Solar cell welding method and solar cell

Abstract

The present application provides a method for welding a solar cell and a solar cell, the welding method comprising: placing solder paste on a pad, the solder paste comprising a first solder; melting the first solder to weld the first solder and the pad; laying a solder strip on the first solder, the solder strip comprising a substrate and a second solder, the second solder covering the substrate; and melting the second solder to weld the solder strip and the first solder, wherein the liquidus temperature of the first solder is greater than the liquidus temperature of the second solder, and when the second solder is in a molten state, part of the first solder melts. In the welding method of the present application, only part of the first solder melts during welding the solder strip and the first solder, thereby improving the welding stability between the first solder and the pad; the thickness of the first alloy layer is less than the thickness of the pad, thereby preventing the pad from falling off the battery cell; using a tunnel furnace to melt the solder paste can reduce the amount of slurry used.

Description

Technical Field

[0001] The present application mainly relates to the field of photovoltaic technology, and in particular to a welding method for solar cells and a solar cell. Background Art

[0002] Solar cells are the core of solar power generation systems. Solar cells mainly include cells, pads and ribbons. The ribbons connect multiple cells in series to increase the output voltage. In the manufacturing process of solar cells, the welding stability between the ribbon and the pad directly affects the performance and service life of the solar cell. How to improve the welding stability between the ribbon and the pad is one of the important research directions in this field. Summary of the invention

[0003] The technical problem to be solved by the present application is to provide a solar cell welding method and a solar cell, wherein the solar cell welding method and the solar cell can improve the welding stability between the welding ribbon and the welding pad.

[0004] To solve the above technical problems, the present application provides a welding method for a solar cell, wherein the solar cell includes a welding pad, and further includes: placing a solder paste on the welding pad, wherein the solder paste includes a first solder; melting the first solder to weld the first solder to the welding pad; laying a welding strip on the first solder, wherein the welding strip includes a substrate and a second solder, and the second solder covers the substrate; and melting the second solder to weld the welding strip to the first solder, wherein the liquidus temperature of the first solder is greater than the liquidus temperature of the second solder, and when the second solder is in a molten state, part of the first solder melts.

[0005] In an embodiment of the present application, the liquidus temperature of the first solder is at least 7° C. higher than the liquidus temperature of the second solder.

[0006] In an embodiment of the present application, a difference between a liquidus temperature of the first solder and a liquidus temperature of the second solder is equal to or less than 72° C.

[0007] In an embodiment of the present application, the temperature for melting the second solder is greater than the melting point liquidus temperature of the second solder and less than the melting point liquidus temperature of the first solder.

[0008] In an embodiment of the present application, after welding the first solder and the welding pad, the first solder is flush with or higher than the insulating glue, wherein the insulating glue is located between the welding strip and the battery cell.

[0009] In an embodiment of the present application, a tunnel furnace is used to melt the first solder.

[0010] In an embodiment of the present application, the solder paste further includes flux and / or solvent.

[0011] In an embodiment of the present application, the method of melting the second solder includes: melting the second solder during the process of laminating the solar cells.

[0012] On the other hand, the present application also proposes a solar cell, comprising: a cell and a soldering pad located on the cell; a first solder located on the soldering pad, a first alloy layer being formed between the first solder and the soldering pad by remelting; a soldering strip located on the first solder, the soldering strip comprising a substrate and a second solder covering the substrate, a second alloy layer being formed between the first solder and the second solder by remelting, wherein the melting point liquidus temperature of the first solder is greater than the melting point liquidus temperature of the second solder.

[0013] In one embodiment of the present application, the melting point liquidus temperature of the first solder is at least 7° C. higher than the melting point liquidus temperature of the second solder.

[0014] In an embodiment of the present application, the thickness of the first alloy layer is smaller than the thickness of the pad.

[0015] In an embodiment of the present application, the solar cell further includes an insulating adhesive located between the soldering ribbon and the cell sheet, and the insulating adhesive is flush with or lower than the first solder.

