A weather-resistant film for a solar cell back sheet and a method of manufacturing the same

Abstract

This application discloses a weather-resistant film for solar cell backsheets, comprising a PVDF film. The PVDF film has multiple equally spaced, parallel, isosceles triangular serrated stripes on both sides. A white protective layer is formed on the surface of the serrated stripes facing the solar cell by vacuum sputtering, while a black protective layer is formed on the surface of the serrated stripes away from the solar cell by vacuum sputtering. A thermally conductive metal film is adhered to the side of the PVDF film with the white protective layer. The weather-resistant film for solar cell backsheets of this application, with its serrated stripes, significantly improves adhesion and prevents delamination, exhibits excellent thermal conductivity, increases the contact angle of the outer surface, enhances self-cleaning ability, and possesses excellent dust resistance.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, particularly to the field of solar cell backsheet technology, and especially to a weather-resistant film for solar cell backsheets and its preparation method. Background Technology

[0002] Solar cell modules typically consist of a front panel, solar cells, encapsulation materials, and a backsheet. The solar cells are encapsulated between the front panel and the backsheet using encapsulation materials. Currently, widely used solar cells include crystalline silicon solar cells and thin-film solar cells. Flexible solar cells, a type of thin-film solar cell, are widely used in building-integrated photovoltaics (BIPV). The backsheet, as the encapsulation structure of the solar cell, plays a crucial role in extending the lifespan of the solar cell module. CN 101359695 A discloses a solar cell backsheet, including a substrate and a weather-resistant layer, the weather-resistant layer mainly composed of fluorinated resin. The technology of using fluorinated resin to form a weather-resistant film is described in the background section of CN 101582458 A, which mentions that a common backsheet structure is the TPT structure, where T usually refers to polyvinyl fluoride (PVF) film and P usually refers to polyethylene terephthalate (PET) film, i.e., a PVF / PET / PVF structure. The main function of PVF film is weather resistance, but it is expensive and has low surface energy, making it prone to delamination.

[0003] CN 103563096 B discloses a backsheet for a solar cell module, comprising a polyester film layer and a fluorine coating applied to at least one surface of the polyester film layer. The backsheet is formed on the upper surface of the polyester film layer and includes a polyethylene film layer attached to the ethylene vinyl acetate (EVA) plate of the solar cell module. As repeatedly mentioned in this prior art, the adhesion of the existing fluorinated films is poor, resulting in insufficient adhesion between the weather-resistant fluorinated film covering the backsheet and the substrate, or even the EVA plate of the solar cell module. Therefore, even if the fluorinated film has excellent weather resistance, its weak adhesion leads to poor barrier properties and inadequate moisture protection. This prior art uses an outer fluorinated coating to reduce costs and improve adhesion; however, the coating contains relatively few effective weather-resistant components, and because it is located on the outermost side of the backsheet, it is difficult to resist wind and sand erosion for extended periods, and the coating is prone to peeling off. In addition, in order to reduce costs and improve adhesion, the existing technology also emphasizes that the coating should not be too thick. Therefore, the weather resistance at the same thickness will obviously be weaker than that of fluorinated films. If better protection is to be achieved, the coating thickness can only be increased. However, a thicker coating will reduce the ability to withstand changes in thermal stress on the backing plate. Under alternating hot and cold conditions, the coating is more likely to peel off.

[0004] In addition, the backsheet of the aforementioned prior art requires not only a thicker fluorine-containing coating, but also a white polyethylene film layer on the inside. Although the adhesion is enhanced, the structure is further thickened, making it difficult to apply to the field of flexible solar cells, which have greater flexibility requirements. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a weather-resistant film for solar cell backsheets and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0006] To address the aforementioned technical problems, this application proposes a weather-resistant film for a solar cell backsheet, comprising a PVDF film. The PVDF film has multiple equally spaced, parallel serrated stripes with isosceles triangular cross-sections formed on both sides. A white protective layer is formed on the surface of the serrated stripes facing the solar cell by vacuum sputtering, while a black protective layer is formed on the surface of the serrated stripes away from the solar cell by vacuum sputtering. A thermally conductive metal film is adhered to the side of the PVDF film with the white protective layer.

