JP7476786B2 - Organic electroluminescence element, its manufacturing method, display device and lighting device - Google Patents

Description

The present invention relates to an organic electroluminescence element, a manufacturing method thereof, a display device, and a lighting device.
More specifically, the present invention relates to an organic electroluminescence element or the like that does not require individual electrodes or banks, has a low driving voltage, and has high luminous efficiency.

Organic electroluminescence (EL) elements (hereinafter also referred to as "organic EL elements") are surface light sources that have advantages in terms of lightness, flexibility, etc., and have been used in a wide range of applications, such as lighting, signage, and displays. However, to realize lighting, signage, and displays that can reproduce multiple colors other than single-color lighting, pixel formation (see Patent Document 1) and separate painting to extract different luminescent colors for each pixel (see Patent Document 2) are required.

However, the technology disclosed in Patent Document 1 is inefficient, and in particular, there is a problem with the reduction in brightness and color purity caused by passing through a color filter. In addition, the technology disclosed in Patent Document 2 requires a complex manufacturing process using a metal mask, and there is a problem with it not being on-demand.

On the other hand, there is an increasing demand for higher pixel resolution, as exemplified by micro LEDs, in which the R (red), G (green), and B (blue) subpixels of a display are each independent LEDs (light emitting diodes), and there has been a demand for a general-purpose method to be established.

As a solution to the above problem, in recent years, methods have been proposed for manufacturing the emission layer (EML) and the like using inkjet recording (e.g., Patent Documents 3, 4, 5, and 6). However, this requires that the pixels be configured with divided electrodes and that banks be formed in all pixels for separate coating, resulting in complex configurations and manufacturing structures, and increased costs due to low yields. A more fundamental solution to pixel formation is therefore required.

As an organic EL element that solves these problems, Non-Patent Document 1 discloses "an organic EL element that has a light-emitting layer formed by ink-jetting a light-emitting ink (ink containing a charge-transporting host compound and a light-emitting compound) onto an ink-receiving layer made of an insulating polymer, and that emits an ejection pattern image by passing a current between a pair of anode and cathode." This organic EL element does not require individual electrodes or banks, and is therefore capable of solving the above problems.

However, because the light-emitting layer of this organic EL element is formed by inkjet ejection of light-emitting ink, the charge-transporting host compound and light-emitting compound tend to have low concentrations in the lower part of the area where the light-emitting ink is ejected. This causes problems such as poor charge transportability and high driving voltage.

Furthermore, to solve this problem, Non-Patent Document 2 discloses an organic EL element having an emissive layer formed by inkjet ejecting ink containing a luminescent compound onto an ink-receiving layer that has already contained a hole-transporting material.

However, even the organic EL element disclosed in Non-Patent Document 2 does not have sufficient luminous efficiency, and there is a demand for an organic EL element that does not require individual electrodes or banks and that has both a low driving voltage and high luminous efficiency.

JP 2006-073219 A JP 2003-272838 A Japanese Patent Application Laid-Open No. 11-271753 JP 2006-223954 A Japanese Patent Application Laid-Open No. 11-54270 JP 2001-189193 A

K. Matsui, J. Yanagi, M. Shibata, S. Naka, H. Okada, T. Miyabayashi, T. Inoue: "Multi-Color Organic Light Emitting Panels Using Self-Aligned Ink-Jet Printing Technology", Mol. Cryst. Liq. Cryst., 471(1), pp.261-268 (2007). R. Satoh, S. Naka, M. Shibata, H. Okada, T. Inoue, T. Miyabayashi:” Self-Aligned Organic Light-Emitting Diodes with Color Changing by Ink-Jet Printing Dots ”, Japanese Journal of Applied Physics, 50 , pp. 01BC09-1-4 (2011)

The present invention has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide an organic electroluminescence element that does not require individual electrodes or banks, has a low driving voltage, and has high luminous efficiency, a manufacturing method thereof, and a display device and a lighting device that include the organic electroluminescence element.

The present inventors have investigated the causes of the above problems in order to solve the above problems, and as a result have found that it is possible to provide an organic electroluminescence element, etc. that does not require individual electrodes or banks, has a low driving voltage and high luminous efficiency, by configuring an emissive layer to contain an ink receiving layer that is present as a continuous phase throughout the entire display area, and at least one luminescent compound that is present with a concentration gradient in the in-plane and thickness directions of the ink receiving layer, and the ink receiving layer to contain at least one insulating polymer and at least one charge transport compound, and further optimize the relationship between the excitation energy levels of the charge transport compound and the luminescent compound, thereby completing the present invention.
That is, the above-mentioned problems of the present invention are solved by the following means.

1. An organic electroluminescence element having a light-emitting layer between at least one pair of an anode and a cathode,
The light-emitting layer contains an ink-receiving layer that exists as a continuous phase throughout the entire display area, and at least one light-emitting compound that exists with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer,
The ink receiving layer contains at least one insulating polymer and at least one charge transporting compound,
The light-emitting compound contains a phosphorescent compound or a delayed fluorescent compound, and
An organic electroluminescence device, characterized in that the lowest excited triplet energy level of any one of the charge transport compounds is higher than the lowest excited triplet energy level of any one of the phosphorescent compounds or delayed fluorescent compounds.

2. The organic electroluminescence element according to paragraph 1, characterized in that the lowest excited triplet energy level of any of the charge transport compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or delayed fluorescent compounds.

3. An organic electroluminescence element having a light-emitting layer between at least one pair of an anode and a cathode,
The light-emitting layer contains an ink-receiving layer that exists as a continuous phase throughout the entire display area, and at least one light-emitting compound that exists with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer,
The ink receiving layer contains at least one insulating polymer and at least one charge transporting compound,
a mass ratio of the charge transporting compound in the ink receiving layer is within a range of 50 to 80%;
The light-emitting compound contains a fluorescent compound, and
An organic electroluminescence device, wherein the lowest excited singlet energy level of any one of the charge transport compounds is higher than the lowest excited singlet energy level of any one of the fluorescent compounds.

4. The organic electroluminescence device according to claim 3, characterized in that the lowest excited singlet energy level of any of the charge transport compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds.

5. The organic electroluminescence element described in item 1 or 2 , wherein the mass ratio of the charge transporting compound in the ink receiving layer is within a range of 20 to 80%.

6. A method for producing the organic electroluminescence element according to any one of items 1 to 5, comprising the steps of:
a step of dropping a solution containing the light-emitting compound onto the ink-receiving layer to form the light-emitting layer.

7. The method for producing an organic electroluminescence element according to claim 6, characterized in that the method for dropping the solution containing the luminescent compound onto the ink receiving layer is an inkjet printing method.

8. A display device comprising an organic electroluminescence element according to any one of claims 1 to 5.

9. A lighting device comprising an organic electroluminescence element according to any one of claims 1 to 5.

The above-mentioned means of the present invention make it possible to provide an organic electroluminescence element that does not require individual electrodes or banks, has a low driving voltage, and has high luminous efficiency, a manufacturing method thereof, and a display device and a lighting device that include the organic electroluminescence element.

Although the mechanism by which the effects of the present invention are expressed or acted upon has not been clarified, it is speculated as follows.

First, in the organic EL element of the present invention, the light-emitting layer is configured to contain an ink-receiving layer that exists as a continuous phase throughout the entire display area, and at least one type of light-emitting compound that exists with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer, thereby eliminating the need for individual electrodes or banks.

In addition, the ink receiving layer is configured to contain at least one type of insulating polymer and at least one type of charge transport compound, making it possible to achieve a low driving voltage.

Furthermore, unlike the light-emitting layer of the organic EL element disclosed in Non-Patent Document 2, the present invention is characterized in that, when a phosphorescent compound or a delayed fluorescent compound is contained as the light-emitting compound, the lowest excited triplet energy level of any of the charge transport compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or delayed fluorescent compounds, and, when a fluorescent compound is contained as the light-emitting compound, the lowest excited singlet energy level of any of the charge transport compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds.

In the light-emitting layer of the organic EL element disclosed in Non-Patent Document 2, the charge transport compound used is the hole transport material 4,4'-bis[N-(1-naphyl)-N-phenyl-amino]biphenyl (α-NPD), and the light-emitting compound used is Bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium III (FIrpic).

The inventors have found that in an organic EL device formed from a combination of the above compounds, the lowest excited triplet energy level of the charge transport compound is lower than the lowest excited triplet energy level of the light emitting compound, resulting in energy transfer from the light emitting compound to the charge transport compound (reverse energy transfer), and thus reducing the luminous efficiency.

In contrast, in the organic EL element of the present invention, the relationship between the excitation energy levels of the charge transport compound and the light-emitting compound is optimized, making it difficult for energy to be transferred from the light-emitting compound to the charge transport compound, thereby increasing the light-emitting efficiency.

It is believed that these mechanisms of expression or action can provide an organic electroluminescence element that does not require individual electrodes or banks, has a low driving voltage, and has high luminous efficiency, a method for manufacturing the same, and a display device and lighting device that include the organic electroluminescence element.

Schematic cross-sectional view of an organic EL element Schematic diagram of a method for manufacturing an organic EL element using an inkjet printing method Schematic perspective view of an inkjet head Schematic bottom view of the inkjet head Schematic diagram of a display device Schematic cross-sectional view of a display device Schematic cross-sectional view of an organic EL element according to Example 1 Schematic cross-sectional view of an organic EL element according to Example 2

As one embodiment, the organic electroluminescent element of the present invention is an organic electroluminescent element having a light-emitting layer between at least one pair of anodes and cathodes, the light-emitting layer containing an ink-receiving layer present as a continuous phase throughout the display area and at least one light-emitting compound present with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer, the ink-receiving layer containing at least one insulating polymer and at least one charge-transporting compound, the light-emitting compound containing a phosphorescent compound or a delayed fluorescent compound, and the lowest excited triplet energy level of any of the charge-transporting compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or the delayed fluorescent compounds.

In the above embodiment, it is preferable that the lowest excited triplet energy level of any of the charge transport compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or delayed fluorescent compounds, in order to further suppress reverse energy transfer.

In one embodiment, the organic electroluminescent element of the present invention is an organic electroluminescent element having a light-emitting layer between at least one pair of anode and cathode, the light-emitting layer containing an ink-receiving layer present as a continuous phase throughout the display area and at least one light-emitting compound present with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer, the ink-receiving layer containing at least one insulating polymer and at least one charge-transporting compound, the light-emitting compound containing a fluorescent compound, and the lowest excited singlet energy level of any of the charge-transporting compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds.

In the above embodiment, it is preferable that the lowest excited singlet energy level of any of the charge transport compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds, in order to further suppress reverse energy transfer.

In the organic electroluminescence device of the present invention, the mass ratio of the charge transporting compound in the ink receiving layer is preferably within a range of 20 to 80%.
When the mass ratio of the charge transporting compound is 20% or more, the driving voltage can be lowered, and when the mass ratio of the charge transporting compound is 80% or less, the liquid flow of the ink receiving layer material can be suppressed and partial thinning of the ink receiving layer can be prevented, thereby preventing failures such as short circuits between electrodes.

The method for producing an organic electroluminescent element of the present invention is a method for producing an organic electroluminescent element of the present invention, and is characterized by having a step of forming the light-emitting layer by dropping a solution containing the light-emitting compound onto the ink-receiving layer.

In the method for producing an organic electroluminescence element of the present invention, the method of dropping the solution containing the luminescent compound onto the ink receiving layer is preferably an inkjet printing method, which is capable of forming small droplets, does not require the formation of a bank, and is simple.

The display device of the present invention is characterized by having the organic electroluminescence element of the present invention.

The lighting device of the present invention is characterized by including the organic electroluminescence element of the present invention.

The present invention, its components, and the forms and modes for implementing the present invention are described in detail below. Note that in this application, "~" is used to mean that the numerical values before and after it are included as the lower and upper limits.

