JP6024359B2 - Dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell that is excellent in heat resistance, shows a high open-circuit voltage value, and is expected to have high photoelectric conversion efficiency.

  Compared to silicon solar cells and compound solar cells, dye-sensitized solar cells have less resource constraints, are cheaper in raw materials, and have a simple manufacturing method. It has the advantage of being able to give flexibility. Because of these advantages, dye-sensitized solar cells are highly expected as next-generation solar cells.

  In this dye-sensitized solar cell, an electrolyte layer containing a pair of oxidizing species and reducing species converts a cathode having a semiconductor layer containing a dye as a photosensitizer, and converts the oxidizing species in the electrolyte layer into reducing species. And having a structure sandwiched between the anode having the catalyst layer. In general, an oxide semiconductor in which a dye such as ruthenium complex is supported on a transparent electrode in which a deposited layer of semiconductor ceramics such as tin-doped indium oxide (ITO) or fluorine-doped tin oxide (FTO) is formed on the surface of a transparent substrate such as glass An electrode in which a layer is formed is used as a cathode, and an electrode obtained by adhering Pt on a substrate such as the above-described transparent electrode or steel by a sputtering method, a vacuum evaporation method, or the like is used as an anode. When light is irradiated onto the dye of the semiconductor layer through the transparent electrode, the dye absorbs light energy to be in an excited state and emits electrons toward the semiconductor. The emitted electrons move from the semiconductor layer to the transparent electrode, and further move from the transparent electrode to the anode via the external circuit. Then, by the action of the anode Pt catalyst layer, the oxidized species in the electrolyte layer receive electrons from the anode and are converted into reduced species, and the reduced species emit electrons to the dye and are converted into oxidized species.

Meanwhile, the dye-sensitized solar cell which has been considered so far exclusively high photoelectric conversion efficiency I ^- / I ₃ ^- redox couple have been used in the electrolyte layer. However, I ^- / I ₃ ^- for redox pairs are two-electron redox system is a complex redox reactions. Also, I ^- / I ₃ ^- electrolyte layer containing a redox pair, strongly corrosive, has a problem that iodine tends to volatilize.

_{^{I - / I 3 -..}} . As an oxidation-reduction pair to replace the redox couple, Co (II / III) an outer sphere complex system redox pairs have been studied (e.g., Non-Patent Document 1 (J Am Chem Soc , 2002, 124 (37), 11215-11222)). The term Co (II / III) means that the valence of cobalt changes between divalent and trivalent by redox.

Since the Co (II / III) outer sphere complex system is a one-electron redox system, the redox reaction is relatively simple. In addition, the electrolyte layer containing this complex-type redox couple is weak in volatility and corrosivity, and has a weak absorption in the visible light region. It can be included in the layer. Furthermore, when comparing the redox level governing the open circuit voltage of the dye-sensitized solar cell, the Co (II / III) an outer sphere complex system redox couple, I ^- is the redox couple as much ^- / I ₃ Or having a lower redox level, it is expected that a dye-sensitized solar cell having a high open-circuit voltage and high photoelectric conversion efficiency can be obtained by using this complex-based redox level. . However, according to a report in Patent Document 1, an electrolyte layer containing tris (4,4′-di-t-butyl-2,2′-bipyridyl) Co (II / III) perchlorate which exhibits the best characteristics is used. even dye-sensitized solar cell had, the open voltage is only about 450mV~550mV, I ^- / I ₃ ^- about 80% of the dye-sensitized solar cell using the electrolyte layer containing a redox couple Only photoelectric conversion efficiency is obtained.

J. et al. Am. Chem. Soc, 2002, 124 (37), 11215-11222

  In the examination of Co (II / III) outer sphere complex-based redox couples so far, metals such as Pt or carbon have been used for the catalyst layer of the anode.

On the other hand, the applicant has continued examination about the conductive polymer layer for the catalyst layer of the dye-sensitized solar cell. And in PCT / JP2012 / 58771 and PCT / JP2012 / 58762, which are unpublished at the time of filing this application, thiophene having substituents at the 3-position and 4-position (hereinafter, thiophene having substituents at the 3-position and 4-position, A polymer composed of at least one monomer selected from the group consisting of a substituted thiophene) and a non-sulfonic acid organic compound as a dopant for the polymer, the molecular weight of the anion of the compound being 200 or more A conductive polymer layer containing an anion generated from at least one kind of compound having excellent heat resistance and excellent catalytic ability to convert oxidized species in the electrolyte layer to reducing species, Furthermore, by limiting the density of the conductive polymer layer to a range of 1.15 to 1.80 g / cm ^3. It was reported that the heat resistance was further improved. Here, the “non-sulfonic acid organic compound” means an organic compound having no sulfonic acid group and / or sulfonic acid group.

  An object of the present invention is to provide a dye-sensitized solar cell that is excellent in heat resistance, has a high open-circuit voltage, and has high photoelectric conversion efficiency based on the above-described knowledge.

As a result of intensive studies, the inventors have used the polymer layer described above as a catalyst layer on the anode in a dye-sensitized solar cell having an electrolyte layer containing a Co (II / III) outer-sphere complex-based redox couple. the, I ^- / I ₃ ^- was found that dye-sensitized solar cell having high open-circuit voltage than the open circuit voltage of the dye sensitized solar cell using the electrolyte layer containing a redox couple is obtained.

