KR20120035841A - Transparent electrode comprising doped graphene, process for preparing the same, and display device and solar cell comprising the electrode - Google Patents

Abstract

A graphene-containing transparent electrode doped with a p-dopant is provided, and the transparent electrode has improved sheet resistance without deterioration in permeability and excellent stability in the atmosphere, and thus can be usefully used in various display devices or solar cells.

Description

Transparent electrode comprising doped graphene, process for preparing the same, and display device and solar cell comprising the electrode}

The present invention relates to a doped graphene-containing transparent electrode, a method of manufacturing the same, and a display device and a solar cell including the same. A method, and a display device and a solar cell having the same.

Various devices such as display devices or solar cells require a transparent electrode, for example, indium tin oxide (ITO). However, ITO has a problem that the price due to resource depletion increases as the consumption of indium increases, and there is a problem that the resistance increases due to cracks generated when bending due to lack of ductility due to the characteristics of the ITO electrode. Therefore, development of an electrode material to replace ITO is required, and research on graphene is being conducted as an alternative.

Since graphene has a metallic or semiconducting property on its own, it is possible to reduce sheet resistance by controlling carrier density by electron transfer through non-chemical bonding of dopants, but to use it as a transparent electrode of various display devices, Permeability has an important meaning. Graphene is a material that causes a decrease in transmittance of about 2.3% per mono-layer. Therefore, in order to obtain effective transmittance as a transparent electrode of a display device, it is impossible to use graphene more than a certain number of layers, thereby failing to obtain sufficient sheet resistance. .

In addition, in the case of nitric acid, which is generally used as a dopant for improving the electrical properties of graphene, sheet resistance is reduced without decreasing permeability, but the molecular weight is low so that it can be easily evaporated in the air. _In the case of ₃ , light absorption occurs in the visible region by the transition between the d-orbitals present in the gold ions, which causes a decrease in transmittance before and after doping, leading to a decrease in transmittance of the doped graphene.

The problem to be solved is to provide a graphene-containing transparent electrode with improved optical and electrical properties.

Another problem to be solved is to provide a display device or a solar cell employing the transparent electrode.

Another problem to be solved is to provide a method for manufacturing the transparent electrode.

Another problem to be solved is to provide a graphene-containing transparent thin film with improved optical and electrical properties.

In order to achieve the above object,

A transparent electrode comprising graphene doped with p-dopant on at least one surface of the transparent substrate, wherein the p-dopant is an acid having a molecular weight of 120 or more, and a transparent electrode having a rate of change of transmittance before and after doping of the doped graphene is about 1% or less. This is provided.

In order to achieve the above another problem,

Provided is a display device or a solar cell having the transparent electrode.

In order to achieve the third object,

Transferring the graphene onto the transparent substrate to form a transparent electrode; And

doping the graphene with a p-dopant solution;

The p-dopant is an acid having a molecular weight of 120 or more, a method of manufacturing a transparent electrode having a permeability change rate of about 1% or less before and after the doping graphene is provided.

In order to achieve the fourth task,

A thin film comprising graphene doped with p-dopant on at least one surface of a transparent substrate, wherein the p-dopant has a molecular weight of 120 or more and a thin film having a permeability change rate of about 1% or less before and after doping of the doped graphene. do.

The transparent electrode containing the graphene doped with the p-dopant may be usefully used in various display devices since the sheet resistance of the graphene is reduced and the stability in the atmosphere is improved without decreasing the permeability of the graphene itself.

1 is a schematic diagram of a dye-sensitized solar cell according to one embodiment.
2 shows surface optical photographs and XPS graphs of the transparent electrodes obtained in Examples 1 and 4.
3 is a graph showing XPS results of the transparent electrode obtained in Example 4. FIG.
4 is a graph showing a change in sheet resistance according to the number of bending of the transparent electrode obtained in Example 4. FIG.

In the transparent electrode in which graphene is formed on at least one surface of the substrate, by doping a certain kind of p-dopant to the graphene, it is possible to reduce the sheet resistance of the transparent electrode without lowering the transmittance and to improve stability in the atmosphere.

The "graphene" refers to a polycyclic aromatic molecule formed by coupling a plurality of carbon atoms covalently to each other, wherein the covalently linked carbon atoms form a 6-membered ring as a basic repeating unit, but a 5-membered ring and / or 7 It is also possible to further include a torus. Thus, the graphene is seen as a single layer of covalently bonded carbon atoms (usually sp ² bonds). The graphene may have a variety of structures, such a structure may vary depending on the content of 5-membered and / or 7-membered rings that may be included in the graphene. The graphene may be formed of a single layer, but they may be stacked with each other to form a plurality of layers.

In general, a single layer of graphene causes a decrease in transmittance of about 2.3%, and when a plurality of these layers are stacked, for example, four layers of graphene have a decrease in transmittance of about 9.2%. Therefore, as the number of layers of graphene included in the transparent electrode increases, the transmittance decreases, thereby lowering the transparency of the transparent electrode.

As the graphene usable in the transparent electrode, light transmittance may be, for example, 75% or more, for example, in a range of 90% to 99%. By securing sufficient light transmittance, it becomes possible to improve photoelectric efficiency and the like.

The p-dopant doped in the graphene causes the electrical interaction with the graphene by the redox potential difference, thereby doping the graphene, thereby increasing the carrier density to reduce the sheet resistance of the graphene. However, when doping a typical dopant to graphene, the transmittance and conductivity have an effect (trade off) each other. When a large amount of dopant is used to increase conductivity (that is, to reduce sheet resistance), the transmittance is lowered to cause a decrease in photoelectric efficiency. In addition, when a small amount of dopant is used to maintain the transmittance, it is difficult to achieve a desired decrease in conductivity.

According to one embodiment, by using a material that does not absorb light in the visible region as the p- dopant, it is possible to reduce the sheet resistance without lowering the transmittance of graphene. Accordingly, it is possible to improve the electrical characteristics (surface resistance) while securing the optical characteristics (transmittance) of the transparent electrode having the doped graphene.

The "doped graphene" refers to a case where an effective doping effect is exhibited by a dopant, and examples of the doping effect include an increase in conductivity, that is, a decrease in sheet resistance. As a range showing effective doping effect in doped graphene, the reduction rate of the sheet resistance according to doping may be defined as, for example, about 20% or more, or about 20% to about 90%, or about 20% to about 80%. . The sheet resistance reduction rate may be expressed by Equation 1 below as a percentage of the sheet resistance measured before the doping with respect to the sheet resistance measured immediately after the doping.

