JP2012201950A - METHOD FOR PRODUCING STAINLESS STEEL SHEET WITH FINELY ROUGHENED SURFACE AND THIN FILM Si SOLAR CELL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology that allows uniform formation of finely roughened surface texture on the surface of a stainless steel sheet, and especially technology suitable for a substrate of a thin film Si solar cell.SOLUTION: A method for producing a stainless steel sheet with finely roughened surface includes: a step (cathode electrolysis step) of allowing a film thickness of a passivation film to be 4.0 nm or less by performing cathode electrolysis of a ferritic stainless steel sheet in an aqueous solution having pH of 11.0 or more at electric potential of -0.5 to -2.2 Vvs.SCE; and a step (etching step) of allowing a projected area ratio (pit occupied area ratio) to be 40% or more and average surface roughness SPa to be 0.05 or more and less than 0.30 μm in a pit generation portion covering the surface by immersing the steel sheet which completed the cathode electrolysis step in a mixed aqueous solution of ferric chloride and hydrochloric acid having FeClconcentration of 2-50 mass% and HCl concentration of 0.1-20 mass% and generating pits on the surface.

Description

  The present invention relates to a method for producing a roughened stainless steel plate having a fine texture formed on the surface, a substrate for a thin film Si solar cell comprising the roughened stainless steel plate, and a thin film Si solar using the roughened stainless steel plate. The present invention relates to a battery manufacturing method.

  Attempts have been made to form fine irregularities on the thin-film Si solar cell substrate in order to improve the efficiency by lengthening the optical path of the light absorption layer formed thereon. Further, in order to cope with flexibility, application of metal materials such as stainless steel plates has been attempted. By applying a metal substrate, it is possible to manufacture by roll-to-roll, and productivity is greatly improved.

As a method for forming irregularities on the surface of stainless steel, it is difficult to form fine irregularities uniformly by an electrolytic etching method or a mechanical polishing method that is generally performed conventionally.
Surface roughening by shot blasting or honing can form a surface having a relatively large anchor effect, but is not suitable for forming fine irregularities at low cost. In addition, there is an environmental problem that dust is generated, and workability is poor. In order not to adversely affect the subsequent process, a process for removing the powder of the base material removed by blasting is also required, and the work efficiency is reduced. Furthermore, in the case of a thin plate having a thickness of 0.5 mm or less, there is a problem that warpage is likely to occur.
Roughening by dull roll rolling is to transfer the irregularities formed on the rolling roll during rolling, and it is difficult to form irregularities with a fine pitch.
Pickling with an acid solution such as nitric hydrofluoric acid is effective for removing a weakened surface layer, but is not suitable as a means for forming a fine uneven texture.

  Etching by immersing in ferric chloride aqueous solution or spraying ferric chloride aqueous solution is a relatively simple method, but these methods are originally intended to make patterns by opening through holes or half-etching It is suitable for performing large volume etching. In these methods, in order to prevent side etching, it is customary to perform etching so that the etched surface is not rough as much as possible to finish the surface smoothly. Therefore, these methods are not suitable as a method for forming fine irregularities.

  Surface roughening by electrolysis in an acid solution or ferric chloride aqueous solution can form a surface with a high anchoring effect, but the processing time is long, productivity is low, and equipment costs are high. There is a problem that becomes.

As a technique for roughening the surface of stainless steel using electrolysis, Patent Document 1 discloses a direct current having a current density of ^{20 to} 100 mA / cm ² using stainless steel as an anode in a 0.02 to 2.0 wt% sodium chloride aqueous solution. In the aqueous solution further containing 0.02 to 20% by weight of sodium chloride and 0.03 to 3.0% by weight of hydrochloric acid, the direct current having a current density of ^{20 to} 100 mA / cm ² is obtained again using stainless steel as an anode. The surface of the non-pitting portion is roughened by chemical surface corrosion or mechanical surface polishing, or a thin oxide film layer on the surface by short-time heating in various high-temperature atmospheres. A method for forming the film is disclosed. However, in this method, electrolytic treatment is performed for 40 minutes in order to obtain a target form, and productivity is low.

  Patent Document 2 discloses that stainless steel is subjected to anodic electrolysis or anodic electrolysis + cathodic electrolysis in a nitric acid solution, so that it is coarsened by passivation with nitric acid and overpassive dissolution by anodic electrolysis, or further active dissolution by cathodic electrolysis. A method of forming a surface is disclosed. However, since the active region, passive region, and hyperpassive region are different depending on the steel type and surface condition, the potential and electrolytic current must be set according to the individual materials in order to control the roughening form with high accuracy. It is necessary to perform strictly, and the process becomes complicated. For this reason, this method is not always easy to implement industrially.

