JP2009239301A - Substrate and photoelectric conversion device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate comprising a transparent conductive film that has asperity suitable for confinement of light and absorbs less short wavelength light of visible region so as to increase an amount of incident light to a photoelectric conversion layer of a solar cell, as well as a photoelectric conversion device using the substrate. <P>SOLUTION: The substrate comprises: a glass plate containing alkaline components, an underlayer film, formed on the glass plate, including (i) a first underlayer being 35 to 100 nm in thickness and containing tin oxide, (ii) an amorphous second underlayer, formed on the first underlayer, being thinner than the first underlayer and 5 to 50 nm in thickness, the under layer film having asperity; a non-doped buffer layer, formed on the underlayer film, being 10 to 250 nm in thickness and containing tin oxide as a main component; and a doped transparent conductive film, formed on the buffer layer, containing tin oxide as a main component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a substrate provided with a transparent conductive film used for a photoelectric conversion element or the like. Furthermore, the present invention relates to a photoelectric conversion device using the same.

Solar cells are attracting attention against the background of energy problems and environmental problems in recent years. There are various types of solar cells. Above all, thin-film solar cells are considered to become mainstream from the viewpoint of resource saving. The general structure of a thin film solar cell is as follows. A transparent conductive film made of tin oxide (SnO ₂ ), a photoelectric conversion layer made of an amorphous semiconductor such as amorphous silicon or amorphous silicon germanium, and a conductive film are sequentially laminated on a transparent substrate such as a glass plate. .

Solar cells are constantly required to improve the photoelectric conversion efficiency, and various techniques have been developed and put into practical use. A typical example is a technique that exhibits a so-called light confinement effect by making the surface of the transparent conductive film uneven so that incident light is scattered there to increase the optical path length in the photoelectric conversion layer. Such irregularities on the surface of the transparent conductive film are derived from crystal growth of tin oxide. In order to grow the crystal grains of the tin oxide film greatly, it is effective to form the film at a high temperature and / or to thicken the film. For example, Patent Document 1 describes a conductive film solar cell substrate formed by atmospheric pressure chemical vapor deposition using SnCl ₄ , H ₂ O, CH ₃ OH and HF as raw materials and having a large number of protrusions on the surface. Yes.

  Furthermore, in order to increase the photoelectric conversion efficiency of the solar cell, it is indispensable to increase the amount of incident light to the photoelectric conversion layer, and there is a technique for reducing the reflectance of the incident light and a technique for reducing the absorption rate of the transparent conductive film. Has been developed. For example, Patent Document 2 proposes a tin oxide film that has a low absorption coefficient in a wavelength region in which a solar cell can be effectively used.

Japanese Patent No. 2862174 JP 2001-35262 A

  However, in Patent Document 1, which aims to further develop the crystal grains of the tin oxide film using tin chloride as a raw material and to improve the productivity by increasing the film formation rate, it is higher than 615 ° C. A transparent conductive film having a thickness of 350 nm or more is formed on the surface of the glass substrate at a temperature by a thermal decomposition method. When the film is formed at such a high temperature, the crystal grains are not uniformly formed in the surface, so that the transparent conductive film having a very high haze and white turbidity is obtained. When a photoelectric conversion device is configured by forming an amorphous silicon layer on the transparent conductive film, there is a problem that the amorphous silicon film as the photoelectric conversion layer is not uniformly formed, and the efficiency of the solar cell is lowered.

  Furthermore, when dimethyltin dichloride or monobutyltin trichloride is used as a tin raw material other than the above, although it does not become cloudy, the wavelength range of 400 to 700 nm where the amount of sunlight spectrum reaching the ground is large, especially its short wavelength Since the absorptance on the side increases, there is a problem that the amount of incident light on the photoelectric conversion layer of the solar cell eventually decreases. For example, Patent Document 2 describes the absorption coefficient of a tin oxide film using dimethyltin dichloride or monobutyltin trichloride as a raw material. The absorption coefficient is lowest at a wavelength of about 600 to 700 nm, and the absorption coefficient at 400 nm. Is more than 1.8 times the above range.

  The present invention has been made paying attention to such problems existing in the prior art. The purpose is to provide a transparent surface with an optimal concavo-convex shape for demonstrating the light confinement effect in order to increase the amount of light incident on the photoelectric conversion layer of the solar cell and with little absorption in the short wavelength region of visible light. It is providing the board | substrate provided with an electrically conductive film. Furthermore, it is providing the photoelectric conversion apparatus using the board | substrate.

In order to solve such problems in the prior art, the substrate of the present invention is
A glass plate containing an alkaline component;
Formed on the glass plate, (i) has a film thickness in the range of 35 to 100 nm, and includes a first underlayer containing tin oxide as a main component; and (ii) formed on the first underlayer, A base film having irregularities, including an amorphous second base layer having a thickness in the range of 5 to 50 nm and thinner than the first base layer;
A non-doped buffer layer formed on the base film, having a thickness in the range of 10 to 250 nm and containing tin oxide as a main component;
And a doped transparent conductive film formed on the buffer layer and containing tin oxide as a main component.

The transparent conductive film has an absorption coefficient in a wavelength range of 400 to 700 nm of 1 × 10 ³ cm ⁻¹ or less, a maximum value of the absorption coefficient of 1.7 times or less of a minimum value, and a sheet resistance of 15Ω / □ or less, a film thickness of 1,000 nm or less, and a haze ratio of 12% or more.

  The second underlayer may contain silicon oxide as a main component.

  The buffer layer may have a film thickness in the range of 50 to 150 nm.

  Moreover, the photoelectric conversion device of the present invention uses the substrate of the present invention.

