Organic EL element, organic EL display panel, and method for manufacturing organic EL element

Abstract

To prolong a lifetime by improving light emission efficiency at a high temperature and maintaining high light emission efficiency over an operation temperature range in an organic EL element.SOLUTION: The present invention relates to an organic EL element configured by successively laminating a positive electrode, a light-emitting layer, an intermediate layer and a negative electrode. In the organic EL element, an electron implantation control layer which is disposed in the intermediate layer at a side of the light-emitting layer is further included, and a trap site is formed on an interface between the intermediate layer and the electron implantation control layer. A trap level of the trap site is lower than a lowest unoccupied molecular orbital (LUMO) of a functional material contained in the intermediate later by 35 meV or more, and density of the trap site is equal to or greater than 0.1% of electron density in the intermediate layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to improvements in luminous efficiency and lifetime in organic EL devices that use a fluorescent material as a light-emitting material. [Background technology]

[0002] In recent years, display devices using organic EL elements have become widespread.

[0003] An organic EL element has a structure in which at least a light-emitting layer is sandwiched between an anode and a cathode. In the light-emitting layer, the energy of excitons generated by the recombination of electrons and holes is converted into light. Conventionally, in order to improve the light-emitting efficiency of organic EL elements, efforts have been made such as adjusting the balance between electrons and holes (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-187205 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the luminous efficiency of organic EL elements is temperature dependent, making it difficult to maintain high luminous efficiency over the entire operating temperature range. In particular, the luminous efficiency decreases as the operating temperature increases.

[0006] An object of the present disclosure is to improve the luminous efficiency at high temperatures, maintain high luminous efficiency over the entire range of operating temperatures, and extend the life of an organic EL element. [Means for solving the problem]

[0007] An organic EL element according to one embodiment of the present disclosure is an organic EL element comprising an anode, an emitting layer, an intermediate layer, and a cathode stacked in this order, further comprising an electron injection control layer arranged in contact with the emitting layer side of the intermediate layer, wherein a trap site is formed at the interface between the intermediate layer and the electron injection control layer, a trap level of the trap site is 35 meV or more lower than a lowest unoccupied molecular orbital (LUMO) level of a functional material contained in the intermediate layer, and a density of the trap sites is 0.1% or more of the electron density in the intermediate layer.

[0008] In this specification, a high LUMO (Lowest Unoccupied Molecular Orbital) level, a high highest occupied molecular orbital (HOMO; Highest Occupied Molecular Orbital) level, or a trap level means that the difference between the level and the vacuum level of electrons is small, that is, the potential energy of electrons present at the level is large. Effect of the Invention

[0009] In the organic EL element according to one embodiment of the present disclosure, when electrons are injected from the intermediate layer to the electron injection control layer, the electrons pass through a trap site, and the difference between the trap level and the LUMO level of the intermediate layer is sufficiently high relative to the energy of thermal excitation. Therefore, the improvement of the electron injection from the intermediate layer to the electron injection control layer due to thermal excitation is suppressed, and the balance of electrons and holes in the light-emitting layer does not depend on temperature. This configuration makes it easy to maintain the balance of electrons and holes regardless of the temperature of the organic EL element, and high luminous efficiency can be maintained over the entire operating temperature range, which is expected to extend the life of the organic EL element. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view that illustrates a schematic configuration of an organic EL element 1 according to an embodiment. [Diagram 2] FIG. 2 is a simplified schematic diagram showing band diagrams of a hole transport layer, a light emitting layer, an electron injection control layer, and an electron transport layer in the example. [Diagram 3]1 is a graph showing the relationship between applied voltage and current density and its temperature dependency for each of Comparative Example 1, Comparative Example 2, and Comparative Example 3. [Figure 4] 1 is a graph showing the relationship between current density and the rate of change in current relative to voltage, and the temperature dependency thereof, for each of Comparative Examples 1, 2, and 3. [Diagram 5] 13 shows the results of comparing the actual measured values ​​and the simulation results for the relationship between the applied voltage and the current density and the temperature dependency thereof for each of an example and a comparative example 4. [Figure 6] FIG. 2 is a simplified schematic diagram showing band diagrams of a hole transport layer, a light emitting layer, an electron injection control layer, and an electron transport layer in accordance with examples and comparative examples. [Figure 7] FIG. 1 is a partial cross-sectional view showing a schematic diagram of a part of a manufacturing process of an organic EL element according to an embodiment, in which (a) shows a state in which a TFT layer is formed on a substrate, (b) shows a state in which an interlayer insulating layer is formed on a substrate, (c) shows a state in which a pixel electrode material is formed on the interlayer insulating layer, (d) shows a state in which a pixel electrode is formed, and (e) shows a state in which a partition material layer is formed on the interlayer insulating layer and the pixel electrode. [Figure 8] FIG. 1 is a partial cross-sectional view showing a schematic diagram of a part of a manufacturing process of an organic EL element according to an embodiment, in which (a) shows a state in which a partition wall is formed, (b) shows a state in which a hole injection layer is formed on a pixel electrode, and (c) shows a state in which a hole transport layer is formed on the hole injection layer. [Figure 9] FIG. 1 is a partial cross-sectional view showing a schematic diagram of a part of a manufacturing process of an organic EL device according to an embodiment, in which (a) shows a state in which a light-emitting layer is formed on a hole-transport layer, (b) shows a state in which an electron injection control layer is formed on the light-emitting layer and the partition layer, and (c) shows a state in which an electron transport layer is formed on the electron injection control layer. [Figure 10] FIG. 1 is a partial cross-sectional view showing a schematic diagram of a part of a manufacturing process of an organic EL device according to an embodiment, in which (a) shows a state in which an electron injection layer is formed on an electron transport layer, (b) shows a state in which a counter electrode is formed on the electron injection layer, and (c) shows a state in which a sealing layer is formed on the counter electrode. [Figure 11] 4 is a flowchart showing a manufacturing process of the organic EL element according to the embodiment. [Figure 12] 1 is a block diagram showing a configuration of an organic EL display device including an organic EL element according to an embodiment. [Figure 13] 1A is a band diagram of a hole transport layer, a light emitting layer, an electron transport layer, an electron injection control layer, and an electron injection layer according to a modified example, and FIG. 1B is a band diagram of a hole transport layer, a hole injection control layer, a light emitting layer, and an electron transport layer according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <<How one aspect of the present disclosure was arrived at>> In order to use an organic EL element as a light-emitting element, it is essential to generate excitons that are the initial state of light emission. Therefore, in the past, the hole injection from the hole transport layer to the light-emitting layer and the electron injection from the electron transport layer to the light-emitting layer have been improved, and the carrier density in the light-emitting layer has been improved to increase the probability of recombination of electrons and holes. In addition, as a configuration for further improving the carrier density in the light-emitting layer, a functional layer is selected in which the HOMO (Highest Occupied Molecular Orbital) level of the electron transport layer and / or the LUMO (Lowest Unoccupied Molecular Orbital) level of the hole transport layer are adjusted so that hole leakage from the light-emitting layer to the electron transport layer and electron leakage from the light-emitting layer to the hole transport layer can be suppressed. This is because such a configuration can improve the carrier density in the light-emitting layer and increase the probability of recombination of electrons and holes. In addition, in order to improve the luminous efficiency, it is important not only to simply improve the carrier density in the light-emitting layer, but also to adjust the balance between electrons and holes.

[0012] It has been known that the luminous efficiency of an organic EL element decreases as the operating temperature increases. Therefore, the inventors have focused on the temperature dependence of the electron injection property into the light-emitting layer and the hole injection property into the light-emitting layer. Then, they have found that when the temperature dependence of the hole injection property into the light-emitting layer is low, the decrease in the luminous efficiency can be suppressed by suppressing the temperature dependence of the electron injection property into the light-emitting layer, and have arrived at the embodiment of the present disclosure.

