JP2011159685A - Method of manufacturing solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell including a photoelectric conversion layer formed of at least one compound semiconductor consisting of a group Ib element, a group IIIb element and a group VIb element, and an insulating layer formed by anodizing Al, in which degradation of insulating characteristics caused by a crack in the insulating layer can be prevented even when the photoelectric conversion layer is formed at a high temperature exceeding 500°C. <P>SOLUTION: The problem can be solved by cleaning a surface of the Al to be anodized using an acidic cleaning solution before forming the insulating layer by anodizing Al. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solar cell that can suitably prevent performance degradation caused by a decrease in insulating properties.

Conventionally, in solar cells, Si-based solar cells using bulk single-crystal Si or polycrystalline Si or thin-film amorphous Si have been mainstream, but in recent years, research on compound semiconductor-based solar cells that do not depend on Si has been conducted. Development is underway.
Compound semiconductor solar cells include CIS (Cu-In-Se) -based and CIGS (Cu-In-Ga-Se) -based bulk systems such as GaAs and the like, and Ib group elements, IIIb group elements, and VIb group elements. ) And other thin film systems are known. The CIS system and the CIGS system have high light absorptance, and high photoelectric conversion efficiency has been reported.

Currently, glass substrates are mainly used as substrates for solar cells, but the use of flexible metal substrates has been studied.
A compound thin film solar cell using a metal substrate may be applicable to a wider range of applications than the one using a normal glass substrate due to the light weight and flexibility of the substrate. There is. In addition, a metal substrate can withstand high-temperature processes, so it is possible to form a photoelectric conversion layer (light absorption layer) at high temperatures, which improves photoelectric conversion characteristics and increases the efficiency of solar cells. Can be expected.

  By the way, the solar cell (solar cell module) can improve the efficiency as a module by connecting the solar cells in series on the same substrate and integrating them. In this case, when a metal substrate is used, it is necessary to form an insulating layer on the metal substrate and provide a semiconductor circuit layer that performs photoelectric conversion.

For example, in Patent Document 1, an iron-based material such as stainless steel is used as a solar cell substrate, and an insulating layer is formed by coating an oxide of Si or Al by a vapor phase method such as CVD or a liquid phase method such as a sol-gel method. It is described to form.
However, these methods are prone to pinholes and cracks due to the manufacturing method, and have an essential problem as a method for stably producing a large-area thin film insulating layer.

On the other hand, in the case of Al (aluminum), by forming an anodic oxide film (AAO) on the surface, an insulating film having no pinholes and good adhesion can be obtained.
Therefore, as described in Patent Document 2, a solar cell module using a substrate in which an anodized film is formed as an insulating layer on the surface of an Al substrate has been studied.

Here, as described in Non-Patent Document 1, it is known that the anodized film formed on the surface of Al is cracked when heated to 120 ° C. or higher.
However, in the case of a compound semiconductor-based photoelectric conversion layer, in particular, a CIGS-based compound semiconductor photoelectric conversion layer, in order to obtain high photoelectric conversion efficiency, it is better that the film formation temperature is high. The film temperature is 500 ° C. or higher.

Therefore, when a substrate having an anodic oxide film of Al as an insulating layer is used as a substrate of a solar cell having a compound semiconductor-based photoelectric conversion layer, the anode is formed during the formation of the photoelectric conversion layer or in the cooling process after the film formation. Cracks or peeling of the oxide film will occur.
Once a crack is generated, there is a problem in that insulation, in particular, a leakage current increases, a satisfactory light conversion efficiency cannot be obtained, and dielectric breakdown occurs.

In addition, since Al softens at about 200 ° C., an Al substrate that has experienced this temperature or more has a very low strength and is likely to undergo permanent deformation (plastic deformation) such as creep deformation or buckling deformation.
Therefore, a solar cell using an Al substrate needs to be severely restricted in handling, including at the time of manufacture. This makes it difficult to apply solar cells using an Al substrate to outdoor solar cells and the like.

  On the other hand, in Patent Document 3, a layer made of an anodizable metal such as Al is provided as an intermediate layer on the surface of a metal substrate such as stainless steel, Cu, Al, Ti, Fe, or an iron alloy. A heat-resistant insulating substrate is described in which an anodized film is used as an insulating layer.

JP 2001-339081 A JP 2000-49372 A JP 2009-132996 A

Masae Takashima, Masakatsu Tsuji, Tokyo Metropolitan Industrial Technology Research Institute, Research Report, No. 3, February 2000, p21

It is considered that the cause of cracks in the anodic oxide film on the Al layer is that the linear expansion coefficient (linear thermal expansion coefficient) of Al is larger than the linear expansion coefficient of the anodic oxide film.
That is, the linear expansion coefficient of Al is 23 × 10 ⁻⁶ / ° C. On the other hand, although the exact numerical value of the linear expansion coefficient of the anodic oxide film of Al is unknown, it is estimated that the value is close to aluminum oxide (α alumina) and is about 7 × 10 ⁻⁶ / ° C. Considering this point, since the anodic oxide film cannot withstand the stress caused by a large difference in linear expansion coefficient of about 16 × 10 ⁻⁶ / ° C., if the anodic oxide film on the Al material is cracked as described above. Conceivable.

On the other hand, as shown in Patent Document 3, an Al layer is formed on the surface of a metal substrate, and a substrate on which an insulating layer is formed by anodizing the surface of the Al layer is used as a substrate for a solar cell. By using, the metal substrate bears the strength and the linear expansion coefficient of the entire substrate, and further, the stress caused by the difference in thermal expansion between the metal substrate and the insulating layer that is an anodic oxide film of Al is reduced. Absorption can be achieved by interposing an Al layer having a smaller Young's modulus than the insulating layer.
This suppresses cracks in the insulating layer, that is, the anodic oxide coating of Al due to the difference in coefficient of linear expansion, and can also eliminate handling limitations due to softening of Al due to high-temperature treatment.

  However, even when a substrate having such a metal substrate and an Al layer is used, if a photoelectric conversion layer is formed at a film formation temperature of 500 ° C. or more, an insulating layer, that is, an Al anodic oxide film is formed. In many cases, cracks are generated that significantly reduce the insulation performance.

  An object of the present invention is to solve the above-described problems of the prior art, and in a method for manufacturing a solar cell using a substrate that uses an Al anodic oxide film as an insulating layer, a photoelectric conversion layer such as a CIGS layer is formed. A method for manufacturing a solar cell in which even when subjected to a thermal history of 500 ° C. or higher suitable for cracking, the generation of cracks in the insulating layer can be more reliably suppressed, and the insulating layer can maintain good insulating characteristics. It is to provide.

  In order to achieve the above object, a method for producing a solar cell of the present invention includes a step of cleaning a surface of an aluminum substrate with an acidic cleaning liquid, a step of anodizing the cleaning surface of the aluminum, And forming a thin-film solar cell having a photoelectric conversion layer made of at least one compound semiconductor composed of a group Ib element, a group IIIb element and a group VIb element on the substrate using the anodized film as an insulating layer. A method for manufacturing a solar cell is provided.

