JP2021012949A - Transparent electrode substrate and solar battery - Google Patents

Abstract

To provide a transparent electrode substrate which is used as a cathode of a solar battery, can uniformly cover a very thin film such as an n-type layer, and can realize high battery efficiency.SOLUTION: A transparent electrode substrate used for a solar battery includes a glass substrate and a transparent conductive film, and the transparent conductive film includes a conductive layer located on the glass substrate side and a surface layer, and has a substantially hemispherical convex portion on the surface of the surface layer.SELECTED DRAWING: Figure 4

Description

The present invention relates to a transparent electrode substrate used for a solar cell and a solar cell having the transparent electrode substrate.

A solar cell is a type of semiconductor that directly converts light energy from the sun into electrical energy. Holes generated by light irradiation move to a p-type semiconductor (p-type layer), and electrons move to an n-type semiconductor (n-type layer), so that a current flows through the external circuit connecting the p-type layer and the n-type layer. Will flow. As described above, in the solar cell, the p-type layer acts as the anode side and the n-type layer acts as the cathode side.

Solar cells are roughly classified into silicon-based, compound-based, III-V group-based, and organic-based solar cells. One of the compound-based solar cells is a CdTe solar cell made from Cd / Te as a raw material. CdTe solar cells can be mass-produced with resource saving, and their manufacturing cost is relatively low, so they have been put into practical use, and various studies have been conducted.

Generally, a CdTe solar cell has a structure in which a transparent electrode (cathode), an n-type layer, a p-type layer, and an electrode (anode) are laminated in this order. For example, Patent Document 1 focuses on a glass substrate constituting a transparent electrode and aims to improve the conversion efficiency (power generation efficiency) of a CdTe solar cell. That is, in Patent Document 1, a glass substrate for a CdTe solar cell satisfies a specific composition and physical properties, so that it has a high transmittance, a high glass transition temperature, a predetermined average coefficient of thermal expansion, a high glass strength, and a low glass density. It is disclosed that the properties of solubility, moldability, and devitrification prevention during the production of flat glass can be well-balanced, and the power generation efficiency of the CdTe solar cell can be increased.

International Publication No. 2013/0472446

The power generation principle of a CdTe solar cell is that light energy such as sunlight is incident from the transparent electrode substrate side, light is absorbed by the p-type layer, and carriers such as electrons and holes are generated. That is, the generated carriers move to and flow into the p-type layer and the n-type layer, respectively, and are extracted as electrical energy.

Of these, the thickness of the p-type layer is generally about 3 to 5 μm, while the thickness of the n-type layer is generally very thin, about 30 nm to 50 nm. Therefore, it is considered that the film formation state of the n-type film on the transparent electrode substrate has a very sensitive effect on the battery characteristics.
Assuming that the surface of the transparent electrode substrate is not sufficiently coated with respect to the film which is an n-type layer such as CdS, the film thickness of the n-type layer is significantly uneven although the coating is performed, or the n-type is formed. If there is a defect in a part of the film that is the layer, it becomes difficult for electrons to flow, which causes a decrease in battery efficiency. Further, there is a possibility that the battery may be short-circuited through a minute portion such as an uncoated portion or a defective portion, and in that case, the battery efficiency is greatly reduced. This tendency is seen not only in CdTe solar cells but also in solar cells having a very thin layer formed on the surface of the transparent electrode substrate.

Therefore, an object of the present invention is to provide a transparent electrode substrate that is used as a cathode of a solar cell, can uniformly cover a very thin film such as an n-type layer, and can realize high battery efficiency.

The present invention relates to the following [1] to [8].
[1] A transparent electrode substrate used in a solar cell, which includes a glass substrate and a transparent conductive film, and the transparent conductive film is composed of a conductive layer located on the glass substrate side and a surface layer. A transparent electrode substrate having substantially hemispherical protrusions on the surface of the surface layer.
[2] The sharpness (Kurtosis) obtained by processing the data obtained by measuring the surface layer at 1024 × 1024 points of an arbitrary 8 μm square using an atomic force microscope using SPIP image analysis software. ): The transparent electrode substrate according to the above [1], wherein the value of Sk is smaller than 3.00.
[3] The transparent electrode substrate according to the above [1] or [2], wherein the haze ratio measured from the glass substrate side is 4% or less.
[4] The transparent electrode substrate according to any one of [1] to [3], wherein the surface roughness of the surface layer is 25 nm or less.
[5] The transparent electrode substrate according to any one of [1] to [4], wherein the conductive layer is a layer containing SnO ₂ as a main component.
[6] The transparent electrode substrate according to any one of [1] to [5], wherein the transparent conductive film has a film thickness of 300 to 800 nm and the surface layer has a thickness of 10 to 80 nm.
[7] The transparent electrode substrate according to any one of [1] to [6], further comprising an undercoat layer between the glass substrate and the transparent conductive film.
[8] A solar cell having the transparent electrode substrate according to any one of [1] to [7] above.

