JP2022075153A - Organic el element, organic el panel, and manufacturing method for organic el element - Google Patents

Abstract

To provide an organic EL element, an organic EL panel, and a manufacturing method for an organic EL element, in which the increase in driving voltage is suppressed even if the carrier injection property to a light-emitting layer decreases due to deterioration of a functional layer.SOLUTION: An organic EL element 1 includes an anode 13, a plurality of functional layers including a light-emitting layer 17, and a cathode 20 that are stacked in this order. For each of the functional layers, when the value obtained by dividing the thickness of the functional layer by the effective carrier mobility, which is the addition value of the effective electron mobility of the functional layer and the effective hole mobility, is the effective film thickness of the functional layer, the effective film thickness of the light-emitting layer is 30% or less of the total value of the effective film thicknesses of all the functional layers.SELECTED DRAWING: Figure 1

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 (see, for example, Patent Document 1). ). 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.

Japanese Unexamined Patent Publication No. 2016-115748

However, metal materials with a low work function are highly reactive and tend to be deteriorated by contact with moisture or oxygen. On the other hand, when the electron injection property from the cathode to the light emitting layer is lowered, a high drive voltage is required for the organic EL element to function. Similarly, when the hole injection property from the anode to the light emitting layer is lowered, a high drive voltage is required for the organic EL element to function as well. Therefore, there is a problem that the voltage to be applied to the organic EL element increases as the carrier injection property into the light emitting layer decreases, the deterioration of the functional layer further accelerates, and the life of the organic EL element tends to be shortened.

The present disclosure has been made in view of the above problems, and the organic EL element, the organic EL panel, and the organic EL element and the organic EL panel in which the drive voltage is difficult to increase even if the carrier injection property into the light emitting layer is deteriorated due to the deterioration of the functional layer. An object of the present invention is to provide a method for manufacturing an EL element.

The organic EL element according to one aspect of the present disclosure is an organic EL element in which an anode, a plurality of functional layers including a light emitting layer, and a cathode are laminated in this order, and each of the functional layers has the above-mentioned function. When the value obtained by dividing the film thickness of the functional layer by the effective carrier mobility, which is the sum of the effective electron mobility and the effective hole mobility of the layer, is taken as the effective film thickness of the functional layer, the effective film of the light emitting layer is used. The thickness is 30% or less of the total effective film thickness of all the functional layers.

According to the organic EL device according to one aspect of the present disclosure, when the carrier injection property into the light emitting layer is lowered, the ratio of the applied voltage (divided voltage) to the light emitting layer to the driving voltage is improved, so that the inside of the light emitting layer is increased. The electric field strength of is increased. Therefore, even when the carrier injection property into the light emitting layer is lowered, the carrier density in the light emitting layer is suppressed from being lowered, and the luminous efficiency is increased by improving the carrier mobility, so that the light emitting brightness is hard to be lowered and the driving is performed. The degree of voltage rise can be reduced. Therefore, even if carrier injection into the light emitting layer is deteriorated due to deterioration of the functional layer, the drive voltage is unlikely to increase, and the life of the organic EL element can be extended while suppressing the decrease in luminance.

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 transport layer, the light emitting layer, the electron transport layer, and the electron injection layer which concerns on Example. It is a graph which shows the electron injection property into a light emitting layer, and the relationship between the film thickness of a light emitting layer, and a drive voltage. (A) is a graph showing the relationship between the potential distribution in the film thickness direction and the electron injection property according to the embodiment, and (b) is the electron injection property according to the example and the voltage applied to each functional layer. It is a graph which shows the relationship with. (A) is a graph showing the relationship between the potential distribution in the film thickness direction and the electron injection property according to the comparative example, and (b) is the electron injection property according to the comparative example and the voltage applied to each functional layer. It is a graph which shows the relationship with. (A) is a graph showing the electron density in the film thickness direction for each electron injecting property according to the example, and (b) is a graph showing the electron density in the film thickness direction for each electron injecting property according to the comparative example. be. (A) is a graph showing the electron density at each of the interface on the hole transport layer side of the light emitting layer and the interface on the electron injection transport layer side of the light emitting layer for each electron injection property according to the embodiment (b). ) Is a graph showing the electron densities at the interface on the hole transport layer side of the light emitting layer and the interface on the electron injection transport layer side of the light emitting layer for each electron injection property according to the comparative example. (A) is a graph showing the current flowing through the light emitting layer for each electron injecting property according to the embodiment, and (b) is a graph showing the current flowing through the light emitting layer for each electron injecting property according to the comparative example. Relationship between the ratio of the effective film thickness Left (EML) of the light emitting layer to the total Effective film thickness Ref (ALL) of all the functional layers constituting the organic EL element and the increase value of the drive voltage when the electron injection property decreases. It is a graph which shows. 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 electron injection transport layer is formed on the light emitting layer and the partition wall layer, and (c) shows the state in which the optical adjustment layer is formed on the electron injection 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. FIG. The state where the sealing layer is formed on the electrode is shown. 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.