In such a solar cell manufacturing method, the group Ib element of the compound semiconductor is at least one of Cu and Ag, and the group IIIb element is at least one selected from the group consisting of Al, Ga, and In. Preferably, the group VIb element is at least one element selected from the group consisting of S, Se and Te.
The acidic cleaning liquid is an acidic cleaning liquid containing sulfuric acid having a temperature of 60 ° C. or higher and a concentration of 300 g / L or higher, and the surface of the aluminum is immersed in the acidic cleaning liquid for 3 seconds or more. It is preferable to perform the cleaning.
The photoelectric conversion layer is preferably formed at a film formation temperature of 500 ° C. or more, and the intermetallic compound existing on the aluminum surface is removed by 50% or more per unit area by washing with the acid. Is preferred.
Moreover, it is preferable that the said board | substrate is a board | substrate formed by forming the aluminum layer in the surface of a metal base material, and it is preferable in this case that the said metal base material is stainless steel.
In addition, the formation of the insulating layer by anodizing of the Al is preferably performed using an acidic electrolyte, and the substrate is formed by pressure bonding an aluminum plate to the metal base material. preferable.

According to the method for manufacturing a solar cell of the present invention having the above-described configuration, by treating the surface of Al of the substrate serving as the insulating layer with an acidic cleaning liquid such as high-concentration sulfuric acid, prior to the anodic oxidation of Al (aluminum), Intermetallic compounds present on the surface of Al can be removed. Therefore, when forming a photoelectric conversion layer made of a compound semiconductor such as a CIGS compound, even if the film is formed at a high temperature of 500 ° C. or higher, the insulating layer (Al anodic oxide film) starts from the intermetallic compound. It can suppress that a crack enters into.
Therefore, according to the present invention, even when the photoelectric conversion layer is formed at a high temperature, it is possible to suppress a decrease in insulation caused by cracks in the insulating layer and to maintain good insulating characteristics of the insulating layer.

Moreover, according to this invention, as above-mentioned, even if it passes through the film-forming process of the photoelectric converting layer at 500 degreeC or more, high insulation can be maintained. That is, the photoelectric conversion layer can be formed at a film formation temperature of 500 ° C. or higher.
As described above, compound semiconductors such as CIGS can improve photoelectric conversion characteristics when formed at a high temperature. Therefore, according to the present invention, it is possible to obtain a solar cell having a photoelectric conversion layer that is formed at a temperature of 500 ° C. or higher and has improved photoelectric conversion characteristics.
Moreover, even when the manufacturing process includes a manufacturing process at a high temperature of 500 ° C. or higher, sufficient strength of the substrate can be ensured, so that it is possible to eliminate restrictions on handling during manufacturing.

It is a figure which shows notionally an example of the solar cell of this invention.

  Hereinafter, a method for manufacturing a solar cell of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

In FIG. 1, an example of the solar cell module manufactured with the manufacturing method of the solar cell of this invention is notionally shown with sectional drawing.
A solar cell module 10 (hereinafter, referred to as a solar cell 10) shown in FIG. 1 includes a lower electrode 32, a photoelectric conversion layer on an insulating metal substrate 18 having a metal base 12, an Al layer 14, and an insulating layer 16. 34, a module type solar cell in which a plurality of solar cells (thin film solar cells) 40 including a buffer layer 36 and an upper electrode 38 are joined in series. Further, on the lower electrodes 32 at both ends in the arrangement direction of the solar cells 40, the first conductive member 42 and the second conductive member 42 for taking out the electric power generated by the solar cells 40 connected in series to the outside. A conductive member 44 is formed.

In the solar cell 10, the insulating substrate 18 (hereinafter referred to as the substrate 18) has an anodic oxide film of Al (aluminum) as the insulating layer 16. As a preferable configuration, the metal substrate 12 and the Al layer 14 are included. And an insulating layer 16.
In addition, the board | substrate used by this invention is not limited to the thing which has such a metal base material 12, For example, it does not have the metal base material 12, but is comprised only from Al layer 14 and the insulating layer 16. There may be. That is, in the present invention, substrates having various configurations can be used as long as the plate has Al on the surface.

There is no limitation in particular in the metal base material 12 (henceforth the base material 12), Various metal materials can be utilized. Preferably, a material having a thermal expansion coefficient (linear thermal expansion coefficient) approximating that of the photoelectric conversion layer 34 described later, particularly a material having a thermal expansion coefficient approximating that of a CIGS compound such as CIGS is used.
Considering this point, as the base material 12, austenitic stainless steel (linear expansion coefficient: 17 × 10 ⁻⁶ / ° C.), carbon steel (same as 10.8 × 10 ⁻⁶ / ° C.), ferritic stainless steel (Same as above: 10.5 × 10 ⁻⁶ / ° C.), 42 Invar alloy and Kovar alloy (same as 5 × 10 ⁻⁶ / ° C.), 36 Invar alloy (same as: <1 × 10 ⁻⁶ / ° C.), Ti ( I.e., 9.2 × 10 ⁻⁶ / ° C.).
Of these, stainless steel is particularly preferred.

The thickness of the substrate 12 is not particularly limited, and may be set as appropriate according to the manufacturing process of the solar cell 10 (semiconductor device) and the handling properties (strength and flexibility) required during operation. .
Considering this point, the thickness of the substrate 12 is preferably 10 to 1000 μm.

Further, the strength of the substrate 12 is not particularly limited, but it is necessary to have a strength that has an elastic limit stress that does not cause plastic deformation. Considering this point, the base material 12 preferably has a 0.2% proof stress value of 250 to 900 MPa at room temperature, although it depends on the degree of machining and tempering of the base material 12. In addition, when there is a high-temperature process at the time of manufacturing the solar cell 10, the temperature dependency of 0.2% proof stress is also important. As described above, steel and Ti are about 70% of room temperature at 500 ° C. Maintain proof strength. Thereby, even when the substrate 18 receives a thermal history of 500 ° C. that is the film forming temperature of the photoelectric conversion layer, it is possible to secure an elastic limit stress that does not cause plastic deformation.
The 0.2% proof stress value and its temperature dependence are described in “Iron and Steel Material Handbook (Japan Institute of Metals, Japan Iron and Steel Institute, Maruzen Co., Ltd.)”.

An Al layer 14 is provided on the surface of the substrate 12.
The Al layer 14 is a layer mainly composed of Al, and various types of Al and Al alloys can be used. In particular, Al having a purity of 99% by mass or more with few impurities is preferable. As purity, for example, 99.99 mass% Al, 99.96 mass% Al, 99.9 mass% Al, 99.85 mass% Al, 99.7 mass% Al, 99.5 mass% Al, etc. are preferable. .

In the substrate 18 of the present invention, the insulating layer 16 formed by anodizing Al is formed on the surface of the Al layer 14 formed on the base material 12.
Here, as also shown in Non-Patent Document 1 described above, when the anodic oxide coating of Al formed on the surface of Al is heated to 120 ° C. or higher, cracks are generated. Further, as described above, it is considered that the cause of cracks in the anodic oxide film on the Al layer is that the linear expansion coefficient (linear thermal expansion coefficient) of Al is larger than the linear expansion coefficient of the anodic oxide film. .
Therefore, in a solar cell using a substrate having an insulating layer formed by anodizing the surface of an Al material, an insulating layer is formed by heating when forming a photoelectric conversion layer made of a compound semiconductor that requires a film forming temperature of 500 ° C. or higher. Cracks and peeling will occur, and sufficient insulation performance cannot be obtained.

