JP2013131458A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element offering a high short circuit current density and capable of being manufactured at low cost.SOLUTION: The photoelectric conversion element includes a translucent substrate, a photoelectric conversion layer provided on the translucent substrate, a collector electrode provided on at least a portion of the photoelectric conversion layer, a counter electrode conductive layer facing the translucent substrate, a catalyst layer provided on the translucent substrate-side surface of the counter electrode conductive layer, and a carrier transport material provided between the translucent substrate and the catalyst layer. The photoelectric conversion layer contains a first porous semiconductor layer provided on the translucent substrate, a second porous semiconductor layer provided on the first porous semiconductor layer, and a photosensitizer adsorbed in the first porous semiconductor layer and the second porous semiconductor layer. The porosity of the first porous semiconductor layer is higher than the porosity of the second porous semiconductor 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 photoelectric conversion element using a photo-induced electron transfer of a metal complex as a new type of solar cell. In this photoelectric conversion element, a photosensitizing dye is adsorbed between the electrodes of two glass substrates on which electrodes (first electrode and second electrode) are formed, and an absorption spectrum is provided in the visible light region. It has a structure in which the conversion layer and the electrolytic solution are sandwiched. In this photoelectric conversion element, when light is irradiated to the transparent first electrode side, electrons are generated in the photoelectric conversion layer, and the generated electrons move from one first electrode to the opposing second electrode through an external electric circuit. Then, a phenomenon occurs in which the moved electrons are carried by the ions in the electrolyte and return to the photoelectric conversion layer. By repeating such a series of electron movements, electric energy can be extracted.

  In Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-352870), in a porous film composed of a plurality of layers formed on a transparent electrode, the porous film is disposed at a position farthest from a layer disposed at a position closest to the transparent electrode. There has been proposed a dye-sensitized solar cell in which the pore size distribution is increased over the layers. The purpose of this is to ensure the adsorption amount of the sensitizing dye and to quickly supply the reactant to the reaction site inside the semiconductor electrode.

  Moreover, since the basic structure of the photoelectric conversion element described in Patent Document 1 is a structure using a substrate (TCO substrate) on which a transparent conductive film is formed, there is a problem that the cost is high. In order to solve this problem, for example, Patent Document 3 (Japanese Patent No. 4415448) proposes a photoelectric conversion element that does not use a TCO substrate. In the photoelectric conversion element described in Patent Document 3, a porous semiconductor layer is formed on a light-transmitting substrate instead of using a TCO substrate, and a perforated current collecting electrode having an eye roughness of 20 to 500 mesh is formed thereon. Forming.

However, a photoelectric conversion element that does not use a TCO substrate has a problem that a short-circuit current density (J _sc ) is lower than a photoelectric conversion element having a conventional structure.

Japanese Patent No. 2664194 JP 2002-352870 A Japanese Patent No. 4415448

  In view of the above circumstances, an object of the present invention is to provide a photoelectric conversion element capable of manufacturing a photoelectric conversion element exhibiting a high short-circuit current density at low cost.

  The present invention provides a light-transmitting substrate, a photoelectric conversion layer provided on the light-transmitting substrate, a current collecting electrode provided on at least a part of the photoelectric conversion layer, and a light-transmitting substrate. A counter electrode conductive layer, a catalyst layer provided on the surface of the counter electrode conductive layer on the side of the light-transmitting substrate, and a carrier transporting material provided between the light-transmitting substrate and the catalyst layer. The layer includes a first porous semiconductor layer provided on the translucent substrate, a second porous semiconductor layer provided on the first porous semiconductor layer, a first porous semiconductor layer, and A photoelectric conversion element comprising a photosensitizer adsorbed on each of the second porous semiconductor layers, wherein the porosity of the first porous semiconductor layer is larger than the porosity of the second porous semiconductor layer. .

  Here, in the photoelectric conversion element of this invention, it is preferable that a 1st porous semiconductor layer consists of semiconductor fine particles with an average particle diameter of 50 nm or less.

  In the photoelectric conversion element of the present invention, the thickness of the first porous semiconductor layer is preferably 50% or less of the thickness of the photoelectric conversion layer.

  Moreover, in the photoelectric conversion element of this invention, it is preferable that the porosity of the 1st porous semiconductor layer is 55% or more.

  The photoelectric conversion element of the present invention further includes a third porous semiconductor layer provided on the second porous semiconductor layer, and the average particle size of the semiconductor fine particles constituting the third porous semiconductor layer is The average particle diameter of the semiconductor fine particles constituting the second porous semiconductor layer is preferably larger.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion element which can manufacture the photoelectric conversion element which has a high short circuit current density at low cost can be provided.

It is typical sectional drawing of the photoelectric conversion element of 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 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 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 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 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 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 of the present embodiment includes a translucent substrate 1, a photoelectric conversion layer 5 provided on the translucent substrate 1, and a collecting electrode 6 provided on at least a part of the photoelectric conversion layer 5. The counter electrode conductive layer 7 provided so as to face the translucent substrate 1, the catalyst layer 11 provided on the surface of the counter electrode conductive layer 7 on the side of the translucent substrate 1, the translucent substrate 1 and the catalyst layer 11 and the carrier transporting material 8 provided between the two.

  Here, the translucent substrate 1 and the counter electrode conductive layer 7 are arranged at a predetermined distance so as to face each other, and the carrier transport material 8 is interposed between the translucent substrate 1 and the counter electrode conductive layer 7. A sealing material 9 for bonding the translucent substrate 1 and the counter electrode conductive layer 7 is disposed so as to surround the substrate.

