JP2014133680A - Glass plate for thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass plate that contributes to improvement in conversion efficiency of a thin film solar cell.SOLUTION: A glass plate for a thin film solar cell in this invention is produced by a floating method and has a bvalue to be 7 or more in a coloring test using silver.

Description

  The present invention relates to a glass plate for a thin film solar cell, and more particularly to a glass plate suitable for a chalcopyrite solar cell such as a CIS solar cell and a CdTe solar cell.

  Solar cells are roughly classified into bulk type solar cells and thin film solar cells. A thin film solar cell is a solar cell that uses a semiconductor thin film with a thickness of several microns as a photoelectric conversion film. Compared with a bulk type solar cell, a small amount of semiconductor material is required, and power generation efficiency per manufacturing cost is excellent. . In particular, compound semiconductor solar cells (for example, chalcopyrite solar cells, CdTe solar cells, etc.) have a higher degree of freedom in the manufacturing process than thin-film silicon solar cells, and are therefore superior in power generation efficiency per manufacturing cost. (For example, refer to Patent Document 1).

  A compound semiconductor solar cell generally has an electrode such as molybdenum, a compound semiconductor layer such as CIS and CIGS, a buffer layer such as CdS and ZnS, a ZnO, AZO (aluminum-doped zinc oxide), It has a structure in which a transparent conductive film such as ITO (tin-doped indium oxide) is sequentially laminated.

JP-A-8-330614

  By the way, in a thin film solar cell such as a chalcopyrite solar cell or a CdTe solar cell, when the photoelectric conversion film is formed at a high temperature, the crystal quality of the photoelectric conversion film can be improved. It is known that when the crystal quality of the photoelectric conversion film is high, the conversion efficiency of the thin film solar cell is improved.

  On the other hand, when the photoelectric conversion film is formed at a high temperature, an electrode such as molybdenum formed on the glass plate is likely to be oxidized, and the conversion efficiency is likely to be lowered due to the influence.

  As a result, it has been difficult to sufficiently increase the conversion efficiency of thin film solar cells.

  This invention is made | formed in view of the said situation, The technical subject is creating the glass plate which contributes to the conversion efficiency improvement of a thin film solar cell.

As a result of intensive studies, the present inventors have found that the above technical problem can be solved by regulating the redox state of the surface layer of the glass plate, and propose the present invention. That is, the glass plate for a thin film solar cell of the present invention is formed by a float process, and has a b ^* value of 7 or more when a color development test with silver is performed. Here, the “color development test with silver” is for evaluating the redox state of the surface layer of the glass plate, and the b ^* value is an index of the redox state. In the “color development test with silver”, first, a silver paste was applied to the top surface side of a glass plate so as to have a thickness of 6 μm, then baked at (distortion point −15) ° C. for 1 hour, and then simplified spectral color difference. Using a meter (for example, NF333 manufactured by Nippon Denshoku Industries Co., Ltd.), the b ^* value can be measured from the bottom surface (the surface in contact with the Sn bath) side of the glass plate. In the present invention, a color development test is performed with silver because the silver paste is easily available and can be easily tested. In addition, it is thought that another metal material shows the same tendency as silver.

  The glass plate of the present invention is made by a float process. The float process is a method of making a plate in a float bath in a reducing atmosphere. For this reason, if it manufactures with a float glass process, a reduction layer can be formed in the surface layer of a glass plate. This reduction layer interacts with an electrode such as molybdenum when the photoelectric conversion film is formed, and can suppress oxidation of the electrode. As a result, the conversion efficiency of the thin film solar cell can be increased.

In order to increase the b ^* value in the color development test with silver, (1) a method for increasing the hydrogen concentration in the float bath, (2) a method for increasing the residence time of the glass ribbon in the float bath, (3) in the float bath And (4) a method for reducing the strain point of the glass plate. The b ^* value can be increased by appropriately selecting these methods. However, when the strain point of the glass plate is lowered, the heat resistance of the glass plate is likely to be lowered. As a result, it becomes difficult to form the photoelectric conversion film at a high temperature, and the crystal quality of the photoelectric conversion film is easily lowered.

Second, the glass plate for a thin film solar cell of the present invention preferably has a b ^* value of 14 or more when a color development test with silver is performed.

