JP2007141621A - Lead wire for solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead wire for solar battery damaging no conductivity, preventing warp and crack of a cell after soldering, free from breakage even when receiving stress repeatedly. <P>SOLUTION: The lead wire is composed of a tape-shaped main body 16 formed by annealing electrolytic copper foil, and a solder plated layer 18 formed on a surface of the main body. By this constitution, the main body 16 has very low bearing load, and easily deformed by small stress. Moreover, indentation 22 formed on a deposition face 24 of the main body 16 preforms as if it is a cushion, apparent elasticity is reduced. Bending stress added to a cell 12 accompanied by thermal contraction of the lead wire 10 in cooling after soldering is thereby relaxed, and the cell 12 of the solar battery is prevented from warp and crack. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lead wire that electrically connects cells of a solar cell module and extracts current.

  Generally, a solar cell module is formed by electrically connecting cells made of a single crystal or polycrystalline silicon substrate with lead wires.

  In a conventional solar cell, a solder wire is applied to a rectangular copper wire having a width of 1 to 3 mm obtained by slitting a rolled copper foil having a thickness of 0.05 to 0.2 mm as a lead wire for connecting cells. When this lead wire is joined to a solar cell, the lead wire and the cell are heated to melt the solder plating provided on the surface of the lead wire, and then, these are brought into close contact with each other. I was trying to cool.

  Here, since the linear expansion coefficient of the flat copper wire constituting the lead wire is much larger than the linear expansion coefficient of the silicon substrate constituting the cell of the solar battery, the lead wire welded to the surface of the cell is cooled. The lead wire extended by heating shrinks and bending stress is applied to the cell. As a result, the cell in which the lead wire is welded is warped, and in the worst case, the cell is cracked. Such a problem has been recognized as more prominent with the shift to lead-free solder having a high melting temperature and the progress of thinning of the cell.

  As a technique that can solve such a problem, a technique has been proposed in which a lead wire is formed by a twisted wire and this lead wire is point-joined at a plurality of locations in a cell (for example, see Patent Document 1).

According to this technique, the influence of expansion and contraction due to thermal expansion when welding the lead wire is reduced in the longitudinal direction of the lead wire, and the warpage of the cell can be reduced. Further, the warp of the cell can be reduced more effectively by joining the lead wire and the cell at a plurality of points.
Japanese Patent Laid-Open No. 11-251613

  However, the above-described technique has a problem in that the current flow from the cell to the lead wire is deteriorated because there are few contacts between the cell and the lead wire.

  In addition, since solar cells are installed outdoors during use and are always exposed to changes in solar radiation and temperature, the lead wires naturally undergo repeated heat expansion and contraction in response to thermal history due to solar radiation and temperature changes. It becomes like this. For this reason, when a lead wire is formed by twisting together fine wires, the fine wire subjected to the stretching stress breaks and repeats fine thermal expansion and contraction for a long period of time, and the electrical resistance increases (i.e., conductivity is impaired). There is a risk of becoming. Further, in the above-described technology, since there are few contacts between the cell and the lead wire, if such fine expansion and contraction is repeated for a long time, the contact point between the cell and the lead wire is broken, and a current does not flow to the lead wire. Is also a concern.

  In addition, there is a problem that it takes time to manufacture the lead wire and to join the lead wire and the cell, and the solar cell cannot be manufactured economically.

  Therefore, the main problem of the present invention is that it is possible to prevent warping and cracking of a cell after soldering, and it does not break even when subjected to repeated stress, and does not impair electrical conductivity. Is to provide lead wires.

  The invention described in claim 1 is a solar cell lead wire 10 for electrically connecting the cells 12 of the solar cell module 14, “the tape-shaped main body 16 formed by annealing the electrolytic copper foil 34, The solar cell lead wire 10 is characterized by comprising a solder plating layer 18 provided on the surface of the main body 16.

  Moreover, the invention described in claim 2 relates to a method for manufacturing the solar cell lead wire 10 described in claim 1, in which “plated copper is electrodeposited on the rotating drum 30 serving as a cathode and then peeled off. The obtained electrolytic copper foil 34 is cut into a tape shape with a predetermined width and then annealed in a non-oxidizing atmosphere, or the electrolytic copper foil 34 is annealed in a non-oxidizing atmosphere and then taped with a predetermined width. The main body 16 is formed by cutting it into a shape, and thereafter, the main body 16 is immersed in a solder bath to form a solder plating layer 18 on the surface of the main body 16 ".

