JP2013251377A - Substrate with transparent conductive film for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent conductive substrate for a solar cell, high in haze rate and high in light transmittance, and capable of achieving high open voltage (V) and high short circuit current (J) in a solar cell manufactured using a substrate with a transparent conductive film.SOLUTION: In a transparent conductive substrate for a solar cell, a transparent conductive oxide film is formed on a substrate. The transparent conductive oxide film is made of tin oxide or fluorine-containing tin oxide, irregularities formed of a facet of a substantially triangular pyramid, a substantially quadrangular pyramid or a substantially four or more polygonal pyramid are present on a surface of the transparent conductive oxide film. A ratio of an area (an area projected in a horizontal direction) of the facet having a facet surface angle of 70° or more relative to an area (an area projected in a horizontal direction) of the transparent conductive oxide film, the areas being measured by an atomic force microscope (AFM), is 0.05-0.25%, and a ratio of an area (an area projected in a horizontal direction) of the facet having a facet surface angle of 20° or less is 16% or less.

Description

  The present invention relates to a substrate with a transparent conductive film for solar cells.

For solar cells, it is desired to increase the photoelectric conversion efficiency in order to make the most of the energy of solar incident light.
One means for increasing the photoelectric conversion efficiency is to increase the current flowing through the substrate with a transparent conductive film for a solar cell used as an electrode for the solar cell. For this purpose, it is known to increase the haze ratio. For example, a method of providing irregularities on the surface of a transparent conductive film is known. By providing appropriate irregularities on the surface of the transparent conductive film, more effective light absorption can be achieved in the photoelectric conversion layer formed on the transparent conductive film. In other words, incident light is scattered at the interface between the transparent conductive film and the photoelectric conversion layer due to the unevenness, and a so-called light confinement effect that increases the optical path length in the photoelectric conversion layer is exhibited (see, for example, Patent Documents 1 and 2). .

JP 2006-005021 A JP 2010-262931 A

Patent Documents 1 and 2 show preferable shapes of unevenness imparted to the surface of the transparent conductive film. According to this, since there is a sharp V-shaped valley in the concavo-convex shape on the surface of the transparent conductive film, the open-circuit voltage (V _OC ) deteriorates. It would be preferable not to exist.

  As a result of intensive studies on the relationship between the uneven shape on the surface of the transparent conductive film and the characteristics as the substrate with the transparent conductive film for solar cells, the inventors of the present application have made facets that have the uneven shape, that is, the abbreviations that make the uneven shape It has been found that the facet face angle of a triangular pyramid, a substantially quadrangular pyramid, or a larger polygonal pyramid facet has an important influence on the characteristics as a substrate with a transparent conductive film for solar cells.

Specifically, when the ratio of the facet area (projection area in the horizontal direction) whose facet surface angle is greater than a specific angle to the area of the transparent conductive oxide film (projection area in the horizontal direction) is transparent, Cracks are likely to occur on the surface of the conductive film, and the open circuit voltage (V _OC ) of a solar cell produced using a substrate with a transparent conductive film is lowered.
However, if there is no facet whose facet surface angle is greater than a specific angle, the haze ratio of the transparent conductive film is lowered. Moreover, the adhesiveness of a transparent conductive film and the photoelectric converting layer formed on this transparent conductive film falls. As the photoelectric conversion layer formed on the transparent conductive film, a thin film containing silicon (Si) as a main component is used. However, since a thin film containing Si as a main component has a large film stress, When the adhesiveness with the photoelectric conversion layer formed on the conductive film is lowered, the photoelectric conversion layer may be peeled off from the transparent conductive film. Therefore, peeling of the photoelectric conversion layer can be reduced due to the presence of facets having a specific angle or more.
On the other hand, in the facet whose facet surface angle is a specific angle or less, the film thickness of the p layer directly formed on the transparent conductive film among the photoelectric conversion layers (p-i-n layers) formed on the transparent conductive film. However, it is relatively increased as compared with the case where the facet surface angle is larger than a specific angle. For this reason, when the ratio of the facet area (projection area in the horizontal direction) whose facet angle is below a specific angle to the surface area (horizontal projection area) of the transparent conductive oxide film is high, Since the p layer in the portion has a high light absorptance, the light reaching the i layer decreases due to the increase in the thickness of the p layer, the use efficiency of the light in the photoelectric conversion layer decreases, and a short circuit in the photoelectric conversion layer The current (J _sc ) decreases.

