JP2010283138A - Solar cell lead wire, manufacturing method thereof, and solar cell using the same - Google Patents

Abstract

The present invention provides a lead wire for a solar cell, which has a high cell cracking suppressing effect and a high bonding reliability, and suppresses a decrease in conversion efficiency, a manufacturing method thereof, and a solar cell using the same.
In a solar cell lead wire (or 20) in which molten solder is supplied to the surface of a strip-like conductive material to form molten solder plating layers 13a and 13b, corner portions are chamfered in a cross-sectional shape. The strip-shaped conductive material 12 (or 21) is formed, molten solder is supplied to the upper and lower surfaces of the strip-shaped conductive material 12 (or 21), and the upper and lower molten solder plating layers 13a and 13b (or 22a and 22b) are provided. ) Is formed flat.
[Selection] Figure 1

Description

  The present invention relates to a solar cell lead wire, and in particular, a solar cell lead wire excellent in bondability (strength, short-time bonding, reliability) with a solar battery cell, a manufacturing method thereof, and a solar cell using the same. It is about.

  In solar cells, polycrystalline and single crystal Si cells are used as semiconductor substrates.

  As shown in FIGS. 8A and 8B, the solar cell 100 includes a predetermined region of the semiconductor substrate 102, that is, a front surface electrode 104 provided on the surface of the semiconductor substrate 102 and a back surface provided on the back surface. The solar cell lead wires 103a and 103b are joined to the electrode 105 with solder. The electric power generated in the semiconductor substrate 102 is transmitted to the outside through the solar cell lead wire 103.

  As shown in FIGS. 9A and 9B, a conventional solar cell lead wire 103a (or 103b) includes a strip-shaped conductive material 112 having a rectangular cross-sectional shape and the strip-shaped conductive material. 112 and a molten solder plating layer 113 formed on the upper and lower surfaces of 112. The strip-shaped conductive material 112 is, for example, a strip-shaped conductor formed by rolling a conductor having a circular cross section, and is also referred to as a flat conductor or a flat wire.

  The molten solder plating layer 113 is formed by supplying molten solder to the upper and lower surfaces of the strip-like conductive material 112 by a hot dipping method.

  In the hot dipping method, the upper and lower surfaces 112a and 112b of the strip plate-like conductive material 112 are cleaned by pickling or the like, and the strip plate-like conductive material 112 is passed through a molten solder bath, thereby In this method, solder is laminated on the lower surfaces 112a and 112b. As shown in FIG. 9B, the molten solder plating layer 113 is formed on the side portions in the width direction by the action of surface tension when the molten solder adhering to the upper and lower surfaces 112a and 112b of the strip plate-like conductive material 112 solidifies. It is formed in a so-called mountain shape that swells from the center to the center.

  The conventional solar cell lead wire 103a (or 103b) shown in FIGS. 9A and 9B has a molten solder plating layer 113 swelled in a mountain shape on the upper and lower surfaces 112a and 112b of the strip-like conductive material 112. FIG. Is formed. In this solar cell lead wire 103, since the molten solder plating layer 113 swells in a chevron shape, it is difficult to obtain a stable laminated state when it is wound around a bobbin, and it is likely to collapse. In addition, the lead wire may become entangled due to collapse, and may not be pulled out.

  The solar cell lead wire 103 is cut into a predetermined length, adsorbed by air, moved onto the surface electrode 104 of the semiconductor substrate 102, and soldered to the surface electrode 104 of the semiconductor substrate 102. An electrode strip (not shown) that is electrically connected to the surface electrode 104 is formed on the surface electrode 104 in advance. The surface electrode 104 is brought into contact with the molten solder plating layer 113 of the solar cell lead wire 103a, and soldered and joined in this state. The same applies to the case where the solar cell lead wire 103 b is joined to the back electrode 105 of the semiconductor substrate 102.

  At this time, the solar cell lead wire 103 in FIGS. 9A and 9B has a small contact area with the air adsorption jig and a small adsorption force because the molten solder plating layer 113 swells and becomes uneven. Insufficient, there is a problem of falling when moving. Further, the contact area between the surface electrode 104 and the molten solder plating layer 113 is reduced. When the contact area between the surface electrode 104 and the molten solder plating layer 113 is small, heat conduction from the semiconductor substrate 102 to the molten solder plating layer 113 becomes insufficient, resulting in poor soldering. Generally, in soldering, the solder fillet formed at the end of the lead wire (edge portion) affects the bonding reliability. However, in the lead wire according to the prior art in which the chevron is formed in the width direction of the lead wire, the solder fillet is formed. Can be inadequate. Conversely, if sufficient fillets are to be formed, more bonding time is required. Furthermore, since the bonding area is increased by the amount of fillet formation, there is a concern that the solar light receiving area of the semiconductor substrate 102 is reduced and the power generation efficiency is reduced.