Third, the glass plate for a thin film solar cell of the present invention preferably has a b ^* value of 30 or less when a color development test with silver is performed. When the b ^* value is too high, the metal ions in the photoelectric conversion film cause an ion exchange reaction with the metal ions (particularly alkali metal ions) in the glass plate during film formation, and are easily diffused into the glass plate. As a result, the diffused metal ions are reduced by the reduction layer to become metal atom colloids, which color the glass plate. In the super straight type and tandem type thin film solar cells, sunlight is absorbed by the glass plate due to the coloring of the glass plate, and the conversion efficiency tends to decrease.

Fourth, the glass plate for a thin-film solar cell of the present invention has a glass composition, in _mass%, Na 2 O _1~15%, preferably contains K 2 O 0~9%.

Fifth, a glass plate for thin-film solar cell of the present invention has a glass composition, in _{mass%, SiO 2 45~65%, Al} 2 O 3 1~20%, MgO + CaO + SrO + BaO 1~40%, Na 2 O + K 2 O It is preferable to contain 1 to 20%. Here, “MgO + CaO + SrO + BaO” refers to the total amount of MgO, CaO, SrO and BaO. “Na ₂ O + K ₂ O” refers to the total amount of Na ₂ O and K ₂ O.

Sixth, a glass plate for thin-film solar cell of the present invention has a glass composition, in _{mass%, SiO 2 45~60%, Al} 2 O 3 8 super _{to 20%} B 2 O 3 less than 0 to 15%, It is preferable that MgO + CaO + SrO + BaO 1 to 40%, Na ₂ O + K ₂ O 1 to 20% and the strain point be higher than 590 ° C. Here, the “strain point” refers to a value measured based on ASTM C336-71.

  Seventh, the glass plate for a thin-film solar cell of the present invention preferably has a substantially unpolished surface, more preferably the entire top surface is substantially unpolished, and the entire surface is substantially the same. In particular, it is particularly preferably unpolished. Here, “substantially unpolished” refers to the case where the surface polishing amount is less than 1.0 μm.

  Eighth, it is preferable that the glass plate for thin film solar cells of the present invention is subjected to a chemical strengthening treatment.

  Ninthly, it is preferable that the glass plate for thin film solar cells of the present invention is not subjected to chemical strengthening treatment.

  10thly, it is preferable to use the glass plate for thin film solar cells of this invention for a chalcopyrite solar cell.

  Eleventh, the glass plate for a thin film solar cell of the present invention is preferably used for a CdTe solar cell.

In the glass plate for a thin film solar cell of the present invention, the b ^* value when the color development test with silver is 7 or more, preferably more than 8, 10 or more, 14 or more, 15 or more, 17 or more, 19 or more, 21 or more, especially 23-30. If the b ^* value is too small, the reduction layer of the glass plate does not easily interact with an electrode such as molybdenum when the photoelectric conversion film is formed, and thus it is difficult to suppress oxidation of the electrode. If the b ^* value is too large, the glass plate is likely to be colored when the photoelectric conversion film is formed.

When making a plate by the float process, the hydrogen concentration in the float bath is over 1%, 1.5% or more, 1.9% or more, 3% or more, 4% or more, 4.5% or more, especially 5% or more Is preferred. If the hydrogen concentration is too low, the b ^* value becomes small and it becomes difficult to suppress oxidation of the electrode.

When manufacturing the plate by a float process, 0 ° C., the flow rate of the hydrogen gas in 1atm is space 1 m ³ per float bath, 0.4 m ³ / time or more, 0.5 m ³ / time or more, particularly 0.6 m ³ / More than time is preferred. If the flow rate of the hydrogen gas is too small, the b ^* value becomes small and it becomes difficult to suppress the oxidation of the electrode.

When making a plate by the float process, the residence time of the glass ribbon in the float bath is preferably 10 minutes or more, 13 minutes or more, particularly preferably 15 minutes or more. If the staying time of the glass ribbon is too short, the b ^* value becomes small and it becomes difficult to suppress the oxidation of the electrode.

When making a plate by the float process, the temperature in the float bath is preferably 1120 ° C. or higher, 1150 ° C. or higher, particularly 1160 ° C. or higher. If the temperature in the float bath is too low, the b ^* value becomes small and it becomes difficult to suppress oxidation of the electrode.

