silicon oxide are preferably used. The moisture permeation preventing layer (gas barrier layer) can be formed by, for example, a high frequency sputtering method.
When a thermoplastic substrate is used, a hard coat layer, an undercoat layer, or the like may be further provided as necessary.

(Protective layer)
In the present invention, the entire organic EL element may be protected by a protective layer.
As a material contained in the protective layer, any material may be used as long as it has a function of preventing materials that promote device deterioration such as moisture and oxygen from entering the device.
Specific examples thereof include metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni, MgO, SiO, SiO ₂ , Al ₂ O ₃ , GeO, NiO, CaO, BaO, and Fe ₂ O. ₃ , metal oxides such as Y ₂ O ₃ and TiO ₂ , metal nitrides such as SiN _x and SiN _x O _y , metal fluorides such as MgF ₂ , LiF, AlF ₃ and CaF ₂ , polyethylene, polypropylene, polymethyl Monomer mixture containing methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, tetrafluoroethylene and at least one comonomer A copolymer obtained by copolymerization of a copolymer having a cyclic structure in the copolymer main chain. Copolymer, 1% by weight of the water absorbing water absorption material, water absorption of 0.1% or less of moisture-proof material, and the like.

  The method for forming the protective layer is not particularly limited, and for example, vacuum deposition, sputtering, reactive sputtering, MBE (molecular beam epitaxy), cluster ion beam, ion plating, plasma polymerization (high frequency) Excited ion plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, coating method, printing method, transfer method can be applied.

(Sealing)
Furthermore, the organic electroluminescent element of this invention may seal the whole element using a sealing container.
Further, a moisture absorbent or an inert liquid may be sealed in a space between the sealing container and the light emitting element. Although it does not specifically limit as a moisture absorber, For example, barium oxide, sodium oxide, potassium oxide, calcium oxide, sodium sulfate, calcium sulfate, magnesium sulfate, phosphorus pentoxide, calcium chloride, magnesium chloride, copper chloride Cesium fluoride, niobium fluoride, calcium bromide, vanadium bromide, molecular sieve, zeolite, magnesium oxide and the like. The inert liquid is not particularly limited, and examples thereof include fluorinated solvents such as paraffins, liquid paraffins, perfluoroalkanes, perfluoroamines, perfluoroethers, chlorinated solvents, and silicone oils. It is done.

The organic electroluminescence device of the present invention emits light by applying a direct current (which may include an alternating current component as necessary) voltage (usually 2 to 15 volts) or a direct current between the anode and the cathode. Obtainable.
The driving durability of the organic electroluminescent element in the present invention can be measured by the luminance half time at a specific luminance. For example, using a source measure unit 2400 made by KEITHLEY, a DC voltage is applied to an organic EL element to emit light, a continuous drive test is performed under the condition of an initial luminance of 2000 cd / m ² , and the luminance becomes 1000 cd / m ² Can be obtained by comparing the luminance half-life time with a conventional light emitting device. This numerical value was used in the present invention.
An important characteristic value of this organic electroluminescence device is external quantum efficiency. The external quantum efficiency is calculated by “external quantum efficiency φ = number of photons emitted from the device / number of electrons injected into the device”, and it can be said that the larger this value, the more advantageous the device in terms of power consumption.

  The external quantum efficiency of the organic electroluminescent element is determined by “external quantum efficiency φ = internal quantum efficiency × light extraction efficiency”. In an organic EL device using fluorescence emission from an organic compound, the limit value of the internal quantum efficiency is 25%, and the light extraction efficiency is approximately 20%. Therefore, the limit value of the external quantum efficiency is approximately 5%. Has been.

The external quantum efficiency of the device is preferably 6% or more, and particularly preferably 12% or more, from the viewpoint of reducing power consumption and driving durability.
Figures external quantum efficiency, the maximum value of the external quantum efficiency when the device is driven at 20 ° C., or around 100~300cd / m ² when the device is driven at 20 ° C. (preferably 200 cd / m ²⁾ The value of external quantum efficiency at can be used.
In the present invention, using a source measure unit type 2400 manufactured by Toyo Technica, a DC constant voltage is applied to the EL element to emit light, and the luminance is measured using a luminance meter BM-8 manufactured by Topcon Corporation, and is 200 cd / m ^2. A value obtained by calculating the external quantum efficiency at is used.

