KR20160078202A

KR20160078202A - Silver nanowires and copper nanowires composite networks as colorless transparent polyimide electrodes and it's fabrication

Info

Publication number: KR20160078202A
Application number: KR1020150030437A
Authority: KR
Inventors: 김일두; 윤두영; 이다솜
Original assignee: 한국과학기술원
Priority date: 2014-12-23
Filing date: 2015-03-04
Publication date: 2016-07-04

Abstract

Disclosed are a colorless transparent polyimide electrode formed of a network wherein a Ag nanowire and a Cu nanowire are combined and a manufacturing method thereof. In a conductive colorless transparent polyimide electrode formed of an Ag-Cu composite network, a junction between a plurality of Ag nanowires and a plurality of Cu nanowires is fused and each junction between Ag nanowire-Ag nanowire, Ag nanowire-Cu nanowire, and Cu nanowire-Cu nanowire is sintered together and co-exists each other. The conductive colorless transparent polyimide electrode can be embedded on one side of a colorless transparent substrate as a shape in which the Ag nanowires and the Cu nanowires are connected.

Description

Technical Field [0001] The present invention relates to a colorless transparent polyimide electrode comprising a network in which silver (Ag) nanowires and copper (Cu) nanowires are combined,

More particularly, the present invention relates to a transparent electrode, and more particularly, to a method of manufacturing a transparent electrode by combining silver (Ag) nanowires and copper (Cu) nanowires to significantly reduce the cost of materials, The present invention relates to a transparent electrode having excellent conductivity by connecting junctions. In particular, nanowires are embedded in the upper layer of a transparent plastic substrate to provide a transparent electrode excellent in mechanical stability and long life reliability.

Recently, as the use of optoelectronic devices such as touch panels, solar cells, and organic light emitting diodes is increasing, research on transparent electrodes, an essential component of optoelectronic devices, It is actively proceeding. Until now, ITO (Sn-doped Indium Oxide), one of transparent conductive oxide materials, has been widely used for transparent electrodes. The use of ITO metal oxide as a transparent electrode can have high electrical conductivity (10 Ω / sq) and good transparency (> 85%), while indium (In: Indium) There is a burden on the increase of the price. ZnO (Zinc Oxide) has been used as an alternative to overcome the disadvantages of ITO. ZnO has an n-type semiconductor property and a band gap of 3.4 eV, which is known as a material having good transparency in the visible light region. In addition, ZnO is doped with Group 3 elements such as Al, In and Ga to enhance conductivity . However, ZnO transparent conductive oxide doped with Al or Ga is also deposited through a thin film deposition process such as sputtering, resulting in a low deposition yield, and not only a process cost is high but also a dense thin film having a crystalline structure is formed Therefore, cracks may be generated in the process of repeatedly bending when the transparent electrode is deposited on a plastic substrate, or the transparent conductive oxide electrode may peel off from the lower substrate. Due to these problems, research on alternative conductive materials such as graphene, carbon nanotube, conducting polymer, and metal nanowire has been actively conducted to replace transparent conductive oxides ought. In particular, the silver (Ag) nanowire has a high resistivity of 15.87 nΩ · m for the silver (Ag) material itself and the lowest electrical resistance value in the natural world. If such silver (Ag) is made in the form of a wire, the silver nanowires can be networked together with very small amounts of use due to the very large shortening ratio, and many parts are empty without the nanowires, And it is attracting attention as a most suitable material to replace ITO. In addition, silver (Ag) nanowires can easily be mass-synthesized in a polyol solution process in the atmosphere, and can be coated on a substrate using a printing process and a spray process. The copper nanowire, another metal nanowire, has electrical conductivity similar to that of silver, and is 100 times more expensive than silver (Ag). Due to its abundance of reserves, it is seen as a next-generation transparent electrode material have. Copper (Cu) nanowires also have advantages in that they can be easily manufactured by a solution-phase process, while they are more easily oxidized than silver (Ag) nanowires after the process and coating process, There is a great limitation in practical use.

Polyimide (PI) is a polymer having an imide group in the main chain of a molecule. It has strong imidization due to imide groups, strong structure, resonance stabilization, and normal angular structure. Therefore, it has excellent thermal stability, mechanical properties, And is a representative high-performance polymer material having insulating properties. The polyimide has an amorphous structure because it has a low crystallinity when it contains an aromatic structure and becomes transparent. The first polyimide was synthesized by the condensation polymerization of 4-amino phthalic anhydride in 1908. The polyimide film developed by DuPont in 1962 was widely known as 'Kapton' . 'Kapton' synthesizes polyamic acid (PAA) by polymerizing pyromellitic dianhydride and 4,4'oxydiphenylamine, and then reacting at 200 ~ 300 ℃ Imidized and synthesized as polyimide. Since the colorless transparent polyimide undergoes an imidization process at about 250 캜, the plastic substrate is not deformed even at a high temperature of about 300 캜, which is advantageous in durability. However, if the nanowire materials are coated together on a colorless transparent polyimide substrate and subjected to a heat treatment, it is important to overcome this because surface oxidation of silver (Ag) or copper (Cu) nanowires can occur. It is also important to fabricate nanowire-based transparent electrodes in which the contact areas between the nanowires are welded together to greatly reduce the contact resistance value, since high contact resistance occurs at the contact between the nanowires.

