JP2008218972A - Organic electroluminescence device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence device having high light-emission efficiency and superior drive durability. <P>SOLUTION: The organic electroluminescence device has an organic compound layer including at least one light-emitting layer between a pair of electrodes arranged in an opposite configuration, the light-emitting layer containing at least a light-emitting material and electrically inactive material which has an energy gap Eg of 4.0 eV or larger, between the highest of the energy-levels of the occupied orbits and the lowest of the energy-levels of the unoccupied orbits; in which the light-emitting material includes at least a first light-emitting material and a second light-emitting material, with the first light-emitting material being an electron-transporting material and a second light-emitting material being a positive hole transporting material, and the light-emitting layer is 5 nm or larger to 20 nm or smaller in thickness. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element (hereinafter abbreviated as an organic EL element). In particular, the present invention relates to an organic EL element having high luminous efficiency and excellent driving durability.

  An organic electroluminescent element using a thin film material that emits light when excited by passing an electric current is known. Since organic electroluminescent devices can emit light with high brightness at low voltage, they are widely used in a wide range of fields including mobile phone displays, personal digital assistants (PDAs), computer displays, automobile information displays, TV monitors, or general lighting. It has potential applications and has advantages such as thinning, lightening, miniaturization, and power saving of devices in these fields. For this reason, the expectation as a leading role of the future electronic display market is great. However, in order to be practically used in these fields in place of conventional displays, many technical improvements such as light emission luminance and color tone, durability under a wide range of usage conditions, low cost and large productivity are problems. ing.

  One of the particular issues is improving luminous efficiency and driving durability. Many of the above-described devices have a problem of achieving high brightness first in reducing the thickness, weight, and size. In reducing the thickness and weight, not only the device but also the drive power source must be made compact and lightweight. In particular, when power is supplied from a primary battery or a secondary battery, power saving is a major issue, and there is a strong demand for high brightness with a low driving voltage. Conventionally, in order to achieve high brightness, a high voltage is required, resulting in faster power consumption. Also, high brightness and high voltage have resulted in a loss of device durability.

Attempts have been made to use a phosphorescent dopant and two or more phosphorescent host materials as the light-emitting layer (see, for example, Patent Document 1). The two phosphorescent host materials preferably have a triplet energy difference of 2.3 eV to 3.5 eV and a mixing ratio of 3: 1 to 1: 3 in terms of mass ratio. However, the combined use of such two types of host materials cannot provide a sufficient improvement effect in any respect with respect to luminous efficiency and driving durability.
It has been proposed to use a light-emitting material and a host material containing a polyaromatic hydrocarbon compound and a fluorescent dye as the light-emitting layer (see, for example, Patent Document 2). The polyaromatic hydrocarbon compound has a higher hole mobility than the host material, and was used for the purpose of suppressing the accumulation of holes in the light emitting layer. However, with such a composition, a sufficient improvement effect cannot be obtained regardless of the luminous efficiency and driving durability.

On the other hand, a light-emitting layer containing a phosphorescent light-emitting dopant material and a charge-carrying dopant material doped in an inert host material is disclosed for a blue light-emitting organic EL device (see, for example, Patent Document 3). According to the disclosure, a plurality of hosts having an energy gap of 3.5 eV or more are used in combination to produce a blue light-emitting organic EL element. However, this means increases the resistance of the light emitting layer and greatly increases the driving voltage, and if the thickness of the light emitting layer is reduced to reduce the driving voltage, the driving durability is deteriorated.
Also disclosed is an organic electroluminescent device in which the light emitting layer contains a light emitting material and an electrically inactive material having an energy difference (Eg) between the highest occupied orbital and the lowest unoccupied orbital of 4.0 eV or more ( For example, see Patent Document 4.) However, this means also has a problem that the resistance of the light emitting layer is increased and the driving voltage is greatly increased, and if the thickness of the light emitting layer is reduced to reduce the driving voltage, the driving durability is deteriorated.
JP 2006-135295 A JP 2000-106277 A JP-T-2004-526284 JP 2005-294250 A

  An object of the present invention is to provide an organic EL element having particularly high luminous efficiency and high durability.

The above-described problems of the present invention have been solved by the following means.
<1> An organic compound layer including at least one light emitting layer is provided between a pair of opposing electrodes, and the light emitting layer has at least a light emitting material and an energy difference (Eg) of 4 between the highest occupied orbit and the lowest unoccupied orbit. An organic electroluminescence device containing an electrically inactive material of 0.0 eV or more, wherein the light emitting material includes at least a first light emitting material and a second light emitting material, and the first light emitting material is an electron transporting light emitting device. An organic electroluminescent element, characterized in that the second light emitting material is a hole transporting light emitting material, and the thickness of the light emitting layer is 0.5 nm or more and 20 nm or less.