According to the transparent electrode substrate according to the present invention, since the surface layer has a surface shape having substantially hemispherical protrusions, even a film such as an n-type layer having a very thin film thickness can be sufficiently without defects. And it can be coated uniformly. Therefore, it is possible to prevent a short circuit without obstructing the flow of electrons as a solar cell, and to realize high battery efficiency.

FIG. 1 is a schematic cross-sectional view showing the configuration of a transparent electrode substrate. FIG. 2 is an image diagram for explaining the sharpness (Kurtosis): Sku of a substantially hemispherical convex portion which is the surface shape of the surface layer. FIG. 3 is a schematic cross-sectional view showing the configuration of a CdTe solar cell. FIG. 4 is a scanning electron microscope (SEM) image of the surface layer of the transparent electrode substrate of Example 1 when the sample inclination angle is 60 °. FIG. 5 is an SEM image of the surface layer of the transparent electrode substrate of Example 2 when the sample inclination angle is 60 °. FIG. 6 is an SEM image of the surface layer of the transparent electrode substrate of Example 3 when the sample inclination angle is 60 °. FIG. 7 is an SEM image of the surface layer of the transparent electrode substrate of Comparative Example 1 when the sample inclination angle is 60 °. FIG. 8 is an SEM image of the surface layer of the transparent electrode substrate of Comparative Example 2 when the sample inclination angle is 60 °. FIG. 9 is an SEM image of the surface layer of the transparent electrode substrate of Comparative Example 3 when the sample inclination angle is 60 °.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and carried out without departing from the gist of the present invention. Further, "~" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

As shown in FIG. 1, the transparent electrode substrate 1 according to the present invention includes a glass substrate 10 and a transparent conductive film 20, and the transparent conductive film 20 includes a conductive layer 21 located on the glass substrate 10 side and a surface thereof. A solar cell composed of a layer 22 and having a substantially hemispherical convex portion on the surface of the surface layer 22, and forming a very thin layer on the surface of a transparent electrode substrate such as a solar cell, preferably a CdTe solar cell. Used for. Further, if desired, an undercoat layer 30 may be provided between the glass substrate 10 and the transparent conductive film 20.

(Surface layer)
In the case of a CdTe solar cell, a thin film such as CdS or CdSe is used as the n-type layer, but the thickness of the n-type layer is as thin as 30 to 50 nm. Therefore, the state of film formation on the transparent electrode substrate serving as the cathode has a very sensitive effect on the battery characteristics.

Focusing on the surface shape of the outermost surface of the transparent electrode substrate, conventionally, it has been a chevron-shaped surface shape having sharp vertices like a cone or a pyramid.
With such a surface shape, when a thin film such as a very thin n-type layer is formed, it is difficult to cover the valley portion of the chevron, and it is not covered, or even if it is covered, it is concentrated near the apex of the chevron. Therefore, the film thickness is uneven and tends to be non-uniform.

On the other hand, in the transparent electrode substrate according to the present invention, a thin film such as an n-type layer is provided by providing a surface layer having a substantially hemispherical convex portion on the surface of the conductive layer of the transparent conductive film. When forming a film, even if the film thickness is very thin, uniform coating is possible.

Having a substantially hemispherical convex portion on the surface is synonymous with having a fine curved surface shape, and a chevron shape consisting of a cone or a pyramid whose apex is curved (or curved) without being sharpened. It means that it has a surface shape.
By adopting such a surface shape, it is possible to prevent the thin film such as the n-type layer from being concentratedly covered near the apex of the chevron, and the entire surface region of the surface layer is evenly covered with the thin film such as the n-type layer. Easy to be covered.

