JP2011065751A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a complete solid photoelectric conversion element superior in long-time stability and productivity. <P>SOLUTION: In the photoelectric conversion element provided with a first electrode with an electron transport compound covered, a second electrode facing the electron transport compound of the first electrode, and a hole transport layer composed of a hole transport material between the electron transport compound of the first electrode and the second electrode, the hole transport layer is laminated with a compound having different molecular weight, and a hole transport material near a second electrode side is a polymer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion element.

  There are several types of solar cells, but most of them are diode type using silicon semiconductor junctions. These solar cells are currently expensive to manufacture, which is a factor that hinders their spread.

Recently, Graetzel et al. Of Lausanne University of Technology, Switzerland, announced the possibility of lowering costs, and the expectation for practical use has increased (for example, Patent Document 1, Non-Patent Document 1, 2).
The structure of this high-efficiency solar cell includes a porous metal oxide semiconductor provided on a transparent conductive glass substrate, a dye adsorbed on the surface thereof, an electrolyte having a redox pair, and a counter electrode.
Graetzel et al. Significantly improved the photoelectric conversion efficiency by making a metal oxide semiconductor electrode such as titanium oxide porous to increase the surface area, and by adsorbing a ruthenium complex as a dye on a single molecule basis.
However, since these solar cells use an electrolytic solution having a high vapor pressure such as acetonitrile, there is a problem in volatilization and leakage of the electrolytic solution.

In order to compensate for this drawback, the following completely solid dye-sensitized solar cell has been announced.
1) Using an inorganic semiconductor (for example, see Non-Patent Documents 3 and 4)
2) A material using a low molecular weight organic hole transport material (for example, see Patent Document 2, Non-Patent Documents 5 and 6)
3) Using conductive polymer (for example, see Patent Document 3 and Non-Patent Document 7)

In the solar cell described in Non-Patent Document 3, copper iodide is used as a constituent material of the p-type semiconductor layer.
However, there is a problem that the generated current is reduced due to deterioration due to an increase in crystal grains of copper iodide.
Therefore, in the solar cell described in Non-Patent Document 4, the crystallization of copper iodide is suppressed by adding an imidazolinium salt. However, long-term stability is lacking, and further improvement in durability is required. Yes.

A solid type solar cell using the organic hole transport material described in Non-Patent Document 5 has been reported by Hagen et al. And improved by Graetzel et al. (Non-Patent Document 6).
However, the conversion efficiency is very low as compared with the liquid electrolyte, and the solid solar cell using the triphenylamine compound described in Patent Document 2 forms a charge transport layer by vacuum-depositing the triphenylamine compound. ing. For this reason, the triphenylamine compound cannot reach the internal pores of the porous semiconductor, and only low conversion efficiency is obtained.

As a solid-state solar cell of a type using a conductive polymer, Osaka University Yanagida et al. Have reported that using polypyrrole (see Non-Patent Document 7).
However, even in these cases, the conversion efficiency is low, and the solid solar cell using the polythiophene derivative described in Patent Document 3 is provided with a charge transfer layer using an electrolytic polymerization method on a porous titanium oxide electrode adsorbed with a dye. However, there is a problem that the pigment is desorbed from the titanium oxide or the pigment is decomposed. Further, the polythiophene derivative has a very problem in durability.
As described above, none of the perfect solid-state photoelectric conversion elements that have been studied so far have been obtained with satisfactory characteristics.

  An object of the present invention is to solve the above-described problems, and to provide a complete solid-state photoelectric conversion element that is excellent in long-term stability and productivity as compared with the conventional one.

As a result of intensive studies to solve the above problems, it has been found that a high-performance photoelectric conversion element can be provided, and the present invention has been achieved.
The said subject is solved by following (1)-(9) of this invention.
(1) “a first electrode coated with an electron transporting compound, a second electrode facing the electron transporting compound of the first electrode, an electron transporting compound of the first electrode, and the second electrode In the photoelectric conversion element having a hole transport layer made of a hole transport material between the two layers, the hole transport layer is laminated with compounds having different molecular weights, and the hole transport material close to the second electrode side is a polymer. Photoelectric conversion element characterized by
(2) "The photoelectric conversion element according to (1) above, wherein the electron transporting compound is coated with a photosensitizer",
(3) "The photoelectric conversion element according to (1) or (2), wherein a metal oxide is present between the hole transport layer and the second electrode",
(4) "The photoelectric conversion element according to (3), wherein the metal oxide layer contains molybdenum oxide",
(5) "The photoelectric conversion element according to any one of (1) to (4) above, wherein the hole transport layer contains at least one of a metal compound and an ionic liquid" ,
(6) "The photoelectric conversion element according to (5) above, wherein the metal compound is one or more of a metal halide, a metal thiocyanide, and an amidation metal"
(7) "The photoelectric conversion element according to (6) above, wherein the ionic liquid is an imidazolinium compound",
(8) "The photoelectric conversion element according to any one of (1) to (7) above, wherein the electron transporting compound is an n-type oxide semiconductor",
(9) “The photoelectric conversion element according to (8), wherein the oxide semiconductor is selected from at least one of titanium oxide, zinc oxide, tin oxide, and niobium oxide”.

