Skin film for photovoltaic module and preparation method of skin film

Abstract

The invention discloses a skin film for a photovoltaic module and a preparation method of the skin film, the skin film for the photovoltaic module comprises a weather-proof polyolefin resin outer layer, a weather-proof polyethylene resin inner layer and an excimer ultraviolet curing layer, and the excimer ultraviolet curing layer is located on one side close to a welding strip. The excimer ultraviolet curing layer is arranged on the side close to the welding strip, the crosslinking curing depth is 0.5-3 m, the overall hardness is not improved, a skin film can be prevented from flowing and overflowing to the position below the welding strip at the lamination temperature, the problems of hidden cracks and fragments of a battery piece during conventional skin film lamination are solved, and the problem of no bubbles during lamination is solved; by introducing an aromatic group into the excimer ultraviolet curing layer and introducing a branched cross-linking group into the weather-resistant polyethylene resin inner layer, gradient increase of refractive index from the weather-resistant polyolefin resin outer layer to the excimer ultraviolet curing layer is formed, which is beneficial to absorption of the photovoltaic module to weak light. The contribution of low-angle sunlight in the morning and evening periods to power generation of the photovoltaic module is increased, and the daily generating capacity of the photovoltaic module is improved.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology, specifically relating to a skin film for photovoltaic modules and its preparation method. Background Technology

[0002] To reduce the cost of photovoltaic modules, OBB (Obstacle-Free) technology and low-temperature welding technology have been introduced in recent years. Instead of infrared welding, low-temperature solder ribbons are used, with initial fixation achieved through dispensing or coating, followed by alloying through lamination. Since lamination is an essential process in photovoltaic module production, this approach not only saves on the cost of infrared welding but also reduces stress on the cells, lowering the probability of microcracks.

[0003] Commercially available coating materials generally use existing encapsulating film formulations, optimizing them with equipment to achieve thinner films, and then pre-crosslinking them through irradiation. Pre-crosslinking can prevent the film material from overflowing under the solder strip during lamination, causing poor soldering. However, besides increasing process costs, pre-crosslinking also increases material hardness, raising the probability of microcracks and fragmentation during lamination. Furthermore, the pre-crosslinked skin film is highly prone to generating air bubbles during lamination, reducing the process window for module lamination.

[0004] Therefore, there is an urgent need to develop a skin film for photovoltaic modules that can achieve low-temperature welding without radiation crosslinking, thus solving the technical problems existing in the current process route. Summary of the Invention

[0005] To address the problems in the prior art, the present invention aims to provide a skin film for photovoltaic modules and a method for preparing the same.

[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: A skin film for photovoltaic modules, wherein the skin film is located above the photovoltaic cell solder strip and is used to fix the solder strip, comprising a weather-resistant polyolefin resin outer layer, a weather-resistant polyethylene resin inner layer and an excimer ultraviolet curing layer arranged sequentially from the outside to the inside, wherein the excimer ultraviolet curing layer is located on the side close to the solder strip.

[0007] Furthermore, the refractive indices of the three layers—the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer—are 1.48-1.60, with the refractive indices increasing in that order.

[0008] Furthermore, the matrix resin of the weather-resistant polyolefin resin outer layer is selected from one or more of polyethylene, ethylene-α-olefin random copolymer, ethylene-α-olefin block copolymer, and ethylene-acrylate copolymer, and its resin component DSC curve should contain at least one set of melting peaks with a temperature >120°C.

[0009] Furthermore, the matrix resin of the weather-resistant polyethylene resin inner layer is selected from branched crosslinked polymers, specifically from one or more of branched crosslinked polyethylene, branched crosslinked ethylene-α-olefin random copolymers, and branched crosslinked ethylene-α-olefin block copolymers.

[0010] Furthermore, the raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 80-99.6 parts of resin I, 0.1-5 parts of initiator, 0.1-5 parts of monomer I, 0.1-5 parts of comonomer I, and 0.1-2 parts of antioxidant.

[0011] Furthermore, the preparation steps of the branched crosslinked polymer include: Resin I is added to a mixer, followed by monomer I, comonomer I, and antioxidant. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes and allowed to stand for 1-4 hours. An initiator is then added and the mixture is mixed in a low-speed mixer for 2-10 minutes. The mixture is then fed into a twin-screw extruder and extruded and granulated at 150-200°C. After cooling, the branched crosslinked polymer is obtained.

