Photovoltaically active solder, gate-line-free heterojunction cell and module and method of manufacture

Abstract

The application provides a photovoltaic active solder, a grid line-free heterojunction cell and a module and a preparation method, wherein the photovoltaic active solder comprises a first component and a matrix, the first component can increase the solder wetting performance of the matrix and strengthen the beta-Sn phase / In phase / Zn phase grains in the solder matrix, the soldering strength is improved, the risk of grid breakage of the module is reduced after the module is prepared, and the reliability of the module is enhanced. The ultra-fine active solder wire prepared by using the aforementioned photovoltaic active solder replaces the grid line in the prior art, printing and curing of the grid line are not required in the cell manufacturing process, the slurry and the printing and curing process and equipment thereof are omitted, in addition, the transmission resistance and the contact resistance on the current output path of the cell after soldering are small, and the electrical performance of the cell can be improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell technology, specifically to a photovoltaic active solder, a gridless heterojunction photovoltaic cell and photovoltaic module prepared using the photovoltaic active solder, and a method for preparing the aforementioned photovoltaic cell and photovoltaic module. Background Technology

[0002] Heterojunction (HJT) photovoltaic cells possess advantages such as high bifaciality, low temperature coefficient, low degradation rate, minimal thermal damage, and significant potential for efficiency improvement. However, existing problems include: limited by the formation temperature of amorphous silicon thin films, HJT photovoltaic cells are not suitable for high-temperature processes, requiring low-temperature electrode pastes. In these pastes, silver particles can only be bonded together by polymers. To ensure low connection resistance, the silver particles must be made smaller in diameter and have a larger specific surface area, resulting in higher costs for low-temperature silver pastes compared to high-temperature pastes. Furthermore, the printing characteristics of low-temperature pastes lead to higher paste consumption in HJT photovoltaic cells. The organic carrier coating of silver particles in the low-temperature paste provides overall bonding, resulting in weak welding force between the welding wire and the paste. Although existing methods using silver-coated base metals combined with gridless technology can reduce paste costs to some extent, the cost reduction is far from sufficient and remains the primary factor limiting cost reduction in HJT photovoltaic cells.

[0003] Gridless heterojunction photovoltaic modules have emerged. Chinese invention patents with publication numbers CN116581193A and CN113013296B describe gridless heterojunction photovoltaic modules that use a solder ribbon interconnect film to fix the solder wires. This method requires the preparation of the solder ribbon interconnect film in advance, which not only adds a new film material but also adds new processes and equipment. Chinese utility model patent with publication number CN214672644U describes a gridless heterojunction photovoltaic module that uses solder pads on the cells for welding or bonding of solder wires. Although this method does not print grid lines, it still requires printing the paste for the solder pads. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a photovoltaic active solder, a gridless heterojunction photovoltaic cell and module prepared using the photovoltaic active solder, and a method for preparing the aforementioned photovoltaic cell and module. The present invention proposes a photovoltaic active solder with a specific formulation. Ultrafine active welding wires prepared from this photovoltaic active solder can be directly welded onto the transparent conductive oxide (TCO) film on the surface of a heterojunction photovoltaic cell to replace the grid lines of existing technologies, eliminating the need for paste preparation and its printing and curing processes and equipment. Furthermore, the welding wire can form a continuous and robust weld with the heterojunction photovoltaic cell, resulting in high welding tensile strength between the entire ultrafine active welding wire and the cell after welding. The ultrafine active welding wire also simultaneously possesses the dual functions of collecting and transmitting current, improving contact resistance during current extraction and reducing transmission resistance, thus improving module power.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] According to a first aspect of the present invention, a photovoltaic active solder is provided, comprising a matrix and a first component;

[0007] The matrix is ​​selected from Sn-Ti, Sn-Ti-In, Sn-Ti-Ag, Sn-Ti-Bi, Sn-Ti-Pb, Sn-Ti-Ag-In, Sn-Ti-Ag-Pb, Sn-Ti-Ag-Bi, Sn-Ti-Ag-Bi-Pb, Sn-Ti-Ga -X, Sn-Ti-Ag-Ga-X, Sn-Ti-Bi-Ga-X, Sn-Ti-Pb-Ga-X, Sn-Ti-Ag-Pb-Ga-X, Sn-Ti-Ag-Bi-Ga-X, Sn-Ti-Bi-Pb-Ga-X, Sn-Ti-Ag-Bi- Pb-Ga-X, Sn-Zn, Sn-Zn-Sb, Sn-Zn-Sb-Pb, Zn-Ag, Zn-Ag-Ti, Sn-Mg, Sn-Mg-In, Sn-Mg-Ag, Sn-Mg-Bi, Sn-Mg-Pb, Sn-Mg-Bi-In, Sn-Mg-Zn, Sn-Mg-Zn-In, Sn-Mg-Zn-Bi, Sn-Mg-Zn-Bi-Ag, Sn-Mg-Zn-Bi-In, In-Mg, In-Mg-Ag, In-Mg-Zn, wherein X is Ce or La or Ce-La;

[0008] The first component is selected from any at least one of NiFe2O4, NiCo2O4, CoFe2O4, BaTiO3, SrTiO3, CaTiO3, MgTiO3, and POSS.

