Preparation method of photovoltaic module and photovoltaic module

Abstract

The invention relates to the technical field of photovoltaic, and discloses a preparation method of a photovoltaic module and the photovoltaic module. The photovoltaic module preparation method comprises the steps that a plurality of battery pieces and a low-temperature welding strip are provided, the low-temperature welding strip comprises a copper substrate and welding flux wrapping the copper substrate, and the welding flux comprises metallic tin; the battery pieces and the low-temperature welding strips are pre-fixed, so that the multiple battery pieces are connected through the low-temperature welding strips to form a battery string; packaging materials are arranged on the two sides of the cell string to form a to-be-laminated piece, and the to-be-laminated piece is laminated and solidified at a preset heating rate, so that the welding flux is melted to form an interconnection alloy layer between the copper substrate and the grid line electrode of the cell piece; wherein the preset heating rate is greater than 5 DEG C / min. According to the preparation method of the photovoltaic module and the photovoltaic module provided by the invention, the connection effect between the welding strip and the battery piece can be ensured, so that the use performance of the photovoltaic module is prevented from being influenced.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic technology, and particularly relates to a preparation method of a photovoltaic module and a photovoltaic module. Background Art

[0002] With the continuous development of new energy technologies, the installed capacity of photovoltaic modules is also continuously increasing. Photovoltaic modules can convert solar energy into electrical energy, thereby realizing power generation. Moreover, no polluting products will appear during the power generation process of photovoltaic modules, which is relatively friendly to the environment. Photovoltaic modules are formed by encapsulating solar cells, and the solar cells play a role in photovoltaic conversion and are an important part of photovoltaic modules. During the production process of photovoltaic modules, multiple solar cells are connected together.

[0003] When connecting multiple solar cells, welding tapes are used to form an integral body between the welding tapes and the solar cells. The welding tapes rely on the solder on the surface to form a connection with the grid electrodes of the solar cells. The connection effect between the welding tapes and the solar cells affects the use performance of the photovoltaic module. Therefore, how to ensure the connection effect between the welding tapes and the solar cells to avoid affecting the use performance of the photovoltaic module is an important issue. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a preparation method of a photovoltaic module and a photovoltaic module, which can help ensure the connection effect between the welding tapes and the solar cells to avoid affecting the use performance of the photovoltaic module.

[0005] To solve the above technical problems, an embodiment of the present application provides a preparation method of a photovoltaic module. The preparation method of the photovoltaic module includes:

[0006] Providing a plurality of solar cells and low-temperature welding tapes. The low-temperature welding tapes include a copper substrate and solder wrapping the copper substrate, and the solder includes metallic tin;

[0007] Pre-fixing the solar cells and the low-temperature welding tapes so that a plurality of solar cells are connected via the low-temperature welding tapes to form a battery string;

[0008] Setting encapsulation materials on both sides of the battery string to form a laminate to be laminated, and performing a lamination curing process on the laminate to be laminated at a preset heating rate, so that the solder melts to form an intermetallic alloy layer between the copper substrate and the grid electrodes of the solar cells;

[0009] Wherein, the preset heating rate is greater than 5°C / min.

[0010] Embodiments of the present application also provide a photovoltaic module prepared by using the above photovoltaic module preparation method. The photovoltaic module includes a battery string and encapsulation materials located on both sides of the battery string. The battery string includes a plurality of solar cells and low-temperature solder tapes connecting the plurality of solar cells. The low-temperature solder tape includes a copper matrix and solder wrapping the copper matrix. The solder includes metallic tin. The solder is melted to form an intermetallic alloy layer between the copper matrix and the grid line electrode of the solar cell.

[0011] For the photovoltaic module preparation method and the photovoltaic module provided by the embodiments of the present application, during the preparation of the photovoltaic module, the temperature during the lamination process is controlled so that the lamination environment where the workpiece to be laminated is located reaches the lamination temperature at a preset heating rate. By controlling the heating rate in the lamination process, the copper diffusion process at the solder interface of the solder tape can be promoted, and a Cu6Sn5 alloy with higher tensile strength can be generated. At the same time, the overall thickness of the copper-tin alloy in the alloy layer is reduced, and the adverse effect of the copper-tin alloy with relatively low tensile strength compared to other alloys on the alloy layer is reduced. Furthermore, in the case where new elements are introduced into the solder to reduce the melting point of the solder, the connection effect between the solder tape and the solar cell is ensured, so as to avoid affecting the service performance of the photovoltaic module.

[0012] In some embodiments, the preset heating rate is greater than or equal to 10 °C / min and less than or equal to 20 °C / min. In this way, by controlling the preset heating rate within the range of 10 °C / min to 20 °C / min, it is beneficial to accelerate the diffusion of metallic copper during welding and effectively ensure the mechanical properties at the welding point.

[0013] In some embodiments, after the workpiece to be laminated is subjected to lamination and curing treatment, it further includes cooling at a preset cooling rate, and the preset cooling rate is greater than 20 °C / min. In this way, by controlling the cooling rate after the lamination and curing treatment, it can assist in promoting the diffusion of metallic copper.