On the other hand, in the substrate 18 of the illustrated example, the base material 12 bears the strength and linear expansion coefficient of the entire substrate, and a minute thermal expansion difference between the base material 12 and the insulating layer 16 which is an anodic oxide film of Al. Is absorbed by interposing an Al layer 14 having a smaller Young's modulus than the base material 12 and the insulating layer 16. Thereby, the crack of the insulating layer 16, ie, the anodic oxide film of Al, resulting from the difference in linear expansion coefficient can be suppressed.
Moreover, although the yield strength of Al at room temperature is 300 MPa or more, at 500 ° C., the yield strength decreases to 1/20 or less of room temperature. On the other hand, the proof stress of stainless steel or the like is maintained at about 70% of room temperature even at 500 ° C. Therefore, the base material 12 is dominant in the elastic stress limit and thermal expansion of the substrate 18 at a high temperature. That is, by configuring the substrate 18 by combining the Al layer 14 and the base material 12, sufficient rigidity of the substrate 18 can be ensured even when experiencing high heat of 500 ° C. or higher. In addition, even when a manufacturing process at a high temperature of 500 ° C. or higher is included, since sufficient rigidity of the substrate can be secured, it is possible to eliminate restrictions on handling during manufacturing.

There is no particular limitation on the thickness of the Al layer.
Here, if the Al layer 14 is too thin, a sufficient stress relaxation effect cannot be obtained, and the insulating layer 16 may directly come into contact with the substrate 12. On the other hand, if it is too thick, the residual warp becomes large when subjected to a high-temperature heat history, which may interfere with the subsequent manufacturing process, which is also disadvantageous in terms of material cost.
Considering the above points, the thickness of the Al layer is preferably 5 to 150 μm, more preferably 10 to 100 μm, and particularly preferably 20 to 50 μm.

Here, the thickness of the Al layer 14 decreases due to pretreatment of the Al surface, formation of the insulating layer 16 by anodic oxidation, etc. (Al is consumed).
Therefore, it is necessary to set the thickness at the time of forming the Al layer 14 to be described later in anticipation of the thickness reduction caused by these.

An insulating layer 16 is formed on the Al layer 14 (on the side opposite to the substrate 12). The insulating layer 16 is an Al anodic oxide film formed by anodizing the surface of the Al layer 14. In the method for manufacturing a solar cell of the present invention, the surface of the Al layer 14 is cleaned with an acidic cleaning solution prior to the formation of the insulating layer 16. This will be described in detail later.
In the present invention, various films formed by anodizing Al can be used as the insulating layer 16, but a porous anodic oxide film using an acidic electrolytic solution, which will be described later, is preferable. This anodic oxide film is an alumina oxide film having pores of several tens of nanometers. Since the Young's modulus of the film is low, the anodic oxide film has high resistance to bending and crack resistance caused by a difference in thermal expansion at high temperatures.

The thickness of the insulating layer 16 is preferably 2 μm or more, and more preferably 5 μm or more. When the thickness of the insulating layer 16 is excessively large, it is not preferable because flexibility is lowered and cost and time required for forming the insulating layer 16 are required. In practice, the thickness of the insulating layer 16 is 50 μm or less, preferably 30 μm or less at maximum. For this reason, the preferable thickness of the insulating layer 16 is 2-50 micrometers.
Further, the surface roughness of the surface 18a of the insulating layer 16 is, for example, an arithmetic average roughness Ra of 1 μm or less, preferably 0.5 μm or less, more preferably 0.1 μm or less.

In addition, the board | substrate 18 becomes flexible as the board | substrate 18 whole by making all the base material 12, the Al layer 14, and the insulating layer 16 have flexibility, ie, a flexible thing. Thereby, for example, the lower electrode 32, the photoelectric conversion layer 34, the upper electrode 36, and the like can be formed on the insulating layer 16 side of the substrate 18 by a roll-to-roll method.
In the present invention, a solar cell structure may be produced by continuously forming a plurality of layers from one roll unwinding to winding, or roll unwinding, film forming, winding The solar cell structure may be formed by performing the taking step a plurality of times. In addition, as will be described later, a solar cell in which a plurality of solar cells are electrically connected in series by adding a scribe process for separating and accumulating elements between the film forming processes to the roll-to-roll method. Can be produced.

  In the present invention, the Al layer 14 and the insulating layer 16 are not limited to be formed on only one surface of the substrate 12, but the Al layer 14 or further the insulating layer 16 is formed on both surfaces of the substrate 12. The substrate may be used in the production method of the present invention.

The solar cell 10 in the illustrated example includes a plurality of thin-film solar cells (solar cells) 40 including a lower electrode 32, a photoelectric conversion layer 34, a buffer layer 36, and an upper electrode 38 on such a substrate 18. It is a solar cell module (module type solar cell) formed by serial joining.
A first conductive member 42 and a second conductive member 44 are formed on the lower electrode 32 at both ends in the arrangement direction.

Here, in the illustrated example, as a preferred embodiment, an alkali supply layer 50 is provided between the insulating layer 16 (substrate 18) and the lower electrode 32.
It is known that when an alkali metal (particularly Na) is diffused into the photoelectric conversion layer 34 made of CIGS or the like, the photoelectric conversion efficiency is increased. The alkali supply layer 50 is a layer for supplying alkali metal to the photoelectric conversion layer 34 and is a layer of a compound containing an alkali metal. By having such an alkali supply layer 50, the alkali metal diffuses into the photoelectric conversion layer 34 through the lower electrode 32 when the photoelectric conversion layer 34 is formed, and the conversion efficiency of the photoelectric conversion layer 34 can be improved.

The alkali supply layer 50 is not limited, and a main component is a compound containing an alkali metal (a composition containing an alkali metal compound) such as Na ₂ O, Na ₂ S, Na ₂ Se, NaCl, NaF, or sodium molybdate. Various types of devices are available. In particular, a compound containing SiO ₂ (silicon nitride) as a main component and Na ₂ O (sodium oxide) is preferable.

The method for forming the alkali supply layer 50 is not particularly limited, and various known methods can be used. As an example, a vapor deposition method such as sputtering or CVD, or a liquid deposition method such as sol-gel method is exemplified.
For example, in the case of a compound containing SiO ₂ as a main component and containing Na ₂ O, the alkali supply layer 50 is formed by sputtering using soda lime glass as a target or sol-gel reaction using alkoxide containing Si and Na. A film may be used. Furthermore, these methods may be used in combination.

In the solar cell 10, the lower electrode 32 is formed on the alkali supply layer 50 by being arranged with a predetermined gap 33 with the adjacent lower electrode 32. A photoelectric conversion layer 34 is formed on the lower electrode 32 while filling the gap 33 between the lower electrodes 32. A buffer layer 36 is formed on the surface of the photoelectric conversion layer 34.
The photoelectric conversion layer 34 and the buffer layer 36 are arranged on the lower electrode 32 with a predetermined gap 37. Note that the gap 33 between the lower electrode 32 and the photoelectric conversion layer 34 (buffer layer 36) are formed at different positions in the arrangement direction of the solar cells 40.

