Back contact cell string and preparation method thereof

Abstract

The invention relates to a preparation method of a back contact cell string. The preparation method comprises the following steps: S1, printing insulation paste; s2, printing and curing a conductive material; s3, solder strip laying and preliminary curing: a main grid of the battery piece comprises a positive electrode main grid and a negative electrode main grid which are arranged in a staggered manner, UV glue is printed on the positive electrode main grid and the negative electrode main grid of the battery piece, and the printing position of the UV glue covers the surfaces of the insulation glue, the positive electrode main grid and the negative electrode main grid at the same time; a flat low-temperature welding strip is laid in the length direction of the positive electrode main grid and the negative electrode main grid, the melting point of the low-temperature welding strip is smaller than 155 DEG C, pre-pressing is conducted through a pressing tool, and then pre-fixing is conducted through ultraviolet irradiation curing UV glue; and S4, welding strip connection. The method has the advantages that the situation that the battery strings tilt due to the fact that the single faces of the battery pieces are welded is reduced, and then the effects of piece merging and piece cracking in the laminating process are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of preparing cell strings of photovoltaic modules, and in particular to a back-contact cell string and a preparation method thereof. Background Art

[0002] Back-contact cells (BC cells) are a type of solar cell technology whose main feature is the placement of both the PN junction and the metal contact on the back of the solar cell, leaving the front of the cell unobstructed by electrodes. This increases the area of ​​sunlight absorbed by the cell, thereby improving conversion efficiency and generating more electricity. The innovative design of BC cells lies in their front-side unobstructed structure. This feature eliminates the light energy loss caused by traditional grid lines, ensuring maximum utilization of incident photons, and achieving higher conversion efficiency. BC cells offer significant structural advantages and multiple benefits. For example, thanks to the front-side grid-free design, the short-circuit current of BC cells can be increased by approximately 7%. This significant gain is due to the unique back-side electrode layout. With the development of solar cells and modules, back-contact photovoltaic modules have become popular among photovoltaic companies because they have no grid lines obstructing the front (light-receiving) side and both the positive and negative electrodes are located on the back (non-light-receiving) side, thereby increasing the power of the photovoltaic module.

[0003] Back-contact cells and modules have become a key development direction in the photovoltaic industry. Back-contact photovoltaic modules primarily consist of a laminate consisting of a back cover, back film, back-contact cell array, front film, and front cover. The cell array is a string of multiple back-contact cells connected by solder ribbons. In the cell structure, metal grids are responsible for directing the photocurrent generated within the cell to the outside of the cell.

[0004] Since the current conventional battery string welding ribbon connection is basically a high-temperature welding method, on the one hand, the grid is prone to breakage in the existing process, and the tin on the welding ribbon melts and forms a tin-silver alloy with the main grid silver paste, resulting in the undesirable phenomenon of excessively high resistance in this area, which in turn causes damage to the internal electrodes of the battery cell, directly affecting the power attenuation of the component, reducing the life of the component or causing it to be scrapped. On the other hand, it will bring about problems such as warping and micro-cracks on the surface of the battery due to thermal stress. Since the back-contact battery is single-sided welded, combined with the different thermal expansion coefficients of the solder ribbon and the silicon material, after the battery cell and the solder ribbon alloy are welded, the battery and the battery string will have obvious warping, which will cause adverse improvements in the laying, lamination and other processes. It is particularly serious in single-glass modules. Using the conventional laying method, that is, battery string layout and convergence welding, film laying, backboard laying and other processes, the current back-contact batteries will show warping after being strung together. The back of the single-glass module is a polymer material backboard with a small weight. The warped battery string cannot be flattened after laying. Therefore, it is easy for the battery cells to come into contact with each other during lamination, which in turn causes adverse effects such as cracking, resulting in an increase in the defective rate. Summary of the Invention

[0005] In order to reduce the problem of increased defective rate of battery strings caused by warping of battery strings due to high-temperature welding of one side of battery cells, which may lead to adverse effects such as cell paralleling and cell splitting during lamination, the present application provides a back-contact battery string and a preparation method thereof.