[0012] Furthermore, the matrix resin of the excimer UV-curable layer is selected from polymers crosslinked with aromatic groups, specifically from one or more of the following: polyethylene crosslinked with aromatic groups, ethylene-α-olefin random copolymer crosslinked with aromatic groups, ethylene-α-olefin block copolymer crosslinked with aromatic groups, and ethylene-vinyl acetate copolymer crosslinked with aromatic groups.

[0013] Furthermore, the raw materials for preparing the crosslinked polymer containing aromatic groups include the following components in parts by weight: 80-99.6 parts of resin II, 0.1-5 parts of initiator, 0.1-5 parts of monomer II, 0.1-5 parts of comonomer II, and 0.1-2 parts of antioxidant.

[0014] Furthermore, the preparation steps of the polymer containing aromatic crosslinking groups include: Resin II is added to a mixer, followed by monomer II, comonomer II, and antioxidant. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes, allowed to stand for 1-4 hours, and then an initiator is added. The mixture is then mixed in a low-speed mixer for 2-10 minutes, fed into a twin-screw extruder, and extruded and granulated at 150-200°C. After cooling, a polymer containing aromatic crosslinked groups is obtained.

[0015] This invention also discloses a method for preparing a skin film for photovoltaic modules, comprising the following steps: 1) Prepare the base resins for the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer; 2) The matrix resins of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer and the excimer UV-cured layer obtained in step 1) are respectively compounded with additives to obtain particle mixtures of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer and the excimer UV-cured layer respectively. 3) The particle mixtures of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer obtained in step 2) are fed into a multi-layer co-extrusion extruder to extrude the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer. After cooling and shaping, the excimer UV-cured layer is irradiated with a 254nm excimer UV lamp. After the crosslinking and curing depth is 0.5-3µm, the desired photovoltaic module skin film is obtained.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a skin film for photovoltaic modules and its preparation method. An excimer UV-cured layer is set on the side near the solder strip. Due to the cross-linking curing depth of 0.5-3µm, the overall hardness is not increased, but it can prevent the skin film from flowing and overflowing under the solder strip at the lamination temperature. This solves the problem of microcracks and fragmentation of the battery cells during conventional skin film lamination, and eliminates the problem of air bubbles during lamination. By introducing aromatic groups into the excimer UV-cured layer and branched cross-linked groups into the inner layer of weather-resistant polyethylene resin, a refractive index gradient with increasing from the outer layer of weather-resistant polyolefin resin to the excimer UV-cured layer is formed. This is beneficial for the absorption of weak light by the photovoltaic module, increases the contribution of low-angle sunlight to the power generation of the photovoltaic module during the morning and evening, and improves the daily power generation of the photovoltaic module. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0019] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0020] like Figure 1As shown, the present invention discloses a skin film for photovoltaic modules, which is located above the photovoltaic cell solder strip and plays a role in fixing the solder strip. It includes a weather-resistant polyolefin resin outer layer 1, a weather-resistant polyethylene resin inner layer 2, and an excimer ultraviolet curing layer 3 arranged sequentially from the outside to the inside. The excimer ultraviolet curing layer 3 is located on the side close to the solder strip.

[0021] In some embodiments, the refractive index of the three layers—the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3—is between 1.48 and 1.60, and the refractive index of the three layers increases in that order.

[0022] In some embodiments, the matrix resin of the weather-resistant polyolefin resin outer layer 1 is selected from one or more of polyethylene, ethylene-α-olefin random copolymer, ethylene-α-olefin block copolymer, and ethylene-acrylate copolymer, and its resin component DSC curve should contain at least one set of melting peaks with a temperature >120°C.

[0023] In some embodiments, the matrix resin of the weather-resistant polyethylene resin inner layer 2 is selected from a branched crosslinked polymer, specifically from one or a combination of several of branched crosslinked polyethylene, branched crosslinked ethylene-α-olefin random copolymers, and branched crosslinked ethylene-α-olefin block copolymers.

[0024] In some specific embodiments, the raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 80-99.6 parts of resin I, 0.1-5 parts of initiator, 0.1-5 parts of monomer I, 0.1-5 parts of comonomer I, and 0.1-2 parts of antioxidant.

