JP2006294767A - Substrate for solar cell and solar cell employing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for solar cell in which stripping of an insulation layer formed on a substrate can be suppressed even in a heating/cooling process and to provide the solar cell using the same. <P>SOLUTION: The substrate for solar cell comprises a base material 11, an electric insulation layer (first layer) 13 formed above the base material 11, and a softening layer (second layer) 12 arranged between the base material 11 and the insulation layer 13 wherein the softening temperature of the softening layer 12 is lower than those of the base material 11 and the insulation layer 13. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solar cell substrate and a solar cell using the same.

Conventionally, various substrates have been proposed as substrates for solar cells. For example, a substrate is disclosed in which an insulating layer, a low melting point layer, and a molybdenum thin film (lower electrode) are sequentially laminated on the substrate (for example, paragraph [0025] in Patent Document 1 and FIG. 2). The low melting point layer is formed to prevent peeling of the molybdenum thin film.
JP 2004-103663 A

  However, in the conventional substrate described above, peeling between the insulating layer and the molybdenum thin film can be suppressed, but peeling may occur between the substrate and the insulating layer.

  Therefore, it is an object of the present invention to provide a solar cell substrate that can suppress peeling of an insulating layer formed on the substrate, and a solar cell using the solar cell substrate.

  In order to achieve the above object, a solar cell substrate of the present invention is a substrate used for a solar cell, comprising a base material, an electrically insulating first layer laminated on the base material, A second layer disposed between the substrate and the first layer, wherein the temperature at which the second layer softens is lower than the temperature at which the substrate and the first layer soften .

  The solar cell of the present invention is a solar cell comprising a substrate and a photovoltaic layer formed on the substrate, and the substrate is the solar cell substrate of the present invention.

  According to the solar cell substrate of the present invention, peeling of the insulating layer formed on the substrate can be suppressed. Further, according to this substrate, even when the conductive layer is formed on the insulating layer, the conductive layer can be prevented from being separated from the substrate. The solar cell of the present invention using this solar cell substrate has a high yield during production and high reliability after production.

  Hereinafter, embodiments of the present invention will be described with examples. In the following description, specific materials, specific layer thicknesses, and specific laminated structures may be exemplified, but these are merely examples, and the present invention is not limited to these examples.

  The substrate of the present invention is a substrate used for a solar cell, and is disposed between a base material, an electrically insulating first layer laminated on the base material, and the base material and the first layer. And a second layer. The temperature at which the second layer softens is lower than the temperature at which the substrate and the first layer soften. According to this configuration, it is possible to prevent the insulating layer formed on the substrate from being peeled off due to a difference in thermal expansion during the heating (for example, heating at 400 ° C. or higher) or cooling.

Substances include substances having a predetermined melting point and substances not having a predetermined melting point (for example, amorphous substances). In this specification, “softening temperature” means a melting point when the substance has a predetermined melting point, and means a softening point (softening temperature) when the substance does not have a predetermined melting point. . The softening point means a temperature at which the viscosity (η) becomes 4.5 × 10 ⁷ poise.

  The solar cell substrate of the present invention may further include a conductive third layer laminated on the side opposite to the second layer with respect to the first layer. That is, the first to third layers are arranged in the order of the second layer, the first layer, and the third layer from the substrate side. The third layer is made of a conductive material such as metal. The thickness of the third layer is not particularly limited, and may be, for example, about 0.2 μm to 1 μm. The third layer can be used as a back electrode of a solar cell.

  In the case of a CIS solar cell or CIGS solar cell substrate, a layer made of molybdenum (Mo) is preferably used as the third layer. The molybdenum layer can be in ohmic contact with the CIS film or the CIGS film, and there is no fear of diffusion into the compound semiconductor layer such as the CIS film or the CIGS film. In addition, since the difference between the thermal expansion coefficient of the molybdenum layer and the thermal expansion coefficient of the compound semiconductor layer such as the CIS film or the CIGS film is relatively small, the compound semiconductor layer is less likely to be separated from the molybdenum layer.

  In the solar cell substrate of the present invention, the temperature at which the second layer softens may be 400 ° C. or less. According to this configuration, peeling caused by heating at 400 ° C. or higher can be suppressed. The temperature at which the second layer softens is preferably in the range of 200 ° C to 400 ° C, for example in the range of 250 ° C to 300 ° C.

In the solar cell substrate of the present invention, the second layer may be made of glass. As the glass, for example, PbO—SiO ₂ or PbO—B ₂ O ₃ can be used. In the solar cell substrate of the present invention, the second layer may be made of any one of In, Sn, In alloy, or Sn alloy.

