JP2011108465A - Dye-sensitized solar cell having visible light transmittance, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell which has a see-through appearance while applying a metal material to both of a photoelectrode and the counter electrode and has good manufacturability with a low cost. <P>SOLUTION: The dye-sensitized solar cell has a photoelectrode having a stainless steel sheet A with through holes as a current collector material and a counter electrode having a stainless steel sheet B with through holes as a conductive material opposed to each other through an electrolyte in a cell interposed between a pair of translucent plates. The stainless steel sheets A, B are made of a stainless steel containing Cr: 16 mass% and Mo: 0.3 mass%, and have the through holes of which the surface area ratio of the through hole part occupied in a projected area when the stainless steel sheet is viewed in thickness direction is 5-80% and the average diameter of the through hole part is 5-500 μm. The dye-sensitized solar cell has visible light transmittance. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell having visible light permeability using a conductive member made of stainless steel for both a photoelectrode and a counter electrode, and a method for producing the same.

  Conventionally, solar cells using mainly silicon as a photoelectric conversion element have been used, but the practical application of “dye-sensitized solar cells” has been studied as a more economical next-generation solar cell.

  FIG. 1 schematically shows the configuration of a general dye-sensitized solar cell. A translucent conductive film 3 is provided on the surface of the translucent plate-like body 2, and a porous semiconductor layer 4 carrying a sensitizing dye is formed on the surface of the translucent conductive film 3. A photoelectrode 10 is constituted by the translucent conductive film 3 and the porous semiconductor layer 4. The translucent conductive film 3 is composed of an oxide conductive film such as ITO (indium-tin oxide), FTO (fluorine-doped tin oxide), TO (tin oxide), ZnO (zinc oxide), and the like. The plate-like body 2 is made of glass or plastic film. A counter electrode 20 is disposed so as to face the photoelectrode 10, and the dye-sensitized solar cell 1 is configured by the photoelectrode 10, the counter electrode 20, and the electrolytic solution 8 interposed between the two electrodes. The counter electrode 20 is composed of a conductive material 6 and a catalyst layer 7 provided on the surface thereof. A substrate 5 for supporting the counter electrode 20 is provided as necessary.

The porous semiconductor layer 4 constituting the photoelectrode 10 is a porous layer using semiconductor particles such as TiO ₂ having a large specific surface area, and a sensitizing dye such as a ruthenium complex is supported on the surface of the semiconductor particles. In general, an electrolytic solution containing iodine (I ₂ ) and iodide ions is used. When the incident light 30 reaches the sensitizing dye supported on the porous semiconductor layer 4, the sensitizing dye (for example, ruthenium complex) is excited by absorbing light, and the electrons are converted into semiconductor particles (for example, TiO ₂ ). Injected. The sensitizing dye that is in an oxidized state by injecting excited electrons receives electrons from ions (for example, iodide ions I ⁻ ) in the electrolyte 8 and returns to the ground state. At this time, ions (for example, I ⁻ ) in the liquid are oxidized to ions having different valences (for example, I ₃ ⁻ ), diffuse to the counter electrode 20, receive electrons from the counter electrode 20, and receive original ions (for example, I ^−). Return to). As a result, electrons move along the path “porous semiconductor layer 4 → translucent conductive film 3 → load 40 → conductive material 6 → catalyst layer 7 → electrolytic solution 8 → porous semiconductor layer 4”. As a result, a current for operating the load 40 is generated.

  As the conductive material 6 constituting the counter electrode 20, a light-transmitting oxide conductive film such as ITO or FTO may be used in the same manner as the light-transmitting conductive film 3. In this case, when the catalyst layer 7 is a thin film layer having many pinholes, visible light can be transmitted through the counter electrode 20, so that the dye-sensitized solar cell 1 itself can have visible light transmittance. . That is, a so-called “see-through” appearance is obtained in which the opposite side can be seen through to some extent through the dye-sensitized solar cell 1. In a solar cell using silicon as a photoelectric conversion element, it is basically difficult to realize a solar panel exhibiting a see-through appearance, but in a dye-sensitized solar cell, this is possible. For this reason, dye-sensitized solar cells, for example, enable the installation of solar panels that take advantage of see-through properties (visible light transmission), such as the windows of buildings and the roofs of bicycle parking lots and parking lots. It is also expected to be used in the field. In addition, the dye-sensitized solar cell having see-through property has an advantage that incident light inserted from the counter electrode 20 side can also be used for power generation.

  In order to construct a cell of a dye-sensitized solar cell having such see-through property, it is necessary to configure both the photoelectrode and the counter electrode with a translucent member. In the conventional dye-sensitized solar cell using an oxide conductive film such as FTO as the light-transmitting conductive film 3 and the conductive material 6 in FIG. 1, both electrodes have a light-transmitting property, so that a see-through appearance is obtained. It was possible.

  However, since the light-transmitting oxide conductive film has low conductivity compared to the metal material, using such a light-transmitting conductive film for both electrodes increases the photoelectric conversion efficiency of the dye-sensitized solar cell. It is disadvantageous in improving. Further, since the catalyst layer 7 covers the surface of the conductive material 6, the visible light transmittance of the counter electrode 20 is weakened, and a desired see-through appearance may be difficult to obtain.

  On the other hand, a dye-sensitized solar cell using a stainless steel plate for either the photoelectrode or the counter electrode is known (Patent Document 4). In this type of dye-sensitized solar cell, the conductivity is improved as compared with the case where an oxide conductive film is used for both electrodes. However, see-through appearance cannot be obtained.

