KR20200077479A - Silver nanowire-graphene complex nanofilm and method of preparing the same - Google Patents

Abstract

The present invention relates to a method for manufacturing a composite nano thin film by using a silver nanowire and graphene, the composite nano thin film manufactured thereby, and a flexible electrode including the composite nano thin film. The method for manufacturing a composite nano thin film by using a silver nanowire and graphene comprises: a step of forming a silver nanowire network layer on a substrate; a graphene layer forming step of laminating a graphene layer by using wet transfer on the silver nanowire network layer; and a light irradiation step of irradiating an electron beam.

Description

Silver nanowire-graphene complex nanofilm and method of preparing the same}

The present invention relates to a method for manufacturing a composite nano thin film using silver nanowires and graphene, a composite nano thin film prepared therefrom, and a flexible electrode comprising the composite nano thin film.

A transparent flexible electrode is a core technology for realizing a next-generation wearable device. Indium-tin oxide (ITO) is commonly used as a transparent electrode used in a conventional device, but there has been a limitation in implementing a wearable device requiring flexibility of the electrode.

To replace this, various nanomaterials such as metal nanowires, carbon nanotubes, and graphene have been developed, but they do not have electrical conductivity of ITO level, but also have a problem of not being able to stably implement performance in the atmosphere.

Accordingly, it is necessary to research and develop a flexible electrode material having excellent atmospheric stability that can improve electrical characteristics including electrical conductivity and at the same time stably secure performance in the air.

The present invention has been made to solve the above problems,

To provide a composite nano-thin film using silver nanowires and graphene, the present invention is to provide a method for manufacturing a composite nano-thin film that dramatically reduces the contact resistance of these components and has a remarkable improvement in electrical properties including electrical conductivity.

In addition, an object of the present invention is to provide a method of manufacturing a composite nano-thin film that enables a stable performance in the air by encapsulating the silver nanowire network layer using graphene.

In addition, another object of the present invention is to provide a flexible electrode comprising a composite nano-thin film prepared by the above manufacturing method.

In order to achieve the above object, an aspect of the present invention,

Forming a silver nanowire network layer on the substrate,

A graphene layer forming step of stacking a graphene layer using wet transfer on the silver nanowire network layer, and

Light irradiation step of irradiating electron beam

It is to provide a method of manufacturing a composite nano-thin film using silver nanowires and graphene containing.

In the method of manufacturing a composite nano-thin film according to an embodiment of the present invention, the graphene lamination step is carried out by transferring the graphene layer adhered to one surface of the polymer film onto the silver nanowire network layer and then removing the polymer film. It may be.

In the method of manufacturing a composite nano-thin film according to an embodiment of the present invention, the irradiation step may be to irradiate electron beams under conditions of an acceleration voltage of 1 to 10 MeV and an irradiation dose of 20 to 200 Gy.

In the method of manufacturing a composite nano thin film according to an embodiment of the present invention, the step of forming the silver nanowire network layer may include coating a silver nanowire dispersion.

In the method of manufacturing a composite nano-thin film according to an embodiment of the present invention, the substrate may be a hydrophilic silicon substrate.

In the method of manufacturing a composite nano thin film according to an embodiment of the present invention, the silver nanowire may have a diameter of 2 to 100 nm and a length of 1 to 100 μm.

In the method of manufacturing a composite nano-thin film according to an embodiment of the present invention, the graphene layer is selected from graphene materials such as graphene particles, graphene quantum dots, graphene ribbons, graphene flakes, and mixtures thereof It may be formed of any one component.

In addition, another aspect of the present invention is manufactured by the above manufacturing method, and includes a substrate, a silver nanowire network layer, and a graphene layer, wherein the graphene layer is encapsulated with silver nanowires to encapsulate the silver nanowire network layer. It is to provide a composite nano thin film.

The composite nano-thin film according to an embodiment of the present invention may have an average sheet resistance of 100 ohm/sq or less and a sheet resistance increase rate of 50% or less according to a 10,000 bending test with a radius of curvature of 1 cm.

In addition, another aspect of the present invention is to provide a flexible electrode comprising the composite nano-thin film.