[0014] In some embodiments, pre-fixing the solar cells and the low-temperature solder tape includes: arranging a plurality of solar cells in the same direction and making the surfaces with the same polarity of the plurality of solar cells face the same side; applying glue dots on the surfaces of the plurality of solar cells, and laying the low-temperature solder tape at the glue dot positions on the surfaces of the solar cells so that the low-temperature solder tape bends between adjacent two solar cells; or laying the low-temperature solder tape on the surface of the solar cell so that the low-temperature solder tape bends between adjacent two solar cells, and applying glue dots or covering a film on the surface of the low-temperature solder tape. In this way, the solar cells and the low-temperature solder tape can be pre-fixed by applying glue dots or covering a film, so as to accurately control the welding position between the low-temperature solder tape and the solar cell.

[0015] In some embodiments, the laminate is subjected to a lamination and curing process, including: placing the laminate to be laminated on a carrier in a laminator; lifting the carrier to form a gap between the laminate to be laminated and the heating unit; setting the lamination temperature, duration, and pressure, and controlling the laminator to perform a lamination and curing process on the laminate to be laminated at a preset heating rate. In this way, by lifting the laminate to be laminated during the lamination process, it is ensured that the interior of the laminate to be laminated is uniformly heated, and basically consistent mechanical properties are formed at various locations after welding.

[0016] In some embodiments, the lamination temperature is greater than or equal to 160 °C and less than or equal to 200 °C. In this way, by controlling the lamination temperature, the encapsulation effect and welding effect after the lamination process can be ensured.

[0017] In some embodiments, the solder further includes metallic lead, and the difference in the content of metallic lead and metallic tin in the solder is within 10%. In this way, tin-lead solder can be formed using metallic tin and metallic lead to ensure the welding performance after the lamination process.

[0018] In some embodiments, the solder further includes metallic bismuth, and the content of metallic bismuth in the solder is 3 wt% to 20 wt%. In this way, by adding a certain amount of metallic bismuth, the melting point of the solder can be reduced.

[0019] In some embodiments, the melting point of the solder is 120 °C to 160 °C. In this way, by controlling the melting point of the solder, it is avoided that the melting point is too low and affects the welding performance of the solder, and it is also avoided that the melting point is too high and a good welding effect cannot be achieved. Description of the Drawings

[0020] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the drawings in the figures do not constitute a scale limitation.

[0021] Figure 1 is a flowchart of a method for preparing a photovoltaic module provided in some embodiments of the present application;

[0022] Figure 2 is a schematic structural diagram of a laminate to be laminated formed in a method for preparing a photovoltaic module provided in some embodiments of the present application;

[0023] Figure 3 is a schematic structural diagram of a laminate to be laminated formed in a method for preparing a photovoltaic module provided in some other embodiments of the present application;

[0024] Figure 4 is a schematic cross-sectional structural diagram of a low-temperature solder tape provided in a method for preparing a photovoltaic module provided in some embodiments of the present application;

[0025] Figure 5 It is a flowchart for pre-fixing a battery cell and a low-temperature solder tape in a method for manufacturing a photovoltaic module provided by some embodiments of the present application;

[0026] Figure 6 It is a flowchart for laminating and curing a workpiece to be laminated in a method for manufacturing a photovoltaic module provided by some embodiments of the present application;

[0027] Figure 7 It is a schematic structural diagram of a photovoltaic module provided by some embodiments of the present application;

[0028] Figure 8 It is a schematic structural diagram of a photovoltaic module provided by some other embodiments of the present application. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will elaborate on each implementation manner of the present application in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in each implementation manner of the present application, many technical details are presented for the convenience of readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following implementation manners, the technical solutions claimed in the present application can still be achieved. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation manners of the present application. The various embodiments can be combined and cross-referenced with each other without conflict.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above accompanying drawing descriptions are intended to cover non-exclusive inclusion.

[0031] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral body; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0032] The cells in a photovoltaic module can be classified into main-gridless cells, multi-main-grid cells, and ultra-multi-main-grid cells according to the number of main grids. The main grids are arranged in a direction intersecting with the fine grids and usually play the role of current transmission. Since the design of the main grid is eliminated in the main-gridless cells and the solder tapes are directly welded to the fine grids, the single consumption of silver paste can be significantly saved, and the silver paste cost can be effectively reduced.

[0033] Since the design of the main grid is eliminated in the main-gridless cells, the area of the welding points on the cell surface is small, which is not suitable for traditional high-temperature welding and is prone to grid breakage at high temperatures. Based on this, the low-temperature lamination welding technology has become an important option for interconnecting main-gridless cells. The low-temperature lamination welding technology realizes the welding between the solder tape and the cell during the lamination process of the photovoltaic module. When performing low-temperature lamination welding on the laminate to be formed including the cell, the solder tape, and the encapsulation material, the solder on the solder tape can be melted to form an alloy with the grid electrode on the cell surface, thereby forming an electrical connection between the solder tape and the cell. However, since the control of temperature has a great influence on the effect of the alloy layer formed between the solder tape and the cell, there is a problem of poor alloying effect in the existing main-gridless cells during interconnecting.

[0034] Since the connection between the solder tape and the cell is realized during the lamination process, the melting point of the solder of the solder tape needs to be lower than the lamination temperature to ensure the melting of the solder during the lamination process. Currently, the method of reducing the melting point of the solder mainly adopts the method of adding metallic bismuth or metallic silver to the tin-based solder, and by adjusting the ratio between various elements, the melting point of the solder is reduced below the lamination temperature. However, the addition of Bi (bismuth) or Ag (silver) introduces new elements, which have a negative impact on the tensile strength and reliability of the alloy layer formed between the solder tape and the cell. This makes the prepared photovoltaic module products prone to TC (high-low temperature environment) failure and DH (high temperature and high humidity environment) failure phenomena.

