TW201724539A - Solar cell glass substrate and solar cell - Google Patents

Abstract

The present invention provides a glass substrate for a solar cell which is excellent in alkali diffusion energy and has high power generation efficiency, and a solar cell using the same. A glass substrate for a solar cell, comprising a ruthenium-containing glass substrate at least on a first main surface, wherein the ruthenium-containing layer has an atomic percentage of 15% or more and 45% or less with respect to the total atomic weight and 0.4 % or more and 30% or less of carbon, and the surface roughness Ra of the ruthenium-containing layer is 0.3 nm or more and less than 2 nm.

Description

Solar cell glass substrate and solar cell

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

In a compound solar cell, a film of a semiconductor is formed on a glass substrate as a photoelectric conversion layer. As a semiconductor for a solar cell, a group semiconductor of a chalcopyrite crystal structure, a group 11-13, a group 11-16 compound semiconductor, or a cubic crystal system or a hexagonal system group 12-16 compound semiconductor, etc. Light in the wavelength range of near infrared rays has a large absorption coefficient. Therefore, it is expected to be a material for high-efficiency thin film solar cells. A representative example is Cu(In,Ga)Se ₂ (hereinafter, referred to as "CIGS").

As the glass substrate for a solar cell, it is known that the photoelectric conversion efficiency of a solar cell can be improved by using an alkali metal, particularly a glass substrate containing sodium (Na) or potassium (K). In the case where a photoelectric conversion layer such as a CIGS film is formed on a glass substrate, the glass substrate is subjected to heat treatment in the step of forming the photoelectric conversion layer, and the alkali metal atoms contained in the glass substrate are gradually diffused from the surface of the glass substrate to Photoelectric conversion layer. Therefore, the defect density of the photoelectric conversion layer is lowered, and the carrier concentration is increased, with the result that the photoelectric conversion efficiency can be improved.

From the viewpoint of reducing the environmental burden, it is desired to save energy in the manufacture of a solar cell, and to seek a low-temperature process of heat treatment in the formation step of the photoelectric conversion layer. Further, the demand for the cost reduction of the solar cell substrate has been increasing year by year, and in particular, it has been sought to provide a glass substrate which is inexpensive to provide most of the weight of the solar cell panel. In the low-temperature process, alkali metal is likely to diffuse into the photoelectric conversion layer, and as an example of a glass substrate which is inexpensive, it is widely known as soda-lime glass which is widely used for construction glass and the like. Advanced technical literature

Patent Document 1: Japanese Patent No. 5575163 Patent Document 2: Japanese Patent Publication No. 2015-506890

SUMMARY OF THE INVENTION Problems to be Solved by the Invention A predetermined film is sometimes formed on the surface of a soda lime glass substrate. In the past, there is a method of preventing deterioration of characteristics such as optical characteristics due to diffusion of an alkali component, particularly a sodium component, by using such a film-attached glass substrate. Therefore, the film-attached glass substrate is used for solar cell applications to prevent deterioration of various characteristics, but on the other hand, there is a demand for an increase in alkali diffusion.

Patent Document 1 proposes that when high strain point glass is used for a glass substrate of a CIS-based thin film solar cell in order to prevent deformation, since the glass alkali concentration at a high strain point is low, 3 to 12 nm is thinly formed on a glass substrate. Further, as the ceria film of the alkali control layer, Na is further added to the metal precursor film forming the CIS-based light absorbing layer. In Patent Document 1, the cerium oxide film functions to suppress the diffusion of the alkali component as the alkali control layer, but promotes the diffusion of the alkali component by making the film thickness thin. However, in Patent Document 1, only Na is not added to the metal precursor film because there is no sufficient alkali component to diffuse. Further, in Patent Document 1, a high strain point glass having a low Na amount is used, and the alkali control in the soda lime glass is not reviewed.

Patent Document 2 proposes that when sodium ions are diffused from a substrate made of borosilicate glass or soda lime glass to a functional thin layer on the surface, the characteristics of the thin layer of the function may be deteriorated, so that the glass substrate is deteriorated. The surface forms a layer of yttria (SiO _x C _y ). In Patent Document 2, in the automotive sheet glass or the residential sheet glass, the oxycarbonitride layer is formed into a two-layer structure having different carbon contents depending on the coloring problem. In Patent Document 2, in order to prevent the diffusion of sodium ions, the total thickness of the oxynitride layer is 10 to 200 nm, and particularly preferably 40 to 70 nm. As disclosed in Patent Document 2, the oxynitride layer is used to prevent sodium ions from diffusing from the glass substrate. Further, since the oxynitride layer is made thick to prevent the diffusion of sodium ions, there is a problem that the alkali diffusion energy cannot be sufficiently obtained once the glass substrate as described above is transferred to a solar cell.

An object of the present invention is to provide a glass substrate for a solar cell which is excellent in alkali diffusion energy and has high power generation efficiency, and a solar battery using the same. Means to solve the problem

The present invention is based on the following constitution. (1) A glass substrate for a solar cell, comprising a ruthenium-containing glass substrate at least on a first main surface, wherein the ruthenium-containing layer has an atomic percentage of 15% or more and 45% or less with respect to the total atomic weight. Thereafter, the carbon is 0.4% or more and 30% or less, and the surface roughness Ra of the ruthenium-containing layer is 0.3 nm or more and less than 2 nm. (2) The glass substrate for a solar cell according to the above aspect, wherein the ruthenium-containing layer further contains, in atom%, oxygen of 30% or more and 65% or less with respect to the total atomic weight. (3) The glass substrate for a solar cell according to (1) or (2), wherein an absolute difference in reflectance between the surface of the ruthenium-containing layer and the surface of the bismuth glass substrate of the glass substrate at an incident angle of 5° and a wavelength of 550 nm The value is 0.02% or more. (4) The glass substrate for a solar cell according to any one of (1) to (3), wherein the glass having a depth of 5000 nm or more from the first main surface of the glass substrate has a composition based on oxidation The mass percentage of the substance is expressed as: 60 to 75% of SiO ₂ , 0.25 to 8% of Al ₂ O ₃ , 7 to 20% of Na ₂ O, more than 0 and less than 9% of K ₂ O, 0 to 10 % of MgO, and 0 to 15% of CaO. (5) A solar cell for a solar cell according to any one of (1) to (4), wherein the photoelectric conversion layer is provided on a surface of the glass substrate having a ruthenium-containing layer. (6) The solar cell according to (5), wherein the photoelectric conversion layer is composed of a Cu(In,Ga)Se ₂ compound semiconductor. In the present specification, the "~" of the numerical range is used as the lower limit and the upper limit, and unless otherwise specified, the following "~" in the present specification is the same. The meaning to use. Effect of the invention

According to the present invention, it is possible to provide a glass substrate for a solar cell which is excellent in alkali diffusion energy and has high power generation efficiency, and a solar battery using the same.

MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described. The glass substrate for a solar cell according to an embodiment of the present invention is a glass substrate having a ruthenium-containing layer at least on the first main surface, wherein the ruthenium-containing layer has an atomic weight relative to the entire atomic percentage. It is 15% or more and 35% or less of ruthenium and 0.4% or more and 30% or less of carbon, and the surface roughness Ra of the ruthenium-containing layer is 0.3 nm or more and less than 2 nm. According to the present embodiment, it is possible to provide a glass substrate for a solar cell which is excellent in alkali diffusion energy and has high power generation efficiency.

By doping the alkali metal such as a Na atom and a K atom toward a photoelectric conversion layer such as a CIGS film, the solar cell defect density can be lowered and the carrier concentration can be increased. The Na atom and the K atom are diffused from the surface of the glass substrate to the photoelectric conversion layer by heat treatment in the forming step of the photoelectric conversion layer. The doping of the alkali metal is made possible by including an oxide containing an alkali metal such as Na ₂ O or K ₂ O in the glass substrate raw material in which the photoelectric conversion layer is formed. In the present embodiment, the alkali diffusion energy can be further improved by forming a ruthenium-containing layer having a specific surface roughness and a predetermined composition on the glass substrate. Further, when the soda lime glass itself is used as a glass substrate for a solar cell, since the blending ratio of the alkali metal or the alkaline earth metal is high, the surface of the glass substrate is likely to precipitate carbonate, which causes a problem of coking. On the other hand, by forming the ruthenium-containing layer as described above, it is possible to suppress the coking and enhance the alkali diffusion energy.

When the ruthenium-containing layer is formed thickly on the glass substrate, the ruthenium-containing layer functions as an alkali component barrier layer to lower the alkali diffusion energy. However, since the ruthenium-containing layer is formed to some extent on the glass substrate, the alkali diffusion energy can be improved. The ruthenium containing layer which increases the degree of alkali diffusion energy can be evaluated by its surface roughness and film composition. In the present invention, it has been found that the surface roughness Ra of the ruthenium-containing layer is 0.3 nm or more, which can enhance the alkali diffusion energy. Here, the surface roughness Ra is based on JIS B0601-2001. It is presumed that this is caused by the following reasons: the surface of the ruthenium-containing layer is formed with a nano-scale irregular shape, so that the surface area of the surface of the glass substrate is increased, and the interaction between the glass surface and the element containing the ruthenium layer is formed. The surface of the glass is activated, or the surface of the glass is covered to some extent by the ruthenium-containing layer, so that alkali desorption due to SO ₂ gas is suppressed. It is speculated that in this way, the alkali component is promoted to diffuse from the glass substrate to the ruthenium containing layer. The surface roughness Ra of the ruthenium-containing layer is preferably 0.4 nm or more, more preferably 0.5 nm or more. If the surface of the ruthenium-containing layer becomes too thick, there is a problem that the battery characteristics are deteriorated. From this point of view, the surface roughness Ra of the ruthenium containing layer is preferably less than 2 nm, and preferably 1.8 nm or less, more preferably 1.5 nm or less. Here, the surface roughness Ra can be measured using an atomic force microscope (AFM).

The ruthenium-containing layer formed on the glass substrate is a layer containing ruthenium as an essential component, and is preferably a layer containing SiO ₂ . The preferred form of the ruthenium-containing layer is a layer containing three or more elements including ruthenium. The element constituting the ruthenium-containing layer is preferably a layer containing ruthenium, oxygen, and carbon, and preferably contains a layer of carbon in SiO ₂ as a main component (hereinafter, simply referred to as "SiOC layer"). The ruthenium containing layer preferably contains SiO ₂ or SiOC as a main component. The "main component" means the amount of each element constituting SiO ₂ or SiOC is 50 atom% or more with respect to the total amount of elements. In the ruthenium-containing layer, the ruthenium component is preferably 15 to 45 atom%, preferably 17 to 35 atom%, based on the total number of atoms constituting the ruthenium-containing layer. That is, in the ruthenium-containing layer, the ruthenium component, that is, the ruthenium atom is preferably 15 to 45 atom%, preferably 17 to 35 atom%, based on the total number of atoms constituting the ruthenium-containing layer. In the ruthenium-containing layer, the carbon component, that is, the carbon atom is preferably 0.4 to 30 atom% with respect to the total number of atoms constituting the ruthenium-containing layer. The carbon component is preferably 0.5 atom% or more, more preferably 0.6 atom% or more, and more preferably 0.7 atom% or more. It is preferably 1 to 20 atom%. It is presumed that the formation of irregularities on the glass surface is promoted by containing a carbon component in this range. Further, it is also presumed that the surface area of the glass is useful for activation. In the ruthenium-containing layer, the oxygen component, that is, the oxygen atom is preferably 30 to 65 atom%, preferably 50 to 62 atom%, based on the total number of atoms constituting the ruthenium-containing layer. Here, the method of measuring the atomic content can be measured using, for example, X-ray photoelectron spectroscopy (XPS). The measurement method is not limited to XPS.

The absolute value of the difference between the reflectance at the wavelength of 550 nm and the reflectance at the wavelength of 550 nm on the surface of the glass substrate having the ruthenium-containing layer on the glass substrate is preferably 0.02% or more at 5° incidence. Hereinafter, there is a case where the difference is called a difference in reflectance. In the present invention, the term "primary glass substrate" means a state having the same composition as that of a glass substrate having a ruthenium-containing layer, and a film containing a ruthenium-containing layer is not formed on both surfaces thereof. The reflectance difference can be obtained by first measuring the reflectance of the surface of the glass substrate, secondly forming a germanium-containing layer on the glass substrate, and then measuring the reflectance of the germanium-containing layer formed on the glass substrate. The reflectance of the surface of the glass substrate measured at the beginning means the reflectance of the glass substrate to be the reference, and even if it is a glass substrate other than the glass substrate having the ruthenium layer, as long as it has a glass containing a ruthenium layer. If the substrate has the same composition, it can also be replaced by its reflectance. The reflectance can be measured using a spectroscope and measuring at a wavelength of 550 nm and 5°.

It was confirmed that the yttrium-containing layer was formed by the difference in reflectance of 0.02% or more. The difference in reflectance is preferably 2% or less from the viewpoint that the film thickness is increased to impair the alkali diffusion.

Next, the thickness of the ruthenium-containing layer formed on the glass substrate will be described. Here, the thickness of the ruthenium containing layer can be determined by X-ray total reflection (XRR). However, in the state in which the tantalum layer is a nanometer-scale thin film, the influence of the error may become large, and the visible light reflectance of the glass substrate containing the tantalum layer may be formed by the surface roughness Ra or The difference in film thickness is represented by the difference in visible light reflectance from the surface of the self-containing layer.

