JP5361612B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a gold cluster-modified metal oxide semiconductor, a photoelectrode using the same, and a photoelectric conversion element including the photoelectrode. More specifically, the present invention relates to a gold cluster-modified metal oxide semiconductor having visible light responsiveness, a photoelectrode using the same, and a photoelectric conversion element including the photoelectrode and having high photoelectric conversion efficiency.

Metal oxide semiconductors such as titanium oxide (TiO ₂ ) and zinc oxide (ZnO) are known as photocatalysts and photoelectric conversion materials. When irradiated with light having energy greater than the band gap, electrons in the valence band Is excited in the conduction band, generating electrons and holes in the conduction band and valence band, respectively. Already applied as photocatalysts and photoelectric conversion materials using the generated electrons and holes, most of them respond only to ultraviolet light.

  In order to impart visible light responsiveness to these metal oxide semiconductors, methods have been proposed in which titanium oxide is doped with metal ions or lattice oxygen is replaced with other elements such as nitrogen, carbon, and sulfur (for example, And Patent Documents 1 to 4).

  Moreover, there exists a dye-sensitized solar cell as a visible light-responsive photoelectric conversion element (for example, refer patent documents 5 and 6). A dye-sensitized solar cell is a photoelectric conversion element using an electrode in which a visible light-responsive dye is adsorbed on an oxide semiconductor such as titanium oxide, and photoelectrons excited in the dye by sunlight are oxide semiconductors. The photoelectrons move through the oxide semiconductor and reach the counter electrode via an external circuit having a load, thereby generating electric energy.

JP 2001-87654 A JP 2005-169216 A JP 2005-177548 A JP 2009-66594 A Japanese Patent No. 2664194 JP 2009-129574 A

The above-described method of doping titanium oxide with metal ions or replacing lattice oxygen with other elements necessitates high-temperature firing in an atmosphere-controlled furnace.
In addition, in dye-sensitized solar cells, the durability (weather resistance, heat resistance, etc.) of the dye used is often insufficient, and the dye is decomposed with photoexcitation of titanium oxide, and its synthesis is costly. Such a problem remains to be solved.

  Under such circumstances, an object of the present invention is to provide a metal oxide semiconductor having visible light responsiveness and usable for a photocatalyst or a photoelectric conversion element, the metal oxide semiconductor, a photoelectrode using the metal oxide semiconductor, and the It is providing the photoelectric conversion element provided with the photoelectrode.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the following inventions meet the above object, and have reached the present invention.

That is, the present invention relates to the following inventions.
<1> A photoelectric conversion element comprising an anode and a cathode arranged via an electrolyte containing an electron donor,
The anode is formed by supporting gold clusters of 15 to 33 mer on the surface of a metal oxide semiconductor, and a layer containing a gold cluster modified metal oxide semiconductor having visible light response is formed on a conductive electrode. A photoelectric conversion element which is a photoelectrode formed.
<2> The photoelectric conversion element according to <1>, wherein the metal oxide semiconductor is titanium oxide.
<3> The photoelectric conversion element according to <1> or <2>, wherein the metal oxide semiconductor has a granular or film-like shape.
<4> The photoelectric conversion element according to any one of < 1 > to <3>, wherein the gold cluster is a 25-mer gold cluster.
<5> The photoelectric conversion element according to any one of <1> to <4>, wherein the gold cluster is coated with a protective agent.
<6> The photoelectric conversion element according to <5>, wherein the protective agent is glutathione.

  The gold cluster-modified metal oxide semiconductor of the present invention has visible light response and exhibits excellent photoelectrochemical reactivity. Therefore, the granular body or film-like body containing the gold cluster-modified metal oxide semiconductor can be used for a photocatalyst or a photoelectric conversion element.

It is a schematic sectional drawing of the photoelectrode of this invention. It is a schematic sectional drawing of the photoelectric conversion element of this invention. It is a figure which shows the electric current-voltage curve of the photoelectric conversion element (Example 4) of this invention. A photocurrent action spectrum of the photoelectric conversion element of the present invention (Example 4), showing the absorption spectra of Au ₂₅ clusters solution.

