TW201416335A - Glass substrate for solar cell and solar cell using same - Google Patents

Abstract

The present invention provides a glass substrate for a solar cell and a solar cell using the same, which satisfies a high power generation efficiency, a high glass transition point temperature, a predetermined average thermal expansion coefficient, a high glass strength, a low glass density, and the like. In the production of sheet glass, it has high meltability, good formability, and good resistance to devitrification. A glass substrate for a solar cell, which is represented by a mass percentage based on the following oxides, and contains: 50 to 65% of SiO2, 8 to 15% of Al2O3, 0 to 1% of B2O3, and 0 to 10% of MgO, 1~. 12% CaO, 6-12% SrO, 0~3% BaO, 1~7% ZrO2, 2~8% Na2O, 0~8% K2O, 15~30% MgO+CaO+SrO +BaO; and SrO/Na2O is 0.8~2.5.

Description

Glass substrate for solar cell and solar cell using same Field of invention

The present invention relates to a glass substrate for a solar cell in which a photoelectric conversion layer is formed between glass substrates, and a solar cell using the same. More specifically, the present invention relates to a Cu-In-Ga-Se solar cell or CdTe for forming a photoelectric conversion layer of Cu-In-Ga-Se or a photoelectric conversion layer of CdTe between glass substrates. A glass substrate such as a solar cell or a solar cell using the same.

Background of the invention

a compound semiconductor having a chalcopyrite crystal structure of Groups 11-13, 11-16th compound semiconductor or a cubic crystal system or a hexagonal system of Group 12-16, which has a light having a wavelength range from visible to near infrared rays The absorption coefficient is large. Therefore, it is expected to be a material for high-efficiency thin film solar cells. Typical examples include Cu(In,Ga)Se ₂ (hereinafter referred to as "CIGS" or "Cu-In-Ga-Se") and CdTe.

For CIGS thin film solar cells (hereinafter also referred to as "CIGS solar cells") and CdTe thin film solar cells (hereinafter, also referred to as "CdTe solar cells"), the average thermal expansion coefficient and the average thermal expansion coefficient of CIGS compound semiconductors are cheap. Similar, so the use of soda lime glass as a base Plate to make solar cells.

In recent years, a glass material which can withstand heat treatment at a high temperature has been proposed as a glass substrate for a CIGS solar cell (see, for example, Patent Documents 1 to 5).

Advanced technical literature Patent literature

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 11-135819

Patent Document 2: Japanese Laid-Open Patent Publication No. 2010-118505

Patent Document 3: Japanese Patent Laid-Open No. Hei 8-290938

Patent Document 4: Japanese Laid-Open Patent Publication No. 2008-280189

Patent Document 5: Japanese Laid-Open Patent Publication No. 2010-267965

Summary of invention

In the CIGS solar cell, a CIGS photoelectric conversion layer (hereinafter also referred to as "CIGS layer") is formed between the glass substrates, but in order to produce a solar cell system with good power generation efficiency, heat treatment at a relatively high temperature is preferable, and thus glass is required. The substrate needs to be able to withstand the heat treatment. However, in the patent documents 1 to 4, a glass composition having a high cold point is proposed, but the inventions described in Patent Documents 1 to 4 are not necessarily said to have high power generation efficiency.

More specifically, in the inventions described in Patent Documents 2 and 4, a glass for a solar cell having a high strain point and satisfying a predetermined average thermal expansion coefficient is proposed. However, the subject of Patent Document 2 is to ensure heat resistance and improve productivity, and the subject of Patent Document 4 is to improve the surface texture and to improve the resistance to devitrification, and it is not intended to solve the problem of power generation efficiency. Therefore, Patent Document 2 The invention described in 4 may not necessarily be said to have high power generation efficiency.

Further, in Patent Document 3, there is a proposal for a glass substrate having a high strain point similar to that of Patent Document 2. However, this proposal is focused on the use of a plasma display device, and the invention described in Patent Document 3 may not be possible. It is said to have high power generation efficiency.

Further, in Patent Document 4, a glass containing a large amount of boron oxide and having a high strain point and satisfying a predetermined average thermal expansion coefficient is proposed. However, when a large amount of boron is present in the glass, as disclosed in Patent Document 5, boron diffuses into the CIGS layer which is a p-type semiconductor and acts as a host, which may cause a decrease in power generation efficiency. In other words, there is a problem that the cost of the boron is easily increased due to the need for the removal device of boron.

In Patent Document 5, although boron in the glass is reduced, power generation efficiency is insufficient in the glass composition specifically described. Therefore, there is room for improvement in that power generation efficiency is further improved.

On the other hand, in order to prevent peeling of the photoelectric conversion layer (CIGS layer) on the glass substrate during or after film formation, the glass substrate is required to have a predetermined average thermal expansion coefficient.

Furthermore, from the viewpoint of the manufacture and use of the CIGS solar cell, it is required to increase the strength and weight of the glass substrate, and to have good meltability and formability when producing sheet glass, and to prevent devitrification.

However, in a glass substrate used for a CIGS solar cell, it is difficult to balance high power generation efficiency, high alkali diffusibility, high glass transition point temperature, predetermined average thermal expansion coefficient, high glass strength, low glass density, and production of sheet glass. High meltability, good formability and good devitrification Characteristics such as discontinuity.

An object of the present invention is to provide a glass substrate which can be suitably used for a CIGS solar cell and a solar cell using the same, which has a high power generation efficiency, a high alkali diffusion property, a high glass transition point temperature, and a predetermined average thermal expansion. Coefficient, high glass strength, low glass density, and high meltability in the production of sheet glass, good formability, and good resistance to devitrification.

In order to solve the above-mentioned problems, the inventors of the present invention have found that the glass substrate for a solar cell can be made into a balanced composition with high power generation efficiency and high alkali diffusion property by setting it as a specific composition range. A glass substrate having high glass transition point temperature, predetermined average thermal expansion coefficient, high glass strength, low glass density, and high meltability in sheet glass production, good formability, and good resistance to devitrification.

That is, the present invention is as follows:

(1) A glass substrate for a solar cell, which comprises: 50 to 65% of SiO ₂ , 8 to 15% of Al ₂ O ₃ , and 0 to 1% of B ₂ O ₃ based on the mass percentage based on the following oxides. 0 to 10% of MgO, 1 to 12% of CaO, 6 to 12% of SrO, 0 to 3% of BaO, 1 to 7% of ZrO ₂ , 2 to 8% of Na ₂ O, 0 to 8% K ₂ O, 15~30% of MgO+CaO+SrO+BaO; and SrO/Na ₂ O is 0.8~2.5.

(2) The glass substrate for a solar cell according to the above (1), wherein the glass transition point temperature is 640 ° C or higher.

(3) The glass substrate for a solar cell according to the above (1) or (2), which has an average thermal expansion coefficient of 70 × 10 ^-7 to 90 × 10 ^-7 / °C.

(4) The glass substrate for a solar cell according to any one of the above items (1) to (3), wherein the viscosity is 10 ⁴ dPa. The temperature of s (T ₄ ) is below 1230 ° C, and the viscosity becomes 10 ² dPa. The temperature (T ₂ ) of s is 1650 ° C or less, and the relationship between the above T ₄ and the devitrification temperature (T _L ) is T ₄ -T _L ≧ -30 ° C.

