CN104080749A - Glass substrate for Cu-In-Ga-Se solar cells, and solar cell using same - Google Patents

Abstract

The glass substrate for CIGS solar cells of the present invention is produced by a selenization method. The ratio of Ca+Sr+Ba in the surface layer to the inside of the glass substrate is 0.7 or less. The Na ₂ O content ratio between the surface and the inside of the glass substrate is 0.4 to 1.1. The ratio of Na in the surface layer of the glass substrate before and after heat treatment is 1.1 or more. Contains 50-72% of SiO ₂ , 1-15% of Al ₂ O ₃ , 0-10% of MgO, and 0.1-11% of the following oxides at a depth of 5000 nm or more from the surface of the glass substrate CaO, 0-13% SrO, 0-11% BaO, 1-11% Na ₂ O, 2-21% K ₂ O, 0-10.5% ZrO ₂ , 4-25% MgO+ CaO+SrO+BaO, 2-23% CaO+SrO+BaO, 8-22% Na ₂ O+K ₂ O, and Na ₂ O/(CaO+SrO+BaO)≤1.2. The glass transition temperature of the glass substrate is 580°C or higher, and the average thermal expansion coefficient is 70×10 ^-7 to 100×10 ^-7 /°C. This glass substrate can achieve both high power generation efficiency and high glass transition temperature.

Description

Glass substrate for Cu-In-Ga-Se solar cell and solar cell using same

technical field

The present invention relates to a glass substrate for a solar cell in which a photoelectric conversion layer is formed between glass plates, and a solar cell using the glass substrate. More specifically, it typically has a glass substrate and a cover glass as a glass plate, and a photoelectric conversion layer mainly composed of group 11, 13, and 16 elements is formed between the glass substrate and the cover glass by a selenization method. A glass substrate for at least a part of Cu-In-Ga-Se solar cells and a solar cell using the same.

Background technique

Group 11-13, Group 11-16 compound semiconductors having a chalcopyrite crystal structure, Group 12-16 compound semiconductors having a cubic crystal system or a hexagonal crystal system have a large absorption coefficient for light in a wavelength range from visible to near infrared. Therefore, it is expected to be a material for high-efficiency thin-film solar cells. Typical examples include Cu(In,Ga)Se ₂ (hereinafter also referred to as “CIGS” or “Cu—In—Ga—Se”) and CdTe.

For CIGS thin-film solar cells, soda lime glass is used as a substrate to obtain solar cells from the viewpoint of low cost and a thermal expansion coefficient close to that of CIGS compound semiconductors.

In addition, in order to obtain a solar cell with high efficiency, glass materials capable of withstanding high heat treatment temperatures have also been proposed (refer to Patent Document 1).

prior art literature

patent documents

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

Contents of the invention

The problem to be solved by the invention

A CIGS photoelectric conversion layer (hereinafter also referred to as "CIGS layer") was formed on the glass substrate. As disclosed in Patent Document 1, in order to produce a solar cell with good power generation efficiency, heat treatment at a higher temperature is preferable, and the glass substrate is required to be able to withstand high temperature heat treatment. Patent Document 1 proposes a glass composition having a high annealing point, but the invention described in Patent Document 1 cannot be said to have high power generation efficiency.

The inventors of the present invention found that the power generation efficiency can be increased by increasing the alkali of the glass substrate within a predetermined range, but there is a problem that the glass transition temperature (Tg) decreases due to the increase of the alkali.

It can be seen that for the glass substrate used in CIGS solar cells, it is difficult to balance high power generation efficiency and high glass transition temperature.

An object of the present invention is to provide a glass substrate for a Cu-In-Ga-Se solar cell that is particularly compatible with high power generation efficiency and high glass transition temperature.

means of solving problems

The gist of the present invention lies in the following configurations.

(1) a Cu-In-Ga-Se solar cell glass substrate made by selenization method, wherein,

The difference between the average total amount (atomic %) of Ca, Sr and Ba at a depth of 10 to 40 nm from the surface of the glass substrate and the total amount (atomic %) of Ca, Sr and Ba at a depth of 5000 nm from the surface of the glass substrate The ratio is 0.7 or less,

The ratio of the Na ₂ O content (mass %) measured from the glass substrate surface by fluorescent X-rays to the Na ₂ O content (mass %) measured from the surface after removing 5000 nm of glass from the glass substrate surface by fluorescent X-rays is 0.4～1.1,

The ratio of the average Na amount (atomic %) at a depth of 10 to 40 nm from the surface of the glass substrate before and after heat treatment at 600° C. for 1 hour under _N atmosphere is 1.1 or more,

Contains 50 to 72% of SiO ₂ , 1 to 15% of Al ₂ O ₃ , 0 to 10% of MgO, and 0.1 to 11% at a depth of 5000 nm or more from the surface of the glass substrate, based on the mass percentage of the following oxides CaO, 0-13% SrO, 0-11% BaO, 1-11% Na ₂ O, 2-21% K ₂ O, 0-10.5% ZrO ₂ , 4-25% MgO+ CaO+SrO+BaO, 2-23% CaO+SrO+BaO, 8-22% Na ₂ O+K ₂ O, and Na ₂ O/(CaO+SrO+BaO)≤1.2,

The glass substrate has a glass transition temperature of not less than 580°C, and an average coefficient of thermal expansion of not less than 70×10 ^-7 and not more than 100×10 ^-7 /°C.

(2) The Cu-In-Ga-Se solar cell glass substrate produced by the selenization method as described in said (1), wherein,

The depth from the surface of the glass substrate is the average total amount (atomic %) of Ca, Sr and Ba between 10 and 40 nm and the total amount (atomic %) of Ca, Sr and Ba at the depth of 5000 nm from the surface of the glass substrate ) ratio is 0.5 or less,

Ratio of the Na ₂ O content (mass %) measured from the surface of the glass substrate by fluorescent X-rays to the Na ₂ O content (mass %) measured by fluorescent X-rays from the surface after removing 5000 nm of glass from the glass substrate surface 0.5～0.87,

The ratio of the average Na amount (atomic %) at a depth of 10 to 40 nm from the surface of the glass substrate before and after heat treatment at 600° C. for 1 hour under _N atmosphere is 1.5 or more,

At a depth of 5000 nm or more from the surface of the glass substrate, 0.5-9% of ZrO ₂ , 2.5-19% of CaO+SrO+BaO, and 0-16% of SrO+BaO are contained in the mass percentage based on the following oxides.

(3) The Cu-In-Ga-Se solar cell glass substrate produced by the selenization method as described in the above (1) or (2), wherein,

The depth from the surface of the glass substrate is the average total amount (atomic %) of Ca, Sr and Ba between 10 and 40 nm and the total amount (atomic %) of Ca, Sr and Ba at the depth of 5000 nm from the surface of the glass substrate ) ratio is 0.35 or less,

Ratio of the Na ₂ O content (mass %) measured from the surface of the glass substrate by fluorescent X-rays to the Na ₂ O content (mass %) measured by fluorescent X-rays from the surface after removing 5000 nm of glass from the glass substrate surface is 0.6～0.84,

The ratio of the average Na amount (atomic %) at a depth of 10 to 40 nm from the surface of the glass substrate before and after heat treatment at 600° C. for 1 hour under _N atmosphere is 2.0 or more,

At a depth of 5000 nm or more from the glass substrate surface, 3 to 15% of CaO+SrO+BaO and 0 to 8% of SrO+BaO are contained in mass percentages based on the following oxides.

(4) A solar cell having a glass substrate, a cover glass, and a photoelectric conversion layer of Cu-In-Ga-Se produced by a selenization method disposed between the glass substrate and the cover glass,

Among the glass substrate and the cover glass, at least the glass substrate is the Cu-In-Ga-Se solar cell glass substrate produced by the selenization method according to any one of the above (1) to (3).

Invention effect

The glass substrate for Cu-In-Ga-Se solar cells of the present invention can take into account both high power generation efficiency and high glass transition temperature. By using the glass substrate for CIGS solar cells of this invention, the solar cell with low cost and high efficiency can be provided.

Description of drawings

FIG. 1 is a cross-sectional view schematically showing an example of an embodiment of a solar cell of the present invention.

FIG. 2A shows a solar battery cell fabricated on a glass substrate for evaluation in Examples.

Fig. 2B is a cross-sectional view along line A-A' of the solar cell shown in Fig. 2A.

FIG. 3 shows a CIGS solar cell for evaluation on a glass substrate for evaluation in which eight solar cells shown in FIG. 2A are arrayed.

Detailed ways

Hereinafter, the glass substrate for Cu-In-Ga-Se solar cells of this invention is demonstrated.