<2> The electron affinity (Ea1) of the first light emitting material is larger than the electron affinity (Ea2) of the second light emitting material, and the ionization potential (Ip1) of the first light emitting material is ionized by the second light emitting material. The organic electroluminescence device according to <1>, wherein the organic electroluminescence device is larger than potential (Ip2).
<3> The organic electroluminescent element according to <1> or <2>, wherein the first light emitting material is a platinum complex.
<4> The organic electroluminescent element according to any one of <1> to <3>, wherein the second light emitting material is an iridium complex.
<5> The organic electroluminescent element according to <4>, wherein the first light emitting material is a platinum complex, and the second light emitting material is an iridium complex.
<6> The organic electroluminescent element according to any one of <1> to <5>, wherein the light emitting layer has a thickness of 1 nm to 10 nm.
<7> The ratio of the light emitting material to the total amount of the light emitting material and the electrically inactive material in the light emitting layer is 5% to 40% by mass ratio. <1> to <6 > The organic electroluminescent element in any one of>.
<8> The organic electric field according to any one of <1> to <7>, wherein the electrically inactive material is an organic compound, and an ionization potential (Ip) thereof is larger than that of the light emitting material. Light emitting element.
<9> The organic electric field according to any one of <1> to <8>, wherein the electrically inactive material is an organic compound and has an electron affinity (Ea) smaller than that of the light emitting material. Light emitting element.
<10> The organic electroluminescent element according to any one of <1> to <9>, wherein the electrically inactive material is an aromatic hydrocarbon compound.
<11> The organic electroluminescent device according to <10>, wherein the aromatic hydrocarbon compound is a compound represented by the following general formula (1):
General formula (1) L- (Ar) _m
(In general formula (1), Ar represents a group represented by the following general formula (2), L represents a trivalent or higher benzene skeleton, and m represents an integer of 3 or higher);

(In General Formula (2), R ¹ represents a substituent, and when a plurality of R ¹ are present, they may be the same or different from each other. N1 represents an integer of 0 to 9).
<12> The organic electroluminescent device according to <10>, wherein the aromatic hydrocarbon compound is a compound represented by the following general formula (3):

(In General Formula (3), R ² represents a substituent, and when a plurality of R ² are present, they may be the same or different from each other. N2 represents an integer of 0 to 20).
<13> The organic electroluminescent element according to any one of <1> to <7>, wherein the electrically inactive material is an insulating inorganic compound.
<14> The organic compound layer has at least one of a hole injection layer and a hole transport layer from the anode side, the light emitting layer, and an electron transport layer or an electron injection layer, and the hole injection layer and At least one layer of a positive hole transport layer contains an electron-accepting material, The organic electroluminescent element in any one of <1>-<13> characterized by the above-mentioned.
<15> The organic compound layer has at least one of a hole transport layer, the light emitting layer, and an electron transport layer and an electron injection layer from the anode side, and the electron transport layer or the electron injection layer is an electron donor. The organic electroluminescent element according to any one of <1> to <14>, which contains a functional material.

  ADVANTAGE OF THE INVENTION According to this invention, the organic EL element excellent in driving durability with high luminous efficiency is provided. In particular, according to the present invention, an improved organic EL element having a low driving voltage and high driving durability is provided.

  Hereinafter, the organic EL device of the present invention will be described in detail.

(Constitution)
The organic electroluminescent element of the present invention has an organic compound layer including at least a light emitting layer between a pair of electrodes (anode and cathode), and more preferably, a hole transport layer is provided between the anode and the light emitting layer. In addition, an electron transport layer is provided between the cathode and the light emitting layer.
From the nature of the light emitting element, it is preferable that at least one of the pair of electrodes is transparent.

  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, a hole injection layer is provided between the hole transport layer and the anode, and / or an electron transporting intermediate layer is provided between the light emitting layer and the electron transport layer. Further, a hole transporting intermediate layer may be provided between the light emitting layer 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 (1) a hole injection layer, a hole transport layer (the hole injection layer and the hole transport layer may serve as both). Good), a hole transporting intermediate layer, a light emitting layer, an electron transport layer, and an electron injection layer (the electron transport layer and the electron injection layer may serve both), (2) hole injection layer, hole Transport layer (hole injection layer and hole transport layer may serve as well), light emitting layer, electron transport intermediate layer, electron transport layer, and electron injection layer (electron transport layer and electron injection layer may serve as well) (3) hole injection layer, hole transport layer (hole injection layer and hole transport layer may be combined), hole transport intermediate layer, light emitting layer, electron transport intermediate layer, This is an embodiment having an electron transport layer and an electron injection layer (the electron transport layer and the electron injection layer may serve as each other).

The hole transporting intermediate layer preferably has at least one of a function of accelerating hole injection into the light emitting layer and a function of blocking electrons.
The electron transporting intermediate layer preferably has at least one of a function of promoting electron injection into the light emitting layer and a function of blocking holes.
Furthermore, it is preferable that at least one of the hole transporting intermediate layer and the electron transporting intermediate layer has a function of blocking excitons generated in the light emitting layer.
In order to effectively express the functions of hole injection promotion, electron injection promotion, hole block, electron block, and exciton block, the hole transporting intermediate layer and the electron transporting intermediate layer are formed of a light emitting layer. It is preferable that it adjoins.
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.
The organic electroluminescent element of the present invention has an organic compound layer including at least one light emitting layer. As the organic compound layer other than the light emitting layer, as described above, a hole injection layer, a hole transport layer, and the like. , Hole transporting intermediate layer, light emitting layer, electron transporting intermediate layer, electron transporting layer, electron injection layer and the like.

