JP5863380B2 - Stainless steel foil with insulating coating for solar cell and method for producing the same - Google Patents

Description

  The present invention relates to a stainless steel foil with an insulating coating for solar cells and a method for producing the same.

  Stainless steel foils with coatings are expected to be applied to electronic paper, organic EL displays, organic EL lighting, solar cell device substrates, etc. In solar cell substrates, heat resistance and insulation are important characteristics. .

  In particular, in a compound semiconductor solar cell such as CIGS (CuInGaSe), the substrate is exposed to a temperature of 500 ° C. or higher in the heating step of the manufacturing process. The stainless steel foil itself does not change in properties such as weight, Young's modulus, and hardness even when exposed to the CIGS process temperature, but heat resistance to heating temperatures of 500 ° C or higher is important for the coating coated with stainless steel. Become.

  Since the electromotive force and current obtained from one solar battery cell are small, it is necessary to connect a plurality of cells in series or in parallel. In the case of a solar battery substrate using a stainless steel foil, a method of forming cells directly on the stainless steel foil, cutting the whole substrate and connecting the target cells to each other with a conductive wire, etc., and a stainless steel foil having an insulating film as a glass substrate In the latter method, cells are formed to produce integrated modules, and the latter is highly productive due to its simple module structure. However, if the insulation of the coating is insufficient, multiple cells are connected. In this case, it is important to produce a film free from defects such as pinholes because the solar cell characteristics as designed cannot be obtained.

  Now, on the surface of the stainless steel foil, there are protrusions due to rolling stripes and wrinkles, adhered foreign matter due to altered oil wound in the rolling process, and the like. When these heights are sufficiently lower than the film thickness, a sound film is formed, but when there are protrusions or heights of adhering foreign matter that exceed the film thickness, there are cracks in the film. In many cases, short circuits occur due to the occurrence of repelling or pinholes during film formation. The existence probability of such high protrusions and foreign matters depends on the manufacturing process of the stainless steel foil, but generally speaking, it is very difficult to make one or less within 10 cm square. It is not unusual to have more than one. An example of a protrusion by a scissors is shown in FIG.

  Although the leakage current is measured with the configuration shown in FIG. 4, since there are film defects such as cracks, the leakage current often depends on the electrode area of the electrode 3, and the leakage current increases as the electrode area increases. Easy to connect to. Further, as the applied voltage increases, a high voltage is applied to a film having a thin film defect, and a short circuit is likely to occur.

In order to fabricate an integrated device, a large area has a low leakage current when a high voltage is applied, for example, 1 × 10 ⁻⁶ A / cm ² or less when a 50 V is applied at a 10 × 10 cm square, and 1 × 10 ⁶ when a 200 V is applied at a 1 × 1 cm square. It is required to be ⁻⁸ A / cm ² or less. Although the required area and leakage current vary depending on the device to be manufactured, 1 × 10 ⁻⁵ A / cm ² is one general-purpose index when applying 100 V at a 3 × 3 cm square. However, softening of the coating is effective in reducing the influence of rolling stripes, wrinkles, and adhering foreign matter on the surface of the stainless steel foil, but organic resin coatings rich in flexibility cannot be used because of their low heat resistance.

  Patent Document 1 discloses a stainless steel foil coated with an inorganic / organic hybrid that has higher heat resistance than an organic resin. However, in the coated stainless steel foil disclosed in Patent Document 1, the upper electrode has a 1 × 1 cm square. When a low voltage of about 10V is applied, there is a problem that even if insulation is maintained, a short circuit occurs at 100V.

  Patent Document 2 discloses a stainless steel foil coated with a plurality of inorganic polymer films. However, in the coated stainless steel foil disclosed in Patent Document 2, the coating with the inorganic polymer film is made of stainless steel foil and the upper electrode is 1 ×. In the case of forming 1 cm square, insulation is maintained by applying a low voltage of about 5V, but there is a problem that a short circuit occurs at 100V.

  In the stainless steel with a coating disclosed in Patent Document 1 and Patent Document 2, the coating is not clearly disclosed in terms of heat resistance in an environment of 500 ° C. or higher.

  The HT film disclosed in Non-Patent Document 1 as having a heat resistance of 500 ° C. or higher is an inorganic-organic hybrid film, but there is a problem that cracks occur when the film thickness exceeds 1 μm, and the film thickness is 1 μm. Even if it is below, if there is a protrusion on the stainless steel foil, a crack as shown in FIG. 5 occurs, causing a short circuit.