[0006] In a first aspect, the present application provides a method for preparing a back-contact battery string, using the following technical solution:

[0007] A method for preparing a back-contact battery string comprises the following steps:

[0008] S1. Printing insulation glue: Printing insulation glue on the back of the cell with main grid and auxiliary grid and then drying it;

[0009] S2. Printing and curing conductive material: After printing and curing the conductive material on the back of the cell, the cured conductive material is dried to a semi-dried state;

[0010] S3. Laying and Preliminary Curing of Welding Strips: The main grid of the cell includes staggered positive and negative main grids. UV glue is printed on the positive and negative main grids of the cell. The printing position of the UV glue covers the insulating glue, the positive and negative main grids at the same time. Then, a flat low-temperature welding strip with a melting point of less than 155°C is laid along the length direction of the positive and negative main grids. The low-temperature welding strip is pre-pressed by a press and then pre-fixed by curing the UV glue with ultraviolet light.

[0011] S4, welding ribbon connection.

[0012] By adopting the above technical solution, a stable connection can be achieved during the process of laying the welding tape to fix it to the battery cell without the need for high-temperature hot welding. By printing UV glue on the surface of the insulating glue and the main grid, and then laying the low-temperature welding tape and pre-pressing it with a press to increase the contact area between the low-temperature welding tape, UV glue and the positive main grid and the negative main grid, and then irradiating it with ultraviolet light to achieve UV glue curing and thereby increase the pre-fixing effect.

[0013] Optionally, during S3, strip laying and preliminary curing, the UV irradiation intensity is 900-1100 mw / cm 2 , the wavelength of ultraviolet light is 360-370nm.

[0014] Optionally, the UV irradiation intensity can be 900 mw / cm 2 , 950 mw / cm 2 、1000 mw / cm 2 、1050mw / cm 2 、1100 mw / cm 2The wavelength of ultraviolet light can be 360 ​​nm, 365 nm, 370 nm, etc. The ultraviolet light irradiation area is 240*260 mm.

[0015] Optionally, in S1, printing insulating adhesive, insulating adhesive is printed on the back of a cell with multiple main grids and auxiliary grids, where the main grids and auxiliary grids on the cell are perpendicular to each other. The insulating adhesive is dotted on both sides of the main grids and covers the auxiliary grids, and then dried at a temperature of 230-250°C for 7-9 minutes. The drying temperature may be, but is not limited to, 230°C, 235°C, 240°C, 245°C, etc. The drying time may be, but is not limited to, 7 minutes, 7.5 minutes, 8 minutes, 8.5 minutes, 9 minutes, etc.

[0016] By adopting the above technical solution, by applying insulating glue dots on both sides of the main grid and covering the auxiliary grid, on the one hand, it plays a limiting role in the subsequent laying of the welding strip to prevent the welding strip from being offset. On the other hand, the insulating glue prevents the welding strip from contacting the auxiliary grid and causing a short circuit.

[0017] Optionally, the spacing between adjacent main grids is 9.3-9.4 mm, the spacing from the main grid to the edge of the cell is 11.3-11.4 mm, and the spacing between adjacent auxiliary grids is 0.5-0.6 mm.

[0018] Optionally, in the S2, printed and cured conductive material, the auxiliary grid of the battery cell includes a staggered positive auxiliary grid and a negative auxiliary grid, the PAD point is located between the positive auxiliary grid and the negative auxiliary grid and coincides with the main grid, and the low-temperature solder paste is printed at the PAD point on the back of the battery cell and then dried. The drying temperature is 165-175°C and the drying time is 0.5-1.5 minutes, so that the low-temperature solder paste is in a semi-dried state. Among them, the drying temperature can be but not limited to 165°C, 166°C, 167°C, 168°C, 169°C, 170°C, 171°C, 172°C, 173°C, 174°C, 175°C, etc., and the drying time can be but not limited to 0.5 minutes, 0.8 minutes, 1 minute, 1.2 minutes, 1.5 minutes, etc.

[0019] By adopting the above technical solution, low-temperature solder paste, as a conductive material with a melting point of 145-155°C, can form an alloy contact between the low-temperature solder paste and the PAD points at the drying temperature of this application. In the subsequent lamination environment, the solder ribbon and the solder paste can form an alloy contact through lamination, thereby achieving the fixation of the solder ribbon. In addition, by controlling the drying time of the low-temperature solder paste so that the low-temperature solder paste achieves alloy contact while being in a semi-dried state, it helps to improve the connection stability between the solder ribbon and the solder paste, thereby reducing the phenomenon of the solder ribbon slipping and short circuiting caused by the solder paste being completely dried.

