JP2020129454A - Coating ink, and electronic device and electroluminescent element using coating ink - Google Patents

Abstract

To provide a coating ink improved in efficiency of a thermal reduction process and capable of achieving the low drive voltage and long life of an electronic device.SOLUTION: A coating ink containing a metal-doped heteropolyoxometalate and an ink solvent is characterized in that an element contained in the coating ink consists only of an element constituting a metal-doped heteropolyoxometalate and an element constituting an ink solvent.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a metal-doped heteropolyoxometallate coating ink and an electronic device using the heteropolyoxometallate.

Organic EL (electroluminescence) is a phenomenon that self-luminesces due to current injection, and an organic EL device (OLED) utilizing this phenomenon has a high viewing angle, high contrast, ultra-thin structure, low voltage drive, and high response speed. As such, it is expected to be applied to lighting and displays as a next-generation surface emitting device.

A wet process is used for manufacturing such an organic EL device (OLED) because it can have a large area or is easy to process. For example, the light emitting layer is formed by a coating method, or the partition wall for partitioning the OLED is formed by a photolithography method. In order to realize a mass-produced coating type organic EL device that enables future large-area organic devices, OLEDs that emit light stably on the substrate are required. For a large organic EL display of 50 inches or more, a vapor deposition tandem type (multi-photon type) device is already known, but establishment of a coating type device manufacturing technique is essential.

In order to obtain high light emission efficiency, it is necessary to efficiently recombine electrons and holes in the light emitting layer. Therefore, conventionally, a charge transport material is contained in the light emitting layer, or an anode and a light emitting layer are combined. A hole transport layer is provided between them, an electron transport layer is provided between the cathode and the light emitting layer, or the work function of the anode or the cathode is optimized so that the electrode and the organic functional layer (hole transport layer, electron transport layer) The energy barrier with the (layer) is being reduced. In order to form these organic functional layers by a wet process, there is a demand for a technique of forming a laminated structure with a material having excellent solvent resistance, heat resistance, and controllability of molecular structure.

As a coating type hole injecting layer that constitutes such an OLED, in Patent Document 1, a hole transporting material in which polyoxometallate containing phosphomolybdic acid is dissolved in water is coated, and at 200° C. for 10 minutes, It is reported that the hole transport layer formed by heating and drying can be stably driven for a long time. However, in the hole transport layer, the driving voltage is high, and the high temperature process of 200° C. leads to an increase in running cost such as electricity bill in industrial use. For this reason, improvements in technologies such as reduction of driving voltage and fabrication in low temperature process are required.

On the other hand, the present inventors have found that an ink in which phosphomolybdic acid powder that has been heated and reduced is dissolved can realize a low driving voltage without requiring treatment after film formation (Non-Patent Document 1). However, there is a problem that the efficiency of the heat reduction process of the sample is very poor. Further, further reduction of the driving voltage is required.

JP, 2011-23711, A

Inorg.Chem. 2018, 857, 1950 (Published February 2018)

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a coating ink which can improve the efficiency of the heating and reduction process, and can achieve lower driving voltage and longer life of electronic devices. ..

The coating ink of the present invention contains a metal-doped heteropolyoxometalate, and an ink solvent, and an element constituting the metal-doped heteropolyoxometallate, and only an element constituting the ink solvent. It is characterized by consisting of.
The heteropolyoxometallate is preferably phosphomolybdic acid.
The ink solvent is preferably a compound having a nitrile group.
The metal is preferably any one of magnesium, aluminum, titanium, manganese, cobalt, nickel, copper, zinc, molybdenum, silver, tin, antimony and tungsten.

The electronic device of the present invention includes one or more thin films, and at least one of the thin films is a metal-doped heteropolyoxometalate thin film.
The heteropolyoxometallate is preferably phosphomolybdic acid.
The metal-doped phosphomolybdic acid thin film preferably functions as a charge acceptor layer when electric charges are generated inside the device.
The metal is preferably one of magnesium, aluminum, titanium, manganese, cobalt, nickel, copper, zinc, molybdenum, silver, tin, antimony and tungsten.

