JP6911833B2 - Electrodes for solar cells, their manufacturing methods, and solar cells - Google Patents

Description

The present invention relates to an electrode for a solar cell, a method for manufacturing the electrode, and a solar cell.

In recent years, solar cells have been attracting attention as photoelectric conversion elements that convert light energy into electric power. Among them, organic solar cells that use organic materials for light absorption and organic-inorganic hybrid solar cells that use a combination of organic and inorganic materials for light absorption are more flexible than silicon (Si) -based solar cells. It is attracting particular attention because it can be manufactured using inexpensive materials with excellent properties.

For example, a dye-sensitized solar cell, which is a kind of organic solar cell, has a light electrode and a counter electrode, and an electrolyte layer interposed between these two electrodes. Then, when the sensitizing dye in the light electrode is excited by receiving light, the electrons of the sensitizing dye are taken out. The electrons exit the photoelectrode, travel through an external circuit to the counter electrode, and then to the electrolyte layer via its catalyst layer.

Here, in order to improve the performance of the solar cell, the electrodes used in the solar cell are being improved. For example, Patent Document 1 discloses a dye-sensitized solar cell counter electrode including a catalyst layer containing carbon nanotubes having predetermined properties on a support.

Japanese Unexamined Patent Publication No. 2014-120219

Here, the solar cell is required to maintain excellent photoelectric conversion efficiency for a long period of time. The conventional electrodes have room for improvement in that the durability of the solar cell is enhanced and the solar cell exhibits excellent photoelectric conversion efficiency for a long period of time. Therefore, an object of the present invention is to provide an electrode for a solar cell that can impart excellent durability to a solar cell, and a solar cell having excellent durability.

The present inventors have made extensive studies to achieve the above object. Then, the present inventors use an electrode including a support and a catalyst layer having an average thickness within a predetermined range and a standard deviation of the thickness of a predetermined value or less, so that the durability of the solar cell can be obtained. We have found that it is possible to increase the above, and completed the present invention.

That is, the present invention aims to advantageously solve the above problems, and the solar cell electrode of the present invention includes a support and a catalyst layer formed on the support. The electrode for use is characterized in that the average value of the thickness of the catalyst layer is 0.5 μm or more and 3.0 μm or less, and the standard deviation of the thickness of the catalyst layer is 0.2 μm or less. As described above, if the electrode including the support and the catalyst layer having the average thickness within a predetermined range and the standard deviation of the thickness being equal to or less than a predetermined value is used, the durability of the solar cell can be enhanced. It is possible to make a solar cell exhibit excellent photoelectric conversion efficiency for a long period of time.

Here, in the solar cell electrode of the present invention, the difference between the maximum value and the minimum value of the thickness of the catalyst layer is preferably 50% or less of the average value of the thickness of the catalyst layer. When the difference between the maximum value and the minimum value of the thickness of the catalyst layer is 50% or less of the average value of the thickness, the durability of the solar cell can be further improved.

Further, in the electrode for a solar cell of the present invention, it is preferable that the catalyst layer contains fibrous carbon nanostructures. By using a catalyst layer containing fibrous carbon nanostructures such as carbon nanotubes, the production cost can be reduced without using a precious metal such as platinum which is generally used for the catalyst layer.

Further, in the electrode for a solar cell of the present invention, it is preferable that the t-plot of the fibrous carbon nanostructure obtained from the adsorption isotherm shows an upwardly convex shape. The photoelectric conversion efficiency of a solar cell can be increased by using a fibrous carbon nanostructure in which the t-plot shows an upwardly convex shape.

Then, in the electrode for a solar cell of the present invention, the amount of the fibrous carbon nanostructure contained in the catalyst layer is preferably 0.1 mg / m ² or more and 20000 mg / m ² or less. If a catalyst layer having a fibrous carbon nanostructure content within the above range is used, the photoelectric conversion efficiency of the solar cell can be increased.

Here, in the electrode for a solar cell of the present invention, the catalyst layer is preferably formed by a screen printing method using a metal mask. By using the catalyst layer formed by the screen printing method using a metal mask, the durability of the solar cell can be further improved.

Further, the present invention aims to advantageously solve the above-mentioned problems, and the solar cell of the present invention includes two electrodes facing each other, and at least one of the two electrodes is any of the above-mentioned ones. It is characterized by being an electrode for a solar cell. A solar cell provided with any of the above-mentioned electrodes for a solar cell has excellent durability and maintains excellent photoelectric conversion efficiency for a long period of time.

Here, in the solar cell of the present invention, the distance between the supports of the two electrodes is preferably 70 μm or less. When the distance between the supports is 70 μm or less, the durability of the solar cell can be further improved.

Further, the present invention aims to advantageously solve the above problems, and the method for producing an electrode for a solar cell of the present invention uses a dispersion liquid containing fibrous carbon nanostructures and a metal mask. It is characterized by including a step of applying it on a support by a screen printing method, and a step of drying a dispersion liquid containing the applied fibrous carbon nanostructures to form a catalyst layer. Through the above steps, it is possible to efficiently manufacture an electrode for a solar cell capable of increasing the durability of the solar cell.

According to the present invention, it is possible to provide an electrode for a solar cell capable of increasing the durability of the solar cell.
Further, according to the present invention, it is possible to provide a solar cell having excellent durability.
According to the present invention, it is possible to provide a method for manufacturing a solar cell electrode, which can manufacture a solar cell electrode capable of increasing the durability of the solar cell.

It is a graph which shows an example of the t-plot of the sample which has pores on the surface. It is a figure which shows the schematic structure of an example of a dye-sensitized solar cell.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the electrode for a solar cell of the present invention has flexibility, and is a solar cell, preferably an organic solar cell such as a dye-sensitized solar cell, or an organic-inorganic hybrid solar cell such as a perovskite type solar cell. It can be suitably used as an electrode. Further, the electrode for a solar cell of the present invention can be manufactured by using, for example, the method for manufacturing an electrode for a solar cell of the present invention. The solar cell of the present invention is characterized by including the electrode for the solar cell of the present invention.

(Electrodes for solar cells)
The electrode for a solar cell of the present invention includes a support and a catalyst layer formed on the support, and the average value of the thickness of the catalyst layer is 0.5 μm or more and 3.0 μm or less, and the thickness of the catalyst layer. The standard deviation of is 0.2 μm or less. In the catalyst layer having such a predetermined thickness and having a standard deviation of the thickness of a predetermined value or less, the layer thickness unevenness is sufficiently small. Therefore, if an electrode having this catalyst layer is used, it is possible to prevent a partial short circuit caused by, for example, a portion having a convex thickness coming into contact with the other electrode (optical electrode or the like) side inside the solar cell. In particular, when a film is used as a support, when a load is applied to the battery cell, the distance between the electrodes becomes narrow and a short circuit is likely to occur. However, even in such a case, if the electrode for a solar cell of the present invention provided with the catalyst layer having a sufficiently small layer thickness unevenness as described above is used, a short circuit of the electrode can be sufficiently prevented. Therefore, if an electrode provided with such a catalyst layer is used, it is possible to impart excellent durability to the solar cell and exhibit excellent photoelectric conversion efficiency over a long period of time.

<Support>
The support plays a role of supporting the catalyst layer. In the present invention, a conductive film is not always required between the support and the catalyst layer, but at least in contact with the catalyst layer from the viewpoint of ensuring better energization and increasing the photoelectric conversion efficiency of the solar cell. It is preferable that a conductive film is formed on the surface portion of the support.
As such a support, a conductive sheet formed of a metal, a metal oxide, a carbon material, a conductive polymer, or the like, or a non-conductive sheet made of resin or glass is used. Among them, since a solar cell that is lightweight and has excellent photoelectric conversion efficiency can be efficiently formed, a non-conductive sheet made of resin or glass is preferable as the support, and the support is lightweight and excellent in photoelectric conversion efficiency. , A transparent resin is more preferable because an inexpensive solar cell can be easily obtained.
Examples of the transparent resin used include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PAr), and polysulfone (PSF). Examples thereof include synthetic resins such as polyester sulfone (PES), polyetherimide (PEI), and transparent polyimide (PI). These may be used alone or in combination of two or more.