[0009] In this technical solution, "POSS" refers to polyhedral oligomeric silsesquioxanes. The photovoltaic active solder provided by this technical solution comprises a specially selected matrix and a first component. The addition of the first component can increase the wettability of the matrix solder and strengthen the β-Sn / In / Zn phase grains in the solder matrix, thereby improving the welding strength and reducing the risk of grid breakage in the prepared module. This results in better reliability of the prepared module when used in windy and snowy weather or when hot spot effects occur.

[0010] It should be noted that, based on the experimental data provided in the embodiments of this invention, it can be confirmed that the addition of the first components NiFe2O4, BaTiO3, and POSS can help improve the welding strength. Among the other first components, SrTiO3, CaTiO3, and MgTiO3 are titanates of the same group as BaTiO3, and NiCo2O4 and CoFe2O4 are acid salts of the same group as NiFe2O4. Therefore, their interaction mechanism with the matrix in the solder is the same as that of BaTiO3 and NiFe2O4, and thus they have the same effect of improving the welding strength.

[0011] Preferably, the substrate accounts for 55wt% to 99.99wt% of the photovoltaic active solder content;

[0012] The matrix is ​​selected from any at least one of Sn-Ti-Ag-Bi-Ga-X, Sn-Ti-Bi-Ga-X, Sn-Ti-Ag-Ga-X, Sn-Zn-Sb-Pb, and Sn-Mg-Pb;

[0013] When the matrix contains Sn, the Sn content in the matrix accounts for 20wt% to 99.9wt% of the matrix content, and the Ti, Zn, or Mg content accounts for 0.01wt% to 20wt% of the matrix content.

[0014] In this technical solution, more preferably, the Sn content in the matrix accounts for 40wt%~60wt% of the matrix content, and the Ti or Zn or Mg content accounts for 1wt%~5wt% of the matrix content.

[0015] Preferably, the first component is selected from at least one of NiFe2O4, BaTiO3, and POSS; the first component accounts for 0.01wt% to 5wt% of the photovoltaic active solder content.

[0016] In this technical solution, more preferably, the first component accounts for 1wt% to 3wt% of the photovoltaic active solder content.

[0017] Preferably, the photovoltaic active solder further includes a second component and / or a third component, wherein the second component is selected from at least one of Zr, V, Nb, and Hf, and the third component is selected from at least one of Cu, Al, Ni, Cr, Mo, and Ta;

[0018] The second component accounts for 0 wt% to 20 wt% of the photovoltaic active solder content, and the third component accounts for 0 wt% to 20 wt% of the photovoltaic active solder content.

[0019] In this technical solution, more preferably, the second component accounts for 1wt% to 5wt% of the photovoltaic active solder content, and the third component accounts for 1wt% to 5wt% of the photovoltaic active solder content. In this technical solution, the addition of the second component can assist Ti, Zn, and Mg to diffuse to the welding interface, and the addition of the third component can improve the thermal stability of the solder, thereby further improving the welding strength.

[0020] According to a second aspect of the present invention, a method for preparing a grid-free heterojunction photovoltaic cell is provided, comprising the following steps:

[0021] The silicon wafer is sequentially texturized, non-crystalline / microcrystalline silicon coated, TCO coated, and welded with ultrafine active welding wire to obtain a grid-free heterojunction photovoltaic cell.

[0022] The specific steps of welding the ultrafine active welding wire are as follows: define the extension directions parallel to the two intersecting edges of the silicon wafer as the X direction and the Y direction, respectively, and weld the ultrafine active welding wire directly onto the TCO film along the X direction and / or the Y direction. The ultrafine active welding wire includes a welding wire core and a coating layer wrapped around the welding wire core. The coating layer is the photovoltaic active solder as described in any one of the first aspects of the present invention.

[0023] In this technical solution and application, regarding the definitions of the X and Y directions, in the prior art, silicon wafers are typically rectangular or square. For two sides where they intersect at right angles, the X direction is the extension direction parallel to one of the right-angled sides of the silicon wafer, and the Y direction is the extension direction parallel to the other right-angled side. Based on consistency in the preceding and following descriptions, in the embodiments shown later in this invention, when the silicon wafer is placed horizontally, the extension direction parallel to its horizontal right-angled side is defined as the X direction, and the extension direction parallel to its vertical right-angled side is defined as the Y direction. This technical solution uses ultra-fine active welding wire to replace the grid lines in the prior art. During battery manufacturing, there is no need to print and cure the grid lines, completely eliminating electrode paste and saving the paste and its printing and curing processes and equipment. Furthermore, the transmission resistance and contact resistance on the current outflow path of the battery cell are small after welding, which can improve the electrical performance of the battery cell.