One mode of the electroluminescence element of the present invention is a plurality of light emitting units stacked in a tandem shape, and is arranged between two light emitting units of the plurality of light emitting units, and electrically connects the light emitting units. And an intermediate layer that is formed of a phosphomolybdic acid thin film doped with silver.

In the present invention, it has been found that phosphomolybdic acid solution can be easily reduced by reacting the phosphomolybdic acid solution with the metal powder, and the reduced phosphomolybdic acid does not precipitate in the coating ink and stably exists. By applying the coating ink to the intermediate layer of the device, it is possible to realize a low temperature process and low driving voltage of the device by a simple solution process.
Since the coating ink of the present invention can be coated at room temperature, it can be used on a substrate having low heat resistance such as a PET substrate and can greatly contribute to the development of a flexible electroluminescence device. Further, it exhibits superior performance as a conventional material for the intermediate layer of the coating type tandem element, compared to the conventional one.

FIG. 1 shows PMA (phosphomolybdic acid) in Example 1 of 10 wt% metal (Mg, Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Sn, Sb or W) 30 mg. /ML acetonilyl solution and PMA: 10 wt% 30 mg/mL 1-butanol solution of metal (Mg, Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Sn, Sb or W). 3 is a photograph showing the appearance of a coating ink, and a photograph showing the appearance of PMA's 10 mg/mL acetonylyl solution and 10 mg/mL 1-butanol solution. FIG. 2 shows the XPS measurement results of the coating ink prepared in Example 1. In FIG. 2, PMA (3.61%) (2a), Bakerd PMA (25.63%) (2b), PMA:Mg (24.50%) (2c), PMA:Al (7.82%) ( 2d), PMA:Ti (2.82%) (2e), PMA:Mn (19.28%) (2f), PMA:Fe (8.98%) (2g), PMA:Co (44.95%). ) (2h), and the ratio of Mo(V) calculated by fitting is shown in parentheses. FIG. 3 shows the XPS measurement results of the coating ink prepared in Example 1. In FIG. 3, PMA:Ni (7.04%) (3a), PMA:Cu (9.96%) (3b), PMA:Zn (44.91%) (3c), PMA:Mo (44.98). %) (3d), PMA:Ag (6.12%) (3e), PMA:Sn (7.85%) (3f), PMA:Sb (11.69%) (3g), PMA:W(10 0.88%) (3 h), and the ratio in the parentheses of Mo(V) calculated by fitting is shown.

FIG. 4 shows an element configuration according to an embodiment of the present invention.

FIG. 5 shows the current density-voltage characteristics of the device. FIG. 6 shows a tandem element structure according to an embodiment of the present invention. FIG. 7 shows current density-voltage characteristics (7a), luminance-voltage characteristics (7b), power efficiency-current density characteristics (7c), and current efficiency-current density characteristics (7d) of the tandem element. FIG. 8 shows external quantum efficiency-luminance characteristics (8a), EL spectrum (8b), external quantum efficiency-current density characteristics (8c) before and after light distribution correction, and external quantum efficiency-current density after light distribution correction of the tandem element. A characteristic (8d) is shown.

[Coating ink]
The coating ink of the present invention contains a metal-doped heteropolyoxometalate, and an ink solvent, and an element constituting the metal-doped heteropolyoxometallate, and only an element constituting the ink solvent. It is characterized by consisting of. That is, the coating ink of the present invention is composed only of a metal-doped heteropolyoxometalate and an ink solvent.

Oxo metallate is also called polyacid, and is a molecular metal oxide composed of transition metal ions (Mo ⁶⁺ , W ⁶⁺ , V ^5+, etc.) and oxide ions (O ²⁻ ). The structure of oxometallates is endless. Oxometallates containing other metals and elements (P, Si, etc.) in addition to the transition metal ions are called heteropolyoxometalates.
The hetero polyoxometalate, phosphomolybdic acid _{(H 3 [PMo 12 O 40} ]), silicomolybdic acid _{(H 4 [SiMo 12 O 40} ]), phosphotungstic acid _{(H 3 [PW 12 O 40} ]), Kay Examples thereof include tungstic acid (H ₄ [SiW ₁₂ O ₄₀ ]) and phosphorus tungstomolybdic acid (H ₃ [PW ₆ Mo ₆ O ₄₀ ]). Of these, phosphomolybdic acid (H ₃ [PMo ₁₂ O ₄₀ ]) having the following structural formula is preferable in terms of solubility, stability, and easy availability. The heteropolyoxometallate may be synthesized by a conventionally known method, or a commercially available product may be obtained.