[0016] In an embodiment of the present application, during the process of forming the second alloy layer between the first solder and the second solder by remelting, the thickness of the first alloy layer does not substantially increase.

[0017] In one embodiment of the present application, the first solder includes one or more of Sn39Pb39Bi22, Sn43Pb43Bi14, Sn50Pb50, and the second solder includes Sn37Pb37Bi26.

[0018] Compared with the prior art, this application has the following advantages:

[0019] (1) During the welding process between the solder strip and the first solder, only a portion of the first solder is melted, thereby preventing the thickness of the first alloy layer from increasing, thereby improving the welding stability between the first solder and the solder pad.

[0020] (2) The thickness of the first alloy layer is smaller than the thickness of the pad, which can prevent the pad from falling off the battery cell.

[0021] (3) Using a tunnel furnace to melt the first solder can ensure that the melting degree of the solder paste is the same when the thickness of the solder paste is small, thereby reducing the amount of slurry used. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are included to provide a further understanding of the present application. They are included and constitute a part of the present application. The accompanying drawings illustrate embodiments of the present application and together with the present specification serve to explain the principles of the present application. In the accompanying drawings:

[0023] Figure 1 is a schematic flow chart of a solar cell welding method in one embodiment of the present application;

[0024] Figures 2 to 5 is a schematic diagram of the structure of a solar cell during the process of welding a welding ribbon to a solar cell according to the welding method of the present application;

[0025] Figure 6 is a cross-sectional schematic diagram of a solar cell in one embodiment of the present application;

[0026] Figures 7 to 9 is an energy spectrum diagram at the fusion zone of the first solder and the second solder in different embodiments of the present application;

[0027] Fig.10 is an energy spectrum diagram at the fusion zone of the first solder and the second solder in the comparative example;

[0028] Fig.11 yes Figures 7 to 10 The tensile test results of the fusion zone between the first solder and the second solder in the embodiments and comparative examples. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0030] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0031] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0032] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0033] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0034] In addition, it should be noted that the use of words such as "first" and "second" to define components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above words have no special meaning and cannot be understood as limiting the scope of protection of this application. In addition, although the terms used in this application are selected from well-known and commonly used terms, some terms mentioned in the specification of this application may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this article. In addition, it is required to understand this application not only by the actual terms used, but also by the meaning implied by each term.

[0035] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, various steps may be processed in reverse order or simultaneously. At the same time, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0036] Next, the solar cell welding method and the solar cell of the present application are described through embodiments.

[0037] Figure 1 A schematic diagram of a process for welding a solar cell in an embodiment of the present invention is shown in FIG. Figure 1 As shown, the welding method in this embodiment includes the following steps:

[0038] Step S110: placing solder paste on the pad, where the solder paste includes a first solder;

[0039] Step S120: melting the first solder to weld the first solder and the pad;

[0040] Step S130: Laying a solder strip on the first solder, the solder strip comprising a substrate and a second solder, the second solder covering the substrate;

[0041] Step S140: Melting the second solder to weld the solder strip and the first solder, wherein the liquidus temperature of the first solder is greater than the liquidus temperature of the second solder, and when the second solder is in a molten state, a portion of the first solder is melted.

[0042] Next, steps S110 to S140 are described in detail.

[0043] refer to Figure 2As shown, the solar cell includes a cell 110 and a pad 120, and the pad 120 is electrically connected to the grid line in the cell 110. The present application does not limit the number of pads 120, for example, a plurality of pads 120 can be arranged at intervals on a grid line according to demand. The material of the pad 120 may include metallic silver. In some embodiments, the solar cell may be a gridless solar cell, in which case the pad 120 may be electrically connected to the emitter.

[0044] In step S110, solder paste 130 is placed on pad 120. Solder paste 130 includes a first solder. The first solder may include a binary alloy and / or a ternary alloy. The first solder serves to connect pad 120 with a solder strip, which will be described in detail later.

