JP2008034110A - Electrode material of dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode material of a dye-sensitized solar cell which is made of a metallic material of low cost. <P>SOLUTION: The electrode material of the dye-sensitized solar cell is composed of a ferrite system steel which has a composition in which in mass%, C:0.15% or less, Si:1.2% or less, Mn:1.2% or less, Cr:17-32%, Mo:0.8-3%, and N:0.025% and, as required, which includes one kind or more of Cu:1% or less, Nb:1% or less, and Ti:1% or less, and the rest is, in substance, Fe; or austenite system steel or austenite+ferrite two-phase steel which has a composition in which C:0.15% or less, Si:4% or less, Mn:2.5% or less, Ni:3-28%, Cr:17-32%, Mo:0.8-7%, N:0.30.3% or less, and, as required, which includes one kind or more of Cu:3.5% or less, Nb:1% or less, and Ti:1% or less, and the rest is, in substance, Fe. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a metal material constituting an electrode of a dye-sensitized solar cell, and particularly an electrode material suitable for a “counter electrode” for directly contacting an electrolyte solution containing iodine and passing electrons to ions in the solution. About.

  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. .

  FIG. 1 schematically shows the structure of a conventional dye-sensitized solar cell. (A) is a type having a photoelectric conversion layer on an electrode on the incident light side, and (b) is a type in which the electrode on the incident light side is a “counter electrode”.

In the type of FIG. 1A, the solar cell 1 is configured by the photoelectrode 3 formed on the surface of the glass 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). . 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. Since the counter electrode 5 needs to exhibit excellent corrosion resistance with respect to the electrolyte solution 9 containing iodide ions, the counter electrode 5 is made of noble metal such as platinum, ITO, FTO, or TO. A load 10 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 10 → counter electrode 5 → electrolyte solution 9 → Ru dye 8. As a result, a current for operating the load 10 is generated.

  In the type of FIG. 1B, 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. . The photoelectrode 3 in this case is not necessarily a transparent film, and a noble metal plate or the like may be used. The other configuration is basically the same as the type shown in FIG. The principle of current generation is the same as described above.

JP 2003-123858 A JP 2004-3111197 A JP 2005-235664 A Hironori Arakawa, “Elemental Technology of High-Performance Dye-Sensitized Solar Cell”, Applied Physics, 2004, Vol. 73, No. 12, p. 1519-1523

  In order to promote the spread of dye-sensitized solar cells, there is a strong demand for the construction of technology that can further improve performance and reduce costs. One of the important matters is the development of elemental technology that improves the electrical conductivity of the electrode by a method that is as inexpensive as possible.

  In the type shown in FIG. 1 (a), if a transparent electrode is used for both the “photoelectrode” and the “counter electrode”, the decrease in conductivity increases. Therefore, in order to alleviate this, it is not necessary to transmit light. It is advantageous that the “counter electrode” is made of a metal material having a low electric resistance. However, since an electrolyte solution containing iodide ions is used, it is necessary to employ a metal material having sufficient corrosion resistance against iodide ions.

  Stainless steel is a metal material that is inherently excellent in corrosion resistance. However, the corrosion resistance in an electrolyte solution containing iodide ions is not sufficiently grasped, and it is known that at least general-purpose stainless steel types such as SUS430 and SUS304 cause severe corrosion in the electrolyte solution. For this reason, stainless steel cannot be easily adopted as the counter electrode material of the dye-sensitized solar cell. Patent Document 3 lists various corrosion resistant materials such as gold, silver, copper, platinum, nickel, titanium, tantalum, tungsten, aluminum, and stainless steel as the counter electrode metal material (paragraph 0015). Only platinum plates are used in the examples. In fact, a dye-sensitized solar cell that has succeeded in using stainless steel as a counter electrode material has not been seen yet.

  In this way, noble metals such as platinum are currently used as the metal material for the counter electrode, and in order to improve the conductivity at the counter electrode, the cost is increased by using an expensive noble metal material. Accompanying.

  On the other hand, in the type shown in FIG. 1B, it is effective for improving the conductivity to form the “photoelectrode” with a metal material. Since the photoelectric conversion layer covering the surface of the “photoelectrode” is a porous substance, a material exhibiting high corrosion resistance against an electrolyte solution containing iodide ions may be employed as the photoelectrode material in this case as well. is important.

