Preparation method and system of three-dimensional graphene film photoelectric detector

Abstract

The invention belongs to the technical field of semiconductor photoelectric integration, and discloses a preparation method of a three-dimensional graphene film photoelectric detector, a three-dimensional graphene film keeps the characteristics of zero band gap and high light absorption of graphene, has the characteristic of wide spectrum absorption, and can realize effective absorption from ultraviolet to infrared to microwave bands. The three-dimensional graphene thin film has a rough surface and a three-dimensional porous internal structure, the utilization rate of light can be greatly improved, efficient migration of carriers can be achieved through construction of a three-dimensional network, oxygen defects existing in a system can promote separation of photo-generated electron hole pairs and limit photo-generated holes, and therefore the obvious optical gain effect is generated, and the photoelectric conversion efficiency is improved. The photoconductive effect is enhanced, and larger photocurrent is obtained.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic integration technology, and particularly relates to a method and system for preparing a three-dimensional graphene thin film photodetector. Background Technology

[0002] Traditional photodetectors are mostly based on rigid silicon, mercury cadmium telluride, and other inorganic materials, which cannot be compatible with flexible substrates and are expensive. Graphene, as a two-dimensional nanomaterial, has excellent carrier transport performance (mobility up to 200,000 cm² / V·s), and its zero bandgap characteristic allows for broadband light absorption, making it an ideal material for flexible photodetectors.

[0003] Patent application number 202011614322.7 developed a graphene broadband detector including a substrate layer, an insulating isolation layer, a resonant cavity waveguide structure, and a heterojunction. By combining graphene with titanium dioxide to form a heterojunction, the spectral response of the photodetector can be extended from infrared to visible light and even to violet light. Furthermore, the high carrier mobility and other properties of graphene itself can also improve the photoresponsivity and photogain of the detector.

[0004] Patent application number 202110797165.6 mentions that by setting a slit waveguide with a Bragg resonant cavity, the optical signal is localized into the graphene layer, thereby improving the photoelectric detection responsivity of the photodetector during operation.

[0005] The patent application number 202210694742.3 mentions that the substrate is first photolithographically etched to form a device pattern, wherein the device pattern includes a first part pattern and a second part pattern, wherein the connection is a pointed shape, and then a metal catalyst layer is prepared on the device pattern. Graphene is grown on the surface of the catalyst layer at a preset temperature to obtain a graphene device.

[0006] Based on the above analysis, the problems and shortcomings of the existing technology are as follows: While existing photodetectors based on two-dimensional graphene and its heterojunctions have shown some potential in broadband detection, the developed graphene-based photodetectors are mainly based on single-layer or few-layer graphene, and their light absorption capacity is still limited by atomic-level thickness. In addition, the fabrication process is complex and difficult to scale up to a large area. Most existing technologies use complex processes of mechanical peeling and artificial stacking to prepare two-dimensional heterojunctions, which makes it difficult to achieve large-scale uniform production. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for fabricating a three-dimensional graphene thin film photodetector.

[0008] This invention is achieved as follows: a method for fabricating a three-dimensional graphene thin-film photodetector includes: Step 1: Use polyimide double-sided tape to stick the two sides of the glass slides together.

[0009] Step 2: Prepare a graphene oxide (GO) solution, fill it into a polytetrafluoroethylene liner, and then place it into a high-pressure hydrothermal reactor. Immerse the glued glass slides in the solution and allow it to stand under vacuum for a period of time to allow the GO solution to fully penetrate the glass interlayer.

[0010] Step 3: Perform a solvothermal reaction, then allow it to cool naturally to room temperature. Peel off the double-layered glass sheet, remove the graphene film in the middle, wash it repeatedly with ethanol, then transfer it to a flexible substrate using a wet method, dry it to obtain a flexible three-dimensional graphene film material, and cut it into the specific size required for the device.

[0011] Step 4: High work function metal electrode A and low work function metal electrode B are deposited on both sides of the device using a mask to obtain a flexible broadband photodetector with an asymmetric structure.

[0012] Furthermore, the thickness of the polyimide double-sided tape in step 1 is 100-1000 μm.

