Grid-like silver nanowire flexible transparent electrode based on nanometer thin film device and preparation method thereof

Abstract

The application discloses a kind of grid-like silver nanowire flexible transparent electrode based on nanometer film device and preparation method thereof, the electrode includes PET substrate and silver nanowire conductive network supported thereon, the silver nanowire conductive network has orthogonal arrangement structure of grid-like, and silver nanowire intersection node has the nanoweld interface formed by mechanical pressure treatment;Its grid-like structure is induced by electrostatic adsorption effect by anionic polyelectrolyte or zwitterionic surfactant as dispersant to form silver nanowire self-assembly.Form flexible transparent electrode by the synergistic effect of dispersant regulation silver nanowire grid-like assembly and mechanical pressure induced nanowelding, the sheet resistance and surface roughness of electrode are significantly reduced, the mechanical stability, high-temperature stability and substrate adhesion of electrode are improved, suitable for flexible organic electroluminescence diode, flexible solar cell, flexible touch screen and flexible sensor and other nanometer film devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic technology, and relates to a flexible transparent electrode for nanofilm devices, particularly a silver nanowire flexible transparent electrode with dispersant-controlled mesh structure assembly and mechanical pressure-induced welding, and its preparation method. Background Technology

[0002] With the rapid development of the flexible electronic device industry and materials science, high-performance and high-stability transparent conductive electrode materials have become key basic materials in emerging fields such as flexible displays, flexible lighting, wearable electronics and electronic skin. Their performance directly determines the photoelectric conversion efficiency, mechanical flexibility and long-term stability of the above devices.

[0003] Traditional indium tin oxide (ITO) transparent conductive electrodes, while possessing excellent conductivity and light transmittance, suffer from poor flexibility, brittleness, and low bending cycle stability. Furthermore, the scarcity and high cost of indium resources make it difficult to meet the long-term reliability requirements of electrode materials in flexible electronic devices. Among numerous alternative materials, silver nanowires (AgNWs) exhibit a theoretical conductivity as high as 3 × 10⁻⁶. 5 With a silver transmittance (S / cm) several times that of existing carbon-based transparent electrodes, and thanks to its abundant silver reserves, high optical transmittance, and environmental friendliness, it is considered one of the flexible transparent conductive electrode systems with great research value and application prospects.

[0004] However, silver nanowire electrodes still face many technical challenges, such as high network contact resistance due to random stacking of silver nanowires, easy breakage of nodes during bending, and peeling due to weak adhesion between silver nanowires and the substrate. To address these issues, existing technologies mainly employ direct spin-coating of silver nanowire dispersions. However, the randomly stacked silver nanowire network structure struggles to form effective conductive pathways, often requiring additional high-temperature sintering or chemical treatment to improve interconnection, increasing fabrication costs and process complexity.

[0005] CN 104134484A proposes a structure of silver nanowire network + nanoparticle filling + optical adhesive coating. It improves flatness and stability by embedding some silver nanowires into optical adhesive and bridging with nanoparticles, but it does not achieve mesh-like control, so its conductivity optimization is limited, and it lacks system stability research under harsh conditions such as high temperature, large area uniformity and high cyclic bending. CN 102087886A enhances the bonding between silver nanowires and substrate through organic polymer adhesion layer, but it only relies on macroscopic adhesion and does not perform microscopic welding of nodes or network structure optimization. Therefore, it is still easy to break when bent and has insufficient mechanical strength.

[0006] Regarding the control of the mesh-like structure, CN 113383398A improved the dispersibility of silver nanowires by adding a dispersant and used first and second external coating matrices to coat the nanostructure to improve the flatness and contact resistance of the film. However, this approach only achieved passive coating and did not perform mesh-like orthogonal control of the silver nanowire arrangement, resulting in a high sheet resistance of the electrode. Although Sun, Y., et al. (Flexible High-Performance and Solution-Processed Organic Photovoltaics with Robust Mechanical Stability). Advanced Functional Materials , 2021, 31(16): 2010000.)A flexible transparent electrode with both high photoelectric conversion efficiency and excellent mechanical stability was obtained by introducing anionic polyelectrolyte PSSNa. However, the surface roughness of the prepared film is large (>30nm), which cannot meet the stringent requirements of flexible OLED devices for electrode flatness (<10nm). Summary of the Invention

[0007] The purpose of this invention is to provide a flexible transparent electrode with a mesh-like structure of silver nanowires and its preparation method. By controlling the distribution and assembly behavior of silver nanowires during the film formation process through a dispersant, and combining it with mechanical pressure-induced nano-welding, the comprehensive performance optimization of the flexible transparent electrode is achieved, including low sheet resistance, high light transmittance, low roughness, and high mechanical stability.