  Further, the contact area between the surface electrode 104 and the molten solder plating layer 113 is small because the solar cell soldered to the surface electrode 104 when the solar cell lead wires 103a and 103b are bonded to the front and back surfaces of the semiconductor substrate 102. A positional misalignment is generated between the lead wire 103a for solar cell and the lead wire 103b for solar cell soldered to the back electrode 105, and the cell misalignment (semiconductor substrate 102 is cracked) due to the misalignment. Since the semiconductor substrate 102 is expensive, cell cracking is not preferable.

  In order to improve the solderability between the surface electrode 104 and the solar cell lead wire 103, a concave portion is formed in the strip-like conductive material 112, and this is hot-plated to fill the concave portion with solder so that the lead wire width There has been proposed a method for preventing the formation of plating chevron in the direction and improving the wiring yield at the time of assembling a solar cell (see, for example, Patent Document 1). Further, a method has been proposed in which the solar cell bonding surface of the strip-shaped conductive material 112 is roughened to obtain a high adhesive force (see, for example, Patent Document 2).

  As shown in FIG. 10, the solar cell lead wire 30 of Patent Document 1 is obtained by forming a concave portion in a strip-shaped conductive material 31 with a roll or the like and then performing hot dipping. When such a solar cell lead wire 30 is soldered to the front surface electrode 104 or the back surface electrode 105 of the semiconductor substrate 102 with the molten solder plating layer 32, the lead wire can be wired with a high yield without positional deviation. Become. Moreover, as shown in FIG. 11, in the solar cell lead wire 50 of Patent Document 2, the solar cell joint surface of the strip-shaped conductive material 51 is roughened by polishing or etching. As a result, the substantial bonding area is increased, so that the solar cell lead wire 50 is firmly bonded to the semiconductor substrate 102, and the durability is excellent.

International Publication WO2004 / 105141 Pamphlet International Publication WO2006 / 128203 Pamphlet

  As described above, according to the solar cell lead wire 30 of Patent Document 1, since the conductive material cross-section is recessed, the molten solder plating layer 32 from the side in the width direction to the center is also flat. Misalignment with respect to the electrodes hardly occurs, and cell cracks due to misalignment hardly occur. However, since more solder stays in the center in the width direction of the conductive material, solder fillet formation at the end of the conductive material is small, and the problem that the module output decreases due to peeling of the lead wire is completely solved in terms of bonding reliability. is not. In addition, according to the solar cell lead wire 50 of Patent Document 2, since the strip plate-like conductive material 51 is roughened, the strip plate-like conductive material 51 and the strip plate-like conductive material 51-solar cell surface electrode. Although the improvement of the joining property with the brazing material such as solder existing between 104 and 105 can be expected, the problem of the reduction of the sunlight receiving area due to the fillet formation has not been solved.

  Since the semiconductor substrate 102 occupies most of the cost of the solar cell, the semiconductor substrate 102 has been considered to be thin. However, the thinned semiconductor substrate 102 is easily warped and cracked when the solar cell lead wire is bonded to the electrode. Cheap. For example, when the thickness of the semiconductor substrate 102 is 200 μm or less, the rate at which cell cracking due to warping or flat wire peeling occurs increases. If the module output is reduced due to cell cracking or peeling of the flat wire due to the solar cell lead wire, the semiconductor substrate 102 cannot be thinned.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and to provide a solar cell lead wire that has a high effect of suppressing cell cracking and has high bonding reliability, minimizes a decrease in the solar light receiving area of the cell, and can be wired in a short time. And a manufacturing method thereof and a solar cell using the same.

  The present invention has been devised to achieve the above object, and the invention of claim 1 is a solar cell lead wire in which a molten solder plating layer is formed by supplying molten solder to the surface of a strip-like conductive material. In which a strip-shaped conductive material having a cross-sectional shape with chamfered corners is formed, molten solder is supplied to the upper and lower surfaces of the strip-shaped conductive material, and the upper and lower molten solder plating layers are formed flat. This is a battery lead wire.

  The invention according to claim 2 is the lead wire for solar cell according to claim 1, wherein the plating temperature is set to the liquidus temperature of the used solder + 120 ° C. or less, and the thickness of the oxide film on the surface of the molten solder plating layer is set to 7 nm or less. It is.

  A third aspect of the present invention is the solar cell lead according to the first or second aspect, wherein the strip-shaped conductive material is a rectangular wire having a volume resistivity of 50 μΩ · mm or less.