  In addition, the current collecting electrode 6 passes through the upper surface and side surfaces of the photoelectric conversion layer 5 and the surface of the light transmissive substrate 1 so that a current can be taken out of the photoelectric conversion element, and the light transmissive substrate 1 and the sealing material 9. It extends from the space between and outside.

  Furthermore, the photoelectric conversion layer 5 includes a first porous semiconductor layer 2 provided on the translucent substrate 1, a second porous semiconductor layer 3 provided on the first porous semiconductor layer 2, and The third porous semiconductor layer 4 provided on the second porous semiconductor layer 3 has a laminated structure. Here, a photosensitizer is adsorbed to each of the first porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4.

  In the photoelectric conversion element of the present embodiment, the porosity of the first porous semiconductor layer 2 is larger than the porosity of the second porous semiconductor layer 3. Thereby, in the photoelectric conversion element of this Embodiment, in order to show a high short circuit current density even if it does not use a TCO board | substrate, it can manufacture at low cost compared with the photoelectric conversion element using the conventional TCO board | substrate. it can.

<Translucent substrate>
As the light-transmitting substrate 1, at least a light-transmitting material can be used. However, any material may be used as long as it is a material that substantially transmits light having a wavelength that has an effective sensitivity to at least a dye described later, and is not necessarily transparent to light in all wavelength regions.

  Examples of the light-transmitting material used for the light-transmitting substrate 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. be able to.

  Examples of the flexible film used for the translucent substrate 1 include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PA), and polyether. A film such as imide (PEI), phenoxy resin, or polytetrafluoroethylene (PTFE) can be used.

  As a flexible film used for the translucent substrate 1, it is preferable to use a PTFE film. Since the PTFE film has a heat resistance of 250 ° C. or higher, when the surface of the translucent substrate 1 is heated to, for example, about 250 ° C., thermal damage to the translucent substrate 1 tends to be suppressed.

  Moreover, although the thickness of the translucent board | substrate 1 is not specifically limited, It is preferable that they are 0.2 mm or more and 5 mm or less. When the thickness of the translucent substrate 1 is 0.2 mm or more, the translucent substrate 1 tends to exhibit a function as a support. When the thickness of the translucent substrate 1 is 5 mm or less, the amount of light transmitted through the translucent substrate 1 increases and the short-circuit current density of the photoelectric conversion element tends to increase.

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

<Photoelectric conversion layer>
As the photoelectric converting layer 5, what contains a porous semiconductor layer and the pigment | dye adsorb | sucked to a porous semiconductor layer can be used. The carrier transport material 8 can move freely inside and outside the photoelectric conversion layer 5. The thickness T of the photoelectric conversion layer 5 is not particularly limited, but is preferably 1 μm or more and 50 μm or less, and more preferably 5 μm or more and 30 μm or less.

<Porous semiconductor layer>
The porous semiconductor layer (the first porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4) used for the photoelectric conversion layer 5 is composed of a porous semiconductor. Is not particularly limited, for example, titanium oxide, zinc oxide, tin oxide, iron oxide, niobium oxide, cerium oxide, tungsten oxide, barium titanate, strontium titanate, cadmium sulfide, lead sulfide, zinc sulfide, phosphide A layer made of a porous semiconductor containing at least one selected from the group consisting of indium, copper indium sulfide (CuInS ₂ ), CuAlO ₂ and SrCu ₂ O ₂ can be used. Among these, titanium oxide is preferably used from the viewpoint of improving the stability and safety of the porous semiconductor layer.

  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. As the titanium oxide, it is preferable to use an anatase type content of 80% or more.

  As the porous semiconductor layer, for example, a single crystal or a polycrystalline semiconductor can be used. From the viewpoint of improving the stability of the porous semiconductor layer, easiness of crystal growth, and reducing manufacturing costs, the polycrystalline semiconductor layer can be used. The semiconductor is preferably used, and the form of polycrystalline semiconductor fine particles is particularly preferable. Here, the average particle diameter of the semiconductor fine particles is, for example, not less than 1 nm and not more than 1000 nm.

  Accordingly, it is particularly preferable to use fine particles of titanium oxide (average particle diameter: 1 nm or more and 1000 nm or less) as the porous semiconductor layer. The fine particles of titanium oxide can be produced by a known method such as a gas phase method or a liquid phase method (hydrothermal synthesis method, sulfuric acid method). It can also be produced by high-temperature hydrolysis of chlorides developed by Degussa.

  As the semiconductor fine particles, a mixture of two or more different types of semiconductor fine particles made of the same or different semiconductors may be used. It is considered that semiconductor fine particles having a large particle diameter scatter incident light and contribute to an improvement in the light capture rate, and semiconductor fine particles having a small particle diameter contribute to an improvement in the amount of dye adsorbed by increasing the number of adsorption points. Here, the ratio of the average particle diameter of the semiconductor fine particles having different particle diameters is preferably 10 times or more, and the average particle diameter of the semiconductor fine particles having a large particle diameter is 100 nm to 500 nm, and the semiconductor having a small particle diameter The average particle size of the fine particles is more preferably 5 nm or more and 50 nm or less. In the case of using mixed particles composed of two or more kinds of semiconductor fine particles of different semiconductors, it is effective to make semiconductor fine particles having a stronger dye adsorption action into semiconductor fine particles having a small particle diameter.

