JP2013102054A - Solar cell lead wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell lead wire capable of suppressing nonuniform deformation when wound to a bobbin and delivered from the bobbin.SOLUTION: The solar cell lead wire is a copper wire covered with a solder plating layer, consisting of pure copper or copper alloy and having a cross section perpendicular to the length direction which is approximately a rectangle with a long side and a short side. In the cross section of the copper wire perpendicular to the length direction, an occupancy of a crystal orientation<100>±10° is 5 area% or more and 50 area% or less; an occupancy of a crystal orientation<111>±10° is 5 area% or more and 50 area% or less; and an occupancy of a crystal orientation<101>±10° is 5 area% or more and 50 area% or less. The total occupancy of the crystal orientation<100>±10°, the crystal orientation<111>±10° and the crystal orientation<101>±10° is 100 area% or less.

Description

  The present invention relates to a lead wire used for a solar cell.

  Solar cells generally have silicon cells and lead wires (also referred to as interconnectors), and a plurality of silicon cells are electrically connected via lead wires. As this lead wire, a solder-plated copper wire is frequently used.

  In recent years, silicon cells of solar cells have been made thinner for cost reduction and the like. In a thin silicon cell, there is a problem that the solder-plated copper wire expands due to heating during soldering or a temperature rise during use of the solar cell, and the cell is deformed or damaged by the load stress generated by this expansion. .

  Various techniques have been proposed to deal with the above problems. For example, Patent Documents 1 to 3 describe a technique for reducing the yield strength by improving the proportion of a specific crystal orientation of a copper wire in order to prevent deformation or breakage of the cell.

JP 2008-168339 A JP 2009-016593 A JP 2010-073445 A

  However, in the solar cell lead wire in which the ratio of the specific crystal orientation of the copper wire is improved as in the prior art, when the solar cell lead wire is wound around the bobbin, and the solar cell lead wire wound around the bobbin , Undesirably uneven deformation (deformation only in a specific direction) may occur in the solar cell lead.

  The present invention has been made paying attention to the above-described circumstances, and its object is to provide a solar cell lead wire capable of suppressing non-uniform deformation during winding onto a bobbin and feeding from the bobbin. There is to do.

  As a result of intensive studies by the present inventors, the above object can be achieved by suppressing the development of a specific crystal orientation in the cross section of the copper wire, in other words, by randomly presenting various crystal orientations. I found. The present invention based on such knowledge is as follows.

[1] A solar cell lead wire in which a copper wire is coated with a solder plating layer,
The copper wire is made of pure copper or a copper alloy, and the cross section perpendicular to the length direction is a substantially rectangular shape having a long side and a short side,
In the cross section of the copper wire that is perpendicular to the length direction,
Occupancy ratio of crystal orientation <100> ± 10 ° is 5 area% or more and 50 area% or less,
Occupancy of crystal orientation <111> ± 10 ° is 5 area% or more and 50 area% or less,
Occupancy of crystal orientation <101> ± 10 ° is 5 area% or more and 50 area% or less,
The total of the crystal orientation <100> ± 10 ° occupancy, the crystal orientation <111> ± 10 ° occupancy, and the crystal orientation <101> ± 10 ° occupancy is 100 area% or less. Lead wire for solar cell.
[2] The solar cell lead wire according to [1], wherein the 0.2% proof stress is 90 MPa or less.
[3] The above-mentioned [1] or [2], wherein the body portion has a winding diameter of 80 to 120 mm, a flange diameter of 150 to 200 mm, and a width between the flanges of 80 to 120 mm. Solar cell lead wires.

  In the lead wire for solar cell of the present invention, uneven deformation during winding onto the bobbin and feeding from the bobbin is suppressed.

Fig.1 (a)-FIG.1 (c) are schematic which shows the shape of the various cross sections of the lead wire for solar cells of this invention. FIG. 2 is a schematic view showing the shape of a bobbin for winding the solar cell lead wire of the present invention. FIG. 3 is a schematic view showing a manufacturing process of the solar cell lead wire of the present invention.

  The lead wire for solar cell of the present invention is obtained by coating a copper wire with a solder plating layer. Below, a copper wire is demonstrated first and then a solder plating layer is demonstrated.

[Copper wire]
The copper wire is made of pure copper or a copper alloy. From the viewpoint of obtaining a low 0.2% proof stress, pure copper is preferred. Here, pure copper means what consists of copper and an unavoidable impurity, for example, tough pitch copper, deoxidized copper, and oxygen-free copper are mentioned.

