WO2013042699A1 - Spirobifluorene compound, colorant for photoelectric transducer, and photoelectric transducer using same - Google Patents

Abstract

A colorant for a photoelectric transducer, containing a spirobifluorene compound represented by general formula (1). The colorant exhibits excellent photoelectric conversion characteristics and is useful not only for a semiconductor electrode for a photoelectric transducer but also for a photoelectric transducer and a photoelectrochemical cell. In general formula (1), R¹ and R² are each independently a hydrogen atom, a substituted or unsubstituted alkyl or alkoxy group, or a hydroxyl group; Z is a π-conjugated linking group; and X is an organic group having an acid group.

Description

Spirobifluorene compound, dye for photoelectric conversion element, and photoelectric conversion element using the same

The present invention relates to a spirobifluorene compound, a dye for a photoelectric conversion element, a semiconductor electrode for a photoelectric conversion element using the same, a photoelectric conversion element, and a photoelectrochemical cell.

Due to the large amount of fossil fuels represented by petroleum so far, global warming has become a serious problem due to the increase in CO ₂ concentration, and there is a concern about the depletion of fossil fuels. Therefore, how to meet future demand for large amounts of energy has become a very important issue on a global scale. Under such circumstances, the use of light energy that is infinite and clean with respect to nuclear power generation is being actively studied. Solar cells that convert light energy into electrical energy include inorganic solar cells that use inorganic materials such as single crystal silicon, polycrystalline silicon, and amorphous silicon, and organic solar cells that use organic dyes and conductive polymer materials. Solar cells have been proposed.

Under such circumstances, a dye-sensitized solar cell (Gretzel solar cell) (Non-patent Document 1 and Patent Document 1) proposed by Dr. Gretzer et al. In 1991 of Switzerland is produced by a simple manufacturing process. It is expected as a next-generation solar cell because it can achieve the same conversion efficiency. A Gretzel type solar cell includes a semiconductor electrode in which a semiconductor layer having a dye adsorbed thereon is formed on a conductive substrate, a counter electrode made of a conductive substrate opposite to the electrode, and an electrolyte layer held between the electrodes. And.

In this Gretzel type solar cell, the adsorbed dye absorbs light and enters an excited state, and electrons are injected from the excited dye into the semiconductor layer. The dye that is in an oxidized state due to the emission of electrons returns to the original dye by transferring electrons to the dye by the oxidation reaction of the redox agent in the electrolyte layer. Then, the redox agent that has donated electrons to the dye is reduced again on the counter electrode side. This series of reactions functions as a battery.

In this Gretzel type solar cell, the effective reaction surface area increased about 1000 times by using porous titanium oxide in which fine particles were sintered in the semiconductor layer, and a photocurrent larger than the conventional one could be taken out. It is a big feature.

In a Gretzel type solar cell, a metal complex such as a ruthenium complex is used as a sensitizing dye. Specifically, for example, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ) Ruthenium (II) ditetrabutylammonium complex, cis-bis (isothiocyanato) -bis- (2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium (II), etc. And tris (isothiocyanato) (2,2 ′: 6 ′, 2 ″ -terpyridyl-4,4 ′, 4 ″ -tricarboxylic acid) ruthenium (II) tritetrabutylammonium complex.

Japanese Patent No. 2664194

Nature, 353, p. 737-740 (1991)

The problem with dye-sensitized solar cells using metal complexes is that noble metals such as ruthenium are used as a raw material for the dye. When mass-producing a dye-sensitized solar cell using such a metal complex, resource restrictions become a problem, and the solar cell becomes expensive and hinders its spread.

Therefore, the development of organic dyes that do not contain noble metals such as ruthenium is required as sensitizing dyes in dye-sensitized solar cells. In general, organic dyes have a higher molar extinction coefficient than metal complexes such as ruthenium complexes, and further have a high degree of freedom in molecular design, so that development of dyes with high photoelectric conversion efficiency is expected.

The present invention has been made in order to solve the above problems, and provides a dye for a photoelectric conversion element having excellent photoelectric conversion characteristics, a semiconductor electrode for a photoelectric conversion element, a photoelectric conversion element and a photoelectrochemical cell using the same. It is to provide.

As a result of intensive studies to solve the above problems, the present inventors have found that spirobifluorene compounds can be dyes for photoelectric conversion elements having excellent photoelectric conversion characteristics.

That is, the compound of the present invention is a spirobifluorene compound represented by the following general formula (1), a tautomer or a stereoisomer thereof.

(In Formula (1), R ¹ and R ² each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, an alkoxy group, or a hydroxy group. Z represents a π-conjugated linking group. , X represents an organic group having an acidic group.)

The dye for a photoelectric conversion device of the present invention includes at least one of the spirobifluorene-based compound of the present invention, a tautomer or a stereoisomer thereof.
The semiconductor electrode for photoelectric conversion elements of the present invention has a semiconductor layer containing the dye for photoelectric conversion elements of the present invention.
The photoelectric conversion element of the present invention has the semiconductor electrode for a photoelectric conversion element of the present invention.
Moreover, the photoelectrochemical cell of the present invention has the photoelectric conversion element of the present invention.

According to the present invention, a spirobifluorene compound having excellent photoelectric conversion characteristics can be provided. In addition, the compound can provide a dye for a photoelectric conversion element having excellent photoelectric conversion characteristics, a semiconductor electrode for a photoelectric conversion element using the same, a photoelectric conversion element, and a photoelectrochemical cell.

It is sectional drawing which shows typically the structure of an example of the photoelectric conversion element by one Embodiment of this invention. It is a figure which shows the absorption spectrum curve of the spirobifluorene type compound (SP-1) of Example 1 by one Embodiment of this invention. It is a figure which shows the electric current-voltage curve of the photoelectric conversion element (cell) using the spirobifluorene type compound (SP-1) of Example 1 by one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail.

<Spirobifluorene compounds>
A spirobifluorene compound suitable for the photoelectric conversion dye according to the present embodiment is a compound represented by the following general formula (1).

