JP2013041736A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element having an excellent durability and capable of suppressing reduction in photoelectric conversion efficiency.SOLUTION: A photoelectric conversion element has: a light transmissive supporting body; a transparent conductive layer provided on the light transmissive supporting body; a photoelectric conversion layer including a porous semiconductor layer provided on the transparent conductive layer; a conductive layer provided to at least a part of the photoelectric conversion layer; a counter electrode conductive layer provided so as to face the transparent conductive layer; and a carrier transportation material provided between the transparent conductive layer and the counter electrode conductive layer. The carrier transportation material contains a hardly volatile solvent and a redox species. The conductive layer is electrically connected to the transparent conductive layer.

Description

  The present invention relates to a photoelectric conversion element.

  As an energy source that replaces fossil fuel, a battery that can convert sunlight into electric power, that is, a solar cell, has attracted attention. At present, some solar cells and thin film silicon solar cells using a crystalline silicon substrate are beginning to be put into practical use.

  However, a solar cell using a crystalline silicon substrate has a problem that the manufacturing cost of the silicon substrate is high. In addition, the thin film silicon solar cell has a problem in that the manufacturing cost is high because it is necessary to use many kinds of semiconductor manufacturing gases and complicated devices. For this reason, in any solar cell, efforts have been made to increase the efficiency of photoelectric conversion in order to reduce the cost per power generation output, but the above problem has not yet been solved sufficiently.

  Further, for example, Patent Document 1 (Japanese Patent No. 2664194) discloses a wet type solar cell to which photoinduced electron transfer of a metal complex is applied as a new type of solar cell. For example, Patent Document 2 (Japanese Patent Laid-Open No. 2008-287900) discloses a wet solar cell using quantum dots as a new type of solar cell.

  In these wet solar cells, electrodes are respectively formed on the surfaces of two glass substrates, two glass substrates are arranged so that these electrodes are inside, and a photoelectric conversion layer and an electrolytic solution are placed between the electrodes. It is made so as to be sandwiched. The photoelectric conversion layer is composed of a semiconductor layer in which a photosensitizing dye is adsorbed to give an absorption spectrum in the visible light region. Such a wet solar cell is also called a dye-sensitized solar cell.

  When light enters the wet solar cell as described above, electrons are generated in the photoelectric conversion layer, and the electrons generated in the photoelectric conversion layer reach the electrode through the photoelectric conversion layer. Then, the electrons that have reached the electrodes move to the other electrode through an external electric circuit that connects the electrodes, are supplied to the electrolytic solution, are carried by the ions in the electrolytic solution, and return to the photoelectric conversion layer again. In a wet solar cell, electric energy is taken out by such a flow of electrons.

  Patent Document 3 (Japanese Patent Laid-Open No. 2001-357897) discloses a wet solar cell using two conductive substrates. In this wet solar cell, a porous semiconductor layer, which is a photoelectrode, is formed on one conductive substrate, a catalyst layer is formed on the other conductive substrate, and the side surfaces of the wet solar cell are overlapped so as to match each other. It is produced by sealing with an epoxy adhesive.

Japanese Patent No. 2664194 JP 2008-287900 A JP 2001-357897 A

  From the viewpoint of improving the durability of the wet solar cell, it is preferable to use a hardly volatile solvent as the solvent for the electrolyte of the wet solar cell. However, when a hardly volatile solvent is used as the solvent for the electrolyte of the wet solar cell, the photoelectric conversion efficiency of the wet solar cell is higher than that when a volatile solvent such as acetonitrile is used as the solvent for the electrolyte. There was a problem of a significant drop.

  In view of the above circumstances, an object of the present invention is to provide a photoelectric conversion element that is excellent in durability and can suppress a decrease in photoelectric conversion efficiency.

  The present invention provides a light transmissive support, a transparent conductive layer provided on the light transmissive support, a photoelectric conversion layer including a porous semiconductor layer provided on the transparent conductive layer, and at least a photoelectric conversion layer. A carrier layer comprising: a conductive layer provided in part; a counter electrode conductive layer provided to face the transparent conductive layer; and a carrier transport material provided between the transparent conductive layer and the counter electrode conductive layer. The material includes a hardly volatile solvent and a redox species, and the conductive layer is a photoelectric conversion element that is electrically connected to the transparent conductive layer.

  Here, in the photoelectric conversion element of this invention, it is preferable that a hardly volatile solvent does not have a boiling point, or the boiling point of a hardly volatile solvent is 100 degreeC or more.

  Moreover, in the photoelectric conversion element of this invention, it is preferable that the thickness of a photoelectric converting layer is 4 micrometers or more and 30 micrometers or less.

  Moreover, in the photoelectric conversion element of this invention, it is preferable that the viscosity of a hardly volatile solvent is 1 cp or more.

  Moreover, in the photoelectric conversion element of this invention, it is preferable that the electrical conductivity of a carrier transport material is 1.5 S / m or less.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in durability and can provide the photoelectric conversion element which can suppress the fall of a photoelectric conversion efficiency.

It is typical sectional drawing of the photoelectric conversion element of this Embodiment. It is typical sectional drawing illustrating a part of manufacturing process of an example of the manufacturing method of the photoelectric conversion element of this Embodiment. It is typical sectional drawing illustrating other one part of the manufacturing process of an example of the manufacturing method of the photoelectric conversion element of this Embodiment. It is typical sectional drawing illustrating other one part of the manufacturing process of an example of the manufacturing method of the photoelectric conversion element of this Embodiment. It is typical sectional drawing illustrating other one part of the manufacturing process of an example of the manufacturing method of the photoelectric conversion element of this Embodiment.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Photoelectric conversion element>
FIG. 1 shows a schematic cross-sectional view of a photoelectric conversion element of the present embodiment which is an example of the photoelectric conversion element of the present invention. The photoelectric conversion element according to the present embodiment is provided between the transparent electrode plate 11, the counter electrode 12 disposed at a predetermined distance so as to face the transparent electrode plate 11, and the transparent electrode plate 11 and the counter electrode 12. And a sealing material 6 for joining the transparent electrode plate 11 and the counter electrode 12 between the transparent electrode plate 11 and the counter electrode 12. The sealing material 6 is disposed between the transparent electrode plate 11 and the counter electrode 12 so as to surround the carrier transporting material 8 and seals the carrier transporting material 8.

