JP5018951B2 - electrode - Google Patents

Description

  The present invention relates to an electrode.

  For example, an organic electroluminescence element (hereinafter referred to as “organic EL element”) is mainly composed of an anode composed of a transparent electrode, a cathode, and holes placed between these electrodes, and holes injected from the anode and electrons injected from the cathode. The transparent electrode generally has a film made of indium-tin oxide (hereinafter referred to as “ITO”) on a transparent substrate. In such an organic EL element, it is desirable to improve the hole injection efficiency from the ITO film of the transparent electrode to the light emitting layer. For that purpose, it is desirable that the work function of the ITO film surface is higher. Has been.

  Conventionally, for example, those disclosed in the following Patent Documents 1 to 3 are known as transparent electrodes having such an ITO film. Patent Document 1 discloses a transparent electrode having a high work function on the surface of a transparent conductive part manufactured by exposing a transparent conductive part provided on a transparent substrate to a gas containing active oxygen. No. 2 discloses a transparent electrode having a high work function on the surface of a transparent conductive part, which is manufactured by implanting plasma-ized oxygen ions into a transparent conductive part provided on a transparent substrate.

Patent Document 3 discloses a method for forming an ITO film on a glass substrate by an ion plating method using an ITO sintered body having a SnO ₂ content of 4 to 6% by mass. .

JP 2001-284059 A JP 2001-284060 A Japanese Patent No. 2002-83893

  However, although all of the transparent electrodes described in Patent Documents 1 to 3 can increase the work function, they have the following problems.

  That is, the transparent electrodes described in Patent Documents 1 and 2 have a problem that the manufacturing cost increases because they are manufactured using a special plasma generator or an ion source.

  Moreover, since the transparent electrode described in Patent Document 3 is manufactured by an ion plating apparatus that requires a large vacuum vessel, the vacuum vessel such as a sputtering method cannot be downsized or inlined, and the running cost increases. There was a problem that the manufacturing cost was high.

  This invention is made | formed in view of the said situation, and it aims at providing the electrode which can fully enlarge the work function of the metal oxide electroconductive part surface at low cost.

  As a result of intensive studies to achieve the above object, the inventors of the present invention have a first conductive part containing a metal oxide on a substrate and a difference between the first conductive part on the first conductive part. It has been found that the above-described problems can be solved by making the second conductive part including a metal oxide and the second conductive part have a specific configuration, and the present invention has been completed.

That is, the present invention provides a first conductive part including a first metal oxide on a substrate and a second conductive part including a second metal oxide different from the first metal oxide on the first conductive part. The thickness of the second conductive part is 15 nm or less, the first metal oxide is tin-added indium oxide, and the second metal oxide is fluorine-added tin oxide. It is an electrode characterized in that the above can be solved.

  According to the above electrode, since it is not necessary to use oxygen ions or active oxygen or to use an ion plating method, the manufacturing cost can be reduced. In addition, the ionization potential of the second conductive portion of the electrode can be made sufficiently larger than the ionization potential of the first conductive portion or the second conductive portion when each electrode is disposed on the substrate. That is, the ionization potential on the surface of the conductive part can be sufficiently increased at low cost. Moreover, according to the electrode which concerns on this invention, the electrode stabilized in the state with the high ionization potential of the 2nd electroconductive part of an electrode irrespective of the use environment of an electrode can be obtained. In the present specification, the concept of “ionization potential” includes “work function”.

  According to the electrode of the present invention, in the configuration of the electrode, the ionization potential of the second conductive part of the electrode is sufficiently higher than the ionization potential of the first conductive part or the second conductive part in the case where they are individually arranged on the substrate. Can be bigger. For this reason, since it is not necessary to use oxygen ions or active oxygen or to use an ion plating method, the manufacturing cost can be reduced. In addition, the ionization potential of the second conductive portion of the electrode is stabilized in a high state regardless of the use environment of the electrode.