In order to overcome the surface oxidation of the metal nanowires, researches for forming a thin (<several tens of nm) oxidation-preventing film on the surface of the nanowires have been actively conducted. When the metal oxide thin film is deposited on the plastic substrate to a thickness of 20 to 30 nm or less, it is possible to maintain excellent flexibility. The conductive oxide thin layer or the graphene layer including ITO, ZnO, Ga-doped ZnO, In-doped ZnO, and Al-doped ZnO is used as an oxidation preventing layer for preventing the oxidation of the silver (Ag) nanowire- , It is possible to prevent surface oxidation of the material formed by heat and atmospheric oxygen exposure.

The present invention relates to a method of forming a network of silver (Ag) nanowires (X) and copper (Cu) nanowires (Y) in a relative proportion selected from the range of 99: 1 to 10: And a method of manufacturing the same. More particularly, silver (Ag) nanowires having high oxidation resistance and excellent electrical conductivity in a copper (Cu) nanowire having a disadvantage of being cheap but not having good oxidation resistance are compounded in a range of 99: 1 to 10:90 (Cu) nanowire composite network in which electrons move through a silver nanowire even when the surface of the copper (Cu) nanowire is oxidized, and a manufacturing method thereof.

Among the metal nanowires, silver (Ag) nanowires are not only very high in electric conductivity, but also can be easily manufactured by a polyol process, while the cost of raw materials due to the use of silver is disadvantageous.

The substrate used as a transparent electrode mainly uses glass, but is fragile and does not bend, which is disadvantageous as a substrate for a flexible device. The substrates used as flexible substrates are PET (polyethylene terephthalate), PES (polyethersulfone), and PEN (polyethylene naphthalate), but have physical properties that are insufficient for working at temperatures of 200 ° C or higher, which is the limit of plastic substrates. Polyimide is a substrate which can be used stably even in a high temperature process (relatively higher temperature than other plastic substrates), but has a property of absorbing light of a short wavelength by a resonance structure phenomenon due to pi-pi bonding, There are disadvantages. Colorless polyimide prepared by securing the structure of an anhydride and a diamine, which are monomers of polyimide, is currently used as a substitute material for a high heat-resistant transparent film.

Although polyimide and colorless transparent polyimide have the advantage of excellent physical properties, they have a drawback that the polymerization process must go through the intermediate polymer differently from the general polymer. The presence of such an intermediate leads to an increase in the process cost, because the process must be increased in terms of time and energy.

Therefore, in the present invention, in the process of imidization, which is the last step of forming a colorless transparent polyimide-based conductive substrate in order to drastically reduce the process cost in the production of a transparent electrode, (Ag) - copper (Cu) nanowires with excellent electrical conduction characteristics by welding the junctions of the copper (Cu) nanowires and the copper (Cu) nanowires to produce a colorless transparent polyimide conductive film I want to.

In the present invention, the price competitiveness of materials is increased by using copper (Cu) nanowires as well as silver (Ag) nanowires, and the ratio of silver (Ag) nanowires to copper While providing a flexible transparent electrode substrate that is inexpensive. This silver (Ag) -copper (Cu) composite nanowire electrode has a relatively low standard reduction level and the copper is in contact with the silver (Ag) to prevent the oxidation of silver (Ag) (Core) of the copper nanowire whose surface is oxidized.

As the polyimide used in the present invention, it is possible to embed metal nanowires using the intermediate of polyamic acid (PAA). A polyamic acid intermediate film containing silver (Ag) -copper (Cu) composite nanowires instead of silver (Ag) -copper (Cu) composite nanowires laminated on top of the completed colorless transparent polyimide film Transparent conductive polyimide electrode in which silver (Ag) -copper (Cu) composite nanowires are firmly embedded in a skin layer of a colorless transparent polyimide film and bound together as imidized. As a result, silver (Ag) -copper (Cu) composite nanowires are embedded in one surface of a colorless transparent polyimide substrate, thereby providing a colorless transparent polyimide conductive substrate having a very smooth surface.

Since the imidization process of the colorless transparent polyimide is carried out at about 250 ° C., the junction between the silver nanowires, the junction between the copper (Cu) nanowires, the silver (Ag) -copper (Ag), copper (Cu) -copper (Cu), silver (Ag) -copper (Cu), and the like by the sintering by heat at the junction where the wires ) Junctions are welded together to provide a polyimide-based transparent electrode interconnected with the networks. This provides a conductive transparent electrode that is electrically conductive along the center even if some surface oxidation occurs.

The present invention provides a conductive transparent electrode further comprising a layer of an anti-oxidation metal oxide layer or a graphene layer on an upper layer of a colorless transparent polyimide substrate having a built-in silver (Ag) -copper (Cu) composite nanowire network.