When the spirobifluorene compound of the present invention has isomers such as tautomers or stereoisomers (eg, geometric isomers, conformers and optical isomers), any isomers It can be used in the present invention.

R ¹ and R ^{2 in} the general formula (1) each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, an alkoxy group, or a hydroxy group. Examples of the substituted or unsubstituted alkyl group include methyl group, ethyl group, propyl group, iso-propyl group, n-butyl group, t-butyl group, pentyl group, neo-pentyl group, cyclopentyl group, hexyl group and cyclohexyl group. A linear, branched or cyclic alkyl group having 1 to 8 carbon atoms such as a heptyl group and an octyl group, an aralkyl group such as a benzyl group in which the alkyl group is substituted with a phenyl group, and the like, and a hydroxy group substituted on the alkyl group Examples thereof include a hydroxyalkyl group and an alkoxyalkyl group obtained by substituting an alkoxy group (for example, an alkoxy group having 1 to 4 carbon atoms) with these alkyl groups. Examples of the substituted or unsubstituted alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an iso-propoxy group, an n-butoxy group, a t-butoxy group, an n-hexyloxy group, a cyclohexyloxy group, and an n-octyloxy group. A linear, branched or cyclic alkoxy group having 1 to 8 carbon atoms, an aralkyloxy group such as a benzyloxy group in which the alkoxy group is substituted with a phenyl group, or the like, or a hydroxyalkoxy group in which the alkoxy group is substituted with a hydroxy group And an alkoxyalkoxy group in which an alkoxy group (for example, an alkoxy group having 1 to 4 carbon atoms) is substituted for these alkoxy groups.

Z represents a π-conjugated linking group, specifically, a substituted or unsubstituted aromatic ring, a substituted or unsubstituted heterocyclic ring, a vinylene group (—CH═CH—), an ethynylene group (—C≡C— ) Represents a linking group containing at least one selected from the group consisting of The linking group Z is not particularly limited, but is preferably an atomic group that can be conjugated with the spirobifluorene ring to which Z is bonded and the organic group X having an acidic group. The linking group Z is preferably a linking group having a structure represented by at least the following general formula (2).

In the general formula (2), R ³ and R ⁴ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group, and R ³ and R ⁴ are connected to each other. A ring may be formed. Examples of the substituted or unsubstituted alkyl group include a methyl group, an ethyl group, a propyl group, an iso-propyl group, an n-butyl group, a t-butyl group, a pentyl group, a neo-pentyl group, a hexyl group, a heptyl group, and an octyl group. Examples of the substituent bonded to the alkyl group include a hydroxy group and an alkoxy group. Examples of the substituted or unsubstituted alkoxy group include linear or branched alkoxy groups having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an iso-propoxy group, a butoxy group, and a t-butoxy group. In addition, examples of the ring formed by connecting R ³ and R ⁴ include a cycloheptane ring, a cyclohexane ring, a tetrahydrofuran ring, a tetrahydropyran ring, a dioxane ring, and a dioxepane ring. These rings may have a substituent which the alkyl group and alkoxy group may have.

In the general formula (2), Y represents an oxygen atom, a sulfur atom or NRa, and Ra represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituted or unsubstituted alkyl group include the same alkyl groups as the substituted or unsubstituted alkyl groups of R ¹ and R ² described above. Examples of the unsubstituted aryl group include a phenyl group and a naphthyl group. Examples of the substituent bonded to the aryl group include an alkyl group, a hydroxy group, an alkoxy group, and an N, N-dialkylamino group. Examples of the substituted aryl group include a tolyl group, 4-t-butylphenyl group, 3,5-di-t-butylphenyl group, 4-methoxyphenyl group, 4- (N, N-dimethylamino) phenyl group and the like. It is done. * Indicates a bond.

In addition to these, two structures represented by the general formula (2) may be linked, and the substituents may be bonded to each other to form a tricyclic linking group. It may be another bonding part such as a (or diaryl) silyl group. Furthermore, a structure in which two or more 5-membered ring structures of the general formula (2) are condensed, for example, a thienofuran, a thienothiophene, a thienopyrrole structure, or the like may be used.

Specific examples of the linking group Z are shown in the chemical formulas (Z1) to (Z29), but are not limited thereto. When there are a plurality of heterocycles and aromatic rings, carbons constituting the rings are directly bonded to each other or bonded by forming a condensed ring. Further, a group in which a plurality of these linking groups are linked may be used. In these examples, the spirobifluorene ring is shown as being bonded to the left bond and the organic group X having an acidic group is bonded to the right bond, but it may be in the opposite direction.

Further, X in the formula (1) represents an organic group having an acidic group. Examples of the acidic group of the organic group X include a carboxy group, a sulfonic acid group, a phosphonic acid group, or a salt thereof, and among them, a carboxy group or a salt thereof is particularly preferable. In addition, at least one acidic group may be included, but a plurality of acidic groups may be included. When the acidic group is a salt, a monovalent or divalent metal salt, ammonium salt or organic ammonium salt is preferred. Examples of the monovalent or divalent metal salt include alkali metal salts such as Li, Na, K, and Cs, and alkaline earth metal salts such as Mg, Ca, and Sr. Examples of the organic group of the organic ammonium salt include an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 1 to 8 carbon atoms, and an aryl group having 6 to 12 carbon atoms.

The spirobifluorene compound represented by the general formula (1) preferably has a functional group that can be adsorbed to the semiconductor layer from the viewpoint of adsorbing to the semiconductor layer used in the semiconductor electrode, and the acidic group of the organic group X is a functional group. Can play the role of a group. Specific examples of the organic group X having an acidic group are shown by chemical formulas (X1) to (X16) in Tables 3 and 4, but are not limited thereto. These organic groups X have a carbon-carbon double bond in addition to the acidic group, and one bond of the linking group Z is bonded to one carbon of the carbon-carbon double bond, and the other carbon. A cyano group, a carbonyl group, or another carbon-carbon double bond carbon is bonded to.

The organic group X having an acidic group is preferably a group represented by the following general formula (3).

　式（３）中、Ｍは、水素原子または塩形成性陽イオンを表す。

In formula (3), M represents a hydrogen atom or a salt-forming cation.

