JP4595337B2 - Method for producing negative electrode in dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a method for producing a negative electrode in a dye-sensitized solar cell, and more specifically, production of a negative electrode in a dye-sensitized solar cell in which a semiconductor porous layer is formed by heating using a microwave. Regarding the law.

  Currently, there is great expectation for photovoltaic power generation from the viewpoint of global environmental problems and fossil energy resource depletion problems, and single crystal and polycrystalline silicon photoelectric conversion elements are put into practical use as solar cells. However, this type of solar cell is expensive and has a problem of supply of silicon raw materials, and the practical application of solar cells using materials other than silicon is desired.

  From the above viewpoint, recently, a dye-sensitized solar cell has attracted attention as a solar cell using a material other than silicon. As shown in FIG. 1, this dye-sensitized solar cell uses a transparent conductive film 1b (for example, ITO film) as an electrode substrate 1 on a transparent substrate 1a such as transparent glass or a transparent resin film. A porous layer 3 made of a metal oxide semiconductor such as titanium dioxide is provided on the transparent conductive film 1b, and a sensitizing dye (for example, Ru dye) 5 is adsorbed on the surface of the porous layer 3 as the negative electrode 7. Such a negative electrode 7 has a structure in which the positive electrode 10 is opposed to the electrolyte solution 8 therebetween.

  In the dye-sensitized solar cell having such a structure, when visible light is irradiated from the negative electrode 7 side, the dye 5 is excited and transitions from the ground state to the excited state. It is injected into the conduction band of the porous layer 3 and moves to the positive electrode 10 through the external circuit 12. The electrons that have moved to the positive electrode 10 are carried by the ions in the electrolytic solution and return to the dye 5. Electric energy is extracted by repeating such a process. The power generation mechanism of such a dye-sensitized solar cell differs from that of a pn junction photoelectric conversion element in that light capture and electron conduction are performed at different locations, which is very similar to a plant photoelectric conversion process. ing.

By the way, in the negative electrode 7 of the dye-sensitized solar cell as described above, a metal oxide semiconductor paste is applied on the transparent conductive film 1b of the transparent substrate 1a and baked to form the semiconductor porous layer 3. It is manufactured by applying a dye solution thereon, adsorbing the dye to the porous layer 3, and then removing the solvent of the dye solution (Patent Documents 1 and 2), and baking the semiconductor paste. Is also known to be performed by microwave irradiation (Non-patent Document 1).
Japanese Patent No. 2664194 Japanese Patent Publication 8-15097 Functional Materials June 2003 Vol.23 No.6 pp.58-63

  The method of firing semiconductor paste by microwave irradiation as in Patent Document 3 has the advantage that firing can be completed in a very short time compared to firing in an electric furnace. Since the semiconductor paste and the underlying transparent conductive layer are heated rapidly to a high temperature, the temperature of the transparent substrate supporting the transparent conductive layer is increased. For example, a transparent resin film using a transparent resin film as the transparent substrate is used. In the case of electrodes, there is a drawback that deformation occurs due to thermal expansion and contraction. For this reason, as a microwave to be irradiated, a microwave having a special oscillation frequency (for example, 28 GHz) is used instead of a generally used frequency of 2.45 GHz, and the selective heating property is enhanced.

  However, when microwaves with special oscillation frequencies as described above are used, special microwave oscillators, waveguides, etc. are used to satisfy the restrictions on the output and leakage electric field strength specified by the Radio Law. Equipment is required, resulting in a significant increase in manufacturing costs.

  Therefore, the object of the present invention is to form a semiconductor porous layer by heating by microwave irradiation with a commonly used oscillation frequency of 2.45 GHz, and to effectively deform the transparent resin electrode during heating and firing. It is providing the manufacturing method of the negative electrode in the dye-sensitized solar cell which can be suppressed.

