Conductive ink based on PEDOT: PSS and carboxylated carbon nanotubes

Abstract

The invention belongs to the field of conductive ink, and discloses conductive ink based on PEDOT: PSS and carboxylated carbon nanotubes, and the conductive ink is prepared from PEDOT: PSS, carboxylated carbon nanotubes, [EMIM] [TCB], polyacrylate, salicylic acid and DMSO. According to the conductive ink with PEDOT: PSS as the main body, [EMIM] [TCB], carboxylated carbon nanotubes, salicylic acid and DMSO are introduced to improve the performance of the ink, the obtained conductive ink is high in conductivity, high in oxidation resistance and good in printing performance, and a flexible transparent electrode prepared from the conductive ink is high in conductivity and light transmittance and can be well suitable for the fields of human body wearable, robot electronic skin and the like.

Description

Technical Field

[0001] The present invention belongs to the field of conductive inks, and particularly relates to a conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes. Background Art

[0002] Flexible transparent electrodes (TCEs) have attracted much attention in various applications, such as touch interfaces, organic light-emitting diodes (OLEDs), interactive displays, energy storage, and energy harvesting. So far, indium tin oxide (ITO) has been the most commonly used TCE material due to its excellent optoelectronic properties, such as high transparency (>85%) and low sheet resistance (10–100 Ω / sq). However, ITO has obvious defects and is difficult to meet the requirements of new flexible electronics: it requires high-temperature and vacuum processes, but plastic substrates are not resistant to high temperatures, which limits the improvement of optoelectronic properties; it is brittle and prone to cracking or peeling when bent, and cannot adapt to dynamic deformation scenarios such as foldable screens and wearable devices; it is easily damaged when etching circuits on flexible substrates, and the large-area processing cost is high and the yield is low. These defects have promoted the research and development of new transparent conductive materials, which are required to have both the excellent optoelectronic characteristics of ITO and flexible reliability. In this regard, metals (nanoparticles or nanowires), carbon nanotubes, graphene and its derivatives, and conductive polymers have been explored.

[0003] Patent CN119092180A proposes a preparation method for a silver nanowire composite transparent electrode resistant to ultraviolet ozone treatment, which improves the stability of the silver nanowire electrode through a three-layer structure design. First, a conductive network is formed by spin-coating silver nanowires on a transparent substrate, then an aluminum-doped zinc oxide (AZO) protective layer is constructed on the silver nanowires by electrochemical deposition, and finally a tin dioxide (SnO 2 )nanocrystalline protective layer is spin-coated by the sol-gel method. Through the synergistic protection of the AZO / SnO 2 double-layer oxides, the high carrier mobility of AZO is utilized to maintain conductivity, and the dense structure of SnO 2 is used to block oxidation erosion, so that the electrode still maintains a low sheet resistance after 15 minutes of ultraviolet ozone treatment, and the antioxidant ability is significantly improved compared with the unprotected silver nanowires. However, this solution has the problem of optoelectronic performance loss, and the transmittance drops from 83.73% of pure silver nanowires to 70.26%. In addition, the strict control of temperature, concentration, and voltage in the electrodeposition process and the double-layer spin-coating heat treatment process increase the process complexity and may affect the mass production stability.

[0004] Patent CN119305286A proposes a preparation method for a multi-layer composite electrode. Its core innovation lies in using a multi-walled carbon nanotube film as the heating layer. First, by preheating the base layer, a wet-curing polyurethane adhesive (PUR) is sprayed using a dispensing machine along a specific path. Through a hot pressing process, the lower waterproof layer, the carbon nanotube film / electrode layer, the upper waterproof layer, and the antibacterial layer are sequentially bonded, finally forming a five-layer composite structure. By arranging multi-walled carbon nanotubes in the same direction, a directional conductive film with a longitudinal conductivity (>0.8×10 5 S / m) significantly higher than the transverse direction is formed. Combined with a copper flexible electrode arranged in a warp and weft cross pattern, uniform heating with low power consumption is achieved while maintaining an ultra-thin thickness and bendable flexibility. Although the conductive anisotropy of the carbon nanotube film improves the longitudinal current efficiency, insufficient transverse conductivity may cause local heat accumulation, especially a decrease in the heat conduction efficiency in the direction of non-parallel electrodes. Secondly, the visible light absorption rate of about 80% of the carbon nanotube material itself results in a light transmittance of less than 40%, limiting its application in transparent or semi-transparent electrodes.