  Further, the external quantum efficiency of the light emitting element can be calculated from the result and the relative luminous efficiency curve obtained by measuring the light emission luminance, the light emission spectrum, and the current density. That is, the number of input electrons can be calculated using the current density value. The emission luminance can be converted into the number of photons emitted by integral calculation using the emission spectrum and the relative visibility curve (spectrum). From these, the external quantum efficiency (%) can be calculated by “(number of photons emitted / number of electrons input to the device) × 100”.

  The driving method of the organic electroluminescence device of the present invention is described in JP-A-2-148687, JP-A-6-301355, JP-A-5-29080, JP-A-7-134558, JP-A-8-234585, and JP-A-8-2441047. The driving methods described in each publication, Japanese Patent No. 2784615, US Pat. Nos. 5,828,429, 6023308, and the like can be applied.

  The organic EL element of the present invention can be suitably used for display elements, displays, backlights, electrophotography, illumination light sources, recording light sources, exposure light sources, reading light sources, signs, signboards, interiors, optical communications, and the like.

  The present invention will be described using examples, but is not limited thereto.

Example 1
Using an ITO target having an In ₂ O ₃ content of 95% by mass on a glass substrate of 0.5 mm thickness and 2.5 cm square, DC magnetron sputtering (conditions: substrate temperature 100 ° C., oxygen pressure 1 × 10 ^-3 Pa), an ITO thin film (thickness 0.2 μm) was formed as a transparent anode. The surface resistance of the ITO thin film was 10Ω / □.
Next, the substrate on which the transparent anode was formed was placed in a cleaning container and subjected to IPA cleaning, and then UV-ozone treatment was performed for 30 minutes. On this transparent anode, copper phthalocyanine was provided with a 10 nm hole injection layer at a rate of 0.5 nm / second by vacuum deposition.
On top of that, 4,4 ′, 4 ″ -tris (2-methylphenylphenylamino) triphenylamine (m-MTDATA) is vacuum-deposited at a rate of 0.5 nm / second to a 40 nm hole transport layer. Was provided.
On top of this, m-MTDATA as the hole transport material in the light emitting layer, the following electron transport host 1 as the electron transport material in the light emitting layer, and the following iridium complex 1 (Ir complex 1) as the light emitting material are formed by vacuum deposition. Co-evaporated at a ratio of 50/8 and co-evaporated to obtain a 30 nm light emitting layer.

On the light-emitting layer, Balq ₂ as an electron transport material in the electron transport layer is deposited by vacuum deposition at a rate of 0.5 nm / second to 10 nm, and on that, Alq ₃ is deposited by vacuum deposition as an electron transport material. The film was deposited at a rate of 0.2 nm / second to provide a 35 nm electron transport layer.
Further, a patterned mask (a mask having a light emission area of 2 mm × 2 mm) was placed on the electron transport layer, and lithium fluoride was deposited by a vacuum deposition method to provide a 1 nm electron injection layer.
Aluminum was vapor-deposited thereon by a vacuum vapor deposition method to provide a 0.15 μm cathode.
Aluminum lead wires were respectively connected from the anode and the cathode to form a light emitting laminate.

The obtained light emitting laminate is put in a glove box substituted with argon gas, and sealed with a stainless steel sealing can provided with a desiccant and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba). Thus, a light emitting device of the present invention was obtained.
The operations from the deposition of copper phthalocyanine to the sealing were performed in a vacuum or nitrogen atmosphere, and the device was fabricated without exposure to the atmosphere.

[Evaluation]
The hole transport material in the hole transport layer used above, the hole transport material in the light emitting layer, the electron transport material in the light emitting layer, the electron transport material in the electron transport layer, the electron transport layer, and the hole transport layer, respectively. The ionization potential (Ip) and electron affinity (Ea) of each were measured as a single layer film (single layer) by the following method. The results are shown in Table 1 below.