The size of each convex portion of the substantially semi-shaped shape is such that the diameter of the circumscribed circle of the portion that becomes the bottom surface of the pyramid or the cone is about 40 to 330 nm, and the height is about 50 to 200 nm.

For the substantially hemispherical convex part, the data obtained when the surface layer is measured at an arbitrary 8 μm square 1024 × 1024 point using an atomic force microscope (AFM) is obtained by using SPIP image analysis software (Image Technology). It is preferable that the sharpness (Kurtosis): Sku value obtained by the treatment using the above satisfies the following relationship.
Sku is an index representing surface roughness defined by ISO25178, and has z (x, y) at a reference length that is dimensionless by the square of the root mean square height Sq in the plane using the following formula. ) Means the sharpness (Kurtosis) that represents the mean square. The surface shape (see FIG. 2) showing a value smaller than 3.00 (Sku <3.00) is preferable, and the Sku is more preferably 2.90 or less.

Further, when coating with a thin film such as an n-type layer, the surface roughness of the surface layer is preferably 25 nm or less, more preferably 20 nm or less, from the viewpoint of more even and uniform coating.
The surface roughness of the surface layer can be measured by AFM.

The surface layer is not particularly limited as long as it has translucency as a transparent electrode substrate. Specifically, SnO ₂ , ZnO, and In ₂ O ₃ are preferable, SnO ₂ or ZnO is more preferable, and SnO ₂ is even more preferable. Further, it may be the same component as the conductive layer, for example, the main components are preferably SnO ₂ , ZnO, In ₂ O ₃ , more preferably SnO ₂ or ZnO, further preferably SnO ₂ , and the dopant is doped. It may have been.
The composition of the surface layer can be identified by X-ray photoelectron spectroscopy (XPS) or secondary ion mass spectrometry (SIMS).

The surface layer is formed on the conductive layer by adjusting the composition and thickness in order to realize a preferable surface shape.
The preferred thickness of the surface layer depends on the composition of the surface layer. For example, when the specific resistance of the surface layer is as high as 0.1 Ωcm or more, the resistance increases and may hinder the electron transfer which is a function of the electrode. Therefore, the thickness of the surface layer is preferably 100 nm or less, preferably 80 nm or less. Is more preferable. Further, for example, when the specific resistance of the surface layer is as low as 0.001 Ωcm or less, the thickness of the surface layer is not particularly limited, but is usually 10 nm or more.
The thickness of the surface layer can be measured by a stylus type step meter, a fluorescent X-ray analyzer, X-ray photoelectron spectroscopy (XPS), or secondary ion mass spectrometry (SIMS).

(Conductive layer)
The conductive layer is not particularly limited as long as it has translucency and conductivity as a transparent electrode substrate, but for example, the main components are preferably SnO ₂ , ZnO, In ₂ O ₃ , and SnO ₂ or ZnO. Is more preferable, and SnO ₂ is further preferable. The main component of the conductive layer means that it is 50% by weight or more of the components constituting the conductive layer, preferably 70% by weight or more, and 85% by weight or more with respect to the entire conductive layer. Is more preferable. The upper limit is not particularly limited, but when the main component is doped with a dopant, it is preferably 99.9% by weight or less.

(Transparent conductive film)
The transparent conductive film is composed of a conductive layer located on the glass substrate side and a surface layer.
The specific resistance of the transparent conductive film is preferably 0.001 Ωcm or less, more preferably 0.0008 Ωcm or less, and 0.0006 Ωcm or less as a whole of the conductive layer and the surface layer because it does not obstruct the flow of electrons as an electrode. Is even more preferable. Further, the lower the specific resistance of the transparent conductive film, the more preferable, but 0.0001 Ωcm or more is practical.
In the present specification, the resistivity ( _Rt ) of the transparent conductive film can be measured by using a Hall effect measuring device with respect to the transparent electrode substrate.

The film thickness of the transparent conductive film is preferably 800 nm or less, more preferably 600 nm or less, from the viewpoint of ensuring high transmittance. Further, from the viewpoint of not increasing the resistance too much, 300 nm or more is preferable, and 400 nm or more is more preferable. The film thickness of the transparent conductive film can be measured by using a stylus type step meter or a fluorescent X-ray analyzer.

