WO2013011786A1 - Dye for dye-sensitized solar cell, photoelectric conversion element including said dye, and dye-sensitized solar cell - Google Patents

Abstract

[Problem] To provide a dye for dye-sensitized solar cells which is useful as a sensitizing dye for improving thermal durability, a photoelectric conversion element including the dye, and a dye-sensitized solar cell. [Solution] Ru(4,4'-di(9-nonenyl)-2,2'-bipyridine)(4,4'- dicarboxy-2,2'-bipyridine)(NCS)₂ is used as a sensitizing dye.

Description

Dye for dye-sensitized solar cell, photoelectric conversion element using the dye, and dye-sensitized solar cell

The present invention relates to a dye for a dye-sensitized solar cell for improving the thermal durability of a dye-sensitized solar cell, a photoelectric conversion element using the dye, and a dye-sensitized solar cell.

In recent years, in order to solve the problem of exhaustion of fossil fuels such as oil and natural gas and the global warming problem due to greenhouse gases, attention has been focused on photovoltaic power generation using clean and safe natural energy. Research and development of devices are actively conducted. At present, silicon photoelectric conversion elements are put into practical use as silicon-based solar cells, but there is a view that it is difficult to spread them due to restrictions such as price and material supply. Therefore, research and development of solar cells using materials other than silicon is being promoted as an effort to expand the use of solar cells, and low-cost next-generation solar cells that are manufactured using inexpensive raw materials and simple processes. As a candidate, a dye-sensitized solar cell is expected.

As for dye-sensitized solar cells, a group of Prof. Gretzel of Lausanne University of Technology in Switzerland in 1991 found an iodine-based electrolyte between a porous titanium oxide (TiO ₂ ) electrode carrying a ruthenium dye and a counter electrode. Since the announcement that a dye-sensitized solar cell encapsulating bismuth can provide a conversion efficiency as high as 10%, much attention has been paid. Dye-sensitized solar cells are characterized by low cost in terms of raw materials and manufacturing, high designability such as colorfulization, and high output under fluorescent lamps. A dye-sensitized solar cell is a solar cell that generates electricity based on a chemical reaction similar to plant photosynthesis, and when irradiated with visible light, the sensitizing dye absorbs light and enters an excited state. The electrons are injected into the conduction band of the titanium oxide semiconductor, the injected electrons move to the counter electrode through an external circuit, and the transferred electrons are carried by the ions in the electrolyte and return to the sensitizing dye. Is repeated to extract electric energy.

One of the issues for the widespread use of dye-sensitized solar cells is the improvement of thermal durability. Temperature has been pointed out as a degradation environment factor of dye-sensitized solar cells, and the phenomenon of dye detachment at electrodes caused by high temperatures is considered to be one of the causes of deterioration of solar cell characteristics. Conventionally, many efforts have been made to improve the thermal durability of dye-sensitized solar cells. For example, a K19 dye (Ru (4,4′-dicarboxylic acid-2,2′-bipyridine) (4,4′-bis (p-hexyloxystyryl) -2,2′-bipyridine) (NCS) ₂ ) used as a sensitizing dye, as an electrolytic solution, 1 Puropiru 3- methylimidazolium iodide, iodine, employing 3-methoxy propionitrile solution containing guanidine thiocyanate and N- methylbenzimidazole, the porous TiO ₂ film The nanocrystalline TiO ₂ dye-sensitized solar cell co-grafted with 1-decylphosphonic acid on the surface of the sensitizing dye showed a conversion efficiency of 8% or more after 1000 hours of thermal stress at 80 ° C. Has been reported (see Non-Patent Document 1).

In addition, a current collector wiring type ionic liquid dye-sensitized solar cell manufactured using a multi-layer wiring protective layer having a reinforced wiring protective layer and a moisture-resistant package that prevents moisture from entering is 85 ° C., 85% RH. It has been reported that the durability evaluation items defined in JIS such as 1000 hours can be cleared (see Non-Patent Document 2).

The sensitizing dye used in the dye-sensitized solar cell is improved to a ruthenium dye containing a crosslinkable olefin group polymerizable on a porous TiO ₂ electrode, and an acetonitrile / tert-butanol mixed solution containing this ruthenium dye is prepared. It is applied to a TiO ₂ layer on a fluorine-doped tin oxide (FTO) substrate, and together with methacrylic acid, an azobisisobutyronitrile (AIBN) solution, which is a polymerization initiator, is added and photocopolymerized by ultraviolet irradiation, and the ruthenium A crosslinked product of a dye and methacrylic acid is prepared and bonded to the surface of the porous TiO ₂ film, and polymethacrylic acid powder is added to an acetonitrile solution containing lithium iodide, lithium, and 4-tert-butylpyridine. Heat-gelled polymethacrylate gel electrolyte is used as the electrolyte solution, and this is sealed between the electrodes. DOO-like hot melt by sealant dye-sensitized solar cell sealing the inlet of the electrolyte solution, N3 dye containing no crosslinkable olefinic groups (Ru (4,4' Jikarubokishi 2,2'-bipyridine) ₂ (NCS) ₂ ) papers have been published that report that the conversion efficiency is improved by 5% or more, the shelf life is prolonged, and the durability is improved (Non-patent Document 3). reference). However, the durability test only reported the deterioration at room temperature.

