JP5396851B2 - Photoelectric conversion element and solar cell - Google Patents

Description

  The present invention relates to a photoelectric conversion element and a solar cell, and more particularly to a dye-sensitized photoelectric element and a solar cell using the same.

  In recent years, the use of sunlight, which is infinite and does not generate harmful substances, has been energetically studied. What is currently put into practical use as solar energy, which is a clean energy source, includes residential single crystal silicon, polycrystalline silicon, amorphous silicon, and inorganic solar cells such as cadmium telluride and indium copper selenide. .

  However, the disadvantages of these inorganic solar cells are that, for example, silicon-based solar cells are required to have a very high purity. Naturally, the purification process is complicated, the number of processes is large, and the production cost is high.

  On the other hand, many solar cells using organic materials have been proposed. As an organic solar cell, a Schottky photoelectric conversion element that joins a p-type organic semiconductor and a metal having a low work function, a p-type organic semiconductor and an n-type inorganic semiconductor, or a p-type organic semiconductor and an electron-accepting organic compound are joined. There are heterojunction photoelectric conversion elements, and organic semiconductors used are synthetic dyes and pigments such as chlorophyll and perylene, conductive polymer materials such as polyacetylene, or composite materials thereof. These are thinned by a vacuum deposition method, a casting method, a dipping method, or the like to form a battery material. Although organic materials have advantages such as low cost and easy area enlargement, there are many problems that the photoelectric conversion efficiency is as low as 1% or less, and the durability is poor.

  Under such circumstances, a solar cell exhibiting good characteristics has been reported by Dr. Gretzell of Switzerland (see, for example, Non-Patent Document 1). The proposed battery is a dye-sensitized solar cell, which is a wet solar cell using a titanium oxide porous thin film spectrally sensitized with a ruthenium complex as a working electrode. The advantage of this method is that it is not necessary to purify inexpensive oxide semiconductors such as titanium oxide to high purity, and therefore, it is inexpensive and the available light extends over a wide visible light range, and the sun is rich in visible light components. It is that light can be effectively converted into electricity.

  On the other hand, since these wet solar cells are electrically connected between the working electrode and the counter electrode by the electrolyte solution, there is a problem in durability in terms of volatilization of the electrolyte solution, liquid leakage, detachment of the sensitizing dye, and the like. In order to solve this problem, a solid dye-sensitized solar cell using a solid electrolyte has been reported (for example, see Patent Document 1).

  However, there is a problem that the photoelectric conversion efficiency of the dye-sensitized photoelectric conversion element using a solid solid electrolyte instead of the electrolyte solution is very low.

For such a problem, Patent Document 2 proposes to provide a conductive layer, but the photoelectric conversion efficiency is still not sufficient.
JP 2007-115665 A JP 2001-203377 A B. O'Regan, M.M. Gratzel, Nature, 353, 737 (1991)

  This invention is made | formed in view of the said subject, The objective is to provide a photoelectric conversion element with high photoelectric conversion efficiency, and a solar cell using the same.

  The above object of the present invention is achieved by the following configurations.

  1. In the photoelectric conversion element in which at least the substrate, the first electrode, the semiconductor layer in which the dye is adsorbed on the semiconductor, the charge transport layer, and the counter electrode disposed to face the first electrode are disposed in this order, The transport layer contains a low molecular charge transport agent having a molecular weight of 2,000 or less and a polymer charge transport agent having a molecular weight of 5,000 or more, and the content (A) of the low molecular charge transport agent and the polymer A ratio A: B of the content (B) of the charge transfer agent is 1: 3 to 3: 1.

  2. 2. The photoelectric conversion element as described in 1 above, wherein the molecular weight of the low molecular charge transport agent is 400 to 1,500.

  3. A solar cell comprising the photoelectric conversion element as described in 1 or 2 above.

  ADVANTAGE OF THE INVENTION According to this invention, a photoelectric conversion element with a high photoelectric conversion efficiency and a solar cell using the same can be provided.

