An attachable transparent phase change thermal management film, its preparation method and application in photovoltaic modules

Abstract

The application discloses a preparation method of an attachable transparent phase change heat management film, which comprises the following steps: uniformly mixing a phase change material, an epoxy resin matrix and glass microspheres by heating to obtain a prepared mixed solution; adding an acid anhydride curing agent, an accelerator and an ultraviolet absorber into the prepared mixed solution, uniformly mixing and heating, and then vacuum deaerating; and injecting the deaerated mixed solution into a mold, and then performing stage heating and curing at a temperature range of 50-160 DEG C for 2-24 hours, so that the film is obtained. The film can be attached to a front surface of an existing photovoltaic module in a laminating or pressure-sensitive adhesive mode, so that the synergistic heat management of radiation refrigeration, phase change energy storage and heat diffusion is realized. The working temperature of the photovoltaic module using the film is significantly reduced, the photoelectric conversion efficiency is improved, and the optical performance remains stable in repeated heat cycles. The film has the advantages of simple preparation process, low cost and stable optical performance, and can be widely applied to passive cooling and performance improvement of single-glass, double-glass, double-sided and building integrated photovoltaic modules.

Description

Technical Field

[0001] This invention belongs to the field of new materials and photovoltaic technology, specifically relating to an attachable transparent phase change thermal management film and its preparation method, as well as the application of this film in passive cooling of photovoltaic modules. This film maintains high light transmittance in the visible light band while achieving passive cooling of photovoltaic modules through the synergistic effects of phase change energy storage, infrared radiation, and heat diffusion. Background Technology

[0002] Global warming is ongoing, impacting not only human lives but also the balance of natural ecosystems. Solar photovoltaic (PV) technology, as a core pathway for low-carbon energy transition, is being deployed globally on an unprecedented scale. However, during actual outdoor operation, the continuous absorption of solar radiation by PV modules leads to heat accumulation inside the modules, significantly increasing cell temperature. For crystalline silicon cells, the photoelectric conversion efficiency decreases by approximately 0.4–0.5% for every 1°C increase in temperature. High temperatures also accelerate the aging of encapsulation materials and defect formation, shortening module lifespan. As PV applications expand into hot climate zones and building-integrated applications, traditional active cooling methods are unsuitable due to their high energy consumption and complex structures, necessitating the development of scalable passive thermal management technologies.

[0003] In recent years, researchers have proposed various passive cooling strategies. Radiative cooling materials radiate heat into outer space by achieving high infrared emission in the atmospheric window band (8–13 μm), but existing high-efficiency radiative coolers are mostly opaque or reflective structures, which can block the absorption of visible light required by photovoltaic modules. Hydrogel evaporative cooling can achieve significant cooling, but it requires millimeter-thickness to maintain moisture, necessitating frequent water replenishment in arid regions, limiting its practicality. Phase change materials buffer temperature fluctuations through latent heat storage, but traditional phase change cooling layers are thick, heavy, and prone to leakage and fatigue failure. These existing technologies generally suffer from a trade-off between light transmittance, cooling efficiency, and stability, making it difficult to balance transparency and thermal management performance.

[0004] Therefore, developing an attachable thin film that combines high light transmittance, efficient thermal management, and long-term stability to achieve passive cooling without altering the existing photovoltaic module structure is of significant scientific importance and engineering application value.

[0005] Based on this, this application was developed. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide an attachable transparent phase change thermal management film that combines high light transmittance, efficient thermal management, and long-term stability. Without changing the existing photovoltaic module structure, it can achieve passive cooling of the photovoltaic module through the synergistic effect of radiation cooling, phase change energy storage, and heat diffusion mechanisms, thereby improving photoelectric conversion efficiency and extending service life.

[0007] The present invention also provides a method for preparing the above-mentioned attachable transparent phase change thermal management film and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an attachable transparent phase change thermal management thin film includes the following steps: 1) The phase change material, epoxy resin matrix and glass microspheres are heated and stirred at 50-160 °C to obtain a pre-prepared mixture; the phase change material is selected from at least one of polyethylene glycol, fatty acid, polyol, paraffin, organic carboxylic acid ester, etc. 2) Add anhydride curing agent, accelerator and UV absorber to the premixed liquid, heat and mix evenly, and then degas under vacuum; 3) Inject the degassed mixture into the mold, heat and solidify to obtain a transparent composite film.

[0009] Specifically, in step 1), the phase change material is selected from polyethylene glycol (molecular weight 1000-8000), fatty acids (such as at least one of lauric acid, palmitic acid, stearic acid, decanoic acid, etc., or their binary / ternary eutectic mixtures; melting point 40-70℃, refractive index 1.43-1.48), polyols (such as at least one of pentaerythritol, trimethylolethane, trimethylolpropane, etc., or their binary / ternary eutectic mixtures; phase change temperature 40-80℃, refractive index about 1.45-1.52, undergoing solid-solid phase change, with no risk of leakage), paraffin wax (selected from at least one of 52# paraffin wax, 58# paraffin wax, n-octadecane, n-eicosane, etc., melting point 40-70℃, refractive index 1.45-1.50), organic carboxylic acid esters (such as at least one of octadecyl acrylate, methyl stearate, butyl stearate, etc., phase change temperature -25-80℃, latent heat 100-250℃), and organic carboxylic acid esters (such as at least one of octadecyl acrylate, methyl stearate, butyl stearate, etc., phase change temperature -25-80℃, latent heat 100-250℃). The phase change material (PCM) is at least one of the following: (kJ / kg, refractive index approximately 1.44–1.50), or a binary / ternary eutectic mixture of any two of the aforementioned. These PCMs exist stably within the epoxy network in a microcrystalline / amorphous coexistence or microphase separation form through molecular confinement induced by anhydride-based curing agents, achieving reversible solid-liquid phase change thermal storage. The mass ratio of the PCM to the epoxy resin is (1–3):1; the epoxy resin includes at least one of EP51 type epoxy resin, EP44 type epoxy resin, etc.

