JP2022123516A - Glass substrate for solar cells and solar cell - Google Patents

Abstract

To provide a glass substrate that can give a solar cell with reduced color irregularities.SOLUTION: A glass substrate for solar cells has a glass plate, on which an undercoat layer, a first functional transparent film layer and a second functional transparent film layer are arranged in the stated order. The first functional transparent film layer comprises fluorine-doped tin oxide; the second functional transparent film layer comprises tin oxide; and the total thickness of the first functional transparent film layer and the second functional transparent film layer is 550-1000 nm.SELECTED DRAWING: None

Description

The present invention relates to a solar cell glass substrate and a solar cell using the solar cell glass substrate.

A solar cell converts light energy into electrical energy by absorbing light in a predetermined wavelength band of sunlight. There are various types of solar cells, such as amorphous silicon (a-Si) solar cells, cadmium telluride (CdTe) solar cells, CIS solar cells, and CIGS solar cells, depending on the difference in the wavelength band they absorb.

A solar cell is configured by laminating a light absorption layer on a solar cell glass substrate, and a glass substrate suitable for the type of solar cell is used. A glass substrate used for a solar cell is generally obtained by sequentially laminating an undercoat layer, a transparent conductive film layer and a surface layer on a glass plate.

Various studies have been made on glass substrates used in solar cells. For example, Patent Document 1 discloses a glass plate, a base film containing silicon, oxygen, and carbon formed on the glass plate, and tin oxide formed on the base film so as to be in contact with the base film. A glass plate with a transparent conductive film, wherein the transparent conductive film has an adhesive force of 90 mN or more as measured according to JIS R3255-1997 “Test of adhesion of thin film using glass as substrate”. A glass plate with a transparent conductive film has been proposed.

Fluorine-doped tin oxide (metal oxide in which F is added to SnO ₂ , FTO) is used for the transparent conductive film layer of the glass substrate used for the cadmium tellurium solar cell. For example, Non-Patent Document 1 describes a cadmium telluride solar cell using a glass substrate having an FTO film with a thickness of 400 nm.

JP-A-2005-29463

Amit H. Munshi, et al., "Polycrystalline CdTe photovoltaics with efficiency over 18% through improved absorber passivation and current collection." current collection)", "Solar Energy Materials and Solar Cells", Volume 176, March 2018, Pages 9-18

A conventional glass substrate has a large in-plane film thickness distribution, and when used in a cadmium tellurium solar cell, for example, color spots may become large. In recent years, there has been a need for a glass substrate that can suppress color spots, since there are applications that require designability in solar cells.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a glass substrate from which a solar cell in which color spots are suppressed can be obtained.

The present inventors have worked diligently to solve the above problems, and have found that the above problems can be solved by placing two specific types of functional transparent film layers on the undercoat layer and setting the total film thickness of these layers to a specific range. We found that the problem can be solved, and arrived at the present invention.

The present invention relates to the following <1> to <10>.
<1> An undercoat layer, a first functional transparent film layer, and a second functional transparent film layer are arranged in this order on a glass plate, and the first functional transparent film layer is fluorine-doped tin oxide. The second functional transparent film layer is made of tin oxide, and the total thickness of the first functional transparent film layer and the second functional transparent film layer is 550 to 1000 nm. Glass substrate for batteries.
<2> The glass substrate for a solar cell according to <1> above, wherein the undercoat layer contains at least one selected from the group consisting of silicon carbide oxide, titanium oxide and silicon oxide.
<3> The glass substrate for solar cells according to <1> or <2>, wherein the color difference variation ΔE of the glass substrate for solar cells is 8.0 or less.
<4> The glass substrate for a solar cell according to any one of <1> to <3> above, which has a haze value of 6.0% or less.
<5> The above <1> to <4>, wherein the thickness of the first functional transparent film layer is 500 to 900 nm, and the thickness of the second functional transparent film layer is 6 to 150 nm. Any one glass substrate for solar cells.
<6> Any one of <1> to <5>, wherein the total thickness of the first functional transparent film layer and the second functional transparent film layer is 600 to 1000 nm. Glass substrate for solar cells.
<7> The solar cell glass substrate according to any one of <1> to <6>, which is formed in a float glass manufacturing process.
<8> The glass substrate for a solar cell according to any one of <1> to <7>, wherein the first functional transparent film layer and the second functional transparent film layer are in contact with each other.
<9> A solar cell comprising the glass substrate for a solar cell according to any one of <1> to <8>.
<10> The solar cell according to <9> above, which is a cadmium tellurium solar cell.

The glass substrate for a solar cell of the present invention can suppress the in-plane variation of the reflected color of the obtained solar cell, so that the color spots of the solar cell can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing of the glass substrate for solar cells as an example for demonstrating the structure of the glass substrate for solar cells of this invention. It is a figure which shows the simulation result of the relationship between the total film thickness of the 1st functional transparent film layer of a glass substrate for solar cells, and a 2nd functional transparent film layer, and the color spot of a cadmium telluride solar cell.

The present invention will be described below, but the present invention is not limited by the exemplifications in the following description.

