JP2016100488A - Semiconductor layer and dye-sensitized solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor layer for a dye-sensitized solar cell, capable of increasing photoelectric conversion efficiency, and to provide a dye-sensitized solar cell.SOLUTION: A semiconductor layer 13 provided in a dye-sensitized solar cell 10 comprises a semiconductor having a surface including a first binding site and a second binding site, a first dye adsorbed on the surface and absorbing light in a first wavelength region, and a second dye adsorbed on the surface and absorbing light in a second wavelength region. The first binding site has chemical characteristics different from those of the second binding site. A sensitizing dye bound to the first binding site is contained in the first dye. A sensitizing dye bound to the second binding site is contained in the second dye. The first wavelength region is wider than the second wavelength region. The ratio of the amount of adsorption of the second dye to the amount of adsorption of the first dye is 0.5 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor layer used in a dye-sensitized solar cell, and a dye-sensitized solar cell including the semiconductor layer.

  A dye-sensitized solar cell is known as a type of solar cell that converts light energy into electrical energy. The dye-sensitized solar cell includes a semiconductor layer and an electrolyte layer between two electrodes facing each other. The semiconductor layer is a layer formed by adsorbing a sensitizing dye on the semiconductor surface. When the sensitizing dye absorbs photons, the electrons contained in the sensitizing dye are excited. The excited electrons are injected into the semiconductor and taken out from the electrode connected to the semiconductor layer. On the other hand, the sensitizing dye that has lost electrons receives electrons from the reducing agent in the electrolyte layer, and the oxidant in the electrolyte layer generated thereby is reduced by receiving electrons from the electrode connected to the electrolyte layer. . By repeating such a reaction, electric power is generated.

  In order to efficiently obtain power from the solar cell, it is important to increase the light absorption rate and the photoelectric conversion efficiency. Sunlight contains light of various wavelengths from the short wavelength region to the long wavelength region. Therefore, in order to achieve a high light absorption rate in a dye-sensitized solar cell, as a sensitizing dye, a wide range of wavelengths is possible. It is desirable to use a dye that absorbs the light in the region.

  However, the energy of light that can be absorbed by the sensitizing dye is the band gap energy inherent to the dye, that is, the energy that causes the electrons to transition from the ground state (HOMO) to the excited state (LUMO), and can be absorbed by the sensitizing dye. The wavelength region of light is a specific wavelength region corresponding to the band gap energy. At present, there is no single sensitizing dye that can efficiently absorb all of light having a wavelength of 300 nm to 1000 nm contained in sunlight. Therefore, in the configuration using a single type of sensitizing dye, there is a limit in improving the light absorption rate.

  Therefore, dye-sensitized solar cells using a plurality of types of sensitizing dyes having different wavelength ranges of light that can be absorbed have been developed (see, for example, Patent Document 1 and Non-Patent Documents 1 to 3). In particular, Non-Patent Document 3 describes a configuration in which a fixing group, which is a functional group bonded to a semiconductor surface, is different between types of sensitizing dyes. When multiple types of sensitizing dyes have the same fixing group, it has been reported that competition of adsorption of sensitizing dyes to binding sites on the semiconductor surface occurs. Since plural kinds of sensitizing dyes bind to different binding sites on the semiconductor surface, adsorption competition can be suppressed.

Japanese Patent No. 43807779

H. Ozawa, R. Shimizu and H. Arakawa., RSC. Adv., 2012, 2, 3198. G. D. Sharma, M. S. Roy and Surya Prakash Shingh., J. Mater. Chem., 2012, 22, 18788. N. Shibayama, H. Ozawa, M. Abe, Y. Ooyama and H. Arakawa., Chem. Commun., 2014, 50, 6398.

  However, when multiple types of sensitizing dyes are mixed in one semiconductor layer, electrons are transferred between the sensitizing dyes or recombination of electrons and holes occurs, or the sensitizing dyes are transferred from the sensitizing dye to the semiconductor. The electrons may be captured by another type of sensitizing dye. Such a phenomenon reduces the number of electrons that reach the electrode from the sensitizing dye, and as a result, the ratio at which a current is obtained from the absorbed photons, that is, the quantum yield, decreases, leading to a decrease in photoelectric conversion efficiency.

  In the dye-sensitized solar cell described in Patent Document 1, a combination of sensitizing dyes capable of suppressing the sensitizing dyes from exerting the strong interaction as described above has been proposed. On the other hand, there are many unclear parts regarding the interaction between sensitizing dyes, and there is still room for improvement in photoelectric conversion efficiency.

  For example, when a plurality of types of sensitizing dyes are used, it has been reported that association of dyes occurs between different types of sensitizing dyes. Many sensitizing dyes that absorb light in the wavelength region from the visible region to the near infrared region have a long π-conjugated system in the dye and have a cyclic structure. Non-Patent Document 2 describes that when such a plurality of types of sensitizing dyes are used, the association of the dyes occurs on the semiconductor surface.

In addition, since it is suggested that the association of the dye occurs in the structure in which charge transfer occurs between the sensitizing dyes, the semiconductor layer having a structure capable of suppressing the association of the dye in improving the photoelectric conversion efficiency. Development is desired.
An object of this invention is to provide the semiconductor layer for dye-sensitized solar cells which can improve a photoelectric conversion efficiency, and a dye-sensitized solar cell.

  A semiconductor layer for solving the above-described problem is a semiconductor having a surface including a first binding site and a second binding site, and adsorbs on the surface and absorbs light in the first wavelength region. And a second dye that adsorbs on the surface and absorbs light in the second wavelength region, wherein the first binding site is the second binding site. A sensitizing dye having different chemical properties and bound to the first binding site is included in the first dye, and a sensitizing dye bound to the second binding site is the second binding site. It is contained in the dye, the first wavelength region is wider than the second wavelength region, and the ratio of the adsorption amount of the second dye to the adsorption amount of the first dye is 0.5 or less. .

The dye-sensitized solar cell for solving the above problems includes the semiconductor layer, the electrolyte layer, the first electrode, the first electrode, the second electrode facing each other with the semiconductor layer and the electrolyte layer interposed therebetween, Is provided.
According to the above configuration, since the association of sensitizing dyes is suppressed, unnecessary charge transfer between sensitizing dyes can be suppressed. As a result, the photoelectric conversion efficiency in the dye-sensitized solar cell is increased.

  In the dye-sensitized solar cell, the first binding site is a Bronsted acid site, the second binding site is a Lewis acid site, and the sensitizing dye bonded to the first binding site is The sensitizing dye that has an ester bond with the Bronsted acid site and does not bind to the Lewis acid site and is bonded to the second binding site is coordinated to the Lewis acid site. It is preferable.

According to the above configuration, since the sensitizing dye that binds to the first binding site has a structure that does not bind to the second binding site, the sensitizing dye can be selectively bound to the first binding site. Easy on the semiconductor surface.
In the dye-sensitized solar cell, the sensitizing dye bonded to the second binding site preferably includes a pyridine group that coordinates to the Lewis acid site.
According to the said structure, about the sensitizing dye couple | bonded with a 2nd binding site, the coupling | bonding to the semiconductor surface in a preferable conformation is implement | achieved.

In the dye-sensitized solar cell, the first dye may have a ruthenium complex structure.
According to the said structure, a photoelectric conversion efficiency can be improved in the dye-sensitized solar cell which has a ruthenium complex structure as a sensitizing dye.
In the dye-sensitized solar cell, the second dye may be an organic dye.
According to the said structure, a photoelectric conversion efficiency can be improved in the dye-sensitized solar cell which has an organic dye as a sensitizing dye.