  The present inventors have examined the cause of the low photoelectric conversion efficiency of the dye-sensitized photoelectric conversion element using a conventional solid electrolyte, and found that the solid electrolyte does not penetrate well into the oxide semiconductor matrix, Similarly to the electrolyte, the charge transport layer made of a charge transport agent having a charge transport ability has a high crystallinity of the charge transport layer itself, and it is difficult to obtain a uniform film. It was found that a high photoelectric conversion efficiency could not be obtained. On the other hand, it was also found that in a charge transport layer in which a low molecular charge transport agent is dispersed in a binder, the uniformity of the film is improved but the charge mobility is lowered, and as a result, the photoelectric conversion efficiency is not improved.

  Therefore, by using a charge transport layer in which a low molecular charge transport agent having a molecular weight of 2,000 or less and a high molecular charge transport agent having a molecular weight of 5,000 or more are used in a ratio of 1: 3 to 3: 1, It has been found that a photoelectric conversion efficiency higher than that expected from the molecular charge transfer agent alone or the polymer charge transfer agent alone can be obtained. It is anticipated that the combined use suppresses the crystallization of the low molecular charge transport agent and makes the film quality of the charge transport layer uniform, so that the high charge mobility of the low molecular charge transport agent can be fully expressed. Yes.

  Hereinafter, the present invention will be described in detail.

[Photoelectric conversion element]
The photoelectric conversion element of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing an example of the photoelectric conversion element of the present invention. As shown in FIG. 1, the photoelectric conversion element of the present invention includes a substrate 1, a transparent conductive film 2 as a first electrode, a semiconductor layer 6, a charge transport layer 7, a counter electrode 8, and the like.

  Production examples of the photoelectric conversion element of the present invention will be described below. A semiconductor 5 having pores formed by sintering after forming an insulating layer 3 on a transparent substrate 1 (also referred to as a conductive support) provided with a transparent conductive film 2 as a first electrode, if necessary. The semiconductor layer 6 is formed by adsorbing the dye 4 on the surface of the pores. Furthermore, a charge transport layer 7 containing a p-type semiconductor as a main component is provided on the semiconductor layer 6, and a counter electrode 8 is provided thereon. At this time, a terminal is attached to the first electrode and the counter electrode 8 to extract a photocurrent. FIG. 2 shows an example of a cross-sectional view of an element provided with an insulating layer.

(Charge transport layer)
A solid dye-sensitized solar cell in which electrical connection between the first electrode and the counter electrode is performed by a solid electrolyte has a problem that the photoelectric conversion efficiency is very low. The cause is presumed that the electrolyte is not sufficiently in contact with the semiconductor layer, and the low molecular charge transport agent that is not an electrolyte easily enters the pores of the semiconductor and has high charge mobility, but is a film that is easily crystallized. Has the disadvantage of being easily broken. In addition, the polymer charge transport agent alone does not easily enter the semiconductor vacancies and has low charge mobility.

  Therefore, in the present invention, a charge transport layer in which a low molecular charge transport agent and a polymer charge transport agent are used in combination is used. Specifically, it contains a low molecular charge transport agent having a molecular weight of 2,000 or less and a polymer charge transport agent having a molecular weight of 5000 or more, and the content (A) of the low molecular charge transport agent and the polymer charge transport agent. A charge transport layer having a ratio A: B of 1: 3 to 3: 1 is used. The molecular weight of the low molecular charge transport agent is preferably 400 to 1,500. The molecular weight of the polymeric charge transport agent is 5,000 or more, preferably 5,000 to 150,000. The molecular weight without molecular weight distribution can be obtained from the chemical formula, and with molecular weight distribution, the weight average molecular weight is defined as molecular weight in the present invention, and can be measured by gel permeation chromatography.

  The charge transport layer is a layer having a function of rapidly reducing the oxidized oxidant and transporting holes injected at the interface with the dye to the counter electrode. The charge transport layer according to the present invention is composed mainly of a p-type compound semiconductor as a hole transport material. The band gap of the p-type compound semiconductor is preferably large because it does not hinder dye absorption. The band gap of the p-type compound semiconductor used in the present invention is preferably 2 eV or more, and more preferably 2.5 eV or more. Also, the ionization potential of the p-type compound semiconductor needs to be smaller than the dye adsorption electrode ionization potential in order to reduce the dye hole. Although the preferable range of the ionization potential of the p-type compound semiconductor used for the charge transport layer varies depending on the dye used, it is generally preferably 4.5 eV or more and 5.5 eV or less, and more preferably 4.7 eV or more and 5.3 eV or less.

