JP7691884B2 - Electronic device, organic electroluminescence device, display device, and lighting device - Google Patents

Description

The present invention relates to an electronic device, and an organic electroluminescence (hereinafter, electroluminescence (field emission) may be abbreviated as "EL") device, display device, and lighting device that use the electronic device.

In recent years, there has been active research and development into display devices and lighting devices that use organic electroluminescence elements (hereinafter sometimes abbreviated as "organic EL elements"), which utilize the light emitted when an electric field is applied to organic materials, and their widespread use is progressing rapidly. In addition, in recent years, in order to further improve their performance, there has been active development of organic-inorganic hybrid elements that use inorganic materials with lower resistance than organic materials as the charge transport layer. Among these, there has been particularly active development of metal oxide conductive films formed by solution processing.

In general, in order to obtain good characteristics in an organic EL element, it is necessary to properly control the optical interference inside the element, and for this purpose, a charge transport layer with a thickness of several tens of nm or more is required. However, with the exception of some transparent conductive films, general metal oxides absorb light in the visible light range, so when a thick metal oxide layer is provided inside an organic EL element, the light emitted by the recombination of charges is absorbed by the metal oxide layer, reducing the luminous efficiency. Therefore, there is a problem that it is difficult to obtain high luminous efficiency when using a metal oxide in a thick film of several tens of nm or more. Moreover, this problem is not limited to organic EL elements, but can be said to be a general problem in electronic elements such as organic solar cells (especially optical elements).

Phosphotungstic acid (PWA), which is made of phosphoric acid and tungsten trioxide, is known as a colorless and transparent metal oxide in the visible light region that can be used in solution processes. The tungsten trioxide contained in this PWA has high electrical resistance, but once an electric current is passed through it, the tungsten is reduced and the electrical resistance decreases. However, when tungsten is reduced in this PWA, it enters a mixed valence state, which causes the PWA to be colored blue, which is a problem.

On the other hand, in the case of tin-doped indium oxide (ITO), which is well known as a transparent conductive film formed by a dry process, the metal valence is controlled by changing conditions such as the oxygen partial pressure during sputtering film formation, achieving high transparency in the visible light region (Non-Patent Document 1).

"Transparent Conductive Film Technology", Ohmsha Publishing

As mentioned above, in the case of tin-doped indium oxide (ITO), the metal valence can be controlled by changing conditions such as the oxygen partial pressure during sputtering deposition, but it is difficult to control the metal valence in a solution process. Therefore, the challenge is to develop an electronic device that can be deposited by a solution process and has a charge transport layer that contains metal oxide and yet has both high conductivity and high transparency in the visible light range.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide an electronic device having a charge transport layer that contains a metal oxide and has both high electrical conductivity and high transparency in the visible light region.
Another object of the present invention is to provide an organic EL element, a display device, and a lighting device that use such an electronic element.

The gist of the present invention, which solves the above problems, is as follows:

The electronic device of the present invention is an electronic device comprising an anode, a cathode, and a charge transport layer located between the anode and the cathode,
the charge transport layer comprises a metal oxide and a compound having a higher reducing ability than the metal oxide,
The content of the compound having a higher reducing ability than the metal oxide is 10 parts by mass or less per 100 parts by mass of the metal oxide.
The electronic device of the present invention contains a metal oxide and yet is capable of achieving both high electrical conductivity and high transparency in the visible light region.

In a preferred embodiment of the electronic device of the present invention, the metal oxide is phosphotungstic acid represented by the formula: H ₃ PW ₁₂ O _40. In this case, the transparency of the charge transport layer in the visible light region is further improved, and the smoothness of the charge transport layer is also improved.

In another preferred embodiment of the electronic device of the present invention, the compound having a higher reducing ability than the metal oxide is at least one selected from the group consisting of molybdic acid, copper(I) iodide, and dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN). In this case, the transparency of the charge transport layer can be maintained at a high level.