The glass substrate for a solar cell according to any one of the above items (1) to (4), which has a density of 2.75 g/cm ³ or less.

The glass substrate for a solar cell according to any one of the above items (1) to (5) wherein the content of Al ₂ O ₃ is 8.5 to 14.5%.

(7) The glass substrate for a solar cell according to any one of the above (1), wherein the content of CaO is from 3 to 11%.

The glass substrate for a solar cell according to any one of the above items (1) to (6) wherein the content of CaO is from 3 to 10%.

The glass substrate for a solar cell according to any one of the above items (1) to (8) wherein the content of Na ₂ O is 4 to 7%.

(10) A glass base for a solar cell according to any one of the above items (1) to (9) The sum of the contents of MgO+CaO+SrO+BaO is 17-23%.

The glass substrate for a solar cell according to any one of the above items (1) to (10) wherein the content of BaO is 2% or less.

The glass substrate for a solar cell according to any one of the above items (1) to (11), wherein the value represented by the formula 9SiO ₂ +15Al ₂ O ₃ is in the range of 570% to 840%. Contains SiO ₂ and Al ₂ O ₃ .

The glass substrate for a solar cell according to any one of the above items (1) to (12), wherein the value represented by the formula of 3Na ₂ O+2K ₂ O is in the range of 14% to 44%. Contains Na ₂ O and K ₂ O.

(14) A Cu-In-Ga-Se solar cell comprising: a glass substrate; a cover glass; and a Cu-In-Ga-Se photoelectric conversion layer disposed between the glass substrate and the cover glass; In the glass substrate and the cover glass, at least the glass substrate is a glass substrate for a solar cell according to any one of the above items (1) to (13).

(15) A CdTe solar cell comprising: a glass substrate; a back sheet glass; and a CdTe photoelectric conversion layer disposed between the glass substrate and the back sheet glass; and the glass substrate and the back sheet glass The glass substrate for a solar cell according to any one of the above items (1) to (13).

The glass substrate for a solar cell of the present invention has high power generation efficiency, high alkali diffusibility, high glass transition point temperature, predetermined average thermal expansion coefficient, high glass strength, low glass density, and high meltability when producing sheet glass. Good formability and good resistance to devitrification. Moreover, by using the glass substrate for a solar cell of the present invention, it is possible to provide a solar cell having high power generation efficiency. In particular, the glass substrate for a solar cell of the present invention is useful as a Cu-In-Ga-Se solar cell or as a CdTe solar cell system.

1‧‧‧CIGS solar cell

5, 5a‧‧‧ glass substrate

7, 7a‧‧‧ positive electrode

9, 9a‧‧‧ CIGS layer

11, 11a‧‧‧ buffer layer

13, 13a‧‧‧Transparent conductive film

15, 15a‧‧‧ negative electrode

16a‧‧‧negative terminal

17‧‧‧Anti-reflective film

19‧‧‧ Cover glass

21‧‧‧CdTe solar cell

22‧‧‧ glass substrate

23‧‧‧Transparent conductive film

24‧‧‧buffer layer

25‧‧‧CdTe layer

26‧‧‧Back electrode

27‧‧‧back glass

Fig. 1 is a cross-sectional view showing an example of an embodiment of a solar cell (CIGS solar cell) using the glass substrate for a solar cell of the present invention.

Fig. 2 is a view showing a solar battery cell (a) and a cross-sectional view (b) thereof produced on the glass substrate for evaluation in the examples.

Fig. 3 shows an evaluation CIGS solar cell on an evaluation glass substrate of eight solar cell units shown in Fig. 2 side by side.

Fig. 4 is a cross-sectional view showing an example of an embodiment of a solar cell (CdTe solar cell) using the glass substrate for a solar cell of the present invention.

Form for implementing the invention

<The glass substrate for a solar cell of the present invention>

Hereinafter, the glass substrate for a solar cell of the present invention will be described.

The glass substrate for a solar cell of the present invention has a composition of 50% to 65% SiO ₂ , 8 to 15% Al ₂ O ₃ , and 0 to 1% by mass percentage based on the following oxides. B ₂ O ₃ , 0 to 10% of MgO, 1 to 12% of CaO, 6 to 12% of SrO, 0 to 3% of BaO, 1 to 7% of ZrO ₂ , 2 to 8% of Na ₂ O, 0 to 8% of K ₂ O, 15 to 30% of MgO+CaO+SrO+BaO; and SrO/Na ₂ O is 0.8 to 2.5.

The glass transition point temperature (Tg) of the glass substrate for a solar cell of the present invention is preferably higher than the glass transition point temperature of the soda lime glass, and specifically, it is preferably 640 ° C or higher. When the glass substrate for a solar cell of the present invention is used as a glass substrate of a CIGS solar cell or a CdTe solar cell, the photoelectric conversion layer of CIGS at a high temperature is secured (hereinafter, "the photoelectric conversion layer of CIGS" is also referred to as a "CIGS layer". Or the formation of a photoelectric conversion layer of CdTe (hereinafter, also referred to as "CdTe photoelectric conversion layer" is simply referred to as "CdTe layer"), and the glass transition point temperature (Tg) is preferably 645 ° C or more, and more preferably 650 ° C or more, 655 Above °C is especially good. In order to make the viscosity at the time of melting not rise too high, it is preferable to set it as 750 degreeC or less. More preferably, it is 720 ° C or less, and 690 ° C or less is particularly preferable.

The average thermal expansion coefficient of the glass substrate for a solar cell of the present invention at 50 to 350 ° C is preferably 70 × 10 ^-7 to 90 × 10 ^-7 / ° C. When the glass substrate for a solar cell of the present invention is used as a glass substrate of a CIGS solar cell, if the coefficient is less than 70 × 10 ^-7 / ° C or more than 90 × 10 ^-7 / ° C, the difference in thermal expansion from the CIGS layer becomes If it is too large, it will become prone to peeling off defects. Therefore, it is preferably 85 × 10 ^-7 / ° C or less.

The glass substrate for a solar cell of the present invention has a viscosity of 10 ⁴ dPa. The relationship between the temperature (t ₄ ) of s and the devitrification temperature (T _L ) is preferably T ₄ -T _L ≧ -30 °C. When T ₄ -T _{L is} less than -30 ° C, devitrification is likely to occur during the formation of the sheet glass, which may cause difficulty in forming the glass sheet. Therefore, T ₄ -T _{L is} preferably -20 ° C or higher, more preferably -10 ° C or higher, and particularly preferably 0 ° C or higher, and most preferably 10 ° C or higher. Here, the "devitrification temperature" refers to the maximum temperature at which crystals are not formed on the surface and inside of the glass when the glass is held at a specific temperature for 17 hours.

When considering the formability of the glass sheet, that is, considering the improvement of flatness and productivity, T _{4 is} preferably 1230 ° C or less. Further, T _{4 is} preferably 1220 ° C or lower, more preferably 12 10 ° C or lower.