  As the p-type compound semiconductor, an aromatic amine derivative having an excellent hole transport capability is preferable. For this reason, photoelectric conversion efficiency can be improved more by comprising a charge transport layer mainly with an aromatic amine derivative. As the aromatic amine derivative, it is particularly preferable to use a triphenyldiamine derivative. Triphenyldiamine derivatives are particularly excellent in the ability to transport holes among aromatic amine derivatives. Moreover, such an aromatic amine derivative may use any of a monomer, an oligomer, a prepolymer, and a polymer, and may mix and use these. Monomers, oligomers, and prepolymers have a relatively low molecular weight, and thus have high solubility in solvents such as organic solvents. For this reason, when forming a charge transport layer by the apply | coating method, there exists an advantage that preparation of charge transport layer material can be performed more easily. Among these, it is preferable to use a dimer or a trimer as the oligomer.

  Specific aromatic tertiary amine compounds include N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl; N, N′-diphenyl-N, N′-bis (3- Methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1-bis (4-di) -P-tolylaminophenyl) cyclohexane; N, N, N ', N'-tetra-p-tolyl-4,4'-diaminobiphenyl; 1,1-bis (4-di-p-tolylaminophenyl)- 4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N′-diphenyl-N, N′-di (4 -Methoxyphenyl -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadriphenyl; N, N, N- Tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenylamino- (2-diphenylvinyl) Benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and two fused aromatic rings described in US Pat. No. 5,061,569 For example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), described in JP-A-4-308688 That triphenylamine units are linked to three starburst 4,4 ', 4 "- tris [N- (3- methylphenyl) -N- phenylamino] triphenylamine (MTDATA) and the like.

  Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

  Examples of charge transport agents other than aromatic amine derivatives include condensed polycyclic aromatic compounds and conjugated compounds.

  As the condensed polycyclic aromatic compound, for example, anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, sarkham anthracene, bisanthene, zestrene, heptazelene, Examples thereof include compounds such as pyranthrene, violanthene, isoviolanthene, cacobiphenyl, anthradithiophene, and derivatives thereof.

  Examples of the conjugated compound include polythiophene and its oligomer, polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, tetrathiafulvalene compound, quinone Compounds, cyano compounds such as tetracyanoquinodimethane, fullerenes and derivatives or mixtures thereof.

  In particular, among polythiophene and oligomers thereof, thiophene hexamer α-seccithiophene, α, ω-dihexyl-α-secthiothiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3 Oligomers such as -butoxypropyl) -α-sexithiophene can be preferably used.

  The molecular weight measurement method is preferably measured by GPC (gel permeation chromatography) using THF (tetrahydrofuran) as a solvent. That is, 1.0 ml of THF is added to 0.5 to 5 mg of a measurement sample, more specifically 1 mg, and the mixture is sufficiently dissolved by stirring at room temperature using a magnetic stirrer or the like. Subsequently, after processing with a membrane filter having a pore size of 0.45 to 0.50 μm, the solution is injected into a GPC column. The measurement conditions of GPC are measured by stabilizing the column at 40 ° C., flowing THF at a flow rate of 1.0 ml / min, and injecting about 100 μl of a sample having a concentration of 1 mg / ml. The column is preferably used in combination with a commercially available polystyrene gel column. For example, Shodex GPC KF-801, 802, 803, 804, 805, 806, 807 manufactured by Showa Denko KK, TSKgel G1000H, G2000H, G3000H, G4000H, G5000H, G6000H, G7000H, TSKguard column manufactured by Tosoh Corporation A combination etc. can be mentioned. As a detector, a refractive index detector (IR detector) or a UV detector may be used. In the measurement of the molecular weight of a sample, the molecular weight distribution of the sample is calculated using a calibration curve created using monodisperse polystyrene standard particles. About 10 points may be used as polystyrene for preparing a calibration curve.