  The second layer is in a solid state at a relatively low temperature (a temperature lower than the temperature at which the second layer softens), and maintains a predetermined shape. It is preferable that a 2nd layer consists of an inorganic substance which does not deteriorate at the high temperature of 500-600 degreeC. Examples of such inorganic materials include metals and glasses having a melting point or softening point of 400 ° C. or less.

  When a metal is used as the material for the second layer, In, Sn, or an alloy thereof is particularly preferable. The melting point of In is about 157 ° C., the melting point of Sn is about 232 ° C., and these alloys have a lower melting point. Moreover, the thin film which consists of these metals is easy to produce.

  Examples of the Sn alloy include Sn—Pb, Sn—Bi, Sn—In—Ag, Sn—Bi—Zn, Sn—Zn, Sn—Ag—Bi, Sn—Bi—Ag—Cu, Sn having a melting point of 400 ° C. or less. -Ag-Cu, Sn-Ag-Cu-Sb, Sn-Ag, Sn-Cu, Sn-Sb etc. are mentioned. Other Sn alloys may be used.

  The solar cell substrate of the present invention may further include a fourth layer disposed between the first layer and the third layer. The temperature at which the fourth layer softens is lower than the temperature at which the substrate, the first layer, and the third layer soften. According to this structure, it can suppress that an insulating layer (1st layer) and a conductive layer (3rd layer) peel in the process of a heating or cooling.

  The fourth layer is a layer having properties similar to those of the second layer, and can be formed using the same material as that of the second layer. That is, the temperature at which the fourth layer softens may be 400 ° C. or less. The temperature at which the fourth layer softens is preferably in the range of 200 ° C to 400 ° C, for example, in the range of 250 ° C to 300 ° C. Further, the fourth layer may be made of any of In, Sn, In alloy, or Sn alloy, or may be made of another material described as the material of the second layer. Good.

  In the solar cell substrate of the present invention, the base material may be made of at least one material selected from the group consisting of stainless steel, titanium, and copper. Since the base material which consists of these materials has high heat resistance, the board | substrate excellent in heat resistance is obtained.

  The base material may be a base material made of a material other than stainless steel, titanium, and copper. For example, a heat-resistant base material such as an aluminum foil, a cobalt film, or a polyimide film is preferable. Stainless steel thin films are suitable as a substrate for solar cells because they have the advantages of being relatively inexpensive, lightweight, resistant to high temperatures, and excellent in strength. The thickness of the substrate varies depending on the type of material and is not particularly limited, but is usually selected from the range of 20 μm to 1 mm in consideration of strength, weight, and the like.

  Since these substrates are lightweight, construction is easy even when the solar cell is bent and attached. In addition, since the thin substrate has flexibility, the solar cell can be continuously formed by rolling the substrate. As a result, production becomes easy, and the produced solar cell can be wound up and stored in a roll shape, so that productivity including storage and transportation is excellent.

In the solar cell substrate of the present invention, the first layer may be made of at least one oxide selected from the group consisting of SiO ₂ , TiO _2, and Al ₂ O ₃ . These materials are preferable because of their excellent electrical insulation. Note that the first layer may be formed using another insulator.

  There is no particular limitation on the thickness of the first layer, but if the first layer is too thick, flow and deformation may occur when the second layer is melted or softened. Therefore, the thickness of the first layer is usually preferably about 0.01 μm to 0.5 μm.

  There is no limitation in the formation method of a 1st-4th layer, A well-known method is applicable. For example, the first layer (insulating layer) can be formed by a thermal spraying method, a sputtering method, or a method of melting a glass material. The second and fourth layers (softening layers) can be formed by, for example, a sputtering method, a sol-gel method, or a vapor deposition method. The third layer (conductive layer) can be formed by, for example, a sputtering method or a vapor deposition method.

  The solar cell of the present invention is a solar cell comprising a substrate and a photovoltaic layer formed on the substrate, and the substrate is the solar cell substrate of the present invention. There is no particular limitation on the photovoltaic layer, and a multilayer film including a junction that generates an electromotive force by light irradiation is applied. For example, a multilayer film including a semiconductor layer made of a CIS layer or a CIGS layer as a light absorption layer can be used as the photovoltaic layer. The CIS layer and the CIGS layer are I-III-VI group compound semiconductor layers composed of a group 1B element such as Cu, a group 3B element such as In or Ga, and a group 6B element such as Se or S. , Including Ga is a CIGS layer. A photovoltaic layer can be constructed by combining a p-type CIS layer or CIGS layer and an n-type semiconductor layer. In this case, a ZnO layer, a CdS layer, or the like can be used for the n-type semiconductor layer.

