JP5635430B2 - Substrate with transparent conductive film, solar cell, and production method thereof - Google Patents

Description

  The present invention relates to a substrate with a transparent conductive film, a solar cell, and a method for producing them, and more specifically, a substrate with a transparent conductive film for a solar cell that enables fine texture in a transparent conductive film made of a ZnO-based material, The present invention relates to batteries and methods for manufacturing them.

  When energetic particles called photons contained in sunlight hit the i layer, electrons and holes are generated by the photovoltaic effect, and the electrons move toward the n layer and the holes move toward the p layer. A solar cell is an element that takes out electrons generated by the photovoltaic effect with the upper electrode and the back electrode and converts light energy into electric energy.

  FIG. 20 is a schematic cross-sectional view of an amorphous silicon solar cell. The solar cell 100 includes a glass substrate 101 constituting the surface, an upper electrode 103 made of a zinc oxide-based transparent conductive film provided on the glass substrate 101, a top cell 105 made of amorphous silicon, and a top cell 105 And an intermediate electrode 107 made of a transparent conductive film, a bottom cell 109 made of microcrystalline silicon, a buffer layer 110 made of a transparent conductive film, and a back electrode 111 made of a metal film. And are stacked.

  The top cell 105 has a three-layer structure of a p layer (105p), an i layer (105i), and an n layer (105n), of which the i layer (105i) is formed of amorphous silicon. Similarly to the top cell 105, the bottom cell 109 has a three-layer structure of a p layer (109p), an i layer (109i), and an n layer (109n), of which the i layer (109i) is made of microcrystalline silicon. It is configured.

In such a solar cell 100, sunlight incident from the glass substrate 101 side is reflected by the back electrode 111 through the upper electrode 103, the top cell 105 (p-i-n layer), and the buffer layer 110. In order to improve the conversion efficiency of light energy in the solar cell, the purpose is to reflect the sunlight by the back electrode 111 or to extend the optical path of the incident sunlight to the upper electrode 103 and to confine the light. Ingenuity such as providing a structure called texture has been made. The buffer layer 110 is intended to prevent diffusion of the metal film used for the back electrode 111.

Although the wavelength band used for the photovoltaic effect varies depending on the device structure of the solar cell, in any case, the transparent conductive film constituting the upper electrode transmits light for absorption by the i layer and light. Electrical conductivity for extracting electrons generated by electromotive force is required, and FTO or ZnO-based oxide semiconductor thin films in which fluorine is added as an impurity to SnO ₂ are used. The buffer layer is also required to have the property of transmitting the light reflected by the back electrode and the light reflected by the back electrode in order to absorb the i layer and the electrical conductivity for transferring holes to the back electrode.

The characteristics required for the transparent conductive film used for solar cells are roughly divided into three elements: conductivity, optical characteristics, and texture structure. In the first conductivity, a low electric resistance is required to take out the generated electricity. FTO generally used for a transparent conductive film for solar cells is obtained by adding F to SnO ₂ with a transparent conductive film formed by CVD, whereby F substitutes O to obtain conductivity. Further, a ZnO-based material that is attracting attention as post-ITO can be formed by sputtering, and conductivity is obtained by adding a material containing oxygen deficiency and Al or Ga to ZnO.

Secondly, since the transparent conductive film for solar cells is mainly used on the incident light side, optical characteristics that transmit the wavelength band absorbed by the power generation layer are required.
Third, a texture structure that scatters light is necessary to efficiently absorb sunlight in the power generation layer, and a ZnO-based thin film created by a sputtering process usually has a flat surface state. A texture forming process is required.

Substrates with a transparent conductive film in which a transparent conductive film having such a texture is arranged on a transparent substrate have been developed by various glass manufacturers and the like (for example, see Patent Documents 1 and 2).
Conventionally, a substrate with a transparent conductive film with a predetermined texture commercially available from a glass maker is purchased, and a solar cell manufacturer manufactures a solar cell by forming a desired photoelectric conversion unit or the like on the substrate. There was a need to do.

However, in such a substrate with a transparent conductive film that is generally sold, the texture shape of the surface of the transparent conductive film is defined in advance, the degree of freedom of selection is low, and the transparent conductive film having a fine texture with a desired roughness and shape. Obtaining a substrate with a film has been difficult. For this reason, even if a solar cell manufacturer develops a photoelectric conversion unit having a unique laminated structure, a substrate with a transparent conductive film having a texture suitable for the laminated structure cannot be obtained flexibly. It has been difficult to produce a solar cell that exhibits the best power generation characteristics provided by the laminated structure.
For this reason, the development of a substrate with a transparent conductive film having a fine texture having a high degree of freedom and a desired roughness and shape on the surface and a method for producing the same has been expected.

JP 2009-140930 A JP 2002-1583665 A

The present invention has been devised in view of such a conventional situation, with a transparent conductive film provided with appropriate unevenness (texture structure) for each photoelectric conversion unit comprising various laminated structures constituting a solar cell. The first object is to provide a substrate.
Further, the present invention has fine irregularities (texture structure) having a desired degree of roughness and shape on the surface of the transparent conductive film, and sufficiently obtains the prism effect and the light confinement effect by this texture structure. A second object of the present invention is to provide a method for producing a substrate with a transparent conductive film.
Furthermore, the present invention utilizes a substrate with a transparent conductive film provided with irregularities (texture structure) suitable for a characteristic laminated structure, and a photoelectric conversion unit having a characteristic laminated structure (for each solar cell manufacturer) on the substrate. A third object of the present invention is to provide a solar cell that achieves the best power generation characteristics provided by the laminated structure.
Furthermore, according to the present invention, fine irregularities (texture structure) suitable for a characteristic laminated structure can be formed on the surface of the transparent conductive film with a desired roughness and shape with a high degree of freedom of selection. A fourth object is to provide a method of manufacturing a solar cell that can sufficiently obtain a prism effect and a light confinement effect due to the structure and has high conversion efficiency.