<First porous semiconductor layer>
The first porous semiconductor layer 2 is a porous semiconductor layer formed in contact with the translucent substrate 1 among the porous semiconductor layers formed on the translucent substrate 1. As described above, the porosity of the first porous semiconductor layer 2 is made larger than the porosity of the second porous semiconductor layer 3 formed on the first porous semiconductor layer 2. Thereby, in the photoelectric conversion element which does not have a TCO substrate in which the current collecting electrode 6 is formed on the side opposite to the light receiving surface of the photoelectric conversion layer 5, the distribution of electrons generated by the dye absorbing the light is collected. It is considered that the current collection effect is increased and a high short-circuit current density is exhibited.

  The porosity of the first porous semiconductor layer 2 is preferably 55% or more. When the porosity of the 1st porous semiconductor layer 2 is 55% or more, it exists in the tendency for the short circuit current density of a photoelectric conversion element to become higher.

  The porosity of the first porous semiconductor layer 2 is preferably 75% or less. When the porosity of the first porous semiconductor layer 2 is 75% or less, the first porous semiconductor layer 2 retains sufficient strength, and the first porous semiconductor from the translucent substrate 1 The peeling of the layer 2 can be effectively suppressed.

In the present specification, the “porosity” can be obtained by the following equation (a).
Porosity (%) = 100 × (mass of porous semiconductor layer) / ((volume of porous semiconductor layer) × (density of semiconductor material constituting porous semiconductor layer)) (a)
When the first porous semiconductor layer 2 is composed of semiconductor fine particles, the average particle diameter of the semiconductor fine particles constituting the first porous semiconductor layer 2 is preferably 50 nm or less, and is 30 nm or less. It is more preferable. When the average particle size of the semiconductor fine particles constituting the first porous semiconductor layer 2 is 50 nm or less, particularly when it is 30 nm or less, more light that has entered from the translucent substrate 1 side is the first light. Since the light is transmitted to the collecting electrode 6 side without being scattered by the porous semiconductor layer 2, the photoelectric conversion element tends to exhibit a larger short-circuit current density.

  The thickness T1 of the first porous semiconductor layer 2 is preferably 50% or less of the thickness T of the photoelectric conversion layer 5. Since the photoelectric conversion layer 5 can absorb more light when the thickness T1 of the first porous semiconductor layer 2 is 50% or less of the thickness T of the photoelectric conversion layer 5, photoelectric conversion The device tends to exhibit a larger short circuit current density.

<Second porous semiconductor layer>
The 2nd porous semiconductor layer 3 is a porous semiconductor layer formed on the 1st porous semiconductor layer 2, The porosity of the 2nd porous semiconductor layer 3 is the 1st porous semiconductor layer. The porosity is smaller than 2. Note that the porosity of the second porous semiconductor layer 3 is smaller than that of the first porous semiconductor layer 2 can be confirmed by SEM (Scanning Electron Microscope) observation of the cross section of the photoelectric conversion layer 5.

<Third porous semiconductor layer>
The third porous semiconductor layer 4 is a porous semiconductor layer formed on the second porous semiconductor layer 3. When the second porous semiconductor layer 3 and the third porous semiconductor layer 4 are each composed of semiconductor fine particles, the average particle diameter of the semiconductor fine particles constituting the third porous semiconductor layer 4 is the second The average particle diameter of the semiconductor fine particles constituting the porous semiconductor layer 3 is preferably larger. When the average particle size of the semiconductor fine particles constituting the third porous semiconductor layer 4 is larger than the average particle size of the semiconductor fine particles constituting the second porous semiconductor layer 3, the light scattering effect is further enhanced. The light utilization efficiency tends to improve and the short circuit current density tends to improve.

  The third porous semiconductor layer 4 may have a structure in which a plurality of porous semiconductor layers made of semiconductor fine particles having different average particle diameters are stacked. In this case, in order to improve the light scattering effect. In addition, it is preferable to form a porous semiconductor layer made of fine particles having a large average particle diameter in a portion far from the light receiving surface. Further, when the third porous semiconductor layer 4 has a structure in which a plurality of porous semiconductor layers made of semiconductor fine particles having different average particle diameters are stacked, a plurality of the plurality of porous semiconductor layers 4 constituting the third porous semiconductor layer 4 are formed. At least one of the porous semiconductor layers is preferably composed of semiconductor fine particles having an average particle diameter of 300 nm or more. If the photoelectric conversion layer 5 has sufficient light absorption with only the two-layer structure of the first porous semiconductor layer 2 and the second porous semiconductor layer 3, the third porous semiconductor layer 4 is It does not have to be formed.

<Photosensitizer>
As the photosensitizer adsorbed on the porous semiconductor layer, for example, one of dyes such as an organic dye and / or a metal complex dye that can absorb light having a wavelength in the visible light region and / or the infrared light region. Species or two or more can be selectively used.

  Examples of organic dyes include azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, porphyrin dyes, and perylenes. At least one selected from the group consisting of a system dye, an indigo dye, and a naphthalocyanine dye 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.

  As the metal complex dye, one in which a metal is coordinated to a molecule can be used. Here, examples of the molecule include porphyrin dyes, phthalocyanine dyes, naphthalocyanine dyes, ruthenium dyes, and the like. Examples of the metal 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 done. Among these, as the metal complex dye, those in which a metal is coordinated to a phthalocyanine dye or ruthenium dye are preferable, and those in which a metal is coordinated to a ruthenium metal complex dye are particularly preferable.

