Stealth biomimetic high-conductivity transparent electrodes for optoelectronic devices and methods for their fabrication

Abstract

The application relates to the field of biosensors, and particularly relates to a stealth biomimetic high-conductivity transparent electrode for photoelectric devices and a preparation method thereof, which comprises the following steps: processing a leaf blade into a vein network template; growing graphene on the surface of the vein network template; forming a metal nanowire network on the surface of the graphene; growing vertical graphene on the surface of the metal nanowire network to obtain a hybrid electrode; performing constant voltage electroplating with the hybrid electrode as one electrode, and coating the hybrid electrode with conductive hydrogel to obtain the stealth biomimetic high-conductivity transparent electrode for photoelectric devices. The preparation method of the biomimetic high-conductivity transparent electrode provides a preparation strategy for constructing a transparent electrode with high conductivity, transparency, mechanical stability and gas permeability. The super flexibility and light weight characteristics of the prepared novel transparent electrode are also crucial for the development of low-cost and large-scale commercial applications of flexible photoelectric devices.

Description

Technical Field

[0001] This application relates to the field of biosensors, and mainly to a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices and its fabrication method. Background Technology

[0002] Stretchable transparent electrodes are indispensable components in future deformable optoelectronic devices, playing a crucial role in smart touchscreens, perovskite solar cells / light-emitting diodes, electrochromic windows, thin-film transistors, electronic skin, and photodetectors. However, due to the lack of effective methods for synthesizing inherently stretchable and transparent highly conductive materials, existing methods for fabricating stretchable transparent electrodes involve processing non-stretchable conductive materials (such as carbon nanomaterials, conductive polymers, metal nanowires, and metals) into transparent conductive films and then bending these transparent conductors to achieve stretchability. A more preferable method involves assembling conductive materials into interconnect networks. Among these conductive materials, metal nanowire meshes exhibit high conductivity under large strain, making them the most promising candidates for stretchable transparent electrodes. However, traditional fabrication of metal nanowire meshes requires vacuum-based metal evaporation, and the resulting meshes need to be thermally fused at high temperatures to reduce contact resistance at the mesh junctions. These physical methods are not suitable for the plastic and elastomeric sub-substrates involved in deformable devices, especially non-planar sub-substrates, thus significantly limiting the application of metal nanowire meshes. To address this issue, scientists have made some progress in developing low-temperature chemical methods, such as directly depositing metal nanowire meshes onto two-dimensional transparent templates. However, existing fabrication processes still suffer from insufficient flexibility and low conductivity, making them unsuitable for stretchable transparent electrodes. Therefore, current technologies require further improvement and development. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this application is to provide a stealthy biomimetic highly conductive transparent electrode for optoelectronic devices and its preparation method, aiming to solve the problems of complex manufacturing process of existing stretchable transparent electrodes, poor flexibility of the electrodes, toxicity and poor bending resistance.

[0004] The technical solution of this application is as follows: In a first aspect, this application provides a method for fabricating a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices, comprising the following steps: The leaf blades were processed into leaf vein network templates; Graphene is grown on the surface of the leaf vein network template; A network of metal nanowires is formed on the surface of the graphene. Vertical graphene is grown on the surface of the metal nanowire network to obtain a hybrid electrode; Using the hybrid electrode as one electrode, constant voltage electroplating is performed, and the hybrid electrode is coated with conductive hydrogel to obtain the invisible biomimetic highly conductive transparent electrode for optoelectronic devices.

[0005] This application proposes a transparent conductive mesh electrode with layered conductive hydrogel-coated graphene / metal nanowire interwoven leaf vein fibers using a biomimetic method. The inner graphene and metal nanowire network can effectively improve the conductivity of the leaf vein network structure, while the outer vertically grown graphene increases the contact area between the electrode and the outside world. The conductive hydrogel can ensure the tight bonding of graphene and metal nanowires, which can effectively solve the problems of transparent electrodes being fragile, having poor flexibility, and having low conductivity.

[0006] Furthermore, the step of processing the leaf blade into a leaf vein network template includes: Dissolve 8-15g of sodium hydroxide in a container containing 80-100ml of distilled water, add the leaves, heat rapidly to 100℃ and continue for 3-4 hours until the leaf mesophyll is removed to obtain the leaf veins, wash and dry at 60-80℃ for 3-5 hours to obtain the leaf vein network template.

[0007] Further, the step of growing graphene on the surface of the leaf vein network template includes: A thin copper film is sputtered onto the leaf vein network template; The leaf vein network template sputtered with a copper film was placed in the quartz tube of the CVD system and kept at 1 mbar. Hydrogen and methane were introduced at a flow rate of 1-3 sccm and 15-20 sccm respectively. The temperature was raised to 950-1050℃ and the growth was carried out for 10-30 minutes. Then the methane was stopped and the graphene was cooled to room temperature in a hydrogen atmosphere to complete the graphene growth. Remove the leaf vein network template containing a copper film and graphene on its surface, spin-coat the PMMA solution onto the leaf vein network template containing a copper film and graphene on its surface, and let it stand at room temperature for 30-60 minutes. The leaf vein network template is immersed in a 0.1M-0.3M ammonium persulfate solution to remove the copper film, and then washed with deionized water 4-6 times. The separated graphene and leaf vein network template are gently bonded together at room temperature, then immersed in acetone and left to stand for 11-13 hours to remove the PMMA, and then immersed in ethanol for 5-8 minutes to complete the cleaning.

