KR20110001854A - Manufacturing method for carbon base nano material transparent electrode - Google Patents

Abstract

PURPOSE: A manufacturing method for a carbon base nano material transparent electrode is provided to control the work function of a carbon-based nanomaterial transparent electrode by depositing metal o n the surface of the carbon-based nanomaterial transparent electrode. CONSTITUTION: An aluminum(111) or an organic compound is doped on the surface of the carbon-based nanomaterial transparent electrode to control the work function of the carbon-based nanomaterial transparent electrode. The aluminum or the organic compound is doped in a vacuum chamber. The evaporation height of the aluminum or the organic compound is 0.1nm to 0.3nm. A carbon-based nanomaterial is a nanotube or a grapheme.

Description

Manufacturing method for carbon base nano material transparent electrode

The present invention relates to a method for manufacturing a carbon-based nanomaterial transparent electrode, and more particularly to a method for manufacturing a carbon-based nanomaterial transparent electrode applicable to a variety of devices by controlling the work function of the transparent electrode.

In general, the panel using the organic light emitting device (OLED) has the advantages of low voltage driving, high luminous efficiency, wide viewing angle, fast response speed, etc. As one, technology development is actively progressing.

6 is a cross-sectional view of a conventional organic electroluminescent device. In FIG. 6, the organic electroluminescent device includes a glass substrate 10 through which light is emitted, and one surface of the glass substrate 10 is transparent, such as ITO, having a high work function and applying a positive voltage. The positive electrode 11 which is an electrode, an organic light emitting layer 18 in which light emission is generated by voltages applied at both ends, a metal having a low work function (Ca, Li, Al, Mg, Ag, etc.) and a negative voltage are applied thereto The negative electrodes 17 are sequentially stacked.

In this case, the organic light emitting layer 18 is a hole injection layer 12, a hole transport layer 13, a light emitting layer 14, an electron transport layer 15, an electron injection layer 16 on the ITO transparent electrode (anode) 11 It consists of a structure laminated one by one.

When a forward voltage is applied to the organic EL device, electrons and holes are injected from the negative electrode 17 and the positive electrode 11.

The injected electrons and holes are combined in the organic light emitting layer 18 to form a pair and then disappear. In this process, light is generated in the organic light emitting layer 18 and emitted to the glass substrate 10.

However, since the ITO transparent electrode may have a weak mechanical strength and may cause cracking or cracking, the ITO transparent electrode is not suitable for a flexible display as a scroll display or a next-generation display for mobile communication.

On the other hand, the carbon nanotube transparent electrode has an advantage that it is easy to apply to a scroll display or a flexible display because of the bending property of the material itself.

Therefore, in order to make up for the shortcomings of the ITO transparent electrode, research is being actively conducted to replace the ITO with the carbon nanotube transparent electrode and apply it to the flexible display.

On the other hand, the research to use the carbon nanotube transparent electrode as the anode of the OLED device is being actively conducted, but in order to apply the carbon nanotube transparent electrode to the characteristics of various devices, a technique that can be used as a cathode is required. .

The present invention devised in view of the above, by controlling the work function by depositing a very small amount of metal on the surface of the carbon-based nano-material transparent electrode, the control of the work function that can be used as the cathode as well as the anode of the OLED The purpose is to provide a method of manufacturing a carbon-based nanomaterial transparent electrode is possible.

The present invention is applied to a variety of devices such as double-sided light emitting OLED, fully transparent solar cell, fully transparent display that can be mounted on the windshield of the car, or an electrode having a work function optimized for device design,

Preparation of carbon-based nanomaterial transparent electrode that can control work function of carbon-based nanomaterial transparent electrode by controlling doping thickness of metal or organic material on surface of carbon-based nanomaterial transparent electrode such as carbon nanotube and graphene Provide a method.

Referring to the advantages of the method of manufacturing a carbon-based nanomaterial transparent electrode of the present invention according to the above problem solving means.

By controlling the doping thickness of metal or organic material to the transparent electrode of the carbon-based nanomaterials, the work function of the transparent electrode can be controlled and applied to various devices.