It is sectional drawing which shows roughly one Embodiment of the electrode of this invention. It is a top view which shows roughly the surface state of the conduction part of an electrode. It is a series of process diagrams showing an embodiment of a method for manufacturing an electrode. It is a figure which shows the surface state of the electroconductive part by SEM about the electrode which concerns on Example 1. FIG. It is a figure which shows the surface state of the electroconductive part by SEM about the electrode which concerns on Example 2. FIG. It is a figure which shows the surface state of the electroconductive part by SEM about the electrode which concerns on the reference example 3. FIG. It is a figure which shows the surface state of the electroconductive part by SEM about the electrode which concerns on the comparative example 13. FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a cross-sectional view schematically showing an embodiment of the electrode of the present invention, and FIG. 2 is a view showing a state where the surface of the electrode on the conductive part side is observed with an SEM. As shown in FIG. 1, the electrode 10 includes a substrate 2, a first conductive portion 4 disposed on the substrate 2, and a second conductive portion 6 disposed on the first conductive portion 4. .

  Further, as shown in FIG. 2, the second conductive portion 6 has a plurality of island-shaped portions 8 made of the second metal oxide. The island portions 8 are formed on the particles 7 made of the first metal oxide constituting the first conductive portion 4. The particles 7 are formed on the substrate 2 (not shown), and the particles are in close contact with each other.

  Here, the thickness of the second conductive portion 6 is 30 nm or less.

  According to such an electrode 10, it is stabilized in a state where the ionization potential of the second electrode portion 6 is high regardless of the use environment. In other words, even if it is placed in a strict reducing atmosphere or oxidizing atmosphere, the lowering of the second conductive portion 6 of the electrode is sufficiently prevented.

  The substrate 2 is not particularly limited as long as it can be used as a substrate for the electrode and the first conductive portion and the second conductive portion can be formed on the substrate.

  When the electrode 10 is an electrode transparent to the wavelength of light to be transmitted (hereinafter referred to as “transparent electrode”), the substrate 2, the first conductive unit, and the second conductive unit are configured to transmit the wavelength of light to be transmitted. Must be transparent.

  As the transparent electrode substrate 2, for example, a transparent glass substrate, a glass substrate whose surface is appropriately roughened to prevent light reflection, a polished glass-like translucent glass substrate, or the like that transmits light is the substrate 2. As one of the constituent materials. In this case, the material may not be glass as long as it transmits light, and may be a transparent plastic or a transparent crystal. The substrate 2 is not particularly limited as long as it is transparent to the wavelength of light to be transmitted.

  The first metal oxide and the second metal oxide for the transparent electrode have high light transmissivity in the visible region and low electrical resistivity, so that indium, tin, zinc, gallium, lead, cadmium are used. The main component is preferred. For example, tin-doped indium oxide, germanium-doped indium oxide, molybdenum-doped indium oxide, iron-doped indium oxide, titanium-doped indium oxide, zirconium-doped indium oxide, hafnium-doped indium oxide, niobium-doped indium oxide, tantalum-doped indium oxide, tungsten-doped oxide Indium, tellurium added indium oxide, fluorine added tin oxide, antimony added tin oxide, niobium added tin oxide, tantalum added tin oxide, aluminum added zinc oxide, gallium added zinc oxide, bismuth added zinc oxide, indium added zinc oxide, yttrium added oxide Zinc, scandium added zinc oxide, iron added zinc oxide, vanadium added zinc oxide, silicon added zinc oxide, germanium added zinc oxide, titanium added zinc oxide, zirconium Addition zinc oxide, hafnium addition zinc oxide, tin addition gallium oxide, bismuth addition lead oxide, indium addition cadmium oxide, tin addition cadmium oxide, zinc-tin oxide, indium-tin oxide, zinc-indium oxide, tin-zinc -Indium oxide, etc.

  Next, an embodiment of the electrode 10 shown in FIG. 1 will be described with reference to FIGS. 3A to 3C are a series of process diagrams for manufacturing the electrode 10. In the present embodiment, the case where the electrode 10 is a transparent electrode will be described. A case where the first metal oxide is tin-added indium oxide and the second metal oxide is fluorine-added tin oxide will be described.

  First, the substrate 2 is prepared (see FIG. 3A). Then, as shown in FIG. 3B, the first conductive portion 4 made of tin-added indium oxide is formed on the surface of the substrate 2.

