KR102722103B1 - Fabrication method of conductive nanonetworks using nanomask - Google Patents

Abstract

The present invention relates to a method for manufacturing a transparent conductive network using a nanomask, which can improve the electrical and optical characteristics of a transparent conductive network by eliminating contact resistance between nanowires and minimizing surface roughness of the transparent conductive network when forming a transparent conductive network. The method for manufacturing a transparent conductive network using a nanomask according to the present invention comprises the steps of: laminating a conductive thin film on a substrate; forming a nanomask in the form of a nanowire network on the conductive thin film; performing anisotropic etching on the entire surface of the substrate to etch and remove the conductive thin film in an area where the nanomask is not provided; and removing the nanomask. The method is characterized in that the conductive thin film in an area where the nanomask is provided is a conductive network.

Description

{Fabrication method of conductive nanonetworks using nanomask}

The present invention relates to a method for manufacturing a transparent conductive network using a nanomask, and more specifically, to a method for manufacturing a transparent conductive network using a nanomask, which can improve the electrical and optical characteristics of a transparent conductive network by eliminating contact resistance between nanowires and minimizing surface roughness of the transparent conductive network when forming the transparent conductive network.

ITO (indium tin oxide) is widely used as a transparent electrode for various display modules, which has a transmittance of about 85% and a sheet resistance of 15 Ω/sq. However, the indium component that composes ITO is limited in reserves and locations, so its supply is unstable and its price is relatively high. In addition, expensive and bulky vacuum equipment and high maintenance costs are required to perform the ITO deposition process, and it is not suitable for application to flexible electrodes due to the characteristics of the oxide that breaks.

Recently, research on transparent conductive films using flexible metal nanowires that can be processed at low temperatures has been actively conducted. For example, Korean Patent No. 1011447 proposes a technology for manufacturing a metal polymer film by drying a metal polymer solution having metal nanowires dispersed therein on a mold and for stretching the metal polymer film in one direction. In addition, U.S. Patent No. US 10831233 proposes a technology for forming a patterned conductive layer by coating a conductive layer including nanowires on a matrix, forming a resist pattern on the conductive layer, overcoating a peelable polymer layer, and then removing the peelable polymer layer so that the conductive layer is removed in an area where the resist pattern is not formed.

However, the technology disclosed in Korean Patent No. 1011447 has the disadvantage of inevitably having contact resistance between the metal nanowires and having a large surface roughness because the transparent conductive film is formed in the form of overlapping metal nanowires. In addition, post-processing such as heat treatment and laser treatment is required to reduce the contact resistance between the metal nanowires, but this is a process that is not bonded to a polymer flexible substrate. In addition, the wet process according to the conventional technology is difficult to apply to a substrate that is extremely hydrophobic.

The technology disclosed in U.S. Patent No. US 10831233 does not have the problems of Korean Patent No. 1011447 because it does not utilize a metal polymer solution in which metal nanowires are dispersed, but has the disadvantage of requiring a complex process, such as the formation of a resist pattern and a polymer layer.

Korean Patent No. 1011447 (announced on January 28, 2011) US Patent No. US 10831233 (announced on November 10, 2020)

The present invention has been made to solve the above problems, and the purpose of the present invention is to provide a method for manufacturing a transparent conductive network using a nanomask, which can improve the electrical and optical characteristics of a transparent conductive network by eliminating contact resistance between nanowires and minimizing the surface roughness of the transparent conductive network when forming a transparent conductive network.

In addition, another purpose of the present invention is to provide a method for manufacturing a transparent conductive network using a nanomask, which can control the electrical and optical properties of the conductive network by controlling not only the thickness of the conductive thin film but also the material of the nanomask, nanomask process conditions, etc. during the process of manufacturing the conductive network.

In order to achieve the above object, the present invention provides a method for manufacturing a transparent conductive network using a nanomask, comprising: a step of laminating a conductive thin film on a substrate; a step of forming a nanomask in the form of a nanowire network on the conductive thin film; a step of performing anisotropic etching on the entire surface of the substrate to etch and remove the conductive thin film in an area where the nanomask is not provided; and a step of removing the nanomask. The method is characterized in that the conductive thin film in an area where the nanomask is provided is a conductive network.

The above nanomask is a nanowire network made of metal nanowires or a nanowire network made of nanofibers. The nanomask made of the metal nanowires can be formed using a spray coating or spin coating method, and the nanowire network made of the nanofibers can be formed using an electrospinning method.

