JP2022080879A - Organic el element, organic el panel, and organic el element manufacturing method - Google Patents

Abstract

To provide an organic EL element having lifespan which is increased by suppressing deterioration of a function layer caused by deactivation reaction between carriers and excitons.SOLUTION: An organic EL element is provided, comprising: an anode; a first functional layer disposed above the anode and including an organic material; a second functional layer disposed on and in contact with the first functional layer and including the organic material; a light emitting layer disposed on and in contact with the second functional layer; and a cathode disposed on the light emitting layer. A highest occupied molecular orbital (HOMO) level of the organic material included in the second functional layer has an energy level at least 0.2 eV lower than that of the HOMO level of the organic material included in the first functional layer, and a film thickness of the second functional layer is 15 nm or less.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to suppressing an increase in drive voltage and improving the life of an organic EL device using a carrier-injectable material.

In recent years, display devices using organic EL elements that utilize the electroluminescence phenomenon of organic materials are becoming widespread.

The organic EL element has a basic structure in which a light emitting layer is arranged between a pair of electrodes, and when a voltage is applied between the electrodes, holes and electrons are recombined and the light emitting layer emits light. More specifically, holes are injected into the light emitting layer from the anode, electrons are injected into the light emitting layer from the cathode, and holes and electrons are recombined in the light emitting layer. On the other hand, in many cases, the difference between the Fermi level of the cathode material and the energy level of the lowest unoccupied molecular orbital (LUMO) of the light emitting material contained in the light emitting layer is large. Therefore, in order to facilitate the injection of electrons from the cathode into the light emitting layer, a configuration is used in which a functional layer containing a metal material having a low work function is provided between the cathode and the light emitting layer. Similarly, in order to facilitate the injection of holes from the anode into the light emitting layer, a configuration is used in which a functional layer containing a material having a hole injecting property is provided between the anode and the light emitting layer. Further, a layer for suppressing the outflow of holes from the light emitting layer to the cathode is provided between the cathode and the light emitting layer, and a layer for suppressing the outflow of electrons from the light emitting layer to the anode is provided with the anode and light emission. A configuration provided between the layers may be used (see, for example, Patent Documents 1-3).

Japanese Unexamined Patent Publication No. 2009-267392 Japanese Unexamined Patent Publication No. 2001-85166 International Publication No. 2011/92939

"Operational degradation of organic light-emitting diodes: Mechanism and identification of chemical products", D. Y. Kondakov, et al., JOURNAL OF APPLIED PHYSICS 101, 024512 (2007) "Intrinsic luminance loss in phosphorescent small-molecule organic light emitting devices due to bimolecular annihilation reactions", N.C. Giebink, et al., JOURNAL OF APPLIED PHYSICS 103, 044509 (2008)

However, in order to efficiently generate recombination in the light emitting layer, it is necessary to increase the density of carriers (electrons and / or holes) in the light emitting layer, so that the anode side interface and / or the light emitting layer is generally used. At the interface on the cathode side, the carrier density and exciton density become high. Therefore, excitons tend to increase in the functional layer due to the movement of excitons from the light emitting layer to the functional layer or the generation of excitons in the functional layer due to the leakage of carriers from the light emitting layer. Then, the energy of the excitons is transferred to the polaron which is the carrier in the functional layer material, so that the polaron becomes high energy and the chemical bond in the functional layer material is destroyed to generate a dissociation product, and the carrier transport property of the functional layer is generated. There is a problem that the function of the functional layer is deteriorated due to the dissociation product forming carrier traps and quenching sites (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

The present disclosure has been made in view of the above problems, and is an organic EL element, an organic EL panel, and an organic EL element having a long life by suppressing deterioration of the functional layer due to a deactivation reaction between excitons and carriers. It is an object of the present invention to provide the manufacturing method of.

The organic EL element according to one aspect of the present disclosure is arranged above the anode, the first functional layer containing the organic material, and is arranged in contact with the first functional layer, and includes the organic material. A second functional layer, a light emitting layer arranged in contact with the second functional layer, and a cathode arranged above the light emitting layer are provided, and the maximum cover of the organic material contained in the second functional layer is provided. The occupied orbital (HOMO) level is characterized in that the energy level is 0.2 eV or more lower than the HOMO level of the organic material contained in the first functional layer, and the film thickness of the second functional layer is 15 nm or less. And.

According to the organic EL device according to one aspect of the present disclosure, since the hole injection property from the first functional layer to the second functional layer is lowered, the hole density in the second functional layer can be lowered. Therefore, since the deactivation reaction between the hole and the exciton can be suppressed in the second functional layer and the deterioration of the functional layer can be suppressed, the life of the organic EL element can be expected to be extended. Further, by limiting the film thickness of the second functional layer, it is possible to suppress an increase in the drive voltage even if the hole injection property from the first functional layer to the second functional layer is lowered.

It is sectional drawing which shows typically the structure of the organic EL element 1 which concerns on embodiment. It is a simplified schematic diagram which shows the band diagram of the hole injection layer, the hole transport layer, the light emitting layer, and the first electron transport layer which concerns on Example. (A) to (c) schematically show the band diagram of the hole injection layer, the hole transport layer, the light emitting layer, the first electron transport layer, and the distribution of electrons, holes, and excitons according to Examples and Comparative Examples. It is a simplified schematic diagram shown in. (A) is a graph showing the distribution of the hole density when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. (B) is a graph showing the distribution of the recombination rate of electrons and holes when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. .. (C) is a graph showing the distribution of excitons when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. (A) is a graph showing the relationship between the applied voltage and the current value in each of the examples and the comparative examples. (B) shows the relationship between the applied voltage and the current value for each film thickness of the hole transport layer 16 in the organic EL element having the same thickness as that of the example and the example except for the film thickness of the hole transport layer 16. It is a graph shown. (A) is a graph showing the value of Hg (htl) and the hole density in the hole transport layer 16. (B) is a graph showing the relationship between the value of Hg (htl) and the drive voltage of the organic EL element. It is a graph which shows the relationship between the value of Hg (htl), and the drive voltage of an organic EL element for obtaining the current density required as an organic EL element. (A) is a graph showing the relationship between the film thickness of the hole transport layer 16 and the hole density in the hole transport layer 16. (B) is a graph showing the relationship between the film thickness of the hole transport layer 16 and the drive voltage. (A) shows the relationship between the operating time and the brightness for each hole injection barrier Hg (htl) in the example and the organic EL element having the same thickness as the hole transport layer 16 except for the film thickness of the example. FIG. (B) is a graph showing the relationship between the value of the hole injection barrier Hg (htl) and the 50% luminance life. It is a partial cross-sectional view schematically showing a part of the manufacturing process of the organic EL element which concerns on embodiment. FIG. The state in which the interlayer insulating layer is formed, (c) is the state in which the pixel electrode material is formed on the interlayer insulating layer, (d) is the state in which the pixel electrode is formed, and (e) is the state in which the interlayer insulating layer and the interlayer insulating layer are formed. The state where the partition wall material layer is formed on the pixel electrode is shown. It is a partial cross-sectional view schematically showing a part of the manufacturing process of the organic EL element which concerns on embodiment. FIG. The state in which the layer is formed, (c) shows the state in which the hole transport layer is formed on the hole injection layer. It is a partial cross-sectional view schematically showing a part of the manufacturing process of the organic EL element which concerns on embodiment. FIG. The state in which the first electron transport layer is formed on the light emitting layer and the partition wall layer, and (c) shows the state in which the second electron transport layer is formed on the first electron transport layer. It is a partial cross-sectional view schematically showing a part of the manufacturing process of the organic EL element which concerns on embodiment, (a) is the state which the optical adjustment layer was formed on the 2nd electron transport layer, (b). Indicates a state in which a counter electrode is formed on the optical adjustment layer, and (c) shows a state in which a sealing layer is formed on the counter electrode. It is a flowchart which shows the manufacturing process of the organic EL element which concerns on embodiment. It is a block diagram which shows the structure of the organic EL display apparatus provided with the organic EL element which concerns on embodiment. It is a simplified schematic diagram which shows the relationship between the band diagram of the hole transport layer, the light emitting layer, the first electron transport layer, and the second electron transport layer and the recombination position of an electron and a hole, which are related to the modified example.

