KR20100108237A - Compositions for photoelectric conversion devices and photoelectric conversion devices using the same - Google Patents

Abstract

PURPOSE: A composition for the photoelectric conversion element and a photoelectric conversion element using the same are provided to generate the electromotive force between a transparent electrode layer and a opposite electrode by irradiating solar light from a side of the transparent layer. CONSTITUTION: A pigment layer(12) is formed on one side of a semiconductor layer(11). A transparent electrode layer(13) is formed on the side of the semiconductor. An opposite electrode(14) is arranged to oppose the pigment layer. An electrolyte layer(15) is arranged between the pigment layer and the opposite layer.

Description

Composition for photoelectric conversion device and photoelectric conversion device using same {Compositions for photoelectric conversion devices and photoelectric conversion devices using the same}

The present invention relates to a composition for photoelectric conversion elements. Moreover, this invention relates to the photoelectric conversion element using the said composition for photoelectric conversion elements.

Silicon-based solar cells using single crystal silicon, polycrystalline silicon and amorphous silicon have excellent photoelectric conversion efficiency of up to 20%, and have been put into practical use as the main technology of solar power generation systems. However, this silicon-based solar cell is expensive due to the high energy cost for manufacturing the material, and is limited by the viewpoint of price and material supply. On the other hand, the dye-sensitized solar cell proposed by Gratzel et al. Has recently attracted attention. This has a structure in which an electrolyte solution is interposed between a titanium oxide porous electrode on which a sensitizing dye is supported and an opposite electrode, and thus, a significant cost reduction in terms of materials, manufacturing methods, and the like is possible.

As this dye-sensitized solar cell, the electrolyte solution which melt | dissolved the halogen and electrolyte which comprise a halogen redox band in the organic solvent or ionic liquid (normal temperature molten salt), such as a nitrile type and a carbonate type, is used normally. Used as electrolytes are quaternary halide salts with nitrogen-based cations, such as mainly imidazolium halides, pyridinium halides, quaternary ammonium halides, pyrrolidinium halides, piperidinium halides. However, since the nitrogen-based cation of such a quaternary halogen salt has an active site in its molecular structure, when used as an electrolyte of a dye-sensitized solar cell, there is a possibility of causing decomposition of the electrolyte solution.

On the other hand, quaternary phosphonium halides mainly composed of phosphorus quaternary phosphonium cations are also known. Quaternary phosphonium halides are known to be chemically and thermally stable, and are also known to have indigestion (self-extinguishing) by further containing phosphorus. Regarding the application of the quaternary phosphonium halide to the electrolytic solution of dye-sensitized solar cells, for example, in Patent Documents 1 to 3, quaternary ammonium salts and phosphonium salts composed of alkyl or alkenyl groups bonded to a nitrogen atom or a phosphorus atom An electrolyte composition comprising a is described. However, the dye-sensitized solar cell using the electrolyte containing quaternary phosphonium halides described in these documents needs further improvement in terms of photoelectric conversion efficiency and stability of the electrolyte solution.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-29139 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-35253 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003092153

The present invention provides an electrolyte composition for a photoelectric conversion element and a photoelectric conversion element using the same, which can solve various drawbacks of the aforementioned prior art.

The present invention contains a quaternary phosphonium salt represented by the following formula (1) and an imidazolium salt represented by the following formula (2), and the quaternary phosphonium salt is 20 to 80 mol%, based on the total amount of both. It is to provide an electrolyte composition for a photoelectric conversion element, characterized in that 20 to 80 mol% of the dazolium salt is contained.

In the above formula, R ₁ , R ₂ , R ₃ and R ₄ represent an alkyl group having 1 to 6 carbon atoms, may be the same or different from each other, and R ₁ and R ₂ may form a ring. X ₁ ^- represents a monovalent anion.

In the above formula, R ₅ to R ₉ represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and may be the same or different from each other. X ₂ ⁻ represents a monovalent anion.

The electrolyte composition for photoelectric conversion elements of the present invention provides high photoelectric conversion efficiency. In addition, the composition has good solubility and is rich in heat resistance and inferiority.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the structure of one Embodiment of the photoelectric conversion element using the electrolyte composition of this invention.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated based on the preferable embodiment. The electrolyte composition for photoelectric conversion elements (hereinafter, simply referred to as "electrolyte composition") of the present invention is characterized by containing the above-described quaternary phosphonium salt and imidazolium salt. In the electrolyte composition of the present invention, the quaternary phosphonium salt and imidazolium salt are used in combination at a predetermined ratio, thereby achieving high photoelectric conversion efficiency. Hereinafter, these compounds are demonstrated, respectively.

