JP5206092B2 - Photoelectric conversion element and solar cell - Google Patents

Description

  The present invention relates to a photoelectric conversion element, 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 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, ruthenium complexes with limited resources are used, so when this solar cell is put to practical use, the supply of ruthenium complexes is in danger. Further, this ruthenium complex is expensive and has problems in stability over time, and this problem can be solved if it can be changed to an inexpensive and stable organic dye.

  It is known that a dye molecule having both a π-electron conjugated system having an electron donating ability and an acidic adsorbing group having an electron withdrawing property gives an element having high photoelectric conversion efficiency. Triarylamine derivatives are widely used as the electron-donating π-electron system (see, for example, Patent Documents 1 to 4). However, the solution absorption peak of these dyes is 500 nm or less, and the problem remains that the absorption on the long wave side of visible light is weak.

Furthermore, it has been found that these dyes have poor adsorption to titanium oxide and have not yet achieved a high sensitization effect, and have a problem with durability.
JP 2005-123033 A JP 2006-079898 A JP 2006-134649 A JP 2006-156212 A B. O'Regan, M.M. Gratzel, Nature, 353, 737 (1991)

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

  1. The photoelectric conversion element characterized by containing the compound represented by following General formula (1).

(In the formula, R ₁ and R _{2 each} represents an alkyl group, an aralkyl group, an alkenyl group, an aryl group, or a heterocyclic ring, and may have a substituent. R ₁ and R ₂ combine to form a ring. R ₃ and R ₄ each represents an alkyl group having 3 to 18 carbon atoms, an alkoxy group or an aralkyl group, and L ₁ represents a carbon-carbon double bond, a divalent aromatic hydrocarbon or a divalent aromatic hydrocarbon. It represents a heterocyclic ring or a linked structure thereof, and the carbon-carbon double bond may be either E type or Z type, n represents an integer of 0 to 3. X represents an organic group having an acidic group. Represents a residue.)
2. 2. The photoelectric conversion device according to 1, wherein in the photoelectric conversion element in which at least a semiconductor layer and an electrolyte layer are provided between the counter electrodes, the semiconductor layer contains a compound represented by the general formula (1). Conversion element.

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

  By using the novel sensitizing dye of the present invention, it was possible to provide a dye-sensitized photoelectric conversion element having high photoelectric conversion efficiency and excellent light durability, and a solar cell using the same.

  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, it is composed of substrates 1, 1 ', transparent conductive films 2, 7, semiconductor 3, sensitizing dye 4, electrolyte 5, partition wall 9 and the like.

  As a photoelectrode, a semiconductor layer having pores formed by sintering particles of the semiconductor 3 is formed on a substrate 1 (also referred to as a conductive support) provided with a transparent conductive film 2, and the surface of the pores The sensitizing dye 4 is adsorbed on the surface.

  As the counter electrode 6, a transparent conductive film 7 formed on a substrate 1 ′ and platinum 8 deposited thereon is used, and an electrolyte 5 is filled between both electrodes as an electrolyte layer.

  In the dye of the present invention, during power generation, the sensitizing dye generates a current by repeating the photooxidation reaction. In order to improve durability, a sensitizing dye excellent in light stability is required. The present inventors have a donor unit containing nitrogen with high photoelectric conversion efficiency as a mother nucleus of a sensitizing dye, and in order to efficiently transfer photoexcited electrons to a titanium oxide electrode, an acidic group is added, The structure can be adsorbed to titanium oxide. In addition, it is considered that the sensitizing dye is stabilized in the excited state and the photostability is improved by the formation of the aggregate. By having a structure in which a highly planar fluorene unit is directly connected to a nitrogen-containing donor unit that is expected to play a central role in the photoelectric conversion function of sensitizing dyes, It is considered that the aggregation of the water can be promoted. Further, an alkyl group having 3 to 18 carbon atoms, an alkoxy group, and an aralkyl group were introduced into the fluorene unit of the general formula (1).