  When manufacturing a solar cell, the substrate is usually heated to a high temperature of 500 to 600 ° C. to form a semiconductor layer and then cooled. At this time, in the conventional substrate, the insulating layer may peel from the substrate when the substrate is cooled due to the difference between the thermal expansion coefficient of the substrate and the thermal expansion coefficient of the insulating layer. On the other hand, when the substrate of the present invention is used, the second layer that softens at a relatively low temperature exists between the base material and the insulating layer (first layer). The stress generated between the substrate and the insulating layer is relaxed. As a result, it can suppress that an insulating layer peels from a base material by the difference of heating and cooling.

  In the present invention, a fourth layer that softens at a relatively low temperature is formed between the insulating layer (first layer) and the conductive layer (third layer), so that heating and cooling can be performed. The conductive layer can be prevented from peeling from the insulating layer. Note that by forming the insulating layer on the base material, a structure in which a plurality of solar cells are connected in series can be formed on one substrate even if the base material is conductive. With such a series connection structure, a solar cell with a high output voltage can be obtained.

  In another aspect, the present invention relates to a method for manufacturing a solar cell in a manufacturing process including a process of heating to a temperature equal to or higher than a temperature at which a softened layer is softened using the substrate of the present invention. The step of heating at a temperature equal to or higher than the temperature at which the softened layer softens (for example, a temperature equal to or higher than 400 ° C.) is a step for forming a semiconductor layer, for example. According to this manufacturing method, solar cells can be manufactured with a high yield.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts may be denoted by the same reference numerals and redundant description may be omitted.

<Example of substrate>
An example of the substrate of the present invention is shown in FIG. A substrate 10 in FIG. 1 includes a base material 11, and a softening layer (second layer) 12 and an insulating layer (first layer) 13 that are sequentially stacked on the base material 11.

  Another example of the substrate of the present invention is shown in FIG. The substrate 20 in FIG. 2 includes a base material 11 and a softening layer 12, an insulating layer 13, and a conductive layer (third layer) 14 that are sequentially stacked on the base material 11.

  Another example of the substrate of the present invention is shown in FIG. A substrate 30 in FIG. 3 includes a base material 11, a softening layer 12, an insulating layer 13, a softening layer (fourth layer) 15, and a conductive layer 14 that are sequentially stacked on the base material 11. The base material and the first to fourth layers are formed of the materials described above.

<Example of solar cell>
FIG. 4 shows a cross-sectional view of an example of the solar cell of the present invention using the substrate 30 of FIG. The solar cell 40 in FIG. 4 uses a molybdenum layer as the conductive layer (third layer) 14.

  The solar cell 40 includes a substrate 30, a p-type semiconductor layer 41, an n-type semiconductor layer 42, a window layer 43, and a transparent electrode 44 that are sequentially stacked on the substrate 30. The conductive layer 14 of the substrate 30 is made of molybdenum. The solar cell 40 includes an n-side extraction electrode 45 formed on the transparent electrode 44 and a p-side extraction electrode 46 formed on the conductive layer 14.

  The p-type semiconductor layer 41 is a light absorption layer, and a CIGS layer or the like can be applied. The n-type semiconductor layer 42 can be formed of CdS or the like, the window layer 43 can be formed of ZnO or the like, and the transparent electrode 44 can be formed of ITO (indium-tin-oxide) or the like.

  When forming the CIS layer and CIGS layer used as the p-type semiconductor layer 41, it is necessary to set the temperature of the substrate to a high temperature of about 500 to 600 ° C. Since the softening layers 12 and 15 are present in the substrate 30 of the present invention, the stress generated between the base material 11 and the insulating layer 13 during heating and cooling, and the space between the insulating layer 13 and the conductive layer 14. Can relieve stress. Therefore, it can suppress that peeling arises in the interface of those layers, when the board | substrate 30 is heated and cooled.

  Another example of the solar cell of the present invention is shown in FIG. The solar cell 50 in FIG. 5 includes a plurality of unit cells 50a connected in series.

  The solar cell 50 includes a substrate 30, a p-type semiconductor layer 41, an n-type semiconductor layer 42, a window layer 43, and a transparent electrode 44 that are sequentially stacked on the substrate 30. The conductive layer 14 of the substrate 30 is made of molybdenum. Since examples of materials other than the conductive layer 14 have been described above, description thereof will be omitted.