In the quaternary phosphonium salt represented by the formula (1), the four alkyl groups may be the same or different, provided that they have 1 to 6 carbon atoms. In some cases, among four alkyl groups, R ₁ and R ₂ may be bonded to form a ring. By using a quaternary phosphonium salt having a structure in which such a relatively short-chain alkyl group is directly bonded to a phosphorus atom as an electrolyte composition for a photoelectric conversion element together with an imidazolium salt represented by the formula (2), the photoelectric conversion efficiency is significantly higher than before. The result of the examination by the present inventors etc. was revealed. It has also been found that the chemical stability and heat resistance of the electrolyte composition containing the same are improved by using the quaternary phosphonium salt represented by the formula (1). The inventors believe that the reason is that the phosphonium cation represented by the formula (1) does not have an active hydrogen moiety as the imidazolium cation. Furthermore, quaternary phosphonium salts represented by the general formula (1) are advantageous in that the solubility in solvents is higher than that of the corresponding nitrogen-based cationic salts and it is easy to increase the concentration of anions.

In particular, it is preferable from the point which improves photoelectric conversion efficiency further that three alkyl groups of R <_1> -R <_3> are the same alkyl group among four alkyl groups, and R <_4> is an alkyl group different from R <_1> -R <_3> . In this case, it was found that the case where the carbon number of R ₄ is smaller than the carbon number of R ₁ to R ₃ is higher than the case where the carbon number of R ₄ is larger than the carbon number of R ₁ to R ₃ . In the former case, the difference between the carbon number of R _{4 and} the carbon number of R ₁ to R ₃ is preferably 1 to 5, and particularly preferably 2 to 4. The reason why photoelectric conversion efficiency improves when carbon number of R <_4> is smaller than carbon number of R <_1> -R <_3> is not fully understood at present. The present inventors believe that this is because the presence of the quaternary phosphonium cation represented by the formula (1) increases the redox efficiency of the redox band and the efficiency of the charge transfer in the electrolyte composition.

Specific examples of the alkyl group of the formula (1) of R ₁ to R _4, methyl, ethyl, n- propyl, n- butyl, n- hexyl, i- propyl, i- butyl, n- pentyl group, a hexyl i- A real group, a cyclopentyl group, a cyclohexyl group, etc. are mentioned. In the case where R ₁ and R ₂ form a ring, for example, a tetrahydrophosphos ring, a pentahydrophosphorine ring, a 9-H-9-phosphacyclocyclononane ring, etc. may be mentioned. have. Such alkyl groups may be substituted with monovalent substituents. Examples of such a substituent include an alkenyl group, alkynyl group, alkoxy group, carboxyl group, alkylcarbonyloxy group, alkoxycarbonyl group, sulfoxy group, alkyl sulfoxy group, hydroxy group, hydroxysulfonyl group, aryl group, aryl oxy group, acyl oxy group , Carbamoyl group, sulfonic acid group, sulfamoyl group, cycloalkyl group, cyano group, nitro group, amino group, alkyl amino group, heterocyclic group, aminosulfon group, halogen atom, 2-butoxyethyl group, 6-bromo hexyl group, 2 -Carboxyethyl group, 3-sulfoxypropyl group, 4-sulfoxybutyl group, 2-hydroxyethyl group, phenyl methyl group, 4-butoxyphenylmethyl group, etc. are mentioned.

In the case where R ₁ to R ₃ are the same alkyl group and carbon number of R ₄ is smaller than that of R ₁ to R ₃ , R ₁ to R ₃ are, for example, an ethyl group, n-propyl group, n-butyl group, n -Hexyl group, i-propyl group, i-butyl group, n-pentyl group, i-hexyl group, cyclopentyl group, cyclohexyl group, etc. are mentioned. Such alkyl groups may be substituted with one substituent. As an example of such a substituent, the same thing as the above-mentioned is mentioned. On the other hand, roneun R _4, carbon atoms on condition that is less than R ₁ to R _3, methyl, ethyl, n- propyl, n- butyl, i- propyl, i- butyl, n- pentyl group, a cycloalkyl Pentyl group etc. are mentioned. R ₄ may also be substituted with the same substituent as R ₁ to R ₃ .

As a particularly preferable combination of R ₁ to R ₄ , R ₁ to R ₃ are ethyl groups, R ₄ is a methyl group, R ₁ to R ₃ is an n-propyl group, R ₄ is a methyl group, and R ₁ to R ₃ are i-propyl R ₄ is a methyl group; R ₁ to R ₃ are n-butyl groups, R ₄ is a methyl group; R ₁ to R ₃ are i-butyl groups and R ₄ is a methyl group; R ₁ to R ₃ are n-pentyl groups R ₄ is methyl group; R ₁ to R ₃ are cyclopentyl groups, R ₄ is methyl group; R ₁ to R ₃ are n-hexyl group, R ₄ is methyl group; R ₁ to R ₃ is cyclohexyl group, and R ₄ is methyl group Phosphorus combination is mentioned. A particularly preferable combination is a combination in which R ₁ to R ₃ are n-butyl groups and R ₄ is a methyl group.

