JP2014220164A - Dye-sensitized solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve photoelectric conversion efficiency of a dye-sensitized solar cell.SOLUTION: A dye-sensitized solar cell includes a photoelectrode 12 comprising: a transparent electrode 18; an oxide semiconductor layer 20 laminated on the transparent electrode 18; and a light scattering layer 22 which is laminated on the counter electrode side of the oxide semiconductor layer 20 and scatters light incident from the transparent electrode 18 side. The light scattering layer 22 is constituted of core-shell type composite particles 24 comprising: base particles 26 made of, for example, a polymer; and inorganic fine particles 28 which are carried on the surface of the base particles 26 and have light scattering properties.

Description

  The present invention relates to a dye-sensitized solar cell.

  In dye-sensitized solar cells, it has been studied to improve photoelectric conversion efficiency by confining light incident on an oxide semiconductor layer of a photoelectrode so as not to escape to the outside. For example, as a light confinement technique used for thin film solar cells, the nano-sized uneven structure is formed on the surface of the transparent conductive film formed on the transparent insulating substrate, thereby improving the light conversion efficiency of the thin film solar cells. (See, for example, Patent Document 1). The light confinement technology based on the concavo-convex structure is such that light incident from the transparent insulating substrate side enters the oxide semiconductor layer after being scattered at the interface between the transparent conductive film having the concavo-convex structure and the oxide semiconductor layer. Incidently incident on the physical semiconductor layer. In this manner, when light is incident on the oxide semiconductor layer obliquely, a substantial optical path of the light is extended and the amount of light absorption is increased, so that the photoelectric conversion characteristics of the photovoltaic element are improved and the output current is increased. Will increase.

  As another light confinement technique, the oxide semiconductor layer is mixed with light-scattering particles having a different particle diameter from the light-absorbing particles carrying the dye, and the light incident on the oxide semiconductor layer is scattered to oxidize. A configuration has been proposed in which a substantial optical path of light in the physical semiconductor layer is extended (see, for example, Patent Document 2). As such light scattering particles, inorganic fine particles that refract light such as titanium oxide having a particle size of about 20 nm to 1000 nm are used. It has also been proposed that the oxide semiconductor layer is composed of normal semiconductor particles such as titanium oxide and titanium oxide particles having a specific shape (star shape) as light scattering particles (see Patent Document 3). .

  As another optical confinement technique, a light reflecting layer is provided on the surface of the oxide semiconductor layer facing the counter electrode, and light passing through the oxide semiconductor layer is reflected by the light reflecting layer and reenters the oxide semiconductor layer. The structure to be made is proposed (for example, refer patent document 4). The light reflecting layer disclosed in Patent Document 3 is composed of inorganic fine particles such as titanium oxide having shape anisotropy.

JP 2009-217970 A JP 2003-303629 A JP 2010-1212 A JP 2008-258011 A

  As for the light confinement technique using the concavo-convex structure, it has been studied to form an concavo-convex structure for ideal light confinement by a nanoimprint technique. However, the light confinement technology using the concavo-convex structure requires a lithography technology used in the state-of-the-art semiconductor technology in consideration of the fabrication of a mold and the like, and is extremely expensive at present. Light confinement technology using light scattering particles dispersed in an oxide semiconductor layer makes it difficult to uniformly disperse the light scattering particles in the oxide semiconductor layer, and the light scattering particles are located near the transparent insulating substrate in the oxide semiconductor layer. If present, the light is reflected on the surface before entering the oxide semiconductor layer, so that loss occurs. The light confinement technique using the light reflecting layer is likely to cause aggregation of inorganic fine particles, and it is difficult to uniformly arrange the inorganic fine particles having shape anisotropy, so that the light reflecting layer can provide a sufficient light scattering effect. Absent.

  That is, the present invention has been proposed in order to suitably solve these problems related to the prior art, and an object of the present invention is to provide a dye-sensitized solar cell with high photoelectric conversion efficiency.

In order to overcome the above-mentioned problems and achieve the intended object, the dye-sensitized solar cell of the invention according to claim 1 of the present application,
A dye sensitizer comprising a transparent electrode, an oxide semiconductor layer laminated on the transparent electrode, and a light scattering layer laminated on the counter electrode side of the oxide semiconductor layer and scattering light incident from the transparent electrode side. In sensitive solar cells,
The gist of the invention is that the light scattering layer is composed of core-shell type composite particles comprising mother particles and inorganic fine particles having light scattering properties supported on the surface of the mother particles.
According to the first aspect of the present invention, since a uniform light scattering layer can be formed by the core-shell type composite particles, the confinement effect of incident light can be improved. Thus, the photoelectric conversion efficiency can be improved.

The gist of the invention according to claim 2 is that the base particles are spherical.
According to the invention which concerns on Claim 2, light can be more suitably scattered by the inorganic fine particle arrange | positioned along the surface of a mother particle in the light-scattering layer.

The gist of the invention according to claim 3 is that the mother particles have an anionic group or a cationic group on the surface.
According to the invention of claim 3, inorganic fine particles can be appropriately supported on the surface of the mother particle.

  According to the dye-sensitized solar cell according to the present invention, the photoelectric conversion efficiency can be improved.

