A highly transparent all-dielectric radiative cooling visible window

Abstract

The present invention relates to the technical field of optical materials, and specifically to a highly transparent all-dielectric radiative cooling visible window, whose film system structure is: (HfO2 / SiO2) 6 / HfO2 / substrate / HfO2 / (SiO2 / HfO2) 6 . The film system structure of the present invention has the characteristics of high ultraviolet reflection, high near-infrared reflection, and high visible light transmittance, and also has the advantages of higher thermal infrared emission and better radiative cooling effect. In addition, compared with the composite photonic crystal structure, the present invention also has the characteristics of improved ultraviolet reflection, improved infrared reflection, and improved visible light transmittance.

Description

Technical Field

[0001] The present invention relates to the technical field of optical materials, and specifically to a highly transparent all-dielectric radiative cooling visible window. Background Art

[0002] In daily life, people will choose a suitable ambient temperature to achieve a comfortable feeling. To maintain a suitable temperature in a closed space, various technical means need to be adopted. For example, modern buildings use a large number of structures such as glass doors, windows, and curtain walls. In winter, internal heating is required through heat sources, and in summer, cooling is achieved through means such as air conditioners, while minimizing heat conduction in the building to reduce energy consumption. In the above means, the sources of heat and electricity mainly come from fossil fuels such as coal. The weakest link in building insulation and heat preservation is the doors, windows, and curtain walls. The energy consumption of the outer windows accounts for 65.21% in summer; the energy consumption of the outer windows accounts for 23.42% in winter. It can be seen that reducing the energy consumption of doors, windows, and curtain walls has become the key to reducing building operation energy consumption.

[0003] When it comes to modern means of transportation such as cars commonly used by people, the glass usage area is also very large, and the temperature inside the vehicle fluctuates greatly with the outside world. In particular, continuous refrigeration is required to keep the temperature inside the vehicle within a comfortable range. Especially for new energy vehicles, a large amount of electrical energy needs to be consumed to keep the air conditioner running. Since the total capacity of the vehicle battery remains unchanged, the energy consumed for refrigeration will cause a reduction in the vehicle's cruising range. Reducing the energy consumption of vehicle air conditioners has also become the key to reducing vehicle operation energy consumption.

[0004] Glass can transmit sufficient sunlight and is also the main medium for heat transfer between the internal and external environments. We hope to obtain a medium that can effectively reflect sunlight without any additional energy input, and through the atmospheric window, radiate the excess energy into outer space to achieve cooling, thereby regulating the temperature inside the vehicle and the room, and achieving the dual purposes of low solar transmission and thermal infrared radiative cooling. This medium should have the characteristics of high ultraviolet reflection, high visible light transmission, high near-infrared reflection, and high thermal infrared emission. Thereby reducing the usage frequency of air conditioners, saving the use of fossil fuels, reducing greenhouse gas emissions, and promoting the solution of global climate problems.

[0005] In the existing solutions, (SiO2-HfO2) is mainly adopted m SiO2 / glass / (TiO2-Ag) nOne-dimensional composite photonic crystal structure of TiO2. The reflectivity of this structure is up to 95.44% in the wavelength range of 300 nm - 20,000 nm, the transmittance is up to 90.80% in the visible light band (380 nm - 780 nm), the absorptance is up to 100% in the thermal infrared band (8000 nm - 12,000 nm), and the surface emissivity is 72.15% in the range of 8000 nm - 13,000 nm at a temperature of 300 K. The direct transmittance ratio of the solar spectrum is 39.52%, the direct reflectance ratio is 53.19%, and the direct absorptance ratio is 7.29%. This structure has good radiative cooling performance and can be applied to visual windows to achieve the effect of energy conservation and emission reduction. However, due to (SiO2 / HfO2) 3 SiO2 / glass / (TiO2 / Ag) 2 In the TiO2 structure, due to the presence of the Ag film, the transmittance of visible light is about 90% at most, and the transmittance is relatively low, which is not conducive to observation, and the surface emissivity is not high enough.

