JP5407061B2 - Solar cell lead, manufacturing method thereof, and solar cell using the same - Google Patents

Description

  The present invention relates to a solar cell lead, and more particularly to a solar cell lead having a high cell crack suppression effect, a method for manufacturing the same, and a solar cell using the same.

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

  As shown in FIGS. 6A and 6B, 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 FIG. 7, the conventional solar cell lead wire 103 includes a strip plate conductive material 112 and a molten solder plating layer 113 formed on the upper and lower surfaces of the strip plate conductive material 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. 7, the molten solder plating layer 113 is formed from the side in the width direction to the center by the action of surface tension when the molten solder adhering to the upper and lower surfaces 112 a and b of the strip plate-like conductive material 112 solidifies. It is formed into a so-called mountain shape that swells over.

  In the conventional lead wire 103 for a solar cell shown in FIG. 7, a molten solder plating layer 113 swelled in a mountain shape is formed on the upper and lower surfaces 112 a and 112 b of the strip plate-like conductive material 112. 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. The lead wire may become entangled due to unwinding and may not be pulled out.

  The solar cell lead wire 103 is cut to a predetermined length, adsorbed with 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 soldering is performed in this state. The same applies to the case where the solar cell lead wire 103 b is soldered to the back electrode 105 of the semiconductor substrate 102.

  At this time, since the molten solder plating layer 113 swells and becomes uneven in thickness, the solar cell lead wire 103 in FIG. 7 has a small contact area with the air suction jig and has insufficient suction force, and drops when moving. There is a problem to do. 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.

  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 solve the problem that the contact area between the surface electrode 104 and the molten solder plating layer 113 is small, a concave surface is formed on the lower surface of the strip-like conductive material, and molten solder is supplied to the concave surface to form a molten solder plating layer. A method of forming it flat has been proposed (Patent Document 1).

  As shown in FIG. 8, the solar cell lead wire 203 of Patent Document 1 uses a strip-shaped conductive material 212 having a concave surface on the lower surface 212b. The upper surface 212a of the strip-shaped conductive material 212 is a convex surface or a flat surface. In this way, the molten solder plating layers 213 and 214 are formed on the upper and lower surfaces 212a and 212b of the strip-shaped conductive material 212 by passing the strip-shaped conductive material 212 having a concave surface only on the lower surface 212b through the molten solder bath. The molten solder plating layer 212 on the lower surface 212b formed on the concave surface of the strip-shaped conductive material 212 becomes flat. When such a solar cell lead wire 203 is soldered to the front or back electrode of the semiconductor substrate on the flat lower surface 214b of the molten solder plating layer 214, the solar cell lead wire 203 is firmly bonded to the semiconductor substrate. The solar cell lead wire 203 is not easily detached from the semiconductor substrate and has excellent durability.

International Publication WO2004 / 105141 Pamphlet

  As described above, in order to firmly join the solar cell lead wire to the semiconductor substrate, the molten solder plating layers 113 and 214 may be formed flat. However, according to Patent Document 1, in order to form a concave surface on the lower surface 212b of the strip-shaped conductive material 212, the strip-shaped conductive material 212 is subjected to appropriate plastic working and bending. For example, the concave surface is formed by passing the strip-shaped conductive material 212 through a mold roll. In addition, when the flat clad material is slit to obtain a strip-like conductive material, bending is performed by adjusting the interval and the rotational speed of the rotary blades. In this way, a conductive material 212 having a concave bottom surface is obtained.

  However, since plastic processing and bending are intermittent processes, they are inferior in mass productivity. Moreover, since it is difficult to adjust the pressure with respect to the strip-shaped conductive material 212 when the strip-shaped conductive material 212 is passed through the mold roll, the strip-shaped conductive material 212 having a concave bottom surface is inferior in cross-sectional dimension accuracy.

  When a concave surface is formed on the strip-shaped conductive material 212 by slit processing, burrs are generated on both sides of the lower surface 212b of the strip-shaped conductive material 212. If burrs are present in the strip-shaped conductive material 212 and the plating layer 214 is thin at that portion, the burrs and cells are melted by the solder plating layer 214 when the solar cell lead wire 203 is bonded to the semiconductor substrate. Contact, stress concentration occurs at the contact portion between the burr and the cell, and the semiconductor substrate 102 is cracked.

  Moreover, in the solar cell lead wire 203 of Patent Document 1, from the back electrode of the first semiconductor substrate to the surface electrode of the second semiconductor substrate, from the back electrode of the second semiconductor substrate to the surface electrode of the third semiconductor substrate. Connected to. Thus, when joining the solar cell lead wire 203 to both front and back surfaces of the semiconductor substrate, between the solar cell lead wire 203 soldered to the front electrode and the solar cell lead wire 203 soldered to the back electrode. The problem of misalignment has not been solved. The problem of cell cracking in the semiconductor substrate due to this misalignment remains.

