Preparation Method of Conductive Film Based on PEDOT:PSS and Silver Nanowires

Abstract

The present invention belongs to the field of conductive films, and discloses a preparation method of a conductive film based on PEDOT:PSS and silver nanowires. Specifically, after the surface of silver nanowires AgNWs is hydroxylated, under the action of a silane coupling agent 3-(trimethoxysilyl)propyl methacrylate TMSPMA, it is mixed with PEDOT:PSS to obtain a PEDOT:PSS / AgNWs base solution; after the pH of the base solution is adjusted to near neutral by sodium citrate, it is then mixed with a PEA emulsion and spin-coated into a film, and finally the conductivity is improved by ultrafast laser treatment, thereby obtaining a conductive film based on PEDOT:PSS and silver nanowires. The conductive film provided by the present invention has a high conductivity (>1200 S / cm), good stability and excellent mechanical properties, and is suitable for stable operation in flexible electronic devices and a certain humidity environment.

Description

Technical Field

[0001] The present invention belongs to the field of conductive films, and particularly relates to a method for preparing a conductive film based on PEDOT:PSS and silver nanowires. Background Art

[0002] In recent years, with the rapid development of flexible electronic devices, the demand for high-performance conductive films has been increasing. Although traditional indium tin oxide (ITO) films have excellent electrical conductivity and light transmittance, their high brittleness, high cost and scarcity of indium resources limit their application in flexible devices.

[0003] Therefore, researchers are committed to developing new conductive materials. Among them, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) has become a research hotspot due to its good electrical conductivity, solution coating ability, excellent thermal stability, flexibility and solution processability. However, the electrical conductivity of pure PEDOT:PSS films is still not sufficient to meet the requirements of some high-performance devices. Silver nanowires (AgNWs) are regarded as ideal alternative materials due to their high electrical conductivity, excellent mechanical flexibility and light transmittance. However, problems such as uneven resistance distribution caused by rough surface, easy oxidation and high interfacial contact resistance still need to be solved. Therefore, combining PEDOT:PSS with AgNWs to construct a synergistic conductive network has become an effective strategy to improve the comprehensive performance of the film. When PEDOT:PSS is incorporated into the AgNWs network, PEDOT:PSS forms a continuous conductive path by filling the gaps between silver nanowires, thus significantly improving the overall electrical conductivity of the network. At the same time, the flexibility and tunability of PEDOT:PSS make the film surface more uniform and smooth, effectively reducing the poor contact and interfacial defects between nanowires, and further improving the performance of the film. The combination of this composite material not only endows the silver nanowire network with excellent electrical conductivity characteristics, but also gives it better mechanical stability and surface quality, making it more suitable for the application of various electronic devices. In recent years, much work has been done on the research of transparent conductive films of PEDOT:PSS and AgNWs:

[0004] The academic paper "Zhao Y, Zhang S, Yu T, et al. Ultra-conformal skinelectrodes with synergistically enhanced conductivity for long-time and low-motion artifact epidermal electrophysiology[J]. Nature Communications, 2021,12(1): 4880." proposed that by adding surfactants and ionic compounds, using the synergistic effect of PEDOT molecular packing improvement and underlying graphene charge transfer, a thin, uniform, continuous and conductive PEDOT:PSS layer was prepared on the top layer of graphene. The optimized dry electrode of PEDOT:PSS transferred CVD graphene film (PTG) exhibited a total thickness of ~100 nm, a sheet resistance of ~24 Ω / sq (4142 S / cm), high optical transparency and sufficient skin electro-mechanical electrical stability.

[0005] The academic paper "Chen S, Song L, Tao Z, et al. Neutral-pH PEDOT: PSS as over-coating layer for stable silver nanowire flexible transparent conductivefilms[J]. Organic Electronics, 2014, 15(12): 3654-3659." proposed a multi-step preparation of AgNWs / PEDOT:PSS transparent conductive electrodes using neutralized PEDOT:PSS (guanidine as the neutralizing agent) as an over-coating layer. However, the conductivity of the neutralized PEDOT:PSS was low (about 60% lower than the original), and the resulting AgNWs hybrid film showed poor uniformity and high surface roughness.

[0006] The academic paper "Jin W Y, Ginting R T, Ko K J, et al. Ultra-smooth, fully solution-processed large-area transparent conducting electrodes for organic devices[J]. Scientific reports, 2016, 6(1): 36475." proposed to use a combination of embedded AgNWs metal grid and PEDOT:PSS conductive polymer in a polymer substrate to achieve high transparency (transmittance at 550 nm wavelength ~ 90%), low roughness (root mean square roughness ~ 1 nm), and high flexibility (bending radius ~ 1 mm). However, it did not solve the corrosion of embedded AgNWs caused by the acidity and hygroscopicity of PEDOT:PSS, resulting in poor stability of the fabricated thin film.

