CN115832092A

CN115832092A - Flexible solar cell back plate and preparation method thereof

Info

Publication number: CN115832092A
Application number: CN202211491236.0A
Authority: CN
Inventors: 吴培服; 吴迪; 孙化斌; 吴和坡; 高升
Original assignee: Jiangsu Shuangxing Color Plastic New Materials Co Ltd
Current assignee: Jiangsu Shuangxing Color Plastic New Materials Co Ltd
Priority date: 2022-11-25
Filing date: 2022-11-25
Publication date: 2023-03-21

Abstract

The application discloses a flexible solar cell back plate and a preparation method thereof, and the flexible solar cell back plate comprises a base film, an adhesive layer and a weather-resistant film, wherein the weather-resistant film comprises a PVDF film, and a plurality of equally-spaced saw-tooth stripes which are arranged in parallel and have isosceles triangle-shaped sections are formed on the surfaces of two sides of the PVDF film; the base film comprises a base material layer, two side surfaces of the base material layer are respectively provided with an online coating layer, and the outer side of the online coating layer is sputtered to form a barrier layer; the substrate layer comprises a transmission film and a heat conduction film, and a plurality of prism structures which are arranged in parallel at equal intervals are formed on the transmission film. The utility model provides a backplate not only can assemble light through the substrate layer that sets up the reflection prism structure that has physical structure, has still increased heat radiating area and heat conduction efficiency. In addition, the weather-resistant film can increase the contact area with the adhesive through the arranged sawtooth stripes, so that the overall adhesive force of the weather-resistant film is increased, the problem that the weather-resistant film is easy to delaminate is solved, and the weather-resistant film also has excellent heat-conducting property and self-cleaning capability.

Description

Flexible solar cell back plate and preparation method thereof

Technical Field

The application relates to a flexible solar cell back plate and a preparation method thereof.

Background

The solar cell module is generally composed of a front plate, a solar cell, an encapsulating material and a back plate, wherein the solar cell is encapsulated between the front plate and the back plate through the encapsulating material. Solar cells widely used at present include crystalline silicon solar cells and thin film solar cells. The flexible solar cell is one of thin-film solar cells and is widely applied to the field of building integration. The back plate is used as a packaging structure of the solar cell and plays an important role in prolonging the service life of the solar cell module. CN 101359695A discloses a solar cell back sheet, which comprises a substrate and a weather-resistant layer, wherein the weather-resistant layer mainly comprises fluorine-containing resin. The technology of forming weather resistant film with fluorine-containing resin is described in the background section of CN 101582458A, wherein the common structure of the back sheet is referred to as TPT structure, wherein T generally refers to polyvinyl fluoride (PVF) film, and P generally refers to polyethylene terephthalate (PET) film, i.e. PVF/PET/PVF structure. The main function of PVF films is weather resistance, but they are relatively expensive and have low surface energy, low surface energy and are easily delaminated.

CN 114536906A discloses a black photovoltaic back plate, which comprises a black layer, an inner coating, a supporting layer and an outer layer sequentially arranged from inside to outside. The position of the black layer corresponds to the cell gap of the photovoltaic module; the inner coating is white and is used for reflecting light; the support layer contains a thermally conductive filler. The black layer in the prior art mainly plays a role in beauty, reflects little light and is difficult to be folded to the cell for utilization. The white inner coating on the inner side of the battery piece is a surface mainly reflecting light, and is mainly made of materials with poor heat conductivity, such as white titanium dioxide, glass beads and resin. However, the particles such as titanium dioxide and glass beads have a diffuse reflection effect, a large amount of light is actually absorbed by the inner coating, the thermal conductivity of the inner coating is relatively poor, and the efficiency of conducting the absorbed heat to the supporting layer is low. This prior art's backplate, the ability that relies on internal coating reflection light is limited, and the efficiency of heat conduction for the supporting layer is lower, and the leakproofness of coating is also relatively poor.

CN 114156357A discloses a flexible solar cell back sheet, comprising: the first grid layer comprises weather-resistant resin, nano-scale filler A, isocyanate and a solvent; the second grid layer comprises weather-resistant resin, nano-scale filler B, isocyanate and a solvent; a bonding layer; a substrate layer; a weatherable layer; wherein the grain diameter of the nano-scale filler A is larger than that of the nano-scale filler B. The reflection method of the prior art also utilizes nano-scale particles, which actually play a role of diffuse reflection, so that a large amount of light cannot be directly reflected back to the cell, but is absorbed by the resin in the grid, and the absorbed heat is difficult to be conducted to the substrate layer.

Disclosure of Invention

The technical problem to be solved by the present application is to provide a flexible solar cell back sheet and a method for manufacturing the same, so as to reduce or avoid the aforementioned problems.

In order to solve the technical problem, the application provides a flexible solar cell backboard, which comprises a base film close to the back surface of a solar cell and a weather-resistant film positioned on the outer side of the base film, wherein the weather-resistant film and the base film are bonded into a whole through a bonding layer; the weather-resistant film comprises a PVDF film, wherein a plurality of equally-spaced parallel saw tooth stripes with isosceles triangle-shaped cross sections are formed on the surfaces of two sides of the PVDF film, a white protective layer is formed on the surface of the saw tooth stripe facing one side of the solar cell piece through vacuum sputtering, and a black protective layer is formed on the surface of the saw tooth stripe far away from one side of the solar cell piece through vacuum sputtering; one side of the PVDF film with the white protective layer is bonded with a layer of heat-conducting metal film; the base film comprises a base material layer, two side surfaces of the base material layer are respectively provided with an online coating layer, and the outer side of the online coating layer is sputtered to form a barrier layer; the substrate layer includes towards the transmission membrane of solar wafer one side and keeps away from the heat conduction membrane of solar wafer one side, be formed with a plurality of equidistant parallel arrangement's prism structure on the transmission membrane, prism structure comprises the body part that the cross-section is isosceles triangle and the fin that upwards extends from the top of body part, and the prism structure outside is formed with one deck metal reflection stratum through vacuum sputtering, and the sunken cavity between heat conduction membrane and the metal reflection stratum has the heat conduction to glue, and it is as an organic whole to fill in heat conduction membrane and the metal reflection stratum through heat conduction glue connection.