For example, the present invention can be applied to a double-sided light emitting OLED, a fully transparent solar cell, a fully transparent display that can be mounted on a vehicle windshield, or an electrode having a work function optimized for device design.

1 is a schematic view of applying a carbon nanotube transparent electrode deposited with an aluminum metal on the double-sided light emitting OLED according to an embodiment of the present invention
Figure 2 shows the work function of the initial SWNT and the measured UPS spectrum during the stepwise deposition of aluminum. (a) shows the balance band spectrum from which the spectrum and background of the normal secondary electron cutoff region are removed, and (b) shows the work function of the initial SWNT with increasing aluminum thickness.
3 shows the key level spectra of C 1s, Al 2p, and O 1s measured at initial SWNTs during the stepwise deposition of aluminum.
4 is a graph showing a work function of a carbon nanotube thin film deposited on an actual plastic substrate as an aluminum deposition thickness increases as another embodiment of the present invention.
5 shows the work function of graphene and the measured UPS spectrum during the stepwise deposition of aluminum. (a) shows a balance band spectrum in which the spectrum and background of a normal secondary electron cutoff region are removed, and (b) shows the work function of graphene with increasing aluminum thickness.
6 is a schematic view showing an OLED according to the prior art.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view of applying a carbon nanotube transparent electrode on which an aluminum metal is deposited on a double-sided light emitting OLED according to an embodiment of the present invention.

The present invention relates to a transparent electrode of a carbon nanotube controllable by various work functions, by controlling the work function by controlling the deposition thickness of the metal on the surface of the transparent electrode 110, the anode of the carbon nanotube transparent electrode 110 It relates to a carbon nanotube transparent electrode 110 that can be used as both a and a cathode.

Since the carbon nanotubes do not change their electrical properties even when they are pulled or bent, the carbon nanotube transparent electrode 110 may be used to form a display that may be folded or bent as well.

That is, the carbon nanotubes can be used in computers, bracelets, cellular phones, electronic papers, etc. rolled around or folded.

The transparent electrode 110 according to the present invention uses the carbon nanotubes as a material, and by controlling a metal such as aluminum 111 on the surface of the electrode to a very thin deposition thickness (ongstrong unit), Work function can be controlled. In this case, the work function of the transparent electrode 110 may be controlled by depositing an organic material, an insulator, etc. in addition to the metal.

For example, when the aluminum 111 is adjusted to a deposition thickness in the range of 0.1 nm to 0.3 nm on a single-walled carbon nanotube (SWNT) transparent conductive film according to an embodiment of the present invention, the carbon nanotube transparent electrode 110 The work function of can be controlled to range from 3.97 eV to 4.43 eV (see FIG. 3B).

That is, when the aluminum 111 is not deposited, the work function of the carbon nanotube transparent electrode 110 is 4.43 eV, and if the deposition thickness of the aluminum 111 is gradually increased to 0.3 nm or less, the carbon nanotube transparent electrode The work function of 110 decreases from 4.43 eV to 3.97 eV.

When the small amount of aluminum 111 is deposited on the surface of the carbon nanotube transparent electrode 110, a work function may be reduced due to a surface existing on the surface of the carbon nanotube transparent electrode 110 before deposition of the aluminum 111. Due to oxygen.

This is because, when the small amount of aluminum 111 is deposited, chemical reaction with surface oxygen forms alumina (Al ₂ O _x ), and the alumina reduces the work function of the carbon nanotube transparent electrode 110. .

4 is a graph showing a work function of a carbon nanotube thin film deposited on an actual plastic substrate with an increase in aluminum deposition thickness as another embodiment of the present invention.

Referring to Figure 4, it can be seen that the work function of the carbon nanotube thin film on the plastic substrate according to the thickness of the aluminum deposited on the carbon nanotube thin film is 3.7 ~ 4.8 eV.

In general, the range of work function that can be used as a cathode when manufacturing OLED devices is 3.7 ~ 4.2eV, and the range of work function that can be used as an anode is 4.8 ~ 5.2eV.