Hereinafter, the present invention will be described in detail.
The present invention relates to a gold cluster-modified metal oxide semiconductor characterized in that an 8-250 mer gold cluster is supported on the surface of a metal oxide semiconductor and has visible light responsiveness.

  Examples of the metal oxide constituting the metal oxide semiconductor include titanium oxide, zinc oxide, tin oxide, zirconium oxide, hafnium oxide, strontium oxide, indium oxide, yttrium oxide, lanthanum oxide, vanadium oxide, niobium oxide, and tantalum oxide. And mixed oxides or oxide mixtures of these metals such as chromium oxide, molybdenum oxide, tungsten oxide, or strontium titanate. Among these, titanium oxide, zinc oxide, tin oxide, and tungsten oxide are preferable, and titanium oxide is particularly preferable. These metal oxides may be doped with other elements, oxygen deficiency, or metal deficiency from the viewpoint of changing conductivity.

  A feature of the gold cluster-modified metal oxide semiconductor of the present invention is that an 8-250 mer gold cluster is supported on a metal oxide semiconductor.

The gold cluster means an aggregate of gold atoms, and usually refers to an aggregate of gold atoms of about 3 to 500 mer. Hereinafter, x-mer (x is a positive integer) may be referred to as a gold clusters with Au _x clusters.
In the present invention, from the viewpoint of visible light responsiveness, applicable gold clusters are 8-250 mer, preferably 15-33 mer. In particular, it is particularly preferable that the gold cluster is substantially only a 25-mer because the responsiveness to visible light is particularly high.
A gold cluster having such an atom number can be produced by a conventionally known production method as disclosed in, for example, JP-A-2007-45791.

The excitation level of the gold cluster is higher in energy than the conduction band of the metal oxide semiconductor, and charge separation occurs when electrons are injected from the gold cluster into the metal oxide semiconductor by light irradiation. Oxidation reactions and reduction reactions can occur on metal oxide semiconductors. In the present invention, “visible light responsiveness” in a metal oxide semiconductor means that a photoelectromotive force is generated by irradiating visible light, and a photoelectrochemical reaction (including a photocatalytic reaction) proceeds. To do.
Moreover, the metal oxide semiconductor according to the present invention may exhibit photoelectrochemical reactivity with respect to not only visible light but also ultraviolet rays and infrared rays other than visible light.

  The amount (adsorption amount) of the gold cluster supported on the metal oxide semiconductor is not particularly limited, and is appropriately determined depending on the intended use within a range that does not inhibit the reduction reaction in the metal oxide semiconductor. Specifically, it is desirable that the oxide semiconductor surface carry an amount such that the gold cluster becomes a monolayer.

The gold cluster is preferably coated with a protective agent.
Here, the protective agent is a compound that is chemically or physically bonded and adsorbed around the gold cluster, and suppresses and stabilizes the aggregation of the gold cluster.
Since the gold clusters are coated with the protective agent, the aggregation of the gold clusters is suppressed. Therefore, the dispersibility of the gold clusters is increased, and the aggregation is difficult to occur after being adsorbed on the metal oxide semiconductor.
Further, the gold cluster coated with the protective agent has an advantage that a gold cluster with the number of atoms selectively controlled can be obtained by combining with an appropriate separation means.

The protective agent is roughly classified into a physical adsorption protective agent and a chemical adsorption protective agent.
Physiological adsorption protective agent is a compound that can coat gold clusters by van der Waals force or electrostatic interaction. Polyvinyl pyrrolidone, polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polyallylamine hydrochloride, citric acid Etc.
On the other hand, the chemisorption protective agent is a compound that can chemically bond with the gold atom of the gold cluster. Specifically, a thiol compound having a mercapto group (—SH group) is applicable, and a strong chemical bond can be formed through a gold cluster and a sulfur atom, which is preferable.
As such a thiol compound, a thiol compound having a molecular weight of about 100 to 1000 is preferable. Specifically, a mercapto organic acid such as phenylethanethiol, mercaptopropionic acid, 3-mercaptobenzoic acid, (N, N- Examples include mercaptoamines such as (dimethylamino) ethanethiol hydrochloride, amino acids and peptides having mercapto groups such as mercaptopropionylglycine and glutathione (γ-Glu-Cys-Gly). In order to make these thiol compounds water-soluble, they can also be used as salts such as alkali metal salts and hydrochlorides. Among these, a peptide having a mercapto group is preferable, and glutathione is particularly preferable.