  Various techniques for utilizing a metal material as a current collecting member while ensuring the translucency of the photoelectrode have been proposed. In this case, a metal film (Patent Document 1), a grid (Patent Document 2), a metal wire (Patent Document 3), a stainless steel mesh (Non-Patent Document 1) provided with a large number of holes so as not to disturb the incidence of light as much as possible. ) Etc. apply. These methods are considered to be applicable not only to the photoelectrode but also to the counter electrode. However, a complicated process is required to form an electrode having a configuration as described in Patent Documents 1 to 3, which necessitates an increase in cost. Further, the stainless steel mesh is expensive because it is a woven fabric made of stainless steel fine wires, and cannot be easily adopted in order to promote the spread of dye-sensitized solar cells.

JP 2003-123858 A JP 2003-203682 A JP 2005-158726 A JP 2009-26532 A

Yoshikazu Yoshida et al. , APPLIED PHYSICS LETTERS 94,093301 (2009)

  The present invention is to provide a dye-sensitized solar cell that has a see-through appearance while applying a metal material to both a photoelectrode and a counter electrode, and that has good manufacturability and low cost.

  As a result of detailed studies, the inventors have used a stainless steel sheet having a large number of through holes as a current collecting material for a photoelectrode, and a stainless steel having a large number of through holes as a conductive material for a counter electrode. We have found that this can be achieved by using a sheet. It was also found that such a stainless steel sheet can be efficiently produced by etching in a ferric chloride aqueous solution.

That is, in the present invention,
In a cell sandwiched between a pair of translucent plates, a photosensitized solar cell in which a photoelectrode and a counter electrode face each other through an electrolyte,
The photoelectrode is obtained by integrating a stainless steel sheet A having a through hole and a porous semiconductor layer carrying a sensitizing dye, and the counter electrode is a catalyst layer on at least one surface of the stainless steel sheet B having a through hole. Is formed,
The stainless steel sheets A and B are made of stainless steel containing Cr: 16% by mass or more and Mo: 0.3% by mass or more, and the area of the penetrating portion in the projected area when the stainless steel sheet is viewed in the thickness direction. Provided is a dye-sensitized solar cell having visible light permeability, which has a through hole having a rate of 5 to 80% and an average diameter of the through part of 5 to 500 μm.
The through holes of the stainless steel sheet are preferably formed by immersing the rolled sheet in an aqueous electrolyte solution to grow pitting corrosion pits.

As standard steel types, the following steels are suitable for the stainless steel sheet.
[1] Steel that belongs to a ferritic steel type specified in JIS G4305: 2005, has a Cr content of 16 to 32 mass%, and a Mo content of 0.3 to 3 mass%.
[2] Steel that belongs to the austenitic steel grade specified in JIS G4305: 2005, has a Cr content in the range of 16 to 32 mass%, and a Mo content in the range of 0.3 to 7 mass%.
The stainless steel sheets A and B may be steel having the same composition or may be steel having different compositions. Further, either one of the stainless steel sheets A and B may be steel corresponding to the above [1], and the other may be steel corresponding to the above [2].

Specifically, when the content range of each element is shown, the following steels are suitable targets.
[3] By mass%: C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, P: 0.04% or less, S: 0.03% or less, Ni: 0.0 6% or less, Cr: 16 to 32%, Mo: 0.3 to 3%, Cu: 0 to 1%, Nb: 0 to 1%, Ti: 0 to 1%, Al: 0 to 0.2%, Ferritic stainless steel consisting of N: 0.025% or less, B: 0-0.01%, balance Fe and inevitable impurities.
[4] By mass% C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, P: 0.045% or less, S: 0.03% or less, Ni: 6 to 28% Cr: 16 to 32%, Mo: 0.3 to 7%, Cu: 0 to 3.5%, Nb: 0 to 1%, Ti: 0 to 1%, Al: 0 to 0.1%, N : Austenitic stainless steel consisting of 0.3% or less, B: 0 to 0.01%, balance Fe and inevitable impurities.
In this case, both the stainless steel sheets A and B may be steel corresponding to [3], or both may be steel corresponding to [4]. Further, either one of the stainless steel sheets A and B may be steel corresponding to the above [3], and the other may be steel corresponding to the above [4].

  The photoelectrode of the dye-sensitized solar cell of the present invention is preferably disposed so that the porous semiconductor layer faces the translucent plate.

Moreover, as a method for producing the dye-sensitized solar cell of the present invention as described above,
After obtaining a stainless steel sheet A having through holes by the following through hole forming method X, a porous semiconductor layer composed of an oxide semiconductor is formed on at least one side of the stainless steel sheet A, and then the porous semiconductor A step of preparing a photoelectrode by carrying a sensitizing dye in the layer (photoelectrode preparation step),
After obtaining a stainless steel sheet B having a through hole by the following through hole forming method X, a step of producing a counter electrode by forming a catalyst layer on at least one side of the stainless steel sheet B (opposite electrode production step),
In the space sandwiched between a pair of translucent plates, the photoelectrode and the counter electrode are arranged facing each other so that they do not contact each other, and at least between both electrodes in the space and the porous semiconductor Filling the electrolyte in the voids in the layer (battery forming step),
A method for producing a dye-sensitized solar cell having the following is provided.
[Through hole forming method X]
A stainless steel rolled sheet having a thickness of 0.005 to 0.2 mm is immersed in an aqueous ferric chloride solution having a trivalent iron ion concentration of 30 to 100 g / L and a hydrochloric acid concentration of 0 to 50 g / L, Through the growth of pitting corrosion-like pits, through holes with an area ratio of the penetrating portion occupying the projected area of the sheet in the thickness direction of 5 to 80% and an average diameter of the penetrating portion of 5 to 500 μm Let it form.