<< Aspects of disclosure >>
The organic EL element according to one aspect of the present disclosure is an organic EL element in which an anode, a plurality of functional layers including a light emitting layer, and a cathode are laminated in this order, and each of the functional layers has the above-mentioned function. When the value obtained by dividing the film thickness of the functional layer by the effective carrier mobility, which is the sum of the effective electron mobility and the effective hole mobility of the layer, is taken as the effective film thickness of the functional layer, the effective film of the light emitting layer is used. The thickness is 30% or less of the total effective film thickness of all the functional layers.

Further, in the method for manufacturing an organic EL element according to one aspect of the present disclosure, a substrate is prepared, an anode is formed above the substrate, and a plurality of functional layers including a light emitting layer are formed above the anode. A method for manufacturing an organic EL element that forms a cathode above the functional layer, which is an execution carrier mobility that is an addition value of the effective electron mobility and the effective hole mobility of the functional layer for each of the functional layers. When the value obtained by dividing the film thickness of the functional layer is taken as the effective film thickness of the functional layer, the effective film thickness of the light emitting layer is 30% or less of the total effective film thickness of all the functional layers. The film thickness of the light emitting layer is set so as to be.

According to the organic EL device according to one aspect of the present disclosure or the method for manufacturing the same, when the carrier injection property into the light emitting layer is lowered, the ratio of the applied voltage (divided voltage) to the light emitting layer to the drive voltage is improved. , The electric field strength in the light emitting layer increases. Therefore, even when the carrier injection property into the light emitting layer is lowered, the carrier density in the light emitting layer is suppressed from being lowered, and the luminous efficiency is increased by improving the carrier mobility, so that the light emitting brightness is hard to be lowered and the driving is performed. The degree of voltage rise can be reduced. Therefore, even if carrier injection into the light emitting layer is deteriorated due to deterioration of the functional layer, the drive voltage is unlikely to increase, and the life of the organic EL element can be extended while suppressing the decrease in luminance.

The organic EL device according to one aspect of the present disclosure may include an electron injection layer containing a metal material as the functional layer between the light emitting layer and the cathode.

With this configuration, even when the metal material contained in the electron injection layer is deteriorated due to oxidation or the like, the degree of increase in the drive voltage can be reduced.

In the organic EL element according to one aspect of the present disclosure, the metal material contained in the electron injection layer may be selected from an alkali metal, an alkaline earth metal, and a rare earth metal.

With this configuration, since the electron injection layer before deterioration has high electron inflow property, the luminous efficiency of the organic EL element can be improved, and the metal material contained in the electron injection layer is deteriorated due to oxidation or the like. However, the degree of increase in the drive voltage can be reduced.

In the organic EL element according to one aspect of the present disclosure, the anode is a light-reflecting electrode, and the organic EL element includes an intermediate layer between the light emitting layer and the anode as the functional layer. The film thickness of the layer may be 40 nm or less.

With this configuration, it is possible to facilitate the design of an optical resonator structure in which the surface of the anode on the light emitting layer side is one of the reflecting surfaces without increasing the optical path length from the anode to the light emitting center.

In the organic EL element according to one aspect of the present disclosure, the cathode is a light translucent electrode, and the organic EL element includes a transparent conductive layer between the light emitting layer and the cathode as the functional layer. May be.

With this configuration, it is possible to properly design the optical path length from the cathode to the light emitting center, and then facilitate the design of the optical resonator structure in which the surface of the cathode on the light emitting layer side is one of the reflecting surfaces.

The organic EL element according to one aspect of the present disclosure has an optical resonator structure 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 an ITO. Alternatively, it may include IZO.

With this configuration, it is possible to design an optical resonator structure having a large optical path length while suppressing an increase in the impedance of the entire organic EL element, so that the light extraction efficiency can be increased.

The organic EL panel according to one aspect of the present disclosure may include a plurality of organic EL elements according to 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 as an anode, a hole injection layer 15, a hole transport layer 16, a light emitting layer 17, an electron injection transport layer 18, an optical adjustment layer 19, and a counter electrode 20 as a cathode. ..

In the organic EL element 1, the pixel electrode 13 and the counter electrode 20 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 20. ..

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. A hole injection layer 15 is formed between the hole transport layer 16 and the pixel electrode 13.

On the counter electrode 20 side of the light emitting layer 17, an electron injection transport layer 18 is formed in contact with the light emitting layer 17. An optical adjustment layer 19 is formed between the electron injection transport layer 18 and the counter electrode 20.

[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 (zinc oxide) is laminated on the metal layer. May be good.

When the counter electrode 20 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, for example, a coating film, and is formed by coating and drying a hole injection material and a solution as a solute. 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. In one embodiment, the hole injection layer 15 has a film thickness of 10 nm.

Alternatively, the hole injection layer 15 may be formed of a thin-film deposition film. The hole injection layer 15 is made of, for example, an oxide such as Ag, Mo, chromium (Cr), vanadium (V), tungsten (W), nickel (Ni), and iridium (Ir).

