JP6531977B2 - Electrolyte for dye-sensitized solar cell and dye-sensitized solar cell using the electrolyte - Google Patents

Description

  The present invention relates to an electrolyte for a dye-sensitized solar cell and a dye-sensitized solar cell using the electrolyte.

  Dye-sensitized solar cells, a new type of solar cell developed by Gratzel et al. At the Lausanne Institute of Technology in 1990, can be manufactured inexpensively and have superior features such as performance equal to or better than amorphous solar cells. It is noted worldwide for having it. As a subject of this dye-sensitized solar cell, the further improvement of a photoelectric conversion efficiency (it may only be called conversion efficiency hereafter), the improvement of durability, etc. are mentioned.

  In order to obtain high durability, it is required that the electrolyte does not generate gas by decomposition or volatilization. The outer peripheral edge of the cell of the dye-sensitized solar cell is sealed with a sealing material so that the electrolyte does not leak. If the electrolyte is decomposed or volatilized to generate gas, the cell may be broken due to the rise in internal pressure, and the electrode portion containing bubbles due to the gas generation does not cause photovoltaic generation, and the conversion efficiency is lowered. It is because it

  Particularly in the case of a highly volatile electrolyte, the vapor pressure of the electrolyte rises under high temperature conditions, so it is difficult to completely seal the cell for a long period and maintain airtightness. Therefore, the electrolyte for dye-sensitized solar cells is required to be hard to evaporate even under high temperature conditions and to have high stability.

  Conventionally, as electrolyte solution for dye-sensitized solar cells, one in which lithium iodide or iodide salt and iodine are dissolved in methoxypropionitrile or acetonitrile is generally used (Patent Document 1). However, although the nitrile solvent has a high initial conversion efficiency, it has a high vapor pressure and is volatilized from the cell, so there is a problem that sufficient durability can not be obtained.

  The electrolyte solution for dye-sensitized solar cells using propylene carbonate or (gamma) -butyrolactone as a solvent is also disclosed (patent documents 3 and 4). However, even if these electrolytes are used, they volatilize particularly in a situation where they are used outdoors, and the usable temperature range is narrow. In addition, carbonates react with iodine and iodide salts to be decomposed, and furthermore, lactones have a fatal defect as a solar cell that is decomposed by light, and these solvents generate gas when decomposed And there is a problem that the durability is inferior.

  In order to obtain practical durability as an electrolyte for dye-sensitized solar cells, solvents and additives which have a high boiling point of 200 ° C. or higher, and which are chemically, electrochemically or photochemically stable are used. Is required. As measures against the problem of durability, some of the present inventors have found an electrolyte for a dye-sensitized solar cell using a chain sulfone as a solvent as a novel high-durability electrolyte (Non-patent Literature 1). However, for the electrolytic solution using the linear sulfone solvent, further improvement in conversion efficiency has been required.

(A) Improvement of photoelectric conversion efficiency With regard to improvement of photoelectric conversion efficiency, the photoelectric conversion efficiency of a dye-sensitized solar cell using the electrolytic solution by adding a basic additive to the electrolytic solution for a dye-sensitized solar cell It is reported that it can improve (patent documents 1-19).

  It is described that the open circuit voltage can be increased by preventing the reverse current flowing from the porous semiconductor layer to the liquid electrolyte layer regardless of the light irradiation by the addition of such a basic additive. (For example, paragraph 0006 of patent document 14 and paragraph 0006 of patent document 15).

(Difference in the effect of solvent interaction)
However, when the additive is added, the interaction between the additive and the solvent and the other electrolyte acts to change the viscosity as the electrolytic solution. If a solvent with a low viscosity is used, even if the interaction between the additive and the solvent works, the original viscosity is low, so that the movement of the electrolyte can still be maintained at a sufficient speed, but a highly heat resistant electrolyte In order to achieve this, when using a high boiling point solvent such as chain sulfone, the viscosity of the solvent itself increases with the improvement of the boiling point, so the influence of the viscosity by the addition of the additive becomes large I will. As a result, the diffusion of the electrolyte is inhibited, and the short circuit current density tends to be low. Even if the open circuit voltage is improved by the additive, if the current value is reduced more than the effect, the conversion efficiency is reduced.

  Patent Document 5 discloses that an electron donor compound having a noncovalent electron pair is used as an additive, and various organic solvents are disclosed as a solvent at that time. However, the examples given as examples are extremely durable. Acetonitrile is used as the solvent because it lacks the viscosity and the viscosity of the additive and the viscosity is negligible so that the molecular size can be ignored, and only the amino-pyrimidine and t-butylpyridine are used as the electron donor compound. is there. Since the effect of the interaction differs depending on the solvent, it is impossible to deduce from this patent what basic additive is effective for improving the conversion efficiency in any organic solvent, not the high boiling point solvent. That is, it is difficult to select an additive suitable for the chain sulfone solvent based on the evaluation with acetonitrile.

  Similarly, all of the additives in Patent Documents 6 to 9 and 13 to 16 are also evaluated with acetonitrile, and as described above, it is difficult to estimate the effect of using a high boiling point solvent.

(Boiling point difference due to additive skeleton between additives of similar molecular weight)
Patent Document 11 discloses an example using, as an additive, a nitrogen-containing heterocyclic compound composed of a 5- or 6-membered aromatic ring containing two or more nitrogen atoms and having no substituent.

  The patent specification paragraph 0016 states that it is preferable to add a basic compound with a molecular size as small as possible so as not to increase the viscosity of the electrolyte as much as possible, and further, as such a basic compound, a substituent It is said that cyclic bases having a small size and therefore small molecular size are used, specifically imidazole, pyrazole, triazole, pyridazine, pyrimidine, pyrazine, triazine as a six-membered ring in a five-membered ring. Further, in the patent specification paragraph 0019, the boiling points of pyrazole, imidazole, triazole and pyridine having substantially the same molecular weight are largely different, and it is preferable to use those having high boiling points.

  As described in the patent document, it can also be generally assumed that the smaller the molecular size of the additive, the lower the viscosity of the electrolyte solution. However, as pyrazole and imidazole have almost the same molecular weight as pyridine, that is, almost the same molecular size but different boiling points of these compounds, those having different main structures also differ in physical properties such as boiling point and viscosity. The molecular sizes can be compared only when the ones having the same main structure are compared with one another in the solvent having the same or a similar structure. Furthermore, the patent documents and Patent Documents 1, 2 and 10 also disclose additives evaluated with methoxypropionitrile having a relatively low boiling point and low viscosity, and studies on high boiling point solvents are conducted at all. It is impossible to determine the structure of the additive suitable for the high boiling point organic solvent and the molecular size thereof.