The thickness of the ruthenium containing layer should preferably exceed 3 nm. Thereby, the alkali diffusion can also be improved. This is presumed to be because the surface of the glass substrate on the surface of the ruthenium-containing layer is activated as long as the ruthenium-containing layer exceeds the thickness of 3 nm, and the alkali component tends to move to the surface of the glass at the time of high-temperature treatment. On the other hand, the thickness of the ruthenium containing layer is preferably less than 10 nm. When the ruthenium-containing layer is thickened, it becomes a tendency to prevent the alkali component from diffusing from the glass substrate to the photoelectric conversion layer. Further, at the stage where the ruthenium-containing layer is formed thick, the surface of the ruthenium-containing layer is flattened, and there is a case where the range of the surface roughness is not satisfied. Therefore, in order to obtain sufficient alkali diffusion energy, the thickness of the ruthenium containing layer is preferably less than 10 nm. The thickness of the germanium-containing layer is preferably 4 nm or more, more preferably 5 nm or more, and more preferably 6 nm or more. Further, the thickness of the ruthenium containing layer is preferably 9 nm or less. From the viewpoint of alkali diffusion energy, the thickness of the ruthenium-containing layer is preferably 7 to 9 nm.

The ruthenium-containing layer may be formed to cover the entire surface of the glass substrate, or may be formed in an island shape partially covering the glass substrate. It is presumed that the ruthenium-containing layer is formed in an island shape in the ultra-thin film, and as the amount of adhesion to the surface of the film-forming material increases, the density and size of the island change, and once a certain amount of adhesion is reached, it becomes close. It can be roughly regarded as a state of a continuous film. At this time, although the surface roughness Ra is a predetermined value in the island shape, once the film is formed, the surface is flattened, so that it is expected to gradually become smaller. When the surface roughness Ra of the ruthenium-containing layer satisfies the above range, the surface of the glass substrate may be exposed in the concave portion of the ruthenium-containing layer. Thus, by exposing the glass substrate, the surface area of the substrate surface is increased, and the diffusion of the alkali component toward the photoelectric conversion layer can be promoted. As long as the surface roughness Ra of the ruthenium-containing layer satisfies the above range, the surface of the glass substrate may be covered with the ruthenium-containing layer. By covering the entire surface of the glass substrate as described above, it is possible to promote the diffusion of the alkali component to the photoelectric conversion layer without functioning as an alkali barrier layer.

Next, a method of forming a ruthenium-containing layer will be described. The ruthenium-containing layer can be formed by various film formation methods such as a chemical vapor deposition (CVD) method, an electron beam evaporation method, a vacuum deposition method, a sputtering method, and a spray coating method. Among them, a ruthenium-containing layer satisfying the above range of physical properties (hereinafter, a ruthenium-containing layer is also referred to as "SiOC layer") can be satisfactorily formed by using a CVD method. As a method of specifically forming a SiOC layer by a CVD method, a SiOC layer is formed by spraying a raw material gas of an SiOC and an oxidizing gas on a glass substrate. The SiOC layer is formed, and as the material gas, a decane gas such as decane gas or tetraethoxy decane can be used. In addition to decane gas, carbon-containing gases can also be sprayed. As the carbon-containing gas, methane gas, ethylene gas, acetylene gas or the like can be used. Further, carbonic acid gas can also be used as a carbon material. Further, as the diluent gas of the material gas, nitrogen gas, argon gas or the like can be used. The flow rate of each gas can be adjusted within the following range: the flow rate of the decane gas is in the range of 0.01 to 2.4 kg/hour; the flow rate of the carbon-containing gas is in the range of 0 to 9 kg/hour; and the flow rate of the carbonic acid gas is 0.3~ Within the range of 3kg/hour; the flow rate of nitrogen is in the range of 0~12kg/hour. The surface roughness, composition, reflectance, and thickness of the ruthenium-containing layer can be adjusted by adjusting the film formation temperature, gas ambient pressure, gas flow rate, and film formation time. When forming a film, the temperature of the glass substrate should be adjusted to 600 to 1100 °C. Further, the film formation system can be carried out under normal pressure.

Hereinafter, the composition of a glass substrate according to an embodiment of the present invention will be described. In the following description, the composition of the glass substrate is expressed by a percentage of the oxide based on the percentage of the oxide in the region from the surface of the first main surface of the glass substrate to a depth of 5000 nm or more. In the description of the content ratio of the composition of the glass substrate, the mass percentage (% by mass) based on the oxide is also simply referred to as "%". The composition of the glass substrate according to the present embodiment is not limited. However, by using at least one of Na ₂ O and K ₂ O as the main component of SiO ₂ , it is possible to obtain a photovoltaic excellent in a glass substrate for a solar cell. Conversion efficiency. Preferably, it contains 7 to 20% of Na ₂ O and more than 0% and less than 9% of K ₂ O, more preferably 10 to 20% of Na ₂ O + K ₂ O.

As an example of a composition of a preferred glass substrate, the composition of the glass having a depth of 5000 nm or more from the surface of the first main surface of the glass substrate is represented by a mass percentage based on the following oxide, and contains: 60 to 75%. SiO ₂ , 0.25 to 8% of Al ₂ O ₃ , 7 to 20% of Na ₂ O, more than 0 and less than 9% of K ₂ O, 0 to 10% of MgO, and 0 to 15% of CaO.

The reason why the glass substrate according to the present embodiment is limited to the above composition is as follows: SiO ₂ : a component which forms a structure of glass, and when it is less than 60%, heat resistance and chemical durability of the glass are lowered, and a glass substrate is feared. The average linear expansion coefficient (hereinafter, also referred to as "average linear expansion coefficient" or "CTE") at 50 to 350 °C is increased. Therefore, it should be more than 65%, preferably more than 68%.

However, if it exceeds 75%, the high-temperature viscosity of the glass will rise, and there is a fear that the problem of deterioration of the meltability will occur. Therefore, it should be 73% or less, preferably 72% or less.

Al ₂ O ₃ : a component that increases the Young's modulus by increasing the glass transition temperature and improving weather resistance (baking and aging), heat resistance, and chemical durability. Further, when the photoelectric conversion layer is formed, it also has an effect of promoting diffusion of alkali inside the glass. If the content is less than 0.25%, there is a fear that the glass transition temperature is lowered. Also, there is a fear that the average coefficient of thermal expansion will increase. Therefore, it is preferably 0.5% or more, preferably 0.75% or more, more preferably 1% or more.

However, if it exceeds 8%, the high-temperature viscosity of the glass will rise, and there is a fear that the meltability will deteriorate. Also, the devitrification temperature will rise, and there is a fear that the formability will deteriorate. Further, the alkali component diffused from the glass substrate to the photoelectric conversion layer is caught, and there is a fear that the amount of alkali diffusion is lowered. Therefore, it is preferably 7% or less, preferably 6% or less, more preferably 5.5% or less.

Na ₂ O: Na ₂ O is a component for helping to increase the power generation efficiency of a solar cell having a photoelectric conversion layer such as CIGS. Further, since it has an effect of lowering the viscosity at the glass melting temperature and facilitating the melting, it may contain 7 to 20%. Although Na diffuses in the photoelectric conversion layer formed on the glass substrate to improve power generation efficiency, if the content is less than 7%, the amount of Na diffusion into the photoelectric conversion layer on the glass substrate may become insufficient, and power generation may be insufficient. Efficiency has also become inadequate. When the content is 8% or more, the content is preferably 10% or more, more preferably 12% or more, and particularly preferably 13% or more.