  Patent Document 3 describes that the reduction of Fe in the hydroxide film is promoted by the cathode electrolysis by pretreatment by alkaline electrolysis, and the Cr concentration in the hydroxide film increases. However, there is no description about roughening treatment in an acid solution after cathodic electrolysis.

  Patent Document 4 describes that cathodic electrolysis is performed in an alkaline solution on a chemically or electrically roughened surface. This method is said to improve the adhesion of the coated film after roughening. However, it is difficult to obtain a fine roughened texture by such a procedure.

  Patent Document 5 discloses an amorphous silicon solar cell in which an amorphous silicon layer and a transparent electrode layer are sequentially formed on the surface of an aluminum substrate roughened by electrochemical etching or chemical etching. However, the conditions for forming irregularities on the stainless steel plate are not described.

JP 56-77400 A JP-A-6-136600 JP 2002-275658 A JP 2005-42130 A JP 59-14682 A

  The present invention is a technique for uniformly forming a fine roughened texture on the surface of a stainless steel plate, and is intended to provide a technique particularly suitable for a substrate of a thin-film Si solar cell.

The purpose is mass%, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.01 to 2.0%, P: 0.001 to 0.050. %, S: 0.0005 to 0.030%, Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 11.0 to 32.0%, Mo: 0 to 3.0% , Al: 0 to 1.0%, Nb: 0 to 1.0%, Ti: 0 to 1.0%, N: 0 to 0.0025%, B: 0 to 0.01%, V: 0 0.5%, W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth element) total: 0 to 0.1%, balance Fe and unavoidable impurity composition, outermost surface A ferritic stainless steel sheet having a passive film on the surface is subjected to cathodic electrolysis in an aqueous solution having a pH of 11.0 or more at a potential of -0.5 to -2.2 V vs. SCE, whereby the depth direction from the outermost surface by AES Elemental profile to Takes half the oxygen concentration position of SiO ₂ in terms depth by determined step of less 4.0nm thickness of the passivation film (cathode electrolysis step),
The steel plate that has undergone the cathodic electrolysis step is dipped in a mixed aqueous solution of ferric chloride and hydrochloric acid having an FeCl ₃ concentration of 2 to 50% by mass and an HCl concentration of 0.1 to 20% by mass to generate pits on the surface, A step (etching step) of setting the ratio of the projected area of the pit generation portion on the surface (pit occupation area ratio) to 40% or more and the average surface roughness SPa to less than 0.05 to 0.30 μm;
It is achieved by a method for producing a fine-roughened stainless steel sheet having

Moreover, in this invention, the board | substrate for thin film Si solar cells which consists of a fine-roughened stainless steel plate obtained by the said manufacturing method is provided. In that case, it is particularly preferable that the pit occupation area ratio is 85% or more and the average surface roughness SPa is 0.05 to 0.20 μm in the etching step.
Moreover, the manufacturing method of the thin film Si solar cell which manufactures a fine roughening stainless steel plate with said manufacturing method, and forms the film for photoelectric conversion on the fine roughening surface by using the steel plate as a board | substrate is provided.

Here, the “ferritic stainless steel sheet having a passive film on the outermost surface” means one that is not coated with a coating film or other various coating layers or oxide scales formed by heat treatment. For example, those having pickled skin and those having surface skin finished by cold rolling after pickling are targeted.
“1/2 oxygen concentration position” means a depth position at which the oxygen detection amount becomes 1/2 of the maximum value for the first time in an element profile from the outermost surface to the depth direction by AES (Auger electron spectroscopy). .

  “Surface roughness SPa” is obtained by measuring the arithmetic average height Pa of the cross-sectional curve defined in JIS B0601-2001 for a surface area of a certain area and taking the average value. Specifically, SPa is one of the surface roughness parameters obtained by analyzing the data of the three-dimensional surface profile measured by the scanning confocal laser microscope, and the elevation of the cross-sectional curved surface relative to the average surface of the cross-sectional curved surface. Means the average of absolute values. The surface area for measuring the three-dimensional surface profile may be a rectangular surface area having a side of 50 μm. It is desirable that the resolution in the depth direction of the scanning confocal laser microscope is 0.01 μm or less. On the other hand, in the stylus type roughness meter defined in JIS, the tip diameter of the stylus is 5 μm, and the tip of the stylus does not enter the recess on the surface where the fine irregularities are formed as in the present application. Therefore, it is not suitable for surface roughness measurement.

