JP2013016360A - Photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element capable of realizing high output with an electrolyte containing water.SOLUTION: The photoelectric conversion element includes a photoelectric conversion layer (1), a counter electrode (2), and a charge transport layer (3) in which an electrolyte containing water, a metal complex, and an oxoammonium salt is included.

Description

  The present invention relates to a photoelectric conversion element.

  Conventionally, various solar cells have been proposed as photoelectric conversion elements that convert light energy into electrical energy. Among such solar cells, a dye-sensitized solar cell was developed by Gretzel et al. Of Lausanne University of Technology in Switzerland in 1991, and is generally a photoelectric conversion layer made of a semiconductor in which a dye is adsorbed on a conductive substrate. A counter electrode made of a conductive base material provided opposite to the semiconductor electrode, and a charge transport layer (electrolyte layer) held between the semiconductor electrode and the counter electrode. Become.

  Photoelectric conversion elements formed from a semiconductor electrode having a semiconductor layer adsorbed with a dye, a charge transport layer (electrolyte layer), a counter electrode, and the like can be applied to energy devices such as dye-sensitized solar cells and optical sensors. Expected. Among them, dye-sensitized solar cells are attracting wide attention because they exhibit high conversion efficiency among organic solar cells. As the semiconductor layer made of a photoelectric conversion material used in the dye-sensitized solar cell, a semiconductor layer in which a spectral sensitizing dye having absorption in the visible light region is adsorbed on the semiconductor surface is used.

  Conventionally, the charge transport layer (electrolyte layer) has been formed by injecting an electrolytic solution in which iodine / iodide ions are dissolved in an organic solvent between a semiconductor electrode and a counter electrode. For this reason, the composition of the electrolytic solution may change due to volatilization of the solvent, which may cause a problem in long-term stability. In addition, in an electrolyte containing an organic solvent, the manufacturing process must be performed in a non-aqueous environment, preferably in a dehydrated state. Therefore, the manufacturing process becomes complicated and the manufacturing cost required for environmental maintenance increases. There was a problem.

  The development of electrolytes containing water is eagerly desired. Thus, several inventions for replacing the organic solvent with water have been disclosed so far. Patent Documents 1 and 2 propose an electrolyte containing no organic solvent, specifically, an electrolytic solution containing lithium iodide, iodine and water. By using this, an electromotive force of about 0.7 V is proposed. Is obtained. However, when the solvent is changed from organic to water, the output tends to decrease. Although many patent documents suggest the use of an electrolyte containing water, there is no patent document that describes a highly efficient photoelectric conversion element using an electrolyte that actually contains water.

In recent years, Non-Patent Document 1 proposes an electrolytic solution in which 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radical is substituted for iodine / iodide ions. Gretzell et al. Proposed using the redox reaction of the TEMPO radical, but at the same time, the nitrosonium tetrafluoroborate (NOBF ₄ ), which is a deleterious reagent, does not work and cannot be handled safely. there were. Patent Documents 3 to 6 disclose dye-sensitized solar cells using a cyclic nitroxyl radical compound as an electrolyte.

In addition, an electrolytic solution using a redox species (reduced form) other than iodine has been reported. For example, in Non-Patent Document 2, acetonitrile (ACN) is used as an electrolyte solvent, and a metal complex (tris (2,2′-bipyridyl) cobalt (II)) is used as a redox species (reduced form). The redox species (oxidant) in this electrolyte is tris (2,2′-bipyridyl) cobalt (III) BF ₄ . This redox species (oxidant) is made by adding NOBF ₄ to the electrolyte and oxidizing the reduced redox species (tris (2,2′-bipyridyl) cobalt (II)) in the electrolyte. . According to Non-Patent Document 2, 7.2% is realized as the power generation efficiency of the dye-sensitized solar cell using this redox species.

JP 2003-308889 A JP 2003-308890 A JP 2009-021212 A JP 2009-076369 A JP 2009-098225 A JP 2010-205704 A

Z. Zhang, P. Chen, T. N. Murakami, S. M. Zakeeruddin, M. Gratzel, Adv. Funct. Mater. 2008, 18, 341 Sandra M. Feldt et.al., J.Am.Chem.Soc. 2010, 132, 16714

In the method using a metal complex redox compound instead of iodide ion, the method of adding NOBF ₄ is carried out as described above. However, since NOBF ₄ reacts violently with water, it is applied to an electrolyte containing water. It is difficult. On the other hand, the redox species of iodine ions (I ⁻ / I ₃ ⁻ ) applied to electrolytes containing water have not yet provided a highly efficient device.
Therefore, an object of the present invention is to provide a photoelectric conversion element having an electrolyte containing water capable of high output.

The photoelectric conversion element according to the present invention for solving the above problems is
A photoelectric conversion layer, a counter electrode, and a charge transport layer are provided, and the charge transport layer includes an electrolyte containing water, a metal complex, and an oxoammonium salt.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion element in which high output is possible using the electrolyte containing water can be provided.

1 is a schematic view of a photoelectric conversion element according to the present invention. The schematic cross section which shows the basic structure of the dye-sensitized solar cell which concerns on one Embodiment of the photoelectric conversion element of this invention. The figure which shows the specific example of the photoelectric conversion system which concerns on one Embodiment of the photoelectric conversion element of this invention. The schematic cross section which shows the structure of a W-type stack module as a photoelectric conversion element stack used for a photoelectric conversion system. The schematic cross section which shows the structure of an S-type stack module as a photoelectric conversion element stack used for a photoelectric conversion system. The schematic cross section which shows the structure of a Z-type stack module as a photoelectric conversion element stack used for a photoelectric conversion system. The schematic cross section which shows the structure of a grid wiring type stack module as a photoelectric conversion element stack used for a photoelectric conversion system. The figure which shows the circuit structural example of the optical sensor using the photoelectric conversion element of this invention. The graph which shows the result of the IV measurement in Example 1 and Comparative Example 1. The graph which shows the result of the IV measurement in Example 2 and Comparative Example 2.