  According to the present invention, photoelectric conversion efficiency can be increased in a dye-sensitized solar cell.

It is sectional drawing which shows the whole structure of the dye-sensitized solar cell of one Embodiment. It is an energy diagram for demonstrating the principle of operation in the dye-sensitized solar cell of one Embodiment. It is a figure which shows the IPCE spectrum of Examples 1, 2, and 3 and Comparative Examples 1 and 3. FIG. It is a figure which shows the IPCE spectrum of Examples 4, 5, and 6 and Comparative Examples 2 and 3.

  One embodiment of a dye-sensitized solar cell and a semiconductor layer used in the solar cell will be described with reference to FIGS. 1 and 2.

[Overall configuration of dye-sensitized solar cell]
With reference to FIG. 1, the whole structure of a dye-sensitized solar cell is demonstrated.
As shown in FIG. 1, the dye-sensitized solar cell 10 includes a first electrode 12 supported by a first substrate 11, and a second electrode 15 supported by a second substrate 16 and facing the first electrode 12. In between, a semiconductor layer 13 having a plurality of types of sensitizing dyes and an electrolyte layer 14 are provided. The semiconductor layer 13 is in contact with the first electrode 12, the electrolyte layer 14 is in contact with the second electrode 15, and the semiconductor layer 13 and the electrolyte layer 14 are in contact with each other between the first electrode 12 and the second electrode 15. The first electrode 12 is an electrode that supplies electrons received from the semiconductor layer 13 to an external circuit, and is an electrode for taking out electrons from the dye-sensitized solar cell 10. The second electrode 15 is an electrode that delivers electrons received from an external circuit to the electrolyte layer 14.

  In the above configuration, it is preferable that the first substrate 11 and the first electrode 12 are formed of a transparent material, and the light L is incident on the first substrate 11 from the side opposite to the first electrode 12 side. The second substrate 16 and the second electrode 15 may be formed of a transparent material, and light may be incident on the second substrate 16 from the side opposite to the second electrode 15 side. Alternatively, the first substrate 11 and the first electrode 12, and the second substrate 16 and the second electrode 15 are formed of a transparent material, and light is transmitted from both the first substrate 11 and the second substrate 16 to these. It may be incident.

[Configuration of sensitizing dye]
The detailed structure of the sensitizing dye that the semiconductor layer 13 has will be described. The sensitizing dye included in the semiconductor layer 13 includes a basic dye that is a first dye and an auxiliary dye that is a second dye.

  At least part of the wavelength range of light absorbed by the basic dye is different from the wavelength range of light absorbed by the auxiliary dye, and the wavelength range of light absorbed by the basic dye is greater than the wavelength range of light absorbed by the auxiliary dye. Is also wide. The minimum excitation energy from the ground state (HOMO) to the excited state (LUMO) preferably has a sufficient difference between the basic dye and the auxiliary dye. Specifically, it is desirable that the minimum excitation energy of the basic dye and the minimum excitation energy of the auxiliary dye have a difference of 0.172 eV or more, preferably 0.209 eV or more.

  The basic dye and the auxiliary dye are adsorbed on the semiconductor surface on the electrolyte layer 14 side by bonding to different bonding sites of the semiconductor constituting the semiconductor layer 13. In order to realize such a configuration, the basic dye and the auxiliary dye have different fixing groups as fixing groups which are functional groups bonded to the semiconductor surface. The basic dye is composed of a fixing group and a basic structure that is a part other than the fixing group, and the basic structure of the basic dye imparts photosensitivity to the semiconductor through the fixing group. The auxiliary dye is composed of a fixing group and a basic structure that is a part other than the fixing group, and the basic structure of the auxiliary dye also imparts photosensitivity to the semiconductor through the fixing group. The ratio (molar ratio) of the adsorbing amount of the auxiliary dye to the adsorbing amount of the basic dye on the semiconductor surface is 0.5 or less.

  Specifically, the basic dye preferably has a carboxyl group or a phosphono group as a fixing group. Among them, the basic dye preferably has a carboxyl group as a fixing group to form an ester bond with the semiconductor surface. The auxiliary dye has a nitrogen-containing aromatic heterocyclic compound group as a fixing group. The nitrogen-containing aromatic heterocyclic compound group is a cyclic compound group having aromaticity composed of two or more elements containing nitrogen. Specific examples of the nitrogen-containing aromatic heterocyclic compound group include pyridine group, pyridazine group, pyrimidine group, 1,3,5-triazine group, imidazole group, pyrazole group, thiazole group, thiadiazole group, triazole group, 1, An 8-naphthyridine group, a purine group, etc. are mentioned. Since these compounds have an imine nitrogen (—C═N—) in the ring, they have an electron accepting property. Of these, the auxiliary dye preferably has a pyridine group as a fixing group.

  The basic dye is a complex dye having the property of causing MLCT (Metal Ligand Charge Transfer), and the auxiliary dye is preferably an organic dye having the property of intramolecular CT (Charge Transfer). CT means charge transfer transition, and MLCT means charge transfer transition from the metal center of the complex dye to the ligand. Intramolecular CT mainly means a charge transfer transition from an electron donating group to an electron accepting group in the molecule.

  Examples of the complex dye having the property of causing MLCT include polypyridine complexes such as a bipyridine complex, a biquinoline complex, and a terpyridine complex. For example, black dye and N719 are preferable. A porphyrin complex or the like can also be used.

As the organic dye having the property of intramolecular CT, a molecule having an electron donating group and an electron accepting group can be used. However, an aromatic conjugated molecule or the like arranged in a straight line directly or via a conjugated system is preferable. Further, when the auxiliary dye is adsorbed on the semiconductor surface in the semiconductor layer 13, if an electron-accepting group is arranged on the semiconductor layer 13 side and an electron-donating group is arranged on the electrolyte layer 14 side, The auxiliary dye is preferably a molecule having such a structure because it advantageously acts on the transfer of electrons into the semiconductor layer 13. This is because the charge transfer path and transfer direction in the organic dye having the property of intramolecular CT differ from the charge transfer path and transfer direction in the inorganic complex dye that causes MLCT.
Hereinafter, specific materials used as basic dyes and specific materials used as auxiliary dyes will be described.

  As the basic dye, an aromatic conjugated molecule having a carboxyl group (—COOH) is preferably used. The carboxyl group forms an ester bond through a dehydration reaction with a Bronsted acid site on the semiconductor surface in the semiconductor layer 13. The Bronsted acid site is an example of a first binding site.

  The basic dye is preferably a polypyridine complex having a carboxyl group among aromatic conjugated molecules. As the polypyridine complex, a bipyridine complex, a biquinoline complex, or a terpyridine complex can be used. For example, cis-bis (isothiocyanato) bis (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetrabutylammonium complex (common name: N719), which is a kind of bipyridine complex, is a sensitizing dye. As a result, it is generally used. Further, cis-bis (isothiocyanato) bis (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) (common name: N3), which is a kind of bipyridine complex, and tris ( Isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex (common name: black dye) may be used.

  As the following chemical formula (1), a structural formula of cis-bis (isothiocyanato) bis (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II) ditetrabutylammonium complex (N719) is shown.

  As shown in the following chemical formula (2), tris (isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex (black dye) The structural formula is shown.