[0035] In order to ensure the connection effect between the solder tape and the cell and avoid affecting the use performance of the photovoltaic module, some embodiments of the present application provide a method for preparing a photovoltaic module. When preparing the photovoltaic module, the temperature control during the lamination process is carried out such that the lamination environment where the laminate to be formed is located reaches the lamination temperature at a preset heating rate. By controlling the heating rate in the lamination process, the copper diffusion process at the solder interface of the solder tape can be promoted, and a Cu6Sn5 alloy with higher tensile strength can be generated. At the same time, the overall thickness of the copper-tin alloy in the alloy layer is reduced, and the adverse effect of the copper-tin alloy with relatively lower tensile strength compared with other alloys on the alloy layer is reduced. Furthermore, when new elements are introduced to the solder tape to reduce the melting point of the solder, the connection effect between the solder tape and the cell is ensured.

[0036] The following combines Figures 1 to 6 to illustrate the method for preparing a photovoltaic module provided by some embodiments of the present application. Among them, Figure 2And Figure 3 shows the structure of the laminate-to-be formed during the preparation of a photovoltaic module, Figure 4 and shows the structure of the solder tape provided when preparing a photovoltaic module.

[0037] As Figure 1 shown, the method for preparing a photovoltaic module provided by some embodiments of the present application includes the following steps:

[0038] Step S110, provide a plurality of cell wafers 11 ( Figure 2 and Figure 3 shown) and low-temperature solder tape 12 ( Figures 2 to 4 shown). The low-temperature solder tape 12 includes a copper substrate 121 and a solder 122 wrapping the copper substrate 121, and the solder 122 includes metallic tin.

[0039] The cell wafers 11 may be main-gridless cell wafers, and the surface of the cell wafers 11 has a plurality of fine grids arranged at intervals in the same direction. The number of fine grids on the surface of the cell wafers 11 may be 45, 50, 55, 60, 65, 70 or 75. The cell wafers 11 may be whole cell wafers or sliced cell wafers formed by a scribing process. The sliced cell wafers are formed by cutting a whole cell wafer into a plurality of independent parts along the extension direction of the fine grids. In actual situations, the cell wafers 11 may also be main-grid cell wafers with a small number of main grids. The type of the cell wafers 11 may be any one of PERC cells (Passivated Emitter and Rear Cell), PERT cells (Passivated Emitter and Rear Totally-diffused cell), TOPCon cells (Tunnel Oxide Passivated Contact), HIT / HJT cells (Heterojunction Technology), perovskite cells and BC cells (Back Contact). The BC cells may be IBC cells (Interdigitated Back Contact), HPBC cells (Hybrid Passivated Back Contact photovoltaic cells), TBC cells with superimposed TOPCon technology and IBC technology, or HBC cells with superimposed HIT / HJT technology and IBC technology. Of course, they may also be other types of back-contact photovoltaic cells. For example, the cell wafers 11 may be main-gridless TOPCon cells or main-gridless BC cells.

[0040] The low-temperature solder tape 12 is a solder tape used for laminating and welding with the solar cell 11. The melting point of the solder 122 on the surface of the low-temperature solder tape 12 is within the laminating temperature. For example, the melting point of the solder 122 can be controlled within 160 °C. By using the laminating welding in a low-temperature environment, the thermal stress during the welding process can be reduced, and the phenomenon of hidden cracks in the solar cell 11 can be reduced. The copper matrix 121 in the low-temperature solder tape 12 has good electrical conductivity and can better realize the interconnection between multiple solar cells 11. The low-temperature solder tape 12 is formed by plating a layer of solder 122 on the copper matrix 121. The solder 122 uses a tin-based solder 122. In order to reduce the melting point of the solder 122, metallic bismuth or metallic silver can be added to the solder 122. The cross-sectional shape of the low-temperature solder tape 12 can be a regular shape such as a circle, a rectangle, or a square, or an irregular shape with a special shape.

[0041] Step S120: Pre-fix the solar cell 11 and the low-temperature solder tape 12 so that multiple solar cells 11 are connected via the low-temperature solder tape 12 to form a battery string 10.

[0042] To ensure that the matching positions between the grid electrodes on the solar cell 11 and the low-temperature solder tape 12 are accurately corresponding, the solar cell 11 and the low-temperature solder tape 12 can be pre-fixed in advance. A certain connection relationship is maintained between the solar cell 11 and the low-temperature solder tape 12. The pre-fix between the solar cell 11 and the low-temperature solder tape 12 can be realized by means of dispensing or laminating. Multiple solar cells 11 are connected in series via the low-temperature solder tape 12 to form a battery string 10. After the battery string 10 is formed by pre-fixation, encapsulation materials can be set on both side surfaces of the battery string 10 to cover the surface of the battery string 10 for subsequent laminating treatment.

[0043] Step S130: Set encapsulation materials on both sides of the battery string 10 to form a laminate 100, and perform a laminating and curing treatment on the laminate 100 at a preset heating rate so that the solder 122 melts to form an intermetallic alloy layer between the copper matrix 121 and the grid electrodes of the solar cell 11; wherein, the preset heating rate is greater than 5 °C / min.