The organic electroluminescent element of the present invention comprises the electronic element described above and a light-emitting layer, and is characterized in that the light-emitting layer is located between the anode and the cathode. Such an organic electroluminescent element of the present invention has high light-emitting efficiency.

The display device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a display device of the present invention has high luminous efficiency.

The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a lighting device of the present invention has high luminous efficiency.

According to the present invention, it is possible to provide an electronic device having a charge transport layer that contains a metal oxide and has both high electrical conductivity and high transparency in the visible light region.
Furthermore, according to the present invention, it is possible to provide an organic EL element, a display device, and a lighting device using such an electronic element.

The absorption spectrum of a thin film of PWA and the absorption spectrum of a thin film containing PWA and HAT-CN, formed by adding 0.5 parts by mass, 1 part by mass, 3 parts by mass, or 10 parts by mass of HAT-CN to 100 parts by mass of PWA. The absorption spectrum of a thin film of PWA and the absorption spectrum of a thin film containing PWA and PMA, formed by adding 0.5 parts by mass, 1 part by mass, 3 parts by mass, or 10 parts by mass of PMA to 100 parts by mass of PWA. 1 shows the absorption spectrum of a thin film of PWA, and the absorption spectrum of a thin film containing PWA and CuI, formed by adding 0.5 parts by mass, 1 part by mass, or 3 parts by mass of CuI to 100 parts by mass of PWA. 1 is an XPS spectrum of W4f of a thin film of PWA. 1 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of HAT-CN to 100 parts by mass of PWA. 1 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of PMA to 100 parts by mass of PWA. 1 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of CuI to 100 parts by mass of PWA. FIG. 2 is a schematic cross-sectional view for explaining an example of an electronic element according to the present embodiment. 1 is a graph showing the difference in absorption spectrum before and after voltage application of a device having a charge transport layer made of PWA (Comparative Example 1-1). 1 is a graph showing the difference in absorption spectrum before and after voltage application for elements (Examples 1-1 to 1-4) having a charge transport layer containing PWA and HAT-CN. 1 is a graph showing the difference in absorption spectrum before and after voltage application for elements (Examples 1-5 to 1-8) having a charge transport layer containing PWA and PMA. 1 is a graph showing the difference in absorption spectrum before and after voltage application for elements (Examples 1-9 to 1-11) having a charge transport layer containing PWA and CuI.

The electronic device, organic electroluminescence device, display device, and lighting device of the present invention will be described in detail below with reference to their embodiments.

<Electronic elements>
The electronic device of the present invention includes an anode, a cathode, and a charge transport layer located between the anode and the cathode, and is characterized in that the charge transport layer contains a metal oxide and a compound having a higher reducing ability than the metal oxide, and the content of the compound having a higher reducing ability than the metal oxide is 10 parts by mass or less per 100 parts by mass of the metal oxide.

In the electronic device of the present invention, the charge transport layer contains a metal oxide and a compound more reducible than the metal oxide, and when a current flows, the compound more reducible than the metal oxide is reduced, thereby suppressing the reduction of the metal oxide. By suppressing the reduction of the metal oxide, coloring of the charge transport layer can be prevented and high transparency in the visible light region can be maintained. In addition, in the electronic device of the present invention, the content of the compound more reducible than the metal oxide is small, at 10 parts by mass or less relative to 100 parts by mass of the metal oxide, so that the effect on electrical conductivity properties is small.
Therefore, the charge transport layer of the electronic device of the present invention can achieve both high electrical conductivity and high transparency in the visible light region while containing a metal oxide.

Here, in the present invention, the "reducibility" of a compound that is more reducible than a metal oxide is determined by XPS. Specifically, a compound that, when added to a metal oxide, has the effect of lowering the spectral intensity on the low binding energy side after a current is applied is considered to be a compound that is more reducible than a metal oxide. As an example, when the metal oxide is a metal oxide that contains tungsten (W), the "reducibility" of a compound that is more reducible than a metal oxide can be evaluated by measuring the XPS spectrum of W4f.