[0007] Preferably, the base of the isosceles triangle of the sawtooth stripe has a length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes of 0-5 μm.

[0008] Preferably, the maximum thickness of the PVDF film is 20-30 μm.

[0009] Preferably, the white protective layer is made of titanium dioxide; the black protective layer is made of silicon carbide.

[0010] Preferably, the thicknesses of the white protective layer and the black protective layer are 1-3 μm, respectively.

[0011] Preferably, the serrated stripes on both sides of the PVDF film are arranged perpendicularly to each other; the angle between the length direction of the serrated stripes and the four rectangular sides of the PVDF film is 45 degrees.

[0012] This application also proposes a method for preparing a weather-resistant film for a solar cell backsheet, comprising the following steps: providing a PVDF film; forming multiple equally spaced parallel serrated stripes with isosceles triangular cross-sections on both sides of the PVDF film by hot pressing; forming a white protective layer on one side of the serrated stripes by vacuum sputtering, and forming a black protective layer on the other side of the serrated stripes by vacuum sputtering; and bonding a thermally conductive metal film to the side with the white protective layer, thereby forming the weather-resistant film.

[0013] Preferably, the specific steps for forming the serrated stripes are as follows: using two rollers with patterns matching the shape of the serrated stripes placed vertically opposite each other, passing the heated PVDF film between the two rollers, and then air-cooling or water-cooling the PVDF film to obtain the cured serrated stripes on the PVDF film.

[0014] Preferably, the length directions of the patterns on the surfaces of the two rollers, which are positioned vertically opposite each other and match the shape of the sawtooth stripes, are perpendicular to each other.

[0015] Preferably, the pattern orientation on the surfaces of the two rollers forms a 45-degree angle with the direction in which the PVDF film is advanced.

[0016] The weather-resistant film of this application, through its serrated stripes, increases the contact area with the adhesive, thereby enhancing the overall adhesion of the weather-resistant film and preventing delamination. The weather-resistant film for solar cell backsheets of this application, with its serrated stripes, significantly improves adhesion, prevents delamination, exhibits excellent thermal conductivity, increases the contact angle of the outer surface, enhances self-cleaning ability, and possesses excellent dust resistance. Attached Figure Description

[0017] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0018] Figure 1 The diagram shown is a cross-sectional schematic of a weather-resistant film for a solar cell backsheet according to a specific embodiment of this application.

[0019] Figure 2 The diagram shown is a structural schematic of a PVDF film for a weather-resistant film used as a backsheet of a solar cell according to another specific embodiment of this application. Detailed Implementation

[0020] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0021] As described in the background section, existing fluorinated films used as weather-resistant films are expensive and suffer from low surface energy, insufficient adhesion, and easy delamination. Therefore, this application proposes a weather-resistant film for solar cell backsheets, such as... Figure 1 As shown, the weather-resistant film includes a PVDF film 1. Multiple equally spaced parallel sawtooth stripes 11 with cross-sections of isosceles triangles are formed on both sides of the PVDF film 1. A white protective layer 12 is formed on the surface of the sawtooth stripes 11 facing the solar cell by vacuum sputtering, and a black protective layer 13 is formed on the surface of the sawtooth stripes 11 away from the solar cell by vacuum sputtering.

[0022] The PVDF membrane contains at least 90% PVDF by mass. To improve its performance, ultraviolet absorbers and wear-resistant fillers can be added. Preferably, the serrated stripes 11 formed on both sides of the PVDF membrane 1 are identical. The dimensions of the weather-resistant membrane shown in the figure have been enlarged for easier observation and understanding; the actual serrated stripes are relatively small, with only barely perceptible texture on the surface. In one specific embodiment, the maximum thickness of the PVDF membrane 1 is 20-30 μm.