Further, the hole injection layer 15 may have a laminated structure in which a coating film is formed on the thin-film deposition film.

<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, and is specifically formed by coating and drying a solution containing a hole transport material as a solute. In one embodiment of the embodiment, the hole transport layer 16 has a film thickness of 13 nm. In order not to make the optical path length between the light emitting center and the pixel electrode 13 excessive in forming the optical cavity structure, the total 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.
Alternatively, the hole transport layer 16 may be formed of a thin-film deposition film. For example, polyfluorene or a derivative thereof, or a polymer compound such as polyarylamine or a derivative thereof can be used.

<Light emitting layer>
The light emitting layer 17 has a function of emitting light by recombination of holes and electrons. As will be described later, the impedance of the light emitting layer 17 is preferably not too large with respect to the impedance of the hole injection layer 15, the hole transport layer 16, the electron injection transport layer 18, and the optical adjustment layer 19, and the film thickness of the light emitting layer is adjusted. It is preferable to design it thin. In one embodiment of the embodiment, the film thickness of the light emitting layer 17 is 25 nm.

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.

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.

<Electron injection transport layer>
The electron injecting and transporting layer 18 is formed on the light emitting layer 17, 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 metal atoms or metal ions is preferably uniform, and the metal atoms or metal ions are preferably not aggregated. The metal material is preferably selected from alkali metals, alkaline earth metals, and rare earth metals. Further, the doping amount of the metal material in the electron injection 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 small molecule organic materials such as an oxadiazole derivative (OXD), a triazole derivative (TAZ), and a phenanthroline derivative (BCP, Bphen).

In one embodiment of the embodiment, the electron injection transport layer 18 has a film thickness of 30 nm.

The electron injection transport layer 18 does not necessarily have to be formed of one layer, and may have, for example, a multi-layer structure including an electron injection layer containing a metal material and an electron transport layer made of an electron transportable material. Alternatively, for example, it may have a multi-layer structure including a layer containing a metal material or a compound thereof as a main component and an electron transport layer. Alternatively, for example, it may have a multi-layer structure including a layer containing a compound of a metal material as a main component and a layer for injecting electrons into the metal material to exhibit electron injectability.

<Optical adjustment layer>
The optical adjustment layer 19 is made of a light translucent conductive material and is formed on the electron injection transport layer 18.

The light reflecting surface at the interface of the counter electrode 20 with the optical adjustment layer 19 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 20 from the optical adjustment layer 19, a part of the light needs to be reflected to the optical adjustment layer 19. Therefore, it is preferable that the refractive index differs between the counter electrode 20 and the optical adjustment layer 19. For example, when the counter electrode 20 is a metal thin film, the optical adjustment layer 19 is preferably an oxide conductor such as ITO or IZO. Further, for example, when the counter electrode 20 is an oxide conductor such as ITO or IZO, the optical adjustment layer 19 is preferably a metal thin film such as Ag or Al. In one embodiment of the embodiment, the material of the optical adjustment layer 19 is IZO, and the film thickness thereof is 104 nm.

<Counter electrode>
The counter electrode 20 is made of a light translucent conductive material and is formed on the optical adjustment layer 19. In this embodiment, the counter electrode 20 functions as a cathode.

The light reflecting surface at the interface of the counter electrode 20 with the optical adjustment layer 19 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 20 from the optical adjustment layer 19, a part of the light needs to be reflected to the optical adjustment layer 19. Therefore, it is preferable that the refractive index differs between the counter electrode 20 and the optical adjustment layer 19. In one embodiment of the embodiment, the counter electrode 20 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 20 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. In this embodiment, the counter electrode 20 is a thin film of Ag.

Further, the counter electrode 20 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 20 may be a light-reflecting electrode. At this time, the counter electrode 20 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 formed 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 21 is formed on the organic EL element 1. The sealing layer 21 has a function of suppressing the exposure of organic layers such as the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, and the electron injection transport layer 18 to moisture or air. It has 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 21 needs to be formed 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 21 via a sealing resin. By laminating the upper substrate, the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, and the electron injection transport layer 18 can be protected from moisture, air, and the like.

[2. Relationship between electron injection and drive voltage]
The organic EL device 1 according to one aspect of the present disclosure is characterized in that an increase in the drive voltage can be suppressed even if the electron injection property from the cathode to the light emitting layer decreases. Hereinafter, the relationship between the electron injection property from the cathode into the light emitting layer and the drive voltage of the organic EL element 1 is compared with the organic EL element 1 (hereinafter referred to as “Example”) according to one aspect of the present disclosure. It is shown in the comparison explanation with. The electrical characteristics of the examples and comparative examples shown in [2.2] 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]
The organic EL element 1 according to the embodiment and the organic EL element according to the comparative example have the same energy band structure. FIG. 2 is a band diagram showing an energy band structure of the organic EL element 1 according to the embodiment and the organic EL element according to the comparative example. 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 energy level (hereinafter referred to as “LUMO level”) and the HOMO energy level of the hole transport layer 16, the light emitting layer 17, the electron injection transport layer 18, and the optical adjustment layer 19 are shown. (Hereinafter referred to as "HOMO level"), and the description is omitted for 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 Examples and Comparative Examples, the LUMO level 191 of the optical adjustment layer 19, the LUMO level 181 of the electron injection transport layer 18, the LUMO level 171 of the light emitting layer 17, and the LUMO level 161 of the hole transport layer 16 are respectively. , -2.5 eV, -2.4 eV, -2.4 eV, -2.1 eV. Therefore, the energy barrier Eg (etl) for injecting electrons from the optical adjustment layer 19 into the electron injection transport layer 18 and the energy barrier Eg (eml) for injecting electrons from the electron injection transport layer 18 into the light emitting layer 17 are used. Both are 0.1 eV or less. Further, the energy barrier for injecting electrons from the light emitting layer 17 into the hole transport layer 16 is about 0.3 eV.

