JP5397415B2 - Solar cell module - Google Patents

Description

The present invention relates to a solar cell interconnector, a method for manufacturing the same, and a solar cell module using the solar cell interconnector .

  Since the solar cell is a power generation method that directly converts infinite solar energy into electric energy, technological development has recently become active as a technology for greatly reducing energy problems, and the market has greatly increased.

  In the solar cell modules which are currently mainstream, solar cells using a single crystal or polycrystalline silicon substrate having a size of several tens of centimeters are arranged, and these are connected by electric conductors to collect current. Yes. For the connection between the substrate and the electric conducting wire, melt liquid phase bonding using solder is the mainstream, and as the electric conducting wire, a rectangular copper wire covered with solder is used as an interconnector for collecting current. The interconnector is solder-connected to the solar battery cell via an electrode formed by applying and baking silver or aluminum paste.

JP 2006-80217 A JP 2008-21831 A JP 2008-168339 A

Hirotoshi Endo, et al., Hitachi Cable: 2007, Vol. 26, No. 1, p15

  Since the solar cell module is an energy device, the cross-sectional area of the interconnector itself and the connection area between the interconnector and the solar cell also need an area corresponding to the amount of current. On the other hand, when the width of the rectangular copper wire is increased, sunlight is reflected by the interconnector and this portion becomes a shadow, which is a cause of reducing the power generation efficiency of the solar battery cell.

  In the case of a solar cell using a polycrystalline silicon substrate, the thermal expansion coefficient of copper, which is the main material of the interconnector, is about five times that of silicon, which is the main structure of the solar cell. Therefore, when the temperature is raised and liquid phase bonding is performed and then cooled to room temperature, thermal stress is generated, which causes deformation and breakage of the solar battery cell (see Non-Patent Document 1). In recent years, due to the tightness of silicon materials, the thickness of silicon substrates used in solar cells has been reduced, and silicon substrates with a thickness of 180 μm are now being used. The corruption problem has become a big problem.

  In order to solve this problem, an attempt has been made to reduce the 0.2% yield strength (yield stress) of the interconnector so as to make it softer (see Non-Patent Document 1). However, it is expected that softening by normal annealing will be difficult to cope with the severe usage situation in the future, and it has been proposed to respond by improving the interconnector structure and mounting structure and controlling the texture. (See Patent Documents 1 to 3). In Patent Document 1, a wavy structure is provided in the length direction of an interconnector, and stress is released at the bellows portion. Patent Document 2 provides a non-connecting portion that does not form electrodes at arbitrary intervals in the length direction of the electrode of the solar battery cell, and relieves stress by adding a notch to the interconnector that faces the non-contacting portion. To do. Further, in Patent Document 3, the crystal orientation (plating line axis orientation) at the center of the conductor is oriented at a ratio of 30% or more to the (211) orientation, thereby reducing the 0.2% proof stress and reducing the variation. It is supposed to be possible.

  Of the above techniques, the stress relaxation technique based on the structure of the interconnector is considered to be an effective means. However, the method of Patent Document 1 has a problem that a necessary interconnector becomes long, and material cost and electrical resistance value increase. In the methods of Patent Documents 1 and 2, there is an increase in connection resistance due to a reduction in junction area, and there is a problem that the electrical resistance value of the notch portion increases.

  When the interconnector is mounted on a semiconductor substrate such as a solar battery cell, soldering is performed by applying pressure from the interconnector toward the cell electrode with hot air, a heating holding jig, a soldering iron or the like. At this time, if the supply of solder is not sufficient, the entire surface is not welded, and the electrons and holes generated in the solar cell cannot be collected, or the solar cell is damaged due to local heat generation. There is a case. Therefore, it is necessary to supply a sufficient amount of solder, but if the clearance between the electrode on the photovoltaic cell formed of a paste of silver or aluminum and the interconnector is not appropriate or partially small, Molten solder protrudes in the width direction of the interconnector, and in some cases protrudes beyond the electrodes on the solar cells. Accordingly, there is a problem that the light receiving area is reduced and the power generation efficiency is lowered.

The present invention has been made to solve the above problems, the electrical conductor portion and the bonding target (e.g., a semiconductor substrate typified by silicon) of the rectangular distance between, i.e. in the surface layer after bonding While maintaining a uniform thickness of the bonding layer , it is possible to obtain an electrically uniform and good bond, and thermal expansion between the material of the electrical conductor (for example, copper) and the material to be bonded (for example, a semiconductor represented by silicon) Reduces the thermal stress and thermal distortion that occurs after solder mounting due to the difference, suppresses the warping and cracking of the object to be joined, and applies the flat conductor to the interconnector of the solar cell module. It aims at providing the flat conducting wire which suppresses the fall of the power generation efficiency resulting from it, its manufacturing method, and a solar cell module.

