JP2008108710A - Organic luminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element having high external quantum efficiency. <P>SOLUTION: In this electroluminescent element, a luminescent layer is held between a pair of electrodes, the luminescent layer is divided into at least three layers in its thickness direction. The electroluminescent element has at least two intermediate layers containing electron block materials between the divided luminescent layers, the electron block ability of the intermediate layer is the highest in the layer closer to an anode, and is the lowest in the layer closer to a cathode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic light emitting device having improved external quantum efficiency. In particular, the present invention relates to an organic light emitting device that can be effectively used for a surface light source such as a full color display, a backlight, and an illumination light source, and a light source array such as a printer.

  An organic light emitting element (hereinafter abbreviated as an organic EL element) is composed of a light emitting layer or a plurality of organic functional layers including a light emitting layer, and a counter electrode sandwiching these layers. In the organic EL element, electrons injected from the cathode and holes injected from the anode are recombined in the light-emitting layer, and the generated light is emitted from at least one of the excitons and other excitons. It is an element for obtaining light emission utilizing light emission from molecular excitons.

  Until now, organic EL elements have been developed with greatly improved brightness and element efficiency by using a laminated structure with separated functions. For example, a two-layer stacked device in which a hole transport layer and a light-emitting / electron transport layer are stacked, a three-layer stacked device in which a hole transport layer, a light-emitting layer, and an electron transport layer are stacked, a hole transport layer, a light-emitting layer, and a hole blocking layer A four-layer stacked element in which a layer and an electron transport layer are stacked is often used (for example, see Non-Patent Document 1).

  However, many problems still remain in practical use of organic EL elements. The first is to achieve high external quantum efficiency, and the second is to achieve high driving durability.

  For example, an interface layer of 0.1 nm to 5 nm is provided as a barrier layer between the light-emitting layer and the hole transport layer, and attempts are made to increase the external quantum efficiency by adjusting the movement balance of holes and electrons by slowing the movement of holes. Has been proposed (see, for example, Patent Document 1). However, with this means, since the movement of the carrier as a whole is reduced, the luminance is lowered, the drive voltage is increased, and the dwell time in the element of the carrier is increased, so that there is a concern that the drive durability is lowered.

  Further, a configuration in which one light emitting unit is laminated in multiple layers is known. For example, the structure which isolate | separated the light emission unit of the some organic light emitting element by the insulating layer, and has arrange | positioned the electrode which each faces each light emission unit is disclosed (for example, refer patent document 2). However, in this configuration, since the insulating layer and the electrode between the light emitting units hinder the extraction of the light emission, the light emission from each light emitting unit cannot substantially be utilized sufficiently. In addition, it is not a means for improving the low external quantum efficiency inherent to each light emitting unit.

  In addition, a configuration in which a single light emitting unit including a light emitting layer called a multiphoton and a functional layer is stacked in multiple layers is known. The multi-photon organic EL element is one in which a plurality of light emitting layers are separated from each other by an electrically insulating charge generation layer (see, for example, Patent Document 3). However, even in this configuration, a plurality of light emitting units are simply stacked, and it is not a means for improving the low external quantum efficiency inherent to each light emitting unit.

To achieve both high external quantum efficiency and high driving durability is an extremely important issue in designing a practically useful organic EL device, and has always been a demand for improvement.
Science, 267, 3, 1995, p. 1332 JP 2003-123984 A JP-A-6-310275 JP 2003-45676 A

  An object of the present invention is to provide an organic EL device having improved external quantum efficiency and driving durability.

It has been found that the above-mentioned problems of the present invention can be solved by the following means.
<1> An organic electroluminescent device comprising at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided into at least three layers in the thickness direction, and an electron block material is contained between the divided light emitting layers An organic light emitting device comprising at least two intermediate layers, wherein the intermediate layer has the largest electron blocking ability near the anode and the smallest layer near the cathode. <2> An organic electroluminescent device comprising at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided into at least three layers in the thickness direction, and a hole blocking material is contained between the divided light emitting layers An organic light emitting device comprising at least two intermediate layers, wherein the intermediate layer has the smallest hole blocking ability near the anode and the smallest layer near the cathode.
<3> The organic light-emitting device according to <1>, wherein Ea (electron affinity) of the electron block material is the smallest in the layer close to the anode and the largest in the layer close to the cathode.
<4> The organic light-emitting device according to <2>, wherein the hole block material has a minimum Ip (ionization potential) in a layer close to the anode and a maximum in a layer close to the cathode.
<5> The organic light-emitting device according to <1>, wherein the concentration of the electron block material in the intermediate layer is highest in a layer close to the anode and lowest in a layer close to the cathode.
<6> The organic light-emitting device according to <2>, wherein the concentration of the hole blocking material in the intermediate layer is lowest in a layer close to the anode and highest in a layer close to the cathode.
<7> The organic light-emitting device according to <1>, wherein the electron mobility of the intermediate layer is lowest in a layer close to the anode and highest in a layer close to the cathode.
<8> The organic light-emitting device according to <2>, wherein the hole mobility of the intermediate layer is highest in a layer close to the anode and lowest in a layer close to the cathode.
<9> The organic light-emitting element according to <1>, wherein the intermediate layer is thickest in a layer close to the anode and thinnest in a layer close to the cathode.
<10> The organic light-emitting element according to <2>, wherein the intermediate layer is thinnest in a layer close to the anode and thickest in a layer close to the cathode.
<11> The organic light-emitting device according to any one of <1> to <10>, wherein the light-emitting material of the light-emitting layer is a phosphorescent material.
<12> The organic light-emitting device according to any one of <1> to <11>, wherein the intermediate layer contains a light-emitting material.
<13> The organic light-emitting device according to <12>, wherein the light-emitting material contained in the intermediate layer is a phosphorescent material.

  According to the present invention, an organic EL device with dramatically improved external quantum efficiency is provided. Furthermore, an organic EL device with improved driving durability as well as improved external quantum efficiency is provided.