The substrate with a transparent conductive film according to claim 1 of the present invention is a substrate with a transparent conductive film in which a transparent conductive film based on ZnO is arranged so as to be in contact with an insulating transparent substrate, the transparent conductive film is a crystal grain aggregate having a shape extending in a thickness direction, wherein the intergranular grain, there is an interface at least in the thickness direction, with on the surface having fine irregularities In the film thickness direction, the crystal grains include crystal grains having a crystal grain size that increases with distance from the transparent substrate .
A substrate with a transparent conductive film according to a second aspect of the present invention is the substrate according to the first aspect , wherein the transparent conductive film contains hydrogen.
The method for manufacturing a substrate with a transparent conductive film according to claim 3 of the present invention is a method for manufacturing a substrate with a transparent conductive film in which a transparent conductive film based on ZnO is arranged so as to be in contact with an insulating transparent substrate. a method, in a film forming space was set to the desired process gas atmosphere, subjected to sputtering by applying a sputtering voltage to the coater g e t preparative constituting the base material of the transparent conductive film, the transparent substrate having a predetermined temperature At least a step α1 for forming the transparent conductive film thereon, a material mainly composed of ZnO is used as the base material, and the pressure [Pa] in the film formation space is in the range of 1 to 10. The mixed gas comprising an inert gas and hydrogen gas is used as the process gas, and the addition amount of the hydrogen gas is set to 1 to 6 [%] .
The method for producing a substrate with a transparent conductive film according to claim 4 of the present invention is characterized in that, in claim 3 , a mixed gas composed of an inert gas and hydrogen gas is used as the process gas in the step α1. To do.
The method for producing a substrate with a transparent conductive film according to claim 5 of the present invention is characterized in that, in claim 3 or 4 , the temperature [° C.] of the transparent substrate in the step α1 is in the range of 150 to 400 . And
The method for manufacturing a substrate with a transparent conductive film according to claim 6 of the present invention includes, in any one of claims 3 to 5 , a step α2 of post-heating treatment in the atmosphere after the step α1. It is characterized by that.
The solar cell according to claim 7 of the present invention uses a substrate with a transparent conductive film, a p-type semiconductor layer (p layer), a substantially intrinsic i-type semiconductor layer (i layer), and an n-type semiconductor layer (n A pin-type photoelectric conversion unit laminated in order on the transparent conductive film, the transparent conductive film is disposed in contact with an insulating transparent substrate, and has a basic structure of ZnO. the thickness is a grain aggregate having a shape extending in a direction, said between crystal grains of the grain, there is an interface at least in the thickness direction, with the surface thereof to have a fine uneven (texture structure), its In the film thickness direction, the p-layer, the i-layer, and the n-layer that include crystal grains having a larger crystal grain size as they move away from the transparent substrate and are included in the photoelectric conversion unit are made of an amorphous silicon-based thin film, , Constituting the photoelectric conversion unit A buffer layer made of a silicon-based thin film is disposed between the p layer and the p layer.
The method for manufacturing a solar cell according to claim 8 of the present invention uses a substrate with a transparent conductive film, a p-type semiconductor layer (p layer), a substantially intrinsic i-type semiconductor layer (i layer), and an n-type semiconductor. A solar cell manufacturing method in which a pin-type photoelectric conversion unit in which layers (n layers) are stacked is provided on a transparent conductive film in this order via a buffer layer. In the film space, a sputtering voltage is applied to the target that forms the base material of the transparent conductive film to perform sputtering, and the transparent conductive film is formed in contact with an insulating transparent substrate at a predetermined temperature β1 And using a material mainly composed of ZnO as the base material, the pressure [Pa] in the film formation space is in the range of 1 to 10, and an inert gas and a hydrogen gas are used as the process gas. Mixed ga Using, characterized in that the amount of hydrogen gas was 1-6%.
The method for manufacturing a solar cell according to claim 9 of the present invention is characterized in that, in claim 8 , a mixed gas comprising an inert gas and hydrogen gas is used as the process gas in the step β1.
The method for producing a solar cell according to claim 10 of the present invention is characterized in that, in claim 8 or 9 , the temperature [° C.] of the transparent substrate in the step β1 is in the range of 150 to 400.
According to Claim 11 of the present invention, in the method for manufacturing a solar cell according to Claim 10 , after the step β1 and before the step β2 of forming the buffer layer, post-heating treatment is performed in the atmosphere. Step β4 is provided.

  In the substrate with a transparent conductive film of the present invention, the transparent conductive film is an aggregate of crystal grains having a shape extending in the film thickness direction, and there is at least an interface in the film thickness direction between the crystal grains. Since the surface has fine irregularities (texture structure), the prism effect and the light confinement effect due to the texture structure can be sufficiently obtained.

The transparent conductive film-coated substrate manufacturing method of the present invention, when forming the transparent conductive film, in the film formation space a desired process gas atmosphere, the sputtering voltage to terpolymers g e t preparative forming the base material of the transparent conductive film At least a step α1 for forming the transparent conductive film on the transparent substrate at a predetermined temperature by applying and sputtering, using a material mainly composed of ZnO as the base material, and The pressure [Pa] in the membrane space is in the range of 1-10. The transparent conductive film obtained by this is an aggregate of crystal grains having a shape extending in the film thickness direction, and there is an interface at least in the film thickness direction between the crystal grains, and the surface is fine. It has unevenness (texture structure). As a result, in the manufacturing method of the present invention, a fine texture suitable for a characteristic laminated structure can be formed with a high degree of freedom and a desired roughness and shape, and the prism effect and light confinement effect due to the texture structure are sufficiently obtained. It becomes possible to produce the board | substrate with a transparent conductive film which can be obtained to this.

In the solar cell of the present invention, the transparent conductive film is an aggregate of crystal grains having a basic configuration of ZnO and extending in the film thickness direction, and at least between the crystal grains in the film thickness direction. There is an interface, and the surface has fine irregularities (texture structure). Thereby, the prism effect and the light confinement effect due to the texture structure are obtained, and as a result, the solar cell of the present invention has a high conversion efficiency.
Moreover, in the solar cell of this invention, p layer, i layer, and n layer which comprise the said photoelectric conversion unit consist of an amorphous silicon-type thin film, The said transparent conductive film, The said p layer which comprises the said photoelectric conversion unit, Since a buffer layer made of a silicon-based thin film is disposed between the layers, mismatch at the interface between the transparent conductive film and the p-layer made of an amorphous silicon-based thin film can be alleviated. Thereby, the fill factor (FF) of a photoelectric conversion unit can be improved. As a result, the solar cell light of the present invention has high conversion efficiency.

In the method of manufacturing the solar cell of the present invention, when forming the transparent conductive film, in the film formation space a desired process gas atmosphere by applying a sputtering voltage to the coater g e t preparative forming the base material of the transparent conductive film At least a step α1 for performing sputtering to form the transparent conductive film on the transparent substrate at a predetermined temperature, and using a material mainly composed of ZnO as the base material, The pressure [Pa] is in the range of 1-10. The transparent conductive film obtained by this is an aggregate of crystal grains having a shape extending in the film thickness direction, and there is an interface at least in the film thickness direction between the crystal grains, and the surface is fine. It has unevenness (texture structure). As a result, in the manufacturing method of the present invention, a fine texture suitable for a characteristic laminated structure can be formed with a high degree of freedom and a desired roughness and shape, and the prism effect and light confinement effect due to the texture structure are sufficiently obtained. Thus, a solar cell with high conversion efficiency can be manufactured.

Sectional drawing which shows an example (1st embodiment) of the solar cell which concerns on this invention. Sectional drawing which expands and shows a transparent conductive film typically in the solar cell of this invention. The schematic block diagram which shows the film-forming apparatus suitable for the manufacturing method of the solar cell of this invention. Sectional drawing which shows the principal part of the film-forming chamber in the film-forming apparatus of FIG. Sectional drawing which shows another example of the film-forming apparatus. The schematic diagram which shows an example of a continuous film-forming apparatus. Sectional drawing which shows an example (2nd embodiment) of the solar cell which concerns on this invention. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows collectively the relationship between a film thickness, a haze rate, and the power generation efficiency of a solar cell about the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the SEM image of the transparent conductive film obtained in the Example. The figure which shows the result of a SIMS analysis about the transparent conductive film obtained in the Example. The figure which shows the result of a SIMS analysis about the transparent conductive film obtained in the Example. For the transparent conductive film obtained in Example are summarized and added amount of H ₂ gas at the time of film formation, the relationship between the power generation efficiency of the haze ratio and the solar cell FIG. The figure which shows collectively the relationship between the substrate temperature at the time of film-forming, a haze rate, and the power generation efficiency of a solar cell about the transparent conductive film obtained in the Example. Sectional drawing which shows an example of the conventional solar cell.