[0023] Existing PVDF weather-resistant films suffer from low surface energy and insufficient adhesion, leading to a tendency to delaminate. To overcome this problem, this application forms serrated stripes on the surface of the PVDF film. These serrated stripes increase the contact area with the adhesive 3 (which will be described in more detail later). For example, when the apex angle of the isosceles trapezoid of the serrated stripes is 60 degrees, the serrated stripes can double the surface area, thereby increasing the overall adhesion of the PVDF film and preventing the weather-resistant film from easily delaminating.

[0024] It should be noted that improving the overall adhesion of the weather-resistant film actually only requires setting serrated stripes on the inner side of the PVDF film. However, since the stripes are very small and difficult to observe, the inventors chose to form the same serrated stripes on both sides of the PVDF film simultaneously for ease of assembly, so that film coating can be performed on both sides, thus increasing the applicability of the weather-resistant film. The inventors believed that the serrated stripes originally located on the outer side did not seem to have any intended function. However, during actual laying experiments, it was found that if the scale of the serrated stripes formed on the PVDF film surface is smaller than a certain range, it can play a self-cleaning role, reducing the adhesion of dust to the weather-resistant film surface, and rainwater can easily wash away the attached dust. For example, in a specific embodiment, the isosceles triangle of the serrated stripe 11 preferably has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent serrated stripes 11 of 0-5 μm. Forming identical serrated stripes on both sides of the PVDF film not only reduces manufacturing costs, but also allows for better adhesion on the inner side and excellent dust resistance on the outer side when the serrated stripes are selected within this size range. Furthermore, the serrated stripes on the outer side increase the surface area, thereby increasing the heat dissipation area and further improving the overall heat dissipation performance of the weather-resistant film.

[0025] Furthermore, to improve the adhesion of the PVDF film and prevent delamination, this application selects an angle of 45 degrees between the length direction of the serrated stripes and the four rectangular sides of the weather-resistant film. Figure 2As shown. Generally, solar panels are designed in a rectangular shape with four perpendicular sides. If the length direction of the sawtooth stripes is perpendicular to one pair of rectangular sides of the weather-resistant film, then the other pair of rectangular sides will be parallel to the length direction of the sawtooth stripes. Since the stiffness of the sawtooth stripes differs in the length and width directions, their expansion rates also differ, which can cause one pair of rectangular sides of the weather-resistant film to warp and delaminate. This application directs the direction of the sawtooth stripes at a 45-degree angle to the four rectangular sides. This makes the proportion of stiffness differences in different directions caused by the sawtooth stripes spreading to the four rectangular sides more even, thus avoiding the delamination problem of the weather-resistant film caused by the sawtooth stripe arrangement and further improving the structural performance of the weather-resistant film.

[0026] Furthermore, if the same serrated stripes are formed on both sides, and the serrated stripes on both sides are oriented in the same direction (i.e., the length directions of the serrated stripes on both sides are parallel), the different thermal expansion rates on both sides will be concentrated in the same direction, which may lead to stress concentration and delamination. To avoid the delamination problem caused by the serrated stripes on both sides being oriented in the same direction, this application further proposes a special design in which the serrated stripes 11 on both sides of the PVDF film 1 are arranged perpendicular to each other, thereby avoiding the problem of stress bias in one direction causing delamination.

[0027] Furthermore, to avoid the problem that the excessively thick backsheets of existing technologies are difficult to apply to flexible solar cells with higher flexibility requirements, this application forms a white protective layer 12 and a black protective layer 13 on the PVDF film with a serrated stripe structure via vacuum sputtering. Since the bonding strength of the sputtered layer formed by vacuum sputtering is much greater than that of adhesive bonding, a very thin protective layer can achieve the protective function. For example, the white protective layer 12 can be made of titanium dioxide; the black protective layer 13 can be made of silicon carbide. Preferably, the thicknesses of the white protective layer 12 and the black protective layer 13 are 1-3 μm, respectively.

