JP2006245153A - Electrode connecting wire material for solar cell, and solar cell connected with wire material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrode connection wire materials of which a solder is hard to stick on the rear surface of a solar cell element when connecting electrode terminals of different polarity provided to the end of the rear surface of solar cell elements adjoined each other, for discouraged damage on the elements due to thermal stress. <P>SOLUTION: An electrode connection wire material 1 connects the electrode terminals of different polarity together provided to the end of the rear surface of solar cell elements adjoined each other. It comprises a core material 2 formed from Fe base alloy of low thermal expansion, a separation band 3 stacked at the center of the surface of core material 2, and connecting solders 4 and 4 coated on the core material surfaces on both sides of the separation band 3. The separation band 3 comprises a passive coat on its surface, and the connecting solders are formed from molten solder plating. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode connecting wire for connecting electrodes having different polarities of solar cell elements arranged adjacent to each other and a solar cell connected thereby.

  The solar cell element includes a semiconductor substrate formed of a silicon semiconductor having a PN junction, and electrode connection wires are soldered to a plurality of surface electrodes (light-receiving surface electrodes) provided linearly on the surface. A solar cell usually has a structure in which a plurality of solar cell elements are connected in series in order to obtain a desired electromotive force. A solar cell element is connected by soldering the said electrode connection wire to the back surface electrode of the other solar cell element adjacent to the surface electrode of one solar cell element. As shown in FIG. 4, the electrode connecting wire 31 is obtained by subjecting a core material 32 formed of a thin copper strip to molten solder plating, and expands in an arc shape on the outer peripheral surface of the core material 32. Solder portions 34, 35 and 36 are formed.

In recent years, the thickness of a semiconductor substrate has been reduced, and due to the difference in thermal expansion coefficient between the semiconductor substrate and the electrode connecting wire, a large thermal stress is generated in the semiconductor substrate when the electrode connecting wire is soldered. There is a risk of breakage. Therefore, a material having a small difference in thermal expansion coefficient from the semiconductor material has been used as the core material 32 of the electrode connecting wire 31. As such a material, for example, Japanese Patent Laid-Open No. 60-15937 (Patent Document 1) discloses an intermediate layer formed of Invar (typical composition: Fe-36% Ni) which is an alloy of Fe and Ni. A clad material in which copper layers are laminated and integrated on both sides has been proposed.
Japanese Unexamined Patent Publication No. 60-15937

  As in the prior art, when the front electrode of the solar cell element is connected in series to the back electrode of the adjacent solar cell by the electrode connecting wire, it is necessary to connect the electrode connecting wire by moving from the upper side to the lower side of the solar cell element. For this reason, the soldering work is complicated, resulting in high production costs. Further, in the connection method, it is necessary to provide an interval of about 3 to 4 mm between the solar cell elements, the area ratio of the solar cell element in the total area of the solar cell is reduced, and the power generation efficiency is reduced due to the reduction in the mounting rate. Has been invited.

  For this reason, the thing which provided the electrode terminal from which each polarity differs in the both ends of the back surface of a solar cell element is examined. Regarding the connection of the solar cell elements, the solar cell elements are arranged adjacently so that the electrode terminals having different polarities face each other, and the electrode terminals having different polarities of the adjacent arranged solar cell elements are similar to the electrode connecting wire 31. Attempts have been made to solder using an electrode connecting wire having the following structure. In this type of solar cell element, the elements can be arranged adjacent to each other with an interval of about 1 mm, so that the mounting rate of the element can be increased and the electrode connecting wire must be connected from the front side to the back side. Since there is no, connection work becomes easy. A back electrode (aluminum paste electrode) is formed on the back surface of the solar cell element, and an electrode terminal is formed at the end of the back surface of the element while being insulated from the back electrode. The electrode terminal is formed at the other end of the back surface of the element.

  However, as shown in FIG. 5, when the electrode terminals B and A of the adjacent solar cell elements C1 and C2 are soldered to each other using the electrode connecting wire, the solder portion 34 having a swelled central portion is melted. There is a problem that the molten solder adheres to the back surfaces of the solar cell elements C1 and C2. When the solder 34A adheres to the back surfaces of the solar cell elements (semiconductor substrates) C1 and C2, the solar cell element is electrically short-circuited, and the performance is deteriorated. Further, the electrode connecting wire 31 has a large difference in thermal expansion coefficient from that of the semiconductor substrate, and the thickness of the substrate is thinned to about 200 μm, so that the semiconductor substrate may be damaged by thermal stress during soldering. There is.