  Hereinafter, embodiments of the photoelectric conversion element of the present invention will be described in detail with reference to the drawings. Note that various embodiments can be implemented within the scope of the present invention.

[First embodiment]
For example, as shown in FIG. 1, the photoelectric conversion element according to this embodiment includes a photoelectric conversion layer 1, a counter electrode 2, and a charge transport layer 3 that performs charge transport between the photoelectric conversion layer 1 and the counter electrode 2. And an electrolyte containing water, a metal complex, and an oxoammonium salt in the charge transport layer 3.

1. Photoelectric Conversion Layer The photoelectric conversion layer 1 usually has a structure in which a dye functioning as a photosensitizer is adsorbed on a semiconductor layer.

1-1. Semiconductor layer 1-1-1. Semiconductor Layer Material / Structure Semiconductor materials constituting the semiconductor layer include known semiconductors such as titanium oxide, zinc oxide, tungsten oxide, barium titanate, strontium titanate, and cadmium sulfide. Two or more kinds of these semiconductor materials can be mixed and used. Among these, titanium oxide is particularly preferable in terms of conversion efficiency, stability, and safety. Examples of such titanium oxide include anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, various titanium oxides such as metatitanic acid, orthotitanic acid, and titanium oxide-containing composites. Among these, anatase type titanium oxide is preferable.

  Examples of the shape of the semiconductor layer include a porous semiconductor layer obtained by sintering semiconductor fine particles, a thin-film semiconductor layer obtained by a sol-gel method, a sputtering method, a spray pyrolysis method, and the like, and other fibers. It can be appropriately selected according to the purpose of use of the photoelectric conversion element such as a semiconductor layer or a semiconductor layer made of needle crystals.

  The semiconductor layer of the present invention is preferably a semiconductor layer having a large specific surface area such as a porous semiconductor layer or a needle-like semiconductor layer from the viewpoint of the amount of dye adsorption. A porous semiconductor layer formed from semiconductor fine particles is preferable from the viewpoint that the utilization factor of incident light can be adjusted by the particle size of the semiconductor fine particles.

  Further, the semiconductor layer may be a single layer or a multilayer. By using a multilayer structure, a semiconductor layer having a sufficient thickness can be easily formed. The porous multilayer semiconductor layer may be composed of semiconductor fine particle layers having different average particle diameters. For example, by making the average particle size of the semiconductor fine particles constituting the semiconductor layer closer to the light incident side (first semiconductor layer) smaller than that of the farther semiconductor layer (second semiconductor layer), the first semiconductor layer A large amount of light is absorbed, and the light that has passed through the first semiconductor layer is scattered by the second semiconductor layer, returned to the first semiconductor layer, and absorbed by the first semiconductor layer, thereby improving the overall light absorption rate. be able to. Although the film thickness of a semiconductor layer is not specifically limited, About 0.5-45 micrometers is desirable from viewpoints, such as permeability | transmittance and conversion efficiency.

The specific surface area of the semiconductor layer is preferably 10 to ²⁰⁰ m ² / g in order to adsorb a large amount of dye. Further, the porosity is preferably 40 to 80% in order to adsorb the dye and to carry out charge transport by sufficiently diffusing ions in the electrolyte. Note that the porosity means the ratio of the volume occupied by the pores in the semiconductor layer in% in the volume of the semiconductor layer.

1-1-2. Next, a method for forming the semiconductor layer will be described by taking a porous semiconductor layer as an example. The porous semiconductor layer is prepared, for example, by adding a semiconductor fine particle together with an organic compound such as a polymer and a dispersing agent to a dispersion medium such as an organic solvent or water, and preparing a suspension, and using this suspension as a conductive support substrate It can be formed by coating on top, drying and firing.

  When an organic compound is added to the dispersion medium together with the semiconductor fine particles, the organic compound burns during firing, and a gap can be secured in the porous semiconductor layer. Moreover, the porosity can be changed by controlling the molecular weight and the addition amount of the organic compound combusted during firing. The type and amount of the organic compound can be appropriately selected and adjusted depending on the state of the fine particles used, the total weight of the entire suspension, and the like. However, when the proportion of the semiconductor fine particles is 10 wt% or more with respect to the total weight of the whole suspension, the strength of the produced film can be sufficiently increased, and the proportion of the semiconductor fine particles is the total weight of the whole suspension. If the amount is 40 wt% or less, a porous semiconductor layer having a large porosity can be obtained. Therefore, the ratio of the semiconductor fine particles is preferably 10 to 40 wt% with respect to the total weight of the entire suspension.

  Examples of the semiconductor fine particles include single or compound semiconductor particles having an appropriate average particle size, for example, an average particle size of about 1 nm to 500 nm. Among them, those having an average particle diameter of about 1 to 50 nm are preferable from the viewpoint of increasing the specific surface area. Moreover, you may add a semiconductor particle with a large average particle diameter of about 200-400 nm from the point of raising the utilization factor of incident light.

  Examples of the method for producing semiconductor fine particles include a sol-gel method such as a hydrothermal synthesis method, a sulfuric acid method, a chlorine method, and the like, and any method can be used as long as it can produce the desired fine particles. From the viewpoint of crystallinity, it is preferably produced by a hydrothermal synthesis method.

  Any organic compound can be used as long as it dissolves in the suspension and can be removed by burning when baked. Examples thereof include polymers such as polyethylene glycol and ethyl cellulose. Examples of the dispersion medium for the suspension include glyme solvents such as ethylene glycol monomethyl ether, alcohols such as isopropyl alcohol, mixed solvents such as isopropyl alcohol / toluene, and water.