Phosphomolybdic acid has a structure called Keggin type, and since it has phosphoric acid, it exhibits excellent solubility in a polar solvent and can be formed by coating. In addition, since molybdenum (Mo) in phosphomolybdic acid is oxidized to the maximum oxidation number of 6 ^+, it shows high oxidizing power.

In the present invention, the heteropolyoxometallate is reduced by doping the heteropolyoxometalate with a metal. In the case of phosphomolybdic acid, by doping with a metal, electrons move from the metal to Mo and Mo is reduced. Specifically, Mo in phosphomolybdic acid (H ₃ [PMo ₁₂ O ₄₀ ]) is reduced from hexavalent to pentavalent.

Here, in semiconductors and insulators, the Fermi level (Ef) exists in the band gap (Eg) of the forbidden band between the conduction band and the valence band, and the valence electrons are given energy exceeding the band gap. And conduction electrons are obtained by exciting from the valence band to the conduction band. In the present invention, by doping the heteropolyoxometalate with a metal, a new level is formed in the band gap (Eg) of the forbidden band between the conduction band and the valence band, and the undoped heteropolyoxometalate is formed. Excitation from the valence electrons into the conduction band is more likely to occur than in the case where an energy equivalent to is given. In an electroluminescent device including a charge transfer layer formed by applying an ink containing such a metal-doped heteropolyoxometallate, high mobility can be imparted to both electron and hole carriers, and driving is possible. This will lead to a drop in voltage.

The metal is not limited as long as it can reduce the heteropolyoxometalate, but Mg, Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Sn, Sb or W is preferable. , Co and Sb are more preferred. These metals may be used alone or in combination of two or more.

The ratio (weight ratio) of the heteropolyoxometallate to the metal is usually 80:20 to 99:1, preferably 85:15 to 95:5. When the ratio of the metal is in the above range, the solubility is good, so that the driving voltage of the electroluminescence element can be lowered.

The ink solvent may be any solvent that dissolves the material, and examples thereof include compounds having a nitrile group such as acetonitrile and propanenitrile, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol and Examples thereof include alcohols such as s-butanol, ethers such as tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate, butyl acetate and ethyl cellosolve acetate. Among these, a compound having a nitrile group is preferable, and acetonitrile is more preferable, because the heteropolyoxometallate is easily reduced.
The ratio (weight ratio) of the ink solvent and the metal-doped heteropolyoxometallate is usually 1:1 to 99.9:0.1.

In the present invention, a metal-doped heteropolyoxometallate is applied to the charge generation layer. Metal-doped heteropolyoxometalates are suitable as a substitute material for molybdenum trioxide, which has been conventionally used for the charge generation layer, because they can be formed by coating and do not require high temperature heating during film formation. Can be used.

[Electronic devices and electroluminescent elements]
The electronic device of the present invention includes one or more thin films, at least one of which is a metal-doped heteropolyoxometalate thin film.
Phosphomolybdic acid is preferably used for the heteropolyoxometallate, and the metal-doped phosphomolybdic acid thin film functions as a charge acceptor layer when electric charges are generated inside the device.
The electroluminescent element of the present invention includes a plurality of light emitting units stacked in a tandem shape, and an intermediate layer disposed between two light emitting units of the plurality of light emitting units and electrically connecting the light emitting units. And at least one of the intermediate layers is a charge acceptor layer made of a silver-doped phosphomolybdic acid thin film.