The organic EL device of the present invention is an organic electroluminescent device comprising at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided into at least three layers in the thickness direction, and between the divided light emitting layers. It has at least two intermediate layers containing an electron blocking material, and the intermediate layer has the largest electron blocking ability near the anode and the smallest layer near the cathode. The electron blocking ability of the intermediate layer can be adjusted by using materials having different Ea values from the electron blocking material.
The electron blocking ability of the intermediate layer can also be adjusted by changing the concentration of the electron blocking material in each layer. Alternatively, the electron blocking ability of the intermediate layer can be adjusted by changing the thickness of each layer.
Preferably, the electron mobility of the intermediate layer is the lowest in the layer close to the anode and the highest in the layer close to the cathode. In another aspect of the organic EL device of the present invention, the hole blocking ability of the intermediate layer is the smallest in the layer close to the anode, and the layer close to the cathode has the largest hole blocking ability.
The hole blocking ability of the intermediate layer can be adjusted by using materials having different Ip values.
The hole blocking ability of the intermediate layer can also be adjusted by changing the concentration of the hole blocking material in each layer. Alternatively, the hole blocking ability of the intermediate layer can be adjusted by changing the thickness of each layer.
Preferably, the hole mobility of the intermediate layer is the highest in the layer close to the anode and the lowest in the layer close to the cathode.

That is, the organic EL device of the present invention has a multi-layered structure in which two or more intermediate layers are sandwiched between light emitting layers subdivided into three or more thin layers in the thickness direction, and the electrons of the two or more intermediate layers. Block ability or hole block ability is different from each other.
When the number of intermediate layers in the present application is three or more, the above thickness condition may be satisfied when any three of them are selected. For example, when an intermediate layer containing an electron blocking material is used, the intermediate layer closest to the anode has the highest electron blocking ability, and the intermediate layer closest to the cathode has the lowest electronic blocking ability. The electron blocking ability of the intermediate layer existing in the intermediate layer may be between those of the intermediate layer.
Further, the electron blocking ability of the plurality of intermediate layers between the intermediate layer closest to the anode and the intermediate layer closest to the cathode preferably increases in order from the cathode side toward the anode side.

As a result of analyzing the cause of the low external quantum efficiency in the light-emitting element, the present inventors have found that main light emission occurs near a very limited interface between the light-emitting layer and the adjacent layer, and the charge is limited to this limit. As a result of localization at the interface, it was estimated that the deterioration was caused gradually until recombination.
As a result of earnest search for improvement means, the present inventors subdivided the light-emitting layer into a plurality of thin light-emitting layers in the thickness direction, arranged an intermediate layer having charge blocking ability between each of the subdivided light-emitting layers, and If the layer has an electron blocking ability, the intermediate layer close to the anode has a large electron blocking ability, the intermediate layer close to the cathode is small, and if the layer has a hole blocking ability, the intermediate blocking layer close to the anode is small. It was found that the intermediate layer close to the cathode can be improved by increasing the size. That is, the distance between the regions where electrons and holes are localized is shortened, the recombination speed is increased, the leakage of carriers from each light emitting layer is improved, and the light emission efficiency is improved. In addition, the light-emitting unit of each thin layer is connected to an intermediate layer having a charge blocking ability, and the light generated by each element can be efficiently extracted outside without greatly increasing the driving resistance. .
Preferably, by further containing a light emitting material in the intermediate layer, the layer can emit light, and light emission with higher luminance can be obtained.
Preferably, the light emitting material contained in the light emitting layer is a phosphorescent material. Further preferably, the light emitting material contained in the intermediate layer is a phosphorescent material.

1. Light emitting layer The organic EL device of the present invention is an organic EL device having at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided in the thickness direction, and an intermediate layer is formed between the divided light emitting layers. Have The intermediate layer functions as a charge blocking layer. In the present application, the light emitting layer subdivided in the thickness direction is hereinafter referred to as “unit light emitting layer”.
The thickness of the unit light emitting layer in the present invention is preferably 2 nm to 50 nm, more preferably 2 nm to 40 nm, and still more preferably 2 nm to 30 nm.
The light emitting layer in the present invention is preferably subdivided into 3 or more and 50 or less, more preferably 4 or more and 30 or less in the thickness direction.
The unit light emitting layers in the present invention are connected by an intermediate layer. Preferably, it has at least four unit light emitting layers in the thickness direction and three intermediate layers connecting them.
The intermediate layer in the present invention preferably contains a light emitting material. The charge blocking material contains a hole blocking material or an electron blocking material.
Preferably, the intermediate layer contains a phosphorescent material as a light emitting material.

(Middle layer)
The intermediate layer in the present invention will be described in more detail.
The intermediate layer in the present invention functions as a charge blocking layer.
The intermediate layer functioning as a charge blocking layer in the present invention is a hole that suppresses electrons transported from the cathode side to the light emitting layer side from passing through the anode side or is transported from the anode side to the light emitting layer. However, it is a layer having a function of suppressing the passage to the cathode side, and is not a layer for completely stopping carrier movement.
The intermediate layer in the present invention preferably further contains a light emitting material.

1) Electron Block Material in Intermediate Layer The electron block material in the intermediate layer used in the present invention is a material having an Ea value in the range of 1.5 eV or more and 3.0 eV or less. More preferably, it is the range of 2.0 eV or more and 2.8 eV or less.
As the electron blocking material in the intermediate layer in the present invention, the smallest material among the materials used for Ea is used for the layer close to the anode, and the largest material used for Ea is used for the layer near the cathode. Is preferred.
The electron blocking ability of the intermediate layer in the present invention is such that the smaller the Ea value of the electron blocking material in the layer, the higher the electron blocking material concentration in the layer, the thicker the layer, the smaller the electron mobility in the layer, large.

Examples of electron block materials that satisfy these conditions include N, N′-dicarbazolyl-3,5-benzene (hereinafter referred to as “mCP”) and N, N′-dicarbazolyl-4,4′-biphenyl. A hole transporting material such as a carbazole derivative (hereinafter referred to as “CBP”), an azacarbazole derivative, an indole derivative, an azaindole derivative, a pyrene derivative, a pyrrole derivative, a triazole derivative, or an oxazole derivative is preferable. Particularly preferred are hole transport materials such as carbazole derivatives and pyrene derivatives such as mCP and CBP, but the material is not limited to these as long as it can be controlled so that electrons can be appropriately introduced into the light emitting layer.
Specific examples of the electron block material include, but are not limited to, the following hole transport materials.

2) Hole block material in the intermediate layer The hole block material in the intermediate layer used in the present invention is a material having an Ip value in the range of 5.0 eV to 8.0 eV. More preferably, it is the range of 5.5 eV or more and 7.0 eV or less.
As the hole blocking material in the intermediate layer in the present invention, the smallest material among Ip is used for the layer near the anode, and the largest material among the Ip is used for the layer near the cathode. Is preferred.
The hole blocking ability of the intermediate layer in the present invention is such that the larger the Ip value of the hole blocking material in the layer, the higher the concentration of the hole blocking material in the layer, the thicker the layer, and the smaller the hole mobility in the layer. ,large.