In order to solve the above-mentioned problems of the prior art, the present invention provides a high open-circuit voltage (V _OC) in a solar cell having a high haze ratio, a high light transmittance, and a transparent conductive film-coated substrate. And a transparent conductive substrate for solar cells that can achieve a high short-circuit current (J _sc ).

In order to achieve the above-described object, the present invention is a transparent conductive substrate for solar cells in which a transparent conductive oxide film is formed on a substrate,
The transparent conductive oxide film is made of tin oxide or tin oxide containing fluorine,
On the surface of the transparent conductive oxide film, there are irregularities consisting of facets of a substantially triangular pyramid, a substantially quadrangular pyramid, or a substantially more polygonal pyramid,
Measured with an atomic force microscope (AFM),
The ratio of the facet area (projection area in the horizontal direction) having a facet angle of 70 ° or more to the area (projection area in the horizontal direction) of the transparent conductive oxide film is 0.05 to 0.25%. Yes,
Transparent for solar cells in which the ratio of the facet area (projection area in the horizontal direction) whose facet angle is 20 ° or less to the area (projection area in the horizontal direction) of the transparent conductive oxide film is 16% or less A conductive substrate is provided.

  Further, in the transparent conductive substrate for a solar cell of one embodiment of the present invention, in the unevenness existing on the surface of the transparent conductive oxide film, a recess formed between a plurality of adjacent protrusions When the height difference (the difference between the height of the convex portion from the substrate surface and the height of the concave portion from the substrate surface) is taken, the ratio that the maximum height difference falls within the range of 50 to 200 nm is 60% or more. In addition, it is preferable that the C light source haze ratio of the transparent conductive substrate for solar cells is 7% or more and less than 20%.

In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the mode angle of the facet surface angle on the surface of the transparent conductive oxide film is in the range of 30 to 51 °, and the mode angle is relative to the mode angle. The standard deviation of the facet surface angle is 12 ° or less,
In the unevenness present on the surface of the transparent conductive oxide film, a difference in height from a recess formed between a plurality of adjacent protrusions (the height of the protrusion from the substrate surface and the substrate surface). The ratio of the maximum height difference in the range of 200 to 800 nm when taking the difference between the height of the concave portions of the first and second recesses is preferably 60% or more.

  Moreover, it is preferable that the transparent conductive substrate for solar cells of one embodiment of the present invention has a C light source haze ratio of 20% or more.

  Further, in the transparent conductive substrate for a solar cell of one embodiment of the present invention, the parallel direction to the surface on which the transparent conductive oxide film of the substrate is formed has an angle of 0 °, and the surface on which the oxide film is formed When measuring the X-ray diffraction pattern with the angle 90 ° in the vertical direction, the peak intensity at the angle of 40 ° is the peak intensity at the angle 90 ° with respect to the peak intensity of the diffraction peak due to the (110) plane in the X-ray diffraction pattern. It is preferably 5 times or more.

  In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the integrated intensity of the diffraction peak due to the (301) plane in the X-ray diffraction pattern of the transparent conductive oxide of the substrate is a diffraction peak due to another plane. It is preferably stronger than the integral intensity.

In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the substrate is preferably a soda lime silicate glass substrate having a light transmittance of 80% or more in a wavelength region of 350 to 1200 nm.
In the soda lime silicate glass substrate, the iron content is preferably 0.05 wt% or less in terms of the amount of iron oxide.

  In the transparent conductive substrate for a solar cell of one embodiment of the present invention, at least one of a titanium oxide layer and a silicon oxide layer is formed between the substrate and the transparent conductive oxide film. Preferably it is.

In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the transparent conductive oxide film is preferably formed using an atmospheric pressure CVD method.
In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the transparent conductive oxide film is preferably formed using atmospheric pressure CVD method using tin tetrachloride and water as main raw materials. .

  The transparent conductive substrate for a solar cell of one embodiment of the present invention preferably has an average light transmittance of 80% or more in a wavelength region of 450 to 1200 nm.

  The transparent conductive substrate for a solar cell of one embodiment of the present invention preferably has a sheet resistance of 7 to 20Ω / □.

  Another embodiment of the present invention provides a solar cell using the transparent conductive substrate for solar cell of one embodiment of the present invention.

  Still another embodiment of the present invention provides a tandem solar cell using the transparent conductive substrate for a solar cell of one embodiment of the present invention.