[0008] Furthermore, the metal nanowires of the metal nanowire network are one of silver nanowires, silver nanosheets, gold nanowires, and nickel nanowires.

[0009] Further, the step of forming a metal nanowire network on the graphene surface includes: A metal nanowire film solution with a concentration of 5-8 mg / mL was spin-coated onto the graphene surface at 1000 rpm for 70-90 seconds, air-dried, and then placed at a temperature of 100℃ and a pressure of 12 MPa for 15 seconds. Finally, it was cooled to room temperature within 15-25 minutes to complete the annealing process.

[0010] Further, the step of preparing the metal nanowire film solution includes: A metal salt is added to ethylene glycol and stirred at 400-600 rpm using a magnetic stirrer to obtain a nanowire solution. The nanowire solution is then filtered using a glass filter, and the collected nanowires are redispersed in methanol to obtain the metal nanowire film solution.

[0011] Further, the step of growing vertical graphene on the surface of the metal nanowire network includes: The leaf vein network template, on which the metal nanowire network and the graphene are grown, is placed on the cathode plate in a quartz tube within a microwave plasma chemical vapor deposition system. Hydrogen gas is introduced at a flow rate of 110 sccm, and a microwave power of 550 W is applied to generate plasma. A DC bias is applied between the anode and the cathode plate, and then methane is introduced at a flow rate of 10 sccm. The chamber pressure is maintained at 230 Pa, and the DC bias is increased to -200 V to grow vertical graphene. After growth for 20-30 minutes, the introduction of hydrogen gas and methane is stopped, and the mixture is cooled to room temperature in a vacuum to obtain the hybrid electrode.

[0012] Furthermore, the step of performing constant voltage electroplating using the hybrid electrode as one electrode and coating the hybrid electrode with conductive hydrogel includes: The hybrid electrode is immersed in an electrolyte mixture as the working electrode, with an Ag / AgCl electrode as the reference electrode and a Pt wire electrode as the counter electrode. A constant voltage of 0.5V is set, and electroplating is performed for 200-400 seconds using a constant voltage electroplating method to obtain the invisible biomimetic highly conductive transparent electrode coated with conductive hydrogel.

[0013] Furthermore, the electrolyte mixture is composed of a polymer monomer solution and a catalyst; the concentration of the polymer monomer solution in the electrolyte mixture is 0.3M-0.6M, and the mass fraction of the catalyst in the electrolyte mixture is 0.5wt%-1.5wt%. The polymer is one of PEDOT:PSS, polythiophene, polypyrrole, and polyaniline; the catalyst is Ti(ClO4)4.

[0014] Secondly, this application provides a stealth biomimetic highly conductive transparent electrode for optoelectronic devices, which is prepared by the method described above for preparing a stealth biomimetic highly conductive transparent electrode for optoelectronic devices. The stealth biomimetic highly conductive transparent electrode for optoelectronic devices includes a hybrid electrode and a conductive hydrogel. The hybrid electrode includes, from bottom to top, a leaf vein network template, graphene, a metal nanowire network, and vertical graphene. The conductive hydrogel coats the surface of the hybrid electrode.

[0015] This application has the following beneficial effects: (1) This application proposes a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices. Inspired by the hollow interconnected structure of leaf veins, a layered transparent conductive mesh electrode of polymer-coated graphene / metal nanowires interwoven with leaf vein fibers is proposed using a biomimetic method. The biomimetic conductive mesh electrode forms a layered structure, wherein the macroscopically interwoven graphene / leaf vein conductive fibers along the leaf veins serve as the first layer, the mesoscopic stitching structure of the graphene / leaf vein structure sheets interwoven with metal nanowires serves as the second layer, the microscopic intrinsic structure perpendicular to the graphene conductive material serves as the third layer, and the polymer-coated fully flexible conductive gel serves as the fourth layer. The transparent conductive mesh has great potential in high-performance wearable optoelectronics and camouflage electronics.

[0016] (2) This application develops a unique sandwich structure for fabricating high-performance and fully flexible graphene / metal nanowire polymer transparent electrodes. The metal nanowires are completely encapsulated between a single layer of graphene and a hybrid polymer matrix using a specific bottom-up fabrication process. This unique hybrid electrode exhibits advantages in various aspects. First, as the main framework of the electrode, the polymer ensures a tight bond between the graphene and metal nanowires, as well as a strong connection between the metal nanowires. Simultaneously, due to the properties of the hybrid polymer matrix, the entire hybrid film exhibits ultrathin, lightweight, and fully flexible characteristics. Furthermore, the graphene and polymer layers protect the buried metal nanowires from oxidation and corrosion, which is beneficial for maintaining the high conductivity of the transparent electrode device. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the fabrication method of a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices according to an embodiment of this application.

[0018] Figure 2 This is a schematic diagram illustrating the method for fabricating a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices according to an embodiment of this application.

[0019] Figure 3 This is a schematic diagram illustrating the textual description of the preparation method of growing graphene on a leaf vein network template according to an embodiment of this application.

