JP2010157606A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element having a high luminous efficiency by means of mixed luminescence. <P>SOLUTION: This organic electroluminescent element includes: a pair of electrodes constituted of a positive electrode and a negative electrode; and at least a luminescent layer arranged between the pair of electrodes, a hole transport layer arranged between the positive electrode and the luminescent layer, and an electron transport layer arranged between the negative electrode and the luminescent layer. In the organic electroluminescent element, (1) the luminescent layer contains an electron transporting luminescent material and a hole transporting host material; (2) the concentration of the electron transporting luminescent material in the luminescent layer is gradually reduced toward the positive electrode side of the luminescent layer from the negative electrode side thereof; and (3) at least one kind of a luminescent material low in triplet energy level relative to the electron transporting luminescent material is included in a region reduced in the electron transporting luminescent material concentration in the luminescent layer and in a region having a thickness of 1/100-1/2 of the total thickness of the luminescent layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element (hereinafter abbreviated as an organic EL element). In particular, it relates to a white light-emitting organic EL element.

  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.

In addition, the organic EL element is also characterized in that light emission of various emission colors is possible by color mixture combining a plurality of emission colors.
Among the luminescent colors, the need for white light emission is particularly high. White light emission can be used as power saving in general lighting, an in-vehicle display, or a backlight. Furthermore, it can be divided into blue, green, and red pixels using a color filter, and a full-color display device is also possible.

For example, it has been proposed that two layers of a blue light emitting layer that emits short wavelength light and a red light emitting layer that emits long wavelength light are stacked to obtain white light emission as a mixed color of both light emitting layers ( For example, see Patent Documents 1 and 2).
However, such a laminated structure of light emitting layers with different color development (that is, different energy levels) has a low carrier injection property due to a barrier between the respective layers, and the performance such as an increase in driving voltage and a decrease in durability. In addition to the above problems, production problems such as an increase in the deposition process (chamber) during production also arise.
JP-A-7-142169 JP 2008-85363 A

  The subject of this invention makes it a subject to provide the organic EL element by the mixed light emission which has especially high luminous efficiency. In particular, it is an object of the present invention to provide an organic EL device capable of efficiently generating three-color light emission having different emission peaks, for example, three-color light emission of blue, green, and red, and obtaining white light emission at a low voltage. .

It has been found that the above-mentioned problems of the present invention can be solved by the following means.
<1> A pair of electrodes composed of an anode and a cathode, at least a light emitting layer disposed between the pair of electrodes, a hole transport layer disposed between the anode and the light emitting layer, and the cathode and the above An electron transport layer disposed between the light emitting layer and
1) The light emitting layer contains an electron transporting light emitting material and a hole transporting host material,
2) The concentration of the electron-transporting light-emitting material in the light-emitting layer gradually decreases from the cathode side to the anode side of the light-emitting layer,
3) In the region where the concentration of the electron-transporting light-emitting material in the light-emitting layer is reduced and in a region having a thickness of 1/100 or more and 1/2 or less of the total thickness of the light-emitting layer, triple the electron transporting light-emitting material. An organic electroluminescent device comprising at least one light emitting material having a low term energy level.
<2> The electron-transporting light-emitting material is a blue light-emitting material, and the light-emitting material having a lower triplet energy level than the electron-transporting light-emitting material is at least one of a green light-emitting material and a red light-emitting material. The organic electroluminescent element of description.
<3> The organic electroluminescent element according to <2>, wherein the light emitting material having a triplet energy level lower than that of the electron transporting light emitting material is a green light emitting material and a red light emitting material.
<4> A region containing a light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material in the light-emitting layer in which the concentration of the light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material And the organic electroluminescent element as described in <1>-<3> which is constant in the thickness direction.
<5> A region containing a light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material in the light-emitting layer in which the concentration of the light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material And the organic electroluminescent element as described in <1>-<3> which is gradually decreasing toward the cathode side from the anode side of the said light emitting layer.
<6> The organic material according to <1> to <5>, wherein the concentration of the hole transporting host material in the light emitting layer is gradually decreased from the anode side to the cathode side of the light emitting layer. Electroluminescent device.
<7> The organic electroluminescent element according to <1> to <6>, wherein the electron-transporting light-emitting material is a metal complex having platinum as a central metal.