The silver (Ag) - copper (Cu) composite nanowire network formed by the present invention can be formed by using silver (Ag) and copper (Cu) nanowires at the same time, An electrode can be formed at a low cost. By incorporating silver (Ag) - copper (Cu) composite nanowires in a colorless transparent polyimide substrate, it is expected to be applicable to transparent electrodes for high heat resistance flexible devices required in solar cell and display market by improving oxidation resistance and heat resistance .

1 is a flowchart schematically illustrating a method of manufacturing a colorless transparent polyimide electrode having silver (Ag) - copper (Cu) composite nanowires embedded therein according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a colorless transparent polyimide electrode of a silver (Ag) -copper (Cu) composite nanowire network in which a nanowire junction is melted in an embodiment of the present invention.
Figure 3 is a scanning electron microscope (SEM) photograph of silver (Ag) nanowires prepared according to one embodiment of the present invention.
4 is a scanning electron microscope (SEM) photograph of copper (Cu) nanowires manufactured according to an embodiment of the present invention.
FIG. 5 is a scanning electron microscope (SEM) photograph showing a silver (Ag) -copper (Cu) nanowire network in which a junction of a nanowire is photo-welded after a light sintering process according to an embodiment of the present invention.
6 is a photograph of a colorless transparent polyimide prepared according to an embodiment of the present invention.
FIG. 7 is a cross-sectional view of a silver (Ag) -copper (Cu) nanowire bonded after a heat treatment in the process of embedding silver (Ag) -copper (Cu) nanowire in a colorless transparent polyimide according to an embodiment of the present invention. Network.
Figure 8 is a schematic diagram of a silver nanowire network fabricated in accordance with one embodiment of the present invention, silver (Ag) -copper (Cu) with 1: 1 and 1: 3 copper ratios, A graph of the conductivity, transmittance and transparent electrode of each of the composite nanowire network and the copper (Cu) nanowire network.

Hereinafter, a method of manufacturing a silver (Ag) - copper (Cu) composite nanowire network transparent electrode in which a junction between nanowires is melted will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view illustrating a method of manufacturing an Ag-Cu composite nanowire according to an exemplary embodiment of the present invention. The nanowire is then subjected to optical sintering using a Xenon flash lamp. (Ag) - silver (Ag) - copper (Cu) nanowire, and copper (Cu) - copper (Cu) nanowires through the heat treatment in the process of embedding in the colorless transparent polyimide (Sintering) the junctions of the transparent electrodes with each other in order.

The method for manufacturing a silver (Ag) - copper (Cu) composite nanowire network transparent electrode in which the junction of the nanowire of FIG. 1 is melted is merely to illustrate the present invention, and the present invention is not limited thereto.

As shown in FIG. 1, a method of manufacturing a silver (Ag) -copper (Cu) composite nanowire transparent electrode in which a junction between nanowires is melted includes the steps of i) (Iii) coating a silver (Ag) - copper (Cu) nanowire network on a glass substrate (S30), iv) colorless transparent A step S50 of forming a polyamic acid solution which is an intermediate of polyimide, v) a step S50 of embedding the silver (Ag) -copper composite nanowire network prepared in the step S30 into a colorless transparent polyimide, vi) converting the polyamic acid to polyimide (S60), and vii) separating the colorless transparent polyimide film containing the (Ag) -copper (Cu) composite nanowire (S70).

At this time, in order to improve the conductivity, a photo-sintering process step S35 using a xenon flash lamp may be selectively added to increase the junction of the nanowire network fabricated in step S30 and remove the organic material.

First, in step S10, a silver (Ag) nanowire (for example, silver (Ag) nanowire 110 in FIG. 2) can be synthesized in a polyol manner.

Silver (Ag) nanowire synthesis step

First, a solvent (eg, ethylene glycol) capable of reacting with a reducing reaction of Ag ⁺ ions in a solution phase without boiling at a high temperature of 100 to 200 ° C. adheres to a specific crystal plane of silver to selectively inhibit growth in a specific direction (Such as polyvinylpyrrolidone, PVP (C ₆ H ₉ NO) _x ) and an additive that keeps the concentration of Ag ⁺ ions constant on the solution to stabilize the rate of Ag ⁺ ion reduction (Eg, potassium bromide (KBr)) is dissolved in a certain ratio and stabilized at a high temperature of 130 to 170 ° C.

After creating the Ag precursor (AgCl) to first dissolve silver (Ag) nanowires are nucleated place to grow, primary reactants (e.g., AgNO ₃₎ a constant infusion to Ag ⁺ ions in a specific crystal plane that adhere the PVP polymer material different To allow silver (Ag) nanowires to be formed, and the silver (Ag) nanowires to grow sufficiently to hold the reaction for a predetermined time to complete the reaction. At this time, most of the reactants used in the reaction participate in the reaction, so that a large amount of silver (Ag) nanowires can be produced at one time.