The gold cluster-modified metal oxide semiconductor of the present invention itself may have various shapes, and examples thereof include a granular body and a film-like body.
In addition, in this invention, a granular material means a powder and its aggregate, Although there is no restriction | limiting in particular in the particle size and density, Usually, it is about 0.01-500 micrometers.
The granular material may be used as it is, but it is preferably used as a raw material for the film-shaped material by sintering at an appropriate temperature to use as a sintered material or by dispersing in a suitable solvent.
The film-like body is a thin film or a laminate thereof, and the thickness thereof is not particularly limited, but a preferable film thickness when formed on a substrate is about 0.01 to 500 μm.

  In addition, in order to further enhance photocatalytic property and photoresponsiveness, and to give another functionality, these granular materials and film-like materials may contain other components. As other components, other oxides such as silica and alumina, or other inorganic substances, metal fine particles such as platinum, and organic substances such as resins can be used as a binder component and a functional component.

The manufacturing method of the gold cluster modified metal oxide semiconductor of the present invention will be described.
The gold cluster used in the present invention is produced according to a known method and is not particularly limited. A preferred example is a method in which the above-mentioned protective agent is added to an aqueous chloroauric acid solution as necessary, and reduction is performed with a reducing agent such as sodium borohydride in an ice bath. Although the usage-amount of a protective agent is not specifically limited, It is about 0.5-10 mol normally with respect to 1 mol of gold clusters, It is 1-5 mol suitably.
Although the manufacturing method of a gold cluster modified metal oxide semiconductor is not particularly limited, a method of immersing a metal oxide semiconductor of an appropriate shape such as a granular material or a film in a solution in which the manufactured gold cluster is dispersed, or a metal oxide semiconductor The method of dripping the solution containing a gold cluster in is mentioned.
Alternatively, the metal oxide semiconductor may be immersed in a gold cluster precursor solution, and then gold clusters may be deposited.
Note that, from the viewpoint of improving the bondability between the metal oxide semiconductor and the gold cluster, heat treatment may be performed after the gold cluster is supported on the metal oxide semiconductor. The conditions (temperature, atmosphere) for performing the heat treatment are appropriately determined under conditions where the gold clusters do not aggregate.

  The gold cluster-modified metal oxide semiconductor of the present invention can be used as a photoelectric conversion element electrode, an electrochromic display substrate, a pollutant decomposition substrate that can decompose pollutants in the atmosphere using a photocatalytic reaction, and the like.

In particular, the gold cluster-modified metal oxide semiconductor of the present invention can be suitably used for a photoelectrode for a photoelectric conversion element.
As shown in FIG. 1, the photoelectrode 1 of the present invention has a structure in which a conductive electrode 1b and a gold cluster modified metal oxide semiconductor layer 1c are sequentially formed on a substrate 1a. In particular, it is preferable that the substrate 1a and the conductive electrode 1b are both transparent. In such a configuration, the current from the light irradiated from either the substrate 1a side or the gold cluster modified metal oxide semiconductor layer 1c side Can be taken out. In the present invention, “transparent” means that at least a part of visible light passes through the irradiated light.
On the other hand, when only the light irradiated from the gold cluster modified metal oxide semiconductor layer 1c side is used, both the substrate 1a and the conductive electrode 1b do not need to be transparent, and those that are not transparent can also be used.

The substrate 1a is preferably made of a material having high transparency of irradiated light, particularly visible light, and examples thereof include glass, acrylic, polyester, polycarbonate, and the like. From the viewpoint of durability, a glass substrate is preferable. used. Moreover, in order to improve adhesiveness with the conductive electrode 1b, you may use the board | substrate 1a which has an undercoat layer on the surface.
The thickness of the substrate 1a is not particularly limited, but is usually 0.1 to 10 mm, and is appropriately determined in consideration of necessary strength and light transmittance.