(Determination of carrier transport between high boiling point solvent and ionic liquid, various mechanisms such as solvation, etc.)
Moreover, in patent document 11, the effect of the additive with respect to an ionic liquid electrolyte solution is also compared. Similarly, Patent Document 17 also reports an example in which benzimidazole or the like in an ionic liquid electrolytic solution is used as an additive. However, the mechanism of carrier transport of iodine redox is different between the ionic liquid electrolyte used for these and the organic solvent electrolyte using a nonionic molecule as a solvent, and the concentration of the iodine redox is appropriate for both. From the results of the ionic liquid electrolyte, it is not possible to distinguish the additive suitable for the high boiling point organic solvent. In addition, the ionic liquid forms an ion pair, and the interaction with the additive and the state of solvation are completely different from those of the organic solvent-based electrolyte solution, and furthermore, the volatilization and gas generation itself hardly occur. Therefore, also from the fact that the degradation mechanism itself as a solar cell device is different from that of the organic solvent-based electrolyte solution, etc., the additive suitable for the organic solvent-based electrolyte solution is the result of the additive in the ionic liquid electrolyte Can not be determined in the first place.

  As described above, with regard to how much the viscosity changes depending on the additive, the interaction differs depending on the combination of the solvent or electrolyte used and the additive, and the concentration and composition ratio thereof. It is impossible to predict in advance the viscosity change of the resulting electrolyte, and even if additives that did not pose a problem when using a low viscosity solvent, a high boiling point solvent was used. In this case, it can not be guessed what kind of adverse effect on the current value or the form factor (abbreviated as "ff").

  In addition to the problem of current value, the basicity of the solvent itself and the electron acceptability are different, so the open circuit voltage of the solar cell is different depending on the solvent used for the electrolyte solution, so It is unclear if it can be used to effectively improve the open circuit voltage among the high boiling point solvents used.

  Therefore, it is possible to evaluate the quality of the characteristics of the electrolytic solution of the composition only by actually preparing the electrolytic solution and assembling the solar cell. Based on the above-mentioned prior art documents, no excellent electrolyte solution can be obtained.

(Difference of appropriate additives between high boiling point solvents)
Patent Document 12 exemplifies a nitrogen-containing aromatic 5- or 6-membered ring compound having a specific structure having a specific substituent at the α-carbon of the ring nitrogen. As the solvent, a high boiling point solvent having a boiling point of 200 ° C. or higher is mentioned in paragraph 0032, and solvents of S-5 and S-6 are mentioned as being particularly preferable among them, and further, a combination with an additive suitable for each is mentioned in paragraph It is described in Table 3 of 0135. However, although these additives considered to be suitable for S-5 and S-6 solvents were added to the linear sulfone electrolyte of the present invention, it has not been possible to obtain excellent electrolyte performance. (See comparative example). That is, as described above, in the prior art, the molecular structure of the solvent is different, even if certain additives are suitable for certain high boiling solvents, as well as low viscosity, low boiling solvents. Then, it can be said that it can not be guessed at all whether the additive is also suitable for the linear sulfone used as a solvent in the present invention. That is, even based on the prior art documents, no excellent electrolytic solution was obtained.

(B) Improvement of Durability On the other hand, there is almost no prior art concerning the durability of a dye-sensitized solar cell using an electrolytic solution to which a basic additive is added, in particular, the improvement of the durability by a basic additive. For example, although there is a report on an example in which the light resistance test by light irradiation in the case of an electrolytic solution using acetonitrile as a solvent is reported, there is no example regarding the heat resistance test, that is, the durability against volatilization etc. 9, 13-16). Also from this fact, it can be easily estimated that the electrolyte using acetonitrile as the solvent is practically durable, in particular, the heat resistance is low. Therefore, the durability of the solvent is less than the durability of each additive, and the durability of each additive has not been evaluated.

  Patent Document 17 reports that the durability of the dye-sensitized solar cell is further improved by adding a benzimidazole derivative to the electrolytic solution. However, the document does not at all demonstrate the durability improvement effect by the benzimidazole derivative in the examples, and the performance is greatly reduced by the heat resistance test, and the durability remains insufficient.

  In Patent Document 10, a pyridine having an alkyl substituent in which 1-position is a tertiary carbon as an additive of an electrolytic solution for improving high-temperature durability, and a t-butylpyridine exemplified as another example in another patent document Is disclosed. However, the solvent used in the patent document has a boiling point lower than that of the additive, and it is still unclear whether sufficient durability can be obtained even in a high boiling point solvent. In addition, pyridines have a strong odor and there is a problem that the handling environment at the time of production is deteriorated.

  Furthermore, as an additive superior to t-butylpyridine, in Patent Document 16, when various specific aromatic ring hetero compounds are added to the electrolyte, it is higher than t-butylpyridine or 2-vinylpyridine. It is reported to have found that it has an open circuit voltage and its durability is also high. Although there is no technical explanation in the document, when the substituent bonded to the monocyclic aromatic heterocycle is an organic residue having 2 or less carbon atoms, it is added to the electrolyte of a wet solar cell. However, since high durability and the like can not be obtained (paragraph 0011), the boiling point of the basic additive is increased by having a certain molecular weight, thereby improving the durability of the electrolyte. It is considered to be intended.

  Similarly, Patent Document 11 discloses a nitrogen-containing heterocyclic compound comprising a 5- or 6-membered ring containing two or more nitrogen atoms and having no substituent. Although no example is given regarding durability, as described in paragraphs 0020 and 0057, it is considered desirable that the boiling point of the additive be as high as possible.

  Therefore, it is naturally desirable that the additive has as high a boiling point as possible, but these patent documents disclose the additive combined with a low boiling point and low viscosity methoxypropionitrile, or an electrolytic solution as described above The mechanism is an effect that is matched to different ionic liquid electrolytes, and no studies have been conducted on non-ionic high boiling point solvents. That is, since methoxypropionitrile listed as the optimum solvent in the patent documents and the like has a low boiling point and the durability is compared in a state where sufficient durability as a solar cell can not be obtained, the basic addition thereof Not only the effect of improving the conversion efficiency in the high boiling point solvent of the agent but also how the durability changes depending on the type of basic additive remains essentially unknown.

JP 2005-327515 A JP, 2011-28918, A JP 2007-220608 A JP, 2000-277182, A Japanese Patent Application Publication No. 2006-12848 JP, 2005-216490, A JP, 2005-38711, A Japanese Patent Application Laid-Open No. 2003-331936 Unexamined-Japanese-Patent No. 2004-47229 Unexamined-Japanese-Patent No. 2010-218902 JP, 2006-134615, A JP 2000-90991 A JP, 2004-273272, A Unexamined-Japanese-Patent No. 2006-331995 JP, 2005-108664, A Japanese Patent Application Publication No. 2003-331646 JP, 2009-231008, A JP, 2013-54879, A WO 2007/091525 Electrochemistry, 3, 163 (2011)

  Among these, some of the present inventors, in Patent Document 18, add an additive that exhibits excellent conversion efficiency while having sufficient durability against a high boiling point chain sulfone solvent. Although it has been found, further performance improvement is required.