Solar cell module of the present invention includes a semiconductor substrate constituting a solar cell, an electrode formed on a surface of the semiconductor substrate, and the interconnector connected solar cell and the electrode, the solar cell The interconnector has a flat electrical conductor portion and a wide surface of the electrical conductor portion, and has a surface layer with a thickness of 10 μm to 40 μm on one surface. It is made of a material in which a granular filler having a maximum diameter higher than that of the solder and having a maximum diameter of 10 μm to 40 μm is dispersed, and a portion covering the one surface is defined by the maximum diameter of the filler. and it is, the are formed uneven surface due to the presence of less the filler amount of the solder than the other part covering the parts the one surface covering the surface of the wide, in for the solar cell Through the one surface of the surface layer of the over connector, the said electrical conductor portion electrode are electrically connected, and the electrode and the other surface of the surface layer in the light-receiving surface side of the electric wire portion It becomes a non-connection part .

  According to the present invention, the gap between the flat electrical conductor portion and the object to be joined (for example, a semiconductor substrate typified by silicon), that is, the thickness of the surface layer is kept constant, and an electrically uniform and satisfactory joining is obtained. At the same time, the thermal stress and thermal strain generated after mounting by solder due to the difference in thermal expansion between the material of the electrical conductor portion (for example, copper) and the material to be joined (for example, a semiconductor typified by silicon) are reduced, It is possible to suppress the occurrence of warpage and cracking of the joining target, and to suppress the decrease in power generation efficiency caused by the interconnector when the flat conducting wire is applied to the interconnector of the solar cell module.

It is a schematic sectional drawing which shows the structure of the flat conducting wire by this embodiment. It is a schematic diagram which shows the apparatus structure for manufacturing the flat conducting wire by this embodiment. It is a schematic diagram which shows the other apparatus structure for manufacturing the flat conducting wire by this embodiment. It is a perspective view which shows schematic structure of the solar cell module which mounted the flat conducting wire by this embodiment as an interconnector. It is a schematic sectional drawing which shows the mode of the cross section orthogonal to the longitudinal direction of the interconnector in FIG.

  Hereinafter, specific embodiments of a rectangular conductive wire, a method for manufacturing the same, and a solar cell module will be described in detail with reference to the drawings. In addition, the flat conducting wire according to the present embodiment can be applied to semiconductor mounting materials used for small semiconductor devices such as LSIs and LEDs other than solar cell modules.

FIG. 1 is a schematic cross-sectional view showing the configuration of a flat conducting wire according to the present embodiment, and shows a cross section orthogonal to the longitudinal direction of the flat conducting wire.
This flat conducting wire comprises a flat electric conducting wire portion, here a copper wire portion 1, and a surface layer 2 covering at least one wide surface of the copper wire portion 1, here the entire surface. As the electrical conductor portion, in addition to the copper wire portion 1 made of copper, a material made of a copper alloy, or other electrically conductive material such as aluminum or silver is used. Here, the wide surface means a surface including a wide side in a cross section orthogonal to the longitudinal direction of the copper wire portion 1 in the surface of the copper wire portion 1.
The surface layer 2 is formed by dispersing granular fillers 2b made of a material having a melting point higher than that of the solder in the solder plating 2a. The surface layer 2 may be formed on only one or two of the wide surfaces of the copper wire portion 1 depending on the object to be joined with the flat wire.

As the solder of the solder plating 2a, Pb—Sn eutectic solder, Sn—Ag—Cu-based lead-free solder, and other types can be used.
The filler 2b may be made of any material as long as it has a melting point higher than that of the above-described solder and functions as a spacer when the flat conductor is mounted (when the flat conductor is joined to the joining object). If the material of the filler 2b is a metal such as copper, aluminum or silver, there is an advantage that the electrical resistance value is low and the electrical resistance value of the surface layer 2 is lowered. If the material of the filler 2b is stainless steel, alumina, silica or the like, the thermal expansion coefficient is smaller than that of solder, for example, a value between silicon and copper, so that the surface layer 2 acts as a thermal stress relaxation layer after mounting. When the material of the filler 2b is ceramics, the effect of improving the wettability with the solder plating 2a can be obtained by coating the surface of the filler 2b with an active metal such as titanium or tungsten.