[0025] In some specific embodiments, the preparation steps of the branched crosslinked polymer include: Resin I is added to a mixer, followed by monomer I, comonomer I, and antioxidant in sequence. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes and allowed to stand for 1-4 hours. Initiator is then added and the mixture is mixed in a low-speed mixer for 2-10 minutes. The mixture is then fed into a twin-screw extruder (screw length-to-diameter ratio > 44:1) and extruded and granulated at 150-200°C. After cooling, the branched crosslinked polymer is obtained.

[0026] This invention improves the crosslinking density and mechanical properties of materials by adding polymers of unsaturated silanes. Compared to directly adding unsaturated silanes, this method offers advantages such as better mixing, reduced agglomeration, fewer material defects, and a lower risk of precipitation.

[0027] In some more specific embodiments, resin I is selected from one or a combination of several of polyethylene, ethylene-α-olefin random copolymers, and ethylene-α-olefin block copolymers.

[0028] In some more specific embodiments, monomer I is selected from one or a combination of several of diethylenetriamine, divinylethylene glycol, and divinyldimethylsilane.

[0029] In some more specific embodiments, comonomer I is a polymer (oligomer, dimer, trimer, or tetramer) of an unsaturated silane, and the unsaturated silane is one or a combination of several of vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and allyltrimethoxysilane.

[0030] In some more specific embodiments, the initiator is one or a combination of several of azobisisobutyronitrile, benzoyl peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0031] In some embodiments, the matrix resin of the excimer UV-curable layer 3 is selected from polymers crosslinked with aromatic groups, specifically from one or more of the following: polyethylene crosslinked with aromatic groups, ethylene-α-olefin random copolymer crosslinked with aromatic groups, ethylene-α-olefin block copolymer crosslinked with aromatic groups, and ethylene-vinyl acetate copolymer crosslinked with aromatic groups.

[0032] In some specific embodiments, the raw materials for preparing the polymer containing aromatic crosslinking groups include the following components in parts by weight: 80-99.6 parts of resin II, 0.1-5 parts of initiator, 0.1-5 parts of monomer II, 0.1-5 parts of comonomer II, and 0.1-2 parts of antioxidant.

[0033] In some specific embodiments, the preparation steps of the polymer containing aromatic crosslinking groups include: Resin II is added to a mixer, followed by monomer II, comonomer II, and antioxidant. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes and allowed to stand for 1-4 hours. An initiator is then added and the mixture is mixed in a low-speed mixer for 2-10 minutes. The mixture is then fed into a twin-screw extruder (screw length-to-diameter ratio > 44:1) and extruded and granulated at 150-200°C. After cooling, a polymer containing crosslinked aromatic groups is obtained.

[0034] In some more specific embodiments, resin II is selected from one or a combination of several of polyethylene, ethylene-α-olefin random copolymer, ethylene-α-olefin block copolymer, and ethylene-vinyl acetate copolymer.

[0035] In some more specific embodiments, monomer II is selected from one or a combination of several of divinylbenzene, styrene, vinyl ethylbenzene, vinyl benzyl chloride, and 4-vinylbiphenyl.

[0036] In some more specific embodiments, comonomer II is a polymer (oligomer, dimer, trimer or tetramer) of an unsaturated silane, and the unsaturated silane is one or a combination of several of vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and allyltrimethoxysilane.

[0037] In some embodiments, the excimer UV-cured layer 3 is obtained by 254 nm UV irradiation, and the depth of its cross-linked cured portion 4 is 0.5-3 µm.

[0038] In some embodiments, the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are prepared by their respective matrix resins and additives.

[0039] In some embodiments, the additive is selected from one or a combination of several of antioxidants, light stabilizers, ultraviolet absorbers, nucleating agents, crosslinking agents, crosslinking aids, and photoinitiators.

[0040] In some specific embodiments, the antioxidant is one or a combination of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0041] In some specific embodiments, the light stabilizer is one or a combination of several of light stabilizer 770, light stabilizer 292, and light stabilizer 622.

[0042] In some specific embodiments, the ultraviolet absorber is one or a combination of several of UV234, UV360, and UV531.

[0043] In some specific embodiments, the crosslinking agent is one or a combination of several of tert-butyl peroxycarbonate-2-ethylhexyl ester (TBEC), tert-butyl peroxycarbonate isopropyl ester, and tert-amyl peroxycarbonate; In some specific embodiments, the crosslinking aid is one or a combination of several of the following: trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTMA), triallyl isocyanate (TAIC), propoxyglycerol triacrylate (GPTA), silane coupling agent (KH570), and silane coupling agent (A171).