Further, an upper electrode 38 is formed on the surface of the buffer layer 36 so as to fill the gap 37 of the photoelectric conversion layer 34 (buffer layer 36).
The upper electrode 38, the buffer layer 36 and the photoelectric conversion layer 34 are arranged with a predetermined gap 39. The gap 39 is provided at a position different from the gap between the lower electrode 32 and the gap between the photoelectric conversion layer 34 (buffer layer 36).
In the solar battery 10, each solar battery cell 40 is electrically connected in series in the longitudinal direction (arrow L direction) of the substrate 18 by a lower electrode 32 and an upper electrode 38.

The lower electrode 32 is composed of, for example, a Mo electrode. The photoelectric conversion layer 34 is composed of a compound semiconductor having a photoelectric conversion function, for example, a CIGS layer. Further, the buffer layer 36 is made of, for example, CdS, and the upper electrode 38 is made of, for example, ZnO.
The solar battery cell 40 is formed to extend long in the width direction orthogonal to the longitudinal direction L of the substrate 18. For this reason, the lower electrode 32 and the like also extend long in the width direction of the substrate 18.

As shown in FIG. 1, a first conductive member 42 is connected on the lower electrode 32 at the right end. The first conductive member 42 is for taking out an output from a negative electrode to be described later.
The first conductive member 42 is, for example, an elongated belt-like member, extends substantially linearly in the width direction of the substrate 18, and is connected to the lower electrode 32 at the right end. As shown in FIG. 1, the first conductive member 42 is, for example, a copper ribbon 42a covered with an indium copper alloy coating 42b. The first conductive member 42 is connected to the lower electrode 32 by, for example, ultrasonic soldering.

On the other hand, a second conductive member 44 is formed on the lower electrode 32 at the left end.
The second conductive member 44 is for taking out the output from the positive electrode, which will be described later, to the outside. Like the first conductive member 42, the second conductive member 44 is a strip-like member that extends substantially linearly in the width direction of the substrate 18. And connected to the lower electrode 32 at the left end.
The second conductive member 44 has the same configuration as the first conductive member 42. For example, a copper ribbon 44a is covered with a coating material 44b of indium copper alloy.

  In the solar cell 10, when light is incident on the solar cell 40 from the upper electrode 38 side, this light passes through the upper electrode 38 and the buffer layer 36, and an electromotive force is generated in the photoelectric conversion layer 34. A current is generated from the upper electrode 38 toward the lower electrode 32. The arrows shown in FIG. 1 indicate the direction of current, and the direction of movement of electrons is opposite to the direction of current. For this reason, in the photoelectric conversion unit 48, the leftmost lower electrode 32 in FIG. 1 is a positive electrode (positive electrode), and the rightmost lower electrode 32 is a negative electrode (negative electrode).

In the present embodiment, the electric power generated in the solar cell 10 can be taken out of the solar cell 10 from the first conductive member 42 and the second conductive member 44.
In the present embodiment, the first conductive member 42 is a negative electrode, and the second conductive member 44 is a positive electrode. In addition, the first conductive member 42 and the second conductive member 44 may have opposite polarities, and are appropriately changed according to the configuration of the solar cell 40, the configuration of the solar cell 10, and the like.
Moreover, in this embodiment, although each photovoltaic cell 40 was formed so that it might be connected in series with the longitudinal direction L of the board | substrate 18 by the lower electrode 32 and the upper electrode 38, it is not limited to this. For example, each solar battery cell 40 may be formed such that each solar battery cell 40 is connected in series in the width direction by the lower electrode 32 and the upper electrode 38.

  In the solar cell 40, the lower electrode 32 and the upper electrode 38 are both for taking out the current generated in the photoelectric conversion layer 34. Both the lower electrode 32 and the upper electrode 38 are made of a conductive material. The upper electrode 38 on the light incident side needs to have translucency.

The lower electrode (back electrode) 32 is made of, for example, Mo, Cr, or W, and a combination thereof. The lower electrode 32 may have a single layer structure or a laminated structure such as a two-layer structure. The lower electrode 32 is preferably made of Mo.
The lower electrode 32 preferably has a thickness of 100 nm or more, and more preferably 0.45 to 1.0 μm.
The method for forming the lower electrode 32 is not particularly limited, and can be formed by a vapor phase film forming method such as an electron beam evaporation method or a sputtering method.

The upper electrode (transparent electrode) 38 is made of, for example, ZnO to which Al, B, Ga, Sb or the like is added, ITO (indium tin oxide), SnO ₂ , or a combination thereof. The upper electrode 38 may have a single layer structure or a laminated structure such as a two-layer structure. Further, the thickness of the upper electrode 38 is not particularly limited, and is preferably 0.3 to 1 μm.
The formation method of the upper electrode 38 is not particularly limited, and can be formed by a vapor deposition method such as an electron beam evaporation method or a sputtering method, or a coating method.

The buffer layer 36 is formed to protect the photoelectric conversion layer 34 when the upper electrode 38 is formed and to transmit light incident on the upper electrode 38 to the photoelectric conversion layer 34.
The buffer layer 36 is made of, for example, CdS, ZnS, ZnO, ZnMgO, ZnS (O, OH), or a combination thereof.
The buffer layer 36 preferably has a thickness of 0.03 to 0.1 μm. The buffer layer 36 is formed by, for example, a CBD (chemical bath deposition) method.

  The photoelectric conversion layer (light absorption layer) 34 is a layer that absorbs light that has passed through the upper electrode 38 and the buffer layer 36 and generates a current, and has a photoelectric conversion function. In the present invention, the photoelectric conversion layer 34 is at least one compound semiconductor composed of a group Ib element, a group IIIb element, and a group VIb element.

Among these, since the light absorption rate is high and high photoelectric conversion efficiency is obtained, the photoelectric conversion layer 34 is composed of at least one type Ib element selected from the group consisting of Cu and Ag, and Al, Ga, and In. Preferably, it is at least one compound semiconductor composed of at least one group IIIb element selected from the group consisting of and at least one group VIb element selected from the group consisting of S, Se and Te.
Examples of the compound semiconductor include CuAlS ₂ , CuGaS ₂ , CuInS ₂ , CuAlSe ₂ , CuGaSe ₂ , CuInSe ₂ (CIS), AgAlS ₂ , AgGaS ₂ , AgInS ₂ , AgAlSe ₂ , AgGaSe ₂ , AgInSe ₂ e, AgInSe ₂ , AgInSe ₂ , AgInSe ₂ , AgInTe ₂ , Cu (In _1-x Ga _x ) Se ₂ (CIGS), Cu (In _1-x Al _x ) Se ₂ , Cu (In _1-x Ga _x ) (S, Se) ₂ , Ag (In _1-x Ga _x ) Se ₂ , Ag (In _1-x Ga _x ) (S, Se) _{2 and the} like.