[0044] The encapsulation materials include a front adhesive film 13 and a front cover plate 14 on the front side of the solar cell 11 in the battery string 10, and a back adhesive film 15 and a back cover plate 16 on the back side of the solar cell 11 in the battery string 10. The front cover plate 14 and the back cover plate 16 are located on the outermost sides of the laminate and are used to isolate the influence of the external environment on the solar cell 11. The front cover plate 14 and the back cover plate 16 can be glass cover plates, plastic cover plates, etc. with good light transmission functions and are not easily damaged. Among them, the good light transmission function means that the cover plate has a light transmittance of more than 80% for light with a wavelength greater than 400 nm or a light transmittance of more than 85% for light with a wavelength greater than 450 nm and other characteristics.

[0045] The front adhesive film 13 and the back adhesive film 15 are used to form an encapsulation film 17 that wraps the battery string 10 after the lamination process, and play a role in connecting the front cover plate 14 and the back cover plate 16, bonding the cover plates to the battery string 10. The front adhesive film 13 and the back adhesive film 15 can be ethylene-vinyl acetate copolymer (EVA) adhesive films, polyolefin thermoplastic elastomer (POE) adhesive films, polyethylene glycol terephthalate (PET) adhesive films, or PolyVinylButyral Film (PVB) adhesive films.

[0046] The lamination and curing process can be carried out in a laminator. The heating system of the laminator can adopt an oil heating method or an electric heating method. The oil heating method circulates heat transfer oil or other media through the construction of an oil circuit system to heat the carrier for placing the workpiece to be laminated 100. The control of the heating rate can be achieved by changing the flow rate of the heat transfer oil or the circulation temperature of the heat transfer oil. The electric heating method uses electric heating elements to heat the carrier, with a faster heating response and simple operation. The control of the heating rate can be achieved by changing the magnitude of the current or the number of electric heating elements.

[0047] As the temperature continuously rises during the lamination process, the diffusion rate of elements in the solder 122 alloy and the copper substrate 121 accelerates, resulting in the formation of a Cu6Sn5 alloy with higher tensile strength at the brazing joint interface of the low-temperature solder tape 12. Even if eutectic reaction occurs between metallic tin and metallic copper during the welding process to form the Cu6Sn5 alloy. The Cu6Sn5 alloy in the alloy layer has sufficient mechanical properties, and its tensile strength can meet the usage requirements. At the same time, an AgSn alloy is formed at the brazing joint interface of the grid line electrodes on the surface of the battery cell 11. Since the tensile strength of the AgSn alloy itself is sufficient, the mechanical properties of the alloy at the grid line electrodes on the surface of the battery cell 11 can be ensured.

[0048] After the lamination and curing process, each battery cell 11 forms an integral body after low-temperature welding and is in a complete electrical path, and the current is transmitted through the low-temperature solder tape 12. The low-temperature solder tape 12 can connect multiple battery cells 11 in series to form a stable connection structure.

[0049] The method for manufacturing a photovoltaic module provided by some embodiments of the present application controls the temperature during the lamination process when manufacturing the photovoltaic module 110, so that the lamination environment where the workpiece to be laminated 100 is located reaches the lamination temperature at a preset heating rate. By controlling the heating rate in the lamination process, the copper diffusion process at the interface of the solder 122 of the solder strip can be promoted, and a Cu6Sn5 alloy with higher tensile strength can be generated. At the same time, the overall thickness of the copper-tin alloy in the alloy layer is reduced, and the adverse effect of the copper-tin alloy with relatively low tensile strength compared to other alloys on the alloy layer is reduced. Furthermore, in the case where new elements are introduced into the solder strip to lower the melting point of the solder 122, the connection effect between the solder strip and the battery cell 11 is ensured. To avoid affecting the service performance of the photovoltaic module 110.

[0050] In some embodiments, the preset heating rate can be greater than or equal to 10 °C / min and less than or equal to 20 °C / min.

[0051] By controlling the temperature during the lamination process to increase at a rate of greater than or equal to 10 °C per minute, the diffusion rate of metallic copper at the solder 122 can be effectively accelerated, which is beneficial to the reaction to generate a Cu6Sn5 alloy with higher tensile strength. By controlling the temperature during the lamination process to increase at a rate of less than or equal to 20 °C per minute, it is possible to avoid the short heating time from affecting the diffusion degree of metallic copper at the solder 122. At the same time, it also avoids excessive heating energy consumption during the lamination process from affecting energy conservation. Through actual tests, when the preset heating rate is 5 °C / min, the alloy layer is mainly composed of Cu3Sn alloy, and the tensile strength of the alloy layer is 25 MPa. When the preset heating rate is 11 °C / min, the alloy layer is mainly composed of Cu6Sn5 alloy, and the tensile strength of the alloy layer is 34 MPa. When the preset heating rate is increased to 22 °C / min, the alloy layer is mainly composed of Cu6Sn5 alloy, and the tensile strength of the alloy layer is 36 MPa.

[0052] In addition, after the lamination and curing treatment of the workpiece to be laminated 100, it may further include cooling at a preset cooling rate, and the preset cooling rate is greater than 20 °C / min.