  The transparent electrode plate 11 includes a light transmissive support 1 and a transparent conductive layer 2 provided on one surface of the light transmissive support 1. The photoelectric conversion layer 3 is provided on the surface of the transparent conductive layer 2, and the conductive layer 4 is provided on at least a part of the photoelectric conversion layer 3. The conductive layer 4 is electrically connected to the transparent conductive layer 2 of the transparent electrode plate 11. In addition, a hole for injecting the carrier transport material 8 may be provided in a part of the transparent electrode plate 11.

  The counter electrode 12 includes a counter electrode conductive layer 5 and a catalyst layer 7 provided on one surface of the counter electrode conductive layer 5. Here, the counter electrode conductive layer 5 and the catalyst layer 7 of the counter electrode 12 are configured to face the transparent conductive layer 2 of the transparent electrode plate 11, respectively.

<Light transmissive support>
Since the light transmissive support 1 constitutes at least a part of the light receiving surface of the photoelectric conversion element of the present embodiment, the light transmissive support 1 is, for example, the light receiving surface of the photoelectric conversion element. A material having at least light transparency in the portion can be used. However, any material can be used as long as it is a material that substantially transmits light having a wavelength having effective sensitivity to at least a photosensitizer described later, and is not necessarily transparent to light in all wavelength regions.

  Examples of the light transmissive material used for the light transmissive support 1 include glass substrates such as soda lime float glass, fused silica glass, and crystal quartz glass, or heat resistant resin plates such as flexible films. Can be used.

  Examples of the flexible film used for the light transmissive support 1 include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polycarbonate (PC), and polyarylate (PA). , Polyetherimide (PEI), phenoxy resin, or polytetrafluoroethylene (PTFE) can be used.

  As the flexible film used for the light transmissive support 1, it is preferable to use a PTFE film. Since the PTFE film has a heat resistance of 250 ° C. or more, when the transparent conductive layer 2 is formed by heating the surface of the light transmissive support 1 to about 250 ° C., for example, the light transmissive support 1 is damaged by heat. There is a tendency to be able to suppress.

  The thickness of the light transmissive support 1 is not particularly limited, but is preferably 0.2 mm or more and 5 mm or less. When the thickness of the light transmissive support 1 is 0.2 mm or more, the light transmissive support 1 tends to exhibit a function as a support. When the thickness of the light transmissive support 1 is 5 mm or less, the amount of light transmitted through the light transmissive support 1 is increased and the photoelectric conversion efficiency of the photoelectric conversion element tends to be improved.

  When attaching the photoelectric conversion element of this Embodiment to another structure, it can attach using the transparent support body 1. FIG. For example, when the light transmissive support 1 is made of a glass substrate, the peripheral portion of the light transmissive support 1 can be easily attached to another structure with screws or the like.

<Transparent conductive layer>
Since the transparent conductive layer 2 constitutes at least a part of the light receiving surface of the photoelectric conversion element of the present embodiment, the transparent conductive layer 2 may be, for example, at least a portion of the light receiving surface of the photoelectric conversion element. A material having transparency and conductivity can be used. However, any material can be used as long as it is a material that substantially transmits light having a wavelength having effective sensitivity to at least a photosensitizer described later, and is not necessarily transparent to light in all wavelength regions.

  As the light-transmitting material used for the transparent conductive layer 2, for example, indium tin composite oxide (ITO), fluorine-doped tin oxide (FTO), zinc oxide (ZnO), or the like can be used.

  A metal wire may be provided on the transparent conductive layer 2. When a metal wire is provided on the transparent conductive layer 2, the resistance of the transparent conductive layer 2 tends to be lowered. As the metal wire, for example, a metal wire containing at least one metal selected from the group consisting of platinum, gold, silver, copper, aluminum, nickel and titanium can be used. From the viewpoint of avoiding a decrease in the amount of incident light due to the metal wire provided in the transparent conductive layer 2, the thickness of the metal wire is preferably about 0.1 to 4 mm, for example.

  The thickness of the transparent conductive layer 2 is preferably 0.02 μm or more and 5 μm or less. When the thickness of the transparent conductive layer 2 is 0.02 μm or more, the resistance of the transparent conductive layer 2 is reduced and the amount of current that can be taken out of the photoelectric conversion element is increased. Photoelectric conversion efficiency tends to improve. Further, when the thickness of the transparent conductive layer 2 is 5 μm or less, the amount of transmitted light of the transparent conductive layer 2 increases and the amount of photoelectrons generated in the photoelectric conversion layer 3 increases. Efficiency tends to improve.

  Further, the surface resistance of the surface of the transparent conductive layer 2 is preferably 40Ω / □ or less. When the surface resistance of the transparent conductive layer 2 is 40Ω / □ or less, the amount of current that can be taken out of the photoelectric conversion element increases, and thus the photoelectric conversion efficiency of the photoelectric conversion element tends to be improved.

<Transparent electrode plate>
A transparent electrode plate 11 is composed of the light transmissive support 1 and the transparent conductive layer 2. As the transparent electrode plate 11, for example, a transparent conductive material made of FTO is formed on a light transmissive support material 1 made of soda-lime float glass. A transparent electrode plate 11 on which the layer 2 is laminated can be used.

<Photoelectric conversion layer>
As the photoelectric conversion layer 3, a layer including a porous semiconductor layer and a photosensitizer that is held by being adsorbed on the porous semiconductor layer can be used.

  The porous semiconductor layer used for the photoelectric conversion layer 3 is not particularly limited as long as it is made of a porous semiconductor. For example, the porous semiconductor layer is made of a porous semiconductor having various shapes such as a bulk shape, a particle shape, or a film shape. Can be used. Especially, it is preferable to use a film-like porous semiconductor as the porous semiconductor layer. In this case, the light receiving area of the photoelectric conversion layer 3 is increased, the photoelectric conversion efficiency of the photoelectric conversion element is improved, and the thinning of the photoelectric conversion element tends to be promoted.

