A photovoltaic encapsulant film, a preparation method thereof and a photovoltaic module

Abstract

The present application relates to photovoltaic packaging material technical field, disclose a kind of photovoltaic encapsulant film and its preparation method and photovoltaic module.The adhesive film includes quantitative encapsulation resin matrix, black colorant, heat-conducting filler, infrared reflective thermochromic microcapsule (is with temperature-induced infrared reflectivity reversible change thermochromic spiropyran compound as core, with phase change heat-conducting polymer or copolymer as shell core-shell structure material) and silane coupling agent;Heat-conducting filler includes primary filler (is spherical alumina with surface coating carbon black or black metal oxide, average particle size is 20-45 μm), secondary filler (is average particle size 2-8 μm of insulating heat-conducting material of sheet or two-dimensional appearance) and tertiary filler (is TiN nanoparticle or AlN@C nanoparticle with average particle size <80nm).The adhesive film effectively solves the serious heat absorption, high temperature and other problems of dark photovoltaic module while not affecting dark appearance and adhesive film performance.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic encapsulation materials technology, specifically to a photovoltaic encapsulation film, its preparation method, and a photovoltaic module. Background Technology

[0002] Due to their superior aesthetics and architectural adaptability, the demand for dark-colored, especially black, photovoltaic (PV) modules is growing in the building-integrated photovoltaic (BIPV) and high-end residential markets. However, dark-colored PV encapsulant films or backsheets lead to a significant increase in the absorption rate of the solar spectrum (especially in the infrared band), resulting in a much higher thermal effect than conventional PV modules. This causes the cell operating temperature to become too high, leading to a significant decrease in the photoelectric conversion efficiency of dark-colored PV modules (power loss of PV modules is approximately 0.3-0.5% for every 1°C increase in temperature), and also accelerates material aging, inducing the risk of hot spots, severely restricting the performance and reliability of dark-colored PV modules.

[0003] Current technologies often improve heat dissipation by adding conventional white thermally conductive fillers (such as alumina) to dark encapsulation layers (such as photovoltaic films) (as shown in publication number CN112321933A). However, this method has a fundamental contradiction: a large amount of white filler will severely dilute the color, making it difficult to meet the aesthetic requirements of dark colors, especially black; while the addition of small amounts of white thermally conductive fillers such as alumina will result in limited heat dissipation. In addition, conventional dark photovoltaic films are passive and cannot dynamically adjust in response to temperature changes.

[0004] Therefore, there is an urgent need to develop a photovoltaic encapsulating film that combines a dark appearance with efficient thermal management in order to unlock the application potential of dark photovoltaic modules. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a photovoltaic encapsulation film, its preparation method, and a photovoltaic module.

[0006] Based on this, the present invention discloses a photovoltaic encapsulation film, comprising the following raw materials in parts by weight: 70-95 parts of encapsulation resin matrix, 5-30 parts of black colorant, 25-46 parts of thermally conductive filler, 8-20 parts of infrared reflective thermochromic microcapsules, and 0.5-1.2 parts of silane coupling agent.

[0007] The thermally conductive filler is a multi-level gradient thermally conductive filler system, comprising 18-30 parts of primary filler, 6-12 parts of secondary filler, and 1-4 parts of tertiary filler. The primary filler is spherical alumina coated with carbon black or dark metal oxide (such as ferrous metal oxide) with an average particle size of 20-45 μm. The secondary filler is a sheet-like or two-dimensional insulating thermally conductive material with an average particle size of 2-8 μm. The tertiary filler is titanium nitride nanoparticles with an average particle size of <80 nm or carbon-coated aluminum nitride nanoparticles.

[0008] The infrared reflective thermochromic microcapsule is a core-shell structure material with a thermochromic spiropyran compound whose infrared reflectance changes reversibly with temperature, and a phase change thermally conductive polymer or copolymer as its outer shell.

[0009] The silane coupling agent is at least one of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-methacryloyloxypropyltrimethoxysilane (KH-570) (preferably γ-methacryloyloxypropyltrimethoxysilane, KH-570).

[0010] Preferably, the primary filler is Al2O3@C or Al2O3@Fe3O4 with an average particle size of 20-45 μm. This gives the low-cost, high-thermal-conductivity spherical alumina a dark appearance, allowing it to blend into dark film systems without creating visual clashes, while maintaining its thermal conductivity.

[0011] Al2O3@C (carbon black-coated alumina) is prepared by modifying the surface of spherical alumina with a silane coupling agent to introduce organic functional groups and enhance its affinity with carbon black nanoparticles. Then, through controlled adsorption in a liquid phase environment, the carbon black nanoparticles uniformly coat the spherical alumina. Subsequent heat treatment removes residual organic matter and stabilizes the structure, yielding a uniform dark gray to black composite powder (Al2O3@C). The preparation process of Al2O3@C includes:

[0012] S11. Raw material preparation:

[0013] Spherical alumina (α phase, D50 = 10-35 μm): 100 parts by weight;

[0014] Carbon black nanoparticles (particle size <50nm, such as high pigment carbon black C111 provided by Tianjin Baochi Chemical Technology Co., Ltd.): 3-8 parts by weight;

[0015] Silane coupling agent (such as KH-570 or KH-550; CAS number of KH-550 is 919-30-2): 0.5-1.5 parts by weight;

[0016] Anhydrous ethanol: used as a solvent;

[0017] Deionized water, etc.

[0018] S12. Pretreatment and dispersion: Place the spherical alumina in a high-speed mixer and preheat to 100±5℃; dilute the silane coupling agent with 5-10 times its mass of anhydrous ethanol, and slowly add it to the stirred spherical alumina in the form of spray, and modify it for 15-20 minutes to activate the surface of the spherical alumina.

[0019] S13. Preparation of carbon black dispersion: Carbon black nanoparticles are added to a water-ethanol mixed solution containing a dispersant (such as polyethylene glycol 400, the amount of which is 1-2% of the mass of carbon black nanoparticles) (the amount of which is 5-10% of the mass concentration of carbon black nanoparticles, preferably the mass ratio of water to ethanol is 7:3), and treated with an ultrasonic cell disruptor for 20-30 minutes to form a uniform and stable carbon black suspension.

[0020] S14. Liquid phase coating: Transfer the activated spherical alumina to a reactor equipped with heating and stirring, add deionized water (60-80% of the mass of the spherical alumina) to form a slurry; control the temperature to 60-70℃, and under continuous stirring, slowly drip the carbon black suspension into the slurry, with the dripping time controlled at 1-2 hours.

[0021] S15. Adsorption and fixation: After the addition is complete, adjust the pH to weakly acidic (e.g., pH≈5), and continue to keep warm and stir for 2-3 hours so that the carbon black nanoparticles can be uniformly attached to the outer surface of the spherical alumina through electrostatic adsorption and the action of the silane coupling agent on the surface of the spherical alumina.

[0022] S16. Drying and heat treatment: After filtering and separating the solid, wash it several times with ethanol, and dry it in a forced-air drying oven at 100-110℃ for 10-12 hours. Then, under the protection of nitrogen or argon, calcine it at 450-550℃ for 1-2 hours to make the carbon black layer bond more firmly with the surface of the spherical alumina and form a stable coating layer, thus obtaining Al2O3@C.