1 is a schematic view of an apparatus used in an online CVD method. It is the figure which image-processed the photograph which image | photographed the buffer layer of thickness 90nm using SEM at the dip angle of 30 degrees to the black-and-white binary. It is the figure which image-processed the photograph which image | photographed the buffer layer of thickness 140nm using the SEM at the dip angle of 30 degrees into the black-and-white binary. It is the figure which image-processed the photograph which image | photographed the buffer layer of thickness 190nm using the SEM at the dip angle of 30 degrees to the black-and-white binary.

  Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiment.

  When forming a transparent conductive film by thermal decomposition using tin chloride as a raw material on a transparent substrate such as a glass plate having a temperature higher than 615 ° C., the present inventors previously form a buffer layer having a thickness of 250 nm or less. And it discovered that a transparent conductive film did not become a cloudy, high haze state. This phenomenon is considered to occur as follows. Since tin chloride is more reactive than organotin compounds such as dimethyltin dichloride and monobutyltin trichloride, it is not suitable for glass plates and silicon oxide films at high temperatures where the reaction is more activated in the thermal decomposition method. When directly supplied onto the amorphous film, crystal nuclei are not uniformly generated on the surface, and crystal growth proceeds starting from the locally formed crystal nuclei. Crystal particles are formed. And this huge crystal particle macroscopically exhibits a cloudy high haze state. On the other hand, if a buffer layer is formed in advance on a transparent substrate, the surface of the buffer layer functions as a starting point for crystal growth, and a large number of crystal growths proceed at the same time. Is not formed, and the transparent conductive film does not become a cloudy high haze state.

  Since the buffer layer is a thin film mainly composed of crystalline metal oxide or metal and includes a large portion of crystal growth of the transparent conductive film formed thereon, at least from the transparent conductive film Needs to have a smooth surface and a large number of minute irregularities derived from a metal oxide or metal crystal on the surface. Examples of the metal oxide include, but are not limited to, tin oxide, titanium oxide, zinc oxide, zirconium oxide, or tin oxide doped with indium (ITO). Examples of the metal include tin, titanium, silicon, and alloys thereof. Among these, the buffer layer mainly composed of tin oxide has the same main component as the transparent conductive film, so that the starting point of crystal growth is increased in the formation of the transparent conductive film, and the thickness hardly varies. Become. Furthermore, the adhesive strength between the buffer layer and the transparent conductive film increases, and the durability and weather resistance of the substrate and the photoelectric conversion device are improved. The “main component” refers to a state where the composition component content is 50% by mass or more according to common usage.

  The thickness of the buffer layer is desirably 10 nm or more so that the entire surface of the substrate can be covered. If the thickness is less than 10 nm, it is difficult to cover the entire surface of the substrate. On the other hand, if it is too thick, minute irregularities on the surface of the buffer layer become large and affect the uniformity of the transparent conductive film, and therefore it is preferably 250 nm or less, more preferably 150 nm or less. Since this point is closely related to the surface state of the substrate or the base film, it will be described in detail later.

  When the buffer layer is formed by the same thermal decomposition method as that of the transparent conductive film, the buffer layer is formed by making the film formation rate slower than the film formation rate of the transparent conductive film. For example, when a transparent conductive film is formed by a chemical vapor deposition method (CVD method), the film is formed at a temperature lower than the reaction system temperature at the time of forming the transparent conductive film, or a raw material that is less reactive than the raw material of the transparent conductive film Or using a raw material having a lower concentration than the raw material of the transparent conductive film. Further, when a film is formed on the glass ribbon in the float bath by the CVD method using the same raw material, the film formation rate can be reduced by making the buffer layer thinner than the transparent conductive film. Even if the film formation rate of the buffer layer itself is slow, the thickness is 250 nm or less, which is considerably thinner than the transparent conductive film, so that the overall film formation rate including the transparent conductive film does not significantly decrease. Rather, the existence of the buffer layer can increase the film formation rate of the transparent conductive film. Therefore, if the buffer layer is relatively thin and the transparent conductive film is formed faster at a higher temperature, the overall film formation rate can be increased. it can. The buffer layer may be formed by a method different from the method for forming the transparent conductive film. For example, the buffer layer may be formed by uniformly applying a fine powder to the substrate surface using a powder spray method.

  The buffer layer is a stone for increasing the film forming speed of the transparent conductive film, and the film forming speed is compensated. However, when the buffer layer is formed by the CVD method, the film forming speed can be increased by roughening the surface on which the buffer layer is formed, that is, the surface of the substrate or the surface of the base film. For example, if the substrate is a glass plate, the surface can be roughened on the nanometer order by immersing the glass plate in an acid solution or an alkali solution for a predetermined time. Further, in the case where a base film is formed on the substrate, minute irregularities can be formed on the surface by using a crystalline base film. Thus, if the surface on which the buffer layer is formed is roughened, that is, not smooth, in the CVD method, the non-smooth surface is buffered in the same manner as the buffer layer increases the deposition rate of the transparent conductive film. Increase the deposition rate of the layer.