From these, the stainless steel foil having the coating disclosed in Patent Document 1, Patent Document 2 and Non-Patent Document 1 has a leakage current of less than 10 ⁻⁵ A / cm ² when 100 V is applied to the upper electrode 3 × 3 cm. It is difficult to satisfy the heat resistance of 500 ° C. or higher.

  Patent Document 3 discloses an electronic material substrate having a surface insulating layer on a substrate such as aluminum or titanium. The substrate surface is anodized to form a film, and then a non-conductive substance is formed on the surface. This layer is formed to fill the pores of the anodic oxide film.

However, Patent Document 3 can also be suitably used for a solar cell that satisfies both a leakage current of less than 10 ⁻⁵ A / cm ² and a heat resistance of 650 ° C. or higher when 100 V is applied to the upper electrode 3 × 3 cm. An insulating coated stainless steel foil is not taught.

Japanese Patent No. 3882008 Japanese Patent No. 4245394 Japanese Patent Laid-Open No. 11-229187

N. Yamada, T. Ogura, S. Ito and Y. Kubo, “Surface Morphology and Reliability Evaluation of Insulating Films on Stainless Steel Foil,” Proc. IDW’09, pp. 775-778 (2009)

The present invention has been made to solve the above-mentioned problems, and the leakage current is less than 10 ⁻⁵ A / cm ² when 100 V is applied to the upper electrode 3 × 3 cm, and at least 500 ° C., more preferably 650 ° C. or more. It is providing the stainless steel foil which has the film which has the heat resistance in the temperature of this, and its manufacturing method.

The gist of the present invention for achieving the above object is as follows.
(1) A stainless steel foil with an insulating coating for solar cells having an insulating coating formed in the order of a first layer and a second layer on a stainless steel foil as a substrate,
The first layer has higher heat resistance than the second layer,
The first layer is a metal oxide film, and the thickness of the metal oxide film is 0.1 to 0.4 μm in the case of ZrO ₂ , and 0.1 to 0.4 in the case of other metal oxide films. 0.2 μm,
The second layer is a methyl group-containing silica-based film represented by (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) (where 0 <x <1.0) , The methyl group-containing silica-based coating has a thickness of 0.5 to 2.0 μm,
The weight loss rate at 500 ° C. heating with respect to 100 ° C. heating of the insulating coating is less than 1.0%,
A stainless steel foil with an insulating coating for solar cells, wherein a leakage current when a voltage of 100 V is applied to an area of 3 × 3 cm of the stainless steel foil with an insulating film is less than 10 ⁻⁵ A / cm ² .

(2) The metal oxide film is composed of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , MgO, V ₂ O ₅ , Ta ₂ O ₅ , Cr ₂ O _3. And a stainless steel foil with an insulating coating for solar cells according to (1).

(3) The stainless steel foil with an insulating coating for solar cells according to (1) or (2), wherein the metal oxide coating is a thermal oxide film on the surface of the stainless steel foil.
  (4) The stainless steel foil with an insulating coating for solar cells according to (3), wherein the stainless steel foil contains aluminum or silicon, and the thermal oxide film contains alumina or silica.

( 5 ) The range of said x is 0.2 <= x <= 0.8, The stainless steel foil with an insulating film for solar cells as described in ( 1)-(4 ) characterized by the above-mentioned.

( 6 ) The stainless steel with an insulating coating for solar cells according to any one of (1) to ( 5 ), wherein the weight reduction rate during heating at 650 ° C. of the insulating coating at 100 ° C. is less than 1.0%. Foil.

( 7 ) The stainless steel foil with an insulating coating for solar cells according to (1) to ( 6 ), wherein the solar cell is for CIGS solar cells.

( 8 ) Form the first layer and the second layer in this order on the stainless steel foil as the base material,
The first layer has higher heat resistance than the second layer,
The first layer is a metal oxide film, and the thickness of the metal oxide film is 0.1 to 0.4 μm in the case of ZrO ₂ , and 0.1 to 0.4 in the case of other metal oxide films. 0.2 μm,
The second layer is a methyl group-containing silica-based film represented by (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) (where 0 <x <1.0) , The method for producing a stainless steel foil with an insulating coating for solar cells according to (1) to (7), wherein the methyl group-containing silica-based coating has a thickness of 0.5 to 2.0 μm.