  In view of such a current situation, an object of the present invention is to provide an inexpensive material having high corrosion resistance suitable for an electrode material of a dye-sensitized solar cell.

  In order to achieve the above object, in the present invention, by mass, C: 0.15% or less, Si: 1.2% or less, Mn: 1.2% or less, Cr: 17 to 32%, Mo: 0 Provided is an electrode material for a dye-sensitized solar cell made of steel having a composition of 0.8 to 3%, N: 0.025% or less, and the balance being substantially Fe and having a ferrite phase structure. In the above composition, if necessary, Cu: 1% or less can be further contained.

  Further, in mass%, C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, Ni: 3 to 28%, Cr: 17 to 32%, Mo: 0.8 to 7% , N: 0.3% or less, and the balance is substantially Fe, and an electrode material for a dye-sensitized solar cell made of steel having an austenite phase structure or an austenite + ferrite two-phase structure is provided. In this case, if necessary, Cu: 3.5% or less can be further contained.

  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. This electrode material is used, for example, by exposing the steel surface to an electrolyte solution containing iodine.

  Since the electrode material of the dye-sensitized solar cell of the present invention is composed of an Fe-based metal material, it has a higher conductivity than a transparent conductive film such as ITO, FTO, or TO, and is much higher than a noble metal material such as platinum. Inexpensive. This Fe-based metal material has been adjusted to a stainless steel composition exhibiting excellent corrosion resistance against the electrolyte solution of the dye-sensitized solar cell. Conventionally, such an inexpensive material is an electrode material for the dye-sensitized solar cell. It was not known to have applicable properties. Therefore, the present invention can contribute to the cost reduction of the dye-sensitized solar cell.

  In dye-sensitized solar cells that are currently being studied for practical use, an electrolyte solution containing iodide ions in an organic solvent is used. Therefore, the electrode needs to be made of a material that exhibits stable and excellent corrosion resistance for a long time against iodide ions. Since the counter electrode 5 of FIG. 1A type and the photoelectrode 3 of FIG. 1B type do not need to transmit light, they are not transparent oxide-based materials such as ITO, FTO, TO, It is desirable to use a metal material with low electrical resistance. However, in dye-sensitized solar cells at the stage of practical use, even such electrodes use oxide-based materials such as ITO and FTO whose reliability is known from past data and the like. . As for metal materials, little attention is paid to other than noble metal materials such as platinum.

  As a result of various studies, the inventors have found that in Fe-based metallic materials having a composition as stainless steel, dissolution in an iodine-containing electrolyte solution using an organic solvent is almost achieved by containing a certain amount or more of Cr and Mo. It was discovered that excellent corrosion resistance that does not progress can be imparted. By utilizing this property, it becomes possible to construct an electrode material for a dye-sensitized solar cell using a stainless steel material. That is, a new application has been found in a stainless steel material having a specific composition.

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 found that severe corrosion occurs in SUS304, which is a general-purpose steel grade, and the application of stainless steel materials to applications that are directly exposed to the electrolyte solution has been avoided. This was a factor that motivated me to make a detailed examination.

  As a result of detailed studies, the inventors have applied the present invention to a dye-sensitized solar cell when the Cr content in the Fe-based metal material is 17% by mass or more and the Mo content is 0.8% by mass or more. It was found that excellent corrosion resistance that hardly dissolves in the iodine-containing electrolyte solution is expressed. As described above, even when the application is an everyday hot water environment, in order to provide corrosion resistance that can sufficiently withstand it, it is necessary to add a relatively large amount of Mo, for example, 1.75% by mass or more. 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. Moreover, this tendency is not significantly affected by steel types such as austenitic and ferritic, and is less affected by other additive elements. This point is very different from the corrosion resistance tendency of stainless steel against chloride ions. Therefore, it is considered that the mechanism for improving corrosion resistance caused by Cr, Mo and the like cannot be equated with the case of chloride ions.

  In the present invention, ferritic steel types and austenitic and austenite + ferrite two-phase steel types are intended for steels having the following composition ranges, respectively. Unless otherwise specified, “%” with respect to the alloy element content means “mass%”.