<< Aspects of disclosure >>
The organic EL device according to at least one aspect of the present disclosure is arranged above the anode, the first functional layer containing the organic material, and the first functional layer, and is arranged in contact with the first functional layer. A second functional layer including, a light emitting layer arranged in contact with the second functional layer, and a cathode arranged above the light emitting layer, and the organic material contained in the second functional layer. The highest occupied orbital (HOMO) level has an energy level 0.2 eV or more lower than the HOMO level of the organic material contained in the first functional layer, and the film thickness of the second functional layer is 15 nm or less. It is characterized by.

In the method for manufacturing an organic EL element according to at least one aspect of the present disclosure, an anode is formed on a substrate, a first functional layer containing an organic material is formed above the anode, and the first functional layer is placed on the first functional layer. A method for manufacturing an organic EL element in which a second functional layer containing an organic material is formed so as to be in contact with the light emitting layer, a light emitting layer is formed so as to be in contact with the second functional layer, and a cathode is formed above the light emitting layer. The maximum occupied orbital (HOMO) level of the organic material contained in the second functional layer is 0.2 eV or more lower than the HOMO level of the organic material contained in the first functional layer. The second functional layer is characterized in that the film thickness is 15 nm or less.

In the organic EL element or the method for manufacturing an organic EL element according to at least one aspect of the present disclosure, the hole injectability from the first functional layer to the second functional layer is lowered, so that the hole density in the second functional layer is reduced. Can be reduced. Therefore, since the deactivation reaction between the hole and the exciton can be suppressed in the second functional layer and the deterioration of the functional layer can be suppressed, the life of the organic EL element can be expected to be extended. Further, by limiting the film thickness of the second functional layer, it is possible to suppress an increase in the drive voltage even if the hole injection property from the first functional layer to the second functional layer is lowered.

The organic EL device according to at least one aspect of the present disclosure may have a hole mobility in the second functional layer of 1 × 10 ^-9 cm ² / Vs or more.

In the organic EL element of the above aspect, since the hole mobility of the second functional layer is sufficiently high and the impedance is low, the drive voltage of the organic EL element is reduced by setting the film thickness of the second functional layer to 15 nm or less. Can be done.

In the organic EL device according to at least one aspect of the present disclosure, the electron mobility in the light emitting layer may be larger than the hole mobility in the light emitting layer.

The organic EL device of the above aspect has high luminous efficiency because the exciton density is high at the interface of the light emitting layer with the second functional layer, while the second functional layer is deteriorated by the coupling between the exciton and the hole. Since it can be suppressed, the life can be extended.

In the organic EL element according to at least one aspect of the present disclosure, the energy of the singlet excitons in the organic material contained in the second functional layer is larger than the energy of the singlet excitons in the functional material contained in the light emitting layer. , May be.

Since the organic EL device of the above embodiment can prevent the singlet excitons in the light emitting layer from moving to the second functional layer, it suppresses the decrease in luminous efficiency and deteriorates the second functional layer. It can be suppressed and the life can be extended.

In the organic EL element according to at least one aspect of the present disclosure, the energy of triplet excitons in the organic material contained in the second functional layer is larger than the energy of triplet excitons in the functional material contained in the light emitting layer. , May be.

Since the organic EL element of the above aspect can prevent the triplet excitons in the light emitting layer from moving to the second functional layer, deterioration of the second functional layer is suppressed and the life is extended. Can be done.

In the organic EL device according to at least one aspect of the present disclosure, the anode is a light-reflecting electrode, and the distance between the surface of the anode on the light emitting layer side and the surface of the light emitting layer on the anode side is 40 nm or less. It may be.

The organic EL element of the above aspect can be configured to have improved light extraction efficiency.

In the organic EL device according to at least one aspect of the present disclosure, an optical resonator structure is formed between the surface of the anode on the light emitting layer side and the surface of the cathode on the light emitting layer side, and the transparent conductive layer is formed. , ITO or IZO may be included.

In the organic EL element of the above aspect, the resonator structure can be easily realized while the thickness of each functional layer existing between the cathode and the anode is optimally designed, so that the luminous efficiency and the light extraction efficiency are improved. It is possible to easily achieve both.

In the organic EL element according to at least one aspect of the present disclosure, the highest occupied orbital (HOMO) level of the organic material contained in the second functional layer is the HOMO level of the organic material contained in the first functional layer. The energy level may be low in the range of 0.6 eV or less, and the thickness of the second functional layer may be 5 nm or more.

The organic EL device of the above aspect can secure the current density required for the organic EL device and can satisfy the dielectric breakdown electric field strength of the organic semiconductor material constituting the second functional layer. At the same time, the second functional layer can be formed by using a thin film of an organic semiconductor, and can secure dielectric strength and carrier transport / injection properties.

The organic EL display panel according to at least one aspect of the present disclosure includes a plurality of organic EL elements according to at least one aspect of the present disclosure on a substrate.

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

[1. Configuration of organic EL element]
FIG. 1 is a diagram schematically showing a cross-sectional structure of the organic EL element 1 according to the present embodiment. The organic EL element 1 includes a pixel electrode 13, a hole injection layer 15, a hole transport layer 16, a light emitting layer 17, a first electron transport layer 18, a second electron transport layer 19, an optical adjustment layer 20, and an anode. The counter electrode 21 which is a cathode is provided.

In the organic EL element 1, the pixel electrode 13 and the counter electrode 21 are arranged so as to face each other so that the main surfaces face each other, and a light emitting layer 17 is formed between the pixel electrode 13 and the counter electrode 21. ..

On the pixel electrode 13 side of the light emitting layer 17, a hole transport layer 16 is formed in contact with the light emitting layer 17. On the pixel electrode 13 side of the hole transport layer 16, the hole injection layer 15 is formed in contact with the hole transport layer 16.

A first electron transport layer 18 is formed in contact with the light emitting layer 17 on the opposite electrode 21 side of the light emitting layer 17. A second electron transport layer 19 is formed in contact with the first electron transport layer 18 on the counter electrode 21 side of the electron transport layer 18. An optical adjustment layer 20 is formed between the second electron transport layer 19 and the counter electrode 21.

[1.1 Each component of the organic EL element]
<Pixel electrode>
The pixel electrode 13 is formed on the interlayer insulating layer 12. The pixel electrode 13 is provided for each pixel and is electrically connected to the TFT layer 112 through a contact hole provided in the interlayer insulating layer 12.

In this embodiment, the pixel electrode 13 functions as an anode.

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

The pixel electrode 13 may be composed of a metal layer alone, but as 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 the metal layer. May be good.

When the counter electrode 21 is a light-reflecting electrode, the pixel electrode 13 may be a light-transmitting electrode. In this case, the pixel electrode 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 pixel electrode 13 is set as thin as about 1 nm to 50 nm and has light transmission. The metal material is a light-reflecting material, but light transmission can be ensured by thinning the thin film of the metal layer to 50 nm or less. Therefore, a part of the light from the light emitting layer 17 is reflected by the pixel electrode 13, but the remaining part is transmitted through the pixel electrode 13.

At this time, examples of the metal material forming the metal layer contained in the pixel electrode 13 include a silver alloy containing Ag and Ag as main components, and an Al alloy containing Al and Al as main components. Examples of the Ag alloy include magnesium-silver alloy (MgAg) and indium-silver alloy. Ag basically has a low resistivity, and Ag alloy is preferable in that it has excellent heat resistance and corrosion resistance and can maintain good electrical conductivity for a long period of time. Examples of the Al alloy include a magnesium-aluminum alloy (MgAl) and a lithium-aluminum alloy (LiAl). Examples of other alloys include lithium-magnesium alloys and lithium-indium alloys.