で表されるジピラジノ［２，３－ｆ：２’，３’－ｈ］キノキサリン－２，３，６，７，１０，１１－ヘキサカルボニトリル（ＨＡＴ－ＣＮ）、リンモリブデン酸（ＰＭＡ）、ヨウ化銅（Ｉ）（ＣｕＩ）が特に好ましい。 The compound having a higher reducing ability than the metal oxide (hereinafter, sometimes referred to as a "coloring inhibitor") is preferably one having a low light absorption in the visible light region, and is represented by the following structural formula:

Dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) represented by the following formula: phosphomolybdic acid (PMA) and copper(I) iodide (CuI) are particularly preferred.

Next, as an example of the charge transport layer of the electronic device of the present invention, a thin film containing phosphotungstic acid (PWA) as a metal oxide and dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), phosphomolybdic acid (PMA), or copper(I) iodide (CuI) as a compound (coloration inhibitor) with higher reducing properties than metal oxides will be described in detail.

FIG. 1 shows the absorption spectrum of a thin film of phosphotungstic acid (PWA) and the absorption spectrum of a thin film containing phosphotungstic acid (PWA) and HAT-CN, and formed by adding 0.5 parts by mass, 1 part by mass, 3 parts by mass, or 10 parts by mass of HAT-CN to 100 parts by mass of PWA.
FIG. 2 shows the absorption spectrum of a thin film of phosphotungstic acid (PWA) and the absorption spectrum of a thin film containing phosphotungstic acid (PWA) and phosphomolybdic acid (PMA) formed by adding 0.5 parts by mass, 1 part by mass, 3 parts by mass, or 10 parts by mass of PMA to 100 parts by mass of PWA.
FIG. 3 shows the absorption spectrum of a thin film of phosphotungstic acid (PWA) and the absorption spectrum of a thin film containing phosphotungstic acid (PWA) and CuI, and formed by adding 0.5 parts by mass, 1 part by mass, or 3 parts by mass of CuI to 100 parts by mass of PWA.

Figures 1 to 3 show that when the metal oxide is phosphotungstic acid (PWA), the addition of HAT-CN, PMA, or CuI does not increase absorption in the visible light region.

In order to suppress coloration when an electronic device having a charge transport layer containing phosphotungstic acid (PWA) is driven, the additive (coloration inhibitor) must be more easily reduced than PWA, and this ease of reduction can be evaluated by measuring the XPS spectrum of W4f, as described above.

FIG. 4 is an XPS spectrum of W4f of a thin film of phosphotungstic acid (PWA).
FIG. 5 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of HAT-CN to 100 parts by mass of phosphotungstic acid (PWA).
FIG. 6 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of PMA to 100 parts by mass of phosphotungstic acid (PWA).
FIG. 7 shows an XPS spectrum of W4f of a thin film formed by adding 3 parts by mass of CuI to 100 parts by mass of phosphotungstic acid (PWA).

The XPS spectrum of the thin film of PWA shown in Figure 4 shows that the intensity of the shoulder on the low binding energy side is greater than that of the XPS spectra of the thin films formed by adding HAT-CN, PMA, or CuI to PWA shown in Figures 5 to 7. Here, the part on the low binding energy side represents the presence of tungsten, which has a smaller valence. Peak separation was performed, and the abundance ratio of the valence of W is summarized in Table 1.

As can be seen from Table 1, in the PWA thin film (without additives), 89.0% of the tungsten (W) has a valence of 6, and the remaining 11% has a lower valence.
On the other hand, in the thin film in which HAT-CN was added to PWA, 95.5% of the tungsten (W) had a valence of 6, in the thin film in which PMA was added to PWA, 93.3% of the tungsten (W) had a valence of 6, and in the thin film in which CuI was added to PWA, 90.8% of the tungsten (W) had a valence of 6. In either case, the proportion of tungsten (W) with a high valence is greater than that of the thin film of PWA (without additives), and it is found that it is oxidized. Therefore, it can be seen that HAT-CN, PMA, and CuI all have the ability to oxidize PWA (the ability to suppress the reduction of PWA). In addition, from this, it can be seen that when PWA is reduced, HAT-CN, PMA, and CuI are reduced instead.
In the present invention, by adding a compound having a higher reducing ability than the metal oxide as a discoloration inhibitor to the metal oxide, not limited to HAT-CN, PMA, or CuI, the reduction of the metal oxide can be suppressed and discoloration of the metal oxide can be prevented.