According to the configurations (1) to (4) of the present invention, a photoelectric conversion element having excellent cost performance and good conversion efficiency is provided.
According to the configurations (5) to (7), hole movement of the hole transport layer becomes efficient, and a photoelectric conversion element exhibiting further excellent conversion efficiency is provided.
With the configurations of (8) and (9) above, by using an n-type oxide semiconductor for the electron transport layer, electron transfer becomes efficient, and a photoelectric conversion element exhibiting excellent conversion efficiency is provided.

  According to the photoelectric conversion element of the present invention, a photoelectric conversion element having good characteristics can be obtained by laminating a hole transport material and providing a metal oxide layer between the hole transport compound layer and the second electrode. Is possible.

It is the schematic of an example showing the structure of the photoelectric conversion element which concerns on this invention. It is the schematic of another example showing the structure of the photoelectric conversion element which concerns on this invention.

The present invention will be described in detail below.
The structure of the photoelectric conversion element will be described with reference to FIGS.
1 and 2 are cross-sectional views of the photoelectric conversion element.
In the embodiment shown in FIG. 1, an electrode (3) is provided on a substrate (1), an electron transport layer (5) comprising a dense electron transport layer (6), a granular electron transport layer (7), and then the first A hole transport layer (8) composed of one hole transport material layer (9) and a second hole transport material layer (10) which is a polymer material is laminated, and a metal oxide layer (11), an electrode (3), The substrate (1) is sequentially provided.
In the embodiment shown in FIG. 2, an electrode (3) is provided on a substrate (1), an electron transport layer (5) comprising a dense electron transport layer (6), a granular electron transport layer (7), and then the first A structure in which a hole transport layer (8) composed of one hole transport material layer (9) and a second hole transport material layer (10) which is a polymer is laminated, and an electrode (3) and a substrate (1) are sequentially provided. Have taken.
A photoelectric conversion element generally comprises an electron collector electrode, an electron acceptor / electron transport layer (hereinafter simply referred to as an electron transport layer), an electron donor / hole transport layer (hereinafter simply referred to as a hole transport layer), and a hole current collector electrode. Is done.

The electron collecting electrode (4) used in the present invention is not particularly limited as long as it is a conductive material transparent to visible light, and is known for use in ordinary photoelectric conversion elements or liquid crystal panels. Can be used.
For example, indium tin oxide (hereinafter referred to as ITO), fluorine-doped tin oxide (hereinafter referred to as FTO), and the like can be given. Of these, FTO is preferred.
The thickness of the electron collector electrode is preferably 5 nm to 100 μm, more preferably 50 nm to 10 μm.
In addition, the electron collector electrode is preferably provided on a substrate made of a material transparent to visible light in order to maintain a certain hardness. For example, glass, a transparent plastic plate, a transparent plastic film, an inorganic transparent crystal, or the like is used. .

For example, FTO coated glass, ITO coated glass, zinc oxide: aluminum coated glass, FTO coated transparent plastic film, ITO coated transparent plastic film, etc. can be used. Is mentioned.
In addition, a transparent electrode obtained by doping cations or anions with different valences into tin oxide or indium oxide, or a metal electrode having a structure capable of transmitting light, such as a mesh shape or a stripe shape, provided on a substrate such as a glass substrate Good. These may be used singly or as a mixture of two or more kinds or laminated ones.
Further, a metal lead wire or the like may be used for the purpose of reducing the resistance of the substrate (1).
Examples of the material of the metal lead wire include metals such as aluminum, copper, silver, gold, platinum, and nickel. For example, the metal lead wire may be provided on the substrate by vapor deposition, sputtering, pressure bonding, or the like, and ITO or FTO may be provided thereon.

The photoelectric conversion element of this invention forms the thin film which consists of semiconductors as an electron carrying layer (5) on said electron current collection electrode (4).
The electron transport layer (5) has a laminated structure in which a dense electron transport layer (6) is formed on the electron collector electrode (4), and a porous electron transport layer (7) is further formed thereon. Preferably there is.
The dense electron transport layer (6) is formed for the purpose of preventing electronic contact between the electron collector electrode (4) and the hole transport layer (8). Therefore, if the electron current collecting electrode and the hole transport layer are not in physical contact, pinholes, cracks, or the like may be formed.
Moreover, although there is no restriction | limiting in the film thickness of this precise | minute electron carrying layer, 10 nm-1 micrometer are preferable and 20 nm-700 nm are more preferable.
The “dense” of the electron transport layer (6) means that the inorganic oxide semiconductor is filled at a higher density than the packing density of the semiconductor fine particles in the electron transport layer (7).

