A silver nanowire transparent composite conductive film with high antioxidant property and a preparation method thereof

Abstract

The present invention belongs to the field of conductive films, and discloses a highly antioxidant silver nanowire transparent composite conductive film and a preparation method thereof. The transparent composite conductive film is sequentially provided with an ultraviolet-resistant layer and a hydrophobic protective layer on both sides of a conductive film containing silver nanowires; the conductive film containing silver nanowires is an AgNWs / PEDOT:PSS conductive film obtained by forming a film from a mixed solution of silver nanowires AgNWs and modified PEDOT:PSS; the ultraviolet-resistant layer is a nano-ZnO / PI layer obtained by forming a film from a mixed solution of nano-ZnO and polyimide PI; the hydrophobic protective layer is an OTS layer formed by immersing the conductive film with the ultraviolet-resistant layer formed thereon in octadecyltrichlorosilane OTS. The transparent composite conductive film of the present invention significantly improves its antioxidant performance while maintaining a high light transmittance, and exhibits good mechanical flexibility and conductive ability, and has broad application prospects in the fields of electronic devices and transparent electrodes.

Description

Technical Field

[0001] The present invention belongs to the field of conductive films, and particularly relates to a silver nanowire transparent composite conductive film with high antioxidant property and a preparation method thereof. Background Art

[0002] Silver nanowires (AgNWs) have been widely used in the fields of transparent conductive films (TCFs), touchscreens, solar cells, flexible displays, etc. due to their excellent electrical conductivity, transparency, mechanical flexibility, and chemical stability. Although AgNWs have extremely high electrical conductivity, their electrical conductivity in thin films is often limited by factors such as high contact resistance between nanowires, uneven dispersion, and air oxidation. In addition, silver nanowires are prone to oxidation reactions in a humid and hot environment, resulting in the destruction of the conductive network structure and a decrease in light transmittance, seriously affecting the long-term stability of devices. Currently, common improvement methods include: introducing other conductive materials to reduce the percolation network of junctions between nanowires, thereby reducing the high resistance of junctions between nanowires in AgNWs transparent conductive films; and at the same time developing protection technologies such as surface coating and alloying treatment to inhibit their oxidation degradation process. In recent years, a lot of work has been done on improving the electrical conductivity and antioxidant property of AgNWs transparent conductive films.

[0003] A preparation method of an AgNWs conductive film and an additive thereof disclosed in Patent CN110289125B prepare a flexible transparent conductive film through an inkjet printing technique, solving the problem that it is difficult to achieve large-scale production of flexible transparent conductive films, and discloses a ratio of an additive to ensure the optical properties, electrical properties, and mechanical stability of the conductive film with specific proportions and raw materials. However, the additive contains a polymer block polymer with multiple pigment anchoring groups and a surfactant, which affects the electrical conductivity of the film, resulting in low electrical conductivity of the film, and the film prepared by this patent has not been subjected to antioxidant treatment, and AgNWs are prone to cause signal instability during long-term use.

[0004] An AgNWs conductive film and a preparation method thereof disclosed in Patent CN110689995B use a soluble linear polymer PI layer instead of the existing insoluble three-dimensional polymer material protective layer by coating, which can not only well protect AgNWs, but also enable AgNWs to overlap with silver paste, ensuring the electrical conductivity and reliability of the AgNWs conductive film, and solving the technical problem that the organic polymer protective layer of the existing AgNWs conductive film cannot take into account the electrical conductivity of overlapping with silver paste and water and oxygen barrier. The prepared film does not solve the problem of oxidation of the upper and lower surfaces of the film in the air, and only by the method of coating different layers, the upper and lower surfaces of the prepared film use different materials, resulting in poor electrical stability and consistency of the film.

[0005] Patent CN119092180A discloses an anti-ultraviolet ozone-treated AgNWs composite transparent electrode and its preparation method. By electro-depositing an aluminum-doped zinc oxide (AZO) protective layer on AgNWs and then coating a layer of tin dioxide nanocrystals (SnO2), an anti-ultraviolet ozone-treated AgNWs composite transparent electrode is obtained after heat treatment, significantly improving the antioxidant ability and mechanical stability of the AgNWs transparent conductive film. However, this prepared film does not solve the problems of random packing arrangement and free dispersion of AgNWs.