The method of manufacturing a composite nano-thin film using silver nanowires and graphene according to the present invention has an effect of significantly improving the electrical conductivity of the composite nano-thin film by dramatically reducing the contact resistance between the silver nanowires and graphene.

In addition, by encapsulating the silver nanowire network layer using a graphene layer, it has an effect capable of realizing stable performance in the long term.

In addition, it has an effect of providing a flexible electrode applicable to various fields by using a composite nano thin film having excellent electrical properties as well as durability and atmospheric stability.

1 schematically shows a composite nano thin film according to an aspect of the present invention.
FIG. 2(a) shows the composite nano thin film according to Example 1 by SEM, and FIG. 2(b) shows the composite nano thin film according to Example 1 by TEM.
3 is a graph showing the XPS Ag 3d core level spectra according to the electron beam irradiation dose of Comparative Example 1 (left) and Example 1 (right).
4 is a graph showing sheet resistance stability over time of the composite nano thin film according to Comparative Example 1 (Ag/SiO ₂ ) and Example 1 (G/Ag/SiO ₂ ).
5 shows a photograph of a bending test for a composite nano thin film.
6 is a graph showing the results of the bending test of the composite nano-thin film according to Example 1.

Hereinafter, a method of manufacturing a composite nano thin film using silver nanowires and graphene of the present invention, a composite nano thin film prepared therefrom, and a flexible electrode including the composite nano thin film will be described in detail with reference to the accompanying drawings. The present invention can be better understood by the following examples. The following examples are for illustrative purposes of the present invention and are not intended to limit the scope of protection defined by the appended claims. At this time, the technical terms and scientific terms to be used, unless otherwise defined, has a meaning commonly understood by those of ordinary skill in the art to which this invention belongs.

The inventors of the present invention have excellent electrical conductivity and are deepening research on nanomaterials that can secure performance stability in the air, and have a low sheet resistance by significantly lowering the contact resistance occurring at the intersection between silver nanowires. A silver nanowire network layer having a, and formed on the network layer, while providing an additional charge transfer path, and at the same time encapsulating the network layer, realizing high electrical conductivity and providing excellent electrical properties and performance stability without increasing long-term sheet resistance. The present invention was completed by discovering a method capable of manufacturing a composite nano-thin film of silver nanowires and graphene.

Method of manufacturing a composite nano-thin film using silver nanowires and graphene according to an aspect of the present invention

Forming a silver nanowire network layer on the substrate,

A graphene layer forming step of stacking a graphene layer using wet transfer on the silver nanowire network layer, and

And a light irradiation step of irradiating the electron beam.

Specifically, the step of forming the silver nanowire network layer includes a process of coating the silver nanowire dispersion on the substrate.

The silver nanowire network layer has a plurality of silver nanowires individually intersecting other silver nanowires and has at least one intersection point, and these intersection points are formed by bonding by a light irradiation step of a post process.

The silver nanowire is a nano thin film, but the diameter or length is not limited in a range in which physical properties are not significantly reduced, but the diameter may be 2 to 100 nm, specifically 5 to 90 nm, more specifically 10 to 80 nm, and length It may be 1 to 100 μm, specifically 2 to 50 μm, and more specifically 5 to 30 μm. In the above range, by diversifying the movement path of the charge through the intersection formed between the silver nanowires, it has the property of not only improving electrical conductivity but also securing performance stability in physical deformation such as bending, but this is only a non-limiting example. , It is not limited to the above numerical range.

According to an aspect of the present invention, the silver nanowire network layer may be formed by coating a silver nanowire dispersion, but may be formed by coating or deposition by a known method within a range that does not impair the properties of the nano thin film. , But is not limited thereto.

