CN112951485A

CN112951485A - Metal grid stretchable transparent electrode with shell-core structure, and preparation method and application thereof

Info

Publication number: CN112951485A
Application number: CN202110104201.6A
Authority: CN
Inventors: 朱晓阳; 张厚超; 兰红波; 李红珂; 孙銮法
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2021-01-26
Filing date: 2021-01-26
Publication date: 2021-06-11
Anticipated expiration: 2041-01-26
Also published as: CN112951485B

Abstract

The invention relates to a metal grid stretchable transparent electrode with a shell-core structure, and a preparation method and application thereof. The transparent electrode comprises a flexible substrate, a base material, a metal layer and a polymer layer, wherein the base material is provided with a groove structure, the metal layer is arranged on the inner side wall of the groove and is in the shape of the groove, and the polymer layer is filled in the metal layer. The transparent flexible electrodes with different structures are provided, and the preparation method comprises the steps of 3D printing of the submicron-scale polymer structure, chemical plating of the surface layer of the polymer structure and transfer printing preparation of the embedded electrode. The preparation of the superfine ordered structure with any shape and large aspect ratio is realized, and the conductive performance and the mechanical performance are excellent.

Description

Metal grid stretchable transparent electrode with shell-core structure, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of flexible transparent electrodes, and particularly relates to a metal grid stretchable transparent electrode with a shell-core structure, and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The transparent electrode is the key to realize transparent nano electronic and photoelectronic devices, and has the characteristics of high conductivity, transparency, mechanical flexibility and the like. In recent years, the film has very wide application in the fields of touch screens, electronic paper, intelligent windows, flexible photoelectric display/conversion devices, electronic skins, transparent electric heating, flexible sensors, electromagnetic shielding, wearable equipment and the like. Indium tin oxide (ITO, having excellent photoelectric properties) and other metal transparent oxides as traditional transparent electrode materials occupy the market leading position of transparent electrodes, however, the application of ITO in the field of flexible transparent electrodes is greatly limited due to the problems of intrinsic brittleness, high sheet resistance on flexible substrates, high temperature and vacuum sputtering preparation processes and the like. Therefore, the research and development of the high-performance flexible transparent electrode capable of replacing ITO is a key problem to be solved and broken through in the emerging fields of flexible electronics and the like.

Scholars at home and abroad propose several transparent electrodes as substitutes of traditional Indium Tin Oxide (ITO) electrodes, such as graphene, carbon nanotubes, metal nets, solution-grown metal nanowires and the like. Graphene has excellent light transmission, flexibility, high mechanical strength, and high temperature stability. Carbon nanotubes have high thermal conductivity, high mechanical strength and good chemical stability. However, the carbon nanotubes (with a sheet resistance of 60-300 Ω/sq) and graphene (with a sheet resistance of 50-500 Ω/sq) have relatively high resistance, and the synthesis of graphene and carbon nanotubes is applied to various complex processes such as chemical vapor deposition and the like, so that the application of the graphene and carbon nanotubes in production is limited. The conductive polymer has the characteristics of high transparency, high energy efficiency and high flexibility, but the conductivity (the sheet resistance is 150-500 omega/sq) is very weak, so that the application of the conductive polymer in high-performance devices is severely limited. Metal nanowires (e.g., AgNWs) are suitable as transparent electrodes due to their simple and highly profitable preparation process and low resistivity (1.67 μ Ω/cm). However, metal nanowires still have many problems, such as: large surface roughness, poor mechanical properties, poor adhesion to substrates, large haze, large junction resistance, and the like. Besides the advantages and defects of the transparent electrode materials such as the carbon-based material, the conductive polymer and the metal nanowire, the contradiction that the light transmittance and the conductivity of the flexible transparent electrode are difficult to be improved together exists, namely, certain light transmittance is usually sacrificed when the conductivity is improved, and on the contrary, the conductivity is reduced when essential for increasing the light transmittance.

In order to solve the inherent defects of the transparent electrode material, a metal grid electrode material is proposed, wherein a metal grid is made to have high conductivity by preparing patterned metal wires on the surface (relief type) or inside (embedded type) of a flexible substrate with high light transmittance, a mesh area without patterns is a transparent substrate, and light can normally penetrate through the metal grid.

Although the transparent electrode based on the metal grid has a remarkable advantage in solving the contradiction between the light transmittance and the conductivity of the traditional electrode, the surface roughness of the electrode is high due to the structure with a large aspect ratio prepared by the existing method, and short circuits of an OLED (organic light emitting diode) and a photovoltaic device are easily caused; the adhesion force between the electrode material and the substrate is poor, so that the electrode material is easy to fall off and the device is easy to lose efficacy; the mechanical property is poor, when the steel plate is bent for more than 5000 times, the resistance change is large and the steel plate is not stretch-proof; and the high-temperature treatment is needed to remove the polymer auxiliary agent in the metal slurry to ensure that the metal slurry has good conductivity, so that the application of the metal slurry to a flexible substrate which is not high in temperature resistance is limited. Although researchers at home and abroad make various attempts and researches on the manufacturing technology of the embedded metal grid transparent electrode, the main manufacturing process is still difficult to get rid of yellow light process, electroplating process and other processes, the process is complex and high in cost, more waste products and liquid waste are produced, resources are wasted, the environment is polluted, and efficient and low-cost green manufacturing of the embedded metal grid with superfine and large aspect ratio is difficult to realize.

Disclosure of Invention

In view of the problems in the prior art, the present invention aims to provide a metal grid stretchable transparent electrode with a shell-core structure, and a preparation method and applications thereof.

In order to solve the technical problems, the technical scheme of the invention is as follows:

in a first aspect, the metal grid stretchable transparent electrode with the shell-core structure comprises a flexible substrate, a base material, a metal layer and a polymer layer, wherein the base material is a transparent and flexible material, the base material covers the surface of the flexible substrate, a groove structure is formed in the base material, the metal layer is arranged on the inner side wall of the groove, the metal layer is in the shape of the groove, and the polymer layer is filled in the metal layer.