[0006] The paper "A highly conductive and smooth AgNW / PEDOT:PSS film treated by hot-pressing as electrode for organic light emitting diode" (Wei B, Wu X, Lian L, et al. Organic Electronics, 2017, 43: 182-188.) develops a highly conductive, smooth and transparent electrode by coating poly(3,4-ethylenedioxythiophene):p-toluenesulfonate (PEDOT:PSS) on AgNWs and then performing hot-pressing treatment. The obtained hot-pressed AgNW / PEDOT:PSS film exhibits excellent properties, with a low sheet resistance of 12 Ω / sq, a transmittance of 83% at 550 nm and a smooth surface. The melting of AgNWs promoted by the mechanical hot-pressing process improves the conductivity and smoothness of the film. Although sintering of the AgNWs connection points by hot-pressing treatment enhances the stability of the AgNWs lap joints, the problem of random distribution of AgNWs is not solved, resulting in a lack of effective electrical connection in the blank area between the lines and no antioxidant treatment of the film.

[0007] The paper "A robust and flexible silver nanowire / silica sol / poly(3,4-ethylene dioxythiophene) / poly(styrene sulfonate) transparent conductive film for film heater" (Zhang X Y, Shan J Q, Bai S C, Guo X Z, et al. Thin Solid Films, 2022, 749: 139178.) prepared a robust, flexible and transparent AgNWs / silica sol / PEDOT:PSS composite film by spraying AgNWs ink, silica sol and PEDOT:PSS onto the surface of a polyethylene terephthalate substrate in sequence. The capillary effect caused the silica sol nanoparticles to be absorbed by AgNWs, effectively improving the connection between AgNWs. PEDOT:PSS covered the surface of the AgNWs / silica sol layer to increase the network conduction path and protect the AgNWs / silica sol layer. Due to the hygroscopicity of PEDOT:PSS, its electrical stability and consistency deteriorated during long-term use. The hygroscopicity caused the film to swell, thereby affecting the performance of the AgNWs / silica sol layer.

[0008] The paper "Solution processed transparent conductive hybrid thin films based on silver nanowires, zinc oxide and graphene" (Arat R, Jia G, Dellith J, et al. Materials Today Communications, 2021, 26: 102162.) deposited AgNWs and nano-ZnO by spin coating with fixed parameters, while the deposition of graphene was completed through a double self-assembly (DSA) process. The article showed that the spin-coated ZnO particles were located on the top or bottom of the AgNWs network, improving the conductivity of the hybrid film without causing a loss in transmittance. The article used nano-ZnO to improve the conductivity of AgNWs, ignoring its anti-ultraviolet function, and improved the conductivity of AgNWs by coating without modifying the AgNWs film, so its mechanical properties could not be guaranteed.

[0009] The paper "One-step fabrication of highly stable, durable, adhesion-enhanced, flexible, transparent conducting films based on silver nanowires and neutralized PEDOT:PSS" (Subramani D, Aruna K M, Du-hyun W, et al. Materials Advances. 2023, 4(7): 1769-1776.) prepared a flexible and bendable transparent conductive electrode with good mechanical stability and excellent optoelectronic properties by mixing a mixture of AgNWs and neutralized PEDOT:PSS through a simple one-step roll coating method. The article used imidazole to neutralize commercial PEDOT:PSS to reduce conductivity loss. Hydroxypropyl methylcellulose was used as a binder to improve the dispersion of the mixture and enhance its adhesion to the substrate. In addition, polysiloxane was used as a surface protection layer for the AgNWs-neutralized PEDOT:PSS transparent conductive film to improve its stability against oxidation and corrosion. Although the article enhanced the conductivity, mechanical properties, and stability of the AgNWs conductive film, adding too many non-conductive polymer materials to the sensor reduced its conductivity, and the film had poor resistance to ultraviolet oxidation.

[0010] In summary, although researchers are committed to improving the conductivity and antioxidant properties of AgNWs transparent conductive films, the following problems still exist in AgNWs transparent conductive films:

[0011] 1. During the use of AgNWs with rough surfaces, due to their random packing or cross arrangement, problems such as poor contact between nanowires and inter-wire gaps are likely to occur, leading to current jumps and discontinuities, which reduces the charge transport efficiency. In addition, the deposition of AgNWs usually does not form a perfect plane but a conductive network, resulting in the lack of effective AgNWs connections in some areas. These areas not covered by AgNWs will form non-conductive blank areas, further affecting charge transport.