  Each layer constituting the organic compound layer can be suitably formed by any of dry film forming methods such as vapor deposition and sputtering, transfer methods, printing methods, coating methods, ink jet methods, and spray methods.

(Light emitting layer)
The light emitting layer receives holes from the anode, hole injection layer, hole transport layer, or hole transport intermediate layer when an electric field is applied, and receives electrons from the cathode, electron injection layer, electron transport layer, or electron transport intermediate layer. It is a layer having a function of receiving and providing a field for recombination of holes and electrons to emit light.
The organic electroluminescent element in the present invention has at least a light emitting material and a light emitting layer containing an electrically inactive material having an energy difference (Eg) of 4.0 eV or more between the highest occupied orbital and the lowest unoccupied orbital. The light emitting material includes at least a first light emitting material and a second light emitting material, the first light emitting material is an electron transporting light emitting material, the second light emitting material is a hole transporting light emitting material, and the light emission The thickness of the layer is 0.5 nm or more and 20 nm or less.

The light emitting layer may be one 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, at least one layer of the light emitting layer includes the electrically inactive material, the first light emitting material, and the second light emitting material.
Preferably, the electron affinity (Ea1) of the first light emitting material is larger than the electron affinity (Ea2) of the second light emitting material, and the ionization potential (Ip1) of the first light emitting material is the ionization potential of the second light emitting material. Greater than (Ip2). More preferably, the Ea1 is greater than the Ea2 by 0.01 eV or more, and more preferably 0.02 eV or more. More preferably, the Ip1 is greater than the Ip2 by 0.01 eV or more, and more preferably 0.02 eV or more.

In the present invention, the content ratio of the inactive material of the light emitting layer, the first light emitting material, and the second light emitting material varies depending on the specific structure of each material, but the carrier mobility of the light emitting layer is kept appropriate, The ratio is selected within a range that keeps the balance between mobility and electron mobility, but generally, the ratio of the total amount of the light emitting material including the first light emitting material and the second light emitting material to the amount of the inert material is 5% or more by mass ratio. 40% or less is preferable. More preferably, the mass ratio is 5% or more and 35% or less.
The content ratio of the first light-emitting material and the second light-emitting material varies depending on the specific structure of each material, but is selected within a range that maintains a balance between hole mobility and electron mobility. The ratio of the two light emitting materials is preferably 30% or more and 70% or less by mass ratio. More preferably, the mass ratio is 40% or more and 60% or less.
The thickness of the light emitting layer is 0.5 nm or more and 20 nm or less, preferably 1 nm or more and 15 nm or less, more preferably 1 nm or more and 10 nm. If the thickness of the light emitting layer is less than 0.5 nm, it is not preferable in terms of deterioration of light emission efficiency and durability, and if it exceeds 20 nm, it is not preferable in terms of increase in driving voltage.

1) Inactive Material The light emitting layer in the present invention contains an electrically inactive material having an energy difference (Eg) of 4.0 eV or more between the highest occupied orbital and the lowest unoccupied orbital.
The Eg is preferably 4.1 eV or more and (a) 5.0 eV or less, more preferably 4.2 eV or more and 5.0 eV or less. When the Eg is less than 4.0 eV, holes and electrons enter the inert material, and the carrier mobility cannot be maintained properly. As a result, it is not preferable in terms of deterioration of luminous efficiency and durability.

<Material>
The electrically inactive material in which the energy difference (Eg) between the highest occupied orbit and the lowest unoccupied orbit in the present invention is 4.0 eV or more is selected from organic compounds or inorganic compounds.
As the electrically inactive compound selected from the organic compounds, those having an ionization potential (Ip) larger than that of the first light emitting material are preferable. More preferably, the Ip of the electrically inactive compound is 0.1 eV or more, more preferably 0.2 eV or more larger than the first light emitting material.
The electrically inactive compound preferably has an electron affinity (Ea) smaller than that of the second light emitting material. More preferably, the Ea of the electrically inactive compound is 0.1 eV or less, more preferably 0.2 eV or less smaller than the second light emitting material.
A preferred specific compound is selected from aromatic hydrocarbon compounds, and one compound group is a compound represented by the following general formula (1).
General formula (1) L- (Ar) _m
In general formula (1), Ar represents a group represented by the following general formula (2), L represents a trivalent or higher benzene skeleton, and m represents an integer of 3 or higher.

In General Formula (2), R ¹ represents a substituent, and when a plurality of R ¹ are present, they may be the same as or different from each other. n1 represents the integer of 0-9.
Another preferred compound group is a compound represented by the following general formula (3).

In General Formula (3), R ² represents a substituent, and when a plurality of R ² are present, they may be the same as or different from each other. n2 represents an integer of 0 to 20.

First, the general formula (1) will be described in detail.
L contained in the general formula (1) represents a trivalent or higher benzene skeleton. Ar represents a group represented by the general formula (2), and m represents an integer of 3 or more. m is preferably 3 or more and 6 or less, and more preferably 3 or 4.