The glass plate for a thin-film solar cell of the present invention preferably contains Na ₂ O 1-15% and K ₂ O 0-9% in terms of glass composition, SiO ₂ 45-65%, Al _{2. O 3 1~20%, Na 2 O} + K 2 O 1~20%, preferably contains 1~40% MgO + CaO + SrO + BaO. The reason why the content of each component is regulated as described above is shown below.

SiO ₂ is a component that forms a glass network. The content of SiO ₂ is preferably 45 to 65%, 45 to 60%, 45 to 54%, particularly 49 to 52%. When the content of SiO ₂ is too large, the high-temperature viscosity becomes unduly high and the meltability and moldability are liable to decrease, and the thermal expansion coefficient becomes too low, so that the electrode of the thin film solar cell, photoelectric conversion It becomes difficult to match the thermal expansion coefficient of the film. On the other hand, if the content of SiO ₂ is too small, devitrification resistance is liable to decrease. Furthermore, since the thermal expansion coefficient becomes too high, the thermal shock resistance of the glass plate is likely to be lowered, and as a result, the glass plate is easily cracked in a high-temperature film forming process.

Al ₂ O ₃ is a component that increases the strain point and also increases weather resistance and chemical durability. The content of Al ₂ O ₃ is preferably 1 to 20%, 5 to 18%, more than 8 to 18%, more than 10 to 15%, more than 11 to 14.5%, particularly preferably 11.5 to 14%. When the content of Al ₂ O ₃ is too large, the high temperature viscosity becomes unduly high, the meltability and the formability tends to decrease. On the other hand, when the content of Al ₂ O ₃ is too small, the strain point tends to decrease.

SiO ₂ —Al ₂ O ₃ is a difference between SiO _{2 as} a main component and Al ₂ O ₃ that greatly contributes to increase the strain point among components constituting the glass network. When the content of SiO ₂ -Al ₂ O ₃ is too large, the strain point tends to decrease. On the other _hand, if the content of SiO 2 _-Al 2 _{O 3} is too small, devitrification resistance is liable to decrease. Therefore, the content of SiO ₂ —Al ₂ O ₃ is preferably 28 to 50%, less than 30 to 45%, 32 to 43%, particularly preferably 34 to 40%.

Na ₂ O is a component that adjusts the thermal expansion coefficient, and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. Na ₂ O is an effective component for the growth of chalcopyrite crystals and is an important component for increasing the conversion efficiency. The content of Na ₂ O is preferably 1 to 15%, 2.5 to 13%, 4 to 11%, particularly more than 4.3 to 9%. When the content of Na 2 _O is too large, in addition to the strain point tends to decrease, the thermal expansion coefficient becomes too high, the thermal shock resistance of the glass plate is liable to lower. As a result, the glass plate is likely to undergo thermal shrinkage or thermal deformation or cracks are likely to occur during the high temperature film formation process.

K ₂ O is a component that adjusts the thermal expansion coefficient, and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. K ₂ O is an effective component for the growth of chalcopyrite crystals and is an important component for increasing the conversion efficiency. However, in a glass system containing more than 10% Al ₂ O ₃ , if the content of K ₂ O is too large, KAlSiO-based devitrified crystals are likely to precipitate. If the content of K 2 _O is too large, easily strain point is lowered, also too high thermal expansion coefficient, the thermal shock resistance of the glass plate is liable to lower. As a result, the glass plate is likely to undergo thermal shrinkage or thermal deformation or cracks are likely to occur during the high temperature film formation process. Therefore, the content of K ₂ O is preferably 0 to 9%, 0.1 to 8%, particularly preferably 1 to 7%.

Na ₂ O + K ₂ O is a component that adjusts the thermal expansion coefficient, and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. Na ₂ O + K ₂ O is an effective component for the growth of chalcopyrite crystals and is an important component for increasing the conversion efficiency. The content of Na ₂ O + K ₂ O is preferably 1 to 20%, 2 to 20%, 4 to 18%, more than 4.3 to 15%, and particularly preferably 7 to 12%. When the content of Na 2 O _{+ K} 2 _O is too large, in addition to the strain point tends to decrease, the thermal expansion coefficient becomes too high, the thermal shock resistance of the glass plate is liable to lower. As a result, the glass plate is likely to undergo thermal shrinkage or thermal deformation or cracks are likely to occur during the high temperature film formation process. On the other _hand, when the content of Na 2 O + _{K 2} O is too small, it becomes difficult to enjoy the above-mentioned effects.