Examples of the salt-forming cation include various cations capable of forming a salt with a carboxy group. Examples of such a cation include an ammonium cation (NH ₄ ⁺ ); an organic ammonium cation derived from an amine (A ¹ A ² A ³ A ⁴ N ⁺ , and A ¹ to A ⁴ are a hydrogen atom or an organic group. shown, but at least one of which is an organic ^{group); Li +, Na +,} K +, alkali metal ions Cs ^{+, etc.; 1 / 2Mg 2+, 1 /} 2Ca 2+, 1 / 2Sr alkaline earth metals such as ²⁺ A metal ion etc. are mentioned. Examples of the organic group represented by A ¹ to A ⁴ of the organic ammonium cation include an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 1 to 8 carbon atoms, and an aryl group having 6 to 12 carbon atoms.

Examples of the combination of Z and X in the spirobifluorene compound represented by the general formula (1), the tautomer or stereoisomer thereof include, for example, a-1 to a-29, b-1 to b-29, c-1 to c-29, d-1 to d-13, e-1 to e-13, f-1 to f-13, g-1 to g- 13, h-1 to h-13, and i-1 to i-13, but are not limited thereto.

The compounds of the present invention are, for example, spirobifluorene compounds such as compounds SP-1 to SP-12 shown in Table 8 and Table 9 below, tautomers or stereoisomers thereof, or salts thereof. Particularly preferred.

These compounds SP-1 to SP-12 can be used by those skilled in the art by referring to the production methods and examples of compounds SP-1 and SP-2 to be described later. Without being easily prepared and used according to the compounds SP-1 and SP-2. Moreover, the compound of this invention is not limited to these examples, The combination of R < ¹ >, R < ² >, Z, X can be made arbitrary within the defined range, respectively.

<Photoelectric conversion element>
FIG. 1 schematically shows a cross-sectional structure of an example of the photoelectric conversion element according to the present embodiment. The photoelectric conversion element shown in FIG. 1 includes a semiconductor electrode 4, a counter electrode 8, and an electrolyte layer (charge transport layer) 5 held between both electrodes. The semiconductor electrode 4 includes a conductive substrate including the light transmissive substrate 3 and the transparent conductive layer 2, and the semiconductor layer 1. The counter electrode 8 includes a catalyst layer 6 and a substrate 7. The semiconductor layer 1 is adsorbed with a spirobifluorene compound according to the present invention, a dye containing at least one of its tautomers or stereoisomers.

When light is incident on this photoelectric conversion element, the dye adsorbed on the semiconductor layer 1 is excited and emits electrons. The electrons move to the conduction band of the semiconductor, and further move to the transparent conductive layer 2 by diffusion. The electrons in the transparent conductive layer 2 move to the counter electrode 8 via an external circuit (not shown). And the pigment | dye which emitted the electron (oxidized pigment | dye) receives an electron from the electrolyte layer 5 (reduced), returns to the original state, and a pigment | dye reproduce | regenerates. On the other hand, the electrons moved to the counter electrode are given to the electrolyte layer 5 and the electrolyte is reduced. In this manner, the photoelectric conversion element functions as a battery. Hereinafter, each component will be described by taking the photoelectric conversion element shown in FIG. 1 as an example.

<Semiconductor electrode>
The semiconductor electrode 4 includes a conductive substrate including the light transmissive substrate 3 and the transparent conductive layer 2, and the semiconductor layer 1. As shown in FIG. 1, a light transmissive substrate 3, a transparent conductive layer 2, and a semiconductor layer 1 are laminated in this order from the outside to the inside of the element. A dye (not shown) is adsorbed on the semiconductor layer 1.

<Conductive substrate>
The conductive substrate of the semiconductor electrode 4 may have a single layer structure in which the substrate itself has conductivity, or a two-layer structure in which a conductive layer is formed on the substrate. The conductive substrate of the photoelectric conversion element shown in FIG. 1 has a two-layer structure in which a transparent conductive layer 2 is formed on a light transmissive substrate 3.

Examples of the substrate used for the conductive substrate include a glass substrate, a plastic substrate, and a metal plate. Among them, a substrate having high light transmittance, such as a transparent glass substrate and a plastic substrate, is particularly preferable. Examples of the material for the transparent plastic substrate include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polycycloolefin, polyphenylene sulfide, and the like. In particular, when the semiconductor layer is formed by sintering as described later, it is preferable to use a glass substrate having excellent heat resistance.

Further, the conductive layer (for example, the transparent conductive layer 2) formed on the substrate (for example, the light transmissive substrate 3) is not particularly limited, but for example, indium tin oxide (Indium-Tin-Oxide: ITO), A transparent conductive layer made of a transparent material such as fluorine-doped tin oxide (FTO), indium-zinc oxide (IZO), tin oxide (SnO ₂ ), or the like is preferable. The conductive layer formed over the substrate can be formed into a film shape over the entire surface or a part of the surface of the substrate. The thickness of the conductive layer can be selected as appropriate, but is preferably about 0.02 μm or more and 10 μm or less. Such a conductive layer can be formed using a normal film formation technique.

It should be noted that the conductive substrate in this embodiment can also use a metal lead wire for the purpose of reducing the resistance of the conductive substrate. Examples of the metal lead wire include metals such as aluminum, copper, gold, silver, platinum, and nickel. The metal lead wire can be produced by vapor deposition, sputtering, or the like. After a metal lead wire is formed on a substrate (for example, light transmissive substrate 3), a conductive layer (for example, transparent conductive layer 2 such as ITO or FTO) can be provided on the metal lead wire. Alternatively, after providing a conductive layer (for example, transparent conductive layer 2) on a substrate (for example, light transmissive substrate 3), a metal lead wire may be formed on the conductive layer.

The following description of the present embodiment is based on an example in which a conductive substrate having a two-layer structure in which the transparent conductive layer 2 is formed on the light-transmitting substrate 3 is used as the conductive substrate of the semiconductor electrode. It is not limited to examples.