Next, the group represented by the general formula (2) will be described.
R ¹ contained in the general formula (2) represents a substituent. Here, examples of the substituent include an alkyl group (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, and particularly preferably 1 to 10 carbon atoms such as methyl, ethyl, iso-propyl, tert. -Butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl, cyclopentyl, cyclohexyl, etc.), an alkenyl group (preferably having 2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably Has 2 to 10 carbon atoms, and examples thereof include vinyl, allyl, 2-butenyl, and 3-pentenyl, and alkynyl groups (preferably having 2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably Has 2 to 10 carbon atoms, and examples thereof include propargyl and 3-pentynyl, and aryl groups (preferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenyl, p- methylphenyl, naphthyl, and the like and anthranyl),

An amino group (preferably having 0 to 30 carbon atoms, more preferably 0 to 20 carbon atoms, particularly preferably 0 to 10 carbon atoms, such as amino, methylamino, dimethylamino, diethylamino, dibenzylamino, diphenylamino, and Such as ditolylamino), an alkoxy group (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy, and 2-ethylhexyl). Siloxy and the like), an aryloxy group (preferably having 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenyloxy, 1-naphthyloxy, and 2 -Naphthyloxy etc. are mentioned), heteroaryloxy group (preferably C1-C30) More preferably, it is C1-C20, Most preferably, it is C1-C12, for example, pyridyloxy, pyrazyloxy, pyrimidyloxy, quinolyloxy etc. are mentioned, acyl group (preferably C1-C30, more preferably C1-C20, Most preferably, it is C1-C12, for example, acetyl, benzoyl, formyl, pivaloyl etc. are mentioned, alkoxycarbonyl group (preferably C2-C30, more preferably C2-C2) To 20 and particularly preferably 2 to 12 carbon atoms, such as methoxycarbonyl and ethoxycarbonyl, and aryloxycarbonyl groups (preferably 7 to 30 carbon atoms, more preferably 7 to 20 carbon atoms, particularly preferably Has 7 to 12 carbon atoms, such as phenyloxycarbonyl Etc., and the like),

An acyloxy group (preferably having 2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 2 to 10 carbon atoms, such as acetoxy and benzoyloxy), an acylamino group (preferably having 2 carbon atoms) To 30, more preferably 2 to 20 carbon atoms, particularly preferably 2 to 10 carbon atoms, and examples thereof include acetylamino and benzoylamino, and alkoxycarbonylamino groups (preferably 2 to 30 carbon atoms, more preferably Has 2 to 20 carbon atoms, particularly preferably 2 to 12 carbon atoms, and examples thereof include methoxycarbonylamino and the like, and aryloxycarbonylamino group (preferably 7 to 30 carbon atoms, more preferably 7 to 20 carbon atoms). Particularly preferably, it has 7 to 12 carbon atoms, such as phenyloxycarbonylamino Mentioned are),

A sulfonylamino group (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methanesulfonylamino, benzenesulfonylamino, etc.), a sulfamoyl group (preferably Is 0 to 30 carbon atoms, more preferably 0 to 20 carbon atoms, particularly preferably 0 to 12 carbon atoms, and examples thereof include sulfamoyl, methylsulfamoyl, dimethylsulfamoyl, and phenylsulfamoyl. A carbamoyl group (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl, and phenylcarbamoyl). An alkylthio group (preferably having 1 to 30 carbon atoms, More preferably, it is C1-C20, Most preferably, it is C1-C12, for example, methylthio, ethylthio etc. are mentioned, Arylthio group (Preferably C6-C30, More preferably C6-C20, Particularly preferably, it has 6 to 12 carbon atoms, for example, phenylthio and the like, and a heteroarylthio group (preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms). For example, pyridylthio, 2-benzimidazolylthio, 2-benzoxazolylthio, 2-benzthiazolylthio and the like),

A sulfonyl group (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms such as mesyl and tosyl), a sulfinyl group (preferably having 1 to 1 carbon atoms). 30, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methanesulfinyl, benzenesulfinyl and the like, ureido group (preferably 1 to 30 carbon atoms, more preferably carbon numbers) 1 to 20, particularly preferably 1 to 12 carbon atoms, such as ureido, methylureido, phenylureido and the like, phosphoric acid amide group (preferably 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms) Particularly preferably, it has 1 to 12 carbon atoms, and examples thereof include diethyl phosphoric acid amide and phenyl phosphoric acid amide)

Hydroxy group, mercapto group, halogen atom (eg fluorine atom, chlorine atom, bromine atom or iodine atom), cyano group, sulfo group, carboxyl group, nitro group, hydroxamic acid group, sulfino group, hydrazino group, imino group, hetero A cyclic group (preferably having 1 to 30 carbon atoms, more preferably 1 to 12 carbon atoms, and having, for example, a nitrogen atom, an oxygen atom, a sulfur atom, etc. as a hetero atom, specifically, for example, imidazolyl, pyridyl, quinolyl , Furyl, thienyl, piperidyl, morpholino, benzoxazolyl, benzimidazolyl, benzthiazolyl, carbazolyl group, azepinyl group and the like), silyl group (preferably having 3 to 40 carbon atoms, more preferably 3 to 30 carbon atoms). Particularly preferably having 3 to 24 carbon atoms, such as trimethylsilyl, Such as Li triphenylsilyl and the like) and the like.

When a plurality of R ¹ are present, they may be the same as or different from each other, and these may be bonded to each other to form a ring. R ¹ may be further substituted.

  n1 represents an integer of 0 to 9. n1 is preferably an integer of 0 to 6, and more preferably 0 to 3.

