JP2000053662A - Electrolyte, electrolyte for photo-electrochemical cell, photoelectrochemical cell and oxazolium compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrolyte that is useful for cells having excellent photoelectric transfer characteristics and durability, particularly useful for a photoelectrochemical cell by admixing a specific compound thereto. SOLUTION: The objective electrolyte contains a compound of formula I (Z is nitrogen, an atomic group that links to E and can form a cation of aromatic five-membered ring; E is oxygen or sulfur, R1 is an alkyl or alkenyl; R51 is H, a substituent; a is 1, 3), for example, a compound of formula II, preferably in an amount of >=50 wt.%, preferably >=90 wt.%. The compound of formula I is a salt, preferably a liquid at 25 deg.C or melting at a lower temperature, preferably melting at 60 deg.C and lower and boils higher than 400 deg.C. The compound of formula I is obtained, for example, by allowing an alkyl iodide, for example, octane iodide to react with a nitrogen-containing 5-membered ring compound such as oxazole or the like (for example, a compound of formula III).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel compound used for an electrolyte of a battery, particularly for an electrolyte of a photoelectrochemical cell. Furthermore, the present invention relates to a photoelectrochemical cell using the same.

[0002]

2. Description of the Related Art Single-crystal silicon solar cells, polycrystalline silicon solar cells, amorphous silicon solar cells, and compound solar cells such as cadmium telluride and indium copper selenide are used for photovoltaic power generation that converts light energy into electric energy. Or, it is an object of research and development, but it is necessary to overcome problems such as production cost, securing of raw materials, and long energy payback time in order to spread it. On the other hand, there have been proposed many solar cells using an organic material intended to have a large area and a low price, but have a problem that conversion efficiency is low and durability is poor.

Under these circumstances, Nature (Vol. 353,
737-740, 1991) and U.S. Pat. No. 4,492,721 and the like, a photoelectric conversion element using an oxide semiconductor sensitized with a dye (hereinafter, abbreviated as a dye-sensitized photoelectric conversion element) and light using the same. Techniques for electrochemical cells have been disclosed. This battery includes a photoelectric conversion element functioning as a negative electrode, a charge transfer layer, and a counter electrode. The photoelectric conversion element includes a conductive support and a photosensitive layer, and the photosensitive layer includes a semiconductor having a surface on which a dye is adsorbed. The charge transfer layer is made of an oxidation-reduction body, and performs charge transport between the negative electrode and the counter electrode (positive electrode). The photoelectrochemical battery proposed in the above patent is a battery using an aqueous solution (electrolyte solution) using a salt such as potassium iodide as an electrolyte as a charge transfer layer. This method is inexpensive and is promising in that relatively high energy conversion efficiency (photoelectric conversion efficiency) can be obtained. However, since the charge transfer layer uses an electrolyte containing a large amount of a low boiling point solvent such as an aqueous solution of potassium iodide, the like. However, when used for a long period of time, there is a problem that the photoelectric conversion efficiency is remarkably reduced due to evaporation and depletion of the electrolytic solution, and the battery does not function as a battery.

[0004] As a method for preventing the depletion of the electrolytic solution, WO 95/18456 describes a method using an imidazolium salt or a triazolium salt, which is a low-melting compound, as an electrolyte. According to this method, water or an organic solvent, which has been conventionally used as a solvent for the electrolyte, is not necessary or is small, so that the durability has been improved, but the durability is still insufficient, and the imidazolium is still insufficient. When the concentration of the salt is increased, there is a problem that the photoelectric conversion efficiency decreases.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolyte for a battery having excellent photoelectric conversion characteristics and durability, particularly an electrolyte for a photoelectrochemical battery, and a novel compound used therein. It is to provide. Another object is to provide a photoelectrochemical cell having excellent photoelectric conversion efficiency and durability.

[0006]

The above object has been attained by the following items which specify the present invention and preferable items thereof. (1) An electrolyte comprising a compound represented by the general formula (I).

[0007]

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[In the general formula (I), Z represents an atomic group capable of forming a cation of an aromatic 5-membered ring by bonding to nitrogen and E, and E represents oxygen or sulfur. R ₁ represents an alkyl group or an alkenyl group, R ₅₁ represents hydrogen or a substituent, and a is 1 or 3. (2) The compound represented by the general formula (I) is a compound represented by the general formula (II)
The electrolyte according to the above (1), which is a compound represented by the formula:

[0009]

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[In the general formula (II), E represents oxygen or sulfur. R ₁ represents an alkyl group or an alkenyl group. R ₂
Represents a substituent, and b is an integer of 0 to 3. However, when b is 2 or more, R ₂ may be the same substituent or different substituents. a is 1 or 3. (3) The compound represented by the general formula (II) is
The electrolyte according to the above (2), which is a compound represented by I).

[0011]

