JP2006073706A - Solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction of yield even when crack is easily generated in a solar cell battery element due to lamination during the process, for example, in the pressing under the evacuated pressure under the condition that the solar cell module is manufactured while warp is generated in the solar cell element. <P>SOLUTION: In the solar cell module where an area between a transparent substrate and a rear surface sheet is sealed with a filler and a plurality of solar cell elements electrically connected with connection tab are allocated, the connection tab is formed of a three-layer clad consisting of copper/covar/copper or copper/invar/copper. Almost entire surface is coated with solder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solar cell module, and more particularly to a solar cell module in which a connection tab for electrically connecting solar cell elements is improved, thereby improving its reliability and manufacturing yield. .

  A solar cell element is often manufactured using a single crystal silicon substrate or a polycrystalline silicon substrate, and the solar cell element itself is a structure that is vulnerable to physical impact. Furthermore, when solar cells are installed outdoors, it is necessary to protect them from rain.

  On the other hand, a single solar cell element generates a small electrical output. For this reason, a plurality of solar cell elements are connected in series and parallel so that a practical electrical output can be taken out.

  From such a need, a plurality of solar cell elements are electrically connected using a connection tab, and the plurality of solar cell elements are connected to a light-transmitting substrate and an ethylene vinyl acetate copolymer (EVA). A solar cell module is formed by encapsulating with a filler mainly composed of, for example.

  A solar cell element which is the basic structure of such a solar cell module will be described with reference to FIG.

  FIG. 1 shows an example of a cross-sectional structure of a solar cell element. According to this solar cell element 1, reference numeral 2 denotes a silicon substrate, and a light receiving surface side electrode 3 is formed on one main surface of the silicon substrate 2. And the back surface side electrode 4 is formed in the other main surface.

  The light receiving surface side electrode 3 and the back surface side electrode 4 are formed by silver paste by a screen printing method or the like.

  Further, the surfaces of these electrodes 3 and 4 are solder-coated over almost the entire surface in order to facilitate the protection and attachment of the connection tabs.

  When the silicon substrate 2 is composed of a single crystal or polycrystal, for example, the substrate has a thickness of about 0.3 to 0.4 mm and a size of about 150 mm square.

  Inside the silicon substrate, a PN junction (not shown) is formed in which a P layer containing a large amount of P-type impurities such as boron and an N layer containing a large amount of N-type impurities such as phosphorus are in contact. Also, a high concentration P layer 5 containing a high concentration of P-type impurities such as aluminum is formed on almost the entire back surface of the silicon substrate.

  In the solar cell element 1 having the above-described configuration, the high concentration P layer 5 is formed on the silicon substrate 2, so that the high concentration P layer 5 on the back surface side of the substrate is contracted. There is a problem that the back surface side contracts and warps so that the light receiving surface side extends.

  In particular, in the solar cell element 1 used in recent solar cell modules, the substrate 2 of the solar cell element 1 tends to be thinner due to its cost reduction. There is a tendency for the size of the film to become large, and due to these, the warpage is more remarkable.

  In the solar cell module, a plurality of solar cell elements 1 are electrically connected using conductive connection tabs.

  Such a connection tab is usually used by cutting a copper foil having a thickness of about 0.1 to 1.0 mm and a width of about 2 to 8 mm into a predetermined length after solder coating.

When this electrode of the solar cell element and the electrode of the adjacent solar cell element are connected by soldering using the connection tab, the connection tab is disposed on the electrode of the solar cell element, and the connection tab is In a state where the electrode is pressed against the electrode of the battery element with a pin or the like, both the solder is melted by heating with hot air or a lamp, and the electrode of the solar cell element and the connection tab are soldered (refer to the conventional technique of Patent Document 1). ).
Japanese Patent Laid-Open No. 11-312820

  As described above, in soldering the connection tab to the electrode of the solar cell element, the conditions (soldering temperature, time, etc.) for soldering the connection tab to the light receiving surface side electrode 3 and the back surface side electrode 4 are described. There is a slight difference between the two and the conditions for soldering the connection tab, and the warpage of the solar cell element before and after the connection tab is soldered may be further increased.