[0012] 2. Uniformly dispersing AgNWs in a solution to form a conductive network can improve the conductivity and light transmittance of the prepared flexible transparent conductive film. During the uniform dispersion process, irreversible agglomeration is likely to occur due to reasons such as mutual attraction between particles and van der Waals forces between molecules. Utilizing the strong mechanical shear force generated by the high-frequency oscillation of ultrasonic waves can help AgNWs disperse uniformly in water, but long-term ultrasonic treatment is likely to cause AgNWs to break, fragment, and surface oxidation.

[0013] 3. In the overlapping area, due to the lack of sufficient physical connection force or chemical bonding force, the overlapping part of the structure is loose. The loose contact area not only affects the conductivity but may also cause loosening or fracture in these areas during long-term use, resulting in unstable electrical properties.

[0014] 4. AgNWs have a strong absorption of ultraviolet light in the ultraviolet band, especially at the 380 nm band. Under photon irradiation, the surface plasmon effect is generated on the silver surface, enhancing the local electric field of silver, which promotes the transition of electrons on the silver surface. The excited silver atoms or electrons react with oxygen (O2) molecules to generate silver ions (Ag + ), or silver oxide (Ag2O). The oxide adheres to the surface of the silver wire, resulting in a decrease in the electrical contact performance of the silver wire, causing embrittlement and fracture of the silver wire, and reducing the conductivity and stability of the transparent conductive film.

[0015] 5. PI has a certain hydrophilicity, resulting in insufficient waterproof performance. And AgNWs are unstable under oxygen-containing water conditions. The heterogeneous oxidation on the silver surface leads to the oxidation and dissolution of nano-silver and the release of Ag + , and silver ions can react with hydroxide ions (OH - ) in water to form silver hydroxide (AgOH). Under further oxidation conditions, silver hydroxide may be converted into silver oxide (Ag2O), increasing the resistance of AgNWs and reducing their conductivity and light transmittance. Summary of the Invention

[0016] Aiming at the problems existing in the existing AgNWs transparent conductive film, the present invention designs a highly antioxidant silver nanowire transparent composite conductive film, aiming to improve the problems of unstable conductivity and poor conductivity caused by the oxidation, loose overlapping, and dispersion of the existing AgNWs transparent conductive film.

[0017] To solve the above problems, the present invention adopts the following technical solutions:

[0018] The present invention first provides a highly antioxidant silver nanowire transparent composite conductive film, which is characterized in that: the transparent composite conductive film is sequentially provided with an anti-ultraviolet layer and a hydrophobic protective layer on both sides of the conductive film containing silver nanowires;

[0019] The conductive film containing silver nanowires is an AgNWs / PEDOT:PSS conductive film obtained by forming a film from a mixed solution of silver nanowires AgNWs and modified PEDOT:PSS;

[0020] The anti-ultraviolet layer is a nano-ZnO / PI layer obtained by forming a film from a mixed solution of nano-ZnO and polyimide PI;

[0021] The hydrophobic protective layer is an OTS layer formed by immersing a conductive thin film with an ultraviolet-resistant layer in octadecyltrichlorosilane (OTS).

[0022] The present invention also provides a method for preparing the highly antioxidant silver nanowire transparent composite conductive thin film, comprising the following steps:

[0023] Step 1: Fabricate the nano-ZnO / PI layer

[0024] Add 0.01 g of silane coupling agent and 0.1 - 0.3 g of ZnO nanoparticles into 10 - 20 mL of a mixed solution with a volume ratio of ethanol to water of 9:1, stir at 50 - 60 °C until evenly dispersed to obtain a nano-ZnO solution;

[0025] Add 1.7 - 1.9 g of PI powder into 20 - 30 mL of N,N-dimethylformamide (DMF), stir at 60 - 80 °C until dissolved, then add the nano-ZnO solution and ultrasonicate until evenly dispersed to obtain a nano-ZnO / PI mixed solution;

[0026] Spin-coat the nano-ZnO / PI mixed solution on the surface of a glass substrate treated with oxygen plasma, and then dry it in an oxygen-free environment at 60 - 100 °C for 2 - 4 hours to form a nano-ZnO / PI layer on the glass substrate surface.