[0045] In some embodiments, the solder paste 130 may further include flux and / or solvent. The flux has the function of assisting and promoting soldering during the soldering process, and may also have the function of preventing oxidation. The solvent has the function of dissolving the flux. During the soldering process, the solvent in the solder paste 130 will volatilize due to heat. Therefore, for the solder paste containing solvent, after the solder paste is melted and solidified by heat, there is no (or substantially no) solvent in the solder paste, and the main component of the solder paste is the first solder.

[0046] refer to Figure 2 and Figure 3 As shown, in step S120, the first solder in the solder paste 130 is melted, and the melted first solder 150 and the melted pad 120 form a first alloy layer 140. The first alloy layer 140 serves to connect the first solder 150 and the pad 120. It can be understood that the elements in the first alloy layer 140 come from the first solder 150 and the pad 120. As mentioned above, if the solder paste 130 contains a solvent, after the solder paste 130 is melted and solidified by heat, the solvent in the solder paste 130 is volatilized by heat. In addition, the first solder 150 is the main component of the solder paste 130 that forms the first alloy layer 140. For the convenience of explanation and understanding, other components in the solder paste 130 (such as flux, residual solvent, etc.) are ignored. Figure 3 The first solder in the solder paste located above the pad 120 is marked as 150.

[0047] In one embodiment, a tunnel furnace is used to melt the first solder. In the prior art, a string soldering machine is often used to melt the solder paste 130. In order to solve the problem of different melting degrees of solder pastes caused by the uneven temperature of the string soldering machine, the height of the solder paste needs to be increased, which will lead to an increase in the amount of slurry used. The above embodiment uses a tunnel furnace to melt the first solder. Thanks to the higher temperature uniformity of the tunnel furnace than the string soldering machine, the melting degree of the solder paste can be ensured to be the same when the thickness of the first solder is small, which can reduce the amount of slurry used.

[0048] In one embodiment, reference Figure 3 As mentioned above, the solar cell further includes an insulating adhesive (not shown), and after the first solder 150 is soldered to the solder pad 120, the first solder 150 is flush with or higher than the insulating adhesive. This will be described in detail later.

[0049] refer to Figure 3 As shown, in one embodiment, the thickness of the first alloy layer 140 is less than the thickness of the pad 120. The first alloy layer 140 serves to connect the first solder 150 and the pad 120. Increasing the thickness of the first alloy layer 140 can improve the stability of the connection between the first solder 150 and the pad 120. However, if the thickness of the first alloy layer 140 is equal to or greater than the thickness of the pad 120, the lower surface of the first alloy layer 140 will contact the battery cell 110, and the bonding force between the first alloy layer 140 and the battery cell 110 is low. Therefore, the lower surface of the first alloy layer 140 contacts the battery cell 110, which may cause the pad 120 to fall off from the battery cell 110. The thickness of the first alloy layer 140 is less than the thickness of the pad 120 to prevent the pad 120 from falling off from the battery cell 110.

[0050] refer to Figure 3 and Figure 4 As shown, in step S130, a solder strip 160 is laid on the first solder 150, and the solder strip 160 includes a substrate 161 and a second solder 162, and the second solder 162 covers the substrate 161. The material of the substrate 161 may include metallic copper, and the second solder 162 may include a binary alloy and / or a ternary alloy.

[0051] refer to Figure 4 and Figure 5 As shown, in step S140, the second solder 162 is melted, part of the first solder 150 is melted, and the melted second solder 162 and the melted first solder 150 form a second alloy layer 170, and the second alloy layer 170 serves to connect the first solder 150 and the second solder 162. The liquidus temperature of the first solder 150 is greater than the liquidus temperature of the second solder 162. When the second solder 162 is in a molten state, only part of the first solder 150 is melted. Since the first solder 150 is not completely melted during the welding of the welding strip 160, the thickness of the first alloy layer 140 does not increase or substantially does not increase, so that the thickness of the first alloy layer 140 can be prevented from increasing to contact with the battery cell 110, thereby preventing the pad 120 from falling off.

