Patent Application
20070044831
1. Field of the Invention
The present invention relates to an electrolyte composition and a dye-sensitized solar cell using for the solid electrolyte layer thereof the electrolyte composition.
2. Description of the Related Art
Dye-sensitized solar cells usually contain in the electrolyte layer thereof a liquid electrolyte including a low molecular weight solvent, and accordingly, a problem is raised in that the photoelectric conversion rate is degraded due to the liquid leakage and the solvent evaporation.
For the purpose of solving the above described problem, solidification (gelation) of the electrolyte layer has been studied.
As a method for solidifying the electrolyte layer, there has been proposed a method in which nanoparticles are added to an electrolytic solution (electrolyte solution) (for example, see Non-patent Document 1).
However, although the solidification becomes remarkable with the addition of a nanoparticles, there is such a problem that the photoelectric current or the photoelectric conversion rate is significantly reduced with the addition of nanoparticles.
Alternatively, for the purpose of improving the photoelectric conversion rate, there has been proposed a method in which an electrolyte composition containing an imidalzolium salt is used for the electrolyte solution (for example, see Patent Document 1).
Needless to say, this method cannot attain the solidification of the electrolyte layer.
In a contrast to these method, there has been proposed a method in which an electrolyte composition containing nanoparticles and an imidazolium cation is used for the electrolyte layer for the purpose of simultaneously realizing the solidification of the electrolyte layer and the prevention of degradation of the photoelectric conversion rate caused by the solidification of electrolyte layers (for example, see Non-patent Document 2). In this case, the situation involved is such that the imidazolium cations are adsorbed on the surface of the nanoparticles.
[Patent Document 1]: Japanese Patent Laid-Open No. 2001-160427.
[Non-patent Document 1]: J. H. Kim, M-S. Kang, Y. J. Kim, J. Won, N-G. Park and Y. S, Kang, Chem. Comm., 2004, 1662.
[Non-patent Document 2]: H. Usui, H. Matsui, N. Tanabe and S. Yanagida, J. Photochem. Photobiol., A: Chem., 164(2004), 97.
However, a dye-sensitized solar cell having an electrolyte layer comprising an electrolyte composition in the form of the above described nanoparticles having imidazolium cations adsorbed on the surface thereof cannot sufficiently overcome a significant reduction in photoelectric conversion rate caused by the solidification of electrolyte layers.
The present invention has been achieved in view of the above described problem, and an object of the present invention is to provide an electrolyte composition that can simultaneously realize solidification of the electrolyte layer and alleviation of a reduction in photoelectric conversion rate caused by the solidification of electrolyte layers, and a dye-sensitized solar cell having a solid electrolyte layer comprising the electrolyte composition.
The electrolyte composition according to the present invention is characterized in that the electrolyte composition includes nanoparticles with an ammonium group or a nitrogen-containing heterocyclic group bound thereto, or a porous inorganic film with an ammonium group or a nitrogen-containing heterocyclic group bound thereto.
The electrolyte composition according to the present invention is also characterized in that the nanoparticles and the porous inorganic film each are formed of a metal oxide.
Further, the electrolyte composition according to the present invention is characterized in that: the nitrogen-containing heterocyclic group includes one or more groups selected from the group consisting of an imidazolium group represented by the following general formula (1), a pyridinium group represented by the following general formula (2), a triazolium group represented by the following general formula (3), and a guanidinium group represented by the following general formula (4); and the counter anion group is selected from the group consisting of F−, Cl−, Br−, I− and a compound represented by the following general formula (5)
wherein R1 to R4 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R5 to R9 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R10 to R12 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R13 to R17 each are a hydrogen atom or a phenyl group, and may be the same or different from each other; and n is an integer of 4 to 20;
Y—(CH2)n—COOH (5)
wherein Y represents —SO3− or —COO−, and n is an integer of 4 to 20.