&Quot; (1) "

Sheet resistance reduction rate (%) = absolute value of {(sheet resistance of doped graphene immediately after doping-sheet resistance of graphene before doping) / 100}

As described above, the graphene doped with the p-dopant according to the embodiment of the present invention increases the conductivity (decreases in sheet resistance) and hardly causes a decrease in the transmittance before and after doping, and thus the transmittance change rate is about 0% to about 0.5%, or from about 0.001% to about 0.3%. The change rate of permeability refers to a percentage of a value obtained by subtracting the permeability of graphene after the doping from the permeability of the graphene before doping, as shown in Equation 2 below.

<Equation 2>

Permeability change rate (%) = (graphene before doping-graphene after doping) / 100

As described above, by doping the graphene with the p-dopant, it is possible to prevent the light transmittance of the graphene from being lowered and to reduce the sheet resistance. Due to the reduction in sheet resistance of graphene, sufficient conductivity can be ensured, thus making it possible to use fewer layers of graphene. This makes it possible to manufacture a transparent electrode having a higher light transmittance.

As such a p-dopant, an acid having a molecular weight of 120 or more, for example, 120 to 400, can be used, and as the acid, for example, an organic acid or an inorganic acid can be used. Acids having a molecular weight in such a range is to prevent evaporation in graphene to ensure the stability in the atmosphere. Accordingly, the sheet resistance change of the doped graphene doped with the p-dopant is suppressed. Such a change in sheet resistance can be expressed by a change rate of sheet resistance, and can be defined as a percentage of the value obtained by subtracting sheet resistance immediately after doping from sheet resistance measured after leaving doping graphene in air for 14 days as shown in Equation 3 below. Therefore, when such a sheet resistance change rate is small, it means that stability in the air is secured.

&Quot; (3) &quot;

% Change in sheet resistance = (sheet resistance of doped graphene left for 14 days after doping-sheet resistance immediately after doping) / 100

In the case of doping the p- dopant having the molecular weight range as described above, the sheet resistance change rate after 14 days of doping graphene may have a value of about 25% or less, for example, have a sheet resistance change rate of about 20% to -10%. Can be.

As such a p-dopant, an acid such as an organic acid or an inorganic acid may be used, and the organic or inorganic acid may include metal ions. The metal ions may be substituted with hydrogen ions present in the organic acid or the inorganic acid, or included in the form of metal complexes.

As such metal ions, metal ions which do not generate a transition between d-orbitals that cause light absorption in the visible region may be used. For example, metal ions filled with all of the d-orbitals may be used. As the metal ions filled with all of the d-orbital functions, Ag ⁺ , Zn ²⁺ , Ce ³⁺ , K ⁺ , lanthanide metal ions, and actinium metal ions can be exemplified.

The organic acid means a compound consisting of carbon, hydrogen, and oxygen, and hydrogen atoms of the compounds may be substituted with halogen group elements, and the bonds between the carbon atoms included in the compound may be all formed as a single bond. When the bond between carbon atoms is a single bond, transitions such as π-> π ^* , n-> π ^* do not occur, thereby suppressing light absorption in the visible region, thereby preventing a decrease in the transmittance of the doped graphene.

As such an organic acid, an organic material including an electron withdrawing group may be used, and an oxalic acid organic acid, lactic acid organic acid, propionic acid organic acid, acetic acid organic acid, citric acid may be used. (citric acid) organic acid, or trifluoroacetate organic acid may be used one or more, but is not limited to these.

Examples of the oxalic acid-based organic acid include oxalyl chloride and oxalyl bromide. Examples of the lactic acid-based organic acid include silver lactate, and the propionic acid-based organic acid is silver pentafluor. For example, rotropionate may be cited. The acetic acid organic acid may include methyl chlorooxoacetate, ethyl chlorooxoacetate, and the like, and the citric acid organic acid is citric acid. Lithium citrate, potassium citrate, zinc citrate, and the like can be exemplified. Examples of the trifluoroacetate-based organic acid include cesium trifluoroacetate, ethyl trifluoroacetate, trifluoroacetic anhydride, silver trifluoroacetate, anhydrous trifluoroacetic acid and trifluoromethanesulfonic acid (CF ₃ SO ₃ COCF ₃ ) etc. can be illustrated.

As an inorganic acid having a molecular weight of 120 or more as a p-dopant doped with the graphene, a material containing an electron withdrawing group is a triflate-based (CF ₃ SO _3- ) inorganic acid, sulfonimide-based inorganic acid, sulfonamide-based inorganic acid , Tetrafluoroborate-based inorganic acid, perchlorate-based inorganic acid, hexafluorophosphate-based inorganic acid, fluoroantimonic acid-based inorganic acid, silver-based inorganic acid, tellurium-based inorganic acid and the like, but is not limited thereto.

Examples of the triflate-based inorganic acid include silver trifluoromethanesulfonate, scandium (III) triflate, trifluoromethanesulfonic anhydride, and the like.

Examples of the sulfonimide inorganic acid include bis (trifluoromethane) sulfonimide ((CF ₃ SO ₂ ) ₂ NH), bis (trifluoromethane) sulfonimide lithium salt, and silver bis (trifluoromethane sulfone Mead), bis (pentafluoroethylsulfonyl) imide, a nitrosyl bis (trifluoromethane) sulfonimide, etc. can be illustrated.

Examples of the sulfonamide inorganic acid include trifluoromethanesulfonamide, 2,2,2-trichloroethoxysulfonamide, and the like.

Examples of the tetrafluoroborate acid include nitrosyl tetrafluoroborate, nitronium tetrafluoroborate, silver tetrafluoroborate, and the like.

As said perchlorate type inorganic acid, silver perchlorate etc. can be illustrated.

Examples of the hexafluorophosphate-based inorganic acid include potassium hexafluorophosphate, silver hexafluorophosphate, hexafluorophosphoric acid, lithium hexafluorophosphate, and the like.

Examples of the fluoroantimonic acid-based inorganic acid include fluoroantimonic acid (HSbF ₆ ), nitronium hexafluoroantimonate, nitrosonium hexafluoroantimonate, potassium hexafluoroantimonate, and fluorosulfuric acid-antimony penta. Fluoride, silver hexafluoroantimonate and the like can be exemplified.

