JPWO2010032490A1 - Solar cell and manufacturing method thereof - Google Patents

Abstract

The method for manufacturing a solar cell according to the present invention is a solar cell in which a transparent conductive film made of a film-forming material obtained by adding a substance containing Al or Ga to ZnO is formed on a substrate as a power extraction electrode on the light incident side. A manufacturing method, comprising: a transparent conductive film forming step of forming the transparent conductive film on the substrate by applying a sputtering voltage and sputtering a target made of the film forming material, the transparent conductive film The conductive film forming step is performed at least in order, with the first pressure as the sputtering pressure, forming the first layer constituting the transparent conductive film, and the first pressure. A second film forming step of forming a second layer constituting the transparent conductive film at a high second pressure.

Description

The present invention relates to a solar cell and a method for manufacturing the solar cell, and more specifically, a solar cell having a fine texture structure and high conversion efficiency, and a solar cell having high conversion efficiency and capable of forming a fine texture. The present invention relates to a method for manufacturing a solar cell.
This application claims priority on September 19, 2008 based on Japanese Patent Application No. 2008-241136 for which it applied to Japan, and uses the content here.

  In the solar cell, when energetic particles called photons contained in sunlight hit the i layer, electrons and holes are generated by the photovoltaic effect, the electrons move toward the n layer, and the holes are p. Move towards the layer. Electrons generated by the photovoltaic effect are taken out by the upper electrode and the back electrode, and light energy can be converted into electric energy.

  FIG. 16 is a schematic cross-sectional view of an amorphous silicon solar cell. The solar cell 100 is composed of 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, and amorphous silicon in order from the top to the bottom of the drawing. A top cell 105 configured, 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 are laminated. (For example, refer to Patent Document 1). Among them, the intermediate electrode 107 is provided between the top cell 105 and the bottom cell 109.

  The top cell 105 has a three-layer structure of a p layer 105p, an i layer 105i, and an n layer 105n. Among them, 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. Among them, the i layer 109i is made of microcrystalline silicon.

  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 the light energy of the solar cell 100, a contrivance is made such that the sunlight is reflected by the back electrode 111 or a texture structure is provided on the upper electrode 101. Among them, the texture structure has a prism effect for extending the optical path of incident sunlight and an effect for confining light. The buffer layer 110 is intended to prevent diffusion of a metal film used for the back electrode 111 (see, for example, Patent Document 2).

The wavelength band used for the photovoltaic effect varies depending on the device structure of the solar cell 100. However, in any solar cell 100, the transparent conductive film constituting the upper electrode 103 is required to have a property of transmitting light for absorption by the i layer and an electric conductivity for extracting electrons generated by the photovoltaic power. ing. The transparent conductive film constituting the upper electrode 103, FTO and that the fluorine SnO ₂ was added as an impurity, such as ZnO-based oxide semiconductor film is used. The buffer layer 110 is also required to have the property of transmitting the light reflected by the back electrode and the light reflected by the back electrode for absorption by the i layer and the electrical conductivity for moving holes to the back electrode 111. The

The characteristics required for the transparent conductive film used in the solar cell 100 are roughly divided into three elements: (1) conductivity, (2) optical characteristics, and (3) texture structure. Among them, (1) Regarding electrical conductivity, low electrical resistance is required to extract generated electricity. FTO (fluorine-doped tin oxide) generally used for transparent conductive films for solar cells is a transparent conductive film formed by CVD, and F is added to SnO _{2 so} that F replaces O. Thus, conductivity is obtained. In addition, a ZnO-based material that is attracting attention as post-ITO (tin-doped indium oxide) can be formed by sputtering, and conductivity is obtained by adding a material containing oxygen deficiency and Al or Ga to ZnO.

(2) Regarding the optical characteristics, 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.
(3) Regarding the texture structure, a texture structure that scatters light is required to efficiently absorb sunlight in the power generation layer. Usually, since a ZnO-based thin film prepared by a sputtering process has a flat surface state, a texture forming process such as wet etching is required.

  However, when a TCO (translucent conductive oxide film) for solar cells is formed by sputtering a ZnO-based material and then wet etching, a fine texture is formed because the ZnO-based material has a remarkable C-axis orientation. Difficult to do.