[0020] Optionally, the distance between the PAD point and the edge of the battery cell is 4.1-4.2 mm, and the distance between adjacent PAD points is 12.4-12.5 mm.

[0021] Optionally, the spacing between the PAD points and the edge of the battery cell may be, but is not limited to, 4.11 mm, 4.12 mm, 4.13 mm, 4.14 mm, 4.15 mm, 4.16 mm, 4.17 mm, 4.18 mm, 4.19 mm, 4.2 mm, etc. The spacing between adjacent PAD points may be, but is not limited to, 12.4 mm, 12.41 mm, 12.42 mm, 12.43 mm, 12.44 mm, 12.45 mm, 12.46 mm, 12.47 mm, 12.48 mm, 12.49 mm, 12.5 mm, etc.

[0022] Optionally, in the S4, solder strip connection, the solder paste enters the lamination equipment for lamination curing, and the UV glue on the top of the solder paste diffuses to both sides so that there is no glue on the top of the solder paste, forming an alloy contact with the low-temperature solder strip. The positive main grid and the negative main grid on the two adjacent battery cells are arranged opposite to each other, and one end of the low-temperature solder strip is connected to the positive main grid of one of the battery cells, and the other end is connected to the negative main grid on the other battery cell to form a battery string.

[0023] Optionally, the lamination temperature is 150-155° C., and the lamination pressure is 70-25 MPa.

[0024] Optionally, the lamination temperature may be, but is not limited to, 150°C, 151°C, 152°C, 153°C, 154°C, 155°C, etc., and the lamination pressure may be, but is not limited to, 25 Mpa, 30 Mpa, 35 Mpa, 40 Mpa, 45 Mpa, 50 Mpa, 55 Mpa, 60 Mpa, 65 Mpa, 70 Mpa, etc.

[0025] By adopting the above technical solution, the battery string formed by connecting the battery cells with the welding tape of the present application has the effects of good curing effect, high bonding strength, high yield, and the power of the component is not easy to attenuate. By first printing the insulating glue on both sides of the main grid and the position covered by the auxiliary grid and then drying it, the situation of short circuit caused by the subsequent laying of the welding tape and contact with the auxiliary grid is reduced, and the effect of regional insulation is achieved. At the same time, it plays a limiting role in the laying of the long strip of low-temperature welding tape, ensuring that the connection between the welding tape and the main grid always remains in an overlapping state; then print the low-temperature solder paste at the PAD point, and dry the low-temperature solder paste to a semi-dried state. At this time, the low-temperature solder paste and the PA Point D reacts to form an alloy contact. UV glue is then printed on the main grid, with the UV glue printing location coinciding with the insulating glue printing location. Low-temperature solder tape is then applied along the length of the main grid, which helps ensure a tighter bond during application. Pre-pressing with a press further increases the contact area, improving bond stability. UV light is then used to cure the low-temperature solder tape, pre-fixing the cells and interconnecting them into a string. Finally, the process is cured in a laminating environment, causing the low-temperature solder tape to react with the low-temperature solder paste at the point of contact, forming an alloy contact and ensuring the bond strength between the low-temperature solder tape and the positive and negative main grids. This eliminates the need for high-temperature welding to secure the tape, forming a stable connected string without warping. This reduces the risk of paralleling during lamination, significantly improving the production yield of the string.

[0026] In a second aspect, the present application provides a back-contact battery string, which adopts the following technical solution:

[0027] A back-contact battery string is prepared using the above-mentioned method for preparing a back-contact battery string.

[0028] In summary, this application has the following beneficial effects:

[0029] 1. The high-temperature welding process without the need for welding ribbons effectively avoids the problem of cell deformation caused by high-temperature welding and reduces the phenomenon of affecting component power attenuation.

[0030] 2. It solves the problem of easy chipping during lamination, which in turn causes defects such as chip splitting, greatly improving the yield rate of component production.