  Examples of the method for applying the suspension include known methods such as a doctor blade method, a squeegee method, a spin coating method, and a screen printing method. Thereafter, the coating film is dried and fired. The drying and firing conditions may be about 10 seconds to 12 hours in the range of about 50 to 800 ° C. in the air or in an inert gas atmosphere. This drying and baking can be performed once at a single temperature or twice or more by changing the temperature.

  Although the method for forming the porous semiconductor layer has been described in detail here, other types of semiconductor layers can also be formed using various known methods.

1-2. Photosensitizer In the present invention, a dye can be used as a photosensitizer. A dye functioning as a photosensitizer (hereinafter simply referred to as “dye”) has absorption in various visible light regions and infrared light regions, and is strongly adsorbed to the semiconductor layer. Those having an interlock group such as a COOH group, an alkoxy group, a hydroxyl group, a hydroxyalkyl group, a sulfonic acid group, an ester group, a mercapto group, and a phosphonyl group in the dye molecule are preferable. Of these, those having a COOH group are particularly preferred.

  The interlock group provides an electrical bond that facilitates electron transfer between the excited dye and the semiconductor conduction band. Examples of the dye containing an interlock group include a ruthenium metal complex dye (such as a ruthenium bipyridine metal complex dye, a ruthenium terpyridine metal complex dye, and a ruthenium quarterpyridine metal complex dye), an azo dye, and a quinone dye. Quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, porphyrin dyes, phthalocyanine dyes, perylene dyes, indigo dyes, naphthalocyanine dyes Examples thereof include dyes and coumarin dyes. Of these, organic dyes are preferred.

  Examples of the method for adsorbing the dye on the semiconductor layer include a method in which a semiconductor layer formed on a substrate is immersed in a solution in which the dye is dissolved. Solvents used to dissolve the dye include alcohols such as ethanol, ketones such as acetone, ethers such as diethyl ether and tetrahydrofuran, nitrogen compounds such as acetonitrile, halogenated aliphatic hydrocarbons such as chloroform, and hexane. Examples thereof include aliphatic hydrocarbons, aromatic hydrocarbons such as benzene, and esters such as ethyl acetate. These solvents may be used as a mixture of two or more.

The dye concentration in the solution can be adjusted as appropriate depending on the type of the dye and the solvent to be used. In order to improve the adsorption function, it is preferable that the concentration is somewhat high. For example, the concentration can be 5 × 10 ⁻⁵ mol / L or more.

  When the semiconductor is immersed in the solution in which the dye is dissolved, the temperature and pressure of the solution and the atmosphere are not particularly limited, and examples include room temperature and atmospheric pressure, and the immersion time is the dye and solvent to be used. It can be appropriately adjusted depending on the kind of the solution, the concentration of the solution, and the like. In order to effectively perform the immersion, the immersion may be performed under heating. Thereby, a pigment | dye can be made to adsorb | suck to a semiconductor layer.

When adsorbing the dye, deoxycholic acid or guanidine is added to the solution in which the dye is dissolved in order to control the dye and its adsorption state, the surface of fine particles such as TiO ₂ constituting the porous semiconductor layer, and the like. Organic compounds such as thiocyanate, tert-butylpyridine, ethanol, and the like may be added.
As a photosensitizer, semiconductor fine particles, so-called quantum dots, can be used instead of a dye.

2. Counter electrode Examples of the counter electrode 2 include those having a metal catalyst such as platinum or a carbon film. In particular, platinum is preferable. These film thicknesses should just be the thickness which can express a catalyst function, and about 1-2000 nm is desirable.

3. Charge Transport Layer The charge transport layer 3 according to the present invention includes an electrolyte containing water, a metal complex, and an oxoammonium salt.
3-1. Metal Complex As the metal complex, one that is stable in a liquid medium containing water is selected from known metal complexes that can be used in dye-sensitized solar cells.

  In particular, a metal complex having a metal atom selected from Group 8 to 10 elements (formerly Group 8B) of the Periodic Table as the metal atom is preferable, and in particular, a metal complex containing a metal atom selected from Fe, Co, Ni, Os. More preferred. For example, iron complexes that form redox pairs such as ferrocyanate / ferricyanate and ferrocene / ferricinium ions are known as metal complexes containing Fe. Examples of the metal complex containing Co include cobalt complexes described in Non-Patent Document 2, J. AM. CHEM. SOC. 2002, 124, 11215-11222 (the following formulas (1-a) to (1-c)). And cobaltcene. Examples of the metal complex containing Ni include nickel complexes and nickelocene described in J. AM. CHEM. SOC. 2010, 132, 4580-4582. Examples of the metal complex containing Os include osmocene.

  Among these, metallocenes that are metal bispentadienyl complexes, such as ferrocene, cobaltcene, nickelocene, osmocene, and derivatives thereof are preferable, and ferrocene is particularly preferable.

  It is preferable that at least a part of the metal complex in the charge transport layer 3 forms an oxidation-reduction pair (redox pair) in the charge transport layer 3. For example, ferrocene shows an equilibrium state between ferricinium ion (oxidized substance) and ferrocene (reduced form) as shown in the following formula (2).

  Note that at least a part of the metal complex contained in the electrolyte needs to form a redox pair, and all of the metal complexes to be added need not form a redox pair.

3-2. Oxoammonium salt An oxoammonium salt consists of an oxoammonium cation represented by> N ⁺ = O and an anion represented by X ⁻ . Specifically, a cyclic oxoammonium salt represented by the following formula is preferable.

(In General Formula (3), A is a divalent group constituting a 5- to 7-membered heterocyclic ring together with the nitrogen atom of nitroxide and the two carbon atoms to which R ^{1 to} R ⁴ are bonded, R ¹ , R ² , R ³ , R ⁴ may be the same or different and each represents a substituted or unsubstituted alkyl group, where X is a metal chloride, fluorine, chlorine , Bromine, iodine, BF ₄ , PF ₆ , CF ₃ SO _3, N (SO ₂ CF ₃ ) ₂ , N (SO ₂ F) ₂ , CF ₃ COO, N (C ₂ F ₅ SO ₂ ), or ClO ₄ Is shown.)