Manufacturing process of silver (Ag) nanowire dispersion solution

Pure silver (Ag) nanowire dispersion solution is prepared so that it can be coated in impurity mixed silver (Ag) nanowire synthesis solution. In order to remove only the pure silver (Ag) nanowire, the silver nanoparticles are washed with a certain amount of ethanol purified water in a solution that can be mixed with the solvent, the polymer substance and the additive, Followed by dilution and centrifugation. This cleaning procedure can be repeated several times for impurity removal and effective silver (Ag) nanowire separation.

In step S20, a copper (Cu) nanowire (for example, copper (Cu) nanowire 120 of FIG. 2) can be synthesized by a hydrothermal synthesis method.

Copper (Cu) nanowire synthesis step

The hydrothermal synthesis method is a liquid phase synthesis method and collectively refers to a process of synthesizing a substance using water or an aqueous solution under high temperature and high pressure. The hydrothermal synthesis method is advantageous in that it can mass-produce copper nanowires and does not use toxic hydrazine.

CuCl ₂ dehydrate as a copper precursor, hexadecylamine as a capping agent, and glucose as a reducing agent. Copper has a face centered cubic structure, and copper seeds exist in the form of {111} crystal faces exposed in a decahedral structure. Since the {111} crystal face of the Cu seed is most unstable and exposed energetically, the capping agent preferentially protects the {111} crystal face. Therefore, when copper seeds are bound by copper atoms, copper (Cu) grows mainly in the [100] crystal direction, forming a wire-like structure. The copper (Cu) precursors are all put into purified water and stirred. Then, the copper (Cu) nanowires are synthesized by heat treatment at 120 ° C for 24 hours in a hydrothermal synthesis vessel.

Manufacturing process of copper (Cu) nanowire dispersion solution

Pure copper (Cu) nanowire dispersion solution is prepared so that it can be coated in impurity mixed copper (Cu) nanowire synthesis solution like silver (Ag) nanowire. In order to remove the pure copper (Cu) nanowires from the polymeric materials used for the synthesis of copper (Cu) nanowires, it is diluted in purified water, ethanol, hexane solvent and centrifuged several times to wash do.

This cleaned copper (Cu) nanowire is still surrounded by a large number of organics and does not exhibit conductivity by itself. Therefore, in order to remove organic matter, copper (Cu) nanowires must be transferred onto a substrate and then annealed at a temperature of 200 ° C or more for 1 hour or more. This process may be performed in a subsequent light sintering process or a colorless transparent polyimide- It is not necessary to carry out the process separately in the embodiments of the present invention because it is an accompanying process inevitably.

In step S30, a silver (Ag) -copper (Cu) composite nanowire network formed by mixing silver (Ag) nanowires and copper (Cu) nanowires can be fabricated. The silver (Ag) nanowire (X) prepared in step S10 and the copper (Cu) nanowire (Y) prepared in step S20 are mixed in a ratio of X: Y of 99: 1 to 10: (Ag) nano-particles are dispersed again in a solution such as ethanol, methanol, isopropanol or the like in order to coat the mixed nanowires on a glass, metal or plastic substrate, Wire and copper (Cu) nanowires are mixed and uniformly dispersed to prepare a silver (Ag) -copper (Cu) composite nanowire dispersion solution. At this time, a dispersant or other additives which do not affect the electrode formation may be additionally added. There is no restriction on the additive surface-specific additives that do not interfere with the coating and can improve the dispersion characteristics. On the other hand, the lower the concentration of the silver (Ag) nanowire or the copper (Cu) nanowire dispersion solution is, the more favorable the dispersion is, so that it can be used by being diluted as much as possible. The silver (Ag) - copper (Cu) composite nanowire dispersion solution prepared in this way is transferred onto a nylon filter through a vacuum filtration transfer method, and then pressed together with a substrate using a compactor. Ag) -copper (Cu) composite nanowire network is transferred onto the substrate. A process such as screen printing or spray coating can be used to form a silver (Ag) -copper (Cu) composite nanowire network on a glass substrate or a plastic substrate, and a silver (Ag) If the process can form a nanowire network, there is no restriction on a specific process.

Step S35 is a process for the photo-sintering process. The step S35 is a process for the photo-sintering process to melt the junction between the nanowires in the silver (Ag) -copper (Cu) nanowire network on the substrate manufactured in step S30, It may be a step of applying light sintering for the purpose of removing it. This step is a step that can be selectively added as needed to reduce the oxidation of the silver (Ag) - copper (Cu) composite nanowire network. The silver (Ag) May be performed before being embedded in the mid substrate. Intensive Pulsed Light Sintering (XPS) is a process in which a voltage is applied to a xenon lamp having a wavelength of 420 to 1200 nm to transfer energy at a low temperature in a very short time (0.1 ms) . The number of pulses can be adjusted from 1 to 99, and the energy can be controlled by controlling the interval between the voltage and the pulse. When the wavelength range of 420 to 1200 nm including the visible ray region is deviated, very high energy is transferred to cause thermal damage to the transparent substrate, and the transparent plastic substrate may be deformed. In the case of using a xenon lamp having a visible light range of 420 to 1200 nm, the transparent substrate is allowed to pass through and the light energy is transmitted only to the opaque silver (Ag) nanowire, The surface temperature of the nanowire is instantaneously increased to 1000 to 1500 ° C. In some cases, it is also possible to additionally remove some wavelength regions using a filter in a wavelength range of 420 to 1200 nm. This momentary high heat melts the junctions of the nanowires and at the same time removes the polymers covering the copper (Cu) nanowires. Silver (Ag), silver (Ag), copper (Cu), copper (Cu), and copper (Cu) wires through a light sintering process in the case of silver (Ag) The electrical conduction characteristics can be improved through the melting process at junctions between the electrodes and the residual polymer or organic matter can be effectively removed.