Compared with the prior transparent electrode, the structure is different. Compared with the existing electrode, the structure that the high-conductivity metal shell wraps the high-elasticity polymer core increases the elasticity, reduces the resistance and improves the photoelectric and mechanical properties.

In some embodiments of the invention, the polymer has a line width of 500nm to 2 μm and an aspect ratio of 2 to 5. The method has the advantages of large height-width ratio and larger surface area, and the deposition of the high-conductivity metal layer is favorable for improving the electrical property.

In some embodiments of the invention, the polymer is poly (4-vinylpyridine) (P4VP) and Dimethylformamide (DMF) in a mass ratio of 3-4: 4-5. The poly (4-vinylpyridine) is a white powdery high molecular polymer and can be well dissolved in an organic solvent; DMF is a benign solvent for P4VP, and has a high dielectric constant, which tends to reduce beading formation during printing and decrease print line width diameter. The combination of the two polymers is advantageous for obtaining low line width arrays.

In some embodiments of the present invention, the material of the metal layer is gold, silver, copper, nickel, or the like. The metal layer can be replaced by various metals and can be selected according to performance requirements. Or the thickness of the metal layer is 400nm-2 μm.

In some embodiments of the present invention, the matrix material is a photosensitive resin, a thermosetting material, or the like.

In some embodiments of the present invention, the flexible substrate is a material such as polyethylene terephthalate (PET), polyimide, polyvinyl chloride, polystyrene, polyurethane, or the like.

The transparent electrode has a shell-core structure (a high-conductivity metal shell wraps a high-elasticity polymer core), overcomes the defects of high material cost, large surface resistance, brittleness and the like of the traditional electrode material, not only has a printed submicron-scale structure with a large height-width ratio, but also can greatly improve the light transmittance; and the large aspect ratio enables it to have a large surface area, with excellent electrical properties after deposition of highly conductive metals; and the high-elasticity polymer core provides excellent bending performance and has certain stretchability, so that the electrode is a novel transparent conductive material, and the problem of poor mechanical performance of the conventional metal grid transparent electrode is solved.

In a second aspect, the preparation method of the metal grid stretchable transparent electrode with the shell-core structure comprises the following specific steps:

1) printing a polymer structure on a printing substrate by using an electric field driven jet deposition micro-nano 3D printing method;

2) depositing a metal layer on the surface layer of the polymer structure by using a chemical plating method to obtain a shell-core structure;

3) and embedding the obtained shell-core structure into the impression material by using a roller auxiliary transfer method and taking a transparent flexible material as the impression material, and removing the printing substrate to obtain the electrode.

The method is combined with the technologies of electric field driven jet deposition micro-nano 3D printing, electroless plating and roller auxiliary transfer printing, and the efficient low-cost green manufacturing of the embedded flexible and stretchable embedded metal grid transparent electrode with any shape, superfine (submicron scale) and large aspect ratio is realized.

The electric field driven jet deposition micro-nano 3D printing technology is adopted to realize the manufacture of the random-shaped superfine and large-aspect-ratio ordered structure, and has the advantages of high precision, low cost, direct forming and the like, and the printed polymer structure has excellent mechanical properties (bending and stretching properties). By adopting the electroless plating technology, the problem that the traditional metal grid can have excellent conductivity only by high-temperature sintering is solved, the preparation of the high-conductivity transparent electrode at normal temperature is realized, and the 3D printed structure has a large height-width ratio, so that the surface area is large, and the deposited metal has excellent conductivity. On the other hand, processes such as electroplating and yellow light processing are not needed, and efficient, low-cost and green manufacturing is realized. The roller auxiliary transfer printing technology is adopted, and the problems that the electrode with a large height-width ratio has large surface roughness and poor adhesion with a substrate are solved.

In some embodiments of the invention, the method of printing the polymer structure is printing with a polymer solution comprising poly (4-vinylpyridine), dimethylformamide and ethanol, the mass fraction of ethanol in the polymer solution being between 15 and 30%. Optionally, the polymer viscosity is 500 to 30000 cps.

In some embodiments of the invention, the submicron-scale polymer structure is printed in step 1) with a line width of 500nm to 2 μm.

In some embodiments of the invention, step 1) is performed at least 3 times layer-by-layer additive printing.

In some embodiments of the invention, the polymer structure in step 1) is a wire grid, a grid of squares or diamonds, a fractal curve, or the like.

In some embodiments of the present invention, the distance between the printing needle and the printing substrate in step 1) is 50 to 100 μm, the power voltage is 500 to 1500V, and the printing speed is 10 to 30 mm/s.

In some embodiments of the invention, after the polymer structure is printed, the polymer structure is treated in a UV irradiation device to expose the surface of the polymer structure to UV/O₃Oxidized under treatment. Optionally, the intensity of UV radiation is 13-16mWcm^-2The time is 3-6 min. The polymer structure is prevented from swelling in the subsequent chemical plating solution, and the structure precision is ensured.

In some embodiments of the present invention, the specific process of step 2) is: placing the polymer structure obtained in the step 1) in a pre-immersion liquid, taking out the polymer structure after a complexing reaction, placing the polymer structure in a reducing solution for a reducing reaction, then placing the polymer structure in a plating solution to obtain a plated piece, and then carrying out anti-oxidation treatment on the plated piece to obtain a shell-core structure.

The transparent flexible electrode can be prepared at normal temperature by adopting a chemical plating method, and compared with an electroplating process, a high-temperature treatment process is not needed. The chemical plating process comprises the following steps: and coating a metal layer on the polymer structure, wherein the metal layer and the polymer have the adsorption effect on metal ions through pyridine groups.

Optionally, the pre-immersion liquid is metal salt solution, specifically copper sulfate pentahydrate aqueous solution, HAuCl₄、AgNO₃、CuSO₄、NiSO₄Etc.; optionally, the reducing solution is a solution containing a reducing agent, and the reducing agent is hypophosphite (NaH)₂PO₂) Hydrazine hydrate, amine borane (DMAB), sodium borohydride, and the like; optionally, the plating solution is a solution of a metal salt, a complexing agent, a reducing agent, and a PH adjusting agent, wherein the complexing agent may be Triethanolamine (TEA), potassium sodium tartrate (Tart), disodium Ethylenediaminetetraacetate (EDTA), tetraethyldiamine, phenylenediaminetetraacetic acid (CDTA), citric acid, and the PH adjusting agent may be sodium hydroxide or potassium hydroxide.