Here, the specific surface area (surface area per unit mass) of the porous semiconductor layer used for the photoelectric conversion layer 3 is preferably 0.5 m ² / g or more and 300 m ² / g or less. When the specific surface area of the porous semiconductor layer of the photoelectric conversion layer 3 is 0.5 m ² / g or more, the photoelectric conversion layer 3 can hold many photosensitizers, so that light is efficiently absorbed. Tend to be able to. When the specific surface area of the porous semiconductor layer of the photoelectric conversion layer 3 is 300 m ² / g or less, the durability of the photoelectric conversion layer 3 tends to be improved. The specific surface area of the porous semiconductor layer used for the photoelectric conversion layer 3 can be calculated by, for example, the BET method (JIS Z8830: 2001) which is a gas adsorption method.

  The porosity of the porous semiconductor layer used for the photoelectric conversion layer 3 (ratio of the volume of voids provided in the porous semiconductor layer to the total volume of the porous semiconductor layer) is preferably 20% or more. . When the porosity of the porous semiconductor layer of the photoelectric conversion layer 3 is 20% or more, the carrier transporting material 8 tends to be sufficiently diffused inside the porous semiconductor layer of the photoelectric conversion layer 3. . The porosity of the porous semiconductor layer used for the photoelectric conversion layer 3 is, for example, the volume calculated from the film thickness and area of the porous semiconductor layer, the mass of the porous semiconductor layer, and the material of the porous semiconductor layer It can be calculated from the density.

Examples of the porous semiconductor layer used for the photoelectric conversion layer 3 include titanium oxide, zinc oxide, tin oxide, iron oxide, niobium oxide, cerium oxide, tungsten oxide, nickel oxide, strontium titanate, cadmium sulfide, lead sulfide, A layer made of a porous semiconductor containing at least one selected from the group consisting of zinc sulfide, indium phosphide, copper indium sulfide (CuInS ₂ ), CuAlO ₂ and SrCu ₂ O ₂ can be used.

  Especially, it is preferable that the porous semiconductor layer of the photoelectric converting layer 3 contains at least 1 sort (s) selected from the group which consists of a titanium oxide, a zinc oxide, a tin oxide, and niobium oxide, and it is especially preferable that a titanium oxide is included. In this case, the stability and safety of the porous semiconductor layer of the photoelectric conversion layer 3 are improved, and the photoelectric conversion efficiency of the photoelectric conversion element tends to be improved.

  In this specification, “titanium oxide” is not limited to various narrowly defined oxides of titanium, such as anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, metatitanic acid, and orthotitanic acid. In addition, it is a concept including a titanium compound containing oxygen such as titanium oxide, titanium hydroxide and hydrous titanium oxide, and these can be used alone or in combination. Titanium oxide can be in any of two types of crystal systems, anatase type and rutile type, depending on the production method and thermal history, but anatase type is common.

  Moreover, the porous semiconductor layer of the photoelectric conversion layer 3 may be made of a polycrystalline sintered body. In this case, the stability of the porous semiconductor layer of the photoelectric conversion layer 3 is improved and the crystal growth is facilitated, so that the manufacturing cost of the photoelectric conversion element tends to be reduced.

  When the porous semiconductor layer of the photoelectric conversion layer 3 is made of a polycrystalline sintered body, the average particle size of the crystallites constituting the polycrystalline sintered body is preferably 5 nm or more and less than 50 nm, preferably 10 nm or more and 30 nm. The following is more preferable. In this case, since an effective surface area sufficiently large with respect to the projected area can be obtained, there is a tendency that it can be converted into electric energy with high efficiency by increasing the amount of incident light. The average particle diameter of the crystallite can be calculated by applying Scherrer's equation to the X-ray diffraction spectrum of the porous semiconductor layer obtained by X-ray diffraction measurement, for example.

  The light scattering property of the photoelectric conversion layer 3 can be adjusted by the particle diameter (average particle diameter) of the semiconductor particles used for forming the porous semiconductor layer.

  For example, in the case where the photoelectric conversion layer 3 includes a porous semiconductor layer formed of semiconductor particles having a large average particle diameter, the light capturing property is high and more light is scattered, so that the light capture rate can be improved. It tends to be possible. For example, when the photoelectric conversion layer 3 includes a porous semiconductor layer formed of semiconductor particles having a small average particle diameter, the light scattering property is lowered, but the number of places where the photosensitizer can be held increases. There is a tendency that the amount of the photosensitizing element held in the photoelectric conversion layer 3 can be increased.

  The porous semiconductor layer of the photoelectric conversion layer 3 is, for example, a semiconductor layer made of semiconductor particles having an average particle diameter of 50 nm or more, more preferably an average particle diameter of 50 nm or more and 600 nm or less on the polycrystalline sintered body. It is good also as a structure which provided. Thus, the porous semiconductor layer of the photoelectric conversion layer 3 is not limited to a single layer, and may be a laminated structure of at least two layers.

  As a photosensitizer element hold | maintained at the porous semiconductor layer of the photoelectric converting layer 3, a pigment | dye and / or a quantum dot etc. can be used, for example.

  As the dye, for example, one or more of dyes such as organic dyes and / or metal complex dyes that can absorb light in the visible light region and / or infrared light region are selectively used. Can do.

  Examples of organic dyes include azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, perylene dyes, and indigo. At least one selected from the group consisting of system dyes can be used.

  In general, the extinction coefficient of an organic dye is larger than the extinction coefficient of a metal complex dye having a form in which molecules are coordinated to a transition metal.

  Examples of the metal complex dye include Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, La, W, Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac, Tc, Te, Rh, etc. It is possible to use at least one kind of dye having molecules coordinated to the metal. Examples of such metal complex dyes include porphyrin dyes, phthalocyanine dyes, and naphthalocyanine dyes.