[0020] Figure 4This is a schematic diagram of the structure of the invisible biomimetic highly conductive transparent electrode for optoelectronic devices prepared according to an embodiment of this application.

[0021] Labeling explanations: 1. Leaf vein network template; 2. Graphene; 3. Metal nanowire network; 4. Vertical graphene; 5. Conductive hydrogel. Detailed Implementation

[0022] This application provides a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices and a method for its fabrication. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] Specifically, refer to Figures 1-2 This application provides a method for preparing a stealth biomimetic highly conductive transparent electrode, comprising the following steps: S1. Process the leaf blade into a leaf vein network template.

[0024] S2. Graphene is grown on the surface of a leaf vein network template.

[0025] S3. Forming a network of metal nanowires on the surface of graphene.

[0026] S4. Vertical graphene is grown on the surface of a metal nanowire network to obtain a hybrid electrode.

[0027] S5. Using the hybrid electrode as one electrode, constant voltage electroplating is performed, and the hybrid electrode is coated with conductive hydrogel to obtain a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices.

[0028] This application proposes a layered polymer-coated transparent conductive mesh electrode of graphene / metal nanowire interwoven leaf vein fibers using a biomimetic method. The inner graphene and metal nanowire network can effectively improve the conductivity of the leaf vein network structure, while the outer vertically grown graphene increases the contact area between the electrode and the outside world. The polymer can ensure the tight bonding between the graphene and the metal nanowires, which can effectively solve the problems of transparent electrodes being fragile, having poor flexibility, and having low conductivity.

[0029] In nature, plant leaves have two-dimensional branching and extending veins. During photosynthesis, light passes through the veinless regions and is absorbed by the mesophyll cells of the leaf, while necessary substances and produced nutrients are efficiently transported through the veins. Over billions of years of evolution, the vein structure has gradually optimized to achieve a balance between transparency, substance transport, and mechanical stability. Given these properties, the veins in leaves are ideal templates for fabricating stretchable transparent electrodes.

[0030] Under strongly alkaline conditions, the organic matter in the leaf mesophyll will be corroded, while the fibrous veins will be partially preserved. Specifically, step S1 includes: dissolving 8-15g of sodium hydroxide in a container containing 80-100ml of distilled water, adding the leaves, rapidly heating to 100℃ and continuing for 3-4 hours until the leaf mesophyll is removed to obtain the veins, repeatedly washing the veins with distilled water, and drying them at 60-80℃ for 3-5 hours to obtain a vein network template.

[0031] During this process, the leaf mesophyll is gradually corroded by the alkali solution until it is almost completely removed, while the leaf vein structure is preserved and presents a transparent network of veins.

[0032] Furthermore, the leaves are preferably young maple leaves. Maple leaves have a good fractal structure, and the young maple leaves should be newly grown fresh leaves, preferably 5-10 days old. Younger maple leaves have better flexibility, and using young maple leaves to prepare the vein network template is also more conducive to improving the flexibility of the electrode material.

[0033] Stretchable transparent electrodes are key components of optoelectronic devices, but traditional indium tin oxide (ITO) electrodes are hampered in their further application in flexible optics and electronic devices due to insufficient indium sources and the brittleness of ITO. To overcome these limitations, many alternative transparent electrode materials have been investigated, such as conductive polymers, carbon nanotubes, graphene, and random metal nanowires. However, the oxidation and corrosion problems of metal nanowires, exposed to the atmosphere and harsh environments, persist and severely affect the electrical performance of stretchable transparent electrodes.

[0034] To address the aforementioned problems, this application develops a hybrid structure combining graphene and metal nanowires. Graphene possesses advantages such as high chemical and thermal stability, high mechanical properties, high optical transparency, and ease of fabrication, providing an effective protective barrier for the metal matrix. This effectively solves the corrosion problem of metal nanowires. Specifically, a layer of graphene is first prepared on the surface of a leaf vein network template, referring to... Figure 1 and Figure 3 ( Figure 1 (Step S23 is not shown), Step S2 includes: S21. Sputter a copper thin film onto the leaf vein network template. Specifically, the leaf vein network template is laid flat on a silicon substrate, and then a copper thin film with a thickness of 100-200 μm is deposited by magnetron sputtering. By sputtering a copper thin film onto the leaf vein network template before growing graphene, it helps to improve the decomposition rate of methane during graphene growth, thereby promoting graphene growth. The magnetron sputtering method for depositing the copper thin film is existing technology and will not be described in detail here.

[0035] S22. Place the leaf vein network template sputtered with copper film in the quartz tube of the CVD system, maintain it at 1 mbar, and introduce hydrogen at a flow rate of 1-3 sccm and methane at a flow rate of 15-20 sccm. Raise the temperature to 950-1050℃, grow for 10-30 minutes, then stop introducing methane and cool to room temperature in a hydrogen atmosphere to complete the graphene growth.

[0036] S23. Take out the leaf vein network template containing copper film and graphene on the surface, spin-coat the PMMA solution onto the leaf vein network template containing copper film and graphene on the surface, so that the graphene surface is coated with PMMA solution, and let it stand at room temperature for 30-60 minutes.