[0007] Although some progress has been made in the modification research on the mechanical and electrical properties of PEDOT:PSS / AgNWs flexible thin films, there are still the following deficiencies:

[0008] 1. Since the PSS chains in PEDOT:PSS contain unstable sulfonic acid groups (-SO3H), these groups will undergo dissociation reactions in water, releasing hydrogen ions (H + +), resulting in the PEDOT:PSS solution being acidic. In an acidic environment, silver nanowires are prone to oxidation reactions, generating silver oxides (such as Ag2O), which increases the resistance of silver nanowires and reduces the overall conductivity of the composite thin film.

[0009] 2. In the composite system of PEDOT:PSS and silver nanowires (AgNWs), the binding between the two is poor. As a hydrophilic conductive polymer, the sulfonic acid groups (-SO3 - -) of PEDOT:PSS are difficult to form a stable interface with the inert metal surface of AgNWs, resulting in a reduction in charge transfer efficiency and easy delamination under mechanical stress.

[0010] 3. The conductivity of PEDOT:PSS thin films prepared from the PEDOT:PSS stock solution is usually low, mainly because the presence of the insulating PSS phase restricts the transport of carriers. When PEDOT:PSS is combined with AgNWs, PEDOT:PSS fills the voids in the AgNWs network. However, due to its low conductivity, the transport of carriers in the PEDOT:PSS region is severely restricted, thus affecting the overall conductivity of the composite film. To improve the conductivity of PEDOT:PSS thin films, additives (such as dimethyl sulfoxide DMSO or ethylene glycol EG) are usually added to the stock solution, or the film is post-treated with strong acids (such as sulfuric acid) and ionic solutions. However, these methods may cause certain damage to the stability and adhesion of AgNWs and the stability of the substrate, limiting their application in flexible electronic devices.

[0011] 4. When the PEDOT:PSS material is exposed to air, the sulfonic acid groups (-SO3H) in the PSS groups have strong hydrophilicity and easily form hydrogen bonds with water molecules, making the material have strong water absorption ability. This water absorption will cause PEDOT:PSS to swell and even partially decompose in a humid environment, thus causing device performance degradation and limiting its stability in long-term use. Summary of the Invention

[0012] To solve the above technical problems, the present invention provides a method for preparing a conductive film based on PEDOT:PSS and silver nanowires. The acidity of PEDOT:PSS is neutralized by sodium citrate to promote the dispersion of silver nanowires. By using the silane coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) to bridge AgNWs and PEDOT:PSS, efficient charge transport and interface strengthening are achieved, and ultrafast laser treatment is used to enhance the overall conductivity. At the same time, by adding a PEA network, excessive swelling of PSS due to water absorption and detachment from the substrate are prevented, so that the conductive film can work in a certain humidity environment.

[0013] To solve the above problems, the present invention adopts the following technical solutions:

[0014] A method for preparing a conductive film based on PEDOT:PSS and silver nanowires, characterized in that: after the surface of AgNWs is hydroxylated, under the action of the silane coupling agent TMSPMA, it is mixed with PEDOT:PSS to obtain a PEDOT:PSS / AgNWs base liquid; after the pH of the base liquid is adjusted by sodium citrate, it is mixed with a PEA emulsion and spin-coated into a film, and finally the conductivity is improved by laser treatment to obtain a conductive film based on PEDOT:PSS and silver nanowires. The specific steps are as follows:

[0015] Step 1. Surface hydroxylation treatment of silver nanowires

[0016] Disperse 8 - 10 mg of AgNWs in 10 mL of nitric acid solution with a concentration of 0.01 - 0.03 M, stir at 25 °C for 5 - 8 min to form silver oxide Ag2O on some areas of the AgNWs surface, centrifuge to remove the supernatant, wash with deionized water, then disperse the precipitate in 10 mL of deionized water, and gradually add 0.1 M - 0.2 M sodium hydroxide solution until the pH = 8 - 9, and perform ultrasonic treatment at 45 - 55 °C for 10 - 15 min to promote the hydrolysis of Ag2O to generate surface hydroxyl groups OH - After centrifuging again and removing the supernatant, wash with deionized water to completely remove the residual Ag + Disperse the obtained precipitate in 10 mL of deionized water to obtain a hydroxylated AgNWs dispersion;