In the formula, the divalent group represented by A is a group that forms a 5- to 7-membered heterocyclic ring together with the nitrogen atom of nitroxide and the two carbon atoms to which R ^{1 to} R ⁴ are bonded, A C2-C4 alkylene group or alkenylene group can be illustrated. In addition, some of the carbon atoms of the alkylene group may be replaced with oxygen atoms, nitrogen atoms, sulfur atoms, silicon atoms, phosphorus atoms, or boron atoms. Each carbon atom of the alkylene group may have a substituent, such as an aliphatic group, aromatic group, hydroxyl group, alkoxy group, aldehyde group, carboxyl group, alkoxycarbonyl group, cyano group, amino group, nitro group. Group, nitroso group and the like. Examples of the substituent in the substituted alkyl group represented by R ¹ , R ² , R ³ , or R ⁴ include the substituents that A may have. R ¹ , R ² , R ³ and R ⁴ are preferably each independently a linear alkyl group. Moreover, from a viewpoint of stability, a C1-C4 unsubstituted alkyl group, especially a methyl group are preferable.

  Preferably, A is an oxoammonium salt represented by the following general formula (4), which is a propylene chain forming a 6-membered ring.

(In the general formula (4), R ^{1 to} R ⁴ and X have the same meaning as in the general formula (3), and R ⁵ and R ⁶ are each independently a hydrogen atom, aliphatic group, aromatic group, hydroxyl group. , An alkoxy group, an aldehyde group, a carboxyl group, an alkoxycarbonyl group, a cyano group, an amino group, a nitro group, and a nitroso group, and C = O may be formed by a carbon atom bonded to R ⁵ and R ^6. In addition, R ⁵ and R ⁶ may be bonded to form a cyclic structure.)

  In addition, in the charge transport layer 3, a part of the oxoammonium salt supplies an anion to the metal complex, and a redox pair showing an equilibrium state between the nitroxyl radical and the nitroxyl cation as shown in the following formula (5). It may be formed.

  Examples of such oxoammonium salts are preferably 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radicals represented by the following formulas (6) to (9) and oxoammonium salts of derivatives thereof. Can be mentioned.

  By simultaneously containing a metal complex and an oxoammonium salt in a liquid medium containing water, for example, a reduced redox species such as ferrocene is an oxidized redox species such as ferricinium ion as shown in the above formula (2). Can be oxidized to. Since the oxoammonium salt exists stably in water, it can be suitably used for an electrolyte containing water.

3-3. Electrolyte Solution The charge transport layer 3 contains the above-described metal complex and oxoammonium salt, and includes a liquid electrolyte (electrolyte solution). This electrolytic solution contains water as a solvent. The electrolytic solution may also be contained in the porous semiconductor layer and the counter electrode.

  Moreover, an organic solvent can be appropriately added to the electrolytic solution. For example, as an organic solvent to be added, nitrogen-containing compounds such as N-methylpyrrolidone and N, N-dimethylformamide, nitrile compounds such as methoxypropionitrile and acetonitrile, lactone compounds such as γ-butyrolactone and valerolactone, ethylene carbonate , Carbonate compounds such as diethyl carbonate, dimethyl carbonate, propylene carbonate, ethers such as tetrahydrofuran, dioxane, diethyl ether, ethylene glycol dialkyl ether, alcohols such as methanol, ethanol, isopropyl alcohol, and further imidazoles, etc. These can be used alone or in admixture of two or more. In particular, when the solubility of the metal complex or oxoammonium salt in water is low, it is preferable to include an organic solvent capable of dissolving them.

3-4. Electrolytic Solution Preparation Method In order for the metal complex and the oxoammonium salt according to the present invention to be simultaneously present in the electrolytic solution, there is a method in which each is dissolved in water. However, in the case of a material having poor solubility in water, a method in which the material is compatible with water in advance and the material is dissolved in a soluble solvent and mixed with water can be used. As usage-amount of water, 50 Vol% or more is preferable with respect to the whole solvent, and 70 Vol% or more is more preferable.

  Furthermore, as a method for preparing the electrolytic solution, a method of dissolving the metal complex and the oxoammonium salt in water, a method of mixing an aqueous solution in which one of the metal complex and the oxoammonium salt is dissolved, and an organic solvent in which the other is dissolved, or And a method of dissolving a metal complex and an oxoammonium salt in a mixed solvent of water and an organic solvent.

Second Embodiment Next, a dye-sensitized solar cell will be described as an embodiment of the photoelectric conversion element of the present invention.
FIG. 2 is a schematic cross-sectional view showing the basic structure of a dye-sensitized solar cell according to an embodiment of the photoelectric conversion element of the present invention. As shown in the figure, this dye-sensitized solar cell includes a transparent substrate (11) having light transmittance, a transparent conductive film (12) having light transmittance formed on the surface of the transparent substrate (11), and A semiconductor electrode (18) composed of a photoelectric conversion layer (13), which is a porous semiconductor layer adsorbing a dye formed on the transparent conductive film (12), and provided at a position facing the semiconductor electrode (18). A counter electrode (19), and a charge transport layer (14) held between the semiconductor electrode (18) and the counter electrode (19). The counter electrode (19) is made of a transparent substrate or support substrate (17) on which a conductive film (16) is formed, and a platinum catalyst layer (15) is formed on the surface of the conductive film (16). The charge transport layer (14) includes an electrolyte containing water, a metal complex, and an oxoammonium salt. In the present invention, a layer containing an electrolyte may be referred to as an electrolyte layer.