In Formula 1, the monovalent anion represented by X ₁ ^- is, for example, a halide ion, tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ), bis (trifluoromethylsulfonyl) imide (N (SO ₂ CF ₃ ) ₂ ), bis (fluorosulfonyl) imide (N (SO ₂ F) ₂ ), tetra cyanoborate (B (CN) ₄ ), trifluoromethanesulfonate (SO ₃ CF ₃ ), pentafluoroethanesulfonate (SO ₃ CF ₂ CF ₃ ), tetrafluoroethanesulfonate (SO ₃ CHFCF ₃ ), methanesulfonate (SO ₃ CH ₃ ), ethanesulfonate (SO ₃ C ₂ H ₅ ), tris (pentafluoroethyl) trifluoro phosphate ((C ₂ F ₅ ) ₃ PF ₃ ), trifluoro acetic acid (CF ₃ COO), amino acids, bisoxalate borate (B (C ₂ O ₄ ) ₂ ), p-toluene sulfonate (SO ₃ C ₆ H ₄ CH ₃ ), thiocyanate (SCN), dicyanamid (N (CN) ₂ ), dialkylphosphoric acid ((RO) ₂ POO), Dialkyldithiophosphoric acid ((RO) ₂ PSS), aliphatic carboxylic acid (R COO) etc. are mentioned. Among these anions, it is preferable to use halide ions from the viewpoint of further improving the photoelectric conversion efficiency. In particular, the use of iodide ions in combination with the imidazolium salt represented by the formula (2) is preferable because excellent photoelectric conversion efficiency can be achieved.

Preferred specific examples of the quaternary phosphonium salt represented by the formula (1) include tetramethylphosphonium chloride, tetramethylphosphonium bromide, tetramethylphosphonium iodide, tetraethylphosphonium chloride, tetraethylphosphonium bromide, and tetraethylphosphonium. Odide, triethylmethylphosphonium chloride, triethylmethylphosphonium bromide, triethylmethylphosphonium iodide, tetra-n-propyl phosphonium chloride, tetra-n-propyl phosphonium bromide, tetra-n-propyl phosphate Phosphorium iodide, tri-n-propyl methylphosphonium chloride, tri-n-propyl methylphosphonium bromide, tri-n-propyl methylphosphonium iodide, tri-n-propyl ethylphosphonium iodide, tetra -n-butylphosphonium chloride, tetra-n-butylphosphonium bromide, tetra-n-butylfoam Phosphorium iodide, tri-n-butylmethylphosphonium chloride, tri-n-butylmethylphosphonium bromide, tri-n-butylmethylphosphonium iodide, tri-n-butylethylphosphonium iodide, tri -i-butylmethylphosphonium chloride, tri-i-butylmethylphosphonium bromide, tri-i-butylmethylphosphonium iodide, tetra-n-pentylphosphonium chloride, tetra-n-pentylphosphonium bromide, tetra -n-pentylphosphonium iodide, tri-n-pentylmethylphosphonium chloride, tri-n-pentylmethylphosphonium bromide, tri-n-pentylmethylphosphonium iodide, and tri-n-pentylethylphospho Nium iodide, tri-n-pentyl-n-propyl phosphonium iodide, tricyclopentylmethylphosphonium iodide, tetra-n-hexyl phosphonium chloride, tetra-n-hexyl phosphonium bromide, tetra-n -Hexyl phosphonium iodide De, tri-n-hexyl methyl phosphonium chloride, tri-n-hexyl methyl phosphonium bromide, tri-n-hexyl methyl phosphonium iodide, tri-n-hexyl ethyl phosphonium iodide, tri-n- Hexyl-n-propyl phosphonium iodide, tri-n-hexyl-n-butylphosphonium iodide, tri-n-hexyl-i-butylphosphonium iodide, tricyclohexylmethylphosphonium iodide Etc. can be mentioned. Among these compounds, triethylmethylphosphonium iodide, tri-n-propyl methylphosphonium iodide, tri-i-propyl methylphosphonium iodide, tri-n-butylmethylphosphonium iodide, Tri-i-butylmethylphosphonium iodide, tri-n-pentylmethylphosphonium iodide, tricyclopentylmethylphosphonium iodide, tri-n-hexylmethylphosphonium iodide, tricyclohexylmethyl Phosphonium iodide and the like are particularly preferred in that they exhibit high chemical stability and heat resistance. Moreover, among these, tri-n- butylmethyl phosphonium iodide is preferable since it shows the outstanding photoelectric conversion efficiency especially.