Further, in Examples and Comparative Examples, the HOMO level 162 of the hole transport layer 16, the HOMO level 172 of the light emitting layer 17, the HOMO level 182 of the electron injection transport layer 18, and the HOMO level 192 of the optical adjustment layer 19 are , -5.3 eV, -5.5 eV, -5.3 eV, and -5.3 eV, respectively. Therefore, the energy barrier Hg (eml) for injecting holes from the hole transport layer 16 into the light emitting layer 17 is about 0.2 eV. Further, the energy barrier Hg (etl) for injecting holes from the light emitting layer 17 into the electron injection transport layer 18 and the energy barrier for injecting the optical adjustment layer 19 holes from the electron injection transport layer 18 are −0. It is 2 eV and 0.0 eV.

[2.2 Electron injection and drive voltage of the entire light emitting element]
FIG. 3 is a graph showing the relationship between the electron injection property from the counter electrode 20 (cathode) into the light emitting layer 17 and the drive voltage of the organic EL element 1 for each film thickness of the light emitting layer 17. As shown in FIG. 3, the larger the film thickness of the light emitting layer 17, the higher the drive voltage. It is considered that the reason is that as the film thickness of the light emitting layer 17 increases, the electric resistance of the light emitting layer 17 increases, and the voltage required for passing the same current increases. Further, as shown in FIG. 3, the higher the electron injection property from the counter electrode 20 to the light emitting layer 17, the lower the drive voltage, and the lower the electron injection property, the higher the drive voltage. The reason is that if the voltage applied to the organic EL element 1 is the same, the electron density in the light emitting layer 17 decreases if the electron injection property from the counter electrode 20 to the light emitting layer 17 becomes low, and the exciton generation efficiency. It is considered that the lower the electron injection property, the higher the voltage required to obtain the same amount of light emission, because the light emission efficiency is lowered.

[2.3 Light emitting layer film thickness and voltage distribution]
FIG. 4A shows, as an example, in the organic EL element 1 in which the film thickness of the light emitting layer 17 is 25 nm, each position in the film film direction is shown according to the degree of electron injection from the counter electrode 20 to the light emitting layer 17. It is a graph which showed the electric potential (electrical potential). FIG. 4B is a graph showing the relationship between the degree of electron injection and the voltage (voltage division) applied to each functional layer when the organic EL element 1 is driven. Further, FIG. 5A shows, as a comparative example, in an organic EL element having a light emitting layer having a film thickness of 81 nm, at each position in the film film direction according to the degree of electron injection from the counter electrode 20 to the light emitting layer 17. It is a graph which showed the electric potential (electrical potential). FIG. 5B is a graph showing the relationship between the degree of electron injection and the voltage (divided voltage) applied to each functional layer when the organic EL element according to the comparative example is driven. In FIGS. 4 (a) and 5 (a), the degree of electron injectability is highest in A, lower in the order of B, C, D, E, and F, and lowest in F. Further, in FIGS. 4 (a) and 5 (a), when the degree of electron injection property is indicated by the same character, it indicates that the characteristics of the electron injection transport layer 18 are the same. That is, the organic EL element according to the degree A of electron injectability in FIG. 4A and the organic EL element according to the degree A of electron injectability in FIG. 5A differ only in the film thickness of the light emitting layer 17. There is no difference in other configurations.

As shown in FIGS. 4A and 5A, when the electron injection transport layer 18 deteriorates and the electron transportability decreases, more specifically, when the electron mobility decreases, the impedance of the electron injection transport layer 18 decreases. As it rises, the voltage drop in the electron injection transport layer 18 becomes large, and as shown in FIGS. 4 (b) and 5 (b), the voltage applied to the electron injection transport layer 18 rises. Due to the increase in impedance of the electron injection transport layer 18, the current flowing with respect to the applied voltage decreases.