The metal layer included in the pixel electrode 13 may be composed of, for example, a single layer of an Ag layer or an MgAg alloy layer, a laminated structure of an Mg layer and an Ag layer (Mg / Ag), or an MgAg alloy layer and an Ag layer. May be a laminated structure (MgAg / Ag).

Examples of the metal oxide forming the metal oxide layer contained in the pixel electrode 13 include ITO (indium tin oxide) and IZO (zinc oxide).

Further, the pixel electrode 13 may be composed of a metal layer alone or a metal oxide layer alone, but may have a laminated structure in which a metal oxide layer is laminated on a metal layer, or a metal on a metal oxide layer. It may be a laminated structure in which layers are laminated.

<Hole injection layer>
The hole injection layer 15 has a function of promoting the injection of holes (holes) from the pixel electrode 13 which is an anode into the light emitting layer 17. The hole injection layer 15 is formed, for example, by applying and drying a solution as a solute with the hole injection material. The hole injection layer 15 is made of a conductive polymer material such as PEDOT: PSS (mixture of polythiophene and polystyrene sulfonic acid), polyfluorene or a derivative thereof, or polyarylamine or a derivative thereof. As will be described later, in the material of the hole injection layer 15, the HOMO level of the material of the hole injection layer 15 is 0.2 eV or more higher than the HOMO level of the material of the hole transport layer 16 (close to the vacuum level). ) The material is selected. Further, in one embodiment, the film thickness of the hole injection layer 15 is 10 nm.

Further, an inorganic layer having a hole-injecting property may be provided between the hole-injecting layer 15 and the pixel electrode 13. As the inorganic layer, for example, oxides such as Ag, Mo, chromium (Cr), vanadium (V), tungsten (W), nickel (Ni), and iridium (Ir) can be used.

<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 formed, for example, by applying and drying a solution containing a hole transport material as a solute. The hole transport layer 16 is made of, for example, a polymer compound such as polyfluorene or a derivative thereof, or polyarylamine or a derivative thereof, and does not have a hydrophilic group. As the material of the hole transport layer 16, a material whose HOMO level of the material of the hole transport layer 16 is 0.2 eV or more lower than the HOMO level of the material of the hole injection layer 15 is selected. Further, in one aspect of the embodiment, the film thickness of the hole transport layer 16 is 15 nm.

When the hole mobility of the hole transport layer 16 is low, the impedance of the hole transport layer 16 tends to increase and the drive voltage of the organic EL element 1 tends to increase. Therefore, in order to suppress an increase in the drive voltage of the organic EL element 1, the hole mobility of the hole transport layer 16 is preferably 1 × 10 ^-9 cm ² / Vs or more.

Further, the movement of excitons from the light emitting layer 17 to the hole transport layer 16 due to the energy of the excitons of the light emitting material of the light emitting layer 17 being transferred to the hole transport material of the hole transport layer 16 is the emission efficiency. It is not preferable because it causes both a decrease in the hole transporting material and deterioration of the hole transporting material of the hole transporting layer 16. Therefore, it is preferable that the energy S1 (htl) of the singlet excitons of the hole transport material of the hole transport layer 16 is larger than the energy S1 (eml) of the singlet excitons of the light emitting material of the light emitting layer 17. Similarly, the energy of the triplet excitons of the hole transport material of the hole transport layer 16 is preferably larger than the energy of the triplet excitons of the light emitting material of the light emitting layer 17.

In order to prevent the optical path length between the light emitting center and the pixel electrode 13 from being excessive in forming the optical resonator structure, the total film thickness of the functional layers existing between the pixel electrode 13 and the light emitting layer 17, that is, The total thickness of the hole injection layer 15 and the hole transport layer 16 is preferably 40 nm or less.

Further, the film thickness of the hole transport layer 16 is preferably 5 nm or more. The hole transport layer 16 is composed of a thin film of an organic semiconductor made of polycrystalline or amorphous. Polycrystals are composed of small crystals with a size of several nm to several mm. In order to use a thin film of an organic semiconductor as the hole transport layer 16 and obtain electrical functions such as insulation withstand voltage and carrier transport / injectability, the film is composed of relatively fine crystals and the hole transport layer 16 is formed. A film thickness of about 5 nm is required as the minimum film thickness.

Therefore, by setting the film thickness of the hole transport layer 16 to 5 nm or more, the hole transport layer 16 is configured by using a thin film of an organic semiconductor, and the dielectric strength and carrier transport / injection property are ensured. Can be done.

The hole transport layer 16 is not limited to the coating film, but may be a thin-film deposition film.

<Light emitting layer>
The light emitting layer 17 has a function of emitting light by recombining holes and electrons. The light emitting layer 17 is, for example, a coating film, and is formed by, for example, coating and drying a material forming the light emitting layer and a solution as a solute. Alternatively, the light emitting layer 17 may be formed of a thin-film deposition film.

Further, it is preferable that at least one of the electron mobility and the hole mobility of the light emitting layer 17 is large in terms of increasing excitons. Further, when the electron mobility in the light emitting layer 17 is higher than the hole mobility, the density of excitons is high on the interface side of the light emitting layer 17 with the hole transport layer 16, so that the hole transport layer 16 in the embodiment of the present disclosure has a high electron mobility. The effect of extending the life can be expected more.

As a material for forming the light emitting layer 17, an organic material which is a known fluorescent substance can be used. For example, oxinoid compounds, perylene compounds, coumarin compounds, azacumine compounds, oxazole compounds, oxadiazole compounds, perinone compounds, pyrolopyrrole compounds, naphthalene compounds, anthracene compounds, fluorene compounds, fluoranthene compounds, tetracene compounds, pyrene compounds, coronene compounds, Kinolone compound and azaquinolone compound, pyrazoline derivative and pyrazolone derivative, rhodamine compound, chrysen compound, phenanthrene compound, cyclopentadiene compound, stilben compound, diphenylquinone compound, styryl compound, butadiene compound, dicyanomethylenepyrane compound, dicyanomethylenethiopyran compound, fluorescein Compounds, pyrylium compounds, thiapyrylium compounds, selenapyrylium compounds, tellropyrylium compounds, aromatic aldaziene compounds, oligophenylene compounds, thioxanthene compounds, cyanine compounds, acrydin compounds and the like can be used. The light emitting material is not limited to a fluorescent substance, and may be a known phosphorescent substance such as a metal complex that emits phosphorescence such as tris (2-phenylpyridine) iridium.

Further, the light emitting layer 17 may be configured by doping a host material having high carrier mobility with a light emitting material. Here, high carrier mobility means high electron mobility and / or high hole mobility. As the host material, for example, an amine compound, a condensed polycyclic aromatic compound, or a heterocyclic compound can be used. As the amine compound, for example, a monoamine derivative, a diamine derivative, a triamine derivative, or a tetraamine derivative can be used. As the condensed polycyclic aromatic compound, for example, an anthracene derivative, naphthalene derivative, naphthalene derivative, phenanthrene derivative, chrysene derivative, fluoranthene derivative, triphenylene derivative, pentacene derivative, and perylene derivative can be used. Examples of the heterocyclic compound 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, and azaindole derivatives. Azacarbazole derivative, pyrazoline derivative, pyrazolone derivative and phthalocyanine derivative can be used. In the case where the light emitting layer is formed of the fluorescent material and the host material, in one embodiment, the concentration of the fluorescent material is 1 wt% or more. Further, in one embodiment, the concentration of the fluorescent material is 10 wt% or less. Further, in one embodiment, the concentration of the fluorescent material is 30 wt% or less.