The glass substrate for Cu-In-Ga-Se solar cells of the present invention is a glass substrate for Cu-In-Ga-Se solar cells made by selenization method, wherein the depth from the surface of the glass substrate is between 10 and 40nm The average total amount (atomic %) of Ca, Sr, and Ba (hereinafter also referred to as "the amount of Ca+Sr+Ba in the surface layer of the glass substrate") and the total amount of Ca, Sr, and Ba at a depth of 5000 nm from the surface of the glass substrate The ratio of the amount (atomic %) (hereinafter also referred to as "the amount of Ca+Sr+Ba inside the glass substrate") (hereinafter also referred to as "the ratio of the surface layer of the glass substrate to the inside of Ca+Sr+Ba") is 0.7 or less , the Na ₂ O content (mass %) measured from the surface of the glass substrate by fluorescent X-rays (hereinafter also referred to as "Na ₂ O content (mass %) on the surface of the glass substrate") is the same as that measured from the surface of the glass substrate by fluorescent X-rays. The ratio of the Na ₂ O content (mass %) (hereinafter also referred to as "Na ₂ O content (mass %) inside the glass substrate") measured on the surface after removing 5000 nm of glass (hereinafter also referred to as "glass substrate surface to internal The ratio of _Na2O content ") is 0.4 to 1.1, and the depth from the surface of the glass substrate is 10 to 40nm. The ratio of the average Na content (atomic %) before and after heat treatment at 600°C for 1 hour under _N2 atmosphere ( Hereinafter also referred to as "the ratio of Na in the surface layer of the glass substrate before and after heat treatment") is 1.1 or more, at a depth of 5000 nm or more from the surface of the glass substrate, and contains 50 to 72% by mass percentage based on the following oxides SiO ₂ , 1-15% Al ₂ O ₃ , 0-10% MgO, 0.1-11% CaO, 0-13% SrO, 0-11% BaO, 1-11% Na ₂ O, 2-21 % K ₂ O, 0~10.5% ZrO ₂ , 4~25% MgO+CaO+SrO+BaO, 2~23% CaO+SrO+BaO, 8~22% Na ₂ O+K ₂ O , and Na ₂ O/(CaO+SrO+BaO)≤1.2, the glass transition temperature of the glass substrate is above 580°C, and the average thermal expansion coefficient is 70×10 ^-7 to 100×10 ^-7 /°C.

It is preferable that the glass substrate for Cu-In-Ga-Se solar cells is the glass substrate for Cu-In-Ga-Se solar cells manufactured by the selenization method.

The Cu-In-Ga-Se produced by the selenization method refers to Cu-In-Ga-Se in which at least a part of the CIGS layer which is the photoelectric conversion layer of the solar cell is formed into a film by the selenization method.

In the glass substrate for CIGS solar cells of the present invention, the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior is 0.7 or less, preferably 0.5 or less, more preferably 0.35 or less, further preferably 0.3 or less, particularly preferably 0.25 the following.

In addition, regarding the ratio of Ca+Sr+Ba in the surface layer of the above-mentioned glass substrate to the inside, the amount of Ca+Sr+Ba in the surface layer of the glass substrate can be compared with the amount of Ca+Sr+Ba in the inside of the glass substrate in the form of relative ratio . That is, when the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior is 0.7 or less, it means that the amount of Ca+Sr+Ba in the surface layer of the glass substrate is smaller than the amount of Ca+Sr+Ba in the inside of the glass substrate. , specifically refers to the state in which atoms of Ca, Sr, and Ba are detached from the vicinity of the surface of the glass substrate.

In the glass substrate for solar cells of the present invention, the Na ₂ O content ratio between the surface and the inside of the glass substrate is 0.4 to 1.1. When the above-mentioned Na ₂ O content ratio is less than 0.4, the ratio of Na in the surface layer of the glass substrate described later before and after heat treatment is too small, which is not preferable. Preferably it is 0.5 or more, More preferably, it is 0.6 or more. In addition, when the above Na ₂ O content ratio exceeds 1.1, the amount of Ca, Sr, and Ba atoms detached from the vicinity of the glass substrate surface is small, so the ratio of Na in the surface layer of the glass substrate described later before and after heat treatment becomes small, so it is not preferable. . The above Na ₂ O content ratio is preferably 0.9 or less, more preferably 0.87 or less, and still more preferably 0.84 or less.

When the Na ₂ O content ratio is less than 1.1, it means a state in which Na atoms are detached from the vicinity of the glass substrate surface (detached state).

In the present invention, the _Na2O content on the surface of the glass substrate is quantified from the surface of the glass substrate using a standard sample for quantification measured by fluorescent X-rays (bulb voltage 50kV50mA) and a calibration curve method using the fluorescent X-ray method. The Na ₂ O content (mass %) is a value obtained by measuring the average content in the range from the surface of the glass substrate to about 3000 nm. In addition, the Na ₂ O content inside the glass substrate refers to the Na ₂ O content (mass %) measured from the surface after removing the glass up to 5000 nm from the surface of the glass substrate using fluorescent X-rays (bulb voltage 50 kV 50 mA). The value obtained from the average content in the range to about 3000 nm from the surface after removing glass.

In the present invention, the degree of Na exfoliation from the surface of the glass substrate to a depth of about 3000 nm is defined by using the ratio of the Na ₂ O content on the surface of the glass substrate to the Na ₂ O content inside the glass substrate.

The inventors of the present invention have found that Na and atoms of Ca, Sr, and Ba, or atoms of Ca, Sr, and Ba are detached from the vicinity of the surface of the glass substrate (detached state) and Na in the surface layer of the above-mentioned glass substrate described later is heat-treated. The front-to-back ratio is large, and when the glass substrate for CIGS solar cells of the present invention is used for CIGS solar cells, in the heat treatment process in the solar cell manufacturing process (generally, under an atmosphere containing selenium and sulfur and oxygen-free, at about 100°C ~600° C., heat treatment conditions of 10 minutes or more), when at least a part of CIGS as the photoelectric conversion layer of the solar cell is formed by the selenization method, the power generation efficiency of the solar cell improves.

The inventors of the present invention have found that the state in which atoms of Na, Ca, Sr, and Ba, or atoms of Ca, Sr, and Ba are detached from the vicinity of the surface of the glass substrate refers to the first half of the heat treatment in the solar cell manufacturing process produced by the selenization method. Partly, specifically, in the process of selenization and sulfidation with hydrogen selenide and hydrogen sulfide while heating the precursor film of the In-CuGa alloy, the diffusion of Na is reduced at the initial stage of the selenization and sulfidation reactions. When using such a substrate in which the ratio of Na in the surface layer of the above-mentioned glass substrate before and after heat treatment is large, the second half of the heat treatment process in the solar cell manufacturing process (generally, at about 500°C to 600°C for 10 minutes or more ), the amount of Na diffused from the vicinity of the glass substrate surface to the photoelectric conversion layer increases, and the power generation efficiency improves.

The inventors of the present invention conducted in-depth studies on the above-mentioned effects of Na diffusion, and found that when the amount of Na diffusion was small in the initial stage of the selenization and sulfidation reactions and the amount of Na diffusion was ensured in the second half of the heat treatment process, the crystallization grade of CIGS improve. The increase in crystalline grade can be confirmed by the increase in free carrier density in CIGS.

In the sample in which free carriers were increased, it was confirmed that the cell characteristics of the solar cell were an increase in the open circuit voltage (Voc) and the curve factor (FF), which will be described later, and as a result, the power generation efficiency was improved. The reason for the increase in FF is that the conductivity of the CIGS film increases and the series resistance (Rser) decreases mainly by increasing the free carrier density. Series resistance (Rser) is the resistance component when current flows through the element, and the lower the better.

In the present invention, "the average total amount (atomic %) of Ca, Sr and Ba at a depth of 10 to 40 nm from the surface of the glass substrate" or "the average Na at a depth of 10 to 40 nm from the surface of the glass substrate Amount (atomic %)" to specify the amount of Ca+Sr+Ba or the amount of Na (atomic %) in the surface layer of the glass substrate because: the atoms of Ca, Sr and Ba in this region are detached and the Na near the surface of the glass substrate is When the ratio before and after the heat treatment is large, the diffusion of Na to the surface layer of the glass substrate after the heat treatment becomes remarkable. In addition, in consideration of the influence of external air on compositional fluctuations, the region of 0 to less than 10 nm was not included in the measurement object.

The Na ₂ O content indicates how much Na is less in the range from the surface of the glass substrate to about 3000 nm in the initial state of the substrate, and it strongly affects the initial stage of the heat treatment process. On the other hand, as an index showing how easily Na diffuses into the photoelectric conversion layer, the ratio of Na in the surface layer of the glass substrate before and after heat treatment is appropriate, so two indexes were introduced for the amount of Na near the surface of the glass substrate.

In addition, the reason for specifying the amount of Ca+Sr+Ba inside the glass substrate as "the total amount at a depth of 5000 nm from the surface of the glass substrate" is that this is a part where the detachment of atoms of Ca, Sr, and Ba hardly occurs.

The reason why the "Na ₂ O content inside the glass substrate" is defined by the Na ₂ O content measured from the surface after removing the glass up to 5000 nm from the surface of the glass substrate by fluorescent X-rays is that the part deeper than 5000 nm is basically not The part where detachment of the atom of Na occurs.