The conductive film includes metals such as platinum, gold, silver, copper, aluminum, indium and titanium; conductive metal oxides such as tin oxide and zinc oxide; indium-tin oxide (ITO) and indium-zinc oxide. Examples thereof include composite metal oxides such as (IZO); carbon materials such as graphene; and combinations of two or more of these;

The surface resistance value of the conductive film is preferably 500 Ω / □ or less, more preferably 150 Ω / □ or less, and further preferably 50 Ω / □ or less.
The conductive film can be formed by a known method such as a sputtering method or a coating method.

The thickness of the support may be appropriately determined depending on the intended use, but is usually 10 μm or more and 10000 μm or less.
The light transmittance (measurement wavelength: 500 nm) of the support is preferably 60% or more, more preferably 75% or more, still more preferably 80% or more. When the light transmittance of the support is 60% or more, a solar cell having excellent photoelectric conversion efficiency can be obtained.

<Catalyst layer>
The catalyst layer is a layer responsible for electron transfer between electrodes, and for example, in a dye-sensitized solar cell, it functions as a catalyst when electrons are transferred from the counter electrode to the electrolyte layer. Such a catalyst layer usually contains catalyst components such as conductive polymers, carbon materials, and noble metals. These may be used individually by 1 type or in combination of 2 or more types. For example, a carbon material such as carbon black or carbon nanotubes on which a precious metal such as platinum is supported can also be used.
Examples of the conductive polymer include poly (thiophene-2,5-diyl), poly (3-butylthiophene-2,5-diyl), poly (3-hexylthiophene-2,5-diyl), and poly (3-hexylthiophen-2,5-diyl). Polythiophenes such as 2,3-dihydrothieno- [3,4-b] -1,4-dioxin) (PEDOT); polyacetylenes and their derivatives; polyaniline and its derivatives; polypyrol and its derivatives; poly (p-xylenetetrahydrothiofe) Nium chloride), poly [(2-methoxy-5- (2'-ethylhexyloxy))-1,4-phenylene vinylene], poly [(2-methoxy-5- (3', 7', 7'-dimethyloctyloxy)). ) -1,4-phenylene vinylene)], poly-phenylene vinylenes such as poly [2-2', 5'-bis (2''-ethylhexyloxy) phenyl] -1,4-phenylene vinylene]; Can be done.
Examples of the carbon material include natural graphite, activated carbon, artificial graphite, graphene, carbon nanotubes (CNT), carbon nanobuds, vapor-grown carbon fibers, and a tape-like portion in which the inner walls are close to each other or adhered to each other over the entire length. Examples thereof include graphene nanotapes (hereinafter, may be referred to as “GNT”, which will be described in detail later), which are single-walled or multi-layered flat tubular fibrous carbon nanostructures. In the present invention, "having a tape-shaped portion over the entire length" means "continuously over 60%, preferably 80% or more, more preferably 100% of the length (overall length) in the longitudinal direction". Or it has a tape-like part intermittently. "
The noble metal is not particularly limited as long as it has a catalytic action, such as a thin film formed by sputtering or the like, a colloid, a noble metal complex, a noble metal particle, or the like, and a known noble metal can be appropriately selected and used. The shape is not particularly limited, for example, a thin film formed by sputtering, a spherical shape such as a colloid, a rod shape, or a plate shape. For example, platinum, palladium and ruthenium can be mentioned. Sputtering and precious metal particles are preferable.

[Fibrous carbon nanostructures]
Among the above-mentioned catalyst components, the catalyst layer is a fibrous carbon nanostructure from the viewpoint of ease of handling during screen printing, drying, and storage, from the viewpoint of productivity, and from the viewpoint of further enhancing the durability of the solar cell. It is preferable to include it. The catalyst layer containing the fibrous carbon nanostructures can also function as a conductive layer.
Among the fibrous carbon nanostructures, it is preferable to use fibrous carbon nanostructures containing CNTs. The use of fibrous carbon nanostructures containing CNTs can further enhance the durability of the solar cell.

The fibrous carbon nanostructures containing CNTs are not particularly limited, and those consisting of CNTs alone may be used, or a mixture of CNTs and fibrous carbon nanostructures other than CNTs may be used. You may.

Further, as the fibrous carbon nanostructure, from the viewpoint of increasing the photoelectric conversion efficiency of the solar cell, it is preferable that the t-plot obtained from the adsorption isotherm shows an upward convex shape.
Here, in general, adsorption is a phenomenon in which gas molecules are removed from the gas phase to the solid surface, and is classified into physical adsorption and chemisorption according to the cause. Then, in the nitrogen gas adsorption method used for acquiring the t-plot, physical adsorption is used. Normally, if the adsorption temperature is constant, the number of nitrogen gas molecules adsorbed on the fibrous carbon nanostructure increases as the pressure increases. The horizontal axis plots the relative pressure (the ratio of the pressure P in the adsorption equilibrium state to the saturated vapor pressure P0), and the vertical axis plots the amount of nitrogen gas adsorbed. The case where the amount is measured is called "adsorption isotherm", and the case where the amount of nitrogen gas adsorbed while reducing the pressure is called "desorption isotherm".
Then, the t-plot is obtained by converting the relative pressure into the average thickness t (nm) of the nitrogen gas adsorption layer in the adsorption isotherm measured by the nitrogen gas adsorption method. That is, the above conversion is performed by obtaining the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure from a known standard isotherm obtained by plotting the average thickness t of the nitrogen gas adsorption layer with respect to the relative pressure P / P0. Provides a t-plot of fibrous carbon nanostructures (t-plot method by de Boer et al.).

Here, a typical t-plot of a sample having pores on its surface is shown in FIG. In a sample having pores on the surface, the growth of the nitrogen gas adsorption layer is classified into the following processes (1) to (3). Then, as shown in FIG. 1, the slope of the t-plot changes due to the following processes (1) to (3).
(1) Single-molecule adsorption layer formation process of nitrogen molecules on the entire surface (2) Multi-molecule adsorption layer formation and accompanying capillary condensation and filling process in the pores (3) Apparently the pores are filled with nitrogen Process of forming a multi-molecule adsorption layer on a non-porous surface

Then, in the t-plot of the suitable fibrous carbon nanostructure used in the present invention, as shown in FIG. 1, the plot is located on a straight line passing through the origin in the region where the average thickness t of the nitrogen gas adsorption layer is small. On the other hand, when t becomes large, the plot is positioned downward from the straight line and shows an upwardly convex shape. The shape of the t-plot is that the ratio of the internal specific surface area to the total specific surface area of the fibrous carbon nanostructures is large, and a large number of openings are formed in the carbon nanostructures constituting the fibrous carbon nanostructures. As a result, it is inferred that the fibrous carbon nanostructures exhibit excellent properties.

The bending point of the t-plot of the fibrous carbon nanostructure is preferably in the range satisfying 0.2 ≦ t (nm) ≦ 1.5, and 0.45 ≦ t (nm) ≦ 1.5. It is more preferably in the range satisfying, and further preferably in the range satisfying 0.55 ≦ t (nm) ≦ 1.0. When the position of the bending point of the t-plot is in the above range, the characteristics of the fibrous carbon nanostructures are further improved, so that the durability of the solar cell can be further improved.
Here, the "position of the bending point" is an intersection of the approximate straight line A of the process of (1) described above and the approximate straight line B of the process of (3) described above.