Examples of the inorganic acid containing the silver ion include silver nitrate, silver sulfate, silver thiocyanate, silver hexafluorophosphate, silver hexafluoroantimonate, silver hexafluoroarsenate, silver cyanide, silver tetrafluoroborate, Silver perchlorate, and the like.

Examples of the tellurium-based inorganic acid may include teflic acid, telluric acid, and the like.

In the inorganic acid as described above, it may include a carbon atom as a member element, it may be used that the carbon atom is saturated carbon (carbon atoms form only a single bond). When unsaturated carbons, for example carbon atoms having double bonds or triple bonds, are included in the inorganic acid, light absorption occurs in the visible region due to transitions such as π-> π ^* , n-> π ^* . It may lead to a decrease in permeability. Therefore, when an inorganic acid containing no unsaturated carbon is used as a p-dopant, light absorption can be suppressed in the visible region to prevent a decrease in transmittance.

The organic acid or inorganic acid as mentioned above can be used 1 or more types, and can also mix and use 2 or more types.

The p-dopant containing an organic acid or an inorganic acid as described above may be doped to an appropriate content in the graphene, and 0.000025 to 0.0175 mmol for one layer of graphene (size 1 cm X 1 cm) in consideration of sufficient doping effect and economy. / cm ² , for example from 0.000125 to 0.00875 mmol / cm ² .

Meanwhile, when the graphene is excessively doped using the p-dopant, an undoped dopant may be further present on the surface of the graphene, and the dopant of the undoped region may form a surface coating layer having a thin film structure. Thereby acting as a protective layer to prevent evaporation of the doped dopant present therein.

As described above, the transparent electrode having graphene doped by the p-dopant doping has a reduced sheet resistance while hardly causing a decrease in light transmittance of the graphene. The light transmittance of the graphene doped with the dopant may have a light transmittance of 75% or more, for example, 90% to 99%.

In addition, since the graphene doped with the p-dopant hardly decreases the transmittance, the light transmittance reduction rate is about 0% to about 0.5%, or about 0.001% to about 0.3% compared to the undoped graphene. You can have

As described above, by doping the graphene with the p-dopant, it is possible to prevent the light transmittance of the graphene from being lowered and to reduce the sheet resistance. The reduction in sheet resistance of graphene makes it possible to use fewer layers of graphene, thereby making it possible to manufacture transparent electrodes with higher light transmittance.

The sheet resistance of the graphene doped with the p-dopant may have a value of 500 Ω / □ or less, for example, 1 to 500 Ω / □.

In addition to the reduced sheet resistance, the graphene doped with the p-dopant may have a work function of 4.5 to 5.5 eV.

As the graphene doped with the p-dopant, a sheet-like graphene manufactured by a known manufacturing method may be used, and considering the inherent light transmittance of graphene, for example, 1 to 10 layers, or 1 Layers to four layers of graphene can be used. The number of layers of the graphene may be selected by using an appropriate light transmittance according to the intended use. In addition, the graphene of a plurality of layers may be formed by sequentially stacking one layer of graphene. When doping two or more layers of graphene with p-dopant, the p-dopant may also be present between the layers.

Graphene doped with the p-dopant is formed on at least one surface of the transparent substrate to form a transparent electrode, and as the transparent substrate, a plastic substrate, a glass substrate, or the like may be used. In order to provide flexibility to bend the transparent electrode, a transparent flexible substrate may be used as the transparent substrate, and as such a transparent flexible substrate, polyethylene terephthalate (PET), polycarbonate (PC), and polyimide ( PI), or polyethylene naphthalate (PEN), polystyrene (PS), polyether sulfone (PES) substrate, or the like.

As described above, the doped graphene-containing transparent electrode has improved optical and electrical properties, and is excellent in stability in the atmosphere, and thus is useful for various display devices such as organic light emitting devices, electronic paper, liquid crystal display devices, or solar cells. .

The graphene-containing transparent electrode can be manufactured by the following method.

First, a graphene is transferred onto a transparent substrate to form a transparent electrode, and then, the doped graphene is doped with a p-dopant solution to prepare a transparent electrode. The p-dopant is an inorganic acid or an organic acid having a molecular weight of 120 or more. After 14 days of doping of the doped graphene, the sheet resistance change rate may have a value of 25% or less.

The graphene may be prepared using a known production method, for example, a graphitized sheet on the surface of the catalyst by heat-treating a graphitized catalyst having a sheet shape at a predetermined temperature with a gaseous or liquid carbon source. After forming, it can be used separately.

When the graphene is transferred to a transparent substrate, a transparent electrode is obtained, and in this case, graphene may be used having graphene having a structure of 1 to 10 layers, for example, 1 to 4 layers. In the case where a plurality of layers of graphene are formed on the transparent substrate, it is also possible to transfer the graphene having a desired number of layers by repeatedly laminating monolayers of graphene on the transparent substrate.

The transparent substrate may be a glass substrate or a plastic substrate, a transparent flexible substrate may be used as the plastic substrate, for example polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), or Polyethylene naphthalate (PEN), polystyrene (PS) substrate, etc. can be used.

As described above, after the graphene is transferred onto the transparent substrate to form a transparent electrode, the graphene may be doped with a p-dopant solution.

In this case, the p-dopant solution usable may be one in which one or more of the above-described p-dopants are dissolved or dispersed in a polar solvent.As a polar solvent usable as the solvent having a dielectric constant of 5 or more, for example, water and nitro Methane, dimethylformamide, N-methyl-2-pyrrolidinone, tetrahydrofuran, acetonitrile, dimethyl sulfoxide, ethanol (ethanol) and the like can be used.

The concentration of the p-dopant solution may determine the amount of dopant doped in the graphene, and in consideration of sufficient doping effect and economy, 0.001M to 0.1M, for example, for 1 layer of graphene (1cm X 1cm). 0.005M to 0.05M can be used. As the graphene layer increases, the concentration of the dopant solution may be increased.

The doping process of the p-dopant solution to the graphene may be performed by an immersion or dropping process, and in consideration of economics, the dropping process may be performed. In the case of the dropping process, a p-dopant solution having the above-described concentration with respect to one layer of graphene (1 cm X 1 cm) may be used, for example, in an amount of 0.025 ml to 0.175 ml in consideration of the doping effect and economic efficiency. When the content of the p-dopant solution is 0.025 ml of the dopant solution of 0.001 M concentration with respect to 1 cm ² of graphene, the mole number of the dopant is 0.000025 mmol, and the molar number of the dopant is 0.175 ml of the 0.1 M dopant solution. 0.0175 mmol.