[0031] 3. The battery string formed by connecting the battery cells with the welding ribbon of the present application has good curing effect, high bonding strength, high yield, and the power of the component is not easy to attenuate. By first printing insulating glue on both sides of the main grid and the position covering the secondary grid and then drying it, the situation of short circuit caused by the subsequent laying of the soldering tape and contact with the secondary grid is reduced, thereby achieving the effect of regional insulation. At the same time, it plays a limiting role in the laying of the long low-temperature soldering tape, ensuring that the connection between the soldering tape and the main grid always remains in an overlapping state; then the low-temperature solder paste is printed on the PAD point, and the low-temperature solder paste is dried to a semi-dried state. At this time, the low-temperature solder paste reacts with the PAD point to form an alloy contact; then UV glue is printed, and the UV glue printing position covers the position of the insulating glue and the main grid, and then the low-temperature soldering tape is laid along the length direction of the main grid, which helps to make the soldering tape more tightly bonded during laying, and further increases its contact area through pre-pressing by the press, thereby improving the stability of the bonding; then ultraviolet light is used for curing, so that the low-temperature soldering tape pre-fixes the battery cells and interconnects them into battery strings, and finally is cured in a laminating environment, so that the position where the low-temperature soldering tape contacts the low-temperature solder paste reacts to form an alloy contact, thereby ensuring the bonding strength of the low-temperature soldering tape with the positive and negative main grids. The soldering ribbon can be fixed without high-temperature welding to form a stable connected battery string without the battery string warping phenomenon. When the battery string is laminated, the battery string is not prone to parallelization, which greatly improves the production yield of the battery string. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the main grid and auxiliary grid of the battery cell.

[0033] Figure 2 This is a schematic diagram of the structure of the battery cell after printing the insulating glue.

[0034] Figure 3 Schematic diagram of the structure of the battery cell after printing and curing the conductive material.

[0035] Figure 4 Schematic diagram of the structure of the battery cell after the solder ribbon is laid and initially cured.

[0036] Figure 5 Schematic diagram of the structure of the battery string after lamination and curing. DETAILED DESCRIPTION

[0037] The experimental methods in the following examples of this application, where specific conditions are not specified, are generally carried out under conventional conditions or conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0038] Source of raw materials:

[0039] Insulation glue: curing parameters: temperature is 240℃, time is 350 seconds, viscosity is 16000mpas.

[0040] UV glue: viscosity 8000mpas, curing time 2-3 seconds, tensile test 0.3~0.4N.

[0041] The melting point of low-temperature solder paste is 145-155°C.

[0042] The melting point of low temperature solder strip is less than 155℃.

[0043] The PAD point described in this application refers to a metal contact point.

[0044] Example 1

[0045] A method for preparing a back-contact battery string comprises the following steps:

[0046] S1, Printed insulation adhesive: refer to Figure 1 and Figure 2 The back of the battery cell has multiple mutually perpendicular main grids and sub-grids. The main grids are parallel and equidistant to each other. The spacing between adjacent main grids is 9.35mm, and the spacing between the main grid and the edge of the battery cell is 11.35mm. The sub-grids are parallel and equidistant to each other; the spacing between adjacent sub-grids is 0.52mm. Insulating glue is printed on both sides of each main grid. The spacing between the insulating glue and the main grid is 1mm, and the insulating glue covers the sub-grid. The printing distance of the insulating glue is consistent with the position of the sub-grid. Then put it into the plug furnace to dry the insulating glue. The drying temperature is 240℃ and the drying time is 8 minutes.

[0047] S2. Printing and curing conductive material: refer to Figure 1 and Figure 3 The secondary grid on the back of the cell includes staggered positive and negative secondary grids. PAD points (metal contact points) are set between the positive and negative secondary grids, and the PAD points coincide with the main grid. The spacing from the PAD point to the edge of the cell is 4.16mm, and the spacing between adjacent PAD points is 12.48mm.

[0048] After printing the low-temperature solder paste on the PAD point on the back of the battery cell, put it into the drying oven for drying. The drying oven has 6 drying temperature zones, and the drying temperatures are 165℃, 170℃, 175℃, 175℃, 175℃, and 170℃, respectively. The drying time is 1 minute, so that the low-temperature solder paste is in a semi-dried state.