  In the dye-sensitized solar cell having this structure, when light (sunlight) is irradiated from the transparent substrate (11) side, the light passes through the transparent substrate (11) and the transparent conductive film (12), and photoelectric The dye adsorbed on the conversion layer (13) is irradiated, and the dye absorbs light and is excited. Electrons generated by this excitation move from the photoelectric conversion layer (13) to the transparent conductive film (12). The electrons moved to the transparent conductive film (12) move to the counter electrode (19) through the external circuit, and return to the dye from the counter electrode (19) through the charge transport layer (14). In this way, current flows and photoelectric conversion (power generation) can be performed.

Semiconductor electrode (18)
Transparent substrate (11)
Examples of the transparent substrate include highly transparent substrates such as a glass substrate and a plastic substrate.

Transparent conductive film (12)
Type of transparent conductive film formed on the transparent substrate (11) (12) include, but are not limited to, for example ITO, FTO, a transparent conductive film made of a metal oxide such as SnO ₂ preferred. The production method and film thickness of the transparent conductive film can be selected as appropriate, but those having a film thickness of about 1 nm to 5 μm can be used.

Photoelectric conversion layer (13)
As the photoelectric conversion layer, a layer obtained by adsorbing a dye to the semiconductor layer described in the first embodiment can be suitably used.

Charge transport layer (14)
The charge transport layer (14) includes an electrolytic solution in which the metal complex and oxoammonium salt exemplified in the first embodiment are dissolved in a liquid medium mainly containing water as a solvent.

  In addition, an ionic liquid, that is, a molten salt can be appropriately added to the electrolytic solution. Examples of the ionic liquid are disclosed in “Inorg. Chem.” 1996, 35, p1168-1178, “Electrochemistry” 2002.2, p130-136, JP-T-9-507334, JP-A-8-259543, and the like. Although it will not specifically limit if it can generally be used in the well-known battery, solar cell, etc. which have a melting point lower than room temperature (25 degreeC) or higher than room temperature However, a salt that liquefies at room temperature by dissolving other molten salt or additives other than the molten salt is preferably used.

Specifically, as the cation of the molten salt, ammonium, imidazolium, oxazolium, thiazolium, piperidinium, pyrazolium, isoxazolium, thiadiazolium, oxadiazolium, triazolium, pyrrolidinium, pyridinium, pyrimidinium, pyridazinium, pyrazinium, Triazinium, phosphonium, sulfonium, carbazolium, indolium, and derivatives thereof are preferable, and ammonium, imidazolium, pyridinium, piperidinium, pyrazolium, and sulfonium are particularly preferable. The anion of the molten salt includes metal chlorides such as AlCl ₄ ⁻ and Al ₂ Cl ₇ ^— , PF ₆ ⁻ , BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , CF _3. Fluorine-containing materials such as COO ⁻ , NO ₃ ⁻ , CH ₃ COO ⁻ , C ₆ H ₁₁ COO ⁻ , CH ₃ OSO ₃ ⁻ , CH ₃ OSO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CH ₃ SO ₂ ⁻ , (CH Non-fluorine compounds such as ₃ O) ₂ PO ₂ ^— , chlorine, bromine. And halides such as iodine.

  The molten salt can be synthesized by methods known in various literatures and publications. Taking a quaternary ammonium salt as an example, a quaternization of an amine is performed using a tertiary amine as an alkylating agent as an alkylating agent as a first step, and an ion exchange from a halide anion to a target anion is performed as a second step. Can be used. Alternatively, there is a method in which a tertiary amine is reacted with an acid having a target anion to obtain the target compound in one step.

  The charge transport layer may contain a gel electrolyte or a solid electrolyte in addition to the electrolyte solution. As such a gel electrolyte or solid electrolyte, a polymer of a cyclic nitroxyl radical represented by the following general formula (10) can be used.

(In the formula, E, R ¹ , R ² , R ³ and R ⁴ represent the same meaning as A, R ¹ , R ² , R ³ and R ^{4 in the} general formula (3), and R ⁷ represents oxygen. An atom or a carbonyloxy group, R ⁸ , R ⁹ and R ¹⁰ represent a hydrogen atom or an alkyl group, n represents an integer of 10 or more and 10,000 or less, and * represents a bond.

  The polymer may be a homopolymer or a copolymer. The copolymer may be a block copolymer or a random copolymer. Preferred examples of these polymers include TEMPO polymers as shown in the following formulas (11) to (13).

  In addition to the nitroxyl radical polymer, a polymer compound for solidifying the liquid electrolyte may be used. It is not particularly limited as long as it is a polymer compound that can hold a liquid electrolyte, and includes a compound having a polyoxyalkylene chain, and can be gelled or solidified, and usually a polymer precursor having a polyoxyalkylene chain. The body (polymer gelling agent) is used. For example, (i) alkylenes such as trifunctional terminal acryloyl modified alkylene oxide polymers and tetrafunctional terminal acryloyl modified alkylene oxide polymers disclosed in JP-A-5-109311 and JP-A-11-176442 Examples include acryloyl-modified polymer compounds having an oxide polymer chain. (B) In addition, it contains compound A having at least one type of isocyanate group and compound B that is reactive with at least one type of isocyanate group, and at least one of compound A and compound B has a polyoxyalkylene chain. (See JP 2002-289271 A, etc.). As the compound having a polyoxyalkylene chain, a compound having a polymer structure having a molecular weight of 500 to 50,000 is preferably used.

  The trifunctional or tetrafunctional terminal acryloyl-modified alkylene oxide polymer (i) is, for example, glycerol or trimethylolpropane in the case of trifunctional, diglycerin or pentaerythritol in the case of tetrafunctional. Etc. as starting materials, alkylene oxides such as ethylene oxide and propylene oxide are added thereto, and an unsaturated organic acid such as acrylic acid and methacrylic acid is further esterified, or acrylic acid chloride and methacrylic acid chloride It is a compound obtained by carrying out dehydrochlorination reaction of acid chlorides, such as.

