Metal mesh flexible transparent conductive film, method for preparing same and use thereof

Abstract

The application discloses a metal grid flexible transparent conductive film and a preparation method and application thereof, and comprises a flexible substrate and a sputtered metal grid, wherein the metal grid forms various required patterns on the flexible substrate. The application adopts a magnetron sputtering method to accurately control the thickness of the metal grid layer by controlling the deposition time, thereby preparing the flexible transparent conductive film with good quality, high transmittance, high conductivity and high bending resistance, which can be used as a flexible transparent electrode material with excellent properties, can meet the requirements of a flexible display screen or a flexible electronic, and the preparation process is simple, safe and non-toxic, and can conveniently prepare a large-area metal grid.

Description

Technical Field

[0001] This invention belongs to the field of metal thin film technology, and more specifically, relates to a flexible transparent conductive metal mesh film, its preparation method, and its application. Background Technology

[0002] Transparent electrodes (TEs) play a crucial role in many modern devices, including solar cells, light-emitting diodes (LEDs), touchscreens, wearable electronics, and transparent heaters. For a long time, the field of transparent electrodes has been dominated by transparent conductive oxides (TCOs). In the early 1950s, wide-bandgap semiconductor materials with high optical transparency, such as SnO2 and In2O3, were reported, and their conductivity could be enhanced through impurity doping. After more than 60 years of extensive research, indium tin oxide (ITO) films emerged as a representative transparent electrode material with excellent optical and electronic properties and have been widely commercialized. However, in recent years, the demand for flexibility, stretchability, and foldability in flexible electronic devices has increased significantly. ITO is not only limited in production by the severe shortage of indium resources, but also suffers from poor mechanical flexibility, making it prone to cracking under strain or bending. Although there are ITO / PET substrates available on the market for use in flexible optoelectronic devices, the brittleness of ITO and its insufficient bending strain tolerance and cyclic fatigue resistance on flexible substrates make it difficult for flexible ITO / PET substrates to be practically applied in stretchable, foldable, or bendable optoelectronic devices.

[0003] Therefore, the search for new materials with higher performance and additional properties has become one of the most popular research topics. New materials need to possess better flexibility and stability, more abundant and available raw materials, and lower processing costs. Based on this goal, some emerging transparent conductive materials have emerged as alternatives to traditional ITO, mainly including three categories: i) carbon nanomaterials, such as carbon nanotubes (CNTs) or graphene; ii) conductive polymers (such as PEDOT:PSS); and iii) metal nanomaterials, such as metal nanofilms, metal nanowire networks, and metal meshes. These materials have been extensively studied and have proven to have high potential in overcoming the shortcomings of ITO. Among all the emerging materials that replace ITO, metal nanomaterials exhibit higher optical and electrical properties than carbon nanomaterials (such as graphene or carbon nanotubes). Furthermore, metal nanomaterials have attracted widespread attention due to their significant additional advantages, such as good mechanical properties (e.g., good flexibility and tensile strength), low cost, ease of fabrication, flexibility, and wide applicability.

[0004] In metallic mesh nanomaterials, the commonly used methods for fabricating metallic meshes are based on photolithography techniques, such as optical lithography and nanoimprint lithography. Photolithography can precisely control the mesh pattern, but optical lithography has a relatively large linewidth, which easily causes Murray interference, limiting its application in high-resolution smartphones, tablets, and other products. Nanoimprint lithography, another technique, can reduce the linewidth, but it requires the simultaneous use of electron beam etching or focused ion beam etching, or electron beam evaporation, increasing fabrication time and cost.

[0005] Other methods for fabricating metal meshes include templated electrodeposition and imprint transfer processes. By embedding metal meshes within polymer molecules, high-performance transparent metal mesh electrodes with excellent surface smoothness can be obtained. However, such processes typically involve complex multiple transfer and stripping steps, which can lead to reduced cost-effectiveness in large-scale manufacturing and may present issues with process repeatability and uniformity.