  As the dye, a phthalocyanine dye or a ruthenium metal complex dye is preferably used, more preferably a ruthenium metal complex dye, and particularly, a ruthenium metal complex represented by the following formulas (I) to (III): It is preferable to use a dye. When a phthalocyanine dye or a ruthenium metal complex dye is used as the dye, particularly when a ruthenium metal complex dye represented by the following formulas (I) to (III) is used, light having a wavelength in the near infrared region is used. Therefore, the photoelectric conversion efficiency of the photoelectric conversion element can be increased. In the following formulas (II) and (III), “TBA” represents tetrabutylammonium.

  Moreover, in order to make a pigment | dye adsorb | suck firmly to the porous semiconductor layer of the photoelectric converting layer 3, a pigment | dye is a carboxylic acid group, a carboxylic anhydride, an alkoxy group, a hydroxyl group, a hydroxyalkyl group, a sulfonic acid group, an ester group. It preferably contains at least one selected from the group consisting of a mercapto group and a phosphonyl group, and particularly preferably contains a carboxylic acid group and / or a carboxylic acid anhydride. When the dye contains a carboxylic acid group and / or a carboxylic acid anhydride, the adsorptivity with the porous semiconductor layer is stable, and electron injection from the dye into the porous semiconductor layer tends to be performed efficiently. It is in. Note that these functional groups provide an electrical bond that facilitates electron transfer between the excited dye and the conduction band of the porous semiconductor layer.

  In addition, as the quantum dots, for example, at least one kind of fine particles selected from the group consisting of CdS, CdSe, PbS, and PbSe can be used. The particle diameter of the fine particles constituting the quantum dot is appropriately adjusted according to the absorption wavelength or the like, but is preferably 1 nm or more and 10 nm or less from the viewpoint of functioning as a quantum dot.

  The thickness of the photoelectric conversion layer 3 is preferably 4 μm or more and 30 μm or less. When the thickness of the photoelectric conversion layer 3 is 4 μm or more, the moving distance of electrons in the photoelectric conversion layer 3 becomes long, and thus the effect of providing the conductive layer 4 tends to be sufficiently exhibited. In addition, when the thickness of the photoelectric conversion layer 3 is 30 μm or less, a sufficient amount of light can be irradiated to the photosensitizer that is in contact with the photoelectric conversion layer 3, and thus the photoelectric conversion efficiency of the photoelectric conversion element Tend to improve.

<Conductive layer>
The conductive layer 4 can be used without particular limitation as long as it is a conductive material. For example, at least one metal selected from the group consisting of silver, copper, aluminum, indium, titanium, nickel, tantalum, and iron, or Two or more kinds of alloys can be used, and among them, it is preferable to use a material that can make ohmic contact with the photoelectric conversion layer 3. When a material that can make ohmic contact with the photoelectric conversion layer 3 is used for the conductive layer 4, the contact resistance between the photoelectric conversion layer 3 and the conductive layer 4 can be reduced, and the conductive layer 4 can be taken out of the photoelectric conversion element. Since the amount of current can be increased, the photoelectric conversion efficiency of the photoelectric conversion element tends to be improved.

  Examples of the conductive layer 4 include transparent conductive metal oxides such as zinc oxide doped with at least one selected from the group consisting of boron, gallium, and aluminum, titanium oxide doped with niobium, ITO, or FTO. Etc. can be used.

  When a material having a strong corrosive force such as iodine is used for the carrier transport material 8, it is preferable to use at least one selected from the group consisting of ITO, FTO, titanium and tantalum as the conductive layer 4. In this case, corrosion of the conductive layer 4 due to the carrier transport material 8 can be effectively suppressed. In addition, in the conductive layer 4, only the interface with the carrier transport material 8 is required to have corrosion resistance with respect to the carrier transport material 8, so that only the surface of the conductive layer 4 is covered with a material having corrosion resistance. Also good.

<Carrier transport material>
In the photoelectric conversion element of the embodiment shown in FIG. 1, the space sealed with the sealing material 6 between the transparent conductive layer 2 and the counter electrode conductive layer 5 is filled with a carrier transport material 8. The photoelectric conversion layer 3 is provided in the carrier transport material 8. That is, the carrier transport material 8 enters the pores of the photoelectric conversion layer 3.

  As the carrier transport material 8, a material containing a hardly volatile solvent and a redox species can be used. For example, a material in which a redox species is dissolved in a hardly volatile solvent can be used.

  Examples of the hardly volatile solvent include ionic liquids having no boiling point such as ethylmethylimidazolium bis (trifluoromethanesulfonyl) imide, carbonate compounds such as propylene carbonate, nitrile compounds such as 3-methoxypropionitrile, or water. It is preferable to use a solvent having a boiling point of 100 ° C. or higher. When an ionic liquid having no boiling point or a solvent having a boiling point of 100 ° C. or higher is used as the hardly volatile solvent, the durability of the photoelectric conversion element tends to be improved. Moreover, not only one type of solvent but also two or more types can be mixed and used as the hardly volatile solvent. In the present specification, “boiling point” means a boiling point at a pressure of 1 atm.

  Here, the viscosity of the hardly volatile solvent is preferably 1 cp (0.001 Pa · s) or more. When the viscosity of the hardly volatile solvent is 1 cp or more, since the loss at the time of electron transport due to carrier transport in the carrier transport material 8 is large, the effect of forming the conductive layer 4 is easily obtained. There is a tendency. The viscosity of the hardly volatile solvent can be measured, for example, with a conventionally known viscometer.

As the redox species, for example, at least one selected from the group consisting of I ⁻ / I ³⁻ series, Br ²⁻ / Br ³⁻ series, Fe ²⁺ / Fe ³⁺ series and quinone / hydroquinone series is used. be able to.

As the redox species, it is preferable to use a combination of metal iodide and iodine (I ₂ ), a combination of tetraalkylammonium salt and iodine (I ₂ ), or a combination of metal bromide and bromine (Br ₂ ). . In this case, for example, a better IV curve can be obtained as compared with a case where a cobalt complex or ferrocene is used as a redox species.

