JP2009200008A - Electrode material, its manufacturing method, and electrode of dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive material for an electrode, which can secure an excellent electric conduction and a high conversion efficiency, in a dye-sensitized solar cell; and to provide an electrode using the same. <P>SOLUTION: The material for the electrode used in the dye-sensitized solar cell comprises a stainless steel plate having a pitting recess in an average opening bore diameter D: 0.5 to 5 μm on a surface in the proportion of an area percentage over 50%. The stainless steel plate is preferably made of a steel material containing Cr in 17 to 32 mass% and Mo in 0.8 to 3 mass%. For example, in a ferrite-based steel material prescribed in JIS Z4305:2005, the material can be selected as Cr in 17 to 32 mass% and Mo in 0.8 to 3 mass%. Using the material as a base member, the dye-sensitized solar cell can be constituted by forming a catalyst layer on the surface of the stainless steel plate having the pitting recess. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a material constituting an electrode of a dye-sensitized solar cell, an electrode material used for a “counter electrode” or “photoelectrode” that is not required to be provided on the side opposite to the light receiving surface, and a method for producing the same And an electrode of a dye-sensitized solar cell using the electrode material.

  Currently, solar cells using silicon as the photoelectric conversion element are the mainstream, but the practical application of “dye-sensitized solar cells” is being studied as a more economical next-generation solar cell to replace this. .

  1 and 2 schematically show the structure of a conventional dye-sensitized solar cell. FIG. 1 shows a type in which a photoelectric conversion layer is provided on the incident light side electrode, and FIG. 2 shows a type in which the incident light side electrode is a “counter electrode” for passing electrons to ions in the solution.

In the type of FIG. 1, the solar cell 1 is configured by the photoelectrode 3 formed on the surface of the transparent substrate 2 and the counter electrode 5 formed on the surface of the substrate 4 facing each other. Since this type of photoelectrode 3 needs to transmit light, it is usually composed of a transparent conductive film such as ITO (indium-tin oxide), FTO (fluorine-doped tin oxide), or TO (tin oxide). . Glass or the like is used for the transparent substrate 2. A photoelectric conversion layer 6 is formed on the surface of the photoelectrode 3. The photoelectric conversion layer 6 are porous layer made of large TiO ₂ particles 7 of the specific surface area, the surface of the TiO ₂ particles 7 Ru dyes 8 is doped. An electrolyte solution 9 containing iodide ions is filled between the photoelectric conversion layer 6 and the counter electrode 5. On the counter electrode side, a counter electrode 5 made of a transparent conductive film is provided on the substrate 4, and a catalyst layer 10 made of a noble metal such as platinum is formed thereon. A load 11 is connected by a conducting wire between the photoelectrode 3 and the counter electrode 5 outside the solar cell 1 to form a circuit.

When the incident light 20 reaches the Ru dye 8, the Ru dye 8 absorbs light and is excited, and its electrons are injected into the TiO ₂ particles 7. The excited Ru dye 8 receives electrons from the iodide ion I ^{− in} the electrolyte solution 9 and returns to the ground state. I ⁻ is oxidized to I ³⁻ , diffuses to the counter electrode 5, receives electrons from the counter electrode 5, and returns to I ⁻ . As a result, electrons move along the route of Ru dye 8 → TiO ₂ particles 7 → photoelectrode 3 → load 11 → catalyst layer 10 → counter electrode 5 → electrolyte solution 9 → Ru dye 8. As a result, a current for operating the load 11 is generated.

  In the type of FIG. 2, the counter electrode 5 is made of a transparent conductive film such as ITO, FTO, or TO that transmits light, and the photoelectric conversion layer 6 is formed on the surface of the photoelectrode 3 that is the other electrode. In this case, the photoelectrode 3 is not necessarily transparent. The principle of current generation is basically the same as that of the type shown in FIG.

  Patent Documents 1 to 6 describe that a conductive film made of a corrosion-resistant metal such as platinum is used for an electrode of a dye-sensitized solar cell. There is also an example in which the counter electrode is formed of a platinum plate having a thickness of 1 mm (Patent Document 6).