The porous electron transport layer (7) formed on the dense electron transport layer (6) may be a single layer or multiple layers.
In the case of multiple layers, a dispersion of semiconductor fine particles having different particle diameters can be applied in multiple layers, or different types of semiconductors, and application layers having different compositions of resins and additives can be applied in multiple layers.
Multi-layer coating is an effective means when the film thickness is insufficient with a single coating.
In general, as the film thickness of the electron transport layer increases, the amount of the photosensitized compound carried per unit projected area increases, so that the light capture rate increases. Loss due to coupling also increases. Therefore, the film 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 single semiconductor such as silicon or germanium, a compound semiconductor typified 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 oxides, cadmium, zinc, lead, silver, antimony, bismuth. Sulfide, cadmium, lead selenide, cadmium telluride and the like.
Other compound semiconductors are preferably phosphides such as zinc, gallium, indium, cadmium, gallium arsenide, copper-indium-selenide, copper-indium-sulfide, and the like.
As the compound having a perovskite structure, strontium titanate, calcium titanate, sodium titanate, barium titanate, potassium niobate and the like are preferable.
Among these, an oxide semiconductor is preferable, and titanium oxide, zinc oxide, tin oxide, and niobium oxide are particularly preferable, and 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.
Although there is no restriction | limiting in particular in the size of a semiconductor fine particle, 1-100 nm is preferable and, as for the average particle diameter of a primary particle, 5-50 nm is more preferable.
It is also possible to improve efficiency by mixing semiconductor fine particles having a larger average particle diameter and scattering incident light. In this case, the average particle size of the semiconductor is preferably 50 to 500 nm.

There is no restriction | limiting in particular in the preparation methods of an electron carrying layer, The method of forming a thin film in vacuum, such as sputtering, and the wet film forming method are mentioned.
In view of the manufacturing cost and the like, a wet film forming method is particularly preferable, and a method in which a paste in which semiconductor fine particle powder or sol is dispersed is prepared and applied onto an electron collecting electrode substrate is preferable.
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 wet printing methods such as relief printing, offset, gravure, intaglio printing, rubber printing, screen printing, etc. Can be used.

When a dispersion is prepared by mechanical pulverization or using a mill, it is formed by dispersing at least semiconductor fine particles alone or a mixture of semiconductor fine particles and a resin in water or an organic solvent.
As the resin used at this time, polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, acrylic acid ester, methacrylic acid ester, silicon resin, phenoxy resin, polysulfone resin, polyvinyl butyral resin, polyvinyl formal resin, Examples include polyester resin, cellulose ester resin, cellulose ether resin, urethane resin, phenol resin, epoxy resin, polycarbonate resin, polyarylate resin, polyamide resin, polyimide resin, and the like.

  Solvents for dispersing the semiconductor fine particles include water, alcohol solvents such as methanol, ethanol, isopropyl alcohol, and α-terpineol, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethyl formate, ethyl acetate, and n acetate. Ester solvents such as butyl, ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, etc. Amide solvents, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromo Halogenated hydrocarbon solvents such as benzene, iodobenzene or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o Examples thereof include hydrocarbon solvents such as xylene, m-xylene, p-xylene, ethylbenzene, and cumene. These can be used alone or as a mixed solvent of two or more.

In order to prevent re-aggregation of particles, a paste of semiconductor fine particles obtained by a dispersion of semiconductor fine particles or a sol-gel method is used, such as acids such as hydrochloric acid, nitric acid, acetic acid, polyoxyethylene (10) octylphenyl ether, etc. Surfactants, chelating agents such as acetylacetone, 2-aminoethanol, and ethylenediamine 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.

After the semiconductor fine particles are applied, the particles are brought into electronic contact with each other, and firing, microwave irradiation, electron beam irradiation, laser light irradiation, or press treatment is performed in order to improve film strength and adhesion to the substrate. It is preferable. These processes may be performed alone or in combination of two or more.
When firing, the range of the firing temperature is not particularly limited, but if the temperature is raised too much, the resistance of the substrate may be increased or the substrate may be melted. Moreover, although there is no restriction | limiting in particular also in baking time, 10 minutes-10 hours are preferable.
For the purpose of increasing the surface area of the semiconductor fine particles after firing and increasing the efficiency of electron injection from the photosensitizing compound to the semiconductor fine particles, for example, chemical plating using titanium tetrachloride aqueous solution or mixed solution with organic solvent, titanium trichloride Electrochemical plating using an aqueous solution may be performed.
Microwave irradiation may be performed from the electron transport layer forming side or from the back side.
Although there is no restriction | limiting in particular in irradiation time, It is preferable to carry out within 1 hour.
The press treatment is preferably 100 kg / cm ² or more, more preferably 1000 kg / cm ² . There is no particular limitation on the pressing time, but it is preferably within 1 hour. Further, heat may be applied during the pressing process.

