KR20150075173A - Transparent electrode comprising transparent conductive oxide and Ag nanowire and the fabrication method thereof - Google Patents

Abstract

The present invention relates to a transparent electrode including transparent conductive oxide (TCO) and an Ag nanowire and a manufacturing method thereof and, more particularly, to a transparent electrode which includes a first conductive layer with the Ag nanowire and a second conductive layer which is formed on the first conductive layer by over coating, and a manufacturing method thereof. Wherein, the second conductive layer includes the TCO made by a combustion method.

Description

TECHNICAL FIELD [0001] The present invention relates to a transparent electrode including a transparent conductive oxide and a silver nanowire, and a transparent electrode comprising the transparent conductive oxide and Ag nanowire and the fabrication method thereof.

The present invention relates to a transparent electrode including a transparent conductive oxide (TCO) and a silver (Ag) nanowire, and more particularly, to a transparent electrode comprising a first conductive layer including silver nanowires, And a second conductive layer formed over the first conductive layer, wherein the second conductive layer comprises a TCO produced by a combustion method. ≪ / RTI >

In general, a transparent electrode is a light-transmissive and electrically conductive electrode. The transparent electrode may be a flat liquid crystal display, a touch panel, an electroluminescent device, or a thin film photovoltaic cell. Its importance is increasing day by day for applications.

Currently, vacuum deposited metal oxides, such as indium tin oxide (ITO), are used for optical transparency and electrical conductivity for dielectric surfaces such as glass and polymeric films Are industry standard materials to provide. However, metal oxide films require a high deposition temperature or a high annealing temperature in order to achieve high conductivity levels, and are susceptible to fragility and brittle fracture by external physical stimulation. Also, when the substrate is coated on the polymer substrate, the film is broken when the substrate is bent.

Conductive polymers, carbon nanotubes, graphene, and metal nanowires are attracting attention as a solution to these problems.

In the case of silver (Ag) or copper (Cu) nanowire among the metal nanowires, the solution is based on a coating having a high transmittance in a visible light region and a surface resistance similar to that of ITO. Particularly, when silver nanowires are coated on a transparent substrate while forming a network like a network, they can be manufactured as transparent electrodes having high conductivity with high light transmittance.

However, in the case of the silver electrode, when exposed to the atmosphere, the silver electrode is oxidized in the form of Ag ₂ O, AgO, Ag ₂ O ₂ or the like to form a silver oxide film on the electrode surface. Therefore, when exposed to oxygen in the atmosphere for a long time, the silver color changes to black, and the electrical resistance increases rapidly by 500 times or more. This oxidation of silver significantly lowers the reliability of the transparent electrode.

Also, when a transparent conductive film is formed using only silver (Ag) nanowires, the silver nanowires are broken under high temperature process conditions, and the conductivity is rapidly lowered. In addition, it is very difficult to perform lamination printing of the next material for the implementation of a device such as a TFT (thin film transistor) when the surface of the transparent electrode is made of silver nanowire only, and the haze increases, . Therefore, attempts have been made to fill or coat (laminate) the rough surface of the silver nanowire layer with another transparent electrode material.

For example, Patent Document 1 (WO 2007/022226) discloses an entire transparency in which a network of silver nanowires is overcoated with an optically transparent polymer matrix material, and Patent Document 2 2013-0048333) discloses a transparent electrode comprising a silver nanowire network layer and a polymeric protective film.

According to the above methods, since the silver (Ag) nanowire is formed between the transparent substrate and the polymer layer, the contact with oxygen and moisture in the atmosphere is minimized, thereby suppressing an increase in resistance due to oxidation of silver and a decrease in electrical conductivity It can fill the rough surface of the silver nanowire and solve the problem caused by the protruding silver nanowire.

However, the polymer is disadvantageous in that it is inferior in conductivity compared with materials of ITO or metal nanostructures, and has poor stability including light stability.

WO2007 / 022226 A KR 2013-0048333 A

A problem to be solved by the present invention is to provide a transparent electrode improved in physical, optical and electrical characteristics by including silver nanowires overcoated with a TCO produced by a combustion method.