  The first conductive portion 4 can be formed using, for example, a spray pyrolysis film forming method. The spray pyrolysis film-forming method sprays a tin-added indium oxide forming raw material (hereinafter referred to as “ITO film forming raw material”) on the surface of the substrate 2 while heating the substrate 2. Thereby, the material which comprises the raw material for ITO film formation is decomposed | disassembled on the surface of the board | substrate 2. FIG. At this time, a special atmosphere such as a vacuum is not required. Thus, the first conductive portion 4 made of tin-added indium oxide is formed on the surface of the substrate 2.

The raw material for forming the ITO film can be composed of an indium-containing compound, a tin-containing compound, and a solvent for dissolving them. Examples of indium-containing compounds include indium chloride, indium nitrate, indium hydroxide, indium acetate, indium acetylacetonate, 2-ethylhexaneindium, and indium isopropoxide. Examples of tin-containing compounds include tin chloride. , Tin hydroxide, tin acetate, tetrabutyltin, tin acetylacetonate, dibutyltin diacetate, 2-ethylhexanetin, tin octylate, tin ethoxide, tin isopropoxide, tin isobutoxide and the like. The solvent is not particularly limited as long as it is a liquid that can dissolve the indium-containing compound and the tin-containing compound. For example, ethanol, methanol, propanol, butanol, methoxyethanol, acetone, hexane, benzene, toluene, water, or these two Combinations of more than one species can be used.

  Moreover, the temperature of the board | substrate 2 at this time should just be a temperature which can decompose | disassemble and oxidize an indium containing compound and a tin containing compound, for example, should just be 200-700 degreeC.

  Subsequently, as shown in FIG. 3C, the second conductive portion 6 made of the second metal oxide is formed on the surface of the first conductive portion 4. At this time, the thickness of the second conductive portion 6 is set to 30 nm or less. Similarly to the case of forming the first conductive portion 4, the second conductive portion 6 can be formed using a spray pyrolysis film forming method.

  In the spray pyrolysis film forming method, a fluorine-added tin oxide forming raw material (hereinafter referred to as “FTO film forming raw material”) is sprayed on the surface of the substrate 2 while heating the substrate 2. Thereby, the material constituting the raw material for forming the FTO film is decomposed on the surface of the first conductive portion 4. At this time, a special atmosphere such as a vacuum is not required. Thus, the second conductive portion 6 made of fluorine-added tin oxide is formed on the surface of the first conductive portion 4.

  The raw material for forming the FTO film can be composed of a fluorine-containing compound, a tin-containing compound, and a solvent for dissolving them. Examples of the fluorine-containing compound include ammonium fluoride and hydrofluoric acid. Examples of the tin-containing compound include tin chloride, tin hydroxide, tin acetate, tetrabutyltin, tin acetylacetonate, dibutyltin diacetate, and 2-ethyl. Examples include hexane tin, tin octylate, tin ethoxide, tin isopropoxide, and tin isobutoxide. The solvent is not particularly limited as long as it is a liquid that can dissolve the fluorine-containing compound and the tin-containing compound. For example, ethanol, methanol, propanol, butanol, methoxyethanol, water, or a combination of two or more thereof may be used. Can do. The formation of the second conductive portion 6 is performed by repeatedly spraying the FTO film material. To reduce the thickness of the second conductive portion 6 to 30 nm or less, the amount of spray per spray or the number of sprays should be adjusted. That's fine.

  Moreover, the temperature of the board | substrate 2 at this time should just be a temperature which can decompose | disassemble and oxidize a fluorine-containing compound and a tin-containing compound, for example, should just be 200-700 degreeC.

  In this way, the electrode 10 shown in FIG. 3C is obtained.