The silver nanowire dispersion is a solution in which silver nanowires are dispersed in a solvent. The solvent is not particularly limited as long as it can disperse the silver nanowires well. For example, water, isopropyl alcohol, methanol, ethanol, butanol, 2-ethoxy ethanol, 2-butoxy ethanol, 2-methoxy Propanol, cyclohexanone, N-methyl-2-pyrrolidone (NMP), acetone, dimethylformamide (DMF), dimethylsulfoxide (DMSO, Dimethylsulfoxide), cyclohexyl pi Cyclohexyl-pyrrolidinone (CHP), chloroform, chlorobenzene, benzonitrile, quinoline, benzyl ether, tetrahydrofuran (THF), ethylene glycol, N-vinylpyrrolidone, methyl ethyl ketone, ethyl acetate and acrylic It may be any one or more selected from the group consisting of nitrile, but is not limited thereto. At this time, the solvent may have a content in the dispersion of 0.1 to 5% by weight, specifically 0.2 to 3% by weight. In the above range, it is effective in improving the coatability of the silver nanowire dispersion and the dispersibility of the silver nanowire, but is not limited thereto.

As an aspect of forming the silver nanowire network layer, a process of spin coating the silver nanowire dispersion may be performed.

The silver nanowire network layer formed by the above-described coating process is only in which silver nanowires are in physical contact with each other, and since there are no junctions at the crossing parts, the sheet resistance due to application is very large. This has the property of significantly reducing the resistance as a charge transfer path by joining the intersection point through light irradiation in a post process.

The substrate on which the silver nanowire network layer is formed is not particularly limited, but may be any one selected from a glass substrate, a polymer film substrate, and a silicon substrate. The polymer film may include polyethylene terephthalate (PET), but is not limited thereto.

According to an aspect of the present invention, the substrate may be a silicon substrate, specifically, a hydrophilic silicon transparent substrate, specifically SiO ₂ /Si. This is more effective in that the coating property of the silver nanowire dispersion is improved, the silver nanowire can be uniformly enhanced on the substrate, and the silver nanowire network layer can be stably formed. no.

According to an aspect of the present invention, silver nanowires have low electrical resistance, have ITO-level electrical conductivity and transparency, and are effective because they can implement excellent flexibility and mechanical stability compared to ITO, which has poor bending characteristics, but the present invention Metal nanowires other than silver nanowires can be used in combination within a range that does not deviate from the intended purpose of. The metal nanowire may include any one or more selected from the group consisting of copper nanowires, nickel nanowires, gold nanowires, and iron nanowires, and is not particularly limited as long as it has a conductive material.

When the silver nanowire network layer is formed, a graphene layer forming step of stacking a graphene layer on the silver nanowire network layer is performed.

At this time, graphene may be formed using a known method. As an example, the method of forming graphene may be synthesized and deposited by thermal chemical vapor deposition (thermal CVD), but is not limited thereto. Further, the graphene may be a single layer or a laminate in which a plurality of single layers are stacked.

According to an aspect of the present invention, the graphene layer forming step includes a process of transferring the graphene layer adhered to one surface of the polymer film onto the silver nanowire network layer and then removing the polymer film.

The transfer method may be performed through a wet transfer process. This is to form a graphene layer on top of a silver nanowire network, and to form a graphene layer very densely compared to applying a coating solution containing graphene, which can further improve the mechanical strength, especially flexibility, of the composite nano thin film. At the same time, the surface resistance that can be generated at the contact point of silver nanowires and graphene formed through light irradiation in the post process can be significantly lowered, and thus it has the characteristics of realizing excellent electrical conductivity.

Furthermore, the silver nanowires can be easily oxidized by moisture or oxygen in the atmosphere, and the graphene layer formed by wet transfer effectively enhances the encapsulation of the silver nanowire network layer, thereby effectively reducing the silver nanowire network layer. It is possible to protect the oxidation, and thus it is more effective in securing atmospheric stability and long-term performance stability of the composite nano-thin film of silver nanowires and graphene. At this time, encapsulation means that the silver nanowire network layer is sealed so as not to be exposed to the outside due to the graphene layer formed on the silver nanowire network layer.

As the wet transfer process, a known method may be used, and in one embodiment, after spin coating methyl methacrylate (PMMA) on the graphene surface synthesized on a copper substrate through thermal chemical vapor deposition, copper etchant is used. It may be a method of removing copper by using it, placing it on a desired substrate, and removing PMMA using acetone to transfer it to a desired substrate, but is not limited thereto.

