KR20100068019A - Solar cell using carbon nanotube complex material and fabrication method thereof - Google Patents

Abstract

PURPOSE: A solar cell using carbon nanotube complex material and a fabrication method thereof are provided to implement a power generation layer and a charge transport layer by attaching a nono particle to a nonotube. CONSTITUTION: A lower electrode(120) is formed on a substrate(110). A hole-transport layer(130) is formed on the lower electrode. An active layer(140) is formed on the hole-transport layer and is formed with a carbon nonotube having a carbon particle of a core shell. An upper electrode(150) is formed on the active layer.

Description

Solar cell using carbon nanotube composite material and manufacturing method thereof {Solar cell using carbon nanotube complex material and fabrication method}

The present invention relates to a solar cell, and more particularly, to a solar cell using nanoparticles and carbon nanotubes.

Recently, interest in renewable energy is increasing due to global environmental problems, depletion of fossil energy, waste disposal of nuclear power generation, and location selection due to the construction of new power plants. Among them, research on solar power generation as a pollution-free energy source Development is underway at home and abroad.

Solar cells are semiconductor devices that convert solar energy directly into electrical energy. It is common to manufacture a solar cell with a p-n junction structure using amorphous silicon or polycrystalline silicon, and its basic structure is similar to that of a diode.

When solar light is irradiated to a solar cell having a structure in which p-type semiconductors and n-type semiconductors having different electrical properties are bonded to each other, electron-hole pairs are generated by light energy, and electrons and holes Electromotive force is generated by a photovoltaic effect in which current moves through an n-type semiconductor layer and a p-type semiconductor layer, and current flows to an externally connected load.

Specifically, when light is incident on the solar cell from outside, the valence band electrons of the p-type semiconductor of the p-n junction are excited to the conduction band by the incident light energy. The excited electrons generate one electron-hole pair inside the p-n junction. The electrons and holes in the electron-hole pairs are transferred to the n-type and p-type semiconductors by electric fields existing between p-n junctions, respectively, to supply current to the outside.

Although solar cells made of such silicon materials exhibit higher photovoltaic efficiency than other materials, even though commercialization has been made early, the price of solar cells has increased due to the use of expensive silicon to manufacture solar cells. It is used only in a limited field, and solar cells using new materials and structures such as carbon nanotubes and nanoparticles have been researched to solve the problem of silicon solar cells.

Among them, carbon nanotubes have high electrical conductivity and are used as charge transport layers and transparent electrodes in solar cells. However, carbon nanotubes cannot form electrons and holes when irradiated with sunlight, and thus cannot generate power directly. Therefore, a separate power generation layer (power generation layer) is required for power generation. Therefore, carbon nanotubes are mainly used for dye-sensitized solar cells with relatively low efficiency.

Unlike carbon nanotubes, nanoparticles can be used in power generation layers that produce power directly from solar cells. And nanoparticles have the advantage that can be formed simply by a method such as spin coating using a polymer solution. However, in order to increase the power efficiency of solar cells using nanoparticles, it is necessary to form a separate charge transport layer. In addition, in order to manufacture nanoparticles, a complicated process is required, resulting in a high production cost.

In order to overcome these shortcomings and take advantage of the advantages of nanoparticles and carbon nanotubes, new structures of solar cells using carbon nanotubes with nanoparticles attached have been proposed. However, the proposed solar cell is also a dye-sensitized solar cell, and carbon nanotubes to which nanoparticles are attached are used to increase power generation efficiency, but are not used as a power generation layer that directly generates power. In addition, in order to manufacture the carbon nanotubes to which the nanoparticles are attached, there is a problem in that the production cost increases due to an excessively complicated manufacturing process and a lot of equipment.

The technical problem to be solved by the present invention is a solar cell that serves as a charge transport layer for transporting electrons while the carbon nanotube composite material in which the nanoparticles are attached to the carbon nanotubes serves as a power production layer for generating electron-hole pairs. And a method for manufacturing such a solar cell in a simpler and cheaper method.

In order to solve the above technical problem, a solar cell according to the present invention is a substrate; A lower electrode formed on the substrate; A hole transport layer formed on the lower electrode; An active layer formed on the hole transport layer and made of carbon nanotubes to which core-shell structure nanoparticles are attached; And an upper electrode formed on the active layer.

