A three-band spectral synergistic regulation radiation cooling film for the front surface of a photovoltaic module

Abstract

This invention belongs to the field of photovoltaic thermal management, radiation cooling, and spectrally selective functional thin film technology, specifically relating to a three-band spectrally synergistically modulated radiation cooling thin film for the front surface of a photovoltaic module. The film is disposed on the outer surface of the front cover plate of the photovoltaic module and, from the air side to the photovoltaic module side, sequentially includes a polymer functional layer, an upper dielectric layer, a metal reflective layer, and a lower dielectric layer. The polymer functional layer enhances infrared emission in the mid-infrared band; the upper dielectric layer, metal reflective layer, and lower dielectric layer constitute a dielectric / metal / dielectric spectrally selective modulation structure, used to improve transmittance in the 0.3~1.1μm band and reflectivity in the 1.1~2.5μm band. This thin film can suppress ineffective near-infrared heat input in the sub-bandgap while ensuring effective photovoltaic incidence and enhance mid-infrared radiative heat dissipation, thereby reducing the operating temperature of the photovoltaic module and improving power generation efficiency. It has the advantages of simple structure, diverse material combinations, ease of large-area continuous fabrication, and suitability for engineering application.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic thermal management, radiation cooling and spectrally selective functional thin film technology, specifically relating to a three-band spectral synergistic modulation radiation cooling thin film for the front surface of a photovoltaic module. Background Technology

[0002] As the installed capacity of photovoltaic (PV) power generation continues to expand, PV modules commonly face the problem of heat accumulation during long-term outdoor operation. Under strong solar irradiation, the temperature of PV modules rises, which not only leads to a decrease in cell output power but also accelerates the aging of encapsulation materials, affecting the long-term stability and power generation revenue of the modules. Existing research shows that for every 1°C increase in the temperature of crystalline silicon modules, their output power typically decreases by about 0.4% to 0.45%. High temperature has become a significant factor restricting the efficient power generation and long-life operation of PV systems.

[0003] Existing photovoltaic cooling technologies mainly include active cooling methods such as air cooling and water cooling, as well as passive cooling methods such as enhanced thermal conductivity, phase change thermal storage, and radiative cooling. While active cooling methods can reduce module temperature to some extent, they typically suffer from high additional energy consumption, system complexity, and high maintenance costs. In contrast, passive cooling methods require no additional energy input and are more suitable for long-term outdoor applications.

[0004] In passive cooling approaches, radiative cooling is considered a promising direction for photovoltaic thermal management because it can radiate heat into the outside space through an 8-13 μm atmospheric window. However, traditional radiative cooling materials typically focus on increasing the overall reflectivity across the solar wavelength range to reduce solar heat absorption. This design approach is suitable for ordinary building roofs, exterior walls, or the back of devices, but it has significant limitations for the front surface of photovoltaic modules. This is because the front surface of photovoltaic modules must ensure effective solar transmittance within the 0.3-1.1 μm wavelength range as much as possible to maintain cell power generation efficiency; simply increasing the reflectivity across the entire solar wavelength range would directly weaken the cell's absorption of effective photons, reducing power generation performance. For a long time, the photovoltaic field has generally believed that the front surface film should maximize the transmittance of solar light across the entire wavelength range, while ignoring the fact that photovoltaic modules also experience ineffective heat input from sub-bandgap near-infrared radiation in the 1.1-2.5 μm wavelength range. This radiation cannot be effectively converted into electrical energy but increases the module's thermal load. Therefore, the thermal management film suitable for the front surface of photovoltaic modules should simultaneously meet the following requirements: high transmittance in the 0.3~1.1μm band, high reflectivity in the 1.1~2.5μm band to suppress ineffective heat input, and high emissivity in the 8~13μm band to enhance long-wave heat radiation dissipation capability.

