A heat-conducting insulating photovoltaic encapsulant film, a preparation method and application thereof

Abstract

This invention relates to the field of photovoltaic encapsulant film technology, and discloses a thermally conductive and insulating photovoltaic encapsulant film, its preparation method, and its application. The film is an integrated structure formed by double-layer co-extrusion, comprising upper and lower functional layers (each including 100 parts of matrix resin, 5-25 parts of BN@SiO2 core-shell composite filler, and 1.5-8 parts of functional microcapsules); the BN@SiO2 core-shell composite filler includes a BN@SiO2 core-shell structure with h-BN as the core and amorphous SiO2 as the shell, and a gradient interface layer grafted onto its outer surface (which, from the inside out, includes an anchoring layer covalently bonded to the SiO2 shell, a flexible stress-buffering crosslinking layer, and a hydrophobic outer layer); the fillers in the upper and lower functional layers have different orientations. The thermal conductivity of this film exceeds 1.0 W / (m·K), reducing the operating temperature of photovoltaic modules by nearly 20°C, and the volume resistivity after deflection exceeds 10¹. 5 It has a strength of Ω·cm and also possesses excellent resistance to PID, high-voltage insulation, and interfacial adhesion.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic encapsulant technology, specifically to a thermally conductive and insulating photovoltaic encapsulant film, its preparation method, and its application. Background Technology

[0002] Photovoltaic encapsulation films need to possess multiple properties, including high light transmittance (or specific light absorption), strong adhesion, aging resistance, and high insulation. With the increasing power density of photovoltaic modules and the widespread adoption of bifacial power generation technology, the heat dissipation and insulation issues of photovoltaic encapsulation films are becoming increasingly prominent. These two aspects often conflict: photovoltaic encapsulation films (such as black photovoltaic encapsulation films) absorb a significant amount of heat, resulting in higher operating temperatures; conventional fillers (such as carbon black) have poor thermal conductivity, accelerating aging and leading to increased power loss in photovoltaic modules.

[0003] Existing technologies, such as those disclosed in CN112321933A, which involve adding metals or high-dielectric-constant fillers (e.g., aluminum nitride, thermally conductive oxides) to improve thermal conductivity, may introduce ionic impurities or form leakage current pathways, reducing the volume resistivity of the photovoltaic encapsulation film (especially after humid heat aging), increasing its potential-induced degradation (PID) risk and electrical breakdown hazard. In humid heat environments, the filler-resin interface easily becomes a channel for moisture and ion permeation, causing the insulation performance of the photovoltaic encapsulation film to deteriorate rapidly over time. Therefore, there is currently a lack of systematic and synergistic technical solutions on the market for addressing the "high thermal conductivity" and "high insulation" of materials like black photovoltaic encapsulation films. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a thermally conductive and insulating photovoltaic encapsulating film, its preparation method, and its application.

[0005] Based on this, the present invention discloses a thermally conductive and insulating photovoltaic encapsulating film, which is an integrated structure formed by double-layer co-extrusion, comprising an upper functional layer and a lower functional layer. Both the upper and lower functional layers comprise the following raw materials in parts by weight: 100 parts matrix resin, 5-25 parts BN@SiO2 core-shell composite filler, and 1.5-8 parts functional microcapsules. The BN@SiO2 core-shell composite filler includes a BN@SiO2 core-shell structure with hexagonal boron nitride (h-BN) as the core and amorphous SiO2 as the shell, and a gradient interface layer grafted onto the outer surface of the BN@SiO2 core-shell structure. The gradient interface layer includes, from the inside to the outside, an anchoring layer covalently bonded to the SiO2 shell, a flexible stress buffer crosslinking layer, and a hydrophobic outer layer. The filler orientations in the upper and lower functional layers are different.

[0006] Preferably, the thickness of the SiO2 shell in the BN@SiO2 core-shell structure is 20-100 nm, and it is fabricated using atomic layer deposition technology; The process involves reacting a silane coupling agent with the silanol groups on the surface of the SiO2 shell to form a covalently bonded anchoring layer. A flexible stress-buffered crosslinking layer is then formed on the anchoring layer by grafting a flexible segment polymer to create a crosslinked network. A hydrophobic outer layer is formed by grafting fluorinated silanes and / or molecules containing voltage-stabilizing groups onto the surface of the flexible stress-buffered crosslinking layer. The h-BN core provides extremely high in-plane thermal conductivity and excellent insulation. The SiO2 shell serves as an insulating reinforcement layer and reaction platform; its amorphous structure effectively blocks leakage current paths, and the silanol groups on its surface facilitate in-depth chemical modification. The gradient interface layer achieves a modulus transition from rigid to flexible between the filler and the matrix resin, significantly reducing interfacial thermal resistance and stress concentration, while introducing hydrophobic and / or voltage-stabilizing functions, fundamentally improving the long-term reliability of the film.

[0007] More preferably, the amount of the silane coupling agent added is 1-3% of the mass of the BN@SiO2 core-shell structure, and at least one of KH-550 and γ-aminopropyltriethoxysilane is selected. The amount of the flexible segment polymer added is 5-30% of the mass of the BN@SiO2 core-shell structure, and at least one of terminal hydroxyl polydimethylsiloxane and polyurethane prepolymer is selected. The amount of the fluorinated silane and / or the molecule containing the voltage stabilizing group added is 0.5-3% of the mass of the BN@SiO2 core-shell structure. The fluorinated silane is perfluorooctyltriethoxysilane, and the molecule containing the voltage stabilizing group is a nitrogen-containing heterocyclic compound.