When the Na ₂ O content exceeds 20%, the glass transition temperature is lowered, and the average thermal expansion coefficient is increased, or the chemical durability is deteriorated. In addition, there is a fear of deterioration in weather resistance. When the content is 18% or less, the content is preferably 16% or less, more preferably 15.5% or less, and particularly preferably 15% or less.

K ₂ O: Since it has the same effect as Na ₂ O, it may contain more than 0 and less than 9%. However, if it exceeds 9%, the power generation efficiency will decrease, that is, the diffusion of Na will be hindered, and the glass transition temperature will decrease, which may cause the CTE to become larger. It is preferably 0.1% or more, more preferably 0.2% or more, more preferably 0.3% or more, and particularly preferably 0.4% or more. On the other hand, it is preferably 8.0% or less, preferably 7.0% or less, more preferably 6.0% or less, and particularly preferably 5.0% or less.

MgO is a component which stabilizes the glass and improves the meltability, and is a component which can reduce the content of the alkali metal and suppress the increase in the average thermal expansion coefficient by adding the component, and can be contained in an amount of 10% or less. It is preferably 0.01% or more, and preferably 1.0% or more, preferably 2.0% or more, more preferably 3.0% or more, and particularly preferably 4.0% or more. However, if it exceeds 10%, there is a fear that CTE will increase. It is also fearful that the temperature of devitrification will rise. Therefore, it is preferably 9.5% or less, preferably 9.0% or less, more preferably 8.5% or less, and particularly preferably 8.0% or less.

CaO: It is a component which stabilizes glass, prevents devitrification by the presence of MgO, and has an effect of suppressing the rise of CTE while improving the meltability, and therefore may be contained in an amount of 15% or less. It is preferably 1.0% or more, and preferably 2.0% or more, preferably 2.5% or more, more preferably 3.0% or more, and particularly preferably 3.5% or more. However, if it exceeds 15%, there is a fear that the CTE of the glass will increase. Therefore, it is preferably 14.5% or less, preferably 12% or less, more preferably 9% or less, and particularly preferably 8% or less.

SrO: It is used to reduce the viscosity of the glass and the devitrification temperature of the active ingredient. However, since the raw material cost is high and the specific gravity of the glass is increased compared with MgO and CaO, even in the case of being contained, it is preferably 1% or less. When it is set to 1% or less, the meltability is improved, and the CTE and the density are prevented from rising excessively. However, it is more preferable that the glass substrate does not substantially contain SrO from the viewpoint of cost.

BaO: It is the same as SrO and is an active ingredient for reducing the viscosity and devitrification temperature of glass. However, since the raw material cost is high and the specific gravity of the glass is increased compared with MgO and CaO, even in the case of being contained, it is preferably 1% or less. When it is set to 1% or less, the meltability is improved, and the CTE and the density increase can be suppressed to be more than necessary. However, from the viewpoint of cost, it is more desirable that the glass substrate does not substantially contain BaO.

ZrO ₂ will increase the Tg, which is detrimental to the low temperature process of the glass substrate. In addition, since it is feared to remain as an unmelted material during melting, the blending amount is preferably limited to 1.0% or less, preferably 0.8% or less. More preferably, it is 0.5% or less. It is more preferable that ZrO ₂ is substantially not contained in the glass substrate.

The total amount of SrO, BaO and ZrO ₂ is preferably 1.0% or less, preferably 0.5% or less, more preferably 0.1% or less, based on the above viewpoint.

The glass substrate according to the present embodiment is preferably composed of the above-described composition. However, it is also possible to contain other components in a total amount of 5% or less in a range which does not detract from the object of the present invention. For example, for the purpose of improving weather resistance, meltability, devitrification, and ultraviolet ray concealing, 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 and the like.

The B ₂ O ₃ system is used to increase the meltability and the like, and may also contain an amount of not more than 0.8%. When the content is 0.8% or more, the glass transition temperature is lowered or the average thermal expansion coefficient is small, which is not preferable for the process of forming a photoelectric conversion layer such as a CIGS film. Preferably, the content is less than 0.8%. When the content is 0.5% or less, it is particularly preferable, and more preferably it is not contained. In addition, "substantially not contained" means that it is not contained except for the unavoidable impurities which are mixed in from raw materials, etc., that is, it means intentionally not to contain. The same is true below.

Li ₂ O is a component which lowers the viscosity at the glass melting temperature and improves the meltability. However, since the raw material cost is higher than Na ₂ O and the Na and K are inhibited from diffusing to the photoelectric conversion layer, it is preferable not to contain. Even in the case of inclusion, the content is preferably less than 1%, preferably less than 0.05%, and particularly desirably less than 0.01%.

In addition, in order to improve the meltability and the clarification property of the glass, the content of the glass matrix of the glass substrate to be described later may be 100% by mass, and the total content of SO ₃ , F, Cl, and SnO ₂ may be 2% by mass or less. These raw materials are added to the parent constituent raw materials.

Further, in order to increase the chemical durability of the glass, Y ₂ O ₃ , La ₂ O ₃ and TiO ₂ may be contained in the glass in a total amount of 5% or less. Among these, Y ₂ O ₃ , La ₂ O ₃ and TiO ₂ also contribute to the Young's modulus of the glass. There are many TiO ₂ in natural raw materials, and it is known as a yellow color source. When TiO ₂ is contained, it is preferably less than 1%, preferably 0.5% or less, more preferably 0.2% or less.

Further, in order to adjust the color tone of the glass, the glass may contain a coloring agent such as Fe ₂ O ₃ . The content of the coloring agent is preferably 100% by mass based on the glass mother composition, and the ratio is 1% by mass or less. Here, the "glass mother composition of the glass substrate" means the total amount of the above-mentioned SiO ₂ , Al ₂ O ₃ , MgO, CaO, Na ₂ O, and K ₂ O.

The glass transition temperature (Tg) of the glass substrate according to the present embodiment is preferably 580 ° C or lower. Thereby, in the production of the solar cell, alkali diffusion from the glass substrate to the photoelectric conversion layer at a low temperature can be promoted during the heat treatment of the photoelectric conversion layer forming step. Moreover, the viscosity at the time of melting a glass raw material can be moderately lowered, and it can manufacture easily. The Tg is preferably 575 ° C or lower, preferably 570 ° C or lower. The Tg is preferably 535 ° C or higher, preferably 540 ° C or higher, more preferably 550 ° C or higher. When the Tg is less than 535 ° C, the warpage, deformation, and heat shrinkage of the substrate during the production of the photoelectric conversion layer are not sufficiently suppressed, and the film characteristics may not be ensured. Tg can be adjusted to an appropriate range by adjusting the composition blended on the glass substrate.

The average linear expansion coefficient (CTE) of the glass substrate according to the present embodiment at 50 to 350 ° C is preferably 70 × 10 ^-7 to 110 × 10 ^-7 / ° C. By this range, it is possible to prevent the difference in thermal expansion from the CIGS film or the like formed on the glass substrate from becoming excessive, and it is possible to prevent film peeling, film breakage, and the like. Further, when the solar cell is assembled (specifically, when the glass substrate having the CIGS photoelectric conversion layer and the cover glass are heated and bonded), the glass substrate can be prevented from being deformed.

