JP2014042065A - Lead wire for solar battery, and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead wire for a solar battery which is low in cost, and superior in designability and bondability with a cell.SOLUTION: A lead wire for a solar battery comprises: a strip-like conductive material 2; a plating layer 4 on a surface of the strip-like conductive material 2; and a coating layer 5 located outside the plating layer 4. In the lead wire, the plating layer 4 includes a Sn-based solder or a Sn-based solder alloy which includes Sn as a first component, and as a second component, no less than 0.1 mass% of at least one element selected from a group consisting of Pb, In, Bi, Sb, Ag, Zn, Ni and Cu; the coating layer 5 includes a resin consisting of any one of a phenoxy resin, a polyvinyl butyral resin, a polyamide resin, an epoxy resin and a polyester resin; and the plating layer 4 has, on its surface, an oxide film having a thickness of 7 nm or less.

Description

  The present invention relates to a solar cell lead wire and a solar cell, and particularly relates to a solar cell lead wire and a solar cell that are low in cost, excellent in design properties, and excellent in bonding properties with cells.

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

  As shown in FIG. 4A and FIG. 4B, the solar cell 40 includes a predetermined region of the semiconductor substrate 41, that is, a surface electrode 42 provided on the surface of the semiconductor substrate 41 and a back surface provided on the back surface. The solar cell lead wires 44a and 44b are joined to the electrode 43 with solder. The electric power generated in the semiconductor substrate 41 is transmitted to the outside through the solar cell lead wires 44a and 44b.

  As shown in FIG. 5, the conventional solar cell lead wire 44 (44 a, 44 b) includes a strip-shaped conductive material 45 and a plating layer 47 formed on the upper and lower surfaces 46 a, 46 b of the strip-shaped conductive material 45. With. The strip-shaped conductive material 45 is formed by rolling a conductor having a circular cross section into a strip shape, and is also called a flat conductor or a flat wire.

  The plating layer 47 is formed by supplying molten solder to the upper and lower surfaces 46a and 46b of the strip-like conductive material 45 by a hot dipping method.

  In the hot dipping method, the upper and lower surfaces 46a and 46b of the strip plate-like conductive material 45 are cleaned by pickling or the like, and the strip plate-like conductive material 45 is passed through a molten solder bath, thereby In this method, solder is laminated on the lower surfaces 46a and 46b. The plated layer 47 swells from the side in the width direction to the center as shown in FIG. 5 due to the action of surface tension when the molten solder adhering to the upper and lower surfaces 46a and 46b of the strip plate-like conductive material 45 solidifies. It is formed in a so-called mountain shape.

  The solar cell lead wire 44 is cut to a predetermined length, adsorbed with air, moved onto the surface electrode (grid) 42 of the semiconductor substrate 41, and soldered to the surface electrode 42 of the semiconductor substrate 41. On the surface electrode 42, an electrode band (finger) (not shown) that is electrically connected to the surface electrode 42 is formed in advance. The plating layer 47 of the solar cell lead wire 44a is brought into contact with the surface electrode 42, and soldering is performed in this state. The same applies to the case where the solar cell lead wire 44b is soldered to the back electrode 43 of the semiconductor substrate 41.

  Conventionally, in order to obtain good solderability between the surface electrode 42 of the semiconductor substrate 41 and the solar cell lead wire 44a, the surface electrode 42 is impregnated with the same quality solder as the plating layer 47 of the solar cell lead wire 44a. However, since the semiconductor substrate 41 has been made thinner in recent years, the problem of damage to the semiconductor substrate 41 when the surface electrode 42 is impregnated with solder has been surfaced. Therefore, in order to avoid damage to the semiconductor substrate 41, the solder impregnation step for the surface electrode 42 is being omitted.