  Furthermore, even if the plating layer is flat and there are no burrs in the conductor, if the conductor has a corner like a rectangular parallelepiped, the conductor tilts when the solder is melted, and the contact between the corner of the conductor and the cell is generated. Stress concentration occurs at the contact portion between the cell and the cell, and there remains a problem that cell cracking occurs in the semiconductor substrate.

  Since the semiconductor substrate occupies most of the cost of the solar cell, the thinning of the semiconductor substrate has been studied, but the thinned semiconductor substrate is easily broken. For example, when the thickness of the semiconductor substrate is 200 μm or less, the rate of cell cracking increases. If cell cracks occur in the semiconductor substrate due to the solar cell lead wires, the semiconductor substrate cannot be thinned.

  Then, the objective of this invention is providing the solar cell lead using the lead wire for solar cells which solves the said subject and has a high cell crack suppression effect, its manufacturing method, and it.

In order to achieve the above object, the invention according to claim 1 is directed to a solar cell lead wire having a molten solder plating layer formed by supplying molten solder to the surface of a strip-shaped conductive material. conductive material is a flat top and bottom surfaces, side surfaces is a curved surface bulging convex, wherein the melt solder-plated layer formed on at least upper and lower surfaces of the strip-shaped conductive material is flat It is a lead wire for solar cells.

According to the invention of claim 2, a strip-shaped conductive material is formed by rolling a strand having a circular cross section to form a flat upper surface and a lower surface, and a curved surface whose side surfaces bulge. Then, a molten solder is supplied and solder-plated on the strip-shaped conductive material, and the plated strip-shaped conductive material is sandwiched between a pair of lower rolls and a pair of upper rolls to provide a molten solder plating layer. Is a method for producing a solar cell lead wire.

  The invention according to claim 3 is a solar cell characterized in that the lead wire for solar cell according to claim 1 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, an excellent effect that a solar cell lead wire having a high cell crack suppressing effect can be obtained is exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the present invention, in which (a) is a cross-sectional view of a solar cell lead wire, and (b) is a schematic perspective view of a strip-like conductive material used as a material for a solar cell lead wire. It is a cross-sectional view of the lead wire for solar cells which shows other embodiment of this invention. It is a cross-sectional view of the lead wire for solar cells showing still another embodiment of the present invention. In this invention, it is the schematic of the hot dipping equipment which forms a hot-dip solder plating layer. The solar cell of this invention is shown, (a) is a cross-sectional view, (b) is a top view of the solar cell. The conventional solar cell is shown, (a) is a cross-sectional view, (b) is a top view of the solar cell. It is a cross-sectional view of a conventional solar cell lead wire. It is a side cross-sectional view of the conventional lead wire for solar cells.

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

  As shown in FIG. 1 (a), a solar cell lead wire 10 according to the present invention supplies a molten solder to the upper and lower surfaces of the strip plate-like conductive material 12 and is plated at the solder bath outlet. The upper and lower molten solder plating layers 13 and 13 are formed flat by sandwiching 12 with a roll and adjusting the plating thickness. Here, “flat” means that the unevenness of the plating surface is 3 μm or less.

  The strip-shaped conductive material 12 is formed by rolling an element wire (wire having a circular cross-section), and is formed by heat-treating it with a continuous energizing heating furnace, a continuous heating furnace, or a batch heating facility.

  FIG. 1B shows a perspective view of the strip-shaped conductive material 12, where the upper surface 12 a and the lower surface 12 b are flat surfaces, the side surfaces 12 c are formed to bulge in a convex shape, and the end surface 12 d is timely Cut to length to form.

  FIG. 4 shows a hot-dip plating facility for flattening the hot-dip solder plating layers 13, 13, and a reverse roller 16 is provided in the solder bath 15. A pair of upper and lower rollers 17a, 17b, 18a, and 18b are provided above the solder bath 15 positioned above 16, and a pulling roller 19 is provided above them.

  The strip-shaped conductive material 12 is immersed in the solder bath 15 so that the solder is supplied to the upper and lower surfaces, reversed by the reversing roller 16 and directed upward, and the plating layer is sandwiched between the lower rolls 17a and 17b, Furthermore, it is sandwiched between the upper rolls 18a and 18b, and the final plating thickness is adjusted by the upper rolls 18a and 18b, whereby the molten solder plating layers 13 and 13 are flattened as shown in FIG. The lead wire 10 is manufactured.

  Upper and lower rolls 17 a, 17 b, 18 a, 18 b for flatly forming the molten solder plating layers 13, 13 on the strip-shaped conductive material 12 sandwich the upper and lower surfaces of the strip-shaped conductive material 12 at the outlet of the plating bath 15. By arranging the distance between the upper and lower rolls 17a, 17b, 18a, 18b finely, the plating thickness of the molten solder plating layers 13, 13 and the cross-sectional shape of the plating layer 13 can be adjusted. .