Further, in the fibrous carbon nanostructure, the ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from the t-plot is preferably 0.05 or more and 0.30 or less. When S2 / S1 is 0.05 or more and 0.30 or less, the characteristics of the fibrous carbon nanostructure can be further improved while sufficiently suppressing the formation of the bundle, so that the durability of the solar cell is further improved. Can be enhanced.
The total specific surface area S1 and the internal specific surface area S2 of the fibrous carbon nanostructure are not particularly limited, but individually, S1 is ^{preferably 600 m 2} / g or more and 1400 m ² / g or less, and 800 m ^{2 or less.} It is more preferably / g or more and 1200 m ² / g or less. On the other hand, S2 is ^{preferably 30 m 2} / g or more and 540 m ² / g or less.
Here, the total specific surface area S1 and the internal specific surface area S2 of the fibrous carbon nanostructure can be obtained from the t-plot. Specifically, to explain by the t-plot shown in FIG. 1, first, the total specific surface area S1 is obtained from the slope of the approximate straight line in the process (1), and the external specific surface area S3 is obtained from the slope of the approximate straight line in the process (3). Can be obtained respectively. Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

Incidentally, the measurement of the adsorption isotherm of the fibrous carbon nanostructure, the creation of the t-plot, and the calculation of the total specific surface area S1 and the internal specific surface area S2 based on the analysis of the t-plot can be performed by, for example, a commercially available measuring device. "BELSORP (registered trademark) -mini" (manufactured by Nippon Bell Co., Ltd.) can be used.

When a fibrous carbon nanostructure containing CNT is used, the CNT in the fibrous carbon nanostructure is not particularly limited, and single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used. However, the CNTs are preferably single-walled to five-walled carbon nanotubes, and more preferably single-walled carbon nanotubes. When single-walled carbon nanotubes are used, the durability of the solar cell can be further improved as compared with the case where multi-walled carbon nanotubes are used.

It is more preferable that the fibrous carbon nanostructures containing CNTs are not subjected to CNT opening treatment, and the t-plot shows an upwardly convex shape.

Further, as the fibrous carbon nanostructure, the ratio (3σ / Av) of the value (3σ) obtained by multiplying the standard deviation (σ) of the diameter by 3 with respect to the average diameter (Av) is more than 0.20 and less than 0.60. It is preferable to use the fibrous carbon nanostructures of the above, and it is more preferable to use the fibrous carbon nanostructures having a 3σ / Av of more than 0.25, and the fibrous carbon nanostructures having a 3σ / Av of more than 0.40. Is more preferable to use. If a fibrous carbon nanostructure having a 3σ / Av of more than 0.20 and less than 0.60 is used, the durability of the solar cell can be further improved.
The "average diameter of the fibrous carbon nanostructures (Av)" and the "standard deviation of the diameters of the fibrous carbon nanostructures (σ: sample standard deviation)" were randomly selected using a transmission electron microscope, respectively. It can be obtained by measuring the diameter (outer diameter) of 100 fibrous carbon nanostructures selected in 1. The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures may be adjusted by changing the manufacturing method and manufacturing conditions of the fibrous carbon nanostructures, or may be obtained by different manufacturing methods. It may be adjusted by combining a plurality of types of the obtained fibrous carbon nanostructures.

As the fibrous carbon nanostructures, those measured as described above are usually plotted with the diameter measured on the horizontal axis and the frequency on the vertical axis, and when approximated by Gaussian, a normal distribution is usually used. Will be done.

Further, the fibrous carbon nanostructures preferably have a Radial Breathing Mode (RBM) peak when evaluated using Raman spectroscopy. RBM does not exist in the Raman spectrum of the fibrous carbon nanostructure composed of only three or more layers of multi-walled carbon nanotubes.

Further, the fibrous carbon nanostructure preferably has a ratio (G / D ratio) of G band peak intensity to D band peak intensity in the Raman spectrum of 1 or more and 20 or less. When the G / D ratio is 1 or more and 20 or less, the durability of the solar cell can be further improved.

Further, the average diameter (Av) of the fibrous carbon nanostructures is preferably 2 nm or more, more preferably 2.5 nm or more, more preferably 10 nm or less, and further preferably 6 nm or less. preferable. When the average diameter (Av) of the fibrous carbon nanostructure is 2 nm or more and 10 nm or less, the durability of the solar cell can be further improved.

Further, the fibrous carbon nanostructure preferably has an average length of 100 μm or more at the time of synthesis. The longer the length of the structure at the time of synthesis, the more easily the fibrous carbon nanostructure is damaged such as breakage or cutting at the time of dispersion. Therefore, the average length of the structure at the time of synthesis should be 5000 μm or less. Is preferable.
The aspect ratio (length / diameter) of the fibrous carbon nanostructures preferably exceeds 10. For the aspect ratio of the fibrous carbon nanostructures, the diameter and length of 100 fibrous carbon nanostructures randomly selected using a transmission electron microscope were measured, and the ratio (length) of the diameter to the length was measured. It can be obtained by calculating the average value of (aspect ratio / diameter).

Further, the fibrous carbon nanostructures preferably have a plurality of micropores. The fibrous carbon nanostructure preferably has micropores having a pore diameter smaller than 2 nm, and the abundance thereof is the micropore volume determined by the following method, preferably 0.40 mL / g or more. It is preferably 0.43 mL / g or more, more preferably 0.45 mL / g or more, and the upper limit is usually about 0.65 mL / g. When the fibrous carbon nanostructure has the above-mentioned micropores, the durability of the solar cell can be further enhanced. The micropore volume can be adjusted, for example, by appropriately changing the preparation method and preparation conditions of the fibrous carbon nanostructure.
Here, the "micropore volume (Vp)" is the nitrogen adsorption amount at a relative pressure P / P0 = 0.19 by measuring the nitrogen adsorption / desorption isotherm at the liquid nitrogen temperature (77K) of the fibrous carbon nanostructure. Let V be, and it can be calculated from the formula (I): Vp = (V / 22414) × (M / ρ). In addition, P is the measured pressure at the time of adsorption equilibrium, P0 is the saturated vapor pressure of liquid nitrogen at the time of measurement, and in the formula (I), M is the molecular weight of the adsorbent (nitrogen) 28.010 and ρ is the adsorbent (nitrogen). ) Has a density of 0.808 g / cm ³ at 77 K. The micropore volume can be determined using, for example, "BELSORP (registered trademark) -mini" (manufactured by Nippon Bell Co., Ltd.).

The fibrous carbon nanostructure having the above-mentioned properties and containing CNT that can be suitably used as the fibrous carbon nanostructure used for the catalyst layer is, for example, a catalyst layer for producing carbon nanotubes (for producing CNT). When a raw material compound and a carrier gas are supplied onto a substrate having a catalyst layer on the surface to synthesize CNTs by a chemical vapor phase growth method (CVD method), a trace amount of oxidizing agent (catalyst activation) is introduced into the system. In the method of dramatically improving the catalytic activity of the catalyst layer for CNT production by the presence of the substance) (super growth method; see International Publication No. 2006/011655), the catalyst layer for CNT production on the surface of the substrate. Is formed by a wet process, so that it can be efficiently produced. In the following, the carbon nanotubes obtained by the super growth method may be referred to as "SGCNT".

The fibrous carbon nanostructures produced by the super growth method may be composed of only SGCNTs, or may be composed of SGCNTs and non-cylindrical carbon nanostructures having conductivity. .. Specifically, the fibrous carbon nanostructure includes a single-layer or multi-layered flat tubular carbon nanostructure (GNT described above) having a tape-like portion in which inner walls are close to each other or adhered to each other over the entire length. It may be.

Here, it is presumed that GNT is a substance in which a tape-like portion in which the inner walls are close to each other or adhered to each other is formed over the entire length from the time of its synthesis, and a six-membered ring network of carbon is formed in a flat tubular shape. NS. The fact that the GNT has a flat tubular shape and that there is a tape-shaped portion in the GNT in which the inner walls are close to each other or adhered to each other means that, for example, the GNT and the fullerene (C60) are sealed in a quartz tube. When the fullerene-inserted GNT obtained by heat treatment (fullerene insertion treatment) under reduced pressure is observed with a transmission electron microscope (TEM), there is a part (tape-like part) in the GNT where the fullerene is not inserted. You can check.

