JP6677078B2 - Hole transport material, photoelectric conversion element, and solar cell - Google Patents

Description

  The present invention relates to a hole transport material, a photoelectric conversion element, and a solar cell including the same.

  In recent years, drive power in electronic circuits has become extremely small, and various electronic components such as sensors can be driven with weak power. Further, when utilizing sensors, applications to self-sustained power sources (energy-generating elements) that can generate and consume power on the spot are expected, and among them, solar cells are attracting attention as elements that can generate power anywhere with light.

Among solar cells, dye-sensitized solar cells announced by Graetzel et al. Of the Swiss University of Technology Lausanne have been reported to have higher photoelectric conversion characteristics than amorphous silicon solar cells in a weak indoor light environment (non- Patent Document 1).
In a dye-sensitized solar cell using a conventional electrolytic solution having high power generation performance, there is a concern that the electrolytic solution may volatilize or leak. Therefore, when assuming practical use, solidification of the electrolytic solution is desired. Many reports have been made, such as those using low molecular weight organic hole transport materials (see, for example, Patent Document 1, Non-Patent Documents 2 and 3). Non-Patent Document 4 discloses that 9,9 ′-([1,1′-biphenyl] -4,4′-diyl) bis (N ³ , N ³ , N ⁶ , N ⁶ − tetrakis (4-methoxyphenyl) -9H-carbazole-3,6-diamine) is described.
It has been reported that when weak light such as room light is converted into electricity, the loss current due to the internal resistance of the photoelectric conversion element is significant (see Non-Patent Document 5).

  As described above, in all of the solid-state photoelectric conversion elements studied so far, only the power generation performance in simulated sunlight is reported, and the power generation performance in indoor light is not reported. Further, cost reduction of a hole transport material called spiro-OMeTAD described in Non-Patent Document 2 is desired. A 60 ° C. heat resistance test on a solar cell using spiro-OMeTAD has been reported (Non-Patent Document 6). The results of the test show that the output decreases with time.

  In view of the above problems, an object of the present invention is to provide a hole transporting material capable of obtaining a photoelectric conversion element having excellent photoelectric conversion properties even under weak irradiation light such as room light even under high-temperature storage. And

In order to solve the above problems, the hole transport material of the present invention is as follows.
A hole transport material represented by the following general formula (1).
(In the formula, R ₁ represents a methoxy group or an ethoxy group. R ₂ represents a hydrogen atom, a methyl group, or a methoxy group. R ₃ represents a hydrogen atom or a methyl group.)

  According to the present invention, it is possible to provide a hole transport material capable of obtaining a photoelectric conversion element having excellent photoelectric conversion properties even under low-temperature storage even under low-temperature storage.

FIG. 1 is a schematic view of an example showing a structure of a photoelectric conversion element according to the present invention. It is an IR spectrum of the hole transport material (Compound No. 1-1) obtained in Example I-1.

The hole transport material of the present invention is represented by the following general formula (1).
(In the formula, R ₁ represents a methoxy group or an ethoxy group. R ₂ represents a hydrogen atom, a methyl group, or a methoxy group. R ₃ represents a hydrogen atom or a methyl group.)

When conventional hole transport materials are used, the morphology of the hole transport material in the hole transport layer and the constituent materials such as basic compounds and lithium salts as additives change during the high-temperature process, and the output is considered to decrease. I have.
In order to suppress the morphological change, it is considered that one solution is to make the hole transport material a material with high crystallinity, but the hole transport material in the solid-state dye-sensitized solar cell has a high output unless it is in an amorphous state. Can not be obtained.
The hole transport material 9,9 ′-([1,1′-biphenyl] -4,4′-diyl) bis (N ³ , N ³ , N ⁶ , N ⁶ -tetrakis (4 -methoxyphenyl) -9H-carbazole-3,6-diamine) is a compound having the following structure and having a carbazole skeleton and a triphenylamine skeleton.
The carbazole skeleton has high planarity, low solubility, and easy crystallization. Therefore, as a result of intensive studies, it was found that by using a triphenylamine structure instead of a carbazole skeleton, stericity was enhanced, solubility was increased, crystallization was difficult, and high amorphousness and hole transportability were obtained. It has become possible. As a result, even under storage at a high temperature of 85 ° C., a photoelectric conversion element having excellent photoelectric conversion properties under weak irradiation light such as room light could be obtained.

Specific exemplary compounds of the hole transporting material represented by the general formula (1) are described below, but are not limited thereto.

  Hereinafter, a photoelectric conversion element and a solar cell according to the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiment described below, and can be changed in other embodiments, additions, modifications, deletions, and the like within a range that can be conceived by those skilled in the art. The present invention is also included in the scope of the present invention as long as the functions and effects of the present invention are exhibited.

The photoelectric conversion element of the present invention has a first electrode, a hole blocking layer, an electron transport layer, a hole transport layer, and a second electrode, wherein the hole transport layer is a hole transport material of the present invention. including.
The configuration of the photoelectric conversion element and the solar cell will be described with reference to FIG. FIG. 1 is an example of a cross-sectional view of a photoelectric conversion element and a solar cell.
In the embodiment shown in FIG. 1, a first electrode 2 is formed on a substrate 1, a hole blocking layer 3 is formed on the first electrode 2, an electron transport layer 4 is formed on the hole blocking layer 3, An example of a configuration in which the photosensitizing material 5 is adsorbed on the electron transporting material in the electron transporting layer 4 and the hole transporting layer 6 is interposed between the first electrode 2 and the second electrode 7 opposed to the first electrode 2 is illustrated. ing. FIG. 1 shows an example of a configuration in which the lead lines 8 and 9 are provided so that the first electrode 2 and the second electrode 7 conduct. Hereinafter, the details will be described.