In particular, as the “photoelectrode manufacturing process”,
After obtaining the stainless steel sheet A having through holes by the through hole forming method X, a paste containing oxide semiconductor particles is applied to at least one surface of the stainless steel sheet A to form a coating film. A porous semiconductor layer formed by sintering oxide semiconductor particles by firing the film is formed on the surface of the stainless steel sheet A, and then a photosensitizing dye is supported on the porous semiconductor layer. Manufacturing process (photoelectrode manufacturing process),
Can be adopted.

In addition, as the “battery forming step”
In the space between the pair of translucent plates, the photoelectrode and the counter electrode are arranged such that the porous semiconductor layer of the photoelectrode faces the translucent plate and the electrodes do not contact each other. So as to face each other and fill the electrolyte in the space between at least both electrodes in the space and in the porous semiconductor layer (battery forming step),
Can be adopted.

According to the present invention, the following advantages can be obtained.
(1) Since both the current collecting material of the photoelectrode and the conductive material of the counter electrode are metal materials, the conductivity inside the cell is superior to that of a dye-sensitized solar cell using a conventional translucent conductive film, and the photoelectric This is advantageous for improving the conversion efficiency.
(2) In the counter electrode, visible light is transmitted through the portion of the through hole of the stainless steel sheet, so that the see-through property is not inhibited by the catalyst layer.
(3) Since it is not necessary to use a translucent conductive film for both electrodes, it is advantageous for cost reduction.
(4) Since the perforated stainless steel sheet used in the present invention is obtained by etching a rolled stainless steel sheet in an aqueous solution without applying the resist method, the productivity is high and suitable for mass production. This is also advantageous for cost reduction.

The figure which showed typically the structure of the general dye-sensitized solar cell. The figure which illustrated typically the composition of the dye sensitizing type solar cell of the present invention. The figure which illustrated typically the composition of the dye sensitizing type solar cell of the present invention. The figure which illustrated typically the composition of the dye sensitizing type solar cell of the present invention.

FIG. 2 schematically illustrates the configuration of the dye-sensitized solar cell of the present invention.
The photoelectrode 10 includes a stainless steel sheet A having a through hole 50 and a porous semiconductor layer 4 attached to one surface thereof. In the dye-sensitized solar cell 1 using the photoelectrode 10, the photoelectrode 10 can be arranged so that the porous semiconductor layer 4 faces the translucent plate-like body 2 as illustrated. That is, conventionally, a dye-sensitized solar of the type in which a metal current collecting material is disposed on the surface of the translucent plate 2 or in contact with the translucent conductive film 3 shown in FIG. Compared with a battery (for example, Patent Documents 1 to 3), in the dye-sensitized solar cell of the present invention, without light shielding by a metal current collecting material or slight dimming by a translucent conductive film, Since the incident light 30 reaches the porous semiconductor layer 4 directly, it is advantageous for improving the photoelectric conversion efficiency. In addition, it is easy to ensure the adhesion between the stainless steel and the semiconductor layer as compared with a dye-sensitized solar cell using a stainless steel mesh (see Non-Patent Document 1).

  The counter electrode 20 is constituted by a stainless steel sheet B having a through hole 50 ′ and a catalyst layer 7 formed on one surface thereof. The through hole 50 ′ is not blocked by the catalyst layer 7. In the dye-sensitized solar cell 1 using the counter electrode 20, incident light 30 'incident through the through hole 50' can be used for power generation as necessary. That is, one or both of the incident light 30 from the photoelectrode 10 side and the incident light 30 ′ from the counter electrode 20 side can be used for power generation. A translucent plate-like body 2 ′ is provided outside the counter electrode 20 for the purpose of sealing the electrolytic solution 8. As the translucent plate-like body 2 ′, a plate or a film made of a translucent material such as glass or plastic can be applied in the same manner as the translucent plate-like body 2 on the photoelectrode 10 side.

  In the dye-sensitized solar cell 1 of the present invention, the photoelectrode 10 can pass visible light through the through hole 50 of the stainless steel sheet A and the counter electrode 20 can pass through the through hole 50 ′ of the stainless steel sheet B. Therefore, the cell sandwiched between the pair of translucent plate-like bodies 2, 2 ′ has a see-through property. The through hole 50 of the stainless steel sheet A is responsible for the passage of ions in addition to the passage of visible light.

  In the example of the battery shown in FIG. 2, electrons move along the path of “porous semiconductor layer 4 → stainless steel sheet A → load 40 → stainless steel sheet B → catalyst layer 7 → electrolytic solution 8 → porous semiconductor layer 4”. To do. As a result, a current for operating the load 40 is generated.

  In FIG. 3, the structure of the dye-sensitized solar cell of another aspect of this invention is illustrated typically. In this case, porous semiconductor layers 4 and 4 ′ are attached to both sides of the stainless steel sheet A. The porous semiconductor layers 4, 4 ′ on both sides may be connected via the through hole 50 or may be separated. In this case, incident light 30 ′ from the counter electrode 20 side can be received particularly efficiently at the portion of the porous semiconductor layer 4 ′.

As long as a gap is secured between the counter electrode 20 and the photoelectrode 10, the counter electrode 20 does not necessarily have to be in close contact with the surface of the translucent plate 2 '. What is necessary is just to hold | maintain in the optimal position in consideration of design property and productivity.
FIG. 4 illustrates a configuration of a dye-sensitized solar cell in which the counter electrode 20 is disposed in a state where it is not in contact with the translucent plate-like body 2 ′. In this case, the catalyst layer 7 may be formed on one surface of the stainless steel sheet B as illustrated, or may be formed on both surfaces.