Further, in the dye-sensitized solar cell, when an ionic liquid based on tetracyanoborate anion and organic cation was used as an electrolyte, 90% of the initial value of conversion efficiency after 1000 hours of heat history at 80 ° C. It has been reported that the supermarket has been suspended (see Patent Document 1). *

Special table 2009-527074

As described above, the thermal durability of the conventional dye-sensitized solar cell is limited to 85 ° C., and the thermal durability is still insufficient for commercialization as a solar cell product. The improvement of this was one of the issues to be overcome.
Accordingly, in view of such circumstances, the present invention provides a dye for a dye-sensitized solar cell for improving the thermal durability of a dye-sensitized solar cell, a photoelectric conversion element using the dye, and a dye-sensitized solar. An object is to provide a battery.

As a result of repeated studies to solve the above problems, the present inventors synthesized a novel ruthenium complex dye having a long alkyl group having a vinyl group introduced at the terminal as a sensitizing dye, and as an electrolyte, A dye-sensitized solar cell was fabricated by heat treatment at a temperature higher than the conventional range of 100 to 120 ° C using an ionic liquid with high heat durability instead of an organic solvent such as acetonitrile. The present inventors have found that the thermal durability is improved from 85 ° C. to 120 ° C., and have completed the present invention based on such knowledge.

That is, the present invention relates to a dye comprising Ru (4,4′-di (9-nonenyl) -2,2′-bipyridine) (4,4′-dicarboxy-2,2′-bipyridine) (NCS) ₂ It is a dye for sensitized solar cells.

The present invention also provides a photoelectric conversion element comprising a transparent conductive substrate and a porous film formed on the transparent conductive substrate, wherein the porous film adsorbs the dye for dye-sensitized solar cells. a photoelectric conversion element is composed of TiO ₂ particles.

Furthermore, the present invention is a dye-sensitized solar cell using the photoelectric conversion element.

According to the present invention, dye detachment that occurs in a high-temperature environment is significantly suppressed as compared with conventional dyes, so that the thermal durability of the dye-sensitized solar cell is dramatically improved. Therefore, the present invention greatly contributes to the future spread of dye-sensitized solar cells.

It is a figure which shows the change with respect to the elapsed time of the open circuit voltage of a dye-sensitized solar cell. It is a figure which shows the change with respect to the elapsed time of the short circuit current density of a dye-sensitized solar cell. It is a figure which shows the change with respect to the elapsed time of the fill factor of a dye-sensitized solar cell. It is a figure which shows the change with respect to the elapsed time of the conversion efficiency of a dye-sensitized solar cell. Is a diagram showing the absorbance of the porous was supported in TiO ₂ film porous TiO ₂ electrode N719 dye, the horizontal axis represents units wavelength nm, the vertical axis represents the absorbance. Is a diagram showing the absorbance of the porous was supported in TiO ₂ film porous TiO ₂ electrode Z907 dye, the horizontal axis represents units wavelength nm, the vertical axis represents the absorbance. Is a diagram showing the absorbance of the porous was supported in TiO ₂ film porous TiO ₂ electrode SG1051 dye, the horizontal axis represents units wavelength nm, the vertical axis represents the absorbance. Is a diagram showing the absorbance of the porous was supported in TiO ₂ film porous TiO ₂ electrode SG1051 dye heated at 125 ° C., the horizontal axis represents units wavelength nm, the vertical axis represents the absorbance. Is a diagram showing the absorbance of the porous was supported in TiO ₂ film porous TiO ₂ electrode SG1051 dye was heated at 250 ° C., the horizontal axis represents units wavelength nm, the vertical axis represents the absorbance.

Hereinafter, the present invention will be described in detail.
The dye for a dye-sensitized solar cell of the present invention is Ru (4,4′-di (9-nonenyl) -2,2′-bipyridine) (4,4′-dicarboxy-2,2′-bipyridine). (NCS) ₂ (hereinafter abbreviated as “SG1051 dye”), which is represented by the following formula.

Since the dye for a dye-sensitized solar cell is surrounded by an electrolyte solution, it is easily detached from the surface of the TiO ₂ electrode. However, since the dye of the present invention is strongly bonded to the surface of the porous TiO ₂ , It is possible to obtain a dye-sensitized solar cell that generates less dye in the environment and thus has excellent thermal durability. In addition, the dye of the present invention is combined with an electrolyte solution composed of a predetermined ionic liquid described later, and further, the dye is adsorbed on the electrode and then heated in a predetermined temperature range, thereby heating the dye-sensitized solar cell. Durability can be further improved.