It is a schematic diagram of the dye-sensitized solar cell according to the present invention. It is a schematic diagram of a composite particle. It is a scanning electron micrograph of the PAA-PMA particle of an Example. It is a scanning electron micrograph of the PAAm-PMA particle of an Example. It is a figure which shows the infrared absorption spectrum of the PAA-PMA particle of an Example. It is a scanning electron micrograph of the composite particle of an Example. It is a figure which shows the electric current-voltage (IV) characteristic of a solar cell.

  As shown in FIG. 1, a dye-sensitized solar cell (hereinafter simply referred to as a solar cell) 10 according to the present invention includes a photoelectrode 12, a counter electrode 14 disposed to face the photoelectrode 12, a photoelectrode 12, And an electrolyte 16 filled between the counter electrodes 14. In the following description, the direction of the solar cell 10 is designated with the light incident side as a table. That is, in the solar cell 10, the photoelectrode 12 side is the front side, and the counter electrode 14 side is the back side. In the solar cell 10, a spacer (not shown) made of glass or synthetic resin is provided between the photoelectrode 12 and the counter electrode 14, and the distance between the two is maintained by the spacer. Also good. The photoelectrode 12 has a multilayer structure having a transparent electrode 18, an oxide semiconductor layer 20 formed on the back surface of the transparent electrode 18, and a light scattering layer 22 formed on the back surface of the oxide semiconductor layer 20. It has become. Thus, the light scattering layer 22 is formed on the photoelectrode 12 on the side of the counter electrode 14 opposite to the side on which light is incident, and the light incident from the front side is confined by the light scattering layer 22. .

The transparent electrode 18 includes, for example, a substrate and a conductive layer formed on the back surface of the substrate. The substrate is not particularly limited as long as it is a material having optical transparency and electrical insulation properties. For example, transparent glass, transparent ceramics such as titanium oxide and alumina, transparent plastics, and the like can be used. Examples of the plastic include polypropylene, polyethylene terephthalate, polycarbonate, polyimide, and polyethersulfone. As the conductive layer, an inorganic conductive material such as a metal or a metal oxide, a polymer conductive material, an inorganic-organic composite conductive material, or a composite material obtained by mixing these materials can be used. As the conductive layer, for example, indium / tin composite compound (ITO), fluorine-doped tin oxide (FTO), tin oxide (SnO ₂ ), zinc oxide (ZnO), gallium-doped zinc oxide (GZO), aluminum-doped zinc oxide ( AZO), antimony / tin composite compound (ATO), or the like can be used. When forming a conductive layer from such a metal oxide, an appropriate thin film forming method such as a sputtering method, a CVD method, an SPD method, or an evaporation method is selected. The conductive layer is formed with a thickness of about 0.01 μm to 10 μm. In addition, as the transparent electrode 18, not only the thing in which the conductive layer was formed in the board | substrate, but the board | substrate is not provided but the whole may consist of a conductive layer.

  The oxide semiconductor layer 20 is configured by combining a sensitizing dye with a porous metal oxide layer made of a metal oxide. Here, when the sensitizing dye is combined with the metal oxide layer, the sensitizing dye is chemically bonded to the metal oxide layer (chemical adsorption), or the sensitizing dye is physically held in the metal oxide layer. Or a state in which a sensitizing dye is supported on a metal oxide layer, such as being absorbed (physical adsorption). As the metal oxide, titanium oxide, zinc oxide, tin oxide, indium oxide, niobium oxide, tungsten oxide, zirconium oxide, strontium titanate, barium titanate, calcium titanate, etc. can be used. Zinc oxide is preferred. Note that the metal oxide is not limited to one type, and may be composed of two or more metal oxides. The metal oxide layer is formed by applying a suspension containing metal oxide particles on the back surface of the transparent electrode, drying and baking, or immersing the transparent electrode 18 in a colloidal solution and electrophoresing the metal. After the oxide particles are attached to the back surface of the transparent electrode 18, the foaming agent is mixed and applied to the colloidal solution or dispersion and then sintered to make it porous, or the polymer microbeads are mixed and applied. Appropriate methods such as removing the polymer microbeads by heat treatment or chemical treatment to form voids can be applied. Further, when applying the metal oxide particles or the dispersion containing the metal oxide particles to the transparent electrode 18, the squeegee method, gravure coating method, screen printing method, ink jet method, roll coating method, doctor blade method, spin coating method. Method, spray coating method and the like can be employed. Here, the metal oxide particles preferably have an average particle size of 1 nm to 100 μm, and more preferably 1 nm to 1000 nm. When the average particle diameter of the metal oxide particles is 100 μm or less, a metal oxide layer having a surface area sufficient to secure the amount of the sensitizing dye to be adsorbed can be formed.

  You may form a metal oxide layer by apply | coating to the transparent electrode 18 in the state which disperse | distributed the metal oxide particle to the solvent, and vaporizing a solvent. As the solvent, those which can be vaporized at a temperature of less than 50 ° C. are preferable. For example, a nitrile compound such as acetonitrile, alcohol such as ethanol, water, or a mixed solution thereof can be employed. Thus, by evaporating the solvent at a low temperature, the metal oxide layer can be formed while maintaining the crystallinity of the metal oxide particles dispersed in the solvent. The state in which the degree of crystallinity of the metal oxide particles is maintained is not a state in which the metal oxide is sintered by a conventional high-temperature heat treatment but an amorphous state in the metal oxide particles. A state in which the ratio of the crystalline component to the component does not change.