The core-shell structured nanoparticles are CdSe / ZnTe, CdSe / ZnSe, CdSe / ZnS, InP / ZnTe, InP / ZnSe, InP / GaAs, InP / CdS, InP / CdSe, AlSb / GaP, AlSb / ZnO, AlSb / ZnS, AlSb / ZnSe, AlSb / CdS, AlSb / CdSe, InGaAs / GaAs, PbTe / PbS, CdTe / ZnTe, GaAs / GaP, GaAs / InP, GaAs / CdSe, GaSb / GaP, GaSb / Ind, GaSb / CdS GaSb / CdSe, ZnTe / GaP, ZnTe / ZnO, ZnTe / ZnS, ZnTe / ZnSe, ZnTe / CdS, and ZnTe / CdSe, and at least one of the lower electrode and the upper electrode may be Al, Au, Cu , Pt, Ag, W, Ni, Zn, TI, Zr, Hf, Cd, Pd, ITO (indium-tin oxide), Al-doped ZnO (AZO), Ga-doped ZnO (GZO) and It may be any one of Mg-doped ZnO (MZO).

In the method of manufacturing a solar cell according to the present invention, after forming a lower electrode on a substrate, a hole transport layer is formed on the lower electrode, and an active layer made of carbon nanotubes to which core-shell structured nanoparticles are attached on the hole transport layer. To form. Then, an upper electrode is formed on the active layer.

The forming of the active layer may include preparing a solution in which carbon nanotubes to which core-shell structured nanoparticles are attached are dispersed in a solvent, and then spin coating the solution on the hole transport layer to form a film, and then Removing the solvent. In this case, preparing the solution in which the carbon nanotubes to which the core-shell structure nanoparticles are attached is dispersed in a solvent, treating the carbon nanotubes with an acid and then in the solvent, the carbon nanotubes and the core-shell structure nanoparticles And mixing the particles and reacting the carbon nanotubes with the core-shell structure nanoparticles to attach the core-shell structure nanoparticles to the surface of the carbon nanotubes. Here, the step of treating the carbon nanotubes with an acid may include forming a carboxyl group (-COOH) while simultaneously removing impurities on a surface by heat treating the carbon nanotubes in a nitric acid solution at 60 ° C .; Diluting the nitric acid solution containing the carbon nanotubes with deionized water and filtering only the carbon nanotubes using a filter; And drying the filtered carbon nanotubes, wherein the solvent is 1,2-dicloroethane (C ₂ H ₄ Cl ₂ ), toluene, acetone, chloroform, ethylene glycol, isoprophenol (isopropanol). ) And xylene.

According to the present invention, since the solar cell is manufactured using a carbon nanotube composite material consisting of carbon nanotubes to which core-shell structured nanoparticles are attached, the carbon nanotube composite material serves as a power production layer and an electron transporting layer. There is no need to fabricate a separate electron transport layer, which makes the structure of the solar cell very simple. The carbon nanotube composite material can be formed into a thin film by an easy method such as spin coating, and the structure of the solar cell is simple, so that a high efficiency solar cell can be manufactured at low cost.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention and to those skilled in the art. It is provided for complete information.

1 is a view showing a schematic structure of a preferred embodiment for a solar cell according to the present invention.

Referring to FIG. 1, the solar cell 100 according to the present invention includes a lower electrode 120, a hole transport layer 130, an active layer 140, and an upper electrode 150 sequentially formed on the substrate 110 and the substrate 110. ).

The substrate 110 is made of an insulating inorganic material or an insulating organic material. Insulating inorganic material is any one of Si, GaAs, InP, InSb, AlAs, AlSb, CdTe, ZnTe, ZnS, CdSe, CdSb, GaP, SiC, Al ₂ O ₃ , ZnO, glass and quartz Can be. Insulating organic materials include PET (polyethylene terephtalate), PS (poly styrene), PI (poly imide), PVC (poly vinyl chloride), PVP (poly vinyl pyrrolidone), PMMA (poly methyl methacrylate) and PE (poly ethylene) Either can be used.

The lower electrode 120 is formed on the substrate 110 and includes Al, Au, Cu, Pt, Ag, W, Ni, Zn, TI, Zr, Hf, Cd, Pd, indium-tin oxide (ITO), and Al. Can be formed of any one of -doped ZnO (AZO), Ga-doped ZnO (GZO) and Mg-doped ZnO (MZO), especially when the substrate 110 is a transparent substrate such as glass or quartz As the lower electrode 120, it is preferable to use ITO, AZO, GZO or MZO made of a transparent material.