By omitting the solder impregnation step that provided good solderability between the surface electrode 42 of the semiconductor substrate 41 and the solar cell lead wire 44a, even among the solar cell lead wires that conventionally had no problem with the bondability, Many cases where a good bondability cannot be obtained have been seen. The semiconductor substrate 41 and the solar cell lead wire 44 are joined by an intermetallic compound (eg, Ag ₃ Sn) between the electrode material (eg, Ag) of the surface electrode 42 and the joining material (eg, Sn) of the plating layer 47. For this purpose, the oxide film is removed from the surface of the plating layer 47 and the surface of the surface electrode 42 by the action of the flux, so that the metal atoms (Sn) of the solder and the metal atoms (Ag) of the electrode are removed. ) And the Sn atoms in the solder must be easily diffused into the lattice of other atoms (Ag) by heating. That is, when the thickness of the oxide film on the surface of the plating layer 47 is thick, the removal of the oxide film by the flux becomes insufficient, resulting in poor soldering.

  If a soldering failure occurs between the surface electrode 42 and the plating layer 47, the semiconductor substrate 41 and the solar cell lead wire 44 are not sufficiently bonded to each other. And the output of a module incorporating the solar cell 40, which is a joined body of the solar cell lead wire 44, is caused.

  On the other hand, there is a problem that the metallic luster of the solar cell lead wire 44 impairs the appearance, and as a countermeasure, a method of covering the light receiving surface of the solar cell lead wire 44 with resin or the like has been proposed (for example, Patent Documents 1 to 4). 3).

  Patent Document 1 describes a method in which an inter-cell wiring of a thin-film solar cell is colored so as not to be conspicuous, and a bonding portion with the cell is not coated for coloring in terms of bonding properties. Patent Document 2 discloses a method of coating the surface of a wiring member of a crystalline solar cell with a colored resin layer. Patent Document 3 discloses that only the light receiving surface of the wiring member of the crystalline solar cell has a high reflectance. A method of coloring with a coating is described.

JP-A-8-312089 JP 2001-339089 A JP-A-2005-243972

  As described above, in order to firmly join the solar cell lead wire 44 to the semiconductor substrate 41, the surface thickness of the plating layer 47 may be reduced, and the metallic luster of the solar cell lead wire 44 is inconspicuous. In order to achieve this, a colored resin or the like may be coated. However, since soldering cannot be performed at the coated part, as in Patent Documents 1 to 3, only the part other than the soldered part is coated, and there is a problem that the process is very complicated and the manufacturing cost is high. Therefore, in order to prevent an increase in manufacturing cost, a method has been adopted in which a black mask is provided on the glass plate on the module surface so that the metallic luster of the solar cell lead wire 44 is inconspicuous. However, this method also covers the light-receiving surface of the semiconductor substrate (silicon cell) 41 that contributes to power generation, causing shadow loss and lowering power generation efficiency compared to conventional modules that do not cover the solar cell lead wires 44. There is a problem to do. Further, the surface of the plating layer 47 of the solar cell lead wire 44 is oxidized before the module is assembled, and when the module cannot be joined to the electrode on the surface of the semiconductor substrate 41 or when the contact resistance increases due to poor bonding, the module There was also a problem that the power generation efficiency of the system decreased.

  Accordingly, an object of the present invention is to provide a solar cell lead wire and a solar cell that solve the above-described problems, are low in cost, excellent in design properties, and excellent in bonding properties with cells.

In order to achieve the above object, the invention of claim 1 is the use of Sn-based solder on the surface of the strip-shaped conductive material, or Sn as the first component and Pb, In, Bi, Sb, Ag, Zn as the second component. , Having a plating layer made of a Sn-based solder alloy containing at least one element selected from Ni and Cu in an amount of 0.1 mass% or more, and having a phenoxy resin, a polyvinyl butyral resin, a polyamide resin on the outside of the plating layer, A solar cell lead wire having a coating layer containing a resin composed of either an epoxy resin or a polyester resin, and having an oxide film thickness of 7 nm or less on the surface of the plating layer.

  According to the solar cell lead wire of the present invention, it is possible to obtain a solar cell lead wire that suppresses the growth of the oxide film on the surface of the plating layer and has excellent bonding properties with the cell.