  Accordingly, the present invention provides a cathode having a semiconductor layer containing a dye as a photosensitizer, an electrolyte layer stacked on the semiconductor layer of the cathode and containing a pair of oxidized species and reduced species, and the electrolyte. A dye-sensitized solar cell comprising a conductive polymer layer that acts as a catalyst for converting the oxidized species to the reduced species, and the conductive polymer layer in the anode comprises: A polymer composed of at least one monomer selected from the group consisting of thiophene having substituents at the 3-position and 4-position, and a non-sulfonic acid organic compound as a dopant for the polymer, the anion of the compound And an anion generated from at least one compound having a molecular weight of 200 or more, and the oxidizing and reducing species forming a pair in the electrolyte layer are 2,2′-bipyridine Co (III) outer sphere having a ligand selected from the group consisting of 4,4'-dimethyl-2,2'-bipyridine and 4,4'-di-t-butyl-2,2'-bipyridine Provided is a dye-sensitized solar cell which is a complex and a Co (II) reductant of the complex. Since the photoelectric conversion efficiency of the dye-sensitized solar cell is proportional to the value of the open circuit voltage, it is expected that a dye-sensitized solar cell having high photoelectric conversion efficiency can be obtained by the present invention.

  The conductive polymer layer contains, as a dopant, an anion generated from a non-sulfonic acid organic compound having a molecular weight of 200 or more. Anions generated from inorganic compounds, or organic compounds that are organic compounds that do not have sulfonate groups and / or sulfonate groups generated from compounds having sulfonate groups and / or sulfonate groups Even so, an anion generated from a compound having a molecular weight of less than 200 does not give a conductive polymer layer having excellent heat resistance (see PCT / JP2012 / 58761 and PCT / JP2012 / 58762).

（式中、ｍが１〜８の整数、好ましくは１〜４の整数、特に好ましくは２を意味し、ｎが１〜８の整数、好ましくは１〜４の整数、特に好ましくは２を意味し、ｏが２又は３を意味する）で表わされるスルホニルイミド酸及びこれらの塩から選択された化合物は、特に耐熱性に優れた導電性ポリマー層を与えるため好ましい。 Among the non-sulfonic acid organic compounds whose anion molecular weight is 200 or more, borodisalicylic acid, borodisalicylate, formula (I) or formula (II)

(In the formula, m represents an integer of 1 to 8, preferably an integer of 1 to 4, particularly preferably 2, and n represents an integer of 1 to 8, preferably an integer of 1 to 4, particularly preferably 2. In addition, a compound selected from sulfonylimidic acid represented by (2) or (3) and salts thereof is particularly preferable because it provides a conductive polymer layer excellent in heat resistance.

  The monomer for forming the conductive polymer layer is not particularly limited as long as it is a compound selected from the group consisting of substituted thiophenes, that is, thiophenes having substituents at the 3-position and 4-position. The substituents at the 3-position and 4-position of the thiophene ring may form a ring together with the carbons at the 3-position and 4-position. In particular, when the monomer is EDOT, it is preferable because a conductive polymer layer having excellent catalytic stability for converting oxidized species in the electrolyte layer into reducing species can be obtained in addition to excellent environmental stability.

The density of the conductive polymer layer is preferably in the range of 1.15~1.80g / cm ^3, more preferably in the range of 1.20~1.80g / cm ^3, 1.60~ A range of 1.80 g / cm ³ is particularly preferred. When the density is less than 1.15 g / cm ³ , the heat resistance is drastically lowered, and it is difficult to produce a conductive polymer layer having a density exceeding 1.80 g / cm ³ . When obtaining a flexible anode, if the density of the conductive polymer layer is too high, the conductive polymer layer becomes hard and lacks flexibility, so the density of the conductive polymer layer is 1.75 g / cm. ^It is preferably ³ or less, particularly preferably 1.70 g / cm ³ or less.

The conductive polymer layer having a density in the range of 1.15 to 1.80 g / cm ³ comprises a solvent composed of 100 to 80% by mass of water and 0 to 20% by mass of an organic solvent, a substituted thiophene as a monomer, It can be obtained by electrolytic polymerization using a polymerization solution containing the above-mentioned specific range non-sulfonic acid organic compound. Since this specific range of non-sulfonic acid-based organic compound acts as a supporting electrolyte in the polymerization solution, it is also referred to as a “non-sulfonic acid-based organic supporting electrolyte”. A solvent composed of 100 to 80% by mass of water and 0 to 20% by mass of an organic solvent is hereinafter referred to as “water-rich solvent”. In the water-rich solvent, the total amount of water and the organic solvent is 100% by mass. When the content of the organic solvent in the water-rich solvent is increased, the conductive polymer layer in which the polymer particles are densely packed becomes difficult to be formed on the substrate by electrolytic polymerization. When it exceeds, the heat resistance of the obtained conductive polymer layer will fall remarkably (refer to PCT / JP2012 / 57661 and PCT / JP2012 / 58762). The surface resistance of the conductive polymer layer obtained by electrolytic polymerization is 10Ω / □ or less. The lower the surface resistance, the lower the resistance of the entire dye-sensitized solar cell and the higher the photoelectric conversion efficiency of the battery. This low surface resistance is preferable because it leads to high photoelectric conversion efficiency.

  The semiconductor layer in the cathode may be formed using any material used for the semiconductor layer in the conventional dye-sensitized solar cell, but it is preferable to use titanium oxide having high photoelectric conversion efficiency. . Although there is no strict restriction | limiting in the thickness of a semiconductor layer, Generally it is 1-100 micrometers, Preferably it is 3-50 micrometers, Most preferably, it is the range of 3-20 micrometers. If the thickness of the semiconductor layer is less than 1 μm, light absorption may be insufficient. If the thickness of the semiconductor layer is greater than 100 μm, the distance from which the electrons reach the conductive portion of the base becomes long, and the electrons Is not preferable because of inactivation.

