Heat-conducting and insulating BN / Al2O3 / EVA photovoltaic packaging adhesive film as well as preparation method and application thereof

Abstract

The invention discloses a heat-conducting and insulating BN / Al2O3 / EVA photovoltaic packaging adhesive film, a preparation method and application, flaky boron nitride and spherical aluminum oxide are adopted as heat-conducting fillers, an ethylene vinyl acetate copolymer and the heat-conducting fillers are dispersed in xylene by adopting a high-speed shearing method, and glass is coated with the xylene in a blade coating manner, so that the heat-conducting and insulating photovoltaic packaging adhesive film is formed. The flaky boron nitride and the spherical aluminum oxide are in contact with each other to form a three-dimensional heat conduction path, and meanwhile, the shear strength of the packaging adhesive film is effectively improved due to the addition of the inorganic particles. The in-plane heat conductivity can reach 2.71 W / m.K, the out-plane heat conductivity can reach 1.01 W / m.K, heat conduction can be conducted quickly, and heat accumulation of the photovoltaic module is effectively relieved. Under the irradiation of sunlight, the photovoltaic module can be cooled by 2 DEG C, and the working voltage of 5 mV is increased. In addition, the packaging adhesive film has excellent electrical insulation property and mechanical property, and ensures stable and safe operation of the photovoltaic module in practical application.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive photovoltaic encapsulation film technology, specifically relating to thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film; it also relates to the preparation method and application of thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film. Background Technology

[0002] Solar cells have been developed as a low-cost power generation source and are expected to become a major power source between 2040 and 2050. Typically, only 13% to 20% of the solar energy absorbed by solar photovoltaic (PV) panels is converted into electricity; the remainder is inevitably converted into heat, leading to increased operating temperature and negatively impacting the conversion efficiency of the PV panels. For every 1°C increase in the temperature of a solar PV panel, its power generation efficiency decreases by approximately 0.4-0.5%. Reducing the operating temperature of solar PV panels is one of the key factors in improving their photoelectric conversion efficiency, thus creating an urgent need for efficient solar PV panel cooling technologies. Currently, the industry employs various solutions to reduce the operating temperature of PV modules. These include liquid cooling, finned heat dissipation, forced convection, and phase change materials. However, these heat dissipation methods typically consume other forms of energy, require specific operating conditions, and have complex structures. Considering economic costs, technical requirements, energy consumption, and stability, the application of these cooling methods in practical scenarios still faces some difficulties and has not yet been widely adopted. Therefore, reducing the operating temperature of photovoltaic modules without changing the existing structure of the modules or consuming other forms of energy is a good strategy to solve this problem.

[0003] The EVA encapsulation layer in photovoltaic modules has extremely low thermal conductivity, making it the primary thermal resistance layer. It cannot quickly dissipate the heat generated by the solar cells, causing heat buildup and a continuous rise in the operating temperature of the photovoltaic cells, ultimately reducing the module's power generation efficiency. Although many researchers have introduced high thermal conductivity fillers into the EVA matrix to improve its thermal conductivity, most of these methods enhance thermal conductivity by introducing single-dimensional fillers, which is not conducive to efficient heat dissipation of photovoltaic modules. Therefore, the preparation of thermally conductive and insulating EVA photovoltaic encapsulation films by introducing multi-dimensional thermally conductive particle composites to construct three-dimensional thermally conductive pathways has significant technical value. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method for preparing a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film, thereby solving the problem of poor thermal conductivity of conventional EVA films.

[0005] Another objective of this invention is to provide a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film.

[0006] Another objective of this invention is to provide the application of thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film.

[0007] The first technical solution adopted in this invention is a method for preparing a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film, the specific operation steps of which are as follows: Step 1: Disperse boron nitride and aluminum oxide in xylene and stir evenly by high-speed shearing to obtain dispersion A; Step 2: Add 15-20 parts of EVA to dispersion A, heat and stir magnetically until the EVA is completely dissolved, and record this as dispersion B; Step 3: Pour dispersion B onto the upper surface of the coating machine and obtain thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film by coating.

[0008] The invention is further characterized in that, Preferably, the high-speed shearing time in step 1 is 30-40 min, and the rotation speed is 7000-8000 r / min.

[0009] Preferably, the duration of magnetic stirring in step 2 is 30-40 minutes, and the heating temperature is 70-80℃.

[0010] Preferably, the coating speed in step 3 is 70~80 mm / s, and the drying time after coating is 1~2 hours at a temperature of 50~60℃.

[0011] Preferably, the mass ratio of boron nitride, aluminum oxide and xylene in step 1 is 2~8:2~8:70~80.