[0017] Step 2: Prepare the PEDOT:PSS / AgNWs base liquid

[0018] Dissolve 400 - 450 μL of silane coupling agent TMSPMA in 10 mL of a mixture of ethanol and water with a volume ratio of 8 - 9:1, add acetic acid to adjust the pH to 4.5 - 5.2, and stir to make it hydrolyze fully to generate Si - OH active groups to obtain a coupling agent hydrolysis solution;

[0019] Mix the coupling agent hydrolysis solution with the hydroxylated AgNWs dispersion in Step 1, stir and react at 30 °C - 40 °C for 80 - 100 min under nitrogen protection, then centrifuge to remove the supernatant, wash more than 3 times with a mixed solution of ethanol and water with a volume ratio of 4:1 to completely remove the unreacted silver ions and TMSPMA, and then disperse the precipitate in 3 - 5 mL of deionized water containing 0.05 wt% sodium dodecylbenzenesulfonate SDBS (the introduction of SDBS can prevent electrostatic repulsion during subsequent PEDOT:PSS coating) to obtain a TMSPMA - AgNWs dispersion;

[0020] Pump 2 mL of the TMSPMA - AgNWs dispersion and 10 - 15 mL of a 1 wt% PEDOT:PSS solution into the flow channel through a microfluidic device at a total flow rate of 0.2 mL / min according to the volume ratio for mixing; after mixing, stir in the dark at 25 °C for 40 - 60 min under nitrogen protection to enable the other end of TMSPMA to achieve interfacial binding with PEDOT:PSS through hydrogen bonding to prepare the PEDOT:PSS / AgNWs base liquid;

[0021] Step 3: Adjust the pH and increase the dispersibility of AgNWs

[0022] While stirring, add 0.05 M sodium citrate solution to the PEDOT:PSS / AgNWs base solution prepared in Step 2 to adjust the pH to 6.0 - 6.3, and continue stirring at room temperature for 30 - 60 minutes;

[0023] Step 4: Synthesis of PEA emulsion

[0024] Mix 72 g of ethyl acrylate (EA) and 17.1 - 20 μL of TMSPMA and ultrasonically treat for 5 - 10 min to remove dissolved oxygen. Add the resulting mixture to a round-bottom flask, and then add 0.4 - 0.45 g of sodium dodecyl sulfate (SDS), 0.015 - 0.02 g of ammonium persulfate (APS), and 168 - 200 g of distilled water. Flush the mixture with nitrogen and stir at a speed of 300 rpm for 10 - 15 min, then seal the round-bottom flask with a septum plug. Insert a syringe needle connected to the balloon into the septum plug to balance the additional pressure generated by the exotherm during polymerization. Place the round-bottom flask in an oil bath at 65 - 70 °C and stir in a magnetic stirrer at 300 rpm for 8 - 10 h to obtain the PEA emulsion. Store the prepared PEA emulsion in a plastic tank made of high-density polyethylene at room temperature;

[0025] Step 5: Preparation and post-treatment of the film

[0026] Take 10 mL of the PEDOT:PSS / AgNWs base solution with adjusted pH in Step 3, and add 3.5 - 4 g of the PEA emulsion prepared in Step 4 thereto. After stirring evenly, perform vacuum degassing to obtain a composite solution. Clean the glass substrate with oxygen plasma, and then spin-coat the composite solution on the surface of the substrate and cure it gradiently. Perform ultrafast laser treatment on the substrate with the formed film on the processing table of an ultrafast laser, and then take it out and put it into an oven for curing at 80 - 100 °C to obtain a conductive film based on PEDOT:PSS and silver nanowires.

[0027] Preferably, in Step 5, the gradient curing is completed by drying in ventilation at 25 - 30 °C for 1 - 1.5 h, vacuum drying at 60 - 70 °C for 30 - 50 min, and annealing at 100 - 130 °C for 10 - 20 min.

[0028] Preferably, in Step 5, the parameters of the ultrafast laser treatment are set as follows: laser power 8.5 W - 9.5 W, line scanning speed 950 mm / s - 1150 mm / s, and filling pitch 32 μm - 37 μm. Ultrafast laser treatment shows unique advantages compared with continuous laser in the processing of PEDOT:PSS films. Its ultrashort pulse (10 -15 ~10 -12In (seconds), non-thermal dominant localized processing is achieved through the non-linear absorption effect, significantly suppressing the influence of heat diffusion on materials, thereby avoiding the excessive carbonization of the PSS insulating phase or the degradation of the PEDOT conductive phase caused by heat accumulation in continuous lasers, and maximizing the retention of the conductivity and mechanical flexibility of the thin film. This property enables ultrafast lasers to achieve precise patterning with micron-scale or even sub-micron resolution on the surface of PEDOT:PSS (such as the preparation of electrode microstructures), while avoiding common thermal stress cracks or edge ablation defects in continuous laser processing, and is particularly suitable for local doping regulation of transparent conductive thin films and high-resolution device integration (such as flexible electronics, biosensors).

