JP2010067542A - Photoelectric conversion element, manufacturing method thereof, and solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element having a high photoelectric conversion efficiency and a high durability, to provide a manufacturing method thereof, and to provide a solar cell using the photoelectric conversion element. <P>SOLUTION: The photoelectric conversion element of dye-sensitized type has a counter electrode, a semiconductor electrode which has at least one kind of dye adsorbed, and a solid hole transporting layer on a substrate. The surface of the semiconductor electrode is formed of a dye phase and an inorganic oxo acid phase or a metal hydroxide phase. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  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 the like, 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 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 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. An advantage of this method is that an inexpensive metal semiconductor such as titanium oxide can be used without the need to purify it to high purity, and thus a solar cell can be produced at low cost. In addition, the spectral sensitization effect of the dye can effectively convert sunlight with many visible light components into electricity.

The above dye-sensitized solar cell uses, as a charge transport layer, an electrolytic solution in which an electrolyte containing iodine is dissolved in an organic solvent, but has problems such as volatilization and leakage of the electrolytic solution or corrosion by iodine. . In order to compensate for these drawbacks, a substance using an aromatic amine solid p-type semiconductor as a charge transport layer (for example, see Non-Patent Document 2) has been reported. However, there are many cases where there is no report about durability, and even if there is, it did not satisfy the level of practical durability. A cause of low durability is that the dye adsorbed on the semiconductor thin film such as titanium oxide is decomposed by the photocatalytic action of the semiconductor, and this decomposition action is remarkable when the electrolyte is solid.
B. O'Regan, M.M. Gratzel, Nature, 353, 737 (1991) U. Bach, M.M. Gratzel, Nature, 395, 583 (1998)

  An object of the present invention is to provide a photoelectric conversion element having high photoelectric conversion efficiency and high durability, a method for producing the photoelectric conversion element, and a solar cell using the photoelectric conversion element.

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

  1. In a dye-sensitized photoelectric conversion element in which a counter electrode, a semiconductor electrode formed by adsorbing at least one dye and a solid hole transport layer are provided on a substrate, the surface of the semiconductor electrode is a dye phase, And a photoelectric conversion element formed of an inorganic oxoacid phase or a metal hydroxide phase.

  2. 2. The photoelectric conversion element as described in 1 above, wherein the semiconductor forming the semiconductor electrode is titanium oxide.

  3. 3. The photoelectric conversion element as described in 1 or 2 above, wherein the oxo acid phase is phosphoric acid or sulfuric acid.

  4). 4. The photoelectric conversion element according to any one of 1 to 3, wherein the hydroxide forming the metal hydroxide phase is aluminum hydroxide or zirconium hydroxide.

  5. 5. The photoelectric conversion element according to any one of 1 to 4, wherein the hole transport layer contains an aromatic amine compound.

  6). The photoelectric conversion element according to any one of 1 to 5, wherein the dye has a carboxyl group.

  7). In the method for producing a dye-sensitized photoelectric conversion element comprising a counter electrode, a semiconductor electrode on which at least one kind of dye is adsorbed on a substrate, and a solid hole transport layer, the dye is adsorbed. A method for producing a photoelectric conversion element, wherein the semiconductor electrode is obtained by being immersed or brought into contact with an oxoacid salt solution or a metal hydroxide-containing solution.

  8). A solar cell comprising the photoelectric conversion device according to any one of 1 to 6 or the photoelectric conversion device obtained by the method for producing a photoelectric conversion device according to 7.

  According to the present invention, a photoelectric conversion element having high photoelectric conversion efficiency and high durability, a manufacturing method thereof, and a solar cell using the photoelectric conversion element can be provided.

  As a result of intensive studies, the present inventors have found that in a dye-sensitized photoelectric conversion element in which a counter electrode, a semiconductor electrode on which a dye is adsorbed, and a solid hole transport layer are provided on a substrate, the semiconductor It has been found that a photoelectric conversion element having high photoelectric conversion efficiency and high durability can be obtained by a photoelectric conversion element in which the surface of the electrode is formed of a dye phase and an inorganic oxo acid phase or metal hydroxide phase. It was.

  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 comprises a substrate 1, a transparent conductive film 2, an insulating layer 3, a semiconductor electrode 6, a hole transport layer 7, a counter electrode 8, and the like.