[0008] To achieve the above objectives, this invention first provides a method for preparing a smooth, strong, and highly adhesive flexible transparent silver nanowire electrode by using anionic polyelectrolytes or zwitterionic surfactants as dispersants to regulate a quasi-mesh structure combined with mechanical pressure-induced nanowelding. Charge regulation is achieved through the electrostatic adsorption between the dispersant and the surface of the silver nanowires, causing the silver nanowires to form a quasi-mesh orthogonal network structure on the surface of a PET substrate. Combined with mechanical pressure-induced nanowelding technology, the contact points of the silver nanowires undergo plastic deformation and embed into the substrate. Based on the synergistic effect of the dispersant and mechanical pressure, the surface roughness and contact resistance of the electrode are significantly reduced, improving the electrode's mechanical stability, high-temperature stability, and substrate adhesion.

[0009] Specifically, the method for preparing the mesh-like silver nanowire flexible transparent electrode of the present invention includes:

[0010] S1: An anionic polyelectrolyte or amphoteric surfactant is added to the silver nanowire dispersion and mixed evenly to obtain a composite solution.

[0011] S2: The composite solution is coated onto a PET substrate and then annealed to obtain a silver nanowire network film with a mesh-like structure.

[0012] S3: Apply mechanical pressure to the silver nanowire network film to cause local plastic deformation at the intersection of the silver nanowires and form a nano-welding interface. At the same time, the silver nanowire network is partially embedded in the surface of the PET substrate to form a mesh-like flexible transparent silver nanowire electrode.

[0013] In the preparation method of the present invention, the anionic polyelectrolyte is preferably sodium polystyrene sulfonate (PSSNa), and the zwitterionic surfactant is preferably 3-[(3-cholamidopropyl)dimethylamino]propanesulfonic acid inner salt (CHAPS).

[0014] In the preparation method of this invention, the length of the silver nanowires is preferably 5-100 μm, and the diameter is preferably 20-100 nm.

[0015] More specifically, the silver nanowire dispersion can be obtained by dispersing in water, isopropanol, ethanol or a mixture thereof as a dispersion medium, and the concentration of the dispersion is preferably 1.0 to 2.0 mg / mL.

[0016] In the preparation method of the present invention, the coating of the composite solution can be carried out by solution film formation method, including but not limited to spin coating, drop coating, spray coating, blade coating or slot coating.

[0017] More specifically, the present invention preferably employs spin coating to coat the composite solution. Furthermore, the preferred spin coating speed is 1500–3500 rpm. It should be understood that the choice of the above coating method does not affect the essence of the technical solution of the present invention, and those skilled in the art can select an appropriate coating method based on the substrate size, the properties of the composite solution, and mass production requirements.

[0018] Furthermore, after the composite solution is uniformly coated on the surface of the PET substrate, it is preferably annealed at 100-150°C to evaporate the solvent and form a silver nanowire network film. The annealing time is preferably 5-20 minutes.

[0019] In the preparation method of this invention, the pressure applied during the mechanical pressure treatment is preferably 10–50 MPa, more preferably 20 MPa, and the holding time is preferably 5–30 s, more preferably 15 s. This pressure can achieve physical compaction and embedding of the silver nanowire network, forming a flexible transparent electrode with good nano-welding.

[0020] More specifically, the mechanical pressure treatment can be carried out using a hydraulic press, a pneumatic press, or a precision tablet press, with the surface of the pressure plate being a mirror-polished metal plate to avoid introducing additional roughness.

[0021] Furthermore, the preparation method of the present invention also includes surface pretreatment of the PET substrate, specifically by ultrasonically cleaning the PET substrate sequentially with deionized water, acetone and isopropanol and then drying it, followed by ultraviolet-ozone treatment for 5 to 15 minutes, so that the PET surface forms abundant oxygen-containing functional groups, thereby enhancing the interfacial interaction between the silver nanowire network and the substrate.

[0022] Secondly, the present invention also provides a quasi-grid silver nanowire flexible transparent electrode prepared by the above method, comprising a PET substrate and a silver nanowire conductive network loaded thereon. The silver nanowire conductive network has a quasi-grid orthogonal arrangement structure, and the silver nanowire intersections have nano-welding interfaces formed by mechanical pressure treatment. The quasi-grid orthogonal arrangement structure is formed by the self-assembly of silver nanowires induced by anionic polyelectrolytes or zwitterionic surfactant dispersants through electrostatic adsorption.

[0023] The flexible transparent silver nanowire electrode described in this invention has excellent comprehensive optoelectronic properties, with a sheet resistance of less than 15 Ω / sq, a transmittance of more than 90% at a wavelength of 550 nm, a quality factor (FOM) of more than 380, and a surface roughness (RMS) of less than 10 nm.

[0024] The present invention also provides the application of the aforementioned mesh-like silver nanowire flexible transparent electrode as an anode material in the fabrication of nanofilm devices, including but not limited to flexible organic light-emitting diodes, flexible solar cells, flexible touch screens, or flexible sensors.