The electroluminescent element is a preferred embodiment of the electronic device of the present invention. Therefore, the electroluminescent element of the present invention will be described.
The electroluminescent element has an anode, a cathode, and at least one thin film layer sandwiched between the anode and the cathode. The thin film layers are a light emitting layer and a charge transfer layer, and the charge transfer layer is a hole injection layer, a hole transport layer, an electron blocking layer, an electron transport layer, an electron injection layer, a hole blocking layer, or the like. Of the hole injection layers, those that receive electrons, such as molybdenum trioxide, are called charge acceptor layers, and the hole transport layer that adjoins them is called charge donor layer. It is called a charge generation layer.

The element structure of the electroluminescent element includes (1) anode/light-emitting layer/cathode, (2) anode/light-emitting layer/electron transport layer/cathode, (3) anode/hole-transport layer/light-emitting layer/cathode, ( 4) Anode/hole transport layer/light emitting layer/electron transport layer/cathode, (5) Anode/hole transport layer/light emitting layer/electron transport layer/electron injection layer/cathode, (6) Anode/hole injection layer /Hole transport layer/light emitting layer/electron transport layer/cathode, (7) anode/hole injection layer/hole transport layer/(electron blocking layer/)light emitting layer/(hole blocking layer/)electron transport layer/ Examples include an electron injection layer/cathode. However, it is not limited to these element configurations. Further, the charge transfer layer may be composed of a plurality of layers.

The electroluminescent element of the present invention may be a tandem type element in which a plurality of light emitting layers and an intermediate layer are laminated in series. The intermediate layer is a charge generation layer. The tandem element can have higher performance in accordance with the number of light emitting units (leu), and can produce high brightness with less current compared to the non-tandem element.
A typical device configuration of the tandem structure is anode/first light emitting unit/charge transfer layer/second light emitting unit/charge transfer layer/third light emitting unit/cathode. The first light emitting unit, the second light emitting unit and the third light emitting unit may be the same or different. Further, for example, the two light emitting layers may be the same and the remaining one may be different.

Next, the constituent material of each layer will be described.
<Anode 1>
In the case of a bottom emission type electroluminescence element, an electrode having light transmittance is used for the anode 1. Examples of the anode 1 include thin films of metal oxides, metal sulfides, or metals having high electric conductivity. Specifically, indium oxide, zinc oxide, tin oxide, indium tin oxide (ITO), Examples of the thin film include indium zinc oxide (IZO), gold, platinum, silver, copper, and the like. Further, an organic transparent conductive film such as polyaniline or its derivative, or polythiophene or its derivative may be used as the anode 1.
In the case of a top emission type electroluminescence element, a material that reflects light may be used for the anode 2, and examples of such a material include a metal having a work function of 3.0 eV or more, a metal oxide, and a metal sulfide. preferable.

<Hole injection layer 2>
The coating ink of the present invention is used as the hole injection material. In addition to the coating ink, other oxides such as vanadium oxide, molybdenum oxide, ruthenium oxide, and aluminum oxide, phenylamine-based, starburst-type amine-based, phthalocyanine-based, amorphous carbon, polyaniline, and poly(3,4- A polythiophene derivative such as ethylenedioxythiophene) (PEDOT:PSS) may be used.

<Hole transport layer 3>
Examples of the hole transport material include poly(9,9-dioctylfluorene-alto-N-(4-butylphenyl)diphenylamine) (TFB) and 4,4′-cyclohexylidenebis[N,N-bis( 4-Methylphenyl)benzenamine] (TAPC), N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (TPD), N,N'-di(1-naphthyl)-N,N '-Diphenylbenzidine (α-NPD), (4,4',4'' tri-9-carbazolyltriphenylamine (TCTA)) and (4,4',4'' tris[phenyl(m-tolyl) Amino]triphenylamine)) and the like. Of these, poly(9,9-dioctylfluorene-alto-N-(4-butylphenyl)diphenylamine) (TFB) is preferable from the viewpoint of coating film formation and improvement of life.