FIG. 1 is a cross-sectional view of a solar cell glass substrate as an example for explaining the structure of the solar cell glass substrate of the present invention.
As shown in FIG. 1, the solar cell glass substrate 10 of the present invention comprises an undercoat layer 3, a first functional transparent film layer 5 and a second functional transparent film layer 7 formed on a glass plate 1. They are arranged in this order. The first functional transparent film layer 5 is made of fluorine-doped tin oxide, the second functional transparent film layer 7 is made of tin oxide, and the first functional transparent film layer 5 and the second functional transparent film layer are formed. The total film thickness of 7 is 550 to 1000 nm. Each layer will be described below.

(glass plate)
The glass plate 1 is a support base material of the glass substrate 10 for solar cells.
The same glass plate as used in conventional solar cells can be used. Examples thereof include glass plates containing _SiO2 , _{Al2O3 , B2O3 ,} MgO, CaO, SrO, BaO, _ZrO2 , _Na2O and _K2O as base compositions. More specifically, SiO ₂ is 60 to 75%, Al ₂ O ₃ is 1 to 7.5%, B ₂ O ₃ is 0 to 1%, and MgO is 8.5 in terms of molar percentages based on oxides. ~12.5% CaO _1-6.5 % SrO 0-3% BaO 0-3% ZrO2 0-3% _Na2O 1-8% _K2O A glass plate containing 2 to 12% may be mentioned. However, it is not limited to these compositions.

Considering the power generation efficiency of a solar cell, the glass plate preferably has an average transmittance of 90.3% or more, more preferably 90.4% or more, and more preferably 90% or more in terms of a thickness of 2 mm for light with a wavelength of 500 to 800 nm. 0.5% or more is more preferable.

Moreover, since the glass substrate for solar cells is sometimes subjected to heat treatment when producing the solar cell, the glass plate preferably has good heat resistance.
Specifically, the glass transition temperature (Tg) is preferably 640° C. or higher, more preferably 645° C. or higher, and even more preferably 655° C. or higher. On the other hand, the glass transition temperature is preferably 750° C. or lower, more preferably 720° C. or lower, so as not to increase the viscosity too much during melting.

In addition, the average thermal expansion coefficient of the glass plate at 50 to 350° C. is preferably 70×10 ⁻⁷ /° C. or more, more preferably 80×10 ⁻⁷ /° C. or more, from the viewpoint of suppressing warpage of the module when modularized. is more preferred. On the other hand, it is preferably 90×10 ⁻⁷ /° C. or less, more preferably 85×10 ⁻⁷ /° C. or less, from the viewpoint of suppressing peeling and the like.

Although the thickness of the glass plate is not particularly limited, it is preferably in the range of 1 to 5 mm from the viewpoint of the balance between mechanical strength and light transmittance. The thickness of the glass plate is more preferably 2 mm or more, still more preferably 2.5 mm or more, more preferably 4.5 mm or less, even more preferably 4 mm or less, and particularly preferably 3.5 mm or less.

The shape of the glass plate is not particularly limited, and can be appropriately selected according to the shape of the solar cell manufactured using the glass substrate for solar cell of the present invention. For example, the cross-sectional shape may be a flat flat plate shape, a curved surface shape, or other irregular shape.

(undercoat layer)
The undercoat layer 3 is provided to suppress reflection between the glass plate 1 and the functional transparent film layers including the first functional transparent film layer 5 and the second functional transparent film layer 7. . In addition, the presence of the undercoat layer prevents the diffusion of alkali from the glass plate and prevents deterioration of the functional transparent film layer even when heat treatment is performed in the production of the solar cell.

Materials constituting the undercoat layer include silicon carbide oxide (SiOC), titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), silicon nitride oxide (SiON), tin oxide (SnO ₂ ), and the like. It is preferable to include one or more of Among them, from the viewpoint of facilitating flat deposition on a glass substrate, it is possible to contain at least one selected from the group consisting of silicon oxide carbide (SiOC), titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ). preferable.

The undercoat layer may consist of one layer, or may have a structure in which two or more layers are laminated. Specific examples of the undercoat layer include a single layer of silicon carbide oxide (SiOC), and a first undercoat layer of titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ). Examples include those having a laminated structure including a second undercoat layer.

When a silicon carbide oxide (SiOC) layer is used as the undercoat layer, the thickness of the SiOC layer is preferably 10 to 150 nm. When the film thickness of the SiOC layer is 10 nm or more, the surface of the glass plate can be uniformly covered, and when it is 150 nm or less, flatness can be ensured.
The film thickness of the SiOC layer is more preferably 20 nm or more, more preferably 25 nm or more, particularly preferably 30 nm or more, and more preferably 100 nm or less, further preferably 90 nm or less, and particularly preferably 80 nm or less. .

When a titanium oxide (TiO ₂ ) layer is used as the undercoat layer, the thickness of the TiO ₂ layer is preferably 3 to 50 nm. When the thickness of the TiO ₂ layer is 3 nm or more, the surface of the glass plate can be uniformly coated, and when it is 50 nm or less, sufficient alkali barrier properties can be ensured.
The thickness of the TiO ₂ layer is more preferably 4 nm or more, more preferably 5 nm or more, particularly preferably 6 nm or more, more preferably 30 nm or less, even more preferably 25 nm or less, particularly 20 nm or less. preferable.