  FIG. 2 shows another shape of the solar cell lead wire according to the present invention.

  The solar cell lead wire 20 in FIG. 2A is formed by forming the molten solder plating layer 23 on the upper surface 12a of the strip-like conductive material 12 so that the central portion 23o is flat and both side portions 23s are rounded. The molten solder plating layer 24 on the lower surface 12b is formed flat on the entire surface.

  In addition, the solar cell lead wire 20 of FIG. 2B is formed by flattening the central portions 23o and 24o of the molten solder plating layers 23 and 24 on the upper surface 12a and the lower surface 12b of the strip plate-like conductive material 12, and both side portions 23s and 24s. Are formed in a round shape.

  The lead wire 20 for solar cell in FIG. 2 (c) is formed by forming a molten solder plating layer 25 so as to cover the outer periphery of the strip-shaped conductive material 12 and melting the upper surface 12 a and the lower surface 12 b of the strip-shaped conductive material 12. The solder plating layers 25a and 25b are formed so as to be flat.

  The shapes shown in FIGS. 2A and 2B can be formed by adjusting the amount of molten solder plating, the distance between the upper and lower rolls 17a, 17b, 18a, and 18b, and the position thereof. Moreover, the shape of FIG.2 (c) can be formed by adjusting the pulling-up speed | rate of the strip | belt-shaped conductive material 12 at the time of performing molten solder plating in addition to adjustment of the space | interval and position of a roll.

  That is, when the molten solder plating layers 23 and 24 are formed on the upper and lower surfaces of the strip plate-like conductive material 12 in the hot dipping equipment of FIG. The upper and lower rolls 17a, 17b, 18a, and 18b are finely adjusted with respect to the path to finely adjust the positions and intervals of the upper and lower rolls 17a, 17b, 18a, and 18b. The layer thickness of the layer 24 can be adjusted and the entire layer thickness can be adjusted. The total layer thickness is determined by the distance between the lower rolls 17a and 17b, and the distance between the upper rolls 18a and 18b. To determine the final thickness. Further, when the strip-like conductive material 12 is reversed by the pulling roller 19, the upper surface becomes the upper molten solder plating layer 23 and the lower surface becomes the lower molten solder plating layer 24. As for the roll for determining the flatness, the upper and lower rolls 17a and 18a on the left side determine the flatness of the upper molten solder plating layer 23, and the upper and lower rolls 17b and 18b on the right side of the lower molten solder plating layer 23 as shown in the figure. Since the flatness is determined, the flatness of the molten solder plating layer can be adjusted by adjusting the positions of the rolls 17a, 17b, 18a, and 18b with respect to the path. Moreover, if the pulling-up speed of the strip-shaped conductive material 12 when performing the molten solder plating is slowed, the amount of solder that flows down to the solder bath increases because the solder attached to the strip-shaped conductive material 12 is removed. In addition, the amount of adhesion to the strip plate-like conductive material 12 can be reduced, and conversely, if the pulling speed is increased, the solder attached to the strip plate-like conductive material 12 is rapidly cooled, so that the amount of solder flowing down to the solder bath is reduced. In addition, the amount of adhesion to the strip-like conductive material 12 can be increased.

  That is, in order to form both sides 23s of the molten solder plating layer 23 on the upper part of the solar cell lead wire 20 in FIG. 2A in a rounded shape, the upper roll 18a is formed to be slightly away from the path. In order to form both sides 23s and 24s of the upper and lower molten solder plating layers 23 and 24 of the solar cell lead wire 20 of FIG. 2B in a rounded shape, the upper rolls 18a and 18b are slightly moved from the respective paths. It can be formed by separating. At this time, the thickness and solidification state of the molten solder plating layer can be controlled by changing the pulling speed in accordance with the position of the rolls 17 and 18 and the interval adjustment, so that the flatness of the molten solder plating layer can be freely formed. Can do. In order to form the molten solder plating layer so as to cover the outer periphery of the solar cell lead wire 20 of FIG. 2C, the pulling speed of the strip-like conductive material 12 when performing the molten solder plating is shown in FIG. It can be formed by making it faster than the pulling speed when forming.

  When the conductor width and the electrode width of the strip-like conductive material 12 shown in FIG. 2 are the same, the amount of solder to be supplied is suppressed, that is, by adopting the shape of FIGS. 2 (a) and 2 (b), Solder contributing to the bonding between the strip-shaped conductive material and the semiconductor substrate is excessively supplied to the bonding portion between the front surface electrode and the back surface electrode, and is prevented from flowing out to a portion other than the electrode and reducing the cell light receiving surface. Thereby, the lead wire 20 for solar cells excellent in shadow loss suppression is obtained.