<Light emitting layer 4>
In the light emitting layer 4, it is preferable to use a host compound together with a light emitting material, as in the case of other light emitting layers used in an electroluminescence element. Examples of the light emitting material include bis[2-(4-n-hexylphenyl)quinoline](acetylacetonate)iridium(III)(HexIr(phq) ₃ ) and tris(2-phenylpyridinato)iridium(III). )(Ir(ppy) ₃ ), bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)(FIrpic), tris[1-phenylisoquinoline-C2,N]iridium. (III)(Ir(piq) ₃ ), (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) 10,10'-(4. 4′-sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine)) (DMAC-DPS) and the like. Examples of the host compound include ICTRZ-1, bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO), 3,6-bis(diphenylphophoryl)-9-phenylcarbazole (PO9), 4, 4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), 3,3'-bis(N-carbazolyl)-1,1'-biphenyl (mCBP), tris(4-carbazoyl-9-) Ilphenyl)amine (TCTA), 2,8-bis(diphenylphosphoryl)dibenzothiophene (PPT), adamantane anthracene (Ad-Ant), rubrene, and 2,2′-bi(9,10-diphenylanthracene)( TPBA) and the like.

<Electron injection layer 5>
Examples of the electron injection material include cesium carbonate (Cs ₂ CO ₃ ); zinc oxide (ZnO); polyethyleneimine derivative (PEIE); sodium 8-quinolinolato (Naq), lithium 8-hydroxyquinolinolato (Liq), lithium. Alkali metal salts such as lithium phenolate salts such as 2-(2-pyridyl)phenolate (Lipp) and lithium 2-(2′,2″-bipyridin-6′-yl)phenolate (Libpp) are known. ing. Of these, Liq is particularly suitable as a coating type electron injecting material because it is stable in the atmosphere and can lower the voltage and increase the efficiency than Cs ₂ CO _{3 which} cannot be exposed to the atmosphere. These known electron injection materials may be added to the electron injection layer 5 used in the present invention in a desired amount.

<Charge generation layer 6>
The charge generation layer 6 is a charge donor layer and a charge acceptor layer. The same material as the hole transport layer 3 can be used as the material of the charge donor layer. On the other hand, the charge acceptor layer includes metal oxides such as hexaazatriphenylene carbonitril (HAT-CN), tungsten trioxide, molybdenum trioxide, heteropolyoxometalates such as phosphomolybdic acid, silicomolybdic acid, and the like of the present invention. Examples include metal-doped heteropolyoxometalates.

<Cathode 9>
A metal electrode of Al is generally used for the cathode 9, but other metal such as silver may be used. This metal electrode is formed by a vapor deposition method or a coating method. In addition, for example, a thin film made of a conductive resin such as PEDOT:PSS and a thin film made of a resin and a conductive filler are used.
In the case of a thin film composed of a resin and a conductive filler, a conductive resin can be used as the resin, and fine metal particles, a conductive wire or the like can be used as the conductive filler. Au, Ag, Al, Cu, C, etc. can be used for a conductive filler.

The electroluminescent element is formed by sequentially laminating the constituent materials of the layers. Each layer is laminated by a vacuum vapor deposition method or a coating method. When the vacuum vapor deposition method is used, the vapor deposition is usually heated in an atmosphere reduced to 10 ⁻³ Pa or less. When the coating method is used, the constituent material of each layer is dissolved in, for example, chloroform, methylene chloride, dichloroethane, tetrahydrofuran, toluene, xylene, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, ethyl cellosolve acetate, water, or the like, and publicly known coating Each layer is formed by the method. Examples of the coating method include a bar coating method, a capillary coating method, a slit coating method, an ink jet method, a spray coating method, a nozzle coating method, and a printing method. The same coating method may be used for forming each layer, or an optimal coating method may be used individually depending on the type of ink.