The reason why the photostability is further improved by introducing an alkyl group having 3 to 18 carbon atoms, an alkoxy group or an aralkyl group to the fluorene unit in the general formula (1) is not clear, but its hydrophobicity It is presumed that the stability in the excited state is further increased by further promoting the molecular aggregation due to the effect. When the number of carbon atoms is 2 or less, the hydrophobic effect is small, which is insufficient for aggregate formation. On the other hand, when the number of carbon atoms is 19 or more, the hydrophobic effect becomes excessive and aggregates are formed. L ₁ represents a carbon-carbon double bond, a divalent aromatic hydrocarbon or a divalent heterocycle, and n represents an integer of 0 to 3. When n is 4 or more, the molecular chain becomes more flexible, so that aggregate formation is inhibited and the light durability cannot be improved.

n is more preferably 1 to 3. The reason is that L ₁ is present between the acidic group and the fluorene structure, so that the donor group containing nitrogen and the acidic group which is an adsorption group of titanium oxide can be spatially separated, and charge separation is performed. Since the state is improved, an improvement in photoelectric conversion efficiency can be achieved, which is more preferable.

  Hereinafter, the present invention will be described in detail.

<< Compound Represented by Formula (1) >>
The compound represented by the general formula (1) (hereinafter also referred to as a sensitizing dye of the present invention) will be described in more detail.

In the general formula (1), R ₁ and R ₂ are an alkyl group such as a methyl group, an ethyl group or an isopropyl group, an aralkyl group such as a benzyl group or a 1-naphthylmethyl group, an alkenyl such as a vinyl group or a cyclohexenyl group. And heterocyclic residues such as aryl groups such as a group, phenyl group and naphthyl group, furyl group, thienyl group and indolyl group. R ₁ and R ₂ may have a substituent, and examples of the substituent include the same alkyl groups as R ₁ and R ₂ , alkoxy groups such as a methoxy group, an ethoxy group, and an n-hexyloxy group. Alkylthio groups such as methylthio group and n-hexylthio group, aryloxy groups such as phenoxy group and 1-naphthyloxy group, arylthio groups such as phenylthio group, halogen atoms such as chlorine and bromine, dimethylamino group, diphenylamino group and the like disubstituted amino group, the same aryl group as R _1, R _2, same heterocycle and R _1, R _2, carboxyl group, carboxyalkyl carboxyalkyl group such as methyl group, sulfonyl group such as sulfonyl propyl , Acidic groups such as phosphoric acid groups and hydroxamic acid groups, and electron withdrawing groups such as cyano groups, nitro groups and trifluoromethyl groups. Kill.

Examples of R ₃ and R ₄ include alkyl groups such as n-propyl group, isopropyl group, n-butyl group, and isobutyl group, and alkoxy groups such as n-propoxy group, isopropoxy group, n-butoxy group, and isobutoxy group. be able to.

  X represents an organic residue having an acidic group. Examples of the acidic group include a carboxyl group, a sulfo group, a sulfino group, a sulfinyl group, a phosphoryl group, a phosphinyl group, a phosphono group, a thiol group, a hydroxy group, a phosphonyl group, a sulfonyl group, and salts thereof. As the acidic group, a carboxyl group is preferable.

  Examples of the organic residue having an acidic group include those listed below, or combinations thereof.

  Moreover, you may have a substituent in the site | part which can be substituted of the said compound. The organic residue having an acidic group preferably has an electron withdrawing site. Examples of the electron withdrawing moiety include a fluoro group, a chloro group, a bromo group, a nitro group, a cyano group, an alkylsulfonyl group, an arylsulfonyl group, a perfluoroalkylsulfonyl group, a perfluoroarylsulfonyl group, and a rhodanine ring. In particular, a cyano group or a rhodanine ring having a high electron-withdrawing property is preferable because it can effectively inject photoelectrons into an oxide semiconductor.

  X is particularly preferable in the case of a compound having a carboxyl group having a high adsorptive ability for an oxide semiconductor, since the flow of electric charge to the oxide semiconductor becomes smooth and exhibits favorable characteristics. Moreover, an electron withdrawing group is preferable as a substituent of X.