[0029] The conductive thin film of the present invention is prepared from AgNWs, PEDOT:PSS, sodium citrate, TMSPMA, and polyethyl acrylate PEA. By introducing the silane coupling agent TMSPMA, a stable "silver-silane-PEDOT:PSS" bridging structure is constructed. By adding sodium citrate, the pH of the solution can be adjusted to near neutrality, and a complexation reaction occurs with the silver ions on the surface of the silver nanowires, effectively inhibiting the oxidation of silver ions and the corrosion of the nanowires. Sodium citrate also promotes the uniform dispersion of silver nanowires in the PEDOT:PSS aqueous solution through electrostatic repulsion and steric hindrance effects. In addition, the hydrophobic elastic network of the PEA emulsion further locks the PEDOT:PSS chains, preventing the failure of PEDOT:PSS due to water absorption and swelling. The thin film is treated with an ultrafast laser, which significantly improves the conductivity of the thin film by selectively removing part of the PSS insulating layer and increasing the oxidation degree of PEDOT. The conductive thin film provided by the present invention has a high conductivity (>1200 S / cm), good stability (the conductivity retention rate is >65% in a high-humidity environment), and excellent mechanical properties (the conductivity decreases by <10% when the bending radius <5 mm), and is suitable for the stable operation of flexible electronic devices and in an environment with a certain humidity. The beneficial effects of the present invention are specifically reflected in:

[0030] 1. Introducing sodium citrate into the PEDOT:PSS emulsion can protect AgNWs from corrosion in the water environment through a multi-level cooperative mechanism, and its mechanism of action strictly follows the principles of electrochemistry and surface chemistry: First, sodium citrate acts as a pH buffer to neutralize the inherent acidity (pH 2-3) of PEDOT:PSS, raising the system pH to near neutrality and inhibiting the oxidation reaction of silver by reducing the H + concentration; Second, citrate (C6H5O7 3- ) forms a stable complex ([Ag(C6H5O7)] + ) with the dissolved Ag 2- through the multidentate coordination ability of three carboxyl groups (-COO-) and one hydroxyl group (-OH), and reduces the free Ag +Concentration inhibits the continuous progress of the corrosion reaction; finally, citrate forms a dense and extremely thin molecular layer on the surface of AgNWs through physical adsorption and chemical coordination. The tunneling resistance slightly increases, but the steric hindrance effect of citrate makes the dispersion of AgNWs more uniform, forming a denser conductive network. Moreover, this layer effectively blocks the direct contact of H2O / O2, and at the same time, the negative charge of the carboxyl group repels erosive ions such as Cl - to form a dual physicochemical barrier. This three-level protection mechanism significantly reduces the corrosion current density of silver, providing a theoretical basis and process guarantee for the stability of the AgNWs-PEDOT:PSS composite system in aqueous processing.

[0031] 2. As Figure 1 shown, the silane coupling agent TMSPMA realizes the uniform dispersion and stable composite of AgNWs in the PEDOT:PSS aqueous solution through a two-step cooperative mechanism: First, its inorganic end (trimethoxysilyl group -Si-OCH3) hydrolyzes to generate silanol (-Si-OH), which condenses with the pre-treated hydroxyl group (-OH) on the surface of AgNWs to form a covalent bond (Ag-O-Si), endowing AgNWs with hydrophilicity to inhibit the aggregation caused by van der Waals forces. Subsequently, the organic end (methacryloyloxy group) dynamically cross-links with the sulfonic acid group (-SO3H) in PEDOT:PSS through hydrogen bonds, and at the same time, its hydrophobic chain segment (acrylate) is compatible with the hydrophobic region of PEDOT, thus significantly enhancing the interfacial binding. Finally, the synergistic effect of covalent bonds and hydrogen bonds combined with the steric hindrance effect of the silane chain segment enables AgNWs to form a sterically stable dispersion system in PEDOT:PSS, providing a controllable strategy for the interface engineering of high-performance flexible conductive composites.