(1) Structure of Organic EL Element Representative examples of the structure of the organic EL element of the present invention include the following examples, but are not limited to these.
(i) anode/light-emitting layer/cathode (ii) anode/light-emitting layer/electron transport layer/cathode (iii) anode/hole transport layer/light-emitting layer/cathode (iv) anode/hole transport layer/light-emitting layer/electron transport layer/cathode (v) anode/hole transport layer/light-emitting layer/electron transport layer/electron injection layer/cathode (vi) anode/hole injection layer/hole transport layer/light-emitting layer/electron transport layer/cathode (vii) anode/hole injection layer/hole transport layer/(electron blocking layer/)light-emitting layer/(hole blocking layer/)electron transport layer/electron injection layer/cathode Of the above, the configuration (i) is preferably used, but is not limited thereto.

Figure 1 is a cross-sectional schematic diagram of an organic EL element having the configuration (i). From the bottom, it is composed of a glass substrate (107) with a transparent electrode (anode), a light-emitting layer (106), and a cathode (105). The light-emitting layer (106) is composed of an ink-receiving layer (201) and a light-emitting compound (202).

The light-emitting layer according to the present invention is composed of a single layer or multiple layers. When multiple light-emitting layers are used, a non-light-emitting intermediate layer may be provided between each of the light-emitting layers. If necessary, a hole-blocking layer (also called a hole-blocking layer) or an electron-injecting layer (also called a cathode buffer layer) may be provided between the light-emitting layer and the cathode, and an electron-blocking layer (also called an electron-blocking layer) or a hole-injecting layer (also called an anode buffer layer) may be provided between the light-emitting layer and the anode.

The "electron transport layer" according to the present invention is a layer that has the function of transporting electrons, and in a broad sense, the electron transport layer also includes an electron injection layer and a hole blocking layer. It may also be composed of multiple layers.

The "hole transport layer" according to the present invention is a layer that has the function of transporting holes, and in a broad sense, hole injection layers and electron blocking layers are also included in the hole transport layer. It may also be composed of multiple layers.

In the above typical device configuration, layers other than the anode and cathode, including the light-emitting layer, are referred to as "organic functional layers."

(2) Light-emitting layer The light-emitting layer of the organic EL element of the present invention is characterized in that it contains an ink-receiving layer which is present as a continuous phase throughout the entire display area, and at least one light-emitting compound which is present with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer.

"An ink-receiving layer that exists as a continuous phase over the entire display area" refers to, for example, an ink-receiving layer that exists as a continuous solid phase (a solid phase whose chemical composition and physical state are entirely and substantially uniform) over the entire surface of the light-emitting region of an organic EL element.

"At least one luminescent compound that exists with a concentration gradient in the in-plane and thickness directions of the ink receiving layer" refers to a luminescent compound that is not continuously attached or contained on the ink receiving layer at a uniform concentration, but is intermittently attached at a non-uniform concentration to each microscopic location that constitutes the surface of the ink receiving layer.
The phrase "existing with a concentration gradient in the in-plane direction" refers to a state in which the luminescent compound is attached or contained in a dot-like (point-like) form when viewed from the light-emitting surface side.
"Existing with a concentration gradient in the thickness direction" refers to a state in which, for example, when the cross section of the light-emitting layer is viewed with the light-emitting surface facing down, the concentration of the light-emitting compound is high in the upper part of the light-emitting layer and low in the lower part of the light-emitting layer. Or, it refers to a state of concentration gradient with the opposite effect. Usually, the concentration is higher on the side where the inkjet lands, which will be described later.

Although there is no clear boundary, the area of the light-emitting layer where the light-emitting compound is the main component and exists in the form of dots (points) is called the "dot area."

In an embodiment of the present invention, from the viewpoint of manifesting the effects of the present invention, it is preferable that the maximum emission luminance is at least twice the minimum emission luminance in the in-plane direction of the ink receiving layer.

The light-emitting layer according to the present invention is a layer that provides a field where electrons and holes injected from an electrode or an adjacent layer recombine and emit light via excitons, and the light-emitting portion may be within the light-emitting layer or at the interface between the light-emitting layer and an adjacent layer.

There is no particular limit to the total thickness of the light-emitting layer, but from the viewpoints of the homogeneity of the layer to be formed, preventing the application of unnecessary high voltage during light emission, and improving the stability of the emitted color relative to the driving current, it is preferably adjusted to within the range of 2 nm to 5 μm, more preferably within the range of 2 to 500 nm, and even more preferably within the range of 5 to 200 nm.

The thickness of each light-emitting layer is preferably adjusted to within the range of 2 to 1000 nm, more preferably within the range of 2 to 200 nm, and even more preferably within the range of 3 to 150 nm.

The ink receiving layer according to the present invention is characterized by a composition containing at least one insulating polymer and at least one charge transporting compound. By containing a charge transporting compound in the ink receiving layer, the driving voltage of the organic EL element can be reduced.

In the organic EL element of the present invention, the mass ratio of the charge transporting compound in the ink receiving layer is preferably within the range of 20 to 80%.
When the mass ratio of the charge transporting compound is 20% or more, the driving voltage can be lowered, and when the mass ratio of the charge transporting compound is 80% or less, the liquid flow of the ink receiving layer material can be suppressed and partial thinning of the ink receiving layer can be prevented, thereby preventing failures such as short circuits between electrodes.

Details about insulating polymers and charge transport compounds will be provided later.

The light-emitting compound is contained in the light-emitting layer in an amount ranging from 1 to 80% by mass, and preferably in an amount ranging from 5 to 40% by mass.

In the present invention, the luminescent compound refers to a fluorescent compound, a delayed fluorescent compound, and a phosphorescent compound. These will be described in detail later.

The luminescent compounds used in the present invention may be used in combination of multiple types, such as a combination of different phosphorescent compounds or a combination of a phosphorescent compound and a fluorescent compound. This allows any luminescent color to be obtained.

The light-emitting layer according to the present invention preferably contains a plurality of light-emitting compounds with different light-emitting colors and emits white light. The combination of light-emitting compounds that emit white light is not particularly limited, but examples include combinations of blue and orange, blue, green and red, etc. The white color in the present invention is preferably a color in the range of x=0.39±0.09, y=0.38±0.08 in the CIE1931 color system at 1000 cd/m2 when the ^2- degree viewing angle front luminance is measured by the method described below.

The color of light emitted by the organic EL element of the present invention and the compound used in the present invention is determined by the color measured using a spectroradiometer CS-1000 (manufactured by Konica Minolta, Inc.) and applied to the CIE chromaticity coordinates in Figure 3.16 on page 108 of "New Color Science Handbook" (edited by the Color Science Association of Japan, University of Tokyo Press, 1985).

The light-emitting layer and ink-receiving layer according to the present invention may contain other materials and additives. Examples of additives include halogen elements such as bromine, iodine, and chlorine, halogenated compounds, alkali metals such as Pd, Ca, and Na, alkaline earth metals, and transition metal compounds, complexes, and salts. In addition, various functional additives contained in the light-emitting ink described below may be contained.

(3) Excitation Energy Levels of Charge Transport Compound and Light Emitting Compound The conditions for the excitation energy levels of the charge transport compound and light emitting compound are as follows.
Condition (A): The lowest excited triplet energy level of any charge transporting compound is higher than the lowest excited triplet energy level of any phosphorescent compound or delayed fluorescent compound.
Condition (B): The lowest excited triplet energy level of any of the charge transport compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or delayed fluorescent compounds.
Condition (C): The lowest excited singlet energy level of any of the charge transport compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds.
Condition (D): The lowest excited singlet energy level of each charge transport compound is higher than the lowest excited singlet energy level of each fluorescent compound.

The organic EL element of the present invention is characterized in that, when it contains a phosphorescent compound or a delayed fluorescent compound as a light-emitting compound, it satisfies the above-mentioned condition (A), and, when it contains a fluorescent compound as a light-emitting compound, it satisfies the above-mentioned condition (C).
This makes it possible to make it difficult for energy to be transferred from the light-emitting compound to the charge-transporting compound (reverse energy transfer), thereby making it possible to increase the luminous efficiency.

In addition, when at least one of the charge transport layer compound and the light-emitting compound is a plurality of types, if the light-emitting compound contains a phosphorescent compound or a delayed fluorescent compound, it is preferable to satisfy the above condition (B), and if the light-emitting compound contains a fluorescent compound, it is preferable to satisfy the above condition (D).
This makes it possible to further suppress the reverse energy transfer.

When a phosphorescent compound or a delayed fluorescent compound is contained as the luminescent compound, the above condition (A) needs to be satisfied, and when a fluorescent compound is contained as the luminescent compound, the above condition (C) needs to be satisfied. Therefore, when a phosphorescent compound or a delayed fluorescent compound and a fluorescent compound are used in combination, either the above condition (A) or the above condition (C) needs to be satisfied.

In addition, when using a phosphorescent compound or delayed fluorescent compound in combination with a fluorescent compound, it is preferable to satisfy both the above condition (A) and the above condition (C) in order to further suppress reverse energy transfer.

Furthermore, when at least one of the charge transport layer compounds or the light emitting compounds is of multiple types and a phosphorescent compound or a delayed fluorescent compound and a fluorescent compound are used in combination, it is preferable to satisfy either the above condition (B) or the above condition (D), and it is more preferable to satisfy both the above condition (B) and the above condition (D).

<Method of measuring excitation energy levels (S ₁ , T ₁ )>
The lowest excited singlet energy level _S1 and the lowest excited triplet energy level T1 can be measured using Gaussian ₀₉ (Revision C.01, MJ Frisch, et al., Gaussian, Inc., 2010.), a molecular orbital calculation software manufactured by Gaussian, Inc., USA.
The lowest excited singlet energy level S 1 and the lowest excited triplet energy level T 1 can be obtained by performing structure optimization calculations using _B3LYP as the functional and 6-31G(d) as the basis function for charge transport compounds and LanL2DZ as the basis function for light-emitting compounds, and further performing excited state calculations using time-dependent density functional theory ( _TDDFT ).

(4) Luminescent Compound The “luminescent compound” according to the present invention includes a “fluorescent compound”, a “phosphorescent compound” and a “delayed fluorescent compound”. Each of these will be described below.

<Fluorescent Compounds>
In the present invention, the term "fluorescent compound" refers to a compound that emits fluorescence other than delayed fluorescence. "Fluorescence" refers to light emitted when returning from a singlet excited state to a ground state, and "fluorescence other than delayed fluorescence" refers to fluorescence excluding "delayed fluorescence" such as "thermally activated delayed fluorescence (TADF)" and "triplet-triplet annihilation (TTA) delayed fluorescence". In other words, in the present invention, the term "fluorescent compound" does not include "delayed fluorescent compounds" such as "thermally activated delayed fluorescent compounds" and "triplet-triplet annihilation delayed fluorescent compounds", and refers to compounds that do not undergo upconversion due to reverse intersystem crossing from the lowest excited triplet energy level to the lowest excited singlet energy level.

Fluorescent compounds do not necessarily have to be heavy metal complexes like phosphorescent compounds; so-called organic compounds consisting of combinations of common elements such as carbon, oxygen, nitrogen and hydrogen can be used. In addition, other non-metallic elements such as phosphorus, sulfur and silicon can also be used. Complexes of typical metals such as aluminum and zinc can also be used, so the diversity is almost limitless.

The fluorescent compound can be appropriately selected from known fluorescent compounds used in the light-emitting layer of an organic EL element.

Examples of known fluorescent compounds that can be used in the present invention include anthracene derivatives, pyrene derivatives, chrysene derivatives, fluoranthene derivatives, perylene derivatives, fluorene derivatives, arylacetylene derivatives, styrylarylene derivatives, styrylamine derivatives, arylamine derivatives, boron complexes, coumarin derivatives, pyran derivatives, cyanine derivatives, croconium derivatives, squarium derivatives, oxobenzanthracene derivatives, fluorescein derivatives, rhodamine derivatives, pyrylium derivatives, perylene derivatives, polythiophene derivatives, and rare earth complex compounds.

