KR20150080220A - a method of preparing Ag nanowire, Ag nanowire prepared thereby, and transparent electrode including the same - Google Patents

Abstract

The present invention relates to a method of preparing metal nanowires and metal nanowires prepared by the same. The method of preparing metal nanowires includes: a step of providing a reaction solution by dissolving a capping agent in a reducing solvent; a step of purging the reaction solution with nitrogen; a step of injecting a metal precursor to the reaction solution after the nitrogen purging step; and a step of heating the reaction solution injected with the metal precursor. The present invention allows the preparation of metal nanowires smaller than 50 nm, thereby allowing the preparation of a transparent electrode with a reduced haze.

Description

METHOD FOR MANUFACTURING METAL NANO-WIRE, METHOD FOR MANUFACTURING METALLIC NANO-WIRE AND TRANSPARENT ELECTRODE CONTAINING THE SAME,

The present invention relates to a process for producing metal nanowires having a diameter of 50 nm or less, a metal nanowire produced thereby, and a haze reduced transparent electrode including metal nanowires having a diameter of 50 nm or less.

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 made of transparent electrodes having excellent conductivity with a relatively high light transmittance, but still require improved light transmittance and conductivity.

In addition, the transparent electrode to which the metal nanowire is applied has a problem that the haze is high due to the diameter of the metal nanowire or the transparent electrode surface is not smooth.

To solve this problem, it is urgently required to develop silver (Ag) nanowires having a small diameter.

1. Korean Patent Publication No. 10-1307967

In order to solve the above-mentioned problems, the present invention provides a method for producing metal nanowires having an average diameter of 50 nm or less and metal nanowires produced thereby.

The present invention seeks to provide a metal nanowire transparent electrode having an average diameter of 50 nm or less.

According to one aspect of the present invention, there is provided a method for producing a metal complex, comprising the steps of: providing a reaction solution in which a capping agent is dissolved in a reducing solvent; purging the reaction solution; introducing a metal precursor into the nitrogen purged reaction solution; And heating the solution to form a metal nanowire.

Another aspect of the present invention may be a metal nanowire fabricated according to the method of the preceding aspect.

Another aspect of the present invention may be a transparent electrode comprising metal nanowires on the front side.

According to the present invention, metal nanowires having an average diameter of 50 nm or less can be synthesized.

According to the present invention, a transparent electrode having reduced haze can be realized by using a metal nanowire having an average diameter of 50 nm or less.

Figure 1 is a scanning electron micrograph of silver (Ag) nanowires prepared according to an embodiment.
2 is a scanning electron microscope (SEM) image of silver (Ag) nanowires prepared according to a comparative example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: providing a reaction solution in which a capping agent is dissolved in a reducing solvent; purging the reaction solution; injecting a metal precursor into the nitrogen- purged reaction solution; And heating the reaction solution to form a metal nanowire.

A nanowire is a structure having a nano-level diameter and a wire shape with an aspect ratio of more than one. For example, silver (Ag) nanowire is a single crystal structure composed of silver (Ag) and having a diameter of nanometer level.

First, a reaction solution can be prepared by dissolving a capping agent in a reducing solvent.

The metal nanowires can be prepared by reducing a precursor containing a metal in a reducing solvent. For example, in the case of a silver (Ag) nanowire, a silver nitrate (AgNO ₃ ) precursor can be produced by reduction.

The metal precursor may be a salt form containing a metal component of the nanoparticles to be produced and may be used without limitation as long as it is commonly used in the production of solution nanoparticles. As such a metal precursor, an organic acid salt, an inorganic acid salt or a halide including at least one metal selected from the group consisting of gold, silver, copper, nickel and palladium may be used.

Examples of the reducing solvent include water, ethylene glycol, 1,2-propyleneglycol, 1,3-propyleneglycol, diethyleneglycol (DEG) At least one selected from the group consisting of dipropyleneglycol (DPG), polyethylene glycol (PEG), glycerol and pentaerythritol may be used.

The capping agent acts on the side of the wire to promote the growth in a specific direction to form a wire. Examples of the capping agent include water-soluble polymers such as polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymaleic acid (PMA) and polymethylmethacrylic acid (PMMA) One or more selected from the group can be used. Of these, polyvinylpyrrolidone is preferably used. The capping agent can be selected according to the length of the nanowire to be produced, and is preferably a material having a molecular weight (Mw) of 1,000 to 1,500,000. By using the capping agent, nanoscale wires can be stably formed.

The amount of the capping agent relative to the metal precursor is preferably in the range of 100: 10 to 100: 300 by weight. If the amount of the capping agent is less than the lower limit, the production rate of the nanorod increases, and when the upper limit is exceeded, the electrical conductivity of the manufactured nanowire may decrease.

The reaction solution may further contain an additive. As the additive, a halogen compound including tetrabutylammonium chloride or a metal salt of a typical or transition element series (for example, NaCl, CuCl ₂ ) may be used. The halogen compound can facilitate nanowire formation by effectively inhibiting lateral growth of the nanowire with the capping agent. By using a halogen compound, generation of nanostructures in particle form, plate form or rod form can be inhibited. The weight ratio of the metal precursor and the halogen compound is 100: 0.01 to 100: 3, preferably 100: 0.01 to 100: 2.