  Further, it may be preferable to perform a reduction treatment after the electrode 10 is formed. Due to the reduction treatment, the electrical resistivity of the obtained electrode 10 may decrease, or the ionization potential of the second conductive portion of the electrode 10 may increase. Specifically, when the first metal oxide is tin-added indium oxide and the second metal oxide is fluorine-added tin oxide, the electrical resistivity of the electrode is reduced, and the ionization potential of the second conductive portion is large. Become. Specifically, the reduction treatment can be performed by heating in a reducing atmosphere. The reducing atmosphere can be formed by, for example, hydrogen gas, carbon monoxide gas, nitrogen gas, rare gas, or a mixed gas thereof. Moreover, what is necessary is just to let heating temperature be 100-800 degreeC, for example.

  When the electrode 10 is formed as described above, the ionization potential of the second conductive portion 6 of the electrode 10 is sufficiently higher than the ionization potential of the first conductive portion or the second conductive portion when each electrode is disposed on the substrate 2 alone. Can be large. In addition, since it is not necessary to use oxygen ions or active oxygen or use an ion plating method, the manufacturing cost can be reduced. That is, the ionization potential on the surface of the conductive portion of the electrode 10 can be sufficiently increased at low cost. Furthermore, since the phenomenon in which the ionization potential of the second conductive portion 6 of the electrode 10 increases is caused by the configuration of the conductive portion of the electrode 10, the second conductive portion of the electrode 10 regardless of the usage environment of the electrode 10. 6 is stable while the ionization potential remains high.

  Such an electrode 10 has a sufficiently large ionization potential of the second conductive part. Therefore, among the electrodes 10, in particular, in the case of a transparent electrode that is transparent with respect to a necessary light wavelength, for example, organic It can utilize for the transparent electrode as an anode of EL element, and the transparent electrode of a compound solar cell. Moreover, since the electrode 10 can be manufactured at low cost by the above forming method, the cost of the organic EL element and the compound solar cell can be reduced.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, in the second conductive portion 6, the thickness of the second conductive portion 6 is 30 nm or less and the second conductive portion 6 is composed of a plurality of island-shaped portions. The 2 conductive part 6 should just satisfy | fill either the requirements that the thickness of the said 2nd conductive part 6 is 30 nm or less, and the 2nd conductive part is comprised from the several island-shaped part.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
An electrode having the same configuration as that of the electrode 10 shown in FIG. 1 was produced by the following procedure.

  First, on a glass substrate transparent to visible light (thickness: about 1 mm, 26 mm × 50 mm) as a substrate, a spray-pyrolysis deposition method is used to form tin-added indium oxide (hereinafter “ITO”). And a fluorine-added tin oxide (hereinafter referred to as “FTO”) part to form a conductive part transparent to visible light. As a glass substrate, a Corning # 7059 glass flat plate was used.

  At this time, the ITO part and the FTO part were formed as follows.

  When forming the ITO part, a raw material for ITO film made of indium chloride, tin chloride and ethanol was prepared. The raw material for the ITO film was adjusted so that the molar ratio of indium atoms and tin atoms was 95: 5, and the total number of moles of indium and tin in ethanol was 0.1 mol / L. Then, this ITO film material was sprayed onto the surface of the glass substrate using a spray nozzle having a hole diameter of about 0.1 mm. At this time, the temperature of the glass substrate was set to 320 to 350 ° C., and spraying was performed 200 times intermittently. At this time, the spray time was 0.2 to 0.3 seconds, and the spray interval was about 5 seconds. Thus, an ITO film having a thickness of about 400 nm was formed on the glass substrate.

  When the FTO part was formed, an FTO film material consisting of tin chloride, ammonium fluoride, 2M-hydrochloric acid and ethanol was prepared. The raw material for the FTO film is such that the fluorine atom and the tin atom are in a molar ratio of 1: 2, and the volume ratio of 2M-hydrochloric acid and ethanol is 5:95, and a mixed solvent of ethanol and 2M-hydrochloric acid. It adjusted so that the number-of-moles of tin might become 0.1 mol / L. And this raw material for FTO films | membranes was sprayed on the surface of the ITO part using the spray nozzle with a hole diameter of 0.1 mm. At this time, spraying was performed twice intermittently. The temperature, spray time, and spray interval of the glass substrate were the same as in forming the ITO part. Thus, an FTO portion having a thickness of about 6 nm was formed on the ITO portion.