Further, the electrolyte composition according to the present invention is characterized in that the ammonium group is a compound represented by the following general formula (6), and the counter anion group is F−, Cl−, Br− or I−:
wherein R18 to R20 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20.
Further, the electrolyte composition according to the present invention is characterized in that the electrolyte composition is formed of the nanoparticles or the porous inorganic film chemically modified by the ammonium group or the nitrogen-containing heterocyclic group through the intermediary of an acyclic hydrocarbon group straight chain having a functional group at one end thereof.
Furthermore, the dye-sensitized solar cell according to the present invention is a dye-sensitized solar cell which includes a semiconductor electrode with a dye adsorbed on the surface thereof, a counter electrode disposed so as to face the semiconductor electrode, and an electrolyte layer disposed between the semiconductor electrode and the counter electrode, characterized in that the electrolyte layer includes the above described electrolyte composition.
The electrolyte composition according to the present invention includes nanoparticles with an ammonium group or a nitrogen-containing heterocyclic group bound thereto or a porous inorganic film with an ammonium group or a nitrogen-containing heterocyclic group bound thereto. Herewith, a dye-sensitized solar cell having an electrolyte layer comprising this electrolyte composition can simultaneously realize solidification of the electrolyte layer and alleviation of a reduction in photoelectric conversion rate caused by the solidification of electrolyte layers.
Hereinbelow, embodiments of the present invention are described.
First, the electrolyte composition of the present invention is described.
The electrolyte composition of the present invention includes nanoparticles with an ammonium group or a nitrogen-containing heterocyclic group bound thereto or a porous inorganic film with an ammonium group or a nitrogen-containing heterocyclic group bound thereto.
The nanoparticles and the porous inorganic film are not particularly constrained with respect to material type as long as they can realize solidification of the electrolyte layer, but each are preferably formed of a metal oxide. The metal element of the metal oxide emcompasses Si. Examples of the metal oxide may include TiO2, Al2O3, ZnO, ZrO2 and SiO2.
The particle size (diameter) of the nanoparticles is not particularly limited from the viewpoint of solidification of the electrolyte layer, but it is preferably 5 to 100 nm from the viewpoint that a sufficient quantity of a modifier such as an ammonium group or the like should be bound to the surface of the nanoparticles and the like.
The nitrogen-containing heterocyclic group is not particularly limited for type from the viewpoint of improving the electric conductivity of the electrolyte layer. However, the nitrogen-containing heterocyclic group is preferably one or more groups selected from the group consisting of an imidazolium group represented by the following general formula (1), a pyridinium group represented by the following general formula (2), a triazolium group represented by the following general formula (3), and a guanidinium group represented by the following general formula (4); and the counter anion group is selected from the group consisting of F−, Cl−, Br−, I− and a compound represented by the following general formula (5)
wherein R1 to R4 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R5 to R9 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R10 to R12 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20;
wherein R13 to R17 each are a hydrogen atom or a phenyl group, and may be the same or different from each other; and n is an integer of 4 to 20; and
Y—(CH2)n—COOH (5)
wherein Y represents —SO3− or —COO−, and n is an integer of 4 to 20.
The ammonium group is also not particularly limited for type from the viewpoint of improving the electric conductivity of the electrolyte layer; however, the ammonium group is preferably a compound represented by the following general formula (6), and the counter anion group is F−, Cl−, Br− or I−:
wherein R18 to R20 each are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and may be the same or different from each other; and n is an integer of 4 to 20.
Examples of the imidazolium group represented by the above described general formula (1) may include the following compounds:
Examples of the pyridinium group represented by the above described general formula (2) may include the following compounds:
Examples of the triazolium group represented by the above described general formula (3) may include the following compounds:
Examples of the guanidinium group represented by the above described general formula (4) may include the following compounds:
Examples of the ammonium group represented by the above described general formula (6) may include the following compounds:
The respective groups and the nanoparticles or porous inorganic film may be directly bound to each other, or may be indirectly bound to each other in such a manner that the ammonium group or the nitrogen-containing heterocyclic group chemically modifies the nanoparticles or the porous inorganic film through the intermediary of an acyclic hydrocarbon group straight chain having a functional group at one end thereof.