  In the flat conducting wire according to the present embodiment, the melting point of the filler 2b constituting the surface layer 2 is higher than that of the solder plating 2a. By setting the processing temperature at the time of mounting the flat conductive wire to be equal to or higher than the melting point of the solder plating 2a and lower than the melting point of the filler 2b, the filler 2b is not melted when the solder plating 2a is melted. Therefore, at the time of the mounting, the filler 2b functions as a spacer between the copper wire part 1 and the object to be joined, and the distance between the copper wire part 1 and the object to be joined is defined by the largest diameter of the fillers 2b. The thickness of the surface layer 2 is kept at a constant value. That is, by forming the surface layer 2 using the filler 2b having the maximum diameter equal to a desired value as the distance between the copper wire portion 1 and the object to be joined, that is, the thickness of the solder plating 2a, solder plating is easily and accurately performed. The thickness of 2a can be controlled.

The thickness of the solder plating 2a when the flat wire is mounted, that is, the thickness of the surface layer 2 is preferably a value within a range of 10 μm to 40 μm, for example, as will be described later. The thickness of the surface layer 2 after mounting of the flat conductor, since it is defined by the maximum diameter of the filler 2 b, the filler 2 b, it is preferable that the maximum diameter has a value between 10Myuemu～40myuemu. The particle size distribution of the filler 2b is not particularly specified, but it is preferable as the spacer to spheroidize and narrow the particle size distribution. However, a filler having a larger diameter than this may be mixed with an extremely small probability. For example, when the diameter distribution follows a normal distribution, the upper limit of 3σ of the diameter distribution of the filler is set as the maximum diameter (σ: standard deviation). In the case of a filler whose upper limit diameter that has been sieved is cut, the upper limit diameter is the maximum diameter. For example, 99.85% of the filler diameter counted from the smallest is the maximum diameter. There is no problem even if a filler having a larger diameter is mixed.

FIG. 2 is a schematic view showing a device configuration for manufacturing the rectangular conducting wire according to the present embodiment.
This manufacturing apparatus is applied to a technique called a hot dipping method. As shown in FIG. 2 (a), a molten solder plating bath 21 that accommodates molten solder plating 2a, a copper wire guide 22 that regulates the supply of a flat copper wire portion 1, and a filler 2b that is supplied to the solder plating 2a. And a filler guide 24 serving as a supply path for the filler 2b.

  In order to manufacture the flat conducting wire according to the present embodiment using the manufacturing apparatus of FIG. 2A, the copper wire guide 22 is driven and the copper wire portion 1 is placed in the molten solder plating 2a of the molten solder plating bath 21. The solder plating 2a is supplied to the surface of the copper wire portion 1 through the wires. The copper wire part 22 supplied with the solder plating 2a is sent out by the copper wire guide 22. Immediately after delivery to the outside of the copper wire part 1, the filler 2 b is supplied from the filler hopper 23 through the filler guide 24 in contact with the solder plating 2 a covering the copper wire part 1. The solder plating 2a containing the filler 2b is cooled and completely solidified. By the above, the surface layer 2 is formed in the surface of the copper wire part 1, and a flat conducting wire is produced.

  Here, as shown in FIG. 2B, a pressure contact roller 25 for pressing the copper wire portion 1 may be provided in the manufacturing apparatus. In this case, for example, the solder plating 2a supplied with the filler 2b is forcibly pressed against the copper wire portion 1 by the pressing roller 25 rotating in the direction of the arrow. Thereby, the solder plating 2a can be reliably regulated to a desired thickness. Thereafter, the solder plating 2a containing the filler 2b is cooled and solidified completely, whereby the surface layer 2 is formed, and a flat conductor is produced.

FIG. 3 is a schematic view showing another apparatus configuration for manufacturing the flat conducting wire according to the present embodiment.
This manufacturing apparatus is applied to a technique called aerosol or cold spray, and includes a mixture chamber 31 for generating a mixture 30 of solder powder and filler, and a nozzle 32 for supplying the mixture to the copper wire portion 1. And.

In order to manufacture the flat conducting wire according to the present embodiment using the manufacturing apparatus of FIG. 3, the copper wire portion 1 is made to travel in the direction of the arrow, for example, and the mixture 30 of the solder powder and filler generated in the mixture chamber 31 is From the nozzle 32, it supplies to the surface of the copper wire part 1 at high speed with a solid state. Thereby, the surface layer 2 is formed in the copper wire part 1, and a flat conducting wire is produced.
In the example of FIG. 3, the mixture chamber 31 and the nozzle 32 are installed corresponding to each wide surface of the copper wire portion 1, but for example, by installing only one mixture chamber 31 and the nozzle 32, the copper wire portion The surface layer 2 can be formed by supplying the mixture 30 to only one of the wide surfaces.