[0010] Furthermore, in step 1), the glass microspheres are used to enhance the thermal diffusivity of the film, and their refractive index is 1.45–1.55, matching the refractive indices of the epoxy resin and the phase change material. The glass microspheres include one or more of borosilicate glass microspheres, soda-lime glass microspheres, and quartz glass microspheres; the amount of glass microspheres added accounts for 2.5–15 wt% of the total mass of the phase change material and epoxy resin. When the glass microsphere content is 10 wt%, the film maintains high visible light transmittance (>88%) while increasing in-plane thermal conductivity by more than 40%, achieving a good balance between optical and thermal properties.

[0011] Specifically, in step 2), the anhydride curing agent includes one or more of phthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride; the mass ratio of the pre-mixed liquid to the anhydride curing agent is 5:(0.8-1.2). The anhydride curing agent undergoes a cross-linking reaction with the epoxy resin to form a three-dimensional network structure. Simultaneously, through the physical confinement of molecular chain segments, it inhibits the crystallization and growth of the phase change material, allowing it to be stably dispersed in the epoxy network in a microcrystalline / amorphous coexistence form.

[0012] Further, in step 2), the accelerator is at least one of tertiary amines, imidazoles, and organometallic compounds, including but not limited to one or more of 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 2-methylimidazole, 2-ethyl-4-methylimidazole, stannous octoate, and aluminum acetylacetonate. The mass ratio of the anhydride curing agent to the accelerator is (10-30):1, preferably (15-25):1.

[0013] Furthermore, in step 2), the ultraviolet absorber is a triazine ultraviolet absorber (model UV-1500) or a benzotriazole ultraviolet absorber, and the amount of the ultraviolet absorber added accounts for 0.5 to 3 wt% of the total mass of the phase change material and epoxy resin, preferably 1 to 2 wt%. The introduction of this ultraviolet absorber can effectively delay the yellowing phenomenon of the film during outdoor use and improve its long-term optical stability.

[0014] Specifically, in step 3), the temperature is gradually increased and cured in stages within the range of 50–160 °C for 2–24 hours. A preferred technical solution could be maintaining the temperature at 60 °C for 1–3 h, 70 °C for 1–3 h, and 80 °C for 20–28 h; maintaining the temperature at 70 °C for 1–3 h, 80 °C for 1–3 h, and 90 °C for 20–28 h; maintaining the temperature at 80 °C for 1–3 h, 90 °C for 1–3 h, and 100 °C for 18–24 h; or maintaining the temperature at 130 °C for 1–3 h, 140 °C for 1–3 h, and 150 °C for 20–24 h, etc.

[0015] As a preferred technical solution, the film further includes a polydimethylsiloxane functional layer coated on its surface (i.e., a polydimethylsiloxane precursor solution is spin-coated or blade-coated onto the surface of the cured transparent composite film, and a polydimethylsiloxane functional layer with a thickness of 10-100 μm is formed after curing). The polydimethylsiloxane functional layer is used to improve the visible light transmittance of the film, enhance the infrared emissivity, and impart hydrophobic self-cleaning properties to the film surface. Specifically: A polydimethylsiloxane prepolymer and a curing agent are mixed at a mass ratio of (8–12):1, dissolved in an organic solvent to prepare a solution with a mass fraction of 8–20%. This solution is then spin-coated onto the surface of a film and subsequently cured to form a polydimethylsiloxane functional layer with a thickness of 10–100 μm (preferably 35–60 μm). The curing agent is an organosilicon curing agent, etc. The organic solvent includes, but is not limited to, n-hexane, toluene, ethyl acetate, etc.

[0016] This invention provides an attachable transparent phase-change thermal management film prepared by the above-described method. Further, the film has a thickness of 0.5–2.0 mm. The film exhibits high transmittance in the visible light band and high emissivity in the 8–13 μm infrared atmospheric window. The in-plane thermal conductivity of the film is higher than that of a pure epoxy resin matrix.

[0017] This invention also provides the application of the aforementioned thin film in photovoltaic modules, which is attached to the surface of the photovoltaic module via pressure-sensitive adhesive or lamination. The thin film is adhered to the front surface of the photovoltaic module to reduce its operating temperature. Furthermore, the photovoltaic module includes single-glass modules, double-glass modules, bifacial photovoltaic modules, or building-integrated photovoltaic modules, etc.

[0018] The attachable transparent phase change thermal management film of the present invention comprises an epoxy resin matrix, microregions of phase change material (such as polyethylene glycol, paraffin or fatty acid) dispersed in the epoxy resin matrix, and glass microsphere filler dispersed in the epoxy resin matrix.