[0023] Al2O3@Fe3O4 (Fe3O4-coated alumina) is prepared by co-precipitation to generate Fe3O4 nanocrystals in situ on the surface of spherical alumina. A hydrothermal process then allows the Fe3O4 nanocrystals to grow and form a continuous, highly crystalline coating layer. The Fe3O4 itself is black and magnetic, which is beneficial for controlling the dispersion stability of subsequent fillers in the film. The preparation process of Al2O3@Fe3O4 includes:

[0024] S21. Raw material preparation:

[0025] Spherical alumina (α phase, D50 = 10-35 μm): 100 parts by weight;

[0026] Ferric chloride hexahydrate (FeCl3·6H2O): 5-15 parts by weight (adjust according to coating thickness);

[0027] Ferrous sulfate heptahydrate (FeSO4·7H2O): according to Fe³ + with Fe² + Weigh out in a molar ratio of 2:1;

[0028] Ammonia solution (25-28% by mass): used to adjust pH;

[0029] Surfactant (such as sodium citrate): 1-3 parts by weight.

[0030] S22. Alumina dispersion: Disperse spherical alumina in deoxygenated deionized water (the amount of which is 3-4 times the mass of the spherical alumina) to form a uniform slurry, add surfactant, and ultrasonically disperse for 20-30 minutes to obtain alumina slurry.

[0031] S23. Preparation of iron salt solution: Dissolve FeCl3·6H2O and FeSO4·7H2O in another portion of deoxygenated deionized water (controlling the total concentration of iron salt to 0.2-0.3 mol / L) in proportion to obtain a mixed iron salt solution.

[0032] S24. Co-precipitation Coating: Under nitrogen protection and vigorous stirring (stirring speed 800-1200 rpm), the iron salt mixed solution is slowly added to the alumina slurry. The mixture is heated in a water bath to 60-70℃, and ammonia is slowly added dropwise to maintain the pH of the system between 9 and 10. During this process, Fe³⁺… + and Fe² + Fe3O4 precursor is generated by co-precipitation on the surface of spherical alumina, thus obtaining the mixed slurry.

[0033] S25, Hydrothermal: The above mixed slurry is transferred to a hydrothermal reactor and reacted at 180-220℃ for 6-12 hours. The high temperature and high pressure (1.5-2MPa) environment promotes the better growth and crystallization of Fe3O4 crystals on the surface of spherical alumina, forming a dense and firm magnetic black coating layer.

[0034] S26. Post-processing: After the reaction is complete, the product is cooled naturally, separated with the aid of a magnet, and repeatedly washed with deionized water and ethanol until neutral. It is then dried in a vacuum drying oven at 70-80℃ to obtain Al2O3@Fe3O4.

[0035] Preferably, the insulating and thermally conductive material includes, but is not limited to, at least one of the following: sheet-like hexagonal boron nitride with high thermal conductivity, sheet-like aluminum nitride, mica sheet coated with boron nitride, mica sheet coated with aluminum nitride, and fluorinated graphene.

[0036] More preferably, the secondary filler is a sheet-like hexagonal boron nitride with an average particle size of 2-8 μm or a dark mica sheet (such as a black mica sheet) with a surface coated with nano-boron nitride (here, nano-boron nitride is not sheet-like hexagonal boron nitride, but ordinary nano-sized boron nitride).

[0037] Among them, dark mica sheets coated with nano-boron nitride are a low-cost alternative filler for hBN that combines high thermal conductivity bridging function with a dark appearance. They are produced by chemical vapor deposition (CVD) using a gaseous boron source precursor on a high-temperature substrate (mica sheet) surface, forming a solid film (nano-hBN layer). The perfect sheet-like structure of the mica sheet provides an excellent template for the heteroepitaxial growth of nano-hBN. The formed nano-hBN layer inherits its high in-plane thermal conductivity and insulation. The dark mica sheet substrate ensures the overall dark color of the material, while the surface nano-hBN layer provides crucial bridging and thermal conductivity. This method realizes the design of a composite material with low-cost dark mica sheets as the core and high-performance nano-hBN grafted onto the surface. The preparation process of this dark mica sheet coated with nano-boron nitride includes:

[0038] S31. Raw material preparation:

[0039] Dark mica flakes (particle size D50=1-7μm, aspect ratio>30, select natural black mica flakes or dark-dyed white mica flakes): 100 parts by weight;

[0040] Boron source precursor: borane-ammonia complex (NH3BH3) or boron trichloride (BCl3, CAS No. 10294-34-5): for example, borane-ammonia complex in 2.0-3.5 parts by weight;

[0041] Nitrogen source: ammonia (NH3) or nitrogen (N2, or as a carrier gas if a nitrogen-boron source is used, CAS No. 7727-37-9).

[0042] Carrier gas / protective gas: High-purity (≥99.999%) argon (Ar).

[0043] S32. Mica sheet pretreatment: Soak and clean the dark mica sheets in dilute hydrochloric acid (mass concentration 5-15%) to remove surface impurities, then wash with deionized water, dry at 100-120℃, and perform plasma treatment to increase surface active sites, thus obtaining pretreated dark mica sheets.

[0044] S33. The pretreated dark mica sheets are laid flat in the quartz boat of the CVD tube furnace. After the system is sealed, it is repeatedly flushed with argon gas to remove air.

[0045] S34, Deposition process:

[0046] Taking borane-ammonia complex as an example: 2.0-3.5 parts by weight of solid borane-ammonia complex are placed in the low-temperature evaporation zone upstream of the tubular furnace, with the temperature set at 80-100℃. The reaction zone of the tubular furnace is heated to 900-1100℃ (optimally 1000℃), and argon gas is introduced as a carrier gas to carry the evaporated borane-ammonia complex vapor (gas-phase boron source precursor) to the high-temperature reaction zone, where it contacts the surface of dark mica sheets. Simultaneously, ammonia gas (NH3) is continuously introduced as a supplementary nitrogen source and reaction gas. At the high temperature in the reaction zone, the gas-phase boron source precursor decomposes and reacts on the surface of the dark mica sheets, depositing a nano-hexagonal boron nitride (hBN) layer. The deposition time is typically 30-120 minutes to control the thickness of the nano-boron nitride layer.

[0047] S35. Cooling and Collection: After the reaction is completed, the product is naturally cooled to room temperature under argon protection. The product is then removed, and a dark mica composite material with a uniformly coated layer of nano-sized hBN is obtained, which is a dark mica sheet with nano-sized boron nitride on the surface.

[0048] The tertiary filler is a dark-colored nanofiller, selected from titanium nitride (TiN) nanoparticles or carbon-coated aluminum nitride (AlN@C) nanoparticles. This achieves the goal of filling the gaps between micron-sized fillers with a dark-colored nanofiller without introducing color clashes. The preparation process of the titanium nitride (TiN) nanoparticles includes:

[0049] S41. Raw material preparation:

[0050] Titanium dioxide nanopowder (TiO2 nanopowder, anatase type, <50nm): 100 parts by weight;

[0051] Magnesium powder (Mg powder, 200-300 mesh): 150-180 parts by weight (excess);

[0052] MgCl2-NaCl mixed molten salt (molar ratio 1:4): 300-400 parts by weight.

[0053] S42. Mixing: Thoroughly mix TiO2 nanopowder, Mg powder and MgCl2-NaCl mixed molten salt in a mortar or mixer to obtain a mixture.