[0052] In one embodiment, the liquidus temperature of the first solder 150 is at least 7°C higher than the liquidus temperature of the second solder 162. For example, the liquidus temperature of the first solder 150 is 7°C, 10°C, 20°C, 40°C, 60°C or 72°C higher than the liquidus temperature of the second solder 162. The liquidus temperature of the first solder 150 is at least 7°C higher than the liquidus temperature of the second solder 162. On the one hand, it can increase the temperature window for melting the second solder 162. On the other hand, it can also reduce the melted volume of the first solder 150 during the melting of the second solder 162, thereby slowing down the growth rate of the first alloy layer 140.

[0053] In one embodiment, the difference between the liquidus temperature of the first solder 150 and the liquidus temperature of the second solder 162 is equal to or less than 72° C.

[0054] In one embodiment, the temperature for melting the second solder 162 is greater than the liquidus temperature of the second solder 162 and less than the liquidus temperature of the first solder 150. For example, assuming that the liquidus temperature of the first solder 150 is 180° C. and the liquidus temperature of the second solder 162 is 160° C., the temperature for melting the second solder 162 is 170° C. In this way, the first solder 150 can be prevented from melting during the melting of the second solder 162.

[0055] In one embodiment, reference Figure 3 The solar cell further includes an insulating adhesive (not shown). After the first solder 150 is soldered to the solder pad 120, the insulating adhesive is not higher than the first solder 150, or the highest point of the insulating adhesive is not higher than the first solder 150. In this way, it is prevented that when the soldering ribbon 160 is laid on the first solder 150, the insulating adhesive will suspend the soldering ribbon 160, thereby causing the soldering ribbon 160 not to contact the first solder 150. In some embodiments, the height of the first solder 150 is 35μm to 150μm, for example, the height of the first solder 150 is 55μm, 75μm, 95μm, 115μm or 135μm.

[0056] In one embodiment, the first solder includes one or more of Sn39Pb39Bi22, Sn43Pb43Bi14, Sn50Pb50, and the second solder includes Sn37Pb37Bi26.

[0057] In order to more clearly understand the present application, two embodiments are given here.

[0058] Embodiment 1

[0059] First, refer to Figures 2 to 5As shown, solder paste 130 is applied on pad 120 by printing or spraying, the thickness of solder paste 130 is greater than the thickness of pad 120, the liquidus temperature of the first solder in solder paste 130 is A, solder paste 130 is heated at a temperature higher than A, for example, the cell with solder paste 130 is heated by infrared and tunnel furnace, so that the solvent in solder paste 130 is volatilized and the first solder in solder paste 130 is melted. The first solder 150 forms a first alloy layer 140 with the silver paste in pad 120.

[0060] Next, a soldering tape 160 is placed on the first solder 150. The soldering tape 160 wraps the copper and the second solder 162 covering the copper surface. The thickness of the second solder 162 can be 2μm~30μm, for example, the thickness of the second solder 162 is 5μm, 10μm, 15μm, 20μm or 25μm. The battery cell with the soldering tape 160 is sent to the welding machine. The soldering tape 160 can be heated by infrared, hot air or thermal contact welding to melt the second solder 162. The second solder 162 and the first solder 150 form a second alloy layer 170. In the process of heating the soldering tape 160, the first solder 150 is not completely melted, so that the growth rate of the first alloy layer 140 is limited, thereby preventing the pad 120 from falling off.

[0061] The first solder 150 can be Sn63Pb37, the liquidus temperature is 183°C, and the temperature for heating the solder paste 130 is any temperature between 183°C and 300°C. The second solder 162 can be Sn43Pb43Bi14, the melting range of the second solder 162 is 138°C to 163°C, and the temperature for heating the second solder 162 is any temperature between 162°C and 183°C. The starting temperature of the "melting range" refers to the temperature at which the solid phase in the phase diagram begins to transform into the liquid phase, and the ending temperature of the "melting range" refers to the temperature at which the solid phase in the phase diagram completely transforms into the liquid phase, or the "melting range" refers to the temperature range in which solid and liquid coexist in the phase diagram. The liquidus temperature in the above text refers to the ending temperature of the melting range.