Another embodiment of the present invention is a method for producing a transparent conductive substrate for a solar cell according to one embodiment of the present invention, wherein a transparent conductive oxide film is formed on a substrate by a normal pressure CVD method. In the CVD method, a process gas supplied onto the substrate contains tin tetrachloride (SiCl ₄ ) and water (H ₂ O), and the flow rates of H ₂ O and SiCl ₄ in the process gas Production of transparent conductive substrate for solar cell having a ratio (H ₂ O (m / sec) / SiCl ₄ (m / sec)) of 23 times or less and a contact time of the process gas to the substrate of 90 seconds or more Provide a method.

The transparent conductive substrate for a solar cell of one embodiment of the present invention has a facet area angle of 70 ° or more on the surface of the transparent conductive oxide film, which is as low as 0.25% or less. In a solar cell manufactured using a substrate with a transparent conductive film, cracks are hardly generated, and a high open circuit voltage (V _OC ) can be achieved. On the other hand, when the area ratio of facets having a facet angle of 70 ° or more on the surface of the transparent conductive oxide film is 0.05% or more, the photoelectric conversion layer formed on the transparent conductive oxide film Adhesion is improved, and the possibility that the photoelectric conversion layer is peeled off from the transparent conductive oxide film is eliminated.
In addition, the transparent conductive substrate for solar cells of one embodiment of the present invention has a facet area ratio of a facet angle of 20 ° or less on the surface of the transparent conductive oxide film, which is as low as 16% or less. Of the formed photoelectric conversion layer (p-i-n layer), there is no influence of an increase in the thickness of the p layer formed directly on the transparent conductive film. For this reason, the utilization efficiency of the light in the photoelectric converting layer formed on a transparent conductive film becomes high, and the short circuit current ( _Jsc ) in a photoelectric converting layer improves.

FIG. 1 is a schematic diagram for explaining a facet surface angle in a transparent conductive substrate for a solar cell of one embodiment of the present invention.

  Hereinafter, the transparent conductive substrate for solar cells of one embodiment of the present invention will be described.

  The transparent conductive substrate for solar cells of one embodiment of the present invention is obtained by forming a transparent conductive oxide film on a substrate. Each structure of the transparent conductive substrate for a solar cell of one embodiment of the present invention is described below.

<Board>
Although the material of a board | substrate is not specifically limited, Glass and a plastic are suitably illustrated by the point which is excellent in translucency (light transmittance) and mechanical strength. Among these, inorganic glass is preferable because it is excellent in translucency, mechanical strength, and heat resistance and is excellent in cost.

  The kind of inorganic glass is not particularly limited, and examples thereof include soda lime silicate glass, aluminosilicate glass, lithium aluminosilicate glass, quartz glass, borosilicate glass, and alkali-free glass. Among them, soda lime silicate glass is preferable because it is colorless and transparent, is inexpensive, and can be easily obtained by specifying specifications such as area, shape, and plate thickness in the market. The soda-lime silicate glass substrate has an iron content of 0.05 wt% or less in terms of the amount of iron oxide, because absorption of visible light on the substrate is reduced and light transmittance in the visible light region is improved. preferable.

  In the case of a glass substrate containing an alkali component such as soda lime silicate glass, an alkali barrier layer for minimizing the diffusion of the alkali component from the glass to the transparent conductive oxide film formed on the upper surface thereof As at least one of the titanium oxide layer and the silicon oxide layer is preferably formed between the glass substrate and the transparent conductive oxide film. In addition, it is better to form a titanium oxide layer and a silicon oxide layer in this order from the substrate to have an antireflection effect.

When the substrate is made of glass, the thickness is preferably 0.2 to 6.0 mm. Within the above range, the balance between mechanical strength and translucency is excellent.
The substrate is preferably excellent in light transmittance in a wavelength region of 350 to 1200 nm. Specifically, the light transmittance in the wavelength region of 350 to 1200 nm is preferably 80% or more, and more preferably 85% or more.
Moreover, it is preferable that the substrate is excellent in insulation, and it is preferable that the substrate is also excellent in chemical durability and physical durability.

  The shape of the substrate is not particularly limited, and can be appropriately selected according to the shape of the solar cell manufactured using the transparent conductive substrate for solar cell of one embodiment of the present invention. For example, the cross-sectional shape may be a flat plate shape, a curved surface shape, or another different shape.

<Transparent conductive oxide film>
The transparent conductive oxide film is required to be transparent in the visible light region and to have conductivity.
In order to have high transmittance in the visible light region, the refractive index of the transparent conductive oxide film is preferably 1.8 to 2.2 at a wavelength of 400 to 800 nm, and further 1.9 to 2. 1 is preferred.
Moreover, regarding electroconductivity, it is preferable that the sheet resistance of a transparent conductive oxide film is 7-20 ohms / square, More preferably, it is 8-12 ohms / square.