<First electron transport layer>
The electron transport layer 18 is formed on the light emitting layer 17, and has a function of transporting electrons injected from the second electron transport layer 19 to the light emitting layer 17. The first electron transport layer 18 is, for example, a thin-film vapor deposition film and is made of an organic material having electron transport properties. The first electron transport layer 18 is made of a π-electron small molecule organic material such as an oxadiazole derivative (OXD), a triazole derivative (TAZ), and a phenanthroline derivative (BCP, Bphen).

<Second electron transport layer>
The second electron transporting layer 19 is formed on the first electron transporting layer 18, and the organic material having electron transporting property is doped with a metal material for improving electron injecting property. Here, doping refers to the substantially even distribution of metal atoms or metal ions of a metal material in an organic material, specifically forming a single phase containing the organic material and a trace amount of the metal material. Point to that. It is preferable that no other phase, particularly a phase consisting only of a metal material such as a metal piece or a metal film, or a phase containing a metal material as a main component exists. Further, in a single phase containing an organic material and a trace amount of metal material, the concentration of the metal atom or the metal ion is preferably uniform, and the metal atom or the metal ion is preferably not aggregated. The metal material is preferably selected from alkali metals, alkaline earth metals, and rare earth metals. The doping amount of the metal material in the second electron transport layer 18 is preferably 3 to 60 wt%. The doped metal is not limited to the simple substance of the metal, and may be doped as a compound such as a fluoride (for example, NaF) or a quinolinium complex (for example, Alq ₃ , Liq). Examples of the dope metal include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), which correspond to alkali metals, and calcium, which corresponds to alkaline earth metals. (Ca), strontium (Sr), barium (Ba), radium (Ra), yttrium (Y) corresponding to rare earth metals, yttrium (Sm), europium (Eu), itterbium (Yb) and the like.

Examples of the organic material having an electron transport property include π-electron low molecular weight organic materials such as an oxadiazole derivative (OXD), a triazole derivative (TAZ), and a phenanthroline derivative (BCP, Bphen).

A single electron transport layer may be formed in place of the first electron transport layer 18 and the second electron transport layer 19.

<Optical adjustment layer>
The optical adjustment layer 20 is made of a light translucent conductive material and is formed on the second electron transport layer 19.

The light reflecting surface at the interface of the counter electrode 21 with the optical adjustment layer 20 is paired with the light reflecting surface at the interface with the hole injection layer 15 of the pixel electrode 13 to form a resonator structure. Therefore, when the light emitted from the light emitting layer 17 is incident on the counter electrode 21 from the optical adjustment layer 20, a part of the light needs to be reflected to the optical adjustment layer 20. Therefore, it is preferable that the refractive index differs between the counter electrode 21 and the optical adjustment layer 20. For example, when the counter electrode 21 is a metal thin film, the optical adjustment layer 20 is preferably an oxide conductor such as ITO or IZO. Further, for example, when the counter electrode 21 is an oxide conductor such as ITO or IZO, the optical adjustment layer 20 is preferably a metal thin film such as Ag or Al. In one embodiment of the embodiment, the material of the optical adjustment layer 20 is IZO, and the film thickness thereof is 104 nm.

<Counter electrode>
The counter electrode 21 is made of a light translucent conductive material and is formed on the optical adjustment layer 20. In this embodiment, the counter electrode 21 functions as a cathode.

As described above, the light reflecting surface at the interface of the counter electrode 21 with the optical adjustment layer 20 is paired with the light reflecting surface at the interface with the hole injection layer 15 of the pixel electrode 13 to form a resonator structure. Therefore, it is preferable that the refractive index differs between the counter electrode 21 and the optical adjustment layer 20. In one embodiment of the embodiment, the counter electrode 21 is a metal thin film. The film thickness of the metal layer is about 1 nm to 50 nm in order to ensure light translucency.

Examples of the material of the counter electrode 21 include a silver alloy containing Ag and Ag as main components, and an Al alloy containing Al and Al as main components. Examples of the Ag alloy include magnesium-silver alloy (MgAg) and indium-silver alloy. Examples of the Al alloy include a magnesium-aluminum alloy (MgAl) and a lithium-aluminum alloy (LiAl). Examples of other alloys include lithium-magnesium alloys and lithium-indium alloys. In this embodiment, the counter electrode 21 is a thin film of Ag.

Further, the counter electrode 21 may be composed of a metal layer alone or a metal oxide layer alone, but may have a laminated structure in which a metal oxide layer is laminated on a metal layer, or a metal on a metal oxide layer. It may be a laminated structure in which layers are laminated.

When the pixel electrode 13 is a light-transmitting electrode, the counter electrode 21 may be a light-reflecting electrode. At this time, the counter electrode 21 includes a metal layer made of a light-reflecting metal material. Specific examples of the metal material having light reflectivity include silver, aluminum, aluminum alloy, molybdenum, APC, ARA, MoCr, MoW, NiCr and the like.

<Others>
The organic EL element 1 is formed on the substrate 11. The substrate 11 is made of a base material 111 which is an insulating material. Alternatively, the wiring layer 112 may be formed on the base material 111 which is an insulating material. As the base material 111, for example, a glass substrate, a quartz substrate, a silicon substrate, a plastic substrate, or the like can be adopted. 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 fluororesins, styrene-based, polyolefin-based, polyvinyl chloride-based, polyurethane-based, Examples thereof include various thermoplastic elastomers such as fluororubber and chlorinated polyethylene, epoxy resins, unsaturated polyesters, silicone resins, polyurethanes, etc., or copolymers, blends, polymer alloys, etc. mainly containing these. A laminated body in which one type or two or more types are laminated can be used. Materials constituting 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 arsenic, anthracene and rubrene. Examples thereof include organic semiconductor materials such as polyparaphenylene vinylene, and a TFT (Thin Film Transistor) layer formed by using these in combination may be used.

Further, 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 is for flattening a step on the upper surface of the TFT layer 112. Examples of the resin material include positive photosensitive materials. Moreover, as such a photosensitive material, an acrylic resin, a polyimide resin, a siloxane resin, and a phenol resin can be mentioned. Further, a contact hole is formed for each pixel in the interlayer insulating layer 12.

When the organic EL display panel 100 is a bottom emission type, the base material 111 and the interlayer insulating layer 12 need to be made of a light-transmitting material. Further, when the TFT layer 112 is present, at least a part of the region existing below the pixel electrode 13 in the TFT layer 112 needs to have light transmission.

Further, a sealing layer 22 is formed on the organic EL element 1. In the sealing layer 22, the organic layers such as the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, the first electron transport layer 18, and the second electron transport layer 19 are exposed to moisture or air. It has a function of suppressing bleaching, and is formed by using a translucent material such as silicon nitride (SiN) and silicon oxynitride (SiON). Further, 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 by using a material such as silicon nitride (SiN) or silicon oxynitride (SiON).

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 bonded onto the sealing layer 22 via a sealing resin. By laminating the upper substrate, the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, the first electron transport layer 18, and the second electron transport layer 19 can be protected from moisture, air, and the like.

[2. Relationship between hole injection and drive voltage]
The organic EL device according to one aspect of the present disclosure is characterized in that deterioration of the functional layer due to excitons can be suppressed. Hereinafter, as one aspect of the present disclosure, a comparative example of the relationship between the hole injection barrier and the hole density and the relationship with the drive voltage of the organic EL device 1 in which the deterioration of the hole transport layer 16 is suppressed by excitons. It is shown in the comparison explanation with. The electrical characteristics of the examples and comparative examples shown in [2.3] and subsequent examples are calculated using the device model having the energy band structure shown in [2.1] in the device simulation TCAD manufactured by SILVACO. ..

[2.1 Energy band structure]
FIG. 2 is a band diagram showing an energy band structure of the organic EL element 1 according to the embodiment. In addition, for the sake of simplification of the description, the energy level of the organic material forming the layer is abbreviated as "the energy level of the layer" below. For layers made of multiple types of materials, the energy level of a typical organic material responsible for transporting electrons and / or holes is referred to as the "layer energy level".