FIG. 4 is a perspective view showing a schematic configuration of a solar cell module in which the flat conducting wire according to the present embodiment is mounted as an interconnector. FIG. 5 is a schematic cross-sectional view showing a state of a cross section orthogonal to the longitudinal direction of the interconnector in FIG.
As shown in FIG. 4, this solar cell module includes a plurality of solar cells 11 provided side by side and an interconnector 13 that is electrically connected to electrodes 12 formed on the surface of each solar cell 11. I have. As the interconnector 13, the flat conducting wire according to the present embodiment is applied. The interconnector 13 collects each solar battery cell 11 through the electrode 12.

The cross-sectional state of the solar cell module is shown in FIG. FIG. 5 is a schematic cross-sectional view showing a state of a cross section orthogonal to the longitudinal direction of the interconnector 13.
Electrodes 12 are respectively formed on the front surface and the back surface of the solar battery cell 11 made of a single crystal or polycrystalline silicon substrate. As the material of the electrode 12, for example, silver paste is used on the front surface side (light receiving surface side) and silver and aluminum paste are used on the back surface side. The electrode 12 is formed by firing the metal paste. Since the light receiving surface receives sunlight, the electrode area should be as small as possible within the range where the collected current can sufficiently flow.

The interconnector 13 is a flat conductive wire as described above, and has a flat copper wire portion 1 and a surface layer 2 covering at least one of the wide surfaces of the copper wire portion 1. The interconnector 13 mounted on the surface of the solar battery cell 11 has the surface layer 2 formed on the lower wide surface and the upper wide surface of the copper wire portion 1, respectively. They are electrically and mechanically connected by solder plating 2a on the surface layer 2 of the wide surface on the side. Of the surface layer 2 , in the bonding layer with the electrode 12 on the solar battery cell 11 , the filler 2b functions as a spacer, and the thickness of the surface layer 2 is defined by the filler 2b having the maximum diameter. In the interconnector 13 mounted on the back surface of the solar battery cell 11, the bonding layer of the surface layer 2 is formed on the wide surface on the upper side of the copper wire portion 1, and the copper wire portion 1 is soldered between the electrode 12 and the surface layer 2. They are connected by plating 2a. Similarly, in the surface layer 2, the filler 2b functions as a spacer, and the thickness of the surface layer 2 is defined by the filler 2b having the maximum diameter. The interconnector in which the surface layer is formed only on one wide surface of the copper wire portion can also be applied to a case where the interconnector is mounted only on one surface, such as a back contact solar cell module.

  An EVA (ethylene vinyl acetate) adhesive layer 14 is provided on each of the front and back surfaces of the solar battery cell 11 to seal the interconnector 13. The EVA adhesive layer 14 on the front surface (light receiving surface) side is covered with a protective glass 15, and for example, a back film 16 is provided on the EVA adhesive layer 14 on the back surface side.

  In general, when manufacturing a solar cell module, it is desirable to supply enough solder when soldering the interconnector. However, if the amount of supplied solder is excessive, the solder will protrude from the electrodes and receive light. The area will decrease. Since the junction length between the interconnector and the solar battery cell is long and two-dimensional, it is difficult to keep the solder thickness uniform in the length direction. When the interval between the solders is reduced due to non-uniform pressure or the like when mounting the interconnector, the amount of solder supplied from the layer previously coated on the interconnector is constant, so the solder is laterally It protrudes and the light receiving area is reduced. On the other hand, if the supply amount of solder is too large, the solder has a higher electrical resistance value than copper, so that the electrical resistance value becomes high. Further, in this case, since the height of the interconnector is high, the shadow of the interconnector greatly extends to the light receiving surface in a situation where sunlight is received obliquely. If the amount of solder at the time of interconnector connection is excessive due to the above factors, the power generation efficiency of the solar cell module is reduced.

  On the other hand, if the supply amount of solder is small, it becomes difficult to supply the solder uniformly, and the effect of alleviating the thermal expansion difference between the copper of the wiring and the silicon of the solar cell by interposing a soft solder. Becomes smaller. Therefore, thermal stress and thermal strain increase, and warpage and cracking of the solar battery cell are increased.

In the solar cell module according to the present embodiment, the filler 2b is not melted even when the solder plating 2a is melted when the interconnector 13 is joined to the electrode 12, and the filler 2b is a spacer between the copper wire portion 1 and the electrode 12. The distance between the copper wire portion 1 and the electrode 12 is defined by the maximum diameter of the fillers 2b, and the thickness of the bonding layer of the surface layer 2 is maintained at a desired and appropriate constant value. .
By using the value of the thickness of the surface layer 2 in the range of 10 μm to 40 μm, in other words, the filler 2 b having the maximum diameter in the range of 10 μm to 40 μm, The reduction in power generation efficiency of the solar cell module and the warpage / cracking of the solar cell can be suppressed.