  Hereinafter, the best mode of a solar cell and a manufacturing method thereof according to the present invention will be described with reference to the drawings. The present embodiment is specifically described for better understanding of the gist of the invention, and does not limit the invention unless otherwise specified.

<First embodiment>
(Solar cell)
In the present embodiment, one embodiment of the solar cell 1 according to the present invention is an amorphous silicon type solar cell as the first photoelectric conversion unit 6 (top cell), and a microcrystalline silicon type as the second photoelectric conversion unit 7 (bottom cell). A case of a tandem solar cell stacked as a solar cell will be described with reference to the drawings.
First, the solar cell of this invention is demonstrated based on FIG. FIG. 1 is a cross-sectional view showing an example of the configuration of the solar cell 1A (1).
The solar cell 1A (1) includes an insulating transparent substrate 2 made of a glass substrate or the like constituting the surface, an upper electrode 3 made of a zinc oxide-based transparent conductive film 4 provided on the transparent substrate 2, and amorphous silicon. Are stacked, a first photoelectric conversion unit 6 made of (2), a second photoelectric conversion unit 7 made of microcrystalline silicon, a buffer layer 11 made of a transparent conductive film, and a back electrode 12 made of a metal film. . The transparent substrate 2 and the transparent conductive film 4 provided on the transparent substrate 2 constitute the substrate 10 with a transparent conductive film of the present invention.

Since the transparent conductive film 4 is formed by a manufacturing method described later, a fine texture suitable for a laminated structure having a characteristic of a solar cell is formed with a high degree of freedom and a desired roughness and shape. .
Here, FIG. 2 is a cross-sectional view schematically showing an enlarged transparent conductive film 4 in the solar cell 1A (1) of the present invention. Specifically, the transparent conductive film 4 is an aggregate of crystal grains 4a having a basic configuration of ZnO and extending in the film thickness direction, and at least an interface is formed between the crystal grains 4a in the film thickness direction. 4b, and the surface has fine irregularities (texture structure). Thereby, solar cell 1A (1) of the present invention has sufficient prism effect and light confinement effect due to the texture structure, and has high conversion efficiency.

  The solar cell 1 is an a-Si / microcrystalline Si tandem solar cell. In the solar cell 1 having such a tandem structure, power generation efficiency can be improved by absorbing short wavelength light with the first photoelectric conversion unit 6 and long wavelength light with the second photoelectric conversion unit 7. The upper electrode 3 is formed with a thickness of 2000 to 10,000 mm.

  The 1st photoelectric conversion unit 6 is comprised by the 3 layer structure of p layer (6p), i layer (6i), and n layer (6n), These p layer (6p), i layer (6i), and n layer (6n) is formed of amorphous silicon. Similarly to the first photoelectric conversion unit 6, the second photoelectric conversion unit 7 has a three-layer structure of a p layer (7p), an i layer (7i), and an n layer (7n). 7p), i layer (7i) and n layer (7n) are made of microcrystalline silicon.

In the solar cell 1A (1) of the present invention, a buffer layer 5 made of a silicon thin film is disposed between the transparent conductive film 4 and the p layer (6p) constituting the photoelectric conversion unit. Yes.
Since the buffer layer 5 made of a crystalline silicon-based thin film is disposed between the transparent conductive film 4 and the p layer (6p) constituting the first photoelectric conversion unit 6, the transparent conductive film 4 and the amorphous The mismatch at the interface with the p layer (6p) made of the silicon-based thin film can be alleviated. Thereby, the fill factor (FF) of a 1st photoelectric conversion unit can be improved. As a result, the solar cell 1A (1) of the present invention has high conversion efficiency.

  In the solar cell 1A (1) having such a configuration, when energetic particles called photons contained in sunlight hit the i layer, electrons and holes are generated due to the photovoltaic effect, and the electrons are in the n layer. The hole moves toward the p-layer. Electrons generated by the photovoltaic effect can be taken out by the upper electrode 3 and the back electrode 63 to convert light energy into electric energy.

  Moreover, the sunlight which entered from the transparent substrate 2 side passes through each layer, and is reflected by the back surface electrode 12. In order to improve the conversion efficiency of light energy, the solar cell 1 employs a texture structure for the purpose of a prism effect for extending the optical path of sunlight incident on the upper electrode 3 and a light confinement effect.

As will be described later, in the present invention, in the formation of the transparent conductive film 4 constituting the upper electrode 3, the transparent conductive film 4 is formed on the transparent substrate 2 by performing sputtering using a material mainly composed of ZnO as a base material. Is deposited. At this time, in the film formation space a desired process gas atmosphere, the perform sputtering by applying a sputtering voltage to the coater g e t preparative constituting the base material of the transparent conductive film 4, the transparent substrate is a predetermined temperature 2 Steps α1 for forming the transparent conductive film 4 thereon are provided, and a material mainly composed of ZnO is used as the base material, and the pressure [Pa] in the film formation space is in the range of 1 to 10. It is said.

Thereby, the transparent conductive film 4 is an aggregate of crystal grains 4a extending in the film thickness direction, and there is at least an interface 4b in the film thickness direction between the crystal grains 4a. It has fine unevenness (hereinafter also referred to as “texture structure”) (see FIG. 2).
As a result, the substrate 10 with the transparent conductive film for solar cell of the present invention thus obtained has a high degree of freedom on the surface of the transparent conductive film 4 with a fine texture suitable for the characteristic laminated structure of the solar cell. It is formed with a desired roughness and shape. Thereby, the board | substrate 10 with a transparent conductive film for solar cells of this invention can fully acquire the prism effect and light confinement effect by a texture structure.

  Moreover, it is preferable that the transparent conductive film 4 includes crystal grains 4 a having a crystal grain size that increases with distance from the transparent substrate 2 in the film thickness direction. Thereby, the fine texture suitable for the laminated structure with the characteristic of a solar cell will be formed with the desired roughness and shape with a high freedom degree.

  The transparent conductive film 4 preferably contains hydrogen. As will be described in detail later, when forming the transparent conductive film 4, a mixed gas composed of an inert gas and hydrogen gas is used as a process gas, which is suitable for a unique laminated structure of the solar cell 1A (1). A fine texture can be formed with a high degree of freedom and a desired roughness and shape. Further, as shown in Examples described later, the transparent conductive film 4 formed in this way includes hydrogen in the film.

  An intermediate electrode 8 may be provided between the first photoelectric conversion unit 6 and the second photoelectric conversion unit 7. By providing the intermediate electrode 8 between the first photoelectric conversion unit 6 and the second photoelectric conversion unit 7, a part of the light that passes through the first photoelectric conversion unit 6 and reaches the second photoelectric conversion unit 7 is intermediate. Since the light is reflected by the electrode 8 and is incident again on the first photoelectric conversion unit 6 side, the sensitivity characteristic of the cell is improved and the power generation efficiency is improved.