The method for producing the dye for a dye-sensitized solar cell of the present invention will be described. The dye for a dye-sensitized solar cell of the present invention comprises 4,4′-di (9-nonenyl) -2,2′-bipyridine, using dichloro (p-cymene) ruthenium (II) dimer as a starting material, It can be prepared by sequentially reacting with 4,4′-dicarboxy-2,2′-bipyridine and sodium thiocyanate. In addition, the manufacturing method of the said pigment | dye is not limited to this.

4,4′-di (9-nonenyl) -2,2′-bipyridine can be prepared, for example, as follows. First, a hexane solution of n-butyllithium was added to a tetrahydrofuran solution of diisopropylamine at 0 to 5 ° C. and stirred for 0.5 to 1.0 hour, followed by addition of 4,4′-dimethyl-2,2′-bipyridine in tetrahydrofuran. Add the solution dropwise. After the dropwise addition, the mixture is stirred at -70 to -60 ° C for 3 to 4 hours. Next, a tetrahydrofuran solution of 9-iodinated nonene is added at −78 to −60 ° C. and reacted at the same temperature for 12 to 15 hours. Thereafter, the mixture was cooled with methanol, and the resulting tan solution was poured into cold water and extracted with diethyl ether, and then the diethyl ether was evaporated and recrystallized from hexane to obtain 4,4 ′. -Di (9-nonenyl) -2,2'-bipyridine is obtained. Incidentally, 9-iodinated nonene may be prepared by using a known technique for iodination of alcohol. For example, triphenylphosphine, imidazole is added to a mixed solution of starting material 9-nonen-1-ol in diethyl ether / acetonitrile. , And iodine to obtain alcohol by iodination.

Next, a commercially available [(p-cymene) RuCl (μ-Cl)] ₂ solution in N, N-dimethylformamide (DMF) was added to 4,4′-di (9-nonenyl) -2,2′-bipyridine. After stirring at 50-80 ° C. for 0.5-2.0 hours under an argon atmosphere, commercially available 4,4′-dicarboxy-2,2′-bipyridine was added thereto, and the mixture was added at 100-140 ° C. For 10 to 20 hours with stirring. Next, excess NH ₄ NCS is added to the reaction product and reacted at 120 to 140 ° C. for 2 to 10 hours, and then the DMF solution as a solvent is evaporated by a rotary evaporator. Thereafter, excess NH ₄ NCS is removed with water, and the insoluble product is washed with water and diethyl ether and then dried. The obtained crude product is dissolved in methanol and purified by gel filtration chromatography (eluent: methanol or the like). Thus, Ru (4,4′-di (9-nonenyl) -2, which is a dye for dye-sensitized solar cells of the present invention, which makes it possible to produce a dye-sensitized solar cell with excellent heat durability. 2′-bipyridine) (4,4′-dicarboxy-2,2′-bipyridine) (NCS) ₂ can be obtained.

The photoelectric conversion element of the present invention uses the above-described dye, and can be produced, for example, by the following method.
First, a transparent conductive substrate having a transparent conductive film formed on an electrode substrate is prepared. The electrode substrate is preferably light transmissive, and examples thereof include plates and films made of glass, ceramics, plastics, and the like.

As the transparent conductive film, a film in which tin oxide is doped with fluorine (FTO film), a film in which a small amount of tin oxide is added to indium oxide (ITO film), a film in which tin oxide is doped with antimony (ATO film), oxidation Tin etc. are mentioned.
The transparent conductive substrate is produced by forming a transparent conductive film on one surface, both surfaces, or the entire surface of the electrode substrate by a spray pyrolysis method, a vapor deposition method, a sputtering method, an ion plating method, a hydrolysis method, or the like.

Next, a porous film is produced on the transparent conductive film of the transparent conductive substrate. As the porous film, an n-type metal oxide semiconductor film made of titanium oxide or the like is preferable, and a porous TiO ₂ film obtained by applying and baking a TiO ₂ paste is particularly preferable. The TiO ₂ paste is prepared by adding and mixing TiO ₂ particles in an aqueous solvent to prepare a dispersion, and adding a thickener, a dispersant, and the like to the dispersion and mixing them uniformly.

Next, a method for forming a porous film will be described. On the transparent conductive film of the transparent conductive substrate, for example, the TiO ₂ paste is applied by a doctor blade method, a squeegee method, a spin coating method, a screen printing method, an electrodeposition method, a spray method, and the like, dried, and then placed in an electric furnace. The porous film is formed on the transparent conductive film by firing at 300 to 700 ° C. for 10 to 60 minutes in the air. This porous film constitutes a photoelectric conversion element together with the transparent conductive substrate and the dye. If the firing temperature is less than 300 ° C., sintering of the TiO ₂ particles becomes insufficient, so that the adsorption of the dye is hindered and high photoelectric conversion characteristics cannot be obtained, and if it exceeds 700 ° C., the transparent conductive substrate may be defective. is there. Further, if the firing time is less than 10 minutes, the sintering becomes insufficient, and if it exceeds 60 minutes, the grain growth due to firing proceeds so much that the specific surface area may be lowered.