[0062] Embodiment 2

[0063] The main difference between the second embodiment and the first embodiment is that after placing the solder ribbon 160 on the first solder 150, the battery cells with the solder ribbon 160 are connected into a string, and then the lamination process is performed. The adhesive film and glass are laid on the front and back sides of the battery string to form a laminated part, and the laminated part is sent to the laminator. The laminated part is heated by the temperature of the lamination process. The highest temperature of the lamination process is higher than the liquidus temperature of the second solder 162 and lower than the liquidus temperature of the first solder 150. The second solder 162 melts and forms a second alloy layer 170 with the first solder 150, and the first solder 150 is not completely melted. The incomplete melting of the first solder 150 can limit the growth of the first alloy layer 140, thereby preventing the pad 120 from falling off.

[0064] On the other hand, the present application also proposes a solar cell, Figure 5 As shown, the solar cell includes a cell 110 , a solder pad 120 located on the cell 110 , a first solder 150 and a solder ribbon 160 .

[0065] Specifically, the first solder 150 is located on the pad 120, and the first alloy layer 140 is formed between the first solder 150 and the pad 120 by remelting, that is, the first solder 150 and the pad 120 are heated to melt, and then cooled and solidified to form the first alloy layer 140, and the first alloy layer 140 contains the components of the first solder 150 and the pad 120.

[0066] In one embodiment, the thickness of the first alloy layer 140 is less than the thickness of the pad 120. For example, the thickness of the first alloy layer 140 is 0.5 μm, 1 μm or 1.5 μm, and the thickness of the pad 120 is 3 μm, 4 μm or 5 μm. The thickness of the first alloy layer 140 is less than the thickness of the pad 120 to prevent the pad 120 from falling off the battery cell 110.

[0067] The soldering strip 160 is located on the first solder 150. The soldering strip 160 includes a substrate 161 and a second solder 162 covering the substrate 161. The second alloy layer 170 is formed between the first solder 150 and the second solder 162 by remelting, that is, the first solder 150 and the second solder 162 are heated and melted, and then cooled and solidified to form the second alloy layer 170, and the second alloy layer 170 contains the components of the first solder 150 and the second solder 162. The liquidus temperature of the first solder 150 is at least 7°C higher than the liquidus temperature of the second solder 162. During the remelting process, when the second solder 162 is in a molten state, part of the first solder 150 melts (the first solder 150 is not completely melted). In this way, the thickness of the first alloy layer 140 does not increase or substantially does not increase during the remelting process, which can prevent the thickness of the first alloy layer 140 from increasing to contact with the battery cell 110, thereby preventing the pad 120 from falling off.

[0068] refer to Figure 6 As shown, in one embodiment, the solar cell further includes an insulating glue 180 located between the soldering ribbon 160 and the cell 110, and the insulating glue 180 covers the grid line 190, thereby preventing a short circuit between the grid line 190 and the soldering ribbon 160. The apex of the insulating glue 180 is flush with or lower than the apex of the first solder 150, so that the insulating glue 180 can be prevented from being too high, thereby becoming the main force-bearing part supporting the soldering ribbon 160, and reducing the risk of the soldering ribbon 160 piercing through the insulating glue 180 and contacting the grid line 191 to cause a short circuit.

[0069] In one embodiment, the first solder 150 may be Sn63Pb37, whose liquidus temperature is 183°C, and the temperature of the molten solder paste may be any temperature between 183°C and 300°C, and the corresponding second solder 162 may be Sn32Pb42Bi26, whose melting range is 136°C to 143°C, and the highest temperature of the lamination process is greater than 143°C and less than 183°C. The first solder 150 may also be Sn43Pb43Bi14, whose melting range is 136°C to 163°C (liquidus temperature is 163°C), and the corresponding second solder 162 may be Sn42Bi57Ag1, whose liquidus temperature is 138°C, and the highest temperature of the lamination process is greater than 138°C and less than 163°C, and the first solder 150 is only partially melted during the lamination process.