[0019] When the thin film of this invention is applied to solar cell modules, it significantly reduces the module's operating temperature through the synergistic effect of radiative cooling, phase change energy storage, and thermal diffusion. Outdoor testing shows that compared to a reference module without the film coating, the photovoltaic module using the film of this invention exhibits an average operating temperature reduction of 5–7 °C, with a peak temperature reduction exceeding 10 °C, effectively mitigating the adverse effects of high temperatures on battery performance. This film can be attached to the front surface of existing photovoltaic modules via lamination or pressure-sensitive adhesive to achieve synergistic thermal management of radiative cooling, phase change energy storage, and thermal diffusion. The photovoltaic module using this film exhibits a significantly reduced operating temperature, improved photoelectric conversion efficiency, and stable optical performance during repeated thermal cycling. The thin film of this invention has a simple manufacturing process, low cost, and stable optical performance, and can be widely applied to passive cooling and performance enhancement of single-glass, double-glass, bifacial, and building-integrated photovoltaic modules.

[0020] The thin film of this invention significantly improves photoelectric conversion efficiency while reducing the operating temperature of photovoltaic modules. Since the open-circuit voltage of crystalline silicon cells decreases with increasing temperature, this invention effectively increases the open-circuit voltage by lowering the cell's operating temperature. Tests show that photovoltaic modules using the thin film of this invention exhibit approximately a 4% increase in relative photoelectric conversion efficiency, while maintaining a essentially unchanged short-circuit current density, demonstrating that the thin film achieves a cooling effect without significantly impacting light absorption.

[0021] The thin film of this invention can delay the performance degradation of photovoltaic modules under continuous illumination. Compared with a reference module without the thin film coating, the photovoltaic module with the thin film of this invention exhibits a slower efficiency decline trend in long-term illumination tests, indicating that the cooling effect helps to reduce thermal stress damage to the cells and extend the module's lifespan.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) This invention utilizes the molecular confinement effect induced by anhydride curing agents to stably disperse phase change materials (such as polyethylene glycol, paraffin, or fatty acids) in an epoxy network in a microcrystalline / amorphous coexistence form. Compared with conventional amine curing agents, the anhydride curing agents used in this invention can form a tighter cross-linked network, providing stronger physical constraints on the chain segment movement of phase change materials (such as polyethylene glycol, paraffin, or fatty acids), effectively inhibiting crystallization nucleation and growth during the cooling process. This avoids the light scattering problem caused by large-size crystals during the solid-liquid phase transition of traditional phase change materials, ensuring that the film maintains stable high light transmittance before and after the phase transition. 2) This invention utilizes glass microspheres (refractive index 1.45–1.55) with matching refractive index to improve the in-plane thermal conductivity of the film while maintaining high light transmittance, thus achieving rapid heat diffusion. Compared to pure polymer films without fillers, the composite film of this invention has a higher thermal diffusivity, effectively preventing the formation of local hot spots and achieving a more uniform temperature distribution. 3) The thin film of this invention has high emissivity in the 8–13 μm infrared atmospheric window, which can dissipate heat to outer space through radiative cooling. Compared with existing opaque or reflective radiative cooling materials, this invention achieves efficient infrared radiation while maintaining high visible light transmittance, thus resolving the contradiction between light transmittance and thermal management performance in traditional cooling materials. 4) The polydimethylsiloxane surface functional layer that can be used in this invention can further improve visible light transmittance (by reducing reflection loss through refractive index gradient matching) and infrared emissivity (by enhancing radiation absorption through the inherent vibration of Si-O bonds), while giving the film surface hydrophobic self-cleaning properties, reducing dust adhesion, and extending outdoor service life. 5) Unlike existing cooling solutions that need to be integrated into the module, the film of this invention can be directly attached to the surface of existing photovoltaic modules by pressure-sensitive adhesive or lamination without changing the original structure of the module. It has good operability and universality and is suitable for upgrading and retrofitting existing photovoltaic power plants. 6) The preparation process of this invention is simple, the raw materials are readily available, the cost is low, and it can be mass-produced, thus having broad application prospects in the field of photovoltaic thermal management. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the attachable transparent phase change thermal management film prepared in Example 1 of the present invention; Figure 2 The transmission spectrum of the thin film prepared in Example 1 of the present invention in the visible light band shows that the thin film maintains high light transmittance at different temperatures; Figure 3 The image shows the reflectance spectrum of the thin film prepared in Example 1 of this invention in the 8-13 μm infrared atmospheric window, indicating that the thin film has low reflectance (high emissivity) characteristics. Figure 4 The temperature-time curves of the thin film prepared in Example 1 of the present invention and the uncoated reference battery under outdoor light are compared, showing that the thin film of the present invention significantly reduces the battery operating temperature. Figure 5 The image shows a comparison of the water contact angles of the thin film surface prepared in Example 1 of this invention before and after PDMS modification, indicating that the modified surface has hydrophobic properties. Figure 6 The images are scanning electron microscope images of the thin film prepared in Example 1 of the present invention, wherein (a) is the surface morphology and (b) is the morphology of the frozen fracture cross section, showing the micron-scale uniform dispersion of polyethylene glycol in the epoxy matrix and the smooth surface. Figure 7 The images shown are SEM images (a) of the frozen fracture cross section of the composite film after incorporating borosilicate glass microspheres in Example 1 of the present invention and the corresponding EDS surface distribution map of silicon elements (b), showing the uniform dispersion of glass microspheres in the matrix. Detailed Implementation

[0024] The technical solutions of the present invention will be described in detail below with reference to the embodiments. However, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the protection scope of the present invention.