The transparent conductive film has an absorption coefficient of 1 × 10 ³ cm ⁻¹ or less in a wavelength range of 400 to 700 nm, a maximum value of the absorption coefficient of 1.7 times or less of a minimum value, and sheet resistance. It is desirable for the transparent conductive film for solar cells to be 15Ω / □ (square) or less. The wavelength range of 400 to 700 nm is a region where the amount of light of the solar spectrum reaching the ground is large, and is a wavelength region that should be emphasized in order to increase the photoelectric conversion efficiency of the solar cell. Reducing the absorption of the transparent conductive film over the entire wavelength range leads to an increase in the amount of light incident on the photoelectric conversion layer. As a result of studies by the present inventors, when a tin oxide film is formed on a glass plate at a high temperature using tin chloride, an extra impurity component is not added, so that the tin oxide film is absorbed in a wavelength region of 400 to 700 nm. It was possible to reduce. Since the transparent conductive film also serves as a solar cell electrode, it is preferable that the sheet resistance is low. However, in the conventional case, when the sheet resistance is reduced, absorption in the long wavelength region increases due to absorption of free electrons and short. Absorption in the wavelength range also increased. When a tin oxide film is formed on a substrate at a high temperature using tin chloride, the absorption coefficient of the tin oxide film in the wavelength region of 400 to 700 nm is 1 × 10 ³ cm while maintaining a sheet resistance of 15Ω / □ or less. ⁻¹ or less, and the absorption coefficient can be reduced so that the maximum value is 1.7 times or less of the minimum value.

  Moreover, if the surface of a transparent conductive film is uneven | corrugated as above-mentioned, the light confinement effect will be show | played and the photoelectric conversion efficiency of the photoelectric conversion apparatus represented by the solar cell can be improved. Conventionally, a thick transparent conductive film has been formed as means for forming the unevenness. Since the transparent conductive film is mainly composed of tin oxide, it is crystalline. As the transparent conductive film becomes thicker, individual crystals become larger and the surface irregularities thereof become larger. However, if the transparent conductive film becomes thick, the problem of absorption occurs as described above. Therefore, the transparent conductive film is required to be thin and have relatively large and uniform surface irregularities. In order to form such a transparent conductive film, it is effective to increase the thickness of the buffer layer. If the buffer layer is made thicker, the minute irregularities on the surface can be enlarged, and the transparent conductive film formed thereon has the large minute irregularities as the starting point for crystal growth. However, the surface unevenness can be increased. However, if the micro unevenness of the buffer layer becomes larger than necessary, the transparent conductive film becomes cloudy as described above, or even if the transparent conductive film can be formed at a high speed, the overall film formation speed including the buffer layer is increased. Various problems occur, such as slowing down. Therefore, the buffer layer is not necessarily thick, and the preferred range of the thickness is limited to a range in which the surface unevenness of the transparent conductive film can be appropriately increased. That is, the thickness of the buffer layer needs to be 250 nm or less, preferably 100 to 200 nm, and most preferably 140 to 150 nm. For reference, a sample of a first base layer made of tin oxide, a second base layer made of silicon oxide, and a buffer layer made of tin oxide formed in this order on a glass substrate by scanning the buffer layer is scanned. FIGS. 2 to 4 show images obtained by processing a photograph taken at a depression angle of 30 ° using a scanning electron microscope (SEM) into a monochrome binary image. 2 shows a case where the buffer layer is 90 nm, FIG. 3 shows a case where the buffer layer is 140 nm, and FIG. 4 shows a case where the buffer layer is 190 nm. These have the same configuration except that the thickness of the buffer layer is different. As is clear from the comparison of FIGS. 2 to 4, it can be seen that the thicker the buffer layer, the larger the micro unevenness on the surface. In addition, the transparent conductive film formed on the buffer layer is easily expected to have surface irregularities corresponding to the surface shape of the buffer layer.

  Specifically, the sheet resistance of the transparent conductive film is preferably 5 to 15Ω / □. Considering this value, the preferable film thickness of the conductive film is 500 to 2,000 nm. However, considering the absorption of visible light as described above, a more preferable film thickness is 500 to 1,000 nm.

  Further, a first underlayer having a refractive index of 1.6 to 2.5 and a thickness of 5 to 100 nm, a refractive index of 1.4 to 2.0, and a film thickness of 5 to 100 nm between the substrate and the buffer layer. When a base film composed of two base layers is formed, the reflectance can be reduced, and the amount of light incident on the photoelectric conversion layer of the photoelectric conversion device can be increased. In addition to the role of reducing the reflectance and reflection interference color, the base film diffuses into the buffer layer and the transparent conductive film if the substrate is a glass plate containing an alkali component. It also plays a role in suppressing the decrease in conductivity. The first underlayer in contact with the substrate is preferably composed mainly of at least one selected from the group consisting of tin oxide, titanium oxide, zinc oxide and aluminum oxide. The second underlayer in contact with the buffer layer is preferably composed mainly of at least one selected from the group consisting of silicon oxide, aluminum oxide, silicon oxynitride, silicon oxycarbide, and tin oxide. When the base film is too thin, the function of preventing diffusion of the alkali component is not sufficiently exhibited. On the other hand, if it is too thick, the reflectance reduction effect is lost and the transmittance is lowered.

  Further, when the first underlayer is a crystalline thin film containing tin oxide or titanium oxide as a main component, the surface roughness due to crystal growth can be increased as the thickness is increased. Since the surface irregularities of the first underlayer are reflected on the surface of the second underlayer, the first underlayer is thickened to 40 to 100 nm, while the dense and amorphous second underlayer is thinned to 5 to 50 nm. By doing so, it is possible to reliably prevent the alkali component contained in the glass plate from diffusing into the buffer layer and the transparent conductive film while increasing the surface roughness of the base film.

