JP2012243721A - Photoelectric conversion element - Google Patents

Abstract

Provided is a photoelectric conversion element that is excellent in conversion efficiency, excellent in design without impairing color, and suitable for solar cells.
A photoelectric conversion element comprising a semiconductor electrode in which a semiconductor layer is provided on a transparent conductive film, a counter electrode, and an electrolyte layer held between the two electrodes, wherein the semiconductor layer is a metal oxide. 2 is a laminated film formed by laminating two or more layers having different average particle diameters of physical semiconductor particles, and the electrolyte layer is added with 1.0 mM to 1.0 M of both a benzoquinone derivative and a hydroquinone derivative as a redox pair, respectively. A photoelectric conversion element comprising 1.0 mM to 2.0 M of an ammonium salt as an agent.
[Selection] Figure 1

Description

  The present invention relates to a photoelectric conversion element for a dye-sensitized solar cell.

  As a next-generation solar cell, development of an organic solar cell that can be manufactured at a low temperature and at a lower cost is expected. Among organic solar cells, dye-sensitized solar cells have the potential to significantly reduce manufacturing costs, have the same performance as amorphous silicon solar cells, and can produce colored transparent solar cells. It has attracted particular attention because of its attractiveness not found in batteries.

  In general, a dye-sensitized solar cell includes a semiconductor electrode having a photoelectric conversion layer made of a semiconductor having a dye adsorbed on a conductive substrate, and a counter electrode having a catalyst layer provided on a conductive substrate provided oppositely. The electrolyte layer is held between the semiconductor electrode and the counter electrode. As the electrolyte layer, an iodine-based redox couple dissolved in an organic solvent is generally used. Iodine-based redox couples have excellent performance, such as high ion conductivity and a high rate of reducing oxidized dyes, while low reactivity on the conductive glass surface and titanium oxide surface of the working electrode. ing.

However, iodine-based electrolytes can obtain high conversion efficiency, but have the following problems.
-It is very difficult to seal because of its high volatility.
-Since it has high corrosivity, the material which can be used as an electrode is limited.
・ Iodine-based redox couples have a very large absorbance coefficient in the visible light region, impeding the light absorption of the dye, causing performance degradation, and when emphasizing the design of solar cells, the iodine color This prevents the vividness of the pigment from being fully utilized.

Thus, although the iodine-based redox couple has high performance as a redox couple, it also has drawbacks, so a redox couple that replaces the iodine-based one is required. For example, bromine-based, sulfur-based, selenium-based, Redox couples such as iron complex system, cobalt complex system, benzoquinone / hydroquinone system, (SCN) ⁻ / (SCN) ₂ , (SeCN) ⁻ / (SeCN) ₂ system have been proposed. However, it is difficult to say that the practicality is high because the change efficiency is low and there are problems in stability and safety.

  In addition, in order to improve the conversion efficiency of the dye-sensitized solar cell, a film composed of small-diameter metal oxide semiconductor particles having a high adsorption ability of the sensitizing dye is formed on the conductive film, and further light scattering properties are formed thereon. It has been proposed to stack films made of excellent large-diameter metal oxide semiconductor particles (see Non-Patent Documents 1 and 2). However, the electrolyte is an iodine-based redox couple, and there are concerns about the same problems as described above. In addition, even if a film made of large-diameter metal oxide semiconductor particles is provided to lengthen the optical path and provide a light containment effect, the light absorption effect is sufficiently large because the absorbance coefficient due to the iodine-based redox couple is too large. I can't get it.

M. Graetzel, Chem. Lett. 34 (2005), pp8-13 M. Graetzel, et al, Adv. Mater. 18 (2005), pp1202-1205

  The present invention has been made in view of such a situation, and an object thereof is to provide a photoelectric conversion element that is excellent in conversion efficiency, excellent in design without impairing color, and suitable for solar cells. .