  The sensitizing dye is not particularly limited as long as it can generate an electromotive force. For example, transition metal complexes such as ruthenium and osmium, ruthenium-bipyridyl complexes, porphyrins, phthalocyanines, dithiolate complexes, cyanine dyes, rhodamines, coumarins. Derivatives, stilbene derivatives and the like can be employed. As a method of compounding a sensitizing dye on the surface of the metal oxide layer, a solution obtained by dissolving the sensitizing dye in an organic solvent is obtained by forming a metal oxide layer on the back surface of the transparent electrode 18. Immersion, dipping method, roller method, air knife method, etc. can be applied, the mixed solution is applied to the metal oxide layer, wire bar method, application method, spin method, spray method, offset printing method, screen printing method, etc. Can be applied. As a method for adsorbing the sensitizing dye to the metal oxide layer, a method in which the transparent electrode on which the metal oxide layer is formed is immersed in a dye solution in which the sensitizing dye is dissolved in a solvent is preferable. In addition, as a solvent of a pigment | dye solution, organic solvents, such as ethanol, toluene, acetonitrile, chloroform, can be used.

  The thickness of the oxide semiconductor layer 20 is preferably set in the range of 1 μm to 1000 μm. If the thickness of the oxide semiconductor layer 20 is 1 μm or more, light that is sufficient to obtain suitable photoelectric conversion efficiency can be absorbed. Further, when the thickness of the oxide semiconductor layer 20 is 1000 μm or less, the loss due to recombination of electrons generated by photoelectric conversion at a position away from the conductive layer of the transparent electrode 18 hardly occurs, and the photoelectric conversion efficiency due to this loss It is hard to be affected by the decline of

  The light scattering layer 22 is composed of composite particles 24 composed of mother particles 26 and inorganic fine particles 28 supported on the surface of the mother particles 26 and having light scattering properties that change the traveling direction of light striking the mother particles 26. (See FIGS. 1 and 2). The composite particle 24 has a so-called core-shell structure in which the surface of the mother particle 26 is covered with a large number of inorganic fine particles 28, and is preferably formed in a spherical shape. The light scattering layer 22 is composed of composite particles 24 that are uniformly arranged on the back surface of the oxide semiconductor layer 20, and is incident on the photoelectrode 12 due to the light scattering effect of inorganic fine particles 28 that form the outline of the composite particles 24. It is confined so that light does not escape behind. The light scattering layer 22 has a thickness in the range of 1 μm to 50 μm. When the light scattering layer 22 is thinner than 1 μm, a sufficient light scattering effect cannot be obtained. When the light scattering layer 22 is thicker than 50 μm, the movement of electrons between the oxide semiconductor layer 20 and the electrolyte 16 is hindered, and the obtained solar cell 10 is obtained. The effect of improving the open-circuit voltage (Voc) is reduced.

  The mother particle 26 preferably has a spherical or ellipsoidal surface with a curved surface. The mother particles 26 are not particularly limited as long as they can be formed from organic compounds such as polymers, inorganic materials such as ceramics, carbon beads, and the like, and can carry the inorganic fine particles 28 on the surface. For example, if the mother particle 26 has an anionic group or a cationic group on the surface, the inorganic particle 28 can be appropriately supported. Note that the presence or absence of conductivity of the mother particle 26 is not particularly limited. However, from the viewpoint of preventing a short circuit in the oxide semiconductor layer 20, the mother particle 26 is not conductive or low enough not to cause a short circuit even if conductive. It is desirable. The mother particles 26 preferably have an average particle size in the range of 2 μm to 100 μm, more preferably in the range of 5 μm to 30 μm. When the average particle size of the mother particles 26 is smaller than 2 μm, the number of inorganic fine particles 28 that can be carried on the surface of the mother particles 26 is decreased, and a suitable light scattering effect by the inorganic fine particles 28 cannot be obtained. When it becomes larger than 100 μm, the effect of improving the open circuit voltage (Voc) of the obtained solar cell 10 becomes low. Since the inorganic fine particles 28 are very small as compared with the mother particles 26, the average particle size of the composite particles 24 is substantially the same as the particle size of the mother particles 26. When the mother particle 26 is composed of an inorganic material, silica, glass, zirconia, alumina, or the like can be used.

前記化学式１および化学式２のＲは、脂肪族または芳香族の炭化水素基から選択される疎水性の官能基を表す。 When an organic polymer is used for the mother particle 26, it is preferable to use a crosslinked polyacrylic acid ester represented by the following chemical formula 1 or a derivative of a crosslinked polymethacrylic acid ester represented by the following chemical formula 2. Here, R in Chemical Formula 1 and Chemical Formula 2 is an alkyl group such as methyl, ethyl, propyl, or butyl, a phenyl group, a benzyl group, or the like, and is a hydrophobic functional group selected from aliphatic or aromatic hydrocarbon groups. Represents a group. The polyacrylic acid ester and the cross-linked polymethacrylic acid ester are collectively referred to as poly (meth) acrylic acid ester particles below. In this case, the mother particle 26 is basically composed of crosslinked poly (meth) acrylate particles, and the mother particle 26 having an anionic group is one of the carboxylic acid esters in the crosslinked poly (meth) acrylate ester. It has a structure in which the part is hydrolyzed. Further, the mother particle 26 having a cationic group has a structure in which, for example, an amino group is introduced into a part of a carboxylic acid ester by an aminolysis reaction with an amine compound. Examples of amine compounds include diamine compounds and dimethylamino compounds. Further, the mother particle 26 has a spherical shape, and the shape of the crosslinked poly (meth) acrylate particles formed in a spherical shape is approximately maintained. In the mother particle 26, the carboxylate ester present on the spherical surface of the crosslinked poly (meth) acrylate particle is hydrolyzed, so that a carboxyl group and an amino group are present on the spherical surface portion, and the spherical inner portion is hydrophobic. A carboxylic acid ester having a group is configured to be present.