[0027] Step 2: Prepare the AgNWs / PEDOT:PSS conductive thin film

[0028] Add 5 g of AgNWs into 10 - 20 mL of a solution containing 0.1 - 1 wt% of sodium dodecyl sulfate (SDS) at room temperature, stir for 30 - 60 minutes, ultrasonicate at 50 - 100 W for 20 - 30 minutes, then centrifuge at 3000 - 5000 rpm for 10 - 20 minutes to remove the supernatant, wash with absolute ethanol 3 - 5 times to remove excess SDS, and then disperse the product in 15 - 25 mL of absolute ethanol to obtain an AgNWs dispersion;

[0029] Add 0.04 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid and 0.6 - 1.5 g of poly(butyl acrylate) (PBA) into 20 - 30 g of a 1.5% PEDOT:PSS solution, stir magnetically for 30 - 60 minutes to obtain a modified PEDOT:PSS solution;

[0030] Add the AgNWs dispersion into the modified PEDOT:PSS solution, with a mass ratio of AgNWs dispersion to modified PEDOT:PSS solution of 1:2 - 4, stir magnetically at 60 - 80 °C until completely dispersed to obtain an AgNWs / PEDOT:PSS conductive paste;

[0031] Coat the AgNWs / PEDOT:PSS conductive paste on the glass substrate formed with the nano-ZnO / PI layer, then insert two electrodes into the paste, apply a voltage of 5 - 30 V for deposition for 10 - 30 minutes; after the deposition is completed, clean the surface with absolute ethanol, then anneal in an oven at 100 - 150 °C for 10 - 30 minutes, and then use a hot press to hot press and sinter at 0.5 - 1.5 Mpa and 100 - 120 °C for 0.5 - 1 h, that is, form an AgNWs / PEDOT:PSS conductive film on the nano-ZnO / PI layer; the light transmittance of the prepared AgNWs / PEDOT:PSS conductive film is not less than 85%, and the thickness is 0.05 - 0.1 mm.

[0032] Step 3. Fabricate the nano-ZnO / PI layer again

[0033] Spin-coat the nano-ZnO / PI mixture in Step 1 on the surface of the AgNWs / PEDOT:PSS conductive film, and then dry it in an oxygen-free environment at 60 - 100 °C for 2 - 4 hours to form a nano-ZnO / PI layer on the AgNWs / PEDOT:PSS conductive film;

[0034] Step 4. Fabricate the OTS layer

[0035] Immerse the sample in OTS for 10 - 15 min; after the immersion is completed, take out the sample and thoroughly clean the surface with deionized water to remove the unreacted OTS, and then put it into the oven to dry thoroughly, thus obtaining a highly antioxidant silver nanowire transparent composite conductive film.

[0036] Furthermore, in Step 1 and Step 3, the spin-coating speed of the nano-ZnO / PI mixture is 3000 - 5000 rpm, the spin-coating time is 1 - 2 min, the thickness of the obtained nano-ZnO / PI layer is 5 - 30 μm, the visible light transmittance is not less than 85%, and it can effectively absorb ultraviolet light.

[0037] In the above preparation method of the present invention: by adding an ionic liquid to the AgNWs dispersion to enhance the conductivity of the PEDOT:PSS solution, a carrier migration path with high conductivity is provided for the poor contact between AgNWs and the lack of AgNWs parts, effectively improving the conductivity and conductive stability of the AgNWs transparent conductive film. And, because AgNWs are treated with SDS in advance, AgNWs are more easily uniformly dispersed, and the problem of uneven dispersion of AgNWs is effectively solved by combining with ultrasonic technology. The post-treatment of the AgNWs / PEDOT:PSS conductive film is carried out by hot pressing, solving the problem that the lap joint area of AgNWs is prone to looseness and fracture during long-term use. The antioxidant property of the AgNWs / PEDOT:PSS conductive film is improved by coating the nano-ZnO / PI layer and the OTS layer.

[0038] Compared with the prior art, the highly antioxidant silver nanowire transparent composite conductive film of the present invention has excellent antioxidant properties while maintaining high light transmittance, and exhibits good mechanical flexibility and conductivity, showing broad application prospects in the fields of electronic devices and transparent electrodes. Specifically, the beneficial effects of the present invention are as follows:

