Spectrally selective black photovoltaic encapsulant film and preparation method and application thereof

Abstract

The present application relates to the technical field of photovoltaic encapsulation adhesive film, and discloses a spectrum-selective black photovoltaic encapsulation adhesive film, a preparation method and application thereof. The adhesive film is designed by a three-layer functional decoupling structure of a visible light absorption layer (A layer), an infrared reflection and charge blocking layer (B layer) and a diffuse reflection adhesive layer (C layer), and a proper amount of light absorber is introduced into the A layer, a proper amount of infrared reflection particles with core-shell structure and ion capturing agent are introduced into the B layer, and a proper amount of diffuse reflection particles are introduced into the C layer, so that multiple balances of pure black appearance, high-efficiency infrared reflection and high diffuse reflection are realized, and the industry problems such as temperature rise, power loss and potential-induced degradation caused by heat absorption of traditional black photovoltaic modules are solved. While maintaining the black appearance, the adhesive film can reduce the temperature of the module, improve the power output, has good adhesive performance, high volume resistivity and excellent PID resistance, and has high reliability, and is particularly suitable for high-end BIPV and distributed photovoltaic modules.

Description

Technical Field

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

[0002] The application scenarios for photovoltaic power generation are rapidly expanding from large-scale ground-mounted power plants to building-integrated photovoltaics (BIPV) and high-end distributed rooftop systems. In these applications, the aesthetics of photovoltaic modules and their integration with the building environment have become important considerations. Black photovoltaic modules are particularly favored by the market due to their uniform appearance and good visual concealment.

[0003] However, as shown in publication number CN112980353A, the conventional method to achieve a black appearance is to add light-absorbing agents such as carbon black to the photovoltaic encapsulation film (such as EVA film and POE film). This brings two serious problems: First, while absorbing visible light, carbon black also strongly absorbs near-infrared light, which accounts for about 50% of the solar energy. This causes a sharp increase in the temperature of the photovoltaic encapsulation film and the entire photovoltaic module. Studies have shown that for every 1°C increase in the operating temperature of a photovoltaic module, its output power can decrease by 0.3-0.5%, and the power loss of traditional black photovoltaic modules can reach 3-5%. Second, the addition of a large amount of carbon black may affect the volume resistivity of the photovoltaic encapsulation film and exacerbate the migration of metal ions such as sodium ions in harsh environments of high humidity, high temperature, and high voltage, causing severe potential-induced degradation (PID), threatening the reliability of the photovoltaic module's 25-year lifespan.

[0004] To reduce the operating temperature of photovoltaic (PV) modules, the industry has developed high-reflectivity white encapsulant films. These films effectively reduce the operating temperature of PV modules by reflecting or directly reflecting light that is not absorbed by the solar cells (especially infrared light). However, white encapsulant films cannot meet the requirements for a black appearance, limiting their application scenarios. Furthermore, some existing improvements, such as mixing white reflective or thermally conductive fillers into black encapsulant films (as shown in CN112980353A), often result in low reflectivity due to filler agglomeration and poor interfacial compatibility, and the electrical insulation performance of the encapsulant film deteriorates, increasing the risk of PID (Potential Inhibition) in PV modules. Additionally, black encapsulant films using a black / white dual-layer composite structure (as shown in CN114149769A) suffer from low reflectivity due to weak interfacial bonding, a grayish-black appearance, and interference of the upper absorption layer with the reflective layer's function. Therefore, developing a new black PV encapsulant film that simultaneously satisfies the requirements of an ultra-black appearance, efficient infrared reflection to reduce operating temperature, and excellent electrical insulation to ensure long-term PID resistance has become a critical technological bottleneck that the industry urgently needs to overcome. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a spectrally selective black photovoltaic encapsulating film, its preparation method and application, so as to solve the contradiction between power, reliability and aesthetics of black photovoltaic modules in one stop.

[0006] Based on this, the present invention discloses a spectrally selective black photovoltaic encapsulating film, which is a multilayer composite structure, comprising a visible light absorption layer (layer A), an infrared reflection and charge blocking layer (layer B), and a diffuse reflection adhesive layer (layer C).

[0007] The visible light absorbing layer comprises a matrix resin and a light absorber formulated at a weight ratio of 100:0.3-1.2; the average transmittance of the visible light absorbing layer to visible light in the 380-780nm range is less than 5%.

[0008] The infrared reflective and charge-blocking layer comprises a matrix resin, core-shell structured infrared reflective particles, and an ion trapping agent prepared in a weight ratio of 100:8-25:0.1-0.8. The core-shell structured infrared reflective particles have at least one of TiO2, ZrO2, and SiO2 as the core and at least one of ZnO, Al2O3, and MgO as the shell. The infrared reflective and charge-blocking layer has an average reflectivity of not less than 93% for 800-1200nm infrared light and a volume resistivity of not less than 1×10¹. 6 Ω·cm;

[0009] The diffuse reflective adhesive layer comprises a matrix resin and diffuse reflective particles formulated at a weight ratio of 100:3-15; the average diffuse reflectance of the diffuse reflective adhesive layer for light in the 380-1200nm wavelength band is not less than 95%.

