JP2011108463A - Photoelectrode of dye-sensitized solar cell, its manufacturing method, and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectrode of a dye-sensitized solar cell applying a metal material as a current collector member, which does not require concurrently a translucent conductive film and is of low cost and in which a high photoelectric transfer efficiency can be obtained. <P>SOLUTION: The photoelectrode of a dye-sensitized solar cell has a stainless steel sheet having through holes and a porous semiconductor layer carrying sensitized dyes integrated together. The stainless steel sheet contains Cr: 16 mass% or more and Mo: 0.3 mass% or more, and has a through hole of which the surface area ratio of the penetrating part occupied in a projected area viewed in thickness direction of the stainless steel sheet is 5% or more and the average diameter of the penetration part is 5-500 μm. The through hole can be formed by a method in which a stainless steel rolled sheet is immersed in a ferric chloride aqueous solution of trivalent iron concentration of 30-100 g/L and hydrochloric acid concentration of 0-50 g/L, and a pitting corrosion-like pit is grown in the solution. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photoelectrode of a dye-sensitized solar cell, which uses stainless steel as a current collecting member, a manufacturing method thereof, and a dye-sensitized solar cell using the photoelectrode.

  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.

  When the photoelectrode 10 requires a conductive material that functions as a current collecting member, the conductive material is disposed on the light receiving surface side (the side into which incident light is inserted) of the porous semiconductor layer 4 as shown in FIG. In general, a light-transmitting oxide conductive film such as ITO or FTO is employed. However, these conductive films have lower conductivity than metal materials, which is one factor that hinders improvement in power generation efficiency. Therefore, various methods using a metal material as a current collecting member have been proposed. In this case, in order to dispose the current collecting member on the light receiving surface side of the porous semiconductor layer 4, a metal film (Patent Document 1) provided with a large number of holes and a grid (Patent Document) so as not to disturb the incidence of light as much as possible. 2) It is necessary to apply a metal wire (Patent Document 3). Forming the photoelectrode having such a configuration requires a complicated process, and the cost is inevitably increased.

On the other hand, in order to arrange the current collecting member inside the porous semiconductor layer 4 or between the porous semiconductor layer 4 and the electrolyte 8, it is necessary to avoid the current collecting member and ensure charge transfer by ions. Therefore, it is not possible to simply apply a metal sheet. Therefore, a technique using a stainless steel mesh as a current collecting member for a photoelectrode is known. However, in this case, there is a problem that it is difficult to improve the photoelectric conversion efficiency. This is because the difference in thermal expansion coefficient between TiO ₂ and stainless steel is large in the firing step (heating temperature: about 450 to 500 ° C.) for forming the TiO ₂ semiconductor layer on the surface of the stainless steel mesh. The main reason is that TiO ₂ cracks occur on the surface of the steel mesh. Unlike the plate-like material, the wire constituting the mesh is poor in restraining force in a plane, and thus it can be said that it has an essential problem that it tends to cause a length change due to thermal expansion. In order to solve this problem, Non-Patent Document 1 proposes a method of forming a TiO _x layer having a gradient composition on the surface of a stainless steel mesh. However, this method requires complicated processing such as plasma deposition while changing the composition, and industrial practical application is not easy in terms of productivity and cost.

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 provides a photoelectrode for a dye-sensitized solar cell to which a metal material is applied as a current collecting member, which does not require the use of a light-transmitting conductive film, is low in cost, and has high photoelectric conversion efficiency. And a dye-sensitized solar cell using the same.