  The photoelectric conversion element of this invention is formed with the following structures. An insulating layer 3 is formed on a substrate 1 (also referred to as a conductive support) to which a transparent conductive film 2 is attached, and then a semiconductor layer 5 having pores formed by sintering is formed. The semiconductor electrode 6 is formed by adsorbing the sensitizing dye 4. A hole transport layer 7 mainly composed of a p-type semiconductor is provided on the semiconductor electrode 6, and a counter electrode 8 is attached thereon. A terminal is attached to the transparent conductive film 2 and the counter electrode 8, and a photocurrent is taken out.

(Oxo acid phase or metal hydroxide phase)
In the present invention, the surface of the semiconductor used for the semiconductor electrode is formed of a dye phase having a dye and an inorganic oxo acid phase or metal hydroxide phase in order to suppress decomposition of the dye due to photocatalysis. And

  In the present invention, the dye phase refers to the portion where the dye is adsorbed on the semiconductor surface, the inorganic oxo acid phase refers to the portion where the inorganic oxo acid ion is adsorbed to the semiconductor surface, and the metal hydroxide phase refers to the semiconductor The part where the surface reacted or adsorbed with the metal hydroxide. Therefore, when the surface of the semiconductor electrode according to the present invention is schematically shown, as shown in FIG. 2, the surface of the semiconductor particles constituting the semiconductor electrode is composed of a dye adsorption phase 11, an inorganic oxo acid phase, or a metal hydroxide phase. 12 is comprised.

  With such a configuration, it is presumed that the generation of active oxygen species is suppressed by reducing the exposure of the semiconductor particle surface to the atmosphere, and decomposition by the photocatalyst can be suppressed while maintaining the photoelectric conversion function. . In particular, in the case of a dye-sensitized solar cell having a solid charge transport layer in which the semiconductor electrode and the charge transport layer may be microscopically separated, the decomposition suppression effect by the photocatalyst is large, and the remarkable durability. We think that improvement was achieved. When the charge transport layer is a liquid, ions in the electrolyte suppress the photocatalytic action, so that the adsorbed sensitizing dye is hardly decomposed.

  The durability improvement effect is particularly remarkable in the case of titanium oxide among the semiconductor electrodes. This is presumed to be because the reaction suppression effect becomes more remarkable because titanium oxide has a high photocatalytic action.

  In order to obtain such a semiconductor, for example, a semiconductor electrode is treated with a dye solution to adsorb dye molecules on the surface, and a dye adsorbing phase is formed as a region where the dye molecules are adsorbed. Next, when this semiconductor electrode is treated with an inorganic oxo acid solution, an inorganic oxo acid phase is formed at the dye non-adsorption site on the surface of the semiconductor particles without desorbing the already adsorbed dye molecules. Similarly, when a semiconductor electrode having a dye adsorbed is treated with a metal hydroxide-containing liquid, a metal hydroxide phase is formed.

  In the present invention, the surface of the semiconductor electrode is formed of a dye phase and an inorganic oxo acid phase or metal hydroxide phase. A part of the surface of the semiconductor particles constituting the semiconductor electrode is a dye phase and an inorganic oxo acid. It is not excluded that the phase is not a phase or a metal hydroxide phase, as long as the portion obtained by subtracting the dye phase from the entire semiconductor surface is partially changed to an inorganic oxo acid phase or metal hydroxide phase. . However, from the viewpoint of durability, it is preferable that the portion where the dye phase is subtracted from the entire semiconductor surface is changed to 50% or more of the oxo acid phase or metal hydroxide phase, and 70% or more of the oxo acid phase or metal hydroxide. What has changed into the physical phase is more preferable.

  In order to form an inorganic oxo acid phase or metal hydroxide phase, the sensitized semiconductor electrode is immersed or brought into contact with an inorganic oxo acid salt solution or a metal hydroxide-containing solution. An inorganic oxo acid phase or a metal hydroxide phase is formed at the dye non-adsorption site on the surface of the semiconductor particle without desorption of the dye molecules that have already been adsorbed. The semiconductor electrode after the immersion or contact is dried to remove the solvent.

  Inorganic oxo acid salts include hypochlorous acid, chlorous acid, chloric acid, perchloric acid, perbromic acid, iodic acid, periodic acid, boric acid, carbonic acid, silicic acid, nitrous acid, nitric acid, phosphorous acid Examples thereof include salts of acid, phosphoric acid, sulfurous acid, sulfuric acid and the like, and among inorganic oxoacid salts, phosphate or sulfate is preferable. There are no particular restrictions on the counter-cationic species of the oxoacid salt.

  Similarly, as the metal hydroxide, aluminum hydroxide or zirconium hydroxide is preferable.