The electrolyte composition of the present invention contains, for example, an appropriate amount of an electrolytic solution containing, as a redox substance in addition to the above described components, a component composed of a combination of iodide ion and iodine. Specifically, there may be used combinations of metal iodides such as LiI, NaI and CaI2 and iodine. Alternatively, examples of the other combinations may include bromide ion-bromine, thallium ion (III)-thallium ion (I), mercury ion (II)-mercury ion (I) and the like. Here, containing an appropriate amount of an electrolytic solution means that the electrolyte composition includes an electrolyte in such a range that the electrolyte composition maintains solidification (gelation) condition and the efficiency of the solar cell is not drastically decreased.
The electrolyte composition of the present invention that is composed as described above remains solid (gel).
Next,
A separator 20 is interposed between the two electrodes, more strictly, between the metal oxide semiconductor layer 16 and the transparent conductive film 14b, to form and define an enclosed space. Inside the enclosed space, an electrolyte layer 22 is disposed.
The components of the cell 10, other than the electrolyte layer 22, are not particularly limited for material types, but can be formed of some materials appropriately selected from common materials. The film thickness and the like can also be appropriately set.
The transparent substrates 12a and 12b each may be, for example, a glass plate or a plastic plate.
The transparent conductive films 14a and 14b each may be made of, for example, ITO, SnO2 or the like.
For the metal oxide semiconductor layer 16, for example, titanium, tin, zirconium, zinc, indium, tungsten, iron, nickel, silver or the like may be used as the metal thereof.
For the dye of the sensitizing dye layer 18, for example, the metal dyes or non-metal dyes such as complexes of transition metals such as ruthenium, phthalocyanines, porphins or the like may be used.
Good conductive materials to be deposited by sputtering, such as platinum, conductive polymers and substances free from corrosion by iodine such as carbon may be used as well as gold.
The electrolyte layer 22 is formed between the metal oxide semiconductor layer 16 and the transparent conductive film 12b with the electrolyte composition, gelated beforehand, of the present invention by a coating method, a printing method or the like. The formation of the electrolyte layer 22 is thereby facilitated, and mass production and area enlargement of the dye-sensitized solar cell can be expected.
The dye-sensitized solar cell of the present invention is free from a reduction in photoelectric conversion rate caused by the liquid leakage and the solvent evaporation which may occur if the electrolyte layer comprises a liquid electrolyte containing a low molecular weight solvent, and can alleviate a reduction in photoelectric conversion rate which may occur in solidification of electrolyte layers.
The present invention will be described in more detail with reference to examples and comparative examples. However, it is construed that the present invention is not limited to the examples described below.
On a transparent substrate (manufactured by Nippon Sheet Glass Co., Ltd.; 30 ohm/sq) on which a transparent conductive film made of SnO2 was vacuum deposited, the D paste manufactured by Solaronix SA (trade name: Ti-Nanoxide D) was coated and baked at 450° C. for 30 minutes to prepare a 9 μm thick titania electrode (titanium dioxide semiconductor layer). Subsequently, the transparent substrate with the titania electrode formed thereon was soaked in an ethanol solution in which 0.1% by mass of cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarbox ylato)ruthenium(II) (manufactured by Kojima Chemicals Co., Ltd.) was dissolved.
Aside from this, a transparent substrate with a platinum-containing transparent conductive film sputtered thereon was prepared as the counter electrode.
An electrolyte composition was obtained in the following manner.