On the other hand, when comparing FIG. 4 (b) and FIG. 5 (b), the organic EL element 1 according to the embodiment shown in FIG. 4 (b) is more electron-injected than the comparative example shown in FIG. 5 (b). The degree of increase in the voltage applied to the transport layer 18 and the degree of increase in the voltage applied to the light emitting layer 17 are both large. The reason may be that the impedance of the light emitting layer 17 is different. As shown in FIG. 5B, in the comparative example, the voltage applied to the light emitting layer 17 is applied to the electron injection transport layer 18 even when the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 is high. Greater than the voltage to be applied. That is, since the impedance of the light emitting layer 17 is larger than the impedance of the electron injection transport layer 18, the electron mobility of the electron injection transport layer 18 decreases due to the deterioration of the electron injection transport layer 18, so that the electron injection transport layer 18 has a higher impedance. Even if the impedance rises, the voltage applied to the light emitting layer 17 hardly changes. Therefore, when the electron injection transport layer 18 deteriorates, the voltage applied to the light emitting layer 17 does not change, and the current decreases due to the deterioration of the electron injection property. As a result, if the voltage applied to the organic EL element is the same, the emission brightness decreases due to the decrease in current, and it is necessary to increase the drive voltage to compensate for the decrease. On the other hand, as shown in FIG. 4B, in the embodiment, the impedance of the light emitting layer 17 is about the same as the impedance of the electron injection transport layer 18, so that the electrons from the electron injection transport layer 18 to the light emitting layer 17 are received. The voltage applied to the light emitting layer 17 and the voltage applied to the electron injection transport layer 18 are about the same regardless of whether the injection property is high or low. That is, when the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 is lowered, both the voltage applied to the electron injection transport layer 18 and the voltage applied to the light emitting layer 17 increase. Therefore, by reducing the degree of decrease in electron density of the light emitting layer 17 and improving the luminous efficiency of the light emitting layer 17, it is possible to compensate for the decrease in emission luminance by increasing the applied voltage. As a result, even when the voltage applied to the organic EL element is the same and the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 is deteriorated, the degree of the decrease in emission brightness can be reduced. Therefore, the degree of increase in the drive voltage can be reduced.

[2.4 Changes in electron density and current]
Hereinafter, the relationship between the decrease in electron injection property and the change in current will be described in more detail.

FIG. 6 is a graph showing the electron density at each position in the film thickness direction for each degree of electron injection property from the electron injection transport layer 18 to the light emitting layer 17, and FIG. 6A corresponds to the embodiment. , FIG. 6B corresponds to a comparative example. As for the degree of electron injection, A is the highest, B, C, D, E, and F are the lowest, and F is the lowest, as in FIGS. 4 (a) and 5 (a).

In the comparative example, even if the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 is lowered, the voltage (divided voltage) applied to the light emitting layer 17 hardly changes. Therefore, as shown in FIG. 6B, the electron density in the light emitting layer 17 decreases due to the decrease in electron injection property. On the other hand, in the embodiment, when the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 decreases, the voltage (partial pressure) applied to the light emitting layer 17 increases. Therefore, even in the examples, the electron density in the light emitting layer 17 decreases due to the decrease in electron mobility, but the electric field strength increases because the film thickness of the light emitting layer 17 is smaller and the voltage rise is larger than in the comparative example, and light emission occurs. Since the electron mobility in the layer 17 increases, the degree of decrease in the electron density in the light emitting layer 17 becomes small.

FIG. 7 shows the relationship between the electron density at the interface of the light emitting layer 17 on the hole transport layer 16 side and the interface of the light emitting layer 17 on the electron injection transport layer 18 side and the electron injection property from the counter electrode 20 to the light emitting layer 17. 7 (a) corresponds to an embodiment, and FIG. 7 (b) corresponds to a comparative example. As shown in FIGS. 7 (a) and 7 (b), when the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 is lowered, both the comparative example and the example are on the hole transport layer 16 side of the light emitting layer 17. Although the electron density at the interface decreases, it does not change significantly. The reason is considered to be that the electron density at the interface of the light emitting layer 17 on the hole transport layer 16 side is greatly affected by the electron injection barrier from the light emitting layer 17 to the hole transport layer 16. On the other hand, the electron density at the interface of the light emitting layer 17 on the electron injection transport layer 18 side decreases in both the examples and the comparative examples. The reason is considered to be that the electron density at the interface of the light emitting layer 17 on the electron injection transport layer 18 side is directly affected by the degree of electron injection property from the electron injection transport layer 18 to the light emitting layer 17. However, in the examples, the electron density at the interface on the hole transport layer 16 side of the light emitting layer 17 is higher than that in the comparative example. The reason is that, as described above, in the embodiment, the voltage gradients of the electron injection transport layer 18 and the light emitting layer 17 are large and the electric field strength is large, so that the electron mobility in the electron injection transport layer 18 and the light emitting layer 17 is large. Is considered to be due to an increase in the number of electrons injected into the light emitting layer 17 as compared with the comparative example.