[0005] In existing technologies, a single transparent film layer usually cannot simultaneously achieve the above three spectral properties; simple dielectric films or polymer films can often only meet some light transmission or emission requirements, and it is difficult to achieve near-infrared high reflectivity at the same time; although conventional multilayer optical films can achieve modulation of a specific wavelength band, they are not designed in a coordinated manner for photovoltaic front surface application scenarios, and therefore still have shortcomings in terms of comprehensive light transmission, heat insulation and radiative heat dissipation.

[0006] Furthermore, existing related structures still have certain limitations in terms of fabrication processes. Some high-performance spectrally modulated thin films rely on complex laboratory-scale micro / nano fabrication methods, making it difficult to simultaneously meet the requirements of continuous, large-area, and low-cost fabrication. For applications on the front surface of photovoltaic modules, the relevant functional films should not only meet spectral performance requirements but also possess process routes suitable for industrial continuous fabrication and large-area integration. Existing reports also indicate that complex micro / nano structures or too many film layers can lead to problems such as manufacturing complexity, high cost, and insufficient commercial applicability.

[0007] Therefore, it is necessary to provide a functional thin film suitable for the front surface of photovoltaic modules to achieve synergistic control of three bands: high visible light transmittance, high near-infrared reflectance, and high mid-infrared emissivity, and to have the potential for large-area continuous fabrication, thereby reducing module heat accumulation and improving overall operating performance. Summary of the Invention

[0008] To address the aforementioned problems in the prior art, this invention provides a three-band spectral synergistic modulation radiation cooling film for the front surface of photovoltaic modules, thereby solving the problem that existing front surface thermal management materials cannot simultaneously achieve high transmittance in the effective power generation band of photovoltaics, high reflectance in the sub-bandgap near-infrared, and high emission in the mid-infrared atmospheric window.

[0009] The present invention discloses a three-band spectral synergistic modulation radiation cooling film for the front surface of a photovoltaic module, which is disposed on the outer surface of the front cover plate of the photovoltaic module, thereby reducing the temperature on the back of the module by more than 10°C and increasing the output power by more than 4%. The film comprises, from the air side to the photovoltaic module side, a polymer functional layer, an upper dielectric layer, a metal reflective layer and a lower dielectric layer.

[0010] The polymer functional layer is made of one or more of the following materials, including but not limited to polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene-vinyl acetate copolymer (EVA), polyurethane (PU), and polylactic acid (PLA), which have high mid-infrared emissivity. The polymer functional layer enhances infrared emission performance in the mid-infrared band, providing high emissivity within the mid-infrared atmospheric window, thereby enhancing long-wave radiation heat dissipation.

[0011] The material of the metal reflective layer can be selected from one or more of silver, aluminum, gold, copper, nickel, chromium, titanium, platinum and their alloys, or a composite metal thin layer composed of the above metals. The metal reflective layer is used to achieve high reflectivity in the near-infrared subbandgap band (1.1~2.5μm band) to suppress ineffective heat input; at the same time, due to its thin thickness and the thin-film interference modulation with the upper and lower dielectric layers, it can maintain high transmittance in the visible-near-infrared effective power generation band (0.3~1.1μm band).

[0012] The materials of the upper and lower dielectric layers can be selected from one or more combinations of transparent dielectric materials with suitable refractive indices, such as alumina (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), zinc oxide (ZnO), hafnium dioxide (HfO2), tantalum pentoxide (Ta2O5), magnesium fluoride (MgF2), zinc sulfide (ZnS), silicon nitride (Si3N4), and indium tin oxide (ITO). The materials of the upper and lower dielectric layers can be the same or different, and can be flexibly selected according to specific spectral control requirements.

[0013] The upper dielectric layer, the metal reflective layer, and the lower dielectric layer together constitute a dielectric / metal / dielectric spectrally selective tuning structure. Through thin-film interference and impedance matching, the transmittance in the 0.3~1.1μm band and the reflectance in the 1.1~2.5μm band are improved, thereby reducing the ineffective heat input in the sub-bandgap near-infrared region.