  Invention of Claim 4 is a lead wire for solar cells in any one of Claims 1-3 whose 0.2% yield strength value in a tensile test is 90 Mpa or less.

  A fifth aspect of the present invention is the solar cell lead according to any one of the first to fourth aspects, wherein the strip-like conductive material is made of any one of Cu, Al, Ag, and Au.

  According to a sixth aspect of the present invention, the strip-shaped conductive material comprises any one of tough pitch Cu, low oxygen Cu, oxygen free Cu, phosphorus deoxidized Cu, and high purity Cu having a purity of 99.9999% or more. 4. The solar cell lead wire according to claim 4.

  In the invention of claim 7, the molten solder plating layer is selected from Sn solder, Sn as the first component, and Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component. It is a lead wire for solar cells in any one of Claims 1-6 which consists of Sn type solder alloy which contains 0.1 mass% or more of at least 1 element.

  The invention of claim 8 is to form a strip-shaped conductive material having a chamfered corner in the cross section by rolling or dicing the strand, and the strip-shaped conductive material is continuously energized or heated continuously. Heat treatment in a batch-type heating furnace or batch-type heating equipment, and then supply molten solder and solder-plating the strip-shaped conductive material, and the plated strip-shaped conductive material is in a molten state with a flat roll. It is the manufacturing method of the lead wire for solar cells which forms a flat part in a molten solder plating layer by pinching.

  The invention of claim 9 is a solar cell in which the lead wire for solar cell according to any one of claims 1 to 7 is soldered to the front electrode and the back electrode of the semiconductor substrate by the solder of the molten solder plating layer.

  According to the present invention, it is possible to obtain a solar cell lead wire that has a high effect of suppressing cell cracking and high bonding reliability, minimizes a decrease in the solar light receiving area of the cell, and can be wired in a short time. It is effective.

It is a figure of the lead wire for solar cells which shows one Embodiment of this invention, (a) is a top view, (b) is an AA sectional view. In this invention, it is the schematic of the rolling roll used for manufacture of a strip-shaped electroconductive material. It is a figure of the strip | belt-plate-shaped electrically conductive material used as the material of the lead wire for solar cells of FIG. 1, (a) is a top view, (b) is a BB sectional drawing. In this invention, it is the schematic of the hot dipping equipment which forms a hot-dip solder plating layer. It is a figure of the lead wire for solar cells which shows other embodiment of this invention, (a) is a top view, (b) is CC sectional view taken on the line. It is a figure of the strip | belt-plate-shaped electrically conductive material used as the material of the lead wire for solar cells of FIG. 5, (a) is a top view, (b) is DD sectional view taken on the line. The solar cell of this invention is shown, (a) is a top view of a solar cell, (b) is a cross-sectional view. A conventional solar cell is shown, (a) is a top view of the solar cell, and (b) is a cross-sectional view. It is a figure which shows the conventional lead wire for solar cells, (a) is a top view, (b) is EE sectional view taken on the line. It is a cross-sectional view of a conventional solar cell lead wire. It is a cross-sectional view of a conventional solar cell lead wire.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  As shown in FIGS. 1 (a) and 1 (b), a solar cell lead wire 10 according to the present invention is obtained by rolling or dicing a strand in advance to form a cross-sectional shape with four corners chamfered. The strip-shaped conductive material 12 is formed, molten solder is supplied to the upper and lower surfaces of the strip-shaped conductive material 12, and the strip-shaped conductive material 12 plated at the solder bath outlet is melted in a flat state. A flat part is formed on the upper and lower molten solder plating layers 13a and 13b while adjusting the plating thickness with a roll.

  The strip-shaped conductive material 12 is formed, for example, by rolling an element wire (wire having a circular cross section). At this time, in order to obtain a shape in which the four corners of the conductor cross section are chamfered, a rolling roll For example, a rolling roll 14 having the shape shown in FIG. 2 is used. Thereafter, the formed (rolled) conductor is formed by heat treatment in a continuous energizing heating furnace, a continuous heating furnace, or a batch-type heating facility.

  3 (a) and 3 (b) show the strip-like conductive material 12, the upper surface 12a and the lower surface 12b are flat, the side surfaces 12c and 12d form slopes, The shape is just chamfered at the four corners. The end surface 12e is formed by being cut to a suitable length.

  FIG. 4 shows a hot dipping apparatus for forming flat portions in the hot solder plating layers 13a and 13b, and a reversing roller 16 is provided in the solder bath 15 so as to reverse the strip plate-like conductive material 12 and to face upward. A pair of upper and lower rolls 17a, 17b, 18a, 18b is provided above the solder bath 15 located above the roller 16, and a pulling roller 19 is provided above the pair. All the rollers have a flat surface shape.