[0024] Preferably, the base material of the welding wire core is selected from at least one of the following substances: copper, aluminum, zinc, nickel, tungsten, titanium, chromium, cobalt, magnesium, and alloys containing any of the foregoing substances; or

[0025] The base material of the welding wire core is selected from any two of the following substances: copper, aluminum, zinc, nickel, tungsten, titanium, chromium, cobalt, magnesium and alloys containing any of the aforementioned substances, and the structure of the welding wire core is a core-shell cladding structure or a laminated structure composed of the selected substances.

[0026] In this technical solution, the so-called core-shell encapsulation structure refers to a concentric structure in which the base material of the welding wire core forms a core with other materials forming the shell, layer by layer. For example, when the base material of the welding wire core is selected from two materials, one material is the core and the other material is the shell encapsulating the core material, thus forming a core-shell encapsulation structure. Similarly, when the base material of the welding wire core is selected from three materials, material 1 is the core, material 2 is the shell encapsulating material 1, and material 3 further encapsulates material 2, thus forming a core-shell encapsulation structure. The so-called layered structure refers to a structure in which the base material of the welding wire core forms a layered structure. For example, when the base material of the welding wire core is selected from two materials, one material forms the lower layer and the other material forms the upper layer, stacked on top of the lower material, thus forming a layered structure. And when the base material of the welding wire core is selected from three materials, material 1 is the first layer, material 2 is the second layer stacked on top of the first material 1, and material 3 is the third layer stacked on top of the second material 2, thus forming a layered structure.

[0027] Preferably, the cross-sectional width of the ultrafine active welding wire is 10~120μm and the cross-sectional thickness is 10~120μm; the thickness of the coating layer is 1~50μm.

[0028] This technical solution does not limit the cross-sectional shape of the welding wire; it can be any one or more combinations of circular, elliptical, triangular, rectangular, trapezoidal, and flat shapes. As a further preferred embodiment, the cross-sectional width of the ultrafine active welding wire is 10-50 μm, the cross-sectional thickness is 10-50 μm, and the coating thickness is 5-20 μm. The ultrafine active welding wire of this technical solution has a small diameter, which can significantly reduce the basis weight of the encapsulation film during packaging, thus achieving further cost reduction.

[0029] Preferably, the number of ultrafine active welding wires welded on the same surface is 20 to 300; the welding method is any one of the following: hot welding, ultrasonic welding, laser welding; the welding temperature is 100℃ to 400℃.

[0030] In this technical solution, the number of ultrafine active welding wires welded on the same surface is more preferably 30 to 150. The welding wires can be welded only in the X or Y direction on the surface of the battery cell, or they can be welded in both the X and Y directions in a mesh welding manner.

[0031] According to a third aspect of the present invention, a gridless heterojunction photovoltaic cell is provided, which is prepared by the method for preparing a gridless heterojunction photovoltaic cell as described in any one of the second aspects.

[0032] According to a fourth aspect of the present invention, a gridless heterojunction photovoltaic module is provided, which is obtained by welding the gridless heterojunction photovoltaic cells described in the third aspect of the present invention into strings and then encapsulating them.

[0033] According to a fifth aspect of the present invention, a method for fabricating a grid-free heterojunction photovoltaic module is provided, comprising the following steps:

[0034] The silicon wafer is sequentially texturized, non-crystalline / microcrystalline silicon coated, and TCO coated to obtain a grid-free heterojunction photovoltaic cell body.

[0035] The gridless heterojunction photovoltaic cell body is directly welded into strings using ultra-fine active welding wire, and then encapsulated to obtain a gridless heterojunction photovoltaic module.

[0036] The specific steps of welding the ultrafine active welding wire are as follows: define the extension directions parallel to the two intersecting edges of the silicon wafer as the X direction and the Y direction, respectively, and weld the ultrafine active welding wire directly onto the TCO film along the X direction and / or the Y direction. The ultrafine active welding wire includes a welding wire core and a coating layer wrapped around the welding wire core. The coating layer is the photovoltaic active solder as described in any one of the first aspects of the present invention.