By controlling the geometric shape of the above nanomask, the geometric shape of the conductive network can be changed, thereby controlling the electrical and optical properties of the conductive network.

In forming a nanomask using an electrospinning method, the geometric shape of the nanofibers formed on the substrate can be controlled by controlling at least one of the needle diameter of the electrospinning device, the voltage applied to the needle, and the concentration of the solution containing the material forming the nanofibers.

The conductive thin film is one or a combination of a conductive metal, a carbon-based conductive material, a conductive polymer, and a conductive nanoparticle.

The method for manufacturing a transparent conductive network using a nanomask according to the present invention has the following effects.

Since the conductive network is formed by patterning a conductive thin film using a nanomask in the form of a nanowire network, the surface roughness characteristics are excellent and the contact resistance between metal nanowires can be fundamentally eliminated. In addition, since a post-processing process such as heat treatment or laser treatment to improve the electrical resistance characteristics is not required, there is no limitation on the use of a flexible substrate, and the conductive network process can be applied regardless of the properties of the substrate. In addition, the geometric shape of the conductive network can be changed by controlling the thickness of the conductive thin film and the process conditions of the nanomask, and thereby the optical and electrical characteristics of the conductive network can be controlled.

FIG. 1 is a flowchart illustrating a method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention.
FIG. 2 is a process schematic diagram illustrating a method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention.
FIGS. 3A to 3D are process reference diagrams for explaining a method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention.
FIG. 4a and FIG. 4b are reference drawings showing the form of a metal nanowire of the prior art and a conductive network according to the present invention.
Figures 5a and 5b and Figures 6a and 6b are SEM images of the nanomask and conductive network.
Figure 7 shows the experimental results showing the optical transmittance characteristics of the conductive network manufactured by Experimental Example 1.
Figure 8 is an experimental result showing the photoelectric conversion efficiency of a solar cell in which a conductive network manufactured by Experimental Example 1 was applied as an electrode.
Figure 9 shows the experimental results showing the electrical resistance characteristics over time of the conductive network manufactured by Experimental Example 1.

The present invention proposes a technique for manufacturing a transparent conductive network through a novel process.

As described above in the 'Background Technology of the Invention', a transparent conductive film made of metal nanowires has been proposed to replace the existing ITO transparent electrode, and such a metal nanowire transparent conductive film is typically manufactured through a wet process using a nanowire solution. The wet process using a nanowire solution is a process of forming a transparent conductive film in which the metal nanowires are connected to each other by applying a solution in which metal nanowires are distributed on a substrate and removing the solvent. A transparent conductive film made of metal nanowires can be manufactured through this process; however, since the metal nanowires randomly dispersed in the solution are connected in an overlapping form, the surface roughness of the final manufactured metal nanowire transparent conductive film is large and contact resistance between the nanowires inevitably exists. In addition, the height of the metal nanowire transparent conductive film cannot be controlled.

The present invention manufactures a transparent conductive network using a nanomask, thereby fundamentally eliminating the problem of contact resistance between nanowires and minimizing the surface roughness of the final manufactured transparent conductive network.

Meanwhile, the 'conductive network' in the present invention means a conductive material forming a nano-sized network. The 'conductive network' of the present invention corresponds to a transparent conductive film, just like the 'metal nanowires forming a mesh shape' of the prior art. However, the reason the term 'conductive network' is used in the present invention is because there is a difference in configuration from the prior art using metal nanowires. While the prior art is a method of inducing a connection between metal nanowires, the present invention excludes the use of metal nanowires and directly forms a 'conductive material forming a nano-sized network'. Therefore, the 'conductive network' of the present invention and the 'metal nanowires forming a mesh shape' of the prior art can be said to have different technical configurations.

Hereinafter, a method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention will be described in detail with reference to the drawings.

Referring to Fig. 1, first, a substrate (110) is prepared. The substrate (110) is not limited in material and type. A semiconductor substrate (110) of various materials may be used, or an insulating substrate (110) such as a glass substrate (110) may be used, and a flexible polymer substrate (110) or an elastic substrate (110) may be applied. Since one purpose of the present invention is to manufacture a transparent electrode that can be applied to a large area and a flexible substrate (110), a flexible substrate (110) may be applied as an example.