  The strip-shaped conductive material 12 having the chamfered shape at the four corners of the cross section is immersed in the solder bath 15 so that the solder is supplied to the upper and lower surfaces 12a and 12b, reversed by the reversing roller 16 and directed upward. The plating layer is sandwiched between the rolls 17a and 17b to form a flat portion. By adjusting the position of the core material (Cu) with the upper rolls 18a and 18b, flat portions are formed in the molten solder plating layers 13a and 13b as shown in FIGS. 1 (a) and 1 (b), and the belt plate The solar cell lead wire 10 having a larger amount of solder plating than the flat portion is manufactured at the four corners of the cross section of the conductive material.

  The upper and lower rolls 17a, 17b, 18a, 18b for forming the molten solder plating layers 13a, 13b having flat portions on the strip-like conductive material 12 are the upper and lower surfaces of the strip-like conductive material 12 at the outlet of the plating bath 15. Are arranged so as to sandwich the upper and lower rolls 17a, 17b, 18a, 18b, and finely adjust the distance between the molten solder plating layers 13a, 13b and the cross-sectional shape of the molten solder plating layers 13a, 13b. Can be adjusted.

  FIG. 5 shows another shape of the solar cell lead wire according to the present invention.

  As shown in FIG. 6, the solar cell lead wire 20 in FIG. 5 is processed by using a roll having R shapes at the four corners of the cross section, as shown in FIG. Then, hot-dip solder plating is performed to form hot-dip solder layers 22a and 22b.

  These shapes can be formed by changing the shape of the rolling roll, adjusting the amount of molten solder plating, the distance between the upper and lower rolls 17a, 17b, 18a, and 18b, and the position thereof when the wire is rolled.

  That is, when the molten solder plating layers 13a and 13b (or 22a and 22b) are formed on the upper and lower surfaces of the strip-shaped conductive material 12 (or 21) in the hot-dip plating facility of FIG. 4, the strip-shaped conductive material 12 ( Or 21) is determined by the reversing roller 16 and the pulling roller 19, and the position and interval of the upper and lower rolls 17a, 17b, 18a, 18b are finely adjusted with respect to the path. The layer thickness of the upper molten solder plating layer 13a (or 22a) and the layer thickness of the lower molten solder plating layer 13b (or 22b) can be adjusted and the entire layer thickness can be adjusted. The layer thickness is determined by the interval between the lower rolls 17a and 17b, and the position of the strip-like conductive material 12 (or 21) as the core material is determined by the interval between the upper rolls 18a and 18b.

  The height of the roll with respect to the solder plating furnace is fixed at a position where the solder plating is not completely solidified, so that a flat portion is formed in the solder plating in the molten state. Is not work hardened and its 0.2% proof stress can be kept low.

  As described above, the solar cell lead wires 10 and 20 according to the present invention are provided at the four corners of the conductor cross section so that the semiconductor substrate can be easily installed on the front and back electrodes of the semiconductor substrate and sufficient bonding properties are ensured. Is a chamfered shape, and the amount of molten solder plating in the portion is positively secured. Furthermore, since the flat portions are formed in the plating layers 13a, 13b, 22a, and 22b in the molten state of the solder, the core material is not work-hardened, can maintain a low 0.2% proof stress, and is less likely to warp the cell when connected to the cell. Since cell warpage is unlikely to occur, lead wires are less likely to peel when the cell is warped. In addition, since there is sufficient molten solder at the four corners of the conductor cross section, rapid fillet formation is possible, and bonding with a strong and suppressed solder spread in the conductor width direction after bonding to the front and back electrodes ( Forming a fillet on the conductor chamfered portion).

  In addition, since the molten solder plating layers 13a, 13b, 22a, and 22b are flat, the adhesiveness with the air suction jig is high, and falling during movement is unlikely to occur. Furthermore, since the molten solder plating layers 13a, 13b, 22a, and 22b are flat, a stable laminated state is easily obtained when winding on the bobbin, and the collapse is not likely to occur. Therefore, the problem that the solar cell lead wires are tangled and cannot be pulled out due to the collapse of winding is also solved.

  For the strip-like conductive materials 12 and 21, for example, an element wire (wire material having a circular cross section) having a volume resistivity of 50 μΩ · mm or less is used. By rolling or dicing this strand, the strip-like conductive materials 12 and 21 having a cross-sectional shape as shown in FIGS. 3B and 6B can be obtained.

  The strip-like conductive materials 12 and 21 are made of Cu, Al, Ag, or Au, or tough pitch Cu, low oxygen Cu, oxygen free Cu, phosphorus deoxidized Cu, high purity Cu having a purity of 99.9999% or more. Consists of either.