The shape of the GNT is preferably a shape having a tape-shaped portion in the central portion in the width direction, and the shape of the cross section orthogonal to the extending direction (axial direction) is the cross-sectional length in the vicinity of both ends in the cross-sectional longitudinal direction. It is more preferable that the maximum dimension in the direction orthogonal to the direction is larger than the maximum dimension in the direction orthogonal to the longitudinal direction of the cross section in the vicinity of the central portion in the longitudinal direction of the cross section, and the shape is particularly dumbbell-shaped. preferable.
Here, in the cross-sectional shape of the GNT, "near the central portion in the longitudinal direction of the cross section" means the width in the longitudinal direction of the cross section from the longitudinal center line of the cross section (a straight line passing through the center of the longitudinal direction of the cross section and orthogonal to the longitudinal line). The region within 30% of the above, and the "near the end portion in the longitudinal direction of the cross section" means the region outside the longitudinal direction of the "near the central portion in the longitudinal direction of the cross section".

The fibrous carbon nanostructure containing GNT as a non-cylindrical carbon nanostructure has a catalyst layer on the surface when CNT is synthesized by the super growth method using a base material having a catalyst layer on the surface. It can be obtained by forming a base material (hereinafter, may be referred to as "catalyst base material") by a predetermined method. Specifically, in the fibrous carbon nanostructure containing GNT, a coating liquid A containing an aluminum compound is applied onto a base material, and the applied coating liquid A is dried to form an aluminum thin film (catalyst) on the base material. After forming the supporting layer), a coating liquid B containing an iron compound is applied onto the aluminum thin film, and the applied coating liquid B is dried at a temperature of 50 ° C. or lower to dry the coated coating liquid B on the aluminum thin film (catalyst layer). ) Can be obtained by synthesizing CNTs by the super growth method using the catalyst base material obtained by forming).

[Characteristics of catalyst layer]
When the catalyst layer contains fibrous carbon nanostructures, it has sufficient activity even if it does not contain metal. Therefore, the catalyst layer may not necessarily contain a metal, but may contain a fibrous carbon nanostructure carrying a trace amount of nano-sized platinum or the like. In that case, improvement of the catalytic effect is expected. The metal can be supported on the fibrous carbon nanostructures such as carbon nanotubes according to a known method.

Here, the average value of the thickness of the catalyst layer needs to be 0.5 μm or more and 3.0 μm or less, preferably 1.0 μm or more, and more preferably 1.5 μm or more. It is preferably 5.5 μm or less. If the average thickness of the catalyst layer is less than 0.5 μm, the surface area of the catalyst layer is insufficient and the photoelectric conversion efficiency of the solar cell is lowered. On the other hand, if the average thickness of the catalyst layer exceeds 3.0 μm, the catalyst layer becomes brittle when the electrolytic solution is infiltrated, and the durability of the solar cell is lowered. Therefore, if the average value of the thickness of the catalyst layer is out of the above range, the photoelectric conversion efficiency and / or durability of the solar cell cannot be ensured.
Further, the standard deviation of the thickness of the catalyst layer needs to be 0.2 μm or less, and preferably 0.15 μm or less. If the standard deviation of the thickness of the catalyst layer exceeds 0.2 μm, the possibility of short-circuiting of the electrodes increases, and the durability of the solar cell cannot be ensured. The standard deviation of the thickness of the catalyst layer is usually 0.03 μm or more.
The difference between the maximum value and the minimum value of the thickness of the catalyst layer is preferably 50% or less, more preferably 40% or less, and more preferably 30% or less of the average value of the thickness of the catalyst layer. It is more preferably 20% or less, and particularly preferably 20% or less. When the difference between the maximum value and the minimum value of the thickness of the catalyst layer is 50% or less of the average value of the thickness, the possibility of short circuit can be further reduced and the durability of the solar cell can be further improved. The difference between the maximum value and the minimum value of the thickness of the catalyst layer is usually 1% or more of the average value of the thickness of the catalyst layer.
The "average value of the thickness of the catalyst layer", "standard deviation of the thickness of the catalyst layer (sample standard deviation)", and "difference between the maximum value and the minimum value of the thickness of the catalyst layer" are randomly selected for the catalyst layer. It can be obtained by measuring the thickness of 100 selected points.

The amount of the fibrous carbon nanostructure contained in the catalyst layer ^{is preferably 0.1 mg / m 2} or more, more preferably 1 mg / m ² or more, and 20000 mg / m ² or less. It is preferably 5000 mg / m ² or less, and more preferably 5000 mg / m 2. If a catalyst layer having a fibrous carbon nanostructure content within the above range is used, the photoelectric conversion efficiency of the solar cell can be increased.

<Manufacturing method of electrodes for solar cells>
The method for producing the electrode for a solar cell of the present invention is not particularly limited. For example, a solar cell electrode containing a fibrous carbon nanostructure in a catalyst layer has a step of applying a dispersion liquid containing the fibrous carbon nanostructure on a support (coating step) and a step of applying the fibrous carbon nanostructure. It can be produced through a step of drying a dispersion liquid containing a body to form a catalyst layer (catalyst layer forming step).

[Dispersion containing fibrous carbon nanostructures]
The dispersion containing the fibrous carbon nanostructures (fibrous carbon nanostructures dispersion) uses a known dispersion treatment method, preferably in the presence of a dispersant, in which the fibrous carbon nanostructures are placed in a solvent. It can be prepared by dispersing. Above all, from the viewpoint of satisfactorily dispersing the fibrous carbon nanostructures and satisfactorily forming the catalyst layer by using the fibrous carbon nanostructures dispersion liquid having excellent dispersibility, the fibrous carbon nanostructures and the fibrous carbon nanostructures are contained in the solvent. It is preferable that the crude dispersion liquid to which a dispersant is optionally added is subjected to a dispersion treatment for obtaining a cavitation effect or a crushing effect to prepare a fibrous carbon nanostructure dispersion liquid.

− Solvent −
Here, the solvent of the fibrous carbon nanostructure dispersion liquid (dispersion medium of the fibrous carbon nanostructure) is not particularly limited, and is, for example, water, methanol, ethanol, n-propanol, isopropanol, n-. Alcohols such as butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, diethyl Ethers such as ether, dioxane and tetrahydrofuran, amide-based polar organic solvents such as N, N-dimethylformamide and N-methylpyrrolidone, aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene and paradichlorobenzene Can be mentioned. Only one type of these may be used alone, or two or more types may be used in combination.

-Dispersant-
Further, the dispersant used for preparing the fibrous carbon nanostructure dispersion liquid is particularly limited as long as the fibrous carbon nanostructures can be dispersed and dissolved in a solvent for dispersing the fibrous carbon nanostructures. Surfactants such as anionic, nonionic, cationic, and betaine-based surfactants, synthetic polymers, or natural polymers can be used without this.

Examples of the surfactant include sodium dodecylsulfonate, sodium deoxycholate, sodium cholic acid, sodium dodecylbenzenesulfonate and the like.
Examples of the synthetic polymer include polyether diol, polyester diol, polycarbonate diol, polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, acetal group-modified polyvinyl alcohol, butyral group-modified polyvinyl alcohol, and silanol group-modified. Polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl alcohol-vinyl acetate copolymer resin, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, acrylic resin, epoxy resin, modified epoxy resin, phenoxy resin, modified phenoxy Examples thereof include resins, phenoxy ether resins, phenoxy ester resins, fluororesins, melamine resins, alkyd resins, phenol resins, polyacrylamides, polyacrylic acids, polystyrene sulfonic acids, polyethylene glycols, polyvinylpyrrolidones and the like.
Further, as natural polymers, for example, polysaccharides starch, pullulan, dextran, dextrin, guar gum, xanthan gum, amylose, amylopectin, alginic acid, arabic gum, carrageenan, chondroitin sulfate, hyaluronic acid, curdlan, chitin, chitosan, etc. Examples include cellulose and its salts or derivatives.
These dispersants can be used alone or in admixture of two or more. The dispersant is not particularly limited, but usually 10 to 2000 parts by mass can be used with respect to 100 parts by mass of the fibrous carbon nanostructure.

