Conductive films and photovoltaic modules

Abstract

The present invention provides a conductive film and photovoltaic module. The conductive film comprises: a base film, the base film comprising at least a first region and a second region, the first region and the second region being distributed along the thickness of the base film, the first region having a greater viscosity than the second region, and the viscosity of the first region being greater than 10,000 Pa·s, while the viscosity of the second region being less than 100,000 Pa·s; and a conductor bonded to the second region of the base film. By controlling the viscosity of the base film in different regions where the conductor is provided and where it is not provided, the two regions have different fluidities, with the first region having a higher viscosity and lower fluidity, thereby maintaining the stability of the transparent base film, and the second region having a lower viscosity and higher fluidity, thereby ensuring that the conductor is firmly bonded to the battery cell using the base film during hot pressing of the battery assembly, and effectively preventing solder joint defects caused by excessive fluidity of the base film.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a conductive film and a photovoltaic module. Background Art

[0002] Busbarless technology replaces the cell's silver busbar and flat solder ribbons with multiple thin copper wires (ribbons) coated with a special coating. This significantly reduces the frontal shading area of ​​the cell while also reducing silver paste consumption, thereby improving the conversion efficiency of photovoltaic modules and lowering manufacturing costs. However, this technology requires laying dozens of thin tinned copper wires (ribbons) on the cell and welding them to the fine grid lines. A film material is required to pre-arrange and secure the tinned copper wires (ribbons) and support them in place during the welding process.

[0003] During the lamination process of modules using busbar-less technology, the special coating on the outer surface of the thin copper wire melts and welds to the fine grid lines. If the transparent film material and the upper encapsulation film have high fluidity, the copper wires may be poorly soldered. This means that the film penetrates between the copper wires and the fine grid lines, resulting in insulation. Therefore, it is necessary to develop a film material that meets the low fluidity requirements while ensuring high bonding performance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a conductive film and a photovoltaic module to solve the problem of copper wire cold soldering easily occurring during the lamination of modules using busbar-free technology in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a conductive film is provided, which includes: a base film, the base film includes at least a first region and a second region, the first region and the second region are distributed along the thickness direction of the base film, the viscosity of the first region is greater than the viscosity of the second region, and the viscosity of the first region is greater than 10,000 Pa·s, and the viscosity of the second region is less than 100,000 Pa·s; a conductor, the conductor is adhered to the second region on the base film.

[0006] Furthermore, the cross-linking degree of the first region is greater than or equal to 30%, preferably greater than or equal to 50%, and more preferably between 50 and 80%.

[0007] Furthermore, the crosslinking degree of the second region is less than 30%, preferably less than 15%, and more preferably between 0 and 10%. Preferably, the difference between the crosslinking degree of the first region and the crosslinking degree of the second region is 55% to 80%.

[0008] Furthermore, the thickness of the first region is 20 to 80% of the thickness of the basement film, and preferably the thickness of the first region is 65 to 80% of the thickness of the basement film.

[0009] Furthermore, the thickness of the second region is 20 to 80% of the thickness of the base film, and preferably the thickness of the second region is 20 to 35% of the thickness of the base film.

[0010] Furthermore, the thickness of the base film is 20 to 500 μm, preferably 40 to 300 μm, and more preferably 50 to 150 μm.

[0011] Furthermore, the base film is formed of one or more of polyethylene, polyolefin elastomer, polyvinyl butyral, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene ester copolymer, nylon, and ionomer.

[0012] Furthermore, the conductor is any one of copper wire, conductive paste, TCO coating, metal coating, and conductive polymer.

[0013] According to another aspect of the present invention, a photovoltaic module is provided, which includes a transparent front support plate, a transparent packaging film, a battery unit, a packaging film and a back support plate stacked in sequence, and the battery unit includes: at least two battery cells, each battery cell having fine grid lines on both surfaces; a plurality of conductive films of any one of the above, bonded to the two surfaces of each battery cell in a one-to-one correspondence, and the fine grid lines are electrically connected to the conductors of the corresponding conductive films, and the surface of the conductive film having the first area is bonded to the packaging film.

[0014] Furthermore, the extension direction of the above-mentioned conductor is the first direction, dividing the battery unit into multiple sub-units, each sub-unit includes multiple battery cells and corresponding conductive films arranged along the first direction, and the conductor of the conductive film in the same sub-unit connects adjacent battery cells in series.