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

In order to further improve the light conversion efficiency, it is preferable to adsorb the photosensitizing compound (12) on the electron transport layer.
The photosensitizing compound (12) is not particularly limited as long as it is a compound that is photoexcited by the excitation light used, and specific examples thereof include the following compounds.
The metal complex compounds described in JP 7-500630 A, JP 10-233238 A, JP 2000-26487 A, JP 2000-323191 A, JP 2001-59062 A, etc. 10-93118, JP-A No. 2002-164089, JP-A No. 2004-95450, J. Phys. Chem. C, 7224, Vol. 111 (2007), and the like. No. 95450, Chem. Commun., 4887 (2007), etc., JP 2003-264010 A, JP 2004-63274 A, JP 2004-115636 A, JP 2004-200068 A. J. Am. Chem. Soc., 12218, Vol. 126 (2004), Chem. Commun., 3036 (2003), Angew. Chem. Int. Ed., 1923, Vol. 47 (2008) etc. Compounds, J. Am. Chem. Soc., 16701, Vol. 128 (2006), thiophene compounds described in J. Am. Chem. Soc., 14256, Vol. 128 (2006), etc., JP-A-11-86916 Cyanine dyes described in JP-A-11-214730, JP-A-2000-106224, JP-A-2001-76773, JP-A-2003-7359, etc., JP-A-11-214731, Merocyanine dyes described in Kaihei 11-238905, JP-A-2001-52766, JP-A-2001-76775, JP-A-2003-7360, etc., JP-A-10-92477, JP-A-11-273754 , 9-arylxanthene compounds described in JP-A-11-273755, JP-A-2003-3273, etc., JP-A-10-93118, JP-A-2003-31273, etc. The described triarylmethane compounds, JP-A-9-199744, JP-A-10-233238, JP-A-11-204821, JP-A-11-265738, J. Phys. Chem., 2342, Vol.91 (1987), J. Phys. Chem. B, 6272, Vol. 97 (1993), Electroanal. Chem., 31, Vol. 537 (2002), JP 2006-032260, J. Porphyrins Phthalocyanines, 230, Examples include phthalocyanine compounds and porphyrin compounds described in Vol. 3 (1999), Angew. Chem. Int. Ed., 373, Vol. 46 (2007), Langmuir, 5436, Vol. 24 (2008), etc. .
Among these, it is particularly preferable to use metal complex compounds, coumarin compounds, polyene compounds, indoline compounds, and thiophene compounds.

As a method of adsorbing the photosensitizing compound (12) to the electron transport layer (7), a method of immersing an electron current collecting electrode containing semiconductor fine particles in a photosensitizing compound solution or dispersion, solution or dispersion Can be applied to the electron transport layer and adsorbed onto the electron transport layer.
In the former case, dipping method, dipping method, roller method, air knife method, etc. can be used, and in the latter case, wire bar method, slide hopper method, extrusion method, curtain method, spin method, spray method, etc. Can be used.
Further, it may be adsorbed in a supercritical fluid using carbon dioxide or the like.

When adsorbing the photosensitizing compound, a condensing agent may be used in combination.
The condensing agent has a catalytic action that seems to physically or chemically bond the photosensitizing compound and the electron transport compound to the inorganic surface, or acts stoichiometrically to favorably shift the chemical equilibrium. Either may be sufficient.
Furthermore, a thiol or a hydroxy compound may be added as a condensation aid.

  Solvents for dissolving or dispersing the photosensitizing compound are water, methanol, ethanol, alcohol solvents such as isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, or methyl isobutyl ketone, ethyl formate, ethyl acetate, or acetic acid. Ester solvents such as n-butyl, ether solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone Amido solvents, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromoben Halogenated hydrocarbon solvents such as ethylene, iodobenzene or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o Examples include hydrocarbon solvents such as -xylene, m-xylene, p-xylene, ethylbenzene, and cumene, and these can be used alone or as a mixture of two or more.

In addition, depending on the type of photosensitizing compound, there are compounds that work more effectively when aggregation between the compounds is suppressed, and therefore, an aggregation dissociator 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 according to the dye used. The addition amount of these aggregating and dissociating agents is preferably 0.01 to 500 parts by mass, more preferably 0.1 to 100 parts by mass with respect to 1 part by mass of the dye.

The temperature at which these are used to adsorb the photosensitizing compound or the photosensitizing compound and the aggregation / dissociation agent is preferably −50 ° C. or more and 200 ° C. or less.
Moreover, this adsorption may be carried out while standing or stirring.
Examples of the stirring method include, but are not limited to, a stirrer, a ball mill, a paint conditioner, a sand mill, an attritor, a disperser, and ultrasonic dispersion.
The time required for adsorption is preferably 5 seconds or more and 1000 hours or less, more preferably 10 seconds or more and 500 hours or less, and further preferably 1 minute or more and 150 hours.
Adsorption is preferably performed in a dark place.

