Structurally colored photonic crystal radiative cooling device and method of making the same

Abstract

The application discloses a kind of structural colored photonic crystal radiation refrigeration devices and preparation method thereof, the device includes double-layer micro-circular platform three-dimensional grating located at top and multilayer film structure located at bottom, wherein the included angle between the bus of micro-circular platform three-dimensional grating of upper and lower two layers and bottom surface is different angle respectively, and the multilayer film structure at bottom includes metal layer, dielectric layer and substrate from bottom to top.The preparation method is: spin coating a layer of photoresist on the substrate, pre-baking, contact exposure under mask plate, post-baking, developing in solution, obtaining the substrate with micro-grating complementary structure on the surface, evaporating a layer of MgF2 on the surface, obtaining the substrate with MgF2 microstructure deposited on the surface, then depositing surface SiO2 and bottom dielectric layer, and finally depositing metal layer.The angle combination of the application can neutralize the emissivity peak and valley of the two microstructure angles, realize the effect of wide spectrum infrared radiation regulation, has good color effect in different light environment, and the average reflectivity and average emissivity in infrared band are both above 0.9, realizing an average decrease of 6.1-7.7℃ compared with ambient temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to a refrigeration device and a preparation method thereof, in particular to a structural colored photonic crystal radiation refrigeration device and a preparation method thereof. BACKGROUND

[0002] With the continuous development of global industrialization, energy crisis and global warming have become two major problems that cannot be ignored in today's world. At the same time, the quality of life of residents in many emerging economies has been improved unprecedentedly, and the demand for air conditioning refrigeration has increased significantly. Traditional steam compression refrigeration, steam absorption refrigeration, adsorption refrigeration and other technologies have high energy demand and will discharge waste heat into the atmosphere, causing global warming and exacerbating urban heat island effect, which cannot fully meet the demand for new energy-saving and environmentally friendly refrigeration.

[0003] Radiative cooling is a passive cooling technology. Due to its unique thermodynamic mechanism, it can release the thermal energy of an object to the largest cold object, space, without any additional energy input. Passive radiative cooling technology is attracting more and more attention due to its environmental protection and energy-free characteristics. To achieve passive radiative cooling during the day, it is necessary to meet the conditions of high reflectivity in the solar spectrum band (0.3-2.5 μm) and high emission in the infrared band (2.5-20 μm). This spectral selective absorption optical property is achieved through micro-nano engineering of specific materials and coatings. Many reported radiative coolers have achieved good results in cooling performance, but whether it is a photonic crystal film or a polymer polymer film, most of them present a white or mirror-like appearance in order to maximize the broadband high reflectivity in the solar spectrum band. This single color tone is a visual aesthetic drawback for some consumer-oriented industries, such as building and automotive applications, and a colorful appearance can be more attractive.

[0004] However, some color radiative cooling devices in the industry have the problems of incompatible color appearance and high cooling performance, environmental hazards of dyeing agents, and poor color stability. Therefore, it is of great application prospect to develop a structural colored photonic crystal radiation refrigeration device with low absorption in the visible light range. SUMMARY

[0005] The purpose of the present application is to provide a structural colored photonic crystal radiation refrigeration device with low absorption in the visible light range.

[0006] The second purpose of the present application is to provide a preparation method of the structural colored photonic crystal radiation refrigeration device.

[0007] Technical solution: The structural colored photonic crystal radiation refrigeration device provided by the application comprises a top double-layer angle combined micro-circular platform three-dimensional grating and a bottom multilayer film structure, and the bottom multilayer film structure comprises a metal layer, a dielectric layer and a substrate from bottom to top.

[0008] The double-layer angle combined micro-circular platform three-dimensional grating comprises an upper circular platform and a lower circular platform, the included angle between the generatrix of the lower circular platform and the bottom surface is 30-40°, and the included angle between the generatrix of the upper circular platform and the bottom surface is 60-70°, and the grating period is 4-7 μm.

[0009] The metal layer is a high-reflectivity material with stable physical and chemical properties, such as at least one of Ag, Au and Al, and the dielectric layer material is Si3N4 and / or HfO2; and the substrate is a SiO2 substrate.

