Preparation method for tunable transparent terahertz absorbing film for enhancing thermal radiation and use

Abstract

Disclosed in the present invention are a preparation method for a tunable transparent terahertz absorbing film for enhancing thermal radiation and a use. The method comprises evaporating / sputtering indium tin oxide (ITO) on one surface of a polyimide film; transferring graphene to the other surface of the polyimide film; manufacturing an electrode on the graphene and spin-coating the graphene with an ion gel; and finally manufacturing another electrode on the ion gel to obtain a tunable transparent terahertz absorbing film. The bias voltage across two ends of each electrode is changed, a terahertz time domain signal of the tunable transparent terahertz absorbing film is collected, the absorption rate of the tunable transparent terahertz absorbing film under a corresponding bias voltage condition is obtained, and the tunable transparent terahertz absorbing film is placed under sunlight / an infrared lamp to obtain a heating effect. According to the present invention, a transparent absorbing film formed by graphene-polyimide-ITO is used for absorbing terahertz waves of multiple bands to improve the heating effect; the method of the present invention does not involve a photoetching step; the tunable transparent terahertz absorbing film has high transmittance to visible light; the device manufacturing steps are simplified; and the growing demand for passive energy saving can be met.

Description

Preparation method and application of tunable transparent terahertz absorption film for enhanced thermal radiation Technical Field

[0001] The present invention belongs to the technical field of thermal insulation films, and in particular relates to a preparation method and application of an adjustable transparent terahertz absorption film for enhancing thermal radiation. Background Art

[0002] With the continuous improvement of the living standards of Chinese residents, people's demand for off-season fruits / vegetables is gradually increasing. In order to ensure the normal growth of off-season fruits / vegetables in greenhouses, a large amount of energy needs to be consumed to increase the temperature. Existing greenhouses can achieve normal production in an environment of minus 20 degrees by improving the lighting angle, heat preservation and heat storage performance. However, greenhouse films still have the problem of high transmittance to infrared electromagnetic waves and difficulty in utilizing infrared electromagnetic wave energy (such as energy in the terahertz band). Therefore, there is an urgent need for a greenhouse film with high transmittance to visible light and the ability to utilize infrared electromagnetic wave energy to ensure the normal growth of off-season fruits / vegetables in greenhouses, effectively reduce energy consumption and greenhouse gas emissions, achieve passive energy saving, and contribute to the "dual carbon" goals. However, the existing technology lacks a greenhouse film that can efficiently utilize infrared electromagnetic wave energy. Summary of the Invention

[0003] To address the problems in the prior art, the present invention provides a method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation and its application. The method of the present invention has the characteristics of dynamic tunability, high terahertz wave absorption rate, and simple production steps.

[0004] The technical solution adopted by the present invention is as follows, comprising the following steps:

[0005] Step 1: Preparation of an adjustable transparent terahertz absorption film: preparing an adjustable transparent terahertz absorption film comprising, from top to bottom, an electrode, an ion gel, an electrode, graphene, a polyimide film, and indium tin oxide (ITO);

[0006] In the step 1, the tunable transparent terahertz absorption film is prepared in the following manner:

[0007] Step 1) Evaporation / sputtering of ITO on the surface of the dielectric film;

[0008] First, a cleaned transparent polyimide film is taken, and indium tin oxide (ITO) is evaporated / sputtered on the lower surface of the polyimide film;

[0009] Step 2) Then, graphene is transferred onto the upper surface of the polyimide film;

[0010] Step 3) Next, a first electrode is fabricated on one end of the graphene top surface;

[0011] Step 4) spin coating the ion gel on the upper surface of the graphene;

[0012] Step 5) Finally, a second electrode is fabricated on the upper surface of the ion gel, ultimately producing a tunable transparent terahertz absorption film.