As a quaternary phosphonium salt represented by General formula (1), a commercial item can be used. As such a commercial item, the hischoline PX-4MI etc. which this applicant manufactures and sells are mentioned. In addition, the quaternary phosphonium salt represented by General formula (1) can also be synthesize | combined by the following method. That is, when the salt is, for example, a halide, it can be synthesized by nucleophilic reaction of trialkylphosphine and the corresponding alkyl halide. For example, an alkyl halide is preferably added 0.5 to 2 times mole, more preferably 0.9 to 1.2 times mole to trialkylphosphine, and is preferably in an inert solvent free of chlorine, for example in toluene. Preferably it is made to react at 20-150 degreeC, More preferably, 30-100 degreeC, Preferably it is 3 hours or more, More preferably, it is 5-12 hours. Since trialkylphosphine is easily oxidized, the reaction atmosphere is preferably an atmosphere in which oxygen is not present. For example, nitrogen atmosphere or argon atmosphere is preferable. When trialkylphosphine and halogenated alkyl are reacted in the presence of oxygen, oxygen may bind to trialkylphosphine to generate trialkylphosphine oxide, which may lower the yield. Although trialkylphosphine oxide can be removed by washing with a suitable organic solvent, it is difficult to remove the quaternary phosphonium halide because the quaternary phosphonium halide tends to dissolve in the organic solvent when the total number of carbon atoms of the quaternary phosphonium halide is increased. do. Therefore, in order not to produce trialkylphosphine oxide, it is suitable to perform reaction in inert atmosphere.

The obtained quaternary phosphonium halide can be refine | purified by recrystallization. It is preferable to perform recrystallization preferably repeatedly until an impurity content falls. Examples of the impurities to be removed by recrystallization include unreacted raw materials, trialkylphosphine oxides, and the like. As an organic solvent which can be used for recrystallization, it is preferable to use water, methanol, acetone, toluene, hexane, etc. individually or in combination.

The quaternary phosphonium halide purified by recrystallization is preferably dried in order to remove water or an organic solvent. As a drying method, the vacuum drying method which can prevent mixing of impurities and can remove moisture and an organic solvent at once is preferable. In the vacuum drying method, the drying temperature is 70 to 120 ° C, more preferably 80 to 100 ° C, and the degree of vacuum is 0.1 to 1.0 kPa, more preferably 0.1 to 0.5 kPa. Drying time is about 2 to 8 hours, More preferably, it is about 5 to 12 hours.

Next, the imidazolium salt represented by General formula (2) which is a compound used together with the quaternary phosphonium salt represented by General formula (1) is demonstrated. R ₅ to R ₉ in this imidazolium salt represent hydrogen or an alkyl group having 1 to 8 carbon atoms and may be the same or different from each other.

When R <_5> -R <_9> is an alkyl group, as a specific example, a methyl group, an ethyl group, n-propyl group, n-butyl group, n-hexyl group, i-propyl group, i-butyl group, n-pentyl group, i- Hexyl group, n-heptyl group, i-heptyl group, n-octyl group, i-octyl group, cyclopentyl group, cyclohexyl group, etc. are mentioned. Such an alkyl group may be substituted with a monovalent substituent. Examples of such a substituent include an alkenyl group, alkynyl group, alkoxy group, carboxyl group, alkyl carbonyl oxy group, alkoxy carbonyl group, sulfoxy group, alkylsulfonyl group, hydroxy group, hydroxy sulfonyl group, aryl group, aryl oxy group, acyl oxy group, Carbamoyl group, sulfonic acid group, sulfamoyl group, cycloalkyl group, cyano group, nitro group, amino group, alkylamino group, heterocyclic group, amino sulfonyl group, halogen atom, 2-butoxyethyl group, 6-bromohexyl group, 2-carboxy Ethyl group, 3- sulfoxy propyl group, 4- sulfoxy butyl group, 2-hydroxyethyl group, a phenylmethyl group, 4-butoxy phenylmethyl group, etc. are mentioned.

In general formula (2), it is preferable that R <_8> and R <_9> is hydrogen among R <_5> -R <_9> in the point which achieves high photoelectric conversion efficiency. In this case, R ₅ to R ₇ are preferably hydrogen or an alkyl group having 1 to 8 carbon atoms. In particular, it is preferable that R <_5> -R <_7> is (i) two of which are alkyl groups, and the other one is hydrogen, or (ii) all three are alkyl groups. In the case of (i), it is preferable that R <_5> and R <_7> is an alkyl group, and R <_6> is hydrogen. R ₅ and R ₇ may be the same or different, but one is a methyl group and the other is preferably an alkyl group having 1 to 8 carbon atoms. In the case of (ii), R ₅ and R ₆ are the same alkyl group, and R ₇ is preferably an alkyl group different from R ₅ and R ₆ . In this case, R ₇ is preferably an alkyl group having a larger carbon number than R ₅ and R ₆ . It is especially preferable that R <_5> and R <_6> is a methyl group and R <_7> is a C2-C4 alkyl group.