[Steel grades of stainless steel sheets A and B]
An organic solvent containing iodine (I ₂ ) and iodide ions is usually used for the electrolyte solution of the dye-sensitized solar cell. The stainless steel sheets A and B applied to the present invention need to be made of a material that exhibits stable and excellent corrosion resistance for a long time in such an electrolytic solution. As a result of investigations by the inventors, it has been found that it is extremely effective to apply stainless steel having a property that the corrosion weight loss when immersed in the electrolyte heated to 80 ° C. for 500 hours is 1 g / m ² or less. It was. Stainless steel with a corrosion weight loss of 1 g / m ² or less in the above-mentioned severe test environment in the so-called bare state (in which no coating layer is formed) is a popular dye-sensitized solar mounted on personal use equipment. In constructing a battery, it usually has sufficient durability. In addition, stainless steel having a property that the corrosion weight loss when immersed in the above solution for 1000 hours is 1 g / m ² or less is further advantageous in constructing a highly reliable dye-sensitized solar cell.

As a result of detailed studies, the inventors have found that in stainless steel, by containing a certain amount or more of Cr and Mo, dissolution in an electrolyte solution containing iodine (I ₂ ) and iodide ions using an organic solvent is almost impossible. It has been confirmed that excellent corrosion resistance that does not progress can be imparted. Specifically, in the stainless steel material, when the Cr content is 16% by mass or more and the Mo content is 0.3% by mass or more, iodine (I ₂ ) applied to the dye-sensitized solar cell and It has been found that it exhibits excellent corrosion resistance with little dissolution in an iodide ion-containing electrolyte. When the Cr content is 17% by mass or more and the Mo content is 0.8% by mass or more, a more reliable dye-sensitized solar cell can be constructed. This tendency is not significantly affected by the steel types such as austenite and ferritic, and is less affected by other additive elements.

  In the present invention, stainless steels having the following composition ranges can be applied to ferritic steel types and austenitic steel types. Unless otherwise specified, “%” with respect to the alloy element content means “mass%”.

Ferritic steel grades;
“C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, P: 0.04% or less, S: 0.03% or less, Ni: 0.6% or less, Cr : 16-32%, preferably 17-32%, Mo: 0.3-3%, preferably 0.8-3%, Cu: 0-1%, Nb: 0-1%, Ti: 0-1%, Ferritic stainless steel having a composition of Al: 0 to 0.2%, N: 0.025% or less, B: 0 to 0.01%, balance Fe and inevitable impurities "
When using a standard steel grade, for example, it is a ferritic steel grade specified in JIS G4305: 2005, Cr: 16-32 mass%, preferably 17-32 mass%, Mo: 0.3-3 mass%, preferably 0.3. What is necessary is just to apply the stainless steel containing 8-3 mass%.

Austenitic grades;
“C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, P: 0.045% or less, S: 0.03% or less, Ni: 6 to 28%, Cr: 16 to 32%, preferably 17-32%, Mo: 0.3-7%, preferably 0.8-7%, Cu: 0-3.5%, Nb: 0-1%, Ti: 0-1%, Al : 0 to 0.1%, N: 0.3% or less, B: 0 to 0.01%, the balance being Fe and an inevitable impurity composition austenitic stainless steel "
When using a standard steel grade, for example, it is an austenitic steel grade defined in JIS G4305: 2005, Cr: 16-32 mass%, preferably 17-32 mass%, Mo: 0.3-7 mass%, preferably 0.3. What is necessary is just to apply the stainless steel containing 8-7 mass%.

When the Cr content is less than 16% or the Mo content is less than 0.3%, the material is hardly dissolved in the electrolyte solution containing iodine (I ₂ ) and iodide applied to the dye-sensitized solar cell. It becomes difficult to stably obtain excellent corrosion resistance that does not occur. In order to further improve the reliability, in the case of ferrite, it is preferable to contain 17% or more of Cr and 0.8% or more of Mo, and it is more preferable to contain 18% or more of Cr and 1% or more of Mo. In the case of an austenitic system, it is preferable to contain 17% or more of Cr and 0.8% or more of Mo, and more preferably to contain 18% or more of Cr and 2% or more of Mo. However, when the content of Cr or Mo is excessively increased, the adverse effects such as the manufacturability are remarkable. For this reason, the Cr content is desirably 32% or less, and more preferably 30% or less. In addition, the Mo content is preferably 3% or less in the case of ferrite, and is preferably 7% or less in the case of austenite. In addition, the lower limit “0%” of the element content means that the content of the element is equal to or lower than the measurement limit in an analysis method at a normal steelmaking site.

  As elements other than the above, mixing of elements such as V: 0.3% or less, Zr: 0.3% or less, Ca, Mg, Co, and REM (rare earth elements): 0.1% or less in total is allowed. These may be inevitably mixed from raw materials such as scrap, but if mixed within the above range, the effect of the present invention is not hindered.

The stainless steel of various compositions, which illustrate the results of examining the corrosion resistance to a test liquid containing a simulated iodine (I ₂₎ and iodide ion electrolyte of the dye-sensitized solar cell.
Various stainless steels having the compositions shown in Table 1 were melted, and cold rolled annealed steel sheets (2D finishing materials) having a thickness of 0.28 to 0.81 mm were manufactured by a general stainless steel sheet manufacturing process. It was. In Table 1, in the structure column, “α” means ferrite and “γ” means austenite. The hyphen “-” in the table means that it is below the measurement limit by a normal analysis method in the steelmaking field.