[0013] Furthermore, the graphene oxide mentioned in step 2 is single-layer graphene oxide or multi-layer (2-10 layers) graphene oxide, preferably single-layer graphene oxide; the concentration of graphene oxide in the graphene oxide solution is 0.2-10 mg / mL.

[0014] The vacuum settling time mentioned in step 2 is 1-6 hours.

[0015] Furthermore, in step 3, the solvent for the solvothermal process is selected from one or more of water, methanol, ethanol, ethylene glycol, n-butanol, isobutanol, tert-butanol, n-propanol, isopropanol, N,N-dimethylformamide, and acetone in any proportion; the additive for the solvothermal reaction is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid, and the addition ratio is 0.01%-1% of the solvent volume; the use of a small amount of acid can effectively enhance the hydrogen bonds in the solvothermal process, realize the effective cross-linking of the three-dimensional graphene structure, and enhance the mechanical strength of the product.

[0016] Furthermore, in step 3, the solvothermal reaction temperature is 80-200ºC, and the reaction time is 12-24h. After the solvothermal reaction, the double-layer glass slide is peeled off in an ethanol solution, the three-dimensional graphene film is taken out, and it is repeatedly cleaned with ethanol.

[0017] In step 3, the substrates for wet transfer include flexible substrates such as polyester (PET), polyimide (PI), polyvinyl alcohol (PVA), polyethylene naphthalate (PEN), and textile materials. After transfer, vacuum drying is performed at a temperature of 50-150ºC for 6-48 hours.

[0018] The thickness of the three-dimensional porous graphene film material after wet transfer in step 3 is 3-50 micrometers.

[0019] Furthermore, in step 4, the high work function metal electrode A is selected from one of gold, cobalt, nickel, and rhodium, and the low work function metal electrode B is selected from one of silver, lead, aluminum, vanadium, titanium, manganese, and zinc, with an electrode thickness of 50-500 nm.

[0020] In step 4, the width of the channel between the two electrodes is 100 micrometers to 1 centimeter, and the operating voltage is 0-5V.

[0021] Furthermore, an external electric or magnetic field with a strength of 0.1 to 1 Tesla is applied to the graphene oxide solution before the solvothermal reaction to induce the oriented stacking of graphene oxide sheets. This method can significantly reduce the sheet defect density and improve carrier mobility and device response speed.

[0022] Furthermore, during the solvothermal process, 0.01 to 0.5 mol / L of ascorbic acid or hydrazine solution is added as a synergistic reducing agent to partially reduce graphene oxide to graphene and form a π-conjugated network, thereby improving the light absorption coefficient and conductivity, and enhancing the photoelectric conversion efficiency.

[0023] Furthermore, before wet transfer, a polyvinyl alcohol stress buffer layer with a thickness of 50 to 300 nanometers is spin-coated on the surface of the flexible substrate, which can disperse strain concentration, prevent crack propagation caused by bending, and significantly improve the cyclic bending stability and service life of the device.

[0024] Another object of the present invention is to provide a fabrication system for a three-dimensional graphene thin film photodetector, comprising: The adhesive module is used to bond the two sides of two glass slides together using polyimide double-sided tape.

[0025] The impregnation module is used to prepare graphene oxide (GO) solution, which is then placed in a polytetrafluoroethylene liner and then into a high-pressure hydrothermal reactor. The glued glass sheets are then impregnated in the solution and left to stand under vacuum for a period of time to allow the GO solution to fully penetrate the glass interlayer.

[0026] The exfoliation module is used to perform a solvothermal reaction, followed by natural cooling to room temperature to peel off the double-layer glass sheet, remove the graphene film in the middle, repeatedly wash it with ethanol, then wet transfer it to a flexible substrate, dry it to obtain a flexible three-dimensional graphene film material, and cut it into the specific size required for the device.

[0027] The vapor deposition module is used to deposit a high work function metal electrode A and a low work function metal electrode B on both sides of the device through a mask, to obtain a flexible broadband photodetector with an asymmetric structure.

[0028] Another object of the present invention is to provide a computer device comprising a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the method for preparing the three-dimensional graphene thin film photodetector.