The hole transport layer 130 is formed on the lower electrode 120 and may be made of a material such as PEDOT: PSS (poly (3,4-ethylenedioxy-thiophene) -poly (styrene sulfonate)). The hole transport layer 130 serves to transport holes generated in the active layer 140 when sunlight is irradiated.

The active layer 140 is formed on the hole transport layer 130 and is made of the carbon nanotube composite material 145 without any other material. The carbon nanotube composite material 145 has a configuration in which the core-shell structured nanoparticles 141 are attached to the carbon nanotubes 142.

Carbon nanotubes 142 may be single-walled carbon nanotubes, double-walled carbon nanotubes or multi-walled carbon nanotubes, and combinations thereof are of course possible. . 2 shows a single walled carbon nanotube 142. As shown in FIG. 1, a bundle of a plurality of carbon nanotubes may be used, but a single carbon nanotube may be used. The core-shell structured nanoparticle 141 has a core material / shell material combination of CdSe / ZnTe, CdSe / ZnSe, CdSe / ZnS, InP / ZnTe, InP / ZnSe, InP / GaAs, InP / CdS, InP / CdSe, AlSb / GaP, AlSb / ZnO, AlSb / ZnS, AlSb / ZnSe, AlSb / CdS, AlSb / CdSe, InGaAs / GaAs, PbTe / PbS, CdTe / ZnTe, GaAs / GaP, GaAs / InP, GaAs / CdSe GaP, GaSb / InP, GaSb / CdS, GaSb / CdSe, ZnTe / GaP, ZnTe / ZnO, ZnTe / ZnS, ZnTe / ZnSe, ZnTe / CdS, and ZnTe / CdSe. 2 shows CdSe / ZnSe core-shell structured nanoparticles 141 whose core is CdSe and the shell is ZnSe.

In the core-shell structure nanoparticles 141, the shell structure acts as a protective film for the core material, which can be used in processes impossible when fabricating devices using only the core material, and the electrical and optical properties of the nano structure of the core material. This can be improved. In particular, when the core-shell structure is a p-n junction, it can be used as a photovoltaic structure can be utilized in solar cells. Therefore, when sunlight is irradiated, the core-shell structured nanoparticles 141 attached to the carbon nanotubes 142 receive sunlight and generate electrons and holes to generate power, and the core-shell structured nanoparticles ( Since 141 surrounds the carbon nanotubes 142 in the form of a shell, electrons produced from the core-shell structured nanoparticles 141 may directly move to the electrode through the carbon nanotubes 142. Therefore, the carbon nanotubes 142 serve to transport electrons. Since the carbon nanotubes 142 have very high electrical conductivity and low resistance, power loss due to internal resistance of the device in the process of transporting electrons to the electrode. Can be minimized.

As such, the solar cell using the carbon-nanotube composite material composed of the core-shell structured nanoparticles and carbon nanotubes proposed in the present invention has a structure capable of increasing power generation efficiency. Core-shell structured nanoparticles can be used in the power generating layer to generate electricity, thereby forming electrons and holes in the nanoparticles more efficiently. The core-shell structured nanoparticles attached to the surface of the carbon nanotubes serve as a power generation layer, and the electrons generated from the core-shell structured nanoparticles are quickly moved to the electrode through the carbon nanotubes, so the carbon nanotubes are electrons. It serves as a transport layer. Therefore, by using the carbon-nanotube composite material composed of core-shell structured nanoparticles and carbon nanotubes as in the present invention, power generation efficiency and electron transport efficiency may be increased to increase the power production efficiency of the entire solar cell.

By using core-shell structured nanoparticles, unlike nanoparticles that cannot be attached directly to carbon nanotubes, they can be attached to carbon nanotubes, allowing a wider variety of materials to be used in solar cell fabrication. In addition, since the material used for the shell can be fixed and only the material used for the core can be replaced with other materials, it is possible to use various materials to obtain higher photovoltaic efficiency. Particularly, when the energy band of the core material that generates electricity is larger than the energy band of the shell material among the core material / shell material combinations mentioned above, the leakage of the produced electrons and holes is small, and thus higher generation efficiency may be obtained.