The basis for the work function range of the material that can be used as the cathode and anode of the OLED is aluminum, which is a representative material that is commonly used as the cathode of OLED, and the work function of aluminum is 4.2 eV or less, It is gold, but its work function is about 5.2 eV.

Therefore, when aluminum is deposited on the surface of the carbon nanotube transparent electrode 110 at a thickness of 0.3 nm, the work function decreases to 3.97 eV, so that it can be used as the cathode of the OLED (see FIG. 2B), and the carbon nanotube transparent When aluminum is not deposited on the surface of the electrode, since the work function is 4.8 eV, it can be used as the anode of the OLED (see FIG. 4).

Therefore, the work function can be controlled by depositing a small amount of metal on the carbon nanotube transparent electrode 110, and the carbon nanotube transparent electrode 110 whose work function is controlled is used for the anode and the cathode of the OLED to emit light on both sides. Type OLED can be realized.

In addition, by applying the carbon nanotube transparent electrode 110 that can control the work function to a variety of devices, a new concept of application devices such as double-sided light emitting OLED, fully transparent solar cell, fully transparent display that can be mounted on the windshield of the car Can be produced.

As shown in FIG. 1, a double-sided light emitting OLED according to an embodiment of the present invention is a flexible substrate 100 from below, a carbon nanotube transparent electrode 110 (anode) on which aluminum 111 is deposited, and hole injection. The organic light emitting layer 18 having the layer 12, the hole transporting layer 13, the light emitting layer 14, the electron transporting layer 15, the electron injection layer 16, and the aluminum (111) metal deposited on the carbon nanotube transparent electrode ( 110 (cathode), the flexible substrate 100 is formed in a deposited form.

In this case, the aluminum 111 may not be deposited on the carbon nanotube transparent electrode 110 used as the anode.

Here, when voltage is applied to both ends of the organic light emitting layer 18, holes and electrons are injected from the anode and the cathode.

The injected holes and the electrons are combined in the organic light emitting layer 18 to form a pair, and then disappear. As the light is emitted from the organic light emitting layer 18, light is emitted to the flexible substrate 100 on both sides.

Hereinafter, the present invention will be described in more detail based on the following examples, but the present invention is not limited by the following examples.

Example

First, a work function of a carbon nanotube (CNT) transparent conductive film is measured by using an ultraviolet photoelectron spectroscopy (UPS), and then a small amount of metal such as aluminum 111 is deposited on the carbon nanotube transparent conductive film.

As such, by depositing a small amount of aluminum 111 on the carbon nanotube transparent conductive film, the carbon nanotube transparent conductive film can be used for the anode and cathode of the OLED device by controlling the work function of the carbon nanotube transparent conductive film.

To investigate the effect of aluminum (111) on the work function of carbon nanotubes, an ultra-violet photoelectron spectroscopy (UPS) and XPS (during each step of thin deposition of aluminum 111 on a SWNT film without breaking the vacuum) X-ray photoelectron spectroscopy) was used to measure the changes in the electronic structure and the respective work functions of the prepared SWNTs.

Spectra were measured on a VG ESCALAB 220i system using monochrome x-ray (Al Kα) and UV (He I) radiation sources. The base pressure of the analytical chamber was 2 ㅧ 10 ^-9 Torr.

For the UPS spectrum, measurements were taken at -10V (secondary electron cutoff region) and -5V (balance band region) of sample bias to accelerate low energy secondary electrons.

In order to evaporate the thin layer of aluminum, a Nudsen type effusion cell was used, and a typical deposition rate of aluminum 111 was 0.1 nm / sec, which was applied to a quartz crystal microbalance. Were carefully monitored.

Figure 2 shows the work function of the initial SWNT and the measured UPS spectrum during the stepwise deposition of aluminum. (a) shows the normalized secondary electron cutoff region spectrum and the balance band spectrum with the background removed, and (b) shows the work function of the initial SWNT with increasing aluminum thickness.

Before depositing the aluminum 111, the π band characteristic of SWNTs is clearly shown around 3eV.