[0013] The dielectric film is a polyimide film;

[0014] In step 1), the transparent polyimide film is cleaned in the following manner: a complete polyimide film is taken, cleaned with acetone, isopropyl alcohol and deionized water in sequence, and then blown dry with nitrogen to obtain a cleaned polyimide film.

[0015] The thickness of the polyimide film is 10-200 microns.

[0016] In the step 1), the thickness of indium tin oxide (ITO) is 50-300 nm.

[0017] In the step 2), the graphene is obtained by chemical vapor deposition or mechanical exfoliation, and the number of layers of the graphene is 1 to 5.

[0018] In step 4), the spin coating speed of the ion gel is 1500-4000 rpm.

[0019] In step 4), the ion gel is spin-coated to cover the first electrode prepared in step 3);

[0020] The first electrode and the second electrode are respectively located on both sides of the adjustable transparent terahertz absorption film.

[0021] In step 2), the specific method of transferring graphene on the polyimide film is:

[0022] Release the graphene into water for at least 2 hours, then use tweezers to clamp the ITO-coated polyimide film and place the polyimide film obliquely into the water; at the same time, place the non-ITO-coated side of the polyimide film on the graphene in the water. After the graphene is adjusted to the middle position of the polyimide film, remove the polyimide film with graphene from the water, place it vertically for 3-5 minutes to drain excess water, and then let it dry for 30-40 minutes. Then, dry it in an oven at 100-120 °C for 20-30 minutes to obtain a dry polyimide film with graphene attached.

[0023] A polyimide film is used in the preparation of radiation heating devices, warm clothing or greenhouses.

[0024] Step 2: Verify the thermal radiation absorption efficiency of the tunable transparent terahertz absorber film

[0025] Step 1) Collect the terahertz time domain signal of the tunable transparent terahertz absorption film:

[0026] In a nitrogen atmosphere, the terahertz time domain signals of the tunable transparent terahertz absorption film and the total reflection mirror were collected in the spectral bandwidth range of 0.1~10 THz.

[0027] Step 2) changing the bias voltage across the electrodes to collect the terahertz time domain signal of the tunable transparent terahertz absorption film;

[0028] In step 1), when collecting the terahertz time domain signal of the tunable transparent terahertz absorption film, the humidity of the measurement environment is less than 2%. In step 2), the bias voltage across the two electrodes is -3.0V to 3.0V;

[0029] Step 3) Obtain the absorption peak intensity of the tunable transparent terahertz absorption film from the terahertz time domain signal:

[0030] The terahertz time domain signal is converted into a frequency domain signal using fast Fourier transform, and the absorptivity of the tunable transparent terahertz absorption film under the corresponding bias conditions is obtained by frequency domain signal processing;

[0031] Step 4) Place the tunable transparent terahertz absorber film and the ordinary film under sunlight / infrared light conditions and monitor the temperature rise of both.

[0032] In the preferred embodiment of the present invention, Trivial Transfer Graphene produced by ACS Material can be selected, but is not limited thereto. The graphene of the present invention can be replaced by a semi-metal, such as tungsten ditelluride.

[0033] In the specific implementation of the preferred ionic liquid of the present invention, the ionic liquid with the product number 711691-100G produced by Sigma Company can be selected, but it is not limited thereto.

[0034] In the specific implementation of the preferred P(VDF-HFP) copolymer of the present invention, the P(VDF-HFP) copolymer with the product number 427160-100G produced by Sigma can be selected, but it is not limited thereto.

[0035] In the specific implementation of the preferred infrared camera of the present invention, an infrared camera with the product number DS-2TD2636-10 produced by Hikvision can be selected, but it is not limited thereto.

[0036] The preferred polyimide film of the present invention can be a transparent polyimide film produced by South China Xiangcheng Technology Co., Ltd., but is not limited thereto. The polyimide film of the present invention can be replaced by other dielectric materials such as photoresist, such as SU-8 photoresist, polyethylene terephthalate (PET).