[0008] The preparation process of BN@SiO2 core-shell composite filler includes: Preparation of S1.BN@SiO2 core-shell structure: The BN@SiO2 core-shell structure was prepared using atomic layer deposition (ALD) technology. The specific preparation process is as follows: h-BN (hexagonal boron nitride) powder is immersed in concentrated nitric acid (HNO3) or aqua regia and refluxed at 80°C for 4-6 hours to remove metallic impurities and some amorphous carbon from the h-BN surface. It is then washed with deionized water until neutral and vacuum dried (e.g., vacuum dried at 120°C for 12 hours). The dried h-BN powder is then placed in a tube furnace and heat-treated at 400-500°C for 2-4 hours in an oxygen-containing atmosphere (O2 / Ar mixture) or a steam atmosphere to generate uniform silanol (-Si-OH) and boronol (-B-OH) groups on the h-BN surface (especially at edges and defects) to serve as active sites for subsequent ALD (atomic layer deposition) growth. Then, a vibrating fluidized bed ALD reactor was used to induce a self-limiting reaction cycle on the h-BN surface by alternately introducing a silicon source precursor (tris(dimethylamino)silane, 3DMAS) and an oxygen source (ozone or water vapor). The process parameters for the self-limiting reaction cycle are as follows: reaction temperature 150-200°C, equilibrium reaction rate and byproduct desorption; precursor pulse time: silicon source 0.5-2s, oxygen source 0.2-1s; purging time: thorough purging after each pulse, such as 30-60s, to prevent parasitic gas-phase reactions; number of cycles: calculated and set according to the target thickness, such as 450 cycles required to grow 50nm. Growing 80nm requires approximately 650 cycles. The fluidizing gas is high-purity nitrogen or argon to maintain a stable fluidization state. The silicon source precursor reacts with the -OH groups on the h-BN surface to form a chemisorption monolayer (i.e., a silane layer). The oxygen source reacts with the adsorbed silane layer to generate SiO2 and regenerate the surface -OH groups. By controlling the number of cycles (e.g., 200-800 cycles), a 20-100nm thick silane shell (an amorphous SiO2 insulating shell, or simply SiO2 shell) is formed on the outer surface of h-BN, thus creating a BN@SiO2 core-shell structure with h-BN as the core and amorphous SiO2 as the insulating shell.

[0009] S2. Interface Modification: After forming the BN@SiO2 core-shell structure, a gradient interface layer is constructed on the outer surface of the BN@SiO2 core-shell structure through a multi-step surface grafting reaction. (This gradient interface layer includes, from the inside out, an anchoring layer covalently bonded to the SiO2 shell, a flexible stress-buffering crosslinking layer, and a fluorinated hydrophobic outer layer.) The specific interface modification process is as follows: Silane coupling agents (such as KH-550 or γ-aminopropyltriethoxysilane, at 1-3% of the mass of the BN@SiO2 core-shell structure) react with the silanol groups on the surface of the SiO2 shell to form strong Si-O-Si covalent bonds, with amino groups (-NH2) introduced at the ends to form an anchoring layer covalently bonded to the SiO2 shell (e.g., reaction temperature 90℃, reaction time 6 hours. Solvent selection: Toluene, n-butanol, or ethanol are usually chosen as the reaction medium to disperse silica and dissolve the silane coupling agent; an anhydrous system is used, such as using toluene dehydrated by molecular sieves, to avoid premature hydrolysis and self-polymerization of the silane coupling agent in the aqueous phase, thereby improving grafting efficiency). This anchoring layer provides reaction sites for subsequent interface modification. On the anchoring layer, flexible segment polymers (such as hydroxyl-terminated polydimethylsiloxane, isocyanate-terminated PDMS, polyurethane prepolymers, etc., accounting for 5-30% of the mass of the BN@SiO2 core-shell structure) are grafted onto the anchoring layer. The introduced amino groups undergo dehydration condensation with the hydroxyl groups of the hydroxyl-terminated polydimethylsiloxane (reaction temperature 70-120℃, reaction time 2-4 hours. Catalyst and atmosphere: Dehydration condensation of hydroxyl and amino groups usually requires a catalyst. Adding an alkaline catalyst, such as potassium hydroxide or potassium silanolate, and conducting the reaction under nitrogen protection, prevents oxidation and promotes the reaction), or reacting the amino groups with isocyanate-terminated PDMS to form polyurea bonds, the resulting flexible siloxane segments entangle with each other in the interfacial region, further forming a cross-linked network. This forms a flexible stress-buffered cross-linked layer on the outer surface of the anchoring layer, which buffers thermal and mechanical stresses and prevents interfacial debonding; or the amino groups react with polyurethane prepolymers (usually isocyanate-terminated) to rapidly generate a polyurea structure. Finally, a fluorinated silane (such as perfluorooctyltriethoxysilane, accounting for 0.5-3% of the mass of the BN@SiO2 core-shell structure) is grafted onto the outer surface of the flexible stress-buffered crosslinking layer. The remaining amino groups or the active groups at the ends of the flexible stress-buffered crosslinking layer are then grafted with the fluorinated silane (e.g., stirred at 40°C for 5 hours; solvent and dispersion: typically, the aminated or flexible stress-buffered crosslinked silica shell is ultrasonically dispersed in an alcohol solvent such as ethanol), and then the fluorinated silane (perfluorooctyltriethoxysilane) is added for reaction. Ultrasonic dispersion helps prevent particle aggregation and ensures uniform modification. This forms a fluorinated hydrophobic outer layer on the outer surface of the flexible stress-buffered crosslinking layer. After steps S1-S2, the BN@SiO2 core-shell composite filler is obtained. The perfluoroalkyl chain in the hydrophobic outer layer has extremely low surface energy. Like a raincoat, it wraps around the outermost layer of the filler, giving it superhydrophobicity. It can effectively block water vapor from penetrating to the interface, giving the filler hydrophobicity and voltage stability, and resisting the PID (potential-induced decay) effect.

[0010] Preferably, the functional microcapsules comprise 0.5-3 parts of type A thermo-repair microcapsules and 1-5 parts of type B voltage-sensitive discharge microcapsules; the core of the type A thermo-repair microcapsules contains a curable siloxane resin, and the core of the type B voltage-sensitive discharge microcapsules contains zinc oxide varistor microcrystals. The BN@SiO2 core-shell composite filler provides intrinsic and continuous high thermal conductivity insulation. The type A thermo-repair microcapsules address physical damage (microcracks), while the type B voltage-sensitive discharge microcapsules address electrical overstress (overvoltage). The gradient interface ensures long-term stable bonding between all fillers and the matrix, providing a reliable environment for the microcapsules to function effectively.