Preferably, the sawtooth stripes on the two side surfaces of the PVDF film are mutually and vertically arranged; the included angle between the length direction of the sawtooth stripes and the four rectangular sides of the PVDF film is 45 degrees.

Preferably, the length of the base of the isosceles triangle of the sawtooth stripes is 5-10 μm, the vertex angle is 45-135 degrees, the height is 5-10 μm, and the minimum gap between adjacent sawtooth stripes is 0-5 μm.

Preferably, the isosceles triangle of the cross-section of the body portion of the prism structure has a base length of 20-30 μm, a vertex angle of 45-135 degrees and a height of 25-50 μm, and the minimum gap between adjacent prism structures is 0-50 μm.

Preferably, the height of the fin is 15 to 50 μm, and the thickness is 2 to 10 μm.

In addition, the application also provides a preparation method of the flexible solar cell backboard, which comprises a preparation step of a base film, a preparation arrangement of a weather-resistant film and a bonding step of the base film and the weather-resistant film; wherein the preparation of the base film comprises: providing a transmission film facing one side of the solar cell, and forming an online coating layer and a barrier layer on one side surface of the transmission film; providing a heat conducting film at one side far away from the solar cell slice, and forming an online coating layer and a barrier layer on one side surface of the heat conducting film; curing to form a plurality of prism structures which are arranged in parallel at equal intervals on one side of the transmission film on which the online coating layer and the barrier layer are not formed, wherein each prism structure consists of a body part with an isosceles triangle section and a fin extending upwards from the top of the body part; forming a metal reflecting layer on the prism structure by vacuum sputtering; filling heat-conducting glue in the concave cavity at the outer side of the metal reflecting layer, and attaching a layer of heat-conducting film at one side far away from the solar cell piece to the outer sides of the metal reflecting layer and the filled heat-conducting glue; wherein the side of the heat-conducting film, on which the on-line coating layer and the barrier layer are not formed, faces the metal reflecting layer for bonding; and curing the heat-conducting glue by heating, and simultaneously connecting the heat-conducting film and the metal reflecting layer into a whole through the heat-conducting glue, thereby preparing the base film.

Preferably, the method further comprises the steps of: the method comprises the steps of taking PET slices as raw materials for preparing a PET film, obtaining a single-layer thick sheet through melt extrusion, longitudinally stretching the PET slices into the film after preheating, coating a mixture of components forming an online coating layer on one side of the film through a coating machine after longitudinally stretching, transversely stretching, sizing, cooling and rolling to form the online coating layer on the surface of the film, and forming a barrier layer formed by silicon dioxide on the outer side of the online coating layer in a sputtering mode, so that the transmission film with the online coating layer and the barrier layer is obtained.

Preferably, the method further comprises the steps of: the preparation method comprises the steps of taking PET slices and-wt% of heat-conducting filler particles as raw materials for preparing a PET film, carrying out melt extrusion to obtain a single-layer thick sheet, longitudinally stretching the single-layer thick sheet into a film after preheating, carrying out longitudinal stretching, then carrying out online coating on one side of the film by a coating machine to form a mixture of components of an online coating layer, transversely stretching, shaping, cooling and rolling the mixture to form the online coating layer on the surface of the film, and then sputtering the outer side of the online coating layer to form a barrier layer formed by silicon dioxide, thereby obtaining the heat-conducting film with the online coating layer and the barrier layer.

Preferably, the preparation step of the weatherable film comprises: providing a PVDF film; forming a plurality of saw-tooth stripes with isosceles triangle-shaped sections which are arranged in parallel at equal intervals on the surfaces of two sides of the PVDF film through hot press molding; forming a white protective layer on the sawtooth stripes on one side through vacuum sputtering, and forming a black protective layer on the sawtooth stripes on the other side through vacuum sputtering; and adhering a heat-conducting metal film on the side with the white protective layer to form the weather-resistant film.

Preferably, the specific steps of forming the sawtooth stripes are as follows: adopting two rollers which are opposite up and down and are provided with patterns matched with the shape of the sawtooth stripes, enabling the heated PVDF film to pass between the two rollers, and then carrying out air cooling or water cooling on the PVDF film, thereby obtaining the solidified sawtooth stripes on the PVDF film; the length directions of the patterns matched with the shape of the sawtooth stripes on the surfaces of the two rollers which are opposite up and down are mutually vertical; the pattern direction of the two roller surfaces makes an angle of 45 degrees with the advancing direction of the PVDF film.

The utility model provides a backplate not only can assemble light through the substrate layer that sets up the reflection prism structure that has physical structure, has still increased heat radiating area and heat conduction efficiency. In addition, the weather-resistant film can increase the contact area with the adhesive through the arranged sawtooth stripes, so that the overall adhesive force of the weather-resistant film is increased, the problem that the weather-resistant film is easy to delaminate is solved, and the weather-resistant film also has excellent heat-conducting property and self-cleaning capability.

Drawings

The drawings are only for purposes of illustrating and explaining the present application and are not to be construed as limiting the scope of the present application.

Fig. 1 shows a schematic cross-sectional view of a flexible solar cell backsheet according to one embodiment of the present application.

Fig. 2 shows a schematic cross-sectional view of a weatherable film that can be used in a flexible solar cell backsheet of the present application, according to one embodiment of the present application.

Fig. 3 shows a schematic structural view of a PVDF film used as a weatherable film for a flexible solar cell backsheet according to one embodiment of the present application.

Figure 4 shows a schematic cross-sectional view of a base film that can be used in the flexible solar cell backsheet of the present application, according to one embodiment of the present application.

Fig. 5 shows a schematic cross-sectional view of a weatherable film that can be used in the flexible solar cell backsheet of the present application, according to another specific embodiment of the present application.

Fig. 6 shows an exploded perspective schematic view of a base film that can be used in a flexible solar cell backsheet of the present application, according to yet another embodiment of the present application.

Fig. 7 is a partially enlarged schematic view of a base film that can be used in a flexible solar cell backsheet according to yet another embodiment of the present application.

Detailed Description

In order to more clearly understand the technical features, objects, and effects of the present application, embodiments of the present application will now be described with reference to the accompanying drawings. Wherein like parts are given like reference numerals.