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[In the general formula (III), R ₃ has 4 to 4 carbon atoms.
Represents 24 unsubstituted alkyl groups. R ₄ represents an alkyl group, and c is an integer of 0 to 3. However, when c is 2 or more, R ₄ may be the same alkyl group or different alkyl groups. a is 1 or 3. (4) The electrolyte according to the above (3), wherein in the general formula (III), R ₃ is an unsubstituted alkyl group having 4 to 12 carbon atoms. (5) The electrolyte according to the above (3) or (4), wherein in the general formula (III), R ₄ is an unsubstituted alkyl group having 1 to 12 carbon atoms. (6) In the general formula (III), R ₃ is an unsubstituted straight-chain alkyl group having 8 to 12 carbon atoms, R ₄ is a methyl group or an ethyl group, c is 2, and R ₄ is the same. The electrolyte according to any one of the above (3) to (5), wherein R ₄ is bonded to the 2- and 4-positions of the oxazolium ring. (7) The electrolyte according to any one of the above (1) to (6), which contains the compound represented by the general formula (I) in an amount of 50% by weight or more. (8) The electrolyte according to the above (7), which contains the compound represented by the general formula (I) in an amount of 80% by weight or more. (9) The electrolyte according to the above (8), which is in a liquid state at 25 ° C. (10) The electrolyte according to any one of the above (1) to (9), wherein the compound represented by the general formula (I) is a liquid at 25 ° C. (11) The above (1), wherein the compound represented by the general formula (I) is a solid at 25 ° C. and has a melting point of 100 ° C. or less.
To (9). (12) An electrolyte for a photoelectrochemical battery, wherein the electrolyte according to any of the above (1) to (11) is used for a photoelectrochemical battery. (13) A photoelectrochemical cell having a charge transfer layer containing the electrolyte for a photoelectrochemical cell according to (12), and further having a semiconductor sensitive to radiation and a counter electrode. (14) The photochemical battery according to (13), wherein the semiconductor is a fine particle semiconductor sensitized by a dye. (15) The photoelectrochemical cell according to (14), wherein the particulate semiconductor is a metal chalcogenide. (16) The metal chalcogenide containing titanium oxide (1)
5) Photoelectrochemical battery. (17) The photoelectrochemical battery according to any one of (14) to (16), wherein the dye is a metal complex dye and / or a polymethine dye. (18) An oxazolium compound represented by the general formula (IV).

[0013]

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[In the general formula (IV), R ₅ is a group having 8 to 8 carbon atoms.
Represents 12 unsubstituted linear alkyl groups, and R ₆ and R ₇ each independently represent a methyl group or an ethyl group. a is 1
Or 3. ]

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The electrolyte containing the compound represented by the general formula (I) [preferably the general formula (II), more preferably the general formula (III)] of the present invention can be used as a reaction solvent for chemical reaction and metal plating, CC
It can be used for a D (charge coupled device) camera and various batteries, but is preferably used for a lithium secondary battery or a photoelectrochemical battery using the following semiconductor, and more preferably for a photoelectrochemical battery.

The compounds represented by the general formulas (I) to (III) and the electrolytes using the same will be described later in detail, but these compounds are liquids or solids having a low melting point at room temperature (25 ° C.). It is a certain salt, so-called molten salt. These compounds have an extremely high boiling point as compared with general low-molecular solvents, and therefore have little volatilization when used for an electrolyte. Therefore, when used in a photoelectrochemical battery, performance degradation of the battery can be prevented. Further, the charge transport performance is sufficient, and particularly, the photoelectric conversion efficiency when used in a photoelectrochemical cell is excellent. Such a performance is represented by the general formula (I)
Similar to some of the compounds (1) and (2), the solvent is an electrolyte which does not require any other compound (for example, an imidazolium salt or a triazolium salt).

Hereinafter, a photoelectrochemical cell in which the electrolyte of the present invention is preferably used will be described.

The photoelectrochemical cell of the present invention has a semiconductor sensitive to radiation, a charge transfer layer, and a counter electrode, and the charge transfer layer contains the electrolyte of the present invention.

In the present invention, the semiconductor is a so-called photoreceptor, which plays a role of absorbing light to separate electric charges to generate electrons and holes.

As the semiconductor, in addition to a simple semiconductor such as silicon and germanium, a so-called compound semiconductor represented by a metal chalcogenide (eg, oxide, sulfide, selenide, etc.) or perovskite can be used. Preferably titanium as a metal chalcogenide,
Tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxides, cadmium, sulfides such as zinc, lead, silver, antimony, bismuth, cadmium, Examples include selenides such as lead and telluride of cadmium, and other compound semiconductors include phosphides such as zinc, potassium, indium and cadmium, gallium arsenide, copper-indium-selenide, copper-indium-sulfide and the like. Is mentioned.

Further, as the perovskite, strontium titanate, calcium titanate, sodium titanate, barium titanate, potassium niobate and the like are preferably mentioned.

More preferably, the semiconductor used in the present invention is, specifically, Si, TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , Zn
O, Nb ₂ O ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, GaP, InP, Ga
As, CdTe, CuInS ₂ , CuInSe _{2 and the} like, more preferably TiO ₂ , ZnO, SnO ₂ , Fe ₂ O ₃ , WO ₃ , Nb ₂ O ₅ , CdS, Pb
S, CdSe, InP, GaAs, CuInS ₂ , CuInSe _{2 and the} like.

The semiconductor used in the present invention may be single crystal or polycrystal. Although a single crystal is preferable as the conversion efficiency, a polycrystal is preferable in terms of manufacturing cost, securing of raw materials, energy payback time, and the like, and a fine particle semiconductor having a nanometer to micrometer size is particularly preferable.

The particle size of these semiconductor fine particles is preferably 5 to 200 nm as a primary particle as an average particle size using a diameter when the projected area is converted into a circle, and particularly preferably 8 to 1 nm.
Preferably it is 00 nm. Further, the average particle size of the semiconductor fine particles in the dispersion is preferably 0.01 to 100 μm.

Further, the fine particle semiconductor is preferably used after being sensitized with a dye, and in that case, a metal oxide is preferable. Specifically, TiO ₂ , ZnO, SnO ₂ , Fe ₂ O ₃ , WO _2
3 , Nb ₂ O ₅ is preferred, and TiO ₂ is more preferred.

A photoelectrochemical cell using semiconductor fine particles sensitized with a dye will be described below.

Such a photoelectrochemical cell is a dye-sensitized photoelectric conversion element comprising a conductive support, and a layer (photosensitive layer) of semiconductor fine particles having a dye adsorbed thereon, which is coated on the conductive support. Having the general formula (I) [preferably the general formula (I
I), more preferably a charge transfer layer containing an electrolyte containing a compound represented by the general formula (III)] and a counter electrode. In this case, the charge transfer layer does not have to be a clear layer, and the layer of the semiconductor fine particles may be partially or entirely impregnated or impregnated with the electrolyte.

