JP2015071513A - Insulated substrate for cigs solar battery and cigs solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulated substrate which is excellent in surface smoothness, has high-temperature heat resistance and enables compatibility of insulation suitable for applications in CIGS-system solar batteries and Na supply contributable to enhancement of the conversion efficiency and a CIGS solar battery using the insulated substrate.SOLUTION: In an insulated substrate for CIGS solar batteries, a glass layer of a thickness of 10-50 μm is formed on the surface of a steel sheet or steel foil by using a paste of an alkali metal-containing bismuth-based glass having a thermal expansion coefficient of 8-13x10/°C. An available alkali metal-containing bismuth-based glass has a glass transition point of 500°C or lower, a softening temperature of 550°C or higher and a crystallization temperature of 800°C or higher or a not crystallizing composition and comprises 30-90 mass% of BiO, 3-55 mass% of SiO+BOand a combined content of 0.5-20 mass% of one or more of LiO, NaO and KO.

Description

  The present invention relates to an insulating substrate of a CIGS solar cell and a CIGS solar cell using the insulating substrate.

The CIGS solar cell is a compound semiconductor solar cell having a structure in which a chalcopyrite type compound layer is a light absorbing layer (photoelectric conversion layer) and zinc oxide (ZnO) is a window layer. FIG. 1 schematically illustrates a cross-sectional structure of a conventional general CIGS solar cell. A lower electrode layer 2 made of metal Mo is formed on the surface of the substrate 1. As the substrate 1, soda lime glass is generally applied. The soda lime glass contains Na, which diffuses into the CIGS layer during the CIGS layer formation, and improves the characteristics of the CIGS solar cell. A CIGS layer 3 is formed as a light absorption layer on the surface of the lower electrode layer 2. Further thereon, a zinc oxide layer 5 as a window layer and a translucent conductive layer 6 made of ITO (indium tin oxide) or the like are formed via a buffer layer 4 made of CdS. An upper electrode layer 7 made of metal is provided on a part of the surface of the translucent conductive layer 6. Conductive wires 8 are connected to the lower electrode layer 2 and the upper electrode layer 7, respectively, and power is supplied to the load 9.

JP 2000-164909 A JP 2009-267335 A JP-A-62-276883 JP 2006-80370 A Japanese Patent Laid-Open No. 10-74966 Japanese Patent Laid-Open No. 10-74967 JP-A-9-55378 Japanese Patent Application Laid-Open No. 10-125941 Japanese Patent Laid-Open No. 2006-210424 JP 2005-1117012 A WO2009-116626

In CIGS solar cells, glass substrates are generally used as substrates, but solar cells using metal substrates such as stainless steel plates in addition to glass substrates have also been reported as light-weight and flexible solar cells. ing. A solar cell using a metal substrate can be applied to a wide range of uses because the substrate can be reduced in weight and flexible. In addition, since the metal substrate has resistance to a high temperature process of 400 ° C. or higher, high efficiency of the solar cell can be expected.
However, when a conductive substrate such as a stainless steel plate is used, in order to connect the solar cells in series, a complicated manufacturing process such as cutting of the substrate and wiring with a conductive wire is required, and there is a problem in cost reduction. Therefore, in order to connect a plurality of unit cells in series on the substrate, it is essential to provide an insulating layer on the metal substrate.

As a method for forming an insulating layer, for example, Patent Document 1 describes a method for forming an insulating layer by a sol-gel method. However, it is difficult to obtain a sufficient withstand voltage with a thin film produced by the sol-gel method. In addition, the temperature at which the CIGS semiconductor layer is manufactured is 500 ° C. or higher, and an insulating layer having a small difference in thermal expansion coefficient from the semiconductor layer is necessary in order to prevent cracks in the insulating layer even when exposed to this temperature. .
Patent Document 2 describes a substrate having an anodized film on a metal substrate and having pores formed on the surface of the anodized film. When such a porous anodic oxide film is used as an insulating layer, an oxide film that is difficult to generate cracks can be obtained. However, since it is porous, there is a problem that moisture is easily adsorbed and a leak current easily flows. ing.

