WO2009064133A2

WO2009064133A2 - Conductivity enhanced transparent conductive film and fabrication method thereof

Info

Publication number: WO2009064133A2
Application number: PCT/KR2008/006727
Authority: WO
Inventors: Young Kyu Chang; Seung Yong Bae; Young Sil Lee; Young Hee Lee; Hong Zhang Geng
Original assignee: Cheil Industries Inc.
Priority date: 2007-11-14
Filing date: 2008-11-14
Publication date: 2009-05-22
Also published as: WO2009064133A3

Abstract

Disclosed herein is a method of fabricating a transparent conductive film, including preparing a carbon nanotube composite composition by blending a carbon nanotube in a solvent; coating the carbon nanotube composite composition on a base substrate to form a carbon nanotube composite film, and acid-treating the carbon nanotube composite film by dipping the carbon nanotube composite film in an acid solution, followed by washing the carbon nanotube composite film with distilled water and drying the washed carbon nanotube composite film to form a transparent electrode on the base substrate. The transparent conductive film is imparted with excellent conductivity, transparency and bending properties through acid treatment, so that it can be applied to touch screens and transparent electrodes of foldable flat panel displays. Further, the carbon nanotube composite conductive film has improved conductivity while maintaining transparency after acid treatment.

Description

[DESCRIPTION] [Invention Title]

CONDUCTIVITY ENHANCED TRANSPARENT CONDUCTIVE FILM AND FABRICATION METHOD THEREOF

[Technical Field]

The present invention relates to transparent conductive films formed using a carbon nanotube composite composition. More particularly, the present invention relates to a conductivity enhanced transparent conductive film, and a method of fabricating the same by dispersing a carbon nanotube in a polymer binder dissolved in a solvent to form an electrically conductive carbon nanotube composite composition, followed by coating and acid-treating the carbon nanotube composite composition on a base substrate.

[Background Art]

In recent years, advances in technology for developing a thin and light- weight display have generated a great deal of interest in materials for transparent electrodes.

Transparent conductive films have been generally applied to advanced displays such as flat panel displays, touch screen panels, and the like.

For the flat panel displays, a transparent electrode is formed by coating a metal oxide such as indium tin oxide (ITO) and indium zinc oxide (IZO) on a glass or plastic substrate via a coating process such as sputtering and the like.

The transparent electrode film formed using such a metal oxide has high conductivity and transparency, but also suffers low friction resistance and is vulnerable to bending. Furthermore, indium adopted as one main material for the transparent film does not allow easy treatment and is very expensive due to limited natural reserves thereof.

Hence, the use of electrically conductive polymers, such as polyaniline, polythiophen, and the like, has been investigated to develop a transparent electrode that has polymers' merits in terms of easy processibility and bending properties.

A transparent electrode film formed of the conductive polymer has high electrical conductivity by doping, good adhesion of a coating layer, and good bending properties. However, the conductivity of the conductive polymer-based transparent film is not sufficient for the transparent film to be applied to the transparent electrode, and the conductive polymer-based transparent film provides low transparency.

Thus, a carbon nanotube is developed as a material which can substitute ITO. The carbon nanotube is used in many fields, and particularly, the application of the carbon nanotube to an electrode material exhibiting excellent electrical conductivity has been actively studied.

The carbon nanotube is based on carbon and has a tube shape formed by rolling a graphene sheet in a spiral shape. As currently known in the related art, carbon-based materials include diamond, graphite, and fullerene. Compared with these carbon-based materials, the carbon nanotube has a lower density and exhibits higher strength, stability and electrical properties, thereby attracting considerable attentions from many fields. In particular, investigation for the application of the carbon nanotube has been conducted to develop not only materials for field emission devices, light emitting devices, displays, and the like using the electrical properties of the carbon nanotube, but also composite materials for use as general materials.

For these applications, attempts have been made to enhance dispersibility and adhesive properties of the carbon nanotube to improve the electrical conductivity of the carbon nanotube.

However, the carbon nanotube still does not have the conductivity of ITO (several tens of Ω /cm²).