[0010] The matrix resins in layers A, B, and C can be independently selected from resins commonly used in photovoltaic encapsulation films, including but not limited to at least one of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE). They can be selected and compounded according to the different requirements of each layer for weather resistance, adhesion, and processability. For example, the matrix resins in layers A, B, and C can all be EVA. Alternatively, the matrix resins in layers A, B, and C can all be POE. Or, the matrix resins in layers A and C can be EVA, while the matrix resin in layer B can be POE, to form a spectrally selective black photovoltaic encapsulation film with an EPE (EVA-POE-EVA) structure. The melt index of EVA is preferably 20-25 g / min, and its VA content is preferably 24-28%. The melt index of POE is preferably 5-14 g / 10min.

[0011] Preferably, the light absorber is nano-carbon black with a particle size D50 of 20-80 nm, and more preferably nano-carbon black with a particle size D50 ≤ 50 nm.

[0012] Preferably, the infrared reflective particles of the core-shell structure have a particle size of 100-500 nm and a shell thickness of 10-80 nm. The core of the infrared reflective particles of the core-shell structure is a high-refractive-index metal oxide such as TiO2 or ZrO2, and the shell is a wide-bandgap, high-resistivity metal oxide such as ZnO or Al2O3.

[0013] More preferably, the infrared-reflecting particles with the core-shell structure are ZnO@TiO2 core-shell particles. The preparation process of these ZnO@TiO2 core-shell particles via the sol-gel method specifically includes the following steps:

[0014] (1) Pretreatment of nuclear material: Take 100 parts by weight of rutile TiO2 (nuclear material) powder with a particle size of 100-300 nm, and vacuum dry it at 100-130℃ for 3-6 hours to remove surface adsorbed water. Disperse the dried nuclear material powder in 800-1500 mL of anhydrous ethanol, add 2-8 parts by weight of silane coupling agent KH-570, and ultrasonically disperse it at 300-800 W for 15-45 minutes to allow the silane coupling agent to be fully adsorbed on the surface of the nuclear material. Stir and react in a water bath at 50-70℃ for 1-3 hours. After the reaction, centrifuge at 6000-10000 rpm for 8-15 minutes, discard the supernatant, and wash the precipitate with anhydrous ethanol 2-5 times. After each washing, centrifuge under the same conditions. Collect the precipitate and dry it in a vacuum drying oven at 60-100℃ for 8-16 hours to obtain surface-modified nuclear material.

[0015] (2) Preparation of shell precursor solution: Weigh out 6-40 parts by weight of the shell metal salt precursor, which is selected from at least one of zinc acetate dihydrate, zinc nitrate, aluminum isopropoxide, and aluminum nitrate. Dissolve the shell metal salt precursor in 40-200 mL of anhydrous ethanol, heat to 50-70 °C, stir until dissolved, adjust the pH of the solution to 4.0-5.5 with acetic acid, add 1-50 mL of deionized water, stir evenly to obtain the shell precursor solution.

[0016] (3) Sol-gel coating reaction: Take 100 parts by weight of the surface-modified core material obtained in step (1), disperse it in 800-1500 mL of anhydrous ethanol, and ultrasonically disperse it for 15-30 minutes at a power of 300-800 W. Transfer it to a reaction vessel and place it in a constant temperature water bath at 50-70℃. Stir at a speed of 200-500 rpm to obtain a core material suspension. Add the shell precursor solution prepared in step (2) dropwise to the core material suspension at a rate of 3-10 mL / min. During the dropwise addition, add 0.05-0.2 mol / L NaOH ethanol solution simultaneously to maintain the pH value of the reaction system in the range of 6.0-7.5. After the dropwise addition is completed, continue to stir the reaction in a water bath at 50-70℃ for 1-3 hours to allow the shell precursor to fully hydrolyze and condense on the surface of the surface-modified core material to form a uniform gel coating layer. After the reaction is complete, the mixture is left to stand and age for 6-18 hours to further densify the gel coating.

[0017] (4) Separation and washing: Centrifuge the aged mixture at 6000-10000 rpm for 8-15 minutes and discard the supernatant. Wash the precipitate with anhydrous ethanol 3-5 times, then centrifuge at 6000-10000 rpm for 8-15 minutes. Wash with deionized water 2-3 times until the pH of the washing solution reaches 6.5-7.5. Collect the washed precipitate.

[0018] (5) Drying and calcination: Place the washed precipitate in a vacuum drying oven and dry it at 60-100℃ for 8-16 hours. Place the dried precipitate powder in a ceramic crucible, put it in a muffle furnace, heat it to 400-500℃ at a heating rate of 1-5℃ / min, hold it at that temperature for 1-3 hours, and then let it cool naturally to room temperature. Take out the calcined core-shell particles.