Specifically, TiO2 nanoparticles (trade name: P25; manufactured by Japan Aerosil Co., Ltd.; particle diameter: 21 nm) were added to an acetonitrile solution in which 8-bromooctanoic acid was dissolved, and the mixture was stirred at room temperature all day in a dark room. The mixture thus obtained was filtered to obtain a solid, which was washed with acetonitrile to remove the remaining 8-bromooctanoic acid, and was further dried to obtain TiO2 nanoparticles with 8-bromooctanoic acid bound thereto. The TiO2 nanoparticles with 8-bromooctanoic acid bound thereto were added to an acetonitrile solution in which methylimidazole was dissolved, and the solution was stirred at room temperature for one day in a dark room. The mixture thus obtained was filtered to obtain a solid, which was washed with acetonitrile, and dried under reduced pressure (under vacuum) to obtain TiO2 nanoparticles chemically modified with an adduct (bound molten salt molecule A) of methylimidazole (methylimidazole group) and 8-bromooctanoic acid (8-bromooctanoic acid group). To an electrolytic solution composed of methylpropylimidazolium iodide (water content: 5% by mass) containing 300 mM I2, 500 mM LiI, and 580 mM t-butylpyridine, the modified particles were added with a ratio (particles/electrolytic solution=1) shown in Table 1 to yield a gelled electrolyte composition.
The electrolyte composition was coated on the titania electrode formed on the transparent substrate, the counter electrode was superposed through the electrolyte composition on the transparent substrate with the titania electrode formed thereon by using 50-μm Himilan (trade name; a resin manufactured by Mitsui-Dupont Chemicals Co.) as a spacer and adhesive, to fabricate a cell.
The area of the fabricated cell was 0.25 cm2, and the solar cell efficiency (photoelectric conversion rate) was measured with a solar simulator (YSS-50A; manufactured by Yamashita Denso Corp.; AM1.5; 100 mW/cm2).
The conditions of preparation of the electrolyte composition and the solar cell efficiency, respectively, are shown in Table 1.
Cells were fabricated and their solar cell efficiencies were measured in the same manner as in Example 1 except that, in each example, the types of nanoparticles and bound molten salt molecule were changed as shown in Table 1 to 3. The conditions of preparation of the electrolyte compositions and the solar cell efficiencies, respectively, are shown in Tables 1, 2 and 3.
Here, in each table, the bound molten salt molecules A to E are the compounds having the following structural formulas, respectively; A is an imidazolium group-containing compound, B is a pyridinium group-containing compound, C and E are a compound containing an ammonium group, and D is a guanidinium compound. It is to be noted that in D, Ph represents a phenyl group.
As illustrated in Table 2, the nanoparticle with bound modifier molecules thereon in each Example has such a form that the surface of the nanoparticle (M1) is covered with a large number of long chain compound (M2) molecules each having a functional group at one end thereof, and a bound molten salt molecule (M3) is bound to the other end of each long chain compound (M2) molecule.
As Comparative Example 1, a cell was fabricated in the same manner as in Example 1 except that an electrolyte composition containing a gelled solid containing TiO2 as nanoparticle and methylimidazole ion as molten salt ion was used. As Comparative Example 2, a cell was fabricated in the same manner as in Example 1 except that an electrolyte composition containing only the electrolytic solution used in Examples was used. The conditions of the preparation of the electrolyte composition and the solar cell efficiency of each of Comparative Examples are shown in Table 1, respectively.
As can be seen from Tables 1 to 3, as compared to Comparative Example 1 in which no molten salt is bound to the nanoparticles, each of Examples is significantly larger in solar cell efficiency.
As also can be seen from these tables, with an increasing number of carbon atoms (the hydrocarbon chain length), the solar cell efficiency is increased.
As also can be seen from these tables, as compared to Comparative Example 2 in which only an electrolytic solution was used and thus contained neither nanoparticles nor bound molten salt molecules, Comparative Example 1 is largely decreased in solar cell efficiency, but each Example is significantly alleviated in a reduction in solar cell efficiency.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-251348 | Aug 2005 | JP | national |