(Method for manufacturing solar cell)
Next, a method for manufacturing such a solar cell 1A (1) will be described.
The method of manufacturing a solar cell of the present invention, when forming the transparent conductive film 4, the film-forming space was desired process gas atmosphere, the sputtering voltage to terpolymers g e t preparative forming the base material of the transparent conductive film 4 At least a step α1 for forming the transparent conductive film 4 on the transparent substrate 2 that is applied and sputtered to a predetermined temperature is used, and a material mainly composed of ZnO is used as the base material, The pressure [Pa] in the film formation space is in the range of 1 to 10.

  The transparent conductive film 4 obtained by the production method of the present invention is an aggregate of crystal grains 4a having a shape extending in the film thickness direction, and at least an interface 4b is provided between the crystal grains 4a in the film thickness direction. And the surface has fine irregularities (texture structure). As a result, in the manufacturing method of the present invention, it is possible to form a fine texture suitable for a laminated structure having a characteristic of a solar cell with a desired degree of roughness and shape with a high degree of freedom. It becomes possible to produce the substrate 10 with a transparent conductive film that can sufficiently obtain the confinement effect.

In the present invention, the buffer layer 5 made of a silicon-based thin film is formed between the transparent conductive film 4 and the p layer (6p) constituting the first photoelectric conversion unit 6.
In the present invention, since the buffer layer 5 made of a silicon-based thin film is formed between the transparent conductive film 4 and the p layer (6p) that forms the first photoelectric conversion unit 6 and is made of an amorphous silicon-based thin film. The mismatch at the interface between the transparent conductive film 4 and the p layer (6p) made of an amorphous silicon thin film can be alleviated. Thereby, the fill factor (FF) of the first photoelectric conversion unit 6 can be improved. As described above, in the solar cell 1A (1) of the present invention, the FF can be improved by inserting the buffer layer 5, and the power generation efficiency of the first photoelectric conversion unit 6 can be improved. As a result, it is possible to improve the photoelectric conversion efficiency.
As a result, in the manufacturing method of the present invention, the prism effect and the light confinement effect due to the texture structure can be sufficiently obtained, and the solar cell 1A (1) with high conversion efficiency can be manufactured.

  The thickness of the buffer layer 5 is preferably in the range of 50 to 10 nm, for example. For example, it can be 50 mm. When the thickness of the buffer layer 5 is in the range of 50 to 10 nm, the fill factor (FF) and voltage (Voc) increase, and the effect of increasing the photoelectric conversion efficiency is recognized.

First, an example of a sputtering apparatus (film forming apparatus) suitable for forming the zinc oxide-based transparent conductive film 4 forming the upper electrode 3 in the solar cell manufacturing method of the present invention will be described.
(Sputtering device 1)
FIG. 3 is a schematic configuration diagram showing an example of a sputtering apparatus (film forming apparatus) used in the method for manufacturing the solar cell 1 of the present invention, where (a) is a top view and (b) is a cross-sectional view. FIG. 4 is a cross-sectional view showing the main part of the film forming chamber of the sputtering apparatus. The sputtering apparatus 20 is an inter-back type sputtering apparatus. For example, a loading / unloading chamber 22 for loading / unloading a substrate such as an alkali-free glass substrate (not shown), and a zinc oxide-based transparent conductive film on the substrate. 4 and a film forming chamber (vacuum vessel) 23 for forming a film.

  The preparation / removal chamber 22 is provided with a roughing exhaust means 24 such as a rotary pump for roughly evacuating the chamber, and a substrate tray 25 for holding and transporting the substrate is movably disposed in the chamber. ing.

On the other hand, a heater 31 for heating the substrate 26 is vertically provided on one side surface 23a of the film forming chamber 23, and a target 27 of a zinc oxide-based material is held on the other side surface 23b to provide a desired sputtering voltage. A sputtering cathode mechanism (target holding means) 32 to be applied is provided in a vertical type, and further, a high vacuum evacuation means 33 such as a turbo molecular pump for evacuating the interior of the chamber, a power supply 34 for applying a sputtering voltage to the target 7, Gas introduction means 35 for introducing gas into the room is provided.
In particular, in this sputtering apparatus, a plurality (four in the figure) of heaters 31 and sputtering cathode mechanisms 32 are provided. By providing a plurality of heaters 31 and sputtering cathode mechanisms 32 and performing sputtering while moving the substrate 26, even a thick transparent conductive film can be formed without unevenness.

The sputter cathode mechanism 32 is made of a plate-like metal plate, and is used for fixing the target 7 by bonding (fixing) with a mouth material or the like.
The power source 34 is for applying a sputtering voltage in which a high frequency voltage is superimposed on a DC voltage to the target 27, and includes a DC power source and a high frequency power source (not shown).

Gas introduction means 35 introduces a Supattaga scan introducing means 35a for introducing a sputtering gas such as Ar, a hydrogen gas introduction means 35b for introducing the hydrogen gas, and oxygen gas introducing means 35c for introducing the oxygen gas, water vapor steam And introducing means 35d.

  In the gas introduction means 35, the hydrogen gas introduction means 35b to the water vapor introduction means 35d may be selectively used as necessary. For example, the hydrogen gas introduction means 35b, the oxygen gas introduction means 35c, and the hydrogen gas introduction means You may comprise by two means like 35b and the water vapor introducing means 35d.

(Sputtering equipment)
FIG. 5 is a cross-sectional view showing an example of another sputtering apparatus used in the method for manufacturing a solar cell of the present invention, that is, the main part of a film forming chamber of an inter-back type magnetron sputtering apparatus. The magnetron sputtering apparatus 40 shown in FIG. 5 differs from the sputtering apparatus 20 shown in FIGS. 3 and 4 in that a target 27 made of zinc oxide material is held on the negative side surface 23a of the film forming chamber 23 to generate a desired magnetic field. A sputter cathode mechanism (target holding means) 42 is provided in a vertical shape.

  The sputter cathode mechanism 42 includes a back plate 43 in which the target 27 is bonded (fixed) with a brazing material or the like, and a magnetic circuit 44 disposed along the back surface of the back plate 43. The magnetic circuit 44 generates a horizontal magnetic field on the surface of the target 27. A plurality of magnetic circuit units (two in FIG. 5) 44a and 44b are connected and integrated by a bracket 45, and the magnetic circuit unit 44a, Each of 44b includes a first magnet 46 and a second magnet 47 having different polarities on the surface on the back plate 43 side, and a yoke 48 for mounting them.

  In the magnetic circuit 44, a magnetic field represented by a magnetic force line 49 is generated by the first magnet 46 and the second magnet 47 having different polarities on the back plate 43 side. Thereby, on the surface of the target 7 between the first magnet 46 and the second magnet 47, a position 50 where the vertical magnetic field is 0 (the horizontal magnetic field is maximum) is generated. The high-density plasma is generated at the position 50, so that the film forming speed can be improved.