[0019] (6) Dispersion treatment: The calcined core-shell particles are mixed with anhydrous ethanol at a mass-to-volume ratio (i.e., solid-liquid ratio, unit g / mL) of 1:5 to 1:10, and placed in a planetary ball mill. The mixture is ball-milled at 200-400 rpm for 1-3 hours to break up the agglomerates generated during the calcination process. The ball-milled slurry is then centrifuged at 6000-10000 rpm for 8-15 minutes. The supernatant is discarded, and the precipitate is dried in a vacuum drying oven at 60-100℃ for 8-16 hours. The precipitate is then passed through a 100-300 mesh sieve to obtain ZnO@TiO2 core-shell particles.

[0020] More preferably, the shell thickness accounts for 8-40% (more preferably 10-30%) of the overall particle size of the infrared reflective particles in the core-shell structure, which can provide better insulation and encapsulation effects while ensuring optical performance. If the shell is too thin, the following defects will occur: ① Incomplete encapsulation: When the shell is too thin, it cannot completely cover the core surface, and pinholes or uncovered areas are likely to appear, resulting in direct exposure of the core material (such as TiO2); ② Formation of conductive pathways: The exposed TiO2 particles may come into direct contact with each other, forming a local conductive network, which will significantly reduce the overall volume resistivity. If the shell is too thick, the following defects will occur: ① Reduced effective refractive index: The refractive index of the shell material (such as ZnO, refractive index -2.0) is lower than that of the core material (TiO2, refractive index -2.5). An excessively thick shell will reduce the overall effective refractive index of the particles, weaken the refractive index difference with the polymer matrix, and thus reduce the infrared reflectivity; ② Increased scattering loss: An excessively thick shell may cause additional light absorption or scattering, especially in the infrared band, which will cause the infrared reflectivity to fail to meet the requirement of ≥93%.

[0021] Preferably, the ion-scavenging agent is at least one selected from aminosilane coupling agents, epoxysilane coupling agents, and vinylsilane coupling agents. The ion-scavenging agent is preferably an aminosilane coupling agent (such as KH-550).

[0022] Preferably, the diffuse reflective particles are at least one of the following: smooth solid or hollow glass microspheres, ceramic microspheres (such as SiO2 or Al2O3 microspheres), and polymer microspheres, with a particle size of 0.5-15 μm (preferably 1-10 μm) and a refractive index of 1.8-2.5.

[0023] Preferably, the visible light absorption layer, the infrared reflection and charge blocking layer, and the diffuse reflection adhesive layer all further include a crosslinking agent and an anti-aging agent, and the weight ratio of the matrix resin, crosslinking agent, and anti-aging agent is 100:0.5-1.2:0.3-0.8.

[0024] This invention also discloses a method for preparing a spectrally selective black photovoltaic encapsulating film, comprising the following preparation steps:

[0025] S1. Prepare premixes for the visible light absorption layer, infrared reflection and charge blocking layer and diffuse reflection adhesive layer according to the raw material formulas for each layer.

[0026] S2. The premixed materials of each layer are melt-co-extruded through a co-extrusion die with independent flow channels, and after casting and cooling, a spectrally selective black photovoltaic encapsulation film is obtained.

[0027] Preferably, in step S2, the premix of each layer is fed into three independent single-screw extruders for melting and plasticizing. The extrusion temperature of the premix of the visible light absorption layer is 100-130℃, the extrusion temperature of the premix of the infrared reflection and charge blocking layer is 110-140℃, and the extrusion temperature of the premix of the diffuse reflection adhesive layer is 100-130℃. The molten material of each layer is conveyed to a three-layer co-extrusion casting die with three independent flow channels. The three layers of melt converge in the die or at the outlet, are extruded through the co-extrusion die, and formed into a film by casting. The film is then cooled and shaped by a 20-35℃ cooling roller to obtain a spectrally selective black photovoltaic encapsulation film.

[0028] Preferably, in step S3, the total thickness of the spectrally selective black photovoltaic encapsulating film is 0.40-0.65 mm; the thickness ratio of the visible light absorption layer, the infrared reflection and charge blocking layer and the diffuse reflection adhesive layer is 0.8-1.2:1.8-2.2:1.8-2.2.