[0025] Compared with the prior art, the present invention has the following outstanding advantages:

[0026] This invention utilizes anionic polyelectrolytes or zwitterionic surfactants as dispersants. The electrostatic adsorption between the dispersant and the surface of silver nanowires regulates the alignment behavior of the silver nanowires during film formation, forming a near-grid-like orthogonal conductive network with an angle close to 90°, distinct from the traditional randomly overlapping network. This structure not only effectively reduces the number of intersections between silver nanowires but also increases the continuity of parallel conductive pathways, significantly reducing the overall contact resistance of the conductive network from a geometric perspective and improving charge transport efficiency.

[0027] This invention utilizes a synergistic approach combining electrostatically regulated self-assembly and pressure-induced nanowelding. First, silver nanowires are guided to form an ordered mesh framework. Then, mechanical pressure induces metallurgical-bonded plastic deformation at the mesh nodes, creating a stable nanowelding interface and further reducing node resistance. Simultaneously, the entire network is pressed into a PET substrate, achieving physical anchoring. This synergistic strategy resolves the contradictions inherent in single methods regarding conductivity, roughness, and adhesion, reducing the surface roughness of the flexible transparent electrode to below 10 nm.

[0028] The flexible transparent silver nanowire electrode prepared by this invention not only achieves ultra-low sheet resistance, high transmittance, extremely high quality factor, and extremely low surface roughness, but also reduces the number of weak nodes due to the mesh-like structure. The metallurgical bonding and physical riveting effect formed by pressure welding greatly enhance the connection strength between silver nanowires and the interfacial bonding force between the conductive network and the PET substrate. This enables the flexible transparent electrode to exhibit excellent stability under application scenarios such as repeated bending, high temperature heating, and mechanical peeling, and comprehensively overcomes the reliability problem of flexible transparent silver nanowire electrodes in practical use.

[0029] Experiments have shown that the flexible OLED device based on the silver nanowire flexible transparent electrode of this invention is significantly superior to the traditional ITO device in terms of luminous efficiency, large area uniformity and bending durability, which fully demonstrates its feasibility in replacing ITO and realizing commercial application. Attached Figure Description

[0030] Figure 1 These are atomic force microscopy (AFM) images of the surface morphology of AgNWs, Pressing-AgNWs, and PP-AgNWs flexible transparent electrodes prepared in Examples 1 and Comparative Examples 1-2.

[0031] Figure 2 These are scanning electron microscope (SEM) images of the surface morphology of AgNWs, Pressing-AgNWs, and PP-AgNWs flexible transparent electrodes prepared in Examples 1 and Comparative Examples 1-2.

[0032] Figure 3 The images show the SEM surface morphology of the flexible transparent electrodes (ITO, AgNWs, Pressing-AgNWs, and PP-AgNWs) prepared in Examples 1 and Comparative Examples 1-3 after 1000 bending cycles (R=3mm).

[0033] Figure 4 This is an AFM surface morphology image of the PC-AgNWs flexible transparent electrode prepared in Example 2.

[0034] Figure 5 This is a SEM image of the surface morphology of the PC-AgNWs flexible transparent electrode prepared in Example 2.

[0035] Figure 6 This is a photograph of a green phosphorescent flexible OLED device prepared using PP-AgNWs as the anode in Example 1.

[0036] Figure 7 yes Figure 6 Brightness-voltage-current density (LVJ) characteristic curves of green phosphorescent flexible OLED devices.

[0037] Figure 8 yes Figure 6 External quantum efficiency-voltage (EQE-V) characteristic curve of green phosphorescent flexible OLED device.

[0038] Figure 9 This is a photograph of a green phosphorescent flexible OLED device fabricated using PC-AgNWs as the anode in Example 2.

[0039] Figure 10 yes Figure 9 LVJ characteristic curve of green phosphorescent flexible OLED device.

[0040] Figure 11 yes Figure 9 EQE-V characteristic curve of green phosphorescent flexible OLED device. Implementation

[0041] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and specific examples. It should be noted that the embodiments are merely illustrative and are intended to provide a thorough understanding of the technical solutions of the present invention and to provide guidance for those skilled in the art to implement and apply the present invention. It should be understood that these descriptions do not constitute any limitation on the scope of protection of the present invention.

[0042] Unless otherwise expressly stated, the production processes, experiments, tests or analysis methods involved in the embodiments of the present invention are all considered to be conventional methods known to those skilled in the art, and only need to be implemented in accordance with conventional conditions or relevant product instructions. The steps and names involved are also generally clear and unambiguous in the art.

[0043] The instruments, equipment, raw materials, reagents, or samples used in the embodiments are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels or prepared by known methods, and their source does not have a substantial impact on the implementation results of the present invention.

[0044] Unless otherwise expressly defined, the scientific and technical terms used in this invention have the meanings commonly understood by one of ordinary skill in the art. In case of any conflict, the definitions in this specification shall prevail.