  Next, the solar cell lead wire 30 of FIG. 3 is formed by forming the strip-shaped conductive material 32 so that the lower surface 32b is concave by slit processing, and the upper and lower surfaces 32a and 32b of the strip-shaped conductive material 32, The molten solder plating layers 33 and 34 are respectively formed using the hot dipping equipment described with reference to FIG.

  In this case, the lower molten solder plating layer 34 is formed so that the thickness of both ends of the lower molten solder plating layer 34 is 5 μm or more in consideration of burrs.

  As described in Patent Document 1, the strip-shaped conductive material 32 having a concave bottom surface 32b is formed by adjusting the interval and the rotation speed of the slitting blades when slitting the flat plate to obtain the strip. The strip-shaped conductive material 32 can have a concave shape 32b and a slightly convex upper surface 32a.

  The strip-shaped conductive material 32 obtained by slit processing can correspond to materials having various widths. In other words, even if the strip plate-like conductive material 32 is not uniform in the longitudinal direction or when various strip plate-like conductive materials 32 having different widths are used, they are long and uniform in the longitudinal direction by slit processing. Can be formed.

  In this reference form, when a wide conductor such as a backside wiring is required, it is necessary to use a strip-like conductive material 32 formed by slit processing. The lead wire 30 for solar cells is further excellent in shadow loss suppression (applicable as a backside wiring) by forming the plating thickness of the end portion to 5 μm or more so as not to cause cracking and forming the molten solder plating layer 34 flat. Is obtained.

  As described above, the solar cell lead wires 10, 20, and 30 according to the examples and the reference examples of the present invention can be easily installed on the front surface electrode and the back surface electrode of the semiconductor substrate, and have heat conduction necessary for bonding. The molten solder plating layers 13, 23, 24, 33, and 34 are formed flat so as to be sufficiently secured. Thereby, it can install orderly with respect to a surface electrode and a back surface electrode, and enables firm soldering. In addition, since the plating layer is flat, the adhesiveness with the air suction jig is high, and it does not easily drop during movement. Furthermore, since the plating layer is flat, a stable laminated state can be easily obtained when winding on the bobbin, and the winding collapse hardly occurs. Therefore, the problem that the lead wire is tangled and cannot be pulled out due to the winding collapse is also solved.

  For the strip-shaped conductive material 12, for example, a rectangular wire having a volume resistivity of 50 μΩ · mm or less is used. By rolling this flat wire, a strip-shaped conductive material 12 having a cross-sectional shape as shown in FIG. 1B is obtained, or a strip-shaped conductive material 32 shown in FIG. 3 is obtained by slitting. Can do.

  The strip-like conductive materials 12 and 32 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 layer, 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 effect of the present invention will be described.

  When soldering the solar cell lead wire 10 shown in FIG. 1A to the front electrode 54 and the back electrode 55 of the semiconductor substrate 52 shown in FIG. 5, the heating temperature of the solar cell lead wire 10 and the semiconductor substrate 52 Is controlled to a temperature in the vicinity of the melting point of the solder of the molten solder plating layer 13. The reason is that the thermal expansion coefficient of the strip-like conductive material 12 (for example, copper) of the solar cell lead wire 10 and the thermal expansion coefficient of the semiconductor substrate (Si) are greatly different. Due to the difference in thermal expansion coefficient, thermal stress that causes cracks in the semiconductor substrate 52 is generated. In order to reduce this thermal stress, it is preferable to perform low-temperature bonding. Therefore, the heating temperature of the solar cell lead wire 10 and the semiconductor substrate 52 is controlled to a temperature near the melting point of the solder of the molten solder plating layer 13.

  The heating method at the time of joining is a method in which the semiconductor substrate 52 is placed on a hot plate, and heating from the hot plate is combined with heating from above the solar cell lead wire 10 placed on the semiconductor substrate 52. is there.

  In order to increase the contact area between the front surface electrode 54 and the rear surface electrode 55 of the semiconductor substrate 52 and the molten solder plating layer 13, and to ensure sufficient heat conduction from the semiconductor substrate 52 to the molten solder plating layer 13, the molten solder plating layer The shape of the solar cell lead wire 10 including 13 is preferably a rectangular shape.

  However, the conventional solar cell lead wire 103 shown in FIG. 7 has a mountain shape in which the central portion in the longitudinal direction swells, and as shown in FIG. 6, the front surface electrode 104 and the back surface electrode 105 of the semiconductor substrate 102. When soldering, the contact area between the front surface electrode 104 and the back surface electrode 105 of the semiconductor substrate and the molten solder plating layer 113 of the solar cell lead wire 103 is small. For this reason, if the heat conduction becomes insufficient or the solar cell lead wire 103 is placed on the front electrode 104 and the back electrode 105, the position becomes unstable, and the position of the solar cell lead wire 103 on the front and back of the semiconductor substrate 102 May shift. These cause cell cracks.