  As the molten solder plating layers 13a, 13b, 22a, and 22b, Sn-based solder (Sn-based solder alloy) is used. Sn-based solder uses Sn as the first component having the heaviest component weight, and 0.1 mass% of at least one element selected from Pb, In, Bi, Sb, Ag, Zn, Ni, and Cu as the second component. Including the above.

  Next, the operation of the present invention will be described.

  When the solar cell lead wire 10 shown in FIGS. 1A and 1B is joined to the front electrode 44 and the back electrode 45 of the semiconductor substrate 42 shown in FIG. 7, the solar cell lead wire 10 and the semiconductor The heating temperature of the substrate 42 is controlled in the vicinity of the melting point of the solder of the molten solder plating layers 13a and 13b. The reason is that the thermal expansion coefficient of the strip-like conductive material 12 (for example, Cu) of the solar cell lead wire 10 and the thermal expansion coefficient of the semiconductor substrate (Si) are greatly different. The difference in thermal expansion coefficient causes thermal stress that causes warpage and cracks in the semiconductor substrate 42. In order to reduce this thermal stress, the 0.2% yield strength of the lead wire may be reduced. Thereby, when the lead wire heated at the time of bonding is cooled, the compressive stress generated in the cell can be lowered, so that the warpage of the cell is reduced and the peeling of the lead wire caused by the cell warpage can be prevented. Therefore, the 0.2% yield strength of the lead wire is desirably 90 MPa or less. Moreover, in order to reduce the thermal expansion distortion at the time of joining, it is good to perform joining temperature as low as possible. Therefore, the heating temperature of the solar cell lead wire 10 and the semiconductor substrate 42 is controlled to a temperature near the melting point of the solder of the molten solder plating layers 13a and 13b.

  As the heating method at the time of bonding, for example, the semiconductor substrate 42 is placed on a hot plate, and heating from the hot plate and heating from above the solar cell lead wire 10 placed on the semiconductor substrate 42 are used in combination. Is.

  In order to increase the bonding strength between the front electrode 44 and the rear electrode 45 of the semiconductor substrate 42 and the solar cell lead wire 10, the four corners of the cross section of the solar cell lead wire 10 are chamfered, and this is subjected to solder plating. It is preferable that the fillet 13c can be positively formed at the conductor chamfered portion when the front surface electrode 44 and the rear surface electrode 45 of the semiconductor substrate 42 are joined. And in order to prevent peeling of the lead wire due to cell warpage, the 0.2% yield strength of the solar cell lead wire 10 must be 90 MPa or less.

  However, in the conventional solar cell lead wire 30 shown in FIG. 10, since the solder remains in the central portion of the cross section of the lead wire, the fillet formation at the end portion of the lead wire is not sufficient, and the surface electrode 44 of the semiconductor substrate 42 is formed. In addition, since it is difficult to say that the bonding strength between the back electrode 45 and the solar cell lead wire 30 is sufficiently secured, peeling occurs between the solar cell lead wire 30 and the semiconductor substrate 42, and sufficient conduction is achieved. The module output cannot be obtained and the module output is reduced. On the other hand, since the solar cell lead wire 10 of the present invention sufficiently secures the bonding strength between the front electrode 44 and back electrode 45 of the semiconductor substrate 42 and the solar cell lead wire 10, the formation of solder fillets at the end of the lead wire is quick. In addition, the four corners of the cross section of the lead wire are chamfered so that they can be sufficiently formed.

  According to the present invention, uneven thickness of the plating layer that occurs when hot-dipping is performed at high speed can be suppressed by squeezing the molten solder with the rolls 17 and 18, so that a predetermined plating thickness can be formed at a higher speed than before. It is excellent in mass productivity. Moreover, the plating thickness of the four corners of the conductor can be increased by plating with this method. As a result, the present invention can provide a solar cell lead wire 10 that minimizes the reduction in the solar light receiving area of the cell, can be wired in a short time, and has the most effective effects on cell crack suppression and connection reliability. it can. Although the effect of the solar cell lead wire 10 has been described here, the solar cell lead wire 20 can also achieve the same effect.

  Next, Table 1 shows the physical properties of the material of the strip-like conductive materials 12 and 21 used in the present invention.

  The strip-like conductive materials 12 and 21 are preferably materials having a relatively small volume resistivity. As shown in Table 1, Cu, Al, Ag, Au, or the like is used for the strip-like conductive materials 12 and 21.