(9) The method for producing a stainless steel foil with an insulating coating for solar cells according to (8), wherein the metal oxide coating is formed by thermally oxidizing the surface of the stainless steel foil.
(10) The stainless steel foil with an insulating coating for solar cells according to (9), wherein the stainless steel foil contains aluminum or silicon, and the metal oxide coating formed by the thermal oxidation contains alumina or silica. Manufacturing method.
( 11 ) The stainless steel with an insulating coating for solar cells according to any one of ( 8) to (10) , wherein the weight reduction rate when the insulating coating is heated at 650 ° C. with respect to the heating at 100 ° C. is less than 1.0%. Foil manufacturing method.

( 12 ) The method for producing a stainless steel foil with an insulating coating for solar cells according to ( 8) to (11 ), wherein the solar cell is for CIGS solar cells.
According to the present invention, there is provided a stainless steel foil with a solar cell insulating coating having a leakage current of less than 10 ⁻⁵ A / cm ² when applied with 100 V at an upper electrode 3 × 3 cm and having heat resistance of at least 500 ° C., particularly 650 ° C. or more. There is a remarkable effect that it is provided.

It is a figure which shows the stainless steel foil with the insulating film for solar cells of this invention. (A) It is the figure showing the stainless steel foil which has a processus | protrusion. (B) A stainless steel foil in which a methyl group-containing silica-based film is formed on the stainless steel foil shown in (a). (C) A stainless steel foil in which a metal oxide film is formed on the stainless steel foil shown in (a). (D) A stainless steel foil in which a methyl group-containing silica-based film is formed on the stainless steel foil of (c). (A) It is a light micrograph of the stainless steel foil surface. (B) It is a laser microscope photograph of the stainless steel foil surface. (C) It is the height measurement result of the cross section with the stainless steel foil surface shown in (b). It is a figure explaining the measuring method of leak current and applied voltage. It is a figure which shows the example place where the crack generate | occur | produced due to the adhering foreign material on stainless steel foil when a methyl group containing silica type coating film was formed on stainless steel foil. It is a figure which shows the structural example of a CIGS solar cell.

As shown in FIG. 1, the present inventors coat the stainless steel foil 1 with a coating 2 composed of a first layer 21 and a second layer 22, and in forming the coating in the order of the first layer and the second layer, In order to suppress the occurrence of cracks and foreign matter on the surface of the stainless steel foil during the formation of the layer, a metal oxide film layer is provided as the first layer in order to reduce the influence of large protrusions and foreign matter on the stainless steel surface. The two layers are made of a methyl group-containing silica-based coating layer that is compatible with a device having a balance of smoothness, heat resistance, and insulation, so that the leakage current is 10 ⁻⁵ when 100 V is applied to the upper electrode 3 × 3 cm. It has been found that heat resistance at a heating temperature of less than A / cm ² and at least 500 ° C., particularly 650 ° C. or more can be realized.

  In the evaluation of heat resistance, thermogravimetric analysis is used, and the value obtained by subtracting the weight reduction rate at 100 ° C. from the weight reduction rate of the coating at a predetermined temperature (500 ° C. and 650 ° C. in the present invention) is used. When it is 1% or less, it is evaluated that there is heat resistance at the temperature (500 ° C., further 650 ° C.). When the first layer and the second layer are stacked as in the present invention, the heat resistance of the coating is measured by peeling the two layers together and measuring with a thermal analyzer. The reason for subtracting the weight reduction rate at 100 ° C. is that the weight reduction up to 100 ° C. is mostly derived from the adsorbed water, and is distinguished from degassing due to decomposition of the organic components of the coating, which is a problem in device fabrication.

  The stainless steel foil with an insulating coating for solar cells of the present invention has an insulating coating formed in the order of a first layer and a second layer on a stainless steel foil as a base material, and the first layer is more heat resistant than the second layer. The stainless steel foil with an insulating coating for solar cells, wherein the first layer is a metal oxide coating and the second layer is a methyl group-containing silica-based coating.

Specifically, the metal oxide film is composed of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , MgO, V ₂ O ₅ , Ta ₂ O ₅ , Cr ₂ O _3, etc. The methyl group-containing silica-based coating is (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) 0 <x <1.0
It is a substance that can be expressed by
(Coating cracks and leakage current)
The surface of the stainless steel foil has wrinkles / spikes associated with rolling and attached foreign substances that are thought to occur during the process, and this is a cause of coating defects. Leakage current is likely to increase or a short circuit is likely to occur. Further, when the applied voltage is increased, an excessive voltage is applied to the thin part of the coating, and the short circuit is likely to occur.