In order to obtain a glass substrate in which the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior is 0.7 or less and the Na ₂ O content ratio in the surface of the glass substrate to the interior is 0.4 to 1.1, so that the composition of the glass substrate reaches the specified Each raw material component is used in a manner within a range, and the melting, clarification process, and forming process are performed in the same manner as in the production of conventional solar cell glass substrates, and the SO ₂ treatment of the present invention is performed in the subsequent annealing process. The composition of the glass substrate for CIGS solar cells of the present invention (each raw material component) and the SO ₂ treatment of the present invention will be described in detail later.

In addition, the present inventors found that in the glass substrate for CIGS solar cells of the present invention, the ratio of Na in the surface layer of the glass substrate before and after heat treatment needs to be 1.1 or more, preferably 1.2 or more, more preferably 1.5 or more. This increases the amount of Na diffused from the glass substrate to the CIGS photoelectric conversion layer during the heat treatment in the CIGS solar cell manufacturing process, and when used in a CIGS solar cell, the power generation efficiency of the solar cell increases. The ratio of Na in the surface layer of the glass substrate before and after heat treatment is more preferably 1.8 or more, still more preferably 2.0 or more, particularly preferably 2.4 or more.

However, the amount of Na in the surface layer of the glass substrate after the heat treatment is preferably 0.3 atomic % or more. This is because if it is less than 0.3 atomic %, sufficient diffusion into the photoelectric conversion layer cannot be performed, and thus there is a possibility that sufficient power generation efficiency cannot be obtained. More preferably, it is 0.5 atomic % or more, Still more preferably, it is 1.0 atomic % or more, Especially preferably, it is 2.5 atomic % or more.

The upper limit of the ratio of Na in the surface layer of the glass substrate before and after heat treatment is 5. When the ratio of Na in the surface layer of the glass substrate before and after the heat treatment is greater than 5, the Na in the surface layer of the glass substrate before the heat treatment decreases, and as a result, the amount of Na diffusing from the glass substrate to the photoelectric conversion layer of CIGS decreases, so the power generation efficiency may decrease. The ratio of Na in the surface layer of the glass substrate before and after heat treatment is preferably 4.5 or less, more preferably 4 or less.

It should be noted that the ratio of Na in the surface layer of the glass substrate before and after heat treatment was specified under the conditions of heat treatment at 600° C. for 1 hour under N ₂ atmosphere for the following reason. The inventors of the present invention have confirmed that when the diffusion of Na to the surface layer of the glass substrate is sufficient under the conditions of heat treatment at 600°C for 1 hour in _a N atmosphere, even if the conditions of the heat treatment process in the solar cell manufacturing process are slightly changed, the Good influence on power generation efficiency.

The composition of the glass substrate is the composition specified in the present invention, and the ratio of Ca+Sr+Ba in the surface layer of the above-mentioned glass substrate to the inside is 0.7 or less, preferably 0.5 or less, more preferably 0.35 or less, further preferably 0.3 or less, particularly preferably 0.25 When the _Na2O content ratio between the surface and the inside of the glass substrate is 0.4 to 1.1, preferably 0.5 to 0.87, and more preferably 0.6 to 0.84, the ratio of Na in the surface layer of the glass substrate before and after heat treatment can be easily made 1.1 or more. , preferably 1.5 or more, more preferably 1.8 or more, still more preferably 2.0 or more, particularly preferably 2.4 or more.

The glass transition temperature (Tg) of the glass substrate for CIGS solar cells of this invention is 580 degreeC or more. The glass transition temperature of the glass substrate for CIGS solar cells of the present invention is higher than that of soda lime glass. In order to ensure the formation of the photoelectric conversion layer at high temperature, the glass transition temperature (Tg) of the glass substrate for CIGS solar cells of the present invention is preferably 600°C or higher, more preferably 610°C or higher, still more preferably 620°C or higher, particularly preferably It is above 630°C. The upper limit of the glass transition temperature is 750°C. If the glass transition temperature is 750° C. or lower, the viscosity at the time of melting can be appropriately suppressed to be low, and thus production is easy, which is preferable. The glass transition temperature is more preferably 700°C or lower, further preferably 680°C or lower.

The average coefficient of thermal expansion at 50 to 350°C of the glass substrate for a CIGS solar cell of the present invention is 70×10 ^-7 to 100×10 ^-7 /°C. When the average coefficient of thermal expansion is less than 70×10 ^-7 /°C or more than 100×10 ^-7 /°C, the difference in thermal expansion from the CIGS layer and the like becomes too large, and disadvantages such as peeling tend to occur. In addition, when a solar cell is assembled (specifically, when a glass substrate having a CIGS photoelectric conversion layer and a cover glass are bonded together by heating), the glass substrate may be easily deformed. The average thermal expansion coefficient is preferably 95×10 ^-7 /°C or less, more preferably 90×10 ^-7 /°C or less.

In addition, the average coefficient of thermal expansion is preferably 73×10 ^-7 /°C or higher, more preferably 75×10 ^-7 /°C or higher, and still more preferably 80×10 ^-7 /°C or higher.

In the glass substrate for CIGS solar cells of this invention, the reason why each raw material component is limited to the said composition is as follows.

In addition, the percentage (%) in the following shows mass % unless otherwise indicated.

SiO ₂ : SiO ₂ is a component that forms the skeleton of glass, and if the content thereof is less than 50 mol %, the heat resistance and chemical durability of the glass substrate may decrease and the average thermal expansion coefficient may increase. Its content is preferably 52% or more, more preferably 54% or more, still more preferably 56% or more, particularly preferably 58% or more.

However, when the content exceeds 72%, the high-temperature viscosity of the glass may increase and the meltability may deteriorate. Its content is preferably 70% or less, more preferably 68% or less, still more preferably 67% or less, particularly preferably 66% or less.

Al ₂ O ₃ : Al ₂ O ₃ increases the glass transition temperature, improves weather resistance (light exposure), heat resistance, and chemical durability, and increases Young's modulus. When the content is less than 1%, the glass transition temperature may be lowered. In addition, it is possible to increase the average thermal expansion coefficient. The content thereof is preferably 2% or more, more preferably 3% or more, still more preferably 4% or more, particularly preferably 5% or more.

However, if the content exceeds 15%, the high-temperature viscosity of glass may increase and the meltability may deteriorate. In addition, the devitrification temperature may increase and the moldability may be deteriorated. In addition, the power generation efficiency may decrease, that is, the amount of Na diffusion described later may decrease. Its content is preferably 14% or less, more preferably 13% or less, still more preferably 12% or less, particularly preferably 11.5% or less.

B ₂ O ₃ : ₃ to 2% of B ₂ O may be contained in order to improve the meltability and the like. When the content thereof exceeds 2%, the glass transition temperature decreases, or the average thermal expansion coefficient becomes small, which is not preferable for the process of forming a CIGS layer. The content thereof is more preferably 1% or less. The content thereof is particularly preferably 0.5% or less. _Moreover , it is preferable not to contain _B2O3 substantially.

In addition, "it does not contain substantially" means that it does not contain except the unavoidable impurity mixed from a raw material etc., ie, does not contain intentionally. In addition, it has the same meaning about other components.

MgO: MgO has the effect of reducing the viscosity at the time of glass melting and accelerating melting, so it may be contained. The content thereof is preferably 0.5% or more, more preferably 1% or more, still more preferably 2% or more, particularly preferably 3% or more.

However, when the content exceeds 10%, the average thermal expansion coefficient may increase. In addition, the devitrification temperature may be increased. The content thereof is preferably 9.5% or less, more preferably 9.0% or less, still more preferably 8.5% or less, particularly preferably 8.0% or less.

CaO: CaO has the effect of reducing the viscosity at the time of glass melting and accelerating melting, so it may be contained in an amount of 0.1% or more. The content thereof is preferably 0.5% or more, more preferably 1% or more, still more preferably 2% or more, particularly preferably 3% or more. However, when the content exceeds 11%, the average thermal expansion coefficient of glass may increase. In addition, the power generation efficiency may be reduced, that is, the amount of Na diffusion described later may be reduced. The content thereof is preferably 10% or less, more preferably 9% or less, further preferably 8% or less, particularly preferably 7% or less.

SrO: SrO has the effect of reducing the viscosity at the time of glass melting and promoting melting, so it may be contained. However, if more than 13% of SrO is contained, the power generation efficiency may decrease, that is, the amount of Na diffusion described later may decrease, and the average thermal expansion coefficient of the glass substrate may increase. The content thereof is preferably 11% or less, more preferably 9% or less, further preferably 7% or less, particularly preferably 5% or less. In addition, the content thereof is preferably 0.5% or more, more preferably 1% or more.