[0029] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method for preparing the three-dimensional graphene thin film photodetector.

[0030] Another objective of this invention is to provide an information data processing terminal for implementing the fabrication system of the three-dimensional graphene thin film photodetector.

[0031] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows: This invention proposes a novel flexible three-dimensional graphene thin-film-based photodetector. By designing a three-dimensional porous structure to increase the light absorption path and enhancing charge collection efficiency through a continuous conductive network, it maintains the broad spectral response characteristics of graphene, thereby solving the aforementioned technical challenges and promoting the development of broad spectral photodetectors towards high performance, high stability, and practical application.

[0032] (1) Three-dimensional graphene films retain the high light absorption characteristics of graphene with zero band gap and have broad spectrum absorption characteristics, which can achieve effective absorption from ultraviolet to infrared to microwave range.

[0033] (2) Three-dimensional graphene films have a rough surface and a three-dimensional porous internal structure, which can greatly improve the utilization rate of light. The construction of three-dimensional network can realize the efficient migration of charge carriers. The oxygen defects in the system can promote the separation of photogenerated electron-hole pairs and restrict photogenerated holes, thereby generating a significant light gain effect, enhancing the photoconductivity effect, and obtaining a larger photocurrent.

[0034] (3) The design of asymmetric electrodes with high work function and low work function promotes the separation and flow of photogenerated electron-hole pairs under bias voltage, thereby obtaining a higher photoresponse current.

[0035] (4) Compared with traditional two-dimensional graphene, three-dimensional graphene films not only have good flexibility, but also have considerable mechanical strength, and are easy to prepare on a large scale and transfer to flexible substrates. Attached Figure Description

[0036] Figure 1 This is a flowchart of the fabrication method of the three-dimensional graphene thin film photodetector provided in the embodiments of the present invention.

[0037] Figure 2 This is a structural block diagram of the fabrication system for a three-dimensional graphene thin film photodetector provided in an embodiment of the present invention.

[0038] Figure 3 This is a process diagram for preparing flexible three-dimensional graphene films provided in an embodiment of the present invention.

[0039] Figure 4 This is a scanning electron microscope image of the cross-section of a flexible three-dimensional graphene film provided in an embodiment of the present invention.

[0040] Figure 5 This is a schematic diagram of a flexible three-dimensional graphene thin film photodetector provided in an embodiment of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] like Figure 1 As shown, the method for fabricating a three-dimensional graphene thin-film photodetector provided in this embodiment of the invention includes the following steps: S101, use polyimide double-sided tape to stick the two sides of the two glass slides together.

[0043] S102, prepare graphene oxide (GO) solution, fill it into a polytetrafluoroethylene liner, then fill it into a high-pressure hydrothermal reactor, immerse the glued glass slides in it, and let it stand under vacuum for a period of time to allow the GO solution to fully penetrate into the glass interlayer.

[0044] S103 is subjected to a solvothermal reaction, and then naturally cooled to room temperature. The double-layer glass sheet is peeled off, the graphene film in the middle is taken out, and it is repeatedly washed with ethanol. Then it is wet-transferred to a flexible substrate, dried to obtain a flexible three-dimensional graphene film material, and cut into the specific size required for the device.

[0045] S104, by evaporating a high work function metal electrode A and a low work function metal electrode B on both sides of the device through a mask, a flexible broadband photodetector with an asymmetric structure is obtained.

[0046] The thickness of the polyimide double-sided tape in S101 provided in this embodiment of the invention is 100-1000 μm.

[0047] The graphene oxide described in S102 of the present invention is a single-layer graphene oxide or a multi-layer (2-10 layers) graphene oxide, preferably a single-layer graphene oxide; the concentration of graphene oxide in the graphene oxide solution is 0.2-10 mg / mL.

[0048] The vacuum settling time described in S102 is 1-6 hours.