As the conductive support, a support such as a metal which has conductivity, or a glass or plastic support having a conductive agent layer on its surface can be used. In the latter case, preferred conductive agents include metals (eg, platinum, gold, silver, copper, aluminum, rhodium,
Indium, etc.), carbon, or a conductive metal oxide (indium-tin composite oxide, tin oxide doped with fluorine, and the like). Of these, conductive glass in which a conductive agent layer made of tin dioxide doped with fluorine is deposited on a transparent substrate made of low-cost soda-lime float glass is particularly preferable. The conductive agent layer preferably has a thickness of about 0.02 to 10 μm.

The lower the surface resistance of the conductive support, the better. The preferred range of the surface resistance is 100 Ω / cm ² or less, and more preferably 40 Ω / cm ² or less. The lower limit is not particularly limited, but is usually about 0.1 Ω / cm ² .

Preferably, the conductive support is substantially transparent. Substantially transparent means that light transmittance is 10%
The above means that it is preferably at least 50%, particularly preferably at least 70%. As the transparent conductive support, glass or plastic coated with a conductive metal oxide is preferable. The coating amount of conductive metal oxide in this case the support 1 m ² per 0.01~100g glass or plastic is preferred. When a transparent conductive support is used, light is preferably incident from the support side.

The method of coating the semiconductor fine particles on the conductive support includes a method of coating a dispersion or a colloid solution of the semiconductor fine particles on the conductive support, and a method of coating the precursor of the semiconductor fine particles on the conductive support. Method of obtaining semiconductor fine particle film by applying and hydrolyzing with moisture in the air (sol-gel method)
And the like. In addition to the sol-gel method described above, a method of preparing a dispersion of semiconductor fine particles, a method of grinding in a mortar, a method of dispersing while crushing using a mill, or a method of depositing fine particles in a solvent when synthesizing a semiconductor. And a method of using it as it is. Examples of the dispersion medium include water and various organic solvents (eg, methanol, ethanol, isopropyl alcohol, dichloromethane, acetone, acetonitrile, ethyl acetate, etc.). At the time of dispersion, a polymer, a surfactant, an acid, a chelating agent, or the like may be used as a dispersing aid, if necessary.

It is preferable that the semiconductor fine particles have a large surface area so that many dyes can be adsorbed. For this reason, the surface area in the state where the semiconductor fine particle layer is coated on the support is preferably at least 10 times, more preferably at least 100 times the projected area. The upper limit is not particularly limited, but is usually about 1000 times.

In general, as the thickness of the layer containing semiconductor fine particles increases, the amount of dye carried per unit projected area increases, so that the light capture rate increases. However, the diffusion distance of the generated electrons increases, and the loss due to charge recombination also increases. growing. Therefore, the semiconductor fine particle layer has a preferable thickness, but typically has a thickness of 0.1 to 100 μm. When used as a photoelectrochemical cell, the thickness is preferably 1 to 30 μm,
More preferably, it is 3 to 20 μm. It is preferable that the semiconductor fine particles are applied to a support, then the particles are brought into electronic contact with each other, and baked to improve the strength of the coating film and the adhesion to the substrate. A preferred range of the firing temperature is 40 ° C. or more and less than 700 ° C., more preferably 40 ° C.
It is not less than 650 ° C and not less than ℃. The firing time is 10 minutes to 1
It is about 0 hours.

After firing, for the purpose of increasing the surface area of the semiconductor particles, increasing the purity in the vicinity of the semiconductor particles, and increasing the efficiency of injecting electrons from the dye into the semiconductor particles, for example, chemical plating using titanium tetrachloride aqueous solution or titanium plating. Electrochemical plating using an aqueous solution of titanium chloride may be performed.

The coating amount of the semiconductor fine particles per 1 m ² of the support is preferably 0.5 to 500 g, more preferably 5 to 100 g.

The dye used in the present invention is preferably a complex dye, particularly a metal complex dye and / or a polymethine dye. Such a dye preferably has an appropriate interlocking group for the surface of the semiconductor fine particles. Preferred linking groups, COOH groups, SO ₃ H group, a cyano group, -P (O) (OH) 2 group, -OP (O) (OH) 2 group, or, oxime, dioxime, hydroxyquinoline, salicylate and Chelating groups having π conductivity, such as α-keto enolate. Among them, COOH group, -P (O) (OH) ₂
The group, -OP (O) (OH) _2, is particularly preferred. These groups may form a salt with an alkali metal or the like, or may form an intramolecular salt. In the case of a polymethine dye, if the methine chain contains an acidic group as in the case of forming a squarylium ring or a croconium ring, this portion may be used as a bonding group.

When the dye used in the present invention is a metal complex dye, it is preferably a ruthenium complex dye, and more preferably a dye represented by the following formula (V). Formula _{(V) (Y 1) p} RuB a B b B c

In the formula, p is 0 to 2, preferably 2. Ru represents ruthenium. Y ₁ is Cl, SCN,
H ₂ O, a ligand selected Br, I, CN, -NCO, and from SeCN. B _a, B _b, B _c is an organic ligand selected from the following B-1 to B-8 independently.

[0039]

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[0040]

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Here, Ra is hydrogen, halogen, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms (hereinafter referred to as C number), a substituted or unsubstituted aralkyl group having 7 to 12 carbon atoms, or A substituted or unsubstituted aryl group is represented by 6 to 12 carbon atoms. The alkyl portion of the above alkyl group and aralkyl group may be linear or branched, and the aryl portion of the aryl group and aralkyl group may be monocyclic or polycyclic (condensed ring, ring assembly ).

The ruthenium complex dyes used in the present invention include, for example, US Pat.
Complex dyes described in 5084365, 5350644, 5463057, 5525440 and JP-A-7-249790.

Preferred specific examples of the metal complex dye used in the present invention are shown below, but the present invention is not limited to these.

[0044]

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[0045]

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[0046]

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When the dye used in the present invention is a polymethine dye, a dye represented by the following formula (VI) or (VII) is preferable.