By the way, in the past, soda lime glass is frequently used as a glass substrate in CIGS solar cells, and when sodium is diffused into the photoelectric conversion semiconductor layer when the photoelectric conversion semiconductor layer is formed, it contributes to improvement in power generation efficiency. Based on knowledge. However, when a metal substrate having the above-described insulating layer is used as a solar cell substrate, there is a problem that conversion efficiency does not increase because sodium cannot be supplied from the substrate.
In Patent Document 3 and Patent Document 4, an attempt is made to provide a glass layer on a metal substrate to ensure insulation when the metal substrate is used, and to contain Na in the insulating layer. However, the bag of Patent Document 3 contains lead and impairs the safety of the product, and the thermal expansion coefficient cannot be brought close to the thermal expansion coefficient of the steel sheet. The glass layer provided in Patent Document 4 is also a silica-based glass, and even if it can increase the withstand voltage, it has not reached the thermal expansion coefficient. Further, in order to diffuse Na and promote crystal growth of the CIGS layer, there is a description (paragraph 0009) that NaF or Na ₃ AlF ₆ is included. Are considered to be small (Table 1).

As a general technique for supplying alkali metal ions to the photoelectric conversion semiconductor layer, for example, Patent Documents 5 and 6 use Na ₂ Se, Patent Document 7 uses Na ₂ O ₂ , and Patent Document 8 uses Na ₂ S. A method of co-evaporation with an element constituting a photoelectric conversion semiconductor layer is described. Patent Document 9 describes a method of depositing sodium phosphate on molybdenum (Mo), and Patent Document 10 describes a method of forming a Na layer by immersing in Na ₂ MoO ₄ . Furthermore, Patent Document 11 proposes a method of providing a silicate layer between a substrate and a lower electrode layer. The silicate layer is formed by a magnetron sputtering method, and the alkali metal derived from the silicate layer passes through the back electrode layer and diffuses into the CIGS thin film. Is possible. However, in any case, it is necessary to further form a submicron order thin film on the insulating layer by vapor deposition, and it is impossible to give both characteristics of insulation and increase in conversion efficiency by supplying Na.

The present invention provides an insulating substrate that has both excellent surface smoothness and high-temperature heat resistance, and is capable of satisfying both the insulating properties suitable for CIGS solar cell applications and the supply of alkali metals that contribute to increased conversion efficiency, and An object of the present invention is to provide a CIGS solar cell using the insulating substrate.

  As a result of detailed research by the inventors, when a glass layer of 10 to 50 μm is formed using a paste of an alkali metal-containing bismuth glass using a steel plate / steel foil as a substrate material, insulation required for a solar cell is obtained. It was found that a CIGS solar cell having a high conversion efficiency due to breakdown voltage and alkali metal diffusion can be obtained. In addition, the adhesion between the oxide film formed on the steel sheet surface and bismuth-based glass is good, and the difference in thermal expansion coefficient can be reduced. It becomes. Furthermore, since the leveling property of the glass at the time of heating is good and a flat surface is obtained, there are few defects in the CIGS layer which is a thin film, and the battery performance is also good. In addition, in order to serve as a solar cell substrate, it is necessary to form a metal electrode on the insulating film, and it must be an insulating layer that does not cause migration, while only a bismuth-based glass composition contains an alkali metal. The effect of preventing migration is shown. The present invention has been completed based on such findings.