The CTE is preferably 100 × 10 ^-7 / ° C or less, preferably 96 × 10 ^-7 / ° C or less, more preferably 93 × 10 ^-7 / ° C or less. On the other hand, the average linear expansion coefficient is preferably 80 × 10 ^-7 / ° C or more, preferably 83 × 10 ^-7 / ° C or more, more preferably 85 × 10 ^-7 / ° C or more.

The Young's modulus of the glass substrate according to the present embodiment is preferably 68 GPa or more, preferably 70 GPa or more, more preferably 72 GPa or more. Thereby, thermal deformation can be prevented during the heat treatment.

The density of the glass substrate according to the present embodiment is preferably 2.480 g/cm ³ or more, preferably 2.485 g/cm ³ or more, more preferably 2.490 g/cm ³ or more. The density of the glass substrate is preferably 2.50 g/cm ³ or less, preferably 2.540 g/cm ³ or less, more preferably 2.520 g/cm ³ or less from the viewpoint of the weight of the solar cell module.

<Method for Producing Glass Substrate> A method for producing a glass substrate according to an embodiment of the present invention will be described. In the method for producing a glass substrate according to the present embodiment, the floating glass plate method can be suitably used because it is excellent in productivity and cost. The floating glass plate method which is an example of the method for producing a glass substrate of the present embodiment has a method of melting a glass raw material, forming a molten glass on a molten tin to form a glass substrate, and cooling the glass substrate. .

In the melting of the glass raw material, the raw material is adjusted according to the composition of the glass substrate to be obtained, and the raw material is continuously introduced into a melting furnace and heated to obtain a molten glass. It is also desirable to adjust the raw material so that the composition of the glass substrate becomes the aforementioned glass composition.

The melting temperature of the glass raw material can be usually set to 1450 to 1700 ° C, preferably 1500 to 1650 ° C. The melting time is not particularly limited and is usually from 1 to 48 hours.

A clarifying agent can be utilized in the melting step. In the case where an alkali glass substrate containing an alkali metal oxide (Na ₂ O, K ₂ O) is used as the glass substrate, SO ₃ can be effectively utilized as a clarifying agent from the above-mentioned clarifying agent.

In the forming step of the glass substrate, the molten glass may be formed on the molten tin in the molten tin bath to form a plate-shaped glass substrate. In detail, on the molten tin bath surface which has been filled with molten tin, the molten glass continuously flows from the melting kiln to form a glass ribbon. Next, the glass ribbon is advanced while floating along the bath surface of the molten tin bath, and the glass ribbon is formed into a plate shape while the temperature is lowered. After that, the glass substrate that has been plated is taken out by the take-up roll and transferred to the quench furnace.

As the ambient gas in the molten tin bath, a mixed gas composed of hydrogen and nitrogen can be used. The hydrogen concentration is preferably from 1 to 10% by volume. And the molten tin bath should be positive pressure.

The temperature of the molten tin bath should be 500~1200 °C. Further, the temperature of the molten tin bath should be adjusted so that the temperature of the molten glass flowing into the molten tin bath is 950 to 1200 ° C upstream and 500 to 950 ° C downstream. The residence time of the glass ribbon in the molten tin bath is preferably from 1 to 10 minutes.

Prior to or after the slow cooling step therebetween, SO ₂ may be implemented by the following process step, the SO ₂ treatment step based at least one surface of the glass substrate in contact with the side of the SO ₂ gas. When the process based on the SO ₂ in the slow cooling step of the glass substrate conveying roller, the processing roller pair to prevent injuries caused by the surface of the glass substrate. The SO ₂ treatment step is to apply a SO ₂ gas (sulfurous acid gas) to a glass plate having a high temperature in the atmosphere to react with the glass component and precipitate a sulfate on the surface of the glass, thereby protecting the transfer surface of the glass substrate. . Examples of the barium sulfate include Na salt, K salt, Ca salt, Sr salt, and Ba salt, and are usually precipitated as a complex of these salts.

After the SO ₂ treatment, the glass substrate is preferably washed to remove a film such as sulfate. The method for washing the glass substrate is not particularly limited. For example, it can be washed with water, washed with a detergent, and washed with a brush while pulverizing the slurry containing cerium oxide. When washing with a slurry containing cerium oxide, it is preferably washed with an acidic detergent such as hydrochloric acid or sulfuric acid.

It is preferable that the surface of the glass substrate after the cleaning is not so as to have micron-sized irregularities on the surface of the glass substrate due to contamination or deposits such as the above-mentioned cerium oxide. This is because, when the film is formed on the electrode film or the underlayer thereof by the unevenness of the micron-scale, there is no possibility that the surface of the film is uneven, the thickness of the film is changed, or the pinhole of the film is generated, and the power generation efficiency is lowered. . After washing, it is cut into a predetermined size to obtain a glass substrate.

In the present embodiment, a step of forming a ruthenium-containing layer on the glass substrate by a CVD method can be provided while the glass substrate is being formed. Thereby, before the glass substrate is stored or transported, the characteristics of the haze or the like can be prevented from being deteriorated by covering the glass substrate with the ruthenium-containing layer.

<Glass substrate for solar cell> The glass substrate according to the present embodiment can be suitably used as a glass substrate for a solar cell. The ruthenium-containing layer is formed on one side or both sides of a glass substrate for a solar cell. Further, on the side of the glass substrate having the ruthenium-containing layer, a photoelectric conversion layer is preferably formed. Since the ruthenium-containing layer is formed on both surfaces of the glass substrate, the weather resistance during the storage and transportation of the glass substrate and the back side of the glass substrate after the solar cell has been assembled can be improved.

As the photoelectric conversion layer of the solar cell, a Group 12-13, a Group 11-16 compound semiconductor or a cubic crystal system or a hexagonal system Group 12-16 compound semiconductor having a chalcopyrite crystal structure can be suitably used. Typical examples include a CIGS-based compound (Cu (In, Ga) Se ₂ compound), a CdTe-based compound, a CIS-based compound, and a CZTS-based compound. Particularly desirable are CIGS compounds. As the photoelectric conversion layer of the solar cell, a lanthanoid compound, an organic compound, or the like can also be used.

When the glass substrate according to the present embodiment is used for a glass substrate for a CIGS solar cell, the thickness of the glass substrate is preferably 3 mm or less, preferably 2.5 mm or less, more preferably 2 mm or less. Further, the method of forming the photoelectric conversion layer of the CIGS film on the glass substrate is preferably a method in which at least a part of the CIGS film is formed by a selenization method or a vapor deposition method.

<Solar Cell> Next, a solar cell according to an embodiment of the present invention will be described. A solar cell according to the present embodiment is characterized by comprising: the glass substrate according to the embodiment; and a photoelectric conversion layer on the surface of the glass substrate having the ruthenium containing layer.