Next, one embodiment of the electronic element of the present invention will be described in detail with reference to the drawings. Figure 8 is a schematic cross-sectional view illustrating an example of the electronic element of this embodiment.

In the electronic element 1 of this embodiment shown in FIG. 8, an electrode 20 (cathode 20 in FIG. 8) that serves as an anode or cathode is provided on a substrate 10. In addition, in the electronic element 1 shown in FIG. 8, a charge transport layer 30 made of a metal oxide to which a coloring inhibitor has been added, and a functional layer 40 are laminated in that order on top of the electrode 20 (cathode 20 in FIG. 8), and finally an electrode 50 (anode 50 in FIG. 2) that serves as the opposing electrode of the electrode 20 is laminated. Here, the functional layer 40 may or may not be present.

(Substrate 10)
The substrate 10 is made of a material such as glass, resin, etc., and can be appropriately used. The material of the substrate 10 can be made of one type alone or a combination of two or more types.
Examples of glass materials used for the substrate 10 include quartz glass and soda glass.
On the other hand, examples of the resin material used for the substrate 10 include polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, etc. When a resin material is used as the material for the substrate 10, an electronic device 1 having excellent flexibility can be obtained.
The average thickness of the substrate 10 is not particularly limited, but is preferably 0.1 to 30 mm, and more preferably 0.1 to 10 mm.

(electrode 20)
For the electrode 20, an electrode material generally used in electronic devices can be suitably used.
For example, a highly conductive transparent electrode made of ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), InSnZnO (indium zinc tin oxide, ITZO), In ₃ O ₃ , SnO ₂ , Sb-containing SnO ₂ , Al-containing ZnO, or the like, or an electrode having high reflectivity and high conductivity made of aluminum, silver, or the like can be appropriately used.
The average thickness of the electrode 20 (cathode 20 in FIG. 2) is not particularly limited, but is preferably 10 to 500 nm, and more preferably 50 to 200 nm.

(Charge transport layer 30)
The material for the charge transport layer 30 is the above-mentioned metal oxide to which a compound (coloring inhibitor) having a higher reducing ability than the metal oxide has been added.

--Metal oxides--
The metal oxide is preferably a polyoxometalate, more preferably a heteropolyoxometalate, which is a compound having a structure in which a heteroatom (P5 ⁺ , Si4 ⁺ , Ge4 ⁺ , Bi3 ⁺ , etc.) is at the center and polyatoms (W6 ⁺ , Mo6 ⁺ , V5 ⁺ , etc.) are coordinated to the heteroatom via oxygen, and structures such as Keggin type and Dawson type are known.

As the polyoxometalate, acids such as phosphotungstic acid (PWA), phosphomolybdic acid (PMA), silicotungstic acid (SWA), and the like, as well as the sodium salts of these acids, such as the sodium salt of PWA (PWA-Na) and the sodium salt of PMA (PMA-Na), can be used.
The polyoxometalate has high solubility in a solvent, and can be dissolved in a solvent to form an ink, which can be applied to form a film to easily form a charge transport layer having a thickness of several hundred nanometers. The film thus formed preferably has a smooth surface.

The metal oxide is preferably phosphotungstic acid (PWA) represented by the formula: H ₃ PW ₁₂ O _40. Phosphotungstic acid (PWA) has particularly high solubility in solvents and high transparency in the visible light region. Furthermore, when phosphotungstic acid (PWA) is used to form a charge transport layer, the smoothness of the film (charge transport layer) formed is improved. Note that, since the smoothness of the film produced varies depending on the concentration of impurities, it is preferable to appropriately select and use raw materials that provide a smoother film.