  The present invention has been made in view of such problems, and when the electrode terminals having different polarities provided at the end portions of the back surface of the adjacent solar cell elements are electrically connected to each other, solder is applied to the back surface of the solar cell element. It is an object of the present invention to provide an electrode connecting wire which is difficult to adhere and damages due to thermal stress on the element, and a solar cell connected by the electrode connecting wire.

  The electrode connecting wire of the present invention connects electrode terminals having different polarities provided at the end of the back surface of the solar cell elements arranged adjacent to each other, and includes a core formed of a low thermal expansion material and the core A separation band formed in a central portion of the surface of the material, and a connecting solder portion coated on the surface of the core on both sides of the separation band, the separation band being in a passive state on the surface It has a film, and the connecting solder part is formed by hot-dip solder plating.

  According to this electrode connection wire, since the core material of the electrode connection wire is formed of a low thermal expansion material, when the electrode connection wire is soldered to the electrode terminal of the solar cell element, the thermal stress generated in the semiconductor substrate of the solar cell element Can be reduced, and breakage of the semiconductor substrate can be prevented. Further, since no solder part is formed in the separation band part at the center part of the surface of the core material, there is no possibility that the molten solder adheres to the back surface of the solar cell element during the soldering, and the soldering work Excellent in properties. Further, since the separation band portion has a passive film on the surface thereof, the wettability with molten solder is poor, and the molten solder plating portion is formed on the surface of the separation band portion by high-productivity molten solder plating. Therefore, the connecting solder portions can be easily and easily formed on both sides, and the productivity is excellent.

As the low thermal expansion material forming the core material, it is preferable to use an Fe-based alloy which is easily available and has a thermal expansion coefficient of 1 to 5 ppm / ° C. which is close to the thermal expansion coefficient of the semiconductor substrate.
In addition, the low thermal expansion material is not limited to a single layer, and an outer layer formed of the low thermal expansion Fe base alloy is laminated on both sides of an intermediate layer formed of pure Cu or a Cu base alloy containing Cu as a main component. Multiple layers may be used. By providing such an intermediate layer, the conductivity of the core material can be improved, and the power generation loss of the solar cell can be reduced.

  The separation band portion can be formed of pure Al or an Al-based alloy containing Al as a main component (collectively referred to as “aluminum-based metal”) or an Al—Fe intermetallic compound. Aluminum-based metals are easy to obtain and low in cost, and a passive film (dense oxide film) is easily formed on the surface thereof. For this reason, it is possible to easily form a solder part (molten solder plating part) around the surface of the separation band part by simply immersing the composite material in which the separation band part is formed in the core material in the molten solder bath. Can do. In addition, since the Al—Fe intermetallic compound has a passive film easily formed and is black like the aluminum metal, the gap between the black solar cell elements can be made inconspicuous.

  In addition to the connection solder portion, the solder portion can be formed by coating the solder portions for covering on both side surfaces and the back surface of the core material. By providing the solder part for coating, the corrosion resistance of the core material can be improved, and the conductivity can be improved. These coated solder portions can also be easily formed integrally by molten solder plating.

In the solar cell of the present invention, solar cell elements in which electrode terminals having different polarities are formed at both ends of the back surface are arranged adjacent to each other so that electrode terminals having different polarities face each other, and the polarities of the solar cell elements arranged adjacent to each other are Different electrode terminals are solar cells connected by the electrode connecting wire, wherein one connecting solder portion of the electrode connecting wire is soldered to the electrode terminal of the one solar cell element, and the electrode connecting wire The other connecting solder portion is soldered to the electrode of the other solar cell terminal.
According to this solar cell, when different electrode terminals of adjacent solar cell elements are connected by soldering with the electrode connecting wire, a separation band portion having no solder portion is formed at the center of the surface of the electrode connecting wire. Therefore, there is no fear that the solder adheres to the back surface of the solar cell element, the soldering operation is easy, and defective products are hardly generated.

  According to the electrode connection wire for solar cell of the present invention, the separation band portion having the passive film having poor wettability with the molten solder is formed in the center portion of the surface of the core material formed of the low thermal expansion material. When soldering the electrode connecting wire to the electrode terminals of the adjacent solar cell elements, the thermal stress generated on the semiconductor substrate of the solar cell element can be reduced, and the molten solder may adhere to the back surface of the solar cell element Excellent soldering workability, and it is difficult for defective products to occur. Furthermore, since the passive band is formed on the surface of the separation band part, the molten solder plating with high productivity can be performed on both sides without forming the molten solder plating part on the surface of the separation band part. The solder part for joining can be formed easily and easily, and the productivity is excellent.