Japanese Patent Laid-Open No. 11-273753 JP 2004-3111197 A JP 2006-147261 A JP 2007-48659 A JP 2004-165015 A JP 2005-235644 A

  The conversion efficiency of current dye-sensitized solar cells is lower than that of silicon solar cells, and increasing efficiency is one of the major issues. As a technique aiming at high efficiency of the dye-sensitized solar cell, for example, in Patent Document 1, a plurality of electrode pairs are stacked, and the counter electrode farthest from the light incident side is used as a reflective electrode layer, thereby converting Techniques for improving efficiency and increasing the amount of power supply per unit area are disclosed. That is, the incident light is absorbed by the plurality of electrode layers, and the reflected light reflected by the reflective counter electrode is absorbed by the reverse path, thereby achieving high efficiency.

  However, the technique of Patent Document 1 has a drawback that the material cost becomes very high because an expensive metal such as platinum, gold, silver, titanium, or an alloy thereof having excellent corrosion resistance against the electrolyte solution is used as the reflective electrode layer. is there. In particular, platinum is highly effective as a counter electrode material because it has high conductivity and exhibits a catalytic action, but it is extremely expensive. Therefore, it is strongly desired to reduce its use amount to the minimum necessary.

  Patent Document 3 discloses a method of forming a corrosion-resistant metal material film such as titanium or tantalum having a concavo-convex structure with a scale of 1 to 1000 nm on the surface of a resin counter electrode by sputtering, and forming a platinum film on the surface. ing. According to this method, since the contact area between the counter electrode and the electrolyte solution is increased, the surface resistance is reduced, and even if the thickness of the platinum film is reduced, the reduction in the total electric resistance is alleviated. However, as long as a resin substrate is used by this method, it is necessary to supply electricity at the counter electrode only with a platinum film, and a considerable amount of platinum is still necessary to ensure sufficient conductivity. There is a need for a structure that can reduce costs.

  As described above, a considerable amount of noble metal such as platinum is currently used for the electrode of the dye-sensitized solar cell, which is accompanied by an increase in cost due to the use of an expensive noble metal. In the type of electrode in which a “film” is formed of platinum, carbon black or other materials, there is room for improvement in electrical conductivity within the electrode.

  In view of such a current situation, the present invention is composed of a metal material exhibiting excellent corrosion resistance in an electrolyte solution containing iodide ions of a dye-sensitized solar cell, and is inexpensive in which good electrical conduction and high conversion efficiency are ensured. An electrode material and an electrode using the same are provided.

  In order to achieve the above object, the inventors have studied various metal materials as an electrode substrate used on the side that does not need to transmit light of the dye-sensitized solar cell, and as a result, the surface has an appropriate size. It has been found that a stainless steel plate provided with a large number of hemispherical recesses can be used. In particular, high Cr ferritic stainless steel containing an appropriate amount of Mo has good corrosion resistance to an electrolyte solution, and is useful in constructing a highly durable dye-sensitized solar cell.

  That is, the present invention provides an electrode material for a dye-sensitized solar cell comprising a stainless steel plate having a pitting-corrugated recess having an average opening diameter D of 0.5 to 5 μm at a surface area ratio of 50% or more. The surface having the pitting-like recesses has, for example, a surface roughness SRa of 0.1 to 1.5 μm, preferably 0.3 to 1.5 μm. The stainless steel plate preferably employs a steel type containing Cr in a range of 17 to 32% by mass and Mo in a range of 0.8 to 3% by mass. For example, in the ferritic steel types specified in JIS Z4305: 2005, a steel containing Cr in the range of 17 to 32 mass% and Mo in the range of 0.8 to 3 mass% can be selected.

  As a more specific stainless steel plate, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0.8 to 3%, N: 0.025% or less, the balance being substantially Fe, and exhibiting a ferrite phase structure. In addition to the above elements, Al: 5% or less, Ti: 1% or less Nb: not more than 1%, Cu: not more than 3%, Ni: not more than 5% may be used.