In some embodiments of the invention, the concentration of the pre-immersion liquid is 10-20g/L, and the time for immersion in the pre-immersion liquid is 1-9 h; preferably 6-9 h.

In some embodiments of the invention, the volume concentration of the reducing agent in the reducing solution is 5-15mL/L, and the soaking time in the reducing solution is 1.5-5 min; preferably 2-3 min.

In some embodiments of the invention, the soaking time in the plating solution is 30-100 min; preferably 60-90 min.

By controlling the thickness of the metal layer by varying the soaking time, a shell-core structure is finally formed, wherein the polymer core structure provides good mechanical properties (bending, stretching) and the metal shell structure provides electrical conductivity.

In some embodiments of the present invention, the transparent flexible material in step 3) is polyethylene terephthalate (PET), polyimide, polyvinyl chloride, polystyrene, polyurethane, or the like;

or, the thickness of the printing substrate ranges from 50 μm to 500 μm.

In some embodiments of the present invention, the specific process of step 3) is: and placing a base material, performing secondary imprinting by using a roller, performing secondary imprinting by using dislocation rotation of the roller, and then curing to separate the substrate to obtain the flexible electrode. Through secondary imprinting, the influence of uneven imprinting force between the air groove on the surface of the roller and the imprinting surface can be eliminated.

Optionally, the base material is a photosensitive resin or a thermosetting material, etc.

Optionally, the second embossing is performed, and the rollers rotate 45 degrees in a staggered manner.

Alternatively, the imprinting force is 10-100N.

In a third aspect, the metal mesh stretchable transparent electrode of the shell-core structure is applied to the fields of touch screens, electronic paper, smart windows, flexible photoelectric display/conversion devices, electronic skins, transparent electric heating, flexible sensors, electromagnetic shielding, wearable devices and the like.

One or more technical schemes of the invention have the following beneficial effects:

(1) the transparent electrode has the advantages of low cost and high efficiency in manufacturing. The invention utilizes the outstanding advantages of the electric field driven jet deposition micro-nano 3D printing technology in the aspect of manufacturing the microstructure with high resolution (superfine) and high aspect ratio, overcomes the defects of complex process, resource waste, high cost, environmental pollution and the like in the prior art (such as ink-jet printing, gravure printing, self-assembly, electroplating, nano-imprinting, blade coating process, molding process, ink-jet printing, electrostatic spinning and the like), does not need photoetching, electroplating and other processes, does not need to manufacture masks and molds, is easy to realize the high-precision, low-cost and high-efficiency manufacture of the submicron-scale grid transparent electrode with high aspect ratio, and is green and pollution-free.

(2) The problem that the conductivity and the light transmittance are mutually restricted is solved. The invention utilizes the electric field to drive the injection deposition micro-nano 3D printing technology, overcomes the problem that the electrical conductivity and the light transmittance are mutually restricted commonly existing in the traditional transparent electrode preparation process, can ensure excellent light transmittance by adjusting the printed line width and period, and can ensure good electrical conductivity on the premise of not sacrificing the light transmittance (unchanged line width) when printing a grid with a large aspect ratio.

(3) Any shape structure can be printed according to performance requirements. According to the invention, the electric field driven jet deposition micro-nano 3D printing technology is utilized to print ordered grid structures with various shapes (squares, rhombic grids, fractal curves and the like), periods and line widths at high precision according to performance requirements. The method provided by the invention overcomes the defects that a nanofiber network prepared by the traditional electrostatic spinning technology and the like is disordered and has poor stability, poor conduction uniformity and mechanical stability and large contact resistance between wires, greatly reduces the node resistance and has good photoelectric property and mechanical stability.

(4) Can be prepared at room temperature and has various metal plating types. The electroless plating process can prepare the high-conductivity transparent electrode at normal temperature, overcomes the defect that the traditional metal grid electrode has good conductivity only by removing the polymer additive in the metal slurry through high-temperature treatment, realizes the application on the flexible substrate which is not resistant to high temperature, and can select plated metal according to the performance requirement.

(5) The electroless plating process has good controllability, uniform plating and low cost. The pyridine group contained in the printed P4VP structure has the characteristic of adsorbing metal ions, and a layer of high-conductivity metal is plated on the surface of the P4VP polymer structure through complexing of nitrogen in the pyridine group and the metal ions and then in-situ reduction, so that the plating layer is uniform and compact, has low roughness, has average roughness lower than 30nm, and is tightly combined with the polymer and not easy to separate.

(6) Has excellent photoelectric and mechanical properties. The shell-core structure (the high-conductivity metal shell wraps the high-elasticity polymer core) grid transparent electrode manufactured by the invention overcomes the defects of high material cost, large surface resistance, brittleness and the like of the traditional electrode material, not only is the printed large aspect ratio submicron scale structure, but also the light transmittance can be greatly improved (the light transmittance can be more than 95%); and the large aspect ratio enables the high-conductivity metal to have a large surface area, and excellent electrical properties (the sheet resistance is lower than 30 omega) after the high-conductivity metal is deposited; and the high-elasticity polymer core provides excellent bending performance and has certain stretchability (the resistance is increased by less than 0.4 percent after the electrode is bent for 3000 times), so that the electrode is a novel transparent conductive material, and the problem of poor mechanical performance of the conventional metal grid transparent electrode is solved.

(7) The embedded electrode manufactured by the invention has low surface roughness, is tightly combined with the substrate and is not easy to fall off. The roughness of the surface of the transparent electrode prepared by the traditional method is often very large, and the large surface roughness can directly cause higher current leakage in an OLED device; the adhesion force between the electrode material and the substrate is poor, the electrode material is easy to fall off, and the failure of the device is easy to cause. According to the invention, a roller auxiliary transfer printing technology is adopted, the prepared shell-core structure electrode is embedded into the flexible material, the surface roughness (average surface roughness is lower than 100nm) is greatly reduced, and the adhesion with the substrate is improved.