As shown in fig. 1, the present application proposes a flexible solar cell back sheet, which includes a base film 100 adjacent to a back surface of a solar cell (not shown in the figure) and a weather-resistant film 200 located outside the base film 100, wherein the weather-resistant film 200 and the base film 100 are integrally bonded by an adhesive layer 300. In a specific embodiment, the total thickness of the backing plate is about 170-332 μm; the thickness of the base film 100 is about 120 to 250 μm; the weatherable film 200 has a thickness of about 45-72 μm; the adhesive layer 300 has a thickness of about 5 to 10 μm.

The adhesive layer 300 may be a conventional EVA adhesive, or an ultraviolet light curing adhesive. The weatherable film on the outside of the flexible solar cell backsheet may provide good resistance to environmental attack. The weather-resistant film 200 can be prepared by selectively using a PVDF film, for example, a commercially available PVDF film with a thickness of 20-30 μm can be used, or a PVDF film can be formed by adding an ultraviolet absorber, an abrasion-resistant filler and the like to PVDF raw material particles with a mass content of 90% or more, performing melt co-extrusion, and then performing biaxial stretching.

Further, since the prior art fluorine-containing thin film used as a weatherable film is expensive and has the problems of low surface energy, insufficient adhesion and easy delamination, the present application proposes a weatherable film 200 that can be used in the flexible solar cell backsheet of the present application, as shown in fig. 2 to 3, wherein the weatherable film 200 includes a PVDF film 201, a plurality of equally spaced and parallel saw-tooth stripes 211 having isosceles triangle-shaped cross sections are formed on both side surfaces of the PVDF film 201, a white protective layer 212 is formed on the surface of the saw-tooth stripe 211 facing the solar cell by vacuum sputtering, and a black protective layer 213 is formed on the surface of the saw-tooth stripe 211 facing away from the solar cell by vacuum sputtering.

The PVDF film 201 contains PVDF in an amount of 90% by mass or more, and an ultraviolet absorber, an abrasion resistant filler, and the like may be added to improve the performance of the PVDF film. It is preferable that the both side surfaces of the PVDF film 201 are formed with the sawtooth stripes 211 which are identical. The weatherable film 200 is shown enlarged in size to facilitate viewing and understanding, the actual sawtooth streaks 211 are relatively fine in size, and the surface has only a small texture that is not noticeable. In one embodiment, the maximum thickness of PVDF membrane 201 is 20-30 μm.

The existing PVDF weather-resistant film has the problems of easy delamination due to low surface energy and insufficient adhesive force. In order to overcome the technical problem, the present application forms a sawtooth stripe 211 on the surface of the PVDF film 201, and the contact area with the adhesive 203 (which will be described in further detail later) can be increased by the sawtooth stripe 211, for example, when the isosceles trapezoid of the sawtooth stripe 211 has an apex angle of 60 degrees, the sawtooth stripe 211 can double the surface area, thereby increasing the overall adhesion of the PVDF film 201 and avoiding the problem that the weather-resistant film is easily delaminated.

It should be noted that, in practice, the whole adhesion of the weatherable film 200 only needs to be improved by providing the sawtooth stripes 211 on the inner side of the PVDF film 201, but since the stripes are very small and difficult to observe, and for the convenience of assembly operation, the inventors have chosen to form the same sawtooth stripes 211 on both surfaces of the PVDF film 201, so that both sides can be coated with the film, and the application range of the weatherable film 200 can be improved. The inventor thinks that the originally located sawtooth stripes 211 on the outer side do not assume any effect, however, in the actual laying experiment process, the inventor finds that if the scale of the sawtooth stripes 211 formed on the surface of the PVDF film 201 is smaller than a certain range, the PVDF film can play a self-cleaning effect, the adhesion force of dust on the surface of the weather-resistant film 200 can be reduced, and the rainwater can easily flush the adhered dust. For example, in one embodiment, it is preferable that the isosceles triangle of the sawtooth stripes 211 has a length of 5 to 10 μm, a vertex angle of 45 to 135 degrees and a height of 5 to 10 μm, and a minimum gap between adjacent sawtooth stripes 211 is 0 to 5 μm. The same saw-tooth stripes 211 formed on both surfaces of the PVDF film 201 not only can reduce the manufacturing cost, but also can obtain better bonding performance on the inner side and excellent dust adsorption resistance on the outer side by selecting the saw-tooth stripes 211 in the size range. In addition, the surface area of the outer surface is further increased by the sawtooth stripes 211 on the outer side, the heat dissipation area is increased, and the overall heat dissipation performance of the weather-resistant film is further improved.

Further, in order to improve the adhesion of the PVDF film 201 and avoid delamination, the angle between the length direction of the sawtooth stripes 211 and the four rectangular sides of the weatherable film is selected to be 45 degrees, as shown in fig. 3. In general, the solar cell panel is generally designed to be rectangular, four sides are perpendicular to each other, and if the length direction of the sawtooth stripes 211 is perpendicular to one pair of rectangular sides of the weatherable film 200, the other pair of rectangular sides will be parallel to the length direction of the sawtooth stripes 211. Since the rigidity in the longitudinal direction and the width direction of the zigzag stripes 211 are different, the expansion rates are also different, which causes one pair of rectangular sides of the weather-resistant film 200 to be easily warped and delaminated. The direction of the sawtooth stripes 211 is turned to form 45-degree included angles with the four rectangular sides, the proportion of the rigidity difference in different directions caused by the sawtooth stripes 211 diffusing to the four rectangular sides tends to be average, so that the problem of delamination of the weather-resistant film 200 caused by the arrangement of the sawtooth stripes 211 can be avoided, and the structural performance of the weather-resistant film 200 is further improved.

In addition, when the same saw-tooth stripes 211 are formed on both sides, if the saw-tooth stripes 211 on both sides are oriented in the same direction, that is, the saw-tooth stripes 211 on both sides are arranged in parallel to each other in the longitudinal direction, different thermal expansion coefficients on both sides are concentrated in the same direction, and thus stress concentration may occur, which may cause delamination. In order to avoid the delamination problem caused by the consistent directions of the sawtooth stripes 211 on both sides, the present application further proposes a special design, in which the sawtooth stripes 211 on both sides of the PVDF film 201 are perpendicular to each other, so as to avoid the delamination problem caused by the formation of a profit bias in one direction at the same time.