[0006] In order to achieve higher ultraviolet reflectivity, higher near-infrared reflectivity, and thermal infrared emissivity (absorptance), the prior art also adopts a all-dielectric film stack structure (HfO2 / SiO2) / HfO2 / substrate / HfO2 / (SiO2 / HfO2) to integrate the reflection layer and emission layer of the solar spectrum in its structure design. Summary of the Invention

[0007] The present invention aims to provide a visual window that combines solar spectrum reflection and radiative cooling, reduces the energy consumption of visual windows in buildings, automobiles, etc., and thus effectively reduces greenhouse gas emissions and promotes the comprehensive green transformation of economic and social development.

[0008] The technical solution of the present invention is a highly transparent all-dielectric radiative cooling visual window, and its structure is: (HfO2 / SiO2) 6 / HfO2 / substrate / HfO2 / (SiO2 / HfO2) 6 . The substrate is glass. The substrate is PET. The overall structure schematic diagram is as Figure 1 .

[0009] When the substrate is glass, its film layer thickness is (nm):

[0010] 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / glass / 134 / 170 / 134 / 170 / 134 / 170 / 134 / 170 / 134 / 170 / 134 / 170 / 134.

[0011] When the substrate is PET, its film layer thickness is (nm):

[0012] 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / PET / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474。

[0013] A Distributed Bragg reflector (DBR) is composed of periodic arrangements of thin films of two different refractive-index media. A DBR usually consists of an odd number of layers, with the first and last layers being high-refractive-index films. This can achieve a higher reflectivity. When light passes through different media, reflection occurs at the interfaces. The magnitude of the reflectivity is related to the difference in refractive indices between the media. By stacking thin films of different refractive indices alternately and periodically, when light passes through the thin films of different refractive indices, due to the change in the phase angle of the reflected waves from each layer, coherent interference occurs, enhancing the reflection. Therefore, two DBR structures based on ultraviolet and near-infrared are designed to achieve the purpose of high reflection for ultraviolet and near-infrared. At the same time, by utilizing the intrinsic properties of HfO2 and SiO2, radiative cooling for thermal infrared is achieved.

[0014] Compared with the prior art, the present invention has the following technical effects:

[0015] (1) The film system structure (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 Compared with the metal-containing (SiO2 - HfO2) m SiO2 / glass / (TiO2 - Ag) n TiO2 structure, the transmittance in the visible light band is higher. The highest transmittance is increased from 90.80% to 99.99%, an increase of 9.19%, proving that the transmittance of the final structure is better and the application range is wider. The highest ultraviolet reflectivity is increased from 85.44% to 87.58%, an increase of 2.14%, proving that the final structure has a stronger ability to resist ultraviolet rays and better performance. The highest near-infrared reflectivity is increased from 88.11% to 95.12%, an increase of 7.01%, proving that the final structure can reflect heat more effectively and has a better refrigeration effect. The highest emission (absorption) rate in the thermal infrared band is increased from 91.09% to 99.23%, an increase of 8.14%, proving that the final structure can absorb heat better and prevent heat from passing through the film into the room or vehicle.

[0016] (2) The film system structure (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6The emissivity is 89.95%. When the direct transmittance, direct reflectance, and direct absorptance of the final film system are not very different, the overall surface emissivity is higher, by 43.16%. This film system structure has the characteristics of high reflectance in the ultraviolet range, high reflectance in the near-infrared range, and high transmittance in the visible light range, and also has higher thermal infrared emission and better radiative cooling effect.