[0015] By applying the technical solution of the present invention, by controlling the viscosity of different areas of the base film where conductors are provided and where conductors are not provided, the two areas have different fluidities, wherein the viscosity of the first area is greater and the fluidity is smaller, thereby maintaining the stability of the transparent base film, and the viscosity of the second area is smaller and the fluidity is larger, thereby achieving the goal of using the base film to firmly bond the conductors to the battery cells when the battery assembly is hot pressed, and effectively avoiding cold solder joints caused by excessive fluidity of the base film. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 shows a schematic diagram of a longitudinal cross-sectional structure of a conductive adhesive film according to an embodiment of the present invention; and

[0018] Figure 2shows a top view of a conductive adhesive film according to an embodiment of the present invention;

[0019] Figure 3 A schematic diagram of the disassembled structure of a photovoltaic module according to the present invention is shown.

[0020] The above drawings include the following reference numerals:

[0021] 10. Basement membrane; 11. First region; 12. Second region; 20. Conductor;

[0022] 1. Transparent front support plate; 2. Encapsulation film; 3. Battery cell; 4. Back support plate; 31. Battery cell; 32. Conductive film. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] As analyzed in the background of this application, the existing film materials and upper encapsulation films have high fluidity, which can cause copper wire solder joints to become cold, that is, the film penetrates between the copper wire and the fine grid lines, resulting in insulation. To solve this problem, this application provides a conductive film and photovoltaic module.

[0025] In a typical embodiment of the present application, a conductive film is provided, such as Figure 1 and 2 As shown, the above-mentioned conductive film includes a base film 10 and a conductor 20, the base film 10 includes at least a first area 11 and a second area 12, the first area 11 and the second area 12 are distributed along the thickness direction of the base film 10, the viscosity of the first area 11 is greater than the viscosity of the second area 12, and the viscosity of the first area 11 is greater than 10000 Pa·s, and the viscosity of the second area 12 is less than 100000 Pa·s; the conductor 20 is bonded to the second area 12 on the base film 10.

[0026] The present application controls the viscosity of different areas of the base film 10 where the conductor 20 is provided and where the conductor 20 is not provided, so that the two areas have different fluidities. The first area 11 has a higher viscosity and a lower fluidity, thereby maintaining the stability of the transparent base film 10. The second area 12 has a lower viscosity and a higher fluidity, thereby achieving the goal of using the base film 10 to firmly bond the conductor 20 to the battery cell when the battery assembly is hot pressed, and effectively avoiding cold solder joints caused by excessive flow of the base film 10.

[0027] There are many ways to adjust the viscosity of the base film 10, such as selecting materials with different compositions, selecting materials with different melt indexes, or performing different degrees of pre-crosslinking treatment on the same material. In order to make the dimensional stability of the base film 10 better and effectively block the flow of the packaging film during the lamination of the battery components, the crosslinking degree of the above-mentioned first region 11 is preferably greater than or equal to 30%, preferably greater than or equal to 50%, and further preferably between 50 and 80%.

[0028] To better coordinate the viscosities of the two regions, the crosslinking degree of the second region 12 is preferably less than 30%, preferably less than 15%, and more preferably between 0 and 10%. Furthermore, the difference between the crosslinking degrees of the first region 11 and the second region 12 is preferably between 55% and 80%.

[0029] The distribution of the first region 11 and the second region 12 of the transparent conductive film of the present application is primarily controlled by thickness, and the balance between thickness and viscosity is utilized to achieve an ideal balance between dimensional stability and viscosity performance. Preferably, the thickness of the first region 11 is 20-80% of the thickness of the base film 10. To more stably resolve the problem of cold solder joints, the thickness of the first region 11 is preferably 65-80% of the thickness of the base film 10. The majority of the conductive film is the first region 11, thereby ensuring the dimensional stability of the conductive film.

[0030] The first region 11 and the second region 12 may constitute the conductive film of this application, or a transition region may be provided between the first region 11 and the second region 12. To simplify the structure and more stably control product quality, the thickness of the second region 12 is preferably 20-80% of the thickness of the base film 10, and more preferably 20-35% of the thickness of the base film 10. The above thickness range of the second region 12 can achieve sufficient coverage of the thickness of the conventional conductor 20 and sufficient adhesion to the battery cell.