[0045] The terms “comprising,” “including,” “having,” etc., used in this invention should be understood as open-ended, meaning “including but not limited to.” The term “and / or” includes any and all combinations of one or more of the associated listed items. Quantitative terms such as “a,” “one,” etc., do not exclude multiples; “multiple” or “a variety” refers to quantities greater than or equal to two.

[0046] This invention relates to the description of numerical parameters (such as quantity, concentration, temperature, time, etc.), and it should be understood that reasonable deviations naturally exist due to measuring instruments, operational errors, statistical fluctuations, etc. The range of such deviations should be within limits acceptable to those skilled in the art based on common sense.

[0047] The key to this invention is to transform the random overlapping of silver nanowires during film formation into a grid-like orthogonal arrangement through the electrostatic regulation effect of the dispersant. This reduces the number of nodes and increases the continuity of parallel conductive pathways in terms of geometry. Then, through mechanical pressure welding, local plastic deformation occurs at the intersection nodes of the silver nanowires to form a metallurgical bonding interface. The conductive network is then pressed into the PET surface to achieve physical anchoring, thereby simultaneously solving the three major problems of contact resistance, surface roughness, and interface adhesion.

[0048] Based on the above ideas, the present invention provides the following specific implementation schemes.

[0049] PET substrates require cleaning and surface activation treatment before use. The PET film is ultrasonically cleaned sequentially in deionized water, acetone, and isopropanol, then dried, and subsequently treated with ultraviolet-ozone irradiation to generate polar oxygen-containing functional groups on the substrate surface, thereby enhancing interfacial bonding with the subsequent conductive network. The above cleaning and activation treatments are standard procedures in this field, and specific process parameters can be adjusted appropriately according to the substrate material and size.

[0050] Anionic polyelectrolytes or zwitterionic surfactants are added as dispersants to the silver nanowire dispersion. After thorough mixing, the mixture is allowed to stand and react, allowing the dispersant molecules to fully adsorb onto the surface of the silver nanowires, forming a composite solution. Through the electrostatic adsorption of the anionic polyelectrolytes or zwitterionic surfactants onto the surface of the silver nanowires, the surface charge state of the silver nanowires in the dispersion is altered, causing them to spontaneously align orthogonally rather than randomly overlap during the coating process. This is a crucial prerequisite for achieving a mesh-like structure. Those skilled in the art can select an appropriate amount of dispersant based on the desired mesh regularity.

[0051] The composite solution described above was coated onto the surface of a PET substrate using a solution film-forming method, and then annealed at a set temperature to allow the solvent to evaporate and form a mesh-like conductive network of silver nanowires. The annealing temperature and time can be controlled based on the thermal stability of the dispersant.

[0052] The annealed silver nanowire network film is placed between two mirror-polished metal plates, and mechanical pressure is applied and held for a certain period of time. This pressure treatment achieves three functions simultaneously: localized plastic deformation occurs at the intersections, forming a nano-welding interface and reducing contact resistance; the conductive network portion is pressed into the PET surface, forming a physical anchor and enhancing interfacial adhesion; and the network protrusions are flattened, reducing surface roughness. The pressure magnitude and holding time can be selected synergistically based on the silver nanowire diameter, network density, and substrate hardness.

[0053] The aforementioned mesh-like silver nanowire flexible transparent electrode can be directly used as the anode material for nanofilm devices. Taking a flexible organic light-emitting diode (OLED) as an example, after patterning the electrode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a metal cathode are sequentially deposited to construct a complete flexible OLED device. The material selection and thickness design of each functional layer can be adapted according to the device structure, and those skilled in the art should not be limited to the specific materials listed in the embodiments. Furthermore, this electrode is also suitable for other nanofilm devices requiring transparent conductive electrodes, such as flexible solar cells, flexible touchscreens, and flexible sensors.

[0054] The specific process parameters for each step in the above preparation process description, including dispersant concentration, spin coating speed, annealing temperature and time, pressure and holding time, are only for reference by those skilled in the art when carrying out specific implementations, and should not be construed as limiting the present invention.

[0055] The following embodiments of the present invention provide a detailed description of the above-described solution. In these embodiments, AFM and SEM were used to characterize the electrode surface morphology and microstructure. The stability of the electrodes was verified through bending tests, high-temperature heating, and tape peeling. The practical application effect of the electrodes was verified through photoelectric performance testing of OLED devices. The accompanying drawings in each embodiment correspond to the respective characterization results and device performance data. Example

[0056] Example 1: Preparation of flexible transparent silver nanowire electrode (PP-AgNWs) treated with sodium poly4-styrene sulfonate (PSSNa)

[0057] After gently wiping the PET substrate in one direction with a lint-free cotton ball soaked in a special cleaning agent, rinse it with deionized water, and then ultrasonically clean it in deionized water, acetone and isopropanol for 20 minutes each. Transfer it to a constant temperature oven and dry it at 60°C until there are no residues on the surface.