[0029] This invention also discloses the application of a spectrally selective black photovoltaic encapsulating film, which is used as an encapsulating film in photovoltaic modules. The photovoltaic module's cell types include, but are not limited to, high-efficiency crystalline silicon cells such as PERC, TOPCon, HJT, and IBC, as well as novel cells such as perovskite tandem cells. In application, this spectrally selective black photovoltaic encapsulating film can be used in single-glass or double-glass photovoltaic modules, and can be encapsulated using conventional lamination processes.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The spectrally selective black photovoltaic encapsulating film of this invention employs a three-layer functional decoupled structure design (i.e., a visible light absorption layer, an infrared reflection and charge blocking layer, and a diffuse reflection adhesive layer). An appropriate amount of light absorber is introduced into layer A, along with an appropriate amount of core-shell structured infrared reflective particles and ion trapping agents introduced into layer B, and an appropriate amount of diffuse reflection particles introduced into layer C. This achieves a balance between a pure black appearance and high efficiency in infrared and diffuse reflection. The spectrally selective black photovoltaic encapsulating film exhibits a pure black appearance due to its efficient absorption in the visible light band, while its efficient reflection in the infrared band reduces thermal effects. Simultaneously, it possesses extremely high resistance to block charge migration and efficiently diffusely reflects the light source back to the solar cell for secondary absorption, ensuring its adhesive performance. Therefore, while maintaining a deep black appearance (L* value ≤ 25), this spectrally selective black photovoltaic encapsulating film can significantly reduce the operating temperature of photovoltaic modules by 10-15℃, increase the power output of photovoltaic modules by 3-5%, and possesses good adhesive performance, high volume resistivity, and excellent anti-PID performance, resulting in high reliability. Therefore, this spectrally selective black photovoltaic encapsulating film solves the industry problems of traditional black photovoltaic modules, such as temperature rise, power loss and potential-induced degradation caused by heat absorption. This spectrally selective black photovoltaic encapsulating film is particularly suitable for application scenarios with strict requirements for aesthetics, such as building-integrated photovoltaic (BIPV) modules and high-end residential distributed photovoltaic modules. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] This embodiment provides a spectrally selective black photovoltaic encapsulating film, which has a three-layer co-extruded composite structure, comprising a visible light absorption layer (layer A), an infrared reflection and charge blocking layer (layer B), and a diffuse reflection adhesive layer (layer C).

[0035] The visible light absorption layer (layer A) has an average transmittance of less than 5% in the 380-780nm wavelength range. Layer A comprises the following raw materials in parts by weight:

[0036] 100 parts POE (polyolefin elastomer, Wanhua Chemical WANSUPER® 9147, melt index 14g / 10min), 0.7 parts nano carbon black (particle size D50 of 30nm, Orion Printex® 35), 0.5 parts anti-aging agent (0.25 parts anti-aging agent 770, called bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, BASF-770 + 0.25 parts anti-aging agent 1076, called β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate octadecyl alcohol ester, Rianon RIANOX® 1076), 0.8 parts crosslinking agent (2-ethylhexyl carbonate tert-butyl peroxide, Arkema's Luperox® TBEC-H).

[0037] Among them, the infrared reflective and charge-blocking layer (B layer) has an average reflectivity of not less than 93% in the 800-1200nm wavelength band, and a volume resistivity of not less than 1×10¹. 6 Ω·cm. Layer B comprises the following raw materials in parts by weight:

[0038] 100 parts POE (polyolefin elastomer, Wanhua Chemical WANSUPER® 9147, melt index 14g / 10min), 15 parts ZnO@TiO2 core-shell particles (self-made, average particle size of TiO2 core is 200nm, thickness of ZnO shell is 25nm), 0.3 parts KH-550 (3-aminopropyltriethoxysilane, Shandong Silicon Science & Technology Co., Ltd.'s KH-550), 0.5 parts anti-aging agent (0.25 parts anti-aging agent 770, BASF-770 + 0.25 parts anti-aging agent 1076, RIANORON RIANOX® 1076), 0.8 parts crosslinking agent (Arkema's Luperox® TBEC-H).

[0039] The preparation process of ZnO@TiO2 core-shell particles specifically includes the following steps:

[0040] (1) TiO2 core pretreatment: Take 50g of rutile TiO2 (DuPont R-105, average particle size 200nm), vacuum dry at 120℃ for 4 hours, then disperse it in 500mL of anhydrous ethanol, add 2.5g of silane coupling agent KH-570, ultrasonically disperse at 500W for 30 minutes, and stir the reaction with a magnetic stirrer at 60℃ for 2 hours. Centrifuge the product after reaction at 8000rpm for 10 minutes, wash the obtained precipitate with anhydrous ethanol 3 times, and centrifuge under the same conditions after each wash; vacuum dry the precipitate at 80℃ for 12 hours to obtain pretreated TiO2.

[0041] (2) Preparation of shell precursor solution: Weigh 8.8g of zinc acetate dihydrate, dissolve it in 100mL of anhydrous ethanol, stir at 60℃ to dissolve, adjust the pH of the solution to 4.8 with acetic acid, add 1.4mL of deionized water, stir evenly to obtain shell precursor solution (zinc acetate solution).

[0042] (3) Sol-gel coating reaction: Take 30g of pretreated TiO2 from step (1), disperse it in 300mL of anhydrous ethanol, and sonicate it for 20 minutes at 500W. Then transfer it to a 1L three-necked flask and stir it in a 60℃ water bath at 400rpm to obtain a core material suspension. Add the shell precursor solution (zinc acetate solution) prepared in step (2) to the core material suspension at a rate of 6mL / min, and simultaneously add 0.1mol / L NaOH ethanol solution to maintain the pH value to 6.8. After the addition is complete, continue stirring the reaction in a 60℃ water bath for 2 hours, and then let it stand for 12 hours.