In order to solve the above problems, the present invention provides the following photoelectric conversion element.
(1) A photoelectric conversion element comprising a semiconductor electrode provided with a semiconductor layer on a transparent conductive film, a counter electrode, and an electrolyte layer held between the two electrodes,
The semiconductor layer is a laminated film formed by laminating two or more layers having different average particle diameters of metal oxide semiconductor particles,
A photoelectric conversion element, wherein the electrolyte layer contains 1.0 mM to 1.0 M of both a benzoquinone derivative and a hydroquinone derivative as a redox pair, and 1.0 mM to 2.0 M of an ammonium salt as an additive, respectively.
(2) The photoelectric conversion element as described in (1) above, wherein the laminated film is laminated such that a layer having a larger average particle diameter is located toward the counter electrode.
(3) In the laminated film, the average particle diameter of the metal oxide semiconductor particles in the layer closest to the transparent conductive film is 100 nm or less, and the average particle diameter of the metal oxide semiconductor particles in the layer farthest from the transparent conductive film is 200 to The photoelectric conversion element as described in (1) or (2) above, which has a thickness of 700 nm.
(4) The photoelectric conversion according to (3) above, wherein the thickness of the layer closest to the transparent conductive film is 5 μm or more and the thickness of the layer farthest from the transparent conductive film is 3 μm or more. element.
(5) The photoelectric conversion element as described in any one of (1) to (4) above, wherein the ammonium salt has a basic skeleton represented by the following general formula (A).
_{^{NH 4 + X - ···· (A}} )
(Wherein, X ^- is an inorganic anion or an organic anion)

  In the present invention, a hydroquinone / benzoquinone-based redox pair is used. However, compared with an iodine charge transport material, although coloring can be suppressed, there is a problem that power generation efficiency is inferior. Therefore, by adding a specific ammonium salt, it is possible to achieve high performance and stability as a charge transport material, and furthermore, it is possible to achieve a redox couple in which coloring is suppressed as compared with iodine. In addition, the semiconductor layer is a semiconductor layer in which a layer made of small-sized metal oxide semiconductor particles having a high ability to adsorb a dye and a layer made of large-sized metal oxide semiconductor particles having an excellent light containment effect thereon are laminated, Conversion efficiency increases.

  In the photoelectric conversion element of the present invention, the hydroquinone derivative / benzoquinone derivative and ammonium salt mixed charge transport material contained in the electrolyte layer not only have high performance and stability as an oxidation-reduction pair, but also compared with an iodine-based charge transport material. Since it is a light color, high conversion efficiency is obtained by a semiconductor layer composed of metal oxide semiconductor particles having high efficiency and excellent design without impairing the color of the photoelectric conversion element, and having different average particle diameters.

It is sectional drawing which shows the photoelectric conversion element of this invention.

  Hereinafter, the photoelectric conversion element of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a photoelectric conversion element A of the present invention. A transparent conductive film 2 is formed on one surface of the transparent substrate 1, and a semiconductor layer 3 is formed on the surface of the transparent conductive film 2 to constitute a semiconductor electrode 9. The semiconductor layer 3 is composed of a laminated film in which layers made of metal oxide semiconductor particles are laminated. The layer closer to the transparent conductive film 2 is laminated so that the average particle diameter becomes smaller. That is, in the example of the figure, the second semiconductor layer 5 made of large-sized metal oxide semiconductor particles is formed on the first semiconductor layer 4 made of small-sized metal oxide semiconductor particles in contact with the transparent conductive film 2. Laminated. The semiconductor layer 3 is not limited to the two layers shown in the figure, but may be three or more layers. For example, in the case of three layers, the first layer having the smallest average particle diameter in order from the side closer to the transparent electrode film 2 A first semiconductor layer, a second semiconductor layer having an average particle diameter larger than that of the first semiconductor layer, and a third semiconductor layer having an average particle diameter larger than that of the second semiconductor layer. A sensitizing dye is adsorbed on the metal oxide semiconductor particles constituting each semiconductor layer.

  As the sensitizing dye, any dye that can be excited by sunlight and can inject electrons into the semiconductor layer 3 can be used. In general, a dye used in a photoelectric conversion element can be used, but in order to improve conversion efficiency. It is desirable that the absorption spectrum overlaps with the sunlight spectrum in a wide wavelength region and has high light resistance. Examples of the sensitizing dye include metal complex dyes such as ruthenium complexes, iron complexes, and copper complexes. Further examples include cyan dyes, porphyrin dyes, polyene dyes, coumarin dyes, cyanine dyes, squaric acid dyes, methine dyes, xanthene dyes, indoline dyes, and the like.

