JP2000357544A - Coloring matter sensitizing type solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coloring matter sensitizing type solar battery with high photoelectric transfer efficiency and stable performance for a long time. SOLUTION: In a coloring matter sensitizing type solar battery having an electrolyte layer between a coloring matter sensitizing type semiconductor electrode and a counter electrode, a solid material for holding an electrolyte solution is arranged in the electrolyte layer between the semiconductor electrode and the counter electrode, the solid material is a fibrous material, the presence ratio of the solid material is 25-98% based on the volume of the electrolyte layer, and the presence ratio of the solid electrolyte is increased with approaching the semiconductor electrode and decreased with approaching the the semiconductor electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell for converting light energy into electric energy, and more particularly to a dye-sensitized solar cell.

[0002]

2. Description of the Related Art In recent years, global environmental problems have become apparent as represented by global warming. Such does not emit CO ₂ gas which is the cause of global warming in such, or less emissions, there has been a growing demand for so-called clean energy. Looking at solar cells, which are the most promising as clean energy, the ones that are currently commercialized are mainly made of crystalline (single-crystal, polycrystalline) silicon p.
This uses an n-junction. The silicon used for this solar cell needs to be very high purity, and the purification process for removing impurities requires a great deal of energy and a complicated process. As a result, the solar cell system as a whole is very expensive. Therefore, the power generation cost is higher in the photovoltaic power generation system than in the electric power from the existing commercial power supply, and there is a problem for widespread use. Also,
Although amorphous silicon solar cells have been put to practical use, they are suitable for calculators and the like in terms of durability and the like, but are not suitable as a power source.

On the other hand, solar cells other than silicon-based ones are also being developed, and Gretzwell et al. Adsorb a ruthenium complex-based organic dye on a porous titanium oxide film having a large surface area to form a dye-sensitized type as a photoelectrode. And the conversion efficiency was shown to be as high as silicon-based solar cells (J. Am. Chem. Soc. Vol. 115, 63).
82-6390, 1993). This dye-sensitized solar cell is expected to be a low-cost solar cell because the materials used are inexpensive and can be manufactured by a simple process.

In such a solar cell of the Gretzell type, a dye is adsorbed on a porous film having a very large surface area, so that the amount of the dye contributing to power generation increases, and a conventional dye-sensitized solar cell is used. It is considered that the conversion efficiency is improved as compared with that of the prior art. The structure of the Gretzell-type solar cell uses a porous film of a metal oxide semiconductor as one electrode, and an electrolyte solution is filled between the electrode and the counter electrode. The periphery of the solar cell is sealed with a sealing material so that the electrolyte solution does not leak. However, since this solar cell is a wet type solar cell in which an electrolyte solution is sealed between a titanium oxide film on which a dye is adsorbed and a counter electrode, there is a problem of deterioration due to liquid leakage. In particular, the electrolyte solution may expand, shrink, evaporate, etc. due to a change in the temperature of the battery under the usage environment, which may cause deformation of the components of the battery or breakage of the sealing portion, so that there is still a problem with the long-term stability.

Japanese Patent Application Laid-Open No. 9-27352 discloses that long-term stability is achieved by using a solid polymer electrolyte in an electrolyte solution layer and by allowing a solid polymer electrolyte to be present in pores of a porous metal oxide semiconductor. It is described that a battery having high reliability can be obtained. However, this battery uses a polymer solid electrolyte, and the pores are filled with the same substance. Therefore, considering the performance of the polymer solid electrolyte, the ion conductivity is not sufficient and the conversion efficiency is low. Becomes

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dye-sensitized solar cell capable of maintaining high performance and stable performance for a long period of time.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a dye-sensitized solar cell having an electrolyte layer disposed between a dye-sensitized optical semiconductor electrode and a counter electrode has a semiconductor electrode. A dye-sensitized solar cell with a structure in which a solid material such as a fibrous substance is placed in the electrolyte layer between the electrode and the counter electrode, and the electrolyte solution is held in this, is a battery that has a small amount of electrolyte expansion and contraction and has a long life. It has been found that the performance can be maintained, and the present invention has been completed.