Examples of L ₁ include an alkylene group, an alkenylene group, an arylene group, a heterocyclic group, and combinations thereof, and specific examples thereof include alkenylene groups such as 1,2-vinylene group and 1,4-butadienylene group, , 4-phenylene group, arylene group such as 1,4-naphthylene group, and heterocycle such as 2,5-thienylene group. Examples of the organic residue having a preferable acidic group include -alkylene-COOH, -arylene-COOH, -alkylene-PO (OH) ₂ , -CH = C (CN) COOH, -heterocyclic-alkylene-COOH,- CH = heterocycle-alkylene-COOH and the like can be mentioned.

  Specific examples of the sensitizing dye of the present invention are shown below, but the present invention is not limited thereto.

  The sensitizing dye of the present invention can be synthesized by a general synthesis method, and synthesis examples are described below.

[Synthesis of A-1]
Exemplified Compound A-1 was synthesized according to the following scheme.

  While stirring a mixture of 5.00 g of 9,9-dibutyl-2,7-dibromofluorene, 120 ml of tetrahydrofuran and 0.85 g of tetrakis (triphenylphosphine) palladium (0), 1.88 g of thiophene boronic acid, potassium carbonate, 3. 39 g was added, and the reaction was carried out under a nitrogen stream for 15 hours under reflux conditions. After standing to cool, water was added to terminate the reaction. The organic phase was separated, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The resulting residue was purified by column chromatography to obtain 4.25 g of compound (1).

  Compound (1) 4.11 g, diphenylamine 2.02 g, sodium-t-butoxide 1.44 g, bis (dibenzylideneacetone) palladium (0) 58 mg, tri-t-butylphosphine 30.4 mg and toluene 40 ml in a mixture of 80 The reaction was carried out at 0 ° C. for 8 hours. After standing to cool, water was added to terminate the reaction. The organic phase was separated, dried by adding anhydrous sodium sulfate, concentrated under reduced pressure, and the resulting residue was purified by column chromatography to obtain 4.02 g of compound (2).

  1 g of compound (2) was dissolved in 20 ml of terahydrofuran and cooled to −78 ° C. with stirring. 1.5 ml of n-butyllithium (1.6M hexane solution) was added dropwise over 10 minutes. The temperature was raised to 0 ° C. over 1 hour and further stirred at 0 ° C. for 1 hour. The mixture was cooled again to -78 ° C, and 1 ml of N, N-dimethylformamide was added. After slowly returning to room temperature, the mixture was stirred overnight. The reaction was completed by pouring into dilute hydrochloric acid (hydrochloric acid 1 ml, water 20 ml). The organic phase was separated, dried by adding anhydrous sodium sulfate, concentrated under reduced pressure, and the resulting residue was purified by column chromatography to obtain 0.75 g of compound (3).

  A mixture of 0.53 g of compound (3), 0.17 g of cyanoacetic acid, 17 mg of ammonium acetate and 10 ml of acetic acid was reacted under reflux conditions for 4 hours. After allowing to cool, the mixture was concentrated under reduced pressure, and the resulting residue was washed with water, then washed with toluene, and 0.48 g of Exemplified Compound A-1 was obtained by reprecipitation from ethyl acetate and toluene. Exemplified Compound A-1 was confirmed in structure by nuclear magnetic resonance spectrum and mass spectrum.

  Other compounds can be synthesized in the same manner.

  The sensitizing dye thus obtained is sensitized by supporting it on a semiconductor, and the effects described in the present invention can be achieved. Here, loading a sensitizing dye on a semiconductor means adsorption to the surface of the semiconductor, and when the semiconductor has a porous structure such as a porous structure, the semiconductor has a porous structure filled with the sensitizing dye. Various embodiments are mentioned.

The total amount of the sensitizing dye of the present invention per 1 m ² of the semiconductor layer (which may be a semiconductor) is preferably in the range of 0.01 to 100 mmol, more preferably 0.1 to 50 mmol, particularly preferably. 0.5-20 mmol.

  When sensitizing treatment is performed using the sensitizing dye of the present invention, the sensitizing dye may be used alone or in combination, and other compounds (for example, U.S. Pat. No. 4,684). No. 5,537, No. 4,927,721, No. 5,084,365, No. 5,350,644, No. 5,463,057, No. 5,525. , 440, JP-A-7-249790, JP-A-2000-150007, etc.) can also be used as a mixture.

  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.