  In order to reduce the leakage current, a countermeasure is taken by increasing the film thickness. However, since the film defect occurs when the inorganic film is thickened, the leakage current per unit area is kept low to increase the film thickness. It ’s difficult. Organic coatings tend to be thicker, but have low heat resistance, and increasing heat resistance results in a composition close to that of an inorganic film, making it difficult to increase the film thickness. Therefore, it has been difficult to increase the film thickness while maintaining high heat resistance.

Therefore, conventionally, a solar cell having a heat resistance of 500 ° C. or higher, particularly 650 ° C. or higher, and a low leakage current of less than 10 ⁻⁵ A / cm ² when a voltage of 100 V is applied to an area of 3 × 3 cm. No stainless steel foil with an insulating coating has been obtained.

As a result of intensive research and development, the present inventors have formed a metal oxide film with a predetermined thickness as a first layer and then formed a methyl group-containing silica-based film with a predetermined thickness as a second layer. The film defects of the group-containing silica-based film are reduced, the leakage current caused by cracks in the film is reduced, and the leakage current when a voltage of 100 V is applied to an area of 3 × 3 cm is 10 ⁻⁵ A / cm ^2. It was found that a film having a heat resistance of 500 ° C. or higher, particularly 650 ° C. or higher can be formed.

  The methyl group-containing silica-based film is excellent in heat resistance and leakage current, and is formed on an ideal smooth surface of stainless steel with a film thickness of up to about 2.0 μm, preferably about 1.5 μm. Although a film can be formed, protrusions and adhering foreign matters having a height of about 1 to 2 μm are frequently seen on the rolled stainless steel foil, and further, protrusions and adhering foreign matters having a height of 2 to 3 μm are also seen. If there are such protrusions and attached foreign matter, the insulating film formed thereon locally becomes thin or cracks are generated, so that the leakage current increases. However, if the metal oxide film is thinly formed as a base layer before forming the methyl group-containing silica film, cracks derived from protrusions on the stainless steel foil in the form shown in FIG. 2 are suppressed. In addition, the present inventors have found that the metal oxide film and the methyl group-containing silica film can reduce the leakage current value to a desired value in a wide unit area while maintaining high heat resistance.

Since protrusions and adhered foreign substances existing on the rolled stainless steel foil include large ones, as in the present invention, the metal oxide film is maintained with high heat resistance of 500 ° C. or higher, particularly 650 ° C. or higher. A combination of methyl group-containing silica-based coatings has a leakage current value of less than 10 ⁻⁵ A / cm ² and more preferably 10 ⁻⁶ A / cm ² when a voltage of 100 V is applied in a unit area of 3 × 3 cm. Less than 10 ⁻⁷ A / cm ² is unexpected from the knowledge of the prior art.

Furthermore, according to the present invention, even when the leakage current value is 10 × 10 cm in a unit area, the leakage current when a voltage of 100 V is applied is less than 10 ⁻⁵ A / cm ^2, less than 10 ⁻⁶ A / cm ² , It is also possible to decrease to less than 10 ⁻⁷ A / cm ² .

(Stainless steel foil)
As the stainless steel foil, austenite SUS304, SUS316, ferrite SUS430, SUS444, or the like can be used. Since these available stainless steel foils are manufactured by rolling, there are protrusions and adhered foreign substances on the foil.

  When the metal oxide film is formed by a sol-gel method or a sputtering method, it is better to have a smaller difference in thermal expansion coefficient from the metal oxide film, so that a ferrite system is preferable.

(Metal oxide coating)
The first layer of the present invention uses a metal oxide film.
Examples of the metal oxide film include Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , MgO, V ₂ O ₅ , Ta ₂ O ₅ , Cr ₂ O _{3 and the} like. These metal oxides have no adverse effect on the formation process of the methyl group-containing silica film because no weight change (1% or less as defined in the examples) is observed at temperatures lower than 650 ° C. In addition, there is no problem even if it is exposed to a device formation process temperature such as a solar cell.

A metal oxide has a smaller thermal expansion coefficient than a stainless steel foil, which is about 7.5 × 10 ⁻⁶ / ° C. for alumina and about 0.5 × 10 ⁻⁶ / ° C. for silica. For this reason, the film thickness which can form a metal oxide film without a crack is very thin, and is about 0.1-0.2 micrometer. If there are protrusions on the substrate, the portion becomes thick, but cracks may occur as shown in FIG. FIG. 5 is a photomicrograph of the surface of the stainless steel foil on which the methyl group-containing silica-based coating is formed, and there are protrusions and foreign matters having a size of several μm or less on the stainless steel surface up to the methyl group-containing silica-based coating. Cracks are seen in the coating starting from protrusions and foreign matter.