<Semiconductor layer>
As a material constituting the semiconductor layer 1, a single semiconductor such as silicon or germanium, a compound semiconductor such as a metal chalcogenide, a compound having a perovskite structure, or the like can be used.

Metal chalcogenides include oxides such as titanium, tin, zinc, iron, tungsten, indium, zirconium, vanadium, niobium, tantalum, strontium, hafnium, cerium, lanthanum; cadmium, zinc, lead, silver, antimony, bismuth, etc. Sulfides; selenides such as cadmium and lead; tellurides of cadmium and the like. Examples of other compound semiconductors include phosphides such as zinc, gallium, indium, and cadmium; gallium arsenide; copper-indium-selenide; copper-indium-sulfide, and the like. Examples of the compound having a perovskite structure include commonly known semiconductor compounds such as barium titanate, strontium titanate, and potassium niobate. These semiconductor materials can be used alone or in combination of two or more.

Among these semiconductor materials, from the viewpoint of conversion efficiency, stability, and safety, a semiconductor material containing titanium oxide or zinc oxide is preferable, and a semiconductor material containing titanium oxide is more preferable. Examples of titanium oxide include various types of titanium oxide such as anatase type titanium oxide, rutile type titanium oxide, amorphous titanium oxide, metatitanic acid, orthotitanic acid, and a titanium oxide-containing complex can be used. . Among these, anatase type titanium oxide is preferable from the viewpoint of further improving the stability of photoelectric conversion.

Examples of the form of the semiconductor layer include a porous semiconductor layer obtained by sintering semiconductor fine particles, a thin film semiconductor layer obtained by a sol-gel method, a sputtering method, a spray pyrolysis method, and the like. Moreover, it is good also as a semiconductor layer which consists of a fibrous semiconductor layer or an acicular crystal | crystallization. The form of these semiconductor layers can be appropriately selected according to the purpose of use of the photoelectric conversion element. Among these, a semiconductor layer having a large specific surface area such as a porous semiconductor layer and a needle-like semiconductor layer is preferable from the viewpoint of the amount of dye adsorbed. Furthermore, a porous semiconductor layer formed from semiconductor fine particles is preferable from the viewpoint that the utilization factor of incident light and the like can be adjusted by the particle size of the semiconductor fine particles. Further, the semiconductor layer may be a single layer or a multilayer. By forming a multilayer, a sufficiently thick semiconductor layer can be more easily formed. Moreover, when the porous semiconductor layer formed from semiconductor fine particles is a multilayer, it may consist of a plurality of semiconductor layers having different average particle diameters of the semiconductor fine particles. For example, the average particle diameter of the semiconductor fine particles of the semiconductor layer closer to the light incident side (first semiconductor layer) may be smaller than that of the semiconductor layer farther from the light incident side (second semiconductor layer). In this way, the first semiconductor layer absorbs a lot of light, and the light that has passed through the first semiconductor layer is efficiently scattered by the second semiconductor layer and returned to the first semiconductor layer, and the returned light is returned to the first semiconductor layer. By making it absorb with 1 semiconductor layer, the whole optical absorptance can be improved further.

The film thickness of the semiconductor layer is not particularly limited, but can be set to, for example, not less than 0.5 μm and not more than 45 μm from the viewpoints of permeability and conversion efficiency. The specific surface area of the semiconductor layer can be set to, for example, 10 m ² / g or more and 200 m ² / g or less from the viewpoint of adsorbing a large amount of dye.

In the case where the dye is adsorbed on the porous semiconductor layer, the porosity of the porous semiconductor layer is, for example, 40% or more and 80 from the viewpoint that ions in the electrolyte are further sufficiently diffused and charge transport is performed. % Or less is preferable. Here, the porosity is a percentage of the volume of the semiconductor layer occupied by the pores in the semiconductor layer.

<Method for forming semiconductor layer>
Next, a method for forming the semiconductor layer 1 will be described by taking a porous semiconductor layer as an example. The porous semiconductor layer can be formed, for example, as follows.

First, a suspension is prepared by adding semiconductor fine particles together with an organic compound such as a resin and a dispersant to a dispersion medium such as an organic solvent and water. And this suspension is apply | coated on a conductive substrate (in FIG. 1, the transparent conductive layer 2), this is dried and baked, and a semiconductor layer is obtained. When an organic compound is added to the dispersion medium together with the semiconductor fine particles, the organic compound burns during firing, and it becomes possible to secure a further sufficient gap (void) in the porous semiconductor layer. Moreover, the porosity can be changed by controlling the molecular weight and the addition amount of the organic compound combusted during firing.

The organic compound to be used is not particularly limited as long as it can be dissolved in a suspension and burned and removed during firing. For example, polyethylene glycol, cellulose ester resin, cellulose ether resin, epoxy resin, urethane resin, phenol resin, polycarbonate resin, polyarylate resin, polyvinyl butyral resin, polyester resin, polyvinyl formal resin, silicon resin, styrene, Examples thereof include polymers and copolymers of vinyl compounds such as vinyl acetate, acrylic acid esters, and methacrylic acid esters. The type and amount of the organic compound can be appropriately selected according to the type and state of the fine particles used, the composition ratio of the suspension, the total weight, and the like. At that time, when the ratio of the semiconductor fine particles is 10% by mass or more with respect to the total weight of the whole suspension, the strength of the prepared film can be further sufficiently increased, and the ratio of the semiconductor fine particles is If the total weight is 40% by mass or less, a porous semiconductor layer having a large porosity can be obtained more stably. Therefore, the ratio of the semiconductor fine particles is based on the total weight of the entire suspension. It is preferable that it is 10 mass% or more and 40 mass% or less.

As the semiconductor fine particles, single or plural compound semiconductor particles having an appropriate average particle diameter, for example, an average particle diameter of about 1 nm to 500 nm can be used. Among these, from the viewpoint of increasing the specific surface area, those having an average particle diameter of about 1 nm to 50 nm are desirable. In order to increase the utilization factor of incident light, semiconductor particles having a relatively large average particle diameter of about 200 nm to 400 nm may be added.