Japanese Unexamined Patent Publication No. 58-57756 Japanese National Table No. 2-503615

The present invention has been devised in view of such a conventional situation. Even when a transparent conductive film made of a ZnO-based material is formed by sputtering, a fine texture can be formed and converted. It aims at providing the manufacturing method of the solar cell which can produce a solar cell with high efficiency.
Another object of the present invention is to provide a solar cell having a fine texture structure on the light extraction electrode on the light incident side and high conversion efficiency.

In the method for manufacturing a solar cell according to the embodiment of the present invention, a solar conductive film made of a film-forming material obtained by adding a substance containing Al or Ga to ZnO is formed on a substrate as a power extraction electrode on the light incident side. A method for manufacturing a battery, comprising: forming a transparent conductive film on the substrate by applying a sputtering voltage and sputtering a target made of the film forming material; The film forming step of the transparent conductive film is performed at least in order, and a first film forming step of forming a first layer constituting the transparent conductive film at a first pressure as a sputtering pressure; A second film forming step of forming a second layer constituting the transparent conductive film at a second pressure higher than the pressure.
A configuration in which the sputtering voltage is applied to generate a horizontal magnetic field on the surface of the target and the target is sputtered may be employed.
A configuration in which the first pressure is less than 10 mTorr and the second pressure is 10 mTorr or more may be employed.
You may employ | adopt the structure further provided with the process of performing the wet etching process with respect to the said transparent conductive film after the film-forming process of the said transparent conductive film.
A solar cell according to an embodiment of the present invention includes a glass substrate that constitutes a surface of the solar cell, an upper electrode that is provided on the glass substrate and made of a film-forming material obtained by adding a substance containing Al or Ga to ZnO, A top cell provided on the upper electrode and including an amorphous silicon layer, an intermediate electrode provided on the top cell, a bottom cell provided on the intermediate electrode and including a microcrystalline silicon layer, and provided on the bottom cell A solar cell comprising: a buffer layer made of a transparent conductive film; and a metal electrode provided on the buffer layer, wherein the upper electrode has a conductive first layer conductive film and a fine texture structure And a second layer conductive film.
The first layer conductive film of the upper electrode has a thickness of 100 nm or more and 1000 nm or less, and the second layer conductive film of the upper electrode has a thickness of 50 nm or more and 500 nm or less. It may be adopted.

  According to the present invention, when sputtering a ZnO-based material in forming a transparent conductive film, the first layer for obtaining conductivity is formed by sputtering at low pressure, and then the second layer for forming texture is formed by high pressure. Sputter film formation is performed. Thereby, the orientation of the formed film is disturbed, and a fine texture can be formed. 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 a solar cell with high conversion efficiency can be manufactured.

It is sectional drawing which shows an example of the solar cell formed by the manufacturing method of the solar cell which concerns on this invention. It is a schematic block diagram which shows the film-forming apparatus suitable for the manufacturing method of the solar cell which concerns on this invention. It is sectional drawing which shows the principal part of the film-forming chamber which comprises the film-forming apparatus shown in FIG. It is sectional drawing which shows another example of the film-forming apparatus suitable for the manufacturing method of the solar cell which concerns on this invention. It is a schematic diagram which shows another example of the film-forming apparatus suitable for the manufacturing method of the solar cell which concerns on this invention. It is a schematic diagram which shows another example of the film-forming apparatus suitable for the manufacturing method of the solar cell which concerns on this invention. It is a side surface schematic diagram which shows another example of the film-forming apparatus suitable for the manufacturing method of the solar cell which concerns on this invention. It is a schematic diagram which shows an example of DC power supply of the film-forming apparatus shown to FIG. 7A. It is a schematic diagram which shows an example of AC power supply of the film-forming apparatus shown to FIG. 7A. FIG. 3 is a view showing an SEM image of a transparent conductive film according to Example 1. 6 is a view showing an SEM image of a transparent conductive film according to Example 2. FIG. It is a figure which shows the SEM image of the transparent conductive film which concerns on the comparative example 1. FIG. It is a figure which shows the SEM image of the transparent conductive film which concerns on the comparative example 2. It is a figure which shows the SEM image of the transparent conductive film which concerns on the comparative example 3. It is a figure which shows the SEM image of the transparent conductive film which concerns on the comparative example 4. It is a figure which shows the XRD measurement result of the transparent conductive film which concerns on Example 2. FIG. It is a figure which shows the XRD measurement result of the transparent conductive film which concerns on the comparative example 1. It is 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.