Moreover, considering the melting property of the glass, that is, considering the improvement of homogeneity and improving productivity, the glass substrate for a solar cell of the present invention has a viscosity of 10 ² dPa. The temperature (T ₂ ) of s is preferably 1650 ° C or less. Further, T _{2 is} preferably 1630 ° C or lower, and more preferably 1620 ° C or lower.

The glass substrate for a solar cell of the present invention preferably has a density of 2.75 g/cm ³ or less. If the density exceeds 2.75 g/cm ³ , the quality of the glass substrate becomes heavy and it is not preferable. The density is preferably 2.73 g/cm ³ or less, more preferably 2.71 g/cm ³ or less. Further, when a glass substrate is produced by a usual method such as a floating glass plate method or a melt-blown method, it is usually 2.4 g/cm ³ or more in consideration of a glass composition range which can be easily produced.

In the glass substrate for a solar cell of the present invention, the brittleness index value is preferably less than 7000 m ^-1/2 . When the brittleness index value is 7000 m ^-1/2 or more, the glass substrate may be easily cracked in the manufacturing process of the solar cell. It is preferably 6900m ^-1/2 or less, 6800m ^-1/2 or less more preferably, 6700m ^-1/2 or less is preferred, more preferably less based 6600m ^-1/2. Further, when a glass substrate is produced by a usual method such as a floating glass plate method or a melt-blown method, it is usually 5000 m ^-1/2 or more in consideration of a glass composition range which can be easily produced.

In the present invention, the brittleness index value of the glass substrate for a solar cell is obtained by "B" defined by the following formula (1) (J. Sehgal, et al., J. Mat. Sci. Lett., 14, 167). (1995)).

c/a=0.0056B ^2/3 P ^1/6 (1)

Here P is the Vickers indenter, and the a and c are the diagonal length of the Vickers indentation and the length of the crack from the four corners (including the symmetrical 2 crack of the indenter). full length). The brittleness index value B was calculated by using the size of the Vickers indentation applied to various glass surfaces and the formula (1).

The reason why the glass substrate for a solar cell of the present invention is limited to the above composition is as follows:

SiO ₂ :

SiO ₂ is a component which forms a skeleton of glass, and is less than 50% by mass (hereinafter, "% by mass" is simply referred to as "%". The same applies hereinafter), the heat resistance and chemical durability of the glass substrate are lowered, and the average thermal expansion coefficient is feared. Increase the considerations. Therefore, it is preferably 52% or more, preferably 53% or more, more preferably 53.5% or more, and even more preferably 54% or more.

However, if it exceeds 65%, the high-temperature viscosity of the glass will rise, and there is a fear that the meltability is deteriorated. Therefore, it is preferably 63% or less, preferably 62% or less, more preferably 61% or less, and particularly preferably 59% or less, more preferably 57.5% or less.

Al ₂ O ₃ :

Al ₂ O ₃ can increase the temperature of the glass transition point, improve the solarization, heat resistance and chemical durability, and increase the Young's modulus. If the content is less than 8%, the glass transition point temperature may be lowered. There is also the fear that the average coefficient of thermal expansion will increase. Therefore, it is preferably 8.5% or more, preferably 9% or more, more preferably 10% or more, and more preferably 11% or more, and more preferably 12% or more.

However, if it exceeds 15%, the high-temperature viscosity of the glass will rise, and there is a fear that the meltability is deteriorated. Moreover, the devitrification temperature will rise, and there is a fear that the formability will deteriorate. Therefore, it is preferably 14.5% or less, and preferably 14% or less.

SiO ₂ and Al ₂ O ₃ :

Since SiO ₂ and Al ₂ O _{3 are} components which increase the heat resistance of the glass substrate, it is preferable to use 9SiO ₂ +15Al ₂ O ₃ (that is, (% of SiO ₂ is contained in the range of 9) and (containing of Al ₂ O ₃ ) The total of % × 15) is contained in a range of 570% or more. It is preferably 600% or more, more preferably 630% or more, and particularly preferably 660% or more. However, since SiO ₂ and Al ₂ O ₃ have an effect of increasing the high-temperature viscosity of the glass and deteriorating the meltability, it is preferable to contain 9SiO ₂ +15Al ₂ O _{3 in} a range of 840% or less. And 800% or less is better, 760% or less is better, and 720% or less is particularly preferable.

B ₂ O ₃ :

The B ₂ O ₃ system may be added to 1% in order to improve the meltability and the like. If the content exceeds 1%, there is a fear that the temperature of the glass transition point is lowered, or the average thermal expansion coefficient is small, which is not preferable for the process for forming the photoelectric conversion layer. Further, the devitrification temperature rises and becomes devitrified, making it difficult to form the sheet glass. Therefore, the content is preferably 0.5% or less. It is not particularly preferable.

In addition, "substantially does not contain" means that it is not mixed with raw materials or the like. It is not contained other than the impurities to be avoided, that is, it means intentionally not to contain it. The same as below.

MgO:

Since MgO can reduce the viscosity at the time of glass melting and has an effect of promoting melting, it can be contained. It is preferably 0.5% or more, preferably 1% or more. As long as it is 10% or less, the desired average coefficient of thermal expansion can be obtained. It is also ideal that there will be no devitrification temperature rise. It is preferably 7% or less, and 5% is more preferable, more preferably 3% or less, and particularly preferably 2.5% or less.

CaO:

Since CaO can reduce the viscosity at the time of glass melting and has an effect of promoting melting, it can contain 1 to 12%. It is preferably 2% or more, preferably 3% or more, more preferably 4% or more, and more preferably 5% or more. However, if it exceeds 12%, there is a fear that the average thermal expansion coefficient of the glass substrate increases. Further, sodium (Na) is less likely to move in the glass substrate, which may cause a decrease in power generation efficiency. Therefore, it is preferably 11% or less, preferably 10% or less, more preferably 9% or less, and particularly preferably 8.5% or less.

SrO:

Since SrO can reduce the viscosity at the time of glass melting and has an effect of promoting melting, it contains 6 to 12%. Further, when SrO is contained in the glass substrate, when the glass substrate for a solar cell of the present invention is used as a glass substrate of a CIGS solar cell, there is an effect of promoting diffusion of sodium (Na) onto the CIGS layer on the glass substrate. It is preferably 6.3% or more, preferably 6.5% or more, more preferably 7% or more. However, if it contains more than 12%, there is a fear that the density of the glass substrate increases and the value of the brittleness index increases. Therefore, it should be 11% or less, preferably 10% or less, and more preferably 9%. Below, 8.5% or less is particularly preferable.

BaO:

BaO can be contained because it can reduce the viscosity at the time of glass melting and has an effect of promoting melting. However, if it contains more than 3%, there is a fear that the average thermal expansion coefficient of the glass substrate increases, the density increases, and the brittleness index value increases. Also, there is a fear that the Young's modulus will decrease. Therefore, it is preferably 2.5% or less, and preferably 2% or less.