The porous film on the transparent conductive film can be not only a single layer but also a multilayer structure of two or more layers. For example, when the porous film has two layers, as the first layer film provided on the transparent conductive film of the transparent conductive substrate, the average particle diameter using the diameter when the projected area is converted into a circle is 5 to 5 as primary particles. A transparent layer composed of 200 nm TiO ₂ particles is formed, and a light scattering layer composed of TiO ₂ particles having an average particle diameter of 100 to 600 nm is formed thereon. By forming such a two-layer TiO ₂ film, the conversion efficiency can be further improved.

Next, a transparent conductive substrate having a porous film formed on the transparent conductive film is immersed in a dye solution, thereby adsorbing and fixing the dye to the porous film. The dye solution is obtained by mixing the dye of the present invention with hydrocarbons such as hexane, octane, toluene and xylene, aliphatic alcohols such as methanol, ethanol, propanol and normal butanol, nitriles such as acetonitrile and propionitrile, acetone and methyl ethyl ketone. Ketones such as ethyl acetate and butyl acetate, carbonates such as diethyl carbonate and propylene carbonate, carbonates such as dimethyl carbonate and diethyl carbonate, lactones, amides such as dimethylformamide and dimethylacetamide, caprolactam And a single solvent such as sulfones such as dimethyl sulfoxide and sulfolane or a mixed solvent thereof. Preferably, aliphatic alcohols and nitriles are used. The dye concentration in the dye solution is 0.01 mM or more, preferably 0.1 to 10 mM. The transparent conductive substrate is immersed in the dye solution at 10 to 40 ° C. for about 1 to 24 hours. In addition, ultrasonic vibration can be applied to improve the efficiency of dye adsorption to the porous film. In this case, the immersion can be performed at room temperature for 5 to 60 minutes. The porous membrane surface adsorbing the dye is washed and then dried. Thus, a photoelectric conversion element including a transparent conductive substrate having light transparency and a porous film formed on the transparent conductive substrate, wherein the porous film adsorbs at least the dye of the present invention. _A photoelectric conversion element composed of _two particles is obtained.

After immersing the transparent conductive substrate in a dye solution and adsorbing the dye of the present invention to the porous film, the temperature is 120 to 300 ° C., preferably 150 to 300 ° C., for 0.5 to 60 minutes. By performing the heat treatment, at least a part of the porous film is composed of a reaction product obtained by polymerizing the dyes of the present invention, whereby the thermal durability can be further improved. As will be described later, this heat treatment may be performed as a main seal or end seal treatment in producing a dye-sensitized solar cell. It is considered that the above heat treatment causes the polymerization between the dyes of the present invention to progress so that the SG1051 dye is not further desorbed, and the dye desorption, which is the main cause of the deterioration of the characteristics of the dye-sensitized solar cell, is reduced. In addition, when the pigment | dye of this invention is superposed | polymerized on a porous membrane, the polymerization reaction using a polymerization initiator is unnecessary.

The photoelectric conversion element of the present invention is strongly bonded to TiO ₂ particles by forming a bond between the dye molecules or between the dye and the TiO ₂ particle surface by two terminal vinyl functional groups having the appropriate length of the dye of the present invention. Since it is adsorbed, dye desorption that occurs in a high-temperature environment is greatly reduced as compared with conventional dyes, so that heat durability is excellent. Moreover, since the pigment | dye which does not require the polymerization reaction using a polymerization initiator for adsorption | suction to a porous membrane is used, it can produce easily. Furthermore, even if the dye is desorbed by continuous use of the photoelectric conversion element, a complicated process is not required to restore the original state. Therefore, the photoelectric conversion element of the present invention is very useful as a photoelectric conversion element such as a dye-sensitized solar cell.

Next, the manufacturing method of the dye-sensitized solar cell using the said photoelectric conversion element is demonstrated.
First, a transparent conductive substrate having a transparent conductive film formed on an electrode substrate is prepared, and a counter electrode is produced by forming a conductive film on the transparent conductive film. The electrode substrate is preferably light transmissive, and examples thereof include plates and films made of glass, ceramics, plastics, and the like.

As the transparent conductive film, a film in which tin oxide is doped with fluorine (FTO film), a film in which a small amount of tin oxide is added to indium oxide (ITO film), a film in which tin oxide is doped with antimony (ATO film), oxidation Tin etc. are mentioned.
The transparent conductive substrate is produced by forming a transparent conductive film on one surface, both surfaces, or the entire surface of the electrode substrate by a spray pyrolysis method, a vapor deposition method, a sputtering method, an ion plating method, a hydrolysis method, or the like.

Examples of the conductive film formed on the transparent conductive film include a thin film made of platinum, carbon, or the like. The conductive film is formed by a vapor deposition method, a sputtering method, an ion plating method, a hydrolysis method, or the like. The thickness of the conductive film is generally several nm.