[0013] <Mode of Disclosure> An organic EL element according to one embodiment of the present disclosure is an organic EL element comprising an anode, an emitting layer, an intermediate layer, and a cathode stacked in this order, further comprising an electron injection control layer arranged in contact with the emitting layer side of the intermediate layer, wherein a trap site is formed at the interface between the intermediate layer and the electron injection control layer, a trap level of the trap site is 35 meV or more lower than a lowest unoccupied molecular orbital (LUMO) level of a functional material contained in the intermediate layer, and a density of the trap sites is 0.1% or more of the electron density in the intermediate layer.

[0014] In the organic EL element according to one embodiment of the present disclosure, when electrons are injected from the intermediate layer to the electron injection control layer, the electrons pass through a trap site, and the difference between the trap level and the LUMO level of the intermediate layer is sufficiently high relative to the energy of thermal excitation. Therefore, the improvement of the electron injection from the intermediate layer to the electron injection control layer due to thermal excitation is suppressed, and the balance of electrons and holes in the light-emitting layer does not depend on temperature. This configuration makes it easy to maintain the balance of electrons and holes regardless of the temperature of the organic EL element, and high luminous efficiency can be maintained over the entire operating temperature range, which is expected to extend the life of the organic EL element.

[0015] In the organic EL element according to the embodiment of the present disclosure, the trap level may be lower than a lowest unoccupied molecular orbital (LUMO) level of the functional material contained in the intermediate layer by 50 meV or more.

[0016] With the above configuration, it is possible to further reduce the temperature dependency of the light emission efficiency and to increase the upper limit of the operating temperature.

[0017] In the organic EL element according to the aspect of the present disclosure, the electron injection control layer may have a thickness of 1 nm or more.

[0018] With the above-mentioned configuration, it is possible to prevent the function of the trap site from being deteriorated due to electrons tunneling through the electron injection control layer and flowing directly from the intermediate layer into the light emitting layer.

[0019] In the organic EL element according to the embodiment of the present disclosure, the intermediate layer may have a thickness of 1 nm or more.

[0020] With the above-mentioned configuration, it is possible to prevent the function of the trap site from being deteriorated due to electrons tunneling through the intermediate layer and flowing directly from the cathode side into the electron injection control layer.

[0021] In the organic EL element according to one aspect of the present disclosure, the electron injection control layer may be in contact with the light-emitting layer, and a LUMO level of the functional material contained in the electron injection control layer may be higher than a LUMO level of the functional material contained in the light-emitting layer and also higher than a LUMO level of the functional material contained in the intermediate layer.

[0022] With the above-described configuration, the electron injection property from the cathode side to the light-emitting layer can be controlled by the electron injection barrier from the intermediate layer to the electron injection control layer, and deterioration of the electron injection control layer due to concentration of electrons at the interface on the light-emitting layer side of the electron injection control layer can be suppressed.

[0023] In the organic EL element according to the embodiment of the present disclosure, the highest occupied molecular orbital (HOMO) level of the functional material contained in the electron injection control layer may be lower than the HOMO level of the functional material contained in the light-emitting layer.

[0024] With the above-mentioned structure, the electron injection control layer also functions as a hole blocking layer that prevents holes from flowing out from the light emitting layer to the electron injection control layer, thereby improving the light emitting efficiency.

[0025] Furthermore, the organic EL element according to one embodiment of the present disclosure may further include a second intermediate layer disposed in contact with the electron injection control layer on the side of the light emitting layer, and the LUMO level of the functional material contained in the electron injection control layer may be higher than the LUMO level of the functional material contained in the second intermediate layer and higher than the LUMO level of the functional material contained in the intermediate layer.

[0026] With the above configuration, the electron injection from the cathode side to the light-emitting layer can be controlled by the electron injection barrier from the intermediate layer to the electron injection control layer, and deterioration of the second intermediate layer due to concentration of electrons in the second intermediate layer can be suppressed.

[0027] Furthermore, the organic EL display panel according to an embodiment of the present disclosure may include a plurality of organic EL elements according to an embodiment of the present disclosure on a substrate.

[0028] An organic EL element according to one embodiment of the present disclosure is an organic EL element including an anode, an intermediate layer, an emitting layer, and a cathode stacked in this order, and further including a hole injection control layer disposed in contact with the emitting layer side of the intermediate layer, wherein trap sites are formed at the interface between the intermediate layer and the hole injection control layer, a trap level of the trap site is 35 meV or more higher than a HOMO level of a functional material contained in the intermediate layer, and a density of the trap sites is 0.1% or more of the hole density in the intermediate layer.

[0029] In the organic EL element according to one embodiment of the present disclosure, holes are injected from the intermediate layer to the hole injection control layer via a trap site, and the difference between the trap level and the HOMO level of the intermediate layer is sufficiently high relative to the energy of thermal excitation. Therefore, the improvement of hole injection from the intermediate layer to the hole injection control layer due to thermal excitation is suppressed, and the balance of electrons and holes in the light-emitting layer does not depend on temperature. This configuration makes it easy to maintain the balance of electrons and holes regardless of the temperature of the organic EL element, and high luminous efficiency can be maintained over the entire operating temperature range, which is expected to extend the life of the organic EL element.

[0030] A method for manufacturing an organic EL element according to one embodiment of the present disclosure includes preparing a substrate, forming an anode above the substrate, forming an emitting layer above the anode, forming an electron injection control layer above the emitting layer, forming an intermediate layer on the electron injection control layer, and forming a cathode above the intermediate layer, and is characterized in that trap sites having a level 35 meV or more lower than a lowest unoccupied molecular orbital (LUMO) level of a functional material contained in the intermediate layer are formed at an interface between the electron injection control layer and the intermediate layer, with a density of 0.1% or more of the electron density in the intermediate layer.

[0031] <Embodiment> The organic EL element according to the embodiment will be described below. Note that the following description is an example for explaining the configuration and the action and effect according to one aspect of the present invention, and the present invention is not limited to the following embodiment except for the essential part.

[0032] [1. Structure of organic EL element] 1 is a diagram showing a schematic cross-sectional structure of an organic EL element 1 according to the present embodiment. The organic EL element 1 includes an anode 13, a hole injection layer 15, a hole transport layer 16, an emitting layer 17, an electron injection control layer 18, an electron transport layer 19, an electron injection layer 20, and a cathode 21. In the present embodiment, the electron transport layer 19 corresponds to the intermediate layer of the present invention.

[0033] In the organic EL element 1, the anode 13 and the cathode 21 are disposed so as to face each other with their principal surfaces facing each other, and a light-emitting layer 17 is formed between the anode 13 and the cathode 21.

[0034] A hole transport layer 16 is formed on the anode 13 side of the light emitting layer 17 so as to be in contact with the light emitting layer 17. A hole injection layer 15 is formed between the hole transport layer 16 and the anode 13.

[0035] On the cathode 21 side of the light-emitting layer 17, an electron injection control layer 18 is formed in contact with the light-emitting layer 17, and an electron transport layer 19 is formed in contact with the electron injection control layer 18. An electron injection layer 20 is formed between the electron transport layer 19 and the cathode 21.

[0036] [1.1 Components of an organic EL element] The anode 13 is formed on the interlayer insulating layer 12. The anode 13 is formed as a pixel electrode provided for each pixel, and is electrically connected to the TFT layer 112 through a contact hole provided in the interlayer insulating layer 12.

[0037] In this embodiment, the anode 13 functions as a light-reflective electrode.

[0038] Specific examples of metal materials having light reflectivity include Ag (silver), Al (aluminum), aluminum alloys, Mo (molybdenum), APC (an alloy of silver, palladium, and copper), ARA (an alloy of silver, rubidium, and gold), MoCr (an alloy of molybdenum and chromium), MoW (an alloy of molybdenum and tungsten), and NiCr (an alloy of nickel and chromium).

[0039] The anode 13 may be composed of a metal layer alone, or may have a laminated structure in which a layer made of a metal oxide such as ITO (indium tin oxide) or IZO (indium zinc oxide) is laminated on a metal layer.