ZrO ₂ :

Since ZrO ₂ can reduce the viscosity at the time of glass melting and has an effect of promoting melting, it can be contained in an amount of 1% or more. As long as the power generation efficiency is 7% or less, it will be good, and there will be no devitrification temperature rise and devitrification, and the sheet glass is easy to form. Therefore, it is preferably 6% or less, preferably 5% or less, and more preferably 4.5% or less. Further, it is preferably 2% or more, preferably 2.5% or more, more preferably 3% or more, and particularly preferably 3.5% or more.

TiO ₂ :

Since the devitrification temperature rises if TiO ₂ is contained, it is preferable to contain no TiO ₂ . However, the glass substrate for a solar cell of the present invention is more likely to form a bubble layer on the surface of the molten glass than the usual soda lime glass when the glass substrate is easily produced. When the bubble layer is formed, the temperature of the molten glass does not rise, resulting in difficulty in clarification and a tendency to deteriorate in productivity. In order to thin or even disappear the bubble layer formed on the surface of the molten glass, there is a case where a titanium compound is supplied to the bubble layer formed on the surface of the molten glass as an antifoaming agent. The titanium compound is incorporated into the molten glass and exists as TiO ₂ . The titanium compound may be an inorganic titanium compound (for example, titanium tetrachloride or titanium oxide) or an organic titanium compound. Examples of the organic titanium compound include titanate or a derivative thereof, a titanium chelate compound or a derivative thereof, titanium telluride or a derivative thereof, and titanium oxalate. For the reasons described above, 0.2% or less of TiO ₂ is allowed to be contained as an impurity in the glass substrate.

MgO, CaO, SrO and BaO:

The MgO, CaO, SrO, and BaO may contain CaO and SrO from the viewpoint of lowering the viscosity at the time of melting the glass and promoting melting, and may be at least 1 selected from the group consisting of MgO and BaO. The components are set to have a total amount of these (that is, the total amount of the alkaline earth metal oxides (RO) is also referred to as (MgO + CaO + SrO + BaO)) to be 15% or more. However, if the total amount exceeds 30%, the devitrification temperature will rise, which may result in deterioration of formability. Therefore, it is preferably 16% or more, and 17% or more is preferred. Further, it is preferably 26% or less, and preferably 23% or less, more preferably 20% or less, and particularly preferably 18% or less.

Na ₂ O:

When the glass substrate for a solar cell of the present invention is used as a glass substrate of a CIGS solar cell, the Na ₂ O system is an essential component for contributing to the improvement of the power generation efficiency of the CIGS solar cell. Further, since the viscosity in the glass melting temperature can be lowered, the effect of facilitating the melting is facilitated, so that it contains 2 to 8%. Although sodium (Na) diffuses into the CIGS layer formed on the glass substrate, the power generation efficiency can be improved. However, if the content is less than 2%, the diffusion of Na into the CIGS layer on the glass substrate is insufficient, and power generation efficiency is feared. It has also become inadequate. The content may be 3% or more, and the content is preferably 4% or more.

When the Na ₂ O content exceeds 8%, the average thermal expansion coefficient increases, and the glass transition point temperature tends to decrease. Or there is a tendency to deteriorate chemical durability. Also, there is a fear that the Young's modulus will decrease. Therefore, the content is preferably 7.5% or less, more preferably 7% or less, and even more preferably 6.5% or less.

K ₂ O:

Since K ₂ O has the same effect as Na ₂ O, it contains 0 to 8%. However, if the content exceeds 8%, there is a fear that the glass transition point temperature is lowered, the average thermal expansion coefficient is increased, and the specific gravity is increased. Therefore, it is preferably 0.5% or more, and preferably 1% or more, and more preferably 3.5% or more. Further, it is preferably 7% or less, preferably 6% or less, more preferably 5% or less, and particularly preferably 4.5% or less.

Na ₂ O and K ₂ O:

Na ₂ O and K ₂ O are components that help to increase the power generation efficiency of CIGS solar cells. Further, since the viscosity in the glass melting temperature is lowered to facilitate the melting, it is preferable to use 3Na ₂ O+2K ₂ O (that is, (% of Na ₂ O) and (K ₂ O). The total of %×2) is contained in a range of 14% or more. It is preferably 16% or more, more preferably 18% or more, and more preferably 20% or more. Since Na ₂ O and K ₂ O tend to lower the glass transition point temperature by increasing the average thermal expansion coefficient, it is preferable to contain 3Na ₂ O+2K ₂ O in a range of 44% or less. It is preferably 40% or less, more preferably 36% or less, and particularly preferably 32% or less.

The ratio of SrO to Na ₂ O:

The ratio of SrO to Na ₂ O (SrO/Na ₂ O) is 0.8 or more. If the amount of SrO is small relative to the amount of Na ₂ O, the effect of promoting the diffusion of Na into the CIGS layer on the glass substrate tends to be weakened when the CIGS solar cell is fabricated. Therefore, it is preferably 0.9 or more, preferably 1.0 or more, and more preferably 1.1 or more. However, if it is 2.5 or more, the specific gravity of the glass substrate may become excessive. Therefore, it is preferably 2.1 or less, preferably 1.8 or less, more preferably 1.6 or less, and particularly preferably 1.4 or less.

The glass substrate for a solar cell of the present invention is substantially composed of the above-described mother material (containing SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, ZrO ₂ , Na ₂ O, and K _{2 in the above range).} The glass mother composition of O is composed of, but not limited to the purpose of the present invention, the following other components may be contained in an amount of 1% or less with respect to the inner percentage of the glass mother composition, and the total amount is 5% or less of the aforementioned TiO ₂ . For example, for the purpose of improving weather resistance, meltability, devitrification, ultraviolet shielding, refractive index, etc., it may contain ZnO, Li ₂ O, WO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Bi _{2 .} Cases such as O ₃ , MoO _{3 ,} and P ₂ O ₅ .

Also, to improve the meltability and fining glass, can also cause the glass contained in the ratio (outer percentage) than the mother glass composition in terms of the individual is 1% or less, and a total amount of 2% or less of SO _3, A clarifying agent such as F, Cl or SnO _{2 is} added to the parent constituent raw material.

Moreover, in order to improve the chemical durability of the glass substrate, the glass may contain Y ₂ O ₃ and La ₂ O _{3 in a} total amount of 2% or less based on the internal ratio of the glass mother composition.

Further, the glass substrate for a solar cell of the present invention contains SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, and the like in order to secure the transmittance and improve the power generation efficiency. The glass mother composition of BaO, ZrO ₂ , Na ₂ O, and K ₂ O is 100 parts by mass, and preferably contains iron oxide in an amount of 0.06 part by mass or less in terms of Fe ₂ O ₃ . It is preferably 0.055 parts by mass or less, more preferably 0.05 parts by mass or less, and particularly preferably 0.045 parts by mass or less. However, when the transmittance is not required (for example, when it is used as a substrate of a CIGS solar cell, etc.), it is 100 parts by mass with respect to the above-mentioned mother composition from the viewpoint of using a raw material having a small iron content and heating easiness at the time of melting. The iron oxide is preferably 0.2 parts by mass or less in terms of Fe ₂ O ₃ , more preferably 0.15 parts by mass or less, more preferably 0.12 parts by mass or less.