Next, in a state where the photoelectric conversion element and the counter electrode are opposed to each other with a predetermined gap, they are bonded together via a sealing material (main sealing material), and an electrolyte solution is injected between the electrodes to form an electrolyte layer. Finally, the electrolyte inlet is sealed with a sealing material (end seal material), and if necessary, the end seal material is sealed with a cover material made of glass or the like. Thereby, a dye-sensitized solar cell is produced. Examples of the main sealing material include a hot melt material, an ultraviolet curable resin, a thermosetting resin, and a glass frit. In the present invention, sealing is performed by heating at a temperature of 120 to 300 ° C., preferably 150 to 300 ° C. for a time range of 0.5 to 60 minutes, using a main seal material made of a hot melt material. Is preferable from the viewpoint of improving thermal durability. Specific examples of the main seal material made of hot melt material include hot melt gasket made of ionomer resin (Surlyn 1702, trade name, thickness 25 μm, manufactured by DuPont), hot melt gasket made of polyethylene resin (Bynel, trade name) And a thickness of 25 μm, manufactured by DuPont).

The electrolytic solution sealed between the photoelectric conversion element and the counter electrode includes a supporting electrolyte made of a cation such as lithium ion or an anion such as iodine ion, and a redox pair such as iodine-iodine compound or bromine-bromine compound. It is prepared by mixing with a solvent. Examples of the solvent include water, alcohols, nitriles, ethers, esters, ketones, lactones, heterocyclic compounds, amides, nitromethane, halogenated hydrocarbons, dimethyl sulfoxide, sulfolane, N-methylpyrrolidone, Examples thereof include single solvents or mixed solvents such as 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, and hydrocarbons. In the present invention, tetraalkyl-based, pyridinium-based, imidazolium-based borate, quaternary ammonium, and the like. An ionic liquid such as a salt is preferable, and an imidazolium borate is more preferable. In particular, 1-ethyl-3-methylimidazolium tetracyanoborate is preferable from the viewpoint of improving thermal stability. An ionic liquid is a salt composed only of positive and negative ions, and since it has a low melting point, it is liquid at room temperature, is not volatile, and is effective in preventing deterioration of the characteristics of a dye-sensitized solar cell over time. . Particularly suitable electrolyte compositions include 0.2-2M 1-ethyl-3-methylimidazolium iodide, 0.2-2M 1,3-dimethylimidazolium iodide, 0.1-1M guanidine. Examples are 1-ethyl-3-methylimidazolium tetracyanoborate solution containing thiocyanate, 0.1-1M N-butylbenzimidazole, 0.05-0.5M iodine. This electrolytic solution is excellent in thermal stability and hardly causes electrode alteration.

After injecting the electrolyte into the gap between the photoelectric conversion element and the counter electrode, for example, a through hole (injection port) is opened in at least one of the photoelectric conversion element and the counter electrode, The electrolytic solution is injected through the through hole, and after the injection, the through hole is sealed with a sealing material (end seal material). In addition, for example, a method of reducing the pressure in a state of being immersed in the electrolytic solution and then releasing the pressure to normal pressure is exemplified, and thus, the space between the photoelectric conversion element and the counter electrode can be easily filled with the electrolytic solution.

Examples of the material of the sealing material (end seal material) that seals the through hole (injection port) after injecting the electrolytic solution include a hot melt material, an ultraviolet curable resin, a thermosetting resin, and a glass frit. .

In the dye-sensitized solar cell having such a structure, the dye of the present invention has two terminal vinyl functional groups having an appropriate length, thereby forming a bond between the dye molecules or between the dye and the TiO ₂ particle surface. Excellent chemical durability due to strong chemical adsorption on TiO ₂ particles. Moreover, since the pigment | dye which does not require the polymerization reaction using a polymerization initiator for adsorption | suction to a porous membrane is used, it can produce comparatively easily. Moreover, even if a pigment | dye remove | desorbs by continuous use of a photoelectric conversion element, a complicated process is not required to return to the original state.