  Examples of (B) compound A include aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and xylylene diisocyanate; aliphatic isocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; fats such as isophorone diisocyanate and cyclohexyl diisocyanate. Examples thereof include cyclic isocyanates, which may be multimers such as dimers and trimers, or modified products. Further, low molecular alcohols and adducts of these isocyanates, and compounds obtained by addition reaction of polyoxyalkylene and these isocyanates in advance are also included. Examples of the compound B include compounds having an active hydrogen group such as a carboxyl group, a hydroxyl group, and an amino group. More specifically, examples of the compound having a carboxyl group include hexanoic acid, adipic acid, phthalic acid, and azelaic acid. Carboxylic acids such as: hydroxyl group-containing compounds such as ethylene glycol, diethylene glycol, glycerin, pentaerythritol, sorbitol, sucrose polyols; amino group-containing compounds such as ethylenediamine, tolylenediamine, diphenylmethanediamine, diethylenetriamine, etc. These organic amines are listed. Compound B also includes a compound having one or more active hydrogen groups as described above in one molecule and a polyoxyalkylene chain.

Stabilizing additive The metal complex in the electrolyte is oxidized and reduced in an oxidized state and a reduced state, as shown in the above-mentioned formula (2). Further, a part of the oxoammonium salt may be added to the electrolyte for the purpose of stabilizing the above-mentioned formula nitroxyl radical and its oxidation state (cationic state). As a salt to be used, as a cation, lithium, sodium, potassium, ammonium, imidazolium, oxazolium, thiazolium, piperidinium, pyrazolium, isoxazolium, thiadiazolium, oxadiazolium, triazolium, pyrrolidinium, pyridinium, pyrimidinium, pyridazinium, Pyrazinium, triazinium, phosphonium, sulfonium, carbazolium, indolium, and derivatives thereof are preferable, and ammonium, imidazolium, pyridinium, piperidinium, pyrazolium, and sulfonium are particularly preferable. As anions, fluorine-containing materials such as PF ₆ ⁻ , BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , F (HF) _n ⁻ and CF ₃ COO ⁻ , NO ₃ ⁻ , CH ₃ COO ⁻ , C ₆ H ₁₁ COO ⁻ , CH ₃ OSO ₃ ⁻ , CH ₃ OSO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CH ₃ SO ₂ ⁻ , (CH ₃ O) ₂ PO ₂ ⁻ , SbCl ₆ ⁻ And non-fluorine compounds such as iodine, bromine and the like. The aforementioned molten salt may function as a stabilizing additive.

  The charge transport layer may include a porous insulating material such as a separator. By impregnating the separator with the above electrolytic solution, the photoelectric conversion layer and the counter electrode can be prevented from being in direct contact with each other, and charge transport between the two can be performed.

Counter electrode (19)
Examples of the support substrate (17) include glass, a polymer film, a semiconductor substrate such as Si, and a metal plate (foil). When light is also incident from the counter electrode, a highly transparent substrate is used. In the case of a conductive substrate, the conductive film (16) can be omitted.

  When the support substrate (17) is insulative or semi-insulating, a conductive film (16) is provided. The conductive film (16) is preferably a material resistant to an electrolyte containing water, and a metal oxide conductive material used for the transparent conductive film (12) is preferably used.

  The platinum catalyst layer (15) formed on the surface of the conductive film (16) may be formed in a film shape on the entire surface or a part of the conductive film (16). The platinum catalyst layer is formed to a thickness capable of exhibiting a catalytic function, for example, about 1 to 2000 nm.

  In the above description, an example in which the photoelectric conversion layer (13) and the platinum catalyst layer (15) are formed on different substrates has been described. However, on the transparent substrate (11) having the same transparent conductive film (12), After providing the conversion layer (13) and the platinum catalyst layer (15), the transparent conductive film (12) between them may be cut by laser scribing or the like to obtain a lateral electric field type element.

(Other embodiments)
A plurality of photoelectric conversion elements according to the present invention can be combined and used as a photoelectric conversion element stack in a photoelectric conversion (photovoltaic power generation) system.
FIG. 3 is a diagram illustrating a specific example of the photoelectric conversion system. In the photoelectric conversion system 150 illustrated in FIG. 3, electrons generated in the photoelectric conversion element stack 100 move to the battery 154 via the charge / discharge control device 152. A load 153 that is driven by a direct current is connected to the charge / discharge control device 152. Further, the direct current from the battery 154 is DA-converted by the inverter 155 and flows to the load 156 driven by the alternating current.

  Although there is no restriction | limiting in particular in the structure of the photoelectric conversion element stack 100, For example, a structure like FIGS. 4-7 can be illustrated. 4 to 7 are cross-sectional views illustrating a configuration example of the photoelectric conversion element stack 100.

FIG. 4 shows a W-type stack module 101.
In FIG. 4, a plurality of photoelectric conversion elements each including a photoelectric conversion layer 161, an electrolyte (charge transport layer) 163, and a counter electrode (counter electrode) 162 are disposed between the transparent substrate 163 and the transparent substrate 164. . The photoelectric conversion layer 161 is, for example, the photoelectric conversion layer 13 described in the second embodiment. A transparent conductive film 166 and a transparent conductive film 167 are provided between the transparent substrate 163 and the photoelectric conversion layer 161 and between the transparent substrate 164 and the counter electrode 162, respectively. These transparent conductive films are provided in common to the photoelectric conversion layer 161 of one element and the counter electrode 162 of the adjacent element, and the adjacent elements are connected. Further, the space between the plurality of transparent conductive films 166 and the space between the transparent conductive films 167 are sealed with a sealing material 170 made of an insulating material. The transparent conductive film 166 is connected to the anode (minus electrode) 168 and the cathode (plus electrode) 169 at both ends.

FIG. 5 shows an S-type stack module 102.
In FIG. 5, the photoelectric conversion layer 161 is provided on the transparent conductive film 166, the separator 171 that covers the photoelectric conversion layer 161 from the upper surface to the side surface of the photoelectric conversion layer 161, and the counter electrode 162 that covers the entire surface of the separator 171. The space is filled with the electrolytic solution 163 to constitute an element. Also in FIG. 5, the photoelectric conversion layer 161 and the other counter electrode 162 of one adjacent element are disposed on one transparent substrate 163 via a common transparent conductive film 166.