[0031] The aforementioned degree of crosslinking can be achieved by pre-crosslinking the base film 10 through radiation and controlling the degree of pre-crosslinking. For example, the degree of crosslinking or the depth of each region can be adjusted by adjusting the dose or duration of the radiation crosslinking. Furthermore, the additives in the first and second regions can be adjusted, and the films can be simultaneously extruded and cast using a dual-layer co-extrusion method, thereby achieving different degrees of pre-crosslinking under the same radiation crosslinking process conditions.

[0032] The base film 10 of the present application is primarily used as a support structure for the conductor 20. Its thickness can be smaller than that of conventional encapsulation films. Preferably, the base film 10 has a thickness of 20 to 500 μm, more preferably 40 to 300 μm, and even more preferably 50 to 150 μm. Tests have shown that this thickness range provides superior adhesion and ensures welding performance.

[0033] The base film 10 of the conductive film of the present application can be made of commonly used transparent film materials. Preferably, the base film 10 is formed of one or more of polyethylene, polyolefin elastomer, polyvinyl butyral, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene ester copolymer, nylon, and ionomer, so as to facilitate compatible bonding with conventional EVA encapsulating film or POE encapsulating film.

[0034] The conductor 20 of the present application can be made of copper wire commonly used in the prior art, which may be coated; or any one of conductive paste, solder tape, ITO coating, metal coating, and conductive polymer can be used as the conductor 20. For example, the conductor 20 can be formed by printing a conductive paste; forming an ITO coating by physically or chemically coating a transparent substrate with a conductive metal oxide; forming a metal coating by physically or chemically coating a transparent substrate with a metal; or forming a conductive polymer by printing or printing a conductive polymer paste. The thickness of the various conductors 20 described above can be flexibly controlled, so that the appropriate thickness can be set according to the mechanical properties of different materials, ensuring sufficient electrical connection while avoiding cell cracking caused by excessive lamination stress. Preferably, when a soldering strip is selected as the conductor 20, when the outer diameter of the soldering strip is 100-300, the thickness of the first region is preferably 50-350, and the thickness of the second region is preferably 30-150; when a conductive paste is selected as the conductor, when the thickness of the conductive paste is 50-200, the thickness of the first region is preferably 50-350, and the thickness of the second region is 20-150; when an ITO coating is selected as the conductor, when the thickness of the ITO coating is 30-200, the thickness of the first region is preferably 50-350, and the thickness of the second region is 10-150.

[0035] In another typical embodiment of the present application, a photovoltaic module is provided, such as Figure 3 As shown, the photovoltaic module includes a transparent front support plate 1, a packaging film 2, a battery unit 3, a packaging film 2 and a back support plate 4 stacked in sequence, wherein the battery unit 3 includes at least two battery cells 31 and a plurality of conductive films 32 of any of the above types, and each battery cell 31 has fine grid lines on both surfaces; the conductive films 32 are bonded to the two surfaces of each battery cell 31 in a one-to-one correspondence, and the fine grid lines are electrically connected to the conductor 20 of the corresponding conductive film 32, and the surface of the conductive film 32 having the first area 11 is bonded to the packaging film 2.

[0036] The conductive film 32 of the present application has a conductor 20, which is used as a main grid line and a welding strip to electrically connect with the fine grid of the battery cell, so that there is no need to weld the main grid line and the welding strip on the battery cell 31, effectively controlling the negative impact of high-temperature welding on the battery cell 31; and the conductive film 32 of the present application controls the viscosity of different regions, on the one hand, effectively improving the dimensional stability of the conductive film 32, avoiding its excessive flow or cold welding caused by excessive flow of the packaging film 2, and on the other hand, having sufficient fluidity in the area where the conductor 20 is set, ensuring that the base film 10 covers and fixes the conductor 20 and adheres to the battery cell 31.

[0037] The conductive films on both sides of the battery cell 31 can be the same, for example, both are transparent conductive films, or they can be different. For example, the conductive film on the side close to the transparent front support plate 1 is a transparent conductive film, and the conductive film on the side close to the back support plate 4 is selected to have similar optical transparency properties as the back support plate 4, for example, both are transparent or both are opaque. The opaque setting is achieved by doping with pigments, and the details will not be repeated here. The packaging films 2 on both sides of the battery cell are transparent films on the side close to the transparent front support plate 1, and the packaging film 2 on the side close to the back support plate 4 is selected to have similar optical transparency properties as the back support plate 4, for example, both are transparent or both are opaque. The opaque setting is achieved by doping with pigments, and the details will not be repeated here.