In order to satisfy the above-described refractive index and sheet resistance, in one embodiment of the present invention, the transparent conductive oxide film contains tin oxide that substantially contains fluorine, tin oxide that does not contain fluorine, and fluorine. Containing tin oxide. In a preferred embodiment, in order to increase the mobility and the light transmittance, and simultaneously increase the haze ratio, a layer made of tin oxide containing no fluorine is first formed to a thickness of 100 to 1000 nm, and fluorine is formed thereon. A layer made of tin oxide is formed to a thickness of 300 to 1000 nm. The fluorine content in the layer made of tin oxide containing fluorine or the transparent conductive oxide film made of tin oxide containing fluorine is preferably such that the fluorine content relative to tin oxide is 0.01 to 4 mol%. 0.02 to 2 mol% is more preferable.
In addition, a tin oxide layer having a fluorine content of 1 ppm or less, referred to as an intermediate layer between the transparent conductive oxide film made of tin oxide containing fluorine and the photoelectric conversion layer, or a fluorine content of 0.01 to A layer made of a material having a work function higher than that of tin oxide containing 4 mol% is preferably formed with a thickness of 1 to 50 nm. This intermediate layer is preferably installed to improve the Voc of the photovoltaic layer.

As described above, in order to increase the photoelectric conversion efficiency of the solar cell, it is preferable to increase the haze ratio of the transparent conductive substrate for solar cell, and by providing irregularities on the surface of the transparent conductive oxide film, The haze ratio of the transparent conductive substrate for batteries can be increased. For this reason, the surface of the transparent conductive oxide film of one embodiment of the present invention has irregularities formed by facets of a substantially triangular pyramid, a substantially quadrangular pyramid, or more.
Note that the transparent conductive substrate for a solar cell of one embodiment of the present invention has a C light source haze ratio of 7% or more.
Since the haze value is deeply related to the height difference of the unevenness, the height difference between the protrusions and the recesses formed between a plurality of adjacent protrusions (the height of the protrusions from the substrate surface). When the ratio of the maximum height difference when the difference between the height of the recesses from the substrate surface is within the range of 50 to 200 nm is 60% or more, the C light source haze ratio is 7% or more. Less than 20%. On the other hand, the height difference (the difference between the height of the convex portion from the substrate surface and the height of the concave portion from the substrate surface) with respect to the concave portion formed between the convex portions and the adjacent convex portions was taken. When the ratio of the maximum height difference in the range of 200 to 800 nm is 60% or more, the haze ratio is preferably 20% or more, and more preferably 20% to 60%.
Further, when the X-ray diffraction pattern was measured with the direction parallel to the surface on which the transparent conductive oxide film was formed at an angle of 0 ° and the direction perpendicular to the surface on which the oxide film was formed at an angle of 90 °, Regarding the peak intensity of the diffraction peak due to the (110) plane in the X-ray diffraction pattern, when the peak intensity at an angle of 40 ° is 5 times or more of the peak intensity at an angle of 90 °, the haze ratio is preferably 20% or more. 20% to 60% is more preferable.
In addition, the height difference (the difference between the height of the convex portion from the substrate surface and the height of the concave portion from the substrate surface) with respect to the concave portion formed between the convex portions and the adjacent convex portions was taken. The maximum height difference is formed between the height from the substrate surface of the convex portion and the plurality of convex portions adjacent to the convex portion with respect to the concave and convex portions present on the surface of the transparent conductive oxide film. The maximum height difference value when the difference (height difference) between the height of the recess from the substrate surface is taken.

Moreover, in order to make C light source haze rate 20% or more, it is preferable that there is little dispersion | variation in the facet surface angle in the surface of a transparent conductive oxide film.
Specifically, it is preferable that the mode angle of the facet surface angle is in the range of 30 to 51 °, and the standard deviation of the facet surface angle with respect to the mode angle is 12 ° or less.
The most frequent angle of the facet surface angle is more preferably in the range of 35 to 48 °, and still more preferably in the range of 40 to 45 °.
Further, the standard deviation of the facet surface angle with respect to the mode angle is more preferably 10 ° or less, and further preferably 8 ° or less.