[0037] According to a sixth aspect of the present invention, a gridless heterojunction photovoltaic module is provided, which is prepared by the method for preparing a gridless heterojunction photovoltaic module as described in the fifth aspect of the present invention.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The gridless heterojunction photovoltaic cell provided by this invention directly welds ultrafine active welding wire onto the TCO to replace the grid lines of the prior art. The gridless heterojunction photovoltaic module provided by this invention uses gridless heterojunction photovoltaic cells and ultrafine active welding wire to further prepare the module, or uses ultrafine active welding wire to directly weld the gridless heterojunction photovoltaic cell body after TCO coating into strings to further prepare the module. The electrode paste is completely eliminated, saving the paste and its printing and curing processes and equipment.

[0040] 2. The gridless heterojunction photovoltaic cell and photovoltaic module provided by the present invention, by flexibly matching the composition of the photovoltaic active solder used in the ultrafine active welding wire, enables the ultrafine active welding wire to form a continuous and firm weld with the heterojunction photovoltaic cell. No flux is needed during welding. After welding, the welding tensile force between the entire welding wire and the cell is large. Moreover, the ultrafine active welding wire has the dual function of collecting current and transmitting current, improving the contact resistance when conducting current and reducing the transmission resistance. Therefore, it can improve the electrical performance of the photovoltaic cell and module.

[0041] 3. The photovoltaic active solder provided by the present invention can increase the wettability of the base solder by adding the first component, and strengthen the β-Sn phase / In phase / Zn phase grains in the solder matrix, thereby improving the welding strength, reducing the risk of grid breakage in the module, and making the module more reliable when used in windy and snowy weather or when hot spot effect occurs. Attached Figure Description

[0042] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0043] Figure 1 Here are simplified structural diagrams of the gridless heterojunction photovoltaic cells prepared in Examples 1-2 of this invention;

[0044] Figure 2 This is a simplified structural diagram of the gridless heterojunction photovoltaic cell prepared in Example 3 of the present invention;

[0045] Figure 3 This is a simplified structural diagram of the gridless heterojunction photovoltaic cell prepared in Example 4 of the present invention;

[0046] Figure 4 Here are simplified structural diagrams of the cell bodies used in the gridless heterojunction photovoltaic modules prepared in Examples 5-8 of this invention;

[0047] Figure 5 The following are simplified structural diagrams of the cell strings required for the gridless heterojunction photovoltaic modules prepared in Examples 5-6 and 8 of this invention.

[0048] Figure 6 This is a simplified structural diagram of the cell string required for the gridless heterojunction photovoltaic module prepared in Example 7 of the present invention.

[0049] The diagram shows:

[0050] 1- Gridless heterojunction photovoltaic cell;

[0051] 2-Ultra-fine active welding wire;

[0052] 3-Battery cell body Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0054] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0055] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, all directional indications (such as up, down, left, right, front, back, bottom, etc.) in this application are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the figures). If the specific orientation changes, the directional indication will also change accordingly. Further, the descriptions involving "first," "second," etc., in this application are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0056] Example 1

[0057] This embodiment provides a grid-free heterojunction photovoltaic cell, such as... Figure 1 As shown, 100 parallel ultrafine active welding wires 2 are arranged on the surface of the battery cell 1 along the X direction. The ultrafine active welding wires 2 serve as the metal electrodes of the battery cell, eliminating the grid lines in the prior art.

[0058] The fabrication method of this gridless heterojunction photovoltaic cell 1 includes the following steps: texturing the silicon wafer, non-crystalline / microcrystalline silicon coating, TCO coating, and welding with ultrafine active welding wire 2. The metallization process after TCO coating is achieved by welding with ultrafine active welding wire 2, eliminating the need for paste in the prior art, and this step does not use existing screen printing technology, thus eliminating the need for printing and curing processes and equipment.

[0059] The preparation method of the ultrafine active welding wire used in this embodiment includes the following steps: a specially made photovoltaic active solder is used to prepare the ultrafine active welding wire. Specifically, the specially made photovoltaic active solder ingot is melted in a molten pool, the temperature of the molten pool is maintained at 280°C, and a copper wire with a circular cross-section and a diameter of 25μm is pulled out from the molten pool after annealing and surface treatment. The thickness of the photovoltaic active solder on the surface of the copper wire is controlled by an air knife to obtain a 5μm thick coating layer. After cooling, the wire is wound up and vacuum-packed to obtain the ultrafine active welding wire.

[0060] The preparation method of the specially made photovoltaic active solder in this embodiment includes the following steps: Referring to Table 1, weigh 60g Sn, 4g Zn, 1g Sb, 40g Pb, 1g NiFe2O4, 1g BaTiO3, and 1g POSS. Place all the weighed raw materials into a crucible made of graphite and prepare it in a vacuum high-frequency induction furnace. The solder manufacturing temperature is 1100℃. Melt it three times in the crucible and cool the crucible in water to form a photovoltaic active solder ingot.