[0037] The solvent in the PMMA solution is toluene or chloroform, the mass fraction of PMMA in the PMMA solution is 10wt%-20wt%, and the coating amount of the PMMA solution is 10-15mL / cm. 2 In the embodiments of this application, the solvent used in the PMMA solution is toluene, the mass fraction of PMMA in the PMMA solution is 15 wt%, and the coating amount of the PMMA solution is 12 mL / cm². 2 .

[0038] In this application, PMMA can be cured during the standing process at room temperature for 30-60 minutes, avoiding the impact of heating on the strength of the leaf vein network template. By applying PMMA as a transfer medium for the bonding of graphene and the leaf vein network template, the applied PMMA causes the graphene to redissolve in the early stage of standing, which helps to reduce the interaction force between graphene and the copper film, facilitating the removal of the copper film and enhancing the contact between graphene and the leaf vein network template, thereby ensuring the integrity of graphene. After standing and curing at room temperature, the solvent evaporates, and the PMMA chains recombine, promoting the conformal bonding of graphene and the leaf vein network template. Through the glass transition of the polymer, graphene spreads and wets the surface of the leaf vein network template, successfully achieving the complete transfer of the graphene film.

[0039] S24. Immerse the leaf vein network template in a 0.1M-0.3M ammonium persulfate solution to etch and remove the copper film. Wash with deionized water 4-6 times. Gently press and bond the separated graphene and leaf vein network template at room temperature. Then immerse in acetone and let stand for 11-13 hours to remove PMMA. Then transfer to ethanol and keep for 5-8 minutes to complete the cleaning. Graphene is obtained on the surface of the leaf vein network template.

[0040] The transfer of graphene is similar to that of most two-dimensional materials. PMMA is used to fix and support the graphene film, forming a sandwich structure of PMMA + graphene + copper foil. The copper film is then removed by immersion in ammonium persulfate solution, and the PMMA is removed by immersion in acetone solution, thus obtaining the transferred graphene sample. The curing of PMMA has a significant impact on the transfer quality, effectively supporting and protecting the graphene and reducing wrinkles and damage during the transfer process. To avoid insufficient bonding strength, light pressing bonding can be performed at room temperature before PMMA removal, allowing the graphene to conformally adhere to the target substrate. This conformal adhesion increases the bonding force between the graphene and the leaf vein network template.

[0041] This application prepares a layer of two-dimensional conformally bonded and well-morphologically good continuous graphene on the surface of a leaf vein network template. This not only provides protection for the subsequently prepared nanowire structure, but the strong interfacial interaction between the plant fiber and the graphene conductive unit helps to orderly construct a layered and interwoven conductive mesh on a flexible and lightweight texture. This can provide a good electron transport channel to further improve electrical performance, while maintaining high transparency and effectively avoiding the trade-off between photoelectric performance.

[0042] Furthermore, the metal nanowires in the metal nanowire network are one of silver nanowires, silver nanosheets, gold nanowires, and nickel nanowires. The selected metal nanowires have high conductivity and strong chemical stability. Preferably, the metal nanowires are silver nanowires, which have excellent conductivity and light transmittance, making them more suitable for transparent electrodes.

[0043] Furthermore, step S3 specifically includes: spin-coating a metal nanowire film solution with a concentration of 5-8 mg / mL onto the graphene surface at 1000 rpm for 70-90 seconds to form a metal nanowire network, air drying, then placing it under conditions of 100°C and 12 MPa for 15 seconds, and then cooling it to room temperature within 15-25 minutes to complete the annealing, thereby forming a metal nanowire network on the graphene surface.

[0044] Spin coating creates a randomly dispersed network of metal nanowires, which are interconnected and improve overall conductivity. Annealing ensures a tight bond between the metal nanowire network and the graphene.

[0045] Graphene possesses advantages such as high chemical and thermal stability, high mechanical properties, high optical transparency, and ease of fabrication, providing an effective protective barrier for metal matrices. Furthermore, the two-dimensional graphene structure can improve the additional electron channels in hybrid films, while graphene and metal nanowires can effectively enhance the conductivity of leaf vein network structures.

[0046] The metal nanowire film solution is manufactured using a solution treatment method with a polyol process. The steps include: adding the corresponding metal salt to ethylene glycol according to the metal nanowires, stirring with a magnetic stirrer at 400-600 rpm to obtain a nanowire solution, filtering the nanowire solution with a glass filter, and redispersing the collected nanowires in methanol to obtain the metal nanowire film solution.

[0047] The collected nanowires can be dispersed in methanol at the desired concentration for later use. The appropriate metal salt, such as silver salt (silver nitrate) or gold salt (chloroaurate (AuCl4), is selected based on the desired metal nanowire network. - ), gold nitrate (Au(NO3)4) - (and nickel salts (nickel nitrate hexahydrate)). Filtering the nanowire solution through a glass filter can remove particles that reduce transmittance.