In addition, in order to avoid the problem that the back plate in the prior art is too large in thickness and difficult to apply to the field of flexible solar cells with larger flexibility requirements, the white protective layer 212 and the black protective layer 213 are formed on the sawtooth stripes in a vacuum sputtering mode on the basis of the PVDF film with the sawtooth stripe structure, and the binding force of the sputtering layer formed by vacuum sputtering is far greater than that of adhesion, so that the protection function can be achieved through very thin thickness. For example, the white protective layer 212 may be composed of titanium dioxide; the black protective layer 213 may be made of silicon carbide. Preferably, the white protective layer 212 and the black protective layer 213 have a thickness of 1 to 3 μm, respectively.

The white passivation layer 212 can provide a good light reflection function, and can reflect the light transmitted from the front surface of the solar cell back to the solar cell as much as possible, thereby improving the light conversion efficiency. Meanwhile, the white protective layer 212 is integrally sputtered on the surface of the sawtooth stripes 211, so that an additional white polyethylene film layer is not required, the structure of the weather-resistant film 200 is simplified, and the film thickness is reduced.

The black overcoat 213 is also a very thin sputtered layer that can be used to improve the abrasion resistance and the ability of the weathering film 200 to resist wind and sand. In addition, the black protection layer 213 has better heat radiation capability, so as to facilitate the heat absorbed by the back plate to be radiated out as soon as possible, so as to reduce the temperature of the solar cell module. Meanwhile, the combination force is improved by a sputtering layer mode, an additional film layer structure is reduced, and the thickness and the cost are reduced.

Further, in order to better improve the heat dissipation capability of the backplane, a layer of heat-conducting metal film 202 is bonded to one side of the PVDF film 201 having the white protection layer 212, for example, the heat-conducting metal film 202 and the PVDF film 201 can be bonded into a whole by a suitable adhesive 203, the heat absorbed by the backplane can be conducted to the PVDF film 201 through the heat-conducting metal film 202, and the heat can be efficiently radiated out through the surface area increased by the outer side sawtooth stripes. In one embodiment, the heat conductive metal film 202 may be a metal aluminum foil with a thickness of 8-16 μm, and the adhesive 203 may be a commercially available EVA adhesive or acrylic adhesive with a maximum thickness of 15-20 μm.

Examples 1 to 6

Weatherable films for the flexible solar cell backsheet of the present application were prepared according to the following table parameters.

In examples 1 to 3, the included angles between the sawtooth stripes and the rectangular sides of the weatherable film are both 45 degrees, and in examples 4 to 6, the included angles between the sawtooth stripes and the rectangular sides of the weatherable film are both 0/90 degrees, that is, the included angles between the sawtooth stripes and one pair of rectangular sides are 0 degree, and the included angles between the sawtooth stripes and the other pair of rectangular sides are 90 degrees. The white protective layer is made of titanium dioxide; the black protective layer is made of silicon carbide.

Comparative examples 1 to 6

Comparative examples 1-6 used PVDF films without sawtooth stripes and bonded with a thermally conductive metal film as a weatherable film, with the following parameters. In examples 1 to 6 and comparative examples 1 to 6, an EVA adhesive was used, and a metal aluminum foil was used as a heat conductive metal film.

	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6
							PVDF film thickness μm	20	22	24	26	28	30
Maximum thickness of adhesive	15	16	17	18	19	20
							Thickness of heat conducting metal film	8	10	12	12	14	16

The weatherable films of examples 1 to 6 and comparative examples 1 to 6 were respectively adhered to the surface of a 188 μm PET base film, and the parametric properties of the examples in which the weatherable film was measured were compared as follows.

As can be seen by the comparison of performance parameters of the embodiment, the weather-resistant film for the flexible solar cell backboard can obviously improve the bonding performance and avoid layering under the condition of having the sawtooth stripes, has excellent heat conduction performance, can increase the contact angle of the outer surface, improves the self-cleaning capability, and has excellent dust-resistant adsorbability.

The base film on the inner side of the flexible solar cell backboard has good insulating property and mechanical property. The base film in the back plate in the prior art usually only plays a simple supporting role, reflection and heat transfer of transmitted light rays need to be realized by other coatings, the process is complex, the coating structure is unstable, and the back plate is easy to age and delaminate under the condition of long-term heating.

The present application thus proposes an improved base film that can be used in the flexible solar cell backsheet of the present application. In one embodiment of the present application, the base film 100 may be made of a PET film, which may be a single-layer or multi-layer structure that is biaxially stretched. The PET film can provide excellent insulation, water resistance, mechanical properties and dimensional stability. However, for solar cells, especially for CI (G) S flexible solar cells, which are mainstream products, the requirements for the back sheet are high due to the process characteristics of the solar cells requiring stronger barrier property to protect the internal circuits, and the barrier property is usually required to be 10 ^- ³ g/m ² Day level. The general idea for enhancing barrier properties is to increase the thickness of the material, which results in increased material costs, while increasing the unit weight and decreasing the flexibility of the material, and too thick a material also results in slippage leakage when the edges of the sheet are bent.

In view of this, in one embodiment of the base film 100 shown in fig. 4, the base film 100 includes a substrate layer 101, an in-line coating layer 102 is formed on both surfaces of the substrate layer 101, and a barrier layer 103 is formed on the outside of the in-line coating layer 102 by sputtering. The substrate layer 101 has a thickness of about 120 to 250 μm, and may be formed of, for example, 188 μm biaxially oriented PET film having a single layer structure, or may be formed by laminating a plurality of films (as will be described in further detail below). The barrier layer 23 is preferably composed of silicon dioxide; the thickness was 200nm.

The barrier property of the substrate layer 101 can be improved by arranging the barrier layer 103, the thickness of the substrate layer 101 does not need to be increased, and the adaptability of the flexible solar cell is improved. In order to improve the surface smoothness and the adhesion of the barrier layer 103, it is preferable to perform an in-line coating process on both surfaces of the base material layer 101 before forming the barrier layer 103 by sputtering, and to form an in-line coating layer 102 having a thickness of preferably 0.1 to 0.3 μm on each of both sides.

The online coating can be directly through online coating machine with the coating of chemical article on the substrate layer in the production process of substrate layer 101, and online coating can be directly formed in the later stage of the production process of substrate layer, need not launch the operation again with the coiled material, and the coating forms evenly, fast, efficient, and is with low costs.