In FIG. 2, the LUMO level (hereinafter referred to as “LUMO level”) of the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, and the first electron transport layer 18 and the energy level of HOMO are shown. The rank (hereinafter referred to as “HOMO level”) is indicated, and the description is omitted for the other layers. Although the vacuum level of electrons is not shown in FIG. 2, the lower the LUMO level and the HOMO level are, the larger the difference from the vacuum level of electrons is, and the energy level is large. Is low.

In the embodiment, the energy barrier for injecting electrons from the first electron transport layer 18 into the light emitting layer 17 is defined by the difference between the LUMO level 171 of the light emitting layer 17 and the LUMO level 181 of the first electron transport layer 18. Will be done. Further, the energy barrier Eg (htl) for injecting electrons from the light emitting layer 17 into the hole transport layer 16 is defined by the difference between the LUMO level 161 of the hole transport layer 16 and the LUMO level 171 of the light emitting layer 17. Will be done.

Further, the energy barrier Hg (htl) for injecting holes from the hole injection layer 15 into the hole transport layer 16 is the HOMO level 152 of the hole injection layer 15 and the HOMO level 162 of the hole transport layer 16. It is defined by the difference between. In the embodiment, the energy barrier Hg (htl) preferably satisfies the following (Equation 1).

Hg (htl) ≧ 0.2 eV …… (Equation 1)
In the examples, Hg (htl) is 0.3 eV.

Further, the energy barrier Hg (eml) for injecting holes from the hole transport layer 16 into the light emitting layer 17 is defined by the difference between the HOMO level 162 of the hole transport layer 16 and the HOMO level 172 of the light emitting layer 17. Will be done. Further, the energy barrier Hg (etl1) for injecting holes from the light emitting layer 17 into the electron transport layer 18 is defined by the difference between the HOMO level 172 of the light emitting layer 17 and the HOMO level 182 of the first electron transport layer 18. Will be done.

In the comparative example, Hg (htl) was set to 0 eV, and the other electron injection barrier, hole injection barrier, and singlet exciton energy S1 which is the difference between the LUMO level and the HOMO level were set to be the same. ..

[2.2 Expected effects from design]
3 (a) to 3 (b) and (c) show the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, and the first electron transport layer 18, respectively, according to Examples and Comparative Examples. It is a simple schematic diagram which showed the band diagram and the recombination of an electron and a hole.

In the organic EL device according to the embodiment, as shown in the schematic diagram of FIG. 3A, a part of the electrons injected into the cathode side of the light emitting layer 17 is consumed by recombination, and the rest is consumed by the light emitting layer 17. Moves to the vicinity of the interface with the hole transport layer 16. On the other hand, as shown in FIG. 3B, since the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 is as large as 0.2 eV or more, the hole density in the hole transport layer 16 is large. Is small. Further, the holes in the hole transport layer 16 move to the vicinity of the interface with the light emitting layer 17, and then are injected into the light emitting layer 17 through the hole injection barrier Hg (eml), and a part of them is consumed by recombination. The rest moves to the vicinity of the interface of the light emitting layer 17 with the first electron transport layer 18. Therefore, the hole density in the hole transport layer 16 can be reduced, and deterioration of the hole transport material due to the interaction between the holes and excitons can be suppressed.

On the other hand, FIG. 3C is a schematic diagram when the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 is set to less than 0.2 eV. Also in this case, a part of the electrons injected into the cathode side of the light emitting layer 17 is consumed by recombination, and the rest moves to the vicinity of the interface of the light emitting layer 17 with the hole transport layer 16. On the other hand, since the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 is as small as less than 0.2 eV, the hole density in the hole transport layer 16 becomes large. Further, the holes in the hole transport layer 16 move to the vicinity of the interface with the light emitting layer 17, and then are injected into the light emitting layer 17 through the hole injection barrier Hg (eml), and a part of them is consumed by recombination. The rest moves to the vicinity of the interface of the light emitting layer 17 with the first electron transport layer 18. Therefore, since the hole density in the hole transport layer 16 is high, excitons are likely to be generated in the hole transport layer 16. Further, since many excitons are present near the interface of the light emitting layer 17 with the hole transport layer 16, exciton energy is transferred from the light emitting material in the light emitting layer 17 to the hole transport material in the hole transport layer 16. This also tends to increase excitons in the hole transport layer 16. Due to such a cause, both the hole density and the exciton density become high in the hole transport layer 16. Therefore, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, the energy of excitons of the hole transport material in the hole transport layer 16 is a hole transport in the hole transport layer 16. The phenomenon of moving to the material polaron can occur. Due to this phenomenon, some of the chemical bonds in the polaron of the hole transport material in the high energy state may be released, and a dissociation product may be produced. Since the dissociation product is generated at the site where the hole transport material was present before dissociation, the loss of the hole transport material due to dissociation not only reduces the hole transport property of the hole transport layer 16. It is also possible that the hole transportability of the hole transport layer 16 is reduced by the dissociation product trapping the holes. Further, since the dissociation product is generated near the interface of the hole transport layer 16 with the light emitting layer 17, the excitation energy in the light emitting layer 17 is transferred to the dissociation product in the hole transport layer 16. Since it can also be a quenching site that causes non-emission deactivation, it may also bring about a decrease in the quantum efficiency of the organic EL element 1. Due to these factors, when the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 is set to less than 0.2 eV, the hole transportability of the hole transport layer 16 deteriorates and the organic EL element 1 The quantum efficiency of the organic EL element 1 is lowered, the drive voltage of the organic EL element 1 is increased, the quantum efficiency is lowered, and the life is likely to be shortened due to these.

[2.3 Hall Density and Exciton Density]
Hereinafter, the hole density and the exciton density in the organic EL device according to the embodiment will be described by comparing the simulation results according to each of the example and the comparative example.

FIG. 4A is a graph showing the distribution of the hole density when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. FIG. 4A shows a simulation result in which Hg (htl) = 0.3 eV is shown by a broken line as an example, and a simulation result in which Hg (htl) = 0.0 eV is set and other conditions are the same is a comparative example. It is shown by a solid line. As shown in FIG. 4A, in the comparative example, since the hole injection barrier Hg (htl) between the hole injection layer 15 and the hole transport layer 16 is small, the hole injection layer 15 to the hole transport layer Holes are smoothly injected into 16, and there is almost no difference in hole density between the hole injection layer 15 and the hole transport layer 16. On the other hand, in the embodiment, since the hole injection barrier Hg (htl) between the hole injection layer 15 and the hole transport layer 16 is as large as 0.3 eV, the hole injection layer 15 moves to the hole transport layer 16. The injection of holes is suppressed, the hole density increases near the interface of the hole injection layer 15 with the hole transport layer 16, and the density of the hole transport layer 16 decreases. That is, in the comparative example, the holes are almost evenly present from the hole injection layer 15 to the hole transport layer 16, whereas in the embodiment, the holes are unevenly distributed in the hole injection layer 15 and the hole transport layer. The hole density of 16 is reduced. On the other hand, the hole density in the light emitting layer 17 is substantially the same regardless of the value of the hole injection barrier Hg (htl). The reason is that when the hole density of the hole transport layer 16 decreases, the electrical resistance of the hole transport layer 16 increases, a larger voltage is applied to the hole transport layer 16, and the inside of the hole transport layer 16 is applied. Generates a larger electric field. Therefore, the hole mobility inside the hole transport layer 16 becomes larger due to this larger electric field, and even if the hole density is lowered, the hole current is not reduced by the amount that the hole density is lowered, and the hole current is holed. Feedback is applied to bring it closer to the case where the injection barrier is small. Therefore, if the current flowing through the organic EL element is the same, it is considered that the amount of holes injected from the anode (pixel electrode 13) into the light emitting layer 17 is the same. That is, in the example, as compared with the comparative example, if the current flowing through the entire organic EL element is the same, the hole density in the hole transport layer 16 is reduced without lowering the hole density in the light emitting layer 17. Can be done.