(Solar cell)
First, the solar cell manufactured by this embodiment is demonstrated based on FIG. FIG. 1 is a cross-sectional view showing an example of the configuration of the solar cell 50.
The solar cell 50 includes, in order from the top to the bottom of the drawing, a glass substrate 51 constituting the surface thereof, an upper electrode 53 made of a zinc oxide-based transparent conductive film 54 provided on the glass substrate 51, and amorphous silicon. A top cell 55 made of (a-Si), an intermediate electrode 57 made of a transparent conductive film, a bottom cell 59 made of microcrystalline silicon (microcrystalline Si), a buffer layer 61 made of a transparent conductive film, A back electrode 63 made of a metal film is laminated. Among them, the intermediate electrode 57 is provided between the top cell 55 and the bottom cell 59.

  That is, the solar cell 50 is an a-Si / microcrystalline Si tandem solar cell. In the solar cell 50 having such a tandem structure, the short-wavelength light is absorbed by the top cell 55 and the long-wavelength light is absorbed by the bottom cell 59, so that the power generation efficiency can be improved. The film thickness of the upper electrode 53 is 150 nm to 1500 nm. Further, the upper electrode 53 may be formed to a thickness of 200 nm to 1000 nm. As shown in FIG. 1, the transparent conductive film 54 constituting the upper electrode 53 includes a first layer 54a having conductivity and a second layer 54b having a texture structure. Among them, the conductive first layer 54a is formed with a film thickness of 100 nm or more and 1000 nm or less. Among them, the film thickness of the first layer 54a of the transparent conductive film (for example, AZO film) can be set to 100 nm or more so that the sheet resistance of the TCO substrate for solar cells is 50Ω / □ (ohm / Square) or less. Further, the film thickness of the first layer 54a can be set to 1000 nm or less so that the total light transmittance of 80% or more (only the transparent conductive film) can be achieved in the state before the texture treatment. The second layer 54b having a texture structure is formed with a film thickness of 50 nm or more and 500 nm or less. Among them, in addition to forming a texture structure on the second layer 54b, when etching the first layer 54a using the second layer 54b as a mask, the characteristics of the high-pressure sputtered film can be realized. The film thickness can be set to 50 nm or more. In consideration of the productivity of the transparent conductive film, the thickness of the second layer 54b can be set to 500 nm or less. However, the film thickness of the said transparent conductive film is not limited to this, The said numerical value can be set appropriately according to the solar cell to manufacture.

  The top cell 55 has a three-layer structure of a p layer 55p, an i layer 55i, and an n layer 55n. Among them, the i layer 55i is formed of amorphous silicon. Similarly to the top cell 55, the bottom cell 59 has a three-layer structure of a p layer 59p, an i layer 59i, and an n layer 59n. Among them, the i layer 59i is made of microcrystalline silicon.

  In the solar cell 50 having such a configuration, 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. Then, the holes move toward the p layer. Electrons generated by the photovoltaic effect are taken out by the upper electrode 53 and the back electrode 63, and light energy can be converted into electric energy.

  Further, by providing the intermediate electrode 57 between the top cell 55 and the bottom cell 59, a part of the light that passes through the top cell 55 and reaches the bottom cell 59 is reflected by the intermediate electrode 57, and the top cell 55 side again. Therefore, the sensitivity characteristic of the cell is improved and the power generation efficiency is improved.

  Moreover, the sunlight which entered from the glass substrate 51 side passes through each layer, and is reflected by the back surface electrode 63. In order to improve the light energy conversion efficiency of the solar cell 50, a texture structure is adopted for the upper electrode 53. This texture structure has a prism effect for extending the optical path of sunlight incident on the upper electrode 53 and an effect for confining light.