(8) Has very good expandability. Can meet the requirements of different applications.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.

Fig. 1 is a schematic view of a shell-core structured embedded stretchable metal mesh transparent electrode.

Fig. 2 is a schematic diagram of the electric field driven jet deposition micro-nano 3D printing in embodiment 1.

FIG. 3 is a schematic view of roll-assisted transfer.

Fig. 4 a composite nanoimprint lithography machine.

Fig. 5 is a flow chart for preparing an embedded stretchable metal mesh transparent electrode having a shell-core structure.

Fig. 6 is a schematic view of the preparation of the transparent electrode based on the proposed method.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. The invention will be further illustrated by the following examples

Example 1

Fig. 1 is a schematic diagram of an embedded stretchable metal mesh transparent electrode with a shell-core structure to be manufactured by the present invention (1 is a polymer core structure, 2 is a metal shell, 3 is photoresist, and 4 is PET). Parameters of the transparent electrode to be manufactured in this embodiment example: the line width is 500 nm; the period is 100 mu m; the aspect ratio is 2; the structure is in a grid shape; the metallization is copper.

The specific process of the proposed method based preparation is specifically described by taking the transparent electrode described in the examples as an example and combining fig. 2-6.

Step 1: preparing a polymer structure printing solution.

Printing solutions were prepared from poly (4-vinylpyridine) (P4VP, average Mw-160000) from Sigma-Aldrich, N-Dimethylformamide (DMF) of Aladdin, and ethanol (C)₂H₆O) preparation.

The specific process comprises the following steps:

(1) 30 weight percent of white powdery poly (4-vinylpyridine) (P4VP) is weighed by a precision electronic balance and placed in a glass beaker, then 50 weight percent of N, N-Dimethylformamide (DMF) is weighed and mixed with P4VP (DMF is a benign solvent of P4VP and has higher dielectric constant and is easy to reduce the formation of beads and the fiber diameter in the printing process), a glass rod is used for stirring until P4VP is completely dissolved in DMF, and finally 20 weight percent of ethanol is weighed as a volatile solvent and dropped into the beaker and stirred uniformly.

(2) And transferring the printing solution from the beaker to a printing material cylinder of the electric field driven jet deposition micro-nano 3D printer by using a suction pipe.

Step 2: 3D printing of sub-microscale polymer structures (core structures).

An electric field is used for driving a jet deposition micro-nano 3D printer to print a submicron-scale polymer structure, the pattern area is 100mm multiplied by 100mm, and the line width is 500 nm.

The specific process comprises the following steps:

(1) and (4) preprocessing. The grid structure was drawn with a cycle of 100 μm using CAD drawing software, and then converted into a processing code using data preprocessing software and input into a printer. Subsequently, the printing substrate is laid on the printing platform and the printer is started.

(2) A polymer structure is printed. According to design data, the printing is carried out layer by layer on a flexible PET substrate, the printing speed is 20mm/s, the voltage is 1400V, the distance from a printing nozzle to the substrate is 50 micrometers, the printing line width is 500nm, and the number of printing layers is 10.

(3) And (5) post-treatment. Taking down the printed structure from the printing platform, and placing the printed structure in a UV lamp box for irradiation, wherein the illumination intensity is 15mWcm^-2Irradiating for 5min to make the surface of the polymer structure in UV/O₃Oxidized under treatment, thereby preventing the chemical plating solution from swelling in the subsequent chemical plating solution and ensuring the structural precision.

And step 3: and chemically plating the surface layer of the polymer structure.

Copper (Cu) is selected as the metal to be plated in the embodiment, and copper sulfate (CuSO) from Aladdin is selected as the main salt₄·5H₂O), the complexing agent is potassium sodium tartrate (C) from Sigma-Aldrich company₄H₄KNaO₆·4H₂O), the reducing agent is sodium hypophosphite (NaH) from Aladdin company₂PO₂) The PH regulator is sodium hydroxide (NaOH) from Fuchen chemical reagent company, and chemical plating process is combined to chemically plate copper on the surface layer of the polymer structure.

The specific process comprises the following steps:

(1) and preparing a chemical plating solution. Preparing a pre-immersion liquid: weighing 10g of CuSO by using a precision electronic scale₄·5H₂O was dissolved in 500ml of deionized water and thoroughly stirred with a glass rod to completely dissolve it. Preparing a reducing solution: weighing 8g of NaOH by using a precision electronic scale, dissolving the 8g of NaOH in 500ml of deionized water, and then weighing 5ml of N by using a measuring cylinder₂H₄·H₂O was mixed with an aqueous sodium hydroxide solution and stirred with a glass rod. Preparing plating solution: firstly, respectively weighing 5.2g of CuSO by using a precision electronic scale₄·5H₂O and 7.15g of sodium potassium tartrate were dissolved in 500ml of deionized water and stirred with a glass rod until the copper ions and potassium tartrate were sufficiently dissolvedSodium is fully complexed to prevent the subsequent addition of NaOH from generating CuOH flocculent precipitate), then 8.75g of NaOH is weighed and dissolved in the mixed solution to provide an alkaline environment for chemical copper plating, and finally 15g of NaH is added₂PO₂As a reducing agent.

(2) And (4) chemical plating. Placing the printed polymer structure in a pre-soaking solution for 8h to fully complex the pyridine group in the P4VP with copper metal ions; then taking out and repeatedly washing with deionized water to remove uncomplexed Cu²⁺(ii) a Then placing in prepared reducing solution for 3min to complex Cu on the surface of the polymer²⁺Reducing the Cu into metal Cu which is attached to the surface of P4VP to provide a reduction site for the subsequent thickening process; and finally, placing the alloy in the prepared plating solution for 80min to thicken, and controlling the thickness of the plating layer to reach 500 nm. The process has the advantages of low plating speed, compact and uniform crystal grains and surface roughness of 30 nm.