  In the film forming apparatus shown in FIG. 5, since the sputtering cathode mechanism 42 that generates a desired magnetic field is provided on the one side surface 23 a of the film forming chamber 23 in the vertical type, the sputtering voltage is set to 340 V or less and the surface of the target 27 is By setting the maximum value of the horizontal magnetic field strength to 600 gauss or more, it is possible to form the zinc oxide-based transparent conductive film 4 in which the crystal lattice is arranged. This zinc oxide-based transparent conductive film 4 is not easily oxidized even if annealing is performed at a high temperature after film formation, and can suppress an increase in specific resistance, and the zinc oxide-based transparent conductive film that forms the upper electrode of the solar cell 1. The conductive film 4 can be made excellent in heat resistance.

Next, as an example of the manufacturing method of the solar cell of the present invention, a zinc oxide-based transparent conductive film 4 forming the upper electrode 3 of the solar cell 1 is formed on the transparent substrate 2 by using the sputtering apparatus 1 shown in FIGS. A method for forming a film is illustrated.
First, the target 27 is bonded and fixed to the sputtering cathode mechanism 32 with a brazing material or the like. Here, as the target material, zinc oxide-based material, for example, aluminum added zinc oxide (AZO) added with 0.1 to 10% by mass of aluminum (Al), 0.1 to 10% by mass of gallium (Ga) added. Gallium-added zinc oxide (GZO) and the like. Among them, aluminum-added zinc oxide (AZO) is preferable because a thin film having a low specific resistance can be formed.

  Next, with the substrate 26 (transparent substrate 2) of the solar cell 1 made of glass, for example, stored in the substrate tray 25 of the preparation / removal chamber 22, the roughing exhaust means 4 moves the preparation / removal chamber 22 and the film formation chamber 23. After rough vacuuming, the substrate 26 is transferred from the preparation / removal chamber 22 to the deposition chamber 23 after the preparation / removal chamber 22 and the film formation chamber 23 reach a predetermined degree of vacuum, for example, 0.27 Pa (2.0 mTorr). Then, this substrate 26 is disposed in front of the heater 31 in a state in which the setting is turned off, the substrate 26 is opposed to the target 27, and the substrate 26 is heated by the heater 31, so that the temperature of 100 to 600 ° C. Within the temperature range.

Next, the film forming chamber 23 is evacuated by the high vacuum exhaust means 33, and the film forming chamber 23 has a predetermined high vacuum, for example, 2.7 × 10 ⁻⁴ Pa (2.0 × 10 ⁻³ mTorr). After that, a sputtering gas such as Ar is introduced into the film forming chamber 23 by the sputtering gas introducing means 35 to set the inside of the film forming chamber 23 to a predetermined pressure (sputtering pressure).

  Next, a sputtering voltage, for example, a sputtering voltage obtained by superimposing a high frequency voltage on a DC voltage is applied to the target 27 by the power supply 34. When a sputtering voltage is applied, plasma is generated on the substrate 26, and ions of sputtering gas such as Ar excited by the plasma collide with the target 27. From the target 7, aluminum-added zinc oxide (AZO), gallium-added zinc oxide The atoms constituting the zinc oxide-based material such as (GZO) are ejected, and the transparent conductive film 4 made of the zinc oxide-based material is formed on the substrate 26.

  At this time, in the present invention, the pressure [Pa] in the film formation space during sputtering is set to a range of 1 to 10. As shown in Examples described later, by setting the film forming pressure within the above range, it is possible to form a fine texture suitable for a laminated structure having a characteristic of a solar cell with a high degree of freedom and a desired roughness and shape. it can. As a result, the solar cell 1A (1) which can obtain the maximum prismatic effect of extending the optical path of incident sunlight and the light confinement effect, and realizes the highest power generation characteristics brought about by the characteristic laminated structure of the solar cell. Can be produced.

  Further, it is preferable to use a mixed gas composed of an inert gas and hydrogen gas as a process gas at the time of sputtering. The ratio [%] of hydrogen gas at this time is not particularly limited, but is, for example, in the range of 0.5 to 7. A fine texture suitable for a laminated structure having a characteristic solar cell can be formed with a high degree of freedom and a desired roughness and shape.

Moreover, it is preferable that the temperature [° C.] of the transparent substrate 2 during sputtering is in the range of 200 to 500. By setting the temperature of the substrate in the above range, a fine texture suitable for a laminated structure having a characteristic solar cell can be formed with a high degree of freedom and a desired roughness and shape.
Thus, in the present invention, when the transparent conductive film 4 made of a zinc oxide-based material is formed by sputtering, the aggregate of crystal grains 4a having a shape extending in the film thickness direction is controlled by controlling the pressure and other conditions. A transparent conductive film 4 is obtained which has an interface 4b at least in the film thickness direction between the crystal grains 4a and has fine irregularities (texture structure) on the surface thereof (see FIG. 2).

Here, the relationship between the film forming pressure and the film forming speed during sputtering will be described.
Although depending on the type of the target material and the process gas, when the film is formed by the magnetron sputtering method, a film formation pressure between 2 mTorr and 10 mTorr is generally selected. When the film forming pressure is low, the plasma impedance is high and cannot be discharged, or the plasma becomes unstable even if it can be discharged. On the other hand, when the deposition pressure is high, the process gas and the sputtered target material are scattered, so that the deposition efficiency (deposition rate) on the substrate is reduced or the target material sputtered on the cathode peripheral component is reduced. By depositing the film, the cathode and the ground are short-circuited, and the productivity is lowered.

  After the transparent conductive film 4 made of a zinc oxide-based material is formed on the substrate 26 as described above, the substrate 26 (transparent substrate 2) is transferred from the film formation chamber 23 to the preparation / removal chamber 2, and this preparation is performed. / The vacuum in the take-out chamber 2 is broken, and the substrate 26 (transparent substrate 2) on which the zinc oxide-based transparent conductive film 4 is formed is taken out.

Thus, the substrate 10 with a transparent conductive film in which the zinc oxide-based transparent conductive film 4 is formed on the transparent substrate 2 is obtained. The transparent conductive film 4 has a fine texture suitable for a laminated structure having a characteristic of a solar cell and has a high degree of freedom and a desired roughness and shape. As a result, it becomes possible to produce the substrate 10 with a transparent conductive film that can sufficiently obtain the prism effect and the light confinement effect by the texture structure.
Moreover, it is preferable to provide the step of post-heat-treating in air | atmosphere with respect to the formed transparent conductive film 4. Thereby, the transparency of the transparent conductive film 4 can be increased.
By using such a substrate 10 with a transparent conductive film for the solar cell 1A (1), the prism effect for extending the optical path of incident sunlight and the light confinement effect can be obtained to the maximum. The solar cell 1A (1) that realizes the best power generation characteristics brought about by can be produced.

Next, a method for manufacturing a tandem solar cell 1A (1) using such a substrate 10 with a transparent conductive film will be described in the order of steps.
First, on the transparent conductive film 4 of the substrate 10 with a transparent conductive film, the buffer layer 5, the p-type semiconductor layer 6p of the first photoelectric conversion unit 6, the i-type semiconductor layer 6i, the n-type semiconductor layer 6n, and the second photoelectric conversion. The p-type semiconductor layer 7p of the unit 7 is formed in a separate plasma CVD reaction chamber. That is, the solar cell first intermediate product in which the p-type semiconductor layer 7 p constituting the second photoelectric conversion unit 7 is provided on the n-type semiconductor layer 6 n of the first photoelectric conversion unit 6 is formed.