The photoelectric conversion layer 34 particularly preferably contains CuInSe ₂ (CIS) and / or Cu (In, Ga) Se ₂ (CIGS) in which Ga is dissolved. CIS and CIGS are semiconductors having a chalcopyrite crystal structure, have high light absorption, and high photoelectric conversion efficiency has been reported. Moreover, there is little degradation of efficiency by light irradiation etc. and it is excellent in durability.

The photoelectric conversion layer 34 contains impurities for obtaining a desired semiconductor conductivity type. Impurities can be contained in the photoelectric conversion layer 34 by diffusion from adjacent layers and / or active doping. In the photoelectric conversion layer 34, the constituent elements and / or impurities of the I-III-VI group semiconductor may have a concentration distribution, and a plurality of layers having different semiconductor properties such as n-type, p-type, and i-type An area may be included.
For example, in the CIGS system, when the Ga amount in the photoelectric conversion layer 34 has a distribution in the thickness direction, the band gap width / carrier mobility and the like can be controlled, and the photoelectric conversion efficiency can be designed high.

The photoelectric conversion layer 34 may include one or more semiconductors other than the I-III-VI group semiconductor. As a semiconductor other than the I-III-VI group semiconductor, a semiconductor composed of a group IVb element such as Si (group IV semiconductor), a semiconductor composed of a group IIIb element such as GaAs and a group Vb element (group III-V semiconductor), and Examples thereof include semiconductors (II-VI group semiconductors) composed of IIb group elements such as CdTe and VIb group elements. The photoelectric conversion layer 34 may contain an optional component other than a semiconductor and impurities for obtaining a desired conductivity type as long as the characteristics are not hindered.
Further, the content of the I-III-VI group semiconductor in the photoelectric conversion layer 34 is not particularly limited. 75 mass% or more is preferable, as for content of the I-III-VI group semiconductor in the photoelectric converting layer 34, 95 mass% or more is more preferable, and 99 mass% or more is especially preferable.

  In addition, in this example, when the photoelectric converting layer 34 is comprised with the compound semiconductor whose main component (75 mass% or more) is CdTe, it is preferable that the base material 12 is comprised by carbon steel or a ferritic stainless steel. .

  When a CIGS layer is used as the photoelectric conversion layer 34, the film formation method includes 1) a multi-source co-evaporation method, 2) a selenization method, 3) a sputtering method, 4) a hybrid sputtering method, and 5 ) The mechanochemical process method is known.

1) As a multi-source simultaneous vapor deposition method,
Three-stage method (JRTuttle et.al, Mat.Res.Soc.Symp.Proc., Vol.426 (1996) p.143. Etc.) and EC group co-evaporation method (L. Stolt et al .: Proc. 13th ECPVSEC (1995, Nice) 1451, etc.).
In the former three-stage method, In, Ga, and Se are first co-deposited at a substrate temperature of 300 ° C. in a high vacuum, and then heated to 500 to 560 ° C., and Cu and Se are co-evaporated. In this method, Ga and Se are further vapor-deposited. The latter EC group simultaneous vapor deposition method is a method in which Cu-excess CIGS is vapor-deposited in the early stage of vapor deposition and In-rich CIGS is vapor-deposited in the latter half.

In order to improve the crystallinity of the CIGS film, as a method of improving the above method,
a) a method using ionized Ga (H. Miyazaki, et.al, phys.stat.sol. (a), Vol.203 (2006) p.2603, etc.),
b) Method of using cracked Se (68th Japan Society of Applied Physics Academic Lecture Proceedings (Autumn 2007, Hokkaido Institute of Technology) 7P-L-6 etc.),
c) Method using radicalized Se (Proceedings of the 54th Japan Society of Applied Physics (Aoyama Gakuin University) 29P-ZW-10 etc.)
d) A method using a photoexcitation process (the 54th Japan Society of Applied Physics Academic Lecture Proceedings (Spring 2007 Aoyama Gakuin University) 29P-ZW-14 etc.) is known.

2) The selenization method is also called a two-step method. First, a metal precursor of a laminated film such as a Cu layer / In layer or a (Cu—Ga) layer / In layer is formed by sputtering, vapor deposition, or electrodeposition. This is a method for producing a selenium compound such as Cu (In _1-x Ga _x ) Se ₂ by a thermal diffusion reaction by forming a film and heating it to about 450 to 550 ° C. in selenium vapor or hydrogen selenide. . This method is called a vapor phase selenization method. In addition, there is a solid-phase selenization method in which solid-phase selenium is deposited on a metal precursor film and selenized by a solid-phase diffusion reaction using the solid-phase selenium as a selenium source.

  In the selenization method, in order to avoid the rapid volume expansion that occurs during selenization, a method of previously mixing selenium in a metal precursor film at a certain ratio (T. Nakada et.al, Solar Energy Materials and Solar Cells 35 (1994) 204-214, etc.), and multilayer precursor film with selenium sandwiched between thin metal layers (for example, Cu layer / In layer / Se layer ... stacked with Cu layer / In layer / Se layer) (T. Nakada et.al, Proc. Of 10th European Photovoltaic Solar Energy Conference (1991) 887-890. Etc.) is known.

  In addition, as a method for forming a graded band gap CIGS film, a Cu—Ga alloy film is first deposited, an In film is deposited thereon, and when this is selenized, natural thermal diffusion is used to form Ga. There is a method in which the concentration is inclined in the film thickness direction (K. Kushiya et.al, Tech.Digest 9th Photovoltaic Science and Engineering Conf. Miyazaki, 1996 (Intn. PVSEC-9, Tokyo, 1996) p.149.).

3) As a sputtering method,
A method using CuInSe ₂ polycrystal as a target, a two-source sputtering method using Cu ₂ Se and In ₂ Se ₃ as targets and a H ₂ Se / Ar mixed gas as a sputtering gas (JHErmer, et.al, Proc. 18th IEEE Photovoltaic Specialists Conf. (1985) 1655-1658. Etc.), and a three-source sputtering method in which a Cu target, an In target, and a Se or CuSe target are sputtered in Ar gas (T. Nakada, et.al, Jpn. J. Appl. Phys. 32 (1993) L1169-L1172.

  4) As the hybrid sputtering method, in the sputtering method described above, Cu and In metal are DC sputtering, and only Se is vapor deposition (T. Nakada, et.al., Jpn.Appl.Phys.34 ( 1995) 4715-4721.

  5) In the mechanochemical process method, raw materials corresponding to the CIGS composition are put into a planetary ball mill container, and the raw materials are mixed by mechanical energy to obtain CIGS powder, which is then applied onto the substrate by screen printing and annealed. To obtain a CIGS film (T. Wada et.al, Phys.stat.sol. (A), Vol.203 (2006) p2593, etc.).

  Other CIGS film formation methods include screen printing, proximity sublimation, MOCVD, and spray (wet film formation). For example, a fine particle film containing a group Ib element, a group IIIb element, and a group VIb element is formed on a substrate by a screen printing method (wet film forming method) or a spray method (wet film forming method), and then pyrolyzed ( At this time, a crystal having a desired composition can be obtained by performing a thermal decomposition treatment in a VIb group element atmosphere (JP-A-9-74065, JP-A-9-74213, etc.).