The graphene layer may be a single-layer graphene or two or more multi-layer graphene layers, and the thickness thereof is not particularly limited in a range that does not depart from the scope of the present invention, specifically 1 to 10 nm, more specifically 2 to 5 nm It may be. It is more effective in securing optical transmittance and flexibility in terms of utilizing the transparent flexible electrode as well as improving the electrical conductivity, encapsulation and durability of the silver nanowire network layer in the above range.

According to an aspect of the present invention, the graphene layer may be formed of any one or more of graphene or reduced graphene oxide, graphene particles, graphene quantum dots, graphene ribbon, graphene flakes, and mixtures thereof It may be formed of any one component selected from, but is not necessarily limited to.

When a graphene layer is formed on the silver nanowire network layer, a light irradiation step of irradiating electron beams to the stack is performed.

According to an aspect of the present invention, the light irradiation step is a graphene and silver nanowires of the graphene layer formed on the silver nanowire network layer as well as individual silver nanowires inside the silver nanowire network layer by irradiating high energy electron beams. Nano welding is performed at the junction or contact point that is in physical contact, and these are more effective in improving the mechanical stability as well as the flexibility of the thin film, as well as significantly lowering the sheet resistance through solid bonding. Nano-welding through such light irradiation can be performed without damaging the substrate in connecting the silver nanowires and the contact portion between the silver nanowires and graphene, and is advantageous for a substrate having high selectivity and a large area or flexibility. It has characteristics.

The light irradiation is not significantly limited in the range of achieving the object of the present invention, but the irradiation dose is 20 to 200 Gy at an acceleration voltage of 1 to 10 MeV, specifically 30 to 190 Gy, more specifically 50 to It is effective to irradiate electron beams to be 180 Gy. The nano-welding in the above range is more effective because the bonding of the silver nanowire through the contact portion of the graphene is well made, which can significantly lower the sheet resistance and further improve the mechanical properties and durability. However, if it is less than the above range, a desired effect may not be achieved, or if it exceeds the above range, a part of the silver nanowire may be damaged, and performance according to the combination of the silver nanowire network layer and graphene layer including electrical conductivity may deteriorate. Preferably, it is effective to be carried out within the above irradiation conditions.

The irradiation of the electron beam may use a large pulsed electron beam (LPEB), but is not limited thereto.

In addition, another aspect of the present invention relates to a composite nano thin film manufactured using silver nanowires and graphene. The composite nano-thin film is manufactured by the above-described manufacturing method, and as shown in FIG. 1, the silver nanowire and graphene are bound through electron beam irradiation on a graphene layer stacked on a silver nanowire network layer formed on a substrate. will be. Specifically, it includes a substrate, a silver nanowire network layer and a graphene layer, and the graphene layer is encapsulated with a silver nanowire to encapsulate the silver nanowire network layer.

The graphene layer is stacked on top of the silver nanowire network layer through a wet transfer process, and the number of junction points between the silver nanowire and graphene can be further increased, and the continuous and robust layer improves the mechanical stability and flexibility of the composite nano thin film. Have Furthermore, it is more effective in that it has the property of realizing excellent electrical conductivity because it can significantly lower the resistance at the junction.

That is, the graphene layer tightly and tightly surrounds the silver nanowire network layer, and thus, through efficient encapsulation of the silver nanowire network layer, the anti-oxidation effect of the silver nanowire is excellent, and furthermore, the surface resistance is significantly lowered, and the air stability and performance stability It has more effective characteristics to secure it.

The composite nano-thin film has an average sheet resistance of 100 ohm/sq or less, and a sheet resistance increase rate (ΔR/R ₀ -ΔR: resistance change value, R ₀ : initial resistance value) according to a 10,000 bending test with a radius of curvature of 50%. It may be the following. At this time, the bending test was performed so that the curvature radius of the sample was 1 cm for the composite nano thin film having a thickness of 1 to 10 nm.

In addition, the present invention can provide a flexible electrode comprising the composite nano thin film. The flexible electrode can be manufactured by a known method, and has characteristics that can secure excellent electrical conductivity and mechanical stability despite physical deformation of the electrode. In addition, the flexible electrode has excellent air stability and has characteristics that can secure long-term performance stability, and thus can be applied to various fields such as electronic devices to which flexibility is provided.