<Substrate>
The substrate 1 used in the present invention is not particularly limited, and a known substrate can be used. The substrate 1 is preferably made of a transparent material, and examples thereof include glass, a transparent plastic plate, a transparent plastic film, and an inorganic transparent crystal.

<First electrode>
The first electrode 2 used in the present invention is not particularly limited as long as it is a conductive material that is transparent to visible light, and is a known material used in ordinary photoelectric conversion elements or liquid crystal panels. Can be used.
As a material of the first electrode, for example, indium tin oxide (hereinafter, referred to as ITO), fluorine-doped tin oxide (hereinafter, referred to as FTO), antimony-doped tin oxide (hereinafter, referred to as ATO), indium Examples include zinc oxide, niobium / titanium oxide, and graphene, and these may be used alone or in a plurality of layers.
The thickness of the first electrode is preferably from 5 nm to 10 μm, more preferably from 50 nm to 1 μm.

The first electrode is preferably provided on a substrate 1 made of a material transparent to visible light in order to maintain a certain degree of hardness. Examples of the substrate include glass, a transparent plastic plate, a transparent plastic film, and a transparent inorganic material. Crystals and the like are used.
Known ones in which the first electrode and the substrate are integrated can also be used. For example, FTO coated glass, ITO coated glass, zinc oxide: aluminum coated glass, FTO coated transparent plastic film, ITO coated transparent plastic film And the like.
In addition, a transparent electrode in which tin oxide or indium oxide is doped with a cation or anion having a different valence, a metal electrode having a structure in which light can be transmitted, such as a mesh or a stripe, is provided on a substrate such as a glass substrate. May be.

These may be used alone or as a mixture of two or more kinds, or may be a layered one. For the purpose of lowering the resistance, a metal lead wire or the like may be used in combination.
Examples of the material of the metal lead wire include metals such as aluminum, copper, silver, gold, platinum, and nickel. The metal lead wire can be formed by a method in which the metal lead wire is provided on a substrate by vapor deposition, sputtering, pressure bonding, or the like, and ITO or FTO is provided thereon.

<Hole blocking layer>
The material constituting the hole blocking layer 3 used in the present invention is not particularly limited as long as it is transparent to visible light and has an electron transporting property, but titanium oxide is particularly preferable. The hole blocking layer is provided in order to suppress a decrease in power due to recombination (so-called reverse electron transfer) of holes in the electrolyte and electrons on the electrode surface when the electrolyte is in contact with the electrode. The effect of the hole blocking layer 3 is particularly remarkable in a solid-type dye-sensitized solar cell. This is because, compared to a wet dye-sensitized solar cell using an electrolyte, a solid-type dye-sensitized solar cell using an organic hole transport material or the like recombines holes in the hole transport material with electrons on the electrode surface ( (Reverse electron transfer) speed is high.

  Although the method for forming the hole blocking layer is not limited, a high internal resistance is required to suppress the loss current in room light, and the film forming method is also important. In general, a sol-gel method for wet film formation is mentioned, but the film density is low and the loss current cannot be sufficiently suppressed. For this reason, a dry film forming method such as a sputtering method is more preferable, and the film density is sufficiently high to suppress the loss current.

  This hole blocking layer is also formed for the purpose of preventing electronic contact between the first electrode 2 and the hole transport layer 6. The thickness of the hole blocking layer is not particularly limited, but is preferably 5 nm to 1 μm, more preferably 500 to 700 nm for wet film formation, and more preferably 10 nm to 30 nm for dry film formation.

<Electron transport layer>
The photoelectric conversion element and the solar cell of the present invention have a porous electron transport layer 4 formed on the hole blocking layer 3. The electron transport layer may be a single layer or a multilayer. Is also good.
The electron transport layer is composed of an electron transport material, and semiconductor particles are preferably used as the electron transport material.
In the case of a multilayer, a dispersion of semiconductor particles having different particle diameters can be applied in multiple layers, or a coating layer having different types of semiconductors, resins, and additives having different compositions can be applied in multiple layers.
When the film thickness is insufficient by one application, multilayer application is an effective means.
In general, as the thickness of the electron transport layer increases, the amount of photosensitized material carried per unit projected area increases, so that the light capture rate increases. The loss due to coupling also increases.
Therefore, the thickness of the electron transport layer is preferably 100 nm to 100 μm.

The semiconductor is not particularly limited, and a known semiconductor can be used.
Specifically, a simple semiconductor such as silicon or germanium, a compound semiconductor represented by a metal chalcogenide, a compound having a perovskite structure, or the like can be given.
Metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, or tantalum oxide, cadmium, zinc, lead, silver, antimony, bismuth Sulfide, cadmium, lead selenide, cadmium telluride, and the like.
As other compound semiconductors, phosphides such as zinc, gallium, indium and cadmium, gallium arsenide, copper-indium-selenide, copper-indium-sulfide and the like are preferable.
Further, as the compound having a perovskite structure, strontium titanate, calcium titanate, sodium titanate, barium titanate, potassium niobate and the like are preferable.
Of these, oxide semiconductors are preferred, and titanium oxide, zinc oxide, tin oxide, and niobium oxide are particularly preferred. They may be used alone or in combination of two or more. The crystal type of these semiconductors is not particularly limited, and may be single crystal, polycrystal, or amorphous.

The size of the semiconductor particles is not particularly limited, but the average particle size of the primary particles is preferably 1 to 100 nm, more preferably 5 to 50 nm.
Further, efficiency can be improved by mixing or laminating semiconductor particles having a larger average particle diameter to scatter incident light. In this case, the average particle size of the semiconductor is preferably 50 to 500 nm.