[0058] The dried PET substrate was placed in a UV ozone cleaner and irradiated with UV lamps for 10 minutes to perform surface activation treatment, thereby increasing the surface energy of the substrate and improving the adhesion and spreadability of the subsequent silver nanowire film.

[0059] Weigh sodium polystyrene sulfonate (PSSNa, Mw approximately 70,000) into deionized water, stir magnetically until completely dissolved, and prepare a 10 mg / mL PSSNa aqueous solution.

[0060] Add 60 μL of the above PSSNa solution to 1 mL of silver nanowire isopropanol dispersion with a concentration of 1.9 mg / mL, sonicate for 10 s, and let stand to allow PSSNa to be fully adsorbed on the surface of silver nanowires, thus obtaining PSSNa@AgNWs composite solution.

[0061] The above PSSNa@AgNWs composite solution was dropped onto the treated PET substrate and spin-coated at 1500 rpm for 30 s. Then, it was placed on a hot plate at 120°C for annealing for 10 min to remove the solvent and enhance the interfacial bonding, resulting in a silver nanowire network film with a mesh-like structure and good dispersion.

[0062] The above-mentioned silver nanowire network film was placed between two mirror-polished metal plates, and a mechanical pressure of 20 MPa was applied in a hydraulic press for 15 seconds. After the pressure was released, the film was removed, and a flexible transparent electrode film of Pressing PSSNa@silver nanowires (PP-AgNWs) with good nano-welding was obtained.

[0063] The PP-AgNWs flexible transparent electrode film prepared above has excellent photoelectric properties.

[0064] The sheet resistance of the flexible transparent electrode film was measured to be 12.4 Ω sq using a four-probe tester. -1 The UV-Vis spectrophotometer recorded that the transmittance of the thin film at a wavelength of 550 nm was 91.8%. Based on this, the quality factor (FOM) of the flexible transparent electrode film was calculated to be 388.78, indicating that the film achieved a good balance between conductivity and transmittance.

[0065] Furthermore, regarding 4×4cm 2 Shear resistance was measured at multiple points within a large-area flexible transparent electrode film, with a standard deviation of 1.66 Ω sq. -1 This indicates that the large-area electrode film has good uniformity.

[0066] The surface roughness of the flexible transparent electrode film was measured using atomic force microscopy. Figure 1 AFM images showed that the silver nanowires were arranged in a mesh-like pattern on the substrate, with a uniform distribution and a smooth surface; the root mean square roughness (RMS) was 7.22 nm. The microstructure of the flexible transparent electrode film was then observed under a scanning electron microscope. Figure 2 SEM images showed that the silver nanowires formed a uniform orthogonal mesh structure. The nodes were tightly connected after being mechanically pressure welded and underwent plastic deformation, exhibiting a fused welded morphology, with no obvious cracks or gaps observed.

[0067] A flexible transparent electrode film was fixed on a bending test platform with a bending radius of 3 mm. After 1000 repeated bending cycles, the resistivity change rate DR / R0 of the film was measured to be only 0.07. The microstructure of the flexible transparent electrode film was observed again after 1000 bending cycles. Figure 3 SEM images show that the silver nanowire network remains intact and continuous after bending, with no obvious cracks or node breakage.

[0068] The flexible transparent electrode film was heated on a 150°C hot stage, and the sheet resistance was measured at regular intervals. The results showed that the film resistance remained almost unchanged after 6 hours of heating.

[0069] 3M tape was applied to the surface of a flexible transparent electrode film, uniform pressure was applied, and then the film was peeled off. This process was repeated a certain number of times, and the sheet resistance change was measured afterward. The results showed that the film resistance increased by only 0.13 times after 20 peels.

[0070] Example 2: Preparation of flexible transparent silver nanowire electrodes (PC-AgNWs) treated with 3-[(3-cholamidopropyl)dimethylamino]propanesulfonic acid inner salt (CHAPS)

[0071] The PET substrate was cleaned and pretreated with UV-ozone activation according to the method in Example 1.

[0072] Weigh 8 mg of CHAPS powder and add it to 2 mL of deionized water. Stir gently at room temperature until completely dissolved to obtain a 4 mg / mL CHAPS aqueous solution.

[0073] Take 1 mL of a 1.9 mg / mL aqueous dispersion of silver nanowires, add 100 μL of the above CHAPS solution, shake to mix evenly, and let stand at room temperature for 4 h to obtain a CHAPS@AgNWs composite solution.

[0074] 60 μL of the above CHAPS@AgNWs composite solution was dropped onto the treated PET substrate and spin-coated at 2000 rpm for 30 s. Then, it was placed on a hot plate at 120 °C for annealing for 15 min to remove the solvent and enhance the interfacial bonding, resulting in a silver nanowire network film with good dispersion and a mesh-like structure.