[0017] (3) The film system structure (HfO2 / SiO2) of the present invention 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 The overall performance is better than that of (SiO2-HfO2) m SiO2 / glass / (TiO2-Ag) n The one-dimensional composite photonic crystal structure of TiO2. The reflectance in the ultraviolet band (200nm - 380nm) increases from 85.44% to 97.58%, an increase of 12.14%. The transmittance in the visible light band (380nm - 780nm) increases from 90.80% to 99.01%, an increase of 8.21%. The reflectance in the near-infrared band (780nm - 2500nm) increases from 88.11% to 97.12%, an increase of 9.01%. The absorptance in the thermal infrared band (8000nm - 12000nm) increases from 91.09% to 91.23%, an increase of 0.14%. Description of the Drawings

[0018] Figure 1 is (HfO2 / SiO2) 6 / HfO2 / substrate / HfO2 / (SiO2 / HfO2) 6 Schematic diagram of the film system structure;

[0019] Figure 2 is (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 Curves of reflectance, transmittance, and absorptance of the film system structure;

[0020] Figure 3 is (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 Curves of enlarged reflectance, transmittance, and absorptance of the film system structure in the visible light band;

[0021] Figure 4 is the absorptance curve of the overall film system of HfO2 at different film thicknesses in the ultraviolet band;

[0022] Figure 5 is (HfO2 / SiO2) after the first optimization 6 / HfO2 / Glass / HfO2 / (SiO2 / HfO2) 6 Reflectivity, transmittance, and absorptance curves of the film stack structure;

[0023] Figure 6 After the first optimization (HfO2 / SiO2) 6 / HfO2 / Glass / HfO2 / (SiO2 / HfO2) 6 Magnified reflectivity, transmittance, and absorptance curves of the film stack structure in the visible light band;

[0024] Figure 7 Reflectivity curves for different film thicknesses of SiO2 before the PET substrate in the 200 nm - 380 nm wavelength range;

[0025] Figure 8 Transmittance curves for different film thicknesses of SiO2 before the PET substrate in the 380 nm - 780 nm wavelength range;

[0026] Figure 9 Absorptance curves for different film thicknesses of SiO2 before the PET substrate in the 780 nm - 13000 nm wavelength range;

[0027] Figure 10 Reflectivity curves for different film thicknesses of HfO2 before the PET substrate in the 200 nm - 380 nm wavelength range;

[0028] Figure 11 Transmittance curves for different film thicknesses of HfO2 before the PET substrate in the 380 nm - 780 nm wavelength range;

[0029] Figure 12 Absorptance curves for different film thicknesses of HfO2 before the PET substrate in the 780 nm - 13000 nm wavelength range;

[0030] Figure 13 Reflectivity curves for different film thicknesses of HfO2 after the PET substrate in the 200 nm - 380 nm wavelength range;

[0031] Figure 14 Transmittance curves for different film thicknesses of HfO2 after the PET substrate in the 380 nm - 780 nm wavelength range;

[0032] Figure 15 Absorptance curves for different film thicknesses of HfO2 after the PET substrate in the 780 nm - 13000 nm wavelength range;

[0033] Figure 16Reflectivity curve of different film thicknesses of SiO2 after PET substrate in the wavelength range of 200nm - 380nm;

[0034] Figure 17 Transmittance curve of different film thicknesses of SiO2 after PET substrate in the wavelength range of 380nm - 780nm;

[0035] Figure 18 Absorbance curve of different film thicknesses of SiO2 after PET substrate in the wavelength range of 780nm - 13000nm;

[0036] Figure 19 For (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 Reflectivity, transmittance and absorbance curves of the film structure in the wavelength range of 200nm - 10000nm when the substrate is PET after the second optimization. Detailed implementation method

[0037] Comparative example 1

[0038] Design of the first DBR structure: According to the formula When λ is 300nm, the film thickness of each layer of HfO2 and SiO2 is 37nm and 50nm respectively;

[0039] Design of the second DBR structure: According to the formula When λ is 1000nm, the film thickness of each layer of HfO2 and SiO2 is 134nm and 170nm respectively.

[0040] Table 1 (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 Film thickness of the film structure

[0041]

[0042] (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 Schematic diagram of the structure is as Figure 1 shown, and the reflectivity, reflectivity, transmittance and absorbance are as Figure 2 shown.

[0043] (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 Magnified reflectivity, transmittance and absorbance of the structure in the visible light band are as Figure 3 shown.