Examples of hole block materials that satisfy these conditions include aluminum complexes such as Aluminum (III) bis (2-methyl-8-quinolinato) -4-phenylphenolate (hereinafter referred to as “BAlq”), triazole derivatives, 2 , 9-dimethyl-4,7-diphenyl-1,10-phenanthrolin (hereinafter referred to as “BCP”), and electron transport materials such as imidazopyridine derivatives are preferred. An electron transport material of an imidazopyridine derivative is particularly preferable, but the material is not limited to these as long as the material can be controlled so as to appropriately enter holes in the light emitting layer.
Specific examples of the hole block material include, but are not limited to, the following electron transport materials.

3) Structure of intermediate layer The ratio of the intermediate layer in the present invention is generally 5% to 90% by volume for the charge blocking material, 0% to 30% by volume for the light emitting material, and 0% for the charge transporting material. % To 95% by volume (the total of the light emitting material and the charge transporting material is 10% to 95% by volume), the charge blocking material is 10% to 80% by volume, and the light emitting material is 0% to 30% by volume. %, The charge transport material is preferably 0% by volume to 90% by volume (the total of the light emitting material and the charge transport material is 20% by volume to 80% by volume), the charge blocking material is 30% by volume to 70% by volume, and the light emission More preferably, the material is 0% by volume to 30% by volume, and the charge transporting material is 0% by volume to 70% by volume (the total of the light emitting material and the charge transporting material is 30% by volume to 70% by volume).
If the charge blocking material exceeds 90% by volume, there is a problem that the movement of carriers is largely inhibited and the driving voltage is increased, which is not preferable. If the charge blocking material is less than 5% by volume, there is a problem that the effect of improving the external quantum efficiency does not appear because the charge blocking performance is almost lost.

4) Thickness The thickness of the intermediate layer in the present invention is generally preferably 3 nm to 100 nm and more preferably 5 nm to 50 nm in order to suppress an increase in driving voltage.
If the thickness exceeds 100 nm, it is not preferable because the movement of carriers is greatly hindered and the drive voltage increases. If the thickness is less than 3 nm, the formation of the layer becomes insufficient, and the intermediate layer loses the function as the charge blocking layer partially or entirely, which is not preferable.
5) Number of layers The number of intermediate layers in the present invention is preferably 2 to 49, more preferably 3 to 29, and still more preferably 4 to 14.

(Split layer)
The division of the light emitting layer used in the present invention will be described. The composition of each light emitting layer will be described in detail in the description of the light emitting layer described later.
In the structure of the present invention, the light emitting layer is subdivided into 3 or more unit light emitting layers in the thickness direction, preferably 4 or more and 30 or less, more preferably 5 or more and 15 or less unit light emitting layers. Subdivided. When the intermediate layer contains an electron block material, the thickness of the unit light emitting layer decreases in order from the cathode side toward the anode side. On the other hand, when the intermediate layer contains a hole blocking material, the thickness of the unit light emitting layer is gradually decreased from the anode side toward the cathode side.
In the present invention, the unit light emitting layer is a very thin layer having a thickness of 2 nm to 50 nm, more preferably 2 nm to 40 nm, and further preferably 2 nm to 30 nm.
If the thickness of the unit light emitting layer in the present invention is less than 2 nm, sufficient light emission cannot be obtained, and if it exceeds 50 nm, the effect of subdividing the light emitting layer cannot be sufficiently exhibited.

  The multilayer light-emitting layer in the present invention may be a light-emitting layer having a material structure that emits light having the same wavelength or a light-emitting layer having a material structure that emits light having different wavelengths. For example, if the light-emitting layer has a material structure that emits light of the same wavelength, highly efficient light emission of the same wavelength can be extracted. On the other hand, when light having different wavelengths is emitted, light having a desired color tone can be extracted or white light can be obtained depending on the combination of the respective emission wavelengths.

(Divided layer structure)
The layer structure will be described with reference to the drawings. The layer configuration shown in FIGS. 1 to 5 shows only the layers necessary for explaining the intention of the present application. Elements that are necessary for the light emitting element but are not directly necessary for the description of the present application are omitted.
FIG. 1 is a schematic view of a layer structure of a comparative light emitting device. An anode electrode 1 made of ITO or the like is provided on a substrate (not shown), and a hole injection layer 2, a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, an electron injection layer 6 and aluminum are sequentially formed thereon. A cathode 7 made of a metal such as is disposed.
FIG. 2 is a schematic diagram of a layer structure of another comparative light-emitting element, in which the light-emitting layer is divided into three layers of a first light-emitting layer 4a, a second light-emitting layer 4b, and a third light-emitting layer 4c, with an intermediate layer 8a interposed therebetween. And 8b. The total thickness including the three light emitting layers and the two intermediate layers in FIG. 2 is substantially equal to the thickness of the light emitting layer 4 in FIG.
FIG. 3 shows an example of the light emitting device of the present application, in which the light emitting layer is divided into three parts, a first light emitting layer 4a, a second light emitting layer 4b, and a third light emitting layer 4c, and intermediate layers 8a and 8b are arranged therebetween. It is. The intermediate layer 8a contains an electron block material having a large electron blocking ability, and the intermediate layer 8b contains an electron block material having a small electronic blocking ability. The total thickness including the three light emitting layers and the two intermediate layers in FIG. 3 is substantially equal to the light emitting layer 4 in FIG.
FIG. 4 shows another example of the layer structure of the present application. The light emitting layer is divided into 4a, 4b, 4c, and 4d, and intermediate layers 8a, 8b, and 8c are arranged between the divided light emitting layers, respectively. The intermediate layer 8a contains a hole blocking material with the smallest hole blocking ability, the intermediate layer 8c contains a hole blocking material with the largest hole blocking ability, and the intermediate layer 8b has a hole blocking ability with an intermediate hole blocking ability. Contains material. The total thickness including the four divided light emitting layers and three intermediate layers in FIG. 4 is substantially the same as that of the light emitting layer 4 in FIG.
FIG. 5 shows another example of the layer structure of the present application. The light emitting layer is divided into 4a, 4b, 4c, and 4d, and intermediate layers 8a, 8b, and 8c are arranged between the divided light emitting layers, respectively. The intermediate layers 8a, 8b, and 8c contain an electron block material, with the intermediate layer 8a having the thickest thickness, 8c having the thinnest thickness, and the thickness of 8b being between them. The total thickness including the four divided light emitting layers and three intermediate layers in FIG. 5 is substantially the same as that of the light emitting layer 4 in FIG.