Here, as the metal iodide, for example, at least one selected from the group consisting of lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), and calcium iodide (CaI ₂ ) is used. Can be used.

  The tetraalkylammonium salt is selected from the group consisting of, for example, tetraethylammonium iodide (TEAI), tetrapropylammonium iodide (TPAI), tetrabutylammonium iodide (TBAI), and tetrahexylammonium iodide (THAI). At least one selected from the above can be used.

Further, as the metal bromide, for example, at least one selected from the group consisting of lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), and calcium bromide (CaBr ₂ ) is used. Can do.

Of these, a combination of LiI and I ₂ is preferably used as the redox species. This is because when the carrier transport material 8 contains Li cations, the electron injection efficiency from the excited dye to the porous semiconductor layer increases, and as a result, the obtained current density tends to increase. Because there is.

  Moreover, you may add an additive to the carrier transport material 8 as needed. Examples of such additives include aromatic compounds containing nitrogen such as t-butylpyridine (TBP) and / or dimethylpropylimidazole iodide (DMPII), methylpropylimidazole iodide (MPII), ethyl Imidazole salts such as methylimidazole iodide (EMII), ethylimidazole iodide (EII), and hexylmethylimidazole iodide (HMII) can be used.

  The concentration of the redox species in the carrier transport material 8 is appropriately selected depending on the type of the solvent, electrolyte, etc., and is preferably 0.001 mol / liter to 1.5 mol / liter. It is preferably from 01 mol / liter to 0.7 mol / liter. In this case, the redox species in the carrier transport material 8 tend to be transported efficiently.

  The electric conductivity of the carrier transport material 8 is preferably 1.5 S / m or less. When the electric conductivity of the carrier transport material 8 is 1.5 S / m or less, the electron transfer from the carrier transport material 8 to the photosensitizer is not efficiently performed, so the conductive layer 4 was formed. There exists a tendency which can fully express the effect by this.

<Counter electrode>
The counter electrode 12 includes a counter electrode conductive layer 5 and a catalyst layer 7 provided on the surface of the counter electrode conductive layer 5. The counter electrode conductive layer 5 collects electrons and can be electrically connected to an adjacent photoelectric conversion element. Further, the catalyst layer 7 has catalytic ability and can reduce holes in the carrier transport material 8.

  In the present embodiment, the counter electrode 12 is composed of the counter electrode conductive layer 5 and the catalyst layer 7. However, when the counter electrode conductive layer 5 has catalytic ability, or the catalyst layer 7 has high conductivity. In this case, the counter electrode 12 may be constituted by only one of the counter electrode conductive layer 5 and the catalyst layer 7.

  As the counter electrode conductive layer 5, a conductive material can be used. For example, at least one of metal oxides such as ITO, FTO, and ZnO, and / or titanium, tungsten, gold, silver, copper, nickel, and the like can be used. A conductive material containing at least one kind of metal can be used. Especially, it is preferable to use titanium as the counter electrode conductive layer 5. When titanium is used as the counter electrode conductive layer 5, the strength of the counter electrode conductive layer 5 can be significantly improved.

  For example, platinum and / or carbon is preferably used as the catalyst layer 7. When the catalyst layer 7 is made of carbon, examples of carbon used in the catalyst layer 7 include a group consisting of carbon black, graphite, glass carbon, amorphous carbon, hard carbon, soft carbon, carbon whisker, carbon nanotube, and fullerene. It is preferable to use at least one selected from

<Encapsulant>
The sealing material 6 can suppress the volatilization of the carrier transport material 8 and can suppress the intrusion of a liquid such as water into the photoelectric conversion element. Moreover, the sealing material 6 can absorb the stress (impact) which acts on the transparent support body 1, and can absorb the bending etc. which act on the transparent support body 1 at the time of long-term use of a photoelectric conversion element. .

  As the sealing material 6, for example, a single layer including at least one selected from the group consisting of a silicone resin, an epoxy resin, a polyisobutylene resin, a hot melt resin, and a glass frit, or the single layer is made into two or more layers. A plurality of stacked layers can be used. When a nitrile solvent or a carbonate solvent is used as the hardly volatile solvent of the carrier transport material 8, the sealing material 6 is a silicone resin, a hot melt resin (for example, an ionomer resin), or a polyisobutylene resin. And at least one selected from the group consisting of glass frit. In this case, corrosion of the sealing material 6 with respect to the carrier transporting material 8 tends to be suppressed.

<Manufacturing method>
Hereinafter, an example of a method for manufacturing the photoelectric conversion element of the embodiment will be described with reference to the schematic cross-sectional views of FIGS.

  First, as shown in FIG. 2, a step of preparing a transparent electrode plate 11 in which a transparent conductive layer 2 is provided on the surface of a light-transmissive support 1 is performed. Here, the step of preparing the transparent electrode plate 11 may be, for example, a commercially available one. For example, the transparent conductive layer 2 is formed on the surface of the light-transmissive support 1 by, for example, sputtering or thermal CVD. You may prepare by laminating | stacking by methods, such as a method.

Next, as shown in FIG. 3, a step of forming a porous semiconductor layer 3a on the surface of the transparent conductive layer 2 is performed. Here, the step of forming the porous semiconductor layer 3a is not particularly limited, but can be performed by, for example, at least one of the following methods (i) to (iv).
(I) A porous semiconductor layer 3a is formed on the surface of the transparent conductive layer 2 by applying a paste containing fine particles made of a semiconductor material on the surface of the transparent conductive layer 2 by a screen printing method or an ink jet method and then baking the paste. How to form.
(Ii) A method of forming the porous semiconductor layer 3a on the surface of the transparent conductive layer 2 by a CVD method or an MOCVD method using a desired source gas.
(Iii) A method of forming the porous semiconductor layer 3a on the surface of the transparent conductive layer 2 by a PVD method, a vapor deposition method or a sputtering method using a solid material.
(Iv) A method of forming the porous semiconductor layer 3a on the surface of the transparent conductive layer 2 by a sol-gel method or a method utilizing an electrochemical redox reaction.