  As the photosensitizer, it is particularly preferable to use ruthenium-based metal complex dyes represented by the following formulas (I) to (III). When a ruthenium-based metal complex dye represented by the following formulas (I) to (III) is used as a photosensitizer, light having a wavelength in the near-infrared region can be absorbed. The short circuit current density of the element can be increased.

  Examples of commercially available ruthenium-based metal complex dyes include trade name Ruthenium 535 dye, Ruthenium 535-bisTBA dye, Ruthenium 620-1H3TBA dye manufactured by Solaronix. In the following formulas (II) and (III), “TBA” represents tetrabutylammonium.

  In order to firmly adsorb the dye to the porous semiconductor layer, at least selected from the group consisting of a carboxyl group, an alkoxy group, a hydroxyl group, a sulfo group, an ester group, a mercapto group, and a phosphonyl group in the dye molecule. Those having one type of interlocking group are preferred. The interlock group is generally present when the dye is fixed to the porous semiconductor layer, and provides an electrical bond that facilitates the movement of electrons between the excited dye and the semiconductor conduction band. To do.

<Collector electrode>
As the collector electrode 6, indium tin composite oxide (ITO), tin oxide (SnO ₂ ), tin oxide doped with fluorine (FTO), zinc oxide (ZnO), titanium, nickel, tantalum, or the like is used. be able to.

  The thickness of the current collecting electrode 6 is preferably 0.02 μm or more and 5 μm or less, and the electric resistance of the current collecting electrode 6 is preferably as low as possible, and more preferably 40Ω / □.

  The collecting electrode 6 is preferably provided with a small hole. When the collecting electrode 6 is provided with a small hole, when the collecting electrode 6 is formed, when the electrode is immersed in a solution containing a dye or infiltrated with an electrolyte, the solution or the electrolyte containing the dye Therefore, the short circuit current density of the photoelectric conversion element tends to be increased.

  The small holes of the current collecting electrode 6 can be formed by, for example, a mechanical method or laser processing. Here, the small hole of the current collecting electrode 6 is preferably an opening having a diameter of 0.1 μm or more and 100 μm or less, and more preferably an opening of 1 μm or more and 50 μm or less. The interval between adjacent small holes is preferably 1 μm or more and 200 μm or less, and more preferably 10 μm or more and 300 μm or less.

<Carrier transport material>
As the carrier transport material 8, a conductive material capable of transporting ions can be used. For example, a liquid electrolyte, a solid electrolyte, a gel electrolyte, a molten salt gel electrolyte, or the like can be used. The carrier transport material 8 is present in a form that fills the voids of the structure formed between the translucent substrate 1 and the counter electrode conductive layer 7.

  The liquid electrolyte is not particularly limited as long as it is a liquid substance containing a redox species, and can be generally used in a battery, a solar battery, or the like. Examples of the liquid electrolyte include those comprising a redox species and a solvent capable of dissolving the same, those comprising a redox species and a molten salt capable of dissolving the same, or a redox species and a solvent and molten salt capable of dissolving the same. The thing which consists of can be used.

Examples of the redox species include I ⁻ / I ³⁻ series, Br ²⁻ / Br ³⁻ series, Fe 2 ⁺ / Fe ³⁺ series, and quinone / hydroquinone series. As the redox species, among others, combinations of metal iodides such as lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), calcium iodide (CaI ₂ ) and iodine (I ₂ ) Tetraalkylammonium iodide (TEAI), Tetrapropylammonium iodide (TPAI), Tetrabutylammonium iodide (TBAI), Tetrahexylammonium iodide (THAI) and other combinations of tetraalkylammonium salts and iodine, and lithium bromide A combination of a metal bromide such as (LiBr), sodium bromide (NaBr), potassium bromide (KBr), calcium bromide (CaBr ₂ ) and bromine is preferable, and among these, a combination of LiI and I ₂ is particularly preferable.

  Examples of the redox species solvent include carbonate compounds such as propylene carbonate, nitrile compounds such as acetonitrile, alcohols such as ethanol, water, and aprotic polar substances. Among these, carbonate compounds and nitrile compounds are particularly preferable. Two or more of these solvents can be used in combination.

  The solid electrolyte is a conductive material that can transport electrons, holes, and ions, and can be used as an electrolyte of a solar cell and has no fluidity. Examples of the solid electrolyte include a hole transport material such as polycarbazole, an electron transport material such as tetranitrofluororenone, a conductive polymer such as polyroll, a polymer electrolyte obtained by solidifying a liquid electrolyte with a polymer compound, and copper iodide. A p-type semiconductor such as copper thiocyanate, or an electrolyte obtained by solidifying a liquid electrolyte containing a molten salt with fine particles can be used.

  The gel electrolyte is usually composed of an electrolyte and a gelling agent. Examples of gelling agents include polymer gelation such as crosslinked polyacrylic resin derivatives, crosslinked polyacrylonitrile derivatives, polyalkylene oxide derivatives, silicone resins, and polymers having a nitrogen-containing heterocyclic quaternary compound salt structure in the side chain. An agent or the like can be used.

  The molten salt gel electrolyte is usually composed of the gel electrolyte as described above and a room temperature molten salt. Examples of the room temperature molten salt include nitrogen-containing heterocyclic quaternary ammonium salt compounds such as pyridinium salts and imidazolium salts.