In order to improve the performance, as in Patent Document 11, there is a directionality of using an additive with the smallest possible molecular size so as not to raise the viscosity of the electrolyte as much as possible. However, when the molecular size is reduced, the boiling point generally decreases, and the heat resistance as the electrolyte solution is reduced. Conversely, means to increase the molecular weight is effective to raise the boiling point of the additive. However, as in the case where the boiling point of the solvent itself is increased, when the molecular weight of the additive itself is increased, for example, the boiling point is increased by a method which simply increases the carbon number of the organic residue of the basic additive. the elevated base additives, viscosity of the electrolyte also increases, redox electrolyte (e.g. I ₃ ^- / I ^-) to work in the direction preventing the diffusion, as originally solvent viscosity than conventional nitrile solvent In the case of a high chain sulfone solvent, it is considered to be a factor that particularly reduces the photoelectric conversion efficiency.

  In addition to the heat resistance, the durability, such as the chemical, electrochemical, photochemical stability, and the like, of the basic additive affect the durability when assembling the solar cell as an electrolytic solution and a device. Other factors may also be present.

  Therefore, the object of the present invention is to use an electrolyte solution which can achieve both compatibility with such durability, particularly heat resistance improvement and photoelectric conversion efficiency improvement, which can be in such a reciprocal relationship, by using a high boiling point solvent. It is providing the dye-sensitized solar cell used.

A first aspect of the present invention is an electrolyte solution for a dye-sensitized solar cell, comprising a redox electrolyte, a basic additive, and a solvent,
The basic additive is
1- (Arylmethyl) imidazole of the following formula (1):

In the formula (1), Ar represents an unsubstituted 5- or 6-membered aromatic group,
The said solvent is a chain | strand-shaped sulfone compound of following formula (2) as a solvent:

At least including
In the above formula (2), R ₁ and R _{2 each} independently may be partially substituted with at least one substituent selected from the group consisting of a halogen group, an alkoxy group and an aromatic ring group; It is an electrolyte solution for dye-sensitized solar cells, characterized by showing 1 to 12 alkyl groups or aryl groups.

  A second aspect of the present invention is a dye-sensitized solar cell characterized in that the electrolyte for a dye-sensitized solar cell of the first aspect of the present invention is used.

  By using the electrolytic solution of the present invention, it becomes possible to form a dye-sensitized solar cell in which high durability and high conversion efficiency are more compatible.

(A) About the 1st aspect of this invention This aspect is an electrolyte solution for dye-sensitized solar cells containing a redox electrolyte, a basic additive, and a solvent.

(A-1) Basic Additive (A-1-1)
The basic additive used in the present invention is
1- (Arylmethyl) imidazole of the following formula (1):

  It is a basic additive which has the chemical structure of, and in said Formula (1), Ar represents an unsubstituted and 5- or 6-membered ring aromatic group.

The structural features of the basic additive added to the electrolyte of the present invention are:
(A) having no substituent other than one nitrogen atom on the imidazole ring, and (b) the one nitrogen atom on the imidazole ring being unsubstituted and having a five-membered ring or the like via a methylene group It is to be bonded to a six-membered aromatic group.

  By using the basic additive having such a characteristic structure, high durability and high conversion efficiency could be better achieved.

(A-1-2)
Ar in the formula (1) represents an unsubstituted 5-membered or 6-membered aromatic group, and as such an aromatic group, a 6-membered ring aromatic group such as a phenyl group or a pyridyl group (for example, And 2-pyridyl group, 3-pyridyl group, 4-pyridyl group etc., and examples of 5-membered ring aromatic group include imidazoyl group (eg, 1-imidazoyl group, 4-imidazoyl group etc.), pyrrolyl group For example, 1-pyrrolyl group etc. etc. can be illustrated.

  Here, the term "unsubstituted" means that the aromatic ring has no substituent other than bonding through an imidazole ring and a methylene group.

  From the viewpoint of obtaining a basic additive having a relatively low molecular weight but a high boiling point, it is preferable to use a heterocyclic ring such as a pyridyl group, an imidazoyl group or a pyrrolyl group as the aromatic group.

  Also, from the viewpoint of the chemical stability of the basic additive, it is preferable to use a phenyl group as the aromatic group. More specifically, 1-benzylimidazole of the following formula (1-1) can be exemplified.

(A-1-3)
The boiling point at 1 atmosphere pressure of the basic additive of the present invention is preferably 160 ° C. or more, more preferably 200 ° C. or more, and still more preferably 250 ° C. or more from the viewpoint of sealing property. Incidentally, the boiling point at 1 atmosphere of the compound of the above formula (1-1) is 310 ° C.

  Moreover, when using a solvent, it is preferable to have a boiling point higher than the boiling point of a solvent.

  The concentration of the basic additive of the present invention in the electrolytic solution is not particularly limited because the amount of irradiated light varies depending on the environment used and the concentration of the appropriate electrolyte varies, but, for example, outdoors, Even if it is indoors, when relatively high light is irradiated, such as at the window, 0.01 mol / L or more is preferable from the viewpoint of improving the cell open circuit voltage, 0.1 mol / L or more is more preferable, electrolyte stability, dye It is preferable that it is 1 mol / L or less from a viewpoint of desorption suppression etc., and it is more preferable that it is 0.5 mol / L or less. However, since the linear sulfone compound [see below (A-2)] used as a solvent is a solvent having a relatively high viscosity, the viscosity increase due to the addition of the basic additive, and the photoelectric conversion efficiency thereby It is preferable to avoid the decrease of From such a viewpoint, the concentration of the basic additive of the present invention in the electrolytic solution is more preferably 0.45 mol / L or less, and still more preferably 0.3 mol / L or less.

  From the viewpoint of the low concentration of the basic additive, 1- (arylmethyl) imidazole used in the present invention is a basic additive that can contribute to the increase in cell voltage even at a low concentration, and is a chain sulfone compound [ The technical significance used in combination with the following (A-2) is large.

  Moreover, the basic additive of the present invention may be used alone or in combination of two or more. Further, conventionally known basic additives may optionally be used in combination within a small amount that does not impair the effects of the present invention.

(A-2) Solvent (A-2-1)
The solvent of the present invention is used to dissolve at least the redox electrolyte and the basic additive. The amount and composition of the solvent are selected so as to effectively perform the function of the solvent.

  The solvent that can be used in the present invention is, as a solvent, at least a chain sulfone compound of the following formula (2):

Including
In the above formula (2), R ₁ and R _{2 each} independently may be partially substituted with at least one substituent selected from the group consisting of a halogen group, an alkoxy group and an aromatic ring group; 1 to 12 alkyl or aryl groups are shown.

