JP6673360B2 - Glass substrate for solar cell and solar cell - Google Patents

Description

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

In a compound solar cell, a semiconductor film is formed as a photoelectric conversion layer on a glass substrate. As semiconductors used for solar cells, group 11-13 and 11-16 group compound semiconductors having a chalcopyrite crystal structure and cubic or hexagonal group 12-16 group compound semiconductors have wavelengths from visible to near infrared. It has a large absorption coefficient for light in the range. Therefore, it is expected as a material for a high-efficiency thin-film solar cell. A typical example is Cu (In, Ga) Se ₂ (hereinafter, may be referred to as CIGS).

  It is known that by using a glass substrate containing an alkali metal, particularly sodium (Na) or potassium (K) as such a glass substrate for a solar cell, the photoelectric conversion efficiency of the solar cell can be improved. When 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 photoelectric conversion layer forming step, so that alkali metal atoms contained in the glass substrate are transferred from the glass substrate surface to the photoelectric conversion layer. It spreads. Thereby, the defect density of the photoelectric conversion layer decreases, the carrier concentration increases, and as a result, the photoelectric conversion efficiency can be improved.

From the viewpoint of reducing environmental load, energy saving in the production of solar cells is desired, and a low-temperature process of heat treatment is required in the process of forming the photoelectric conversion layer. In addition, the demand for cost reduction of the solar cell substrate is increasing year by year, and in particular, it is required to provide a glass substrate occupying most of the weight of the solar cell panel at a low cost.
Alkali metal diffusion into the photoelectric conversion layer easily occurs in a low-temperature process, and as an example of an inexpensive glass substrate, soda-lime glass widely used for architectural glass and the like is known.

Japanese Patent No. 5575163 JP-T-2015-506890A

  A predetermined film may be formed on the soda lime glass substrate surface. Conventionally, for architectural uses and the like, there is a method of preventing deterioration of various characteristics such as optical characteristics due to diffusion of an alkali component, particularly a sodium component, by using such a glass substrate with a film. For this reason, there is a demand to increase alkali diffusion while preventing deterioration of various characteristics by applying the glass substrate with a film to a solar cell application.

Patent Literature 1 discloses that when a high strain point glass is used for a glass substrate of a CIS based thin-film solar cell to prevent distortion, the high strain point glass has a low alkali concentration, and is used as an alkali control layer on the glass substrate. It has been proposed to form a thin silica film having a thickness of 3 to 12 nm and further add Na to a metal precursor film forming a CIS-based light absorbing layer.
In Patent Literature 1, the silica film functions as an alkali control layer to suppress the diffusion of an alkali component. However, the thickness of the silica film is reduced to promote the diffusion of the alkali component. However, in Patent Literature 1, it is not sufficient to diffuse a sufficient alkali component by itself, so it is necessary to further add Na to the metal precursor film.
Patent Document 1 uses a high strain point glass having a low Na content, and does not discuss alkali control in soda-lime glass.

Patent Document 2 discloses that if sodium ions diffuse from a substrate made of borosilicate glass or soda-lime glass to a functional thin layer on the surface, the characteristics of the functional thin layer may be deteriorated. It has been proposed to form a _(SiO x _{C y)} layer.
In Patent Literature 2, in a glass sheet for automobiles and a glass sheet for houses, the silicon oxycarbide layer has a two-layer structure having different carbon contents from the viewpoint of coloring problem.
In Patent Document 2, the total thickness of the silicon oxycarbide layer is 10 to 200 nm, particularly preferably 40 to 70 nm, in order to prevent diffusion of sodium ions.
As disclosed in Patent Document 2, a silicon oxycarbide layer is used to prevent diffusion of sodium ions from a glass substrate.
In addition, since the diffusion of sodium ions is prevented by increasing the thickness of the silicon oxycarbide layer, there is a problem that when such a glass substrate is used for a solar cell, sufficient alkali diffusing ability cannot be obtained.

  An object of the present invention is to provide a glass substrate for a solar cell, which has excellent alkali diffusing ability and high power generation efficiency, and a solar cell using the same.

The gist of the present invention is as follows.
(1) A glass substrate provided with a silicon-containing layer on at least a first main surface, wherein the silicon-containing layer contains 15% or more and 45% or less of silicon and 0.4% or less of carbon in atomic% based on the total atomic weight. %, And the surface roughness Ra of the silicon-containing layer is 0.3 nm or more and less than 2 nm.
(2) The glass substrate for a solar cell according to (1), wherein the silicon-containing layer further has oxygen in an amount of 30% or more and 65% or less in atomic% based on the total atomic weight.
(3) The absolute value of the reflectance difference between the surface of the silicon-containing layer of the glass substrate and the surface of the base glass substrate at a wavelength of 550 nm at 5 ° incidence is 0.02% or more, (1) or (2). The glass substrate for a solar cell according to the above.
(4) The glass in a region at a depth of 5000 nm or more from the first main surface of the glass substrate has a SiO ₂ content of 60 to 75% and an Al ₂ O ₃ content of 0.25 to Any of (1) to (3), which has a composition containing 8%, 7 to 20% of Na ₂ O, more than 0 to 9% of K ₂ O, 0 to 10% of MgO, and 0 to 15% of CaO. A glass substrate for a solar cell as described in Crab.
(5) A solar cell, comprising: the glass substrate for a solar cell according to any one of (1) to (4); and a photoelectric conversion layer on a surface of the glass substrate having a silicon-containing layer.
(6) the photoelectric conversion layer is composed of Cu (In, Ga) Se ₂ compound semiconductor solar cell according to (5).
In the present specification, `` to '' indicating a numerical range is used in a meaning including the numerical values described before and after it as a lower limit and an upper limit, and unless otherwise specified, `` to '' in the present specification is hereinafter referred to as , With similar meanings.

  ADVANTAGE OF THE INVENTION According to this invention, the glass substrate for solar cells with high power generation efficiency with excellent alkali diffusion ability and a solar cell using the same can be provided.