BaO: BaO has the effect of reducing the viscosity at the time of glass melting and promoting melting, so it can be contained. However, if more than 11% of BaO is contained, the power generation efficiency may decrease, that is, the amount of Na diffusion described later may decrease, and the average thermal expansion coefficient of the glass substrate may increase. In addition, the specific gravity also increases. The content thereof is preferably 7% or less, more preferably 3% or less, still more preferably 0.5% or less. It is especially preferable not to contain BaO substantially.

ZrO ₂ : ZrO ₂ has the effect of lowering the viscosity of glass when it is melted, promoting melting, and increasing Tg, so it may be contained. It is preferable to contain 0.5% or more of ZrO ₂ . The content thereof is more preferably 1% or more, still more preferably 1.5% or more, particularly preferably 2% or more. However, if ZrO ₂ is contained in excess of 10.5%, the power generation efficiency may decrease, that is, the amount of Na diffusion described later may decrease, the devitrification temperature may increase, and the average thermal expansion coefficient of the glass substrate may increase. Its content is preferably 9% or less, more preferably 7% or less, still more preferably 5% or less, particularly preferably 4% or less.

MgO, CaO, SrO and BaO: From the viewpoint of reducing the viscosity of the glass during melting and promoting melting, the total amount (MgO+CaO+SrO+BaO) contains 4-25% of MgO, CaO, SrO and BaO. However, when the total amount exceeds 25%, the average thermal expansion coefficient may increase and the devitrification temperature may increase. The total amount thereof is preferably 6% or more, more preferably 9% or more. In addition, the total amount thereof is preferably 21% or less, more preferably 20% or less, further preferably 18% or less, particularly preferably 15% or less.

From the viewpoint of making the ratio of Ca+Sr+Ba in the surface layer of the glass substrate after the _SO2 treatment to 0.7 or less, CaO, SrO, and BaO are contained in a total amount of 2% or more. The total amount of CaO, SrO, and BaO is preferably 2.5% or more, more preferably 3% or more, still more preferably 3.5% or more, particularly preferably 4% or more. When the total amount of CaO, SrO, and BaO is less than 2%, the viscosity of the glass when it melts is lowered, and the glass transition temperature is raised. Therefore, it is necessary to add a large amount of MgO, which may raise the devitrification temperature.

However, when the total amount exceeds 23%, the amount of Na diffusion after heat treatment may decrease. That is, it is considered that since the ionic radius of Ca is close to that of Na, it tends to compete with the migration of Na in the glass, and the amount of diffusion of Na tends to decrease. In addition, Ba has a large ionic radius, so it is easy to suppress the migration of Na, and it is considered that it is easy to reduce the diffusion amount of Na. Sr is considered to have the properties of both Ca and Ba described above. Therefore, the total amount thereof is preferably 19% or less, more preferably 15% or less, further preferably 12% or less, particularly preferably 10% or less.

SrO and BaO form sulfate films (SrSO ₄ , BaSO ₄ ) when subjected to SO ₂ treatment, which are less soluble in water than other sulfate films (MgSO ₄ , CaSO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ ) , Therefore, the sulfate film is not easily removed when cleaning the sulfate film. Therefore, the total amount of SrO and BaO is preferably 16% or less, more preferably 8% or less, still more preferably 6% or less, particularly preferably 4% or less.

Na ₂ O: Na ₂ O is a component that contributes to improving the power generation efficiency of a CIGS solar cell and is an essential component. In addition, it has the effect of lowering the viscosity at the melting temperature of glass and facilitating melting, so it is contained in an amount of 1 to 11%. Na diffuses into the photoelectric conversion layer of CIGS formed on glass to improve power generation efficiency, but when the content is less than 1%, the amount of Na diffusion into the photoelectric conversion layer of CIGS on the glass substrate may not be sufficient, resulting in poor power generation efficiency. also become inadequate. The content thereof is preferably 2% or more, more preferably 2.5% or more, still more preferably 3% or more, particularly preferably 3.5% or more.

When the Na ₂ O content exceeds 11%, the glass transition temperature decreases, the average thermal expansion coefficient increases, or the chemical durability deteriorates. The content thereof is preferably 10% or less, more preferably 9% or less, still more preferably 8% or less. It is particularly preferred that its content is less than 7%.

K ₂ O: K ₂ O has the same effect as Na ₂ O, so it is contained in 2 to 21%. However, when the content exceeds 21%, the power generation efficiency may decrease, that is, the diffusion of Na may be suppressed, the amount of Na diffusion described later may decrease, the glass transition temperature may decrease, and the average thermal expansion coefficient may increase. Preferably it is 3% or more, more preferably 4% or more, still more preferably 5% or more, particularly preferably 6% or more. Its content is preferably 16% or less, more preferably 12% or less, still more preferably 10% or less, particularly preferably 8% or less.

Na ₂ O and K ₂ O: In order to sufficiently reduce the viscosity at the melting temperature of the glass and to increase the power generation efficiency of CIGS solar cells, the total content of Na ₂ O and K ₂ O (Na ₂ O+K ₂ O) is set 8 to 22%. The total amount is preferably 9% or more, more preferably 10% or more, still more preferably 11% or more, particularly preferably 12% or more.

However, if the total amount exceeds 22%, Tg may be too low and the average thermal expansion coefficient may be too high. The total amount thereof is preferably 20% or less, more preferably 17% or less, further preferably 16% or less, particularly preferably 15% or less.

Na ₂ O/(CaO+SrO+BaO): When Na ₂ O/(CaO+SrO+BaO) exceeds 1.2, during SO ₂ treatment, the precipitation reaction of Na ₂ SO ₄ proceeds, and on the other hand, it is difficult to proceed with CaSO _4. Precipitation reaction of SrSO ₄ and BaSO ₄ , as a result, detachment of Ca, Sr and Ba in the surface layer of the glass substrate is less likely to occur. Na ₂ O/(CaO+SrO+BaO) is preferably 1.0 or less, more preferably 0.9 or less, even more preferably 0.8 or less.

The lower limit of Na ₂ O/(CaO+SrO+BaO) is preferably 0.1. When Na ₂ O/(CaO+SrO+BaO) is less than 0.1, the amount of Na ₂ O becomes too small, which may lower the battery efficiency. Na ₂ O/(CaO+SrO+BaO) is more preferably 0.2 or more, still more preferably 0.3 or more, still more preferably 0.5 or more.

The glass substrate for CIGS solar cells of the present invention essentially has a basic composition: 50 to 72% of SiO ₂ , 1 to 15% of Al ₂ O ₃ , 0 to 10 % MgO, 0.1-11% CaO, 0-13% SrO, 0-11% BaO, 1-11% Na ₂ O, 2-21% K ₂ O, 0-10.5% ZrO ₂ , 4-25% MgO+CaO+SrO+BaO, 2-23% CaO+SrO+BaO, 8-22% Na ₂ O+K ₂ O, and Na ₂ O/(CaO+SrO+BaO) ≤1.2. Among them, in terms of mass percentage based on the following oxides, 0.5-9% of ZrO ₂ , 2.5-19% of CaO+SrO+BaO, 0-16% of SrO+BaO, or 3-15% of A combination of CaO+SrO+BaO, 0-8% of SrO+BaO.

The glass substrate for CIGS solar cells of the present invention essentially contains the above-mentioned basic composition, but may contain other components typically at a total amount of 5% or less within a range that does not impair the object of the present invention. For example, B ₂ O ₃ , ZnO, Li ₂ O, WO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Bi ₂ O ₃ , MoO ₃ , P ₂ O ₅ , etc.

In addition, in order to improve the meltability and clarity of the glass, SO ₃ , F, Cl and/or SnO ₂ raw materials may be added to the basic composition raw materials so that the total amount of these substances in the glass is 2% or less.

In addition, in order to improve the chemical durability of glass, ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ , TiO ₂ and/or SnO ₂ may be contained in the glass in a total amount of 5% or less. Among them, Y ₂ O ₃ , La ₂ O ₃ and TiO ₂ also help to increase the Young's modulus of the glass.

In addition, in order to adjust the color tone of the glass, coloring agents such as Fe ₂ O ₃ may be contained in the glass. The content of such a colorant is preferably 1% or less in total.

_Moreover , in consideration of environmental load, _it is preferable that the glass substrate for CIGS solar cells of this invention does not contain _As2O3 and _Sb2O3 substantially. In addition, in consideration of stable float forming, it is preferable not to contain ZnO substantially. However, the glass substrate for a CIGS solar cell of the present invention is not limited to float molding, and may be manufactured by fusion molding.

The manufacturing method of the glass substrate for CIGS solar cells of this invention is demonstrated.

The glass substrate for CIGS solar cells of the present invention can be obtained by performing the melting, clarification, and molding steps in the same manner as in the production of conventional solar cell glass substrates, using each raw material component of the glass substrate so as to achieve the above-mentioned composition, In the subsequent annealing step, the SO ₂ treatment shown below is performed.