FIG. 4B is a graph showing the distribution of the recombination rate of electrons and holes when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. Is. FIG. 4B shows a simulation result in which Hg (htl) = 0.3 eV is shown by a broken line as an example, and a simulation result in which Hg (htl) = 0.0 eV is set and other conditions are the same is a comparative example. It is shown by a solid line. As shown in FIG. 4B, the recombination rate in the hole transport layer 16 is lower in the examples as compared with the comparative example. The reason is considered to be that, as described above, in the examples, the hole density in the hole transport layer 16 is lower than that in the comparative example. On the other hand, as described above, the recombination rate in the light emitting layer 17 is almost the same between the example and the comparative example. The reason is considered to be that, as described above, there is no difference in the hole density in the light emitting layer 17 between the example and the comparative example.

FIG. 4C is a graph showing the distribution of excitons when a voltage is applied so as to have the same current density in each of the examples and the comparative examples along the film thickness direction. FIG. 4C shows a simulation result in which Hg (htl) = 0.3 eV is shown by a broken line as an example, and a simulation result in which Hg (htl) = 0.0 eV is set and other conditions are the same is a comparative example. It is shown by a solid line. As shown in FIG. 4 (c), the exciton densities in the light emitting layer 17 are almost the same between the examples and the comparative examples. It is considered that the reason is that, as described above, there is no difference in the hole density in the light emitting layer 17 and there is no difference in the recombination rate between the example and the comparative example. Further, also in the hole transport layer 16, there is almost no difference in exciton density between the examples and the comparative examples. The reason is that, in the examples, although the hole density and the recombination rate are low and the amount of excitons generated is small in the hole transport layer 16, many excitons are excited near the interface of the light emitting layer 17 with the hole transport layer 16. Since the children are generated, it is considered that the exciton density does not decrease even in the hole transport layer 16 due to the energy transfer from the light emitting layer 17 to the hole transport layer 16. However, in the examples, the exciton density in the hole transport layer 16 is not large and the hole density is low as compared with the comparative example, so that the deactivation reaction due to the bond between the exciton and the hole is suppressed, and the hole transport layer 16 is used. Deterioration of the material can be suppressed.

[2.4 Voltage-Current Characteristics]
Hereinafter, the effects of Hg (htl) and the film thickness of the hole transport layer 16 on the voltage-current characteristics of the organic EL device according to the embodiment will be described with simulation results.

FIG. 5A is a graph showing the relationship between the applied voltage and the current value in each of the above-mentioned Examples and Comparative Examples. FIG. 5A shows a simulation result in which Hg (htl) = 0.3 eV is shown by a broken line as an example, and a simulation result in which Hg (htl) = 0.0 eV is set and other conditions are the same is a comparative example. It is shown by a solid line. As shown in FIG. 5A, when the same amount of current is to be passed, the example requires a higher voltage than the comparative example. It is considered that the reason is that the impedance of the hole transport layer 16 increases because the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 is large. That is, when the conditions other than the value of the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 are the same, the embodiment requires a higher drive voltage than the comparative example.

On the other hand, FIG. 5B shows an applied voltage and a current value for each film thickness of the hole transport layer 16 in the organic EL element having the same thickness as that of the embodiment and the example except for the film thickness of the hole transport layer 16. It is a graph showing the relationship with. As shown in FIG. 5B, the smaller the film thickness of the hole transport layer 16, the smaller the applied voltage when trying to pass the same amount of current. It is considered that the reason is that the impedance of the hole transport layer 16 becomes smaller as the film thickness of the hole transport layer 16 becomes smaller. That is, the smaller the film thickness of the hole transport layer 16, the lower the drive voltage of the organic EL element.

[2.5 Optimal value of hole injection barrier and hole transport layer film thickness]
FIG. 6A is a graph showing the value of Hg (htl) and the hole density in the hole transport layer 16. As shown in FIG. 6A, the hole density in the hole transport layer 16 hardly changes when Hg (htl) is 0.15 eV or less, and significantly decreases when Hg (htl) is 0.2 eV or more. Therefore, in order to reduce the hole density in the hole transport layer 16, the Hg (htl) is preferably 0.2 eV or more.

On the other hand, FIG. 6B is a graph showing the relationship between the value of Hg (htl) and the drive voltage of the organic EL element. Here, the drive voltage refers to the voltage required to set the current value to a predetermined value. As shown in FIG. 6B, the drive voltage hardly changes when Hg (htl) is 0.15 eV or less, and increases remarkably at 0.2 eV or more. Therefore, if the influence of the increase in the drive voltage due to the increase in Hg (htl) can be offset by the decrease in the drive voltage due to the reduction in the film thickness of the hole transport layer 16, the drive voltage of the entire organic EL element does not increase. , The life of the hole transport layer 16 can be extended.

FIG. 7 is a graph showing the relationship between the value of Hg (htl) and the drive voltage of the organic EL element for obtaining the current density required for the organic EL element. The thickness of the hole transport layer 16 is 15 nm, and the characteristics are calculated by changing the value of Hg (htl). When the required current density is 20 mA / cm ² , the drive for obtaining the current density is obtained. The relationship between the voltage and the value of Hg (htl) is as shown in FIG.

Here, the current density of 20 mA / cm ² required for the organic EL element is calculated by the following. That is, the organic EL element is required to have a high brightness of about 1000 cd / m ² as a white peak brightness. Even in monochromatic light emission, a brightness of about several hundred cd / cm ² is required. For example, a blue light emitting element having the lowest energy efficiency requires a brightness of 300 to 400 cd / m ² . Considering the efficiency of the blue light emitting element (2 cd / A to 10 cd / A, 2 cd / m ² in this example), a current density of 20 mA / cm ² is required to obtain a brightness of 400 cd / m ² .

On the other hand, considering the distance between the anode and cathode electrodes of the organic EL element (100 nm to 200 nm, 200 nm in this example), the dielectric breakdown electric field strength of the organic semiconductor material constituting the organic EL element is about 1 × 10 ⁶ V / cm ² . The corresponding applied voltage is 20V. From FIG. 7, it can be seen that the applied voltage is 20 V when the Hg (htl) value is 0.62 eV, and when the Hg (htl) value is 0.6 eV or more and a drive voltage exceeding 20 V is applied. Insulation breakdown is likely to occur.

From the above, in order to obtain the current density of 20 mA / cm ² required for the organic EL device at a drive voltage of 20 V or less that satisfies the dielectric breakdown electric field strength of the organic semiconductor material, the value of Hg (htl) is about 0. It can be seen that 6 eV is the upper limit.

As a result, in the organic EL element 1, the Hg (htl) value is set to 0.6 eV or less to secure the current density required for the organic EL element and to make the hole transport layer 16 of the organic semiconductor material. The insulation breakdown electric field strength can be satisfied.

Here, it is confirmed that the hole density in the hole transport layer 16 does not increase due to the reduction in the film thickness of the hole transport layer 16. FIG. 8A is a graph showing the relationship between the film thickness of the hole transport layer 16 and the hole density in the hole transport layer 16. Here, the hole density in the hole transport layer 16 is a value on the anode (pixel electrode 13) side of the hole transport layer 16 by 1 nm from the interface with the light emitting layer 17. As shown in FIG. 8A, the hole density in the hole transport layer 16 hardly depends on the film thickness of the hole transport layer 16. That is, even if the film thickness of the hole transport layer 16 is reduced, the hole density in the hole transport layer 16 does not increase, so that the degree of deterioration in the hole transport layer 16 does not change and only the drive voltage is reduced. be able to.