R in Chemical Formula 1 and Chemical Formula 2 represents a hydrophobic functional group selected from an aliphatic or aromatic hydrocarbon group.

  The crosslinked poly (meth) acrylic acid ester particles used as the starting material for the mother particles 26 are fine spherical particles obtained by crosslinking an acrylic acid ester monomer with a crosslinking agent. The method for producing spherical cross-linked poly (meth) acrylic acid ester particles includes, as a cross-linking agent, alkane diacrylate, phenyl diacrylate, alkane triacrylate, alkane tetraacrylate or alkane dimethacrylate, alkane trimethacrylate, alkane tetramethacrylate, Examples thereof include emulsion copolymerization and suspension copolymerization of acrylic acid esters using a bifunctional or polyfunctional cross-linking agent such as phenyl dimethacrylate and divinylbenzene. In addition, although there exist methacrylic acid ester and acrylic acid ester in an acrylic resin, any of acrylic acid ester and methacrylic acid ester may be used as a starting material.

  The mother particle 26 has a structure in which a part or all of the carboxylic acid produced by partially hydrolyzing the crosslinked poly (meth) acrylate particles is metallized with an alkali metal, and is insoluble in water. It is. As the alkali metal, it is preferable to use an alkali metal or an alkaline earth metal of a hydroxide, and in particular, sodium by sodium hydroxide, potassium by potassium hydroxide, magnesium by magnesium hydroxide, and the like are preferable.

Examples of the inorganic fine particles 28 include titanium oxide (TiO ₂ ), zirconia (zirconium dioxide: ZrO ₂ ), diamond, iron oxide (Fe ₃ O ₄ , Fe ₂ O ₃ ), copper oxide (Cu ₂ O), tungsten, and ceria. Those having a refractive index of 2 or more, such as (CeO ₂ ) and boron nitride (h-BN, c-BN), are suitable. Titanium oxide may be either anatase type or rutile type. The inorganic fine particles 28 have an average particle size in the range of 100 nm to 1000 nm, preferably in the range of 200 nm to 500 nm, and the size of the inorganic fine particles 28 is related to the wavelength of light in the visible region incident on the solar cell 10. Is set in. In the composite particles 24, the inorganic fine particles 28 are supported so as to be arranged on the surface of the mother particles 26. For example, in the case of the spherical mother particles 26, the inorganic fine particles 28 are arranged on the curved surface of the mother particles 26. The entire composite particle 24 has a spherical shape. That is, the outer shape of the composite particle 24 is derived from the outer shape of the mother particle 26.

  Next, an example of a method for producing the composite particle 24 will be described. The aforementioned crosslinked poly (meth) acrylic acid ester particles are prepared. In addition, a reaction solvent obtained by mixing an alkali solution and an organic solvent is separately prepared. The alkali solution used here is one in which an alkali metal, alkaline earth metal hydroxide or the like is dispersed in water. Moreover, as an organic solvent, 1 type, or 2 or more types, such as alcohol, such as ethanol and methanol, a protic solvent mixed with these, or aprotic solvents, such as acetone, tetrahydrofuran, and a dioxane, are used. Then, the poly (meth) acrylate particles are immersed in a reaction solvent composed of an alkali solution and an organic solvent, and the carboxylic acid ester in the poly (meth) acrylate particles is hydrolyzed under the temperature conditions of the predetermined reaction solvent. To do. After the immersion treatment in the reaction solvent, the mother particles 26 obtained from the reaction solvent are taken out, and the mother particles 26 are washed with water. In addition, freeze-drying is good if it is dried when it is recovered only by washing with water. When the mother particles 26 are recovered by solvent substitution, after washing with water, they are substituted with methanol, diethyl ether or the like and dried. Then, the mother particles 26 in the desired average particle size range are isolated by a collection method such as filtration. The method for collecting the mother particles 26 is not limited to filtration, and other methods such as centrifugation can be employed.

The composite particles 24 are generated by supporting the inorganic fine particles 28 on the surfaces of the mother particles 26 by electrostatic interaction between the inorganic fine particles 28 and the mother particles 26. When the functional group on the surface of the mother particle is an anionic group, hydrogen ions bind to TiOH on the surface of titanium oxide under acidic conditions of pH 7 to 1, preferably between pH 4 and 2, and TiOH ²⁺ It becomes a positive charge, and ion exchange occurs between the hydrogen ions existing in the vicinity of the anionic group and the titanium oxide particles, and the titanium oxide particles are bonded to the anionic group. In this case, as the anionic group, a weakly acidic cation exchange group such as a carboxyl group or a silanol group, or a strongly acidic cation exchange group such as a sulfonic acid group, a sulfuric acid group or a phosphoric acid group can be selected. . When the functional group on the surface of the mother particle is a cationic group, hydrogen ions are dissociated from TiOH on the surface of titanium oxide under a basic condition of pH 7 to 13, preferably between pH 9 and 12, It becomes TiO ⁻ and ion exchange occurs with the hydroxide ion existing in the vicinity of the ammonium group, and the titanium oxide particles are bonded to the cationic group. In this case, the cationic group is a weakly basic anion exchange group such as a primary amino group or a secondary amino group, or a strongly basic anion exchange group such as a tertiary amino group or a quaternary amino group. You can choose. In this way, the ion exchange reaction occurs on the surface of the mother particle 26 due to electrostatic interaction, the inorganic fine particles are collected on the surface of the mother particle 26, and the composite particle in which the surface of the mother particle 26 is coated with a plurality of inorganic fine particles 28. 24 is generated. And the core-shell type composite particle 24 is obtained by performing treatments such as washing and drying.