The conductive electrode 1b is a conductive electrode made of a conductive oxide or a metal thin film, and is preferably transparent from the viewpoint that light can be irradiated from the substrate 1a side.
Examples of the conductive oxide include tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO). Among these, it is preferable to use ITO because it is transparent and has high conductivity.
Examples of the metal thin film include thin films made of gold, silver, platinum, copper, and alloys thereof, and are manufactured by a vapor deposition method or a sputtering method.
The thickness of the conductive electrode 1b is not particularly limited as long as it has sufficient conductivity, but the preferred thickness is 20 to 1000 nm in the case of a metal oxide, and 5 nm in the case of a metal thin film. ~ 400 nm. The conductive electrode 1b is usually a single layer made of one kind of raw material, but may be a layer made of two or more kinds of raw materials or a plurality of layers.

The gold cluster modified metal oxide semiconductor layer 1c is made of the gold cluster modified metal oxide semiconductor of the present invention, and the preferred film thickness is about 50 to 5000 nm, but it is thicker by mixing a conductive material. You can also
The amount of gold clusters supported on the metal oxide semiconductor when used as a photoelectrode tends to improve the visible light absorption, but if it is too large, it becomes difficult to transfer charges to the metal oxide semiconductor. There is a case. Therefore, the preferable loading amount of the gold cluster is about 1 to 100 gold clusters with respect to 1 nm ² of the film.

  As a preferred example of the method for forming a photoelectrode of the present invention, a dispersion of a metal oxide semiconductor is applied to a substrate 1a provided with a conductive electrode 1b by using a conventionally known method such as spin coating, dip coating, or squeegee method. A film containing the gold cluster was dropped on the thin film made of the metal oxide semiconductor, or a substrate on which the thin film was formed was formed by the method described above and heat-treated at 120 to 800 ° C. in an air atmosphere. What is necessary is just to immerse in the solution containing a gold cluster.

  Hereinafter, a photoelectric conversion element having the photoelectrode of the present invention as an anode (hereinafter referred to as a photoelectric conversion element of the present invention) will be described with reference to the drawings. In addition, the structure shown here is one Embodiment of the photoelectric conversion element using the photoelectrode of this invention as an anode. The photoelectric conversion element of this invention is applicable not only to this form but to any photoelectric conversion element.

A schematic cross-sectional view of the photoelectric conversion element of the present invention is shown in FIG.
The photoelectric conversion element 10 according to the present invention is a so-called sandwich type cell in which an anode 1A as a photoelectrode and a cathode 2 are arranged to face each other with an electrolyte 3 interposed therebetween. The anode 1A is the same as the photoelectrode 1 described above.
The planar shape of the photoelectric conversion element 10 is not particularly limited, and it is preferable that the photoelectric conversion element 10 has a shape such as a square, a rectangle, a rhombus, and a regular hexagon arranged without gaps. As the size, for example, when the planar shape is a square, one side is about 5 mm to 50 cm.

  In the photoelectric conversion element 10 of the present invention, the substrate 1a and the conductive electrode 1b are used, light is irradiated from either the anode 1A side or the cathode 2 side, and light is emitted from the gold cluster modified metal oxide semiconductor layer 1c in the anode 1A. It is absorbed and converted from light energy to electrical energy, a potential difference is generated between the anode 1A and the cathode 2, and the generated electrons are taken out to produce an effect as a photoelectric conversion element.

  Hereinafter, each structure of the photoelectric conversion element 10 which concerns on this invention is demonstrated.

  The anode 1A is made of the photoelectrode of the present invention, and the details thereof are the same as described above, and thus detailed description thereof is omitted here. In the present embodiment, the substrate 1a and the conductive electrode 1b are both transparent, but when light is irradiated from the cathode 2 side (the gold cluster modified metal oxide semiconductor layer 1c side), each is not transparent. You may use anything.