[0006] As the use of ITO in the transparent electrode market declines, the fabrication technology of metal meshes and other ITO alternatives is expected to continue to grow. Due to the high tunability of its microstructure, metal meshes can exhibit better optical and electrical properties than ITO films, and compared with other metal materials (such as ultrathin metal films), optical transmittance and conductivity can be optimized individually, achieving an optimal balance between optical and electrical properties.

[0007] However, metal meshes still face some challenges: 1) the relative trade-off between transparency and conductivity needs to be addressed in a simpler way during fabrication; 2) the fabrication process still needs improvement, including reducing costs and increasing pattern accuracy. Therefore, how to solve these problems and improve the overall performance of flexible transparent conductive films made from metal meshes, thereby expanding their applications, has become a hot research topic. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a flexible transparent conductive film with a metal mesh, its preparation method, and its application. The conductive film of this invention exhibits optimal transparency and conductivity, and is particularly suitable for use in stretchable, foldable, or bendable optoelectronic devices.

[0009] Specifically, the present invention provides the following technical solution:

[0010] A flexible transparent conductive film with a metal mesh, the film comprising a flexible substrate and a sputtered metal mesh, the metal mesh being formed on the flexible substrate in various desired patterns.

[0011] In one embodiment of the present invention, the flexible substrate is selected from soft PET substrate, CPI substrate, or flexible ultrathin glass. PET substrate has high visible light transmittance and strong bending resistance, making it a high-performance transparent electrode substrate material.

[0012] In one embodiment of the present invention, the metal mesh is an Ag metal mesh. Studies have found that Ag metal has strong conductivity, enabling the fabrication of electrodes with extremely low sheet resistance, and its high ductility makes it suitable for fabricating high-performance flexible mesh electrodes.

[0013] In one embodiment of the present invention, the metal mesh is formed on a flexible substrate using different mesh patterns such as square metal mesh, triangular metal mesh, brick wall-shaped metal mesh, honeycomb metal mesh, and circular metal mesh. Different geometric shapes of the metal mesh can serve as important factors in controlling the balance between conductivity and transparency.

[0014] In one embodiment of the present invention, the thickness of the metal mesh is 50 nm to 600 nm.

[0015] For example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 500nm or 600nm.

[0016] In one embodiment of the present invention, the metal linewidth of the metal mesh is 1μm to 50μm, preferably 5μm to 30μm.

[0017] For example, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm.

[0018] In one embodiment of the present invention, the size and area of ​​the metal mesh ranges from 2cm×2cm to 20cm×20cm.

[0019] In one embodiment of the present invention, the sheet resistance of the flexible transparent conductive film with metal mesh is 4 to 10 Ωsq. -1 .

[0020] In one embodiment of the present invention, the light transmittance of the metal mesh at 550 nm reaches more than 90%, specifically, it can reach more than 92%, and even more specifically, it can reach more than 93.5%.

[0021] In one embodiment of the present invention, the overall light transmittance of the metal mesh flexible transparent conductive film at 550nm reaches more than 80%, specifically, it can reach more than 82%.

[0022] According to another aspect of the present invention, a method for preparing a flexible transparent conductive film with a metal mesh is also provided, comprising the following steps:

[0023] S1. Prepare a polymer template and cut out the desired hollow stripe pattern from the center of the polymer template;

[0024] S2. Prepare a flexible substrate, attach it tightly to the substrate to form a flexible substrate / substrate combination, and fix the polymer template prepared in step S1 onto the flexible substrate to form a template / substrate / substrate combination.

[0025] S3. Place the template / substrate / base plate assembly into a magnetron sputtering coating apparatus, introduce rare gas under vacuum conditions, adjust the power, and use magnetron sputtering to deposit the metal target material onto the flexible substrate. Remove the template to obtain the flexible transparent conductive film of the metal mesh.