The upper electrode 150 is formed on the active layer 140 and, like the lower electrode 120, Al, Au, Cu, Pt, Ag, W, Ni, Zn, TI, Zr, Hf, Cd, Pd, ITO, It may be formed of any one of AZO, GZO and MZO. In particular, when the substrate 110 is a transparent substrate such as glass or quartz, it is preferable to use ITO, AZO, GZO or MZO of a transparent material as the upper electrode 150. .

The lower electrode 120 and the upper electrode 150 may be configured in various forms, and may be a straight line extending in a predetermined direction. When the lower electrode 120 and the upper electrode 150 have a straight line extending in a predetermined direction, the lower electrode 120 and the upper electrode 150 may be formed to cross each other. In FIG. 1, the lower electrode 120 has a straight line extending in a direction parallel to the ground, and the upper electrode 150 has a straight line extending in a direction perpendicular to the ground so as to cross perpendicularly thereto.

As described above, the solar cell 100 using the carbon nanotube composite material 145 generates carbon and electrons at the same time as electrons and holes are generated in the core-shell structured nanoparticles 141 included in the carbon nanotube composite material 145. The carbon nanotubes 142 provided on the nanotube composite material 145 serve to transport electrons. Therefore, the solar cell 100 using the carbon nanotube composite material 145 does not need a separate electron transport layer, thereby simplifying the structure of the solar cell 100.

The method of manufacturing such a solar cell may follow the following process sequence with reference to the flowcharts of FIGS. 3A and 3B.

In order to remove impurities such as dust and grease on the surface of the substrate 110, the intrinsic Si substrate in the undoped (100) direction, the de-ionized water is washed with TCE (trichloroethylene) solution. Prepare by washing. Then, a lower electrode 120, as an embodiment, an Al electrode is formed using thermal evaporation (step S1 in Fig. 3A).

Substrate 110 is formed of GaAs, InP, InSb, AlAs, AlSb, CdTe, ZnTe, ZnS, CdSe, CdSb, GaP, SiC, Al ₂ O ₃ , ZnO, glass, quartz, PET, PS, PI , PVC, PVP, PMMA or PE may be used, and the lower electrode 120 may also use Au, Cu, Pt, Ag, W, Ni, Zn, TI, Zr, Hf, Cd, Pd, ITO, AZO in addition to Al as an example. , GZO or MZO. The lower electrode 120 may be formed of a thermal evaporation method for a metal electrode and a sputtering method for a transparent electrode.

Next, a hole transport layer 130 is formed on the lower electrode 120 (step S2 of FIG. 3A). The hole transport layer 130 may be formed of PEDOT: PSS as a thin film for transporting holes. In this case, the PEDOT: PSS hole transport layer 130 may be formed through spin coating.

Subsequently, the active layer 140 is formed on the hole transport layer 130 (step S3 of FIG. 3A).

At this time, first, a solution in which the carbon nanotubes 142 to which the core-shell structure nanoparticles 141 are attached is dispersed is prepared (step S3_1 of FIG. 3A). In this case, the following t1 to t4 order as shown in FIG. 3B can be followed.

First, the carbon nanotubes 142 having the structure as shown in FIG. 2 are treated with an acid to remove impurities on the surface, and at the same time, a carboxyl group (-COOH) is formed as a functional group so that other materials can be bonded. As an example, single walled carbon nanotubes are stirred in an nitric acid solution using an ultrasonic stirrer while heating at 60 ° C. for 30 hours. In this process, the carbon nanotubes are split into small portions by ultrasonic agitation, and at the same time, impurities present in the carbon nanotubes are removed. After diluting the acid treated carbon nanotube solution with deionized water, the filter is used to filter out only the carbon nanotubes (step t1 in FIG. 3b).

The filtered carbon nanotubes are dried by heating at 100 DEG C for 24 hours. The dried carbon nanotubes are in a state in which impurities on the surface are oxidized and disappeared by the acid. After oxidation, the carbon nanotubes are shortened and at the same time have a carboxyl group (-COOH) on the surface as shown in FIG. 4 (step t2 of FIG. 3b).

Next, as shown in FIG. 2, the core-shell structured nanoparticle 141, the core is CdSe and the shell is ZnSe, is CdSe / ZnSe nanoparticles, and carbon nanotubes treated through steps t1 and t2 are used as general solvents. For example, 1,2-dicloroethane (C ₂ H ₄ Cl ₂ ), toluene, acetone, chloroform, ethylene glycol, isoprophenol (isopropanol), xylene, preferably mixed in chloroform (step of Figure 3b) t3).