FIG. 1 is a cross-sectional view schematically illustrating an example of a solar cell according to an embodiment of the present invention. FIG. 2 is a graph showing a ΔHaze value of each glass substrate. Is a graph showing the Na diffusion amount of each glass substrate of Examples 1 to 4. Is a graph showing the amount of K diffusion of each glass substrate of Examples 1 to 4. 9 is a graph showing the amount of Na diffusion of each of the glass substrates of Examples 1, 5, 6, and 7. Is a graph showing the amount of K diffusion of each of the glass substrates of Examples 1, 5, 6, and 7. 9 is an AFM image of the glass substrate of Example 3.

Hereinafter, an embodiment of the present invention will be described.
<Glass substrate>
The glass substrate for a solar cell according to one embodiment of the present invention is a glass substrate provided with a silicon-containing layer on at least a first main surface, wherein the silicon-containing layer contains 15% or more of silicon in atomic% based on the total atomic weight. , 35% or less, and 0.4% or more and 30% or less of carbon, and the surface roughness Ra of the silicon-containing layer is 0.3 nm or more and less than 2 nm.
According to this embodiment, it is possible to provide a glass substrate for a solar cell having excellent alkali diffusing ability and high power generation efficiency.

By doping a photoelectric conversion layer such as a CIGS film with an alkali metal such as Na atom or K atom, the solar cell can reduce the defect density and increase the carrier concentration. These Na atoms and K atoms are diffused from the glass substrate surface to the photoelectric conversion layer by the heat treatment in the step of forming the photoelectric conversion layer. Alkali metal doping can be achieved by including an oxide containing an alkali metal such as Na ₂ O or K ₂ O in a raw material of a glass substrate on which a photoelectric conversion layer is formed.
In the present embodiment, by forming a silicon-containing layer having a specific surface roughness and a predetermined composition on a glass substrate, the alkali diffusing ability can be further increased.
Further, when soda lime glass itself is used as a glass substrate for a solar cell, the proportion of an alkali metal or an alkaline earth metal is high, so that a carbonate easily precipitates on the surface of the glass substrate, and there is a problem of burning. On the other hand, by forming the silicon-containing layer as described above, it is possible to improve alkali diffusion ability while suppressing burn.

If the silicon-containing layer is formed thick on the glass substrate, the silicon-containing layer may act as a barrier layer for an alkali component, and the alkali diffusing ability may be reduced. However, the alkali diffusing ability can be improved by forming the silicon-containing layer to some extent thin on the glass substrate. Such a silicon-containing layer whose alkali diffusing ability can be improved can be evaluated by its surface roughness and film composition.
In the present invention, it has been found that when the surface roughness Ra of the silicon-containing layer is 0.3 nm or more, the alkali diffusing ability can be improved. Here, the surface roughness Ra is based on JIS B0601-2001.
This is because nano-level irregularities are formed on the surface of the silicon-containing layer, which increases the surface area of the glass substrate surface and activates the glass surface by the interaction between the glass surface and the elements that constitute the silicon-containing layer. It is considered that this is because the glass surface is covered to some extent with the silicon-containing layer, so that alkali elimination by SO ₂ gas is suppressed. It is considered that the diffusion of the alkali component from the glass substrate to the silicon-containing layer is promoted in this manner.
The surface roughness Ra of the silicon-containing layer is more preferably 0.4 nm or more, and even more preferably 0.5 nm or more.
If the surface of the silicon-containing layer becomes excessively rough, there is a problem that battery characteristics deteriorate. In this respect, the surface roughness Ra of the silicon-containing layer is preferably less than 2 nm, more preferably 1.8 nm or less, and still more preferably 1.5 nm or less.
Here, the surface roughness Ra can be measured using an atomic force microscope (AFM).

The silicon-containing layer formed on the glass substrate is a layer containing silicon as an essential component, and is preferably a layer containing SiO ₂ .
A preferred form of the silicon-containing layer is a layer containing three or more elements containing silicon. The element constituting the silicon-containing layer is preferably a layer containing silicon, oxygen, and carbon, and is preferably a layer containing carbon as a main component of SiO ₂ (hereinafter sometimes simply referred to as an SiOC layer). .
The silicon-containing layer preferably contains SiO ₂ or SiOC as a main component. The main component means that the total amount of each atom constituting SiO ₂ or SiOC is 50 atomic% or more based on the total amount of elements.
In the silicon-containing layer, the silicon component is preferably 15 to 45 atomic%, more preferably 17 to 35 atomic%, based on the total number of atoms constituting the silicon-containing layer.
That is, in the silicon-containing layer, the silicon component, that is, silicon atoms, is preferably 15 to 45 atomic%, more preferably 17 to 35 atomic%, based on the total number of atoms constituting the silicon-containing layer.
In the silicon-containing layer, the carbon component, that is, the carbon atom is preferably 0.4 to 30 atomic% based on the total number of atoms constituting the silicon-containing layer. The carbon component is more preferably at least 0.5 at%, further preferably at least 0.6 at%, and still more preferably at least 0.7 at%. More preferably, it is 1 to 20 atomic%.
It is presumed that the inclusion of the carbon component in this range promotes the formation of irregularities on the glass surface. It is also considered that this contributes to activation in the extremely surface region of the glass.
In the silicon-containing layer, the oxygen component, that is, the oxygen atom is preferably 30 to 65 atomic%, more preferably 50 to 62 atomic%, based on the total number of atoms constituting the silicon-containing layer.
Here, the atomic content can be measured by, for example, X-ray photoelectric spectroscopy (XPS). The measuring method is not limited to XPS.

At 5 ° incidence, the absolute value of the difference between the reflectance at a wavelength of 550 nm of the surface of the glass plate having the silicon-containing layer at a wavelength of 550 nm and the reflectance at a wavelength of 550 nm of the surface of the elementary glass substrate described below is 0.02% or more. Is preferred. Hereinafter, this difference may be referred to as a reflectance difference. In the present invention, the elementary glass substrate refers to a glass substrate having the same composition as a glass substrate provided with a silicon-containing layer and having no film containing a silicon-containing layer formed on both main surfaces thereof.
The reflectance difference can be determined by first measuring the reflectance of the glass substrate surface, then forming a silicon-containing layer on the glass substrate, and then measuring the reflectance of the silicon-containing layer formed on the glass substrate. . The reflectance of the glass substrate surface to be measured first means the reflectance of the base glass substrate serving as a reference, and even if the glass substrate having a silicon-containing layer is different from the glass substrate provided with the silicon-containing layer, it is a silicon-containing layer. If the composition is the same as that of the glass substrate provided with, the reflectance may be used instead.
The reflectance can be measured using a spectroscope at a measurement wavelength of 550 nm and 5 ° incidence.