MgO is a component that increases the meltability and moldability by reducing the high-temperature viscosity. Moreover, MgO is a component with a large effect which makes a glass plate hard to break among alkaline-earth oxides. However, when MgO coexists with ZrO ₂ , it is a component that remarkably lowers the liquid phase viscosity by precipitating ZrO ₂ -based devitrified crystals. Further, when coexisting with CaO, it is a component that easily deposits a CaMgSiO-based devitrified crystal. Therefore, the content of MgO is preferably 0 to 10%, 0 to less than 3.7%, 0.01 to 3%, 0.02 to 2%, particularly 0.03 to 0.5%.

  CaO is a component that increases the meltability and moldability by reducing the high-temperature viscosity. Moreover, CaO is a component with a large effect which makes a glass plate hard to break among alkaline-earth oxides. The content of CaO is preferably 0 to 10%, 0.1 to 9%, more than 2.9 to 8%, 3 to 7.5%, and particularly preferably 4.2 to 6%. When there is too much content of CaO, devitrification resistance will fall easily and it will become difficult to shape | mold into a glass plate.

MgO + CaO, among alkaline earth metal oxides, increases the moving speed of the upward flow, downward flow, and backward flow toward the batch inlet in the glass melting furnace by reducing the high-temperature viscosity, making the glass homogeneous Is the sum of the two components to be converted. Moreover, MgO + CaO is the total of the two components that can most maintain the difficulty of breaking the glass plate and reduce the density most among the alkaline earth metal oxides. When the density is lowered, the cost of the support member of the thin film solar cell can be reduced. The content of MgO + CaO is preferably 0 to 10%, 0.1 to 9.9%, more than 2.9 to 9.5%, particularly more than 3.4 to less than 9.4%. When the content of MgO + CaO is too large, devitrification resistance, tends to particularly devitrification crystals ZrO ₂ system is deposited. In addition, when there is too little content of MgO + CaO, the moving speed of the molten glass in a glass melting furnace will fall, a molten glass will not be homogenized, and there exists a tendency for a meltability and a moldability to fall as a result. Here, “MgO + CaO” refers to the total amount of MgO and CaO.

The mass ratio CaO / MgO is a ratio of MgO and CaO having a large effect of reducing the high temperature viscosity among the alkaline earth oxides. From the point of view of resistance to devitrification, against easy MgO especially to generate devitrification crystals ZrO ₂ system, which is the ratio of hard CaO which caused the devitrification crystals ZrO ₂ system as compared with MgO. The mass ratio CaO / MgO is preferably more than 1, more than 2, more than 2.5, particularly more than 3.4 in order to reduce the high temperature viscosity while suppressing the precipitation of ZrO ₂ -based devitrified crystals.

SrO is a component that increases the meltability and moldability by reducing the high-temperature viscosity. Also, SrO, when coexisting with ZrO _2, is a component that hardly deposited devitrification crystals ZrO ₂ system. The content of SrO is preferably 0 to 20%, 0.1 to 15%, more than 4 to 15%, 5 to 14%, more than 7 to 13%, particularly preferably 9.2 to 12.5%. If the content of SrO is too large, feldspar group devitrified crystals are likely to precipitate, and the raw material cost increases.

  The content of CaO + SrO is preferably 0 to 30%, 0.1 to 25%, 6.92 to 23%, 8 to 21%, particularly preferably 9 to 20%. When there is too much content of CaO + SrO, devitrification resistance will fall easily. In addition, when there is too little content of CaO + SrO, the moving speed of the molten glass in a glass melting furnace will fall, a molten glass will not be homogenized, and there exists a tendency for a meltability and a moldability to fall as a result.

  BaO is a component that lowers the high-temperature viscosity and improves the meltability and moldability. The BaO content is preferably 0 to 20%, 0.1 to 15%, more than 2 to less than 14%, more than 2 to less than 8%, particularly preferably more than 2 to less than 5%. When there is too much content of BaO, the devitrification crystal | crystallization of a barium feldspar group will become easy to precipitate, and raw material cost will rise. Furthermore, the density increases, and the cost of the support member is likely to increase. In addition, when there is too little content of BaO, high temperature viscosity will become high and there exists a tendency for a meltability and a moldability to fall.