[0043] (4) Separation and washing: Centrifuge the aged mixture from step (3) (8000 rpm, 10 minutes), and wash it three times with ethanol and twice with deionized water until the pH reaches 7.0.

[0044] (5) Drying and calcination: The washed precipitate was vacuum dried at 80°C for 12 hours. The dried product was placed in a muffle furnace and heated to 450°C at a heating rate of 2°C / min. It was then kept at this temperature for 2 hours and allowed to cool naturally to room temperature. The calcined core-shell particles were then removed.

[0045] (6) Dispersion treatment: Take 20g of calcined core-shell particles, add 160mL of anhydrous ethanol and mix. Place the mixture in a planetary ball mill and ball mill at 300rpm for 2 hours. Centrifuge the slurry after ball milling at 8000rpm for 10 minutes and collect the precipitate. Dry the precipitate in a vacuum drying oven at 80℃ for 12 hours, and then pass it through a 200-mesh sieve to obtain ZnO@TiO2 core-shell particles.

[0046] The diffuse reflectance adhesive layer (C layer) has an average diffuse reflectance of not less than 95% in the 380-1200nm wavelength band. The C layer comprises the following raw materials in parts by weight:

[0047] 100 parts POE (polyolefin elastomer, Wanhua Chemical WANSUPER® 9147, melt index 14g / 10min), 8 parts hollow glass microspheres (average particle size 3μm, Saint-Lite hollow glass microspheres HM10), 0.5 parts anti-aging agent (0.25 parts anti-aging agent 770, BASF-770 + 0.25 parts anti-aging agent 1076, RIANORON RIANOX® 1076), 0.8 parts crosslinking agent (Arkema Luperox® TBEC-H).

[0048] This embodiment describes a method for preparing a spectrally selective black photovoltaic encapsulating film, the preparation process of which includes:

[0049] According to the raw material formulas for each layer, all raw materials for layers A, B, and C were premixed in a high-speed mixer and then melt-plasticized in three independent single-screw extruders. The extrusion temperature for layer A was 115°C, for layer B it was 120°C, and for layer C it was 110°C. The extrusions were then co-extruded through a die, cast into a film, cooled and shaped by a 20°C cooling roller, embossed, and finally measured, trimmed, and wound to obtain the spectrally selective black photovoltaic encapsulating film of Example 1. The average thickness ratio of layers A, B, and C was 1:2:2.

[0050] Example 2

[0051] This embodiment describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight of nano-carbon black in layer A is changed to 0.3 parts.

[0052] Example 3

[0053] This embodiment provides a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight of nano-carbon black in layer A is changed to 1.2 parts.

[0054] Example 4

[0055] This embodiment describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight fraction of ZnO@TiO2 core-shell particles in layer B is changed to 8 parts.

[0056] Example 5

[0057] This embodiment describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight fraction of ZnO@TiO2 core-shell particles in layer B is changed to 25 parts.

[0058] Example 6

[0059] This embodiment provides a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Embodiment 1, the difference between Embodiment 1 and Embodiment 1 is that the weight fraction of hollow glass microspheres in the C layer is changed to 3 parts.

[0060] Example 7

[0061] This embodiment provides a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Embodiment 1, the difference between Embodiment 1 and Embodiment 1 is that the weight fraction of hollow glass microspheres in the C layer is changed to 15 parts.

[0062] Comparative Example 1

[0063] This comparative example describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight of nano-carbon black in layer A is changed to 0.2 parts.

[0064] Comparative Example 2

[0065] This comparative example describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight of nano-carbon black in layer A is changed to 1.5 parts.

[0066] Comparative Example 3

[0067] This comparative example describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 2 is that the ZnO@TiO2 core-shell particles in layer B of Example 1 are replaced with the same weight proportions of conventional TiO2 particles (DuPont R105).

[0068] Comparative Example 4

[0069] This comparative example describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight fraction of ZnO@TiO2 core-shell particles in layer B is changed to 5 parts.

[0070] Comparative Example 5

[0071] This comparative example describes a spectrally selective black photovoltaic encapsulating film and its preparation method. Referring to Example 1, the difference between Example 1 and Example 1 is that the weight fraction of the hollow glass microspheres in layer C is changed to 1 part.