  In order to carry the sensitizing dye of the present invention on a semiconductor, a method in which the compound is dissolved in an appropriate solvent (ethanol or the like) and a well-dried semiconductor is immersed in the solution for a long time is generally used.

  When using a plurality of sensitizing dyes of the present invention in combination or sensitizing treatment with other sensitizing dyes in combination, a mixed solution of each sensitizing dye may be prepared and used. It is also possible to prepare different solutions for the sensitizing dye and immerse them in each solution in order. When preparing a separate solution for each sensitizing 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 sensitizing dye is included in the semiconductor. Can do. Alternatively, it may be prepared by mixing fine particles of semiconductor adsorbed with the sensitizing dye alone.

  The details of the semiconductor sensitization process according to the present invention will be specifically described in the photoelectric conversion element described later.

  In the case of a semiconductor having a high porosity, it is preferable to complete the adsorption treatment of a sensitizing dye or the like before water is adsorbed on the semiconductor thin film and in the voids inside the semiconductor thin film due to moisture, water vapor, etc. .

  Next, the photoelectric conversion element of the present invention will be described.

<< Photoelectric conversion element >>
The photoelectric conversion element of the present invention comprises a photoelectrode in which a dye is contained in a semiconductor on a conductive support, and a counter electrode arranged to face each other with an electrolyte layer interposed therebetween. Hereinafter, the semiconductor, the photoelectrode, the electrolyte, and the counter electrode will be sequentially described.

〔semiconductor〕
Examples of semiconductors used for the photoelectrode include silicon, germanium, compounds having elements of Group 3 to Group 5 and Group 13 to 15 of the periodic table (also referred to as Periodic Table of Elements), and metal chalcogenides. (For example, oxides, sulfides, selenides, and the like), metal nitrides, and the like 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 compound semiconductors include phosphides such as zinc, gallium, indium and cadmium, gallium-arsenic or copper-indium selenide, copper-indium sulfide, titanium nitride, and the like.

Specific examples include TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , ZnO, Nb 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 can be mentioned, but TiO ₂ , ZnO, SnO ₂ , Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , CdS, and PbS are preferably used, and more preferably used. Is TiO ₂ or Nb ₂ O ₅ , among which 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 metal oxides or metal sulfides described above can be used in combination, or 20% by mass of titanium nitride (Ti ₃ N ₄ ) may be mixed and used in the titanium oxide semiconductor. 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.

  Further, the semiconductor according to the present invention may be surface-treated using an organic base. Examples of the organic base include diarylamine, triarylamine, pyridine, 4-t-butylpyridine, polyvinylpyridine, quinoline, piperidine, and amidine, among which pyridine, 4-t-butylpyridine, and polyvinylpyridine are preferable. .

  When the organic base is a liquid, the surface treatment can be carried out by preparing a solution dissolved in an organic solvent and immersing the semiconductor according to the present invention in a liquid amine or an amine solution.

[Conductive support]
The conductive support (substrate) used in the photoelectric conversion element of the present invention and the solar cell of the present invention is conductive to 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 substance can be used. Examples of materials used for the conductive support include metal (for example, platinum, gold, silver, copper, aluminum, rhodium, indium) or conductive metal oxide (for example, indium-tin composite oxide, tin oxide doped with fluorine) And carbon). The thickness of the conductive support is not particularly limited, but is preferably 0.3 to 5 mm.

  The conductive support is preferably substantially transparent, and substantially transparent means that the light transmittance is 10% or more, more preferably 50% or more, and 80%. The above is most preferable. 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 surface resistance of the conductive support is preferably 50 Ω / cm ² or less, and more preferably 10 Ω / cm ² or less.

[Production of photoelectrode]
A method for producing a photoelectrode according to the present invention will be described.

  When the semiconductor of the photoelectrode according to the present invention is in the form of particles, the photoelectrode may be produced 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 photoelectrode by bonding the semiconductor onto the conductive support.

  As a preferred embodiment of the photoelectrode according to the present invention, a method of forming a semiconductor fine particle on the conductive support by firing is exemplified.

  When the semiconductor according to the present invention is produced by firing, the sensitizing treatment (adsorption, filling into the porous layer, etc.) of the semiconductor using a sensitizing dye is preferably performed after firing. It is particularly preferable to perform the compound adsorption treatment quickly after the firing and before the water is adsorbed to the semiconductor.