[0005] Patent CN117860255A proposes a preparation method for a screen-printed flexible electrode based on flash graphene. Its core process is to ball-mill and mix the disordered structure flash graphene prepared by the Joule heat flash evaporation method with a specific binder in a certain proportion to form a conductive paste with a nano-channel structure, which is screen-printed onto a flexible fiber cloth and then dried at a low temperature to form a shape. Using disordered graphene with a high specific surface area to construct a three-dimensional conductive network, a low sheet resistance of 125Ω / sq is achieved while maintaining 98% of the original air permeability of the fabric; the wear resistance is improved through the mechanical interlocking structure between the fiber cloth substrate and the paste, and the resistance fluctuation is <5% after ten thousand times of friction. Although the initial conductivity of this electrode is better than that of traditional gel electrodes, the light transmittance is low, limiting its application in transparent wearable scenarios; the lack of light transmittance makes it impossible to balance the optical transparency and conductive requirements, and there are limitations in medical scenarios where visual monitoring of skin conditions is required. In addition, although a high binder content can ensure adhesion, it will hinder the close stacking of graphene, making it difficult to further improve the conductivity to the level of metal electrodes.

[0006] Conductive polymers have gradually attracted the attention of researchers due to their inherent flexibility, adjustable optoelectronic properties, simple synthesis, and low-temperature processing. Among them, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has become the most commonly used conductive polymer for flexible transparent electrodes due to its advantages of high conductivity, high biocompatibility, non-toxicity, and low cost. Its conductivity and light transmittance are comparable to those of traditional electrode materials.

[0007] Patent CN119371642A provides a preparation method for regulating the properties of PEDOT:PSS dispersion by adding different emulsifiers. Its core process is to introduce amphiphilic emulsifiers during the oxidative polymerization of EDOT monomer and polystyrene sulfonic acid (PSS) to regulate the molecular structure of PEDOT: The emulsifier forms microdroplets by reducing the surface tension, providing a better chain growth environment, enabling PEDOT molecules to form a more ordered linear structure, and ultimately achieving a film conductivity of 377 - 387 S / cm, which is significantly improved compared to traditional methods. However, there is still a large gap between the conductivity of the dispersion obtained in this patent and commercial products.

[0008] Patent CN119530995A proposes a preparation method for PEDOT:PSS-based composite fibers with silver nanoparticles loaded on the surface. Mix the silver nanowire solution and the PEDOT:PSS solution to form a spinning solution. Through the synergistic effect of solvent evaporation induction and Ag - S bonds, high-density silver nanoparticles are in-situ generated on the fiber surface, and the internal silver nanowires form a conductive network (conductivity 1019 S / cm). Although high-concentration silver nanowires increase the conductivity to the metal level, the excessive metal components may cause a significant decrease in the transmittance, limiting its application potential in transparent flexible devices; at the same time, the dense silver particles on the surface may exacerbate the light scattering effect, further weakening the optical transparency and making it difficult to meet the requirements of transmissive optical sensing.

[0009] Patent CN104212243A provides a preparation method for neutralizing PEDOT:PSS conductive ink. The production process is to directly add an alkaline regulator to adjust the pH of the system to 5.0 - 9.0 after the polymerization of EDOT and PSS, naturally form a viscosity of 1000 - 50000 mPa•s during the aging stage, and then remove inorganic salts through an ion exchange resin to finally obtain a neutral dispersion without a thickening agent. This process synchronizes neutralization and viscosity adjustment, avoiding the damage to performance caused by non-conductive additives in traditional post-thickening processes. By adding guanamine-formaldehyde condensate and a water-insoluble polyester adhesive, the coating adhesion and solvent resistance are significantly improved while maintaining the conductivity (the lowest surface resistance reaches 537 Ω / sq). However, there are still challenges in balancing the conductivity and transmittance of this conductive ink: when the adhesive addition amount exceeds 2 wt%, the surface resistance rises above 800 Ω / sq, and the transmittance decreases by about 3% simultaneously. In addition, the pH control accuracy during the neutralization process directly affects the stability of the dispersion. If it exceeds the preferred range of 6.5 - 7.2, the conductivity will decay by 10 - 15%.