Examples of the method for producing semiconductor fine particles include a sol-gel method such as a hydrothermal synthesis method, a sulfuric acid method, and a chlorine method. The method is not limited as long as the method can produce the desired fine particles, but from the viewpoint of crystallinity. Is preferably synthesized by a hydrothermal synthesis method.

Examples of the dispersion medium for the suspension include glyme solvents such as ethylene glycol monomethyl ether; alcohols such as isopropyl alcohol; mixed solvents such as isopropyl alcohol / toluene; water and the like.

The suspension can be applied by a usual application method such as a doctor blade method, a squeegee method, a spin coating method, or a screen printing method. The conditions for drying and baking the coating film after application of the suspension can be, for example, about 10 seconds to 12 hours in the range of about 50 ° C. to 800 ° C. in the air or in an inert gas atmosphere. . This drying and baking can be performed once at a single temperature or twice or more at different temperatures.

Other types of semiconductor layers other than the porous semiconductor layer can be formed using a normal method for forming a semiconductor layer used in a photoelectric conversion element.

<Dye>
As the dye in the photoelectric conversion device according to the present embodiment, at least one of the above-described spirobifluorene compounds represented by the general formula (1), tautomers or stereoisomers thereof is used. Two or more kinds may be used in combination. Furthermore, other organic pigments can be combined.

As a method for adsorbing the dye to the semiconductor layer 1, for example, a method in which a semiconductor substrate (that is, a conductive substrate having the semiconductor layer 1) is immersed in a solution in which the dye is dissolved, or a dye solution is applied to the semiconductor layer. The method of making it adsorb | suck is mentioned.

Solvents for this dye solution include nitrile solvents such as acetonitrile, propionitrile, methoxyacetonitrile; alcohol solvents such as methanol, ethanol, isopropyl alcohol; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; acetic acid Ester solvents such as ethyl and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methyl-2-pyrrolidone; dichloromethane, chloroform, And halogen solvents such as dichloroethane, trichloroethane, and chlorobenzene; hydrocarbon solvents such as toluene, xylene, and cyclohexane; and water. These may be used alone or in combination of two or more.

When the semiconductor substrate is immersed in this dye solution, the solution can be stirred, heated to reflux, or ultrasonic waves can be applied.

After performing the dye adsorption treatment, it is desirable to wash with a solvent such as acetonitrile in order to remove the dye remaining without being adsorbed.

The amount of the dye supported can be set in the range of 1 × 10 ⁻¹⁰ mol / cm ² or more and 1 × 10 ⁻⁴ mol / cm ² or less, and 1 × 10 ⁻⁹ mol / cm ² or more and 9.0 × 10 ^−6. A range of less than mol / cm ² is preferred. Within this range, the effect of improving the photoelectric conversion efficiency can be obtained economically and sufficiently.

Further, in order to widen the wavelength range where photoelectric conversion can be performed and to increase the conversion efficiency, two or more types of dyes may be mixed and used. It is preferable to select the type and ratio as appropriate.

Further, an additive may be used in combination when adsorbing the dye in order to suppress a decrease in conversion efficiency due to the association between the dyes. Examples of such additives include steroidal compounds having a carboxy group (for example, deoxycholic acid, cholic acid, chenodeoxycholic acid, etc.).

<Counter electrode>
The counter electrode 8 in the photoelectric conversion element according to the present embodiment has the catalyst layer 6 on the substrate 7. In this photoelectric conversion element, holes generated from the dye adsorbed on the semiconductor layer 1 due to the incidence of light are carried to the counter electrode 8 through the electrolyte layer 5, but the counter electrode 8 efficiently annihilates electrons and holes. There is no limit to the material as long as it can fulfill its function.

The catalyst layer 6 of the counter electrode 8 can be formed as a metal vapor deposition film on the substrate 7 by vapor deposition or the like. For example, a Pt layer formed on the substrate 7 may be used. Further, the catalyst layer 6 of the counter electrode 8 may contain a nanocarbon material. For example, the catalyst layer 6 of the counter electrode 8 may be formed by sintering a paste containing carbon nanotubes, carbon nanohorns, or carbon fibers on the porous insulating film. Nanocarbon materials have a large specific surface area and can improve the probability of annihilation of electrons and holes.

Examples of the substrate 7 include transparent substrates such as glass and polymer films, and metal plates (foil). In the case of producing the light-transmitting counter electrode 8, a glass with a transparent conductive film is selected as the substrate 7, and platinum, carbon, or the like is formed as the catalyst layer 6 using a vapor deposition method or a sputtering method. be able to.

<Electrolyte layer>
The electrolyte layer 5 in the photoelectric conversion element according to the present embodiment has a function of transporting holes generated from the dye adsorbed on the semiconductor layer 1 due to incidence of light to the counter electrode 8. As such an electrolyte layer, an electrolyte solution in which a redox couple is dissolved in an organic solvent, a gel electrolyte in which a polymer matrix is impregnated with a liquid in which the redox couple is dissolved in an organic solvent, a molten salt containing the redox couple, a solid electrolyte Organic hole transport materials and the like can be used.

The electrolyte layer can be composed of an electrolyte, a solvent, and an additive.
As the electrolyte, LiI, NaI, KI, CsI , CaI 2 , etc. of the metal iodides, tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide iodide and _{I 2,} such as iodine salts of quaternary ammonium compounds such as id A combination of a bromide such as a bromide of a quaternary ammonium compound such as a metal bromide such as LiBr, NaBr, KBr, CsBr or CaBr ₂ or a tetraalkylammonium bromide or pyridinium bromide with Br ₂ ; Metal complexes such as ferricyanate and ferrocene-ferricinium ions; sulfur compounds such as sodium polysulfide and alkylthiol-alkyl disulfides; viologen dyes; hydroquinone-quinone and the like. Among these, a combination of LiI and pyridinium iodide, or a combination of imidazolium iodide and I ₂ is preferable. Moreover, said electrolyte may be used independently or may be used in mixture of 2 or more types. In addition, a molten salt that is in a molten state at room temperature can be used as the electrolyte. In this case, a solvent need not be used.