In a state where the substrate (110) is prepared, a conductive thin film (120) is laminated on the substrate (110) (S101) (see FIG. 2 (a) and FIG. 3a). The conductive thin film (120) is a constituent material of a conductive network (120a) described below, and as the conductive thin film (120), a conductive metal such as Ag, Au, Al, Cu, or Ga, a carbon-based conductive material such as graphene or CNT, a conductive polymer, a conductive nanoparticle, or the like can be used, and a combination of these conductive materials can also be used.

Next, a nanomask (130) having a nanowire network shape is formed on the conductive thin film (120) (S102) (see FIG. 2 (b) and FIG. 3b). The nanomask (130) serves as a mask for patterning the conductive thin film (120).

The above nanomask (130) may be composed of a nanowire network formed of metal nanowires or a nanowire network formed of nanofibers. When forming the nanomask (130) with metal nanowires, a solution process, such as spray coating or spin coating, may be used, and when forming the nanomask (130) with nanofibers, an electrospinning method may be used. In addition, when forming the nanomask (130) with metal nanowires, the metal nanowires may use the same material as the conductive thin film (120) or a material having etching selectivity compared to the conductive thin film (120). In addition, the nanofibers may use PAN (Polyacrylonitrile), PMMA (Poly(methyl methacrylate)), PVP (poly(N-vinylpyrrolidone), etc.

In a state where a nanomask (130) in the form of a nanowire network is formed on a conductive thin film (120), anisotropic dry etching is performed on the entire surface of the substrate (110) (S103) (see FIG. 2 (c) and FIG. 3c). By the anisotropic dry etching, the conductive thin film (120) in the area where the nanomask (130) is provided is not etched, and the conductive thin film (120) in the area where the nanomask (130) is not provided is etched and removed. That is, only the conductive thin film (120) in the area where the nanomask (130) is provided by the anisotropic dry etching remains, and as the nanomask (130) forms a nanowire network, the conductive thin film (120) under the nanomask (130) also forms a nanowire network.

The conductive thin film (120) under the nanomask (130) forming a nanowire network shape is called a 'conductive network (120a)', and the conductive network (120a) is completed by the anisotropic dry etching (see FIG. 2 (d) and FIG. 3d).

When the conductive network (120a) is completed by anisotropic dry etching, and the nanomask (130) provided on the conductive network (120a) is removed (S104), the method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention is completed.

As can be seen from the above manufacturing method, while the conventional technology is a method of inducing the connection of metal nanowires, the conductive network of the present invention is formed by patterning a conductive thin film using a nanomask, and therefore, it can be seen that the conventional 'metal nanowires forming a mesh shape' and the 'conductive network' of the present invention have different technical configurations.

In addition, since the conductive network of the present invention excludes connections between metal nanowires, the surface roughness of the conductive network is minimized and the electrical and optical characteristics are improved compared to the conventional technology. In addition, referring to FIG. 4a, in the case of the structure in which the metal nanowires of the conventional technology form a mesh shape, protruding metal nanowires may exist due to the process characteristics, which may cause problems such as shorts, but the conductive network of the present invention has a flat surface since the conductive thin film is patterned, thereby avoiding problems such as shorts (see FIG. 4b).

Meanwhile, since the conductive network of the present invention is formed by patterning a conductive thin film of a certain thickness by a nanomask as described above, it is possible to control the geometric shape such as the height, diameter, and structure of the conductive network. Specifically, the height of the conductive network can be controlled by controlling the thickness of the conductive thin film, the diameter of the conductive network can be controlled by controlling the diameter of the electrospun nanofibers, and the structure of the conductive network can be selectively controlled through the structure of the metal nanowire formed through the solution process or the electrospun nanofibers.

Furthermore, as previously mentioned, PAN (Polyacrylonitrile), PMMA (Poly(methyl methacrylate)), PVP (poly(N-vinylpyrrolidone), etc. are used as materials for nanofibers. Depending on the type of material of the nanofiber or the mixing ratio of the materials, the height, diameter, and structure of the nanomask change. In addition, the diameter, size, and structure of the nanofiber change depending on the diameter of the needle that spins the solution during electrospinning of the nanofiber and the voltage applied to the needle. For reference, the electrospinning device is composed of a needle that spins the solution and a high voltage generator that applies voltage to the needle.