  According to the present invention, it is possible to efficiently produce a stainless steel plate having a fine roughened texture on the surface. Cathodic electrolysis according to the present invention does not require severe selection of the liquid concentration and electrolysis conditions depending on the natural potential and corrosion resistance which vary depending on the steel type, and is easy to apply widely to various ferritic stainless steel types. Further, the obtained roughened surface has a fine and uniform texture, and the photoelectric conversion efficiency can be improved by using this as a substrate for a thin film Si solar cell.

The SEM photograph of the stainless steel plate surface which has the fine unevenness | corrugation texture obtained according to this invention.

  The inventors have conducted research on a method for forming a uniform uneven texture on the surface of stainless steel. As a result, it was found that it is extremely effective to modify the passive film of stainless steel in advance before chemical etching with a mixed aqueous solution of ferric chloride and hydrochloric acid. This modification process of the passive film is a process that should be referred to as a pretreatment for chemical etching, and specifically, cathodic electrolysis is performed in an alkaline aqueous solution.

  Regarding Fe and Cr, which are the main elements constituting the passive film of stainless steel, the potential-pH relationship in the aqueous solution is seen. In the high pH range, the Fe oxide becomes unstable at the lower potential side. However, for Cr oxide, there is a region that is still stable even in the low potential region. If the surface of the stainless steel is held in such a region where the Fe oxide becomes unstable compared with the Cr oxide, the passive film can be modified to a thin film rich in Cr oxide. Specifically, for a ferritic stainless steel having a composition range to be described later, a Cr oxide-rich thin film is formed by holding in a region of potential: −0.5 V vs. SCE or lower and pH: 11.0 or higher. A passive film can be formed. If the potential is too low, a large amount of hydrogen is generated, which is uneconomical. Therefore, the lower limit of the potential is desirably -2.2 V vs. SCE.

  Fine ferritic pits are uniformed by subjecting the ferritic stainless steel plate, in which the passive film is modified to a thin film rich in Cr oxide by cathodic electrolysis, to a chemical etching process in which it is immersed in a mixed aqueous solution of ferric chloride and hydrochloric acid Thus, the fine uneven texture distributed on the surface can be formed in a short time. Although the mechanism is not necessarily clear at present, the following may be considered. In the ordinary passive film of stainless steel, there are many Fe oxides particularly in the portions where surface defects are present, and the distribution of Fe oxides is non-uniform. On the other hand, in the film modified by the cathodic electrolysis, much of the existing Fe oxide is removed, and the component distribution in the film is made more uniform. Therefore, a large number of pits (pitting corrosion) are generated simultaneously from many locations on the surface of the film by the etching solution. These pits grow in the depth direction while expanding the openings, and the opening diameter of each pit ends when the openings of adjacent pits collide with each other. In this way, it is assumed that the surface of the stainless steel plate is covered with fine pits that are deep with respect to the opening diameter. Also, since the passive film is thin, the steel substrate starts to dissolve quickly, so that a fine uneven texture can be formed in a short time. This fine asperity texture has been confirmed to bring about an improvement in photoelectric conversion efficiency when used as a substrate of a thin film Si solar cell, for example.

Hereinafter, matters for specifying the present invention will be described.
[Chemical composition of stainless steel]
In the present invention, a ferritic stainless steel having a relatively low thermal expansion coefficient among steels is targeted. Depending on the required properties, various stainless steel types in the following composition ranges are widely applicable. Among them, many known standard steel types are included.
Composition range;
By mass%, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.01 to 2.0%, P: 0.001 to 0.050%, S: 0.0005 to 0.030%, Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 11.0 to 32.0%, Mo: 0 to 3.0%, Al: 0 -1.0%, Nb: 0-1.0%, Ti: 0-1.0%, N: 0-0.0025%, B: 0-0.01%, V: 0-0.5% , W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth elements) total: 0 to 0.1%, balance Fe and inevitable impurities

[Cathode electrolysis process]
As described above, in the present invention, prior to the etching step, cathodic electrolysis in an alkaline aqueous solution is performed in order to modify the passive film of stainless steel. At that time, it is important that the pH of the electrolytic solution is 11.0 or more. In an electrolytic solution having a lower pH than that, the potential condition that can stabilize the Cr oxide while sufficiently reducing the Fe oxide is narrowed. When the pH is 11.0 or more, the degree of freedom in setting an appropriate potential and electrolysis time is expanded in the steel types having the above composition range, which is suitable for industrial production. However, it is not necessary to set the pH to an excessively high level, and it may be usually in the range of pH 13.0 or less.