In the manufacturing method of the glass substrate for CIGS solar cells of this invention, it is important to perform the _SO2 treatment of this invention in an annealing process. By making the composition of the glass substrate into the range specified by the present invention and performing the following _SO2 treatment, the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the inside can be 0.7 or less, and the _Na2 ratio in the surface and inside of the glass substrate can be obtained. A glass substrate for a CIGS solar cell having an O content ratio of 0.4 to 1.1 and a ratio of Na in the surface layer of the glass substrate before and after heat treatment of 1.1 or more.

Hereinafter, the SO ₂ treatment of the present invention will be described.

In a conventional glass substrate manufacturing method, in order to prevent scratches on the glass surface during glass conveyance in the annealing step, it is known to blow SO ₂ gas to form a protective film made of sulfate. However, for the conventional blowing conditions, it is preferable to set the minimum necessary sulfate film in consideration of the prevention of yellowing when the silver electrode for display substrate is provided, the ease of cleaning the sulfate film, and the prevention of equipment corrosion. i.e. with as little _SO2 treatment as possible.

However, in the present invention, it is preferable that the ratio of Ca+Sr+Ba in the surface layer to the inside of the glass substrate is 0.7 or less, the _Na2O content ratio in the surface layer of the glass substrate to the inside is 0.4 to 1.1, and the Na2O content ratio in the surface layer of the glass substrate is reduced before and after heat treatment. The ratio of 1.1 or more makes the glass composition within the composition range specified in the present application, and the glass surface temperature is 500 to 700 ° C, the _SO concentration is 0.01 to 5 (volume) %, and the treatment time is 1 to 10 minutes. Under SO ₂ treatment.

In the SO ₂ treatment, the higher the glass surface temperature, the higher the SO ₂ gas concentration, and the longer the SO ₂ treatment time. In addition, the higher the airtightness of the annealing furnace, the easier it is to make the Ca+Sr+Ba in the surface layer and the inside of the glass substrate ratio and the Na ₂ O content ratio between the surface and interior of the glass substrate become smaller. In addition, even if the SO ₂ treatment is not performed in the annealing furnace, the SO ₂ treatment can be performed by reheating the annealed glass.

In addition, when the glass surface temperature is low, it is more difficult to reduce the ratio of Ca+Sr+Ba on the surface of the glass substrate to the inside than the ratio of Na ₂ O content on the surface of the glass substrate to the inside, so the desired surface may not be achieved. state.

In addition, since the glass substrate for CIGS solar cells of the present invention is an alkali glass substrate containing alkali metal oxides (Na ₂ O and K ₂ O), SO ₃ can be effectively used as a clarifier, and as a forming method, a float method is suitable and fusion method (pull down method).

In the manufacturing process of the glass substrate for solar cells, as a method of forming glass into a plate shape, it is preferable to use a float method that can easily and stably form a large-area glass substrate as solar cells increase in size.

A preferable embodiment of the manufacturing method of the glass substrate for CIGS solar cells of this invention is demonstrated.

First, molten glass obtained by melting raw materials is formed into a plate shape. For example, raw materials are prepared so that the obtained glass substrate has the above-mentioned composition, and the above-mentioned raw materials are continuously charged into a melting furnace and heated to about 1450° C. to about 1700° C. to obtain molten glass. Then, the molten glass is formed into a ribbon-shaped glass sheet using, for example, a float method.

Next, after the strip-shaped glass plate is pulled out from the float forming furnace, it is treated with SO ₂ in an annealing furnace when it is cooled to room temperature, and then cleaned to remove films such as sulfate, and cut to obtain CIGS solar cells. Glass base board.

In the solar cell manufacturing process, when forming an electrode film such as Mo or its base layer (such as SiO ₂ ) on the surface of a glass substrate, if the surface of the glass substrate is contaminated, the film may not be formed properly. Therefore, it is preferable to wash the glass substrate.

The method of cleaning is not particularly limited, and examples include cleaning with water, cleaning with a cleaning agent, cleaning with a brush or the like while spreading a slurry containing cerium oxide, and the like. When cleaning with a slurry containing cerium oxide, it is preferable to perform cleaning with an acidic cleaning agent such as hydrochloric acid or sulfuric acid thereafter.

On the surface of the glass substrate after cleaning, it is preferable that there are no unevenness on the surface of the glass substrate caused by dirt, the above-mentioned deposits such as cerium oxide, and the like. This is because unevenness on the film surface, variation in film thickness, pinholes in the film, and the like may occur when forming the above-mentioned electrode film, its underlayer, etc., and the power generation efficiency may decrease. The unevenness is preferably 20 nm or less in height difference.

The Na amount (atomic %) and/or Na ₂ O content ratio of the surface layer of the glass substrate is preferably uniform over the entire region of the glass substrate for CIGS solar cells. This is because if the Na content and/or Na ₂ O content ratio of the surface layer of the glass substrate is not uniform, there will be parts with low power generation efficiency, and the power generation efficiency of the solar cell may decrease due to the influence of these parts.

The glass substrate for CIGS solar cells of this invention is suitable also as a glass substrate for CIGS solar cells and a cover glass.

When the glass substrate for CIGS solar cells of the present invention is applied to a glass substrate, the thickness of the glass substrate is preferably 3 mm or less, more preferably 2 mm or less, further preferably 1.5 mm or less. In addition, the method of providing a CIGS photoelectric conversion layer on a glass substrate is preferably a method of producing at least a part of the CIGS layer as a photoelectric conversion layer by a selenization method. By using the glass substrate for CIGS solar cells of this invention, the heating temperature at the time of forming a photoelectric conversion layer can be made into 500-650 degreeC.

When using the glass substrate for CIGS solar cells of this invention only as a glass substrate, cover glass etc. are not specifically limited. As another example of the composition of a cover glass, soda lime glass etc. are mentioned.

When the glass substrate for a CIGS solar cell of the present invention is used as a cover glass, the thickness of the cover glass is preferably 3 mm or less, more preferably 2 mm or less, even more preferably 1.5 mm or less. In addition, the method of assembling the cover glass on the glass substrate having the photoelectric conversion layer is not particularly limited. By using the glass substrate for CIGS solar cells of this invention, the heating temperature can be made into 500-650 degreeC at the time of heating assembly.

When the glass substrate for a CIGS solar cell of the present invention is used in combination with a glass substrate for a CIGS solar cell and a cover glass, since the average thermal expansion coefficients are the same, thermal deformation during solar cell assembly does not occur, which is preferable.

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

The solar cell of the present invention has a glass substrate, a cover glass, and a photoelectric conversion layer disposed between the glass substrate and the cover glass. Moreover, at least a part of the photoelectric conversion layer is a Cu-In-Ga-Se photoelectric conversion layer formed by a selenization method, and at least the glass substrate among the above-mentioned glass substrate and the above-mentioned cover glass is Cu-In-Ga-Se of the present invention. Glass substrate for Se solar cells.

Hereinafter, the solar cell of the present invention will be described in detail using the drawings. It should be noted that the present invention is not limited to the accompanying drawings.

FIG. 1 is a cross-sectional view schematically showing an example of an embodiment of a solar cell of the present invention.

In FIG. 1 , a solar cell (CIGS solar cell) 1 of the present invention has a glass substrate 5 , a cover glass 19 , and a CIGS layer 9 between the glass substrate 5 and the cover glass 19 . It is preferable that the glass substrate 5 contains the glass substrate for CIGS solar cells of this invention demonstrated above. The solar cell 1 has a rear electrode layer of Mo film as a positive electrode 7 on a glass substrate 5 and a photoelectric conversion layer as a CIGS layer 9 thereon. The composition of the CIGS layer can be exemplified by Cu(In _1-X Ga _x )Se ₂ . x represents the composition ratio of In and Ga, and 0<x<1.

On the CIGS layer 9, there is a transparent conductive film 13 of ZnO or ITO via a CdS (cadmium sulfide) or ZnS (zinc sulfide) layer as a buffer layer 11, and there is an Al electrode (aluminum electrode) as a negative electrode 15 thereon. ) etc. Take out the electrodes. An antireflection film may be provided at necessary locations between these layers. In FIG. 1 , an antireflection film 17 is provided between the transparent conductive film 13 and the negative electrode 15 .

In addition, a protective glass 19 may be provided on the negative electrode 15, and if necessary, the negative electrode and the protective glass may be sealed with a resin or bonded with a transparent resin for adhesive. As a cover glass, the glass substrate for CIGS solar cells of this invention can be used.

In the present invention, the end of the photoelectric conversion layer or the end of the solar cell may be sealed. As a material used for sealing, the same material as the glass substrate for CIGS solar cells of this invention, other glass, resin, etc. are mentioned, for example.

It should be noted that the thickness of each layer of the solar cell shown in the drawings is not limited to the drawings.

Example

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

Examples (Examples 1-5, 7-29, 46-48) and comparative examples (Examples 6, 30-45, 49-50) of the glass substrate for CIGS solar cells of this invention are shown.

