JP2007273240A - Dye-sensitized solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar battery of a tandem type which has high light transparency and can make a highly efficient photoelectric conversion by using a counter electrode considering a rate determining of an electron supply. <P>SOLUTION: The coloring matter sensitizing solar battery is provided with a counter electrode 13 which is arranged between an n-type semiconductor electrode 11 in which a first coloring element is absorbed and an n-type semiconductor electrode 12 in which a second coloring element having a different absorbing wavelength from the first coloring element and an electrolyte solution 15 filled between the n-type semiconductor electrode and the counter electrode. The counter electrode 13 is formed as a repeating pattern of lines and spaces and when a line width and a space between lines are xμm and yμm respectively, conditions of 0.5≤y/(x+y)≤0.85 and 0≪y≪320 shall be satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell in which a dye is adsorbed and sensitized by adsorbing a dye to a metal oxide semiconductor material. It relates to solar cells.

Global environmental problems such as the depletion of fossil fuels and the global warming that accompanies the combustion have become issues for all mankind. Under such circumstances, solar cells that use non-depleting solar energy are fuels. Full-scale practical use is progressing as unnecessary and inexhaustible clean energy. Solar cells are classified into silicon-based, compound semiconductor-based, organic semiconductor-based, metal oxide semiconductor-based, etc., depending on the semiconductor material used. Metal oxide semiconductor solar cells use less energy for material purification than silicon, have less impact on environmental issues than compound semiconductors, and have good photoelectric conversion efficiency due to dye adsorption Therefore, as a low-cost, environmentally compatible solar cell, research and development are being promoted for practical use (see, for example, Patent Documents 1-4).
JP 2000-260492 A JP 2005-129580 A JP 2000-1000048 A JP 2001-167808 A

  N / n parallel tandem type in which a translucent counter electrode is arranged between a first electrode made of an n-type semiconductor adsorbing a first dye and a second electrode made of an n-type semiconductor adsorbing a second dye A dye-sensitized solar cell is known (Patent Document 1-2). In such a tandem dye-sensitized solar cell, sunlight transmitted through the first electrode generates power at the first electrode, transmits through the counter electrode, and further generates power at the second electrode. As the amount of light increases, the amount of power generated by the second electrode increases and the conversion efficiency also improves. For this reason, about the mesh and wire as a counter electrode, it is calculated | required that the transmittance | permeability of light is high. However, as the aperture ratio of the mesh or wire increases, the mesh or wire becomes coarser, so that the diffusion distance of the redox pair necessary for supplying electrons from the counter electrode to the first electrode or the second electrode side becomes longer. . For this reason, when the aperture ratio of the counter electrode increases, the supply of electrons becomes rate-determined, and the power generation efficiency may decrease. Moreover, conversion efficiency may fall by reaction rate control by insufficient surface area, so that an aperture ratio rises.

  The present invention has been made in view of the above-described circumstances. A tandem dye-sensitized solar cell capable of highly efficient photoelectric conversion by using a counter electrode with high translucency and considering the rate-limiting of electron supply. The purpose is to provide. It is another object of the present invention to provide a dye-sensitized solar cell with higher efficiency by adjusting the concentration of the electrolyte solution in order to reduce the rate of electron supply.

The dye-sensitized solar cell of the present invention includes an n-type semiconductor electrode on which a first dye is adsorbed and a counter electrode between an n-type semiconductor electrode on which a second dye having an absorption wavelength different from that of the first dye is adsorbed. In the dye-sensitized solar cell in which the electrolyte solution is filled between the n-type semiconductor electrode and the counter electrode, the counter electrode is formed as a repetitive pattern of lines and spaces, and the line width and the line interval are set to x μm, respectively. And y μm, 0.5 ≦ y / (x + y) ≦ 0.85 and 0 <y <320 are satisfied.
The counter electrode is formed as a repeating pattern of polygonal openings, and when the line width and the line interval are x μm and y μm, respectively, 0.5 ≦ y ² / (x + y) ² ≦ 0.85, 0 <y < It is characterized by satisfying 320 conditions.
The counter electrode is formed as a repeating pattern of circular openings, and 0.5 ≦ 0.906 × y ² / (x + y) ² ≦ 0.85, 0 <0, where the line width and the line interval are x μm and y μm, respectively. The feature is that the condition of y <320 is satisfied.