[0010] Although great progress has been made in the research of PEDOT:PSS conductive ink, there are still the following problems: 1. The conductivity of PEDOT:PSS is mainly determined by PEDOT, while PSS is the component that enables the dissolution, stabilization, and dispersion of PEDOT, but it itself is not conductive. Excessive PSS will limit the flow of charges, thereby reducing the conductivity of the thin film. How to reduce the influence of PSS or optimize its distribution is the key to improving conductivity. The conductivity of the PEDOT:PSS conductive thin film not only depends on the composition of the material, but also on its molecular structure and the packing state of the chains. If the packing between PEDOT molecular chains is not tight, the charge transport path becomes discontinuous, resulting in a decrease in conductivity.

[0011] 2. Due to its rigid conjugated main chain and strong intermolecular interactions, the thin film prepared from PEDOT:PSS inherently has poor stretchability, low elongation at break, exhibits low ductility, and is prone to brittle fracture under external forces. PSS has strong hydrophilicity and ionic properties, which limits the mechanical properties of the thin film under external forces. To improve the mechanical properties of PEDOT:PSS, it is usually necessary to introduce mechanical modification reagents to enhance its elasticity and ductility. However, these mechanical modification reagents often introduce additional interfacial impedance or hydrophobicity, hindering the flow of electrons or ions, and also causing excessive cross-linking or aggregation of PEDOT:PSS chains, which will reduce the degree of freedom of PEDOT segments and lower the conductivity of PEDOT:PSS.

[0012] 3. The conductive properties of PEDOT:PSS are very sensitive to environmental humidity. In a high-humidity environment, the conductivity of the PEDOT:PSS thin film will be affected, resulting in unstable performance. When the humidity increases, moisture and oxygen in the air will promote the oxidation reaction of PEDOT chains, forming an oxidized form of PEDOT with poor conductivity. The oxidation process reduces the conductivity of PEDOT chains, thereby decreasing the overall conductivity of the thin film. In addition, the oxidation causes a change in the structure of PEDOT chains, further affecting the conduction path. In the conductive mechanism of PEDOT:PSS, there is both electron conduction and ionic conduction. When the humidity is too high, the hydration enhances the ionic conductivity, but at the same time, the electron conduction may be limited by the effects of oxidation and structural changes, resulting in a competition in the conduction efficiency between the two, and thus affecting the conductive performance of the PEDOT:PSS conductive ink when prepared into a flexible transparent electrode.

[0013] 4. PEDOT:PSS is formed by the copolymerization of PEDOT and PSS. In an alkaline environment, PEDOT will degenerate (such as deprotonation or oxidation), resulting in a decrease in conductivity. The alkaline environment will also cause the interaction between PSS and PEDOT to weaken, thereby affecting the stability of the ink. In an overly acidic environment (pH < 4), it will cause the degradation or chemical reaction of PEDOT molecules, reducing its conductivity. At the same time, the excessive dissociation of PSS will also have a negative impact on the conductive network.

[0014] 5. For different printing methods, the rheological properties of the ink are key factors to ensure printing suitability and film-forming uniformity. As an easily solution-processable formulation, PEDOT:PSS has become an ideal material for digital printing technology. However, the inherent rheological properties of the original PEDOT:PSS suspension, characterized by low viscosity and high surface tension, make it less than ideal as an ink for printing applications. Summary of the Invention

[0015] In view of the deficiencies of the above-mentioned prior art, the present invention provides a conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes, aiming to effectively improve the problems existing in the conductive ink mainly composed of PEDOT:PSS, such as low conductivity, poor printability, and poor humidity sensitivity, so that the prepared conductive ink can be widely applied to the fields of wearable electronics and electronic skin.

[0016] To solve the above problems, the present invention adopts the following technical solutions: The conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes has the following components by mass percentage: PEDOT:PSS 55-65%, carboxylated carbon nanotubes 7.5%, 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] 15-25%, polyacrylate 5%, salicylic acid 2.5%, DMSO 5%.

[0017] Most preferably, the components of the conductive ink are composed by mass percentage as follows: PEDOT:PSS 60%, carboxylated carbon nanotubes 7.5%, [EMIM][TCB] 20%, polyacrylate 5%, salicylic acid 2.5%, DMSO 5%.