  In addition, a catalyst layer 7 is formed on one surface of the electrode base 8 to constitute the counter electrode 10. The transparent electrode film 2 of the semiconductor electrode 9 and the catalyst layer 7 of the counter electrode 10 are disposed so as to face each other, and the electrolyte layer 5 is interposed therebetween.

  Below, each component is explained in detail.

[Transparent substrate 1]
As the transparent substrate 1, one that transmits visible light can be used, and transparent glass can be preferably used. Moreover, incident light can be utilized with high efficiency by processing the surface on the side where the transparent conductive film 2 is formed and scattering incident light. Moreover, not only glass but a plastic plate, a plastic film, etc. can be used if it transmits light.

  The thickness of the transparent substrate 1 is not particularly limited because it varies depending on the shape and use conditions of the photoelectric conversion element A. For example, glass or plastic that requires rigidity and durability, such as a solar cell panel for outdoor installation, etc. Then, about 1 mm to 1 cm is preferable, and about 1 μm to 1 mm is preferable for a plastic film or the like that is used for small home appliances or the like and is required to have flexibility.

[Transparent conductive film 2]
The transparent conductive film 2 can be made of a material that transmits visible light and has conductivity. An example of such a material is a metal oxide. Although not particularly limited, for example, tin oxide doped with fluorine (hereinafter abbreviated as “FTO”), indium oxide, a mixture of tin oxide and indium oxide (hereinafter abbreviated as “ITO”), antimony, and the like. Oxide-doped tin oxide, zinc oxide, and the like can be suitably used.

  In addition, an opaque conductive material can be used as long as visible light is transmitted through a treatment such as dispersion. Such materials include carbon materials and metals. Although it does not specifically limit as a carbon material, For example, graphite (graphite), carbon black, glassy carbon, a carbon nanotube, fullerene, etc. are mentioned. Further, the metal is not particularly limited, and examples thereof include platinum, gold, silver, ruthenium, copper, aluminum, nickel, cobalt, chromium, iron, molybdenum, titanium, tantalum, and alloys thereof.

  The thickness of the transparent conductive film 2 is not particularly limited because the conductivity varies depending on the material to be used, but is generally 0.01 μm to 5 μm, preferably 0.1 μm to 1 μm in the FTO coated glass generally used. It is. Further, the required conductivity varies depending on the area of the electrode to be used, and it is required that the wider the electrode, the lower the resistance. In general, the sheet resistance (surface resistivity) is 100Ω / □ or less, preferably 10Ω. / □ or less, more preferably 5Ω / □ or less. This sheet resistance is an electrical resistance value of a thin film or film-like substance, and its unit is Ω, but is conventionally described as “Ω / □ (ohm / square)” to indicate that it is a sheet. Since the thickness of the laminated body of the transparent substrate 1 and the transparent conductive film 2 or the thickness obtained by integrating the transparent substrate 1 and the transparent conductive film 2 varies depending on the shape and use conditions of the photoelectric conversion element A as described above. Although not particularly limited, it is generally about 1 μm to 1 cm.

[Semiconductor layer 3]
The semiconductor layer 3 is formed by laminating layers of metal oxide semiconductor particles having different average particle diameters in multiple layers. The type of the metal oxide semiconductor is not particularly limited, and examples thereof include titanium oxide, zinc oxide, tin oxide, and titanium dioxide, and more particularly anatase type titanium dioxide are preferable. Further, it is desirable that the metal oxide has few grain boundaries in order to reduce the electric resistance value.