In the case of using the coating method, a supporting substrate having an anode 1 formed on its surface in advance is prepared, and an ink containing a hole injecting material is applied and formed on the supporting substrate to form a hole injecting layer 2. An ink containing a hole transport material is applied and formed into a film to form the hole transport layer 3. Next, an ink containing a material to be the light emitting layer 4 is applied on the hole transport layer 3 to form a film, and after forming the light emitting layer 4, an ink containing an electron injection material is applied to form a film. 5′ is formed, an ink containing a charge acceptor material is applied and formed on the electron injection layer 5, a charge generating layer 6 is formed, and an ink containing a charge donor material is applied and formed on the charge generating layer 6, The charge generation layer 6'is formed. Further, an ink containing a material to be the light emitting layer 7 is applied and formed on the charge generation layer 6′ to form the light emitting layer 7, and then an ink containing an electron injection material is applied and formed to form the electron injection layers 8 and 8′. Then, an ink containing a cathode material is applied on the electron injection layer 8 to form a cathode 9 to form an electroluminescence element. The cathode 9 is formed by applying an ink containing a cathode material to form a film, or by transferring a conductive thin film that becomes the cathode 9. The cathode 9 may be formed by a so-called laminating method or a vapor deposition method instead of the coating film forming method. The anode 1 may be formed by a sputtering method, an ion plating method, a plating method, or the like.

The thickness of each layer varies depending on the type of layer and the material used, but is usually about 100 nm for the anode 1 and the cathode 9 and less than 50 nm for the other layers including the light emitting layer 4. The electron injection layer 5 and the like may be formed with a thickness of 1 nm or less, for example.

The electroluminescent element of the present invention may be formed by, for example, a roll-to-roll method instead of forming each layer by a single-wafer method.

The above-mentioned manufacturing process of the electroluminescence element can be performed in the atmosphere, for example, in a clean room. In addition, you may perform the said manufacturing process in inert gas atmosphere as needed.

Hereinafter, the present invention will be described more specifically based on Examples, but the present invention is not limited to the following Examples.
[Example 1] Preparation of coating ink For phosphomolybdic acid (PMA), 14 kinds of metals (Mg, Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ag, Sn, Sb) were used. Alternatively, W) was added to each so as to have a concentration of 10 wt% and then dissolved in acetoniryl to prepare a coating ink having a concentration of 30 mg/mL.
[Example 2] Preparation of coating ink A coating ink was prepared in the same manner as in Example 1 except that 1-butanol was used in place of acetonitrile.

[Comparative Example 1]
Phosphomolybdic acid (PMA) was dissolved in acetonitrile to prepare an ink having a concentration of 10 mg/mL.
[Comparative Example 2]
A coating ink was prepared in the same manner as in Comparative Example 1 except that 1-butanol was used instead of acetonitrile.

[Example 3] Evaluation of coating ink A thin film having a thickness of 30 nm was formed using the coating inks obtained in Example 2 and Comparative Example 2, and XPS (X-ray photoelectron spectroscopy) measurement was performed. , Mo was found to be reduced from hexavalent to pentavalent. The darker the color, the higher the degree of reduction, and the Zn-doped solution reduced about 45%. Further, the degree of color change was different between the acetonitrile solution and the 1-butanol solution, and the color was more strongly changed in the acetonitrile solution.
In Table 1, “Baked PMA” is a sample in which a thin film was formed by baking at 200° C. after applying the solution.
The results are shown in FIGS.

Table 1 shows the color (%) of each sample and Mo(V).

[Example 4] Application to electroluminescence element An electroluminescence element was produced using the coating ink obtained in Example 2 and the ink of Comparative Example 2.
The structure of the device is shown below (FIG. 4). The HIL (hole injection layer) has a PMA film (no bake), a PMA film (bake at 200° C.), and a PMA: 10 wt% (Mg, Al, Ti, Mn, Fe, Co, Ni, Cu, Zn). , Mo, Ag, Sn, Sb or W) were formed. The film thickness (nm) is shown in parentheses.
ITO (130) / HIL (10 ) / NPD (30) / CBP: 8wt% Ir (ppy) 3 (30) / BAlq 2 (10) / Alq 3 (40) / Liq (1) / Al (100)

The results of the current density-voltage characteristics of the device are shown in FIG. When the hole injecting layer is formed by using the coating ink containing Mn, Co, Cu, Zn, Mo or Sb (the circled portion 1 in FIG. 5), among the circled portions 1, It was driven at a lower voltage than the heat-reduced PMA represented by a black square. In the case of the ink reacted in butanol, the ink reduced with another metal (circled portion 2 in FIG. 5) was driven at a higher voltage than the heat-reduced PMA.