The steps (S40), (S50), (S60), and (S70) are performed by embedding a silver (Ag) -copper composite nanowire network in a colorless transparent polyimide to fabricate a flexible transparent electrode A transparent electrode having a junction of nanowires is formed by a heat treatment process performed in step S40. In step S40, an anhydride and an amine are stirred to prepare a polyamic acid which is a precursor of a colorless transparent polyimide. In order to effectively stir anhydrides and amines, a solvent must be added. Examples of the solvent include ethanol, water, chloroform, N, N'-dimethylformamide, dimethyl sulfoxide Dimethylsulfoxide, N, N'-dimethylacetamide, N-methylpyrrolidone and the like can be used.

The anhydride used in step S40 is an anhydride capable of synthesizing a colorless transparent polyamic acid. The anhydride may be 4,4'-Oxydiphthalic Dianhydride (ODPA), pyromellitic dianhydride (PMDA), 3,3 ', 4,4'-diphenylsulfonetetracar- 4,4'- (4,4'-isopropylidenediphenoxy) bis (phthalic anhydride) (BPADA), 4,4'- (hexafluoroisopropylidene) diphthalic anhydride (6FDA ), 4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 1,2,3,4-cyclobutanetetracaroxylic dianhydride (CBDA) and 1,4-cyclohexanedicarboxylic acid (CHDA). In addition, transparent polyamic acid If an anhydrous substance is available, it does not limit the specific substance.

The amine used in step S40 is an amine capable of synthesizing a colorless transparent polyamic acid. Examples of the amine include 3,3'-bis (4-aminophenoxy) biphenyl (M-BAPB) and 1,3-bis (3-aminophenoxy) benzene p-BAPB), 2,2-bis (4-aminophenyl) hexafluoropropane (BAHFP), meta-amino bis metabisaminophenoxy diphenyl sulfone (m-BAPS), ammonium persulfate (APS) bis (trifluoromethyl) benzidine (TFB), or a mixture of two or more of the following compounds: And in addition, if the amine is capable of synthesizing a transparent polyamic acid, there is no restriction on a specific substance.

The reason why the polyimide has a specific yellow color can be explained by the charge transfer complex theory. As the number of resonance structures increases in the imide structure, the transition of the pi (pi) electrons becomes easy, so the energy level is low It is the theory that yellow light is absorbed by the high wavelength, that is, visible light region. The anhydrides and amines that can synthesize colorless transparent polyamic acids should be substances that prevent the transition of these pi electrons. Typically, there is a method of lowering the resonance effect by restricting the movement of the pi electrons by introducing an element having relatively high electronegativity such as trifluoromethyl, sulfone, and ether, , A colorless transparent polyimide film can be produced by reducing the density of pi electrons present in the main chain by introducing an olefinic cycloolefin structure.

Step S50 is a step of embedding a silver (Ag) - copper (Cu) composite nanowire network coated on the glass substrate or the plastic substrate manufactured in step S30 inside a colorless transparent polyimide. Polyamic acid mixed by polymerization reaction of anhydride and amine in an organic solvent is applied on a substrate coated with a silver (Ag) - copper (Cu) composite network by screen printing using a doctor blade, spin coating or the like. In step S60, the polyamic acid is thermally treated at 100 ° C, 200 ° C, and 300 ° C for 1 hour in order to imidize the polyamic acid to polyimide, and dropped to room temperature. This results in the completion of colorless transparent polyimide with embedded silver (Cu) composite nanowires. In addition, during the heat treatment up to 300 ° C, the nanowires' junction is melted, as well as the polymers surrounding the copper (Cu) nanowires are removed. The schematic diagram of FIG. 2 briefly shows the surface and cross-section of a colorless transparent polyimide having silver (Ag) -copper (Cu) composite nanowires embedded therein. As seen from the surface of the schematic diagram, silver (Ag) nanowires 110 and copper (Cu) nanowires 120 are networked in a colorless transparent polyimide substrate 140, and these two types of nanowires are made to meet The types of junctions that can be used include copper (Cu) -nano wire contact 131, copper-silver (Ag) nanowire contact 132, silver (Ag) There may be a nanowire contact 133. These junctions have the same shape as the junctions where the contact points between the nanowires are united with each other due to melting by heat treatment accompanying the imidization process. In addition, in the cross-sectional view, silver (Ag) nanowires 110, copper nanowires 120, and three kinds of contacts 131, 132, and 133 are all embedded in the colorless transparent polyimide 140 Can be seen. Imidization of polyamic acid can be achieved by light and chemical treatment as well as by heat. If polyimidation is to be performed instead of the thermal method, step S35 must be proceeded. If you do not go through this step, you will get low conductivity.