  As will be described later, in the present embodiment, in the formation of the transparent conductive film 54 constituting the upper electrode 53, the first layer 54a for obtaining conductivity when the ZnO-based material forming the transparent conductive film 54 is sputtered. Then, the second layer 54b for forming the texture is sputtered at a high pressure. Thereby, a fine texture by wet etching can be formed. The solar cell 50 thus manufactured can sufficiently obtain the prism effect and the light confinement effect due to the texture structure, and the photoelectric conversion efficiency is increased.

(Method for manufacturing solar cell)
Next, the manufacturing method of the said solar cell is demonstrated.
The method for manufacturing a solar cell according to the present embodiment is a method for manufacturing a solar cell in which the upper electrode 53 is made of a transparent conductive film 54 having ZnO as a basic constituent element. Among them, the upper electrode 53 functions as a power extraction electrode on the light incident side. This solar cell manufacturing method includes at least a transparent conductive film forming step for forming the upper electrode 53. In the transparent conductive film forming step, a sputtering voltage is applied to the target made of the material for forming the transparent conductive film 54, and a horizontal magnetic field is generated on the surface of the target to perform sputtering, thereby producing a glass substrate 51 (substrate). The transparent conductive film 54 is formed thereon.

  In the solar cell manufacturing method according to the present embodiment, the material for forming the transparent conductive film 54 is a film forming material obtained by adding a substance containing Al or Ga to ZnO. The transparent conductive film forming process for forming the upper electrode 53 includes a first film forming process and a second film forming process which are performed at least in order. Among them, in the first film forming step, the first layer 54a constituting the transparent conductive film 54 is formed at a first pressure as a sputtering pressure. In the second film formation step, the second layer 54b constituting the transparent conductive film 54 is formed at a second pressure higher than the first pressure. The first pressure is preferably 2 mTorr or more and less than 10 mTorr. If the pressure is 2 mTorr or less, it may be difficult to obtain a stable discharge. The second pressure is preferably 10 mTorr or more. Furthermore, the second pressure is preferably 30 mTorr or more. The upper limit of the second pressure is not particularly limited, but preferably does not exceed 50 mTorr. When the pressure is 50 mTorr or more, there is a possibility that a decrease in the film formation rate due to scattering will become remarkable.

  In the present embodiment, when sputtering the ZnO-based material in forming the transparent conductive film 54, first, the first layer 54a for obtaining conductivity is formed by sputtering at a low pressure. Next, the second layer 54b for forming the texture is formed by sputtering at a high pressure. Thereby, a fine texture by wet etching can be formed. Thereby, in this embodiment, the prism effect and light confinement effect by a texture structure can fully be acquired, and a solar cell with high photoelectric conversion efficiency can be produced.

First, an example of a growth apparatus (sputtering apparatus) suitable for forming the zinc oxide-based transparent conductive film 54 constituting the upper electrode 53 in the solar cell manufacturing method of the present embodiment will be described.
(Example of growth device)
FIG. 2 is a schematic configuration diagram showing an example of a growth apparatus (sputtering apparatus) used in the method for manufacturing the solar cell 50 of the present embodiment. FIG. 3 is a cross-sectional view showing the main part of the film forming chamber constituting the film forming apparatus 1 shown in FIG. The growth apparatus 1 is an inter-back type sputtering apparatus. For example, a loading / unloading chamber 2 for loading / unloading a substrate such as an alkali-free glass substrate (not shown), and a zinc oxide-based sputtering substrate on the substrate. And a film forming chamber (vacuum container) 3 for forming a transparent conductive film.

  The preparation / removal chamber 2 is provided with a roughing exhaust unit 4 such as a rotary pump used to depressurize the chamber. A substrate tray 5 for holding and transporting the substrate is movably disposed in the preparation / removal chamber 2.