  Here, “the balance is substantially Fe” means that mixing of elements other than the above is allowed unless the effect of the present invention is inhibited, and there are cases where “the balance consists of Fe and inevitable impurities”. included. “Ferrite phase structure” refers to a metal structure in which a metal matrix excluding precipitates and inclusions is composed of a ferrite phase. “At an area ratio of 50% or more” means an area in which a pitting-corrugated recess is formed (that is, no pit is generated) that occupies the projected area of the observation area when the steel plate surface is viewed in a direction parallel to the plate thickness direction. The ratio of the projected area of the region excluding the portion) is 50% or more. The surface roughness SRa means the average roughness in the center plane (reference plane) when the surface roughness curve is approximated by a sine curve, and was obtained using a stylus type three-dimensional surface roughness meter, a laser microscope, or the like. It is a value obtained by measuring the height of each point and performing a three-dimensional surface roughness analysis on these measured values. The measurement area may be a rectangular area (for example, 50 μm × 50 μm) having a side of 40 μm or more.

  In FIG. 3, the SEM photograph of the surface which has a pitting corrosion-like recessed part about an example of the electrode material consisting of the stainless steel material of this invention is illustrated. Each pitting corrosion-like recessed part is comprised by the pit (pitting corrosion) which has a circular shaped opening part. Circular shape refers to the diameter of the longest part in the outline of the opening when the surface of the steel sheet is viewed in a direction parallel to the plate thickness direction. When the diameter is called “minor axis”, it means a shape having an aspect ratio represented by major axis / minor axis of 2 or less. There are some pits where the overall shape of the opening can be clearly seen by the outline of the pit opening, but there are also pits where the overall image does not appear in the outline at the part where multiple pits are connected to form a recess. To do. However, even with such pits, there are many pits that can estimate the entire image (that is, the shape of the circular opening) from the outline with relatively high accuracy.

  The average opening diameter D can be determined as follows. That is, a straight line is drawn on an image obtained by viewing the surface of the steel plate in a direction parallel to the plate thickness direction, and from the pit where the outline of the pit intersects the straight line, an overall image of the shape of the opening appears in the outline. Randomly select a total of 30 pits that can be estimated from the outline of the shape of the opening from the pit or its outline, measure the maximum diameter in the direction parallel to the straight line for each pit, and calculate the arithmetic average of those values The value obtained by doing this is defined as the average opening diameter D. A total of 30 pits may be selected by drawing a plurality of straight lines. As a method for “selecting a total of 30 randomly”, for example, a method of picking up all the pits in which the entire image of the opening shape appears along the straight line and the pits from which the entire image of the opening shape can be estimated You can pick up a total of 100 pits and select 30 pits randomly.

  FIG. 4 schematically shows the form of pitting pits appearing in a cross section parallel to the plate thickness direction. The opening distance (D1 to D5 in the figure) of each pit that appears in this cross section does not mean the above-mentioned “maximum diameter of each pit in the linear direction”.

In the present invention, as a method for producing the above electrode material, a stainless steel plate having the above composition and exhibiting a ferrite phase structure, in a ferric chloride aqueous solution having a Fe ³⁺ concentration of 1 to 50 g / L, 1.0~10.0kA / m ² current density during the anodization, the current density during cathodic electrolysis by applying an alternating electrolysis 1~20Hz which was 0.1~3.0kA / m ^2, the steel plates Provided is a method for producing an electrode material for a dye-sensitized solar cell in which a pitting corrosion-shaped recess having an average opening diameter D of 0.5 to 5 μm is formed on the surface at a ratio of 50% or more.

  Furthermore, the present invention provides an electrode of a dye-sensitized solar cell in which the above electrode material is used as a base material and a catalyst layer is formed on the surface of a stainless steel plate having a pitting corrosion-like recess. This electrode is an electrode on the side that does not need to transmit light.

When the electrode material of the dye-sensitized solar cell of the present invention is used, the following merits are obtained.
(1) The conversion efficiency by the diffuse reflection effect of incident light can be improved by optimizing the concave area ratio and the aperture diameter.
(2) By increasing the surface area due to the large number of recesses provided on the surface on the side on which the catalyst layer is formed, the amount of catalyst supported such as platinum can be reduced, and the cost can be reduced.
(3) Since it is based on a stainless steel plate, it has higher conductivity than transparent conductive films such as ITO, FTO, and TO.
(4) Since the stainless steel of the substrate itself exhibits excellent corrosion resistance in the electrolyte solution used in the dye-sensitized solar cell, it is strong against the presence of defects and surface flaws in the catalyst layer.
(5) Since it is strong against the presence of defects and surface flaws in the catalyst layer, the thickness of the catalyst layer (the amount of catalyst material such as platinum) used can be minimized and the cost can be reduced.
(6) Since the stainless steel plate is the base, this electrode material itself has the function of a substrate and has higher strength than a conventional general glass substrate.
Therefore, the present invention contributes to the spread of dye-sensitized solar cells.