When a silicon oxide (SiO ₂ ) layer is used as the undercoat layer, the thickness of the SiO ₂ layer is preferably 10-200 nm. When the thickness of the SiO ₂ layer is 10 nm or more, the surface of the glass plate can be uniformly covered, and when it is 200 nm or less, sufficient alkali barrier properties can be ensured.
The thickness of the _SiO2 layer is more preferably 12 nm or more, more preferably 15 nm or more, particularly preferably 20 nm or more, more preferably 120 nm or less, even more preferably 100 nm or less, particularly 70 nm or less. Preferably, 60 nm or less is most preferable.

The thickness of the entire undercoat layer is preferably 10 to 300 nm. When the total thickness of the undercoat layer is 10 nm or more, sufficient alkali barrier properties can be ensured, and when it is 300 nm or less, color spots due to optical interference can be suppressed in the undercoat layer.
The total thickness of the undercoat layer is more preferably 20 nm or more, further preferably 25 nm or more, particularly preferably 30 nm or more, more preferably 150 nm or less, further preferably 100 nm or less, and 80 nm or less. It is particularly preferred, and 70 nm or less is most preferred.

(First functional transparent film layer)
In the present invention, the first functional transparent film layer 5 is a semiconductor film layer having conductivity and transparency. The first functional transparent film layer consists of fluorine-doped tin oxide (FTO).

The content of fluorine (F) in the FTO film, which is the first functional transparent film layer, is 0.01 to 10 mol% from the viewpoint of appropriate electrical conductivity and transmittance as a solar cell substrate. Preferably, 0.1 to 5 mol % is more preferable, and 0.2 to 1 mol % is even more preferable.

The composition of the FTO film can be identified by X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectroscopy (SIMS).

The film thickness of the first functional transparent film layer is preferably 500 to 950 nm. When using an FTO film in a cadmium telluride solar cell, the FTO film was generally used with a film thickness of less than 500 nm. However, according to the knowledge of the present inventors, it was found that the color mottling of the solar cell can be suppressed by setting the film thickness of the first functional transparent film layer to 500 nm or more. In addition, when the film thickness of the FTO film (first functional transparent film layer) is 950 nm or less, productivity can be secured.
The film thickness of the first functional transparent film layer is preferably 520 nm or more, more preferably 530 nm or more, still more preferably 550 nm or more, and preferably 930 nm or less, more preferably 920 nm or less, and 900 nm. More preferred are:

(Second functional transparent film layer)
The second functional transparent film layer 7 is a layer for preventing recombination of light holes generated in the solar cell and conductive carriers in the first functional transparent film layer to improve the efficiency of the solar cell. be. The second functional transparent film layer consists of non-doped tin oxide (SnO ₂ ).

The composition of the second functional transparent film layer can be similarly identified by X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectroscopy (SIMS).

The film thickness of the second functional transparent film layer is preferably 6 to 150 nm. When the film thickness of the second functional transparent film layer is 6 nm or more, the first functional transparent film layer can be uniformly coated. It is preferably 150 nm or less because it becomes a direct resistance component for .
The thickness of the second functional transparent film layer is more preferably 8 nm or more, more preferably 9 nm or more, particularly preferably 10 nm or more, particularly preferably 12 nm or more, most preferably 15 nm or more, and 100 nm. It is more preferably 90 nm or less, particularly preferably 80 nm or less.

In the present invention, the total thickness of the first functional transparent film layer and the second functional transparent film layer is 550-1000 nm. When the total film thickness of the first functional transparent film layer and the second functional transparent film layer is 550 nm or more, the effect of suppressing color spots of the solar cell is exhibited when used in the solar cell, and when the total film thickness is 1000 nm or less. If there is, the transmittance of the entire substrate can be increased.
The total thickness of the first functional transparent film layer and the second functional transparent film layer is preferably 600 nm or more, more preferably 650 nm or more, still more preferably 670 nm or more, and 950 nm or less. is preferred, 930 nm or less is more preferred, and 900 nm or less is even more preferred.

The glass substrate for a solar cell of the present invention may have other functional transparent film layers in addition to the first functional transparent film layer and the second functional transparent film layer.
Other functional transparent film layers include transparent semiconductor film layers mainly containing metal oxides other than FTO, and transparent oxide layers mainly containing oxides other than SnO ₂ . Note that "mainly containing" means that the metal oxide or oxide is 50% by mass or more, preferably 70% by mass or more, and 85% by mass or more with respect to the entire other functional transparent film layer. is more preferable. The upper limit is not particularly limited, but when the main component of the semiconductor film layer is doped with a dopant (impurity metal), it is preferably 99.9% by weight or less.