After performing the doping process, a drying process is performed to evaporate the organic solvent and the like. Such a drying process may perform natural drying in the air, and for efficient drying process, it is also possible to use mechanical drying using a spin coater or the like.

According to one embodiment, after the transparent electrode is formed, it may further include a step of acid-treating the graphene-containing transparent electrode before the doping step. This acid treatment gives polarity to graphene so that doping of graphene can be performed more easily. The acid treatment may be performed by dipping graphene transferred on the transparent substrate using an acid solution such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, or spraying or dropping the acid directly on the graphene, and drying appropriately. The process may be involved.

As described above, the doped graphene-containing transparent electrode decreases sheet resistance without deteriorating transmittance and improves stability in the atmosphere, and thus is useful for display devices such as organic light emitting diodes, liquid crystal displays, and electronic papers, and dye-sensitized solar cells. It is also useful as a solar cell, such as an organic solar cell, and a transparent electrode of LED.

An example of a solar cell employing the doped graphene-containing transparent electrode is a dye-sensitized solar cell as shown in FIG. 1, wherein the dye-sensitized solar cell includes a semiconductor electrode 10, an electrolyte layer 13, and an opposite electrode ( 14), wherein the semiconductor electrode is made of a conductive transparent substrate 11 and a light absorption layer 12, coated with a colloidal solution of nanoparticle oxide (12a) on a conductive glass substrate and heated in a high temperature electric furnace It is completed by adsorbing the dye 12b.

The transparent electrode is used as the conductive transparent substrate 11. Such a transparent electrode is obtained by transferring a reduced product of graphene oxide doped with the dopant onto a transparent substrate. Examples of the transparent substrate include polyethylene terephthalate, polycarbonate, polyimide, or polyethylene naphthalate. Transparent polymeric materials or glass substrates can be used. This also applies to the counter electrode 14 as it is.

In order to make the dye-sensitized solar cell bendable structure, for example, a cylindrical structure, it is preferable that in addition to the transparent electrode, the counter electrode and the like are all soft.

The nanoparticle oxide 12a used in the solar cell is preferably an n-type semiconductor in which conduction band electrons become carriers and provide an anode current under optical excitation as semiconductor fine particles. Specific examples include TiO ₂ , SnO ₂ , ZnO ₂ , WO ₃ , Nb ₂ O ₅ , Al ₂ O ₃ , MgO, TiSrO ₃ , and the like, and particularly preferably anatase TiO ₂ . In addition, the said metal oxide is not limited to these, These can be used individually or in mixture of 2 or more types. Such semiconductor fine particles preferably have a large surface area in order for the dye adsorbed on the surface to absorb more light, and for this purpose, the particle size of the semiconductor fine particles is preferably about 20 nm or less.

In addition, the dye 12b may be used without limitation as long as it is generally used in the solar cell or photovoltaic field, but ruthenium complex is preferable. As the ruthenium complex, RuL ₂ (SCN) ₂ , RuL ₂ (H ₂ O) ₂ , RuL ₃ , RuL _2, etc. may be used (wherein L is 2,2′-bipyridyl-4,4′-dicar). Carboxylate and the like). However, the dye 12b is not particularly limited as long as it has a charge separation function and exhibits a sensitive action. In addition to the ruthenium complex, for example, xanthine-based pigments such as rhodamine B, rosebengal, eosin, erythrosine, and quinocyanine Cyanine-based pigments such as Cryptocyanin, basic dyes such as phenosafranin, cabrioblue, thiocin and methylene blue, porphyrin-based compounds such as chlorophyll, zinc porphyrin, magnesium porphyrin, other azo dyes, phthalocyanine compounds, Ru Complex compounds such as trisbipyridyl, anthraquinone dyes, polycyclic quinone dyes, and the like, and the like can be used alone or in combination of two or more thereof.

The thickness of the light absorption layer 12 including the nanoparticle oxide 12a and the dye 12b is 15 microns or less, preferably 1 to 15 microns. Because the light absorption layer has a large series resistance due to its structural reasons, and the increase in series resistance leads to a decrease in conversion efficiency. The film thickness is 15 microns or less, so that the series resistance is kept low while maintaining its function. Can be prevented from deteriorating.

Examples of the electrolyte layer 13 used in the dye-sensitized solar cell include a liquid electrolyte, an ionic liquid electrolyte, an ionic gel electrolyte, a polymer electrolyte, and a composite therebetween. Representatively, it is made of an electrolyte solution, and includes the light absorption layer 12, or is formed so that the electrolyte solution is infiltrated into the light absorption layer. As the electrolyte, for example, an acetonitrile solution of iodine may be used, but the present invention is not limited thereto, and any electrolyte may be used without limitation as long as it has a hole conduction function.

In addition, the dye-sensitized solar cell may further include a catalyst layer, such a catalyst layer is for promoting the redox reaction of the dye-sensitized solar cell, platinum, carbon, graphite, carbon nanotubes, carbon black, p-type semiconductor and Composites therebetween and the like can be used, and they are located between the electrolyte layer and the counter electrode. It is preferable that such a catalyst layer increases the surface area by a microstructure, for example, it is preferable that it is a platinum black state for platinum, and it is a porous state for carbon. The platinum black state can be formed by anodic oxidation of platinum, platinum chloride treatment, or the like, and carbon in the porous state can be formed by sintering of carbon fine particles or firing of an organic polymer.

The dye-sensitized solar cell as described above is superior in conductivity and has excellent light efficiency and processability by employing a flexible graphene sheet-containing transparent electrode.

Examples of the display device using the doped graphene-containing transparent electrode include an electronic paper display device, an organic light emitting display device, and a liquid crystal display device. Among these, the organic light emitting display device is an active light emitting display device using a phenomenon in which light is generated when electrons and holes are combined in an organic film when a current flows through a fluorescent or phosphorescent organic compound thin film. A general organic electroluminescent device has an anode in which an anode is formed on a substrate, and a hole transporting layer, a light emitting layer, an electron transporting layer and a cathode are sequentially formed on the anode. In order to more easily inject electrons and holes, an electron injection layer and a hole injection layer may be further provided, and a hole blocking layer and a buffer layer may be further provided as necessary. The anode is preferably a transparent material having excellent conductivity, and the graphene sheet-containing transparent electrode according to the present invention may be usefully used.