[0044] In some specific embodiments, the photoinitiator is one or a combination of several of the following: diaryliodonium salt, triarylsulfonium salt, and iron aromatic salts.

[0045] In some embodiments, the thicknesses of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 10-50µm, 20-80µm, and 10-30µm, respectively.

[0046] This invention also discloses a method for preparing a skin film for photovoltaic modules, comprising the following steps: 1) Prepare the matrix resins for the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3; 2) The matrix resins of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer ultraviolet curing layer 3 obtained in step 1) are respectively compounded with additives to obtain particle mixtures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer ultraviolet curing layer 3. 3) The particle mixture of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 obtained in step 2) is fed into a multi-layer co-extrusion extruder to extrude the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3. After cooling and shaping, the excimer UV-cured layer 3 is irradiated with a 254nm excimer UV lamp until the depth of its cross-linked curing portion 4 reaches 0.5-3µm, thus obtaining the skin film for photovoltaic modules.

[0047] Example 1 like Figure 1 As shown, a skin film for photovoltaic modules is located above the photovoltaic cell solder strip and serves to fix the solder strip. It includes a weather-resistant polyolefin resin outer layer 1, a weather-resistant polyethylene resin inner layer 2, and an excimer ultraviolet curing layer 3 arranged sequentially from the outside to the inside. The excimer ultraviolet curing layer 3 is located on the side close to the solder strip.

[0048] The thicknesses of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 30µm, 50µm, and 20µm, respectively.

[0049] A method for preparing a skin film for photovoltaic modules includes the following steps: 1) The base resin of the weather-resistant polyolefin resin outer layer 1 is polyethylene, 99.5 parts; The matrix resin for preparing the weather-resistant polyethylene inner layer 2: The raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 98.25 parts polyethylene, 0.15 parts benzoyl peroxide, 1 part diethylenetriamine, 0.5 parts vinyltrimethoxysilane trimer, and 0.1 parts antioxidant 1076; The preparation steps of the branched crosslinked polymer include: adding 98.25 parts of polyethylene to a mixer, then adding 1 part of diethylenetriamine, 0.5 parts of vinyltrimethoxysilane trimer, and 0.1 parts of antioxidant 1076 in sequence, mixing in a high-speed mixer for 0.5 min, letting it stand for 1 h, then adding 0.15 parts of benzoyl peroxide, mixing in a low-speed mixer for 2 min, feeding it into a twin-screw extruder (screw length-to-diameter ratio 45:1), extruding and granulating at 150°C, and cooling to obtain the branched crosslinked polymer; The matrix resin for preparing the excimer UV-curable layer 3: The raw materials for preparing the crosslinked polymer containing aromatic groups include the following components in parts by weight: 98.25 parts of resin II (a mixture of block copolymers of polyethylene and ethylene-1-hexene in a weight ratio of 8:2), 0.15 parts of benzoyl peroxide, 1 part of divinylbenzene, 0.5 parts of trimer of vinyltrimethoxysilane, and 0.1 parts of antioxidant 1010; The preparation steps of polymers crosslinked with aromatic groups include: Resin II was added to a mixer, followed by 1 part divinylbenzene, 0.5 parts vinyltrimethoxysilane trimer, and 0.1 parts antioxidant 1010. The mixture was then mixed in a high-speed mixer for 0.5 min and allowed to stand for 1 h. 0.15 parts benzoyl peroxide were then added and mixed in a low-speed mixer for 2 min. The mixture was then fed into a twin-screw extruder (screw length-to-diameter ratio 45:1) and extruded and granulated at 150 °C. After cooling, a polymer containing aromatic crosslinked groups was obtained.