  5 and 6 schematically show structural examples of a dye-sensitized solar cell using the electrode material of the present invention. FIG. 5 shows a conventional dye-sensitized solar cell of the type shown in FIG. 1, in which the substrate 4 and the counter electrode 5 are changed to a counter electrode 30 made of the electrode material of the present invention. The counter electrode 30 includes a stainless steel plate substrate 21 and a catalyst layer 10 provided on the surface thereof. FIG. 6 shows a conventional dye-sensitized solar cell of the type shown in FIG. 2, in which the substrate 4 and the photoelectrode 3 are replaced with a photoelectrode 40 made of the electrode material of the present invention. The photoelectrode 40 includes a stainless steel plate substrate 21 and a catalyst layer 10 provided on the surface thereof. 5 and 6, the surface of the stainless steel plate substrate 21 on the side of the electrolyte solution 9 is a roughened surface having pitting corrosion-like recesses. The catalyst layer 10 is formed on this roughened surface.

(Roughened form)
According to the inventors' research, in a dye-sensitized solar cell using a stainless steel plate with a number of pitting corrosion-like recesses formed on the surface as an electrode material on the side that does not need to transmit light, a smooth surface electrode material It has been found that the conversion efficiency is higher than in the case of. And it discovered that the opening diameter of a recessed part and the area ratio (namely, roughening form) of a recessed part had much larger influence on the conversion efficiency rather than the catalyst carrying amount.

  As a result of detailed studies, it was found that the effect of improving the conversion efficiency is large when the average opening diameter D is 0.5 to 5 μm.

  There are many unexplained parts about the mechanism, but the following can be considered. A part of the light incident from the transparent electrode side is absorbed by the pigment, and the rest reaches the electrode using the stainless steel plate substrate on the opposite side. At this time, since light is diffusely reflected in many directions on the surface of many concave portions formed on the stainless steel plate, the reflected light is more efficiently absorbed by the pigment than in the case of only regular reflection. Conceivable. However, in practice, when very fine recesses having an average opening diameter D of less than 0.5 μm are formed, it is understood that the conversion efficiency is reduced compared to the case of a smooth surface. It was.

  The reason is presumed as follows. Ru dye used as a sensitizing dye has a property of being excited by light in a wavelength range of 350 to 800 nm which is a visible light region of sunlight. However, if there are many concave portions with openings smaller than this wavelength on the surface of the electrode that reflects incident light, the amount of reflected light decreases because light is absorbed in the concave portions due to the standing wave resonance phenomenon. For this reason, the conversion efficiency decreases rather than in the case of a smooth electrode.

  As shown in FIGS. 5 and 6, a catalyst layer such as platinum is formed on the roughened surface of the stainless steel plate substrate. Then, the catalytic substance is coated on the inner wall surface of the pitting corrosion-shaped recess formed on the surface of the stainless steel plate substrate, so that the opening diameter of the recess is smaller than that of the substrate on the electrode surface in which the catalyst is supported. Therefore, in order to reflect light having a wavelength of 350 to 800 nm, it is effective to set the average aperture diameter D to 0.5 μm or more, which is larger than 350 nm (0.35 μm), at the stage of the stainless steel plate of the substrate. . More preferably, it is 1 μm or more.

  On the other hand, when the opening diameter of the concave portion is increased, absorption due to standing wave resonance does not occur, and the above-described effect of improving the conversion efficiency can be obtained by sufficient diffuse reflected light. However, when the opening diameter of the concave portion becomes excessively large, the effect of diffuse reflection itself is reduced. As a result of various studies, when the average opening diameter D at the stage of the stainless steel plate of the substrate is larger than 5 μm, it is difficult to obtain a substantial conversion efficiency improvement effect. Therefore, the average opening diameter D of the stainless steel plate is specified to be 5 μm or less.