In one embodiment, the primer solution forming the in-line coating layer 102 can be applied to the thick sheet before or during the stretching of the polyester film forming the substrate layer 101, and then the primer solution applied to the surface of the thick sheet is cured at a high temperature during the stretching process to form the in-line coating layer 102 as the thick sheet is stretched to a film with a desired thickness.

In one embodiment, the in-line coating layer 102 is formed by uniformly mixing acrylic resin, silica nanoparticles having a particle size of 5 to 10nm, 1, 4-dioxane, polyethylene oxide, and ethylene-vinyl acetate copolymer into a primer solution, and then curing by in-line coating.

Specifically, the mass ratios of the components of the online coating layer 102 are, respectively, acrylic resin: silica nanoparticles: 1, 4-dioxane: polyethylene oxide: the ethylene-vinyl acetate copolymer is 100: (10-15): (20 to 30): (10-15): (5-10). Wherein the ethylene-vinyl acetate copolymer can be ethylene-vinyl acetate copolymer which is sold by Mitsui corporation of Japan and has the trade name of Evaflex 550, and the mass percentage of the contained vinyl acetate polymer is 14 percent.

According to the weight ratio of the raw materials in the following table, on-line coating layers are respectively prepared on the two side surfaces of a 188-micron biaxially oriented PET film, and then a layer of barrier layer made of silicon dioxide is respectively sputtered on the outer sides of the on-line coating layers.

	Example 7	Example 8	Example 9	Example 10	Example 11
						Acrylic resin	100	100	100	100	100
Silica nanoparticles	10	11.5	12.5	13.5	15
						1, 4-dioxane	20	22	25	28	30
Polyethylene oxide	10	12	13	14	15
						Ethylene-vinyl acetate copolymer	5	6	7.5	8	10
On-line coating layer thickness (nm)	100	150	200	250	300
						Thickness of barrier layer (nm)	200	200	200	200	200

For comparison, barrier layers of 200nm thick silica were formed by sputtering directly on both side surfaces of a 188 μm biaxially oriented PET film as comparative examples. The 180 degree peel force (N/25 mm) of the barrier layers of examples 7-11 was measured to be 34.5%, 36.2%, 35.1%, 34.8%, and 36.1% higher than the comparative examples, respectively.

Further, as shown in fig. 5, the present application proposes another embodiment of a base film that can be used in the flexible solar cell backsheet of the present application, and similar to the embodiment shown in fig. 4, the base film 100 of the present embodiment also includes a substrate layer 101, an in-line coating layer 102 is respectively disposed on both sides of the substrate layer 101, and a barrier layer 103 is formed on the outside of the in-line coating layer 102 by sputtering. Unlike the embodiment shown in fig. 2, the substrate layer 101 of the present embodiment is formed by laminating a plurality of films, and the on-line coating layer 102 and the barrier layer 103 may have the same structure and composition as those of the previous embodiment. Only the substrate layer 101 of the multilayer composite structure of the present embodiment will be described in detail below.

As shown in fig. 5-7, the substrate layer 101 of the present embodiment includes a transmission film 1 facing one side of the solar cell and a heat conduction film 2 away from one side of the solar cell, wherein the transmission film 1 is formed with a plurality of prism structures 3 arranged in parallel at equal intervals, the prism structures 3 are composed of a body portion 31 having an isosceles triangle cross section and fins 32 extending upward from the top of the body portion 31 (see fig. 7 in particular), a metal reflection layer 4 is formed on the outer side of the prism structures 3 by vacuum sputtering, a concave cavity between the heat conduction film 2 and the metal reflection layer 4 is filled with a heat conduction glue 5, and the heat conduction film 2 and the metal reflection layer 4 are connected into a whole through the heat conduction glue 5. In fig. 3, the thickness of the fin 32 is enlarged for clarity, and the actual thickness is small, substantially concentrated at the apex of the body portion 31, and does not substantially destroy the triangular cross-sectional shape of the body portion 31.

The substrate layer 101 of the application adopts a multilayer composite structure, a reflection prism structure of a physical structure is arranged between the diaphragms (the transmission film 1 and the heat conduction film 2) of the two-layer overall structure, light rays at different angles can be converged to be reflected, the reflection surface deflected by the angle can not only converge the light rays, but also enlarge the reflection area. The metal reflecting layer on the back of the reflecting prism structure not only has a reflecting function, but also has a heat conduction function, and the reflecting surface is bent along with the reflecting surface, so that the reflectivity is increased, and the heat dissipation area is also increased. In addition, in order to further enlarge the heat dissipation area, the top of the body part of the prism structure is extended with fins, and the metal reflection layer is formed on the surfaces of the fins, so that the fins attached with the metal reflection layer become heat dissipation fins, and the heat dissipation area and the heat conduction efficiency are further enlarged.

The transmission film 1 can be made of PET with light transmittance of more than 85%, the heat conduction film 2 can be made of PET added with heat conduction filler, and the PET film with a double-layer structure can provide excellent insulation, water resistance, mechanical property and dimensional stability. The transmission film 1 and the heat conduction film 2 integrally package the middle prism structure, the metal reflection layer 4 sputtered on the back of the prism structure isolates the heat dissipation structure on the outer side, the bent metal reflection layer 4 prolongs the isolation channel, and the water resistance and the air tightness are enhanced.

In a particular embodiment, the prismatic structure 3 is made of uv curable acrylic. The metallic reflective layer 4 may be formed by sputtering metallic silver having excellent reflection effect and heat conduction effect. The heat conductive adhesive 5 may be made of an ultraviolet-curable acrylic resin to which a heat conductive filler is added, or, in order to avoid poor ultraviolet curing effect due to influence of the heat conductive filler on light transmittance, the heat conductive adhesive 5 is preferably made of a thermosetting resin to which a heat conductive filler is added.

The solar panels are usually fixed and non-orientable after installation, so that the efficiency is greatly affected by the direction of the sunlight, generally speaking the direct sunlight is the most efficient, but the time is short, and the direction of the sunlight is inclined for a large period of time. The prism structure is arranged and formed in the substrate layer 101, light rays enter the prism structure and then are reflected by the metal reflecting layer on the outer side on the inclined triangular edge, the reflected light rays are gradually collected to the bottom of the triangle and finally are reflected back to the direction perpendicular to the solar cell piece as far as possible, and therefore even if the inclined light rays can be collected and reflected for use, and therefore the utilization rate of sunlight is improved. In addition, for the flexible solar cell laid on the roof, the efficiency of the stripes of the prism structure pointing to the north-south direction is better, and the utilization rate of the light rays facing the east-west direction at morning and evening can be improved. For the flexible solar cell laid on the vertical wall, the efficiency of the stripes of the prism structure pointing to the east-west direction is better, and the utilization rate of light rays obliquely irradiating the wall from the top when the sunlight is strongest at noon can be improved.