[0014] As a further technical solution of the present invention: the thickness of the lower dielectric layer is 10~300nm, the thickness of the metal reflective layer is 3~30nm, the thickness of the upper dielectric layer is 10~300nm, and the thickness of the polymer functional layer is 20~500μm. Within the above thickness range, it can be flexibly adjusted according to the substrate type, application scenario, and specific spectral modulation target.

[0015] As a preferred embodiment of the present invention: the polymer functional layer is a polydimethylsiloxane layer, the upper dielectric layer and the lower dielectric layer are both alumina layers, and the metal reflective layer is a silver layer; the thickness of the lower alumina layer is 50 nm, the thickness of the silver layer is 8 nm, the thickness of the upper alumina layer is 50 nm, and the thickness of the polydimethylsiloxane layer is 100 μm.

[0016] As a further technical solution of the present invention: the average transmittance of the thin film in the 0.3~1.1μm band is not less than 70%, the average reflectance in the 1.1~2.5μm band is not less than 70%, and the average emissivity in the 8~13μm band is not less than 80%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) This invention organically combines a polymer functional layer with a dielectric / metal / dielectric spectrally selective modulation structure to form a polymer / dielectric / metal / dielectric four-layer film system, achieving three-band spectral synergistic modulation of high visible light transmittance, high sub-bandgap near-infrared reflectance, and high mid-infrared emission for photovoltaic front surface scenarios. While ensuring full utilization of photovoltaic effective incident light, it suppresses ineffective sub-bandgap infrared heat input and enhances mid-infrared radiation heat dissipation, thereby significantly reducing the operating temperature of photovoltaic modules and improving power generation efficiency.

[0019] (2) The materials and thicknesses of each functional layer in the thin film of the present invention have a wide range of options and can be flexibly configured according to the application scenario to meet the differentiated needs of different substrate types, different photovoltaic module structures and different environmental conditions.

[0020] (3) The present invention adopts a planar layered structure, which is more suitable for continuous production than complex surface micro-nano structure schemes, and can reduce the risk of surface structure degradation caused by dust deposition, rain erosion and long-term service. Its inorganic / metal functional layer can be continuously prepared by roll-to-roll physical vapor deposition process, and combined with a variety of mature polymer coating processes to form an outer layer, which can meet the needs of large-area and batch engineering applications. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of the three-band spectral synergistic modulation radiation-cooling thin film described in Embodiment 1 of the present invention;

[0022] Figure 2 The image shows a schematic curve of the transmittance and reflectance of the thin film described in Example 1 of this invention in the 0.3~2.5μm wavelength range.

[0023] Figure 3 This is a schematic curve of the infrared emissivity of the thin film described in Example 1 of the present invention in the 8~13μm band;

[0024] In the diagram, 1-front cover of photovoltaic module; 2-lower dielectric layer; 3-metal reflective layer; 4-upper dielectric layer; 5-polymer functional layer. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto. Equivalent substitutions, improvements, and modifications made by those skilled in the art based on the essence of the present invention should all be included within the scope of protection of the present invention.

[0026] In specific embodiments, the substrate material can be selected from flexible polymer substrates, flexible release substrates, glass substrates, or photovoltaic module front covers.

[0027] Example 1

[0028] This embodiment provides a three-band spectral synergistic modulation radiation-cooling thin film for the front surface of a photovoltaic module. For example... Figure 1 As shown, in this embodiment, a photovoltaic module front cover plate 1 is used as the substrate. The thin film, from the air side to the photovoltaic module side, includes a polymer functional layer 5, an upper dielectric layer 4, a metal reflective layer 3, and a lower dielectric layer 2.

[0029] In the thin film described in this embodiment, the polymer functional layer is polydimethylsiloxane (PDMS), the upper and lower dielectric layers are both made of aluminum oxide (Al2O3), and the metal reflective layer is made of silver (Ag). The lower Al2O3 layer has a thickness of 50 nm, the Ag layer has a thickness of 8 nm, the upper Al2O3 layer has a thickness of 50 nm, and the PDMS layer has a thickness of 100 μm.