  The invention of claim 2 uses Sn-based solder on the surface of the strip-shaped conductive material, or Sn as the first component, and is selected from Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component. A solar cell lead wire having a plating layer made of an Sn-based solder alloy containing 0.1 mass% or more of at least one element, and a semiconductor substrate joined to the solar cell lead wire. The lead wire is joined to the electrode provided on the semiconductor substrate by the solder of the plating layer, and on the side surface of the solar cell lead wire, a phenoxy resin, a polyvinyl butyral resin, a polyamide resin, an epoxy resin And a solar cell having a coating layer containing a resin made of any one of polyester resins.

  According to the present invention, it is possible to obtain an excellent effect of being able to obtain a solar cell lead wire that is low in cost, excellent in design properties, and excellent in bondability with a cell.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one embodiment of this invention, (a) is a cross-sectional view of the lead wire for solar cells, (b) is an external appearance perspective view of the strip-shaped electroconductive material used as the material of the lead wire for solar cells. is there. In this invention, it is the schematic of the hot dipping equipment which forms a plating layer. In this invention, it is the schematic of the coating equipment which apply | coats a self-bonding material. It is a figure which shows the solar cell which concerns on one embodiment of this invention, (a) is a cross-sectional view, (b) is a top view. It is a cross-sectional view which shows 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), the solar cell lead wire 1 according to the present invention supplies molten solder to the upper and lower surfaces 3a, 3b of the strip-like conductive material 2, and plating by plating at the solder bath outlet. The layer 4 is formed, and a self-bonding material is coated on the outside of the plating layer 4.

  FIG. 1B shows a perspective view of the strip-shaped conductive material 2. The strip-shaped conductive material 2 is formed by, for example, forming an upper surface 3a and a lower surface 3b as flat surfaces, a side surface 3c bulging in a convex shape, and an end surface 3d cut to a suitable length.

  Table 1 shows the physical properties of the material of the strip-shaped conductive material 2 used in the present invention.

  The strip-shaped conductive material 2 is preferably made of a material having a relatively low volume resistivity. Examples of the material having a low volume resistivity include Cu, Al, Ag, and Au.

  Among Cu, Al, Ag, and Au, Ag has the lowest volume resistivity. Therefore, when Ag is used as the material of the strip-like conductive material 2, the power generation efficiency of the solar cell using the solar cell lead wire 1 can be maximized. Moreover, when Al is used as the strip-like conductive material 2, the weight of the solar cell lead wire 1 can be reduced. In addition, when Cu is used as the material of the strip-shaped conductive material 2, the solar cell lead wire 1 can be reduced in cost. When Cu is used as the material of the strip-shaped conductive material 2, 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. May be. In order to minimize the 0.2% proof stress of the strip-like conductive material 2, 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-like conductive material 2 can be reduced. When tough pitch Cu or phosphorus deoxidized Cu is used, the solar cell lead wire 1 can be reduced in cost.

  From the above, the strip-like conductive material 2 is either Cu, Al, Ag, or Au, or a tough pitch Cu, low oxygen Cu, oxygen free Cu, phosphorus deoxidized Cu, high purity of 99.9999% or more. It may be made of any one of Cu.

  For the strip-shaped conductive material 2, for example, a rectangular wire having a volume resistivity of 50 μΩ · mm or less is used. By rolling this flat wire, a strip-like conductive material 2 having a cross-sectional shape as shown in FIGS. 1A and 1B can be obtained. In order to increase the contact area between the front surface electrode 42 and the rear surface electrode 43 of the semiconductor substrate 41 and the plating layer 4 and to ensure sufficient heat conduction from the semiconductor substrate 41 to the plating layer 4, the shape of the plating layer 4 is a rectangular shape. Is preferable.

  The plating layer 4 is formed in a so-called mountain shape that swells from the side in the width direction to the center due to the action of surface tension when the molten solder adhering to the upper and lower surfaces 3a, 3b of the strip-like conductive material 2 solidifies. Any of them may be used, or may be formed in a substantially flat shape.

  The plating layer 4 is formed of Sn-based solder (Sn-based solder alloy). 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. These solders may further contain a trace element of 1000 ppm or less.