  In addition, when the substrate is a glass plate containing an alkali component, when the first underlayer is formed by a pyrolysis method, a material containing halogen is used to derive crystal growth on the surface of the first underlayer. A convex portion or a concave portion larger than the concave and convex portions to be formed can be formed. About this comparatively large convex part thru | or a recessed part, the alkali component of a glass plate and the halogen contained in the raw material of a 1st base layer react, and an alkali-halogen particle is formed, and this is taken in in a 1st base layer. A convex part is formed by this, or a concave part is formed by disappearing with heat. These convex portions and concave portions are reflected in the surface shape of the second underlayer. Therefore, if the crystalline first underlayer and the amorphous second underlayer are formed by the thermal decomposition method, the surface shape of the underlayer reflects the irregularities resulting from the crystal growth and the protrusions or depressions. Can be made. This means that the base film can be processed to a non-smooth surface. From this, it can be said that if the base film is formed by a thermal decomposition method, the film formation rate of the buffer layer can be increased as described above.

  Further, as a method for producing such a transparent conductive film, the cut glass plate may be heated to a temperature higher than 615 ° C. However, in the glass ribbon in the float glass plate production process, the glass temperature becomes higher. In addition, the effects of the present invention are more effectively exhibited. When the present inventors examined in detail, when forming a transparent conductive film in the state without a buffer layer, the higher the temperature of the substrate such as cut glass or glass ribbon, the more the area of the cloudy state is expanded. confirmed. That is, the higher the temperature of the transparent substrate or base film, the greater the effect of the buffer layer.

  The raw material of the transparent conductive film used in the thermal decomposition method desirably contains tin chloride in a gaseous state and a reactive gas. The tin chloride and the reactive gas may be in a gas state in the vicinity of the substrate, and may be in a liquid state or a solid state in the supply path. In other words, the thermal decomposition method is preferably a CVD method in which tin chloride is supplied in a gaseous state, but it may be a solution spray method in which the route is supplied in liquid or a powder spray method in which it is supplied in a solid state. Absent. Further, in the CVD method, the gaseous tin chloride and the reactive gas may be supplied through different paths so that they react in the vicinity of the substrate, or the separation gas is provided between the gaseous tin chloride and the reactive gas. May be supplied at the same time. However, when the gaseous tin chloride and the reactive gas are premixed in the middle of the path, a cloudy, high haze state occurs at a larger area or at a lower temperature. It becomes. In the case of the premix, since the mixing of the gaseous tin chloride and the reactive gas is fast, the reaction takes place quickly, and if there is no buffer layer, the crystal growth base (in this case mainly, Before the crystal nuclei) are formed, it is thought that individual crystals grow rapidly and cause a cloudy state.

  Further, from the viewpoint of energy efficiency and film formation on a large area, an on-line CVD method is preferable in which film formation is performed in a float bath in a glass manufacturing process of the float method. In this manufacturing method, since the substrate is a molten glass ribbon, the temperature is as high as about 620 to 750 ° C., and the buffer layer of the present invention is used to form a film using gaseous tin chloride. There is a need to.

  An embodiment of an apparatus for on-line CVD is shown in FIG. In this apparatus, a predetermined number of coaters 16 (shown in the figure) are separated from the surface of the glass ribbon 10 which flows out from a melting furnace (float kiln) 11 into a tin float bath (float bath) 12 and moves in a strip shape on the tin bath 15. In this configuration, three coaters 16a, 16b, 16c) are arranged in the tin float tank. From these coaters, a gaseous raw material is supplied, and a thin film is continuously formed on the glass ribbon 10. If a plurality of coaters are used, the base film, the buffer layer, and the transparent conductive film can be continuously formed on the glass ribbon 10. The glass ribbon 10 after the thin film formation is pulled up by the roller 17 and fed into the slow cooling furnace 13. The glass ribbon slowly cooled in the slow cooling furnace 13 is cut into a glass plate of a predetermined size by a cutting device (not shown).

  Note that the transparent conductive film may be formed by using both the online CVD method and the spray method. For example, an online CVD method and a spray method may be performed in this order. (For example, film formation by the CVD method is performed in the float bath space, and film formation by the spray method is performed downstream of the float bath space in the glass ribbon traveling direction)

  Examples of tin chloride that can be used in the pyrolysis method include stannous chloride and stannic chloride, but stannic chloride that is easy to handle and has high stability is desirable. The same raw material may be used for the buffer layer and the transparent conductive film, or different raw materials may be used for the purpose of slowing the film formation rate of the buffer layer. For example, organotin compounds such as dimethyltin dichloride and monobutyltin chloride are preferable as a raw material for the buffer layer because they are less reactive than stannic chloride. In addition, although using an organic tin compound as a raw material of a transparent conductive film is also considered, when simplification of an installation is considered, it is preferable to use stannic chloride.

  In the formation of the transparent conductive film, it is desirable to use stannic chloride in a gaseous state as tin chloride and use water vapor as a reactive gas in combination as an oxidation raw material. Water vapor is convenient for decomposing stannic chloride by a hydrolysis reaction. In addition, oxygen, air, alcohols such as methyl alcohol and ethyl alcohol can also be used as the oxidation raw material. Further, these gases may be used in combination with water vapor. Incidentally, the absorption coefficient in the wavelength 600-800 nm of a transparent conductive film can be reduced by using water vapor | steam and oxygen together, or raising the density | concentration of water vapor | steam. When water vapor and oxygen are used in combination, the concentration of water vapor is preferably 30 to 70 mol / L and the concentration of oxygen is preferably 5 to 30 mol / L. When only water vapor is used, the concentration is 40 to 95 mol / L. Is preferred.

  In order to improve the conductivity of the transparent conductive film, it is preferable to add an antimony or fluorine compound. Examples of the antimony compound include antimony trichloride and antimony pentachloride, and examples of the fluorine compound include hydrogen fluoride, trifluoroacetic acid, bromotrifluoromethane, and / or chlorodifluoromethane. In order to further increase the conductivity, addition of fluorine is preferable. A preferable fluorine concentration in the transparent conductive film is 0.2% by mass or less. At this time, the refractive index of the transparent conductive film is about 1.9. The transparent conductive film may contain other trace components such as silicon, aluminum, zinc, copper, indium, bismuth, gallium, boron, vanadium, manganese and / or zirconium. However, the concentration of these trace components is preferably 0.02% by mass or less.