[0075] The above-mentioned silver nanowire network film was placed between two mirror-polished metal plates, and a mechanical pressure of 20 MPa was applied in a hydraulic press for 15 seconds. After the pressure was released, the film was removed, and a flexible transparent electrode film with well-welded Pressing CHAPS@silver nanowires (PC-AgNWs) was prepared.

[0076] The performance of the PC-AgNWs electrode was tested according to the test method in Example 1. The results showed that the sheet resistance of the electrode was 12.2 Ω / sq, the transmittance at 550 nm was 91.3%, and the calculated FOM value was 414.7.

[0077] and then, Figure 4 The AFM characterization results show that its surface RMS is 9.0 nm. Figure 5 The SEM images also confirmed that the silver nanowires formed a regular mesh structure and well-welded nodes.

[0078] Stability test results show that the PC-AgNWs electrode performs essentially the same as in Example 1 in stability tests involving bending, high temperature, and mechanical glass. Of particular note is that after placing the PC-AgNWs electrode in anhydrous ethanol and treating it with ultrasound at 40 kHz and 100 W for 30 minutes, its resistance showed only a slight change, indicating that this electrode has outstanding resistance to solvent-resistant ultrasound.

[0079] Comparative Example 1: Preparation of untreated pure silver nanowire flexible transparent electrodes (AgNWs)

[0080] The PET substrate was cleaned and pretreated with UV-ozone activation according to the method in Example 1.

[0081] Using only a 1.9 mg / mL aqueous dispersion of silver nanowires without adding any dispersant, after sonication for 10 seconds, the nanowires were directly spin-coated onto a PET substrate according to the method in Example 1 and then annealed without mechanical pressure treatment to obtain pure silver nanowire flexible transparent electrodes (AgNWs).

[0082] The performance was tested according to the test method in Example 1. The sheet resistance of the AgNWs electrode was 19.825 Ω / sq, the transmittance at 550 nm was 94.5%, and its FOM value was calculated to be only 211.82.

[0083] Figure 1 The AFM characterization results showed that the surface RMS of the AgNWs electrode reached 31.4 nm, which is much higher than the 7.22 nm surface RMS of the PP-AgNWs electrode. Figure 2 The results show that, compared with the PP-AgNWs electrode, the AgNWs electrode does not have a significant mesh structure.

[0084] After bending the AgNWs electrode 1000 times, its sheet resistance was measured again, and it remained essentially unchanged. Figure 3 It can also be seen that the corresponding surface morphology changes are very small. This result fully demonstrates that AgNWs electrodes can effectively maintain the integrity of their internal structure and conductivity when subjected to mechanical bending.

[0085] However, when the AgNWs electrode was heated at 150°C for 6 hours and its resistance was measured again, it showed a significant increase (DR / R0 > 35%), and after being peeled off 20 times with 3M tape, the silver nanowires were basically peeled off.

[0086] The above test results are consistent with existing reports on silver nanowire electrodes, namely that silver nanowire films without effective composite regulation or protection treatment usually have significant shortcomings in mechanical durability and adhesion.

[0087] Comparative Example 2: Fabrication of Flexible Transparent Silver Nanowire Electrodes Treated Only by Mechanical Pressure (Pressing AgNWs)

[0088] The PET substrate was cleaned and pretreated with UV-ozone activation according to the method in Example 1.

[0089] Using only a 1.9 mg / mL aqueous dispersion of silver nanowires without adding any dispersant, after sonication for 10 seconds, the nanowires were directly spin-coated onto a PET substrate according to the method in Example 1 and then annealed. Finally, they were subjected to mechanical pressure treatment according to the method in Example 1 to obtain mechanically pressure-treated silver nanowire flexible transparent electrodes (Pressing AgNWs).

[0090] The performance was tested according to the method in Example 1. The sheet resistance of the Pressing AgNWs electrode was 24.4 Ω / sq, the transmittance at 550 nm was 91.8%, and its FOM value was calculated to be 212, which is significantly lower than that of the PP-AgNWs electrode in Example 1.

[0091] Figure 1 AFM characterization results showed that, compared to AgNWs electrodes, the surface RMS of the Pressing AgNWs electrode decreased to 12.01 nm, but was still higher than that of the PP-AgNWs electrode; and its 4×4 cm 2 The standard deviation of the resistance of the large-area electrode is 5.33 Ωsq. -1 All were significantly higher than the PP-AgNWs electrode of Example 1, which is consistent with Figure 2 It exhibits a relatively poor mesh structure. However, thanks to the good flexibility of silver nanowires, after being bent 1000 times, Figure 3 The SEM images of the Pressing AgNWs electrodes did not show significant changes.

[0092] The test results above show that although pressure treatment alone can improve the conductivity of the electrode, it is still inferior to the synergistic solution of "dispersant regulation + pressure welding" in terms of uniformity and overall performance.