  Further, the metal oxide semiconductor particles constituting the semiconductor layer closest to the transparent conductive film 2 (first semiconductor layer 4 in the illustrated example) have the smallest average particle diameter, preferably 100 nm or less, more preferably 10 ~ 80 nm. Further, the semiconductor layer farthest from the transparent conductive film 2 (second semiconductor layer 5 in the example shown in the figure) has the largest average particle diameter, preferably 200 to 700 nm, and more preferably 300 to 600 nm. As the metal oxide semiconductor particles become smaller, the surface area becomes larger and the adsorption amount of the sensitizing dye becomes larger. On the other hand, the light scattering property becomes smaller and the conversion efficiency becomes smaller. Therefore, in the present invention, the increase in the adsorption amount of the sensitizing dye by the small-diameter metal oxide semiconductor particles and the light scattering effect by the large-diameter metal oxide semiconductor particles are combined. By arranging the particles closer to the transparent conductive film 2 to increase the amount of the sensitizing dye, and disposing the large-diameter metal oxide semiconductor particles far away to further enhance the light scattering effect, Increase conversion efficiency. In order to reliably obtain such an effect, the size of the metal oxide semiconductor particles in each semiconductor layer is defined as described above. That is, when the average particle diameter of the metal oxide semiconductor particles constituting the semiconductor layer closest to the transparent conductive film 2 exceeds 100 nm, the adsorption amount of the sensitizing dye is not sufficient, and the semiconductor layer farthest from the transparent conductive film 2 is formed. When the average particle diameter of the metal oxide semiconductor particles to be performed is smaller than 200 nm, the light scattering effect cannot be sufficiently obtained. In addition, a large-sized metal oxide semiconductor particle having an average particle diameter exceeding 700 nm has a remarkably small surface area on which a sensitizing dye can be adsorbed, resulting in not only low photoelectric conversion efficiency but also poor film-formability and uniformity. No semiconductor film 3 can be obtained.

In order to further increase the adsorption amount of the sensitizing dye, the BET specific surface area of the metal oxide semiconductor particles constituting the semiconductor layer closest to the transparent conductive film 2 is 50 to 200 m ² / g, the semiconductor farthest from the transparent conductive film 2 It is preferable that the metal oxide semiconductor particles constituting the layer have a BET specific surface area of 5 to ²⁰ m ² / g.

  The thickness of the semiconductor layer closest to the transparent conductive film 2 is preferably 5 μm or more, and the thickness of the semiconductor layer farthest from the transparent conductive film 2 is preferably 3 μm or more. The thickness of the semiconductor layer varies depending on the average particle diameter of the metal oxide semiconductor particles constituting the semiconductor layer. By using such a thickness, the adsorption amount of the sensitizing dye and the light scattering effect can be sufficiently obtained, and the photoelectric conversion efficiency can be obtained. Will improve.

  Such a semiconductor layer 3 can be provided on the transparent conductive film 2 by a known film formation method, and examples thereof include a sol-gel method, a dispersion paste application, a method of electrodeposition and electrodeposition. At that time, the film forming process is repeated in order from the layer made of the metal oxide semiconductor particles having a small average particle diameter so as to obtain the multilayer structure.

[Electrolyte layer 6]
The electrolyte layer 6 has a composition in which a hydroquinone derivative, a benzoquinone derivative, and an ammonium salt represented by the following general formula (A) are mixed as a redox pair.
_{^{NH 4 + X - ···· (A}} )
In the formula, X ⁻ is an inorganic anion or an organic anion, and an organic anion is preferable in consideration of solubility in an organic solvent. The type of organic anion is not particularly limited, but carboxylate ions represented by acetate ion, propionate ion, benzoate ion, and the like are preferable because the acid dissociation constant is small and NH ₄ ⁺ can stably exist. Examples of inorganic anions include chlorine ions, bromine ions, iodine ions and the like.

  The concentration of the ammonium salt in the redox composition is in the range of 1.0 mM to 2.0 M with respect to the solvent. When the concentration is smaller than 1.0 mM, the effect of adding an ammonium salt is hardly obtained, and the conversion efficiency is hardly improved. On the other hand, even if the concentration is higher than 2.0M, the conversion efficiency is hardly improved, and ammonium salts may be precipitated in the solution due to solubility problems. A preferred concentration is 20 mM to 2.0 M.