In addition, when the content of the iron oxide is 0.01 parts by mass or more, it is preferable to use industrial materials which are inevitable in the incorporation of the iron oxide component, which makes industrial production easy. In addition, when the content of the iron oxide is 0.01 parts by mass or more, the absorption of radiation during melting is remarkably increased, and the temperature of the molten glass is likely to rise without causing an obstacle to production. Therefore, it is preferably 0.015 parts by mass or more, more preferably 0.02 parts by mass or more.

Further, in the present invention, red dan, iron oxide powder or the like may be mentioned as the iron oxide.

Further, the glass substrate for a solar cell of the present invention preferably contains substantially no As ₂ O _{3 or} Sb ₂ O _{3 in} consideration of an environmental load. Further, in consideration of stable floating molding, it is preferable that ZnO is not substantially contained. However, the glass substrate for a solar cell of the present invention is not limited to the formation by the floating glass plate method, and may be produced by molding by a melt injection method.

<Method for Producing Glass Substrate for Solar Cell of the Present Invention>

A method of producing a glass substrate for a solar cell of the present invention will be described.

When the glass substrate for a solar cell of the present invention is produced, the melting, clarification step, and molding step are carried out in the same manner as in the case of producing a conventional glass substrate for a solar cell. Further, since the glass substrate for a solar cell of the present invention contains an alkali-containing glass substrate containing an alkali metal oxide (Na ₂ O, K ₂ O), SO ₃ can be effectively used as a clarifying agent, and the forming method is suitable for floating. Glass plate method and melting method (overflow downdraw).

In the manufacturing process of the glass substrate for a solar cell, as the method of forming the glass into a plate shape, the method of forming the glass substrate into a plate shape is a floating glass plate method which can form a large-area glass substrate easily and stably. It is better.

An ideal aspect of the method for producing a glass substrate for a solar cell of the present invention will be described.

First, the molten glass obtained by melting a predetermined glass raw material is formed into a plate shape. For example, the raw material is prepared so that the obtained glass substrate can have the aforementioned composition, and the above-mentioned raw materials are continuously introduced into a melting furnace, and heated to 1550 to 1700 ° C to obtain molten glass. Then, the molten glass is formed into a strip-shaped glass plate by, for example, a floating glass plate method.

Next, the strip-shaped glass plate was taken out from the floating forming furnace, and then cooled to room temperature by a cooling mechanism, and a glass substrate for a solar cell was obtained after cutting.

<Use of Glass Substrate for Solar Cell of the Present Invention>

The glass substrate for a solar cell of the present invention has a predetermined average thermal expansion coefficient, high glass strength, low glass density, high meltability in the production of sheet glass, good formability, and good devitrification resistance, and glass. Since the transfer point temperature is high and the alkali diffusibility is also high, it is advantageous for power generation efficiency when used for a CIGS solar cell, and therefore it can be suitably used as a glass substrate for a CIGS solar cell.

When the glass substrate for a solar cell of the present invention is applied to a glass substrate of a CIGS solar cell, the thickness of the glass substrate is preferably set to 3 mm or less, and is preferably It is 2 mm or less, and more preferably 1.5 mm or less.

Further, the method of forming the CIGS layer on the glass substrate is not particularly limited. However, since the glass transition temperature is high, the heating temperature at the time of forming the CIGS layer can be 500 to 700 ° C, and preferably 550 to 700 ° C. It is 580 to 700 ° C, more preferably 600 to 700 ° C, and is preferably 620 to 700 ° C.

When the glass substrate for a solar cell of the present invention is used only for a glass substrate of a CIGS solar cell, the cover glass or the like is not particularly limited. Other examples of the composition of the cover glass include soda lime glass and the like.

When the glass substrate for a solar cell of the present invention is used as a cover glass of a CIGS solar cell, the thickness of the cover glass is preferably 3 mm or less, preferably 2 mm or less, and more preferably 1.5 mm or less.

Further, in the manufacture of a CIGS solar cell, the method of assembling the cover glass on the glass substrate having the CIGS layer is not particularly limited, but when it is assembled after heating, the heating temperature can be set to 500 to 700. °C, and should be set to 600~700 °C.

When the glass substrate for a solar cell of the present invention is used for a glass substrate and a cover glass of a CIGS solar cell, it is preferable that the average thermal expansion coefficient is equal, and thermal deformation during assembly of the solar cell does not occur.

Moreover, the glass substrate for a solar cell of the present invention has a predetermined average thermal expansion coefficient, high glass strength, low glass density, high meltability in the production of sheet glass, good formability, and good devitrification resistance. It is suitably used as a glass substrate for CdTe solar cells.

In the superstrate type structure used in the CdTe solar cell, since the glass substrate is exposed to the outside, it has a high glass strength. The glass substrate for a solar cell of the invention is also suitably used as a glass substrate for a CdTe solar cell.

Moreover, since it has a high glass transition point temperature, it can form a film at a high temperature when a CdTe layer is formed, which is beneficial to the power generation efficiency of the CdTe solar cell.

When the glass substrate for a solar cell of the present invention is applied to a glass substrate of a CdTe solar cell, the thickness of the glass substrate is preferably 3 mm or less, more preferably 2 mm or less, and still more preferably 1.5 mm or less. The method of forming the CdTe layer on the glass substrate is not particularly limited, but since the glass transition point temperature is high, the heating temperature at the time of forming the CdTe layer can be set to 500 to 700 ° C, and preferably set to 550 to 700 ° C. It is preferably 580 to 700 ° C, more preferably 600 to 700 ° C, and more preferably 620 to 700 ° C.

When the glass substrate for a solar cell of the present invention is used only for a glass substrate of a CdTe solar cell, the back glass or the like is not particularly limited. Other examples of the composition of the back sheet glass include soda lime glass and the like.

When the glass base for a solar cell of the present invention is used as a back sheet glass of a CdTe solar cell, the thickness of the back sheet glass is preferably 3 mm or less, more preferably 2 mm or less, and still more preferably 1.5 mm or less.

Further, in the manufacture of a CdTe solar cell, the method of assembling the back sheet glass to the glass substrate having the CdTe layer is not particularly limited, but when it is assembled after heating, the heating temperature can be set to 500 to 700 ° C. And should be set to 600~700 °C.

When the glass substrate for a solar cell of the present invention is used for both the glass substrate and the back glass of the CdTe solar cell, it is preferable that the average thermal expansion coefficient is equal, and thermal deformation during assembly of the solar cell does not occur.

<CIGS Solar Cell of the Invention>

Next, the CIGS solar cell of the present invention will be described.

The CIGS solar cell of the present invention includes: a glass substrate; a cover glass; and a Cu-In-Ga-Se photoelectric conversion layer disposed between the glass substrate and the cover glass; and the glass substrate and the cover glass At least the glass substrate is a glass substrate for a solar cell of the present invention.

Hereinafter, the CIGS solar cell of the present invention will be described in detail using the drawings. Further, the invention is not limited to the drawings.