When the reflectance difference is 0.02% or more, it can be confirmed that the silicon-containing layer is formed.
The reflectance difference is preferably 2% or less from the viewpoint of increasing the film thickness and inhibiting alkali diffusion.

Next, the thickness of the silicon-containing layer formed on the glass substrate will be described.
Here, the thickness of the silicon-containing layer can be measured by an X-ray reflectivity method (XRR). However, when the silicon-containing layer is a very thin film having a thickness of several nanometers, there is a concern that the influence of an error or the like may be increased. Therefore, the surface roughness Ra and the visible light from the glass substrate surface on which the silicon-containing layer is not formed. The difference between the film thickness and the reflectance can be expressed by the difference between the reflectance and the visible light reflectance from the surface of the silicon-containing layer.

Preferably, the thickness of the silicon-containing layer is greater than 3 nm. Thereby, the alkali diffusing ability can be improved. This is probably because if the thickness of the silicon-containing layer exceeds 3 nm, the surface of the glass substrate is activated on the surface on which the silicon-containing layer is formed, and the alkali component easily moves to the glass surface during high-temperature treatment.
On the other hand, the thickness of the silicon-containing layer is preferably less than 10 nm. When the silicon-containing layer becomes thicker, the diffusion of the alkali component from the glass substrate to the photoelectric conversion layer is rather prevented. Further, at the stage of forming the silicon-containing layer thickly, the surface of the silicon-containing layer may be flattened, and may be out of the above range of the surface roughness. Therefore, in order to obtain a sufficient alkali diffusing ability, the thickness of the silicon-containing layer is preferably less than 10 nm.
The thickness of the silicon-containing layer is more preferably 4 nm or more, still more preferably 5 nm or more, and still more preferably 6 nm or more.
Further, the thickness of the silicon-containing layer is more preferably 9 nm or less.
From the viewpoint of alkali diffusing ability, the thickness of the silicon-containing layer is preferably from 7 to 9 nm.

The silicon-containing layer described above may be formed so as to cover the entire surface of the glass substrate, or may be formed in an island shape so as to partially cover the glass substrate.
The silicon-containing layer is formed as an island in a very thin film, and the density and size of the island change as the amount of adhesion to the surface of the film-forming material increases. It is considered that the films are in a state close enough to be regarded as a film. At this time, the surface roughness Ra takes a predetermined value in the island shape, but it is assumed that the surface roughness Ra becomes smaller again because the surface is smoothed when the film is formed.
As long as the surface roughness Ra of the silicon-containing layer satisfies the above range, the surface of the glass substrate may be exposed in the concave portion of the silicon-containing layer. By exposing the glass substrate in this manner, the surface area of the substrate surface is increased, and the diffusion of the alkali component into the photoelectric conversion layer can be promoted.
As long as the surface roughness Ra of the silicon-containing layer satisfies the above range, the entire surface of the glass substrate surface may be covered with the silicon-containing layer. By covering the entire surface of the glass substrate in this manner, the function as an alkali barrier layer is not achieved, and the diffusion of an alkali component into the photoelectric conversion layer can be promoted.

Next, a method for forming the silicon-containing layer will be described.
The silicon-containing layer can be formed by various film forming methods such as a chemical vapor deposition (CVD) method, an electron beam evaporation method, a vacuum evaporation method, a sputtering method, and a spray method.
In particular, by using the CVD method, a silicon-containing layer satisfying the above-mentioned range of physical properties (hereinafter, the silicon-containing layer is also referred to as an SiOC layer) can be preferably formed.
Specifically, as one method of forming the SiOC layer using the CVD method, a SiOC material gas and an oxidizing gas are sprayed on a glass substrate to form the SiOC layer.
In order to form the SiOC layer, silane gas such as silane gas and tetraethoxysilane can be used as a source gas. In addition to the silane gas, a carbon-containing gas may be sprayed. As the carbon-containing gas, methane gas, ethylene gas, acetylene gas and the like can be used. Further, carbon dioxide may be used as a carbon raw material.
Further, a nitrogen gas, an argon gas, or the like can be used as a diluting gas for the source gas.
The flow rate of the silane gas is 0.01 to 2.4 kg / hour, the flow rate of the carbon-containing gas is 0 to 9 kg / hour, the flow rate of the carbon dioxide gas is 0.3 to 3 kg / hour, and the flow rate of the nitrogen gas is 0 to 0 kg / hour. It can be adjusted within the range of 12 kg / hour.
The surface roughness, composition, reflectance, thickness, and the like of the silicon-containing layer can be adjusted by adjusting the film forming temperature, ambient pressure, gas flow rate, and film forming time. At the time of film formation, it is preferable to adjust the temperature of the glass substrate to 600 to 1100 ° C. Further, film formation can be performed at normal pressure.

Hereinafter, the composition of the glass substrate according to one embodiment of the present invention will be described. In the following description, the composition of the glass substrate is expressed in terms of an oxide-based mass percentage for glass in a region at a depth of 5000 nm or more from the surface of the first main surface of the glass substrate. In the expression of the content ratio of the composition of the glass substrate, the expression of mass percentage (% by mass) based on the oxide is also simply described as “%”.
Although the composition of the glass substrate according to the present embodiment is not limited, the main component is SiO ₂ , and by including at least one of Na ₂ O and K ₂ O, excellent photoelectric conversion efficiency as a solar cell glass substrate can be obtained. Obtainable.
More preferably, Na ₂ O and 7 to 20% _{K 2} O 0 percent, including 9% or less, more preferably 10 to 20% of _{Na 2} O + _K 2 O.

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

The reason for limiting to the above composition in the glass substrate according to the present embodiment is as follows.
SiO ₂ : a component that forms the skeleton of glass. If less than 60%, the heat resistance and chemical durability of the glass are reduced, and the average linear expansion coefficient of the glass substrate at 50 to 350 ° C. (hereinafter simply referred to as the average linear expansion coefficient) Or CTE) may increase. It is preferably at least 65%, more preferably at least 68%.