  Subsequently, after the p-type semiconductor layer 7p of the second photoelectric conversion unit 7 is exposed to the atmosphere, the i-type silicon layer constituting the second photoelectric conversion unit 7 is formed on the p-type semiconductor layer 7p exposed to the atmosphere. (Crystalline silicon layer) 7i and n-type semiconductor layer 7n are formed in the same plasma CVD reaction chamber. That is, the second intermediate product of the solar cell provided with the second photoelectric conversion unit 7 is formed on the first photoelectric conversion unit 6.

Then, by forming the buffer layer 11 and the back electrode 12 on the n-type semiconductor layer 7n of the second photoelectric conversion unit 7, a solar cell 1A (10) as shown in FIG. 1 is obtained.
In particular, in the present invention, by forming the buffer layer 5 in a separate film forming chamber between the transparent conductive film 4 and the p layer 6p of the first photoelectric conversion unit 6, the solar cell 1A having good characteristics ( 10) can be obtained.

Next, the manufacturing system of this solar cell 1A (10) is demonstrated based on drawing.
The solar cell 1 manufacturing system according to the present invention includes a p-type semiconductor layer 6p, an i-type silicon layer (amorphous silicon layer) 6i, an n-type semiconductor layer 6n, and a second photoelectric conversion unit in the first photoelectric conversion unit 6. A so-called in-line type first film-forming device 60 in which a plurality of film-forming reaction chambers called chambers for forming each of the seven p-type semiconductor layers 7p are connected in a straight line, and a second photoelectric conversion unit 7 in the same film formation reaction chamber, the exposure device for exposing the p layer of 7 to the atmosphere, the i-type silicon layer (crystalline silicon layer) 7i, and the n-type semiconductor layer 7n in the second photoelectric conversion unit 7. A so-called batch-type second film forming apparatus 70 is formed by sequentially processing and forming the substrates at the same time.

This solar cell manufacturing system is shown in FIG.
As shown in FIG. 6, the manufacturing system exposes the first film forming apparatus 60, the second film forming apparatus 70, and the substrate processed by the first film forming apparatus 60 to the atmosphere, and then the second film forming apparatus 70. And an exposure device 80 that moves to
The first film forming apparatus 60 in the manufacturing system is provided with a charging (L) chamber 61 in which a substrate is first loaded and placed in a reduced pressure atmosphere. Note that a heating chamber for heating the substrate temperature to a certain temperature may be provided in the subsequent stage of the L chamber according to the process. Subsequently, a p-layer film-forming reaction chamber 62 for forming a buffer layer 5 made of a crystalline silicon-based thin film on the transparent conductive film 4, and a p-layer film-forming reaction for forming a p-type semiconductor layer 6p of the first photoelectric conversion unit 6 Chamber 63, i-layer deposition reaction chamber 64 for forming i-type silicon layer (amorphous silicon layer) 6i, n-layer deposition reaction chamber 65 for forming n-type semiconductor layer 6n, second photoelectric conversion unit 7 The p-layer film formation reaction chamber 66 for forming the p-type semiconductor layer 7p is continuously arranged linearly. Finally, a decompression state is returned to the air atmosphere, and an unload (UL) chamber 67 for unloading the substrate is arranged.
At this time, a substrate 10 with a transparent conductive film in which the transparent conductive film 4 is formed on the transparent substrate 2 is prepared at a point A in FIG. In addition, at point B in FIG. 6, the buffer layer 5, the p-type semiconductor layer 6 p of the first photoelectric conversion unit 6, and the i-type silicon layer (non-crystalline) are formed on the transparent conductive film 4 formed on the transparent substrate 2. The first intermediate product of the solar cell provided with each of the silicon layer 6i, the n-type semiconductor layer 6n, and the p-type semiconductor layer 7p of the second photoelectric conversion unit 7 is formed.

The second film forming apparatus 70 in the manufacturing system carries in the first intermediate product 10a of the solar cell 1 first processed by the first film forming apparatus 60 and puts it under a reduced pressure atmosphere or a substrate under reduced pressure. A loading / unloading (L / UL) chamber 71 for unloading the substrate as an atmospheric atmosphere is arranged. Subsequently, the i-type silicon layer (crystalline silicon layer) 7i of the second photoelectric conversion unit 7 is formed on the p-type semiconductor layer 7p of the second photoelectric conversion unit 7 through the preparation / removal (L / UL) chamber 71. The n-type semiconductor layer 7n is sequentially formed in the same reaction chamber, and a film formation reaction chamber 72 capable of simultaneously processing a plurality of substrates is arranged.
At this time, a solar cell second intermediate product in which the second photoelectric conversion unit 7 is provided is formed on the first photoelectric conversion unit 6 at a point C in FIG.

  In FIG. 6, the in-line type first film forming apparatus 60 is shown so that two substrates are processed simultaneously, and the i-layer film forming reaction chamber 64 is constituted by four reaction chambers 64a, 64b, 64c, and 64d. Shown as configured. In FIG. 6, the batch-type second film forming apparatus 70 is shown so that six substrates are processed simultaneously.

<Second embodiment>
Next, a second embodiment of the present invention will be described.
In the following description, portions different from the above-described first embodiment will be mainly described, and descriptions of portions similar to the first embodiment will be omitted.
FIG. 7 is a structural cross-sectional view showing the layer configuration of the solar cell 1B (1) according to this embodiment.

In the first embodiment described above, the solar cell having the tandem structure has been described. However, the present invention is not limited to the tandem structure, and can be applied to a solar cell having a single structure.
This solar cell 1B (10) uses a substrate 10 with a transparent conductive film, a p-type semiconductor layer (p layer) 9p, a substantially intrinsic i-type semiconductor layer (i layer) 9i, an n-type semiconductor layer (n layer) ) A pin type third photoelectric conversion unit 9 in which 9n is stacked is provided on the transparent conductive film 4 in order.

In the solar cell 1B (10) of the present invention, the transparent conductive film 4 is an aggregate of crystal grains 4a having a shape extending in the film thickness direction, and at least the film thickness is between the crystal grains 4a. There is an interface 4b in the direction, and the surface has fine unevenness (texture structure) (see FIG. 2).
Also in this solar cell 1B (10), a fine texture having a high degree of freedom and a desired roughness and shape is formed on the surface of the transparent conductive film 4. Since this texture structure brings about a prism effect and a light confinement effect, the solar cell 1B (10) according to the present invention has high conversion efficiency.

  Further, in this solar cell 1B (10), the p layer 9p, i layer 9i, and n layer 9n constituting the third photoelectric conversion unit 9 are made of an amorphous silicon thin film, and the transparent conductive film 4 and the p layer 9p are formed. In between, a buffer layer 5 made of a silicon thin film is disposed.

  Also in this solar cell 1B (10), since the buffer layer 5 made of a crystalline silicon thin film is disposed between the transparent conductive film 4 and the p layer 9p, the transparent conductive film 4 and the amorphous The mismatch at the interface with the p layer (9p) made of a silicon-based thin film can be alleviated. Thereby, the fill factor (FF) of the 3rd photoelectric conversion unit 9 can be improved. As a result, the solar cell 1B (1) of the present invention has high conversion efficiency.