  You may add an additive to said electrolyte as needed. Additives include nitrogen-containing aromatic compounds such as t-butylpyridine (TBP), or dimethylpropylimidazole iodide (DMPII), methylpropylimidazole iodide (MPII), ethylmethylimidazole iodide (EMII), ethylimidazole An imidazole salt such as iodide (EII) or hexylmethylimidazole iodide (HMII) can be used.

  The electrolyte concentration in the electrolyte is preferably 0.001 mol / L or more and 1.5 mol / L or less, and more preferably 0.01 mol / L or more and 0.7 mol / L or less.

<Counter electrode conductive layer>
As the counter electrode conductive layer 7, a conductive material can be used, which may or may not have optical transparency. However, in the case where the counter electrode conductive layer 7 side is the light receiving side, it is necessary to have the same light transmissivity as that of the translucent substrate 1 described above.

Examples of the material constituting the counter electrode conductive layer 7 include indium tin composite oxide (ITO), tin oxide (SnO ₂ ), tin oxide doped with fluorine (FTO), and zinc oxide (ZnO). It is done. Moreover, you may use the metal which does not show corrosivity with respect to the carrier transport material 5, such as titanium, nickel, or tantalum.

  The thickness of the counter electrode conductive layer 7 is preferably 0.02 μm or more and 5 μm or less, and the electric resistance of the counter electrode conductive layer 7 is more preferably 40Ω / □ or less. In order to facilitate the injection of the carrier transport material 8, it is preferable to form a plurality of small holes for the injection of the carrier transport material 8 in the counter electrode conductive layer 7.

  The small holes of the counter conductive layer 7 can be formed by, for example, a mechanical technique or laser processing. Here, the small hole of the counter electrode conductive layer 7 is preferably an opening having a diameter of 0.1 μm to 100 μm, and more preferably an opening of 1 μm to 50 μm. The interval between adjacent small holes is preferably 1 μm or more and 300 μm or less, and more preferably 10 μm or more and 200 μm or less. The same effect can be obtained by forming a stripe-shaped opening in the counter electrode conductive layer 7. The interval between the stripe-shaped openings formed in the counter electrode conductive layer 7 is preferably 1 μm or more and 300 μm or less, and more preferably 10 μm or more and 200 μm or less.

<Catalyst layer>
The catalyst layer 11 may be any material that can transfer electrons on the surface of the catalyst layer 11. For example, a noble metal material such as platinum or palladium, or a carbon-based material such as carbon black, ketjen black, carbon nanotube, or fullerene. Etc. can be used.

<Encapsulant>
As the sealing material 9, for example, a single layer including at least one selected from the group consisting of silicone resin, epoxy resin, polyisobutylene resin, hot melt resin, and glass frit, or the single layer into two or more layers A plurality of stacked layers can be used. Specifically, a model number manufactured by ThreeBond: 31X-101, a model number manufactured by ThreeBond: 31X-088, or a commercially available epoxy resin can be used. .

  When a silicone resin, an epoxy resin, or a glass frit is used as the sealing material 9, it can be formed using a dispenser. Moreover, when using hot-melt resin as the sealing material 9, it can form by opening the hole patterned in the sheet-like hot-melt resin. Moreover, the material for sealing the hole for injection | pouring of the carrier transport material 8 formed in the counter electrode conductive layer 7 can also be formed using said material.

<Manufacturing method>
Hereinafter, an example of the method for manufacturing the photoelectric conversion element of the present 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 translucent substrate 1 is performed. The process of preparing the translucent board | substrate 1 can be performed by preparing what is marketed, for example.

  Next, as shown in FIG. 3, the first porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4 are formed in this order on the surface of the translucent substrate 1. The process to perform is performed. Here, the step of forming the first porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4 is not particularly limited, but for example, a suspension containing the above-described semiconductor fine particles The liquid can be applied on the surface of the light-transmitting substrate 1 and then subjected to at least one of drying and baking.

  Specifically, first, the semiconductor fine particles are suspended in an appropriate solvent to obtain a suspension. As such a solvent, for example, a glyme solvent such as ethylene glycol monomethyl ether, an alcohol such as isopropyl alcohol, an alcohol mixed solvent such as a mixed solvent of isopropyl alcohol and toluene, or water can be used. In order to adjust the porosity of the porous semiconductor layer, a polymer material may be added to the suspension. As such a polymer material, ethyl cellulose or the like can be used. In addition, the porosity of the porous semiconductor layer can be controlled by controlling the molecular weight and the amount of the polymer material added to the suspension. In addition, as the polymer material added to the suspension, a plurality of polymer materials having different molecular weight distributions may be used.

  Further, instead of such a suspension, a commercially available titanium oxide paste (for example, Solaronix, Ti-nanoxide, T, D, T / SP, D / SP, R / SP) may be used.

  Next, the suspension obtained as described above is applied onto the surface of the light-transmitting substrate 1, and at least one of drying and baking is performed on the surface of the light-transmitting substrate 1, so that the first The porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4 are formed in this order. Here, the first porous semiconductor layer 2 is formed by adjusting the suspension or the like so that the porosity of the second porous semiconductor layer 3 is larger than the porosity of the second porous semiconductor layer 3.

  As a method for applying the suspension, for example, a known method such as a doctor blade method, a squeegee method, a spin coating method, or a screen printing method can be used.