In the present embodiment, the difference in linear expansion coefficient between the substrate 12 and the photoelectric conversion layer 34 is preferably less than 3 × 10 ⁻⁶ / ° C.
The linear expansion coefficient of the main compound semiconductor used for the photoelectric conversion layer 34 is 5.8 × 10 ⁻⁶ / ° C. for GaAs, which is representative of III-V group, and 4 for CdTe, which is representative of II-VI group. 5 × 10 ⁻⁶ / ° C. and 10 × 10 ⁻⁶ / ° C. for Cu (InGa) Se ₂ , which is representative of the I-III-VI group.
When the compound semiconductor is formed as a photoelectric conversion layer 34 on the substrate 18 at a high temperature of 500 ° C. or higher and then cooled to room temperature, if the difference in thermal expansion from the base material 12 is large, film formation defects such as peeling occur. . Moreover, the photoelectric conversion efficiency of the photoelectric converting layer 34 may fall by the strong internal stress in the compound semiconductor resulting from the thermal expansion difference with the base material 12. When the difference in linear expansion coefficient between the substrate 12 and the photoelectric conversion layer 34 (compound semiconductor) is less than 3 × 10 ⁻⁶ / ° C., film formation defects such as peeling are unlikely to occur, which is preferable. More preferably, the difference in coefficient of linear expansion is less than 1 × 10 ⁻⁶ / ° C. Here, the linear expansion coefficient and the difference between the linear expansion coefficients are both room temperature (23 ° C.) values.

  Hereinafter, the manufacturing method of this invention which manufactures such a solar cell 10 is demonstrated.

First, the base material 12 is prepared. The base material 12 is formed in a predetermined shape and size depending on the size of the substrate 18 to be formed.
Next, an Al layer 14 is formed on the surface of the substrate 12. The method for forming the Al layer 14 on the surface of the base material 12 is not particularly limited as long as an integrated bond capable of ensuring the adhesion between the base material 12 and the Al layer 14 is achieved. As an example, a vapor phase method such as a vapor deposition method or a sputtering method, an electric Al plating method using a nonaqueous electrolytic solution, a molten plating method immersed in molten Al, a pressure bonding method after surface cleaning, or the like can be used. When the Al layer 14 is formed using the hot dipping method, an intermetallic compound is highly likely to be formed at the interface between the substrate 18 and the Al layer 14, so that the intermetallic compound does not become thick. It is necessary to.
As a method for forming the Al layer 14, pressure bonding by roll rolling or the like is preferable from the viewpoints of cost, mass productivity, and the like.

  Next, if necessary, the surface other than the surface of the Al layer is masked, and the surface of the Al layer 14 (the surface on which the insulating layer 16 is formed by the anodic oxidation of Al) is washed with an acidic cleaning solution and is present on the surface of the Al layer 14 Removing intermetallic compounds.

As described above, when the substrate having the insulating layer formed by anodizing Al on the surface of the Al layer is heated to 120 ° C. or higher, the insulating layer is cracked and the insulating property is lowered. . This is due to the difference in thermal expansion coefficient between Al (23 × 10 ⁻⁶ / ° C.) and an anodic oxide film of Al (estimated to be about 7 × 10 ⁻⁶ / ° C.).
Here, as described above, the crack of the insulating layer due to the difference in the thermal expansion coefficient forms the Al layer 14 on the base material 12 and forms the insulating layer formed by anodizing the Al layer 14. By doing so, it can be largely avoided. However, even when the substrate 18 having such a base material 12 is used, if the thermal history of 500 ° C. or higher is received during the film formation of the photoelectric conversion layer 34, the insulating layer 16 is greatly improved in insulation performance. In many cases, cracks that can be easily reduced occur.

This inventor earnestly examined about this cause. As a result, cracks in the insulating layer 16 due to heating include the intermetallic compound (IMC) on the Al layer surface in addition to the difference in linear expansion coefficient between the Al and Al anodized films. And found that it is the cause of cracks.
Even if the purity is 99.99% (4N), an intermetallic compound such as Al ₃ Fe, Al ₆ Fe, Al ₂ Cu, α-AlFeSi, and β-AlFeSi is present on the surface. With such an intermetallic compound remaining, anodic oxidation is performed to form the insulating layer 16, and the lower electrode 32 and the like are formed. Thereafter, a photoelectric conversion layer such as a CIGS layer is formed at a high temperature such as 500 ° C. When the film 34 is formed, an intermetallic compound present on the surface of the Al layer 14 is a starting point during the film formation, and a crack occurs in the insulating layer 16. Due to the occurrence of this crack, in some cases, the insulation performance is significantly reduced.

In contrast, in the solar cell manufacturing method of the present invention, the Al layer is cleaned with an acidic cleaning solution prior to the formation of the insulating layer 16 by the anodic oxidation of Al.
Many of the above-mentioned intermetallic compounds existing on the surface of the Al layer 14 can be dissolved with an acid. Therefore, according to the present invention, by this cleaning, the intermetallic compound remaining in the Al layer 14 can be greatly reduced, and the insulating layer 16 can be formed by the anodic oxidation of Al. Therefore, even if film formation of the photoelectric conversion layer 34 at a high temperature of 500 ° C. or higher is performed thereafter, the generation of cracks due to the intermetallic compound of the Al layer 14 is significantly reduced, and the insulating characteristics are maintained. be able to.
In addition, a high insulating property can be maintained even after a film forming step at 500 ° C. or higher, that is, a photoelectric conversion layer can be formed at a film forming temperature of 500 ° C. or higher. Therefore, according to the present invention, since the photoelectric conversion layer 34 such as a CIGS layer can be formed at a high temperature of 500 ° C. or higher, a solar cell having excellent conversion characteristics can be manufactured.

In the present invention, the acidic cleaning solution for cleaning the surface of the Al layer 14 includes various acids such as sulfuric acid, nitric acid, phosphoric acid, perchloric acid, mixtures of these acids, and solutions containing these acids, Is available.
Among them, sulfuric acid can be suitably used in that a high effect of removing an intermetallic compound can be obtained. Particularly, sulfuric acid having a concentration of 300 g / L (liter) or more (acidic acid containing 300 g / L or more of sulfuric acid). The cleaning liquid is preferably used.

  Further, the temperature of the acidic cleaning solution for cleaning the surface of the Al layer 14 is not particularly limited. Similarly, an acidic cleaning solution of 60 ° C. or higher is used in that a high intermetallic compound removal effect can be obtained. Is preferred.

  Further, the cleaning method is not particularly limited, and various methods such as a method of immersing the cleaning surface in an acidic cleaning solution, a method of spraying an acidic cleaning solution, and a method of applying an acidic cleaning solution can be used. In particular, similarly, it is preferable to perform cleaning by immersing the surface (cleaning surface) of the Al layer 14 in an acidic cleaning solution for 3 seconds or more in that a high intermetallic compound removal effect is obtained.

  In consideration of the above points, the present invention preferably uses sulfuric acid having a temperature of 60 ° C. or higher and a concentration of 300 g / L or higher as the acidic cleaning liquid, and the surface of the Al layer 14 is kept for 3 seconds or longer. It is preferable to clean the surface of the Al layer 14 by immersing in Al.