[0018] In the conductive ink with PEDOT:PSS as the main body provided by the present invention, [EMIM][TCB], carboxylated carbon nanotubes, salicylic acid, and DMSO are introduced to improve the ink properties. [EMIM][TCB] induces efficient ion exchange within PEDOT:PSS; carboxylated carbon nanotubes promote the transport of electrons in the PEDOT:PSS network through the π-π stacking interaction between their carboxyl functional groups and the PEDOT chains; salicylic acid forms interactions with the sulfonic acid groups in PSS through hydrogen bonds, π-π bonds, and electrostatic interactions, optimizing the interaction between PEDOT and PSS, helping to form a more uniform and stable conductive network, thereby improving the overall conductivity of the ink, and at the same time reducing the surface tension of the ink and improving the wettability and spreadability of the ink on the surfaces of various substrates. The large number of ions provided in [EMIM][TCB] enhances the hydration effect, increases the diffusivity of the ions in the ionic liquid in the film, improves the co-conduction of ions and electrons, reduces the degree of oxidation of PEDOT, and thus improves the antioxidant property of the conductive ink. Using DMSO as a solvent can, on the one hand, increase the conductivity of the ink, and on the other hand, reinforce the mechanical properties of the ink.

[0019] Furthermore, the mass ratio of PSS to PEDOT in the PEDOT:PSS is 2.5:1. This ratio results in a moderate steric hindrance effect of PSS, which not only ensures the full dispersion of PEDOT but also reduces the inhibition of conductivity by the insulating layer. Secondly, the synergistic effect of carboxylated carbon nanotubes and salicylic acid can partially replace the dispersion function of PSS. The interaction between their carboxyl groups and the sulfonic acid groups of PSS can weaken the strong Coulomb attraction between PEDOT-PSS, enabling the maintenance of system stability even when the proportion of PSS is reduced. In addition, the electrostatic interaction between the cations in the [EMIM][TCB] ionic liquid and PSS can further promote the phase separation of PEDOT chains. At this ratio, the size and density of the PEDOT conductive domains reach an equilibrium, maximizing the proportion of the quinoid structure and further increasing the conductivity.

[0020] The present invention further provides a preparation method of a conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes, comprising the following steps: Step 1, at a concentration of 5 mg·mL -1While stirring, [EMIM][TCB] and salicylic acid were successively added to the ethanol dispersion of carboxylated carbon nanotubes, and then ultrasonically dispersed evenly. Then, stirring was continued for 1 to 3 hours at room temperature to obtain mixture A. Ultrasonic treatment can utilize the cavitation effect of ultrasonic waves to fully mix [EMIM][TCB], salicylic acid, and carboxylated carbon nanotubes, break the agglomeration of particles, and improve the uniformity and stability of the solution. Continuous stirring helps to further promote the interaction between components, enabling the additive to better coat the surface of carboxylated carbon nanotubes and form a stable mixed system.

[0021] Step 2: Filter the ethanol dispersion of PEDOT:PSS with a mass concentration of 1 - 2% through a syringe filter. Add the filtered ethanol dispersion of PEDOT:PSS, polyacrylate, and DMSO to the above-mentioned mixture A, and stir for 1 to 3 hours at room temperature to obtain the conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes. Filtration can remove impurities, agglomerates, or large particle substances present in the ethanol dispersion of PEDOT:PSS, ensuring the purity and uniformity of the PEDOT:PSS solution, thereby improving the performance of the final conductive ink. During the stirring at room temperature, PEDOT:PSS, polyacrylate, DMSO, and mixture A are fully mixed, and the components interact with each other.