  In particular, in recent solar cell modules, due to environmental considerations, there is a tendency to use solder that does not substantially contain lead. In the case of using solder that does not substantially contain lead, The soldering temperature is increased due to the physical properties of the solder, and thus the degree of warping of the solar cell element is further increased before and after soldering the connection tab as described above.

  In this way, in addition to warping due to shrinkage of the high-concentration P layer of the solar cell element, when the manufacturing process of the solar cell module proceeds in a state where there is warping after tab attachment, Cracking of the solar cell element is likely to occur due to the laminate pressed by the above, and as a result, the production yield is reduced or cracking is likely to occur.

  This invention is completed in view of the said situation, The objective is to improve the curvature condition of a solar cell element, and to provide a highly reliable and high quality solar cell module.

  Another object of the present invention is to provide a solar cell module that prevents the occurrence of cracks, improves the production yield, and achieves cost reduction.

  In order to achieve the above object, the present invention provides a solar cell module in which a plurality of solar cell elements sealed with a filler and electrically connected by connection tabs are arranged between a light-transmitting substrate and a back sheet, The connection tab is made of a three-layer clad material consisting of a copper layer, a Kovar layer, and a copper layer, or is made of a three-layer clad material consisting of a copper layer, an invar layer, and a copper layer. It is characterized by solder coating over substantially the entire surface.

  Another solar cell module of the present invention is characterized in that the thickness is different between one copper layer and the other copper layer in the three-layer clad material.

The thermal expansion coefficient of copper metal is 16.7 × 10 ⁻⁶ , and the thermal expansion coefficient of silicon metal is 2.6 × 10 ⁻⁶ .

Copper metal has a larger coefficient of thermal expansion than silicon metal, but there is a three-layer clad material consisting of a copper layer, a kovar layer, and a copper layer (when the layer thickness ratio of each layer is 1: 1: 1). The thermal expansion coefficient is 12.6 × 10 ⁻⁶ .

On the other hand, a thermal expansion coefficient of 11.2 × 10 ⁻⁶ is obtained by using a three-layer clad material composed of a copper layer, an invar layer, and a copper layer (when the layer thickness ratio of each layer is 1: 1: 1). .

  By using the three-layer clad material having such a configuration, the thermal thermal expansion coefficient becomes smaller than that of the copper layer. In addition, both the three-layer clad materials have good electrical conductivity and solderability.

  By using the three-layer clad material having such a configuration according to the present invention for the connection tab for connecting the solar cell element, the warpage of the solar cell element after the connection tab is attached is limited to the copper material. It can be reduced from the connection tab.

  Furthermore, according to the present invention, it is desirable to have a structure in which the thickness is different between one copper layer and the other copper layer of the three-layer clad material, whereby the solar cell before the connection tab is attached. Warpage due to shrinkage of the high-concentration P layer on the back side of the element can be corrected after tabbing.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Example 1)
FIG. 1 shows a state in which a solar cell element according to the present invention is connected in series using a connection tab, and is an example particularly when viewed from the light-receiving surface side.

  FIG. 2 shows an example of a cross section of a solar cell element according to the present invention in a state where two solar cell elements are connected in series using a connection tab.

  1 and 2, 11 is a connection tab, 12a and 12b are solar cell elements, 13 is a light receiving surface side bus bar electrode of the solar cell element, 14 is a finger electrode, and 15 is a back side bus bar electrode.

  The solar cell elements 12a and 12b are made of a monocrystalline or polycrystalline silicon substrate as described above. Further, a light receiving surface side electrode and a back surface side electrode are formed on the light receiving surface side and the back surface side of the silicon substrate.

  That is, on the light receiving surface side and the back surface side, a bus bar electrode and finger electrodes are respectively formed by silver paste using a screen printing method or the like. Also, these electrode surfaces are solder coated over almost the entire surface in order to provide protection and easy attachment of the connection tabs.

  According to the finger electrode 14 on the light receiving surface side, a large number are formed to collect photogenerated carriers with a width of about 0.1 to 0.2 mm and parallel to the side of the solar cell element. Finger electrodes are formed.

  The light receiving surface side bus bar electrode 13 and the back side bus bar electrode 15 collect the collected carriers, but have a width of about 2 mm for attaching a connection tab, and 2 so as to intersect the finger electrode 14 perpendicularly. About 3 are formed.

  Further, the connection tab 11 has the following configuration.