Examples of such metal oxides include ZnO (zinc oxide), In ₂ O ₃ (indium oxide), SnO ₂ (tin oxide), etc. These metal oxides include Al (aluminum), Impurity metals such as B (boron), Ga (gallium), In (indium), Sn (tin), Sb (antimony), and F (fluorine) may be included.
Specific examples of metal oxides containing such impurity metals include ITO (tin-doped indium oxide, a metal oxide obtained by adding Sn to In ₂ O ₃ ), AZO (aluminum-doped zinc oxide, ZnO with Al ), IZO (indium-doped zinc oxide, metal oxide in which In is added to ZnO), niobium-doped titanium oxide, tantalum-doped titanium oxide, antimony-doped tin oxide, and the like.
Examples of the oxide include ZnO (zinc oxide), In ₂ O ₃ (indium oxide), TiO ₂ (titanium oxide), CdO (cadmium oxide), and the like.

One layer may be sufficient as another functional transparent film layer, and two or more layers may be sufficient as it.
In addition, the position where the other functional transparent film layer is provided is not particularly limited. For example, between the undercoat layer and the first functional transparent film layer, between the first functional transparent film layer and the second functional transparent film layer Between the transparent film layer, the surface of the second functional transparent film layer, and the like.

In the present invention, the first functional transparent film layer and the second functional transparent film layer are preferably in contact with each other, and the first functional transparent film layer and the second functional transparent film layer are formed on the undercoat layer. It is more preferable to have a structure in which the transparent film layers are laminated in this order.

(Method for producing glass substrate for solar cell)
The glass substrate for solar cells of the present invention can be produced, for example, by sequentially forming an undercoat layer, a first functional transparent film layer and a second functional transparent film layer on the surface of a glass plate.

A glass plate is produced by heating frit to obtain molten glass, fining by removing bubbles from the molten glass, forming the molten glass into a plate to obtain a glass ribbon, and slowly cooling the glass ribbon to room temperature. It can be obtained by a slow cooling process. Alternatively, the molten glass may be formed into a block shape, slowly cooled, and then cut and polished to produce a glass plate.
Conventionally known methods can be used for each of the above steps. The manufacturing method is not limited to the embodiment, and suitable modifications and improvements are possible as long as the object of the present invention can be achieved.

The undercoat layer, the first functional transparent film layer, and the second functional transparent film layer are all formed by a CVD (Chemical Vapor Deposition) method, a sputtering method, a chemical plating method, a wet coating method, or the like. can be formed. The sputtering method is a method of forming a film on a manufactured glass plate, and the chemical plating method is a method of making a mirror.

CVD methods include an online CVD method and an offline CVD method.
The online CVD method is a method of forming a film directly on the surface of a glass plate during the manufacturing process of the glass plate on a float line. That is, the functional transparent film layer or the like is formed during the process of obtaining the glass plate, rather than forming the functional transparent film layer or the like after obtaining the glass plate.
Specifically, in the production of glass sheets, glass sheets are continuously produced by moving the glass ribbon over a molten tin bath and then slowly cooling it. , the film-forming process of a desired layer is continuously carried out on the upper surface of the glass ribbon.

More specifically, before the slow cooling step in the above glass plate manufacturing method, that is, while the glass on the float line is still hot in the forming step, the gaseous raw material is blown onto the glass surface and reacted. , a glass substrate for a solar cell can be obtained by forming a desired layer.
The online CVD method can form the undercoat layer, the first functional transparent film layer and the second functional transparent film layer in a series of steps for manufacturing the glass plate, so that the manufacturing cost can be kept low. Therefore, it is preferable.

On the other hand, in the offline CVD method, a glass plate that has been once manufactured in a glass manufacturing process and cut into an appropriate size is put into an electric furnace and transported while supplying gaseous raw materials in the same manner as in the online CVD method. This is a method of forming a desired layer using a reaction. Although there is an advantage that the transport speed and the substrate temperature can be set according to the film formation, the manufacturing cost is higher than that of the on-line CVD method.

When the sputtering method is used, a very small amount of special gas is injected into an evacuated container and a voltage is applied to form a desired functional transparent film layer on the glass plate, thereby forming a solar cell glass substrate. can get.
Since the sputtering method forms a layer on a glass plate that has been manufactured once, it is possible to form layers with various desired compositions, although the production cost is high.

In the case of the CVD method, the thickness of the undercoat layer, the first functional transparent film layer, and the second functional transparent film layer depends on the type of raw material, the concentration of the raw material gas, the flow rate of the raw material gas blown onto the glass ribbon, the substrate It can be controlled by the temperature, the reaction gas residence time derived from the coating beam structure, and the like. In the case of the sputtering method, the thickness can be controlled by the sputtering time, voltage and the like.

A method for producing a solar cell glass substrate by the off-line CVD method will be described below.
In the following manufacturing method, an undercoat layer is formed on the surface of a glass plate, and then an FTO film as a first functional transparent film layer and a tin oxide layer as a second functional transparent film layer are formed. do.

When forming a silicon carbide oxide layer as an undercoat layer, it is preferable to use a mixed gas containing, for example, monosilane (SiH ₄ ), ethylene and carbon dioxide as the raw material.
The temperature for forming the silicon carbide oxide layer is preferably 700 to 1000°C, more preferably 850 to 950°C.

When forming a titanium oxide layer as an undercoat layer, examples of raw materials include tetraisopropyl orthotitanate (TTIP) and titanium tetrachloride. Among them, tetraisopropyl orthotitanate (TTIP) is more preferable.
The temperature for forming the titanium oxide layer is preferably 500 to 800.degree. C., more preferably 550 to 700.degree.