  The transparent conductive film is likely to be clouded and has a large area when the glass ribbon is at a temperature higher than 615 ° C. and the film forming rate is 600 nm / min or more. This invention can exhibit the effect effectively in formation of the transparent conductive film in the said environment.

  In addition, when forming a thin film mainly composed of silicon oxide as a base film by the CVD method, the raw materials are monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, 1,2-dimethylsilane, 1,1,2- Examples thereof include trimethyldisilane, 1,1,2,2-tetramethyldisilane, tetramethylorthosilicate and / or tetraethylorthosilicate. In this case, examples of the oxidation raw material include oxygen, water vapor, dry air, carbon dioxide, carbon monoxide, nitrogen dioxide and / or ozone. In addition, when using silane, you may use unsaturated hydrocarbon gas, such as ethylene, acetylene, or toluene, in order to suppress the reaction of silane until it reaches the glass surface.

  Similarly, when a thin film mainly composed of aluminum oxide is formed by CVD as a base film, the raw materials include trimethylaluminum, aluminum triisopropoxide, diethylaluminum chloride, aluminum acetylacetonate and / or aluminum chloride. It is done. In this case, examples of the oxidation raw material include oxygen, water vapor, and / or dry air.

  Hereinafter, the case where a substrate provided with a buffer layer and a transparent conductive film is used for a photoelectric conversion element will be described in detail. A photoelectric conversion element is obtained by sequentially forming a base film, a buffer layer, a transparent conductive film, a photoelectric conversion layer such as amorphous silicon or a crystalline silicon thin film, and a conductive film (back electrode) on a substrate. In addition, a photoelectric conversion device in which a photoelectric conversion element is incorporated and each component is linked and unitized to a state where electric energy can be extracted from light energy as a solar cell is referred to as a photoelectric conversion device.

  The photoelectric conversion layer may have a single layer configuration, or may have a configuration in which several layers are stacked. Further, it may be a conventional amorphous silicon thin film or a crystalline silicon thin film. Further, a so-called hybrid tandem type may be formed by combining an amorphous silicon thin film and a crystalline silicon thin film. In the case of the hybrid tandem type, an amorphous silicon thin film is usually formed on a transparent conductive film, and a crystalline silicon thin film is formed thereon.

The amorphous silicon thin film is formed by depositing each semiconductor layer by plasma CVD in the order of pin type. Specifically, a p-type microcrystalline silicon-based layer doped with 0.01 atomic% or more of boron, which is a conductivity type determining impurity atom, an intrinsic amorphous silicon layer mainly responsible for photoelectric conversion, and a conductivity type determining impurity atom. An example is one in which n-type microcrystalline silicon-based layers doped with 0.01% or more of certain phosphorus are deposited in this order. However, these layers are not limited to the above. For example, an amorphous silicon-based layer may be used for the p-type layer, or aluminum or the like may be used for impurity atoms in the p-type microcrystalline silicon-based layer. Further, an alloy material such as amorphous or microcrystalline silicon carbide or silicon germanium may be used for the p-type layer. The film thickness of the conductive (p-type, n-type) microcrystalline silicon-based layer is preferably 3 to 100 nm, and more preferably 5 to 50 nm. The film thickness of the intrinsic amorphous silicon layer is preferably 0.05 to 0.5 μm. However, in a photoelectric conversion element including an amorphous silicon thin film, an amorphous silicon carbide layer (for example, amorphous silicon containing 10 atomic% or less of carbon) is used instead of an intrinsic amorphous silicon layer. An amorphous silicon carbide layer) or an amorphous silicon germanium layer (for example, an amorphous silicon germanium layer made of amorphous silicon containing 30 atomic% or less of germanium) may be used. The intrinsic amorphous silicon layer is preferably formed by a plasma CVD method at a substrate temperature of 450 ° C. or lower. This layer is formed as a thin film that is substantially an intrinsic semiconductor having a conductivity type determining impurity atom density of 1 × 10 ¹⁸ cm ⁻³ or less.

  The crystalline silicon thin film can be formed by depositing the p-i-n type semiconductor layers in this order by the plasma CVD method in the same procedure as the amorphous silicon thin film. Alternatively, it can be formed by electron beam evaporation using silicon as a raw material, plasma CVD method using glow discharge using monosilane diluted with hydrogen gas as a raw material, or thermal CVD method using monosilane or dichlorosilane. The film thickness of the crystalline silicon thin film is preferably 0.1 to 10 μm, particularly preferably 5 μm or less. Since this thin film is formed at a low temperature of 450 ° C. or less, for example, in the plasma CVD method, it contains a relatively large amount of hydrogen atoms for terminating or inactivating defects in crystal grain boundaries and grains. The hydrogen content in the layer is preferably in the range of 0.5 to 30 atomic%, particularly 1 to 20 atomic%.

  In the case of a hybrid tandem photoelectric conversion element, although it depends on the configuration of the photoelectric conversion device, the thickness of the amorphous silicon thin film is preferably 0.05 to 0.4 μm, and the thickness of the crystalline silicon thin film is 0.5 to 5 μm is preferable.

  Incidentally, the spectral sensitivity characteristic of the amorphous silicon thin film is maximized in a wavelength range of about 500 to 600 nm, and has sensitivity only up to a wavelength range of about 800 nm due to an optical energy gap. On the other hand, the crystalline silicon thin film has sensitivity up to about 1,100 nm.