[0054] S43. Reduction Nitriding Reaction: The mixture is placed in an alumina crucible and then placed in a tube furnace. Under a flowing atmosphere of high-purity (≥99.999%) nitrogen or ammonia (N2 / NH3 mixture), the temperature is increased to 900-1000℃ at a rate of 10℃ / min and held for 2-4 hours. During this process, the mixed molten salt (MgCl2-NaCl) melts to form a liquid phase medium (eutectic point approximately 450℃). The liquid phase medium accelerates the diffusion of Mg and the reduction of TiO2. The reduced Ti reacts with nitrogen dissolved in the mixed molten salt to form TiN. Reaction Mechanism: TiO2 dissolves in the mixed molten salt → Mg is reduced to form Ti → Ti combines with N to form TiN (dissolution-precipitation mechanism).

[0055] S44. Purification: After the reaction is complete, cool to room temperature, crush the product block, soak and stir in dilute hydrochloric acid or dilute acetic acid (mass concentration 5-15%) for 2-4 hours to dissolve excess Mg, by-product MgO and molten salt (MgCl2 and NaCl are both soluble in water).

[0056] S45. Post-treatment: Wash repeatedly with deionized water and ethanol until neutral, and dry under vacuum at 60-80℃ to obtain dark gray to black TiN nanoparticles.

[0057] The preparation principle of titanium nitride (TiN) nanoparticles: This method is based on molten salt-assisted magnesothermic reduction, using TiO2 nanoparticles as the titanium source and magnesium powder as the reducing agent. The reaction is carried out in a MgCl2-NaCl mixed molten salt medium. MgCl2 and NaCl (molar ratio 1:4) form a eutectic liquid phase at around 450℃, providing a fluid environment for the reaction. At a high temperature of 800-1000℃, the molten salt liquid phase greatly promotes the diffusion and mass transfer of substances: TiO2 partially dissolves in the molten salt, and magnesium powder reduces the dissolved titanium species to form Ti. Simultaneously, flowing nitrogen dissolves in the molten salt and reacts with Ti to form TiN. Finally, TiN nanocrystals are formed through a "dissolution-precipitation" mechanism. The molten salt medium not only lowers the reaction temperature (200-400℃ lower than traditional solid-state reactions) but also prevents product agglomeration, ensuring the uniformity of TiN nanoparticles. After the reaction is complete, the byproduct MgO and excess Mg are dissolved in dilute hydrochloric acid or dilute acetic acid, while the molten salts (MgCl2, NaCl) are dissolved in water and washed away, finally yielding high-purity TiN nanoparticles.

[0058] In this process, carbon-coated aluminum nitride (AlN@C) nanoparticles are adsorbed onto the surface of AlN nanoparticles in the liquid phase to form a uniform organic carbon precursor, which is then transformed into a continuous amorphous carbon shell through controlled pyrolysis. This carbon shell provides a dark appearance and improves the interfacial compatibility between AlN and the polymer matrix, potentially helping to reduce interfacial thermal resistance and, to some extent, isolating AlN from moisture in the environment, thus improving its stability. The preparation process of AlN@C nanoparticles includes:

[0059] S51. Raw material preparation:

[0060] Aluminum nitride nanoparticles (AlN nanoparticles, <60nm): 100 parts by weight;

[0061] Carbon source precursor: at least one of glucose, phenolic resin (CAS No. 9003-35-4), and polyvinylpyrrolidone (CAS No. 9003-39-8): 10-30 parts by weight;

[0062] Solvent: Deionized water or ethanol.

[0063] S52, AlN dispersion: AlN nanoparticles are dispersed in a solvent (the mass ratio of AlN to solvent is 1:15 to 1:25), and ultrasonic treatment is performed to form a stable suspension (the solid content of the suspension is 4-6%).

[0064] S53. Carbon source introduction and adsorption: Add a carbon source (such as glucose aqueous solution), stir continuously, and evaporate the solvent at a certain temperature (such as 80-90℃) to make the carbon source precursor uniformly adsorbed and coated on the surface of AlN nanoparticles.

[0065] S54. Pre-carbonization: The coated AlN nanoparticles are subjected to pre-oxidative stabilization treatment in air at 200-300℃ (for polymer carbon sources), or the next step is carried out directly in an inert atmosphere.

[0066] S55. High-temperature carbonization: The coated AlN nanoparticles are placed in a tube furnace and heated to 600-800℃ at a rate of 5-10℃ / min under argon or nitrogen protection. The temperature is maintained for 1-2 hours. During this process, the carbon source precursor is pyrolyzed to form an amorphous carbon layer, which is uniformly coated on the surface of the AlN nanoparticles.

[0067] S56. Cooling: Cool to room temperature under a protective atmosphere to obtain black or dark gray AlN@C nanoparticles (which are core-shell structured nanocomposite powders).

[0068] Preferably, the infrared-reflective thermochromic microcapsules have an average particle size of 4-18 μm, a shell thickness of 0.5-3 μm, a temperature response threshold of 58-65°C, and a shell-to-core mass ratio of 4-4.5:1. The core is 1-alkyl-3,3-dimethylindoline-6'-nitrospirobenzopyran, wherein the alkyl group is ethyl and / or propyl. The shell is at least one of aliphatic polyester, polyether, paraffin-polymer composite material, or copolymer thereof, with a melting point or glass transition temperature of 50-70°C. When the temperature exceeds its response threshold, the infrared-reflective thermochromic microcapsules exhibit a significant increase in reflectivity to near-infrared light (780-1100 nm) to maintain the film's dark visual appearance.

[0069] More preferably, the infrared reflective thermochromic microcapsules are prepared by in-situ free radical polymerization microencapsulation reaction at the interface; the core of the infrared reflective thermochromic microcapsules is 1-ethyl-3,3-dimethylindoline-6'-nitrospirobenzopyran, and its shell is a composite material of n-tetracosane and LDPE; the mass ratio of n-tetracosane to LDPE in the shell is 3-5:1.

[0070] Among them, the infrared reflective thermochromic microcapsules are core-shell structure materials with a thermochromic spiropyran compound (1-alkyl-3,3-dimethylindoline-6'-nitrospirobenzopyran, wherein the alkyl group is ethyl or propyl, or a mixture of two or more thereof) as the core and an aliphatic polyester, polyether, paraffin-polymer composite material or copolymer thereof with a melting point or glass transition temperature in the range of 50-70℃ as the outer shell. The phase transition temperature of the outer shell matches the color change temperature of the thermochromic spiropyran compound. The preparation process of the infrared reflective thermochromic microcapsules includes:

[0071] S61. Raw material preparation:

[0072] Oil phase composition:

[0073] Core material: thermochromic spiropyran compound (color change temperature 60±2℃), 10-15 parts (parts by weight, the same below);

[0074] The shell material includes the following components:

[0075] Tetracosane (melting point 50.9℃, phase change paraffin): 15-25 parts;

[0076] Low-density polyethylene (LDPE, MI=20-25g / 10min): 5-6 parts;

[0077] Styrene (monomer): 15-20 parts;

[0078] Divinylbenzene (crosslinking agent, DVB): 2-4 parts;

[0079] Benzoyl peroxide (BPO, oil-soluble initiator): 0.3-1 part;

[0080] Toluene (solvent): 30-50 parts.

[0081] Aqueous phase composition:

[0082] Deionized water: 200-300 parts;

[0083] Polyvinyl alcohol (PVA-1788, film-forming agent / emulsifier): 2.5-4 parts;

[0084] Sodium dodecylbenzenesulfonate (SDBS, emulsifier): 0.5-1 part;

[0085] Sodium chloride (electrolyte, used to adjust the density and stability of the aqueous phase): 3-5 parts.