However, the crack in the metal oxide film can be filled with the coating solution when the second layer methyl group-containing silica-based film is formed. In addition, although the protrusions and foreign matters remain on the metal oxide film, the height of the protrusions and foreign matters is reduced. Furthermore, although the reason is not clear, surprisingly, unexpectedly from the height of the protrusions and foreign matters and the film thicknesses of the first layer and the second layer, according to the present invention, the CIGS solar cell has a large leak current in a large unit area. It has been found that a desired leakage current value required for a battery can be suppressed.
The reason is not clear, but it may be surprising that there are many protrusions and foreign matters that prevent the occurrence of cracks by the first layer and the second layer, and the first layer and the second layer in places where there are protrusions and foreign matters. It is conceivable that it is effective even for larger ones by raising.

The thicker the metal oxide film is, the better, but if it is too thick, many cracks will occur in the metal oxide film itself and the film will peel off. desirable. Among metal oxide coatings, zirconia, which has a thermal expansion coefficient of 10.5 × 10 ⁻⁶ / ° C. and is close to ferritic stainless steel and has high toughness, can be easily formed to a thickness of 0.3 to 0.4 μm without cracks. So especially desirable.

Examples of the method for forming the metal oxide film include a sol-gel method and a sputtering method. For example, in the case of the sol-gel method, a zirconia film is made of zirconium alkoxide as a raw material, and a sol hydrolyzed in an organic solvent is applied onto stainless steel. An acid catalyst such as hydrochloric acid or acetic acid may be used for the hydrolysis. Examples of the coating method include spin coating, dip coating, and roll coating. Application may be performed on both sides of the stainless steel foil or only on one side. After application, the film is dried at 70 to 150 ° C. and heat-treated at 300 to 600 ° C. The atmosphere for drying and heat treatment may be air or an inert gas atmosphere. Examples of the zirconium alkoxide include zirconium ethoxide, zirconium propoxide, zirconium butoxide and the like. In addition, when hydrolyzing the zirconium alkoxide, the metal alkoxide of yttrium, magnesium or calcium is simultaneously hydrolyzed to produce a solid solution of ZrO ₂ —Y ₂ O ₃ , ZrO ₂ —MgO or ZrO ₂ —CaO, respectively. Also good. At this time, the molar ratio of Y to Zr + Y, the molar ratio of Mg to Zr + Mg, and the molar ratio of Ca to Zr + Ca are preferably 1 to 20%. This is because the addition of Y, Mg, and Ca suppresses the volume change accompanying the phase transition of zirconia, so that it can be expected that cracks are less likely to occur even when a thick film is formed.

  Similarly, an alumina film, a titania film, a silica film, and the like can be manufactured using aluminum alkoxide, titanium alkoxide, and silicon alkoxide, respectively. In the case of sputtering, a metal oxide film can be produced using a metal oxide target to be formed.

  As for the metal oxide film, a stainless steel can be thermally oxidized at a high temperature to form a metal oxide film on the surface. When forming a metal oxide film by high-temperature thermal oxidation, it is easy to form an alumina or silica film on the surface if a material containing a relatively high concentration of Al or Si in stainless steel is used. Specifically, YUS205M1 containing about 5% aluminum in steel is used to form an alumina coating, and NSSCFH11 containing about 2.5% silicon is used to form a silica coating. it can. Thermal oxidation may be performed in the air or in an inert gas atmosphere, but in an inert gas atmosphere that does not contain oxygen is desirable in order to suppress the formation of iron oxide having low insulating properties. An inert gas may raise a dew point by bubbling in water. The thermal oxidation temperature is desirably 500 ° C. or higher. The second layer may be formed on stainless steel that has been previously thermally oxidized, but a methyl silica film is applied directly on YUS205M1, and the dehydration condensation of the methyl silica film is performed during the heat treatment of the methyl silica film. While advancing the reaction, the first layer of metal oxide film and the second layer of methyl-based silica film may be formed simultaneously such that alumina is deposited on the surface layer from stainless steel YUS205M1.