[0028] The white protective layer 12 provides excellent light reflection, reflecting as much light transmitted from the front of the solar cell back to the solar cell as possible, thus improving light conversion efficiency. Furthermore, since the white protective layer 12 is integrally sputtered onto the serrated surface, an additional white polyethylene film layer is unnecessary, simplifying the weather-resistant film structure and reducing film thickness.

[0029] The black protective layer 13 is also a very thin sputtered layer, which can be used to improve wear resistance and enhance the weather-resistant film's ability to resist wind and sand erosion. In addition, the black protective layer 13 has better thermal radiation capabilities, facilitating the rapid dissipation of heat absorbed by the backsheet to reduce the temperature of the solar cell module. Simultaneously, the sputtering method improves adhesion while reducing additional film layers, thus lowering thickness and cost.

[0030] Furthermore, to further improve the heat dissipation capacity of the backplate, this application adheres a thermally conductive metal film 2 to the side of the PVDF film 1 with the white protective layer 12. For example, the thermally conductive metal film 2 can be bonded to the PVDF film 1 as a single unit using a suitable adhesive 3. Through the thermally conductive metal film 2, the heat absorbed by the backplate can be conducted to the PVDF film 1, and the heat can be efficiently radiated away through the increased surface area of ​​the outer serrated stripes. In a specific embodiment, the thermally conductive metal film 2 can be made of aluminum foil with a thickness of 8-16 μm, and the adhesive 3 can be commercially available EVA adhesive or acrylic adhesive with a maximum thickness of 15-20 μm.

[0031] The preparation method of the weather-resistant film for solar cell backsheets of this application is further described in detail below with reference to the accompanying drawings. Specifically, the preparation method of this application includes the following steps:

[0032] First, a PVDF membrane is provided. This PVDF membrane can be a commercially available PVDF membrane with a thickness of 20-30μm, or it can be formed by melt co-extrusion and biaxial stretching of PVDF raw material particles with a mass content of ≥90%, with the addition of UV absorbers, wear-resistant fillers, etc.

[0033] Then, multiple equally spaced parallel serrated stripes 11 with isosceles triangular cross-sections are formed on both sides of the PVDF film by hot pressing. For example, two rollers with patterns matching the shape of the serrated stripes can be used, one above the other, to pass the heated PVDF film between the two rollers, and then the PVDF film is air-cooled or water-cooled to obtain the cured serrated stripes 11 on the PVDF film. The length directions of the patterns matching the shape of the serrated stripes on the surfaces of the two rollers are perpendicular to each other, thus forming mutually perpendicular serrated stripes 11 on both sides of the PVDF film. For example, if the pattern direction on the surfaces of the two rollers forms a 45-degree angle with the direction of the PVDF film's movement, serrated stripes 11 at a 45-degree angle to the four rectangular sides of the weather-resistant film can be formed.

[0034] Subsequently, a white protective layer 12 is formed on one side of the serrated stripe 11 by vacuum sputtering, and a black protective layer 13 is formed on the other side of the serrated stripe 11 by vacuum sputtering. For example, a layer of titanium dioxide with a thickness of 1-3 μm can be formed on one side of the serrated stripe 11 by vacuum sputtering to form the white protective layer 12; and a layer of silicon carbide with a thickness of 1-3 μm can be formed on the other side of the serrated stripe 11 by vacuum sputtering to form the black protective layer 13. Since the thickness of the formed protective layer is relatively very thin, Figure 2 The protective layer is not shown in the image, and at the same time, Figure 1The protective layers 12 and 13 have also been enlarged for easier understanding.

[0035] Finally, a thermally conductive metal film 2 is bonded to the side with the white protective layer 12 to form the weather-resistant film. For example, an acrylic adhesive with a thickness of 15-20 μm can be coated on the side with the white protective layer 12, the surface can be smoothed, and then an 8-16 μm metal aluminum foil can be bonded.

[0036] Examples 1-6

[0037] The weather-resistant film for solar cell backsheets was prepared according to the parameters in the table below.