[0011] More preferably, the outer shell of the type A thermotropic repair microcapsule is a thermoplastic resin, and the core is an incompletely cured siloxane resin containing a catalyst. When microcracks occur locally in the film due to heat or stress, the cracks propagate, causing the type A thermotropic repair microcapsule to rupture. The siloxane resin flows out and cures under the action of the catalyst, achieving self-repair of the crack. The type A thermotropic repair microcapsule is preferably 0.5-3 parts (i.e., 0.5-3% of the matrix resin mass). Too little will result in insufficient repair points, while too much may affect the continuity and initial properties of the matrix.

[0012] More preferably, the preparation process of the type A thermotropic repair microcapsules includes emulsification-polymerization coating-post-treatment, specifically as follows: a mixture of siloxane prepolymer core material (at least one of a mixture of hydroxyl-terminated silicone oil, hydrogen-containing silicone oil, and vinyl silicone oil) and a catalyst (the amount of catalyst added is 0.1-1% of the mass of the siloxane prepolymer core material, and platinum catalyst or tin-type catalyst is selected) is used as the oil phase. This mixture is then subjected to high-speed shearing or homogenization at 3000-10000 rpm in an aqueous solution containing an emulsifier (the amount of emulsifier added is 0.5-2% of the mass of the aqueous phase, and at least one of sodium dodecyl sulfate and polyvinyl alcohol is selected) to form oil particles with uniform particle size. A water-in-oil emulsion is prepared by adding methyl methacrylate monomer and an oil-soluble initiator (the amount of oil-soluble initiator added is 0.5-1.5% of the mass of methyl methacrylate monomer, benzoyl peroxide is selected) to the emulsion. Under stirring and heating conditions (heating temperature is 60-90℃, stirring speed is 3000-12000 rpm), the methyl methacrylate monomer (MMA monomer) gradually diffuses and aggregates on the surface of the oil phase, undergoing an in-situ polymerization reaction to form a solid polymethyl methacrylate shell to encapsulate the liquid siloxane prepolymer core material. After filtration, washing and drying, white powdery A-type thermotropic repair microcapsules with a particle size of 5-50 micrometers are obtained. The mass ratio of siloxane prepolymer core material to methyl methacrylate monomer wall material is 60-80:40-20. For example, if a batch aims to produce 100 grams of type A thermo-repair microcapsules, then 60-80 grams of siloxane prepolymer and 40-20 grams of MMA monomer are used.

[0013] More preferably, the outer shell of the type B voltage-sensitive discharge microcapsule is a polymer with a suitable dielectric constant, and the core is zinc oxide varistor microcrystals; the polymer with a suitable dielectric constant is at least one of polystyrene, polyacrylates, and ethyl cellulose. When an abnormally high electric field is generated locally in the film due to PID effect or lightning strike induction, the outer shell of the type B voltage-sensitive discharge microcapsule undergoes dielectric breakdown, and the released ZnO microcrystals form local conductive channels under the electric field, dissipating charge and protecting the solar cell. The type B voltage-sensitive discharge microcapsule is preferably 1-5 parts (i.e., 1-5% of the matrix resin mass), and needs to be precisely controlled to ensure that its threshold voltage is higher than the normal operating voltage of the photovoltaic module, but lower than the breakdown voltage of the solar cell.

[0014] More preferably, the preparation process of the type B voltage-sensitive discharge microcapsule includes: placing zinc oxide microcrystalline powder as the core material in the cavity of a fluidized bed coating device, and using clean hot air to make it uniformly suspended in a fluidized state (the process conditions are as follows: clean hot air rises uniformly through the bottom airflow distribution plate, and the material is suspended and fluidized under the action of airflow. The inlet air temperature is controlled at 40-100℃, the bed temperature is maintained at 30-60℃, and the outlet air temperature is 20-50℃); and atomizing the polymer solution into fine droplets through a nozzle at an atomization pressure of 0.2-0.8MPa. The spraying rate is 10-500 mL / min, and the atomized droplets are 10-100 μm, sprayed onto the fluidized zinc oxide particles. When the droplets contact the surface of the zinc oxide particles, the solvent evaporates rapidly, leaving a uniform polymer film as a coating. By continuously cycling this coating process, the polymer film gradually thickens to 0.5-3 μm. After coating, hot air is continuously introduced to completely solidify the polymer solution (e.g., solidification temperature 90℃, solidification time 2h). Type B voltage-sensitive release microcapsules with a particle size of 250-850 μm and uniform particle size distribution are obtained by sieving. The concentration of the polymer solution is 5-15% (solvent: toluene for polystyrene, acetone for certain acrylates, water). The polymer in the polymer solution is used as the wall material. The core-to-wall ratio directly affects the breakdown voltage threshold. The thicker the wall, the higher the breakdown voltage. The mass ratio of core material to wall material is 70-90:30-10. For example, to produce 100 grams of type B voltage-sensitive discharge microcapsules, 70-90 grams of ZnO and 30-10 grams of wall material polymer are used (calculated based on the solid content in the polymer solution).

[0015] Preferably, the lower functional layer further includes 0.5-5 parts of magnesium oxide whiskers; magnesium oxide whiskers have extremely high axial thermal conductivity and insulation, and are easily vertically oriented under tensile flow, constructing a "thermal short circuit" path from the solar cell outwards. The upper functional layer is rich in horizontally oriented BN@SiO2 core-shell composite filler, while the lower functional layer is rich in vertically oriented BN@SiO2 core-shell composite filler and magnesium oxide whiskers.