[Disclosure] [Technical Problem]

An aspect of the present invention is to provide a transparent conductive film that is formed using a carbon nanotube composite composition and can be applied to a transparent electrode of a foldable flat panel display by enhancing electric conductivity, transparency, and bending properties.

Another aspect of the present invention is to provide a transparent conductive film that is formed using a carbon nano composite composition through acid treatment to enhance electric conductivity and adhesive force while maintaining transparency of the transparent conductive film, and to provide a method of fabricating the same.

It should noted that the present invention is not limited to the above aspects and that other aspects of the present invention not referred to herein will be more clearly understood by those skilled in the art from the following disclosure.

[Technical Solution]

In accordance with an aspect of the present invention, a method of fabricating a transparent conductive film includes: preparing a carbon nanotube composite composition by blending a carbon nanotube in a solvent; coating the carbon nanotube composite composition on a base substrate to form a carbon nanotube composite film; and acid-treating the carbon nanotube composite film to form a transparent electrode on the base substrate by dipping the carbon nanotube composite film in an acid solution, followed by washing the carbon nanotube composite film with distilled water and drying the washed carbon nanotube • composite film. In accordance with another aspect of the present invention, a transparent conductive film including a transparent electrode formed of a carbon nanotube on a base substrate is provided.

The transparent electrode may have a transmittance of 80% or more as measured at a wavelength of 550 nm using a UV/Vis spectrometer.

The transparent electrode may have a surface resistance of 1000 Ω /ciif or less as measured by a 4-point probe method.

[Advantageous Effects]

According to an embodiment of the invention, the transparent conductive film may be formed using a carbon nanotube composite to have enhanced electrical conductivity without deterioration of transparency.

According to the embodiment of the invention, the transparent conductive film may have improved bending properties to be used for a transparent electrode of a foldable flat panel display. According to the embodiment of the present invention, the method may be used to fabricate a transparent conductive film having enhanced electric conductivity and surface flatness without deteriorating transparency of the film through surface modification, that is, acid treatment.

[ Description of Drawings ]

Fig. 1 is a view of a transparent conductive film according to an embodiment of the present invention;

Figs. 2 to 5 are flow diagrams of a method of fabricating a transparent conducive film according to an embodiment of the present invention;

Fig. 6 is a flow chart of the method of fabricating the transparent conducive film according to the embodiment of the present invention; Fig. 7 is a graph depicting surface resistance of inventive transparent conductive films according to transparency thereof; and

Figs. 8 and 9 are SEM images of a transparent conductive film of Example 10 before and after acid treatment, respectively.

[Best Mode]

Embodiments of the present invention will hereinafter be described with reference to the accompanying drawings.

Fig. 1 is a view of a transparent conductive film according to an embodiment of the present invention. Referring to Fig. 1, a transparent conductive film 10 according to the embodiment of the invention includes a base substrate 100 and a transparent electrode 110 formed thereon.

The base substrate 100 may be formed of a polymer film or glass substrate.

The polymer film may be a polyester, polycarbonate, polyether sulfone or acrylate-based transparent film. More specifically, the polymer film may be selected from polyethylene terephtalate (PET), polyethylene naphtalate (PEN) or polyether sulfone (PES).

The transparent electrode 110 may be formed by dispersing a carbon nanotube in a surfactant or polymer binder to form a carbon nanotube composite composition, and coating the composition on the base substrate 100.

Here, acid treatment may be performed on the carbon nanotube composite composition to enhance an adhesive force between the base substrate 100 and the carbon nanotube. The acid treatment will be described in detail below in description of a method of fabricating the transparent conductive film. The carbon nanotube has a very low electric resistance due to inherent structural characteristics thereof, and has a very long shape. The carbon nanotube is used for many applications, and has been investigated, particularly, for application to an electrode material due to its superior electrical conductivity.

The carbon nanotube may be one selected from a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), a multi-walled carbon nanotube (MWCNT), and a rope carbon nanotube. Advantageously, the carbon nanotube may be the single-walled carbon nanotube.