  The oxide film thickness on the surface of the plating layer 4 is preferably 7 nm or less. When the oxide film thickness on the surface of the plating layer 4 is increased, the removal of the oxide film by flux becomes insufficient at the time of solder joining with the front surface electrode 42 and the back surface electrode 43 of the semiconductor substrate 41 shown in FIG. As a result, there are problems such as mechanical peeling and insufficient output due to poor conduction.

  Here, “self-bonding” means that the resin is melted by heat or a solvent without using a bonding material such as solder, and is adhered to the solar cell. Examples of the resin having a heat-bonding property include, for example, resins having a heat-fusible property such as polyvinyl butyral, polyamide-based, epoxy-based, and polyester-based resins, and resins having an alcohol-welding property, such as a polyamide-based modified to be soluble in alcohol. It is done. In addition, as the paint having self-bonding property, a phenoxy resin such as polyhydroxy polyether resin and a colorant such as carbon black or titania can be used. As the phenoxy resin, one having a sulfone group and improved heat resistance can be used. Further, in order to improve solderability, a flux component such as rosin can be contained in the self-bonding material.

  The covering layer 5 may be composed mainly of a material containing a predetermined amount of other additives in the self-bonding material as long as it can be joined to the cell.

  By coating the self-bonding material, the growth of the oxide film on the surface of the plating layer 4 can be delayed under storage conditions, and the oxide film thickness can be suppressed to 7 nm or less. In other words, by coating the outer layer of the plating layer 4 with a self-bonding material, the growth of the oxide film on the surface of the plating layer 4 is suppressed, and the quality is maintained without sacrificing the bondability even during long-term storage before module assembly. can do.

  In addition, as long as the solar cell lead wire of the present invention can be joined to the cell, the coating layer 5 and the plating layer 4 do not necessarily have to be in direct contact with each other. A structure having an intervening layer in addition to a flux or the like may be used.

  Next, the manufacturing method of the lead wire 1 for solar cells of this invention is demonstrated.

  First, a strip-like conductive material 2 is formed by rolling a wire having a circular cross-section as a raw material or slitting a flat plate, and heat-treating it.

  Thus, as a processing method for processing the raw material into the strip-shaped conductive material 2, both rolling and slit processing are applicable. Rolling is a method of flattening by rolling a round wire. When the strip-like conductive material 2 is formed by rolling, a long and uniform width in the longitudinal direction can be formed. Slit processing can be applied to materials of various widths. That is, even if the width of the conductive material of the raw material is not uniform in the longitudinal direction, even when using various raw material conductive materials having different widths, a long and uniform width in the longitudinal direction can be formed by slit processing. .

  By heat-treating the strip-shaped conductive material 2, the softening characteristics of the strip-shaped conductive material 2 can be improved. Improving the softening characteristics of the strip-shaped conductive material 2 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 plating layer 4 is formed on the upper and lower surfaces 3a and 3b of the strip-like conductive material 2 using the molten solder plating facility shown in FIG. Here, it is necessary to set the temperature of the solder bath 20 higher than the melting point of the solder used. However, in the molten state, Sn in the solder is easily diffused and combined with oxygen in the air, so that oxide film formation is remarkable. Proceed to In addition, the temperature of the working atmosphere and the high humidity contribute to the promotion of oxide film generation. Therefore, the temperature of the solder bath 20 is the liquidus temperature of the solder used + 120 ° C. or lower (the lower limit is the liquidus temperature + 50 ° C. or higher), the temperature of the plating work atmosphere is 30 ° C. or lower (the lower limit is 10 ° C. or higher), The relative humidity in the plating work atmosphere is desirably 60% or less (the lower limit is 10% or more). However, the temperature of the solder bath 20 is measured within 5 cm from the entrance or exit of the strip-like conductive material 2 to the solder bath 20 by a contact thermometer, and the temperature and relative humidity of the plating work atmosphere are measured at a position 5 cm from the plating work line. Indicates the value.