[0022] Compared with the existing technology, in the conductive ink with PEDOT:PSS as the main body provided by the present invention, [EMIM][TCB], carboxylated carbon nanotubes, salicylic acid, and DMSO are introduced to improve the ink performance. The obtained conductive ink has high conductivity, strong antioxidant performance, good printing performance, and the flexible transparent electrode prepared therefrom has high light transmittance. The beneficial effects of the present invention are specifically embodied in: 1. The conductivity of the conductive ink provided by the present invention is not less than 500 S / cm, and the conductivity of the flexible transparent electrode with a thickness not greater than 10 μm prepared from the conductive ink is not less than 1500 S / cm. The excellent conductive performance mainly comes from the following aspects: (1) The strong interactions between the hydrophilic cations of [EMIM][TCB] and hydrophilic PSS, and between the hydrophobic anions and hydrophobic PEDOT clusters respectively induce efficient ion exchange within PEDOT:PSS. This spontaneous ion exchange triggers the separation of PEDOT and PSS, and at the same time, the π-stacking order in the PEDOT domain is also improved. On the one hand, the hydrophobic anions covering the surface of the PEDOT polymer are expected to hinder the attachment of PSS anions to the PEDOT surface. The hydrophilic, non-planar cations remain in the aqueous phase and do not embed with the hydrophobic anions within the π-stacked PEDOT clusters, thus promoting the generation of more crystalline and interconnected PEDOT nanofiber structures. The induced structural change of the PEDOT chain, from the benzenoid structure to the quinoid structure with a flatter chain conformation, contributes to denser molecular packing. These microscopic changes promote carrier transport by enhancing the charge carrier mobility and density, ultimately increasing the conductivity. (2) The introduction of carboxylated carbon nanotubes can promote the transport of electrons in the PEDOT:PSS network through the π-π stacking interaction between its carboxyl functional groups and PEDOT chains, enhancing the conductive performance of PEDOT. The functional groups on the carboxylated carbon nanotubes weaken the Coulomb attraction between PEDOT and PSS, and the conductive network of carboxylated carbon nanotubes and the conductive chains of PEDOT:PSS form an electron migration channel. This composite structure forms a relatively dense conductive network through the connection of carboxylated carbon nanotubes, providing an additional electron migration path, thereby increasing the conductivity of the conductive ink. (3) Salicylic acid further optimizes the interaction between PEDOT and PSS by forming hydrogen bonds or other weak interactions with the sulfonic acid groups of PSS, forming a more uniform and stable conductive network, and thus increasing the overall conductivity of the ink.

[0023] 2. The elongation at break of the flexible transparent electrode with a thickness not greater than 10 μm prepared from the conductive ink provided by the present invention is not higher than 10%. The excellent mechanical properties mainly come from the following aspects: (1) The introduction of salicylic acid forms interactions with the sulfonic acid groups in PSS through hydrogen bonds, π-π bonds, and electrostatic interactions, etc. This interaction enhances the structural stability of PEDOT:PSS and also improves the microscopic arrangement of the film. The hydrophilicity and dispersibility of salicylic acid improve the uniform dispersion degree of PEDOT:PSS molecules in the solution, thereby forming a more uniform film, effectively reducing the pores and defects in the film, and improving the mechanical strength and durability of the film. (2) The introduction of DMSO can effectively improve the rheological properties of the ink, enabling the ink to form a uniform and firm network structure during the curing process. Since stress is generated during the curing process of PEDOT:PSS, the presence of DMSO can effectively reduce this stress, thereby improving the crack resistance and flexibility of the ink.

[0024] 3. After being tested in an oxidation environment, the conductivity of the flexible transparent electrode with a thickness not greater than 10 μm prepared from the conductive ink provided by the present invention remains above 90% of the initial value, and the oxidation loss is less than 10%. By introducing [EMIM][TCB], the conductivity of PEDOT is stabilized, and the oxidation of PEDOT chains is reduced. The cations and anions in [EMIM][TCB] interact with PEDOT chains, optimizing the electron conduction path of PEDOT chains, reducing the oxidation degree of PEDOT, and improving the electron migration efficiency in PEDOT chains, thereby enhancing the conductivity of the film. A large number of ions in [EMIM][TCB] can enhance the hydration of the film, making it easier for the PSS chains in the PEDOT:PSS film to exchange with the ions of [EMIM][TCB]. This enhanced hydration increases the diffusibility of ions in the ionic liquid in the film and improves the co - conduction of ions and electrons. [EMIM][TCB] can not only improve the conductivity of the film through ionic conduction but also further optimize its electron transport performance by improving the hydration of PEDOT:PSS.

[0025] 4. The pH value of the conductive ink provided by the present invention is approximately 5.5. By introducing salicylic acid, the alkalinity can be neutralized, and the pH of the ink system can be adjusted to a milder value, making the PEDOT:PSS system in the ink more stable and avoiding the negative impact of overly strong acidity on the viscosity and fluidity of the ink. An appropriate acidic environment helps the ionization of PEDOT, promotes its conductivity, and at the same time avoids the damage or excessive degradation of the PEDOT polymer chain structure caused by excessive acidity. The interaction between salicylic acid and the sulfonic acid group of PSS further enhances the stability of the ink, avoiding the phenomenon of uneven film formation or ink precipitation caused by changes in the pH value, thereby ensuring the uniformity and stability of the final printed pattern or film layer.