Hereinafter, the electrode connecting wire of the present invention will be described with reference to the drawings.
FIG. 1 shows an electrode connecting wire 1 according to a first embodiment of the present invention. The electrode connecting wire 1 is in the form of a strip and has a single-layer core 2 and the surface is flush with the center of the surface of the core 2. The separation band part 3 is press-bonded so as to be, and the soldering parts 4 and 4 are joined on the surface of the core member 2 and are swelled in an arc shape and coated on both sides of the separation band part 3. In addition, the soldering portions 5 and 6 for coating are formed on the side surfaces and the back surface of the core material 2.

  FIG. 2 shows an electrode connecting wire 1A according to the second embodiment. The electrode connecting wire 1A has a strip-like and multi-layered core material 2A. The core material 2A is made of pure Cu or Cu having good conductivity. Outer layers 21 and 23 are laminated on both sides of an intermediate layer 22 formed of a Cu-based alloy containing 90 mass% or more as a main component (sometimes collectively referred to as “copper metal”). . Other configurations are the same as those of the first embodiment, and the same reference numerals are given.

  The single-layer core material 2 and the outer layers 21 and 23 of the multilayer core material 2A are formed of an Fe-based alloy having a thermal expansion coefficient of about 1 to 5 ppm / ° C. Such an Fe-based alloy approximates the thermal expansion coefficient of a semiconductor substrate of a solar cell element (about 3 ppm / ° C. for a silicon substrate) and can be easily obtained. Specifically, an FeNi alloy of 36 to 50 wt% Ni and the remaining Fe, 20 to 30 wt% Ni, 1 to 20 wt% Co, and an FeNiCo alloy of the remaining Fe are suitable.

  In the case of the multilayer core material 2A, the thicker the intermediate layer 22, the more the conductivity is improved, but the thermal expansion coefficient of the core material 2A as a whole increases. For this reason, the ratio of the thickness of the intermediate layer 22 to the total thickness of the core material 2A is about 20 to 40%, preferably about 25 to 35%. Of course, it is preferable that the thicknesses of the outer layers 21 and 23 on both sides of the intermediate layer 22 be equal in order to prevent warping. The core material 2A can be easily manufactured by superposing the material thin plates of the outer layers 21 and 23 on both sides of the material thin plate of the intermediate layer 22 and performing roll pressure contact and annealing.

  The separation band portion has a passive film (dense oxide film) and is formed of a material that forms the passive film. As such a material, for example, pure Al, an Al-based alloy containing Al as a main component, preferably 90 mass% or more, for example, JIS 1050, 1060, 1085, 1080, 1070, 1N99, 1N90 can be used. In addition to the aluminum-based metal, pure Ti, a Ti-based alloy containing Ti as a main component, and other metals such as stainless steel, on which the passive film is naturally formed, can be used. In particular, an aluminum-based metal is preferable because it is easily available and low in cost. In addition, when the outer layer of a single-layer core material or a multi-layer core material is formed of a low thermal expansion Fe-based alloy, the aluminum-based metal easily reacts with Al and Fe by heat treatment to form a black Al-Fe intermetallic compound. It can be easily formed white by etching and etching the surface, and can be colored in various colors by alumite treatment. Further, the separation band portion 3 is usually set to a width of about 40 to 70% with respect to the entire width of the core materials 1 and 1A.