  Among Cu, Al, Ag, and Au, Ag has the lowest volume resistivity. Therefore, when Ag is used as the strip-like conductive materials 12 and 21, the power generation efficiency of the solar cell using the solar cell lead wires 10 and 20 can be maximized. When Cu is used as the strip-like conductive materials 12 and 21, the solar cell lead wires 10 and 20 can be reduced in cost. When Al is used as the strip-like conductive materials 12 and 21, the solar cell lead wires 10 and 20 can be reduced in weight.

  When Cu is used for the strip-shaped conductive materials 12 and 21, any of tough pitch Cu, low oxygen Cu, oxygen free Cu, phosphorus deoxidized Cu, and high purity Cu having a purity of 99.9999% or more is used as the Cu. Also good. In order to minimize the 0.2% proof stress of the strip-shaped conductive materials 12 and 21, it is advantageous to use Cu having a high purity. Therefore, when high-purity Cu having a purity of 99.9999% or more is used, the 0.2% proof stress of the strip-shaped conductive materials 12 and 21 can be reduced. When tough pitch Cu or phosphorus deoxidized Cu is used, the solar cell lead wires 10 and 20 can be reduced in cost.

  The solder used for the molten solder plating layers 13a and 13b is selected from Sn-based solder or Sn as the first component and Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component. An Sn-based solder alloy containing 0.1 mass% or more of at least one element can be used. These solders may contain a trace element of 1000 ppm or less as the third component.

  Next, the manufacturing method of the lead wire 10 for solar cells of this invention is demonstrated.

  First, by rolling a wire rod (not shown) having a circular cross section as a raw material using a rolling roll 14 as shown in FIG. Form. This strip-like conductive material 12 is heat-treated in a continuous energizing heating furnace, a continuous heating furnace, or a batch type heating facility. Thereafter, a molten solder is supplied using a hot dipping equipment as shown in FIG. 4 to form flat portions in the hot solder plated layers 13a and 13b.

  As a processing method for processing the raw material into the strip-like conductive material 12, both rolling and dicing are applicable. Rolling is a method of rolling a round wire to obtain a predetermined cross-sectional shape. When a strip-shaped conductive material is formed by rolling, a long and uniform cross-sectional shape in the longitudinal direction can be formed. Die drawing is a processing method in which a round wire is passed through a die having a desired cross-sectional shape, and this processing method can also form a long and uniform cross-sectional shape in the longitudinal direction. In any of the processing methods, the strip plate-shaped conductive material 12 is shaped using a rolling roll, a die or the like in which the four corners of the cross section are chamfered.

  By heat-treating the strip-shaped conductive material 12, the softening characteristics of the strip-shaped conductive material 12 can be improved. Improving the softening characteristics of the strip-shaped conductive material 12 is effective in reducing the 0.2% proof stress. Examples of the heat treatment method include continuous energization heating, continuous heating, and batch heating. For continuous heat treatment over a long length, continuous energization heating and continuous heating are preferred. Batch heating is preferred when stable heat treatment is required. From the viewpoint of preventing oxidation, it is preferable to use a furnace having an inert gas atmosphere such as nitrogen or a hydrogen reducing atmosphere.

  A furnace having an inert gas atmosphere or a hydrogen reduction atmosphere is provided by a continuous energizing heating furnace, a continuous heating furnace, or a batch heating facility.

  Here, although the manufacturing method of the lead wire 10 for solar cells was described, the lead wire 20 for solar cells is obtained by the same manufacturing method except using the rolling roll and die | dye whose cross-sectional four corner parts become R shape.

  Next, the solar cell of the present invention will be described in detail.

As shown in FIG. 7A and FIG. 7B, the solar cell 40 of the present invention has the above-described solar cell lead wire 10 formed on the semiconductor substrate 42 by soldering the molten solder plating layers 13a and 13b. It is joined to the front electrode 44 and the back electrode 45. However, in the case of solder bonding, it is desirable that the oxide film thickness on the surface of the solder plating is 7 nm or less. In general, when the thickness of the oxide film exceeds 7 nm, it becomes difficult to remove the oxide film when the solar cell lead wires are soldered to the electrodes 44 and 45 on the cell. Insufficient soldering. The thickness of the oxide film can be defined by, for example, the time during which the oxygen peak value is reduced by half in the depth profile obtained by Auger analysis, with the sputtering rate converted to SiO ₂ . As a method of setting the oxide film thickness on the surface of the solder plating to 7 nm or less, there is a method in which the plating temperature is set to the liquidus temperature of the used solder + 120 ° C. or less to perform hot dipping.