[0086] S62. Oil phase preparation: In a water bath at 40-50℃, mix n-tetracosane, LDPE and toluene, and stir until LDPE is completely dissolved to form a homogeneous and transparent mixed solution; after the mixed solution is cooled to 40℃, add the thermochromic spiropyran compound, styrene, divinylbenzene and benzoyl peroxide (BPO) in sequence, and continue stirring until all components are completely dissolved to obtain a homogeneous oil phase mixture.

[0087] S63. Aqueous phase preparation: PVA is added to deionized water at 80-90℃ and stirred until completely dissolved. After cooling to 40-50℃, SDBS and sodium chloride are added and stirred until dissolved evenly to obtain a clear aqueous phase.

[0088] S64. Emulsification process: Pour the aqueous phase into a reactor equipped with mechanical stirring and a constant temperature water bath, maintain the temperature at 40-50℃, and slowly add the oil phase mixture dropwise to the aqueous phase under medium-speed stirring at 400-700 rpm. After the addition is complete, increase the stirring speed to 3000-3500 rpm and perform high-speed shear emulsification for 20-30 minutes to form a uniform and stable oil-in-water (O / W) emulsion with droplet size controlled at 5-20 μm.

[0089] S65. In-situ polymerization reaction: After emulsification, the temperature of the reaction system is slowly raised to 75±2℃. At this temperature, the system is continuously stirred at a speed of 250-300 rpm for 6-8 hours to carry out free radical polymerization. During the reaction, styrene and divinylbenzene copolymerize at the oil-water interface to form a cross-linked polystyrene network structure. At the same time, the molten phase change paraffin (n-tetracosane) and LDPE are locked in the polystyrene network structure to form a composite shell to encapsulate the core material (thermochromic spiropyran compound).

[0090] S66. Post-processing: After the reaction is complete, allow the product to cool naturally to room temperature. Filter the product and wash it repeatedly with warm water (40-50℃), ethanol, and deionized water 3-5 times in sequence to remove unreacted monomers, emulsifiers, and electrolytes. Place the filter cake in a vacuum drying oven at 35-40℃ and dry it for 20-24 hours to avoid excessive temperature causing phase change in the core or shell material. After sieving (200 mesh), you will obtain free-flowing white or light yellow powder microcapsules (i.e., infrared reflective thermochromic microcapsules).

[0091] Phase change paraffin (n-tetracosane) melts at 51°C, but is confined within the polymer network and cannot flow macroscopically. When the temperature reaches the thermochromic temperature (e.g., 60°C), two simultaneous responses are triggered: (1) Optical response: The core of the thermochromic spiropyran compound undergoes reversible molecular isomerization, changing its color from dark (e.g., black or dark blue, high light absorption state) to light or colorless (high reflectivity state). This directly increases the reflectivity of the film to incident sunlight (especially near-infrared light that generates more heat), reduces the light energy absorbed by the solar cell and the film itself, and suppresses heat generation from the source; (2) Thermal response: LDPE softens (glass transition and partial melting), and in synergy with the molten phase change paraffin, significantly improves the overall thermal conductivity of the composite shell and improves its interfacial contact with the thermally conductive filler. The polystyrene network ensures that the infrared reflective thermochromic microcapsules maintain structural integrity after the phase change. The synergistic improvement in light and heat performance creates a dual suppression effect on the temperature rise of photovoltaic modules, effectively controlling the operating temperature of the cells within an optimal range. When the temperature drops below the threshold, the color and shell phase of the infrared reflective thermochromic microcapsules return to their original state, awaiting the next response. This response mechanism is dynamic, reversible, and adaptive.

[0092] Preferably, the encapsulating resin matrix includes, but is not limited to, at least one of EVA, POE, and PVB.

[0093] Preferably, the black colorant is carbon black masterbatch.

[0094] Preferably, the photovoltaic encapsulating film further includes the following raw materials in parts by weight: 0.7-1.2 parts of crosslinking agent and 0.5-1.5 parts of stabilizer.

[0095] The crosslinking agent is at least one of bis-tert-butylperoxyisopropylbenzene (BIPB), tert-butyl peroxide-2-ethylhexyl carbonate (TBEC), and tert-amyl peroxide-2-ethylhexyl carbonate (TAEC) (preferably tert-butyl peroxide-2-ethylhexyl carbonate, TBEC).

[0096] The stabilizers include ultraviolet absorbers (such as UV-531, UV-234, etc.) and / or light stabilizers (such as Tinuvin 783, Tinuvin 791, etc.).

[0097] Therefore, the photovoltaic encapsulation film of the present invention forms a spatially complementary structure of microspheres-microsheets-nanodots by controlling the particle size, morphology and ratio of the three-level fillers: spherical alumina with black coating of carbon black or black metal oxide on the surface constitutes a low-cost, continuously thermally conductive dark-colored skeleton filler (i.e., primary filler); sheet-like or two-dimensional insulating thermally conductive materials serve as efficient bridging fillers (i.e., secondary fillers), establishing rapid thermal conduction channels in the gaps between the primary fillers; the remaining microscopic voids are filled with dark-colored, nano-sized compatible tertiary fillers (AlN nanoparticles with an average particle size <80nm or carbon-coated aluminum nitride nanoparticles), significantly reducing the interfacial thermal resistance between fillers and between fillers and the matrix, forming a multi-level gradient thermally conductive filler system. This maximizes the construction of a thermally conductive network with a relatively low total amount of conductive filler, and minimizes the impact on the target color of the encapsulation film by treating the fillers themselves with a dark color.

[0098] Moreover, the photovoltaic encapsulation film of the present invention also possesses a novel thermochromic system (i.e., based on a multi-level gradient thermally conductive filler system, it is also equipped with infrared reflective thermochromic microcapsules). When the temperature exceeds the threshold, a phase change occurs inside the infrared reflective thermochromic microcapsules, accompanied by microstructural reorganization, resulting in a sharp increase in its reflectivity or backscattering rate to near-infrared and mid-infrared light. Thus, without significantly changing the color in the visible light region (maintaining dark vision), it greatly reduces the absorption of solar heat. At the same time, the solid-liquid phase change of the polymer or copolymer of the outer shell of the infrared reflective thermochromic microcapsules occurs simultaneously, significantly improving the interfacial thermal conductivity and forming a dual response of reducing heat absorption and enhancing heat dissipation. This response is a reversible process, and the initial state is restored when the temperature drops, realizing dynamic and adaptive closed-loop regulation of the photovoltaic module temperature.

[0099] This invention also discloses a method for preparing a photovoltaic encapsulating film, comprising:

[0100] Step 1: Preparation of thermally conductive filler premix: Coupling treatment is performed on the primary and secondary fillers; all the tertiary fillers are mixed evenly with some of the coupled secondary fillers, and then all the coupled primary fillers and the remaining coupled secondary fillers are added and mixed again to obtain the thermally conductive filler premix.

[0101] Step 2: After mixing the encapsulating resin matrix with the black colorant, add the thermally conductive filler premix, infrared reflective thermochromic microcapsules and silane coupling agent, mix, and then cast and extrude to obtain the photovoltaic encapsulating film.

[0102] Preferably, step one specifically includes: preheating the primary and secondary packings to 100-110°C in a high-speed mixer, spraying an anhydrous ethanol solution containing a silane coupling agent (such as KH-570) for coupling treatment (for example, preparing a coupling agent solution by mixing KH-570 with anhydrous ethanol and deionized water at a mass ratio of 1:10-20:1, wherein the amount of KH-570 is 1.0-1.5% of the total mass of the primary and secondary packings); mixing all the tertiary packings with a portion of the coupled secondary packings (such as 30-50% coupled secondary packings) in a three-dimensional mixer for 60-90 minutes to achieve the adhesion of nanoparticles to micron-sized sheets; then adding all the coupled primary packings and the remaining coupled secondary packings, and continuing to mix for more than 90 minutes to obtain a thermally conductive packing premix with uniform color and reasonable gradation.