  Thus, an electrode 10 having a laminated conductive portion formed on the substrate was obtained.

  The electrode thus obtained was observed using a scanning electron microscope (SEM) under conditions of a magnification of 100,000 times and an acceleration voltage of 10 kV. The observation results are shown in FIG. FIG. 4 is a view showing the surface form of the electrode by SEM.

  As shown in FIG. 4, the electrode according to this example has a configuration in which a large number of island-shaped second conductive portions are in contact with a first conductive portion having a structure in which large particles are in close contact. It was confirmed. Here, the average particle diameter of the island-shaped particles of the second conductive portion was about 6 nm.

In addition, it was also confirmed by SEM morphology observation of the cross section of the electrode (not shown) that the thickness of the second conductive portion and the average particle diameter of the island-shaped particles of the second conductive portion determined from the surface morphology were almost the same. . For this reason, the thickness of the second conductive portion was set to 6 nm. The thickness of the first conductive portion was about 400 nm, and this value was obtained from the interference pattern of the spectral transmittance of the electrode, and the certainty was confirmed by morphological observation by SEM of the cross section. The results regarding the thickness are shown in Table 1. In Table 1, the numerical value in parentheses in each column of the first conductive part indicates the thickness of the first conductive part, and the numerical value in parenthesis in each column of the second conductive part is the thickness of the second conductive part. (The same applies to Examples 2 , 4 and 5, Reference Examples 3 and 6, and Comparative Examples 1 to 6).

(Example 2)
An electrode was produced in the same manner as in Example 1 except that the number of sprays of the FTO film forming raw material was set to 5. And about the obtained electrode, it carried out similarly to the Example, and observed the surface form of the electrode. As an observation result, FIG. 5 is a diagram showing the surface morphology of the electrode by SEM.

  From FIG. 5, the electrode according to the present embodiment has a form in which a large number of island-shaped second conductive portions are in contact with a first conductive portion having a structure in which large particles are in close contact. It was confirmed that Here, the thicknesses of the first conductive portion and the second conductive portion were measured in the same manner as in Example 1. The results regarding thickness are shown in Table 1.

( Reference Example 3)
An electrode was produced in the same manner as in Example 1 except that the number of sprays of the FTO film forming raw material was 10 times. And about the obtained electrode, it carried out similarly to the Example, and observed the surface form of the electrode. As an observation result, a diagram showing the surface morphology of the electrode by SEM is shown in FIG.

From FIG. 6, the electrode according to this reference example has a form in which a large number of island-shaped second conductive portions are in contact with a first conductive portion having a structure in which large particles are in close contact. It was confirmed that Here, the thicknesses of the first conductive portion and the second conductive portion were measured in the same manner as in Example 1. The results regarding thickness are shown in Table 1.

(Comparative Example 1)
An electrode was produced in the same manner as in Example 1 except that only the ITO film was formed. And about the obtained electrode, it carried out similarly to the Example, and observed the surface form of the electrode. As an observation result, a diagram showing the surface morphology of the electrode by SEM is shown in FIG. The thickness of the ITO film was measured in the same manner as in Example 1. The results regarding thickness are shown in Table 1.

(Comparative Example 2)
An electrode was produced in the same manner as in Example 1 except that only the FTO film was formed. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the FTO film | membrane. The results regarding thickness are shown in Table 1.

(Comparative Example 3)
An electrode was produced in the same manner as in Example 1 except that the number of sprays of the FTO film forming raw material was 20 times. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the 1st conductive part and the 2nd conductive part. The results regarding thickness are shown in Table 1.

Example 4
The same electrode as in Example 1 was produced, and the obtained electrode was reduced by heat treatment at 600 ° C. for 60 minutes in an atmosphere of a mixed gas of hydrogen gas and nitrogen gas (hydrogen gas 0.2%). And a new electrode was obtained. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the 1st conductive part and the 2nd conductive part. The results regarding thickness are shown in Table 1.

(Example 5)
The same electrode as in Example 2 was produced, and the obtained electrode was subjected to reduction treatment in the same manner as in Example 4 to obtain a new electrode. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the 1st conductive part and the 2nd conductive part. The results regarding thickness are shown in Table 1.

