WO2014084206A1

WO2014084206A1 - Organic el element

Info

Publication number: WO2014084206A1
Application number: PCT/JP2013/081770
Authority: WO
Inventors: 賢太郎渡邉; 竜徳篠; 伸浩名取; 光正岩本; 孝彰間中; 大田口
Original assignee: 昭和電工株式会社
Priority date: 2012-11-27
Filing date: 2013-11-26
Publication date: 2014-06-05

Abstract

This organic EL element has a light-emitting layer between an anode and a cathode, and is provided with an electron injection layer and an electron transport layer, in that order from the cathode side, between the cathode and the light-emitting layer; the electron mobility of the electron transport layer being less than the electron mobility of the electron injection layer, and the electron mobility of the light-emitting layer being greater than the electron mobility of the electron transport layer.

Description

Organic EL device

The present invention relates to an organic EL element.
This application claims priority based on Japanese Patent Application No. 2012-258907 filed in Japan on November 27, 2012, the contents of which are incorporated herein by reference.

Electron injection layers with very high electron mobility have been reported as techniques for increasing the voltage and efficiency of organic EL elements, and it has been confirmed that the use of these can significantly reduce the voltage of organic EL elements ( For example, see Patent Documents 1 and 2).

However, in the case of the techniques described in Patent Documents 1 and 2, the amount of electrons injected into the light emitting layer becomes excessive than the amount of holes, and the balance between the amount of electrons and the amount of holes is lacking. In many cases, the rate at which electrons pass through the light emitting layer increases. Therefore, since the current is a combination of the flow of holes and electrons, a large amount of current flows, but the amount of light emission does not increase so much. That is, there is a problem that sufficient luminous efficiency cannot be obtained and the lifetime is short.

In order to solve the above problem, in Patent Document 3, by combining an electron injection layer having a high electron mobility and an electron injection suppression layer, the balance between the amount of electrons and the amount of holes is improved, and an organic EL element is obtained. It has been reported that the light emission efficiency and lifetime of this product are improved. That is, from the viewpoint of electron mobility, since the electron mobility of the electron injection suppression layer is smaller than the electron mobility of the electron injection layer, the amount of electrons injected into the light-emitting layer is suppressed, so that It is thought that it contributed to the improvement of luminous efficiency and lifetime in balance with the amount.

Japanese Patent Laid-Open No. 9-087616 JP-A-9-194487 JP 2009-239309 A

However, in the configuration of Patent Document 3, charges accumulate at the interface between the electron injection suppression layer and the light emitting layer, preventing further improvement in light emission efficiency, and such charges become chemically unstable radicals. The organic layer (light emitting layer) was deteriorated, preventing further improvement of the device lifetime.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an organic EL element having high luminous efficiency and improved lifetime.

The inventors of the present invention have made extensive studies to solve the above problems. As a result, with respect to the above electron mobility, the light emitting layer is further configured to have a higher electron mobility than the electron transport layer (electron injection suppression layer), thereby promoting charge recombination and improving light emission efficiency. It has been found that the lifetime can be improved by reducing chemically unstable radicals in the vicinity of the light emitting layer. Furthermore, similarly, regarding the hole mobility, the light emitting layer is configured to have a higher hole mobility than the hole transport layer (hole injection suppression layer), thereby promoting charge recombination. Thus, the present inventors have found that the luminous efficiency can be improved and the lifetime can be improved by reducing chemically unstable radicals in the vicinity of the light emitting layer.
That is, in order to achieve the above object, the present invention provides the following means.

[1] An organic EL device having a light emitting layer between an anode and a cathode, comprising an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the light emitting layer, An organic EL element, wherein an electron mobility is smaller than an electron mobility of the electron injection layer, and an electron mobility of the light emitting layer is larger than an electron mobility of the electron transport layer.
[2] The organic EL device according to [1], wherein a hole injection layer and a hole transport layer are provided in this order from the anode side between the anode and the light emitting layer.
[3] An organic EL device having a light emitting layer between an anode and a cathode, comprising a hole injection layer and a hole transport layer in that order from the anode side between the anode and the light emitting layer, The hole mobility of the transport layer is smaller than the hole mobility of the hole injection layer, and the hole mobility of the light emitting layer is larger than the hole mobility of the hole transport layer EL element.
[4] The organic EL device according to [3], wherein an electron injection layer and an electron transport layer are provided in this order from the cathode side between the cathode and the light emitting layer.
[5] An organic EL device having a light emitting layer between an anode and a cathode, comprising an electron injection layer and an electron transport layer in that order from the cathode side between the cathode and the light emitting layer, Between the light emitting layer, a hole injection layer and a hole transport layer are provided in this order from the anode side, the electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer, and the electron mobility of the light emitting layer The mobility of the electron transport layer is greater than the mobility of the hole transport layer, the mobility of the hole transport layer is smaller than the mobility of the hole injection layer, and the mobility of the light emitting layer is greater than the positive mobility. An organic EL element characterized by being larger than the hole mobility of the hole transport layer.

[6] An organic EL device having a plurality of light emitting layers between an anode and a cathode, comprising an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the plurality of light emitting layers, The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer, and the electron mobility of the light emitting layer disposed at a position closest to the electron transport layer among the plurality of light emitting layers is the electron transport. An organic EL element characterized by being larger than the electron mobility of the layer.
[7] The organic EL device according to [6], wherein a hole injection layer and a hole transport layer are provided in this order from the anode side between the anode and the plurality of light emitting layers.
[8] An organic EL device having a plurality of light emitting layers between an anode and a cathode, wherein a hole injection layer and a hole transport layer are arranged in order from the anode side between the anode and the plurality of light emitting layers. A hole mobility of the hole transport layer is smaller than a hole mobility of the hole injection layer, and a light emitting layer disposed at a position closest to the hole transport layer among the plurality of light emitting layers. An organic EL device having a hole mobility larger than that of the hole transport layer.
[9] The organic EL device according to [8], wherein an electron injection layer and an electron transport layer are provided between the cathode and the light emitting layers in order from the cathode side.
[10] An organic EL device having a plurality of light emitting layers between an anode and a cathode, and having an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the plurality of light emitting layers. And a hole injection layer and a hole transport layer in order from the anode side between the anode and the plurality of light emitting layers, and the electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer. The electron mobility of the light emitting layer disposed at the position closest to the electron transport layer among the plurality of light emitting layers is larger than the electron mobility of the electron transport layer, and the hole mobility of the hole transport layer is The hole mobility of the light-emitting layer that is smaller than the hole mobility of the hole-injection layer and is arranged closest to the hole-transport layer among the plurality of light-emitting layers is the hole of the hole-transport layer. An organic EL element characterized by being larger than a mobility.

[11] An organic EL device having a plurality of light emitting layers between an anode and a cathode, and having an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the plurality of light emitting layers. And a hole injection layer and a hole transport layer in order from the anode side between the anode and the plurality of light emitting layers, and the electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer. The electron mobility of the light emitting layer disposed at a position closest to the electron transport layer among the plurality of light emitting layers is larger than the electron mobility of the electron transport layer, and the hole of the plurality of light emitting layers is the hole. The electron mobility of the light emitting layer disposed closest to the transport layer is smaller than the electron mobility of the light emitting layer disposed closest to the electron transport layer, and the hole mobility of the hole transport layer is greater than the positive mobility. Less than the hole mobility of the hole injection layer, Among the layers, the hole mobility of the light emitting layer disposed at a position closest to the hole transport layer is larger than the hole mobility of the hole transport layer, and the electron transport layer among the plurality of light emitting layers. An organic EL element, wherein the hole mobility of the light emitting layer disposed at a position closest to the hole is smaller than the hole mobility of the light emitting layer disposed at a position closest to the hole transport layer.

According to the organic EL device of the present invention, in the structure having the light emitting layer between the anode and the cathode as described above, the electron injection layer and the electron transport layer are provided between the cathode and the light emitting layer from the cathode side. A structure is adopted in which the electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer, and the electron mobility of the light emitting layer is larger than the electron mobility of the electron transport layer. Alternatively, a hole injection layer and a hole transport layer are sequentially provided between the anode and the light emitting layer from the cathode side, and the hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer. The structure in which the hole mobility of the light emitting layer is larger than the hole mobility of the hole transport layer is adopted. By adopting at least one of the above-mentioned structures, charge recombination is promoted, luminous efficiency is improved, and lifetime is also improved by reducing chemically unstable radicals in the vicinity of the light emitting layer. Can do. Therefore, it is possible to realize an organic EL element with high luminous efficiency and long life.