  When ceramic is used for the mother particles 26, any of silica, glass, zirconia, alumina and the like may be used. However, in the case of silica or glass, silanol groups are present on the surface, so that the pH condition is acidic. The inorganic fine particles 28 can be supported under the condition. In the case of zirconia or alumina, the surface charge can be controlled by setting the pH condition to 2 or less, or 12 or more, and the inorganic fine particles 28 can be supported.

  As the counter electrode 14, platinum, gold, carbon, conductive polymer, a substrate provided with a conductive layer similar to the photoelectrode 12, or the like can be used. The electrolyte 16 is not particularly limited as long as it is a substance capable of transporting electrons, holes, ions, and the like, and is a redox electrolyte such as iodine / iodide, bromine / bromide, potassium iodide (KI), copper iodide (CuI). ), Copper thiocyanate (CuSCN), nickel oxide (NiO) and other P-type semiconductors in an organic solvent can be used. As the organic solvent, acetonitrile, 3-methoxypropionitrile, γ-ptyrolactone, polyethylene glycol, propylene carbonate, diethyl carbonate and the like can be employed. The electrolyte 16 is not limited to a liquid, and may be a gel body, a solid, or the like.

  The size of the inorganic fine particles 28 is set in relation to the wavelength of light to be scattered. In order to appropriately scatter light in the visible region, it is desirable to use nano-sized inorganic fine particles 28. Such nano-sized inorganic fine particles 28 have many restrictions in handling and are likely to be aggregated. Therefore, it is very difficult to form a uniform light scattering layer on the back side of the oxide semiconductor layer 20 by using only the inorganic fine particles 28. It is difficult to. According to the solar cell 10 of the present invention, since the inorganic fine particles 28 can be handled in the form of the composite particles 24 supported on the mother particles 26 larger than the inorganic fine particles 28, the light scattering layer 22 can be easily formed. In addition, since the composite particles 24 are less likely to aggregate than the inorganic fine particles 28, the light scattering layer 22 in which the composite particles 24 are densely arranged on the back side of the oxide semiconductor layer 20 can be formed uniformly. Further, even if the shape of the inorganic fine particles 28 supported on the surface of the mother particle 26 is indefinite, the composite particles are not affected by the shape of the inorganic fine particles 28 when forming the light scattering layer 22 with the composite particles 24. 24 can be uniformly arranged, and as a result, the inorganic fine particles 28 constituting the outline of the composite particle 24 are uniformly arranged on the back side of the oxide semiconductor layer 20. Therefore, the light passing through the oxide semiconductor layer 20 can be scattered by the inorganic fine particles 28 of the light scattering layer 22 and confined in the oxide semiconductor layer 20, and the optical path length in the oxide semiconductor layer 20 can be extended. Photoelectric conversion efficiency can be improved. In addition, since the inorganic fine particles 28 are carried on the front-side curved surface of the mother particle 26 formed in a spherical shape, the inorganic fine particles 28 are arranged in various directions in the light scattering layer 22, and light is transmitted through the light scattering layer 22. The light can be reflected so as to diffuse in various directions, and the light confinement effect by the light scattering layer 22 can be improved.

  Since the composite particles 24 are spherical, the light scattering layer 22 in which the composite particles 24 are densely arranged on the back side of the oxide semiconductor layer 20 can be formed more uniformly and easily.

  Next, the dye-sensitized solar cell according to the present invention will be described below with reference to preferred examples.

  The solar cell according to the example is manufactured by the following procedure.

(Generation of mother particles having an anionic group)
First, the production of crosslinked polyacrylic acid ester particles (referred to as PAA-PMA particles) having a structure obtained by hydrolyzing a part of a carboxylic acid ester, which is a mother particle of the composite particles, will be described. 75.0 g of sodium hydroxide was added to an ethanol water mixed solvent (distilled water / ethanol = 525 ml / 200 ml), and polymethyl acrylate particles (Sekisui Plastics Co., Ltd .: trade name ARX15, average particle size of 15 μm as a starting material) ) Is added to prepare a mixed solution. This mixed solution is heated to 60 ° C. and subjected to a hydrolysis treatment while stirring at 350 rpm for 2 hours. Thereafter, centrifugation is repeated using distilled water, and solid-liquid separation is performed to perform washing until the pH of the washing liquid becomes neutral. Thus, polymethyl acrylate particles (called NaPAA-PMA particles) having a structure obtained by hydrolyzing a part of the carboxylic acid ester are obtained. Further, the NaPAA-PMA particles are washed with 0.1 M hydrochloric acid, and then centrifuged with distilled water to perform solid-liquid separation, thereby washing until the pH of the washing solution becomes neutral. Then, the recovered particles are lyophilized to obtain crosslinked polyacrylate particles (PAA-PMA particles) having a structure in which a part of the carboxylic acid ester is hydrolyzed. The recovered amount of PAA-PMA particles was 74 g, and the recovery rate of PAA-PMA particles relative to the starting material was 92%. FIG. 3 shows a photograph of PAA-PMA particles taken with a scanning electron microscope (S-4000 manufactured by Hitachi High-Technologies Corporation).