  In these inventions, the main body 16 of the solar cell lead wire 10 is formed by annealing an electrolytic copper foil 34 formed by growing and precipitating copper crystal grains in a substantially rod shape in the thickness direction. Therefore, the proof load (that is, the load when the main body 16 changes from elastic deformation to plastic deformation) is extremely low. For this reason, it can be easily plastically deformed with less stress.

  Further, the electrolytic copper foil 34 constituting the main body 16 has a smooth glossy surface 20 (commonly referred to as an S surface) formed by transferring the surface shape of the rotary drum 30 on one surface, but the other surface is made of copper. A precipitation surface 24 (commonly referred to as M-plane) is formed in which the irregularities 22 remain when crystal grains are precipitated. For this reason, as for the main body 16, the unevenness | corrugation 22 formed in the precipitation surface 24 can work like a cushion, and can reduce an apparent elasticity modulus.

  Therefore, in the solar cell lead wire 10 configured as described above, when the lead wire 10 is welded (soldered) to the surface of the cell 12 by heating and melting the solder 18a of the solder plating layer 18, the main body 16 is Although it is thermally expanded by heating, it undergoes plastic deformation beyond the elastic deformation region due to the expansion stress during thermal expansion. Further, the apparent elastic modulus of the main body 16 is low. Therefore, the bending stress applied to the cell 12 with the thermal contraction of the lead wire 10 during cooling after cooling (in other words, the tension in the contraction direction on the surface of the cell 12 on which the lead wire 10 is soldered). ) Can be mitigated, and warpage and cracking of the solar cell 12, more specifically, the solar cell module 14 can be prevented.

  Further, the electrolytic copper foil 34 constituting the main body 16 has a smooth glossy surface 20 on one surface as described above, and a precipitation surface 24 having irregularities 22 on the other surface. When the lead wire 10 and the cell 12 are soldered so that the deposition surface 24 side of the main body 16 faces the cell 12 of the solar cell module 14 through the plating layer 18, the lead effect is caused by the anchor effect of the unevenness 22 in the deposition layer 24. The line 10 and the cell 12 can be firmly bonded.

  Furthermore, since the solar cell lead wire 10 of the present invention can join the solar cell 12 and the lead wire 10 with a large surface area, the junction reliability can be improved and the cell 12 can be improved. Current can flow smoothly from the lead wire 10 toward the lead wire 10.

  The solar cell lead wire 10 of the present invention has a uniform cross-sectional area in the width direction at any position in the longitudinal direction, and therefore breaks when repeatedly subjected to stress by repeated thermal expansion and contraction. In addition, there is no loss of conductivity in the longitudinal direction through which electricity flows.

  According to the present invention, since the main body of the solar cell lead wire is made of annealed electrolytic copper foil, the main body has an extremely low proof load and can be easily plastically deformed with a small amount of stress. In addition, the unevenness formed on the deposition surface of the main body works like a cushion, and the apparent elastic modulus can be lowered. For this reason, the bending stress given to a cell with the thermal contraction of the lead wire at the time of cooling after soldering can be relieved, and the curvature and the crack of the cell of a solar cell can be prevented.

  In addition, the cells of the solar battery and the lead wires can be joined to each other with a large surface area, so that the joining reliability can be improved and a current can smoothly flow from the cells toward the lead wires.

  Furthermore, since the cross-sectional area in the width direction of the solar cell lead wire according to the present invention is almost uniform at any position in the longitudinal direction, it breaks even when subjected to repeated stress by repeated thermal expansion and contraction. In addition, there is no loss of conductivity in the longitudinal direction through which electricity flows.

  Therefore, it is possible to prevent warping and cracking of a cell after soldering, more specifically, a solar cell module, and it does not break even when subjected to repeated stress, and does not impair electrical conductivity. Lead wires can be provided.

  Hereinafter, the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, the solar cell lead wire 10 of the present invention (hereinafter simply referred to as “lead wire 10”) electrically connects the cells 12 made of a single crystal or polycrystalline silicon substrate. The solar cell module 14 is connected to take out current from the cell 12.