  As the cathode 2, for example, a cathode of a conventional photoelectric conversion element disclosed in JP 2001-35551 A can be used. Specifically, those having a conductive layer formed on the substrate surface are preferably used. Examples of the conductive layer include conductive oxides, metal thin films, carbon, metal-supported carbon, and conductive polymers.

The electrolyte 3 is an electrolytic solution containing a supporting salt and an electron donor, and the form thereof may be a gel as well as a liquid.
Examples of the solvent for the electrolyte 3 include water, acetonitrile, methoxyacetonitrile, propylene carbonate, ethylene carbonate, dimethoxyethane, and mixtures thereof.

  The supporting salt is not particularly limited as long as it provides sufficient conductivity to the electrolytic solution. However, tetrabutylammonium perchlorate, tetraethylammonium perchlorate, lithium perchlorate, lithium tetrafluoroborate, and hexafluoride. Lithium phosphate, sodium sulfate and the like are preferably used. The concentration of the supporting salt in the electrolyte 3 is about 0.1M to a saturated concentration.

  As the electron donor, hydroquinone, catechol, phenol, triethanolamine, ferrocene, lithium iodide, iron (II) sulfate, potassium ferrocyanide are preferably used, the redox potential is appropriate, and the oxidant is stable. In view of this, hydroquinone is particularly preferred. The concentration of the electron donor in the electrolyte 3 is preferably 10 mM to a saturated concentration. When the concentration of the electron donor is 10 mM or more, sufficient photoelectric conversion efficiency is easily obtained.

  In addition, the electrolyte 3 may contain additives such as a crosslinking agent and a thickener as other compounds other than the supporting salt and the electron donor.

  The photoelectric conversion element of the present invention is produced according to a known method. Specifically, the anode 1A and the cathode 2 are arranged so as to face each other while maintaining a predetermined interval. An electrolyte 3 is injected between the anode 1A and the cathode 2 to seal the whole. Thereby, the photoelectric conversion element 10 shown in FIG. 2 can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, unless it exceeds the summary of this invention, it is not limited to a following example.

The gold cluster was synthesized according to the method described in a previous report (J. Am. Chem. Soc. 2005, 127, 5261; Small 2007, 3, 835).
0.25 mmol of tetrachloroauric acid was dissolved in 50 mL of methanol, 1 mmol of glutathione was added, and the mixture was ice-cooled. To this, 12.5 mL of an ice-cooled 0.2M NaBH ₄ aqueous solution was added all at once with vigorous stirring and allowed to react for 1 hour. The resulting precipitate was removed by centrifugation (3000 G, 5 minutes) and washed with methanol (3 times). The precipitate was vacuum-dried at room temperature to obtain Au cluster powder protected by dark brown glutathione.

The size separation of Au clusters was performed by polyacrylamide gel electrophoresis (J. Phys. Chem. B 2006, 110, 12218). 4 mL of 1.5 M Tris-HCl buffer (pH 8.8) was added to 12 mL of 40 wt% monomer aqueous solution in which acrylamide and N, N′-methylenebisacrylamide were mixed at 93: 7, and 100 μL of a polymerization initiator (10% ammonium persulfate) was added. Then, after pouring an aqueous solution containing 10 μL of a polymerization accelerator (N, N, N ′, N′-tetramethylethylenediamine) between two glass plates with a spacer of 1 mm, pure water is gently overlaid and left for several hours. By doing so, a separation gel was prepared. Discard the layered pure water, wash it together with the monomer aqueous solution for the concentrated gel, pour the monomer aqueous solution for the concentrated gel, gently layer the pure water, and let stand for several hours for electrophoresis that separates the separated gel and the concentrated gel A gel was made.
As a monomer aqueous solution for concentrated gel, 5 mL of a 6 wt% monomer aqueous solution in which acrylamide and N, N′-methylenebisacrylamide were mixed at 94: 6, 2.5 mL of 1.5 M Tris-HCl buffer (pH 6.8) and pure water were added. 2.5 mL was added, and a polymerization initiator (10% ammonium persulfate) 50 μL and a polymerization accelerator (N, N, N ′, N′-tetramethylethylenediamine) 10 μL were used.
The sample was gently overlaid on an electrophoresis gel prepared by preparing a sample prepared by dissolving 8 mg of Au cluster in 2 mL of a glycerin-water (5:95 in vol) mixed solvent, and a voltage of 150 V was applied for 9 hours in 192 mM glycine and 25 mM trishydroxymethylamine aqueous solution. Electrophoresis. Each polyacrylamide gel containing Au clusters separated in each size was immersed in pure water for 12 hours to elute the Au clusters. By passing through a filter having a pore diameter of 0.2 μm, 15-mer, 18-mer, 22-mer, 25-mer, 29-mer, and 33-mer Au cluster aqueous solutions from which gel was removed were obtained.