The method for forming the electron transport layer is not particularly limited, and examples thereof include a method of forming a thin film in a vacuum such as sputtering and a wet film forming method.
In consideration of the production cost and the like, a wet film forming method is particularly preferable, and a method of preparing a paste in which powder or sol of semiconductor particles is dispersed and applying the paste on an electron collecting electrode substrate is preferable.
When this wet film forming method is used, the coating method is not particularly limited, and the coating can be performed according to a known method.
For example, dip method, spray method, wire bar method, spin coating method, roller coating method, blade coating method, gravure coating method, and various wet printing methods such as letterpress, offset, gravure, intaglio, rubber plate, screen printing, etc. Various methods can be used.

When a dispersion of semiconductor particles is prepared by mechanical pulverization or using a mill, at least semiconductor particles alone or a mixture of semiconductor particles and a resin are dispersed in water or an organic solvent.
As the resin used at this time, for example, a polymer or copolymer of a vinyl compound such as styrene, vinyl acetate, acrylate, methacrylate, silicone resin, phenoxy resin, polysulfone resin, polyvinyl butyral resin, polyvinyl Formal resins, polyester resins, cellulose ester resins, cellulose ether resins, urethane resins, phenol resins, epoxy resins, polycarbonate resins, polyarylate resins, polyamide resins, polyimide resins, and the like.
As a solvent for dispersing the semiconductor particles, for example, water, an alcohol solvent such as methanol, ethanol, isopropyl alcohol, α-terpineol, a ketone solvent such as acetone, methyl ethyl ketone, or methyl isobutyl ketone, ethyl formate, ethyl acetate, or Ester solvents such as n-butyl acetate, ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolan or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone Amide solvents such as dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene Bromobenzene, iodobenzene, or a halogenated hydrocarbon solvent such as 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, Examples thereof include hydrocarbon solvents such as o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene. These can be used alone or as a mixed solvent of two or more.

A semiconductor particle dispersion or a paste of semiconductor particles obtained by a sol-gel method or the like is used to prevent reaggregation of the particles, and is preferably an acid such as hydrochloric acid, nitric acid, or acetic acid, or a polyoxyethylene (10) octylphenyl ether or the like. Surfactants, chelating agents such as acetylacetone, 2-aminoethanol, ethylenediamine and the like can be added.
It is also an effective means to add a thickener for the purpose of improving the film forming property.
Examples of the thickener added at this time include polymers such as polyethylene glycol and polyvinyl alcohol, and thickeners such as ethyl cellulose.

  The semiconductor particles are preferably subjected to baking, microwave irradiation, electron beam irradiation, or laser light irradiation in order to electronically contact the particles after application and to improve film strength and adhesion to a substrate. . These treatments may be performed alone or in combination of two or more.

  In the case of firing, the range of the firing temperature is not particularly limited. However, if the temperature is too high, the resistance of the substrate may be increased or the substrate may be melted. Therefore, the temperature is preferably 30 to 700 ° C, more preferably 100 to 600 ° C. preferable. The firing time is not particularly limited, but is preferably 10 minutes to 10 hours.

The microwave irradiation may be performed from the side on which the electron transport layer is formed or from the back side.
The irradiation time is not particularly limited, but is preferably performed within one hour.

  After firing, for example, chemical plating using an aqueous solution of titanium tetrachloride or a mixed solution with an organic solvent or titanium trichloride for the purpose of increasing the surface area of the semiconductor particles and increasing the electron injection efficiency from the photosensitizing material to the semiconductor particles. Electrochemical plating using an aqueous solution may be performed.

A film in which semiconductor particles having a diameter of several tens of nm are stacked by sintering or the like forms a porous state. This nanoporous structure has a very high surface area, which can be described using a roughness factor.
The roughness factor is a numerical value representing the actual area inside the porous body with respect to the area of the semiconductor particles applied to the substrate. Therefore, the roughness factor is preferably as large as possible, but it is also preferably 20 or more in the present invention because of the relationship with the film thickness of the electron transport layer.

<Photosensitizing material>
In the present invention, in order to further improve the conversion efficiency, it is preferable that the photosensitizing material is adsorbed on the surface of the electron transporting material that is the electron transporting layer 4.

The photosensitizing material 5 is not limited to the above as long as it is a compound that is photoexcited by the excitation light to be used, and specific examples include the following compounds.
JP-A-7-500630, JP-A-10-233238, JP-A-2000-26487, JP-A-2000-323191, JP-A-2001-59062, etc. JP-A-10-93118, JP-A-2002-164089, JP-A-2004-95450, J.P. Phys. Chem. C, 7224, Vol. Coumarin compounds described in JP-A-2004-95450, Chem. Commun. , 4887 (2007), and the like, JP-A-2003-264010, JP-A-2004-63274, JP-A-2004-115636, JP-A-2004-200068, and JP-A-2004-235052. Gazette, J.A. Am. Chem. Soc. , 12218, Vol. 126 (2004), Chem. Commun. , 3036 (2003), Angew. Chem. Int. Ed. , 1923, Vol. 47 (2008) and the like. Am. Chem. Soc. , 16701, Vol. 128 (2006); Am. Chem. Soc. , 14256, Vol. 128 (2006), JP-A-11-86916, JP-A-11-214730, JP-A-2000-106224, JP-A-2001-76773, and JP-A-2003-7359. And the merocyanine described in JP-A-11-214731, JP-A-11-238905, JP-A-2001-52766, JP-A-2001-76775, JP-A-2003-7360 and the like. Dyes, 9-aryl xanthene compounds described in JP-A-10-92477, JP-A-11-273754, JP-A-11-273755, JP-A-2003-31273, JP-A-10-93118 , JP-A-2003-31273, etc. JP-9-199744, JP-A No. 10-233238, JP-A No. 11-204821, JP-A No. 11-265738, JP-J. Phys. Chem. , 2342, Vol. 91 (1987); Phys. Chem. B, 6272, Vol. 97 (1993), Electronal. Chem. , 31, Vol. 537 (2002), JP-A-2006-032260, J.P. Porphyrins Phthalocyanines, 230, Vol. 3 (1999), Angew. Chem. Int. Ed. , 373, Vol. 46 (2007), Langmuir, 5436, Vol. 24 (2008), porphyrin compounds and the like. In particular, it is preferable to use a metal complex compound, a coumarin compound, a polyene compound, an indoline compound, and a thiophene compound.