[0040] In addition, when the cathode 21 is a light-reflective electrode, the anode 13 may be a light-transmitting electrode. In this case, the anode 13 includes at least one of a metal layer formed of a metal material and a metal oxide layer formed of a metal oxide. The film thickness of the anode 13 is set to be thin, about 1 nm to 50 nm, and has light transmittance. Although the metal material is a light-reflective material, the light transmittance can be ensured by making the thin film of the metal layer thin, 50 nm or less. Therefore, a part of the light from the light-emitting layer 17 is reflected by the anode 13, but the remaining part passes through the anode 13.

[0041] In this case, examples of the metal material forming the metal layer included in the anode 13 include Ag, a silver alloy mainly composed of Ag, Al, and an Al alloy mainly composed of Al. Examples of Ag alloys include magnesium-silver alloy (MgAg) and indium-silver alloy. Ag basically has a low resistivity, and Ag alloys are preferable in that they have excellent heat resistance and corrosion resistance and can maintain good electrical conductivity for a long period of time. Examples of Al alloys include magnesium-aluminum alloy (MgAl) and lithium-aluminum alloy (LiAl). Other examples of alloys include a lithium-magnesium alloy and a lithium-indium alloy.

[0042] The metal layer included in the anode 13 may be, for example, a single layer of Ag or MgAg alloy, or may have a laminated structure of an Mg layer and an Ag layer (Mg / Ag), or a laminated structure of an MgAg alloy layer and an Ag layer (MgAg / Ag).

[0043] Examples of metal oxides that form the metal oxide layer included in the anode 13 include ITO and IZO.

[0044] In addition, the anode 13 may be composed of a metal layer alone or a metal oxide layer alone, or may have a laminated structure in which a metal oxide layer is laminated on a metal layer, or a laminated structure in which a metal layer is laminated on a metal oxide layer.

[0045] <Hole injection layer> The hole injection layer 15 has a function of promoting the injection of holes from the anode 13 to the light emitting layer 17. The hole injection layer 15 is, for example, a coating film, and is formed, for example, by coating and drying a solution containing a hole injection material as a solute. The hole injection layer 15 may be formed of a vapor deposition film. The hole injection layer 15 is made of, for example, a conductive polymer material such as PEDOT:PSS (a mixture of polythiophene and polystyrene sulfonic acid), polyfluorene or a derivative thereof, or polyarylamine or a derivative thereof, or an oxide of Ag, Mo, chromium (Cr), vanadium (V), tungsten (W), nickel (Ni), iridium (Ir), or the like.

[0046] <Hole transport layer> The hole transport layer 16 has a function of transporting holes injected from the hole injection layer 15 to the light emitting layer 17. The hole transport layer 16 is, for example, a coating film, specifically formed by coating and drying a solution containing a hole transport material as a solute. Alternatively, the hole transport layer 16 may be formed as a vapor deposition film. For example, a polymer compound such as polyfluorene or a derivative thereof, or polyarylamine or a derivative thereof can be used.

[0047] <Light-emitting layer> The light-emitting layer 17 has a function of emitting light by recombination of holes and electrons. Since the recombination positions of holes and electrons in the light-emitting layer have a distribution, it is preferable that the thickness of the light-emitting layer is larger than the recombination distribution width, and in one embodiment, the thickness of the light-emitting layer 17 is 30 nm or more. In one embodiment, the thickness of the light-emitting layer 17 is 40 nm or more. In addition, the mobility of a light-emitting material is generally smaller than that of a charge transport material, and designing the thickness of the light-emitting layer to be thin contributes to reducing the driving voltage of the device, so in one embodiment, the thickness of the light-emitting layer 17 is 80 nm or less. In one embodiment, the thickness of the light-emitting layer 17 is 120 nm or less.

[0048] The light-emitting layer 17 is, for example, a coating film, and is formed, for example, by coating and drying a solution containing a material for forming the light-emitting layer and a solute. Alternatively, the light-emitting layer 17 may be formed as a vapor-deposited film.

[0049] Known organic fluorescent materials can be used as materials for forming the light-emitting layer 17. For example, oxinoid compounds, perylene compounds, coumarin compounds, azacoumarin compounds, oxazole compounds, oxadiazole compounds, perinone compounds, pyrrolopyrrole compounds, naphthalene compounds, anthracene compounds, fluorene compounds, fluoranthene compounds, tetracene compounds, pyrene compounds, coronene compounds, quinolone compounds and azaquinolone compounds, pyrazoline derivatives and pyrazolone derivatives, rhodamine compounds, chrysene compounds, phenanthrene compounds, cyclopentadiene compounds, stilbene compounds, diphenylquinone compounds, styryl compounds, butadiene compounds, dicyanomethylenepyran compounds, dicyanomethylenethiopyran compounds, fluorescein compounds, pyrylium compounds, thiapyrylium compounds, selenapyrylium compounds, telluropyrylium compounds, aromatic aldadiene compounds, oligophenylene compounds, thioxanthene compounds, cyanine compounds, acridine compounds, and the like can be used.

[0050] As described later, the light-emitting layer 17 preferably has a higher hole mobility than an electron mobility, and it is preferable to use a fluorescent material having such characteristics, or to use an organic material having such characteristics as a host material. When a fluorescent material is used as a dopant, for example, an amine compound, a condensed polycyclic aromatic compound, or a heterocyclic compound can be used as the host material. For example, a monoamine derivative, a diamine derivative, a triamine derivative, or a tetraamine derivative can be used as the amine compound. For example, an anthracene derivative, a naphthalene derivative, a naphthacene derivative, a phenanthrene derivative, a chrysene derivative, a fluoranthene derivative, a triphenylene derivative, a pentacene derivative, or a perylene derivative can be used as the condensed polycyclic aromatic compound. Examples of the heterocyclic compound that can be used include carbazole derivatives, furan derivatives, pyridine derivatives, pyrimidine derivatives, triazine derivatives, imidazole derivatives, pyrazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, pyrrole derivatives, indole derivatives, azaindole derivatives, azacarbazole derivatives, pyrazoline derivatives, pyrazolone derivatives, and phthalocyanine derivatives.

[0051] In the case where the light-emitting layer is formed from a fluorescent material and a host material, in one embodiment, the concentration of the fluorescent material is 1 wt% or more, in one embodiment, the concentration of the fluorescent material is 10 wt% or less, and in one embodiment, the concentration of the fluorescent material is 30 wt% or less.

[0052] The thickness of the light-emitting layer 17 is, for example, 20 to 60 nm in the case of a blue light-emitting layer, and, for example, 50 to 150 nm in the case of a green light-emitting layer or a red light-emitting layer.

[0053] <Electron injection control layer> The electron injection control layer 18 has a function of restricting the outflow of holes from the light-emitting layer 17 to the electron injection control layer 18, and also of controlling the injection of electrons from the electron injection control layer 18 to the light-emitting layer 17. The function of restricting the outflow of holes from the light-emitting layer 17 to the electron injection control layer 18 is realized by designing the energy band structure described below.

[0054] Moreover, it is preferable that the material of the electron injection control layer 18 has a larger energy difference (band gap) between the LUMO level and the HOMO level, i.e., the energy of singlet excitons, than the energy difference (energy of singlet excitons) between the LUMO level and the HOMO level of the material of the light-emitting layer 17. With this configuration, when singlet excitons are generated in the material of the electron injection control layer 18, they easily transition to singlet excitons in the fluorescent material of the light-emitting layer 17, and it is possible to prevent the singlet excitons of the fluorescent material of the light-emitting layer 17 from flowing out to the electron injection control layer 18, which contributes to improving the light-emitting efficiency. Similarly, it is preferable that the energy of triplet excitons in the material of the electron injection control layer 18 is larger than the energy of triplet excitons in the material of the light-emitting layer 17.