-Ionization potential (Ip)-
The ionization potential (Ip) was measured by an ultraviolet photoelectron analyzer AC-1 (manufactured by Riken Keiki).

-Electron affinity (Ea)-
For the electron affinity (Ea), the band gap was calculated from the absorption spectrum of the single layer film, and the electron affinity (Ea) was calculated from the value of the ionization potential (Ip).

Using the light emitting device obtained as described above, the external quantum efficiency was measured by the following method.
-External quantum efficiency-
The waveform of the emission spectrum of the manufactured light-emitting element was measured using a multi-channel analyzer PMA-11 manufactured by Hamamatsu Photonics. The wavelength value of the emission peak was determined from this measurement data. Further, the external quantum efficiency was calculated from the waveform of the emission spectrum and the current / brightness (200 cd / m ² ) at the time of measurement, and evaluated according to the following criteria. The results are shown in Table 1 below.

[Evaluation criteria]
◎: 12% or more ○: 6% or more and less than 12% △: 3% or more and less than 6% ×: Less than 3%

-Driving durability test-
Using a KEITHLEY source measure unit type 2400, a direct current voltage was applied to the organic EL element to emit light. The luminance was measured using a luminance meter BM-8 manufactured by Topcon Corporation, and the external quantum efficiency at 2000 cd / m ² was calculated.
Subsequently, the light-emitting device was a continuous driving test under the condition of the initial luminance 2000 cd / m ^2, the luminance was the luminance half-life T (1/2) time became 1000 cd / m ^2. The luminance half time was evaluated according to the following evaluation criteria.

[Evaluation criteria]
A: 500 hr or more ○: 250 hr or more and less than 500 hr Δ: 100 hr or more and less than 250 ×: Less than 100 hr

(Example 2)
In Example 1, a light-emitting element was obtained in the same manner as in Example 1 except that the light-emitting dopant was changed to Ir (ppy) ₃ instead of the iridium complex 1, and a similar evaluation test was performed. The results are shown in Table 1 below.

(Example 3)
In Example 1, except having changed into the rubrene instead of the iridium complex 1 of a luminescent dopant, it carried out similarly to Example 1 and obtained the light emitting element, and performed the same evaluation test. The results are shown in Table 1 below.

Example 4
A light emitting device was obtained in the same manner as in Example 2 except that BAlq ₂ was changed to the electron transport host 1 in Example 2, and the same evaluation test was performed. The results are shown in Table 1 below.

(Example 5)
In Example 4, the hole transport layer was changed to 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (NPD) instead of m-MTDATA, and the positive transport layer in the light emitting layer was changed. The hole transport material is changed to the following hole transport host 2 instead of m-MTDATA, the electron transport material in the light emitting layer is changed to the following electron transport host 2 instead of the electron transport host 1, and the light emitting material is Ir (ppy) ) A blue light-emitting device was obtained in the same manner as in Example 4 except that the following Ir complex 2 was used instead of ₃ , and the same evaluation test was performed. The results are shown in Table 1 below.

(Comparative Example 1)
In Example 1, the light-emitting element was obtained in the same manner as in Example 1 except that the electron transport host 1 was not used and that the Ir (ppy) ₃ was changed to the light-emitting dopant Ir complex 1. A similar evaluation test was conducted. The results are shown in Table 1 below.

(Comparative Example 2)
In Example 2, the Alq ₃ was used instead of the electron transport host 1, and 4,4′-bis [N- (1-naphthyl) -N-phenyl was used instead of m-MTDATA in the light emitting layer and the hole transport layer. A light emitting device was obtained in the same manner as in Example 2 except that -amino] biphenyl (NPD) was used, and the same evaluation test was performed. The results are shown in Table 1 below.

(Comparative Example 3)
In Example 3, the Alq ₃ was used instead of the electron transport host 1, and 4,4′-bis [N- (1-naphthyl) -N-phenyl was used instead of m-MTDATA in the light-emitting layer and the hole transport layer. A light emitting device was obtained in the same manner as in Example 3 except that -amino] biphenyl (NPD) was used, and the same evaluation test was performed. The results are shown in Table 1 below.