More preferred are D131 represented by the following structural formula (3), D102 represented by the following structural formula (4), and D358 represented by the following structural formula (5) manufactured by Mitsubishi Paper Mills.

The method for adsorbing the photosensitizing material 5 to the electron transport layer 4 includes a method of immersing an electron collecting electrode containing semiconductor particles in a solution or a dispersion of the photosensitizer material, and a method of applying the solution or dispersion to the electron transport layer. And a method of applying and adsorbing it on the surface.
In the former case, an immersion method, a dipping method, a roller method, an air knife method, or the like can be used.
In the latter case, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, a spray method, or the like can be used.
Further, the adsorption may be performed in a supercritical fluid using carbon dioxide or the like.

When adsorbing the photosensitizing material, a condensing agent may be used in combination.
The condensing agent acts as a catalyst that seems to physically or chemically bind the photosensitizer and the electron transport compound to the inorganic surface, or acts stoichiometrically to shift the chemical equilibrium advantageously. Any of these may be used.
Further, a thiol or a hydroxy compound may be added as a condensation aid.

As a solvent for dissolving or dispersing the photosensitizing material, for example, water, methanol, ethanol, or an alcohol solvent such as isopropyl alcohol,
Ketone solvents such as acetone, methyl ethyl ketone or methyl isobutyl ketone,
Ester solvents such as ethyl formate, ethyl acetate, or n-butyl acetate;
Ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolan, or dioxane,
An amide solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone;
Halogenated hydrocarbon solvents such as dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene, or 1-chloronaphthalene;
Hydrocarbons such as n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene System solvents can be mentioned, and these can be used alone or as a mixture of two or more.

In addition, some types of photosensitizing materials work more effectively when the coagulation between the compounds is suppressed, so that an aggregating / dissociating agent may be used in combination.
The aggregating / dissociating agent is preferably a steroid compound such as cholic acid or chenodeoxycholic acid, a long-chain alkyl carboxylic acid or a long-chain alkyl phosphonic acid, and is appropriately selected depending on the photosensitizing material to be used.
The addition amount of these aggregation dissociation agents is preferably 0.01 to 500 parts by mass, more preferably 0.1 to 100 parts by mass, per 1 part by mass of the photosensitizing material.

The temperature at which these are used to adsorb the photosensitizing material or the photosensitizing material and the coagulation / dissociation agent is preferably from -50 ° C to 200 ° C.
In addition, this adsorption may be carried out with standing or stirring.

Examples of the method of stirring include, but are not limited to, a stirrer, a ball mill, a paint conditioner, a sand mill, an attritor, a disperser, and an ultrasonic dispersion.
The time required for the adsorption is preferably from 5 seconds to 1,000 hours, more preferably from 10 seconds to 500 hours, even more preferably from 1 minute to 150 hours.
The adsorption is preferably performed in a dark place.

<Hole transport layer>
Generally, as the hole transport layer, an electrolytic solution in which a redox couple is dissolved in an organic solvent, a gel electrolyte in which a liquid in which a redox couple is dissolved in an organic solvent is impregnated in a polymer matrix, a molten salt containing a redox couple, a solid An electrolyte, an inorganic hole transport material, an organic hole transport material, or the like is used. The hole transport layer 6 of the photoelectric conversion element of the present invention contains an organic hole transport material represented by the following general formula (1).
(In the formula, R ₁ represents a methoxy group or an ethoxy group. R ₂ represents a hydrogen atom, a methyl group, or a methoxy group. R ₃ represents a hydrogen atom or a methyl group.)

The hole transport layer preferably contains the organic hole transport material represented by the general formula (1) in an amount of 50 to 95% by mass, more preferably 70 to 85% by mass.
The hole transport material of the present invention can obtain photoelectric conversion characteristics excellent in storage properties under a high-temperature environment. Furthermore, it has been verified that when photoelectric conversion is performed on weak light such as room light, which has been rarely reported, particularly superiority appears.

Further, in the present invention, it is preferable to add a basic compound represented by the following general formula (2) to the hole transport layer 6, and it is possible to obtain a particularly high open-circuit voltage by adding the basic compound. it can. Further, the internal resistance of the photoelectric conversion element is increased, and the loss current in weak light such as room light can be reduced. Therefore, a higher open-circuit voltage than the conventional basic compound can be obtained.
(Wherein, R ₄ and R ₅ each independently represent an alkyl group or an aromatic hydrocarbon group, provided that R ₄ and R ₅ are bonded to each other to form a heterocyclic group containing a nitrogen atom. Including cases.)
R ₄ and R ₅ may be the same.
The alkyl group is preferably an alkyl group having 1 to 12 carbon atoms, and may have a branched chain. As the aromatic hydrocarbon group, a phenyl group and a naphthyl group are preferable. The alkyl group includes a substituted alkyl group and a non-substituted alkyl group, and the aromatic carbohydrate group includes a substituted aromatic hydrocarbon group and a non-substituted aromatic hydrocarbon group. including. Examples of the substituent include a phenyl group.
When R ₄ and R ₅ are bonded to each other to form a heterocyclic group containing a nitrogen atom, the heterocyclic group may contain an oxygen atom or a nitrogen atom. In addition, the heterocyclic group includes a heterocyclic group having a substituent and a heterocyclic group having no substituent, and examples of the substituent include a phenyl group.