[0055] The electron injection control layer 18 is composed of, for example, a vapor deposition film. Examples of materials for the electron injection control layer 18 include π-electron low-molecular organic materials such as pyridine derivatives, pyrimidine derivatives, triazine derivatives, imidazole derivatives, oxadiazole derivatives, triazole derivatives, quinazoline derivatives, and phenanthroline derivatives. As described below, at the interface between the electron injection control layer 18 and the electron transport layer 19, an electron trap level that is 50 meV or more lower than the LUMO level of the electron transport layer 19 exists at 0.1% or more of the electron density of the electron transport layer 19 during operation. Therefore, it is preferable that the crystal lattices between the electron injection control layer 18 and the electron transport layer 19 are mismatched so that the trap level is easily generated. The energy and relative state density of the trap level can be measured by low-energy inverse photoelectron spectroscopy.

[0056] As will be described later, in order to reduce the accumulated charge Q at the interface between the electron injection control layer 18 and the electron transport layer 19, the dielectric constant of the electron transport layer 19 is set to ε 19 , conductivity is σ 19 , the dielectric constant of the electron injection control layer 18 is ε 18 , conductivity is σ 18 Then, ΔT(=ε 19 / σ 19 -ε 18 / σ18 ) is preferably small, and is preferably 1 / 2 or less than that of conventional materials.

[0057] The film thickness of the electron injection control layer 18 is at least 1 nm or more in order not to allow tunneling of electrons from the electron transport layer 19 to the light emitting layer 17. In the embodiment, the film thickness is, for example, 10 to 30 nm.

[0058] <Electron transport layer> The electron transport layer 19 has a function of transporting electrons from the cathode 21 to the light emitting layer 17 via the electron injection control layer 18. The electron transport layer 19 is made of an organic material having high electron transport properties. The electron transport layer 19 is formed of, for example, a vapor deposition film. Examples of organic materials used in the electron transport layer 19 include π-electron low molecular weight organic materials such as pyridine derivatives, pyrimidine derivatives, triazine derivatives, imidazole derivatives, oxadiazole derivatives, triazole derivatives, quinazoline derivatives, and phenanthroline derivatives.

[0059] The film thickness of the electron transport layer 19 is at least 1 nm or more in order not to allow tunneling of electrons from the electron injection layer 20 to the electron injection control layer 18. In the embodiment, the film thickness is, for example, 20 to 60 nm.

[0060] <Electron injection layer> The electron injection layer 20 has a function of injecting electrons supplied from the cathode 21 to the light emitting layer 17. The electron injection layer 20 is formed of, for example, a vapor deposition film. The electron injection layer 20 is formed by doping an organic material having high electron transportability with a doping metal selected from alkali metals, alkaline earth metals, rare earth metals, and the like. The doping metal is not limited to a simple metal, and may be doped as a compound such as a fluoride (for example, NaF) or a quinolinium complex (for example, Alq3, Liq). In the embodiment, Li is doped as Liq. Examples of doping metals include alkali metals such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr); alkaline earth metals such as calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra); and rare earth metals such as yttrium (Y), samarium (Sm), europium (Eu), and ytterbium (Yb).

[0061] Examples of organic materials used in the electron injection layer 20 include π-electron low-molecular organic materials such as oxadiazole derivatives (OXD), triazole derivatives (TAZ), and phenanthroline derivatives (BCP, Bphen).

[0062] <Cathode> The cathode 21 is made of a light-transmitting conductive material, and is formed on the electron injection layer 20. The cathode 21 is formed as a common counter electrode that faces the anode 13 of each organic EL element in common.

[0063] The material of the cathode 21 includes at least one of a metal layer made of a metal material and a metal oxide layer made of a metal oxide.

[0064] Examples of the metal material forming the metal layer included in the cathode 21 include Ag, a silver alloy mainly composed of Ag, Al, and an Al alloy mainly composed of Al. Examples of the Ag alloy include a magnesium-silver alloy and an indium-silver alloy. Examples of the Al alloy include a magnesium-aluminum alloy and a lithium-aluminum alloy. Other examples of the alloy include a lithium-magnesium alloy and a lithium-indium alloy.

[0065] The metal layer included in the cathode 21 may be, for example, a single layer of Ag or MgAg alloy, or may have a laminated structure of an Mg layer and an Ag layer, or a laminated structure of an MgAg alloy layer and an Ag layer.

[0066] Examples of metal oxides that form the metal oxide layer included in the cathode 21 include ITO and IZO.

[0067] In addition, the cathode 21 may be composed of a metal layer alone or a metal oxide layer alone, or may have a laminated structure in which a metal oxide layer is laminated on a metal layer, or a laminated structure in which a metal layer is laminated on a metal oxide layer.

[0068] When the anode 13 is a light-transmitting electrode, the cathode 21 may be a light-reflective electrode. In this case, the cathode 21 includes a metal layer made of a light-reflective metal material. Specific examples of the metal material having light reflectivity include silver, aluminum, aluminum alloy, molybdenum, APC, ARA, MoCr, MoW, and NiCr.

[0069] <Other> The organic EL element 1 is formed on a substrate 11. The substrate 11 is made of a base material 111 which is an insulating material. Alternatively, a wiring layer 112 may be formed on the base material 111 which is an insulating material. For example, a glass substrate, a quartz substrate, a silicon substrate, a plastic substrate, or the like may be adopted as the base material 111. As the plastic material, either a thermoplastic resin or a thermosetting resin may be used. For example, polyethylene, polypropylene, polyamide, polyimide (PI), polycarbonate, acrylic resin, polyethylene terephthalate (PET), polybutylene terephthalate, polyacetal, other fluorine-based resins, various thermoplastic elastomers such as styrene-based, polyolefin-based, polyvinyl chloride-based, polyurethane-based, fluorine rubber-based, and chlorinated polyethylene-based, epoxy resin, unsaturated polyester, silicone resin, polyurethane, etc., or copolymers, blends, polymer alloys, etc. mainly made of these may be used, and a laminate in which one or more of these are laminated may be used. Materials that can be used to form the wiring layer 112 include metal materials such as molybdenum sulfide, copper, zinc, aluminum, stainless steel, magnesium, iron, nickel, gold, and silver, inorganic semiconductor materials such as gallium nitride and gallium arsenide, and organic semiconductor materials such as anthracene, rubrene, and polyparaphenylenevinylene, and a TFT (Thin Film Transistor) layer may be formed by using a combination of these materials.

[0070] Although not shown, an interlayer insulating layer 12 is formed on the substrate 11. The interlayer insulating layer 12 is made of a resin material and serves to flatten steps on the upper surface of the TFT layer 112. Examples of the resin material include positive-type photosensitive materials. Examples of such photosensitive materials include acrylic resins, polyimide resins, siloxane resins, and phenol resins. In the interlayer insulating layer 12, a contact hole is formed for each pixel.

[0071] When the organic EL display panel 100 is of a bottom emission type, the substrate 111 and the interlayer insulating layer 12 need to be made of a light-transmitting material. Furthermore, when the TFT layer 112 is present, at least a part of the region of the TFT layer 112 that is present below the anode 13 needs to be light-transmitting.

[0072] In addition, a sealing layer 22 is formed on the organic EL element 1. The sealing layer 22 has a function of preventing organic layers such as the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, the electron injection control layer 18, the electron transport layer 19, and the electron injection layer 20 from being exposed to moisture or air, and is formed using a light-transmitting material such as silicon nitride (SiN) or silicon oxynitride (SiON). In addition, a sealing resin layer made of a resin material such as an acrylic resin or a silicone resin may be provided on a layer formed using a material such as silicon nitride (SiN) or silicon oxynitride (SiON).

[0073] When the organic EL display panel 100 is a top-emission type, the sealing layer 22 needs to be made of a light-transmitting material. Although not shown in Fig. 1, a color filter or an upper substrate may be attached onto the sealing layer 22 via a sealing resin. By attaching the upper substrate, the hole injection layer 15, the hole transport layer 16, the light-emitting layer 17, the electron injection control layer 18, the electron transport layer 19, and the electron injection layer 20 can be protected from moisture, air, and the like.