[0016] Preferably, both the upper and lower functional layers further include the following raw materials in parts by weight: 1-3 parts black colorant, 0.5-2 parts crosslinking agent, 0.5-2 parts antioxidant, and 0.5-2 parts light stabilizer; The matrix resin is at least one of ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), ethylene-olefin copolymer, and their modified forms. The black colorant is at least one of carbon black, black organic dye, and black composite pigment; The crosslinking agent is a peroxide initiator, such as 2-ethylhexyl carbonate tert-butyl peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, etc. The antioxidants include, but are not limited to, at least one of antioxidant 1010 and antioxidant 1076; The light stabilizers include, but are not limited to, at least one of UV622, UV531, UV292, and UV770.

[0017] This invention also discloses a method for preparing a thermally conductive and insulating photovoltaic encapsulating film, comprising the following preparation process: The raw material melts of the upper and lower functional layers are respectively conveyed to a multi-cavity laminar flow distribution die (flexible lip die) through two sets of flow channels of a co-extrusion device (which includes extruder A and extruder B). Laminar flow co-extrusion is performed in the die, and by controlling the geometry and temperature zone of the flow channels, the sheet-like BN@SiO2 core-shell composite filler in the raw material melt of the upper functional layer is mainly horizontally oriented, while the BN@SiO2 core-shell composite filler and magnesium oxide whiskers in the raw material melt of the lower functional layer are mainly vertically oriented. Then, the raw material melts of the upper and lower functional layers converge at the die outlet and are laminated in a laminar flow manner. After being cooled and shaped by the casting roller, they are formed into a thermally conductive and insulating photovoltaic encapsulation film with a strong interface fusion through one-step double-layer co-extrusion casting.

[0018] The mechanism for achieving the upper functional layer (horizontal orientation): The BN@SiO2 core-shell composite filler lamellars are made as parallel as possible to the film plane (i.e., the XY plane). Before entering the confluence mold lip, the raw material melt of the upper functional layer undergoes intense shear flow (e.g., through a narrow, flat flow channel). The velocity gradient direction of the shear flow field is perpendicular to the flow direction. This forces the lamellar BN@SiO2 core-shell composite filler to spread out like playing cards along the flow direction (MD) and transverse direction (TD), thus achieving in-plane orientation. The mechanism for achieving the lower functional layer (vertical orientation): The BN@SiO2 core-shell composite filler lamellars and MgO whiskers are rotated 90° within the film plane, making their normal direction (thickness direction) perpendicular to the film plane, i.e., standing upright. The raw material melt of the lower functional layer undergoes a unidirectional or bidirectional strong tensile flow during the critical molding stage (mold lip exit). When the melt is rapidly stretched and thinned (e.g., from a thicker flow channel to the final film thickness), the lamellar filler tends to orient its plane perpendicular to the stretching direction to reduce flow resistance. For unidirectional stretching perpendicular to the film plane (Z-axis thinning), the filler will orient its plane in the XY direction. By designing and creating an in-plane extended stretching flow (e.g., fan-shaped expansion at the die lip exit), the lamellar crystals are induced to rotate around an axis perpendicular to the flow direction, thereby aligning their normal direction (i.e., the thickness direction) with the normal direction of the film (Z-axis), forming a vertical orientation.

[0019] For example, the temperatures of extruders A and B (extruder A corresponds to the raw material melt of the upper functional layer, and extruder B corresponds to the raw material melt of the lower functional layer), each section of the die, and the die lip are independently controlled. Extruder A (temperature: 75℃-80℃-85℃-85℃-85℃) → Multi-layer co-extrusion distributor (independent flow channel A, temperature: 87℃) → Die (upper flow channel, temperature: 87℃); Extruder B (temperature: 75℃-85℃-87℃-87℃-89℃) → Multi-layer co-extrusion distributor (independent flow channel B, temperature: 88℃) → Die (lower flow channel, temperature: 89℃). In this way, the raw material melt temperature of the lower functional layer is slightly higher than that of the upper functional layer to reduce its viscosity, making it easier to deform and orient during stretching flow.

[0020] This invention also discloses an application of a thermally conductive and insulating photovoltaic encapsulating film, in which the thermally conductive and insulating photovoltaic encapsulating film described above is used as an encapsulating material in photovoltaic modules (at least one layer of the above-mentioned thermally conductive and insulating photovoltaic encapsulating film is used to encapsulate the solar cells).

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: The photovoltaic encapsulation film achieves "thermal conductivity without electrical conductivity" through the following synergistic design: (1) it is paired with BN@SiO2 core-shell composite filler to achieve "thermal conductivity without electrical conductivity"; (2) the gradient interface layer of BN@SiO2 core-shell composite filler ensures stable interface insulation under long-term humid and hot conditions; (3) the filler orientations in the upper and lower functional layers are different, optimizing the heat flow path while ensuring overall insulation; (4) functional microcapsules (such as type A thermally induced repair microcapsules and type B voltage-sensitive discharge microcapsules) provide active insulation protection. Thus, the present invention provides a photovoltaic encapsulation film that can significantly improve the thermal conductivity and insulation reliability (especially long-term insulation stability) of the film, constructing a composite functional system that is "thermal conductive without charge conduction and insulating without blocking heat flow", creatively solving the multiple requirements of photovoltaic encapsulation films for efficient heat dissipation, reliable insulation, long-term stability and active protection under harsh environments such as high temperature, high humidity and high voltage. Therefore, the thermal conductivity of the photovoltaic encapsulating film of the present invention exceeds 1.0 W / (m·K), the operating temperature of photovoltaic modules using this photovoltaic encapsulating film is reduced by nearly 20°C, and the volume resistivity after damp heat aging remains at 10¹ for a long period of time. 5 With a strength exceeding Ω·cm, it exhibits excellent resistance to PID, high-voltage insulation, and interfacial bonding performance, significantly improving the power generation efficiency, safety, and service life of black photovoltaic modules.

[0022] Furthermore, the preparation method of this photovoltaic encapsulating film embodies a high degree of integration from nanoscale interface control to macroscopic flow field processing, and has significant innovation and industrial application value. Detailed Implementation

[0023] 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.

[0024] Example 1 This embodiment provides a thermally conductive and insulating photovoltaic encapsulating film, which is an integrated structure formed by double-layer co-extrusion, comprising an upper functional layer and a lower functional layer.