<Phosphorescent Compound>
In the present invention, the term "phosphorescent compound" refers to a compound that emits phosphorescence, and is specifically defined as a compound that emits phosphorescence at room temperature (25° C.) and has a phosphorescence quantum yield of 0.01 or more at 25° C. The phosphorescence quantum yield is preferably 0.1 or more. "Phosphorescence" refers to light emitted when returning from a triplet excited state to the ground state.

The above phosphorescence quantum yield can be measured by the method described in Spectroscopy II, 4th Edition, Experimental Chemistry Lectures 7, p. 398 (1992 edition, Maruzen). The phosphorescence quantum yield in a solution can be measured using various solvents, but the phosphorescent compound used in the present invention may be any solvent that achieves the above phosphorescence quantum yield (0.01 or more).

When excited by an electric field, as in organic EL elements, triplet excitons are generated with a 75% probability and singlet excitons with a 25% probability, so phosphorescence can achieve higher luminous efficiency than fluorescence, making it an excellent method for achieving low power consumption.

In terms of luminous efficiency, phosphorescence is theoretically three times more advantageous than fluorescence. However, energy deactivation from the triplet excited state to the singlet ground state (= phosphorescence) is a forbidden transition, and similarly, intersystem crossing from the singlet excited state to the triplet excited state is also a forbidden transition, so the rate constant is usually small. In other words, because the transition is difficult to occur, the phosphorescence lifetime is long, on the order of milliseconds to seconds, making it difficult to obtain the desired emission.

However, when complexes using heavy metals such as iridium or platinum emit light, the rate constant of the forbidden transition increases by three orders of magnitude or more due to the heavy atom effect of the central metal, and depending on the selection of the ligand, it is possible to obtain a phosphorescence quantum yield of 100%.

The phosphorescent compound can be appropriately selected from known compounds used in the light-emitting layer of an organic EL device. Specific examples of known phosphorescent compounds that can be used in the present invention include compounds described in the following documents:
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Among them, preferred phosphorescent compounds are organometallic complexes having Ir as a central metal, and more preferred are complexes having at least one of the coordination modes of a metal-carbon bond, a metal-nitrogen bond, a metal-oxygen bond, and a metal-sulfur bond.

Furthermore, examples of phosphorescent compounds that can be suitably used in the present invention are given below. The phosphorescent compounds described in the examples below can also be suitably used in the present invention.

<Delayed Fluorescence Compound>
In the present invention, the term "delayed fluorescent compound" refers to a compound that emits delayed fluorescence. The term "delayed fluorescence" refers to light emitted when returning from a singlet excited state to a ground state as a result of upconversion caused by reverse intersystem crossing from the lowest excited triplet energy level to the lowest excited singlet energy level.
Up-conversion from the lowest excited triplet energy level to the lowest excited singlet energy level by reverse intersystem crossing occurs when the energy level difference ΔE _ST between the lowest excited triplet energy level and the lowest excited singlet energy level is extremely small.

"Delayed fluorescence" includes "thermally activated delayed fluorescence" and "triplet-triplet annihilation delayed fluorescence", in other words, "delayed fluorescent compounds" include "thermally activated delayed fluorescent compounds" and "triplet-triplet annihilation delayed fluorescent compounds".

(Thermal activation delayed fluorescent compound)
The term "thermally activated delayed fluorescent compound" refers to a compound that emits thermally activated delayed fluorescence (TADF). The term "thermally activated delayed fluorescence (TADF)" refers to light emitted when a compound returns from a singlet excited state to a ground state as a result of upconversion from the lowest excited triplet energy level to the lowest excited singlet energy level due to reverse intersystem crossing caused by the absorption of ambient thermal energy.

Since thermally activated delayed fluorescence compounds have an extremely large rate constant for deactivation (=fluorescence emission) from the singlet excited state to the ground state, it is kinetically more advantageous for triplet excitons to return to the ground state while emitting light via the singlet excited state, rather than thermally deactivating (non-radiative deactivation) themselves to the ground state. Therefore, thermally activated delayed fluorescence (TADF) theoretically allows for 100% emission.

Examples of thermally activated delayed fluorescent compounds include those described in WO 2011/156793, JP 2011-213643, JP 2010-93181, Japanese Patent No. 5,366,106, WO 2013/161437, WO 2016/158540, etc., but the present invention is not limited to these.

As the thermally activated delayed fluorescent compound, compounds having structures represented by the following general formulas (1) to (6) are preferred.

[In general formula (1), Ar ¹ to Ar ³ each independently represent a substituted or unsubstituted aryl group, and at least one of them represents an aryl group substituted with a group having a structure represented by the following general formula (2)]

[In general formula (2), R ¹ to R ⁸ each independently represent a hydrogen atom or a substituent. Z represents O, S, O═C, Ar ⁴ —N, or a chemical bond. Ar ⁴ represents a substituted or unsubstituted aryl group. Adjacent groups among R ¹ to R ⁸ may form a bond with each other or form a ring via a linking group.]

[In the general formula (3), at least one of R ¹ to R ⁵ represents a cyano group, at least one of R ¹ to R ⁵ represents a group having a structure represented by the following general formula (4), and the remaining R ¹ to R ⁵ represent a hydrogen atom or a substituent.]

In the general formula (4), R ²¹ to R ²⁸ each independently represent a hydrogen atom or a substituent, provided that at least one of the following requirements (A) or (B) is satisfied:
Requirement (A): R ²⁵ and R ²⁶ form a single bond.
Requirement (B): R ²⁷ and R ²⁸ each represent an atomic group necessary to form a substituted or unsubstituted benzene ring.

[In the general formula (5), R ¹ and R ² each independently represent a group having a structure represented by the following general formula (6)]

[In general formula (6), R ¹ to R ⁸ each independently represent a hydrogen atom or a substituent. Z represents O, S, O═C, Ar ⁴ —N, or a bond. Ar ⁴ represents a substituted or unsubstituted aryl group. Adjacent groups among R ¹ to R ⁸ may form a bond with each other or form a ring via a linking group.]

The following are examples of thermally activated delayed fluorescent compounds, but the present invention is not limited to these.

(Triplet-triplet annihilation delayed fluorescent compound)
"Triplet-triplet annihilation delayed fluorescent compound" refers to a compound that emits triplet-triplet annihilation delayed fluorescence (TTA delayed fluorescence). "Triplet-triplet annihilation delayed fluorescence (TTA delayed fluorescence)" refers to light emitted when returning from a singlet excited state to a ground state as a result of upconversion caused by reverse intersystem crossing from the lowest excited triplet energy level to the lowest excited singlet energy level due to collision between excited triplets.

The generation of singlet excitons by collisions between excited triplets can be described by the following general formula:
General formula: T ^* +T ^* →S ^* +S
(In the formula, T ^* represents a triplet exciton, S ^* represents a singlet exciton, and S represents a ground state molecule.)

Any known triplet-triplet annihilation delayed fluorescent compound can be used.

(5) Charge Transporting Compound The charge transporting compound used in the light emitting layer of the present invention is a compound that mainly transports charges to the light emitting compound in the light emitting layer, and light emission by itself is not substantially observed in the organic EL device.

The charge transporting compound may be used alone or in combination of two or more kinds. By using two or more kinds of charge transporting compounds, it is possible to adjust the movement of the charge, and the efficiency of the organic electroluminescence element can be increased.

From the viewpoint of driving stability, it is preferable that the charge transport compound can exist stably in all active species states, including the cation radical state, the anion radical state, and the excited state, and does not undergo chemical changes such as decomposition or addition reactions. Furthermore, it is preferable that the charge transport compound molecules do not move at the angstrom level in the layer over time when a current is applied.

In terms of luminous efficiency, it is preferable that the charge transport compound according to the present invention has a ratio of electron mobility [cm ² /(V·s)] to hole mobility [cm ² /(V·s)], that is, electron mobility/hole mobility, in the range of 0.5 to 2.0.

The electron mobility [cm ² /(V·s)] and hole mobility [cm ² /(V·s)] can be calculated by preparing an electron-only device (example configuration: ITO anode/calcium layer/charge transport compound layer/potassium fluoride layer/aluminum cathode) and a hole-only device (example configuration: ITO anode/charge transport compound layer/α-NPD layer/aluminum cathode), measuring the current density-voltage characteristics of these devices, plotting them as log-log graphs, and using the current density and applied voltage obtained from these graphs and the space charge limited current equation.

The space charge limited current formula is J = (9/8) ε _r ε ₀ μ (V ² /L ³ ), where J is the current density, ε _r is the dielectric constant of the charge transport compound layer, ε ₀ is the dielectric constant of a vacuum, μ is the electron mobility [cm ² /(V·s)] or hole mobility [cm ² /(V·s)], L is the thickness of the charge transport compound layer, and V is the applied voltage.

When a known charge transporting compound is used in the organic EL device of the present invention, specific examples thereof include the compounds described in the following documents, but the present invention is not limited thereto.
JP-A-2001-257076, JP-A-2002-308855, JP-A-2001-313179, JP-A-2002-319491, JP-A-2001-357977, JP-A-2002-334786, JP-A-2002-8860, JP-A-2002-334787, No. 2002-15871, No. 2002-334788, No. 2002-43056, No. 2002-334789, No. 2002-75645, No. 2002-338579, No. 2002-105445, No. 2002-343568, No. 20 No. 2002-141173, No. 2002-352957, No. 2002-203683, No. 2002-363227, No. 2002-231453, No. 2003-3165, No. 2002-234888, No. 2003-27048, No. 2002 -255934, 2002-260861, 2002-280183, 2002-299060, 2002-302516, 2002-305083, 2002-305084, 2002-308837, 2016 US Patent Application Publication No. 2003/0175553, US Patent Application Publication No. 2006/0280965, US Patent Application Publication No. 2005/0112407, US Patent Application Publication No. 2009/0017330, US Patent Application Publication No. 2009/0030202, US Patent Application Publication No. 2005/0238919, International Publication No. 2001/039234, International Publication No. 2009/021126, International Publication No. 2008/056746, International Publication No. 2004/093207, International Publication No. 2005/089025, International Publication No. 2007/063796 No. , WO 2007/063754, WO 2004/107822, WO 2005/030900, WO 2006/114966, WO 2009/086028, WO 2009/003898, WO 2012/023947, JP 2008-074939 A, JP 2007-254297 A, EP 2034538 A, WO 2011/055933, WO 2012/035853, JP 2015-38941 A, and U.S. Patent Application Publication No. 2017/056814.

Furthermore, examples of charge transport compounds that can be suitably used in the present invention are given below. The charge transport compounds described in the examples below can also be suitably used in the present invention.

(6) Insulating Polymer The "insulating" property of the insulating polymer used in the present invention means that the electrical resistivity is 1 x ¹⁰⁶ Ω·m or more, preferably 1 x ¹⁰⁸ Ω·m or more, and more preferably 1 x ¹⁰¹⁰ Ω·m or more.
It is believed that when the electrical resistivity of the insulating polymer alone is 1×10 ⁶ Ω·m or more, the leakage current flowing through the light-emitting layer can be suppressed.

The type of insulating polymer is not particularly limited as long as it is capable of forming an ink receiving layer. In one embodiment, the insulating polymer is a polymer whose main chain is made up of carbon atoms, which is more stable.

In order to form an ink receiving layer containing an insulating polymer by a coating method, the insulating polymer is preferably a soluble polymer and preferably exhibits solubility in aprotic polar solvents. Specifically, the solubility of the insulating polymer in 1 g of N,N-dimethylformamide at 25°C is preferably 0.5 mg or more, more preferably 1.0 mg or more, and even more preferably 2.0 mg or more.