(Methyl group-containing silica coating)
The second layer of the present invention uses a methyl group-containing silica-based coating.
The methyl group-containing silica-based film is a film formed of a siloxane skeleton modified with a methyl group,
(SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) 0 <x <1.0
Can be expressed as

  According to the temperature-programmed desorption spectrum, the degassing start temperature is 600 ° C. or higher regardless of the range of x. The value obtained by subtracting the weight reduction rate at 100 ° C. from the weight reduction rate at 500 ° C. by thermogravimetric analysis is less than 1% regardless of x, and has heat resistance that can withstand the CIGS solar cell manufacturing process. . As x increases, the amount of methyl groups in the film increases, so that the film becomes soft and the limit of increasing the film thickness that can be formed without cracks can be increased, but the heat resistance tends to decrease. A preferable range of x is 0.2 ≦ x ≦ 0.8, and further 0.4 ≦ x ≦ 0.6.

  The methyl group-containing silica-based film can be produced by a sol-gel method. A manufacturing method will be described. At least one selected from tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and at least one selected from methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxytitanium, and methyltributoxysilane. More than one kind of silane is mixed and hydrolyzed in an organic solvent. As the organic solvent, methanol, ethanol, propanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, MEK, MIBK, or the like can be used alone or in combination. It is desirable that the water used for the hydrolysis is 0.3 mol to 3 mol times the total alkoxy groups. At the time of hydrolysis, a metal alkoxide catalyst other than silicon, an organic acid, or an inorganic acid may be used. In order to apply the prepared coating solution onto the stainless steel foil coated with the first layer of metal oxide, there are methods such as spin coating, dip coating, and roll coating. A methyl group containing silica-type coating film can be obtained by heat-processing for 0.5 to 10 hours in nitrogen at 400-600 degreeC after drying for 0.5 to 5 minutes at about 80-150 degreeC after application | coating.

  The preferred film thickness of the methyl group-containing silica-based coating is 2.0 μm or less, more preferably 1.8 μm or less. When this film thickness is increased, cracks may occur in the film and the leakage current may be undesirably increased. The preferable lower limit of the film thickness is 0.5 μm, more preferably 0.9 μm, and further 1.2 μm. When the film thickness is thin, the leakage current is low.

(Solar cell)
The stainless steel foil with an insulating coating for solar cells of the present invention can be suitably used for CGIS solar cells.

The structure and manufacturing method of CIGS solar cells are known. FIG. 6 shows an example of a typical structure. In FIG. 6, 41 is a substrate, 42 is a back electrode such as Mo, 43 is a CuIGeSe ₂ light absorption layer, 44 is a CdS buffer layer, 45 is a ZnO semi-insulating layer, 46 is a ZnO: Al window layer, 47 is an Al electrode, Reference numeral 48 denotes an MgF ₂ antireflection film. Examples of film thickness are 0.8 μm, 1.7 μm, 50 nm, 0.1 μm, and 0.6 μm in order from the back electrode 42 to the window layer order 46.

(Measurement of leakage current)
The leakage current was measured by forming a 3 × 3 cm gold upper electrode on the stainless steel foil with the first and second layers and applying 100V. FIG. 4 shows an example of the measuring apparatus, wherein 1 is a stainless steel foil, 2 is an insulating coating, 3 is an upper electrode, 4 is a voltmeter, 5 is an ammeter, and 6 is a power source.

(Evaluation of heat resistance)
Using thermogravimetric analysis, when the value obtained by subtracting the weight reduction rate at 100 ° C. from the weight reduction rate of the coating at a predetermined heating temperature is 1% or less, it is evaluated that the film has heat resistance at that temperature. When the value obtained by subtracting the weight reduction rate at 100 ° C. from the weight reduction rate of the film at 650 ° C. was 1% or less, it was evaluated that the film had heat resistance of at least 650 ° C.

(Stainless steel foil)
SUS430: Stainless steel made of iron containing 16-18% Cr YUS205M1: NS containing about 5% of aluminum in stainless steel NSSCH11: NS containing about 2.5% of silicon in stainless steel NSSC190SB: NSSC190 is NS It is a unique stainless steel grade that is almost the same as SUS444, and SB stands for Nippon Steel Materials with a super bright finish.

(Invention Examples 1 to 15)
The stainless steel foil used in Invention Examples 1 to 10 was NSSC190SB.
A method for forming the first layer of the present invention will be described.
Inventive Examples 1 to 3 were prepared by mixing 1 mol of aluminum butoxide with 2 mol of ethyl acetoacetate in 10 mol of butanol, spin-coating a sol hydrolyzed with 2 mol of water at 1000 rpm, and baking at 550 ° C. for 30 minutes in the atmosphere. A sol-gel alumina film was used. The film thickness obtained was 100 nm.