[0049] The solvent in the solvothermal process of S103 provided in this embodiment of the invention is selected from one or more of water, methanol, ethanol, ethylene glycol, n-butanol, isobutanol, tert-butanol, n-propanol, isopropanol, N,N-dimethylformamide, and acetone in any proportion; the additive for the solvothermal reaction is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid, and the addition ratio is 0.01%-1% of the solvent volume; the use of a small amount of acid can effectively enhance the hydrogen bonds in the solvothermal process, realize the effective cross-linking of the three-dimensional graphene structure, and enhance the mechanical strength of the product.

[0050] In the embodiment of the present invention, the solvothermal reaction temperature in S103 is 80-200ºC, and the reaction time is 12-24h. After the solvothermal reaction, the double-layer glass sheet is peeled off in an ethanol solution, the three-dimensional graphene film is taken out, and it is repeatedly cleaned with ethanol.

[0051] The substrates for wet transfer in S103 include flexible substrates such as polyester (PET), polyimide (PI), polyvinyl alcohol (PVA), polyethylene naphthalate (PEN), and textile materials. After transfer, vacuum drying is performed at a temperature of 50-150ºC for 6-48 hours.

[0052] The thickness of the three-dimensional porous graphene film material after wet transfer of S103 is 3-50 micrometers.

[0053] In the S104 provided in this embodiment of the invention, the high work function metal electrode A is selected from one of gold, cobalt, nickel, and rhodium, and the low work function metal electrode B is selected from one of silver, lead, aluminum, vanadium, titanium, manganese, and zinc. The electrode thickness is 50-500 nm.

[0054] The width of the channel between the two electrodes in the S104 is 100 micrometers to 1 centimeter, and the operating voltage is 0-5V.

[0055] like Figure 2 As shown, the fabrication system for a three-dimensional graphene thin-film photodetector provided in this embodiment of the invention includes: The adhesive module is used to bond the two sides of two glass slides together using polyimide double-sided tape.

[0056] The impregnation module is used to prepare graphene oxide (GO) solution, which is then placed in a polytetrafluoroethylene liner and then into a high-pressure hydrothermal reactor. The glued glass sheets are then impregnated in the solution and left to stand under vacuum for a period of time to allow the GO solution to fully penetrate the glass interlayer.

[0057] The exfoliation module is used to perform a solvothermal reaction, followed by natural cooling to room temperature to peel off the double-layer glass sheet, remove the graphene film in the middle, repeatedly wash it with ethanol, then wet transfer it to a flexible substrate, dry it to obtain a flexible three-dimensional graphene film material, and cut it into the specific size required for the device.

[0058] The vapor deposition module is used to deposit a high work function metal electrode A and a low work function metal electrode B on both sides of the device through a mask, to obtain a flexible broadband photodetector with an asymmetric structure.

[0059] Another object of the present invention is to provide a computer device comprising a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the method for preparing the three-dimensional graphene thin film photodetector.

[0060] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method for preparing the three-dimensional graphene thin film photodetector.

[0061] Another objective of this invention is to provide an information data processing terminal for implementing the fabrication system of the three-dimensional graphene thin film photodetector.

[0062] Specific implementation of the present invention: Example 1: Use polyimide double-sided tape to adhere the two sides of two glass slides together. The polyimide double-sided tape should be 100 micrometers thick. Prepare 50 ml of a 2 mg / ml monolayer graphene oxide ethanol solution and add it to a 100 ml hydrothermal reactor (e.g., ...). Figure 3 As shown), a double-layered glass slide was immersed in a solution, vacuumed and allowed to stand for 60 minutes, followed by a solvothermal reaction at 160°C for 12 hours. Afterward, it was allowed to cool naturally to room temperature. The glass slide was then peeled off, and the middle film was removed. The film was washed multiple times with ethanol to transfer the three-dimensional graphene film onto a polyester (PET) substrate. Vacuum drying was then performed at 80°C for 10 hours. Figure 4 The image shown is a scanning electron microscope (SEM) image of a cross-section of a flexible three-dimensional graphene film. The substrate was cut to 6*10 mm, and a gold electrode with a thickness of 300 nm was deposited on one side of the device using a mask. Then, a silver electrode with a thickness of 300 nm was deposited on the other side. The channel width was 3 mm, thus fabricating a flexible three-dimensional graphene film photodetector. Figure 5 (As shown).