  Moreover, in order to obtain the effect of diffuse reflection by the recesses having the appropriate dimensions, it is desirable that the area ratio of the recesses on the steel plate surface is higher. In the present invention, the lower limit of the area ratio at which a practical effect is obtained is set to 50%. Moreover, since the substantial surface area (actual surface area) of the steel plate surface increases as the area ratio increases, the amount of platinum supported can be reduced at the same time.

  As the surface having such a pitting corrosion-like recess, the surface roughness SRa is preferably in the range of 0.1 to 1.5 μm. By setting SRa to 0.1 μm or more, the effect of diffuse reflection can be obtained more effectively. SRa is more preferably 0.3 μm or more. However, it is not easy to obtain a roughened surface with SRa of 1.5 μm or more by electrolytic roughening.

[Alternative electrolytic treatment]
The above-mentioned unique roughening form is a ferric chloride solution for a stainless steel plate having a non-roughened surface such as normal annealing / pickling finish, BA annealing finish, or skin pass rolling finish. It can obtain by performing the alternating electrolysis process in.

The Fe ³⁺ concentration in the aqueous ferric chloride solution can be 1 to 50 g / L. A range of 10 to 40 g / L is more preferable.

The current density during anode electrolysis can be set to 1.0 to 10.0 kA / m ² . If the anode current density is too low, pitting corrosion (pits) is not generated. If the anode current density is too high, the decomposition reaction of the electrolyte occurs, leading to a reduction in efficiency. The current density during cathode electrolysis can be set to 0.1 to 3.0 kA / m ² . If the cathode current density is too low, hydrogen gas that promotes the formation of pitting corrosion is difficult to generate, and if it is too high, the pitting corrosion generated by excessive hydrogen generation tends to be lost. Further, the cycle of alternating electrolysis affects the size of the generated pits, and in the present invention, it may be adjusted in the range of 1 to 20 Hz. When the alternating electrolysis cycle is reduced, the energization time per cycle is increased, so that the size of pitting corrosion can be increased. Conversely, when the alternating electrolysis cycle is increased, the size of pitting corrosion can be reduced. The temperature of the electrolytic solution can be adjusted in the range of 30 to 70 ° C. What is necessary is just to adjust electrolysis time so that said roughening form may be obtained. Usually, optimum conditions can be found in the range of 10 to 300 seconds.

[Stainless steel as base material]
In the present application, “stainless steel” refers to steel having a Cr content of 10.5 mass% or more (number 4201 of JIS G0203). Even if a steel type having a particularly high corrosion resistance is not adopted, a catalyst layer having a sufficient film thickness can be formed by platinum coating or the like, so that it can be used as an electrode substrate of a dye-sensitized solar cell. However, when the platinum coating or the like is applied as thinly as possible, defects such as pinholes are likely to occur in the coating layer. Therefore, in order to construct a more reliable electrode, it has excellent durability with respect to the electrolyte solution of the dye-sensitized solar cell in the state of a bare stainless steel plate (the state where the catalyst layer is not formed). It is more preferable to use the stainless steel type to be used for the electrode substrate. As a result of various studies, the stainless steel species containing Cr in the range of 17 to 32 mass% and Mo in the range of 0.8 to 3 mass% has excellent durability against the electrolyte solution containing iodine ions of the dye-sensitized solar cell. It turns out that it exhibits sex.

Generally stainless steel chloride ion Cl ^- is to have a weak point in corrosion resistance to an aqueous solution containing, to improve its corrosion resistance the addition of increasing or Mo and Cr is to be effective. For example, in ferrite type SUS444 suitable for water heaters, Cr: 17% by mass or more and Mo: 1.75% by mass or more are ensured. Even in SUS316, which is a high corrosion resistance austenitic general-purpose steel grade, Cr: 16% by mass. As mentioned above, Mo: Content of 2 mass% or more is ensured. However, there are surprisingly few reports on the corrosion resistance of stainless steel against iodide ions. The reason for this is that there is almost no environment exposed to iodide ions in nature or in daily life. In particular, regarding the iodide ion-containing electrolyte solution when the solvent is not water but an organic substance, the relationship between the composition of stainless steel and the corrosion resistance is hardly grasped. It has been known that SUS430 and SUS304, which are general-purpose steel types, corrode severely against the electrolyte solution in the bare state, and the application of stainless steel materials for electrode applications of dye-sensitized solar cells has been avoided. This was a factor that motivated me to make a detailed examination.