[0025] The upper functional layer comprises the following raw materials by weight: Matrix resin (POE): 100 parts; Black colorant (carbon black): 2 parts; BN@SiO2 core-shell composite filler: 15 parts; Type A thermo-repair microcapsules: 1 part; Type B voltage-sensitive discharge microcapsules: 1.5 parts; Crosslinking agent (2-ethylhexyl tert-butyl peroxide): 1.5 parts; Antioxidant (Antioxidant 1010): 0.5 parts; Light stabilizer (UV622): 0.5 parts.

[0026] The raw material formula of the lower functional layer is the same as that of the upper functional layer, and magnesium oxide whiskers are added to the raw material formula of the lower functional layer: 0.5 parts.

[0027] This embodiment provides a method for preparing a thermally conductive and insulating photovoltaic encapsulating film, comprising the following preparation steps: Preparation of S1.BN@SiO2 core-shell structure: The BN@SiO2 core-shell structure was prepared using atomic layer deposition (ALD) technology. The specific preparation process is as follows: h-BN (hexagonal boron nitride) powder was immersed in 68% concentrated nitric acid (HNO3) at a mass ratio of 1:50 to h-BN, and refluxed at 80°C for 4 hours to remove metallic impurities and some amorphous carbon from the h-BN surface. The powder was then washed with deionized water until neutral and vacuum dried at 120°C for 12 hours. The dried h-BN powder was then placed in a tube furnace and heat-treated at 500°C for 2 hours in an oxygen-containing atmosphere (O2 / Ar mixture, O2 / Ar mass ratio 5:95) to generate uniform boron hydroxyl groups (-B-OH) on the h-BN surface (especially at edges and defects) to serve as active sites for subsequent ALD (atomic layer deposition) growth. Then, a vibrating fluidized bed ALD reactor was used to induce a self-limiting reaction cycle on the h-BN surface by alternately introducing a silicon source precursor (tris(dimethylamino)silane, 3DMAS) and an oxygen source (ozone). The process parameters for the self-limiting reaction cycle were as follows: reaction temperature 180°C, equilibrium reaction rate and byproduct desorption; precursor pulse time: 1s for silicon source, 0.5s for oxygen source; purging time: thorough purging after each pulse (e.g., 60s) to prevent parasitic gas-phase reactions; number of cycles: calculated and set according to the target thickness, e.g., 4 cycles are required to grow 50nm. 50 cycles. The fluidizing gas is high-purity nitrogen or argon to maintain a stable fluidization state. The silicon source precursor reacts with the -OH groups on the surface of h-BN to form a chemisorption monolayer (i.e., a silane layer). The oxygen source reacts with the adsorbed silane layer to generate SiO2 and regenerate the surface -OH groups. Through 450 cycles, a 50nm thick silane shell layer (which is an amorphous SiO2 insulating shell layer, referred to as the SiO2 shell) is formed on the outer surface of h-BN. This results in a BN@SiO2 core-shell structure with h-BN as the core and amorphous SiO2 as the insulating shell.

[0028] S2. Interface Modification: After forming the BN@SiO2 core-shell structure, a gradient interface layer is constructed on the outer surface of the BN@SiO2 core-shell structure through a multi-step surface grafting reaction. (This gradient interface layer includes, from the inside out, an anchoring layer covalently bonded to the SiO2 shell, a flexible stress-buffering crosslinking layer, and a fluorinated hydrophobic outer layer.) The specific interface modification process is as follows: The silane coupling agent KH-550 (1% of the mass of the BN@SiO2 core-shell structure) reacts with the silanol groups on the surface of the SiO2 shell to form strong Si-O-Si covalent bonds, with amino groups (-NH2) introduced at the ends to form an anchoring layer covalently bonded to the SiO2 shell (the process conditions for forming the anchoring layer are as follows: reaction temperature 90℃, reaction time 6 hours. Solvent selection: n-Butanol organic solvent is used as the reaction medium to disperse silica and dissolve the silane coupling agent; using an anhydrous system (such as toluene dehydrated by molecular sieves) can avoid premature hydrolysis and self-polymerization of the silane coupling agent in the aqueous phase, thereby improving grafting efficiency). (This anchoring layer provides reaction sites for subsequent interface modification.) On the anchoring layer, a flexible segment polymer (hydroxyl-terminated polydimethylsiloxane, also known as hydroxyl-terminated PDMS, at 10% of the mass of the BN@SiO2 core-shell structure) is grafted onto it. The introduced amino groups undergo dehydration condensation with the hydroxyl groups of the hydroxyl-terminated PDMS (reaction conditions are as follows: reaction temperature between 80°C and 4 hours; catalyst and atmosphere: dehydration condensation of hydroxyl and amino groups usually requires a catalyst. Potassium hydroxide, an alkaline catalyst, is added, and the reaction is carried out under nitrogen protection to prevent oxidation and promote the reaction). The resulting flexible siloxane segments become entangled in the interfacial region, further forming a cross-linked network. This forms a flexible stress-buffering cross-linked layer on the outer surface of the anchoring layer, which buffers thermal and mechanical stresses and prevents interfacial debonding. Finally, perfluorooctyltriethoxysilane (1% of the mass of the BN@SiO2 core-shell structure) is grafted onto the outer surface of the flexible stress-buffered crosslinking layer. The remaining amino groups or active groups such as hydroxyl groups at the ends of the flexible stress-buffered crosslinking layer are then grafted onto the perfluorooctyltriethoxysilane (reaction conditions are as follows: stirring at 40°C for 5 hours; solvent and dispersion: typically, the aminated or flexible stress-buffered crosslinked silica shell is ultrasonically dispersed in ethanol, and then a fluorinated silane, perfluorooctyltriethoxysilane, is added for reaction. Ultrasonic dispersion helps prevent particle aggregation and ensures uniform modification). This forms a fluorinated hydrophobic outer layer on the outer surface of the flexible stress-buffered crosslinking layer. After steps S1-S2, the BN@SiO2 core-shell composite filler is obtained.