  The width may be the same as or less than the width of the bus bar electrode 13 so that the connection tab 11 itself does not shadow the light receiving surfaces of the solar cell elements 12a and 12b when soldering to the solar cell elements 12a and 12b.

  Further, the length of the connection tab 11 is made to overlap almost all of the light receiving surface side bus bar electrode 13 and the back surface side bus bar electrode 15.

  When a general 150 mm square polycrystalline silicon solar cell element is used, the connection tab 11 has a width of about 1 to 3 mm and a length of about 150 to 250 mm. The reason why the connection tab 11 overlaps almost all of the light receiving surface side bus bar electrode 13 and the back surface side bus bar electrode 15 is to reduce the resistance component.

  Further, according to the connection tab 11 according to the present invention, the structure is as follows.

  The connection tab consists of a three-layer clad material consisting of a copper layer, a Kovar layer and a copper layer.

  Or it consists of a three-layer clad material which consists of a copper layer, an Invar layer, and a copper layer.

  FIG. 3 shows a cross-sectional structure of a three-layer clad material used as a connection tab according to the present invention.

  In the figure, 20 is an upper copper portion (copper layer), 21 is a portion composed of a Kovar layer or Invar layer, 22 is a lower copper portion (copper layer), and 23 and 24 are solder layers which are the above-mentioned solder coats. .

  The Kovar material forming the Kovar layer is an alloy having a composition of Fe-29% Ni-17% Co.

  The invar material forming the other invar layer is an alloy having a composition of Fe-36% Ni.

  Moreover, these Kovar materials and Invar materials are known as low thermal expansion metals, and the tolerance in a preferred ratio thereof is ± 10%.

  In the three-layer clad material according to the present invention, the layer thickness ratio of the upper copper portion 20 / the Kovar or the invar portion 21 / the lower copper portion 22 is (3/1) as a result of various experiments by the inventors. / 3) or a ratio of (1/1/1) or (1/6/1), and it is preferable to define the ratio within the range.

  That is, when the copper layers 20 and 22: Kovar layer (invar layer) 21 = 3: 1 to 1: 6, warping can be eliminated most preferentially.

  Moreover, about the total thickness which is the whole thickness of these three-layer clad materials, if it is set to 0.1-1.0 mm, it is sufficient at the point that curvature is eliminated most predominately.

  When the ratio of the copper portion of the upper layer 20 and the lower layer 21 is larger than (3/1/3) with respect to the portion 21 made of Kovar or Invar of the intermediate layer, it is soldered as a connection tab of the solar cell element from its thermal expansion coefficient In some cases, the effect of suppressing the warpage cannot be expected.

  Further, when the ratio of the copper portion of the upper layer 20 and the lower layer 21 is smaller than (1/6/1) with respect to the portion 21 made of Kovar or Invar of the intermediate layer, the electrical resistance increases if it is less than the ratio. When used as a connection tab, the output of the solar cell module tends to decrease due to an increase in the resistance component of this portion.

  In addition, when the total thickness of the three-layer clad material is less than 0.1 mm, the layer thickness ratio can reduce both the effect of suppressing the warpage of the solar cell element and the output of the solar cell module. I can't be satisfied.

  Further, when the total thickness exceeds 1.0 mm, in the laminate pressed under reduced pressure in the manufacturing process of the solar cell module, the solar cell element is cracked or cracked due to the thickness of the connection tab, so that the solar cell module May be defective.

  According to the present invention, solder layers 23 and 24 having a surface of about 20 to 70 μm are formed on such a three-layer clad material by plating or dipping.

  This solder layer may be coated on substantially the entire surface of the surface and the back surface except for the portion that cannot be coated in a spot shape due to oxidation of copper on the surface or the end surface when cut out.

  Thus, according to the present invention, the warp of the solar cell element after the connection tab is attached due to its low thermal expansion coefficient is obtained by using the solder coat on the three-layer clad material as described above as the connection tab 11. Can be reduced from a connection tab made of only copper.

  Furthermore, since the main surface is copper, the solderability is good, and the apparatus for attaching the connection tab using only the current copper can be used without the need for modification or major condition changes.

  Next, another embodiment of the present invention will be described.

(Example 2)
FIG. 4 shows a cross-sectional structure of a three-layer clad material used as another connection tab according to the present invention.