( Reference Example 6)
The same electrode as in Reference Example 3 was produced, and the obtained electrode was subjected to a reduction treatment in the same manner as in Example 4 to obtain a new electrode. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the 1st conductive part and the 2nd conductive part. The results regarding thickness are shown in Table 1.

(Comparative Example 4)
The same electrode as Comparative Example 1 was produced, and the obtained electrode was subjected to reduction treatment in the same manner as in Example 4 to obtain a new electrode. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the ITO film | membrane. The results regarding thickness are shown in Table 1.

(Comparative Example 5)
The same electrode as Comparative Example 2 was produced, and the obtained electrode was subjected to reduction treatment in the same manner as in Example 4 to obtain a new electrode. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the FTO film | membrane. The results regarding thickness are shown in Table 1.

(Comparative Example 6)
The same electrode as Comparative Example 3 was produced, and the obtained electrode was subjected to reduction treatment in the same manner as in Example 4 to obtain a new electrode. And about the obtained electrode, it carried out similarly to Example 1, and measured the thickness of the 1st conductive part and the 2nd conductive part. The results regarding thickness are shown in Table 1.

(Measurement of ionization potential on the surface of the conductive part of the electrode)
For the electrodes obtained in Examples 1 , 2, 4, 5, Reference Examples 3 and 6, and Comparative Examples 1 to 6, the ionization potential on the surface of the conductive part was measured using a photoelectron spectrometer. The results are shown in Table 1.

In Table 1, the electrodes obtained in Examples 1 and 2 and Reference Example 3 are the ionization potential of the conductive part of a single film made only of ITO, which is the first metal oxide obtained in Comparative Example 1, and the comparison. The ionization potential is sufficiently larger than the work function of the conductive portion of the single film made only of FTO, which is the second metal oxide obtained in Example 2. The electrode obtained in Comparative Example 3 does not have a sufficiently large ionization potential because the thickness of the second conductive portion is different from that of the present invention. That is, the electrodes obtained in Examples 1 and 2 can sufficiently increase the ionization potential on the surface of the conductive portion at a low cost by adopting the configuration of the conductive portion of the present invention.

In Table 1, the electrodes obtained in Examples 4 and 5 and Reference Example 6 were subjected to reduction treatment , and the ionization potential was larger than the ionization potential of the conductive part of the electrodes obtained in Examples 1 and 2 and Reference Example 3. have.

Further, in Table 1, the electrodes obtained in Examples 4 and 5 and Reference Example 6 are ionization potentials of conductive parts of a single film made only of ITO, which is the first metal oxide obtained in Comparative Example 4, and The ionization potential is sufficiently larger than the ionization potential of the conductive portion of the single film made only of FTO, which is the second metal oxide obtained in Comparative Example 5. The electrode obtained in Comparative Example 6 does not have a sufficiently large ionization potential because the thickness of the second conductive portion is different from that of the present invention. That is, in the electrodes obtained in Examples 4 and 5 , the ionization potential on the surface of the conductive part can be sufficiently increased at low cost by adopting the structure of the conductive part according to the present invention.

(Measurement of ionization potential after oxidation treatment)
The electrodes obtained in Examples 1 , 2, 4, 5, Reference Examples 3 and 6, and Comparative Examples 1 to 6 were subjected to an oxidation treatment by heat treatment at 450 ° C. for 60 minutes in the air. For these electrodes, the ionization potential on the surface of the conductive portion was measured using a photoelectron spectrometer as in the case before the oxidation treatment. The results are shown in Table 2.

As can be seen from Table 2, even after the oxidation treatment, the electrodes of Examples 1 and 2 and Reference Example 3 have the ionization potential of the conductive part of the single film made only of ITO which is the first metal oxide of Comparative Example 1, And it has an ionization potential sufficiently larger than the ionization potential of the conductive part of the single film made only of FTO which is the second metal oxide of Comparative Example 2. The electrode of Comparative Example 3 does not have a sufficiently large ionization potential because the thickness of the second conductive portion is different from that of the present invention. That is, the ionization potential on the surface of the conductive part of the electrodes of Examples 1 and 2 is sufficiently large and stable even after the oxidation treatment by adopting the structure of the conductive part according to the present invention.