[0037] The thickness of indium tin oxide (ITO) is at least 50 nm. The reason is that when the thickness is less than 50 nm, terahertz waves can penetrate ITO, and the transparent terahertz absorption film made therefrom has a weaker effect of absorbing terahertz radiation.

[0038] The use of ion gel to make transparent terahertz absorption film can achieve large-scale modulation of terahertz waves through low voltage (<3V). Compared with laser modulation and ordinary voltage modulation (modulation voltage reaches tens or even hundreds of volts), the equipment used is simpler and the operation is safer.

[0039] Compared to traditional terahertz absorption films, visible light can pass through the ion gel, graphene, dielectric material, and ITO in transparent terahertz absorption films, resulting in high transmittance. Since terahertz waves cannot penetrate ITO, when terahertz waves are incident on the transparent terahertz absorption film, multiple frequency bands of terahertz waves are absorbed by the absorber structure composed of graphene, dielectric material, and ITO. The absorption rate can be adjusted by applying a bias voltage above and below the ion gel. In summary, transparent terahertz absorption films can improve the absorption and utilization of terahertz waves without affecting crop photosynthesis.

[0040] In a specific implementation, the preferred terahertz time-domain spectroscopy system of the present invention is recommended to be a terahertz time-domain spectroscopy system of model TAS7500 produced by ADVANTEST.

[0041] Terahertz waves refer to waves with a frequency of 0.1-10 THz (1 THz=10 12 Terahertz (THz) electromagnetic waves belong to the far-infrared band. Terahertz waves are widely present in nature, and human radiation contains energy in this band. The terahertz time-domain spectroscopy (THz-TDS) technique employed in this invention is a spectroscopy technology that has rapidly developed and spread internationally in recent years.

[0042] The tunable transparent terahertz absorption film of the present invention features a graphene-dielectric material-ITO anti-transmission layer structure. This structure boasts high transmittance in the visible light band and meets impedance matching requirements in the terahertz band. It can absorb terahertz waves across multiple bands, converting them into heat energy to enhance the warming effect. Compared to conventional plastic agricultural films, terahertz waves have greater penetration through dielectric materials such as plastics and clothing, making it difficult for conventional plastic agricultural films to absorb and utilize terahertz energy, thus reducing the greenhouse's warming effect.

[0043] The outstanding advantages of the present invention are that the tunable transparent terahertz absorption film has high transmittance for visible light and can absorb terahertz waves of multiple wavelengths and convert them into heat energy. The absorption film does not require photolithography of periodic metal structures, has a smooth surface, and is easy to process.

[0044] The present invention utilizes the technology of adjustable transparent terahertz absorption film, which has the following beneficial effects:

[0045] 1. The present invention adopts an adjustable transparent terahertz absorption film and utilizes a transparent absorber structure formed by graphene-polyimide-ITO to absorb terahertz waves of multiple bands to improve the warming effect.

[0046] 2. Compared with traditional plastic films, the method of the present invention can significantly improve the utilization rate of far-infrared radiation and enhance the warming effect; compared with ordinary terahertz absorbers, the adjustable transparent terahertz absorption film in this method does not require a photolithography step, has a high transmittance to visible light, simplifies the device manufacturing steps, and can meet the growing demand for passive energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG1 is a schematic structural diagram of an adjustable transparent terahertz absorption film according to the present invention;

[0048] FIG2 is a graph showing the terahertz transmission and reflection curves of ITO used in the present invention;

[0049] FIG3 is a terahertz reflection curve diagram of the transparent terahertz absorption film and dielectric layer-ITO structure of the present invention;

[0050] FIG4 is a terahertz reflection curve diagram of the tunable transparent terahertz absorption film under different bias voltages in Example 1 of the present invention;

[0051] FIG5 is a graph showing simulated terahertz reflection curves of the tunable transparent terahertz absorption film at different Fermi levels in Example 1 of the present invention;

[0052] FIG6 is a graph showing changes in the reflectivity of the lowest point of the tunable transparent terahertz absorption film under different bias conditions in Example 1 of the present invention;

[0053] FIG7 is a diagram showing the reflectivity simulation results of the transparent terahertz absorption film in Example 2 of the present invention within the 0.2 to 5 THz frequency range;

[0054] FIG8 is a temperature variation trend diagram of the transparent terahertz absorption film and glass during the heating process with an infrared lamp in Example 2 of the present invention;

[0055] FIG9 is a diagram showing the transmittance of the transparent terahertz absorption film in the visible light band in Example 2 of the present invention.