[0093] Comparative Example 3: Commercial ITO Flexible Transparent Electrode

[0094] Using a commercially available ITO flexible transparent electrode as a control electrode, from Figure 3 As can be seen, after being bent 1000 times with a bending radius of 3mm, the electrode suffered severe mechanical damage.

[0095] Meanwhile, the conductivity of the ITO electrode showed a significant decline after approximately 500 bends, with DR / R0 > 1850%. Furthermore, after 1000 bends, its conductivity deteriorated further, with DR / R0 > 2680%. Consequently, the brightness retention of green and red flexible OLED devices based on ITO electrodes was only 40.6% and 40%, respectively, after 1200 bends.

[0096] Public information shows that although ITO is widely used in the field of transparent conductivity, it is prone to brittleness in flexible devices, and its bending reliability is generally not as good as that of silver nanowire network electrodes.

[0097] Application Example 1: Fabrication of a green phosphorescent OLED device based on PP-AgNWs flexible transparent electrode film

[0098] Using the PP-AgNWs flexible transparent electrode film prepared in Example 1 as the anode, a green flexible phosphorescent OLED device was prepared. The device structure is: PET / PP-AgNWs / MoO3 (3nm) / TAPC (100nm) / TCTA:Bepp2 (1:1, 20nm) :6wt% Ir(ppy)3 / TPBi (45nm) / LiF (1nm) / Al (100nm).

[0099] A patterned PP-AgNWs flexible transparent electrode film with an effective light-emitting area of ​​3mm×3mm was sequentially ultrasonically cleaned with deionized water, acetone, and isopropanol, dried with nitrogen, and then transferred to a high-vacuum multi-source organic evaporation system. The process was continued until the cavity vacuum level was below 5×10⁻⁶. -4 At Pa, each functional layer is sequentially thermally vapor-deposited. During the vapor deposition process, the deposition rate is controlled by a quartz crystal film thickness monitor. The deposition rate of MoO3 and organic materials is controlled at 0.5–1 Å / s, LiF at 0.1 Å / s, and Al electrode at 3–6 Å / s.

[0100] To comprehensively evaluate the performance advantages of PP-AgNWs electrodes, green phosphorescent OLED devices with the same structure based on PressingAgNWs electrodes in Comparative Example 2 and commercial ITO electrodes in Comparative Example 3 were also fabricated as comparisons.

[0101] The optoelectronic performance of the device was characterized using a combined testing system of a Keithley 2400 digital source meter, a BM-7A luminance colorimeter, and a PR655 spectroradiometer. The external quantum efficiency (EQE) was calculated from JVL data and electroluminescence spectral data.

[0102] Figure 6 This is a photograph of the green flexible phosphorescent OLED device in its lit state, showing that the device emits light uniformly with no obvious dark areas or brightness differences.

[0103] Figure 7 and Figure 8 The LVJ characteristic curves and external quantum efficiency-voltage (EQE-V) curves of the devices corresponding to the three anodes are given respectively.

[0104] Depend on Figure 7 The LVJ characteristic curves show that, although the three anodes correspond to different device turn-on voltages (brightness = 1 cd / m²), the actual brightness of the device varies. 2 Both devices operate at a voltage of 2.7V, but under the same driving voltage, the device based on PP-AgNWs electrodes exhibits superior brightness and current density compared to the two comparative devices, with a maximum brightness exceeding 14000 cd / m². 2 The maximum luminance of Pressing AgNWs devices and ITO devices is 12020 cd / m², respectively. 2 and 6554cd / m 2 .

[0105] and then, Figure 8 The EQE-V curves show that the maximum external quantum efficiency of the PP-AgNWs device reaches 24.68%, while the maximum external quantum efficiencies of the Pressing AgNWs device and the ITO device are only 19.48% and 19.36%, respectively. Throughout the entire voltage range, the EQE of the PP-AgNWs device is significantly better than that of the two comparative devices.

[0106] The green flexible phosphorescent OLED device fabricated with PP-AgNWs was subjected to 1200 reciprocating bends with a bending radius of 4mm, and its photoelectric performance was tested again. The brightness retention rate was 80.5%. In contrast, the brightness retention rate of the Pressing AgNWs device under the same conditions was approximately 60.3%, and that of the ITO device was only 40.6%, which is significantly lower than that of the green OLED device fabricated with PP-AgNWs flexible transparent electrodes.

[0107] A large-area OLED was fabricated using a mask with an effective luminescent area of ​​25mm×25mm according to the above method. Under a driving voltage of 5V, the PP-AgNWs device emitted light uniformly, and no obvious dark spots were observed.