The change in the? Band characteristic can be neglected after 0.3 nm of aluminum 111 and disappeared when the thickness of the aluminum layer is increased.

As shown in the secondary electron cut off region of FIG. 2 (a), the secondary electron cut off of SWNTs was shifted toward higher binding energy with aluminum deposition of 0.1 nm. The maximum change in the secondary electron cutoff occurred at 0.3 nm aluminum deposition, and the total change shifted towards high binding energy.

After 0.3 nm of aluminum deposition, the secondary electron cutoff was somewhat reduced to lower binding energy. As a result, according to the UPS spectrum, the work function of the initial SWNT was changed according to the deposition thickness of aluminum 111 as shown in FIG. 2B.

According to the results of the UPS, the work function of the initial SWNT before the deposition of aluminum 111 after hydrogen heat treatment was 4.43 eV, and then the work function of the initial SWNT according to the deposition thickness of aluminum 111 was 4.06 eV (at 0.1 nm aluminum). ), 3.97 eV (at 0.3 nm aluminum), 4.03 eV (at 0.9 nm aluminum), and 4.15 eV (at 2.7 nm aluminum).

After the deposition of aluminum 111 at 0.9 nm, the work function converges to the work function of aluminum 111 due to the predominant amount of aluminum 111 at the SWNT surface. As a result, it can be seen that the work function of SWNT can be changed to 3.97 to 4.43 eV by deposition of a thin aluminum layer on the surface of SWNT.

3 shows the cabinet electron level spectra of C 1s, Al 2p, and O 1s measured at initial SWNTs during the stepwise deposition of aluminum.

According to the spectral measurement of the cabinet electrons using the XPS, the chemical reaction between the CNT and aluminum 111 can be seen.

Before depositing the small amount of aluminum 111, it was observed that a certain amount of surface oxygen exists on the surface of the initial SWNT. After depositing 0.1 nm of aluminum 111, the peak of the O 1s core level was shifted toward a higher binding energy.

This means that surface oxygen deposited on the initial SWNT reacted with aluminum 111 to form alumina. The formation of alumina was also confirmed in the Al 2p cabinet level spectrum.

In the initial stage of aluminum 111 deposition, alumina is more dominant than aluminum 111, but after deposition of 0.9 nm aluminum 111, the aluminum 111 is predominant in the spectrum of the Al 2p cabinet level due to the depletion of surface oxygen. .

As the thickness of the aluminum 111 increased, there was no significant peak change at the C 1s core level.

As a result, surface oxygen is present in the initial SWNT according to the cabinet level spectrum. In addition, alumina (Al ₂ O _x ) was formed between SWNT and aluminum 111 by the surface oxygen. Therefore, the alumina plays an important role to reduce the work function of SWNT by depositing a small amount of aluminum (111).

In the present invention, by depositing a metal, such as aluminum (111) in a small amount on the carbon nanotube transparent electrode 110, it is possible to control the work function of the carbon nanotube transparent electrode 110 according to the deposition thickness of the metal. .

In particular, when the aluminum is deposited on the carbon nanotube transparent electrode with a thickness of 0.1 to 0.3 nm or less, the work function of the transparent electrode may be adjusted to 4.06 to 3.97 eV, which may be used as a cathode of the OLED.

In addition, according to the results of measuring the chemical reaction and the change of work function between SWNT and aluminum 111 using the UPS and XPS, deposition of aluminum 111 less than 0.5 nm controls the work function of the SWNT transparent conductive film. It can be seen that it is sufficient to.

Therefore, the carbon nanotube transparent electrode 110 capable of controlling the work function may be applied to optoelectronics, sensors, solar cells, and nanotechnology systems as well as electronics.

Although the above description focuses on the work function control and manufacturing method of the carbon nanotube transparent electrode, the thickness of the metal, for example, aluminum is controlled on the transparent electrode of carbon-based nanomaterials, such as graphene, in addition to the transparent electrode of the carbon nanotube material. It is possible to control the work function of the transparent electrode.

5 shows the work function of graphene and the measured UPS spectrum during the stepwise deposition of aluminum. (a) shows the spectrum of the normalized normal secondary electron cutoff region and the balance band spectrum with the background removed, and (b) shows the work function of graphene with increasing aluminum thickness.