There is no particular limitation on the type of insulating polymer, and examples thereof include nonionic polymers such as polystyrene, polymethylmethacrylate, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, polyvinylpolypyrrolidone, polyethylene glycol, polymethylvinylether, and polyisopropylacrylamide; cationic polymers such as sodium polyacrylate, sodium polystyrenesulfonate, sodium polyisopropylenesulfonate, polynaphthalenesulfonic acid condensate salt, and polyethyleneimine xanthate salt; anionic polymers such as dimethylaminomethyl (meth)acrylate quaternary salt, dimethyldiallylammonium chloride, polyamidine, polyvinylimidazoline, dicyandiamide condensate, epichlorohydrin dimethylamine condensate, and polyethyleneimine; and amphoteric polymers such as dimethylaminoethyl (meth)acrylate quaternary salt acrylic acid copolymer and Hofmann decomposition product of polyacrylamide. Preferably, polystyrene and polymethylmethacrylate.
The insulating polymer may contain two or more different repeat units.

The weight average molecular weight of the insulating polymer is not particularly limited, but is preferably 5×10 ³ or more, more preferably 10×10 ³ or more. Also, it is preferably 1000×10 ³ or less, more preferably 400×10 ³ or less. It is considered that the weight average molecular weight within this range makes it possible to appropriately control the diffusion of the luminescent compound in the ink receiving layer.

(7) Components other than the light-emitting layer The electrodes (anode and cathode) that the organic EL element of the present invention has and components other than the light-emitting layer that may be provided will be described below.

<Anode>
As the anode in an organic EL element, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function (4 eV or more, preferably 4.5 V or more) is preferably used as the electrode material. Specific examples of such electrode materials include metals such as Au, CuI, indium tin oxide (ITO), SnO ₂ , ZnO, and other conductive transparent materials. In addition, a material that is amorphous and can be used to prepare a transparent conductive film, such as IDIXO (In ₂ O ₃ -ZnO), may also be used.

The anode may be prepared by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering, and then forming a pattern of a desired shape by a photolithography method. Alternatively, when high pattern accuracy is not required (approximately 100 μm or more), a pattern may be formed through a mask of a desired shape during vapor deposition or sputtering of the electrode material.
Alternatively, when a coatable substance such as an organic conductive compound is used, a wet film formation method such as a printing method or a coating method can be used. When light is extracted from this anode, it is preferable that the transmittance is greater than 10%, and the sheet resistance of the anode is preferably several hundred Ω/sq. or less.
The thickness of the anode varies depending on the material, but is usually selected within the range of 10 nm to 1 μm, preferably 10 to 200 nm.

<Cathode>
The cathode may be made of a metal (referred to as an electron injecting metal) with a small work function (5 eV or less), an alloy, an electrically conductive compound, or a mixture of these. Specific examples of such electrode materials include sodium, a sodium-potassium alloy, magnesium, lithium, silver, a magnesium/copper mixture, a magnesium/silver mixture, a magnesium/aluminum mixture, a magnesium/indium mixture, an aluminum/aluminum oxide (Al ₂ O ₃ ) mixture, indium, a lithium/aluminum mixture, aluminum, and rare earth metals.

Among these, from the standpoint of electron injectability and durability against oxidation, etc., preferred are mixtures of an electron injecting metal and a second metal which has a larger and more stable work function than the electron injecting metal, such as a magnesium/silver mixture, a magnesium/aluminum mixture, _a magnesium/indium mixture, an aluminum/aluminum oxide ( _Al2O3 ) mixture, a lithium/aluminum mixture, and aluminum.

The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. Alternatively, when a coatable material such as metal nanoparticles is used, a wet film formation method such as a printing method or a coating method can be used. The sheet resistance of the cathode is preferably several hundred Ω/sq. or less, and the thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.
In order to transmit the emitted light, it is advantageous for either the anode or the cathode of the organic EL element to be transparent or semi-transparent, since this improves the luminance of the emitted light.
In addition, after forming the above metal in a thickness of 1 to 20 nm as the cathode, a conductive transparent material as described in the explanation of the anode can be formed thereon to prepare a transparent or semitransparent cathode. By applying this, it is possible to prepare an element in which both the anode and cathode are transparent.

<Electron Transport Layer>
The electron transport layer is made of a material having a function of transporting electrons, and is a layer having a function of transmitting electrons injected from the cathode to the light emitting layer.

There are no particular limitations on the thickness of the electron transport layer, but it is usually in the range of 2 nm to 5 μm, more preferably in the range of 2 to 500 nm, and even more preferably in the range of 5 to 200 nm.

The material used in the electron transport layer (hereinafter also referred to as "electron transport material") may have any of the following properties: electron injectability or transportability, and hole barrier properties. Any material may be selected from conventionally known compounds and used.
Examples of the conventionally known compounds include nitrogen-containing aromatic heterocyclic derivatives (carbazole derivatives, azacarbazole derivatives (one or more of the carbon atoms constituting the carbazole ring are substituted with a nitrogen atom), pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, pyridazine derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, azatriphenylene derivatives, oxazole derivatives, thiazole derivatives, oxadiazole derivatives, thiadiazole derivatives, triazole derivatives, benzimidazole derivatives, benzoxazole derivatives, benzothiazole derivatives, etc.), dibenzofuran derivatives, dibenzothiophene derivatives, silole derivatives, aromatic hydrocarbon ring derivatives (naphthalene derivatives, anthracene derivatives, triphenylene, etc.).

In addition, metal complexes having a quinolinol skeleton or a dibenzoquinolinol skeleton in the ligand, such as tris( ₈ -quinolinol)aluminum (Alq), tris(5,7-dichloro-8-quinolinol)aluminum, tris(5,7-dibromo-8-quinolinol)aluminum, tris(2-methyl-8-quinolinol)aluminum, tris(5-methyl-8-quinolinol)aluminum, bis(8-quinolinol)zinc (Znq), and metal complexes in which the central metal of these metal complexes is replaced with In, Mg, Cu, Ca, Sn, Ga, or Pb can also be used as the electron transport material.

In addition, metal-free or metal phthalocyanine, or those in which the terminals are substituted with an alkyl group, a sulfonic acid group, etc., can also be preferably used as the electron transport material. Distyrylpyrazine derivatives can also be used as the electron transport material, and inorganic semiconductors such as n-type Si and n-type SiC can also be used as the electron transport material, as in the hole injection layer and hole transport layer.
Furthermore, it is also possible to use polymer materials in which these materials are introduced into the polymer chain or in which these materials form the polymer main chain.

In the electron transport layer according to the present invention, a dopant may be doped into the electron transport layer as a guest material to form an electron transport layer with high n-type (electron-rich) properties. Examples of the dopant include n-type dopants such as metal complexes and metal compounds such as metal halides. Specific examples of electron transport layers having such a configuration include those described in Japanese Patent Application Laid-Open Nos. 4-297076, 10-270172, 2000-196140, and 2001-102175, and J. Appl. Phys., 95, 5773 (2004), etc.

Specific examples of well-known preferred electron transport materials that can be used in the organic EL device of the present invention include compounds described in the following documents, but the present invention is not limited thereto.
U.S. Patent No. 6,528,187, U.S. Patent No. 7,230,107, U.S. Patent Publication No. 2005/0025993, U.S. Patent Publication No. 2004/0036077, U.S. Patent Publication No. 2009/0115316, U.S. Patent Publication No. 2009/0101870, U.S. Patent Publication No. 2009/0179554, International Publication No. 2003/060956, International Publication No. 2008/132085, Appl. Phys. Lett. 75, 4 (1999), Appl. Phys. Lett. 79, 449 (2001), Appl. Phys. Lett. 81, 162 (2002), Appl. Phys. Lett. 81, 162 (2002), Appl. Phys. Lett. 79, 156 (2001), U.S. Pat. No. 7,964,293, U.S. Patent Publication No. 2009/030202, International Publication No. 2004/080975, International Publication No. 2004/063159, International Publication No. 2005/085387, International Publication No. 2006/067931, International Publication No. 2007/086552, International Publication No. 2008/114690, International Publication No. 2009/069442, International Publication No. 2009/066779, International Publication No. 2009/054253, International Publication No. 2011/086935, International Publication No. WO 2010/150593, International Publication No. WO 2010/047707, EP2311826, JP2010-251675A, JP2009-209133A, JP2009-124114A, JP2008-277810A, JP2006-156445A, JP2005-340122A, JP2003-45662A, JP2003-31367A, JP2003-282270A, International Publication No. WO 2012/115034, and the like.

More preferred electron transport materials include pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, carbazole derivatives, azacarbazole derivatives, and benzimidazole derivatives.
The electron transporting materials may be used alone or in combination of two or more kinds.

<Hole Blocking Layer>
In a broad sense, the hole blocking layer is a layer that has the function of an electron transport layer, and is preferably made of a material that has the function of transporting electrons but has little ability to transport holes, and is a layer that can improve the probability of recombination of electrons and holes by transporting electrons while blocking holes.
Furthermore, the above-mentioned configuration of the electron transport layer can be used as a hole blocking layer, if necessary.

The hole blocking layer is preferably provided adjacent to the cathode side of the light emitting layer. The thickness of the hole blocking layer is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.

The materials used for the hole blocking layer are preferably the same as those used for the electron transport layer.

<Electron injection layer>
The electron injection layer (also referred to as "cathode buffer layer") refers to a layer provided between the cathode and the light-emitting layer in order to reduce the driving voltage and improve the luminance of emitted light, and is described in detail in "Electrode Materials" (pp. 123-166, Chapter 2, Volume 2) of "Organic EL Elements and Their Industrialization Frontiers" (published by NTS Corporation on Nov. 30, 1998).
The electron injection layer is provided as necessary, and may be present between the cathode and the light emitting layer, or between the cathode and the electron transport layer, as described above.
The electron injection layer is preferably a very thin layer, and the thickness is preferably within the range of 0.1 to 5 nm, depending on the material, and may be a non-uniform layer in which the constituent materials are intermittently present.

The electron injection layer is described in detail in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, etc., and specific examples of materials preferably used for the electron injection layer include metals such as strontium and aluminum, alkali metal compounds such as lithium fluoride, sodium fluoride, potassium fluoride, etc., alkaline earth metal compounds such as magnesium fluoride, calcium fluoride, etc., metal oxides such as aluminum oxide, metal complexes such as lithium 8-hydroxyquinolate (Liq), etc. The above-mentioned electron transport materials can also be used.
The above-mentioned materials for use in the electron injection layer may be used alone or in combination of two or more kinds.

<Hole transport layer>
The hole transport layer is made of a material having a function of transporting holes, and is a layer having a function of transmitting holes injected from the anode to the light emitting layer.
The thickness of the hole transport layer is not particularly limited, but is usually within the range of 5 nm to 5 μm, more preferably within the range of 2 to 500 nm, and further preferably within the range of 5 to 200 nm.

The material used in the hole transport layer (hereinafter referred to as "hole transport material") may be any material that has hole injection or transport properties or electron barrier properties, and may be selected from among conventionally known compounds.

For example, porphyrin derivatives, phthalocyanine derivatives, oxazole derivatives, oxadiazole derivatives, triazole derivatives, imidazole derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, hydrazone derivatives, stilbene derivatives, polyarylalkane derivatives, triarylamine derivatives, carbazole derivatives, indolocarbazole derivatives, isoindole derivatives, acene derivatives such as anthracene and naphthalene, fluorene derivatives, fluorenone derivatives, and polyvinylcarbazole, polymeric materials or oligomers with aromatic amines introduced into the main chain or side chain, polysilane, conductive polymers or oligomers (e.g. PEDOT:PSS, aniline-based copolymers, polyaniline, polythiophene, etc.), etc.