[0026] In one embodiment of the present invention, in step S1, a laser is used to cut out the desired hollow stripe pattern at the center of the polymer template.

[0027] In one embodiment of the present invention, different polymer template patterns are obtained by adjusting the laser cutting parameters, the cutting parameters including cutting energy, cutting spacing and cutting length.

[0028] In one embodiment of the present invention, the cutting energy is 8-20W, the cutting spacing is 100-500μm, and the cutting length is 2-20cm.

[0029] In one embodiment of the present invention, step S2 further includes: cleaning the flexible substrate sequentially with a 1:1 volume ratio of acetone and ethanol solution and deionized water, drying it with nitrogen, and fixing the polymer template onto the flexible substrate with high-temperature tape.

[0030] In one embodiment of the present invention, in step S3, the template is positioned facing the Ag target, and the vacuum is evacuated to 10... -5 ~10 - 9 Torr, magnetron sputtering of Ar gas to bombard the target, with a power of 300-500W and a deposition time of 30-900s, preferably 90s-600s.

[0031] Examples include 30s, 60s, 90s, 120s, 180s, 240s, 300s, 360s, 420s, 480s, 540s, 600s, or 900s.

[0032] Preferably, the partial pressure of Ar is controlled at 60% to 70%.

[0033] In one embodiment of the present invention, the polymer template is a polyimide sheet; the overall size of the polymer template is 4cm×4cm to 24cm×24cm, and the thickness is 30 to 90μm.

[0034] In one embodiment of the present invention, the metal target is at least one of Ag target, Cu target, Al target, and Au target.

[0035] In one embodiment of the present invention, the polymer template has a parallel hollow stripe pattern, and in step S3, conductive films with square, triangular or intersecting metal grid patterns are obtained by coating 2, 3 or 4 times respectively.

[0036] According to another aspect of the invention, the application of the aforementioned flexible transparent conductive film with metal mesh in flexible displays or flexible electronic devices is also provided.

[0037] Specifically, it can be used on mobile phone screens.

[0038] This invention designs and prepares templates for magnetron sputtering and obtains different internal patterns of the templates by adjusting the cutting parameters. By selecting a suitable substrate and sputtering parameters, the thickness of the metal mesh layer can be precisely controlled (e.g., controlled between 50 nm and 600 nm) by controlling the sputtering time, thereby optimizing and achieving the best film transparency and conductivity.

[0039] The beneficial effects of this invention are:

[0040] 1) This invention employs magnetron sputtering to prepare a flexible transparent conductive film composed of a flexible substrate (PET) and a metal mesh. Magnetron sputtering can accurately control the microstructure of the metal mesh and the thickness of the film, thereby optimizing the conductivity, light transmittance, and bending performance of the transparent conductive film. Specifically, through the effective combination of template design (e.g., designing it as hollow parallel stripes) and magnetron sputtering, the shape of the microstructure of the metal mesh, such as squares and triangles, can be precisely controlled, as can the size of the microstructure, such as linewidth, size, and shape.

[0041] For example, in a square metal grid, light transmittance (excluding the influence of the substrate) can be approximately given by the percentage of space between the metal lines, and can be quantified, for example, by the following formula: Light transmittance = (grid spacing - line width) 2 / Grid spacing 2 Furthermore, it can be easily adjusted by modifying the geometric parameters (line width and line spacing) of the mesh microstructure.

[0042] Electrical conductivity depends not only on linewidth and spacing but also on the height of the metal wires (i.e., the thickness of the metal mesh). Therefore, by adjusting the linewidth, spacing, and thickness of the metal mesh, the balance between conductivity and light transmittance can be easily optimized. This conductivity can be characterized by sheet resistance, which is calculated as: Sheet Resistance = (Resistivity * Mesh Spacing) / (Line Height * Linewidth).