  As a result of detailed studies, the inventors have found that the above object can be achieved by using a stainless steel sheet having a large number of through holes as a current collecting member of a photoelectrode. 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,
A photoelectrode of a dye-sensitized solar cell in which a stainless steel sheet having a through hole and a porous semiconductor layer carrying a sensitizing dye are integrated,
The stainless steel sheet contains Cr: 16% by mass or more, Mo: 0.3% by mass or more, and has a chemical composition corresponding to a ferritic steel type defined in JIS G4305: 2005. The area ratio of the penetrating portion occupying the projected area seen in the vertical direction is 5 to 80%, and the through hole has an average diameter of 5 to 500 μm,
The porous semiconductor layer is attached to at least one side of the stainless steel sheet,
A photoelectrode for a dye-sensitized solar cell is provided.
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 the steel types of the stainless steel sheet, the following are suitable targets when standard steel types are listed.
(1) Cr: 16 to 32% by mass, Mo: 0.3 to 3% by mass, and corresponding to a ferritic steel type specified in JIS G4305: 2005.
(2) Cr: 16 to 32% by mass, Mo: 0.3 to 7% by mass, and corresponding to the austenitic steel grade specified in JIS G4305: 2005.

When the content range of each element is specifically shown, the following 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: 6-28% 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.
Here, the element whose lower limit of content is 0% is an optional element.

Moreover, as a manufacturing method of said photoelectrode,
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 are formed. Forming (through hole forming step),
A step of forming a porous semiconductor layer composed of an oxide semiconductor (for example, TiO ₂ ) on at least one surface of the stainless steel sheet in which the through hole is formed (porous semiconductor layer forming step);
A step of supporting a sensitizing dye on the porous semiconductor layer (dye supporting step),
There is provided a method for producing a photoelectrode of a dye-sensitized solar cell comprising:

In particular, as the “porous semiconductor layer forming step”,
Applying a paste containing oxide semiconductor (for example, TiO ₂ ) particles on at least one surface of the stainless steel sheet having the through holes to form a coating film (coating film forming process);
A step of firing the coating film to form a porous semiconductor layer formed by sintering oxide semiconductor particles (firing step);
The manufacturing method having a suitable target.

  Moreover, in this invention, a dye-sensitized solar cell provided with said photoelectrode is provided.

According to the present invention, the following advantages can be obtained.
(1) Since the current collecting member of the photoelectrode is a metal material, the electroconductivity is better than that of a conventional photoelectrode using a translucent conductive film, which is advantageous in improving the photoelectric conversion efficiency.
(2) Since it is not necessary to use a light-transmitting conductive film in combination with the photoelectrode, it is advantageous for cost reduction.
(3) Compared with a photoelectrode using a stainless steel mesh as a current collector, oxide semiconductor cracks due to thermal expansion differences are less likely to occur during the firing process of oxide semiconductor coatings, improving conductivity and thus photoelectric conversion. This is advantageous for improving efficiency. It is extremely advantageous in terms of cost.
(4) Moreover, since the perforated stainless steel sheet used in the present invention is obtained by etching a stainless steel rolled sheet in an aqueous solution without applying a 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 structure of the photoelectrode of this invention, and a dye-sensitized solar cell using the same. The figure which illustrated typically the structure of the photoelectrode of this invention, and a dye-sensitized solar cell using the same. The figure which illustrated typically another aspect of the photoelectrode of this invention, and the structure of the dye-sensitized solar cell using the same.

  In FIG. 2, the structure of the photoelectrode of this invention and a dye-sensitized solar cell using the same is illustrated typically. The photoelectrode 10 is constituted by a stainless steel sheet 9 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 porous semiconductor layer 4 can be disposed on the stainless steel sheet 9 on the side on which the incident light 30 is incident. 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), when the photoelectrode of the present invention is used, it is directly porous without being shielded by a metal current collecting material or slightly dimmed by a translucent conductive film. Since the incident light 30 reaches the quality semiconductor layer 4, 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).

  In the photoelectrode of the present invention, the through hole 50 formed in the stainless steel sheet 9 is used for charge transfer by ions. In the example of the battery shown in FIG. 2, electrons move along the path “porous semiconductor layer 4 → stainless steel sheet 9 → load 40 → conductive material 6 → catalyst layer 7 → electrolyte solution 8 → porous semiconductor layer 4”. . As a result, a current for operating the load 40 is generated.