[0103] Preferably, step two specifically includes: mixing the encapsulating resin matrix, black colorant, and stabilizer uniformly in a mixer at 85-95°C, maintaining the temperature, adding thermally conductive filler premix, infrared reflective thermochromic microcapsules, and silane coupling agent, and mixing in a vacuum environment for 20-30 minutes to ensure full dispersion; cooling the material to below 70°C, then adding a crosslinking agent and mixing quickly (<5 minutes); the material is then formed into a uniform black film with a thickness of 0.4-0.7 mm through a cold casting extruder, and wound up for later use to obtain the photovoltaic encapsulating film.

[0104] The present invention also discloses a photovoltaic module, comprising a photovoltaic front panel, a first encapsulating film, a photovoltaic cell, a second encapsulating film, and a photovoltaic back panel stacked sequentially; the second encapsulating film is a photovoltaic encapsulating film as described above in the present invention.

[0105] Compared with the prior art, the present invention has at least the following beneficial effects:

[0106] The photovoltaic encapsulation film of this invention, through the darkening of the thermally conductive filler (e.g., black coating) and optimization of its spatial gradation (e.g., the complementary spatial structure of primary, secondary, and tertiary fillers forming microspheres-microsheets-nanodots), constructs a highly efficient thermally conductive network with low filler content and low cost. Furthermore, by combining it with infrared-reflective thermochromic microcapsules, the synergistic effect of the infrared high reflectivity state triggered by the microcapsules at a threshold temperature and the phase transition of its outer shell allows for dynamic reduction of photothermal absorption and enhanced heat dissipation without altering the dark appearance of the photovoltaic module (compatible with dark backgrounds) and ensuring the peel strength and other properties of the encapsulation film. This enables adaptive and reversible temperature control of the photovoltaic module. Therefore, the photovoltaic encapsulation film of this invention effectively suppresses the temperature rise of dark-colored photovoltaic modules, effectively solving the problems of severe heat absorption and high operating temperature in dark-colored photovoltaic modules, contributing to improved power generation efficiency and reliability, and showing broad market application prospects. Detailed Implementation

[0107] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0108] Example 1

[0109] The photovoltaic encapsulation film of this embodiment comprises the following raw materials by weight:

[0110] Encapsulating resin matrix: EVA, 80 parts;

[0111] Carbon black masterbatch (Polydi Functional Materials Research Institute, grade PA-10118-A1): 20 parts;

[0112] Crosslinking agent: tert-butyl peroxide-2-ethylhexyl carbonate (TBEC), 0.9 parts;

[0113] Silane coupling agent: γ-methacryloyloxypropyltrimethoxysilane (KH-570), 0.7 parts;

[0114] Primary filler (dark skeleton filler): 20 parts of spherical alumina (Al2O3@C) with an average particle size of 30μm and a dark carbon black coating on the surface;

[0115] Secondary packing material (high-efficiency bridging packing material): 8 parts of plate-shaped hexagonal boron nitride (plate-shaped hBN) with an average particle size of 5μm;

[0116] Tertiary filler (nano-interface filler): 2 parts of titanium nitride (TiN) nanoparticles with an average particle size of <80nm;

[0117] Infrared reflective thermochromic microcapsules: average particle size 12 μm, response threshold 60 °C, core is 1-ethyl-3,3-dimethylindoline-6'-nitrospirobenzopyran, shell is a composite material of n-tetracosane and LDPE (shell thickness is 1.5 μm), 15 parts;

[0118] Stabilizers: UV absorber (UV-531) and light stabilizer (Tinuvin783), 0.7 parts each.

[0119] The preparation process of Al2O3@C (carbon black coated alumina) specifically includes:

[0120] S11. Raw material preparation:

[0121] Spherical alumina (α phase, D50=25μm, spherical alumina powder from Jiangsu Shengtian New Materials Co., Ltd.): 100 parts by weight;

[0122] Carbon black nanoparticles (particle size <50nm, high pigment carbon black grade C111 provided by Tianjin Baochi Chemical Technology Co., Ltd.): 5 parts by weight;

[0123] Silane coupling agent (KH-570, CAS No. 2530-85-0): 1.5 parts by weight;

[0124] Anhydrous ethanol: (as a solvent, CAS No. 64-17-5);

[0125] Deionized water.

[0126] S12. Pretreatment and dispersion: Place the spherical alumina in a high-speed mixer and preheat to 100°C; dilute the silane coupling agent with 10 times its mass of anhydrous ethanol and slowly add it to the stirred spherical alumina in the form of a spray, and modify it for 20 minutes to activate the surface of the spherical alumina.

[0127] S13. Preparation of carbon black dispersion: Carbon black nanoparticles are added to a water-ethanol mixed solution containing a dispersant (polyethylene glycol 400, the amount of which is 2% of the mass of carbon black nanoparticles) (the amount of which is 10% of the mass concentration of carbon black nanoparticles, and the mass ratio of water to ethanol is 7:3), and treated with an ultrasonic cell disruptor for 30 minutes to form a uniform and stable carbon black suspension.

[0128] S14. Liquid phase coating: The activated spherical alumina is transferred to a reactor equipped with heating and stirring. Deionized water (80% of the mass of the spherical alumina) is added to form a slurry. The temperature is controlled to 60°C. Under continuous stirring, the carbon black suspension is slowly dripped into the slurry. The dripping time is controlled to be 1.5 hours.

[0129] S15. Adsorption and fixation: After the addition is complete, adjust the pH to weakly acidic (pH≈5), and continue to keep warm and stir for 3 hours so that the carbon black nanoparticles can be uniformly attached to the outer surface of the spherical alumina through electrostatic adsorption and the action of the silane coupling agent on the surface of the spherical alumina.

[0130] S16. Drying and heat treatment: After filtering and separating the solid, wash it several times with ethanol, dry it in a 110℃ forced-air drying oven for 12 hours, and then calcine it at 500℃ for 1.5 hours under nitrogen protection to make the carbon black layer bond more firmly with the surface of the spherical alumina and form a stable coating layer, thus obtaining Al2O3@C.

[0131] The preparation process of titanium nitride (TiN) nanoparticles specifically includes:

[0132] S41. Raw material preparation:

[0133] Titanium dioxide nanopowder (TiO2 nanopowder, anatase type, <50nm, nano titanium dioxide (anatase) from Guangzhou Hongwu Materials Technology Co., Ltd.): 100 parts by weight;

[0134] Magnesium powder (Mg powder, 300 mesh, CAS No. 7439-95-4): 180 parts by weight;

[0135] MgCl2-NaCl mixed molten salt (molar ratio 1:4; CAS number of MgCl2 is 7786-30-3, CAS number of NaCl is 7647-14-5): 400 parts by weight.

[0136] S42. Mixing: TiO2 nanoparticles, Mg powder and MgCl2-NaCl mixed molten salt are thoroughly mixed in a mixer to obtain a mixture.

[0137] S43. Reduction nitriding reaction: Place the mixture in an alumina crucible, put it in a tube furnace, and heat it to 1000℃ at a rate of 10℃ / min under a flowing high-purity (purity ≥99.999%) nitrogen (N2) atmosphere, and hold it at that temperature for 4 hours.