[0039] 1. The AgNWs / PEDOT:PSS conductive film of the present invention is prepared by mixing a modified PEDOT:PSS solution with an AgNWs dispersion. PEDOT:PSS can penetrate into the grids and gaps of AgNWs, forming a good ohmic contact with AgNWs, providing a conductive channel for electron transport between AgNWs, thereby reducing the resistance. When PEDOT:PSS wraps around the network nodes of AgNWs, it can significantly reduce the node spacing, further promoting electron transport. PEDOT:PSS has good adhesion, which can composite AgNWs to improve conductivity while effectively and synergistically solving problems such as the easy shedding of AgNWs on flexible substrates and the easy oxidation when exposed to air. Using ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate and PBA to modify PEDOT:PSS, the ionic liquid acts as an efficient conductivity enhancer and plasticizer, which can promote the formation of ordered crystals and conductive networks in a larger range, trigger the gelation of PEDOT:PSS by increasing its viscosity, thereby improving the mechanical properties. Strong counterion exchange leads to the formation of a highly ordered nanofiber structure of PEDOT chains, which is based on a more expanded conformation and a shorter π-π stacking distance, further improving the conductivity. The flexible chain segments of PBA are complementary to the rigid structure of PEDOT:PSS, enhancing the mechanical flexibility of the film and the adhesion to the substrate (nano-ZnO / PI layer).

[0040] 2. For the silver nanowire transparent composite conductive film proposed by the present invention, by combining the use of SDS as a surfactant with ultrasonic dispersion technology, the dispersion of AgNWs in the solution is effectively improved. The sulfate group of SDS is negatively charged, causing the surface of AgNWs to carry negative charges. Due to the same-charge interaction between AgNWs, they repel each other, thus preventing the aggregation of AgNWs. The imidazolium ionic liquid not only has a good plasticizing effect on the AgNWs flexible transparent conductive film, improving its conductivity, but also can modify AgNWs to improve its dispersion and compatibility in the solution. In addition, short-time ultrasonic dispersion causes cavitation effects, destroying the aggregated structure of AgNWs and further promoting the dispersion of AgNWs. The uniform dispersion of AgNWs can significantly reduce the defects in the PEDOT:PSS system, thereby improving the conductivity and mechanical properties.

[0041] 3. The silver nanowire transparent composite conductive film proposed by the present invention is post-treated by using a hot pressing method. The hot pressing promotes the sintering of AgNWs at the contact points, reduces the contact resistance, and enhances the conductance path between the nanowires. The pressure helps to promote the close contact between the nanowires, reduces the resistance and critical temperature at the nanowire contact points, and can effectively improve the conductivity at a lower temperature, thereby avoiding the problem of structural deformation at high temperatures, maintaining the structural stability, and enhancing the overall conductivity of the film.

[0042] 4. The silver nanowire transparent composite conductive film proposed by the present invention enhances the antioxidant property and stability by coating a nano-ZnO / PI mixed solution on the surface of the AgNWs / PEDOT:PSS conductive film. PI has excellent radiation resistance, hydrolysis stability, corrosion resistance, as well as excellent atomic oxygen resistance and light transmittance, and can maintain good stability even in harsh environments; the bandgap value of nano-ZnO is about 3.36 eV, corresponding to an absorption wavelength of about 369 nm, which enables nano-ZnO to absorb ultraviolet radiation and be transparent in the visible light band. In addition, nano-ZnO has antioxidant property and can effectively prevent the direct contact between oxygen and moisture and the surface of PEDOT:PSS to reduce the oxidation reaction. This organic-inorganic composite layer can not only prevent the intrusion of oxides, but also improve the surface hydrophobicity of the conductive film and reduce the influence of moisture on the film performance.

[0043] 5. The silver nanowire transparent composite conductive film proposed by the present invention immerses the AgNWs / PEDOT:PSS conductive film formed with a nano-ZnO / PI layer into OTS. After the solvent evaporates, the alkylsilane molecules form covalent bonds with the surface of nano-ZnO through their silyl groups, and form a chemically bonded hydrophobic alkylsilane transparent film on the material surface, changing the surface hydrophilicity, reducing the adsorption and penetration of moisture, thereby effectively protecting the material from the influence of moisture and further enhancing the antioxidant performance of the film. Description of the Drawings

[0044] Figure 1 are the effect diagrams before and after doping PEDOT:PSS with AgNWs and hot pressing, where: Figure 1 a in corresponds to the individual AgNWs, Figure 1 b in corresponds to AgNWs doped with PEDOT:PSS before hot pressing, Figure 1 c in corresponds to AgNWs doped with PEDOT:PSS after hot pressing.

[0045] Figure 2 is a schematic diagram of PEDOT:PSS penetrating into the grids and gaps of AgNWs.

[0046] Figure 3It is a graph showing the relationship between the mass concentration of the doped ionic liquid and the conductivity of PEDOT:PSS.