  The basic dye may be an organic dye. When the basic dye is an organic dye, the carboxyl group in the organic dye also functions as an electron-accepting group, and considering the energy level of the basic dye, it is most likely that the carboxyl group constitutes a cyanoacrylate group. preferable.

  As the auxiliary dye, an aromatic conjugated molecule having a nitrogen-containing aromatic heterocyclic compound group as a functional group having a loan pair (lone electron pair) is preferably used. The nitrogen-containing aromatic heterocyclic compound group provided in the auxiliary dye is bonded to the Lewis acid site on the semiconductor surface in the semiconductor layer 13 by a coordinate bond. The Lewis acid site is an example of a second binding site. The nitrogen-containing aromatic heterocyclic compound group functions as an electron-accepting group. In particular, the auxiliary dye is preferably an aromatic conjugated molecule having a pyridine group as a nitrogen-containing aromatic heterocyclic compound group from the viewpoint of the conformation at the time of bonding with the Lewis acid site on the semiconductor surface. A structural formula of a pyridine group is shown as the following chemical formula (3).

The electron-donating group possessed by the auxiliary dye is not particularly limited as long as it has a higher electron-donating group than the nitrogen-containing aromatic heterocyclic compound group, but the auxiliary dye has a carbazole group as the electron-donating group. It is preferable to have. A structural formula of a carbazole group is shown as the following chemical formula (4). In the chemical formula (4), R1 to R7 are hydrogen or C _n H _{2n + 1} (n represents an integer of 1 to 16) or OC _n H _{2n + 1} (n represents an integer of 1 to 16) Indicates.

  In the auxiliary dye, a conjugated linking group such as a thiophene group, an oligothiophene group, an N-alkylcarbazole group, or a 9,9-dialkylfluorene group is provided as a linking group between the electron-accepting group and the electron-donating group. It may be introduced. By introducing a linking group having a conjugated system, the wavelength region of light that can be absorbed by the auxiliary dye can be adjusted.

A thiophene group is preferably used as the linking group. The structural formula of the thiophene group is shown as the following chemical formula (5). In the chemical formula (5), n represents an integer of 1 to 10, a represents any of _{1, 2, and 0} , Rx represents hydrogen or C _n H _{2n + 1} (n represents an integer of 1 to 16) Indicates. Rx is preferably bonded to the 2nd or 5th position, and different substances may be bonded to each of the repeating structures.
Note that the electron-accepting group and the electron-donating group may be directly linked without using a linking group.

  As an aromatic conjugated system molecule having a pyridine group, which is a preferred example of the auxiliary dye, for example, a compound having a structural formula represented by the following chemical formula (6) (common name: NI5) or a structural formula represented by the following chemical formula (7) And a compound (common name: YNI-2). NI5 is described in, for example, Reference 1 (Y. Ooyama, S. Inoue, T. Nagano, K. Kushimoto, J. Ohshita, I. Imae, K. Komaguchi and Y. Harima., Angew. Chem. Int. Ed. , 2011, 50, 7429.). YNI-2 is described in, for example, Reference 2 (Y. Ooyama, N. Yamaguchi, I. Imae, K. Komaguchi, J. Ohshita and Y. Harima., Chem. Commun., 2013, 49, 2548.). Has been.

  The wavelength range of light absorbed by the basic dye is different from the wavelength range of light absorbed by the auxiliary dye, and the wavelength range of light absorbed by the basic dye is wider than the wavelength range of light absorbed by the auxiliary dye. The absorption wavelength region of these dyes is not particularly limited. The basic dye and the auxiliary dye may be in a relationship in which the auxiliary dye assists light absorption in a region where the absorbance of the basic dye is insufficient. For example, a dye having a wide absorption wavelength region and a small molar absorption coefficient is selected as the basic dye, and a dye having an absorption wavelength region in the short wavelength region and a large molar absorption coefficient is selected as the auxiliary dye.

Specifically, when a black dye is used as the basic dye and NI5 or YNI-2 is used as the auxiliary dye, according to the IPCE (Incident Photo-to-current Conversion Efficiency) spectrum, the absorption peak wavelength of the black dye is It exists in the wavelength region of 400 nm or more and the long wavelength side end of the absorption wavelength region is near 860 nm, whereas the absorption peak wavelength of NI5 or YNI-2 exists in the wavelength region of 500 nm or less, and the length of the absorption wavelength region The wavelength side end is in the vicinity of 600 nm. This indicates that the band gap energies of these dyes are greatly different. It is considered that the large difference in band gap energy contributes to suppression of charge transfer between dyes.
In this way, the light absorption rate is improved by using a plurality of types of dyes of the basic dye and the auxiliary dye as the sensitizing dye.

  In such a configuration in which the basic dye and the auxiliary dye are used, as described above, the fixing group of the basic dye selectively binds to the Bronsted acid site in a monodentate or multidentate manner with respect to the semiconductor surface in the semiconductor layer 13. The fixing group of the auxiliary dye is bonded to the Lewis acid site. At this time, the binding structure between the basic dye and its binding site is different from the binding structure between the auxiliary dye and its binding site. Therefore, it is suppressed between the dyes that the conjugated systems of these dyes are adjacent on the semiconductor surface to such an extent that they exert a strong interaction. Therefore, it is suppressed that these pigments inhibit each other's photoelectric conversion performance. And between the basic dye and the auxiliary dye, the chemical properties of the binding sites on which they adsorb are different from each other, so the adsorption competition of these dyes is suppressed, compared to the case where a single dye is used, It is possible to increase the total adsorption amount of the dye located on the semiconductor surface. As a result, the photoelectric conversion efficiency is increased.

  In addition, two sites having different chemical characteristics, that is, the first binding site and the second binding site are normally repeated alternately at a predetermined cycle on the surface of the semiconductor that is a periodic structure. It is. Therefore, each of the one type of dye is likely to intervene between the other type of dye, and the association of the same type of dye is suppressed. For example, when the auxiliary dye is interposed between the basic dyes, the association between the basic dyes is suppressed, and when the basic dye is interposed between the auxiliary dyes, the association between the auxiliary dyes is suppressed. This suppresses unnecessary charge transfer between the same kind of dyes.

  However, even if the binding mode with the binding site is different from each other, if the ratio of the amount of adsorbed dye to the amount of adsorbed basic dye located on the semiconductor surface increases, the distance between the basic dye and the auxiliary dye becomes closer. As a result, dye association occurs between different types of dyes of the basic dye and the auxiliary dye, resulting in a decrease in photoelectric conversion efficiency.

  Specifically, in the association between the basic dye and the auxiliary dye, the association between the dyes bonded to the semiconductor surface, and the dye bonded to the semiconductor surface and the dye not bonded to the semiconductor surface are physically adsorbed. And meetings that occur by waking up. Among these, the association between the dyes bound to the semiconductor surface is a phenomenon that occurs as a result of an increase in the amount of dye adsorbed on the semiconductor surface. Thus, the influence of dye association on the photoelectric conversion efficiency is small.

  On the other hand, when the ratio of the amount of the auxiliary dye to the amount of the basic dye increases, association between the basic dye bonded to the semiconductor surface and the auxiliary dye not bonded to the semiconductor surface occurs. In the state in which this association occurs, when the basic dye absorbs light and is excited, the excited electrons are not injected into the semiconductor layer 13, and the electrons are delivered to the auxiliary dye associated with the basic dye. A phenomenon occurs in which electrons move from the auxiliary dye to the electrolyte layer 14, and the photoelectric conversion efficiency is remarkably lowered.