-Coarse dispersion-
The crude dispersion liquid is not particularly limited, and can be obtained by mixing the above-mentioned fibrous carbon nanostructure, the above-mentioned dispersant used arbitrarily, and the above-mentioned solvent by a known method. The fibrous carbon nanostructure, the dispersant, and the solvent can be mixed in any order. For example, the fibrous carbon nanostructure, the dispersant, and the solvent may be mixed at the same time. Then, the fibrous carbon nanostructures may be added to the mixed solution of the dispersant and the solvent and mixed. Further, in addition to the above-mentioned components, an additive generally used for producing a fibrous carbon nanostructure dispersion liquid and a molded product may be further added to the crude dispersion liquid. Additives include hardeners, antioxidants, heat stabilizers, light stabilizers, UV absorbers, pigments, fillers such as silica, colorants, foaming agents, antistatic agents, flame retardants, lubricants, softeners, etc. Examples thereof include antistatic agents, plasticizers, mold release agents, deodorants, and fragrances.

-Distributed processing that provides cavitation effect-
Here, the dispersion treatment for obtaining the cavitation effect is a dispersion method using a shock wave generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid. By using this dispersion method, the fibrous carbon nanostructures can be dispersed well.

Specific examples of the dispersion treatment for obtaining the cavitation effect include dispersion treatment by ultrasonic waves, dispersion treatment by jet mill, and dispersion treatment by high shear stirring. Only one of these distributed processes may be performed, or a plurality of distributed processes may be combined. More specifically, for example, an ultrasonic homogenizer, a jet mill and a high shear agitator are preferably used. As these devices, conventionally known devices may be used.

When an ultrasonic homogenizer is used to disperse the fibrous carbon nanostructures, the crude dispersion liquid may be irradiated with ultrasonic waves by the ultrasonic homogenizer. The irradiation time may be appropriately set depending on the amount of the fibrous carbon nanostructures and the like. For example, 3 minutes or more is preferable, 30 minutes or more is more preferable, 5 hours or less is preferable, and 2 hours or less is more preferable. .. Further, for example, the output is preferably 20 W or more and 500 W or less, more preferably 100 W or more and 500 W or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

When a jet mill is used, the number of treatments may be appropriately set depending on the amount of the fibrous carbon nanostructures and the like. For example, 2 times or more is preferable, 100 times or less is preferable, and 50 times or less is more preferable. Further, for example, the pressure is preferably 20 MPa or more and 250 MPa or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

Further, when high shear stirring is used, stirring and shearing may be added to the crude dispersion liquid by a high shear stirring device. The faster the turning speed, the better. For example, the operating time (the time during which the machine is rotating) is preferably 3 minutes or more and 4 hours or less, the peripheral speed is preferably 5 m / sec or more and 50 m / sec or less, and the temperature is preferably 15 ° C. or more and 50 ° C. or less.

The dispersion treatment for obtaining the above-mentioned cavitation effect is more preferably performed at a temperature of 50 ° C. or lower. This is because the change in concentration due to the volatilization of the solvent is suppressed.

-Dispersion treatment that provides crushing effect-
Further, in the dispersion treatment for obtaining the crushing effect, the fibrous carbon nanostructures can be uniformly dispersed in the solvent, and of course, compared with the dispersion treatment for obtaining the cavitation effect described above, the fibers due to the shock wave when the bubbles disappear. It is advantageous in that damage to the state carbon nanostructures can be suppressed.

In the dispersion treatment to obtain this crushing effect, a shearing force is applied to the crude dispersion liquid to crush and disperse the aggregates of the fibrous carbon nanostructures, and further, a back pressure is applied to the coarse dispersion liquid, and it is necessary. Therefore, by cooling the crude dispersion liquid, the fibrous carbon nanostructures can be uniformly dispersed in the solvent while suppressing the generation of bubbles.
When the back pressure is applied to the crude dispersion liquid, the back pressure applied to the crude dispersion liquid may be lowered to atmospheric pressure at once, but it is preferable to lower the pressure in multiple steps.

Here, in order to further disperse the fibrous carbon nanostructures by applying a shearing force to the crude dispersion liquid, for example, a dispersion system having a disperser having the following structure may be used.
That is, the disperser has a disperser orifice having an inner diameter of d1, a dispersion space having an inner diameter of d2, and a terminal portion having an inner diameter of d3 from the inflow side to the outflow side of the crude dispersion liquid (however, d2>d3>. d1), are sequentially provided.
Then, in this disperser, the inflowing high-pressure (for example, 10 to 400 MPa, preferably 50 to 250 MPa) coarse dispersion liquid passes through the disperser orifice to become a fluid having a high flow velocity while reducing the pressure. Inflow into the dispersed space. After that, the high-velocity coarse dispersion liquid that has flowed into the dispersion space flows at high speed in the dispersion space, and receives a shearing force at that time. As a result, the flow velocity of the crude dispersion liquid is reduced, and the fibrous carbon nanostructures are well dispersed. Then, a fluid having a pressure (back pressure) lower than the pressure of the inflowing crude dispersion liquid flows out from the terminal portion as a dispersion liquid of the fibrous carbon nanostructures.

The back pressure of the coarse dispersion liquid can be applied to the crude dispersion liquid by applying a load to the flow of the coarse dispersion liquid. The desired back pressure can be applied to the dispersion.
Then, by lowering the back pressure of the crude dispersion in multiple steps with a multi-step step-down device, bubbles are generated in the dispersion when the dispersion of the fibrous carbon nanostructure is finally released to atmospheric pressure. Can be suppressed.

Further, the disperser may include a heat exchanger for cooling the crude dispersion liquid and a coolant supply mechanism. This is because the generation of bubbles in the coarse dispersion can be further suppressed by cooling the crude dispersion which has become hot due to the shearing force applied by the disperser.
It should be noted that the generation of bubbles in the solvent containing the fibrous carbon nanostructures can be suppressed by pre-cooling the crude dispersion liquid instead of arranging the heat exchanger or the like.

As described above, in the dispersion treatment that obtains this crushing effect, the occurrence of cavitation can be suppressed, so that damage to the fibrous carbon nanostructures due to cavitation, which is sometimes a concern, especially when bubbles disappear. Damage to the fibrous carbon nanostructures caused by shock waves can be suppressed. In addition, the fibrous carbon nanostructures can be uniformly and efficiently dispersed by suppressing the adhesion of bubbles to the fibrous carbon nanostructures and the energy loss due to the generation of the bubbles.

Examples of the distributed system having the above configuration include the product name "BERYU SYSTEM PRO" (manufactured by Bitsubu Co., Ltd.). Then, the dispersion processing in which the crushing effect can be obtained can be carried out by using such a dispersion system and appropriately controlling the dispersion conditions.

[Applying process]
The method of applying the fibrous carbon nanostructure dispersion obtained as described above onto the support is not particularly limited, and is, for example, a spin coating method, a dipping method, a roll coating method, a gravure coating method, or a knife. A coating method, an air knife coating method, a roll knife coating method, a die coating method, a screen printing method, a spray coating method, a gravure offset method, or the like can be used. Among these, the screen printing method is preferable from the viewpoint of obtaining a catalyst layer having less thickness unevenness (small value of standard deviation of thickness).