  In the present invention, since the molten solder plating layer 13 that becomes the upper and lower surfaces of the solar cell lead wire 10 is flattened, the above-described conventional problems are solved.

  In the solar cell lead wire 203 of Patent Document 1 shown in FIG. 8, the molten solder plating layer 214 is flattened by accommodating the molten solder on the concave lower surface 212 b of the strip plate-like conductive material 212. However, if the flat plate is slit to form the lower surface concave strip-shaped conductive material 212, burrs are generated on both sides of the lower surface strip-shaped conductive material 212. Due to the burrs, stress concentrates on the joint between the solar cell lead wire 203 and the semiconductor substrate 102, and cell cracking occurs.

  Moreover, the strip-shaped conductive material 212 having a concave bottom surface used for the solar cell lead wire 203 of Patent Document 1 has a concave surface only on the bottom surface 212b, and the top surface 212a is a relatively flat surface. When the molten solder plating layers 213 and 214 are formed on such a strip-shaped conductive material 212, the molten solder plating layer 214 on the lower surface 212b becomes flat, but the molten solder plating layer 213 on the upper surface 212a swells in a mountain shape. That is, in the solar cell lead wire 203 of Patent Document 1, the lower surface of the molten solder plating layer 214 is flat, and the upper surface of the molten solder plating layer 213a swells in a mountain shape. When such a solar cell lead wire 103 is to be bonded to both the front and back surfaces of the semiconductor substrate 102, the position of the solar cell lead wire 203 is shifted between the front and back surfaces. This misalignment causes cell cracks in the semiconductor substrate 203.

  Next, the reason why this cell crack occurs will be described.

  The belt-like conductive material 212 and the semiconductor substrate 102 are bonded to each other with a predetermined pressure by sandwiching the solar cell lead wire 203 and the semiconductor substrate 102 in accordance with the bonding portions (the front electrode 104 and the back electrode 105) and heating them. To join. At this time, if burrs exist in the strip-shaped conductive material 212, high pressure is generated on the semiconductor substrate 102 due to the burrs, and cell cracking occurs. Further, when a strip-shaped conductive material 212 having a bonding surface swelled in a mountain shape is bonded to the semiconductor substrate 102, as shown in FIG. , 105 and the solar cell lead wire 203 are easily displaced. Due to the deviation, the front and back surfaces of the semiconductor substrate 103 are alternately sandwiched between the strip-shaped conductive materials 212, and cell cracks occur.

  However, when the upper and lower molten solder plating layers 33 and 34 shown in FIG. 3 according to the reference example of the present invention are joined to the semiconductor substrate 50 with the strip plate-like conductive material 32 having a flat joining surface, the solar cell lead wire 30. Is difficult to shift on the front electrode 54 and the back electrode 55. If there is no deviation, the semiconductor substrate 52 is sandwiched between the solar cell lead wires 30 having a flat joining surface at substantially the same position on the front surface and the back surface, the stress on the semiconductor substrate 52 is reduced, and cell cracking does not occur.

  Thus, in the solar cell lead wires 10, 20, and 30 according to the examples and the reference examples of the present invention, the molten solder plating is rolled on the upper and lower surfaces of the strip plate-like conductive materials 12 and 32 formed by rolling or slitting. 17 and 18 so as to be flat. Thereby, there is no burr | flash and a junction surface with a semiconductor substrate becomes flat. Therefore, cell cracking is suppressed.

  In addition, since the present invention can suppress the uneven thickness of the plating layer that occurs when performing hot dipping at a high speed by squeezing the molten solder with the rolls 17 and 18, the predetermined plating thickness is formed at a higher speed than in the past. Can be produced and is excellent in mass productivity. As a result, the present invention can provide a solar cell lead wire that is most effective in suppressing cell cracking.

  Furthermore, in the present invention, the molten solder plating layers 13, 23, 24, 33, and 34 are formed flat by adjusting the rolls 17 and 18 by supplying molten solder to the upper and lower surfaces of the strip-like conductive materials 12 and 32. The solar cell lead wires 10, 20, and 30 have flat upper and lower surfaces. Therefore, when the solar cell lead wires 10, 20, 30 are bonded to the front and back surfaces of the semiconductor substrate 52, the solar cell lead wires 10, 20, 30 to be soldered to the front electrode 54 and the back electrode 55 are soldered. No misalignment occurs between the solar cell lead wires 10, 20, and 30.

  Further, according to the present invention, even if flat solder plating is formed thickly on the upper and lower surfaces of the strip-like conductive materials 12 and 32, the positional deviation does not occur unlike the conventional solder plating wire, and sufficient solder can be supplied at the time of joining. Therefore, it is also possible to make the solder fillet formed on the Si cell surface electrode after lead wire bonding into a stable chevron shape. Fillet refers to wax or solder that protrudes from the gap between joints that have been brazed or soldered.