  Specific examples of the low molecular charge transport agent having a molecular weight of 2,000 or less are shown below, but the present invention is not limited thereto.

  Specific examples of the polymeric charge transfer agent having a molecular weight of 5,000 or more are shown below, but the present invention is not limited to these.

(Preparation of charge transport layer)
The charge transport layer is coated on the semiconductor layer with a mixed solution dissolved in a solvent capable of dissolving both the low molecular charge transport agent and the polymer charge transport agent, and then left at room temperature in the atmosphere, and then evacuated. It can be made by drying. The application method is appropriately set depending on the material and the viscosity of the solution, and is not particularly limited. For example, various coating methods such as dipping, dripping, doctor blade, spin coating, brush coating, spray coating, roll coater and the like can be mentioned. The mixed solution of the low molecular charge transport agent and the polymer charge transport agent may be mixed after dissolving each charge transport agent in a solvent, or may be mixed after dissolving each in a solution. In addition, after applying a solution in which a low molecular charge transport agent is dissolved, a solution in which a polymer charge transport agent is dissolved is applied and dried, or after applying a low molecular charge transport agent solution and drying, a polymer charge transport agent solution May be applied and dried. Further, the order of application of the charge transport agent may be reversed.

  The photoelectric conversion element of the present invention is formed by arranging a semiconductor layer in which a dye is adsorbed on a semiconductor on a conductive support and a counter electrode so as to face each other via a charge transport layer. Hereinafter, the substrate, the semiconductor layer, and the counter electrode will be described.

(substrate)
The substrate used for the photoelectric conversion element of the present invention or the solar cell of the present invention has a structure in which a conductive material is provided on a conductive material such as a metal plate or a non-conductive material such as a glass plate or a plastic film. Things can be used. When the substrate is transparent, light can enter from here. When the substrate is opaque, the counter electrode is transparent and light can enter from this side. Any of them may be transparent.

(First electrode)
Examples of the material used for the first electrode include metal (for example, platinum, gold, silver, copper, aluminum, rhodium, indium) or conductive metal oxide (for example, indium-tin composite oxide, tin oxide with fluorine. And doped carbon). The thickness of the conductive support is not particularly limited, but is preferably 0.0003 to 5 mm.

  Further, the conductive support is preferably substantially transparent, and substantially transparent means that the light transmittance is 10% or more, more preferably 50% or more, Most preferably, it is 80% or more. In order to obtain a transparent conductive support, it is preferable to provide a conductive layer made of a conductive metal oxide on the surface of a glass plate or a plastic film. When a transparent conductive support is used, light is preferably incident from the support side.

The conductive support preferably has a surface resistance of 50 Ω / cm ² or less, and more preferably 10 Ω / cm ² or less.

(Semiconductor layer)
A method for manufacturing a semiconductor layer (6 in FIG. 1) according to the present invention will be described.

  The semiconductor layer according to the present invention comprises a semiconductor, a dye, and, if necessary, an additive.

  When the semiconductor according to the present invention is produced by firing, it is preferable that the semiconductor sensitization treatment (adsorption, penetration into the porous body, etc.) using a dye is performed after the semiconductor is fired. It is particularly preferable to perform the dye adsorption treatment quickly after the firing and before the water is adsorbed to the semiconductor.

  When the semiconductor according to the present invention is in the form of particles, the semiconductor layer is preferably manufactured by coating or spraying the semiconductor on a conductive support. In addition, when the semiconductor according to the present invention is in a film form and is not held on the conductive support, it is preferable to manufacture the semiconductor by pasting onto the conductive support.

  In the photoelectric conversion element of the present invention, as the semiconductor, a compound having a Group 3 to Group 5, Group 13 to Group 15 element of a periodic table (also referred to as an element periodic table), a metal chalcogenide (for example, Oxides, sulfides, selenides, etc.), metal nitrides, etc. can be used.

  Preferred metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxides, cadmium, zinc, lead, silver, antimony or Bismuth sulfide, cadmium or lead selenide, cadmium telluride and the like. Examples of other semiconductors include phosphides such as zinc, gallium, indium, and cadmium, gallium-arsenic or copper-indium selenides, copper-indium sulfides, and titanium nitrides.