As the material of the hole transport layer, a material commonly used may be used. Preferably, polytriphenylamine may be used, but is not limited thereto.

As a material of the electron transport layer, a material commonly used may be used. Preferably, polyoxadiazole may be used, but is not limited thereto.

As the light emitting material used in the light emitting layer, a fluorescent or phosphorescent light emitting material generally used may be used without limitation, but may be selected from the group consisting of at least one polymer host, a mixture host of polymers and low molecules, a low molecular host, and a non-light emitting polymer matrix. It may further include one or more. Herein, the polymer host, the low molecular host, and the non-luminescent polymer matrix may be used as long as they are commonly used in forming an emission layer for an organic EL device. Examples of the polymer host include poly (vinylcarbazole), polyfluorene, and poly (p-phenylene vinylene), polythiophene, and the like, and examples of low molecular weight hosts include CBP (4,4'-N, N'-dicarbazole-biphenyl), 4,4'-bis [9- (3,6-biphenylcarbazolyl)]-1-1,1'-biphenyl {4,4'-bis [9- (3,6-biphenylcarbazolyl)]-1-1,1'- Biphenyl}, 9,10-bis [(2 ', 7'-t-butyl) -9', 9 ''-spirobifluorenyl anthracene, tetrafluorene and the like, and a non-luminescent polymer matrix Examples of the polymethyl methacrylate and polystyrene include, but are not limited to. The light emitting layer described above may be formed by a vacuum deposition method, a sputtering method, a printing method, a coating method, an inkjet method, or the like.

Fabrication of the organic electroluminescent device according to the present invention does not require a special device or method, it can be produced according to the manufacturing method of the organic electroluminescent device using a conventional light emitting material.

The graphene-containing transparent electrode doped with the dopant may improve electrical properties without deterioration of permeability, and since the stability in the air is improved, such a transparent electrode may be used in various display devices and solar cells.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Preparation Example 1 Preparation of Graphene Transparent Electrode

Cu foil (75 μm, manufactured by Wacopa) was placed in a chamber and heat-treated at 1,000 ^o C for 30 minutes with H ₂ 4 sccm, and then flowed with CH _{4 20} sccm / H _{2 4} sccm for 30 minutes, and the inside of the chamber was naturally cooled. Monolayer graphene is formed to a size of 2 cm x 2 cm.

Subsequently, a chlorobenzene solution (5 wt%) in which polymethyl methacrylate (PMMA) was dissolved was coated on the graphene sheet at a speed of 1,000 rpm for 60 seconds, followed by an etchant (CE-100, Transene). Co. Inc.) was immersed for 1 hour to remove the Cu foil to separate the graphene sheet attached to the PMMA. The graphene sheet attached on the PMMA is dried on a plastic substrate (PEN, DPont Teijin) and dried, and then the PMMA is removed with acetone to obtain a transparent electrode having a single layer graphene formed on the substrate.

On the graphene transparent electrode formed as described above, a process of additionally stacking the separated graphene sheet attached to PMMA and removing it with acetone was repeated to form a transparent electrode having two, three, and four graphene layers. Each is prepared.

Production Example 2

Cu foil (75 μm, manufactured by Wacopa) was placed in a chamber and heat-treated at 1,000 ^o C for 30 minutes with H ₂ 4 sccm, and then flowed with CH _{4 20} sccm / H _{2 4} sccm for 30 minutes, and the inside of the chamber was naturally cooled. Monolayer graphene is formed to a size of 1.5 cm x 1.5 cm.

Subsequently, a chlorobenzene solution (5 wt%) in which polymethyl methacrylate (PMMA) was dissolved was coated on the graphene sheet at 60 rpm for 60 seconds, followed by an etchant (CE-100, Transene). Co. Inc.) was immersed for 1 hour to remove the Cu foil to separate the graphene sheet attached to the PMMA. The graphene sheet attached on the PMMA is dried on a plastic substrate (PEN, DPont Teijin) and dried, and then the PMMA is removed with acetone to obtain a transparent electrode having a single layer graphene formed on the substrate.

Production Example 3

Cu foil (75 μm, manufactured by Wacopa) was placed in a chamber and heat-treated at 1,005 ^° C. for 2 hours with H ₂ 4 sccm, followed by flowing 20 mL of CH ₄ 20 sccm / H _{2 4} sccm for 20 minutes, and naturally cooling the inside of the chamber. Monolayer graphene is formed to a size of 1.5 cm x 1.5 cm.

Subsequently, a chlorobenzene solution (5 wt%) in which polymethyl methacrylate (PMMA) was dissolved was coated on the graphene sheet at a speed of 1,000 rpm for 60 seconds, followed by an etchant (CE-100, Transene). Co. Inc.) was immersed for 1 hour to remove the Cu foil to separate the graphene sheet attached to the PMMA. The graphene sheet attached on the PMMA is dried on a plastic substrate (PEN, DPont Teijin) and dried, and then the PMMA is removed with acetone to obtain a transparent electrode having a single layer graphene formed on the substrate.

On the graphene transparent electrode formed as described above, a process of additionally stacking the separated graphene sheet attached to PMMA and removing it with acetone is repeated to prepare a transparent electrode having four graphene layers.

Example 1

The Preparative Example 1 1 layer, 2 layers obtained, TFSI the number of layers of three-layer and four-layer graphene transparent electrodes each having (Bis (trifluoromethane) sulfonimide, (CF ₃ SO _{2) 2} NH, Aldrich Co.) nitro 0.4 ml of 0.01 M TFSI solution dissolved in methane (Aldrich) was added dropwise, and left for 5 minutes, followed by drying at a spin coater at 2000 rpm for 30 sec.

Example 2

PMMA 1 layer (monolayer) graphene formed in Example 1 doped with 0.4ml of 0.01M TFSI solution as in Example 1, and then separated graphene sheet (1 layer) attached on PMMA ) Is further laminated and the PMMA is removed with acetone and doped again with 0.4 ml of 0.01 M TFSI solution as in Example 1. As described above, the lamination of the graphene, the PMMA removal, and the doping are repeated two more times to form a transparent electrode in which four layers of doped graphene are stacked.

Example 3

The graphene transparent electrode in which the four layers of graphene obtained in Preparation Example 1 were laminated was immersed in 48.8% HNO ₃ aqueous solution, left for 5 minutes, dried, and doped with 0.05 M TFSI solution (0.4) ml. Form an electrode.