  Conventionally, some compounds classified as basic compounds represented by the general formula (2) are known. Further, it is known that some of the compounds are used as basic compounds in iodine electrolyte type dye-sensitized solar cells. However, it has been reported that the iodine electrolyte type dye-sensitized solar cell using the basic compound has a high open-circuit voltage, but has a significantly reduced short-circuit current density and significantly deteriorates photoelectric conversion characteristics.

  The hole transport layer in the present invention uses an organic hole transport material, and is different from the hole transport model using the iodine electrolyte or the like. Therefore, even when the basic compound represented by the general formula (2) is used, an excellent photoelectric conversion characteristic can be obtained by a small decrease in short-circuit current density and a high open-circuit voltage. Furthermore, it has been verified that when photoelectric conversion is performed on weak light such as room light, which has been rarely reported, particularly superiority appears.

Specific examples of the compound represented by the general formula (2) are shown below, but are not limited thereto. In addition, when a number is described next to the following structural formula, the number means a compound number in the chemical substance database “Japan Chemical Substance Dictionary” published by the Japan Science and Technology Agency.

  The amount of the basic compound represented by the general formula (2) in the hole transport layer is preferably 1 part by mass or more and 30 parts by mass or less, and more preferably 5 parts by mass with respect to 100 parts by mass of the organic hole transport material. It is more preferable that the amount be not less than 20 parts by mass and not more than 20 parts by mass.

The organic hole transport layer in the present invention may have a single layer structure or a laminated structure composed of different compounds. In the case of a laminated structure, it is preferable to use a polymer material for the organic hole transporting material layer near the second electrode 7.
This is because the surface of the porous electron transport layer can be further smoothed and the photoelectric conversion characteristics can be improved by using a polymer material having excellent film-forming properties.
In addition, since it is difficult for the polymer material to penetrate into the inside of the porous electron transport layer, it is also excellent in coating the surface of the porous electron transport layer, and is also effective in preventing a short circuit when an electrode is provided. , It is possible to obtain higher performance.

  Examples of the organic hole transporting material used in the single layer structure and the organic hole transporting material used in the organic hole transporting layer far from the second electrode in the laminated structure include the organic hole transporting compound represented by the general formula (1). Used.

As the polymer material used for the organic hole transport layer near the second electrode 7 used in the laminated structure, a known hole transport polymer material is used.
Specific examples thereof include poly (3-n-hexylthiophene), poly (3-n-octyloxythiophene), poly (9,9′-dioctyl-fluorene-co-bithiophene), poly (3,3 ″). '-Didodecyl-quarterthiophene), poly (3,6-dioctylthieno [3,2-b] thiophene), poly (2,5-bis (3-decylthiophen-2-yl) thieno [3,2-b ] Thiophene), poly (3,4-didecylthiophene-co-thieno [3,2-b] thiophene), poly (3,6-dioctylthieno [3,2-b] thiophene-co-thieno [3, 2-b] thiophene), poly (3,6-dioctylthieno [3,2-b] thiophene-co-thiophene), poly (3.6-dioctylthieno [3,2-b] thiophene-co-bithiophene) Polythiophene compounds such as
Poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene], poly [2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylenevinylene], poly Polyphenylene vinylene compounds such as [(2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene) -co- (4,4′-biphenylene-vinylene)];
Poly (9,9'-didodecylfluorenyl-2,7-diyl), poly [(9,9-dioctyl-2,7-divinylenefluorene) -alt-co- (9,10-anthracene)] , Poly [(9,9-dioctyl-2,7-divinylenefluorene) -alt-co- (4,4′-biphenylene)], poly [(9,9-dioctyl-2,7-divinylenefluorene) -Alt-co- (2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylene)], poly [(9,9-dioctyl-2,7-diyl) -co- (1,4- (2,5-dihexyloxy) benzene)] and the like,
Polyphenylene compounds such as poly [2,5-dioctyloxy-1,4-phenylene] and poly [2,5-di (2-ethylhexyloxy-1,4-phenylene)];
Poly [(9,9-dioctylfluorenyl-2,7-diyl) -alt-co- (N, N'-diphenyl) -N, N'-di (p-hexylphenyl) -1,4-diamino Benzene], poly [(9,9-dioctylfluorenyl-2,7-diyl) -alt-co- (N, N′-bis (4-octyloxyphenyl) benzidine-N, N ′-(1, 4-diphenylene)], poly [(N, N′-bis (4-octyloxyphenyl) benzidine-N, N ′-(1,4-diphenylene)], poly [(N, N′-bis (4- (2-ethylhexyloxy) phenyl) benzidine-N, N '-(1,4-diphenylene)], poly [phenylimino-1,4-phenylenevinylene-2,5-dioctyloxy-1,4-phenylenevinylene- 1,4-phenylene], poly p-tolylimino-1,4-phenylenevinylene-2,5-di (2-ethylhexyloxy) -1,4-phenylenevinylene-1,4-phenylene], poly [4- (2-ethylhexyloxy) phenylimino- Polyarylamine compounds such as 1,4-biphenylene],
Poly [(9,9-dioctylfluorenyl-2,7-diyl) -alt-co- (1,4-benzo (2,1 ′, 3) thiadiazole], poly (3,4-didecylthiophene- And polythiadiazole compounds such as co- (1,4-benzo (2,1 ′, 3) thiadiazole).
Among them, polythiophene compounds and polyarylamine compounds are particularly preferable in consideration of carrier mobility and ionization potential.