[0061] Example 2

[0062] This embodiment provides a grid-free heterojunction photovoltaic cell, which is prepared using the same method as in Example 1. The difference is that when preparing the photovoltaic active solder, refer to Table 1, the formula is: 60g Sn, 4g Zn, 1g Sb, 40g Pb, 5g V, 5g Cr, 1g NiFe2O4, 1g BaTiO3, 1g POSS.

[0063] Example 3

[0064] This embodiment provides a grid-free heterojunction photovoltaic cell, prepared using the same method as in Example 1, with the difference being:

[0065] (1) such as Figure 2 As shown, in this embodiment, the ultrafine active welding wire 2 is arranged in 200 strands along the Y direction on the surface of the battery cell 1.

[0066] (2) As shown in Table 1, in this embodiment, the formulation of photovoltaic active solder is: 60g Sn, 40g Pb, 5g Mg, 3g NiFe2O4.

[0067] Example 4

[0068] This embodiment provides a grid-free heterojunction photovoltaic cell, prepared using the same method as in Example 1, with the difference being:

[0069] (1) such as Figure 3 As shown, in this embodiment, the distribution direction of the ultrafine active welding wires 2 on the surface of the battery cell 1 is changed to 80 wires in the X direction and 24 wires in the Y direction;

[0070] (2) As shown in Table 1, in this embodiment, the formulation of photovoltaic active solder is: 60g Sn, 40g Pb, 5g Mg, 3g BaTiO3.

[0071] Comparative Example 1

[0072] The same method as in Example 1 was used, except that instead of the specially prepared photovoltaic active solder described in Example 1, ordinary ultrafine solder was used. This ordinary ultrafine solder was prepared using commercially available solder, as shown in Table 1. The formula of this commercially available solder is: 60g Sn, 40g Pb. During the preparation process, it was found that the ultrafine solder could not be successfully bonded to the cell body, therefore, a gridless heterojunction photovoltaic cell could not be obtained.

[0073] Table 1 shows the solder formulations and welding directions of the welding wires in Examples 1-4 and Comparative Example 1 above, where the content of each substance is expressed in grams (g).

[0074] Table 1

[0075]

[0076] Example 5

[0077] This embodiment provides a gridless heterojunction photovoltaic module. The heterojunction photovoltaic cells used in this module have no grid lines on their surface. The cells are directly used in module fabrication after TCO coating. The metallization process of the cells and the stringing process of the module are performed simultaneously. The resulting photovoltaic module has no grid lines on its surface and is directly interconnected by ultra-fine active welding wires. The fabrication method of this gridless heterojunction photovoltaic module includes the following steps: Figure 4 and Figure 5 As shown, 150 ultra-fine active welding wires 2 are drawn from the welding machine and directly welded to the TCO film on the surface of the gridless solar cell body 3. They are welded into strings along the Y direction of the solar cell body 3. The welding method is thermal welding (specifically infrared welding) at a welding temperature of 180℃. After being welded into strings, the solar cell strings are arranged, busbars are welded, film glass is laid, laminated, framed, and junction box is installed to produce a gridless heterojunction photovoltaic module.

[0078] The preparation method of the ultrafine active welding wire used in this embodiment includes the following steps: using a special photovoltaic active solder for the preparation of ultrafine active welding wire. Specifically, the special photovoltaic active solder ingot is melted in a molten pool, and the temperature of the molten pool is maintained at 280°C. A copper wire with a circular cross-section and a diameter of 25μm is annealed and surface treated before being pulled out from the molten pool. The thickness of the photovoltaic active solder on the surface of the copper wire is controlled by an air knife to obtain a 5μm thick coating layer. After cooling, the wire is wound up and vacuum-packed to obtain the ultrafine active welding wire.

[0079] The preparation method of the specially made photovoltaic active solder in this embodiment includes the following steps: Referring to Table 2, weigh 60g Sn, 4g Zn, 1g Sb, 40g Pb, 1g NiFe2O4, 1g BaTiO3, and 1g POSS. Place all the weighed raw materials into a crucible made of graphite and prepare it in a vacuum high-frequency induction furnace. The solder manufacturing temperature is 1100℃. Melt it three times in the crucible and cool the crucible in water to form a photovoltaic active solder ingot.

[0080] Example 6

[0081] This embodiment provides a gridless heterojunction photovoltaic module, which is prepared using the same method as in Example 5. The difference is that when preparing the photovoltaic active solder, refer to Table 2, the formula is: 60g Sn, 40g Pb, 5g Mg, and 3g POSS.

[0082] Example 7

[0083] This embodiment provides a grid-free heterojunction photovoltaic module, which is prepared using the same method as in Embodiment 5, with the difference being:

[0084] (1) such as Figure 6 As shown, in this embodiment, the ultrafine active welding wire 2 is led out in the welding equipment in the following directions: 80 wires along the X direction and 24 wires along the Y direction.