  In the battery using the photoelectrode 10 of the present invention, a light-transmitting conductive film such as FTO can be used for the counter electrode 20 as the conductive material 6 shown in FIG. Therefore, the conductive material 6 can be made of a metal material having excellent conductivity. For example, as disclosed in Patent Document 4, a counter electrode using a stainless steel plate as the conductive material 6 can be employed. In this case, since the stainless steel plate can have a substrate function, a material corresponding to the substrate 5 in FIG. 2 can be omitted.

  FIG. 3 illustrates the configuration of such a dye-sensitized solar cell. As the counter electrode 20, one having a catalyst layer 7 formed on the surface of a stainless steel plate 60 is employed. In this case, the stainless steel sheet 60 can be the same as the stainless steel sheet 9 as described later. Further, the surface of the stainless steel plate 60 can be applied with a surface roughened to such an extent that a through hole is not generated by etching described later. This increases the surface area, which is advantageous in reducing the internal resistance of the battery.

  FIG. 4 schematically illustrates another embodiment of the photoelectrode of the present invention and the configuration of a dye-sensitized solar cell using the same. In this case, porous semiconductor layers 4 and 4 ′ are attached to both sides of the stainless steel sheet 9. The porous semiconductor layers 4, 4 ′ on both sides may be connected via the through hole 50 or may be separated. When the light is received only from the photoelectrode 10 side as in the incident light 30 shown in FIG. 3, the porous semiconductor layer 4 ′ attached to the surface of the stainless steel sheet 9 on the counter electrode 20 side passes through the through hole 50. Photoelectric conversion is performed using the incident light 30 to be inserted. In this case, the through hole 50 is responsible not only for charge transfer by ions but also for transmission of incident light. On the other hand, when both the counter electrode 20 and the substrate 5 are translucent materials, it is possible to receive light not only from the photoelectrode 10 side but also from the counter electrode 20 side. In such a case, the porous semiconductor layer 4 ′ adhering to the surface on the counter electrode 20 side of the stainless steel sheet 9 acts particularly effectively on incident light from the counter electrode 20 side.

[Steel grade of stainless steel sheet]
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 sheet applied to the present invention needs 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.

[Stainless steel sheet form]
The stainless steel sheet 9 constituting the photoelectrode 10 of the present invention has a function of holding the porous semiconductor layer 4 (semiconductor layer holding function) and a function of receiving electrons transferred from the sensitizing dye to the oxide semiconductor (current collecting function). In order to construct a solar cell in which the porous semiconductor layer 4 is disposed on the light-receiving surface side with respect to the stainless steel sheet 9, the ions pass through the through holes 50 during battery operation. It must fulfill the function (ion passage function) that facilitates the movement of. If the area ratio of the penetrating portion is too small, the photoelectric conversion efficiency is lowered, which is not preferable. Here, the area ratio of the penetrating portion can be represented by the area ratio of the penetrating portion (hereinafter sometimes referred to as “penetration ratio”) in the projected image when the stainless steel sheet 9 is viewed in the thickness direction. . The area of the through portion for each through hole 50 is a projected area of a portion where the other side is seen through the hole when the through hole 50 is viewed in the thickness direction of the stainless steel sheet 9. The penetration rate is defined as 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 in which the penetrating part in at least thirty through holes 50 is completely included. And the total area is divided by the area (projected area) of the rectangular region.

  The through hole 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, it has been found that in any of these through holes, when the penetration rate is less than 5%, the photoelectric conversion efficiency is rapidly lowered. For this reason, the perforated stainless steel sheet used in the present invention needs 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. When the through hole 50 is required to transmit incident light, 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, the strength for achieving the semiconductor layer holding function is insufficient. As a result of various studies, it was found that the penetration rate should be 80% or less. You may manage to 70% or less.

In addition, if the size of each through hole 50 is excessive, it becomes difficult to apply the semiconductor particle-containing paint when forming the porous semiconductor layer 4, and current collection from the porous semiconductor layer 4 is not uniform. It can be considered that the internal resistance of the photoelectrode 10 increases. The average diameter of the penetrating portion needs 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 hole 50 is made too fine, it does not lead to improvement in characteristics such as improvement in current collecting property, and it is difficult to form a large number of such fine through holes 50. 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.