Next, general formula (3) will be described.
R ² in the general formula (3) represents a substituent. The substituent R ² is synonymous with the substituent R ^{1 including} preferred embodiments.
n2 represents an integer of 0 to 20. The preferable range of n2 is 0 to 10, more preferably 0 to 5.

  Although the example of a compound of General formula (1) or General formula (3) is shown below, this invention is not limited to these.

Another group of the electrically inactive materials used in the present invention are insulating inorganic compounds.
The insulating inorganic compound used in the present invention is not particularly limited as long as it is an inorganic compound having substantially no conductivity. For example, metal oxide, metal nitride, metal carbide, metal halide, metal sulfate, metal nitrate, metal phosphate, metal sulfide, metal carbonate, metal borohalide, or metal phosphorus halide can be used. It is. Among these, from the viewpoint of compatibility with light emitting materials and film forming suitability, silicon oxide, silicon dioxide, silicon nitride, silicon oxynitride, silicon carbide, germanium oxide, germanium dioxide, tin oxide, tin dioxide, barium oxide, fluoride Lithium, lithium chloride, cesium fluoride, cesium chloride, or the like is preferable. More preferred are silicon nitride, silicon oxynitride, silicon oxide, and silicon carbide.

2) First light emitting material The light emitting material that can be used in the present invention may be either a phosphorescent light emitting material or a fluorescent light emitting material. A phosphorescent light emitting material is preferable.
<Phosphorescent material>
In general, examples of the phosphorescent light-emitting material 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, more preferably rhenium, iridium, and platinum. More preferred are iridium and platinum.
Examples of the lanthanoid atom 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), aromatic carbocyclic ligands (eg, cyclopentadienyl anion, benzene anion, or naphthyl anion), Nitrogen-containing heterocyclic ligand (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, or phenanthroline), diketone ligand (eg, acetylacetone), carboxylic acid ligand (eg, acetic acid ligand) , Alcoholate ligands (eg, phenolate ligands), carbon monoxide ligands, isonitrile ligands, and cyano ligands, more preferably nitrogen-containing heterocyclic ligands.
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 light emitting material include, for example, US6303238B1, US6097147, WO00 / 57676, WO00 / 70655, WO01 / 08230, WO01 / 39234A2, WO01 / 41512A1, WO02 / 02714A2, WO02 / 15645A1, WO02 / 44189A1, Japanese Patent Application Laid-Open No. 2001-247859, Japanese Patent Application No. 2000-33561, Japanese Patent Application No. 2002-117978, Japanese Patent Application Laid-Open No. 2002-225352, Japanese Patent Application No. 2002-233501, Japanese Patent Application No. 2001-239281, Japanese Patent Application Laid-Open No. 2002-170684, Japanese Patent Application Laid-Open No. JP, 2002-234894, JP, 2001-247859, JP, 2001-298470, JP, 2002-173673, JP, 2002-203. 78, JP 2002-203679, JP 2004-357791, JP 2006-256999, and the like phosphorescent compounds described in patent documents such as Japanese Patent Application No. 2005-75341.

<Fluorescent material>
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. ), Metal complexes of 8-quinolinol, various metal complexes represented by pyromethene complexes and rare earth complexes, polythiophene, polyphenylene, polyphenylene bi Polymeric compounds Ren like, organic silanes, and the like, and their derivatives.
The first light emitting material in the present invention is an electron transporting light emitting material.
Preferably, the electron-transporting light-emitting material has an electron affinity (Ea) of 2.5 eV to 3.5 eV and an ionization potential (Ip) of 5.7 eV to 7.0 eV.
As the first light emitting material in the present invention, a conventionally known electron transporting light emitting material can be used.
Materials that can be preferably used are ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, platinum, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, And lutesium complexes. More preferred are ruthenium, rhodium, palladium, or platinum complexes, and most preferred is a platinum complex.
Although the example of a specific platinum complex is illustrated below, this invention is not limited to these.

3) Second light emitting material As the second light emitting material in the present invention, a conventionally known hole transporting light emitting material can be used. Preferably, the hole transporting light emitting material has an electron affinity (Ea) of 2.4 eV or more and 3.4 eV or less and an ionization potential (Ip) of 5.0 eV or more and 6.3 eV or less.
Materials that can be preferably used are ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, platinum, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, And lutesium complex, more preferably iridium complex.
Although the example of a specific iridium complex is illustrated below, this invention is not limited to these.

  In a particularly preferred combination in the present invention, the first light emitting material is a platinum complex, and the second light emitting material is an iridium complex.

(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.

  The hole injection layer preferably contains an electron-accepting material that serves as a carrier for hole movement. As the electron-accepting material to be introduced into the hole injection layer, an inorganic compound or an organic compound can be used as long as it has an electron-accepting property and oxidizes an organic compound. Specifically, the inorganic compound is ferric chloride. Lewis acid compounds such as aluminum chloride, gallium chloride, indium chloride, and antimony pentachloride can be suitably used.