Specific examples include TiO ₂ , ZrO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , ZnO, Nb ₂ O ₅ , Ta ₂ O ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, CdTe, GaP. , InP, GaAs, CuInS ₂ , CuInSe ₂ , Ti ₃ N _{4 and the} like, but TiO ₂ , ZnO, SnO ₂ , Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , CdS, etc. are preferably used. PbS is more preferably used, and TiO ₂ or SnO ₂ is used. Of these, TiO ₂ is particularly preferably used.

As the semiconductor used for the photoelectrode, a plurality of the above-described semiconductors may be used in combination. For example, several kinds of the above-described metal oxides or metal sulfides can be used in combination, and a titanium oxide semiconductor may be used by mixing 20% by mass of titanium nitride (Ti ₃ N ₄ ). In addition, J.H. Chem. Soc. Chem. Commun. 15 (1999). At this time, when a component is added as a semiconductor in addition to the metal oxide or metal sulfide, the mass ratio of the additional component to the metal oxide or metal sulfide semiconductor is preferably 30% or less.

(Preparation of coating liquid containing semiconductor fine powder)
First, a coating solution containing fine semiconductor powder is prepared. The finer the primary particle diameter of this semiconductor fine powder, the better. The primary particle diameter is preferably 1 to 5,000 nm, more preferably 2 to 50 nm. The coating liquid containing the semiconductor fine powder can be prepared by dispersing the semiconductor fine powder in a solvent. The semiconductor fine powder dispersed in the solvent is dispersed in the form of primary particles. The solvent is not particularly limited as long as it can disperse the semiconductor fine powder.

  Examples of the solvent include water, an organic solvent, and a mixed solution of water and an organic solvent. As the organic solvent, alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone, acetone and acetyl acetone, hydrocarbons such as hexane and cyclohexane, and the like are used. A surfactant and a viscosity modifier (polyhydric alcohol such as polyethylene glycol) can be added to the coating solution as necessary. The range of the semiconductor fine powder concentration in the solvent is preferably 0.1 to 70% by mass, and more preferably 0.1 to 30% by mass.

(Application of coating liquid containing semiconductor fine powder and baking treatment of the formed semiconductor)
The semiconductor fine powder-containing coating solution obtained as described above is applied or sprayed onto a conductive support, dried, etc., and then baked in air or an inert gas to provide a conductive support. A semiconductor is formed on top.

  The film obtained by applying and drying the coating liquid on the conductive support is composed of an aggregate of semiconductor fine particles, and the particle size of the fine particles corresponds to the primary particle size of the used semiconductor fine powder. is there.

  Since the semiconductor fine particle aggregate film formed on the substrate such as the conductive support in this way has a low bonding strength with the conductive support or between the fine particles and a low mechanical strength. In order to increase the mechanical strength and to obtain a fired product film firmly adhered to the substrate, the semiconductor fine particle aggregate film is preferably subjected to a firing treatment.

  In the present invention, the fired product film obtained by this firing treatment may have any structure, but is preferably a porous structure film (also referred to as a porous layer having voids).

  Here, the porosity of the semiconductor thin film according to the present invention is preferably 10% by volume or less, more preferably 8% by volume or less, and particularly preferably 0.01 to 5% by volume or less. The porosity of the semiconductor means a porosity that is penetrable in the thickness direction of the dielectric, and can be measured using a commercially available apparatus such as a mercury porosimeter (Shimadzu Polarizer 9220 type).

  10 nm or more is preferable and, as for the film thickness of the semiconductor used as the baked material film | membrane which has a porous structure, More preferably, it is 100-10000 nm.

  From the viewpoint of appropriately preparing the actual surface area of the fired product film during the firing treatment and obtaining a fired product film having the above porosity, the firing temperature is preferably lower than 1000 ° C, more preferably in the range of 200 to 800 ° C. Especially preferably, it is the range of 300-800 degreeC.