  MgO + CaO + SrO + BaO is a component that lowers the high temperature viscosity without lowering the strain point. When there is too much content of MgO + CaO + SrO + BaO, devitrification resistance will fall easily and raw material cost will rise. On the other hand, when the content of MgO + CaO + SrO + BaO is too small, the high temperature viscosity becomes too high. Therefore, the content of MgO + CaO + SrO + BaO is preferably 1 to 40%, 15 to 40%, more than 17 to 40%, 18 to 30%, and particularly preferably 19 to 25%.

  Furthermore, it is preferable to have the following component content and component ratio.

B ₂ O ₃ is a component that lowers the melting temperature and molding temperature by lowering the viscosity of the glass, but it is a component that lowers the strain point, and with the component volatilization at the time of melting, the furnace refractory material is changed. It is a component to be consumed. Therefore, the content of B ₂ O ₃ is preferably 0 to less than 15%, 0 to 1.5%, 0 to less than 1%, particularly preferably less than 0 to 0.1%.

Li ₂ O is a component that adjusts the thermal expansion coefficient, and is a component that lowers the high-temperature viscosity and improves the meltability and moldability. Li ₂ O is an effective component for the growth of chalcopyrite crystals in the same manner as Na ₂ O and K ₂ O. However, Li ₂ O is a component that significantly lowers the strain point in addition to the high raw material cost. Therefore, the content of Li ₂ O is preferably 0 to 10%, 0 to 2%, 0 to less than 1%, particularly preferably 0 to less than 0.1%.

The mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is the total amount of components having a large effect of reducing the high-temperature viscosity (MgO, CaO, SrO, BaO, Li ₂ O, Na ₂ O and K ₂ O total amount). ) To Na ₂ O content useful for precipitation of chalcopyrite crystals. The mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is 0.005 to 0.5, 0.05 to 0.4, 0.1 to 0.38, 0.137 to 0.355,. 140 to 0.300, especially more than 0.158 to 0.250 are preferable. If the mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is too large, it will be difficult to maintain a high strain point, and meltability and moldability will tend to be reduced. On the other hand, if the mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is too small, the conversion efficiency of the thin-film solar cell tends to decrease. In addition, if the mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is too small, the high-temperature viscosity is lowered, so the content of Li ₂ O and K ₂ O must be increased, and as a result Raw material costs will soar. Note that when the content of K ₂ O is preferentially increased, KAlSiO-based devitrified crystals are likely to precipitate in a glass system containing more than 10% Al ₂ O ₃ . Furthermore, even if the mass ratio Na ₂ O / (MgO + CaO + SrO + BaO + Li ₂ O + Na ₂ O + K ₂ O) is too small, it is difficult to maintain a high strain point, and devitrification resistance is lowered, and the liquid phase viscosity is likely to be lowered. .

  ZnO is a component that lowers the high temperature viscosity. When there is too much content of ZnO, devitrification resistance will fall easily. Therefore, the content of ZnO is preferably 0 to 10%, particularly preferably 0 to 5%.

ZrO ₂ is a component that increases the strain point without increasing the high-temperature viscosity. However, if the content of ZrO ₂ is too large, the density tends to increase, the glass plate tends to break, ZrO ₂ -based devitrified crystals tend to precipitate, and it becomes difficult to form the glass plate. Therefore, the content of ZrO ₂ is preferably 0 to 15%, 0 to 10%, 0 to 7%, 0.1 to 6.5%, particularly preferably 2 to 6%.

Fe in the glass exists in the state of Fe ²⁺ or Fe ³⁺ , but both ions cause glass coloring. Therefore, the content of Fe ₂ O ₃ is preferably 0.001 to 0.07%, particularly preferably 0.005 to 0.05%. Here, “Fe ₂ O ₃ ” refers to a value obtained by converting the total Fe amount to the Fe ₂ O ₃ amount regardless of the valence.

TiO ₂ is a component that prevents coloring by ultraviolet rays and enhances weather resistance. However, when the content of TiO ₂ is too large, or glass is devitrified, glass tends colored brown. Therefore, the content of TiO ₂ is preferably 0 to 10%, 0 to less than 1%, particularly preferably 0 to less than 0.1%.