  The potential of cathodic electrolysis is in the range of −0.5 to −2.2 V vs. SCE. Fe oxide is likely to be insufficiently removed on a higher potential side than −0.5 V vs. SCE. On the other hand, generation of hydrogen is intense on a lower potential side than −2.2 V vs. SCE, which is not industrially suitable.

The electrolytic solution is not particularly limited as long as the pH is 11.0 or higher, and examples thereof include a sodium hydroxide-containing aqueous solution, a sodium silicate-containing aqueous solution, a sodium carbonate-containing aqueous solution, and a mixed aqueous solution containing two or more of these substances. Suitable target. The liquid temperature during electrolysis is preferably in the range of 20 to 90 ° C., and the electrolysis current density is preferably in the range of ^{2 to} 10 A / dm ² .

Depending on these conditions, it is important to terminate the electrolysis in an electrolysis time when the thickness of the passive film after cathodic electrolysis is 4.0 nm or less. The film thickness here means the film thickness (described above) determined by the SiO ₂ equivalent depth at the 1/2 oxygen concentration position. When the film thickness exceeds 4.0 nm, the removal of Fe oxide is still insufficient, and the generation of pits becomes non-uniform in the subsequent etching, making it difficult to form a fine roughened texture. However, too thin a film is a factor that impairs productivity, so it is desirable to end electrolysis so that the film thickness becomes 2.0 to 4.0 nm. With such thinning, the coating composition changes to Cr oxide rich. The molar ratio of Cr / Fe in the film is preferably 1.0 or more, and more preferably in the range of 1.0 to 3.0. In addition, the range of the electrolysis conditions in which the passive film with a predetermined film thickness is formed according to the steel type can be grasped in advance in a preliminary experiment.

[Etching process]
Next, the steel plate that has undergone the cathodic electrolysis step is chemically etched by a method of immersing it in a ferric chloride + hydrochloric acid mixed aqueous solution.
Ferric chloride has the action of generating pitting corrosion on the stainless steel surface, and hydrochloric acid has the action of completely dissolving the stainless steel surface. According to the method of immersing a ferritic stainless steel sheet in an aqueous solution in which these two substances are mixed in a well-balanced manner, fine irregularities can be uniformly formed on the surface as compared with the case of immersing in a conventional aqueous solution of ferric chloride. Is possible. Immediately after being immersed in the etching solution, fine pits are generated on the entire surface of the steel sheet, and the inner walls of the pits generated on the steel sheet surface are etched with time, and deep pits are formed with respect to the opening diameter. As the pit grows, the wall surfaces of adjacent pits collide with each other, and as a result, the boundary becomes an edge shape.

When the mixing amount of ferric chloride in the etching solution is small, the entire surface is etched, but sufficient SPa and area increase rate cannot be obtained. For example, when used for a substrate of a thin film Si solar cell The effect of improving the photoelectric conversion efficiency is reduced. When the mixing amount of hydrochloric acid is small, pitting corrosion is formed on the surface, but many pit non-occurrence portions remain, and also in this case, the effect of improving the photoelectric conversion efficiency is reduced. According to the inventors' detailed study, the composition of the ferric chloride + hydrochloric acid mixed aqueous solution was adjusted to the surface by adjusting the FeCl ₃ concentration in the range of 2 to 50% by mass and the HCl concentration in the range of 0.1 to 20% by mass. Roughened texture having a projected area ratio (pit occupied area ratio) of 40% or more and an average surface roughness SPa of less than 0.05 to 0.30 μm, preferably 0.05 to 0.25 μm. Can be obtained. Such a fine roughening texture has not been obtained by conventional general roughening techniques. It is easy to find optimum conditions in the range of FeCl ₃ concentration of 10 to 20% by mass and HCl concentration of 1 to 10% by mass in the ferritic steel types having the above composition range. When used as a substrate for a thin-film Si solar cell, it is particularly desirable that the pit occupation area ratio is 85% or more and the average surface roughness SPa is 0.05 to 0.20 μm. The temperature of the etching solution is desirably in the range of 10 to 90 ° C. The immersion time is adjusted so that the pit occupying area ratio and SPa are in a predetermined range according to the application.