(3) And (5) post-treatment. And (3) placing the plated part in 0.02mol/L aqueous solution of benzotriazole for carrying out anti-oxidation treatment for 5min, finally repeatedly washing the plated part with deionized water, removing impurities remained on the substrate, and drying at room temperature.

And 4, step 4: and (4) transferring to prepare the embedded electrode.

In this embodiment, a method for manufacturing an embedded electrode by using a composite nanoimprint lithography machine (fig. 4) and combining an imprint process and optimized process parameters includes:

(1) and (4) preprocessing. High-flexibility and high-transparency PET is selected as a transfer substrate. Firstly, a spin coater is utilized to spin a layer of liquid UV-6110 photoresist on PET with the thickness of 10cm multiplied by 10cm, the rotating speed is 500r/min, and the spin coating is carried out for 60 s. Then placing the wafer on a wafer bearing table, and fixing the wafer on the wafer bearing table in an adsorption manner in a vacuum adsorption manner; wrapping a printing substrate printed with a polymer structure on the outer surface of the roller, and introducing negative pressure into an air inlet hole in the side surface of the roller through a vacuum pipeline so as to adsorb the substrate on the outer surface of the roller; and then the transfer printing substrate is driven by the wafer bearing table to move from the initial station to the stamping station, and the roller and the polymer structure wrapped on the roller are driven by the stamping mechanism to move from the initial station to the stamping station.

(2) And (3) paving a polymer structure. The roller rotates, air holes at the bottom are sequentially switched from negative pressure to positive pressure, the negative pressure is changed into normal pressure after a moment, and meanwhile, the polymer structure adsorbed on the roller and the substrate are laid on the substrate coated with the impression material in a progressive line contact mode by matching with the relative horizontal movement of the wafer bearing table. The moving speed of the wafer bearing table is 15mm/s, and the linear speed of the rotation of the adsorption roller is 15 mm/s. The line contact type laying greatly reduces or even eliminates bubble defects generated in imprinting.

(3) And (6) stamping. The roller applies 50N impressing force downwards and rotates, and meanwhile, the roller synchronously moves in cooperation with the sheet bearing table, and impressing is carried out in a line contact mode, so that the first impressing is completed. And then, after the roller rotates by 45 degrees in a staggered way, coining is carried out again to finish secondary coining. Wherein the moving speed of the wafer bearing table is 10mm/s, and the linear speed of the rotation of the adsorption roller is 10 mm/s. The influence of uneven stamping force between the air groove on the surface of the roller and the stamping surface during primary stamping can be eliminated through the staggered rotation of the roller and the secondary stamping.

(4) And (5) curing. After the imprinting is finished, the roller is lifted upwards by 20cm, and a UV light source (power of 2000W and wavelength of 365nm) is turned on to irradiate for 1min so as to completely cure the photosensitive resin.

(5) And removing the substrate. The roller is lowered to a working station, rotates, and the air holes with the bottoms contacted with the substrate are sequentially switched from normal pressure to negative pressure, and simultaneously, the substrate is separated from the imprinting material in an uncovering mode by matching with the synchronous horizontal movement of the wafer bearing table, and the polymer structure on the substrate is kept in a state of being embedded in photosensitive resin and is not separated along with the substrate. Wherein the moving speed of the wafer bearing table is 15mm/s, and the linear speed of the rotation of the adsorption roller is 15 mm/s.

The transparent electrode prepared by embedding the copper-P4 VP (shell-core) structure into the photoresist by the transfer printing technology has a very flat surface, so the transparent electrode has extremely low average surface roughness which can reach 80 nm.

The copper-P4 VP (shell-core) structure embedded transparent electrode manufactured in the embodiment has excellent photoelectric and mechanical properties, and the light transmittance of the electrode exceeds 95% when an ultraviolet-visible spectrophotometer is used for testing the optical properties (light transmittance); the electrical property (sheet resistance) of the electrode is measured and characterized by using a four-probe measurement method, the sheet resistance of the electrode reaches 30 omega/sq, and the sheet resistance is only increased by 0.3 percent after the electrode is bent for 3000 times, so that the electrode has excellent photoelectric property and mechanical property.

The equipment used in this embodiment mainly includes: the electric field drives the micro-nano 3D printer for jet deposition; a spin coater; a UV curing machine; composite nano-imprint machines, etc.

Example 2

Parameters of the transparent electrode to be manufactured in this embodiment example: the line width is 500 nm; the aspect ratio is 3; the structural shape is a fractal curve; the metallization is copper.

Based on the specific process of preparation of the proposed method.

Step 1: preparing a polymer structure printing solution.

The specific process comprises the following steps:

(1) weighing 40 wt% of white powdery poly (4-vinylpyridine) (P4VP) by using a precision electronic balance, placing the weighed white powdery poly (4-vinylpyridine) (P4VP) in a glass beaker, then weighing 40 wt% of N, N-Dimethylformamide (DMF) and mixing the N, N-Dimethylformamide (DMF) with P4VP (DMF is a benign solvent of P4VP and has a high dielectric constant and is easy to reduce the formation of beading and the fiber diameter), stirring by using a glass rod until P4VP is completely dissolved in DMF, and finally weighing 20 wt% of ethanol as a volatile solvent, dripping the ethanol in the beaker, and stirring uniformly.

Step 2: 3D printing of sub-microscale polymer structures (core structures).

The specific process comprises the following steps:

(2) and (4) preprocessing. Drawing a fractal curve by using CAD drawing software, converting the fractal curve into a processing code by using data preprocessing software, and inputting the processing code into a printer. Subsequently, the printing substrate is laid on the printing platform and the printer is started.

(2) A polymer structure is printed. According to design data, the printing is carried out layer by layer on a flexible polyimide substrate, the printing speed is 15mm/s, the voltage is 1300V, the distance from a printing nozzle to the substrate is 50 micrometers, the printing line width is 500nm, and the number of printing layers is 10.

And step 3: and chemically plating the surface layer of the polymer structure.