By the above manufacturing method, the oxide film thickness on the surface of the plating layer 4 can be set to 3.0 nm or less (the lower limit is 0.5 nm or more). The oxide film thickness shown here can be defined as the time during which the oxygen peak value is halved in the depth profile obtained by performing Auger analysis on the surface (upper surface or lower surface) of the plating layer 4. That is, the oxide film thickness is a value obtained by averaging data obtained by Auger analysis. The components of the oxide film shown here are Sn oxides (SnO: tin (II) oxide, SnO ₂ : tin oxide (IV)) by SERA (Sequential Electrochemical Analysis: continuous electrochemical reduction method). It can be confirmed that the oxide film thickness obtained by adding the SnO film thickness and the SnO ₂ film thickness obtained by the SERA analysis substantially corresponds to the oxide film thickness obtained by the Auger analysis.

  After the molten solder plating, a self-fusing material is applied to the surface of the plating layer 4 with the equipment as shown in FIG. 3, and the coating thickness is adjusted with a die or the like, followed by baking. At this time, if the baking temperature of the self-bonding material is suppressed below the liquidus line of the solder, the growth of the oxide film thickness on the surface of the plating layer 4 can be suppressed to 7 nm or less (lower limit is 0.5 nm or more). . In addition, it is possible to reduce the manufacturing cost by combining with the above-described molten solder plating equipment by making the line consistent. Through the above steps, the solar cell lead wire 1 of the present invention is obtained.

  Next, the effect | action of the lead wire 1 for solar cells of this invention is demonstrated.

  When the solar cell lead wire 1 of the present invention is soldered to the front surface electrode 42 and the back surface electrode 43 of the semiconductor substrate 41 shown in FIG. 4, the heating temperature of the solar cell lead wire 1 and the semiconductor substrate 41 depends on the plating layer. 4 is controlled to a temperature near the melting point of the solder. The reason is that the thermal expansion coefficient of the strip-like conductive material 2 (for example, copper) of the solar cell lead wire 1 is greatly different from the thermal expansion coefficient of the semiconductor substrate 41 (Si). Due to the difference in thermal expansion coefficient, thermal stress that causes cracks in the semiconductor substrate 41 is generated. In order to reduce this thermal stress, it is preferable to perform low-temperature bonding. For these reasons, the heating temperature of the solar cell lead wire 1 and the semiconductor substrate 41 is controlled to a temperature near the melting point of the solder of the plating layer 4. Here, the plating layer 4 is formed in a substantially flat shape.

  The heating method at the time of bonding is a method in which the semiconductor substrate 41 is placed on a hot plate, and heating from the hot plate and heating from above the solar cell lead wire 1 placed on the semiconductor substrate 41 are combined. is there.

  By this heating, the coating layer 5 containing the self-bonding material and the plating layer 4 are melted, and the solar cell lead wire 1 is soldered to the front electrode 42 and the rear electrode 43 of the semiconductor substrate 41.

  In the solar cell lead of the present invention, since the coating layer is mainly composed of a self-bonding resin, the plating is connected to the surface electrode or the back electrode of the semiconductor substrate after melting by heat, The resin flows and adheres to the solar cell lead wire in the vicinity of the front or back electrode of the semiconductor substrate. That is, there is an advantage that the light receiving area can be secured without the resin leaking more than necessary.

  If the coating layer 5 containing the self-bonding material is melted first and the plating layer 4 is formed in a mountain shape, the coating layer 5 containing the self-bonding material is used as the solar cell lead wire 1. The plating layer 4 that flows and adheres to the side surface of the substrate and is then melted is soldered to the front electrode 42 and the back electrode 43 more reliably.

  On the other hand, the conventional solar cell lead wire 44 has a thick oxide film on the surface of the plating layer 47 during storage until the module is assembled. Therefore, the oxide film can be removed by flux when soldering to the surface electrode 42. Insufficient soldering occurs, resulting in problems such as mechanical peeling and insufficient output due to poor conduction.