[0010] The preparation method of the structural colored photonic crystal radiation refrigeration device comprises the following steps:

[0011] (1) washing and drying the substrate;

[0012] (2) spin coating a layer of photoresist on the substrate, pre-baking, then performing contact exposure under a mask plate, and then post-baking; after post-baking, developing in a solution to obtain a substrate with a micro-grating complementary structure on the surface;

[0013] (3) evaporating a layer of MgF2 on the surface of the substrate with the micro-grating complementary structure on the surface, and then immersing in a stripping solution to strip the residual photoresist, to obtain a substrate with MgF2 microstructure deposited on the surface;

[0014] (4) depositing SiO2 on the surface and depositing a dielectric layer at the bottom of the substrate with the MgF2 microstructure deposited on the surface by using ion enhanced chemical vapor deposition, and then evaporating a metal layer on the dielectric layer to obtain the structural colored photonic crystal radiation refrigeration device.

[0015] In step (1), the substrate is a SiO2 substrate; the SiO2 substrate is placed in an ethanol solution for ultrasonic cleaning, and then taken out for drying.

[0016] In step (2), the photoresist is NR77-6000PY negative photoresist; the spin coating speed of the photoresist is 4500-5000 rpm; the pre-baking is performed on a hot table at 90-120 ℃ for 120-150 s; the post-baking is performed on a hot table at 90-120 ℃ for 90-120 s; and the contact exposure time is 0.4-0.5 s.

[0017] In step (2), the developing solution is a 2.38% TMAH aqueous solution, and the developing time is 5-6 s.

[0018] The MgF2 in step (3) has a thickness of 1.6-2 microns.

[0019] The SiO2 in step (4) has a thickness consistent with that of MgF2, the dielectric layer has a thickness of 0.5-1.2 microns, and the metal layer has a thickness of more than 100 nm.

[0020] In step (4), the substrate with the MgF2 microstructure on the surface is transferred to a plasma-enhanced chemical vapor deposition device for deposition of SiO2 on the surface and deposition of a dielectric layer at the bottom, and then transferred to a vacuum evaporation device for deposition of a metal layer.

[0021] The main role of the deposition of MgF2 is to prepare the required surface microstructure without affecting the spectral performance, and the deposition stability and controllability of MgF2 are much better than those of SiO2, so it is easier to form the target microstructure.

[0022] Beneficial effects: Compared with the prior art, the present application has the following remarkable effects:

[0023] (1) The present application is a SiO2-based microstructure radiative cooler, and the three-dimensional micrograting with the angle combination at the top can neutralize the emissivity peaks and troughs of the two kinds of microstructure angles, greatly reduce the impedance mismatch of bulk SiO2 in the atmospheric window band, and the dielectric layer can further enhance the infrared emissivity to achieve the effect of wide-spectrum infrared radiation regulation; and the bottom metal reflection layer can achieve high reflectivity of the solar spectrum.

[0024] (2) The present application uses common materials as raw materials, which are abundant and easy to obtain.

[0025] (3) The present application adopts a preparation process of photolithography-coating-peeling, and the prepared micro-dome grating has a period of 4-7 microns and a large line width, and reasonable control of exposure and development time can obtain a high preparation success rate.

[0026] (4) The prepared micro-dome grating has a height of 1.6-2 microns and good structural stability, and the material usage is controllable.

[0027] (5) The structural colored photonic crystal radiative cooling device prepared by the present application utilizes the multiple interference of the micrograting and the silver reflection layer to form a rainbow color feature, which has good color effect in different light environments and has no obvious absorption peak in the visible light band.

[0028] (6) The structural colored photonic crystal radiative cooling device prepared by the present application has an average reflectivity of more than 0.9 in the solar band and an average emissivity of more than 0.9 in the infrared band.