In the present invention, in cleaning the surface of the Al layer 14 using such an acidic cleaning liquid, it is preferable to remove 50% or more of intermetallic compounds per unit area, for example, 5 mm ² .
By cleaning the surface of the Al layer 14 in this way, a sufficient cleaning effect is obtained, and more preferably, the generation of cracks in the insulating layer 16 during the subsequent formation of the photoelectric conversion layer 34 is suppressed more appropriately. Can do.

  After the surface of the Al layer 14 is cleaned in this manner, the acidic cleaning solution is sufficiently removed by washing with water, and the surface (cleaned surface) of the Al layer 14 is anodized to form the insulating layer 16. Thereby, the substrate 18 is obtained.

Various known methods can be used for the anodic oxidation of Al. Hereinafter, an example of a method for forming the anodic oxide film that is the insulating layer 16 will be described.
As described above, the insulating layer 16 is an anodized film formed by anodizing the surface of the Al layer 14. The anodic oxide film can be formed by immersing the base material 12 as an anode in an electrolytic solution together with a cathode and applying a voltage between the anode and the cathode.
At this time, when the base material 12 comes into contact with the electrolytic solution, the Al layer 14 and the local battery are formed. Therefore, it is necessary to insulate the base material 12 in contact with the electrolytic solution. That is, it is necessary to insulate the end surface and the back surface of the substrate 12 other than the surface of the Al layer 14 (the reverse surface of the Al layer 14 formation surface) using a masking film or the like.

  Before the anodizing treatment, the surface of the Al layer 14 may be subjected to a cleaning treatment using an alkali or the like, a polishing smoothing treatment such as mechanical polishing or electrolytic polishing, etc., if necessary.

Carbon, Al, or the like is used as a cathode during anodization.
There is no particular limitation on the electrolytic solution, and an acidic solution containing one or more acids such as sulfuric acid, phosphoric acid, chromic acid, oxalic acid, malonic acid, tartaric acid, sulfamic acid, benzenesulfonic acid, and amidosulfonic acid. It is preferable to use an electrolytic solution. In particular, sulfuric acid, phosphoric acid, oxalic acid, or a mixture thereof is preferable.
Anodizing conditions are not particularly limited by the type of electrolyte used. As anodizing conditions, for example, electrolyte concentration is 1 to 80% by mass, liquid temperature is 5 to 70 ° C., current density is 0.005 to 0.60 A / cm ² , voltage is 1 to 200 V, and electrolysis time is 3 to 500 minutes. is there.

During the anodic oxidation process, an oxidation reaction proceeds in a substantially vertical direction from the surface of the Al layer 14, and an anodic oxide film is generated on the surface of the Al layer 14. When the above acidic electrolytic solution is used, the anodic oxide film has a fine columnar body having a substantially regular hexagonal shape in plan view arranged without gaps, and has a round bottom at the center of each fine columnar body. Holes are formed, and a porous type in which a barrier layer (usually 0.02 to 0.1 μm in thickness) is formed at the bottom of the fine columnar body.
As described above, the anodic oxide film having such a porous structure has high resistance to bending and crack resistance caused by a difference in thermal expansion at high temperatures.

For the purpose of increasing the thickness of the barrier layer, a pore filling method in which a porous anodic oxide film is formed with an acidic electrolytic solution and then re-electrolyzed with a neutral electrolytic solution may be used. By increasing the thickness of the barrier layer, it is possible to obtain a coating with higher insulation.
Further, in such anodization of Al, when an electrolytic treatment is performed with a neutral electrolytic solution such as boric acid without using such an acidic electrolytic solution, a dense anode is formed instead of an anodized film in which porous fine columnar bodies are arranged. It becomes an oxide film (non-porous aluminum oxide simple substance film).

The preferable thickness of the anodic oxide film that is the insulating layer 16 is 2 to 50 μm as described above. This thickness is controllable by constant current electrolysis, constant voltage electrolysis current, voltage magnitude, and electrolysis time.
The anodizing treatment can be performed by, for example, a known so-called roll-to-roll anodizing apparatus.

  After the anodizing treatment, the masking film is peeled off. Thereby, the board | substrate 18 is producible.

  When the substrate 18 is manufactured in this manner, the solar battery cell 40 is formed on the substrate 18. In addition, the formation method of the following photovoltaic cell may be the same as that of the manufacturing method of a well-known solar cell (solar cell module) fundamentally.

First, the alkali supply layer 50 is formed on the surface of the insulating layer 16 of the substrate 18 by, for example, sputtering using soda lime glass as a target or a sol-gel method using an alkoxide containing Si and Na.
Next, a Mo film to be the lower electrode 32 is formed on the surface of the alkali supply layer 50 by sputtering using, for example, a film forming apparatus.
Next, using a laser scribing method, for example, a predetermined position of the Mo film is scribed to form a gap 33 extending in the width direction of the substrate 18. Thereby, the lower electrodes 32 separated from each other by the gap 33 are formed.

Next, a photoelectric conversion layer 34 (p-type semiconductor layer) is formed so as to cover the lower electrode 32 and fill the gap 33.
The photoelectric conversion layer 34 is a CIGS layer, for example, and may be formed by a known method by any of the film forming methods described above.

Here, the photoelectric conversion layer 34 made of a compound semiconductor such as CIGS is preferably formed at a high temperature in terms of conversion efficiency of the solar cell, as described above, at a film formation temperature of 500 ° C. or higher. It is preferable to form a film.
Here, in the present invention, prior to the formation of the insulating layer 16 by the anodic oxidation of Al, the surface of the Al layer 14 is washed with an acidic cleaning solution to remove the intermetallic compounds present on the surface of the Al layer 14. Even if the photoelectric conversion layer 34 is formed at a temperature of 500 ° C. or higher, the generation of cracks in the insulating layer 16 starting from the intermetallic compound can be suitably suppressed, and excellent insulating characteristics can be maintained. Can do.

After the photoelectric conversion layer 34 is formed, next, a CdS layer (n-type semiconductor layer) that becomes the buffer layer 36 is formed on the CIGS layer by, for example, a CBD (chemical bath deposition) method. Thereby, a pn junction semiconductor layer is formed.
Next, a predetermined position different from the gap 33 in the arrangement direction of the solar cells 40 is scribed using, for example, a laser scribing method to form a gap 37 extending in the width direction of the substrate 18 and reaching the lower electrode 32. To do.

Next, a ZnO layer added with, for example, Al, B, Ga, Sb or the like, which becomes the upper electrode 38, is formed on the buffer layer 36 so as to fill the gap 37 by a sputtering method or a coating method.
Next, the gaps 33 and 37 are gaps that reach the lower electrode 32 extending in the width direction of the substrate 18 by scribing, for example, using a laser scribing method at different predetermined positions in the arrangement direction of the solar cells 40. 39 is formed. Thereby, the photovoltaic cell 40 is formed.

Next, the solar cells 40 formed on the lower electrodes 32 at the left and right ends in the longitudinal direction L of the substrate 18 are removed by, for example, laser scribing or mechanical scrubbing to expose the lower electrodes 32. Next, the first conductive member 42 is connected to the lower electrode 32 at the right end, and the second conductive member 44 is connected to the lower electrode 32 at the left end using, for example, ultrasonic soldering.
Thereby, as shown in FIG. 2, the solar cell 10 by which the several photovoltaic cell 40 was electrically connected in series can be manufactured.