FIG. 1 is a cross-sectional view schematically showing an organic EL element 1 according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an organic EL element 3 according to the second embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing an organic EL element 5 according to the third embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing an organic EL element 6 according to the fourth embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing an organic EL element 8 according to the fifth embodiment of the present invention. FIG. 6 is a sectional view schematically showing an organic EL element 10 according to the sixth embodiment of the present invention. FIG. 7 is a cross-sectional view schematically showing an organic EL element 1A according to a seventh embodiment of the present invention. FIG. 8 is a cross-sectional view schematically showing the organic EL element 2 in the first embodiment of the present invention. FIG. 9 is a cross-sectional view schematically showing the organic EL element 4 in the second embodiment of the present invention. FIG. 10 is a cross-sectional view schematically showing an organic EL element 7 according to the fourth embodiment of the present invention. FIG. 11 is a cross-sectional view schematically showing an organic EL element 9 according to the fifth embodiment of the present invention.

Hereinafter, embodiments of the organic EL element of the present invention will be described with reference to FIGS. 1 to 11 as appropriate.
1 to 11, an arrow 101 (upward arrow in the figure) shown in each figure is an arrow showing a flow of holes, and an arrow 102 (downward arrow in the figure) is an electron flow. It is the arrow which shows a flow. In addition, the inequality symbols shown in FIGS. 1 to 11 (indicated by vertical writing in the respective drawings) indicate the relationship between the mobility of electrons or holes between the layers, and the opening of the inequality symbol is This indicates that the facing layer has a higher mobility than the opposite layer.
In addition, about a layer with unknown mobility, it can measure by the time of flight method (TOF method), for example.

[First Embodiment]
As illustrated in FIG. 1, the organic EL element 1 described in the present embodiment includes a light emitting layer 14 between an anode 11 and a cathode 17, and a cathode 17 between the cathode 17 and the light emitting layer 14. An electron injection layer 16 and an electron transport layer 15 are provided in order from the side, and are schematically configured. In the organic EL element 1, an anode 11, a light emitting layer 14, an electron transport layer 15, an electron injection layer 16, and a cathode 17 are sequentially stacked on a support substrate (not shown) that supports the organic EL element. Here, an arrow 102 shown in FIG. 1 is an arrow indicating the direction of the flow of electrons e ⁻ . The inequality sign 201a is an inequality sign indicating the magnitude of the electron mobility between the electron transport layer 15 and the light emitting layer 14. The inequality sign 201b is an inequality sign indicating the magnitude of the electron mobility between the electron injection layer 16 and the electron transport layer 15.

Then, in the organic EL device 1 of the present embodiment, as the electron mobility _{mu E_ETL} of the electron transport layer 15 is smaller than the electron mobility _{mu E_EIL} of the electron injection layer 16, and the electron mobility of the light-emitting layer 14 The material used for each layer is selected so that μ _{e_EML} is larger than the electron mobility of the electron transport layer 15.
Here, the electron mobility described in the present invention is a value indicating the ease of movement of electrons in the solid material, and is defined as the ratio V1 / E of the electron velocity V1 and the electric field E.

Examples of the support substrate used in the present invention include a substrate made of a translucent material, and the organic EL element 1 of the present embodiment has the above layer structure formed on the translucent substrate. As the above-described light-transmitting supporting substrate, a transparent substrate having a transmittance of visible light of 400 to 700 nm of 50% or more is preferable. Specific examples of such a support substrate include a glass plate and a polymer plate. Here, examples of the glass plate material include soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the material for the polymer plate include polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyether sulfide, polysulfone and the like.

The anode 11 is for injecting holes into the light emitting layer 14 and is preferably made of an electrode material having a work function of 4.5 eV or more. Specifically, a material such as indium tin oxide alloy (ITO), indium zinc oxide alloy (IZO), tin oxide (NESA), gold, silver, platinum, or copper can be used for the anode 11. The anode 11 can be formed by depositing the electrode material as a thin film on a supporting substrate using a method such as vapor deposition or sputtering.

Here, when light emitted from the light emitting layer 14 is taken out from the anode 11, it is preferable to optimize the anode material and the film thickness so that the transmittance of the light emitted from the anode 11 exceeds 10%.
The sheet resistance of the anode 11 is preferably several hundred Ω / □ or less.
Further, although the film thickness of the anode 11 depends on the material, it can be generally in the range of about 10 nm to 1 μm, more preferably in the range of 50 to 200 nm in consideration of the above-described transmittance and sheet resistance.

The light emitting layer 14 is a layer for generating an excited state mainly by recombining electrons supplied from the cathode and holes supplied from the anode, and connecting this to light emission. Moreover, the light emitting layer 14 provided in the organic EL element 1 of the present embodiment is configured to have a higher electron mobility than an electron transport layer 15 described later.

The light-emitting layer 14 has a transport function of moving injected charges (electrons and holes) by the force of an electric field. Further, as described above, the light-emitting layer 14 has a charge recombination of electrons and holes. By providing a field, it has a light emitting function to connect it to light emission.
However, in the light emitting layer 14 of the present embodiment, the transport ability of both charges represented by the mobility of holes and electrons may be large or small, but it is preferable to transport at least one of the charges.

The light emitting layer 14 is made of a material that actually emits light called a light emitter and a material that transports charges called a host. As the material used for the light-emitting layer 14, a conventionally known light-emitting material having a long lifetime can be used. For example, a material described in Japanese Patent Application Laid-Open No. 2011-139044 (particularly, in paragraph 0100 of the same publication). The organic materials described in the above, and the organometallic complex materials described in paragraph 0101) can be used.
Examples of the host material used for the light-emitting layer 14 include materials described in JP-A-2009-260308 (in particular, host materials having hole transport properties described in paragraph 0049 of the same publication, and paragraph 0054). Or a host material having an electron transporting property described in 1).
For the light-emitting layer 14, a material whose electron mobility is _higher than the electron mobility μ _{e_ETL} of the electron transport layer 15 is selected from the materials that can be used for the light-emitting layer 14.

In addition, as a method of forming the light emitting layer 14 provided in the organic EL element 1 of the present embodiment, for example, a known method such as a vapor deposition method, a spin coating method, or an LB method is applied to form the above material into a film. The method can be adopted. In this case, the light emitting layer 14 is particularly preferably a molecular deposition film. Here, the molecular deposition film refers to a thin film formed by deposition from a material compound in a gas phase state or a film formed by solidifying from a material compound in a solution state or a liquid phase state. Such a molecular deposition film can be generally distinguished from a thin film (molecular accumulation film) formed by the LB method by a difference in an agglomerated structure and a higher-order structure and a functional difference resulting therefrom.
In addition to the above method, for example, a light emitting layer can be obtained by applying a method in which a binder such as a resin and a material compound are dissolved in a solvent to form a dispersion solution and then thinned by a spin coating method or the like. 14 can be formed.

The electron transport layer 15 relates to electrons injected from the cathode 17 into the light-emitting layer 14 via the electron injection layer 16, and the electrons injected from the electron injection layer 16 are flowed with appropriate mobility. This layer is transported to the light emitting layer 14 while adjusting, and is a layer for balancing the electrons injected from the cathode 17 and the holes injected from the anode 11. For this reason, in this embodiment, the electron mobility of the electron transport layer 15 is made smaller than the electron mobility of the electron injection layer 16 described later, and smaller than the electron mobility of the light emitting layer 14 described above. .

Even if the material used for the electron transport layer 15 is a material that suppresses the transport of electrons, it should not be a material that does not allow electrons to flow. As such a material, a material having a lower electron mobility than the electron injection layer used in the organic EL device of the present invention can be used. For example, as such a material, a heterocyclic derivative, for example, a heterocyclic compound in which a 6-membered ring and a 5-membered ring are condensed, such as an imidazole derivative and an imidazopyridine derivative, can be suitably used. Furthermore, a nitrogen-containing ring compound, a silicon-containing ring compound, a boron compound, and the like that can be used as an electron injection layer to be described later can also be suitably used. Specifically, 8-hydroxyquinoline or a metal complex of a derivative thereof is preferable. Specific examples include metal chelate oxinoid compounds containing a chelate of oxine (generally 8-quinolinol or 8-hydroxyquinoline). For example, (8-quinolinolato) aluminum complex (Alq) can be used.