According to the present invention, a transparent resin electrode substrate provided with a transparent conductive layer on a transparent resin film is prepared, and a metal oxide semiconductor is dispersed in an organic solvent on the transparent conductive layer of the transparent resin electrode. A semiconductor paste is applied to form a semiconductor coating layer, and the semiconductor coating layer is baked to form a semiconductor porous layer, and a dye solution is brought into contact with the semiconductor coating layer before baking or the semiconductor porous layer after baking. In the method for producing a negative electrode in a dye-sensitized solar cell that performs adsorption treatment of
The semiconductor coating layer is baked by heating with microwave irradiation in a state where the transparent resin electrode is placed on the liquid film formed on the sample stage so that the semiconductor coating layer is on the surface side. There is provided a manufacturing method characterized in that it is performed.

In the present invention,
(1) Use a microwave whose oscillation frequency is 2.45 GHz.
(2) the liquid film is formed of water;
(3) The transparent resin film is polyethylene terephthalate or polyethylene naphthalate,
Is preferred.

  In the present invention, a heat treatment (firing) for making a semiconductor paste porous is performed by microwave irradiation. When microwave irradiation is performed, a transparent resin electrode supporting a semiconductor coating layer irradiated with microwaves is provided. It is an important feature that the substrate is placed on a liquid film formed on the sample stage. That is, due to the cooling action of the liquid film, the temperature rise of the transparent resin film in the electrode substrate can be effectively avoided. Moreover, due to the nature of the liquid film, the back surface of the transparent resin film (the side on which the transparent conductive layer is formed) Since the liquid film is always in contact with the entire surface on the opposite side, the uniform cooling effect can be ensured, and deformation due to local temperature unevenness of the transparent resin film can be effectively avoided. In addition, even if the transparent conductive film is subjected to thermal deformation, it is a liquid film, so the space between the sample stage and the film can be maintained constantly filled with liquid, which greatly reduces the damage caused by microwaves. be able to. Therefore, in the present invention, the dye-sensitized solar cell can be fired by using microwaves with a particularly wide frequency of 2.45 GHz, requires no special equipment, and is manufactured at an extremely low manufacturing cost. The negative electrode can be manufactured.

  Hereinafter, the manufacturing process of the negative electrode in the dye-sensitized solar cell using the semiconductor fine particle paste of the present invention will be described with reference to FIG. 1 and FIG.

  First, the transparent resin electrode substrate 1 shown in FIG. 1 is prepared. This electrode substrate 1 is provided with a transparent conductive film 1b on a transparent resin film 1a, and any transparent resin film 1a may be used as long as it is transparent. A random or block copolymer of α-olefins such as density polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene, etc. Polyolefin resin; ethylene-vinyl compound copolymer resin such as ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene-vinyl chloride copolymer; polystyrene, acrylonitrile-styrene copolymer, ABS, α -Styrenic resin such as methylstyrene-styrene copolymer; polyvinyl alcohol, Polyvinyl resins such as polyvinylpyrrolidone, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate; nylon 6, nylon 6-6 Polyamide resins such as nylon 6-10, nylon 11 and nylon 12; polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate; polycarbonate; polyphenylene oxide; cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; oxidized starch and ether A film made of starch such as modified starch or dextrin; and a resin made of a mixture thereof can be used. In general, a polyethylene terephthalate film or polyethylene naphthalate is preferably used from the standpoint of strength, heat resistance, and the like. Further, the thickness and size of the transparent resin film 1a are not particularly limited, and are appropriately determined according to the use of the dye-sensitized solar cell to be finally used.

  The transparent conductive film 1b is typically a film made of an indium oxide-tin oxide alloy (ITO film) or a film in which tin oxide is doped with fluorine (FTO film). Is preferred. These are formed on the transparent substrate 1a by vapor deposition, and the thickness is usually about 0.5 to 0.7 μm.

  Next, a semiconductor paste is applied on the transparent conductive film 1b of the transparent resin electrode substrate 1 to form a semiconductor coating layer. This coating layer forms the semiconductor porous layer (titania porous layer) 3 in FIG. 1 by firing.