FIG. 8 is a graph showing the relationship between the current flowing through the light emitting layer 17 and the electron injection property from the electron injection transport layer 18 to the light emitting layer 17, and FIG. 8 (a) corresponds to an embodiment and FIG. 8 (b). ) Corresponds to the comparative example. As shown in FIGS. 8A and 8B, when the electron injection property from the electron injection transport layer 18 to the light emitting layer 17 decreases, the current flowing through the light emitting layer 17 decreases. However, in the examples, as compared with the comparative example, the decrease in the current flowing through the light emitting layer 17 is small even if the electron injection property from the counter electrode 20 into the light emitting layer 17 is decreased. The reason is that, as described above, in the examples as compared with the comparative example, the electron mobility is increased due to the large voltage gradient of the electron injection transport layer 18 and the large electric field strength, and the electrons are injected into the light emitting layer 17. The number of electrons increases. Further, as the mobility of the electrons in the light emitting layer 17 increases, the recombination coefficient (recoupling probability) of the electrons and holes in the light emitting layer 17 also increases, so that the luminous efficiency in the light emitting layer 17 also increases. Therefore, in the examples, the degree of decrease in the current is reduced even if the electron injection property from the counter electrode 20 to the light emitting layer 17 is lowered as compared with the comparative example, and the organic EL is improved by improving the luminous efficiency of the light emitting layer 17. The degree of decrease in the luminous efficiency of the element 1 can be reduced.

[2.5 Relationship between the film thickness of the light emitting layer and the film thickness of other functional layers]
As described above, when the electron injection property from the cathode to the light emitting layer is lowered, the ratio of the voltage (divided voltage) applied to the light emitting layer to the drive voltage of the organic EL element is improved, so that the drive voltage is increased. The degree can be reduced. Hereinafter, the conditions for determining the configuration are examined in detail.

The ratio of the voltage (divided voltage) applied to the light emitting layer to the drive voltage of the organic EL element can be defined by the relationship between the total impedance of the organic EL element and the impedance of the light emitting layer. Here, as factors that determine the impedance of the functional layer, the film thickness of the functional layer, the carrier mobility in the functional layer, the electric field strength in the functional layer, and the carrier density in the functional layer can be considered. Here, the electric field strength in the functional layer is defined by the partial pressure of the functional layer and the film thickness of the functional layer, and the carrier density in the functional layer depends on the carrier mobility and the electric field strength in the functional layer. Consider the film thickness and carrier mobility in the functional layer as a reference. Generally, as the film thickness of the functional layer increases, the electric resistance increases, that is, the impedance increases. On the other hand, the higher the carrier mobility in the functional layer, the smoother the carrier moves and the larger the current value, that is, the lower the impedance. Therefore, the effective film thickness Leaf obtained by dividing the film thickness L of the functional layer by the carrier mobility μ of the functional layer is defined as an index indicating the impedance of the functional layer. That is, the effective film thickness Leaf of the functional layer where the electron mobility is μe, the hole mobility is μh, and the film thickness is L is defined as follows.

Ref = L / (μe + μh)
Then, the relationship between the ratio of the effective film thickness Leaf (EML) of the light emitting layer to the total Leaf (ALL) of the effective film thickness of all the functional layers and the increase value of the drive voltage was investigated. FIG. 9 shows the ratio of the effective film thickness Leaf (EML) of the light emitting layer to the total Leaf (ALL) of the effective film thickness of all functional layers, and the driving voltage when the electron injection property from the cathode to the light emitting layer is lowered. It is a graph which shows the relationship with the rise value ΔV. Here, the total effective film thickness Ref (ALL) of all functional layers is the effective film of each of the hole injection layer 15, the hole transport layer 16, the light emitting layer 17, the electron injection transport layer 18, and the optical adjustment layer 19. It is the total value of the thickness Leaf.

As shown in FIG. 9, the drive voltage increases as the ratio of the effective film thickness Left (EML) of the light emitting layer to the total effective film thickness of all functional layers (ALL) increases, and the drive voltage increases as the ratio decreases. The voltage drops. The reason is as follows. The ratio of the voltage (divided voltage) applied to the light emitting layer to the drive voltage of the organic EL element increases as the ratio of the effective film thickness Left (EML) of the light emitting layer to the total effective film thickness of all functional layers Ref (ALL) increases. Therefore, even if the electron injection property from the cathode to the light emitting layer is lowered, the voltage (divided voltage) applied to the light emitting layer with respect to the drive voltage of the organic EL element does not increase. Therefore, since the electron injection property from the cathode to the light emitting layer is lowered, the electron density in the light emitting layer is lowered and the luminous efficiency is lowered, so that it is necessary to increase the drive voltage. On the other hand, the voltage (divided voltage) applied to the light emitting layer with respect to the drive voltage of the organic EL element decreases as the ratio of the effective film thickness Left (EML) of the light emitting layer to the total Effective film thickness of all functional layers decreases. Therefore, when the electron injection property from the cathode to the light emitting layer is lowered, the voltage (divided voltage) applied to the light emitting layer with respect to the drive voltage of the organic EL element tends to increase. Therefore, even if the electron injection property from the cathode to the light emitting layer is reduced, the electron density in the light emitting layer is compensated by the increase in the voltage (divided voltage) applied to the light emitting layer, so that the degree of decrease in the luminous efficiency is low and the drive voltage is low. The degree of increase is low. That is, the lower the ratio of the effective film thickness Left (EML) of the light emitting layer to the total effective film thickness of all functional layers is, the better. For example, this ratio should be 30% (0.3) or less. Therefore, the increase in the drive voltage can be suppressed to 2 V or less. Generally, in an organic EL panel provided with an organic EL element, the voltage margin in an increase in the drive voltage of the organic EL element is about 2 V. Therefore, the above configuration suppresses a decrease in brightness even if the organic EL panel is driven for a long time. can do. The voltage margin is driven when the output voltage of the drive circuit is allocated to each voltage such as the drive voltage of the organic EL element, the drive voltage of a circuit other than the organic EL element (for example, TFT), and the voltage drop due to wiring. It is a voltage designed as a surplus in preparation for a voltage rise. For example, when the drive voltage of the organic EL element before deterioration is 11 V, the drive voltage of the TFT is 10 V, and the voltage drop due to wiring is 0.5 V, while the output voltage of the drive circuit is about 20 to 30 V, the organic EL The upper limit of the voltage margin when the drive voltage of the element rises is about 1 to 2 V.