Further, as can be seen from Table 2, even after the oxidation treatment, the electrodes of Examples 4 and 5 and Reference Example 6 are ionized in the conductive part of a single film made only of ITO which is the first metal oxide of Comparative Example 4. The ionization potential is sufficiently larger than the potential and the ionization potential of the conductive portion of the single film made of only FTO which is the second metal oxide of Comparative Example 5. The electrode of Comparative Example 6 does not have a sufficiently large ionization potential because the thickness of the second conductive portion is different from that of the present invention. That is, the ionization potential on the surface of the conductive part of the electrodes of Examples 4 and 5 is sufficiently large and stable even after the oxidation treatment by adopting the structure of the conductive part according to the present invention.

From the results of Examples 1 , 2, 4, 5, Reference Examples 3 and 6 and Comparative Examples 1 to 6, according to the electrode of the present invention, the first conductive part containing the first metal oxide on the substrate is used. A second conductive part including a second metal oxide different from the first metal oxide on the first conductive part, and a thickness of the second conductive part being 15 nm or less, or A first conductive part including a first metal oxide on the substrate; a second conductive part including a second metal oxide different from the first metal oxide on the first conductive part; A structure in which the two conductive portions are formed of a plurality of island-shaped portions, and each of the first metal oxide film constituting the first conductive portion or the second metal oxide constituting the second conductive portion independently on the substrate. It was confirmed that the ionization potential on the surface of the conductive portion when the material film was formed can be made sufficiently larger. Furthermore, according to the electrode of the present invention, it is confirmed that the ionization potential on the surface of the conductive portion can be maintained sufficiently large even by reduction treatment or oxidation treatment, and that the ionization potential of the electrode is stabilized in a high state. did it.

The reason why the effect of the present invention occurs, that is, a first conductive part including a first metal oxide and a second conductive part including a second metal oxide different from the first metal oxide on the first conductive part. The thickness of the second conductive portion is 15 nm or less, or the first conductive portion containing the first metal oxide on the substrate and the first metal on the first conductive portion The ionization potential on the surface of the conductive portion of the electrode having a configuration in which the second conductive portion including a second metal oxide different from the oxide and the second conductive portion is composed of a plurality of island-shaped portions is independently on the substrate, The effect is that the ionization potential of the surface of the conductive part when the first metal oxide film constituting the first conductive part or the second metal oxide film constituting the second conductive part is formed is larger. The reason for this was considered as follows.

  It was considered that the reason why the effect occurs can be explained by using an isotype heterojunction band model having many interface orders such as a double Schottky barrier band model. Here, the isotype means that the main carrier responsible for the electrical conduction of the substances on both sides in contact with the joint surface is the same for both substances. In other words, it means that the main carrier is an electron or a hole in both substances.

  In concretely explaining the reason why the effect is produced using the above model, the first metal oxide shown in “Best Mode for Carrying Out the Invention” in this specification is tin-doped indium oxide (ITO), Consider the case where the second metal oxide is fluorine-added tin oxide (FTO). Here, both ITO and FTO are n-type semiconductors whose main carriers are electrons. However, actually, the phenomenon described below is not limited to the first metal oxide being ITO and the second metal oxide being FTO. The first metal oxide and the second metal oxide are respectively Any metal oxide having the characteristics described below may be used.

The ITO single film of Comparative Example 1 and the FTO single film of Comparative Example 2 each have a high carrier density. In the measurement by the four-probe method using the Hall effect using ReyoTest 8300 manufactured by Toyo Technica, the carrier concentrations of the ITO single film and the FTO single film are 4.7 × 10 ²⁰ cm ⁻³ and 3.0 × 10 ²⁰ cm, respectively. ^-3 . Thus, when the carrier concentration is as high as 1 × 10 ²⁰ cm ⁻³ or more, it is considered that the Fermi level of the ITO single film and the FTO single film is in the conduction band. Therefore, the Fermi levels of the ITO single film and the FTO single film coincide with the maximum levels of the conduction band occupied electrons.