  On the other hand, if the ratio between the adsorption amount of the basic dye located on the semiconductor surface and the adsorption amount of the auxiliary dye is 1, the adsorption amount of the auxiliary dye is 0.5 or less when the basic dye adsorption amount is 1, The association between the basic dye bonded to the surface and the auxiliary dye not bonded to the semiconductor surface is suppressed. The amount of adsorption includes the amount of dye adsorbed by chemical adsorption on the semiconductor surface and the amount of dye adsorbed by physical adsorption on the semiconductor surface.

  In particular, when the ratio exceeds 0.55, the photoelectric conversion efficiency is significantly reduced. However, it has been confirmed that the photoelectric conversion efficiency is improved when the ratio is 0.5 or less. When the adsorption amount of the dye in the semiconductor layer 13 satisfies the above ratio, the association between the auxiliary dye bonded to the semiconductor surface and the auxiliary dye not bonded to the semiconductor surface can be suppressed.

  As described above, the present inventor paid attention to the association between different types of dyes as a factor for reducing the photoelectric conversion efficiency of the dye-sensitized solar cell, and determined the ratio of the adsorption amount of the dye capable of suppressing such association. By finding out, it was possible to further improve the photoelectric conversion efficiency in a dye-sensitized solar cell using a plurality of types of sensitizing dyes.

[Detailed structure of dye-sensitized solar cell]
A configuration other than the above-described sensitizing dye in the dye-sensitized solar cell 10 and a method for manufacturing the dye-sensitized solar cell 10 will be described in detail. In the following, a configuration in which the first substrate 11 and the first electrode 12 are formed from a transparent material on the assumption that light is incident from the first substrate 11 side will be described. The light incident direction and the configuration of the substrate and the electrodes are not limited to this.

  The first substrate 11 is formed of a material that easily transmits light, and the configuration is not particularly limited as long as the first substrate 11 has a shape that easily transmits light. Although it can be used, it is particularly preferable to use a material having a high visible light transmittance. Further, a material that has a high blocking performance for blocking moisture and gas that tries to enter from the outside and that is excellent in solvent resistance and weather resistance is more preferable. Specifically, as the material of the first substrate 11, transparent inorganic substrates such as quartz and glass, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polyethylene, polypropylene, polyphenylene sulfide, polyvinylidene fluoride, acetyl cellulose, bromo Examples thereof include transparent plastic substrates such as modified phenoxy, aramids, polyimides, polystyrenes, polyarylates, polysulfones, and polyolefins. The thickness of the first substrate 11 is not particularly limited, and may be appropriately selected in consideration of the light transmittance and the performance of blocking the inside and outside of the dye-sensitized solar cell 10. The first substrate 11 and the second substrate 16 may have flexibility.

As a material for forming the first electrode 12, a known transparent conductive material can be used. Specifically, indium-tin composite oxide (ITO), fluorine-doped tin oxide (IV) SnO ₂ (FTO ), tin oxide (IV) SnO _2, zinc oxide (II) ZnO or indium - zinc oxide (IZO) and the like. In addition, the formation material of the 1st electrode 12 is not limited to the said material, Two or more types of materials may be combined and used. The first electrode 12 is formed on the upper surface of the first substrate 11 by a sputtering method or the like.

  The surface resistivity of the first electrode 12 is preferably as small as possible. Specifically, the surface resistivity is preferably 500Ω / □ (Ω / sq.) Or less, and more preferably 100Ω / □ or less. The surface resistivity was measured using Loresta-GP (model number MCP-T610) manufactured by Mitsubishi Chemical Analytech. This device complies with JIS K7194-1994. The unit of surface resistivity is Ω / □ or Ω / sq. Is substantially Ω (□ and sq. Are dimensionless). The surface resistivity means a numerical value obtained by dividing the potential gradient in the direction parallel to the current flowing along the surface of the test piece by the current per unit width of the surface. This numerical value is defined in JIS K6911-1995 to be equal to the surface resistance between two electrodes having opposite sides of a square of 1 cm on each side as electrodes.

  The first electrode 12 may be formed by patterning a highly conductive metal wiring for the purpose of reducing the resistance of the electron extraction path and improving the current collection efficiency. The material of the metal wiring is not particularly limited, but it is preferable to use a material having high corrosion resistance and oxidation resistance and low leakage current of the metal material itself. Further, even a material with low corrosion resistance can be used as a material for metal wiring by providing a separate protective layer. For the purpose of reducing dark current from the first substrate 11, various oxide thin film barrier layers may be provided on the metal wiring constituting the first electrode 12.

The semiconductor layer 13 is a layer in which a sensitizing dye is adsorbed on a base layer made of a semiconductor. As the base layer, a porous film obtained by sintering semiconductor fine particles is preferably used. As a semiconductor material which is a material constituting the base layer, a compound semiconductor material, a material having a perovskite structure, or the like can be used in addition to a single semiconductor material typified by silicon. These semiconductor materials are preferably n-type semiconductor materials in which conduction band electrons become carriers under photoexcitation and generate an anode current. Specifically, as a semiconductor material, titanium oxide (TiO ₂ ), zinc oxide (ZnO), tungsten oxide (WO ₃ ), niobium oxide (Nb ₂ O ₅ ), strontium titanate (SrTiO ₃ ), or oxide Tin (SnO ₂ ) is preferably used, and in particular, anatase type titanium oxide is preferably used.

  Note that the semiconductor material is not limited to the above materials, and other than this, a single semiconductor material or a semiconductor material in which two or more kinds are mixed or combined can be used. Further, the semiconductor fine particles can take various forms such as a granular shape, a tube shape, and a rod shape as required.

  Although there is no restriction | limiting in particular in the film forming method of a base layer, When the physical property, the convenience, manufacturing cost, etc. are considered, the film forming method by a wet is preferable. Specifically, a paste-like dispersion liquid in which a powder or sol of semiconductor fine particles is uniformly dispersed in a solvent such as water is prepared, and this dispersion liquid is formed on the upper surface of the first electrode 12 laminated on the first substrate 11. The base layer is preferably formed by a method of applying or printing. There is no restriction | limiting in particular in the coating method or the printing method, What is necessary is just to use a well-known method. For example, as a coating method, a dip method, a spray method, a wire bar method, a spin coating method, a roller coating method, a blade coating method, a gravure coating method, or the like can be used. A printing method, an offset printing method, a gravure printing method, an intaglio printing method, a rubber plate printing method, a screen printing method, or the like can be used.

  When an anatase-type titanium oxide is used as a semiconductor material in preparing the dispersion, a commercially available product in the form of powder, sol, or slurry may be used as the titanium oxide, or a titanium oxide alkoxide may be added with water. Semiconductor fine particles having a predetermined particle diameter may be generated by a known method such as decomposition. When using a commercially available powder, it is preferable to eliminate secondary aggregation of the particles, and it is preferable to pulverize the particles using a mortar, ball mill, or the like when preparing the dispersion. At this time, acetylacetone, hydrochloric acid, nitric acid, a surfactant, a chelating agent, or the like may be added to the dispersion in order to prevent the particles from which secondary aggregation has been eliminated from aggregating again. In order to increase the viscosity of the dispersion, a polymer such as polyethylene oxide or polyvinyl alcohol, or various thickeners such as a cellulose-based thickener may be added to the dispersion.