As shown in the secondary electron cutoff region of FIG. 5 (a), the secondary electron cutoff of graphene was moved toward the high binding energy with aluminum deposition of 0.1 nm. The maximum change in the secondary electron cutoff occurred at 0.1 nm aluminum deposition, and the total change shifted towards high binding energy.

After 0.1 nm of aluminum deposition, the secondary electron cutoff was somewhat reduced to lower binding energy. As a result, according to the UPS spectrum, the work function of graphene is changed according to the deposition thickness of aluminum as shown in FIG. 4B.

According to the UPS measurement, after hydrogen heat treatment, the graphene work function was 4.43 eV before aluminum deposition, and then the graphene work function was 4.18 eV (at 0.1 nm aluminum), 4.24 eV (0.3) nm aluminum), 4.25 eV (at 0.9 nm aluminum) and 4.24 eV (at 2.7 nm aluminum).

After deposition of 0.3 nm of aluminum 111, the work function converges to the work function of aluminum 111 due to the predominant amount of aluminum 111 at the graphene surface. As a result, it can be seen that the work function of graphene can be changed to 4.18 to 4.43 eV by deposition of a thin aluminum layer on the surface of graphene.

In addition, the work function of the transparent electrode may be controlled by doping organic materials in addition to the metal to the transparent electrode of the carbon-based nanomaterial.

For example, the organic material is 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane, copper hexadecafluorophthalocyanine And cobaltocene can be used.

In this case, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane or copper hexadecafluorophthalocyanine ( When p-doped copper hexadecafluorophthalocyanine, the fermi level (the distribution of the number of electrons with any energy in the crystal is based on Fermi-Dirac's stats, in which case the energy level at which electrons are present). At this level, the distribution of electrons changes remarkably) and the work function increases.

In addition, when the carbon-based nanomaterial transparent electrode is n-doped with cobaltocene, the Fermi level rises and the work function decreases, thereby adjusting the work function of the transparent electrode.

Here, the metal or organic material is doped to the surface of the carbon-based nanomaterial transparent electrode in the vacuum chamber. This is because the vacuum evaporation method is suitable for doping a very small amount of high purity material.

12: hole injection layer 13: hole transport layer
14 light emitting layer 15 electron transport layer
16: electron injection layer 18: organic light emitting layer
100: flexible substrate 110: carbon nanotube transparent electrode
111: aluminum

Claims (10)

In the method of manufacturing a carbon-based nanomaterial transparent electrode,
Method of manufacturing a carbon-based nanomaterial transparent electrode, characterized in that to adjust the work function of the transparent electrode by doping a metal or organic material on the surface of the carbon-based nanomaterial transparent electrode.
The method of claim 1, wherein the work function of the carbon-based nanomaterial transparent electrode is adjusted by adjusting the doping depth of the metal or organic material.
The method of manufacturing a carbon-based nanomaterial transparent electrode according to claim 1, wherein the metal is aluminum (111).
The method of manufacturing a carbon-based nanomaterial transparent electrode according to claim 3, wherein the thickness of the aluminum (111) is controlled to be 0.3 nm or less so that the work function can be used as a cathode.
The method of claim 1, wherein the organic material is p-doped 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane doped with a carbon-based nanomaterial transparent electrode Or copper hexadecafluorophthalocyanine, or a cobaltocene n-doped to the carbon-based nanomaterial transparent electrode.
The method of claim 1, wherein the metal or organic material is doped in a vacuum chamber.
The method of claim 1, wherein the carbon-based nanomaterial is carbon nanotubes.
The method of claim 1, wherein the carbon-based nanomaterial is graphene.
The carbon-based nanomaterial transparent electrode manufactured by the manufacturing method of any one of claims 1 to 8.
A double-sided light emitting OLED, transparent solar cell, and transparent display that can be mounted on the windshield of a carbon-based nanomaterial transparent electrode that can control the work function by controlling the deposition thickness of metal on the surface.

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