  As the hydroquinone derivative, those having a basic skeleton represented by the following general formula (I) are preferable.

  In the formula, R represents an alkyl group or an aryl group, and the subscript n represents 0 or more substituents. The type of alkyl group or aryl group is not particularly limited, but an alkyl group is more preferable in consideration of solubility in an organic solvent and absorption of visible light caused by an increase in conjugation length.

  Further, as the structure of the general formula (I), not only a monocyclic aromatic ring but also a polycyclic aromatic hydroquinone derivative can be applied. The type of polycyclic aromatic is not particularly limited, but in consideration of solubility in an organic solvent and absorption of visible light due to an increase in conjugation length, a condensed ring number of 3 or less is preferable. Conceivable. Examples of the compound having 3 or less condensed rings include naphthohydroquinone derivatives in which two rings are condensed and anthrahydroquinone derivatives in which three rings are condensed.

  The concentration of the hydroquinone derivative in the oxidized ring base composition is in the range of 1.0 mM to 1.0 M with respect to the solvent. When the concentration is smaller than 1.0 mM, the addition effect is hardly obtained, and the conversion efficiency is hardly improved. On the other hand, even if the concentration is higher than 1.0M, not only the conversion efficiency is hardly improved, but also the hydroquinone derivative may be precipitated in the solution due to the solubility of the hydroquinone derivative. A preferred concentration is 10 mM to 1.0 M.

  As the benzoquinone derivative, those having a basic skeleton represented by the following general formula (II) are preferable.

  In the formula, R represents an alkyl group or an aryl group, and the subscript n represents 0 or more substituents. The type of alkyl group or aryl group is not particularly limited, but an alkyl group is more preferable in consideration of solubility in an organic solvent and absorption of visible light caused by an increase in conjugation length.

  Further, as the structure of the general formula (II), not only a monocyclic aromatic ring but also a polycyclic aromatic hydroquinone derivative can be applied. The type of polycyclic aromatic is not particularly limited, but in consideration of solubility in an organic solvent and absorption of visible light due to an increase in conjugation length, a condensed ring number of 3 or less is preferable. Conceivable. Examples of the compound having 3 or less condensed rings include a naphthoquinone derivative in which two rings are condensed and an anthraquinone derivative in which three rings are condensed.

  The concentration of the benzoquinone derivative in the oxidized ring base composition is in the range of 1.0 mM to 1.0 M with respect to the solvent. When the concentration is smaller than 1.0 mM, the addition effect is hardly obtained, and the conversion efficiency is hardly improved. On the other hand, even if the concentration is higher than 1.0M, not only the conversion efficiency is hardly improved, but the benzoquinone derivative may be precipitated in the solution due to the solubility problem of the benzoquinone derivative. A preferred concentration is 10 mM to 1.0 M.

  The combination of hydroquinone derivative and benzoquinone derivative is preferably a combination in which Rn in the general formulas (I) and (II) are the same substituent.

The mixing ratio of hydroquinone derivative, benzoquinone derivative, and ammonium salt is not particularly limited. However, when the molar concentration of hydroquinone derivative is x, the molar concentration of benzoquinone derivative is y, and the molar concentration of ammonium salt is z, the following formula is satisfied. Is preferred.
0.05 ≦ x / y ≦ 20, 0.5 ≦ (x + y) /z≦2.0

  The solvent for dissolving the redox couple is not particularly limited as long as it is a compound capable of dissolving the redox couple, and can be arbitrarily selected from a non-aqueous organic solvent, a room temperature molten salt, a protic organic solvent, and the like. In addition, the ammonium salt may be hardly soluble in an organic solvent. In that case, the ammonium salt can be dissolved by adding a carboxylic acid to the solvent.

  Examples of organic solvents include nitrile compounds such as acetonitrile, methoxyacetonitrile, parelonitrile, and 3-methoxypropionitrile, lactone compounds such as γ-butyllactone and parerolactone, carbonate compounds such as ethylene carbonate and propylene carbonate, dioxane, diethyl ether, and ethylene. Examples include glycol dialkyl ethers, ethers such as low-polymerization polyethylene glycol, alcohols such as methanol and ethanol, and dimethylformamide and imidazoles. Among them, acetonitrile, pareronitrile, 3-methoxypropionitrile, propylene carbonate, low Polymerization degree polyethylene glycol etc. can be used conveniently.