In the case of an organic compound, a compound having a nitro group, a halogen, a cyano group, a trifluoromethyl group, or the like as a substituent, a quinone compound, an acid anhydride compound, or fullerene can be preferably used.
Specifically, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, 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-dinitrobenzene, o-dinitrobenzene, p-cyanonitrobenzene, m-cyanonitrobenzene, o-cyanonitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1 Nitronaphthalene, 2-nitronaphthalene, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9-cyanoanthracene, 9-nitroanthracene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, Examples include 2,4,7-trinitro-9-fluorenone, 2,3,5,6-tetracyanopyridine, maleic anhydride, phthalic anhydride, fullerene C60, and C70.

  Among these, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil, p-bromanyl, p-benzoquinone, 2,6-dichlorobenzoquinone, 2 , 5-dichlorobenzoquinone, 1,2,4,5-tetracyanobenzene, 1,4-dicyanotetrafluorobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,3-dinitronaphthalene, 1,5-dinitronaphthalene, 9,10-anthraquinone, 1,3,6,8-tetranitrocarbazole, 2,4,7-trinitro-9- Preferred are luolenone, 2,3,5,6-tetracyanopyridine, or C60, hexacyanobutadiene, hexacyanobenzene, tetracyanoethylene, tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, p-fluoranyl, p-chloranil. P-bromanyl, 2,6-dichlorobenzoquinone, 2,5-dichlorobenzoquinone, 2,3-dichloronaphthoquinone, 1,2,4,5-tetracyanobenzene, 2,3-dichloro-5,6-dicyanobenzoquinone Or 2,3,5,6-tetracyanopyridine is particularly preferred.

These electron-accepting materials may be used alone or in combination of two or more.
Although the usage-amount of an electron-accepting dopant changes with kinds of material, it is preferable that it is 0.01 mass%-50 mass% with respect to hole injection layer material, and it is 0.05 mass%-20 mass%. It is further more preferable and it is especially preferable that it is 0.1 mass%-10 mass%. When the amount used is less than 0.01% by mass relative to the hole injecting material, the effect of the present invention is insufficient because it is insufficient, and when it exceeds 50% by mass, the hole injecting ability is impaired. .

  Specific examples of materials for the hole injection layer and the hole transport layer include pyrrole derivatives, carbazole derivatives, pyrazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, Pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, A layer containing a porphyrin compound, an organic silane derivative, carbon, or the like is preferable.

The thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of driving voltage reduction, light emission efficiency improvement, durability improvement, The thickness is further preferably 5 nm to 1 μm, and particularly preferably 10 nm to 500 nm.
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. .

(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.

The electron-donating material introduced into the electron-injecting layer or the electron-transporting layer may be any electron-donating material that has the property of reducing organic compounds with an electron-donating property, such as alkali metals such as Li and alkaline earth metals such as Mg. Transition metals including rare earth metals are preferably used.
In particular, a metal having a work function of 4.2 eV or less can be preferably used. Specifically, Li, Na, K, Be, Mg, Ca, Sr, Ba, Y, Cs, La, Sm, Gd, Yb, and the like Is mentioned.

These electron donating materials may be used alone or in combination of two or more.
The amount of the electron donating dopant varies depending on the type of material, but is preferably 0.1% by mass to 99% by mass, and 1.0% by mass to 80% by mass with respect to the electron transport layer material. Is more preferable, and 2.0 mass% to 70 mass% is particularly preferable. When the amount used is less than 0.1% by mass with respect to the electron transport layer material, the effect of the present invention is insufficient because it is insufficient, and when it exceeds 99% by mass, the electron transport ability is impaired.

  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. Heterocyclic tetracarboxylic anhydrides such as pyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine-substituted aromatic compounds, naphthaleneperylene, phthalocyanines, and their derivatives (form condensed rings with other rings) Or metal complexes of 8-quinolinol derivatives, metal phthalocyanines, metal complexes having benzoxazole or benzothiazol as ligands, and the like.

The thicknesses of the electron injecting layer and the electron transporting layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of lowering driving voltage, improving luminous efficiency, and improving durability. It is more preferably 1 μm, and particularly preferably 10 nm to 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.

(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 a hole block layer is not specifically limited, Specifically, aluminum complexes, such as BAlq, a triazole derivative, a pyraza ball derivative, etc. can be contained.
In addition, the thickness of the hole blocking layer is generally preferably 50 nm or less, preferably 1 nm to 50 nm, and more preferably 5 nm 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 described in detail in the book “New Development of Transparent Electrode Films” published by CMC (1999), supervised by Yutaka Sawada, 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 (for example, Li, Na, K, or Cs), alkaline earth metals (for example, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys, And a rare earth metal such as magnesium-silver alloy, indium, and ytterbium. 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% by mass to 10% by mass of alkali metal or alkaline earth metal, or a mixture thereof (for example, lithium-aluminum alloy, magnesium-aluminum alloy). Etc.).

  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 nm 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 nm 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. , Norbornene resins, and organic materials such as poly (chlorotrifluoroethylene).
For example, when glass is used as the substrate, it is preferable to use non-alkali glass 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. Metal oxide such as O ₃ , Y ₂ O ₃ , or TiO ₂ , metal nitride such as SiN _x , SiN _x O _y , metal fluoride such as MgF ₂ , LiF, AlF ₃ , or CaF ₂ , polyethylene, polypropylene Polymethyl methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, a copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, tetrafluoroethylene and at least one comonomer. Copolymer obtained by copolymerizing monomer mixture containing And a fluorine-containing copolymer having a cyclic structure in the copolymer main chain, a water-absorbing substance having a water absorption of 1% or more, and a moisture-proof substance having a water absorption of 0.1% or less.