  However, if it exceeds 75%, the high-temperature viscosity of the glass increases, and there is a possibility that the problem of deterioration in solubility may occur. It is preferably at most 73%, more preferably at most 72%.

Al ₂ O ₃ : A component that raises the glass transition temperature, improves weather resistance (burn or solarization), heat resistance and chemical durability, and raises the Young's modulus. Further, it also has a function of promoting alkali diffusion inside the glass when forming the photoelectric conversion layer. If the content is less than 0.25%, the glass transition temperature may decrease. Also, the average coefficient of thermal expansion may increase. It is preferably at least 0.5%, more preferably at least 0.75%, further preferably at least 1%.

  However, if it exceeds 8%, the high-temperature viscosity of the glass may increase, and the melting property may deteriorate. Further, the devitrification temperature may increase, and the moldability may deteriorate. Furthermore, there is a possibility that the alkali component diffused from the glass substrate to the photoelectric conversion layer is trapped, and the amount of alkali diffusion is reduced. It is preferably at most 7%, more preferably at most 6%, even more preferably at most 5.5%.

Na ₂ O: Na ₂ O is a component that contributes to improving the power generation efficiency of a solar cell including a photoelectric conversion layer such as CIGS. Further, it has the effect of lowering the viscosity at the glass melting temperature and facilitating melting, so that 7 to 20% can be contained. Na diffuses into the photoelectric conversion layer formed on the glass substrate and can improve the power generation efficiency. However, if the content is less than 7%, the amount of Na diffused into the photoelectric conversion layer on the glass substrate becomes insufficient, and the power generation becomes insufficient. The efficiency may also be insufficient. The content is preferably 8% or more, more preferably 10% or more, further preferably 12% or more, and particularly preferably 13% or more.

If the Na ₂ O content exceeds 20%, the glass transition temperature decreases, the average thermal expansion coefficient increases, or the chemical durability deteriorates. Further, the weather resistance may be deteriorated. The content is preferably 18% or less, more preferably 16% or less, further preferably 15.5% or less, and particularly preferably less than 15%.

K ₂ O: Since it has the same effect as Na ₂ O, it can contain more than 0 and 9% or less. However, if it exceeds 9%, the power generation efficiency is reduced, that is, the diffusion of Na is hindered, and the glass transition temperature is lowered, and the CTE may be increased. It is preferably at least 0.1%, more preferably at least 0.2%, even more preferably at least 0.3%, particularly preferably at least 0.4%. On the other hand, it is preferably at most 8.0%, more preferably at most 7.0%, further preferably at most 6.0%, particularly preferably at most 5.0%.

  MgO: a component that stabilizes glass, improves solubility, and can reduce the content of alkali metal by adding the same to suppress an increase in average thermal expansion coefficient. Can be included. It is preferably at least 0.01%, preferably at least 1.0%, more preferably at least 2.0%, further preferably at least 3.0%, particularly preferably at least 4.0%. However, if it exceeds 10%, the CTE may increase. Further, the devitrification temperature may increase. It is preferably at most 9.5%, more preferably at most 9.0%, further preferably at most 8.5%, particularly preferably at most 8.0%.

  CaO: a component that stabilizes glass, has the effect of preventing devitrification due to the presence of MgO, and improving the solubility while suppressing an increase in CTE, and can be contained at 15% or less. It is preferably at least 1.0%, preferably at least 2.0%, more preferably at least 2.5%, further preferably at least 3.0%, particularly preferably at least 3.5%. However, if it exceeds 15%, the CTE of the glass may increase. It is preferably at most 14.5%, more preferably at most 12%, further preferably at most 9%, particularly preferably at most 8%.

  SrO: A component effective for lowering the viscosity and devitrification temperature of glass, and can be contained. However, since the raw material cost is higher than MgO and CaO and the specific gravity of the glass is increased, it is preferable that the content is 1% or less even if it is contained. By setting the content to 1% or less, the solubility becomes good, and it is possible to suppress the CTE and the density from unnecessarily increasing. However, from the viewpoint of cost, it is more preferable that SrO is not substantially contained in the glass substrate.

  BaO: Similar to SrO, BaO is a component effective for lowering the viscosity and devitrification temperature of glass, and can be contained. However, since the raw material cost is higher than MgO and CaO and the specific gravity of the glass is increased, it is preferable that the content is 1% or less even if it is contained. By setting the content to 1% or less, the solubility becomes good, and it is possible to suppress the CTE and the density from unnecessarily increasing. However, from the viewpoint of cost, it is more preferable that BaO is not substantially contained in the glass substrate.

ZrO ₂ raises Tg and adversely affects the low-temperature process of the glass substrate. In addition, ZrO ₂ may remain unmelted during melting, and thus the amount is preferably limited to 1.0% or less. , More preferably 0.8% or less, still more preferably 0.5% or less. More preferably, ZrO ₂ is not substantially contained in the glass substrate.

In view of the above, the total amount of SrO, BaO, and ZrO ₂ is preferably equal to or less than 1.0%, more preferably equal to or less than 0.5%, and still more preferably equal to or less than 0.1%. .

It is preferable that the glass substrate according to the present embodiment consist essentially of the above composition, but may contain other components, typically in a total of 5% or less, as long as the object of the present invention is not impaired. For example, weather resistance, solubility, devitrification, aims to improve the ultraviolet blocking _{such, 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 or the like may be contained.

B ₂ O ₃ may be contained in an amount not exceeding 0.8% in order to improve the solubility. When the content is 0.8% or more, the glass transition temperature decreases or the average thermal expansion coefficient decreases, which is not preferable for the process of forming a photoelectric conversion layer such as a CIGS film. More preferably, the content is less than 0.8%. It is particularly preferred that the content is 0.5% or less, and more preferably, it is substantially not contained.
In addition, "substantially not contained" means that it is not contained except for inevitable impurities mixed from raw materials and the like, that is, it is not intentionally contained. The same applies hereinafter.

Li ₂ O is a component that lowers the viscosity of glass at the melting temperature and improves the solubility. However, the raw material cost is higher than that of Na ₂ O, and the diffusion of Na and K to the photoelectric conversion layer may be suppressed. Therefore, it is preferably not contained, and even if it is contained, its content is preferably less than 1%, more preferably 0.05% or less, particularly preferably less than 0.01%. is there.