  As a result of detailed studies, the inventors have found that when the Cr content in the stainless steel material is 17% by mass or more and the Mo content is 0.8% by mass or more, the iodine applied to the dye-sensitized solar cell. It has been found that excellent corrosion resistance that hardly dissolves in a fluoride-containing electrolyte solution is exhibited. As described above, even when the application is a daily hot water environment, in order to give the stainless steel sufficient corrosion resistance, it is necessary to add a relatively large amount of Mo, for example, 1.75% by mass or more. is there. Compared to this, it has been clarified that the corrosion resistance of the dye-sensitized solar cell in which iodide ions are present in the organic solvent to the electrolyte solution is remarkably improved from a smaller Mo addition range.

  Therefore, as the electrode material of the present invention, it is more desirable to apply a stainless steel type containing Cr in a range of 17 to 32% by mass and Mo in a range of 0.8 to 3% by mass. In particular, in the present invention, a ferritic steel type that is less expensive than an austenitic steel type can be employed. Specifically, as such steel, for example, it corresponds to existing steel types such as SUS434, SUS436L, SUS444, SUS445J1, SUS445J2, SUS447J1, and SUSXM27 specified in JIS G4305: 2005, and in particular, Cr is 17 to 32% by mass, Stainless steel having a composition containing Mo in the range of 0.8 to 3% by mass can be employed.

  When the Cr content is less than 17% or the Mo content is less than 0.8%, it is excellent that the material hardly dissolves in the iodide-containing electrolyte solution applied to the dye-sensitized solar cell. It becomes difficult to stably obtain corrosion resistance. In order to further improve the reliability, it is preferable to contain 18% or more of Cr and 1% 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. The Mo content is preferably 3% or less, and more preferably 2% or less.

More specifically, ferritic stainless steel as shown in the following (i) and (ii) can be employed.
(I) By mass%, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0.8 to 3%, N: 0 0.025% or less, the balance being substantially Fe
(Ii) By mass%, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0.8 to 3%, N: 0 0.025% or less, and further containing at least one of Al: 5% or less, Ti: 1% or less, Nb: 1% or less, Cu: 3% or less, Ni: 5% or less, and the balance substantially Fe

In the case of (ii) above, a more preferable content range of each selected element is Al: 0.03.
-5%, Ti: 0.05-0.4%, Nb: 0.05-0.8%, Cu: 0.4-3%, Ni: 0.4-5%.

The elements that can be mixed in the balance are P: 0.04 mass% or less, S: 0.03 mass% or less, V: 0.5 mass% or less, B: 0.1 mass% or less, Ca: 0.1 Mass% or less, Mg: 0.1 mass% or less, Y: 0.1 mass% or less, REM (rare earth element): 0.1 mass% or less.
The balance can be limited to Fe and inevitable impurities.

〔electrode〕
An electrode can be obtained by providing a catalyst layer on the surface of the stainless steel plate on the side where the concave portion is formed. Examples of the catalyst substance include transition metals having high catalytic activity such as platinum and palladium, and organometallic complexes such as carbon black and porphyrin. As a method for forming a catalyst layer using platinum, known methods such as sputter coating and electroplating can be used. Sputter coating is suitable in terms of forming a platinum film that is as thin and uniform as possible. In the case of carbon black, the catalyst layer can be formed by a method of applying and drying a paste mixed with a binder. This metal plate having a catalyst layer on the surface is used as a “counter electrode” or “photoelectrode” of the dye-sensitized solar cell in such a state that the surface on the side where the catalyst layer is formed is in contact with the electrolyte solution.

  Stainless steel having the composition shown in Table 1 was melted, and a cold-rolled annealed steel sheet (No. 2D finish) having a thickness of 0.2 mm was manufactured by a general stainless steel sheet manufacturing process. In each steel, the content of P, which is an impurity, is suppressed to 0.04 mass% or less, and the content of S is suppressed to 0.002 mass% or less.