[0138] S44. Impurity Removal: After the reaction is complete, cool to room temperature, crush the product block, soak it in dilute hydrochloric acid (10% mass concentration) and stir for 2 hours to dissolve excess Mg, by-product MgO and molten salt (MgCl2 and NaCl are both soluble in water).

[0139] S45. Post-treatment: Wash repeatedly with deionized water and ethanol until neutral, and dry under vacuum at 60℃ to obtain dark gray to black TiN nanoparticles.

[0140] The preparation process of infrared reflective thermochromic microcapsules specifically includes:

[0141] S61. Raw material preparation:

[0142] Oil phase composition:

[0143] Core material (core): 10 parts (parts by weight, the same below) of 1-ethyl-3,3-dimethylindoline-6'-nitrospirobenzopyran (the preparation method is referred to "Synthesis and Photochromic Properties of Indoline Spiropyran" DOI:10.3969 / j.issn.1006-3536.2010.08.019, and the color change temperature is 60℃).

[0144] The shell material includes the following components:

[0145] Tetracosane (melting point 50.9℃, phase change paraffin, provided by Hubei Wande Chemical Co., Ltd.): 20 parts;

[0146] Low-density polyethylene (LDPE, MI=25g / 10min, provided by Sinopec Yanshan Petrochemical, grade LD400): 5 parts;

[0147] Styrene (monomer, CAS No. 100-42-5): 15 parts;

[0148] Divinylbenzene (crosslinking agent, DVB, provided by Jiangsu Zhengdan Chemical Industry Co., Ltd.): 2 parts;

[0149] Benzoyl peroxide (BPO, oil-soluble initiator, CAS No. 94-36-0): 0.3 parts;

[0150] Toluene (solvent, CAS No. 108-88-3): 30 parts.

[0151] Aqueous phase composition:

[0152] Deionized water: 200 parts;

[0153] Polyvinyl alcohol (PVA-1788, film-forming agent / emulsifier, CAS No. 9002-89-5, provided by Anhui Wanwei High-Tech Materials Co., Ltd.): 2.5 parts;

[0154] Sodium dodecylbenzenesulfonate (SDBS, emulsifier, CAS No. 25155-30-0): 0.5 parts;

[0155] Sodium chloride (electrolyte, used to adjust the density and stability of the aqueous phase, CAS No. 7647-14-5): 5 parts.

[0156] S62. Oil phase preparation: In a 50°C water bath, n-tetracosane, LDPE and toluene are mixed and stirred until LDPE is completely dissolved to form a homogeneous and transparent mixed solution. After the mixed solution is cooled to 40°C, thermochromic spiropyran compound, styrene, divinylbenzene and benzoyl peroxide (BPO) are added in sequence and stirred continuously until all components are completely dissolved to obtain a homogeneous oil phase mixture.

[0157] S63. Aqueous phase preparation: PVA is added to deionized water at 80°C and stirred until completely dissolved. After cooling to 40°C, SDBS and sodium chloride are added and stirred until dissolved evenly to obtain a clear aqueous phase.

[0158] S64. Emulsification process: Pour the aqueous phase into a reactor equipped with mechanical stirring and a constant temperature water bath, maintain the temperature at 40℃, and slowly add the oil phase mixture dropwise to the aqueous phase under medium-speed stirring at 400 rpm. After the addition is complete, increase the stirring speed to 3000 rpm and emulsify at high speed for 20 minutes to form a uniform and stable oil-in-water (O / W) emulsion with droplet size controlled at 15 μm.

[0159] S65. In-situ polymerization reaction: After emulsification, the temperature of the reaction system is slowly raised to 75°C. At this temperature, the system is continuously stirred at 300 rpm for 6 hours to carry out free radical polymerization. During the reaction, styrene and divinylbenzene copolymerize at the oil-water interface to form a cross-linked polystyrene network structure. At the same time, molten phase change paraffin (n-tetracosane) and LDPE are locked in the polystyrene network structure to form a composite shell to encapsulate the core material (1-ethyl-3,3-dimethylindoline-6'-nitrospirobenzopyran).

[0160] S66. Post-processing: After the reaction is complete, the product is naturally cooled to room temperature. The product is then filtered and washed three times in sequence with warm water at 40°C, ethanol, and deionized water to remove unreacted monomers, emulsifiers, and electrolytes. The filter cake is then dried in a vacuum drying oven at 40°C for 24 hours to avoid excessive temperature causing phase changes in the core or shell material. After sieving (200 mesh), a free-flowing white or light yellow powder microcapsule (i.e., infrared reflective thermochromic microcapsule) is obtained.

[0161] This embodiment of a method for preparing a photovoltaic encapsulating film includes the following preparation steps:

[0162] Step 1: Preparation of Dark-Colored Thermally Conductive Filler Premix: The primary filler (Al2O3@C) and secondary filler (sheet-like hBN) are preheated to 110°C in a high-speed mixer. An ethanol solution containing silane coupling agent (KH-570) is sprayed on the filler for coupling treatment (KH-570 is prepared by mixing anhydrous ethanol and deionized water at a mass ratio of 1:10:1, with KH-570 accounting for 1.5% of the total mass of the primary and secondary fillers). All tertiary filler (TiN nanoparticles) and 50% of the secondary filler are mixed in a three-dimensional mixer for 60 minutes to achieve adhesion of nanoparticles (such as TiN nanoparticles) onto the micron-sized sheets (sheet-like hBN). Then, all primary filler and the remaining secondary filler are added, and mixing continues for at least 90 minutes to obtain a dark-colored thermally conductive filler premix with uniform color and reasonable gradation.

[0163] Step 2: The encapsulating resin matrix, carbon black masterbatch, ultraviolet absorber (UV-531), and light stabilizer (Tinuvin783) are mixed evenly in a mixer at 90°C. While maintaining the temperature, silane coupling agent, dark thermally conductive filler premix, and infrared reflective thermochromic microcapsules are added. The mixture is then mixed under vacuum for 25 minutes to ensure full dispersion. The material is cooled to below 70°C, and crosslinking agent (TBEC) is added. The mixture is then quickly mixed (<5 minutes). The mixture is then formed into a uniform black film with a thickness of 0.42 mm using a cold casting extruder. The film is then wound up for later use, thus obtaining a photovoltaic encapsulating film of this embodiment.

[0164] A dark-colored photovoltaic module according to this embodiment includes a photovoltaic front panel, a first encapsulating film, a photovoltaic cell, a second encapsulating film, and a photovoltaic back panel stacked from top to bottom; the second encapsulating film is a photovoltaic encapsulating film as described above in this embodiment.

[0165] Example 2

[0166] This embodiment provides a photovoltaic encapsulation film, its preparation method, and a dark-colored photovoltaic module. Referring to Embodiment 1, the difference between Embodiment 1 and Embodiment 1 is that the encapsulation resin matrix (EVA) in Embodiment 1 is replaced with the same weight of POE; the other raw material composition and preparation steps are the same as in Embodiment 1.

[0167] Example 3

[0168] This embodiment provides a photovoltaic encapsulation film, its preparation method, and a dark-colored photovoltaic module. Referring to Embodiment 1, the difference between Embodiment 1 and Embodiment 1 is that: the primary filler in Embodiment 1 is replaced with the same weight of Al2O3@Fe3O4, the secondary filler in Embodiment 1 is replaced with the same weight of black mica sheets with nano-boron nitride on the surface, and the tertiary filler in Embodiment 1 is replaced with the same weight of AlN@C; other raw material compositions and preparation steps are the same as in Embodiment 1.