  A ferritic stainless steel sheet (bright annealing material) having a thickness of 0.2 mm having the composition shown in Table 1 was prepared.

Each stainless steel plate was subjected to cathodic electrolysis at various potentials using electrolytic solutions adjusted to various pHs. The current density was in the range of ^{2 to} 10 A / dm2. The type of electrolytic solution and electrolysis conditions are listed in Table 2. For the steel sheet after the cathodic electrolysis treatment, the film thickness measurement and composition analysis of the passive film were carried out by the following methods.

[Measurement of Passive Film Thickness]
The film thickness was determined by collecting the element profile from the outermost surface of the coating in the depth direction by AES. The apparatus used was JEMP; JAMP-9500. The film thickness in terms of SiO ₂ was determined by the sputtering time in which the oxygen profile in terms of SiO ₂ was ½ of the peak. The results are shown in Table 2.

[Composition analysis of passive film]
After the above electrolytic treatment, the composition of the passive film was investigated by XPS (X-ray photoelectron spectroscopy) for the sample immediately after being washed with water and dried. The apparatus was manufactured by Kratos; AXIS-NOVA was used, the excitation line of AlKα (single color) was used, the photoelectron extraction angle was set to 90 °, and the outermost surface of the coating was analyzed without sputtering. The amount of information in the depth direction by the analysis of the analyzer used is about 5 nm, and it can be determined that the information of the entire passive film is taken in. The composition of the passive film was indicated by the molar ratio of Cr and Fe existing in the film (Cr / Fe molar ratio). The results are shown in Table 2.

  As shown in Table 2, it is possible to adjust the film thickness of the passive film to 4.0 nm or less and the Cr / Fe molar ratio to 1.0 or more by cathodic electrolysis in a predetermined pH range. Met. Nos. 13, 33, and 53 in Table 2 are obtained by measuring the surface of the stainless steel plate before electrolytic treatment. In the example of the subject of the invention, the passive film is made thin with a Cr oxide-rich film by cathodic electrolysis. It can be seen that the film has been modified.

  On the other hand, Nos. 2, 22, and 42 had insufficient modification of the passive film due to insufficient electrolysis time. Nos. 5, 11, 12, 25, 31, 32, 45, 51, and 52 have electrolyte pH too low, and Nos. 8, 28, and 48 have electrolysis potentials too high. Passive film is not modified.

  Next, by using a part of the sample obtained in Example 1, an etching process was performed by immersing in a mixed aqueous solution of ferric chloride and hydrochloric acid to try to form a fine roughened surface. Etching conditions are listed in Table 3. For the sample after etching, the average surface roughness SPa, the surface area increase rate, and the pit occupation area rate were determined. Moreover, the thin film Si solar cell which used the steel plate after an etching for the board | substrate was produced, the photoelectric conversion efficiency was measured, and the performance was evaluated. These experimental methods are as follows.

[Measurement of average surface roughness SPa]
The roughened surface is observed with a scanning confocal laser microscope (Olympus; OLS1200), the surface profile of a rectangular region of 50 μm × 50 μm is captured with a resolution of 0.01 μm in the depth direction, and isolated points are removed as image processing 1 The average surface roughness SPa was calculated after performing the image averaging and the image luminance averaging once. The results are shown in Table 3.

[Measurement of surface area increase rate]
The surface area in a rectangular area of 50 μm × 50 μm was measured with the above-described scanning confocal laser microscope, and the area increase rate was determined by dividing the value by the projected area. The results are shown in Table 3.

[Measurement of pit occupation area ratio]
By observing the roughened surface with a scanning electron microscope at a magnification of 2000 times, the area of the pit occurrence portion (portion where the pit opening exists) in the projected image is obtained, and this is calculated as the pit occupation area ratio ( %). The results are shown in Table 3.

[Production of thin-film Si solar cells]
Using a steel plate after etching as a substrate, a 0.3 μm thick Ag layer is formed on the roughened surface by DC magnetron sputtering without heating the substrate, and a 50 nm thick ZnO layer is further formed thereon. Formed. Thereafter, the substrate was put in a plasma CVD apparatus, the substrate temperature was set to 200 ° C. under a reduced pressure of 1.5 × 10 ⁻⁵ Pa, and an n-type Si thin film having a thickness of 0.3 μm was formed using hydrogen gas and monosilane gas. An i-type Si thin film having a thickness of 1 μm was formed thereon at a substrate temperature of 200 ° C. Further, a p-type Si thin film having a thickness of 0.3 μm was formed thereon. Next, an ITO layer having a thickness of 50 nm was formed at a substrate temperature of 180 ° C. by high-frequency magnetron sputtering. Thereafter, the film was taken out into the atmosphere, a comb-like mask was attached, and a thin film Si solar cell was constructed by forming a 500 nm Ag thin film by DC magnetron sputtering without heating the substrate.