[0032] 3. Using ultrafast laser to treat the AgNWs / PEDOT:PSS composite conductive film, the increase in the conductivity of PEDOT:PSS is attributed to the fact that laser treatment improves the oxidation degree of PEDOT and reduces the content of PSS. Compared with traditional solvent addition and post-treatment methods, ultrafast laser treatment of the film is a green, pollution-free, and low-cost treatment method. Compared with continuous lasers, ultrafast laser pulses have the advantages of short action time, high peak power, and low heat generation. When processing materials, ultrafast lasers do not bring heat to the surrounding materials. Ultrafast lasers can selectively process the PEDOT:PSS film to form electrode patterns. By selecting an appropriate power, ultrafast lasers can selectively remove the PEDOT:PSS film without damaging the surrounding PEDOT:PSS film or substrate. Since no solvents are added, both cost is saved and the adhesion and flexibility of the film are increased.

[0033] 4. As Figure 2As shown, in the dry PEDOT:PSS / PEA / AgNWs film, PSS presents as a glassy polymer, while PEDOT behaves as a crystalline polymer, and PEA has rubber-like properties. When the PEDOT:PSS / AgNWs base liquid is mixed with the PEA emulsion, as the water evaporates, the TMSPMA silyl groups condense into siloxane bonds, and the siloxane bonds crosslink the PEA chains. The emulsion particles gradually fuse to form a continuous solid structure, which contains two main domains: the PEDOT:PSS domain and the PEA domain, and the characteristic sizes of these two domains are approximately in the micrometer range. The PSS chains remain continuous in the film and are not crosslinked. The PEDOT nanocrystals are embedded in the PSS and between the silver nanowires, and their sizes are much smaller than the emulsion particles. This structure enables the PEDOT nanocrystals in the film prepared from the mixed emulsion to form a percolation network for electron transport, which is not disturbed by the hydrophobic and rubbery PEA chains, thus endowing the film with high conductivity. In addition, the presence of the PEA network effectively prevents the excessive swelling of PSS, avoids the detachment of PSS from the substrate, and ensures the stability of the film in a certain humidity environment. Description of the Drawings

[0034] Figure 1 Schematic diagram of the interfacial enhancement mechanism of TMSPMA bridging PEDOT:PSS and silver nanowires.

[0035] Figure 2 Schematic diagram of the mechanism for improving the stability of the PEA-chain-fixed PEDOT:PSSD film in a certain humidity environment.

[0036] Figure 3 Variation of the film resistance with the placement time of the AgNWs film, AgNWs / PEDOT:PSS film, and AgNWs / PEDOT:PSS / PEA film when placed at a temperature of 85 °C and a humidity of 30%.

[0037] Figure 4 Variation of the film resistance with the placement time of the AgNWs film, AgNWs / PEDOT:PSS film, and AgNWs / PEDOT:PSS / PEA film when placed at a temperature of 25 °C and a humidity of 85%. Detailed Embodiment

[0038] The embodiments of the present invention will be described in detail below in conjunction with the drawings and embodiments. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0039] The PEDOT:PSS used in the following embodiments was purchased from Shanghai Macklin Biochemical Co., Ltd. (containing 0.5 wt% PSS);

[0040] The silver nanowires (AgNWs) used in the following examples were purchased from Shanghai Macklin Biochemical Co., Ltd. (diameter 90 nm, length 20 - 60 μm);

[0041] The sodium citrate used in the following examples was purchased from Shanghai Macklin Biochemical Co., Ltd. (AR 99%);

[0042] The ethyl acrylate used in the following examples was purchased from Shanghai Macklin Biochemical Co., Ltd. (AR 99%);

[0043] The 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) used in the following examples was purchased from Sigma-Aldrich (AR 98%);

[0044] The sodium dodecylbenzenesulfonate (SDBS) used in the following examples was purchased from Sigma Aldrich.

[0045] The sodium dodecyl sulfate (SDS) used in the following examples was purchased from Shanghai Macklin Biochemical Co., Ltd. (AR ≥ 99%);

[0046] The ammonium persulfate (APS) used in the following examples was purchased from Shanghai Macklin Biochemical Co., Ltd. (AR 98.5%).

[0047] Example 1

[0048] In this example, a conductive film based on PEDOT:PSS and silver nanowires was prepared according to the following steps:

[0049] Step 1. Hydroxylation treatment of the silver nanowire surface

[0050] Disperse 10 mg of silver nanowires (AgNWs) in 10 mL of 0.02 M nitric acid (HNO3) solution, place it in a 25°C constant temperature water bath and stir for 6 minutes to form silver oxide Ag2O in some areas on the surface of AgNWs. Then centrifuge at 8000 rpm for 10 minutes, remove the supernatant, wash it 6 times repeatedly with deionized water, and then disperse the precipitate in 10 mL of deionized water. Subsequently, slowly add 0.1 M sodium hydroxide solution to adjust the pH to 8 - 9, and perform ultrasonic treatment at 50°C for 10 min to promote the hydrolysis of Ag2O to generate OH - , centrifuge again at 8000 rpm, remove the supernatant, wash it 5 times with deionized water, and disperse the obtained precipitate in 10 mL of deionized water to obtain a hydroxylated AgNWs dispersion.