[Ferrite type]
“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, balance A composition of “Fe” can be employed.
Among these, C, Si, Mn, and N are elements that are unavoidable in the melting process at the mass production site of stainless steel, and are allowed to be contained within the above range. However, considering various properties such as manufacturability, for example, C: 0.01% or less, Si: 0.5% or less or 0.3% or less, Mn: 0.5% or less or 0.3% or less, N: It is effective to control to 0.020% or less.

  Excellent corrosion resistance such that when the Cr content is less than 17% or the Mo content is less than 0.8%, the material hardly dissolves in the iodine-containing electrolyte solution applied to the dye-sensitized solar cell. It becomes difficult to obtain a stable. 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.

  As another optional element, a composition containing Cu: 1% or less, for example, 0.01 to 1% can be adopted. In this case, the Cu content may be more severely controlled, for example, within a range of 0.1% or less.

The remainder other than these may be substantially composed of Fe, but the following elements can be generally listed as elements that are allowed to be mixed into stainless steel. The allowable range is also shown.
P: 0.04% or less, S: 0.03% or less, preferably 0.005% or less, Ni: 0.6% or less, preferably 0.25% by mass or less, Nb: 1% or less, preferably 0.5% Ti: 1% or less, preferably 0.3% or less, Al: 0.2% or less, O: 0.005% or less, B: 0.01% or less, V: 0.3% or less, Zr: 0 .3% or less, Ca, Mg, Co, and REM (rare earth elements): 0.1% or less in total

[Austenitic, austenitic + ferrite two-phase]
“C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, Ni: 3 to 28%, Cr: 17 to 32%, Mo: 0.8 to 7%, N: 0.00. A composition of 3% or less and the balance substantially Fe "can be employed.
Among these, C, Si, Mn, and N are elements that are unavoidable in the melting process at the mass production site of stainless steel, and are allowed to be contained within the above range. However, considering various properties such as manufacturability, for example, C: 0.08% or less or 0.03% or less, Si: 1% or less or 0.6% or less, Mn: 2% or less, N: 0.00 It is effective to control to 03% or less or 0.01% or less.
In the case of an austenitic system, Ni is contained in an amount of 7% or more, preferably 10% or more.

  When the Cr content is less than 17% or the Mo content is less than 0.8%, the material is hardly dissolved in the iodine-containing electrolyte solution applied to the dye-sensitized solar cell as in the case of the ferrite type. It becomes difficult to stably obtain excellent corrosion resistance that does not occur. In order to further improve the reliability, it is preferable to contain 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. The Mo content is preferably 7% or less, and more preferably 4% or less.

As another optional element, a composition containing Cu: 3.5% or less, for example, 0.01 to 3.5% can be adopted. In this case, the Cu content may be more severely controlled, for example, within a range of 0.1% or less.
In this case, the Cu content may be more severely controlled, for example, within a range of 1% or less, or 0.5% or less.

The remainder other than these may be substantially composed of Fe, but the following elements can be generally listed as elements that are allowed to be mixed into stainless steel. The allowable range is also shown.
P: 0.045% or less, S: 0.03% or less, preferably 0.005% or less, Nb: 1% or less, preferably 0.5% or less, Ti: 1% or less, preferably 0.3% or less, Al : 0.1% or less, preferably 0.01% or less, O: 0.01% or less, preferably 0.005% or less, B: 0.01% or less, V: 0.3% or less, Zr: 0.3 % Or less, Ca, Mg, Co and REM (rare earth elements): 0.1% or less in total

  The Fe-based metal material whose composition is adjusted as described above may be a steel plate having a necessary thickness by a general stainless steel plate manufacturing process. Using this as an electrode material, a “counter electrode” used by exposing the surface of the steel to an electrolyte solution, or a “photoelectrode” by forming a photoelectric conversion layer on the surface of the steel, a dye-sensitized solar cell Can be built.

  In FIG. 2, the structural example of the dye-sensitized solar cell using the electrode material of this invention is shown typically. FIG. 2A shows a conventional dye-sensitized solar cell of the type shown in FIG. 1A 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. FIG. 2B shows a conventional dye-sensitized solar cell of the type shown in FIG. 1B in which the substrate 4 and the photoelectrode 3 are replaced with a photoelectrode 40 made of the electrode material of the present invention. is there.