In this solar cell module, the surface layer 2 is also formed on the wide surface on the upper side of the interconnector 13 mounted on the surface of the solar cell 11.
When the filler 2b is dispersed in the solder plating 2a on both sides of the wide surface of the copper wire part 1, a part of the solder plating 2a supplied to the upper surface of the copper wire part 1 is caused by gravity and surface tension. Move to the bottom. As a result, unevenness is formed in the upper surface layer 2 that is not used for bonding to the electrode 12 due to the presence of the filler 2b. On the surface (light-receiving surface) side of the solar battery cell 11, the incident sunlight 10 is irregularly reflected by the unevenness of the wide surface on the upper side of the interconnector 13, and a part thereof is an interface between the EVA adhesive layer 14 and the protective glass 15, protection. The light is reflected again at the interface between the glass 15 and the atmosphere, and enters the solar battery cell 11. Thereby, the light normally lost by reflection by the interconnector is also used as electric power, and the power generation efficiency of the solar cell module is further improved.

  As described above, according to the present embodiment, the surface layer is formed by dispersing the granular filler having a melting point higher than that of the solder contained in the solder. Thereby, the filler plays the role of a spacer, the distance between the electrode on the solar battery cell and the surface of the flat copper wire portion is kept at an appropriate level, and an electrically uniform and good bonding is obtained. At the same time, it reduces the thermal stress and thermal strain generated after mounting by solder due to the difference in thermal expansion between copper and silicon, reduces the warpage and cracking of the solar cell, and reduces the solar cell and the flat conductor (interconnector). Electrical and mechanical joining by soldering can be improved. By selecting a filler with a diameter smaller than the thickness of the solder and bringing the coefficient of thermal expansion of the solder closer to that of the solar battery cell, thermal stress and thermal strain generated after mounting with solder are reduced, and warpage and cracking of the solar battery cell are reduced. In addition, it is possible to improve the electrical and mechanical joining of the solar battery cell and the flat conductive wire by soldering.

  Furthermore, by keeping the distance between the electrode on the solar battery cell and the surface of the flat wire at an appropriate distance, it becomes possible to hold a sufficient and uniform molten solder between the solar battery cell and the copper wire portion, and to receive light. It is possible to prevent the solder from protruding to the surface and to prevent the power generation efficiency of the solar cell module from decreasing. Also, the opposite surface of the joint surface with the flat conductor is uneven due to the presence of the filler, so that the sunlight incident on the flat conductor on the light receiving surface side is irregularly reflected, and the irregularly reflected light is regenerated at the protective glass interface of the solar cell module. The power generation efficiency is improved by reflecting and entering the light receiving surface of the solar battery cell.

  Hereinafter, specific examples of the present invention will be described.

Example 1
In this example, a rectangular conductor (interconnector) having a solder plated surface layer containing a stainless filler was prepared. As the copper core material, a rectangular copper wire portion having a thickness of 0.2 mm and a width of 2 mm by rolling a tough pitch copper round wire having a diameter of 1.5 mm was used. The copper wire portion was passed through an annular furnace heated to 600 ° C. in which nitrogen containing 40% hydrogen was passed, and the copper wire portion was inserted in the molten solder plating tank at the outlet side of the copper wire portion of the annular furnace. The wire was drawn out and hot-dip plated. As a solder material, Sn-3.0 wt% Ag-0.5 wt% Cu was used, and the temperature of the hot dipping bath was set to 300 ° C. The copper wire portion that has passed through the hot dipping bath is drained in the vertical direction using a copper wire guide, but a square hole having a thickness of 0.3 mm and a width of 2.4 mm is formed in the liquid surface of the plating bath. An aperture die is installed and moves upward through the hole. The copper wire portion immediately after passing through the drawing die rides in a state where the solder is melted, and the solder cools and solidifies as it moves upward. The thickness of the solder covering the copper wire portion that passes through at a speed of 0.5 mm / min was 25 μm on one side in the plate thickness direction, and this was used as a comparative material. This is designated as sample A.

  On the other hand, a feeder for supplying a stainless steel filler was provided immediately above the drawing die, the stainless steel filler was brought into contact with the surface of the molten solder, and the stainless steel filler was press-fitted into the solder plating layer immediately after the press roller, thereby producing a rectangular conductor. . The stainless steel filler was classified by sieving, and the maximum diameter was 20 μm. As a result of wiring at a speed of 0.5 mm / min, the thickness of the solder was 25 μm, and the volume ratio of the stainless steel filler in the solder was 10%. The flat conducting wire thus produced is designated as sample B.