  Although there is no restriction | limiting in particular in the particle size of semiconductor fine particle, It is preferable that they are 1 nm or more and 200 nm or less by average particle diameter of primary particles, and it is especially preferable that they are 5 nm or more and 100 nm or less. Further, by mixing particles having a size larger than the semiconductor fine particles in the base layer, it is possible to scatter incident light and improve the quantum yield. In this case, it is preferable that the average particle diameter of the separately mixed particles is 20 nm or more and 500 nm or less. The average particle size was calculated by measuring the particle size with an image taken using a scanning electron microscope (SEM).

  The base layer is preferably as large as the actual surface area including the fine particle surface facing the pores inside the porous film so that a large amount of sensitizing dye can be adsorbed. The actual surface area in the state where the base layer is formed on the first electrode 12 is preferably 10 times or more, more preferably 100 times or more the projected area which is the area of the outer surface of the base layer. preferable. Although there is no particular upper limit to this ratio, the base layer formed by the above-described materials and manufacturing method can ensure an actual surface area of about 1000 times the projected area.

  In general, as the thickness of the base layer increases and the number of semiconductor fine particles contained per unit projected area increases, the actual surface area increases and the amount of dye that can be held in the unit projected area increases. Become. On the other hand, when the thickness of the base layer increases, the distance by which electrons transferred from the sensitizing dye to the inside of the semiconductor layer 13 diffuse until reaching the first electrode 12 increases. Therefore, electrons due to charge recombination inside the semiconductor layer 13 Loss also increases. Therefore, the thickness of the base layer is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 50 μm or less, and particularly preferably 3 μm or more and 30 μm or less. Note that since the increase in the thickness of the semiconductor layer 13 due to adsorption of the sensitizing dye is minute, the thickness of the base layer can be regarded as the thickness of the semiconductor layer 13.

  The base layer electrically connects the semiconductor fine particles, improves the mechanical strength of the semiconductor layer 13, and improves the adhesion between the semiconductor layer 13 and the first electrode 12. The first electrode 12 is preferably formed by being applied or printed on the upper surface and then baked. There is no particular limitation on the range of the firing temperature, but the firing temperature should not be too high in order to reduce the electrical resistance of the first electrode 12, that is, the increase in surface resistivity and the possibility of melting the first electrode 12. Is preferred. Specifically, the firing temperature is preferably 40 ° C. or higher and 700 ° C. or lower, and more preferably 40 ° C. or higher and 650 ° C. or lower. Moreover, although there is no restriction | limiting in particular also in baking time, It is preferable that it is about 10 minutes-10 hours.

  For example, a dip treatment with a titanium tetrachloride aqueous solution or a titanium oxide ultrafine particle sol having a diameter of 10 nm or less may be performed for the purpose of increasing the actual surface area of the base layer or increasing necking between semiconductor fine particles after firing.

  When a plastic substrate is used as the first substrate 11, a titanium oxide layer is formed on the upper surface of the first electrode 12 using a paste-like dispersion liquid that does not contain a binder, and then a base layer is formed by a pressure press. May be. This method is described in, for example, Reference 3 (T. Yamaguchi, N. Tobe, D. Matsumoto, T. Nagai and H. Arakawa., Sol. Energy Mater. Sol. Cells, 94 (2010), 812.). Has been.

  The method for adsorbing the sensitizing dye to the base layer is not particularly limited, but the sensitizing dye is dissolved in a solvent and the base layer is immersed in the dye solution, or the dye solution is applied to the base layer. The sensitizing dye is preferably adsorbed on the base layer. Examples of the solvent include alcohols, nitriles, nitromethane, halogenated hydrocarbons, ethers, dimethyl sulfoxide, amides, N-methylpyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters, Examples thereof include carbonates, ketones, hydrocarbons, THF (tetrahydrofuran), and water.

  In order to reduce association between the dyes, a co-adsorbent may be added to the dye solution. As the co-adsorbent, for example, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid salt, 1-decylphosphonic acid or the like can be used, and chenodeoxycholic acid is preferably used. The concentration of the coadsorbent in the dye solution is generally 10 μM (M: mol / L) or more and 0.5 M or less, but preferably 0.3 μM or more and 0.2 M or less.

  When adsorbing two types of dyes, the basic dye and the auxiliary dye, to the base layer, the basic dye is adsorbed to the base layer as the first step, and then the auxiliary dye is adsorbed to the base layer as the second step. preferable. When the base layer contains titanium oxide as a semiconductor material, the nitrogen-containing aromatic heterocyclic compound group that the auxiliary dye has generates a hydrogen bond with the titania hydroxyl group. Adsorption is likely to be hindered. In addition, since the auxiliary dye generally has an adsorption rate about 10 times that of the basic dye, when the basic dye and the auxiliary dye are adsorbed simultaneously, the basic dye can bind to the Bronsted acid site. Nevertheless, the auxiliary dye previously bonded to the semiconductor surface may become a spatial obstacle, and the basic dye may not be bonded to the semiconductor surface.

  However, as long as the ratio of the adsorbing amount of the auxiliary dye to the adsorbing amount of the basic dye on the semiconductor surface can be 0.5 or less, the adsorption procedure of the basic dye and the auxiliary dye is not limited to the above procedure. .

As the electrolyte layer 14, an electrolytic solution or a gel or solid electrolyte can be used. Examples of the electrolytic solution include a solution containing a redox system (redox pair). Specifically, a solution containing a combination of iodine (I ₂ ) and a metal or organic iodide salt, bromine (Br ₂ ), or the like. And a solution containing a combination of metal and organic bromide salts. The cation constituting the metal salt is lithium ion (Li ⁺ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), cesium ion (Cs ⁺ ), magnesium ion (Mg ²⁺ ), or calcium ion (Ca ^2+). The cation constituting the organic salt is preferably a quaternary ammonium ion such as tetraalkylammonium ions, pyridinium ions, or imidazolium ions, but the type of cation is limited to these. In addition, it can be used alone or in combination of two or more.

  In addition to the above substances, as an electrolyte, a metal complex such as a combination of ferrocyanate and ferricyanate, a combination of ferrocene and ferricinium ion, cobalt complex, sodium polysulfide, alkylthiol and alkyldisulfide A sulfur compound such as a combination, a viologen dye, a combination of hydroquinone and quinone, or the like can be used.

As the electrolyte, in particular, an electrolyte combining iodine (I ₂ ) and a quaternary ammonium compound such as lithium iodide (LiI), sodium iodide (NaI), or imidazolium iodide is used. preferable.

The concentration of the electrolyte salt is preferably 0.05 M or more and 10 M or less, and more preferably 0.2 M or more and 3 M or less with respect to the solvent. The concentration of iodine (I ₂ ) or bromine (Br ₂ ) is preferably 0.0005 M or more and 1 M or less, and more preferably 0.001 M or more and 0.5 M or less with respect to the solvent.

  When a cobalt complex is used instead of iodine as an electrolyte, metal corrosion is less likely to occur than when iodine is used, so that metal wiring or the like can be used inside the dye-sensitized solar cell 10. become.

Solvents constituting the electrolyte include water, alcohols, ethers, esters, carbonates, lactones, carboxylic esters, phosphate triesters, heterocyclic compounds, nitriles, ketones, amides Nitromethane, halogenated hydrocarbons, dimethyl sulfoxide, sulfolane, N-methylpyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, or hydrocarbons, but the solvent is not limited thereto. As the solvent, one type of solvent may be used alone, or two or more types of solvents may be mixed and used. Further, a room temperature ionic liquid of a tetraalkyl, pyridinium, or imidazolium quaternary ammonium salt may be used as the solvent. In order to prevent electrolyte leakage, a solid metal salt such as CuI ₂ may be used.