  Furthermore, if necessary, a sealing adhesive layer, a water vapor barrier layer, and a surface protective layer are disposed on the surface side of the obtained solar cell 10 and sealed on the back side of the solar cell 10, that is, on the back side of the substrate 18. The adhesive layer and the back sheet are arranged, and are laminated by, for example, a vacuum laminating method to integrate them.

  As mentioned above, although the manufacturing method of the solar cell of this invention was demonstrated in detail, this invention is not limited to the above-mentioned example, You may perform various improvement and a change in the range which does not deviate from the summary of this invention. Of course.

Hereinafter, specific examples of the insulating substrate of the present invention will be given to describe the present invention in more detail.
[Example 1]
A 99.5% purity Al plate and a stainless steel plate (SUS430) are pressure bonded, and the base material 12 (stainless steel) has a thickness of 50 μm and the Al layer 14 has a thickness of 30 μm (two layers) clad A material was used.
The surface of the Al layer 14 of the clad material was immersed in sulfuric acid having a concentration of 500 g / L at 60 ° C. for 10 seconds to clean the surface of the Al layer.
After washing, the surface of the Al layer 14 is thoroughly washed with water, and the substrate surface and the end surface are covered with a masking film, and then subjected to constant voltage electrolysis at 40 V in an oxalic acid solution at a temperature of 16 ° C. and 0.5 mol / L. Thus, a 9 μm-thick insulating layer 16 (Al anodic oxide film) was formed, and a substrate 18 having a base material 12, an Al layer 14, and an insulating layer 16 as shown in FIG. 1 was produced.

[Example 2]
A substrate 18 as shown in FIG. 1 was produced in the same manner as in Example 1 except that the cleaning time (immersion time) with sulfuric acid was 20 seconds.

[Example 3]
A substrate 18 as shown in FIG. 1 was produced in the same manner as in Example 1 except that the cleaning time (immersion time) with sulfuric acid was 40 seconds.

[Example 4]
A substrate 18 as shown in FIG. 1 was produced in the same manner as in Example 3 except that an Al plate having a purity of 99.99% was used.

[Comparative Example 1]
A substrate 18 as shown in FIG. 1 was produced in the same manner as in Example 1 (purity of Al layer 99.5%) except that the surface of the Al layer 14 was not cleaned with sulfuric acid.

[Comparative Example 2]
A substrate 18 as shown in FIG. 1 was produced in the same manner as in Example 4 (purity of Al layer 99.99%) except that the surface of the Al layer 14 was not cleaned with sulfuric acid.

  About each board | substrate produced in this way, the crack generation of the insulating layer 16 by the effect of the sulfuric acid washing | cleaning of the Al layer surface and the heat processing imitating at the time of forming the CIGS layer as the photoelectric converting layer 34 was evaluated.

[Effect of washing with sulfuric acid]
Before and after cleaning with sulfuric acid, the same position on the surface of the Al layer 14 was photographed with an SEM, and the intermetallic compound removed and the remaining metal were removed at the same position of an area 5 mm ² arbitrarily selected in the photographed image. The ratio (removal rate) with the compound was examined.

[Crack generation due to heat treatment]
Each substrate was hold | maintained for 15 minutes in the infrared heating furnace of 400 degreeC, 450 degreeC, 500 degreeC, 530 degreeC, and 560 degreeC imitating film-forming of the CIGS layer as the photoelectric converting layer 34. FIG.
From each heat-treated substrate, the base material 12 (stainless steel) and the Al layer 14 were dissolved by iodomethanol treatment, and a single film of the insulating layer 16 (Al anodic oxide film) was taken out.
The insulating layer 16 was visually observed to evaluate the occurrence of cracks. The evaluation is as follows.
○: No cracking.
Δ: There are cracks, but there are 3 or more cracks in 2 cm ² , 2 or more crossed cracks, 2 or more connected cracks, and 2 or more connected cracks. None of them exist.
×: There is a crack that satisfies one or more of the conditions of Δ.

As shown in Table 1 above, according to the present invention, it is possible to suitably suppress cracks in the insulating layer 16 even when processing is performed at a high temperature. For example, in the manufacture of solar cells, as the light absorption layer 34 Even when the CIGS layer is formed, sufficient insulation characteristics can be secured. In addition, if evaluation is (triangle | delta), even if there exists a crack in the insulating layer 16, there is no problem practically as an insulating characteristic requested | required of the insulating layer of a solar cell.
Furthermore, according to the present invention, by using an Al plate having a purity of 99.99%, the photoelectric conversion layer 34 can be formed at a high temperature of 560 ° C., and the photoelectric conversion layer 34 is formed at a high temperature. It is possible to manufacture a highly efficient solar cell.
From the above results, the effects of the present invention are clear.

  The present invention can be used in various fields in which solar cells such as power generators are used.

DESCRIPTION OF SYMBOLS 10 Solar cell 12 Base material 14 Al layer 16 Insulating layer 18 Substrate 30 Solar cell 32 Lower electrode 33, 37, 39 Gap 34 Photoelectric conversion layer 36 Buffer layer 38 Upper electrode 40 Thin film solar cell 42 1st electrically-conductive member 44 2nd Conductive member 50 Alkali supply layer

Claims (9)

A step of cleaning the surface of the substrate having an aluminum surface with an acidic cleaning liquid;
Anodizing the cleaned surface of the aluminum;
And forming a thin-film solar cell having a photoelectric conversion layer made of at least one compound semiconductor composed of a group Ib element, a group IIIb element and a group VIb element on the substrate using the anodized film as an insulating layer. A method for producing a solar cell, comprising: The group Ib element of the compound semiconductor is at least one of Cu and Ag;
The group IIIb element is at least one element selected from the group consisting of Al, Ga and In;
The method for manufacturing a solar cell according to claim 1, wherein the group VIb element is at least one element selected from the group consisting of S, Se, and Te. The acidic cleaning liquid is an acidic cleaning liquid having a temperature of 60 ° C. or higher and containing sulfuric acid having a concentration of 300 g / L or higher,
The method for manufacturing a solar cell according to claim 1 or 2, wherein the surface of the aluminum is cleaned by immersing the surface of the aluminum in the acidic cleaning solution for 3 seconds or more.   The method for manufacturing a solar cell according to claim 1, wherein the photoelectric conversion layer is formed at a film formation temperature of 500 ° C. or higher.   The manufacturing method of the solar cell in any one of Claims 1-4 which removes 50% or more per unit area of the intermetallic compound which exists in the aluminum surface by the washing | cleaning by the said acid.   The method for manufacturing a solar cell according to claim 1, wherein the substrate is a substrate formed by forming an aluminum layer on a surface of a metal base material.   The method for manufacturing a solar cell according to claim 6, wherein the metal substrate is stainless steel.   The method for manufacturing a solar cell according to claim 1, wherein the formation of the insulating layer by anodization of Al is performed using an acidic electrolytic solution.   The method for manufacturing a solar cell according to any one of claims 6 to 8, wherein the substrate is formed by pressure bonding an aluminum plate to the metal base material.