The hole transport layer (8) in the present invention has a structure in which different hole transport material layers (9, 10) are laminated, and a polymer material is used for the hole transport material layer (10) close to the second electrode (3). Yes.
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 to penetrate into the porous electron transport layer, it is excellent in covering the surface of the porous electron transport layer, and also effective in preventing a short circuit when an electrode is provided. As a result, higher performance can be obtained.

  As the hole transporting compound used in the hole transporting layer (10) close to the second electrode (3), known hole transporting compounds are used, and specific examples thereof are shown in JP-B No. 34-5466. Oxadiazole compounds, triphenylmethane compounds shown in JP-B-45-555, pyrazoline compounds shown in JP-B-52-4188, JP-B-55-42380, etc. Hydrazone compounds shown, oxadiazole compounds shown in JP-A-56-123544, tetraarylbenzidine compounds shown in JP-A-54-58445, JP-A-58-65440 And stilbene compounds disclosed in JP-A-60-98437.

As the polymer material used for the hole transport layer (10) close to the second electrode (3), a known hole transport polymer material is used, and 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-dioctyl) Thieno [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) and other polythiophene compounds, poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylene vinylene], poly [2-methoxy-5- (3,7-dimethyloctyloxy) -1,4-phenylene vinylene], poly [(2-methoxy-5- (2-ethylphenyloxy) ) -1,4-phenylene vinylene) -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, -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 Polyfluorene compounds, poly [2,5-dioctyloxy-1,4-phenylene], poly [2,5-di (2-ethylhexyloxy-1,4-phenylene] and other polyphenylene compounds, poly [(9,9- Dioctylfluorenyl-2,7-diyl) -alt-co- (N, N′-diphenyl) -N, N′-di (p-hexylphenyl) -1,4-diaminobenzene], poly [(9 , 9-Diocti Rufluorenyl-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) phenyl Polyarylamine compounds such as mino-1,4-biphenylene], poly [(9,9-dioctylfluorenyl-2,7-diyl) -alt-co- (1,4-benzo (2,1 ′, And polythiadiazole compounds such as poly (3,4-didecylthiophene-co- (1,4-benzo (2,1 ′, 3) thiadiazole)).
Of these, polythiophene compounds and polyarylamine compounds are particularly preferred in consideration of carrier mobility and ionization potential.

Moreover, in the photoelectric conversion element of this invention, you may add various additives to the hole transport compound shown above.
Additives include iodine, lithium iodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide, copper iodide, iron iodide, silver iodide and other metal iodides, tetraalkylammonium iodide, Quaternary ammonium salts such as pyridinium iodide, metal bromides such as lithium bromide, sodium bromide, potassium bromide, cesium bromide and calcium bromide, quaternary ammonium compounds such as tetraalkylammonium bromide and pyridinium bromide Metal chlorides such as bromine salts, copper chloride and silver chloride, metal acetates such as copper acetate, silver acetate and palladium acetate, metal sulfates such as copper sulfate and zinc sulfate, ferrocyanate-ferricyanate, ferrocene -Sulfur compounds such as metal complexes such as ferricinium ions, sodium polysulfide, alkylthiol-alkyl disulfides Viologen dye, hydroquinone, 1,2-dimethyl-3-n-propylimidazolinium iodide, 1-methyl-3-n-hexylimidazolinium iodide, 1,2-dimethyl-3-ethylimidazo Inorg. Chem. 35 (1996) such as 1-methyl-3-butylimidazolium nonafluorobutylsulfonate, 1-methyl-3-ethylimidazolium bis (trifluoromethyl) sulfonylimide, and the like. The ionic liquid according to 1168, basic compounds such as pyridine, 4-t-butylpyridine and benzimidazole, and lithium compounds such as lithium trifluoromethanesulfonylimide and lithium diisopropylimide can be exemplified.

Moreover, you may add the oxidizing agent for making a part of hole transport compound into a radical cation for the purpose of improving electroconductivity.
As the oxidizing agent, tris (4-bromophenyl) aminium hexachloroantimonate, silver hexafluoroantimonate, nitrosonium tetrafluorate and the like are preferable.
It is not necessary for all hole transport materials to be oxidized by the addition of the oxidizing agent, and only a part of the hole transporting material needs to be oxidized. The added oxidizing agent may be taken out of the system after the addition or may not be taken out.