[0074] [2. Energy band structure] The organic EL element 1 is characterized by the energy band structures of the light-emitting layer 17, the electron injection control layer 18, and the electron transport layer 19. For ease of explanation, the term "energy level of a layer" is used, which is an abbreviation of the energy level of the organic material forming the layer. For layers made of multiple types of materials, the energy level of a representative organic material responsible for transporting electrons and / or holes is used as the "energy level of a layer."

[0075] Fig. 2 is a band diagram showing the energy band structure of the organic EL element 1. Fig. 2 shows the LUMO energy level (hereinafter referred to as "LUMO level") and the HOMO energy level (hereinafter referred to as "HOMO level") of the hole transport layer 16, the light emitting layer 17, the electron injection control layer 18, and the electron transport layer 19, as well as the level of the trap site (hereinafter referred to as "trap level") at the interface between the electron injection control layer 18 and the electron transport layer 19, and omits the rest. Note that although Fig. 2 does not show the vacuum level of electrons, the LUMO level, the HOMO level, and the trap level each have a larger difference from the vacuum level of electrons and a lower energy level as they are located further down in the band diagram.

[0076] [2.1 Electron injection barrier] An energy barrier for injecting electrons from the cathode 21 side to the light-emitting layer 17 exists at the interface of each layer from the cathode 21 to the light-emitting layer 17. This energy barrier is caused by the difference in LUMO level between the layer on the anode 13 side of the interface and the layer on the cathode 21 side. Hereinafter, the energy barrier for injecting electrons from the cathode 21 side to the anode 13 side at the interface between two adjacent layers is referred to as the "electron injection barrier."

[0077] The electron injection barrier Eg(eicl) from the electron transport layer 19 to the electron injection control layer 18 is determined by the difference between the LUMO level 181 of the organic material of the electron injection control layer 18 and the trap level 185. In this embodiment, the difference between the LUMO level 181 and the LUMO level 191 is 0.2 eV, and the difference Et between the trap level 185 and the LUMO level 191 is 50 meV, so that the electron injection barrier Eg(eicl) is 0.25 eV.

[0078] The electron injection barrier Eg(eml) from the electron injection control layer 18 to the light-emitting layer 17 is determined by the difference between the LUMO level 171 of the organic material of the light-emitting layer 17 and the LUMO level 181 of the organic material of the electron injection control layer 18. In this embodiment, the electron injection barrier Eg(eml) is −0.1 eV.

[0079] [2.2 Hole injection barrier] Meanwhile, an energy barrier for injecting holes from the anode 13 to the cathode 21 side through the light-emitting layer 17 exists at the interface of each layer from the anode 13 to the second electron transport layer 19. This energy barrier is caused by the difference in HOMO level between the layer on the cathode 21 side and the layer on the anode 13 side of the interface. Hereinafter, the energy barrier for injecting holes from the anode 13 side to the cathode 21 side at the interface between two adjacent layers is referred to as a "hole injection barrier."

[0080] The hole injection barrier Hg(eml) from the hole transport layer 16 to the light emitting layer 17 is determined by the difference between the HOMO level 172 of the organic material of the light emitting layer 17 and the HOMO level 162 of the organic material of the hole transport layer 16. In this embodiment, the hole injection barrier Hg(eml) is 0.11 eV.

[0081] The hole injection barrier Hg(eicl) from the light-emitting layer 17 to the electron injection control layer 18 is determined by the difference between the HOMO level 182 of the organic material of the electron injection control layer and the HOMO level 172 of the organic material of the light-emitting layer. It is preferable that Hg(eicl) satisfies the following formula (1). In this embodiment, the hole injection barrier Hg(etl1) is 0.31 eV. It is more preferable that Hg(etl1) satisfies the following formula (2).

[0082] Hg(etl1)≧0.2eV …Formula (1) Hg(etl1)≧0.4eV …Formula (2) [3. Effects of composition] [3.1 Temperature dependence of electron injection characteristics and hole injection characteristics] The relationship between the applied voltage and the current density and its temperature dependency for each of the comparative examples which adopt only a part of the examples are shown below. Fig. 3 is a graph showing the relationship between the applied voltage and the current density for each temperature for each of the comparative examples 1, 2, and 3. Fig. 4 shows the relationship between the applied voltage and the current density for each temperature for each of the comparative examples 1, 2, and 3 in terms of the relationship between the current density and the rate of change, and shows only the voltage dependency of the carrier injection degree, excluding the influence of temperature (the increase in conductivity due to the increase in carrier density).

[0083] Here, Comparative Example 1 is a HOD (Hole Only Device) in which the electron injection control layer 18, the electron transport layer 19, and the electron injection layer 20 are omitted, and the cathode 21 is in direct contact with the light emitting layer 17. This configuration significantly reduces the electron injection from the cathode 21 to the light emitting layer 17, so that all carriers in Comparative Example 1 can be considered to be holes. Therefore, the current density in Comparative Example 1 can be considered to be almost the same as the hole density in the examples.

[0084] FIG. 3(a) is a graph showing the relationship between applied voltage and current density and its temperature dependency in Comparative Example 1. That is, this shows the relationship between applied voltage and current density and its temperature dependency in the Example. As shown in FIG. 3(a), the increase in current density with respect to voltage change (the slope and tendency of the graph) does not change significantly between the case of 25° C. and the case of 85° C. This is more evident in the relationship between current density and the increase in current density with respect to voltage change shown in FIG. 4(a). That is, in the Example, the temperature dependency of hole injection characteristics is low.

[0085] Comparative Example 2 is an EOD (Electron Only Device) in which the hole injection layer 15 and the hole transport layer 16 are omitted and the light emitting layer 17 is in direct contact with the anode 13. This configuration significantly reduces the hole injection from the anode 13 to the light emitting layer 17, so that all carriers in Comparative Example 2 can be considered to be electrons. Therefore, the current density in Comparative Example 2 can be considered to be almost the same as the electron density in the examples.

[0086] Next, Comparative Example 3 is an EOD in which the hole injection layer 15, the hole transport layer 16, and the electron injection control layer 18 are omitted, the light emitting layer 17 is in direct contact with the anode 13, and the light emitting layer 17 is in direct contact with the electron transport layer 19. Therefore, the current density in Comparative Example 3 can be considered to be almost the same as the electron density in Comparative Example 4 in which the electron injection control layer 18 is omitted from the example.

[0087] Comparing Comparative Example 2 and Comparative Example 3, as shown in FIG. 3(b), in Comparative Example 2, the increase in current density with respect to the voltage change does not change significantly between 25° C. and 85° C. That is, the temperature dependency of the electron injection characteristics is low. In contrast, as shown in FIG. 3(c), in Comparative Example 3, the increase in current density with respect to the voltage change is large at 85° C. compared to 25° C. This difference is more remarkable in the relationship between the current density and the increase in current density with respect to the voltage change shown in FIG. 4(b) and (c). In Comparative Example 2, the temperature dependency of the relationship between the current density and the increase in current density with respect to the voltage change is low as in Comparative Example 1, whereas in Comparative Example 3, the temperature dependency of the relationship between the current density and the increase in current density with respect to the voltage change is high. Therefore, in the Comparative Example in which the electron injection control layer 18 is omitted, as the operating temperature increases, the increase in electron injection is large relative to the increase in hole injection. That is, when the injection balance between holes and electrons is optimized at 25° C., when the device is operated at 85° C., the luminous efficiency decreases due to an excess supply of electrons in the light-emitting layer. On the other hand, when the hole and electron injection balance is optimized at 85°C, the light-emitting layer is supplied with insufficient electrons when the device is operated at 25°C, resulting in a decrease in light-emitting efficiency. In other words, in Comparative Example 4, in which the electron injection control layer 18 is omitted from the embodiment, the hole and electron injection balance cannot be optimized at all operating temperatures, and there is a limit to the improvement of light-emitting efficiency. In contrast, in the configuration of the embodiment, when the operating temperature increases, the hole injection property and the electron injection property increase to the same extent. That is, when the hole and electron injection balance is optimized at 25°C, the hole and electron injection balance is maintained at a suitable level even when the device is operated at 85°C. In other words, since the hole and electron injection balance can be optimized at all operating temperatures, the light-emitting efficiency can be improved, and in particular, the decrease in light-emitting efficiency at high temperatures can be suppressed.