According to an exemplary embodiment of the invention, the transparent conductive film comprises at least 90% by weight or more of single-walled or double- walled carbon nanotubes.

The carbon nanotube may have an outer diameter of 0.5-4 nm and a length of 10-5,000 nm. The carbon nanotube may be refined by a metal catalysis treatment process using a strong acid.

When the carbon nanotubes are coated on the glass substrate or polymer film, the adhesion between the carbon nanotubes can be weakened so as to cause a reduction of electrical conductivity and a failure of the electrode.

Thus, after the formation of the transparent conductive film, pressing or over-coating is generally carried out to enhance the adhesion between the carbon nanotubes. In these cases, however, since thin carbon nanotubes of 100 nm or less in thickness are physically processed, there is a possibility of damaging the surface of the conductive film.

In this invention, the transparent conducive film is fabricated to have good electrical properties without undergoing transparency deterioration through acid treatment in order to enhance the properties of a transparent electrode formed of the carbon nanotubes.

Figs. 2 to 5 are flow diagrams of a method of fabricating a transparent conducive film according to an embodiment of the present invention, and Fig. 6 is a flow chart of the method of fabricating the transparent conducive film according to the embodiment of the present invention.

Herein, the method of the fabrication of the transparent conducive film will be described with reference to the flow diagrams and the flowchart together. Referring to Figs. 2 and 6, first, a carbon nanotube composite composition

210 comprising carbon nanotubes 220 is prepared to perform coating a base substrate 100 (see Fig. 3) with the carbon nanotube composite composition 210 in order to form a transparent conductive film in operation S310.

According to embodiments of the invention, the carbon nanotube composite composition 210 may be formed by blending the carbon nanotubes 220 with a mixture solution 250.

In a first embodiment of the invention, the mixture solution 250 contains a surfactant and a solvent, and in a second embodiment of the invention, the mixture solution 250 contains a polymer binder and a solvent. The mixture solution 250 according to the first embodiment may have a composition of 0.01-2 parts by weight of the surfactant and 0.01-2 parts by weight of the carbon nanotubes with respect to 100 parts by weight of the solvent.

The mixture solution 250 according to the second embodiment may have a composition of 0.05-1 part by weight of the polymer binder and 0.05-1 part by weight of the carbon nanotubes with respect to 100 parts by weight of the solvent.

The polymer binder and the carbon nanotubes may be mixed in a ratio of 1 :5 - 5:1.

For the mixture solution of the first embodiment, the solvent may be water, which permits more environmentally friendly preparation. For the mixture solution of the second embodiment, the solvent may be a mixture of water and isopropyl alcohol as prepared by considering solubility of the polymer binder. In this case, the mixture of water and isopropyl alcohol may have a volume ratio of 20:80 to 80:20. In terms of an environmental engineering approach, it is suggested to use water, and when used with water, the solvent may provide high dispersibility of the carbon nanotubes.

According to this invention, the surfactant is an amphiphilic material containing both a hydrophilic moiety and a hydrophobic moiety. In the solution, the hydrophobic moiety of the surfactant exhibits affinity to the carbon nanotubes and the hydrophilic moiety of the surfactant exhibits affinity to water provided as one component of the solvent so as to be conducive to stable dispersion of the carbon nanotubes in the solution.

The hydrophobic moiety may take the form of a long alkyl chain, and the hydrophilic moiety may take the form of a salt, such as sodium salt, potassium salt, or the like.

In this invention, the hydrophobic moiety has a chain structure composed of 10 or more carbon elements, and the hydrophilic moiety may have either an ionic or non-ionic shape. The surfactant may be one selected from sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (NaDDBS), and the like.

The polymer binder may be composed of hydrophobic elements while allowing ion conduction or ion exchange.

Although any resin having ionic conductivity or ion exchange properties can be used as the polymer binder, the resin having ionic conductivity is sensitive to moisture due to its hydrophilic properties and can cause a reduction of the adhesive force after processing.