That is, in this invention, ordinary steel or stainless steel-foil having a coefficient of thermal expansion 9~13x10 ^-6 / ℃, insulating CIGS solar cells thermal expansion coefficient is coated with 8~13x10 ^-6 / ℃ of bismuth glass A substrate is provided. Here, the film of bismuth glass has a softening temperature of 550 ° C. or higher and a crystallization temperature of 800 ° C. or higher or a composition that does not crystallize. For example, Bi ₂ O ₃ : 30 to 90% by mass, SiO ₂ + B ₂ O ₃ : _{3 to} 55% by mass, and any one or more of Li ₂ O, Na ₂ O, and K ₂ O are combined in a total of 0. The thing of the glass composition containing 5-20 mass% is mentioned. Range up to 10% by weight may be added _TiO 2, _Al 2 _{O 3} or the like. Various steel types are applicable as the base steel, and examples thereof include ordinary steel and ferritic stainless steel. The specific component composition is exemplified as follows.
[Regular steel]
% By mass, C: 0.001 to 0.15%, Si
: 0.001-0.1%, Mn: 0.005-0.6%, P: 0.001-0.05%, S: 0.001-0.5%, Al: 0.001-0 0.5%, Ni: 0.001 to 1.0%, Cr: 0.001 to 1.0%, Cu: 0 to 0.1%, Ti: 0 to 0.5%, Nb: 0 to 0. 5%, N: 0 to 0.05%, steel composed of the balance Fe and inevitable impurities.
[Ferrite stainless steel]
In mass%, C: 0.0001 to 0.15%, Si: 0.001 to 1.2%, Mn: 0.001 to 1.2%, P: 0.001 to 0.04%, S: 0.0005% to 0.03%, Ni: 0 to 0.6%, Cr: 11.5 to 32.0%, Mo: 0 to 2.5%, Cu: 0 to 1.0%, Nb: 0 to 1.0%, Ti: 0 to 1.0%, Al: 0 to 0.2%, N: 0 to 0.025%, B: 0 to 0.01%, V: 0 to 0.5 %, W: 0 to 0.3%, Ca, Mg, Y, REM (rare earth elements) total: 0 to 0.1%, the balance Fe and steel consisting of inevitable impurities.
Here, an element whose lower limit is 0% is an arbitrary element, and “0%” means a case where an analysis value in a normal steelmaking process is equal to or less than a measurement limit.

Moreover, in this invention, the electrode substrate for CIGS solar cells which has Mo film | membrane on the glass layer of said board | substrate is provided. In addition, a CIGS solar cell having a Cu (In, Ga) Se ₂ type compound layer on the Mo film of the electrode substrate is provided.

In the present invention, by providing an alkali metal-containing bismuth glass as the insulating layer of the insulating substrate of the CIGS solar cell, it has a dielectric breakdown voltage of 500 V or more and is as high as a CIGS solar cell using a soda lime glass substrate. Efficiency is obtained. High-temperature heating at 500 ° C. or higher is possible during film formation, and the degree of freedom in film formation conditions is greatly expanded as compared with the case where a polymer film is used as a substrate. Moreover, it becomes flexible by using a foil-shaped stainless steel plate. The thermal expansion coefficient of ferritic stainless steel is 9 to 13 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the alkali metal-containing bismuth glass is also adjusted to 8 to 13 × 10 ⁻⁶ / ° C. It is possible to prevent the insulating layer from being deteriorated due to cracks in the insulating layer during the formation and further when used as a solar cell for a long time (cooling cycle). Further, since the glass composition has a relatively low softening temperature, it can be leveled during firing to obtain a smooth surface. Therefore, this invention contributes to the weight reduction, flexibility, and cost reduction of a CIGS solar cell.

The figure which illustrated typically the section structure of the conventional general CIGS solar cell. The figure which illustrated typically the section structure of the CIGS solar cell using the substrate of the present invention.

FIG. 2 schematically illustrates a cross-sectional structure of a CIGS solar cell using the substrate of the present invention. A significant difference from the conventional general CIGS solar cell shown in FIG. 1 is that a stainless steel plate 11 having an alkali metal-containing bismuth glass layer 12 is used instead of the substrate 1 made of soda lime glass (FIG. 1). There is to be. In the present invention, a substrate for a CIGS solar cell having an alkali metal-containing bismuth glass layer 12 on the surface of the steel plate 11 is referred to as an insulating substrate 12. A lower electrode layer 2 made of metal Mo is formed on the surface of the glass layer by, for example, sputtering. By setting the glass layer to have a predetermined thickness or more, which will be described later, it is possible to prevent stainless steel component elements such as Fe and Cr from diffusing into the CIGS layer 3 from the stainless steel plate 11 by high-temperature heating when forming the CIGS layer 3. And withstand voltage of 500 V or more required as a solar cell substrate. Further, since alkali metal is contained in the alkali metal-containing bismuth-based glass layer 12, it functions as a group Ia alkali metal element supply source to the CIGS layer 3 and brings about improvement in battery performance.
The plate thickness of the insulating substrate 12 may be about 0.02 to 2.00 mm, for example. In particular, in order to place importance on flexibility, it is desirable that the thickness is 0.02 to 0.5 mm.