[0029] The preparation process of S3.A type thermo-repair microcapsules includes emulsification-polymerization-coating-post-treatment. The specific preparation process is as follows: A mixture of siloxane prepolymer (hydroxyl-terminated silicone oil) and catalyst (platinum catalyst, 0.5% of the mass of the core siloxane prepolymer) is used as the oil phase. In an aqueous solution containing emulsifier (sodium dodecyl sulfate, 1% of the mass of the aqueous phase), a high-speed shearing or homogenization at 6000 rpm is carried out to form an O / W (water-in-oil) emulsion with uniform particle size. Methyl methacrylate (MMA) monomer and an oil-soluble initiator (benzoyl peroxide, 1% of the MMA monomer mass) were added to the above O / W type emulsion. Under stirring and heating conditions (heating temperature 70℃, stirring speed 6000 rpm), the MMA monomer gradually diffused and accumulated on the surface of the oil phase (siloxane prepolymer droplets), and an in-situ polymerization reaction was carried out for 4 hours to form a solid PMMA (polymethyl methacrylate) shell to encapsulate the liquid siloxane prepolymer core material. After the reaction, after filtration, washing, and drying, white powdery A-type thermotropic repair microcapsules with a particle size of 20 micrometers were obtained. The mass ratio of core material (core material is siloxane prepolymer) to wall material (wall material is MMA) was 70:30.

[0030] The preparation process of S4.B type voltage-sensitive discharge microcapsules includes fluidization, atomization and coating, solidification and sieving. The specific preparation process is as follows: ZnO microcrystalline powder (core material) is placed in the cavity of a fluidized bed coating device, and clean hot air is used to make it uniformly suspended in a fluidized state (the process conditions are as follows: clean hot air rises uniformly through the bottom airflow distribution plate, and the material is suspended and fluidized under the action of airflow. The inlet air temperature is controlled at 60℃, the bed temperature is maintained at 40℃, and the outlet air temperature is 30℃). The wall material polymer solution (polystyrene, mass concentration 10%, solvent is toluene) is atomized into fine droplets through a nozzle located at the bottom. The atomization pressure is 0.5MPa, the spray rate is 200mL / min, and the atomized droplets are 20μm, which are sprayed onto the fluidized ZnO particles. When the droplets contact the surface of the ZnO particles, the solvent evaporates rapidly, leaving a uniformly coated polymer film. Through continuous circulation of this process, the wall layer (i.e., the polymer film) gradually thickens to 1 micrometer. After coating, hot air was continuously introduced to completely cure the wall material at 90℃ for 2 hours. Finally, B-type voltage-sensitive discharge microcapsules with a uniform particle size distribution (500μm) were obtained by sieving. The core-to-wall ratio (mass ratio of core material to wall material, where the core material is ZnO microcrystalline powder and the wall material is polymer solution-polystyrene, calculated based on the solid polystyrene content in the polymer solution) was 80:20.

[0031] S5. Bilayer Co-extrusion and Structural Orientation: All raw materials for the upper functional layer (including matrix resin, black colorant, BN@SiO2 core-shell composite filler, type A thermotropic repair microcapsules, type B voltage-sensitive discharge microcapsules, crosslinking agent, antioxidant, and light stabilizer) and all raw materials for the lower functional layer (including matrix resin, black colorant, BN@SiO2 core-shell composite filler, type A thermotropic repair microcapsules, type B voltage-sensitive discharge microcapsules, magnesium oxide whiskers, crosslinking agent, antioxidant, and light stabilizer) are fed into a co-extrusion unit equipped with two sets of flow channels and a flexible lip die. The materials are then transported to the appropriate locations through the two flow channels of the co-extrusion unit. A flexible lip die with multi-cavity laminar flow distribution; laminar co-extrusion is performed within the die, and the geometry and temperature zone of the flow channels of the raw material melts of the two functional layers before laminar flow convergence are controlled (extruder A screw speed 10 rpm, extruder B screw speed 11 rpm; by adjusting the screw speed of each extruder, the volumetric flow rate of the raw material melts of the upper and lower functional layers is controlled, so that the linear velocity difference between the two melts before convergence is less than 5%, ensuring the stability of the interlayer interface. The temperature of extruders A / B (extruder A corresponds to the raw material melt of the upper functional layer, extruder B corresponds to the raw material melt of the lower functional layer), each zone of the die, and the die lip are independently controlled: Extruder A (temperature: (75℃-80℃-85℃-85℃-85℃) → Multi-layer co-extrusion distributor (independent flow channel A, temperature: 87℃) → Die head (upper flow channel, temperature: 87℃); Extruder B (temperature: 75℃-85℃-87℃-87℃-89℃) → Multi-layer co-extrusion distributor (independent flow channel B, temperature: 88℃) → Die head (lower flow channel, temperature: 89℃); Thus, the raw material melt temperature of the lower functional layer is slightly higher than that of the raw material melt of the upper functional layer to reduce its viscosity, making it easier to deform and orient during stretching flow. The shrinkage ratio (inlet cross-sectional area / outlet cross-sectional area) of the flow channel in the die lip area is controlled between 4:1 to produce A tensile stress field sufficient to induce filler orientation is generated, causing the upper functional layer material (such as sheet-like BN@SiO2 core-shell composite filler) to mainly exhibit in-plane (MD / TD) orientation (i.e., horizontal orientation), while the lower functional layer material (such as BN@SiO2 core-shell composite filler and magnesium oxide whiskers) mainly exhibits thickness (ND) orientation (vertical alignment). Then, the melt of the upper functional layer material and the melt of the lower functional layer material converge at the die exit and are laminated in a laminar flow manner. After being cooled and shaped by the casting roller, a one-step double-layer co-extrusion and casting process is completed to form a thermally conductive and insulating photovoltaic encapsulation film (400μm thick) with a strong interface fusion and an integrated structure.

[0032] S6. Post-processing: Cooling, winding.