[Measurement of conversion efficiency]
The obtained solar cell was irradiated with simulated solar light of AM 1.5, 100 mW / cm ² using “Solar simulator; YSS-100” manufactured by Yamashita Denso Co., Ltd. The -V characteristic was measured, and the values of short circuit current density Jsc, open circuit voltage Voc, and form factor FF were obtained. From these values, the value of photoelectric conversion efficiency η was determined by the following formula (1).
Photoelectric conversion efficiency η (%) = short circuit current density Jsc (mA / cm ² ) × open circuit voltage Voc (V) × {form factor FF / incident light 100 (mW / cm ² )} × 100 (1)
The photoelectric conversion efficiency eta ₀ in the solar cell of the same structure using a flat conventional type substrate not roughened as a standard, the ratio eta / eta ₀ value of photoelectric conversion efficiency eta of the thin film Si solar cell for eta ₀ (Referred to as “conversion efficiency ratio”). The results are shown in Table 3.

  As can be seen from Table 3, according to the present invention, a fine uneven texture in which SPa, pit occupying area ratio, and area increase rate are appropriately controlled can be formed on the surface of the stainless steel plate, and a thin film using it as a substrate. In the Si solar cell, the conversion efficiency ratio clearly exceeded 1.00, and an improvement in photoelectric conversion efficiency was observed. The area increase rate is preferably 1.20 or more.

  On the other hand, Nos. 2-9 and 2-17 were subjected to etching with a mixed aqueous solution of ferric chloride and hydrochloric acid without performing the cathodic electrolysis, which was a pretreatment, and the SPa increased to cause a short circuit. . Nos. 2-2, 2-10, and 2-18 have a small pit occupation area ratio due to a short immersion time in etching, and Nos. 2-6, 2-14, and 2-22 Since the immersion time was long, SPa was lowered, and any of these showed no improvement in photoelectric conversion efficiency or remained at an insufficient level.

  For reference, FIG. 1 illustrates an SEM photograph of the surface of a stainless steel plate having a fine uneven texture obtained according to the present invention (Example of Table 3, No. 2-12).

Claims (4)

By mass%, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.01 to 2.0%, P: 0.001 to 0.050%, S: 0.0005 to 0.030%, Ni: 0 to 2.0%, Cu: 0 to 1.0%, Cr: 11.0 to 32.0%, Mo: 0 to 3.0%, Al: 0 -1.0%, Nb: 0-1.0%, Ti: 0-1.0%, N: 0-0.0025%, B: 0-0.01%, V: 0-0.5% , W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth elements) total: 0 to 0.1%, remaining Fe and unavoidable impurities, composition on the outermost surface Elemental profile from the outermost surface to the depth direction by AES by cathodic electrolysis of a ferritic stainless steel plate having a pH of −0.5 to −2.2 V vs. SCE in an aqueous solution having a pH of 11.0 or more 1/2 in The step of the thickness of passive film determined by SiO ₂ conversion depth of iodine concentration position than 4.0 nm (cathodic process),
The steel plate that has undergone the cathodic electrolysis step is dipped in a mixed aqueous solution of ferric chloride and hydrochloric acid having an FeCl ₃ concentration of 2 to 50% by mass and an HCl concentration of 0.1 to 20% by mass to generate pits on the surface, A step (etching step) of setting the ratio of the projected area of the pit generation portion on the surface (pit occupation area ratio) to 40% or more and the average surface roughness SPa to less than 0.05 to 0.30 μm;
A method for producing a fine-roughened stainless steel sheet having   The method for producing a fine-roughened stainless steel sheet according to claim 1, wherein the pit occupation area ratio is 85% or more and the average surface roughness SPa is 0.05 to 0.20 µm in the etching step.   A thin film Si solar cell substrate made of a fine-roughened stainless steel plate obtained by the production method according to claim 1.   A method for producing a thin-film Si solar cell, wherein a fine-roughened stainless steel plate is produced by the production method according to claim 1 or 2, and a film for photoelectric conversion is formed on the fine-roughened surface using the steel plate as a substrate.