Further, sheet resistance is important as the electrical characteristics of the transparent conductive film, and this is the electrical resistance as a substantial electrode film defined by specific resistance / film thickness. By adjusting the above-mentioned specific resistance and film thickness, the sheet resistance can be set to a preferable value. The sheet resistance of the transparent conductive film for a CdTe solar cell is preferably 20 Ω / □ or less, and more preferably 12 Ω / □ or less from the viewpoint of reducing voltage loss in wiring.

(Glass substrate)
As the glass substrate, the same one as that conventionally used for a solar cell can be used. For example, a glass substrate containing SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO, ZrO ₂ , Na ₂ O and K ₂ O as a mother composition can be mentioned. More specifically, in the oxide-based molar percentage display, SiO ₂ is 60 to 75%, Al ₂ O ₃ is 1 to 7.5%, B ₂ O ₃ is 0 to 1%, and Mg O is 8.5. ~ 12.5%, CaO 1 to 6.5%, SrO 0 to 3%, BaO 0 to 3%, ZrO ₂ 0 to 3%, Na ₂ O 1 to 8%, K ₂ O Examples thereof include a glass substrate containing 2 to 12%. However, the composition is not limited to these.

Considering the power generation efficiency of the solar cell, the glass substrate preferably has an average transmittance of 90.3% or more, more preferably 90.4% or more, and 90.5% in terms of 2 mm thickness for light having a wavelength of 500 to 800 nm. The above is more preferable.

Further, since the transparent electrode substrate may be heat-treated when the solar cell is manufactured, it is preferable that the glass substrate has good heat resistance.
Specifically, the glass transition temperature (Tg) is preferably 640 ° C. or higher, more preferably 645 ° C. or higher, and even more preferably 655 ° C. or higher. On the other hand, the glass transition temperature is preferably 750 ° C. or lower, more preferably 720 ° C. or lower, and even more preferably 690 ° C. or lower so as not to increase the viscosity at the time of melting too much.

The average coefficient of thermal expansion of the glass substrate at 50 to 350 ° C. is preferably 70 × ^10-7 / ° C. or higher, preferably 80 × ^10-7 / ° C. or higher, from the viewpoint of suppressing warping of the module during modularization. Is more preferable. On the other hand, from the viewpoint of suppressing peeling and the like, 90 × 10 ^-7 / ° C. or lower is preferable, and 85 × 10 ^-7 / ° C. or lower is more preferable.

The thickness of the glass substrate is not particularly limited, but from the viewpoint of strength and transmittance, 0.7 mm or more is preferable, 1.1 mm or more is more preferable, 6.0 mm or less is preferable, and 4.0 mm or less is more preferable. preferable.

(Undercoat layer)
As shown in FIG. 1, an undercoat layer 30 may be further included between the glass substrate and the transparent conductive film, if desired. The undercoat layer 30 can improve the conversion efficiency by preventing the reflection of light. Further, even when heat treatment is performed in the production of the solar cell, it is possible to prevent the diffusion of alkali from the glass substrate 10 and prevent the deterioration of the conductive layer 21.
As the undercoat layer, a conventionally known one can be used. For example, SiO ₂ , SiOxCy, SnO ₂ , TiO _{2 and the} like can be mentioned.

The thickness of the undercoat layer is preferably 10 nm or more, and more preferably 20 nm or more from the viewpoint that the above effects can be preferably obtained. Further, from the viewpoint of suppressing light absorption of the material itself, 100 nm or less is preferable, and 80 nm or less is more preferable.

<Manufacturing method of transparent electrode substrate>
The transparent electrode substrate 1 can be obtained by laminating the conductive layer 21 and the surface layer 22 in this order on the glass substrate 10. Further, the undercoat layer 30 may be laminated if desired before the conductive layer 21 is laminated.
Specifically, the glass substrate has a melting step of heating a glass raw material to obtain molten glass, a clarification step of removing bubbles from the molten glass, a molding step of forming a molten glass into a plate shape to obtain a glass ribbon, and a glass ribbon at room temperature. It can be obtained by a slow cooling step of slowly cooling to a state. Further, the molten glass may be formed into a block shape, slowly cooled, and then cut and polished to produce a glass substrate.

For each of the above steps, conventionally known methods can be used. An example thereof is shown below, but the manufacturing method is not limited to these embodiments, and modifications and improvements can be made as appropriate within the range in which the object of the present invention can be achieved.