Another object of the present invention is to provide a method of fabricating a semiconductor device, which comprises forming a first conductive layer including silver nanowires on a transparent substrate through a solution process and a second conductive layer including the TCO capable of low temperature firing, And to provide a transparent electrode manufacturing method which is effectively reduced.

According to an aspect of the present invention, A first conductive layer formed on the transparent substrate, the first conductive layer including a plurality of silver (Ag) nanowires; And a second conductive layer formed by overcoating the silver nanowires protruding from the surface of the first conductive layer as a whole, wherein the second conductive layer is formed of a transparent conductive material produced by a combustion method, And a transparent conductive oxide (TCO).

The surface resistivity of the transparent conductive oxide (hereinafter referred to as " Combustion TCO ") produced by the above combustion method is preferably 10 to 500 ohm / sq and the average thickness is preferably 10 to 1000 nm. Firing can be performed at a temperature of preferably 100 to 200 ° C.

The present invention also provides a method of manufacturing a silver nanowire dispersion, comprising: a first coating step of coating a silver nanowire dispersion solution on a transparent substrate; A first heat treatment step of removing the solvent from the coated silver nanowire dispersion solution to form a first conductive layer; A second coating step of overcoating a Combustion TCO dispersion solution on the first conductive layer; And a low temperature firing step of forming a second conductive layer by performing a second heat treatment on the first conductive layer coated with the Combustion TCO dispersion solution.

 According to the invention, it is possible to provide a transparent electrode having high electrical conductivity while preventing oxidation of silver by overcoating silver nanowires vulnerable to oxidation by Combustion TCO.

Since the combustion TCO included in the overcoat layer fills the empty space of the silver nanowire and covers the rough surface, the surface roughness of the first conductive layer formed of the silver nanowire can be reduced, and the haze reduction And a high transmittance effect can be obtained. In addition, it is also possible to obtain an effect of improving the adhesion with the next material for implementing devices such as TFTs.

Since the silver nanowires are physically bound by a combustion TCO, the silver nanowires can be broken even at a high process temperature, thereby preventing a sharp decrease in conductivity.

In addition, since the first conductive layer made of silver nanowires and the second conductive layer formed of Combustion TCO are formed on the transparent substrate using the solution process, the manufacturing cost can be lowered compared with the vacuum sputtering process.

1 is a schematic view showing an embodiment of a transparent electrode manufactured according to the present invention.
2 is a scanning electron microscope (SEM) photograph of silver nanowires according to a heat treatment temperature.
FIG. 3 is a scanning electron microscope (SEM) image of silver nanowires overcoated with ITO (right) and silver nanowires (left) not coated with a heat treatment at 250 ° C.

The present invention relates to a transparent electrode; A first conductive layer formed on the transparent electrode, the first conductive layer including a plurality of silver (Ag) nanowires; And a second conductive layer formed by overcoating the silver nanowires protruding from the surface of the first conductive layer as a whole, wherein the second conductive layer is formed of a transparent conductive material produced by a combustion method, And a transparent conductive oxide (TCO).

The combustion method is a method that was established in 1966 by AG Merzhanov of Russia to establish combustion theory and to nano-scale synthesis of oxide ceramic materials such as aluminates, ferrites and chromites. The principle is that when heat is applied to a precursor solution containing an oxidizing agent (metal nitrate) and a reducing agent (fuel) at a temperature of 300 ° C or less, it instantaneously and locally explodes due to an exothermic reaction caused by the oxidation / 2,000 ℃) It is possible to make fine powder easily at relatively low temperature and short time. Particularly, in the case of powders produced by the combustion synthesis method, very fine particles are uniformly obtained in comparison with the solid phase reaction method. This is because, in the exothermic reaction process, a large amount of environmentally friendly gases such as N ₂ , CO ₂ and H ₂ O are generated, And the heat is dispersed evenly.

In the present invention, any one of the direct combustion method, the catalytic combustion method, the solution combustion method and the sol-gel combustion method may be used as the combustion method, and more preferably, the sol-gel combustion method is used.