Accordingly, it is desirable that the resin for the polymer binder of the present invention be composed of the hydrophobic elements while exhibiting the ionic conductivity or ion exchange properties.

Specifically, the polymer binder may be so-called Nafion as expressed by the following Chemical Formula 1, that is, fluorinated polyethylene that comprises fluorine elements and contains a sulfonyl functional group. Additionally, the polymer binder may be a thermoplastic polymer that contains one or more functional groups selected from carboxyl, sulfonyl, phosphonyl, and sulfone imides. Also, the polymer binder may be a salt of potassium, sodium or the like combined with one or more functional groups selected from carboxyl, sulfonyl, phosphonyl, and sulfone imides.

Chemical formula 1

C! ., ~™" Cf' '

! ^J " R -Ct- O

O-ϊ- CI-,- CF, - C) 4- CV,- CF, - S -OH

O

(where R is a fluorinated alkyl group of C1-C8 with fluorine or an alkyl group between Cl-Cl substituted, and m is an integer between 0 to 3, n is a degree of polymerization, advantageously in the range of 10-10,000, and can be optionally adjusted during polymerization as needed.)

The carbon nanotube 220 has a nano size (shape), forming a large surface area.

As such, since the carbon nanotubes 220 provide a large surface area, the carbon nanotubes 220 agglomerate and have a tendency of becoming energetically stable via surface area reduction. In other words, since the carbon nanotubes 200 agglomerate in the form of a rope and exhibit the tendency of becoming stable via the surface area reduction so as to have a reduced surface energy, the agglomeration of the carbon nanotubes is relieved when the carbon nanotubes become stable.

Therefore, it is important to evenly disperse nano-size materials, such as the carbon nanotubes, which exhibit a tendency of agglomeration. A solution of the carbon nanotube composite composition 210 containing the carbon nanotubes 220 is dispersed by ultrasound dispersion and the like.

Then, as shown in Figs. 3 and 6, the carbon nanotube composite composition 210 prepared as in Fig. 2 is coated on the base substrate 100 in operation S320. Coating of the carbon nanotube composite composition 210 on the base substrate 100 can be achieved by a spray coating process, an ink-jet coating process, and the like. The spray coating process may be advantageously used for the coating operation. In this manner, a carbon nanotube composite layer 210a is formed on the base substrate 100 by coating the carbon nanotube composite composition 210 on the base substrate 100.

Here, a substrate having the carbon nanotube composite layer 210a formed on the base substrate 100 will be defined as a carbon nanotube composite film 200. As for the base substrate 100, a polymer film or a glass substrate may be used. The polymer film may be a polyester, polycarbonate, polycther sulfone or acrylate-based transparent film. More specifically, the polymer film may be selected from polyethylene terephtalate (PET), polyethylene naphtalate (PEN) and polyether sulfone (PES). Then, as shown in Figs. 4 and 6, the carbon nanotube composite film 200 is subjected to acid treatment in operation S330.

For acid treatment, the carbon nanotube composite film 200 may be dipped in an acid solution. In the drawings, the acid treatment is schematically shown for convenience of description. The acid solution may have a pH of 3 or less, and more advantageously a pH in the range of -1~1 to exhibit high efficiency. When the acid solution has a pH above 3, suitable acid treatment cannot be performed due to a long acid treatment time.

Further, the acid solution used for the acid treatment may comprise one selected from the group consisting of, but not limited to, perchloric acid, nitric acid, hydrochloric acid, sulfuric acid, and mixtures thereof.

During the acid treatment, the carbon nanotube composite film 200 is dipped in the acid solution for 1 minute to 24 hours. More advantageously, the dipping time is adjusted to be 30 minutes or more to 5 hours to increase electrical conductivity or to reduce a process time.

Next, the carbon nanotube composite film 200 is taken out, washed with distilled water, and dried. If the carbon nanotube composite film 200 is made from the combination of the carbon nanotubes, polymer binder and solvent as in the first embodiment described above, the carbon nanotubes 220, which protrude from the surface of the carbon nanotube composite film 200 due to partial detachment of the polymer binder from the surface thereof by the acid treatment, may be conducive to enhancement of conductivity.