Further, in order to improve the solubility and clarity of the glass, the total amount of SO ₃ , F, Cl, and SnO ₂ in the glass is 2% by mass based on 100% by mass of the glass base composition of the glass substrate described later. These raw materials may be added to the base composition raw material so as to be contained at not more than 10%.

Further, in order to improve 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. Of these, Y ₂ O ₃ , La ₂ O ₃ and TiO ₂ also contribute to improving the Young's modulus of the glass.
TiO ₂ is known to be present abundantly in natural materials and to be a yellow coloring source. When TiO ₂ is contained, the content is preferably less than 1%, more preferably 0.5% or less, further preferably 0.2% or less.

Further, in order to adjust the color tone of the glass, a colorant such as Fe ₂ O ₃ may be contained in the glass. The content of such a coloring agent is preferably not more than 1% by mass based on 100% by mass of the above-mentioned glass base composition.
Here, the glass mother composition of the glass substrate is 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 less.
Thereby, in the production of the solar cell, the alkali diffusion from the glass substrate to the photoelectric conversion layer at a low temperature can be promoted at the time of the heat treatment in the photoelectric conversion layer forming step. In addition, the viscosity of the glass material at the time of melting can be suppressed to an appropriately low level, and the glass material can be easily manufactured.
Tg is preferably 575 ° C. or lower, more preferably 570 ° C. or lower.
Tg is preferably 535 ° C. or higher, more preferably 540 ° C. or higher, and further preferably 550 ° C. or higher.
If the Tg is lower than 535 ° C., warpage, deformation and thermal shrinkage of the substrate during the production of the photoelectric conversion layer cannot be sufficiently suppressed, and the properties of the film may not be ensured.
Tg can be adjusted to an appropriate range by adjusting the components mixed in 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 being in this range, it is possible to prevent the thermal expansion difference from the CIGS film or the like formed on the glass substrate from becoming too large, and to prevent film peeling and film cracking.
Further, when the solar cell is assembled (specifically, when the glass substrate having the CIGS photoelectric conversion layer and the cover glass are bonded by heating), the glass substrate can be prevented from being deformed.

This CTE is preferably 100 × 10 ⁻⁷ / ° C. or less, more preferably 96 × 10 ⁻⁷ / ° C. or less, and even more preferably 93 × 10 ⁻⁷ / ° C. or less. On the other hand, the average coefficient of linear expansion is preferably at least 80 × 10 ⁻⁷ / ° C., more preferably at least 83 × 10 ⁻⁷ / ° C., and even more preferably at least 85 × 10 ⁻⁷ / ° C.

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

The density of the glass substrate according to the present embodiment, is preferably 2.480g / cm ³ or more, more preferably 2.485g / cm ³ or more, more preferably 2.490g / cm ³ or more.
The density of the glass substrate, from the viewpoint of the weight when it is used for a solar cell module, is preferably 2.550g / cm ³ or less, more preferably 2.540g / cm ³ or less, more preferably 2.520g / Cm ³ or less.

<Glass substrate manufacturing method>
A method for manufacturing a glass substrate according to an embodiment of the present invention will be described.
In the method for manufacturing a glass substrate according to the present embodiment, the float method is preferably used because it is excellent in productivity and cost.
As a float method as an example of the method for manufacturing a glass substrate of the present embodiment, there is a method in which a glass material is melted, molten glass is formed on a molten tin into a glass substrate, and the glass substrate is gradually cooled.

  In the melting of the glass raw material, the raw material is adjusted according to the composition of the obtained glass substrate, and the raw material is continuously charged into a melting furnace and heated to obtain a molten glass. It is preferable to adjust the raw materials so that the composition of the glass substrate has the above-mentioned glass composition.

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

A fining agent can be used in the melting process. When 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 used as a fining agent from the above fining agents.

In the glass substrate forming step, the molten glass can be formed into a plate-like glass substrate on molten tin in a molten tin bath.
Specifically, molten glass is continuously flown from a melting furnace onto a bath of molten tin filled with molten tin to form a glass ribbon. Next, the glass ribbon is advanced while floating along the bath surface of the molten tin bath, whereby the glass ribbon is formed into a plate shape with a decrease in temperature. Thereafter, the formed glass substrate is pulled out by a drawer roll and transported to a lehr.

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

  The temperature of the molten tin bath is preferably from 500 to 1200C. The temperature of the molten tin bath is preferably 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 1 to 10 minutes.

Before and after the annealing step, or during, it can be carried out SO ₂ treatment step of contacting the SO ₂ gas to at least one surface of the glass substrate.
The SO ₂ treatment is a treatment for preventing the glass substrate surface from being scratched by the roll when the glass substrate is transported in a roll in the slow cooling step. In the SO ₂ treatment step, SO ₂ gas (sulfurous acid gas) is sprayed on a glass plate having a high temperature in the air to react with a component of the glass to precipitate a sulfate on the glass surface. Can be protected. Representative examples of the sulfate include a Na salt, a K salt, a Ca salt, a Sr salt, and a Ba salt, and are usually precipitated as a composite of these salts.

After the SO ₂ treatment, the glass substrate is preferably washed to remove a film of sulfate or the like.
The method for cleaning the glass substrate is not particularly limited, and examples thereof include cleaning with water, cleaning with a cleaning agent, and cleaning with a brush or the like while spraying a slurry containing cerium oxide. In the case of cleaning with a slurry containing cerium oxide, it is preferable that the cleaning is performed thereafter using an acidic cleaning agent such as hydrochloric acid or sulfuric acid.

It is preferable that the glass substrate surface after the cleaning be free of dirt and irregularities on the glass substrate surface at the micron level due to deposits such as cerium oxide. Since there is no micron-level unevenness, when the above-mentioned electrode film or its underlying layer is formed, unevenness on the film surface, deviation in film thickness, pinhole of the film, and the like are generated, and there is no possibility that power generation efficiency is reduced. It is.
After washing, the glass substrate can be cut into a predetermined size to obtain a glass substrate.

  In the present embodiment, a step of forming a silicon-containing layer on a glass substrate by using a CVD method simultaneously with the production of the glass substrate can be provided. Thereby, before the glass substrate is stored or transported, deterioration of characteristics such as haze can be prevented by covering the glass substrate with the silicon-containing layer.