Hereinafter, an example of a solar cell according to the present embodiment will be described with reference to the drawings. In addition, the thickness of each layer of the solar cell shown in the drawings is indicative of the display. Fig. 1 is a schematic cross-sectional view showing a CIGS solar cell 10 according to an embodiment of the present embodiment. In Fig. 1, a solar cell (CIGS solar cell) 10 is sequentially laminated with a glass substrate 1, a germanium-containing layer 1a, and a CIGS film 3 as a photoelectric conversion layer. The ruthenium-containing layer 1a is formed on one surface of the glass substrate 1. A Mo film 2 which is a positive electrode is formed as a back electrode layer on the germanium-containing layer 1a of the glass substrate 1, and a CIGS film 3 is formed thereon. Although not shown, the weather resistance of the back side of the glass substrate 1 can be improved by forming a ruthenium containing layer on the other surface side of the glass substrate 1.

The CIGS film 3 is a photoelectric conversion layer containing a CIGS-based compound. As a composition of the CIGS-based compound, for example, Cu(In _1-X Ga _x )Se ₂ . Here, x represents the composition ratio of In to Ga and 0 < x < 1. Although the CIGS film 3 may contain a CIGS-based compound alone, it may contain a CdTe-based compound, a CIS-based compound, an anthraquinone-based compound, and a CZTS-based compound.

On the CIGS film 3, a CdS (cadmium sulfide) or ZnS (zinc sulfide) layer, which is a buffer layer 4, has a transparent conductive film 5 of ZnO or ITO or the like, and has an Al electrode belonging to a negative electrode thereon. The electrode 6 is taken out (aluminum electrode) or the like. An anti-reflection film may also be provided at a necessary place between the layers. In FIG. 1, an anti-reflection film 7 is provided between the transparent conductive film 5 and the extraction electrode 6.

Further, a cover glass 8 is provided on the take-out electrode 6, and if necessary, the take-out electrode 6 and the cover glass 8 are sealed with a resin or adhered with a transparent resin for adhesion. In addition, the cover glass 8 may not be provided. For the cover glass 8, soda lime glass or the like can be used. It is preferable to use a glass substrate having the same composition as that of the glass substrate 5 for the cover glass 8, and to make the average linear expansion coefficient equal to prevent thermal deformation during assembly of the solar cell. Although not shown, a ruthenium-containing layer may be formed on one side or both sides of the cover glass 8. Thereby, the alkali diffusion energy of the cover glass 8 can be improved.

In the present embodiment, the end portion of the photoelectric conversion layer or the end portion of the solar cell may be sealed. Examples of the material to be sealed include the same materials as those of the glass substrate according to the present embodiment, other glass, resin, and the like.

Hereinafter, an example of a method of forming the CIGS film 3 will be specifically described. In the formation of the CIGS film 3, first, a CuGa alloy layer is formed on the Mo film 2 by using a sputtering device, and a CuGa alloy layer is formed, and then an In layer is formed by using an In target to form a film of In-CuGa. Pioneer membrane. Although the film formation temperature is not particularly limited, it is usually formed at room temperature.

The composition of the precursor film is preferably measured by a fluorescent X-ray analysis method: the ratio of (Cu + In) is 0.7 to 0.95, and the ratio of Ga In (Ga + In) is 0.1 to 0.5. . This composition can be achieved by adjusting the film thickness of the CuGa alloy layer and the In layer.

Next, the precursor film was subjected to heat treatment using an RTA (Rapid Thermal Annealing) apparatus. In the first step, the heat treatment is carried out at 200 to 700 ° C for 1 to 120 minutes in a hydrogen selenide mixed gas atmosphere to cause Cu, In, and Ga to react with Se. The hydrogen selenide mixed gas atmosphere preferably contains hydrogen selenide at 1 to 20% by volume in an inert gas such as argon or nitrogen.

Thereafter, in the second stage, the hydrogen selenide mixed gas atmosphere is replaced with a hydrogen sulfide mixed gas atmosphere, and further held at 200 to 700 ° C for 1 to 120 minutes, and the CIGS film is formed by crystallizing the CIGS. The hydrogen sulfide mixed gas atmosphere preferably contains hydrogen sulfide in an inert gas such as argon or nitrogen at 1 to 30% by volume. The thickness of the CIGS film is preferably 1 to 5 μm. Example

Hereinafter, the present invention will be described in more detail by way of examples, but the invention should not be construed as limited. Example 1 is a reference example, and Examples 2 to 7 are examples.

<Production of Glass Substrate> The composition of the glass substrate is shown below. Each component is represented by a mass percentage based on an oxide in a glass region having a depth of 5000 nm or more from the surface of the glass substrate. SiO ₂ 71.4% Al ₂ O ₃ 1.1% MgO 5.5% CaO 7.8% Na ₂ O 13.6% K ₂ O 0.4%

The glass frit which has been blended into the glass composition is heated at a temperature of 1,450 to 1,700 ° C to obtain a molten glass. Next, the molten glass is poured into a molten tin bath which has been filled with molten tin, and is formed into a plate-shaped glass ribbon. The tin bath system is a mixed gas atmosphere of H ₂ and N ₂ , and the temperature is 950 to 1200 ° C on the upstream side and 500 to 950 ° C on the downstream side. In the cold step of the glass ribbon, the SO ₂ treatment was simultaneously performed in the Xu cold furnace. Further, a mixed gas of SO ₂ gas and air is blown from the bottom surface of the glass ribbon (the surface in contact with the tin bath). After the SO ₂ treatment, the glass substrate is washed with a mixture of calcium carbonate and water and a mixture of a neutral detergent and water to remove the protective layer of sulfate attached to both sides of the glass substrate to prepare a glass substrate. The glass substrates of Examples 1 to 7.

Using the glass substrates prepared as described above, the glass substrates 1 to 7 of Examples 1 to 7 were produced as described below. (Example 1) A glass substrate 1 on which the SiOC layer was not formed on the glass substrate was prepared. <Formation of SiCl Layer> (Example 2) A glass substrate 2 was prepared by forming a SiOC layer on a surface on one side of the glass substrate by using a CVD apparatus. Specifically, the SiOC layer is formed by blowing a mixed gas of the following raw material gases which have been previously mixed at a normal pressure on a glass substrate which has been heated to a substrate temperature. Raw material gases: decane gas (0.097 kg/hr), ethylene gas (2.57 kg/hr), carbonic acid gas (7.7 kg/hr), and nitrogen gas (2.6 kg/hr). Substrate temperature: 600~1100 °C. Film formation pressure: atmospheric pressure. (Example 3) A glass substrate 3 having a thickness and a surface roughness of the SiOC layer different from that of Example 2 was prepared in the same manner as in Example 2 except that the flow rate of the decane gas was 0.058 kg/hr. (Example 4) A glass substrate 4 having a thickness and a surface roughness of the SiOC layer different from those of Examples 2 and 3 was prepared in the same manner as in Example 2 except that the flow rate of the decane gas was 0.029 kg/hr.