[0050] 2) Add 99.5 parts of the base resin polyethylene of the weather-resistant polyolefin resin outer layer 1 obtained in step 1) to 0.05 parts of antioxidant 1010 and 0.2 parts of light stabilizer 292 into a low-temperature mixer and mix for 30 min. Keep warm at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyolefin resin outer layer 1 for later use. 99.5 parts of the crosslinked polymer of the matrix resin of the weather-resistant polyethylene resin inner layer 2 obtained in step 1) and 0.2 parts of light stabilizer 292 were put into a low mixer and mixed for 30 min. The mixture was kept at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyethylene resin inner layer 2 for later use. 99.35 parts of the matrix resin of the excimer UV-curable layer 3 obtained in step 1) containing aromatic crosslinked polymer, 0.15 parts of diaryliodonium salt, 0.25 parts of triallyl isocyanate TAIC, and 0.25 parts of propoxylated glycerol triacrylate GPTA were added to a low-temperature mixer and mixed for 30 min. The mixture was then kept at 40°C for 12 h to obtain a particle mixture of the excimer UV-curable layer 3 for later use.

[0051] 3) The particle mixtures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 obtained in step 2) are fed into a multi-layer co-extrusion extruder. The processing temperatures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 180℃, 185℃, and 190℃, respectively. The weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are extruded with thicknesses of 30µm, 50µm, and 20µm, respectively. After cooling and shaping by cooling rollers, the excimer UV-cured layer 3 is irradiated with a 254nm excimer UV lamp until the depth of its cross-linked curing portion 4 reaches 1µm, thus obtaining the desired photovoltaic module skin film.

[0052] Example 2 like Figure 1 As shown, a skin film for photovoltaic modules is located above the photovoltaic cell solder strip and serves to fix the solder strip. It includes a weather-resistant polyolefin resin outer layer 1, a weather-resistant polyethylene resin inner layer 2, and an excimer ultraviolet curing layer 3 arranged sequentially from the outside to the inside. The excimer ultraviolet curing layer 3 is located on the side close to the solder strip.

[0053] The thicknesses of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 30µm, 50µm, and 20µm, respectively.

[0054] A method for preparing a skin film for photovoltaic modules includes the following steps: 1) The base resin of the weather-resistant polyolefin resin outer layer 1 is polyethylene, 99.5 parts; The matrix resin for preparing the weather-resistant polyethylene inner layer 2: The raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 98.05 parts of resin I (a mixture of polyethylene and ethylene-1-octene random copolymer in a weight ratio of 7:3), 0.15 parts of benzoyl peroxide, 1.2 parts of divinyldimethylsilane, 0.5 parts of the trimer of vinyltrimethoxysilane, and 0.1 parts of antioxidant 1076; The preparation steps of the branched crosslinked polymer include: adding 98.05 parts of resin I into a mixer, then adding 1.2 parts of divinyldimethylsilane, 0.5 parts of vinyltrimethoxysilane trimer, and 0.1 parts of antioxidant 1076 in sequence, mixing in a high-speed mixer for 0.5 min, letting it stand for 1 h, then adding 0.15 parts of benzoyl peroxide, mixing in a low-speed mixer for 2 min, feeding into a twin-screw extruder (screw length-to-diameter ratio 45:1), extruding and granulating at 150 °C, and cooling to obtain the branched crosslinked polymer; The matrix resin for preparing the excimer UV-curable layer 3: The raw materials for preparing the crosslinked polymer containing aromatic groups include the following components in parts by weight: 98.2 parts of resin II (a mixture of block copolymers of polyethylene and ethylene-1-hexene in a weight ratio of 8:2), 0.2 parts of dicumyl peroxide, 1 part of divinylbenzene, 0.5 parts of vinyltrimethoxysilane trimer, and 0.1 parts of antioxidant 1010; The preparation steps of polymers crosslinked with aromatic groups include: Resin II was added to a mixer, followed by 1 part divinylbenzene, 0.5 parts vinyltrimethoxysilane trimer, and 0.1 parts antioxidant 1010. The mixture was then mixed in a high-speed mixer for 0.5 min and allowed to stand for 1 h. 0.2 parts dicumyl peroxide were then added and the mixture was mixed in a low-speed mixer for 2 min. The mixture was then fed into a twin-screw extruder (screw length-to-diameter ratio 45:1) and extruded and granulated at 150 °C. After cooling, a polymer containing aromatic crosslinked groups was obtained.