  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, or 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 time required to decrease to a certain luminance at a specific luminance. For example, using a source measure unit 2400 manufactured by KEITHLEY, a direct current voltage is applied to the organic EL element to emit light, and a continuous driving test is performed under the condition of an initial luminance of 2000 cd / m ² , and the luminance becomes 1000 cd / m ² . The luminance half time can be obtained by comparing the luminance half 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.

It figures external quantum efficiency, the maximum value of the external quantum efficiency when the device is driven at 20 ° C., or around 100cd ^{/ m 2} ~300cd ^/ m 2 when the device is driven at 20 ° C. (preferably 200 cd / The value of the external quantum efficiency at m ² ) can be used.
In the present invention, by using a Toyo source measure unit MODEL 2400, manufactured by DC constant voltage is applied to cause light emission to the EL element, the luminance was measured using Topcon luminance meter BM-8, 200cd / 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 emitted photons / 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 method described in each publication, Japanese Patent No. 2784615, US Pat. Nos. 5,828,429, 6023308, and the like can be applied.

(Use of the organic electroluminescence device of the present invention)
The organic electroluminescent element of the present invention can be suitably used for a display element, a display, a backlight, electrophotography, an illumination light source, a recording light source, an exposure light source, a reading light source, a sign, a signboard, an interior, or optical communication.

  Examples of the organic electroluminescence device of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
1. Preparation of organic EL element 1) Element No. 1. Preparation of 1 Put a glass substrate having an indium tin oxide (abbreviated as ITO) vapor deposition layer (manufactured by Geomatic Co., Ltd., surface resistance 10Ω / □, size: 0.5 mm thickness, 2.5 cm square) into a washing container. -After ultrasonic cleaning in propanol, UV-ozone treatment was performed for 30 minutes. The following layers were sequentially deposited on this transparent anode by a vacuum deposition method. The vapor deposition rate in the examples of the present invention is 0.2 nm / second unless otherwise specified. The deposition rate was measured using a quartz resonator. The film thicknesses described below were also measured using a crystal resonator.

-Hole injection layer-
2,3,5,6-tetrafluoro-7,7,8,8-tetra to 4,4 ′, 4 ″ -tris (2-naphthylphenylamino) triphenylamine (abbreviated as 2-TNATA) Cyanoquinodimethane (abbreviated as F4-TCNQ) was doped by 1.0 mass%, and was deposited on the ITO film to a thickness of 160 nm.
-Hole transport layer-
N, N′-dinaphthyl-N, N′-diphenyl- [1,1′-biphenyl] -4,4′-diamine (abbreviated as α-NPD) was deposited on the hole injection layer. The film thickness was 1 nm.

-Light emitting layer-
A layer containing the following inactive compound 1 as an electrically inactive material, the following luminescent material A as a first luminescent material, and Ir (ppy) ₃ as a second luminescent material was co-evaporated to a thickness of 5 nm. The composition ratio of the inert compound 1, the first light emitting material, and the second light emitting material was 70:15:15 by mass ratio.

-Electron transport layer-
Aluminum (III) bis (2-methyl-8-quinolinato) -4-phenylphenolate (abbreviated as Balq) was deposited to a thickness of 1 nm.
-Electron injection layer-
Co-evaporation was performed so that tris (8-hydroxyquinoninate) aluminum (abbreviated as Alq) and Alq were lithium (Li) 1 mass%. The deposition thickness was 30 nm.
-Cathode-
A patterned mask (mask with a light emitting area of 2 mm × 2 mm) was placed thereon, lithium fluoride (LiF) was deposited by 0.5 nm, and metal aluminum was further deposited by 100 nm to form a cathode.

  The produced laminate was put in a glove box substituted with argon gas, and sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.).

2) Element No. of the present invention. Preparation of 2-9 The above-mentioned element No. 1, the thickness of the light emitting layer and the type of the electrically inactive material were changed as shown in Table 1, and the element No. 1 of the present invention was changed. 2-9 were produced.

3) Production of comparative element Comparative element a: In element 1, the thickness of the light emitting layer was set to 30 nm.
Comparative element b: fabricated in the same manner as in the element 1, except that a layer having the following composition was used as the light emitting layer in the element 1.
Comparative light emitting layer: CBP and Ir (ppy) ₃ were co-deposited at a ratio of 15 mass% with respect to CBP. The thickness was 10 nm. CBP is a hole transporting host material, and Ir (ppy) ₃ is a hole transporting light emitting material.
Comparative element c: fabricated in the same manner as in the element 1, except that a layer having the following composition was used as the light emitting layer in the element 1.
Comparative light emitting layer: Inactive compound 1, CBP at a ratio of 40% by mass with respect to inactive compound 1, and Ir (ppy) ₃ at a ratio of 15% by mass with respect to inactive compound 1 were co-evaporated. The thickness was 10 nm. CBP is a hole transporting host material, and Ir (ppy) ₃ is a hole transporting light emitting material. Therefore, the structure of the light emitting layer in the comparative element c is different from the structure of the present invention because it contains two kinds of hole transport materials with respect to the inert material.