In the dye-sensitized solar cell having the electrolyte layer containing the Co (II / III) outer sphere complex system of the present invention, the specific range of the conductive polymer layer used as the anode catalyst layer is selected from the oxidized species in the electrolyte layer. In addition to excellent catalytic ability to convert to reducing species, it also has excellent heat resistance. Further, the dye-sensitized solar cell of the present invention with an anode having a conductive polymer layer in this particular range, I ^- / I ₃ ^- open circuit voltage of the dye sensitized solar cell using the electrolyte layer containing a redox couple Has a higher open circuit voltage. Therefore, it is expected that a dye-sensitized solar cell having high photoelectric conversion efficiency can be obtained.

It is a figure which shows the relationship between the thickness of a conductive polymer layer, and surface resistance.

  First, the anode provided with the conductive polymer layer in the specific range described above will be described, and then the entire dye-sensitized solar cell will be described.

A: Anode The anode for the dye-sensitized solar cell of the present invention is a non-sulfonic acid organic compound as a dopant composed of at least one monomer selected from substituted thiophenes and a dopant for the polymer. And an anion generated from at least one compound having a molecular weight of 200 or more of the anion of the compound. The conductive polymer layer is prepared by introducing a preparation step for obtaining a polymerization solution for electrolytic polymerization containing the monomer and the non-sulfonic acid organic compound, and a substrate having a conductive portion in the obtained polymerization solution. By conducting electrolytic polymerization, it can be produced by a method including a polymerization step of forming a conductive polymer layer obtained by polymerization of the monomer on a conductive portion of the substrate. Hereinafter, each step will be described.

(1) Preparation Step The polymerization solution for electrolytic polymerization prepared in this step contains a water-rich solvent, a substituted thiophene as a monomer, and the above-mentioned specific range non-sulfonic acid organic compound as essential components.

  For the preparation of the polymerization solution, water having a small environmental load and economically excellent is used as a main solvent. In addition to water, this polymerization solution may contain an organic solvent such as methanol, ethanol, isopropanol, butanol, ethylene glycol, acetonitrile, acetone, tetrahydrofuran, and methyl acetate. Is water. Water is preferably 90% by mass or more of the whole solvent, more preferably 95% by mass or more of the whole solvent, and particularly preferably the solvent consists of water alone. When the content of the organic solvent in the water-rich solvent increases, the conductive polymer layer in which the polymer particles are densely packed becomes difficult to be formed on the substrate by electrolytic polymerization, and the content of the organic solvent is reduced to 20% by mass of the whole solvent. When it exceeds, the heat resistance of the obtained conductive polymer layer will fall remarkably.

  As the monomer, a substituted thiophene, that is, a monomer selected from thiophenes having substituents at the 3-position and the 4-position is used. The substituents at the 3-position and 4-position of the thiophene ring may form a ring together with the carbons at the 3-position and 4-position. Examples of monomers that can be used include 3,4-dialkylthiophenes such as 3,4-dimethylthiophene and 3,4-diethylthiophene, 3,4 such as 3,4-dimethoxythiophene and 3,4-diethoxythiophene. -Dialkoxythiophene, 3,4-methylenedioxythiophene, EDOT, 3,4-alkylenedioxythiophene such as 3,4- (1,2-propylenedioxy) thiophene, 3,4-methyleneoxythiathiophene, 3,4-alkyleneoxythiathiophene such as 3,4-ethyleneoxythiathiophene, 3,4- (1,2-propyleneoxythia) thiophene, 3,4-methylenedithiathiophene, 3,4-ethylenedithia 3,4-alkylene such as thiophene, 3,4- (1,2-propylenedithia) thiophene Alkylthieno [3,4-b] thiophenes such as thiathiophene, thieno [3,4-b] thiophene, isopropylthieno [3,4-b] thiophene, t-butyl-thieno [3,4-b] thiophene Can be mentioned. A single compound may be used as the monomer, or two or more compounds may be mixed and used. In particular, it is preferable to use EDOT.

（式中、ｍが１〜８の整数、好ましくは１〜４の整数、特に好ましくは２を意味し、ｎが１〜８の整数、好ましくは１〜４の整数、特に好ましくは２を意味し、ｏが２又は３を意味する）で表わされるスルホニルイミド酸及びこれらの塩を好ましく使用することができる。塩としては、リチウム塩、ナトリウム塩、カリウム塩などのアルカリ金属塩、アンモニウム塩、エチルアンモニウム塩、ブチルアンモニウム塩などのアルキルアンモニウム塩、ジエチルアンモニウム塩、ジブチルアンモニウム塩などのジアルキルアンモニウム塩、トリエチルアンモニウム塩、トリブチルアンモニウム塩などのトリアルキルアンモニウム塩、テトラエチルアンモニウム塩、テトラブチルアンモニウム塩などのテトラアルキルアンモニウム塩を例示することができる。これらの支持電解質は、特に耐熱性に優れた導電性ポリマー層を与える。中でも、ビス（ペンタフルオロエタンスルホニル）イミド酸の塩、例えばカリウム塩、ナトリウム塩、アンモニウム塩は、極めて高い耐熱性を有する導電性ポリマー層を与える。 As the supporting electrolyte in the polymerization solution, a non-sulfonic acid organic compound having an anion molecular weight of 200 or more is used. The anion of these supporting electrolytes is contained in the conductive polymer film as a dopant in the process of electrolytic polymerization shown below. In particular, borodisalicylic acid, borodisalicylate, formula (I) or formula (II)

(In the formula, m represents an integer of 1 to 8, preferably an integer of 1 to 4, particularly preferably 2, and n represents an integer of 1 to 8, preferably an integer of 1 to 4, particularly preferably 2. And o means 2 or 3) and salts thereof can be preferably used. Examples of the salt include alkali metal salts such as lithium salt, sodium salt and potassium salt, alkyl ammonium salts such as ammonium salt, ethyl ammonium salt and butyl ammonium salt, dialkyl ammonium salts such as diethyl ammonium salt and dibutyl ammonium salt, and triethyl ammonium salt. And trialkylammonium salts such as tributylammonium salt, and tetraalkylammonium salts such as tetraethylammonium salt and tetrabutylammonium salt. These supporting electrolytes provide a conductive polymer layer that is particularly excellent in heat resistance. Among them, salts of bis (pentafluoroethanesulfonyl) imidic acid, such as potassium salt, sodium salt, and ammonium salt, give a conductive polymer layer having extremely high heat resistance.