Step S70 is a step of removing the colorless transparent polyimide film containing the silver (Ag) -copper (Cu) composite nanowire fabricated in step S60 from the glass substrate. BOE (Buffered oxide etchants) solution is used to etch the substrate to cause the film to fall off. Store the film that has fallen off with purified water through a sufficient washing process.

Hereinafter, the present invention will be described in detail by way of examples. These embodiments are merely illustrative of the present invention, and the present invention is not limited thereto.

[Example 1] Production of silver (Ag) nanowire

First, 40 ml of ethylene glycol, a polyvinylpyrrolidone (PVP) polymer and 0.02 g of KBr additive, which are high boiling point solutions capable of withstanding temperatures of 170 ° C or higher, are mixed in a three neck flask to form a magnetic bar bar) and heated to 170 ° C. to stabilize for 30 minutes. At this time, PVP helps to grow into a wire shape by interfering with a specific growth surface of silver nanowire, and KBr as an additive helps to keep silver ion in solution constantly.

Next, 0.02 g of finely polished AgCl powder ball-milled into a stable solution to form an initial precursor. The remaining AgCl powder, which does not participate in the reaction, may remain on the bottom, and the silver nanowire growth affinity varies depending on the degree of fine grinding and the abrasive crystal plane. After 1 hour, 0.440 g of AgNO _{3 as a} main reaction material is titrated. At this time, AgNO ₃ may be firstly dissolved in 5 ml of ethylene glycol, and injected into the solution at a constant rate of 5 ml / hour using a syringe. It is then heated to 170 ° C for 2 hours. 3 is a scanning electron microscope (SEM) image of a silver (Ag) nanowire synthesized according to an embodiment of the present invention. As shown in FIG. 3, uniform silver nanowires (30 to 60 nm in diameter, 10 to 50 μm in length) were very well synthesized.

In order to separate pure silver (Ag) nanowire from grown silver (Ag) nanowire solution from ethylene glycol and PVP, it was diluted with purified water or ethanol at a ratio of 1: 4 and then centrifuged and then washed. Since separation was not smooth at once, the above procedure was repeated 3 to 5 times. First, centrifuge at 2000 rpm in purified water for 30 minutes, discard the underlying silver particles, use a floating solution, centrifuge at 2000 rpm for 30 minutes in purified water, The process of repeating the process of using the silver nanowires that are floating down and discarding the floating silver particles is repeated three times. After washing with purified water, the above procedure was repeated 4 times in ethanol.

[Example 2] Production of copper (Cu) nanowire

To 80 mL of purified water was added 0.17 g of CuCl ₂ dihydrate, 0.1 g of D - (+) Glucose and 1.44 g of hexadecylamine, and the mixture was stirred at 500 rpm for 12 hours. The solution was placed in a Teflon container, placed in an autoclave device, heated to 120 ° C at a rate of 10 ° C per minute, and allowed to react for 24 hours. After cooling to room temperature, 20 mL of the solution and 15 mL of deionized water were mixed and centrifuged at 2000 rpm for 1 hour. The supernatant was discarded and 35 mL of deionized water, ethanol, and hexane were added and dispersed well. The cells were centrifuged at 2000 rpm for 30 minutes each time for 2 times, and finally ethanol was added thereto.

[Example 3] Production of transparent electrodes in which a junction of nanowires was melted through photo-sintering in a silver (Ag) -copper (Cu) composite nanowire network

The silver (Ag) nanowire fabricated in Example 1 and the copper (Cu) nanowire fabricated in Example 2 were mixed. The mixture ratio of silver nanowire: copper (Cu) nanowire was 400 μl: 400 μl (1: 1) or 200 μl: 600 μl (1: 3) in a falcon tube using a micropipette, and the remainder of the falcon tube was filled with ethanol or methanol. Subsequently, silver (Ag) - copper (Cu) nanowire dispersion solution was transferred onto a glass substrate using a vacuum filtration method and a compactor. Vacuum filtration is a method of separating the solid particles contained in the liquid by applying a vacuum to the back surface. The solid is deposited on the surface or inside of the filter medium, and the liquid is separated from the filtrate by filtration. A nylon filter having a pore size of 0.2 μm was placed on a vacuum filtration apparatus and a silver (Ag) -copper (Cu) nanowire composite dispersion solution was injected to filter the ethanol or methanol. - Copper (Cu) composite nanowire network is left. The silver (Ag) -copper (Cu) composite nanowire placed on the nylon filter was pressed with a load of 3 kgf / cm ² using a presser for about several seconds at room temperature while being in contact with the substrate to be transferred. (Cu) composite nanowires are transferred from the nylon filter to the substrate. Then, a junction between silver (Ag) and copper (Cu) composite nanowires coated on a glass substrate was photo-welded, and a photo-sintering treatment was performed to remove residual organic matter or residual polymer. This allows the silver (Ag) - copper (Cu) nanowire networks to be photolyzed to form silver (Ag) - silver (Ag) nanowires, silver (Ag) The intersections between the nanowires are welded to each other to form a network layer. FIG. 5 is a photograph of a silver (Ag) -copper (Cu) nanowire network in which a junction between nanowires is photo-welded after a photo-sintering process according to an embodiment of the present invention.