  As the back electrode, at least one metal layer made of at least one material selected from aluminum (Al), silver (Ag), gold (Au), copper (Cu), platinum (Pt) and chromium (Cr) is used. It is preferably formed by a sputtering method or a vapor deposition method. In addition, a layer made of a conductive oxide such as ITO, tin oxide, or zinc oxide may be formed between the photoelectric conversion element and the back electrode.

  In addition, the photoelectric conversion element provided with the crystalline silicon thin film has a low open-circuit voltage generated and a high short-circuit current density as compared with the one provided with the amorphous silicon thin film. Therefore, in the photoelectric conversion device provided with the crystalline silicon thin film, the transmittance has a greater influence on the photoelectric conversion efficiency than the sheet resistance value of the transparent conductive film.

  Hereinafter, the present invention will be described specifically by way of examples. However, it is not limited to the following examples.

(Reference Example 1)
A 4 mm thick soda lime glass plate cut to 150 × 150 mm was placed on a mesh belt, passed through a heating furnace, and heated to about 600 ° C. While this heated glass plate is further conveyed, a mixed gas consisting of monosilane, oxygen and nitrogen is supplied from a coater installed above the conveyance path to form a 25 nm thick silicon oxide thin film (underlayer film) on the glass plate. did. After this glass plate was slowly cooled, it was again placed on a mesh belt, passed through a heating furnace, and heated to about 620 ° C. While further transporting the heated glass plate, a mixed gas composed of stannic chloride (steam), oxygen, water vapor, and nitrogen is supplied from a coater installed above the transport path, and a buffer with a film thickness of 30 nm is formed on the base film. The layer was formed at a deposition rate of 50 nm / min. After this glass plate was slowly cooled, it was again placed on a mesh belt, passed through a heating furnace, and heated to about 620 ° C. While further transporting this heated glass plate, a mixed gas consisting of stannic chloride (steam), water vapor, nitrogen and hydrogen fluoride is supplied from a coater installed above the transport path, and a thickness of 800 nm is formed on the buffer layer. A transparent conductive film made of fluorine-containing tin oxide (SnO ₂ : F) was formed at a film formation rate of 670 nm / min. Further, the distance between the coater and the glass plate was set to 10 mm, and nitrogen gas was supplied to the side of the exhaust portion in a curtain shape so that outside air was not mixed inside the coater during the formation of the transparent conductive film.

  About the glass plate provided with this transparent conductive film, when the haze rate was measured using the integrating sphere, it was 22%, and the cloudy high haze state was not seen. The reflectance, absorption coefficient, and sheet resistance are shown in “Table 1” below. The reflectance was measured in the wavelength range of 400 to 1,100 nm from the surface of the glass plate on which the transparent conductive film was not provided, and obtained by averaging the values at a 10 nm pitch. The absorption coefficient was determined for each wavelength of 400, 500, 600 and 700 nm by the following method.

[Measurement of absorption coefficient]
On the transparent conductive film produced by the above means, methylene iodide having a refractive index of 1.79 is applied, and a 1 mm thick cover glass (# 7059 manufactured by Corning Inc.) is further adhered thereon, so that the transparent conductive film The sample which eliminated the scattering loss by the surface unevenness of was manufactured. The transmittance and reflectance of this sample in the visible light range were measured using a spectrophotometer, and the absorption rate was obtained from the result. On the other hand, methylene iodide is applied to a soda lime glass plate having only the base film, and the cover glass is adhered to the sample so as to produce a reference sample. Absorption rate was determined. And the absorption coefficient of the electrically conductive film was calculated | required by subtracting the absorption rate of the sample for a reference from the absorption rate of a sample, and also solving the equation which considered multiple reflection.

(Reference Example 2)
A glass plate provided with a transparent conductive film was prepared in the same manner as in Reference Example 1 except that the conditions were changed as follows. A 20 nm thick silicon oxide thin film (underlying film) was formed on a glass plate, and a 100 nm thick buffer layer was formed thereon at a deposition rate of 170 nm / min. A transparent conductive film made of fluorine-containing tin oxide (SnO ₂ : F) having a thickness of 720 nm is formed on the buffer layer by supplying a mixed gas consisting of stannic chloride (vapor), oxygen, water vapor, nitrogen and hydrogen fluoride. The film was formed at a film speed of 480 nm / min. This glass plate had a haze ratio of 17%, and no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

(Reference Example 3)
A glass plate provided with a transparent conductive film was prepared in the same manner as in Reference Example 1 except that the conditions were changed as follows. A mixed gas composed of stannic chloride (steam), water vapor and nitrogen was supplied, and a buffer layer having a thickness of 50 nm was formed on the base film at a deposition rate of 510 nm / min. When this buffer layer was observed with an electron microscope, it was confirmed that tin oxide was granular on the base film (a state where each crystal was clearly larger than the buffer layer of Reference Example 1). Supplying a mixed gas consisting of stannic chloride (vapor), oxygen, water vapor, nitrogen and hydrogen fluoride, and forming a transparent conductive film made of fluorine-containing tin oxide (SnO ₂ : F) with a thickness of 950 nm on the base film The film was formed at a film forming speed of 8,120 nm / min. This glass plate had a haze ratio of 29%, but no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