  As carboxylic acid, saturated carboxylic acid represented by formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, unsaturated carboxylic acid represented by acrylic acid, methacrylic acid, 2-ethylpropenoic acid, benzoic acid, Examples include aromatic carboxylic acids such as phthalic acid, hydroxy acids such as lactic acid, malic acid, and citric acid.

  The composition of the solvent only needs to dissolve the ammonium salt, but the conversion efficiency tends to decrease as the amount of the carboxylic acid component added increases. Therefore, the amount of the carboxylic acid component added is preferably as small as possible. When the ammonium salt is dissolved in the organic solvent used, it is not necessary to add a carboxylic acid component.

Further, the electrolyte layer 6 can be made pseudo-solid to further enhance durability and reliability. For example, a nanocomposite gel is formed by dispersing metal oxide nanoparticles as crosslinking points. The metal oxide is not limited as long as the charge transport liquid containing the redox _couple and the solvent can be gelled, and is SiO ₂ , TiO ₂ , SnO ₂ , WO ₂ , ZnO ₂ , ITO, BaTiO ₃ , Nb ₂ O. ₅ , metal oxides such as In ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , La ₂ O ₃ , SrTiO ₃ , Y ₂ O ₃ , Ho ₂ O ₃ , Bi ₂ O ₃ , CeO ₂ and Al ₂ O ₃ Is preferably used. These may be used alone or as a mixture of two or more. Although nano-particles can be made into microcomposite gels using polymer nanoparticles such as polymethyl methacrylate and polymethyl acrylate, and carbon-based materials such as carbon fibers and carbon nanotubes, the nanoparticles are used for reducing the color of the electrolyte layer 5. Since carbon must be colorless or white, a carbon-based material is not preferable. In addition, polymer nanoparticles are not preferred because of concerns about solubility in organic solvents.

  The smaller the particle size of the nanoparticles, the better, and 1 to 1000 nm is preferred. If the particle size is less than 1 nm, the production becomes difficult and the cost becomes high. If the particle size exceeds 1000 nm, the holding power of the charge transport liquid becomes small, causing problems such as liquid leakage.

  The addition amount of the nanoparticles is an amount capable of gelling the charge transport liquid, but is preferably 5 to 70% by mass with respect to the weight of the charge transport liquid. If the addition amount is 5% by mass, the charge transport liquid cannot be sufficiently retained, and the electrolyte layer 5 cannot be quasi-solidified. On the other hand, if it exceeds 70 mass%, the charge transport liquid is completely solidified, and the transfer of electrons between the semiconductor electrode 8 and the counter electrode 9 does not proceed smoothly, and the change efficiency may be reduced.

  Furthermore, a lithium salt, an imidazolium salt, a quaternary ammonium salt, a room temperature molten salt, or the like can be added to the electrolyte layer 6 as a supporting electrolyte. These additives can be added to such an extent that the characteristics of the electrolyte layer are not impaired.

[Catalyst layer 7]
The catalyst layer 7 is not particularly limited as long as it has electrode characteristics capable of promptly proceeding with a reduction reaction for reducing the oxidized form of the redox couple in the electrolyte to a reduced form, but chloroplatinic acid is applied. , Heat treated materials, platinum catalyst electrodes deposited with platinum, carbon materials such as activated carbon, glassy carbon and carbon nanotubes, inorganic sulfur compounds such as cobalt sulfide, conductive polymers such as polythiophene, polypyrrole and polyaniline, etc. However, among them, a platinum catalyst electrode can be preferably used. The thickness of the catalyst layer 7 is suitably 5 nm to 5 μm, particularly preferably 50 nm to 2 μm.