<Glass substrate for solar cell>
The glass substrate according to the present embodiment can be preferably used as a glass substrate for a solar cell.
The silicon-containing layer is formed on one or both surfaces of the glass substrate for a solar cell. And it is preferable that the photoelectric conversion layer is formed on the surface side of the glass substrate having the silicon-containing layer. By forming the silicon-containing layers on both surfaces of the glass substrate, it is possible to improve the weather resistance of the back surface side of the glass substrate during storage and transportation of the glass substrate and after assembling the solar cell.

As the photoelectric conversion layer of the solar cell, a group 11-13 or 11-16 group compound semiconductor having a chalcopyrite crystal structure, or a cubic or hexagonal group 12-16 group compound semiconductor can be preferably used. Representative examples include CIGS-based compounds (Cu (In, Ga) Se ₂ compounds), CdTe-based compounds, CIS-based compounds, and CZTS-based compounds. Particularly preferred are CIGS compounds.
As the photoelectric conversion layer of the solar cell, a silicon compound, an organic compound, or the like may be used.

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

<Solar cells>
Next, a solar cell according to an embodiment of the present invention will be described.
The solar cell according to the present embodiment is characterized by having the above-described glass substrate according to the present embodiment and a photoelectric conversion layer on the surface of the glass substrate having the silicon-containing layer.

Hereinafter, an example of the solar cell according to the present embodiment will be described with reference to the drawings. The thickness of each layer of the solar cell shown in the drawings is schematically shown.
FIG. 1 is a schematic cross-sectional view of a CIGS solar cell 10 which is an example of the present embodiment.
In FIG. 1, a solar cell (CIGS solar cell) 10 includes a glass substrate 1, a silicon-containing layer 1a, and a CIGS film 3 as a photoelectric conversion layer, which are stacked in this order.
On one surface of the glass substrate 1, the above-mentioned silicon-containing layer 1a is formed. On the silicon-containing layer 1a of the glass substrate 1, a Mo film 2 serving as a positive electrode is formed as a back electrode layer, and a CIGS film 3 is formed thereon.
Although not shown, a silicon-containing layer is also formed on the other surface side of the glass substrate 1 so that the weather resistance on the back surface side of the glass substrate 1 can be improved.

The CIGS film 3 is a photoelectric conversion layer containing a CIGS-based compound. The composition of the CIGS-based compounds, for _example, a _{Cu (In 1-X Ga x} ) Se 2. Here, x indicates the composition ratio of In and Ga, where 0 <x <1.
The CIGS film 3 can contain a CIGS-based compound alone, but may also contain a CdTe-based compound, a CIS-based compound, a silicon-based compound, a CZTS-based compound, or the like.

  On the CIGS film 3, a transparent conductive film 5 such as ZnO or ITO is provided via a CdS (cadmium sulfide) or ZnS (zinc sulfide) layer as a buffer layer 4, and a negative electrode is further provided thereon. It has an extraction electrode 6 such as an Al electrode (aluminum electrode). An antireflection film may be provided at a necessary place between these layers. In FIG. 1, an antireflection film 7 is provided between the transparent conductive film 5 and the extraction electrode 6.

Further, a cover glass 8 is provided on the extraction electrode 6, and if necessary, the extraction electrode 6 and the cover glass 8 are sealed with a resin or bonded with a transparent resin for bonding. Note that the cover glass 8 need not be provided.
As the cover glass 8, soda lime glass or the like can be used. Preferably, a glass substrate having the same composition as that of the glass substrate 5 is used for the cover glass 8 so that the average linear expansion coefficient is made equal to prevent thermal deformation or the like at the time of assembling the solar cell.
Although not shown, a silicon-containing layer may be formed on one or both surfaces of the cover glass 8. Thereby, the alkali diffusing ability of the cover glass 8 can be improved.

  In the present embodiment, the end of the photoelectric conversion layer or the end of the solar cell may be sealed. As the material for sealing, for example, the same material as the glass substrate according to the present embodiment, other glass, resin, and the like can be used.

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 using a CuGa alloy target using a sputtering apparatus, and then an In layer is formed using an In target. An In-CuGa precursor film is formed. The film forming temperature is not particularly limited, but the film can be usually formed at room temperature.

  The composition of the precursor film is such that the Cu / (Ga + In) ratio (atomic ratio) is 0.7 to 0.95 and the Ga / (Ga + In) ratio (atomic ratio) is 0.1 to 0 in the measurement by the fluorescent X-ray analysis method. .5. This composition can be achieved by adjusting the thicknesses of the CuGa alloy layer and the In layer.

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

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

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. Example 1 is a reference example, and Examples 2 to 7 are working examples.

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

The glass raw material blended to have the above glass composition was heated at a temperature of 1450 to 1700 ° C. to obtain a molten glass.
Next, the molten glass was poured into a tin bath filled with molten tin to form a plate-shaped glass ribbon.
The tin bath was a mixed gas atmosphere of H ₂ and N ₂ , and the temperature was 950 to 1200 ° C. on the upstream side and 500 to 950 ° C. on the downstream side.
In the annealing step of the glass ribbon, the SO ₂ treatment was simultaneously performed in the annealing furnace. A mixed gas of SO ₂ gas and air was blown from the bottom surface (surface in contact with the tin bath) of the glass ribbon.
After SO ₂ treatment, the glass substrate was washed with a mixture and a mixture of water and mild soap calcium carbonate and water, removing the protective layer of sulfate adhered to the glass substrate duplex, the glass substrate subjected to Examples 1-7 Produced.

Using the glass substrates obtained as described above, glass substrates 1 to 7 of Examples 1 to 7 were produced as follows.
(Example 1)
A glass substrate 1 on which no SiOC layer was formed was prepared.
<Formation of SiOC layer>
(Example 2)
An SiOC layer was formed on one surface of the glass substrate using a CVD apparatus, and a glass substrate 2 was prepared.
Specifically, a SiOC layer was formed by spraying a mixed gas of the following raw material gases premixed at normal pressure onto a glass substrate heated to the following substrate temperature.
Raw material gas: silane gas (0.097 kg / hour), ethylene gas (2.57 kg / hour), carbon dioxide gas (7.7 kg / hour), nitrogen gas (2.6 kg / hour).
Substrate temperature: 600-1100 ° C.
Film forming pressure: normal pressure.
(Example 3)
A glass substrate 3 was prepared in the same manner as in Example 2 except that the flow rate of the silane gas was 0.058 kg / hour, and the thickness and surface roughness of the SiOC layer were different from those in Example 2.
(Example 4)
A glass substrate 4 was prepared in the same manner as in Example 2 except that the flow rate of the silane gas was 0.029 kg / hour, and the thickness and surface roughness of the SiOC layer were different from those of Examples 2 and 3.