  Since the flat portions are formed in the molten solder plating layers 13a and 13b that serve as the joint surfaces between the solar cell lead wire 10 and the surface electrode 44, the solar cell lead wire 10 is formed on the electrodes 44 and 45 of the semiconductor substrate 42. The position is stable and displacement is prevented. Further, since the four corners of the cross section of the strip-like conductive material 12 are chamfered at the end portion of the solar cell lead wire 10, there is sufficient solder, and a sufficient fillet 13c is made larger than the lead width. It can be formed without spreading, which is advantageous for securing the bonding strength and suppressing the increase of the lead wire bonding area. In addition, since the 0.2% proof stress of the solar cell lead wire 10 is reduced, the semiconductor substrate 42 is less likely to warp during bonding, and the lead wire is less likely to peel due to warpage.

  According to the solar cell 40 of the present invention, it is possible to ensure the bonding strength between the solar cell lead wire 10 and the semiconductor substrate 42 and to suppress the increase in the bonding area, and to suppress cell cracking during bonding. It is possible to improve the output of the solar cell (improve the conversion efficiency) and improve the yield and the junction reliability. Here, the solar cell 40 using the solar cell lead wire 10 has been described, but the same effect can be obtained even with a solar cell using the solar cell lead wire 20.

Example 1
A Cu material, which is a raw material conductive material, was rolled to form a rectangular strip-shaped conductive material 12 having a width of 1.0 mm, a thickness of 0.2 mm, and a chamfering width of 0.1 mm at each corner of the transverse section. The strip-shaped conductive material 12 is heat-treated in a continuous heating furnace, and Sn-3% Ag-0.5% Cu solder plating is applied around the strip-shaped conductive material 12 using a hot dipping apparatus shown in FIG. As a result, molten solder plating layers 13a and 13b having flat portions on the upper and lower surfaces of the strip-shaped conductive material 12 were formed (the conductor was heat-treated Cu). Thus, the solar cell lead wire 10 shown in FIGS. 1A and 1B was obtained. The 0.2% proof stress was obtained from the SS curve obtained in the tensile test at a tensile speed of 100 mm / min, and divided by the cross-sectional area of the core material (Cu) to obtain a 0.2% proof stress, which was 60 MPa. .

(Example 2, Comparative Examples 1, 2, and 3)
Example 2 was rolled using a strip-shaped conductive material 21 in which the four corners of the cross section of the solar cell lead wire 10 of Example 1 had an R chamfered shape, and Comparative Example 1 was rolled using a roll having a concave shape in the center of the cross section. In Comparative Example 2, the strip-shaped conductive material has a cross-sectional shape as it is, and in Comparative Example 3, the upper and lower surfaces of the strip-shaped conductive material are roughened by polishing and heat-treated in a continuous heating furnace (implemented) Example 2 and Comparative Examples 1, 2 and 3 were heat-treated at the same temperature as in Example 1), and Sn-3% Ag-0.5% around the strip-like conductive material using the hot dipping apparatus shown in FIG. In Cu solder plating, Example 2 and Comparative Examples 1 and 3 use the same flat processing roll as in Example 1, and Comparative Example 2 performs solder plating without using any roll, and the upper and lower surfaces of the strip-like conductive material. In addition, a molten solder plating layer (the four corners of Examples 1 and 2 and the recesses of Comparative Example 1, comparison 2 central, to form a plating thickness 40 [mu] m) of the end and central portions of the Comparative Example 3 (conductor heat treatment Cu). As described above, the lead wire for solar cell shown in FIG. 1 for Example 1, FIG. 5 for Example 2, FIG. 10 for Comparative Example 1, FIG. 9 for Comparative Example 2, and FIG. The 0.2% proof stress was 60 MPa in all cases.

  An appropriate amount of a rosin-based flux is applied to the solar cell lead wires of Examples 1 and 2 and Comparative Examples 1, 2, and 3, and each solar cell lead wire is 150 mm long × 150 mm wide × 180 μm thick semiconductor substrate ( It was placed on the electrode part on the upper surface of the (Si cell) and hot plate heated (held at 260 ° C. for 30 seconds) with a 10 g weight placed thereon and soldered. The state of peeling of the lead wire, the state of carrying the lead wire, and the state of wetting and spreading of the solder, which were caused by the influence of the cell warp generated during the joining, were investigated.

  Table 2 shows the evaluation results of Examples 1 and 2 and Comparative Examples 1, 2, and 3.