2. Organic EL element As a form of lamination | stacking of the organic compound layer in this invention, the aspect laminated | stacked in order of the hole transport layer, the light emitting layer, and the electron carrying layer from the anode side is preferable. Further, at least one of a hole injection layer between the hole transport layer and the anode and an electron transporting intermediate layer between the light emitting layer and the electron transport layer may be provided. 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 (a hole injection layer and a hole transport layer may serve both), a hole A mode having a transportable intermediate layer, a light emitting layer, an intermediate layer, an electron transport layer, and an electron injection layer (the electron transport layer and the electron injection layer may serve as both), (2) a hole injection layer, a hole transport layer (hole Injection layer and hole transport layer), light emitting layer, intermediate layer, electron transport intermediate layer, electron transport layer, and electron injection layer (electron transport layer and electron injection layer may also serve as) Embodiment, (3) hole injection layer, hole transport layer (hole injection layer and hole transport layer may be combined), hole transport intermediate layer, light emitting layer, intermediate layer, electron transport intermediate layer, electron transport layer, and Electron injection layer (also serves as electron transport layer and electron injection layer) Are embodiments having also good).

The hole transporting intermediate layer preferably has at least one of a function of promoting 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 exhibit the functions such as 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 adjacent to the light emitting layer. It is preferable.
Each layer may be divided into a plurality of secondary layers.

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

(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. This layer has a function of emitting light by providing a recombination field of electrons.
The light emitting layer in the present invention contains at least one light emitting dopant and at least one host compound.
It is preferable that each layer of the light emitting layer contains at least one light emitting dopant and at least one host compound.

As the luminescent dopant and host compound contained in the light emitting layer in the present invention, light emission from triplet excitons can be obtained by combining a fluorescent luminescent dopant and host compound that can emit light (fluorescence) from singlet excitons ( It may be a combination of a phosphorescent dopant capable of obtaining (phosphorescence) and a host compound.
The light emitting layer in the present invention can contain two or more kinds of light emitting dopants in order to improve color purity and to broaden the light emission wavelength region.

As the luminescent dopant in the present invention, any of phosphorescent luminescent materials and fluorescent luminescent materials can be used as the dopant.
The luminescent dopant in the present invention further includes 1.2 eV> | host Ip-luminescent dopant ΔIp |> 0.2 eV and 1.2 eV> | host Ea-luminescent dopant with the host compound. A dopant satisfying at least one relationship of Ea |> 0.2 eV is preferable from the viewpoint of driving durability.

《Phosphorescent dopant》
In general, examples of phosphorescent materials include complexes containing transition metal atoms or lanthanoid atoms.
The transition metal atom is preferably ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum, more preferably rhenium, iridium, and platinum, and more preferably iridium, 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 ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, or phenanthroline), carbene ligands, diketone ligands (eg, acetylacetone), carboxylic acid ligands (eg, acetic acid) Ligands, etc.), alcoholate ligands (eg phenolate ligands, etc.), carbon monoxide ligands, isonitrile ligands, cyano ligands, more preferably nitrogen-containing heterocyclic ligands It is.
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 Laid-Open 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, JP2002-234894A, JP2001247478, JP2001298470, JP2002-173684, JP2002-2036 8, 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 luminescent dopant》
Examples of fluorescent light-emitting materials include benzoxazole derivatives, benzimidazole derivatives, benzothiazole derivatives, styrylbenzene derivatives, polyphenyl derivatives, diphenylbutadiene derivatives, tetraphenylbutadiene derivatives, naphthalimide derivatives, coumarin derivatives, perylene derivatives, perinone derivatives, oxalates. Diazole derivatives, aldazine derivatives, pyralidine derivatives, cyclopentadiene derivatives, bisstyrylanthracene derivatives, quinacridone derivatives, pyrrolopyridine derivatives, thiadiazolopyridine derivatives, styrylamine derivatives, aromatic dimethylidene compounds, 8-quinolinol derivative metal complexes and rare earths Various metal complexes represented by complexes, polythiophene derivatives, polyphenylene derivatives, polyphenylene vinylene derivatives, and polymers Polymeric compounds such as fluorene derivatives. These can be used alone or in combination of two or more.

  Among these, specific examples of the luminescent dopant include the following, but are not limited thereto.

  Among these, as the luminescent dopant used in the present invention, D-2 to D-19 and D-24 to D-31 are preferable from the viewpoint of external quantum efficiency and durability, and D-2 to D-8, D -12, D-14 to D-19, D-24 to D-27, or D-28 to D-31 are more preferable, and D-24 to D-27, or D-28 to D-31 are still more preferable. .

  The light-emitting dopant in the light-emitting layer is generally contained in an amount of 0.1% to 30% by volume with respect to the total compound volume forming the light-emitting layer in the light-emitting layer, but from the viewpoint of durability and external quantum efficiency. Is preferably contained in an amount of 2 to 30% by volume, more preferably 5 to 30% by volume.

(Host material)
As the host material used in the present invention, a hole transporting host material having excellent hole transportability (may be described as a hole transportable host) and an electron transporting host compound having excellent electron transportability (described as an electron transporting host) May be used).

《Hall transportable host》
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. It is more preferably 2 eV or less, and further preferably 5.6 eV or more and 6.0 eV or less. 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 transportable host include the following materials.
Pyrrole, carbazole, azacarbazole, indole, azaindole, pyrazole, 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 oligomer thiophene oligomers, conductive polymer oligomers such as polythiophene, organic Examples thereof include silane, carbon film, and derivatives thereof.

Among them, indole derivatives, carbazole derivatives, azaindole derivatives, azacarbazole derivatives, aromatic tertiary amine compounds, and thiophene derivatives are preferable, and in particular, a plurality of carbazole skeleton indole skeletons and / or aromatic tertiary amine skeletons are included in the molecule. Those having one are preferred.
Specific examples of such a hole transporting host include, but are not limited to, the following compounds.

《Electron transporting host》
The electron transporting host in the light emitting layer 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. More preferably, it is 0.4 eV or less, and further preferably 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 pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, and diphenylquinone. , Thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine-substituted aromatic compounds, heterocyclic tetracarboxylic anhydrides such as naphthaleneperylene, phthalocyanines, and their derivatives (forms condensed rings with other rings) Or metal complexes of 8-quinolinol derivatives, metal phthalocyanines, various metal complexes typified by metal complexes having benzoxazole or benzothiazole as a ligand, and the like.