The transparent conductive oxide (hereinafter referred to as " Combustion TCO ") produced by the combustion method can be fired at 100 to 250 ° C, preferably at a low temperature of 100 to 200 ° C. When the firing temperature is less than 100 ° C, the conductivity is insufficient, which makes it difficult to use the transparent electrode. On the other hand, when the firing temperature is higher than 250 ° C, it is difficult to apply it to a flexible plastic substrate.

When a conventional TCO instead of Combustion TCO according to the present invention is used as an overcoat layer of silver nanowires, a sputtering method of a vacuum process has been mainly used, and there has been a limitation in forming a large-area transparent conductive film due to the vacuum process required. Therefore, when a solution process is applied to form a large-area transparent conductive film, a high-temperature firing process is necessary to achieve the level of conductivity required for the transparent electrode. Therefore, it was impossible to apply the present invention to a flexible plastic substrate requiring a temperature condition of 250 DEG C or less.

The use of Combustion TCO capable of low temperature firing as in the present invention as an overcoat layer makes it possible to manufacture a transparent electrode having excellent conductivity even after baking at a temperature of 250 DEG C or less after overcoating and thus can be applied to a flexible plastic substrate .

The conductivity of the transparent electrode is inversely proportional to the surface resistivity of the conductive layer (often referred to as sheet resistance), which can be measured by methods known in the art. Specifically, Table 1 shows that the transparent electrode manufactured according to the embodiment of the present invention has low sheet resistance and excellent conductivity.

The surface resistance of the Combustion TCO may be in the range of 10 to 500 ohm / sq. If the sheet resistance value is within the above range, it can be applied to a conductive material having excellent conductivity.

The average thickness of the Combustion TCO is preferably 1 to 1000 nm, and when the particle size is within the above range, Combustion TCO is preferable because a uniform overcoat layer can be formed on the silver nanowire surface.

Examples of the TCO include indium tin oxide (ITO), indium zinc oxide (IZO), zinc tin oxide (ZTO), aluminum zinc oxide (AZO), and gallium indium oxide (Gallium Indium Oxide (GIO)) may be used.

Hereinafter, a method of manufacturing a transparent electrode of the present invention will be described in detail.

A method of manufacturing a transparent electrode according to the present invention includes: a first coating step of coating a silver nanowire dispersion solution on a transparent substrate; A first heat treatment step of removing the solvent from the coated silver nanowire dispersion solution to form a first conductive layer; A second coating step of overcoating a Combustion TCO dispersion solution on the first conductive layer; And a low-temperature firing step of forming a second conductive layer by performing a second heat treatment on the first conductive layer coated with the Combustion TCO dispersion solution.

The silver nanowire dispersion solution may be obtained by dispersing silver nanowires in at least one solvent selected from the group consisting of water, ethanol, propanol, propylene glycol monomethyl ether acetate (PGMEA), acetone, and THF (tetrahydrofuran) In the silver nanowire dispersion solution, the silver nanowire concentration is preferably 1 to 10 mg / L. When the concentration of the silver nanowire is less than 0.1 mg / L, the conductivity of the silver nanowire may be difficult to develop on the substrate. When the concentration of the silver nanowire is more than 10 mg / L, There is a fear that the formation of the transparent conductive film may be hindered.

The Combustion TCO dispersion solution may be obtained by dispersing Combustion TCO in at least one solvent selected from the group consisting of alcohols, ethers, and glycol ethers. Examples of the alcohols include methanol, ethanol, isopropanol, tallow butanol, ethylene glycol, and propylene glycol. Examples of the ethers include dimethyl ether, diethyl ether, dimethoxyethane, dioxane, tetrahydrofuran 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol and the like can be used as the glycol ethers.

The concentration of Combustion TCO in the Combustion TCO dispersion solution is preferably 1 to 500 g / L. When the concentration of the Combustion TCO is less than 1 g / L, it may be difficult to uniformly overcoat the surface of the first conductive layer formed of nanowires. When the concentration exceeds 500 g / L, There is a possibility that formation of the transparent conductive film may be hindered due to a decrease in transmittance as well as a decrease.