  In the figure, 25 is an upper copper portion (copper layer), 26 is a portion made of Kovar or Invar (Kovar layer or Invar layer), 27 is a lower copper portion (copper layer), and 28 and 29 are solder layers. .

  Then, according to the present example, as shown in FIG. 4, the copper thicknesses of the upper copper portion 25 and the lower copper portion 27 of the three-layer clad material are different. For example, the thickness of the copper portion 27 of the lower copper portion 27 is thicker than the thickness of the upper copper portion 25.

  An example using the connection tab of this example is shown in FIG.

  In the figure, the thickness of the copper portion 25 of the upper layer copper portion 27 and the copper portion 27 of the lower layer copper portion 27 are different from each other, and the thickness of the copper portion of the lower layer copper portion 27 is the upper copper portion 25. The cross section of the state which connected the solar cell element in series using the thing thicker than this thickness as a connection tab is shown.

  In FIG. 5, 12a and 12b are solar cell elements, 13 is a light receiving surface side bus bar electrode of the solar cell element, and 15 is a back side bus bar electrode.

  Reference numeral 30 denotes a connection tab in which the upper copper portion 25 and the lower copper portion 27 of the three-layer clad material have different copper thicknesses. Similarly to FIG. 4, 25 of the connection tab 30 indicates an upper copper portion, and 27 indicates a lower copper portion.

  Here, as described above, the solar cell elements 12a and 12b tend to warp so that the back surface side contracts and the light receiving surface side extends due to the contraction of the high-concentration P layer on the back surface side. In connection with the connection tabs of the battery elements 12a and 12b, a connection tab 30 in which the thickness of the lower copper portion 27 of the three-layer clad material is larger than the thickness of the upper copper portion 25 is used. As shown in the figure, the copper portion of the thicker lower copper portion 27 is connected to the bus bar 13 on the light receiving surface side of the solar cell elements 12a, 12b by soldering, and the bus bar 15 on the back surface side of the same solar cell elements 12a, 12b. The copper portion of the lower copper portion 25 of the thin connection tab 30 connected to the light receiving surface side bus bar electrode of the adjacent solar cell element is connected by soldering. It is configured so as.

  Therefore, when the warped solar cell elements 12a and 12b are placed in a convex shape, the thickness of the three-layer cladding material used as a connection tab on the electrode on the upper surface of the solar cell elements 12a and 12b is The lower copper portion 27 thicker than the upper copper portion 25 is connected, and the thickness of the three-layer clad material used as a connection tab is lower than that of the lower copper portion 27 on the electrodes on the lower surfaces of the solar cell elements 12a and 12b. With the configuration in which the thin upper copper portion 25 is connected, the following operational effects can be obtained.

  That is, when soldering the connection tabs 30 of the solar cell elements 12a and 12b, the temperature of the solar cell elements 12a and 12b and the connection tab 30 rises to near 200 ° C. and decreases to the room temperature after soldering. At this time, the lower copper portion 27 in which the thickness of the three-layer clad material is thicker than the upper copper portion 25 is connected to the light receiving surface side electrodes of the solar cell elements 12a and 12b, and the lower electrode is connected as a connection tab. Since the upper copper portion 25 whose thickness of the three-layer clad material used is thinner than the lower copper portion 27 is connected, the difference in thickness between the upper copper portion 25 and the lower copper portion 27 of the three-layer clad material Due to this, the warpage before the tabs of the solar cell elements 12a and 12b are corrected.

  Since the warpage of the solar cell elements 12a and 12b is corrected in this way, as a result, the solar cell element is cracked due to, for example, a laminate pressed under reduced pressure during the manufacturing process of the solar cell module. The manufacturing yield is improved, and the generation of cracks due to warpage is eliminated, so that the reliability of the completed solar cell module can be improved.

(Example 3)
In Example 2 described above, the light receiving surface side extends because the back surface side contracts, and when the warped solar cell element is placed in a convex shape, the upper surface becomes the light receiving surface side of the solar cell element.

  Instead, other examples are shown in this example.

  For example, when a solar cell element that is warped due to shrinkage of the antireflection film provided on the light receiving surface side of the solar cell element is placed in a convex shape, even if the upper surface becomes the back side of the solar cell element, a connection tab on the back surface It is only necessary to connect a lower copper portion 27 in which the thickness of the three-layer clad material used is higher than that of the upper copper portion 25.