The transparent conductive oxide film in which the mode angle of the facet surface angle and the standard deviation of the facet surface angle with respect to the mode angle satisfy the above-mentioned conditions is such that the facet surface orientation is mainly oriented in the (110) plane It is. In order to obtain such a transparent conductive oxide film, the transparent conductive oxide film is formed so that the crystal growth orientation of tin oxide constituting the transparent conductive oxide film is mainly oriented in the (301) plane. What is necessary is just to form.
The mode angle of the facet surface angle refers to the mode value of the facet surface angle with respect to the horizontal plane described later when measured with an atomic force microscope (AFM).
Further, the orientation of the crystal growth direction of tin oxide can be confirmed by the peak intensity of the diffraction peak in the X-ray diffraction pattern. Specifically, an X-ray diffraction pattern is measured by the θ-2θ method, and the integrated value of 301 diffraction peaks of rutile tin oxide observed when the value of 2θ is around 66 degrees is the integrated value of all diffraction peaks. In the case of the largest of the above, the orientation of crystal growth of tin oxide is strongly oriented mainly in the (301) plane. Further, it can be confirmed that the facet plane orientation is mainly oriented in the (110) plane by measuring an X-ray diffraction pole figure for 110 diffraction. Specifically, when the X-ray diffraction pattern was measured with an angle of 0 ° parallel to the surface on which the transparent conductive oxide film was formed and an angle of 90 ° perpendicular to the surface on which the oxide film was formed, Regarding the diffraction intensity by the (110) plane in the X-ray diffraction pole figure, if the diffraction intensity at an angle of 40 ° is 10 times or more the diffraction intensity at an angle of 90 °, the facet plane orientation of the tin oxide crystal growth is mainly It is oriented in the (110) plane. That is, the transparent conductive oxide film that satisfies the above-described condition is defined by the mode angle of the facet surface angle and the standard deviation of the facet surface angle with respect to the mode angle.

As described above, in order to form a transparent conductive oxide film whose facet plane orientation is mainly oriented in the (110) plane, the crystal growth orientation of tin oxide constituting the transparent conductive oxide film is mainly (301 ) A transparent conductive oxide film may be formed so as to be oriented in the plane. To form a transparent conductive oxide film so that the crystal growth orientation of tin oxide constituting the transparent conductive oxide film is mainly oriented in the (301) plane, The flow rate ratio (H ₂ O (m / sec) / SiCl ₄ (m / sec)) of H ₂ O and SiCl ₄ in the process gas supplied onto the substrate is set to 23 times or less, and the process gas continues to the substrate. The contact time may be 90 seconds or longer.

  The transparent conductive substrate for a solar cell of one embodiment of the present invention has a facet surface angle with respect to the area of the transparent conductive oxide film (projected area in the horizontal direction) measured by an atomic force microscope (AFM). The ratio of the facet area (projection area in the horizontal direction) of 70 ° or more (the facet area ratio of the facet surface angle of 70 ° or more) is 0.05 to 0.25%.

The facet surface angle in one embodiment of the present invention can be obtained by the following procedure.
First, the height of the unevenness on the surface of the transparent conductive oxide film is measured using AFM. As an example, a range of 8 μm × 8 μm is measured with a resolution of 1024 × 1024 points on the surface of the transparent conductive oxide film. From the obtained measurement results, as shown in FIG. 1, the angle formed between the adjacent three points A, B, and C in the XY plane is selected as AB⊥AC, and the three-dimensional vector AB and the three-dimensional vector are selected. AC is obtained from the difference in height and distance between the points. The XY plane is also called a horizontal plane, and when the substrate is in a plate state, the surface of the substrate on which the transparent conductive oxide film is formed becomes the XY plane.
Therefore, the area of the transparent conductive oxide film (projected area in the horizontal direction) measured by an atomic force microscope (AFM) is defined by the area in a plane parallel to the horizontal plane.
A method of a triangular face (facet) composed of two vectors (three-dimensional vector AB, three-dimensional vector AC) by calculating an outer product of the two obtained vectors (three-dimensional vector AB, three-dimensional vector AC). A linear vector (AB × AC) is obtained.
It is composed of two vectors (three-dimensional vector AB and three-dimensional vector AC) by obtaining the angle between the obtained normal vector (AB × AC) and the vertical vector (0, 0, 1). The angle θ of the triangular surface (facet surface angle) is obtained.
The above procedure is performed for all three adjacent points for the entire surface of the transparent conductive oxide film.

  With respect to the facet having a facet angle of 70 ° or more obtained by the above procedure, the horizontal projection area is obtained, and the ratio of the transparent conductive oxide film to the horizontal projection area (the facet plane angle is 70 ° or more). The facet area ratio).