A 35 × 35 mm test piece was cut out from each test material, and the surface (including the end face) was finished by # 600 dry emery polishing to obtain a corrosion resistance test piece.
As a test solution simulating an electrolyte solution of a dye-sensitized solar cell, a solution prepared by dissolving iodine I ₂ : 0.05 mol / L and lithium iodide LiI: 0.5 mol / L in an acetonitrile solvent was prepared.

  10 mL of the test solution was placed in a Teflon (registered trademark) container, and the corrosion resistance test piece was immersed in the solution. The container was covered to suppress the volatilization of the solvent. This container was held in a constant temperature bath at 80 ° C., and a test piece was taken out after 500 hours from the start of immersion. For each steel type, the number of samples was n = 3.

About each test piece after 500-hour immersion, corrosion weight loss (initial test piece mass-test piece mass after immersion) was measured. The largest value among the corrosion weight loss values of n = 3 (that is, the one with the largest metal elution amount) was adopted as the result of the corrosion weight loss of the steel type. Those having a weight loss of 1 g / m ² or less in this 500 hour immersion test were determined to be acceptable. Further, the surface of the test piece after the 500 hour immersion test was visually observed to examine the appearance. Also in this case, the appearance of the test piece having the most severe degree of corrosion among n = 3 was adopted as the grade of the steel type.
For reference, except for steel types that were found to have full-surface corrosion or end-face corrosion in the appearance after 500 hours of immersion, the specimens after observation were again subjected to the above immersion test, and the corrosion weight loss and appearance in the immersion test for a total of 1000 hours I investigated.
The results are shown in Table 2.

As can be seen from Tables 1 and 2, the steel according to the present invention containing Cr: 16% or more and Mo: 0.3% or more is 80 ° C. × 500 h in the iodide ion-containing electrolyte while being bare. It was confirmed that the corrosion weight loss when immersed under severe conditions was 1 g / m ² or less, there was little occurrence of spot rust, and excellent corrosion resistance was exhibited. Those containing Cr: 17% or more and Mo: 0.8% or more have a corrosion weight loss of 1 g / m ² or less even in a total 1000 hour immersion test, and are further excellent in durability.

[Forms of stainless steel sheets A and B]
Both the stainless steel sheet A constituting the photoelectrode 10 and the stainless steel sheet B constituting the counter electrode 20 need to have through holes 50 and 50 ′ sufficient to allow visible light to pass through sufficiently. Also, the passage of ions must be performed smoothly in the through hole 50 of the stainless steel sheet A. For that purpose, it is important to ensure a sufficient area ratio of the penetrating portion. Here, the area ratio of the penetrating part can be represented by the area ratio of the penetrating part (hereinafter sometimes referred to as “penetration ratio”) in the projected image when the stainless steel sheet is viewed in the thickness direction. The area of the through portion for each through hole is a projected area of a portion where the other side is seen through the hole when the through hole is viewed in the thickness direction of the stainless steel sheet. The penetrability is the area of each penetrating part (the penetrating part partially protruding from the rectangular area is the area of the part in the rectangular area) for a rectangular area that completely includes the penetrating part in at least 30 through holes. ) And dividing the total area by the area (projected area) of the rectangular region.

  The through holes 50 and 50 'can be formed by etching in an aqueous electrolyte solution as will be described later. In that case, pitting corrosion-like pits grow from both surfaces of the stainless steel sheet, so that pits grown from one surface may reach the other surface and a through hole may be formed, or pits grown from both sides It may collide in the middle of the thickness and become a through hole.

  According to the study by the inventors, when the penetration rate of either of the stainless steel sheets A and B is less than 5%, it is difficult for the dye-sensitized solar cell 1 to stably exhibit the see-through property. I understood. Moreover, also from the viewpoint of ion permeability in the stainless steel sheet A, it was found that when the penetration rate is less than 5%, the photoelectric conversion efficiency is drastically reduced. For this reason, both the perforated stainless steel sheets A and B used in the present invention are required to have a penetration rate of 5% or more. What is 10% or more is preferable, and what is 20% or more is more preferable. In particular, when emphasizing good see-through properties, the penetration rate is preferably 50% or more, and more preferably 60% or more. On the other hand, when the penetration rate is excessively high, both the stainless steel sheets A and B are liable to be broken during the manufacturing process due to the strength reduction, resulting in poor productivity. Further, in the stainless steel sheet A, it is difficult to stably hold a sufficient amount of the porous semiconductor layer 4 (4 '). As a result of various studies, it was found that the penetration rates of the stainless steel sheets A and B should be 80% or less. You may manage to 70% or less.

Regarding the size of the individual through holes 50 and 50 ′, if the size of the through hole 50 is excessive in the stainless steel sheet A of the photoelectrode 10, the coating of the semiconductor particle-containing paint is applied when the porous semiconductor layer 4 is formed. It may be difficult, or current collection from the porous semiconductor layer 4 may become non-uniform, which may increase the internal resistance of the photoelectrode 10. Further, in the stainless steel sheet B of the counter electrode 20, when the size of the through hole 50 ′ is excessive, the average moving distance until the ions in the electrolytic solution 8 reach the surface of the counter electrode 20 is increased. Thus, it is conceivable that the photoelectric conversion efficiency is likely to be lowered. As a result of various studies, in both cases of the stainless steel sheets A and B, the average diameter of the penetrating portion is desired to be 500 μm or less, and more preferably 200 μm or less, or 100 μm or less. On the other hand, even if the through holes 50 and 50 ′ are too fine, it does not lead to improvement in characteristics such as improvement in photoelectric conversion efficiency, and it is difficult to form a large number of such fine through holes 50 and 50 ′. The average diameter of the penetrating portion may be 5 μm or more. Here, the average diameter of the penetrating part is a penetrating part that is completely included in the rectangular area that satisfies the conditions for obtaining the penetrating ratio (that is, a part of the penetrating part that protrudes from the rectangular area). Excluding) average diameter. An equivalent circle diameter is adopted as the diameter of each penetrating portion. Circle-equivalent diameter refers to the area of the through portion S (μm ^2), when the circular constant [pi, means D ([mu] m) determined by S = πD ^2/4.