[0056] FIG10 is a graph showing simulated terahertz reflection curves of transparent terahertz absorption films with different dielectric layer thicknesses in Example 3 of the present invention.

[0057] In the figure: 1. Electrode; 2. Graphene; 3. Ion gel; 4. Polyimide; 5. Indium tin oxide (ITO). DETAILED DESCRIPTION

[0058] The present invention is described in detail below with reference to specific implementation cases. The following implementation cases will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. Example 1

[0059] (1) Fabrication of tunable transparent terahertz absorption film

[0060] A 50 mm thick polyimide film was ultrasonically cleaned in acetone, isopropanol, and water for 10 min each, dried with nitrogen, and the cleaned polyimide film was evaporated / sputtered with indium tin oxide (ITO5) with a thickness of 50-300 nm on the surface of the polyimide film; then a layer of graphene 2 was transferred to the other side of the polyimide film.

[0061] Among them, the transfer of graphene can be carried out in the following ways;

[0062] After releasing the purchased graphene into water for at least 2 hours, use tweezers to clamp the polyimide film and place it diagonally into the water. If necessary, use another pair of tweezers to press the polyimide film into the water. Use the side not coated with indium tin oxide (ITO5) to fit the graphene in the water. After adjusting to the appropriate position, remove the graphene from the water and place it vertically for 3 minutes to allow excess water to flow out. Then let it dry for 30 minutes, then dry it in an oven at 100 ºC for 20 minutes. After allowing it to cool to room temperature, add acetone and soak it for about 10 minutes. Then, use conductive silver glue to make electrode 1 on the single-layer graphene 2.

[0063] (2) Configuration of ion gel 3

[0064] An ion gel solution was prepared by dissolving the polymer P(VDF-HFP) and the ionic liquid [EMI][TFSA] in acetone. The weight ratio of polymer, ionic liquid, and solvent was set at 1:4:7. The ion gel solution was stirred at 50°C for 2 hours to form a homogeneous solution. The ion gel solution was then spin-coated onto a single-layer graphene at 2500 rpm. To remove the acetone solvent, the polyimide film was heated at 70°C for 24 hours. Another electrode 1 was fabricated on the ion gel 3 using conductive silver paste to form a tunable transparent terahertz absorber film. The schematic structure of the tunable transparent terahertz absorber film is shown in Figure 1.

[0065] (3) Electrical modulation of the active layer

[0066] The active layer (comprising graphene, ion gel, and silver electrodes) can achieve terahertz wave modulation in reflection mode: when the ion gel layer is unbiased (Vg = 0), free cations and anions are randomly distributed within the ion gel. Applying an external bias to the active layer generates an electric field at the silver electrode, attracting oppositely charged ions from the ion gel and forming a thin electric double layer (EDL) near the graphene and top electrode. This structure creates a high-intensity electric field near the graphene, leading to a rapid increase in the carrier concentration on the graphene.

[0067] Based on the above principle, the reflectivity of the tunable transparent terahertz absorber film changes significantly when the impedance matching conditions are changed. Therefore, the Fermi level of graphene can be effectively modulated with a small electrical bias (<3 V), achieving efficient terahertz wave modulation. The terahertz transmission and reflection curves of ITO, as well as the terahertz reflection curves of the transparent terahertz absorber film and the dielectric layer-ITO structure are shown in Figures 2 and 3.