  In the solar cell lead wire 1 of the present invention, the surface of the plating layer 4 is stored at the time of storage before assembling the module by setting the oxide film thickness of the surface of the plating layer 4 to 7 nm or less and coating the outer layer with a self-bonding material. Since the growth of the oxide film is suppressed, the oxide film can be easily removed by the flux at the time of bonding, and the solderability is improved, so that the conventional problem is solved.

  Thus, in the solar cell lead wire 1 according to the present invention, the oxide film thickness on the surface of the plating layer 4 is set to 7 nm or less so that the bonding of the semiconductor substrate 41 to the front surface electrode 42 and the back surface electrode 43 becomes strong. Is preferred. As a result, the oxide film can be easily removed at the time of soldering, and the solar cell lead wire 1 can be firmly soldered to the front electrode 42 and the back electrode 43. That is, it is possible to prevent a decrease in module output due to mechanical peeling or poor conduction. In addition, the metallic luster of the solder can be blocked by the coating of the self-bonding material containing the colorant, and the oxide film growth on the surface of the plating layer 4 can be delayed. Furthermore, since the coating material is a self-bonding material, it is possible to cover the entire longitudinal direction of the plating wire, including the part where the cells are soldered together, and the manufacturing process is complicated while maintaining excellent solderability. It also has a suppressing effect.

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

  In the solar cell of the present invention, the solar cell lead wire 1 described so far is soldered to the front surface electrode 42 and the back surface electrode 43 of the semiconductor substrate 41 with the solder of the plating layer 4 having an oxide film thickness of 7 nm or less on the plating surface. It is a thing. Since the solar cell of the present invention uses the solar cell lead wire 1 having the plating layer 4 with an oxide film thickness of 7 nm or less on the plating surface, the surface electrode 42 and the back electrode 43 of the semiconductor substrate 41 are impregnated with solder. Is unnecessary. Therefore, damage to the semiconductor substrate due to solder impregnation of the thinned semiconductor substrate electrode can be avoided. However, the solar cell lead wire 1 of the present invention can also be applied to a type of semiconductor substrate in which electrodes are impregnated with solder, and its use is not limited to a type of semiconductor substrate in which electrodes are not impregnated with solder. Further, the module type is not limited to the crystal system, and can be applied to the case where the solar cell lead wires of various modules such as a thin film system are colored.

  In the solar cell of the present invention, the surface oxide of the semiconductor substrate 41 is very thin because the oxide film thickness of the surface of the plating layer 4 serving as the joint surface between the solar cell lead wire 1 and the surface electrode 42 and the back electrode 43 is as thin as 7 nm or less. When soldering to 42 and the back electrode 43, the oxide film is easily broken by the action of the flux, and good solder wettability is obtained. Therefore, the solder joint between the plating layer 4, the front electrode 42 and the back electrode 43 is strong. become. That is, a high bonding strength can be obtained between the solar cell lead wire 1 and the semiconductor substrate 41.

  According to the solar cell of the present invention, since the bonding strength between the solar cell lead wire 1 and the semiconductor substrate 41 is high, it is possible to improve the yield and the module output when manufacturing the solar cell module. Moreover, since the solar cell lead wire 1 can be manufactured in a continuous process and can be joined to the semiconductor substrate 41 with conventional equipment, a module with excellent design can be provided without increasing the manufacturing cost. As a use, it can be applied to in-vehicle use and residential use, which are often touched by human eyes, but the use is not limited to this.

(Example)
A Cu material, which is a raw material conductive material, was rolled to form a rectangular strip-shaped conductive material 2 having a width of 2.0 mm and a thickness of 0.16 mm. This strip-like conductive material 2 is heat-treated with a batch-type heating equipment, and further, the hot-dip plating equipment shown in FIG. 2 (solder bath temperature 340 ° C., work site temperature 30 ° C., Sn-3% Ag-0.5% Cu solder (liquidus temperature 220 ° C.) is plated at a working site humidity of 65 RH%, and the plating layer 4 ( (A chevron structure with a central plating thickness of 20 μm) was formed (the conductor was heat-treated Cu). Further, a self-bonding material containing a polyhydroxy polyether resin in which carbon black was dispersed was baked and coated around the solder plated wire under a heating condition such that no solvent remained in the coating equipment shown in FIG. Thus, the solar cell lead wire 1 of FIG. 1A was obtained. Thereafter, immediately after the production of the solar cell lead wire and after storage for 1 week in an environment of 60 ° C. × 95 RH%, oxide film measurement (Auger analysis), bonding force measurement, and module efficiency measurement were performed. The oxide film thickness was measured by peeling the coated resin.