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, pyridine ligand, bipyridyl ligand, terpyridine ligand, etc.), a hydroxyphenylazole ligand (for example, hydroxyphenylbenzimidazole coordination). And a hydroxyphenyl benzoxazole ligand, a hydroxyphenyl imidazole ligand, a hydroxyphenylimidazopyridine ligand, etc.), an alkoxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 carbon atom). To 20, particularly preferably 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy, 2-ethylhexyloxy), aryloxy ligands (preferably 6 to 30 carbon atoms, more preferably 6-20 carbon atoms, particularly preferably 6-12 carbon atoms, for example phenyl Carboxymethyl, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl oxy, and 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 are described in, 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, JP-A No. 2004-327313, and the like. The compound of this is mentioned.

  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.

  In the light-emitting layer of the present invention, when a phosphorescent dopant is used as the luminescent dopant, the lowest triplet excitation energy T1 (D) of the phosphorescent dopant and the lowest excited triplet energy of the plurality of host compounds It is preferable in terms of color purity, external quantum efficiency, and driving durability that the above T1 (H) min satisfies the relationship of T1 (H) min> T1 (D).

  Further, the content of the host compound in the present invention is not particularly limited, but from the viewpoint of external quantum efficiency and driving voltage, it is 70 vol% or more and 95 vol% or less with respect to the total compound volume forming the light emitting layer. It is preferable that

(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 a dopant which becomes a carrier for hole movement. As a dopant 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 includes ferric chloride, aluminum chloride, Lewis acid compounds such as 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, or a trifluoromethyl group 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, 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 dopants may be used alone or in combination of two or more.
The amount of the electron-accepting dopant used varies depending on the type of material, but is preferably 0.01% by volume to 50% by volume with respect to the hole injection material, and preferably 0.05% by volume to 20% by volume. More preferably, it is particularly preferably 0.1 volume% to 10 volume%. When the amount used is less than 0.01% by volume with respect to the hole injection material, the effect of the present invention is insufficient because it is insufficient, and when it exceeds 50% by volume, the hole injection capability is impaired.

  When a hole injection layer contains an acceptor, it is preferable that a hole transport layer does not contain an acceptor substantially.

  Specific examples of materials for the hole injection layer and the hole transport layer include pyrrole derivatives, carbazole derivatives, azacarbazole derivatives, indole derivatives, azaindole derivatives, pyrazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, and 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, porphyrins A layer containing a 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, external quantum efficiency improvement, and durability improvement. It is more preferably ˜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.

When the carrier transport layer adjacent to the light-emitting layer is a hole transport layer, the Ip (HTL) of the hole transport layer is smaller than the Ip (D) of the dopant contained in the light-emitting layer. Is preferable.
Ip (HTL) in the hole transport layer can be measured by a method of measuring Ip described later.

The carrier mobility in the hole transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point of efficiency, it is preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, preferably 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ or more. ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-3 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less are particularly preferable.
As the carrier mobility, a value measured by a method similar to the method for measuring the carrier mobility of the light emitting layer is adopted.
The carrier mobility of the hole transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoints of driving durability and external quantum efficiency.

(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 dopant introduced into the electron injecting layer or the electron transporting layer only needs to have an electron donating property and a property of reducing an organic compound, such as an alkali metal such as Li or an alkaline earth metal 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 dopants may be used alone or in combination of two or more.
The amount of electron-donating dopant used varies depending on the type of material, but is preferably 0.1% by volume to 99% by volume, and 1.0% by volume to 80% by volume with respect to the electron transport layer material. Is more preferable, and it is particularly preferably 2.0% by volume to 70% by volume. When the amount used is less than 0.1% by volume 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 volume, 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 injection layer and the electron transport layer are not particularly limited, but are preferably 1 nm to 5 μm in thickness from the viewpoint of lowering driving voltage, improving external quantum 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.
When the carrier transport layer adjacent to the light emitting layer is an electron transport layer, the Ea (ETL) of the electron transport layer is greater than the dopant Ea (D) contained in the light emitting layer. Is preferable.

As the Ea (ETL), a value measured by the same method as the Ea measuring method described later is used.
The carrier mobility in the electron transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point of efficiency, it is preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, preferably 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ or more. ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-3 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less are particularly preferable.
The carrier mobility of the electron transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoint of driving durability. The carrier mobility was performed in the same manner as the hole transport layer measurement method.
In the carrier mobility of the light-emitting element in the present invention, the carrier mobility in the hole transport layer, the electron transport layer, and the light-emitting layer is (electron transport layer = hole transport layer)> light-emitting layer. This is preferable.

(Hall block 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 block 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 suppress an increase in 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, It can select suitably from well-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, or nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, polyaniline, polythiophene, and polypyrrole Organic conductive materials such as, 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 volume to 10% by volume 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 EL device of the present invention may be sealed 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 paraffins, liquid paraffins, fluorinated solvents such as perfluoroalkane, perfluoroamine, and perfluoroether, chlorinated solvents, and silicone oils. Can be mentioned.

3. Driving The organic EL device of the present invention emits light by applying a direct current (which may include an alternating current component if necessary) voltage (usually 2 to 15 volts) or a direct current between the anode and the cathode. Obtainable.
The driving durability of the organic EL element in the present invention can be measured by the time required to decrease to a certain luminance at a specific luminance. For example, KEITHLEY Seiso - Sumeja - using Unit 2400, a DC voltage was applied to the organic EL element to emit light, 1500 cd / ^{m 2} if green emission the initial luminance, blue 360 cd / ^{m 2} if the emission of A continuous driving test is performed under the conditions, and the time when the luminance becomes 80% of the initial luminance is set as the luminance decreasing time, and the luminance decreasing time can be obtained by comparing with the conventional light emitting element. This numerical value was used in the present invention. An important characteristic value of the organic EL element 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 EL 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, 20 ² near (preferably 100cd ^{/ m} 2 ~2000cd ^/ m when the device is driven at ° C., red emission if 500 cd / ^{m 2} of, 1500 cd / ^{m 2} if green emission, may be a value of the external quantum efficiency of blue 360 cd / ^{m 2} if emission).
In the present invention, a KEITHLEY source measure unit 2400 type is used to apply a DC constant voltage to an EL element to emit light, and the amount of light is measured using a Topcon luminance meter SR-3. A value obtained by calculating the quantum efficiency is used.

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

  Regarding the driving method of the organic EL device of the present invention, each of JP-A-2-148687, JP-A-6-301355, JP-A-5-290080, JP-A-7-134558, JP-A-8-234658, and JP-A-8-2441047. The driving methods described in the publications, Japanese Patent No. 2784615, US Pat. Nos. 5,828,429 and 6023308, and the like can be applied.