When the area ratio of facets having a facet angle of 70 ° or more is more than 0.25%, the surface of the transparent conductive oxide film is likely to crack, and the transparent conductive substrate for solar cells of one embodiment of the present invention is formed. The open-circuit voltage (V _OC ) of the solar cell manufactured using it decreases.
The area ratio of facets having a facet angle of 70 ° or more is preferably 0.2% or less, more preferably 0.15% or less, and further preferably 0.10% or less.

  On the other hand, when the area ratio of facets having a facet plane angle of 70 ° or more on the surface of the transparent conductive oxide film is less than 0.05%, the haze ratio of the transparent conductive substrate for a solar cell of one embodiment of the present invention is In addition, the adhesion between the transparent conductive oxide film and the photoelectric conversion layer formed on the transparent conductive oxide film decreases. As the photoelectric conversion layer formed on the transparent conductive oxide film, a thin film mainly composed of silicon (Si) is used. However, since the thin film mainly composed of Si has a large film stress, the transparent conductive oxide layer is formed. When the adhesion between the physical film and the photoelectric conversion layer formed on the transparent conductive oxide film is lowered, the photoelectric conversion layer may be peeled off from the transparent conductive oxide film.

Further, for a facet having a facet surface angle of 20 ° or less obtained by the above procedure, the projected area in the horizontal direction is obtained, and the ratio of the transparent conductive oxide film to the projected area in the horizontal direction (the facet surface angle is 20 °). The following facet area ratio) is obtained.
In the transparent conductive substrate for a solar cell of one embodiment of the present invention, the area ratio of facets having a facet angle of 20 ° or less is 16% or less. In the portion where the facet angle is 20 ° or less, the p layer directly formed on the transparent conductive oxide film among the photoelectric conversion layers (p-i-n layers) formed on the transparent conductive oxide film The film thickness increases relatively. Since the p layer has a high light absorptance, the increase in the thickness of the p layer results in a decrease in the amount of light reaching the i layer, a decrease in light utilization efficiency in the photoelectric conversion layer, and a short circuit current (J _sc ) decreases. If the facet surface angle is 20 ° or less and the facet area ratio is more than 16%, a sufficient short-circuit current (J _sc ) cannot be obtained.
The area ratio of facets having a facet surface angle of 20 ° or less is preferably 12% or less, and more preferably 10% or less. In particular, when the mode angle of the facet surface angle on the surface of the transparent conductive oxide film is in the range of 30 to 51 °, and the standard deviation of the facet surface angle with respect to the mode angle is 12 ° or less, The area ratio of facets having a facet surface angle of 20 ° or less is particularly preferably 12% or less.
Further, particularly in the unevenness, the height difference between the protrusions and the recesses formed between a plurality of adjacent protrusions (the height of the protrusions from the substrate surface and the height of the recesses from the substrate surface, When the ratio of the maximum height difference when the difference is taken is in the range of 50 to 200 nm is 60% or more, the area ratio of the facet having a facet angle of 20 ° or less is preferably 12% or less, It is more preferably 8% or less, and further preferably 6% or less.

The haze ratio of the transparent conductive oxide film is the difference in height of the unevenness present on the surface of the transparent conductive oxide film, that is, the height difference between the convex part and the concave part formed between the adjacent convex parts ( The height can be adjusted by the difference between the height of the convex portion from the substrate surface and the height of the concave portion from the substrate surface. The transparent conductive substrate for solar cell according to one embodiment of the present invention has a C light source for a transparent conductive substrate for solar cells when the unevenness is in the range of 50 to 200 nm and the ratio of the convex portions is 60% or more. It is preferable when the haze ratio is 7% or more and less than 20%.
Specifically, in the unevenness present on the surface of the transparent conductive oxide film, a difference in height from the concave portion formed between the convex portions and the plurality of adjacent convex portions (the height of the convex portion from the substrate surface). The ratio of the maximum height difference when the difference between the height of the recess from the substrate surface is taken to be in the range of 50 to 200 nm is preferably 60% or more.
Note that, in the unevenness, a difference in height from a recess formed between a plurality of adjacent protrusions (the difference between the height of the protrusion from the substrate surface and the height of the recess from the substrate surface). The ratio of the maximum height difference in the range of 50 to 200 nm is determined by measuring the surface of the transparent conductive oxide film using AFM, as in the facet face angle evaluation procedure described above. can get. What is necessary is just to measure the surface of the transparent conductive oxide film in a certain range using AFM, and to determine the ratio in the surface, and it is preferable in terms of accuracy to measure a range wider than the range of 8 μm × 8 μm. .
Also, the height difference between the convex portion and the concave portion formed between the adjacent convex portions (the difference between the height of the convex portion from the substrate surface and the height of the concave portion from the substrate surface) was taken. The ratio of the maximum height difference in the range of 50 to 200 nm is preferably 70% or more, and more preferably 80% or more.