[0038] In some embodiments, the conductor 20 extends in a first direction, dividing the battery cell 3 into multiple sub-units. Each sub-unit includes multiple battery cells 31 and corresponding conductive films 32 arranged along the first direction. The conductor 20 of the conductive film 32 in the same sub-unit connects adjacent battery cells 31 in series to achieve current collection. The specific series connection method can be achieved by welding wires or by connecting two adjacent conductive films 32 together through the conductor 20 when the conductive film 32 is installed.

[0039] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0040] Example 1

[0041] 100 parts of EVA resin (VA content 28%), 0.5 parts of cross-linking agent TAIC, 0.6 parts of auxiliary cross-linking agent DCP, 0.2 parts of coupling agent vinyltrimethoxysilane, 0.5 parts of light stabilizer 770, and 0.2 parts of antioxidant 1010 are first thoroughly mixed to form a mixture 1, and the mixture 1 is extruded by an extrusion film forming method to form a base film with a thickness of 100 μm, and the base film is pre-cross-linked by radiation. The base film is irradiated by an electron beam irradiation equipment with an energy of 150 keV, and the radiation treatment is carried out from the surface of the first area with an irradiation dose of 15 kGy; then, an electron beam with an energy of 100 keV is used for irradiation, and the radiation is also incident from the surface of the first area with an irradiation dose of 20 kGy, finally obtaining a base film with two areas with different pre-cross-linking degrees. The thickness of the first region is 70 μm, and the thickness of the second region is 30 μm. A circular solder strip is set on the base film after radiation pre-crosslinking. The material of the circular solder strip is tinned copper, with a diameter of 200 μm and a length of 180 mm to obtain the conductive film of Example 1.

[0042] To determine the degree of pre-crosslinking in two different regions of a basement membrane, a test sample film with the same formulation as the basement membrane is prepared simultaneously. This test sample film consists of two layers, extruded separately and then heat-pressed together at 70°C. The first layer has the same thickness as the first region of the basement membrane, and the second layer has the same thickness as the second region of the basement membrane. Both layers undergo the same radiation pre-crosslinking treatment. When testing the degree of pre-crosslinking, the two layers can be separated and tested individually. The data from this test sample film can be used to characterize the different degrees of pre-crosslinking in the two regions of the basement membrane. The pre-crosslinking data is shown in the table below.

[0043] Example 2

[0044] 100 parts of POE main resin, 0.5 parts of cross-linking agent TAIC, 0.6 parts of auxiliary cross-linking agent DCP, 0.2 parts of coupling agent vinyltrimethoxysilane, 0.5 parts of light stabilizer 770, and 0.2 parts of antioxidant 1010 are fully mixed to form a mixture 2, and the mixture 2 is extruded by extrusion film forming to form a base film with a thickness of 100 μm, and the base film is pre-cross-linked by radiation. The radiation treatment is performed using an electron beam irradiation equipment with an energy of 150 keV, and the radiation is incident from the surface of the first area, with an irradiation dose of 35 kGy; then, an electron beam with an energy of 100 keV is used for irradiation, and the radiation is also incident from the surface of the first area, with an irradiation dose of 50 kGy, to finally obtain a base film with two areas with different pre-cross-linking degrees. The thickness of the first area is 70 μm, and the thickness of the second area is 30 μm. A circular solder strip is set on the base film after radiation pre-crosslinking. The material of the circular solder strip is tin-plated copper, with a diameter of 200 μm and a length of 180 mm to obtain the conductive film of Example 2.

[0045] Example 3

[0046] Mixture 1 was extruded using an extrusion film forming method to form a base film with a thickness of 100 μm. The base film was then pre-crosslinked by radiation. The base film was irradiated using an electron beam irradiation device with an energy of 150 keV, incident on the surface of the first region, with an irradiation dose of 10 kGy. The base film was then irradiated using an electron beam with an energy of 100 keV, also incident on the surface of the first region, with an irradiation dose of 60 kGy. This resulted in a base film having two regions with different pre-crosslinking degrees. The first region had a thickness of 70 μm, and the second region had a thickness of 30 μm. A circular solder strip made of tinned copper, with a diameter of 200 μm and a length of 180 mm, was placed on the pre-crosslinked base film to obtain the conductive film of Example 3.