Specific chain sulfone compounds include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, methyl propyl sulfone, ethyl propyl sulfone, methyl isopropyl sulfone, ethyl isopropyl sulfone, methyl butyl sulfone, ethyl butyl sulfone, methyl isobutyl sulfone, ethyl isobutyl sulfone Sulfone, methyl (2-methylpropyl) sulfone, ethyl (2-methylpropyl) sulfone, methyl tert-pentyl sulfone, ethyl tert-pentyl sulfone, methyl pentyl sulfone, ethyl pentyl sulfone, methyl isopentyl sulfone, ethyl isopentyl Sulfone, (1,2-dimethylpropyl) methylsulfone, (1,2-dimethylpropyl) ethylsulfone, (1-ethylpropyl) methylsulfone Ethyl (1-ethylpropyl) sulfone, methyl (2-methylbutyl) sulfone, ethyl (2-methylbutyl) sulfone, methyl (3-methylbutyl) sulfone, ethyl (3-methylbutyl) sulfone, (2, 2-dimethylpropyl) Examples include methyl sulfone, (2,2-dimethylpropyl) ethyl sulfone, isobutyl isopropyl sulfone, methoxyethyl isopropyl sulfone, fluoroethyl isopropyl sulfone and the like. Among these, ethyl methyl sulfone, ethyl isopropyl sulfone, ethyl isobutyl sulfone, isobutyl isopropyl sulfone, methoxyethyl isopropyl sulfone, fluoroethyl isopropyl sulfone and the like can be suitably used. Compounds in which the total carbon number of R ₁ and R ₂ is 5 or more, preferably 5 to 10, can be used over a wide range of temperatures, and can be particularly preferably used because they are excellent in durability. In addition, even if it is solid at around room temperature such as dimethyl sulfone and ethyl methyl sulfone, freezing point depression occurs by dissolving the electrolyte and additives, or by mixing with other chain sulfone, and the use range If it is liquid at temperature, it can be used as an electrolytic solution, so it may be solid alone. Rather, ethyl methyl sulfone having a small molecular size and an asymmetric molecular structure tends to lower the viscosity of the electrolyte, and can be suitably used.

Other examples of the chain sulfone compound of the above general formula (2) include compounds in which at least one of R ₁ and R ₂ is a phenyl group, and examples thereof include phenyl isopropyl sulfone, phenyl ethyl sulfone, diphenyl sulfone and the like It can be illustrated. Among these, _one of R ₁ and R ₂ is a phenyl group, and one of which may be partially substituted with at least one substituent selected from the group consisting of a halogen group, an alkoxy group and an aromatic ring Compounds having a number of 1 to 12 alkyl groups can be used over a wide range of temperatures, and are preferably used because they are excellent in durability. More preferably, one is an alkyl group having 1 to 5 carbon atoms which is not substituted. It is a compound, and in particular, phenyl isopropyl sulfone can be suitably used.

  One of these substances may be used alone, or a plurality of these substances may be mixed and used. By using such a linear sulfone as a solvent, high durability can be obtained.

  In the solvent of the present invention, other known aprotic polar solvents having a boiling point of 150 ° C. or higher at 1 atmospheric pressure and an ionic liquid are optionally included in a small amount that does not impair the effects of the present invention. It is also good. Such a combined solvent is preferably one having a low viscosity, a high boiling point, a low volatility, and sufficient ion conductivity. Examples of the aprotic organic solvent used in combination include sulfone, cyclic sulfone such as methyl sulfolane, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, ethers such as polypropylene glycol dialkyl ether, butoxy propionitrile, And nitrile compounds such as adiponitrile. Also, N-methyl pyrrolidone, N, N'-dimethyl imidazolidinone, N-methyl oxazolidinone and the like can be mentioned.

  Preferred examples of the ionic liquid used in combination include, for example, 1-ethyl-3-methylimidazolium, 1-methyl-3-propylimidazolium, 1-methyl-3-methylimidazolium, and 1-butyl-3 cation. -Methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-methyl-2,3-dimethylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1 Imidazolium-based such as -hexyl-2,3-dimethylimidazolium, 1-octyl-2,3-dimethylimidazolium, pyridinium-based such as 1-methyl-pyridinium, 1-butyl-pyridinium, 1-hexyl-pyridinium, etc. Pyrazolium type, aliphatic amine type, anion is tetrafluoroborate, hexene Fluorinated sulfonates such as fluoroborate and trifluoromethanesulfonate, fluorinated carboxylic acids such as trifluoroacetic acid, cyanates, thiocyanates, dicyanamides, and sulfonylimides such as bisfluorosulfonylimide and bistrifluoromethanesulfonylimide A certain thing etc. can be mentioned. One of these substances may be used alone, or a plurality of these substances may be mixed and used. The content of the combined solvent in the entire solvent of the electrolytic solution of the present invention varies depending on the type of chain sulfone solvent and the combined solvent used, and the optimum value is different because the viscosity, the number of donors, the interaction, etc. differ. The weight is preferably 50% or less, more preferably 30% or less.

(A-2-2)
The chain sulfone compound of the above-mentioned formula (2) has already been used by some of the present inventors as a high-durability electrolytic solution solvent in dye-sensitized solar cells in Patent Document 18. However, preferred basic additives actually used in Patent Document 18 are compounds having relatively high boiling points despite relatively low molecular weight such as 1,2,4-triazole, 4-methylimidazole, etc. By using it, an electrolytic solution having high photoelectric conversion efficiency and high heat resistance is obtained.

  On the other hand, in the present invention, what is used in combination with the chain sulfone compound is 1- (arylmethyl) imidazole represented by the formula (1), which is preferably used in Patent Document 18 The molecular weight is considerably higher compared to basic additives. As a result of this increase in molecular weight, the boiling point generally rises, and although the improvement in durability due to this is expected, conversely, the viscosity of the electrolyte solution is expected to decrease the initial photoelectric conversion efficiency. The

  However, it goes without saying that the 1- (arylmethyl) imidazole represented by the formula (1), in particular 1-benzylimidazole represented by the formula (1-1), has good durability, of course, On the contrary, in terms of photoelectric conversion efficiency, better results could be obtained as compared with 1,2,4-triazole (see Examples).

(A-3) Examples of the redox electrolyte which can be used in the redox electrolyte present invention, the halogen redox electrolyte (e.g. iodine redox _{^{(I 3 - / I -)}} , bromine redox (Br ₃ ^- / Br ^- ), Metal redox electrolytes (ferrocyanate / ferricyanate, metal complexes such as ferrocene / ferricianium ion, etc.), sulfide electrolytes (poly sodium sulfide, alkyl thiol) Well-known electrolytes can be used as long as the effects of the present invention are not impaired, such as / alkyl disulfides, aromatic electrolytes (viologens, hydroquinones / quinones, etc.), but from the viewpoint of redox potential, halogens A redox electrolyte is preferred.