When forming a silicon oxide layer as an undercoat layer, it is preferable to use, for example, a mixed gas containing monosilane (SiH ₄ ), ethylene and carbon dioxide as the raw material.
The temperature for forming the silicon oxide layer is preferably 500 to 800.degree. C., more preferably 550 to 700.degree.

After forming the undercoat layer, the first functional transparent film layer is subsequently formed.

When forming the FTO film, which is the first functional transparent film layer, it is preferable to use, for example, a mixed gas containing monobutyltin trichloride, oxygen, water, nitrogen and trifluoroacetic acid as the raw material.
The temperature for forming the FTO film is preferably 500 to 800°C, more preferably 550 to 700°C.

After forming the first functional transparent film layer, the second functional transparent film layer is formed continuously.

When forming the tin oxide (SnO ₂ ) layer, which is the second functional transparent film layer, the raw materials include, for example, monobutyltin trichloride, dimethyltin dichloride, tributyltin, trimethyltin, and tin tetrachloride, A gas mixture containing oxygen, water and nitrogen is preferably used.
The temperature for forming the tin oxide film is preferably 400 to 800.degree. C., more preferably 500 to 750.degree.

After forming the second functional transparent film layer, it is slowly cooled, and the undercoat layer, the first functional transparent film layer and the second functional transparent film layer are formed on the glass plate. A battery glass substrate is obtained.

In the present invention, from the viewpoint of manufacturing cost, the number of manufacturing steps, etc., the glass substrate for solar cells is manufactured by the online CVD method, in which the undercoat layer and the functional transparent film layer are manufactured continuously after the manufacturing of the glass substrate. It is preferably manufactured in a process.

The solar cell of the present invention is obtained by forming a light absorption layer on the glass substrate for solar cells of the present invention. film. Since this n-type semiconductor layer has a thin film thickness of 25 to 100 nm, it cannot be formed uniformly if the surface of the glass substrate for solar cell is uneven.
Therefore, in order to obtain a solar cell with high efficiency, it is desirable that the surface flatness of the glass substrate for solar cells is high. Specifically, when evaluating a surface shape of 5 μm × 5 μm with an AFM (Atomic Force Microscope), the difference (Rz) between the maximum height and the minimum height of the substrate surface is smaller than the thickness of the n-type semiconductor layer. is desirable.
The Rz value is preferably 50 nm or less, more preferably 40 nm or less, and particularly preferably 30 nm or less.

In addition, since the surface roughness of a solar cell glass substrate is proportional to the haze value of the substrate, the haze is widely used as an index of surface roughness. When forming the light absorbing layer, the Haze value of the solar cell glass substrate is preferably 6.0% or less in order to uniformly form the light absorbing layer.
The haze value is more preferably 5.5% or less, more preferably 5.0% or less, and particularly preferably 4.5% or less, and the lower limit is not particularly limited, but it is 1.0% or more. is preferred.

The haze value can be measured in accordance with JIS K 7105 (1981) using a haze meter (eg, "HZ-V3" manufactured by Suga Test Instruments Co., Ltd.).

The glass substrate for solar cell of the present invention preferably has a color difference variation ΔE of 8.0 or less. When the color difference variation ΔE is 8.0 or less, the color difference variation in the solar cell structure can be 4.5 or less.
The color difference variation ΔE is more preferably 7.0 or less, even more preferably 6.0 or less, and particularly preferably 5.0 or less. Further, the lower the color difference variation ΔE, the more the color spots are suppressed, so the lower limit is not particularly limited.

The color difference variation ΔE of the solar cell glass substrate is obtained by measuring the distribution of the reflected colors (a ^* , b ^* ) viewed from the glass plate side of the solar cell glass substrate. Specifically, the light source is a D65 light source, both the incident angle and the reflection angle are set at 8° with respect to the substrate, and the light is irradiated from the glass surface side of the substrate. The spot size of the light source is adjusted to about 1 to 4 cm ² on the surface of the glass plate, and the reflection spectrum is measured at intervals of 3 cm in the plane of the glass substrate. The reflected color (a ^* , b ^* ) at each measurement point is calculated from the obtained spectrum. From the obtained reflected color data, Euclidean distance ΔE ₁₂ =((a ₁ ^* -a ₂ ^* ) ² +(b ₁ ^* -b ₂ ^* ) ² ) ^0.5 on the color coordinates is the maximum ( A combination of a ₁ ^* , b ₁ ^* ) and (a ₂ ^* , b ₂ ^* ) is selected, and its ΔE ₁₂ is defined as the color difference variation ΔE of the solar cell glass substrate.

The glass substrate for a solar cell of the present invention preferably has a visible light transmittance of 70% or more. When the transmittance is 70% or more, the light conversion efficiency can be improved when used as a solar cell. The transmittance is more preferably 73% or higher, and even more preferably 76% or higher.

The visible light transmittance of the solar cell glass substrate can be measured with an ultraviolet-visible spectrophotometer.