Further, various additives may be added to the organic hole transporting material described above.
As additives, metal iodides such as iodine, lithium iodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide, copper iodide, iron iodide, silver iodide,
Quaternary ammonium salts such as tetraalkylammonium iodide and pyridinium iodide; metal bromides such as lithium bromide, sodium bromide, potassium bromide, cesium bromide and calcium bromide;
Bromine salts of quaternary ammonium compounds such as tetraalkylammonium bromide and pyridinium bromide,
Copper chloride, metal chlorides such as silver chloride, copper acetate, silver acetate, metal acetates such as palladium acetate,
Copper sulfate, metal sulfates such as zinc sulfate, ferrocyanate-ferricyanate, metal complexes such as ferrocene-ferricinium ion,
Sulfur compounds such as sodium polysulfide, alkyl thiol-alkyl disulfide,
Viologen dyes, hydroquinone, 1,2-dimethyl-3-n-propylimidazoinium iodide, 1-methyl-3-n-hexylimidazolinium iodide, 1,2-dimethyl-3-ethylimidazo Lithium trifluoromethanesulfonate, 1-methyl-3-butylimidazolium nonafluorobutylsulfonate, 1-n-hexyl-3-methylimidazolinium bis (trifluoromethylsulfonyl) imide, 1-methyl-3 Inorg.-ethyl imidazolium bis (trifluoromethyl) sulfonylimide; Chem. 35 (1996) 1168, ionic liquids such as imidazolium compounds, pyridine, 4-t-butylpyridine and basic compounds such as benzimidazole;
Examples thereof include lithium compounds such as lithium trifluoromethanesulfonylimide, lithium diisopropylimide, and lithium bis (trifluoromethanesulfonyl) imide.
An imidazolium compound as an ionic liquid may be used, and specifically, 1-n-hexyl-3-methylimidazolinium bis (trifluoromethylsulfonyl) imide is preferable.

Further, for the purpose of improving conductivity, an oxidizing agent for converting a part of the organic hole transport material into a radical cation may be added.
Examples of the oxidizing agent include tris (4-bromophenyl) aminium hexachloroantimonate, silver hexafluoroantimonate, nitrosonium tetrafluoroborate, silver nitrate, and a cobalt complex compound.
It is not necessary that all the organic hole transporting materials be oxidized by the addition of the oxidizing agent, and only a part of the organic hole transporting material need be oxidized. Further, after the added oxidizing agent is added, it may or may not be taken out of the system.

The organic hole transport layer directly forms a hole transport layer on the electron transport layer 4 supporting the photosensitizing material. The method for forming the organic hole transport layer is not particularly limited, and examples thereof include a method of forming a thin film in a vacuum such as vacuum evaporation and a wet film forming method. In consideration of the production cost and the like, a wet film forming method is particularly preferable, and a method of coating on the electron transport layer is preferable.
When this wet film forming method is used, the coating method is not particularly limited, and the coating can be performed according to a known method. For example, dip method, spray method, wire bar method, spin coating method, roller coating method, blade coating method, gravure coating method, and various wet printing methods such as letterpress, offset, gravure, intaglio, rubber plate, screen printing, etc. Various methods can be used. Further, the film may be formed in a supercritical fluid or a subcritical fluid at a temperature and pressure lower than the critical point.

The supercritical fluid exists as a non-agglomerated high-density fluid in a temperature / pressure region exceeding a limit (critical point) at which a gas and a liquid can coexist, does not aggregate even when compressed, is at or above the critical temperature, and has a critical pressure. There is no particular limitation as long as the fluid is in the above state, and it can be appropriately selected according to the purpose. However, a fluid having a low critical temperature is preferable.
As the supercritical fluid, for example, carbon monoxide, carbon dioxide, ammonia, nitrogen, water, methanol, ethanol, ercol-based solvents such as n-butanol, ethane, propane, 2,3-dimethylbutane, benzene, toluene and the like Preferred are hydrocarbon solvents, halogen solvents such as methylene chloride and chlorotrifluoromethane, and ether solvents such as dimethyl ether. Among them, carbon dioxide is particularly preferable because it has a critical pressure of 7.3 MPa and a critical temperature of 31 ° C., so that it can easily create a supercritical state and is nonflammable and easy to handle.
These fluids may be used alone or as a mixture of two or more.

The subcritical fluid is not particularly limited as long as it exists as a high-pressure liquid in the temperature and pressure regions near the critical point, and can be appropriately selected depending on the purpose.
The compounds listed as supercritical fluids described above can also be suitably used as subcritical fluids.

  The critical temperature and critical pressure of the supercritical fluid are not particularly limited and can be appropriately selected depending on the purpose. The critical temperature is preferably from -273 ° C to 300 ° C, particularly preferably from 0 ° C to 200 ° C. preferable.

Further, in addition to the above-described supercritical fluid and subcritical fluid, an organic solvent and an entrainer can be used in combination.
By adding the organic solvent and the entrainer, the solubility in the supercritical fluid can be more easily adjusted.
Such an organic solvent is not particularly limited, and can be appropriately selected depending on the purpose.
For example, acetone, methyl ethyl ketone, or ketone solvents such as methyl isobutyl ketone,
Ester solvents such as ethyl formate, ethyl acetate, or n-butyl acetate;
Ether solvents such as diisopropyl ether, dimethoxyethane, tetrahydrofuran, dioxolan, or dioxane,
An amide solvent such as N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone;
Halogenated hydrocarbon solvents such as dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene, or 1-chloronaphthalene;
Hydrocarbons such as n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene System solvents and the like.

In the present invention, after the organic hole transporting layer is provided on the first electrode provided with the electron transporting layer supporting the photosensitizing material, a pressing process may be performed.
It is thought that by performing this press treatment, the organic hole transporting material is more closely adhered to the porous electrode, so that the efficiency is improved.
The press treatment method is not particularly limited, and examples thereof include a press molding method using a flat plate typified by an IR tablet shaper and a roll press method using a roller.
The pressure is preferably 10 kgf / cm ² or more, and more preferably 30 kgf / cm ² or more. The pressing time is not particularly limited, but is preferably performed within one hour. Further, heat may be applied at the time of the press treatment.