The electron injection layer 16 is a layer that promotes injection of electrons from the cathode 17 to the electron transport layer 15.
Further, the electron mobility μ _{e_EIL} of the electron injection layer 16 provided in the organic EL element 1 of the present embodiment is larger than the electron mobility μ _{e_ETL} of the electron transport layer 15 described above. Thus, by inserting the electron transport layer 15 having a lower electron mobility than those layers between the electron injection layer and the light emitting layer, the electron transport layer 15 restricts the supply of electrons to the light emitting layer 14, Deterioration of the light emitting layer 14 is suppressed. The material for the electron injection layer 16 is not particularly limited, and a conventionally known material in this field can be used. For example, a nitrogen-containing ring compound, a silicon-containing ring compound, a boron compound, or the like is preferably used. Can do. For the electron injection layer 16, a material having an electron mobility _higher than the electron mobility μ _{e_ETL} of the electron transport layer 15 is selected from the materials described above.

Here, as a material that can realize desired electron mobility and hole mobility described later in each layer constituting the organic EL element, research has been conducted in various fields and many proposals have been made.
For example, the reference “Abhisek P.A. Kulkarni et al .; “Electron Transport Materials Organic Light-Emitting Diodes”; Chem. Mater. 2004, 16, 4556-4573 ”discloses an electron transporting material (see in particular the material described in Table 2 of the same document). The material described in this document can be used as a host material for the electron transport layer 15, the electron injection layer 16, and the electron transporting light-emitting layer 14.

Also, reference documents “Yasuhiko Koshirota et al .;“ Charge Carrier Transporting Molecular Materials and Ther Applications in Devices ”; Chem. Rev. 2007, 107, 953-1010 ”discloses a p-type semiconductor material (see Table 8 in the same document) and an n-type semiconductor material (see Table 9 in the same document) regarding electron mobility and hole mobility. is there. Further, in the same document, in addition to bipolar molecules (see Table 10 in the same document), hole transporting materials (see Table 11 in the same document), electron transporting materials (see Table 12 in the same document), holes There is disclosure about a transportable material (see Table 13 of the same document) and the like. The material described in this document is used as a host material for the electron transport layer 15, the electron injection layer 16, the hole transport layer 13, the hole injection layer 12, and the light-emitting layer 14 having an electron transport property and a hole transport property. Can be used.

In addition, reference literature “Lixin Xiao etc .;“ Recent Progress on Materials for Electrophosphorescent Organic Light-Emitting Devices ”;“ ADVANCED MATERIALS, 2011, 23, 926-952 ” There is a disclosure of a conductive material (see Table 1 of the same document) and an electron transport material (see Table 2 of the same document). Use the material described in this document as a host material for the electron transport layer 15, the electron injection layer 16, the hole transport layer, the hole injection layer, and the light-emitting layer having an electron transport property and a hole transport property. Can do.

In the organic EL element 1 of the present embodiment, the electron transport layer 15 is related to each material forming the light emitting layer 14 in addition to the electron transport layer 15 and the electron injection layer 16 among the materials described with reference to the above references. The material used for each layer is selected so that the electron mobility is lower than that of the electron injection layer 16 and the light emitting layer 14 is higher than the electron transport layer 15. May be. As described above, by making the electron mobility of the electron transport layer 15 smaller than the electron mobility of the electron injection layer 16, supply of excess electrons to the light emitting layer 14 is suppressed. Further, the amount of electrons supplied to the light emitting layer 14 can be adjusted by adjusting the film thickness of the electron transport layer 15. At the same time, in the present embodiment, by making the electron mobility in the electron transport layer 15 smaller than the electron mobility in the light emitting layer 14, electrons supplied from the electron transport layer 15 can enter the light emitting layer 14 without delay. And can be transported. As a result, charge recombination in the light emitting layer 14 can be promoted to improve the light emission efficiency. Furthermore, since the electron mobility of the electron transport layer 15 is smaller than the electron mobility of the light-emitting layer 14, it is possible to suppress accumulation of charges as chemically unstable radicals at the interface between the electron transport layer 15 and the light-emitting layer 14. Therefore, the lifetime of the organic EL element 1 can be improved.

The cathode 17 is for injecting electrons into the electron injection layer 16 or the light emitting layer 14. For example, a metal, an alloy, an electrically conductive compound having a work function as small as 4 eV or less, and a mixture thereof are used as an electrode material. Can do. Specific examples of such electrode materials include, for example, silver, aluminum, platinum, gold, copper, titanium, sodium, sodium-potassium alloy, magnesium, lithium, magnesium / silver alloy, aluminum / aluminum oxide, and aluminum / lithium alloy. , Indium, and rare earth metals.
The cathode 17 can be formed by depositing a thin film on the electron injection layer 16 by using a method such as vapor deposition or sputtering.

Here, when taking out the light emission from the light emitting layer 14 from the cathode 17 side, it is preferable to optimize the electrode material and film thickness so that the transmittance of the cathode 17 with respect to the light emission exceeds 10%.
The sheet resistance of the cathode 17 is preferably several hundred Ω / □ or less.
Further, although the film thickness of the cathode 17 depends on the material, it can be generally in the range of about 10 nm to 1 μm, preferably in the range of 50 to 200 nm, taking into consideration the above-described light transmittance and sheet resistance.

In the present embodiment, the structure is not limited to that shown in FIG. 1. For example, as in the example shown in FIG. 8, between the anode 11 and the light emitting layer 14 and further from the anode 11 side. It is good also as a structure like the organic EL element 2 provided with the positive hole injection layer 12 and the positive hole transport layer 13 in order. Even when the organic EL element 2 is configured, the electron transport layer 15 has a lower electron mobility than the electron injection layer 16 and the light emitting layer 14 has the electron transport layer 15 as described above. By using a layer having a higher electron mobility than that, the effect of improving the light emission efficiency and life characteristics can be obtained.

As a method for manufacturing the organic EL element 1 (2) as described above, for example, the following method can be employed. In the present embodiment, the organic EL element 1 can be manufactured by sequentially forming the anode 11, the light emitting layer 14, the electron transport layer 15, the electron injection layer 16, and the cathode 17 by the materials and methods exemplified in the above description. . Furthermore, in this embodiment, in addition to the above, by forming the hole injection layer 12 and the hole transport layer 13 sequentially from the anode side between the anode 11 and the light emitting layer 14 as necessary, The EL element 2 can be manufactured. Alternatively, each layer can be formed from the cathode 17 to the anode 11 in the reverse order.

Hereinafter, an example of the manufacturing method of the organic EL element 1 having the layer structure shown in FIG. 1 will be described.
First, a thin film made of an anode material is formed on a light-transmitting support substrate (not shown) by a method such as vapor deposition or sputtering so that the film thickness is 1 μm or less, more preferably in the range of 10 to 200 nm. As a result, the anode 11 is formed.

Next, the light emitting layer 14 is formed on the anode 11. The light emitting layer 14 is formed by thinning the light emitting layer material by using, for example, a vacuum deposition method, a sputtering method, a spin coating method, a casting method, or the like, using the organic light emitting material (light emitting layer material) as described above. Can be formed. Thus, when forming the light emitting layer 14, it is preferable to select an appropriate condition in consideration of the compound to be used (organic light emitting material), the crystal structure of the target light emitting layer, and the like.

Next, the electron transport layer 15 is formed on the light emitting layer 14. In forming the electron transport layer 15, it is possible to employ a method of forming a thin film by using, for example, a vacuum deposition method, a sputtering method, a spin coating method, a casting method, or the like using the organic material as described above. Further, as with the light emitting layer 14, appropriate conditions can be selected in consideration of the organic material to be used, the target crystal structure, and the like.

Next, an electron injection layer 16 is formed on the electron transport layer 15. In the formation of the electron injection layer 16, as in the case of the electron transport layer 15, the organic material can be used to form a film by the same film formation method and conditions.