  The joining solder portion 4 and the covering solder portions 5 and 6 are formed by coating the core materials 2 and 2A on which the separation band portion 3 is formed by hot-dip solder plating. The solder material to be applied is preferably a solder material having a low melting point so as to reduce as much as possible the thermal stress generated in the semiconductor substrate of the solar cell element during soldering. As said solder material, melting | fusing point is about 130-300 degreeC, Preferably it is about 180-240 degreeC Sn-Pb alloy, Sn-0.5-5 mass% Ag alloy, Sn-0.5-5 mass% Ag-0. 3-1.0 mass% Cu alloy, Sn-0.3-1.0 mass% Cu alloy, Sn-1.0-5.0 mass% Ag-5-8 mass% In alloy, Sn-1.0-5.0 mass % Ag-40 to 50 mass% Bi alloy, Sn-40 to 50 mass% Bi alloy, Sn-1.0 to 5.0 mass% Ag-40 to 50 mass% Bi-5 to 8 mass% In alloy, etc. are suitable. Since Pb is harmful to the human body and may contaminate the natural environment, Pb-free Sn—Ag alloy, Sn—Ag—Cu alloy, Sn—Cu alloy, Sn—Ag—In alloy are used from the viewpoint of pollution prevention. A solder material such as Sn—Ag—Bi alloy is preferable. Further, in each of the solder materials, in order to prevent the molten solder from being oxidized, one of the P of about 50 to 200 ppm, Ga of several to several tens of ppm, Gd of several to several tens of ppm, and Ge of several to several tens of ppm. Seeds or two or more can be added. Moreover, as said solder part, it is good also as a multilayer structure using various pure metals, such as Sn, Ag, Cu, or these alloys. In this case, the thickness of each layer is adjusted so that the desired alloy composition is obtained after melting. The multilayer structure can be easily formed by sequentially performing predetermined metal plating.

  The dimensions of the electrode connecting wires 1 and 1A are appropriately set according to the size of the solar cell element to be connected. In the case of a rectangular solar cell element having a side of about 120 mm, the core material 1 and 1A has a length of about 120 mm and a width of about 5 mm. The plate thickness is about 200 to 250 μm, the width of the separation band portion 3 is about 3 mm, the thickness is about 10 to 15 μm, and the average height of the connecting solder portion 4 is about 20 to 30 μm.

Here, a method for manufacturing the electrode connecting wire will be briefly described.
First, a material strip that is the basis of the core materials 2 and 2A is prepared, and a material strip that is a material of the separation strip is overlapped on the center of the surface and roll-welded at a rolling reduction of 30 to 60%. The resulting clad material is further finish-rolled to obtain a core material in which the separation band portion is embedded in the center of the surface. When the outer layer 21 of the core material 2 or the core material 2A is made of a low thermal expansion Fe-based alloy and the separation band portion 3 is made of an aluminum-based metal, 700 to Annealing is performed at 800 ° C. for about 1 to 2 minutes. Thereby, Al and Fe react to form a black Fe—Al intermetallic compound. Then, the width direction edge part is slit as needed so that the isolation | separation belt | band | zone part 3 may be arrange | positioned in the center part of the core materials 2 and 2A, and shape is adjusted. Next, flux is applied to the core materials 2 and 2A having the separation band portion 3 to remove the surface oxide film on the surface of the core material, and then immersed in a molten solder bath to remove the separation band portion 3 of the core materials 2 and 2A. Solder portions 4, 5, and 6 are formed on the outer peripheral surface. In addition, in order to whiten the surface of the separation band part 3, it is only necessary to etch the surface of the separation band part 3 by immersing it in an alkaline solution such as an aqueous sodium hydroxide solution after the solder part is coated.

In the electrode connection wires 1 and 1A of the first and second embodiments, the outer peripheral surface of the core material is coated with the solder portions 4, 5, and 6 that are swollen in an arc shape except for the separation band portion 3. The joining solder part 4 should just be formed in the both sides of the separation band part 3 of the core material surface. However, the corrosion resistance of the outer peripheral surfaces of the core materials 2 and 2A can be improved by covering the entire outer peripheral surfaces of the core materials 2 and 2A with the solder portion except for the separation band portion 3 as described above. The conductivity of the connecting wires 1 and 1A can be improved. The solder parts 4, 5, and 6 are molten solder plating parts, and can be easily and easily formed by immersing the core material in a molten solder bath.
Further, in the electrode connecting wires 1 and 1A, the separation band portion 3 is formed so as to be embedded in the surface of the core material because the material metal plate is pressed against the core materials 2 and 2A. There is no need to form it, and a metal layer or an oxide layer that forms a passive film on the core material may be formed on the core by vapor deposition or plating.
In the electrode connecting wire 1A, the intermediate layer 22 is made of a copper-based metal and the outer layers 21 and 23 are made of a low thermal expansion Fe alloy. However, the intermediate layer 22 is made of a low thermal expansion Fe alloy and the outer layers 21 and 23 are made of a copper-based metal. May be formed. Also in this case, the larger the total thickness of the layers formed of the low thermal expansion Fe alloy, the more the thermal stress generated in the solar cell element can be reduced. Therefore, the outer layer (copper metal layer) with respect to the total thickness of the core material The ratio of the total thickness is preferably about 20 to 40%.