[0049] S3, welding tape laying, preliminary curing: refer to Figure 1 and Figure 4The main grid of the battery cell includes staggered positive and negative main grids. UV glue is then printed on the positive and negative main grids of the battery cell. At the same time, the UV glue covers the insulating glue. A flat low-temperature solder tape is then laid along the length of the positive and negative main grids on the back. The melting point of the low-temperature solder tape is less than 155°C. The contact area between the low-temperature solder tape, UV glue, and the positive and negative main grids is increased by pre-pressing with a press. The UV glue is then cured by ultraviolet light for pre-fixation. The UV light intensity is 1000mw / cm 2 , the ultraviolet wavelength is 365nm, and the irradiation area of ​​the lamp is 240*260mm;

[0050] S4, welding ribbon connection: refer to Figure 5 The battery cells after the above steps are placed in a laminator for lamination and curing. The lamination temperature is 152°C, and the lamination pressure includes three pressure zones, namely 70Mpa, 50Mpa, and 25Mpa. The UV glue on the top of the solder paste diffuses to both sides so that there is no glue on the top of the solder paste, forming an alloy contact with the low-temperature solder strip. The positive and negative main grids on the two adjacent battery cells are arranged opposite to each other, and one end of the low-temperature solder strip is connected to the positive main grid on the back of one of the battery cells, and the other end is connected to the negative main grid on the back of the other battery cell to form a battery string.

[0051] Example 2

[0052] A method for preparing a back-contact battery string comprises the following steps:

[0053] S1, Printed insulation adhesive: refer to Figure 1 and Figure 2 The back of the battery cell has multiple mutually perpendicular main grids and sub-grids. The main grids are parallel and equidistant to each other. The spacing between adjacent main grids is 9.3mm, and the spacing between the main grid and the edge of the battery cell is 11.3mm. The sub-grids are parallel and equidistant to each other; the spacing between adjacent sub-grids is 0.5mm. Insulating glue is printed on both sides of each main grid, and the insulating glue covers the sub-grid. The printing distance of the insulating glue is consistent with the position of the sub-grid. Then it is placed in a plug furnace to dry the insulating glue. The drying temperature is 230℃ and the drying time is 9 minutes.

[0054] S2. Printing and curing conductive material: refer to Figure 1 and Figure 3 The secondary grid on the back of the cell includes staggered positive and negative secondary grids. PAD points are set between the positive and negative secondary grids, and the PAD points coincide with the main grid. The spacing from the PAD point to the edge of the cell is 4.1mm, and the spacing between adjacent PAD points is 12.4mm.

[0055] After printing the low-temperature solder paste at the PAD point on the back of the battery cell, put it into the drying oven for drying. The drying oven has 6 drying temperature zones, and the drying temperatures are 165℃, 170℃, 175℃, 175℃, 175℃, and 170℃, respectively. The drying time is 0.5 minutes, so that the low-temperature solder paste is in a semi-dried state.

[0056] S3, welding tape laying, preliminary curing: refer to Figure 1 and Figure 4 The main grid of the cell includes staggered positive and negative main grids. UV glue is then printed on the positive and negative main grids of the cell. At the same time, the UV glue also covers the insulating glue. A flat low-temperature solder tape is then laid along the length of the positive and negative main grids on the back. The melting point of the low-temperature solder tape is less than 155°C. The contact area between the low-temperature solder tape, UV glue, and the positive and negative main grids is increased by pre-pressing with a press. The UV glue is then cured by ultraviolet light for pre-fixation. The UV light intensity is 900mw / cm 2 , the ultraviolet wavelength is 360nm, and the irradiation area of ​​the lamp is 240*260mm;

[0057] S4, welding ribbon connection: refer to Figure 5 The battery cells after the above steps are placed in a laminator for lamination and curing. The lamination temperature is 150°C, and the lamination pressure includes three pressure zones, namely 70Mpa, 50Mpa, and 25Mpa. The UV glue on the top of the solder paste diffuses to both sides so that there is no glue on the top of the solder paste, forming an alloy contact with the low-temperature solder strip. The positive main grid and the negative main grid on the two adjacent battery cells are arranged opposite to each other, and one end of the low-temperature solder strip is connected to the positive main grid on the back of one of the battery cells, and the other end is connected to the negative main grid on the back of the other battery cell to form a battery string.

[0058] Example 3

[0059] A method for preparing a back-contact battery string comprises the following steps:

[0060] S1, Printed insulation adhesive: refer to Figure 1 and Figure 2 Insulating glue is printed on the back of the battery cell. The back of the battery cell has multiple mutually perpendicular main grids and sub-grids. The main grids are parallel and equidistant. The spacing between adjacent main grids is 9.4mm. The spacing between the main grid and the edge of the battery cell is 11.4mm. The sub-grids are parallel and equidistant; the spacing between adjacent sub-grids is 0.6mm. Insulating glue is printed on both sides of each main grid, and the insulating glue covers the sub-grid. The printing distance of the insulating glue is consistent with the position of the sub-grid. Then it is placed in a plug furnace to dry the insulating glue. The drying temperature is 250℃ and the drying time is 7 minutes.