Changes in the geometric shape of the conductive network, such as height, diameter, and structure, are directly related to the electrical and optical properties of the conductive network. Therefore, the electrical and optical properties of the conductive network can be controlled by controlling the geometric shape of the nanomask described above.

Above, a method for manufacturing a transparent conductive network using a nanomask according to one embodiment of the present invention has been described. Hereinafter, the present invention will be described in more detail through experimental examples.

<Experimental Example 1: Manufacturing of conductive network>

After depositing a Ag thin film on a glass substrate, Ag nanowires (AgNWs) were formed on the Ag thin film by spray coating (see Fig. 5a). Separately, after depositing a Ag thin film on a glass substrate, polyacrylonitrile (PAN) was formed on the Ag thin film by electrospinning (see Fig. 6a). In each case, ion beam etching was performed, and then the AgNWs and PAN were removed. As shown in Figs. 5b and 6b, it can be confirmed that Ag networks, i.e., conductive networks, are clearly formed.

<Experimental Example 2: Optical Transmittance and Electrical Characteristics of Conductive Network>

When examining the optical transmittance of the conductive network manufactured by Experimental Example 1, it can be confirmed that the transmittance characteristics by wavelength band are excellent in both the case where the Ag conductive network is manufactured using the spray coating method (see 'Ag ink' in FIG. 7) and the case where the Ag conductive network is manufactured using the electrospinning method (see 'Ag deposition' in FIG. 7), as shown in FIG. 7.

According to Experimental Example 1, conductive networks (Ag networks) were formed on a glass substrate, and then photoactive layers, PEDOT:PSS (2000 rpm) and P3HT:PCBM (700 rpm), were formed on the Ag networks, and Ca/Al electrodes were laminated to manufacture a solar cell. As a result of measuring the photoelectric conversion efficiency of the manufactured solar cell, it was approximately 2.4%, as shown in Fig. 8, confirming that the conductive network of the present invention can be utilized as an electrode of an ultra-thin film device.

In addition, the electrical resistance characteristics of the Ag conductive network manufactured according to Experimental Example 1 and the AgNW manufactured according to the conventional technique over time were examined. Referring to Fig. 9, the Ag conductive network shows almost no change in resistance even after 190 hours, whereas the AgNW shows a pattern in which the resistance increases rapidly from about 20 hours onwards.

110: Substrate 120: Conductive thin film
120a : Conductive network 130 : Nanomask

Claims (6)

A step of laminating a conductive thin film on a substrate;
A step of forming a nanomask in the form of a nanowire network on a conductive thin film;
A step of performing anisotropic etching on the entire surface of the substrate to etch and remove the conductive thin film in an area where the nanomask is not provided; and
It comprises a step of removing the nano mask;
The conductive thin film in the area equipped with the nanomask is a conductive network,
The above nanomask is a nanowire network made of nanofibers.
A method for manufacturing a transparent conductive network using a nanomask, characterized in that the nanowire network made of the above nanofibers is formed using an electrospinning method.
A step of laminating a conductive thin film on a substrate;
A step of forming a nanomask in the form of a nanowire network on a conductive thin film;
A step of performing anisotropic etching on the entire surface of the substrate to etch and remove the conductive thin film in an area where the nanomask is not provided; and
It comprises a step of removing the nano mask;
The conductive thin film in the area equipped with the nanomask is a conductive network,
The above nanomask is a nanowire network made of metal nanowires.
Nanomasks made of metal nanowires are formed using a solution process.
A method for manufacturing a transparent conductive network using a nanomask, characterized in that the solution process utilizes spray coating or spin coating.
delete A method for manufacturing a transparent conductive network using a nanomask, characterized in that in claim 1 or 2, the electrical and optical properties of the conductive network can be controlled by changing the geometric shape of the conductive network through controlling the geometric shape of the nanomask.
A method for manufacturing a transparent conductive network using a nanomask, characterized in that in claim 1, when forming a nanomask using an electrospinning method, the geometric shape of the nanofibers formed on a substrate can be controlled by controlling at least one of the needle diameter of an electrospinning device, the voltage applied to the needle, and the concentration of a solution containing a material forming nanofibers.
A method for manufacturing a transparent conductive network using a nanomask, characterized in that in claim 1, the conductive thin film is one or a combination of a conductive metal, a carbon-based conductive material, a conductive polymer, and a conductive nanoparticle.

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