As the monovalent anion X ₂ ⁻ in formula (2), for example, halide ions, tetrafluoroborate (BF ₄ ), hexafluorophosphate (PF ₆ ), bis (trifluoromethylsulfonyl) imide (N ( SO ₂ CF ₃ ) ₂ ), bis (fluorosulfonyl) imide (N (SO ₂ F) ₂ ), tetracyanoborate (B (CN) ₄ ), trifluoromethanesulfonate (SO ₃ CF ₃ ), Pentafluoroethanesulfonate (SO ₃ CF ₂ CF ₃ ), tetrafluoroethanesulfonate (SO ₃ CHFCF ₃ ), methanesulfonate (SO ₃ CH ₃ ), ethanesulfonate (SO ₃ C ₂ H ₅ ), Tris (pentafluoroethyl) trifluoro phosphate ((C ₂ F ₅ ) ₃ PF ₃ ), trifluoro acetic acid (CF ₃ COO), amino acid, bisoxalate borate (B (C ₂ O ₄ ) ₂ ), p-toluene sulfonate (SO ₃ C ₆ H ₄ CH ₃ ), thiocyanate (SCN), dicyanamid (N (CN) ₂ ), dialkylphosphoric acid ((RO) ₂ POO), dialkyldithi o acid ((RO) ₂ PSS), aliphatic carboxylic acid (RCOO), etc. The can. Among these anions, halide ions are preferable in view of further improving the photoelectric conversion efficiency, and particularly when iodide ions are used in combination with the phosphonium salt represented by the formula (1), excellent photoelectric conversion efficiency can be achieved. It is preferable because it can. In addition, X ₂ ^- X ₁ is of formula ⁽¹⁾ is also preferred and homogeneous. Most preferred is when both X ₁ ^- and X ₂ ^- are iodide ions.

As a preferable specific example of an imidazolium salt, 1, 3- dimethyl imidazolium iodide, 1, 3- diethyl imidazolium iodide, 1-ethyl-3 from a viewpoint of expressing a high opening voltage and a shape factor -Methyl imidazolium chloride, 1-propyl- 3-methyl imidazolium chloride, 1-butyl- 3-methyl imidazolium chloride, 1-hexyl- 3-methyl imidazolium chloride, 1-octyl- 3-methyl Imidazolium chloride, 1-ethyl-3-methyl imidazolium bromide, 1-propyl-3-methyl imidazolium bromide, 1-butyl-3-methyl imidazolium bromide, 1-hexyl-3-methyl imida Sodium bromide, 1-octyl-3-methyl imidazolium bromide, 1-ethyl-3-methyl imidazolium iodide, 1-propyl-3-methyl imidazolium iodide, 1-butyl-3-methyl Imidazolium Iodai , 1-hexyl 3-methyl imidazolium iodide, 1-octyl 3-methyl imidazolium iodide, 1,2-dimethyl-3-ethyl imidazolium iodide, 1,2-dimethyl -3-propyl imidazolium chloride, 1,2-dimethyl-3-propyl imidazolium bromide, 1,2-dimethyl-3-propyl imidazolium iodide, 1,2-dimethyl-3-butyl imida Zolium chloride, 1, 2- dimethyl- 3- butyl imidazolium bromide, 1, 2- dimethyl- 3- butyl imidazolium iodide, etc. are mentioned. Among these compounds, 1-ethyl-3-methyl imidazolium iodide, 1-propyl-3-methyl imidazolium iodide, 1-butyl-3-methyl imidazolium iodide, 1-hexyl- 3-methyl imidazolium iodide, 1-octyl-3-methyl imidazolium iodide, 1,2-dimethyl-3-ethyl imidazolium iodide, 1,2-dimethyl-3-propyl imide Dazolium iodide, 1, 2- dimethyl- 3-butyl imidazolium iodide, etc. are preferable. Moreover, in this, 1, 2- dimethyl- propyl imidazolium iodide expresses especially the photoelectric conversion efficiency excellent, and is preferable.

Imidazolium salts represented by formula (2) are known in the art and are commercially available.

The present invention has the first feature in that the quaternary phosphonium salt represented by the formula (1) and the imidazolium salt represented by the formula (2) are used in a specific ratio. Specifically, 20-80 mol% of quaternary phosphonium salts are used with respect to the total amount of both, Preferably it is 40-60 mol%, and 20-80 mol% of imidazolium salt, Preferably it is 40-60 mol % use. By using both in the above formulation, the electrolyte composition of the present invention exhibits high photoelectric conversion efficiency. In addition, the composition has good solubility and is rich in heat resistance and inferiority. Specifically, by using the electrolyte composition of the present invention, the redox band redox efficiency is increased, the efficiency of charge transfer in the electrolyte composition is increased, the short-circuit photocurrent density is improved, and as a result, the photoelectric conversion efficiency is improved. In addition, the chemical stability and heat resistance of the electrolyte composition are improved due to the combination of the quaternary phosphonium salt and the imidazolium salt. Furthermore, quaternary phosphonium ions represented by the general formula (1) are advantageous in view of higher solubility in solvents than the corresponding nitrogen-based cations, and easy to increase the concentration of anions, particularly halide ions.

In the electrolyte composition of the present invention, when the ratio of the quaternary phosphonium salt is less than 20 mol% or the ratio of the imidazolium salt is more than 80 mol%, the short-circuit photocurrent density is lowered and the photoelectric conversion efficiency is lowered. The chemical stability and the heat resistance derived from the phosphonium salt are lowered. On the contrary, when the ratio of the quaternary phosphonium salt exceeds 80 mol% or the ratio of the imidazolium salt is less than 20 mol%, the opening voltage and the shape factor are lowered, and as a result, the photoelectric conversion efficiency is lowered.