[3. summary]
As described above, the organic EL element according to one aspect of the present disclosure is a light emitting layer when the film thickness L of the functional layer is divided by the carrier mobility μ of the functional layer to obtain the effective film thickness Left of the functional layer. The effective film thickness Leaf (EML) of the above is 30% or less of the total effective film thickness Ref (ALL) of all the functional layers. Here, the carrier mobility μ of the functional layer is the sum of the electron mobility μe of the functional layer and the hole mobility μh of the functional layer. Further, all functional layers refer to all layers existing between the cathode and the anode, and include a light emitting layer. According to this configuration, when the electron injection property from the cathode to the light emitting layer is lowered, the ratio of the voltage (divided voltage) applied to the light emitting layer to the drive voltage is increased, so that the electric field strength in the light emitting layer is strengthened. The degree of decrease in current is reduced. Further, when the electric field strength in the light emitting layer is strengthened, the mobility of the carrier increases and the recombination coefficient increases, so that the luminous efficiency of the light emitting layer 17 is improved and the degree of decrease in the luminous efficiency of the organic EL element 1 is reduced. It can be reduced. Therefore, in the organic EL device according to one aspect of the present disclosure, the degree of increase in the drive voltage is reduced even if the electron injection property from the cathode to the light emitting layer is lowered, and the acceleration of deterioration of the organic EL device can be suppressed. can.

[4. 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 (b) 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, a dry etching method is performed on the source electrode of the TFT layer in the interlayer insulating layer 12 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, 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 sub. A plurality of pixel electrodes 13 partitioned for each pixel are formed (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, and the pixel electrode material layer 130 and the hole injection material layer 150 are etched. The pixel electrode 13 and the hole injection layer 15 may be formed together by patterning with the above.

(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. 12 (a), the ink containing the constituent material of the light emitting layer 17 is ejected 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 Electron Injection Transport Layer 18 Next, as shown in FIG. 12B, an electron injection transport layer 18 is formed on the light emitting layer 17 and the partition wall 14 (step S80). The electron injection transport layer 18 is formed, for example, by forming a film of an organic compound having an electron transport property and a metal material having an electron injection property in common for each subpixel by a co-deposited method.

(8) Formation of Optical Adjustment Layer 19 Next, as shown in FIG. 12 (c), the optical adjustment layer 19 is formed on the electron injection transport layer 18 (step S90). The optical adjustment layer 19 is formed, for example, by forming an oxide conductor such as ITO or IZO in common with each subpixel by a sputtering method.

(9) Formation of Counter Electrode 20 Next, as shown in FIG. 13 (a), the counter electrode 20 is formed on the optical adjustment layer 19 (step S100). The counter electrode 20 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 20 functions as a cathode for each organic EL element.

(10) Formation of Sealing Layer 21 Finally, as shown in FIG. 13B, the sealing layer 21 is formed on the counter electrode 20 (step S110). The sealing layer 21 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 21 and joined.

[5. 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.

[6. Other variants]
(1) In the above embodiment, the case where the electron injection property from the cathode to the light emitting layer is lowered due to the deterioration of the metal material having electron injection property has been described, but the deterioration of the organic material having electron injection property causes the electron injection property from the cathode. Even when the electron injection property into the light emitting layer is lowered, the degree of increase in the drive voltage can be reduced by the same design. The reason is that, as described above, the effective film thickness of the light emitting layer is set to a predetermined ratio or less with respect to the total effective film thickness of all the functional layers, so that the impedance of the functional layer having electron injection property can be obtained. This is because the impedance of the light emitting layer can not be excessive. Due to this configuration, when the electron mobility from the cathode to the light emitting layer is lowered, the applied voltage (divided voltage) ratio to the drive voltage of the light emitting layer and the electron injection layer can be increased, so that electrons are injected into the light emitting layer. The effect of the deterioration of the property can be mitigated by the increase in electron mobility due to the increase in the electric field strength in the light emitting layer and the electron injection layer. The same applies to the case where the electron injection property from the cathode to the light emitting layer is lowered due to the deterioration of the organic material having electron transport property.