According to the present invention, there is provided an organic EL device capable of efficiently generating at least three-color light emission having different emission peaks and obtaining highly efficient white light emission.
Conventionally, a structure in which a short wave light emitting layer is sandwiched between long wave light emitting layers or a structure in which a long wave light emitting layer is sandwiched between short wave light emitting layers is known. For example, PQ2Ir (acac), Btp2Ir (acac), etc. The single-colored red light emitting material is a single color and has a uniform concentration in the thickness direction. Further, the short wave light emitting layer also has a single color doped with one kind of FIrpic and a uniform concentration in the thickness direction.
In the present invention, the light emitting layer contains an electron transporting light emitting material and a hole transporting host material, and the concentration of the electron transporting light emitting material is gradually decreased from the cathode side to the anode side of the light emitting layer. Furthermore, it contains at least one light emitting material having a triplet energy level lower than that of the electron transporting light emitting material, and the light emitting material having a low triplet energy level has a concentration of the electron transporting light emitting material in the light emitting layer. Is reduced, and is contained in a region having a thickness of 1/100 or more and 1/2 or less of the total thickness of the light emitting layer, and by this configuration, without increasing the driving voltage, Each light emitting material can be made to emit light efficiently.

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

(Constitution)
The organic electroluminescent device of the present invention includes at least a light emitting layer between a pair of electrodes (anode and cathode), a hole transport layer between the anode and the light emitting layer, and an electron transport layer between the cathode and the light emitting layer. It has a laminated structure having
From the nature of the light emitting element, it is preferable that at least one of the pair of electrodes is transparent.

  As the form of lamination of the organic compound layer in the present invention, preferably, an electron transport property is further provided between the hole transport layer and the anode, and / or between the light emitting layer and the electron transport layer. Has an intermediate 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, the configuration of the organic EL element of the present invention will be described in detail.

The organic EL device of the present invention includes a pair of electrodes composed of an anode and a cathode, at least a light emitting layer disposed between the pair of electrodes, a hole transport layer disposed between the anode and the light emitting layer, And an electron transport layer disposed between the cathode and the light emitting layer,
1) The light emitting layer contains an electron transporting light emitting material and a hole transporting host material,
2) The concentration of the electron-transporting light-emitting material in the light-emitting layer gradually decreases from the cathode side to the anode side of the light-emitting layer,
3) In the region where the concentration of the electron-transporting light-emitting material in the light-emitting layer is reduced and in a region having a thickness of 1/100 or more and 1/2 or less of the total thickness of the light-emitting layer, triple the electron transporting light-emitting material. It contains at least one light emitting material having a low term energy level.
Preferably, the electron-transporting light-emitting material is a blue light-emitting material, and the light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material is at least one of a green light-emitting material and a red light-emitting material. More preferably, the light emitting material having a triplet energy level lower than that of the electron transporting light emitting material contains at least one green light emitting material and at least one red light emitting material.
Preferably, the concentration of the light emitting material having a lower triplet energy level than that of the electron transporting light emitting material is a region containing a light emitting material having a triplet energy level lower than that of the electron transporting light emitting material in the light emitting layer. It is constant in the thickness direction. Another preferred embodiment is a light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material in the light-emitting layer, wherein the concentration of the light-emitting material having a lower triplet energy level than that of the electron-transporting light-emitting material. In the containing region, the light emitting layer gradually decreases from the anode side toward the cathode side.
Preferably, the concentration of the hole transporting host material in the light emitting layer gradually decreases from the anode side to the cathode side of the light emitting layer.
Preferably, the electron transporting light emitting material is a metal complex having platinum as a central metal.

  In the present invention, the term “gradual decrease” means that the total decreases, and even if it decreases continuously linearly or curvilinearly, it decreases in a stepped or wavy manner. May be. Alternatively, even if there is a region that increases in part, if it decreases overall, it is within the intended range of the present application.

  In the present invention, the term “gradual decrease” means, for example, that it is gradually decreasing from the cathode side to the anode side, that the concentration of the material in the region close to the anode is the cathode of the light emitting layer. It means that it is 0 mass% or more and 50 mass% or less with respect to the density | concentration in the area | region which adjoins, and it is decreasing gradually toward the cathode side from the anode side that it is in the area | region close to the said cathode of this material. It means that the concentration is 0% by mass or more and 50% by mass or less with respect to the concentration in the region adjacent to the anode of the light emitting layer. The value of 0 mass% or more and 50 mass% or less is a value representing the concentration gradient. More preferably, the concentration gradient is 0% by mass or more and 30% by mass or less, and further preferably 0% by mass or more and 20% by mass or less.

  In the present invention, the “region of the light emitting layer close to the cathode or anode” refers to a thickness region of 10% of the light emitting layer thickness from the side of the light emitting layer close to the cathode or anode, and the average concentration in that region Is set to a range that satisfies the above relationship.