[0038]

[0039] In Examples 1-3, the angle between the serrated stripes and the rectangular sides of the weather-resistant film is 45 degrees. In Examples 4-6, the angle between the serrated stripes and the rectangular sides of the weather-resistant film is 0 / 90 degrees, that is, the angle between the serrated stripes and one pair of rectangular sides is 0 degrees, and the angle with the other pair of rectangular sides is 90 degrees. The white protective layer is composed of titanium dioxide; the black protective layer is composed of silicon carbide.

[0040] Comparative Examples 1-6

[0041] Comparative Examples 1-6 used PVDF films without serrated stripes, and bonded thermally conductive metal films as weather-resistant films, with the following parameters. In both Examples 1-6 and Comparative Examples 1-6, EVA adhesive was used, and aluminum foil was used as the thermally conductive metal film.

[0042]

[0043] The weather-resistant films of Examples 1-6 and Comparative Examples 1-6 were respectively bonded to the surface of a 188μm PET support base film. The parameter performance of each example of the weather-resistant film was measured and compared as follows.

[0044]

[0045] As can be seen from the performance parameter comparison of the above embodiments, the weather-resistant film for solar cell backsheets of this application, even with serrated stripes, can significantly improve adhesion performance and avoid delamination, has excellent thermal conductivity, increases the contact angle of the outer surface, improves self-cleaning ability, and has excellent dust resistance.

[0046] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0047] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A weatherable film for a backsheet of a solar cell comprising a layer of PVDF film (1), characterized in that, The PVDF film (1) has multiple equally spaced parallel sawtooth stripes (11) with an isosceles triangle cross section, and the sawtooth stripes (11) on both sides of the PVDF film (1) are arranged perpendicularly to each other; the length direction of the sawtooth stripes (11) forms an angle of 45 degrees with the four rectangular sides of the PVDF film (1); a white protective layer (12) is formed on the surface of the sawtooth stripes (11) facing the solar cell by vacuum sputtering, and a black protective layer (13) is formed on the surface of the sawtooth stripes (11) away from the solar cell by vacuum sputtering; a thermally conductive metal film (2) is bonded to the side of the PVDF film (1) with the white protective layer (12).

2. The weatherable film of claim 1, wherein, The isosceles triangle of the sawtooth stripe (11) has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes (11) of 0-5 μm.

3. The weatherable film of claim 1, wherein, The maximum thickness of the PVDF membrane (1) is 20-30 μm.

4. The weatherable film of claim 1, wherein, The white protective layer (12) is made of titanium dioxide; the black protective layer (13) is made of silicon carbide.

5. The weatherable film of claim 1, wherein, The thicknesses of the white protective layer (12) and the black protective layer (13) are 1-3 μm, respectively.

6. A method for preparing a weather-resistant film for a solar cell backsheet, comprising the following steps: Provide a PVDF membrane; Multiple equally spaced parallel sawtooth stripes (11) with isosceles triangle cross sections are formed on both sides of the PVDF film by hot pressing; the sawtooth stripes (11) on both sides of the PVDF film (1) are arranged perpendicular to each other; the angle between the length direction of the sawtooth stripes (11) and the four rectangular sides of the PVDF film (1) is 45 degrees. A white protective layer (12) is formed on the serrated stripe (11) on one side by vacuum sputtering, and a black protective layer (13) is formed on the serrated stripe (11) on the other side by vacuum sputtering. A thermally conductive metal film (2) is adhered to one side of the white protective layer (12) to form the weather-resistant film.

7. The production method according to claim 6, wherein The specific steps for forming the sawtooth stripes (11) are as follows: two rollers with patterns matching the shape of the sawtooth stripes (11) are placed opposite each other, and the heated PVDF film is passed between the two rollers. Then the PVDF film is cooled by air or water to obtain the cured sawtooth stripes (11) on the PVDF film.

8. The production method according to claim 7, wherein The length directions of the patterns on the surfaces of the two rollers, which are positioned vertically opposite each other and match the shape of the serrated stripes, are set perpendicular to each other.

9. The production method according to claim 8, wherein The pattern orientation on the surfaces of the two rollers forms a 45-degree angle with the direction in which the PVDF film is advanced.

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