Then, by laminating the cathode 17 on the electron injection layer 16, the anode 11, the light emitting layer 14, the electron transport layer 15, the electron injection layer 16, and the cathode 17 are formed on a support substrate made of a translucent material (not shown). Can be produced in sequence. The cathode 17 is composed of the electrode material as described above. For example, a vapor deposition method or sputtering can be used. From the viewpoint of protecting the electron injection layer 16 serving as a base from damage during film formation. It is preferable to use a vacuum deposition method.

In addition, in this embodiment, when manufacturing the organic EL element 2 provided with the positive hole injection layer 12 and the positive hole transport layer 13 in addition to the organic EL element 1, said anode 11 was formed on the support substrate. Thereafter, a hole injection layer 12 is first formed on the anode 11, and a hole transport layer 13 is further formed on the hole injection layer 12. At this time, in forming the hole injection layer 12 and the hole transport layer 13, for example, a method such as a vacuum deposition method, a spin coating method, a casting method, an LB method, or the like can be used using the above materials. Further, regarding the conditions, appropriate conditions can be selected in consideration of the organic material to be used, the target crystal structure, and the like.

Then, the light emitting layer 14 is formed on the hole transport layer 13 by the method described above, and the layers thereon are also formed in the same manner as described above, whereby the anode 11, An organic EL device in which the hole injection layer 12, the hole transport layer 13, the light emitting layer 14, the electron transport layer 15, the electron injection layer 16, and the cathode 17 are sequentially formed can be manufactured.

In addition, the formation method of each layer of the organic EL element which concerns on this invention is not limited to said method, Various formation methods, such as a conventionally well-known vacuum evaporation method and a spin coating method, can be used. The electron injection layer 16, the electron transport layer 15, the light emitting layer 14, the hole injection layer 12, and the hole transport layer 13 are formed by a vacuum evaporation method, a molecular beam evaporation method (MBE method), or a solution dissolved in a solvent. Conventionally known methods by coating methods such as a dipping method, a spin coating method, a casting method, a bar coating method, a roll coating method, and an ink jet method can be employed.

Here, the film thickness of each layer of the organic EL elements 1 and 2 is not particularly limited, but generally, if the film thickness is too thin, defects such as pinholes are likely to occur, and conversely, if it is too thick, a high applied voltage is required. , Luminous efficiency decreases. For this reason, it is usually preferable that the thickness be in the range of several nm to 1 μm.

[Second Embodiment]
Below, 2nd Embodiment of the organic EL element of this invention is described, referring FIG. Note that, in the following description, the same reference numerals are given to configurations common to the organic EL elements 1 and 2 of the first embodiment, and detailed description thereof is omitted.

As illustrated in FIG. 2, the organic EL element 3 of the present embodiment has a light emitting layer 14 between the anode 11 and the cathode 17, and between the anode 11 and the light emitting layer 14 from the anode 11 side. A hole injection layer 12 and a hole transport layer 13 are sequentially provided in order. That is, the organic EL element 3 of the present embodiment includes the hole injection layer 12 and the hole transport layer 13, but does not include the electron transport layer 15 and the electron injection layer 16. Different from the organic EL element 1. Here, an arrow 101 shown in FIG. 2 is an arrow indicating the flow of holes h ⁺ . The inequality sign 202 a is an inequality sign indicating the magnitude of the hole mobility μ _h between the hole transport layer 13 and the light emitting layer 14. The inequality sign 202b is an inequality sign indicating the magnitude of the hole mobility between the hole injection layer 12 and the hole transport layer 13.

Then, the organic EL element 3 of this embodiment, the hole mobility _{mu H_HTL} of the hole transport layer 13 is smaller than the hole mobility _{mu H_HIL} of the hole injection layer 12, and hole mobility of the light-emitting layer 14 The degree _{μh_EML} is larger than the hole mobility of the hole transport layer 13.
Here, the hole mobility described in the present invention is a value indicating the ease of movement of holes in a solid material, and is defined as the ratio V2 / E of the hole velocity V2 and the electric field E. Is done.

In the present embodiment, holes are injected from the anode 11 into the hole injection layer 12.
The hole injection layer 12 is a layer for promoting hole injection into the light emitting layer 14 and transporting it to the light emitting region. The hole injection layer 12 has a high hole mobility and is usually a small ionization energy of 5.5 eV or less. is there. The material of such a hole injection layer 12 is not particularly limited, and a material conventionally used as a charge transport material for holes or a conventionally known material used for a hole injection layer of an organic EL element can be used. It can be appropriately selected from among them. Among these, the material for the hole injection layer 12 is preferably a material that can transport holes to the light emitting layer 14 with lower electric field strength. The material of the hole injection layer 12 is more preferably one having a hole mobility of at least 10 ⁻⁴ cm ² / V · sec when an electric field of 10 ⁴ to 10 ⁶ V / cm is applied. For the hole injection layer 12, a material having a hole mobility _higher than the hole mobility μ _{h_HTL of the} hole transport layer 13 is selected from the materials described above.

The hole injection layer 12 is formed by forming the above-described material into a thin film on the anode 11 by a conventionally known method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. be able to.
The film thickness of the hole injection layer 12 is not particularly limited, but can be, for example, about 1 nm to 1 μm.

The hole transport layer 13 is a layer that suppresses holes injected from the hole injection layer 12 toward the light emitting layer 14. That is, the hole transport layer 13 needs to be made of a material that suppresses holes, but should not be a material that does not allow holes to flow. As such a material of the hole transport layer 13, among those conventionally used for the hole injection layer, the hole mobility is smaller than the material used for the hole injection layer 12, and A material having a hole mobility smaller than that of the light emitting layer 14 is selected and used.

As described above, regarding the hole injection layer 12, the hole transport layer 13, and the light emitting layer 14, the material for realizing the desired hole mobility relationship has been described in the first embodiment. Among the materials described in the respective references, the hole transport layer 13 is a layer having a lower hole mobility than the hole injection layer 12, and the light emitting layer 14 is more positive than the hole transport layer 13. You may select the material used for each layer so that it may become a layer with a large hole mobility.

According to the organic EL element 3 of the present embodiment, as described above, first, the hole transport layer 13 is configured to have a hole mobility smaller than that of the hole injection layer 12, and the light emitting layer 14 is configured to transport holes. By adopting a configuration in which the hole mobility is higher than that of the layer 13, the amount of holes injected into the light emitting layer 14 can be made equal to the amount of electrons. Thereby, by making the hole transport layer 13 have a hole mobility smaller than that of the light emitting layer 14, the holes supplied from the hole transport layer 13 can be transported into the light emitting layer 14 without delay. it can. Accordingly, it is possible to promote the charge recombination in the light emitting layer 14 and improve the light emission efficiency. Furthermore, since the hole mobility μ _{h_HTL} of the hole transport layer 13 is smaller than the hole mobility μ _{h_EML} of the light emitting layer 14, a chemically unstable radical is formed at the interface between the hole transport layer 13 and the light emitting layer 14. As a result, accumulation of electric charges can be suppressed. Therefore, the lifetime of the organic EL element 3 can be improved.

In the present embodiment, the structure is not limited to that shown in FIG. 2, and for example, between the cathode 17 and the light emitting layer 14, as in the modification described in the first embodiment. The organic EL element 4 shown in FIG. 9 may be configured to include the electron injection layer 16 and the electron transport layer 15 in this order from the cathode 17 side. Here, as shown in FIG. 9, the organic EL element 4 of the present embodiment has the same layer structure as the organic EL element 2 described in the first embodiment.
In the present embodiment, even in the case of the layer structure as described above, the hole transport layer 13 is a layer having a hole mobility smaller than that of the hole injection layer 12, and the light emitting layer 14 is a hole. By making the hole mobility higher than that of the transport layer 13, the effect of improving the light emission efficiency and the life characteristics can be obtained.

[Third Embodiment]
Below, 3rd Embodiment of the organic EL element of this invention is described, referring FIG. In the following description, detailed description of the configuration common to the first and second embodiments is omitted. Here, an arrow 101 shown in FIG. 3 is an arrow indicating the flow of holes h ⁺ , an arrow 102 is an arrow indicating the flow of electrons e ⁺ , and an inequality sign 201 a is between the electron transport layer 15 and the light emitting layer 14. An inequality sign indicating the magnitude of electron mobility, the inequality sign 202a is an inequality sign indicating the magnitude of hole mobility between the hole transport layer 13 and the light emitting layer 14, and an inequality sign 202b is a hole injection layer 12 and a hole transport layer. 13 is an inequality sign indicating the magnitude of hole mobility between 13 and 13.