The glass substrate for solar cell of the present invention can be used as a solar cell by forming a light absorption layer on its surface layer.
Examples of the light absorption layer include cadmium telluride (CdTe), cadmium sulfide (CdS), CIGS (Cu/In/Ga/Se), CIS (Cu/In/Se), tin sulfide (SnS), and the like. Among others, the glass substrate for solar cells of the present invention is useful for cadmium tellurium solar cells.

A solar cell using the glass substrate for a solar cell of the present invention preferably has a color difference variation ΔE of 5.0 or less. When the color difference variation ΔE is 5.0 or less, color spots are small, and the design of the solar cell can be improved.
The color difference variation ΔE is more preferably 4.7 or less, more preferably 4.5 or less, and particularly preferably 4.3 or less. Although not limited, it is preferably 0.5 or more.

The color difference variation ΔE of the solar cell is obtained by measuring the distribution of the reflected colors (a ^* , b ^* ) viewed from the glass substrate side of the solar cell in the same manner as the method for measuring the color difference variation of the glass substrate for a solar cell. is obtained by Specifically, the light source is a D65 light source, both the incident angle and the reflection angle are set at 8° with respect to the substrate, and the light is irradiated from the glass surface side of the substrate. The spot size of the light source is adjusted to about 1 to 4 cm ² on the surface of the glass substrate, and the reflection spectrum is measured at intervals of 3 cm in the plane of the glass substrate. The reflected color (a ^* , b ^* ) at each measurement point is calculated from the obtained spectrum. From the obtained reflected color data, Euclidean distance ΔE ₁₂ =((a ₁ ^* -a ₂ ^* ) ² +(b ₁ ^* -b ₂ ^* ) ² ) ^0.5 on the color coordinates is the maximum ( A combination of a ₁ ^* , b ₁ ^* ) and (a ₂ ^* , b ₂ ^* ) is selected, and its ΔE ₁₂ is defined as the color difference variation ΔE of the solar cell.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. As for the examples produced below, Examples 1 to 4, 9 to 13, and 17 to 23 are examples, and Examples 5 to 8, 14 to 16, and 24 to 29 are comparative examples.

The glass substrate, in molar percentage display based on oxides, contains 72% _SiO2 , 1.1% _{Al2O3 ,} the sum of MgO and CaO is 13.5%, and the sum of _Na2O and _K2O is A glass substrate containing 13.5% Fe ₂ O ₃ and FeO with a composition of 0.015% or less was used.

<Experimental example 1>
When a thin film is formed on a glass plate using the CVD method, in-plane variations occur in the film thickness. When a solar cell is formed on this glass plate, the optical reflection spectrum varies within the surface of the glass plate, resulting in color spots.
In Experimental Example 1, the total film thickness (SnO2 _total film thickness) of the first functional transparent film layer (FTO film) and the second functional transparent film layer (tin oxide film), which are functional transparent film layers, was The color mottling of solar cells stacked on different substrates was evaluated using optical simulations. A D65 light source was used as the light source, and both the incident angle and the reflection angle were perpendicular to the substrate.
The size of color mottling was defined as the size of change in ab coordinates of the reflected color of the cadmium telluride solar cell when the SnO ₂ total film thickness varied by ±10%. The structure of the cadmium telluride solar cell is the film composition and film thickness: CdTe: 3500 nm/CdS: 50 nm/SnO ₂ : 45 nm/FTO (F: SnO ₂ ): 155 to 1005 nm/SiOC: 55 nm/glass plate: 3 .2 mm.

FIG. 2 is a graph showing the color difference variation (ΔE) of cadmium telluride solar cells when the total SnO ₂ film thickness is plotted on the horizontal axis.
From FIG. 2, when the total film thickness of the functional transparent film layer exceeds 400 nm, the color difference variation (ΔE) becomes small, and when the total film thickness is 500 nm or more, ΔE becomes less than around 6, and the total film thickness is 600 nm. It was shown above that ΔE is 4 or less.

<Experimental example 2>
In Experimental Example 2, the solar cell glass substrates and solar cells of Examples 1 to 16 were produced.

(Example 1)
Molten glass composed of soda-lime-silica glass was poured into a float bath at 1500 to 1600° C., and sheet glass was formed while continuously flowing the glass ribbon.
An undercoat layer, a first functional transparent film layer (FTO film) and a second functional transparent film layer are formed on a glass ribbon (glass plate) having a thickness of 3.2 mm using an apparatus having a plurality of coating beams. (SnO ₂ film) was formed to prepare a solar cell glass substrate.
A mixed gas consisting of monosilane (SiH ₄ ), ethylene and CO ₂ was supplied from the first coating beam located on the most upstream side where the temperature of the glass ribbon was 700° C., and a SiOC film with a thickness of 55 nm was formed on the glass ribbon. An undercoat layer was formed.
Subsequently, from the second coating beam located downstream where the glass ribbon reaches 600° C., a mixed gas consisting of monobutyltin trichloride, oxygen, water, nitrogen and trifluoroacetic acid is supplied to coat the SiOC film with a film thickness of 855 nm. An FTO film (F: 0.4 mol %) containing F: SnO ₂ as a component was formed.
Furthermore, a mixed gas consisting of monobutyltin trichloride, oxygen, water and nitrogen was supplied from a third coating beam located immediately downstream thereof to form a tin oxide (SnO ₂ ) film having a thickness of 45 nm. , to obtain a glass substrate for a solar cell.