  In addition, the transparent conductive substrate for a solar cell of one embodiment of the present invention has a difference in height from a concave portion formed between a plurality of convex portions adjacent to the convex portion (the height of the convex portion from the substrate surface). When the ratio of the maximum height difference in the range of 200 to 800 nm is 60% or more, the C light source haze of the transparent conductive substrate for solar cells. It is preferable for increasing the rate to 20% or more.

  The transparent conductive oxide film preferably has a film thickness of 450 to 1200 nm in order to achieve the light transmittance and sheet resistance described below, more preferably 300 to 900 nm, still more preferably 300 to 600 nm. is there.

  For the formation of the transparent conductive oxide film, it is preferable to use an atmospheric pressure CVD method because the apparatus cost is low and the film forming speed is high. In order to form a transparent conductive oxide film made of tin oxide, atmospheric pressure CVD may be performed using tin tetrachloride and water as main raw materials. In order to form a transparent conductive oxide film made of tin oxide containing fluorine, in addition to these, atmospheric pressure CVD may be performed using hydrogen fluoride as a main raw material.

  Next, the characteristic which the transparent conductive substrate for solar cells of 1 aspect of this invention has is shown.

  The transparent conductive substrate for solar cell of one embodiment of the present invention has a high haze ratio. Specifically, in the unevenness, the height difference between the protrusions and the recesses formed between the plurality of adjacent protrusions (the height of the protrusions from the substrate surface and the height of the recesses from the substrate surface, When the ratio in which the maximum height difference when the difference is taken is in the range of 50 to 200 nm is 60% or more, the C light source haze ratio is 7% or more and less than 20%, preferably 10 to 15%. It is. Further, in the unevenness, a difference in height from a recess formed between a plurality of adjacent protrusions (the difference between the height of the protrusion from the substrate surface and the height of the recess from the substrate surface). When the ratio of the maximum height difference in the range of 200 to 800 nm is 60% or more, the C light source haze ratio is 20% or more, preferably 20% or more to less than 60%.

  The transparent conductive substrate for solar cell of one embodiment of the present invention is excellent in light transmittance in the visible light region. Specifically, the average light transmittance in a wavelength region of 450 to 1200 nm is 80% or more, preferably 85% or more, more preferably 90% or more. The light transmittance averaged here is a value obtained by averaging the transmittance values obtained by measuring the wavelength region of 450 to 1200 nm at intervals of 5 nm.

  The transparent conductive substrate for solar cell of one embodiment of the present invention is excellent in conductivity. Specifically, the sheet resistance is 7 to 20Ω / □, and preferably 8 to 12Ω / □.

The transparent conductive substrate for a solar cell of one embodiment of the present invention has a difference in the structure of a photoelectric conversion layer such as amorphous silicon or crystalline silicon, or a single structure or a tandem structure. It can be used for a wide variety of solar cells. Therefore, it can be used for an amorphous silicon solar cell having a single structure. However, the C light source haze ratio is 7% or more and less than 20%, or the C light source haze ratio is as high as 20% or more, and the light transmittance in the wavelength region of 450 to 800 nm is as high as 80% or more. In the solar cell manufactured in this way, a high open circuit voltage (V _OC ) and a high short-circuit current (J _sc ) can be achieved. It is particularly preferable to use it for a solar cell having an excellent tandem structure. Of the tandem photoelectric conversion layers, the bottom cell layer thickness is particularly preferably 800 to 3000 nm.

The method for producing a transparent conductive substrate for a solar cell according to one embodiment of the present invention is such that when a transparent conductive oxide film is formed on a substrate by an atmospheric pressure CVD method, the substrate is supplied on the substrate by an atmospheric pressure CVD method. Process gas (raw material gas) contains tin tetrachloride (SiCl ₄ ) and water (H ₂ O), and the flow rate ratio of H ₂ O to SiCl ₄ in the process gas (H ₂ O) (M / sec) / SiCl ₄ (m / sec)) is 23 times or less, and the contact time of the process gas with respect to the substrate is particularly preferably 90 seconds or more.