[0025] In this invention, all raw materials used are ordinary commercially available products that can be purchased directly, or can be prepared using conventional techniques in the field.

[0026] It should be noted that the phase change material described in this invention is not limited to polyethylene glycol. Other organic phase change materials that are transparent or translucent in the visible light band, have a refractive index close to that of the epoxy resin matrix (approximately 1.52) (1.45–1.55), and possess a suitable phase change temperature (typically 30–80°C) can also be used, such as paraffin waxes (e.g., 52# paraffin wax, 58# paraffin wax) and fatty acids (e.g., stearic acid, lauric acid, palmitic acid). These materials can also form stable micro-regions in the anhydride-cured epoxy network through molecular confinement or microphase separation, achieving reversible solid-liquid phase change thermal storage.

[0027] The accelerator described in this invention is not limited to DMP-30. Any substance that can catalyze the ring-opening reaction between acid anhydrides and epoxy groups can be used, including but not limited to: imidazoles (2-methylimidazole, 2-ethyl-4-methylimidazole), tertiary amines (DMP-30, triethylamine), organometallic compounds (stannous octoate, aluminum acetylacetonate), etc.

[0028] The curing temperature described in this invention can be flexibly designed within the range of 50 to 160°C. Low-temperature starting is beneficial for degassing and leveling, while high-temperature curing can improve crosslinking density and network stability. Example 1

[0029] This embodiment provides an attachable transparent phase change thermal management film, the structure of which, from top to bottom, consists of a polydimethylsiloxane surface functional layer and a phase change composite film substrate, wherein the phase change composite film substrate is mainly made of polyethylene glycol, epoxy resin, and borosilicate glass microspheres. The specific preparation steps are as follows; 1) Dry polyethylene glycol (PEG6000) with a molecular weight of 6000 at 30 °C for 2 hours. Weigh 3.0 g of the dried PEG6000, 2.0 g of EP51 epoxy resin, and 0.5 g of borosilicate glass microspheres (average particle size 1-5 μm, refractive index about 1.52) and place them in a 50 mL flask. Stir at 500 rpm for 4 hours in an oil bath at 70 °C to obtain a homogeneous premixed solution. 2) Another 2.0 g of anhydride curing agent methyl hexahydrophthalic anhydride, 0.1 g of accelerator DMP-30, and 0.1 g of ultraviolet absorber (triazine ultraviolet absorber, model UV-1500, Guangzhou Good New Materials Technology) were taken, mixed, and preheated to uniformity at 70 °C to obtain a curing agent solution. The prefabricated mixture was cooled to about 60 °C, and 1.2 g of the above-mentioned curing agent solution was slowly added, stirred at 400 rpm for 10 minutes, and then degassed under vacuum for 10 minutes; 3) The degassed mixture was cast into a polytetrafluoroethylene mold, the film thickness was controlled to be about 1 mm, and it was cured by stepwise heating according to the program of maintaining at 60 °C for 2 h, 70 °C for 2 h, and 80 °C for 24 h to obtain a transparent composite film matrix, denoted as P 60 E-GP10; 4) The polydimethylsiloxane prepolymer and the curing agent were mixed at a mass ratio of 10:1 and dissolved in n-hexane to prepare a 10% PDMS solution by mass fraction. The above-mentioned P 60 E-GP10 film was fixed on a spin coater, and the PDMS solution was spin-coated at a speed of 3000 rpm, and then cured in an oven at 80 °C for 2 hours to form a PDMS surface functional layer with a thickness of about 50 μm, obtaining the final film sample, denoted as P 60 E-G10-P50; The polydimethylsiloxane (PDMS) was Sylgard 184 purchased from Dow Corning, and the curing agent was an organosilicon curing agent. In this example, polymethylhydrosiloxane purchased from Dow Corning of the United States was selected.

[0030] As Figure 1 shown, the schematic diagram of the film structure prepared in this example shows structural features such as a solar light reflection layer (i.e., a transparent composite film matrix) and a thermal emission modulation layer (i.e., a PDMS surface functional layer). In this example, PEG6000 was stably dispersed in the epoxy network in the form of coexistence of microcrystals / amorphous through the molecular confinement effect induced by methyl hexahydrophthalic anhydride curing agent, realizing the reversible solid-liquid phase change heat storage function.

[0031] As Figure 2 shown, the film prepared in this example has high light transmittance in the visible light band. It can be seen from the figure that the transmission spectra of the P 60 E-GP10 film at 25 °C (PEG solid state, T < Tm) and 70 °C (PEG molten state, T > Tm) basically overlap, and the peak transmittance reaches 89~91% at 780 nm, and the transmittance in the entire visible light band remains above 85%, indicating that the P 60 E-GP10 film has stable optical properties before and after phase change and does not produce light scattering due to PEG crystallization. After PDMS surface coating, P 60The E-G10-P50 film achieves an average visible light transmittance of approximately 90.6%, demonstrating excellent anti-reflective properties.