That is, the gist of the present invention is as follows. (1) In a dye-sensitized solar cell having an electrolyte layer disposed between a dye-sensitized optical semiconductor electrode and a counter electrode, a solid holding an electrolyte solution in the electrolyte layer between the semiconductor electrode and the counter electrode A dye-sensitized solar cell comprising a material disposed thereon. (2) The dye-sensitized solar cell according to (1), wherein the solid material is a fibrous substance. (3) The proportion of the solid material is 25 to 25% of the volume of the electrolyte layer.
The dye-sensitized solar cell according to (1) or (2), which has a range of 98%. (4) The dye-sensitized solar cell according to any one of (1) to (3), wherein the proportion of the solid material is higher as being closer to the counter electrode and lower as being closer to the semiconductor electrode.

[0009]

Embodiments of the present invention will be described below. First, a typical dye-sensitized solar cell (Gretzel solar cell) will be briefly described. FIG. 1 shows an example of the configuration of a dye-sensitized solar cell invented by Gretzell et al. For the photoelectrode portion, a metal oxide semiconductor (titanium oxide) porous film (semiconductor electrode) is formed on a glass substrate with a transparent electrode, and the titanium oxide porous film is treated with a titanium tetrachloride aqueous solution or the like. A sensitizing dye is attached. This is used as one electrode, and an electrolyte solution is arranged between the electrode and the counter electrode. A typical Gretzel-type solar cell is sealed around the solar cell with a sealing material so that the electrolyte solution does not leak. This solar cell is a wet type solar cell in which an electrolyte solution is sealed between a titanium oxide film on which a dye is adsorbed and a counter electrode. The electrolyte solution used depends on the use state (temperature, pressure, etc.) and storage state of the battery. May leak or deform. In this case, the power generation performance (conversion efficiency) is reduced, and the battery may not be used. In other words, long-term stability poses a problem for the Gretz-type solar cell at present.

Therefore, the solar cell of the present invention has a structure in which the electrolyte layer is impregnated with a solid material such as a fibrous polymer substance (nonwoven fabric) by swelling the electrolyte solution, thereby expanding, contracting, and vaporizing the electrolyte solution. And the service life of the electrolyte layer is made longer (see FIG. 2). The above is an outline of the dye-sensitized solar cell of the present invention, except that a solid material impregnated with an electrolyte solution is disposed in the electrolyte layer, and may be the same as the structure of a conventional Gretzel solar cell. What is necessary is just to take the structure and manufacturing method of the dye-sensitized solar cell of a normal structure.

The structure, material, manufacturing method, and the like of the dye-sensitized solar cell of the present invention will be described sequentially, including these. [Transparent substrate (commonly called glass substrate)] A transparent substrate used for a silicon solar cell, a liquid crystal panel or the like may be used. Specific examples of the transparent substrate material include a transparent glass substrate, a substrate in which light reflection is prevented by appropriately roughening the surface of the glass substrate, and a substrate that transmits light such as a frosted glass-like translucent glass substrate. The material may not be glass as long as it transmits light, and may be a transparent plastic plate, a transparent plastic film, an inorganic transparent crystal, or the like.

[Transparent electrode] A transparent electrode used for a silicon solar cell, a liquid crystal panel or the like may be used. For example,
Metal oxides such as tin oxide and indium tin oxide (ITO) deposited on a transparent substrate are suitable transparent electrodes. Further, a metal electrode having a structure such as a mesh shape or a stripe shape which can transmit light may be provided on the glass substrate.

[Semiconductor electrode] Metal oxide semiconductors, for example, oxides such as titanium, niobium, zinc, tin, indium, zirconium, yttrium, lanthanum, tantalum, and semiconductors of perovskite-based oxides such as SrTiO ₃ and CaTiO ₃ are preferable. Used for It is preferable that the semiconductor is formed into a thin film. In particular, a titanium oxide film is a preferable semiconductor electrode.