  The ratio of the actual surface area to the apparent surface area can be controlled by the particle size, specific surface area, firing temperature, etc. of the semiconductor fine particles. In addition, after the heat treatment, for example, chemical plating using an aqueous solution of titanium tetrachloride for the purpose of increasing the surface area of the semiconductor particles, increasing the purity in the vicinity of the semiconductor particles, and increasing the efficiency of electron injection from the dye to the semiconductor particles. Alternatively, an electrochemical plating process using a titanium trichloride aqueous solution may be performed.

(Dye)
In the present invention, a dye is adsorbed on a semiconductor. From the viewpoint of efficient injection of charges into the semiconductor, the dye preferably has a carboxyl group. Specific examples of the dye are shown below, but the present invention is not limited thereto.

(Semiconductor sensitization treatment)
The semiconductor sensitization treatment is performed by dissolving a dye in a suitable solvent and immersing the substrate on which the semiconductor is baked and fixed in the solution. In that case, it is preferable that the semiconductor is formed by baking, and the substrate is preliminarily subjected to decompression treatment or heat treatment to remove bubbles in the film so that the dye can enter deep inside the semiconductor. The structure film is particularly preferable. In the case of a semiconductor having a high porosity, the sensitizing dye adsorption treatment (semiconductor sensitization treatment) is performed before water is adsorbed on the semiconductor surface and the voids inside the semiconductor due to moisture, water vapor, etc. Preferably completed.

  The solvent used for dissolving the dye is not particularly limited as long as it can dissolve the dye and does not dissolve the semiconductor or react with the semiconductor, but it is dissolved in the solvent. In order to prevent moisture and gas from entering the semiconductor and hindering the sensitization treatment such as adsorption of the dye, it is preferable to perform deaeration and distillation purification in advance.

  Solvents preferably used include alcohol solvents such as methanol, ethanol, n-propanol, and t-butyl alcohol, ketone solvents such as acetone and methyl ethyl ketone, and ether solvents such as diethyl ether, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane. Solvents, nitrile solvents such as acetonitrile and propionitrile, halogenated hydrocarbon solvents such as methylene chloride and 1,1,2-trichloroethane, and mixed solvents may be used. Particularly preferred are ethanol, t-butyl alcohol, acetonitrile, tetrahydrofuran, toluene and a mixed solvent thereof.

  The time for immersing the substrate on which the semiconductor is baked in the solution containing the dye is such that the dye penetrates deeply into the semiconductor to sufficiently advance adsorption, etc., sufficiently sensitize the semiconductor, and decomposes the dye in the solution. From the viewpoint of suppressing the decomposition product produced by the method from interfering with the adsorption of the dye, it is preferably 1 to 48 hours at 25 ° C., more preferably 3 to 24 hours. This temperature and time are particularly preferred when the semiconductor film is a porous structure film. However, the immersion time is a value at 25 ° C., and this is not the case when the temperature condition is changed.

  In soaking, the solution containing the pigment may be heated to a temperature that does not boil as long as the pigment does not decompose. A preferable temperature range is 10 to 100 ° C., more preferably 25 to 80 ° C., but this is not the case when the solvent boils in the temperature range as described above.

  When the sensitization treatment is performed using a dye, the dye may be used alone or in combination.

  Moreover, the pigment | dye which has a preferable carboxyl group for this invention, and another pigment | dye can also be used together. As the dye that can be used in combination, any dye can be used as long as it can spectrally sensitize the semiconductor according to the present invention. In order to make the wavelength range of photoelectric conversion as wide as possible and increase the photoelectric conversion efficiency, it is preferable to mix two or more kinds of dyes. Moreover, the pigment | dye mixed and the ratio can be selected so that it may match with the wavelength range and intensity distribution of the target light source.

  In particular, when the use of the photoelectric conversion element of the present invention is a solar cell to be described later, two or more types of dyes having different absorption wavelengths so that the wavelength range of photoelectric conversion can be made as wide as possible to effectively use sunlight. It is preferable to mix and use.

  Among the dyes used in combination, metal complex dyes, phthalocyanine dyes, porphyrin dyes, and polymethine dyes are preferably used from the comprehensive viewpoints such as photoelectron transfer reaction activity, light durability, and photochemical stability.