[0051] Step 2. Preparation of the PEDOT:PSS / AgNWs base solution

[0052] Dissolve 400 μL of silane coupling agent TMSPMA in a mixed solvent of 9 mL of ethanol and 1 mL of water, adjust the pH to 4.8 with 0.1 M acetic acid, and stir for 120 minutes to fully hydrolyze it to generate Si-OH active groups, obtaining a coupling agent hydrolysis solution.

[0053] Mix the coupling agent hydrolysis solution with the hydroxylated AgNWs dispersion prepared in step 1, and under nitrogen protection, stir at 40 °C for 90 minutes to complete the grafting reaction. After the reaction, centrifuge at 10000 rpm for 15 minutes, remove the supernatant, wash 5 times with a mixed solution of ethanol and water with a volume ratio of 4:1 to remove unreacted silver ions and TMSPMA, and finally disperse the precipitate in 5 mL of deionized water containing 0.05 wt% SDBS to obtain a TMSPMA-AgNWs dispersion.

[0054] Pump 2 mL of the TMSPMA-AgNWs dispersion and 13 mL of a 1 wt% PEDOT:PSS solution into the flow channel through a microfluidic device at a total flow rate of 0.2 mL / min according to the volume ratio for mixing; after mixing, stir at 25 °C in the dark for 60 min under nitrogen protection to obtain a PEDOT:PSS / AgNWs base solution.

[0055] Step 3: pH adjustment and improvement of AgNWs dispersibility

[0056] While stirring, add 0.05 M sodium citrate solution to the PEDOT:PSS / AgNWs base solution prepared in step 2 to adjust the pH to 6, and continue stirring at room temperature for 60 minutes.

[0057] Step 4: PEA emulsion synthesis

[0058] Mix 72 g of EA and 17.1 μL of TMSPMA and ultrasonically treat for 5 min to remove dissolved oxygen. Add the obtained mixture to a 500 mL round-bottom flask, and add 0.415 g of SDS, 0.016 g of APS, and 168 g of distilled water. Flush nitrogen into the mixture and stir at a speed of 300 rpm for 10 min, then seal the round-bottom flask with a septum plug. Insert a syringe needle connected to a balloon into the septum plug to balance the additional pressure generated by the exotherm during polymerization. Place the round-bottom flask in an oil bath at 65 °C and stir in a magnetic stirrer at 300 rpm for 8 h to obtain a PEA emulsion. Store the prepared PEA emulsion at room temperature in a plastic tank made of high-density polyethylene (VWR, 16125-810).

[0059] Step 5: Preparation and post-treatment of the film

[0060] Take 10 mL of the PEDOT:PSS / AgNWs base solution after adjusting the pH in Step 3, and add 3.5 g of the PEA emulsion prepared in Step 4 thereto. Continuously stir for 2 hours and then degas under vacuum to form a composite solution. Clean the glass substrate with 100 W oxygen plasma for 5 minutes to enhance the surface activity. Subsequently, spin-coat the composite solution on the substrate surface at a speed of 3000 rpm for 30 seconds to form a coating with a wet film thickness of about 200 nm. The coating is cured by ventilation drying at 25°C for 1 hour, vacuum drying at 60°C for 30 minutes, and annealing at 120°C for 15 minutes in sequence. The substrate with the formed thin film is subjected to ultrafast laser treatment on the processing table of an ultrafast laser, taken out and then put into an oven for curing at 80°C for 30 minutes to obtain a conductive thin film based on PEDOT:PSS and silver nanowires.

[0061] Regulate the parameters of the ultrafast laser treatment and test the sheet resistance of the obtained conductive thin films under different parameters:

[0062] 1. Set the filling pitch to 15 microns and the line scanning speed to 1350 mm / s, and regulate the laser powers to 0 W, 8 W, 8.5 W, 9 W, 9.5 W, 10 W, and 11 W respectively. The sheet resistance values of the obtained thin films are shown in Table 1. It can be seen that when the laser processing improves the conductivity of the thin film, the processing power must be within a suitable range. Too high or too low power cannot achieve the ideal effect. When the laser power is 9 W, the sheet resistance value of the thin film is the lowest and the deviation range is the smallest.