The content of metal oxide in the charge transport layer 30 is preferably 90% by mass or more, more preferably 95% by mass or more, and is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99% by mass or less.

--Compounds with higher reducing properties than metal oxides--
The compound having a higher reducing ability than the metal oxide is selected according to the metal oxide to be used, and may be any compound capable of accepting electrons in place of the metal oxide when a current is passed through the electronic device. Here, the "reducibility" of the compound is determined by XPS. The compound having a higher reducing ability than the metal oxide suppresses coloration caused by the reduction of the metal oxide, and acts as a so-called coloration inhibitor.

Examples of compounds having a higher reducing ability than the metal oxides include polyoxometalates such as molybdic acid, copper(I) iodide, and electron-accepting organic compounds such as dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), as well as compounds used as materials for the hole injection layer and charge-accepting layer in the charge generation layer of general organic EL devices. Here, molybdic acid is a compound containing an oxoanion of molybdenum, and the molybdic acid also includes polyoxometalates such as phosphomolybdic acid (PMA).
In addition, when molybdic acid, copper(I) iodide, or HAT-CN is used as a compound having a higher reducing ability than a metal oxide, the effect of suppressing the reduction of the metal oxide is high, and the coloring of the metal oxide is further suppressed, thereby enabling the transparency of the charge transport layer to be maintained at a high level.

In addition, as a compound having a higher reducing ability than the metal oxide, a compound having a high solubility in a polar solvent such as alcohol, acetonitrile, or ester in which the metal oxide dissolves is preferred. Specifically, a compound having a higher reducing ability than the metal oxide is preferably soluble in an amount of 20 mg or more per mL of solvent.

The content of the compound (coloring inhibitor) having a higher reducing property than the metal oxide is 10 parts by mass or less relative to 100 parts by mass of the metal oxide. When the content of the compound having a higher reducing property than the metal oxide is 10 parts by mass or less relative to 100 parts by mass of the metal oxide, the effect on the electrical conductivity properties of the charge transport layer 30 is small, and high electrical conductivity can be maintained.
The content of the compound (coloring inhibitor) having higher reducing ability than the metal oxide is preferably high as long as it does not significantly inhibit the electrical conductivity of the metal oxide. If the content of the compound (coloring inhibitor) having higher reducing ability than the metal oxide is low, the effect of preventing coloring of the metal oxide is small. Specifically, the content of the compound having higher reducing ability than the metal oxide is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the metal oxide. In particular, the content of the compound (coloring inhibitor) having higher reducing ability than the metal oxide is preferably in the range of 1 part by mass or more and 3 parts by mass or less.

The thickness (average thickness) of the charge transport layer 30 is preferably 100 nm or more, more preferably 120 nm or more. The upper limit of the thickness (average thickness) of the charge transport layer 30 is not particularly limited, but is preferably 1000 nm or less, more preferably 500 nm or less, from the viewpoint of the balance between effect and cost.
Here, the thickness (average thickness) of the charge transport layer 30 can be measured by a non-contact optical film thickness measuring device such as a spectroscopic ellipsometry method or a non-contact surface shape measuring device.

(Functional Layer 40)
The electronic element of the present invention may or may not have a functional layer 40, but for example, in the electronic element of the present invention, a layer constituting an organic EL element can be used as a functional layer as described later. In addition, the electronic element of the present invention can also be used in diode elements and solar cell elements composed of inorganic materials other than organic EL elements.

(electrode 50)
If the functional layer 40 is present, the electrode 50 should be able to smoothly exchange charges with the material constituting the functional layer 40. If the functional layer 40 is not present, the electrode 50 should be able to smoothly exchange charges with the material constituting the charge transport layer 30, and a metal material such as aluminum is preferred.
The average thickness of the electrode 50 (anode 50 in FIG. 2) is not particularly limited, but is preferably 10 to 500 nm, and more preferably 50 to 200 nm.