FIG. 6 shows a Z-type stack module 103.
Although the basic configuration of FIG. 6 is common to the W type shown in FIG. 4, in FIG. 6, a plurality of transparent conductive films 165 and transparent conductive films 166 are provided for each element. The photoelectrode 167 of one adjacent element is connected to the counter electrode 169 of the other element through the transparent conductive film 166, the conductive sealant 172, and the transparent conductive film 165 of the other element. The outer periphery of the side surface of the conductive sealing material 172 is covered with the sealing material 170 except for the area in contact with the transparent conductive film 165 and the transparent conductive film 166.

The W, S, and Z types shown in FIGS. 4 to 6 are stack modules in which small cells are connected in series, but may be a grid wiring type module 104 as shown in FIG.
In FIG. 7, an electrolytic solution 163, a transparent conductive film 166, and a transparent conductive film 167 are provided in common for a plurality of elements, and metal is placed at predetermined positions on the transparent conductive film 166 and the transparent conductive film 167. Current collection wiring 174 is arranged. The metal current collector wiring 174 is covered with an insulating film 173 and insulated from the electrolyte solution 163.

  The grid wiring type module 104 is a module that can further reduce the current collection loss when the area of one cell is increased. The grid wiring type can be stacked in Z, W, or S type.

  4 to 7, light enters from the photoelectric conversion layer 161 side. In the W type shown in FIG. 4, light is incident on both sides. By using a highly light-transmitting substrate as the substrate on the counter electrode 162 side, light can be incident from both sides.

  4 to 7 show an example in which the transparent substrate 163 and the transparent substrate 164 are used as the substrate. For example, a material having no transparency may be used for the substrate on the opposite pole side of the W, S, and grid wiring type. Available. Examples of such a material include a resin substrate such as PEEK, a metal substrate such as SUS, and a semiconductor substrate such as Si.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

  For example, the photoelectric conversion element in the present embodiment can be used not only for a solar battery but also for an optical sensor. FIG. 8 is a diagram illustrating a configuration example of a circuit of an optical sensor including the photoelectric conversion element 200.

  Hereinafter, the present invention will be specifically described by way of examples, but the scope of the present invention is not limited thereto. A dye-sensitized solar cell having the laminated structure shown in FIG. 2 was produced as follows.

Example 1
1. Formation of Semiconductor Layer The semiconductor layer was produced by the following procedure. First, 20 mL of an acetic acid aqueous solution having a concentration of 15 vol% was used as a solvent, and 5 g of commercially available titanium oxide powder (P25, Nippon Aerosil Co., Ltd.), 0.1 mL of a surfactant (polyoxyethylene-p-isooctylphenol (trade name: “Triton X-100” (manufactured by Sigma-Aldrich) and 0.3 g of polyethylene glycol (molecular weight 20000) were added, and the mixture was stirred with a stirring mixer for about 1 hour (once for 10 minutes) to prepare a titanium oxide paste.
Next, a glass substrate (2 cm × 1.5 cm, sheet resistance: 10Ω / □) on which a glass substrate was used as the transparent substrate (11) and ITO was sputter-deposited as the transparent conductive film (12) was prepared. This glass substrate was heated to 450 ° C. with a hot plate, and a TAA (diisopropoxytitanium bisacetylacetonate: Sigma-Aldrich) ethanol solution (2 × 10 ⁻² mol / L) was applied 10 times by a spray method.
Next, an appropriate amount of the above titanium oxide paste was applied onto the ITO film of the glass substrate by a doctor blade method so that the film thickness was about 5 μm (application area: 5 mm × 5 mm). This electrode was inserted into an electric furnace and baked at 450 ° C. for about 30 minutes in an air atmosphere to obtain a semiconductor electrode (18).

2. Adsorption of Dye A dye represented by the following formula (trade name “D149”, manufactured by Mitsubishi Paper Industries Co., Ltd.) was dissolved in acetonitrile at a concentration of 3 × 10 ⁻⁴ mol / L to prepare a dye solution for adsorption.

  This adsorption dye solution and the semiconductor electrode obtained above were put in a container and allowed to stand for 1.5 hours to adsorb the dye. Thereafter, it was washed several times with acetonitrile and naturally dried at 50 ° C. for about 30 minutes. This obtained the photoelectric converting layer (13) which the pigment | dye adsorb | sucked to the semiconductor layer.

3. Injection of electrolyte Next, an electrolyte solution was prepared. The composition of the electrolytic solution is shown below.
Electrolytic solution 1
Ferrocene 0.01 mol / L
Solvent: water 70: acetonitrile 30 (Vol%).
Electrolytic solution 2
Ferrocene 0.01 mol / L
TEMPO · BF ₄ 0.0004 mol / L
Solvent: water 70: acetonitrile 30 (Vol%).
Electrolytic solution 3
Ferrocene 0.01 mol / L
Solvent: Water 70: Tetrahydrofuran 30 (Vol%).
Electrolyte 4
Ferrocene 0.01 mol / L
TEMPO · BF ₄ 0.0004 mol / L
Solvent: Water 70: Tetrahydrofuran 30 (Vol%).

  The above electrolytes were dropped into the photoelectric conversion layer (13) of the semiconductor electrode obtained above, and were further evacuated with a rotary pump for about 10 minutes so that the solution was sufficiently immersed in the photoelectric conversion layer. Then, the counter electrode (19) which equipped the platinum catalyst layer (15) was installed, and it fixed with the jig | tool. Then, sealing which avoids a contact with the external world with an epoxy resin was implemented, and the photoelectric conversion element was produced.