[0026] 5. The viscosity of the conductive ink provided by the present invention is 2000 - 3000 mPa·s, which is suitable for inkjet printing, screen printing, etc. As an ionic liquid, [EMIM][TCB] has strong ionic interactions and good solubility, and can interact with PEDOT and PSS molecules in the ink, thereby effectively improving the dispersibility of PEDOT:PSS. This improvement in dispersibility can reduce the agglomeration phenomenon between polymer molecules, making the ink more uniform. The ionic liquid itself has low volatility and moderate viscosity, and its addition can effectively reduce the overall viscosity of the ink and regulate the fluidity of the ink. This helps the fluidity and printability of the ink during the printing process. [EMIM] + and [TCB] - can form hydrogen bonds or ion-dipole interactions with PSS or PEDOT molecules in the ink, reducing the surface tension of the ink, thereby improving the wettability and spreading property of the ink on the surface of various substrates. This improvement in wettability not only avoids the phenomena of sputtering or shedding of the ink during the printing process, but also ensures the uniform coating of the ink, improving the printing quality. Description of the Drawings

[0027] Figure 1 It is a diagram showing the change in the contact angle of the conductive ink provided by the embodiment of the present invention compared with the PEDOT:PSS dispersion liquid.

[0028] Figure 2 It is a schematic diagram of the reaction mechanism of PEDOT:PSS and [EMIM][TCB] in the embodiment of the present invention.

[0029] Figure 3 It is a diagram showing the change in the resistance value of the flexible transparent electrode prepared from the conductive ink of the embodiment of the present invention with the mass percentage of [EMIM][TCB].

[0030] Figure 4 It is a diagram showing the change in the conductivity of the flexible transparent electrode prepared from the conductive ink of the embodiment of the present invention with the mass percentage of [EMIM][TCB].

[0031] Figure 5 Graph of the transmittance of the flexible transparent electrode prepared from the conductive ink of the embodiment of the present invention varying with the mass percentage of [EMIM][TCB].

[0032] Figure 6 Stress-strain curve graph of the flexible transparent electrode prepared from the conductive ink of the embodiment of the present invention.

[0033] Figure 7 Graph of the change in conductivity of the flexible transparent electrode prepared from the conductive ink of the embodiment of the present invention after being placed for 24 h under the accelerated aging conditions of 85% RH (relative humidity) / 60 °C. Detailed implementation manners

[0034] The embodiments of the present invention will be described in detail below 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 processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0035] Embodiment 1 The embodiments of the present invention will be described in detail below 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 processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0036] The conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes provided in this embodiment has the following composition by mass percentage: PEDOT:PSS 60%, carboxylated carbon nanotubes 7.5%, 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] 20%, polyacrylate 5%, salicylic acid 2.5%, DMSO 5%. The specific preparation steps are as follows: Step 1. While stirring, 0.4 g of [EMIM][TCB] and 0.05 g of salicylic acid are successively added to a 30 mL ethanol dispersion solution of carboxylated carbon nanotubes with a concentration of 5 mg·mL -1 (containing 0.15 g of carboxylated carbon nanotubes), and then ultrasonically dispersed evenly, and then stirred at room temperature for 2 hours to obtain a mixed solution A.

[0037] Step 2: Filter the ethanol dispersion of PEDOT:PSS with a mass concentration of 1.5% (where the mass ratio of PSS to PEDOT is 2.5:1) through a syringe filter; add the filtered ethanol dispersion of PEDOT:PSS (containing 1.2 g of PEDOT:PSS), 0.1 g of polyacrylate, and 0.1 g of DMSO to the mixture A, and stir for 2 hours at room temperature to obtain the conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes. After testing, the room-temperature conductivity of the ink obtained in this example is 531 S / cm, the pH value is about 5.5, and the viscosity is 2650 mPa·s.

[0038] Figure 1 This is the contact angle change diagram of the conductive ink provided in this example compared with the PEDOT:PSS dispersion. As can be seen from the figure, the contact angle of the conductive ink is smaller than that of the PEDOT:PSS dispersion, the spreading property of the ink on the substrate surface is better, a more uniform thin film can be formed, reducing pinholes or cracks after printing, thereby reducing the local resistance difference and improving the overall uniformity of the thin film.

[0039] Figure 2 This is the schematic diagram of the reaction mechanism between PEDOT:PSS and [EMIM][TCB] in this example. The strong interactions between the hydrophilic cations of [EMIM][TCB] and hydrophilic PSS, and between the hydrophobic anions and hydrophobic PEDOT clusters respectively induce efficient ion exchange within PEDOT:PSS. The induced change in the PEDOT chain structure, from the benzenoid structure to the quinoid structure with a flatter chain conformation, contributes to denser molecular packing. These microscopic changes promote carrier transport by enhancing the charge carrier mobility and density, ultimately increasing the conductivity.