[Example 4] Manufacture of a transparent electrode in which a junction of a nanowire is melted in the process of embedding a silver (Ag) -copper (Cu) composite nanowire network in a colorless transparent polyimide

First, as a process for preparing a polyamic acid solution which is a precursor of a colorless transparent polyimide, a polyamic acid is produced by polymerization reaction of an anhydride and an amine in an organic solvent. In this experiment, 4.073 g of 6FDA (4,4 '- (hexafluoroisopropylidene) diphthalic anhydride) having a trifluoromethyl group as an anhydride in 8 g of DMF as an organic solvent and ammonium persulfate (APS) 2.276 g was added thereto and stirred at about 20 ° C for 5 hours using a magnetic stirrer to form a liquid polyamic acid. (Cu) composite nanowire network transferred onto a substrate prepared in Example 3 to incorporate a silver (Ag) -copper (Cu) composite nanowire network into a colorless transparent polyimide. doctor's blade) to uniformly apply a liquid polyamic acid to a thickness of 100 탆. The coated polyamic acid was heated to 2 ° C / min and heat-treated at 100 ° C, 200 ° C and 300 ° C for 1 hour, respectively, to form a colorless transparent polyimide film. Finally, a silver (Ag) Thereby making it possible to produce a colorless transparent polyimide transparent electrode film.

6 is a photograph of a colorless transparent polyimide film produced according to an embodiment of the present invention. It can be seen that the colorless transparent polyimide is suitable for use as a transparent electrode substrate as compared with the conventional polyimide. In addition, during the heat treatment process, the junctions of the nanowires are melted. FIG. 7 is a cross-sectional view illustrating a process of welding silver (Ag) -copper (Cu) nanowires after heat treatment in the process of embedding silver (Ag) -copper (Cu) nanowires in colorless transparent polyimide according to an embodiment of the present invention. Displays network pictures of composite nanowires. Finally, to remove the colorless transparent polyimide with silver (Ag) - copper (Cu) mixed nanowires from the substrate, the BOE solution etches the substrate for 3 to 5 minutes, A colorless transparent polyimide film having a copper (Cu) composite nanowire network and a glass substrate are separated from each other. FIG. 8 shows a table showing the electrical and optical characteristics of a colorless transparent polyimide film having a built-in silver (Ag) -couple (Cu) composite network separated from a glass substrate. (Ag) - copper (Cu) composite nanowire with a silver ratio of 1: 1 and 1: 3, a copper (Cu) nanowire It can be seen that the respective conductivities, transmissivities and optical pictures for the network are well compared.

As shown in FIG. 8, it was confirmed that the best electric conduction characteristic was obtained at 16 Ω / sq when silver (Ag) nanowires were embedded among the metal nanowires embedded in the colorless transparent polyimide substrate. Cu (Cu) nanowires and Cu (Cu) nanowires showed a conductivity of 41 Ω / sq when embedded in a colorless transparent polyimide. (Cu) nanowires having a conductivity of 20 Ω / sq and 29 Ω / sq, respectively, when they are mixed with each other at a ratio of 3: 1. The transmittance showed similar transmittance characteristics around 80%. It is expected that a large cost reduction can be expected when forming a silver (Ag) -copper (Cu) nanowire network by appropriately setting the effective mixing ratio of the silver (Ag) nanowire and the copper (Cu) nanowire.

Claims

The junction between a plurality of silver nanowires and a plurality of copper nanowires are fused together to form silver nanowires-Ag nanowires, Ag nanowires- A network configuration in which one or more of the copper (Cu) nanowires and the junctions between the copper (Cu) nanowires and the copper (Cu) nanowires coexist and silver (Ag) and copper Conductive polyimide electrode comprising a silver (Ag) -copper (Cu) composite nanowire network embedded in one side of a polyimide substrate.

The method according to claim 1,
The relative content of the (plurality of silver (Ag) nanowires) X and the (plurality of copper (Cu) nanowires) Y is in the range of 99: 1 to 10: 90 (Cu) composite nanowire network characterized by having a relative ratio selected from the range of from 0.02 to 0.15.

The method according to claim 1,
Wherein the silver (Ag) nanowires and the copper (Cu) nanowires have a diameter in the range of 20 nm to 100 nm and a length in the range of 10 μm to 100 μm. Conductive colorless transparent polyimide electrode composed of copper (Cu) composite nanowire network.