Further, the conductivity may be enhanced due to an increase in adhesion area and adhesive force between the carbon nanotubes 220.

If the carbon nanotube composite film 200 is made from the combination of the carbon nanotubes, surfactant and solvent as in the second embodiment, the surfactant remaining after acid treatment may be neutralized or removed to increase purity of the film, thereby enhancing conductivity.

Namely, the acid solution used for acid treatment of the carbon nanotube composite layer 210a can reduce a large amount of surfactant present between the carbon nanotube composite layer 210a and the base film 100. As a result, the carbon nanotube composite layer can be brought into close contact with the base film 100, so that the adhesive force between the carbon nanotube composite layer and the base film 100 can be increased.

As such, the adhesive force between the carbon nanotubes is increased by removal of the large amount of surfactant present from the film, so that the film has enhanced adhesion and conductivity compared to when a large amount of surfactant remains in the carbon nanotube composite film.

However, a trace of surfactant may remain in the transparent electrode 110 or may be further reduced. Then, as shown in Figs. 5 and 6, the carbon nanotube composite film 200 is subjected to acid treatment and drying, thereby forming a transparent conductive film 10 in operation S340.

The transparent electrode 110 may have a surface resistance of 1,000 Ω Id or less as measured by a 4-point probe method, and may have a transmittance of 80% or more as measured at a wavelength of 550 nm using a UV/Vis spectrometer.

Examples

Next, examples of the present invention will be described in detail to show that acid treatment of a carbon nanotube composite composition leads to excellent electrical conductivity and adhesive characteristics of a transparent conductive film while maintaining transparency thereof.

Herein, a description of configuration apparent to those skilled in the art will be omitted for clarity. 1. Preparation of materials

1) Carbon nanotube: A single- walled carbon nanotube (SAP: purity 60-70%) produced by arc discharge was used. The carbon nanotube has a length of about 20 μm and a thickness of about 1.4 nm.

2) Polymer binder: Nafion™ solution DE 520 (5wt% solution of isopropyl alcohol and water) (commercially available from E.I. Du Pont de

Nemours and Company) was used.

3) Surfactant: Sodium dodecyl sulfate (SDS) (purity 99%) commercially available from Aldrich was used.

4) Base substrate: Skyrol SH34 PET film commercially available from SK Chemical Co., Ltd was used.

The prepared carbon nanotubes and the polymer binder or SDS were added at a predetermined ratio to a mixture solution of water and isopropyl alcohol mixed in a ratio of 40: 60. Then, the carbon nanotubes in the mixture solution were evenly dispersed by ultrasound dispersion to form a carbon nanotube composite composition, which in turn was coated on a PET film by the spray coating process with different coating numbers, thereby producing a carbon nanotube film. The carbon nanotube film was dipped in sulfuric acid, nitric acid or a mixture thereof for a predetermined period of time, followed by measuring electrical conductivity and transparency of the carbon nanotube film after washing and drying.

2. Measurement of electrical conductivity

To determine the electrical conductivity of the transparent conductive film, four corners of the transparent conductive film were coated with gold so as to form electrodes, surface resistance of which was measured in Ω /cnf by the 4-point probe method.

3. Measurement of transmittance

The transmittance of the transparent conductive film was measured at a wavelength of 550 nm with a UV/vis spectrometer with reference to 100 given as a conversion transmittance of the base substrate or glass used for the transparent conductive film.

Herein, the term "transmittance" refers to a degree to which light is transmitted, and is measured in a visible region of 400-800 nm. Herein, to report transmittance measured at a constant wavelength, the transmittance of the film was measured at a wavelength of 400 or 600 nm.

4. Adhesive force

For the adhesive force of the transparent conductive film, scotch tape was attached to the PET film with the transparent electrode formed thereon, and separated therefrom after a predetermined period of time to determine whether the polymer binder or the carbon nanotubes were stuck to the separated scotch tape.