[0053] After the lamination and curing process is maintained for a certain period of time, the environment where the laminate is located can be cooled by water cooling or air cooling. By controlling the cooling rate during cooling, the diffusion effect of metallic copper at the solder 122 can also be controlled. Through actual testing, when the preset cooling rate is 1 °C / min, it will have a certain impact on the diffusion of metallic copper, and Cu3Sn alloy appears in the alloy layer, and the tensile strength of the alloy layer is 28 MPa. When the preset cooling rate is above 20 °C / min, such as 27 °C / min, the alloy layer is mainly composed of Cu6Sn5 alloy, and the tensile strength of the alloy layer is 36 MPa. Therefore, the cooling rate can be controlled to be greater than 20 °C / min to improve the diffusion effect of metallic copper and the tensile strength of the alloy layer.

[0054] In some embodiments, as Figure 5 shown, the pre-fixing of the battery cells 11 and the low-temperature solder tape 12 in step S120 may include the following steps:

[0055] Step S121: Arrange a plurality of battery cells 11 in the same direction and make the surfaces of the plurality of battery cells 11 with the same polarity face the same side.

[0056] When laying the battery cells 11, the front sides of the plurality of battery cells 11 face the same side, and the back sides of the plurality of battery cells 11 face the same side. That is, the front electrodes of the plurality of battery cells 11 face the same side, and the back electrodes of the plurality of battery cells 11 face the same side.

[0057] Step S122: Apply glue dots on the surfaces of the plurality of battery cells 11, and lay the low-temperature solder tape 12 at the glue dot positions on the surfaces of the battery cells 11, so that the low-temperature solder tape 12 is bent between two adjacent battery cells 11; or, lay the low-temperature solder tape 12 on the surfaces of the battery cells 11, so that the low-temperature solder tape 12 is bent between two adjacent battery cells 11, and apply glue dots or cover with a film on the surface of the low-temperature solder tape 12.

[0058] That is, the pre-fixing between the battery cell 11 and the low-temperature solder tape 12 includes glue dot fixing and film covering fixing. The glue dot fixing pre-fixes the low-temperature solder tape 12 on the battery cell 11 through the curing of the glue, and the film covering fixing pre-fixes the low-temperature solder tape 12 on the battery cell 11 through the curing of the glue film.

[0059] The purpose of pre-fixing the solar cell 11 and the low-temperature solder tape 12 is to pre-fix the low-temperature solder tape 12 at a specified position. Thus, during the lamination process, the relative positions between the low-temperature solder tape 12 and the grid line electrodes on the surface of the solar cell 11 do not deviate, and the low-temperature solder tape 12 can be welded at the specified position. When performing pre-fixing, glue can be applied to the area on the surface of the solar cell 11 where the low-temperature solder tape 12 is to be laid, that is, dotting glue on the surface of the solar cell 11. The glue can be a film adhesive in a highly fluid state, or a transparent glue different from the film adhesive material. After the glue application is completed, the low-temperature solder tape 12 is laid on the area where the glue is applied, so that the low-temperature solder tape 12 and the solar cell 11 are bonded. By applying glue to fix the low-temperature solder tape 12 on the surface of the solar cell 11, since the glue itself has adhesive ability, there is no need to heat-treat the solar cell 11, avoiding deformation of the low-temperature solder tape 12 due to heat treatment. Further improving the accuracy of the setting of the low-temperature solder tape 12 facilitates the formation of an accurate fixed connection between the low-temperature solder tape 12 and the grid line electrodes on the surface of the solar cell 11 during the lamination process.

[0060] In actual situations, along the length direction of the low-temperature solder tape 12, the area on the surface of the solar cell 11 corresponding to each low-temperature solder tape 12 is a continuous area. During the glue application process, the glue can cover a part of the continuous area. For example, the continuous area is composed of alternately arranged glue areas and non-glue areas, the glue areas are covered by glue, and the coverage area of glue in the non-glue areas is 0. The glue can also be applied after the low-temperature solder tape 12 is laid.

[0061] After the pre-fixing of the low-temperature solder tape 12 and the solar cell 11 is achieved, the battery string 10 and the encapsulation materials can be arranged and laminated in sequence. A layer of film adhesive is respectively laid on the opposite sides of the battery string 10, and then the front cover plate 14 and the back cover plate 16 are respectively arranged on the surfaces of the film adhesives on different sides of the battery string 10 away from the battery string 10, forming a laminated structure. Then, the laminated structure is transferred to a laminator, and the two layers of film adhesives laid on the opposite sides of the battery string 10 are fused by the way of lamination molding, forming an encapsulation film 17 covering the solar cell 11 and the solder tape, and bonding the front cover plate 14 and the back cover plate 16 to the battery string 10 through the encapsulation film 17. At the same time, the welding between the solar cell 11 and the solder tape is completed, forming an alloy interconnection layer to realize the interconnection between multiple solar cells 11.

[0062] In some embodiments, as Figure 6 shown, the step of performing lamination and curing treatment on the laminate 100 in step S130 may include the following steps:

[0063] Step S131: Place the laminate 100 on the carrier in the laminator.

[0064] The laminator has an inner cavity, and the carrier for placing the workpiece 100 to be laminated is located in the inner cavity of the laminator. The temperature and pressure in the inner cavity of the laminator can be controlled so that the workpiece 100 to be laminated can complete the lamination process in an environment isolated from the outside. The laminator uses a heating system to heat the workpiece 100 to be laminated, and the heat reaches the workpiece 100 in a form of transfer. In actual situations, the glass cover plate in the encapsulation material of the workpiece 100 to be laminated is affected by heat. During the heating process of the laminator, the glass will warp at both ends, forming an arc shape. As a result, the heat conduction path in the middle area is shorter, resulting in a lower temperature in the warped area of the glass cover plate than that in the middle area, making the internal temperature of the laminate uneven, generally about plus or minus 5°C to plus or minus 10°C. This not only easily causes the phenomenon of hidden cracks in the battery chip 11, but also makes the alloying effect between the solder tape and the battery chip 11 uneven after lamination.