Since the composition of this invention contains the quaternary phosphonium salt represented by General formula (1) which is a phosphorus containing component, it exhibits an ovary and self-extinguishing property. In particular, in the quaternary phosphonium salt represented by the general formula (1), since the alkyl group is short-chain (1-6 carbon atoms) and has a low molecular weight, the ratio of phosphorus atoms is high, so that it has moderate ovary and self-extinguishing properties.

As apparent from the above description, the electrolyte composition of the present invention increases the redox efficiency of the redox band, and as a result, high photoelectric conversion efficiency can be obtained, and also has good solubility, and high chemical stability, heat resistance and ovary resistance. Therefore, the electrolyte composition of this invention can be used advantageously as electrolyte composition of a photoelectric conversion element.

The electrolyte composition of the present invention may be composed of only the quaternary phosphonium salt represented by the formula (1) and the imidazolium salt represented by the formula (2), or may include other components in addition thereto. Such other components will be described later. When the electrolyte composition of this invention contains the said other component, the ratio of the total amount of the quaternary phosphonium salt represented by General formula (1) and the imidazolium salt represented by General formula (2) in an electrolyte composition is 0.05-3.0 with respect to the whole electrolyte composition. It is preferable that mol / L, especially 0.1-1.5 mol / L, fully achieves high photoelectric conversion efficiency.

The photoelectric conversion element provided with the electrolyte composition of the present invention includes a device for converting light into electrical energy and a device for converting electrical energy into light. Typical examples of the former include power generation devices such as dye-sensitized solar cells and photodiodes. Typical examples of the latter include light emitting devices such as light emitting diodes and semiconductor lasers. Also in the case where the photoelectric conversion element is both a power generation device and a light emitting device, as shown in FIG. 1, the photoelectric conversion element 10 includes the semiconductor layer 11 and the dye layer 12 provided on one surface of the semiconductor layer 11. ), Between the transparent electrode layer 13 provided on one side of the semiconductor layer 11, the counter electrode 14 disposed to face the dye layer 12, and the dye layer 12 and the counter electrode 14. The electrolyte layer 15 arrange | positioned is provided. The electrolyte layer 15 is made of a composition containing a quaternary phosphonium halide represented by the formula (1). In the case of using the photoelectric conversion element 10 shown in FIG. 1 as a power generation device, between the transparent electrode layer 13 and the counter electrode 14 by irradiating sunlight (visible light) from the side surface of the transparent electrode layer 13. EMF is generated. In the case where the photoelectric conversion element 10 shown in FIG. 1 is used as a light emitting device, a voltage is applied between the transparent electrode layer 13 and the opposite electrode 14 between the semiconductor layer 11 and the dye layer 12. Luminescence occurs. In addition, although the conducting wire is connected to the transparent electrode layer 13 and the counter electrode 14 in FIG. 1, you may connect the conducting wire to the semiconductor layer 11 instead of the transparent electrode layer 13. As shown in FIG. In this case, the transparent electrode layer 13 is not essential.

The photoelectric conversion element 10 using the electrolyte composition of this invention is especially useful as a dye-sensitized solar cell which is a kind of power generation apparatus. In particular, an electrolyte composition containing tri-n-butyl methyl phosphonium iodide as a quaternary phosphonium salt represented by the formula (1) increases the redox efficiency of the redox band, resulting in high photoelectric conversion efficiency. Since excellence can be expected, it is preferable. Moreover, when this electrolyte composition is used for a dye-sensitized solar cell, it is preferable at the point that high chemical and thermal stability can be acquired compared with the case of using the halide of a nitrogen type cation.

When the photoelectric conversion element using the electrolyte composition of this invention is a dye-sensitized solar cell, an example of the specific structure of the said dye-sensitized solar cell is as follows. That is, the dye-sensitized solar cell includes a transparent electrode layer, a nanoporous oxide semiconductor layer coated with the sensitizing dye and a counter electrode, and a redox band disposed on at least part of the transparent electrode layer and the counter electrode. It consists of an electrolyte layer included. When sunlight (for example, visible light) irradiated from the transparent electrode side excites the dye on the oxide semiconductor, the excited dye injects electrons into the conduction band of the oxide semiconductor. The resultant dye oxidant receives electrons from the reducing agent in the electrolyte layer and returns to the ground state dye, which forms the oxidant. Electrons injected into the oxide semiconductor layer donate electrons to the oxidant in the electrolyte layer at the opposite electrode via an external circuit. Through the above cycle, a normal photocurrent flows through the circuit.