The adhesive force of the transparent conductive film was marked by X, Δ, and O after visible determination as to whether the film was entirely, partially or completely not stuck to the scotch tape when separating the scotch tape. 5. Analysis of results

Examples 1-8

After dispersing single-walled CNTs in a solvent prepared using water and SDS or surfactant, ultrasound dispersion was performed to prepare an even dispersion solution. The CNTs and the SDS were present in a ratio of 1 :1, and each was dispersed in a density of 0.1 wt% in the solution.

The dispersion solution was coated on the PET film by the spray coating process with different coating numbers, followed by washing with distilled water three times and drying in an oven at 80 ^°C for 4 hours. The dried film was dipped for 1 hour in 12N nitric acid for acid treatment, followed by washing with distilled water and drying. Then, the electrical conductivity, transparency, and adhesive force of the film were measured.

The same carbon nanotube film was dipped for 1 hour in 12N nitric acid (-1 pH), followed by washing with distilled water and drying. Then, the electrical conductivity and transparency of the film were measured.

Examples 9-14

With single-walled CNTs dispersed in a 40:60 mixture solution of water and isopropyl alcohol, and Nafϊon™ provided as an ionic conductive polymer, the CNTs were mixed in a ratio of 1 : 1. Then, the CNTs and the Nafion™ were dispersed to have a density of 0.1 wt% in the solvent, respectively.

The mixture solution was dispersed by the ultrasound dispersion process, and was then coated on the PET film by the spray coating process with different coating numbers, followed by drying at room temperature for 4 hours. The dried film was dipped for 1 hour in 12N nitric acid solution for acid treatment, followed by washing with distilled water. Then, the electrical conductivity, transparency, and adhesive force of the film were measured. The same carbon nanotube film was dipped for 1 hour in 12N nitric acid (-1 pH), followed by washing with distilled water and drying. Then, the electrical conductivity and transparency of the film were measured. Table 2 shows the deposition (coating) numbers and measurement results. Table 1

From Examples 1 to 8, it can be seen that acid treatment of the film in nitric acid solution led to enhanced electrical conductivity while substantially maintaining transparency of the film before and after the acid treatment.

A degree of conductivity enhancement was about 100%, and there was no difference in adhesive force before and after the acid treatment. However, the use of a suitable binder will increase the adhesive force while enhancing the conductivity.

Table 2

For Examples 9 to 14, the adhesive force between the PET film and the carbon nanotubes was enhanced by the polymer binder. From Table 2, it can be seen that the conductivity was enhanced by 100% or more while the transparency was maintained.

Fig. 7 is a graph depicting surface resistance of inventive transparent conductive films according to transparency thereof, and Figs. 8 and 9 are SEM images of a transparent conductive film of Example 10 before and after acid treatment, respectively.

As shown in Tables 1 and 2, when the carbon nanotube composite film was subjected to acid treatment, there was an effect of highly enhancing the conductivity while maintaining the transparency of the film. Further, as seen from Examples 9 to 14 where the polymer binder was used, the use of the polymer binder enhanced the adhesive force.

Although these results are similar to conductivity enhancement by doping of

CNTs with SOCl₂ (thionly chloride) as reported by Zhang (Nemo Lett. 2006, 6, 1880) and Tomanek (J. Am. Chem. Soc. 2005, 127, 5125), the inventive examples achieved an effect of more noticeable conductivity enhancement than the reported results. Such an increase in conductivity was obtained via improvement of the adhesive force between the carbon nanotubes by removal of the surfactant during acid treatment, and was obtained from a p-doping effect through CNT oxidation during the acid treatment.

Further, it could be seen that the conductivity enhanced film maintained conductivity for 30 days or more after which the film reached a sufficiently stable state.

Referring to Figs. 7, 8, and 9, for the carbon nanotube composite film formed using SDS as the surfactant, the remaining surfactant after acid treatment was neutralized or removed to enhance the conductivity of the film through improvement of purity of the carbon nanotube composite film.