[0169] The preparation process of Al2O3@Fe3O4 specifically includes:

[0170] S21. Raw material preparation:

[0171] Spherical alumina (α phase, D50=25μm): 100 parts by weight;

[0172] Ferric chloride hexahydrate (FeCl3·6H2O, CAS No. 10025-77-1): 10 parts by weight;

[0173] Ferrous sulfate heptahydrate (FeSO4·7H2O, CAS No. 7782-63-0): As Fe³ + with Fe² + Weigh out in a molar ratio of 2:1;

[0174] Ammonia solution (25% concentration, CAS No. 1336-21-6): Appropriate amount, used to adjust pH;

[0175] Surfactant (sodium citrate, CAS No. 68-04-2): 2 parts by weight.

[0176] S22. Alumina dispersion: Disperse spherical alumina in deoxygenated deionized water (the amount of which is 4 times the mass of the spherical alumina) to form a uniform slurry, add surfactant, and ultrasonically disperse for 30 minutes to obtain alumina slurry.

[0177] S23. Preparation of iron salt solution: Dissolve FeCl3·6H2O and FeSO4·7H2O in another portion of deoxygenated deionized water (controlling the total concentration of iron salt to 0.3 mol / L) in proportion to obtain a mixed iron salt solution.

[0178] S24. Co-precipitation coating: Under nitrogen protection and vigorous stirring (1000 rpm), the iron salt mixture solution is slowly added to the alumina slurry. The mixture is heated to 60°C in a water bath, and ammonia is slowly added dropwise to maintain the pH of the system between 1 and 10. During this process, Fe³⁺… + and Fe² + Fe3O4 precursor is generated by co-precipitation on the surface of spherical alumina, thus obtaining the mixed slurry.

[0179] S25, Hydrothermal: The above mixed slurry is transferred to a hydrothermal reactor and reacted at 200°C for 8 hours. The high temperature and high pressure (1.5MPa) environment promotes the better growth and crystallization of Fe3O4 crystals on the surface of spherical alumina, forming a dense and firm magnetic black coating layer.

[0180] S26. Post-processing: After the reaction is complete, the product is cooled naturally, separated with the aid of a magnet, and repeatedly washed with deionized water and ethanol until neutral. It is then dried in a vacuum drying oven at 80℃ to obtain Al2O3@Fe3O4.

[0181] The preparation process of the black mica sheet with nano-boron nitride coating specifically includes:

[0182] S31. Raw material preparation:

[0183] Mica flakes (particle size D50=6μm, aspect ratio>30, selected natural black mica flakes, dark mica from Lingshou County Huayuan Mica Factory): 100 parts by weight;

[0184] Boron source precursor: borane-ammonia complex (Ammonia Borane, NH3BH3, CAS No. 13774-81-7): 3.5 parts by weight;

[0185] Nitrogen source: ammonia (NH3, CAS No. 7664-41-7);

[0186] Carrier gas / protective gas: High-purity argon (99.999% purity) (Ar, CAS No. 7440-37-1).

[0187] S32. Mica sheet pretreatment: The black mica sheet is soaked and cleaned in dilute hydrochloric acid (mass concentration 10%, hydrogen chloride CAS number 7647-01-0) to remove surface impurities, then washed with deionized water, dried at 100℃, and subjected to plasma treatment to increase surface active sites, thus obtaining the pretreated black mica sheet.

[0188] S33. The pretreated black mica sheet is laid flat in the quartz boat of the CVD tube furnace. After the system is sealed, it is repeatedly rinsed with argon gas to remove air.

[0189] S34, Deposition process:

[0190] A solid borane-ammonia complex is placed in the low-temperature evaporation zone upstream of a tubular furnace, with the temperature set at 90°C. The reaction zone of the tubular furnace is then heated to 1000°C, and argon gas is introduced as a carrier gas to carry the evaporated borane-ammonia complex vapor (gas-phase boron source precursor) to the high-temperature reaction zone, where it contacts the surface of black mica sheets. Simultaneously, ammonia gas (NH3) is continuously introduced as a supplementary nitrogen source and reaction gas. At the high temperature in the reaction zone, the gas-phase boron source precursor decomposes and reacts on the surface of the black mica sheets, depositing a nano-hexagonal boron nitride (hBN) layer. The deposition time is typically 80 minutes to control the thickness of the nano-boron nitride layer.

[0191] S35. Cooling and Collection: After the reaction is completed, the product is naturally cooled to room temperature under argon protection. The product is then removed, and a black mica composite material with a uniformly coated layer of nano-sized hBN is obtained, which is a black mica sheet with nano-boron nitride on the surface.

[0192] The preparation process of AlN@C nanoparticles specifically includes:

[0193] S51. Raw material preparation:

[0194] Aluminum nitride nanoparticles (AlN nanoparticles, <60nm, provided by Guangzhou Hongwu Materials Technology Co., Ltd.): 100 parts by weight;

[0195] Carbon source precursor: glucose (CAS No. 50-99-7): 20 parts by weight;

[0196] Solvent: Ethanol.

[0197] S52, AlN dispersion: AlN nanoparticles are dispersed in a solvent (the mass ratio of AlN to solvent is 1:20), and ultrasonic treatment is performed to form a stable suspension (the solid content of the suspension is 6%).

[0198] S53. Carbon source introduction and adsorption: Add a carbon source (such as glucose), stir continuously, and evaporate the solvent at 80°C to allow the carbon source precursor to be uniformly adsorbed and coated on the surface of AlN nanoparticles.

[0199] S54, Pre-carbonization: The coated AlN nanoparticles are pre-oxidized and stabilized in air at 300°C (for polymer carbon sources).

[0200] S55. High-temperature carbonization: The coated AlN nanoparticles are placed in a tube furnace and heated to 800°C at 5°C / min under argon protection. The temperature is maintained for 2 hours. During this process, the carbon source precursor is pyrolyzed to form an amorphous carbon layer, which is uniformly coated on the surface of the AlN nanoparticles.

[0201] S56. Cooling: Cool to room temperature under a protective atmosphere to obtain black or dark gray AlN@C nanoparticles (which are core-shell structured nanocomposite powders).

[0202] Comparative Example 1

[0203] This comparative example provides a photovoltaic encapsulation film and its preparation method, as well as a dark-colored photovoltaic module. Referring to Example 1, the difference between Example 1 and Example 1 is that the primary filler in Example 1 is replaced with the same weight of spherical alumina, the secondary filler in Example 1 is replaced with the same weight of ordinary black mica flakes, and the tertiary filler in Example 1 is replaced with the same weight of aluminum nitride (AlN) nanoparticles; the other raw material composition and preparation steps are the same as in Example 1.

[0204] Comparative Example 2

[0205] This comparative example provides a photovoltaic encapsulating film and its preparation method, as well as a dark-colored photovoltaic module. It is based on Example 1, but differs from Example 1 in that: this comparative example does not add infrared reflective thermochromic microcapsules; the composition of other raw materials and preparation steps are the same as in Example 1.

[0206] Comparative Example 3

[0207] This comparative example provides a photovoltaic encapsulating film and its preparation method, as well as a dark-colored photovoltaic module. It is based on Example 1, but differs from Example 1 in that: no primary, secondary, or tertiary filler is added in this comparative example (i.e., the amount of primary, secondary, and tertiary filler added is 0 parts); the composition of other raw materials and preparation steps are the same as in Example 1.