[Formation of semiconductor electrode (porous film)] Fine particles (particle size [average particle size]) of the metal oxide semiconductor (titanium oxide or the like) are about 1 to 1000 nm, preferably 1 to 1000 nm.
-100 nm) is prepared. The solvent of the dispersion is not particularly limited as long as it can disperse the fine particles, such as water, an organic solvent, or a mixed solvent of both. Further, a surfactant and a viscosity modifier may be added to the dispersion as needed. Next, the dispersion is applied to a glass substrate with a transparent electrode and dried. As a coating method, a bar coater method,
A printing method or the like can be used. This is heated and fired in air or in an inert gas or nitrogen to form a metal oxide semiconductor film (porous film). Firing temperature is 300-80
0 ° C. is suitable. If the sintering temperature is lower than the above, adhesion between the metal oxide semiconductor particles and the adhesion to the substrate are weakened, resulting in insufficient strength. If the firing temperature is too high, the adhesion between the fine particles proceeds, and the surface area of the porous film becomes small. The film thickness is suitably from 0.1 to 100 μm, preferably from 1 to 50 μm. If the thickness is thinner, the amount of the dye adsorbed on the surface decreases, and the light absorption decreases. If the thickness is larger than this, the electrical resistance of the film increases, and the performance of the solar cell thus produced deteriorates.

[Sensitizing Dye] The sensitizing dye in the present invention may be a dye having absorption in a visible light region and / or an infrared light region. Hereinafter, preferred sensitizing dyes of the present invention will be specifically described. As the sensitizing dye, a metal complex or an organic dye can be used. Examples of the metal complex include metal phthalocyanines such as copper phthalocyanine and titanyl phthalocyanine, chlorophyll or derivatives thereof, hemin, JP-A-1-220380 and JP-A-5-504.
No. 023, a complex of ruthenium, osmium, iron and zinc (for example, cis-dicyanate-bis (2,
2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II)). As organic dyes,
Metal-free phthalocyanine, cyanine dyes, metalocyanine dyes, xanthene dyes, triphenylmethane dyes, and the like can be used.

The sensitizing dye may be attached to the surface of the porous film of the metal oxide semiconductor (in any form such as chemical adsorption, physical adsorption, or deposition).
For example, a method such as immersing the porous film in a solution containing a dye can be used as the method of attachment. At this time, the adhesion of the sensitizing dye can be promoted by heating and refluxing the solution.

[Electrolyte solution] I / I ₃ system, Br / Br ₃
And a redox electrolyte such as a quinone / hydroquinone-based solvent dissolved in an electrochemically inert solvent (and a mixed solvent thereof) such as acetonitrile, propylene carbonate, and ethylene carbonate. In particular,
For example, I / I ₃ based electrolyte can be obtained using a mixture of ammonium salt or lithium iodide and iodine iodine. As the electrolyte solution, it is usually preferable to select a solution having no or little solubility or reactivity with a solid material described below. However, this is not the case where the performance as an electrolyte is improved or the stability is chemically and physically stable due to dissolution or reaction in a solid material. For example, it is rather preferable that the change in volume due to temperature is small.

[Counter electrode] The same electrode as that used for a silicon solar cell, a liquid crystal panel or the like may be used.
That is, the same material as the “transparent electrode”, a material obtained by attaching a small amount of platinum to the “transparent electrode”, a metal thin film such as platinum, a conductive film such as carbon, and the like can be used. [Solid Material] As the material of the solid material holding the electrolyte solution, it is usually preferable to select a material having no or little solubility or reactivity with the electrolyte solution. However, this is not the case where the performance of the electrolyte is improved or the electrolyte is chemically and physically stable due to the dissolution or reaction of the electrolyte solution in the solid material. For example, it is rather preferable that the change in volume due to temperature is small. Further, the solid material must be non-conductive. If it is conductive, there is no point in separating the semiconductor electrode and the counter electrode with an electrolyte. In addition, as a form of the solid material that holds the electrolyte solution, it is easy to hold the electrolyte, and the electrolyte layer easily plays its role, that is, ions move easily between the semiconductor electrode and the counter electrode through the electrolyte. The electrolyte layer must have a good (ion-conductive) electrolyte layer.

The following materials are preferably used as a solid material for holding a specific electrolyte solution. As a form of the solid material, a material capable of forming a network structure, a fibrous material, a porous material having continuous pores, a sponge-like material having open cells, and the like are preferable. For example, there are a nonwoven fabric, a fiber, a sponge-like polymer substance, and the like. As its material,
For example, organic materials include rayon, acetate, nylon, polyester, polypropylene, polystyrene,
Examples thereof include polytetrafluoroethylene, polyvinylidene difluoride, and cotton. Materials made of inorganic materials include inorganic materials such as glass wool, asbestos, rock wool, and porous alumina.