For the mixed gas for forming the FTO film and the SnO ₂ film, each substance was supplied in a liquid phase or gas phase state to a mixer, where the substances were mixed while being heated and vaporized to obtain a mixed gas.
The amount of each raw material supplied from the first coating beam when forming the undercoat layer was 0.12 kg/hour (liquid phase) of monosilane, 0.36 kg/hour of ethylene, and 30 kg/hour of CO ₂ .
The amount of each raw material supplied from the second coating beam when forming the FTO film was 20.5 L/hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ /hour of oxygen, and 88.6 kg/hour of water. , trifluoroacetic acid was 4.9 L/hour (liquid phase).
The amount of each raw material supplied from the third coating beam when forming the SnO ₂ film was 5.9 L/hour (liquid phase) of monobutyltin trichloride, 1.27 Nm ³ /hour of oxygen, and 44.6 kg/hour of water. It was time.

After transporting the obtained glass substrate for a solar cell to a vacuum chamber, a cadmium sulfide layer with a thickness of 50 nm and a cadmium tellurium layer with a thickness of 3500 nm were formed on the tin oxide layer by a sublimation proximity method at 440° C. and 650° C., respectively. A film was formed using After that, in order to interdiffuse cadmium tellurium and cadmium sulfide, cadmium chloride is sublimed and then heated at 440° C. to obtain CdTe (3500 nm)/CdS (50 nm)/SnO ₂ (45 nm)/FTO (855 nm)/SiOC. A solar cell having a configuration of (55 nm)/glass plate (3.2 mm) was fabricated.

(Examples 2-8)
A solar cell was prepared in the same manner as in Example 1, except that the film thicknesses of the first functional transparent film layer (FTO film) and the _second functional transparent film layer (SnO2 film) were changed as shown in Table 1. A solar cell having the same structure as in Example 1 was fabricated.

(Example 9)
An undercoat layer, a first functional transparent film layer (FTO film) and a second functional transparent film layer are formed on a glass ribbon (glass plate) having a thickness of 3.2 mm using an apparatus having a plurality of coating beams. (SnO ₂ film) was formed to prepare a solar cell glass substrate.
Tetraisopropyl orthotitanate (TTIP) was supplied from the first coating beam located on the most upstream side where the temperature of the glass ribbon was 650° C., and a first titanium oxide film having a thickness of 8 nm was formed on the glass ribbon. An undercoat layer was formed.
Next, a mixed gas consisting of monosilane (SiH ₄ ), ethylene, and CO ₂ is supplied from the second coating beam located downstream where the glass ribbon reaches 600° C. to form a 33 nm-thickness coating on the titanium oxide film. A second undercoat layer, which is a silicon oxide film, was deposited.
Next, a mixed gas consisting of monobutyltin trichloride, oxygen, water, nitrogen and trifluoroacetic acid is supplied from the third coating beam located downstream where the glass ribbon reaches 600° C., and a film thickness is formed on the silicon oxide film. An FTO film ₍ F: 0.4 mol%) composed of 855 nm F:SnO2 was deposited.
Further, a mixed gas consisting of monobutyltin trichloride, oxygen, water and nitrogen was supplied from a fourth coating beam located immediately downstream thereof to form a tin oxide (SnO ₂ ) film with a thickness of 45 nm. A battery glass substrate was obtained.

For the mixed gas for forming the FTO film and the SnO ₂ film, each substance was supplied in a liquid phase or gas phase state to a mixer, where the substances were mixed while being heated and vaporized to obtain a mixed gas.
The amount of each raw material supplied from the third coating beam when forming the FTO film was 20.5 L/hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ /hour of oxygen, and 88.6 kg/hour of water. , trifluoroacetic acid was 4.9 L/hour (liquid phase).
The amount of each raw material supplied from the fourth coating beam when forming the SnO ₂ film was 5.9 L/hour (liquid phase) of monobutyltin trichloride, 1.27 Nm ³ /hour of oxygen, and 44.6 kg/hour of water. It was time.

After transporting the obtained glass substrate for a solar cell to a vacuum chamber, a cadmium sulfide layer with a thickness of 50 nm and a cadmium tellurium layer with a thickness of 3500 nm were formed on the tin oxide layer by a sublimation proximity method at 440° C. and 650° C., respectively. A film was formed using After that, in order to interdiffuse cadmium telluride and cadmium sulfide, cadmium chloride is sublimated and then heated at 440° C. to form CdTe (3500 nm)/CdS (50 nm)/SnO ₂ (45 nm)/FTO (855 nm)/SiO ₂ (33 nm)/TiO ₂ (8 nm)/glass plate (3.2 mm).

(Examples 10-16)
A solar cell was prepared in the same manner as in Example 9, except that the film thicknesses of the first functional transparent film layer (FTO film) and the _second functional transparent film layer (SnO2 film) were changed as shown in Table 2. A solar cell having the same structure as in Example 9 was fabricated.