  On the other hand, as shown in FIGS. 2 and 3, a heater 11 for heating the substrate 6 is provided in a vertical shape on one side surface 3a of the film forming chamber 3, and a zinc oxide-based material is provided on the other side surface 3b. A sputtering cathode mechanism (target holding unit) 12 for holding a target 7 of material and applying a desired sputtering voltage is provided in a vertical type. Further, on the side surface 3b of the film forming chamber 3, a high vacuum exhaust unit 13 such as a turbo molecular pump for evacuating the inside of the film forming chamber 3, a power source 14 for applying a sputtering voltage to the target 7, and a film forming chamber And a gas introduction unit 15 for introducing gas into the three chambers.

The sputter cathode mechanism 12 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 14 is for applying a sputtering voltage in which a high-frequency voltage is superimposed on a DC voltage to the target 7, and includes a DC power source and a high-frequency power source (not shown).

  The gas introduction unit 15 includes a sputtering gas introduction portion 15a for introducing a sputtering gas such as Ar, a hydrogen gas introduction portion 15b for introducing hydrogen gas, an oxygen gas introduction portion 15c for introducing oxygen gas, and a water vapor for introducing water vapor. And an introduction part 15d.

  The gas introduction unit 15 may be used by selecting the hydrogen gas introduction part 15b to the water vapor introduction part 15d as necessary. For example, the gas introduction unit 15 may be configured by two gas introduction units such as a hydrogen gas introduction unit 15b and an oxygen gas introduction unit 15c, or a hydrogen gas introduction unit 15b and a water vapor introduction unit 15d.

(Another example of film forming apparatus)
FIG. 4 is a cross-sectional view showing another example of a film forming apparatus (sputtering apparatus) used in the method for manufacturing the solar cell 50 of the present embodiment. That is, it is a cross-sectional view showing a main part of a film forming chamber of an inter-back type magnetron sputtering apparatus. The magnetron sputtering apparatus 21 shown in FIG. 4 has the following differences from the film forming apparatus 1 shown in FIGS. That is, a sputtering cathode mechanism (target holding unit) 22 that holds a target 7 made of a zinc oxide material and generates a desired magnetic field is provided vertically on the side surface 3b of the film forming chamber 3.

  The sputter cathode mechanism 22 includes a back plate 23 in which the target 7 is bonded (fixed) with a brazing material or the like, and a magnetic circuit 24 disposed along the back surface of the back plate 23. The magnetic circuit 24 generates a horizontal magnetic field on the surface of the target 7. The magnetic circuit 24 includes a plurality of magnetic circuit units (two in FIG. 4) 24a and 24b, and the plurality of magnetic circuit units 24a and 24b are connected and integrated by a bracket 25. The magnetic circuit units 24 a and 24 b include a first magnet 26, a second magnet 27, and a yoke 28 on which the first magnet 26 and the second magnet 27 are mounted. Among them, the first magnet 26 and the second magnet 27 have different polarities on the surface on the back plate 23 side.

  In the magnetic circuit 24, a magnetic field represented by a magnetic force line 29 is generated by the first magnet 26 and the second magnet 27 having different polarities on the back plate 23 side. As a result, a position 30 where the vertical magnetic field is 0 (the horizontal magnetic field is maximum) is generated on the surface of the target 7 between the first magnet 26 and the second magnet 27. The high-density plasma is generated at the position 30, so that the film forming speed can be improved.

  In the film forming apparatus shown in FIG. 4, since the sputtering cathode mechanism 22 for generating a desired magnetic field is provided on one side surface 3b of the film forming chamber 3 in a vertical type, the sputtering voltage is set to 340 V or less. By setting the maximum value of the horizontal magnetic field strength on the surface of the target 7 to 600 gauss or more, it is possible to form a zinc oxide-based transparent conductive film in which the crystal lattice is arranged. The zinc oxide-based transparent conductive film formed in this manner is hardly oxidized even when annealing is performed at a high temperature after film formation, and an increase in specific resistance can be suppressed. Furthermore, when the upper electrode of a solar cell is comprised with such a zinc oxide type transparent conductive film, the upper electrode of the solar cell excellent in heat resistance can be obtained.