[0044] It can be seen from Figure 2 and Figure 3 that the highest ultraviolet reflectivity of this structure is 95.65%, the highest near-infrared reflectivity is 93.86%, and the highest thermal infrared emissivity (absorptivity) is 72.11%. This structure has high ultraviolet and near-infrared reflectivities, visible light transmittance, but low thermal infrared emissivity.

[0045] Example 1

[0046] The first optimization: Since the SiO2 film thickness has little effect on the absorptivity of the structure, increasing the SiO2 film thickness will reduce the transmittance of the overall film system structure. On the premise of not changing the SiO2 film thickness in the DBR second structure and the DBR first structure, the effect of the HfO2 film thickness on its performance was studied. The research results show that changing the HfO2 film thickness of the DBR first structure has a greater impact on the thermal infrared emissivity, as Figure 4 shown. As the HfO2 film thickness increases, the emissivity of thermal infrared increases accordingly. When the HfO2 film thickness is 296nm, as the HfO2 film thickness increases, the emissivity of thermal infrared no longer increases significantly.

[0047] The structure after the first optimization is shown in Table 2. The reflectivity, transmittance and absorptivity are as Figure 5 shown. After the first optimization (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 The visible light reflectivity, transmittance and absorptivity of the film system structure are as Figure 6 shown.

[0048] Table 2 The film thickness of the structure (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 after the first optimization

[0049]

[0050] It can be seen from Figure 5 and Figure 6 that after the first optimization, the highest ultraviolet (200nm - 380nm) reflectivity is 97.58%, the highest visible light (380nm - 780nm) transmittance is 99.01%, the highest near-infrared (780nm - 2500nm) reflectivity is 97.12%, and the highest thermal infrared (8000nm - 12000nm) absorptivity is 91.23%.

[0051] Comparing Figure 2 and Figure 3 , Figure 5 and Figure 6It can be seen that after the first optimization, the ultraviolet (200nm - 380nm) reflectivity is higher, the visible light (380nm - 780nm) transmittance is higher, the near-infrared (780nm - 2500nm) reflectivity is higher, and the thermal infrared band (8000nm - 12000nm) absorptivity is higher, with better overall performance.

[0052] Example 2

[0053] Second optimization: When the substrate is glass, the absorptivity of the first optimized structure in the thermal infrared band (8000nm - 12000nm) is low, and the emissivity in the wavelength range of 8000nm - 12000nm is relatively low at a temperature of 300K, with the lowest being 8.66% and the highest being 91.23%. In this example, PET is used instead of glass as the substrate. On the one hand, it can improve the emissivity of its structure, and on the other hand, due to the foldability and bendability of PET, it can be widely applied to curved surface occasions.

[0054] After using PET as the substrate, although the emissivity has increased, the increase is not obvious. To solve this problem, an attempt is made to change the film thickness of each layer of material to improve the reflectivity of the overall structure. By periodically increasing the film thickness and periodically increasing the thickness of HfO2 and SiO2 on the substrate PET, the reflectivity, transmittance, and absorptivity of the overall film system are compared for different film thicknesses to obtain the final optimal film layer structure thickness.

[0055] Change the film thickness of each SiO2 film layer before the substrate, keep other film thicknesses unchanged, with a 50nm film thickness as a cycle film thickness, and increase it by 50nm each time, which are 50nm, 100nm, 150nm, 200nm, 250nm, 300nm respectively. Compare the reflectivity in the wavelength range of 200nm - 380nm for different film thicknesses, as Figure 7 shown, the transmittance in the wavelength range of 380nm - 780nm, as Figure 8 shown, and the absorptivity in the wavelength range of 780nm - 13000nm, as Figure 9 shown, to obtain the optimal thickness of the SiO2 film layer before the substrate.

[0056] From Figure 7 it can be seen that the film thickness of SiO2 has an impact on the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6The reflectance impact of the structure varies slightly within the wavelength range of 200nm - 360nm. Considering several peak values comprehensively, when the film thickness of SiO2 is 200nm, the reflectance of the overall structure is the highest. Within the wavelength range of 360nm - 380nm, the reflectance suddenly increases when the film thickness of SiO2 is 150nm. However, within the wavelength range of 200nm - 360nm, the increase in reflectance is not obvious when the film thickness of SiO2 is 150nm. When the wavelength is 375nm, a peak appears, and it can be seen that the peak is the highest when the film thickness of SiO2 is 200nm.