[0032] like Figure 3 As shown, the thin film prepared in this embodiment exhibits high emissivity in the 8–13 μm infrared atmospheric window. As can be seen from the figure, the reflectivity of the P60E-GP10 thin film in this band is approximately 5–7%, corresponding to an emissivity of approximately 0.93–0.95. Compared to ordinary glass and PDMS thin films, the thin film in this embodiment has lower infrared reflectivity (i.e., higher emissivity), which is attributed to the molecular vibrational absorption of the epoxy matrix and the enhanced coupling effect of the glass microspheres on infrared radiation. After PDMS surface coating, P… 60 The E-G10-P50 thin film achieves an average emissivity of approximately 0.942 in the 8–13 μm band, further enhancing its radiative cooling performance.

[0033] like Figure 4 As shown, the thin film P prepared in this embodiment... 60 E-G10-P50 was bonded to the surface of a crystalline silicon solar cell using pressure-sensitive adhesive and tested under outdoor sunlight. As shown in the figures, compared to the uncoated reference cell, the cell coated with the film of this invention exhibited a significantly lower operating temperature. Throughout the test, the average temperature of the coated cell decreased by approximately 5–6°C, with a peak temperature drop exceeding 10°C during peak sunlight hours. Simultaneously, the temperature fluctuations of the coated cell were more gradual, exhibiting a characteristic plateau when the temperature approached the PEG phase transition point (approximately 52°C), indicating that the PEG melting and endothermic action served as a buffer for phase transition energy storage. Electrical performance tests showed that the photoelectric conversion efficiency of the coated cell was relatively improved by approximately 4%, mainly due to the increase in open-circuit voltage, while the short-circuit current density remained essentially unchanged, demonstrating that the film achieved a cooling effect without significantly impacting light absorption.

[0034] like Figure 5 As shown in the figure, the surface wettability of the P60E-G10-P50 film prepared in this embodiment changed significantly after modification with a PDMS surface functional layer. It can be seen from the figure that the surface of the uncoated P60E-GP10 film is hydrophilic, with a water contact angle of approximately 76.5°; while the water contact angle of the PDMS-coated P60E-G10-P50 film increased significantly to approximately 113.8°, exhibiting obvious hydrophobic properties. This change is attributed to the low surface energy of PDMS and the -CH3 groups enriched on its surface, which endow the film with self-cleaning ability, helping to reduce the adhesion of dust and contaminants in outdoor applications and maintain long-term optical performance and thermal management effects.

[0035] like Figure 6As shown, in the transparent phase change heat management film prepared by the present invention, polyethylene glycol is uniformly and densely dispersed in the epoxy resin matrix at the micron level. Figure 6 (a) is a scanning electron microscope image of the surface morphology of the thin film, showing that the surface is smooth and dense, with no obvious phase separation or cracks, which is beneficial to reduce light scattering and improve visible light transmittance; Figure 6 (b) is a scanning electron microscope image of the frozen fracture section of the film, which further confirms that the polyethylene glycol microregions are effectively confined by the epoxy network and no large-sized crystalline regions are formed, thus ensuring that the film maintains high transparency before and after the phase transition.

[0036] like Figure 7 As shown, when borosilicate glass microspheres are incorporated, the glass powder is uniformly dispersed in the matrix. Figure 7 (a) is a scanning electron microscope image of the cross-section of the composite thin film. Figure 7 (b) shows the corresponding silicon energy spectrum distribution, which indicates that the glass microspheres have no obvious agglomeration and are uniformly distributed, which is conducive to the construction of an efficient thermally conductive network and avoids the decline in optical performance caused by filler agglomeration. Example 2

[0037] This embodiment provides an attachable transparent phase change thermal management film, which differs from Embodiment 1 in that it uses phthalic anhydride as the anhydride curing agent and adjusts the type of glass microspheres. The specific preparation steps are as follows; 1) Dry polyethylene glycol (PEG4000) with a molecular weight of 4000 at 30 °C for 2 hours. Weigh 4.0 g of the dried PEG4000, 2.0 g of EP44 epoxy resin, and 0.6 g of soda-lime glass microspheres (average particle size 2-8 μm, refractive index about 1.51) and place them in a 50 mL flask. Stir at 500 rpm for 3 hours in an oil bath at 75 °C to obtain a homogeneous premixed solution. 2) Separately, take 2.2 g of phthalic anhydride curing agent, 0.12 g of DMP-30 accelerator, and 0.1 g of UV absorber (triazine UV absorber, model UV-1500, Guangzhou Good New Material Technology). Mix them and preheat at 80°C until homogeneous to obtain a curing agent solution. Cool the pre-mixed liquid to approximately 65°C, slowly add 1.3 g of the above curing agent solution, stir at 400 rpm for 15 minutes, and then degas under vacuum for 15 minutes. 3) The degassed mixture is poured into a polytetrafluoroethylene mold, the film thickness is controlled to be about 1.2 mm, and the film is cured in stages according to the procedure of holding at 70 °C for 2 h, 80 °C for 2 h, and 90 °C for 20 h to obtain a transparent composite film substrate; 4) The polydimethylsiloxane prepolymer and curing agent were mixed at a mass ratio of 10:1 and dissolved in toluene to prepare a 12% (w / w) PDMS solution. The composite film substrate was fixed on a spin coater, and the PDMS solution was spin-coated at 2500 rpm. It was then cured in a 90°C oven for 1.5 hours to form a PDMS surface functional layer with a thickness of approximately 60 μm, yielding the final film sample. The polydimethylsiloxane (PDMS) used was Sylgard 184 purchased from Dow Corning, and the curing agent was an organosilicon curing agent. In this embodiment, polymethylhydrosiloxane purchased from Dow Corning was used. Example 3