  The shape of the cross section of the copper wire is a substantially rectangular shape having a long side and a short side. That is, the copper wire is a flat wire whose cross-sectional shape is finished into a substantially rectangular shape by plastic working (for example, drawing, wire drawing, rolling, etc.). FIG. 1 illustrates the cross-sectional shapes of a copper wire and a solder-plated copper wire (in FIG. 1, 10 indicates a solder-plated copper wire, 11 indicates a copper wire, and 12 indicates a solder-plated layer). Examples of the substantially rectangular shape include a rectangular shape (FIG. 1A), a rectangular shape with rounded corners (FIG. 1B), and two long sides that are parallel to each other, and the two short sides are outside. The track shape (FIG. 1C) which is a convex curve is mentioned.

  The thickness of the copper wire is preferably 0.1 to 0.5 mm, more preferably 0.1 to 0.3 mm, and the width of the copper wire is preferably 0.8 to 5.0 mm, more preferably 1 0.0-2.0 mm. Here, the thickness of the copper wire refers to the distance between the two long sides in the copper wire cross section, and the width of the copper wire refers to the distance between the two short sides in the copper wire cross section. In addition, as shown in FIG.1 (c), when a short side is a curve, the width | variety of a copper wire says the longest distance between two short sides.

  In the lead wire for solar cell of the present invention, in the cross section of the copper wire perpendicular to the length direction, the occupation ratio of the crystal orientation <100> ± 10 ° is 5 area% or more and 50 area% or less, The occupancy of the crystal orientation <111> ± 10 ° is 5 area% to 50 area%, the occupancy of the crystal orientation <101> ± 10 ° is 5 area% to 50 area%, and the crystal orientation The total of the occupancy of <100> ± 10 °, the occupancy of crystal orientation <111> ± 10 °, and the occupancy of crystal orientation <101> ± 10 ° is 100 area% or less. By having such an occupancy ratio of the crystal orientation, nonuniform deformation of the solar cell lead wire during winding onto the bobbin and feeding from the bobbin is suppressed. The occupancy of the crystal orientation <100> ± 10 ° is 10 to 35 area%, the occupancy of the crystal orientation <111> ± 10 ° is 10 to 35 area%, and the crystal orientation It is preferable that the occupation ratio of <101> ± 10 ° is 10 area% or more and 35 area% or less.

  The occupation ratio in the cross section of the copper wire can be calculated by a back elastic scattering electron diffraction (Electron Back-scattering Diffraction, EBSD) method. Specifically, a solar cell lead wire is cut in a direction perpendicular to its length direction, and the exposed cross section of the copper wire is polished with emery paper, then buffed with alumina, and further electrolytically polished. The occupation ratio can be calculated by mirror-polishing and measuring the cross section by the EBSD method.

[Solder plating layer]
The solder plating layer may be either lead-containing solder or lead-free solder, but lead-free solder is more preferable from the viewpoint of environmental problems. As a lead free solder, Sn-3 mass% Ag-0.5 mass% Cu etc. are mentioned, for example.

  The thickness of the solder plating layer is preferably 5 to 50 μm, more preferably 10 to 40 μm. If this thickness is too thin, the solar cell lead wire cannot be soldered well to a silicon cell or the like. On the other hand, when this thickness is too thick, the yield strength of the solar cell lead wire increases. The thickness of the solder plating layer can be measured by polishing a cross section perpendicular to the axial direction of the solder plating wire and observing with a microscope.

[Solar cell lead wires]
The 0.2% yield strength of the solar cell lead of the present invention is preferably 90 MPa or less, more preferably 60 MPa or less. The solar cell lead wire having a low yield strength can be easily wound on a bobbin, and the effect of the present invention that suppresses non-uniform deformation is further improved. The 0.2% proof stress of the solar cell lead wire is measured by the offset method shown in JIS Z 2241. In the present invention, the cross-sectional area used for calculating the 0.2% yield strength is the cross-sectional area of the copper wire itself that does not include solder.

  The lead wire for solar cell of the present invention has a bobbin whose body part diameter (d) is 80 to 120 mm, collar diameter (D) is 150 to 200 mm, and width (W) between the collars is 80 to 120 mm. It is preferable to be wound around and stored. FIG. 2 shows a schematic view of the bobbin. If the winding diameter of the body part (d) of the bobbin is smaller than 80 mm, the lead wire for solar cell at the beginning of winding tends to be deformed. On the other hand, if it exceeds 120 mm, a large winding device is required. If the bobbin diameter (D) is smaller than 150 mm, it is necessary to frequently replace the bobbin when winding the solar cell lead wire. On the other hand, if the bobbin diameter exceeds 200 mm, a large winding device is required. Become. If the bobbin gap (W) is smaller than 80 mm, it is necessary to frequently replace the bobbin when winding the solar cell lead. On the other hand, if this exceeds 120 mm, the solar cell lead will be deformed. It tends to be easier.

  The bobbin body diameter (d) is preferably 90 to 110 mm, the bobbin collar (D) is preferably 170 to 190 mm, and the bobbin collar width (W) is preferably 90 mm. ~ 110 mm.