Next, as an example of the solar cell manufacturing method of the present embodiment, a zinc oxide-based transparent conductive film constituting the upper electrode of the solar cell is formed on the substrate using the film forming apparatus 1 shown in FIGS. An example of a film forming method will be described.
First, the target 7 is bonded and fixed to the sputtering cathode mechanism 12 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-doped 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, in a state where a substrate 6 (glass substrate 51) of a solar cell made of glass, for example, is stored in the substrate tray 5 of the preparation / removal chamber 2, the preparation / removal chamber 2 and the film formation chamber 3 are roughened by the roughing exhaust unit 4. Evacuate. After the preparation / removal chamber 2 and the film formation chamber 3 reach a predetermined degree of vacuum, for example, 0.27 Pa (2.0 mTorr), the substrate 6 is carried into the film formation chamber 3 from the preparation / removal chamber 2. Is placed in front of the heater 11 in a state in which the setting is turned off, the substrate 6 is opposed to the target 7, and the substrate 6 is heated by the heater 11 to be within a temperature range of 100 ° C. to 600 ° C. .

Next, the film forming chamber 3 is evacuated by the high vacuum exhaust unit 13 so that the film forming chamber 3 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 3 by the sputtering gas introducing unit 15, and the inside of the film forming chamber 3 is set to a predetermined pressure (sputtering pressure).

  Next, a sputtering voltage, for example, a sputtering voltage in which a high frequency voltage is superimposed on a DC voltage is applied to the target 7 by the power source 14. By applying the sputtering voltage, plasma is generated on the substrate 6, and ions of sputtering gas such as Ar excited by the plasma collide with the target 7, and from this target 7 aluminum added zinc oxide (AZO), gallium added oxidation. Atoms constituting a zinc oxide-based material such as zinc (GZO) are ejected to form a transparent conductive film 54 made of a zinc oxide-based material on the substrate 6.

In the present embodiment, at least as a sputtering pressure, a first film forming step of forming the first layer 54a constituting the transparent conductive film 54 at a first pressure and a second pressure higher than the first pressure are used. The second film forming step of forming the second layer 54b constituting the transparent conductive film 54 is sequentially performed.
The first pressure is preferably less than 10 mTorr, and the second pressure is preferably 10 mTorr or more.
That is, the first layer 54a for obtaining conductivity is sputtered at a low pressure, and then the second layer 54b for forming a texture is sputtered at a high pressure. By sputtering the second layer 54b in a high-pressure atmosphere, the orientation of the film to be formed is disturbed, and a fine texture can be formed by wet etching (anisotropic etching) in a subsequent process.

Next, the substrate 6 (glass substrate 51) is transferred from the film formation chamber 3 to the preparation / removal chamber 2, the vacuum in the preparation / removal chamber 2 is broken, and the substrate on which the zinc oxide-based transparent conductive film 54 is formed. 6 (glass substrate 51) is taken out.
Next, a wet etching process is performed on the transparent conductive film 54. Thereby, a fine texture is formed on the surface of the transparent conductive film 54. At this time, the second layer 54b constituting the surface of the transparent conductive film 54 is sputtered and formed in a high-pressure atmosphere, so that the orientation of the film is disturbed. Therefore, during wet etching, etching proceeds in a plurality of directions, and a fine texture can be formed.

In this way, the substrate 6 (glass substrate 51) on which the zinc oxide-based transparent conductive film 54 is formed is obtained. The transparent conductive film 54 has a fine texture structure on its surface.
By using such a substrate for a solar cell, the prism effect that extends the optical path of incident sunlight and the light confinement effect can be maximized, and a solar cell with high photoelectric conversion efficiency can be manufactured.