4). Evaluation of characteristics of photoelectric conversion element Evaluation of the produced photoelectric conversion element was carried out by using a solar simulator to perform IV measurement under irradiation conditions of AM 1.5 and 100 mW / cm ² .

Here, both ends of the photoelectric conversion element were connected to an electronic load device, and potential scanning at a step of 5 mV / sec was repeated until the voltage from the open circuit voltage was zero.
FIG. 9 shows the results using the electrolytic solution 1 (Comparative Example 1) and the electrolytic solution 2 (Example 1), and FIG. 10 shows the results using the electrolytic solution 3 (Comparative Example 2) and the electrolytic solution 4 (Example 2). Respectively.
As shown in FIGS. 9 and 10, it can be seen that when TEMPO · BF4 is added to the electrolyte, the short-circuit current value (Jsc) is dramatically increased.

  The photoelectric conversion element according to the present invention is suitably used as a dye-sensitized solar cell, and can be used not only as a solar cell but also as an optical sensor.

DESCRIPTION OF SYMBOLS 1 Photoelectric conversion layer 2 Counter electrode 3 Charge transport layer 11 ... Transparent substrate 12 ... Transparent conductive film 13 ... Photoelectric conversion layer 14 ... Charge transport layer 15 ... Platinum catalyst layer 16 ... Conductive film 17 ... Transparent substrate or support substrate 18 ... Semiconductor electrode DESCRIPTION OF SYMBOLS 19 ... Counter electrode 100 Photoelectric conversion element stack 101 W-type stack module 102 S-type stack module 103 Z-type stack module 104 Grid wiring type stack module 150 Photoelectric conversion system 152 Charge / discharge control device 153, 156 Load 154 Charger 155 Inverter 161 Photoelectric conversion Layer 162 Counter electrode 163 Electrolytes 164 and 165 Transparent substrates 166 and 167 Transparent conductive film 168 Anode 169 Cathode 170 Sealing material 171 Separator 172 Conductive sealing material 173 Insulating film 174 Metal current collection wiring

Claims (18)

A photoelectric conversion layer;
A counter electrode;
A charge transport layer;
With
A photoelectric conversion element comprising an electrolyte containing water, a metal complex, and an oxoammonium salt in the charge transport layer.   The photoelectric conversion element according to claim 1, wherein the charge transport layer is provided between the photoelectric conversion layer and the counter electrode.   The photoelectric conversion element according to claim 1, wherein the photoelectric conversion layer includes a semiconductor layer provided on a conductive substrate. A semiconductor electrode;
A counter electrode;
An electrolyte layer;
With
A photoelectric conversion element comprising water, a metal complex, and an oxoammonium salt in the electrolyte layer.   The photoelectric conversion element according to claim 4, wherein the electrolyte layer is provided between the semiconductor electrode and the counter electrode.   The photoelectric conversion element according to claim 4, wherein the semiconductor electrode includes a conductive substrate and a semiconductor layer provided on the conductive substrate.   The photoelectric conversion element according to claim 3, wherein the conductive substrate has light transparency.   The photoelectric conversion element according to claim 1, wherein the metal complex includes a metal atom selected from group 8 to 10 elements as a metal atom.   The photoelectric conversion element according to claim 8, wherein the metal atom is selected from Fe, Co, Ni, and Os.   The photoelectric conversion element according to claim 1, wherein the metal complex is metallocene or a derivative thereof.   The photoelectric conversion element according to claim 10, wherein the metal complex is ferrocene. The photoelectric conversion device according to any one of claims 1 to 11, wherein the oxoammonium salt includes one or more selected from compounds represented by the following formula (3).
(In General Formula (3), A is a divalent group constituting a 5- to 7-membered heterocyclic ring together with the nitrogen atom of nitroxide and the two carbon atoms to which R ^{1 to} R ⁴ are bonded, R ¹ , R ² , R ³ , R ⁴ may be the same or different and each represents a substituted or unsubstituted alkyl group, where X is a metal chloride, fluorine, chlorine , Bromine, iodine, BF ₄ , PF ₆ , CF ₃ SO _3, N (SO ₂ CF ₃ ) ₂ , N (SO ₂ F) ₂ , CF ₃ COO, N (C ₂ F ₅ SO ₂ ), or ClO ₄ Is shown.)   The photoelectric conversion device according to claim 1, further comprising an organic solvent in the electrolyte.   The photoelectric conversion element according to claim 13, wherein the organic solvent is a solvent capable of dissolving the metal complex.   The method for preparing the electrolyte in the photoelectric conversion device according to any one of claims 1 to 14, wherein the metal complex and the oxoammonium salt are dissolved in water, and one of the metal complex and the oxoammonium salt. A method for preparing an electrolyte, comprising using a method of mixing an aqueous solution in which an organic solvent is dissolved and an organic solvent in which the other is dissolved, or a method in which a metal complex and an oxoammonium salt are dissolved in a mixed solvent of water and an organic solvent . The electrolyte preparation method according to claim 15, wherein the oxoammonium salt is represented by the following general formula (3).
(In General Formula (3), A is a divalent group constituting a 5- to 7-membered heterocyclic ring together with the nitrogen atom of nitroxide and the two carbon atoms to which R ^{1 to} R ⁴ are bonded, R ¹ , R ² , R ³ , R ⁴ may be the same or different and each represents a substituted or unsubstituted alkyl group, where X is a metal chloride, fluorine, chlorine , Bromine, iodine, BF ₄ , PF ₆ , CF ₃ SO _3, N (SO ₂ CF ₃ ) ₂ , N (SO ₂ F) ₂ , CF ₃ COO, N (C ₂ F ₅ SO ₂ ), or ClO ₄ Is shown.)   The electrolyte preparation method according to claim 15 or 16, wherein the organic solvent is acetonitrile or tetrahydrofuran.   The method for preparing an electrolyte according to any one of claims 15 to 17, wherein 50 vol% or more of the solvent in the electrolyte is water.