Among the halogen redox electrolyte, from the viewpoint of chemical stability in the cell, an iodine redox (I ₃ ^- / I ^- based) are preferred, with iodine redox system, a combination of molecular iodine and an iodide salt Use Examples of the iodide salt include iodide salts with inorganic cations such as LiI, NaI, KI, CsI, CaI ₂ and the like, but the viscosity of the electrolyte is likely to increase due to solvation to inorganic cations by chain sulfone It is desirable that the addition is minimal. Examples of other iodide salts include triethyl methyl ammonium cation, iodide salt with quaternary ammonium cation such as tetrabutyl ammonium cation, and others, pyridinium type cation, imidazolium type cation, pyrazolium type cation, etc., onium cation The well-known iodide salt etc. which consist of can be used preferably. In particular, 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-methyl-3-propylimidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, N-ethyl- The iodide salt of N-methyl pyrrolidinium cation, spiro- (1,1 ')-bipyrrolidinium cation, triethylmethyl ammonium cation is more preferable. Moreover, you may mix and use 2 or more types of electrolytes.

Furthermore, the iodine redox system when adopting the (I ₃ ^{- -} / I system), different irradiation light intensity according to the environment to be used, is not particularly limited because the concentration of appropriate the electrolyte different contrast, for example, outdoor, and in case the light is relatively irradiated Near windows even indoors is strong, I ₃ is oxidant in the electrolytic solution ^- (triiodide ion) concentration, in terms of short-circuit current density 0 .01 mol / L or more is preferable, 0.03 mol / L or more is more preferable, and from the viewpoint of durability, it is preferably 0.5 mol / L or less, and more preferably 0.3 mol / L or less. The electrolyte is a reduced form I in the electrolytic solution ^- (iodide ion) concentration is preferably at least 0.1 mol / L in terms of short-circuit current density, more preferably at least 0.5 mol / L, the viscosity From the viewpoint, it is preferably 5 mol / L or less, more preferably 3 mol / L or less. Further, as another example, it is preferable that the concentration of the triiodide ion and the iodide ion be smaller when the irradiation light is about several hundred lx in the room than in the case where the above-described relatively high irradiation light is strong. More specifically, the concentration of triiodide ion is preferably 0.1 mol / L or less, more preferably 0.05 mol / L or less. The iodide ion concentration is more preferably 2 mol / L or less, and even more preferably 1 mol / L or less.

(B) Second aspect of the present invention This aspect is a dye-sensitized solar cell characterized in that the electrolyte for a dye-sensitized solar cell of the first aspect of the present invention is used. Except for the solution, the configuration of a general dye-sensitized solar cell may be adopted.

  The dye-sensitized solar cell has a structure in which a counter electrode and a semiconductor photoelectrode are disposed opposite to each other via an electrolyte layer containing a redox electrolyte, and the semiconductor photoelectrode contains a photosensitizing dye. .

The photosensitizing dye absorbs light incident into the solar cell, changes from the ground state to an excited state, and injects electrons into the semiconductor photoelectrode. The photosensitizing dye thus oxidized by injecting electrons into the semiconductor photoelectrode side receives electrons from the reductant (eg, I ⁻ ) of the redox electrolyte in the electrolyte layer and returns to the neutral state again. . The reductant of the redox electrolyte deprived of electrons becomes an oxidant (eg, I ₃ ⁻ ), but diffuses to the counter electrode, receives the electron at the counter electrode, and returns to the reductant. The maximum generated voltage (open circuit voltage) of the solar cell generated under the electron cycle as described above is determined by the difference between the Fermi level of the photoelectrode semiconductor and the redox potential of the redox electrolyte.

(B-1) Electrolyte layer The electrolyte layer of this aspect contains the electrolyte solution for a dye-sensitized solar cell described in the first aspect of the present invention. In addition, polymers such as polyacrylonitrile and polyvinylidene fluoride, low molecular weight gelling agents and the like are added to the electrolytic solution of the present invention, or polyfunctional monomers having an ethylenically unsaturated group are polymerized in the electrolytic solution. The electrolyte layer may be formed as a gel electrolyte by a method such as, for example. The polymer for gelling the electrolytic solution may have ionicity, but it is desirable that the polymer not have ionicity in order to prevent migration of the electrolyte. In addition, the present invention is not limited to gelation after preparation of the electrolytic solution, and in the state in which some of the electrolytes and additives are dissolved, or after only the solvent is gelled without containing any electrolyte, etc. The electrolyte layer may be formed by adding an electrolytic solution component.

  Moreover, it is not a polymer, but when it comprises to a cell, you may give solid state, paste property, and gel property by adding particle | grains and giving thixotropy. The material of such particles is not particularly limited, and known materials can be used. For example, indium oxide, a mixture of tin oxide and indium oxide (hereinafter abbreviated as "ITO"), inorganic oxides such as silica, ketjen black, carbon black, carbon materials such as carbon nanotubes, kaolinite And layered inorganic compounds such as montmorillonite, that is, clay minerals. For the details of the electrolyte, refer to the above (A).

(B-2) Semiconductor Photoelectrode The semiconductor photoelectrode is formed, for example, by forming an oxide semiconductor film on a substrate and then incorporating (including adhesion and adsorption) a photosensitizing dye into the oxide semiconductor film. You can get it.

  As the oxide semiconductor, known porous semiconductor materials such as titanium oxide, zinc oxide, tin oxide, indium oxide doped with tin, zirconium oxide, magnesium oxide and the like can be used.

  The oxide semiconductor film can be formed on a substrate by a spin coating method, a spray method, a dipping method, a screen printing method, a doctor blade method, an inkjet method, or the like, but from the viewpoint of simplicity of operation, the spin coating method The spray method and the dipping method are preferably formed by the screen printing method from the viewpoint of mass production.

  The oxide semiconductor film may be formed directly on the surface of the substrate as long as it has electrical conductivity with the outside as an electrode as described below, but may be formed via a conductive layer on the substrate .

  As the substrate, preferably, a resin or glass material can be used. The light-transmitting material is preferably used because light needs to be incident on the photosensitizing dye contained in the oxide semiconductor film. Furthermore, as a solar cell, it is preferable that a conductive layer be formed over the substrate because electrical conduction between the oxide semiconductor film and the outside of the cell needs to be taken.

  It is preferable that such a conductive layer be a light-transmitting material as in the case of a substrate so that light can enter the oxide semiconductor film.

  The material of the conductive layer is titanium oxide, zinc oxide (which may be doped with antimony or aluminum), indium oxide (which may be doped with tin or zinc), tin oxide [antimony-doped (ATO), Or those having a film such as one doped with fluorine (FTO) may be preferably used.