  Inventive Example 4 is a sol-gel silica film obtained by spin-coating a sol obtained by hydrolyzing 1 mol of tetraethoxysilane with 3 mol of water under a hydrochloric acid catalyst in 15 mol of ethanol at 1500 rpm and calcining at 600 ° C. for 30 minutes in the atmosphere. Was used. The film thickness obtained was 70 nm.

  Invention Examples 5 to 7 were prepared by mixing 1 mol of zirconium butoxide with 2 mol of ethyl acetoacetate in 10 mol of butanol, spin-coating a sol hydrolyzed with 4 mol of water at 800 rpm, and baking at 600 ° C. for 30 minutes in the air. A sol-gel zirconia film was used. The film thickness obtained was 250 nm.

  In Invention Examples 8 to 10, films of 100 nm, 100 nm, and 200 nm were formed by magnetron sputtering, using alumina, silica, and zirconia as targets, respectively.

  In Invention Example 11, YUS205M1 was heat-treated at 700 ° C. for 5 hours while flowing nitrogen gas bubbled at room temperature. Invention Example 12 was heat-treated at 700 ° C. for 5 hours while flowing nitrogen gas bubbling NSSC FH11 at room temperature.

  Invention Example 13 was heat-treated at 700 ° C. for 5 hours while flowing nitrogen gas obtained by bubbling SUS430 at room temperature.

  In Invention Examples 14 and 15, YUS205M1 and NSSC FH11 were each heat-treated at 700 ° C. for 5 hours in the atmosphere.

As the second layer of the present invention example, x was changed to 0.05, 0.5, and 0.9 in methyl group-containing silica film (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) . Three types of films were prepared. In any case, in a 2-ethoxyethanol solvent, methyltriethoxysilane is mixed at a ratio of (1-x) mole with respect to x mole of tetramethoxysilane, and equimolar water is added to all alkoxy groups under an acetic acid catalyst. A sol was prepared by hydrolysis.

  The limit film thickness that can be formed without cracks while changing the rotation speed with a spin coater was investigated. When x = 0.05, 1.8 μm, when x = 0.5, 1.1 μm, x = 0. In the case of 9, the film was formed at 0.9 μm. After application, the film was dried at 150 ° C. for 1 minute, and heat-treated in nitrogen at 480 ° C. for 30 minutes.

The results of evaluating Examples 1 to 15 of the present invention are shown in Table 1. As for Inventive Examples 5 and 11, gold was deposited with an ion coater so that the upper electrode area was 5 cm square, and the leakage current was measured. The leakage currents were 2 × 10 ⁻⁸ and 70 × 10 ⁻⁸ A / cm ² , respectively. It was confirmed that the low leakage current was maintained even when the area was increased.
Table 1 shows the results of evaluation on Examples 1 to 15 of the present invention. The properties were good.

(Comparative example)
The evaluation results of the comparative examples are shown in Table 2.
Comparative Example 1 was a case where only the methyl group-containing silica-based film was formed on the first layer, and was short-circuited due to the occurrence of cracks due to protrusions on the stainless steel foil.

  In Comparative Example 2, 0.25 mol of polydimethylsiloxane having an average molecular weight of 3000 in ethanol was mixed with 1 mol of titanium ethoxide and 2 mol of ethyl acetoacetate, and then a sol prepared by adding 2 mol of water was used. It was prepared by spin coating at 1000 rpm and heat treatment in nitrogen at 350 ° C. for 30 minutes. Since the polydimethylsiloxane (PDMS) -based coating thermally decomposes at 300 to 400 ° C., the coating was peeled off during the heat treatment of the second layer, so that it was judged as poor (×) as a characteristic.

  In Comparative Example 3, a sol obtained by hydrolyzing phenyltriethoxysilane in ethanol using an acetic acid catalyst was spin-coated at 1000 rpm, and then heat-treated in nitrogen at 400 ° C. for 30 minutes. Since the phenyl group was decomposed from around 400 ° C. in this film, the film was peeled off during the heat treatment of the second layer.

  Comparative Examples 4 to 5 are examples in which methyl group-containing silica is overcoated. When the first layer was thickly coated as in Comparative Example 4, significant film peeling occurred. In Comparative Example 5, the first layer was thinned, but cracks occurred in the film during the formation of the second layer. It is presumed that the methyl groups contained in the first layer are partially decomposed during the heat treatment for forming the second layer.