  Two flat conductive wires described above were used and mounted on electrodes made by firing silver paste having a width of 3 mm provided in parallel in two rows on a solar cell having a thickness of 200 μm and a 150 mm square at a constant pressure. At the time of mounting, the solder was melted and joined at a temperature higher than the melting point of the solder and lower than the melting point of the stainless filler. The lateral length of the solder protruding from the flat wire and the warpage of the solar battery cell were measured.

  In sample A, the solder locally protruded in the lateral direction of the copper wire portion, the width reached an average of 0.2 mm on one side and a maximum of 1 mm, and the solder protruded from the electrode and spread to the light receiving surface of the solar cell. On the other hand, in the sample B, the amount of protrusion of the solder in the lateral direction was an average of 0.05 mm on one side and a maximum of 0.1 mm.

  Comparing the cross sections of the copper wire portions of Samples A and B, in Sample B, the distance between the electrode of the solar cell and the copper wire portion was maintained at an average of 25 μm by the stainless filler, and the solder did not spread laterally. On the other hand, in the sample A, there is a portion where the solder hardly exists locally between the copper wire portion and the electrode, and the solder protruded greatly in the lateral direction in the portion.

  In addition, the warpage of the solar battery cell using the sample A not mixed with the stainless steel filler was warped 3 mm on the side where the flat wire was mounted, whereas the flat wire of the sample B mixed with the stainless steel filler was used. What was mounted was 0.8 mm. This is because the solidification shrinkage of the solder was small because the stainless steel filler was in a solid phase at the time of solder reflow, the thermal expansion coefficient of stainless steel was small, and the thermal shrinkage after solidification was small. This is because the thermal strain caused by the difference between the thermal expansion coefficients of copper and silicon was alleviated.

(Example 2)
In this example, a rectangular conductive wire (interconnector) having a solder plated surface layer containing a copper filler was produced. As the copper core material, a rectangular copper wire portion having a thickness of 0.2 mm and a width of 2 mm by rolling a tough pitch copper round wire having a diameter of 1.5 mm was used. This copper wire portion was connected to a heated annular furnace in which nitrogen containing 40% hydrogen was passed, and the copper wire portion was led out with the outlet side of the copper wire portion of the annular furnace inserted in the molten solder plating tank. And hot dip plated. As the solder material, a Sn-1.2 wt% Ag-0.5 wt% Cu-0.05 wt% Ni alloy was used, and the copper wire portion that passed through the hot dipping bath maintained at 250 ° C. was a copper wire. Use a guide to pour out hot water and move upward. The copper wire portion immediately after the hot water rides in a state where the solder is melted, and the solder cools and solidifies as it moves upward.

  For supplying the copper filler, a feeder for supplying the copper filler was provided, the copper filler was brought into contact with the surface of the molten solder, and the copper filler was press-fitted into the solder plating layer with a press roller immediately after. The copper filler was classified by sieving, and the maximum diameter was five levels of 5 μm to 50 μm. Adjust the amount of feeder, the temperature of the annular furnace, and the wire speed so that the volume fraction of the copper filler in the solder is 20% and the thickness of the solder is the maximum diameter of the copper filler. A flat rectangular wire having the above structure was produced. The flat conductor wires thus produced are designated as samples C to J. Further, as a comparative material, a rectangular conductor wire having a one-side solder thickness of 40 μm was prepared without adding a copper filler. The flat conductor wire thus produced is designated as sample K.

Two flat conductive wires were used, and each was mounted on an electrode formed by firing silver paste having a size of 3 mm × 5 mm provided in parallel in two rows on a solar cell having a thickness of 190 μm and a 170 mm square at a constant pressure. At the time of mounting, the solder was melted and joined at a temperature higher than the melting point of the solder and lower than the melting point of the copper filler. The length of the mounted flat conducting wire was 170 mm, which was the same as that of the solar battery cell, and was mounted along the center line of the electrode on the solar battery cell. The solar battery cell and the flat conducting wire were joined while being shifted by 5 mm in the mounting length direction. After joining, the solder protruding from the flat wire was observed, and the state of warpage / crack of the solar cell was measured.
The results are shown in Table 1 below.

  The solder protrusion was evaluated based on the degree of wet spreading in the direction perpendicular to the length direction of the flat wire after mounting the flat wire. ○ means that the electrode and the solder were wetted, and the fillet was formed, but the lateral wetting spread was uniform and within the width of the silver electrode. Δ indicates that the solder protrudes locally, but the maximum lateral spread is within 3 mm of the electrode width. In the case of ×, the solder protruded locally, exceeded the electrode, and spread to the light receiving surface of the solar battery cell.