[0063] Flexible broadband photodetectors can detect light signals from the ultraviolet to the microwave band and also possess flexible and stretchable mechanical properties, making them a promising candidate for applications in many emerging fields. In the field of smart healthcare and health monitoring, flexible detectors can be integrated into wearable devices (such as patches and wristbands) to monitor heart rate, blood oxygen, and other parameters in real time by collecting PPG signals. In the field of optical communication and sensing, they can be used in near-infrared optical communication systems to achieve high-speed data transmission. They can also utilize their broadband response characteristics to build imaging systems for security monitoring, material sorting, and other applications.

[0064] Example 1 This embodiment provides a method for fabricating a three-dimensional graphene thin-film photodetector. First, two glass slides measuring 20 mm × 40 mm are selected and bonded together around their perimeter using 500 micrometer-thick polyimide double-sided tape to form a sealed interlayer. Then, a prepared graphene oxide solution is injected into a polytetrafluoroethylene-lined container, the interlayer glass is immersed in it, and the container is placed in a vacuum drying oven and left to stand for 3 hours to allow the graphene oxide to uniformly penetrate the glass interlayer space.

[0065] After being allowed to stand under vacuum, the reaction system was placed in a high-pressure hydrothermal reactor and subjected to a solvothermal reaction at 160 degrees Celsius for 18 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the two glass plates were peeled off to obtain a complete three-dimensional graphene film. After washing and drying with ethanol, the film exhibited continuous, flexible, and highly conductive properties. It was then wet-transferred onto a polyester substrate and dried to form the final product.

[0066] Example 2 In this embodiment, the graphene oxide is prepared by dissolving monolayer graphene oxide powder in deionized water at a concentration of 1 mg / mL, and then ultrasonically dispersing it for 30 minutes to obtain a homogeneous solution. The aforementioned glass sandwich structure is then completely immersed in this solution and left to stand under vacuum for 5 hours to allow the monolayer graphene oxide to fully permeate.

[0067] After a solvothermal reaction, the glass was exfoliated, resulting in a three-dimensional graphene film with a thickness of approximately 15 micrometers and uniform, stable pore distribution. The film's conductivity, measured using the four-probe method, was approximately 550 Siemens per meter, which meets the conductivity requirements for subsequent photodetector fabrication.

[0068] Example 3 In this embodiment, the solvent system uses a 1:1 volume ratio of ethanol and deionized water, with nitric acid as the acidic additive, added at a ratio of 0.2% of the total solvent volume. The introduction of acidic conditions effectively promotes the formation of hydrogen bonds between the graphene oxide sheets, enhancing the mechanical strength and stability of the three-dimensional framework.

[0069] The reaction temperature was controlled at 120 degrees Celsius, and the reaction time was 16 hours. The obtained graphene film exhibited a three-dimensional cross-linked porous structure under a microscope, with an average pore size of approximately 1.5 micrometers. This structure maintained stable electrical conductivity even with a bending radius of 5 millimeters, demonstrating its excellent flexibility.

[0070] Example 4 In this embodiment, ethylene glycol was used as the solvent, the solvothermal reaction temperature was 180 degrees Celsius, and the reaction time was 12 hours. The resulting film was washed with ethanol and then wet-transferred to a flexible polyimide substrate, and dried in a vacuum oven at 100 degrees Celsius for 24 hours.

[0071] Characterization showed that the transferred three-dimensional graphene film had a thickness of 8 micrometers, a smooth and continuous surface, and tightly bonded layers. After 5000 mechanical bending cycles, the resistance change was less than 3%, demonstrating good flexibility and stability, making it suitable for subsequent electrode deposition.

[0072] Example 5 In this embodiment, gold is used as the high work function electrode and aluminum as the low work function electrode. Both electrodes are 200 nanometers thick, and the channel width between the two electrodes is controlled to be 500 micrometers using a mask. The vapor deposition process is carried out under a vacuum of 5 × 10⁻⁶. -4 Completed under Pa conditions.