Claims (16)

A transparent conductive substrate for solar cells in which a transparent conductive oxide film is formed on a substrate,
The transparent conductive oxide film is substantially composed of tin oxide or tin oxide containing fluorine,
On the surface of the transparent conductive oxide film, there are irregularities consisting of facets of a substantially triangular pyramid, a substantially quadrangular pyramid, or a substantially more polygonal pyramid,
Measured with an atomic force microscope (AFM),
The ratio of the facet area (projection area in the horizontal direction) having a facet angle of 70 ° or more to the area (projection area in the horizontal direction) of the transparent conductive oxide film is 0.05 to 0.25%. Yes,
Transparent for solar cells in which the ratio of the facet area (projection area in the horizontal direction) whose facet angle is 20 ° or less to the area (projection area in the horizontal direction) of the transparent conductive oxide film is 16% or less Conductive substrate.   In the unevenness present on the surface of the transparent conductive oxide film, a difference in height from a recess formed between a plurality of adjacent protrusions (the height of the protrusion from the substrate surface and the substrate surface) The ratio of the maximum height difference in the range of 50 to 200 nm is 60% or more, and the C light source haze ratio of the solar cell transparent conductive substrate is 7 The transparent conductive substrate for solar cells according to claim 1, wherein the transparent conductive substrate is at least% and less than 20%. The mode angle of the facet surface angle on the surface of the transparent conductive oxide film is in the range of 30 to 51 °, and the standard deviation of the facet surface angle with respect to the mode angle is 12 ° or less,
In the unevenness present on the surface of the transparent conductive oxide film, a difference in height from a recess formed between a plurality of adjacent protrusions (the height of the protrusion from the substrate surface and the substrate surface). The transparent conductivity for solar cells according to claim 1, wherein the ratio of the maximum height difference when the difference between the height of the concave portions of the first and second recesses is within a range of 200 to 800 nm is 60% or more. substrate.   4. The transparent conductive substrate for solar cells according to claim 3, wherein the substrate having the transparent conductive oxide film formed thereon has a C light source haze ratio of 20% or more.   When the X-ray diffraction pattern was measured with the direction parallel to the surface of the substrate forming the transparent conductive oxide film being an angle of 0 ° and the direction perpendicular to the surface of forming the oxide film being an angle of 90 °, The peak intensity of the diffraction peak due to the (110) plane in the X-ray diffraction pattern is 5 times or more of the peak intensity at an angle of 40 ° than the peak intensity at an angle of 90 °. Transparent conductive substrate.   The integrated intensity of the diffraction peak due to the (301) plane in the X-ray diffraction pattern of the transparent conductive oxide film is stronger than the integrated intensity of the diffraction peak due to the other plane. The transparent conductive substrate for solar cells described in 1.   The transparent conductive substrate for solar cells according to any one of claims 1 to 6, wherein the substrate is a soda lime silicate glass substrate having a light transmittance of 80% or more in a wavelength region of 350 to 1200 nm.   The transparent conductive substrate for solar cells according to claim 7, wherein the soda lime silicate glass substrate has an iron content of 0.05 wt% or less in terms of iron oxide.   The transparent for solar cells according to any one of claims 1 to 8, wherein at least one of a titanium oxide layer and a silicon oxide layer is formed between the substrate and the transparent conductive oxide film. Conductive substrate.   The transparent conductive substrate for solar cells in any one of Claims 1-9 in which the said transparent conductive oxide film is formed using the atmospheric pressure CVD method.   The said transparent conductive oxide film is a transparent conductive substrate for solar cells in any one of Claims 1-10 currently formed using the atmospheric pressure CVD method by using tin tetrachloride and water as a main raw material.   The transparent conductive substrate for solar cells in any one of Claims 1-11 whose average light transmittance in the wavelength range of 450-1200 nm is 80% or more.   The transparent conductive substrate for solar cells in any one of Claims 1-12 whose sheet resistance of the said transparent conductive oxide film is 7-20 ohms / square.   The solar cell using the transparent conductive substrate for solar cells in any one of Claims 1-13.   The solar cell of the tandem structure using the transparent conductive substrate for solar cells in any one of Claims 1-13. The method for producing a transparent conductive substrate for a solar cell according to claim 1, wherein a transparent conductive oxide film is formed on the substrate by atmospheric pressure CVD, wherein the transparent conductive oxide film is formed on the substrate by atmospheric pressure CVD. A method for forming a material film, wherein the process gas supplied onto the substrate by the atmospheric pressure CVD method contains tin tetrachloride (SiCl ₄ ) and water (H ₂ O), The flow rate ratio of H ₂ O to SiCl ₄ in the process gas (H ₂ O (m / sec) / SiCl ₄ (m / sec)) is 23 times or less, and the contact time of the process gas with respect to the substrate The manufacturing method of the transparent conductive substrate for solar cells which is 90 second or more.

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