In this embodiment, when the first layer and the second layer are continuously formed, in the case of an inline type film forming apparatus, an inline buffer chamber type having a buffer chamber as shown in FIG. An in-line slit type film forming apparatus having a slit as shown in FIG. The same applies to a roll-up film forming apparatus.
Specifically, the in-line type film forming apparatus shown in FIG. 5 includes a load chamber for loading a substrate, a heating chamber for heating the substrate, and a low-pressure first layer film forming chamber for forming a first layer of a transparent conductive film. And a buffer chamber, a high-pressure second layer film forming chamber for forming the second layer of the transparent conductive film, and an unload chamber for taking out the substrate.
An in-line slit type film forming apparatus having a slit shown in FIG. 6 includes a load chamber for charging a substrate, a heating chamber for heating the substrate, and a low-pressure first layer film forming chamber for forming a first layer of a transparent conductive film. And a slit, a high-pressure second layer film forming chamber for forming the second layer of the transparent conductive film, and an unload chamber for taking out the substrate.
On the other hand, in the case of a sheet type film forming apparatus, a cluster type film forming apparatus as shown in FIG. 7A can be adopted. In this case, after the first layer is formed, the pressure is adjusted to form the second layer. The same applies to the case of the carousel type film forming apparatus.
Specifically, the film forming apparatus shown in FIG. 7A forms a load chamber for loading a substrate, a cathode mechanism for forming a first layer of a transparent conductive film at a low pressure, and a second layer of the transparent conductive film at a high pressure. A cathode mechanism and an unload chamber for taking out the substrate are provided. 7B and 7C, a DC power supply type or an AC power supply type can be adopted.

As mentioned above, although the manufacturing method of the solar cell of this embodiment was demonstrated, this invention is not limited to this, In the range which does not deviate from the meaning of invention, it can change suitably.
(Example)

Embodiments of the present invention will be described below with reference to the drawings.
A transparent conductive film was formed on the substrate by using a film forming apparatus (sputtering apparatus) 1 as shown in FIGS.
Example 1
First, the target 7 of 5 inches × 16 inches was attached to the sputter cathode mechanism 12. For the target 7, a material obtained by adding 2% by weight of Al ₂ O ₃ as an impurity to ZnO was used. Further, the setting of the heater 11 was adjusted so that the substrate temperature was 250 ° C., and the film formation chamber 3 was heated.

Thereafter, an alkali-free glass substrate (substrate 6) was placed in the charging / unloading chamber 2, exhausted by the roughing exhaust unit 4, and then transferred to the film forming chamber 3. At this time, the film forming chamber 3 is maintained at a predetermined degree of vacuum by the high vacuum exhaust unit 13.
After introducing Ar gas as a process gas from the sputtering gas introduction unit 15 at a desired sputtering pressure (first pressure: 5 mTorr), 1 kW of electric power is applied to the sputtering cathode mechanism 12 from a DC power source, thereby forming the sputtering cathode mechanism 12. A ZnO-based target attached to the substrate was sputtered.

With these operations as a series of flows, a first layer constituting a ZnO-based transparent conductive film was formed to a thickness of 150 nm on an alkali-free glass substrate. Thereafter, the film formation chamber 3 was adjusted again to a vacuum of 30 mTorr with the second pressure, and a ZnO-based target was sputtered to form a second layer having a thickness of 500 nm on the first layer. Thereafter, the substrate was taken out from the charging / unloading chamber 2.
After forming the transparent conductive film, wet etching was performed for 90 seconds using 0.01 wt% hydrochloric acid to form a texture on the surface of the transparent conductive film.

(Example 2)
A transparent conductive film was formed in the same manner as in Example 1 except that the thickness of the first layer was 200 nm, and a texture was formed on the surface of the transparent conductive film.

(Comparative Examples 1 to 4)
Basically the same as in Example 1, but a transparent conductive film having a predetermined thickness was formed by setting the sputtering pressure to a constant pressure of 5 mTorr.
In addition, wet etching was performed for a predetermined time using 0.01 wt% hydrochloric acid to form a texture on the surface of the transparent conductive film.

About the transparent conductive film of the Example produced as mentioned above and a comparative example, those SEM images are shown in FIGS. 8-13, respectively. 8 and 9 are SEM images of Examples 1 and 2, and FIGS. 10 to 13 are SEM images of Comparative Examples 1 to 4. FIG.
Moreover, about the transparent conductive film of Example 2 and Comparative Example 1, the result of the XRD measurement of Example 2 is shown in FIG. 14, and the result of the XRD measurement of Comparative Example 1 is shown in FIG.

Moreover, in order to verify the effect of the texture shape, a minicell solar cell was produced using the obtained transparent conductive film as an upper electrode, and the solar cell performance was evaluated by a solar simulator.
About the transparent conductive film of an Example and a comparative example, those film-forming conditions, etching time, and solar cell characteristic [conversion efficiency (Eff), short circuit current density (Jsc), fill factor (FF)]] are shown in Table 1. Shown together.