  When the concentration of the electron transporting luminescent material gradually decreasing from the cathode side toward the anode side exceeds 50% with respect to the concentration of the light emitting layer in the region adjacent to the cathode, It is not preferable because suppression of omission is insufficient and improvement in luminous efficiency is difficult to obtain. Similarly, the concentration of the hole-transporting host material gradually decreasing from the anode side toward the cathode side is 50% of the concentration in the region adjacent to the anode of the light emitting layer. Exceeding% is not preferable because the suppression of the loss of holes is insufficient and it becomes difficult to improve the light emission efficiency.

In the present invention, the electron-transporting light-emitting material is contained in the entire area of the light-emitting layer while gradually decreasing from the cathode side to the anode side in the light-emitting layer, and emits light uniformly over the entire area of the light-emitting layer. Along with the improvement in efficiency, the light emission distribution approaches the whole light emission, and the durability is improved. As a result of the inclined structure of the present invention, the movement of the electrons injected from the cathode into the light-emitting layer proceeds to the anode side, so that the movement is braked. As a result, holes that have conventionally occurred only on the cathode surface side or anode surface side of the light-emitting layer It is presumed that recombination of electrons has occurred in the center of the light emitting layer.
A light emitting material having a triplet energy level lower than that of the electron transporting light emitting material is a region where the concentration of the electron transporting light emitting material in the light emitting layer is reduced, and is 1/100 or more of the total thickness of the light emitting layer. Inefficient due to interaction between light-emitting materials, such as energy transfer from excitons generated by the electron-transporting light-emitting material to a light-emitting material having a low triplet energy level, because it is contained in a region having a thickness of / 2 or less Does not happen. Therefore, according to the configuration of the present invention, each light emitting material can efficiently emit light without increasing the driving voltage.

  FIG. 1 is a schematic view showing the layer structure of the organic EL device of the present invention. An anode 2 is provided on a substrate 1, and a hole transport layer 3, a light emitting layer 4, and an electron transport layer 5 are sequentially stacked thereon, and a cathode 6 is provided thereon. The light emitting layer 4 contains an electron transporting light emitting material and a hole transporting host material. The concentration of the electron-transporting light-emitting material in the light-emitting layer is gradually decreased from the cathode side toward the anode side, and in the region where the concentration of the electron-transporting light-emitting material is reduced, the triplet than the electron-transporting light-emitting material. It contains a light emitting material with a low energy level. The region containing the light emitting material having a low triplet energy level is a limited region corresponding to a thickness of 1/100 or more and 1/2 or less of the total thickness of the light emitting layer.

The organic EL element in the present invention may have a resonator structure. For example, a multilayer mirror made of a plurality of laminated films having different refractive indexes, a transparent or translucent electrode, a light emitting layer, and a metal electrode are superimposed on a transparent substrate. The light generated in the light emitting layer resonates repeatedly with the multilayer mirror and the metal electrode as a reflection plate.
In another preferred embodiment, a transparent or translucent electrode and a metal electrode each function as a reflector on a transparent substrate, and light generated in the light emitting layer repeats reflection and resonates between them.
In order to form a resonant structure, the optical path length determined from the effective refractive index of the two reflectors and the refractive index and thickness of each layer between the reflectors is adjusted to the optimum value to obtain the desired resonant wavelength. Is done. The calculation formula in the case of the first embodiment is described in JP-A-9-180883. The calculation formula in the case of the second aspect is described in Japanese Patent Application Laid-Open No. 2004-127795.

  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.

  Next, the element which comprises the organic EL element of this invention is demonstrated in detail.

(Light emitting layer)
The light emitting layer receives holes from the anode, hole injection layer, hole transport layer or hole transport buffer layer when an electric field is applied, and receives electrons from the cathode, electron injection layer, electron transport layer or electron transport buffer layer. It is a layer having a function of receiving and providing a field for recombination of holes and electrons to emit light.
The light emitting layer in the present invention contains an electron transporting light emitting material and a hole transporting host material, and the concentration of the electron transporting light emitting material in the light emitting layer is directed from the cathode side to the anode side of the light emitting layer. In the region where the concentration of the electron-transporting light-emitting material in the light-emitting layer is reduced, and in the region of 1/100 or more and 1/2 or less the total thickness of the light-emitting layer, the electron-transporting light-emitting material Also contains at least one light emitting material having a low triplet energy level.

  The total amount of the luminescent material is preferably 0.1% by mass to 30% by mass with respect to the total solid content in the light emitting layer. More preferably. The total amount of the host material is preferably 70% by mass to 99.9% by mass with respect to the total solid content in the light emitting layer, and 85% by mass to 99% by mass from the viewpoint of durability and external quantum efficiency. More preferably.

(Electron transporting luminescent material)

The electron transporting light emitting material is preferably an electron transporting light emitting material having an electron affinity (Ea) of 2.5 eV or more and 3.5 eV or less and an ionization potential (Ip) of 5.7 eV or more and 7.0 eV or less. is there.
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.