[0043] 2) This invention adjusts the linewidth and spacing of the metal mesh by adjusting the width and spacing of the perforated stripes on the template, adjusts the thickness of the metal mesh by adjusting the magnetron sputtering time, and obtains different shapes and patterns by adjusting the number of magnetron sputtering cycles. This allows for the fabrication of metal meshes with different geometric parameters, resulting in high-quality flexible transparent metal mesh films with high light transmittance, high conductivity, and strong bending resistance. The fabrication process is simple, safe, and non-toxic, and can produce films of various sizes as needed. Furthermore, the template of this invention can be prepared by laser cutting, is reusable, and is simple, efficient, and inexpensive.

[0044] 3) The sheet resistance of the flexible transparent conductive film prepared by this invention is 4–10 Ωsq. -1 It has strong conductivity, and the light transmittance of the metal mesh is over 90% (for example, the light transmittance of Ag metal mesh reaches over 93% at 550nm). The substrate material is a soft substrate, and the final prepared metal mesh conductive film can achieve more than 100,000 bending cycles, while maintaining high conductivity stability and visible light transmittance. It can be used as a high-performance flexible transparent electrode material, and has extremely high application prospects in the field of flexible displays or flexible electronic devices, such as mobile phone screens. Attached Figure Description

[0045] Figure 1 An optical microscope image of the surface of the Ag square grid flexible transparent PET film in Example 1;

[0046] Figure 2 An optical microscope image of the Ag triangular mesh flexible transparent PET film surface in Example 2;

[0047] Figure 3 This is a schematic diagram comparing the transmittance results of the Ag triangular grid flexible transparent PET film in Example 2;

[0048] Figure 4 This is a comparison chart showing the conductivity loss test results of the Ag triangular grid flexible transparent PET film of Example 2 and a commercially available ITO-coated flexible PET film after 10,000 bends. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be emphasized that the specific embodiments described herein are only for better illustrating the invention and represent some, not all, embodiments, and therefore are not intended to limit the invention. Furthermore, the technical features involved in the embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[0050] In this invention, light transmittance (also known as light transmittance) is measured using an ultraviolet spectrometer; sheet resistance is measured using a four-probe sheet resistance meter.

[0051] Example 1

[0052] (1) Preparation of PI template: Polyimide (PI) (overall size 20cm×20cm, thickness 70μm) was laser-cut into a template with a central parallel hollow stripe pattern. The cutting energy was 15W, the cutting line spacing was 300μm, and the cutting stripe length was 16cm. The prepared template was then immersed in deionized water and ethanol for cleaning, and dried with nitrogen.

[0053] (2) Preparation of template / substrate / glass plate assembly: The PET substrate is cleaned sequentially with a mixture of acetone and ethanol (volume ratio 1:1), deionized water, and dried with nitrogen. The cleaned flexible substrate is then tightly attached to the glass plate to form a flexible substrate / glass plate assembly.

[0054] (3) The PI template prepared in step (1) is fixed onto the PET substrate after the substrate / glass plate assembly in step (2) using high-temperature tape to obtain a PI / PET / glass plate assembly. This assembly is then placed in the magnetron sputtering chamber with the PI facing the Ag target (Ag target purity is 99.99%). The vacuum of the sputtering system in the magnetron sputtering coating system is evacuated to 10... -5 -10 -9 torr. The target material is bombarded by sputtering Ar gas with a purity of 99.9% using a magnetron sputtering coating machine with a power of 300W.

[0055] (4) Remove the PI / PET / glass plate assembly from step (3), rotate the PI template 90° and fix it back onto the PET substrate, then place it back into the magnetron sputtering chamber for sputtering. The sputtering parameters are the same as above. Finally, a flexible transparent conductive PET film coated with Ag square grids is obtained, such as... Figure 1 As shown.

[0056] The Ag metal mesh has a thickness of approximately 150 nm, a light transmittance of 93.5% (at a wavelength of 550 nm), and a sheet resistance of 8.4 Ωsq. -1 .