Next, the solar cell connected using the electrode connection wire 1 of the first embodiment will be described with reference to FIG.
This solar cell is configured by connecting a large number of solar cell elements in series by the electrode connecting wire 1, and a connection portion between a pair of adjacent left and right solar cell elements is shown in FIG. 3. The electrode terminals A and B having different polarities protrude from both ends of the back surface of the solar cell elements C1 and C2, and in the illustrated example, the electrode terminal B is provided at the right end of the left solar cell element C1 and the right side. An electrode terminal A having a different polarity is provided at the left end of the solar cell element C2, and the left and right solar cell elements C1 and C2 are arranged with an interval of about 1 mm so that the electrode terminals A and B face each other. Yes. The electrode terminals A and B are respectively soldered to connecting solder portions 4 and 4 formed on both sides of the separation band portion 3 of the electrode connecting wire 1 and connected in series. Soldering is performed at a temperature 20 to 30 ° C. higher than the melting point of the solder material forming the connecting solder portion 4.

  According to the electrode connecting wire 1 of the present invention, the separation band portion 3 having a passive film is formed in the center portion in the width direction, and no molten solder plating portion is formed in this portion. The molten solder in which the solder portion is melted does not adhere to the back surface of the solar cell element, and the connecting solder portion 4 formed to be separated from the left and right by the separation band portion 3 is once melted and solidified by the solidified solder portion 4A. Electrode terminals A and B can be soldered. Further, since the core material 2 of the electrode connection wire 1 is formed of a low thermal expansion alloy, the thermal stress generated in the semiconductor substrates of the solar cell elements C1 and C2 during soldering is reduced, and the substrate is damaged. Not likely to occur. In addition, although FIG. 3 connects the electrode terminals of different polarities of the solar cell elements using the electrode connection wire 1 according to the first embodiment, the case where the electrode connection wire 1A of the second embodiment is used. The same effect can be obtained in.

It is a cross-sectional view of the electrode connecting wire according to the first embodiment of the present invention. It is a cross-sectional view of the electrode connection wire material concerning 2nd Embodiment of this invention. It is principal part sectional drawing of the solar cell which shows the connection part of the solar cell element connected in series by the electrode connection wire of this invention. It is a cross-sectional view of the conventional electrode connection wire. It is principal part sectional drawing which shows the connection part of the solar cell element connected in series by the conventional electrode connection wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A Electrode connection wire 2,2A Core material 3 Separation zone part 4 Solder part for connection 22 Intermediate | middle layer 21,23 Outer layer C1, C2 Solar cell element

Claims (7)

An electrode connecting wire for connecting electrode terminals with different polarities provided at the end of the back surface of the solar cell element disposed adjacent to each other,
A core material formed of a low thermal expansion material, a separation band portion formed by lamination at the center of the surface of the core material, and a connecting solder portion formed on the core material surfaces on both sides of the separation band portion. And the separation band portion has a passive film on the surface thereof, and the connection solder portion is formed by molten solder plating. The electrode connection wire for a solar cell according to claim 1, wherein the low thermal expansion material is formed of an Fe-based alloy having a thermal expansion coefficient of 1 to 5 ppm / ° C. In the low thermal expansion material, an outer layer is formed on both sides of an intermediate layer, the outer layer is formed of an Fe-based alloy having a thermal expansion coefficient of 1 to 5 ppm / ° C., and the intermediate layer is mainly composed of pure Cu or Cu. The electrode connection wire for solar cells according to claim 1, which is formed of a Cu-based alloy. The solar cell electrode connecting wire according to any one of claims 1 to 3, wherein the separation band portion is formed of pure Al or an Al-based alloy containing Al as a main component. The solar cell electrode connection wire according to any one of claims 1 to 3, wherein the separation band portion is formed of an Al-Fe intermetallic compound. The electrode connection wire for solar cells according to any one of claims 1 to 5, wherein a coating solder portion is formed on both side surfaces and the back surface of the core material. The solar cell elements in which electrode terminals having different polarities are formed on both ends of the back surface are adjacently arranged so that the electrode terminals having different polarities face each other, and the electrode terminals having different polarities of the adjacent solar cell elements are claimed. A solar cell connected with the electrode connecting wire described in any one of 1 to 6,
One connecting solder portion of the electrode connecting wire is soldered to the electrode terminal of the one solar cell element, and the other connecting solder portion of the electrode connecting wire is soldered to the electrode of the other solar cell terminal. Solar cells.

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