[0085] (2) As shown in Table 2, in this embodiment, the formulation of photovoltaic active solder is: 60g Sn, 4g Zn, 1g Sb, 40g Pb, 5g V, 5g Cr, 1g NiFe2O4, 1g BaTiO3, 1g POSS.

[0086] Example 8

[0087] This embodiment provides a gridless heterojunction photovoltaic module, which is prepared using the same method as in Example 5. The difference is that when preparing the photovoltaic active solder, refer to Table 3. The formula is: 45g Sn, 5g Ti, 1g Ag, 48.8g Bi, 0.1g Ga, 0.1g Ce, 1g NiFe2O4, 1g BaTiO3, and 1g POSS.

[0088] Comparative Example 2

[0089] The same method as in Example 5 was used, except that the ultrafine active welding wire prepared with the special photovoltaic active solder described in Example 5 was not used. Instead, ordinary ultrafine welding wire was used. This ordinary ultrafine welding wire was prepared with commercially available solder, as shown in Table 2. The commercially available solder formula is: 60g Sn, 40g Pb. However, it was found that the ultrafine welding wire could not be welded to the cell body, so gridless heterojunction photovoltaic modules could not be obtained.

[0090] Comparative Example 3

[0091] This comparative example provides a conventional heterojunction photovoltaic module. The heterojunction photovoltaic cells used in this photovoltaic module are conventional heterojunction photovoltaic cells with grid lines printed and cured on the surface. These conventional heterojunction photovoltaic cells are welded into strings using conventional welding wire. After being strung together, the cells are arranged, busbars are welded, encapsulated glass is laid, laminated, framed, and installed in a junction box to form a conventional heterojunction photovoltaic module. The design of this conventional heterojunction photovoltaic module is the same as that in Example 7.

[0092] The preparation method of the conventional welding wire used in this comparative example is the same as that described in Example 5. The difference is that the ultrafine active welding wire prepared by the special photovoltaic active solder described in Example 5 is not used. Instead, conventional welding wire is used. The diameter of the copper wire used in the conventional welding wire is 250 μm and the coating thickness is 15 μm. The conventional welding wire is prepared using commercially available solder, as shown in Table 2. The formula of the commercially available solder is: 60g Sn, 40g Pb.

[0093] Table 2 shows the solder formulations and welding directions of the welding wires in Examples 5-7 and Comparative Examples 2-3 above, where the content of each substance is expressed in grams (g).

[0094] Table 2

[0095]

[0096] Table 3 shows the solder formula and welding direction of the welding wire in Example 8 above, where the content of each substance is expressed in grams (g).

[0097] Table 3

[0098]

[0099] Performance testing

[0100] (1) Peel force test

[0101] A multi-busbar photovoltaic-specific peel force tester was used to test the peel force of the solar cells after welding. The welding wire was clamped with a spring-type fixing device to achieve fixation, and the solar cells were fixed by four rubber strips with magnets at both ends. The test data was automatically operated by a dedicated computer app program, and the average value was recorded.

[0102] (2) Thermal cycling (TC) test

[0103] The fabricated gridless heterojunction photovoltaic module was placed in a thermal cycling environment chamber for testing. The temperature was uniformly reduced from 25°C to -40°C within 1 hour, held for 15 minutes, then uniformly increased from -40°C to 85°C within 3 hours, held for 15 minutes, and then uniformly reduced from 85°C to 25°C within 2 hours. The test was repeated 200 times. Power measurements were performed before and after the initial test, and the recorded data showed the percentage change in power relative to the initial power level.

[0104] (3) Component power test

[0105] The gridless heterojunction photovoltaic module prepared in Example 7 and the conventional heterojunction photovoltaic module prepared in Comparative Example 3 were subjected to power tests using an IV curve power meter. The data was recorded as the difference ΔPmax (W) between the maximum power of Example 7 and Comparative Example 3.

[0106] Test Results

[0107] The results of the peel force test for each group, as well as the percentage change in power (ΔPmax (%)) and the percentage change in series resistance (ΔRs (%)) after the TC test compared to before the test, are listed in Tables 4 and 5. A negative ΔPmax (%) indicates power attenuation after the TC test, while a positive ΔRs (%) indicates an increase in series resistance after the TC test. The module power test results are listed in Table 6, where a positive ΔPmax (W) indicates an increase in module power in Example 7 compared to Comparative Example 3.