[0068] (4) THz time-domain spectroscopy system measurement of tunable transparent terahertz absorption films under different bias voltages

[0069] The reflectivity of the tunable transparent terahertz absorber film was measured using a terahertz time-domain spectroscopy system under different bias conditions. Figure 4 shows that the reflectivity of the tunable transparent terahertz absorber film varies from 0 to 0.42 as the bias voltage increases from -2.5 V to 2.5 V. Because graphene exhibits p-doping properties in air, the reflectivity is not at its highest point at a bias voltage of 0 V.

[0070] (5) Finite-difference time-domain simulation of the reflectivity of tunable transparent terahertz absorption films under different Fermi levels

[0071] The Fermi level of graphene was set between 0 and 500 meV, and simulations were performed using the finite-difference time-domain method. The results, shown in Figure 5, show that as the Fermi level increases from 0 to 300 meV, the reflectivity of the tunable transparent terahertz absorber film decreases from 0.42 to ~0 (nearly perfect absorption), and the impedance mismatch between the tunable transparent terahertz absorber films decreases until it approaches 0. Further increasing the Fermi level increases the impedance mismatch, leading to an increase in reflectivity.

[0072] (6) Reflectivity changes of tunable transparent terahertz absorption films under different bias conditions

[0073] The reflectivity changes of the tunable transparent terahertz absorption film under different bias conditions are further plotted, as shown in Figure 6. The results show that when the electrical bias is set to -1.0 V, the terahertz reflectivity reaches a maximum value (0.42), which means that the Fermi level of the monolayer graphene is close to the charge neutral point (CNP).

[0074] The tunable transparent terahertz absorption film manufactured by the present invention can be modulated by applying a relatively low voltage. Due to the small electrochemical window, applying a larger bias voltage (>3V) should be avoided to avoid irreversible damage to the ion gel. Example 2

[0075] (1) Fabrication of tunable transparent terahertz absorption film

[0076] A 50 mm thick polyimide film was ultrasonically cleaned in acetone, isopropanol, and water for 10 min each, dried with nitrogen, and the cleaned polyimide film was evaporated / sputtered with indium tin oxide (ITO) with a thickness of 50-300 nm on the surface of the polyimide film; then a layer of graphene 2 was transferred to the other side of the polyimide film.

[0077] Among them, the transfer of graphene can be carried out in the following ways;

[0078] After the purchased graphene has been exposed to water for at least 2 hours, hold the polyimide film with tweezers and lower it diagonally into the water. If necessary, use another pair of tweezers to press the polyimide film downward. Place the surface of the film, uncoated with indium tin oxide (ITO5), onto the submerged graphene. Once positioned appropriately, remove the graphene from the water and place it upright for 3 minutes to allow excess water to drain. Allow it to air dry for 30 minutes, then oven dry at 100°C for 20 minutes. Allow it to cool to room temperature and soak in acetone for approximately 10 minutes. Electrode 1 is then fabricated on graphene 2 using conductive silver paste. Next, an ion gel solution is spin-coated at 3500 rpm onto the monolayer graphene 2. Another electrode 1 is fabricated on the ion gel 3 using conductive silver paste, resulting in a tunable transparent terahertz absorption film.

[0079] (2) Temperature rise simulation of transparent terahertz absorption film

[0080] Compared to greenhouses using only glass, transparent terahertz absorber films, provided they meet impedance matching requirements and absorb incident radiation of the corresponding frequencies, have the potential to achieve superior heating performance, converting external radiation into thermal energy. The simulation results, shown in Figure 7, demonstrate that the transparent terahertz absorber film absorbs terahertz waves across multiple frequency bands, including 0.95, 2.10, 3.33, and 4.57 THz, with nearly uniform absorption peaks. This is attributed to multiple reflections within the thin cavity of the transparent terahertz absorber film, which behaves similarly to a Fabry-Pérot cavity (FP cavity). As frequency increases, the absorption intensity weakens due to the damping resonance strength of the FP cavity. These multi-band absorption bands also demonstrate that the device can convert a wide range of terahertz radiation into thermal energy.