  FIG. 3 is a longitudinal sectional view showing the lead wire 10 according to the embodiment of the present invention. As shown in this figure, the lead wire 10 of the present invention is generally composed of a main body 16 and a solder plating layer 18.

  The main body 16 is a long member (wire material) obtained by annealing a tape-shaped member obtained by cutting a copper foil 34 (see FIG. 4) having a thickness of 50 to 300 μm with a predetermined width.

  As described above, the thickness of the main body 16 is preferably in the range of 50 to 300 μm, more preferably in the range of 70 to 250 μm. When the thickness of the main body 16 is less than 50 μm, the conductivity of the main body 16 is deteriorated. Conversely, when the thickness is larger than 300 μm, the conductivity is improved, but the electrolytic copper foil constituting the main body 16 is improved. This is because the manufacturing of the solar cell module 14 is difficult and the flexibility (flexibility) of the main body 16 is lowered, and the workability at the time of manufacturing the solar cell module 14 is deteriorated.

  Moreover, it is preferable that the width | variety of the main body 16 shall be the range of 1-5 mm, More preferably, it is the range of 2-4 mm. When the width of the main body 16 is less than 1 mm, the main body 16 may be disconnected due to the heat cycle when the solar cell module 14 is manufactured or when the solar cell is used. This is because the light receiving area of 12 decreases and the power generation efficiency decreases.

  Since the main body 16 is composed of the electrolytic copper foil 34 as described above, a smooth glossy surface 20 (commonly referred to as S surface) to which the surface shape of the rotary drum 30 (described later) is transferred is provided on one surface. ) And a precipitation surface 24 (commonly referred to as an M surface) is formed on the other surface facing the glossy surface 20, with the irregularities 22 remaining when copper crystal grains precipitate.

  The solder plating layer 18 is a layer having a thickness of about 10 to 40 μm obtained by plating the solder 18 a on the surface of the main body 16. The solder 18a constituting the solder plating layer 18 may be any one of a Pb—Sn eutectic composition used conventionally and a lead-free type whose demand is increasing in recent years.

  Examples of the method for forming the solder plating layer 18 on the surface of the main body 16 include a method in which the main body 16 is immersed in a solder bath in which the solder 18a is dissolved.

  When manufacturing the lead wire 10 configured as described above, first, an electrolytic copper foil that constitutes the main body 16 is manufactured by an electrowinning method using a manufacturing apparatus 26 as shown in FIG. Specifically, a rotating drum 30 made of titanium or stainless steel serving as a cathode is immersed in an electrolytic solution W such as an aqueous copper sulfate solution accommodated in the electrolytic solution tank 28, and lead or lead is formed along the peripheral surface of the rotating drum 30. An anode 32 made of an insoluble material is provided. Then, electric power is supplied between the electrodes while rotating the rotary drum 30. Then, since copper crystal grains grown in a substantially rod shape in the thickness direction are deposited on the surface of the rotary drum 30, the electrolytic copper foil 34 is completed by continuously peeling and winding the deposited copper. . Here, the current density between the electrodes and the rotation speed of the rotating drum are adjusted so that the thickness of the obtained electrolytic copper foil 34 is in the range of 50 to 300 μm.

  Subsequently, the obtained electrolytic copper foil 34 is slit (width-cut) so as to have a width in the range of 1 to 5 mm, and formed into a tape shape. This is formed into a non-oxidizing atmosphere (for example, a nitrogen atmosphere, an argon atmosphere, and one). It is placed in a heat treatment furnace having a carbon oxide atmosphere or the like, and is kept at a temperature of 350 ° C. to 500 ° C. for a predetermined time and annealed. Thereby, the main body 16 of the lead wire 10 is completed.

  Then, the lead body 10 is completed by immersing the obtained main body 16 in a solder bath to form a solder plating layer 18 having a thickness of about 10 to 40 μm on the surface of the main body 16.

  When joining the cells 12 using the lead wire 10 manufactured by the above method, as shown in FIG. 2, the lead wire 10 is disposed so as to be in close contact with a predetermined position on the front surface or the back surface of the cell 12. Using a heating means such as hot air, the lead wire 10 is heated so as to have a temperature equal to or higher than the melting temperature of the solder 18a. Then, the solder 18a of the solder plating layer 18 is melted, and the melted solder 18a is connected to the surface of the main body 16 of the lead wire 10 and the surface (or back surface) of the cell 12. Then, the molten solder 18a cools the main body 16 and the cell 12 in a state where they are cooled, so that the solder 18a is solidified, and the cells 12 are joined to each other using the lead wire 10 (between the lead wire 10 and the cell 12). Joining) is completed.