[0029] (7) The structural colored photonic crystal radiation refrigeration device prepared in the application can realize an average decrease of 6.1-7.7℃ compared with the ambient temperature in a mid-latitude area with an air temperature of 25℃. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The basic structure of the structural colored photonic crystal radiation refrigeration device in Example 1 of the application;

[0031] Figure 2 The SEM image of the micrograting complementary structure constructed on the surface of the SiO2 substrate obtained in step (4) in Example 1 of the application;

[0032] Figure 3 The SEM image of the prepared photonic crystal radiation refrigeration device in Example 1 of the application;

[0033] Figure 4 The spectral characterization curve of the structural colored photonic crystal radiation refrigeration device prepared in Example 1 of the application and the multilayer film structure under the same deposition conditions;

[0034] Figure 5 The emissivity comparison of the structural colored photonic crystal radiation refrigeration device prepared in Example 1 of the application and the SiO2 substrate plated with silver in the local infrared band;

[0035] Figure 6 The theoretical radiation cooling power curve of the structural colored photonic crystal radiation refrigeration device prepared in Example 1 of the application under different non-radiation heat transfer coefficients;

[0036] Figure 7 The color chart of the structural colored photonic crystal radiation refrigeration device prepared in Example 1 of the application under different angles in strong sunlight;

[0037] Figure 8 The detailed variation of the emissivity of different angle combinations calculated in Example 2 of the application;

[0038] Figure 9 The SEM image of the radiation cooling device prepared in Example 3 of the application;

[0039] Figure 10 The detailed variation of the emissivity of different periods and microstructure heights calculated in Example 4 of the application;

[0040] Figure 11 The detailed variation of the emissivity of different medium layer thicknesses calculated in Example 5 of the application;

[0041] Figure 12 The SEM image of the hole structure when the developing time is less than 5s in Example 6 of the application. DETAILED DESCRIPTION

[0042] The present application is described in further detail below.

[0043] Example 1

[0044] This embodiment provides a structure-colored photonic crystal radiation refrigeration device, which comprises a double-layer micro-dome three-dimensional grating at the top and a multilayer film structure at the bottom, wherein the angles between the upper and lower micro-dome three-dimensional grating bus lines and the bottom surface are different, and the bottom multilayer film structure comprises a metal layer, a dielectric layer and a substrate from bottom to top. The basic structure is as shown in Figure 1 , Figure 1 Left in the figure: the upper is a SiO2 double-layer micro-dome three-dimensional grating array, and the lower is a multilayer film structure; Figure 1 Right in the figure: the upper part of A in the figure is a SiO2 double-layer micro-dome three-dimensional grating, the lower part of A in the figure is a MgF2 layer, which is covered inside the SiO2 double-layer micro-dome three-dimensional grating; B is a SiO2 substrate, and C and D are Si3N4 and Ag films respectively. The angle between the upper micro-dome three-dimensional grating bus line and the bottom surface in this embodiment is 70°, the angle between the lower micro-dome three-dimensional grating bus line and the bottom surface is 40°, the double-layer micro-dome three-dimensional grating structure period is 5μm, and the calculated average reflectivity of solar spectrum and average emissivity of atmospheric window are 0.929 and 0.931 respectively. The preparation process comprises the following steps:

[0045] (1) A SiO2 substrate with a size of 30×30×0.5mm 3 is selected, ultrasonic cleaning is carried out in an ethanol solution, and after taking out, it is washed with deionized water and dried;

[0046] (2) A layer of NR77-6000PY negative photoresist is spin-coated on the SiO2 substrate, and then pre-baking is carried out on a hot table at 120℃ for 120s, and the spin-coating parameters are shown in Table 1 below:

[0047] Table 1

[0048] Step Rpm S acceleration / rpm-s -1 ]]> 1 4000 1 4000 2 5000 40 4000 3 0 3 2000

[0049] (3) The photoetching machine is used to carry out 0.4s of contact exposure under the mask, the mask period is 5μm, and then post-baking is carried out on a hot table at 120℃ for 90s, and the micro-dome angle combination obtained under this parameter is 40° and 70°.

[0050] (4) The SiO2 substrate surface is constructed with a micro-grating complementary structure, and the SEM image is as shown in Figure 2 ;

[0051] (5) 1.6 μm thick MgF2 was deposited at an evaporation rate of 0.15 nm / s, after which the same thickness of SiO2 was deposited at an evaporation rate of 0.88 nm / s after removal of the MgF2 in a Remover PG solution at 75 °C, 1 μm thick Si3N4 and 100 nm thick Ag were deposited on the back side at an evaporation rate of 0.3 nm / s and 0.2 nm / s, respectively. The SEM image of the finished photonic crystal radiative cooler is shown in Fig. 6. Figure 3