The proportion of the solid material present in the electrolyte layer is 25 to 98%, more preferably 50 to 98% of the volume of the electrolyte layer.
Is preferably within the range. It is preferable that the proportion of the solid material be higher as the position is closer to the counter electrode and lower as the position is closer to the semiconductor electrode. From the viewpoint of the thermal expansion of the electrolyte, the higher the proportion of the solid material, the better. However, if the proportion of the electrolyte solution is too low, the movement of ions becomes difficult and the function of the electrolyte is hindered. In particular, in order to facilitate the movement of ions near the semiconductor electrode (especially the sensitizing dye) near the semiconductor electrode, it is preferable that the proportion of the electrolyte solution present near the semiconductor electrode is high.

[Assembly of Battery] The solar battery of the present invention has a structure in which an electrolyte layer is disposed between a porous metal oxide semiconductor electrode and a counter electrode. A solid material is superposed between the semiconductor electrode and the counter electrode, and a spacer material is provided at the end of the solid material as necessary, a cell is assembled, and the periphery is sealed with a sealing material such as epoxy. When sealing around the cell, the inlet for the electrolyte solution is left, and after the electrolyte solution is injected, the inlet is sealed with a sealing material such as epoxy to complete the solar cell. As another method, first, the solid material is impregnated with the electrolyte solution or the like to be kept in a state of being held. This is prepared in advance as an electrolyte layer. The dye-sensitized optical semiconductor electrode and the counter electrode are interposed via an electrolyte layer made of a solid material holding this electrolyte solution (a spacer material is arranged at the end as necessary).
A stacked cell is assembled, and the periphery is sealed with a sealing material such as epoxy. If necessary, such as to prevent gas from remaining in the electrolyte layer, leave the electrolyte solution injection port when sealing around the cell, and after further injecting the electrolyte solution, fill the injection port with epoxy or the like. What is necessary is just to seal with a sealing material and to assemble a solar cell.

The solar cell manufactured as described above is a dye-sensitized solar cell according to the present invention in which the mechanical strength and stability of the cell are improved because the cell shape is stabilized against changes in environmental temperature. It becomes a battery. In this solar cell, the porous pores are substantially in the state of only the electrolyte solution (liquid), and the gap between the counter electrode and the counter electrode is a complex of the polymer and the electrolyte solution, so that the ionic conductivity is sufficient. Thus, the battery has high performance, long-term stability, and high reliability.

[0023]

[Example 1]

1. Preparation of Titania Substrate One part by mass of ultra-fine titania (P-25) manufactured by Nippon Aerosol Co., Ltd. was added to a surfactant (Wako Pure Chemicals Triton X-100) at 0.
It was dispersed in 20 parts by mass of water containing 5% by mass. This dispersion was applied to a glass substrate (50 × 50 mm) with a tin oxide transparent electrode doped with fluorine using a bar coater,
And baked at 450 ° C. for 1 hour. The same application, drying and baking as described above were repeated once again to obtain a porous substrate having a thickness of 10 μm. Further, this substrate was immersed in a 1% by mass aqueous solution of titanium tetrachloride overnight, washed with water, dried at 100 ° C. for 1 hour, and baked at 450 ° C. for 1 hour to produce a porous titania substrate.

2. Attachment of sensitizing dye The titania substrate was immersed in an ethanol solution containing 0.3 mmol of a sensitizing dye (cis-dicyanate-bis (2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium (II)). The solution was heated to the boiling point of the solution, and the dye was adhered under reflux conditions for 2 hours to obtain a titania substrate with a sensitizing dye.