  The substrate 10 with a transparent conductive film, the buffer layer 5, the p layer 9p, the i layer 9i, and the n layer 9n constituting the solar cell 1B (10) are all substrates with a transparent conductive film in the first embodiment described above. 10, the buffer layer 5, the p layer 6p, the i layer 6i, and the n layer 6n.

  As mentioned above, although the board | substrate with a transparent conductive film for solar cells of this invention, a solar cell, and those manufacturing methods have been demonstrated, this invention is not limited to this, In the range which does not deviate from the meaning of invention, it changes suitably. Is possible.

Embodiments of the present invention will be described below with reference to the drawings.
A transparent conductive film was formed on the substrate using a film forming apparatus (sputtering apparatus) as shown in FIGS.
In Samples 1 to 6, transparent conductive films were formed by changing the film thickness.
(Sample 1)
First, a 300 mm × 610 mm target 27 was attached to the sputter cathode mechanism 32. For the target 27, a material in which 2% by mass of Al ₂ O ₃ was added as an impurity to ZnO was used. Thereafter, an alkali-free glass substrate (substrate 26) was placed in the charging / unloading chamber 22, exhausted by the roughing exhaust unit 24, and then transferred to the film forming chamber 23. At this time, the film forming chamber 23 is maintained at a predetermined degree of vacuum by the high vacuum exhaust means 33.

After Ar gas is introduced as a process gas from the sputtering gas introducing means 35, the pressure is adjusted to a desired sputtering pressure (5.0 Pa) by a conductance valve, and then a power of 8.4 kW is applied to the sputtering cathode mechanism 32 by a DC power source. Thus, the ZnO-based target attached to the sputtering cathode mechanism 32 was sputtered. The substrate temperature at this time was set to 300 ° C.
As a series of these operations, a ZnO-based transparent conductive film was formed to a thickness of 400 nm on an alkali-free glass substrate. Thereafter, the substrate was taken out from the preparation / removal chamber 22.

Using a transparent conductive film with a fine texture formed on the surface as an upper electrode, a solar cell in which the p-layer, i-layer and n-layer constituting the pin-type photoelectric conversion unit were made of an amorphous silicon-based thin film was produced.
At this time, a buffer layer made of a crystalline silicon-based thin film was formed between the transparent conductive film and the p layer constituting the photoelectric conversion unit.

(Sample 2)
A transparent conductive film was formed in the same manner as in Sample 1, except that the thickness of the transparent conductive film was 600 nm. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 3)
A transparent conductive film was formed in the same manner as Sample 1 except that the thickness of the transparent conductive film was set to 900 nm. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

(Sample 4)
A transparent conductive film was formed in the same manner as Sample 1, except that the thickness of the transparent conductive film was 1300 nm. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 5)
A transparent conductive film was formed in the same manner as in Sample 1, except that the thickness of the transparent conductive film was 1500 nm. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 6)
A transparent conductive film was formed in the same manner as Sample 1 except that the thickness of the transparent conductive film was 1800 nm. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

SEM photographs of the transparent conductive films of Sample 1 (film thickness 400 nm), Sample 2 (film thickness 600 nm), and Sample 3 (film thickness 900 nm) are shown in FIGS.
As is apparent from FIGS. 8 to 10, it can be seen that the transparent conductive film is composed of an aggregate of crystal grains having a shape extending in the film thickness direction. And there exists an interface at least in the film thickness direction between the crystal grains, and fine irregularities (texture structure) are formed on the surface. Further, it can be seen that the unevenness is small when the film thickness is thin, and the unevenness is large when the film thickness is thick. That is, according to the method of the present invention, the fine texture can be formed in a desired roughness and shape with a high degree of freedom by changing the film forming conditions.

Moreover, in order to verify the effect of a texture shape about the transparent conductive film produced in Sample 1 to Sample 6, the haze ratio [%] was obtained as an optical characteristic of a single film by HAZE METER HM-150 (manufactured by Murakami Color Research Laboratory Co., Ltd.). ] Was measured.
Moreover, about the solar cell produced by the sample 1-the sample 6, the electric power generation efficiency [%] was evaluated as solar cell performance with the solar simulator YSS-50A (made by Yamashita Denso Co., Ltd.), respectively.

About the transparent conductive film produced by Sample 1 to Sample 6, the relationship between the film thickness, the haze ratio, and the power generation efficiency of the solar cell is shown together in FIG. In FIG. 11, a commercially available substrate with a transparent conductive film (FTO film) is shown as a comparative sample.
As can be seen from FIG. 11, the haze ratio increases as the film thickness of the transparent conductive film increases. It can also be seen that excellent photoelectric conversion efficiency is obtained when the film thickness is in a certain range. Although this range depends on the laminated structure of the produced solar cell, for example, in the example shown in FIG. 11, when the film thickness of the transparent conductive film is about 600 to 1800 nm, excellent power generation efficiency is obtained. I understand that.

Next, in samples 7 to 13, a transparent conductive film was formed using a gas obtained by mixing H ₂ gas with Ar gas as a process gas. In Samples 7 to 13, the thickness of the transparent conductive film was 800 nm.
(Sample 7)
A transparent conductive film was formed in the same manner as Sample 1 except that Ar gas (without H ₂ gas) was used as the process gas and the substrate temperature during film formation was 220 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 8)
A transparent conductive film was formed in the same manner as Sample 1, except that Ar gas was mixed with H ₂ gas at a rate of 1% as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

(Sample 9)
A transparent conductive film was formed in the same manner as Sample 1 except that a gas obtained by mixing H ₂ gas with Ar gas at a ratio of 2% was used as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 10)
A transparent conductive film was formed in the same manner as Sample 1 except that Ar gas was mixed with H ₂ gas at a ratio of 3% as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 11)
A transparent conductive film was formed in the same manner as Sample 1 except that a gas obtained by mixing 4% of H ₂ gas with Ar gas was used as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

(Sample 12)
A transparent conductive film was formed in the same manner as Sample 1 except that a gas obtained by mixing H ₂ gas with Ar gas at a ratio of 5% was used as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 13)
A transparent conductive film was formed in the same manner as Sample 1, except that Ar gas was mixed with H ₂ gas at a rate of 8% as the process gas. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

SEM photographs of the transparent conductive films of Sample 7 (H ₂ : 0%), Sample 8 (H ₂ : 1%), Sample 9 (H ₂ : 2%), and Sample 10 (H ₂ : 3%) are shown in FIG. To FIG.
As is apparent from FIGS. 12 to 15, it can be seen that the shape of the unevenness can be changed by adding H 2 gas to the process gas at the time of film formation. Specifically, it can be seen that the unevenness is increased by increasing the amount of H ₂ gas added. That is, according to the method of the present invention, the fine texture can be formed in a desired roughness and shape with a high degree of freedom by changing the film forming conditions.