[0070] Next, combine Figures 7 to 11 The energy spectrum diagram at the fusion zone of the first solder and the second solder in the embodiment and the comparative example shown, and Fig.11 The tensile test results of the fusion zone between the first solder and the second solder in the shown embodiments and comparative examples illustrate the welding method of some embodiments of the solar cell of the present application and the technical effect of the solar cell. It can be understood that the fusion zone is located in the second alloy layer.

[0071] The tensile testing method in Examples 3 to 5 and Comparative Example 1 includes: using a 180° peel test, fixing the battery cell on a flat plate (such as a metal plate) perpendicular to a horizontal plane, fixing the solder strip at the starting solder point on a moving module of a tensile testing device, controlling the moving module to move from the starting solder point to the tail solder point at a speed of 10 mm / min, and the moving direction is always perpendicular to the horizontal plane and parallel to the battery cell, recording tensile data and displacement data during the movement of the moving module, and drawing a tensile-displacement curve based on the tensile data and displacement data, and taking the maximum tensile force in the curve as the tensile test result.

[0072] Embodiment 3

[0073] refer to Figure 7 As shown, in Example 3, the first solder is Sn39Pb39Bi22, with a melting range of 136°C to 150°C, and the second solder is Sn37Pb37Bi26, with a melting range of 136°C to 143°C. The liquidus temperature of the first solder is 7°C higher than that of the second solder. Figure 7 From the energy spectrum shown, it can be seen that, thanks to the liquidus temperature of the first solder being 7°C higher than that of the second solder, the bismuth (Bi) element in the fusion zone between the first solder and the second solder is evenly distributed without any segregation zone. Thanks to the even distribution of the bismuth element, the tensile test result of the fusion zone is 1.5N.

[0074] Embodiment 4

[0075] refer to Figure 8 As shown, the first solder in Example 3 is changed to Sn43Pb43Bi14, with a melting range of 136°C to 167°C, and the second solder is still Sn37Pb37Bi26, and the liquidus temperature of the first solder is 24°C higher than that of the second solder. Figure 8 The energy spectrum shown shows that the Bi element is concentrated on the second solder side, and the diffusion amount of the Bi element from the second solder side to the first solder side is significantly reduced. The tensile test result of the fusion zone is 1.4N.

[0076] Embodiment 5

[0077] refer to Fig. 9 As shown, the first solder in Example 4 is changed to Sn50Pb50, with a melting range of 183°C to 215°C, and the second solder is still Sn37Pb37Bi26, and the liquidus temperature of the first solder is 72°C higher than that of the second solder. Fig. 9 As shown in the energy spectrum, the Bi element is concentrated on the second solder side. Figure 8 In comparison, the diffusion amount of Bi element from the second solder side to the first solder side is further reduced, because the difference between the liquidus temperatures of the first solder and the second solder in Example 5 is greater than that in Example 4. The tensile test result of the fusion zone is 0.8N. Although the tensile force in Example 5 is less than that in Example 4, it still has a good connection effect.

[0078] Comparative Example 1:

[0079] refer to Fig.10 As shown, the first solder is pure Sn, the second solder is Sn37Pb37Bi26, and the liquidus temperature of the first solder is 89°C higher than that of the second solder. Fig.10 From the energy spectrum shown, it can be seen that there is almost no Bi element on the side of the first solder, and the tensile test result of the fusion zone is 0.1N, indicating that the tensile strength of the fusion zone is low, and there is almost no connection effect between the first solder and the second solder.