[0208] Comparative Example 4

[0209] This comparative example provides a photovoltaic encapsulating film and its preparation method, as well as a dark-colored photovoltaic module. It is based on Example 1, but differs from Example 1 in that: no primary filler, secondary filler, or tertiary filler is added in this comparative example, nor are infrared reflective thermochromic microcapsules added; the composition of other raw materials and preparation steps are the same as in Example 1.

[0210] Performance testing

[0211] The photovoltaic encapsulating films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Table 1 below:

[0212] (1) Thermal conductivity: The test was conducted in accordance with the standard GB / T 10294-2008 "Determination of steady-state thermal resistance and related properties of thermal insulation materials by protective hot plate method".

[0213] (2) Reflectivity: The test was conducted in accordance with the standard GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastic".

[0214] (3) Simulated photovoltaic module temperature rise test: The test was conducted in accordance with the standard GB / T 45021.1-2024 "Performance testing and energy assessment of photovoltaic modules - Part 1: Irradiance and temperature performance measurement and power assessment".

[0215] (4) Peel strength: The test was conducted in accordance with the standard GB / T 2790-1995 "Test method for peel strength of adhesives at 180°, flexible materials versus rigid materials".

[0216] (5) Crosslinking degree: The test was conducted in accordance with the standard GB / T 29848-2018 "Ethylene-vinyl acetate copolymer (EVA) film for photovoltaic module encapsulation".

[0217] Table 1

[0218]

[0219] By comparing Examples 1-3, it can be seen that within the technical requirements of the present invention, appropriate adjustments to the type of encapsulating resin matrix (as in Example 2) or appropriate adjustments to each level of filler (as in Example 3) can significantly improve the reflectivity and thermal conductivity of the photovoltaic encapsulating film (hereinafter referred to as the film), suppress the temperature rise of the photovoltaic module, and maintain a good dark appearance.

[0220] By comparing Examples 1-3 and Comparative Examples 1-4, it can be seen that the thermal conductivity of the films in Examples 1-3 of the present invention is ≥0.8W / (m·K) at 65℃, while the thermal conductivity of the films in Comparative Examples 1-4 is ≤0.5W / (m·K) at 65℃. It can be seen that the thermally conductive filler formed by the configuration of the primary filler, secondary filler and tertiary filler of the present invention, combined with the infrared reflective thermochromic microcapsules, can significantly increase the thermal conductivity of the film. The films of Examples 1-3 of this invention exhibit a more than 15% increase in reflectivity across the entire solar spectrum after temperatures exceed 65°C, primarily in the near-infrared band (780-1100nm), maintaining the film's dark visual appearance. In this process, the infrared-reflective thermochromic microcapsules play a major optical adjustment role. Simulated temperature rise tests of photovoltaic modules under standard illumination conditions (1000W / m², ambient temperature 25°C) show that the steady-state temperature of the simulated photovoltaic module cells encapsulated with the film of Example 1 is 18.1°C lower than that of the photovoltaic module in Comparative Example 1. The temperatures of Examples 1-3 are generally about 20°C lower than those of Comparative Examples 1-4. This demonstrates that the thermally conductive filler formed by the primary, secondary, and tertiary fillers, combined with the infrared-reflective thermochromic microcapsules, forms a dual temperature control system that enhances heat dissipation and reduces heat absorption, effectively reducing the temperature rise of the photovoltaic module. Moreover, after the encapsulant film was applied to the photovoltaic module lamination, all the encapsulant films in the examples and comparative examples had good crosslinking degree (>80%) and peel strength with photovoltaic glass and photovoltaic backsheet (>100N / cm); indicating that the addition of thermally conductive filler and infrared reflective thermochromic microcapsules does not affect the basic performance of the encapsulant film, and it can be applied to the dark photovoltaic module end with excellent performance.

[0221] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

[0222] The technical solution provided by the present invention has been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A photovoltaic encapsulating film, characterized in that, The raw materials include the following parts by weight: 70-95 parts of encapsulating resin matrix, 5-30 parts of black colorant, 25-46 parts of thermally conductive filler, 8-20 parts of infrared reflective thermochromic microcapsules, and 0.5-1.2 parts of silane coupling agent; The thermally conductive filler comprises 18-30 parts of primary filler, 6-12 parts of secondary filler, and 1-4 parts of tertiary filler; the primary filler is Al2O3@C or Al2O3@Fe3O4 with an average particle size of 20-45 μm; the secondary filler is a sheet-like or two-dimensional insulating thermally conductive material with an average particle size of 2-8 μm; and the tertiary filler is titanium nitride nanoparticles or carbon-coated aluminum nitride nanoparticles with an average particle size of <80 nm. The infrared reflective thermochromic microcapsules are core-shell structure materials with thermochromic spiropyran compounds whose infrared reflectance changes reversibly with temperature as the core and phase change thermally conductive polymers or copolymers as the shell. The insulating and thermally conductive material is at least one of the following: sheet-like hexagonal boron nitride, sheet-like aluminum nitride, mica sheet with boron nitride coating, mica sheet with aluminum nitride coating, and fluorinated graphene. The infrared reflective thermochromic microcapsules have an average particle size of 4-18 μm, a shell thickness of 0.5-3 μm, a temperature response threshold of 58-65℃, and a shell-to-core mass ratio of 4-4.5:

1. The core is 1-alkyl-3,3-dimethylindoline-6'-nitrospirobenzopyran, wherein the alkyl group is ethyl and / or propyl. The shell is a composite material of n-tetracosane and LDPE. The encapsulating resin matrix is ​​at least one of EVA, POE, and PVB; the black colorant is carbon black masterbatch.

2. The photovoltaic encapsulating film according to claim 1, characterized in that, The secondary filler is a sheet-like hexagonal boron nitride with an average particle size of 2-8 μm or a black mica sheet with nano-boron nitride on its surface.

3. The photovoltaic encapsulating film according to claim 1, characterized in that, The infrared reflective thermochromic microcapsules were prepared by in-situ free radical polymerization microencapsulation reaction at the interface; the core of the infrared reflective thermochromic microcapsules is 1-ethyl-3,3-dimethylindoline-6'-nitrospirobenzopyran; the mass ratio of n-tetracosane to LDPE in the shell is 3-5:

1.

4. The photovoltaic encapsulating film according to claim 1, characterized in that, It also includes the following raw materials in parts by weight: 0.7-1.2 parts of crosslinking agent and 0.5-1.5 parts of stabilizer.

5. A method for preparing a photovoltaic encapsulating film according to any one of claims 1-4, characterized in that, include: Step 1: Preparation of thermally conductive filler premix: Coupling treatment of primary and secondary fillers; Mix all the tertiary packing with some of the coupling-treated secondary packing evenly, then add all the coupling-treated primary packing and the remaining coupling-treated secondary packing, and continue mixing to obtain the thermally conductive packing premix. Step 2: After mixing the encapsulating resin matrix with the black colorant, add the thermally conductive filler premix, infrared reflective thermochromic microcapsules and silane coupling agent, mix, and then cast and extrude to obtain the photovoltaic encapsulating film.

6. A photovoltaic module, characterized in that, It includes a photovoltaic front panel, a first encapsulating film, a photovoltaic cell, a second encapsulating film, and a photovoltaic back panel stacked sequentially; the second encapsulating film is a photovoltaic encapsulating film as described in any one of claims 1-4.

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