  In addition, borodisalicylic acid and borodisalicylate are inexpensive and economically advantageous, and are particularly preferable because they provide a conductive polymer layer having excellent heat resistance. However, borodisalicylic acid and borodisalicylate are preferable. It has been found that salicylate ions hydrolyze into salicylic acid and boric acid, which have very low water solubility in water. For this reason, when borodisalicylic acid and / or borodisalicylate is used as a supporting electrolyte, precipitation gradually occurs in the polymerization solution, making it unusable. In order to avoid this, when borodisalicylic acid and / or borodisalicylate is used as the supporting electrolyte, the supporting electrolyte is added to the solution and then subjected to electrolytic polymerization before formation of the precipitate, Used in combination with a stabilizer selected from the group consisting of nitrobenzene and nitrobenzene derivatives, which have the action of inhibiting the hydrolysis of salicylate ions. The stabilizer may be a single compound or two or more compounds. Examples of the nitrobenzene derivative include nitrophenol, nitrobenzyl alcohol, nitrobenzoic acid, dinitrobenzoic acid, dinitrobenzene, nitroanisole, nitroacetophenone, o-nitrophenol, m-nitrophenol, p-nitrophenol, And mixtures thereof are preferred.

  As the supporting electrolyte, a single compound may be used, or two or more compounds may be used, and the amount is sufficient to obtain a sufficient current for electrolytic polymerization at a concentration equal to or lower than the saturated dissolution amount in the polymerization solution. Used, preferably at a concentration of 10 mM or more, particularly preferably at a concentration of 30 mM or more.

  The polymerization solution is prepared by the following method depending on the monomer content. When the monomer is less than the saturated dissolution amount, a water-rich solvent, a substituted thiophene as a monomer, and the above-mentioned specific range of supporting electrolyte are introduced into a container for producing a polymerization solution, and are manually or mechanically A polymerization solution is prepared by dissolving each component in a water-rich solvent using a proper stirring means. If the monomer exceeds the saturated dissolution amount, that is, a water-rich solvent, a substituted thiophene as a monomer, and the above-mentioned specific range of supporting electrolyte are introduced into a container for producing a polymerization solution, and stirred and homogenized. In the case where the monomer phase-separates upon standing, the polymerization solution can be prepared by irradiating the solution with ultrasonic waves and dispersing the phase-separated monomer as oil droplets in the polymerization solution. The polymerization liquid of the present invention is obtained by irradiating a liquid obtained by adding a monomer exceeding the amount of saturated dissolution in a water-rich solvent with ultrasonic irradiation to disperse the monomer as oil droplets, and then adding a supporting electrolyte to the obtained liquid. You can also get If each component in the polymerization solution is stable, there is no limitation on the temperature during preparation. In this specification, “ultrasound” means a sound wave having a frequency of 10 kHz or more.

For ultrasonic irradiation, an ultrasonic oscillator conventionally known for ultrasonic cleaners, cell grinders and the like can be used without particular limitation. In order to obtain a liquid in which monomer oil droplets are stably dispersed in a water-rich solvent by ultrasonic irradiation, the phase-separated monomer must be oil droplets having a diameter of several μm or less. In addition, it is necessary to irradiate the phase separation liquid with ultrasonic waves having a frequency of 15 to 200 kHz that can generate cavitation of several hundred nm to several μm at least having strong mechanical action. The output of the ultrasonic wave is preferably 4 W / cm ² or more. The ultrasonic irradiation time is not strictly limited but is preferably in the range of 2 to 10 minutes. The longer the irradiation time, the more the aggregation of monomer oil droplets is inhibited, and the time until demulsification tends to be longer. However, when the ultrasonic irradiation time is 10 minutes or more, the aggregation effect of oil droplets tends to be saturated. Is recognized. It is also possible to perform multiple irradiations using ultrasonic waves having different frequencies and / or outputs. The monomer content exceeding the saturated dissolution amount may be an amount that can obtain a dispersion in which demulsification is suppressed by ultrasonic irradiation. Not only the type of monomer but also the type and amount of supporting electrolyte, ultrasonic irradiation conditions It also changes depending on.

  The polymerization liquid of the present invention contains a water-rich solvent, a monomer selected from substituted thiophenes, and other additives within a range that does not adversely affect the present invention in addition to the above-mentioned specific range of supporting electrolyte. Also good. Suitable additives include water-soluble nonionic surfactants. Since the monomer is concentrated in the micelles of the nonionic surfactant, electrolytic polymerization proceeds rapidly, and a polymer exhibiting high conductivity is obtained. In addition, the nonionic surfactant itself does not ionize, and does not inhibit doping of the polymer in the specific range with the anion of the supporting electrolyte.