[0048]

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In the formula, Rb and Rf each represent hydrogen, an alkyl group, an aryl group, or a heterocyclic group;
Represents hydrogen or a substituent. Rb to Rf may combine with each other to form a ring. X ₁₁ and X ₁₂ each represent nitrogen, oxygen, sulfur, selenium, or tellurium. n ₁₁ and n
₁₃ represents an integer of 0 to 2; n ₁₂ represents an integer of 1 to 6; The compound represented by the general formula (VI) may have a counter ion depending on the charge of the whole molecule.

The above alkyl group, aryl group and heterocyclic group may have a substituent. The alkyl group may be linear or branched, an aryl group,
The heterocyclic group may be monocyclic or polycyclic (condensed ring, ring assembly). The ring formed by Rb to Rf may have a substituent, and may be a single ring or a condensed ring.

[0051]

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In the formula, Za represents a group of non-metallic atoms necessary for forming a nitrogen-containing heterocyclic ring. Rg is an alkyl group or an aryl group. Q represents a methine group or a polymethine group necessary for the compound represented by the general formula (VII) to form a methine dye. X ₁₃ represents a charge balancing counter ion, and n ₁₄ represents a number from 0 to 10 required to neutralize the charge of the molecule.

The nitrogen-containing heterocyclic ring formed by Za may have a substituent, and may be a single ring or a condensed ring. Further, the alkyl group and the aryl group may have a substituent, the alkyl group may be linear or branched, and the aryl group may be monocyclic or polycyclic (condensed). Ring, ring assembly).

The dye represented by the general formula (VII) is preferably a dye represented by the following general formulas (VIII-a) to (VIII-d).

[0055]

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In the general formulas (VIII-a) to (VIII-d), R
₁₁~ R_Fifteen, R_{twenty one}~ R_{twenty four}, R₃₁~ R₃₃, And R₄₁~ R₄₃
Are each independently hydrogen, an alkyl group, an aryl group, or
Represents a heterocyclic group;₁₁, Y₁₂, Y_{twenty one}, Y_{twenty two}, Y₃₁~ Y
₃₅And Y₄₁~ Y₄₆Are independently oxygen, sulfur,
N, tellurium, -CR₁₆R₁₇-Or -NR₁₈-
You. R₁₆~ R₁₈Are each independently hydrogen, an alkyl group,
Represents a reel group or a heterocyclic group. Y_{twenty three}Is O^-, S^-, S
e^-, Te^-Or -NR^- ₁₈Represents V₁₁, V_{1 Two}, V
_{twenty one}, V_{twenty two}, V₃₁And V₄₁Represents a substituent independently
Then n_Fifteen, N₃₁And n₄₁Are independently 1-6
Represents a number. Represented by the general formulas (VIII-a) to (VIII-d)
Some compounds have a counterion depending on the overall molecular charge.
You may.

The alkyl group, aryl group and heterocyclic group in the above may have a substituent, and the alkyl group may be linear or branched, and may be an aryl group or a heterocyclic group. May be monocyclic or polycyclic (condensed ring, ring assembly).

Specific examples of such polymethine dyes are described in M.
Organic Col by Okawara, T. Kitao, T. Hirasima, M. Matuoka
orants (Elsevier) and others.

Preferred specific examples of the polymethine dyes represented by formulas (VI) and (VII) are shown below, but the present invention is not limited thereto.

[0060]

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[0061]

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[0062]

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[0063]

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[0064]

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[0065]

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[0066]

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[0067]

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[0068]

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The compounds represented by the general formulas (VI) and (VII) are described in "Complex Cyclic Compounds-Cyanine Soybean" by FM Harmer.
AND RELATED COMPOUNDS
mpounds-Cyanine Dyes and Related Compounds), John Wiley & Sons
-New York, London, 1964, DMSturmer, "Complex cyclic
Compoundo Special Topics In Complex Heterocyclic Compounds-Sp
ecial topics in heterocyclic chemistry), 18
Chapter 14, Sections 482-515, John Wiley & Sons, Inc.-New York, London, 1977, "Rodd's Chemistry".
of Carbon Compounds) '' 2nd.Ed.vol.IV, partB, 1977
Published in Chapter 15, Chapters 369-422, Elsevier Science Public Company, Inc.
(Science Publishing Company Inc.), New York, UK Patent No. 1,077,611, and the like.

For adsorbing the dye on the semiconductor fine particles, a method of immersing well-dried semiconductor fine particles in a dye solution for several hours is general. The dye may be adsorbed at room temperature or may be heated and refluxed as described in JP-A-7-249790. The dye may be adsorbed before or after the application of the semiconductor fine particles. Further, the semiconductor fine particles and the dye may be simultaneously applied and adsorbed. It is desirable that unadsorbed dye be removed by washing. In the case of firing the coating film, the dye adsorption is preferably performed after firing.
It is particularly preferable that the dye is quickly adsorbed after the firing and before the water is adsorbed on the coating film surface. The dye to be adsorbed may be one kind or a mixture of several kinds. When the application is a photoelectrochemical cell, a dye to be mixed can be selected so as to make the wavelength range of photoelectric conversion as wide as possible.

The amount of the dye used is preferably 0.01 to 100 mmol per 1 m ² of the support. The amount of the dye adsorbed on the semiconductor fine particles is preferably 0.01 to 1 mmol per 1 g of the semiconductor fine particles.

By using such a dye amount, a sufficient sensitizing effect in a semiconductor can be obtained. In contrast,
If the amount of the dye is small, the sensitizing effect becomes insufficient, and if the amount of the dye is too large, the dye not adhering to the semiconductor floats and causes a reduction in the sensitizing effect.

A colorless compound may be co-adsorbed for the purpose of reducing interaction between dyes such as association. Examples of the hydrophobic compound to be co-adsorbed include steroid compounds having a carboxyl group (for example, cholic acid).