The method according to claim 1,
A silver (Ag) - copper (Cu) alloy in which silver (Ag) nanowires and copper (Cu) nanowires are melted and connected to each other and a silver (Ag) Conductive polyimide electrode composed of a silver (Ag) -couple (Cu) composite nanowire network, characterized in that it forms a junction made.

The method according to claim 1,
Even though the surfaces of copper (Cu) nanowires are oxidized to form copper oxide in a silver (Ag) -copper composite nanowire network, silver (Ag) nanowires and copper (Cu) composite nanowire network, characterized in that it has electrical conductivity along the core of the copper (Cu) nanowire connected to the silver (Ag) nanowires Conductive polyimide electrode.

The method according to claim 1,
(Cu) composite nanowire network characterized by having a transmittance in the range of 80% to 95% and a resistance in the range of 0.1? / Sq to 200? / Sq.

The method according to claim 1,
In order to melt at the junction between the silver nanowires and the copper nanowires, a white light is emitted by an intensified pulsed light (IPL) method using a Xenon flash lamp. (Ag) nanowires, Ag nanowires, Ag nanowires, and the like are annealed at a temperature of 150 to 250 ° C. in a reducing atmosphere in an annealing process for forming a polyimide film by irradiation, optical sintering, A copper (Cu) composite material characterized in that a junction between each of the wire-copper nanowire and the copper nanowire-copper nanowire is formed by sintering or melting. Conductive colorless transparent polyimide electrode composed of a nanowire network.

8. The method according to any one of claims 1 to 7,
(Ag) -copper (Cu) layer characterized by further comprising a metal oxide oxide layer or a graphene layer selected from ITO, ZnO, Al-doped ZnO and Ga-doped ZnO with a thickness of 1 to 30 nm as an oxidation- ) Conductive colorless transparent polyimide electrode composed of a complex nanowire network.

A transparent electrode made of a conductive colorless transparent polyimide having a built-in silver (Ag) -copper (Cu) nanowire network,
(1) synthesizing silver (Ag) nanowires;
(2) synthesizing a copper (Cu) nanowire;
(3) A silver (Ag) -copper (Cu) composite nanowire is coated on a plastic substrate, a metal substrate or a glass substrate to form a transparent electrode step;
(4) is a junction between each of (Ag) nanowires-Ag nanowire, Ag nanowire-copper nanowire, copper nanowire-copper nanowire, Forming a transparent electrode in which silver (Ag) -copper (Cu) composite nanowires in which at least one of the metal nanoparticles and the metal nanoparticles coexist are networked with each other;
(5) A polyamic acid is coated on a transparent electrode made of silver (Ag) -copper (Cu) composite nanowires formed through the steps (3) and (4) Forming a colorless transparent polyimide substrate with embedded (Ag) -copper (Cu) composite nanowires; And
(6) separating the colorless transparent polyimide substrate containing the silver (Ag) -copper (Cu) composite nanowires through the step (5) from the plastic substrate, the metal substrate or the glass substrate
(Cu) composite nanowire network, characterized in that it comprises a silver (Ag) -couple (Cu) nanowire network.

10. The method of claim 9,
(7) The ITO, ZnO, Al-doped ZnO, and Ga-ZnO layers each having a thickness of 1 to 30 nm are formed on the electrode of the conductive colorless transparent polyimide substrate having the separated silver (Ag) doped < RTI ID = 0.0 > ZnO < / RTI >
(Cu) composite nanowire network, characterized in that it further comprises a silver (Ag) -couple (Cu) nanowire network.

10. The method of claim 9,
The silver (Ag) -copper (Cu) composite nanowire mixed solution has a ratio X: Y of 99 (a plurality of silver (Ag) nanowires) X and a plurality (Cu) composite nanowire network characterized in that it is produced by compositing each other in the range of 1: 10 to 90: 1.

10. The method of claim 9,
The step (4)
(Ag) -copper (Cu) composite nanowires are networked to each other by performing photo-sintering using a xenon flash lamp or a heat treatment under a reducing atmosphere at a temperature of 150 to 250 ° C. A method for fabricating a conductive colorless transparent polyimide electrode comprising a silver (Ag) - copper (Cu) composite nanowire network.

13. The method of claim 12,
Wherein the gas used in the reducing atmosphere heat treatment includes a gas heat-treated with nitrogen (N ₂ ) or argon (Ar) gas at a concentration ranging from 0.1 to 50% hydrogen (H ₂ ) A method for fabricating a conductive colorless transparent polyimide electrode comprising a copper (Cu) composite nanowire network.

10. The method of claim 9,
The step (6)
The colorless transparent polyimide substrate containing the silver (Ag) -copper (Cu) composite nanowires is immersed in a BOE (Buffered oxide etch) solution for 1 to 30 minutes, (Cu) composite nanowire network characterized in that it is separated from the silver (Ag) - copper (Cu) nanowire network.