In addition, if the treatment method such as dispersing and supporting a conductive material, or forming a thin wire conductive material such as a mesh shape on a substrate, the light transmittance of the entire electrode can be increased. An opaque conductive material can also be used as the conductive layer. Such materials include carbon materials and metals. The carbon material is not particularly limited, and examples thereof include graphite (graphite), carbon black, glassy carbon, carbon nanotubes and fullerenes. The metal is not particularly limited, and examples thereof include platinum, gold, silver, copper, aluminum, nickel, chromium, iron, molybdenum, titanium, tantalum, niobium and alloys thereof.
Here, in the present invention, it is desirable to use a halogen molecule and a halogen compound salt, more specifically iodine and an iodide salt, or bromine and a bromide salt, as the redox electrolyte contained in the electrolytic solution. It is desirable that the conductive material used be highly resistant to the electrolyte. Therefore, as the conductive material, copper, aluminum, nickel, alloys thereof, titanium, tantalum, niobium, platinum, etc., particularly metal oxides, among which FTO or ITO is particularly preferable, with the surface subjected to a corrosion resistance treatment of the surface. It is.

(B-3) Photosensitizing dye As the photosensitizing dye, various dyes having absorption in the visible region and / or infrared region, such as metal complexes and organic dyes can be used, and an oxide semiconductor film can be used. In order to impart adsorption to the dye, it is preferable that the dye molecule have a functional group such as -CO ₂ H or a salt thereof, -OH, -SO ₃ H or a salt thereof, -PO ₃ H ₂ or a salt thereof .

  Examples of metal complex dyes include ruthenium, osmium, iron, cobalt, zinc, complexes of mercury, metal porphyrins, metal phthalocyanines, chlorophylls and the like.

  Examples of organic dyes include dyes of cyanine type, hemicyanine type, merocyanine type, xanthene type, triphenylmethane type, metal phthalocyanine type, perylene type, coumarin type, polyene type, indoline type, carbazole type and the like.

  As a method of containing a dye in the oxide semiconductor film (including adhesion or adsorption), any known method, for example, a method of dipping an oxide semiconductor thin film such as titanium dioxide in a dye solution at a predetermined temperature (dip method Methods such as roller method and air knife method) and methods of applying a dye solution to the surface of the oxide semiconductor layer (wire bar method, application method, spin method, spray method, offset printing method, screen printing method, etc.).

(B-4) Counter Electrode The counter electrode may be a single layer made of a conductive material, or may be made of a conductive layer made of a conductive material and a substrate.

  The conductive material includes platinum group (Ru, Rh, Pd, Os, Ir or Pt), gold, nickel, titanium, tantalum, niobium, aluminum, copper, silver, tungsten and other metals and any of them. Alloys, carbon materials, conductive organic compounds, FTO films, ITO films and ATO films can be mentioned, but from the viewpoint of requiring corrosion resistance to an electrolytic solution, titanium is particularly preferable as a metal and conductive Among glass materials, one having a conductive film of FTO is preferable.

  The substrate is not particularly limited as long as it has durability to the electrolyte layer to be sealed between the counter electrode and the semiconductor photoelectrode, but various glass, resin, metal (titanium, tantalum, niobium, Nickel, tungsten, etc.) can be used.

  As the catalyst in the counter electrode, known materials such as platinum, graphite, activated carbon, carbon materials such as carbon black, and conductive polymers can be used. In the case of forming a platinum group catalyst layer on a substrate, for example, those prepared by plating, sputtering, application of a solution such as chloroplatinic acid, printing of a paste such as chloroplatinic acid can be mentioned. In particular, for use in a small cell for testing, it is preferable to use one prepared by a sputtering method capable of obtaining a homogeneous film, and in the case of a large module requiring patterning such as a submodule, a screen printing method. Film formation is preferred.

(B-5) Production of Dye-Sensitized Solar Cell A dye-sensitized solar cell can be produced by bonding the semiconductor photoelectrode and the counter electrode to each other via a sealing material.

  For example, a partition wall of a sealing material is formed on a substrate on which the semiconductor photoelectrode is formed. It can be easily formed by using printing technology such as screen printing.

  The sealing material is not particularly limited as long as it has durability to the components in the electrolyte layer, but thermoplastic resins, thermosetting resins, ultraviolet curing resins, electron beam curing resins, metals, rubbers, etc. are exemplified. However, at least the surface is required to be electrically insulating, and when the sealing material is conductive, the surface is coated with an electrically insulating material such as various resins and rubbers.

  Then, the semiconductor photoelectrode and the counter electrode are bonded to each other through the sealing material. At this time, care should be taken so that both electrodes are arranged in parallel under uniform pressure.

  Furthermore, a constant distance is maintained between the semiconductor electrode and the catalyst electrode through the partition wall of the sealing material, and the electrolyte layer is sealed therein, whereby a dye-sensitized solar cell is manufactured.

  The photosensitizing dye can be contained (including adhesion and adsorption) on the semiconductor photoelectrode by immersing the semiconductor electrode in a dye solution or the like before or after the laminating step.

  Hereinafter, the present invention will be more specifically described using examples.

Example 1
Preparation of electrolyte solution and preparation of a dye-sensitized solar cell were performed as follows.

A. Preparation of electrolytic solution 1.35 mol / L of 1-methyl-3-propylimidazolium iodide, 0.15 mol / L of iodine, 1-benzylimidazole as a basic additive [chemical structural formula (1), in the table, “BEI It is abbreviated as ". The solution was dissolved in ethyl isopropyl sulfone at a rate of 0.5 mol / L to prepare an electrolytic solution.

B. Production of Dye-Sensitized Solar Cell A dye-sensitized solar cell using the electrolytic solution prepared in A above was produced according to the following procedures (b-1) to (b-5).

(B-1)
A titanium oxide paste is screen-printed by screen printing on a square area portion of 1 cm on a side of 1 cm on a substrate (a glass plate with a fluorine-doped tin oxide film, 35 mm × 33 mm), and fired at 500 ° C. An oxide semiconductor film consisting of

Power generation layer C
In the screen printing step of titanium oxide paste, the step of screen-printing titanium oxide paste [PST-21 NR made by JGC Catalyst Chemical Co., Ltd.] to a film thickness of 4 μm is repeated twice, and after drying, titanium oxide paste [JGC Catalyst Chemical Made] Power generation layer obtained by screen printing PST-400C] to a film thickness of 4 μm (total applied film thickness: 12 μm).

(B-2) Adsorption of sensitizing dye The electrode formed with the oxide semiconductor film is a dye solution [concentration: 0.3 mmol / L, solvent: mixed solvent of acetonitrile / t-butanol 1/1 (v / v)] The dye was supported on the titanium oxide of the power generation layer by immersion at 40 ° C. for 2 hours to obtain a semiconductor photoelectrode.
Here, a ruthenium complex dye J2 having a structural formula shown below [chemical structural formula (2)] (trade name: SK-1, manufactured by Kobe Natural Products Chemical Co., Ltd.) was used as the dye.

  The complex dye is the ruthenium complex dye J2 of Patent Document 19 and can be prepared based on the same document.