[0072] Performance testing

[0073] Optical, mechanical, and anti-PID tests were conducted on the black photovoltaic encapsulating films prepared in Examples 1-7 and Comparative Examples 1-5, and the corresponding photovoltaic modules. The test results are shown in Table 1 below. The photovoltaic module includes a photovoltaic front panel, a first encapsulating film, a photovoltaic cell, a second encapsulating film, and a photovoltaic back panel stacked sequentially from top to bottom. The second encapsulating film used was a commercially available conventional EPE film (JW-EPE01 film from Taizhou Zhonglai). The first encapsulating film used was the black photovoltaic encapsulating film prepared in Examples 1-7 and Comparative Examples 1-5 (layer A is close to the photovoltaic front panel, and layer C is close to the photovoltaic cell). Thus, the photovoltaic modules corresponding to Examples 1-7 and Comparative Examples 1-5 were obtained.

[0074] Optical performance: The transmittance of the film in the visible light band (380-780 nm), the infrared reflectance in the 800-1200 nm band, and the diffuse reflectance in the 380-1200 nm band were tested using a UV-Vis-NIR spectrophotometer (PerkinElmer Lambda 1050+) equipped with an integrating sphere, according to GB / T 29848-2018 standard. The L* value of the film was measured using a colorimeter (KonicaMinolta CM-3700A) under a D65 light source.

[0075] Among them, peel strength: according to GB / T 2790 standard, the 90° peel strength between the encapsulant film and the photovoltaic cell is tested.

[0076] Volume resistivity: The volume resistivity of the film is tested according to the national standard GB / T 31838.2-2019.

[0077] Among them, the PID test: according to the IEC-61215 standard, a test is conducted for 192 hours under the conditions of 85°C, 85% relative humidity, and -1500V bias voltage to calculate the power degradation rate of the photovoltaic module.

[0078] Among them, the hot spot temperature test: according to the IEC-61215 standard, the hot spot temperature of the photovoltaic module is tested under the following conditions: irradiance 1000±200W / m 2 Spectral distribution AM1.5, temperature 25±5℃.

[0079] Table 1

[0080]

[0081] As can be seen from Table 1:

[0082] (1) Based on the test data of Examples 1-7 (especially Example 1) and Comparative Examples 1-5, it can be concluded that:

[0083] The spectrally selective black photovoltaic encapsulating film of the present invention (hereinafter referred to as black photovoltaic encapsulating film) introduces an appropriate amount of light absorber (such as nano carbon black) in the visible light absorption layer (A layer), introduces infrared reflective particles (ZnO@TiO2 core-shell particles) and ion scavengers (such as KH-550) in the infrared reflective and charge blocking layer (B layer), and introduces diffuse reflective particles (such as hollow glass microspheres) in the diffuse reflective adhesive layer (C layer). In this way, while ensuring the appearance of the deep black photovoltaic module and reducing the L* value, it also improves the infrared reflectivity, diffuse reflectivity, adhesion performance, volume resistivity of the black photovoltaic encapsulating film, as well as the comprehensive performance of the photovoltaic module, such as anti-PID power decay and cooling effect.

[0084] (2) Based on the test data of Examples 1, 4, and 5 (the amount of ZnO@TiO2 core-shell particles in layer B is 15 parts, 8 parts, and 25 parts, respectively) and Comparative Example 3 (the amount of ZnO@TiO2 core-shell particles in layer B is replaced with conventional TiO2 particles) and Comparative Example 4 (the amount of ZnO@TiO2 core-shell particles in layer B is 5 parts), it can be concluded that:

[0085] The black photovoltaic encapsulating film of the present invention incorporates infrared reflective particles such as ZnO@TiO2 core-shell particles in the B layer, which helps to improve its infrared reflectivity. When the amount of ZnO@TiO2 core-shell particles in the B layer is 25 parts (as in Example 5), the infrared reflectivity of the black photovoltaic encapsulating film reaches the highest level of 96.8%.

[0086] However, increasing the amount of ZnO@TiO2 core-shell particles in layer B from 5 parts to 8 parts and then to 15 parts (as shown in Comparative Example 4, Example 4, and Example 1) resulted in a 6.3% increase in the infrared reflectivity of the black photovoltaic encapsulation film, a very significant improvement. In contrast, referring to Examples 1 and 5, increasing the amount of ZnO@TiO2 core-shell particles in layer B from 15 parts to 25 parts only resulted in a 0.3% increase in the infrared reflectivity of the black photovoltaic encapsulation film, a negligible improvement. Furthermore, the volume resistivity of the black photovoltaic encapsulation film in Example 5 was lower than that in Example 1. Therefore, considering all factors, 15 parts of ZnO@TiO2 core-shell particles in layer B of Example 1 is the optimal addition amount. Furthermore, the amount of infrared reflective particles (such as ZnO@TiO2 core-shell particles) introduced into the B layer of the black photovoltaic encapsulating film should not exceed 25 parts, to avoid excessive infrared reflective particles affecting the improvement of its overall performance such as volume resistivity (mainly because: after the concentration of ZnO@TiO2 core-shell particles in the system reaches a certain level, the particle spacing is already small enough, and the interface infrared reflection is close to saturation. Continuing to increase the ZnO@TiO2 core-shell particles will only increase the risk of aggregation, and it is difficult to further improve the infrared reflectivity. When the concentration of ZnO@TiO2 core-shell particles is too high, the average distance between particles decreases. Even with an insulating shell layer, direct contact or tunneling effects may still occur between particles, forming a local conductive network, which may also be one of the reasons for the decrease in volume resistivity). Conversely, the amount of infrared reflective particles (such as ZnO@TiO2 core-shell particles) introduced into the B layer of the black photovoltaic encapsulating film should not be too low (as shown in Comparative Example 4), to avoid affecting the infrared reflectivity and the photovoltaic module's anti-PID power decay and cooling effect.