Copper (Cu) is selected as the metal to be plated in the embodiment, and copper sulfate (CuSO) from Aladdin is selected as the main salt₄·5H₂O), sodium citrate (Na) from Sigma-Aldrich company is selected as complexing agent₃C₆H₅O₇·2H₂O) and ethylenediaminetetraacetic acid (C)₁₀H₁₆N₂O₈) The reducing agent is sodium hypophosphite (NaH) from Aladdin company₂PO₂) The PH regulator is sodium hydroxide (NaOH) from Fuchen chemical reagent company, and chemical plating process is combined to chemically plate copper on the surface layer of the polymer structure.

The specific process comprises the following steps:

(2) and preparing a chemical plating solution. Preparing a pre-immersion liquid: weighing 10g of CuSO by using a precision electronic scale₄·5H₂O was dissolved in 500ml of deionized water and thoroughly stirred with a glass rod to completely dissolve it. Preparing a reducing solution: weighing 8g of NaOH by using a precision electronic scale, dissolving the NaOH in 500ml of deionized water, and then weighing 15g of NaH₂PO₂Mixed with an aqueous solution of sodium hydroxide and stirred with a glass rod. Preparing plating solution: firstly, respectively weighing 5g of CuSO by using a precision electronic scale₄·5H₂Dissolving O and 11.5g of sodium citrate in 500ml of deionized water, stirring with a glass rod until the mixture is fully dissolved (so that copper ions and the sodium citrate are fully complexed to prevent CuOH flocculent precipitate generated by subsequently adding NaOH), then weighing a certain amount of NaOH to dissolve in the mixed solution, adjusting the pH value of the solution to 11 to provide an alkaline environment for electroless copper plating, and finally adding 15gNaH₂PO₂As a reducing agent.

(2) And (4) chemical plating. Placing the printed polymer structure in a pre-soaking solution for 8h to fully complex the pyridine group in the P4VP with copper metal ions; then taking out and repeatedly washing with deionized water to remove uncomplexed Cu²⁺(ii) a Then placing in prepared reducing solution for 3min to complex Cu on the surface of the polymer²⁺Reducing the Cu into metal Cu which is attached to the surface of P4VP to provide a reduction site for the subsequent thickening process; and finally, placing the alloy in the prepared plating solution for 80min to thicken, and controlling the thickness of the plating layer to reach 1 mu m. The process has the advantages of low plating speed, compact and uniform crystal grains and surface roughness of 30 nm.

And 4, step 4: and (4) transferring to prepare the embedded electrode.

(1) and (4) preprocessing. High-flexibility and high-transparency PET is selected as a transfer substrate. Firstly, a layer of liquid PDMS is spin-coated on PET with the thickness of 10cm multiplied by 10cm by a spin coater, the rotating speed is 800r/min, and the spin coating is carried out for 60 s. Then placing the wafer on a wafer bearing table, and fixing the wafer on the wafer bearing table in an adsorption manner in a vacuum adsorption manner; wrapping a printing substrate printed with a polymer structure on the outer surface of the roller, and introducing negative pressure into an air inlet hole in the side surface of the roller through a vacuum pipeline so as to adsorb the substrate on the outer surface of the roller; and then the transfer printing substrate is driven by the wafer bearing table to move from the initial station to the stamping station, and the roller and the polymer structure wrapped on the roller are driven by the stamping mechanism to move from the initial station to the stamping station.

(4) And (5) curing. After the imprinting is finished, the roller is lifted upwards by 20cm, the heating bottom plate is opened, and the PDMS is completely cured by heating at 100 ℃ for 30 minutes.

(5) And removing the substrate. The roller descends to a working station, rotates, and the air holes with the bottoms contacted with the substrate are sequentially switched from normal pressure to negative pressure, and simultaneously, the substrate is separated from the imprinting material in an uncovering mode by matching with the synchronous horizontal movement of the bearing table, and the polymer structure on the substrate is kept embedded in PDMS and is not separated along with the substrate. Wherein the moving speed of the wafer bearing table is 15mm/s, and the linear speed of the rotation of the adsorption roller is 15 mm/s.

The surface of the transparent electrode prepared by embedding the copper-P4 VP (shell-core) structure into PDMS (polydimethylsiloxane) by a transfer printing technology is very flat, so that the surface roughness average is extremely low and can reach 80 nm.

The copper-P4 VP (shell-core) structure embedded transparent electrode manufactured in the embodiment has excellent photoelectric and mechanical properties, and the light transmittance of the electrode can reach 95% when an ultraviolet-visible spectrophotometer is used for testing the optical properties (light transmittance); the electrode sheet resistance reaches 40 omega/sq, the resistance is only increased by 0.35% after bending for 3000 times, and the electrode sheet resistance has certain tensile property, and the sheet resistance has no obvious change when being stretched for more than 2000 times under the stretching limit of 25%, and shows excellent photoelectric property and bending and tensile properties.

Example 3

Parameters of the transparent electrode to be manufactured in this embodiment example: the line width is 1 μm; the period is 500 μm; the aspect ratio is 3; the structure is in a grid shape; the metal plated is silver.

Based on the specific process of preparation of the proposed method.

Step 1: preparing a polymer structure printing solution.

The specific process comprises the following steps:

(1) 30 weight percent of white powdery poly (4-vinylpyridine) (P4VP) is weighed by a precision electronic balance and placed in a glass beaker, then 40 weight percent of N, N-Dimethylformamide (DMF) is weighed and mixed with P4VP (DMF is a benign solvent of P4VP and has higher dielectric constant and is easy to reduce the formation of beading and the fiber diameter), a glass rod is used for stirring until P4VP is completely dissolved in DMF, and finally 30 weight percent of ethanol is weighed as a volatile solvent and dropped into the beaker and stirred uniformly.

Step 2: 3D printing of sub-microscale polymer structures (core structures).

An electric field is used for driving a jet deposition micro-nano 3D printer to print a submicron-scale polymer structure, the pattern area is 100mm multiplied by 100mm, and the line width is 1 mu m.

The specific process comprises the following steps:

(3) and (4) preprocessing. The grid structure was drawn with a period of 500 μm using CAD drawing software, and then converted into a processing code using data preprocessing software and input into a printer. Subsequently, the printing substrate is laid on the printing platform and the printer is started.