[0047] Figure 4 It is a graph showing the relationship between the elongation at break and the tensile strength of PEDOT:PSS modified by different methods after film formation.

[0048] Figure 5 It is a network structure diagram of PI doped with nano-ZnO.

[0049] Figure 6 It is a light transmittance graph of pure PI film, PI film doped with 5 wt% nano-ZnO, and the overall composite conductive thin film obtained in Example 1.

[0050] Figure 7 It is a graph showing the change in the contact angle of water droplets dropped on the surface of the nano-ZnO / PI film after soaking in OTS for different times.

[0051] Figure 8 It is a graph showing the relationship between the tensile strength and the tensile range of the transparent composite conductive thin film obtained in Example 1.

[0052] Figure 9 It is a graph showing the relationship between the mass ratio of AgNWs dispersion liquid and modified PEDOT:PSS solution and the sheet resistance of the prepared transparent composite conductive thin film. Detailed implementation manners

[0053] The following further describes the embodiments of the present invention in detail with reference to the accompanying drawings. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation procedures are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] The highly antioxidant silver nanowire transparent composite conductive thin film of this example is prepared according to the following steps:

[0056] Step 1, fabricate the nano-ZnO / PI layer

[0057] Add 0.01 g of silane coupling agent and 0.1 g of ZnO nanoparticles into 15 mL of a mixed solution with a volume ratio of ethanol to water of 9:1, stir at 60 °C until evenly dispersed to obtain a nano-ZnO solution. Add 1.9 g of PI powder into 25 mL of DMF, stir at 60 °C until dissolved, and then add the nano-ZnO solution and ultrasonicate until evenly dispersed to obtain a nano-ZnO / PI mixed solution.

[0058] The nano-ZnO / PI mixed solution was spin-coated on the surface of the glass substrate treated with oxygen plasma at a spin-coating speed of 4000 rpm and a spin-coating time of 1 min, and then dried in an oxygen-free environment at 80 °C for 3 hours to form a nano-ZnO / PI layer with a thickness of about 10 μm on the glass substrate surface.

[0059] Step 2: Prepare the AgNWs / PEDOT:PSS conductive film

[0060] 5 g of AgNWs was added to 15 mL of a solution of sodium dodecyl sulfate (SDS) with a mass concentration of 0.5 wt%, stirred at room temperature for 30 minutes, sonicated at 60 W for 20 minutes, then centrifuged at 3000 rpm for 20 minutes using a centrifuge, the supernatant was removed, washed 3 times with absolute ethanol to remove excess SDS, and then the product was dispersed in 20 mL of absolute ethanol to obtain an AgNWs dispersion.

[0061] 0.04 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid and 0.6 g of polybutyl acrylate (PBA) were added to 20 g of a PEDOT:PSS solution with a mass concentration of 1.5%, magnetically stirred for 60 minutes to obtain a modified PEDOT:PSS solution, 10 g of the above AgNWs dispersion was added, and magnetically stirred at 60 °C until completely dispersed to obtain an AgNWs / PEDOT:PSS conductive paste.

[0062] The AgNWs / PEDOT:PSS conductive paste was coated on the glass substrate with the nano-ZnO / PI layer formed thereon, then two electrodes were inserted into the paste, and a voltage of 20 V was applied for deposition for 30 minutes; after the deposition was completed, the surface was washed with absolute ethanol, then annealed in an oven at 100 °C for 30 minutes, and then hot-pressed and sintered at 1 Mpa and 100 °C for 0.5 h using a hot press, that is, an AgNWs / PEDOT:PSS conductive film with a thickness of 0.1 mm was formed on the nano-ZnO / PI layer. The transmittance of the prepared AgNWs / PEDOT:PSS conductive film was about 91%.

[0063] Step 3: Fabricate the nano-ZnO / PI layer again

[0064] The mixed solution of nano-ZnO / PI in Step 1 was spin-coated on the surface of the AgNWs / PEDOT:PSS conductive film at a spin-coating speed of 4000 rpm and a spin-coating time of 1 min, and then dried in an oxygen-free environment at 80 °C for 4 hours to form a nano-ZnO / PI layer with a thickness of 10 μm on the AgNWs / PEDOT:PSS conductive film.