  Although the thickness of the stainless steel sheet 9 can be selected in a wide range of about 0.005 to 1 mm, it is necessary to make the stainless steel sheet 9 bear most of the strength of the dye-sensitized solar cell 1 as a whole. As long as there is not, generally the thinner one is preferable. However, it is desirable to secure a thickness of 0.005 mm or more so that the semiconductor holding function can be sufficiently performed. Specifically, for example, it is preferable to form the through hole 50 by a method described later using a 0.005 to 0.2 mm thick stainless steel rolled sheet 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 hole 50 in the stainless steel sheet 9, 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 50 is not formed. That is, in the stainless steel sheet 9 in which the through holes 50 are formed by the etching, the surface of the portion where the through holes 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. In addition, since the pits formed on the surface of the stainless steel sheet 9 have a shape with sharp edges including the through holes 50, the anchor effect on the porous semiconductor layer 4 works, and the stainless steel sheet 9 and the porous This is also effective for improving the adhesion with the 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.

(Formation of oxide semiconductor layer)
The porous semiconductor layer 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 ), tin oxide (SnO) ₂ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO ₂ ), niobium oxide (Nb ₂ O ₅ ), or one containing two or more types of oxide semiconductor particles 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 of the present invention, a paste containing oxide semiconductor particles is applied to at least one surface of the stainless steel sheet 9 having the through hole 50 by a doctor blade method or the like. It is possible to suitably employ a technique in which the substrate is formed, dried and then fired. 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. As a result, the oxide semiconductor particles are sintered to form a porous semiconductor layer. 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. In this way, a plate-like body in which the stainless steel sheet 9 and the porous semiconductor layer 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.

[Formation of catalyst layer on counter electrode]
A catalyst layer 7 is formed on the surface of the counter electrode 20 applied to the dye-sensitized solar cell of the present invention. 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.

  Photoelectrodes were produced using the stainless steel sheets of Nos. 1, 2, 3, 4, 6, 11, and 13 shown in Table 3, and dye-sensitized solar cells using the same were fabricated.

[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 of the above stainless steel sheets by a doctor blade method and allowed to stand at room temperature and dried 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 and the porous semiconductor layer 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 a stainless steel sheet and the porous semiconductor layer.

[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.

[Counter electrode]
As a material used for the counter electrode, a PEN (polyethylene naphthalate) film substrate on which an ITO film was formed (Peccell Technologies, Inc .; PECF-IP) was prepared. Platinum sputtering was performed on the ITO film to obtain a counter electrode. The platinum film has a thickness of about 40 nm.

[Production of battery]
These electrodes were arranged so that the surface of the photoelectrode on the stainless steel sheet side and the platinum film of the counter electrode face each other. At that time, a spacer was inserted around the cell portion to ensure a gap for the electrolyte to enter between the electrodes. A PEN film was disposed at the end in the thickness direction on the photoelectrode side. Then, an electrolytic solution was injected into the gap using a micro cylinder, 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 constructed.

[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)
The results are shown in Table 4.

  As can be seen from Table 4, in the example of the present invention in which the area ratio (penetration ratio) of the through holes formed in the stainless steel sheet was 5% or more, a good photoelectric conversion efficiency η was obtained. On the other hand, in Comparative Example 1, since there was no through hole in the stainless steel sheet, the transport of iodide ions was blocked by the stainless steel sheet, and the battery did not substantially function as a battery. In Comparative Examples 2 and 3, since the area ratio of the through holes in the stainless steel sheet was too small, the charge transfer due to iodide ions was not sufficiently performed, and the photoelectric conversion efficiency η was low.