(Comparative Example 1)
A strip-like conductive material is formed in the same manner as in the solar cell lead wire 1 of the example, heat-treated with a batch-type heating equipment, and the hot-dip plating equipment (solder) shown in FIG. Sn-3% Ag-0.5% Cu solder (liquidus temperature 220 ° C) is plated at a bath temperature of 340 ° C, a worksite temperature of 30 ° C, and a worksite humidity of 65RH%. A plating layer (plating thickness of 20 μm at the center) was formed on the upper and lower surfaces (conductor was heat-treated Cu). Thereafter, immediately after the production of the solar cell lead wire and after storage for 1 week in an environment of 60 ° C. × 95 RH%, oxide film measurement (Auger analysis), bonding force measurement, and module efficiency measurement were performed. The oxide film thickness was measured by peeling the coated resin.

(Comparative Examples 2 and 3)
A strip-like conductive material is formed in the same manner as in the solar cell lead wire 1 of the example, heat-treated with a batch-type heating equipment, and the hot-dip plating equipment (solder) shown in FIG. Sn-3% Ag-0.5% Cu solder (liquidus temperature 220 ° C) is plated at a bath temperature of 340 ° C, a worksite temperature of 30 ° C, and a worksite humidity of 65RH%. A plating layer (plating thickness of 20 μm at the center) was formed on the upper and lower surfaces (conductor was heat-treated Cu). Thereafter, immediately after the production of the solar cell lead wire and after storage for 1 week in an environment of 60 ° C. × 95 RH%, oxide film measurement (Auger analysis), bonding force measurement, and module efficiency measurement were performed. The oxide film thickness was measured by peeling the coated resin.

  Comparative Example 2 is a module in which the produced solar cell lead wire is joined to a semiconductor substrate, and then a surface of the solar cell lead wire opposite to the joint surface (module surface) is covered with a polyester resin containing a black filler. Was made.

  In Comparative Example 3, a module was manufactured using a glass plate in which the corresponding portion on the wiring portion was colored black so as to mask the wiring portion of the solar cell lead wire.

As a result of Auger analysis of the oxide film thickness of the plating layer of the solar cell lead wires of these Examples and Comparative Examples 1 to 3 (immediately after production and after storage at 60 ° C. × 95 RH% × 1 week), all were immediately after production. The oxide film thickness is as thin as 2.5 nm, and after storage at 60 ° C. × 95 RH% × 1 week, the oxide film thickness is as thin as 3.0 nm in the example, whereas the comparative examples 1 to 3 all have the oxide film thickness. It was found to be as thick as 7.2 nm. Here, the oxide film thickness is defined by the time during which the oxygen peak value is halved in the depth profile (sputtering time vs. composition ratio) obtained by Auger analysis, and was calculated by the following equation.
Oxide film thickness (nm) = SiO ₂ conversion sputter rate (nm / min) × Time during which oxygen peak value is halved (min)

  An appropriate amount of rosin-based flux is applied to the solar cell lead wires of these examples and comparative examples 1 to 3, and each solar cell lead wire has a 155 mm × 155 mm × 160 μm semiconductor substrate (previously applied to the electrode). It was placed on a solder-free impregnated plate, heated on a hot plate (held at 260 ° C. for 30 seconds), and the solar cell lead wire was soldered to the semiconductor substrate as in FIG. Further, a 90 ° peel test (test speed: 10 mm / min, peel length: 15 mm) was performed in order to evaluate the bonding strength of the solar cell lead wires soldered to these semiconductor substrates to the semiconductor substrate. Moreover, the produced solar cell lead wire and semiconductor substrate assembly was incorporated into a module, and the module efficiency was compared with a module produced by a conventional method (Comparative Example 1).