[0065] Therefore, before starting the lamination and curing process, the workpiece 100 to be laminated can be lifted by a thimble to make the internal temperature of the workpiece 100 tend to be consistent. And during the lamination process, the heating rate and the cooling rate are controlled to make the alloying effect formed between the low-temperature solder tape 12 and the battery chip 11 better.

[0066] Step S132: Lift the carrier to form a gap between the workpiece 100 to be laminated and the heating unit.

[0067] By lifting the carrier, a gap can be formed between the carrier and the whole workpiece 100 to be laminated and the heating unit, and the way the workpiece 100 to be laminated receives heat is changed from direct transfer to heat radiation. It can ensure that the workpiece 100 to be laminated is heated evenly to prevent the glass cover plate from warping. Furthermore, it can avoid the phenomenon of hidden cracks in the battery chip 11 and avoid affecting the alloying effect formed between the solder tape and the battery chip 11.

[0068] That is, during the lamination process, the bottom plate in the inner cavity of the laminator can be lifted to raise the middle part of the workpiece 100 to be laminated, ensuring that all parts of the workpiece 100 to be laminated are heated evenly. The internal heating temperature of the workpiece 100 to be laminated is consistent, which can make the alloying effect in each part remain the same.

[0069] Step S133: Set the lamination temperature, duration and pressure, and control the laminator to perform lamination and curing treatment on the workpiece 100 to be laminated at a preset heating rate.

[0070] After the workpiece 100 to be laminated is lifted, the laminator can be controlled to perform lamination and curing treatment on the workpiece 100 to be laminated at a certain lamination temperature, duration, vacuum degree and preset heating rate. On the one hand, the forming and fixing of the encapsulation material are completed. On the other hand, the connection between the solder tape and the battery chip 11 is completed to form a welding effect between the solder tape and the battery chip 11.

[0071] In actual situations, the lamination temperature can be greater than or equal to 160°C and less than or equal to 200°C.

[0072] For example, the range of the lamination temperature can be from 160°C to 180°C, or from 180°C to 200°C. Specifically, the lamination temperature can be 160°C, 170°C, 180°C, 190°C, or 200°C. By controlling the lamination temperature of the laminator, it is possible to avoid affecting the welding between the cell 11 and the low-temperature solder tape 12 due to too low a lamination temperature, and it is also possible to avoid affecting the encapsulation effect of the encapsulation material due to too high a lamination temperature.

[0073] In addition, the lamination duration can be controlled within 25 min to 40 min. By controlling the lamination duration, the adhesiveness between the adhesive film and the cover plate can be ensured, and the probability of the encapsulation material falling off and separating can be reduced. When heating and laminating, the inner cavity can be evacuated to discharge the air between the encapsulation materials of the workpiece to be laminated 100, preventing bubbles from appearing in the laminated part after lamination.

[0074] In some embodiments, the solder 122 may further include metallic lead (Pb), and the difference in the content of metallic lead and metallic tin in the solder 122 is within 10%.

[0075] The tin-lead solder 122 is a widely used soft solder. Metallic lead can increase the spreading area of the solder 122 alloy. In addition, since the recrystallization temperature of metallic lead is lower than room temperature and it has good plasticity, metallic lead can also improve the ductility of the solder 122. By controlling the proportion range between metallic lead and metallic tin, the solder 122 can have good welding performance and form good mechanical properties after welding.

[0076] In addition, the solder 122 may further include metallic bismuth (Bi), and the content of metallic bismuth in the solder 122 is 3 wt% to 20 wt%.

[0077] By adding bismuth element to the solder 122, not only can the melting point of the alloy be effectively reduced, but also the wetting performance of the solder 122 on the copper substrate 121 can be effectively improved. At the same time, the maximum addition amount of the bismuth element does not exceed 20 wt%, which can avoid affecting the mechanical properties of the alloy. When the solder 122 has a lower melting point, the breakage rate during the welding of the cell 11 can be reduced. At the same time, the molten solder 122 has good wettability with the copper substrate 121, so that a good weld can be formed. By controlling the content of metallic bismuth in the solder 122, it is possible to avoid being unable to effectively reduce the melting point range of the solder 122 due to too low a content of metallic bismuth, and at the same time, it is also possible to avoid affecting the mechanical properties of the alloy due to too high a content of metallic bismuth.

[0078] Optionally, the content of metallic bismuth in the solder 122 may be 3 wt% to 8 wt%, 8 wt% to 13 wt%, 13 wt% to 17 wt%, or 17 wt% to 20 wt%. Specifically, the content of metallic bismuth in the solder 122 may be 3 wt%, 5 wt%, 7 wt%, 9 wt%, 11 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, or 20 wt%.

[0079] In actual situations, the melting point of the solder 122 may be 120°C to 160°C.

[0080] For example, the melting point of the solder 122 may be 120°C to 140°C, or 140°C to 160°C. Specifically, the melting point of the solder 122 may be 120°C, 130°C, 140°C, 150°C, or 160°C. By controlling the melting point range of the solder 122, it is possible to avoid a decrease in the welding performance of the solder 122 due to too low a melting point, and it is also possible to avoid affecting the welding effect during the lamination process due to too high a melting point.