[0108] Comparing Examples 1-4 with Comparative Example 1, it can be seen from the aforementioned experimental process that the ultrafine active welding wire prepared using the special photovoltaic active solder described in Examples 1-4 can directly weld and prepare gridless heterojunction photovoltaic cells while ensuring welding strength. However, the ultrafine welding wire prepared using the solder in the prior art described in Comparative Example 1 cannot be used to produce gridless heterojunction photovoltaic cells.

[0109] Furthermore, compared with Comparative Example 1, the special photovoltaic active solder used in the preparation of the ultrafine active welding wire in Examples 1-4 of this invention allows the Zn and Mg elements in the solder to diffuse to the welding interface to achieve welding between the ultrafine active welding wire and the solar cell. The addition of NiFe2O4, BaTiO3, and POSS in the solder can improve the wetting effect of the solder matrix, and the increased wetting performance is beneficial to the improvement of welding strength. In addition, during the welding process, NiFe2O4, BaTiO3, and POSS in the solder can interact with Sn, Zn, and Mg in the solder matrix to strengthen the β-Sn phase grains, hinder the formation of SnZn and SnMg alloys, and promote the diffusion of Zn and Mg to the welding interface.

[0110] Furthermore, compared with Example 1, in Example 2, the addition of V can assist the diffusion of Zn, and the addition of Cr can improve the thermal stability of the solder. Therefore, the peel strength of Example 2 is slightly improved.

[0111] Comparing Examples 5-8 with Comparative Example 2, the aforementioned experimental process demonstrates that the ultrafine active welding wire prepared using the specially formulated photovoltaic active solder described in Examples 5-8 can be directly welded into strings to fabricate modules using gridless heterojunction photovoltaic cells, ensuring welding strength. This results in more effective resistance to fatigue damage of the cells and welding wire during TC testing of the fabricated modules. Consequently, power attenuation and series resistance increase are minimal during TC testing, ensuring the reliability of the modules in subsequent use. In contrast, the ultrafine welding wire prepared using the solder from the prior art described in Comparative Example 2 cannot be directly welded into strings to fabricate modules using gridless heterojunction photovoltaic cells.

[0112] Furthermore, compared with Comparative Example 2, in Examples 5-8, the Zn, Mg, and Ti elements in the solder can diffuse to the welding interface to achieve welding of the ultrafine active welding wire and the battery cell. The addition of NiFe2O4, BaTiO3, and POSS in the solder can improve the wetting effect of the substrate, and the increased wetting performance is very beneficial to the improvement of welding strength. In addition, during the welding process, NiFe2O4, BaTiO3, and POSS in the solder can interact with Sn, Zn, Mg, and Ti in the solder matrix to strengthen the β-Sn phase grains, hinder the formation of SnZn, SnMg, and SnTi alloys, and promote the diffusion of Zn, Mg, and Ti to the welding interface.

[0113] Furthermore, compared with Example 5, in Example 7, the addition of V can assist the diffusion of Zn, and the addition of Al can improve the thermal stability of the solder. Example 7 shows a slight increase in peel strength and a slight decrease in TC power attenuation.

[0114] Compared with Comparative Example 3, the gridless heterojunction photovoltaic module prepared in Example 7 has a higher power than the conventional heterojunction photovoltaic module. This is because the ultrafine active welding wire used in the photovoltaic module prepared in Example 7 has the dual function of collecting current and transmitting current, which can improve the contact resistance when discharging current and reduce the transmission resistance, thus improving the power of the module.

[0115] Table 4

[0116]

[0117] Table 5

[0118]

[0119] Table 6

[0120]

[0121] The specific embodiments of the present invention have been described above. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention.

Claims

1. A photovoltaically active solder, characterized in that, Includes the matrix and the first component; The matrix is ​​selected from Sn-Ti, Sn-Ti-In, Sn-Ti-Ag, Sn-Ti-Bi, Sn-Ti-Pb, Sn-Ti-Ag-In, Sn-Ti-Ag-Pb, Sn-Ti-Ag-Bi, Sn-Ti-Ag-Bi-Pb, Sn-Ti-Ga -X, Sn-Ti-Ag-Ga-X, Sn-Ti-Bi-Ga-X, Sn-Ti-Pb-Ga-X, Sn-Ti-Ag-Pb-Ga-X, Sn-Ti-Ag-Bi-Ga-X, Sn-Ti-Bi-Pb-Ga-X, Sn-Ti-Ag-Bi- Pb-Ga-X, Sn-Zn, Sn-Zn-Sb, Sn-Zn-Sb-Pb, Zn-Ag, Zn-Ag-Ti, Sn-Mg, Sn-Mg-In, Sn-Mg-Ag, Sn-Mg-Bi, Sn-Mg-Pb, Sn-Mg-Bi-In, Sn-Mg-Zn, Sn-Mg-Zn-In, Sn-Mg-Zn-Bi, Sn-Mg-Zn-Bi-Ag, Sn-Mg-Zn-Bi-In, In-Mg, In-Mg-Ag, In-Mg-Zn, wherein X is Ce or La or Ce-La; The first component is selected from any one of NiFe2O4, NiCo2O4, CoFe2O4, BaTiO3, SrTiO3, CaTiO3, MgTiO3, and POSS; The substrate comprises 55wt% to 99.99wt% of the photovoltaic active solder content; When the matrix contains Sn, the Sn content in the matrix accounts for 20wt% to 99.9wt% of the matrix content, and the Ti, Zn, or Mg content accounts for 0.01wt% to 20wt% of the matrix content. The first component accounts for 0.01wt% to 5wt% of the photovoltaic active solder content.