Next, by purging the reaction solution with nitrogen, the reaction solution and the nitrogen gas can be brought into contact with each other. Nitrogen gas is dissolved in the reaction solution and nitrogen gas dissolved in the reaction solution can be induced to form a metal single crystal seed having a small size by being involved in formation of a metal single crystal seed.

Nitrogen purging can be carried out by bubbling in the state of being blocked from the outside air. As a method of dissolving nitrogen gas in the reaction solution, there is a method of pressurizing by using a closed container, but it is preferable to use the bubbling method because it can promote the contact of the reaction solution with nitrogen. In addition, when nitrogen gas is pressurized, it is not economical because additional equipment is required for pressurization.

The amount of nitrogen dissolved in the reaction solution by nitrogen purge may depend on the temperature and time of purging. The nitrogen purging is preferably carried out at 20 to 150 DEG C for 5 to 600 minutes. If the nitrogen purging temperature is lower than the lower limit, the effect of nitrogen purging may not be evident. If the nitrogen purging temperature is higher than the upper limit, the solvent may evaporate and the complete nitrogen purging may not proceed. When the nitrogen purging time is shorter than the lower limit, the nitrogen is not sufficiently dissolved and the effect due to the nitrogen purging, that is, the metal nanowires of 50 nm or less can not be produced. The nitrogen purging is preferably carried out for a long time so that the nitrogen sufficiently dissolves, If the purging time is longer than the upper limit, there is little additional effect due to the increased time, which can waste the raw material and be uneconomical.

The nitrogen flow rate is preferably 1 to 1000 ml / min. When the nitrogen flow rate is less than the lower limit, the effect of nitrogen purging is insignificant, so that metal nanowires with diameters of 50 nm or less can not be produced. When the nitrogen flow rate is higher than the upper limit, the effect of nitrogen purge is saturated and an additional effect can not be expected to increase. And can be economical.

Next, a metal precursor can be added to the nitrogen purged reaction solution. For example, when preparing silver (Ag) nanowires, silver nitrate (AgNO ₃ ) can be used as a metal precursor. The introduction of the metal precursor may be performed by dropping a solution obtained by dissolving the metal precursor in a solvent into the reaction solution. When a metal precursor is added to the reaction solution, the metal is reduced from the introduced metal precursor to form a metal single crystal seed. For example, when silver nitrate (AgNO ₃ ) is added, silver (Ag) is reduced from silver nitrate (AgNO ₃ ) to form a silver (Ag) single crystal seed. In order to synthesize a metal nanowire having a small diameter, it is important to control so that the metal single crystal seed is formed small. The size of the single crystal seed is small so that the diameter of the nanowire formed therefrom is small. Existing nitrogen purging was performed to reduce the size of the single crystal seed. In other words, a small size metal single crystal seed may be formed in the reaction solution due to the nitrogen gas dissolved in the reaction solution during nitrogen purging.

Next, the reaction solution into which the metal precursor is introduced can be heated. Through this process, the metal single crystal seed grows in a specific direction with thermal energy as a driving force, and metal nanowires can be formed. As described above, the capping agent and the additive (halide) act on the growth process of the metal single crystal seed to promote the growth in a specific direction of the single crystal seed and suppress the growth in the diameter (thickness) can do.

The heating (temperature profile) may be raised to a specific temperature and then maintained at a constant temperature. Alternatively, a method may be employed in which the temperature is gradually increased stepwise and maintained for a predetermined time at each step. In the case of the former, there is a problem that the driving force due to the temperature difference is very large and thus the growth speed is fast, but the process can not be finely controlled. In the latter case, the driving force is divided and takes a relatively long time, The process can be controlled step by step. In order to precisely control the diameter of the metal nanowire, the latter is preferred.

The heating can be carried out at 50 to 150 ° C for 1 to 24 hours. The physical characteristics (length, diameter, aspect ratio, etc.) of nanowires formed according to heating temperature and time can be determined. An appropriate heating temperature and heating time can be determined to synthesize metal nanowires having desired physical properties. If the heating temperature is high, the heating time is short, and if the heating temperature is low, the heating time may be relatively long. If the heating temperature is lower than the lower limit, the growth rate of the nanowires becomes too slow, which is too slow and uneconomical. If the heating temperature is higher than the upper limit, the nanowire yield may be lowered.

Next, the growth reaction of the metal nanowires can be terminated by introducing water into the reaction solution to quench the reaction solution.

Next, the final metal nanowires can be obtained through washing and drying.

According to the process according to this aspect, metal nanowires having a diameter of 50 nm or less can be synthesized. That is, by adding the nitrogen purging step to the reaction solution, the metal single crystal seed is controlled to be smaller so that a metal nanowire having a small diameter (having a diameter of 50 nm or less) can be synthesized.

Another aspect of the present invention may be a transparent electrode comprising a metal nanowire on the front side. Since the average diameter of the metal nanowires used in this aspect is small (less than 50 nm), the haze caused by the overlap of the metal nanowires can be reduced, thereby improving the optical characteristics of the transparent electrode.