[0048] In one specific embodiment, the steps for preparing the silver nanowire film solution include: first, adding 6.68 g of PVP to 200 mL of ethylene glycol in a three-necked round-bottom flask and stirring at 500 rpm using a magnetic stirrer. Then, heating the mixture to 150°C, adding 0.2 g of KBr, 0.3 g of NaCl, and 3.256 g of AgNO3 to the mixture, and stirring at 300 rpm, then maintaining the mixture at 150°C for 4 hours to allow the reaction to occur and silver nanowires to grow before cooling to room temperature. Filtering the silver nanowire solution using a glass filter to remove particles that would reduce transmittance; dispersing the collected silver nanowires in methanol to the desired concentration to obtain the silver nanowire film solution for later use.

[0049] In one specific embodiment, the steps for preparing the nickel nanowire film solution include: first, adding 5.634 g of PVP to 200 mL of ethylene glycol in a three-necked round-bottom flask and stirring at 400 rpm using a magnetic stirrer. Then, heating the mixture to 120 °C, adding 0.4 g of NaOH and 2.63 g of NiSO4·6H2O to the mixture, and stirring at 200 rpm, followed by holding at 120 °C for 15 min to obtain a light yellow-green Ni(OH)2 precursor, then adding 80 wt% hydrazine hydrate dropwise, and stopping the reaction after the mixture gradually becomes clear to allow nickel nanowire growth to occur before cooling to room temperature. Filtering the nickel nanowire solution using a glass filter to remove particles that would reduce transmittance; dispersing the collected nickel nanowires in methanol at the desired concentration to obtain a nickel nanowire film solution for later use.

[0050] Since the process of preparing metal nanowires from polyols is a relatively mature technology, it will not be described in detail here.

[0051] Vertical graphene is a thin-film composite material with a layered microstructure, specifically comprising graphene containing carbon nanosheets vertically grown on a deposition substrate and several graphene base layers, as well as chemically active atomic defect sites and edges. Due to its excellent electrical and thermal conductivity, chemical stability, and large specific surface area, vertical graphene has been successfully applied in various niche applications closely related to its unique morphology. Various growth processes have been developed to achieve faster and safer large-scale production of vertical graphene for different applications. With the increasing maturity of growth processes, vertical graphene has also been successfully applied in fields including field emission, supercapacitors, fuel cells, batteries, gas sensors, biochemical sensors, electrochemical analysis, strain sensors, wearable electronic devices, light trapping, and terahertz emission.

[0052] In this application, growing vertically aligned graphene on a metal nanowire network increases the chemical stability and specific surface area of ​​the electrode. Further, step S4 specifically includes: A leaf vein network template with graphene and metal nanowire networks was placed on the cathode plate in a quartz tube within a microwave plasma chemical vapor deposition system. Hydrogen gas was then introduced at a flow rate of 110 sccm, and a microwave power of 550 W was applied to generate plasma. A DC bias was applied between the anode and cathode plates, and then methane was introduced at a flow rate of 10 sccm. The chamber pressure was maintained at 230 Pa, and the DC bias was increased to -200 V to grow vertical graphene. After 20-30 minutes of growth, the hydrogen and methane were stopped, and the mixture was cooled to room temperature in a vacuum to obtain a hybrid electrode.

[0053] The leaf vein network template has a relatively large area. This application uses high cavity pressure and bias voltage to ensure that the vertically grown graphene on the metal nanowire network has a good morphology. The mechanism of vertical growth is due to the sheath electric field between the plasma and the substrate. This built-in sheath electric field polarizes the graphene nucleation centers and has a dipole force in the graphene growth direction. The field direction is perpendicular to the substrate. Therefore, by applying a DC bias voltage during the growth process, the graphene can be grown vertically. Applying a DC bias voltage can enhance the plasma energy. The microstructure of the vertically grown graphene material can be adjusted by changing the growth method and growth process parameters. For example, the sheet density and height can be controlled by changing the growth time and methane concentration.

[0054] This application enhances the continuity and flexibility of leaf vein-inspired electrodes by growing vertical graphene. Due to the layered microstructure of vertical graphene and its excellent conductivity, chemical stability, and large specific surface area, the hybrid vertical graphene electrode provides higher conductivity and can significantly improve the electrochemical performance of stretchable transparent electrodes.

[0055] This application develops a hybrid structure combining graphene, metal nanowire networks, and vertical graphene, which can effectively solve the corrosion problem of metal nanowires. Moreover, this hybrid structure can effectively improve conductivity and light transmittance, which is beneficial for fabricating transparent electrode devices with good performance.

[0056] Furthermore, step S5 specifically includes: The hybrid electrode was immersed in an electrolyte mixture as the working electrode, with an Ag / AgCl electrode as the reference electrode and a Pt wire electrode as the counter electrode. A constant voltage of 0.5V was set, and electroplating was performed for 200-400 seconds using a constant voltage electroplating method to obtain an invisible biomimetic highly conductive transparent electrode coated with conductive hydrogel.

[0057] Furthermore, the electrolyte mixture is composed of a polymer monomer solution and a catalyst. The concentration of the polymer monomer is 0.3M-0.6M, and the mass fraction of the catalyst in the electrolyte mixture is 0.5wt%-1.5wt%. The polymer monomer is electrolyzed to form a polymer. The polymer can be one of PEDOT:PSS, polythiophene, polypyrrole, and polyaniline, and the catalyst can be Ti(ClO4)4. The selected polymer has good flexibility and conductivity. By coating the surface of the mixed electrode with the polymer to form a conductive hydrogel, the tight bonding between the graphene and metal nanowire networks can be ensured, and the graphene and polymer layers can protect the buried metal nanowires from oxidation and corrosion, thereby maintaining the conductivity and light transmittance of the metal nanowires.