[0088] In Comparative Example 4, the luminous efficiency at a driving temperature of 85° C. is 94% of that at a driving temperature of 25° C., and in the Example, the luminous efficiency at 85° C. is 99% of that at a driving temperature of 25° C. In addition, when the lifetime (LT80; driving time until the emission brightness decreases to 80% of the initial value) at a driving temperature of 85° C. in Comparative Example 4 is taken as 100, the lifetime (LT80) at a driving temperature of 85° C. in the Example is 2000.

[0089] [3.2 Comparison with simulation] 5(a) shows the relationship between the applied voltage and the current density and its temperature dependence for each of the example and the simulation of the example. For the example, the relationship between the applied voltage and the current density is shown by plotting actual measured values. On the other hand, for the simulation of the example, the number of trap sites having a trap level of a depth Et=50 meV between the electron transport layer 19 and the electron injection control layer 18 is 1×10 11 pieces / cm 3 The figure shows the relationship between the applied voltage and the current density, simulating the distribution of electrons assuming that only one sigma exists. As shown in Figure 5(a), there is little deviation between the simulation results and the actual measurements, indicating that the simulation is highly likely to reproduce the internal state of the embodiment.

[0090] FIG. 5(b) shows the relationship between the applied voltage and the current density and its temperature dependency for each of Comparative Example 4 and the simulation of Comparative Example 4. For Comparative Example 4, the relationship between the applied voltage and the current density is shown by plotting the actual measured values. On the other hand, for the simulation of Comparative Example 4, the relationship between the applied voltage and the current density is shown as the result of simulating the distribution of electrons, assuming that there is no trap between the electron transport layer 19 and the light emitting layer 17. As shown in FIG. 5(b), there is little deviation between the simulation results and the actual measured values, which indicates that the simulation is highly likely to reproduce the internal state of the embodiment.

[0091] From the above results, it is believed that the effect of the embodiment is produced by the trap level existing between the electron transport layer 19 and the electron injection control layer 18.

[0092] [3.3 Considerations regarding trap levels] The reason why the temperature dependency of the electron injection property is reduced by the trap sites is considered as follows.

[0093] First, when the electron injection control layer 18 is not present, as shown in Fig. 6(c), electrons injected from the cathode 21 side into the electron transport layer 19 are injected into the light-emitting layer 17 without any injection barrier. On the other hand, when the electron injection control layer 18 is present, the amount of electrons injected can be controlled by the injection barrier from the electron transport layer 19 to the electron injection control layer 18, as shown in Fig. 6(a) or (b).

[0094] Next, a comparison is made between a case where there are sufficient trap sites between the electron transport layer 19 and the electron injection control layer 18, the trap sites having a trap level lower than the LUMO level of the electron transport layer 19, and a case where there are no such trap sites.

[0095] 6(a), when there are a sufficient number of trap sites having a trap level lower than the LUMO level of the electron transport layer 19 between the electron transport layer 19 and the electron injection control layer 18, electrons injected from the cathode 21 side into the electron transport layer 19 are injected into the electron injection control layer 18 via the trap sites. Therefore, the injection barrier from the trap level to the LUMO level of the electron injection control layer 18 greatly affects the electron injection property.

[0096] Here, when the energy difference Et between the LUMO level and the trap level of the electron transport layer 19 is 50 meV or more, the energy required for the transition from the trap site to the LUMO level of the electron transport layer 19 is sufficiently larger than the thermal energy kT, so that the effect of the trap site on the electron injection property becomes large. If the probability of the existence of electrons follows the Boltzmann distribution, at 95°C, if Et is 35 meV or more, the probability of the existence of electrons transitioning from the trap site to the LUMO level of the electron transport layer 19 is 1 / e or less. That is, it is preferable that the energy difference Et between the LUMO level and the trap level of the electron transport layer 19 satisfies the following formula (3). It is also preferable that the energy difference Et satisfies the following formula (4).

[0097] Et≧35meV…Formula (3) Et≧50meV…Formula (4) Furthermore, when the accumulated charge Q at the interface between the electron transport layer 19 and the electron injection control layer 18 is large, it is believed that the trap does not function sufficiently. When the accumulated charge Q is large, as shown in FIG. 6(b), the probability that the trapped site is occupied by the accumulated charge Q increases, and the proportion of electrons that transition directly from the LUMO level of the electron transport layer 19 to the LUMO level of the electron injection control layer 18 without passing through the trapped site increases. In other words, the control effect of the trap site on electron injection is suppressed by the trap site being occupied by the accumulated charge Q. The density of the trap sites is preferably 0.1% or more of the electron density of the electron transport layer 19. For example, when the electron density of the electron transport layer 19 is 1×10 14 pieces / cm 3 If it is, then 1 x 10 11 pieces / cm 3 It is preferable that the dielectric constant of the electron transport layer 19 is equal to or larger than ε. Furthermore, it is preferable that the stored charge Q is small. 19 , conductivity is σ 19 , the dielectric constant of the electron injection control layer 18 is ε 18 , conductivity is σ 18 Then, the stored charge Q is ΔT(=ε 19 / σ 19 -ε 18 / σ 18) (Maxwell-Wagner effect). Therefore, it is preferable that ΔT is smaller, preferably less than half that of conventional materials.

[0098] When electrons do not pass through the electron transport layer 19 and / or the electron injection control layer 18 due to the tunneling effect, it is considered that the trap site at the interface between the electron transport layer 19 and the electron injection control layer 18 does not function effectively. Therefore, the electron transport layer 19 and the electron injection control layer 18 must have a thickness that does not allow electron tunneling, and the thickness is preferably at least 1 nm.

[0099] [3.4 Luminous center] Here, the luminescence center in the light-emitting layer will be described. The luminescence center refers to a representative position that is the peak of the light emission described below. The position of the light-emitting peak is the position where the excitons of the light-emitting material are concentrated, and is generally either one or both of the interface on the cathode side of the light-emitting layer and the interface on the anode side of the light-emitting layer. When the mobility of holes in the light-emitting layer is sufficiently higher than the mobility of electrons, the holes move to the interface on the cathode side of the light-emitting layer, while the electrons are consumed by recombination near the interface on the cathode side of the light-emitting layer, so that the excitons are generated intensively near the interface on the cathode side of the light-emitting layer. On the other hand, when the mobility of electrons in the light-emitting layer is sufficiently higher than the mobility of holes, the electrons move to the interface on the anode side of the light-emitting layer, while the holes are consumed by recombination near the interface on the anode side of the light-emitting layer, so that the excitons are generated intensively near the interface on the anode side of the light-emitting layer. Depending on the relationship between the mobility of holes and the mobility of electrons in the light-emitting layer, the excitons may be generated intensively both near the interface on the cathode side of the light-emitting layer and near the interface on the anode side. In general, the position where excitons are generated in a concentrated manner corresponds to the position of the emission peak.

[0100] In addition, when the light-emitting material has high exciton diffusion characteristics and a long exciton lifetime, the position where excitons are generated intensively may not necessarily coincide with the position of the emission peak due to exciton diffusion. In this case, the emission center is not the position where excitons are generated intensively, but the position where transition from exciton energy to photon energy occurs intensively.

[0101] [4. Manufacturing method of organic EL element] The method for manufacturing an organic EL element will be described with reference to the drawings. Figures 7(a) to 10(c) are schematic cross-sectional views showing the states in each step in the manufacture of an organic EL display panel including an organic EL element. Figure 11 is a flowchart showing the method for manufacturing an organic EL display panel including an organic EL element.

[0102] In an organic EL display panel, the pixel electrode (lower electrode) functions as an anode of the organic EL element, and the counter electrode (upper electrode, common electrode) functions as a cathode of the organic EL element.