[0057] It can be seen from Figure 8 that for the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure, the transmittance varies significantly for different film thicknesses of SiO2. Comparing different film thicknesses, when the film thickness is relatively thin, the oscillation amplitude of the transmittance is small, and the overall transmittance of the structure is high. When the film thickness is 250nm, the transmittance of the overall structure starts to decline. When the film thickness is 300nm, the decline in the transmittance of the overall structure is the most obvious.

[0058] It can be seen from Figure 9 that for the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure, there are several peaks in the absorption rate within the wavelength range of 780nm - 13000nm. There are 5 obvious peaks, located at the wavelength positions of 2400nm, 5790nm, 7880nm, 9230nm, and 10170nm respectively. At 2400nm, as the film thickness changes, the peak gradually redshifts, and when the film thickness of SiO2 is 200nm, the absorption rate is the highest. At 5790nm, it can be clearly seen that the absorption rate is the highest when the film thickness of SiO2 is 200nm, which is 88.79%. At 7880nm, as the film thickness increases, the absorption rate gradually decreases, but the absorption rate at the film thickness of SiO2 being 200nm is 94.50%, which is relatively high. At 9230nm, as the film thickness increases, the absorption rate also gradually increases, and the absorption rate is the highest when the film thickness of SiO2 is 200nm, approaching 100%. At 10170nm, the peak changes are not obvious for different film thicknesses, and the overall values are relatively high. Considering comprehensively, the optimal film thickness of SiO2 before the substrate PET is 200nm.

[0059] Changing the film thickness of each HfO2 layer before the substrate, with other film thicknesses remaining unchanged, and taking 37nm as the periodic film thickness, increasing by 6×37nm each time, which are 111nm, 333nm, 555nm, 777nm, 999nm, 1221nm, and 1443nm respectively. Comparing the reflectance of different film thicknesses within the wavelength range of 200nm - 380nm, asFigure 10 As shown, the transmittance in the wavelength range of 380 nm - 780 nm is as Figure 11 shown, and the absorbance in the wavelength range of 780 nm - 13000 nm is as Figure 12 shown, to obtain the optimal thickness of the HfO2 film layer in front of the substrate.

[0060] From Figure 10 it can be seen that the influence of HfO2 in front of the substrate on the reflectance of the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure in the wavelength range of 200 nm - 380 nm fluctuates greatly. By synthesizing several peak values, and since too thick a film thickness will affect the transmittance of the overall film system structure, it is concluded that when the film thickness of HfO2 is 999 nm, the reflectance of the overall structure is relatively good.

[0061] From Figure 11 it can be seen that as the film thickness of HfO2 in front of the substrate PET increases, the oscillation amplitude of the transmittance change of structures with different film thicknesses in the wavelength range of 380 nm - 780 nm gradually becomes larger. The larger the film thickness, the smaller the transmittance of the overall structure. When the film thickness of HfO2 is 999 nm, the oscillation change is moderate. Considering the reflectance comprehensively, it is more appropriate to select HfO2 with a film thickness of 999 nm.

[0062] From Figure 12 it can be obtained that the absorbance of the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure has several peaks in the wavelength range of 780 nm - 13000 nm. There are 5 relatively obvious ones, located at the wavelength positions of 3380 nm, 5790 nm, 7980 nm, 9230 nm, and 10280 nm respectively. At 3380 nm, as the film thickness of HfO2 increases, the absorbance gradually increases and reaches the maximum value when the film thickness is 999 nm and 1221 nm. Subsequently, as the film thickness increases, the absorbance begins to decrease. Since the transmittance at a film thickness of 1221 nm is lower than that at 999 nm, the film thickness of 999 nm is better. At 5790 nm, it can be clearly seen that the absorbance is the highest when the film thickness of HfO2 is 999 nm, which is 88.79%. At 7980 nm, as the film thickness increases, the absorbance gradually decreases, but the absorbance at a film thickness of 999 nm of HfO2 is 94.50%, which is relatively high. At 9230 nm, as the film thickness changes, the peak gradually redshifts. When the film thickness of HfO2 is 999 nm, the absorbance is close to 100%. At 10280 nm, as the film thickness of HfO2 increases, the absorbance gradually increases. Considering comprehensively, the optimal film thickness of HfO2 in front of the substrate PET is 999 nm