[0055] 2) Add 99.5 parts of the base resin polyethylene of the weather-resistant polyolefin resin outer layer 1 obtained in step 1) to 0.05 parts of antioxidant 1010 and 0.2 parts of light stabilizer 292 into a low-temperature mixer and mix for 30 min. Keep warm at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyolefin resin outer layer 1 for later use. 99.5 parts of the crosslinked polymer of the matrix resin of the weather-resistant polyethylene resin inner layer 2 obtained in step 1) and 0.2 parts of light stabilizer 292 were put into a low mixer and mixed for 30 min. The mixture was kept at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyethylene resin inner layer 2 for later use. 99.35 parts of the matrix resin of the excimer UV-curable layer 3 obtained in step 1) containing aromatic crosslinked polymer, 0.15 parts of diaryliodonium salt, 0.25 parts of triallyl isocyanate TAIC, and 0.25 parts of propoxylated glycerol triacrylate GPTA were added to a low-temperature mixer and mixed for 30 min. The mixture was then kept at 40°C for 12 h to obtain a particle mixture of the excimer UV-curable layer 3 for later use.

[0056] 3) The particle mixtures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 obtained in step 2) are fed into a multi-layer co-extrusion extruder. The processing temperatures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 180℃, 185℃, and 190℃, respectively. The weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are extruded with thicknesses of 30µm, 50µm, and 20µm, respectively. After cooling and shaping by cooling rollers, the excimer UV-cured layer 3 is irradiated with a 254nm excimer UV lamp until the depth of its cross-linked curing portion 4 reaches 1µm, thus obtaining the desired photovoltaic module skin film.

[0057] The rest is the same as in Example 1.

[0058] Example 3 like Figure 1 As shown, a skin film for photovoltaic modules is located above the photovoltaic cell solder strip and serves to fix the solder strip. It includes a weather-resistant polyolefin resin outer layer 1, a weather-resistant polyethylene resin inner layer 2, and an excimer ultraviolet curing layer 3 arranged sequentially from the outside to the inside. The excimer ultraviolet curing layer 3 is located on the side close to the solder strip.

[0059] The thicknesses of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 30µm, 50µm, and 20µm, respectively.

[0060] A method for preparing a skin film for photovoltaic modules includes the following steps: 1) The base resin of the weather-resistant polyolefin resin outer layer 1 is polyethylene, 99.5 parts; The matrix resin for preparing the weather-resistant polyethylene inner layer 2: The raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 98.25 parts polyethylene, 0.15 parts benzoyl peroxide, 1 part divinyl glycol, 0.5 parts trimer of vinyltrimethoxysilane, and 0.1 parts antioxidant 1076. The preparation steps of the branched crosslinked polymer include: adding 98.25 parts of polyethylene into a mixer, then adding 1 part of divinyl ethylene glycol, 0.5 parts of vinyltrimethoxysilane trimer, and 0.1 parts of antioxidant 1076 in sequence, mixing in a high-speed mixer for 0.5 min, letting it stand for 1 h, then adding 0.15 parts of benzoyl peroxide, mixing in a low-speed mixer for 2 min, feeding into a twin-screw extruder (screw length-to-diameter ratio 45:1), extruding and granulating at 150°C, and cooling to obtain the branched crosslinked polymer; The matrix resin for preparing the excimer UV-curable layer 3: The raw materials for preparing the crosslinked polymer containing aromatic groups include the following components in parts by weight: 98.25 parts of resin II (a mixture of block copolymers of polyethylene and ethylene-1-butene in a weight ratio of 8:2), 0.15 parts of benzoyl peroxide, 1 part of divinylbenzene, 0.5 parts of trimer of vinyltrimethoxysilane, and 0.1 parts of antioxidant 1010; The preparation steps of polymers crosslinked with aromatic groups include: Resin II was added to a mixer, followed by 1 part divinylbenzene, 0.5 parts vinyltrimethoxysilane trimer, and 0.1 parts antioxidant 1010. The mixture was then mixed in a high-speed mixer for 0.5 min and allowed to stand for 1 h. 0.15 parts benzoyl peroxide were then added and mixed in a low-speed mixer for 2 min. The mixture was then fed into a twin-screw extruder (screw length-to-diameter ratio 45:1) and extruded and granulated at 150 °C. After cooling, a polymer containing aromatic crosslinked groups was obtained.