Examples 12 to 14

A substrate layer of the base film, which was used for the flexible solar cell backsheet of the present application, was prepared according to the parameters of the following table.

Comparative examples 12 to 14

Comparative examples 12-14 use a single layer PET film as the base film and a white coating of the second mesh layer referenced CN 114156357A as the reflective coating, with relevant reflection parameters as follows.

	Comparative example 12	Comparative example 13	Comparative example 14
				Thickness of PET film layer	250	250	250
Thickness of the reflection coating	15	10	1

The parametric properties of the examples were measured and compared as follows.

And (3) detecting by referring to GJB 5023.1A-2012 materials and coating reflectivity and emissivity test methods.

As can be seen from the comparison of the performance parameters of the embodiment, the mechanical performance, reflectivity, stripping performance, heat conductivity and the like of the base material layer for the flexible solar cell backboard are greatly improved.

The method for manufacturing the flexible solar cell back sheet of the present application is described in further detail below with reference to the accompanying drawings. As described above, the flexible solar cell back sheet of the present application includes the base film 100 adjacent to the back surface of the solar cell sheet and the weather-resistant film 200 located outside the base film 100, and the weather-resistant film 200 and the base film 100 are integrally bonded by the adhesive layer 300. The base film 100 includes a substrate layer 101, an on-line coating layer 102 is respectively disposed on both side surfaces of the substrate layer 101, and a barrier layer 103 is formed on the outer side of the on-line coating layer 102 by sputtering. Substrate layer 101 is including the transmission membrane 1 towards solar wafer one side and keep away from heat conduction membrane 2 of solar wafer one side, be formed with a plurality of equidistant parallel arrangement's prism structure 3 on the transmission membrane 1, prism structure 3 comprises body part 31 that the cross-section is isosceles triangle and the fin 32 that upwards extends from body part 31's top, prism structure 3 outside is formed with one deck metal reflection stratum 4 through vacuum sputtering, it has heat conduction glue 5 to fill in the sunken cavity between heat conduction membrane 2 and the metal reflection stratum 4, heat conduction membrane 2 is connected as an organic wholely through heat conduction glue 5 with metal reflection stratum 4. The weather-resistant film 200 can comprise a PVDF film 201, wherein a plurality of saw tooth stripes 211 which are arranged in parallel at equal intervals and have isosceles triangle-shaped cross sections are formed on the surfaces of two sides of the PVDF film 201, a white protective layer 212 is formed on the surface of the saw tooth stripe 211 facing one side of the solar cell piece through vacuum sputtering, and a black protective layer 213 is formed on the surface of the saw tooth stripe 211 far away from one side of the solar cell piece through vacuum sputtering; the PVDF film 201 has a heat conductive metal film 2 bonded to the side having the white protective layer 212.

Further, the manufacturing method of the present application includes a manufacturing step of the base film 100, a manufacturing step of the weather-resistant film 200, and a bonding step of the base film 100 and the weather-resistant film 200.

Wherein the preparation of the base film 100 comprises:

first, a transmission film 1 is provided on a side facing the solar cell sheet, and an in-line coating layer 102 and a barrier layer 103 are formed on one side surface thereof. In one embodiment, a PET chip is used as a raw material for preparing a PET film, a single-layer thick sheet is obtained by melt extrusion, the sheet is longitudinally stretched into a film after preheating, a mixture of components constituting the on-line coating layer of the present application is coated on one side of the film on line by a coater after longitudinally stretching, and then the film is transversely stretched, shaped, cooled and wound, so that the on-line coating layer 102 is formed on the surface of the film, and then a barrier layer 103 made of silica is formed on the outer side of the on-line coating layer 102 by sputtering, so that a transmission film 1 with the on-line coating layer 102 and the barrier layer 103 is obtained for standby. The thickness of the transmission film 1 is preferably 40-60 μm, and the visible light transmittance is 85% -95%.

Meanwhile, a heat conducting film 2 is provided on the side far away from the solar cell sheet, and an in-line coating layer 102 and a barrier layer 103 are formed on one side surface of the heat conducting film. In one embodiment, a PET chip and 5 to 10wt% of heat conductive filler particles are used as raw materials for preparing a PET film, a single-layer thick sheet is obtained through melt extrusion, the raw material is longitudinally stretched into a film after preheating, the mixture of the components constituting the on-line coating layer of the present application is coated on one side of the film in an on-line manner through a coating machine after longitudinally stretching, then the on-line coating layer 102 is transversely stretched, shaped, cooled and rolled, and then the on-line coating layer 102 is formed on the surface of the film, and a barrier layer 103 made of silica is formed on the outer side of the on-line coating layer 102 in a sputtering manner, so that the heat conductive film 2 with the on-line coating layer 102 and the barrier layer 103 is obtained for standby. In a specific embodiment, the thermally conductive filler may be one of boron nitride, graphite, and graphene or a mixture thereof, preferably boron nitride.

Then, on the side of the transmission film 1 where the in-line coating layer 102 and the barrier layer 103 are not formed, a plurality of equally spaced prism structures 3 arranged in parallel are cured, the prism structures 3 being composed of a body portion 31 having an isosceles triangle-shaped cross section and fins 32 extending upward from the top of the body portion 31. For example, a roller having a pattern matching the shape of the prism structure may be used, the ultraviolet curable acrylic resin may be applied to the roller, the transmission film 1 may be pressed and rolled along the surface of the roller while the ultraviolet curable acrylic resin is pressed onto the transmission film 1 in accordance with the shape of the prism structure, and then the ultraviolet curable acrylic resin may be cured by irradiating ultraviolet light to form the prism structure 3 of a desired shape on the transmission film 1. The base of the isosceles triangle forming the cross section of the body portion 31 of the prism structure 3 has a length of 20 to 30 μm, a vertex angle of 60 to 120 degrees and a height of 25 to 50 μm, and the minimum gap between adjacent prism structures 3 is 0 to 50 μm. The height of the fin 32 is 15 to 50 μm, and the thickness is 2 to 10 μm.