  The thickness of each of the stainless steel sheets A and B can be selected within a wide range of about 0.001 to 1 mm. However, most of the strength of the dye-sensitized solar cell 1 as a whole is added to these stainless steel sheets. As long as it is not necessary to bear, generally thinner is preferable. However, if it is too thin, it becomes difficult to handle at the time of manufacture due to insufficient strength, so it is desirable to secure a thickness of 0.005 mm or more. Specifically, for example, it is preferable to form the through hole 50 by a method described later using a rolled stainless steel sheet having a thickness of about 0.005 to 0.2 mm as a material. It is more preferable to use a rolled stainless steel sheet having a thickness of 0.005 to 0.1 mm.

(Formation of through holes)
As a method for forming the through holes 50 and 50 ′ of the stainless steel sheets A and B, etching in a ferric chloride aqueous solution is extremely effective. A method of simply immersing the material of the stainless steel sheet in a ferric chloride aqueous solution or a method of adding anode electrolysis or alternating electrolysis as required can be used. When a ferric chloride aqueous solution is used for the electrolyte aqueous solution, a large number of fine pitting corrosion pits can be formed on the stainless steel surface. Since the pitting corrosion pit has a deep shape with respect to the opening diameter, it is possible to open a hole penetrating the thickness of the sheet by growing the pitting corrosion pit. Specifically, a ferric chloride aqueous solution having a trivalent iron ion concentration of 30 to 100 g / L and a hydrochloric acid concentration of 0 to 50 g / L can be used. The temperature is preferably in the range of 20 to 80 ° C., for example. Since there is a difference in the corrosion resistance level depending on the stainless steel type, the concentration and temperature of the aqueous electrolyte solution corresponding to each steel type should be set within the above ranges, and the treatment time and electrolysis conditions for electrolysis should be set optimally. . The penetration rate and the average diameter of the penetration part can be controlled by changing each of the above conditions according to the plate thickness. What is necessary is just to determine optimal conditions by preliminary experiment according to the steel grade and board thickness of a raw material, the target penetration rate, and the average diameter of a penetration part.

  When the through hole 50 is formed by etching in the above ferric chloride aqueous solution, many pitting corrosion pits are also formed on the surface of the portion where the through hole is not formed. That is, in the stainless steel sheets A and B in which the through holes 50 and 50 ′ are formed by the etching, the surface of the portion where the through holes 50 and 50 ′ are not generated is roughened by pitting corrosion pits. . This roughening increases the surface area and is effective in reducing the internal resistance of the battery. Moreover, the pitting corrosion pits (including through-holes) formed on this type of roughened surface have a shape with sharp edges, so that in the stainless steel sheet A of the photoelectrode 10, the porous semiconductor layer 4 The anchor effect for (4 ′) works and is effective for improving the adhesion between the stainless steel sheet A and the porous semiconductor layer 4.

Below, the experiment example which formed the through-hole on various conditions about the stainless steel rolled sheet (annealed material) with a plate | board thickness of 0.01 mm using the steel H of Table 1 is disclosed.
As an aqueous electrolyte solution, an aqueous ferric chloride solution with various concentrations of trivalent iron ions and hydrochloric acid was prepared, and attempts were made to form through holes by immersing the stainless steel rolled sheet in the aqueous electrolyte solution. . The liquid temperature and treatment time were also varied. The stainless steel sheet after the immersion treatment was observed in the plate thickness direction with an optical microscope (manufactured by KEYENCE Corp .; HV-5500), and the average diameter of the penetration portion and the area ratio (penetration rate) of the penetration portion were obtained.
The processing conditions and results are shown in Table 3.

  As can be seen from Table 3, the average diameter of the penetrating part and the area ratio (penetrating ratio) of the penetrating part can be controlled by changing the concentration of the electrolyte aqueous solution, the liquid temperature, and the treatment time. In Nos. 1 and 2, since the trivalent iron ion concentration was too low, the etching force was weak, and the formation of through holes was insufficient. In No. 3, since the hydrochloric acid concentration was too high, the tendency of dissolution of the entire surface increased and the amount of metal elution was large, but pitting corrosion-like deep pits were difficult to grow. As a result, through holes were sufficiently obtained in 60 seconds. There wasn't. In addition, it was confirmed that all the target materials of the present invention were roughened by pitting pits on the surface of the portion where no through hole was generated.

[Production of photoelectrode]
The porous semiconductor layer 4 (4 ′) constituting the photoelectrode 10 may be an oxide semiconductor particle layer constituting the photoelectrode of a general dye-sensitized solar cell. For example, titanium dioxide (TiO ₂ ), One having one or more oxide semiconductor particles of tin oxide (SnO ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO ₂ ) and niobium oxide (Nb ₂ O ₅ ) as a component can be employed. As the sensitizing dye to be supported on the porous semiconductor layer 4, for example, ruthenium complex, porphyrin, phthalocyanine, coumarin, indoline, eosin, rhodamine, merocyanine and the like can be applied.