  Moreover, the evaluation of the crack was evaluated as follows by polishing the cross section of the joint portion between the flat conducting wire and the solar battery cell and observing it with an optical microscope. ○ indicates that no cracks were observed, Δ indicates that cracks were locally generated in the solder, and × indicates that large cracks occurred and the solar cells and the rectangular conductors were partially separated. It was supposed to be.

  In Samples C, D, I, and J, it was recognized that the solder spread to the width of the electrode close to 3 mm, but no protrusion from the electrode was observed in all the rectangular wires. On the other hand, in the flat conductive wire using no copper filler, the solder spreads and reaches the light receiving surface of the solar battery cell. This is the effect of the copper filler. In particular, it was favorable when the thickness of the surface layer was 10 μm to 40 μm. The reason why the copper filler slightly protruded in the sample was considered that the copper filler flowed during the joining. Further, when the solder is thick, it tends to wet and spread in the lateral direction, but it can be considered that this is suppressed by the presence of the copper filler.

  The amount of warpage depends on the maximum diameter of the copper filler, and when the maximum diameter of the copper filler is 10 μm to 40 μm, the amount of warpage is small, and cracks are not observed, and sound bonding is possible. When the maximum diameter of the copper filler was less than 10 μm, the distance between the copper wire and silicon was too small and the thermal stress due to the difference in thermal shrinkage after reflow could not be relieved, resulting in cracks in the solder and solar cells. . However, it was found that cracks were stopped in the vicinity of the copper filler, and the progress of cracks could be suppressed.

  On the other hand, when the maximum diameter of the copper filler is larger than 40 μm, the thickness of the copper wire portion added with solder increases, so the thermal stress due to the difference in thermal shrinkage after reflow increases, and cracks occur in the solar cells. occured. In particular, in sample K not containing a copper filler, peeling occurred between the solar battery cell and the silver electrode interface. This is probably because the thermal stress applied to the interface was the largest.

  Next, the electrical resistance value was measured between the end portion of the flat conducting wire protruding 5 mm from the solar battery cell and the exposed electrode surface not joined to the flat conducting wire. As a result, the electrical resistance value straddling the joint portion where the flat conductor having the surface layer containing the copper filler was mounted was lower than the electric resistance value straddling the joint portion mounted without containing the copper filler. . This is because copper is a better conductor than solder, so that an electric current flows even through a copper filler, thereby lowering the electrical resistance value of the joint portion. In addition, the reason why the electrical resistance value of the rectangular conducting wire not containing the copper filler is high is that the flow of electric current is hindered due to the occurrence of peeling at the joint portion. The electrical resistance value at the joint part was the lowest when the thickness of the surface layer was 10 μm to 40 μm, but this was also because the introduction of cracks was suppressed by the stress relaxation mechanism and the joint part was sound. That is, it has been clarified that the electrical resistance value of the surface layer is lowered by using the copper filler.

  As the thickness of the copper wire portion with the solder increases, the shadow when sunlight enters obliquely becomes longer. Since the light-receiving surface is shielded from light, the power generation efficiency of the solar cell module is lowered. Therefore, the maximum diameter of the copper filler can be said to be the most desirable range from 10 μm to 40 μm from this point.

(Example 3)
In this example, each rectangular conductive wire (interconnector) having a solder plating surface layer with aluminum, silver, nickel, alumina, and silica as the filler material was produced by a hot dipping method and an aerosol method. As the copper core material, a rectangular copper wire portion having a thickness of 0.15 mm and a width of 2 mm was obtained by rolling a tough pitch copper round wire having a diameter of 1.5 mm.

  A sample by a hot dipping method was prepared as follows. The copper wire portion was connected to a heated annular furnace in which nitrogen containing 40% hydrogen was passed, and the copper wire portion was led out in a state where the outlet side of the copper wire portion of the annular furnace was inserted into the molten solder plating tank, Hot-dip plated. As the solder material, Sn-3.0 wt% Ag-0.5 wt% Cu alloy was used, and the copper wire portion that passed through the hot dipping bath maintained at 250 ° C. was perpendicular to the copper wire guide. Move to the hot water. The copper wire portion immediately after the hot water rides in a state where the solder is melted, and the solder cools and solidifies as it moves upward.

For supplying the filler, a feeder for supplying the filler was provided, the filler was brought into contact with the surface of the molten solder, and the filler was press-fitted into the solder plating layer with a press roller immediately after.
The filler was classified by a sieve, and the maximum diameter was 25 μm. As the alumina filler and the silica filler, those coated with about 0.05 μm Ti by vapor deposition were used. Adjusting the amount of feeder, the temperature of the annular furnace, and the wire speed so that the volume ratio of the filler in the solder is 15% and the thickness of the solder is 30 μm, and a rectangular conductor having a surface layer containing each filler is produced. did. The flat conductor wires thus produced are designated as samples L to P. Further, as a comparative material, a rectangular conductor wire having a one-side solder thickness of 30 μm was prepared without adding a filler. The flat conducting wire thus produced is designated as sample Q.