After forming an undercoat layer on the glass substrate as desired, the conductive layer and the surface layer, which are transparent conductive films, are formed in this order.
The undercoat layer, the conductive layer, and the surface layer can all be formed by a CVD (Chemical Vapor Deposition) method, a sputtering method, a chemical plating method, a wet coating method, or the like, and the CVD method is preferable. The sputtering method is a method of forming a film on a plate-made glass substrate, and the chemical plating method is a method of forming a mirror.

The CVD method includes an online CVD method and an offline CVD method.
The online CVD method is a method of forming a film directly on the surface of glass during the manufacturing process of a glass substrate on a float line. That is, unlike the offline CVD method in which a transparent conductive film or the like is formed once after obtaining the glass substrate, the transparent conductive film or the like is formed in the middle of the process of obtaining the glass substrate.
Specifically, when the glass substrate is manufactured, the glass ribbon moves on the molten tin bath and then is slowly cooled to continuously manufacture the glass substrate. During the movement of the glass ribbon, the glass ribbon is continuously manufactured. , The process of forming a desired layer is continuously carried out on the upper surface of the glass ribbon.

When the surface layer is formed by the online CVD method, the surface layer having a substantially hemispherical convex portion can be formed by controlling the composition ratio of the raw material supplied from the coating beam.
For example, when SnO ₂ is formed as a surface layer, the surface shape having substantially hemispherical protrusions can be obtained by reducing the supply amount of oxygen among the raw materials of monobutyltin trichloride, oxygen, and water. it can.
The molar ratio of oxygen / monobutyltin trichloride in the mixed gas of monobutyltin trichloride and oxygen is preferably 2.5 or less, more preferably 2.0 or less. In addition, in order to form SnO ₂ , the molar ratio needs to be 0.5 or more.

When tetrabutyltin is used instead of monobutyltin trichloride, the molar ratio of tetrabutyltin and oxygen in the mixed gas is preferably oxygen / tetrabutyltin of 15 or less, in order to form SnO _2. Must be 1.0 or higher.
In addition, a precursor that becomes SnO ₂ , such as tetramethyltin or tin chloride, can also be used, and the preferable molar ratio in the mixed gas at that time differs depending on the type of the precursor.

As for the undercoat layer and the conductive layer, by using the online CVD method, the same layer can be formed in a series of steps for manufacturing the glass substrate, which is preferable because the manufacturing cost can be kept low. In this case, since the film is formed online, the composition of the layer to be formed is limited. For example, it is preferable that the undercoat layer is SiO ₂ or SiOxCy, the conductive layer is fluorine-doped SnO ₂ , and the surface layer is SnO ₂ .

After forming the conductive layer, the surface layer, and the like by the molding step and the online CVD method, the obtained glass ribbon is cooled to a room temperature state in a slow cooling step under controlled cooling conditions. Then, the slowly cooled glass ribbon is cut to obtain a transparent electrode substrate.

From the viewpoint of obtaining good battery efficiency, the transparent electrode substrate obtained above preferably has a haze ratio of 4% or less, more preferably 3% or less, as measured from the glass substrate side. The haze ratio can be controlled by the composition of the glass substrate, the undercoat layer, and the transparent conductive film constituting the transparent electrode substrate, and the surface roughness and surface shape of the surface layer.
The haze rate is a value measured by a haze meter in accordance with JIS K 7136: 2000.

<Solar cell>
The present invention also relates to a solar cell having the transparent electrode substrate. The configuration and preferred embodiment of the transparent electrode substrate are the same as those described in the above <transparent electrode substrate>.
The solar cell of the present invention is preferably a solar cell having a very thin layer formed on the surface of the transparent electrode substrate, and an example thereof is a CdTe solar cell in which an n-type layer is formed on the surface of the transparent electrode substrate. .. The details in the case of the CdTe solar cell will be described below, but this does not exclude the application of the transparent electrode substrate to other solar cells.

The CdTe solar cell has a configuration in which an n-type layer 40, a p-type layer 50, and a back surface electrode (anode) 60 are laminated in this order on the surface of the transparent electrode substrate 1 on the surface layer 22 side.