  Examples 2 and 3 will be further described in detail.

  A preferred example of the connection tab will be described below.

  In the three-layer clad material in which the copper thickness of the upper copper portion and the lower copper portion is different according to the present invention, the layer thickness of the upper copper portion 25 / the Kovar portion 26 / the lower copper portion 27 The ratio may be (1/1/2) to (1/1/9) as a result of various experiments by the inventors. Further, in such a layer thickness ratio, it is desirable that the total thickness is in the range of 0.1 to 1.0 mm.

  That is, when the thickness of the upper copper portion 25 of the layer thickness ratio is increased by a ratio of (1/1/2), the warpage of the solar cell element is suppressed when soldered as a connection tab of the solar cell element. The effect cannot be expected.

  Further, if the thickness of the upper copper portion 25 of the layer thickness ratio is made smaller by a ratio of (1/1/9), it may be warped in the reverse direction after soldering.

  Furthermore, if the total thickness is smaller than 0.1 mm, the effect of suppressing the warpage of the solar cell element cannot be expected regardless of the total thickness ratio.

  Moreover, the electrical resistance increases, and when used as a connection tab, the output of the solar cell module decreases due to an increase in the resistance component of this portion.

  On the other hand, when the total thickness is larger than 1.0 mm, in the laminate pressed under reduced pressure in the manufacturing process of the solar cell module, the solar cell element is cracked or cracked due to the thickness of the connection tab. Module may be defective.

  Solder layers 28 and 29 having a surface of about 20 to 70 μm are formed on such a three-layer clad material by plating or dipping.

  This solder layer is coated on substantially the entire surface of the front and back surfaces, except for the portions that cannot be coated in the form of dots due to the oxidation of copper on the surface or the end surfaces when cut out.

(Device to connect the connection tab)
FIG. 6 shows an apparatus for connecting a connection tab to a solar cell element according to the present invention.

  In the figure, 12a is a solar cell element, 13 is a bus bar electrode on the light receiving surface side of the solar cell element, 15 is a bus bar electrode on the back side of the solar cell element, 35 is a connection tab, 36 is a pressing pin, and 37 is a hot air blowing nozzle. .

  The process of connecting connection tabs using this device is as follows.

  Attachment of the connection tab 35 to the bus bar electrode 13 on the light receiving surface side of the solar cell element 12a brings the connection tab 35 onto the bus bar electrode 13 of the solar cell element 12a to be attached.

  Thereafter, the pressing pin 36 is lowered, and the connection tab 35 is pressed against the bus bar electrode 13.

  Then, hot air of about 400 to 500 ° C. is blown from the nozzle 37 to the portion where the connection tab 35 is pressed against the bus bar electrode 13 with the pressing pin 36 for several seconds, and the solder of the connection tab 35 and the solder of the bus bar electrode 13 are applied. Melt and connect both.

  Thereafter, when the solder is solidified, the pressing pin 36 is raised. Similarly, another connection tab 35 is connected to the back side bus bar electrode 15 of the solar cell element 12a.

  The connection tab is connected to the solar cell element through the process described above.

  Next, a configuration of a solar cell module in which a connection tab is connected to the solar cell element and a manufacturing method thereof will be described.

(Solar cell module structure and manufacturing method)
FIG. 7 is a diagram showing an example of the structure of the solar cell panel portion of the solar cell module according to the present invention.

  In the figure, 41 is a translucent substrate, 42 is a light receiving surface side sealing material, 43 is a solar cell element, 44 is a back surface side sealing material, 45 is a back surface material, and 46 is a connection tab.

  Each member will be described below.

  As the translucent substrate 41, a substrate made of glass or polycarbonate resin is used.

  As the glass plate, white plate glass, tempered glass, double tempered glass, heat ray reflective glass and the like are used, but generally white plate tempered glass having a thickness of about 3 mm to 5 mm is used.

  On the other hand, when a substrate made of a synthetic resin such as polycarbonate resin is used, a substrate having a thickness of about 5 mm is often used.