[0061] S2. Printing and curing conductive material: refer to Figure 1and Figure 3 The secondary grid on the back of the cell includes staggered positive and negative secondary grids. PAD points are set between the positive and negative secondary grids, and the PAD points coincide with the main grid. The spacing from the PAD point to the edge of the cell is 4.2mm, and the spacing between adjacent PAD points is 12.5mm.

[0062] After printing the low-temperature solder paste at the PAD point on the back of the battery cell, put it into the drying oven for drying. The drying oven has 6 drying temperature zones, and the drying temperatures are 165℃, 170℃, 175℃, 175℃, 175℃, and 170℃, respectively. The drying time is 0.5 minutes, so that the low-temperature solder paste is in a semi-dried state.

[0063] S3, welding tape laying, preliminary curing: refer to Figure 1 and Figure 4 The main grid of the cell includes staggered positive and negative main grids. UV glue is then printed on the positive and negative main grids of the cell. The UV glue also covers the insulating glue. A flat low-temperature solder tape is then laid along the length of the positive and negative main grids on the back. The melting point of the low-temperature solder tape is less than 155°C. The contact area between the low-temperature solder tape, UV glue, and the positive and negative main grids is increased by pre-pressing with a press. The UV glue is then cured by ultraviolet light for pre-fixation. The UV light intensity is 1100mw / cm 2 , the ultraviolet wavelength is 370nm, and the irradiation area of ​​the lamp is 240*260mm;

[0064] S4, welding ribbon connection: refer to Figure 5 The battery cells after the above steps are placed in a laminator for lamination and curing. The lamination temperature is 155°C, and the lamination pressure includes three pressure zones, namely 70Mpa, 50Mpa, and 25Mpa. The UV glue on the top of the solder paste diffuses to both sides so that there is no glue on the top of the solder paste, forming an alloy contact with the low-temperature solder strip. The positive and negative main grids on the two adjacent battery cells are arranged opposite to each other, and one end of the low-temperature solder strip is connected to the positive main grid on the back of one of the battery cells, and the other end is connected to the negative main grid on the back of the other battery cell to form a battery string.

[0065] Comparative Example 1

[0066] A method for preparing a battery string is different from that of Example 1 in that the soldering strip fixing method in step S3 is replaced by thermal welding at a welding temperature of 220° C., and the remaining steps are the same.

[0067] Comparative Example 2

[0068] A method for preparing a battery string is different from that of Example 1 in that, in S1, printing insulating adhesive, the insulating adhesive is printed only on one side of the main grid.

[0069] Comparative Example 3

[0070] A method for preparing a battery string is different from that of Example 1 in that, in S2, printing and curing the conductive material, the printed low-temperature solder paste is dried for 5 minutes to completely dry it.

[0071] Performance testing experiment

[0072] The battery strings prepared in the above embodiment and comparative example were subjected to performance tests respectively, and the test results are as follows.

[0073] 1. Welding ribbon connection strength test

[0074] Table 1 Welding tensile test results of welding strips

[0075]

[0076] 2. Cell warpage test

[0077] Table 2 Cell warpage test results

[0078]

[0079] 3. Battery string performance test

[0080] Table 3 Battery string performance test

[0081]

[0082] Combining Examples 1 to 3 and the test results of Tables 1 to 3, it can be seen that the battery strings of Examples 1 to 3 have good welding tensile strength and greatly reduced warping, while ensuring that the battery strings have good performance and are not prone to power attenuation problems.

[0083] Combining Example 1 and Comparative Example 1 and Tables 1-3, it can be seen that when the traditional thermal welding method is used for welding ribbon connection, although good welding strength can be guaranteed, it will cause the battery cell to warp and then cause the cells to be parallel during the lamination process, which is not conducive to improving the yield of the battery string.