[0012] Preferably, the mass ratio of boron nitride to EVA in step 2 is 2~8:15~20.

[0013] The second technical solution adopted in this invention is a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film, prepared using the above-mentioned method. The thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film comprises the following parts by mass: 70-80 parts xylene solvent, 15-20 parts EVA, 2-8 parts boron nitride, and 2-8 parts alumina. This invention provides a thermally conductive and insulating photovoltaic encapsulating film with a three-dimensional network of thermally conductive pathways synergistically constructed from boron nitride and alumina particles. A polymer is used as the matrix, sheet-like boron nitride as the main thermally conductive filler, and spherical alumina as the structure-regulating thermally conductive particles to synergistically prepare the thermally conductive and insulating photovoltaic encapsulating film. The in-plane thermal conductivity of the BN / Al2O3 / EVA photovoltaic encapsulating film of this invention can reach 2.71 W / m·K, and the out-of-plane thermal conductivity can reach 1.01 W / m·K.

[0014] The third technical solution adopted in this invention is the application of thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film. Photovoltaic modules are prepared using thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film. The BN / Al2O3 / EVA encapsulation film, photovoltaic glass, silicon wafer, and EVA encapsulation film are placed in a vacuum hot press in the order of photovoltaic module composition and hot-pressed to obtain a photovoltaic module encapsulated with insulating and thermally conductive EVA film containing a BN / Al2O3 network.

[0015] Preferably, the hot-pressing temperature of the photovoltaic module encapsulated with the BN / Al2O3 network insulating and thermally conductive EVA film is 100~110℃, and the hot-pressing time is 35~45min.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: 1. The encapsulating film obtained by this invention can be used as the back encapsulation layer of photovoltaic modules, possessing thermal conductivity and insulation properties. Its in-plane thermal conductivity reaches 2.71 W / m·K, and its out-of-plane thermal conductivity reaches 1.01 W / m·K. In photovoltaic module cooling tests, comparative experiments have proven that this film can reduce the operating temperature of photovoltaic modules; simultaneously, it exhibits excellent mechanical stability and volume resistivity, ensuring the stability and safety of the modules in practical applications.

[0017] 2. This invention uses inorganic thermally conductive filler particles as a mixed-dimensional material, namely one-dimensional sheet-like boron nitride and three-dimensional spherical alumina. Compared to using a single thermally conductive filler, the encapsulation film prepared by using mixed-dimensional thermally conductive materials exhibits better thermal conductivity due to their synergistic effect. Under sunlight, it can reduce the operating temperature of photovoltaic modules by 2°C. Detailed Implementation The technical solution and preparation method of the present invention will be clearly and completely described below. The embodiments described below are part of the present invention, but not all of the embodiments.

[0018] The present invention relates to a method for preparing a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film. In this invention, boron nitride is referred to as BN, aluminum oxide as Al2O3, ethylene-vinyl acetate copolymer is simply referred to as EVA, and the mixture of BN and Al2O3 is simply referred to as B. x Al y x and y are the mass ratios of BN and Al2O3.

[0019] Example 1: Step 1: First, disperse 8 parts boron nitride and 2 parts alumina in 70 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B4Al1 dispersion; Step 2: Add 15 parts of EVA to the B4Al1 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B4Al1 / EVA dispersion.

[0020] Step 3: Pour the B4Al1 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h to obtain a thermally conductive and insulating B4Al1 / EVA photovoltaic encapsulation film.

[0021] Testing revealed that the thermally conductive and insulating B4Al1 / EVA encapsulating film prepared in Example 1 had an in-plane thermal conductivity of 3.32 W / m·K, an out-of-plane thermal conductivity of 0.82 W / m·K, and a volume resistivity of 2.74 × 10⁻⁶. 14 The Ω·cm reflectance is 87.38%, the infrared emissivity is 91.67%, the shear strength is 2.71 MPa, the elongation at break is 426.93%, and the breaking strength is 5.58 MPa.

[0022] Example 2: Step a: First, disperse 6 parts boron nitride and 4 parts alumina in 70 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B3Al2 dispersion; Step b: Add 15 parts of EVA to the B3Al2 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B3Al2 / EVA dispersion.

[0023] Step c: Pour the B3Al2 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h, to obtain a thermally conductive and insulating B3Al2 / EVA photovoltaic encapsulation film.

[0024] Testing revealed that the thermally conductive and insulating B3Al2 / EVA encapsulating film prepared in Example 2 had an in-plane thermal conductivity of 2.71 W / m·K, an out-of-plane thermal conductivity of 1.01 W / m·K, and a volume resistivity of 2.97 × 10⁻⁶. 14 Ω·cm, reflectivity 85.72%, infrared emissivity 90.72%, shear strength 3.06 MPa, elongation at break 446.43%, and tensile strength 5.92 MPa.