[Steel substrate]
As the steel plate 11 of the insulating steel plate 12, ordinary steel () having a thermal expansion coefficient relatively close to that of the CIGS layer and ferritic stainless steel are suitable targets. Since stainless steel is excellent in corrosion resistance, it is suitable for applications where high durability and reliability are important. As the standard steel type, in the case of plain steel, for example, a material using a cold-rolled steel sheet (including a steel strip) defined in JIS G3141: 2009 can be applied. In the case of stainless steel, for example, a steel plate (including a steel strip) having a ferritic chemical composition defined in JIS G4305: 2005 can be applied. The specific chemical composition range is as described above.

[Alkali metal-containing bismuth glass]
The composition of the alkali metal-containing bismuth-based glass includes Bi ₂ O ₃ : 30 to 90% by mass, SiO ₂ + B ₂ O ₃ : _{3 to} 55% by mass, and any of Li ₂ O, Na ₂ O, and K ₂ O A glass composition containing a total of 0.5 to 20% by mass of one or more of them is preferred. Range up to 10 _wt%, it may be added TiO 2, _Al 2 _{O 3.} The Bi ₂ O ₃ component plays the role of a glass-forming oxide and greatly contributes to the improvement of the stability of the glass. In particular, the Bi ₂ O ₃ component is indispensable for achieving the object of the present invention having a low glass transition point (Tg) of 500 ° C. or lower. There are no ingredients. In the present invention, since the content of Bi ₂ O ₃ strongly depends on the glass Tg reduction, it is difficult to obtain a glass having a low Tg when the content is small. However, if Bi ₂ O ₃ is contained excessively, the glass stability is impaired, and if it is too small, the object of the present invention cannot be satisfied. Therefore, the Bi ₂ O ₃ content preferably has an upper limit of 90% by mass and a lower limit of 30% by mass.

SiO ₂ or B ₂ O ₃ is a forming oxide of glass and is a useful component for obtaining a stable glass. In order to obtain this effect, the lower limit of the total content of one or two of these components is preferably 3% by mass. In order to obtain a Tg of 500 ° C. or lower, the upper limit of these contents is 55% by mass. % Is preferable. These two components can achieve the object of the present invention even if they are introduced alone into the glass, but the simultaneous use increases the meltability, stability and chemical durability of the glass. Is preferred. In order to maximize the above effect, the ratio of B ₂ O ₃ / SiO ₂ is preferably set in the range of 0.15 to 5.

Any one or more of Li ₂ O, Na ₂ O and K ₂ O are effective components for lowering the softening point of the lead-free glass composition as described above, and are high in the lead-free glass composition. It is an effective component for imparting a thermal expansion coefficient. These total contents which occupy in a glass component shall normally be either in the range of 0.5 to 20% by weight percentage. In addition, these components should just contain any 1 type of them, and 2 types or all 3 types may contain them. For example, if the total content is less than 0.5%, the conversion efficiency during solar cell formation is increased by diffusion of alkali metal into the CIGS layer. The effect of making it not obtain. This is because if it exceeds 20%, it may be difficult to impart sufficient chemical durability to the lead-free glass composition. Addition of TiO ₂ and Al ₂ O ₃ can improve chemical durability.

The thermal expansion coefficient of this glass layer needs to be 8 to 13 × 10 ⁻⁶ / ° C. When the thermal expansion coefficient is less than 8 × 10 ⁻⁶ / ° C., the difference between the thermal expansion coefficient of ordinary steel or stainless steel of the base material becomes large, so that a crack occurs when forming a glass layer or CIGS layer on the base material, An insulating film cannot be obtained. On the other hand, if it exceeds 13 × 10 ⁻⁶ / ° C., the difference from the coefficient of thermal expansion of the CIGS layer is too wide, and defects are likely to occur in the CIGS layer when the CIGS layer is formed.