  Next, consider a composite in which ITO and FTO are joined. Since ITO and FTO are not crystallographically matched at the joint surface, there are many interface states at the joint interface between ITO and FTO. These interface states capture electrons.

  When the thickness or particle size of the FTO is 6 nm, that is, in the case of Example 1 or Example 4, the number of electrons in the conduction band of the FTO is essentially extremely small. It is thought that all of the electrons are trapped at the interface state and depleted. For this reason, many interface states capture electrons in the conduction band of ITO. As a result, the number of electrons in the conduction band of ITO is greatly reduced, so the Fermi level in the vicinity of the joint surface of the composite is lowered, and as a result, it is considered to be smaller than the Fermi level of the ITO single film and the FTO single film. It is done. In the case of the electrode of the present invention, since the Fermi level of the composite is measured as the ionization potential of the composite, the ionization potential increases as the Fermi level decreases. Therefore, the ionization potential of Example 1 or Example 4 is increased. Such a phenomenon that produces an effect occurs in the electrode of Example 1 or Example 4 and is considered to exhibit a high ionization potential.

When the thickness or particle size of the FTO increases to 15 or 30 nm, that is, in the case of Example 2 or Reference Example 3 or Example 5 or Reference Example 6, the number of electrons in the conduction band of the FTO essentially increases. However, even when the junction is formed, it is considered that many electrons in the conduction band of the FTO are not depleted even if they are captured by the interface state. In this case, it is considered that the number of electrons in the conduction band of ITO trapped in the interface state relatively decreases. As a result, the number of electrons in the ITO conductor does not decrease so much, so the decrease in Fermi level in the vicinity of the joint surface of the composite is smaller than the Fermi level of the ITO single film and FTO single film. It is thought that it will not be so large. Therefore, although the ionization potential of Example 2 or Reference Example 3 or Example 5 or Reference Example 6 is large, the magnitude is not as large as that of Example 1 or Example 4.

  When the thickness or particle size of the FTO is further increased to 60 nm, that is, in the case of Comparative Example 3 or Comparative Example 6, the number of electrons in the conduction band of the FTO increases and as shown in Table 1 or Table 2. Because the ionization potential of a single FTO is smaller than the ionization potential of a single ITO, in other words, the Fermi level of a single FTO is higher than the Fermi level of a single ITO, so it is trapped at the interface level. The electrons that are generated are thought to be due to electrons in the conduction band of the FTO. In this case, the Fermi level in the vicinity of the joint surface of the composite is considered to be between the Fermi level of a single ITO and the Fermi level of a single FTO. Therefore, the ionization potential of Comparative Example 3 or Comparative Example 6 does not become larger than the ionization potential of the ITO single film, that is, the ionization potential of Comparative Example 1 or Comparative Example 4.

  Since this phenomenon can be considered as described above, the first metal oxide is not limited to ITO, and the second metal oxide is not limited to FTO.

2 ... substrate, 4 ... first conductive part, 6 ... second conductive part, 10 ... electrode.

Claims (5)

A substrate,
A first conductive part disposed on the substrate and made of a first metal oxide;
An electrode comprising a second conductive part disposed on the first conductive part and made of a second metal oxide different from the first metal oxide,
The first metal oxide and the second metal oxide are both n-type semiconductor or p-type semiconductor at the same time;
And the second conductive portion has a thickness of 15 nm or less,
The electrode, wherein the first metal oxide is tin-added indium oxide, and the second metal oxide is fluorine-added tin oxide.   The electrode according to claim 1, wherein the first metal oxide has a light-transmitting property with respect to visible light.   The electrode according to claim 1, wherein the second metal oxide has a light-transmitting property with respect to visible light. 4. The carrier concentration at room temperature of the film composed of the first metal oxide alone or the second metal oxide alone is 1 × 10 ¹⁹ cm ⁻³ or more, 4. The electrode according to one item. Wherein both the first conductive portion and the second conductive portion, the electrode according to any one of claims 1 to 4, characterized in that one formed by a spray pyrolysis deposition method.

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