Then, in the screen printing method, it is preferable to use a metal mask. Here, as the metal mask, for example, a thin plate of stainless steel or nickel provided with an opening for defining the outer shape and the arrangement position of the catalyst layer can be used. The plate thickness of the metal mask can be set to a value equal to or larger than the thickness of the catalyst layer according to the desired thickness of the catalyst layer. Here, the difference between the thickness of the metal mask and the thickness of the catalyst layer usually corresponds to the difference between the thickness of the coating film before drying and the thickness of the catalyst layer obtained after drying.
The thickness of the metal mask is preferably 50 μm or more and 1000 μm or less. If the plate thickness of the metal mask is less than 50 μm, the durability of the metal mask itself is lowered. On the other hand, when the plate thickness of the metal mask exceeds 1000 μm, the amount of the fibrous carbon nanostructure dispersion liquid applied increases, so that the thickness of the central portion of the obtained catalyst layer decreases and the standard deviation value of the thickness tends to increase. There is. In addition, if a dent is formed in the central portion of the catalyst layer in this way, the battery performance (photoelectric conversion efficiency, etc.) of the solar cell deteriorates.
Further, it is preferable that the surface of the metal mask in contact with the support is surface-treated with a resin coating film, a silicon coating film, or the like. By using a metal mask subjected to such a surface treatment, bleeding of the catalyst layer can be reduced, and a catalyst layer having a small standard deviation value of the thickness can be produced.

In the screen printing method using a metal mask, specifically,
(1) First, a metal mask having an opening corresponding to the shape of the desired catalyst layer is placed on the support.
(2) Next, the fibrous carbon nanostructure dispersion liquid was supplied onto the surface of the placed metal mask, and the liquid was supplied.
(3) Then, the fibrous carbon nanostructure dispersion liquid is filled in the opening of the metal mask by moving the blade along the surface of the metal mask to which the fibrous carbon nanostructure dispersion liquid is supplied.
By going through the steps (1) to (3) above, a thin coating film having a uniform thickness can be formed on the support. The moving speed of the blade on the surface of the metal mask is not particularly limited, but is, for example, 100 mm / sec or more and 1000 mm / sec or less.

[Catalyst layer formation step]
As a method for drying the coating film of the fibrous carbon nanostructure dispersion liquid formed on the support in the coating step, a known drying method can be adopted. Examples of the drying method include an air drying method, a hot air drying method, a vacuum drying method, and an infrared irradiation method. The drying temperature is not particularly limited, but is usually 25 ° C. or higher and 200 ° C. or lower, and the drying time is not particularly limited, but is usually 0.1 minutes or longer and 150 minutes or shorter.

(Solar cell)
The solar cell of the present invention is provided with two electrodes facing each other, and the above-described electrode for a solar cell of the present invention is used as at least one of the two electrodes. Since the solar cell of the present invention includes the electrode for the solar cell of the present invention, it has excellent durability and can exhibit excellent photoelectric conversion efficiency over a long period of time.
The distance between the supports of the two electrodes included in the solar cell is preferably 70 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. When the distance between the supports is 70 μm or less, the durability of the solar cell can be further improved. Here, the lower limit of the distance between the supports is not particularly limited, but is usually 10 μm or more.
The "distance between the supports of the two electrodes" can be obtained as the average value of these values by measuring the distance between the supports of the two electrodes at 10 randomly selected locations.
Hereinafter, the case where the solar cell is a dye-sensitized solar cell will be described as an example, but the present invention is not limited to the organic solar cell such as the dye-sensitized solar cell, and the present invention is not limited to the organic solar cell such as the perovskite type solar cell. It can also be applied to inorganic hybrid solar cells.

<Dye-sensitized solar cell>
FIG. 2 shows an example of a dye-sensitized solar cell as the solar cell of the present invention.
The dye-sensitized solar cell shown in FIG. 2 has a structure in which a light electrode (transparent electrode) 10, an electrolyte layer 20, and a counter electrode 30 are arranged in this order, and the counter electrode 30 is an electrode for a solar cell of the present invention. Is used. The arrows indicate the movement of electrons.

The optical electrode 10 includes an optical electrode substrate 10a, a porous semiconductor fine particle layer 10b formed on the optical electrode substrate 10a, and a sensitizing dye layer 10c formed by adsorbing a sensitizing dye on the surface of the porous semiconductor fine particle layer. Consists of.

The optical electrode substrate 10a plays a role of supporting the porous semiconductor fine particle layer 10b and the like and a role as a current collector.
The optical electrode substrate 10a includes, for example, a composite metal oxide such as indium-tin oxide (ITO) or indium-zinc oxide (IZO) on a support 10d made of a transparent resin or a glass sheet; fibrous. Examples thereof include those obtained by laminating a conductive film 10e made of a carbon material such as a carbon nanostructure or graphene; a metal material such as a silver nanowire or a metal mesh wiring;

The porous semiconductor fine particle layer 10b is a porous layer containing semiconductor fine particles. The porous layer increases the amount of sensitizing dye adsorbed, making it easier to obtain a dye-sensitized solar cell with high conversion efficiency.
Examples of the semiconductor fine particles include particles of metal oxides such as titanium oxide, zinc oxide, and tin oxide.
The particle size of the semiconductor fine particles (average particle size of the primary particles) is preferably 2 to 80 nm, more preferably 2 to 60 nm. The small particle size can reduce the resistance.
The thickness of the porous semiconductor fine particle layer is not particularly limited, but is usually 0.1 to 50 μm, preferably 5 to 30 μm.
The porous semiconductor fine particle layer can be formed by a known method such as a pressing method, a hydrothermal decomposition method, an electrophoretic electrodeposition method, or a binder-free coating method.

The sensitizing dye layer 10c is a layer in which a compound (sensitizing dye) that is excited by light and can transfer electrons to the porous semiconductor fine particle layer 10b is adsorbed on the surface of the porous semiconductor fine particle layer 10b.
Examples of the sensitizing dye include organic dyes such as cyanine dye, merocyanine dye, oxonor dye, xanthene dye, squarylium dye, polymethine dye, coumarin dye, riboflavin dye, and perylene dye; phthalocyanine complex of metal such as iron, copper, and ruthenium, and porphyrin. Metal complex dyes such as complexes; and the like.
The sensitizing dye layer 10c is a known method such as a method of immersing the porous semiconductor fine particle layer 10b in a solution of the sensitizing dye, a method of applying a solution of the sensitizing dye on the porous semiconductor fine particle layer 10b, and the like. Can be formed by

The optical electrode is not limited to the one shown in FIG. 2, and may be any electrode that can emit electrons to the external circuit 40 by receiving light, and a known optical electrode for a dye-sensitized solar cell is used. Can be used.

The electrolyte layer 20 is a layer for separating the light electrode 10 and the counter electrode 30 and efficiently transferring charges.
The electrolyte layer 20 usually contains a supporting electrolyte, a redox pair (a pair of chemical species that can be reversibly converted to each other in the form of an oxidant and a reduced form in the redox reaction), a solvent and the like.

Examples of the supporting electrolyte include salts containing cations such as lithium ion, imidazolium ion, and quaternary ammonium ion.

As the redox pair, known ones can be used as long as they can reduce the oxidized sensitizing dye. As redox pairs, chlorine compound-chlorine, iodine compound-iodine, bromine compound-bromine, tarium ion (III) -talium ion (I), ruthenium ion (III) -ruthenium ion (II), copper ion (II) -Copper ion (I), iron ion (III) -iron ion (II), cobalt ion (III) -cobalt ion (II), vanadium ion (III) -vanadium ion (II), manganate ion-permanganate Examples thereof include ions, ferricocyanide-ferrocyanide, quinone-hydroquinone, fumaric acid-succinic acid and the like.

As the solvent, a solvent known as a solvent for forming the electrolyte layer of the solar cell can be used. Examples of the solvent include acetonitrile, methoxyacetonitrile, methoxypropionitrile, N, N-dimethylformamide, ethylmethylimidazolium bistrifluoromethylsulfonylimide, propylene carbonate, γ-butyl lactone and the like.

The electrolyte layer 20 is formed by applying a solution (electrolyte solution) containing the constituent components on the light electrode 10, forming a cell having the light electrode 10 and the counter electrode 30, and injecting the electrolytic solution into the gap thereof. can do.