After the dye is adsorbed, the surface of the semiconductor fine particles may be treated with amines. Preferred amines include pyridine, 4-tert-butylpyridine, polyvinylpyridine and the like. When these are liquids, they may be used as they are or may be used by dissolving them in an organic solvent.

Next, the electrolyte containing the compound represented by the general formula (I) [preferably the general formula (II), more preferably the general formula (III)] will be described.

The compound represented by the general formula (I) of the present invention is used as an electrolyte in a charge transfer layer in a photoelectrochemical cell, and has a higher boiling point than a general low molecular solvent. , And is preferable in terms of durability.
Since the viscosity is high, it is also preferable from the viewpoint of production suitability.

The electrolyte of the present invention is preferably 50
The compound of the general formula (I) of the present invention may be used in an amount of 70% by weight or more in terms of durability, photoelectric conversion efficiency and production suitability, although it may be used in a mixture with a solvent or the like up to% by weight. Preferably, 80% by weight or more is more preferable,
It is most preferable to use 90% by weight or more.

The compound of the formula (I) is preferably a salt which is a liquid or a solid having a low melting point at 25 ° C., that is, a so-called molten salt. In such a case, the compound of general formula (I) alone can often be used as an electrolyte, and it is often unnecessary to use a solvent. Since the compound of the general formula (I) has a very high boiling point and low volatility as compared with a general solvent, it is preferable because deterioration of the performance of the device due to volatilization can be prevented. In addition to such durability, a short-circuit current density is high, so that a photoelectrochemical cell excellent in photoelectric conversion characteristics and high in viscosity is also excellent in manufacturing suitability.

The compound of the formula (I) preferably has a melting point of 100 ° C. or lower, more preferably 80 ° C. or lower, even more preferably 60 ° C. or lower. As noted above, such compounds include those that are liquid at 25 ° C. Boiling point (standard boiling point) of the compound of the general formula (I)
Is preferably at least 300 ° C., more preferably 4 ° C.
It is 00 ° C or higher.

Further, in the compound of the general formula (I), 2
Compounds that are liquid at 5 ° C., such as F-3 in the compound examples described below, are more preferable in terms of initial performance such as short-circuit current, and conversely, compounds that are solid at 25 ° C. in the compounds of general formula (I), for example, F-1, F-2, F in the compound examples
-5, F-6 and the like are more preferable in terms of durability and the like.

It should be noted that even if the solvent is solid at 25 ° C.,
The addition of water, other additives, etc. often makes it possible to obtain a liquid state and satisfy the performance as an electrolyte.
Depending on the case, it may be heated and dissolved without any addition to penetrate the electrode, or a low boiling point solvent (eg, methanol, acetonitrile, methylene chloride) or the like may be used to penetrate the electrode, and then the solvent is removed by heating. A method of incorporating it into the electrodes of the photoelectric conversion element by a method or the like can also be used.

The compound represented by the general formula (I) often has some hygroscopicity, but is preferably 0.1 to 15% by weight.
It may be used while containing a certain amount of water.

Next, the general formula (I) will be described. In the general formula (I), Z represents an atomic group capable of forming an aromatic 5-membered ring cation by combining with nitrogen and E, and preferably includes carbon, hydrogen, nitrogen, oxygen, and sulfur as constituent atoms. E
Represents oxygen or sulfur, preferably oxygen.

The aromatic 5-membered ring completed by Z is preferably oxazole, thiazole, thiadiazole,
Oxadiazole, more preferably oxazole and thiazole, even more preferably oxazole.

In the general formula (I), R ₅₁ represents hydrogen or a substituent, and examples of the substituent include those similar to the substituents (described later) represented by R ₂ in the general formula (II). Examples include an alkyl group and an aryl group. R ₅₁ is particularly preferably hydrogen or an alkyl group.

In the general formula (I), R ₁ is a substituted or unsubstituted alkyl group (preferably having 1 to 24 carbon atoms (hereinafter referred to as C number), and may be linear or branched. For example, methyl, ethyl, propyl, butyl, i-
Propyl, hexyl, octyl, 2-ethylhexyl,
t-octyl, decyl, dodecyl, benzyl, 2-ethoxyethyl, 2-butoxyethyl, heptafluoropropyl, cyanomethyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, oxazoliumbutyl, thiazoliumbutyl), substituted or unsubstituted It represents an alkenyl group (preferably having 2 to 24 carbon atoms, which may be linear or branched, for example, vinyl or allyl). R ₁ is preferably an alkyl group having 4 to 24 carbon atoms (preferably an unsubstituted alkyl group) or 2 to 18 carbon atoms.
Alkenyl group, more preferably an unsubstituted alkyl group having 4 to 12 carbon atoms, or a vinyl group or an allyl group. Of these, an alkyl group is preferable, and further preferably, 4 to 12 carbon atoms, and Preferably 6 to
It is a 12 unsubstituted linear alkyl group, and particularly preferably an unsubstituted linear alkyl group having 8 to 12 carbon atoms.

In the general formula (I), a represents 1 or 3.
When a is 1, it represents I ⁻ , that is, a reducing substance in the electrolyte, and when a is 3, it represents I ₃ ⁻ , that is, an oxidizing substance.

In the general formula (I), the constituent atoms of Z or R ₁ and R ₅₁ may have the same quaternary salt of a nitrogen-containing 5-membered aromatic ring as in the general formula (I). .

Among the compounds represented by the general formula (I), the compound represented by the general formula (II) is preferable. The general formula (II) will be described. In the general formula (II), E represents oxygen or sulfur, and preferably represents oxygen. R ₁ and a have the same meanings as those in formula (I).