In the dye-sensitized solar cell, the counter electrode is formed as a repetitive pattern of lines and spaces, and when the line width and line interval are x μm and y μm, respectively, 0.8 ≦ y / (x + y) <1, 0 <y <80 and 0 <x <20 are satisfied.
The counter electrode is formed as a repeating pattern of polygonal openings, and when the line width and line interval are x μm and y μm, respectively, 0.8 ≦ y ² / (x + y) ² <1, 0 <y < It is characterized by satisfying the conditions of 80 and 0 <x <20.
Further, the counter electrode is formed as a repetitive pattern of circular openings, when the line width and line interval between each xμm and ^{yμm, 0.8 ≦ 0.906 × y 2} / (x + y) 2 <1,0 < The condition is that y <80 and 0 <x <20.

  According to the present invention, as the repetitive pattern of the openings, the line width and the line interval are within the above ranges, so that the light transmittance is kept high and the first electrode or the second electrode is maintained from the counter electrode. The diffusion distance of the redox pair necessary for supplying electrons to the side can be suppressed, and the rate of electron supply can be prevented from becoming rate limiting. For this reason, power generation efficiency can be improved by balancing the aperture ratio of the counter electrode.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the member or element which has the same effect | action or function, and the overlapping description is abbreviate | omitted.

  FIG. 1 shows a tandem dye-sensitized solar cell according to an embodiment of the present invention. A counter electrode 13 is disposed between an n-type semiconductor electrode 11 that has adsorbed a first dye and an n-type semiconductor electrode 12 that has adsorbed a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode 11 is disposed. This is an n / n parallel tandem dye-sensitized solar cell in which an electrolyte solution 15 is filled between a semiconductor electrode and a counter electrode.

This structure will be described in more detail. The semiconductor electrode 11 is obtained by adsorbing a short wavelength absorbing dye such as a ruthenium-based transition metal complex dye on TiO ₂ (n-type semiconductor). The semiconductor electrode 12 is obtained by adsorbing a long wavelength absorption dye such as a phthalocyanine dye on TiO ₂ (n-type semiconductor). As a dye to be adsorbed on an n-type semiconductor, an organic transition metal complex dye containing at least one bipyridyl group, a phthalocyanine dye, a naphthalocyanine dye, a merocyanine dye, a cyanine dye, a porphyrin dye, a rhodanine dye, an indole System dyes, quinoline dyes, and benzothiazole dyes can be used. Also, ZnO, SnO ₂ , NbO ₂ , WO ₃ or the like can be used as the n-type semiconductor.

  The counter electrode 13 is obtained by coating an inexpensive metal plate with Pt by sputtering, vapor deposition, or plating, and is a punching metal or a mesh. And the repeating pattern of the opening part shown in FIG.2, FIG.3, FIG.4 is provided. The counter electrode may be a Pt wire having a catalytic function, or a mesh formed using carbon fiber, or a mesh formed of metal or fiber or the like coated with Pt or carbon, or a conductive polymer. Good. In addition, the counter electrode may be a punching metal in which a hole is formed in a metal plate and coated with Pt, carbon, or a conductive polymer.

The electrolyte solution 15 is composed of iodine (I ₂ ), lithium iodide (LiI), tertiary butylpyridine (t-BP), dimethylpropylimidazolium iodide (DMPII) in acetonitrile (AN) or methoxyacetonitrile (MAN). It is a dissolved electrolyte. It is preferable that the electrolyte solution is prepared so that the I ₂ concentration is 0.05 to 0.3 mol / l and the iodide salt concentration is 0.6 to 2.4 mol / l. Moreover, you may use the molten salt electrolyte solution which does not contain the volatile component which has imidazolium salt as a main body as electrolyte solution.

  The semiconductor electrodes 11 and 12 are provided on a transparent glass substrate 18 on which a transparent conductive film (ITO film, FTO film) 17 is formed. The side surface between the two glass substrates 18 and 18 is sealed with a thermosetting resin sheet 19, and the electrolyte solution 15 is filled in the internal space. The power generation output of this dye-sensitized solar cell is that the semiconductor electrodes 11 and 12 serve as anodes, so that the positive electrode is taken out from the terminal connected to the transparent conductive film 17 and the counter electrode 13 serves as the cathode. The negative electrode is taken out from the connected terminal.

  Next, the operation of this dye-sensitized solar cell will be described. When sunlight is incident, the light on the short wavelength side is absorbed by the semiconductor electrode 11 to perform a power generation operation, and part of the light transmitted through the transparent semiconductor electrode 11 is blocked by the non-opening portion of the counter electrode. The light that has passed through is incident on the semiconductor electrode 12, and the light on the long wavelength side is absorbed by the semiconductor electrode 12 to perform a power generation operation. Therefore, a wide wavelength range of sunlight can be used for power generation operation by the n / n tandem dye-sensitized solar cell.