Examples of triarylamine derivatives include benzidine types such as α-NPD, starburst types such as MTDATA, and compounds having fluorene or anthracene in the triarylamine linking core portion.
Further, hexaazatriphenylene derivatives as described in JP-T-2003-519432 and JP-A-2006-135145 can also be used as hole transport materials.
Furthermore, a highly p-type hole transport layer doped with impurities may also be used. Examples of such a layer include those described in JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175, and J. Appl. Phys., 95, 5773 (2004), etc.

Also usable are so-called p-type hole transport materials and inorganic compounds such as p-type-Si and p-type-SiC, as described in JP-A-11-251067 and the document by J. Huang et al. (Applied Physics Letters 80 (2002), p. 139). Furthermore, ortho-metalated organometallic complexes having Ir or Pt as the central metal, as typified by Ir(ppy) ₃ , are also preferably used.
As the hole transport material, the above-mentioned materials can be used, but triarylamine derivatives, carbazole derivatives, indolocarbazole derivatives, azatriphenylene derivatives, organometallic complexes, polymeric materials or oligomers having aromatic amines introduced into the main chain or side chain, and the like are preferably used.

Specific examples of well-known preferred hole transport materials that can be used in the organic EL element of the present invention include the compounds described in the documents listed above as well as the following documents, but the present invention is not limited to these.

For example, Appl. Phys. Lett. 69, 2160 (1996), J. Lumin. 72-74, 985 (1997), Appl. Phys. Lett. 78, 673 (2001), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 90, 183503 (2007), Appl. Phys. Lett. 51, 913 (1987), Synth. Met. 87, 171 (1997), Synth. Met. 91, 209 (1997), Synth. Met. 111, 421 (2000), SID Symposium Digest, 37, 923 (2006), J. Mater. Chem. 3, 319 (1993), Adv. Mater. 6, 677 (1994), Chem. Mater. 15, 3148 (2003 ), U.S. Patent Publication No. 2003/0162053, U.S. Patent Publication No. 2002/0158242, U.S. Patent Publication No. 2006/0240279, U.S. Patent Publication No. 2008/0220265, U.S. Patent No. 5,061,569, International Publication No. 2007/002683 No. 2009/018009, EP 650955, U.S. Pat. Publication No. 2008/0124572, U.S. Patent Publication No. 2007/0278938, U.S. Patent Publication No. 2008/0106190, U.S. Patent Publication No. 2008/0018221, International Publication No. 2012/115034, JP 2003-519432 A, Japanese Patent Application Publication No. 2006-135145 and U.S. Patent Application No. 13/585981, etc.
The hole transport material may be used alone or in combination of two or more kinds.

<Electron Blocking Layer>
The electron blocking layer, in a broad sense, is a layer that has the function of a hole transport layer, and is preferably made of a material that has the function of transporting holes but has little ability to transport electrons, and is a layer that can improve the probability of recombination of electrons and holes by blocking electrons while transporting holes.
Furthermore, the above-mentioned structure of the hole transport layer can be used as an electron blocking layer, if necessary.
The electron blocking layer is preferably provided adjacent to the light emitting layer on the anode side, and the thickness of the electron blocking layer is preferably within a range of 3 to 100 nm, and more preferably within a range of 5 to 30 nm.

The materials used for the electron blocking layer are preferably the same as those used for the hole transport layer.

<Hole injection layer>
The hole injection layer (also called "anode buffer layer") is a layer provided between the anode and the light emitting layer to reduce the driving voltage and improve the luminance of light emitted. For example, it is described in detail in "Electrode Materials" (pages 123-166, Chapter 2, Volume 2) of "Organic EL Elements and Their Industrialization Frontiers" (published by NTS Corporation on November 30, 1998).
The hole injection layer is provided as necessary, and may be present between the anode and the light emitting layer or between the anode and the hole transport layer as described above.

The hole injection layer is described in detail in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069, etc., and examples of materials that can be used for the hole injection layer include the materials used for the hole transport layer described above.

Among these, preferred are phthalocyanine derivatives such as copper phthalocyanine, hexaazatriphenylene derivatives as described in, for example, JP-T-2003-519432A and JP-A-2006-135145A, metal oxides such as vanadium oxide, amorphous carbon, conductive polymers such as polyaniline (emeraldine) and polythiophene, ortho-metallated complexes such as tris(2-phenylpyridine)iridium complex, and triarylamine derivatives.
The above-mentioned materials for use in the hole injection layer may be used alone or in combination of two or more kinds.

<Other additives>
The organic functional layer according to the present invention may further contain other additives, such as halogen elements and halogenated compounds, such as bromine, iodine, and chlorine, and compounds, complexes, and salts of alkali metals and alkaline earth metals, such as Pd, Ca, and Na, and transition metals.

The content of the additive can be determined arbitrarily, but is preferably 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 50 ppm or less, based on the total mass % of the layer in which it is contained.
However, depending on the purpose, such as improving the transportability of electrons or holes or making the energy transfer of excitons more advantageous, the content may be outside this range.

<Support substrate>
The supporting substrate (hereinafter also referred to as a base, substrate, substrate, support, etc.) that can be used for the organic EL element is not particularly limited in type, such as glass or plastic, and may be transparent or opaque. When light is extracted from the supporting substrate side, the supporting substrate is preferably transparent. Examples of the transparent supporting substrate that is preferably used include glass, quartz, and transparent resin film. A particularly preferred supporting substrate is a resin film that can provide flexibility to the organic EL element.

Examples of resin films include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose esters or derivatives thereof such as cellulose diacetate, cellulose triacetate (TAC), cellulose acetate butyrate, cellulose acetate propionate (CAP), cellulose acetate phthalate, and cellulose nitrate, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide, polyether sulfone (PES), polyphenylene sulfide, polysulfones, polyetherimide, polyether ketone imide, polyamide, fluororesin, nylon, polymethyl methacrylate, acrylics or polyarylates, and cycloolefin resins such as Arton (registered trademark) (manufactured by JSR Corporation) or APEL (registered trademark) (manufactured by Mitsui Chemicals, Inc.).

A gas barrier film made of an inorganic or organic material or a hybrid gas barrier film made of both may be formed on the surface of the resin film. This gas barrier film is preferably one having a water vapor permeability (25±0.5°C, relative humidity (90±2)% RH) of 0.01 g/( ^m2 ·24 h) or less as measured by a method in accordance with JIS K 7129-1992, and more preferably has high barrier properties such as an oxygen permeability of ^10-3 mL/( ^m2 ·24 h·atm) or less and a water vapor permeability of ^10-5 g/( ^m2 ·24 h) or less as measured by a method in accordance with JIS K 7126-1987.

The material forming the gas barrier film may be any material that has the function of suppressing the intrusion of moisture, oxygen, and other substances that cause deterioration of the element, and examples of materials that can be used include silicon oxide, silicon dioxide, and silicon nitride. To further improve the fragility of the film, it is more preferable to have a laminated structure of layers made of these inorganic layers and organic materials. There are no particular restrictions on the order in which the inorganic layers and organic functional layers are laminated, but it is preferable to laminate the two alternately multiple times.

The method for forming the gas barrier film is not particularly limited, and may be, for example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric plasma polymerization, plasma CVD (chemical vapor deposition), laser CVD, thermal CVD, coating, etc., but atmospheric plasma polymerization as described in JP-A-2004-68143 is particularly preferred.

Examples of the opaque supporting substrate include metal plates such as aluminum and stainless steel, films, opaque resin substrates, and ceramic substrates.
Furthermore, a hue improving filter such as a color filter may be used in combination, or a color conversion filter that converts the emission color from the organic EL element into multiple colors using a phosphor may be used in combination.

<Sealing>
The sealing means used for sealing the organic EL element may be, for example, a method of bonding a sealing member to an electrode and a supporting substrate with an adhesive. The sealing member may be in the form of a concave plate or a flat plate as long as it is disposed so as to cover the display area of the organic EL element. In addition, there is no particular restriction on the transparency and electrical insulation.

Specific examples include glass plates, polymer plates/films, and metal plates/films. Examples of glass plates include soda-lime glass, barium-strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of polymer plates include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, and polysulfone. Examples of metal plates include those made of one or more metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicon, germanium, and tantalum.

In the present invention, a polymer film or a metal film can be preferably used because it allows the organic EL element to be made thin.
It is preferable that the oxygen permeability measured according to a method in accordance with JIS K 7126-1987 is 1 x 10 ^-3 mL/m ² /24 h or less, and the water vapor permeability measured according to a method in accordance with JIS K 7129-1992 (25±0.5°C, relative humidity (90±2)%) is 1 x 10 ^-3 g/(m ² /24 h) or less.

Sandblasting, chemical etching, etc. are used to process the sealing material into a concave shape.

Specific examples of adhesives include photocurable and heat-curable adhesives having reactive vinyl groups such as acrylic acid oligomers and methacrylic acid oligomers, and moisture-curable adhesives such as 2-cyanoacrylic acid esters. Other examples include heat- and chemical-curable adhesives (two-liquid mixtures) such as epoxy systems. Other examples include hot-melt polyamides, polyesters, and polyolefins. Other examples include cationic curable ultraviolet-curable epoxy resin adhesives.
Since the organic EL element may deteriorate due to heat treatment, it is preferable to use an adhesive that can be bonded and cured at a temperature between room temperature and 80° C. A desiccant may be dispersed in the adhesive. The adhesive may be applied to the sealing portion using a commercially available dispenser or by printing such as screen printing.

It is also possible to preferably form a sealing film by covering the outside of the electrode on the side facing the support substrate with the organic functional layer and forming an inorganic or organic layer in contact with the support substrate. In this case, the material for forming the film may be any material that has the function of suppressing the intrusion of moisture, oxygen, and other substances that cause deterioration of the element, and examples of materials that can be used include silicon oxide, silicon dioxide, and silicon nitride.

Furthermore, in order to improve the fragility of the film, it is preferable to provide a laminated structure of these inorganic layers and layers made of organic materials. There are no particular limitations on the method for forming these films, and for example, vacuum deposition, sputtering, reactive sputtering, molecular beam epitaxy, cluster ion beam, ion plating, plasma polymerization, atmospheric pressure plasma polymerization, plasma CVD, laser CVD, thermal CVD, coating, etc. can be used.

In the gas and liquid phase, it is preferable to inject an inert gas such as nitrogen or argon, or an inert liquid such as fluorohydrocarbon or silicone oil into the gap between the sealing member and the display area of the organic EL element. It is also possible to create a vacuum. It is also possible to fill the gap with a hygroscopic compound.

Examples of hygroscopic compounds include metal oxides (e.g., sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, aluminum oxide, etc.), sulfates (e.g., sodium sulfate, calcium sulfate, magnesium sulfate, cobalt sulfate, etc.), metal halides (e.g., calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, magnesium iodide, etc.), and perchlorates (e.g., barium perchlorate, magnesium perchlorate, etc.), and anhydrous salts are preferably used for sulfates, metal halides, and perchlorates.

<Protective film, protective plate>
A protective film or protective plate may be provided on the outer side of the sealing film or the sealing film on the side facing the support substrate with the organic functional layer sandwiched therebetween in order to increase the mechanical strength of the element. In particular, when sealing is performed by the sealing film, the mechanical strength is not necessarily high, so it is preferable to provide such a protective film or protective plate. As materials that can be used for this, glass plates, polymer plates/films, metal plates/films, etc., similar to those used for the sealing, can be used, but it is preferable to use polymer films because they are lightweight and thin.

<Light extraction improvement technology>
It is generally said that organic EL elements emit light within a layer that has a higher refractive index than air (within the range of approximately 1.6 to 2.1), and that only about 15 to 20% of the light generated in the light-emitting layer can be extracted.
This is because light that is incident on the interface (the interface between the transparent substrate and air) at an angle θ equal to or greater than the critical angle undergoes total reflection and cannot be extracted to the outside of the element, and because light undergoes total reflection between the transparent electrode or light-emitting layer and the transparent substrate, and the light is guided through the transparent electrode or light-emitting layer, resulting in the light escaping in the direction of the side of the element.