  Hereinafter, a method for forming a photoelectrode by firing using semiconductor fine powder, which is preferably used in the present invention, will be described in detail.

(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 liquid 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 (also referred to as a semiconductor film) is formed thereover.

  A film obtained by applying and drying a coating solution containing semiconductor fine powder on a conductive support is composed of an aggregate of semiconductor fine particles, and the particle size of the fine particles is equal to the primary particle size of the semiconductor fine powder used. Corresponding.

  Thus, the semiconductor fine particle layer formed on the conductive layer such as the conductive support is weak in bonding strength with the conductive support and fine particles, and has low mechanical strength. The semiconductor fine particle layer is baked to increase the mechanical strength and form a semiconductor layer that is strongly fixed to the substrate.

  In the present invention, the semiconductor layer 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 layer 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. The porosity of the semiconductor layer means a porosity that is penetrable in the thickness direction of the dielectric, and can be measured using a commercially available device such as a mercury porosimeter (Shimadzu Polarizer 9220 type).

  The thickness of the semiconductor layer that is a fired product film having a porous structure is preferably at least 1 μm or more, more preferably 1 to 25 μm.

  From the viewpoint of appropriately preparing the actual surface area of the fired film during the firing treatment and obtaining a fired 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, for the purpose of increasing the surface area of the semiconductor particles after heating, increasing the purity in the vicinity of the semiconductor particles, and increasing the efficiency of electron injection from the dye into the semiconductor particles, for example, chemical plating using a titanium tetrachloride aqueous solution or three An electrochemical plating process using a titanium chloride aqueous solution may be performed.

(Semiconductor sensitization treatment)
The semiconductor sensitization treatment is performed by dissolving the sensitizing dye in an appropriate solvent as described above and immersing the substrate obtained by firing the semiconductor in the solution. In that case, it is preferable that a substrate on which a semiconductor layer (also referred to as a semiconductor film) is formed by baking is subjected to pressure reduction treatment or heat treatment in advance to remove bubbles in the film. Such treatment allows the sensitizing dye to enter deep inside the semiconductor layer (semiconductor film), and is particularly preferable when the semiconductor layer (semiconductor film) is a porous structure film.

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

  Solvents preferably used in dissolving the compound are alcohol solvents such as methanol, ethanol and n-propanol, ketone solvents such as acetone and methyl ethyl ketone, ether ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran and 1,4-dioxane. Solvents and halogenated hydrocarbon solvents such as methylene chloride and 1,1,2-trichloroethane, particularly preferably methanol, ethanol, acetone, methyl ethyl ketone, tetrahydrofuran and methylene chloride.

(Tensing temperature and time)
It is preferable that the time for immersing the semiconductor-baked substrate in a solution containing a sensitizing dye penetrates deeply into the semiconductor layer (semiconductor film) to sufficiently advance adsorption and the like to sufficiently sensitize the semiconductor. In addition, from the viewpoint of suppressing degradation of the sensitizing dye generated in the solution and preventing the degradation product from interfering with the adsorption of the sensitizing dye, 1 to 48 hours are preferable at 25 ° C., more preferably 2 ~ 24 hours. This effect is particularly remarkable when the semiconductor film is a porous structure film. However, the immersion time is a value at 25 ° C., and is not limited to the above when the temperature condition is changed.

  When immersed, the solution containing the sensitizing dye may be used by heating to a temperature at which it does not boil as long as the dye 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.

〔Electrolytes〕
The electrolyte used in the present invention will be described.