  These ions have a great effect of suppressing the action of decomposing organic substances in the semiconductor used for the electrode, and significantly improve the durability of the photoelectric conversion element.

  The solvent used to dissolve the inorganic oxo acid salt or metal hydroxide can dissolve the inorganic oxo acid salt or metal hydroxide, and dissolve the semiconductor or react with the semiconductor. If there is no, there are no special restrictions.

  The photoelectric conversion element of the present invention is formed by disposing a semiconductor electrode formed by adsorbing a dye on a semiconductor layer on a conductive support and a counter electrode through a hole transport layer. Hereinafter, the semiconductor electrode and the counter electrode will be described.

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

  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 electrode may be manufactured by coating or spraying the semiconductor on a conductive support. In addition, when the semiconductor according to the present invention is in the form of a film and is not held on the conductive support, it is preferable to produce a semiconductor electrode by bonding the semiconductor 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.

(substrate)
The substrate used for the photoelectric conversion element of the present invention and the solar cell of the present invention (also referred to as a conductive support) is made of a conductive material such as a metal plate, or a non-conductive material such as a glass plate or a plastic film. A structure provided with a conductive substance can be used. Examples of materials used for the conductive support include metals (for example, platinum, gold, silver, copper, aluminum, rhodium, indium) or conductive metal oxides (for example, indium-tin composite oxide, fluorine for tin oxide) And carbon). The thickness of the conductive support is not particularly limited, but is preferably 0.3 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.

(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 the semiconductor fine powder, the better. The primary particle diameter is preferably 1 to 5000 nm, and 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 solution containing fine semiconductor powder and baking treatment of the formed semiconductor layer)
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 layer (semiconductor film) is formed thereon.

  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 semiconductor fine powder used. 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 thin film 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).

  As for the film thickness of the semiconductor layer used as the baked material film | membrane which has a porous structure, 10 nm or more is preferable, 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 pigment is supported on the semiconductor layer. From the viewpoint of efficient injection of charges into the semiconductor thin film, the sensitizing 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 the dye in an appropriate solvent as described above and immersing the substrate on which the semiconductor is baked and fixed in the solution. In that case, a semiconductor layer (also referred to as a semiconductor film) is formed by baking, and the substrate is subjected to pressure reduction treatment or heat treatment in advance to remove bubbles in the film, so that the dye can enter deep inside the semiconductor layer (semiconductor film). It is preferable that the semiconductor layer (semiconductor film) is a porous structure film.

  The solvent used for dissolving the dye is not particularly limited as long as it can dissolve and does not dissolve the semiconductor or react with the semiconductor. In order to prevent the gas from entering the semiconductor film and hindering the sensitization process such as adsorption of the dye, it is preferable to deaerate and purify 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 and acetonitrile.

  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 layer (semiconductor film) to sufficiently advance adsorption, etc., sufficiently sensitize the semiconductor, and in the solution From the viewpoint of suppressing degradation products generated by the decomposition of the dye and the like from interfering with the adsorption of the dye, it is preferably 1 to 48 hours, more preferably 3 to 24 hours at 25 ° C. 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 layer 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 are used so that sunlight can be used effectively by widening the wavelength range of photoelectric conversion. 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.

  In order to include a dye in the semiconductor layer, a method of dissolving the dye in an appropriate solvent (ethanol or the like) and immersing a well-dried semiconductor in the solution for a long time is general.

  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. When preparing a separate solution for each dye and immersing in each solution in order, the effects described in the present invention can be obtained regardless of the order in which the dye is included in the semiconductor layer. . 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 layer 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.

  In addition, the sensitization treatment of the semiconductor layer according to the present invention is performed by including the sensitizing dye of the present invention in the semiconductor. The details of the sensitization treatment are described in the photoelectric conversion element described later. This will be specifically described.

  In the case of a semiconductor layer having a semiconductor thin film with a high porosity, the sensitizing dye adsorption treatment (before the water is adsorbed on the semiconductor thin film by the water, water vapor, etc., and the voids inside the semiconductor thin film ( It is preferable to complete the sensitization treatment of the semiconductor layer.

(Hole transport layer)
The hole transport layer (also referred to as charge transfer layer) used in the present invention will be described.