Therefore, the semiconductor paste to be applied is obtained by dispersing metal oxide semiconductor particles in an organic solvent. As the metal oxide semiconductor, those conventionally used in dye-sensitized solar cells, specifically, It is possible to use oxides of metals such as titanium, zirconium, hafnium, strontium, tantalum, chromium, molybdenum and tungsten, or composite oxides containing these metals, such as perovskite oxides such as SrTiO ₃ and CaTiO _3. it can. In order to ensure a high conversion rate, titanium dioxide is most preferably used. Such semiconductor oxide particles are preferably fine in terms of porosity, and generally have a particle size of 5 to 500 nm, particularly 5 to 350 nm.

  In addition, as the organic solvent in which the metal oxide semiconductor particles are dispersed, a lower alcohol having 4 or less carbon atoms, for example, methanol, ethanol, isopropanol, n-butanol, sec-butanol, t-butanol or the like may be used alone or in combination. It is suitably used in the above combination.

  Further, the semiconductor paste preferably contains a metal alkoxide corresponding to the metal oxide. Such a metal alkoxide has a function as a so-called dispersant and curing agent, can uniformly and stably disperse the metal oxide semiconductor particles in the organic solvent, and further connects the semiconductor fine particles to each other. It becomes advantageous to form a uniform semiconductor coating layer in a short time by microwave heating described later. In addition, since the metal alkoxide easily forms a corresponding metal oxide by firing for porous formation, which will be described later, performance deterioration due to such metal alkoxide does not occur. In the present invention, as such a metal alkoxide, isopropoxide is suitable, and particularly when titanium dioxide particles are used, tetraisopropoxy titanium is most preferred.

  The metal alkoxide is preferably used in an amount of 10 to 40 parts by weight, particularly 10 to 30 parts by weight per 100 parts by weight of the metal oxide semiconductor particles described above. If it is used too much, the curing effect will increase, but the dispersion effect will not increase, but it tends to cause inconveniences such as lowering the conversion efficiency, and the desired curing effect and dispersion effect can be obtained even with a very small amount. It is not possible.

  Furthermore, the solid content concentration of the above-described semiconductor paste is preferably in the range of 20 to 50% by weight, particularly 25 to 30% by weight. When the amount of the solvent is too large, it becomes difficult to form a coating layer having a stable thickness due to dripping or the like, and when the amount of the solvent is small, the workability is lowered.

  The metal alkoxide-containing semiconductor paste is prepared by preparing an organic solvent solution containing about 1 to 3 moles of metal alkoxide and dispersing the organic solvent solution together with the metal oxide semiconductor particles in the lower alcohol. be able to. In this case, as the organic solvent for the metal alkoxide, in addition to the aforementioned lower alcohol having 4 or less carbon atoms, ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,4-butane. Diol, 1,2-butanediol, 1,3-butanediol, aliphatic glycols such as 2-methyl-1,3-propanediol, ketones such as methylethylketone, and amines such as dimethylethylamine alone or It can also be used in a combination of two or more.

The coating of the semiconductor paste can be performed by a known method such as a doctor blade method, a spin coating method, a screen printing method, or a spray coating method. The thickness after baking is about 5 to 20 μm, and the semiconductor weight is as follows. , 0.001 to 0.005 g / cm ² is preferable.

  After the semiconductor paste of the present invention is coated on the transparent conductive film 1b of the transparent substrate 1 as described above, baking is performed. As described above, this firing is performed by microwave irradiation.

  In FIG. 2 for explaining the firing process by microwave irradiation, a transparent resin electrode substrate 1 on which a semiconductor coating layer 3 ′ is formed is placed on a sample stage 20 in a chamber shielded by a metal wall or the like. In this state, the semiconductor coating layer 3 ′ on the surface is irradiated with microwaves for baking. In the present invention, a liquid film 22 is formed on the sample stage 20, and a transparent resin electrode substrate is formed on the liquid film 22. 1 is placed and irradiated with microwaves.