[0081] (3) Comparison of infrared radiation heating of transparent terahertz absorption film and glass

[0082] To further demonstrate the radiative heating effect of the device, an infrared light source was used to provide external heating radiation. An infrared camera was used to record the surface temperature trends of the transparent terahertz absorber film and glass during irradiation. Figure 8 shows that the surface temperatures of the transparent terahertz absorber film and glass increased with similar trends during the first five seconds. The surface temperature of the glass then reached a threshold, while the surface temperature of the transparent terahertz absorber film continued to rise. After equilibrium (35 seconds), the surface temperature of the transparent terahertz absorber film was ~0.7°C higher than that of the glass. The transparent terahertz absorber film exhibits high transmittance in the visible light band, as shown in Figure 9. Therefore, transparent terahertz absorber films have the potential to capture infrared radiation energy and fabricate radiative heating devices for a variety of applications, such as warm clothing and greenhouses.

[0083] (4) Fabrication of glass terahertz absorbers

[0084] Prepare a PDMS solution by mixing the PDMS base liquid and curing agent in a weight ratio of 15:1. Spin-coat the solution onto an ITO / glass substrate at 2500 rpm and then heat at 60°C for 1 hour. Transfer a layer of graphene onto the PDMS surface.

[0085] Among them, the transfer of graphene can be carried out in the following ways;

[0086] Release the purchased graphene into water for at least 2 hours. Use tweezers to clamp the ITO / glass substrate with the PDMS layer to fit the graphene in the water. After adjusting to the appropriate position, remove the graphene from the water and place it vertically for 3 minutes to allow excess water to flow out. Then let it dry for 30 minutes. Then, dry it in an oven at 100 ºC for 20 minutes. After letting it cool to room temperature, soak it in acetone for about 10 minutes. Remove the PMMA protective layer on the surface. Remove the graphene absorber, rinse it with deionized water, and blow it dry with nitrogen. Then, use conductive silver glue to make electrodes on the single-layer graphene.

[0087] (5) Configuration of ion gel

[0088] An ion gel solution was prepared by dissolving the polymer P(VDF-HFP) and the ionic liquid [EMI][TFSA] in acetone. The weight ratio of polymer, ionic liquid, and solvent was set at 1:4:7. The solution was stirred at 50°C for 2 hours to form a homogeneous solution. The ion gel solution was then spin-coated onto a monolayer graphene at 2500 rpm. To remove the acetone solvent, the ITO / glass substrate was heated at 70°C for 24 hours. Another electrode was then fabricated on the ion gel using conductive silver paste, resulting in a glass terahertz absorber. Example 3

[0089] (1) Fabrication of tunable transparent terahertz absorption film

[0090] A 50-nm-thick PET film was ultrasonically cleaned in acetone, isopropanol, and water for 10 min each, dried with nitrogen, and the cleaned PET film was evaporated / sputtered with indium tin oxide (ITO5) with a thickness of 50-300 nm on the surface of the PET film; then a layer of graphene 2 was transferred to the other side of the PET film.

[0091] Among them, the transfer of graphene 2 can be carried out in the following ways:

[0092] After releasing the purchased graphene into water for at least 2 hours, use tweezers to clamp the PET film and place it diagonally into the water. If necessary, use another pair of tweezers to press the PET film into the water. Use the side not coated with indium tin oxide (ITO5) to fit the graphene in the water. After adjusting to the appropriate position, remove the graphene from the water and place it vertically for 3 minutes to allow excess water to flow out. Then let it dry for 30 minutes, then dry it in an oven at 100 ºC for 20 minutes. After allowing it to cool to room temperature, add acetone and soak it for about 10 minutes. Then, use conductive silver glue to make electrode 1 on the single-layer graphene 2.