[0061] 2) Add 99.5 parts of the base resin polyethylene of the weather-resistant polyolefin resin outer layer 1 obtained in step 1) to 0.05 parts of antioxidant 1010 and 0.2 parts of light stabilizer 292 into a low-temperature mixer and mix for 30 min. Keep warm at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyolefin resin outer layer 1 for later use. 99.5 parts of the crosslinked polymer of the matrix resin of the weather-resistant polyethylene resin inner layer 2 obtained in step 1) and 0.2 parts of light stabilizer 292 were put into a low mixer and mixed for 30 min. The mixture was kept at 40℃ for 12 h to obtain a particle mixture of weather-resistant polyethylene resin inner layer 2 for later use. 99.35 parts of the matrix resin of the excimer UV-curable layer 3 obtained in step 1) containing aromatic crosslinked polymer, 0.15 parts of diaryliodonium salt, 0.25 parts of triallyl isocyanate TAIC, and 0.25 parts of propoxylated glycerol triacrylate GPTA were added to a low-temperature mixer and mixed for 30 min. The mixture was then kept at 40°C for 12 h to obtain a particle mixture of the excimer UV-curable layer 3 for later use.

[0062] 3) The particle mixtures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 obtained in step 2) are fed into a multi-layer co-extrusion extruder. The processing temperatures of the weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are 180℃, 185℃, and 190℃, respectively. The weather-resistant polyolefin resin outer layer 1, the weather-resistant polyethylene resin inner layer 2, and the excimer UV-cured layer 3 are extruded with thicknesses of 30µm, 50µm, and 20µm, respectively. After cooling and shaping by cooling rollers, the excimer UV-cured layer 3 is irradiated with a 254nm excimer UV lamp until the depth of its cross-linked curing portion 4 reaches 1µm, thus obtaining the desired photovoltaic module skin film.

[0063] The rest is the same as in Example 1.

[0064] Comparative Example 1 Commercially available skin masks are made from ethylene-vinyl acetate films through irradiation crosslinking.

[0065] Comparative Example 2 The difference between this comparative example and Example 1 is that the matrix resin of the weather-resistant polyethylene resin inner layer 2 in this comparative example is polyethylene instead of the branched crosslinked polymer in Example 1, and it does not undergo branching crosslinking. The rest is the same as in Example 1.

[0066] Comparative Example 3 The difference between this comparative example and Example 1 is that the matrix resin of the excimer UV-curable layer 3 in this comparative example is a mixture of polyethylene and ethylene-1-hexene block copolymers instead of the aromatic crosslinked polymer in Example 1. It does not undergo aromatic crosslinking. The rest is the same as in Example 1.

[0067] Comparative Example 4 The difference between this comparative example and Example 1 is that this comparative example does not use a 254nm excimer ultraviolet lamp to irradiate the excimer ultraviolet curing layer 3, but otherwise it is the same as Example 1.

[0068] The transmittance at 280-380nm and 380-1100nm was measured using a Shimadzu i2600 UV-Vis spectrophotometer.

[0069] By using an ellipsometry to test the refractive index of each layer, when testing is difficult, each thin film material can be prepared separately for testing.

[0070] The lamination process is verified by laying the skin film on top of the battery solder strip during module lamination and laminating according to the normal process. After lamination, observe whether there is any glue overflow (the skin film melts and overflows below the solder strip) and check for microcracks through EL testing.

[0071] The photovoltaic module power was tested using a photovoltaic module IV power tester. The photovoltaic module was placed in the same location and at the same angle, and the power generation was tracked for 7 days, with the average value taken.

[0072] The test results are shown in Table 1.

[0073] Table 1 Based on the data above, we can conclude that: Examples 1-3 have transmittance comparable to Comparative Example 1, but higher transmittance in the 280-380nm range. This indicates that Examples 1-3 improve transmittance in this wavelength range by disrupting the crystallization of ethylene polymers through crosslinking. In terms of refractive index comparison, Examples 1-3 all show an increase in refractive index from 10 layers to 30 layers. Compared with Comparative Example 1, both module power and power generation are improved, indicating that a progressive increase in refractive index can improve the power generation of photovoltaic modules. Comparative Examples 2-3, however, do not show an increase in refractive index gradient at 20 or 30 layers, thus reducing the effect of increasing power generation. The lamination process was verified, and Examples 1-3 all met the lamination process requirements, with no adhesive overflow and no microcracks. Comparative Example 1, due to its radiation crosslinking curing method, had a higher surface hardness, making the cells prone to microcracks during lamination. Comparative Example 4, because the excimer curing layer was not UV cured, experienced adhesive overflow, leading to poor cell soldering and affecting the module's power generation.