  As the nonionic surfactant, a known water-soluble nonionic surfactant can be used without any particular limitation. Examples include polyalkylene glycol, polyvinyl alcohol, polyoxyalkylene alkyl ether, polyoxyalkylene alkyl phenyl ether, polyoxyalkylene styryl phenyl ether, polyoxyalkylene benzyl phenyl ether, polyoxyalkylene-added alkylphenol formaldehyde condensate, polyoxyalkylene Addition styrylphenol formaldehyde condensate, polyoxyalkylene addition benzylphenol formaldehyde condensate, alkyne diol, polyoxyalkylene addition alkyne diol, polyoxyalkylene fatty acid ester, polyoxyalkylene sorbitan fatty acid ester, polyoxyalkylene castor oil, polyoxyalkylene hydrogenated castor oil , Polyglycerin alkyl agent Le, such as polyglycerol fatty acid esters. These may be used alone or in combination of two or more. Further, for example, alkynediol having high dispersion effect such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol and other nonionic surfactants, preferably polyoxyethylene (9) nonyl Use of a combination with a polyoxyethylene alkylphenyl ether such as a phenyl ether branched type in the polymerization liquid is preferable because the monomer content in the polymerization liquid can be greatly increased.

  When a nonionic surfactant is used in combination, a water-rich solvent, a monomer, the above-mentioned specific range of supporting electrolyte, and a nonionic surfactant are introduced into a container for producing a polymerization solution, and are manually or mechanically stirred. A polymerization solution is prepared by dissolving each component in a water-rich solvent by using or irradiating ultrasonic waves. In addition, a water-rich solvent, a monomer, and a nonionic surfactant are introduced into a container for producing a polymerization solution to prepare a solution in which each component is dissolved in a water-rich solvent. The supporting electrolyte in the specific range may be added and dissolved.

  In any method for producing a polymerization liquid, when borodisalicylic acid and / or borodisalicylate as a supporting electrolyte and nitrobenzene and / or a nitrobenzene derivative as a stabilizer are used in combination, the polymerization liquid is produced. Both are introduced into the container almost simultaneously, or the stabilizer is introduced first. This is because the stabilizer is used to suppress hydrolysis of borodisalicylate ions.

(2) Polymerization step The polymerization solution obtained by the above-described preparation step is substituted by introducing a working electrode (substrate of the conductive polymer layer) having at least a conductive portion on the surface and a counter electrode, and performing electrolytic polymerization. A conductive polymer layer obtained by polymerization of thiophene is formed on the conductive portion of the working electrode to obtain an anode for a dye-sensitized solar cell.

  The material, shape, and size of the working electrode having at least a conductive portion on the surface are appropriately selected according to the application. The conductive portion of the substrate may be a single layer or may include a plurality of different types of layers. For example, a conductive plate or foil of platinum, gold, nickel, titanium, steel, rhodium, ruthenium or the like can be used as a working electrode. However, since the conductive polymer layer obtained in this polymerization step is excellent in transparency, it is transparent and insulating glass substrate such as optical glass, quartz glass, alkali-free glass, or polyethylene terephthalate, polyethylene naphthalate, polycarbonate, poly On the surface of transparent and insulating plastic substrates such as ether sulfone and polyacrylate, indium oxide, tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), tin oxide, antimony-doped tin oxide (ATO), fluorine-doped oxidation It is preferable to use, as a working electrode, a transparent substrate on which a transparent conductive layer such as tin (FTO), zinc oxide, or aluminum-doped zinc oxide (AZO) is provided by vapor deposition or coating. In addition, a substrate in which a metal film such as platinum, nickel, titanium, rhodium, ruthenium, or the like is provided on the glass substrate or plastic substrate described above by vapor deposition or coating can be used as a working electrode.

  As a counter electrode for electrolytic polymerization, a plate of platinum, nickel, or the like can be used.

The electrolytic polymerization is performed by any one of a constant potential method, a constant current method, and a potential sweep method using the polymerization solution obtained in the preparation step. In the case of the constant potential method, depending on the type of monomer, a potential of 1.0 to 1.5 V is suitable for the saturated calomel electrode, and in the case of the constant current method, it depends on the type of monomer. However, a current value of 1 to 10000 μA / cm ² , preferably 5 to 500 μA / cm ² , more preferably 10 to 100 μA / cm ² is suitable, and depending on the type of monomer when the potential sweep method is used. It is preferable to sweep the range of −0.5 to 1.5 V with respect to the saturated calomel electrode at a speed of 5 to 200 mV / sec. The polymerization temperature is not strictly limited, but is generally in the range of 10 to 60 ° C. The polymerization time varies depending on the composition of the polymerization solution and the electrolytic polymerization conditions, but is generally in the range of 0.6 seconds to 2 hours, preferably 1 to 10 minutes, particularly preferably 2 to 6 minutes.

By the electropolymerization, a conductive polymer layer containing the anion of the above-mentioned specific range non-sulfonic acid organic supporting electrolyte as a dopant is formed on the conductive portion of the working electrode. The density of the conductive polymer layer obtained is in the range of 1.15 to 1.80 g / cm ³ . When the density of the conductive polymer layer is less than 1.15 g / cm ³ , the heat resistance is drastically lowered, and it is difficult to produce a conductive polymer layer having a density exceeding 1.80 g / cm ³ . The density of the conductive polymer layer having excellent heat resistance is preferably in the range of 1.20 to 1.80 g / cm ³ , particularly preferably in the range of 1.60 to 1.80 g / cm ³ . When obtaining a flexible anode, if the density of the conductive polymer layer is too high, the conductive polymer layer becomes hard and lacks flexibility, so the density of the conductive polymer layer is 1.75 g / cm. ^It is preferably ³ or less, particularly preferably 1.70 g / cm ³ or less. Moreover, the surface resistance of the conductive polymer layer obtained is 10Ω / □ or less. The lower the surface resistance, the lower the resistance of the entire dye-sensitized solar cell and the higher the photoelectric conversion efficiency of the battery. This low surface resistance is preferable because it leads to high photoelectric conversion efficiency.