  What is necessary is just to set suitably temperature, time, atmosphere, etc. which are required for drying and baking according to the kind of semiconductor fine particle, for example, in air | atmosphere atmosphere or inert gas atmosphere, and the temperature of 50 to 800 degreeC. It can be performed for 10 seconds to 12 hours. This drying and baking may be performed once at a single temperature or twice or more at different temperatures.

  Further, after forming the first porous semiconductor layer 2, the second porous semiconductor layer 3 and the third porous semiconductor layer 4, the electrical connection between the semiconductor fine particles is improved, the surface area of the porous semiconductor layer is increased. Post-treatment may be performed for the purpose of improving the performance, such as increasing or reducing the defect level of the semiconductor fine particles. For example, when the porous semiconductor layer is a titanium oxide film, the performance of the porous semiconductor layer can be improved by treating with a titanium tetrachloride aqueous solution.

  Thereafter, as shown in FIG. 4, a step of forming a collecting electrode 6 on at least a part of the third porous semiconductor layer 4 is performed. Here, the process of forming the current collection electrode 6 can be performed by well-known methods, such as a sputtering method, a spray method, a vapor deposition method, or screen printing, for example.

  Next, as shown in FIG. 5, the photoelectric conversion layer 5 is obtained by adsorbing a photosensitizer to the first porous semiconductor layer 2, the second porous semiconductor layer 3, and the third porous semiconductor layer 4. The process of forming is performed. Here, as a method of adsorbing the photosensitizer, for example, the first porous semiconductor layer 2, the second porous semiconductor layer 3 and the third porous semiconductor layer 3 are added to a solution in which a dye is dissolved (dye adsorption solution). Examples include a method of immersing the translucent substrate 1 after the formation of the porous semiconductor layer 4. At this time, the dye adsorbing solution may be heated in order to penetrate the dye adsorbing solution to the depths of the micropores in the porous semiconductor layer.

The solvent that dissolves the dye may be any solvent that dissolves the dye, and examples thereof include alcohol, toluene, acetonitrile, tetrahydrofuran (THF), chloroform, and dimethylformamide. These solvents are preferably purified and may be used in combination of two or more. The dye concentration in the dye adsorption solution can be appropriately set according to the conditions such as the dye to be used, the type of the solvent, the dye adsorption step, and the like, but is preferably 1 × 10 ⁻⁵ mol / L or more, for example. . Further, an organic compound such as deoxycholic acid may be added as a coadsorbent to the dye adsorption solution in order to change the adsorption state of the dye and the surface state of the porous semiconductor layer.

  Conditions such as the temperature, immersion time, and atmosphere of the dye adsorption solution during adsorption of the dye to the porous semiconductor layer are appropriately set according to the material and state of the porous semiconductor layer, the composition material of the dye adsorption solution, and the like. That's fine. The immersion of the porous semiconductor layer in the dye adsorption solution can be performed, for example, at about room temperature in an air atmosphere, but by immersing it under heating (at a temperature of 30 ° C. or more and 60 ° C. or less), the porous semiconductor layer is immersed. The dye can be efficiently adsorbed to the layer.

  The adsorption of the dye to the porous semiconductor layer may be performed before or after the collector electrode 6 is formed, but is preferably performed after the collector electrode 6 is formed.

  Next, as shown in FIG. 6, after forming the catalyst layer 11 on the counter electrode conductive layer 7, the surface of the counter electrode conductive layer 7 and the surface of the translucent substrate 1 are faced to each other. It seals with the sealing material 9 so that the outer periphery may be surrounded, and the counter electrode conductive layer 7 and the translucent substrate 1 are joined with the sealing material 9.

  Thereafter, as shown in FIG. 1, a step of placing a carrier transport material 8 in a region between the translucent substrate 1 and the counter electrode conductive layer 7 is performed. The step of installing the carrier transporting material 8 is performed by, for example, injecting the carrier transporting material 8 into a region surrounded by the sealing material 9 from the hole provided in the counter electrode conductive layer 7 and then closing the hole. The photoelectric conversion element of embodiment shown to can be produced.

<Action and effect>
As described above, in the photoelectric conversion element of the present embodiment, the porosity of the first porous semiconductor layer 2 is larger than the porosity of the second porous semiconductor layer 3, and thus the TCO substrate. Even without using, a high short-circuit current density is exhibited and it is possible to manufacture at a low cost.

  Examples The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In each example, the film thickness of each layer was measured using a product name: Surfcom 1400A manufactured by Tokyo Seimitsu Co., Ltd. unless otherwise specified.

<Example 1>
First, a porous semiconductor layer was formed on the surface of a translucent substrate made of glass (width 20 mm × length 20 mm × thickness 1 mm, manufactured by Matsunami Glass Industrial Co., Ltd.) by the following method.

  Next, 125 mL of titanium isopropoxide (manufactured by Kishida Chemical Co., Ltd.) and 750 mL of 0.1 M nitric acid aqueous solution (manufactured by Kishida Chemical Co., Ltd.) as a pH adjuster are mixed and heated at 80 ° C. for 8 hours. Then, the hydrolysis reaction of titanium isopropoxide was advanced to prepare a sol solution.

  Next, titanium oxide particles were grown in a titanium autoclave at 240 ° C. for 10 hours. Subsequently, ultrasonic dispersion of the titanium oxide particles is performed for 30 minutes to prepare a colloidal solution I containing titanium oxide particles having an average particle diameter of 15 nm, and then the titanium oxide particles are separated by centrifugation at a rotational speed of 5000 rpm. Precipitated.