As a method for forming the photoelectrode 10, a paste containing oxide semiconductor particles is applied to at least one surface of the stainless steel sheet A having the through holes 50 by a doctor blade method or the like to form a coating film. A method of firing after drying can be suitably employed. When the oxide semiconductor particles are TiO ₂ particles, the firing condition may be, for example, about 450 to 550 ° C. and about 0.5 to 3 hours. In addition, when using the paste of the type in which a porous semiconductor layer is formed by apply | coating and drying a paste, you may abbreviate | omit baking after application | coating. As a result, the oxide semiconductor particles are sintered to form a porous semiconductor layer. In this manner, a plate-like body in which the stainless steel sheet A and the porous semiconductor layer 4 (4 ′) are integrated is obtained. By immersing this plate-like body in a liquid in which the sensitizing dye is suspended, the sensitizing dye can be supported on the porous semiconductor layer 4 (4 ′).

[Preparation of counter electrode]
The counter electrode 20 applied in the present invention is manufactured by forming the catalyst layer 7 on the surface of the perforated stainless steel sheet B. As the catalyst material, platinum, nickel, polyaniline, polyethylenedioxythiophene, carbon and the like can be applied. In the case of a metal film such as platinum or nickel, it can be formed by sputtering, for example. Conductive polymer films such as polyaniline and polyethylenedioxythiophene can be formed by, for example, spin coating. In the case of carbon, for example, it can be formed by spin coating using an activated carbon dispersion solvent. According to the study by the inventors, it was confirmed that even when an extremely thin platinum film having an average film thickness of about 1 nm was formed, it functions as a battery. The average film thickness of the catalyst layer 7 may be about 1 to 300 nm, for example. In order to achieve both conversion efficiency stability and economic efficiency, it is more effective to control the range of 10 to 200 nm or 20 to 100 nm.

  By using the stainless steel sheets of No. 1, 2, 3, 4, 6, 11, and 13 shown in Table 3 as the stainless steel sheet A of the photoelectrode and the stainless steel sheet B of the counter electrode, shown in FIG. A dye-sensitized solar cell having the structure described above was made as a prototype.

[Photoelectrode]
As a material for obtaining a porous semiconductor layer, a TiO ₂ particle-containing paste (Peccell Technologies, Inc .; PECC-01-06) was prepared. This paste was applied to one surface of each stainless steel sheet A by a doctor blade method and allowed to stand at room temperature to dry to form a dry coating film. Then, it inserted in the furnace and baked at 450 degreeC for 1 h, the porous semiconductor layer was formed, and the plate-shaped object which the stainless steel sheet A and the porous semiconductor layer were integrated was obtained. The average thickness of this porous semiconductor layer was 10 μm.
A ruthenium complex dye (manufactured by Solaronix) was prepared as a sensitizing dye, and this was dispersed in a mixed solvent of acetonitrile and tert-butanol to obtain a dye solution.
By immersing the plate-like body in the dye solution, a sensitizing dye was supported on the porous semiconductor layer to obtain a photoelectrode composed of the stainless steel sheet A and the porous semiconductor layer.

[Counter electrode]
A counter electrode was obtained by forming a catalyst layer using one of platinum, nickel, polyaniline, and carbon as a catalyst substance on one surface of each stainless steel sheet B.
In the case of platinum or nickel, the stainless steel sheet B was set in a sputtering apparatus, and a catalyst layer was formed by sputter coating using a metal as a catalyst material as a target. This film thickness was about 20 nm.
In the case of polyaniline, a catalyst layer was formed by a spin coating method in which a toluene solution in which polyaniline was dissolved was dropped onto the surface of stainless steel sheet B. This film thickness is about 30 nm.
In the case of carbon, a catalyst layer was formed by a spin coating method in which a tert-butanol solution in which activated carbon was dispersed was dropped onto the surface of the stainless steel sheet B. This film thickness is about 50 nm.

[Electrolyte]
As an electrolytic solution, a solution prepared by dissolving iodine I ₂ : 0.05 mol / L and lithium iodide LiI: 0.5 mol / L in an acetonitrile solvent was prepared.

[Battery formation]
These electrodes were arranged so that the surface of the photoelectrode on the stainless steel sheet A side and the platinum film of the counter electrode face each other. At that time, a PEN (polyethylene naphthalate) film substrate was disposed as a translucent plate on the outside of each of the electrodes. Spacers were inserted around the part to be the cell, and the cell was constructed so that the distance between the cell inner surfaces of both translucent plates was 50 μm. Then, an electrolytic solution was injected into the cell using a microcylinder, and the space between both electrodes and the gap of the porous semiconductor layer was filled with the electrolytic solution and then sealed. In this way, a dye-sensitized solar cell having the configuration shown in FIG. 2 was obtained.

[Battery characteristics]
Each dye-sensitized solar cell is irradiated with pseudo solar light of AM 1.5, 100 mW / cm ² from the photoelectrode side using a solar simulator (Yamashita Denso Co., Ltd .; YSS-100) “2400” manufactured by KEITHLEY The IV characteristics were measured with a “type source meter” to obtain values of the short circuit current J _SC , the open circuit voltage V _OC , and the form factor FF. From these values, the value of photoelectric conversion efficiency η was determined by the following formula (1).
Photoelectric conversion efficiency η (%) = short circuit current J _SC (mA / cm ² ) × open circuit voltage V _OC (V) × {form factor FF / incident light 100 (mW / cm ² )} × 100 (1)

[See-through]
The produced dye-sensitized solar cell was placed on newspaper, and the see-through property of the battery was evaluated based on whether or not letters on the newspaper could be seen through the battery cell. The case where a newspaper letter could be seen through the cell was judged as ◯ (good), and the other case was judged as x (bad).
These results are shown in Table 4.