The glass layer has a softening temperature exceeding 550 ° C. and a crystallization temperature of 800 ° C. or higher or a composition that does not crystallize. By setting it as the composition whose glass transition point is 500 degrees C or less and whose softening point exceeds 550 degreeC, the glass layer excellent in insulation is formed, without fuse | melting at 550 degreeC which forms a CIGS layer. Further, when the crystallization temperature is 800 ° C. or higher or a composition that does not crystallize, the leveling property is improved when baking at a higher temperature than the softening point, and a smooth surface is obtained.
The migration of the electrode metal on the alkali metal-containing glass is considered to be affected by the elution of the metal accompanying the elution of the alkali metal.
Mo migration can be prevented in the alkali metal-containing bismuth-based glass by containing a proper amount of SiO ₂ and B ₂ O ₃ in a state where a predetermined amount of Bi ₂ O ₃ is contained. Since the metal can exist stably, it is considered that the alkali metal elution is suppressed and the effect of preventing migration is exhibited.

  The alkali metal-containing bismuth glass layer 12 functions as a supply source of the group Ia alkali metal element into the CIGS layer. The group Ia alkali metal element (such as Na) in the glass layer diffuses into the CIGS layer through the lower electrode layer 2 (Mo film) mainly by high-temperature heating at the time of forming the CIGS layer. The average thickness of the alkali metal-containing bismuth glass layer 12 is preferably 5 to 50 μm. If it is thinner than 5 μm, it is difficult to obtain a voltage resistance of 500 V required for a solar cell substrate. If it exceeds 50 μm, cracks occur in the alkali metal-containing bismuth-based glass layer 12 when it is wound by roll coating, etc. Sex is reduced.

The alkali metal-containing bismuth glass layer 12 can be formed by applying and baking a liquid obtained by dispersing finely pulverized glass powder in an organic solvent. For example, after coating on the substrate by bar coating, roll coating, screen printing, etc., the alkali metal-containing bismuth glass layer 12 is formed by baking so that the surface temperature of the substrate 11 is maintained in the range of 570 to 800 ° C. can do.

The coating solution is prepared by mixing finely pulverized glass powder and a vehicle to prepare a paste. The vehicle is obtained by dissolving a resin as a binder component in a solvent. Examples of the resin for the vehicle include cellulose resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose; methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate, butyl acrylate An organic resin such as an acrylic resin obtained by polymerizing one or more acrylic monomers such as 2-hydroxyethyl acrylate is used. Solvents such as terpineol, butyl carbitol acetate, and ethyl carbitol acetate are used in the case of cellulose resins, and solvents such as methyl ethyl ketone, terpineol, butyl carbitol acetate, and ethyl carbitol acetate are used in the case of acrylic resins. Is used.

  The resin component in the vehicle functions as a binder for the glass powder and is removed during firing. The viscosity of the paste may be adjusted to the viscosity corresponding to the apparatus applied to the substrate, and can be adjusted by the ratio of the resin component as the organic binder, the organic solvent, etc., and the ratio of the sealing material and the vehicle. You may add a well-known additive in a glass paste like an antifoamer and a dispersing agent to a paste. For preparing the paste, a known method using a rotary mixer equipped with a stirring blade, a roll mill, a ball mill or the like can be applied.

[Lower electrode (Mo coating)]
By forming a Mo film as the lower electrode layer 2 on the surface of the alkali metal-containing bismuth glass layer 12, an electrode substrate is obtained. As a method for forming the Mo film, a known method such as a sputtering method can be applied. The thickness of the lower electrode layer 2 may be about 0.2 to 3.0 μm.

[Production of solar cells]
On the surface of the lower electrode layer 2 (Mo electrode), a CIGS layer 3, a buffer layer 4, a zinc oxide layer 5, and a light-transmitting conductive layer 6 are formed in this order to produce a solar battery cell. A conventionally known method can be applied as a method of forming each of these layers. For example, the CIGS layer 3 can be formed by a method in which Cu, In, Ga, and Se are vapor-deposited simultaneously or sequentially on the lower electrode layer 2 (Mo film), and a CIGS layer is synthesized by heat diffusion. The heating temperature can be as high as 500 to 550 ° C. Usually, optimum conditions for synthesis of the CIGS layer can be found in this temperature range.