[Electrode substrate 8]
Since the electrode substrate 8 is used as a support and current collector of the catalyst layer 7, it is preferable that the surface portion has conductivity. For example, platinum, gold, silver, ruthenium, copper, aluminum, Nickel, cobalt, chromium, iron, molybdenum, titanium, tantalum, and their alloys, and carbon materials such as graphite (graphite), carbon black, glassy carbon, carbon nanotubes, fullerene, etc., and metal oxides such as FTO and ITO Indium oxide, zinc oxide, antimony oxide, or the like can be used. In addition, an insulator such as glass or plastic can be used if the surface is treated so as to have conductivity.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further, this invention is not restrict | limited at all by this.

<Examples 1-7>
(Preparation of photoelectric conversion element)
A photoelectric conversion element having the structure shown in FIG. 1 was produced as follows.

[Production of semiconductor electrode]
Cut the glass with ITO film (sputtered product) manufactured by Geomat Co., Ltd. into the required size, wash with glass cleaner, rinse the cleaner with pure water, then acetone, hexane, acetone, pure water, pure water in this order Then, ultrasonic cleaning was performed for 5 minutes each. After drying, finish cleaning was performed for 10 minutes using a UV ozone cleaner, and then immersed in an aqueous TiCl ₄ solution at 70 ° C. for 30 minutes. After immersion, it was washed with pure water and dried well.

Next, a small-diameter TiO ₂ paste (“PST-18NR” manufactured by JGC Catalysts &Chemicals; average particle size of 20 nm) is applied to the ITO film surface with a screen printing device (manufactured by Tokai Shoji Co., Ltd.). After being placed and dried, the first semiconductor layer was formed by firing in air in the order of 30 minutes at 80 ° C. and 30 minutes at 450 ° C. Subsequently, a large-diameter TiO ₂ paste (“PST-400C” manufactured by JGC Catalysts &Chemicals; average particle size of 400 nm) is applied on the first semiconductor layer to a predetermined thickness using a screen printing device (manufactured by Tokai Shoji). The first semiconductor layer was formed by baking in the air in the order of 30 minutes at 80 ° C. and 30 minutes at 450 ° C. after standing for 30 minutes and drying.

In the above, the coating thicknesses of the small diameter and large diameter TiO ₂ pastes were adjusted so that the first semiconductor layer and the second semiconductor layer had the thicknesses shown in Table 1.

[Adsorption of sensitizing dye]
As a sensitizing dye, cis-bis (isothiocyanato) bis (2,2′-pybilidyl-4,4′-dicarboxylate) ruthenium (II) (manufactured by Wako Pure Chemical Industries, Ltd.) called N3 was used. The dye solution was a 0.3 mM ethanol solution. And said semiconductor electrode was immersed in the pigment | dye solution, and it left still at about 40 degreeC under light-shielding for 3 hours. Thereafter, the excess pigment was washed with ethanol and air-dried.

[Preparation of counter electrode]
The counter electrode used was a platinum thin film layer deposited on a glass substrate. The thickness of the platinum thin film was about 200 nm.

(Electrolyte layer)
278 mg (2.0 mM) of ammonium benzoate was placed in a glass container subjected to argon substitution, and 1 ml of acetic acid was added. After shaking until the solid is completely dissolved, 220.3 mg (1.0 mM) of 2,5-di-t-butylbenzoquinone and 222.3 mg (1.0 mM) of 2,5-di-t-butylhydroquinone are added. The total volume was adjusted to 20 ml with acetonitrile. Acetic acid and acetonitrile used were freeze-degassed.

[Assembly of photoelectric conversion element]
An electrolyte layer was interposed between the semiconductor electrode and the counter electrode, and the side surfaces were sealed with an epoxy adhesive. This operation was performed in a glove box substituted with argon.

[Evaluation of photoelectric conversion element]
The photoelectric conversion characteristics of the photoelectric conversion element were evaluated using a solar simulator. The simulated sunlight used light of 100 mW / cm ² under AM1.5 conditions, and the conversion efficiency (η1) was calculated from the open circuit voltage, short circuit current, and fill factor. In addition, a comparative photoelectric conversion element was manufactured by forming a semiconductor layer having the same thickness using only the above-described small-diameter TiO ₂ paste. And ratio ((eta) 1 / (eta) 2) with the conversion efficiency ((eta) 2) of the photoelectric conversion element for a comparison was calculated | required.