[0080] Fig.11 The tensile strength of the fusion zone in the examples and comparative examples is shown using a curve. Fig.11 It can be seen that the tensile strength of Example 4 is the highest, and the tensile strength of Comparative Example 1 is 0.1N, which is significantly lower than the tensile strength in the embodiment, mainly because the liquidus temperature in Comparative Example 1 is relatively high (89°C). The liquidus temperature difference in the embodiment of the present application is equal to or greater than 7°C and equal to or less than 72°C, so the fusion effect between the first solder and the second solder is better, thereby improving the tensile strength of the fusion zone.

[0081] The basic concepts have been described above. Obviously, for those skilled in the art, the above application disclosure is only an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present application.

[0082] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0083] Similarly, it should be noted that in order to simplify the description of the disclosure of this application and thus help understand one or more application embodiments, in the above description of the embodiments of this application, multiple features are sometimes merged into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the object of this application are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0084] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used for the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which can be changed according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the method of general digit retention. Although the numerical domains and parameters used to confirm the breadth of the range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0085] Although the present application has been described with reference to the current specific embodiments, ordinary technicians in this technical field should recognize that the above embodiments are only used to illustrate the present application, and various equivalent changes or substitutions may be made without departing from the spirit of the present application. Therefore, as long as the changes and modifications to the above embodiments are within the essential spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A method for welding a solar cell, wherein the solar cell comprises a welding pad, characterized in that: include: placing solder paste on the pad, wherein the solder paste includes a first solder; Melting the first solder to weld the first solder and the pad; Laying a solder strip on the first solder, wherein the solder strip comprises a base material and a second solder, and the second solder covers the base material; as well as The second solder is melted to weld the solder strip and the first solder, wherein the liquidus temperature of the first solder is greater than the liquidus temperature of the second solder, when the second solder is in a molten state, only a portion of the first solder is melted, the difference between the liquidus temperature of the first solder and the liquidus temperature of the second solder is 7°C~72°C, the temperature for melting the second solder is greater than the liquidus temperature of the second solder and less than the liquidus temperature of the first solder, the liquidus temperature refers to the termination temperature of the melting range, and the melting range refers to the temperature range in which solid and liquid coexist in the phase diagram.

2. The method for welding a solar cell according to claim 1, characterized in that: After welding the first solder and the soldering pad, the first solder is flush with or higher than the insulating glue, wherein the insulating glue is located between the soldering ribbon and the battery cell.

3. The method for welding a solar cell according to claim 1, characterized in that: The first solder is melted using a tunnel furnace.

4. The method for welding a solar cell according to claim 1, wherein: The solder paste further comprises flux and / or solvent.

5. The method for welding a solar cell according to claim 1, wherein: The method of melting the second solder includes melting the second solder during lamination of the solar cells.

6. A solar cell, wherein the solar cell uses the welding method according to any one of claims 1 to 5, characterized in that: include: A battery cell and a solder pad located on the battery cell; A first solder is located on the pad, and a first alloy layer is formed between the first solder and the pad by melting; A solder strip is located on the first solder, and the solder strip includes a substrate and a second solder covering the substrate. A second alloy layer is formed between the first solder and the second solder by remelting, wherein the liquidus temperature of the first solder is greater than the liquidus temperature of the second solder, and when the second solder is in a molten state, only a portion of the first solder is melted.

7. The solar cell according to claim 6, characterized in that The liquidus temperature of the first solder is at least 7° C. higher than the liquidus temperature of the second solder.

8. The solar cell according to claim 6, wherein: The thickness of the first alloy layer is smaller than the thickness of the pad.

9. The solar cell according to claim 6, wherein: The solar cell further includes an insulating adhesive located between the soldering ribbon and the cell sheet, and the insulating adhesive is flush with or lower than the first solder.

10. The solar cell according to claim 6, wherein: In the process of forming the second alloy layer between the first solder and the second solder by remelting, the thickness of the first alloy layer does not increase.

11. The solar cell according to claim 6, wherein: The first solder includes one or more of Sn39Pb39Bi22, Sn43Pb43Bi14, Sn50Pb50, and the second solder includes Sn37Pb37Bi26.

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