  In Comparative Example 6, although a single layer of methyl group-containing silica was applied, cracks occurred.

Comparative Examples 7 to 8 are examples in which the thickness of the silica film is increased as the metal oxide film. As seen in Comparative Example 7, when the thickness of the single metal oxide film was increased, cracks occurred and a short circuit occurred in the leakage current measurement. In Comparative Example 8, methyl group-containing silica was overcoated on a thick metal oxide film, but a short circuit occurred and the leakage current could not be reduced.

DESCRIPTION OF SYMBOLS 1 Stainless steel foil 2 Coating 3 Electrode 4 Voltmeter 5 Ammeter 6 Power source 21 First layer coating 22 Second layer coating 31 Metal oxide coating 32 Methyl group-containing silica coating 33 Crack

Claims (12)

A stainless steel foil with an insulating coating for solar cells having an insulating coating formed in the order of a first layer and a second layer on a stainless steel foil as a base material,
The first layer has higher heat resistance than the second layer,
The first layer is a metal oxide film, and the thickness of the metal oxide film is 0.1 to 0.4 μm in the case of ZrO ₂ , and 0.1 to 0.4 in the case of other metal oxide films. 0.2 μm,
The second layer is a methyl group-containing silica-based film represented by (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) (where 0 <x <1.0) , The methyl group-containing silica-based coating has a thickness of 0.5 to 2.0 μm,
The weight loss rate at 500 ° C. heating with respect to 100 ° C. heating of the insulating coating is less than 1.0%,
A stainless steel foil with an insulating coating for solar cells, wherein a leakage current when a voltage of 100 V is applied to an area of 3 × 3 cm of the stainless steel foil with an insulating film is less than 10 ⁻⁵ A / cm ² . The metal oxide film is made of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , MgO, V ₂ O ₅ , Ta ₂ O ₅ , Cr ₂ O _3. Item 12. A stainless steel foil with an insulating coating for solar cells according to item 1. The said metal oxide film is a thermal oxide film of the said stainless steel foil surface, The stainless steel foil with the insulating film for solar cells of Claim 1 or 2 characterized by the above-mentioned. The said stainless steel foil contains aluminum or a silicon | silicone, The said thermal oxide film contains an alumina or a silica, The stainless steel foil with an insulating film for solar cells of Claim 3 characterized by the above-mentioned. The range of said x is 0.2 <= x <= 0.8, The stainless steel foil with an insulating film for solar cells of any one of Claims 1-4 characterized by the above-mentioned. The stainless steel with an insulating coating for solar cells according to any one of claims 1 to 5, wherein a weight reduction rate when the insulating coating is heated at 650 ° C to 100 ° C is less than 1.0%. Foil. A solar cell is for CIGS solar cells, The stainless steel foil with an insulating film for solar cells of any one of Claims 1-6 characterized by the above-mentioned. Formed in the order of the first layer and the second layer on the stainless steel foil as the base material,
The first layer has higher heat resistance than the second layer,
The first layer is a metal oxide film, and the thickness of the metal oxide film is 0.1 to 0.4 μm in the case of ZrO ₂ , and 0.1 to 0.4 in the case of other metal oxide films. 0.2 μm, and the second layer contains (SiO ₂ ) _x- (CH ₃ SiO _3/2 ) _(1-x) (where 0 <x <1.0) a silica-based coating film, according to claim 1 to 7 with the solar cell insulation coating according to any one of, wherein the methyl group-containing silica-based coating is a thickness of 0.5~2.0μm Stainless steel foil manufacturing method. The said metal oxide film is formed by thermally oxidizing the said stainless steel foil surface, The manufacturing method of the stainless steel foil with an insulating film for solar cells of Claim 8 characterized by the above-mentioned. The method for producing a stainless steel foil with an insulating coating for a solar cell according to claim 9, wherein the stainless steel foil contains aluminum or silicon, and the metal oxide film formed by the thermal oxidation contains alumina or silica. . The weight-decreasing rate at the time of 650 degreeC heating with respect to the time of 100 degreeC heating of the said insulating film is less than 1.0%, The stainless steel with an insulating film for solar cells of any one of Claims 8-10 characterized by the above-mentioned. Foil manufacturing method. A solar cell is for CIGS solar cells, The manufacturing method of the stainless steel foil with an insulating film for solar cells of any one of Claims 8-11 characterized by the above-mentioned.