  In particular, the step of forming the porous semiconductor layer 3a is performed by applying a paste containing fine particles made of a semiconductor material on the surface of the transparent conductive layer 2 by the screen printing method (i) and then baking the paste. It is preferable to use a method of forming the porous semiconductor layer 3 a on the surface of the conductive layer 2. In this case, the porous semiconductor layer 3a having a relatively large thickness tends to be produced at a low cost.

When forming the film-like and / or particulate porous semiconductor layer 3a, it is preferable to form the porous semiconductor layer 3a having a specific surface area of 10 m ² / g or more and 200 m ² / g or less. In this case, there is a tendency that the photoelectric conversion efficiency of the photoelectric conversion element can be improved by forming the photoelectric conversion layer 3 holding more photosensitizers.

  Hereinafter, a method for forming a porous semiconductor layer using anatase-type titanium oxide as semiconductor particles will be specifically described.

  First, 125 mL of titanium isopropoxide is dropped into 750 mL of a 0.1 M nitric acid aqueous solution for hydrolysis, and heated at 80 ° C. for 8 hours to prepare a sol solution.

  Next, the sol solution prepared as described above is heated in a titanium autoclave at 230 ° C. for 11 hours to grow titanium oxide particles, and then ultrasonic dispersion is performed at room temperature for 30 minutes to obtain an average particle size. A colloidal solution containing titanium oxide particles having a diameter (average primary particle diameter) of 15 nm is prepared.

  Next, to the colloid solution obtained as described above, ethanol twice the volume of the colloid solution is added, and this is centrifuged at a rotational speed of 5000 rpm to separate the titanium oxide particles and the solvent, Titanium oxide particles are obtained.

  Next, after washing the titanium oxide particles obtained as described above, the titanium oxide particles are dispersed by adding the titanium oxide particles to a solution of ethyl cellulose and terpineol dissolved in absolute ethanol and stirring.

  Next, a titanium oxide paste is obtained by heating the solution in which the above titanium oxide particles are dispersed under vacuum conditions to evaporate ethanol. And as a final composition, a density | concentration is adjusted so that it may become titanium oxide solid concentration 20 mass%, ethyl cellulose 10 mass%, and terpineol 70 mass%, for example. Note that the above-mentioned final composition is illustrative and is not limited to this.

  As a solvent used for preparing a paste containing semiconductor particles (suspended), in addition to the above, for example, a glyme solvent such as ethylene glycol monomethyl ether, an alcohol solvent such as isopropyl alcohol, isopropyl alcohol and the like A mixed solvent such as a mixed solution with toluene, water, or the like can be used.

  Next, the porous semiconductor layer 3a can be produced by screen printing the titanium oxide paste produced as described above on the surface of the transparent conductive layer 2 and then drying and baking the paste. Here, the drying conditions and firing conditions of the titanium oxide paste can be adjusted by appropriately setting conditions such as temperature, time, and atmosphere depending on the type of the light-transmissive support 1 and the semiconductor particles.

Firing of the titanium oxide paste can be performed, for example, in an air atmosphere or an inert gas atmosphere within a range of about 50 to 800 ° C. for about 10 seconds to 12 hours. The titanium oxide paste can be dried and fired, for example, once at a single temperature or twice or more at different temperatures. The specific surface area of the porous semiconductor layer 3a made of titanium oxide produced under the above conditions is in the range of 10 m ² / g or more and 200 m ² / g or less.

  The average particle diameter of the semiconductor particles constituting the porous semiconductor layer 3a is not particularly limited. However, in terms of effectively using incident light for photoelectric conversion, the average particle diameter should be uniform to some extent like a commercially available semiconductor material powder. Is more preferable.

  Next, as shown in FIG. 4, the process of forming the conductive layer 4 on the surface of the photoelectric converting layer 3 and the transparent conductive layer 2 is performed, respectively.

  Here, the conductive layer 4 can be formed on at least a part of the surface of the photoelectric conversion layer 3 by vapor deposition or sputtering, for example, so as to be electrically connected to the transparent conductive layer 2.

  Moreover, the photoelectric converting layer 3 can be formed by making a photosensitizer adsorb | suck to the porous semiconductor layer 3a, for example. Here, as a method for adsorbing the photosensitizer on the porous semiconductor layer 3a, for example, the porous semiconductor layer 3a formed on the surface of the transparent conductive layer 2 is immersed in a solution in which the photosensitizer is dissolved. Can be used. In addition, immersion conditions can be adjusted suitably.

  Solvents that dissolve the photosensitizer include, for example, alcohols such as ethanol, ketones such as acetone, ethers such as diethyl ether and tetrahydrofuran, nitrogen compounds such as acetonitrile, and halogenated aliphatic hydrocarbons such as chloroform. One kind selected from aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, esters such as ethyl acetate, and water, or a mixture of two or more kinds can be used.

When a dye adsorption solution in which a dye is dissolved in the above solvent is used as the solution in which the photosensitizer is dissolved, the dye concentration in the dye adsorption solution is appropriately adjusted according to the type of the dye and the solvent. However, in order to improve the adsorption function (efficiency), the concentration is preferably as high as possible, for example, 5 × 10 ⁻⁴ mol / liter or more.

  Next, as shown in FIG. 5, a step of forming the counter electrode 12 by forming the catalyst layer 7 on the surface of the counter electrode conductive layer 5 is performed. Here, when platinum is used as the catalyst layer 7, the catalyst layer 7 is formed by a known method such as a PVD method such as a vapor deposition method or a sputtering method, thermal decomposition or electrodeposition of chloroplatinic acid, for example. Can do. Here, the thickness of the catalyst layer 7 can be 0.5 nm or more and 1000 nm or less, for example.

  When a carbon material such as carbon black, ketjen black, carbon nanotube, or fullerene is used as the catalyst layer 7, the catalyst layer 7 is, for example, a screen printing method in which carbon dispersed in an arbitrary solvent is pasted. Can be formed by coating on the surface of the counter electrode conductive layer 5. Also here, the thickness of the catalyst layer 7 can be, for example, not less than 0.5 nm and not more than 1000 nm.