FIG. 8B is a graph showing the relationship between the film thickness of the hole transport layer 16 and the drive voltage. Here, the drive voltage refers to the voltage required to set the current value to a predetermined value as described above. As shown in FIG. 8B, the smaller the film thickness of the hole transport layer 16, the smaller the drive voltage. For example, when Hg (htl) is increased from 0.0 eV to 0.2 eV, the drive voltage increases by 0.4 V as shown in FIG. 6 (b), but the film thickness of the hole transport layer 16 is increased from 20 nm to 15 nm. When the voltage is reduced to the above, the drive voltage becomes 0.4 V smaller as shown in FIG. 8 (b), so that the increase in the drive voltage can be suppressed. Therefore, for example, the film thickness of the hole transport layer 16 is preferably 15 nm or less.

[3. effect]
FIG. 9A shows the relationship between the operating time and the brightness for each hole injection barrier Hg (htl) in the organic EL device of the example and the same organic EL device except for the film thickness of the hole transport layer 16. It is a graph shown. The brightness is shown as a relative value with the brightness in the state where the usage time is 0 as 1. As shown in FIG. 9A, the larger the hole injection barrier Hg (htl), the smaller the degree of decrease in luminance. It is considered that the reason is that the hole density of the hole transport layer 16 decreases as the hole injection barrier Hg (htl) increases as described above, so that the deterioration rate of the hole transport layer 16 decreases.

FIG. 9B is a graph showing the relationship between the value of the hole injection barrier Hg (htl) and the 50% luminance life. The 50% luminance life is the luminance time at which the luminance becomes 0.5 when the luminance in the state where the luminance time is 0 is 1, and the luminance time when Hg (htl) = 0.0 eV is 1. It is shown by the relative value. As shown in FIG. 9B, the larger the hole injection barrier Hg (htl), the better the luminance life by 50%, and particularly when the hole injection barrier Hg (htl) is 0.2 eV or more, the luminance life is significantly improved.

[4. summary]
As described above, the organic EL device according to the present embodiment has a hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 of 0.2 eV or more. Therefore, since the hole density in the hole transport layer 16 can be reduced, the deactivation reaction between holes and excitons can be suppressed, and the hole transport material of the hole transport layer 16 due to the deactivation reaction can be suppressed. Deterioration can be suppressed and the life of the organic EL element can be extended.

Further, in the organic EL device according to the present embodiment, the film thickness of the hole transport layer 16 is 15 nm or less. Therefore, the impedance of the hole transport layer 16 can be lowered, and the influence of the increase in the impedance of the hole transport layer 16 due to the large hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16. Can be offset. Therefore, it is possible to suppress an increase in the drive voltage.

[5. Manufacturing method of organic EL element]
A method of manufacturing an organic EL element will be described with reference to the drawings. 10 (a) to 13 (c) are schematic cross-sectional views showing a state in each step in manufacturing an organic EL display panel including an organic EL element. FIG. 14 is a flowchart showing a method of manufacturing an organic EL display panel including an organic EL element.

In the 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.

(1) Formation of Substrate 11 First, as shown in FIG. 10A, a TFT layer 112 is formed on the substrate 111 to form the substrate 11 (step S10). The TFT layer 112 can be formed by a known method for manufacturing a TFT.

Next, as shown in FIG. 10B, the interlayer insulating layer 12 is formed on the substrate 11 (step S20). The interlayer insulating layer 12 can be laminated and formed by using, for example, a plasma CVD method, a sputtering method, or the like.

Next, in the interlayer insulating layer 12, dry etching is performed on the portion of the TFT layer on the source electrode to form a contact hole. The contact hole is formed so that the surface of the source electrode is exposed at the bottom thereof.

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 arranged on the interlayer insulating layer 12. For the formation of the connection electrode layer, for example, a sputtering method can be used, and after forming a metal film, patterning is performed using a photolithography method and a wet etching method.

(2) Formation of the Pixel Electrode 13 Next, as shown in FIG. 10 (c), the pixel electrode material layer 130 is formed on the interlayer insulating layer 12 (step S31). The pixel electrode material layer 130 can be formed by using, for example, a vacuum vapor deposition method, a sputtering method, or the like.

Next, as shown in FIG. 10D, the pixel electrode material layer 130 is patterned by etching to form a plurality of pixel electrodes 13 partitioned by subpixels (step S32). The pixel electrode 13 functions as an anode of each organic EL element.

The method for forming the pixel electrode 13 is not limited to the above method. For example, the hole injection material layer 150 is formed on the pixel electrode material layer 130 by a vapor deposition method, and the pixel electrode material layer 130 and the hole injection material layer 150 are formed. By patterning with the same photoresist, a laminated structure of the pixel electrode 13 and the hole injection layer 15 may be formed.

(3) Formation of the partition wall 14 Next, as shown in FIG. 10 (e), the partition wall material layer 140 is formed by applying the partition wall resin which is the material of the partition wall 14 on the pixel electrode 13 and the interlayer insulating layer 12. do. The partition wall material layer 140 uses a spin coating method or the like on the pixel electrode 13 and the interlayer insulating layer 12 in which a solution obtained by dissolving a phenol resin, which is a resin for the partition wall layer, in a solvent (for example, a mixed solvent of ethyl lactate and GBL) is used. It is formed by uniformly applying it (step S41). Then, the partition wall 14 is formed by pattern exposure and development on the partition wall material layer 140 (FIG. 11A, step S42), and the partition wall 14 is fired. Thereby, the opening 14a which becomes the formation region of the light emitting layer 17 is defined. The partition wall 14 is fired, for example, at a temperature of 150 ° C. or higher and 210 ° C. or lower for 60 minutes.

Further, in the step of forming the partition wall 14, the surface of the partition wall 14 may be further surface-treated with a predetermined alkaline solution, water, an organic solvent, or the like, or may be subjected to plasma treatment. This is done for the purpose of adjusting the contact angle of the partition wall 14 with respect to the ink (solution) applied to the opening 14a, or for the purpose of imparting water repellency to the surface.

(4) Formation of Hole Injection Layer 15 Next, as shown in FIG. 11B, an ink jet head 401 containing the constituent material of the hole injection layer 15 is applied to the opening 14a defined by the partition wall 14. It is discharged from the nozzle of No. 1 and applied onto the pixel electrode 13 in the opening 14a and fired (dried) to form the hole injection layer 15 (step S50).

(5) Formation of Hole Transport Layer 16 Next, as shown in FIG. 11 (c), an ink jet head 402 containing the constituent material of the hole transport layer 16 is applied to the opening 14a defined by the partition wall 14. It is discharged from the nozzle of No. 1 and applied onto the hole injection layer 15 in the opening 14a and fired (dried) to form the hole transport layer 16 (step S60).

(6) Formation of the light emitting layer 17 Next, as shown in FIG. 12A, the ink containing the constituent material of the light emitting layer 17 is discharged from the nozzle of the inkjet head 403 to discharge the hole transport layer in the opening 14a. It is applied onto 16 and fired (dried) to form a light emitting layer 17 (step S70).

(7) Formation of First Electron Transport Layer 18 Next, as shown in FIG. 12 (b), the first electron transport layer 18 is formed on the light emitting layer 17 and the partition wall 14 (step S80). The first electron transport layer 18 is formed, for example, by forming an organic compound as a material of the first electron transport layer 18 in common with each subpixel by a thin film deposition method.

(8) Formation of Second Electron Transport Layer 19 Next, as shown in FIG. 12 (c), a second electron transport layer 19 is formed on the first electron transport layer 18 (step S90). The second electron transport layer 19 is formed, for example, by forming a film of an electron transportable organic material and a doped metal in common for each subpixel by a co-deposited method.

(9) Formation of Optical Adjustment Layer 20 Next, as shown in FIG. 13A, an optical adjustment layer 20 is formed on the second electron transport layer 19 (step S100). The optical adjustment layer 20 is formed by forming an oxide conductor such as IZO or ITO in common for each subpixel by a vapor deposition method or a sputtering method, for example.