  The light-receiving surface side sealing material 42 and the back surface side sealing material 44 are made of an ethylene-vinyl acetate copolymer (hereinafter, ethylene-vinyl acetate copolymer is abbreviated as EVA) and have a thickness of about 0.4 to 1 mm. A sheet-like form is used. These are fused and integrated with other members by applying heat and pressure under reduced pressure using a laminating apparatus.

  EVA may contain titanium oxide, a pigment, etc., and may be colored white. In the light-receiving surface side sealing material 42 according to the present invention, when it is colored, the amount of light incident on the solar cell element 43 tends to decrease and the power generation efficiency tends to decrease.

  In addition, EVA used for the back surface side sealing material 44 may be composed of a transparent material. In addition, titanium oxide, pigment, or the like is contained in accordance with the installation environment around the solar cell module, thereby coloring white or the like. May be.

  As described above, the solar cell element 43 and the connection tab 46 have a structure and a shape.

  The back material 45 is made of a weather-resistant fluorine-based resin sheet sandwiched with an aluminum foil so as not to transmit moisture, a polyethylene terephthalate (PET) sheet deposited with alumina or silica, or the like.

  The manufacturing method of the solar cell module according to the present invention is as follows.

  First, the translucent substrate 41, the light-receiving surface side sealing material 42, the solar cell element 43 to which the connection tab 46 is connected, the back surface side sealing material 44, and the back surface material 45 are superposed and set in a device called a laminator. They are integrated by applying pressure while heating for about 15 to 60 minutes at a temperature of about 100 to 200 ° C. under a reduced pressure of about 150 Pa.

  A terminal box (not shown) having a cable for connecting an external circuit is attached to the back surface of the created solar cell panel portion with an adhesive or the like.

  Furthermore, the required strength as a solar cell module and a module frame (not shown) required for installing the solar cell module in a building or the like are fitted on the outer periphery of the solar cell panel, and the corner is screwed to complete the solar cell module. To do.

  In addition, this invention is not limited to the said embodiment, Many corrections and changes can be added within the range of this invention.

  For example, solar cell elements are not limited to crystalline solar cells such as single crystal and polycrystalline silicon, but can also be applied to thin film solar cells and the like, and further coated with connection tabs and solar cell element electrodes. The solder used may be lead-free solder in addition to eutectic solder containing lead. Furthermore, it is possible to apply a solar cell element without solder coating.

It is a principal part of the solar cell module of this invention, and is a top view which shows an example at the time of seeing the state which connected the solar cell element in series using the connection tab from the light-receiving surface side. It is sectional drawing of the state which connected the solar cell element which connected the solar cell element which concerns on this invention in series using the connection tab. It is sectional drawing of the 3 layer clad material used as a connection tab which concerns on this invention. It is sectional drawing of the other 3 layer clad material used as a connection tab which concerns on this invention. It is sectional drawing of the state which used as another connection tab which concerns on this invention, and connected the solar cell element in series. It is the schematic which shows the apparatus which connects a connection tab to the solar cell element which concerns on this invention. It is a schematic sectional drawing which shows the principal part of the solar cell module which concerns on this invention. It is a schematic sectional drawing which shows the basic structure of a solar cell element.

Explanation of symbols

1: Solar cell element 2: Silicon substrate 3: Light receiving surface side electrode 4: Back surface side electrode 5: High-concentration P layers 11, 30, 35, 46: Connection tabs 12a, 12b: Solar cell element 13: Light receiving surface side busbar electrode 14: Finger electrode 15: Back side bus bar electrode 20, 25: Upper copper portion 21, 26: Intermediate layer portion 22 made of Kovar or Invar, 27: Lower copper portion 23, 24, 28, 29: Solder layer portion 36 : Pressing pin 37: Hot air blowing nozzle 41: Translucent substrate 42: Light receiving surface side sealing material 43: Solar cell element 44: Back surface side sealing material 45: Back surface material

Claims (2)

In a solar cell module in which a plurality of solar cell elements sealed with a filler between a light-transmitting substrate and a back sheet and electrically connected by a connection tab are arranged, the connection tab includes a copper layer, a kovar layer, and a copper layer. Or a three-layer clad material consisting of a copper layer, an invar layer, and a copper layer, and further solder-coated over substantially the entire surface of both main surfaces of the connection tab. Solar cell module. 2. The solar cell module according to claim 1, wherein a thickness is different between one copper layer and the other copper layer in the three-layer clad material.

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