[Example 4] Application to electroluminescence element A tandem element was produced using the coating ink containing phosphomolybdic acid reduced with Ag in Example 2.
The device structure is shown below. LEU represents a light emitting unit.
1st-LEU
Element 1: ITO/PEDOT:PSS/TFB/ICTRZ-1:12 wt% Hex-Ir(phq) ₃ /ZnO/PEIE/Al

2nd-LEU
Element 2: ITO/PMA/TFB/ICTRZ-1: 12 wt% Hex-Ir(phq) ₃ /ZnO/PEIE/Al
Element 3: ITO/PMA:Ag/TFB/ICTRZ-1:12 wt% Hex-Ir(phq) ₃ /ZnO/PEIE/Al

Tandem Element 4: ITO/PEDOT:PSS/TFB/ICTRZ-1:12 wt% Hex-Ir(phq) ₃ /ZnO/PEIE/PMA/TFB/ICTRZ-1:12 wt% Hex-Ir(phq). ₃ /ZnO/PEIE/Al
Element 5: ITO/PEDOT:PSS/TFB/ICTRZ-1:12 wt% Hex-Ir(phq) ₃ /ZnO/PEIE/PMA:Ag/TFB/ICTRZ-1:12 wt% Hex-Ir(phq) ₃ /ZnO /PEIE/Al

The structural formulas of the materials used are as follows.

The elements 1 to 4 were formed by applying the following solutions.
Hole injection layer PEDOT:PSS 60 wt% aqueous solution electron injection layer ZnO 5 mg/ml methanol solution light emitting layer ICTRZ-1:12 wt% Hex-Ir(phq) ₃
10 mg/ml THF solution Electron injection layer PEIE 4 mg/ml 2-propanol solution Charge generation layer PMA 10 mg/ml acetonitrile solution Charge generation layer PMA: Ag 10 mg/ml acetonitrile solution
(Film formation after stirring for 2 hours)
Charge generation layer TFB 7mg/ml p-xylene solution

The results are shown in FIGS. The tandem type element has a lower driving voltage and higher efficiency than the conventional electroluminescent element.

DESCRIPTION OF SYMBOLS 1 anode 2 hole injection layer 3 hole transport layer 4 light emitting layer 5, 5′ electron injection layer 6, 6′ charge generation layer 7 light emitting layer 8, 8′ electron injection layer 9 cathode

Claims (9)

A coating ink containing a metal-doped heteropolyoxometallate, and an ink solvent,
The coating ink, wherein the elements contained in the coating ink consist only of the elements constituting the metal-doped heteropolyoxometallate and the elements constituting the ink solvent. The coating ink according to claim 1, wherein the heteropolyoxometallate is phosphomolybdic acid. The coating ink according to claim 1 or 2, wherein the ink solvent is a compound having a nitrile group. The coating according to any one of claims 1 to 3, wherein the metal is one of magnesium, aluminum, titanium, manganese, cobalt, nickel, copper, zinc, molybdenum, silver, tin, antimony, and tungsten. Ink. An electronic device comprising a thin film of one or more layers, comprising:
An electronic device, wherein at least one of the thin films is a heteropolyoxometalate thin film doped with a metal. The electronic device according to claim 5, wherein the heteropolyoxometallate is phosphomolybdic acid. The electronic device according to claim 5, wherein the metal-doped phosphomolybdic acid thin film functions as a charge acceptor layer when electric charges are generated inside the element. The electronic device according to claim 5, wherein the metal is one of magnesium, aluminum, titanium, manganese, cobalt, nickel, copper, zinc, molybdenum, silver, tin, antimony, and tungsten. .. A plurality of light emitting units stacked in tandem,
Among the plurality of light emitting units, an electroluminescent element, which is disposed between two light emitting units and has an intermediate layer that electrically connects the light emitting units,
At least one of the intermediate layers is a charge acceptor layer formed of a silver-doped phosphomolybdic acid thin film, wherein the electroluminescent element is characterized.