4). Applications Applications of the organic EL device of the present invention are not particularly limited, but can be applied to a wide range of fields such as mobile phone displays, personal digital assistants (PDAs), computer displays, automobile information displays, TV monitors, 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.

Example 1
1. Preparation of organic EL element (production of comparative organic EL element 1)
A 0.5 mm thick, 2.5 cm square ITO glass substrate (manufactured by Geomat Co., Ltd., surface resistance 10 Ω / □) is placed in a cleaning container, subjected to ultrasonic cleaning in 2-propanol, and then subjected to UV-ozone treatment for 30 minutes. went. 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: CuPc was deposited on ITO to a thickness of 10 nm.
Hole transport layer: α-NPD was deposited to a thickness of 10 nm on the hole injection layer.
Light-emitting layer: CBP and Ir (ppy) ₃ were co-deposited so that the volume ratio was 95: 5. The thickness of the light emitting layer was 90 nm.

Electron transport layer: BAlq was deposited on the light-emitting layer to a thickness of 10 nm.
Electron injection layer: Alq was deposited to a thickness of 20 nm on the electron transport layer.

  A patterned mask (a mask having a light emitting area of 2 mm × 2 mm) was placed thereon, and lithium fluoride was deposited by 1 nm at a deposition rate of 0.01 nm / second to form an electron injection layer. Further, metal aluminum was deposited to a thickness of 100 nm to form a cathode.

  The produced laminate is put in a glove box substituted with nitrogen gas, and sealed with a stainless steel sealing can and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba). Element 1 was produced.

(Production of Comparative Organic EL Element 1A)
In the comparative organic EL device 1, the light emitting layer was divided into three as shown below, and the following intermediate layers 1 and 2 were disposed as intermediate layers having the following conductive charge blocking ability between the unit light emitting layers. The light emitting layer 1 -intermediate layer 1 -light emitting layer 2 -intermediate layer 2 -light emitting layer 3 were arranged in order from the hole transport layer.

Light-emitting layer 1: A light-emitting layer having the same composition as Comparative Example 1 was deposited to a thickness of 20 nm.
Intermediate layer 1: <Example of an intermediate layer containing an electron block material>
An intermediate layer was formed such that the hole transport material B as the electron block material and Ir (ppy) ₃ were in a volume ratio of 95: 5.
The Ea value of the hole transport material B, which is an electron blocking material, is 2.5 eV, and the Ea value of CBP that mainly transports electrons in the light emitting layer is 2.7 eV. Out.
The thickness of the intermediate layer was 15 nm.
Light-emitting layer 2: A light-emitting layer having the same composition as that of the light-emitting layer 1 was deposited to a thickness of 20 nm.
Intermediate layer 2: Same as intermediate layer 1. The thickness of the intermediate layer was 15 nm.
Light-emitting layer 3: A light-emitting layer having the same composition as that of the light-emitting layer 1 was deposited to a thickness of 20 nm.

(Production of Comparative Organic EL Element 2)
In the comparative organic EL element 1, CBP used for the light emitting layer was replaced with an electron transport material C, and Ir (ppy) ₃ was replaced with Ir (btp) ₂ (acac), thereby producing a comparative organic EL element 2.
(Production of Comparative Organic EL Element 2A)
In the comparative organic EL element 1A, CBP used for the light emitting layers 1 to ₃ was replaced with the electron transport material A, and Ir (ppy) ₃ was replaced with Ir (btp) ₂ (acac). Further, the hole transport material B used for the intermediate layers 1 and ₂ was replaced with CBP, and Ir (ppy) ₃ was replaced with Ir (btp) ₂ (acac), thereby producing a comparative organic EL element 2A.

(Preparation of the organic EL device 1 of the present invention)
In the comparative organic EL device 1, the light emitting layer was divided into three as shown below, and the following intermediate layers 1 and 2 were disposed as the following conductive charge blocking layers between the unit light emitting layers. The light emitting layer 1 -intermediate layer 1 -light emitting layer 2 -intermediate layer 2 -light emitting layer 3 were arranged in order from the hole transport layer.
Light-emitting layer 1: A light-emitting layer having the same composition as Comparative Example 1 was deposited to a thickness of 25 nm.
Intermediate layer 1: <Example of an intermediate layer containing an electron block material>
An intermediate layer was formed so that the hole transport material C and Ir (ppy) ₃ were in a volume ratio of 95: 5.
The film thickness of the intermediate layer was 5 nm.
Light-emitting layer 2: A light-emitting layer having the same composition as Comparative Example 1 was deposited to a thickness of 25 nm.
Intermediate layer 2: The film thickness was 10 nm with the same composition as the intermediate layer 1.
Light emitting layer 3: A light emitting layer having the same composition as Comparative Example 1 was deposited to a film thickness of 25 nm.

2. Performance Evaluation Results External quantum efficiency was measured for the obtained comparative organic EL elements 1 and 1A and the organic EL element 1 of the present invention under the same conditions by the following means. Further, the luminance reduction time was measured by the means described above.

<Method for measuring external quantum efficiency>
The produced light emitting element was made to emit light by applying a DC voltage to the light emitting element using a source measure unit type 2400 manufactured by KEITHLEY. 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.

  As a result, the external quantum efficiency of the comparative organic EL element 1 was 9.8% and the external quantum efficiency of the comparative organic EL element 1A was 10.4%. However, the external quantum efficiency of the organic EL element 1 of the present invention was 12%. 8%. In addition, the luminance reduction time of the comparative organic EL element 1 was 48 hours and the luminance reduction time of the comparative organic EL element 1A was 51 hours, but the luminance reduction time of the organic EL element 1 of the present invention was 80 hours. Although the total thickness of the two intermediate layers and the three light-emitting layers is equivalent to the light-emitting layer thickness of 90 nm of the comparative organic EL device, high external quantum efficiency and driving durability were exhibited at the same time. Met.