[0058] This application provides a method for fabricating a biomimetic highly conductive transparent electrode, offering a strategy for constructing transparent electrodes with high conductivity, transparency, mechanical stability, and gas permeability. The ultra-flexible and lightweight properties of the novel transparent electrode are also crucial for developing low-cost and large-scale commercial applications of flexible optoelectronic devices.

[0059] Reference Figure 4 This application also provides a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices, comprising a hybrid electrode and a conductive hydrogel. The conductive hydrogel 5 is coated on the surface of the hybrid electrode. The hybrid electrode, from bottom to top, comprises a leaf vein network template 1, graphene 2, a metal nanowire network 3, and vertical graphene 4. The conductive hydrogel coats the entire surface of the hybrid electrode, and can be subsequently cut as needed to obtain a transparent electrode device with the conductive hydrogel only on the surface of the vertical graphene layer.

[0060] This application employs a layered structure consisting of a leaf vein network, monolayer graphene, a metal nanowire network, vertical graphene, and a conductive polymer. The strong interfacial interactions between the plant fibers and the conductive units facilitate the orderly construction of a layered, interwoven conductive mesh on a flexible and lightweight texture, while maintaining high transparency and effectively avoiding the trade-off between photoelectric performance. Graphene possesses advantages such as high chemical and thermal stability, high mechanical properties, high optical transparency, and ease of fabrication, providing an effective protective barrier for the metal matrix. Simultaneously, graphene and silver nanowires effectively enhance the conductivity of the leaf vein network structure, while the chemical stability and large specific surface area of ​​the vertical graphene increase the contact area between the electrode and the external environment. The polymer ensures the tight bonding between the graphene and the metal nanowires. This biomimetic approach provides a strategy for constructing transparent electrodes with high conductivity, transparency, mechanical stability, and gas permeability.

[0061] The following specific examples provide further details.

[0062] Example 1 The leaves were selected from tender maple leaves that had grown for 10 days. First, 10g of sodium hydroxide was dissolved in a beaker containing 100ml of distilled water. The leaves were then added and heated rapidly to 100℃ for 3 hours until the leaf mesophyll was mostly removed to obtain the leaf veins. After repeated washing with distilled water, the leaves were dried at 80℃ for 3 hours to obtain the leaf vein network template.

[0063] A leaf vein network template was laid flat on a silicon substrate, and then a copper thin film with a thickness of 150 μm was deposited by magnetron sputtering.

[0064] A leaf vein network template with a sputtered copper film was placed in the quartz tube of the CVD system and maintained at 1 mbar. Hydrogen and methane were introduced at a flow rate of 1 sccm and 15 sccm respectively. The temperature was raised to 1000℃ and the growth was carried out for 15 minutes. After that, the methane was stopped and the graphene was cooled to room temperature in a hydrogen atmosphere to complete the graphene growth.

[0065] After removal, the PMMA solution was spin-coated onto the leaf vein network template containing a copper film and graphene, so that the graphene surface was coated with PMMA solution. After standing at room temperature for 60 minutes, it was immersed in 0.1M ammonium persulfate solution to etch away the copper film. Then it was washed 4 times with deionized water. The separated graphene and leaf vein network template were gently pressed together at room temperature, then immersed in acetone for 12 hours to remove PMMA. Finally, it was immersed in ethanol for 5 minutes to complete the cleaning, and graphene was obtained on the leaf vein network template.

[0066] A silver nanowire film solution with a concentration of 5 mg / mL was spin-coated onto the graphene surface at 1000 rpm for 70 seconds, air-dried, and then placed at a temperature of 100℃ and a pressure of 12 MPa for 15 seconds. After annealing, the solution was cooled to room temperature within 15 minutes to form a silver nanowire network on the graphene surface.

[0067] A leaf vein network template with silver nanowire network and graphene grown on it was placed on the cathode plate in a quartz tube within a microwave plasma chemical vapor deposition system. Hydrogen gas was introduced at a flow rate of 110 sccm, and a microwave power of 550 W was applied to generate plasma. A DC bias voltage was applied between the anode and cathode plates, and then methane was introduced at a flow rate of 10 sccm. The chamber pressure was maintained at 230 Pa, and the DC bias voltage was increased to -200 V to grow vertical graphene. After 20 minutes of growth, the hydrogen gas and methane were stopped, and the mixture was cooled to room temperature in a vacuum to obtain a hybrid electrode.

[0068] The electrolyte mixture was prepared by mixing the monomer solution of EDOT:PSS and Ti(ClO4)4 in a certain proportion and stirring magnetically at 650 rpm for 15 min to obtain a well mixed electrolyte solution containing a monomer solution of 0.6 M EDOT:PSS and a mass fraction of 0.5 wt% Ti(ClO4)4.

[0069] The hybrid electrode is immersed in the electrolyte mixture solution obtained in the above steps as the working electrode, with an Ag / AgCl electrode as the reference electrode and a Pt wire electrode as the counter electrode. A constant voltage of 0.5V is set, and electroplating is performed for 300 seconds by constant voltage electroplating to obtain the invisible biomimetic highly conductive transparent electrode coated with conductive hydrogel as described in Example 1.