The hole transport layer (8) forms the hole transport layer (9, 10) directly on the electron transport layer (7) carrying the photosensitizing compound.
There is no restriction | limiting in particular in the preparation methods of a hole transport layer, The method of forming a thin film in vacuum, such as sputtering, and the wet film forming method are mentioned.
In consideration of the manufacturing 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 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 wet printing methods such as relief printing, offset, gravure, intaglio printing, rubber printing, screen printing, etc. Can be used. Moreover, you may inject | pour in a supercritical fluid or a subcritical fluid.

As a supercritical fluid, it exists as a non-aggregating high-density fluid in a temperature and pressure range that exceeds the limit (critical point) at which gas and liquid can coexist, and does not aggregate even when compressed. The fluid is not particularly limited as long as it is in the above state, and can be appropriately selected according to the purpose. However, a fluid having a low critical temperature is preferable.
This supercritical fluid includes, for example, carbon monoxide, carbon dioxide, ammonia, nitrogen, water, methanol, ethanol, ercol solvents such as n-butanol, ethane, propane, 2,3-dimethylbutane, benzene, toluene and the like. Hydrocarbon solvents, halogen solvents such as methylene chloride and chlorotrifluoromethane, and ether solvents such as dimethyl ether are preferred.
Among these, 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 in combination 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 according to the purpose.
The compound mentioned as a supercritical fluid mentioned above can be used conveniently also as a subcritical fluid.
The critical temperature and critical pressure of the supercritical fluid are not particularly limited and can be appropriately selected according to the purpose. However, the critical temperature is preferably −273 ° C. or more and 300 ° C. or less, particularly 0 ° C. or more and 200 ° C. or less. preferable.

Furthermore, in addition to the above supercritical fluid and subcritical fluid, an organic solvent or an entrainer can be used in combination.
By adding an organic solvent and an entrainer, the solubility in the supercritical fluid can be adjusted more easily.
Such an organic solvent is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethyl formate, ethyl acetate, and n acetate. Ester solvents such as -butyl, ether solvents such as diisopropyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone Amide solvents, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene Is a halogenated hydrocarbon solvent such as 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m- Examples thereof include hydrocarbon solvents such as xylene, p-xylene, ethylbenzene, and cumene.

  In the present invention, examples of the metal oxide that may be inserted between the hole transport compound and the second electrode include molybdenum oxide, tungsten oxide, vanadium oxide, and nickel oxide, and molybdenum oxide is particularly preferable.

There is no restriction | limiting in particular as a method of providing these metal oxides on a hole transport material, The method of forming a thin film in vacuum, such as sputtering and vacuum evaporation, and the wet film-forming method can be mentioned.
In the wet film forming method, it is preferable to prepare a paste in which a metal oxide powder or sol is dispersed and apply the paste onto 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 wet printing methods such as relief printing, offset, gravure, intaglio printing, rubber printing, screen printing, etc. Can be used. The film thickness is preferably from 0.1 to 50 nm, more preferably from 1 to 10 nm.

The hole collecting electrode is newly applied after the hole transport layer is formed or on the metal oxide.
In addition, the hole collecting electrode can be usually the same as the above-described electron collecting electrode, and the support is not necessarily required in a configuration in which the strength and the sealing performance are sufficiently maintained.
Specific examples of hole collecting electrode materials include metals such as platinum, gold, silver, copper, and aluminum, carbon compounds such as graphite, fullerene, and carbon nanotubes, conductive metal oxides such as ITO and FTO, polythiophene, and polyaniline. And conductive polymers such as
There is no restriction | limiting in particular in the film thickness of a hole current collection electrode layer, and you may use individually or in mixture of 2 or more types.
The hole collecting electrode can be applied by a method such as coating, laminating, vapor deposition, CVD, and bonding on the hole transport layer as appropriate depending on the type of material used and the type of hole transport layer.

In order to operate as a photoelectric conversion element, at least one of the electron collector electrode and the hole collector electrode must be substantially transparent.
In the photoelectric conversion element of the present invention, a method in which the electron collecting electrode side is transparent and sunlight is incident from the electron collecting electrode side is preferable. In this case, it is preferable to use a material that reflects light on the side of the hole collecting electrode, and a metal, glass, plastic, or metal thin film on which a conductive oxide is deposited is preferable.
It is also effective to provide an antireflection layer on the sunlight incident side.

The photoelectric conversion element of the present invention can be applied to a solar cell and a power supply device using the solar cell.
As an application example, any device can be used as long as it has conventionally used a solar cell or a power supply device using the solar cell.
For example, although it may be used for an electronic desk calculator or a solar cell for a wristwatch, examples of utilizing the characteristics of the photoelectric conversion element of the present invention include power supply devices such as a mobile phone, an electronic notebook, and 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.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, embodiment of this invention is not limited to these Examples.