Example 2
1. Production of Organic EL Element 2 In the comparative organic EL element 1, the light emitting layer was divided into the following four unit light emitting layers, and the following intermediate layers 1 to 3 were arranged between the unit light emitting layers. The light emitting layer 11-the intermediate layer 11-the light emitting layer 12-the intermediate layer 12-the light emitting layer 13-the intermediate layer 13-the light emitting layer 14 are arranged in this order from the hole transport layer.
Unit light-emitting layers 11 to 14: vapor-deposited so as to have the same composition as that of the light-emitting layer of the comparative organic EL element 1 and a thickness of 15 nm.
Intermediate layers 11, 12, 13: <Example including hole block material>
An intermediate layer was formed so that the electron transport material B and Ir (ppy) ₃ were in a volume ratio of 95: 5.
The thickness of the intermediate layer 11: 5 nm
The thickness of the intermediate layer 12: 10 nm
The thickness of the intermediate layer 13: 15 nm

  That is, the unit light-emitting layer 11 / intermediate layer 11 / unit light-emitting layer 12 / intermediate layer 12 / unit light-emitting layer 13 / intermediate layer 13 / unit light-emitting layer 14 are subdivided into a total of seven layers, and the total thickness is 90 nm. Yes, it is the same as the light emitting layer of the comparative organic EL element 1.

2. Performance Evaluation Results The obtained organic EL device 2 of the present invention was measured for external quantum efficiency and luminance reduction time in the same manner as in Example 1.

  As a result, the organic EL element 2 of the present invention showed an extremely high value of external quantum efficiency of 13.2% and luminance reduction time of 82 hours.

Example 3
1. Production of Organic EL Element 3 In Example 2, an intermediate layer having the following composition and having an electron blocking ability was used.
The light emitting layer 21-the intermediate layer 21-the light emitting layer 22-the intermediate layer 22-the light emitting layer 23-the intermediate layer 23-the light emitting layer 24 are arranged in this order from the hole transport layer.
Unit light emitting layers 21 to 24: Vapor was deposited with the same composition as the light emitting layer of the comparative organic EL device 1 so that the thickness was 15 nm.
Intermediate layers 21 to 23 were formed so that hole transport materials A to C and Ir (ppy) ₃ were in a volume ratio of 95: 5. Intermediate layer 21: <Hole transport material A (Ea = 2.3 eV)>
Intermediate layer 22: <Hole transport material B (Ea = 2.4 eV)>
Intermediate layer 23: <Hole transport material C (Ea = 2.5 eV)>
Each thickness was 10 nm.

2. Performance Evaluation Result The obtained organic EL device 3 of the present invention was measured for external quantum efficiency and luminance reduction time in the same manner as in Example 1.

  As a result, the organic EL element 3 of the present invention showed an extremely high value of 13.5% for external quantum efficiency and 85 hours for luminance reduction.

Example 4
1. Production of Organic EL Element 4 In Example 2, an intermediate layer having a hole blocking ability having the following composition was used.
The light emitting layer 31—the intermediate layer 31—the light emitting layer 32—the intermediate layer 32—the light emitting layer 33—the intermediate layer 33—the light emitting layer 34 were arranged in this order from the hole transport layer.
Unit light-emitting layers 31 to 34: vapor-deposited with the same composition as the light-emitting layer of the comparative organic EL device 1 so that the thickness was 15 nm.
Intermediate layers 31 to 33 were formed so that electron transport materials A to C and Ir (ppy) ₃ were in a volume ratio of 95: 5. Intermediate layer 31: <Electron transport material A (Ip = 6.2 eV)>
Intermediate layer 32: <electron transport material B (Ip = 6.4 eV)>
Intermediate layer 33: <electron transport material C (Ip = 6.6 eV)>
Each thickness was 10 nm.

2. Performance Evaluation Result The obtained organic EL device 4 of the present invention was measured for external quantum efficiency and luminance reduction time in the same manner as in Example 1.

  As a result, the organic EL element 4 of the present invention showed an extremely high value of 13.4% for external quantum efficiency and 84 hours for luminance reduction.

Example 5
1. Production of Organic EL Element 5 In Example 2, an electron blocking layer having the following composition was used as an intermediate layer having an electron blocking ability having the following composition.
The light emitting layer 41-the intermediate layer 41-the light emitting layer 42-the intermediate layer 42-the light emitting layer 43-the intermediate layer 43-the light emitting layer 44 are arranged in this order from the hole transport layer.
Unit light-emitting layers 41 to 44: vapor-deposited with the same composition as the light-emitting layer of the comparative organic EL device 1 so that the thickness was 15 nm.
Intermediate layer 41: <Concentration change of hole transport material C Volume ratio Hole transport material C: CBP: Ir (ppy) ₃ = 50: 45: 5>
Intermediate layer 42: <Concentration change of hole transport material C Volume ratio Hole transport material C: CBP: Ir (ppy) ₃ = 30: 65: 5>
Intermediate layer 43: <Concentration change of hole transport material C Volume ratio Hole transport material C: CBP: Ir (ppy) ₃ = 10: 85: 5>
Each thickness was 10 nm.

2. Performance Evaluation Results The obtained organic EL device 5 of the present invention was measured for external quantum efficiency and luminance reduction time in the same manner as in Example 1.

  As a result, the organic EL element 5 of the present invention showed an extremely high value of 13.6% for external quantum efficiency and 87 hours for luminance reduction.

Example 6
1. Production of Organic EL Element 6 In Example 2, an intermediate layer having a hole blocking ability having the following composition was used.
The light emitting layer 51-the intermediate layer 51-the light emitting layer 52-the intermediate layer 52-the light emitting layer 53-the intermediate layer 53-the light emitting layer 54 are arranged in this order from the hole transport layer.
Unit light-emitting layers 51 to 54: vapor-deposited with the same composition as the light-emitting layer of the comparative organic EL device 1 so that the thickness was 15 nm.
Intermediate layer 51: <Concentration change of electron transport material B Volume ratio Electron transport material B: CBP: Ir (ppy) ₃ = 10: 85: 5>
Intermediate layer 52: <Concentration change of electron transport material B Volume ratio Electron transport material B: CBP: Ir (ppy) ₃ = 30: 65: 5>
Intermediate layer 53: <Concentration change of electron transport material B Volume ratio Electron transport material B: CBP: Ir (ppy) ₃ = 50: 45: 5>
Each thickness was 10 nm.

2. Performance Evaluation Results The obtained organic EL device 6 of the present invention was measured for external quantum efficiency and luminance reduction time in the same manner as in Example 1.

  As a result, the organic EL element 6 of the present invention showed an extremely high value of 13.7% for the external quantum efficiency and 88 hours for the luminance reduction time.