[0087] Furthermore, compared to Comparative Example 3 (where the ZnO@TiO2 core-shell particles in layer B were replaced with conventional TiO2 particles), Example 1 not only further improved the infrared reflectivity of the black photovoltaic encapsulating film, but also significantly improved the volume resistivity of the black photovoltaic encapsulating film and the anti-PID performance of its photovoltaic module, effectively achieving barrier properties (such as Na+). + Vertical migration.

[0088] It should be noted that, compared to conventional ZnO particles, the introduction of ZnO@TiO2 core-shell particles into the B layer not only results in higher infrared reflectivity but also significantly enhanced anti-PID performance. These ZnO@TiO2 core-shell particles can achieve barrier properties (such as Na+). + Longitudinal migration. However, the reflectivity of conventional ZnO particles is lower than that of core-shell particles; and they cannot simultaneously meet the requirements of high reflectivity and high volume resistivity; when the dosage is high, volume resistivity may be sacrificed, and agglomeration may be severe.

[0089] (3) Based on the test data of Examples 1, 6, 7 and Comparative Example 5 (the amounts of hollow glass microspheres in layer C were 8 parts, 3 parts, 15 parts, and 1 part, respectively), it can be concluded that:

[0090] The black photovoltaic encapsulating film of this invention incorporates hollow glass microspheres in its C-layer, which is crucial for ensuring the diffuse reflectance of the contact surface between the black photovoltaic encapsulating film and the solar cell, enabling secondary absorption and utilization of the light source. As the amount of hollow glass microspheres in the C-layer increases, the diffuse reflectance of the black photovoltaic encapsulating film can reach up to 99.2% (as in Example 7). When the amount of hollow glass microspheres in the C-layer is 1 part (as in Comparative Example 5), the diffuse reflectance of the black photovoltaic encapsulating film is only 92.5%, a parameter that currently cannot meet the needs of most customers, making it difficult to further improve the light absorption utilization rate. Of course, the higher the amount of hollow glass microspheres in the C-layer (as in Example 7), the slightly lower the peel strength and adhesion performance of the black photovoltaic encapsulating film compared to Example 1. Furthermore, it should be noted that excessive amounts of hollow glass microspheres in the C-layer may lead to bubbles in the laminated appearance; increasing the number of hollow glass microspheres also increases process risks, such as excessive pump pressure and other defects; and costs also increase.

[0091] Therefore, when the amount of hollow glass microspheres introduced into the C layer is 8 parts (as shown in Example 1), the black photovoltaic encapsulation film can achieve the best balance of overall performance.

[0092] (4) Based on the test data of Examples 1-3 and Comparative Examples 1-2 (the amount of nano-carbon black in Layer A is 0.7 parts, 0.3 parts, 1.2 parts, 0.2 parts, and 1.5 parts, respectively), it can be seen that if the amount of nano-carbon black in Layer A is too small (as in Comparative Example 1), it will affect the black appearance, visible light absorption rate, and cooling effect of the black photovoltaic encapsulating film and its photovoltaic module. If the amount of nano-carbon black in Layer A is too large (as in Comparative Example 2), it will affect the adhesion performance of the black photovoltaic encapsulating film. Therefore, considering all factors, the amount of nano-carbon black in Layer A should be controlled between 0.3 and 1.2 parts.

[0093] In summary, this invention, by designing a black photovoltaic encapsulating film with a three-layer functional decoupling structure, introduces different functional materials into different functional layers (for example, introducing an appropriate amount of light absorber in layer A, an appropriate amount of infrared reflective particles in layer B, and an appropriate amount of diffuse reflective particles in layer C), which can simultaneously achieve multiple balances between "pure black appearance" and "high efficiency infrared reflection" and "high diffuse reflection". The visible light absorption layer (layer A) is located on the light-illuminated side. It absorbs visible light in the 380-780nm wavelength band by introducing an appropriate amount of light absorber such as nano-carbon black, resulting in a deep black appearance. The average transmittance of this layer in the visible light band is less than 5%. The infrared reflection and charge blocking layer (layer B) incorporates an appropriate amount of infrared reflective particles such as ZnO@TiO2 core-shell particles to achieve efficient reflection of near-infrared light in the 800-1200nm wavelength band. The average reflectance of this layer in the near-infrared light band of 800-1200nm is not less than 93%, which can effectively avoid the power loss of the module caused by the heating of the black photovoltaic encapsulation film and the entire photovoltaic module. Layer B also uses an appropriate amount of infrared reflective particles and ion traps to give the black photovoltaic encapsulation film a high volume resistivity. The diffuse reflection adhesive layer (layer C) incorporates an appropriate amount of diffuse reflection particles such as hollow glass microspheres to efficiently diffusely reflect light back to the solar cell for secondary absorption, while providing strong adhesion between the film and the surface of the solar cell. Therefore, the spectrally selective black photovoltaic encapsulating film of the present invention, while possessing an excellent black appearance, also exhibits high adhesion performance and volume resistivity. Furthermore, its photovoltaic modules also demonstrate excellent resistance to PID power attenuation and cooling effects. This spectrally selective black photovoltaic encapsulating film solves the fundamental contradictions of black photovoltaic modules and possesses extremely high industrialization and commercial value.