[0033] Example 2 This embodiment provides a thermally conductive and insulating photovoltaic encapsulating film and its preparation method, which differs from Embodiment 1 in that: The weight percentage of BN@SiO2 core-shell composite filler in the raw material formulations of both the upper and lower functional layers was changed to 25 parts.

[0034] Example 3 This embodiment provides a thermally conductive and insulating photovoltaic encapsulating film and its preparation method, which differs from Embodiment 1 in that: The weight percentages of BN@SiO2 core-shell composite filler, type A thermotropic repair microcapsules, and type B voltage-sensitive discharge microcapsules in the raw material formulations of the upper and lower functional layers were changed to 25 parts, 3 parts, and 5 parts, respectively. The weight percentage of magnesium oxide whiskers in the raw material formulation of the lower functional layer was also changed to 5 parts.

[0035] Comparative Example 1 This comparative example is a photovoltaic encapsulation film, which is a single-layer conventional black POE photovoltaic encapsulation film without the addition of BN@SiO2 core-shell composite filler, type A thermotropic repair microcapsules, type B voltage-sensitive discharge microcapsules, and magnesium oxide whiskers.

[0036] Comparative Example 2 This comparative example describes a thermally conductive and insulating photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between this example and Example 1 is: Replace the BN@SiO2 core-shell composite filler in the raw material formulations of the upper and lower functional layers with the same weight parts of ordinary h-BN.

[0037] Comparative Example 3 This comparative example describes a thermally conductive and insulating photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between this example and Example 1 is: Replace the BN@SiO2 core-shell composite filler in the raw material formulations of the upper and lower functional layers with the same weight of BN@SiO2 core-shell structure (without a gradient interface layer on its outer surface).

[0038] Performance testing The photovoltaic encapsulating films prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests (such as thermal conductivity and volume resistivity in Table 1). The photovoltaic encapsulating films of Examples 1-3 and Comparative Examples 1-3 were then applied to photovoltaic modules (specifically between the solar cells and the photovoltaic backsheet) to obtain the corresponding photovoltaic modules. The performance of each photovoltaic module was then tested (such as the other performance properties excluding thermal conductivity and volume resistivity in Table 1).

[0039] The test results are shown in Table 1 below: Table 1

[0040] As can be seen from Table 1: (1) The Z-direction thermal conductivity of Examples 1-3 is more than 5 times higher than that of the baseline (Comparative Example 1), and the operating temperature of the photovoltaic module is reduced by nearly 20°C. The electrical insulation performance of Examples 1-3 is also outstanding: the initial volume resistivity is significantly higher, and it still maintains a high insulation level after 1000 hours of stringent double 85 damp heat test (i.e., DH1000h). The power decay after PID test is small, the PID resistance is excellent, and the insulation withstand voltage strength is significantly improved. With the increase of the amount of BN@SiO2 core-shell composite filler, type A thermally induced repair microcapsules, type B voltage-sensitive discharge microcapsules, etc. (as shown in Example 3), the photovoltaic encapsulation film has higher thermal conductivity and insulation performance.

[0041] (2) By comparing Comparative Example 1, Example 1 and Example 2 (the contents of BN@SiO2 core-shell composite filler in Comparative Example 1, Example 1 and Example 2 are 0 parts, 15 parts and 25 parts respectively), it can be seen that: with the increase of the amount of BN@SiO2 core-shell composite filler added, the thermal conductivity of the photovoltaic encapsulation film is significantly improved, and the steady-state operating temperature of the encapsulated photovoltaic module is significantly reduced (the maximum reduction is 19.5°C). Example 1 shows the best balance in terms of comprehensive performance (significantly improved thermal conductivity, less impact on interface peel strength, volume resistivity, volume resistivity after DH1000h and power decay after PID test, etc., and controllable cost).

[0042] (3) By comparing Example 1 and Comparative Examples 2-3, it can be seen that replacing BN@SiO2 core-shell composite filler with BN@SiO2 core-shell structure (without gradient interface layer on its outer surface) or ordinary h-BN has a significant negative impact on the thermal conductivity and insulation performance of photovoltaic encapsulation film. The volume resistivity decreases significantly after long-term aging and the power decay is more serious after PID test. It also significantly reduces the interface peel strength after thermal cycling.

[0043] 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.

[0044] 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 thermally conductive and insulating photovoltaic encapsulating film, characterized in that, It is an integrated structure formed by double-layer co-extrusion, which includes an upper functional layer and a lower functional layer; Both the upper and lower functional layers comprise the following raw materials in parts by weight: 100 parts matrix resin, 5-25 parts BN@SiO2 core-shell composite filler, and 1.5-8 parts functional microcapsules. The BN@SiO2 core-shell composite filler includes a BN@SiO2 core-shell structure with hexagonal boron nitride as the core and amorphous SiO2 as the shell, and a gradient interface layer grafted onto the outer surface of the BN@SiO2 core-shell structure. The gradient interface layer includes, from the inside to the outside, an anchoring layer covalently bonded to the SiO2 shell, a flexible stress buffer crosslinking layer, and a hydrophobic outer layer. The filler orientations in the upper and lower functional layers are different.

2. The thermally conductive and insulating photovoltaic encapsulating film according to claim 1, characterized in that, The SiO2 shell in the BN@SiO2 core-shell structure has a thickness of 20-100 nm and is fabricated using atomic layer deposition technology. The process involves reacting a silane coupling agent with the silanol groups on the surface of the SiO2 shell to form a covalently bonded anchoring layer; on the anchoring layer, a flexible stress-buffered crosslinking layer is formed by grafting a flexible segment polymer to form a crosslinked network; and on the surface of the flexible stress-buffered crosslinking layer, molecules containing fluorinated silanes and / or voltage-stabilizing groups are grafted to form a hydrophobic outer layer.