[0081] When the heating rate during the lamination process is 5°C / min, the diffusion of metallic copper is slow, and the Cu3Sn alloy is formed during the alloying process. By controlling the heating rate to be 10°C / min to 20°C / min, the diffusion of metallic copper is accelerated, and the Cu6Sn5 alloy will be formed. Compared with the Cu3Sn alloy, the tensile strength of the Cu6Sn5 alloy can be increased by about 10 MPa, thereby improving the alloying effect during the lamination process.

[0082] The cooling rate during the cooling stage after the lamination process will also affect the diffusion of metallic copper to a certain extent. Therefore, when starting to cool down after the normal lamination of the laminate is completed, by controlling the cooling rate, the Cu6Sn5 alloy component in the alloy layer can be further increased to optimize the mechanical properties of the alloy layer.

[0083] Table 1 below lists the main components of the CuSn alloy in the alloy layer and the tensile strength of the alloy layer under different heating and cooling rates respectively.

[0084] Table 1. Detection results of the alloy layer under different heating and cooling rates

[0085] Heating and cooling rate Alloy composition Tensile strength Heating rate: 5°C / min <![CDATA[Cu3Sn]]> 25 MPa Heating rate: 11°C / min <![CDATA[Cu6Sn5]]> 34 MPa Heating rate: 22°C / min <![CDATA[Cu6Sn5]]> 36 MPa Cooling rate: 27°C / min <![CDATA[Cu6Sn5]]> 36 MPa Cooling rate: 1°C / min <![CDATA[Cu3Sn]]> 28 MPa

[0086] It can be seen that under different heating and cooling rates, the main components of the CuSn alloy in the alloy layer are different, and the tensile strength of the alloy layer is also different. Under the preset heating rate and preset cooling rate, the thickness of the CuSn alloy formed in the alloy layer is thinner, the alloy component is mainly the Cu6Sn5 alloy, and the tensile strength is higher.

[0087] To adapt to low-temperature lamination welding, metallic bismuth can be added to the solder 122 of the low-temperature solder tape 12, and the overall solder 122 is proportioned by three elements of Sn, Pb, and Bi. The proportion of metallic bismuth is 3 wt% to 20 wt%, and the proportions of metallic tin and metallic lead can remain basically the same. The addition of metallic bismuth can reduce the melting point of the solder 122 to below 160 °C, so as to achieve the welding between the low-temperature solder tape 12 and the grid line electrodes on the surface of the cell 11 during the lamination process.

[0088] In the alloy layer formed between the low-temperature solder tape 12 and the grid line electrodes on the surface of the cell 11, it includes a CuSn alloy formed by the diffusion of metallic copper in the copper matrix 121 of the low-temperature solder tape 12, and an AgSn alloy formed by the diffusion of metallic silver in the grid line electrodes on the surface of the cell 11. And the AgSn alloy itself has a relatively large tensile strength. Therefore, by controlling the thickness and main components of the CuSn alloy in the alloy layer, the alloying effect between the low-temperature solder tape 12 and the cell 11 can be improved to ensure the mechanical properties of the alloy layer. Furthermore, the connection effect between the low-temperature solder tape 12 and the grid line electrodes on the surface of the cell 11 is ensured.

[0089] Some embodiments of the present application also provide a photovoltaic module 110 prepared by using the above-mentioned photovoltaic module preparation method. As Figure 7 and Figure 8 shown, the photovoltaic module 110 includes a battery string 10 and encapsulation materials located on both sides of the battery string 10. The battery string 10 includes a plurality of cells 11 and low-temperature solder tapes 12 connecting the plurality of cells 11. The low-temperature solder tapes 12 include a copper matrix 121 and a solder 122 wrapping the copper matrix 121 ( Figure 4 shown), the solder 122 includes metallic tin, and the solder 122 is melted to form an intermetallic alloy layer between the copper matrix 121 and the grid line electrodes of the cell 11.

[0090] The cell 11 can be a main-gridless cell, and the surface of the cell 11 has a plurality of fine grids arranged at intervals in the same direction. The number of fine grids on the surface of the cell 11 can be 45, 50, 55, 60, 65, 70 or 75. The cell 11 can be a whole cell or a segmented cell formed by a scribing process. The segmented cell is formed by cutting the whole cell into a plurality of independent parts along the extension direction of the fine grids. In actual situations, the cell 11 can also be a main-grid cell with a small number of main grids. The type of the cell 11 can be any one of a PERC cell (Passivated Emitter and Rear Cell), a PERT cell (Passivated Emitter and Rear Totally-diffused cell), a TOPCON cell (Tunnel Oxide Passivated Contact), a HIT / HJT cell (Heterojunction Technology), a perovskite cell, and a BC cell (Back Contact). The BC cell can be an IBC cell (Interdigitated Back Contact), an HPBC cell (Hybrid PassivatedBack Contact), a TBC cell with superimposed TOPCON technology and IBC technology, or an HBC cell with superimposed HIT / HJT technology and IBC technology. Of course, it can also be other types of back-contact photovoltaic cells. For example, the cell 11 can be a main-gridless TOPCon cell or a main-gridless BC cell.