[0108] Application Example 2: Fabrication of a Red Phosphorescent OLED Device Based on PP-AgNWs Flexible Transparent Electrode Thin Film

[0109] The emitting layer of the OLED device in Application Example 1 was replaced with TCTA:Bepp2 (1:1, 20nm): 4wt% Ir-RD, while other materials remained unchanged. A red flexible phosphorescent OLED device was fabricated, and the photoelectric performance of the device was tested. The device showed that the turn-on voltage was 2.7V, the maximum external quantum efficiency was 26.05%, and the brightness retention rate after 1200 bends was 71.2%.

[0110] Application Example 3: Fabrication of Phosphorescent OLED Devices Based on PC-AgNWs Flexible Transparent Electrode Thin Films

[0111] Using the PC-AgNWs flexible transparent electrode film prepared in Example 2 as the anode, a green flexible phosphorescent OLED device was prepared using the same device structure and preparation process as in Application Example 1. At the same time, a green phosphorescent OLED device with the same structure based on the untreated pure silver nanowire flexible transparent electrode AgNWs in Comparative Example 1 was prepared as a comparison.

[0112] Figure 9 A physical image of the light-emitting device is provided. Figure 10 Furthermore, LVJ characteristic curves are provided. Figure 11 EQE-V curves are provided.

[0113] It can be seen that the device based on PC-AgNWs electrodes has a turn-on voltage of 2.7V and a maximum external quantum efficiency of 20.29%, compared to... Figure 7 and Figure 8 The unmodified silver nanowires significantly improved the turn-on voltage of 2.7V and the maximum external quantum efficiency of 19.48% compared to the control device.

[0114] As can be seen from the above embodiments and comparative examples, this invention regulates the assembly behavior of silver nanowires during film formation using anionic dispersants, constructing a uniformly dispersed and well-connected mesh-like conductive network. Furthermore, the combination of mechanical pressure welding significantly improves the contact state between the cross nodes of the silver nanowires, thereby reducing sheet resistance and enhancing film uniformity, adhesion, mechanical stability, and thermal stability. Compared with AgNWs electrodes, Pressing AgNWs electrodes, and commercially available ITO flexible electrodes, the PP-AgNWs and PC-AgNWs electrodes prepared by this invention exhibit superior overall performance in terms of conductivity, transparency, surface smoothness, bending stability, thermal stability, and device applicability, and can be applied to the fabrication of high-performance flexible phosphorescent OLED devices.

[0115] The flexible transparent silver nanowire electrode and its preparation method provided by this invention can be widely used in fields such as flexible organic light-emitting diodes, flexible solar cells, flexible touch screens, flexible sensors and wearable electronic devices, and have extremely high industrial practical value and broad market prospects.

[0116] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible transparent electrode with a mesh-like structure of silver nanowires, comprising: 1) Anionic polyelectrolytes or amphoteric surfactants are added to the silver nanowire dispersion and mixed evenly to obtain a composite solution. 2) The composite solution is coated onto a PET substrate and annealed to obtain a silver nanowire network film with a mesh-like structure; 3) Apply mechanical pressure to the silver nanowire network film to cause local plastic deformation at the intersection of silver nanowires and form a nano-welding interface. At the same time, the silver nanowire network is partially embedded in the surface of the PET substrate to form a mesh-like flexible transparent silver nanowire electrode.

2. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The anionic polyelectrolyte is sodium polystyrene sulfonate, and the amphoteric surfactant is 3-[(3-cholamidopropyl)dimethylamino]propanesulfonic acid inner salt.

3. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The silver nanowires have a length of 5–100 μm and a diameter of 20–100 nm.

4. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The silver nanowire dispersion uses water, isopropanol, ethanol, or a mixture thereof as the dispersion medium, and the dispersion concentration is 1.0–2.0 mg / mL.

5. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The composite solution was coated onto the surface of a PET substrate using a solution film-forming method.

6. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The annealing temperature is 100-150℃, and the annealing time is 5-20 minutes.

7. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: The mechanical pressure is 10–50 MPa, and the pressure holding time is 5–30 seconds.

8. The method for preparing the flexible transparent electrode with a mesh-like silver nanowire according to claim 1, characterized in that: It also includes surface pretreatment of the PET substrate, which involves ultrasonically cleaning the PET substrate sequentially with deionized water, acetone and isopropanol, drying it, and then treating it with ultraviolet-ozone for 5 to 15 minutes.

9. A flexible transparent electrode with a mesh-like structure of silver nanowires prepared by the method of claim 1, comprising a PET substrate and a conductive network of silver nanowires loaded thereon, wherein the conductive network of silver nanowires has a mesh-like orthogonal arrangement structure and the intersections of the silver nanowires have nano-welded interfaces formed by mechanical pressure treatment, wherein the mesh-like orthogonal arrangement structure is formed by the self-assembly of silver nanowires induced by anionic polyelectrolytes or zwitterionic surfactant dispersants through electrostatic adsorption.

10. The application of the mesh-like silver nanowire flexible transparent electrode of claim 9 in the fabrication of nanofilm devices.

Images