As illustrated in FIG. 3, the organic EL element 5 of the present embodiment has a light emitting layer 14 between the anode 11 and the cathode 17, and electrons are sequentially arranged between the cathode 17 and the light emitting layer 14 from the cathode 17 side. An injection layer 16 and an electron transport layer 15 are provided, and a hole injection layer 12 and a hole transport layer 13 are sequentially provided between the anode 11 and the light emitting layer 14 in this order from the anode 11 side.

As shown in FIG. 3, the organic EL element 5 of this embodiment has the same layer structure as the organic EL elements 2 and 4 described in the first and second embodiments. On the other hand, the organic EL element 5, first, similarly to the organic EL element 2 described in the first embodiment, the electron mobility _{mu E_ETL} of the electron transport layer 15 is smaller than the electron mobility _{mu E_EIL} of the electron injection layer 16, and the electron mobility _{mu E_EML} emitting layer 14 is larger configuration than the electron mobility _{mu E_ETL} of the electron transport layer 15. Then, the organic EL element 5 is smaller than the hole mobility _{mu H_HIL} hole mobility _{mu H_HTL} is the hole injection layer 12 of the hole transport layer 13 and hole mobility _{mu H_EML} emitting layer 14 The hole transport layer 13 has a hole mobility _higher than _{μh_ETL} . That is, in the organic EL element 5, the relationship between the electron mobility of each of the electron transport layer 15, the electron injection layer 16, and the light emitting layer 14 is optimized, and the positive hole transport layer 12 and the hole transport layer 13 are positive. The organic EL element 2 described in the first and second embodiments in that the relationship between the hole mobility and the hole mobility between the hole transport layer 13 and the light emitting layer 14 is optimized. 4 is different.

In the present embodiment, when the electron transport layer 15 is a layer having a lower electron mobility than the electron injection layer 16 and the light emitting layer 14 is a layer having a higher electron mobility than the electron transport layer 15, As in the case of the embodiment, by selecting the material, the electron mobility between each layer can be appropriately controlled.
In addition, when the hole transport layer 13 is a layer having a hole mobility smaller than that of the hole injection layer 12 and the light emitting layer 14 is a layer having a hole mobility larger than that of the hole transport layer 13, As in the case of the first and second embodiments, the hole mobility between the layers can be appropriately controlled by selecting the material.

According to the organic EL element 5 of the present embodiment, by adopting the above configuration, as in the organic EL elements 1 to 4 in the first and second embodiments, the charge recombination in the light emitting layer 14 is promoted to increase the luminous efficiency. In addition, the lifetime can be improved by reducing chemically unstable radicals in the vicinity of the light-emitting layer 14.

[Fourth Embodiment]
Below, 4th Embodiment of the organic EL element of this invention is described. In the following description, it will be described with reference to FIGS. 4 and 10, and detailed description of the configuration common to the organic EL elements 1 to 5 in the first to third embodiments will be omitted. Here, an arrow 102 shown in FIG. 4 is an arrow indicating the direction of the flow of electrons e ⁻ . The inequality sign 201a is an inequality sign indicating the magnitude of electron mobility between the electron transport layer 15 and the light emitting layer 14B on the electron transport layer 15 side. The inequality sign 201b is an inequality sign indicating the magnitude of the electron mobility between the electron injection layer 16 and the electron transport layer 15.

The organic EL elements 6 and 7 of the present embodiment are different from the organic EL elements 1 and 2 of the first embodiment in that a plurality of light emitting layers are provided. The organic EL element 6 in the example shown in FIG. 4 includes two light emitting

layers

14A and 14B. In this embodiment, by providing a plurality of light-emitting layers and controlling the wavelength of each light-emitting layer, it is possible to obtain an effect that it is easy to develop a color mixture and obtain an arbitrary color tone. In general, the emission color emitted from the light emitting layer is determined by the band gap of the light emitter (light emitting layer material).

As in the example shown in FIG. 4, the organic EL element 6 of the present embodiment has two light emitting

layers

14A and 14B between the anode 11 and the cathode 17, and the cathode 11 and the

light emitting layers

14A and 14B. The electron injection layer 16 and the electron transport layer 15 are provided in this order from the cathode 17 side. Then, the organic EL device 6 is smaller than the electron mobility _{mu E_EIL} electron mobility _{mu E_ETL} of the electron transport layer 15 is an electron injection layer 16, and a plurality of light-emitting layers 14A, among 14B, the electron transport layer 15 electron mobility _{mu E_EML1} emitting layer 14B which located closest is the larger configuration than the electron mobility _{mu E_ETL} of the electron transport layer 15. That is, the organic EL element 6 of the example shown in FIG. 4 has the same layer structure as that of the organic EL element 1 shown in FIG. 1 except that the light emitting layer is composed of two

layers

14A and 14B. Is.

Further, as shown in FIG. 10, in addition to the configuration of the organic EL element 6 described above, the organic EL element 7 is further provided between the anode 11 and the anode-side light emitting layer 14A among the plurality of light emitting layers. The hole injection layer 12 and the hole transport layer 13 are provided in this order from the anode 11 side. That is, the organic EL element 7 has the same layer structure as that of the organic EL element 2 shown in FIG. 8 except that the light emitting layer is composed of two

layers

14A and 14B.

As the material of the

light emitting layers

14A and 14B, the material as described in the first embodiment (for example, the material described in Japanese Patent Application Laid-Open No. 2011-139044) can be used. It is possible to obtain a desired emission wavelength and intensity by appropriately adopting the dopant and the light emitter described in paragraph 0100 of the publication.
Further, as the host material of the

light emitting layers

14A and 14B, the same material as described above (for example, the material described in JP2009-260308A) can be used, and in particular, the hole described in paragraph 0049 of the same publication. You may select the material which satisfy | fills the above mobility relationships from the material which has transportability, the material which has electron transport property of Paragraph 0054, etc.

[Fifth Embodiment]
Below, 5th Embodiment of the organic EL element of this invention is described, referring FIG.5 and FIG.11. Here, an arrow 101 shown in FIG. 5 is an arrow indicating the flow of holes h ⁺ , and an inequality sign 202 a is an inequality sign or inequality sign indicating the magnitude of hole mobility between the hole transport layer 13 and the light emitting layer 14. 202b is an inequality sign indicating the magnitude of the hole mobility between the hole injection layer 12 and the hole transport layer 13.

The organic EL element 8 (FIG. 5) of this embodiment includes a hole injection layer 12 and a hole transport layer 13 in order from the anode 11 side between the anode 11 and the light emitting layer 14A. smaller than the hole mobility _{mu H_HIL} hole mobility _{mu H_HTL} a hole injection layer 12, luminescent layer 14A of the two layers, among 14B, positive luminescent layer 14A be located closest to the hole transport layer 13 hole mobility _{mu H_HML2} is larger configuration than the hole mobility _{mu H_HTL} of the hole transport layer 13. The organic EL element 8 of the example shown in FIG. 5 has the same layer structure as that of the organic EL element 3 shown in FIG. 2 except that the light emitting layer is composed of two

layers

14A and 14B. Is.

In the present embodiment, in addition to the configuration of the organic EL element 8 described above, the electron injection layer 16 and the electron transport layer 15 are further provided in this order from the cathode 17 side between the cathode 17 and the light emitting layer 14B. It can be set as the organic EL element 9 (refer FIG. 11). Here, the organic EL element 9 of this example has the same layer structure as the organic EL element 7 described above. The organic EL element 9 has the same layer structure as that of the organic EL element 4 shown in FIG. 9 except that the light emitting layer is composed of two

layers

14A and 14B.

As the material of the

light emitting layers

14A and 14B, materials as shown in the first embodiment (for example, materials described in JP2011-139044A) can be used. In particular, a desired emission wavelength and intensity can be obtained by appropriately adopting the dopant and the light emitter described in paragraph 0100 of the publication.
Further, as the host material of the

light emitting layers

14A and 14B, the same material as described above (for example, the material described in JP2009-260308A) can be used, and in particular, the hole described in paragraph 0049 of the same publication. You may select the material which satisfy | fills the above-mentioned mobility relationship from the material which has transportability, the material which has electron transport property of Paragraph 0054, etc.