  Next, Table 1 shows the physical properties of the strip-shaped conductive material used in the present invention.

  The strip-shaped conductive material is preferably a material having a relatively small volume resistivity. As shown in Table 1, the strip-like conductive material includes Cu, Al, Ag, Au, and the like.

  Among Cu, Al, Ag, and Au, Ag has the lowest volume resistivity. Therefore, when Ag is used as the strip-shaped conductive material, the power generation efficiency of the solar cell using the solar cell lead wire 1 can be maximized. When Cu is used as the strip-shaped conductive material, the solar cell lead wire can be reduced in cost. When Al is used as the strip-shaped conductive material, the solar cell lead wires 10, 20, and 30 can be reduced in weight.

  When Cu is used as the strip-shaped conductive material, 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 may be used as the Cu. In order to minimize the 0.2% proof stress of the strip-shaped conductive material, 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 material can be reduced. When tough pitch Cu or phosphorous deoxidized Cu is used, the cost of solar cell lead wires can be reduced.

  As the solder used for the molten solder plating layer, Sn-based solder, or Sn as the first component and at least one selected from Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component Examples thereof include Sn-based solder alloys containing 0.1 mass% or more of elements. These solders may contain a trace element of 1000 ppm or less as the third component.

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

  First, a strip-like conductive material is formed by rolling a wire (not shown) having a circular cross-section as a raw material or slitting a flat plate. This strip-shaped conductive material is heat-treated in a continuous energizing heating furnace, a continuous heating furnace, or a batch-type heating facility. Thereafter, molten solder is supplied using a plating line as shown in FIG. 4 to form a molten solder plating layer flat.

  In general, in a solid or liquid, intermolecular force works between internal molecules, so that it tends to be as small as possible. Since the surface molecules are surrounded by different molecules on one side, they are in a high internal energy state and attempt to stabilize their excess energy. In the case of solder (liquid) in contact with air, the intermolecular force in the air is extremely small compared to the intermolecular force in the solder, so the molecules on the solder surface are not pulled from the air side molecules, only from the molecules inside the solder. Will be pulled. Therefore, the molecules on the solder surface always try to enter the solder, and as a result, the solder surface tends to be spherical with the smallest surface area (the number of elements constituting the solder).

  Due to the force (surface tension) acting to reduce the surface area, the conventional solar cell lead wire 103 shown in FIG. 7 is solidified in a swelled shape on the upper and lower surfaces of the strip-like conductive material 112. A molten solder plating layer 113 is formed. The reason why the solder that is supposed to be spherical does not become spherical is that the interaction force of the interface with the strip plate conductive material 112 (interfacial tension between the solder and the strip plate conductive material 112) is applied to the solder.

  On the other hand, the solar cell lead wires 10, 20, and 30 according to the examples and the reference examples of the present invention are passed between the rolls immediately before the solder solidifies, so that the molten solder plating layers 13, 23, 24, and 33 are passed. , 34 can be formed flat.

  As a processing method for processing a raw material into a strip-shaped conductive material, both rolling and slit processing are applicable. Rolling is a method of flattening by rolling a round wire. When a strip-shaped conductive material is formed by rolling, a long and uniform material in the longitudinal direction can be formed. Slit processing can be applied to materials of various widths. That is, even if the raw material conductive material is not uniform in the longitudinal direction, even when various raw material conductive materials having different widths are used, a long and uniform width in the longitudinal direction can be formed by slit processing.

  By heat-treating the strip-shaped conductive material, the softening characteristics of the strip-shaped conductive material can be improved. Improving the softening properties of the strip-shaped conductive material 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.

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

  As shown in FIGS. 5A and 5B, the solar cell 50 of the present invention is obtained by soldering the solar cell lead wire 10 (or 20, 30) described above with the solder of the molten solder plating layer 13. This is soldered to the front electrode 54 and the back electrode 55 of the semiconductor substrate 52.

  Since the molten solder plating layer 13 serving as a joint surface between the solar cell lead wire 10 and the front electrode 54 and the back electrode 55 is flat, the position of the solar cell lead wire 10 is stabilized on the front and back of the semiconductor substrate 52. Misalignment is prevented.

  According to the solar cell 50 of the present invention, since the bonding strength between the solar cell lead wire 10 and the semiconductor substrate is high and cell cracking at the time of bonding can be suppressed, the yield of the solar cell can be improved.

Example 1
A Cu material, which is a raw material conductive material, was rolled to form a rectangular wire strip-shaped conductive material having a width of 2.0 mm and a thickness of 0.16 mm. This strip-shaped conductive material is heat-treated with a batch-type heating facility, and Sn-3% Ag-0.5% Cu solder plating is applied around the strip-shaped conductive material with a hot dipping facility shown in FIG. A molten solder plating layer (plating thickness of 20 μm at the center) was formed flat on the upper and lower surfaces of the strip-shaped conductive material (the conductor was heat-treated Cu). The solar cell lead wire 10 of FIG. 1A was obtained as described above.