[0074] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0075] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A skin film for photovoltaic modules, characterized in that, The photovoltaic module skin film is located above the photovoltaic cell solder strip and is used to fix the solder strip. It includes a weather-resistant polyolefin resin outer layer, a weather-resistant polyethylene resin inner layer and an excimer ultraviolet curing layer arranged sequentially from the outside to the inside. The excimer ultraviolet curing layer is located on the side close to the solder strip.

2. The skin film for photovoltaic modules according to claim 1, characterized in that, The refractive indices of the three layers—the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer—are 1.48-1.60, with the refractive indices increasing in that order.

3. The skin film for photovoltaic modules according to claim 1, characterized in that, The base resin of the weather-resistant polyolefin resin outer layer is selected from one or more of polyethylene, ethylene-α-olefin random copolymer, ethylene-α-olefin block copolymer, and ethylene-acrylate copolymer, and its resin component DSC curve should contain at least one set of melting peaks with a temperature >120℃.

4. The skin film for photovoltaic modules according to claim 1, characterized in that, The matrix resin of the weather-resistant polyethylene resin inner layer is selected from branched crosslinked polymers, specifically from one or more of branched crosslinked polyethylene, branched crosslinked ethylene-α-olefin random copolymers, and branched crosslinked ethylene-α-olefin block copolymers.

5. A skin film for photovoltaic modules according to claim 4, characterized in that, The raw materials for preparing the branched crosslinked polymer include the following components in parts by weight: 80-99.6 parts of resin I, 0.1-5 parts of initiator, 0.1-5 parts of monomer I, 0.1-5 parts of comonomer I, and 0.1-2 parts of antioxidant.

6. A skin film for photovoltaic modules according to claim 5, characterized in that, The preparation steps of the branched and crosslinked polymer include: Resin I is added to a mixer, followed by monomer I, comonomer I, and antioxidant. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes and allowed to stand for 1-4 hours. An initiator is then added and the mixture is mixed in a low-speed mixer for 2-10 minutes. The mixture is then fed into a twin-screw extruder and extruded and granulated at 150-200°C. After cooling, the branched crosslinked polymer is obtained.

7. A skin film for photovoltaic modules according to claim 1, characterized in that, The matrix resin of the excimer UV-curable layer is selected from polymers crosslinked with aromatic groups, specifically from one or more of the following: polyethylene crosslinked with aromatic groups, ethylene-α-olefin random copolymer crosslinked with aromatic groups, ethylene-α-olefin block copolymer crosslinked with aromatic groups, and ethylene-vinyl acetate copolymer crosslinked with aromatic groups.

8. A skin film for photovoltaic modules according to claim 7, characterized in that, The raw materials for preparing the crosslinked polymer containing aromatic groups include the following components in parts by weight: 80-99.6 parts of resin II, 0.1-5 parts of initiator, 0.1-5 parts of monomer II, 0.1-5 parts of comonomer II, and 0.1-2 parts of antioxidant.

9. A skin film for photovoltaic modules according to claim 8, characterized in that, The preparation steps of the polymer crosslinked with aromatic groups include: Resin II is added to a mixer, followed by monomer II, comonomer II, and antioxidant. The mixture is then mixed in a high-speed mixer for 0.5-3 minutes, allowed to stand for 1-4 hours, and then an initiator is added. The mixture is then mixed in a low-speed mixer for 2-10 minutes, fed into a twin-screw extruder, and extruded and granulated at 150-200°C. After cooling, a polymer containing aromatic crosslinked groups is obtained.

10. A method for preparing a skin film for photovoltaic modules according to any one of claims 1-9, characterized in that, Includes the following steps: 1) Prepare the base resins for the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer; 2) The matrix resins of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer and the excimer UV-cured layer obtained in step 1) are respectively compounded with additives to obtain particle mixtures of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer and the excimer UV-cured layer respectively. 3) The particle mixtures of the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer obtained in step 2) are fed into a multi-layer co-extrusion extruder to extrude the weather-resistant polyolefin resin outer layer, the weather-resistant polyethylene resin inner layer, and the excimer UV-cured layer. After cooling and shaping, the excimer UV-cured layer is irradiated with a 254nm excimer UV lamp. After the crosslinking and curing depth is 0.5-3µm, the desired photovoltaic module skin film is obtained.

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