[0073] After being powered on, the device operates stably within a bias range of 0 to 5 volts. Test results show that it can generate significant photocurrent response in the wavelength range of 400 nm to 2000 nm, with a peak responsivity of 0.85 amps per watt, demonstrating broadband optical response capability.

[0074] Example 6 The preparation system provided in this embodiment consists of five modules: a pasting module, an impregnation module, a reaction module, a transfer module, and a vapor deposition module. The pasting module includes an automatic pressing device to ensure consistent thickness of the double-sided adhesive tape; the impregnation module is equipped with a controllable vacuum chamber, and the vacuum level can be set to 0.05 MPa.

[0075] The reaction module includes a constant-temperature heating vessel and an automatic cooling system, enabling temperature adjustment from 80 to 200 degrees Celsius and programmable reaction time. The transfer module is equipped with a tension control platform, allowing wet transfer while maintaining film integrity; the vapor deposition module features a dual-target vapor deposition structure, enabling precise control of the thickness of different metal electrodes.

[0076] Example 7 In this embodiment, the impregnation module employs a two-stage vacuum structure. First, the pressure is evacuated to 0.08 MPa and maintained stable for 5 hours, then slowly returned to atmospheric pressure, effectively reducing air bubbles in the solution. Through the vacuum control system, graphene oxide forms a uniform deposition layer within the glass interlayer.

[0077] Scanning electron microscopy revealed that the film surface was uniform and smooth, without obvious bubbles or breaks, and the graphene sheets were densely arranged. The use of this module improved the film's conductivity by approximately 20%, supporting the technical feature of "vacuum-controlled chamber promoting solution permeation" in the claim.

[0078] Example 8 In this embodiment, the reaction module uses a stainless steel sealed vessel with a volume of 250 ml, equipped with a temperature control probe and an acid injection channel. The system is heated to 150 degrees Celsius and maintained for 18 hours. After the reaction is completed, it is automatically cooled to 30 degrees Celsius and the reaction solution is discharged.

[0079] The resulting graphene film, after cleaning and drying, exhibits a three-dimensional porous honeycomb structure with lateral dimensions reaching several centimeters and uniform thickness. Mechanical testing shows that its tensile strength is approximately 45 MPa, far exceeding that of ordinary graphene films, supporting the technical effect of "enhancing the stability of the three-dimensional cross-linked structure" in the claims.

[0080] Example 9 The three-dimensional graphene thin-film photodetector fabricated using the above process forms an asymmetric electrode structure with high and low work functions on a flexible polyester substrate. The device generates a significant photocurrent signal under white light illumination, with a response time of approximately 0.03 seconds and a recovery time of 0.05 seconds.

[0081] When the device is bent to a radius of curvature of 10 mm, its photocurrent changes by less than 5%, demonstrating excellent mechanical flexibility. The device can be repeatedly bent more than 5000 times without performance degradation, confirming the combined enhancing effect of the three-dimensional graphene network structure on electrical and mechanical properties.

[0082] Example 10 This embodiment is based on a comprehensive verification of the process parameters obtained in Examples 1 to 9. By changing the graphene oxide concentration and the reaction temperature, the film thickness and porosity can be precisely controlled. A dense film can be formed under higher concentration (10 mg / mL) and lower reaction temperature (100°C), while a porous film is obtained under low concentration and high temperature conditions, which can be applied to high-sensitivity and fast-response applications, respectively.

[0083] Spectroscopic test results show that the device exhibits a continuous and smooth responsivity curve in the 400-2000 nm wavelength range, a quantum efficiency exceeding 65%, and a dark current density below 0.1 μA per square centimeter. These results further validate the overall technical effectiveness of claims 1 to 10 of this invention.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for fabricating a three-dimensional graphene thin-film photodetector, characterized in that, Includes the following steps: Step 1: Use polyimide double-sided tape to bond the two sides of the two glass slides together to form a sandwich structure. Step 2: Prepare a graphene oxide solution and inject it into a polytetrafluoroethylene-lined container. Place the container in a high-pressure hydrothermal reactor and immerse the sandwiched glass sheet in the graphene oxide solution. Allow it to stand under vacuum to promote the solution to fully penetrate the sandwich. Step 3: Perform a solvothermal reaction. After the reaction is complete, cool to room temperature, peel off the two glass plates, take out the graphene film in the middle, clean it with ethanol, transfer it to a flexible substrate by wet method, and dry it to form a flexible three-dimensional graphene film material. Step 4: Asymmetric structure is formed by evaporating high work function metal electrodes and low work function metal electrodes through a mask to obtain a flexible photodetector with a wide spectrum response.