[0103] (1) Formation of the Substrate 11 First, as shown in Fig. 7(a), a TFT layer 112 is formed on a base material 111 to form a substrate 11 (Step S10 in Fig. 11). The TFT layer 112 can be formed by a known method for manufacturing a TFT.

[0104] 7(b), an interlayer insulating layer 12 is formed on the substrate 11 (Step S20 in FIG. 11). The interlayer insulating layer 12 can be formed by laminating layers using, for example, a plasma CVD method, a sputtering method, or the like.

[0105] Next, a contact hole is formed by dry etching at a location on the source electrode of the TFT layer in the interlayer insulating layer 12. The contact hole is formed so that the surface of the source electrode is exposed at the bottom thereof.

[0106] Next, a connection electrode layer is formed along the inner wall of the contact hole. A part of the upper part of the connection electrode layer is disposed on the interlayer insulating layer 12. The connection electrode layer can be formed by, for example, a sputtering method, and after forming a metal film, it is patterned by using a photolithography method and a wet etching method.

[0107] (2) Formation of anode 13 Next, as shown in FIG. 7(c), a pixel electrode material layer 130 is formed on the interlayer insulating layer 12 (step S31 in FIG. 11). The pixel electrode material layer 130 can be formed by, for example, a vacuum deposition method, a sputtering method, or the like. Next, as shown in Fig. 7(d), the pixel electrode material layer 130 is patterned by etching to form anodes 13 as a plurality of pixel electrodes partitioned for each subpixel (step S32 in Fig. 11). The anodes 13 function as the anodes of the respective organic EL elements.

[0108] The method for forming the anode 13 is not limited to the above-mentioned method. For example, the anode 13 and the hole injection layer 15 may be formed collectively by forming the hole injection material layer 150 on the pixel electrode material layer 130 and patterning the pixel electrode material layer 130 and the hole injection material layer 150 by etching.

[0109] (3) Formation of partition wall 14 Next, as shown in FIG. 7(e), a partition resin, which is a material for the partition 14, is applied onto the anode 13 and the interlayer insulating layer 12 to form a partition material layer 140. The partition material layer 140 is formed by uniformly applying a solution in which a phenol resin, which is a partition layer resin, is dissolved in a solvent (e.g., a mixed solvent of ethyl lactate and GBL) onto the anode 13 and the interlayer insulating layer 12 by a spin coating method or the like (step S41 in FIG. 11). Then, the partition material layer 140 is subjected to pattern exposure and development to form the partition 14 (FIG. 8(a), step S42 in FIG. 11), and the partition 14 is baked. As a result, an opening 14a, which is a region in which the light-emitting layer 17 is to be formed, is defined. The partition 14 is baked, for example, at a temperature of 150° C. or higher and 210° C. or lower for 60 minutes.

[0110] In the process of forming the partition wall 14, the surface of the partition wall 14 may be further subjected to surface treatment with a predetermined alkaline solution, water, an organic solvent, or the like, or may be subjected to plasma treatment. This is performed for the purpose of adjusting the contact angle of the partition wall 14 with respect to the ink (solution) applied to the openings 14a, or for the purpose of imparting water repellency to the surface.

[0111] (4) Formation of hole injection layer 15 Next, as shown in FIG. 8(b), ink containing a constituent material of the hole injection layer 15 is ejected from the nozzle of the inkjet head 401 into the opening 14a defined by the partition 14 to coat the anode 13 in the opening 14a, and then baked (dried) to form the hole injection layer 15 (step S50 in FIG. 11).

[0112] (5) Formation of hole transport layer 16 Next, as shown in FIG. 8(c), ink containing a constituent material of the hole transport layer 16 is ejected from the nozzle of the inkjet head 402 into the opening 14a defined by the partition 14 to apply it onto the hole injection layer 15 in the opening 14a, and then baked (dried) to form the hole transport layer 16 (step S60 in FIG. 11).

[0113] (6) Formation of light-emitting layer 17 Next, as shown in FIG. 9(a), ink containing the constituent material of the light-emitting layer 17 is ejected from the nozzle of the inkjet head 403 and applied onto the hole transport layer 16 in the opening 14a, and then baked (dried) to form the light-emitting layer 17 (step S70 in FIG. 11).

[0114] (7) Formation of electron injection control layer 18 Next, as shown in FIG. 9(b), the electron injection control layer 18 is formed on the light-emitting layer 17 and the partition wall 14 (step S80 in FIG. 11). At the interface between the electron injection control layer 18 and the electron transport layer 19, an electron trap level that is 50 meV or more lower than the LUMO level of the electron transport layer 19 exists, which accounts for 0.1% or more of the electron density of the electron transport layer 19 during operation. Therefore, it is preferable to select a material for the electron injection control layer 18 so that the crystal lattices are mismatched between the electron injection control layer 18 and the electron transport layer 19, so that the trap level is easily generated. In addition, the dielectric constant of the electron transport layer 19 is set to ε 19 , conductivity is σ 19 , the dielectric constant of the electron injection control layer 18 is ε 18 , conductivity is σ 18 Then, ΔT(=ε 19 / σ 19 -ε 18 / σ 18 It is preferable to select the material of the electron-injection control layer 18 so that the resistance (distance) is small, particularly so that the resistance is half or less of that of conventional materials.

[0115] The electron injection control layer 18 is formed, for example, by forming an organic compound, which is the material of the electron injection control layer 18, into a film commonly used for each sub-pixel by a vapor deposition method.

[0116] (8) Formation of Electron Transport Layer 19 Next, as shown in FIG. 9(c), the electron transport layer 19 is formed on the electron injection control layer 18 (step S90 in FIG. 11). At the interface between the electron injection control layer 18 and the electron transport layer 19, an electron trap level that is 50 meV or more lower than the LUMO level of the electron transport layer 19 exists, which accounts for 0.1% or more of the electron density of the electron transport layer 19 during operation. Therefore, it is preferable to select a material for the electron transport layer 19 so that the crystal lattices between the electron injection control layer 18 and the electron transport layer 19 are mismatched to facilitate the generation of the trap level. In addition, the dielectric constant of the electron transport layer 19 is set to ε 19 , conductivity is σ 19 , the dielectric constant of the electron injection control layer 18 is ε 18 , conductivity is σ 18 Then, ΔT(=ε 19 / σ 19 -ε 18 / σ18 It is preferable to select a material for the electron transport layer 19 so that the charge transport coefficient (P) is small, particularly, so that the Pt charge transport coefficient (Pt) is half or less that of conventional materials.

[0117] The electron transport layer 19 is formed, for example, by forming a film of an organic material having electron transport properties by a vapor deposition method in common to each sub-pixel.

[0118] (9) Formation of the electron injection layer 20 10(a), the electron injection layer 20 is formed on the electron transport layer 19 (Step S100 in FIG. 11). The electron injection layer 20 is formed, for example, by forming a film of an organic material with electron transport properties and a doped metal or a compound thereof by co-evaporation in common to each subpixel.

[0119] (10) Formation of cathode 21 10(b), a cathode 21 is formed on the electron injection layer 20 (step S110 in FIG. 11). The cathode 21 is formed by depositing ITO, IZO, silver, aluminum, or the like by a sputtering method or a vacuum deposition method. The cathode 21 functions as a common cathode facing the anodes of the organic EL elements.

[0120] (11) Formation of sealing layer 22 Finally, as shown in Fig. 10(c), a sealing layer 22 is formed on the cathode 21 (step S120 in Fig. 11). The sealing layer 22 can be formed by depositing SiON, SiN, or the like by a sputtering method, a CVD method, or the like. Note that a sealing resin layer may be further formed on the inorganic film such as SiON or SiN by coating and baking, or the like.

[0121] A color filter and an upper substrate may be placed on and bonded to the sealing layer 22 .