  Various additives such as 4-tert-butylpyridine and benzimidazoliums may be added to the electrolyte layer 14 for the purpose of improving the open circuit voltage and the short circuit current of the dye-sensitized solar cell 10.

  In order to reduce the leakage of the electrolyte from the dye-sensitized solar cell 10 and the volatilization of the solvent constituting the electrolyte, a gelling agent, a polymer, or a crosslinking monomer is dissolved or dispersed in the electrolyte composition. They may be mixed and used as a gel electrolyte. As for the ratio of the gelling material to the electrolyte composition, the more the electrolyte composition, the higher the ionic conductivity, but the lower the mechanical strength. On the contrary, when there are too few electrolyte components, the mechanical strength increases, but the ionic conductivity decreases. For this reason, the electrolyte composition is preferably 50 wt% or more and 99 wt% or less of the gel electrolyte, and more preferably 80 wt% or more and 97 wt% or less.

  It is also possible to realize the all-solid-state dye-sensitized solar cell 10 by mixing the electrolyte and the plasticizer with the polymer and then volatilizing and removing the plasticizer to make the electrolyte layer 14 a solid. .

  As a material of the second electrode 15, any material can be used as long as it is a conductive material. Further, such a material can be used as the second electrode 15 as long as the conductive layer is formed on the surface of the insulating material in contact with the electrolyte layer 14. However, as the material of the second electrode 15, it is preferable to use an electrochemically stable material. Specifically, it is preferable to use platinum, gold, carbon, a conductive polymer, or the like.

In order to improve the catalytic action for the reduction reaction at the second electrode 15, a fine structure is formed on the surface of the second electrode 15 in contact with the electrolyte layer 14 so that the actual surface area of the second electrode 15 increases. It is preferable that it is comprised. For example, the second electrode 15 is preferably formed in a platinum black state if platinum, or in a porous carbon state if carbon. Platinum black can be formed by anodization of platinum, chloroplatinic acid treatment, etc., and porous carbon can be formed by methods such as sintering of carbon fine particles and baking of organic polymers. .
Since the second substrate 16 may not transmit light, an opaque glass plate, plastic plate, ceramic plate, or metal plate may be used as the material.

  A transparent substrate is used as the second substrate 16, a transparent conductive layer is formed on the upper surface of the second substrate 16, and a wiring made of a metal such as platinum having a high oxidation-reduction catalytic action is formed on the transparent substrate. The second electrode 15 can also be used as a transparent electrode by treating chloroplatinic acid.

  The method for forming the dye-sensitized solar cell 10 by assembling the above-described members is not particularly limited. When the electrolyte layer 14 is liquid, or when a liquid electrolyte is introduced and the electrolyte layer 14 is gelled inside the dye-sensitized solar cell 10, a member other than the electrolyte layer 14 is assembled. It is preferable that the dye-sensitized solar cell 10 is formed by a method in which the periphery is sealed and the electrolytic solution is injected from the provided inlet.

  For example, in the stacked body of the first substrate 11, the first electrode 12, and the semiconductor layer 13 and the stacked body of the second substrate 16 and the second electrode 15, the semiconductor layer 13 and the second electrode 15 are not in contact with each other. The first substrate 11 and the second substrate 16 are bonded and sealed in a region outside the semiconductor layer 13 with an appropriate gap therebetween. The size of the gap between the semiconductor layer 13 and the second electrode 15 is not particularly limited, but the size of the gap in the stacking direction of each member is preferably 1 μm or more and 100 μm or less, and 1 μm or more and 50 μm or less. It is preferable that If the size of the gap is too large, the electrical conductivity is lowered and the generated current is reduced.

  The material of the sealing material is not particularly limited, but a material having light resistance, insulation, and moisture resistance is preferable. Various welding methods, epoxy resin, ultraviolet curable resin, acrylic resin, polyisobutylene resin, EVA (ethylene vinyl acetate) ), Ionomer resin, ceramic, or various heat-sealing resins. The position where the injection port is provided is not particularly limited as long as it is not on the semiconductor layer 13 and the second electrode 15 facing the semiconductor layer 13.

  There is no particular limitation on the method of injecting the electrolytic solution, but a method of dropping a few drops of the electrolytic solution into the injection port and injecting the electrolytic solution by capillary action is simple. Moreover, you may perform injection | pouring operation under pressure reduction or a heating as needed. After the electrolyte is completely injected, the electrolyte remaining in the inlet is removed and the inlet is sealed. Although there is no restriction | limiting in particular also in this sealing method, If necessary, it can also seal by sticking a glass plate or a plastic substrate with a sealing material.

When the electrolyte layer 14 is an electrolyte gelled using a polymer or the like, or an all solid electrolyte, a polymer solution containing an electrolyte and a plasticizer is applied to the upper surface of the semiconductor layer 13 by a casting method or the like. To do. Thereafter, after the plasticizer is volatilized and completely removed, the second substrate 16 and the second electrode 15 are bonded together and sealed with a sealing material in the same manner as described above. This sealing is preferably performed using a vacuum sealer or the like in an inert gas atmosphere or in a reduced pressure. After sealing, heating and pressurizing operations may be performed as necessary so that the electrolyte solution of the electrolyte layer 14 sufficiently permeates the semiconductor layer 13.
In addition, the external shape of the dye-sensitized solar cell 10 can be produced in various shapes depending on the application, and the shape is not particularly limited.

[Operation of dye-sensitized solar cell]
The operation principle of the dye-sensitized solar cell 10 will be described with reference to FIG. In FIG. 2, ITO-PEN film is used as the first substrate 11 and the first electrode 12, titanium oxide TiO ₂ is used as the material of the semiconductor layer 13, and I ⁻ / I ₃ is used as a redox pair contained in the electrolyte layer 14. It is an energy diagram on the assumption that a redox species of ⁻ is used.

  When the sensitizing dye absorbs the photons transmitted through the first substrate 11, the first electrode 12, and the semiconductor layer 13, the electrons in the sensitizing dye are excited from the ground state (HOMO) to the excited state (LUMO). . At this time, since the dye-sensitized solar cell 10 includes the basic dye and the auxiliary dye as the sensitizing dye, light in a wider wavelength region than the dye-sensitized solar cell in which the sensitizing dye is a single dye. Can be absorbed at a higher light absorption rate.

  Excited electrons are drawn to the conduction band of the semiconductor through electrical coupling between the sensitizing dye and the semiconductor constituting the semiconductor layer 13, and reach the first electrode 12 through the semiconductor layer 13. . At this time, the basic dye and the auxiliary dye contained in the sensitizing dye are bonded to different binding sites on the semiconductor surface, and further, the basic dye bonded to the semiconductor surface and the auxiliary not bonded to the semiconductor surface. By suppressing the association with the dye, these dyes can be prevented from decreasing the quantum yield of each other, the amount of current generated is greatly improved, and the photoelectric conversion efficiency is increased.

  When the current-voltage curve is measured, by gradually increasing the voltage value, the Fermi level of the semiconductor layer 13 moves to the LUMO side of the sensitizing dye, and the Fermi level of the semiconductor layer 13 and the LUMO of the sensitizing dye are changed. The level becomes closer. As a result, electrons move from the semiconductor layer 13 to the electrolyte layer 14, and the current value gradually decreases. This is because electron transfer from the semiconductor layer 13 to the electrolyte layer 14 easily occurs. In the dye-sensitized solar cell 10 of this embodiment, the amount of the sensitizing dye adsorbed on the semiconductor surface in the semiconductor layer 13 can be increased by using two kinds of dyes. The movement of electrons to can be suppressed. Thereby, a voltage value and a fill factor can be improved.