  Examples of the dye that can be used in combination with the preferred dye having a carboxyl group in the present invention include, for example, US Pat. Nos. 4,684,537, 4,927,721, 5,084, 365, 5,350,644, 5,463,057, 5,525,440, JP-A-7-249790, JP-A-2000-150007 And the like.

  When sensitizing by using a combination of a plurality of dyes or using a dye other than the dye having a carboxyl group preferable for the present invention, a mixed solution of each dye may be prepared and used. It is also possible to prepare a solution for each dye and immerse in each solution in order. In the case where a separate solution is prepared for each dye and is prepared by sequentially immersing in each solution, the effect described in the present invention can be obtained regardless of the order in which the dye is included in the semiconductor. Alternatively, it may be produced by mixing semiconductor fine particles on which a dye is adsorbed alone.

  The adsorption treatment may be performed when the semiconductor is in the form of particles, or may be performed after forming a film on the support. A solution in which the compound used for the adsorption treatment is dissolved may be used at room temperature, or may be used by heating in a temperature range in which the compound does not decompose and the solution does not boil. Moreover, you may implement adsorption | suction of the said pigment | dye after application | coating of semiconductor fine particles like manufacture of the photoelectric conversion element mentioned later. Moreover, you may implement adsorption | suction of a pigment | dye by apply | coating a semiconductor fine particle and the sensitizing dye of this invention simultaneously. Unadsorbed pigment can be removed by washing.

(Counter electrode)
The counter electrode used in the present invention will be described.

  The counter electrode only needs to have conductivity, and any conductive material is used, but a metal thin film having good contact with the charge transport layer is preferable. A gold thin film that is a chemically stable metal having a small work function difference from the charge transport layer is particularly preferable.

[Solar cell]
The solar cell of the present invention will be described.

  The solar cell of the present invention has a structure in which the optimum design and circuit design for sunlight are performed as one aspect of the photoelectric conversion element of the present invention, and the optimum photoelectric conversion is performed when sunlight is used as a light source. Have. That is, the semiconductor is dye-sensitized and can be irradiated with sunlight. When configuring the solar cell of the present invention, it is preferable that the semiconductor layer, the charge transport layer, and the counter electrode are housed in a case and sealed, or the whole is resin-sealed.

  When the solar cell of the present invention is irradiated with sunlight or an electromagnetic wave equivalent to sunlight, the dye adsorbed on the semiconductor is excited by absorbing the irradiated light or electromagnetic wave. Electrons generated by excitation move to the semiconductor, and then move to the counter electrode via the conductive support to reduce the aromatic amine derivative in the charge transport layer. On the other hand, the dye that has moved the electrons to the semiconductor is an oxidant, but when the electrons are supplied from the counter electrode via the charge transport layer, it is reduced and returned to the original state, and at the same time, the charge transport layer This aromatic amine derivative is oxidized and returned to a state where it can be reduced again by electrons supplied from the counter electrode. In this way, electrons flow, and a solar cell using the photoelectric conversion element of the present invention can be configured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.

Example [Production of Photoelectric Conversion Element 1]
An alkoxy titanium solution (Matsumoto Kosho: TA-25 / IPA dilution) was applied onto a fluorine-doped tin oxide (FTO) conductive glass substrate by spin coating. After standing at room temperature for 30 minutes, baking was performed at 450 ° C. for 30 minutes to form a short-circuit prevention layer (insulating layer). Subsequently, a commercially available titanium oxide paste (particle size: 18 nm) was applied on the short-circuit prevention layer by a doctor blade method, then heat-treated at 60 ° C. for 10 minutes, and then baked at 500 ° C. for 30 minutes. A substrate (semiconductor substrate) in which a semiconductor having a titanium oxide thin film was held on a conductive support was obtained.

Exemplified dye C-1 was dissolved in ethanol to prepare a solution of 3 × 10 ⁻⁴ mol / l. The semiconductor substrate was immersed in this solution at room temperature for 3 hours to perform dye adsorption treatment, and then washed with ethanol and dried to obtain a semiconductor layer carrying the dye.