The counter electrode 30 is the electrode for a solar cell of the present invention, and is composed of a conductive film 30c formed on the support 30a and a catalyst layer 30b formed on the conductive film 30c. Further, the catalyst layer 30b can use the above-mentioned fibrous carbon nanostructure as a constituent material.

In the dye-sensitized solar cell shown in FIG. 2, light energy is converted into electrical energy by repeating the following cycle. That is, (i) when the sensitizing dye 10c is excited by receiving light, the electrons of the sensitizing dye 10c are taken out. (Ii) The electrons exit from the optical electrode 10 and move to the counter electrode 30 through the external circuit 40, and further move to the electrolyte layer 20 via the catalyst layer 30b. (Iii) The redox pair (reducing agent) contained in the electrolyte layer 20 reduces the sensitizing dye in the oxidized state, regenerates the sensitizing dye 10c, and returns to a state in which light can be absorbed again.

The dye-sensitized solar cell as the solar cell of the present invention is not limited to the one shown in FIG. 2, and is a functional layer such as a protective layer, an antireflection layer, and a gas barrier layer in addition to a light electrode, an electrolyte layer, and a counter electrode. May have.
Further, the solar cell of the present invention is not limited to one that uses the sun as a light source, and may be, for example, one that uses indoor lighting as a light source.

<Solar cell module>
By connecting the solar cells of the present invention in series and / or in parallel, a solar cell module can be obtained. Specifically, in the solar cell module, for example, the solar cells of the present invention are arranged in a plane or curved shape, a non-conductive partition wall is provided between the batteries, and the electrodes (optical electrodes and counter electrodes) of the batteries are provided. Can be obtained by electrically connecting using a conductive member.
The number of solar cells to be used is not particularly limited, and can be appropriately determined according to the target voltage.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. The physical properties were evaluated by the following method.

<Thickness of catalyst layer>
Using a laser displacement meter (LT-9500V, manufactured by KEYENCE), the difference in displacement (thickness of the catalyst layer) between the surface of the support and the catalyst layer at 100 randomly selected counter electrodes was measured to determine the thickness. The mean, standard deviation, and the difference between the maximum and minimum values were calculated.
<Distance between supports>
A multi-layer film thickness measuring instrument (SI-T80, manufactured by KEYENCE) was used to measure the distance between the supports of two electrodes (opposite electrode and optical electrode) in the solar cell at 10 randomly selected locations. The average value of these was calculated.
<Photoelectric conversion efficiency>
As a light source, a pseudo-sunlight irradiation device (PEC-L11 type, manufactured by Pexel Technologies Co., Ltd.) in which an AM1.5G filter was attached to a 150 W xenon lamp light source was used. The amount of light was adjusted to 1 sun (AM1.5G, 100mW / cm ² (JIS C8912 class A)). The produced dye-sensitized solar cell was connected to a source meter (2400 type source meter, manufactured by Keithley), and the following current-voltage characteristics were measured.
Under 1 sun light irradiation, the output current was measured while changing the bias voltage from 0 V to 0.8 V in units of 0.01 V. The output current was measured by integrating the values from 0.05 seconds to 0.15 seconds after changing the voltage in each voltage step. A measurement was also performed in which the bias voltage was changed from 0.8 V to 0 V in the reverse direction, and the average value of the measurements in the forward direction and the reverse direction was taken as the photocurrent.
The photoelectric conversion efficiency (%) was calculated from the above measurement results of the current-voltage characteristics and evaluated according to the following criteria.
A: Photoelectric conversion efficiency is 3.0% or more B: Photoelectric conversion efficiency is 2.5% or more and less than 3.0% C: Photoelectric conversion efficiency is less than 2.5% <Durability>
The prepared dye-sensitized solar cell was left in a constant temperature and humidity chamber (60 ° C., 60 RH%) for 2 days. Then, for the dye-sensitized solar cell after being left to stand, the photoelectric conversion efficiency (%) was calculated in the same manner as described above, and evaluated according to the following criteria.
A: Photoelectric conversion efficiency is 3.0% or more B: Photoelectric conversion efficiency is 2.0% or more and less than 3.0% C: Photoelectric conversion efficiency is less than 2.0%

(Example 1)
<Preparation of fibrous carbon nanostructures>
1.9 g of aluminum tri-sec-butoxide, which is an aluminum compound, was dissolved in 100 mL of 2-propanol as an organic solvent. Further, 0.9 g of triisopropanolamine was added as a stabilizer and dissolved to prepare a coating liquid A for forming a catalyst-supporting layer.
Further, 174 mg of iron acetate, which is an iron compound, was dissolved in 100 mL of 2-propanol as an organic solvent. Further, 190 mg of triisopropanolamine was added and dissolved as a stabilizer to prepare a coating liquid B for forming a catalyst layer.
On the surface of Fe-Cr alloy SUS430 substrate (manufactured by JFE Steel Corporation, 40 mm x 100 mm, thickness 0.3 mm, Cr 18%, arithmetic mean roughness Ra ≈ 0.59 μm) as a base material, room temperature 25 ° C., relative humidity The above-mentioned coating liquid A was applied by dip coating under a 50% environment. Specifically, after immersing the base material in the coating liquid A, the base material was held for 20 seconds, and the base material was pulled up at a pulling speed of 10 mm / sec. Then, it was air-dried for 5 minutes, heated for 30 minutes in an air environment at a temperature of 300 ° C., and then cooled to room temperature to form an alumina thin film (catalyst-supporting layer) having a film thickness of 40 nm on the substrate.
Next, the above-mentioned coating liquid B was applied by dip coating on the alumina thin film provided on the base material in an environment of room temperature of 25 ° C. and relative humidity of 50%. Specifically, after immersing the base material containing the alumina thin film in the coating liquid B, the base material containing the alumina thin film was held for 20 seconds, and the base material containing the alumina thin film was pulled up at a pulling speed of 3 mm / sec. Then, it was air-dried for 5 minutes, heated for 20 minutes under the condition of a temperature of 300 ° C., and then cooled to room temperature to form an iron thin film (catalyst layer for CNT production) having a film thickness of 3 nm. In this way, a catalyst base material having an alumina thin film and an iron thin film on the base material in this order was obtained.
The catalytic base fabricated, furnace temperature: 750 ° C., furnace pressure: installed in 1.02 × ¹⁰ 5 reactor of a CVD apparatus which is held in Pa, in the reactor, the He: 100 sccm and H ₂ : A mixed gas of 800 sccm was introduced for 10 minutes. Then, furnace temperature: 750 ° C., furnace pressure: the 1.02 × ¹⁰ 5 reactor held by the Pa, the He: 850 sccm, ethylene: 100 sccm and _{H 2} O containing He (23% relative humidity) : 50 sccm of mixed gas was supplied for 8 minutes.
Then, He: 1000 sccm was supplied into the reactor to eliminate the residual raw material gas and the catalyst activator. As a result, an aggregate of fibrous carbon nanostructures made of CNT was obtained on the catalyst base material. Then, the aggregate of the produced fibrous carbon nanostructures was peeled off from the catalyst base material to obtain a fibrous carbon nanostructure made of CNT.
When the obtained fibrous carbon nanostructures were evaluated and analyzed, the yield was 1.7 mg / cm ² , the G / D ratio was 4.5, and the carbon purity was 99.9%.
In addition, the t-plot of the fibrous carbon nanostructure was bent in an upwardly convex shape. Then, t the position of the bending point is 0.7 nm, total specific surface area S1 is a 1010 m ² / g, the internal specific surface area S2 are a 120m ² / g, S2 / S1 was 0.12. Further, the average diameter (Av) of the obtained fibrous carbon nanostructures was 3.3 nm, and the standard deviation (σ) of the diameter was 0.64 nm, and 3σ / Av was 0.58.
<Manufacturing of counter electrode>
To a 30 ml glass container, 5 g of water, 1 g of ethanol, and 0.0025 g of the fibrous carbon nanostructures described above were added.
The contents of this glass container were dispersed for 2 hours using a bath-type ultrasonic cleaner (5510J-MT (42 kHz, 180 W) manufactured by BRANSON) to obtain a fibrous carbon nanostructure dispersion. rice field.
Next, on the ITO surface of a polyethylene naphthalate film (ITO-PEN film, film thickness: 200 μm, ITO thickness: 200 nm, sheet resistance: 15 Ω / □) sputtered with indium-tin oxide (ITO) as a support. The above-mentioned fibrous carbon nanostructure dispersion liquid was applied to the film by a screen printing method using a metal mask. As the metal mask, a SUS mask having a plate thickness of 250 μm was used. As the blade, a SUS blade having a thickness of 0.5 mm was used, and coating was performed by sweeping at a speed of 500 mm / sec. The obtained coating film was dried at 100 ° C. for 30 minutes to form a catalyst layer to obtain a counter electrode. The thickness of the obtained catalyst layer was measured, and the average value, standard deviation, and difference between the maximum value and the minimum value were calculated. The results are shown in Table 1.
<Manufacturing of optical electrodes>
Binder-free oxidation on the ITO surface of a polyethylene naphthalate film (ITO-PEN film, film thickness 200 μm, ITO thickness 200 nm, sheet resistance 15 Ω / □) sputtered with indium-tin oxide (ITO) as a support. Titanium paste (PECC-C01-06, manufactured by Pexel Technologies) was applied using a baker-type applicator so as to have a coating thickness of 150 μm. The obtained coating film was dried at room temperature for 10 minutes and then heated and dried in a constant temperature layer at 150 ° C. for another 5 minutes to obtain a laminate composed of an ITO-PEN film and a porous semiconductor fine particle layer.
The laminate was cut into a size of 1.2 cm in width and 2.0 cm in length, and a porous semiconductor fine particle layer was formed into a circle having a diameter of 6 mm from the inside of the short side of the laminate by 2 mm. This is immersed in a sensitizing dye solution [sensitizing dye: ruthenium complex (N719, manufactured by Solaronics), solvent: acetonitrile, tert-butanol, concentration: 0.4 mM] at 40 ° C. for 2 hours to sensitize the dye. Was adsorbed on the porous semiconductor fine particle layer. After the dipping treatment, the laminate was washed with acetonitrile and dried to obtain a photoelectrode.
<Preparation of electrolyte>
Iodine 0.05 mol / L, lithium iodide 0.1 mol / L, t-butyl pyridine 0.5 mol / L, and 1,2-dimethyl-3-propylimidazolium iodide 0.6 mol / L. These were dissolved in methoxyacetonitrile to obtain an electrolytic solution.
<Manufacturing of dye-sensitized solar cells>
An alicyclic epoxy resin (manufactured by 3M, manufactured by 3M) on the optical electrode so as to form an electrolyte hole at a position corresponding to the porous semiconductor fine particle layer (titanium oxide layer) provided on the ITO-PEN film (optical electrode substrate). Scotch weld EW2050, curing temperature 120 ° C.) was placed.
Then, when the optical electrode and the counter electrode were bonded to each other on the lower substrate of the aluminum bonding jig, the light electrode having three of the four sides sealed with an alicyclic epoxy resin was placed. A counter electrode was placed on top of it.
Next, under vacuum, an electrolytic solution (PECE-G3 manufactured by Pexel Technologies Co., Ltd.) is filled from the portion where one of the four sides is vacant, and the remaining one of the four sides after filling is UV-cured. A sex resin (polyisobutylene type) was applied, irradiated with UV, cured, and sealed.
The battery performance of the obtained dye-sensitized solar cell was evaluated. The results are shown in Table 1.