P ₂ O ₅ is a component that enhances devitrification resistance, particularly a component that suppresses precipitation of ZrO ₂ -based devitrification crystals, and a component that makes it difficult to break the glass plate. However, when the content of P ₂ O ₅ is too large, easily glass phase separation milky. Therefore, the content of P ₂ O ₅ is preferably 0 to 10%, 0 to less than 1%, 0 to 0.2%, particularly preferably 0 to less than 0.1%.

SO ₃ is a component that acts as a fining agent, and its content is preferably 0 to 1%, particularly preferably 0 to 0.2%. In addition, if it manufactures by a float process, a glass plate can be mass-produced cheaply, but in this case, it is preferable to use mirabilite as a clarifier.

As ₂ O ₃ is a component that acts as a fining agent, but is a component that colors glass when it is made by the float process, and is a component that is concerned about the environmental burden. The content of As ₂ O ₃ is preferably 0 to 1%, particularly preferably less than 0 to 0.1%.

Sb ₂ O ₃ is a component that acts as a refining agent, but is a component that colors glass when it is made by a float process, and it is a component that is concerned about the environmental burden. The content of Sb ₂ O ₃ is preferably 0 to 1%, particularly preferably less than 0 to 0.1%.

SnO ₂ is a component that acts as a fining agent, but is a component that reduces devitrification resistance. The SnO ₂ content is preferably 0 to 1%, particularly preferably 0 to less than 0.1%.

In addition to the above components, F, Cl, and CeO ₂ may be added up to 1% in total in order to enhance solubility, clarity, and moldability. In order to increase chemical durability, Nb ₂ O ₅ , HfO ₂ , Ta ₂ O ₅ , Y ₂ O ₃ , and La ₂ O ₃ may be added up to 3% each.

  In the glass plate for a thin film solar cell of the present invention, the strain point is preferably 580 ° C. or higher, more than 590 ° C., more than 600 to 650 ° C., more than 605 to 650 ° C., particularly preferably more than 610 to 650 ° C. If the strain point is too low, the glass plate is likely to undergo thermal shrinkage or thermal deformation or cracks in the high-temperature film-forming process.

In the glass plate for a thin film solar cell of the present invention, the thermal expansion coefficient is preferably 70 to 100 × 10 ⁻⁷ / ° C., particularly preferably 80 to 90 × 10 ⁻⁷ / ° C. If it does in this way, it will become easy to match with the thermal expansion coefficient of an electrode and a photoelectric conversion film. If the thermal expansion coefficient is too high, the thermal shock resistance of the glass plate tends to be lowered, and as a result, the glass plate is likely to be cracked in a high-temperature film forming process. Here, the “thermal expansion coefficient” refers to a value obtained by measuring an average thermal expansion coefficient at 30 to 380 ° C. using a dilatometer.

In the glass plate for a thin-film solar cell of the present invention, the temperature at 10 ^4.0 dPa · s is preferably 1200 ° C. or less, particularly preferably 1180 ° C. or less. If it does in this way, it will become easy to shape | mold a glass plate at low temperature. The “temperature at 10 ^4.0 dPa · s” can be measured by a platinum ball pulling method.

In the glass plate for a thin film solar cell of the present invention, the temperature at 10 ^2.5 dPa · s is preferably 1520 ° C. or less, particularly preferably 1460 ° C. or less. If it does in this way, it will become easy to melt | dissolve a glass raw material at low temperature. The “temperature at 10 ^2.5 dPa · s” can be measured by a platinum ball pulling method.

  The glass plate for a thin film solar cell of the present invention was prepared by introducing the prepared glass raw material into a continuous melting furnace so as to be in the above glass composition range, heating and melting the glass raw material, and then defoaming the obtained molten glass. Above, it can produce by supplying to a float bath, shape | molding in plate shape, and slow-cooling.

  The glass plate for a thin film solar cell of the present invention preferably has a substantially unpolished surface. If it does in this way, while being able to enjoy the effect by a reduction layer exactly, the manufacturing cost of a glass plate can be reduced.