[0094] 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.

[0095] 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 spectrally selective black photovoltaic encapsulating film, characterized in that, It has a multi-layered composite structure, which includes, in sequence, a visible light absorption layer, an infrared reflection and charge blocking layer, and a diffuse reflection adhesive layer; The visible light absorbing layer comprises a matrix resin and a light absorber formulated at a weight ratio of 100:0.3-1.2; the average transmittance of the visible light absorbing layer to visible light in the 380-780nm range is less than 5%. The light absorber is nano-carbon black with a particle size D50 of 20-80 nm; The infrared reflective and charge-blocking layer comprises a matrix resin, core-shell structured infrared reflective particles, and an ion trapping agent prepared in a weight ratio of 100:8-25:0.1-0.

8. The core-shell structured infrared reflective particles have at least one of TiO2, ZrO2, and SiO2 as the core and at least one of ZnO, Al2O3, and MgO as the shell. The infrared reflective and charge-blocking layer has an average reflectivity of not less than 93% for 800-1200nm infrared light and a volume resistivity of not less than 1×10⁻⁶. 16 Ω·cm; The ion scavenger is at least one of aminosilane coupling agents, epoxysilane coupling agents, and vinylsilane coupling agents; The diffuse reflective adhesive layer comprises a matrix resin and diffuse reflective particles formulated at a weight ratio of 100:3-15; the average diffuse reflectance of the diffuse reflective adhesive layer for light in the 380-1200nm wavelength band is not less than 95%. The diffuse reflective particles are at least one of solid or hollow glass microspheres, ceramic microspheres, and polymer microspheres, with a particle size of 0.5-15 μm and a refractive index of 1.8-2.

5. The matrix resin is selected from at least one of ethylene-vinyl acetate copolymer and polyolefin elastomer.

2. The spectrally selective black photovoltaic encapsulating film according to claim 1, characterized in that, The infrared reflective particles of the core-shell structure have a particle size of 100-500 nm and a shell thickness of 10-80 nm.

3. The spectrally selective black photovoltaic encapsulating film according to claim 2, characterized in that, The infrared reflective particles of the core-shell structure are ZnO@TiO2 core-shell particles; the shell thickness accounts for 8-40% of the overall particle size of the infrared reflective particles in the core-shell structure.

4. The spectrally selective black photovoltaic encapsulating film according to claim 1, characterized in that, The visible light absorption layer, infrared reflection and charge blocking layer, and diffuse reflection adhesive layer all further include crosslinking agents and anti-aging agents, and the weight ratio of the matrix resin, crosslinking agent, and anti-aging agent is 100:0.5-1.2:0.3-0.

8.

5. A method for preparing a spectrally selective black photovoltaic encapsulating film according to any one of claims 1-4, characterized in that, The preparation steps include the following: S1. Prepare premixes for the visible light absorption layer, infrared reflection and charge blocking layer and diffuse reflection adhesive layer according to the raw material formulas for each layer. S2. The premixed materials of each layer are melt-co-extruded through a co-extrusion die with independent flow channels, and after casting and cooling, a spectrally selective black photovoltaic encapsulation film is obtained.

6. The method for preparing a spectrally selective black photovoltaic encapsulating film according to claim 5, characterized in that, In step S2, the extrusion temperature of the premix of the visible light absorption layer is 100-130℃, the extrusion temperature of the premix of the infrared reflection and charge blocking layer is 110-140℃, and the extrusion temperature of the premix of the diffuse reflection adhesive layer is 100-130℃. The total thickness of the spectrally selective black photovoltaic encapsulating film is 0.40-0.65 mm; the thickness ratio of the visible light absorption layer, the infrared reflection and charge blocking layer and the diffuse reflection adhesive layer is 0.8-1.2:1.8-2.2:1.8-2.

2.

7. The application of the spectrally selective black photovoltaic encapsulating film according to any one of claims 1-4, characterized in that, The spectrally selective black photovoltaic encapsulating film is used as an encapsulating film in photovoltaic modules.

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