  As can be seen from Table 4, in the dye-sensitized solar cell of the example of the present invention in which the area ratio (penetration ratio) of the through holes is 5% or more for both the stainless steel sheets A and B, a battery exhibiting a see-through appearance is shown. I was able to build. The battery characteristics were also good.

DESCRIPTION OF SYMBOLS 1 Dye-sensitized solar cell 2, 2 'translucent plate-like body 3 Translucent conductive film 4, 4' Porous semiconductor layer 5 Substrate 6 Conductive material 7 Catalyst layer 8 Electrolytic solution 10 Photoelectrode 20 Counter electrode 30, 30 'incident light 40 load 50, 50' through hole A, B stainless steel sheet

Claims (7)

In a cell sandwiched between a pair of translucent plates, a photosensitized solar cell in which a photoelectrode and a counter electrode face each other through an electrolyte,
The photoelectrode is obtained by integrating a stainless steel sheet A having a through hole and a porous semiconductor layer carrying a sensitizing dye, and the counter electrode is a catalyst layer on at least one surface of the stainless steel sheet B having a through hole. Is formed,
The stainless steel sheets A and B are made of the following [1] or [2] steel, the area ratio of the penetrating portion occupying the projected area when the stainless steel sheet is viewed in the thickness direction, and the penetrating portion. A dye-sensitized solar cell having visible light permeability, having through-holes having an average diameter of 5 to 500 μm.
[1] Steel that belongs to a ferritic steel type specified in JIS G4305: 2005, has a Cr content of 16 to 32 mass%, and a Mo content of 0.3 to 3 mass%.
[2] Steel that belongs to the austenitic steel grade specified in JIS G4305: 2005, has a Cr content in the range of 16 to 32 mass%, and a Mo content in the range of 0.3 to 7 mass%. 2. The dye-sensitized solar cell having visible light transmittance according to claim 1, wherein the stainless steel sheets A and B are made of steel of the following [3] or [4].
[3] By mass%: C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, P: 0.04% or less, S: 0.03% or less, Ni: 0.0 6% or less, Cr: 16 to 32%, Mo: 0.3 to 3%, Cu: 0 to 1%, Nb: 0 to 1%, Ti: 0 to 1%, Al: 0 to 0.2%, Ferritic stainless steel consisting of N: 0.025% or less, B: 0-0.01%, balance Fe and inevitable impurities.
[4] By mass% C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, P: 0.045% or less, S: 0.03% or less, Ni: 6 to 28% Cr: 16 to 32%, Mo: 0.3 to 7%, Cu: 0 to 3.5%, Nb: 0 to 1%, Ti: 0 to 1%, Al: 0 to 0.1%, N : Austenitic stainless steel consisting of 0.3% or less, B: 0 to 0.01%, balance Fe and inevitable impurities.   The through-holes of the stainless steel sheets A and B are formed by immersing a rolled sheet in an electrolyte aqueous solution to grow pitting corrosion-like pits. Sensitized solar cell.   The dye-sensitized solar cell having visible light permeability according to any one of claims 1 to 3, wherein the photoelectrode is disposed such that the porous semiconductor layer faces the translucent plate-like body. After obtaining a stainless steel sheet A having through holes by the following through hole forming method X, a porous semiconductor layer composed of an oxide semiconductor is formed on at least one side of the stainless steel sheet A, and then the porous semiconductor A step of preparing a photoelectrode by carrying a sensitizing dye in the layer (photoelectrode preparation step),
After obtaining a stainless steel sheet B having a through hole by the following through hole forming method X, a step of producing a counter electrode by forming a catalyst layer on at least one side of the stainless steel sheet B (opposite electrode production step),
In the space sandwiched between a pair of translucent plates, the photoelectrode and the counter electrode are arranged facing each other so that they do not contact each other, and at least between both electrodes in the space and the porous semiconductor Filling the electrolyte in the voids in the layer (battery forming step),
The manufacturing method of the dye-sensitized solar cell in any one of Claims 1-3 which have these.
[Through hole forming method X]
A stainless steel rolled sheet having a thickness of 0.005 to 0.2 mm is immersed in an aqueous ferric chloride solution having a trivalent iron ion concentration of 30 to 100 g / L and a hydrochloric acid concentration of 0 to 50 g / L, Through the growth of pitting corrosion-like pits, through holes with an area ratio of the penetrating portion occupying the projected area of the sheet in the thickness direction of 5 to 80% and an average diameter of the penetrating portion of 5 to 500 μm Let it form. As the “photoelectrode manufacturing process”,
After obtaining the stainless steel sheet A having through holes by the through hole forming method X, a paste containing oxide semiconductor particles is applied to at least one surface of the stainless steel sheet A to form a coating film. A porous semiconductor layer formed by sintering oxide semiconductor particles by firing the film is formed on the surface of the stainless steel sheet A, and then a photosensitizing dye is supported on the porous semiconductor layer. Manufacturing process (photoelectrode manufacturing process),
The manufacturing method of the dye-sensitized solar cell of Claim 5 which employ | adopts. As the “battery forming step”,
In the space between the pair of translucent plates, the photoelectrode and the counter electrode are arranged such that the porous semiconductor layer of the photoelectrode faces the translucent plate and the electrodes do not contact each other. So as to face each other and fill the electrolyte in the space between at least both electrodes in the space and in the porous semiconductor layer (battery forming step),
The manufacturing method of the dye-sensitized solar cell of Claim 5 or 6 which employ | adopts.

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