(Example 5) In the same manner as in Example 2 except that it was set to decane gas (0.036 kg/hr), ethylene gas (2.27 kg/hr), carbonic acid gas (6.8 kg/hr), and nitrogen gas (3.7 kg/hr). A glass substrate 5 having a thickness and a surface roughness of the SiOC layer different from those of Examples 2 to 4 was prepared. (Example 6) In the same manner as in Example 2 except that it was set to decane gas (0.036 kg/hr), ethylene gas (2.27 kg/hr), carbonic acid gas (10.2 kg/hr), and nitrogen gas (1.9 kg/hr). A glass substrate 6 having a thickness and a surface roughness of the SiOC layer different from those of Examples 2 to 5 was prepared. (Example 7) In the same manner as in Example 2 except that it was set to decane gas (0.036 kg/hr), ethylene gas (3.41 kg/hr), carbonic acid gas (6.8 kg/hr), and nitrogen gas (3.0 kg/hr). A glass substrate 7 having a thickness and a surface roughness of the SiOC layer different from those of Examples 2 to 6 was prepared.

<Evaluation> The following evaluations were performed for each of the glass substrates prepared as described above. (Surface Thickness of SiOC Layer) The surface roughness Ra of the SiOC layer was measured by the following conditions using the following AFM apparatus. AFM device: "AFM Cypher S" manufactured by Oxford Instruments. Imaging Mode: AC-Air Detector: SI-DF20AL Drive Amplitude (Slave Amplitude): 1V Set Point: ~700mV Scan Size: 2 × 2μm, 5 × 5μm Scan Rate: 1 Hz.

(The difference in reflectance of the SiOC layer) The reflectance difference of the SiOC layer was measured by measuring the reflectance A of the glass substrate 1 (Example 1) in which the SiOC layer was not formed, and measuring the glass substrate on which the SiOC layer was formed (Examples 2 to 4) The reflectance B of the surface of the SiOC layer is determined from "reflectance A - reflectance B". Further, the reflectance A refers to the reflectance of a plain glass substrate having no SiOC layer. Therefore, even if the glass substrate in which the SiOC layer is formed is another glass substrate, if it is a glass substrate of the same composition, the reflectance can be substituted. The reflectance A and the reflectance B were each measured using the following spectrometers under the following conditions. Spectrometer: "ARM-500M" manufactured by JASCO. Measurement conditions: The reflectance was measured under the conditions of a measurement wavelength of 550 nm, an incident angle of 5°, N-polarization, a scan rate of 400 nm/min, and a data interval of 1.0 nm.

(Component of SiOC Layer) The components of the SiOC layer were measured using the following XPS apparatus using the following XPS apparatus for Examples 1 to 3 and Examples 5 to 7. XPS device: "XPS ESCA-5500" manufactured by ULVAC-PHI, INC. Pass energy: 117.4eV step energy: 0.5eV analysis angle: 45° C60 sputtering: depth profile at 10kV 3×3mm (rate: 2.0nm/min as SiO ₂ ) Determination. Further, in order to remove surface contamination, the surface of the SiOC layer was sputtered, and the composition of the SiOC layer having a depth of 2 nm was analyzed.

The measurement results of the respective glass substrates are shown in Table 1.

[Table 1] In addition, the mark "-" of the field of the reflectance and the reflectance difference of Examples 5 to 7 of Table 1 indicates that it was not measured.

(ΔHaze value) The ΔHaze value was obtained by processing the obtained glass substrate into the following dimensions and measuring as follows. Dimensions: 2.5 cm x 2.5 cm x thickness 5 mm. First, the Haze value of the C light source of the glass substrate before the formation of the SiOC layer was measured. On the other hand, a glass substrate in which a plurality of SiOC layers are formed is prepared, and a surface on the opposite side of the surface on which the SiOC layer is formed (the bottom surface in the case of an untreated substrate) is protected by a polyimide film and stored at 60 ° C. -95RH% in a constant temperature and humidity chamber. One glass substrate was taken out after storage for 1 day, 2 days, 4 days, and 7 days, and the polyimide film was peeled off, and the Haze value after formation of the SiOC layer was measured. The Haze value of the glass substrate before and after storage was measured, and the difference was obtained to obtain a ΔHaze value. The Haze value was measured using HZ-2 manufactured by Suga Test Instruments Co., Ltd. The results are shown in Figure 2. ΔHaze value = (Haze value after storage) - (Haze value before storage)

(Na diffusion amount, K diffusion amount) Na diffusion amount is a Mo electrode and an AZO transparent electrode (doped with Al ₂ O) as a positive electrode on the SiOC formation surface of the glass substrate obtained as described above, as described below. A zinc oxide (ZnO) transparent electrode of ₃ was used to prepare a glass substrate for measurement. After that, the glass substrate 1 for measurement was obtained by measuring the amount of Na in the AZO layer as follows.

First, the obtained glass substrate was processed into a size of 5 cm × 5 cm and a thickness of 5 mm. A Mo (molybdenum) film was formed on the SiOC forming surface of the glass substrate by a sputtering apparatus. The film formation was carried out at room temperature, and a Mo film having a thickness of 490 nm was obtained. Next, an AZO film was formed as a transparent electrode by the same sputtering apparatus. The thickness of the AZO film was 150 nm. Thereafter, the glass substrate was heated from room temperature to 450 ° C at a rate of 10 ° C /min in a nitrogen gas atmosphere heat treatment furnace, and maintained at 450 ° C for 10 minutes, and then heated from 450 ° C at a rate of 10 ° C / minute. Heat treatment at 500 ° C for 30 minutes at 500 ° C. Subsequently, the temperature was lowered from 500 ° C to room temperature at a rate of 20 ° C /min, and the obtained glass substrate was supplied as a sample for measuring the amount of Na diffusion.

The obtained sample was subjected to secondary ion mass spectrometry (SIMS) to measure the integrated intensity of ²³ Na and Zn in the AZO layer. The Na diffusion amount is an integrated intensity (Na/Zn) of ²³ Na based on the integrated intensity of Zn. The main component of the Zn-based AZO layer. At this time, in consideration of the difference in film quality between batches, the production of the Mo film and the AZO film was always performed in the same batch as the glass substrate to be measured. Next, when the glass substrate to be measured was subjected to SIMS measurement, the same glass substrate as the reference batch was used as a reference. The Na diffusion amount was performed twice using two glass substrates, and the average value thereof was also determined.

The K diffusion amount was measured in the same manner as the above Na diffusion amount. Specifically, the integrated intensity of ³⁹ K and Zn in the AZO layer was measured by secondary ion mass spectrometry (SIMS). The K diffusion amount is an integrated intensity (K/Zn) of ³⁹ K based on the integrated intensity of Zn. The results of the Na diffusion amount and the K diffusion amount are shown in Fig. 3 (a), Fig. 3 (b), Fig. 4 (a), and Fig. 4 (b).

Further, the sample in which the Na diffusion amount was measured was immersed in a solution of concentrated sulfuric acid and a hydrogen peroxide solution (90:10), and heated at 80 ° C for 30 minutes to dissolve and remove the electrode layer on the surface of the sample. In the glass substrate, the glass substrate was subjected to XPS analysis under the same conditions as those of the SiOC layer, and the composition of the SiOC layer was determined. As a result, the amount of Na equivalent to the result of the secondary ion mass spectrometry (SIMS) described above was observed. On the other hand, for example, the amount of C in Example 3 is 1.6%, and Ra is 1.7 nm, which is a good result compared with Example 1 (ref), and teaches that it can be brought to the SiOC layer. The electrode layer on the surface of the sample is dissolved and removed under the influence of the substance. However, the amount of Na in the SiOC layer after removing the electrode layer is equal to the amount of Na in the SiOC layer in which the electrode layer is not removed, so that it can be estimated that FIGS. 3(a) and (b), FIGS. 4(a) and (b) The result reflects the state of the glass substrate having the SiOC layer after the electrode layer is removed.