[0025] Example 3: Step a: First, disperse 4 parts boron nitride and 6 parts alumina in 70 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B4Al1 dispersion; Step b: Add 15 parts of EVA to the B2Al3 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B2Al3 / EVA dispersion.

[0026] Step c: Pour the B2Al3 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h, to obtain a thermally conductive and insulating B2Al3 / EVA photovoltaic encapsulation film.

[0027] Testing showed that the thermally conductive and insulating B2Al3 / EVA encapsulating film prepared in Example 3 had a thermal conductivity of 1.71 W / m·K, an out-of-plane thermal conductivity of 1.15 W / m·K, and a volume resistivity of 2.82 × 10⁻⁶. 14 The Ω·cm reflectance is 83.74%, the infrared emissivity is 90.63%, the shear strength is 3.32 MPa, the elongation at break is 526.44%, and the tensile strength is 7.37 MPa.

[0028] Example 4: Step a: First, disperse 2 parts boron nitride and 8 parts alumina in 70 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B1Al4 dispersion; Step b: Add 15 parts of EVA to the B1Al4 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B1Al4 / EVA dispersion.

[0029] Step c: Pour the B1Al4 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h to obtain a thermally conductive and insulating B1Al4 / EVA photovoltaic encapsulation film.

[0030] The thermally conductive and insulating B1Al4 / EVA encapsulating film prepared in Example 4 was tested and found to have a thermal conductivity of 2.87 W / m·K, an out-of-plane thermal conductivity of 0.94 W / m·K, and a volume resistivity of 2.63 × 10⁻⁶. 14 Ω·cm, reflectivity 79.37%, infrared emissivity 96.45%, shear strength 2.72 MPa, elongation at break 602.93%, and tensile strength 8.06 MPa.

[0031] Comparative Example 1 Step a: First, disperse 10 parts of boron nitride in 70 parts of xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as BN dispersion; Step b: Add 15 parts of EVA to the BN dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as BN / EVA dispersion.

[0032] Step c: Pour the BN / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h to obtain a thermally conductive and insulating BN / EVA photovoltaic encapsulation film.

[0033] The BN / EVA encapsulating film prepared in Comparative Example 1 was tested and found to have an in-plane thermal conductivity of 2.12 W / m·K, an out-of-plane thermal conductivity of 0.68 W / m·K, and a volume resistivity of 4.09 × 10⁻⁶. 14 The shear strength is 2.48 MPa, the elongation at break is 368.46%, and the breaking strength is 4.94 MPa.

[0034] Comparative Example 2 Step a: First, disperse 10 parts of Al2O3 in 70 parts of xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as Al2O3 dispersion; Step b: Add 15 parts of EVA to the Al2O3 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as Al2O3 / EVA dispersion.

[0035] Step c: Pour the Al2O3 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h to obtain a thermally conductive and insulating Al2O3 / EVA photovoltaic encapsulation film.

[0036] The Al2O3 / EVA encapsulating film prepared in Comparative Example 2 was tested and found to have an in-plane thermal conductivity of 0.87 W / m·K, an out-of-plane thermal conductivity of 0.52 W / m·K, and a volume resistivity of 7.08 × 10⁻⁶. 14 The shear strength is 2.62 MPa, the elongation at break is 705.92%, and the breaking strength is 8.26 MPa.

[0037] Example 5 Step a: First, disperse 3 parts boron nitride and 5 parts alumina in 80 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B3Al5 dispersion; Step b: Add 15 parts of EVA to the B1Al4 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B3Al5 / EVA dispersion.

[0038] Step c: Pour the B3Al5 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h, to obtain a thermally conductive and insulating B3Al5 / EVA photovoltaic encapsulation film.

[0039] Example 6: Step a: First, disperse 5 parts boron nitride and 4 parts alumina in 75 parts xylene, and shear and stir at room temperature for 30 min by high-speed shearing, and record it as B5Al4 dispersion; Step b: Add 15 parts of EVA to the B5Al4 dispersion, heat to 80℃ and stir for 30 min to completely dissolve the EVA, and record it as B5Al4 / EVA dispersion.

[0040] Step c: Pour the B1Al4 / EVA dispersion onto the upper surface of the coating machine, with a coating speed of 70 mm / s, a solvent evaporation temperature of 50℃, and a time of 2 h to obtain a thermally conductive and insulating B5Al4 / EVA photovoltaic encapsulation film.