Table 2 shows the electron affinity (Ea) and ionization potential (Ip) of the materials used in the light emitting layers of the device of the present invention and the comparative device.
Inactive compounds 1 to 5 all have Eg of 4.0 eV or more, whereas all materials used for the comparative elements are less than 4.0 eV.
Further, in the element of the present invention, Ea and Ip of Ir (ppy) ₃ of the first light emitting material and Ir (ppy) ₃ of the second light emitting material are both in the light emitting material A than Ir (ppy) _3. 0.1 eV, 0.4 eV larger. On the other hand, in the two light emitting materials (host and dopant) in the comparative element c, Ir (ppy) ₃ was larger than CBP for Ea, and conversely, CBP was larger than Ir (ppy) _{3 for} Ip.

2. Performance evaluation (evaluation items)
(1) Luminous efficiency The external quantum efficiency of the light-emitting element was calculated from the results and relative luminous efficiency curve obtained by measuring the light emission luminance, light emission spectrum, and current density. The external quantum efficiency (%) was calculated by “(number of photons emitted / number of electrons input to the device) × 100”.
(2) Driving voltage The driving voltage at an illuminance of 2000 cd / m ² was measured.
(3) Driving durability A continuous driving test was performed under the condition of an initial luminance of 2000 cd / m ² , and the time when the luminance was reduced by half was determined as the durability time.

(Evaluation results)
The obtained results are shown in Table 3.
The device of the present invention unexpectedly has extremely high luminous efficiency as compared with the device of the comparative example, and in particular, the driving durability could be extended. Despite the dramatic improvement of these characteristics, the drive voltage was unexpectedly decreased or decreased depending on the element.
In the comparative element a having a light emitting layer thickness of 30 nm, the driving voltage was remarkably increased and the light emission efficiency was low.
Both the comparative elements b and c have low luminous efficiency, and the comparative element c has extremely poor driving durability.

Claims (15)

  An organic compound layer including at least one light emitting layer is provided between a pair of opposed electrodes, and the light emitting layer has at least a light emitting material and an energy difference (Eg) between the highest occupied orbit and the lowest unoccupied orbit is 4.0 eV or more. An organic electroluminescent element containing an electrically inactive material, wherein the light emitting material includes at least a first light emitting material and a second light emitting material, and the first light emitting material is an electron transporting light emitting material. The organic electroluminescent device is characterized in that the second light emitting material is a hole transporting light emitting material and the thickness of the light emitting layer is 0.5 nm or more and 20 nm or less.   The electron affinity (Ea1) of the first light emitting material is larger than the electron affinity (Ea2) of the second light emitting material, and the ionization potential (Ip1) of the first light emitting material is the ionization potential (Ip2) of the second light emitting material. The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is larger.   The organic electroluminescent element according to claim 1, wherein the first light emitting material is a platinum complex.   The organic electroluminescent element according to claim 1, wherein the second light emitting material is an iridium complex.   The organic electroluminescent element according to claim 4, wherein the first light emitting material is a platinum complex and the second light emitting material is an iridium complex.   The organic electroluminescent element according to claim 1, wherein the light emitting layer has a thickness of 1 nm to 10 nm.   The ratio of the light emitting material to the total amount of the light emitting material and the electrically inactive material in the light emitting layer is 5% or more and 40% or less by mass ratio. 2. The organic electroluminescent element according to item 1.   The organic electroluminescence according to any one of claims 1 to 7, wherein the electrically inactive material is an organic compound, and its ionization potential (Ip) is larger than that of the light emitting material. element.   The organic electroluminescence according to any one of claims 1 to 8, wherein the electrically inactive material is an organic compound, and its electron affinity (Ea) is smaller than that of the light emitting material. element.   The organic electroluminescent element according to claim 1, wherein the electrically inactive material is an aromatic hydrocarbon compound. The organic electroluminescent device according to claim 10, wherein the aromatic hydrocarbon compound is a compound represented by the following general formula (1):
General formula (1) L- (Ar) _m
(In general formula (1), Ar represents a group represented by the following general formula (2), L represents a trivalent or higher benzene skeleton, and m represents an integer of 3 or higher);

(In General Formula (2), R ¹ represents a substituent, and when a plurality of R ¹ are present, they may be the same or different from each other. N1 represents an integer of 0 to 9). The organic electroluminescent device according to claim 10, wherein the aromatic hydrocarbon compound is a compound represented by the following general formula (3):

(In General Formula (3), R ² represents a substituent, and when a plurality of R ² are present, they may be the same or different from each other. N2 represents an integer of 0 to 20).   The organic electroluminescent element according to claim 1, wherein the electrically inactive material is an insulating inorganic compound.   The organic compound layer has at least one of a hole injection layer and a hole transport layer from the anode side, the light emitting layer, and an electron transport layer or an electron injection layer, and the hole injection layer and the hole transport The organic electroluminescence device according to claim 1, wherein at least one of the layers contains an electron-accepting material.   The organic compound layer has at least one of a hole transport layer, the light emitting layer, and an electron transport layer and an electron injection layer from the anode side, and at least one layer of the electron transport layer and the electron injection layer is The organic electroluminescent element according to claim 1, comprising an electron donating material.