  Next, the operation of mixing titanium oxide particles and 1000 mL of ethanol and precipitating the titanium oxide particles by centrifugation was repeated three times to produce titanium oxide particles. The average particle diameter of the titanium oxide particles contained in the colloidal solution was determined by analyzing the dynamic light scattering of laser light using a light scattering photometer (manufactured by Otsuka Electronics Co., Ltd.).

  Next, after washing the titanium oxide particles produced by the above-mentioned steps, ethyl cellulose (manufactured by Kishida Chemical Co., Ltd.) and terpineol (manufactured by Kishida Chemical Co., Ltd.) dissolved in absolute ethanol are added and stirred. The titanium oxide particles were dispersed. Thereafter, ethanol was heated to 50 ° C. and evaporated in an atmosphere of a pressure of 40 mbar to prepare a titanium oxide paste (suspension I) from the colloidal solution.

  The concentration of the suspension I was adjusted so that the final composition of the titanium oxide solid was 20% by mass, ethyl cellulose was 16% by mass, and terpineol was 64% by mass.

  The average particle diameter of the titanium oxide particles in the suspension I is the half width of the peak at a diffraction angle of 25.28 ° (corresponding to the (101) plane of anatase-type titanium oxide) measured with an X-ray diffractometer. Was obtained from the half width and Scherrer's formula. The results are shown in Table 1.

  Next, a commercially available suspension is formed on a translucent substrate using a screen plate having a pattern of width 10 mm × length 10 mm and a screen printer (manufactured by Neurong Seimitsu Kogyo Co., Ltd., model number: LS-150). The liquid I was applied, preliminarily dried at 80 ° C. for 30 minutes, and then baked in air at 500 ° C. for 30 minutes to produce a first porous semiconductor layer made of a titanium oxide film having a thickness of 5 μm. The porosity of the first porous semiconductor layer was 55%. Further, the porosity of the first porous semiconductor layer is calculated using the above-described equation (a) based on the result of measurement performed on the first porous semiconductor layer previously formed on another glass substrate. did.

  Next, on the first porous semiconductor layer, by applying a commercially available titanium oxide paste (manufactured by Solaronix, trade name: Ti-Nanoxide T / SP) in the same manner as described above, drying and baking are performed. A second porous semiconductor layer made of a titanium oxide film having a thickness of 8 μm was produced. The porosity of the second porous semiconductor layer was 51%.

  Next, on the second porous semiconductor layer, by applying a commercially available titanium oxide paste (manufactured by Solaronix, trade name: Ti-Nanoxide R / SP) in the same manner as described above, drying and baking are performed. A third porous semiconductor layer made of a titanium oxide film having a thickness of 3 μm was produced. The porosity of the third porous semiconductor layer was 54%.

  As described above, a porous semiconductor layer having a three-layer structure with a total thickness of 16 μm was formed on a translucent substrate made of glass.

  Next, a current collecting electrode was formed by vapor-depositing a Ti film on the surface of the porous semiconductor layer and the surface of the translucent substrate around the porous semiconductor layer.

  Then, after immersing the porous semiconductor layer in a dye adsorbing solution prepared in advance at room temperature for 100 hours, the porous semiconductor layer is washed with ethanol and then dried at about 60 ° C. for about 5 minutes. Thus, a dye was adsorbed on the porous semiconductor layer to produce a photoelectric conversion layer.

The dye adsorbing solution was prepared by mixing a dye represented by the above formula (II) (manufactured by Solaronix, trade name: Ruthenium 620 1H3TBA) with acetonitrile at a volume ratio of 1: 1 so that the concentration was 4 × 10 ⁻⁴ mol / L. It was prepared by dissolving in a mixed solvent with t-butanol.

  Next, a translucent substrate having a photoelectric conversion layer and a collecting electrode formed thereon, and a counter electrode substrate having a platinum film (film thickness: 1 μm) as a catalyst layer on an ITO conductive film as a counter electrode conductive layer, Bonding using a heat-sealing film (DuPont, Himiran 1702), heating for 10 minutes in an oven set at about 100 ° C., pressure-bonding the translucent substrate and the counter electrode substrate, and surrounding a predetermined area An encapsulant was formed.

  Next, an electrolyte prepared in advance is injected into a region surrounded by the sealing material from an electrolyte injection hole provided in advance in the counter electrode substrate, and an ultraviolet curable resin (manufactured by ThreeBond, model number: 31X-101) was used to seal the electrolyte injection hole. This produced the photoelectric conversion element of Example 1.

In the above electrolyte solution, acetonitrile as a solvent has a concentration of 0.1 mol / L of LiI (manufactured by Aldrich) as a redox species and a concentration of 0.01 mol / L of I ₂ (manufactured by Kishida Chemical). In addition, t-butylpyridine (manufactured by Aldrich) was added as an additive so that the concentration was 0.5 mol / L, and dimethylpropylimidazole iodide (manufactured by Shikoku Kasei Kogyo Co., Ltd.) was added at a concentration of 0.6 mol / L. Obtained by dissolution.