[0063] Table 1

[0064]

[0065] 2. When setting the power of the ultrafast laser treatment to 9 W and the filling pitch to 15 microns, regulate the laser line scanning speeds to 650 mm / s, 850 mm / s, 1050 mm / s, 1250 mm / s, and 1450 mm / s respectively. The sheet resistance values of the obtained thin films are shown in Table 2. It can be seen that when the laser line scanning speed is 1050 mm / s, the sheet resistance value of the thin film is the lowest.

[0066] Table 2

[0067]

[0068] 3. When setting the power of the ultrafast laser treatment to 9 W and the line scanning speed to 1050 mm / s, regulate the laser filling pitches to 15 μm, 25 μm, 35 μm, 5 μm, 45 μm, and 55 μm respectively. The sheet resistance values of the obtained thin films are shown in Table 3. It can be seen that when the laser filling pitch is 35 μm, the sheet resistance value of the thin film is the lowest.

[0069] Table 3

[0070]

[0071] The film obtained under the conditions of the parameters of ultrafast laser treatment (power 9 W, line scanning speed 1050 mm / s, filling pitch 35 μm) is denoted as AgNWs / PEDOT:PSS / PEA film.

[0072] For comparison, the following films were also prepared in this example:

[0073] AgNWs film: 10 mg of AgNWs was dispersed in isopropanol and stirred evenly at room temperature to obtain a dispersion with a concentration of 0.5 mg / mL; 10 mL of the dispersion was spin-coated (2000 rpm, 30 s) on the surface of a plasma-treated glass substrate and annealed at 150 °C for 20 minutes to obtain the AgNWs film.

[0074] AgNWs / PEDOT:PSS film: A silver nanowire dispersion (concentration 2 mg / mL) was mixed with an aqueous PEDOT:PSS solution at a volume ratio of 1:7.5, and 2 wt% of dimethyl sulfoxide (DMSO) was added as a conductive enhancer, and the mixture was magnetically stirred for 2 hours to obtain a homogeneous mixture. The spin-coating method was used to spin-coat a wet film with a thickness of about 80 nm on the surface of a plasma-treated glass substrate at a speed of 2500 rpm for 30 s, and then pre-dried on a hot plate at 120 °C for 10 minutes, and then transferred to a vacuum oven and annealed at 150 °C for 30 minutes to form an effective overlapping network of silver nanowires to obtain the AgNWs / PEDOT:PSS film.

[0075] The AgNWs film, AgNWs / PEDOT:PSS film, and AgNWS / PEDOT:PSS / PEA film were placed at a temperature of 85 °C and a humidity of 30%, and the relative change rate of the film resistance with the placement time is as Figure 3 shown. In the figure, R0 is the initial resistance and R is the resistance after placement. It can be seen from the figure that after 40 days, the change rate of the sheet resistance of the AgNWs film and the AgNWs / PEDOT:PSS / PEA film did not show a large change. In contrast, the resistance of the AgNWs / PEDOT:PSS film at high temperature increased by more than 90 times compared to its initial value, because a large amount of H + was generated by PEDOT:PSS under high temperature conditions, corroding the silver nanowires and resulting in poor conductivity. However, the AgNWs / PEDOT:PSS / PEA film of this example significantly improved the high temperature stability due to the addition of sodium citrate.

[0076] The AgNWs film, AgNWs / PEDOT:PSS film, and AgNWs / PEDOT:PSS / PEA film were placed at a temperature of 25 °C and a humidity of 85%, and the relative change rate of the film resistance with the placement time is as Figure 4As shown in the figure, R0 is the initial resistance and R is the resistance after placement. It can be seen from the figure that after 40 days, the change rates of the sheet resistance of the AgNWs film and the AgNWs / PEDOT:PSS film have very large changes. In contrast, the sheet resistance of the AgNWs / PEDOT:PSS / PEA film only increases by 3 times compared to its initial value under high humidity conditions, indicating that the film manufactured in this embodiment can conduct electricity stably under a certain humidity.

[0077] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a conductive thin film based on PEDOT:PSS and silver nanowires, characterized in that: After the surface of silver nanowires (AgNWs) is hydroxylated, under the action of the silane coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), it is mixed with PEDOT:PSS to prepare a PEDOT:PSS / AgNWs base liquid; after adjusting the pH of the base liquid with sodium citrate, it is then mixed with a PEA emulsion and spin-coated into a film, and finally the conductivity is improved by laser treatment to obtain a conductive film based on PEDOT:PSS and silver nanowires.