[0063] Change the thickness of each HfO2 film layer after changing the substrate, keep the thickness of other films unchanged, the film thickness of 134 nm is a periodic film thickness, and increase it by 4×134 nm each time, which are 402 nm, 938 nm, 1474 nm, 2010 nm, 2546 nm respectively. Compare the reflectivity of different film thicknesses in the wavelength range of 200 nm - 380 nm, as Figure 13 shown, the transmittance in the wavelength range of 380 nm - 780 nm, as Figure 14 shown, and the absorbance in the wavelength range of 780 nm - 13000 nm, as Figure 15 shown, to obtain the optimal thickness of the HfO2 film layer after the substrate.

[0064] It can be seen from Figure 13 that the HfO2 after the substrate has a relatively large fluctuation in the reflectivity of the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure in the wavelength range of 200 nm - 380 nm. By synthesizing several peak values, and since too thick a film thickness will affect the transmittance of the overall film system structure, it is concluded that when the film thickness of HfO2 is 1474 nm, the reflectivity of the overall structure is relatively good.

[0065] It can be seen from Figure 14 that as the film thickness of HfO2 after the substrate PET increases, the oscillation amplitude of the transmittance change of structures with different film thicknesses in the wavelength range of 380 nm - 780 nm gradually becomes larger, and the larger the film thickness, the smaller the transmittance of the overall structure. When the film thickness of HfO2 is 1474 nm, the oscillation change is moderate. Considering the reflectivity comprehensively, it is more appropriate to choose HfO2 with a film thickness of 1474 nm.

[0066] It can be seen from Figure 15 that the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6The absorption rate of the structure has several peaks in the wavelength range of 780 nm - 13000 nm. There are 4 relatively obvious ones, located at the wavelength positions of 3390 nm, 5780 nm, 7950 nm, and 9270 nm respectively. At 3390 nm, as the thickness of the HfO2 film increases, the absorption rate gradually increases, reaching the maximum value when the film thickness is 2010 nm. Subsequently, as the film thickness increases, the absorption rate begins to decline. Since the transmittance is relatively low when the film thickness is 2010 nm, the film thickness of 1474 nm is relatively optimal. At 5780 nm, 7950 nm, and 9270 nm, the maximum absorption rates for different HfO2 film thicknesses are equal, which are 89.52%, 94.92%, and 99.47% respectively. In the wavelength range of 11000 nm - 13000 nm, the absorption rate gradually increases. Comparing the absorption rates of different film thicknesses, when the HfO2 film thickness is 1474 nm, the absorption rate can reach the expected value under the condition of relatively high transmittance of the overall film system. Considering the substrate PET comprehensively, the optimal HfO2 film thickness is 1474 nm.

[0067] Change the thickness of each SiO2 film layer after changing the substrate, keep the thicknesses of other films unchanged, with a film thickness of 170 nm as a periodic film thickness, and increase it by 4×170 nm each time, which are 680 nm, 1360 nm, 2040 nm, 2720 nm, and 3400 nm respectively. Compare the reflectivities of different film thicknesses in the wavelength range of 200 nm - 380 nm, as Figure 16 shown, the transmittances in the wavelength range of 380 nm - 780 nm, as Figure 17 shown, and the absorption rates in the wavelength range of 780 nm - 13000 nm, as Figure 18 shown, to obtain the optimal thickness of the SiO2 film layer after the substrate.