Examples of the solvent used in the electrolyte layer include carbonate solvents such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, and propylene carbonate; amide solvents such as N-methyl-2-pyrrolidone and N, N-dimethylformamide; Nitrile solvents such as propionitrile, propionitrile, methoxyacetonitrile, acetonitrile; lactone solvents such as γ-butyrolactone and valerolactone; ether solvents such as tetrahydrofuran, dioxane, diethyl ether, ethylene glycol dialkyl ether; methanol, ethanol Alcohol solvents such as isopropyl alcohol; aprotic polar solvents such as dimethyl sulfoxide and sulfolane; 2-methyl-3-oxazolidinone, 2-methyl Heterocyclic compounds such as 1,3-dioxolane. These solvents may be used alone or in combination of two or more.

A basic compound may be added to the electrolyte layer in order to suppress dark current. The type of basic compound is not particularly limited, and examples thereof include t-butylpyridine, 2-picoline, 2,6-lutidine and the like. The addition concentration in the case of adding a basic compound can be, for example, about 0.05 mol / L or more and 2 mol / L or less.

As the electrolyte, a solid electrolyte can also be used. As this solid electrolyte, a gel electrolyte or a completely solid electrolyte can be used.

As the gel electrolyte, a gelling agent to which an electrolyte or a room temperature molten salt is added can be used. As a gelation method, gelation can be performed by a technique such as addition of a polymer or an oil gelling agent, polymerization of coexisting polyfunctional monomers, or a crosslinking reaction of the polymer.

Examples of the polymer to be gelated by adding a polymer include polyacrylonitrile and polyvinylidene fluoride. As oil gelling agents, dibenzylden-D-sorbitol, cholesterol derivatives, amino acid derivatives, alkylamide derivatives of trans- (1R, 2R) -1,2-cyclohexanediamine, alkylurea derivatives, N-octyl-D-gluconamide benzoate Double-headed amino acid derivatives, quaternary ammonium salt derivatives, and the like.

When gelation is performed by polymerization of a polyfunctional monomer, the monomer used is preferably a compound having two or more ethylenically unsaturated groups, such as divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, Examples include diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, pentaerythritol triacrylate, and trimethylolpropane triacrylate. In the gelation, a monofunctional monomer may be included in addition to the polyfunctional monomer. Monofunctional monomers include esters derived from acrylic acid and α-alkyl acrylic acids such as acrylamide, N-isopropylacrylamide, methyl acrylate, and hydroxyethyl acrylate; amides; dimethyl maleate, diethyl fumarate, dibutyl maleate Esters derived from maleic acid and fumaric acid such as: Dienes such as butadiene, isoprene and cyclopentadiene; Aromatic vinyl compounds such as styrene, p-chlorostyrene and sodium styrenesulfonate; Vinyl esters such as vinyl acetate Nitriles such as acrylonitrile and methacrylonitrile; vinyl compounds having a nitrogen-containing heterocycle such as vinyl carbazole; vinyl compounds having a quaternary ammonium salt; other N-vinylformamide, vinyl sulfone , Vinylidene fluoride, vinyl alkyl ethers, N- phenylmaleimide, and the like. 0.5 mass% or more and 70 mass% or less are preferable, and, as for the polyfunctional monomer which occupies for the monomer whole quantity, 1.0 mass% or more and 50 mass% or less are more preferable.

Polymerization of the monomer for gelation can be performed by radical polymerization. This radical polymerization can be carried out by heating, light, ultraviolet light or electron beam, or electrochemically. Examples of the polymerization initiator used when forming a crosslinked polymer by heating include azo initiators such as 2,2′-azobis (isobutyronitrile) and 2,2′-azobis (dimethylvaleronitrile), Examples thereof include peroxide initiators such as benzoyl peroxide. The addition amount of the polymerization initiator is preferably 0.01% by mass or more and 15% by mass or less, and more preferably 0.05% by mass or more and 10% by mass or less with respect to the total amount of monomers.

When gelation is performed by a crosslinking reaction of a polymer, it is desirable to use a polymer having a reactive group necessary for the crosslinking reaction and a crosslinking agent in combination. Preferred crosslinkable reactive groups are nitrogen-containing heterocycles such as pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, and preferred crosslinkers are alkyl halides, halogenated alkyls. Bifunctional or higher functional compounds capable of electrophilic substitution reaction with nitrogen atoms such as aralkyl, sulfonic acid ester, acid anhydride, acid chloride, isocyanate and the like can be mentioned.

As a complete solid electrolyte, a mixture of an electrolyte and an ion conductive polymer compound can be used. Examples of the ion conductive polymer compound include polar polymer compounds such as polyethers, polyesters, polyamines, and polysulfides.

In the photoelectric conversion element according to the present embodiment, an inorganic hole transport material such as copper iodide or copper thiocyanide can be used as the charge transport material. This inorganic hole transport material can be introduced into the electrode by a method such as a casting method, a coating method, a spin coating method, a dipping method, or electrolytic plating.

In the photoelectric conversion element according to the present embodiment, an organic hole transport material can be used instead of the electrolyte as the charge transport material. Examples of organic hole transport materials include 2,2 ′, 7,7′-tetrakis (N, N-di-p-methoxyphenylamine) -9,9′-spirobifluorene (for example, Adv. Mater. 2005, 17). , 813), aromatic diamines such as N, N′-diphenyl-N, N′-bis (3-methylphenyl)-(1,1′-biphenyl) -4,4′-diamine (for example, Compounds described in US Pat. No. 4,764,625), triphenylamine derivatives (for example, compounds described in JP-A-4-129271), and stilbene derivatives (for example, described in JP-A-2-511262). Compound), hydrazone derivatives (for example, compounds described in JP-A-2-226160) and the like. The organic hole transport material can be introduced into the electrode by a method such as a vacuum deposition method, a cast method, a spin coating method, a dipping method, or an electrolytic polymerization method.