The test piece cut out from the steel sheet was immersed in a ferric chloride aqueous solution with an Fe ³⁺ concentration of 30 g / L and 50 ° C., the anode electrolytic current density was 3 kA / m ² , and the cathode electrolytic current density was 0.3 kA / m ^2. And roughening treatment was carried out at various alternating cycles and electrolysis times. The surface subjected to the roughening treatment was observed with a scanning electron microscope (SEM), and the average opening diameter D of the pitting pits and the area ratio of the pitting pits were measured by the method described above. Moreover, about the roughened surface, the three-dimensional surface profile of a 50 micrometer x 50 micrometer rectangular area was measured using the scanning confocal laser microscope (Olympus Co., Ltd. product; OLS1200). The three-dimensional average surface roughness SRa calculated from the pull file data was determined.

The roughened surface was coated with platinum at an output of 50 W for a predetermined time by sputter coating to form a platinum catalyst layer, and a test material for an electrode was obtained.
Each processing condition and roughening form are shown in Table 2.

  Next, a small battery cell was produced using the above-mentioned sample material having a platinum catalyst layer as a “counter electrode”, and the conversion efficiency was measured. The experiment was performed according to the following procedure.

[1] A PEN film with an ITO film having a size of 20 mm × 20 mm (Peccell Technologies, Inc .; PECF-IP) was prepared. Titanium oxide nanopaste (manufactured by Pexel Technologies, Inc .; PECC-01-06) was applied to a 5 mm × 5 mm region on the film surface by a doctor blade method and dried. The dried film was immersed in a liquid in which N719-based ruthenium complex dye (PECD-07 manufactured by the same company) was dispersed in an acetonitrile-containing solvent to adsorb the dye, thereby producing a photoelectrode.

[2] An ionomer resin film (trade name: High Milan) having a size of 20 mm × 20 mm and a thickness of 50 μm was prepared. A 5 mm × 5 mm region is cut out in the center of the film, and a hole is formed, and this is used as a spacer, and heat fusion is carried out on the surface of the catalyst layer of the above-described test material (catalyst layer formed on a roughened stainless steel plate substrate). Thus, a counter electrode with a spacer was produced.

[3] The photoelectrode and the counter electrode with the spacer are overlapped so that the respective 5 mm × 5 mm regions coincide with each other, and an electrolyte solution (Peccell Technologies, Inc .; PECE-) is formed in the gap between the 5 mm × 5 mm regions. K01) was injected and then fixed with a clip to obtain a battery cell.

[4] Connect each terminal of the IV characteristic measurement device (Peccell Technologies, Inc .; PECK2400-N) to each electrode of the battery cell, and use a solar simulator (Peccell Technologies; PEC-L11) to 100 mW / The conversion efficiency when irradiating cm ² pseudo sunlight was measured.

[5] After measuring the conversion efficiency immediately after production of the battery cell, the cell was stored at room temperature for 1000 h in a glove box purged with argon gas. Thereafter, the conversion efficiency was again measured by the method [4].

  The results are shown in Table 2. Here, the conversion efficiency ratio refers to the conversion efficiency when using a counter electrode in which a Nesa glass (ITO (tin oxide transparent conductive film deposited on a glass substrate) described in the reference column is sputter coated with platinum for 90 min is used. The ratio value is defined as

  As can be seen from Table 2, the conversion efficiency ratio of all of the examples of the present invention exceeded 100 even though the platinum sputtering time was as short as 10 min, showing a higher value than the 90 min sputtered nesa glass, and deteriorated over time. Is also not allowed. Since the conversion efficiency ratio is as low as 90 for nesa glass of 10 min sputtering, the amount of platinum used can be reduced by using the electrode material made of the stainless steel plate of the present invention. Moreover, it is considered that the conversion efficiency is higher than that of Comparative Example No. 11 without electrolysis because of the diffuse reflection effect due to the surface shape.

  On the other hand, Comparative Example No. 6 had a small effect of improving the conversion efficiency because the average opening diameter D of the pitting corrosion-like recesses was large. No. 7 had a lower conversion efficiency than that without electrolysis (No. 11) because the average opening diameter D was too small and the surface roughness SRa was too small. In No. 8, the effect of improving the conversion efficiency was small because the area ratio of the pitting corrosion-like recesses was too low. No. 9 and No. 10 are inferior in corrosion resistance to the electrolytic solution due to the low Mo content or further Cr content of the stainless steel, and the conversion efficiency after 1000 hours is significantly reduced. This is presumed to be because the components in the steel such as Fe and Cr were eluted into the electrolyte through the pinholes in the platinum coating film. This problem can be eliminated by sufficiently increasing the thickness of the platinum coating.