[0093] (2) Configuration of ion gel

[0094] An ion gel solution was prepared by dissolving the polymer P(VDF-HFP) and the ionic liquid [EMI][TFSA] in acetone. The weight ratio of polymer, ionic liquid, and solvent was set at 1:4:7. The ion gel solution was stirred at 50°C for 2 hours to form a homogeneous solution. The ion gel solution was then spin-coated onto a single-layer graphene at 2500 rpm. To remove the acetone solvent, the PET film was heated at 70°C for 24 hours. A second electrode was fabricated on the ion gel using conductive silver paste to form a tunable transparent terahertz absorber film. The fabrication of the transparent terahertz absorber film is now complete. The simulated terahertz reflection curves of transparent terahertz absorber films of different thicknesses are shown in Figure 10.

[0095] From the above implementation, it can be seen that the present invention utilizes the transparent terahertz absorption film with high transmittance in the visible light band and strong absorption characteristics in the terahertz band to enhance the thermal radiation absorption effect, which is expected to reduce energy consumption and greenhouse gas emissions. The production method is simple and can meet the growing demand for passive energy saving.

[0096] The above specific embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a tunable transparent terahertz absorption film for enhancing thermal radiation, characterized in that: The following steps are involved: Step 1) evaporating / sputtering indium tin oxide ITO (5) on the surface of the dielectric film (4); First, a clean dielectric film (4) is taken, and indium tin oxide ITO (5) is evaporated / sputtered on the lower surface of the dielectric film (4); Step 2) Then, the graphene (2) is transferred to the upper surface of the dielectric film (4); Step 3) Next, a first electrode (1) is fabricated at one end of the upper surface of the graphene (2); Step 4) spin coating the ion gel (3) on the upper surface of the graphene (2); Step 5) Finally, a second electrode (1) is fabricated on the upper surface of the ion gel (3), and finally a tunable transparent terahertz absorption film is obtained.

2. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: The dielectric film (4) is a transparent polyimide film; In step 1), the transparent polyimide film is cleaned in the following manner: a complete polyimide film is taken, cleaned with acetone, isopropanol and deionized water in sequence, and then blown dry with nitrogen to obtain a cleaned polyimide film.

3. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 2, characterized in that: The thickness of the polyimide film is 10-200 microns.

4. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: In the step 1), the thickness of indium tin oxide ITO (5) is 50-300 nm.

5. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: In the step 2), the graphene (2) is a graphene material obtained by chemical vapor deposition or mechanical exfoliation, and the number of layers of the graphene (2) is 1 to 5.

6. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: In the step 4), the spin coating speed of the ion gel (3) is 1500-4000 rpm.

7. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: In the step 4), the ion gel (3) is spin-coated to cover the first electrode (1) produced in the step 3).

8. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 1, characterized in that: The first electrode (1) and the second electrode (1) are respectively located on two sides of the adjustable transparent terahertz absorption film.

9. The method for preparing a tunable transparent terahertz absorption film with enhanced thermal radiation according to claim 2, characterized in that: In the step 2), the specific steps of transferring the graphene (2) to the upper surface of the dielectric film (4) are: The graphene (2) is released into water for at least 2 hours, and then the polyimide film coated with indium tin oxide ITO (5) is clamped with tweezers and the polyimide film is placed obliquely into the water; at the same time, the side of the polyimide film that is not coated with indium tin oxide ITO (5) is attached to the graphene (2) in the water. After the graphene (2) is adjusted to the middle position of the polyimide film, the polyimide film attached with the graphene (2) is taken out of the water, placed vertically for 3 to 5 minutes to drain excess water, and then left to dry for 30 to 40 minutes. Then, it is dried in an oven at a temperature of 100 to 120 ° C for 20 to 30 minutes, and finally a dry polyimide film attached with graphene (2) is obtained.

10. Use of a polyimide film prepared by the preparation method according to any one of claims 1 to 9 in the preparation of radiation heating devices, warm clothing or greenhouses.

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