Hereinafter, a method for manufacturing a composite nano thin film according to the present invention, a composite nano thin film prepared therefrom, and a flexible electrode material including the composite nano thin film will be described in more detail. However, the following examples are only one reference for explaining the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

(Example 1)

Silver nanowire network layer formation step

Silica (SiO ₂ )(300nm)/Si(001) substrate whose surface is hydrophilized by irradiating ultraviolet rays with silver nanowires (average diameter: 60nm, average length: 10㎛) dispersed in isopropyl alcohol at a concentration of 0.5wt% Spin coating was performed for 30 seconds at a rotation speed of 30 rpm. Then, heat treatment was performed at 150°C for 5 minutes.

Graphene layer formation step

Graphene was synthesized using thermal chemical vapor deposition. After placing a 25 μm thick copper foil inside the reactor, 200 sccm of hydrogen gas was injected for 2 hours at a temperature of 1050° C. to planarize the surface of copper and remove the oxide film and preliminary annealing for oxide film removal ( pre-annealing). After preliminary annealing, graphene was synthesized under a pressure of 3.6 torr while injecting methane gas and hydrogen gas as carbon sources at 2 sccm and 200 sccm for 80 minutes, respectively.

The synthesized graphene was transferred onto the SiO ₂ /Si substrate on which a silver nanowire network layer was formed through a wet transfer process based on polymethylmethacrylate (PMMA). At this time, the transfer is spin-coated with methyl methacrylate (PMMA) on the graphene surface synthesized on the copper substrate through a thermal chemical vapor deposition method, and then copper is removed using a copper etchant and placed on the desired substrate, followed by acetone. It was carried out by removing PMMA. At this time, graphene was a single layer (thickness of 10 nm), and the size was 2 cm×2 cm.

Light irradiation stage

The electron beam was irradiated on the silver nanowire network layer. As the electron beam, a large pulsed electron beam (LPEB) was used. At this time, the acceleration voltage was set to 2 MeV, and the irradiation dose was set to 150 kGy. In addition, the irradiation environment was set to normal temperature and normal pressure.

(Example 2)

In Example 1, it was carried out in the same manner as in Example 1, except that the irradiation dose was changed from 150 kGy to 180 kGy.

(Example 3)

In Example 1, it was carried out in the same manner as in Example 1, except that the irradiation dose was changed from 150 kGy to 20 kGy.

(Example 4)

In Example 1, it was carried out in the same manner as in Example 1, except that the irradiation dose was changed from 150 kGy to 200 kGy.

(Example 5)

In Example 1, it was carried out in the same manner as in Example 1, except that the irradiation dose was changed from 150 kGy to 10 kGy.

(Example 6)

In Example 1, it was carried out in the same manner as in Example 1, except that the irradiation dose was changed to 30 kGy to 210 kGy.

(Comparative Example 1)

Instead of forming the graphene layer in the wet transfer process in Example 1, it was carried out in the same manner as in Example 1, except that the graphene layer was formed as follows and the light irradiation step was omitted.

0.2 mg of the synthesized graphene was put into a 20 ml DMF solution, mixed by ultrasonic treatment, and then stirred at high speed using a homogenizer to prepare a graphene solution. Thereafter, the graphene solution was spray-coated on the silver nanowire network layer formed on the substrate so that the weight of the silver nanowire was 1 wt% by weight, thereby forming a graphene layer. The formed graphene layer had a thickness of 10 nm.

(evaluation)

The sheet resistance was measured and the values are shown in Table 1 below. In this case, the surface resistance was measured by using a surface resistance meter (4 point probe measurement), and measuring the current and voltage through four probes at the same interval to obtain the resistance value and applying the correction coefficient.

[Table 1]

Figure 2 is a composite nano-thin film of Example 1 analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Figure 2 (a) is between the silver nanowires through wrinkles identified in the silver nanowire junction It can be seen that the binding has been achieved. In addition, in FIG. 2(b), only the graphene is identified as a graphene layer in the left dotted region (only graphene), while the right dotted region can be confirmed that the graphene is bonded to silver nanowires through an electron diffraction pattern (junction). . It can be seen that encapsulation of graphene in a form surrounding the surface of the silver nanowire was made by the graphene layer formed by transferring graphene by wet transfer on the silver nanowire coated on the substrate.