[0052] Figure 4 The spectral characterization curves of the prepared structured colored photonic crystal radiative cooler and the multilayer film structure only under the same deposition conditions, the average reflectivity of the solar spectrum band of the multilayer film structure only under the same deposition conditions is 0.95, and the average emission rate in the infrared is 0.95; according to the Kirchhoff law, the emission rate is equal to the absorption rate, i.e. ε = A = 1 - T - R. The average reflectivity of the solar spectrum band and the average emission rate in the infrared can be calculated according to the following formula:

[0053]

[0054] wherein AM1.5G (Global tilted irradiance AM1.5) refers to the standard solar spectrum irradiance, R(λ) refers to the spectral reflectivity of the sample, I bb (T,λ) refers to the standard blackbody spectral radiation intensity at a temperature of T, and ε(T,λ) refers to the spectral emission rate of the sample. By changing the integral interval, other bands can be calculated. The Planck constant h = 6.626 x 10 -34 J s, the speed of light c = 2.998 x 10 8 m s -1 , and the Stefan-Boltzmann constant k = 1.381 x 10 -23 JK -1 .

[0055] Figure 5 The comparison of the emission rate in the local infrared band between the prepared structured colored photonic crystal radiative cooler and the SiO2 substrate coated with silver only shows that the impedance mismatch of the bulk SiO2 is greatly reduced, and the emission rate is greatly improved.

[0056] Figure 6 The theoretical radiative cooling power curve of the prepared structured colored photonic crystal radiative cooler under different non-radiative heat transfer coefficients shows that the net cooling power per unit area is expected to be 147.1 Wm -2 . The theoretical radiative cooling power P cooling can be calculated according to the following formula:

[0057] P​cooling (T cool )=P rad (T cool )-P solar -P atm (T amb )-P cond+conv (T cool ,T amb )

[0058] wherein P solar is the solar radiation power absorbed by the surface of the radiative cooler, P rad is the thermal radiation power absorbed by the surface, P atm is the atmospheric radiation power absorbed by the surface, P cond+conv is the non-radiative heat transfer power, T cool is the temperature of the surface of the radiative cooler, and T amb is the temperature of the ambient air. In particular:

[0059]

[0060] ε atm =1-t(λ) 1 / cosθ

[0061] P cond+conv (T cool ,T amb )=h c (T amb -T cool )

[0062] wherein Ω is the solid angle, θ is the zenith angle, the atmospheric emissivity ε atm =1-t(λ) 1 / cosθ , t is the spectral transmittance, and h c is the non-radiative heat transfer coefficient.

[0063] Figure 7 is the color map presented by the structure colored photonic crystal under different angles in strong sunlight, which presents red, yellow, green and blue colors respectively as the angle changes.

[0064] Example 2

[0065] On the basis of Example 1, the angle combination of the top double-layer microstructure is modified, Figure 8The detailed variation of emissivity with the angle combination of 30° and 60°, 30° and 70°, 40° and 60°, and 40° and 70° is shown, and the average emissivity is 0.900, 0.913, 0.919 and 0.931 respectively based on the premise of controlling the diameter of the bottom surface of the micro-dome structure. It can be seen that when the included angle between the lower and upper dome generatrix and the bottom surface is in the range of 30°-40° and 60°-70° respectively, the obtained radiation cooling device has a good infrared broadband emission effect, and the combination of 40°-70° has the best effect.

[0066] Example 3

[0067] During the preparation process, the spin coating speed of photoresist and the exposure time can be modified to accurately control the undercut angle of the hollow complementary structure and the height of the vertical part at the bottom of the cavity, so as to realize different angle combinations of the double-layer microstructure. Based on the preparation process of Example 1, the spin coating speed of photoresist is modified to 4500 rpm, and the exposure time is modified to 0.4 s. The SEM image of the prepared radiation cooling device is shown in Figure 9

[0068] Example 4

[0069] Based on Example 1, the period size and height of the top microstructure array are modified, and the detailed variation of emissivity is calculated, Figure 10 when the period is 4 μm, 5 μm, 6 μm, 7 μm and the height is 2 μm. It can be seen that the emissivity will first increase and then decrease with the increase of the period, but all can perfectly cover the working waveband and have a good average emissivity, and the effect is best at 5 μm. The height of the microstructure array in the range of 1.6-2 μm can achieve good broadband emission effect.