(Production of titanium oxide semiconductor electrode)
Titanium tetra-n-propoxide (2 ml), acetic acid (4 ml), ion exchange water (1 ml), and 2-propanol (40 ml) were mixed, spin-coated on an FTO glass substrate, dried at room temperature, and baked at 450 ° C. for 30 minutes in air. Using the same solution again, it was applied on the obtained electrode by spin coating so as to have a film thickness of 100 nm, and baked in air at 450 ° C. for 30 minutes to form a dense electron transport layer.
Bead mill treatment with 3 g of titanium oxide (ST-21 manufactured by Ishihara Sangyo Co., Ltd.), 0.2 g of acetylacetone, and 0.3 g of surfactant (polyoxyethylene octylphenyl ether manufactured by Wako Pure Chemical Industries, Ltd.) together with 5.5 g of water and 1.0 g of ethanol 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 dense electron transport layer so as to have a film thickness of 2 μm, dried at room temperature, and then baked in air at 500 ° C. for 30 minutes to form a porous electron transport layer.

(Preparation of photoelectric conversion element)
N719 dye [cis-bis (isothiocyanato) bis (2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) −] prepared by adjusting the titanium oxide semiconductor electrode to 0.5 mM as a ruthenium complex. Bis-tetra-n-butylammonium, manufactured by Solaronix] in a mixed solution of acetonitrile / t-butanol (1: 1 by volume) at room temperature for 2 days to adsorb the photosensitizing compound. It was.

On a semiconductor electrode carrying a photosensitizer, trifluoromethanesulfonylimide lithium (27 mM) and 4-t-butylpyridine (0.11 M) were added to a chlorobenzene (solid content 10%) solution in which the compound (1) was dissolved. The solution obtained in addition was dropped on a semiconductor electrode carrying a photosensitizer and dried naturally.
Further, a solution obtained by adding trifluoromethanesulfonylimide lithium (27 mM) and 4-t-butylpyridine (0.11 M) to chlorobenzene (2% solids) in which the compound (2) was dissolved was obtained as a hole transport layer. A film was formed thereon by spin coating, and molybdenum oxide (5.0 nm) and silver (50.0 nm) were vacuum-deposited to produce a photoelectric conversion element. The photoelectric conversion efficiency of this photoelectric conversion element under pseudo-sunlight irradiation (AM1.5, 100 mW / cm ² ) is as follows: open-circuit voltage = 0.85V, short-circuit current density 3.9 mA / cm ² , form factor = 0.60, The conversion efficiency = 1.99% was excellent.

A device was prepared in the same manner as in Example 1 except that N719 was replaced with the compound (3) synthesized according to the method described in Chem. Commun., 3036 (2003), and the photoelectric conversion characteristics were measured.
As a result, it showed excellent characteristics of an open circuit voltage = 0.80 V, a short circuit current density of 4.2 mA / cm ² , a form factor = 0.60, and a conversion efficiency = 2.02%.

A device was produced in the same manner as in Example 1 except that trifluoromethanesulfonylimide lithium (27 mM) was replaced with 1-methyl-3-ethylimidazolium bis (trifluoromethyl) sulfonylimide (27 mM), and photoelectric conversion characteristics were obtained. Was measured.
As a result, the excellent characteristics of an open circuit voltage = 0.82 V, a short circuit current density of 3.6 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 1.74% were exhibited.

A device was prepared in the same manner as in Example 1 except that the compound (2) was replaced with the compound (4), and the photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.83 V, a short circuit current density of 3.8 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 1.86% were exhibited.

A device was prepared in the same manner as in Example 1 except that the compound (1) was replaced with the compound (5), and the photoelectric conversion characteristics were measured.
As a result, the excellent characteristics of an open circuit voltage = 0.83 V, a short circuit current density of 4.2 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 2.06% were exhibited.

A device was prepared in the same manner as in Example 1 except that the compound (1) was replaced with the compound (6), and the photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.78 V, a short circuit current density of 3.9 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 1.79% were exhibited.

A device was prepared in the same manner as in Example 1 except that molybdenum oxide was replaced with tungsten oxide, and the photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.75 V, a short circuit current density of 3.8 mA / cm ² , a form factor = 0.61, and a conversion efficiency = 1.74% were exhibited.

A device was prepared in the same manner as in Example 1 except that molybdenum oxide was replaced with vanadium oxide, and photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.78 V, a short circuit current density of 3.5 mA / cm ² , a form factor = 0.61, and a conversion efficiency = 1.67% were exhibited.

A device was prepared in the same manner as in Example 1 except that tris (4-bromophenyl) aminium hexachloroantimonate (0.2 mM) was added to the chlorobenzene solution of the compound (1) in Example 1, and the photoelectric conversion characteristics were obtained. It was measured.
As a result, excellent characteristics of an open circuit voltage = 0.74 V, a short circuit current density of 4.8 mA / cm ² , a form factor = 0.58, and a conversion efficiency = 2.06% were exhibited.