The raw materials of each component were prepared so as to achieve the compositions of Examples 1 to 50 shown in Tables 1 to 6, and 0.4 parts by mass of sulfate was added to the raw materials in terms of SO ₃ with respect to 100 parts by mass of the glass, using platinum The crucible was melted by heating at a temperature of 1600° C. for 3 hours. While melting, a platinum stirrer was inserted and stirred for 1 hour to homogenize the glass. Next, the molten glass is flowed out, formed into a plate shape, and then cooled. Then, it was ground to 30×30×1.1 mm, and both surfaces of 30×30 were mirror-finished and cleaned.

Then, for the glass substrates of Examples 1 to 5, 7 to 34, and 46 to 48, the pulling out from the above-mentioned float forming furnace and the _annealing in the annealing furnace were simulated. After SO treatment under _either condition, remove from the electric furnace and cool to room temperature. In addition, the glass substrates of Examples 6, 35-45, 49, and 50 were not treated with SO ₂ .

(SO ₂ treatment condition A)

Temperature: 600°C

SO _{concentration} : 2.5% by volume

Processing time: 5 minutes

(SO ₂ treatment condition B)

Temperature: 580°C

SO _{concentration} : 2.5% by volume

Processing time: 5 minutes

(SO ₂ treatment condition C)

Temperature: 600°C

_SO2 concentration: 0.2% by volume

Processing time: 10 minutes

(SO ₂ treatment condition D)

Temperature: 650°C

_SO2 concentration: 0.5% by volume

Processing time: 5 minutes

(SO ₂ treatment condition E)

Temperature: 550°C

SO _{concentration} : 2.5% by volume

Processing time: 5 minutes

(SO ₂ treatment condition F)

Temperature: 600°C

_SO2 concentration: 0.5% by volume

Processing time: 5 minutes

(SO ₂ treatment condition G)

Temperature: 600°C

_SO2 concentration: 0.2% by volume

Processing time: 5 minutes

(SO ₂ treatment condition H)

Temperature: 600°C

SO _{concentration} : 2.5% by volume

Processing time: 10 minutes

(SO ₂ treatment condition I)

Temperature: 600°C

SO _{concentration} : 2.5% by volume

Processing time: 5 minutes

The average coefficient of thermal expansion (unit: ×10 ^-7 /°C), the glass transition temperature (Tg) (unit:°C), the Na ₂ O content ratio between the surface and the inside of the glass substrate, and the ratio between the surface layer and the inside of the glass substrate were measured for the glass substrate thus obtained. The ratio of Ca+Sr+Ba in the interior and the ratio of Na in the surface layer of the glass substrate before and after heat treatment are shown in Tables 1 to 5 below.

In addition, the power generation efficiency (unit: %), series resistance (Rser, unit: Ω) and free carrier density (unit: 10 ¹⁵ /cm ³ ) of the obtained glass substrate were evaluated, and are shown in the following Tables 1- Table 5. The measurement method and evaluation method of each physical property are shown below.

(1) Tg: Tg is a value measured using a differential thermal dilatometer (TMA), and is calculated|required by JISR3103-3 (2001 year).

(2) Average coefficient of thermal expansion at 50 to 350°C: Measured using a differential thermal expansion meter (TMA), and obtained from JIS R3102 (1995).

(3) Na ₂ O content ratio between the surface and inside of the glass substrate: Measured under conditions of a bulb voltage of 50 kV and a current of 50 mA using a fluorescent X-ray measuring device (manufactured by Rigaku Co., Ltd., RIX3000). Grinding was performed with an aqueous slurry of cerium oxide in grinding from the surface of the glass substrate to 5000 nm.

(4) The ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the inside:

The amounts (atomic %) of Ca, Sr, and Ba at depths of 10 nm, 20 nm, 30 nm, 40 nm, and 5000 nm from the surface of the glass substrate were measured using an X-ray photoelectron spectrometer (manufactured by Ulvac-phi, ESCA5500). Sputter etching with C ₆₀ ion beam for grinding from the surface of the glass substrate to 10-40nm, grinding to 4000nm with aqueous slurry of cerium oxide for grinding from the surface of the glass substrate to 5000nm Afterwards, sputter etching was performed using a C ₆₀ ion beam.

Calculate the average total amount (atomic %) of Ca, Sr, and Ba at depths of 10 nm, 20 nm, 30 nm, and 40 nm from the surface of the glass substrate and the total amount of Ca, Sr, and Ba at a depth of 5000 nm from the surface of the glass substrate (atomic %) ratio.

(5) The ratio of Na in the surface layer of the glass substrate before and after heat treatment:

The amount of Na (atomic %) at depths of 10 nm, 20 nm, 30 nm, and 40 nm from the surface of the glass substrate was measured using an X-ray photoelectron spectrometer (manufactured by Ulvac-phi, ESCA5500). Sputter etching was performed with a C ₆₀ ion beam for grinding from the surface of the glass substrate to 10 to 40 nm.

Then, the glass substrate was heated up to 600°C at 10°C/min in _N2 atmosphere (simulated oxygen-free state) in an electric furnace, kept at 600°C for 60 minutes, cooled at 2°C/min, and annealed to room temperature.

Then, the amount of Na (atomic %) at depths of 10 nm, 20 nm, 30 nm, and 40 nm from the surface of the glass substrate was measured by the above-mentioned method.

The ratio of the average Na amount (atomic %) at a depth of 10 to 40 nm from the surface of the glass substrate before and after heat treatment at 600° C. for 1 hour in N ₂ atmosphere was obtained.

(6) Power generation efficiency: CIGS solar cell samples produced by the procedure described below were measured by the following procedure using the glass substrates for solar cells of Examples 1 to 50 obtained above.

The obtained glass plate was used as a glass substrate of a solar cell, and a solar cell for evaluation was produced as follows, and the power generation efficiency was evaluated using the solar cell. The results are shown in Table 1.

The preparation of the solar cell for evaluation will be described below using FIGS. 2A , 2B and 3 and their reference numerals. The layer configuration of the solar cell for evaluation is substantially the same as that of the solar cell shown in FIG. 1 except that the solar cell shown in FIG. 1 does not include the cover glass 19 and the antireflection film 17 .

The obtained glass plate was processed into a size of 3 cm x 3 cm and a thickness of 1.1 mm to obtain a glass substrate. A molybdenum film was formed as the positive electrode 7a on the glass substrate 5a using a sputtering apparatus. Film formation was performed at room temperature, and a Mo film with a thickness of 500 nm was obtained.

On the positive electrode 7a (molybdenum film), a CuGa alloy layer was formed using a CuGa alloy target using a sputtering apparatus, and an In layer was subsequently formed using an In target to form an In—CuGa precursor film. Film formation was carried out at room temperature. The composition of the precursor film obtained by fluorescent X-ray measurement was adjusted so that the Cu/(Ga+In) ratio (atomic ratio) was 0.8 and the Ga/(Ga+In) ratio (atomic ratio) was 0.25. layer thickness, a precursor film with a thickness of 650 nm was obtained.

Using RTA (Rapid Thermal Annealing: rapid thermal annealing) equipment, in a mixed atmosphere of argon and hydrogen selenide (hydrogen selenide is 5% by volume relative to argon; hereinafter referred to as "hydrogen selenide atmosphere"), and hydrogen sulfide mixed The precursor film was heat-treated in an atmosphere (5% by volume of hydrogen sulfide relative to argon; hereinafter referred to as "hydrogen sulfide atmosphere"). First, as the first stage, Cu, In, and Ga were reacted with Se at 500° C. for 10 minutes in a hydrogen selenide atmosphere. Then, after replacing it with a hydrogen sulfide atmosphere, as a second stage, the temperature was maintained at 580° C. for 30 minutes to grow CIGS crystals, thereby obtaining CIGS layer 9 a. The resulting CIGS layer 9a had a thickness of 2 μm.

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

Then, a transparent conductive film 13a was formed on the CdS layer by the following method using a sputtering apparatus. First, a ZnO layer was formed using a ZnO target, and then, an AZO layer was formed using an AZO target (ZnO target containing 1.5% by weight of Al ₂ O ₃ ). The film formation of each layer was performed at room temperature, and the transparent conductive film 13a which consists of two layers with a thickness of 480 nm was obtained.

An aluminum film with a film thickness of 1 μm was formed on the AZO layer of the transparent conductive film 13a by EB evaporation method as a U-shaped negative electrode 15a (U-shaped electrode length (8 mm in length, 4 mm in width), and electrode width of 0.5 mm).

Finally, the CIGS layer 9a was scraped from the transparent conductive film 13a side with a mechanical scribe to perform unitization as shown in FIGS. 2A and 2B . FIG. 2A is a plan view of one solar battery cell, and FIG. 2B is an AA' sectional view in FIG. 2A . One cell has a width of 0.6 cm, a length of 1 cm, and an area of 0.51 cm ² excluding the negative electrode 15 a. As shown in FIG. 3 , a total of 8 cells are obtained on one glass substrate 5 a.