That is, the metal oxide semiconductor particles and alkoxide of the semiconductor coating layer 3 ′ are rapidly heated by the microwave, or the transparent conductive film 1b is also heated at the same time, but the liquid film 22 contacts the back surface of the transparent resin film 1a. Therefore, the temperature rise of the transparent resin film 1a is effectively suppressed by the cooling effect, and the deformation is effectively prevented. Moreover, even if the resin film 1a expands and contracts, as is apparent from FIG. 2, the liquid surface follows the back surface of the transparent resin film 1a due to the nature of the liquid film 22 , and the back surface of the transparent resin film 1a is The whole always contacts the liquid film 22 uniformly, and a uniform cooling effect is maintained. Therefore, temperature unevenness of the transparent resin film 1a can be effectively avoided, and for example, wrinkles due to uneven expansion and contraction due to local temperature rise can be effectively avoided. In addition, even if the transparent conductive film is subjected to thermal deformation, it is a liquid film, so the space between the sample stage and the film can be maintained constantly filled with liquid, which greatly reduces the damage caused by microwaves. be able to. In the case where the liquid film 2 is not provided, the transparent resin film 1a partially comes into contact with the sample stage 20, so that temperature unevenness occurs in the transparent resin film 1a and wrinkles due to non-uniform expansion and contraction. The transparent conductive film is subjected to thermal deformation and a space is created between the sample stage and the film. As a result, an electromagnetic field caused by microwaves is intensively formed on the part, and the film is damaged due to discharge and heat generation. Resulting in.

In the present invention, since the liquid film 22 is provided to effectively prevent deformation of the transparent resin film 1a, the frequency of the microwave to be irradiated depends on the metal oxide semiconductor particles or alkoxides in the semiconductor coating layer 3 ′. Is not particularly limited as long as it has an absorption band, but it is a great advantage that a commonly used 2.45 GHz microwave can be used. That is, by using a microwave having such a general frequency, unlike the case of using a special frequency, it is not necessary to use special equipment, and the manufacturing cost can be significantly reduced.

The above-described microwave irradiation may be performed to such an extent that the metal oxide particles in the semiconductor coating layer 3 ′ are appropriately sintered. For example, the metal oxide particles are densified so that the relative density by the Archimedes method reaches 50 to 90%. Just do it. Although the irradiation time varies depending on the type of metal oxide particles used, for example, when a paste containing titanium oxide and tetraisopropoxytitanium is used, it can be easily densified. The irradiation time may be about 3 to 10 minutes, and the size of the transparent conductive film to be irradiated can be selected from 0.25 to 360 cm ² .

The liquid film 22 can be used without particular limitation as long as it does not volatilize during microwave irradiation, but it is usually most preferable to use water in terms of cost. For example, when a microwave of 2.45 GHz is used, water is also heated. However, in the present invention, since baking can be completed by irradiation in an extremely short time, water is present as the liquid film 22 during microwave irradiation. be able to. Further, when water is used as the liquid film 22, the amount may be about 0.2 to 1.0 g / cm ² .

  In addition, as the sample stage 20, glass, a metal plate with good thermal conductivity, or a resin plate is used as necessary.

  The sensitizing dye 5 is adsorbed by bringing the dye solution into contact with the semiconductor porous layer 3 formed by the microwave irradiation as described above. The contact of the dye solution is usually performed by dipping, and the adsorption treatment time (immersion time) is usually about 30 minutes to 24 hours, and after adsorption, the solvent of the dye solution is removed by drying, The negative electrode 7 having the semiconductor porous layer 3 having the sensitizing dye 5 formed on the surface can be obtained.