By using a stainless steel plate (No. 2D finishing material) made of steel H in Table 1 and having a thickness of 0.2 mm as the counter electrode, the prototype dye-sensitized solar cell has the configuration shown in FIG. The experiment was performed under the same conditions as in Example 1 except that the change was made. A platinum catalyst layer having a thickness of about 20 nm is formed on the stainless steel plate surface of the counter electrode by platinum sputtering.
The experimental results are shown in Table 5.

  As shown in Table 5, as in Example 1, in the example of the present invention in which the area ratio (penetration ratio) of the through holes formed in the stainless steel sheet is 5% or more, a good photoelectric conversion efficiency η is obtained. Obtained. Moreover, although the platinum catalyst layer was thinner than Example 1, the photoelectric conversion efficiency η was improved.

DESCRIPTION OF SYMBOLS 1 Dye-sensitized solar cell 2 Translucent plate-shaped body 3 Translucent conductive film 4, 4 'Porous semiconductor layer 5 Substrate 6 Conductive material 7 Catalyst layer 8 Electrolytic solution 9 Stainless steel sheet 10 Photoelectrode 20 Counter electrode 30 Incident light 40 Load 50 Through hole 60 Stainless steel plate

Claims (9)

A photoelectrode of a dye-sensitized solar cell in which a stainless steel sheet having a through hole and a porous semiconductor layer carrying a sensitizing dye are integrated,
The stainless steel sheet contains Cr: 16 to 32% by mass, Mo: 0.3 to 3% by mass, and has a chemical composition corresponding to a ferritic steel type defined in JIS G4305: 2005. Having a through hole with an area ratio of the penetrating portion occupying the projected area as viewed in the thickness direction of 5 to 80% and an average diameter of the penetrating portion of 5 to 500 μm,
The porous semiconductor layer is attached to at least one side of the stainless steel sheet,
Photoelectrode for dye-sensitized solar cell.   The chemical composition of the stainless steel sheet contains Cr: 16 to 32 mass%, Mo: 0.3 to 7 mass%, and corresponds to the austenitic steel grade specified in JIS G4305: 2005. The photoelectrode of the dye-sensitized solar cell described.   The chemical composition of the stainless steel sheet is, 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: 0.6% 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% The light of the dye-sensitized solar cell according to claim 1, which is a ferritic stainless steel comprising 0.2%, N: 0.025% or less, B: 0 to 0.01%, the balance Fe and unavoidable impurities. electrode.   The chemical composition of the stainless steel sheet is, 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 : 6-28%, Cr: 16-32%, Mo: 0.3-7%, Cu: 0-3.5%, Nb: 0-1%, Ti: 0-1%, Al: 0-0 The photoelectrode of a dye-sensitized solar cell according to claim 1, which is an austenitic stainless steel comprising 0.1%, N: 0.3% or less, B: 0 to 0.01%, the balance Fe and inevitable impurities .   The through hole of the stainless steel sheet is formed by immersing a rolled sheet in an aqueous electrolyte solution and growing pitting corrosion-like pits. The dye-sensitized solar cell according to any one of claims 1 to 4 Photoelectrode. 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 are formed. Forming (through hole forming step),
Forming a porous semiconductor layer composed of an oxide semiconductor on at least one surface of the stainless steel sheet in which the through hole is formed (porous semiconductor layer forming step);
A step of supporting a sensitizing dye on the porous semiconductor layer (dye supporting step),
The manufacturing method of the photoelectrode of the dye-sensitized solar cell in any one of Claims 1-4 which has these. As the “porous semiconductor layer forming step”,
Applying a paste containing oxide semiconductor particles to at least one surface of the stainless steel sheet in which the through hole is formed, and forming a coating film (coating film forming process);
A step of firing the coating film to form a porous semiconductor layer formed by sintering oxide semiconductor particles (firing step);
The manufacturing method of the photoelectrode of the dye-sensitized solar cell in any one of Claims 1-4 which has these. The oxide semiconductor manufacturing method of the photoelectrode for a dye sensitizing solar cell as claimed in claim 6 or 7 which is TiO _2.   A dye-sensitized solar cell comprising the photoelectrode according to any one of claims 1 to 5.

Images