The coating methods of the primary and secondary coating steps may be selected from the group consisting of spin coating, bar coating, inkjet printing, slot die coating, gravure printing, Gravure offset printing, and reverse offset printing. In one embodiment, the spin coating may be performed at 500 to 4000 rpm and 10 to 30 Gt; seconds. ≪ / RTI >

The first heat treatment step may be carried out in one step or several steps, and if it proceeds in one step, it may be carried out at 50 ° C to 100 ° C for 30 to 3,000 seconds.

The low-temperature firing may be performed in one step or several stages. If the firing is performed in one step, the heat treatment may be performed at 100 to 250 ° C for 1 to 100 minutes.

The transparent electrode of the present invention manufactured as described above is a structure in which the surface of the first conductive layer from which solvent has been removed is overcoated with a Combustion TCO to lower the surface roughness of the first conductive layer formed of silver nanowires.

1, a transparent electrode 1 (a transparent substrate is not shown) includes a first conductive layer 2 including silver nanowires, a second conductive layer 2 formed of silver nanowires, And a second conductive layer 3 formed on the first conductive layer 2 by overcoating. The second conductive layer 2 is made of Combustion TCO. The Combustion TCO fills the void spaces between the silver nanowires that are the first conductive layer 2 and the silver nanowires protruding from the surface of the first conductive layer 2 Overcoating to cover the wires as a whole to fill the rough surface. In this way, the silver nanowires will have a structure that is bound by the Combustion TCO.

Such a structure prevents the silver nanowire from being broken or aggregated even at high process temperatures.

2, which shows a SEM photograph of a silver nano wire conductive film according to a heat treatment temperature of a first conductive layer that is not overcoated with a second conductive layer, the silver nanowire overlapping portion starts to aggregate from 200 ° C, At temperatures above 250 ° C, silver nanowires are broken.

FIG. 3 is a scanning electron microscope (SEM) image of a silver nanowire (left) overcoated with ITO and a silver nanowire (left) without annealing at 250 ° C. Referring to FIG. 3, In the case of the coated silver nanowire (right), it can be seen that the shape of the nanowire is maintained. Therefore, the composite electrode of the present invention has an advantage in that it has excellent thermal stability and is applied to device manufacturing requiring various temperature process conditions.

In addition, reducing the roughness of the electrode surface facilitates lamination printing of the next material. Therefore, the electrode of the present invention is advantageous in forming a laminated structure for device implementation such as TFTs, for example.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

Example  One

(Manufactured by Combustion TCO)

0.648 g of SnCl ₄ (98.0%) and 4.752 g of In (NO ₃ ) ₃ .5H ₂ O (99.999%) were stirred for 10 minutes in 20 ml of distilled water. To make porosity, 0.4 g of Ketjen Black is added and stirred for 30 minutes. Finally, add a drop of NH ₄ OH aqueous solution as a catalyst and stir the solution for 10 minutes, confirming that the solution turns to the sol state. Drying of the finished sol at 120 ° C for 120 minutes results in a dry gel. The dried gel was sintered for 150 minutes, and the solid resultant was made into a powder form to obtain an ITO nano powder using a sol-gel combustion method.

The ITO nano powder was dispersed in a solvent of 2-methoxyethanol at a concentration of 250 g / L to prepare an ITO ink.

(Transparent electrode manufacturing)

Silver nanowire inks (Cambrios) having a silver nanowire concentration of 0.3 mg / L were coated on a glass substrate (2 cm x 2 cm, eagle glass manufactured by Samsung Corning Precision Materials Co., Ltd.) with a spin coating apparatus (Laurell model: WS-650MZ-8NPP) at 1000 rpm for 10 seconds. The coated silver nanowire layer was subjected to a first heat treatment at 90 DEG C for 90 seconds.

The ITO ink was spin-coated on the silver nanowire layer in the spin coating apparatus at 2000 rpm for 20 seconds. The coated ITO layer was subjected to a second heat treatment at 150 캜 for 30 minutes to complete a transparent electrode.