R ₂ represents a substituent, preferably an alkyl group which may be substituted, linear or branched (preferably having 1 to 24 carbon atoms, for example, methyl, ethyl, i-propyl, butyl, t -Butyl, octyl, 2-methoxyethyl, benzyl, trifluoromethyl, cyanomethyl, ethoxycarbonylmethyl), an alkenyl group which may be substituted or straight-chain or branched (preferably having 2 to 2 carbon atoms)
4, for example, vinyl or allyl), an optionally substituted or condensed aryl group (preferably having 6 to 24 carbon atoms, for example, phenyl, 4-methylphenyl, 3-cyanophenyl, 2-chlorophenyl, 2-chlorophenyl) Naphthyl), a substituted or condensed heterocyclic group (preferably having 2 to 2 carbon atoms)
24, for example, 4-pyridyl, 2-pyridyl, 2-pyrimidyl, 2-imidazolyl, 2-thiazolyl), an alkoxy group (preferably having a C number of 1 to 24, such as methoxy, ethoxy, butoxy), an acyloxy group (preferably having a C number of 24) 1
-24, for example, acetyloxy, benzoyloxy),
Represents an alkoxycarbonyl group (preferably having 2 to 24 carbon atoms, for example, methoxycarbonyl, ethoxycarbonyl), a cyano group or a halogen (for example, chlorine or bromine). R ₂
Are more preferably an alkyl group, an alkenyl group, an alkoxy group, an alkoxycarbonyl group, a cyano group, and a halogen, further preferably an alkyl group and an alkenyl group, and particularly preferably an alkyl group.

In the general formula (II), b is an integer of 0 to 3, preferably an integer of 0 to 2, and more preferably 1
Or 2.

In the general formula (II), R ₁ and R ₂ may have the same oxazolium salt and thiazolium salt as in the general formula (II).

Among the compounds represented by the general formula (II), the compound represented by the general formula (III) is preferable. General formula (I
Explaining II), in the general formula (III), a has the same meaning as in the general formula (I). R ₃ represents an unsubstituted alkyl group having 4 to 24 carbon atoms, preferably an unsubstituted alkyl group having 4 to 12 carbon atoms, and more preferably 6 to 12 carbon atoms.
Represents an unsubstituted alkyl group, and particularly preferably has a C number of 8 to
Represents 12 unsubstituted alkyl groups. The alkyl group is preferably linear. Preferred examples thereof include a hexyl group, an octyl group, a decyl group, and a dodecyl group.Among them, a dodecyl group and a decyl group are preferable in terms of photoelectric conversion efficiency, and an octyl group and a decyl group are preferable in terms of durability. preferable.

In the general formula (III), R ₄ represents an optionally substituted alkyl group, and preferred substituents include halogen, cyano group, alkoxycarbonyl group, alkoxy group, acyloxy group and the like. R ₄ is C number 1-2
It is preferably 4, and more preferably 1-12, more preferably an unsubstituted alkyl group, and most preferably a methyl group.

In the general formula (III), c represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 1
Or 2 is represented.

In the present invention, an oxazolium compound represented by the general formula (IV) is particularly preferred, and the compound represented by the general formula (IV) is a novel compound. The general formula (IV) will be described. In the general formula (IV), a has the same meaning as in the general formula (I), and R ₅ represents an unsubstituted straight-chain alkyl group having 8 to 12 carbon atoms (eg, octyl) , Decyl, dodecyl)
R ₆ and R ₇ may be the same or different and each represents a methyl group or an ethyl group.

Specific examples of the compound represented by formula (I) of the present invention are shown below by combining cations and anions of formula (I), but the present invention is not limited thereto.

[0098]

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[0099]

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[0100]

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[0101]

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The compounds of the present invention represented by the general formula (I) may be used alone or as a mixture. However, it is preferable that I ⁻ and I ₃ ⁻ are mixed at an arbitrary ratio with the same cationic species. Preferably, at that time, I ₃ ⁻ is preferably 0.1 to 50 mol% of I ⁻ , more preferably 0.1 to 20 mol%, and further preferably 0.5 to 10 mol%. It is most preferably 0.5 to 5 mol%.

[0103] Among the compounds represented by formula (I) of the present invention, the anion is I ^- compounds generally oxazole, alkyl iodide or iodide alkenyl such as nitrogen-containing aromatic 5-membered ring compound thiazole like Can be easily synthesized by reacting under heating.

[0104] anion is I ₃ ^- compounds I ^- can be easily synthesized by adding I ₂ to the compound.

[0105] For this reason, pre-anion is I ^-
When the compound is synthesized and used as an electrolyte,
It is preferable to add a predetermined amount of I ₂ to obtain a mixture of the anion of I ⁻ and I ₃ ⁻ .

The compound represented by the general formula (I) of the present invention is used as a compound exhibiting the function of an electrolyte in the electrolyte of the present invention. Although it is preferable to use, LiI, NaI, KI, CsI, metal iodide such as CaI _2, quaternary pyridinium compound iodine salt,
Iodine salt of tetraalkylammonium compound, Br ₂
And LiBr, NaBr, KBr, CsBr, CaBr ₂
Metal bromides such or Br ₂ and tetraalkylammonium bromide, pyridinium bromide, etc. 4
Combined use with bromine salts of quaternary ammonium compounds, metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ion, sulfur compounds such as sodium polysulfide, alkylthiol-alkyldisulfide, viologen dyes, hydroquinone-quinone, etc. It can also be used. When used in combination, the amount of these compounds used is preferably not more than 30% by weight of the entire electrolyte compound.

In the present invention, a solvent can be used together with the compound of the formula (I), preferably up to the same weight as the compound.

The solvent used in the electrolyte of the present invention is a compound which can exhibit excellent ionic conductivity by improving the ionic mobility of a low viscosity or improving the effective carrier concentration by increasing the dielectric constant. Desirably. Examples of such a solvent include carbonate compounds such as ethylene carbonate and propylene carbonate, and 3-methyl-
Heterocyclic compounds such as 2-oxazolidinone, dioxane, ether compounds such as diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, chain ethers such as polypropylene glycol dialkyl ether, methanol, ethanol,
Alcohols such as ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, and polypropylene glycol monoalkyl ether; polyhydric alcohols such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, and glycerin; acetonitrile; Use nitrile compounds such as glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile; esters such as carboxylic acid esters, phosphate esters, and phosphonate esters; aprotic polar substances such as dimethyl sulfoxide and sulfolane; and water. be able to. Among them, ethylene carbonate, carbonate compounds such as propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, nitrile compounds such as benzonitrile, esters are particularly preferable. preferable. These may be used alone or in combination of two or more.