[0047] Example 4

[0048] Mixture 1 was extruded to form a 100 μm thick base film. The base film was then pre-crosslinked by radiation using a 150 keV electron beam irradiation system, incident on the surface of the first region at a dose of 10 kGy. Subsequently, the base film was irradiated using a 50 keV electron beam, also incident on the surface of the first region at a dose of 60 kGy. This resulted in a base film having two regions with different pre-crosslinking levels. The first region had a thickness of 20 μm, and the second region had a thickness of 80 μm. A conductive paste composed of an acrylic resin mixed with 5% by weight silver powder was applied to the pre-crosslinked base film. The paste had a thickness of 50 μm, a width of 0.5 mm, and a length of 180 mm, resulting in the conductive film of Example 4.

[0049] Example 5

[0050] Mixture 1 was extruded to form a 100 μm thick base film. The base film was then pre-crosslinked by radiation using a 150 keV electron beam irradiation system, incident on the first region's surface at a dose of 10 kGy. Subsequently, the base film was irradiated using a 120 keV electron beam, also incident on the first region's surface at a dose of 60 kGy. This resulted in a base film with two regions of varying pre-crosslinking. The first region had a thickness of 80 μm, and the second had a thickness of 20 μm. A conductive paste composed of an acrylic resin mixed with 5% by weight silver powder was applied to the pre-crosslinked base film. The paste had a thickness of 50 μm, a width of 0.5 mm, and a length of 180 mm, yielding the conductive film of Example 5.

[0051] Example 6

[0052] Mixture 2 was extruded to form a 100 μm thick base film. The base film was then pre-crosslinked by radiation using a 150 keV electron beam irradiation system, incident on the surface of the first region at a dose of 15 kGy. Subsequently, the base film was irradiated using a 100 keV electron beam, also incident on the surface of the first region at a dose of 35 kGy. This resulted in a base film with two regions of varying pre-crosslinking. The first region had a thickness of 70 μm, and the second had a thickness of 30 μm. A conductive paste composed of an acrylic resin mixed with 5% by weight silver powder was applied to the pre-crosslinked base film. The paste had a thickness of 50 μm, a width of 0.5 mm, and a length of 180 mm, resulting in the conductive film of Example 6.

[0053] Example 7

[0054] Mixture 2 was extruded to form a 100 μm thick base film. The base film was then pre-crosslinked by radiation using a 150 keV electron beam irradiation system, incident on the first region's surface at a dose of 15 kGy. Subsequently, the base film was irradiated using a 20 keV electron beam, also incident on the first region's surface at a dose of 35 kGy. This resulted in a base film with two regions of varying pre-crosslinking. The first region had a thickness of 10 μm, and the second had a thickness of 90 μm. A conductive paste composed of an acrylic resin mixed with 5% by weight silver powder was applied to the pre-crosslinked base film. The paste had a thickness of 50 μm, a width of 0.5 mm, and a length of 180 mm, yielding the conductive film of Example 7.

[0055] Example 8

[0056] Mixture 2 was extruded using an extrusion film forming method to form a base film with a thickness of 20 μm. The base film was then pre-crosslinked by radiation. The base film was irradiated using an electron beam irradiation device with an energy of 50 keV, incident from the surface of the first region, with an irradiation dose of 15 kGy. Subsequently, the base film was irradiated using an electron beam with an energy of 25 keV, also incident from the surface of the first region, with an irradiation dose of 35 kGy. This resulted in a base film having two regions with different pre-crosslinking degrees. The first region had a thickness of 14 μm, and the second region had a thickness of 6 μm. An indium tin oxide (ITO) with a width of 0.5 mm, a thickness of 80 μm, and a length of 180 mm was deposited on the pre-crosslinked base film, thereby obtaining the conductive film of Example 8.