[Sixth Embodiment]
Hereinafter, a sixth embodiment of the organic EL element of the present invention will be described with reference to FIG. Here, an arrow 101 shown in FIG. 6 is an arrow indicating the flow of holes h ⁺ , and an arrow 102 is an arrow indicating the flow of electrons e ⁺ . The inequality sign 201a is an inequality sign indicating the magnitude of the electron mobility between the electron transport layer 15 and the light emitting layer 14B, and the inequality sign 202a is the magnitude of the hole mobility between the hole transport layer 13 and the light emitting layer 14B. Is an inequality sign. An inequality sign 201b is an inequality sign indicating the magnitude of the electron mobility between the electron injection layer 16 and the electron transport layer 15, and an inequality sign 202b is a hole mobility between the hole injection layer 12 and the hole transport layer 13. It is an inequality sign indicating magnitude.

In the present embodiment, as in the organic EL element 10 shown in FIG. 6, the electron injection layer 16 and the electron transport layer 15 are provided in this order from the cathode 17 side between the cathode 17 and the light emitting layer 14B, and the anode 11 and the light emitting layer. Between 14A, it can also be set as the structure provided with the positive hole injection layer 12 and the positive hole transport layer 13 in order from the anode 11 side. Then, the organic EL element 10 is smaller than the electron mobility _{mu E_EIL} electron mobility _{mu E_ETL} the electron injection layer 16 of the electron transport layer 15, a plurality of light-emitting layers 14A, among 14B, closest to the electron transport layer 15 electron mobility _{mu E_EML1} emitting layer 14B to place the position is greater than the electron mobility _{mu E_ETL} of the electron transport layer 15, the hole mobility _{mu H_HTL} holes move of the hole injection layer 12 of the hole transport layer 13 The hole mobility μ _{h_EML2 of} the light-emitting layer 14A disposed at the position closest to the hole transport layer 13 among the plurality of light-emitting

layers

14A and 14B is smaller than the degree μ _{h_HIL} , and the hole mobility of the hole transport layer 13 The configuration is larger than _{μh_HTL} . The organic EL element 10 has the same layer structure as that of the organic EL element 5 shown in FIG. 3 except that the light emitting layer is composed of two

layers

14A and 14B.

According to the organic EL elements 6 to 10 of the fourth to sixth embodiments as described above, the electron mobility between the layers is similar to the organic EL elements 1 to 5 of the first to third embodiments described above. In addition, by appropriately controlling the hole mobility, the charge recombination in the

light emitting layers

14A and 14B can be promoted to improve the light emission efficiency, and the chemically unstable in the vicinity of the

light emitting layers

14A and 14B. The lifetime can be improved by reducing radicals.

Further, according to the organic EL elements 6 to 10, by adopting a configuration including a plurality of light emitting

layers

14A and 14B, as described above, color mixing is expressed by controlling the wavelength of each light emitting layer, and the like. It becomes easy to obtain an arbitrary color tone.
In the examples shown in FIGS. 4 to 5, the plurality of light emitting layers are represented by two light emitting

layers

14A and 14B. However, in the present embodiment, the present invention is not limited to this, and the desired light emitting characteristics are taken into consideration. However, a light emitting layer having a multilayer structure may be provided.

[Seventh Embodiment]
The seventh embodiment of the organic EL element of the present invention will be described below. In the following description, it will be described with reference to FIG. 7, and detailed description of the configuration common to the description in the first to sixth embodiments will be omitted. Here, an arrow 101 shown in FIG. 7 is an arrow indicating the flow of holes h ⁺ , and an arrow 102 is an arrow indicating the flow of electrons e ⁺ . An inequality sign 201b is an inequality sign indicating the magnitude of electron mobility between the electron injection layer 16 and the electron transport layer 15, and an inequality sign 201c is an electron transfer between the electron transport layer 15 and the light emitting layer (cathode side) 14B. It is an inequality sign indicating the magnitude of degree. The inequality sign 202b is an inequality sign indicating the magnitude of the hole mobility between the hole injection layer 12 and the hole transport layer 13, and the inequality sign 202c is the difference between the hole transport layer 13 and the light emitting layer (anode side) 14A. It is an inequality sign indicating the magnitude of the hole mobility between them. The inequality sign 203b is an inequality sign indicating the size of hole mobility between the light emitting layer (cathode side) 14B and the light emitting layer (anode side) 14A, and the inequality sign 203c is the light emitting layer (cathode side) 14B and the light emitting layer (anode side). ) An inequality sign indicating the magnitude of electron mobility with respect to 14A.

As in the example shown in FIG. 7, the organic EL element 1 </ b> A of the present embodiment has a plurality of light emitting layers 14 </ b> A and 14 </ b> B between the anode 11 and the cathode 17, and a cathode between the cathode 17 and the light emitting layer 14 </ b> B. The electron injection layer 16 and the electron transport layer 15 are provided in this order from the 17th side, and the hole injection layer 12 and the hole transport layer 13 are provided in order from the anode 11 side between the anode 11 and the light emitting layer 14A. .

Then, the organic EL element 1A of the present embodiment is smaller than the electron mobility _{mu E_EIL} electron mobility _{mu E_ETL} of the electron transport layer 15 is an electron injection layer 16, also a plurality of light-emitting layers 14A, among 14B, electronic emitting layer 14B electron mobility _{mu E_EML1} of which located closest to the transport layer 15 is larger configuration than the electron mobility _{mu E_ETL} of the electron transport layer 15.
Furthermore, among the plurality of light emitting

layers

14A and 14B, the electron mobility μ _{e_EML1} of the light emitting layer 14B disposed at the position closest to the electron transport layer 15 is the light emitting layer 14A disposed at the position closest to the hole transport layer 13. The electron mobility is larger than μ _{e_EML2} . The hole mobility _{mu H_HTL} of the hole transport layer 13 is smaller than the hole mobility _{mu H_HIL} of the hole injection layer 12, a plurality of light-emitting layers 14A, among 14B, closest to the hole transport layer 13 emitting layer 14A of the hole mobility _{mu H_EML2} be placed in position, there is a greater configuration than the hole mobility _{mu H_HTL} of the hole transport layer 13. Furthermore, among the plurality of light emitting

layers

14A and 14B, the hole mobility μ _{h_EML1 of} the light emitting layer 14B disposed at the position closest to the electron transport layer 15 is the position of the light emitting layer 14A disposed at the position closest to the hole transport layer 13. The hole mobility is smaller than _{μh_EML2} .

According to the organic EL element 1A of the present embodiment, similarly to the organic EL elements 1 to 10 in the first to sixth embodiments described above, by appropriately controlling the electron mobility and the hole mobility between the respective layers. It is possible to improve the light emission efficiency by promoting charge recombination in the

light emitting layers

14A and 14B, and to improve the lifetime by reducing chemically unstable radicals in the vicinity of the

light emitting layers

14A and 14B. Is possible. In particular, in the present embodiment, by appropriately controlling the electron mobility of the electron injection layer, the electron transport layer, and the light emitting layer 14B, an appropriate amount of electrons transported to the light emitting layer 14B does not penetrate through the light emitting layer 14A. Similarly to the above, by appropriately controlling the hole mobility of the hole injection layer, the hole transport layer, and the light emitting layer 14A, an appropriate amount of holes transported to the light emitting layer 14A penetrates the light emitting layer B. Disappears. Therefore, in the present embodiment, from the viewpoint that there is little penetration of holes and electrons, the probability of charge recombination in each of the light emitting layer 14A and the light emitting layer 14B is improved. It is possible to increase the life improvement effect.