  An energy diagram in each of the above examples and comparative examples is shown in FIG.

As is clear from Table 1, from Example 2 which is a double host (DH) and Comparative Example 1 of a single host (SH), both luminescence characteristics (external quantum efficiency) and driving durability are better than SH. It turns out that it is.
Although both Example 2 and Comparative Example 2 are double hosts (DH), Comparative Example 2 in which ΔIp is 0 is a result in which both driving durability and external quantum efficiency are not good, but it was performed in comparison with them. Example 2 turns out to be good in both.
In comparison between the singlet element and the triplet element, the driving durability and light emission characteristics of Examples 2 and 3 satisfying the requirements compared to Comparative Examples 2 and 3 not satisfying ΔIp> 0 eV and ΔEa> 0 eV ( It can be seen that both (external quantum efficiency) are good.
Also, from Example 4, when the electron affinity Ea (ETL) of the electron transport layer is larger than the electron affinity Ea (D) of the dopant contained in the light emitting layer, good results can be obtained in the same manner. I understand. From Example 5, it can be seen that good results are obtained for the blue phosphorescent dopant as well.

The light emitting device of the present invention can be suitably used in the fields of display devices, displays, backlights, electrophotography, illumination light sources, recording light sources, exposure light sources, reading light sources, signs, signboards, interiors, optical communications, and the like.
The compounds in the present invention can also be applied to medical uses, fluorescent brighteners, photographic materials, UV absorbing materials, laser dyes, recording media materials, inkjet pigments, color filter dyes, color conversion filters, and the like. A compound.

The energy diagram in each Example 1-5 is shown. The energy diagram in each comparative example 1-3 is shown.

Claims (8)

An organic electroluminescent device having an organic compound layer including at least one light emitting layer between a pair of electrodes, the light emitting layer containing at least one luminescent dopant and a plurality of host compounds, ΔIp defined as ΔIp = Ip (D) −Ip (H) min, where Ip (D) is the ionization potential and Ip (H) min is the minimum of the ionization potentials of the plurality of host compounds. Satisfying the relationship of ΔIp> 0 eV, the electron affinity of the dopant is Ea (D), and the maximum of the electron affinity of the plurality of host compounds is Ea (H) max, ΔEa = Ea ( H) An organic electroluminescence device characterized in that ΔEa defined by max−Ea (D) satisfies a relationship of ΔEa> 0 eV. 2. The organic electroluminescence device according to claim 1, wherein the ΔIp satisfies a relationship of 1.2 eV> ΔIp> 0.2 eV and / or the ΔEa satisfies 1.2 eV> ΔEa> 0.2 eV. 3. The fluorescent phosphorescence spectrum measured with a single layer film formed only of the plurality of host compounds is luminescence attributed to a single emission spectrum of each of the plurality of host compounds. 3. The organic electroluminescent element as described. The organic electroluminescent element according to claim 1, wherein the organic compound layer has a carrier transport layer adjacent to the light emitting layer. The carrier transport layer is an electron transport layer, and the electron affinity Ea (ETL) of the electron transport layer is larger than the electron affinity Ea (D) of the dopant contained in the light emitting layer. The organic electroluminescent element as described. The carrier transport layer is a hole transport layer, and an ionization potential Ip (HTL) of the hole transport layer is smaller than an ionization potential Ip (D) of a dopant contained in the light emitting layer. 5. The organic electroluminescent element according to 4. T1 (H) min> T1 between the lowest triplet excitation energy T1 (D) of the dopant and the minimum one among the lowest excited triplet energies of the plurality of host compounds. The organic electroluminescent element according to claim 1, wherein the relationship (D) is satisfied. Content of a some host compound is 15 to 85 mass% with respect to the total compound mass which forms a light emitting layer, respectively, The organic as described in any one of Claims 1-7 characterized by the above-mentioned. Electroluminescent device.

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