  A plurality of grooves 51 are formed substantially in parallel in the softened layer 15 and the conductive layer 14 of the substrate 30. The p-type semiconductor layer 41, the n-type semiconductor layer 42, and the window layer 43 are also formed with a plurality of grooves 52 substantially in parallel. The inside of the groove 52 is filled with the transparent electrode 44. Further, a groove 53 for cutting the transparent electrode 44 from the p-type semiconductor layer 41 is formed. The grooves 51, 52 and 53 are substantially parallel to each other, and are formed so as to be slightly shifted from each other. These grooves can be formed by a known method such as a mechanical scribe method or a laser scribe method.

  On the base material 11, there are a plurality of unit cells 50a divided by these grooves. Adjacent unit cells 50 a are connected in series by transparent electrodes 44 filled in the grooves 52. Thus, a high output voltage is obtained by connecting the plurality of unit cells 50a in series. Although the p-type semiconductor layer 41 is embedded in the groove 51, the conductive layer 14 of one unit cell 50a and the conductive layer of the unit cell 50a adjacent thereto can be obtained by setting the width of the groove 51 to an appropriate width. 14 can be sufficiently high.

  The solar cell 50 can be formed by a known method. Also in the manufacturing process of the solar cell 50, it is possible to suppress the insulating layer 13 and the conductive layer 14 from being peeled, similarly to the solar cell 40.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely using an Example, this invention is not limited to a following example.

Example 1
In Example 1, an example in which the substrate 10 of FIG. 1 is manufactured will be described. First, an Sn film was formed as a softening layer 12 on a stainless steel plate having a thickness of 0.5 mm by an evaporation method. The film thickness of the Sn film was 0.1 μm. Next, a glass layer containing 53 wt% SiO ₂ , 14 wt% B ₂ O ₃ , 13 wt% Na ₂ O, 15 wt% TiO ₂ , and 5 wt% Al ₂ O ₃ on the Sn film. Formed. The glass layer was formed by heating a mixture of the above components at about 800 ° C.

  For the substrate thus obtained, a cycle of heating from room temperature to 1000 ° C. and then cooling to room temperature was repeated 10 times or more, but no peeling of the insulating layer occurred.

  In addition, although the example which used Sn film | membrane as a softening layer was described in the present Example, the same result was obtained even if it used any material mentioned above as a material of the softening layer 12 instead of Sn.

(Example 2)
In Example 2, an example in which a solar cell having the same form as the solar cell 40 shown in FIG. 4 is manufactured will be described. First, an In film was formed as a softening layer 12 on a 50 μm thick stainless steel substrate by a vapor deposition method. The thickness of the In film was 0.1 μm. On top of this, an alumina film was formed by thermal spraying. The thickness of the alumina film was 100 μm. On top of this, an In film was formed as a softening layer 15 by vapor deposition. The thickness of the In film was 0.1 μm. On top of this, a 0.4 μm thick Mo film was formed as a conductive layer 14 by sputtering.

  Next, a CIGS film having a thickness of 2 μm was formed as a p-type semiconductor layer 41 on the Mo film by an evaporation method. The film formation temperature (substrate temperature) of the CIGS film was 600 ° C. In the process of forming the CIGS film, no film peeling was observed.

Next, an aqueous solution containing indium chloride (InCl ₃ ), which is a compound (salt) containing In, and thioacetamide was prepared. The concentration of indium chloride in the aqueous solution was 0.005M, the concentration of thioacetamide was 0.1M, and the pH was 1.9. The container containing the aqueous solution was allowed to stand in a warm water tank maintained at 75 ° C. The substrate on which the CIGS film was formed in this aqueous solution was immersed for about 10 seconds. Thereafter, the substrate was lifted from the solution and washed with pure water. By this operation, a Cu (In, Ga) S ₂ film having a thickness of about 5 nm was formed on the surface of the Cu (In, Ga) Se ₂ film. Since a passivation effect and an all-barrier effect are obtained by the Cu (In, Ga) S ₂ film, a solar cell having high characteristics can be formed.

Next, an aqueous solution containing cadmium sulfate (CdSO ₄ ), which is a compound (salt) containing cadmium, and ammonia was prepared. The concentration of cadmium sulfate in the aqueous solution was 0.001M, and the concentration of ammonia was 1M. The container in which this solution was put was left still in the warm water tank kept at 85 degreeC. The substrate on which the CIGS film was formed was immersed in this solution for about 6 minutes. Thereafter, the substrate was lifted from the solution and washed with pure water to form an n-type semiconductor layer made of CdS.