In the electrolyte of the dye-sensitized solar cell, an oxidation-reduction body (redox couple) of iodine as shown in the following formula is used.
_{^{I 3 - + 2e - = 3I}} - + I 2
The dye absorbs light, and causes electrons to be injected into the conduction band of titania (TiO ₂ ) from the excited dye molecule. Electrons injected into titania reach the cathode through the anode and external circuit. On the other hand, the dye that is in an oxidized state by donating electrons to titania receives electrons from the redox system I ⁻ in the electrolytic solution and returns to neutral molecules. I ⁻ loses electrons and becomes I ₃ ⁻ , but returns to I ⁻ upon receiving electrons flowing through the circuit from the cathode. Such a cycle is repeated inside the dye-sensitized solar cell to convert light into electric current.

  Next, an example of forming the opening pattern of the counter electrode according to the present invention will be described. FIG. 2 shows a counter electrode formed as a repeating pattern of lines and spaces. When the line width and line spacing are xμm and yμm, respectively, by satisfying the condition of 0.5 ≦ y / (x + y) ≦ 0.85 and 0 <y <320, that is, the aperture ratio should be 50-85% As will be described later, the maximum conversion efficiency can be obtained.

FIG. 3 shows a counter electrode formed as a repeating pattern of polygonal openings. In the example shown in the figure, the opening has a quadrangular shape and a hexagonal shape, but may be a triangular shape, a pentagonal shape, an octagonal shape, or the like. By satisfying the conditions of 0.5 ≦ y ² / (x + y) ² ≦ 0.85 and 0 <y <320 when the line width and the line spacing are x μm and y μm, respectively, that is, the aperture ratio is 50-85%. By doing so, the maximum conversion efficiency can be obtained.

In FIG. 4, the counter electrode is formed as a repeating pattern of circular openings. When the line width and line spacing are xμm and yμm, respectively, 0.5 ≦ 0.906 × y ² / (x + y) ² ≦ 0.85 and 0 <y <320, that is, the aperture ratio is 50-85 By setting%, the maximum conversion efficiency can be obtained.

A Pt line pattern of the opening pattern shown in FIG. 2 was formed on an FTO (transparent conductive) substrate by changing the aperture ratio conditions by photolithography, and the aperture ratio was experimentally examined. That is, a dye-sensitized solar cell is formed using this counter electrode, the characteristics of the solar cell irradiated from the TiO ₂ side and the Pt side are measured, and the tendency of the conversion efficiency as the first electrode and the second electrode is experimentally determined. confirmed.

但し、
LiI：ヨウ化リチウム
t-BP：ターシャル-ブチルピリジン
DMPII：ヨウ化ジメチルプロピルイミダゾリウム The experimental conditions are as follows.
Semiconductor electrode: Titanium oxide paste manufactured by Solaronix was used and baked at 450 ° C for 30 minutes.
Dye: N749 (organometallic complex dye) is used.
Electrolyte solution Solvent: Acetonitrile, Component: As shown in the table below.

However,
LiI: Lithium iodide
t-BP: Tertiary-Butylpyridine
DMPII: Dimethylpropylimidazolium iodide

The counter electrode pattern shown in FIG. 2 is formed by Pt sputtering with photolithography on a glass substrate on which a transparent conductive film (FTO) is placed.
Pt line Line width: 20, 40, 60, 80, 100μm
Line spacing: 80, 160, 240, 320, 400μm
Irradiation direction Irradiation from Pt side (Power generation by light transmitted through glass substrate and counter electrode)
Irradiated from TiO ₂ side (power generation by light transmitted through glass substrate)

Using a Pt line for the counter electrode, the line width and line spacing were changed, and the conversion efficiency was confirmed under conditions with different aperture ratios. Table 2 shows the aperture ratio depending on the line width and the line interval.

Table 3 shows the measurement results of conversion efficiency (%) when irradiated from the TiO ₂ side.

Table 4 shows the measurement results of conversion efficiency (%) when irradiated from the Pt side.