[0030] The aforementioned thin film can be prepared as follows: First, the substrate material is sequentially cleaned with ethanol and deionized water and then dried; subsequently, a lower Al2O3 layer, an Ag layer, and an upper Al2O3 layer are sequentially deposited on the substrate surface using a magnetron sputtering process. The Al2O3 layer is formed using radio frequency magnetron sputtering, and the Ag layer is formed using direct current magnetron sputtering. The working gas is argon, and the basic vacuum level is below 5 × 10⁻⁶. -4 The working pressure is 0.1-1.0 Pa. Preferably, the lower Al2O3 layer, Ag layer, and upper Al2O3 layer are continuously deposited using a roll-to-roll magnetron sputtering process to ensure film uniformity and improve the efficiency of large-area preparation. Finally, the PDMS precursor and curing agent are mixed at a mass ratio of 10:1 and vacuum degassed, then coated onto the surface of the upper Al2O3 layer using a spin coating method. The spin coating speed is 1000-2000 rpm, the spin coating time is 20-40 s, and the film is cured at 80℃ for 60 min to obtain the final film.

[0031] Through simulation analysis, such as Figure 2 , 3 As shown, the thin film obtained in this embodiment has an average transmittance of no less than 70% in the 0.3~1.1μm band, an average reflectance of no less than 70% in the 1.1~2.5μm band, and an average emissivity of no less than 80% in the 8~13μm band. After integrating it onto the outer surface of the front cover of the photovoltaic module, it can reduce the subbandgap thermal load and enhance mid-infrared radiation heat dissipation while ensuring effective light incident utilization, thereby reducing the module temperature rise and improving electrical output performance.

[0032] Example 2

[0033] The difference between this embodiment and Embodiment 1 is that: polymethyl methacrylate (PMMA) is used instead of PDMS for the polymer functional layer, silicon dioxide (SiO2) is used instead of Al2O3 for the dielectric layer, and aluminum (Al) is used instead of silver for the metal reflective layer. Specifically, the thickness of the lower SiO2 layer is 40 nm, the thickness of the Al layer is 10 nm, the thickness of the upper SiO2 layer is 40 nm, and the thickness of the PMMA layer is 80 μm.

[0034] This embodiment illustrates that when other common polymers (such as PMMA), dielectric materials (such as SiO2), and metallic materials (such as Al) are used to replace the corresponding components in Example 1, the thin film can still achieve synergistic modulation of the three-band spectrum. Simulation analysis shows that the thin film obtained in this embodiment has an average transmittance of no less than 70% in the 0.3–1.1 μm band, an average reflectance of no less than 70% in the 1.1–2.5 μm band, and an average emissivity of no less than 80% in the 8–13 μm band, demonstrating that the layered structure described in this invention has a certain degree of versatility for material systems.

[0035] Example 3

[0036] The difference between this embodiment and the previous one is that the polymer functional layer is made of polyvinylidene fluoride (PVDF), the dielectric layer is made of titanium dioxide (TiO2), and the metal reflective layer is made of copper (Cu). Specifically, the thickness of the lower TiO2 layer is 30 nm, the thickness of the Cu layer is 12 nm, the thickness of the upper TiO2 layer is 30 nm, and the thickness of the PVDF layer is 150 μm.

[0037] This embodiment is used to illustrate that the metal reflective layer in the four-layer structure of the present invention is not limited to precious metals. Ordinary metals (such as copper and aluminum) can also be used as reflective layers. After being matched with the corresponding dielectric layer, high reflectivity in the near-infrared sub-bandgap band can still be achieved, thereby expanding the range of material selection for the present invention and reducing the material cost for large-scale applications.