Furthermore, according to the organic EL element 1A, by adopting a configuration including a plurality of light emitting

layers

14A and 14B, as in the organic EL elements 6 to 10 of the fourth embodiment, the wavelength of each light emitting layer can be adjusted. It is possible to obtain a mixed color by controlling to obtain an arbitrary color tone.
Furthermore, according to the organic EL element 1A, the luminous efficiency is further improved by suppressing the penetration of electrons from the light emitting layer 14A, that is, the penetration of holes from the light emitting layer 14B. The effect of being obtained.
In the example shown in FIG. 7, the plurality of light-emitting layers are represented by two light-emitting

layers

14A and 14B. However, as in the fourth embodiment, the present invention is not limited to this. Further, a light emitting layer having a multilayer structure may be used in consideration of light emitting characteristics.

According to the organic EL element according to the present invention as described above, the structure of the light emitting layer 14 (14A, 14B) between the anode 11 and the cathode 17 as described above, the cathode 17 and the light emitting layer 14 during, from the cathode side, sequentially and an electron injection layer 16 and the electron transport layer 15, the electron mobility _{mu E_ETL} of the electron transport layer 15 is smaller than the electron mobility _{mu E_EIL} of the electron injection layer 16, luminescent layer 14 ( 14B) is configured so that the electron mobility μ _{e_EML} (μ _{e_EML1} ) of the electron transport layer 15 is larger than the electron mobility μ _{e_ETL} of the electron transport layer 15 or the hole injection layer 12 between the anode 11 and the light emitting layer 14 from the cathode side. and sequentially a hole transport layer 13, the hole mobility _{mu H_HTL} of the hole transport layer 13 is smaller than the hole mobility _{mu H_HIL} of the hole injection layer 12, hole mobility of the light-emitting layer 14 (14A) degree μ _{h_ _ML} (μ _{h_HML2)} is larger configuration than the hole mobility _{mu H_HTL} of the hole transport layer 13, employs at least one of configuration. Thereby, charge recombination is promoted, luminous efficiency is improved, and lifetime can be improved by reducing chemically unstable radicals in the vicinity of the light emitting layer 14 (14A, 14B). Therefore, it is possible to realize an organic EL element with high luminous efficiency and long life.

Next, examples and comparative examples will be shown to describe the present invention more specifically. Note that the scope of the present invention is not limited by this embodiment, and the organic EL device according to the present invention can be implemented with appropriate modifications within a range that does not change the gist of the present invention.

[Measurement of mobility of organic materials used]
First, the time-of-flight method carrier mobility measuring device (OPTEL TOF-401, Sumitomo Shigeru) regarding each organic material used for forming each layer of this example as shown in the following Table 1 and chemical formulas 1 to 12 Hole mobility and electron mobility were measured using a machine industry). Table 1 below shows the measurement results of mobility obtained by applying an electric field of 1 × 10 ⁶ V / cm to the thin film of each organic material formed between the anode (ITO) and the cathode (Au). .

Here, the light emitting layer provided in the organic EL devices prepared in Examples 1 to 3 and Comparative Examples 1 to 3 is composed of a mixture of a light emitter and a host compound. In these light-emitting layers, the main material involved in the charge transport is a host material (a material having a high mixing ratio), so the charge mobility of the light-emitting layer is replaced by the charge mobility of the host compound. In addition, when a mixture is used for the charge injection layer and the charge transport layer, the material having a high mixing ratio is the main material related to the charge transport of the corresponding layer, and therefore the charge mobility of the corresponding layer is Substitute the charge mobility of compounds with a high ratio.

[Preparation of Organic EL Element] (Example 1)
In Example 1, an organic EL device in which the electron mobility of the electron transport layer was smaller than the electron mobility of the electron injection layer and the electron mobility of the light emitting layer was larger than the electron mobility of the electron transport layer was produced. Specifically, a substrate with ITO (Indium Tin Oxide) in which two ITO electrodes with a width of 4 mm serving as an anode are formed in a stripe pattern on one surface of a 25 mm square glass substrate (manufactured by Nippon Electric Co., Ltd.) An organic light emitting device was fabricated using

First, 40 nm of m-MTDATA represented by Chemical Formula 1 was formed on the ITO electrode by a vacuum deposition method to form a hole injection layer and a hole transport layer.
Next, the phosphor PH-1 represented by Chemical Formula 2 and the host compound PyTMB represented by Chemical Formula 3 are co-evaporated to a weight ratio of 10:90 to form a light-emitting layer having a thickness of 20 nm. did.

Next, Alq3 represented by Chemical Formula 4 was deposited to a thickness of 20 nm by vacuum deposition to form an electron transport layer, and then BCP and Cs represented by Chemical Formula 5 were co-deposited (weight) Ratio 20: 1), an electron injection layer having a thickness of 20 nm was stacked and formed.
Next, an aluminum layer having a thickness of 150 nm is stacked on the electron injection layer by an evaporation method, so that 3 mm × 2 cathodes arranged in stripes are orthogonal to the extending direction of the anode. Thus, four organic EL elements having a length of 4 mm and a width of 3 mm in plan view were produced.

Then, using a programmable DC voltage / current source (manufactured by Advantest Co., Ltd .: TR6143), voltage is applied to the organic EL element created by the above procedure to emit light, and the luminance is measured with a luminance meter (Topcon Co., Ltd.). Measured using BM-8).
Table 2 below shows the luminance half-life at the time of constant current driving when the maximum light emission external quantum efficiency and the initial luminance were 1000 cd / m ² obtained in Example 1.

(Comparative Example 1)
In Comparative Example 1, an organic EL device was produced in the same manner as in Example 1 except that OXD-7 represented by Chemical Formula 6 was used instead of PyTMB represented by Chemical Formula 3 as the host material of the light emitting layer. The maximum emission external quantum efficiency and luminance half-life were determined and shown in Table 2 above.

(Example 2)
In Example 2, the hole mobility of the hole transport layer 13 is smaller than the hole mobility of the hole injection layer 12, and the hole mobility of the light emitting layer 14 is the hole mobility of the hole transport layer 13. An organic EL element larger than the above degree was produced.
Specifically, first, pTmTDMPD (synthesized according to the method described in International Publication WO2011 / 052625) (100 parts by mass), which is a triarylamine derivative represented by Chemical Formula 7, and Chemical Formula 8 F4TCNQ (Aldrich) (5 parts by mass), which is an electron-accepting compound, was dissolved in toluene, and a solution was prepared so that the solid content concentration was 0.8% by mass. And this solution was apply | coated by the spin coat method (rotation speed: 3000 rpm, rotation time 30 seconds) on the glass substrate with an ITO film | membrane similar to what was used in Example 1, and the obtained coating film was nitrogen atmosphere. Bottom: heated at 210 ° C. for 1 hour to form a 20 nm thick hole injection layer.

Next, m-TTA represented by Chemical Formula 9 was formed to a thickness of 10 nm on the hole injection layer by a vacuum deposition method to form a hole transport layer.
Next, the phosphor PH-2 represented by the chemical formula 10 and the host compound BFA-1T represented by the chemical formula 11 were co-evaporated so as to have a weight ratio of 10:90, and a light-emitting layer having a thickness of 20 nm was formed. A film was formed.
Next, PyTMB represented by Chemical Formula 3 was formed to a thickness of 40 nm by vacuum deposition to form an electron injection layer and an electron transport layer, and then a 0.5 nm sodium fluoride layer and a 150 nm thickness were further formed. An organic EL element was produced by depositing a cathode made of an aluminum layer in this order to form a laminated film.

Then, in the same manner as in Example 1, the maximum light emission external quantum efficiency and luminance half-life of the organic EL device produced by the above procedure were determined and shown in Table 2.

(Comparative Example 2)
In Comparative Example 2, an organic light emitting device was fabricated in the same manner as in Example 2, except that TPPCz represented by Chemical Formula 12 was used instead of BFA-1T represented by Chemical Formula 11 as the host compound of the light emitting layer. The maximum emission external quantum efficiency and luminance half-life were determined and shown in Table 2 above.

(Example 3)
The organic EL element produced in Example 3 was formed by laminating two light emitting layers. In the organic EL device manufactured in this example, the electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer, and the light emission disposed in the position closest to the electron transport layer among the plurality of light emitting layers. The electron mobility of the layer is larger than the electron mobility of the electron transport layer. Further, among the plurality of light emitting layers, the electron mobility of the light emitting layer disposed at the position closest to the electron transport layer is configured to be greater than the electron mobility of the light emitting layer disposed at the position closest to the hole transport layer. ing. In addition, the hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer, and the hole mobility of the light emitting layer arranged at the position closest to the hole transport layer among the plurality of light emitting layers The degree is higher than the hole mobility of the hole transport layer. Further, among the plurality of light emitting layers, the hole mobility of the light emitting layer disposed at the position closest to the hole transport layer is larger than the hole mobility of the hole transport layer, and among the plurality of light emitting layers, The hole mobility of the light emitting layer disposed at the position closest to the electron transport layer is configured to be smaller than the hole mobility of the light emitting layer disposed at the position closest to the hole transport layer.