(Light emitting material with small triplet energy level)
The light emitting material having a small triplet energy level used in the present invention is a phosphorescent light emitting material having a triplet energy level smaller than the triplet energy level of the electron transporting light emitting material of the light emitting layer. Preferably, the light-emitting material having a small triplet energy level used in the present invention is 1.0 kcal / mol or less, more preferably 2.0 kcal / mol lower than the triplet energy level of the electron-transporting light-emitting material of the light-emitting layer. Smaller than mol, more preferably smaller than 4.0 kcal / mol.
The phosphorescent material is not particularly limited as long as the triplet energy level is lower than that of the electron-transporting light-emitting material of the light-emitting layer, and can be selected from the above platinum complexes, other orthometalated metal complexes, or A porphyrin metal complex can also be used.

  Ortho metalated metal complexes include, for example, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications", pages 150, 232, Hankabosha (published in 1982) and H.C. Yersin's “Photochemistry and Photophysics of Coordination Compounds”, pages 71-77, pages 135-146, Springer-Verlag (published in 1987), etc.

There are various ligands that form the ortho-metalated metal complex, which are also described in the above documents. Among them, preferred ligands include 2-phenylpyridine derivatives, 7,8- Examples include benzoquinoline derivatives, 2- (2-thienyl) pyridine derivatives, 2- (1-naphthyl) pyridine derivatives, and 2-phenylquinoline derivatives. These derivatives may have a substituent if necessary. The orthometalated metal complex may have other ligands in addition to the above ligands.
The orthometalated metal complex used in the present invention can be obtained from Inorg Chem. 1991, 30, 1685, 1988, 27, 3464. 1994, 33, 545, Inorg. Chim. Acta, 1991, No. 181, page 245; Organomet. Chem. 1987, No. 335, 293, J. Am. Am. Chem. Soc. 1985, No. 107, pages 14-31, etc., can be synthesized by various known methods.

Among the orthometalated complexes, orthometalated metal complexes having a 2-phenylpyridine derivative as a ligand are preferable.
The light emitting material having a small triplet energy level used in the present invention may be used alone or in combination of two or more.

  Among these, specific examples of the light emitting material having a small triplet energy level include the following, but are not limited thereto.

(Host material)
The organic EL device of the present invention contains a host material excellent in hole transportability (sometimes referred to as a hole transportable host) in the light emitting layer.

  The hole transporting host used in the organic layer of the present invention preferably has an ionization potential Ip of 5.1 eV or more and 6.4 eV or less from the viewpoint of improving durability and lowering driving voltage. More preferably, it is less than or equal to .3 eV, and even more preferably between 5.6 eV and 6.2 eV. Further, from the viewpoint of improving durability and lowering driving voltage, the electron affinity Ea is preferably 1.2 eV or more and 3.1 eV or less, more preferably 1.4 eV or more and 3.0 eV or less, and 1.8 eV or more. More preferably, it is 2.8 eV or less.

Specific examples of such a hole transporting host include the following materials.
Pyrrole, carbazole, azacarbazole, pyrazole, indole, azaindole, imidazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary Amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N-vinylcarbazole), aniline copolymers, thiophene oligomers, conductive polymer oligomers such as polythiophene, organic silanes, Examples thereof include carbon films and derivatives thereof.

  Among these, a carbazole derivative, an indole derivative, an imidazole derivative, an aromatic tertiary amine compound, or a thiophene derivative is preferable, and in particular, the molecule has a plurality of carbazole skeleton and / or indole skeleton and / or aromatic tertiary amine skeleton. Those are preferred.

  Specific examples of such a hole transporting host include, but are not limited to, the following compounds.

The organic EL device of the present invention may contain an electron transporting host together with the hole transporting host.
The electron transport host used in the present invention preferably has an electron affinity Ea of 2.5 eV or more and 3.5 eV or less from the viewpoint of improving durability and lowering driving voltage, and is 2.6 eV or more and 3.4 eV or less. More preferably, it is 2.8 eV or more and 3.3 eV or less. Further, from the viewpoint of improving durability and reducing driving voltage, the ionization potential Ip is preferably 5.7 eV or more and 7.5 eV or less, more preferably 5.8 eV or more and 7.0 eV or less, and 5.9 eV or more. More preferably, it is 6.5 eV or less.

Specific examples of such an electron transporting host include the following materials.
Pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, Fluorine-substituted aromatic compounds, aromatic ring tetracarboxylic anhydrides such as naphthalene and perylene, phthalocyanines, and derivatives thereof (which may form condensed rings with other rings), metal complexes of 8-quinolinol derivatives, Examples thereof include various metal complexes represented by metal complexes having metal phthalocyanine, benzoxazole or benzothiazol as a ligand.