[0065] Step 4: Fabricate the OTS layer

[0066] The sample was immersed in OTS for 10 minutes. After immersion, the sample was taken out and the surface was thoroughly cleaned with deionized water to remove unreacted OTS molecules and solvents, and then placed in an oven at 60 °C for thorough drying to obtain a highly antioxidant silver nanowire transparent composite conductive film with an overall light transmittance of about 79%.

[0067] Figure 1 Figures of before and after doping PEDOT:PSS into AgNWs and hot pressing. The PEDOT:PSS molecular chains are adsorbed on the surface of AgNWs through van der Waals forces and electrostatic interactions. Under the action of hot pressing, the AgNWs are closely arranged at the intersections, reducing the pores and gaps in the network and increasing the density of the conductive paths. The silver atoms at the contact points are sintered through the contact points, significantly reducing the contact resistance.

[0068] Figure 2 Schematic diagram of PEDOT:PSS penetrating into the grids and gaps of AgNWs. It can be seen that PEDOT:PSS forms a good ohmic contact with AgNWs, providing a conductive channel for electron transport between AgNWs.

[0069] To test the effect of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid on the electrical conductivity of PEDOT:PSS after film formation, 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid with different mass percentages of the PEDOT:PSS solution was added to a PEDOT:PSS solution with a mass concentration of 1.5%, and then spin-coated into a film and the conductivity was measured. The results are as Figure 3 shown. It can be seen that when the mass concentration of the doped ionic liquid is 0.2 wt%, the electrical conductivity of the PEDOT:PSS film is greatly improved.

[0070] To test the effect of doping on the mechanical properties of PEDOT:PSS after film formation, 0.01 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid was added to 20 g of a PEDOT:PSS solution with a mass concentration of 1.5% to obtain a "PEDOT:PSS + 0.05 wt% ionic liquid film", or 0.04 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid was added to obtain a "PEDOT:PSS + 0.2 wt% ionic liquid film", or 0.04 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid and 0.6 g of PBA were added to obtain a "PEDOT:PSS + 0.2 wt% ionic liquid + PBA film", and then the tensile properties of different films were measured. The results are as Figure 4 shown. It can be seen that the pure PEDOT:PSS film without any doping has low tensile strength and elongation at break. Adding ionic liquid and PBA can improve its tensile strength and elongation at break.

[0071] Figure 5It is the network structure diagram of PI doped with nano-ZnO. ZnO nanoparticles are uniformly dispersed in the PI matrix through ultrasonic dispersion and surface modification (such as silane coupling agent), and a continuous network structure is formed between the particles through van der Waals forces and electrostatic interactions.

[0072] Figure 6 The light transmittance of the pure PI film, the PI film doped with 5wt% nano-ZnO, and the overall composite conductive thin film obtained in this example is shown. It can be seen that the cut-off wavelength changes from 357nm of the pure PI film to 386nm of the nano-ZnO / PI film. The ZnO nanocrystals have little effect on the optical transmittance in the visible light range, but enhance the ultraviolet cut-off performance; due to the multi-layer stacking of the overall composite thin film, the visible light transmittance decreases, but it does not affect its ultraviolet shielding ability.

[0073] Figure 7 It is the change of the contact angle of water droplets dropped on the surface of the nano-ZnO / PI film after soaking in OTS for different times. It can be seen that soaking in OTS can increase the contact angle of water droplets on the film surface, and soaking for more than 10 minutes can effectively improve the hydrophobicity of the film.

[0074] Figure 8 It is the relationship diagram between the tensile strength and the tensile range of the overall thin film of the transparent composite conductive thin film obtained in this example. It can be seen that the overall tensile strength of the composite conductive thin film reaches 90MPa and has certain tensile properties, indicating that the overall thin film has good mechanical properties.

[0075] Figure 9 It is the relationship diagram between the mass ratio of the AgNWs dispersion and the modified PEDOT:PSS solution and the sheet resistance of the prepared transparent composite conductive thin film. The density of AgNW has a great influence on the overall conductivity of the film. In this example, when the mass ratio of the AgNWs dispersion and the modified PEDOT:PSS solution is 1:2, the sheet resistance value has been reduced to a small value.