Preferred examples of the solvent will be specifically described below, but it should not be construed that the invention is limited thereto.

[0110]

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The solvent has a boiling point at normal pressure (1 atm) of preferably 200 ° C. or higher, more preferably 250 ° C. or higher, even more preferably 270 ° C. or higher, from the viewpoint of improving durability due to volatility resistance. Therefore, S-5 and S-6 are preferable.

The thickness of the charge transfer layer containing the electrolyte of the present invention is preferably 0.001 to 200 μm, and 0.1 to 1 μm.
00 μm is more preferred.

When the opposing electrode is a photoelectrochemical cell,
It functions as a positive electrode of a photoelectrochemical cell. The counter electrode is usually synonymous with the above-mentioned conductive support, but the support is not necessarily required in a configuration in which the strength is sufficiently maintained. However, having a support is advantageous in terms of hermeticity.

In order for light to reach the photosensitive layer, at least one of the above-described conductive support and the counter electrode must be substantially transparent. In the photoelectrochemical cell of the present invention, it is preferable that the conductive support is transparent and sunlight is incident from the support side. In this case, it is more preferable that the counter electrode has a property of reflecting light.

As the counter electrode of the photoelectrochemical cell, glass or plastic on which a metal or a conductive oxide is deposited can be used, and the metal thin film has a thickness of 5 μm or less, preferably 5 nm to 3 μm. As described above, it can be formed and formed by a method such as vapor deposition or sputtering. In the present invention, it is preferable that glass on which platinum is deposited or a metal thin film formed by deposition or sputtering is used as the counter electrode.

The photosensitive layer is designed according to the purpose and may have a single-layer structure or a multilayer structure. The dye in one photosensitive layer may be one kind or a mixture of many kinds.

In the photoelectrochemical cell of the present invention, the side of the cell may be sealed with a polymer, an adhesive or the like in order to prevent the components from being oxidized and degraded.

[0118]

The present invention will be specifically described below with reference to examples. Example 1 Compounds F-1 and F- of the present invention represented by the general formula (I)
3, Synthesis examples of F-5 are shown. The reaction scheme of these compounds is shown below.

[0119]

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(1) Synthesis of F-1 Oxazole 1; 0.97 g (10 mmol) and octane iodide 4.8 g (20 mmol) were stirred at 140 ° C. for 3 hours in a nitrogen atmosphere. After concentration under reduced pressure, the residue was purified by silica gel column chromatography (methylene chloride: methanol = 5: 1 (volume ratio)) to obtain 3.02 g of F-1 (yield 90%).
I got The structure was confirmed by NMR spectrum.

(2) Synthesis of F-3 F-3 was synthesized in exactly the same manner as in synthesis of F-1, except that dodecane iodide was used in place of octane iodide in an equimolar amount.
57 g (91% yield) were obtained. The structure was confirmed by NMR spectrum.

(3) Synthesis of F-5 In the synthesis of F-1, F-5; 2.94 g (total) was prepared in exactly the same manner except that 1.13 g (10 mmol) of thiazole 2 was used instead of oxazole 1. 83%). The structure was confirmed by NMR spectrum.

[0123] Other I ^- was exemplified compounds to anionic be similarly synthesized. Also, I ₃ ^- which the anion is, the corresponding I ^- I of an anion compound ^- per mole, the I ₂ 1 to 10 moles synthesized in (preferably 1 mol) is added it.

Embodiment 2 1. Preparation of Titanium Dioxide Dispersion Titanium dioxide (Nippon Aerosil Co., Ltd.)
Degussa P-25) 15 g, water 45 g, dispersant (Triton X-100, manufactured by Aldrich) 1
g of zirconia beads having a diameter of 0.5 mm (manufactured by Nikkato Co., Ltd.), and dispersed for 2 hours at 1500 rpm using a sand grinder mill (manufactured by Imex). The zirconia beads were removed by filtration from the dispersion. In this case, the average particle size of the titanium dioxide was 2.5 μm. The particle size at this time was measured with a master sizer manufactured by MALVERN.

[0125] 2. Preparation of dye-adsorbed TiO ₂ electrode (electrode A) On the conductive surface side of conductive glass coated with fluorine-doped tin oxide (TCO glass-U manufactured by Asahi Glass cut into a size of 20 mm x 20 mm) The above dispersion was applied using a glass rod. At this time, an adhesive tape was stretched on a part (3 mm from the end) on the conductive surface side to form a spacer, and glass was lined up so that the adhesive tape came to both ends, and eight sheets were applied at a time. After application, the adhesive tape was peeled off and air-dried at room temperature for one day. Next, this glass was put into an electric furnace (muffle furnace FP-32 manufactured by Yamato Scientific Co., Ltd.) and fired at 450 ° C. for 30 minutes. After the glass was taken out and cooled, it was immersed in an ethanol solution of the dye shown in Table 1 (3 × 10 ⁻⁴ mol / l) for 3 hours. Pigment-dyed glass is 4-te
After being immersed in rt-butylpyridine for 15 minutes, it was washed with ethanol and dried naturally. The thickness of the photosensitive layer thus obtained is 10 μm, and the coating amount of the semiconductor fine particles is 2 μm.
0 g / m ² . The coating amount of the dye was appropriately selected from the range of 0.1 to 10 mmol / m ² according to the type of the dye. The surface resistance of the conductive glass was about 30 Ω / cm ² .