Example 4

A doped transparent electrode was formed by doping treatment with 0.4 ml of 0.05M TFSI solution in 0.4 ml on the graphene transparent electrode in which four layers of graphene obtained in Preparation Example 3 were laminated.

Example 5

Dissolve TFSI (Bis (trifluoromethane) sulfonimide, (CF ₃ SO ₂ ) ₂ NH, manufactured by Aldrich) in a graphene transparent electrode in which one layer of graphene obtained in Preparation Example 2 was laminated, in nitromethane (manufactured by Aldrich). 0.25ml of TFSI solution prepared by adding dropwise to stand for 5 minutes, and then dried for 30sec at a speed of 2000rpm in a spin coater.

Example 6

0.01 made by dissolving trifluoromethanesulfonamide (CF ₃ SO ₂ NH ₂ , manufactured by Aldrich) in nitromethane (manufactured by Aldrich) on a graphene transparent electrode in which one layer of graphene obtained in Preparation Example 2 was laminated. After 0.25 ml of M solution was added dropwise, the mixture was left for 5 minutes and dried in a spin coater at a speed of 2000 rpm for 30 sec.

Example 7

Trifluoromethanesulfonic anhydride ((CF ₃ SO ₂ ) ₂ O, manufactured by Aldrich) was dissolved in nitromethane (manufactured by Aldrich) on the graphene transparent electrode in which one layer of graphene obtained in Preparation Example 2 was laminated. 0.25 ml of the prepared 0.01M solution was added dropwise and left for 5 minutes, and then dried in a spin coater at a speed of 2000 rpm for 30 sec.

Example 8

Anhydrides of trifluoroacetic acid and trifluoromethanesulfonic acid (CF ₃ SO ₃ COCF ₃ , manufactured by Aldrich) were made of nitromethane (manufactured by Aldrich) on a graphene transparent electrode in which one layer of graphene obtained in Preparation Example 2 was laminated. 0.25ml of 0.01M solution prepared by dissolving in water) is added dropwise and left for 5 minutes, and then dried in a spin coater at a speed of 2000rpm for 30sec.

Example 9

0.01 made by dissolving trifluoroacetic anhydride ((CF ₃ CO) ₂ O, manufactured by Aldrich) in nitromethane (manufactured by Aldrich) on a graphene transparent electrode in which one layer of graphene obtained in Preparation Example 2 was laminated. After 0.25 ml of M solution was added dropwise, the mixture was left for 5 minutes and dried in a spin coater at a speed of 2000 rpm for 30 sec.

Comparative Example 1

0.4 ml of 0.01 M AuCl ₃ solution prepared by dissolving AuCl ₃ in nitromethane (manufactured by Aldrich) in a graphene transparent electrode having the number of layers of one, two, three and four layers obtained in Preparation Example 1, respectively. After dropping and standing for 5 minutes, the resultant was dried in a spin coater at 2000 rpm 30 sec.

Comparative Example 2

0.4 ml of 0.01M AuCl ₃ solution was added dropwise to the graphene transparent electrode on which the four layers of graphene obtained in Preparation Example 3 were laminated, and left to dry for 5 minutes to form a doped transparent electrode doped with HNO 3.

Comparative Example 3

Four layers of graphene obtained in Preparation Example 3 were immersed in 48.8% HNO ₃ aqueous solution in a graphene transparent electrode stacked, and dried for 5 minutes to form a doped transparent electrode doped with HNO ₃ .

Experimental Example 1

The graphene transparent electrode obtained in Preparation Example 1, the doped graphene-containing transparent electrode obtained in Example 1, and the doping graphene-containing transparent electrode obtained in Comparative Example 1 were measured immediately after doping, and are shown in Table 1 below. It was.

Graphene
Floor Preparation Example 1 Example 1 Comparative Example 1 % T @ 550nm Sheet resistance
(Ω / □) % T @ 550nm Sheet resistance
(Ω / □) % T @ 550nm Sheet resistance
(Ω / □) First floor 97.6 470.2 97.6 334.2 97.1 269.7 Second floor 94.6 295.3 94.7 142.8 94.1 111.0 3rd Floor 92.7 201.7 92.5 111.6 92.0 80.1 4th floor 90.4 190.3 90.4 95.6 89.7 84.6

The transmittance was measured by measuring the transmittance in the visible region with a UV-Vis spectrometer, and compared with the% transmittance of 550 nm, the sheet resistance was measured by the method of 4 point probe.

As shown in Table 1, Example 1 exhibits an effective doping characteristic by reducing the sheet resistance than the undoped graphene of Preparation Example 1, showing that there is little difference between the undoped graphene of Preparation Example 1 in the case of permeability. However, it can be seen that the transparent electrode doped with AuCl ₃ of Comparative Example 1 has a lower sheet resistance than the transparent electrode doped with TFSI of Example 1 but its transmittance decreases to an amount of more than 0.5%, thereby deteriorating optical characteristics.

Experimental Example 2

Four layers of graphene transparent electrodes obtained in Preparation Example 1, four layers of doped graphene transparent electrodes obtained in Example 1, four layers of doped graphene transparent electrodes (laminated) obtained in Example 2, and Examples 4 layers of doped graphene transparent electrodes (doping after acid treatment) obtained in 3, 4 layers of doped graphene transparent electrodes obtained in Example 4 and 4 layers of doped graphene transparent obtained in Comparative Examples 2 and 3 The sheet resistance was measured immediately after the doping with respect to the electrode and is shown in Table 2 below.

division Dopant Sheet resistance Preparation Example 1 Undoping 190.3 Example 1 TFSI 0.01M 95.6 Example 2 TFSI 0.01M LBL 66.4 Example 3 acidTFSi 0.05M 50.5 Example 4 TFSI 0.05M 47.8 Comparative Example 2 AuCl ₃ 49.6 Comparative Example 3 HNO ₃ 53.5

As shown in Table 2, in Comparative Example 1 doped with AuCl ₃ 0.01M solution, the sheet resistance is reduced compared to the undoped graphene (Preparation Example 1), but the transmittance is reduced from 90.35% to 89.67% optical characteristics This was degraded. In the case of the graphene transparent electrodes of Examples 1 to 3 doped with TFSI, the sheet resistance decreased, and there was almost no difference in transmittance with the manufacturing example, which is an undoped graphene transparent electrode. In order to improve the adsorption of TFSI to improve the performance than the transparent electrode doped with AuCl ₃ layer 2 and doped by a layer (layer by layer), and in the case of Example 3 introduced the method of doping after acid treatment to AuCl ₃ It can be seen that the sheet resistance was further reduced without changing the transmittance of the transparent electrode of Comparative Example 1 doped. In addition, in the case of Example 4 in which the concentration of the dopant is increased, it can be seen that a transparent electrode having a similar or slightly lower sheet resistance is formed when compared with Comparative Example 2.