Example 1
Using an on-line CVD method, a base film, a buffer layer, and a transparent conductive film were formed in this order on a glass ribbon. Specifically, 98% by volume of nitrogen and 2% by volume of hydrogen are supplied into the float bath space so that the inside of the float bath space is maintained at a slightly higher pressure than the outside of the bath, and the inside of the bath is not oxidized. A mixed gas composed of dimethyltin dichloride (vapor), oxygen, nitrogen and helium is supplied from the first coater located on the most upstream side while maintaining a neutral atmosphere, and a tin oxide thin film having a thickness of 35 nm on a glass ribbon (First underlayer) was formed. Subsequently, a mixed gas consisting of monosilane, ethylene, oxygen and nitrogen was supplied from the second coater to form a silicon oxide thin film (second underlayer) having a thickness of 25 nm on the first underlayer. Further, a mixed gas composed of dimethyltin dichloride (steam), oxygen, water vapor and nitrogen is supplied from the third coater, and the tin oxide (SnO ₂ ) having a thickness of 50 nm is formed on the second underlayer having a surface temperature of 690 ° C. A buffer layer was formed at a deposition rate of 1,250 nm / min. Furthermore, using a coater installed on the downstream side, a mixed gas consisting of stannic chloride (steam), water vapor, nitrogen, helium and hydrogen fluoride is supplied at a glass temperature of 630 ° C., and SnO ₂ : F having a thickness of 740 nm is used. A transparent conductive film was formed at a deposition rate of 18,500 nm / min. This glass plate had a haze ratio of 17%, and no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

(Example 2)
In Example 1, the glass plate provided with the transparent conductive film was produced similarly except having changed into the conditions specified below. A mixed gas composed of stannic chloride (steam), water vapor, nitrogen and helium was supplied from the first coater to form a 45-nm-thick tin oxide thin film (first underlayer) on the glass ribbon. A buffer layer made of tin oxide (SnO ₂ ) having a thickness of 90 nm is supplied on a base film having a surface temperature of 680 ° C. by supplying a mixed gas made of stannic chloride (vapor), oxygen, water vapor and nitrogen from the third coater. Was formed at a film forming rate of 1,830 nm / min. Further, using a coater installed on the downstream side, a transparent conductive film made of SnO ₂ : F having a glass temperature of 630 ° C. and a thickness of 690 nm was formed at a deposition rate of 7,030 nm / min. This glass plate had a haze ratio of 20%, and no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

(Example 3)
In Example 2, the glass plate provided with a transparent conductive film was produced similarly except having changed into the conditions specified below. A buffer layer made of tin oxide (SnO ₂ ) having a thickness of 140 nm was formed on the base film at a deposition rate of 2,850 nm / min. A transparent conductive film made of SnO ₂ : F having a thickness of 636 nm was formed at a deposition rate of 6,470 nm / min. This glass plate had a haze ratio of 27%, but no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

Example 4
In Example 2, the glass plate provided with a transparent conductive film was produced similarly except having changed into the conditions specified below. A tin oxide thin film (first underlayer) having a thickness of 80 nm was formed on the glass ribbon. A transparent conductive film made of SnO ₂ : F having a thickness of 710 nm was formed on the buffer layer at a deposition rate of 7,220 nm / min. This glass plate had a haze ratio of 25%, but no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

(Example 5)
In Example 2, the glass plate provided with the transparent conductive film was produced similarly except having changed into the conditions specified below. A transparent conductive film made of SnO ₂ : F having a thickness of 670 nm was formed on the buffer layer at a deposition rate of 6,820 nm / min. This glass plate had a haze ratio of 16%, and no cloudy high haze state was observed. The reflectance, absorption coefficient, and sheet resistance are also shown in Table 1 below.

(Comparative Example 1)
A glass plate provided with a transparent conductive film was prepared in the same manner as in Reference Example 1 except that the conditions were changed to the conditions specified below. A transparent conductive film made of fluorine-containing tin oxide (SnO ₂ : F) was formed without forming a buffer layer on the base film. The glass plate on which this buffer layer was not formed was in a high haze state that was clouded so that the shape of the object on the other side of the glass plate could not be recognized. Therefore, measurement of haze rate, reflectance, absorption coefficient, and sheet resistance value was not performed.

(Comparative Example 2)
In Example 1, the glass plate provided with the transparent conductive film was produced similarly except having changed into the conditions specified below. Without forming the buffer layer on the base film, that is, the supply of the mixed gas to the third coater is stopped, and a transparent conductive film made of SnO ₂ : F having a thickness of 600 nm is formed at a deposition rate of 15,000 nm / min. did. As in Comparative Example 1, the glass plate on which the buffer layer was not formed was in a high haze state that was clouded so that the shape of the object on the other side of the glass plate could not be recognized. Therefore, measurement of haze rate, reflectance, absorption coefficient, and sheet resistance value was not performed.

(Production Example 1)
An amorphous silicon thin film having a thickness of 0.3 μm was formed on the transparent conductive films formed in Reference Examples 1 and 2, Examples 1 to 5 and Comparative Examples 1 and 2 by plasma CVD using monosilane and hydrogen as raw materials. . Thereafter, a silver thin film (back electrode) having a thickness of 300 nm was formed by electron beam evaporation, and a sample of a photoelectric conversion element was manufactured. This sample has a general configuration of a solar cell using an amorphous silicon thin film as a photoelectric conversion layer. About these samples, the result of having measured photoelectric conversion efficiency by a well-known means is combined with following Table 1, and is shown.

(Production Example 2)
A crystalline silicon thin film having a thickness of 2 μm was formed on the transparent conductive films formed in Reference Examples 1 and 2, Example 1 and Comparative Examples 1 and 2 by plasma CVD using monosilane and hydrogen as raw materials. Thereafter, a silver thin film (back electrode) having a thickness of 300 nm was formed by electron beam evaporation, and a sample of a photoelectric conversion element was manufactured. This sample has a general configuration of a solar cell using a crystalline silicon thin film as a photoelectric conversion layer. About these samples, the result of having measured photoelectric conversion efficiency by a well-known means is combined with following Table 1, and is shown.