FIG. 5 shows the correlation between the aperture ratio and the conversion efficiency (%) when irradiated from the TiO ₂ side, and FIG. 6 shows the correlation between the aperture ratio and the conversion efficiency (%) when irradiated from the Pt side. When irradiated from the TiO ₂ side, the area of the counter electrode increased as the aperture ratio decreased, and the fill factor FF and short-circuit current value increased. When irradiated from the Pt side, the fill factor FF increased as the aperture ratio decreased, but the current value decreased as the aperture ratio decreased (by reducing the area contributing to power generation). From the experimental results of the conversion efficiency with respect to the aperture ratio, the first electrode (the electrode that transmits light only through the glass substrate and directly generates electricity) has an aperture ratio of 80% or less, and the second electrode (the glass substrate and the counter electrode opening) It can be seen that the electrode having a high aperture ratio of 60 to 85% provides high efficiency.

In a parallel tandem dye-sensitized solar cell, the aperture ratio is preferably 50 to 85% and particularly preferably 60 to 70% because it is the sum of the current values of the first electrode and the second electrode. Further, in the same opening ratio of 80%, with a result of irradiating the TiO ₂ side, since the line spacing is reduced conversion efficiency at higher 320 .mu.m, the line spacing is high conversion efficiency increased 320 .mu.m smaller range than 0 obtained ing.

Even when the openings of the counter electrode were formed in a repetitive pattern of a honeycomb structure (hexagonal shape), a tendency similar to the tendency of conversion efficiency when a repetitive pattern of lines and spaces was used was observed. Table 5 shows the relationship among line width, line spacing, and aperture ratio.

Table 6 shows the measurement results of the conversion efficiency when irradiated from the TiO ₂ side and the measurement results of the conversion efficiency when irradiated from the Pt side. It can be seen that good conversion efficiency is obtained when the aperture ratio is in the range of 50 to 80%.

In order to promote electron supply in the electrolyte solution, I ⁻ and I ₃ ⁻ concentrations were increased and characteristics were confirmed. As a result, when I ₂ and DPMII concentrations were doubled, conversion efficiency was improved. Table 7 shows the relationship between the material and the concentration, and Table 8 shows the measurement result of the conversion efficiency when the I ₂ and DPMII concentrations are changed. The conversion efficiency improved even when the I ₂ and DPMII concentrations were 3 times, but the improvement rate was lower than 2 times. This is probably because visible light absorption by the electrolyte solution increases as the iodine concentration increases.

Therefore, conversion efficiency can be improved by improving the concentration of the electrolyte solution under conditions where the aperture ratio of the counter electrode is high. As an electrolyte solution concentration capable of improving electron supply, I ₂ and DPMII are preferably 0.05 mol / l to 0.3 mol / l and 0.6 mol / l to 2.4 mol / l, respectively, 0.05 mol / l to 0.15 mol / l, 0.6 Particularly preferred is mol / l to 1.8 mol / l.

  As described above, it can be seen that sufficiently high conversion efficiency can be obtained with a line width of 20 μm, a line interval of 80 μm, and an aperture ratio of 80%. When the line spacing is 80 μm or less, the diffusion rate of the electrolyte solution is not controlled, and the conversion efficiency seems to decrease according to the reaction rate control due to the insufficient surface area of the counter electrode under the condition where the aperture ratio is greater than 80%. However, the surface area per unit area can be increased by increasing the Pt film thickness or making it porous even under counter electrode conditions where the wire diameter is narrower than 20 μm and the aperture ratio is 80% or more in a range shorter than 80 μm. It is possible to achieve high conversion efficiency while maintaining a high aperture ratio by increasing.

That is, by making the counter electrode porous, roughening the surface, or using an elliptical wire, the surface area of the counter electrode is substantially increased without reducing the aperture ratio, thereby promoting the reaction. High conversion efficiency can be realized. From this point of view, when the counter electrode is formed as a repetitive pattern of lines and spaces, 0.8 ≦ y / (x + y) <1, 0 <y <, where the line width and line interval are x μm and y μm, respectively. A good conversion efficiency may be obtained by satisfying the condition of 80 and 0 <x <20. Further, when the counter electrode is formed as a repeating pattern of polygonal openings, 0.8 ≦ y ² / (x + y) ² <1, 0 <y <, where the line width and the line interval are x μm and y μm, respectively. A good conversion efficiency may be obtained by satisfying the condition of 80 and 0 <x <20. Further, when the counter electrode is formed as a repeated pattern of circular openings, when the line width and the line interval are x μm and y μm, respectively, 0.8 ≦ 0.906 × y ² / (x + y) ² <1, 0 < There are cases where good conversion efficiency can be obtained by satisfying the conditions of y <80 and 0 <x <20.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is sectional drawing which shows the dye-sensitized solar cell of one Embodiment of this invention. It is a pattern diagram in the case of forming a counter electrode as a repeated pattern of lines and spaces. It is a pattern diagram in the case of forming a counter electrode as a repeating pattern of polygonal openings. It is a pattern diagram in the case of forming a counter electrode as a repeating pattern of circular openings. It is a graph showing the correlation between the aperture ratio and conversion efficiency when irradiated with light from the TiO ₂ side conditions using a repeating pattern of lines and spaces in the counter electrode. It is a graph which shows the correlation of an aperture ratio and conversion efficiency at the time of light irradiation from the Pt side on the conditions which used the repeating pattern of a line and a space for a counter electrode.