The thickness of the conductive polymer layer is generally in the range of 1 to 10,000 nm. If the thickness of the conductive polymer is 10000 nm or more, the internal resistance becomes high, the reduction reaction rate for converting the oxidized species in the electrolyte to the reduced species becomes insufficient, and it takes time for the electrolytic polymerization, which is economically disadvantageous. When the thickness of the conductive polymer layer is 1 nm or less, the catalytic ability to convert the oxidized species in the electrolyte layer to reduced species becomes insufficient. The thickness of the conductive polymer was calculated as follows. First, an experiment was conducted in which a conductive polymer layer was formed by performing constant current electrolytic polymerization for 1 minute on an ITO electrode under the condition of 0.1 mA / cm ² , and the thickness of the polymer layer was measured with an atomic force microscope. Next, an experiment was conducted in which a conductive polymer layer was formed on the ITO electrode by performing constant-current electrolytic polymerization under the condition of 0.1 mA / cm ² for 28.6 minutes, and the thickness of the polymer layer was measured with a step gauge. From these two experiments, a relational expression between the charge amount and the thickness of the conductive polymer layer was derived. And the amount of electric charge of electrolytic polymerization was converted into the thickness of a conductive polymer layer using the derived | led-out relational expression.

  By washing the conductive polymer layer after electrolytic polymerization with water, ethanol or the like and drying, an anode in which a conductive polymer layer having excellent heat resistance is formed on the substrate with good adhesion can be obtained. The obtained conductive polymer layer of the anode is stable to moisture in the air and exhibits a pH near neutral, so that other components are not corroded in the process of manufacturing or using the solar cell. .

B: Dye-sensitized solar cell A dye-sensitized solar cell includes a cathode having a semiconductor layer containing a dye as a photosensitizer, and a pair of oxidized and reduced species stacked on the semiconductor layer of the cathode. And an electrolyte layer including the anode described above. The conductive polymer layer of the anode described above has sufficient catalytic ability to convert the oxidizing species constituting the redox couple into the reducing species in the electrolyte layer.

  As the conductive substrate and the semiconductor layer constituting the cathode in the dye-sensitized solar cell, the conductive substrate and the semiconductor layer in the conventional dye-sensitized solar cell can be used without any particular limitation.

  As the conductive substrate, a substrate having a conductive portion at least on the surface can be used, and the conductive portion of the substrate may be a single layer or may include a plurality of different types of layers. For example, a plate or foil of a conductor such as platinum, nickel, titanium, steel, chromium, niobium, molybdenum, ruthenium, rhodium, tantalum, tungsten, iridium, or hastelloy can be used as a substrate, or optical glass, quartz On the surface of a transparent and insulating glass substrate such as glass and alkali-free glass, or transparent and insulating plastic substrate such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyethersulfone, polyacrylate, indium oxide, ITO, A transparent substrate provided with a transparent conductive layer such as IZO, tin oxide, ATO, FTO, zinc oxide, and AZO by vapor deposition or coating can also be used. In addition, a substrate in which a metal film such as platinum, nickel, titanium, rhodium, and ruthenium is provided on the above glass substrate or plastic substrate by vapor deposition or coating can be used. When the substrate contained in the anode is opaque, a transparent substrate is used as the cathode substrate. Moreover, even if the base contained in the anode is transparent, an all-transparent solar cell can be constructed by using a transparent base for the cathode.

  Semiconductor layer is titanium oxide, zirconium oxide, zinc oxide, tin oxide, nickel oxide, niobium oxide, magnesium oxide, tungsten oxide, bismuth oxide, indium oxide, thallium oxide, lanthanum oxide, yttrium oxide, phosphonium oxide, cerium oxide, oxide An oxide semiconductor such as aluminum, cadmium sulfide, cadmium selenide, cadmium telluride, calcium titanate, strontium titanate, or barium titanate can be used. As the oxide semiconductor, a single compound may be used, or two or more kinds may be mixed and used. It is preferable to use titanium oxide having high photoelectric conversion efficiency. An oxide semiconductor is usually used in a porous form so that a large amount of dye can be supported on a semiconductor layer.

  As the dye acting as a photosensitizer, an organic dye or a metal complex dye having absorption in the visible light region and / or the infrared light region can be used. Organic dyes include triphenylamine, coumarin, cyanine, merocyanine, phthalocyanine, porphyrin, azo, quinone, quinoneimine, quinacridone, squarylium, triphenylmethane, xanthene, and perylene. Indigo and naphthalocyanine dyes can be used, and triphenylamine dyes are preferably used. As the metal complex dye, an osmium complex, a ruthenium complex, an iron complex, a zinc complex, a platinum complex, a palladium complex, or the like can be used, and in particular, a ruthenium bipyridine complex such as N3 or N719 in that it has a wide absorption band. It is preferable to use a ruthenium terpyridine complex and a ruthenium quarterpyridine complex such as N749. Further, in order to strongly adsorb the dye to the porous oxide semiconductor layer and facilitate the electron transfer between the excited dye and the conduction band of the porous oxide semiconductor layer, a carboxyl group in the dye molecule, Those having an interlock group such as an alkoxy group, a hydroxyl group, a hydroxyalkyl group, a sulfonic acid group, an ester group, a mercapto group, and a phosphonyl group are preferable, and among these, a group having a carboxyl group is particularly preferable. In addition, if an acid functional group such as a carboxyl group is neutralized with an alkali metal hydroxide, a tetraalkylammonium hydroxide, an imidazolium hydroxide, a pyridinium hydroxide, or the like, an anion is obtained. The repulsive force acting between them suppresses the association between the dye molecules, and can greatly reduce the electron trap between the dye molecules. As these dyes, a single compound may be used, or a mixture of two or more kinds may be used.