Methods for improving the efficiency of this light extraction include, for example, a method of forming irregularities on the surface of a transparent substrate to prevent total reflection at the interface between the transparent substrate and the air (for example, U.S. Patent No. 4,774,435), a method of improving efficiency by giving the substrate light-collecting properties (for example, JP-A-63-314795), a method of forming a reflective surface on the side of the element (for example, JP-A-1-220394), a method of introducing a flat layer with an intermediate refractive index between the substrate and the light emitter to form an anti-reflection film (for example, JP-A-62-172691), a method of introducing a flat layer with a lower refractive index than the substrate between the substrate and the light emitter (for example, JP-A-2001-202827), and a method of forming a diffraction grating between the substrate, transparent electrode layer, or light emitter (including between the substrate and the outside world) (JP-A-11-283751).

In the present invention, these methods can be used in combination with the organic EL element. Preferably, however, a method of introducing a flat layer having a lower refractive index than the substrate between the substrate and the light-emitting body, or a method of forming a diffraction grating between any of the substrate, the transparent electrode layer, and the light-emitting layer (including between the substrate and the outside world) can be used.
When a low refractive index medium is formed between a transparent electrode and a transparent substrate with a thickness longer than the wavelength of light, the lower the refractive index of the medium, the higher the efficiency with which light emitted from the transparent electrode can be extracted to the outside.
In the present invention, by combining these means, it is possible to obtain an element having higher luminance or superior durability.

Examples of the low refractive index layer include aerogel, porous silica, magnesium fluoride, fluorine-based polymers, etc. Since the refractive index of a transparent substrate is generally within the range of about 1.5 to 1.7, the refractive index of the low refractive index layer is preferably about 1.5 or less, and more preferably 1.35 or less.
In addition, the thickness of the low refractive index medium is preferably at least twice the wavelength in the medium, because when the thickness of the low refractive index medium becomes approximately the wavelength of light and the electromagnetic waves that have evanescently seeped out enter the substrate, the effect of the low refractive index layer is reduced.

The method of introducing a diffraction grating into an interface or medium where total reflection occurs has the characteristic of being highly effective in improving light extraction efficiency. This method utilizes the property of a diffraction grating that it can change the direction of light to a specific direction different from refraction through so-called Bragg diffraction, such as first-order diffraction or second-order diffraction, to diffract the light generated from the light-emitting layer that cannot escape due to total reflection between layers by introducing a diffraction grating between any of the layers or into the medium (inside the transparent substrate or transparent electrode), thereby attempting to extract the light to the outside.

It is desirable for the diffraction grating to have a two-dimensional periodic refractive index, because the light emitted from the light-emitting layer is generated randomly in all directions, and so with a general one-dimensional diffraction grating that has a periodic refractive index distribution only in one direction, only light traveling in a specific direction is diffracted, and the light extraction efficiency does not increase significantly.
However, by making the refractive index distribution two-dimensional, light traveling in all directions is diffracted, and the light extraction efficiency is increased.

The diffraction grating may be introduced between any of the layers or in the medium (in the transparent substrate or transparent electrode), but is preferably introduced near the organic light-emitting layer where light is generated. In this case, the period of the diffraction grating is preferably within the range of about 1/2 to 3 times the wavelength of the light in the medium. The diffraction grating is preferably arranged in a two-dimensional repeated pattern, such as a square lattice, triangular lattice, or honeycomb lattice.

<Light collecting sheet>
The organic EL element of the present invention can increase the luminance in a specific direction by processing the light extraction side of the supporting substrate (substrate) to have, for example, a microlens array structure, or by combining it with a so-called light-collecting sheet to collect light in a specific direction, for example, in the front direction relative to the light-emitting surface of the element.
As an example of a microlens array, a square pyramid with a side of 30 μm and a apex angle of 90 degrees is arranged two-dimensionally on the light extraction side of the substrate. The side is preferably within the range of 10 to 100 μm. If it is smaller than this, the effect of diffraction occurs and coloring occurs, and if it is too large, the thickness becomes too large, which is not preferable.

The light collecting sheet may be, for example, a sheet that is in practical use in the LED backlight of a liquid crystal display device. For example, brightness enhancing film (BEF) manufactured by Sumitomo 3M may be used as such a sheet. The shape of the prism sheet may be, for example, a base material on which triangle-shaped stripes with an apex angle of 90 degrees and a pitch of 50 μm are formed, or a shape with a rounded apex angle, a shape with a randomly changed pitch, or other shapes.
In order to control the light radiation angle from the organic EL element, a light diffusing plate or film may be used in combination with the light collecting sheet. For example, a light diffusing film (Light Up) manufactured by Kimoto Co., Ltd. may be used.

<Others: Organic EL element having a tandem structure>
The organic EL element of the present invention may be an element having a so-called tandem structure in which a plurality of light-emitting units, each of which includes at least one light-emitting layer, are laminated.
A typical element configuration of the tandem structure is, for example, as follows.
Anode/first light-emitting unit/second light-emitting unit/third light-emitting unit/cathode Anode/first light-emitting unit/intermediate layer/second light-emitting unit/intermediate layer/third light-emitting unit/cathode Here, the first light-emitting unit, the second light-emitting unit, and the third light-emitting unit may all be the same or different. Also, two light-emitting units may be the same and the remaining one may be different.
In addition, the third light-emitting unit may be omitted, while a further light-emitting unit or an intermediate layer may be provided between the third light-emitting unit and the electrode.

The multiple light-emitting units may be stacked directly or via an intermediate layer. The intermediate layer is generally called an intermediate electrode, intermediate conductive layer, charge generation layer, electron extraction layer, connection layer, or intermediate insulating layer. Any known material and configuration can be used as long as the layer has the function of supplying electrons to the adjacent layer on the anode side and holes to the adjacent layer on the cathode side.

Materials used for the intermediate layer include, for example, conductive inorganic compound layers such as ITO (indium tin oxide), IZO (indium zinc oxide), _ZnO2 , _TiN , ZrN, HfN, TiOx, VOx, CuI, InN, GaN, _CuAlO2 , _CuGaO2 , _SrCu2O2 , _LaB6 , _RuO2 , _and Al, bilayer films such as Au/ _{Bi2O3 ,} multilayer films such as _SnO2 /Ag/ _SnO2 , ZnO/ _Ag /ZnO, _Bi2O3 /Au/ _Bi2O3 , _TiO2 /TiN/ _TiO2 , and _TiO2 /ZrN/ _TiO2 , and C. Examples of such conductive organic compounds include fullerenes such as ₆₀ , conductive organic layers such as oligothiophenes, conductive organic compound layers such as metal phthalocyanines, metal-free phthalocyanines, metal porphyrins, and metal-free porphyrins, but the present invention is not limited to these.

Preferred configurations within the light-emitting unit include, for example, configurations (i) to (vii) listed above as typical element configurations, with the anode and cathode removed, but the present invention is not limited to these.

Specific examples of tandem-type organic EL elements include, for example, U.S. Pat. No. 6,337,492, U.S. Pat. No. 7,420,203, U.S. Pat. No. 7,473,923, U.S. Pat. No. 6,872,472, U.S. Pat. No. 6,107,734, U.S. Pat. No. 6,337,492, International Publication No. 2005/009087, JP 2006-228712 A, JP 2006-24791 A, JP 2006-49393 A, JP 2006-49394 A, JP 2006-49396 A, JP 2011-96679 A, Examples of element configurations and constituent materials include those described in JP 2005-340187 A, JP 4711424 A, JP 3496681 A, JP 3884564 A, JP 4213169 A, JP 2010-192719 A, JP 2009-076929 A, JP 2008-078414 A, JP 2007-059848 A, JP 2003-272860 A, JP 2003-045676 A, and International Publication WO 2005/094130, but the present invention is not limited to these.

(8) Manufacturing Method of Organic EL Element The manufacturing method of the organic electroluminescence element of the present invention is a manufacturing method for manufacturing the organic electroluminescence element of the present invention, and is characterized by having a step of forming a light-emitting layer by dropping a solution containing a light-emitting compound (also referred to as "light-emitting ink") onto an ink-receiving layer.

<Formation of Ink Receiving Layer>
The ink receiving layer is preferably formed by a wet process. Examples of wet processes (also called "wet methods") include spin coating, casting, inkjet printing, die coating, blade coating, roll coating, spray coating, curtain coating, and LB (Langmuir-Blodgett) methods. From the viewpoint of easiness in obtaining a homogeneous thin film and high productivity, methods highly suitable for roll-to-roll systems, such as die coating, roll coating, inkjet printing, and spray coating, are preferred.

The liquid medium for dissolving or dispersing the insulating polymer and charge transport compound, which are the constituent materials of the ink receiving layer, is not particularly limited, and examples thereof include halogen-based solvents such as chloroform, carbon tetrachloride, dichloromethane, 1,2-dichloroethane, dichlorobenzene, and dichlorohexanone; ketone-based solvents such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, n-propyl methyl ketone, and cyclohexanone; aromatic solvents such as benzene, toluene, xylene, mesitylene, and cyclohexylbenzene; aliphatic solvents such as cyclohexane, decalin, and dodecane; ester-based solvents such as ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and diethyl carbonate; ether-based solvents such as tetrahydrofuran and dioxane; amide-based solvents such as dimethylformamide and dimethylacetamide; alcohol-based solvents such as methanol, ethanol, 1-butanol, and ethylene glycol; nitrile-based solvents such as acetonitrile and propionitrile; dimethyl sulfoxide, water, and mixtures thereof.

The boiling point of these liquid media is preferably lower than the temperature of the drying process in order to quickly dry the liquid media, and more specifically, is preferably within the range of 60 to 200°C, and more preferably within the range of 80 to 180°C.

The coating liquid may contain a surfactant for the purpose of controlling the coating range or for the purpose of suppressing liquid flow associated with the surface tension gradient after coating (for example, liquid flow that causes a phenomenon called coffee ring).
Examples of the surfactant include anionic or nonionic surfactants from the viewpoints of the effect of moisture contained in the solvent, leveling properties, wettability to the substrate, etc. Specifically, fluorine-containing surfactants and the like, such as those listed in WO 08/146681 and JP-A 2-41308, can be used.

The coating liquid used in the wet method may be a solution in which the material forming the ink receiving layer is uniformly dissolved in the liquid medium, or a dispersion in which the material is dispersed as a solid in the liquid medium. Dispersion methods include ultrasonic, high shear dispersion, and media dispersion.

The concentration of the coating liquid can be appropriately selected depending on the solubility or dispersibility of the material forming the ink receiving layer, and can be selected within the range of, for example, 0.1 to 50%.

The viscosity of the coating liquid can be appropriately selected depending on the solubility or dispersibility of the material forming the ink receiving layer, and can be selected within the range of, for example, 0.3 to 100 mPa·s.

The thickness of the coating film can be appropriately selected depending on the functionality required as an ink receiving layer and the solubility or dispersibility of the organic material, and can be selected within the range of 1 to 90 μm, for example.

After forming the coating film by the wet method, a drying process can be performed to remove the liquid medium. There are no particular limitations on the temperature of the drying process, but it is preferable to perform the drying process at a temperature that does not damage the ink receiving layer, transparent electrode, or substrate. Specifically, the temperature can be, for example, 80°C or higher, and the upper limit is thought to be about 300°C, although it cannot be generalized as it varies depending on the composition of the coating liquid. The drying time is preferably about 10 seconds to 10 minutes. By using such conditions, drying can be performed quickly.

<Dropping of luminous ink onto ink receiving layer>
It is preferable that the luminous ink is dropped onto the ink receiving layer in a patternable manner. A printing method using a mask with patterning openings may be used, but a non-contact method is preferable from the viewpoint of minimizing damage to the ink receiving layer.

The volume of the luminous ink droplets when dropped is preferably 10 μL or less, and more preferably 100 pL or less.