[0057] Example 2

[0058] The preparation method is the same as in Example 1, except that in step (4), the coating process is increased from 2 times to 3 times, and the microstructure of the prepared product changes from a square metal mesh to a triangular metal mesh.

[0059] (4) Remove the PI / PET / glass plate assembly, rotate the PI template 60° clockwise and fix it on the PET surface, then place it back into the magnetron sputtering chamber for sputtering with the same sputtering parameters as above; remove the PI / PET / glass plate assembly again, rotate the PI template 60° clockwise again and fix it on the PET substrate, place it in the magnetron sputtering chamber, and sputter again with the same sputtering parameters as above, finally obtaining a flexible transparent conductive PET film coated with Ag triangular mesh, such as... Figure 2 As shown.

[0060] The metal mesh has a thickness of approximately 150 nm, a light transmittance of 92.3% (at a wavelength of 550 nm), and a sheet resistance of 5.8 Ωsq. -1 .

[0061] Other embodiments

[0062] The other steps are the same as in Example 1 or 2. By simply changing the width of the template cutout stripes, products with different line widths in the metal mesh can be obtained, and / or by changing the spacing of the template cutout stripes, products with different sizes and shapes of squares and triangles can be obtained.

[0063] The sheet resistance and transmittance of the Ag grid PET films prepared in Examples 1-2 were tested using a four-probe and a UV-Vis spectrometer, respectively.

[0064] like Figure 3 As shown, the light transmittance of the metal mesh layer after removing the flexible PET substrate in Examples 1-2 (at 550 nm) can reach 93.5%, and the overall transmittance of the Ag mesh flexible transparent conductive PET film (at 550 nm) can reach more than 82%.

[0065] The sheet resistance of the Ag triangular mesh flexible transparent PET film prepared in Example 2 is 5.806 Ωsq. -1 As can be seen, the sheet resistance of Examples 1-2 is stable at 4-10 Ωsq. -1 .

[0066] Bending resistance tests were conducted on the transparent metal mesh film to demonstrate its suitability for subsequent flexible device applications. A bending machine (purchased from Bofan Technology Co., Ltd.) was used for the bending tests, with a 5mm radius of curvature and a concave bending loading mode, to test the bending resistance of the metal mesh substrate structure. After 10,000 bends, the relative sheet resistance change of the Ag mesh flexible transparent conductive PET film was less than 10%, and it could withstand more than 100,000 bends.

[0067] Figure 4 This is a comparison of the conductivity loss test results of the Ag triangular grid flexible transparent PET film of Example 2 and a commercially available ITO-coated flexible PET film (purchased from South China Xiangcheng Technology Co., Ltd., product model "300*100*0.125mm 6-8 ohms") after 10,000 bends. R is sheet resistance, R0 is the initial sheet resistance, and from... Figure 4 As can be seen from the results, the Ag triangular grid flexible transparent PET film prepared in Example 2 exhibits excellent electrical conductivity stability after bending fatigue testing.

[0068] This invention utilizes magnetron sputtering to prepare a high-quality flexible transparent conductive film with a metal mesh, consisting of a flexible substrate (PET) and a silver mesh. The film exhibits high transmittance, high conductivity, and strong resistance to bending fatigue. Furthermore, the linewidth (1-50 μm) and pattern (square, triangle, etc.) of the metal mesh can be controlled by designing and preparing templates, and the thickness (50-600 nm) of the metal mesh can be controlled by adjusting the deposition time of the sputtering deposition, thereby optimizing the light transmittance and conductivity of the film.

[0069] This invention optimizes the performance of thin films by preparing different grid patterns and adjusting the thickness of the metal grid. By utilizing the high tunability of its microstructure, it can achieve the best balance between optical and electrical properties, making it a high-performance flexible transparent electrode material to meet different application needs, such as flexible displays or flexible electronics.