[0068] It can be seen from Figure 16 that the influence of the SiO2 film thickness on the reflectivity of the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure is relatively small in the wavelength range of 200 nm - 360 nm. Considering several peak values comprehensively, when the SiO2 film thickness is 2040 nm, the reflectivity of the overall structure is the highest. In the wavelength range of 360 nm - 380 nm, the reflectivity peak is the highest when the SiO2 film thickness is 2040 nm.

[0069] It can be seen from Figure 17It can be seen that as the thickness of the SiO2 film after the substrate PET increases, the oscillation amplitude of the transmittance change of the structures with different film thicknesses gradually becomes larger in the wavelength range of 380 nm - 780 nm. The larger the film thickness, the smaller the transmittance of the overall structure. When the SiO2 film thickness is 2040 nm, the oscillation change is moderate. Considering the reflectance comprehensively, it is more appropriate to choose SiO2 with a film thickness of 2040 nm.

[0070] It can be seen from Figure 18 that for the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure, there are several peaks in the absorption rate in the wavelength range of 780 nm - 13000 nm. There are 4 relatively obvious ones, located at the wavelength positions of 3380 nm, 5790 nm, 7960 nm, and 9300 nm respectively. At 3380 nm, as the thickness of the SiO2 film increases, the absorption rate gradually increases and reaches the maximum value when the film thickness is 2720 nm. Subsequently, the absorption rate starts to decrease as the film thickness increases. Since the transmittance is relatively low when the film thickness is 2720 nm, a film thickness of 2040 nm is better. At 5790 nm and 9300 nm, the maximum absorption rates for different SiO2 film thicknesses are equal, being 89.04% and 99.44% respectively. At 7960 nm, the maximum absorption rates are all 94.85% when the SiO2 film thicknesses are 1360 nm, 2040 nm, 2720 nm, and 3400 nm, and the absorption rate is relatively low at 680 nm, being 85.69%. Considering comprehensively, the best SiO2 film thickness after the substrate PET is 2040 nm.

[0071] Comprehensively Figures 7 - 18 it can be obtained that the film thickness of the overall (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure after secondary optimization is (999 / 200) 6 / 999 / PET / 1474 / (2040 / 1474) 6 , as shown in Table 3.

[0072] Table 3 Film thickness of the (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 film system structure with PET as the substrate

[0073]

[0074] The structure after the second optimization is (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2)6 , with film thicknesses of (999 / 200) 6 / 999 / PET / 1474 / (2040 / 1474) 6 , and it can be obtained from Figure 19 that the highest reflectivity of this structure in the ultraviolet band (200nm - 380nm) is 87.58%, the highest transmittance in the visible light band (380nm - 780nm) is 99.99%, the highest reflectivity in the near-infrared band (780nm - 2500nm) is 95.12%, and the highest emissivity (absorptivity) in the thermal infrared band (8000nm - 12000nm) is 99.23%.

[0075] Research on the optical and thermal properties of the solar spectral layer of the film system structure

[0076] According to the national standard GB / T2680 - 94, the direct transmittance τ 6 of the (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) viewing window under the solar spectrum e (Formula 1), direct reflectance ρ e (Formula 2) and direct absorptance α e (Formula 3) are calculated and analyzed. The lower τ e , the better the sunshade effect of the film system structure; the higher ρ e , the better its heat insulation effect; α e represents the heat absorption capacity of the film system structure, and a structure with a smaller α e should be selected to reduce the impact of the thin film on the glass and the environment.

[0077]

[0078]

[0079]

[0080] Where: I AM1.5 —— Relative spectral distribution of solar radiation;

[0081] τ(λ) —— Transmittance of the sample in each band of sunlight;

[0082] ρ(λ) —— Reflectance of the sample in each band of sunlight;

[0083] α(λ) —— Absorptance of the sample in each band of sunlight;

[0084] According to Kirchhoff's law of thermal radiation, the thermal infrared emissivity of a real object is equal to its absorptivity. The thermal infrared emissivity can be characterized by measuring the absorptivity. The relationship between the thermal infrared emissivity and the ratio of absorptivity of a real object is given by the formula α = M / M b , where M is the radiant emittance of the real object, and M b is the radiant emittance of a blackbody at the same temperature. The emissivity ε is defined by the formula ε = M / M b , so α = ε. The emissivity can be characterized by measuring the absorptivity.