(2) A polymer structure is printed. According to design data, the printing is carried out layer by layer on a flexible PET substrate, the printing speed is 15mm/s, the voltage is 1000V, the distance from a printing nozzle to the substrate is 50 micrometers, the printing line width is 1 micrometer, and the number of printing layers is 15.

And step 3: and chemically plating the surface layer of the polymer structure.

The metal plated in this example was silver (Ag), and the main salt was silver nitrate (AgNO) from Aladdin₃) The complexing agent is ammonia water (NH) of Aladdin company₃·H₂O) and ethylenediaminetetraacetic acid (C)₁₀H₁₆N₂O₈) The reducing agent is glucose (C) from Sigma-Aldrich₆H₁₂O₆) And potassium sodium tartrate (C)₄H₄KNaO₆·4H₂O), selecting potassium hydroxide (KOH) of Fuchen chemical reagent company as a pH regulator, and chemically plating silver on the surface layer of the polymer structure by combining a chemical plating process.

The specific process comprises the following steps:

(3) and preparing a chemical plating solution. Preparing a pre-immersion liquid: weighing 5g of AgNO by using a precise electronic scale₃And dissolved in 500ml of deionized water, and sufficiently stirred with a glass rod to be completely dissolved. Preparing a reducing solution: 5g of glucose and 2.5g of potassium sodium tartrate are weighed by a precision electronic scale and dissolved in 500ml of deionized water, and the mixture is stirred uniformly by a glass rod. Preparing plating solution: firstly, weighing 5g of AgNO by using a precise electronic scale₃Dissolving the mixture in 500ml of deionized water, and fully stirring the mixture by using a glass rod to ensure that the mixture is completely dissolved; then, 3g KOH was dissolved in AgNO₃Generating a tan precipitate in the solution; finally, ammonia water is slowly dropped until the precipitate is completely dissolved.

(2) And (4) chemical plating. Placing the printed polymer structure in a pre-soaking solution for 8h to fully complex the pyridine group in the P4VP with silver metal ions; then taking out and repeatedly washing with deionized water to remove uncomplexed Ag⁺(ii) a Then placing in prepared reducing solution for 3min to complex Ag on the surface of the polymer⁺Reducing to metal Ag attached to the surface of P4VP to provide reduction for the subsequent thickening processA locus; and finally, placing the alloy in the prepared plating solution for 60min to thicken, and controlling the thickness of the plating layer to reach 1 mu m. The technological process has relatively slow plating speed, compact and homogeneous crystal grains and surface roughness up to 20 nm.

(3) And (5) post-treatment. And repeatedly cleaning the plated part by using deionized water, removing impurities remained on the substrate, and drying at room temperature.

And 4, step 4: and (4) transferring to prepare the embedded electrode.

The transparent electrode prepared by embedding the silver-P4 VP (shell-core) structure into the photoresist by the transfer printing technology has a very flat surface, so the transparent electrode has extremely low average surface roughness which can reach 80 nm.

The silver-P4 VP (shell-core) structure embedded transparent electrode manufactured in the embodiment has excellent photoelectric and mechanical properties, and the optical property (light transmittance) test is carried out by using an ultraviolet-visible spectrophotometer, wherein the light transmittance of the electrode exceeds 93%; the electrical property (sheet resistance) of the electrode is measured and characterized by using a four-probe measurement method, the sheet resistance of the electrode reaches 15 omega/sq, the sheet resistance is only increased by 0.25 percent after the electrode is bent for 3000 times, and the electrode has excellent photoelectric and mechanical properties.

Comparative example 1

Parameters of the transparent electrode to be manufactured in this embodiment example: the line width is 500 nm; the period is 100 mu m; the aspect ratio is 2; the structure is in a grid shape; the metallization is copper.

Step 1: preparing a polymer structure printing solution.

The specific process comprises the following steps:

(1) 30 weight percent of white powdery poly (4-vinylpyridine) (P4VP) is weighed by a precision electronic balance and placed in a glass beaker, then 50 weight percent of N, N-Dimethylformamide (DMF) is weighed and mixed with P4VP (DMF is a benign solvent of P4VP and has higher dielectric constant and is easy to reduce the formation of beading and the fiber diameter), a glass rod is used for stirring until P4VP is completely dissolved in DMF, and finally 20 weight percent of ethanol is weighed as a volatile solvent and dropped into the beaker and stirred uniformly.

Step 2: 3D printing of sub-microscale polymer structures (core structures).

The specific process comprises the following steps:

(4) and (4) preprocessing. The grid structure was drawn with a cycle of 100 μm using CAD drawing software, and then converted into a processing code using data preprocessing software and input into a printer. Subsequently, the printing substrate is laid on the printing platform and the printer is started.

And step 3: and chemically plating the surface layer of the polymer structure.

Copper (Cu) is selected as the metal to be plated in the embodiment, and copper sulfate (CuSO) from Aladdin is selected as the main salt₄·5H₂O), the complexing agent is potassium sodium tartrate (C) from Sigma-Aldrich company₄H₄KNaO₆·4H₂O), the reducing agent is selected from Aladdin companySodium phosphite (NaH)₂PO₂) The PH regulator is sodium hydroxide (NaOH) from Fuchen chemical reagent company, and chemical plating process is combined to chemically plate copper on the surface layer of the polymer structure.

The specific process comprises the following steps:

(4) and preparing a chemical plating solution. Preparing a pre-immersion liquid: weighing 10g of CuSO by using a precision electronic scale₄·5H₂O was dissolved in 500ml of deionized water and thoroughly stirred with a glass rod to completely dissolve it. Preparing a reducing solution: weighing 8g of NaOH by using a precision electronic scale, dissolving the 8g of NaOH in 500ml of deionized water, and then weighing 5ml of N by using a measuring cylinder₂H₄·H₂O was mixed with an aqueous sodium hydroxide solution and stirred with a glass rod. Preparing plating solution: firstly, respectively weighing 5.2g of CuSO by using a precision electronic scale₄·5H₂Dissolving O and 7.15g of sodium potassium tartrate in 500ml, stirring with a glass rod until the mixture is fully dissolved (so as to fully complex copper ions with the sodium potassium tartrate and prevent the subsequent addition of NaOH from generating CuOH flocculent precipitate), weighing 8.75g of NaOH to dissolve in the mixed solution to provide an alkaline environment for chemical copper plating, and finally adding 15g of NaH₂PO₂As a reducing agent.