[0084] Combining Example 1 and Comparative Example 2 and Tables 1-3, it can be seen that the warping and battery string performance of Example 1 are better than those of Comparative Example 2. The reason for this is that by first printing the insulating glue on both sides of the main grid and the position covered by the auxiliary grid and then drying it, the subsequent laying of the welding tape and the contact with the auxiliary grid to cause short circuits are reduced, thereby achieving the effect of regional insulation. At the same time, it plays a limiting role in the laying of the long low-temperature welding tape, ensuring that the connection between the welding tape and the main grid always remains in an overlapping state, thereby ensuring the accuracy of the welding tape laying and the connection strength.

[0085] Combining Example 1 and Comparative Example 3 and Table 1 and Table 2, it can be seen that Example 1 is better than Comparative Example 3. The reason for this is that when the low-temperature solder paste is dried to a semi-dried state for laying, it can be ensured that it helps to improve the connection stability between the solder ribbon and the solder paste, thereby reducing the phenomenon of the solder ribbon slipping and causing the solder ribbon to deviate and short-circuit due to the complete drying of the solder paste.

[0086] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a back-contact battery string, characterized in that: The following steps are involved: S1. Printing insulation glue: Printing insulation glue on the back of the cell with main grid and auxiliary grid and then drying it; S2. Printing and curing conductive material: After printing and curing the conductive material on the back of the cell, the cured conductive material is dried to a semi-dried state; S3. Laying and Preliminary Curing of Welding Strips: The main grid of the cell includes staggered positive and negative main grids. UV glue is printed on the positive and negative main grids of the cell. The printing position of the UV glue covers the insulating glue, the positive and negative main grids at the same time. Then, a flat low-temperature welding strip with a melting point of less than 155°C is laid along the length direction of the positive and negative main grids. The low-temperature welding strip is pre-pressed by a press and then pre-fixed by curing the UV glue with ultraviolet light. S4, welding ribbon connection.

2. The method for preparing a back-contact battery string according to claim 1, wherein: During S3, strip laying and preliminary curing, the UV irradiation intensity is 900-1100 mw / cm 2 The wavelength of ultraviolet light is 360-370nm, and the ultraviolet light irradiation area is not less than half of the battery cell.

3. The method for preparing a back-contact battery string according to claim 1, wherein: In the S1, printed insulating glue, insulating glue is printed on the back of a battery cell with multiple main grids and auxiliary grids. The main grids and auxiliary grids on the battery cell are perpendicular to each other. The insulating glue is dotted on both sides of the main grid and covers the auxiliary grid, and then dried. The drying temperature is 230-250°C and the drying time is 7-9 minutes.

4. The method for preparing a back-contact battery string according to claim 1, wherein: The spacing between adjacent main grids is 9.3-9.4 mm, the spacing from the main grid to the edge of the cell is 11.3-11.4 mm, and the spacing between adjacent auxiliary grids is 0.5-0.6 mm.

5. The method for preparing a back-contact battery string according to claim 1, wherein: In the S2, printed and cured conductive material, the sub-grid of the battery cell includes a staggered positive sub-grid and a negative sub-grid, the PAD point is located between the positive sub-grid and the negative sub-grid and coincides with the main grid, and low-temperature solder paste is printed at the PAD point on the back of the battery cell and then dried. The drying temperature is 165-175°C and the drying time is 0.5-1.5 minutes, so that the low-temperature solder paste is in a semi-dried state.

6. The method for preparing a back-contact battery string according to claim 5, characterized in that: The distance between the PAD point and the edge of the battery cell is 4.1-4.2 mm, and the distance between adjacent PAD points is 12.4-12.5 mm.

7. The method for preparing a back-contact battery string according to claim 1, characterized in that: In the S4, solder ribbon connection, the solder paste enters the lamination equipment for lamination and curing. The UV glue on the top of the solder paste diffuses to both sides so that there is no glue on the top of the solder paste, forming an alloy contact with the low-temperature solder ribbon. The positive main grid and the negative main grid on the two adjacent battery cells are arranged opposite to each other, and one end of the low-temperature solder ribbon is connected to the positive main grid of one of the battery cells, and the other end is connected to the negative main grid on the other battery cell to form a battery string.

8. The method for preparing a back-contact battery string according to claim 7, characterized in that: The lamination temperature is 150-155° C., and the lamination pressure is 70-25 MPa.

9. A back contact battery string, characterized in that: The back contact battery string is prepared by the preparation method according to any one of claims 1 to 8.

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