FIG. 3 is a graph showing XPS Ag 3d core level spectra according to the radiation dose of electron beams, for confirming whether to effectively inhibit oxidation of silver nanowires that may occur when an electron beam is irradiated at normal temperature and pressure. The peaks associated with silver oxide have a higher binding energy than the peaks of pure silver. In Examples 1, 2 and 4 (Graphene-Ag), the peaks of silver oxide are not observed even when the electron beam irradiation dose is increased, whereas the graphene layer In the case of Comparative Example 1 (Ag), which was not formed, as the electron beam irradiation dose increased, the peaks associated with silver oxide having a high binding energy appeared broadly as in the Examples, and it was found that silver oxide was generated. Examples did not show such a peak pattern, it was confirmed that the composite nano-thin film according to the present invention can effectively inhibit the oxidation of silver nanowires due to the graphene layer encapsulating the silver nanowires.

4 is a graph showing the sheet resistance stability over time of the composite nano-thin film. As a result, in the case of Comparative Example 1 (Ag/SiO ₂ ), after 85 days, the sheet resistance increased by almost 847 times from 51 Ohm/sq to 43212 Ohm/sq, whereas Example 1 (G/Ag/SiO _{2 ).} In the case of ), it was confirmed that after 85 days, the sheet resistance increase rate was almost unchanged by 13.3%, and thus, it had excellent electrical stability.

In addition, Figure 6 shows the results of the bending test for the composite nano-thin film according to Example 1. The bending test was performed by repeating the bending operation over 10,000 times using the bending tester shown in FIG. 5. Prior to the operation, the specimen was fixed between two rolls provided at both ends of the bending tester, and then the curvature radius was adjusted to 1 cm by changing the spacing between both ends, and tests were conducted through repeated length changes based on this. As a result, it was confirmed that the sheet resistance increase rate was less than 50%, and the flexibility was very excellent.

Although the preferred embodiments of the present invention have been described above, it is clear that the present invention can use various changes, modifications, and equivalents, and can be equally applied by appropriately modifying the above embodiments. Therefore, the above description is not intended to limit the scope of the present invention as defined by the following claims.

Claims (10)

Forming a silver nanowire network layer on the substrate,
A graphene layer forming step of stacking a graphene layer using wet transfer on the silver nanowire network layer, and
Light irradiation step of irradiating electron beam
Method of manufacturing a composite nano-thin film using silver nanowires and graphene containing. According to claim 1,
In the step of forming the graphene layer, a graphene layer adhered to one surface of a polymer film is transferred onto a silver nanowire network layer and then removed by removing the polymer film. According to claim 1,
The light irradiation step is a method of manufacturing a composite nano-thin film is to irradiate electron beams under conditions of an acceleration voltage of 1 to 10 MeV and an irradiation dose of 20 to 200 Gy. According to claim 1,
The step of forming the silver nanowire network layer is a method of manufacturing a composite nano thin film comprising coating a silver nanowire dispersion. According to claim 1,
The substrate is a method of manufacturing a composite nano thin film that is a hydrophilic silicon substrate. According to claim 1,
The silver nanowire has a diameter of 2 to 100 nm, and a method of manufacturing a composite nano thin film having a length of 1 to 100 μm. According to claim 1,
The graphene layer is a graphene particle, a graphene quantum dot, a graphene ribbon, a graphene flake, and a method of manufacturing a composite nano thin film formed of any one component selected from mixtures thereof. It includes a substrate, a silver nanowire network layer and a graphene layer,
The graphene layer is a composite nano-thin film that is encapsulated with a silver nanowire to encapsulate a silver nanowire network layer. The method of claim 8,
The composite nano thin film has an average sheet resistance of 100 ohm/sq or less, and a composite nano thin film having an increase in sheet resistance of 50% or less according to a 10,000 bending test with a radius of curvature of 1 cm. A flexible electrode comprising the composite nano-thin film of claim 8.

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