As the steel plate 11, a normal steel cold-rolled steel plate and a SUS430 steel plate having the following chemical composition were prepared.
Normal steel cold-rolled steel sheet:% by mass, C: 0.003%, Al: 0.038%, Si: 0.003%, Mn: 0.12%, P: 0.012%, S: 0.122 %, Ni: 0.02%, Cr: 0.02%, Cu: 0.01%, Ti: 0.073%, N: 0.0023%, balance Fe and inevitable impurities SUS430 steel plate:% by mass, C: 0.01%, Si: 0.52%, Mn: 0.19%, Ni: 0.10%, Cr: 18.4%, balance Fe and inevitable impurities Thermal expansion coefficient of ordinary steel cold-rolled steel sheet Is 10.8 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the SUS430 steel plate is 11.0 × 10 ⁻⁶ / ° C.
Bismuth-based, zinc-based, and silica-based alkali metal-containing glass layers were formed using these steel plates as base materials to obtain an insulating substrate.
The coating material was prepared by mixing the glass material and the vehicle so that the glass material was 80% by mass and the vehicle was 20% by mass. The vehicle is obtained by dissolving ethyl cellulose (2.5% by mass) as a binder component in a solvent (97.5% by mass) made of terpineol. The glass composition was changed as shown in Table 1. The paste was applied to SUS430 having a thickness of 0.1 mm by a bar coater, dried at 300 ° C., and baked at 700 ° C. for 10 minutes. The film thickness of the glass layer was 15 μm.

About the obtained insulating substrate, the relationship between the various characteristics of a glass layer, the presence or absence of the crack generation of an insulating substrate, and the presence or absence of migration generation | occurrence | production was investigated. The results are shown in Table 1.

<Measurement of softening point and crystallization temperature>
Each glass powder sample was put into a platinum cell and measured with a differential thermal analyzer (DTA).
<Measurement of thermal expansion coefficient>
By a measuring method based on JIS R 3102, the glass frit forming the insulating layer was fired into a rod shape, and the thermal expansion coefficient after firing was measured.

<Presence of cracks>
The presence or absence of cracks was evaluated by observing the surface after air-cooling after applying and baking the glass paste. The case where no cracks were observed in both visual observation and observation with an optical microscope was rated as ◯, the case where there were no cracks observed with visual observation and the occurrence of cracks in the observation with an optical microscope was marked as △, and observation with a visual and optical microscope In any of the cases, cracks were observed as x.

<Migration test>
An insulating steel sheet coated with a comb-shaped electrode is held for 96 hours in an environment of a set temperature of 121 ° C., 2 atm, and humidity of 95%, and the insulation resistance value is measured before and after the test, and the resistance does not decrease. The case where the decrease was observed was rated as x.

As can be seen from Table 1, when the thermal expansion coefficient of the glass was less than 8 × 10 ⁻⁶ / ° C., the difference from the thermal expansion coefficient with the steel sheet was too large, and cracks were observed when cooled after firing. Moreover, even when the glass composition has a thermal expansion coefficient of 8 × 10 ⁻⁶ or more and is close to the thermal expansion coefficient of SUS430, the glass composition having a crystallization temperature of less than 800 ° C. shows a decrease in insulation resistance after the migration test, and as a solar cell substrate It turned out that it cannot be used. On the other hand, it was found that by using a bismuth-based glass composition as in the present invention example, an insulating steel sheet free from cracks and having no decrease in insulation resistance due to migration was obtained.

Therefore, the composition of the glass material represents the content of the alkali metal oxide and the glass layer thickness based on Bi ₂ O ₃ : 54 mass%, SiO ₂ : 38 mass%, and B ₂ O ₃ : 8 mass%. 2 and investigated the influence on the conversion efficiency and dielectric strength of the CIGS solar cell.
After producing an insulating steel plate as described above, a Mo film having an average thickness of 1 μm was formed as the lower electrode layer by RF sputtering to obtain an electrode substrate.
A solar battery cell was produced on the Mo film of each insulating substrate by the method described below.
First, a CIGS layer having a thickness of 2 μm was formed by simultaneously depositing Cu, In, Ga, and Se in a state where the temperature of the insulating substrate was about 550 ° C.