2. The photovoltaically active solder of claim 1, wherein, The matrix is ​​selected from any at least one of Sn-Ti-Ag-Bi-Ga-X, Sn-Ti-Bi-Ga-X, Sn-Ti-Ag-Ga-X, Sn-Zn-Sb-Pb, and Sn-Mg-Pb.

3. The photovoltaically active solder of claim 1, wherein, The first component is selected from any one of NiFe2O4, BaTiO3, and POSS.

4. The photovoltaically active solder of claim 1, wherein, The photovoltaic active solder further includes a second component and / or a third component, wherein the second component is selected from at least one of Zr, V, Nb, and Hf, and the third component is selected from at least one of Cu, Al, Ni, Cr, Mo, and Ta. The second component accounts for 0 wt% to 20 wt% of the photovoltaic active solder content, and the third component accounts for 0 wt% to 20 wt% of the photovoltaic active solder content.

5. A method for preparing a gridless heterojunction photovoltaic cell, characterized in that, Includes the following steps: The silicon wafer is sequentially texturized, non-crystalline / microcrystalline silicon coated, TCO coated, and welded with ultrafine active welding wire to obtain a grid-free heterojunction photovoltaic cell. The specific steps of the ultrafine active solder wire welding are as follows: defining the extending directions parallel to two intersecting edges of the silicon wafer as X direction and Y direction, and directly welding the ultrafine active solder wire on the TCO film along the X direction and / or the Y direction, wherein the ultrafine active solder wire comprises a solder wire core and a coating layer wrapped around the periphery of the solder wire core, and the coating layer is the photovoltaic active solder according to any one of claims 1 to 4.

6. The method of claim 5, wherein the method further comprises: The base material of the solder wire core is selected from any at least one of copper, aluminum, zinc, nickel, tungsten, titanium, chromium, cobalt, magnesium and an alloy containing any one of the foregoing. The base material of the solder wire core is selected from any at least two of copper, aluminum, zinc, nickel, tungsten, titanium, chromium, cobalt, magnesium and an alloy containing any one of the foregoing, and the structure of the solder wire core is a core-shell coating structure or a laminated structure composed of the selected materials.

7. The method of claim 5, wherein the method further comprises: The cross-sectional width of the ultrafine active solder wire is 10-120 μm, and the cross-sectional thickness is 10-120 μm; the thickness of the coating layer is 1-50 μm.

8. The method of claim 5, wherein the method further comprises: The number of welds of the ultrafine active solder wire on the same surface is 20-300, and the welding mode is any one of hot welding, ultrasonic welding and laser welding; the welding temperature is 100-400 °C.

9. A gridless heterojunction photovoltaic cell, characterized by The preparation method of the gridless heterojunction photovoltaic cell according to any one of claims 5 to 8 is adopted.

10. A gridless heterojunction photovoltaic module, characterized by, The gridless heterojunction photovoltaic module is obtained by welding the gridless heterojunction photovoltaic cell according to claim 9 into a string and packaging the cell string.

11. A method for fabricating a gridless heterojunction photovoltaic module, characterized in that, The method comprises the following steps: The silicon wafer is sequentially subjected to texturing, amorphous / microcrystalline silicon coating, and TCO coating to obtain a gridless heterojunction photovoltaic cell body; The gridless heterojunction photovoltaic cell body is directly welded into a string by the ultrafine active solder wire, and the cell string is packaged to obtain a gridless heterojunction photovoltaic module; The specific steps of the ultrafine active solder wire welding are as follows: defining the extending directions parallel to two intersecting edges of the silicon wafer as X direction and Y direction, and directly welding the ultrafine active solder wire on the TCO film along the X direction and / or the Y direction, wherein the ultrafine active solder wire comprises a solder wire core and a coating layer wrapped around the periphery of the solder wire core, and the coating layer is the photovoltaic active solder according to any one of claims 1 to 4.

12. A gridless heterojunction photovoltaic module, characterized by The preparation method of the gridless heterojunction photovoltaic module according to claim 11 is adopted.

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