[0040] Ensure that the amounts of carboxylated carbon nanotubes, polyacrylate, salicylic acid, and DMSO in the system remain unchanged, and ensure that the total amount of PEDOT:PSS and [EMIM][TCB] remains unchanged. Adjust the amounts of PEDOT:PSS and [EMIM][TCB] to adjust the mass percentages of PEDOT:PSS and [EMIM][TCB] in the ink. Spin-coat the conductive ink with different mass percentages on the plasma-treated PI film. First, pre-spin at 500 rpm for 10 seconds to spread the ink, then spin at 800 rpm for 30 seconds, and then anneal at 80 °C for 10 minutes to volatilize the solvent to form a uniform film layer, and make a flexible transparent electrode with a thickness of about 7.5 μm.

[0041] Figure 3 and Figure 4The figure shows the variation of the resistance value and conductivity of the flexible transparent electrode prepared from the conductive ink of this embodiment with the mass percentage of [EMIM][TCB]. It can be seen that when the mass percentages of PEDOT:PSS and [EMIM][TCB] in the ink are 60% and 20% respectively, the resistance value of the ink is the smallest (843 Ω) and the conductivity is the largest (1530 S / cm).

[0042] Figure 5 The figure shows the variation of the light transmittance of the flexible transparent electrode prepared from the conductive ink of this embodiment with the mass percentage of [EMIM][TCB]. It can be seen that when the mass percentages of PEDOT:PSS and [EMIM][TCB] in the ink are 40% and 40% respectively, the light transmittance of the ink is the largest (86.2%).

[0043] Figure 6 The figure is the stress-strain curve of the flexible transparent electrode prepared from the conductive ink of this embodiment, where the mass percentages of PEDOT:PSS and [EMIM][TCB] in the ink are 60% and 20% respectively. Figure 6 It shows the tensile properties of the flexible transparent electrode prepared from the conductive ink: when the elongation at break reaches 7.5%, the stress peak is about 400 KPa (corresponding to the elongation at break), and then the stress decreases slowly, indicating that the material maintains strong toughness within 7.5% deformation.

[0044] Figure 7 The figure is the conductivity change curve of the flexible transparent electrode prepared from the conductive ink of this embodiment under the accelerated aging conditions of 85% RH (relative humidity) / 60 °C for 24 h, where the mass percentages of PEDOT:PSS and [EMIM][TCB] in the ink are 60% and 20% respectively. The initial conductivity is 1530 S / cm, and the recorded values every 6 h are 1528.5 S / cm, 1525.4 S / cm, 1523.8 S / cm, 1520.8 S / cm respectively (the total decrease is only 0.6%).

[0045] The above embodiments only 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 modifications 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. Conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes, characterized in that: The components of the conductive ink are composed of 55-65% PEDOT:PSS, 7.5% carboxylated carbon nanotubes, 15-25% 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM] [TCB], 5% polyacrylate, 2.5% salicylic acid, and 5% DMSO by mass percentage.

2. The conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes according to claim 1, characterized in that: The components of the conductive ink are composed of 60% PEDOT:PSS, 7.5% carboxylated carbon nanotubes, 20% [EMIM][TCB], 5% polyacrylate, 2.5% salicylic acid, and 5% DMSO in percentage by mass.

3. The conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes according to claim 1, characterized in that: The mass ratio of PSS to PEDOT in the PEDOT:PSS is 2.5:

1.

4. A method for preparing a conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes according to any one of claims 1 to 3, characterized in that: The steps include: Step 1: At a concentration of 5 mg mL -1 [EMIM] [TCB] and salicylic acid are sequentially added to the ethanol dispersion of carboxylated carbon nanotubes while stirring, and then ultrasonically dispersed uniformly, and then stirred at room temperature for 1 to 3 hours to obtain a mixed solution A; Step 2: Filter the ethanol dispersion of PEDOT:PSS with a mass concentration of 1-2% through a needle filter; add the filtered ethanol dispersion of PEDOT:PSS, polyacrylate and DMSO to the mixed solution A, and stir at room temperature for 1-3 hours to obtain a conductive ink based on PEDOT:PSS and carboxylated carbon nanotubes.

Images