[0085] When the material is in thermal equilibrium, the absorptance of the material is always equal to the emissivity; otherwise, the material itself cannot maintain thermal equilibrium.

[0086]

[0087] Formula (4) represents the surface emissivity of the coating in the wavelength range of λ1 < λ < λ2, where ε(λ) represents the absorptivity of the coating. The greater the surface emissivity in the thermal infrared band, the more heat is radiated to the outside, and the better the passive radiative cooling effect. The infrared emissivity mainly radiates heat through the atmospheric window, and the main atmospheric window is 8μm - 12μm.

[0088] To study the performance of the (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 film structure in the solar spectrum (280nm - 4000nm), the direct transmittance τ 6 、direct reflectance ρ 6 、direct absorptance α 6 of each band of sunlight when the incident angle of sunlight is 0° passing through the (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) e and (HfO2 / SiO2) e / HfO2 / PET / HfO2 / (HfO2 / SiO2) e film structures are calculated by formulas (1), (2), and (3), as shown in the data in Table 4.

[0089] Table 4 Direct transmittance (%), direct reflectance (%), and direct absorptance (%) of composite films

[0090]

[0091] For (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6Compared with the 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 structure, the direct transmittance of the (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 structure is lower. In theory, its heat insulation and sunshade effects are better. However, since the difference in direct transmittance between the two film systems is only 0.59%, the heat insulation and sunshade effects of the two film systems are not very different. The (HfO2 / SiO2) 3 HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure has a relatively large reflectance, which can reduce the heat entering the room, thus achieving better heat insulation and radiative cooling effects. Compared with the (HfO2-SiO2)

[0092] When the substrate is glass / PET, the direct transmittance τ e 、direct reflectance ρ e 、direct absorptance α e of the composite film at different bands of sunlight are as shown in the data in Table 5.

[0093] Table 5 Direct transmittance, direct reflectance and direct absorptance of glass / PET substrate at different bands

[0094]

[0095] It can be seen from Table 5 that the (HfO2 / SiO2) 6 / HfO2 / PET / HfO2 / (SiO2 / HfO2) 6 structure compared with the (HfO2 / SiO2) 6 / HfO2 / glass / HfO2 / (SiO2 / HfO2) 6 structure has a lower direct reflectance, a higher direct transmittance, and a higher direct absorptance in the ultraviolet band (280nm - 380nm). In the visible light band (380nm - 780nm), it has a higher direct reflectance, a lower direct transmittance, and a higher direct absorptance. In the near-infrared band (780nm - 2500nm), it has a lower direct reflectance, a higher direct transmittance, and a higher direct absorptance. In the mid-infrared band (2500nm - 4000nm), it has a higher direct reflectance, a lower direct transmittance, and a higher direct absorptance.

[0096] As described above, it is only the preferred embodiment of the present invention, and it does not impose other forms of restrictions on the present invention. Any person skilled in the art can use the disclosed technical content above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high-transmittance all-dielectric radiation cooling visual window, characterized by The structure is: (HfO2 / SiO2) 6 / HfO2 / substrate / HfO2 / (SiO2 / HfO2) 6 .

2. The high-transmittance all-dielectric radiation cooling visual window according to claim 1 is characterized in that The substrate is glass.

3. The high-transmittance all-dielectric radiation cooling visual window according to claim 1 is characterized in that The substrate is PET.

4. The high-transmittance all-dielectric radiation cooling visual window according to claim 2 is characterized in that When the substrate is glass, the film thickness is (nm): 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / 50 / 296 / glass / 134 / 170 / 134 / 170 / 134 / 170 / 134 / 170 / 134 / 170 / 134.

5. The high-transmittance all-dielectric radiation cooling visual window according to claim 3 is characterized by: When the substrate is PET, the film thickness is (nm): 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / 200 / 999 / PET / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474 / 2040 / 1474.

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