The production of the electrolyte layer 5 of the photoelectric conversion element of the present embodiment can be performed, for example, by the following two methods. One is a method in which the counter electrode 8 is first bonded onto the semiconductor layer 1 on which the dye is adsorbed, and the liquid electrolyte layer 5 is introduced into the gap. The other is a method of forming the electrolyte layer 5 directly on the semiconductor layer 1. In the latter case, the counter electrode 8 is formed on the electrolyte layer 5 after it is formed.

A photoelectrochemical cell can be provided using the photoelectric conversion element described above. This photoelectrochemical cell can be suitably used as a solar cell.

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1
<Synthesis of Spirobifluorene Compound SP-1>
According to the following reaction formula, spirobifluorene compound SP-1 was synthesized as follows.

8 g of R1 (2,2′-bis (3,4-ethylenedioxythiophene), Adv. Mater. 年 1997, No. 10, page 795-798) was added to 300 ml of dry tetrahydrofuran (THF). Then, 21.3 ml of a 1.6 mol / L n-butyllithium hexane solution was added dropwise at −78 ° C. under an argon atmosphere, and the mixture was stirred for 1 hour. Then, 9.221 g of tributyltin chloride was added, stirred at that temperature for 30 minutes, and further stirred overnight at room temperature. 300 ml of water was added to the reaction solvent, and the organic layer was extracted with diethyl ether and dried over magnesium sulfate. The solvent was distilled off under reduced pressure to obtain 14.89 g of A1.

1.7 g of R2 (2-bromo-9,9′-spirobi [9H-fluorene]) and 3.2 g of A1, 0.146 g of tetrakis (triphenylphosphine) palladium (0) were dissolved in 40 ml of dioxane, and 100 ° C. For 2 hours. After allowing to cool, the solvent was distilled off under reduced pressure, and the residue was purified by a silica gel column (elution solvent: toluene / chloroform = 2/1) to obtain 1.7 g of A2.

Next, 1.7 g of A2 was dissolved in 40 ml of dry tetrahydrofuran, and 2.3 ml of a 1.6 mol / L n-butyllithium hexane solution was added dropwise thereto at −78 ° C. in an argon atmosphere, followed by stirring for 1 hour. The temperature is raised to 0 ° C., and a solution prepared by dissolving 0.32 g of N, N-dimethylformamide in 2 ml of dry THF is added dropwise thereto. The mixture is stirred for 1 hour at 0 ° C., water is added to the reaction solution, and the organic layer is extracted with 100 ml of diethyl ether. It dried with magnesium sulfate, the solvent was distilled off under reduced pressure, and 1.05g of A3 was obtained by refine | purifying a residue with a silica gel column (elution solvent: toluene / chloroform = 1/1).

Next, 0.3 g of A3, 0.061 g of cyanoacetic acid and 0.102 g of piperidine were dissolved in 90 ml of chloroform and heated to reflux for 12 hours. After allowing to cool, the solvent is distilled off under reduced pressure, and a small amount of THF is added to the residue, which is added dropwise to 400 ml of water and acidified with dilute hydrochloric acid. The precipitated crystals are filtered off, washed with water and dried. The obtained crystals were washed with hexane to obtain 0.193 g of the target SP-1 (yield 58%).

The measurement results of ¹ H-NMR (THF-d ₈ ) of the obtained spirobifluorene compound SP-1 were as follows: δ was 10.7-10.9 (1H, br), 8. 26 (1H, s), 7.87-7.92 (5H, m), 7.4830-7.37 (3H, m), 7.00-7.19 (4H, m), 6.70 ( 2H, d), 6.58 (1H, d)

Further, FIG. 2 shows an absorption spectrum curve of the obtained spirobifluorene compound SP-1 (dye) in THF. The maximum absorption wavelength (λmax) of the spirobifluorene compound SP-1 was 515 nm.

(Example 2)
<Synthesis of Spirobifluorene Compound SP-2>
According to the following reaction formula, spirobifluorene compound SP-2 was synthesized as follows.

5 g of R3 (3,4'-dihexyl-2,2'-bithiophene) was dissolved in 80 ml of dry THF, and 11.2 ml of a 1.6 mol / L n-butyllithium hexane solution at −78 ° C. in an argon atmosphere. The solution was added dropwise and stirred for 2 hours. Then, 6.324 g of tributyltin chloride was added, stirred at that temperature for 30 minutes, and further stirred overnight at room temperature. 300 ml of water was added to the reaction solvent, and the organic layer was extracted with diethyl ether and dried over magnesium sulfate. The solvent was distilled off under reduced pressure to obtain 8.39 g of B1.

Next, as in Example 1, except that B1 was used instead of compound A1 and reacted with R2 to obtain B2, then reacted with N, N-dimethylformamide to obtain B3, and finally cyanoacetic acid To obtain the target spirobifluorene compound SP-2. Λmax of the obtained spirobifluorene compound SP-2 (dye) was 479 nm.

(Example 3)
<Production of photoelectric conversion element>
A photoelectric conversion element was produced as follows.

(A) Production of Semiconductor Electrode and Counter Electrode First, semiconductor electrodes were produced in the following order.
A glass with FTO (10 Ωcm ² ) having a size of 15 mm × 15 mm and a thickness of 1.1 mm was prepared as a conductive substrate (light transmissive substrate with a transparent conductive layer).

Also, a titanium oxide paste (semiconductor layer material) was prepared as follows. Commercially available titanium oxide powder (trade name: P25, manufactured by Nippon Aerosil Co., Ltd., average primary particle size: 21 nm) 5 g, 15 vol% acetic acid aqueous solution 20 ml, surfactant 0.1 ml (trade name: “Triton” (registered trademark) X-100, manufactured by Sigma-Aldrich Co., Ltd.) and 0.3 g of polyethylene glycol (molecular weight 20000) (manufactured by Wako Pure Chemical Industries, Ltd., product code: 168-11285) were mixed, and this mixture was stirred with a stirring mixer for about 1 hour. A titanium oxide paste was obtained.

Next, this titanium oxide paste was applied on a glass with FTO by a doctor blade method so that the film thickness was about 50 μm (application area: 10 mm × 10 mm).
Thereafter, the glass with FTO coated with the titanium oxide paste was put in an electric furnace, baked at 450 ° C. for about 30 minutes in an air atmosphere, and naturally cooled to obtain a porous titanium oxide film on the glass with FTO. .