Fig. 2 is a graph showing the ΔHaze value of each glass substrate. Fig. 3(a) is a graph showing the amount of Na diffusion of each glass substrate, and Fig. 3(b) is a graph showing the amount of K diffusion. Fig. 4(a) is a graph showing the Na diffusion amount of each glass substrate, and Fig. 4(b) is a graph showing the K diffusion amount. Figure 5 is an AFM image of the glass substrate of Example 3.

As shown in Table 1, in the glass substrates of Examples 2, 3, and 4, it can be said that the flow rate of the decane gas was sequentially decreased, and the thickness of the SiOC layer was also thin. The surface roughness Ra of the SiOC layer was as small as 0.4 nm in the thin example 4 of the SiOC layer, and was larger than 1.0 nm in the example 3 in which the SiOC layer was thick. Further, in Example 2 in which the SiOC layer was thick, the SiOC layer was planarized, and the surface roughness Ra became 0.8 nm, which became smaller than Example 3. In each of the examples 2 to 4 having the SiOC layer, since the reflectance difference was obtained and the surface roughness was also larger than that of the glass substrate of Example 1, it was found that the SiOC layer adhered. Further, since the reflectance difference changes depending on the flow rate of the decane gas, it is presumed that as the flow rate of the decane gas increases, the adhesion of the film-forming material increases, and some structural changes occur. The film thicknesses of the SiOC layers of Examples 5, 6, and 7 are estimated to be equal to the film thickness of Example 4 which is similar to the flow rate of the decane gas. In Examples 5 to 7, the surface roughness was also larger than that of the glass substrate of Example 1, and it was found that the SiOC layer adhered.

As shown in Fig. 3 (a) and Fig. 3 (b), the glass substrates of Examples 2 to 4 can enhance the alkali diffusion energy. For the conventional technique in which the alkali diffusion is lowered when the SiOC layer is formed, the alkali diffusion energy can be improved by setting the surface roughness of the SiOC layer to a predetermined range. In Example 2, Example 3, and Example 4, there is a tendency that the SiOC layer is sequentially thinned, and in this order, the alkali diffusion energy becomes higher. In particular, in Examples 3 and 4, the amount of Na diffusion and the amount of K diffusion can also be increased. In Example 2, it can be inferred that the amount of the SiOC layer is large, and the surface is flattened, so that the alkali diffusion energy is slightly lowered. In the glass substrates of Examples 5 to 7, the film thickness of the SiOC layer was the same as in Example 4. Even if other manufacturing conditions were further changed, the increase in the amount of alkali diffusion was confirmed as shown in Fig. 4 . An AFM image of the glass substrate of Example 3 is shown in FIG. As shown, in the glass substrate of Example 3, a nano-scale uneven shape was formed on the surface of the SiOC layer. As shown in FIG. 2, the glass substrates of Examples 2 and 3 in which the ΔHaze value was thick in the SiOC layer were sufficiently low and weather resistant. Industrial availability

The glass substrate according to the present invention can be suitably used for a glass substrate for a solar cell, in particular, a glass substrate for a CIGS solar cell. For example, it can be used for a glass substrate for a solar cell and/or a cover glass for a solar cell. Thereby, a solar cell excellent in power generation efficiency can be provided. This application is based on Japanese Patent Application No. 2015-185762, which was filed with the Japanese Patent Office on September 18, 2015, and Japanese Patent Application No. 2016-84949, which was filed with the Japanese Patent Office on April 21, 2016. The entire contents of the Japanese Patent Application No. 2015-185762 and the Japanese Patent Application No. 2016-84949 are incorporated herein by reference.

10‧‧‧Solar battery
1‧‧‧ glass substrate
1a‧‧‧矽 layer
2‧‧‧ positive electrode
3‧‧‧CIGS layer
4‧‧‧buffer layer
5‧‧‧Transparent conductive film
6‧‧‧Negative electrode
7‧‧‧Anti-reflective film
8‧‧‧ Cover glass

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view schematically showing an example of a solar cell according to an embodiment of the present invention. Fig. 2 is a graph showing the ΔHaze value of each glass substrate. Fig. 3(a) is a graph showing the amount of Na diffusion of each of the glass substrates of Examples 1 to 4. Fig. 3(b) is a graph showing the amount of K diffusion of each of the glass substrates of Examples 1 to 4. Fig. 4 (a) is a graph showing the amount of Na diffusion of each of the glass substrates of Examples 1, 5, 6 and 7. Fig. 4(b) is a graph showing the K diffusion amount of each of the glass substrates of Examples 1, 5, 6 and 7. Fig. 5 is an AFM (atomic force microscope) image of the glass substrate of Example 3.

10‧‧‧Solar battery

1‧‧‧ glass substrate

1a‧‧‧矽 layer

2‧‧‧ positive electrode

3‧‧‧CIGS layer

4‧‧‧buffer layer

5‧‧‧Transparent conductive film

6‧‧‧Negative electrode

7‧‧‧Anti-reflective film

8‧‧‧ Cover glass

Claims (6)

A glass substrate for a solar cell, comprising a ruthenium-containing glass substrate at least on a first main surface, wherein the ruthenium-containing layer has an atomic percentage of 15% or more and 45% or less with respect to a total atomic weight; 0.4% or more and 30% or less of carbon, and the surface roughness Ra of the above-mentioned ruthenium-containing layer is 0.3 nm or more and less than 2 nm. The glass substrate for a solar cell according to claim 1, wherein the ruthenium-containing layer further contains, in atom%, oxygen of 30% or more and 65% or less with respect to the total atomic weight. The glass substrate for a solar cell according to claim 1 or 2, wherein the absolute value of the difference in reflectance between the surface of the ruthenium-containing layer and the surface of the glass substrate of the glass substrate is 0.02% or more at an incident angle of 5° and a wavelength of 550 nm. The glass substrate for a solar cell according to any one of claims 1 to 3, wherein the composition of the glass having a depth of 5000 nm or more from the first main surface of the glass substrate is represented by a mass percentage based on the following oxide. Contains: 60 to 75% of SiO ₂ , 0.25 to 8% of Al ₂ O ₃ , 7 to 20% of Na ₂ O, more than 0 and less than 9% of K ₂ O, 0 to 10% of MgO, and 0 ~15% CaO. A solar cell comprising: the glass substrate for a solar cell according to any one of claims 1 to 4; and a photoelectric conversion layer on a surface of the glass substrate having a ruthenium containing layer. The solar cell of claim 5, wherein the photoelectric conversion layer is composed of a Cu(In,Ga)Se ₂ compound semiconductor.