  The evaluation results of Examples and Comparative Examples 1 to 3 are shown in Table 2.

  The column of “Designability” in Table 2 indicates whether or not the designability is taken into account by blocking the metallic luster of the solar cell lead wire. The column “Manufacturing cost” indicates the manufacturing cost of the solar cell lead wire and the module based on the conventional manufacturing method (Comparative Example 1) that does not consider design. In the column of “Use of lead wire immediately after manufacture”, the column of “Oxide film thickness” indicates the thickness of the oxide film on the surface of the plating layer (number of samples) obtained from the depth profile (sputter time vs. composition ratio) by Auger analysis. average value of n = 5). The column of “Joint strength” shows the result of testing whether the copper plate and the solar cell lead wire are pulled by a 90 ° peel test, and the tensile strength of the joint is peeled off. , X indicates a tensile force of less than 10N. The column of “module efficiency” is based on the module efficiency obtained by the conventional manufacturing method (Comparative Example 1) that does not take into consideration the design, ○ indicates that the module efficiency does not decrease, and × indicates that the module efficiency decreases. . Also, the column “Use lead after storage at 60 ° C. × 95RH%” shows “Oxide film thickness”, “Joint strength”, “Module efficiency” after storing each lead wire for solar cell at 60 ° C. × 95RH%. The evaluation results are shown.

  As a result of the “designability” evaluation, it was confirmed that the metallic luster of the solar cell lead wire was cut off in the module appearance except for the conventional manufacturing method (Comparative Example 1) that did not consider the designability, and the design was excellent. . As a result of the “manufacturing cost” evaluation, Comparative Example 2 in which the manufacturing process is complicated increases remarkably the manufacturing cost as compared with the conventional manufacturing method (Comparative Example 1). It was found that the manufacturing cost is not significantly different from the conventional (Comparative Examples 1 and 3) because the lead wire for solar cell can be directly soldered to the electrode on the silicon cell that is the semiconductor substrate. . In the case of “use of lead wire immediately after manufacture”, since any of the solar cell lead wires has a thin oxide film thickness on the surface of the plating layer, the bonding strength is excellent. In order to block the metallic luster of the module, black lines are baked and painted on the glass plate on the surface of the module, and a light-shielding tape is applied. As a result of shadow loss, module efficiency is reduced compared to the conventional case. In the case of “use of lead wire after storage at 60 ° C. × 95 RH%”, since the oxide film growth of the plating layer on the surface of the lead wire for solar cell is remarkably reduced except for the examples, the solder wettability is lowered. It has been found that the contact resistance increases with module efficiency.

DESCRIPTION OF SYMBOLS 1 Solar cell lead wire 2 Strip | plate-like electroconductive material 4 Plating layer 5 Covering layer

Claims (2)

  Sn-based solder is used on the surface of the strip-shaped conductive material, or Sn is used as the first component, and at least one element selected from Pb, In, Bi, Sb, Ag, Zn, Ni, Cu is used as the second component. A plating layer made of Sn solder alloy containing 0.1 mass% or more, and a resin made of any of phenoxy resin, polyvinyl butyral resin, polyamide resin, epoxy resin, and polyester resin on the outside of the plating layer A lead wire for a solar cell, comprising: a coating layer including: an oxide film thickness on the surface of the plating layer being 7 nm or less. Sn-based solder is used on the surface of the strip-shaped conductive material, or Sn is used as the first component, and at least one element selected from Pb, In, Bi, Sb, Ag, Zn, Ni, Cu is used as the second component. A solar cell lead wire having a plating layer made of a Sn-based solder alloy containing 0.1 mass% or more;
A semiconductor substrate bonded to the solar cell lead wire,
The solar cell lead wire is bonded to the electrode provided on the semiconductor substrate by the solder of the plating layer,
A solar cell comprising a coating layer containing a resin composed of any one of a phenoxy resin, a polyvinyl butyral resin, a polyamide resin, an epoxy resin, and a polyester resin on a side surface of the solar cell lead wire.

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