The transparent electrode layer is not particularly limited as long as it has good light transmittance and exhibits conductivity by forming a layer made of a conductive material on its surface. For example, glass, polyethylene terephthalate (PET) or a combination of transparent oxide semiconductors such as tin indium oxide (ITO), tin oxide (SnO ₂ ), fluorinated tin oxide (FTO), and zinc oxide (ZnO) alone or in combination. ), Polyethylene naphthalate (PEN), polycarbonate (PC) and the like are preferably formed on a transparent substrate as a thin film. The nanoporous oxide semiconductor layer was used alone or in combination with titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), niobium oxide (Nb ₂ O ₅ ), or the like. It is a porous thin film mainly containing oxide semiconductor fine particles. 1-200 nm is preferable, as for the average diameter of the oxide semiconductor fine particles used, 3-100 nm is more preferable, and 5-50 nm is more suitable. The oxide semiconductor is generally n-type, but is not limited to this and may be p-type. The sensitizing dye supported on the nanoporous oxide semiconductor is not particularly limited as long as it absorbs sunlight (for example, visible light) efficiently. For example, metal complexes such as ruthenium complexes and iron complexes having ligands including a bipyridine structure and a tapyridine structure, metal complexes such as porphyrin-based or phthalocyanine-based organic pigments such as eosin, rhodamine, melocyanine, and coumarin And the like are preferable in terms of light excitation under sunlight irradiation conditions. The counter electrode is not particularly limited as long as it is an electrode that generates electromotive force between the transparent electrode, but a conductive film such as gold, platinum, carbon-based material, conductive polymer material, etc. may be formed by a vacuum film forming method such as a sputtering method or a vapor deposition method, It is preferable to use what was formed on the board | substrate as an electrode in accordance with methods, such as a wet film forming method which adds heat processing after apply | coating platinum solution, such as a coating method and a platinum chloride solution.

When the electrolyte composition of the present invention is used as an electrolyte layer of a dye-sensitized solar cell, a redox band is added to the electrolyte composition in addition to the quaternary phosphonium represented by the formula (1) and the imidazolium salt represented by the formula (2). It is preferable. The redox band is not particularly limited as long as the redox potential is between the reduction potential of the excitation pigment and the oxidation potential of the opposite electrode, but iodide ion (I ⁻ ), bromide ion (Br ⁻ ), chloride ion (Cl ^-) halide ions and Br, such as _{^{3 -, I 3 -, I}} 5 -, I 7 -, Cl 2 I -, ClI 2 -, Br 2 I -, BrI 2 - , such as poly-halides It is preferable to use a halogen-containing redox band composed of ions. As for the density | concentration with respect to the whole redox electrolyte electrolyte composition, 0.05-4.0 mol / L is preferable at molar concentration, 0.1-3.0 mol / L is more preferable, 0.5-2.0 mol / L is still more preferable. This halogen-containing redox band can be obtained by reacting halogen molecules with halide ions such as iodide ions, bromide ions, chloride ions and the like. The ratio of the halogen molecules to the halide ions is not particularly limited, but is preferably 1 to 100% by molar ratio, more preferably 2 to 50% by mole ratio, and still more preferably 3 to 30% by molar ratio.

The quaternary phosphonium salt contained in the electrolyte composition of the present invention functions not only as an electrolyte but also as a source of halide ions constituting the redox band. Of course, substances other than the quaternary phosphonium salt may be added to the electrolyte composition separately as a source of halide ions. For example, lithium halides, sodium halides, quaternary anmonium halides, pyridinium halides, pyrrolidinium halides, piperidinium halides, sulfonium halides and the like can be used alone or in combination.

In the case of using the electrolyte composition of the present invention as an electrolyte layer of a dye-sensitized solar cell, in order to increase the photoelectric conversion efficiency, 4-tert-butyl pyridine (TBP), 2-vinyl pyridine, and N-vinyl are added to the electrolyte composition as necessary. It is preferable to add various additives such as organic nitrogen compounds such as -2-pyrrolidone, lithium salts, sodium salts, magnesium salts, iodides, thiocyanates and water. As exemplified in the examples described below, the use of TBP as an additive or a combination of TBP and lithium iodide is preferable in that the photoelectric conversion efficiency is further improved. Although there is no restriction | limiting in particular in the addition amount of such an additive, As for the density | concentration of each additive in electrolyte composition, 0.01-4.0 mol / L is preferable, 0.05-3.0 mol / L is more preferable, 0.1-2.0 mol / L is further more desirable.

You may add a solvent to the electrolyte composition of this invention as needed. As the solvent, it is preferable to use one having a low viscosity, high ion mobility and excellent ion conductivity. As such a solvent, For example, Carbonate compounds, such as ethylene carbonate and a propylene carbonate; Heterocyclic compounds, such as 3-methyl- 2-oxazolidinone; Ether compounds, such as dioxane and a diethyl ether; Ethylene glycol dialkyl ether, Pro Chain ethers such as pyrene glycol dialkyl ether, polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether; methanol, ethanol, ethylene glycol mono alkyl ether, propylene glycol mono alkyl ether, polyethylene glycol mono alkyl ether, polypropylene glycol mono Alcohols such as alkyl ethers; polyhydric alcohols such as ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, glycerin, nitrile compounds such as acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile and benzonitrile Dime Aprotic polar solvents, such as sulfoxide (DMSO), sulfolane; water; and the like can be mentioned ionic liquid (room temperature molten salt). You may use these solvent in mixture of 2 or more type. It is preferable that the usage-amount of a solvent shall be 5-95 weight% with respect to the whole electrolyte composition.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to these examples.