In the photoelectric conversion element of the present invention, an electrolyte is filled between the counter electrodes to form an electrolyte layer. A redox electrolyte is preferably used as the electrolyte. Here, examples of the redox electrolyte include I ⁻ / I ₃ ⁻ system, Br ⁻ / Br ₃ ⁻ system, and quinone / hydroquinone system. Such redox electrolyte can be obtained by a conventionally known method, for example, I ^- / I ₃ ^- system electrolyte can be obtained by mixing an ammonium salt of iodine and iodine. The electrolyte layer is composed of dispersions of these redox electrolytes. These dispersions are dispersed in liquid electrolytes when they are solutions, solid polymer electrolytes and gel substances when dispersed in polymers that are solid at room temperature. It is called a gel electrolyte. When a liquid electrolyte is used as the electrolyte layer, an electrochemically inert solvent is used as the solvent, for example, acetonitrile, propylene carbonate, ethylene carbonate, or the like is used. Examples of the solid polymer electrolyte include the electrolyte described in JP-A No. 2001-160427, and examples of the gel electrolyte include the electrolyte described in “Surface Science” Vol. 21, No. 5, pages 288 to 293.

[Counter electrode]
The counter electrode used in the present invention will be described.

The counter electrode as long as it has conductivity, but any conductive material is used, I ₃ ^- with catalytic ability to perform fast enough the reduction reaction of oxidation and other redox ions such as ions Is preferably used. Examples of such a material include a platinum electrode, a surface of the conductive material subjected to platinum plating or platinum deposition, rhodium metal, ruthenium metal, ruthenium oxide, and carbon.

《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 photoelectrode, the electrolyte layer and the counter electrode are housed in a case and sealed, or the whole is sealed with resin.

  When the solar cell of the present invention is irradiated with sunlight or an electromagnetic wave equivalent to sunlight, the sensitizing dye according to the present invention carried on a semiconductor absorbs the irradiated light or electromagnetic wave and excites it. Electrons generated by excitation move to the semiconductor, and then move to the counter electrode via the conductive support to reduce the redox electrolyte in the charge transfer layer. On the other hand, the sensitizing dye according to the present invention in which electrons are transferred to a semiconductor is an oxidant, but is reduced by the supply of electrons from the counter electrode via the redox electrolyte of the electrolyte layer, and the original sensitizing dye is reduced. At the same time, the redox electrolyte of the charge transfer 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.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

Example [Production of Photoelectric Conversion Element 1]
A commercially available titanium oxide paste (particle size 18 nm) was applied onto a fluorine-doped tin oxide (FTO) conductive glass substrate by a doctor blade method. The paste was dried by heating at 60 ° C. for 10 minutes, and then baked at 500 ° C. for 30 minutes. Next, exemplary compound A-1 was dissolved in ethanol to prepare a 3 × 10 ⁻⁴ M / L solution. The FTO glass substrate coated and sintered with titanium oxide was immersed in this solution at room temperature for 16 hours for dye adsorption treatment to obtain a photoelectric conversion electrode. Thus, two parts of the photoelectric conversion electrode were prepared, and a part of the photoelectric conversion electrode was subjected to an ozone exposure test for 20 minutes in an ozone atmosphere of 13 ppm, and a photoelectric conversion element was manufactured using the electrodes before and after the exposure.

  As an electrolytic solution, a 3-methylpropionitrile solution containing 0.4 M lithium iodide, 0.05 M iodine, and 0.5 M 4- (t-butyl) pyridine was prepared. A photoelectric conversion element 1 was obtained by using a platinum plate as a counter electrode and assembling the previously prepared photoelectric conversion electrode and the electrolytic solution with a clamp cell.

[Production of photoelectric conversion elements 2 to 7]
Photoelectric conversion electrodes were produced in the same manner as in the production of the photoelectric conversion element 1 except that the compounds shown in Table 1 were used instead of the exemplified compound A-1. Some conducted ozone exposure tests, and photoelectric conversion elements 2 to 7 were prepared in the same manner as the photoelectric conversion element 1 using the electrodes before and after the exposure.

<< Evaluation of photoelectric conversion element >>
(Power generation characteristics)
The produced photoelectric conversion element was 100 mW / cm from a xenon lamp that passed through an AM filter (AM-1.5) using a solar simulator (manufactured by Wacom Denso Co., Ltd., trade name: “WXS-85-H type”). ^This was performed by irradiating ² simulated sunlight. That is, for the photoelectric conversion element, current-voltage characteristics are measured at room temperature using an IV tester, and a short circuit current (J _sc ), an open circuit voltage (V _oc ), and a form factor (FF) are obtained. From these, the photoelectric conversion efficiency (η (%)) was determined. Furthermore, the change in conversion efficiency before and after the ozone exposure test was compared.