Fig. 1 is a cross-sectional view showing an example of an embodiment of a CIGS solar cell of the present invention. In Fig. 1, a CIGS solar cell 1 of the present invention is provided with a glass substrate 5, a cover glass 19, and a CIGS layer 9 which is positioned between the glass substrate 5 and the cover glass 19. Further, the glass substrate 5 is preferably the glass substrate for a solar cell of the present invention described above. The solar cell 1 is a back electrode layer having a Mo film which is a positive electrode 7 on a glass substrate 5, and has a CIGS layer 9 thereon. The composition of the CIGS layer can be exemplified by Cu(In _1-x Ga _x )Se ₂ . The x system shows the composition ratio of In to Ga and 0 < x < 1.

The CIGS layer 9 has a CdS (cadmium sulfide) layer, a ZnS (zinc sulfide) layer, a ZnO (zinc oxide) layer, a Zn(OH) ₂ (zinc hydroxide) layer or the like mixed layer as the buffer layer 11. The transparent conductive film 13 such as ZnO or ITO or ZnO (AZO) doped with Al is interposed between the buffer layer 9 and has an extraction electrode such as an Al electrode (aluminum electrode) of the negative electrode 15 thereon. An anti-reflection film may also be provided at a necessary place between the layers. In the case of FIG. 1, an anti-reflection film 17 is provided between the transparent conductive film 13 and the negative electrode 15.

Moreover, a cover glass 19 may be provided on the negative electrode 15, and is necessary The resin may be sealed between the negative electrode and the cover glass, or may be adhered by a transparent resin for adhesion. The cover glass may also use the glass substrate for solar cells of this invention.

In the present invention, the end portion of the CIGS layer or the end portion of the solar cell may be in a sealed state. The material to be sealed is, for example, the same material as the glass substrate for a solar cell of the present invention, other glass, resin, or the like.

In addition, the thickness of each layer of the solar cell shown in the drawings is not limited by the drawings.

The CIGS solar cell of the present invention uses the glass substrate for a solar cell of the present invention as a glass substrate, and in the second stage of the film formation step of the CIGS layer, the CIGS layer can be formed by heating under conditions of 500 ° C or higher. Get higher power generation efficiency. The heating temperature in the second stage is preferably 550 ° C or higher, preferably 580 ° C or higher, more preferably 600 ° C or higher, and particularly preferably 620 ° C or higher.

The steps other than the film formation step of the CIGS layer in the method of manufacturing the CIGS solar cell, for example, the formation of a buffer layer or a transparent conductive film layer, etc., may be carried out in the same manner as the steps of the general CIGS solar cell manufacturing method. Just fine.

<CdTe Solar Cell of the Invention>

Next, the CdTe solar cell of the present invention will be described.

The solar cell of the present invention includes: a glass substrate; a back sheet glass; and a CdTe photoelectric conversion layer (CdTe layer) disposed between the glass substrate and the back sheet glass; and the glass substrate and the back sheet glass At least the glass substrate is a glass substrate for a solar cell of the present invention. or, In the configuration of the solar cell described above, a solar cell having a water-resistant and oxygen-resistant penetrating back film may be used instead of the back glass.

Hereinafter, the solar cell of the present invention will be described in detail using the drawings. In addition, the invention is not limited by the drawings.

Fig. 4 is a cross-sectional view showing an example of an embodiment of a CdTe solar cell of the present invention.

In Fig. 4, the solar cell (CdTe solar cell) 21 of the present invention comprises: a glass substrate 22 having a thickness of 1 to 3 mm; a back sheet glass 27 having a thickness of 1 to 3 mm; and a CdTe layer having a thickness of 3 to 15 μm . 25, the tie between the glass substrate 22 and the back sheet glass 27. The heating temperature at the time of forming the CdTe layer or the transparent conductive film is 500 ° C or higher, and preferably 550 ° C or higher, preferably 580 ° C or higher, more preferably 600 ° C or higher, and particularly preferably 620 ° C or higher. The glass substrate 22 is preferably composed of the glass substrate for a solar cell of the present invention described above.

The CdTe solar cell 21 has a transparent conductive film 23 having a thickness of 100 to 1000 nm on the glass substrate 22. The heating temperature at the time of forming the CdTe layer or the transparent conductive film is 500 ° C or higher, and preferably 550 ° C or higher, preferably 580 ° C or higher, more preferably 600 ° C or higher, and particularly preferably 620 ° C or higher.

Based transparent conductive film 23 include, for example, the Sn-doped In ₂ O ₃ or the doped In F ₂ O ₃ and the like. A buffer layer 24 (for example, a CdS layer) having a thickness of 50 to 300 nm is provided on the transparent conductive film 23, and a CdTe layer 25 is provided on the buffer layer 24. Further, the CdTe layer 25 has a back electrode layer 26 of 100 to 1000 nm (for example, a carbon electrode doped with Cu or a Mo electrode), and has a back plate glass 27 on the back electrode layer 26. It is preferable to perform resin sealing between the back electrode layer 26 and the back sheet glass 27, otherwise it is preferable to adhere with a resin for adhesion. The glass substrate for a solar cell of the present invention can also be used for the back sheet glass 27.

In the present invention, the end portion of the CdTe layer or the end portion of the solar cell is in a sealed state. The material to be sealed is, for example, the same material as the glass substrate for a CdTe solar cell of the present invention, other glass materials, resins, and the like.

In addition, the thickness of each layer of the solar cell shown in the drawings is not limited by the drawings.

Example

Hereinafter, the present invention will be described in more detail by way of examples and production examples, but the invention is not limited to the examples and the examples.

Further, examples (Examples 1 to 13, 17 to 31) and comparative examples (Examples 14 to 16) of the glass substrate for a solar cell of the present invention are shown.

The raw materials of the respective components are blended so as to have a glass composition as shown in Tables 1 to 4, and a sulfate of 0.1 part by mass in terms of SO ₃ is added to the raw material in an amount of 100 parts by mass based on the raw material of the glass substrate component. It was heated and melted at a temperature of 1650 ° C for 3 hours using a platinum crucible. Further, in Tables 1 to 4, the blending amount of Fe ₂ O ₃ is shown to be relative to the parent composition (containing SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, ZrO _{2 in the above range).} And a glass mother composition of Na ₂ O and K ₂ O) 100 parts by mass parts by mass.

At the time of melting, a platinum stirrer was inserted and stirred for 1 hour to homogenize the glass. Then, the molten glass was poured out, and after being formed into a plate shape, it was cooled, and the glass plate was obtained.

The average thermal expansion coefficient (unit: × 10 ^-7 / ° C), glass transition point temperature Tg (unit: ° C), density (unit: g / cm ³ ), and brittleness index value of the glass plate obtained by the above method were measured. (Unit: m ^-1/2 ), viscosity is 10 ² dPa. The temperature of s (T ₂ ) (unit: ° C), the viscosity becomes 10 ⁴ dPa. The temperature T s ₄ (unit: deg.] C), devitrification temperature (T _L) (unit: ℃), Na diffusion amount and the power generation efficiency, and it is shown in Tables 1 to 4. The measurement method of each physical property will be shown below.

Further, in the examples, the measurement was performed on the glass plate, and the physical properties of the glass plate and the glass substrate were the same. The glass substrate can be produced by subjecting the obtained glass plate to processing and grinding.