[0038] This embodiment provides an attachable transparent phase change thermal management film, which differs from Embodiment 1 in that it uses methyltetrahydrophthalic anhydride as the anhydride curing agent and quartz glass microspheres as the filler. The specific preparation steps are as follows; 1) Dry polyethylene glycol (PEG8000) with a molecular weight of 8000 at 30 °C for 2 hours. Weigh 5.0 g of the dried PEG8000, 2.5 g of EP51 epoxy resin, and 0.8 g of quartz glass microspheres (average particle size 1-3 μm, refractive index about 1.46) and place them in a 50 mL flask. Stir at 600 rpm for 3 hours in an 80 °C oil bath to obtain a homogeneous premixed solution. 2) Separately, take 2.5 g of methyltetrahydrophthalic anhydride curing agent, 0.15 g of accelerator DMP-30, and 0.12 g of UV absorber (triazine UV absorber, model UV-1500, Guangzhou Good New Material Technology). Mix them and preheat at 75 °C until homogeneous to obtain a curing agent solution. Cool the pre-mixed liquid to approximately 70 °C, slowly add 1.5 g of the above curing agent solution, stir at 500 rpm for 15 minutes, and then degas under vacuum for 15 minutes. 3) The degassed mixture is poured into a polytetrafluoroethylene mold, the film thickness is controlled to be about 1.5 mm, and the film is cured in stages according to the procedure of keeping it at 80 °C for 2 h, 90 °C for 2 h, and 100 °C for 18 h to obtain a transparent composite film substrate. 4) The polydimethylsiloxane prepolymer and curing agent were mixed at a mass ratio of 10:1 and dissolved in ethyl acetate to prepare an 8% (w / w) PDMS solution. The composite film substrate was fixed on a spin coater, and the PDMS solution was spin-coated at 3500 rpm. It was then cured in an oven at 85 °C for 2 hours to form a PDMS surface functional layer with a thickness of approximately 40 μm, yielding the final film sample. The polydimethylsiloxane (PDMS) used was Sylgard 184 purchased from Dow Corning, and the curing agent was an organosilicon curing agent. In this embodiment, polymethylhydrosiloxane purchased from Dow Corning was used. Example 4

[0039] This embodiment provides an attachable transparent phase change thermal management film, which differs from Embodiment 1 in that it uses a mixed epoxy resin of EP44 and EP51, and a mixed filler of borosilicate glass microspheres and quartz glass microspheres. The specific preparation steps are as follows; 1) Dry polyethylene glycol (PEG2000) with a molecular weight of 2000 at 30 °C for 2 hours. Weigh 3.5 g of the dried PEG2000, 1.5 g of EP51 epoxy resin, 1.0 g of EP44 epoxy resin, 0.3 g of borosilicate glass microspheres (average particle size 1-5 μm), and 0.3 g of quartz glass microspheres (average particle size 1-3 μm). Place them in a 50 mL flask and stir at 500 rpm for 4 hours in a 70 °C oil bath to obtain a homogeneous premixed solution. 2) Separately, take 1.5 g of methyl methyl hexahydrophthalic anhydride curing agent, 1.0 g of methyl tetrahydrophthalic anhydride, 0.15 g of accelerator DMP-30, and 0.1 g of UV absorber (triazine UV absorber, model UV-1500, Guangzhou Good New Material Technology). Mix them and preheat at 75 °C until homogeneous to obtain a curing agent solution. Cool the pre-mixed liquid to approximately 65 °C, slowly add 1.4 g of the above curing agent solution, stir at 450 rpm for 15 minutes, and then degas under vacuum for 15 minutes. 3) The degassed mixture is poured into a polytetrafluoroethylene mold, the film thickness is controlled to be about 1.0 mm, and the film is cured in stages according to the procedure of keeping it at 60 °C for 2 h, 70 °C for 2 h, and 85 °C for 22 h to obtain a transparent composite film substrate. 4) The polydimethylsiloxane prepolymer and curing agent were mixed at a mass ratio of 10:1 and dissolved in n-hexane to prepare a 10% (w / w) PDMS solution. The composite film substrate was fixed on a spin coater, and the PDMS solution was spin-coated at 3000 rpm. It was then cured in an 80 °C oven for 2 hours to form a PDMS surface functional layer with a thickness of approximately 50 μm, yielding the final film sample. The polydimethylsiloxane (PDMS) used was Sylgard 184 purchased from Dow Corning, and the curing agent was an organosilicon curing agent. In this embodiment, polymethylhydrosiloxane purchased from Dow Corning was used. Example 5