3. The thermally conductive and insulating photovoltaic encapsulating film according to claim 2, characterized in that, The amount of the silane coupling agent added is 1-3% of the mass of the BN@SiO2 core-shell structure, and at least one of KH-550 and γ-aminopropyltriethoxysilane is selected. The amount of the flexible segment polymer added is 5-30% of the mass of the BN@SiO2 core-shell structure, and at least one of terminal hydroxyl polydimethylsiloxane and polyurethane prepolymer is selected. The amount of the fluorinated silane and / or the molecule containing the voltage stabilizing group added is 0.5-3% of the mass of the BN@SiO2 core-shell structure. The fluorinated silane is perfluorooctyltriethoxysilane, and the molecule containing the voltage stabilizing group is a nitrogen-containing heterocyclic compound.

4. The thermally conductive and insulating photovoltaic encapsulating film according to claim 1, characterized in that, The functional microcapsules include 0.5-3 parts of type A thermo-repair microcapsules and 1-5 parts of type B voltage-sensitive discharge microcapsules; the core of the type A thermo-repair microcapsules contains curable siloxane resin, and the core of the type B voltage-sensitive discharge microcapsules contains zinc oxide varistor microcrystals.

5. The thermally conductive and insulating photovoltaic encapsulating film according to claim 4, characterized in that, The outer shell of the type A thermo-repair microcapsule is a thermoplastic resin, and the core is an incompletely cured siloxane resin containing a catalyst. The preparation process of the type A thermotropic repair microcapsules includes: using a mixture of siloxane prepolymer core material and catalyst as the oil phase, and subjecting it to high-speed shearing or homogenization at 3000-10000 rpm in an aqueous solution containing emulsifier to form a water-in-oil emulsion with uniform particle size; adding methyl methacrylate monomer and oil-soluble initiator to the emulsion, and under stirring and heating conditions, the methyl methacrylate monomer gradually diffuses and aggregates on the surface of the oil phase, undergoing an in-situ polymerization reaction to form a solid polymethyl methacrylate shell to encapsulate the liquid siloxane prepolymer core material; and then filtering, washing, and drying to obtain white powder-like type A thermotropic repair microcapsules with a particle size of 5-50 micrometers. The siloxane prepolymer is at least one of a mixture of hydroxyl-terminated silicone oil, hydrogen-containing silicone oil, and vinyl silicone oil; the amount of catalyst added is 0.1-1% of the mass of the siloxane prepolymer core material, and a platinum catalyst or a tin-type catalyst is selected; the amount of emulsifier added is 0.5-2% of the mass of the aqueous phase, and at least one of sodium dodecyl sulfate and polyvinyl alcohol is selected; the amount of oil-soluble initiator added is 0.5-1.5% of the mass of methyl methacrylate monomer, and benzoyl peroxide is selected; the mass ratio of the siloxane prepolymer core material to the methyl methacrylate monomer wall material is 60-80:40-20.

6. The thermally conductive and insulating photovoltaic encapsulating film according to claim 4, characterized in that, The outer shell of the type B voltage-sensitive discharge microcapsule is a polymer with a suitable dielectric constant, and the core is a zinc oxide varistor microcrystal; the polymer with a suitable dielectric constant is at least one of polystyrene, polyacrylates, and ethyl cellulose; The preparation process of the type B voltage-sensitive discharge microcapsules includes: placing zinc oxide microcrystalline powder as the core material in the cavity of a fluidized bed coating device, and using clean hot air to make it uniformly suspended in a fluidized state; atomizing a polymer solution into fine droplets through a nozzle and spraying it onto the fluidized zinc oxide particles; when the droplets contact the surface of the zinc oxide particles, the solvent evaporates rapidly, leaving a uniform polymer film as coating; by continuously cycling this coating process, the polymer film gradually thickens to 0.5-3 micrometers; after coating is completed, hot air is continued to be introduced to completely solidify the polymer solution; and type B voltage-sensitive discharge microcapsules with a particle size of 250-850 μm and uniform particle size distribution are obtained by sieving. The concentration of the polymer solution is 5-15%, and the polymer in the polymer solution is used as the wall material. The mass ratio of the core material to the wall material is 70-90:30-10.

7. The thermally conductive and insulating photovoltaic encapsulating film according to claim 1, characterized in that, The lower functional layer also includes 0.5-5 parts of magnesium oxide whiskers; The upper functional layer contains horizontally oriented BN@SiO2 core-shell composite filler, while the lower functional layer contains vertically oriented BN@SiO2 core-shell composite filler and magnesium oxide whiskers.

8. A thermally conductive and insulating photovoltaic encapsulating film according to any one of claims 1-7, characterized in that, Both the upper and lower functional layers further include the following raw materials in parts by weight: 1-3 parts black colorant, 0.5-2 parts crosslinking agent, 0.5-2 parts antioxidant, and 0.5-2 parts light stabilizer; The matrix resin is at least one of ethylene-vinyl acetate copolymer, polyolefin elastomer, ethylene-olefin copolymer and its modifiers; The black colorant is at least one of carbon black, black organic dye, and black composite pigment; The crosslinking agent is a peroxide initiator; The antioxidant is selected from at least one of antioxidant 1010 and antioxidant 1076; The light stabilizer is selected from at least one of UV622, UV531, UV292, and UV770.

9. A method for preparing a thermally conductive and insulating photovoltaic encapsulating film according to any one of claims 1-8, characterized in that, The preparation process includes the following: The raw material melts of the upper and lower functional layers are respectively transported to the multi-cavity laminar flow distribution die through two sets of flow channels of the co-extrusion device. Laminar flow co-extrusion is carried out in the die, and by controlling the geometry and temperature zone of the flow channels, the sheet-like BN@SiO2 core-shell composite filler in the raw material melt of the upper functional layer is mainly horizontally oriented, while the BN@SiO2 core-shell composite filler and magnesium oxide whiskers in the raw material melt of the lower functional layer are mainly vertically oriented. Then, the raw material melts of the upper and lower functional layers merge at the die outlet and are formed into an integrated thermally conductive and insulating photovoltaic encapsulation film through a one-step double-layer co-extrusion casting process.

10. An application of a thermally conductive and insulating photovoltaic encapsulating film, characterized in that, The thermally conductive and insulating photovoltaic encapsulating film according to any one of claims 1-8 is used as an encapsulation material in photovoltaic modules.

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