The figure which showed typically the structure of the conventional dye-sensitized solar cell (The type which has a photoelectric converting layer in the electrode by the side of incident light). The figure which showed typically the structure of the conventional dye-sensitized solar cell (The type by which the electrode of the incident light side is a counter electrode). The SEM photograph which illustrated the surface form which has the pitting corrosion-like recessed part of the electrode material which consists of a stainless steel plate of this invention. The figure which showed typically the form of the pitting corrosion-like pit which appears in the cross section parallel to the plate | board thickness direction of the stainless steel plate of this invention. The figure which showed typically the structure of the dye-sensitized solar cell (type which has a photoelectric converting layer in the electrode of incident light side) using the electrode material of this invention. The figure which showed typically the structure of the dye-sensitized solar cell (type in which the electrode of incident light side is a counter electrode) using the electrode material of this invention.

Explanation of symbols

1 counter 40 present invention comprising the electrode material of the solar cell 2 transparent substrate 3 photoelectrode 4 substrate 5 counter 6 photoelectric conversion layer 7 TiO ₂ particles 8 Ru dye 9 electrolytic solution 10 catalyst layer 11 loads 20 the incident light 21 stainless steel 30 invention Photoelectrode made of any electrode material

Claims (10)

  An electrode material for a dye-sensitized solar cell comprising a stainless steel plate having a pitting corrosion-like recess having an average opening diameter D of 0.5 to 5 μm at a surface area ratio of 50% or more.   The electrode material for a dye-sensitized solar cell according to claim 1, wherein the stainless steel sheet contains Cr in a range of 17 to 32 mass% and Mo in a range of 0.8 to 3 mass%.   2. The dye-sensitized type according to claim 1, wherein the stainless steel sheet contains 17 to 32 mass% of Cr and 0.8 to 3 mass% of Mo in a ferritic steel type defined in JIS Z4305. Solar cell electrode material.   In mass%, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0.8 to 3%, N: 0.025% Hereinafter, the balance is made of a stainless steel plate substantially having a composition of Fe, exhibiting a ferrite phase structure, and having a pitting corrosion-like recess having an average opening diameter D of 0.5 to 5 μm at a surface area ratio of 50% or more. Electrode material for dye-sensitized solar cells.   The stainless steel sheet further contains at least one of mass%, Al: 5% or less, Ti: 1% or less, Nb: 1% or less, Cu: 3% or less, and Ni: 5% or less. Item 5. An electrode material for a dye-sensitized solar cell according to Item 4.   6. The electrode material for a dye-sensitized solar cell according to claim 1, wherein the surface of the stainless steel plate having a pitting corrosion-like recess has a surface roughness SRa of 0.1 to 1.5 μm. In mass%, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0.8 to 3%, N: 0.025% Hereinafter, the current density during anodic electrolysis is 1 in an aqueous ferric chloride solution having an Fe ³⁺ concentration of 1 to 50 g / L, with respect to a stainless steel plate having a substantially Fe composition and a ferrite phase structure. .0~10.0kA / m ^2, by applying an alternating electrolysis 1~20Hz that the current density during cathodic electrolysis and 0.1~3.0kA / m ^2, an area ratio of 50% or more on the steel sheet surface The manufacturing method of the electrode material of the dye-sensitized solar cell which forms a pitting corrosion-like recessed part with average opening diameter D: 0.5-5 micrometers in a ratio.   The stainless steel sheet further includes one containing at least one of mass%, Al: 5% or less, Ti: 1% or less, Nb: 1% or less, Cu: 3% or less, and Ni: 5% or less. Item 8. A method for producing an electrode material for a dye-sensitized solar cell according to Item 7.   The electrode of the dye-sensitized solar cell which used the electrode material in any one of Claims 1-6 as a base material, and formed the catalyst layer on the stainless steel plate surface which has the pitting corrosion-like recessed part.   The electrode of the dye-sensitized solar cell according to claim 9, wherein the catalyst layer is formed by performing platinum plating.