Various Fe-based metallic materials having the compositions shown in Table 1 are melted at the stainless steel melting site, and cold rolled annealed steel sheets (2D finish materials) having a thickness of 0.28 to 0.81 mm are produced by a general stainless steel sheet manufacturing process. This was manufactured and used as a test material. In Table 1, in the structure column, “α” means ferrite and “γ” means austenite. The hyphen “-” in Cu, Nb, Ti, and Al means that it is below the measurement limit in a normal analysis method at a steelmaking site. The “-” display in B means that no analysis is performed. However, the content of B exceeding 0.01% is not considered from the steelmaking conditions.
By observing the structure of the specimen, it has been confirmed that the ferrite type matrix has a ferrite phase, and the austenitic type matrix has an austenitic phase.

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 hold | maintained in the 80 degreeC thermostat, and the test piece was taken out after 500-hour progress from the immersion start. For each steel type, the number of samples was n = 3.

  About each test piece after 500-hour immersion, the weight change (initial test piece weight-test piece weight after immersion) was measured. The lowest value (that is, the largest weight loss value) among the weight change values of n = 3 was adopted as the result of the weight change of the steel type. Moreover, the surface was visually observed and the external appearance was investigated. 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. Except for the steel type in which the overall corrosion or end face corrosion was recognized in the appearance after immersion for 500 hours, the specimen after observation was again subjected to the above immersion test. At that time, a new test solution was used. The test piece was taken out when the total immersion time from the initial state was 1000 h, and the weight change and appearance were examined in the same manner as described above.

The value of the weight change after the immersion test means that the larger the value on the negative side, the more the amount of dissolution due to corrosion. When the total weight change after the 1000 h immersion test was on the plus side of −0.05 g / m ² , it was evaluated that the dissolution due to corrosion hardly proceeded, and this was determined to be acceptable.
As for the appearance, those having no dissolved part and no rusting were indicated as “no abnormality”, and those evaluated as “no abnormality” after the 1000 h immersion test were determined to be acceptable.
The results are shown in Table 2.

  As can be seen from Tables 1 and 2, in the examples of the present invention containing Cr: 17% or more and Mo: 0.8% or more, dissolution due to corrosion was hardly observed in the iodide ion-containing electrolyte solution. In addition, excellent corrosion resistance with no occurrence of spot rust was observed. Therefore, these are considered to have sufficient durability required for the electrode material of the dye-sensitized solar cell.

A test piece of 100 × 100 mm was cut out from the specimen prepared in Example 1, and the surface was finished by # 600 dry emery polishing. For reference, Nesa glass (a transparent conductive film of TO (tin oxide) deposited on a glass substrate) was prepared.
About these surfaces (nesa glass is a conductive film surface), the surface resistivity was measured by a 4-probe method using a low resistivity meter (manufactured by Mitsubishi Chemical Corporation, Lorester GP). The number of samples was n = 3, and an average value was adopted.
The results are shown in Table 3.

  As can be seen from Table 3, the metal material having a stainless steel composition has a very low surface electrical resistance as compared with the oxide-based conductive film. Therefore, it is considered that the conductivity at the electrode of the dye-sensitized solar cell can be remarkably improved by using the electrode material of the present invention.

The figure which showed typically the structure of the conventional dye-sensitized solar cell. The figure which showed typically the structural example of the dye-sensitized solar cell using the electrode material of this invention.

Explanation of symbols

Photoelectrode consisting of 1 solar cell 2 glass 3 photoelectrode 4 substrate 5 counter 6 photoelectric conversion layer 7 TiO ₂ particles 8 Ru dye 9 electrolytic solution 10 load 20 made of the electrode material of the incident light 30 present invention the electrode material of the counter electrode 40 present invention

Claims (5)

  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 electrode material of the dye-sensitized solar cell made of steel having the balance substantially Fe composition and exhibiting a ferrite phase structure.   Furthermore, the electrode material of Claim 1 containing Cu: 1% or less.   In mass%, C: 0.15% or less, Si: 4% or less, Mn: 2.5% or less, Ni: 3-28%, Cr: 17-32%, Mo: 0.8-7%, N An electrode material for a dye-sensitized solar cell made of steel having an austenite phase structure or an austenite + ferrite two-phase structure having a Fe composition of 0.3% or less and the balance being substantially Fe.   Furthermore, Cu: The electrode material of Claim 3 containing 3.5% or less.   The electrode material according to claim 1, wherein the electrode material is used by exposing the surface of the steel to an electrolyte solution containing iodine.

Images