(Example 5)
Except that silane gas (0.036 kg / hour), ethylene gas (2.27 kg / hour), carbon dioxide gas (6.8 kg / hour), and nitrogen gas (3.7 kg / hour) were used, the same as in Example 2 was used. A glass substrate 5 was prepared in which the thickness and surface roughness of the SiOC layer were different from those of Examples 2 to 4.
(Example 6)
Except that silane gas (0.036 kg / hr), ethylene gas (2.27 kg / hr), carbon dioxide gas (10.2 kg / hr), and nitrogen gas (1.9 kg / hr) were used, the same as in Example 2 was used. A glass substrate 6 was prepared in which the thickness and surface roughness of the SiOC layer were different from those of Examples 2 to 5.
(Example 7)
Except that silane gas (0.036 kg / hour), ethylene gas (3.41 kg / hour), carbon dioxide gas (6.8 kg / hour), and nitrogen gas (3.0 kg / hour) were used, the same as in Example 2 was used. A glass substrate 7 was prepared in which the thickness and surface roughness of the SiOC layer were different from those of Examples 2 to 6.

<Evaluation>
The following evaluation was performed about each glass substrate obtained above.
(Surface roughness of SiOC layer)
The surface roughness Ra of the SiOC layer was measured using the following AFM apparatus under the following conditions.
AFM device: "AFM Cypher S" manufactured by Oxford Instruments.
Imaging Mode: AC-Air, Probe: SI-DF20AL manufactured by SII,
Drive Amplitude: 1V,
Set Point: ~ 700mV,
Scan Size: 2 × 2 μm, 5 × 5 μm,
Scan Rate: 1 Hz.

(Reflectance difference of SiOC layer)
The difference in the reflectance of the SiOC layer is determined by measuring the reflectance A of the glass substrate 1 (Example 1) on which the SiOC layer is not formed and measuring the reflectance A of the glass substrate (Example 2 to Example 4) on which the SiOC layer is formed. The reflectance B was measured and determined from “reflectance A−reflectance B”. In addition, the reflectance A means the reflectance of an elementary glass substrate having no SiOC layer. Therefore, even if it is a glass substrate different from the glass substrate on which the SiOC layer is formed, a glass substrate having the same composition may be substituted by its reflectance.
The reflectance A and the reflectance B were measured using the following spectroscope under the following conditions.
Spectroscope: "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 scanning speed of 400 nm / min, and a data interval of 1.0 nm.

(Component of SiOC layer)
The components of the SiOC layer were measured for Examples 1 to 3 and Examples 5 to 7 using the following XPS apparatus under the following conditions.
XPS apparatus: "XPS ESCA-5500" manufactured by ULVAC-PHI.
Pass energy: 117.4 eV,
Step energy: 0.5 eV,
Analysis angle: 45 °,
C60 sputtering: Measurement of depth profile under the conditions of 10 kV 3 × 3 mm (rate: 2.0 nm / min as SiO ₂ ).
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.

  Table 1 shows the measurement results of each glass substrate.

なお、表１の例５〜7の反射率および反射率差の欄の表示「−」は未測定を表す。

In addition, the display "-" in the column of the reflectance and the reflectance difference of Examples 5 to 7 in Table 1 indicates that no measurement was made.

(ΔHaze value)
The ΔHaze value was obtained by processing the obtained glass substrate into the following sizes and measuring as follows.
Size: 2.5 cm x 2.5 cm x thickness 5 mm.
First, the Haze value of the glass substrate before the formation of the SiOC layer in the C light source was measured.
On the other hand, a plurality of glass substrates after the formation of the SiOC layer are prepared, and the surface opposite to the surface on which the SiOC layer is formed (the bottom surface in the case of an untreated substrate) is protected with a polyimide tape. Stored in a humidity chamber.
After storage for 1 day, 2 days, 4 days, and 7 days, the glass substrates were taken out one by one, the polyimide tape was peeled off, and the haze value after forming the SiOC layer was measured.
The Haze value of the glass substrate before and after storage was measured, and the difference was determined to determine the ΔHaze value.
The Haze value was measured using HZ-2 manufactured by Suga Test Instruments. The results are shown in FIG.
ΔHaze value = (Haze value after storage) − (Haze value before storage)

(Na diffusion amount, K diffusion amount)
The amount of Na diffusion is determined as follows. A Mo electrode and an AZO transparent electrode (Al ₂ O ₃ -doped zinc oxide (ZnO) transparent) are formed on the SiOC-formed surface of the glass substrate obtained as described above. An electrode was formed to obtain a glass substrate for measurement.
Thereafter, the amount of Na in the AZO layer of the glass substrate for measurement 1 was measured and determined as described below.

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 formation surface of the glass substrate by a sputtering device. The film was formed at room temperature to obtain a Mo film having a thickness of 490 nm. Next, an AZO film was formed as a transparent electrode using the same sputtering apparatus. The thickness of the AZO film was 150 nm.
Thereafter, in a heat treatment furnace in a nitrogen atmosphere, the temperature of the glass substrate is raised from room temperature to 450 ° C. at a rate of 10 ° C./min, and the temperature is maintained at 450 ° C. for 10 minutes. And heat-treated at 500 ° C. for 30 minutes. Subsequently, the temperature was lowered at a rate of 20 ° C./min from 500 ° C. to room temperature, and the obtained glass substrate was used as a sample for measuring the amount of Na diffusion.