Further, secondary ion mass spectrometry (SIMS) was performed on the transparent conductive film of Sample 7 in which H ₂ gas was not added to the process gas and the transparent conductive film of Sample 8 in which H ₂ gas was added to the process gas.
The results for sample 7 are shown in FIG. 16, and the results for sample 8 are shown in FIG. Here, in the figure, the right side of the horizontal axis of the graph corresponds to the substrate surface, and the portion where the Si composition rises is the interface between the transparent conductive film and the substrate.
As is clear from comparison between FIG. 16 and FIG. 17, the presence of H is not observed in the transparent conductive film in FIG. 16, but the presence of H is recognized in the transparent conductive film in FIG. 17. It can also be seen that H is present uniformly in the depth direction of the film.
Thus, when forming a transparent conductive film, by using a mixed gas consisting of an inert gas and hydrogen gas as a process gas, it is confirmed that the formed transparent conductive film has H in the film. It was done. It has been confirmed that similar results can be obtained regardless of the H ₂ gas concentration in the process gas.

Further, the transparent conductive film produced in Sample 7 Sample 13, the amount of H ₂ gas at the time of film formation, the relationship between the power generation efficiency of the haze and solar cells, summarized in Figure 18. In FIG. 18, a commercially available substrate with a transparent conductive film (FTO film) is shown as a comparative sample.
The following points became clear from FIG.
(A1) The haze ratio increases as the amount of H ₂ gas added increases.
(A2) Excellent photoelectric conversion efficiency is obtained when the amount of H ₂ gas added is within a certain range.
(A3) This range depends on the laminated structure of the produced solar cell. For example, in the example shown in the figure, when the amount of H ₂ gas added is about 1 to 6%, excellent power generation efficiency is obtained. It is done.

Next, in Samples 14 to 19, a transparent conductive film was formed by changing the substrate temperature during film formation. In Samples 14 to 19, the thickness of the transparent conductive film was 800 nm.
(Sample 14)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 100 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 15)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 220 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

(Sample 16)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 250 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 17)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 300 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

(Sample 18)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 350 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.
(Sample 19)
A transparent conductive film was formed in the same manner as in Sample 1 except that the substrate temperature during film formation was 400 ° C. Moreover, a solar cell was produced using this transparent conductive film as an upper electrode.

About the transparent conductive film produced by the samples 14-19, the relationship between the substrate temperature at the time of film-forming, a haze rate, and the power generation efficiency of a solar cell is collectively shown in FIG. In FIG. 19, a commercially available substrate with a transparent conductive film (FTO film) is shown as a comparative sample.
The following points became clear from FIG.
(B1) The haze rate increases as the substrate temperature increases.
(B2) Excellent photoelectric conversion efficiency is obtained when the substrate temperature is in a certain range.
(B3) Although this range depends on the laminated structure of the produced solar cell, for example, in the example shown in FIG. 19, when the substrate temperature is about 200 to 400 ° C., excellent power generation efficiency is obtained.

  The present invention is widely applied to a substrate with a transparent conductive film for solar cells, a solar cell, and a method for manufacturing the same, in which the upper electrode functioning as a power extraction electrode on the light incident side includes a transparent conductive film containing ZnO as a basic constituent element. Applicable.

  1 solar cell, 2 glass substrate (transparent substrate), 3 upper electrode, 4 transparent conductive film, 4a crystal grain, 4b interface, 5 buffer layer, 6 first photoelectric conversion unit, 7 second photoelectric conversion unit, 10 transparent conductive film Attached substrate, 11 buffer layer, 12 back electrode.

Claims (11)

A substrate with a transparent conductive film in which a transparent conductive film based on ZnO is arranged so as to be in contact with an insulating transparent substrate,
The transparent conductive film is an aggregate of crystal grains having a shape extending in the film thickness direction, and there is an interface in the film thickness direction at least between the crystal grains, and the surface has fine irregularities. And the board | substrate with a transparent conductive film characterized by including a crystal grain with a crystal grain size so large that it leaves | separates from the said transparent substrate in the film thickness direction.   The substrate with a transparent conductive film according to claim 1, wherein the transparent conductive film contains hydrogen. A method for producing a substrate with a transparent conductive film in which a transparent conductive film based on ZnO is arranged so as to be in contact with an insulating transparent substrate,
Sputtering is performed by applying a sputtering voltage to a target that forms the base material of the transparent conductive film in a film formation space in a desired process gas atmosphere, and the transparent conductive film is formed on the transparent substrate at a predetermined temperature. At least a film forming step α1,
As the base material, a material mainly composed of ZnO is used,
The pressure [Pa] in the film-forming space is in the range of 1 to 10, and a mixed gas composed of an inert gas and hydrogen gas is used as the process gas, and the amount of hydrogen gas added is 1 to 6 [%]. The manufacturing method of the board | substrate with a transparent conductive film characterized by the above-mentioned.   The method for manufacturing a substrate with a transparent conductive film according to claim 3, wherein a mixed gas comprising an inert gas and hydrogen gas is used as the process gas in the step α1.   5. The method for producing a substrate with a transparent conductive film according to claim 3, wherein the temperature [° C.] of the transparent substrate in the step α <b> 1 is in a range of 150 to 400. 6.   6. The method for manufacturing a substrate with a transparent conductive film according to claim 3, further comprising a step α2 of performing post-heating treatment in the atmosphere after the step α1. Using a substrate with a transparent conductive film, a pin-type photoelectric conversion unit in which a p-type semiconductor layer (p layer), a substantially intrinsic i-type semiconductor layer (i layer), and an n-type semiconductor layer (n layer) are stacked, Provided in order on the transparent conductive film,
The transparent conductive film is disposed in contact with an insulating transparent substrate, and is an aggregate of crystal grains having a basic configuration of ZnO and extending in the film thickness direction, and at least between the crystal grains. There is an interface in the film thickness direction, and the surface has fine irregularities (texture structure), and in the film thickness direction, the crystal grain has a large crystal grain size as the distance from the transparent substrate increases.
The p layer, i layer and n layer constituting the photoelectric conversion unit are composed of amorphous silicon-based thin films,
A solar cell, wherein a buffer layer made of a silicon-based thin film is disposed between the transparent conductive film and the p layer constituting the photoelectric conversion unit. Using a substrate with a transparent conductive film, a pin-type photoelectric conversion unit in which a p-type semiconductor layer (p layer), a substantially intrinsic i-type semiconductor layer (i layer), and an n-type semiconductor layer (n layer) are stacked, A method for producing a solar cell, wherein the transparent conductive film is stacked in order through a buffer layer,
Sputtering is performed by applying a sputtering voltage to a target that forms the base material of the transparent conductive film in a film formation space in a desired process gas atmosphere, and the transparent film is in contact with an insulating transparent substrate at a predetermined temperature. Comprising at least a step β1 of forming a conductive film;
As the base material, a material mainly composed of ZnO is used,
Pressure [Pa] of the film-forming space, a range of 1 to 10, using a mixed gas consisting of inert gas and hydrogen gas as the process gas, the amount of hydrogen gas 6 [%] A method for producing a solar cell, wherein   The method for manufacturing a solar cell according to claim 8, wherein a mixed gas comprising an inert gas and hydrogen gas is used as the process gas in the step β1.   10. The method for manufacturing a solar cell according to claim 8, wherein the temperature [° C.] of the transparent substrate in the step β1 is in a range of 150 to 400. 10.   The method of manufacturing a solar cell according to claim 10, further comprising a step β4 of performing a post-heating treatment in the atmosphere after the step β1 and before the step β2 of forming the buffer layer. .