The size of the dot regions in which the luminescent compound is present as a dot with the luminescent compound as the main component is preferably within the range of 30 to 300 μm in terms of circular equivalent particle size when measured based on an optical microscope photograph (plan view) taken from the main light-emitting surface side of the light-emitting layer.

<Luminous ink>
A solution containing a luminescent compound (also referred to as a "luminescent ink") is a solution in which a luminescent compound is dissolved or dispersed in a solvent. The concentration of the luminescent compound is not particularly limited, but can be, for example, about 10 mg/mL.

The luminous ink can contain various functional additives depending on the method of dropping the luminous ink. For example, various known additives such as viscosity adjusters, surface tension adjusters, resistivity adjusters, film-forming agents, dispersants, surfactants, UV absorbers, antioxidants, anti-fading agents, anti-fungal agents, and anti-rust agents can be appropriately selected and contained depending on the purpose of improving ejection stability, print head compatibility, storage stability, image storage stability, and other performances.

The luminous ink may also contain a charge transport compound. In this case, it is preferable that the ratio of luminous compound/charge transport compound is 0.03 or more.

The solvent is not particularly limited as long as it can disperse the desired amount of the above material and eject droplets from an inkjet nozzle, but it is preferable to select an appropriate solvent depending on the type of luminescent compound, etc.

Specifically, alcohols such as water, methanol, ethanol, propanol, isopropyl alcohol, butanol, hexanol, heptanol, octanol, decanol, cyclohexanol, and terpineol, hydrocarbon compounds such as n-heptane, n-octane, decane, dodecane, tetradecane, toluene, xylene, cymene, durene, indene, dipentene, tetrahydronaphthalene, decahydronaphthalene, and cyclohexylbenzene, and ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, Examples of such ether compounds include ether compounds such as ether and p-dioxane, glycol ether ester compounds such as ethylene glycol monomethyl ether acetate, glycol oligomer ether esters such as diethylene glycol monomethyl ether acetate and diethylene glycol monobutyl ether acetate, aliphatic or aromatic esters such as ethyl acetate and propyl benzoate, dicarboxylic acid diesters such as diethyl carbonate, alkoxycarboxylic acid esters such as methyl 3-methoxypropionate and ethyl 3-ethoxypropionate, ketocarboxylic acid esters such as ethyl acetoacetate, and polar compounds such as propylene carbonate, γ-butyrolactone, N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, and cyclohexanone.

<Inkjet printing method>
In addition, in the method for producing an organic EL element of the present invention, the method of dropping a solution containing a luminescent compound (luminescent ink) onto an ink-receiving layer is preferably an ink-jet printing method, which is capable of forming small droplets, does not require the formation of a bank, and is simple.

In the inkjet printing method, inkjet printing is performed based on a predetermined dot pattern so that the luminescent compound is present with a concentration gradient in the in-plane and thickness directions of the ink receiving layer.

In the present invention, known inkjet printing methods and inkjet printing devices can be used as appropriate. For example, the IJCS-1 manufactured by Konica Minolta can be used.

The head scan speed is preferably a value that allows the dot pitch in the scanning direction to be set to an appropriate value (50 to 500 μm), preferably 10 to 200 mm/sec, and more preferably 80 to 100 mm/sec.

Figure 2 is a schematic diagram showing an example of a method for forming a light-emitting layer using inkjet printing.

Figure 2 shows an example of a method for depositing luminescent ink onto an ink-receiving layer using an ink-jet printing device equipped with an ink-jet head (30).

In the example shown in FIG. 2, while the substrate (2), which is a transport member carrying an intermediate molded body formed up to the ink receiving layer, is continuously transported, the inkjet head (30) sequentially drops luminous ink onto the ink receiving layer in a predetermined dot pattern controlled by the control unit (35), forming a luminous layer. (1) is the intermediate molded body formed up to the luminous layer.

The inkjet head (30) is connected to a luminous ink supply mechanism and the like. The luminous ink is supplied to the inkjet head (30) by a tank (38A). In this example, the tank liquid level is kept constant so that the pressure of the luminous ink in the inkjet head (30) is always kept constant. This is done by allowing the luminous ink to overflow from the tank (38A) and return to the tank (38B) by natural flow. The luminous ink is supplied from the tank (38B) to the tank (38A) by a pump (31), and is controlled so that the liquid level in the tank (38A) is kept constant and stable according to the ejection conditions.

When the luminous ink is returned to the tank (38A) by the pump (31), it is passed through the filter (32). In this way, it is preferable that the luminous ink is passed at least once through a filter medium with an absolute or quasi-absolute filtration accuracy of 0.05 to 50 μm before being supplied to the inkjet head (30).

In addition, in order to perform operations such as cleaning the inkjet head (30) and filling it with liquid, the luminescent ink from the tank (36) and the cleaning solvent from the tank (37) can be forcefully supplied to the inkjet head (30) by the pump (39). For the inkjet head (30), these tank pumps may be divided into multiple pumps, or a branched pipe may be used, or a combination of these may be used.

In Figure 2, a piping branch (33) is used. Furthermore, in order to thoroughly remove the air from within the inkjet head (30), the luminous ink may be forcibly sent from the tank (36) to the inkjet head (30) using a pump (39), while the luminous ink is extracted from the air vent piping and sent to a waste liquid tank (34).

The inkjet head applicable to the manufacturing method of the organic EL element according to the present invention is not particularly limited, and may be, for example, a shear mode type (piezo type) head having a vibration plate equipped with a piezoelectric element in the ink pressure chamber, ejecting luminous ink by the pressure change in the ink pressure chamber caused by this vibration plate, or a thermal type head having a heating element, ejecting luminous ink from a nozzle by a sudden change in volume caused by film boiling of the luminous ink by thermal energy from this heating element.

Figures 3A and 3B are schematic external views showing an example of the structure of an inkjet head that can be used in an inkjet printing method.

Figure 3A is a schematic perspective view showing an inkjet head (30) applicable to the present invention, and Figure 3B is a schematic bottom view of the inkjet head (30).

The inkjet head (30) shown as an example in Figures 3A and 3B includes a head chip that ejects ink from a nozzle, a wiring board on which the head chip is arranged, a drive circuit board connected to the wiring board via a flexible board, a manifold that introduces ink into the channel of the head chip via a filter, a housing (56) inside which the manifold is housed, a cap receiving plate (57) attached to cover the bottom opening of the housing (56), a first joint and a second joint (81a, 81b) attached to the first ink port and the second ink port of the manifold, a third joint (82) attached to the third ink port of the manifold, and a cover member (59) attached to the housing (56). Also, mounting holes (68) are formed for mounting the housing (56) to the printer body.

The cap receiving plate (57) shown in FIG. 3B is formed as a generally rectangular plate with an elongated outer shape in the left-right direction to correspond to the shape of the cap receiving plate mounting portion (62), and has a nozzle opening (71) that is elongated in the left-right direction to expose the nozzle plate (61) in which multiple nozzles are arranged in its approximate center. For the specific structure inside the inkjet head shown in FIG. 3A, see, for example, FIG. 2 described in JP 2012-140017 A.

Figures 3A and 3B show representative examples of inkjet heads, but other inkjet heads having configurations described in, for example, JP 2012-140017 A, JP 2013-010227 A, JP 2014-058171 A, JP 2014-097644 A, JP 2015-142979 A, JP 2015-142980 A, JP 2016-002675 A, JP 2016-002682 A, JP 2016-107401 A, JP 2017-109476 A, JP 2017-177626 A, etc., can be appropriately selected and applied.

Inkjet heads that can be used in the present invention can be appropriately selected from inkjet heads having the configurations described in, for example, JP 2012-140017 A, JP 2013-010227 A, JP 2014-058171 A, JP 2014-097644 A, JP 2015-142979 A, JP 2015-142980 A, JP 2016-002675 A, JP 2016-002682 A, JP 2016-107401 A, JP 2017-109476 A, JP 2017-177626 A, etc.

In addition, it is preferable for the inkjet head to be capable of producing droplets at the picoliter level, for example, Konica Minolta's KM512 or KM1024.

<Method of forming members other than the light-emitting layer>
There is no particular limitation on the method for forming the electrodes and organic functional layers other than the light-emitting layer (e.g., hole injection layer, hole transport layer, hole blocking layer, electron transport layer, electron injection layer, etc.), and any conventionally known method can be used. For the method for forming the organic functional layer, for example, a formation method using a vacuum deposition method or a wet process can be used. For the wet process, the same method as the method for forming the ink receiving layer can be used.

When a vapor deposition method is employed to form the organic functional layer, the vapor deposition conditions vary depending on the type of compound used, etc., but it is generally desirable to appropriately select the following conditions within the ranges: boat heating temperature 50 to 450° C., vacuum degree 10 ⁻⁶ to 10 ⁻² Pa, vapor deposition rate 0.01 to 50 nm/sec, substrate temperature −50 to 300° C., and thickness 0.1 nm to 5 μm, preferably 5 to 200 nm.

A different formation method may be used for each organic functional layer.

(9) Performance of Organic EL Element <Driving Voltage>
In the organic EL element of the present invention, the driving voltage, which is the voltage at the start of light emission, is preferably 30 V or less, and more preferably 10 V or less.

<External quantum yield>
The external quantum yield (external extraction quantum efficiency) of the light emitted from the organic EL element of the present invention at room temperature (23° C.) is preferably 5% or more, more preferably 9% or more, when a phosphorescent compound or a delayed fluorescent compound is used, and is preferably 1.5% or more, more preferably 1.8% or more, when a fluorescent compound is used.

Here, external quantum yield (%) = number of photons emitted outside the organic EL element / number of electrons flowing into the organic EL element x 100.

The external quantum yield can be measured, for example, using a spectroradiometer CS-2000 (manufactured by Konica Minolta).

(10) Uses of Organic EL Element The organic EL element of the present invention can be suitably used for display devices that emit dot light to reproduce patterns or characters, or emit multi-color light to display high-quality color images with improved color mixing.

The display device of the present invention is characterized by comprising an organic electroluminescence element of the present invention. There are no particular limitations other than the inclusion of an organic electroluminescence element of the present invention, and other configurations may be publicly known.

An embodiment of a display device including the organic EL element of the present invention will be described.
The non-emitting surface of the organic EL element is covered with a glass case, and a 300 μm-thick glass substrate is used as a sealing substrate. An epoxy-based photocuring adhesive (Luxtrack LC0629B, manufactured by Toagosei Co., Ltd.) is applied around the periphery as a sealing material. This is then layered on the cathode and brought into close contact with the transparent support substrate. UV light is then irradiated from the glass substrate side to cure and seal the device, thereby forming a display device as shown in FIGS. 4 and 5.

Figure 4 shows a schematic diagram of a display device (101), in which the organic EL element according to the present invention is covered with a glass cover (102). It is preferable that the sealing operation with the glass cover is performed in a glove box with an atmosphere of high-purity nitrogen gas with a purity of 99.999% or more, without exposing the organic EL element to the air.

Figure 5 shows a schematic cross-sectional view of a display device (101), which includes an organic EL element (100). The organic EL element (100) shown in Figure 5 includes a cathode (105), a light-emitting layer (106), and a glass substrate (107) with a transparent electrode. Nitrogen gas (108) is filled inside the glass cover (102), and a moisture scavenger (109) is provided.

The organic EL element of the present invention can also be suitably used in lighting devices such as home lighting and vehicle lighting.

The lighting device of the present invention is characterized by comprising an organic electroluminescence element of the present invention. There are no particular limitations other than the inclusion of an organic electroluminescence element of the present invention, and other configurations may be publicly known.