As the sensitizing dye to be used, those known per se having a linking group such as a carboxylate group, a cyano group, a phosphate group, an oxime group, a dioxime group, a hydroxyquinoline group, a salicylate group, an α-keto-enol group are used. Those described in Patent Documents 1 to 3 described above, for example, ruthenium complexes, osmium complexes, iron complexes, and the like can be used without any limitation. Ruthenium-tris (2,2′-bispyridyl-4,4′-dicarboxylate), ruthenium-cis-diaqua-bis (2,2′-bispyridyl-4,4) in that it has a particularly broad absorption band. Ruthenium-based complexes such as' -dicarboxylate) are preferred. Such a dye solution of a sensitizing dye is prepared using an alcohol organic solvent such as ethanol or butanol as a solvent, and the dye concentration is usually about 3 × 10 ^{−4 to} 5 × 10 ⁻⁴ mol / l. It is.

  In the manufacturing process, the semiconductor coating layer 3 ′ is fired to form the semiconductor porous layer 3, and then the dye is adsorbed. In the present invention, the firing is performed by microwave irradiation in a short time. Therefore, the baking can be performed after the dye adsorption treatment. That is, after the semiconductor fine particle paste is applied and dried, the dye solution is brought into contact by dipping or the like to adsorb the sensitizing dye and dried, followed by baking. The drying in this case may be natural drying simply by leaving it in the atmosphere, but may be heated to a temperature of less than 100 ° C. if necessary.

  As described above, there is a case where the adsorption of the dye is performed prior to firing, but when using the paste adjusted with the paste material, the toughness having excellent adhesion to some extent after drying in the air for 5 to 10 minutes Since the porous film is obtained, the dye can be adsorbed before firing. In this case, for example, the adsorption treatment can be performed in a short time of about 10 to 15 minutes, and the adsorption treatment is performed after firing. The adsorption process can be completed in half the time or less, which is extremely excellent in terms of productivity and mass productivity.

  As shown in FIG. 1, the negative electrode 7 obtained as described above is used as a dye-sensitized solar cell by facing the positive electrode 10 which is a counter electrode with an electrolyte solution 8 interposed therebetween. .

  As the electrolyte solution 8, various electrolyte solutions containing a cation such as lithium ion and an anion such as chlorine ion can be used. Further, in this electrolyte solution, it is preferable that an oxidation-reduction pair capable of reversibly taking an oxidized structure and a reduced structure exists, and examples of such an oxidized-reduced pair include iodine-iodine compounds, bromine- Examples thereof include bromine compounds and quinone-hydroquinone. The electrolyte solution 8 is generally sealed with an electrically insulating resin or the like so that it does not leak between the electrodes.

  In addition, the positive electrode 10 can use various electrode substrates regardless of whether they are transparent or opaque. For example, a transparent electrode layer such as a platinum layer or ITO is deposited on the surface of a transparent substrate such as a glass substrate or a transparent resin film. Alternatively, it is possible to adopt an arbitrary structure such as a transparent electrode layer such as ITO deposited on the transparent substrate surface and a platinum layer deposited thereon.

A titanium alkoxide solution diluted with an organic solvent butanol is prepared so that titanium isopropoxide is 1 mol / L, and this solution is mixed with titanium dioxide particles (general-purpose titania particles having a particle size of 15 to 350 nm). A titanium dioxide fine particle paste containing titanium isopropoxide in an amount of 20 parts by weight per 100 parts by weight of titanium dioxide fine particles and having a solid content concentration of 30% by weight was prepared.
Then, the above-prepared titanium dioxide paste is applied to a conductive film (product name “OTEC”, manufactured by Tobi Co., Ltd.) in which an ITO film is provided as a conductive film on a polyethylene terephthalate film. Drying was performed for 5 minutes. The dried semiconductor paste (semiconductor coating layer) had a thickness of about 5 μm and a semiconductor weight of about 0.002 g / cm ² .
After that, a dye solution composed of ruthenium complex dye [Ru (dcbpy) ₂ (NCS) ₂ ] · 2H ₂ O dispersed in ethanol of 99.5% purity is dropped and adsorbed onto the titania film coated on the ITO film. Then, water was formed as a liquid film on a glass sample stage in a chamber shielded by a metal wall, and a transparent resin electrode substrate on which a semiconductor coating layer was formed was placed on the water and irradiated with microwaves.
Using the negative electrode obtained as described above, 4-tert-butyl pyridine was added to this and LiI / I ₂ 0.5 mol / 0.05 mol) dissolved in methoxypropionitrile. Thus, a dye-sensitized solar cell was fabricated by sandwiching the prepared electrolyte with a positive electrode composed of an ITO / PET film deposited with platinum. When the conversion efficiency of this battery was measured, it was about 2 to 3%, and it was confirmed that it functions as a solar battery.