  The charge transfer 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 transfer 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 preferred range of the ionization potential of the p-type compound semiconductor used in the charge transfer 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 hole 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. Therefore, for example, when a coating method is used in forming the hole transport layer, there is an advantage that the hole transport layer material can be easily prepared. Among these, as an oligomer, it is preferable to use a dimer or a trimer, and it is particularly preferable to use an oligomer having a spiro structure. Specifically, 2,2 ′, 7,7′-tetrakis (N, N′-di (4-methoxyphenyl) amine) -9,9′-spirobifluorene (spiro-MeOTAD) is preferably used. The

  Although it does not specifically limit as average thickness of a positive hole transport layer, For example, 0.1-100 micrometers is preferable, 0.5-50 micrometers is more preferable, 1-20 micrometers is further more preferable. Thereby, it can prevent more reliably that the efficiency (transmission efficiency) which transmits a hole from a positive hole transport layer to a semiconductor electrode falls.

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

  The counter electrode only needs to have conductivity, and an arbitrary conductive material is used, but a metal thin film having good contact property with the hole transport layer is preferable. A gold thin film that is a chemically stable metal having a small work function difference from the hole 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 constituting the solar cell of the present invention, it is preferable that the semiconductor electrode, the hole transport layer and the counter electrode are housed in a case and sealed, or the whole is sealed with a resin.

  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, then move to the counter electrode via the hole transport layer, and reduce the aromatic amine derivative of the hole transport layer (also referred to as charge transfer 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 hole transport layer, it is reduced and returned to the original state, and at the same time The aromatic amine derivative in the transport layer is oxidized and returned to a state where it can be reduced again by the 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]
A solution obtained by diluting 1.2 ml of tetrakisisoporopoxytitanium and 0.8 ml of acetylacetone in 18 ml of ethanol was dropped onto a fluorine-doped tin oxide (FTO) conductive glass substrate, and after film formation by spin coating, the film was heated at 450 ° C. at 8 ° C. The insulating film was produced on the transparent conductive film (FTO) by heating for minutes. A commercially available titanium oxide paste (particle size: 18 nm) was applied on the insulating film by a screen printing method. After heating at 120 ° C. for 3 minutes to dry the paste, baking was performed at 450 ° C. for 30 minutes to obtain a titanium oxide thin film having a thickness of 3 μm. The whole substrate was immersed in a 0.02 mol / l aqueous solution of titanium tetrachloride overnight and then baked again at 450 ° C. for 10 minutes.

The dye (1) was dissolved in a 1: 1 mixed solvent of t-butyl alcohol and acetonitrile to prepare a 5 × 10 ⁻⁴ mol / l solution. The FTO glass substrate coated and sintered with titanium oxide was immersed in this solution at room temperature for 3 hours, and dye adsorption treatment was performed to obtain a semiconductor electrode. This semiconductor electrode was immersed in an aqueous potassium dihydrogen phosphate solution having a concentration of 1 × 10 ⁻³ mol / l for 1 hour, washed with water, and then dried at 60 ° C. for 10 minutes to form an oxo acid phase. When the spectrum of the energy dispersive X-ray analyzer (EDX) was compared for the sample before and after immersion in the potassium dihydrogen phosphate aqueous solution, a peak derived from phosphorus atoms was newly observed in the sample after immersion treatment. It was judged that phosphate ions were adsorbed on the surface.

Next, in a 19: 1 mixed solvent of chlorobenzene and acetonitrile, 0.17 mol of spiro-MeOTAD is used as a hole transporting agent, 0.33 mmol of N (PhBr) ₃ SbCl ₆ is used as a hole doping agent, Li [(CF ₃ 15 mmol of SO ₂ ) ₂ N] was dissolved, and a hole transport layer was formed on the semiconductor electrode after adsorption of the dye by spin coating, followed by vacuum drying for 30 minutes to form a hole transport layer. 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 3]
Photoelectric conversion elements 2 and 3 were prepared in the same manner as in the production of photoelectric conversion element 1 except that potassium sulfate and sodium hydrogen carbonate were used as the oxoacid salts forming the oxoacid phase, respectively.

[Production of photoelectric conversion elements 4 to 6]
In the production of the photoelectric conversion element 1, photoelectric conversion elements 4 to 6 were produced in the same manner except that aluminum hydroxide, zirconium hydroxide and iron hydroxide were used as the hydroxides forming the metal hydroxide phase, respectively. . In the case of aluminum hydroxide, zirconium hydroxide, and iron hydroxide, the hydroxide is adjusted to pH 7 by adding ammonia water to an aqueous solution of aluminum sulfate, zirconium acetate, and iron (III) chloride at a concentration of 1 × 10 ⁻³ mol / l. The semiconductor electrode was treated with a suspension of

[Production of photoelectric conversion elements 7 to 9]
In the production of the photoelectric conversion element 1, photoelectric conversion elements 7 to 9 were produced in the same manner except that the dye (1) was replaced with the dyes (2) to (4).