A thin film of an n-type layer is formed on the surface of the transparent electrode substrate on the surface layer side. As the n-type layer, conventionally known ones can be used, and examples thereof include CdS, CdSe, and the like. preferable.
The thickness of the n-type layer is preferably 30 nm or more, and preferably 100 nm or less.
The n-type layer can be formed by the proximity sublimation method, and its thickness and film quality can be adjusted by changing the sublimation rate or the substrate temperature.

CdTe is generally used for the p-type layer. The thickness of the p-type layer is preferably 3 μm or more, and preferably 15 μm or less.
The p-type layer can be formed by the proximity sublimation method, and the sublimation rate can be changed, the substrate temperature can be changed, and the thickness and film quality thereof can be adjusted.

The back electrode acts as an anode, but conventionally known ones can be used. For example, an electrode having a structure in which a metal material film such as silver (Ag) or molybdenum (Mo) is laminated, a carbon electrode doped with Cu, or the like can be mentioned. Further, a back plate glass may be further provided on the back electrode. The back plate glass may have water resistance and oxygen permeability, and a back film made of resin may be used instead of the back plate glass.
The back electrode and the back plate glass or the back film are bonded with a resin for sealing or bonding.
The thickness of the back surface electrode is preferably 100 nm or more, and preferably 1000 nm or less. The thickness of the back plate glass or the back film is preferably 1 mm or more, and preferably 3 mm or less.

The end of the p-type layer made of CdTe or the end of the CdTe solar cell may be sealed. Examples of the material for sealing include glass having the same composition as the glass substrate in the transparent electrode substrate, glass having other compositions, resin and the like.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[Example 1]
As shown below, a transparent electrode substrate was obtained by producing a glass substrate by the float method and at the same time forming an undercoat layer, a conductive layer and a surface layer by an online atmospheric pressure CVD (chemical vapor deposition) method.

Fused glass having a soda lime silica glass composition was poured into a float bath at 1500 to 1600 ° C., and the glass on the plate was formed while continuously flowing a glass ribbon.
Monosilane (SiH ₄ ), ethylene, and CO ₂ gases are supplied from the first coating beam located on the most upstream side where the temperature of the glass ribbon reaches 700 ° C., and a SiOC film having a thickness of 30 nm is formed on the glass ribbon. A certain undercoat layer was formed.
Subsequently, a mixed gas composed of monobutyltin trichloride, oxygen, water, nitrogen, nitrate and trifluoroacetic acid is supplied from the second coating beam located on the downstream side where the glass ribbon reaches 600 ° C., and the film is coated on the SiOC film. A conductive layer (fluorine-doped tin oxide film) containing SnO ₂ : F having a thickness of 400 nm was formed.
Further, a mixed gas composed of monobutyltin trichloride, oxygen, water and nitrogen is supplied from a third coating beam immediately downstream thereof to form a surface layer containing SnO ₂ having a film thickness of 15 nm. A transparent electrode substrate was obtained. The thickness of the glass substrate was 3.2 mm.

As the mixed gas for forming the conductive layer and the surface layer, each substance was supplied to the mixer in a liquid phase or a gas phase state, and mixed while being heated and vaporized to obtain a mixed gas.
The amount of each raw material supplied from the second coating beam when forming the conductive layer is monobutyltin trichloride 23.5 L / hour (liquid phase), oxygen 35.7 Nm ³ / hour, water 101.6 kg / hour. , Nitric acid was 23.8 L / hour (liquid phase), and trifluoroacetic acid was 3.8 L / hour (liquid phase).
The amount of each raw material supplied from the third coating beam when forming the surface layer was 2.9 L / hour (liquid phase) of monobutyltin trichloride, 0.62 Nm ³ / hour of oxygen, and 21.7 kg / hour of water. Met.

The surface layer of the obtained transparent electrode substrate was measured at an acceleration voltage of 15.0 kV using a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation: S4800). At this time, the sample inclination angle was set to 60 °. The obtained SEM image is shown in FIG. From this, it can be seen that the surface layer has a surface shape having substantially hemispherical protrusions.
In addition, an atomic force microscope (AFM, manufactured by SII Technology: S-image) was used as a scanning probe microscope to measure the convex portion of an arbitrary 8 μm square field of view. The data was processed using SPIP image analysis software (Image Metrology), and the sharpness (Kurtosis): Sku was calculated. As a result, the Sku was 2.78.
Further, the haze ratio measured from the glass substrate side of the transparent electrode substrate in accordance with JIS K 7136: 2000 by a haze meter is 2.0%, and the surface roughness of the surface layer measured by AFM is 16.7 nm. Met.