  The thickness of the counter electrode conductive layer 5 is preferably selected as appropriate according to the specific resistivity of the material of the counter electrode conductive layer 5. This is because if the counter electrode conductive layer 5 is too thin, the resistance is increased, and if it is too thick, the movement of the carrier transport material 8 is hindered.

  Thereafter, as shown in FIG. 1, a step of installing a carrier transport material 8 in a region between the transparent conductive layer 2 of the transparent electrode plate 11 and the catalyst layer 7 of the counter electrode 12 is performed. The step of installing the carrier transport material 8 includes, for example, installing the sealing material 6 so as to surround the photoelectric conversion layer 3 of the transparent electrode plate 11, the transparent conductive layer 2 of the transparent electrode plate 11, and the counter electrode 12. The transparent electrode plate 11 and the counter electrode 12 are arranged so that the catalyst layer 7 faces each other, and the transparent electrode plate 11 and the counter electrode 12 are fixed by the sealing material 6. Thereafter, the carrier transport material 8 is injected into the region surrounded by the sealing material 6 from the hole provided in the transparent electrode plate 11, and then the hole is closed, whereby the photoelectric conversion element of the embodiment shown in FIG. Can be produced.

<Action and effect>
This inventor considered that the fall of the photoelectric conversion efficiency of the conventional photoelectric conversion element resulting from the high viscosity of a hardly volatile solvent is based on the following mechanisms. That is, since the viscosity of the hardly volatile solvent is high, the rate of diffusion of ions that play a role of reducing the dye excited by absorbing light in the carrier transport material 8 is reduced, and the transparent electrode of the photoelectric conversion layer 3 The time during which the photosensitizer such as a dye existing on the plate 11 side is a cation becomes longer. Thereby, the probability that the photosensitizer present on the counter electrode 12 side of the photoelectric conversion layer 3 absorbs light increases, while the electrons generated on the counter electrode 12 side of the photoelectric conversion layer 3 reach the transparent conductive layer 2. Therefore, the probability that electrons are trapped inside the photoelectric conversion layer 3 is increased, and the current density is significantly reduced.

  Therefore, as a result of intensive studies by the present inventors, in the photoelectric conversion element of the embodiment manufactured as described above, a hardly volatile solvent is used as the solvent of the carrier transport material 8 and the counter electrode 12 of the photoelectric conversion layer 3 is used. The conductive layer 4 is provided on at least a part of the surface on the side, and the conductive layer 4 is electrically connected to the transparent conductive layer 2.

  Thereby, in the photoelectric conversion element of embodiment, the durability of the photoelectric conversion element can be improved, and electrons generated on the counter electrode 12 side of the photoelectric conversion layer 3 are guided from the conductive layer 4 to the transparent conductive layer 2. As a result, the probability that electrons are trapped inside the photoelectric conversion layer 3 can be lowered, so that a significant decrease in current density can be suppressed and a decrease in photoelectric conversion efficiency can be suppressed.

  The present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples. In the following examples and comparative examples, the thickness of each layer was measured with a step gauge (E-VS-S28A manufactured by Tokyo Seimitsu Co., Ltd.).

<Example 1>
In Example 1, a photoelectric conversion element having the structure shown in FIG. 1 was produced. First, a transparent electrode plate 11 having a width of 30 mm × a length of 30 mm × a thickness of 1 mm, in which a transparent conductive layer 2 made of tin oxide (FTO) doped with fluorine is formed on a light-transmitting support 1 made of glass. (Nippon Sheet Glass Co., Ltd. glass with SnO ₂ film) was prepared.

  Next, on the surface of the transparent electrode plate 11 on the transparent conductive layer 2 side, a screen plate having a pattern of a porous semiconductor layer having a width of 5 mm × a length of 5 mm and a screen printing machine (manufactured by Neurong Precision Industry Co., Ltd., model number: LS-150), a commercially available titanium oxide paste (manufactured by Solaronix, trade name: D / SP) was applied and leveled at room temperature for 1 hour.

  Next, the coating film obtained as described above was dried in an oven set at 80 ° C. for 20 minutes, and further using a baking furnace (model number: KDF P-100, manufactured by Denken Co., Ltd.) set at 500 ° C. Baked for 60 minutes in air. The above coating, drying and firing steps were repeated to obtain a porous semiconductor layer having a thickness of about 12 μm. Furthermore, by using a titanium oxide paste (manufactured by JGC Catalysts & Chemicals Co., Ltd., PST-400C) having a different particle size on the obtained porous semiconductor layer, it is finally subjected to the above coating, drying and firing steps, A porous semiconductor layer having a thickness of about 18 μm was formed.

  Next, a metal mask in which rectangular openings with a width of 6 mm and a length of 12 mm are arranged is prepared, and an electron beam evaporator ei-5 (manufactured by ULVAC, Inc.) is formed on the surfaces of the porous semiconductor layer and the transparent conductive layer 2. A conductive film 4 having a thickness of about 300 nm was formed by depositing a titanium film at a deposition rate of 150 nm / sec.

  Next, the transparent electrode plate 11 after the formation of the conductive layer 4 is immersed in a dye adsorption solution prepared in advance at room temperature for 100 hours, and the transparent electrode plate 11 after the formation of the conductive layer 4 is immersed in ethanol. And dried at about 60 ° C. for about 5 minutes, thereby adsorbing the dye to the porous semiconductor layer to form the photoelectric conversion layer 3.

The dye adsorption solution was prepared by dissolving the dye of the above formula (II) (manufactured by Solaronix, trade name: Ruthenium 620 1H3TBA) in a mixed solvent of acetonitrile and t-butanol having a volume ratio of 1: 1. The solution was × 10 ^-4 mol / liter.