<Measurement of color difference variation (ΔE)>
For each of the solar cell glass substrates and solar cells produced in Examples 1 to 16, color difference variation (size of color spots) was measured.
In order to calculate the size of color spots, the distribution of the reflected colors (a ^* , b ^* ) was measured for the solar cell glass substrate viewed from the glass plate side, and for the solar cell viewed from the glass substrate side. A D65 light source was used as the light source, and both the incident angle and the reflection angle were perpendicular to the substrate. Light was applied from the glass surface side of the substrate. The spot size of the light source was adjusted to be approximately 1 cm ² on the surface of the glass plate/glass substrate. Reflection spectra were measured at intervals of 3 cm in the plane of the glass substrate. The reflected color (a ^* , b ^* ) at each measurement point was calculated from the obtained spectrum.
From the obtained reflected color data, Euclidean distance ΔE ₁₂ =((a ₁ ^* -a ₂ ^* ) ² +(b ₁ ^* -b ₂ ^* ) ² ) ^0.5 on the color coordinates is the maximum ( A combination of a ₁ ^* , b ₁ ^* ) and (a ₂ ^* , b ₂ ^* ) was selected, and its ΔE ₁₂ was defined as the color difference variation ΔE of the solar cell glass substrate or solar cell.
The results are shown in Table 1 or Table 2.

From the results in Tables 1 and 2, all of the glass substrates for solar cells produced in Examples 1 to 4 and 9 to 13, in which the total film thickness of the FTO film and the SnO ₂ film is 550 nm or more, had a color difference variation ΔE of 8.5. was 0 or less. Moreover, the solar cells produced in Examples 1 to 4 and 9 to 13 all had a color difference variation ΔE of 5.0 or less, indicating that color mottling was suppressed.

<Experimental example 3>
In Experimental Example 3, solar cell glass substrates and solar cells of Examples 17 to 29 were produced.

(Examples 17-29)
Same as Example 1 of Experimental Example 2, except that the film thicknesses of the first functional transparent film layer (FTO film) and the _second functional transparent film layer (SnO2 film) were changed as shown in Table 3. Then, a solar cell glass substrate was obtained, and a solar cell having the same structure as in Example 1 was produced.

<Measurement of Haze>
For the solar cell glass substrates produced in Examples 17 to 29, the haze value was measured according to JIS K 7105 (1981) using a haze meter "HZ-V3" manufactured by Suga Test Instruments Co., Ltd.
Table 3 shows the results.

<Measurement of color difference variation (ΔE)>
For the solar cell glass substrates and solar cells produced in Examples 17 to 29, the color difference variation ΔE of the solar cell glass substrates and solar cells was measured in the same manner as in Experimental Example 2.
Table 3 shows the results.

From the results in Table 3, even if the thicknesses of the FTO film and the SnO film are changed, by setting the _total film thickness to 550 nm or more, the color difference variation ΔE of the glass substrate for solar cells is 8.0 or less, and the solar cell was 5.0 or less. As a result, it was found that the solar cells produced in Examples 17 to 23 were free from color mottling.
Further, it was found that the solar cell glass substrates of Examples 17 to 23, which are working examples, had a haze value of 6.0% or less, and were excellent in film formability of the light absorbing layer.
Examples 17 to 29 are examples in which a silicon carbide oxide ₍ SiOC) layer was formed as an undercoat layer. It is assumed that the haze value is about the same when using a laminated film (SiO ₂ /TiO ₂ ) in which a titanium oxide (TiO ₂ ) layer and a silicon oxide (SiO ₂ ) layer are laminated in order as the coat layer.

1 glass plate 3 undercoat layer 5 first functional transparent film layer 7 second functional transparent film layer 10 glass substrate for solar cell

Claims (10)

An undercoat layer, a first functional transparent film layer and a second functional transparent film layer are arranged in this order on a glass plate,
The first functional transparent film layer is made of fluorine-doped tin oxide, the second functional transparent film layer is made of tin oxide,
A glass substrate for a solar cell, wherein the total thickness of the first functional transparent film layer and the second functional transparent film layer is 550 to 1000 nm. The glass substrate for solar cell according to claim 1, wherein the undercoat layer contains at least one selected from the group consisting of silicon carbide oxide, titanium oxide and silicon oxide. 3. The glass substrate for solar cells according to claim 1, wherein the glass substrate for solar cells has a color difference variation .DELTA.E of 8.0 or less. 4. The glass substrate for solar cells according to claim 1, which has a Haze value of 6.0% or less. 5. The film according to any one of claims 1 to 4, wherein the first functional transparent film layer has a thickness of 500 to 900 nm, and the second functional transparent film layer has a thickness of 6 to 150 nm. glass substrates for solar cells. 6. The glass substrate for solar cells according to claim 1, wherein the total thickness of said first functional transparent film layer and said second functional transparent film layer is 600-1000 nm. 7. The glass substrate for solar cells according to claim 1, which is formed in a float glass manufacturing process. 8. The glass substrate for solar cell according to claim 1, wherein said first functional transparent film layer and said second functional transparent film layer are in contact with each other. A solar cell comprising the glass substrate for a solar cell according to any one of claims 1 to 8. 10. The solar cell of claim 9, which is a cadmium tellurium solar cell.

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