[0040] This embodiment provides an attachable transparent phase change thermal management film, which differs from Embodiment 1 in that it does not have a PDMS surface functional layer coated and uses a different combination of anhydride curing agents. The specific preparation steps are as follows; 1) Dry polyethylene glycol (PEG6000) with a molecular weight of 6000 at 30 °C for 2 hours. Weigh 4.0 g of the dried PEG6000, 2.5 g of EP51 epoxy resin, and 0.7 g of borosilicate glass microspheres (average particle size 1-5 μm, refractive index about 1.52) and place them in a 50 mL flask. Stir at 500 rpm for 4 hours in an oil bath at 70 °C to obtain a homogeneous premixed solution. 2) Separately, take 1.5 g of methyl hexahydrophthalic anhydride curing agent, 1.0 g of phthalic anhydride, 0.15 g of accelerator DMP-30, and 0.1 g of benzotriazole UV absorber (triazine UV absorber, model UV-1500, (Guangzhou Good New Material Technology)). Mix them and preheat at 80 °C until homogeneous to obtain a curing agent solution. Cool the pre-mixed liquid to about 65 °C, slowly add 1.5 g of the above curing agent solution, stir at 450 rpm for 15 minutes, and then degas under vacuum for 15 minutes. 3) The degassed mixture is poured into a polytetrafluoroethylene mold, and the film thickness is controlled to be about 1.0 mm. The film is cured in stages according to the procedure of keeping it at 60 °C for 2 h, 70 °C for 2 h, and 80 °C for 24 h to obtain a transparent composite film substrate. Example 6

[0041] This embodiment provides an attachable transparent phase change thermal management film, using paraffin as the phase change material, 2-methylimidazole as the promoter, and employing a wide temperature range of 50–150°C step curing. The specific preparation steps are as follows: 1) Place 4.0 g of 52# paraffin wax (refractive index about 1.47) with a melting point of 52℃, 2.0 g of EP51 type epoxy resin, and 0.6 g of borosilicate glass microspheres (average particle size 1-5 μm, refractive index about 1.52) in a flask and stir at 500 rpm for 3 hours in an oil bath at 75℃ to obtain a uniform premixed solution; 2) Separately, take 2.0 g of methylhexahydrophthalic anhydride curing agent, 0.12 g of 2-methylimidazole accelerator, and 0.1 g of triazine UV absorber (UV-1500), mix them, and preheat at 70°C until homogeneous to obtain a curing agent solution. Cool the pre-prepared mixture to approximately 65°C, slowly add 1.3 g of the above curing agent mixture, stir at 400 rpm for 15 minutes, and then degas under vacuum for 15 minutes. 3) Cast the degassed mixture into a polytetrafluoroethylene mold, control the film thickness to about 1.0 mm, and cure it in stages according to the following procedure: 50℃ for 2 h → 70℃ for 2 h → 90℃ for 2 h → 120℃ for 1 h → 150℃ for 2 h, and cool it naturally to room temperature to obtain a transparent composite film substrate. 4) Spin-coat the PDMS surface functional layer (approximately 50 μm thick) using the same method as in Example 1 to obtain the final thin film sample. Example 7

[0042] This embodiment provides an attachable transparent phase change thermal management film, using stearic acid (melting point approximately 69°C, refractive index approximately 1.45) as the phase change material, stannous octoate as the accelerator, and a curing process of 50–160°C. The specific preparation steps are as follows: 1) Place 3.5 g of stearic acid, 2.5 g of EP44 epoxy resin, and 0.5 g of sodium-calcium glass microspheres (average particle size 2-8 μm, refractive index about 1.51) in a flask and stir at 500 rpm for 3 hours in an oil bath at 80℃ until homogeneous to obtain a homogeneous premixed solution. 2) Separately, take 2.2 g of methyltetrahydrophthalic anhydride curing agent, 0.18 g of stannous octoate accelerator, and 0.12 g of triazine UV absorber (UV-1500). Mix them and preheat at 75°C until homogeneous to obtain a curing agent solution. Cool the pre-mixed solution to approximately 65°C, slowly add 1.2 g of the above curing agent mixture to the pre-mixed solution, stir evenly at 400 rpm, and then degas under vacuum for 15 minutes. 3) Inject the mixture into the mold, control the film thickness to about 1.2 mm, and cure the following steps: 50℃ for 1 h → 70℃ for 2 h → 90℃ for 2 h → 120℃ for 1 h → 160℃ for 1 h; 4) Spin-coating the PDMS functional layer (approximately 45 μm thick) as in Example 1. Example 8