前記ＰＡＡｍ−ＰＭＡ粒子のアミノ基は、０．６meq/gであった。図４は、走査型電子顕微鏡(日立ハイテクノロジーズ株式会社製Ｓ-４０００)により倍率５０００倍で撮像した写真を示している。これによれば、エチレンジアミノ化する前のポリアクリル酸エステルの粒子と変わらずに球状形状であり、エチレンジアミノ化反応が進行しても、球状を保ったままであることが確認できる。 (Generation of mother particles having a cationic group)
Next, generation of cross-linked polyacrylic acid ester particles (referred to as PAAm-PMA particles) having amino groups in a part of the carboxylic acid ester, which are the mother particles of the composite particles, will be described. Spherical composite particles in which amino groups are introduced into the polyacrylic acid ester spherical particles by an aminolysis reaction with ethylenediamine are produced. Here, the amount of amino groups can be controlled by adjusting the reaction time for carrying out the aminolysis reaction. Specifically, 20.10 g of polyacrylic acid ester (Sekisui Chemicals Co., Ltd .: trade name ARX15, average particle size 15 μm) is placed in a 300 ml three-necked flask, and then ethylenediamine (manufactured by Nacalai Tesque, 15020- 35) Add 150 ml and heat using an oil bath until the temperature of the mixture reaches 90 ° C. When the mixed solution reaches 90 ° C., the mixture is stirred for a predetermined reaction time at a liquid temperature of 90 ° C. and a rotation speed of 100 rpm using a stirring rod, a three-one motor, an oil bath and a reflux condenser. After a predetermined reaction time has elapsed, the filtrate is washed with water until the pH of the filtrate approaches 7 and freeze-dried to collect particles, whereby ethylene diaminated crosslinked polyacrylate particles (PAAm-PMA particles) are obtained. can get. Here, the reaction time was set to 5 hours, and PAAm-PMA particles having amino groups on the surface were prepared. About the obtained PAAm-PMA particle | grains, the introduction amount of the amino group was computed by back titration. The back titration was performed as follows. Place 0.1 g of sample in a 100 ml Erlenmeyer flask, add 50 ml of 0.01M hydrochloric acid, and stir for 1 hour using a stir bar and stirrer. Filter the Erlenmeyer flask while washing with water, and make up to 100 ml. Then, 20 ml is taken from the Erlenmeyer flask with a whole pipette and titrated with a 0.01 M sodium hydroxide aqueous solution. The amount of functional group introduced (meq / g) is determined by the following formula.

The amino group of the PAAm-PMA particles was 0.6 meq / g. FIG. 4 shows a photograph taken at a magnification of 5000 with a scanning electron microscope (S-4000 manufactured by Hitachi High-Technologies Corporation). According to this, it can confirm that it is spherical shape without changing with the particle | grains of the polyacrylic acid ester before ethylene diamination, and the spherical shape is maintained even if ethylene diamination reaction advances.

About the PAA-PMA particle | grains of an Example, the infrared spectroscopy analysis by the diffuse reflection method was performed, and it was confirmed whether one part of the carboxylic acid ester in PAA-PMA particle | grains was hydrolyzed. In addition, as an infrared spectrometer, the product name FT / IR-6300 manufactured by JASCO Corporation was used. The result is shown in FIG. As shown in FIG. 5, the polymethyl acrylate (PMA) particles (starting raw material) of the reference example showed no hydroxyl peak, whereas the PAA-PMA particles of the example had hydroxyl groups in the vicinity of 3500 cm ⁻¹ . A broad peak appears. Further, as shown in FIG. 5, the PAA particles of the reference example have C═O stretching vibration derived from a carboxyl group in the vicinity of 1710 cm ⁻¹ , whereas the PAA particles of the reference example are hydrolyzed, A carbanion-derived C═O stretching vibration is observed in the vicinity of 1570 cm ⁻¹ . Then, as shown FIG 45, PAA-PMA particles of Example is confirmed disappearance of the C = O stretching vibration derived carbanion around 1570 cm ^-1, a broad peak is observed around 1700 cm ^-1. This is considered that the carbanion is converted to a carboxyl group and the peak is shifted to around 1700 cm −1, and it can be confirmed that the carboxylic acid ester in the crosslinked polyacrylate is hydrolyzed. Further, 100 mg of the PAA-PMA particles of the examples were stirred in 50 ml of distilled water for 1 hour, titrated with 0.05N sodium hydroxide aqueous solution until pH 7 was obtained, and the carboxyl group was calculated. The group was 0.65 meq / g.