Further, a light scattering layer was formed on the titanium oxide film as follows. A titanium oxide paste having an average particle size of 400 nm (trade name: PST-400C, manufactured by JGC Catalysts & Chemicals Co., Ltd.) was applied to the above-described titanium oxide film at a thickness of 20 μm by screen printing. Then, the light-scattering layer on the titanium oxide film was obtained by baking for about 30 minutes at 450 degreeC in air | atmosphere, and allowing it to cool naturally.
As described above, a semiconductor electrode before the dye was adsorbed was obtained.

Meanwhile, a counter electrode was fabricated as follows. A platinum layer having an average film thickness of 1 μm was deposited as a catalyst layer on a soda lime glass plate (thickness: 1.1 mm) by a vacuum deposition method to obtain a counter electrode.

(B) Adsorption of dye Next, the dye was adsorbed to the semiconductor layer composed of the above-described titanium oxide film and light scattering layer. For adsorption of the dye, the spirobifluorene compound SP-1 of Example 1 was dissolved in a mixed solvent of ethanol / tetrahydrofuran (1/1) at a concentration of 0.3 mM, and deoxycholic acid as a coadsorbent was added to 50 mM. The added solution was used. The semiconductor electrode was immersed in this dye solution for 6 hours. Thereafter, the semiconductor electrode was taken out from the dye solution, rinsed with acetonitrile to remove excess dye, and dried in air to obtain a semiconductor electrode on which the dye was adsorbed.

(C) Cell assembly The semiconductor electrode after the dye adsorption treatment and the counter electrode were arranged so that the semiconductor layer and the catalyst layer face each other, thereby forming a cell before electrolyte injection. Next, a thermosetting resin film in which the electrolyte was allowed to penetrate into the gap between the semiconductor electrode and the counter electrode was thermocompression bonded to the outer periphery of the cell.

(D) Injection of electrolyte An iodine-based electrolyte was injected into the above-described cell from the above-mentioned cut and allowed to penetrate between the semiconductor electrode and the counter electrode. The iodine-based electrolyte uses acetonitrile as a solvent, the concentration of iodine is 0.05 mol / L, the concentration of lithium iodide is 0.1 mol / L, 4-tert-butylpyridine is 0.025 mol / L, 1,2- A solution of dimethyl-3-propylimidazolium iodide at a concentration of 0.6 mol / L was used.

(E) Measurement of photocurrent The photoelectric conversion element produced as described above is irradiated with light having an intensity of 100 mW / cm ² under AM1.5 conditions with a solar simulator, and the generated electricity is measured with a current-voltage measuring device. As a result of measuring and evaluating photoelectric conversion characteristics, a photoelectric conversion efficiency of 4.2% was obtained.

(Example 4)
As in Example 3, except that the spirobifluorene dye SP-2 was used instead of the spirobifluorene dye SP-1, a photoelectric conversion element was produced. As a result of evaluating the photoelectric conversion characteristics of the obtained device, a photoelectric conversion efficiency of 4.6% could be obtained.

As is clear from the above description, by using the spirobifluorene compound according to the embodiment of the present invention as a photoelectric conversion dye, a photoelectric conversion element having excellent photoelectric conversion efficiency and a semiconductor electrode used therefor can be obtained. it can. Such a photoelectric conversion element can be applied to a photoelectrochemical cell, and is particularly suitable for a solar cell. Further, the cost can be reduced compared to the case where a metal complex containing a noble metal is used.

As mentioned above, although this invention was demonstrated with reference to embodiment and an Example, this invention is not limited to the said embodiment and Example. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

The photoelectric conversion element according to the present invention is suitably used as a photoelectrochemical cell, and can be used not only as a photoelectrochemical cell but also as a photosensor.

This application claims priority based on Japanese Patent Application No. 2011-204756 filed on September 20, 2011, the entire disclosure of which is incorporated herein.

DESCRIPTION OF SYMBOLS 1 Semiconductor layer 2 Transparent conductive layer 3 Light transmissive substrate 4 Semiconductor electrode 5 Electrolyte layer (charge transport layer)
6 Catalyst layer 7 Substrate 8 Counter electrode

Claims (9)

A spirobifluorene compound represented by the following general formula (1), a tautomer or stereoisomer thereof.

(In Formula (1), R ¹ and R ² each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, an alkoxy group, or a hydroxy group. Z represents a π-conjugated linking group. , X represents an organic group having an acidic group.) The linking group Z includes at least one selected from a substituted or unsubstituted aromatic ring, a substituted or unsubstituted heterocyclic ring, a vinylene group (—CH═CH—), and an ethynylene group (—C≡C—). The spirobifluorene compound according to claim 1, its tautomer or stereoisomer. The spirobifluorene compound, tautomer or stereoisomer thereof according to claim 2, wherein the linking group Z is a linking group having a structure represented by at least the following general formula (2).

(In Formula (2), R ³ and R ⁴ each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, or an alkoxy group, and R ³ and R ⁴ may be linked together to form a ring. Y represents an oxygen atom, a sulfur atom or NRa, Ra represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group, and * represents a bond.) The spirobifluorene compound according to any one of claims 1 to 3, wherein the organic group X having an acidic group is an organic group having a structure represented by the following general formula (3). Mutant or stereoisomer.

(In formula (3), M represents a hydrogen atom or a salt-forming cation.) A dye for a photoelectric conversion element comprising at least one of the spirobifluorene compound according to any one of claims 1 to 4 and a tautomer or stereoisomer thereof. A semiconductor electrode for a photoelectric conversion element, comprising a semiconductor layer containing the dye for a photoelectric conversion element according to claim 5. The semiconductor electrode for a photoelectric conversion element according to claim 6, wherein the semiconductor layer contains titanium oxide or zinc oxide. A photoelectric conversion element comprising the semiconductor electrode for a photoelectric conversion element according to claim 6 or 7. A photoelectrochemical cell comprising the photoelectric conversion element according to claim 8.

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