The dye-sensitized solar cell of the present invention is not limited to the sandwich-type structure described above, but can be integrated into a plurality of structures to form an arbitrary structure such as a W-type integrated structure, a Z-type integrated structure, or a monolithic integrated structure. By accumulating a plurality, the output can be increased.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[Preparation of porous TiO ₂ electrode]
FTO glass substrate (LOF) which is conductive glass substrate with FTO film
Tec7 (trade name, manufactured by Nippon Sheet Glass Co., Ltd.) is cut into a 25 mm × 75 mm square, washed with 50 mM hydrochloric acid for 5 minutes and with acetone for 5 minutes using the ultrasonic bath, and again with hydrochloric acid and acetone for 15 minutes each. Washed one by one. After the washing was completed, it was carefully washed with water and ethanol, dried, and treated with the UV-O ₃ system for 18 minutes. The FTO glass substrate after the UV-O ₃ treatment was placed in a 40 mM TiCl ₄ aqueous solution, held at 70 ° C. for 30 minutes, and then taken out and washed with water and ethanol to prepare an FTO glass substrate.
Next, a TiO ₂ paste (PST-30NRT, trade name, manufactured by JGC Catalysts & Chemicals Co., Ltd.) having a particle size of 20 to 30 nm is applied on the FTO glass substrate by screen printing, dried and fired, and then the transparent layer Formed. The coating, drying and baking operations were performed three times so that the film thickness of the transparent layer was finally 9 μm.
Next, a TiO ₂ paste (PST-400C, trade name, manufactured by JGC Catalysts & Chemicals Co., Ltd.) having a particle size of 400 nm is applied on the transparent layer by screen printing, dried and fired, and a film thickness of 4-5 μm A light scattering layer was formed. Next, the TiO ₂ electrode thus produced was put in an electric furnace, dried and fired at 325 ° C. for 5 minutes, 375 ° C. for 5 minutes, 450 ° C. for 15 minutes, and finally at 500 ° C. for 15 minutes, and FTO glass A porous TiO ₂ film consisting of two layers was formed on the substrate. After removal of the TiO ₂ electrode from the electric furnace, again, the TiO ₂ electrodes were placed in a TiCl ₄ aqueous solution of 40 mM, after maintaining at 70 ° C. 30 minutes, rinse with water and ethanol removed, 50 mM until use It was immersed in hydrochloric acid and stored. In use, the TiO ₂ electrode taken out from hydrochloric acid was rinsed with ethanol and then baked at 500 ° C. for 30 minutes using a heat gun. After air cooling to 80 ° C., the baked TiO ₂ electrode was immersed in an acetonitrile / valeronitrile (1: 1) mixed solution containing 0.3 mM SG1051 dye for 1 hour at room temperature to adsorb the dye. After dye adsorption, the electrode was lifted from the solution and washed with acetonitrile to remove unadsorbed dye. As a result, a porous TiO ₂ electrode in which SG1051 dye was supported on TiO ₂ particles was produced.

[Production of Pt counter electrode]
FTO glass (LOF Tec7, trade name, manufactured by Nippon Sheet Glass Co., Ltd., thickness mm) was cut into a size of 12 mm × 12 mm square. A through hole having a diameter of 1 mm was formed at a position 8 mm × 8 mm from one corner of the FTO glass with a hand drill (U-hoby, trade name, Urawa Kogyo Co., Ltd.). In order to remove dust such as glass pieces from the FTO glass having the through holes, the glass was washed with water for 10 minutes. Next, it was washed with 50 mM hydrochloric acid for 5 minutes, rinsed with acetone, and then washed with acetone for 5 minutes. After this washing, each was washed again with 50 mM hydrochloric acid and acetone for 15 minutes each. The washed FTO glass was carefully washed with water and then immersed in 50 mM hydrochloric acid until use. When used, the FTO glass taken out from hydrochloric acid is placed in a clean box and allowed to air dry. Then, one drop of H ₂ PtCl ₆ solution (containing 2 mg of Pt in 1 ml of ethanol) is dropped onto the FTO glass and applied. Then, a Pt counter electrode in which Pt was coated on FTO glass at 0.5 to 5 nm was prepared by heating at 400 ° C. for 15 minutes using a heat gun.

[Production of dye-sensitized solar cell]
The porous TiO ₂ electrode (size: 0.25 cm ² ) and the Pt counter electrode face each other, and a hot melt gasket (Surlyn 1702, trade name, thickness) made of ionomer resin as a sealing material (main seal material) between them. 25 μm, manufactured by DuPont) was sandwiched and heated at a temperature of 250 ° C. for 1 to 3 minutes to bond the porous TiO ₂ electrode and the Pt counter electrode. The width of the sealing material was 1 mm, and the opening provided was 2 mm larger than the TiO ₂ electrode.
The through hole of the Pt counter electrode was sealed by heating another sealing material at 250 ° C. for 1 to 3 minutes using a hot sealer. After sealing, a through hole was opened in the sealing material using a needle. Then, one drop of the electrolytic solution was dropped in this through hole, placed in a small vacuum chamber, and the electrolytic solution was put into the cell by reverse vacuum transfer. Finally, the through hole was sealed with a hot melt ionomer at a temperature of 250 ° C. for 1 to 3 minutes, and further sealed with a cover glass to produce a sandwich type dye-sensitized solar cell.
Incidentally, as a setup for each measurement to be described later, remove the TiO ₂ film of the connecting portion, in order to improve the electrical contact, shaved little outer end of the FTO glass with sandpaper or film. Solder was applied to both FTO electrodes. The position of the solder was 1 mm outside from the end of the gasket, that is, 4 mm outside from the end of the TiO ₂ layer. In order to reduce scattered light, a black plastic type mask was attached to the assembled cell. A cell antireflection film (Arctop, trade name, manufactured by Asahi Glass Co., Ltd.) was applied to the filter.

The electrolyte includes 0.75M 1-ethyl-3-methylimidazolium iodide, 0.75M 1,3-dimethylimidazolium iodide, 0.2M guanidine thiocyanate, 0.2M N-butylbenzoate. A 1-ethyl-3-methylimidazolium tetracyanoborate solution containing imidazole and 0.1 M iodine was used.