Experimental Example 3

In order to evaluate the atmospheric stability of the undoped transparent electrode of Preparation Example 1, and the doped transparent electrode obtained in Examples 1 to 4, Comparative Example 2 and shown in Table 3 by measuring the sheet resistance per hour. The graphene of Example 1 used graphene in which graphene is laminated in four layers.

division Dopant Sheet resistance immediately after doping
(R ₀ ) Sheet resistance after 14 days
(R) Sheet resistance change rate
(RR ₀ ) / R ₀ * 100) (%) Preparation Example 1 Undoping 190.3 190.3 0.0 Example 1 TFSI 0.01M 95.6 112.8 18.0 Example 2 TFSI 0.01M LBL 66.4 77.7 17.1 Example 3 acidTFSi 0.05M 50.5 57.3 13.5 Example 4 TFSI 0.05M 47.8 47.6 -0.5 Comparative Example 3 HNO ₃ 53.5 72.1 34.7 Comparative Example 2 AuCl ₃ 49.6 62.5 26.0

In the case of the graphene transparent electrode of Comparative Example 2 doped with HNO ₃ , the sheet resistance increased by about 35%, and the examples all increased the resistance of about 25% or less, and particularly, the transparent doped with 0.05M TFSI of Example 4 In the case of the electrode it can be seen that the sheet resistance is stable with time.

Experimental Example 4

Optical photographs were taken by enlarging the surface area of the doped graphene by 1000 times with respect to the four-layered doped graphene transparent electrodes obtained in Examples 1 and 4, and the results are shown in FIG. 2. Also shown together.

The stable property of the sheet resistance shown in Example 4 is considered to be due to the increased doping area of the doped dopant, as shown in the optical photograph shown in FIG. 2, to serve as a passivation function of the transparent electrode of the doped graphene. In addition, considering that the relative strength of the dopant structure of ˜400 eV is increased in XPS N1s, TFSI existing on the surface of graphene without doping is considered to be a passivation role.

Experimental Example 5

The XPS spectrum of the doped graphene transparent electrode obtained in Example 4 was measured and shown in FIG. 3.

As shown in FIG. 3, since the intensity increases from bulk to spectrum in the spectrum measured while changing the angle of XPS N1s, the dopant is adsorbed only on the graphene surface layer in the graphene transparent electrode doped with TFSI. It can be seen that the dopant is included between the graphene layers.

Experimental Example 6

When the graphene transparent electrode doped with 0.05M TFSI obtained in Example 4 was bent 100 times (bending 100 times under 1% strain conditions when bent at a speed of 1 Hz) and then sheet resistance was measured for a total of 1000 bending times (10 The change was measured and shown in FIG. 4. As shown in FIG. 4, a sheet resistance change of about 10% or less is shown, and as a result, the performance of graphene as a flexible transparent electrode can be seen.

Experimental Example 7

In order to determine the doping effects of each of the doped transparent electrodes obtained in Examples 6 to 10 by varying the dopant concentration, the sheet resistance before and after doping was measured and described in Table 4 below.

division Dopant Before Doping
Sheet resistance
(R ₁ ) Immediately after doping
Sheet resistance
(R ₂ ) Sheet resistance change rate
(R _2- R ₁ ) / R ₁ * 100) (%) Example 5 (CF ₃ SO ₂ ) ₂ NH 580 228 -60.6 Example 6 CF ₃ SO ₂ NH ₂ 656 454 -30.8 Example 7 (CF ₃ SO ₂ ) ₂ O 690 269 -61.0 Example 8 CF ₃ SO ₃ COCF ₃ 658 286 -56.6 Example 9 (CF ₃ CO) ₂ O 609 459 -24.7

As shown in Table 4, it can be seen that not only the imide dopant but also the amide-based and anhydride-based compound had a decrease in sheet resistance due to doping, and all of Examples 5 to 9 exhibited a sheet resistivity reduction rate of 20% or more. Can be.

Example 11: Fabrication of Solar Cell

A titanium oxide particle paste having a particle size of about 7 to 25 nm is coated on the transparent electrode obtained in Example 4, and applied to a 4 cm ² area, and a porous titanium oxide film having a thickness of about 15 μm is formed by using a low temperature baking process (150 ° C. or less). To make. Subsequently, dye adsorption treatment was performed on a 0.3 mM Ru (4,4'-dicarboxy-2,2'-bipyridine) ₂ (NCS) ₂ solution dissolved in ethanol at room temperature for at least 12 hours. Thereafter, the porous titanium oxide film to which the dye is adsorbed is washed with ethanol and dried at room temperature to prepare a photocathode.

As the counter electrode, a Pt reduction electrode was deposited on the transparent electrode obtained in Example 1 by using a sputter, and a counter hole was manufactured by making a minute hole using a 0.75 mm diameter drill to inject the electrolyte.

The two electrodes were bonded by pressing a 60 μm-thick thermoplastic polymer film between the photocathode and the counter electrode at 100 ° C. for 9 seconds. A dye-sensitized solar cell is fabricated by injecting a redox electrolyte through the micropores formed in the counter electrode and blocking the micropores using a cover glass and a thermoplastic polymer film. The redox electrolyte used was 21.928 g of tetrapropylammonium iodide and 1.931 g of I ₂ in a solvent consisting of 80% ethylene carbonate and 20% acetonitrile. Use what is dissolved.

Example 12 Fabrication of Organic Electroluminescent Device

An electrode pattern is formed on the transparent electrode obtained in Example 4, and cleaned. The PEDOT is coated on the cleaned transparent electrode to a thickness of about 50 nm, and then baked at 120 ° C. for about 5 minutes to form a hole injection layer.

On top of the hole injection layer, spin coating the green 223 polymer on the hole injection layer, baking at 100 ° C. for 1 hour, and then completely removing the solvent in a vacuum oven to form a light emitting layer having a thickness of 80 nm. To form.