Here, the linear expansion coefficient [17 × 10 ⁻⁶ (/ ° C.)] of copper (Cu) constituting the main body 16 of the lead wire 10 is equal to the linear expansion coefficient [7.6 of silicon (Si) constituting the cell 12. × 10 ⁻⁶ (/ ° C.)], the lead wire 10 and the cell 12 soldered in the expanded state due to heating are cooled, and the bending stress ( In other words, it is considered that a tension in the contraction direction on the surface of the cell 12 on the side where the lead wire 10 is soldered is given.

  However, in the lead wire 10 of the present embodiment, the main body 16 is obtained by annealing the electrolytic copper foil 34 formed by growing and precipitating copper crystal grains in a substantially needle shape or substantially rod shape in the thickness direction. Since it comprises, the proof load is very low. For this reason, it can be easily plastically deformed with less stress.

  The electrolytic copper foil 34 constituting the main body 16 has a smooth glossy surface 20 formed by transferring the surface shape of the rotary drum 30 on one surface, but copper crystal grains are deposited on the other surface. A precipitation surface 24 is formed on which irregularities 22 remain. For this reason, as for the main body 16, the unevenness | corrugation 22 formed in the precipitation surface 24 can work like a cushion, and can reduce an apparent elasticity modulus.

  Therefore, in the lead wire 10 configured as described above, when the lead wire 10 is welded (soldered) to the surface of the cell 12 by heating and melting the solder 18a of the solder plating layer 18, the main body 16 is heated. Although it thermally expands, it undergoes plastic deformation beyond the elastic deformation region due to expansion stress during thermal expansion. Further, the apparent elastic modulus of the main body 16 is low. Therefore, when it is subsequently cooled, the bending stress applied to the cell 12 as the lead wire 10 is thermally contracted during cooling (in other words, the tension in the shrinking direction on the surface of the cell 12 on which the lead wire 10 is soldered). ) Can be mitigated, and warpage and cracking of the solar cell 12, more specifically, the solar cell module 14 can be prevented.

  Further, the electrolytic copper foil 34 constituting the main body 16 has a smooth glossy surface 20 on one surface as described above, and a precipitation surface 24 having irregularities 22 on the other surface. When the lead wire 10 and the cell 12 are soldered so that the deposition surface 24 side of the main body 16 faces the cell 12 of the solar cell module 14 through the plating layer 18, the lead effect is caused by the anchor effect of the unevenness 22 in the deposition layer 24. The line 10 and the cell 12 can be firmly bonded. For this reason, when the cells 12 and the lead wires 10 are arranged in the state as shown in FIG. 2 and are soldered by heating from the upper surface side of the drawing, the deposition surface 24 of the main body 16 faces the upper side of the drawing. If arranged in this way, the cell 12 and the lead wire 10 can be joined with sufficient strength even on the opposite side of the heat source (that is, the lower side in FIG. 2). That is, by appropriately adjusting the surface of the lead wire 10 in contact with the cell 12, the cell 12 and the lead wire 10 can be joined (soldered) in an optimum state according to the manufacturing method and the required joining strength. it can.

  Furthermore, since the solar cell lead wire 10 of the present invention can join the solar cell 12 and the lead wire 10 with a large surface area, the junction reliability can be improved and the cell 12 can be improved. Current can flow smoothly from the lead wire 10 toward the lead wire 10.

  The solar cell lead wire 10 of the present invention has a uniform cross-sectional area in the width direction at any position in the longitudinal direction, and therefore breaks when repeatedly subjected to stress by repeated thermal expansion and contraction. In addition, there is no loss of conductivity in the longitudinal direction through which electricity flows.

  In the above example, when the main body 16 is manufactured, the electrolytic copper foil 34 is cut into a tape shape with a predetermined width and then annealed in a non-oxidizing atmosphere. After annealing in a non-oxidizing atmosphere, it may be cut into a tape shape with a predetermined width. In the method of annealing after cutting the electrolytic copper foil 34, the cut portion of the electrolytic copper foil 34, that is, the longitudinal end of the main body 16 is not work hardened, and the oil of the cutting blade does not remain in the main body 16. Therefore, the main body 16 can be efficiently manufactured by the method of cutting the width after the electrolytic copper foil 34 is annealed.