[Example 2]
The amount of each raw material supplied from the second coating beam was 23.9 L / hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ / hour of oxygen, 107.6 kg / hour of water, and 15.1 L / hour of acetic acid. Liquid phase), trifluoroacetic acid 3.84 L / hour (liquid phase), the film thickness of the conductive layer was 400 nm, and the amount of each raw material supplied from the third coating beam was 3.85 L of monobutyltin trichloride. A transparent electrode substrate was obtained in the same manner as in Example 1 except that the surface layer was changed to 15 nm / hour (liquid phase), oxygen 0.52 Nm ³ / hour, and water 29.1 kg / hour. It was.
The surface layer of the obtained transparent electrode substrate was subjected to SEM observation and AFM observation in the same manner as in Example 1. The SEM image when the sample inclination angle is 60 ° is shown in FIG. 5, and it can be seen that the surface layer has a surface shape having substantially hemispherical protrusions. Moreover, when the Sku was calculated in the same manner as in Example 1, the Sku was 2.89. Further, the haze ratio measured in the same manner as in Example 1 was 2.1%, and the surface roughness of the surface layer was 16.1 nm.

[Example 3]
The amount of each raw material supplied from the second coating beam was 19.5 L / hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ / hour of oxygen, 84.3 kg / hour of water, and 19.8 L / hour of acetic acid (19.8 L / hour). Liquid phase), trifluoroacetic acid 4.47 L / hour (liquid phase), the film thickness of the conductive layer was 420 nm, and the amount of each raw material supplied from the third coating beam was replaced with monobutyltin trichloride. The same as in Example 1 except that tetrabutyltin was changed to 14.4 L / hour (liquid phase), oxygen 11.62 Nm ³ / hour, and water 18.7 kg / hour, and the thickness of the surface layer was 20 nm. , A transparent electrode substrate was obtained.
The surface layer of the obtained transparent electrode substrate was subjected to SEM observation and AFM observation in the same manner as in Example 1. The SEM image when the sample inclination angle is 60 ° is shown in FIG. 6, and it can be seen that the surface layer has a surface shape having substantially hemispherical protrusions. Moreover, when the Sku was calculated in the same manner as in Example 1, the Sku was 2.90. Further, the haze ratio measured in the same manner as in Example 1 was 2.6%, and the surface roughness of the surface layer was 19.4 nm.

[Comparative Example 1]
The amount of each raw material supplied from the second coating beam was 13.5 L / hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ / hour of oxygen, 58.4 kg / hour of water, and 13.7 L / hour of acetic acid (13.7 L / hour). Liquid phase), trifluoroacetic acid 3.10 L / hour (liquid phase), the film thickness of the conductive layer is 300 nm, and the amount of each raw material supplied from the third coating beam is 3.26 L of monobutyltin trichloride. A transparent electrode substrate was obtained in the same manner as in Example 1 except that the thickness of the surface layer was changed to 19 nm by changing to / hour (liquid phase), oxygen 1.23 Nm ³ / hour, and water 24.7 kg / hour. It was.
The surface layer of the obtained transparent electrode substrate was subjected to SEM observation and AFM observation in the same manner as in Example 1. An SEM image when the sample inclination angle is 60 ° is shown in FIG. 7. The surface layer does not have a surface shape having a substantially hemispherical convex portion, and a pyramid or a conical convex portion having a sharp apex. It can be seen that it has. Moreover, when the Sku was calculated in the same manner as in Example 1, the Sku was 4.07. Further, the haze ratio measured in the same manner as in Example 1 was 1.2%, and the surface roughness of the surface layer was 14.7 nm.