Next, a zinc oxide (ZnO) layer having a thickness of 0.1 μm and a thickness of 0.1 μm are formed by a chemical bath deposition method (CBD method) in a state where only the cell portion on the CIGS layer surface is exposed. A 1 μm thick ITO transparent conductive layer was sequentially formed. The size of the solar battery cell is 5 mm × 5 mm.
In a state where only a part of the surface of the ITO translucent conductive layer of the solar battery thus produced is masked, Au serving as an upper electrode layer is formed on the exposed part by a vapor deposition method. A battery was obtained.

<Evaluation of pressure resistance>
The dielectric breakdown voltage of the insulating steel sheet on which the glass layer was formed was measured by a measuring method based on JIS C 2110.
<Evaluation of thermal shock resistance>
After holding the sample temperature at −40 ° C. for 30 minutes and then holding at 250 ° C. for 30 minutes, a thermal shock test was performed for 1000 cycles. Thereafter, the interface between the steel plate and the glass layer after the test was conducted, and the presence or absence of cracks or defects in the glass layer were observed and evaluated using visual observation and an optical microscope. As for crack generation, the case where no crack was generated both visually and by observation with an optical microscope was marked as ◯, the crack was not visually observed, and the case where crack was observed when observed with an optical microscope was marked as △. In addition, the case where cracks were generated in both observations with an optical microscope was marked with x.

<Evaluation of conversion efficiency>
The CIGS solar cell produced by the above method was irradiated with simulated sunlight of AM1.5, 100 mW / cm ² using “Solar Simulator: YSS-100” manufactured by Yamashita Denso Co., Ltd. The IV characteristics were measured with a “meter” to obtain values of the short circuit current density Jsc, the open circuit voltage Voc, and the form factor FF. From these values, the value of photoelectric conversion efficiency η was determined by the following formula (1).
Photoelectric conversion efficiency η (%) = short circuit current density Jsc (mA / cm ² ) × open circuit voltage Voc (V) × {form factor FF / incident light 100 (mW / cm ² )} × 100 (1)
Using the photoelectric conversion efficiency η0 of a CIGS solar cell using soda lime glass as a substrate (test No. 0 in Table 1) as a standard, the ratio η / η0 of the photoelectric conversion efficiency η of each CIGS solar cell with respect to η0 (“conversion Called efficiency ratio).
The above evaluation results are shown in Table 2.

  As can be seen from Table 2, the insulating substrate of the present invention is excellent in withstand voltage, and the conversion efficiency of the CIGS solar cell is a slight decrease in photoelectric conversion efficiency compared to the conventional type CIGS solar cell using soda lime glass as the substrate. In spite of being a flexible substrate, a high-performance CIGS solar cell could be realized.

DESCRIPTION OF SYMBOLS 1 Soda-lime glass substrate 2 Lower electrode layer 3 CIGS layer 4 Buffer layer 5 Zinc oxide layer 6 Translucent conductive layer 7 Upper electrode layer 8 Conductor 9 Load 11 Steel plate 12 Alkali metal-containing bismuth glass layer 20 Insulating substrate

Claims (5)

An alkali metal-containing glass layer having a softening point of 550 ° C. or higher, a crystallization temperature of 800 ° C. or higher, or a thermal expansion coefficient of 8 to 13 × 10 ⁻⁶ / ° C. is formed on the surface of the steel plate. An insulating substrate for CIGS solar cells. The glass is an alkali metal-containing bismuth glass, containing Bi ₂ O ₃ : 30 to 90% by mass, SiO ₂ + B ₂ O ₃ : _{3 to} 55% by mass, and further Li ₂ O, Na ₂ O, K ₂ O. An insulating substrate for CIGS solar cells, comprising a composition containing any one or more of 0.5 to 20% by mass in total. The insulating substrate for CIGS solar cells according to claim 1 or 2, wherein the insulating layer has a thickness of 5 to 50 µm. The electrode substrate for CIGS solar cells which has Mo film | membrane on the insulating substrate in any one of Claims 1-3. On Mo film of the electrode substrate according to claim 4, Cu (In, Ga) CIGS solar cells with Se ₂ type compound layer.

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