Fabrication of the interconnector by the aerosol method was performed by the following method. The copper core material used was the same as that used in hot dipping, but was degreased with acetone before the solder coating was applied.
As the alumina filler, an alumina filler prepared by hot dip plating and having the same particle diameter before coating with Ti was used. The solder used was the same component as the solder used for hot dipping and had a particle size of 35 μm. A mixture of these powders so that the volume fraction of alumina filler was 15% was used as an aerosol injection raw material.

Nitrogen gas is used as the working gas when coating with aerosol, the operating temperature is 150 ° C., the pressure is 2 MPa, the wire feeding speed of the copper wire is 100 mm / s, and the thickness of each side of the copper wire is 35 μm on one side. Thus, both sides were formed into a film. The rectangular conductor wire thus produced was designated as Sample R.
Further, as a comparative material, a rectangular conductive wire was produced using a solder raw material not containing alumina. The flat conductor wire thus produced was designated as Sample S.

Two flat conductive wires were used, and each was mounted on an electrode formed by firing silver paste having a size of 3 mm × 5 mm provided in parallel in two rows on a solar cell having a thickness of 190 μm and a 170 mm square at a constant pressure. At the time of mounting, the solder was melted and joined at a temperature higher than the melting point of the solder and lower than the melting point of each filler. The length of the mounted flat conducting wire was 170 mm, which was the same as that of the solar battery cell, and was mounted along the center line of the silver electrode on the solar battery cell. The solar battery cell and the flat conducting wire were joined while being shifted by 5 mm in the mounting length direction. After joining, the solder protruding from the flat wire was observed, and the state of warpage / crack of the solar cell was measured.
The results are shown in Table 2. Evaluation of solder protrusion and cracks is the same as in Example 2.

    The solder protrusions and cracks differed greatly depending on whether the filler was contained or not. After mounting a flat conductor having a surface layer containing an alumina filler and a flat conductor having a surface layer containing a silica filler, the warpage of the solar battery cell was extremely small, and no cracks were observed. This is because the thermal expansion coefficient of alumina and silica is small, so that the thermal contraction of the joint portion becomes small and approaches to silicon, so that the thermal stress at the joint interface is small. That is, it has been found that when an alumina or silica filler is used, it acts as a thermal stress relaxation layer.

  Next, the electrical resistance value was measured between the end portion of the flat conducting wire protruding 5 mm from the solar battery cell and the exposed electrode surface not joined to the flat conducting wire. As a result, the electrical resistance value of the flat wire having the surface layer containing aluminum and silver as a filler was the lowest. This is because aluminum and silver are good conductors compared to solder, so that current flows even through the filler. Moreover, the electrical resistance value of the flat wire having the surface layer not containing the filler was the highest. This is because the electrode was partially peeled off due to the occurrence of cracks. That is, it has been clarified that when the aluminum or silver filler is used, the electrical resistance value of the surface layer is lowered.

DESCRIPTION OF SYMBOLS 1 Copper wire part 2 Surface layer 2a Solder plating 2b Filler 10 Sunlight 11 Solar cell 12 Electrode 13 Interconnector 14 EVA adhesion layer 15 Protective glass 16 Back film 21 Molten solder plating bath 22 Copper wire guide 23 Filler hopper 24 Filler guide 25 Pressure roller 30 Mixture 31 of solder powder and filler 31 Mixture chamber 32 Nozzle

Claims (1)

A semiconductor substrate constituting a solar battery cell;
An electrode formed on the surface of the semiconductor substrate;
And a interconnector for a solar cell connected to said electrode,
The solar cell interconnector is
A flat electrical conductor,
A surface layer having a thickness of 10 μm to 40 μm, covering both wide surfaces of the electrical conductor portion;
Have
The surface layer is made of a material in which a granular filler having a maximum diameter of 10 μm to 40 μm having a melting point higher than that of the solder is dispersed in the solder, and a portion covering the one surface has the maximum diameter of the filler. It is a constant thickness defined by the thing, the part covering the other surface of the wide is less uneven than the part covering the one surface, the surface is uneven due to the presence of the filler,
The electrical conductor portion and the electrode are electrically connected via the one surface of the surface layer of the solar cell interconnector, and the other surface of the surface layer is a light receiving surface of the electrical conductor portion. A solar cell module, wherein the solar cell module is a non-connected portion with the electrode on the side .

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