Preferred examples of the electron transporting host include metal complexes, azole derivatives (benzimidazole derivatives, imidazopyridine derivatives, etc.), and azine derivatives (pyridine derivatives, pyrimidine derivatives, triazine derivatives, etc.). To metal complex compounds are preferred. The metal complex compound is more preferably a metal complex having a ligand having at least one nitrogen atom, oxygen atom or sulfur atom coordinated to the metal.
The metal ion in the metal complex is not particularly limited, but is preferably beryllium ion, magnesium ion, aluminum ion, gallium ion, zinc ion, indium ion, tin ion, platinum ion, or palladium ion, more preferably beryllium ion, Aluminum ion, gallium ion, zinc ion, platinum ion, or palladium ion, and more preferably aluminum ion, zinc ion, or palladium ion.

  There are various known ligands contained in the metal complex. For example, “Photochemistry and Photophysics of Coordination Compounds”, Springer-Verlag, H.C. Examples include the ligands described in Yersin, published in 1987, “Organometallic Chemistry: Fundamentals and Applications”, Sakai Hanafusa, Yamamoto Akio, published in 1982, and the like.

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. Alternatively, it may be a bidentate or higher ligand, preferably a bidentate or higher and a hexadentate or lower ligand, or a bidentate or higher and lower 6 or lower ligand and a monodentate mixed ligand. preferable.
Examples of the ligand include an azine ligand (for example, a pyridine ligand, a bipyridyl ligand, and a terpyridine ligand), a hydroxyphenylazole ligand (for example, a hydroxyphenylbenzimidazole ligand). Ligands, hydroxyphenylbenzoxazole ligands, hydroxyphenylimidazole ligands, hydroxyphenylimidazopyridine ligands, etc.), alkoxy ligands (preferably having 1 to 30 carbon atoms, more preferably carbon numbers). 1 to 20, particularly preferably 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy and 2-ethylhexyloxy), aryloxy ligands (preferably 6 to 30 carbon atoms, and more). Preferably it has 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, for example Eniruokishi, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl oxy, and the like 4-biphenyloxy and the like.),

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, and quinolyloxy. ), 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 ligands (Preferably 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, such as phenylthio), heteroarylthio ligand (preferably 1 carbon atom) To 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.), a siloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms). Particularly preferably, it has 6 to 20 carbon atoms, and examples thereof include a triphenylsiloxy group, a triethoxysiloxy group, and a triisopropylsiloxy group.), An aromatic hydrocarbon anion ligand (preferably having 6 carbon atoms) To 30, more preferably 6 to 25 carbon atoms, particularly preferably 6 to 20 carbon atoms, such as a phenyl anion, a naphthyl anion, an anthranyl anion, etc.), an aromatic heterocyclic anion ligand (preferably Has 1 to 30 carbon atoms, more preferably 2 to 25 carbon atoms, and particularly preferably 2 to 20 carbon atoms. Pyrrole anion, pyrazole anion, pyrazole anion, triazole anion, oxazole anion, benzoxazole anion, thiazole anion, benzothiazole anion, thiophene anion, benzothiophene anion, etc.), indolenine anion ligand, etc. , Preferably a nitrogen-containing heterocyclic ligand, aryloxy ligand, heteroaryloxy group, or siloxy ligand, more preferably a nitrogen-containing heterocyclic ligand, aryloxy ligand, siloxy coordination Or an aromatic hydrocarbon anion ligand or an aromatic heterocyclic anion ligand.

  Examples of the metal complex electron transporting host include, for example, JP-A No. 2002-235076, JP-A No. 2004-214179, JP-A No. 2004-221106, JP-A No. 2004-221665, JP-A No. 2004-221068. And compounds described in JP-A-2004-327313.

  Specific examples of such an electron transporting host include, but are not limited to, the following materials.

  As the electron transport layer host, E-1 to E-6, E-8, E-9, E-21, or E-22 are preferable, and E-3, E-4, E-6, E-8, E-9, E-10, E-21, or E-22 is more preferable, and E-3, E-4, E-21, or E-22 is still more preferable.

<Film thickness>
The thickness of the light emitting layer is preferably 5 nm or more and 200 nm or less, and more preferably 10 nm or more and 100 nm or less, from the viewpoints of luminance unevenness, driving voltage, and luminance. If the light-emitting layer is thin, it can be driven with high brightness and low voltage, but the device resistance becomes small, so it is more susceptible to changes in brightness due to voltage drop, resulting in increased brightness unevenness. It becomes. If the thickness of the light emitting layer is large, the drive voltage increases, leading to a decrease in light emission efficiency and limiting the application.