(10) Formation of the counter electrode 21 Next, as shown in FIG. 13 (b), the counter electrode 21 is formed on the optical adjustment layer 20 (step S110). The counter electrode 21 is formed by forming a film of silver, aluminum, or the like by a sputtering method or a vacuum vapor deposition method. The counter electrode 21 functions as a cathode for each organic EL element.

(11) Formation of Sealing Layer 22 Finally, as shown in FIG. 13C, the sealing layer 22 is formed on the counter electrode 21 (step S120). The sealing layer 22 can be formed by forming a film of SiON, SiN, or the like by a sputtering method, a CVD method, or the like. A sealing resin layer may be further applied on an inorganic film such as SiON or SiN, and may be formed by firing or the like.

A color filter or an upper substrate may be placed on the sealing layer 22 and joined.

[6. Overall configuration of organic EL display device]
FIG. 15 is a schematic block diagram showing the configuration of the organic EL display device 1000 provided with the organic EL display panel 100. As shown in FIG. 15, the organic EL display device 1000 includes an organic EL display panel 100 and a drive control unit 200 connected to the organic EL display panel 100. The drive control unit 200 includes four drive circuits 210 to 240 and a control circuit 250.

In the actual organic EL display device 1000, the arrangement of the drive control unit 200 with respect to the organic EL display panel 100 is not limited to this.

[7. Other variants]
(1) In the above embodiment, in order to prevent deterioration of the hole transport layer 16, the hole injection barrier Hg (htl) from the hole injection layer 15 to the hole transport layer 16 and the film thickness of the hole transport layer 16 are set. I decided to design it. However, in order to prevent deterioration of the first electron transport layer 18, the electron injection barrier Eg (ettl1) from the second electron transport layer 19 to the first electron transport layer 18 and the film thickness of the first electron transport layer 18 are designed. May be good.

FIG. 16A is a band diagram according to a modified example. In this case, the electron injection barrier Eg (etl1) from the second electron transport layer 19 to the first electron transport layer 18 is set to 0.2 eV or more. That is, each of the first electron transport layer 18 and the second electron transport layer 19 so that the LUMO level 191 of the second electron transport layer 19 is 0.2 eV higher than the LUMO level 181 of the first electron transport layer 18. Select the material of. According to the above configuration, as shown in the schematic diagram of FIG. 16B, the electron density of the first electron transport layer 18 can be reduced without reducing the electron density of the light emitting layer 17, and the electrons and excitons can be reduced. Deterioration of the first electron transport layer 18 can be suppressed by the deactivation reaction due to. Further, in this case as well, the drive voltage increases due to the increase in the impedance of the first electron transport layer 18, but the increase in the drive voltage can be suppressed by thinning the first electron transport layer 18.

In addition, both the embodiment and the configuration of the modified example may be adopted at the same time.

(2) In the above embodiment, the light emitting layer 17 is made of a single organic light emitting material, but the present invention is not limited to this. For example, the light emitting layer 17 may be made of a plurality of materials, such as containing a fluorescent material and a host material.

(3) In the above embodiment, the first electron transport layer 18 and the second electron transport layer 19 are considered to be essential configurations, but the present invention is not limited to this. For example, it may be an organic EL device having a single electron transport layer. Further, an additional functional layer may be provided. For example, a functional layer containing an oxide of a transition metal may be further provided between the pixel electrode 13 and the hole injection layer 15, or an alkali metal may be further provided between the first electron transport layer 18 and the light emitting layer 17. A functional layer containing a fluoride of an alkaline earth metal, a rare earth metal, or a quinolinium complex may be further provided.

Further, the optical adjustment layer 20 is not an indispensable configuration, and may be an organic EL element that does not have the optical adjustment layer 20. Further, the position of the optical adjustment layer 20 is not limited to the embodiment, and may be, for example, between the light emitting layer 17 and the first electron transport layer 18, or between the counter electrode 21 and the sealing layer 22. There may be.

(4) In the above embodiment, the organic EL display panel has a top-emission configuration, but a bottom-emission configuration may be used by using a light-transmitting electrode as the anode and a light-reflecting electrode as the cathode.

Further, in the above embodiment, the anode is a pixel electrode and the cathode is a counter electrode, but the cathode may be a pixel electrode and the anode may be a counter electrode.

Although the organic light emitting panel and the 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 embodiments and modifications. By arbitrarily combining the embodiments obtained by applying various modifications to the above-described embodiments and modifications, and the components and functions of the embodiments and modifications without departing from the spirit of the present invention. The realized form is also included in the present invention.

INDUSTRIAL APPLICABILITY The present invention is useful for manufacturing an organic EL element having a long life, an organic EL display panel including the organic EL element, and a display device.

1 Organic EL element 11 Substrate 12 Interlayer insulation layer 13 Pixel electrode 14 Partition electrode 15 Hole injection layer 16 Hole transport layer 17 Light emitting layer 18 First electron transport layer 19 Second electron transport layer 20 Optical adjustment layer 21 Opposite electrode 22 Sealing Layer 100 Organic EL display panel 200 Drive control unit 210 Drive circuit 250 Control circuit

Claims (11)

With the anode
A first functional layer disposed above the anode and containing an organic material,
A second functional layer, which is arranged in contact with the first functional layer and contains an organic material,
A light emitting layer arranged in contact with the second functional layer and
It is provided with a cathode arranged above the light emitting layer.
The highest occupied orbital (HOMO) level of the organic material contained in the second functional layer has an energy level lower than that of the HOMO level of the organic material contained in the first functional layer by 0.2 eV or more.
An organic EL device characterized in that the film thickness of the second functional layer is 15 nm or less. The organic EL device according to claim 1, wherein the hole mobility in the second functional layer is 1 × 10 ^-9 cm ² / Vs or more. The organic EL device according to claim 1 or 2, wherein the electron mobility in the light emitting layer is larger than the hole mobility in the light emitting layer. Any one of claims 1 to 3, wherein the energy of the singlet excitons in the organic material contained in the second functional layer is larger than the energy of the singlet excitons in the functional material contained in the light emitting layer. The organic EL element according to the section. One of claims 1 to 4, wherein the energy of the triplet excitons in the organic material contained in the second functional layer is larger than the energy of the triplet excitons in the functional material contained in the light emitting layer. The organic EL element according to the section. The anode is a light-reflecting electrode and
The organic EL device according to any one of claims 1 to 5, wherein the distance between the surface of the anode on the light emitting layer side and the surface of the light emitting layer on the anode side is 40 nm or less. An optical resonator structure is formed between the surface of the anode on the light emitting layer side and the surface of the cathode on the light emitting layer side.
The organic EL element according to claim 6, wherein the transparent conductive layer contains ITO or IZO. The maximum occupied orbital (HOMO) level of the organic material contained in the second functional layer has a lower energy level in the range of 0.6 eV or less than the HOMO level of the organic material contained in the first functional layer.
The organic EL device according to any one of claims 1 to 7, wherein the film thickness of the second functional layer is 5 nm or more. An organic EL panel including a plurality of organic EL elements according to any one of claims 1 to 7 on a substrate. Form an anode on the substrate and
A first functional layer containing an organic material is formed above the anode,
A second functional layer containing an organic material is formed so as to be in contact with the first functional layer.
A light emitting layer is formed so as to be in contact with the second functional layer.
A method for manufacturing an organic EL element that forms a cathode above the light emitting layer.
The highest occupied orbital (HOMO) level of the organic material contained in the second functional layer has an energy level lower than that of the HOMO level of the organic material contained in the first functional layer by 0.2 eV or more.
A method for manufacturing an organic EL device, characterized in that the film thickness of the second functional layer is 15 nm or less. The maximum occupied orbital (HOMO) level of the organic material contained in the second functional layer has a lower energy level in the range of 0.6 eV or less than the HOMO level of the organic material contained in the first functional layer.
The method for manufacturing an organic EL device according to claim 10, wherein the film thickness of the second functional layer is 5 nm or more.

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