Then, it is reacted by applying heat at 60 ° C. for 5 hours (step t4 of FIG. 3B). Since the carboxyl group (-COOH) is formed on the surface of the carbon nanotubes, the nanoparticles may be well attached thereto. The concentration of carbon nanotubes and core-shell structured nanoparticles in solution can be easily changed, which means that solar cell properties can be easily adapted to external conditions. In the previous step t3, the two carboxyl groups on the surface of the carbon nanotubes and the Zn ions on the surface of the nanoparticles ZnSe are bonded to each other so that the carbon nanotubes and the nanoparticles are connected to each other. At this time, the core-shell structure nanoparticles and the carbon nanotubes are connected to each other as shown in FIG. 6 while Zn (II) is formed as shown in FIG. 5.

6 is a transmission electron microscope (TEM) image of single-walled carbon nanotubes bonded with CdSe / ZnSe nanoparticles according to the above embodiment.

As described above, the nanoparticles can be attached to the surface of the carbon nanotubes, and the carbon nanotubes to which the nanoparticles are attached are finally included in an organic solvent such as chloroform. It can be formed into a thin film.

Next, spin coating the solution on which the carbon nanoparticles 142 to which the core-shell structure nanoparticles 141 formed through steps t1 to t4 are dispersed in a solvent is formed on the substrate 110 on which the hole transport layer 130 is formed. To form a film (step S3_2 in Fig. 3A). The thickness of the film formed can be changed by adjusting the rotation speed and rotation time at the time of spin coating. For example, spin coating at 4900 rpm for 5 seconds to form a thin film.

Next, heat was evaporated by applying heat at 125 ° C. for 5 minutes to remove the solvent present in the membrane (step S3_3 in FIG. 3A). The heating is performed using an oven or a hot plate. After evaporation of the solvent, the carbon nanotubes 142 to which the core-shell structure nanoparticles 141 are attached are present in a thin film form on the hole transport layer 130 in a structure as shown in FIG. 1. This thin film becomes the active layer 140. As described above, in the present invention, a method of manufacturing a device is simple and inexpensive because a process through a solvent is used, such as spin coating.

Next, an upper electrode 150 and an Al electrode are formed on the active layer 140 in the same manner as in step S1 (step S4 of FIG. 3A). At this time, the direction of the upper Al electrode as the upper electrode 150 is perpendicular to the direction of the lower Al electrode as the lower electrode 120.

As described above, in the solar cell manufacturing method according to the present invention, carbon nanotubes can be included in a solvent by using the properties of carbon nanotubes that can be dissolved in a solvent and formed into a thin film through spin coating. It is not necessary to use the deposition method and the process is very simple. Therefore, the production cost of the solar cell can be reduced by reducing the process cost and shortening the process, and the reproducibility and reliability of the manufactured solar cell can be improved. As described above, the active layer can be formed into a thin film by an easy method such as spin coating, and the structure of the solar cell is simple, so that a high efficiency solar cell can be manufactured at low cost.

The operation of the solar cell shown in FIG. 1 is as follows.

7 is a current-voltage diagram when ultraviolet rays are incident on a solar cell fabricated according to the present invention. The open circuit voltage (V _OC ) of the solar cell when a 6 W ultraviolet ray was incident was 0.7 V, and the short circuit current (I _SC ) density was 46 μA / cm ² . This magnitude of open circuit voltage and short circuit current is sufficient for solar cells. When light is not incident, no current is generated as shown in FIG. 7. Therefore, carbon nanotubes to which core-shell structured nanoparticles are attached can be used as a power generation layer of solar cells.

When light enters the solar cell, the light enters the core-shell structured nanoparticles attached to the surface of the carbon nanotubes in the power generation layer inside the solar cell. Light incident on the nanoparticles is absorbed in the core or shell of the nanoparticles and forms electrons and holes. The formed electrons move out of the nanoparticles as shown in the energy band diagram of FIG. 8 and then move to the electrodes through the carbon nanotubes. In the case of holes, they move to the electrode via the PEDOT: PSS thin film. Core-shell structured nanoparticles attached to the surface of carbon-nanotubes are used for power generation in solar cells. Core-shell structured nanoparticles attached to the surface of carbon nanotubes form electrons and holes in conventional silicon solar cells. To act as a pn junction to generate electricity. The carbon nanotubes transporting electrons and the PEDOT: PSS thin films transporting holes serve as n-type and p-type semiconductors, respectively.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific preferred embodiments described above, and the present invention belongs to the present invention without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

1 is a view showing a schematic structure of a preferred embodiment for a solar cell according to the present invention.