A 25-mer gold cluster (Au ₂₅ cluster) was also produced by the following method according to the method described in the previous report (Small 2007, 3, 835).
4.9 mg of the above Au cluster powder was dissolved in 7 mL of pure water, 130.7 mg of glutathione was added, and the aqueous solution was stirred while bubbling air at 55 ° C. to etch the Au cluster. After 6 hours, the obtained red-brown 25-mer gold cluster (Au ₂₅ cluster) aqueous solution was recovered through a filter having a pore size of 0.2 μm. In order to remove excess glutathione, an Au ₂₅ cluster aqueous solution was placed in a dialysis membrane having a molecular weight cut off of 8000 and dialyzed for 12 hours. The precipitate produced during dialysis was removed with a filter having a pore size of 0.2 μm.

A photoelectrode using titanium oxide as a metal oxide semiconductor was prepared by the following procedure. A slurry obtained by diluting titanium oxide (primary particle size 20 nm, Ishihara Sangyo Co., Ltd., product number: STS-21) three times with pure water is spin-coated on an ITO glass substrate (1500 rpm, 10 sec) and heat-treated at 450 ° C. A titanium oxide thin film having a thickness of about 400 nm was formed on an ITO substrate, and a 15-mer aqueous solution of Au clusters was cast and adsorbed thereto. After leaving still in a dark place for 24 hours, the remaining cast solution was washed away with pure water and then dried to obtain a photoelectrode of Example 1 which is an Au ₁₅ cluster-modified titanium oxide electrode.
In addition, when the pH of the Au cluster aqueous solution was 1 to 6, it was adsorbed well to the titanium oxide electrode.
Further, in the above photoelectrode manufacturing method, by using an 18-mer, 22-mer, 25-mer, 29-mer, or 33-mer Au cluster aqueous solution instead of the 15-mer Au cluster aqueous solution, Example 2 (Au ₁₈ cluster), Example 3 (Au ₂₂ cluster), Example 4 (Au ₂₅ cluster), Example 5 (Au ₂₉ cluster), which are titanium oxide electrodes modified with Au clusters of the number of atoms And the photoelectrode of Example 6 (Au ₃₃ cluster) was obtained.
Further, a photoelectrode of Comparative Example 1 made of a titanium oxide electrode on which no Au cluster was supported was prepared. Furthermore, instead of the Au cluster, the photoelectrode of Example 4 was heat-treated at 500 ° C. in the atmosphere, so that a comparison was made of a titanium oxide electrode on which gold particles with a diameter of about 30 to 100 nm (corresponding to hundreds of thousands of gold atoms) were deposited. The photoelectrode of Example 2 was obtained.

Photoelectrochemical measurement was performed by constructing a sandwich type cell as shown in FIG. The produced photoelectrode (anode) was placed face to face with an ITO electrode (cathode) sputtered with Au (thickness 50 nm) and a spacer (High Milan Film, Mitsui Polydupont Chemical Co., Ltd.) having a thickness of 50 μm. The electrode size was 5 mm × 5 mm. The electrolytic solution was deoxygenated by N ₂ bubbling with 0.1M hydroquinone and 0.1M tetrabutylammonium perchlorate, and then injected through a hole in the counter electrode and sealed. As a light source, a 100 W xenon lamp (LAX-102, Asahi Spectroscopy Co., Ltd.) was used, and white light irradiation or monochromatic light irradiation was performed using an optical filter (SCF-25C-48Y, Sigma Kogyo Co., Ltd.).