(1) Average thermal expansion coefficient from 50 to 350 °C:

The average coefficient of thermal expansion was measured using a differential thermal dilatometer (TMA) and determined according to the specifications of JIS R3102 (1995).

(2) Tg:

Tg is a value measured by TMA and is obtained according to the specifications of JIS R3103-3 (2001).

(3) Density:

The density was determined by using the Archimedes principle using a glass block of about 20 g which was cut out from the glass plate and free of air bubbles.

(4) Brittleness index value:

The brittleness index value was calculated by using the size of the Vickers indentation on the surface of each of the above-mentioned glass sheets and the above formula (1).

(5) Viscosity:

The viscosity was measured using a rotary viscometer, and the viscosity η was measured to be 10 ² dPa. The temperature T ₂ (the reference temperature of the melting property) and the viscosity η become 10 ⁴ dPa. The temperature s T ₄ (moldability of the reference temperature).

(6) Devitrification temperature (T _L ):

The devitrification temperature was carried out by placing 5 g of the glass block cut out from the glass plate on a platinum plate and holding it in an electric furnace for 17 hours. The lowest value of the temperature at which no crystals were precipitated on the surface of the glass block after the holding and the inside was taken as the devitrification temperature.

(7) Power generation efficiency:

Power generation efficiency The obtained glass plate was used for a substrate for a solar cell, and a solar cell for evaluation was produced as shown below, and used for evaluation of power generation efficiency. The results are shown in Tables 1 to 4.

The production of the solar cell for evaluation will be described below using Figs. 2 and 3 and their symbols.

In addition, the layer structure of the solar cell for evaluation is substantially the same as the layer structure of the solar cell shown in FIG. 1 except for the cover glass 19 and the anti-reflection film 17 which do not have the solar cell of FIG.

The obtained glass plate was processed into a size of 3 cm × 3 cm and a thickness of 1.1 mm to prepare a glass substrate. On the glass substrate 5a, a Mo (molybdenum) film is formed as a positive electrode 7a by a sputtering apparatus. The film formation was carried out at room temperature, and a Mo film having a thickness of 500 nm was obtained.

A CuGa alloy layer was formed on the positive electrode 7a (Mo film) by a sputtering apparatus using a CuGa alloy target, and then an In layer was formed using an In target, thereby forming an In-CuGa precursor film. The film formation is carried out at room temperature. The thickness of each layer was adjusted so that the composition of the precursor film was measured by fluorescent X-ray, the ratio of Cu/(Ga+In) was 0.8, and the ratio of Ga/(Ga+In) was 0.25, and a precursor film having a thickness of 650 nm was obtained. .

RTA (Rapid Thermal Annealing) device is used in a mixed gas atmosphere of argon and hydrogen selenide (sodium selenide is 5 bodies with respect to argon) The % of the precursor film was heat treated. First, the reaction was carried out at 500 ° C for 10 minutes, and the reaction with Cu, In, Ga, and Se was carried out as the first step. Thereafter, the CIGS layer was grown by holding at 580 ° C for 30 minutes to obtain the CIGS layer 9a. 2 stages. The thickness of the obtained CIGS layer 9a was 2 μm.

A CdS layer was formed as a buffer layer 11a on the CIGS layer 9a by a CBD (Chemical Bath Deposition) method. Specifically, first, 0.01 M cadmium sulfate, 1.0 M thiourea, 15 M ammonia, and pure water were mixed in a beaker. Next, the CIGS layer was immersed in the above-mentioned mixed solution, and placed in a thermostatic bath having a water temperature of 70 ° C in advance together with a beaker, and the CdS layer was formed into a film of 50 to 80 nm.

Further, the transparent conductive film 13a was formed into a film by a sputtering apparatus on the CdS layer in the following manner. First, a ZnO layer was formed using a ZnO target, and second, an AZO layer (a ZnO target containing 1.5 wt% of Al ₂ O ₃ ) was used to form an AZO layer. The film formation of each layer was carried out at room temperature, and a transparent conductive film 13a having a two-layer structure having a thickness of 480 nm was obtained.

On the AZO layer of the transparent conductive film 13a by the EB vapor deposition method, an aluminum film having a film thickness of 1 μm was formed as the U-type negative electrode 15a (here, the U-shaped electrode length is 8 mm in length and 4 mm in width, and the electrode width is It is 0.5mm).

Finally, it was ground to the CIGS layer 9a from the side of the transparent conductive film 13a by mechanical scribing, and unitization as shown in FIG. 2 was performed. Fig. 2(a) is a view of a solar cell unit as seen from above; Fig. 2(b) is a cross-sectional view taken along line A-A' of Fig. 2(a). One unit has a width of 0.6 cm and a length of 1 cm, and the area of the negative electrode 15a is removed by 0.5 cm ² . As shown in Fig. 3, a total of eight units can be obtained on one glass substrate 5a.

A CIGS solar cell for evaluation (that is, an evaluation glass substrate 5a in which eight units were produced) was provided on a Solar Simulator (YAMASHITA DENSO Co., Ltd., YSS-T80A). The positive terminal (not shown) and the negative terminal 16a are respectively connected to the voltage generator, that is, the positive terminal is connected to the positive electrode 7a to which the InGa solvent has been previously applied, and the negative terminal 16a is connected to The lower end of the U word of the negative electrode 15a. The temperature in the solar simulator is controlled at a fixed temperature of 25 °C with a thermostat. The simulated sunlight was irradiated, and after 60 seconds, the voltage was changed from -1 V to +1 V at intervals of 0.015 V, and individual current values of eight cells were measured.

From the current and voltage characteristics at the time of the irradiation, the power generation efficiency was calculated by the following formula (2). Among the eight units, the value of the most efficient unit is shown in Tables 1 to 4 as the value of the power generation efficiency of each glass substrate. The illuminance of the light source used for the test was 0.1 W/cm ² .

Power generation efficiency [%]=V _oc [V]×J _sc [A/cm ² ]×FF[no dimension]×100/illuminance of the light source used for the test [W/cm ² ]...(2)

The power generation efficiency is obtained by multiplying the open circuit voltage (V _oc ) by the short circuit current density (J _sc ) and the fill factor (FF).

In addition, the open circuit voltage (V _oc ) is the output at the time of opening the terminal, and the short circuit current (I _sc ) is the current at the time of the short circuit. The short-circuit current density (J _sc ) is obtained by dividing I _sc by the area of the cell divided by the negative electrode.

Further, the point at which the maximum output is given is referred to as the maximum output point, and the voltage at this point is referred to as the maximum voltage value (V _max ), and the current is referred to as the maximum current value (I _max ). A value obtained by multiplying the maximum voltage value (V _max ) by the maximum current value (I _max ) by the value of the open circuit voltage (V _oc ) multiplied by the short-circuit current (I _sc ) is obtained as the fill factor (FF). The power generation efficiency is obtained using the above values.