[Method for producing solar cell lead wire]
Regarding the method for producing the solar cell lead wire of the present invention, a method for producing a copper wire will be described first, and then a method for solder plating on the obtained copper wire will be explained. In addition, FIG. 3 is schematic which shows the manufacturing process of the lead wire for solar cells of this invention.

[Manufacturing method of copper wire]
In order to make a rough wire (for example, φ8.0 mm) made of pure copper or a copper alloy into a predetermined wire diameter (φ0.5 mm to φ2.5 mm (working degree: 90.2 to 99.6%)), cold drawing is performed. (Drawing step 1).

Next, the copper wire obtained by cold drawing to a predetermined wire diameter is heat-treated at 200 ° C. to 300 ° C. for 1 to 6 hours in an inert gas atmosphere (CO ₂ , N ₂ , Ar) (heat treatment step) ).

  After the heat treatment step, cold drawing is further performed to obtain a predetermined wire diameter (for example, φ0.3 mm to φ0.8 mm, preferably φ0.4 mm to φ0.7 mm) (drawing step 2).

  Cold-rolling is performed after the wire drawing step 2, and a predetermined cross-sectional shape (for example, thickness 0.2 mm × width 1.0 mm, thickness 0.2 mm × width 2.0 mm, thickness 0.2 mm × A rectangular copper wire having a width of 1.5 mm, a thickness of 0.15 × a width of 2.0 mm, etc.) is produced (rolling step).

[Method of solder plating]
A rectangular copper wire having a predetermined cross-sectional shape is washed to remove processing oil (oils and fats) and foreign matters adhering to the surface of the copper wire (cleaning step).

In addition, when there are fats and oils that could not be removed in the washing step, a step of heating and removing the fats and oils by heating the copper wire in a heating furnace in an air atmosphere after the washing step. It may be provided (heating step).
The heating temperature is, for example, 400 to 800 ° C, preferably 500 to 700 ° C. This temperature is more preferably lower than the temperature at which the copper wire is annealed and softened in the annealing step described later. The heating time is, for example, 0.01 to 30 minutes, preferably 0.01 to 5.0 minutes.

Next, the copper wire is annealed and softened in an annealing furnace under a reducing gas atmosphere (annealing step).
This annealing temperature (temperature in the annealing furnace) is, for example, 300 to 900 ° C. In order to effectively soften the copper wire and to control the crystal orientation of the copper wire, the annealing temperature is preferably set to 500 to 800 ° C. The annealing time is, for example, 0.01 to 30 minutes, preferably 0.01 to 5.0 minutes.

  The annealing of the copper wire is preferably performed in a reducing gas atmosphere. Examples of the reducing gas include hydrogen gas and carbon monoxide gas. Of these, hydrogen gas is preferred from the viewpoint of work environment. Further, when the reducing gas atmosphere is formed, the reducing gas may be diluted with an inert gas. Examples of the inert gas include nitrogen gas and argon gas. Of these, nitrogen gas is preferred from the viewpoint of versatility. When diluting the reducing gas with an inert gas, the concentration of the reducing gas is preferably 10 to 80% by volume, and more preferably 20 to 50% by volume from an economic viewpoint.

  Also, one end of the annealing furnace (the copper wire outlet side) is immersed in molten solder, and the surface of the copper wire is kept in a stable state by making the structure such that the annealed copper wire does not come into contact with the atmosphere. be able to.

  After the annealing step, the copper wire is immersed in molten solder and pulled up to form a solder plating layer to produce a solder-plated copper wire (that is, the solar cell lead wire of the present invention) (solder plating). Process).

  In the solder plating step, it is preferable to pull the copper wire from the solder bath substantially vertically through a turn roll.

  The temperature of the molten solder is, for example, 230 to 300 ° C, preferably 250 to 300 ° C. The temperature of the copper wire when immersed in molten solder is, for example, 100 to 500 ° C., and preferably 150 to 450 ° C. from the viewpoint of suppressing the thickness of the solder plating layer and the crystal orientation of the copper wire. The immersion time of the copper wire in the solder is, for example, 0.005 to 5.0 seconds, preferably 0.01 to 2.0 seconds.