  Moreover, in the above-mentioned example, the case where the manufactured electrolytic copper foil 34 is directly annealed or cut into pieces has been shown. However, before these treatments, a fine copper lump is formed on at least the surface of the electrolytic copper foil 34 on the precipitation surface 24. You may make it perform the roughening process which forms. By performing such a treatment, the lead wire 10 and the cell 12 can be bonded more firmly, and the apparent elastic modulus can be further lowered.

  EXAMPLES Hereinafter, although an Example is shown and this invention is explained in full detail further, this invention is not limited to an Example.

[Example 1]
An electrolytic copper foil having a thickness of 175 μm was prepared, and this was cut into a rectangular wire having a width of 2 mm with a slitter and wound into a coil. Next, the rectangular wire wound in a coil shape was put into a heat treatment furnace, and annealed by holding at 450 ° C. for 4 hours in a nitrogen atmosphere to form a main body. The main body was immersed in a Sn-2.8% Ag-0.5% Cu lead-free solder bath to form a 40 μm thick solder plating layer on the surface of the main body, thereby completing a lead wire.

  And about the obtained lead wire, "cell curvature", "electric resistance", "proof load", and "tensile load" were measured.

  “Cell warpage” was measured by the following method. That is, the obtained lead wire is placed on a square Si plate (cell) having a thickness of 250 μm and a side length of 15 cm, and in this state, hot air of 270 ° C. is blown to solder the lead wire to the cell. I attached. Then, the cell with lead wires after cooling was placed on a surface plate, and the rising of the cell edge was measured to obtain “cell warpage”.

  The “proof load” is a load when the lead wire (specifically, the main body) changes from elastic deformation to plastic deformation, that is, a load at the “yield point”.

  The obtained results are shown in Table 1.

[Comparative Example 1]
A lead wire was completed in the same manner as in Example 1 except that annealing was not performed. And about the obtained lead wire, the curvature of a cell, the electrical resistance, and the tensile load were measured by the same method as what was described in Example 1. FIG. The obtained results are shown in Table 1.

[Comparative Example 2]
A lead wire was completed in the same manner as in Example 1 except that an annealed copper wire having a thickness of 175 μm and a width of 2 mm (a product obtained by annealing a rolled product) was used as the main body. And about the obtained lead wire, the curvature of a cell, the electrical resistance, and the tensile load were measured by the same method as what was described in Example 1. FIG. The obtained results are shown in Table 1.

  As shown in Table 1, the lead wire of the example has an extremely low proof load compared with those of Comparative Examples 1 and 2, although the “electric resistance” and the “tensile load” are almost the same. It can be seen that “cell warpage” can be significantly reduced.

It is a perspective view which shows the outline of the solar cell module using the lead wire of this invention. It is a perspective view which shows the junction structure of the lead wire of this invention, and a photovoltaic cell. It is sectional drawing which shows the lead wire of one Example of this invention. It is the schematic which shows the manufacturing apparatus of the electrolytic copper foil which comprises a main body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Lead wire 12 ... (Solar cell) cell 14 ... Solar cell module 16 ... Main body 18 ... Solder plating layer 18a ... Solder 20 ... Glossy surface 22 ... Concavity / convexity 24 ... Precipitation surface 26 ... (Electrolytic copper foil) manufacturing apparatus

Claims (2)

A solar cell lead wire for electrically connecting cells of a solar cell module,
A lead wire for a solar cell, comprising: a tape-like main body formed by annealing electrolytic copper foil; and a solder plating layer provided on the surface of the main body. Electrodeposited plated copper on a rotating drum that is a cathode, and after stripping the electrolytic copper foil obtained by peeling it into a tape shape with a predetermined width, it was annealed in a non-oxidizing atmosphere, or After annealing the electrolytic copper foil in a non-oxidizing atmosphere, the main body is formed by cutting into a tape shape with a predetermined width,
Thereafter, a method for producing a lead wire for a solar cell, wherein the main body is immersed in a solder bath to form a solder plating layer on the surface of the main body.