On the other hand, the sensitizing dye that has lost electrons receives electrons from the reducing agent in the electrolyte layer 14, such as I ^−, by the following reaction, and oxidants such as I ₃ ⁻ (I ₂ and I ⁻ and To form a conjugate).
2I ⁻ → I ₂ + 2e ⁻
I ₂ + I ⁻ → I ₃ ⁻

The resulting oxidizing agent reaches the second electrode 15 by diffusion, receives electrons from the second electrode 15 by the following reaction, which is the reverse reaction of the above reaction, and is reduced to the original reducing agent.
I ₃ ⁻ → I ₂ + I ⁻
I ₂ + 2e ⁻ → 2I ⁻

  The electrons supplied from the first electrode 12 to the external circuit are sent to the second electrode 15 after performing electrical work in the external circuit. In this way, light energy is converted into electrical energy.

The dye-sensitized solar cell described above will be described using specific examples and comparative examples.
Example 1
In accordance with the procedure described in Reference 3 described above, an ITO-PEN film having a surface resistance of 20Ω / □ is used as the first base material and the first electrode, and a semiconductor made of titanium oxide having a thickness of about 4 μm is formed on the film. A base layer of layers was formed.

Fully purified tris (isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex (black dye) as a basic dye The dye solution A was prepared by dissolving black dye and deoxycholic acid (DCA) as a coadsorbent in 50 ml of 1-propanol to prepare a black dye concentration of 0.2 mM and a DCA concentration of 20 mM.
Further, NI5 (see the above chemical formula (6)) as an auxiliary dye was dissolved in 50 ml of 1-propanol to prepare a dye solution B1 having a NI5 concentration of 0.3 mM.

  The base layer of the semiconductor layer was immersed in the dye solution A at room temperature for 24 hours to adsorb the basic dye to the base layer. The base layer was dried at room temperature, and further immersed in the dye solution B1 for 10 minutes to adsorb the auxiliary dye to the base layer to form a semiconductor layer. This obtained the photoelectrode for dye-sensitized solar cells which consists of a 1st base material, a 1st electrode, and a semiconductor layer. About the produced photoelectrode, it confirmed that the black die and NI5 were adsorb | sucked simultaneously using FT-IR.

  As the second substrate, FTO glass (manufactured by Nippon Sheet Glass Co., Ltd.) was used, and a Pt layer as a second electrode was formed on the FTO layer of this FTO glass using a sputtering method. At this time, the sputtering conditions used were 60 W, 4 sccm, 0.6 Pa, and 60 min.

As an electrolytic solution constituting the electrolyte layer, 0.05M iodine, 0.1M lithium iodide, 0.6M dimethylpropylimidazolium iodine salt, and 0.3M tert-butylpyridine in acetonitrile. The dissolved solution was used.
The prepared semiconductor layer of the photoelectrode and the second electrode were placed facing each other, an electrolyte solution was injected between both electrodes, and sandwiched between clips to obtain a dye-sensitized solar cell of Example 1.
(Example 2)
A dye-sensitized solar cell of Example 2 was obtained in the same procedure as in Example 1 except that the immersion time of the base layer in the dye solution B1 was changed to 15 minutes.
(Example 3)
A dye-sensitized solar cell of Example 3 was obtained in the same procedure as in Example 1 except that the immersion time of the base layer in the dye solution B1 was changed to 30 minutes.

Example 4
As an auxiliary dye, instead of NI5, YNI-2 (see the above chemical formula (7)) was dissolved in 50 ml of 1-propanol to obtain a dye solution B2 having a YNI-2 concentration of 0.3 mM.
A dye-sensitized solar cell of Example 4 was obtained in the same procedure as Example 1 except that the dye solution B2 was used instead of the dye solution B1.
(Example 5)
A dye-sensitized solar cell of Example 5 was obtained in the same procedure as Example 4 except that the immersion time of the base layer in the dye solution B2 was changed to 15 minutes.
(Example 6)
The dye-sensitized solar cell of Example 6 was obtained in the same procedure as in Example 4 except that the immersion time of the base layer in the dye solution B2 was changed to 30 minutes.

(Comparative Example 1)
A dye-sensitized solar cell of Comparative Example 1 was obtained in the same procedure as in Example 1 except that the immersion time of the base layer in the dye solution B1 was changed to 1 hour.
(Comparative Example 2)
A dye-sensitized solar cell of Comparative Example 2 was obtained in the same procedure as in Example 4 except that the immersion time of the base layer in the dye solution B2 was changed to 1 hour.
(Comparative Example 3)
The base layer was immersed in the dye solution A at room temperature for 24 hours and dried at room temperature to obtain a photoelectrode. A dye-sensitized solar cell of Comparative Example 3 was obtained in the same procedure as Example 1 except that only the basic dye was adsorbed on the base layer.

<Evaluation method>
About the dye-sensitized solar cell of each Example and each comparative example, the open circuit voltage at the time of irradiation with pseudo sunlight (AM1.5, 100 mW / cm ² ), the short circuit current in the current-voltage curve, the fill factor, and the photoelectric conversion efficiency Were measured and calculated. The fill factor is also called a shape factor and is one of the parameters indicating the characteristics of the solar cell. In an ideal photoelectric conversion device current-voltage curve, a constant output voltage of the same magnitude as the open circuit voltage is maintained until the output current reaches the same magnitude as the short-circuit current, but the actual solar cell current-voltage curve. Since there is an internal resistance, the shape deviates from the ideal current-voltage curve. The ratio of the maximum output (voltage x current maximum value) in the actual current-voltage curve to the product of the open-circuit voltage and the short-circuit current, which is the maximum output of the ideal current-voltage curve, is called a fill factor. The fill factor indicates the degree of deviation from an ideal current-voltage curve, and is used when calculating actual photoelectric conversion efficiency.

  Further, with respect to the semiconductor layers of the examples and comparative examples, the adsorption amounts of the basic dye and the auxiliary dye in the semiconductor layer were measured using the method described in Non-Patent Document 3 described above, and the adsorption of these dyes in the semiconductor layer. The amount ratio was calculated.

<Evaluation results>
The evaluation results of each Example and each Comparative Example are shown in Table 1 and Table 2. Table 1 shows the measurement results of open-circuit voltage, short-circuit current, fill factor, and photoelectric conversion efficiency, and Table 2 shows the amount of adsorption between the basic dye and the auxiliary dye, and the auxiliary dye relative to the amount of adsorption of the basic dye. The ratio of the amount of adsorption is shown.

また、図３に実施例１、２、３および比較例１、３のＩＰＣＥスペクトルを示し、図４に、実施例４、５、６および比較例２、３のＩＰＣＥスペクトルを示す。

3 shows IPCE spectra of Examples 1, 2, and 3 and Comparative Examples 1 and 3, and FIG. 4 shows IPCE spectra of Examples 4, 5, and 6 and Comparative Examples 2 and 3.

  As shown in Table 1, each example showed higher photoelectric conversion efficiency than Comparative Example 3 using only the black dye as the basic dye as the sensitizing dye. As shown in FIG. 3 and FIG. 4, in each example, an auxiliary dye is included in the semiconductor layer in addition to the basic dye as a sensitizing dye, so that the wavelength around 400 nm to 500 nm is compared with Comparative Example 3. IPCE has been improved. It is suggested that this contributes to the improvement of the photoelectric conversion efficiency in each example. In addition, the fall of IPCE of 370 nm or less originates in absorption of an ITO-PEN film.