On a solar simulator (manufactured by Yamashita Denso Co., Ltd., YSS-T80A), a CIGS solar cell for evaluation (a glass substrate 5a for evaluation on which the above-mentioned 8 cells were produced) was installed, and the positive electrode 7a coated with an InGa solvent in advance The positive terminal (not shown) is connected to the voltage generator, and the negative terminal 16a is connected to the voltage generator at the lower end of the U-shape of the negative electrode 15a. The temperature in the solar simulator was constantly controlled at 25° C. with a temperature regulator. The simulated sunlight was irradiated, and after 10 seconds, the voltage was changed from -1V to +1V at intervals of 0.015V, and the current value of each of the eight cells was measured.

From the current and voltage characteristics at the time of this irradiation, the power generation efficiency was calculated using the formula (1). Table 1 shows the value of the most efficient cell among the eight cells as the value of the power generation efficiency of each glass substrate. The illuminance of the light source used in the test was 0.1 W/cm ² .

Power generation efficiency [%] = Voc [V] × Jsc [A/cm ² ] × FF [dimensionless] × 100 / illuminance of the light source used in the test [W/cm ² ] Formula (1)

The power generation efficiency is obtained by multiplying the open circuit voltage (Voc), the short circuit current density (Jsc) and the curve factor (FF).

It should be noted that the open circuit voltage (Voc) is the output when the terminal is opened, and the short circuit current (Isc) is the current at the time of short circuit. The short-circuit current density (Jsc) is a value obtained by dividing Isc by the area of the cell other than the negative electrode.

In addition, the point at which the maximum output is provided is referred to as the maximum output point, the voltage at this point is referred to as the maximum voltage value (Vmax), and the current is referred to as the maximum current value (Imax). The value obtained by dividing the product value of the maximum voltage value (Vmax) and the maximum current value (Imax) by the product value of the open circuit voltage (Voc) and the short circuit current (Isc) was obtained as a curve factor (FF). Using the above-mentioned values, the power generation efficiency was calculated.

(7) Series resistance (Rser)

The series resistance (Rser) is the resistance component when the current flows through the element, and it is the gradient of the current relative to the voltage when the voltage is equal to the open circuit voltage (Voc) when the light is irradiated. Use this relationship to find the series resistance.

(8) Free carrier density

The carrier density of the CIGS solar cell is obtained by the DLCP (Drive Level Capacitance Profiling) method described in the following document 1. During the measurement, use an LCR meter: E4980A (manufactured by Agilent Technologies Co., Ltd.), set the measurement frequency to 11KHz, measure in the range of Vac+Vdc=-300～+200 [mV], set Vac+Vcd=0[ mV] as the carrier density.

In addition, it is known that the carrier density of CIGS solar cells changes due to light irradiation. Therefore, in order to remove the carriers generated by light irradiation, the analysis chamber was kept at 50°C for more than 30 minutes before measurement, and then The temperature was lowered without irradiating light, and the measurement was started.

The carrier density of the CIGS solar cell was measured while increasing the temperature by 10K in the range of 20K to 300K. On the low temperature side of about 150K or less, the carrier density of free carriers was measured. When the temperature is further increased from about 150K, the carrier density increases due to deep level defects, thereby causing a sharp increase in the carrier density. Therefore, the free carrier density is set as a measured value at 100K before the measured carrier density increases due to deep level defects.

Document 1: Heath, Jennifer T., J.David Cohen, William N. Shafarman."Bulk and MetaStable Defects in CuIn(1-x)Ga(x)Se2 Thin Films Using Drive Level Capacitance Profiling."J.of Applied Physics. 95.3(2004).

The residual amount of _SO3 in the glass is 100-500ppm.

Table 1

weight% example 1 Example 2 Example 3 Example 4 Example 5 Example 6 SiO ₂ 60.6 60.6 60.6 60.6 60.6 60.6 Al ₂ O ₃ 9.5 9.5 9.5 9.5 9.5 9.5 MgO 5.0 5.0 5.0 5.0 5.0 5.0 CaO 6.1 6.1 6.1 6.1 6.1 6.1 SrO 1.6 1.6 1.6 1.6 1.6 1.6 BaO 0.1 0.1 0.1 0.1 0.1 0.1 _ZrO2 2.5 2.5 2.5 2.5 2.5 2.5 Na ₂ O 5.0 5.0 5.0 5.0 5.0 5.0 K ₂ O 9.6 9.6 9.6 9.6 9.6 9.6 MgO+CaO+SrO+BaO 12.8 12.8 12.8 12.8 12.8 12.8 CaO+SrO+BaO 7.8 7.8 7.8 7.8 7.8 7.8 SrO+BaO 1.7 1.7 1.7 1.7 1.7 1.7 _Na2O + _K2O 14.6 14.6 14.6 14.6 14.6 14.6 _Na2O /(CaO+SrO+BaO) 0.64 0.64 0.64 0.64 0.64 0.64 Average thermal expansion coefficient×10 ⁷ /℃ 84 84 84 84 84 84 Tg(°C) 633 633 633 633 633 633 Na ₂ O content on the surface of the glass substrate a (%) 3.7 4.0 4.1 4.2 4.5 5.2 Na ₂ O content b(%) inside the glass substrate 5.2 5.2 5.2 5.2 5.2 5.2 Ratio of Na ₂ O content on the surface of the glass substrate to that in the interior a/b 0.71 0.77 0.79 0.81 0.87 1.00 The amount of Ca+Sr+Ba on the surface of the glass substrate A (atomic %) <0.05 0.10 0.70 0.95 1.27 3.22 Amount B of Ca+Sr+Ba inside the glass substrate (atomic %) 3.3 3.3 3.3 3.3 3.4 3.3 Ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the inside (A/B) less than 0.02 0.03 0.21 0.29 0.37 0.98 Na (before heat treatment) C (atomic %) on the surface of the glass substrate 1.1 0.9 1.1 1.3 2.3 3.3 Na (after heat treatment) D (atomic %) on the surface of the glass substrate 2.8 2.8 2.9 2.9 2.9 3.0 Ratio D/C of Na in the surface layer of the glass substrate before and after heat treatment 2.55 3.11 2.64 2.23 1.24 0.91 SO ₂ treatment conditions A B D. C G - Power Generation Efficiency (%) 14.7 14.9 14.7 14.7 12.9 12.4 Rser(Ω) 2.3 2.3 3.0 2.3 2.7 5.0 Free carrier density (10 ¹⁵ /cm ³ ) 3.9 1.5

Table 6

weight% Example 46 Example 47 Example 48 Example 49 Example 50 SiO ₂ 61.9 53.0 53.0 61.9 53.0 Al ₂ O ₃ 9.6 12.0 12.0 9.6 12.0 MgO 7.0 0.5 0.5 7.0 0.5 CaO 4.4 6.0 6.0 4.4 6.0 SrO 0.8 11.5 11.5 0.8 11.5 BaO 0.6 3.0 3.0 0.6 3.0 _ZrO2 3.4 4.5 4.5 3.4 4.5 Na ₂ O 4.9 5.5 5.5 4.9 5.5 K ₂ O 7.4 4.0 4.0 7.4 4.0 MgO+CaO+SrO+BaO 12.8 21.0 21.0 12.8 21.0 CaO+SrO+BaO 5.8 20.5 20.5 5.8 20.5 SrO+BaO 1.4 14.5 14.5 1.4 14.5 _Na2O + _K2O 12.3 9.5 9.5 12.3 9.5 _Na2O /(CaO+SrO+BaO) 0.84 0.27 0.27 0.84 0.27 Average thermal expansion coefficient×10 ⁷ /℃ 76 84 84 76 84 Tg(°C) 657 665 665 657 665 Na ₂ O content on the surface of the glass substrate a (%) 4.8 6.1 5.9 5.3 5.8 Na ₂ O content b(%) inside the glass substrate 5.3 5.8 5.8 5.3 5.8 Ratio of Na ₂ O content on the surface of the glass substrate to that in the interior a/b 0.91 1.05 1.02 1.00 1.00 The amount of Ca+Sr+Ba on the surface of the glass substrate A (atomic %) 1.00 2.30 4.40 2.01 7.60 Amount B of Ca+Sr+Ba inside the glass substrate (atomic %) 2.1 7.7 7.7 2.1 7.7 The ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the inside (A/B) 0.48 0.30 0.57 0.96 0.99 Na (before heat treatment) C (atomic %) on the surface of the glass substrate 1.8 4.2 4.2 3.1 4.0 Na (after heat treatment) D (atomic %) on the surface of the glass substrate 2.7 4.8 4.7 2.8 4.7 Ratio D/C of Na in the surface layer of the glass substrate before and after heat treatment 1.50 1.14 1.12 0.90 1.18 SO ₂ treatment conditions G E. f - - Power Generation Efficiency (%) 13.4 13.4 13.1 12.9 12.7 Rser(Ω) 6.2 3.0 3.3 4.8 3.7 Free carrier density (10 ¹⁵ /cm ³ ) - 1.9 2.1 - 1.7

As can be seen from Tables 1 to 6, in the glass substrates of the examples (Examples 1 to 5, 7 to 29, and 46 to 48), the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior is 0.7 or less, and the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior The Na ₂ O content ratio of the glass substrate is 0.4 to 1.1, and the ratio of Na in the surface layer of the glass substrate before and after heat treatment is 1.1 or more, and the glass transition temperature Tg is high, the power generation efficiency is also high, and the series resistance is also low. Therefore, both high power generation efficiency and high glass transition temperature can be achieved.