(Example 1 and Comparative Examples 1 and 2)

An electrolyte composition having the composition shown in Table 1 below was prepared.

The dye-sensitized solar cell was produced in the following procedures using the obtained electrolyte composition, and the evaluation was performed by the following method. The results are shown in Table 2.

As a photoanode, a fluorinated tin oxide transparent electrode (FTO; 10.8 Ω cm ^-2 manufactured by Asahi Glass Co., Ltd.) coated with titanium oxide nanoparticles (Solaronix D) with a doctor blade to have a film thickness of 15 µm, The thing baked at 450 degreeC for 30 minutes was used. 0.3 nmol / l N3 pigment | dye (cis- di (thiocyanato) -N, N-bis (2,2'- bipyridyl-4,4'- dicarboxylic acid) ruthenium (II) of this photoanode Complex) It was immersed in ethanol solution at 40 degreeC for several hours, and the pigment was supported. A cell was squeezed (interval: 300 µm) with a photoanode on which a dye was supported and a platinum-supported counter electrode interposed therebetween, and both were filled with the electrolyte compositions obtained in Examples and Comparative Examples. The working area of the photoanode was 0.283 cm ³ , and the other surface was masked. Other than that produced the dye-sensitized solar cell according to the conventional method. In the dye-sensitized solar cell thus obtained, photocurrent-voltage characteristics were measured using an AM1.5 solar simulator (PEC Cell PEC-L10N) equipped with a Caselay 2400 high voltage power supply and a 500 W xenon lamp. . Light intensity was adjusted using an ND filter (100 mWcm ^-2 ). All measurements were performed on the conditions of normal temperature and normal pressure. In addition, the shape factor is an index indicating electrical internal loss, and the larger the value, the higher the value of the battery.

Open voltage (V) Short circuit photocurrent density
(mAcm ^-2 ) Shape factor (%) Photoelectric conversion efficiency (%) Example 1 0.699 18.8 0.59 7.8 Comparative Example 1 0.698 19.2 0.55 7.4 Comparative Example 2 0.714 16.4 0.61 7.1

As is evident from the results shown in Table 2, the solar cell using the electrolyte composition of the example using a quaternary phosphonium salt and an imidazolium salt was prepared using the electrolyte composition of Comparative Example 1 using a quaternary phosphonium salt alone. Compared with a solar cell, it turns out that it exhibits high photoelectric conversion efficiency. Moreover, it turns out that it shows high short circuit photocurrent density and high photoelectric conversion efficiency compared with the solar cell using the electrolyte composition of the comparative example 2 which used imidazolium salt alone.

10 photoelectric conversion element
11 semiconductor layer
12 pigmented layers
13 transparent electrode layer
14 Opposition
15 electrolyte layer

Claims (7)

It contains a quaternary phosphonium salt represented by the following formula (1) and the imidazolium salt represented by the following formula (2), 20 to 80 mol% of the quaternary phosphonium salt relative to the total amount of both, the imidazolium salt is Electrolyte composition for a photoelectric conversion element characterized in that it comprises 20 to 80 mol%.
[Formula 1]

(2)

In the above formula, R ₁ , R ₂ , R ₃ and R ₄ represent an alkyl group having 1 to 6 carbon atoms, may be the same or different from each other, R ₁ and R ₂ may form a ring, X ₁ ^- is 1 A false negative anion;
R ₅ to R ₉ represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and may be the same or different from each other, and X ₂ ⁻ represents a monovalent anion. The electrolyte composition of claim 1, wherein R ₁ , R _2, and R ₃ of Formula 1 are all the same alkyl group, and the carbon number of R ₄ is smaller than the carbon number of each of R ₁ , R _2, and R ₃ . . The electrolyte composition of claim 2, wherein R ₁ , R _2, and R ₃ of Formula 1 are butyl groups, and R ₄ is a methyl group. The electrolyte composition for a photoelectric conversion element according to any one of claims 1 to 3, wherein X ₁ ⁻ in Formula 1 is an iodide ion. The photoelectric conversion element electrolyte according to any one of claims 1 to 3, wherein the electrolyte-containing redox band composed of halide ions and polyhalide ions contains 0.05 to 4.0 mol / L of the composition as a whole. Composition. A semiconductor layer;
A dye layer provided on one side of the semiconductor layer;
An opposite electrode disposed to face the dye layer; And
And an electrolyte layer made of the electrolyte composition of claim 1 disposed between the dye layer and the counter electrode. The photoelectric conversion element according to claim 6, which is a dye-sensitized solar cell.

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