(Formation method)
In the electronic device 1 shown in FIG. 8 , the method for forming all the layers is not particularly limited, and examples of the method that can be used include gas phase film formation methods such as chemical vapor deposition (CVD) methods such as plasma CVD, thermal CVD, and laser CVD, dry plating methods such as vacuum deposition, sputtering, and ion plating, and thermal spraying methods, liquid phase film formation methods such as wet plating methods such as electrolytic plating, immersion plating, and electroless plating, the sol-gel method, the MOD method, the spray pyrolysis method, a doctor blade method using a fine particle dispersion, and printing techniques such as a spin coating method, an inkjet method, and a screen printing method. An appropriate method can be selected and used depending on the material.
It is preferable to select these methods depending on the characteristics of the material of each layer, and the manufacturing method may differ for each layer.

<Electroluminescence element>
The above-mentioned functional layer 40 can be a part of a light-emitting element such as an organic EL element or a quantum dot EL element.
In an EL element having a forward structure, a carrier transport mechanism in which charges are generated inside the EL element and the generated electrons are received by the charge transport layer 30 is preferable.
On the other hand, in an EL element having an inverted structure, a carrier transport mechanism is provided in which electrons are injected and transported from the cathode to the charge transport layer 30, and then injected into the functional layer 40. In order to facilitate the injection of electrons from the charge transport layer 30 to the functional layer 40, it is preferable to insert a layer made of a material having a low work function between the charge transport layer 30 and the functional layer 40. Examples of such materials include metals such as aluminum and silver, and transparent conductive films such as ITO. In order to suppress light absorption and electron conduction in the surface direction of the device, when a metal is used, it is preferable to use a layer made of a material having a low work function with a thickness of 3 nm or less.

<Organic electroluminescence element>
The organic electroluminescence device of the present invention comprises the above-mentioned electronic device and a light-emitting layer, the light-emitting layer being located between the anode and the cathode.
The organic electroluminescence device of the present invention has high luminous efficiency since it includes the electronic element that achieves both high electrical conductivity and high transparency in the visible light region.

The organic EL element according to one embodiment of the present invention is a so-called inverted organic EL element having a cathode on a substrate, and the above-mentioned charge transport layer is provided on the cathode. Here, the charge transport layer contains the above-mentioned metal oxide and a compound having a higher reducing property than the metal oxide. In addition, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, an anode, etc. can be provided in this order on the upper side of the charge transport layer (the opposite side of the substrate).
The configuration of the organic EL element of the present invention is not limited to this example, and it is sufficient that at least one light-emitting layer is included between the cathode and the anode, and the embodiment of the organic EL element of the present invention is not limited to this example.

<Display device>
The display device of the present invention is characterized by comprising the organic electroluminescence element described above.Since the display device of the present invention comprises the organic electroluminescence element described above, it has high luminous efficiency.
The display device can be formed by forming the organic EL element of the present invention on a layer above a TFT circuit or the like that is generally used to drive an organic EL display.

<Lighting equipment>
The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above.Since the lighting device of the present invention comprises the organic electroluminescence element described above, the lighting device has high luminous efficiency.
The lighting device can be formed by incorporating the organic EL element of the present invention into a lighting fixture generally used for organic EL lighting.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(Comparative Example 1-1 and Examples 1-1 to 1-11)
Electronic devices 1 of Comparative Example 1-1 and Examples 1-1 to 1-11 were manufactured as follows.
The structure of the manufactured electronic device 1 is as shown in Fig. 8. However, the manufactured electronic device 1 does not have a functional layer 40.