Comparative example

A titanium alkoxide solution diluted with an organic solvent butanol is prepared so that titanium isopropoxide is 1 mol / L, and this solution is mixed with titanium dioxide particles (general-purpose titania particles having a particle size of 15 to 350 nm). A titanium dioxide fine particle paste containing titanium isopropoxide in an amount of 20 parts by weight per 100 parts by weight of titanium dioxide fine particles and having a solid content concentration of 30% by weight is prepared.
Then, the above-prepared titanium dioxide paste is applied to a conductive film (product name “OTEC”, manufactured by Tobi Co., Ltd.) in which an ITO film is provided as a conductive film on a polyethylene terephthalate film. Drying was performed for 5 minutes. The dried semiconductor paste (semiconductor coating layer) had a thickness of about 5 μm and a semiconductor weight of about 0.002 g / cm ² .
After that, a dye solution composed of ruthenium complex dye [Ru (dcbpy) ₂ (NCS) ₂ ] · 2H ₂ O dispersed in ethanol of 99.5% purity is dropped and adsorbed onto the titania film coated on the ITO film. A transparent resin electrode substrate on which a semiconductor coating layer was formed was placed on a glass sample stage in a chamber shielded by a metal wall and irradiated with microwaves. Then, the transparent resin electrode substrate on which the semiconductor coating layer was formed was thermally deformed and damaged within an irradiation time of 1 minute or less. This is because the substrate on the sample stage is thermally deformed by microwave irradiation, and an electromagnetic field due to microwaves is intensively formed in the space between the substrate and the sample stage that is formed. It is thought that the film was damaged due to the occurrence of the above.

The figure which shows schematic structure of the dye-sensitized solar cell which has a negative electrode manufactured by this invention. The figure for demonstrating the baking process by the microwave irradiation in this invention.

Explanation of symbols

1: Transparent electrode substrate 1a: Transparent substrate 1b: Transparent conductive layer 3: Porous semiconductor layer 3 ′: Semiconductor coating layer 5: Sensitizing dye 7: Negative electrode 8: Electrolyte solution 10: Positive electrode 20: Sample stage 22: Liquid film

Claims (4)

A transparent resin electrode provided with a transparent conductive layer is prepared on a transparent resin film, and a semiconductor paste in which a metal oxide semiconductor is dispersed in an organic solvent is applied onto the transparent conductive layer of the transparent resin electrode to form a semiconductor. A dye layer is formed by forming a coating layer, baking the semiconductor coating layer to form a semiconductor porous layer, and performing an adsorption treatment by bringing a dye solution into contact with the semiconductor coating layer before baking or the semiconductor porous layer after baking. In the method for producing a negative electrode in a sensitive solar cell,
The semiconductor coating layer is baked by heating with microwave irradiation in a state where the transparent resin electrode is placed on the liquid film formed on the sample stage so that the semiconductor coating layer is on the surface side. Manufacturing method characterized by performing.   The manufacturing method according to claim 1, wherein a microwave having an oscillation frequency of 2.45 GHz is used.   The production method according to claim 1, wherein the liquid film is formed of water.   The manufacturing method according to claim 1, wherein the transparent resin film is a polyethylene terephthalate film or a polyethylene naphthalate film.

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