  The glass plate for a thin film solar cell of the present invention is preferably subjected to chemical strengthening treatment, particularly ion exchange treatment. If it does in this way, after installation of a thin film solar cell, the impact resistance with respect to a hail, snowfall, etc. and pressure | voltage resistance can be improved. From the viewpoint of production cost, it is preferable that chemical strengthening treatment, particularly ion exchange treatment is not performed.

  Hereinafter, based on an Example, this invention is demonstrated in detail. The following examples are merely illustrative. The present invention is not limited to the following examples.

Sample no. 1-5 were produced. First, a glass batch prepared to have the glass composition shown in Table 1 was melted in a melting furnace, and the float bath was adjusted while appropriately adjusting the production conditions shown in Table 2 so that a desired b ^* value was obtained. To 1.8 mm thickness. Subsequently, the obtained glass plate was subjected to a color development test with silver while measuring a strain point.

  The strain point is a value measured based on ASTM C336-71.

The color development test with silver was performed as follows. First, a silver paste was applied to the top surface side of the glass plate so as to have a thickness of 6 μm, and then baked at 600 ° C. for 1 hour. Next, b ^* value was measured from the bottom surface side of the glass plate using a simple spectral color difference meter (NF333 manufactured by Nippon Denshoku Industries Co., Ltd.).

As apparent from Table 2, the sample No. 1 to 3 have a large b ^* value, and it is considered that oxidation of the electrode can be suppressed by the reduction layer on the surface layer. On the other hand, sample No. Nos. 4 and 5 have small b ^* values, so it is difficult to suppress oxidation of the electrode by the reduction layer on the surface layer.

In this example, a glass plate having the glass composition shown in Table 1 was used. For example, a glass plate having the glass composition shown in Table 3 is considered to show the same tendency. In addition, in samples a to h, in addition to the strain point, a coefficient of thermal expansion, a temperature at 10 ^4.0 dPa · s, and a temperature at 10 ^2.5 dPa · s were also evaluated.

  A thermal expansion coefficient is the value which measured the average thermal expansion coefficient in 30-380 degreeC with the dilatometer. A cylindrical sample having a diameter of 5.0 mm and a length of 20 mm was used as a measurement sample.

Temperature at 10 ^4.0 dPa · ^s, temperature at ¹⁰ 2.5 dPa · s is a value measured by a platinum ball pulling method. The temperature at 10 ^4.0 dPa · s corresponds to the molding temperature, and the temperature at 10 ^2.5 dPa · s corresponds to the melting temperature.

Claims (11)

A glass plate for a thin-film solar cell, which is made by a float process and has a b ^* value of 7 or more when a color development test with silver is performed. The glass plate for a thin-film solar cell according to claim 1, wherein a b ^* value is 14 or more when a color development test with silver is performed. The glass plate for a thin-film solar cell according to claim 1 or 2, wherein a b ^* value is 30 or less when a color development test with silver is performed. As a glass composition, in _mass%, Na 2 O _1~15%, the glass plate for a thin film solar cell according to any one of claims 1 to 3, characterized in that it contains K 2 O 0 to 9% . As a glass composition, in _{mass%, SiO 2 45~65%, Al} 2 O 3 1~20%, claim 1, characterized in that it contains Na 2 O + K 2 O 1~20 %, MgO + CaO + SrO + BaO 1~40% The glass plate for thin film solar cells as described in any one of -3. As a glass composition, in _{mass%, SiO 2 45~60%, Al} 2 O 3 8 super _{~20%, B} 2 O 3 _0~15 less _{than%, Na 2 O + K 2} O 1~20%, MgO + CaO + SrO + BaO 1~40% The glass plate for thin film solar cells according to any one of claims 1 to 3, wherein the glass plate has a strain point of more than 590 ° C.   The glass plate for a thin-film solar cell according to any one of claims 1 to 6, which has a substantially unpolished surface.   The glass plate for thin film solar cells according to any one of claims 1 to 7, wherein a chemical strengthening treatment is performed.   The chemical strengthening process is not performed, The glass plate for thin film solar cells as described in any one of Claims 1-7 characterized by the above-mentioned.   It uses for a chalcopyrite type solar cell, The glass plate for thin film solar cells as described in any one of Claims 1-9 characterized by the above-mentioned.   It uses for a CdTe type | system | group solar cell, The glass plate for thin film solar cells as described in any one of Claims 1-9 characterized by the above-mentioned.