[0091] The low-temperature solder tape 12 is a solder tape used for laminating and welding with the cell 11. The melting point of the solder 122 on the surface of the low-temperature solder tape 12 is within the lamination temperature. For example, the melting point of the solder 122 can be controlled within 160°C. By using the lamination welding in a low-temperature environment, the thermal stress during the welding process can be reduced, and the phenomenon of cell 11 microcracks can be reduced. The copper matrix 121 in the low-temperature solder tape 12 has good electrical conductivity and can better realize the interconnection between multiple cells 11.

[0092] The encapsulation material includes a front cover plate 14 located on the front side of the cell 11 in the cell string 10, and a back cover plate 16 located on the back side of the cell 11 in the cell string 10. The front cover plate 14 and the back cover plate 16 are located on the outermost sides of the photovoltaic module 110 and are used to isolate the influence of the external environment on the cell 11. The front cover plate 14 and the back cover plate 16 are fixedly connected to the cell string 10 through an encapsulation film 17, and the cover plates are adhered to the cell string 10. At the same time, the encapsulation film 17 covers the cell string 10.

[0093] As the temperature continuously rises during the lamination process, the diffusion rate of the elements in the solder 122 alloy and the copper matrix 121 increases, so that the alloy at the brazing joint interface of the low-temperature solder tape 12 forms a Cu6Sn5 alloy with higher tensile strength. Even if the eutectic reaction occurs between metallic tin and metallic copper during the welding process to form a Cu6Sn5 alloy. The Cu6Sn5 alloy in the alloy layer has sufficient mechanical properties, and the tensile strength can meet the usage requirements. At the same time, an AgSn alloy is formed at the brazing joint interface of the grid line electrode on the surface of the cell 11. Since the tensile strength of the AgSn alloy itself is sufficient, the mechanical properties of the interconnection alloy layer formed by welding at the grid line electrode on the surface of the cell 11 can be ensured.

[0094] Those of ordinary skill in the art can understand that the above-described embodiments are specific examples for implementing the present application, and in practical applications, various changes can be made to it in terms of form and details without departing from the spirit and scope of the present application.

Claims

1. A method for preparing a photovoltaic module, characterized in that, Comprising: Providing a plurality of solar cells and low-temperature solder tapes, the low-temperature solder tapes comprising a copper substrate and a solder wrapping the copper substrate, the solder comprising metallic tin; Pre-fixing the solar cells and the low-temperature solder tapes so that the plurality of solar cells are connected via the low-temperature solder tapes to form a battery string; Disposing encapsulation materials on both sides of the battery string to form a laminate-to-be, and performing a lamination and curing treatment on the laminate-to-be at a preset heating rate so that the solder melts to form an intermetallic alloy layer between the copper substrate and the grid line electrodes of the solar cells; Wherein, the preset heating rate is greater than 5 °C / min.

2. The method for preparing a photovoltaic module according to claim 1, wherein, The preset heating rate is greater than or equal to 10 °C / min and less than or equal to 20 °C / min.

3. The method for preparing a photovoltaic module according to claim 2, wherein After performing the lamination and curing treatment on the laminate-to-be, it further includes cooling at a preset cooling rate, and the preset cooling rate is greater than 20 °C / min.

4. The method for preparing a photovoltaic module according to any one of claims 1 to 3, characterized in that, Pre-fixing the solar cells and the low-temperature solder tapes includes: Arranging the plurality of solar cells in the same direction and making the surfaces of the plurality of solar cells with the same polarity face the same side; Applying glue dots on the surfaces of the plurality of solar cells and laying low-temperature solder tapes at the glue dot positions on the surfaces of the solar cells so that the low-temperature solder tapes are bent between adjacent two solar cells; or, laying low-temperature solder tapes on the surfaces of the solar cells so that the low-temperature solder tapes are bent between adjacent two solar cells, and applying glue dots or laminating films on the surfaces of the low-temperature solder tapes.

5. The method for preparing a photovoltaic module according to claim 1, characterized in that, Performing the lamination and curing treatment on the laminate-to-be includes: Placing the laminate-to-be on a carrier in a laminator; Lifting the carrier so that the laminate-to-be forms a gap with a heating unit; Setting the lamination temperature, duration and pressure, and controlling the laminator to perform the lamination and curing treatment on the laminate-to-be at the preset heating rate.

6. The method for preparing a photovoltaic module according to claim 5, characterized in that, The lamination temperature is greater than or equal to 160 °C and less than or equal to 200 °C.

7. The method for preparing a photovoltaic module according to claim 1, wherein The solder further includes metallic lead, and the content difference between the metallic lead and the metallic tin in the solder is within 10%.

8. The method for preparing a photovoltaic module according to claim 1, wherein, The solder further includes metallic bismuth, and the content of the metallic bismuth in the solder is 3 wt% to 20 wt%.

9. The method for preparing a photovoltaic module according to claim 1, wherein, The melting point of the solder is 120 °C to 160 °C.

10. A photovoltaic module prepared by the method for preparing a photovoltaic module according to any one of claims 1 to 9, characterized in that, Including a battery string, and encapsulation materials located on both sides of the battery string, the battery string including a plurality of solar cells and low-temperature solder tapes connecting the plurality of solar cells, the low-temperature solder tapes including a copper substrate and a solder wrapping the copper substrate, the solder including metallic tin, and the solder being melted to form an intermetallic alloy layer between the copper substrate and the grid line electrodes of the solar cells.

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