(Table 1)

As is clear from FIGS. 8 to 13, fine textures are not formed in the SEM images of Comparative Examples 1 to 4 shown in FIGS. 10 to 13, but Example 1 and FIGS. In the SEM image of Example 2, it can be seen that a fine texture is formed.
As can be seen from FIGS. 14 and 15, in the transparent conductive film of the example, the orientation of the (004) plane is increased, so that etching proceeds in a plurality of directions and a fine texture is formed. It is considered possible.

  Further, as is clear from Table 1, in the example in which the fine texture was formed, the Jsc of the solar cell was higher than that in the comparative example, so that the light scattering effect was improved, and the power generation layer It was confirmed that the amount of power generation was large. Moreover, since the photoelectric conversion efficiency has also increased with the improvement of Jsc, it has been verified that the production method according to the present invention is effective in increasing the efficiency of solar cells.

  A method for forming a transparent conductive film on a substrate using the film forming apparatus shown in FIG. 4 will be briefly described. First, the same target 7 as that of the first embodiment is attached to the sputtering cathode mechanism 22. A sputtering voltage is applied to the target 7 by the sputtering cathode mechanism 22, and a horizontal magnetic field is generated on the surface of the target 7 by the magnetic circuit 24. A target 7 is sputtered at a first pressure, for example, 5 mTorr, to form a first layer of a transparent conductive film. Thereafter, the target 7 is sputtered at a second pressure, for example, 30 mTorr, to form a second layer of the transparent conductive film.

  The present invention is widely applicable to a method for manufacturing a solar cell in which the upper electrode functioning as a power extraction electrode on the light incident side is made of a transparent conductive film containing ZnO as a basic constituent element.

50 Solar cell 51 Glass substrate (substrate)
53 Upper electrode 54 Transparent conductive film 54a First layer 54b Second layer 55 Top cell 59 Bottom cell 57 Intermediate electrode 61 Buffer layer 63 Back electrode

Claims (6)

A method for manufacturing a solar cell, in which a transparent conductive film made of a film forming material in which a substance containing Al or Ga is added to ZnO is formed on a substrate as a power extraction electrode on the light incident side,
Applying a sputtering voltage to sputter a target made of the film forming material, thereby forming a transparent conductive film forming step of forming the transparent conductive film on the substrate;
The film forming step of the transparent conductive film is performed at least in order, and a first film forming step of forming a first layer constituting the transparent conductive film at a first pressure as a sputtering pressure; A second film forming step of forming a second layer constituting the transparent conductive film at a second pressure higher than the pressure,
A method for manufacturing a solar cell. Applying the sputtering voltage to generate a horizontal magnetic field on the surface of the target to sputter the target;
The manufacturing method of the solar cell of Claim 1 characterized by the above-mentioned. The first pressure is less than 10 mTorr;
The second pressure is 10 mTorr or more;
The manufacturing method of the solar cell of Claim 1 characterized by the above-mentioned. The method further includes a step of performing a wet etching process on the transparent conductive film after the transparent conductive film is formed.
The manufacturing method of the solar cell of Claim 1 or 3 characterized by the above-mentioned. A glass substrate constituting the surface of the solar cell;
An upper electrode formed on the glass substrate and made of a film forming material obtained by adding a substance containing Al or Ga to ZnO;
A top cell provided on the upper electrode and including an amorphous silicon layer;
An intermediate electrode provided on the top cell;
A bottom cell provided on the intermediate electrode and including a microcrystalline silicon layer;
A buffer layer provided on the bottom cell and made of a transparent conductive film;
A metal electrode provided on the buffer layer, comprising:
The upper electrode includes a first conductive film having conductivity and a second conductive film having a fine texture structure.
A solar cell characterized by that. The first layer conductive film of the upper electrode has a thickness of 100 nm or more and 1000 nm or less,
The second layer conductive film of the upper electrode has a thickness of 50 nm or more and 500 nm or less.
The solar cell according to claim 5.