(Examples 2, 3, and 4)
A strip plate-like conductive material is formed in the same manner as the solar cell lead wire 10 of Example 1, heat-treated with a batch-type heating facility, and Sn around the strip plate-like conductive material with a hot dipping plating facility shown in FIG. -3% Ag-0.5% Cu solder plating was applied at different pulling speeds, and a molten solder plating layer (plating thickness of 20 μm at the center) was formed flat on the upper and lower surfaces of the strip-like conductive material ( The conductor is heat-treated Cu). In Example 2, the conductor pulling speed was made slower than in Example 1, and the distance between the conductor and the roll was aligned so that the lower surface was smaller. As in Example 2, Example 3 was produced by lowering the conductor pulling speed than Example 1, and performing alignment so that the distance between the conductor and the roll was the same on the upper surface and the lower surface. In Example 4, the conductor was pulled at a higher speed than in Example 1, and the conductor and the roll were aligned so that the distance between the upper surface and the lower surface was the same. Since the solder attached to the conductor is removed by slowing the pulling speed of the conductor, the amount flowing down to the solder bath increases, and as a result, the amount attached to the conductor decreases. In the case of this method, the material cost of solder can be reduced. On the contrary, by increasing the pulling speed, the solder adhering to the conductor is rapidly cooled, so that the amount flowing down to the solder bath decreases, and as a result, the amount adhering to the conductor increases. In the case of this method, it is possible to expect a reduction in the cost of the plating process due to an increase in the plating speed and an improvement in the bondability with the cell by sufficient supply of solder. As described above, the lead wire 20 for solar cell shown in FIG. 2A was obtained in Example 2, FIG. 2B in Example 3, and FIG. 2C in Example 4.

(Reference Example 1)
A Cu-Invar-Cu (ratio 2: 1: 2) material, which is a raw material conductive material, was slit to form a rectangular strip-shaped conductive material having a width of 2.0 mm and a thickness of 0.16 mm. This strip-shaped conductive material was solder-plated with a hot-dip plating facility shown in FIG. 4 to form a molten solder plating layer (plating thickness 20 μm at the center) flat on the upper and lower surfaces of the strip-shaped conductive material. The plating conditions were adjusted so that the end plating thickness was 5 μm. Thus, the solar cell lead wire 30 of FIG. 3 was obtained.

(Comparative Example 1)
A Cu material, which is a raw material conductive material, was rolled to form a rectangular strip-shaped conductive material 112 having a width of 2.0 mm and a thickness of 0.16 mm. The belt-like conductive material 112 is heat-treated with a batch-type heating facility, and further, solder plating is applied to the periphery of the belt-like conductive material 112 so as to swell in a mountain shape on the flat upper and lower surfaces of the belt-like conductive material 112 A solder plating layer 113 (plating thickness of 20 μm at the center) was formed (the conductor was heat-treated Cu). Thus, the solar cell lead wire 103 of FIG. 7 was obtained.

(Comparative Example 2)
A Cu-invar-Cu (ratio 2: 1: 2) material, which is a raw material conductive material, was slit to form a strip-shaped conductive material 212 having a concave bottom surface with a width of 2.0 mm and a thickness of 0.16 mm. Solder plating is applied to the periphery of the strip-shaped conductive material 212 to form a flat molten solder plating layer 214 (plating thickness of 20 μm at the center) on the concave surface 212b of the strip-shaped conductive material 212, and on the flat side surface A molten solder plating layer 213 swelled in a chevron shape (plating thickness at the center portion of 20 μm) was formed. Thus, the solar cell lead wire 203 of FIG. 8 was obtained. The plating thickness at the end was 4 μm.

  As a result of observing the cross sections of the lead wires for solar cells of Examples 1, 2, 3, and 4, Reference Example 1 and Comparative Examples 1 and 2, Examples 1, 2, 3, 4, and Reference Example 1 were formed on a semiconductor substrate. It was confirmed that the upper and lower surfaces to be joined were both flat.

  In Comparative Example 1, the upper and lower surfaces to be bonded to the semiconductor substrate had a chevron-shaped cross section that swelled at the center. In Comparative Example 2, the lower surface to be bonded to the semiconductor substrate was flat and the upper surface was a mountain-shaped cross section swelled at the center.