[0070] Example 2 The leaves were selected from tender maple leaves that had grown for 10 days. First, 10g of sodium hydroxide was dissolved in a beaker containing 100ml of distilled water. The leaves were then added and heated rapidly to 100℃ for 3 hours until the leaf mesophyll was mostly removed to obtain the leaf veins. After repeated washing with distilled water, the leaves were dried at 80℃ for 3 hours to obtain the leaf vein network template.

[0071] A leaf vein network template was laid flat on a silicon substrate, and then a copper thin film with a thickness of 150 μm was deposited by magnetron sputtering.

[0072] A leaf vein network template with a sputtered copper film was placed in the quartz tube of the CVD system and maintained at 1 mbar. Hydrogen and methane were introduced at a flow rate of 1 sccm and 15 sccm respectively. The temperature was raised to 1000℃ and the growth was carried out for 15 minutes. After that, the methane was stopped and the graphene was cooled to room temperature in a hydrogen atmosphere to complete the graphene growth.

[0073] After removal, the PMMA solution was spin-coated onto the leaf vein network template containing a copper film and graphene, so that the graphene surface was coated with PMMA solution. After standing at room temperature for 60 minutes, it was immersed in 0.1M ammonium persulfate solution to etch away the copper film. Then it was washed 4 times with deionized water. The separated graphene and leaf vein network template were gently pressed together at room temperature, then immersed in acetone for 12 hours to remove PMMA. Finally, it was immersed in ethanol for 5 minutes to complete the cleaning, and graphene was obtained on the leaf vein network template.

[0074] A nickel nanowire film solution with a concentration of 6 mg / mL was spin-coated onto the graphene surface at 1000 rpm for 80 seconds, air-dried, and then placed at a temperature of 100℃ and a pressure of 12 MPa for 15 seconds. After annealing, the solution was cooled to room temperature within 20 minutes to form a silver nanowire network on the graphene surface.

[0075] A leaf vein network template with nickel nanowire network and graphene grown on it was placed on the cathode plate in a quartz tube within a microwave plasma chemical vapor deposition system. Hydrogen gas was introduced at a flow rate of 110 sccm, and a microwave power of 550 W was applied to generate plasma. A DC bias was applied between the anode and cathode plates, and then methane was introduced at a flow rate of 10 sccm. The chamber pressure was maintained at 230 Pa, and the DC bias was increased to -200 V to grow vertical graphene. After 20 minutes of growth, the hydrogen and methane were stopped, and the mixture was cooled to room temperature in a vacuum to obtain a hybrid electrode.

[0076] The electrolyte mixture was prepared by mixing pyrrole monomer (Py) solution and Ti(ClO4)4 in a certain proportion and stirring magnetically at 650 rpm for 15 min to obtain a well mixed electrolyte solution containing 0.3 M pyrrole monomer (Py) solution and 1.5 wt% Ti(ClO4)4.

[0077] The hybrid electrode is immersed in the electrolyte mixture solution obtained in the above steps as the working electrode, with an Ag / AgCl electrode as the reference electrode and a Pt wire electrode as the counter electrode. A constant voltage of 0.5V is set, and electroplating is performed for 300 seconds by constant voltage electroplating to obtain the invisible biomimetic highly conductive transparent electrode coated with conductive hydrogel as described in Example 2.

[0078] This application provides a method for fabricating a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices. By employing a layered structure consisting of a leaf vein network, monolayer graphene, a metal nanowire network, vertical graphene, and a conductive polymer, the strong interfacial interaction between plant fibers and conductive units facilitates the orderly construction of a layered, interwoven conductive mesh on a flexible and lightweight texture, while maintaining high transparency and effectively avoiding trade-offs between optoelectronic performance. Graphene possesses advantages such as high chemical and thermal stability, high mechanical properties, high optical transparency, and ease of fabrication, providing an effective protective barrier for the metal matrix. Simultaneously, graphene and silver nanowires effectively enhance the conductivity of the leaf vein network structure, while the chemical stability and large specific surface area of ​​vertical graphene increase the contact area between the electrode and the external environment. The polymer ensures the tight bonding between graphene and metal nanowires. This biomimetic method provides a strategy for constructing transparent electrodes with high electrical conductivity, transparency, mechanical stability, and gas permeability.

[0079] The resulting invisible biomimetic high-conductivity transparent electrode for optoelectronic devices proposes a layered polymer-coated transparent conductive mesh electrode of graphene / metal nanowire interwoven leaf vein fibers through a biomimetic method. This effectively solves the problems of fragility, poor flexibility, and low conductivity of transparent electrodes, and has high conductivity and stability, showing great potential in high-performance wearable optoelectronics and camouflage electronics.