Next, a ZnO film (film thickness 100 nm) as a window layer and an ITO film (film thickness 100 nm) as a transparent electrode were formed by a sputtering method. The sputtering conditions during the formation of the ZnO film were an argon gas pressure of 1.5 × 10 ⁻⁴ Pa (2 × 10 ⁻² Torr) and a high frequency power of 400 W. The sputtering conditions for forming the ITO film were argon gas pressure 6 × 10 ⁻⁵ Pa (8 × 10 ⁻³ Torr) and high frequency power 400 W.

  Next, a NiCr film was formed as a lead electrode on a part of the back electrode (Mo film). Further, an Au film was formed as a lead electrode on a part of the ITO film. These electrodes were formed by electron beam evaporation.

  Thus, the solar cell of the present invention was formed. In the above series of steps, no peeling occurred on the film on the stainless steel substrate.

On the other hand, for comparison, a photovoltaic layer was formed in the same manner as in the above solar cell, using a substrate on which the In film as the softening layers 12 and 15 was not formed. In this case, when the substrate was taken out from the sample preparation chamber after the CIGS film was formed at the substrate temperature of 600 ° C., peeling on the stainless steel substrate surface or the Mo film surface occurred in about 65% of the sample. At this time, when the manufacturing process was further advanced with respect to the sample where peeling did not occur, peeling occurred in an additional 23% of the samples in the process for forming the Cu (In, Ga) S ₂ film. At this time, when the manufacturing process was further advanced with respect to the sample in which peeling did not occur, peeling occurred in an additional 12% of the samples in the process for forming the CdS film. As described above, in the samples using the substrate on which the softened layer was not formed, peeling occurred in all the samples.

About the solar cell of this invention produced with the method mentioned above, AM1.5, the pseudo-sunlight of 100 mW / cm < ² > was irradiated, and the characteristic was evaluated. As a result, the short-circuit current was 34.5 mA / cm ² , the open-circuit voltage was 0.63 V, the fill factor was 0.70, and the conversion efficiency was 15.2%. This characteristic was the same as that of the CIGS solar cell formed on the glass substrate.

  In the present embodiment, the case where In is used as the softening layer has been described. However, the same result was obtained when any of the above-described materials was used as the material of the softening layer 12 instead of In.

  The present invention is applicable to solar cell substrates and solar cells.

It is sectional drawing which shows an example of the board | substrate for solar cells of this invention. It is sectional drawing which shows another example of the board | substrate for solar cells of this invention. It is sectional drawing which shows another example of the board | substrate for solar cells of this invention. It is sectional drawing which shows an example of the solar cell of this invention. It is sectional drawing which shows another example of the solar cell of this invention.

Explanation of symbols

10, 20, 30 Substrate 11 Base material 12 Softened layer (second layer)
13 Insulating layer (first layer)
14 Conductive layer (third layer)
15 Softening layer (fourth layer)
40, 50 Solar cell 41 p-type semiconductor layer 42 n-type semiconductor layer 43 window layer 44 transparent electrode 45, 46 extraction electrode

Claims (10)

A substrate used for solar cells,
A base material, an electrically insulating first layer laminated on the base material, and a second layer disposed between the base material and the first layer,
The solar cell substrate, wherein a temperature at which the second layer is softened is lower than a temperature at which the base material and the first layer are softened.   The solar cell substrate according to claim 1, further comprising a conductive third layer laminated on the opposite side of the first layer from the second layer.   The solar cell substrate according to claim 1 or 2, wherein a temperature at which the second layer is softened is 400 ° C or lower.   The solar cell substrate according to claim 1, wherein the second layer is made of glass.   The solar cell substrate according to claim 1, wherein the second layer is made of any one of In, Sn, an In alloy, and a Sn alloy. A fourth layer disposed between the first layer and the third layer;
The solar cell substrate according to claim 2, wherein a temperature at which the fourth layer is softened is lower than a temperature at which the base material, the first layer, and the third layer are softened.   The solar cell substrate according to claim 6, wherein a temperature at which the fourth layer softens is 400 ° C. or lower.   The solar cell substrate according to any one of claims 1 to 7, wherein the base material is made of at least one material selected from the group consisting of stainless steel, titanium, and copper. The solar cell substrate according to claim 1, wherein the first layer is made of at least one oxide selected from the group consisting of SiO ₂ , TiO _2, and Al ₂ O ₃ . A solar cell comprising a substrate and a photovoltaic layer formed on the substrate,
A solar cell, wherein the substrate is a solar cell substrate according to any one of claims 1 to 9.

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