The present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the embodiments.

Example

Synthesis of silver (Ag) nanowires

A reaction solution was prepared by adding 316 g of propylene glycol (Sigma Aldrich), 1.92 g of polyvinylpyrrolidone (Mw = 55,000) (Sigma Aldrich) and 40 mg of tetrabutylammonium chloride (Sigma Aldrich) .

Next, the reaction solution was purged with nitrogen at a flow rate of 400 ml / min in a bubbling manner for 1 hour while the inflow of external air was blocked.

Next, a solution (1.64 M) of silver nitrate (AgNO ₃ ) (Junsei) dissolved in propylene glycol was added to the reaction solution at a rate of 0.75 ml / min for 20 minutes.

Next, after heating at 100 DEG C for 4 hours, 66.6 g of distilled water was added thereto to terminate the reaction. After completion of the reaction, the reaction solution was mixed with water and spontaneously precipitated. The lower layer was centrifuged to obtain silver (Ag) nanowires.

Fabrication of transparent electrode

A solution prepared by dissolving 2 g of the silver (Ag) nanowire in 100 ml of isopropanol was spin-coated on a 5 cm x 5 cm glass substrate (eagle glss) by 3000 rpm at 150 rpm for 10 minutes And a transparent electrode having a thickness of 200 nm was formed by heating.

Comparative Example

Synthesis of silver (Ag) nanowires

Silver (Ag) nanowires were synthesized in the same manner as in Example except that nitrogen purging was not performed.

Fabrication of transparent electrode

A transparent electrode was prepared using the silver nanowire in the same manner as in Example.

evaluation

Average diameter of nanowires

The results of observing the silver (Ag) nanowires of the examples and comparative examples with a scanning electron microscope are shown in Figs. 1 and 2. Fig. The average diameters of the silver (Ag) nanowires were calculated by measuring 20 points based on the scanning electron microscopic photographs and then arithmetically averaging them.

Referring to FIGS. 1 and 2, the silver (Ag) nanowires synthesized according to the embodiment have a diameter within a range of 35 to 45 nm and an average value thereof is about 40 nm. The diameter of the silver (Ag) nanowires synthesized according to the comparative example is in the range of 50 to 80 nm, and the average value thereof is about 60 nm.

From the above results, it can be confirmed that silver (Ag) nanowires having a diameter of 50 nm or less can be synthesized according to the present invention.

The haze of the transparent electrode

The haze of the transparent electrodes according to Examples and Comparative Examples was measured, and the results are shown in Table 2. Hayes described the average value measured by transmission through a wavelength of 400 to 800 nm using UV-spectroscopy of JASCO V-600 model.

Haze (%) Example 1.0 Comparative Example 2.5

Referring to Table 2, the transparent electrode according to the embodiment exhibits significantly superior characteristics to the transparent electrode according to the comparative example.

From the above results, it can be confirmed that the transparent electrode having reduced haze can be manufactured according to the present invention.

The terms used in the present invention are intended to illustrate specific embodiments and are not intended to limit the invention. The singular presentation should be understood to include plural meanings, unless the context clearly indicates otherwise. The word "comprises" or "having" means that there is a feature, a number, a step, an operation, an element, or a combination thereof described in the specification. The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims. It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

Claims (11)

Dissolving a capping agent in a reducing solvent to prepare a reaction solution;
Purging the reaction solution with nitrogen;
Introducing a metal precursor into the nitrogen purged reaction solution; And
And heating the reaction solution into which the metal precursor is introduced.
The method according to claim 1,
Examples of the reducing solvent include water, ethylene glycol, 1,2-propyleneglycol, 1,3-propyleneglycol, diethyleneglycol (DEG) A metal using at least one member selected from the group consisting of 2-hydroxyethyl ether, diprophyleneglycol (DPG), polyethylene glycol (PEG), glycerol and pentaerythritol. A method of manufacturing a nanowire.
The method according to claim 1,
The capping agent may be selected from the group consisting of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polymaleic acid (PMA), polymethylmethacrylic acid (PMMA) A method for producing a metal nanowire using one or more species.
The method according to claim 1,
Wherein the metal precursor is an organic acid salt, an inorganic acid salt or a halide of at least one metal selected from the group consisting of gold, silver, copper, nickel and palladium.
5. The method of claim 4,
Wherein the reaction solution further comprises tetrabutylammonium chloride or a halogen compound using a metal salt of a typical element or a transition element type.
The method according to claim 1,
Wherein the nitrogen purging is performed by bubbling in a state where the inflow of external air is blocked.
The method according to claim 1,
Wherein the nitrogen purging is performed at 20 to 150 DEG C for 5 to 600 minutes.
The method according to claim 1,
Wherein the step of introducing the metal precursor is carried out by dropping a solution in which the metal precursor is dissolved in the reaction solution.
The method according to claim 1,
Wherein the heating is performed at 50 to 150 DEG C for 1 to 24 hours.
10. A metal nanowire produced by any one of claims 1 to 9.
A transparent electrode comprising the metal nanowire of claim 10.

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