3. Preparation of Solar Cell The titania substrate with a dye that had been subjected to the above surface coating treatment was used as one electrode, and a glass substrate with a doped tin oxide transparent electrode coated as a counter electrode with platinum by sputtering was used. A non-woven fabric made of polypropylene (manufactured by Crecia Co., Ltd.) processed to a thickness of 15 to 20 μm as a solid material is stacked between the electrodes, and a Teflon (registered trademark) having a width of about 3 mm and a thickness of 20 μm is further surrounded as a spacer. 2.) The sheet was sandwiched, and the periphery was sealed with an epoxy adhesive, leaving two injection ports. An electrolyte solution was injected from the injection port under atmospheric pressure, and after the injection, the injection port was sealed with an epoxy adhesive. The volume ratio of the nonwoven fabric in the electrolyte layer was 72%. Thereafter, a lead wire was attached to the electrode to produce a solar cell. The electrolyte solution was prepared by mixing tetrapropylammonium iodide and iodine in a mixed solvent of methoxypropionitrile / ethylene carbonate having a volume ratio of 1: 4 at a concentration of 0.46 mol / L and 0.06 mol, respectively.
What was dissolved so that it might become 1 / L was used.

4. Power generation performance and life test of photovoltaic cells UV cut filter and AM using xenon lamp as light source
The power generation performance was measured by applying 500 W / m ² of simulated sunlight to the solar cell through a 1.5 filter. Further, as a life test, the power generation performance after repeating 50 cycles of leaving the cell at 0 ° C. for 4 hours and 80 ° C. for 4 hours was measured and compared with the performance before leaving.

5. Evaluation results of power generation performance and life The initial open circuit voltage (VOC) is 0.66 V, the short circuit current (ISC) is 6.5 mA / cm ² ,
The fill factor (FF) is 0.61, and the conversion efficiency is 5.2.
%, Which proved to be useful as a solar cell.
As a result of the life test of this cell, VOC, ISC, and FF did not change, and the conversion efficiency was still 5.2%.

Example 2 In the preparation of the solar battery cell of Example 1, polyvinylidene difluoride was used instead of a nonwoven fabric made of polypropylene (Crecia Co., Ltd.) processed to a thickness of 15 to 20 μm as a solid material. Membrane filter (Murapore Durapore, pore size (5 μm
)), And instead of a Teflon sheet having a width of about 3 mm and a thickness of 20 μm as a spacer, a Teflon sheet having a width of about 3 mm and a thickness of 50 μm is sandwiched therearound in the same manner as in Example 1. Was assembled. The volume ratio of the nonwoven fabric in the electrolyte layer was 31%.

When the initial performance of this cell was evaluated, the open circuit voltage (VOC) was 0.66 V, the short circuit current (ISC) was 6.5 mA / cm ² , and the fill factor (FF) was 0. .61, and the conversion efficiency was 5.2%. The results of the life test of this cell were VOC, ISC, F
F did not change and the conversion efficiency remained at 5.2%. Comparative Example A solar cell was produced in the same manner as in Example 1 except that a nonwoven fabric made of polypropylene was not used between the electrodes in producing the solar cell in Example 1. When the initial performance of this cell was evaluated, the open circuit voltage (VOC) was 0.66 V, and the short circuit current (I
SC) is 6.7 mA / cm ² and fill factor (FF)
Was 0.61 and the conversion efficiency was 5.4%. As a result of a life test of this cell, VOC was 0.68 V, ISC was 2.0 mA / cm ² , FF was 0.55, and the conversion efficiency was reduced to 1.5%. Leakage of the electrolyte was observed from a part of the cell seal.

[0030]

The dye-sensitized solar cell manufactured according to the present invention has excellent conversion efficiency and the like, indicating that an effective dye-sensitized solar cell capable of maintaining stable performance for a long time can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a configuration of a Gretzell-type solar cell

FIG. 2 is a conceptual diagram of a configuration (when a nonwoven fabric is used) of a solar cell of the present invention.

Claims (4)

[Claims] 1. A dye-sensitized solar cell having an electrolyte layer disposed between a dye-sensitized optical semiconductor electrode and a counter electrode, wherein an electrolyte solution is held in the electrolyte layer between the semiconductor electrode and the counter electrode. A dye-sensitized solar cell characterized by disposing a solid material. 2. The dye-sensitized solar cell according to claim 1, wherein said solid material is a fibrous substance. 3. The dye-sensitized solar cell according to claim 1, wherein the proportion of the solid material is in the range of 25 to 98% of the volume of the electrolyte layer. 4. The dye-sensitized solar cell according to claim 1, wherein the proportion of the solid material is higher as being closer to the counter electrode and lower as being closer to the semiconductor electrode.