  The column of “conductive material cross-sectional shape” in Table 2 shows the cross-sectional shape of the strip-shaped conductive material before solder plating. The “cross-sectional shape” column indicates which cross-sectional shape is shown in the figure. The column of “solder wetting spreadability” indicates the ratio of the spread width of the solder to the lead wire width at the time of completion of soldering. The column “Conductive material transportability” shows the success rate (transport without dropping) when a certain number of lead wires are sucked with vacuum tweezers after being cut to a standard length and transported for a certain distance. The ratio when 1 is set to 100 is indicated by ◯, 95% or more is indicated by ○, and less than 95% is indicated by ×. In the column of “Joint strength”, a peel test was performed after joining the lead wire and the cell. When the strength of Example 1 was set to 100, 90% or more was given as ◯ and less than 90% was taken as x. In the column of “mass production cost”, the cost for conventional hot dipping is 1.0, and the case where the manufacturing cost is less than 1.2 is given as ◯ and the case where it exceeds 1.5 is given as x.

  As shown in Table 2, it was confirmed that the solar cell lead wires 10 and 20 of Examples 1 and 2 had low 0.2% proof stress and little cell warpage. In addition, since the four corners are chamfered in the cross-section of the conductive material, it can be confirmed that the bonding state with the electrode part on the upper surface of the semiconductor substrate (Si cell) is good and that the spread of solder is suppressed. It was. In the production of the conductive material, it is only necessary to change the roll shape at the time of rolling. Therefore, the mass production cost is almost the same as that of the conventional solder plating wire, which is an industrially excellent method.

  On the other hand, even in the same plating process as in Examples 1 and 2, in Comparative Example 1 having a different cross-sectional shape of the conductive material, the bonding strength was inferior even though the conductive material transportability was good. . In Comparative Example 2, the cross-sectional shape is convex at the center, so that the conductive material transportability and bonding strength are inferior to those of Example 1. Also, the solder wetting spread is larger than other examples. In Comparative Example 3, the bonding strength was sufficiently ensured, but the solder spread was increased.

  As described above, from the evaluation results of Examples 1 and 2 and Comparative Examples 1, 2, and 3, the solar cell lead wires 10 and 20 of the present invention greatly improve the junction reliability while suppressing the area occupied by the junction with the cell. Confirmed to do. In addition, although the shape which chamfered four corners in the cross section of a electrically conductive material is used in the Example, it is not limited to this, When applying to the back surface wiring used for what is called a back contact type photovoltaic cell Chamfers two corners facing the solar cell electrode in the longitudinal direction without chamfering two corners located away from the solar cell electrode among the four corners of the cross section of the conductive material. By doing so, the effects of the present invention can be sufficiently achieved.

10, 20 Solar cell lead wires 12, 21 Strip plate-like conductive materials 13a, 13b, 22a, 22b Molten solder plating layer

Claims (9)

  In a solar cell lead wire in which molten solder is supplied to the surface of a strip-shaped conductive material to form a molten solder plating layer, a strip-shaped conductive material having a cross-sectional shape with chamfered corners is formed, and the strip A lead wire for a solar cell, wherein molten solder is supplied to the upper and lower surfaces of the electrode-like conductive material, and the upper and lower molten solder plating layers are formed flat.   2. The solar cell lead wire according to claim 1, wherein the plating temperature is set to a liquidus temperature of the used solder + 120 ° C. or less, and the thickness of the oxide film on the surface of the molten solder plating layer is set to 7 nm or less.   The lead wire for solar cell according to claim 1 or 2, wherein the strip-shaped conductive material is a flat wire having a volume resistivity of 50 µΩ · mm or less.   The lead wire for solar cell according to any one of claims 1 to 3, wherein a 0.2% proof stress value in a tensile test is 90 MPa or less.   The solar cell lead according to any one of claims 1 to 4, wherein the strip-shaped conductive material is made of any one of Cu, Al, Ag, and Au.   The said strip | belt-plate-shaped electrically-conductive material consists of either tough pitch Cu, low oxygen Cu, oxygen free Cu, phosphorus deoxidation Cu, and high purity Cu of purity 99.9999% or more. Lead wire for solar cell.   The molten solder plating layer uses Sn-based solder or Sn as the first component and at least one element selected from Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component is 0. The lead wire for a solar cell according to any one of claims 1 to 6, wherein the lead wire is made of an Sn-based solder alloy containing 0.1 mass% or more.   A strip-shaped conductive material having a chamfered cross-sectional corner is formed by rolling or dicing the strand, and the strip-shaped conductive material is continuously heated by heating, continuous heating, or batch heating. Heat treatment in equipment, then supplying molten solder and solder plating on the strip-shaped conductive material, and by sandwiching the plated strip-shaped conductive material with a flat roll in the solder molten state, molten solder plating The manufacturing method of the lead wire for solar cells characterized by forming a flat part in a layer.   A solar cell, wherein the lead wire for a solar cell according to any one of claims 1 to 7 is soldered to a front electrode and a back electrode of a semiconductor substrate with solder of a molten solder plating layer.

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