2 is a structural diagram of carbon nanotubes and nanoparticles used in the solar cell according to the present invention.

3A and 3B are flowcharts illustrating a method of manufacturing a solar cell according to the present invention.

4 and 5 are structural diagrams showing a process of attaching nanoparticles to the surface of carbon nanotubes.

Figure 6 is a microstructure photograph observed after attaching nanoparticles to the surface of carbon nanotubes according to the present invention.

7 is a current-voltage diagram when ultraviolet rays are incident on a solar cell fabricated according to the present invention.

8 is an energy band diagram of a solar cell fabricated according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100 Solar cell 110 Substrate 120 Bottom electrode

130 hole transport layer 140 active layer 141 core-shell structured nanoparticles

142 Carbon Nanotubes 145 Carbon Nanotubes Composites

150 ... upper electrode

Claims (8)

Board; A lower electrode formed on the substrate; A hole transport layer formed on the lower electrode; An active layer formed on the hole transport layer and made of carbon nanotubes to which core-shell structure nanoparticles are attached; And And an upper electrode formed on the active layer. The method of claim 1, wherein the core-shell structured nanoparticles are CdSe / ZnTe, CdSe / ZnSe, CdSe / ZnS, InP / ZnTe, InP / ZnSe, InP / GaAs, InP / CdS, InP / CdSe, AlSb / GaP, AlSb / ZnO, AlSb / ZnS, AlSb / ZnSe, AlSb / CdS, AlSb / CdSe, InGaAs / GaAs, PbTe / PbS, CdTe / ZnTe, GaAs / GaP, GaAs / InP, GaAs / CdSe, GaSb / GaP A solar cell comprising any one of InP, GaSb / CdS, GaSb / CdSe, ZnTe / GaP, ZnTe / ZnO, ZnTe / ZnS, ZnTe / ZnSe, ZnTe / CdS, and ZnTe / CdSe. The method of claim 1, wherein at least one of the lower electrode and the upper electrode is Al, Au, Cu, Pt, Ag, W, Ni, Zn, TI, Zr, Hf, Cd, Pd, indium-tin oxide (ITO) And Al-doped ZnO (AZO), Ga-doped ZnO (GZO) and Mg-doped ZnO (MZO). Forming a lower electrode on the substrate; Forming a hole transport layer on the lower electrode; Forming an active layer made of carbon nanotubes to which core-shell structured nanoparticles are attached on the hole transport layer; And Forming an upper electrode on the active layer; solar cell manufacturing method comprising a. The method of claim 4, wherein the forming of the active layer comprises: Preparing a solution in which carbon nanotubes to which core-shell structure nanoparticles are attached are dispersed in a solvent; Spin coating the solution on the hole transport layer to form a film; And Removing the solvent from the membrane. The method of claim 5, wherein the preparing of the solution in which the carbon nanotubes to which the core-shell structure nanoparticles are attached is dispersed in a solvent, Treating the carbon nanotubes with an acid; Mixing the carbon nanotubes and core-shell structured nanoparticles in a solvent; And Reacting the carbon nanotubes with the core-shell structured nanoparticles to attach the core-shell structured nanoparticles to the surface of the carbon nanotubes. The method of claim 6, wherein treating the carbon nanotubes with an acid comprises: Heat-treating the carbon nanotubes in a nitric acid solution to remove impurities from the surface and simultaneously form a carboxyl group (-COOH); Diluting the nitric acid solution containing the carbon nanotubes with deionized water and filtering only the carbon nanotubes using a filter; And A solar cell manufacturing method comprising the step of drying the filtered carbon nanotubes. The method of claim 6, wherein the solvent is any one of 1,2-dicloroethane (C ₂ H ₄ Cl ₂ ), toluene (toluene), acetone, chloroform, ethylene glycol, isoprophenol (isopropanol) and xylene Solar cell manufacturing method.

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