A glass substrate with ITO having a width of 15 mm and a thickness of 150 nm was washed, then subjected to UV ozone treatment, and moved into a glove box filled with nitrogen. An acetonitrile solution of phosphotungstic acid (PWA) (Comparative Example 1-1) adjusted to a predetermined concentration so as to obtain a film thickness of 173 nm was added to the solution.
A solution (Example 1-1) in which 0.5 parts by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA),
A solution in which 1 part by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 1-2);
A solution in which 3 parts by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 1-3);
A solution in which 10 parts by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 1-4);
A solution (Example 1-5) in which 0.5 parts by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA);
A solution (Example 1-6) in which 1 part by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA),
A solution (Example 1-7) in which 3 parts by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA);
A solution (Example 1-8) in which 10 parts by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA),
A solution (Example 1-9) in which 0.5 parts by mass of copper iodide (CuI) was added to 100 parts by mass of phosphotungstic acid (PWA);
A solution (Example 1-10) in which 1 part by mass of copper iodide (CuI) was added to 100 parts by mass of phosphotungstic acid (PWA);
A solution (Example 1-11) in which 3 parts by mass of copper iodide (CuI) was added to 100 parts by mass of phosphotungstic acid (PWA) was prepared.

Each solution was dropped onto a substrate fixed on the spin stage of a spin coater, and spun at 5000 rpm for 180 seconds to form a charge transport layer without the addition of a coloring inhibitor (Comparative Example 1-1) and a charge transport layer with the addition of a coloring inhibitor (Examples 1-1 to 1-11). At this time, the parts not to be coated were covered with a mask, and the mask was removed after coating. Next, a heat treatment was performed at 150°C for 10 minutes under nitrogen to remove the solvent.
Next, the substrate was transferred into a vacuum chamber, and an anode film of 12 nm in thickness was formed by vapor deposition of Al having a width of 10 mm at a film formation rate of 1 to 10 Å/sec.
Next, the substrate was taken out of the vacuum chamber into a glove box filled with nitrogen, and the element was covered with a glass tube coated with a UV-curable adhesive and irradiated with UV light to seal the hollow. The area of the fabricated element was 150 ^mm2 .

<Measurement results for verification: Evaluation of coloring>
The thickness of the Al film of the fabricated element is as thin as 12 nm, and it is possible to evaluate the absorption spectrum because it transmits part of the visible light. In addition, the element area is 10 mm x 15 mm, which is sufficiently larger than the shape of the light used in general absorption spectrum measurement.
First, the ITO electrode of the element was used as the cathode and Al as the anode, and a power source was connected, and the absorption spectrum of the element was measured without applying voltage.
Next, a voltage was applied to the element. The voltage was gradually increased from 0 V to allow current to flow, and was increased up to 7 V. After holding at 7 V for 1 minute, the application of the voltage was stopped. The absorption spectrum of the element was measured again. The difference in the absorption spectra before and after the application of the voltage is shown in Figures 9 to 12, and the difference in absorbance at 685 nm and 480 nm is shown in Tables 2 and 3.

Figures 9 to 12 and Tables 2 and 3 show that in all elements to which a coloring inhibitor was added (Examples 1-1 to 1-11), coloring was suppressed after a voltage was applied to the element to drive it, compared to the element containing only PWA (Comparative Example 1-1). This is because the coloring inhibitor received electrons instead of PWA, suppressing the reduction of tungsten in the PWA.

(Comparative Example 2-1 and Examples 2-1 to 2-6)
The electronic devices 1 of Comparative Example 2-1 and Examples 2-1 to 2-6 were manufactured as follows.
The structure of the manufactured electronic device 1 is as shown in Fig. 8. However, the manufactured electronic device 1 does not have a functional layer 40.

A glass substrate with an ITO film having a width of 3 mm and a thickness of 150 nm was washed, then subjected to UV ozone treatment, and moved into a glove box filled with nitrogen. An acetonitrile solution of phosphotungstic acid (PWA) (Comparative Example 2-1) adjusted to a predetermined concentration so as to obtain a film thickness of 173 nm was added to the solution.
A solution in which 1 part by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 2-1);
A solution in which 3 parts by mass of HAT-CN was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 2-2);
A solution in which 1 part by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA) (Example 2-3);
A solution (Example 2-4) in which 3 parts by mass of phosphomolybdic acid (PMA) was added to 100 parts by mass of phosphotungstic acid (PWA),
A solution (Example 2-5) in which 1 part by mass of copper iodide (CuI) was added to 100 parts by mass of phosphotungstic acid (PWA);
A solution (Example 2-6) in which 3 parts by mass of copper iodide (CuI) was added to 100 parts by mass of phosphotungstic acid (PWA) was prepared.