[Production of Photoelectric Conversion Element 10]
In the production of the photoelectric conversion element 1, a photoelectric conversion element 10 was produced in the same manner except that a tin oxide paste was used instead of the titanium oxide paste.

[Production of Photoelectric Conversion Element 11]
Photoelectric conversion element 11 (comparative example) was prepared in the same manner as in the production of photoelectric conversion element 1 except that immersion in an aqueous potassium dihydrogen phosphate solution was not performed.

[Evaluation of photoelectric conversion element]
About the produced photoelectric conversion element, the initial photoelectric conversion efficiency and the photoelectric conversion efficiency fall rate after a photodegradation test were measured.

(Measurement of initial photoelectric conversion efficiency)
Photoelectric conversion characteristics were measured under the condition that a semiconductor electrode was covered with a 5 × 5 mm ² mask 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.

(Measurement of photoelectric conversion efficiency after light degradation test)
After irradiation with xenon lamp light having an intensity of 100 mW / cm ^{2 in} an open circuit state for 3 hours, the photoelectric conversion efficiency (η (%)) was determined, and the ratio (%) to the initial photoelectric conversion efficiency was calculated.

  The evaluation results are shown in the table.

  From Table 1, the photoelectric conversion elements 1 to 10 of the present invention in which the semiconductor layer was surface-treated with an oxoacid salt or a metal hydroxide were compared with the photoelectric conversion element 11 (comparative example) in which the surface treatment was not performed. It can be seen that the light durability is excellent without impairing the photoelectric conversion characteristics. In particular, among photoelectric conversion elements using a semiconductor electrode made of titanium oxide and a dye having a carboxyl group, the photoelectric conversion elements 1, 2, 7, and 8 in which the oxo acid phase is phosphoric acid or sulfuric acid are initially converted. It is more preferable because the efficiency is as high as 2% or more and the conversion efficiency ratio in the light deterioration test is 0.80 or more and the durability is high. Similarly, the photoelectric conversion elements 4 and 5 in which the metal hydroxide phase is aluminum hydroxide or zirconium hydroxide have an initial conversion efficiency as high as 2% or more, and the conversion efficiency ratio in the photodegradation test is 0.80 or more. It is more preferable because of its high durability.

  From the above results, it was found that treating the semiconductor electrode adsorbed with the dye of the present invention with an oxoacid salt solution or a metal hydroxide-containing solution is effective for improving the durability.

It is sectional drawing which shows an example of the photoelectric conversion element of this invention. It is a schematic diagram which shows the surface of the electrode 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 electrode 6 Semiconductor electrode 7 Hole transport layer 8 Counter electrode 11 Dye adsorption phase 12 Inorganic oxo acid phase or metal hydroxide phase

Claims (8)

In a dye-sensitized photoelectric conversion element in which a counter electrode, a semiconductor electrode formed by adsorbing at least one dye and a solid hole transport layer are provided on a substrate, the surface of the semiconductor electrode is a dye phase, And a photoelectric conversion element formed of an inorganic oxoacid phase or a metal hydroxide phase. The photoelectric conversion element according to claim 1, wherein the semiconductor forming the semiconductor electrode is titanium oxide. The photoelectric conversion element according to claim 1, wherein the oxo acid phase is phosphoric acid or sulfuric acid. 4. The photoelectric conversion element according to claim 1, wherein the hydroxide forming the metal hydroxide phase is aluminum hydroxide or zirconium hydroxide. 5. The photoelectric conversion element according to claim 1, wherein the hole transport layer contains an aromatic amine compound. The photoelectric conversion element according to claim 1, wherein the dye has a carboxyl group. In the method for producing a dye-sensitized photoelectric conversion element comprising a counter electrode, a semiconductor electrode on which at least one kind of dye is adsorbed on a substrate, and a solid hole transport layer, the dye is adsorbed. A method for producing a photoelectric conversion element, wherein the semiconductor electrode is obtained by being immersed or brought into contact with an oxoacid salt solution or a metal hydroxide-containing solution. A solar cell comprising the photoelectric conversion element according to any one of claims 1 to 6 or the photoelectric conversion element obtained by the method for producing a photoelectric conversion element according to claim 7.

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