<Layer structure>
The light emitting layer may be one layer or two or more layers, and each layer may emit light in different emission colors. In the case where the light emitting layer has a laminated structure, the film thickness of each layer constituting the laminated structure is not particularly limited, but it is preferable that the total film thickness of each light emitting layer is in the above-described range.

(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 each preferably 50 nm or less from the viewpoint of lowering the driving voltage.
The thickness of the hole transport layer is preferably 5 nm to 50 nm, and more preferably 10 nm to 40 nm. In addition, the thickness of the hole injection layer is preferably 0.5 nm to 300 nm, and more preferably 1 nm to 200 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 a function of receiving electrons from the cathode or the cathode side and transporting them to the anode side. Specifically, the electron injection layer and the electron transport layer are triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, fluorenone derivatives, anthraquinodimethane derivatives, anthrone derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, Carbodiimide derivatives, fluorenylidenemethane derivatives, distyrylpyrazine derivatives, aromatic tetracarboxylic anhydrides such as naphthalene and perylene, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives, metal phthalocyanines, benzoxazoles and benzothiazoles as ligands It is preferably a layer containing various metal complexes typified by metal complexes, organosilane derivatives, and the like.

The thicknesses of the electron injection layer and the electron transport layer are each preferably 50 nm or less from the viewpoint of lowering the driving voltage.
The thickness of the electron transport layer is preferably 5 nm to 50 nm, and more preferably 10 nm to 50 nm. Moreover, the thickness of the electron injection layer is preferably 0.1 nm to 50 nm, and more preferably 0.5 to 20 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 electron transport layer is a layer adjacent to the light emitting layer, a material having an ionization potential of 6.0 eV or less is used as a material constituting the layer from the viewpoint of improving durability.

(substrate)
The substrate used in the present invention is preferably a substrate that does not scatter or attenuate light emitted from the organic compound layer. Specific examples 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.

(electrode)
<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 doped with antimony and fluorine (ATO, FTO), tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO). 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. Is preferably formed on the substrate. In this case, 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 20 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 (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 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 20 nm to 1 μm.
Further, the cathode may be transparent or opaque. Note that the transparent cathode can be formed by depositing a thin cathode material to a thickness of 1 nm to 20 nm and further laminating a transparent conductive material such as ITO or IZO.

(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.

(Drive)
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 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, The driving methods described in Japanese Patent No. 8-24047, Japanese Patent No. 2784615, US Pat. No. 5,828,429, Japanese Patent No. 6023308, and the like can be applied.

(Use)
The use of the organic EL device of the present invention is not particularly limited, but it can be applied to a wide range of fields such as a mobile phone display, a personal digital assistant (PDA), a computer display, an automobile information display, a TV monitor, or general lighting.

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

(Measurement of triplet energy levels of phosphorescent materials)
First, a measurement method and measurement results of the triplet energy level of the phosphorescent material used in the examples will be described.
Measuring method:
(1) A measurement sample is produced by forming a film in which a host material is doped with a phosphorescent material on a quartz substrate.
(2) Using a spectrofluorometer F7000 (manufactured by Hitachi High-Tech), the quartz substrate is cooled with liquid nitrogen and irradiated with excitation light to emit phosphorescence. The triplet energy level is determined from the obtained phosphorescence spectrum.

  As a result of measurement for the following materials, the blue light emitting material B1 has a triplet energy level of 65 kcal / mol, whereas the green light emitting material G1 has a triplet energy level of 56 kcal / mol and the red light emitting material R1 has a triplet energy. The level is 48 kcal / mol, and the triplet energy levels of the green light-emitting material G1 and the red light-emitting material R1 are 9 kcal / mol to 17 kcal / mol lower than the blue light-emitting material B1.

Example 1
1. Production of organic EL element (production of organic EL element 1 of the present invention)
A glass substrate (manufactured by Geomatic Co., Ltd., surface resistance 10Ω / □) on which 0.5 mm thick and 2.5 cm square indium tin oxide (abbreviated as ITO) is deposited to a thickness of 100 nm is put in a cleaning container, and in 2-propanol After ultrasonic cleaning with, UV-ozone treatment was performed for 30 minutes. The following layers were deposited on this transparent anode by vacuum deposition. 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: 4,4 ′, 4 ″ -tris (2-naphthylphenylamino) triphenylamine (abbreviated as 2-TNATA) and 0.3% by mass of 2,3,2 based on 2-TNATA 5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (abbreviated as F4-TCNQ) was co-evaporated. The thickness was 160 nm.
Hole transport layer: N, N′-dinaphthyl-N, N′-diphenyl- [1,1′-biphenyl] -4,4′-diamine (abbreviated as α-NPD) and deposited to a thickness of 7 nm; Then, the following hole transport agent 1 was deposited to a thickness of 3 nm.