[0057] Example 9

[0058] Mixture 2 was extruded using an extrusion film forming method to form a base film with a thickness of 500 μm. The base film was then pre-crosslinked by radiation. The base film was irradiated using an electron beam irradiation device with an energy of 500 keV, incident from the surface of the first region, with an irradiation dose of 15 kGy. Subsequently, the base film was irradiated using an electron beam with an energy of 400 keV, also incident from the surface of the first region, with an irradiation dose of 35 kGy. This resulted in a base film having two regions with different pre-crosslinking degrees. The first region had a thickness of 350 μm, and the second region had a thickness of 150 μm. An indium tin oxide (ITO) with a width of 0.5 mm, a thickness of 80 μm, and a length of 180 mm was deposited on the pre-crosslinked base film, thereby obtaining the conductive film of Example 9.

[0059] Example 10

[0060] Mixture 2 was extruded using an extrusion film forming method to form a base film with a thickness of 60 μm. The base film was then pre-crosslinked by radiation. The base film was irradiated using an electron beam irradiation device with an energy of 100 keV, incident from the surface of the first region, with an irradiation dose of 15 kGy. Subsequently, the base film was irradiated using an electron beam with an energy of 80 keV, also incident from the surface of the first region, with an irradiation dose of 35 kGy. This resulted in a base film having two regions with different pre-crosslinking degrees. The first region had a thickness of 45 μm, and the second region had a thickness of 15 μm. An indium tin oxide (ITO) with a width of 0.5 mm, a thickness of 80 μm, and a length of 180 mm was deposited on the pre-crosslinked base film, thereby obtaining the conductive film of Example 10.

[0061] Example 11

[0062] Mixture 2 was extruded using an extrusion film forming method to form a base film with a thickness of 60 μm. The base film was then pre-crosslinked by radiation using an electron beam irradiation device with an energy of 25 keV, incident from the surface of the first region, and an irradiation dose of 15 kGy. Subsequently, the base film was irradiated using an electron beam with an energy of 15 keV, also incident from the surface of the first region, and an irradiation dose of 35 kGy, ultimately resulting in a base film having two regions with different pre-crosslinking degrees. The first region had a thickness of 45 μm, and the second region had a thickness of 15 μm. An indium tin oxide (ITO) with a width of 0.5 mm, a thickness of 30 μm, and a length of 180 mm was disposed on the pre-crosslinked base film, thereby obtaining the conductive film of Example 11.

[0063] Comparative Example 1

[0064] The mixture 2 is extruded by an extrusion film forming method to form a base film with a thickness of 100 μm, and the base film is pre-cross-linked by radiation. The radiation treatment is performed using an electron beam irradiation device with an energy of 150 keV, and the radiation is incident from the surface of the first area. The irradiation dose is 85 kGy. A circular welding strip is arranged on the base film after radiation pre-cross-linking. The material of the circular welding strip is tin-plated copper, the diameter is 200 μm, and the length is 180 mm, to obtain the conductive film of comparative example 1.

[0065] Comparative Example 2

[0066] The mixture 1 is formed into a base film with a thickness of 100 μm by extrusion film forming, and the base film is pre-crosslinked by radiation. The radiation treatment is carried out by electron beam irradiation equipment with an energy of 150 keV, and the radiation is incident from the surface of the first area. The irradiation dose is 15 kGy. A circular welding strip is set on the base film after radiation pre-crosslinking. The material of the circular welding strip is tin-plated copper, the diameter is 200 μm, and the length is 180 mm, so as to obtain the conductive film of comparative example 2.

[0067] The viscosity, pre-crosslinking degree and thickness of the first and second regions of each conductive film are tested. The specific testing method is as follows:

[0068] As described in Example 1, in order to determine the pre-crosslinking degree of two different areas of the base membrane, it is necessary to simultaneously prepare a test sample membrane with the same formula as the base membrane. The test sample membrane includes two layers, which are extruded into films separately and hot-pressed together at 70°C. The thickness of the first layer is the same as that of the first area of ​​the base membrane, and the thickness of the second layer is the same as that of the second area of ​​the base membrane, and they undergo the same radiation pre-crosslinking treatment. When testing the pre-crosslinking degree, the two layers can be separated and tested separately, and the data of the test sample membrane can be used to characterize the different pre-crosslinking degrees of the two areas of the base membrane.

[0069] The pre-crosslinking degree test method is as follows: According to the EVA crosslinking degree test method in GB / T 29848-2013, the pre-crosslinking degree of the basement membrane is tested by the xylene extraction method.

[0070] The viscosity is determined according to ASTM D5289 and / or ASTM D6204 and is measured at a frequency of 1 Hz and a strain of 10%. The test results are shown in Table 1.