  In the manufacturing method of the lead wire for solar cells of this invention, it is necessary to perform an annealing process and a solder plating process continuously. Steps other than the annealing step and the solder plating step (hereinafter referred to as “other steps”) may not be performed continuously. For example, in the other steps, the next step may be performed after winding the copper wire around the bobbin.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and appropriate modifications are made within a range that can meet the above and the following purposes. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
Cold drawing of a rough drawn wire having a wire diameter of 8.0 mm was performed to obtain a wire diameter of 1.5 mm, followed by heat treatment at 250 ° C. for 10 hours in a nitrogen atmosphere. Next, cold drawing from a wire diameter of 1.5 mm to a wire diameter of 0.4 mm was performed to produce a rectangular copper wire having a cross-sectional thickness of 0.2 mm and a width of 1.0 mm. The rectangular copper wire was washed and subsequently passed through an annealing furnace (temperature: 550 ° C.) under a reducing atmosphere (hydrogen gas: 30 vol% and argon gas: 70 vol%) (holding time: 0.2 minutes) ) Immediately after that, the copper wire (temperature: 400 ° C.) is plunged into the molten solder bath (temperature of molten solder: 250 ° C.), and the copper wire is pulled up substantially vertically from the solder bath via the turn roll in the solder bath. At the stage where the solder plating layer is formed and solidified, the bobbin is wound around a bobbin (winding diameter (d) of body part: 95 mm, diameter (D): 180 mm, width (W) between ribs: 95 mm). Turned to produce the solar cell lead of the present invention.

(Example 2)
Cold drawing of a rough drawn wire having a wire diameter of 8.0 mm was performed to make the wire diameter 1.5 mm, and then heat treatment was performed at 300 ° C. for 6 hours in a nitrogen atmosphere. Next, cold drawing was performed from a wire diameter of 1.5 mm to a wire diameter of 0.6 mm to produce a rectangular copper wire having a cross-sectional thickness of 0.15 mm and a width of 2.0 mm. The rectangular copper wire was washed and subsequently passed through an annealing furnace (temperature: 600 ° C.) under a reducing atmosphere (hydrogen gas: 30 vol% and argon gas: 70 vol%) (holding time: 0.2 minutes) ) Immediately after that, a copper wire (temperature: 410 ° C.) is plunged into a molten solder bath (temperature of molten solder: 250 ° C.), and the copper wire is pulled up substantially vertically from the solder bath through a turn roll in the solder bath. At the stage where the solder plating layer is formed and solidified, the bobbin is wound around a bobbin (winding diameter (d) of the body portion: 90 mm, heel diameter (D): 180 mm, width between ridges (W): 110 mm). Turned to produce the solar cell lead of the present invention.

  It was visually confirmed that the solar cell lead wire wound around the bobbin produced in Examples 1 and 2 was not deformed in a specific direction even when it was wound from the bobbin.

The occupation ratio of the crystal orientation of the lead wire for solar cell produced in Example 1 and 2 was measured by the EBSD method. The results are shown below.
(EBSD sample making procedure)
The cross section of the lead wire was polished with emery paper, then buffed with alumina, and further mirror finished by electrolytic polishing.
(Measurement method of EBSD method (measurement conditions))
Device name: SEM-EBSD manufactured by Oxford instruments
Count the crystals contained within ± 10 degrees for each orientation.
Counting was performed with data analysis software (INCA Crystal) attached to EBSD.
In addition, using a scanning electron microscope, each measurement point (pixel) within the measurement range on the sample surface is irradiated with an electron beam, and an azimuth difference between adjacent measurement points is determined by orientation analysis by backscattered electron diffraction. The crystal grain boundary was defined between the measurement points at 15 ° or more.

Example 1
Occupancy of crystal orientation <100> ± 10 °: 37 area%
Occupancy of crystal orientation <111> ± 10 °: 41 area%
Occupancy of crystal orientation <101> ± 10 °: 20 area%

(Example 2)
Occupancy of crystal orientation <100> ± 10 °: 35 area%
Occupancy of crystal orientation <111> ± 10 °: 38 area%
Occupancy of crystal orientation <101> ± 10 °: 25 area%

10 Solder-plated copper wire 11 Flat copper wire 12 Solder-plated layer d Winding diameter of body part D Diameter W W Width

Claims (3)

A lead wire for solar cell in which a copper wire is coated with a solder plating layer,
The copper wire is made of pure copper or a copper alloy, and the cross section perpendicular to the length direction is a substantially rectangular shape having a long side and a short side,
In the cross section of the copper wire that is perpendicular to the length direction,
Occupancy ratio of crystal orientation <100> ± 10 ° is 5 area% or more and 50 area% or less,
Occupancy of crystal orientation <111> ± 10 ° is 5 area% or more and 50 area% or less,
Occupancy of crystal orientation <101> ± 10 ° is 5 area% or more and 50 area% or less,
The total of the crystal orientation <100> ± 10 ° occupancy, the crystal orientation <111> ± 10 ° occupancy, and the crystal orientation <101> ± 10 ° occupancy is 100 area% or less. Lead wire for solar cell.   The lead wire for solar cell according to claim 1, wherein 0.2% proof stress is 90 MPa or less.   The lead wire for a solar cell according to claim 1 or 2, wound on a bobbin having a body portion with a winding diameter of 80 to 120 mm, a flange diameter of 150 to 200 mm, and a width between the flanges of 80 to 120 mm. .

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