Moreover, about the PAAm-PMA particle | grains of the Example, the infrared spectroscopic analysis by the diffuse reflection method was performed, and it was confirmed whether one part of the carboxylic acid ester in PAAm-PMA particle | grains was aminated. In addition, as an infrared spectrometer, the product name FT / IR-6300 manufactured by JASCO Corporation was used. The FT-IR spectrum, reduces the absorption of C = O stretching vibration of the ester bond derived from PMA around 1730 cm ^-1, absorption of C = O stretching vibration derived from the amide bond at around 1650 cm ^-1 of the reaction by in results of ethylenediamine And the absorption of N—H stretching vibration near 3400 cm ⁻¹ increased.

(Generation of composite particles from PAA-PMA particles)
10 g of the PAA-PMA particles of Examples are added to 400 ml of distilled water, and the dispersion medium is adjusted to pH 3 by adding hydrochloric acid. Titanium oxide fine particle dispersion obtained by mixing 1.0 g of titanium oxide fine particles (Ishihara Sangyo Co., Ltd .: product name CR50, average particle size 250 nm) as inorganic fine particles in 10 ml of water is added to the dispersion medium, By stirring at 300 rpm for 2 hours under a temperature of 60 ° C., core-shell type composite particles in which the surfaces of PAA-PMA particles are coated with titanium oxide fine particles are generated. After separating the composite particles from the dispersion medium by centrifugation, freeze drying is performed to recover the composite particles of the examples. The recovery amount of the composite particles of the example is 10.8 g, and the recovery rate with respect to the PAA-PMA particles added to the dispersion medium is 97.7 wt%. FIG. 6 shows a scanning electron micrograph of the composite particles of the example. Further, as a result of calculating the composite amount of the titanium oxide fine particles by thermogravimetry (TG) for the composite particles of the example, it was confirmed that 6.7 wt% of the titanium oxide fine particles were composited.

(Generation of composite particles from PAAm-PMA particles)
10 g of the PAAm-PMA particles of Example are added to 400 ml of distilled water, and the dispersion medium is adjusted to pH 12 by adding hydrochloric acid. Titanium oxide fine particle dispersion obtained by mixing 1.0 g of titanium oxide fine particles (Ishihara Sangyo Co., Ltd .: product name CR50, average particle size 250 nm) as inorganic fine particles in 10 ml of water is added to the dispersion medium, By stirring at 300 rpm for 2 hours under a temperature of 60 ° C., core-shell type composite particles in which the surface of PAAm-PMA particles are coated with titanium oxide fine particles are generated. After separating the composite particles from the dispersion medium by centrifugation, the composite particles are recovered by lyophilization. The recovered amount of the composite particles was 10.8 g, and the recovery rate with respect to the PAAm-PMA particles added to the dispersion medium was 98.7 wt%. Further, as a result of calculating the composite amount of the titanium oxide fine particles by thermogravimetry (TG), it was confirmed that 7.0 wt% of the titanium oxide fine particles were composited.

(Production of photoelectrode)
As the transparent electrode, a glass TOC substrate (AGC Fabricec Co., Ltd .: product name A110U80 (U film), 12 to 13 Ω / sq.) Using fluorine-doped tin oxide (FTO) as a conductive layer was used. By cutting a glass TOC substrate 300mm long x 350mm wide x 1.1mm thick, the size is 5mm x 2.5mm. (Sumitomo 3M Co., Ltd., thickness: 58 μm) was attached. After a paste containing 11 wt% of titanium oxide fine particles having an average particle diameter of 8 to 10 nm (manufactured by Solaronix: product name Ti-Nanoxide HT) is dropped on the transparent electrode and applied to the transparent electrode by a squeegee method using a glass rod. Air dried. After drying, the mending tape is peeled off, and the transparent electrode coated with the paste is heat-treated at 450 ° C. for 30 minutes in an electric furnace to sinter titanium oxide fine particles, thereby forming a basic cell in which a metal oxide layer is formed. Got. By immersing the basic cell in an acetonitrile / t-butanol mixed solution in which 0.3 mM sensitizing dye (manufactured by Solaronix: product name Ruthenizer 535 bis-TBA (N719)) is dispersed at 25 ° C. for 24 hours, A sensitizing dye is adsorbed on the oxide layer. Then, the excess sensitizing dye was removed from the basic cell taken out of the mixed solution with acetonitrile and then dried to prepare a photoelectrode of Comparative Example 1 in which a light conversion layer was laminated on a transparent electrode. Moreover, the photoelectrode of Comparative Example 2 was produced by laminating a light scattering layer made of titanium oxide fine particles on the oxide semiconductor layer of the photoelectrode of Comparative Example 1. The light scattering layer of Comparative Example 2 was prepared by dropping a paste containing fine titanium oxide particles (Ishihara Sangyo Co., Ltd .: product name CR50) having an average particle diameter of 250 nm onto the oxide semiconductor layer, applying the paste using a glass rod, and then air drying Formed. The light scattering layer of Comparative Example 2 is formed with a thickness of 25 μm.