Each solution was dropped onto a substrate fixed on the spin stage of a spin coater, and spun at 5000 rpm for 180 seconds to form a charge transport layer without the addition of a coloring inhibitor (Comparative Example 2-1) and a charge transport layer with the addition of a coloring inhibitor (Examples 2-1 to 2-6). At this time, the parts not to be coated were covered with a mask, and the mask was removed after coating. Next, a heat treatment was performed at 150°C for 10 minutes under nitrogen to remove the solvent.
Next, the substrate was transferred into a vacuum chamber, and an electrode having a thickness of 100 nm was formed by vapor deposition of Al having a width of 3 mm at a film formation rate of 1 to 10 Å/sec.
Next, the substrate was taken out of the vacuum chamber into a glove box filled with nitrogen, and a desiccant was attached to a glass tube coated with a UV-curable adhesive, after which the element was covered and irradiated with UV light to seal the hollow. The area of the fabricated element was 9 ^mm2 .

<Measurement results for verification: Evaluation of current density-voltage characteristics>
For each element, first, the characteristics of the element with a normal structure in which ITO was the anode and Al was the cathode were evaluated. The voltage was gradually increased from 0 V, and the current density-voltage characteristics were evaluated. The current density was increased to 22.2 mA/ ^cm2 and held at the same current density for 10 seconds. Then, the current density-voltage measurement was evaluated a second time. The voltage at ^2.5 mA/cm2 is summarized in Table 4.

Next, using measurement points different from those described above, the characteristics of an element with an inverted structure in which ITO was used as the cathode and Al was used as the anode were evaluated in the same manner as described above. The voltage at ^2.5 mA/cm2 is summarized in Table 4.

As can be seen from Table 4, the element to which no coloring inhibitor was added (Comparative Example 2-1) was driven at 0.3 V. All three elements to which 1 part by mass of coloring inhibitor was added (Examples 2-1, 2-3, and 2-5) had almost the same drive voltage of 0.3 V. The elements to which 3 parts by mass of coloring inhibitor were added (Examples 2-2, 2-4, and 2-6) had a slightly higher drive voltage, but the increase in drive voltage was sufficiently small. This shows that the addition of a coloring inhibitor can suppress coloration while suppressing deterioration of electrical characteristics.

The electronic element of the present invention has a charge transport layer that contains a metal oxide but has both high electrical conductivity and high transparency in the visible light region. By applying this to an organic EL element, it is possible to improve the luminous efficiency while driving it at a low voltage. Furthermore, by incorporating such an organic EL element into a display device or lighting device, it is possible to improve the luminous efficiency of the display device or lighting device.

1: Electronic element 10: Substrate 20: Electrode (cathode)
30: Charge transport layer 40: Functional layer 50: Electrode (anode)

Claims (5)

1. An electronic device comprising an anode, a cathode, and a charge transport layer located between the anode and the cathode,
the charge transport layer comprises a metal oxide and a compound having a higher reducing ability than the metal oxide,
The content of the compound having a higher reducing ability than the metal oxide is 3 parts by mass or less per 100 parts by mass of the metal oxide,
An electronic device, wherein the metal oxide is phosphotungstic acid represented by the formula: H ₃ PW ₁₂ O _40. 2. The electronic device according to claim 1, wherein the compound having a higher reducing ability than the metal oxide is at least one selected from the group consisting of molybdic acid, copper (I) iodide, and dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT- CN ). An electronic device comprising the electronic device according to claim 1 or 2 and a light-emitting layer,
The organic electroluminescence element, wherein the light-emitting layer is located between the anode and the cathode. A display device comprising the organic electroluminescence element according to claim 3 . A lighting device comprising the organic electroluminescence element according to claim 3 .

Images