Light emitting layer: 1,3-bis (carbazol-9-yl) benzene (abbreviated as mCP), electron transporting light emitting material B1, light emitting material G1 having a low triplet energy level, and light emitting material having a small triplet energy level Four-element deposition of R1 was performed. For mCP, the co-evaporation ratio of the electron-transporting luminescent material B1, the luminescent material G1, and the luminescent material R1 was changed as the deposition progressed. The thickness of the light emitting layer was 60 nm.
The mixing ratio of the electron transporting light-emitting material B1 is 0% by mass with respect to mCP in the region close to the initial hole transport layer, and 30% by mass in the region close to the electron transport layer at the end of the deposition. The deposition rate was adjusted as follows. The mixing ratio of each component was continuously changed between these regions.
-The light emitting material G1 was vapor-deposited so that it might become 15 mass% with respect to mCP in the 10 nm area | region of the side adjacent to the positive hole transport layer of a light emitting layer.
-The light emitting material R1 was vapor-deposited so that it might become 15 mass% with respect to mCP in the 10 nm area | region of the side adjacent to the positive hole transport layer of a light emitting layer.

Subsequently, the following electron transport layer and electron injection layer were provided on the light emitting layer.
Electron transport layer: bis- (2-methyl-8-quinolinolate) -4- (phenylphenolate) aluminum (abbreviated as BAlq) was deposited to a thickness of 40 nm.
Electron injection layer: LiF, thickness 1 nm.

Furthermore, patterning was performed using a shadow mask to provide Al having a thickness of 100 nm as a cathode.
Each layer was provided by resistance heating vacuum deposition.

  The produced laminate was put in a glove box substituted with nitrogen gas, and sealed with a glass sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by CHI Nagase).

(Preparation of the organic EL element 2 of the present invention)
In the organic EL element 1, the light emitting layer was changed to the following.
Light-emitting layer: Four-element deposition of mCP, electron-transporting light-emitting material B1, light-emitting material G1 having a low triplet energy level, and light-emitting material R1 having a low triplet energy level was performed. For mCP, the co-evaporation ratio of the electron-transporting light-emitting material B1, the light-emitting material G1, and the light-emitting material R1 was changed as the deposition progressed. The thickness of the light emitting layer was 60 nm.
The mixing ratio of the electron transporting light-emitting material B1 is 0% by mass with respect to mCP in the region close to the initial hole transport layer, and 30% by mass in the region close to the electron transport layer at the end of the deposition. The deposition rate was adjusted as follows. The mixing ratio of each component was continuously changed between these regions.
-The light emitting material G1 is 15% by mass with respect to mCP in the 15 nm region on the side adjacent to the hole transport layer of the light emitting layer, in the region close to the hole transport layer at the beginning of deposition, The deposition rate was adjusted to be 0% by mass. The mixing ratio of each component was continuously changed between these regions.
The luminescent material R1 is 15% by mass with respect to mCP in the region adjacent to the hole transport layer at the beginning of vapor deposition in the 15 nm region on the side adjacent to the hole transport layer of the light emitting layer. The deposition rate was adjusted to be 0% by mass. The mixing ratio of each component was continuously changed between these regions.

(Production of Comparative Organic EL Element 1)
In the organic EL device 1 of the present invention, the light emitting layer was changed to the following.
Light-emitting layer: Four-element deposition of mCP, electron-transporting light-emitting material B1, light-emitting material R1 having a low triplet energy level, and light-emitting material G1 having a low triplet energy level was performed. Throughout the entire light emitting layer, the co-evaporation ratios of the electron transporting light emitting material B1, the light emitting material G1, and the light emitting material R1 with respect to mCP were 15% by mass, 4% by mass, and 1.5% by mass, respectively. . The thickness of the light emitting layer was 60 nm.

(Production of Comparative Organic EL Element 2)
In the organic EL device 1 of the present invention, the light emitting layer was changed to the following.
Light-emitting layer: Four-element deposition of mCP, electron-transporting light-emitting material B1, light-emitting material R1 having a low triplet energy level, and light-emitting material G1 having a low triplet energy level was performed. The co-evaporation ratios of the electron-transporting light-emitting material B1, the light-emitting material G1, and the light-emitting material R1 with respect to mCP are 15% by mass, 0.15% by mass, and 0.1% by mass, respectively. there were. The thickness of the light emitting layer was 60 nm.