In addition to the above, the organic EL element of the present invention can be used as a light source for other purposes, such as backlights for clocks and liquid crystal displays, billboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processing machines, and light sources for optical sensors.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

The charge transporting compounds H1 to H7, the phosphorescent compounds Ep1 to Ep4, the delayed fluorescent compound Et1 and the fluorescent compounds Ef1 to Ef3 used in the examples are shown below. The delayed fluorescent compound Et1 is a thermally activated delayed fluorescent compound.
The lowest excited triplet energy level T ₁ [eV] and the lowest excited singlet energy level S ₁ [eV] of each compound are as shown in Tables I to IV.

(1) Example 1
<Preparation of Organic EL Element No. (1-1)>
A 30 mm×30 mm×0.7 mm glass substrate was coated with indium tin oxide (ITO) to a thickness of 100 nm, and the substrate was then patterned. The substrate was then ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and cleaned with UV ozone for 5 minutes to obtain a transparent support substrate provided with an ITO transparent electrode (anode).

On the formed anode, a solution of polystyrene (manufactured by ACROS ORGANICS, molecular weight = 260,000) as an insulating polymer and charge transporting compound H1 in a mass ratio of 1:1 (mass ratio of charge transporting compound in the ink receiving layer: 50%) was used as a solute, and diluted to 1.0% with n-propyl acetate as a solvent was applied by spin coating at 500 rpm for 30 seconds, and then dried at 120°C for 30 minutes to provide an ink receiving layer with a thickness of 50 nm.

A luminescent compound (phosphorescent compound Ep1) was mixed with n-propyl acetate as a solvent at a concentration of 10 mg/mL, and the mixture was ultrasonically heated to maintain a temperature of 90°C for 30 minutes. The mixture was then filtered through a 0.2 μm filter to remove any aggregated components, producing a luminescent ink.

Next, a solution containing the phosphorescent compound Ep1 (luminescent ink) was dropped onto the ink-receiving layer by ink-jet printing under the following conditions to form a luminescent layer having dot regions.
(Inkjet printing conditions)
Inkjet device: Konica Minolta IJCS-1
Inkjet head: Konica Minolta KM512
Number of shots: 2 shots Distance between head ejection nozzles: 140 μm pitch Head scan speed: 90 mm/sec

Next, this was attached to a vacuum deposition apparatus, the vacuum chamber was reduced in pressure to 4×10 ⁻⁴ Pa, and an electron injection layer and a cathode were formed under the following conditions: The electron injection layer was formed by depositing potassium fluoride at a deposition rate of 0.1 Å/sec to a thickness of 2.0 nm, and the cathode was formed by depositing Al at a deposition rate of 4 Å/sec to a thickness of 100 nm.

Organic EL element No. (1-1) was produced by the above process.

Figure 6 is a schematic cross-sectional view of organic EL element No. (1-1). The structure of organic EL element No. (1-1) shown in Figure 6 is the same as the structure of the organic EL element shown in Figure 1, except that it has an electron injection layer (203).

<Preparation of Organic EL Elements No. (1-2) to (1-19)>
Organic EL elements No. (1-2) to (1-19) were prepared in the same manner as organic EL element No. (1-1), except that the types of the charge transport compound and the light emitting compound (phosphorescent compound or delayed fluorescent compound) used were changed as shown in Table I.

<Evaluation of Organic EL Elements No. (1-1) to (1-19)>
The driving voltage [V] and external quantum yield [%] of the produced organic EL device were measured as follows.

The driving voltage [V] of the fabricated organic EL element was measured at a temperature of 23° C. The driving voltage [V] was the voltage value when the current density became 2.5 mA/cm ² at the start of light emission. A spectroradiometer CS-2000 was used to measure the luminance.

The external quantum yield [%] of the produced organic EL element was measured when a constant current of 2.5 mA/ ^cm2 was applied at a temperature of 23° C. A spectroradiometer CS-2000 (manufactured by Konica Minolta, Inc.) was used for the measurement.

The evaluation of the driving voltage [V] and external quantum yield [%] is shown in Table I below. The values of the driving voltage and external quantum yield in Table I are relative values based on the values of organic EL element No. (1-1), which had a driving voltage of 5.5 V and an external quantum yield of 8.5%.

From the results of Example 1 shown in Table I, it can be seen that the present invention has a better external quantum yield than the comparative example.
This is believed to be because, in the comparative example, the lowest excited triplet energy level _T1 of the charge transport compound is lower than the lowest excited triplet energy level _T1 of the phosphorescent compound or delayed fluorescent compound, resulting in reverse energy transfer from the phosphorescent compound or delayed fluorescent compound to the charge transport compound, whereas, in the present invention, the lowest excited triplet energy level _T1 of the charge transport compound is higher than the lowest excited triplet energy level _T1 of the phosphorescent compound or delayed fluorescent compound, thereby suppressing reverse energy transfer.

(2) Example 2
<Preparation of Organic EL Elements No. (2-1) to (2-3)>
A luminous ink containing the phosphorescent compound Ep1 as the luminescent compound A and a luminescent ink containing the phosphorescent compound Ep4 as the luminescent compound B were prepared in the same manner as in Example 1.

Organic EL elements No. (2-1) to (2-3) were produced in the same manner as organic EL element No. (1-1), except that the above two types of luminescent inks were dropped onto the ink receiving layer one shot at a time using different inkjet heads.

Figure 7 is a schematic cross-sectional view of organic EL element No. (2-1). The structure of organic EL element No. (2-1) shown in Figure 6 is similar to the structure of organic EL element No. (1-1) shown in Figure 6, except that it contains two types of dot regions, a dot region made of luminescent compound A (202A) and a dot region made of luminescent compound B (202B).

<Evaluation of Organic EL Elements No. (2-1) to (2-3)>
The driving voltage [V] and external quantum yield [%] of the fabricated organic EL element were measured and evaluated, and are shown in Table II below. The values of the driving voltage and external quantum yield in Table II are relative values based on the values of the organic EL element No. (1-1) of Example 1.

From the results of Example 2 shown in Table II, it can be seen that even when a plurality of phosphorescent compounds are used, when the lowest excited triplet energy level _T1 of the charge transport compound is higher than the lowest excited triplet energy level _T1 of any of the phosphorescent compounds, the driving voltage and external quantum yield are as good as those of the organic EL element No. (1-1) of Example 1.

(3) Example 3
<Preparation of Organic EL Elements No. (3-1) to (3-6)>
Organic EL elements No. (3-1) to (3-6) were prepared in the same manner as organic EL element No. (1-1), except that the types of the charge transporting compound and the luminescent compound (fluorescent compound) used were changed as shown in Table III.

<Evaluation of Organic EL Elements No. (3-1) to (3-6)>
The driving voltage [V] and external quantum yield [%] of the fabricated organic EL elements are shown in Table III below. The values of driving voltage and external quantum yield in Table III are relative values based on the values of organic EL element No. (3-1), and the driving voltage of organic EL element No. (3-1) was 3.8 V and the external quantum yield was 1.8%.

From the results of Example 3 shown in Table III, it can be seen that the present invention has a better external quantum yield than the comparative example.
This is believed to be because, in the comparative example, the lowest excited singlet energy level _S1 of the charge transport compound is lower than the lowest excited singlet energy level _S1 of the fluorescent compound, resulting in reverse energy transfer from the fluorescent compound to the charge transport compound, whereas, in the present invention, the lowest excited singlet energy level _S1 of the charge transport compound is higher than the lowest excited singlet energy level _S1 of the fluorescent compound, thereby suppressing reverse energy transfer.

(4) Example 4
<Preparation of Organic EL Elements No. (4-1) to (4-5)>
Organic EL element No. (4-1) to (4-5) were prepared in the same manner as organic EL element No. (1-1), except that the mass ratio of the charge transporting compound in the ink receiving layer was changed as shown in Table IV. Organic EL element No. (4-3) is the same as organic EL element No. (1-1).

<Evaluation of Organic EL Elements No. (4-1) to (4-5)>
The driving voltage [V] and external quantum yield [%] of the fabricated organic EL element were measured and evaluated, and are shown in Table IV below. The values of the driving voltage and external quantum yield in Table IV are relative values based on the values of organic EL element No. (4-3) as the reference.

From the results of Example 4 shown in Table IV, it can be seen that the mass ratio of the charge transporting compound in the ink receiving layer is preferably within the range of 20 to 80%. When the mass ratio of the charge transporting compound is 0%, the charge transport to the light emitting compound is insufficient, resulting in a high driving voltage. Also, when the mass ratio of the charge transporting compound is 100%, a short circuit occurs and no light is emitted. This is because the rate at which the ink receiving layer material dissolves in the solvent of the light emitting ink, that is, the mass [mg/mL] at which the ink receiving layer material (only the charge transporting compound in the case of organic EL element No. (4-5)) dissolves per unit volume of solvent becomes high, and as a result, most of the dissolved charge transporting compound moves to the periphery to form a coffee ring, and the thickness of the center of the coffee ring becomes extremely thin, causing a short circuit between the upper and lower electrodes.

1 Intermediate molded body with light-emitting layer formed thereon 2 Substrate 30 Inkjet head 31, 39 Pump 32 Filter 33 Pipe branch 34 Waste liquid tank 35 Control unit 36, 37, 38A, 38B Tank 56 Housing 57 Cap receiving plate 59 Cover member 61 Nozzle plate 62 Cap receiving plate mounting portion 68 Mounting hole 71 Nozzle opening 81a First joint 81b Second joint 82 Third joint 100 Organic EL element 101 Display device 102 Glass cover 105 Cathode 106 Light-emitting layer 107 Glass substrate with transparent electrode 108 Nitrogen gas 109 Moisture scavenger 201 Ink receiving layer 202 Light-emitting compound 202A Light-emitting compound A
202B Luminescent compound B
203 Electron injection layer

Claims (9)

An organic electroluminescence element having a light-emitting layer between at least one pair of an anode and a cathode,
The light-emitting layer contains an ink-receiving layer that exists as a continuous phase throughout the entire display area, and at least one light-emitting compound that exists with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer,
The ink receiving layer contains at least one insulating polymer and at least one charge transporting compound,
The light-emitting compound contains a phosphorescent compound or a delayed fluorescent compound, and
An organic electroluminescence device, characterized in that the lowest excited triplet energy level of any one of the charge transport compounds is higher than the lowest excited triplet energy level of any one of the phosphorescent compounds or delayed fluorescent compounds. The organic electroluminescence element according to claim 1, characterized in that the lowest excited triplet energy level of any of the charge transport compounds is higher than the lowest excited triplet energy level of any of the phosphorescent compounds or delayed fluorescent compounds. An organic electroluminescence element having a light-emitting layer between at least one pair of an anode and a cathode,
The light-emitting layer contains an ink-receiving layer that exists as a continuous phase throughout the entire display area, and at least one light-emitting compound that exists with a concentration gradient in the in-plane direction and thickness direction of the ink-receiving layer,
The ink receiving layer contains at least one insulating polymer and at least one charge transporting compound,
a mass ratio of the charge transporting compound in the ink receiving layer is within a range of 50 to 80%;
The light-emitting compound contains a fluorescent compound, and
An organic electroluminescence device, wherein the lowest excited singlet energy level of any one of the charge transporting compounds is higher than the lowest excited singlet energy level of any one of the fluorescent compounds. The organic electroluminescence element according to claim 3, characterized in that the lowest excited singlet energy level of any of the charge transport compounds is higher than the lowest excited singlet energy level of any of the fluorescent compounds. 3. The organic electroluminescence element according to claim 1, wherein the mass ratio of the charge transporting compound in the ink receiving layer is within a range of 20 to 80%. A method for producing the organic electroluminescence element according to any one of claims 1 to 5, comprising the steps of:
a step of dropping a solution containing the light-emitting compound onto the ink-receiving layer to form the light-emitting layer. The method for manufacturing an organic electroluminescence element according to claim 6, characterized in that the method for dropping the solution containing the luminescent compound onto the ink receiving layer is an inkjet printing method. A display device comprising an organic electroluminescence element according to any one of claims 1 to 5. A lighting device comprising an organic electroluminescence element according to any one of claims 1 to 5.

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