Thereafter, a metal reflective layer 4 is formed on the prism structure 3 by vacuum sputtering. For example, a layer of metallic silver having a thickness of 2-10 μm may be formed on the prism structure 3 by vacuum sputtering, and since the thickness of the metallic reflective layer 4 is formed to be relatively very thin, the metallic reflective layer 4 is not shown in fig. 2 and 3.

Then, filling heat-conducting glue 5 in the concave cavity at the outer side of the metal reflecting layer 4, and attaching the heat-conducting film 2 to the outer sides of the metal reflecting layer 4 and the filled heat-conducting glue 5; the side of the heat conductive film 2 where the line coating layer 102 and the barrier layer 103 are not formed is bonded to the metal reflective layer 4. Preferably, the heat conducting glue 5 is filled in the concave cavity at the outer side of the metal reflecting layer 4, and simultaneously the heat conducting glue outside the top of the metal reflecting layer 4 is scraped by a scraper, so that the filled heat conducting glue 5 is flush with the top of the metal reflecting layer 4, and gaps are eliminated, and the bonding between the attached layers is ensured to be firmer, as shown in fig. 3.

And finally, curing the heat-conducting glue 5, and connecting the heat-conducting film 2 and the metal reflecting layer 4 into a whole through the heat-conducting glue 5 while curing the heat-conducting glue 5, thereby preparing the base film 100. In one embodiment, as described above, the heat conductive adhesive 5 may be made of an ultraviolet-curable acrylic resin to which a heat conductive filler is added, and thus the heat conductive adhesive 5 may be cured by irradiating ultraviolet light through the heat conductive film 2. Alternatively, since the heat conductive film 2 and the heat conductive paste 5 are both added with the heat conductive filler, in view of the problem of light transmittance, it is preferable that the heat conductive paste 5 is made of a thermosetting resin to which the heat conductive filler is added, and the heat conductive paste 5 is cured by heating at the time of curing. The heat-conducting glue 5 can be any commercially available bonding resin with a heat-conducting function, or can be prepared by purchasing a heat-conducting filler and adding the heat-conducting filler into the existing bonding resin. In a specific embodiment, the thermally conductive filler may be one of boron nitride, graphite, and graphene or a mixture thereof, preferably boron nitride. The heat-conducting adhesive 5 is preferably a thermosetting resin having a thermal conductivity of 20-25W/(m.K).

The preparation of the weatherable film 200 comprises the steps of:

first, a PVDF film 201 is provided. The PVDF film 201 can be a PVDF film with the thickness of 20-30 μm sold in the market, or a PVDF raw material particle with the mass content of more than or equal to 90 percent is added with an ultraviolet absorber, an abrasion-resistant filler and the like, and then the PVDF film is formed by melt co-extrusion and then two-way stretching.

Then, a plurality of equally spaced saw-tooth stripes 211 having isosceles triangle-shaped cross sections are formed on both side surfaces of the PVDF film 201 by hot press molding. For example, two rollers arranged opposite to each other in the up-down direction and having a pattern matching the shape of the zigzag stripes may be used, the heated PVDF film 201 may be passed between the two rollers, and then the PVDF film 201 may be air-cooled or water-cooled to obtain the cured zigzag stripes 211 on the PVDF film 201. Wherein the longitudinal directions of the patterns matching the shape of the sawtooth stripes of the two roll surfaces facing each other are arranged perpendicular to each other, so that the sawtooth stripes 211 perpendicular to each other can be formed on both side surfaces of the PVDF film 201. For example, the pattern direction of the two roller surfaces forms an angle of 45 degrees with the advancing direction of the PVDF film 201, so that the sawtooth stripes 11 forming an angle of 45 degrees with the four rectangular sides of the weatherable film 200 can be formed.

Thereafter, a white protective layer 212 is formed on the sawtooth stripes 211 on one side by vacuum sputtering, and a black protective layer 213 is formed on the sawtooth stripes 211 on the other side by vacuum sputtering. For example, a layer of titanium dioxide having a thickness of 1 to 3 μm may be formed on the sawtooth stripes 211 of one side by vacuum sputtering to form a white protective layer 212; a black protective layer 213 is formed by vacuum sputtering of silicon carbide having a thickness of 1-3 μm on the sawtooth pattern 211 on the other side, and since the thickness of the formed protective layer is relatively very thin, the protective layer is not shown in fig. 3, and the

protective layers

212 and 213 in fig. 2 are enlarged for easy understanding.

Finally, a thermally conductive metal film 202 is bonded to the side having the white protective layer 212, thereby forming the weatherable film 200. For example, the weather-resistant film 200 may be prepared by coating an acrylic adhesive having a thickness of 15 to 20 μm on the side having the white protective layer 212, leveling the surface, and then attaching a metal aluminum foil having a thickness of 8 to 16 μm as the heat conductive metal film 202.

The bonding step of the base film 100 and the weather-resistant film 200 includes: one side of the heat conductive film 2 of the base film 100 is integrally adhered to the weather-resistant film 200 through an adhesive layer 300.

It should be appreciated by those skilled in the art that while the present application is described in terms of several embodiments, not every embodiment includes only a single embodiment. The description is thus given for clearness of understanding only, and it is to be understood that all matters in the embodiments are to be interpreted as including all technical equivalents which are encompassed by the claims and are to be interpreted as combined with each other in a different embodiment so as to cover the scope of the present application.

The above description is only illustrative of the present invention and is not intended to limit the scope of the present invention. Any equivalent alterations, modifications and combinations that may be made by those skilled in the art without departing from the spirit and principles of this application shall fall within the scope of this application.