[0122] [5. Overall configuration of organic EL display device] 12 is a schematic block diagram showing the configuration of an organic EL display device 1000 including an organic EL display panel 100. As shown in Fig. 12, the organic EL display device 1000 includes the organic EL display panel 100 and a drive control unit 200 connected thereto. The drive control unit 200 is made up of four drive circuits 210-240 and a control circuit 250.

[0123] In an actual organic EL display device 1000, the arrangement of the drive control unit 200 relative to the organic EL display panel 100 is not limited to this.

[0124] [6. Other Modifications] (1) In the above embodiment, the light-emitting layer 17, the electron injection control layer 18, the electron transport layer 19, and the electron injection layer 20 are laminated in this order, but the types of layers and the order of lamination are not limited to this. For example, another intermediate layer such as a hole block layer 40 may be present between the light-emitting layer 17 and the electron injection control layer 18, or the electron transport layer 19 may be present between the light-emitting layer 17 and the electron injection control layer 18. For example, as shown in the band diagram of FIG. 13(a), the light-emitting layer 17, the hole block layer 40, the electron transport layer 19, the electron injection control layer 18, and the electron injection layer 20 may be laminated. In this case, it is preferable that an electron injection barrier exists between the electron injection layer 20 and the electron injection control layer 18, and that trap sites having a trap level 35 meV or more lower or 50 meV or more lower than the LUMO level of the electron injection layer 20 exist at a density of 0.1% or more of the electron density of the electron injection layer 20. An arbitrary intermediate layer may be present between the light-emitting layer 17 and the electron injection control layer 18, or there may be no intermediate layer at all. Similarly, the intermediate layer in contact with the cathode side of the electron injection control layer 18 is not limited to the electron transport layer 19 or the electron injection layer 20, and may be any intermediate layer as long as it satisfies the following conditions: (i) the LUMO level of the intermediate layer is lower than that of the electron injection control layer 18, and (ii) between the electron injection control layer 18 and the intermediate layer, trap sites having a trap level 35 meV or more lower or 50 meV or more lower than the LUMO level of the intermediate layer exist at a density of 0.1% or more of the electron density of the intermediate layer. In order to prevent tunneling of electrons, the film thickness of both the electron injection control layer 18 and the intermediate layer is preferably 1 nm or more.

[0125] (2) In the above embodiment, the hole transport property is higher than the electron transport property in the light-emitting layer 17. However, even when the electron transport property is higher than the hole transport property in the light-emitting layer 17, the configuration according to the present disclosure is possible.

[0126] 13(b) is a band diagram in the case where the electron transport property is higher than the hole transport property in the light emitting layer 17. In this case, a hole injection control layer 31 is provided between the hole transport layer 16 and the light emitting layer 17. In this case, it is preferable that trap sites having a trap level 165 higher than the HOMO level of the hole transport layer 16 by 35 meV or more or by 50 meV or more exist between the hole transport layer 16 and the hole injection control layer 31 at a density of 0.1% or more of the hole density of the hole transport layer 16. With this configuration, it is possible to control the hole injection property into the light emitting layer 17, as in the embodiment.

[0127] As in the above (1), the hole injection control layer 31 does not need to be in direct contact with the light emitting layer 17, and any intermediate layer such as an electron blocking layer may be present between the hole injection control layer 31 and the light emitting layer 17. The intermediate layer in contact with the anode side of the hole injection control layer 31 is not limited to the hole transport layer 16, and may be any intermediate layer as long as it satisfies the following conditions: (i) the HOMO level of the intermediate layer is higher than the HOMO level of the hole injection control layer 31, and (ii) between the hole injection control layer 31 and the intermediate layer, trap sites having a trap level 35 meV or higher or 50 meV or higher than the HOMO level of the intermediate layer exist at a density of 0.1% or higher of the hole density of the intermediate layer. In order to prevent tunneling of holes, the thicknesses of both the hole injection control layer 31 and the intermediate layer are preferably 1 nm or more.

[0128] (3) In the above embodiment, the organic EL display panel has a top emission configuration. However, the organic EL display panel may have a bottom emission configuration by using a light-transmitting electrode as the anode and a light-reflective electrode as the cathode.

[0129] In the above embodiment, the anode is the pixel electrode and the cathode is the counter electrode, but the cathode may be the pixel electrode and the anode may be the counter electrode.

[0130] In addition, in the above embodiment, the hole injection layer, the hole transport layer, and the light emitting layer are formed by a coating method, and the anode, the electron injection control layer, the electron transport layer, the electron injection layer, and the cathode are formed by a deposition method, but the electrodes and each functional layer may be formed by any film formation method.

[0131] Although the organic light-emitting panel and display device according to the present disclosure have been described above based on the embodiments and modifications, the present invention is not limited to the above-mentioned embodiments and modifications. The present invention also includes forms obtained by applying various modifications to the above-mentioned embodiments and modifications that would come to mind by a person skilled in the art, and forms realized by arbitrarily combining the components and functions of the embodiments and modifications within the scope of the present invention. [Industrial Applicability]

[0132] The present invention is useful for producing a long-life organic EL element, and an organic EL display panel and a display device including the same. [Explanation of symbols]

[0133] 1. Organic EL element 13 Anode 15 Hole injection layer 16 Hole transport layer 17 Emitting layer 18 Electron injection control layer 19 Electron transport layer 20 Electron injection layer 21 Cathode 100 Organic EL display panel 1000 organic EL display device

Claims

1. An organic EL element comprising an anode, a light-emitting layer, an electron transport layer, and a cathode laminated in this order, an electron injection control layer disposed in contact with the electron transport layer on the light emitting layer side, the electron injection control layer and the electron transport layer are evaporated films of dielectric materials having mismatched crystal structures, a trap site is formed at the interface between the electron transport layer and the electron injection control layer, a trap level of the trap site is 35 meV or more lower than a lowest unoccupied molecular orbital (LUMO) level of a functional material contained in the electron transport layer and higher than a highest occupied molecular orbital (HOMO) level of a functional material contained in the electron transport layer; The density of the trap sites is 0.1% or more of the electron density in the electron transport layer.

1. An organic electroluminescence (EL) element comprising:

2. The trap level is 50 meV or more lower than the lowest unoccupied molecular orbital (LUMO) level of the functional material contained in the electron transport layer.

2. The organic electroluminescence device according to claim 1 .

3. The thickness of the electron injection control layer is 1 nm or more.

3. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a semiconductor device.

4. The thickness of the electron transport layer is 1 nm or more.

4. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a semiconductor device.

5. the electron injection control layer is in contact with the light emitting layer, The LUMO level of the functional material contained in the electron injection control layer is higher than the LUMO level of the functional material contained in the light emitting layer and is also higher than the LUMO level of the functional material contained in the electron transport layer.

5. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a semiconductor device.

6. The highest occupied molecular orbital (HOMO) level of the functional material contained in the electron injection control layer is lower than the HOMO level of the functional material contained in the light emitting layer.

6. The organic electroluminescence device according to claim 5.

7. Further comprising a hole transport layer, The LUMO level of the functional material contained in the electron injection control layer is higher than the LUMO level of the functional material contained in the hole transport layer and is also higher than the LUMO level of the functional material contained in the electron transport layer.

5. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a semiconductor device.

8. A substrate is provided with a plurality of organic EL elements according to any one of claims 1 to 7. Organic EL display panel.

9. Prepare the substrate, forming an anode above the substrate; forming a light-emitting layer above the anode; forming an electron injection control layer above the light emitting layer; forming an electron transport layer on the electron injection control layer; A method for manufacturing an organic EL element, comprising forming a cathode above the electron transport layer, forming the electron injection control layer, which is a deposition film of a dielectric material having a mismatched crystal structure, above the electron transport layer; At the interface between the electron injection control layer and the electron transport layer, trap sites having a level 35 meV or more lower than a lowest unoccupied molecular orbital (LUMO) level of a functional material contained in the electron transport layer and higher than a highest occupied molecular orbital (HOMO) level of the functional material contained in the electron transport layer are formed at a density of 0.1% or more of the electron density in the electron transport layer.

2. A method for producing an organic EL element comprising the steps of:

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