[0070] Example 5

[0071] Based on Example 1, the thickness of the dielectric layer is modified, and the calculation result of the atmospheric window infrared emissivity is shown in Figure 11 When the thickness is 0.5 μm, 1 μm and 1.2 μm respectively, although there is a slight difference in the emission characteristics, they all have good performance, and the average emissivity can all reach above 0.9. The dielectric layer material has strong transmission in the solar spectrum band, and when the thickness reaches 1.2 μm, the average reflectivity of the cooler in the solar spectrum is still 0.926, so the reflectivity and emissivity performance can be guaranteed.

[0072] Example 6

[0073] Based on Example 1, the development time is modified. When the development time is less than 5 s, the unexposed area of the photoresist does not react sufficiently with the developer, and the cavity with clear structure cannot be obtained. The SEM image in this state is shown in Figure 12 ​When the developing time is higher than 6s, the unexposed area reacts with the developing solution, and the longer the developing time, the stronger the over-developing effect, which will destroy the complete hole structure and cause partial or overall structure to fall off. The developing time controlled in 5-6s is the best, and the ideal hole structure can be obtained.

Claims

1. A structurally colored photonic-crystal radiative cooling device, characterized in that, The application relates to a structure coloring photonic crystal radiation refrigeration device, which comprises a double-layer micro-dome three-dimensional grating on the top and a multi-layer film structure on the bottom, wherein the angles between the upper and lower micro-dome three-dimensional grating bus lines and the bottom surface are different, the multi-layer film structure comprises a metal layer, a dielectric layer and a substrate from bottom to top, the angle between the upper micro-dome three-dimensional grating bus line and the bottom surface is 60 DEG to 70 DEG, and the angle between the lower micro-dome three-dimensional grating bus line and the bottom surface is 30 DEG to 40 DEG; the period of the double-layer micro-dome three-dimensional grating is 4 to 7 mu m.

2. The structurally colored photonic radiative cooling device of claim 1, wherein, The metal layer is at least one of Ag, Au and Al, and the dielectric layer material is Si3N4 and / or HfO2.

3. A method of producing a structurally colored photonic-crystal radiative cooling device as claimed in claim 1, characterized in that, The application further discloses a preparation method of the structure coloring photonic crystal radiation refrigeration device. 1) cleaning and drying the substrate; 2) spin coating a photoresist on the substrate, pre-baking, then performing contact exposure under a mask plate, and then post-baking; developing in a developing solution after post-baking to obtain a substrate with a micro-grating complementary structure on the surface; 3) depositing a MgF2 layer on the substrate with the micro-grating complementary structure on the surface, then immersing in a stripping solution to strip the residual photoresist, and obtaining a substrate with a MgF2 microstructure on the surface; 4) depositing SiO2 on the surface and depositing a dielectric layer on the bottom of the substrate with the MgF2 microstructure on the surface by ion enhanced chemical vapor deposition, then depositing a metal layer on the dielectric layer to prepare the structure coloring photonic crystal radiation refrigeration device.

4. The method of claim 3, wherein the method further comprises: In step 2), the contact exposure time is 0.4 to 0.5 s.

5. The method of claim 3, wherein the method further comprises: In step 2), the developing solution is a 2.38% TMAH aqueous solution, and the developing time is 5 to 6 s.

6. The method of claim 3, wherein the method further comprises: In step 3), the MgF2 deposition thickness is 1.6 to 2 mu m.

7. The method of claim 3, wherein the method further comprises: In step 2), the pre-baking temperature is 90 to 120 DEG C, and the time is 120 to 150 s; the post-baking temperature is 90 to 120 DEG C, and the time is 90 to 120 s.

8. The method of claim 3, wherein the method further comprises: In step 2), the photoresist spin coating rotation speed is 4500 to 5000 rpm.

9. The method of claim 3, wherein the method further comprises: In step 4), the SiO2 deposition thickness is consistent with the MgF2 thickness, the dielectric layer deposition thickness is 0.5 to 1.2 mu m, and the metal layer deposition thickness is greater than 100 nm.

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