FIG. 3 shows a current-voltage curve under irradiation of monochromatic light having a wavelength of 460 nm and a light intensity of 2.6 mW / cm ^{2 in} the photoelectric conversion element (Example 4) of the present invention. A short-circuit photocurrent of 21.5 μA / cm ² and an open-circuit photovoltage of 0.41 V were obtained, and an energy conversion efficiency of 0.078% was obtained.

Further, as shown in FIG. 4, the incident photon-electron conversion efficiency (IPCE) dependence on the irradiation light wavelength (photocurrent action spectrum) in the case of using the photoelectric conversion element of the present invention (Example 4) is Au ₂₅ cluster. It was in good agreement with the absorption spectrum of the aqueous solution. Moreover, since the photoelectric conversion element of the other Example also showed the same tendency, in the photoelectric conversion element of this invention, it was shown that the photocurrent was obtained by the photoexcitation of Au cluster.

Table 1 shows the measurement results of the photoelectric conversion characteristics of the photoelectric conversion elements of Examples 1 to 6. The light irradiation condition is monochromatic light having a wavelength of 460 nm and the light intensity is 2.6 mW / cm ² .
In any of the examples, photocurrent was confirmed, and the 25-mer example 4 showed the largest value.

Table 2 shows the results of the photoelectric conversion characteristics of the photoelectric conversion elements of the present invention (Example 4) and the photoelectric conversion elements of Comparative Examples 1 and 2. The light irradiation condition is white light having a wavelength of 460 to 800 nm and a light intensity of 75 mW / cm ² .
The photoelectric conversion element of Example 4 has a diameter of about 30 to 100 nm (corresponding to hundreds of thousands of gold atoms) instead of the photoelectric conversion element and the gold cluster of Comparative Example 1 including a photoelectrode that does not carry a gold cluster. Compared with the photoelectric conversion element of Comparative Example 2 provided with a photoelectrode carrying gold particles, the photocurrent value was clearly large.

Example 7: Evaluation of photocatalytic activity A sandwich type cell having the same configuration as that of the photoelectric conversion element of Example 4 was prepared except that 0.1 M phenol was used instead of 0.1 M hydroquinone in the electrolytic solution. When white light having a wavelength of 460 to 800 nm and a light intensity of 75 mW / cm ² was irradiated, an oxidation current of 30 μA / cm ² flowed. From this, it was found that phenol can be photocatalyzed by the gold cluster-modified metal oxide semiconductor of the present invention.

  The gold cluster-modified metal oxide semiconductor of the present invention has visible light response and exhibits excellent photoelectrochemical reactivity. Therefore, it can be suitably used as a visible light responsive photocatalyst or a photoelectric conversion element.

1 Photoelectrode 1a Substrate 1b Conductive electrode 1c Gold cluster modified metal oxide semiconductor layer 1A Anode (photoelectrode)
2 Cathode 3 Electrolyte 10 Photoelectric conversion element

Claims (6)

A photoelectric conversion element comprising an anode and a cathode disposed via an electrolyte containing an electron donor,
The anode, the surface of the metal oxide semiconductor, 15-33 mer gold clusters is being carried, the layers conductive electrode on containing Rukin cluster-modified metal oxide semiconductor having a visible light responsive properties A photoelectric conversion element characterized in that it is a photoelectrode formed on the substrate. The photoelectric conversion element according to claim 1, wherein the metal oxide semiconductor is titanium oxide. The photoelectric conversion element according to claim 1, wherein a shape of the metal oxide semiconductor is a granular body or a film-like body. The photoelectric conversion element according to claim 1, wherein the gold cluster is a 25-mer gold cluster. The gold clusters, photoelectric conversion element according to claims 1 consisting coated with a protective agent in any one of 4. The photoelectric conversion element according to claim 5, wherein the protective agent is glutathione.

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