[0038] Example 4

[0039] This embodiment is basically the same as Embodiment 1, except that: the metal reflective layer is replaced by a silver-copper alloy (Ag-Cu alloy) instead of a pure silver layer; the materials and thicknesses of the other layers remain unchanged.

[0040] This embodiment is used to illustrate that the metal reflective layer of the present invention can be made of a single metal, an alloy system of the above metals, or a multilayer composite metal layer, so as to take into account spectral reflectance performance, interface adhesion and long-term chemical stability.

[0041] Example 5

[0042] The difference between this embodiment and the previous one is that the lower dielectric layer is made of Al2O3, and the upper dielectric layer is made of SiO2. That is, the lower and upper dielectric layers use different dielectric materials, and a flexible release substrate is used as the preparation substrate instead of directly using the front cover plate of the photovoltaic module. After preparation, the film can be peeled off from the release substrate and then transferred and bonded to the outer surface of the front cover plate of the photovoltaic module, while the materials and thicknesses of other layers remain unchanged.

[0043] This embodiment illustrates that the upper and lower dielectric layers of the thin film described in this invention can be made of the same or different dielectric materials. By combining heterogeneous upper and lower layers, the interference conditions of the thin film can be more precisely controlled, further optimizing the transmittance and reflectance matching of the target wavelength band. The thin film described in this invention can be directly fabricated on the front cover plate of a photovoltaic module, or it can be fabricated first on a flexible release substrate and then transferred and laminated, to adapt to different production processes and on-site construction requirements.

[0044] Example 6

[0045] The difference between this embodiment and Embodiment 1 is that the polymer functional layer adopts a blend system of PDMS and PMMA, which are mixed at a mass ratio of 7:3 to form a uniform film layer; the materials and thicknesses of other layers remain unchanged; and a flexible release substrate is used as the preparation substrate in this embodiment.

[0046] This embodiment illustrates that the polymer functional layer of the present invention can be formed not only by a single polymer, but also by a blend of two or more polymers or a multilayer composite system. Through the rational design of the polymer components, the emission performance in the mid-infrared atmospheric window band, as well as the mechanical and weather resistance properties of the thin film, can be further optimized.

[0047] In a specific embodiment of the present invention, the thickness of each functional layer is selectable within a range. Specifically, the thickness of the lower dielectric layer can be adjusted within the range of 10~300 nm, the thickness of the metal reflective layer can be adjusted within the range of 3~30 nm, the thickness of the upper dielectric layer can be adjusted within the range of 10~300 nm, and the thickness of the polymer functional layer can be adjusted within the range of 20~500 μm. Different combinations of thicknesses of each layer within the above ranges can form a thin film with three-band spectral synergistic modulation performance.

[0048] When the metal reflective layer is too thin, its near-infrared reflectivity is insufficient, resulting in a weak heat suppression effect; when the metal reflective layer is too thick, it reduces the transmittance of the effective power generation band, which is detrimental to the absorption of effective photons by the photovoltaic cell. The thickness of the dielectric layer and polymer layer is related to the thin-film interference conditions of the target band and the mid-infrared emission characteristics. Those skilled in the art can reasonably select the thickness of each layer within the above range according to the specific application scenario to balance the performance of transmittance, reflectivity, and emissivity.

[0049] To verify the cooling and efficiency improvement effects of the thin film described in this invention on photovoltaic modules, the thin film described in Example 1 was covered on the outer surface of the front cover of a crystalline silicon photovoltaic module, while keeping the internal glass, encapsulation film, and cell structure of the photovoltaic module unchanged. This group was designated as the experimental group, and a photovoltaic module of the same model without the thin film was used as the control group.

[0050] The test conditions are as follows: the photovoltaic modules used are conventional monocrystalline silicon photovoltaic modules, and the simulated solar irradiance conditions are AM1.5G and irradiance of 1000 W / m². 2 The ambient temperature was 25±2℃, and the ambient wind speed was no greater than 1 m / s. The temperature on the back of the module was measured using a T-type thermocouple, and the output power of the photovoltaic module was recorded using an IV tester.