The embossed transparent electrode with the copper-P4 VP (shell-core) structure manufactured in the embodiment is subjected to an optical performance (light transmittance) test by using an ultraviolet-visible spectrophotometer, and the light transmittance of the electrode exceeds 95%; the four-probe measurement method is used for measuring and characterizing the electrical property (sheet resistance) of the electrode, the sheet resistance of the electrode reaches 30 omega/sq, and after the electrode is bent 3000 times, the non-embedded electrode has excellent photoelectric property but poor mechanical property because the electrode is not embedded into a flexible material, part of a conductive structure is broken, dislocated and falls off, and the sheet resistance is increased by 6.5%.

The transparent electrode with the copper-P4 VP (shell-core) structure manufactured in this example does not use a transfer printing technique to manufacture an embedded transparent electrode, so the surface is extremely uneven, the average surface roughness is greater than 1.5 μm, and the copper-P4 VP (shell-core) structure and the substrate are easy to fall off, which is easy to cause device failure.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The metal grid stretchable transparent electrode with the shell-core structure is characterized in that: the flexible substrate comprises a flexible substrate, a base material, a metal layer and a polymer layer, wherein the base material is provided with a groove structure, the metal layer is arranged on the inner side wall of the groove and is in the shape of the groove, and the polymer layer is filled in the metal layer.

2. The shell-core structured metal mesh stretchable transparent electrode according to claim 1, wherein: the line width is 500 nm-2 μm, and the aspect ratio is 2-5.

3. The shell-core structured metal mesh stretchable transparent electrode according to claim 1, wherein: the polymer is poly (4-vinylpyridine) and dimethylformamide with the mass ratio of 3-4: 4-5;

or the metal layer is made of gold, silver, copper and nickel; or the thickness of the metal layer is 400nm-2 μm;

or the matrix material is photosensitive resin or thermosetting material.

4. A method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to any one of claims 1 to 3, characterized in that: the method comprises the following specific steps:

1) printing a polymer structure on a substrate by using an electric field driven jet deposition micro-nano 3D printing method;

5. The method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to claim 4, wherein: the method for printing the polymer structure comprises the step of printing by using a polymer solution, wherein the polymer solution comprises poly (4-vinylpyridine), dimethylformamide and ethanol, and the mass fraction of the ethanol in the polymer solution is 15-30%. Optionally, the viscosity of the polymer is 500-30000 cps;

or printing a submicron-scale polymer structure in the step 1), wherein the line width is 500 nm-2 mu m;

or, performing layer-by-layer accumulation printing for at least 3 times in the step 1);

or, the polymer structure in the step 1) is a wire grid, a square or rhombic grid or a fractal curve;

or, the distance between the printing needle head and the printing substrate in the step 1) is 50-100 μm, the power voltage is 500-1500V, and the printing speed is 10-30 mm/s;

alternatively, after the polymer structure is printed, the polymer structure is placed in a UV irradiation device for treatment.

6. The method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to claim 4, wherein: the specific process of the step 2) is as follows: placing the polymer structure obtained in the step 1) in a pre-immersion liquid, taking out the polymer structure after a complexing reaction, placing the polymer structure in a reducing solution for a reducing reaction, then placing the polymer structure in a plating solution to obtain a plated piece, and then carrying out anti-oxidation treatment on the plated piece to obtain a shell-core structure;

optionally, the pre-immersion liquid is metal salt solution, specifically copper sulfate pentahydrate aqueous solution, HAuCl₄、AgNO₃、CuSO₄、NiSO₄Etc.;

optionally, the reducing solution is a solution containing a reducing agent, and the reducing agent is hypophosphite (NaH)₂PO₂) Hydrazine hydrate, amine borane (DMAB), sodium borohydride, and the like;

optionally, the plating solution is a solution of metal salt, a complexing agent, a reducing agent and a PH adjusting agent, the complexing agent can be Triethanolamine (TEA), potassium sodium tartrate (Tart), disodium Ethylene Diamine Tetraacetate (EDTA), tetraethyl diamine, phenyl ethylene diamine tetraacetic acid (CDTA), citric acid and the like, and the PH adjusting agent is sodium hydroxide or potassium hydroxide.

7. The method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to claim 4, wherein: soaking in the pre-soaking solution for 1-9 h; preferably 6-9 h;

or soaking in reducing solution for 1.5-5 min; preferably 2-3 min;

or, the soaking time in the plating solution is 30-100 min; preferably 60-90 min.

8. The method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to claim 4, wherein: the transparent flexible material in the step 3) is polyethylene terephthalate (PET), polyimide, polyvinyl chloride, polystyrene, polyurethane and other materials;

or, the thickness of the printing substrate ranges from 50 μm to 500 μm.

9. The method for preparing a metal mesh stretchable transparent electrode of a shell-core structure according to claim 4, wherein: the specific process of the step 3) is as follows: and placing a base material, performing secondary imprinting by using a roller, performing secondary imprinting by using dislocation rotation of the roller, and then curing to separate the substrate to obtain the flexible electrode. Through secondary imprinting, the influence of uneven imprinting force between the air groove on the surface of the roller and the imprinting surface can be eliminated;

optionally, the base material is photosensitive resin or thermosetting material, etc.;

optionally, embossing for the second time, and rotating the roller at 45 degrees in a staggered manner;

alternatively, the imprinting force is 10-100N.

10. Use of the metal mesh stretchable transparent electrode of the shell-core structure of any one of claims 1 to 3 in the fields of touch screens, electronic paper, smart windows, flexible photoelectric display/conversion devices, electronic skin, transparent electric heating, flexible sensors, electromagnetic shielding, wearable devices, and the like.