(B-3)
An adhesive is applied to the periphery of the oxide semiconductor film of the above-mentioned semiconductor photoelectrode, and this semiconductor photoelectrode and a platinum-coated titanium plate (counter electrode) having an electrolyte solution injection hole prepared separately are opposed by the adhesive and adhered The two electrodes are arranged in parallel at a constant interval of about 30 μm.

(B-4)
Then, the electrolyte prepared in the above A was injected from the electrolyte injection port on the counter electrode.

(B-5)
Next, the electrolyte injection hole was sealed using an adhesive, and a solder for taking out a terminal was applied on the semiconductor photoelectrode to complete a dye-sensitized solar cell (experimental cell).

(Example 2)
In Example 1, the concentration of 1-methyl-3-propylimidazolium iodide in the electrolytic solution, iodine, 1-benzylimidazole as the basic additive [chemical structural formula (1)] each is 0.99 mol. A solar battery cell is manufactured in the same manner as in Example 1 except that the oxide semiconductor film formed of the following power generation layer D is formed as a power generation layer while replacing with 1 / L, 0.11 mol / L and 0.15 mol / L. did.

Power generation layer D
In the screen printing step of titanium oxide paste, titanium oxide paste [PST-30NR made by JGC Catalysts & Chemicals Co., Ltd.] is screen-printed once to a film thickness of 4 μm, and after drying, titanium oxide paste [PST- A power generation layer obtained by screen printing 400 C] to a film thickness of 4 μm (total applied film thickness: 8 μm).

(Examples 3 to 9)
Ethyl isopropyl sulfone (iodide salt) in a ratio of 1, 3-dimethylimidazolium iodide, 1.1 mol / L, iodine 0.15, mol / L, 1 1-benzylimidazole as a basic additive, 0.15 mol / L Example 3, abbreviated as "EiPS" in the table), ethyl methyl sulfone (example 4, abbreviated as "EMS" in the table), ethyl isobutyl sulfone (example 5, abbreviated as "EiBS" in the table) ), Isopropyl isobutyl sulfone (Example 6, abbreviated as “iPsBS” in the table), ethyl methyl sulfone / ethyl isopropyl sulfone 5/5 (v / v) (Example 7), ethyl isopropyl sulfone / 3-methyl -2-Oxazolidinone (Example 8, abbreviated as "NMO" in the Table) 5/5 (v / v), ethyl isopropyl sulfate On / 3-methyl-2-oxazolidinone 7/3 (v / v), except that an electrolyte solution was prepared by dissolving (Example 9), was A solar cell was produced in the same manner as in Example 1.

(Comparative example 1)
As a basic additive, in place of 1-benzylimidazole, 1-benzyl-2-methylimidazole [chemical structural formula (3), abbreviated as "BMI" in the table. A solar battery cell was produced in the same manner as in Example 1 except that the electrolytic solution was prepared using

(Comparative example 2)
As a basic additive, in place of 1-benzylimidazole, 2-methylimidazole [chemical structural formula (4), abbreviated as "2-MIm" in the table. A solar cell was produced in the same manner as in Example 2 using

(Comparative Examples 3 to 6)
3-Methyl-2-oxazolidinone (comparative example 3), 3-methoxypropionitrile (comparative example 4, abbreviated as “MPN” in the table), γ-butyrolactone (comparative example 5, in the table “GBL” Abbreviated.) A solar battery cell is produced in the same manner as in Example 3 except that an electrolytic solution is prepared by dissolving in S-5 (Comparative Example 6, [Chemical Structural Formula (5)], Patent Document 12). did.

(Comparative Examples 7 to 13)
As a basic additive, 1-benzylimidazole to t-butylpyridine (comparative example 7, respectively abbreviated as "tBP" in the table [chemical structural formula (6)]), 1-benzyl-2-methylimidazole (comparative structure 7). Comparative example 8), 1,2,4-triazole (comparative example 9, abbreviated as "1,2,4-TAz" in the table), 1-methylimidazole (comparative example 10, "1-MI" in the table [Chemical structural formula (7)] abbreviated to, 1-butylimidazole (comparative example 11, abbreviated as "1-BuI" in the table [chemical structural formula (8)].), 2-methylpyridine (comparative example Example 12, abbreviated as "2-MPy" in the table [chemical structural formula (9)]. 2-benzylpyridine (comparative example 13, abbreviated as "2-BPy" in the table [chemical structural formula (10) Change the concentration of each basic additive to 0.15 mol / L or 0). 50 mol / L all used in a proportion except that an electrolyte solution was prepared and was A solar cell was produced in the same manner as in Example 3.

(Comparative Examples 14 to 20)
As a basic additive, 1-benzylimidazole, t-butylpyridine (comparative example 14), 1-benzyl-2-methylimidazole (comparative example 15), 1,2,4-triazole (comparative example 16), respectively Change to 1-methylimidazole (comparative example 17), 1-butylimidazole (comparative example 18), 2-methylpyridine (comparative example 19), 2-benzylpyridine (comparative example 20), and each basic additive concentration is changed A solar battery cell was manufactured in the same manner as in Example 4 except that an electrolytic solution was prepared using a ratio of 0.15 mol / L or 0.50 mol / L.

(Comparative examples 21 to 27)
As a basic additive, t-butylpyridine (comparative example 21), 1-benzyl-2-methylimidazole (comparative example 22), 1,2,4-triazole (comparative example 23) from 1-benzylimidazole, respectively Change to 1-methylimidazole (comparative example 24), 1-butylimidazole (comparative example 25), 2-methylpyridine (comparative example 26), 2-benzylpyridine (comparative example 27), and each basic additive concentration is changed A solar battery cell was manufactured in the same manner as in Example 5, except that an electrolytic solution was prepared using a ratio of 0.15 mol / L or 0.50 mol / L.

(Comparative examples 28 to 30)
As basic additives, 1-benzylimidazole to t-butylpyridine (comparative example 28), 1-benzyl-2-methylimidazole (comparative example 29), 1,2,4-triazole (comparative example 30) A solar battery cell was manufactured in the same manner as in Example 6, except that the electrolyte solution was prepared by changing and using each basic additive concentration at a ratio of 0.15 mol / L or 0.50 mol / L.

(Comparative examples 31 to 33)
As basic additives, 1-benzylimidazole to t-butylpyridine (comparative example 31), 1-benzyl-2-methylimidazole (comparative example 32), 1,2,4-triazole (comparative example 33) A solar battery cell was manufactured in the same manner as in Example 7 except that the electrolyte solution was prepared by changing and using each basic additive concentration at a ratio of 0.15 mol / L or 0.50 mol / L.

(Comparative example 34)
A solar battery cell was manufactured in the same manner as in Example 8, except that 1-benzylimidazole was changed from 0.15 mol / L to 1-benzyl-2-methylimidazole 0.50 mol / L as a basic additive. .