[0076] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A silver nanowire transparent composite conductive film with high antioxidant property, characterized in that: The transparent composite conductive film has an ultraviolet-resistant layer and a hydrophobic protective layer sequentially provided on both sides of the conductive film containing silver nanowires; The conductive film containing silver nanowires is an AgNWs / PEDOT:PSS conductive film obtained by forming a film from a mixed solution of silver nanowires AgNWs and modified PEDOT:PSS; The ultraviolet-resistant layer is a nano-ZnO / PI layer obtained by forming a film from a mixed solution of nano-ZnO and polyimide PI; The hydrophobic protective layer is an OTS layer formed by immersing the conductive film with the ultraviolet-resistant layer in octadecyltrichlorosilane OTS; 2. The preparation method of the highly antioxidant silver nanowire transparent composite conductive film according to claim 1, characterized in that, It includes the following steps: Step 1, fabricate the nano-ZnO / PI layer Add 0.01 g of silane coupling agent and 0.1 - 0.3 g of ZnO nanoparticles into 10 - 20 mL of a mixed solution with a volume ratio of ethanol to water of 9:1, stir at 50 - 60 °C until evenly dispersed to obtain a nano-ZnO solution; Add 1.7 - 1.9 g of PI powder into 20 - 30 mL of N,N-dimethylformamide DMF, stir at 60 - 80 °C until dissolved, then add the nano-ZnO solution and ultrasonically disperse until evenly mixed to obtain a nano-ZnO / PI mixed solution; Spin-coat the nano-ZnO / PI mixed solution on the surface of an oxygen plasma-treated glass substrate, and then dry it in an oxygen-free environment at 60 - 100 °C for 2 - 4 hours to form a nano-ZnO / PI layer on the glass substrate surface; Step 2, prepare the AgNWs / PEDOT:PSS conductive film Add 5 g of AgNWs into 10 - 20 mL of a solution with a mass concentration of 0.1 - 1 wt% of sodium dodecyl sulfate SDS, stir at room temperature for 30 - 60 minutes, ultrasonically treat at 50 - 100 W for 20 - 30 minutes, then centrifuge at 3000 - 5000 rpm for 10 - 20 minutes, remove the supernatant, wash with absolute ethanol 3 - 5 times to remove excess SDS, and then disperse the product in 15 - 25 mL of absolute ethanol to obtain an AgNWs dispersion; Add 0.04 g of 1-hexyl-3-methylimidazolium tetrafluoroborate ionic liquid and 0.6 - 1.5 g of polybutyl acrylate PBA into 20 - 30 g of a PEDOT:PSS solution with a mass concentration of 1.5%, stir magnetically for 30 - 60 minutes to obtain a modified PEDOT:PSS solution; Add the AgNWs dispersion into the modified PEDOT:PSS solution, the mass ratio of the AgNWs dispersion to the modified PEDOT:PSS solution is 1:2 - 4, stir magnetically at 60 - 80 °C until completely dispersed to obtain an AgNWs / PEDOT:PSS conductive paste; Coat the AgNWs / PEDOT:PSS conductive paste on the glass substrate formed with the nano-ZnO / PI layer, then insert two electrodes into the paste, and apply a voltage of 5 - 30 V for deposition for 10 - 30 minutes; after the deposition is completed, clean the surface with absolute ethanol, then anneal in an oven at 100 - 150 °C for 10 - 30 minutes, and then use a hot press to hot press and sinter at 0.5 - 1.5 Mpa and 100 - 120 °C for 0.5 - 1 h, that is, form an AgNWs / PEDOT:PSS conductive thin film on the nano-ZnO / PI layer; Step 3. Fabricate the nano-ZnO / PI layer again Spin-coat the nano-ZnO / PI mixture in Step 1 on the surface of the AgNWs / PEDOT:PSS conductive thin film, and then dry it in an oxygen-free environment at 60 - 100 °C for 2 - 4 hours to form a nano-ZnO / PI layer on the AgNWs / PEDOT:PSS conductive thin film; Step 4. Fabricate the OTS layer Immerse the sample in OTS for 10 - 15 minutes; after the immersion is completed, take out the sample and thoroughly clean the surface with deionized water to remove the unreacted OTS, and then put it into the oven to dry thoroughly, thus obtaining a highly antioxidant silver nanowire transparent composite conductive film.

3. The preparation method according to claim 2, characterized in that, The thickness of the AgNWs / PEDOT:PSS conductive thin film prepared in Step 2 is 0.05 - 0.1 mm.

4. The preparation method according to claim 2, wherein In Steps 1 and 3, the spin-coating speed of the nano-ZnO / PI mixture is 3000 - 5000 rpm, the spin-coating time is 1 - 2 minutes, and the thickness of the obtained nano-ZnO / PI layer is 5 - 30 μm.

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