[Thermal durability test]
The above dye-sensitized solar cell prepared using SG1051 dye is placed in a constant temperature oven (AS ONE) at 120 ° C., and the photoelectric characteristics (open circuit voltage (V), short-circuit current density ( The thermal durability of the dye-sensitized solar cell was evaluated by examining the time course of short circuit current density (mA / cm ² ), fill factor, and conversion efficiency (%). The conversion efficiency (%) was determined by (open circuit voltage × short circuit current × fill factor) / energy of incident light. Further, instead of SG1051 dye, Z907 dye (Ru (4,4′-dicarboxylate-2,2′-bipyridine) (4,4′-dinonyl-2,2′-bipyridine) (NCS) ₂ ) was used. A dye-sensitized solar cell produced in the same manner as described above was used as a comparative control. These results are shown in FIGS. FIG. 1 is a diagram showing a change in the open circuit voltage of the dye-sensitized solar cell with respect to the elapsed time, FIG. 2 is a diagram showing a change in the short-circuit current density of the dye-sensitized solar cell with respect to the elapsed time, and FIG. The figure which shows the change with respect to the elapsed time of the fill factor of a solar cell, FIG. 4 is a figure which shows the change with respect to the elapsed time of the conversion efficiency of a dye-sensitized solar cell.

[Measurement of photoelectric characteristics]
The photoelectric characteristics of the dye-sensitized solar cell are obtained by changing the load between the electrodes of the dye-sensitized solar cell using an AM 1.5 solar simulator (manufactured by Yamashita Denso Co., Ltd.) equipped with a 450 W xenon lamp. The current value and the voltage between the electrodes were plotted on a current-voltage curve obtained by plotting. In order to suppress the error between simulated light and AM 1.5 to 2% or less, a reference Si photodiode equipped with an IR cut-off filter (manufactured by Spectrometer Co., Ltd.) was used, and the output of simulated light was 100 mW / cm ² . The current-voltage curve was created by applying an external bias to the dye-sensitized solar cell and measuring the generated photocurrent with a digital source meter (ADMT). The voltage step was set to 10 mV. The photocurrent delay time was set to 500 ms.

[Evaluation of photoelectric characteristics]
As can be seen from the results shown in FIGS. 1 to 4, the dye-sensitized solar cells using the Z907 dye and the SG1051 dye each show similar photoelectric characteristics until about 30 hours after the start of heating. When it exceeded 200 hours, it turned out that the performance of the dye-sensitized solar cell produced from Z907 dye falls remarkably. SG1051 dye was found to operate at 120 ° C. for about 500 hours. From these results, it was confirmed that the SG1051 dye showed better thermal durability than the Z907 dye. In a high temperature environment of 120 ° C., the Z907 dye is detached from the porous TiO ₂ film, but the SG1051 dye is polymerized with each other, so that even if some of the dye is detached from the porous TiO ₂ film, Therefore, it is considered that they were not completely detached from the porous TiO ₂ film.

[Dye adsorption test]
N719 dye (RuL ₂ (NCS) ₂ · 2TBA: L = 2,2′-bipyridyl-4,4′-dicarboxylate, TBA = tetra-n-butylammonium), Z907 dye and SG1051 dye were supported, respectively. For the porous TiO ₂ electrode, as will be described later, the absorbance before and after the treatment with the aqueous sodium hydroxide solution (or the aqueous sodium hydroxide solution and acetonitrile) is measured, and the strength of the adsorptive power of each dye and the porous TiO ₂ electrode is measured. Were compared. The absorbance of the TiO ₂ electrode was measured by irradiating monochromatic light having a wavelength (380 to 800 nm) with an absorbance meter and measuring the reflection of the monochromatic light.
When the absorbance of the TiO ₂ electrode is measured, if the absorbance decreases, it indicates that the dye is desorbed, and the strength of adsorption between the dye and the porous TiO ₂ electrode is compared according to the degree of change in absorbance. can do. Sodium hydroxide is an effective reagent for removing the dye from the TiO ₂ surface.

[Adsorption power of N719 dye]
To a mixed solution of acetonitrile / tert-butanol (1: 1 (volume ratio)) containing 0.5 mM N719 dye, a TiO ₂ electrode (1 cm × 1 cm square) before dye adsorption prepared in the same manner as described above was placed at 20 ° C. The porous TiO ₂ electrode in which the N719 dye was supported on the porous TiO ₂ film was prepared by soaking for 24 hours. Thereafter, the absorbance of the TiO ₂ electrode was measured. Next, after immersing in a 0.1 M sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with water and dried was measured. Immersion in a sodium hydroxide solution was performed for 30 seconds. The results are shown in FIG. 5 (the horizontal axis represents wavelength, the unit is nm, and the vertical axis represents absorbance).

[Adsorption power of Z907 dye]
To a mixed solution of acetonitrile / tert-butanol (1: 1 (volume ratio)) containing 0.3 mM of Z907 dye, a TiO ₂ electrode (1 cm × 1 cm square) before dye adsorption prepared in the same manner as described above at room temperature. By soaking for 20 hours, a porous TiO ₂ electrode in which the Z907 dye was supported on the porous TiO ₂ film was produced. Thereafter, the absorbance of the TiO ₂ electrode was measured. Next, after immersing in a 0.1 M sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with water and dried was measured. Immersion in a sodium hydroxide solution was performed for 30 seconds. The results are shown in FIG. 6 (the horizontal axis represents wavelength, the unit is nm, and the vertical axis represents absorbance).