2. The preparation method according to claim 1, characterized in that, The thickness of the polyimide double-sided tape mentioned in step 1 is 100 to 1000 micrometers to ensure the stability of the interlayer gap and facilitate solution penetration.

3. The preparation method according to claim 1, characterized in that, The graphene oxide described in step 2 is a single layer or a multilayer structure of 2 to 10 layers. The concentration of the graphene oxide solution is 0.2 to 10 mg per milliliter, and the vacuum settling time is 1 to 6 hours to ensure uniform deposition of the sheets.

4. The preparation method according to claim 1, characterized in that, The solvent in step 3 is selected from any one or a mixture of two or more of water, methanol, ethanol, ethylene glycol, n-butanol, isobutanol, tert-butanol, n-propanol, isopropanol, dimethylformamide, and acetone; an acidic auxiliary agent with a volume ratio of 0.01% to 1% is added to the solvothermal reaction. The acidic auxiliary agent is selected from sulfuric acid, nitric acid, hydrochloric acid, or phosphoric acid, and is used to enhance hydrogen bonding and improve the crosslinking strength of the three-dimensional graphene network.

5. The preparation method according to claim 1, characterized in that, The solvothermal reaction temperature is 80 to 200 degrees Celsius, and the reaction time is 12 to 24 hours; the flexible substrate after wet transfer is selected from polyester, polyimide, polyvinyl alcohol, polyethylene naphthalate, or textile materials, and the vacuum drying temperature is 50 to 150 degrees Celsius, the drying time is 6 to 48 hours, and the thickness of the resulting three-dimensional graphene film is 3 to 50 micrometers.

6. The preparation method according to claim 1, characterized in that, The high work function metal electrode mentioned in step 4 is one of gold, cobalt, nickel or rhodium, and the low work function metal electrode is one of silver, lead, aluminum, vanadium, titanium, manganese or zinc. The electrode thickness is 50 to 500 nanometers, the channel width between the two electrodes is 100 micrometers to 1 centimeter, and the device operating voltage range is 0 to 5 volts.

7. A fabrication system for a three-dimensional graphene thin film photodetector, characterized in that, include: The adhesive module is used to bond the two sides of two glass slides together to form a sandwich layer using polyimide double-sided tape. The impregnation module is used to prepare a graphene oxide solution and place the laminated glass sheet into the solution for vacuum settling. The reaction module is used to perform a solvothermal reaction and then peel off the glass sheet after cooling to room temperature to obtain a graphene film; The transfer module is used to wet transfer graphene films onto a flexible substrate and then dry them to form a three-dimensional thin film material. The vapor deposition module is used to deposit high work function metal electrodes and low work function metal electrodes at both ends of a thin film to form an asymmetric structure.

8. The preparation system according to claim 7, characterized in that, The impregnation module is equipped with a vacuum control chamber, which can maintain a stable negative pressure environment in the range of 0.01 to 0.1 MPa to promote the full penetration of graphene oxide solution into the glass interlayer.

9. The preparation system according to claim 7, characterized in that, The reaction module includes a high-temperature resistant sealed vessel, a temperature control unit, and an acidic additive injection unit. It can achieve a constant temperature reaction for 12 to 24 hours at a set temperature and automatically complete the cooling and drainage operations.

10. A three-dimensional graphene thin film photodetector prepared according to any one of claims 1 to 6, characterized in that, The device uses a flexible three-dimensional graphene film as the photosensitive layer, and a high work function electrode and a low work function electrode form an asymmetric ohmic contact structure. It can achieve a broadband optical response from visible light to near-infrared band under a bias voltage of 0 to 5 volts, while maintaining excellent flexibility and mechanical stability.

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