  Further, as shown in Table 1 and Table 2, when each example is compared with Comparative Examples 1 and 2, in the example in which the ratio of the adsorbing amount of the auxiliary dye to the adsorbing amount of the basic dye is 0.5 or less. In contrast to Comparative Examples 1 and 2 in which the above ratio exceeds 0.5, the photoelectric conversion efficiency is remarkably lowered while high photoelectric conversion efficiency is obtained. This is presumably because, in Comparative Examples 1 and 2, the auxiliary dye physically adsorbs to the basic dye previously bonded to the semiconductor surface, and the association of these dyes occurs. This is because, in each of the examples and the comparative examples, the black die is photoelectrically converted in the comparative examples 1 and 2 as shown in FIGS. This suggests that the IPCE of 600 nm, which is a region contributing to the above, is lower than each example and Comparative Example 1 using only a black die.

  The basic dye and the auxiliary dye bind to binding sites having different chemical properties on the semiconductor surface. Therefore, when the ratio of the adsorbing amount of the auxiliary dye to the adsorbing amount of the basic dye exceeds 0.5, the auxiliary dye is almost completely bonded to the Lewis acid site, which is the bonding site to which the auxiliary dye is bonded, and further to the semiconductor surface. It is thought that physical adsorption occurs to the basic dyes that are bound.

  In Examples 1, 2, and 3, the auxiliary dye has one pyridine group, whereas in Examples 4, 5, and 6, the auxiliary dye has two pyridine groups. Therefore, two pyridine groups can be bonded to the semiconductor surface, but no significant difference was observed in the adsorbed amount of the auxiliary dye. This suggests the possibility that the auxiliary dye is adsorbed monodentate on the semiconductor surface.

  In the above-mentioned examples, a dye having a wide absorption wavelength region is used as the basic dye, and a dye exhibiting a large absorbance in the short wavelength region is used as the auxiliary dye, but the auxiliary dye may be an area where the absorbance of the basic dye is insufficient. For example, a dye having an absorption wavelength region in a long wavelength region may be used. In the configuration in which the basic dye has a wider absorption wavelength region than the auxiliary dye, the basic dye is the main and the auxiliary dye is the subordinate with respect to the photoelectric conversion efficiency. In general, a dye having a wide absorption wavelength region has a smaller molar extinction coefficient than a dye having a narrow absorption wavelength region. Therefore, the amount of the sensitizing dye adsorbed on the semiconductor surface needs to be larger in the basic dye than in the auxiliary dye. In such a relationship, the ratio of the adsorbing amount of the auxiliary dye to the adsorbing amount of the basic dye is 0.5 or less. If so, the association between the basic dye and the auxiliary dye is suppressed, and the photoelectric conversion efficiency can be improved.

  In the above-described examples, a dye having a fixing group that binds to the Bronsted acid site on the semiconductor surface is used as the basic dye, and a dye having a fixing group that binds to the Lewis acid site on the semiconductor surface is used as the auxiliary dye. If the binding sites of the basic dye and the auxiliary dye on the semiconductor surface are different from each other, the type of the binding site is not limited to this. For example, the basic dye may have a fixing group that binds to a Lewis acid site, and the auxiliary dye may have a fixing group that binds to a Bronsted acid site. Further, the semiconductor surface has two types of Bronsted acid sites having different steric structures, the basic dye has a fixing group that binds to one Bronsted acid site, and binds to the other Bronsted acid site. The auxiliary dye may have a fixing group. Further, the semiconductor surface has two types of Lewis acid sites having different steric structures, the basic dye has a fixing group that binds to one Lewis acid site, and a fixing group that bonds to the other Lewis acid site. An auxiliary dye may have.

  The sensitizing dye that the semiconductor layer has may contain two or more kinds of basic dyes or two or more kinds of auxiliary dyes. When these dyes are classified into basic dyes and auxiliary dyes from the binding sites on the semiconductor surface, the ratio of the adsorption amount of the dye classified as the auxiliary dye to the adsorption amount of the dye classified as the basic dye is 0.5. The following is sufficient.

  As described above with reference to the examples, according to the semiconductor layer of the above embodiment and the dye-sensitized solar cell using this semiconductor layer, the effects listed below can be obtained.

  (1) Since the ratio of the adsorption amount of the auxiliary dye to the adsorption amount of the basic dye on the semiconductor surface is 0.5 or less, the association between the basic dye and the auxiliary dye is suppressed. As a result, unnecessary electron transfer between the dyes is suppressed, and the photoelectric conversion efficiency is increased in the dye-sensitized solar cell including such a semiconductor layer 13.

  (2) The basic dye has a structure that forms an ester bond with the Bronsted acid site on the semiconductor surface of the semiconductor layer 13 and does not bond with the Lewis acid site, and the auxiliary dye is arranged at the Lewis acid site on the semiconductor surface. In the configuration in which the base is bonded, it is easy to selectively bond the basic dye to the Bronsted acid site. In addition, since the auxiliary dye includes a pyridine group that coordinates to the Lewis acid site as a fixing group, bonding between the auxiliary dye and the semiconductor surface in a preferable conformation is realized.

  (3) When the basic dye has a ruthenium complex structure, a dye having higher suitability as a sensitizing dye used in a dye-sensitized solar cell can be used as the basic dye. Further, in the configuration in which the auxiliary dye is an organic dye, a dye having higher suitability as the sensitizing dye used in the dye-sensitized solar cell can be used as the auxiliary dye. And photoelectric conversion efficiency can be improved in the dye-sensitized solar cell which has these ruthenium complex structures and organic dye as a sensitizing dye.

  DESCRIPTION OF SYMBOLS 10 ... Dye-sensitized solar cell, 11 ... 1st board | substrate, 12 ... 1st electrode, 13 ... Semiconductor layer, 14 ... Electrolyte layer, 15 ... 2nd electrode, 16 ... 2nd board | substrate.

Claims (6)

A semiconductor having a surface including a first binding site and a second binding site;
A first dye that adsorbs on the surface and absorbs light in a first wavelength region;
A second dye that adsorbs on the surface and absorbs light in the second wavelength region;
With
The first binding site has different chemical properties than the second binding site;
A sensitizing dye bonded to the first binding site is included in the first dye,
A sensitizing dye bonded to the second binding site is included in the second dye,
The first wavelength region is wider than the second wavelength region;
The ratio of the adsorption amount of the second dye to the adsorption amount of the first dye is 0.5 or less. Semiconductor layer. A semiconductor layer according to claim 1;
An electrolyte layer;
A first electrode;
A second electrode facing the first electrode across the semiconductor layer and the electrolyte layer;
A dye-sensitized solar cell comprising: The first binding site is a Bronsted acid site;
The second binding site is a Lewis acid site;
The sensitizing dye bonded to the first binding site has a structure that forms an ester bond with the Bronsted acid site and does not bind to the Lewis acid site,
The dye-sensitized solar cell according to claim 2, wherein the sensitizing dye bonded to the second binding site is coordinated to the Lewis acid site. The dye-sensitized solar cell according to claim 3, wherein the sensitizing dye bonded to the second binding site includes a pyridine group coordinated to the Lewis acid site. The dye-sensitized solar cell according to any one of claims 2 to 4, wherein the first dye has a ruthenium complex structure. The dye-sensitized solar cell according to any one of claims 2 to 5, wherein the second dye is an organic dye.

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