Thereafter, Ag paste (made by Fujikura Kasei Co., Ltd., trade name: Dotite) was applied to the photoelectric conversion element of Example 1 as a terminal electrode portion. Then, a black mask having an opening area of 1 cm ² is installed on the light receiving surface of the photoelectric conversion element of Example 1, and irradiated with light of 1 kW / m ² intensity (AM1.5 solar simulator), Short-circuit current density J _sc (mA / cm ² ), open circuit voltage V _oc (V), FF, and conversion efficiency E _ff (%) were measured. The results are shown in Table 2.

<Example 2>
A photoelectric conversion element of Example 2 was produced in the same manner as in Example 1 except that the thickness of the first porous semiconductor layer was 7 μm and the thickness of the second porous semiconductor layer was 4 μm. Short-circuit current density J _sc , open circuit voltage V _oc , FF, and conversion efficiency E _ff were measured. The results are shown in Table 2.

<Example 3>
Implementation was performed except that the average particle diameter of the titanium oxide particles constituting the first porous semiconductor layer was adjusted to 50 nm and the porosity of the first porous semiconductor layer was set to 55% by adjusting the suspension I. The photoelectric conversion element of Example 3 was produced in the same manner as in Example 1, and the short-circuit current density J _sc , the open circuit voltage V _oc , FF, and the conversion efficiency E _ff were measured. The results are shown in Table 2.

<Example 4>
A photoelectric conversion element of Example 4 was produced in the same manner as in Example 1 except that the porosity of the first porous semiconductor layer was set to 60% by adjusting the suspension I, and the short-circuit current density was J _sc , open circuit voltage V _oc , FF, and conversion efficiency E _ff were measured. The results are shown in Table 2.

<Example 5>
The photoelectric conversion element of Example 5 was changed in the same manner as in Example 1 except that the porosity of the first porous semiconductor layer was changed to 65% by changing the molecular weight and addition amount of ethyl cellulose in suspension I. The short circuit current density J _sc , the open circuit voltage V _oc , FF, and the conversion efficiency E _ff were measured. The results are shown in Table 2.

<Comparative Example 1>
Other than the first porous semiconductor layer and the second porous semiconductor layer having the same porosity by forming the first porous semiconductor layer and the second porous semiconductor layer with the same material. Produced the photoelectric conversion element of Comparative Example 1 in the same manner as in Example 1, and measured the short-circuit current density J _sc , open-circuit voltage V _oc , FF, and conversion efficiency E _ff . The results are shown in Table 2.

<Comparative example 2>
A first porous semiconductor layer is produced using a commercially available titanium oxide paste (manufactured by Solaronix, trade name: Ti-Nanoxide T / SP), and a second porous semiconductor layer is produced using suspension I. Except that, the photoelectric conversion element of Comparative Example 2 was produced in the same manner as in Example 1, and the short-circuit current density J _sc , the open circuit voltage V _oc , FF, and the conversion efficiency E _ff were measured. The results are shown in Table 2. That is, in the photoelectric conversion element of Comparative Example 2, the porosity of the second porous semiconductor layer was larger than the porosity of the first porous semiconductor layer.

As shown in Table 2, in the photoelectric conversion elements of Examples 1 to 5 in which the porosity of the first porous semiconductor layer is larger than the porosity of the second porous semiconductor layer, the first porosity The porosity of Comparative Example 1 and the second porous semiconductor layer in which the porous semiconductor layer and the second porous semiconductor layer have the same porosity are larger than the porosity of the first porous semiconductor layer Compared with the photoelectric conversion element of Comparative Example 2, it was confirmed that a high short-circuit current density J _sc was exhibited.

  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 widely utilized for the photoelectric conversion element containing a solar cell, and can be used suitably especially for a dye-sensitized solar cell.

  DESCRIPTION OF SYMBOLS 1 Translucent board | substrate, 2 1st porous semiconductor layer, 3rd porous semiconductor layer, 4th 3rd porous semiconductor layer, 5 photoelectric converting layer, 6 Current collection electrode, 7 Counter electrode conductive layer, 8 Carrier Transport material, 9 sealing material, 11 catalyst layer.

Claims (5)

A translucent substrate;
A photoelectric conversion layer provided on the translucent substrate;
A collecting electrode provided on at least a part of the photoelectric conversion layer;
A counter electrode conductive layer provided to face the translucent substrate;
A catalyst layer provided on the surface of the counter electrode conductive layer on the light transmitting substrate side;
A carrier transport material provided between the translucent substrate and the catalyst layer,
The photoelectric conversion layer includes a first porous semiconductor layer provided on the translucent substrate, a second porous semiconductor layer provided on the first porous semiconductor layer, and the first And a photosensitizer adsorbed on each of the porous semiconductor layer and the second porous semiconductor layer,
The photoelectric conversion element in which the porosity of the first porous semiconductor layer is larger than the porosity of the second porous semiconductor layer.   The photoelectric conversion element according to claim 1, wherein the first porous semiconductor layer is composed of semiconductor fine particles having an average particle diameter of 50 nm or less.   The photoelectric conversion element according to claim 1 or 2, wherein the thickness of the first porous semiconductor layer is 50% or less of the thickness of the photoelectric conversion layer.   The photoelectric conversion element according to claim 1, wherein the porosity of the first porous semiconductor layer is 55% or more. Further comprising a third porous semiconductor layer provided on the second porous semiconductor layer;
5. The average particle diameter of semiconductor fine particles constituting the third porous semiconductor layer is larger than the average particle diameter of semiconductor fine particles constituting the second porous semiconductor layer. Photoelectric conversion element.

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