3. Preparation of Photoelectrochemical Cell The sensitized TiO ₂ electrode substrate (2 cm × 2 cm) prepared as described above was overlaid with a platinum-deposited glass of the same size (see FIG. 1). Next, an electrolyte (a mixture of an electrolyte compound and a solvent at a weight ratio shown in Table 1 and 2% by mole of iodine added thereto) was impregnated into the gap between the two glasses by capillary action, and TiO was impregnated. _It was introduced into _two electrodes to obtain a photoelectrochemical cell (sample). This step was performed by changing the combination of the dye and the electrolyte composition as shown in Table 1. The compound of the present invention, which is solid at 25 ° C., can be prepared by the above-mentioned method of heating and dissolving, or the method of removing the solvent later using a low-boiling solvent, or the like.
00% by weight of electrolyte was obtained.

According to the present embodiment, as shown in FIG. 1, the conductive glass 1 (the conductive agent layer 2 is provided on the glass), the TiO ₂ electrode 3, the dye layer 4, the electrolyte 5, the platinum layer 6
Then, a photoelectrochemical cell in which the glass 7 and the glass 7 were sequentially laminated was produced.

[0128]

[Table 1]

MHIm; iodine salt of 1-methyl-3-hexylimidazolium (WO95 / 18456)

[0130] 4. Measurement of photoelectric conversion efficiency The light of a 500 W xenon lamp (made by Ushio) was converted to AM1.5.
Simulated sunlight containing no ultraviolet light was generated by passing through a filter (manufactured by Oriel) and a sharp cut filter (Kenko L-42). The intensity of this light was 86 mW / cm ² .

An alligator clip was connected to each of the conductive glass and the platinum-deposited glass of the above-mentioned photoelectrochemical cell, and simulated sunlight was irradiated. The generated electricity was measured with a current / voltage measuring device (Keisley SMU238 type). did. The open-circuit voltage (Voc), short-circuit current density (Jsc), and form factor (FF) of the photoelectrochemical cell obtained by this were [= maximum output / (open-circuit voltage ×
Short-circuit current)], conversion efficiency (η), short-circuit current density after continuous irradiation for 480 hours, and reduction rate of short-circuit current density are collectively shown in Table 2.

[0132]

[Table 2]

A photoelectrochemical cell using a comparative electrolyte containing 50% by weight of a comparative compound of LiI or (C ₄ H ₉ ) ₄ NI has very poor initial performance and durability due to insufficient solubility. When the compound of the present invention represented by the general formula (I) is used at 50% by weight, compatibility with a solvent is good, and initial performance such as short-circuit current density and conversion efficiency, and durability are excellent.
Further, it can be seen that when the weight% of the compound of the present invention in the electrolyte is increased, both initial performance and durability are further increased. Such an effect is seen when any of the dyes is used. The photoelectrochemical cell using the electrolyte containing 50% by weight or more of the compound represented by the general formula (I) of the present invention is particularly resistant to volatilization as compared with a normal electrolyte using a large amount of a solvent (up to 15% by weight). It can be seen that the feature is that the durability based on the properties is excellent. In contrast, the known MH
It can be seen that the short circuit current density and the conversion efficiency are inferior to those of the present invention particularly in the place where the weight ratio of Im is large. Further, it can be seen that as a solvent that can be used in combination with the compound of the present invention, a solvent having a high boiling point such as S-5 and S-6 is preferable in terms of durability.

[0134]

According to the present invention, an electrolyte which is hard to volatilize and which is excellent in charge transport performance can be obtained. As a result, a photoelectrochemical cell having excellent photoelectric conversion characteristics and little deterioration of characteristics over time can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a photoelectrochemical cell prepared in an example.

[Explanation of symbols]

Reference Signs List 1 conductive glass 2 conductive agent layer 3 TiO ₂ electrode 4 dye layer 5 electrolyte 6 platinum layer 7 glass

 ────────────────────────────────────────────────── ─── Continuation of the front page F term (reference) 4C056 AA01 AB01 AC02 AD01 AE03 BA03 BB01 BC02 5F051 AA14 5H032 AA07 AS16 CC17 EE16 EE20 HH00 HH01

Claims (8)

[Claims] 1. An electrolyte comprising a compound represented by the general formula (I). Embedded image [In the general formula (I), Z represents an atomic group capable of forming an aromatic 5-membered ring cation by bonding with nitrogen and E, and E represents oxygen or sulfur. R ₁ represents an alkyl group or an alkenyl group, R ₅₁ represents hydrogen or a substituent, and a is 1 or 3. ] 2. The electrolyte according to claim 1, wherein the compound represented by the general formula (I) is a compound represented by the general formula (II). Embedded image [In the general formula (II), E represents oxygen or sulfur. R ₁ represents an alkyl group or an alkenyl group. R ₂ represents a substituent, and b is an integer of 0 to 3. However, when b is 2 or more, R ₂ may be the same substituent or different substituents. a is 1 or 3. ] 3. The electrolyte according to claim 2, wherein the compound represented by the general formula (II) is a compound represented by the general formula (III). Embedded image [In the general formula (III), R ₃ represents an unsubstituted alkyl group having 4 to 24 carbon atoms. R ₄ represents an alkyl group;
-3. However, when c is 2 or more, R ₄ may be the same alkyl group or different alkyl groups. a is 1 or 3. ] 4. The electrolyte according to claim 1, which contains the compound represented by the general formula (I) in an amount of 50% by weight or more. 5. An electrolyte for a photoelectrochemical cell, wherein the electrolyte according to claim 1 is used for a photoelectrochemical cell. 6. A photoelectrochemical cell having a charge transfer layer containing the electrolyte for a photoelectrochemical cell according to claim 5, and further comprising a radiation-sensitive semiconductor and a counter electrode. 7. The photoelectrochemical cell according to claim 6, wherein the semiconductor is a fine particle semiconductor sensitized by a dye. 8. An oxazolium compound represented by the general formula (IV). Embedded image [In the general formula (IV), R ₅ represents an unsubstituted linear alkyl group having 8 to 12 carbon atoms, and R ₆ and R ₇ each independently represent a methyl group or an ethyl group. a is 1 or 3. ]