[Adsorption power of SG1051 dye]
In a mixed solution of acetonitrile / tert-butanol (1: 1 (volume ratio)) containing 0.3 mM SG1051 dye, a TiO ₂ electrode (1 cm × 1 cm square) before dye adsorption prepared in the same manner as described above was used at room temperature. By soaking for 1 hour, a porous TiO ₂ electrode in which SG1051 dye was supported on the porous TiO ₂ film was produced. Thereafter, the absorbance of the TiO ₂ electrode was measured. Next, after immersing in a 0.1 M sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with water and dried was measured. Immersion in a sodium hydroxide solution was performed for 30 seconds. Further, after the immersion in the sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with acetonitrile and dried was measured. The results are shown in FIG. 7 (the horizontal axis represents wavelength, the unit is nm, and the vertical axis represents absorbance).

[Adsorption power of SG1051 dye heated at 125 ° C.]
To a mixed solution of acetonitrile / tert-butanol (1: 1 (volume ratio)) containing 0.3 mM SG1051 dye, a TiO ₂ electrode (1 cm × 1 cm square) before dye adsorption prepared in the same manner as described above was placed at 20 ° C. The porous TiO ₂ electrode in which SG1051 dye was supported on the porous TiO ₂ film was produced by immersing for 1 hour. Thereafter, absorbance was measured of the TiO ₂ electrode the TiO ₂ electrode was heated for 1 minute at 125 ° C.. Next, after immersing in a 0.1 M sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with water and dried was measured. Immersion in a sodium hydroxide solution was performed for 30 seconds. Further, after the immersion in the sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with acetonitrile and dried was measured. The results are shown in FIG. 8 (the horizontal axis represents wavelength, the unit is nm, and the vertical axis represents absorbance).

[Adsorption power of SG1051 dye heated at 250 ° C.]
To a mixed solution of acetonitrile / tert-butanol (1: 1 (volume ratio)) containing 0.3 mM SG1051 dye, a TiO ₂ electrode (1 cm × 1 cm square) before dye adsorption prepared in the same manner as described above at room temperature. By soaking for 1 hour, a porous TiO ₂ electrode in which SG1051 dye was supported on the porous TiO ₂ film was produced. Thereafter, absorbance was measured of the TiO ₂ electrode the TiO ₂ electrode was heated for 1 minute at 250 ° C.. Next, after immersing in a 0.1 M sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with water and dried was measured. Immersion in a sodium hydroxide solution was performed for 30 seconds. Further, after the immersion in the sodium hydroxide solution, the absorbance of the TiO ₂ electrode washed with acetonitrile and dried was measured. The results are shown in FIG. 9 (the horizontal axis represents wavelength, the unit is nm, and the vertical axis represents absorbance).

[Evaluation of dye adsorption power]
From the results shown in FIGS. 5 to 9, it can be seen that SG1051 dye is not desorbed with sodium hydroxide solution, unlike N719 dye and Z907 dye, but after further washing with organic solvent (acetonitrile), SG1051 dye is It was found that it was detached. Furthermore, before washing with a sodium hydroxide solution and an organic solvent (acetonitrile), it was found that by heating once at 250 ° C., polymerization between SG1051 dyes progressed, and SG1051 dyes were not further detached. Since the SG1051 dye of the present invention is strongly adsorbed to the porous TiO ₂ electrode, there is little dye desorption that is the main cause of the deterioration of the characteristics of the dye-sensitized solar cell, and therefore the heat of the dye-sensitized solar cell It was confirmed that it is very useful as a pigment for improving durability.

Claims (6)

1. Ru (4,4′-di (9-nonenyl) -2,2′-bipyridine) (4,4′-dicarboxy-2,2′-bipyridine) (NCS) ₂ for dye-sensitized solar cell Pigment.
2. A photoelectric conversion element comprising a transparent conductive substrate and a porous film formed on the transparent conductive substrate, wherein the porous film adsorbs the dye for dye-sensitized solar cells according to claim 1. the photoelectric conversion element that consists of the TiO ₂ particles.
3. 2. A dye-sensitized solar cell according to claim 1, comprising a transparent conductive substrate and a porous film formed on the transparent conductive substrate, wherein at least a part of the porous film is a dye-sensitized solar cell according to claim 1. A photoelectric conversion element composed of TiO ₂ particles adsorbing a reaction product obtained by heat treatment at 120 to 300 ° C.
4. A dye-sensitized solar cell using the photoelectric conversion element according to claim 2.
5. The dye-sensitized solar cell according to claim 4, comprising an ionic liquid containing iodine.
6. 6. The dye-sensitized solar cell according to claim 5, wherein the ionic liquid is 1-ethyl-3-methylimidazolium tetracyanoborate.
   
   
   
   
   
   

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