  The evaluation results are shown in Table 1.

  From Table 1, the photoelectric conversion elements 1 to 6 using the sensitizing dye of the present invention have a higher photoelectric conversion efficiency ratio before and after ozone exposure than the photoelectric conversion element 7 using the comparative dye K, and with respect to the fluorene unit. It can be seen that by introducing an alkyl group having 3 to 18 carbon atoms, the sensitizing dye has higher durability than conventional dyes having a small number of carbon atoms.

[Production of photoelectric conversion element 8]
On the same FTO conductive glass substrate as used in the photoelectric conversion element 1, an alkoxytitanium solution (Matsumoto Kosho: TA-25 / IPA dilution) was applied 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. Subsequently, a commercially available titanium oxide paste (particle size: 18 nm) was applied to the substrate by the doctor blade method, heat-treated at 60 ° C. for 10 minutes, and then baked at 500 ° C. for 30 minutes to form a titanium oxide having a thickness of 5 μm. A semiconductor electrode substrate having a thin film was obtained.

Exemplified Compound A-8 was dissolved in ethanol to prepare a 3 × 10 ⁻⁴ mol / L solution. The semiconductor electrode substrate was immersed in this solution at room temperature for 16 hours to perform dye adsorption treatment, then washed with chloroform and vacuum dried to obtain a photoelectric conversion electrode.

Next, in a toluene solvent, 0.17M of the following compound (spiro-MeO TAD) as a hole transport agent, 0.33 mM of N (PhBr) ₃ SbCl ₆ as a hole doping agent, Li [(CF ₃ SO ₂ ) ₂ N] 15 mM was dissolved and spin coated on the photoelectric conversion electrode after dye adsorption to form a hole transport layer. Furthermore, gold was deposited to 30 nm by vacuum deposition to produce a counter electrode.

  The photoelectric conversion element 8 was obtained by assembling the photoelectric conversion electrode and electrolyte solution which were produced previously to the said counter electrode with a clamp cell.

[Production of photoelectric conversion elements 9 to 12]
In the photoelectric conversion element 7, photoelectric conversion elements 9 to 12 were obtained in the same manner except that the exemplified compound A-8 was changed to the sensitizing dyes shown in Table 2.

[Evaluation of photoelectric conversion element]
Each photoelectric conversion element obtained was evaluated in the same manner as the photoelectric conversion element 1. The results are shown in Table 2.

  The photoelectric conversion elements 8 to 11 using the sensitizing dye of the present invention have a higher photoelectric conversion efficiency ratio before and after ozone exposure than the photoelectric conversion element 12 using the comparative dye K, and have 3 to 3 carbon atoms relative to the fluorene unit. It can be seen that introduction of an alkyl group of 18 or the like is a sensitizing dye having higher durability than a conventional dye having a small number of carbon atoms.

It is a structure sectional view showing an example of a photoelectric conversion element used for the present invention.

Explanation of symbols

1, 1 'substrate 2, 7 transparent conductive film 3 semiconductor 4 sensitizing dye 5 electrolyte 6 counter electrode 7 transparent conductive film 8 platinum

Claims (3)

The photoelectric conversion element characterized by containing the compound represented by following General formula (1).

(In the formula, R ₁ and R _{2 each} represents an alkyl group, an aralkyl group, an alkenyl group, an aryl group, or a heterocyclic ring, and may have a substituent. R ₁ and R ₂ combine to form a ring. R ₃ and R ₄ each represents an alkyl group having 3 to 18 carbon atoms, an alkoxy group or an aralkyl group, and L ₁ represents a carbon-carbon double bond, a divalent aromatic hydrocarbon or a divalent aromatic hydrocarbon. It represents a heterocyclic ring or a linked structure thereof, and the carbon-carbon double bond may be either E type or Z type, n represents an integer of 0 to 3. X represents an organic group having an acidic group. Represents a residue.) 2. The photoelectric conversion element in which at least a semiconductor layer and an electrolyte layer are provided between opposing electrodes, wherein the semiconductor layer contains a compound represented by the general formula (1). Photoelectric conversion element. A solar cell comprising the photoelectric conversion element according to claim 1.

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