(Creation of light scattering layer)
The composite particles according to the core-shell type examples using PAA-PMA and titanium oxide are dispersed in a mixed solvent prepared by mixing water and ethylene glycol in a ratio of 1: 2 to make a composite particle paste. The composite particle paste was dropped on the oxide semiconductor layer in the basic cell, applied by a squeegee method using a glass rod, and then air-dried to form the light scattering layer of the example. In addition, the light-scattering layer of an Example is formed with the thickness of 29 micrometers. A metal oxide layer and a light scattering layer of the example were formed in an acetonitrile / t-butanol mixed solution in which 0.3 mM sensitizing dye (manufactured by Solaronix, product name: Ruthenizer 535 bis-TBA (N719)) was dispersed. By immersing the transparent electrode at 25 ° C. for 24 hours, the sensitizing dye is adsorbed on the metal oxide layer. And after removing the excess sensitizing dye with acetonitrile from the metal oxide layer taken out from the mixed solution, the photoelectrode of Example was produced by drying.

Next, by combining the photoelectrode of the example, the photoelectrodes of Comparative Example 1 and Comparative Example 2 with the counter electrode, and injecting an electrolyte between the photoelectrode and the counter electrode, light scattering composed of composite particles The solar cell of the Example provided with the layer, the solar cell of Comparative Example 1 not provided with the light scattering layer, and the solar cell of Comparative Example 2 provided with the light scattering layer made of titanium oxide fine particles were produced. Platinum (Pt) was used as the counter electrode. And in order to avoid a short circuit, the spacer film (about 100 micrometers) was pinched | interposed and fixed between the photoelectrode and the counter electrode. Then, in acetonitrile, 0.5 M lithium iodide (LiI), 0.05 M iodine (I ₂ ), 0.06 M 1,2-dimethyl-3-propylimidazolium iodide, 0.1 M 4 An electrolyte solution containing -tert-butylpyridine was injected into the gap between the photoelectrode and the counter electrode to complete a dye-sensitized solar cell.

  The photoelectrode of the solar cell according to the example includes a transparent electrode, an oxide semiconductor layer stacked on the transparent electrode, and a light that is stacked on the counter electrode side of the oxide semiconductor layer and scatters light incident from the front side. And a light scattering layer, a spherical mother particle composed of a crosslinked polyacrylic acid ester having a structure in which a part of the carboxylic acid ester is hydrolyzed, and titanium oxide supported on the surface of the mother particle. It is composed of core-shell type composite particles composed of fine particles. The photoelectrode of the solar cell according to Comparative Example 1 includes a transparent electrode and an oxide semiconductor layer stacked on the transparent electrode, and does not include a light scattering layer. The photoelectrode of the solar cell according to Comparative Example 2 is laminated on the transparent electrode, the oxide semiconductor layer laminated on the transparent electrode, and the counter electrode side of the oxide semiconductor layer, and scatters light incident from the front side. A light scattering layer, and the light scattering layer is composed only of titanium oxide fine particles.

(Solar cell evaluation)
Embodiment sets the area of the cell to 0.25 cm ^2, for each of the solar cell of Comparative Example 1 and Comparative Example 2, using a solar cell evaluation apparatus (manufactured by JASCO Corporation, product name YQ-250), light Current-voltage (IV) characteristics were measured under the condition of irradiation intensity of 100 mW / cm ² . The results are shown in FIG.

The photoelectric conversion efficiency η of the solar cell is calculated by the following equation.
・ Photoelectric conversion efficiency η = Pmax (mW / cm ² ) / Pin (mW / cm ² ) × 100
= J _SC (mA / cm ² ) x V _OC (V) / 100 (mW / cm ² ) x FF x 100
• Pmax: Maximum output • Pin: Light irradiation intensity • J _SC : Short-circuit current density • V _OC : Open-circuit voltage Here, the short-circuit current density (J _SC ) is the current value when the voltage is 0V, and the open-circuit voltage (V _OC ) is a voltage value when the current is 0 mA. Further, the output of the solar cell is represented by a value obtained by multiplying the set voltage by the generated current, and the maximum output Pmax (mW / cm ² ) is an output when the maximum area can be taken. That is, when the current density and voltage at the maximum output are expressed as Jmax and Vmax, respectively, they are expressed as FF = (Jmax × Vmax) / (J _SC × V _OC ).

  As shown in FIG. 7 and Table 1, the solar cell of the example has a short-circuit current density of 1.54 times and a photoelectric conversion efficiency of 1 compared to the solar cell of Comparative Example 1 that does not include the light scattering layer. It can be confirmed that the performance is significantly improved as compared with Comparative Example 1. The solar cell of the example has a short circuit current density of 1.18 times and a photoelectric conversion efficiency of 1.15 times compared with the solar cell of Comparative Example 2 in which a light scattering layer is formed from titanium oxide fine particles. Compared to Example 2, it can be confirmed that the performance is improved.

14 counter electrode, 18 transparent electrode, 20 oxide semiconductor layer, 22 light scattering layer, 24 composite particle, 26 mother particle, 28 inorganic fine particle

Claims (3)

A transparent electrode (18), an oxide semiconductor layer (20) laminated on the transparent electrode (18), and laminated on the counter electrode side of the oxide semiconductor layer (20), from the transparent electrode (18) side. In a dye-sensitized solar cell comprising a light scattering layer (22) that scatters incident light,
The light scattering layer (22) is composed of core-shell type composite particles (24) composed of mother particles (26) and inorganic fine particles (28) having light scattering properties supported on the surfaces of the mother particles (26). A dye-sensitized solar cell characterized by the above.   The dye-sensitized solar cell according to claim 1, wherein the mother particle (26) is spherical.   The dye-sensitized solar cell according to claim 1 or 2, wherein the mother particle (26) has an anionic group or a cationic group on a surface thereof.

Images