Next, another transparent electrode plate (Nippon Sheet Glass Co., Ltd., glass with SnO ₂ film) is prepared as the counter electrode conductive layer 5, and the catalyst layer 7 is formed on the surface of the SnO ₂ film of the counter electrode conductive layer 5. As a result, a counter electrode 12 was formed by forming a platinum film having a thickness of about 7 nm by sputtering.

  Next, using a heat-sealing film (manufactured by DuPont, High Milan 1855) in which the transparent electrode layer 2 of the transparent electrode plate 11 and the catalyst layer 7 of the counter electrode 12 are cut out to surround the photoelectric conversion layer 3. These were bonded and pressure-bonded by heating in an oven set at about 100 ° C. for 10 minutes.

  Next, an electrolytic solution is injected as a carrier transport material 8 from a hole provided in advance in the transparent electrode plate 11, and then the hole is sealed using an ultraviolet curable resin (manufactured by Three Bond, model number: 31X-101). Thus, the carrier transport material 8 was filled to obtain the photoelectric conversion element of the example.

The above electrolytic solution was prepared by using 3-methoxypropionitrile (boiling point: 165 ° C., viscosity: 1.1 cp) as a solvent, GuSCN (guanidine thiocyanate) as a redox species at a concentration of 0.1 mol / liter, I ₂ (Kishida Chemical Co., Ltd.) N-methylbenzimidazole was added as an additive at a concentration of 0.5 mol / liter, and methylpropylimidazole iodide (manufactured by Shikoku Kasei Kogyo Co., Ltd.) was added as an additive. It was added and dissolved so as to have a concentration of 0.8 mol / liter. The electric conductivity of this electrolytic solution was 1.5 S / m or less.

<Example 2>
In Example 1, the photoelectric conversion element of Example 2 was produced by the same method as Example 1 except that the photoelectric conversion layer 3 (see Table 1) having different pore diameters was formed.

<Comparative Example 1>
In Example 1, the photoelectric conversion element of Comparative Example 1 was produced in the same manner as in Example 1 except that the conductive layer 4 was not formed.

<Comparative example 2>
In Example 2, a photoelectric conversion element of Comparative Example 2 was produced in the same manner as in Example 2 except that the conductive layer 4 was not formed.

<Comparative Example 3>
In Example 1, in place of 3-methoxypropionitrile, acetonitrile (boiling point: 82 ° C., viscosity: 0.341 cp), which is a volatile solvent, was used as a comparative example in the same manner as in Example 1. 3 photoelectric conversion elements were produced.

<Comparative example 4>
In Comparative Example 3, a photoelectric conversion element of Comparative Example 4 was produced by the same method as Comparative Example 3 except that the conductive layer 4 was not formed.

<Measurement of photoelectric conversion efficiency>
Ag paste (made by Fujikura Kasei Co., Ltd., trade name: Dotite) was applied to each of the photoelectric conversion elements of Examples 1 and 2 and Comparative Examples 1 to 4 as a collecting electrode part by a known method. Next, a black mask having an opening area of 0.22 cm ² is installed on the light receiving surface of each photoelectric conversion element, and light of 1 kW / m ² intensity (AM1.5 solar) is applied to each photoelectric conversion element. The photoelectric conversion efficiency was measured by irradiating a simulator.

  As is clear from the results shown in Table 1, the photoelectric conversion elements of Examples 1 and 2 that satisfy the constituent requirements of the present invention are more photoelectrical than the photoelectric conversion elements of Comparative Examples 1 and 2 that are conventional photoelectric conversion elements. It was confirmed that the conversion efficiency was improved. Further, as apparent from Comparative Example 3 and Comparative Example 4, when acetonitrile, which is a volatile solvent having a low boiling point and a low viscosity solvent, is used, the photoelectric conversion efficiency due to the formation of the conductive layer 4 is improved. The improvement effect could not be confirmed.

  In addition, when the solvent viscosity is high, by having the photoelectric conversion layer 3 having a large pore diameter, electrons due to carrier transport in the carrier transporting material 8 as compared with the case having the photoelectric conversion layer 3 having a small pore diameter. It was predicted that the loss during transportation was reduced, and the effect of forming the conductive layer 4 was reduced. However, by comparing the photoelectric conversion elements of Examples 1 and 2 and Comparative Examples 1 and 2, respectively, in the photoelectric conversion element having the photoelectric conversion layer 3 having a large pore diameter, the photoelectric conversion element having the photoelectric conversion layer 3 having a small pore diameter. It was confirmed that the effect of forming the conductive layer 4 was more remarkable than that of the conversion element.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The photoelectric conversion element of this invention can be utilized suitably for wet solar cells, such as a dye-sensitized solar cell.

  DESCRIPTION OF SYMBOLS 1 Light-transmissive support body, 2 Transparent conductive layer, 3 Photoelectric conversion layer, 3a Porous semiconductor layer, 4 Conductive layer, 5 Counter electrode conductive layer, 6 Sealing material, 7 Catalyst layer, 8 Carrier transport material, 11 Transparent electrode plate , 12 Counter electrode.

Claims (5)

A light transmissive support;
A transparent conductive layer provided on the light transmissive support;
A photoelectric conversion layer including a porous semiconductor layer provided on the transparent conductive layer;
A conductive layer provided on at least a part of the photoelectric conversion layer;
A counter electrode conductive layer provided to face the transparent conductive layer;
A carrier transport material provided between the transparent conductive layer and the counter electrode conductive layer,
The carrier transport material includes a hardly volatile solvent and a redox species,
The conductive layer is a photoelectric conversion element electrically connected to the transparent conductive layer.   The photoelectric conversion element according to claim 1, wherein the hardly volatile solvent does not have a boiling point, or the boiling point of the hardly volatile solvent is 100 ° C. or higher.   The photoelectric conversion element of Claim 1 or 2 whose thickness of the said photoelectric converting layer is 4 micrometers or more and 30 micrometers or less.   The photoelectric conversion element according to claim 1, wherein the hardly volatile solvent has a viscosity of 1 cp or more.   The photoelectric conversion element according to claim 1, wherein the carrier transport material has an electric conductivity of 1.5 S / m or less.

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