Similarly, when the hole injection property from the anode to the light emitting layer is lowered due to deterioration of the metal material or the organic material having the hole injection property, the degree of increase in the drive voltage can be reduced by the same design. The reason is that, as described above, the effective film thickness of the light emitting layer is set to a predetermined ratio or less with respect to the total effective film thickness of all the functional layers, so that the impedance of the functional layer having hole injection property can be obtained. This is because the impedance of the light emitting layer can not be excessive. Due to this configuration, when the hole injectability from the anode to the light emitting layer is lowered, the applied voltage (divided voltage) ratio to the drive voltage of the light emitting layer and the hole injection layer can be increased, so that holes in the light emitting layer can be increased. The effect of the decrease in injectability can be mitigated by the increase in hole mobility due to the increase in the electric field strength in the light emitting layer and the hole injection layer. The same applies to the case where the hole injection property from the anode to the light emitting layer is lowered due to the deterioration of the organic material having the hole transport property.

(2) In the above embodiment, the hole injection layer 15 and the hole transport layer 16 are considered to be essential configurations, but the present invention is not limited to this. For example, it may be an organic EL element having no hole transport layer 16. Further, for example, instead of the hole injection layer 15 and the hole transport layer 16, a single hole injection transport layer may be provided.

Further, although the single electron injection transport layer 18 is provided in the above embodiment, the electron injection layer and the electron transport layer may be provided separately.

(3) In the above embodiment, the optical adjustment layer 19 is considered to be an essential configuration, but the present invention is not limited to this. In the above embodiment, since the film thickness of the light emitting layer 17 is small, an optical resonator structure having a minimum optical path length may be formed by designing the film thickness of another functional layer by using 0th-order interference. Further, when the optical adjustment layer is provided, the optical adjustment layer does not have to be one layer or the position shown in the embodiment. For example, the optical adjustment layer is provided between the light emitting layer and the electron injection transport layer. It is also good.

(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 a pixel electrode and a light-reflecting electrode as a counter electrode.

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.

(5) In the above embodiment, the panel provided with the organic EL element is an organic EL display panel, but the present invention is not limited to this. For example, in the case of a panel provided with an organic EL element as a light emitting element, a light emitting panel as a part of a lighting device, a backlight panel of a liquid crystal panel, a multifunction panel that can be used by selecting a light emitting panel function and a display panel function, etc. , May be used for purposes other than display.

Although the organic EL element and the organic EL panel 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 and an organic EL panel including the organic EL element.

1 Organic EL element 11 Substrate 12 Interlayer insulation layer 13 Pixel electrode (anode)
14 Septum 15 Hole injection layer 16 Hole transport layer 17 Light emitting layer 18 Electron injection transport layer 19 Optical adjustment layer 20 Opposite electrode (cathode)
21 Sealing layer 100 Organic EL display panel 200 Drive control unit 210-240 Drive circuit 250 Control circuit 1000 Organic EL display device

Claims (8)

An organic EL element in which an anode, a plurality of functional layers including a light emitting layer, and a cathode are laminated in this order.
For each of the functional layers, the value obtained by dividing the film thickness of the functional layer by the execution carrier mobility, which is the sum of the effective electron mobility and the effective hole mobility of the functional layer, is defined as the effective film thickness of the functional layer. When the light emitting layer is used, the effective film thickness of the light emitting layer is 30% or less of the total effective film thickness of all the functional layers. The organic EL device according to claim 1, wherein an electron injection layer containing a metal material is included as the functional layer between the light emitting layer and the cathode. The organic EL element according to claim 2, wherein the metal material contained in the electron injection layer is selected from an alkali metal, an alkaline earth metal, and a rare earth metal. The anode is a light-reflecting electrode and
The organic EL element includes an intermediate layer as the functional layer between the light emitting layer and the anode.
The organic EL device according to any one of claims 1 to 3, wherein the film thickness of the intermediate layer is 40 nm or less. The cathode is a translucent electrode and
The organic EL element according to any one of claims 1 to 4, wherein the organic EL element includes a transparent conductive layer between the light emitting layer and the cathode as the functional layer. 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 5, wherein the transparent conductive layer contains ITO or IZO. An organic EL panel in which a plurality of the organic EL elements according to any one of claims 1 to 6 are formed on a substrate. Prepare the board,
An anode is formed above the substrate to form an anode.
A plurality of functional layers including a light emitting layer are formed above the anode.
A method for manufacturing an organic EL element that forms a cathode above the functional layer.
For each of the functional layers, the value obtained by dividing the film thickness of the functional layer by the execution carrier mobility, which is the sum of the effective electron mobility and the effective hole mobility of the functional layer, is defined as the effective film thickness of the functional layer. A method for manufacturing an organic EL element, in which the film thickness of the light emitting layer is set so that the effective film film of the light emitting layer is 30% or less of the total value of the effective film thicknesses of all the functional layers.

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