  Next, in a mixed solvent of chlorobenzene: acetonitrile = 19: 1, A-1 (low molecular charge transport agent; charge transport agent 1) 1.0 mass%, B-1 (polymer charge transport agent; charge transport agent 2) Prepare a 0.5% by weight solution, spin-coat at 500 rpm for 60 seconds and then at 2200 rpm for 1 second while filtering through a 0.45 μm filter, leave at room temperature in air for 30 minutes, then vacuum for 10 minutes The charge transport layer was formed by pulling. Further, 90 nm of gold was vapor-deposited by a vacuum vapor deposition method, a counter electrode was produced, and a photoelectric conversion element 1 was produced.

[Production of photoelectric conversion elements 2 to 15]
In the production of the photoelectric conversion element 1, photoelectric conversion elements 2 to 15 were produced in the same manner except that the types and concentrations of the charge transfer agents 1 and 2 and the type of the dye were changed as shown in Table 1.

[Evaluation of photoelectric conversion element]
About the produced photoelectric conversion element, the uniformity of the charge transport layer surface and photoelectric conversion characteristics were measured.

(Uniformity of charge transport layer surface)
For 10 arbitrary surface areas of the charge transport layer, cracks and point defects were observed with a 1000 × optical microscope, an average value was calculated, and evaluated according to the following criteria.

◎: No cracks and point defects in 0.01 mm ² ○: 0.01 mm crack 2 or less in ^2, or point defects 1 or less △: 0.01 mm crack 5 or less in ^2, or point defects 3 X: Cracks exceed 5 in 0.01 mm ² or point defects exceed 3. Δ or less is a practical problem.

(Photoelectric conversion characteristics)
Photoelectric conversion characteristics were measured under conditions where a 5 × 5 mm ² mask was applied to the semiconductor layer under irradiation of a xenon lamp having an intensity of 100 mW / cm ² .

  That is, for a photoelectric conversion element, current-voltage characteristics are measured at room temperature using an IV tester, and a short circuit current (Jsc), an open circuit voltage (Voc), and a form factor (FF) are obtained, and photoelectric conversion is performed from these. Efficiency (η (%)) was determined. The photoelectric conversion efficiency (η (%)) of the photoelectric conversion element was calculated based on the following formula (A).

η = 100 × (Voc × Jsc × FF) / P (A)
Here, P is an incident light intensity [mW · cm ⁻² ], Voc is an open circuit voltage [V], Jsc is a short circuit current density [mA · cm ⁻² ], and FF is a form factor.

  The evaluation results are shown in Table 2.

  From Table 2, the photoelectric conversion efficiency is a charge transport layer with a content ratio of 1: 3 to 3: 1 of a low molecular charge transport agent having a molecular weight of 2,000 or less and a high molecular charge transport agent having a molecular weight of 5,000 or more. It can be seen that all of the photoelectric conversion elements 1 to 6 of the present invention formed with a higher photoelectric conversion efficiency than the comparative photoelectric conversion elements 7 to 12.

  Regarding the uniformity of the surface of the charge transport layer, all of the photoelectric conversion elements 1 to 6 of the present invention were good, and the surface uniformity was confirmed. On the other hand, it was confirmed that the photoelectric conversion elements 12 and 14 of the comparative examples were inferior in surface uniformity because the content ratio of the low molecular charge transport agent alone or the low molecular charge transport agent was high.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent conductive film 3 Insulating layer 4 Dye 5 Semiconductor 6 Semiconductor layer 7 Charge transport layer 8 Counter electrode

Claims (3)

In the photoelectric conversion element in which at least the substrate, the first electrode, the semiconductor layer in which the dye is adsorbed on the semiconductor, the charge transport layer, and the counter electrode disposed to face the first electrode are disposed in this order, The transport layer contains a low molecular charge transport agent having a weight average molecular weight of 2,000 or less and a polymer charge transport agent having a weight average molecular weight of 5,000 or more, and the content of the low molecular charge transport agent (A) The ratio A: B of the content (B) of the polymer charge transporting agent is 1: 3 to 3: 1. 2. The photoelectric conversion element according to claim 1, wherein the low molecular charge transfer agent has a weight average molecular weight of 400 to 1,500. A solar cell comprising the photoelectric conversion element according to claim 1.

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