<Comparative Example 1>
A photoelectric conversion element was produced in the same manner as in Example except that a semiconductor layer having a thickness of 15 μm was formed using only a small diameter TiO ₂ paste, and the conversion efficiency was obtained.

<Comparative example 2>
A photoelectric conversion element was prepared in the same manner as in Example except that a semiconductor layer having a thickness of 10 μm was formed using only a large diameter TiO ₂ paste, and the conversion efficiency was obtained.

<Comparative Example 3>
A photoelectric conversion element was prepared using an iodine-based redox couple for the electrolyte layer, the thickness of the first semiconductor layer being 15 μm, and the thickness of the second semiconductor layer being 10 μm, and the conversion efficiency was determined.

  The photoelectric conversion characteristics of Examples and Comparative Examples are shown in Table 1. In each of the photoelectric conversion elements of Examples, the electrolyte layer is 2,5-di-t-butylbenzoquinone, 2,5-di-t-butylhydroquinone. The conversion efficiency (η1) is a comparative example because it has a first semiconductor layer containing an ammonium salt and further comprising a small-sized metal oxide semiconductor particle and a second semiconductor layer comprising a large-sized metal oxide semiconductor particle. The conversion efficiency ratio (η1 / η2) is large although it is smaller than the iodine electrolyte layer 4. From this, the conversion efficiency is improved by forming the semiconductor layer with the first semiconductor layer made of small-sized metal oxide semiconductor particles and the second semiconductor layer made of large-sized metal oxide semiconductor particles. I understand that. In addition, when the first semiconductor layer is 5 μm or more and the second semiconductor layer is 3 μm or more, the conversion efficiency itself and the effect of improving the conversion efficiency are particularly increased.

  In Comparative Example 3 using a conventional iodine-based electrolyte, the conversion efficiency is higher than in the examples, but the dark brown of the iodine-based redox couple is mixed with the vivid color of the pigment, and the appearance of the photoelectric conversion element is dark brown The design has been greatly impaired. Further, as in Comparative Example 2, even when the electrolyte layer is the same as that in the example, the photoelectric conversion element having a single semiconductor layer made of large-diameter metal oxide semiconductor particles has a low conversion efficiency.

A Photoelectric conversion element 1 Transparent substrate 2 Transparent conductive film 3 Semiconductor layer 4 First semiconductor layer 5 Second semiconductor layer 6 Electrolyte layer 7 Catalyst layer 8 Electrode substrate 9 Semiconductor electrode 10 Counter electrode

Claims (5)

A photoelectric conversion element comprising a semiconductor electrode provided with a semiconductor layer on a transparent conductive film, a counter electrode, and an electrolyte layer held between the two electrodes,
The semiconductor layer is a laminated film formed by laminating two or more layers having different average particle diameters of metal oxide semiconductor particles,
A photoelectric conversion element, wherein the electrolyte layer contains 1.0 mM to 1.0 M of both a benzoquinone derivative and a hydroquinone derivative as a redox pair, and 1.0 mM to 2.0 M of an ammonium salt as an additive, respectively.   2. The photoelectric conversion element according to claim 1, wherein the laminated film is laminated such that a layer having a larger average particle diameter is located toward the counter electrode.   In the laminated film, the average particle diameter of the metal oxide semiconductor particles in the layer closest to the transparent conductive film is 100 nm or less, and the average particle diameter of the metal oxide semiconductor particles in the layer farthest from the transparent conductive film is 200 to 700 nm. The photoelectric conversion element according to claim 1 or 2, wherein   4. The photoelectric conversion element according to claim 3, wherein in the laminated film, the thickness of the layer closest to the transparent conductive film is 5 μm or more, and the thickness of the layer farthest from the transparent conductive film is 3 μm or more. The photoelectric conversion element according to any one of claims 1 to 4, wherein the ammonium salt has a basic skeleton represented by the following general formula (A).
_{^{NH 4 + X - ···· (A}} )
(Wherein, X ^- is an inorganic anion or an organic anion)

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