Particularly, the carbon nanotube composite film made from the combination of the carbon nanotubes, polymer binder and solvent has increased attachment area and adhesive force between the carbon nanotubes via the acid treatment, so that not only does the carbon nanotube composite film have improved conductivity, but also exhibits good adhesive properties due to the increased adhesive force between the film and the carbon nanotubes. Additionally, the acid solution used for the acid treatment causes the base substrate to swell and shrink such that the carbon nanotube composite composition can be brought into close contact with the base substrate, thereby improving the adhesion of the nanotube composite composition. As apparent from the above description, the method of fabricating the transparent conductive film according to the embodiment of the present invention may minimize damage of the surface of the transparent conductive film, and has improved electrical conductivity without undergoing deterioration of transparency through surface modification, that is, acid treatment.

Claims

[CLAIMS]

[Claim 1 ]

A method of fabricating a transparent conductive film, comprising: preparing a carbon nanotube composite composition by blending a carbon nanotube in a solvent; coating the carbon nanotube composite composition on a base substrate to form a carbon nanotube composite film; and acid-treating the carbon nanotube composite film to form a transparent electrode on the base substrate by dipping the carbon nanotube composite film in an acid solution, followed by washing the carbon nanotube composite film with distilled water and drying the washed carbon nanotube composite film.

[Claim 2]

The method according to claim 1 , wherein the solvent is a mixture solution of water and isopropyl alcohol in a volume ratio of 20:80 ~ 80:20.

[Claim 3]

The method according to claim 1, wherein the carbon nanotube composite composition further comprises a surfactant or a polymer binder.

[Claim 4]

The method according to claim 3, wherein the carbon nanotube composite composition comprises 0.01-2 parts by weight of the surfactant and 0.01-2 parts by weight of the carbon nanotube with respect to 100 parts by weight of the solvent.

[Claim 5]

The method according to claim 4, wherein the surfactant is sodium dodecyl sulfate (SDS) or sodium dodecyl benzene sulfonate (NaDDBS).

[Claim 6]

The method according to claim 3, wherein the carbon nanotube composite composition comprises 0.05-1 part by weight of the polymer binder and 0.05-1 part by weight of the carbon nanotube with respect to 100 parts by weight of the solvent.

[Claim 7]

The method according to claim 6, wherein the polymer binder comprises a resin having ionic conductivity or ion exchange properties, the resin comprising fluorine elements and containing at least one functional group selected from carboxyl, sulfonyl, phosphonyl, and sulfone imides.

[Claim 8]

The method according to claim 6, wherein the polymer binder and the carbon nanotube are mixed in a ratio of 1 :5—5:1.

[Claim 9]

The method according to claim 1 , wherein the carbon nanotube composite composition is coated on the base substrate by a spray or ink-jet coating process.

[Claim 10]

The method according to claim 1 , wherein the base film is a polymer film selected from polyester, polycarbonate, polyether sulfone, and acrylate-based polymers.

[Claim 11 ]

The method according to claim 1, wherein the base film is a glass substrate.

[Claim 12]

The method according to claim 1, wherein the acid solution used in the acid- treatment has a pH in the range of -1-3.

[Claim 13]

The method according to claim 1 , wherein the acid solution comprises one selected from the group consisting of perchloric acid, nitric acid, hydrochloric acid, sulfuric acid, and mixtures thereof.

[Claim 14]

The method according to claim 1, wherein the carbon nanotube composite film is dipped in the acid solution for 30 minutes to 5 hours.

[Claim 15]

A transparent conductive film comprising a transparent electrode formed of a carbon nanotube on a base substrate by the method of fabricating a transparent conductive film according to claim 1.

[Claim 16]

The transparent conductive film according to claim 15, wherein the transparent electrode has a transmittance of 80% or more as measured at a wavelength of 550 nm using a UV/Vis spectrometer.

[Claim 17]

The transparent conductive film according to claim 15, wherein the transparent electrode has a surface resistance of 1,000 Ω /cm² or less as measured by a 4-point probe method.