(Example 2)
A counter electrode was produced in the same manner as in Example 1 except that the ITO-PEN film was changed to a PEN film (film thickness 200 μm), and the battery performance of the dye-sensitized solar cell obtained using the counter electrode was evaluated. .. The results are shown in Table 1.

(Comparative Example 1)
A counter electrode was prepared in the same manner as in Example 1 except that the fibrous carbon nanostructure dispersion was applied by a screen printing method using a mesh screen (mesh number: 32, gauze thickness: 460 μm). The battery performance of the dye-sensitized solar cell obtained using the above was evaluated. The results are shown in Table 1.

(Comparative Example 2)
A coating film obtained by applying a fibrous carbon nanostructure dispersion liquid to a coating thickness of 200 μm using a bar coater (manufactured by Tester Sangyo Co., Ltd., SA-203, No. 10) was applied at 100 ° C. for 2 The counter electrode was prepared by drying for a time. The battery performance of the dye-sensitized solar cell obtained by using this counter electrode was evaluated. The results are shown in Table 1.

(Comparative Example 3)
Examples except that the same fibrous carbon nanostructure dispersion liquid as in Example 1 was overlaid on the same portion as the catalyst layer of the counter electrode produced in Example 1 by a screen printing method using a metal mask. A counter electrode was produced in the same manner as in 1. The battery performance of the dye-sensitized solar cell obtained by using this counter electrode was evaluated. The results are shown in Table 1.

From Table 1, Examples 1 to 1 using a counter electrode having a catalyst layer having an average thickness of 0.5 μm or more and 3.0 μm or less and a standard deviation of thickness of 0.2 μm or less on the support. No. 2 is Comparative Examples 1 and 2 using a counter electrode having a catalyst layer having a standard deviation of thickness of more than 0.2 μm, and Comparative Example 2 using a counter electrode having a catalyst layer having an average thickness of more than 3.0 μm. It can be seen that the durability of the dye-sensitized solar cell is superior to that of 3.

According to the present invention, it is possible to provide an electrode for a solar cell capable of increasing the durability of the solar cell.
Further, according to the present invention, it is possible to provide a solar cell having excellent durability.
According to the present invention, it is possible to provide a method for manufacturing a solar cell electrode, which can manufacture a solar cell electrode capable of increasing the durability of the solar cell.

10 ... Optical electrode (transparent electrode)
10a ... Photoelectrode substrate 10b ... Porous semiconductor fine particle layer 10c ... Sensitive dye layer 10d ... Support 10e ... Conductive conductor 20 ... Electrolyte layer 30 ... Counter electrode 30a ...・ ・ Support 30b ・ ・ ・ Catalyst layer 30c ・ ・ ・ conductive film 40 ・ ・ ・ external circuit

Claims (7)

An electrode for a solar cell including a support and a catalyst layer formed on the support.
The average value of the thickness of the catalyst layer is at 0.5μm or 3.0μm or less state, and are standard deviation 0.2μm or less of the thickness of the catalyst layer,
The catalyst layer contains fibrous carbon nanostructures
The t-plot of the fibrous carbon nanostructures obtained from the adsorption isotherm shows an upwardly convex shape.
The bending point of the t-plot is in the range satisfying 0.2 ≦ t (nm) ≦ 1.5.
An electrode for a solar cell in which the ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from the t-plot is 0.05 or more and 0.30 or less. The electrode for a solar cell according to claim 1, wherein the difference between the maximum value and the minimum value of the thickness of the catalyst layer is 50% or less of the average value of the thickness of the catalyst layer. The electrode for a solar cell according to claim 1 or 2 , wherein the amount of the fibrous carbon nanostructure contained in the catalyst layer is 0.1 mg / m ² or more and 20000 mg / m ² or less. The electrode for a solar cell according to any one of claims 1 to 3 , wherein the catalyst layer is formed by using a screen printing method using a metal mask. A solar cell having two electrodes facing each other, wherein at least one of the two electrodes is the electrode for a solar cell according to any one of claims 1 to 4. The solar cell according to claim 5 , wherein the distance between the supports of the two electrodes is 70 μm or less. A process of applying a dispersion liquid containing fibrous carbon nanostructures onto a support by a screen printing method using a metal mask, and
A step of drying the dispersion liquid containing the applied fibrous carbon nanostructures to form a catalyst layer, and
The method for manufacturing an electrode for a solar cell according to any one of claims 1 to 3.

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