[0051] Under the typical steady-state test conditions described above, compared to the control group without the thin film, the back surface temperature of the photovoltaic modules covered with the thin film of the present invention can be reduced by more than 10°C; the corresponding output power is increased by more than 4%; and under conditions of no solar radiation at night, the temperature of the modules covered with the thin film is reduced by about 7°C compared to the control group, which helps to reduce heat retention at night. The results show that the thin film of the present invention can achieve synergistic enhancement of heat suppression and heat dissipation while ensuring effective utilization of incident light.

[0052] The three-band spectral synergistic modulation radiation cooling thin film of this invention can be prepared using mature magnetron sputtering and polymer coating processes. All materials used are commercially available industrial raw materials, and the process has good compatibility with existing photovoltaic module packaging production lines. Large-area, mass production can be achieved through roll-to-roll continuous deposition. This film can be prepared directly on the front cover plate of a photovoltaic module, or it can be prepared first on other substrates such as flexible release substrates and then transferred and laminated, adapting to different production scenarios and demonstrating clear industrial applicability.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention; all equivalent substitutions, improvements and modifications made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-band spectral synergistic modulation radiation-cooling thin film for the front surface of a photovoltaic module, characterized in that: The thin film is disposed on the outer surface of the front cover plate of the photovoltaic module. The thin film includes, from the air side to the photovoltaic module side, a polymer functional layer, an upper dielectric layer, a metal reflective layer, and a lower dielectric layer. The polymer functional layer is used to enhance the infrared emission performance in the mid-infrared band. The upper dielectric layer, the metal reflective layer, and the lower dielectric layer constitute a dielectric / metal / dielectric spectrally selective tuning structure, which is used to improve the transmittance in the 0.3~1.1μm band and the reflectance in the 1.1~2.5μm band.

2. The thin film according to claim 1, characterized in that: The material of the polymer functional layer is selected from one or more combinations of polydimethylsiloxane, polymethyl methacrylate, polyvinylidene fluoride, polyethylene, ethylene-vinyl acetate copolymer, polyurethane, and polylactic acid; the thickness of the polymer functional layer is 20~500μm.

3. The thin film according to claim 1, characterized in that: The material of the metal reflective layer is selected from one or more combinations of silver, aluminum, gold, copper, nickel, chromium, titanium, platinum and their alloys, or is a composite metal layer composed of the above metals; the thickness of the metal reflective layer is 3~30nm.

4. The thin film according to claim 1, characterized in that: The materials of the upper dielectric layer and the lower dielectric layer are each independently selected from one or more combinations of Al2O3, SiO2, TiO2, ZnO, HfO2, Ta2O5, MgF2, ZnS, Si3N4, and ITO; the materials of the upper dielectric layer and the lower dielectric layer may be the same or different; the thickness of the upper dielectric layer is 10~300nm; the thickness of the lower dielectric layer is 10~300nm.

5. The thin film according to claim 1, characterized in that: The average transmittance of the film in the 0.3~1.1μm band is not less than 85%.

6. The thin film according to claim 1, characterized in that: The average reflectivity of the thin film in the 1.1~2.5μm band is not less than 75%.

7. The thin film according to claim 1, characterized in that: The average emissivity of the thin film in the 8-13 μm band is not less than 80%.

8. The thin film according to claim 1, characterized in that: The polymer functional layer is a polydimethylsiloxane layer, the upper and lower dielectric layers are both alumina layers, and the metal reflective layer is a silver layer; the lower alumina layer has a thickness of 50 nm, the silver layer has a thickness of 8 nm, the upper alumina layer has a thickness of 50 nm, and the polydimethylsiloxane layer has a thickness of 100 μm.

9. The thin film according to claim 1, characterized in that: The film is used to cover the outer surface of the front cover of the crystalline silicon photovoltaic module, thereby reducing the temperature on the back of the module by more than 10°C and increasing the output power by more than 4%.

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