The cathode of the dye-sensitized solar cell can be obtained by a known method. For example, a dispersion containing the above-described oxide semiconductor particles and an organic binder such as polytetrafluoroethylene, polyvinylidene fluoride, or carboxymethyl cellulose on a conductive portion of a substrate is wet by spin coating, bar coating, cast coating, or the like. After laminating by the method, heating and drying, the porous layer of the oxide semiconductor is provided on the substrate by firing at a temperature of 400 to 500 ° C. Before providing the porous layer, it is preferable to form a blocking layer composed of a TiO ₂ thin film having a thickness of 10 nm or less on the substrate and to provide the porous layer on the blocking layer. This blocking layer suppresses the Co (III) oxidizing species from being reduced at the transparent substrate portion holding the porous layer, and prevents deterioration of the dye-sensitized solar cell due to dark current. This blocking layer can be suitably formed by an atomic layer volume method using titanium alkoxide and water.

As the oxide semiconductor particles for forming the porous layer, spherical, rod-like, needle-like particles having an average primary particle diameter of 1 to 200 nm are preferably used. Further, in order to improve necking between oxide semiconductor particles, improve electron transport properties, and improve photoelectric conversion efficiency, after immersing the TiCl ₄ solution in the porous layer of the oxide semiconductor and washing the surface with water, You may bake at the temperature of 400-500 degreeC. Next, the substrate after baking is immersed in a solution in which the above-described dye is dissolved in a solvent such as ethanol, isopropyl alcohol, butyl alcohol, etc., taken out from the immersion liquid after a predetermined time, and dried to carry the dye on the oxide semiconductor. Thus, a cathode can be obtained. After supporting a dye on an oxide semiconductor, a reverse electron transfer inhibitor having a functional group such as an imidazolyl group, a carboxy group, or a phosphone group that binds to the semiconductor, such as tert-butylpyridine, 1-methoxybenzimidazole, decanoic acid When the obtained substrate is immersed in a solution in which a phosphonic acid having a long-chain alkyl group (having about 13 carbon atoms) is dissolved and the reverse electron transfer inhibitor is adsorbed in the gap between the dyes on the semiconductor surface, It is preferable because reverse electron transfer in the liquid can be prevented and the dye is less likely to be eluted into the electrolytic solution. The thickness of the semiconductor layer is generally in the range of 1 to 100 μm, preferably 3 to 50 μm, particularly preferably 3 to 20 μm. If the thickness of the semiconductor layer is less than 1 μm, light absorption may be insufficient. If the thickness of the semiconductor layer is greater than 100 μm, the distance from which the electrons reach the conductive portion of the base becomes long, and the electrons Is not preferable because of inactivation.

  The electrolyte layer of the dye-sensitized solar cell has 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, and 4,4′-di-t-butyl-2 as redox couples. Co (III) outer sphere complexes having a ligand selected from the group consisting of 2,2'-bipyridine and Co (II) reductants of the complexes. As the counter anion of the outer sphere complex, perchlorate ion and hexafluorophosphate ion are preferable. The electrolytic solution that forms these redox pairs is reduced to an organic solvent such as acetonitrile, methoxyacetonitrile, 3-methoxypropionitrile, propylene carbonate, ethylene carbonate, γ-butyrolactone, ethylene glycol, and the reduced species ( After the Co (II) complex is dissolved, an oxidizing agent such as nitrosonium borofluoride is added to convert a part of the reduced species into an oxidized species (Co (III) complex). Various additives such as 4-tert-butylpyridine and carboxylic acid can also be added for the purpose of improving the open circuit voltage of the dye-sensitized solar cell. Further, a supporting electrolyte such as lithium iodide or lithium tetrafluoroborate may be added to the electrolytic solution as necessary.

  Moreover, an electrolyte layer can also be formed with the gel electrolyte pseudo-solidified by adding a gelling agent to the electrolyte solution. When used as a physical gel, polyacrylonitrile, polyvinylidene fluoride, or the like can be used as a gelling agent. When used as a chemical gel, an acrylic (methacrylic) ester oligomer or tetra (bromomethyl) benzene as a gelling agent. A combination of polyvinyl pyridine and polyvinyl pyridine can be used.

  The dye-sensitized solar cell can be obtained by a known method using the above-described anode. For example, by disposing a cathode semiconductor layer and an anode conductive polymer layer with a predetermined gap, injecting an electrolyte into the gap, and heating as necessary to form an electrolyte layer, dye sensitization A solar cell can be obtained. The thickness of the electrolyte layer is generally in the range of 1 to 100 μm, preferably 1 to 50 μm, excluding the thickness of the electrolyte layer that has penetrated into the semiconductor layer. If the thickness of the electrolyte layer is less than 1 μm, the semiconductor layer of the cathode may be short-circuited. If the thickness of the electrolyte layer is more than 100 μm, the internal resistance increases, which is not preferable.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

  First, the anode used in the dye-sensitized solar cell of the present invention will be described, and then the dye-sensitized solar cell of the present invention will be described.

(A) Production of anode 50 mL of distilled water was introduced into a glass container, and p-nitrophenol was introduced at a concentration of 0.10 M, EDOT at a concentration of 0.0148 M, and ammonium borodisalicylate at a concentration of 0.08 M. In this order, they were added and stirred to obtain a polymerization solution in which all EDOT was dissolved. An ITO electrode (ITO layer surface resistance: 10Ω / □) having an area of 1 cm ² was introduced into the obtained polymerization solution as a working electrode, and a SUS mesh having an area of 5 cm ² was introduced as a counter electrode, respectively, and 100 μA / cm ² The constant current electropolymerization was performed under the following conditions. The polymerization time was adjusted in the range of 0.2 to 3 minutes so that PEDOT layers having different thicknesses were obtained. The working electrode after polymerization is washed with methanol and then dried at 160 ° C. for 30 minutes to obtain an electrode body in which a PEDOT layer (dopant: borodisalicylate anion) having a thickness of 10 to 105 nm is formed on the ITO electrode. It was. The density of the PEDOT layer was about 1.6 g / cm ³ .