Specifically, first, in the same manner as in Example 2, a hole injection layer, a hole transport layer, and a light emitting layer containing the phosphor PH-2 represented by Chemical Formula 10 were formed on a glass substrate with an ITO film. The layers were sequentially stacked.
Next, on this light emitting layer, a light emitting layer containing the light emitter PH-1 represented by Chemical Formula 2, an electron transport layer, an electron injection layer, and a cathode were laminated in this order by the same method as in Example 1. By forming, an organic EL element was produced.

(Comparative Example 3)
In Comparative Example 3, an organic EL device was produced in the same manner as in Example 3 except that TPPCz represented by Chemical Formula 12 was used instead of BFA-1T represented by Chemical Formula 11 as the host compound of the light emitting layer. The maximum emission external quantum efficiency and luminance half-life were determined and shown in Table 2 above.

(result)
As shown in Tables 1 and 2, in the organic EL devices of Examples 1 to 3 that are produced with the relationship between the electron mobility or the hole mobility between the layers as defined in the present invention, the maximum emission external quantum The efficiency was 11.6 to 15.5%, which was superior to that of Comparative Examples 1 to 3, and the luminance half-life was 2800 to 5900 hours.

On the other hand, in the organic EL elements of Comparative Examples 1 to 3 manufactured with the relationship between the electron mobility or the hole mobility between the respective layers being outside the specified range of the present invention, the maximum light emission external quantum efficiency is 7.5 to 10. 9%, which is inferior to Examples 1 to 3, and the luminance half-life is 300 to 700 hours, which is significantly shorter than Examples 1 to 3.

According to the results of the examples as described above, the relationship between the electron mobility between the electron injection layer, the electron transport layer, and the light emitting layer, in addition to the relationship between the hole injection layer, the hole transport layer, and the light emitting layer. It is clear that both the light emission efficiency and the lifetime characteristics are improved by setting the relationship between the electron mobility or the hole mobility to the conditions defined in the present invention.

Since the organic EL device according to the present invention is excellent in light emission characteristics and lifetime characteristics, for example, various displays used for televisions, computer monitors, consumer TVs, large display displays, mobile phones, various portable terminals, and the like. It is suitable for various lighting devices such as a device, a backlight for liquid crystal, in-vehicle lighting, and indoor lighting.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1A ... organic EL element, 11 ... anode, 12 ... hole injection layer, 13 ... hole transport layer, 14, 14A, 14B ... Light emitting layer, 15 ... electron transport layer, 16 ... electron injection layer, 17 ... cathode, 101 ... arrow indicating the flow of holes, 102 ... arrow indicating the flow of electrons, 201a ... between the electron transport layer and the light emitting layer An inequality sign indicating the magnitude of electron mobility, 201b ... an inequality sign indicating the magnitude of electron mobility between the electron injection layer and the electron transport layer, 201c ... an electron transport layer and a light emitting layer (cathode side) in the seventh embodiment An inequality sign indicating the magnitude of electron mobility between the holes, 202a... An inequality sign indicating the magnitude of hole mobility between the hole transport layer and the light emitting layer, 202b... Between the hole injection layer and the hole transport layer. An inequality sign indicating the magnitude of hole mobility, 202c... Inequality sign indicating the magnitude of hole mobility between layers (anode side), 203b... The magnitude of hole mobility between the light emitting layer (cathode side) and the light emitting layer (anode side) in the seventh embodiment , An inequality sign indicating the magnitude of electron mobility between the light emitting layer (cathode side) and the light emitting layer (anode side) in the seventh embodiment.

Claims

An organic EL device having a light emitting layer between an anode and a cathode,
Between the cathode and the light emitting layer, comprising an electron injection layer and an electron transport layer in order from the cathode side,
The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer,
The organic EL element, wherein the electron mobility of the light emitting layer is larger than the electron mobility of the electron transport layer.
The organic EL device according to claim 1, further comprising a hole injection layer and a hole transport layer in order from the anode side between the anode and the light emitting layer.
An organic EL device having a light emitting layer between an anode and a cathode,
Between the anode and the light emitting layer, comprising a hole injection layer and a hole transport layer in order from the anode side,
The hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer,
The organic EL element, wherein the hole mobility of the light emitting layer is larger than the hole mobility of the hole transport layer.
The organic EL device according to claim 3, further comprising an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the light emitting layer.
An organic EL device having a light emitting layer between an anode and a cathode,
Between the cathode and the light emitting layer, an electron injection layer and an electron transport layer are provided in order from the cathode side, and between the anode and the light emitting layer, a hole injection layer and a hole transport layer are sequentially provided from the anode side. With
The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer,
The electron mobility of the light emitting layer is larger than the electron mobility of the electron transport layer,
The hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer,
The organic EL element, wherein the hole mobility of the light emitting layer is larger than the hole mobility of the hole transport layer.
An organic EL element having a plurality of light emitting layers between an anode and a cathode,
Between the cathode and the plurality of light emitting layers, an electron injection layer and an electron transport layer in order from the cathode side,
The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer,
The organic EL element characterized by the electron mobility of the light emitting layer arrange | positioned in the position nearest to the said electron carrying layer among these light emitting layers being larger than the electron mobility of the said electron carrying layer.
The organic EL device according to claim 6, further comprising a hole injection layer and a hole transport layer in order from the anode side between the anode and the plurality of light emitting layers.
An organic EL element having a plurality of light emitting layers between an anode and a cathode,
Between the anode and the plurality of light emitting layers, a hole injection layer and a hole transport layer are sequentially provided from the anode side,
The hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer,
The organic EL element, wherein a hole mobility of a light emitting layer disposed at a position closest to the hole transport layer among the plurality of light emitting layers is larger than a hole mobility of the hole transport layer.
The organic EL device according to claim 8, further comprising an electron injection layer and an electron transport layer in order from the cathode side between the cathode and the plurality of light emitting layers.
An organic EL element having a plurality of light emitting layers between an anode and a cathode,
Between the cathode and the plurality of light emitting layers, an electron injection layer and an electron transport layer are sequentially provided from the cathode side, and between the anode and the plurality of light emitting layers, a hole injection layer is sequentially provided from the anode side. With a hole transport layer,
The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer,
Among the plurality of light emitting layers, the electron mobility of the light emitting layer disposed at a position closest to the electron transport layer is larger than the electron mobility of the electron transport layer,
The hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer,
The organic EL element, wherein a hole mobility of a light emitting layer disposed at a position closest to the hole transport layer among the plurality of light emitting layers is larger than a hole mobility of the hole transport layer.
An organic EL element having a plurality of light emitting layers between an anode and a cathode,
Between the cathode and the plurality of light emitting layers, an electron injection layer and an electron transport layer are sequentially provided from the cathode side, and between the anode and the plurality of light emitting layers, a hole injection layer is sequentially provided from the anode side. With a hole transport layer,
The electron mobility of the electron transport layer is smaller than the electron mobility of the electron injection layer,
Among the plurality of light emitting layers, the electron mobility of the light emitting layer disposed at a position closest to the electron transport layer is larger than the electron mobility of the electron transport layer,
Among the plurality of light emitting layers, the electron mobility of the light emitting layer disposed at the position closest to the hole transport layer is smaller than the electron mobility of the light emitting layer disposed at the position closest to the electron transport layer,
The hole mobility of the hole transport layer is smaller than the hole mobility of the hole injection layer,
Among the plurality of light emitting layers, the hole mobility of the light emitting layer disposed at the position closest to the hole transport layer is larger than the hole mobility of the hole transport layer,
Among the plurality of light emitting layers, the hole mobility of the light emitting layer disposed at the position closest to the electron transport layer is smaller than the hole mobility of the light emitting layer disposed at the position closest to the hole transport layer,
An organic EL device characterized by that.