Example 7
1. Production of Organic EL Element 7 In Example 2, an intermediate layer containing materials having different electron mobility with different compositions was used.
The light emitting layer 61-the intermediate layer 61-the light emitting layer 62-the intermediate layer 62-the light emitting layer 63-the intermediate layer 63-the light emitting layer 64 are arranged in this order from the hole transport layer.
Unit light-emitting layers 61 to 64: vapor-deposited with the same composition as the light-emitting layer of the comparative organic EL element 2 so that the thickness was 15 nm.
Intermediate layers 61 to 63 were formed so that the volume ratio of Balq, CBP, electron transport material B, and Ir (btp) ₂ (acac) was 95: 5.
Intermediate layer 61: <Balq (electron mobility = 2.5 × 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ )>
Intermediate layer 62: <CBP (electron mobility = 6.0 × 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ )>
Intermediate layer 63: <electron transport material B (electron mobility = 9.0 × 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ )>
(Electron mobility at electric field 10 ⁶ V / cm)
Each thickness was 10 nm.

2. Performance Evaluation Results External quantum efficiency and luminance reduction time of the obtained comparative organic EL elements 2, 2A and the organic EL element 7 of the present invention were measured in the same manner as in Example 1.

  As a result, the external quantum efficiency of the comparative organic EL element 2 was 4.8% and the external quantum efficiency of the comparative organic EL element 2A was 5.2%, but the external quantum efficiency of the organic EL element 7 of the present invention was 7%. The value was extremely high at 4%. Further, the luminance reduction time of the comparative organic EL element 2 was 65 hours, and the luminance reduction time of the comparative organic EL element 2A was 72 hours. However, the luminance reduction time of the organic EL element 7 of the present invention was greatly driven to 93 hours. Improved durability.

Example 8
1. Production of Organic EL Element 8 In Example 2, an intermediate layer containing materials with different electron mobility having different compositions was used.
The light emitting layer 71-the intermediate layer 71-the light emitting layer 72-the intermediate layer 72-the light emitting layer 73 are arranged in this order from the hole transport layer.
Unit light-emitting layers 71 to 73: vapor-deposited with the same composition as the light-emitting layer of the comparative organic EL device 1 so that the thickness was 20 nm.
Intermediate layers 71 and 72: The intermediate layers 71 to 72 were formed so that the hole transport material A, the hole transport material C (mCP), the hole transport material D and Ir (ppy) ₃ were in a volume ratio of 95: 5.
Intermediate layer 71: hole transport material C (hole mobility = 1.7 × 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ )
Intermediate layer 72: hole transport material D (hole mobility = 6.5 × 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ )
The hole mobility is the hole mobility at an electric field of 10 ⁶ V / cm.
Each thickness was 15 nm.

2. Results of Performance Evaluation The obtained organic EL device 8 of the present invention was measured for external quantum efficiency and driving decrease time in the same manner as in Example 1.

  As a result, the external quantum efficiency of the comparative organic EL element 1 was 9.8% and the external quantum efficiency of the comparative organic EL element 1A was 10.4%. However, the external quantum efficiency of the organic EL element 7 of the present invention was 12%. It showed a very high value of 1%. Further, the luminance reduction time of the comparative organic EL element 1 was 48 hours and the luminance reduction time of the comparative organic EL element 1A was 51 hours. However, the luminance reduction time of the organic EL element 8 of the present invention was 81 hours. Improved durability.

  The structure of the compound used for the light-emitting element is shown below.

It is a conceptual diagram of the layer structure of the comparative light emitting element. It is the conceptual diagram of the layer structure of another light emitting element for comparison, and is a structure in which the light emitting layer is divided into three unit light emitting layers, and the same intermediate layer is disposed therebetween. It is a conceptual diagram of an example of the light emitting element of this invention, and is a structure which the light emitting layer was divided | segmented into three unit light emitting layers, and the intermediate | middle layer from which charge blocking ability differs was distribute | arranged between this unit light emitting layer. It is a conceptual diagram of the layer structure of another example of the light emitting element of this invention. The light emitting layer is divided into four parts, and an intermediate layer having different charge blocking ability is arranged between them. It is a conceptual diagram of the layer structure of another example of the light emitting element of this invention. The light emitting layer is divided into four parts, and an intermediate layer having a different thickness is provided between them.

Explanation of symbols

1: Anode 2: Hole injection layer 3: Hole transport layer 4: Light emitting layer 4a, 4b, 4c, 4d: Unit light emitting layer 5: Electron transport layer 6: Electron injection layer 7: Cathode 8: Intermediate layers 8a, 8b, 8c : Intermediate layer that divides the light emitting layer

Claims (13)

  An organic electroluminescent device comprising at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided into at least three layers in the thickness direction, and an intermediate layer containing an electron blocking material between the divided light emitting layers An organic light-emitting device, wherein the intermediate layer has the largest electron blocking ability near the anode and the smallest layer near the cathode.   An organic electroluminescent device comprising at least a light emitting layer sandwiched between a pair of electrodes, wherein the light emitting layer is divided into at least three layers in the thickness direction, and an intermediate layer containing a hole blocking material between the divided light emitting layers An organic light-emitting device characterized in that the intermediate layer has the smallest hole blocking ability near the anode and the smallest layer near the cathode.   2. The organic light emitting device according to claim 1, wherein Ea (electron affinity) of the electron block material is the smallest in the layer close to the anode and the largest in the layer close to the cathode.   3. The organic light emitting device according to claim 2, wherein the hole block material has a minimum Ip (ionization potential) in a layer close to the anode and a maximum in a layer close to the cathode.   2. The organic light emitting device according to claim 1, wherein the concentration of the electron blocking material in the intermediate layer is highest in a layer close to the anode and lowest in a layer close to the cathode.   3. The organic light emitting device according to claim 2, wherein the concentration of the hole blocking material in the intermediate layer is lowest in a layer close to the anode and highest in a layer close to the cathode.   2. The organic light emitting device according to claim 1, wherein the intermediate layer has the lowest electron mobility in a layer close to the anode and the highest in a layer close to the cathode.   The organic light emitting device according to claim 2, wherein the hole mobility of the intermediate layer is highest in a layer close to the anode and lowest in a layer close to the cathode.   2. The organic light emitting device according to claim 1, wherein the intermediate layer is thickest in a layer close to the anode and thinnest in a layer close to the cathode.   The organic light-emitting element according to claim 2, wherein the intermediate layer is thinnest in a layer near the anode and thickest in a layer near the cathode.   11. The organic light-emitting element according to claim 1, wherein the light-emitting material of the light-emitting layer is a phosphorescent material.   The organic light emitting element according to claim 1, wherein the intermediate layer contains a light emitting material.   The organic light-emitting device according to claim 12, wherein the light-emitting material contained in the intermediate layer is a phosphorescent material.