  Regarding the photoelectric conversion efficiencies of Comparative Example 1 and Comparative Example 2 in Production Example 1 and Production Example 2, an attempt was made to measure the photoelectric conversion efficiency, but almost no efficiency was obtained. This is probably because the pin-shaped amorphous silicon film and the crystalline silicon film were not formed uniformly in the plane because of the huge tin oxide particles that appeared in the cloudy state.

  In Examples 1 to 5, the transparent conductive film does not become cloudy even though the film formation rate of the buffer layer greatly exceeds 1,000 nm / min. It is considered that the surface of the base film is not smooth because the particles are taken into the first base layer or disappeared by heat.

  In addition, for reference, it was measured how the absorption coefficient of the transparent conductive film changes when the composition ratio of the raw material of the transparent conductive film is changed (Reference Examples 4 to 6).

(Reference Example 4)
A glass plate provided with a transparent conductive film was produced in the same manner as in Example 2 except that the conditions were changed as follows. A tin oxide thin film (first underlayer) having a thickness of 35 nm was formed on the glass ribbon. A buffer layer made of tin oxide (SnO ₂ ) having a thickness of 110 nm was formed on the base film at a deposition rate of 1,550 nm / min. Further, a mixed gas composed of 1.8 mol% of stannic chloride (vapor), 57 mol% of water vapor, nitrogen, and hydrogen fluoride was supplied to form a transparent conductive film composed of SnO ₂ : F having a thickness of 504 nm on the buffer layer. The film was formed at a film speed of 3,480 nm / min. This glass plate had a haze ratio of 3.3% and an absorption coefficient of 0.53 at 400 nm, 0.36 at 500 nm, 0.26 at 600 nm, and 0.24 at 700 nm.

(Reference Example 5)
In Reference Example 4, a glass plate provided with a transparent conductive film was prepared in the same manner except that the conditions specified below were changed, and the absorption coefficient was measured. As a raw material of the transparent conductive film, a mixed gas composed of 1.8 mol% of stannic chloride (vapor), 57 mol% of water vapor, 23 mol% of oxygen, nitrogen and hydrogen fluoride is used as a raw material of the transparent conductive film, and SnO having a thickness of 500 nm is used. _A transparent conductive film made of ₂ : F was formed at a deposition rate of 3,450 nm / min. This glass plate had a haze ratio of 3% and an absorption coefficient of 0.64 at 400 nm, 0.32 at 500 nm, 0.24 at 600 nm, and 0.17 at 700 nm.

(Reference Example 6)
In Reference Example 4, a glass plate provided with a transparent conductive film was prepared in the same manner except that the conditions specified below were changed, and the absorption coefficient was measured. As a raw material of the transparent conductive film, a mixed gas composed of 1.8 mol% of stannic chloride (vapor), 85.6 mol% of water vapor, nitrogen, and hydrogen fluoride is used as a raw material of the transparent conductive film, and SnO ₂ having a thickness of 453 nm is used. A transparent conductive film made of: F was formed at a deposition rate of 3,120 nm / min. This glass plate had a haze ratio of 3.5% and an absorption coefficient of 0.76 at 400 nm, 0.4 at 500 nm, 0.26 at 600 nm, and 0.17 at 700 nm.

  By comparing Reference Examples 4 to 6, it is understood that the absorption coefficient on the long wavelength side decreases as the content of the oxidizing raw material (oxygen or water vapor) in the mixed gas of the raw material increases.

  Since the present invention is configured as described above, the following effects can be obtained.

  According to the present invention, a substrate with a transparent conductive film which does not cause appearance problems such as white turbidity can be produced at low cost by using a pyrolytic method, particularly a highly productive online CVD method, using a raw material with low toxicity such as tin chloride. Can be manufactured. Furthermore, since this substrate has a low reflectance and a low absorption coefficient, its photoelectric conversion efficiency can be increased by using it for a photoelectric conversion device.

DESCRIPTION OF SYMBOLS 10 Glass ribbon 11 Melting furnace 12 Tin float tank 13 Slow cooling furnace 16 Coater 17 Roller

Claims (7)

A glass plate containing an alkaline component;
Formed on the glass plate, (i) has a film thickness in the range of 35 to 100 nm, and includes a first underlayer containing tin oxide as a main component; and (ii) formed on the first underlayer, A base film having irregularities, including an amorphous second base layer having a thickness in the range of 5 to 50 nm and thinner than the first base layer;
A non-doped buffer layer formed on the base film, having a thickness in the range of 10 to 250 nm and containing tin oxide as a main component;
A doped transparent conductive film formed on the buffer layer and containing tin oxide as a main component;
With a substrate. The transparent conductive film has an absorption coefficient of 1 × 10 ³ cm ⁻¹ or less in a wavelength range of 400 to 700 nm, a maximum absorption coefficient of 1.7 times or less of a minimum value, and a sheet resistance of 15Ω. 2. The substrate according to claim 1, wherein the substrate has a film thickness of 1,000 nm or less and a haze ratio of 12% or more.   The substrate according to claim 1, wherein the second underlayer includes silicon oxide as a main component.   The board | substrate of any one of Claims 1-3 in which the said buffer layer has a film thickness of the range of 50-150 nm.   The substrate according to claim 1, wherein the transparent conductive film contains fluorine as a dopant.   The substrate according to claim 1, wherein the first underlayer is formed by a thermal decomposition method using a halogen-containing raw material.   The photoelectric conversion apparatus using the board | substrate of any one of Claims 1-6.

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