[0043] This embodiment provides an attachable transparent phase change thermal management film, using a eutectic mixture of lauric acid and stearic acid as the phase change material, and employing the anhydride curing system, borosilicate glass microspheres, and PDMS surface functional layer from Example 1. The specific preparation steps are as follows: 1) Lauric acid (purity ≥98%) and stearic acid (purity ≥98%) were mixed at a mass ratio of 70:30 and stirred in an oil bath at 70℃ for 30 minutes to form a homogeneous eutectic mixture (eutectic point approximately 44℃, latent heat approximately 170 kJ / kg). 4.0 g of this eutectic mixture, 2.0 g of EP51 epoxy resin, and 0.6 g of borosilicate glass microspheres (average particle size 1–5 μm, refractive index approximately 1.52) were weighed and placed in a 50 mL flask. The mixture was stirred in an oil bath at 75℃ at 500 rpm for 3 hours to obtain a homogeneous pre-mixed solution. 2) Separately, take 2.0 g of methyl hexahydrophthalic anhydride curing agent, 0.1 g of DMP-30 accelerator, and 0.1 g of triazine UV absorber (model UV-1500), mix them, and preheat at 70°C until homogeneous. Cool the pre-mixed solution to approximately 65°C, slowly add 1.2 g of the above curing agent solution, stir at 400 rpm for 15 minutes, and then degas under vacuum for 15 minutes; 3) The degassed mixture is poured into a polytetrafluoroethylene mold, the film thickness is controlled to be about 1.0 mm, and the film is cured in stages according to the procedure of holding at 60℃ for 2 h, 70℃ for 2 h, and 80℃ for 24 h to obtain a transparent composite film substrate. 4) The polydimethylsiloxane prepolymer and curing agent were mixed at a mass ratio of 10:1 and dissolved in n-hexane to prepare a 10% (w / w) PDMS solution. The composite film substrate was fixed on a spin coater, and the PDMS solution was spin-coated at 3000 rpm. Then, it was cured in an oven at 80°C for 2 hours to form a PDMS surface functional layer with a thickness of about 50 μm, thus obtaining the final film sample.

[0044] In addition, the visible and infrared reflectance spectra of the thin film samples prepared in Examples 2-4 and Examples 6-8 were tested. The test results showed that they all had effects comparable to those in Example 1, achieving passive cooling of photovoltaic modules through the synergistic effect of radiative cooling, phase change energy storage, and thermal diffusion mechanisms, thereby improving photoelectric conversion efficiency and extending service life. The thin film in Example 5 without the PDMS surface functional layer showed reduced visible light transmittance and enhanced infrared emissivity.

Claims

1. A method for preparing an attachable transparent phase change thermal management thin film, characterized in that, The steps include the following: 1) The phase change material, epoxy resin matrix and glass microspheres are heated and mixed evenly to obtain a pre-prepared mixture; the phase change material is selected from at least one of polyethylene glycol, fatty acid, polyol, paraffin, organic carboxylic acid ester, etc. 2) Add anhydride curing agent, accelerator and UV absorber to the premixed liquid, heat and mix evenly, and then degas under vacuum; 3) Inject the degassed mixture into the mold and heat it to solidify.

2. The preparation method according to claim 1, characterized in that, In step 1), the mass ratio of the phase change material to the epoxy resin is (1-3):1; the epoxy resin includes at least one of EP51 type epoxy resin and EP44 type epoxy resin; the fatty acid is selected from at least one of lauric acid, palmitic acid, stearic acid, decanoic acid, etc., or their binary / ternary eutectic mixtures; the polyol is selected from at least one of pentaerythritol, trimethylolethane, trimethylolpropane, etc., or their binary / ternary eutectic mixtures; the paraffin is selected from at least one of 52# paraffin, 58# paraffin, n-octadecane, n-eicosane, etc.; the organic carboxylic acid ester is selected from at least one of octadecyl acrylate, methyl stearate, butyl stearate, etc.

3. The preparation method according to claim 1, characterized in that, In step 1), the refractive index of the glass microspheres is 1.45 to 1.55; the glass microspheres include one or more of borosilicate glass microspheres, soda-lime glass microspheres, and quartz glass microspheres; the amount of glass microspheres added accounts for 2.5 to 15 wt% of the total mass of the phase change material and epoxy resin.

4. The preparation method according to claim 1, characterized in that, In step 2), the anhydride curing agent includes one or more of phthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride; the mass ratio of the pre-mixed liquid to the anhydride curing agent is 5: (0.8-1.2).

5. The preparation method according to claim 1, characterized in that, In step 2), the accelerator includes one or more of 2,4,6-tris(dimethylaminomethyl)phenol, 2-methylimidazole, 2-ethyl-4-methylimidazole, stannous octoate, and aluminum acetylacetonate; the mass ratio of the anhydride curing agent to the accelerator is (10-30):

1.

6. The preparation method according to claim 1, characterized in that, In step 2), the ultraviolet absorber is a triazine ultraviolet absorber or a benzotriazole ultraviolet absorber, and the amount of ultraviolet absorber added accounts for 0.5 to 3 wt% of the total mass of the phase change material and epoxy resin.

7. The preparation method according to claim 1, characterized in that, In step 3), the temperature is gradually increased and cured in stages within the range of 50 to 160°C for 2-24 hours.

8. The preparation method according to claim 1, characterized in that, The film also includes a polydimethylsiloxane functional layer coated on its surface, as follows: The polydimethylsiloxane prepolymer and curing agent are mixed at a mass ratio of (8-12):1, dissolved in an organic solvent to prepare a solution with a mass fraction of 8-20%, and then spin-coated onto the surface of a film, followed by curing to form a polydimethylsiloxane functional layer with a thickness of 10-100 μm.

9. An attachable transparent phase change thermal management film prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the thin film according to claim 9 in a photovoltaic module, characterized in that, It is attached to the surface of the photovoltaic module by pressure-sensitive adhesive or lamination.

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