Moreover, in the glass substrate of the Example (Example 3), the free carrier density was high, and the improvement of the crystal quality was confirmed.

In addition, the average coefficient of thermal expansion of the glass substrates of Examples (Examples 1 to 5, 7 to 29, and 46 to 48) is 70×10 ^-7 to 100×10 ^-7 /°C. Therefore, when assembling the solar cell of the present invention (Concretely, when a glass substrate having a CIGS photoelectric conversion layer is thermally bonded to a cover glass), the glass substrate is less likely to be deformed, and stable power generation efficiency can be easily obtained.

In the glass substrates of comparative examples (Examples 30 to 32), the content of Na ₂ O was as much as 13.1%, so the Tg was lower than 580°C, and the substrate was deformed during CIGS film formation, which might hinder battery production.

In addition, the amount of Na ₂ O in the glass substrates of the comparative examples (Examples 33 and 34) was as little as 0.5%. Therefore, although SO ₂ treatment was performed, the amount of Na after heat treatment on the surface of the glass substrate was less than 0.3 atomic %, and the power generation efficiency Low.

In addition, as can be seen from Tables 1 and 5, in the glass substrates of comparative examples (Examples 6, 35 to 43) that were not treated with SO ₂ , although the composition of each raw material was within the scope of the present invention, it was not treated with SO ₂ , so The ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the interior is 0.90-1.00, which is large, and the ratio of Na in the surface layer of the glass substrate before and after heat treatment is 0.78-1.00, which is small, so it is difficult to obtain power generation efficiency.

The free carrier density of the glass substrate of the comparative example (Example 6) was low, and the improvement of the crystal quality was not confirmed.

The _Na2O /(CaO+SrO+BaO) of the glass substrate of comparative example (example 44) is 1.62, and is big, and also does not carry out SO ₂ process, therefore, the ratio of Ca+Sr+Ba in the surface layer of the glass substrate and inside is 0.97, and the ratio of Na in the surface layer of the glass substrate before and after heat treatment was 0.67, which was small, so it was difficult to obtain power generation efficiency. In addition, since the content of Na ₂ O is as much as 13.1%, the Tg is lower than 580° C., and the substrate may be deformed during CIGS film formation, which may hinder battery production.

The glass substrate of Comparative Example (Example 45) was not treated with SO ₂ , so the ratio of Na in the surface layer of the glass substrate before and after heat treatment was 0.66, which was small, and the amount of Na ₂ O was 0.5%, which was small, so the power generation efficiency was also low.

In addition, as can be seen from Table 6, in the glass substrates of Examples (46-48), the ratio of Ca+Sr+Ba in the surface layer of the glass substrate to the inside is 0.7 or less, and the ratio of Na ₂ O content in the surface layer to the inside of the glass substrate is 0.4-48. 1.1, the ratio of Na in the surface layer of the glass substrate before and after heat treatment is 1.1 or more, and the glass transition temperature Tg is high, and the power generation efficiency is also high. Moreover, the series resistance of the glass substrate of Example (47, 48) was also low. Therefore, both high power generation efficiency and high glass transition temperature can be achieved.

Moreover, the free carrier density of the glass substrate of an Example (Example 47, 48) was high, and the improvement of the crystal quality was confirmed. On the other hand, in the glass substrates of comparative examples (Examples 49 and 50), the ratio of Ca+Sr+Ba in the surface layer to the inside of the glass substrate was 0.96 or more, and the _SO2 treatment was not performed, so the power generation efficiency was also low.

As mentioned above, although this invention was demonstrated in detail, these are only examples, this invention can also be implemented in another form, and various changes can be made in the range which does not deviate from the summary.

This application is based on the JP Patent application (Japanese Patent Application No. 2012-012875) for which it applied on January 25, 2012, The whole content is taken in this specification by reference.

Industrial applicability

The Cu-In-Ga-Se solar cell glass substrate produced by the selenization method of the present invention is suitable as a CIGS solar cell glass substrate and cover glass produced by the selenization method, but it can also be used for other solar cell substrates, Protective glass.

Moreover, by using the glass substrate for Cu-In-Ga-Se solar cells produced by the selenization method of this invention, the solar cell with good power generation efficiency can be provided.

Label description

1 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 pole

17 anti-reflection film

19 protective glass

Claims (4)

1. a Cu-In-Ga-Se used for solar batteries glass substrate of making by selenizing method, wherein,

Apart from the degree of depth of glass baseplate surface, be the average total amount (atom %) of Ca, Sr between 10～40nm and Ba being Ca, Sr and the Ba at 5000nm place with the degree of depth apart from glass baseplate surface, the ratio of total amount (atom %) is below 0.7,

The Na that utilizes fluorescent X-ray to measure from glass baseplate surface ₂o content (quality %) and the Na that utilizes fluorescent X-ray to measure from the face of removing from glass baseplate surface the glass of 5000nm ₂the ratio of O content (quality %) is 0.4～1.1,

Apart from the degree of depth of glass baseplate surface, be that average N a amount (atom %) between 10～40nm is at N ₂ratio under atmosphere, before and after the thermal treatment of 600 ℃, 1 hour is more than 1.1,

More than the degree of depth 5000nm apart from glass baseplate surface, in the quality percentage based on following oxide compound, contain 50～72% SiO ₂, 1～15% Al ₂o ₃, 0～10% MgO, 0.1～11% CaO, 0～13% SrO, 0～11% BaO, 1～11% Na ₂o, 2～21% K ₂o, 0～10.5% ZrO ₂, 4～25% MgO+CaO+SrO+BaO, 2～23% CaO+SrO+BaO, 8～22% Na ₂o+K ₂o, and Na ₂o/ (CaO+SrO+BaO)≤1.2,

The second-order transition temperature of described glass substrate is that 580 ℃ of above, mean thermal expansion coefficientses are 70 * 10 ^-7～100 * 10 ^-7/ ℃.

2. the Cu-In-Ga-Se used for solar batteries glass substrate of making by selenizing method as claimed in claim 1, wherein,

The described degree of depth apart from glass baseplate surface is the average total amount (atom %) of Ca, Sr between 10～40nm and Ba to be Ca, Sr and the Ba at 5000nm place with the degree of depth apart from glass baseplate surface the ratio of total amount (atom %) is below 0.5,

The described Na that utilizes fluorescent X-ray to measure from glass baseplate surface ₂o content (quality %) and the Na that utilizes fluorescent X-ray to measure from the face of removing from glass baseplate surface the glass of 5000nm ₂the ratio of O content (quality %) is 0.5～0.87,

The described degree of depth apart from glass baseplate surface is that the average N a between 10～40nm measures (atom %) at N ₂ratio under atmosphere, before and after the thermal treatment of 600 ℃, 1 hour is more than 1.5,

More than the degree of depth 5000nm apart from glass baseplate surface, in the quality percentage based on following oxide compound, contain 0.5～9% ZrO ₂, 2.5～19% CaO+SrO+BaO, 0～16% SrO+BaO.

3. the Cu-In-Ga-Se used for solar batteries glass substrate of making by selenizing method as claimed in claim 1 or 2, wherein,

The described degree of depth apart from glass baseplate surface is the average total amount (atom %) of Ca, Sr between 10～40nm and Ba to be Ca, Sr and the Ba at 5000nm place with the degree of depth apart from glass baseplate surface the ratio of total amount (atom %) is below 0.35,

The described Na that utilizes fluorescent X-ray to measure from glass baseplate surface ₂o content (quality %) and the Na that utilizes fluorescent X-ray to measure from the face of removing from glass baseplate surface the glass of 5000nm ₂the ratio of O content (quality %) is 0.6～0.84,

The described degree of depth apart from glass baseplate surface is that the average N a between 10～40nm measures (atom %) at N ₂ratio under atmosphere, before and after the thermal treatment of 600 ℃, 1 hour is more than 2.0,

More than the degree of depth 5000nm apart from glass baseplate surface, in the quality percentage based on following oxide compound, contain 3～15% CaO+SrO+BaO, 0～8% SrO+BaO.

4. a solar cell, the photoelectric conversion layer of the Cu-In-Ga-Se that it has glass substrate, protective glass, the selenizing method of passing through between described glass substrate and described protective glass that is disposed at is made,

In described glass substrate and described protective glass, at least described glass substrate is the Cu-In-Ga-Se used for solar batteries glass substrate that in claim 1～3, the selenizing method of passing through described in any one is made.