[0080] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for fabricating a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices, characterized in that, Includes the following steps: The leaf blades were processed into leaf vein network templates; Graphene is grown on the surface of the leaf vein network template; A network of metal nanowires is formed on the surface of the graphene. Vertical graphene is grown on the surface of the metal nanowire network to obtain a hybrid electrode; Using the hybrid electrode as one electrode, constant voltage electroplating is performed, and the hybrid electrode is coated with conductive hydrogel to obtain the invisible biomimetic highly conductive transparent electrode for optoelectronic devices. The step of processing the leaf blade into a leaf vein network template includes: Dissolve 8-15g of sodium hydroxide in a container containing 80-100ml of distilled water, add the leaves, heat rapidly to 100℃ and continue for 3-4 hours until the leaf mesophyll is removed to obtain the leaf veins, wash and dry at 60-80℃ for 3-5 hours to obtain the leaf vein network template. The step of growing graphene on the surface of the leaf vein network template includes: A thin copper film is sputtered onto the leaf vein network template; The leaf vein network template sputtered with a copper film was placed in the quartz tube of the CVD system and kept at 1 mbar. Hydrogen and methane were introduced at a flow rate of 1-3 sccm and 15-20 sccm respectively. The temperature was raised to 950-1050℃ and the growth was carried out for 10-30 minutes. Then the methane was stopped and the graphene was cooled to room temperature in a hydrogen atmosphere to complete the graphene growth. Remove the leaf vein network template containing a copper film and graphene on its surface, spin-coat the PMMA solution onto the leaf vein network template containing a copper film and graphene on its surface, and let it stand at room temperature for 30-60 minutes. The leaf vein network template is immersed in a 0.1M-0.3M ammonium persulfate solution to remove the copper film, and then washed with deionized water 4-6 times. The separated graphene and leaf vein network template are gently bonded together at room temperature, then immersed in acetone and left to stand for 11-13 hours to remove the PMMA solution, and then immersed in ethanol for 5-8 minutes to complete the cleaning.

2. The method for preparing the invisible biomimetic highly conductive transparent electrode for optoelectronic devices according to claim 1, characterized in that, The metal nanowires in the metal nanowire network are one of silver nanowires, silver nanosheets, gold nanowires, and nickel nanowires.

3. The method for preparing the invisible biomimetic highly conductive transparent electrode for optoelectronic devices according to claim 2, characterized in that, The step of forming a metal nanowire network on the graphene surface includes: A metal nanowire film solution with a concentration of 5-8 mg / mL was spin-coated onto the graphene surface at 1000 rpm for 70-90 seconds, air-dried, and then placed at a temperature of 100℃ and a pressure of 12 MPa for 15 seconds. Finally, it was cooled to room temperature within 15-25 minutes to complete the annealing process.

4. The method for preparing the invisible biomimetic highly conductive transparent electrode for optoelectronic devices according to claim 3, characterized in that, The steps for preparing the metal nanowire film solution include: A metal salt is added to ethylene glycol and stirred at 400-600 rpm using a magnetic stirrer to obtain a nanowire solution. The nanowire solution is then filtered using a glass filter, and the collected nanowires are redispersed in methanol to obtain the metal nanowire film solution.

5. The method for preparing a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices according to claim 1, characterized in that, The step of growing vertical graphene on the surface of the metal nanowire network includes: The leaf vein network template, on which the metal nanowire network and the graphene are grown, is placed on the cathode plate in a quartz tube within a microwave plasma chemical vapor deposition system. Hydrogen gas is introduced at a flow rate of 110 sccm, and a microwave power of 550 W is applied to generate plasma. A DC bias is applied between the anode and the cathode plate, and then methane is introduced at a flow rate of 10 sccm. The chamber pressure is maintained at 230 Pa, and the DC bias is increased to -200 V to grow vertical graphene. After growth for 20-30 minutes, the introduction of hydrogen gas and methane is stopped, and the mixture is cooled to room temperature in a vacuum to obtain the hybrid electrode.

6. The method for preparing a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices according to claim 1, characterized in that, The step of performing constant voltage electroplating using the hybrid electrode as one electrode, and coating the hybrid electrode with conductive hydrogel, includes: The hybrid electrode is immersed in an electrolyte mixture as the working electrode, with an Ag / AgCl electrode as the reference electrode and a Pt wire electrode as the counter electrode. A constant voltage of 0.5V is set, and electroplating is performed for 200-400 seconds using a constant voltage electroplating method to obtain the invisible biomimetic highly conductive transparent electrode coated with conductive hydrogel.

7. The method for preparing a stealthy, biomimetic, highly conductive transparent electrode for optoelectronic devices according to claim 6, characterized in that, The electrolyte mixture is composed of a polymer monomer solution and a catalyst; the concentration of the polymer monomer solution in the electrolyte mixture is 0.3M-0.6M, and the mass fraction of the catalyst in the electrolyte mixture is 0.5wt%-1.5wt%. The polymer is one of PEDOT:PSS, polythiophene, polypyrrole, and polyaniline; the catalyst is Ti(ClO4)4.

8. A stealth biomimetic highly conductive transparent electrode for optoelectronic devices, characterized in that, The method described in any one of claims 1-7 for preparing a stealthy biomimetic highly conductive transparent electrode for optoelectronic devices comprises a hybrid electrode and a conductive hydrogel. The hybrid electrode comprises, from bottom to top, a leaf vein network template, graphene, a metal nanowire network, and vertical graphene. The conductive hydrogel coats the surface of the hybrid electrode.

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