(Production of comparative organic EL element 3)
In the organic EL device 1 of the present invention, the light emitting layer was changed to the following two layers.
Light emitting layer 1: 15% by mass of the electron transporting light emitting material B1 was co-deposited with respect to mCP and mCP. The thickness was 30 nm.
Light emitting layer 2: The light emitting material G1 was vapor-deposited at a co-evaporation ratio of 10% by mass and the light emitting material R1 was 10% by mass with respect to mCP and mCP. The thickness was 30 nm.

  The structures of the compounds used in the examples are shown below.

2. Performance Evaluation Results External quantum efficiency and driving durability of the obtained comparative organic EL device and the organic EL device of the present invention were measured under the same conditions by the following means.

<Drive voltage>
A DC voltage reaching a luminance of 1000 cd / m ² was defined as a driving voltage.

<Method for measuring external quantum efficiency>
A direct current voltage was applied to the light emitting element using the source measure unit 2400 made by KEITHLEY, and the light emitting element thus produced was emitted with a luminance of 1000 cd / m ² . The emission spectrum and the amount of light were measured using a luminance meter SR-3 manufactured by Topcon Corporation, and the external quantum efficiency was calculated from the emission spectrum, the amount of light and the current at the time of measurement.

The obtained results are shown in Table 1.
The elements 1 and 2 of the present invention sufficiently emitted blue, green, and red light, and exhibited white light emission with high luminance. The driving voltages were as low as 8.1 V and 7.9 V, and high external quantum yields of 12.4% and 12.6% were exhibited.
On the other hand, the comparative element 1 had a weak blue emission and a yellow to brown emission color composed of green and red emission. The comparative element 2 emitted white light but had a very low light emission efficiency. The comparative element 3 has white light emission and high light emission efficiency, but the drive voltage increased.

Example 2
In Example 1, the green light-emitting material and the red light-emitting material are changed to the materials shown in Table 2 as the electron-transporting light-emitting material of the light-emitting layer and the light-emitting material having a low triplet energy level. Thus, an element of the present invention was produced.
The triplet energy levels were 65 kcal / mol for the electron transporting luminescent material B2, 60 kcal / mol for the luminescent material G2, 58 kcal / mol for the luminescent material G3, and 47 kcal / mol for the luminescent material R2. Therefore, the triplet energy levels of the light emitting materials G1 to G3 and the light emitting materials R1 to R2 are 5 kcal / mol to 18 kcal / mol lower than the electron transporting light emitting materials B1 and B2.

  The results of evaluating the performance in the same manner as in Example 1 are shown in Table 2. Each of the devices of the present invention had a low driving voltage and high external quantum efficiency, like the device of the present invention of Example 1.

It is the schematic which shows the layer structure of this invention organic EL element.

Claims (7)

A pair of electrodes consisting of an anode and a cathode; at least a light emitting layer disposed between the pair of electrodes; a hole transport layer disposed between the anode and the light emitting layer; and the cathode and the light emitting layer. Having an electron transport layer disposed between
1) The light emitting layer contains an electron transporting light emitting material and a hole transporting host material,
2) The concentration of the electron-transporting light-emitting material in the light-emitting layer gradually decreases from the cathode side to the anode side of the light-emitting layer,
3) In the region where the concentration of the electron-transporting light-emitting material in the light-emitting layer is reduced and in a region having a thickness of 1/100 or more and 1/2 or less of the total thickness of the light-emitting layer, triple the electron transporting light-emitting material An organic electroluminescent device comprising at least one light emitting material having a low term energy level.   2. The electron-transporting light-emitting material is a blue light-emitting material, and the light-emitting material having a triplet energy level lower than that of the electron-transporting light-emitting material is at least one of a green light-emitting material and a red light-emitting material. Organic electroluminescent device.   The organic electroluminescent element according to claim 2, wherein the light emitting material having a triplet energy level lower than that of the electron transporting light emitting material is a green light emitting material and a red light emitting material.   The concentration of the light emitting material having a lower triplet energy level than the electron transporting light emitting material is a region containing a light emitting material having a lower triplet energy level than the electron transporting light emitting material in the light emitting layer. The organic electroluminescent element according to any one of claims 1 to 3, which is constant in a direction.   The concentration of the light emitting material having a triplet energy level lower than that of the electron transporting light emitting material is a region containing a light emitting material having a triplet energy level lower than that of the electron transporting light emitting material in the light emitting layer. The organic electroluminescent element according to any one of claims 1 to 3, which gradually decreases from the anode side to the cathode side of the light emitting layer.   The concentration of the hole transporting host material in the light emitting layer is gradually decreased from the anode side to the cathode side of the light emitting layer. Organic electroluminescent element.   The organic electroluminescent element according to any one of claims 1 to 6, wherein the electron-transporting luminescent material is a metal complex having platinum as a central metal.