  An appropriate amount of rosin-based flux was applied to the solar cell lead wires of Examples 1, 2, 3, and 4, Reference Example 1 and Comparative Examples 1 and 2, and each solar cell lead wire was placed on a copper plate. The plate was heated (held at 260 ° C. for 30 seconds), and the solar cell lead was soldered to the copper plate. Furthermore, in order to evaluate the bonding strength of the solar cell lead wire soldered to these copper plates to the copper plate, a 90 ° peel test was performed. Also, these solar cell lead wires are installed on electrode portions on both sides of a semiconductor substrate (Si cell) having a length of 150 mm × width 150 mm × thickness 180 μm, and hot plate heating (260 is carried out in the same manner with a 10 g weight placed thereon. Held at 30 ° C. for 30 seconds) and soldered. The state of cell cracks that occurred during soldering was investigated. About the comparative example 2, the case where the upper surface was joined and the case where the lower surface was joined were performed, and the condition of the cell crack was investigated about each case.

  Table 2 shows the evaluation results of Examples 1, 2, 3, and 4, Reference Example 1 and Comparative Examples 1 and 2.

  The column of “conductor processing” in Table 2 shows a processing method for forming a rectangular wire strip-like conductive material from a raw material conductive material. The column of “end part plating thickness” indicates the plating thickness covered with the bottom face end burr when the conductor is slit. The “cross-sectional shape” column indicates which cross-sectional shape is shown in the figure. The column of “Joint strength” shows the results of a test conducted by pulling a copper plate and a solar cell lead wire by a 90 ° peel test, and by how much tensile force the joint peels off. 20N or more, ○ indicates a tensile force of 10 to 20N, and Δ indicates a tensile force of 10N or less.

In the “cell crack” column, when a square wire is joined to both sides of the cell by a soldering test and the presence or absence of the cell crack is examined, it is determined that there is a cell crack if there is one or more cell cracks that can be visually confirmed. In other cases, it was determined that there was no cell cracking, and when the ratio of no cell cracking in all joints was 90% or more, ○, when the ratio of no cell cracking was 70% or more and less than 90%, Δ, no cell cracking The case where the ratio was less than 70% was evaluated as x. In addition, the ratio without a cell crack was computed by the following formula.

(Percentage without cell cracking) = [(Number of cells without cracking) / (Number of cells subjected to soldering test)] × 100
As shown in Table 2, since the lead wires for solar cells of Examples 1 to 4 and Reference Example 1 supplied molten solder to the upper and lower surfaces and formed the molten solder plating layer flat by rolls, excellent bonding It was confirmed that power was obtained.

  In particular, in the solar cell lead wire 1 of Example 1, the molten solder was sufficiently supplied from the center part to the end part on the upper and lower surfaces to form the molten solder plating layer flat, so that the solder contributing to the bonding was sufficient. The fact that a good fillet is formed is connected to a high bonding force.

  Since the joining surface with the semiconductor substrate of the solar cell lead wire 10 of Example 1 is flat, it is not a point contact like the conventional solar cell (FIG. 6), but the solar cell of the present invention (FIG. 5). In addition, since there is a large amount of solder that contributes to the joining by supplying a sufficient amount of molten solder from the center portion to the end portion, a good solder fillet is formed. Thereby, bondability (strength and electroconductivity) improves.

  Moreover, as shown in Table 2, the solar cell lead wires 10, 20, and 30 of Examples 1 to 4 and Reference Example 1 were formed by flatly forming a molten solder plating layer on the upper and lower surfaces by roll plating. It was confirmed that cracking was suppressed.

  On the other hand, in Comparative Example 1 in which rolling is performed and roll plating is not performed, cell cracks are observed, and the joining force is slightly inferior to that of the present invention. In Comparative Example 2 in which slit processing is performed and roll plating is not performed, cell cracking is observed when the bonding surface is a flat side surface, although the bonding force is excellent. When the joining surface is a swelled side surface, there is no cell cracking, but the joining force is slightly inferior to that of the present invention.

  As described above, from the evaluation results of Examples 1, 2, 3, 4, Reference Example 5 and Comparative Examples 1 and 2, it was confirmed that the present invention has a high cell crack suppressing effect.

10, 20, 30 Lead wire for solar cell 12, 32 Strip plate conductive material 13, 23, 24, 33, 34 Molten solder plating layer

Claims (3)

In the solar cell lead wire having a melt solder-plated layer surface in molten solder strip-shaped conductive material formed by being supplied, the strip-shaped conductive material has an upper surface and a lower surface is flat, the side a curved surface bulging convex, the solar cell lead wire, wherein the melt solder-plated layer formed on at least upper and lower surfaces of the strip-shaped conductive material is flat.
By rolling a wire having a circular cross section, the upper and lower surfaces are formed flat, a strip-like conductive material formed by a curved surface with convex side surfaces is formed, heat-treated, and then melted. Supplying solder and solder-plating the strip-shaped conductive material, and sandwiching the plated strip-shaped conductive material between a pair of lower rolls and a pair of upper rolls to form a flat molten solder plating layer A method for producing a lead wire for a solar cell, which is characterized.
  A solar cell, wherein the lead wire for a solar cell according to claim 1 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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