[0070] The magnetron sputtering method of this invention is simple, low-cost, highly efficient, safe and non-toxic, and can produce metal meshes of various sizes (2cm×2cm-20cm×20cm) and good quality. The pattern templates prepared by laser cutting can be reused, which is simple, efficient and inexpensive.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flexible transparent conductive film with a metal mesh, characterized in that, The thin film includes a flexible substrate and a sputtered metal mesh, wherein the metal mesh is formed into various desired patterns on the flexible substrate; The flexible substrate is selected from soft PET substrate, CPI substrate or flexible ultrathin glass; The metal mesh is an Ag metal mesh; The method for preparing the flexible transparent conductive metal mesh film includes the following steps: S1. Prepare a polymer template and cut out the desired hollow stripe pattern from the center of the polymer template; S2. Prepare a flexible substrate, attach it tightly to the substrate to form a flexible substrate / substrate combination, and fix the polymer template prepared in step S1 onto the flexible substrate to form a template / substrate / substrate combination. S3. Place the template / substrate / base plate assembly into a magnetron sputtering coating apparatus, introduce rare gas under vacuum conditions, adjust the power, and use magnetron sputtering to deposit the metal target material onto the flexible substrate. Remove the template to obtain the metal mesh flexible transparent conductive film. In step S3, the template is positioned facing the Ag target, and the vacuum is evacuated to 10... -5 ~10 -9 Torr, magnetron sputtering of Ar gas to bombard the target, with a power of 300-500W, a deposition time of 90-600s, and the partial pressure of Ar controlled at 60%-70%; The thickness of the metal mesh is 150nm~600nm; The line width of the metal mesh is 1μm to 30μm; The sheet resistance of the flexible transparent conductive film with metal mesh is 4~10Ωsq. -1 .

2. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The metal mesh is formed on a flexible substrate into metal square mesh, metal triangular mesh, metal brick wall-shaped mesh, metal honeycomb mesh, and metal circular mesh patterns.

3. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The size and area of ​​the metal mesh range from 2cm×2cm to 20cm×20cm.

4. The flexible transparent conductive film with metal mesh according to any one of claims 1-3, characterized in that, The metal mesh has a light transmittance of over 90% at 550nm.

5. The flexible transparent conductive film with metal mesh according to claim 4, characterized in that, The light transmittance of the metal mesh at 550nm reaches over 92%.

6. The flexible transparent conductive film with metal mesh according to claim 5, characterized in that, The light transmittance of the metal mesh at 550 nm reaches over 93.5%.

7. The flexible transparent conductive film with metal mesh according to any one of claims 1-3, characterized in that, The overall transmittance of the flexible transparent conductive film with metal mesh at 550nm reaches over 82%.

8. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, In step S1, a laser is used to cut out the desired hollow stripe pattern at the center of the polymer template.

9. The flexible transparent conductive film with metal mesh according to claim 8, characterized in that, Different polymer template patterns can be obtained by adjusting the laser cutting parameters, including cutting energy, cutting spacing, and cutting length; the cutting energy is 8~20W, the cutting spacing is 100~500μm, and the cutting length is 2~20cm.

10. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, Step S2 further includes: cleaning the flexible substrate sequentially with a 1:1 volume ratio of acetone and ethanol solution and deionized water, drying it with nitrogen, and fixing the polymer template onto the flexible substrate with high-temperature tape.

11. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The deposition time for magnetron sputtering is 90s to 300s.

12. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The polymer template is a polyimide sheet; the overall size of the polymer template is 4×4~24×24 cm, and the thickness is 30~90 μm.

13. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The metal target is at least one of Ag, Cu, Al, and Au targets.

14. The flexible transparent conductive film with metal mesh according to claim 1, characterized in that, The polymer template has a parallel hollow stripe pattern, and in step S3, conductive films with square, triangular or intersecting metal grid patterns are obtained by coating 2, 3 or 4 times respectively.

15. The application of the metal mesh flexible transparent conductive film according to any one of claims 1 to 14 in flexible displays or flexible electronic devices.

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