In the above-described press processing, a release material may be interposed between the press and the electrode.
As the release material, polytetrafluoroethylene, polychloroethylene trifluoride, ethylene tetrafluoride hexafluoropropylene copolymer, perfluoroalkoxyfluoride resin, polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, ethylene Examples thereof include fluororesins such as chlorotrifluoroethylene copolymer and polyvinyl fluoride.

After performing the above-described press treatment step, a metal oxide may be provided between the organic hole transport layer and the second electrode before providing the counter electrode. Examples of the metal oxide that may be provided include molybdenum oxide, tungsten oxide, vanadium oxide, and nickel oxide, and molybdenum oxide is particularly preferable.
The method for providing these metal oxides on the hole transport layer is not particularly limited, and examples thereof include a method of forming a thin film in a vacuum such as sputtering or vacuum deposition, and a wet film forming method.
In the wet film forming method, it is preferable to prepare a paste in which powder or sol of a metal oxide is dispersed and apply the paste on the hole transport layer.
When this wet film forming method is used, the coating method is not particularly limited, and can be performed according to a known method.
For example, dip method, spray method, wire bar method, spin coating method, roller coating method, blade coating method, gravure coating method, and various wet printing methods such as letterpress, offset, gravure, intaglio, rubber plate, screen printing, etc. Various methods can be used. The thickness is preferably from 0.1 to 50 nm, more preferably from 1 to 10 nm.

<Second electrode>
The second electrode is newly provided after the formation of the hole transport layer or on the above-described metal oxide.
As the second electrode, the same electrode as that of the above-mentioned first electrode can be usually used, and a support is not necessarily required in a configuration in which strength and sealing property are sufficiently maintained.
Specific examples of the second electrode material include metals such as platinum, gold, silver, copper, and aluminum; carbon-based compounds such as graphite, fullerene, carbon nanotube, and graphene; and conductive metal oxides such as ITO, FTO, and ATO. And conductive polymers such as polythiophene and polyaniline.
The thickness of the second electrode layer is not particularly limited, and may be used alone or in combination of two or more.
The application of the second electrode can be appropriately formed on the hole transport layer by a method such as application, lamination, vapor deposition, CVD, and bonding depending on the type of the material used and the type of the hole transport layer.

In order to operate as a photoelectric conversion element, at least one of the first electrode and the second electrode must be substantially transparent.
In the photoelectric conversion element of the present invention, a method in which the first electrode side is transparent and sunlight is incident from the first electrode side is preferable. In this case, a material that reflects light is preferably used on the second electrode side, and a metal, glass, plastic, or a metal thin film on which a conductive oxide is deposited is preferable.
Providing an antireflection layer on the incident side of sunlight is also an effective means.

<Application>
The photoelectric conversion element of the present invention can be applied to a solar cell and a power supply device having the same.
As an application example, any device can be used as long as it is a device that conventionally uses a solar cell or a power supply device using the same.
For example, it may be used for an electronic desk calculator or a solar cell for a wristwatch, but an example of utilizing the features of the photoelectric conversion element of the present invention is a power supply device such as a mobile phone, an electronic organizer, and an electronic paper. It can also be used as an auxiliary power source for extending the continuous use time of a rechargeable or dry battery type electric appliance. Furthermore, it can be used as a stand-alone power supply for sensors as a substitute for a primary battery combined with a secondary battery.

<Synthesis method of hole transport material of the present invention>
Similarly to the report example (J. Org. Chem., 67 (2002) 3029), it can be easily synthesized from the following route.
(In the formula, R ₁ represents a methoxy group or an ethoxy group. R ₂ represents a hydrogen atom, a methyl group, or a methoxy group. R ₃ represents a hydrogen atom or a methyl group.)

  Hereinafter, the present invention will be described in detail with reference to examples, but embodiments of the present invention are not limited to these examples.

[Example I-1]
(Synthesis of Hole Transport Material (Compound No. 1-1))
4.89 g of N, N, N ', N'-Tetraphenylbenzidine (manufactured by Tokyo Kasei) and 4.52 g of N-Bromosuccinimide (NBS) (manufactured by Tokyo Kasei) are dissolved in 100 ml of chloroform, and the mixture is dissolved at room temperature. Stirred. The reaction was extracted, filtered over magnesium sulfate and concentrated. The crude product was dissolved in acetone: 50 ml, and added dropwise to 500 ml of methanol, followed by reprecipitation purification to obtain 7.85 g of a tetrabromoamine intermediate.

4,4'-Dimethosydiphenylamine (manufactured by Tokyo Kasei): 1.1 g, the above tetrabromoamine intermediate: 0.81 g, palladium acetate (manufactured by Tokyo Kasei): 90 mg, sodium carbonate (manufactured by Kanto Kagaku): 0. 57 g and 15 ml of xylene were weighed and stirred under an argon gas atmosphere. Thereafter, 240 mg of tert-butyl phosphine (manufactured by Kanto Kagaku) was added, and the mixture was stirred under reflux for 5 hours. The reaction was extracted, filtered over magnesium sulfate and concentrated. The crude product was purified by column chromatography (toluene / ethyl acetate = 4/1). The obtained crude product was subjected to reprecipitation treatment with acetone / methanol to obtain a colorless powdery hole transport material (Compound No. 1-1) (1.15 g). FIG. 2 shows the IR spectrum of the obtained hole transport material.