[0071] Table 1

[0072]

[0073] Examples 1, 2, and 3 can ensure low fluidity, and the soldering ribbon and the battery cell are well welded. Examples 4, 5, and 6 use conductive paste, and good ohmic contact can also be achieved between the fine grid of the battery cell and the conductive paste. However, the thickness of the first region of Example 8 is relatively small, and low fluidity cannot be guaranteed, resulting in the flow of adhesive film between the fine grid of the battery cell and the conductive paste, resulting in poor contact and dark stripes on the EL image of the component. Examples 9 to 12 use ITO as the conductor, and the transparent base layer can be set thinner or thicker, which can ensure good adhesion between the base film and the battery cell, and good ohmic contact between the conductor and the fine grid. However, the thickness of the transparent base layer of Example 11 is too thin, and on the one hand, there is a certain degree of poor adhesion, and at the same time, the strength is insufficient. During lamination, the upper layer of adhesive film will flow between the ITO and the fine grid, resulting in poor contact.

[0074] Comparative Examples 1 and 2, the transparent base films had the same viscosity and pre-crosslinking degree. Comparative Example 1 had higher viscosity and lower fluidity, resulting in poor adhesion to the cell. It also exhibited poor wrapping of the circular solder ribbon, with gaps on either side. Comparative Example 2 had lower viscosity and higher fluidity, leading to poor contact between the circular solder ribbon and the cell grids. After module lamination, the EL exhibited numerous dark streaks, indicating a high number of cold solder joints between the ribbon and the cell.

[0075] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A conductive film, characterized in that The conductive film includes: A base film (10), the base film (10) comprising at least a first region (11) and a second region (12), the first region (11) and the second region (12) being distributed along a thickness direction of the base film (10), the viscosity of the first region (11) being greater than the viscosity of the second region (12), and the viscosity of the first region (11) being greater than 10,000 Pa·s, and the viscosity of the second region (12) being less than 100,000 Pa·s; a conductor (20), the conductor (20) being bonded to the second region (12) on the base film (10); The crosslinking degree of the first region (11) is greater than or equal to 30%; The difference between the cross-linking degree of the first region (11) and the cross-linking degree of the second region (12) is 55% to 80%; The thickness of the first region (11) is 65-80% of the thickness of the basement membrane (10); The thickness of the second region (12) is 20-35% of the thickness of the basement membrane (10); The thickness of the basement membrane (10) is 40-500 μm.

2. The conductive film according to claim 1, wherein The cross-linking degree of the first region (11) is greater than or equal to 50%.

3. The conductive film according to claim 2, wherein The cross-linking degree of the first region (11) is between 50% and 80%.

4. The conductive film according to any one of claims 1 to 3, characterized in that The cross-linking degree of the second region (12) is less than 30%.

5. The conductive film according to claim 4, wherein The cross-linking degree of the second region (12) is less than 15%. The conductive film according to claim 5 , wherein: The cross-linking degree of the second region (12) is between 0 and 10%.

7. The conductive film according to claim 1, wherein The thickness of the basement membrane (10) is 40-300 μm.

8. The conductive film according to claim 7, wherein The thickness of the basement membrane (10) is 50-150 μm.

9. The conductive film according to claim 1, wherein The base film (10) is formed of one or more of polyethylene, polyolefin elastomer, polyvinyl butyral, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene ester copolymer, nylon, and ionomer.

10. The conductive film according to claim 1, wherein The conductor (20) is any one of copper wire, conductive paste, TCO coating, metal coating, and conductive polymer.

11. A photovoltaic module comprising a transparent front support plate, a transparent packaging film, a battery cell, a packaging film and a back support plate stacked in sequence, characterized in that: The battery unit comprises: At least two battery cells, each of which has fine grid lines on both surfaces; The conductive films according to any one of claims 1 to 10 are bonded to the two surfaces of each of the battery cells in a one-to-one correspondence, and the fine grid lines are electrically connected to the conductors of the corresponding conductive films, and the surface of the conductive film having the first area is bonded to the packaging film.

12. The photovoltaic module according to claim 11, characterized in that: The extension direction of the conductor is the first direction, dividing the battery unit into multiple sub-units, each of which includes multiple battery cells and corresponding conductive films arranged along the first direction, and the conductor of the conductive film in the same sub-unit connects adjacent battery cells in series.

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