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

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

The sample obtained by measuring the amount of Na diffusion was immersed in a concentrated sulfuric acid and hydrogen peroxide solution (90:10) and heated at 80 ° C. for 30 minutes to dissolve and remove the electrode layer on the sample surface. The substrate was subjected to XPS analysis under the same conditions as when measuring the components of the SiOC layer, and the composition of the SiOC layer was determined. As a result, the same amount of Na as the result by the secondary ion mass spectrometry (SIMS) was observed. On the other hand, for example, the C content in Example 3 was 1.6%, and Ra was 1.7 nm, which was a favorable result as compared with Example 1 (ref), and the sample did not substantially affect the SiOC layer. This suggests that the electrode layer on the surface can be dissolved and removed.
Since the amount of Na in the SiOC layer after the removal of the electrode layer was equal to the amount of Na in the SiOC layer from which the electrode layer was not removed, FIGS. ) And (b) are considered to be the results reflecting the state of the glass substrate provided with the SiOC layer after removing the electrode layer.

FIG. 2 is a graph showing a ΔHaze value of each glass substrate.
FIG. 3A is a graph showing the Na diffusion amount of each glass substrate, and FIG. 3B is a graph showing the K diffusion amount.
FIG. 4A is a graph showing the Na diffusion amount of each glass substrate, and FIG. 4B is a graph showing the K diffusion amount.
FIG. 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, the flow rate of the silane gas is reduced in this order, and the thickness of the SiOC layer is also reduced. The surface roughness Ra of the SiOC layer is as small as 0.4 nm in Example 4 where the SiOC layer is thin, and large at 1.0 nm in Example 3 where the SiOC layer is thick. In Example 2 in which the SiOC layer was further thickened, the SiOC layer was flattened, and the surface roughness Ra was 0.8 nm, which was smaller than that in Example 3.
In each of Examples 2 to 4 including the SiOC layer, there is a difference in reflectivity, and the surface roughness is larger than that of the glass substrate of Example 1, indicating that the SiOC layer is attached. Further, since the reflectance difference changes according to the flow rate of the silane gas, it is conceivable that some structural change occurs while the adhesion of the film-forming material increases as the flow rate of the silane gas increases.
It is considered that the thickness of the SiOC layer in Examples 5, 6, and 7 is equal to the thickness of Example 4 in which the flow rate of the silane gas is close.
Since the surface roughness of Examples 5 to 7 is larger than that of the glass substrate of Example 1, it can be seen that the SiOC layer is attached.

As shown in FIGS. 3A and 3B, the glass substrates of Examples 2 to 4 were able to increase the alkali diffusing ability. In contrast to the prior art in which the formation of the SiOC layer reduces the alkali diffusion, the alkali diffusion ability was able to be increased by setting the surface roughness of the SiOC layer to a predetermined range.
In Examples 2, 3, and 4, the SiOC layer tended to become thinner in this order, and the alkali diffusing ability became higher in this order. In particular, in Examples 3 and 4, both the Na diffusion amount and the K diffusion amount could be increased. In Example 2, it is considered that the amount of the SiOC layer was large, the surface was flattened, and the alkali diffusing ability was slightly lowered.
In the glass substrates of Examples 5 to 7, the thickness of the SiOC layer was equivalent to that of Example 4, and even if other manufacturing conditions were changed, an increase in the amount of alkali diffusion could be confirmed as shown in FIG. .
FIG. 5 shows an AFM image of the glass substrate of Example 3. Thus, in the glass substrate of Example 3, a nano-level uneven shape is formed on the surface of the SiOC layer.
As shown in FIG. 2, the ΔHaze value was sufficiently low for the glass substrates of Examples 2 and 3 where the SiOC layer was thick, and had weather resistance.

The glass substrate according to the present invention can be preferably used as a glass substrate for a solar cell, and particularly, 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 having excellent power generation efficiency can be provided.
This application is based on Japanese Patent Application No. 2015-185762 filed with the Japan Patent Office on September 18, 2015 and Japanese Patent Application No. 2016-84949 filed with the Japan Patent Office on April 21, 2016. Priority is claimed, and the entire contents of Japanese Patent Application No. 2015-185762 and Japanese Patent Application No. 2006-84949 are incorporated herein by reference.

10: solar cell, 1: glass substrate, 1a: silicon-containing layer, 2: positive electrode, 3: CIGS layer, 4: buffer layer, 5: transparent conductive film, 6: negative electrode, 7: antireflection film, 8: cover glass.

Claims (6)

Used for a solar cell including a photoelectric conversion layer containing at least one selected from the group consisting of a CIGS-based compound, a CdTe-based compound, a CIS-based compound, and a CZTS-based compound, wherein SiO ₂ , Na ₂ O and K ₂ O are used. A glass substrate containing at least one of the following,
With a silicon-containing layer on at least the first main surface ,
The silicon-containing layer has 15% or more and 45% or less of silicon and 0.4% or more and 30% or less of carbon in atomic% with respect to the total atomic weight, and has a surface roughness Ra of 0.1% or more. A glass substrate for a solar cell, having a thickness of 3 nm or more and less than 2 nm, wherein the silicon-containing layer is formed in an island shape so as to partially cover the glass substrate.   2. The glass substrate for a solar cell according to claim 1, wherein the silicon-containing layer further has oxygen in an amount of 30% or more and 65% or less in atomic% based on the total atomic weight.   3. The solar cell according to claim 1, wherein an absolute value of a reflectance difference between the surface of the silicon-containing layer of the glass substrate and the surface of the elementary glass substrate at a wavelength of 550 nm at 5 ° incidence is 0.02% or more. 4. Glass substrates for batteries. The glass in a region having a depth of 5000 nm or more from the first main surface of the glass substrate is represented by the following oxide-based mass percentage,
The SiO ₂ 60~75%,
0.25-8% Al ₂ O ₃ ,
Na ₂ O 7-20%
K ₂ O is more than 0, 9% or less,
0-10% MgO,
The glass substrate for a solar cell according to any one of claims 1 to 3, wherein the glass substrate has a composition containing 0 to 15% of CaO. The glass substrate for a solar cell according to any one of claims 1 to 4, and , on a surface of the glass substrate having a silicon-containing layer, a CIGS compound, a CdTe compound, a CIS compound, and a CZTS compound. A solar cell comprising a photoelectric conversion layer including at least one selected from the group consisting of: The photoelectric conversion layer comprises a Cu (In, Ga) Se ₂ compound semiconductor solar cell of claim 5.

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