[Example II-1]
(Production of titanium oxide semiconductor electrode)
A dense hole blocking layer of titanium oxide was formed on the ITO-based glass substrate by reactive sputtering with oxygen gas using a target made of titanium metal.
Next, 3 g of titanium oxide (P90, manufactured by Nippon Aerosil Co., Ltd.), 0.2 g of acetylacetone, 0.3 g of surfactant (polyoxyethylene octylphenyl ether, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed with 5.5 g of water and 1.0 g of ethanol in a bead mill. The treatment was applied for 12 hours.
1.2 g of polyethylene glycol (# 20,000) was added to the obtained dispersion to prepare a paste.
This paste was applied onto the hole blocking layer so as to have a thickness of 1.5 μm, dried at room temperature, and baked in air at 500 ° C. for 30 minutes to form a porous electron transport layer.

(Preparation of photoelectric conversion element)
The titanium oxide semiconductor electrode was immersed in Mitsubishi Paper Mills D102 (0.5 mM, acetonitrile / t-butanol (volume ratio 1: 1) solution) represented by the structural formula (4) as a sensitizing dye, The mixture was allowed to stand in a dark place for a time to adsorb the photosensitizing material.
An organic hole transporting material (exemplified compound No. 1-1) represented by the general formula (1): 183.3 mg of a chlorobenzene solution: 1 ml on a semiconductor electrode carrying a photosensitizing material, manufactured by Kanto Chemical Co., Ltd. A solution obtained by adding 12.83 mg of lithium bis (trifluoromethanesulfonyl) imide and 36.66 mg of the basic compound (compound No. 2-1) represented by the general formula (2) was added to a photosensitizing material. A hole transport layer was formed by spin coating on a semiconductor electrode carrying the compound. Silver was vacuum-evaporated thereon to 100 nm to form a second electrode, and a photoelectric conversion element was manufactured.

(Evaluation of photoelectric conversion element)
The photoelectric conversion efficiency of the obtained photoelectric conversion element under white LED irradiation (50 lux: 12.5 μW / cm ² ) was measured. The white LED was measured by a desk lamp CDS-90α (study mode) manufactured by Cosmo Techno, and the evaluation device was measured by a solar cell evaluation system As-510-PV03 manufactured by NF Circuit Design Block. After measuring the initial characteristics, the photoelectric conversion element was left in a constant temperature bath at 85 ° C. for 4000 hours under vacuum storage. After being taken out, it was allowed to stand at room temperature for 24 hours, and the photoelectric conversion rate was measured in the same manner. The results are shown in Table 1.
Retention rate = (conversion efficiency after storage at 100 ° C. for 1000 hours / initial conversion efficiency) × 100

[Examples II-2 to II-9]
The organic hole transporting material and the basic compound in Example II-1 were identified as compound Nos. A photoelectric conversion device was prepared and evaluated in the same manner as in Example II-1, except that the compound was changed to the above compound. Table 1 shows the results.

[Example II-10]
The basic compound No. in Example II-1. A photoelectric conversion element was prepared and evaluated in the same manner as in Example II-1, except that 2-1 was changed to tert-butylpyridine (tBP: manufactured by Aldrich). Table 1 shows the results.

[Comparative Example 1]
The organic hole transport material compound No. in Example II-1. 1-1 is an organic hole transport material Spiro-MeOTAD (2,2 ', 7,7'-tetrakis (N, N-di-p-methoxyphenylamino) -9,9'-spirobifluorene (SHT-263, manufactured by Merck Ltd.) A photoelectric conversion device was prepared and evaluated in the same manner as in Example II-1, except that the above conditions were changed to (1).

[Comparative Example 2]
The organic hole transport material compound No. in Example II-1. A photoelectric conversion element was prepared and evaluated in the same manner as in Example II-1, except that 1-1 was changed to an organic hole transporting material having the following structure (X51, Dyenamo Corporation). Table 1 shows the results.

  The photoelectric conversion elements of Examples II-1 to II-10 using the hole transporting material represented by the general formula (1) have a slightly lower initial conversion efficiency than the photoelectric conversion elements of Comparative Examples 1 and 2. However, the conversion efficiency after 4000 hours at 85 ° C. was excellent, and the retention was very good. As is clear from the above, it is understood that the photoelectric conversion element of the present invention has excellent photoelectric conversion characteristics in a weak light environment and excellent storage stability at high temperatures.

JP-A-11-144773

Panasonic Technical Report, 56 (2008) 87 J. Am. Chem. Soc., 133 (2011) 18042 J. Am. Chem. Soc., 135 (2013) 7378 Bo Xu, et al., Adv. Mater., 2014 Fujikura Technical Report, 121 (2011) 42 ACS Appl. Mater. Interfaces, 2015, 7 (21), pp 11107-11116

Claims (6)

A hole transport material represented by the following general formula (1).
(In the formula, R _1, .R ₂ representing a methoxy group or an ethoxy group, a hydrogen atom, .R ₃ represent either a methyl group and methoxy group, represents a hydrogen atom or a methyl group.)   A photoelectric conversion element including a first electrode, a hole blocking layer, an electron transport layer, a hole transport layer, and a second electrode, wherein the hole transport layer includes the hole transport material according to claim 1. . The photoelectric conversion device according to claim 2, wherein the hole transport layer contains a basic compound represented by the following general formula (2).
(Wherein, R ₄ and R ₅ each independently represent an alkyl group or an aromatic hydrocarbon group, provided that R ₄ and R ₅ are bonded to each other to form a heterocyclic group containing a nitrogen atom. Including cases.)   The photoelectric conversion device according to claim 2, wherein the electron transport layer includes titanium oxide.   The photoelectric conversion element according to claim 2, wherein the hole blocking layer includes titanium oxide.   A solar cell comprising the photoelectric conversion element according to claim 2.