2. The preparation method according to claim 1, characterized in that, It includes the following steps: Step 1: Hydroxylation treatment of the surface of silver nanowires Disperse 8 - 10 mg of AgNWs in 10 mL of nitric acid solution with a concentration of 0.01 - 0.03 M, stir at 25 °C for 5 - 8 min to form silver oxide Ag2O on some regions of the AgNWs surface, centrifuge to remove the supernatant, wash with deionized water, then disperse the precipitate in 10 mL of deionized water, gradually add 0.1 M - 0.2 M sodium hydroxide solution until the pH = 8 - 9, and ultrasonically treat at 45 - 55 °C for 10 - 15 min to promote the hydrolysis of Ag2O to generate surface hydroxyl groups OH - , after centrifuging again and removing the supernatant, wash with deionized water, and disperse the obtained precipitate in 10 mL of deionized water to obtain a hydroxylated AgNWs dispersion; Step 2: Preparation of PEDOT:PSS / AgNWs base liquid Dissolve 400 - 450 μL of the silane coupling agent TMSPMA in 10 mL of a mixture of ethanol and water with a volume ratio of 8 - 9:1, add acetic acid to adjust the pH to 4.5 - 5.2, stir to make it hydrolyze fully to generate Si-OH active groups, and obtain a coupling agent hydrolysis solution; Mix the coupling agent hydrolysis solution with the hydroxylated AgNWs dispersion liquid in Step 1, under nitrogen protection, stir and react at 30°C - 40°C for 80 - 100 min, then centrifuge to remove the supernatant, wash it with a mixed solution of ethanol and water with a volume ratio of 4:1 for more than 3 times to completely remove unreacted silver ions and TMSPMA, and then disperse the precipitate in 3 - 5 mL of deionized water containing 0.05 wt% sodium dodecylbenzenesulfonate (SDBS) to obtain a TMSPMA-AgNWs dispersion liquid; Pump 2 mL of the TMSPMA-AgNWs dispersion liquid and 10 - 15 mL of a 1 wt% PEDOT:PSS solution into the flow channel through a microfluidic device at a total flow rate of 0.2 mL / min according to the volume ratio for mixing; after mixing, stir in the dark at 25°C under nitrogen protection for 40 - 60 min to enable the other end of TMSPMA to achieve interfacial bonding with PEDOT:PSS through hydrogen bonding to prepare a PEDOT:PSS / AgNWs base liquid; Step 3: pH adjustment and improvement of the dispersibility of AgNWs While stirring, add a 0.05 M sodium citrate solution to the PEDOT:PSS / AgNWs base liquid prepared in Step 2 to adjust the pH to 6.0 - 6.3, and continue to stir at room temperature for 30 - 60 minutes; Step 4: Synthesis of PEA emulsion 72 g of ethyl acrylate (EA) and 17.1 - 20 μL of TMSPMA were mixed and sonicated for 5 - 10 min to remove dissolved oxygen. The resulting mixture was added to a round-bottom flask, and 0.4 - 0.45 g of sodium dodecyl sulfate (SDS), 0.015 - 0.02 g of ammonium persulfate (APS), and 168 - 200 g of distilled water were added. Nitrogen was purged into the mixture and stirred at a speed of 300 rpm for 10 - 15 min, and then the round-bottom flask was sealed with a septum plug. A syringe needle connected to the balloon was inserted into the septum plug to balance the additional pressure generated by the exotherm during polymerization. The round-bottom flask was placed in an oil bath at 65 - 70 °C and stirred in a magnetic stirrer at 300 rpm for 8 - 10 h to obtain a PEA emulsion. The prepared PEA emulsion was stored at room temperature in a plastic tank made of high-density polyethylene; Step 5. Preparation and post-treatment of the film Take 10 mL of the PEDOT:PSS / AgNWs base solution after adjusting the pH in Step 3, and add 3.5 - 4 g of the PEA emulsion prepared in Step 4 thereto. After stirring evenly, it was degassed under vacuum to obtain a composite solution. The glass substrate was cleaned with oxygen plasma, and then the composite solution was spin-coated on the surface of the substrate and cured gradiently. The substrate with the film formed thereon was subjected to ultrafast laser treatment on the processing table of an ultrafast laser, and after taking it out, it was put into an oven and cured at 80 - 100 °C to obtain a conductive film based on PEDOT:PSS and silver nanowires.

3. The preparation method according to claim 2, wherein In Step 5, the gradient curing was completed by drying in ventilation at 25 - 30 °C for 1 - 1.5 h, vacuum drying at 60 - 70 °C for 30 - 50 min, and annealing at 100 - 130 °C for 10 - 20 min.

4. The preparation method according to claim 2, characterized in that, In Step 5, the parameters of the ultrafast laser treatment were set as follows: laser power 8.5 W - 9.5 W, line scanning speed 950 mm / s - 1150 mm / s, and filling pitch 32 μm - 37 μm.

Images