[0041] Performance tests were conducted on the photovoltaic encapsulating films prepared according to Examples 1-4 and Comparative Examples 1-2 above. The test item involved in this invention is: in-plane thermal conductivity λ / / (W / m·K); out-of-plane thermal conductivity λ ⊥ (W / m·K); Volume resistivity ρ (×10 14 Ω·cm); reflectivity R; infrared emissivity E; shear strength σ (MPa); elongation at break e (%); fracture strength σc (MPa).

[0042] Table 1. Test results of the examples and comparative examples.

[0043] Examples 1-4 used BN and Al2O3 dispersed in xylene, followed by the addition of EVA. A three-dimensional thermally conductive network was constructed using the volume repulsion effect of plate-like boron nitride and spherical alumina. The introduction of Al2O3 facilitated the dispersion of boron nitride. Comparative Examples 1-2 used BN or Al2O3 alone introduced into the EVA matrix. The BN / Al2O3 / EVA series encapsulating films prepared in Examples 1-4 have higher in-plane thermal conductivity, out-of-plane thermal conductivity, volume resistivity, reflectivity, infrared emissivity, shear strength, bond-breaking elongation, and fracture strength, exhibiting superior thermal conductivity and enabling rapid conduction of heat from the photovoltaic panel to the external environment through the thermally conductive encapsulating film. In addition, BN / Al2O3 / / EVA possesses excellent mechanical properties and volume resistivity, better ensuring the long-term stable and safe operation of photovoltaic modules.

[0044] When the matrix consists only of lamellar boron nitride, it only provides in-plane thermal conductivity, with a negligible contribution to out-of-plane thermal conductivity. When the matrix consists only of spherical alumina, the spherical thermally conductive filler helps improve out-of-plane thermal conductivity. However, the numerous gaps between the spheres are also detrimental to heat transfer. When lamellar BN and spherical Al2O3 are combined, the spherical Al2O3 has a larger specific surface area, occupying more matrix space and providing more opportunities for the fillers to contact each other. The lamellar BN can only be located in the gaps between the spheres. This sphere-plate structure forms a thermally conductive pathway through mutual contact.

[0045] As shown in Table 1, through comprehensive analysis of the in-plane thermal conductivity, out-of-plane thermal conductivity, shear strength, volume resistivity, elongation at break and fracture strength of each embodiment, the preferred embodiment 2 of the present invention is selected as the best example sample. Its in-plane and out-of-plane thermal conductivity are significantly improved, indicating that it significantly improves the thermal conductivity of the film. Embodiment 2 is used as the back encapsulation layer of the photovoltaic module, and the photovoltaic module is encapsulated by vacuum hot pressing with thermally conductive and insulating BN / Al2O3 / EVA film. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film, characterized in that, The specific operating steps are as follows: Step 1: Disperse boron nitride and aluminum oxide in xylene and stir evenly by high-speed shearing to obtain dispersion A; Step 2: Add 15-20 parts of EVA to dispersion A, heat and stir magnetically until the EVA is completely dissolved, and record this as dispersion B; Step 3: Pour dispersion B onto the upper surface of the coating machine and obtain thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulation film by coating.

2. The method for preparing the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 1, characterized in that, The high-speed shearing time in step 1 is 30-40 min, and the rotation speed is 7000-8000 r / min.

3. The method for preparing the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 1, characterized in that, Step 2: Magnetic stirring should last for 30-40 minutes, and the heating temperature should be 70-80℃.

4. The method for preparing the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 1, characterized in that, The scraping speed in step 3 is 70~80mm / s, and the drying time after scraping is 1~2 hours at a temperature of 50~60℃.

5. The method for preparing the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 1, characterized in that, The mass ratio of boron nitride, aluminum oxide and xylene in step 1 is 2~8: 2~8:70~80.

6. The method for preparing the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 1, characterized in that, The mass ratio of boron nitride to EVA in step 2 is 2~8:15~20.

7. A thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film, characterized in that, The following components are included by mass: 70-80 parts xylene solvent, 15-20 parts EVA, 2-8 parts boron nitride, and 2-8 parts alumina.

8. The application of thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film, characterized in that, Photovoltaic modules are prepared using thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film. The BN / Al2O3 / EVA encapsulating film, photovoltaic glass, silicon wafer, and EVA encapsulating film are placed in a vacuum hot press in the order of photovoltaic module composition and hot-pressed to obtain a photovoltaic module encapsulated with insulating and thermally conductive EVA film containing a BN / Al2O3 network.

9. The application of the thermally conductive and insulating BN / Al2O3 / EVA photovoltaic encapsulating film according to claim 8, characterized in that, The hot-pressing temperature is 100~110℃, and the hot-pressing time is 35~45min.

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