An element was prepared in the same manner as in Example 9 except that tris (4-bromophenyl) aminium hexachloroantimonate was replaced with silver hexafluoroantimonate, and photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.76 V, a short circuit current density of 4.7 mA / cm ² , a form factor = 0.58, and a conversion efficiency = 2.07% were exhibited.

A device was prepared in the same manner as in Example 1 except that iodine (2.5 mM) was added to the chlorobenzene solution of the compound (1) in Example 3, and the photoelectric conversion characteristics were measured.
As a result, it showed excellent characteristics of an open circuit voltage = 0.81 V, a short-circuit current density of 4.4 mA / cm ² , a form factor = 0.58, and a conversion efficiency = 2.07%.

An element was produced in the same manner as in Example 11 except that silver (50 nm) in Example 11 was replaced with gold (50 nm), and photoelectric conversion characteristics were measured.
As a result, excellent characteristics of an open circuit voltage = 0.83 V, a short-circuit current density of 4.3 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 2.11% were exhibited.

A device was prepared in the same manner as in Example 1 except that molybdenum oxide (5.0 nm) was not provided, and the photoelectric conversion characteristics were measured.
As a result, it showed excellent characteristics of an open circuit voltage = 0.86 V, a short circuit current density of 3.4 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 1.73%.

A device was prepared in the same manner as in Example 4 except that the compound (1) was replaced with the compound (7), and the photoelectric conversion characteristics were measured.
As a result, the excellent characteristics of an open circuit voltage = 0.80 V, a short circuit current density of 3.6 mA / cm ² , a form factor = 0.59, and a conversion efficiency = 1.70% were exhibited.

A device was prepared in the same manner as in Example 1 except that the compound (1) was replaced with poly (3-n-hexylthiophene), and the photoelectric conversion characteristics were measured.
As a result, it showed excellent characteristics of an open circuit voltage = 0.82 V, a short circuit current density of 4.3 mA / cm ² , a form factor = 0.60, and a conversion efficiency = 2.12%.

<Comparative Example 1>
A device was produced in the same manner as in Example 1 except that the hole transport layer comprising the compound (2) in Example 1 was not provided.
When the photoelectric conversion characteristics of the obtained device were measured in the same manner as in Example 1, the open circuit voltage = 0.57 V, the short-circuit current density 2.4 mA / cm ² , the form factor = 0.44, and the conversion efficiency = 0.62. %, Which is a characteristic lower than that of the present invention.

<Comparative Example 2>
A device was produced in the same manner as in Example 1 except that the hole transport layer comprising the compound (2) in Example 5 was not provided.
When the photoelectric conversion characteristics of the obtained device were measured in the same manner as in Example 1, the open circuit voltage = 0.55 V, the short-circuit current density 2.2 mA / cm ² , the form factor = 0.47, and the conversion efficiency = 0.57. %, Which is a characteristic lower than that of the present invention.

As apparent from the above, it can be seen that the photoelectric conversion element of the present invention exhibits high efficiency by providing a hole transport layer made of a polymer, as can be seen in Examples 1-15.
As shown in Examples 9 and 10, higher efficiency was obtained when a metal compound was added to the hole transport material, and an ionic liquid was used instead of the lithium compound as shown in Examples 3, 4, 11, and 12. It can be seen that even when used, it shows high efficiency.
Moreover, as shown in Example 13, although high conversion efficiency is shown even if a metal oxide layer is not inserted on the hole transport layer, higher efficiency can be obtained by insertion.

Japanese Patent No. 2664194 Japanese Patent Laid-Open No. 11-144773 JP 2000-106223 A

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Claims (9)

  A first electrode coated with an electron transporting compound; a second electrode facing the electron transporting compound of the first electrode; and between the electron transporting compound of the first electrode and the second electrode In a photoelectric conversion element having a hole transport layer made of a hole transport material, the hole transport layer is laminated with compounds having different molecular weights, and the hole transport material close to the second electrode side is a polymer. Photoelectric conversion element.   The photoelectric conversion element according to claim 1, wherein the electron transporting compound is coated with a photosensitizer.   The photoelectric conversion element according to claim 1, wherein a metal oxide is present between the hole transport layer and the second electrode.   The photoelectric conversion element according to claim 3, wherein the metal oxide layer contains molybdenum oxide.   5. The photoelectric conversion element according to claim 1, wherein the hole transport layer contains at least one of a metal compound and an ionic liquid.   6. The photoelectric conversion element according to claim 5, wherein the metal compound is at least one of a metal halide, a metal thiocyanide, and an amidated metal.   The photoelectric conversion element according to claim 6, wherein the ionic liquid is an imidazolinium compound.   The photoelectric conversion element according to claim 1, wherein the electron transporting compound is an n-type oxide semiconductor.   The photoelectric conversion element according to claim 8, wherein the oxide semiconductor is selected from at least one of titanium oxide, zinc oxide, tin oxide, and niobium oxide.

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