(Comparative example 35)
A solar battery cell was manufactured in the same manner as Example 9, except that 1-benzylimidazole was changed from 0.15 mol / L to 1-benzyl-2-methylimidazole 0.50 mol / L as a basic additive. .

  The compositions of the electrolytes used in Examples 1 to 9 and Comparative Examples 1 to 35 are shown in Table 1.

<Measurement of photoelectric conversion characteristics of solar cells>
C. Initial performance evaluation of dye-sensitized solar cell (C-1)
The dye-sensitized solar cells of Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2 obtained as described above were irradiated with simulated sunlight by a solar simulator [YSS-200, manufactured by Yamashita Denshi K. K., AM 1.5. , 1SUN (100 mW / cm ² )] and its initial performance (measured by preheating overnight at 85 ° C. after solar cell fabrication) were evaluated, and the results shown in Tables 2 and 3 below were obtained.

The photoelectric conversion efficiency was calculated by the following equation.
Photoelectric conversion efficiency (%) =
100 × [(short circuit current density × open voltage × curve factor) / (irradiated light energy density)]

  However, Table 4 below shows the power generation layer, the electrolytic solution and the basic additive used in Examples 1 and 2 and Comparative Examples 1 and 2.

  From the results of the initial performance in Table 2 above, Example 1 using 1-benzylimidazole as the basic additive is better than Comparative Example 1 using 1-benzyl-2-methyl-imidazole as the basic additive. The initial conversion efficiency was good.

  Furthermore, from the results of initial performance in Table 3, Example 2 using 1-benzylimidazole as a basic additive has better initial performance than Comparative Example 2 using 2-methylimidazole having a smaller molecular weight. The

  Considering that the increase in molecular weight of the basic additive generally increases the viscosity of the electrolyte and is expected to adversely affect the photoelectric conversion efficiency, in particular, the results in Table 3 are as basic additives. It can be said that unexpectedly high photoelectric conversion efficiency was exhibited when 1-benzylimidazole was used.

Example 2 gives the result that the photoelectric conversion efficiency is higher than that of Example 1 because the concentration of the additive (basic additive, electrolyte) in the electrolytic solution B (Example 2) is electrolytic. It is considered that the concentration is lower than the additive concentration of the liquid A (Example 1), and the thickness of the power generation layer D (Example 2) is thinner than the thickness of the power generation layer C (Example 1). That is, the lower the additive concentration in the electrolyte solution, the lower the viscosity of the electrolyte solution, and the thinner the power generation layer, the diffusion of the electrolyte I ₃ ⁻ / I ^{− in} the electrolyte solution is It is thought that it is because it is becoming easier.

D. Durability evaluation of dye-sensitized solar cell (D-1-1)
The experimental cells of Examples 3 to 9 and Comparative Examples 3 to 35 were stored in a thermostat at 105 ° C., and the photoelectric conversion efficiency and the change with time of the photoelectric conversion efficiency were measured over 1000 hours.

  The obtained results are shown in Table 5 below.

* 1: Corresponds to the initial photoelectric conversion efficiency measured on the day of solar cell fabrication.
* 2: Conversion efficiency maintenance rate (%) =
100 × [(photoelectric conversion efficiency after 1000 hours) / (initial photoelectric conversion efficiency)]

From the results of the durability evaluation in Table 5, in the experimental cell containing solvents containing various linear sulfone compounds as an electrolytic solution, Examples 3 to 7 using 1-benzylimidazole as the basic additive correspond to each other. The durability was better than Comparative Examples 8, 15, 22, 29 and 32 using 1-benzyl-2-methyl-imidazole. This result is an unexpected result despite the fact that the boiling point of 1-benzyl-2-methylimidazole is expected to be higher than that of 1-benzylimidazole, and accordingly the durability is also expected to be high.
In addition, the corresponding example 3 using 1-benzylimidazole is also used compared to comparative examples 13, 19 and 27 using 2-benzylpyridine, which is expected to have higher molecular weight and higher durability than 1-benzylimidazole. , 4 and 5 were more durable.
The results in Table 5 show that the improvement effect of the durability by the addition of the high boiling point additive is not easily judged from the molecular weight and the boiling point, and although the factor can not be clarified, the chemical in the cell Other factors such as stability may be working.
On the other hand, as a result of the combination of the solvent and 1-benzylimidazole, it is expected that high durability can not be obtained even if the solvent having a medium boiling point and 1-benzylimidazole are combined in Comparative Examples 4 to 6 However, it was also found that the combination of a solvent having a high boiling point and 1-benzylimidazole in Comparative Example 3 was insufficient. As can be seen from Examples 8 and 9, the electrolytic solution containing 1-benzylimidazole was able to obtain high durability only by containing the chain sulfone. In particular, solar cells (Examples 1 to 7) manufactured using an electrolyte solution using only various chain sulfone compounds as a solvent and 1-benzylimidazole as a basic additive have excellent initial performance and durability. And the durability was good as compared with Comparative Examples using other basic additives. It is thought that the effect of the basic additive on the durability of each solar battery cell appears more clearly by making the evaluation condition of the durability of the solar battery cell severe.

Claims (5)

An electrolyte solution for a dye-sensitized solar cell, comprising a redox electrolyte, a basic additive, and a solvent,
The basic additive is
1- (Arylmethyl) imidazole of the following formula (1):
In the formula (1), Ar represents an unsubstituted 5- or 6-membered aromatic group,
The solvent is a chain sulfone compound of the following formula (2):
At least including
In the above formula (2), R ₁ and R _{2 each} independently may be partially substituted with at least one substituent selected from the group consisting of a halogen group, an alkoxy group and an aromatic ring group; 1 to 12 alkyl or aryl group
An electrolyte for dye-sensitized solar cells, characterized in that The basic additive represented by the formula (1) is
1-benzylimidazole of the following formula (1-1):
The electrolyte solution for a dye-sensitized solar cell according to claim 1, having a chemical structure of   The density | concentration of the said basic additive is 0.01-1 mol / L, The electrolyte solution for dye-sensitized solar cells of Claim 1 or 2 characterized by the above-mentioned.   The linear sulfone compound according to claim 1 is at least one selected from the group consisting of ethyl methyl sulfone, ethyl isopropyl sulfone, ethyl isobutyl sulfone, isobutyl isopropyl sulfone, methoxyethyl isopropyl sulfone and fluoroethyl isopropyl sulfone. The electrolyte solution for dye-sensitized solar cells according to any one of claims 1 to 3.   A photoelectrode comprising a porous metal oxide semiconductor layer formed on a conductive layer and containing a dye having a photosensitizing function in the metal oxide semiconductor layer, a counter electrode disposed opposite to the photo electrode, It is a dye-sensitized solar cell which is formed between the said photoelectrode and a counter electrode, and has an electrolyte layer containing an electrolyte solution, Comprising: The said electrolyte solution is an electrolysis for dye-sensitized solar cells in any one of Claims 1-4. A dye-sensitized solar cell characterized by using a liquid.