Comparative Example  One

(Manufactured by Nippon Aerosil Co., Ltd.) on a glass substrate (2 cm x 2 cm, eagle glass manufactured by Samsung Corning Precision Materials) with a spin coating apparatus (Laurell model: WS-650MZ-8NPP) at 1000 rpm for 10 seconds Spin coating. The coated silver nanowire layer was heat-treated at 90 DEG C for 90 seconds to complete a transparent electrode.

Assessment Methods

The properties of the transparent electrode obtained in Example 1 and Comparative Example 1 were measured by the following method, and the results are shown in Table 1 below.

(1) The sheet resistance value

The average value measured using a 4 point probe of the BEGA RS8-1G model was recorded.

(2) Transmittance

The average value measured by transmission through a wavelength of 400 to 800 nm using UV-spectroscopy of JASCO V-600 model was recorded.

(3) Surface roughness

The average value of Ra values measured by a Veeco Instruments Nanoscope I IIa atomic force microscope was recorded.

(4) Adhesion

A 3M magic tape (2.5 cm width) was attached on the transparent electrode and pulled out by hand to remove the tape. The results of tape only bonding were reported as "acceptable" (ie, the coating was not removed) or "failed" (ie, some or all of the coating was removed).

Sheet resistance value Permeability Surface roughness Adhesion Example 1 10 ohm / sq 88% 1.530 nm pass Comparative Example 1 12 ohm / sq 90% 9.210 nm fail

As can be seen from Table 1, the transparent electrode manufactured according to the method of the present invention has excellent conductivity, surface roughness, transparency and adhesion.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments but is to be construed as being limited only by the appended claims. Should be construed as being included in the scope of the present invention.

1: silver nanowires overcoated with Combustion ITO
2: silver nanowire
3: Combustion ITO (indium tin oxide produced by combustion method)

Claims (12)

A transparent substrate;
A first conductive layer formed on the transparent substrate, the first conductive layer including a plurality of silver (Ag) nanowires; And
And a second conductive layer formed by overcoating the silver nanowires protruding from the surface of the first conductive layer as a whole,
Wherein the second conductive layer comprises a transparent conductive oxide (TCO) fabricated by a combustion method. The method according to claim 1,
Wherein the combustion method is any one of a direct combustion method, a catalytic combustion method, a solution combustion method, and a sol-gel combustion method. The method according to claim 1,
Wherein the transparent conductive oxide (hereinafter referred to as " Combustion TCO ") produced by the above combustion method is capable of low-temperature firing at a temperature of 100 to 250 ° C. The method according to claim 1,
Wherein the average thickness of the combustion TCO is 10 to 1000 nm. The method according to claim 1,
Wherein the surface resistance of the Combustion TCO is 10 to 500 ohm / sq. The method according to claim 1,
The TCO may be selected from the group consisting of Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), Zinc Tin Oxide (ZTO), Aluminum Zinc Oxide (AZO) (Gallium Indium Oxide (GIO)). A first coating step of coating a silver nanowire dispersion solution on a transparent substrate;
A first heat treatment step of removing the solvent from the coated silver nanowire dispersion solution to form a first conductive layer;
A second coating step of overcoating a Combustion TCO dispersion solution on the first conductive layer; And
And a low-temperature firing step of forming a second conductive layer by performing a second heat treatment on the first conductive layer coated with the Combustion TCO dispersion solution. The method of claim 7, wherein
The silver nanowire dispersion solution is obtained by dispersing silver nanowires in at least one solvent selected from the group consisting of water, ethanol, propanol, propylene glycol monomethyl ether acetate (PGMEA), acetone and THF (tetrahydrofuran) A method of manufacturing a transparent electrode. 9. The method of claim 8,
Wherein the concentration of the silver nanowires is 0.01 to 0.5 mg / L. 8. The method of claim 7,
Wherein the Combustion TCO dispersion solution is obtained by dispersing Combustion TCO in at least one solvent selected from the group consisting of alcohols, ethers, and glycol ethers. 11. The method of claim 10,
Wherein the concentration of the Combustion TCO is 1 to 500 g / L. 8. The method of claim 7,
Wherein the first heat treatment temperature is 50 to 100 ° C and the second heat treatment temperature is 100 to 250 ° C.

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