Explanation of symbols

11, 12 n-type semiconductor electrode 13 Counter electrode 15 Electrolyte solution 17 Conductive film 18 Glass substrate 19 Thermosetting resin sheet

Claims (16)

A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repetitive pattern of lines and spaces, and satisfies the condition of 0.5 ≦ y / (x + y) ≦ 0.85 and 0 <y <320, where the line width and the line interval are x μm and y μm, respectively. A dye-sensitized solar cell characterized by A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repetitive pattern of polygonal openings, where 0.5 ≦ y ² / (x + y) ² ≦ 0.85, 0 <y <320, where the line width and the line spacing are x μm and y μm, respectively. A dye-sensitized solar cell characterized by satisfying a condition. A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repeating pattern of circular openings, where 0.5 ≦ 0.906 × y ² / (x + y) ² ≦ 0.85, 0 <y <, where the line width and the line interval are x μm and y μm, respectively. A dye-sensitized solar cell characterized by satisfying 320 conditions. A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repetitive pattern of lines and spaces, and 0.8 ≦ y / (x + y) <1, 0 <y <80 and 0 <x <, where the line width and the line spacing are x μm and y μm, respectively. A dye-sensitized solar cell characterized by satisfying 20 conditions. A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repetitive pattern of polygonal openings, and 0.8 ≦ y ² / (x + y) ² <1, 0 <y <80 when the line width and the line interval are x μm and y μm, respectively. A dye-sensitized solar cell characterized by satisfying a condition of 0 <x <20. A counter electrode is disposed between an n-type semiconductor electrode adsorbing the first dye and an n-type semiconductor electrode adsorbing a second dye having an absorption wavelength different from that of the first dye, and the n-type semiconductor electrode In a dye-sensitized solar cell in which an electrolyte solution is filled between a counter electrode and
The counter electrode is formed as a repeating pattern of circular openings, where 0.8 ≦ 0.906 × y ² / (x + y) ² <1, 0 <y <, where the line width and the line interval are x μm and y μm, respectively. A dye-sensitized solar cell characterized by satisfying the conditions of 80 and 0 <x <20.   The dye-sensitized solar cell according to claim 2 or 5, wherein the polygon is a triangle, a quadrangle, a pentagon, a hexagon, or an octagon.   The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the counter electrode is a punching metal or a mesh.   The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the counter electrode is a Pt wire having a catalytic function or a mesh formed using carbon fibers.   The dye-sensitized sun according to any one of claims 1 to 6, wherein the counter electrode is a mesh formed of metal, fiber, or the like, coated with Pt, carbon, or a conductive polymer. battery.   The dye sensitizing method according to any one of claims 1 to 6, wherein the counter electrode is obtained by coating a punching metal having a hole in a metal plate with Pt, carbon, or a conductive polymer. Solar cell.   7. The surface area of the counter electrode is increased without reducing the aperture ratio by making the counter electrode porous, roughening the surface, or using an elliptical wire. The dye-sensitized solar cell according to any one of the above. The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the n-type semiconductor is at least one selected from TiO ₂ , ZnO, SnO ₂ , NbO ₂ , and WO ₃ .   As a dye to be adsorbed on the n-type semiconductor, an organic transition metal complex dye containing at least one bipyridyl group, a phthalocyanine dye, a naphthalocyanine dye, a merocyanine dye, a cyanine dye, a porphyrin dye, a rhodanine dye, The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the dye-sensitized solar cell is at least one selected from indole dyes, quinoline dyes, and benzothiazole dyes.   The dye-sensitized solar cell according to any one of claims 1 to 6, wherein the electrolyte solution is a molten salt electrolyte solution containing no volatile component mainly composed of an imidazolium salt. The electrolyte solution of I ₂ concentration 0.05~0.3mol / l, dye according to any one of claims 1 to 6, characterized in that the iodide salt concentration created in the range of 0.6~2.4mol / l Sensitive solar cell.

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