Then, the polymer in the emission layer Alq _3, while maintaining the degree of vacuum by using a vacuum evaporator to less than 10- ⁶ torr 4 ㅧ vacuum deposited at a rate of 1.0Å / sec to a thickness of 30nm to form an electron transport layer Next, the upper LiF was vacuum deposited at a rate of 0.1 μs / sec to form an electron injection layer having a thickness of 5 nm.

 Subsequently, Al is deposited at a rate of 10 μs / sec to deposit and encapsulate a cathode having a thickness of 200 nm, thereby completing an organic EL device. At this time, the encapsulation process is performed by putting BaO powder in a glove box in a dry nitrogen gas atmosphere, sealing it with a metal can, and then finally treating it with a UV curing agent.

Claims (30)

A transparent electrode comprising graphene doped with p-dopant on at least one surface of the transparent substrate,
The p-dopant is an acid having a molecular weight of 120 or more,
A transparent electrode having a transmittance change rate of about 0.5% or less before and after the doping graphene. The method of claim 1,
The acid is an inorganic acid transparent electrode. The method of claim 2,
The carbon electrode contained in the inorganic acid is a saturated carbon atom to form a single bond. The method of claim 2,
The inorganic acid is one of triflate inorganic acid, trifluorosulfonimide inorganic acid, tetrafluoroborate inorganic acid, perchlorate inorganic acid, hexafluorophosphate inorganic acid, fluoroantimonic acid inorganic acid, silver inorganic acid and tellurium inorganic acid. Transparent electrode that is more than. The method of claim 2,
The inorganic acid is silver trifluoromethanesulfonate, scandium (III) triflate, trifluoromethanesulfonic anhydride, bis (trifluoromethane) sulfonimide, bis (trifluoromethane) sulfonimide lithium, silver bis (Tripulolomethane sulfonimide), bis (pentafluoroethylsulfonyl) imide, nitrosyl bis (trifluoromethane) sulfonimide, trifluoromethanesulfonamide, 2,2,2-trichloro Loethoxysulfonamide, nitrosyl tetrafluoroborate, nitronium tetrafluoroborate, silver tetrafluoroborate, silver perchlorate, potassium hexafluorophosphate, silver hexafluorophosphate, hexafluorophosphoric acid, lithium Hexafluorophosphate, fluoroantimonic acid, nitronium hexafluoroantimonate, nitrosonium hexafluoroantimonate, potassium hexaple Oroantimonate, fluorosulfuric acid-antimony pentafluoride, silver hexafluoroantimonate, silver nitrate, silver sulfate, silver thiocyanate, silver hexafluorophosphate, silver hexafluoroantimonate, silver hexa At least one selected from fluoroarsenate, silver cyanide, silver tetrafluoroborate, silver perchlorate, teflic acid, and telluric acid. The method of claim 1,
Transparent electrode wherein the acid is an organic acid. The method of claim 6,
A transparent electrode in which all the bonds between carbon atoms contained in the organic acid are single bonds. The method of claim 6,
And the organic acid is at least one of oxalic acid organic acid, lactic acid organic acid, propionic acid organic acid, acetic acid organic acid, citric acid organic acid, and trifluoroacetate organic acid. The method of claim 6,
The organic acid is oxalyl chloride, oxalyl bromide, silver lactate, silver pentafluoropropionate, methyl chlorooxoacetate, ethyl chlorooxoacetate, citric acid, lithium citrate, potassium citrate, zinc citrate, cesium trifluor At least one selected from roacetate, ethyl trifluoroacetate, trifluoroacetic anhydride, and silver trifluoroacetate. 7. The method according to claim 2 or 6,
The organic or inorganic acid is a transparent electrode containing a metal ion filled with all the d- orbital function. The transparent electrode of claim 1, wherein the acid has a molecular weight of 120 to 400. 3. The method of claim 1,
The graphene is an acid-treated transparent electrode. The method of claim 1,
The transparent electrode of the graphene doped with the p- dopant is 75% or more. The method of claim 1,
The sheet resistance change rate after 14 days of doping the graphene doped with the p- dopant is about 20% or less with respect to the graphene before doping. The method of claim 1,
The doped graphene has a reduction rate of about 20% or more of sheet resistance,
The reduction rate of the sheet resistance is a transparent electrode according to Equation 1 below:
<Equation 1>
Sheet resistance reduction rate (%) = absolute value of {(sheet resistance of doped graphene immediately after doping-sheet resistance of graphene before doping) / 100} The method of claim 1,
And the p-dopant is further present on the surface of the graphene in a undoped state. The method of claim 1,
And forming a surface coating layer in a state in which the p-dopant is undoped. The method of claim 1,
The graphene is a transparent electrode that is present in a thickness of 1 to 10 layers. The method of claim 1,
The graphene is present in a thickness of 2 to 10 layers, comprising a p-dopant interposed between the layer of the graphene. The method of claim 1,
And a sheet resistance of the graphene doped with the p-dopant is about 500 Ω / □ or less. The method of claim 1,
The graphene doped with the p-dopant comprises a 0.000025 to 0.0175 mmol (mmol) of p- dopant on the basis of 1cm X 1cm graphene having a thickness of one layer. The method of claim 1,
And the transparent electrode is flexible. A solar cell comprising the transparent electrode according to any one of claims 1 to 22. A display device comprising the transparent electrode according to any one of claims 1 to 22. Transferring the graphene onto the transparent substrate to form a transparent electrode; And
and doping the graphene with a p-dopant solution to obtain doped graphene.
Wherein the p-dopant is an acid having a molecular weight of 120 or more, and a rate of change in transmittance before and after doping of the doped graphene is about 0.5% or less. The method of claim 25,
The concentration of the p- dopant solution is a method for producing a transparent electrode in the range of 0.001 to 0.1M per graphene layer. The method of claim 25,
The concentration of the p- dopant solution is a method of manufacturing a transparent electrode in the range of 0.005 to 0.05M per graphene layer. The method of claim 25,
The content of the p-dopant solution is a method for producing a transparent electrode of 0.025ml to 0.175ml per layer of graphene having a size of 1cm X 1cm. The method of claim 25,
After the transparent electrode is formed, before the doping step further comprises the step of acid-treating the graphene-containing transparent electrode. A thin film comprising graphene doped with p-dopant on at least one side of a transparent substrate,
The p-dopant has a molecular weight of 120 or more acid,
A thin film having a transmittance change rate of about 0.5% or less before and after the doping graphene.

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