  About the obtained anode, the surface resistance of the PETOT layer was measured. FIG. 1 shows the relationship between the thickness of the PEDOT layer and the surface resistance. It can be seen that as the PEDOT layer becomes thicker, its surface resistance decreases. The conductive polymer layer obtained by electrolytic polymerization has a surface resistance generally higher than the surface resistance of the conductive portion of the working electrode. However, the conductive polymer layer obtained in the above polymerization step has a conductive portion (ITO) of the working electrode. Layer) surface resistance (10Ω / □). The lower the surface resistance, the lower the resistance of the entire dye-sensitized solar cell and the higher the photoelectric conversion efficiency of the battery. This low surface resistance is preferable because it leads to a high photoelectric conversion efficiency of the battery.

(B) Production of dye-sensitized solar cell Example 1
Methanol containing 3 equivalents of 4,4′-di-t-butyl-2,2′-bipyridine (t-Bu ₂ bpy) obtained by dissolving 1 equivalent of CoCl ₂ .6H ₂ O in a small amount of methanol Added to the solution and stirred for 2 hours. Then, excess NH ₄ PF ₆ was added to precipitate yellow [Co (II) (t-Bu ₂ bpy) ₃ ] [PF ₆ ] ₂ (reducing species). The precipitate was filtered, washed with ethanol, methanol and ether and then dried in vacuo. In acetonitrile, 0.22 M [Co (II) (t-Bu ₂ bpy) ₃ ] [PF ₆ ] ₂ , 0.20 M LiClO ₄ , 0.20 M 4-t-butylpyridine, and 0.02 M Of NOBF ₄ was added to convert some of the reduced species into oxidized species (Co (III) complex) to prepare an electrolytic solution containing a Co (II / III) complex system.

A blocking layer made of a titanium oxide thin film was formed on an FTO electrode having a surface area of 1 cm ² by an atomic layer volume method using titanium isopropoxide and water. Next, a titanium oxide paste (manufactured by JGC Catalysts & Chemicals Co., Ltd.) is applied to the surface of the blocking layer by screen printing so that the film thickness is about 10 μm, pre-dried at 60 ° C. for 30 minutes, and further at 450 ° C. for 15 minutes By firing, a porous titanium oxide layer was formed on the FTO electrode. The thickness of the titanium oxide after firing was 8 μm. Furthermore, after immersing the titanium oxide porous layer in an ethanol solution containing the triphenylamine dye represented by the formula (III) at a concentration of 0.2 mM for 24 hours, the titanium oxide porous layer is dried at room temperature. A dye represented by the formula (III) was added to obtain a cathode of a dye-sensitized solar cell.

  Next, the obtained cathode and an anode having a 105 nm PEDOT layer (dopant: borodisalicylate anion) are laminated so that the titanium oxide porous layer and the conductive polymer layer face each other with a spacer of 50 μm, An electrolyte layer was formed by impregnating the above-mentioned electrolytic solution into the gap to obtain a dye-sensitized solar cell.

Comparative Example 1
Instead of the electrolyte of Example 1, 0.1 M lithium iodide, 0.05 M iodine, 0.6 M 1,2-dimethyl-1,3-propylimidazolium iodide, and 0.5 M 4 The procedure of Example 1 was repeated using an electrolytic solution in which t-butylpyridine was dissolved in acetonitrile.

(C) Evaluation of dye-sensitized solar cell About the dye-sensitized solar cell of Example 1 and the comparative example 1, the current-voltage characteristic under the irradiation conditions of 100 mW / cm < ² > and AM1.5G by a solar simulator was evaluated.

Table 1 shows the obtained open circuit voltage values.

As apparent from Table 1, the dye-sensitized solar cell of the present invention, a conventional I ^- / I ₃ ^- as compared to the dye-sensitized solar cell using the electrolyte layer containing a redox pair, the higher open circuit voltage The value is shown.

  According to the present invention, a dye-sensitized solar cell that is excellent in heat resistance, has a high open-circuit voltage, and is expected to have high conversion efficiency can be obtained.

Claims (3)

A cathode having a semiconductor layer containing a dye as a photosensitizer;
An electrolyte layer comprising a pair of oxidized and reduced species laminated on the cathode semiconductor layer;
An anode having a conductive polymer layer laminated on the electrolyte layer and acting as a catalyst for converting the oxidized species to the reduced species;
A dye-sensitized solar cell comprising:
The conductive polymer layer in the anode is
A polymer composed of at least one monomer selected from the group consisting of thiophene having substituents at the 3-position and 4-position;
An anion generated from at least one compound which is a non-sulfonic acid organic compound and has a molecular weight of 200 or more as a dopant for the polymer;
Including
The non-sulfonic acid organic compound is at least one compound selected from the group consisting of borodisalicylic acid and borodisalicylate;
The oxidizing and reducing species forming a pair in the electrolyte layer are 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, and 4,4′-di-t-butyl-2, A dye-sensitized solar cell comprising a Co (III) outer sphere complex having a ligand selected from the group consisting of 2'-bipyridine and a Co (II) reductant of the complex. The dye-sensitized solar cell according to claim 1, wherein the density of the conductive polymer layer is in the range of 1.15 to 1.80 g / cm ³ . The dye-sensitized solar cell according to claim 1 or 2 , wherein the monomer is 3,4-ethylenedioxythiophene.

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