[Comparative Example 2]
The amount of each raw material supplied from the second coating beam was 23.5 L / hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ / hour of oxygen, 101.6 kg / hour of water, and 23.8 L / hour of acetic acid. Liquid phase), trifluoroacetic acid 3.77 L / hour (liquid phase), the film thickness of the conductive layer was 400 nm, and the amount of each raw material supplied from the third coating beam was 2.87 L of monobutyltin trichloride. A transparent electrode substrate was obtained in the same manner as in Example 1 except that the surface layer was changed to 15 nm / hour (liquid phase), oxygen 3.85 Nm ³ / hour, and water 21.7 kg / hour. It was.
The surface layer of the obtained transparent electrode substrate was subjected to SEM observation and AFM observation in the same manner as in Example 1. An SEM image when the sample inclination angle is 60 ° is shown in FIG. 8. The surface layer does not have a surface shape having substantially hemispherical protrusions, and a pyramid or a conical convex portion having a sharp apex. It can be seen that it has. Moreover, when the Sku was calculated in the same manner as in Example 1, the Sku was 3.02. Further, the haze ratio measured in the same manner as in Example 1 was 2.4%, and the surface roughness of the surface layer was 20.3 nm.

[Comparative Example 3]
The amount of each raw material supplied from the second coating beam was 17.2 L / hour (liquid phase) of monobutyltin trichloride, 35.7 Nm ³ / hour of oxygen, 74.3 kg / hour of water, and 17.4 L / hour of nitrate (17.4 L / hour). Liquid phase), trifluoroacetic acid 3.94 L / hour (liquid phase), the film thickness of the conductive layer was 415 nm, and the amount of each raw material supplied from the third coating beam was 2.77 L of monobutyltin trichloride. A transparent electrode substrate was obtained in the same manner as in Example 1 except that the surface layer was changed to 15 nm / hour (liquid phase), oxygen 3.72 Nm ³ / hour, and water 21.0 kg / hour. It was.
The surface layer of the obtained transparent electrode substrate was subjected to SEM observation and AFM observation in the same manner as in Example 1. Hitachi High-Technologies Corporation: S3400 was used as the SEM, and the acceleration voltage was set to 20.0 kV. An SEM image when the sample inclination angle is 60 ° is shown in FIG. 9. The surface layer does not have a surface shape having substantially hemispherical convex portions, and a pyramid or a conical convex portion having a sharp apex. It can be seen that it has. Moreover, when the Sku was calculated in the same manner as in Example 1, the Sku was 3.74. Further, the haze ratio measured in the same manner as in Example 1 was 1.5%, and the surface roughness of the surface layer was 16.2 nm.

As can be seen from FIGS. 4 to 9, it was found that the surface shape of the formed surface layer can be controlled by controlling the composition ratio of the raw materials when forming the surface layer. That is, when SnO ₂ is formed as the surface layer, the surface shape having substantially hemispherical convex portions can be obtained by reducing the ratio of oxygen in the raw materials.

When applied to a solar cell, the transparent electrode substrate according to the present invention can sufficiently and uniformly cover even a very thin film such as an n-type layer without defects. As a result, short circuits can be prevented without obstructing the flow of electrons, and high battery efficiency can be realized. Therefore, it is excellent as a transparent electrode for a solar cell and is very useful.

1 Transparent electrode substrate 2 CdTe solar cell 10 Glass substrate 20 Transparent conductive film 21 Conductive layer 22 Surface layer 30 Undercoat layer 40 n-type layer 50 p-type layer 60 Back surface electrode

Claims (8)

A transparent electrode substrate used in solar cells.
Including glass substrate and transparent conductive film
The transparent conductive film is composed of a conductive layer located on the glass substrate side and a surface layer.
A transparent electrode substrate having a substantially hemispherical convex portion on the surface of the surface layer. The sharpness (Kurtosis) obtained by processing the data obtained by measuring the surface layer at 1024 × 1024 points of an arbitrary 8 μm square using an atomic force microscope using SPIP image analysis software: Sku. The transparent electrode substrate according to claim 1, wherein the value of is less than 3.00. The transparent electrode substrate according to claim 1 or 2, wherein the haze ratio measured from the glass substrate side is 4% or less. The transparent electrode substrate according to any one of claims 1 to 3, wherein the surface roughness of the surface layer is 25 nm or less. The transparent electrode substrate according to any one of claims 1 to 4, wherein the conductive layer is a layer containing SnO ₂ as a main component. The transparent electrode substrate according to any one of claims 1 to 5, wherein the transparent conductive film has a film thickness of 300 to 800 nm and the surface layer has a thickness of 10 to 80 nm. The transparent electrode substrate according to any one of claims 1 to 6, further comprising an undercoat layer between the glass substrate and the transparent conductive film. A solar cell having the transparent electrode substrate according to any one of claims 1 to 7.