Claims

1. A flexible solar cell backboard comprises a base film (100) close to the back surface of a solar cell and a weather-resistant film (200) positioned on the outer side of the base film (100), wherein the weather-resistant film (200) and the base film (100) are bonded into a whole through a bonding layer (300); the weather-resistant film (200) is characterized by comprising a PVDF film (201), wherein a plurality of equally-spaced and parallelly-arranged sawtooth stripes (211) with isosceles triangle-shaped cross sections are formed on the surfaces of two sides of the PVDF film (201), a white protective layer (212) is formed on the surface of the sawtooth stripe (211) facing one side of a solar cell piece through vacuum sputtering, and a black protective layer (213) is formed on the surface of the sawtooth stripe (211) far away from one side of the solar cell piece through vacuum sputtering; one side of the PVDF film (201) with the white protective layer (212) is bonded with a layer of heat-conducting metal film (2); the base film (100) comprises a base material layer (101), two side surfaces of the base material layer (101) are respectively provided with an online coating layer (102), and a barrier layer (103) is formed on the outer side of the online coating layer (102) in a sputtering mode; substrate layer (101) are including transmission film (1) towards solar wafer one side and keep away from heat conduction membrane (2) of solar wafer one side, be formed with a plurality of equidistant parallel arrangement's prism structure (3) on transmission film (1), prism structure (3) comprise body part (31) that the cross-section is isosceles triangle and fin (32) that upwards extend from the top of body part (31), and prism structure (3) outside is formed with one deck metal reflection stratum (4) through vacuum sputtering, and it has heat conduction glue (5) to fill in the sunken cavity between heat conduction membrane (2) and metal reflection stratum (4), and heat conduction membrane (2) are connected as an organic wholely through heat conduction glue (5) with metal reflection stratum (4).

2. The backsheet according to claim 1, wherein the zigzag stripes (211) of both side surfaces of the PVDF film (201) are arranged perpendicular to each other; the included angle between the length direction of the sawtooth stripes (211) and four rectangular sides of the PVDF film (201) is 45 degrees.

3. The back sheet according to claim 1, wherein the isosceles triangle of the saw-tooth stripes (211) has a length of 5-10 μm at a base angle of 45-135 degrees and a height of 5-10 μm, and a minimum gap between adjacent saw-tooth stripes (211) is 0-5 μm.

4. A backsheet according to claim 1, wherein the isosceles triangle of the cross-section of the body portion (31) of the prism structure (3) has a length of the base of 20-30 μm, a vertex angle of 45-135 degrees and a height of 25-50 μm, and the minimum gap between adjacent prism structures (3) is 0-50 μm.

5. The backing plate of claim 1 wherein the fins (32) have a height of 15-50 μm and a thickness of 2-10 μm.

6. A method for producing a flexible solar cell back sheet as defined in any one of claims 1 to 5, comprising a step of producing the base film (100), a step of producing the weather-resistant film (200), and a step of bonding the base film (100) and the weather-resistant film (200); wherein the preparation step of the base film (100) comprises:

providing a transmission film (1) facing to one side of the solar cell piece, and forming an online coating layer (102) and a barrier layer (103) on one side surface of the transmission film;

providing a heat conducting film (2) at one side far away from the solar cell slice, and forming an online coating layer (102) and a barrier layer (103) on one side surface of the heat conducting film;

curing to form a plurality of equally spaced prism structures (3) arranged in parallel on the side of the transmission film (1) where the online coating layer (102) and the barrier layer (103) are not formed, wherein the prism structures (3) are composed of a body part (31) with an isosceles triangle section and fins (32) extending upwards from the top of the body part (31);

forming a metal reflecting layer (4) on the prism structure (3) through vacuum sputtering;

filling heat-conducting glue (5) in the concave cavity at the outer side of the metal reflecting layer (4), and attaching a layer of heat-conducting film (2) at one side far away from the solar cell piece to the outer sides of the metal reflecting layer (4) and the filled heat-conducting glue (5); wherein one side of the heat-conducting film (2) which is not provided with the on-line coating layer (102) and the barrier layer (103) is attached to the metal reflecting layer (4) in a way of facing the metal reflecting layer;

and (3) curing the heat-conducting glue (5) through heating, and simultaneously connecting the heat-conducting film (2) and the metal reflecting layer (4) into a whole through the heat-conducting glue (5), thereby preparing and obtaining the base film (100).

7. The method of claim 6, further comprising the steps of: the PET chip is taken as a raw material for preparing the PET film, a single-layer thick sheet is obtained through melt extrusion, the single-layer thick sheet is longitudinally stretched into a film after preheating, the mixture of the components forming the on-line coating layer is coated on one side of the film in an on-line mode through a coating machine after the longitudinal stretching, then the on-line coating layer (102) is formed on the surface of the film through transverse stretching, shaping, cooling and rolling, a barrier layer (103) formed by silica is formed on the outer side of the on-line coating layer (102) in a sputtering mode, and the transmission film (1) with the on-line coating layer (102) and the barrier layer (103) is obtained.

8. The method of claim 6, further comprising the steps of: the preparation method comprises the steps of taking PET slices and 5-10wt% of heat-conducting filler particles as raw materials for preparing a PET film, carrying out melt extrusion to obtain a single-layer thick sheet, longitudinally stretching the single-layer thick sheet into a film after preheating, carrying out longitudinal stretching, then carrying out online coating on one side of the film by a coating machine to form a mixture of components of an online coating layer, transversely stretching, shaping, cooling and rolling to form the online coating layer (102) on the surface of the film, and then sputtering and forming a layer of barrier layer (103) made of silicon dioxide on the outer side of the online coating layer (102) to obtain the heat-conducting film (2) with the online coating layer (102) and the barrier layer (103).

9. The method of manufacturing according to claim 6, wherein the step of manufacturing the weatherable film (200) comprises: providing a PVDF film (201);

forming a plurality of saw-tooth stripes (211) which are arranged in parallel at equal intervals and have isosceles triangle-shaped sections on the two side surfaces of the PVDF film (201) through hot press molding;

a white protective layer (212) is formed on the sawtooth stripes (211) on one side through vacuum sputtering, and a black protective layer (213) is formed on the sawtooth stripes (211) on the other side through vacuum sputtering;

and adhering a heat-conducting metal film (202) on one side with the white protective layer (212) to form the weather-resistant film.

10. The method of claim 9, wherein the step of forming the sawtooth striations (211) comprises: adopting two rollers which are opposite up and down and are provided with patterns matched with the shapes of the sawtooth stripes (211), passing the heated PVDF film (201) between the two rollers, and then carrying out air cooling or water cooling on the PVDF film so as to obtain the solidified sawtooth stripes (211) on the PVDF film; the length directions of the patterns matched with the shape of the sawtooth stripes on the surfaces of the two rollers which are opposite up and down are mutually vertical; the pattern direction of the two roller surfaces makes an angle of 45 degrees with the advancing direction of the PVDF film.