(8) Na diffusion amount:

The Na diffusion amount is an effect for observing the alkali diffusibility of the glass substrate, and in the power generation efficiency evaluation, the Na diffusion is measured immediately after the second stage of the heat treatment using the RTA apparatus in the production of the solar cell for evaluation. the amount. The measurement method is as follows:

After the completion of the second stage of the heat treatment by the RTA apparatus, the integrated intensity of ²³ Na in the CIGS film was measured by a secondary ion mass spectrometer (SIMS). The values described in Tables 1 to 4 are relative amounts when the glass substrate used in Example 12 is regarded as 100.

Further, regarding the calculated value of the Na diffusion amount in the present embodiment, for the case where the Na diffusion amount is actually measured in the present embodiment, the regression coefficient is obtained by performing multivariate regression analysis on the Na diffusion amount of each component and is calculated. By.

The residual amount of SO ₃ in the glass is 100 to 500 ppm.

As is clear from Tables 1 to 4, in the glass substrates of the examples (Examples 1 to 13 and Examples 17 to 31), the glass transition point temperature Tg was high and the Na diffusion amount was large. Therefore, it is presumed that the CIGS layer can be formed at a high temperature, whereby the growth of the CIGS crystal is good and the power generation efficiency is high. Further, the glass substrates of the examples (Examples 1 to 9 and Examples 11 to 13) are excellent in devitrification characteristics because T ₄ -T _L is -30 ° C or more, and the average thermal expansion coefficient is 70 × 10 ^{-7 .} ~90 × 10 ^-7 / ° C, the density is 2.75g / cm ³ or less, so the weight is light, and the brittleness index value is less than 7000m - ^1/2, so it has high strength, and the balance has the characteristics of the glass substrate for solar cells.

Therefore, it is understood that the glass substrate for a solar cell of the present invention satisfies all the characteristics of high power generation efficiency, high glass transition point temperature, predetermined average thermal expansion coefficient, high glass strength, low glass density, and good devitrification resistance in sheet glass production. . Therefore, there is no case where the CIGS layer is peeled off from the glass substrate to which the Mo film is attached, and when the solar cell is assembled (specifically, when the glass substrate having the CIGS layer and the cover glass are heated and then bonded), the glass The substrate is not easily deformed. In other words, since T ₂ is 1650 ° C or lower and T ₄ is 1230 ° C or lower, it is excellent in meltability and formability at the time of production of sheet glass.

On the other hand, in the glass substrates of the comparative examples (Examples 14 and 15), since the Na diffusion amount was small when the CIGS solar cell was fabricated, high power generation efficiency was not obtained.

Further, in the glass substrate of Comparative Example (Example 16), since the glass transition point temperature was low, there was a problem in heat resistance. Therefore, it is difficult to form a CIGS layer at a high temperature. Since the ratio is large and the brittleness index value is 7000 m ^-1/2 or more, there is a problem in strength.

Therefore, the glass substrate for solar cells of the present invention can be suitably used for a glass substrate for CIGS solar cells. Further, it can also be suitably used as a glass substrate for a CdTe solar cell.

The glass substrate for a solar cell of the present invention can be used not only for a glass substrate for a CIGS solar cell or a CdTe solar cell, but also for a cover glass and a back glass, and can be used for other solar cell substrates and cover glasses. .

Industrial availability

The glass substrate for a solar cell of the present invention can have high power generation efficiency, high glass transition point temperature, predetermined average thermal expansion coefficient, high glass strength, low glass density, and high meltability and good formability in sheet glass production. In addition to the characteristics such as good devitrification resistance, a solar cell having high power generation efficiency can be provided by using the glass substrate for a solar cell of the present invention. In particular, the glass substrate for a solar cell of the present invention is useful as a Cu-In-Ga-Se solar cell or as a CdTe solar cell system.

In addition, the entire contents of the specification, the drawings, and the abstract of the Japanese Patent Application No. 2012-198334, filed on Sep.

1‧‧‧CIGS solar cell

5‧‧‧ glass substrate

7‧‧‧ positive electrode

9‧‧‧CIGS layer

11‧‧‧buffer layer

13‧‧‧Transparent conductive film

15‧‧‧Negative electrode

17‧‧‧Anti-reflective film

19‧‧‧ Cover glass

Claims (15)

A glass substrate for a solar cell, which has a mass percentage based on the following oxides, and contains: 50 to 65% of SiO ₂ , 8 to 15% of Al ₂ O ₃ , 0 to 1% of B ₂ O ₃ , 0~ 10% MgO, 1-12% CaO, 6-12% SrO, 0~3% BaO, 1~7% ZrO ₂ , 2~8% Na ₂ O, 0~8% K ₂ O, 15~30% of MgO+CaO+SrO+BaO; and SrO/Na ₂ O is 0.8~2.5. The glass substrate for a solar cell according to claim 1 has a glass transition point temperature of 640 ° C or higher. The glass substrate for a solar cell according to claim 1 or 2, which has an average thermal expansion coefficient of 70 × 10 ^-7 to 90 × 10 ^-7 / ° C. The glass substrate for a solar cell according to any one of claims 1 to 3, wherein the viscosity is 10 ⁴ dPa. The temperature of s (T ₄ ) is below 1230 ° C, and the viscosity becomes 10 ² dPa. The temperature (T ₂ ) of s is 1650 ° C or less, and the relationship between the above T ₄ and the devitrification temperature (T _L ) is T ₄ -T _L ≧ -30 ° C. The glass substrate for a solar cell according to any one of claims 1 to 4, which has a density of 2.75 g/cm ³ or less. The glass substrate for a solar cell according to any one of claims 1 to 5, wherein the content of Al ₂ O ₃ is 8.5 to 14.5%. The glass substrate for a solar cell according to any one of claims 1 to 6, wherein the content of CaO is from 3 to 11%. The glass substrate for a solar cell according to any one of claims 1 to 6, wherein the content of CaO is 3 to 10%. The glass substrate for a solar cell according to any one of claims 1 to 8, wherein the content of Na ₂ O is 4 to 7%. The glass substrate for a solar cell according to any one of claims 1 to 9, wherein a sum of content of MgO+CaO+SrO+BaO is 17 to 23%. The glass substrate for a solar cell according to any one of claims 1 to 10, wherein a content of BaO is 2% or less. The glass substrate for a solar cell according to any one of the items 1 to 11, which has a value of 9SiO ₂ +15Al ₂ O ₃ and contains SiO ₂ and Al ₂ O in a range of 570% to 840%. ₃ . The glass substrate for a solar cell according to any one of the items 1 to 12, which has a value of 3Na ₂ O+2K ₂ O and contains Na ₂ O and K _{2 in a} range of 14% to 44%. O. A Cu-In-Ga-Se solar cell comprising: a glass substrate; a cover glass; and a Cu-In-Ga-Se photoelectric conversion layer disposed on the glass substrate and In the above-mentioned cover glass, at least the glass substrate is a glass substrate for a solar cell according to any one of claims 1 to 13. A CdTe solar cell comprising: a glass substrate; a back sheet glass; and a CdTe photoelectric conversion layer disposed between the glass substrate and the back sheet glass; and at least the glass of the glass substrate and the back sheet glass The substrate is a glass substrate for a solar cell according to any one of claims 1 to 13.