JP4552014B2 - Organic transparent conductor material and manufacturing method thereof - Google Patents

Description

The present invention relates to a transparent conductor material having polycarbazole or a derivative thereof as a basic skeleton and a method for producing the same.

The transparent conductive material is used for image display panel surfaces such as liquid crystal displays, electroluminescent displays, and electrochromic displays, and solar cell panel surfaces, and is used as an electrode for voltage application and current injection purposes. It is also widely used for touch panels that are two-dimensional information input devices. Furthermore, there is an application to a packaging material having transparency, and since the contents of the package can be seen, it becomes easy to inspect the safety of the inclusion.

As the material, a panel in which a thin film of inorganic oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), and fluorine-doped tin oxide (FTO) is deposited on a glass substrate or a plastic sheet has been used. It was. However, the cost of materials and film formation is high, and there is a problem that a considerable cost of, for example, an organic electroluminescent element or an organic solar cell is spent on the inorganic transparent electrode. In addition, the electronic (or chemical) interaction with the organic substance is poor, and for example, there is a problem in charge injection efficiency into the charge transport layer of the organic EL element.

From such a viewpoint, there is an attempt to disperse the conductive fine particles in the transparent insulating polymer to form a conductor film. However, since ITO fine particles are used as the conductive particles, the above problem is not solved. (See Patent Documents 1 to 3).

In recent years, there has been an attempt to coat a substrate with a polythiophene-based solvent-soluble conductive polymer thin film (see Patent Documents 4 to 5), but there is a problem that the material becomes expensive. Furthermore, in such conductive polymers, polaron or bipolaron (cation radical or dication) sites that are charge carriers are unavoidably present, but these sites have light absorption in the visible region to the infrared region. It will be colored when made into a film. Therefore, transparency must be sacrificed when a thick film is used in order to increase the mechanical strength.

As described above, there is still an organic transparent conductor material that can maintain good transparency even when the mechanical strength is increased by using a relatively thick film and can be easily manufactured (synthesized), so that the cost can be kept low. Not realized.

Japanese Patent Laid-Open No. 7-219697 JP 2000-123658 A Japanese Patent Laid-Open No. 3-167590 JP 2002-60736 A Japanese Laid-Open Patent Publication No. 2005-146259

The present invention aims to solve the conventional problems as described above and achieve the following objects. In the present invention, an organic film is formed by a simple electropolymerization process using an inexpensive commercially available reagent, and then brought into contact with a metal, so that a current can be injected and drawn with excellent mechanical strength and practical use. The object is to form a possible hybrid transparent conductor.

  When the inventors first deposited a metal such as aluminum or indium on a conductive polymer film (such as an anion-doped polypyrrole film) formed by an electrolytic polymerization method, the polypyrrole film and metal hybridized. It has been shown that the hybrid film has high durability against repetition of current injection (oxidation reduction) (Patent Publication 2004-99640). In the present invention, it has been found that a transparent conductor hybrid film can be formed by adopting polycarbazole and derivatives thereof among these conductive polymers and by setting the ratio of the conductive polymer to the metal to an optimum value. is there.

That is, the present invention electrolyzes a solution of carbazole and its derivatives with respect to a saturated calomel reference electrode in the range of an electrolysis potential of +0.5 V to +1.8 V to form a green polycarbazole film doped with anions on the anode. Formation of an organic transparent conductor characterized by forming a transparent hybrid film having electrical conductivity by contact with a metal having an optimum amount of material relative to the amount of material of the carbazole film after (electrolytic polymerization) Is the method.
In addition, the present invention provides a self-standing type (free standing) by forming an organic transparent conductor on the anode by the above method, coating a transparent general-purpose polymer film, and peeling the organic transparent conductor together with the general-purpose polymer film. ) Transparent conductor film.
Furthermore, in the present invention, after the polycarbazole film is formed on the anode by the above method, a transparent general-purpose polymer film is coated, and the polycarbazole film is peeled off together with the general-purpose polymer film. After forming a polycarbazole film, an organic transparent conductor is obtained by contacting a metal having an optimum amount of material with respect to the amount of material of the carbazole film to obtain a transparent hybrid film having electrical conductivity Is the method.

According to the method of the present invention, since carbazole or a derivative thereof is used, there is no material cost. In addition, electronic (or chemical) interaction with organic substances is high. Furthermore, there is no problem of coloring even if the film is thick. Furthermore, it is possible to form an organic transparent conductor film excellent in mechanical strength that has hardly been prepared so far.

Since the organic transparent conductor film produced by the method of the present invention has a conductivity which is practically used despite being relatively thick, (1) image display such as liquid crystal display, electroluminescent display, electrochromic display, etc. It is useful as an electrode material for the panel surface and (2) an electrode material for the solar cell panel surface. In addition, (3) application to a touch panel which is a two-dimensional information input device, (4) utilization to a packaging material having transparency, and the like can be given.

Hereinafter, embodiments of the present invention (hereinafter referred to as the present invention) will be described.
(Preparation of carbazole solution)
A commercially available carbazole is dissolved in dichloromethane to prepare a carbazole solution.
Although there is no restriction | limiting in particular in the density | concentration of carbazole, 1 mM-10 mM are desirable.
The general formula (1) of carbazole is described below. In general formula (1), R _{1 to} R ₉ may be the same as or different from each other, and represent a hydrogen atom or a substituent. Further, they may be connected to each other to form a ring.
As the solvent for dissolving carbazole, a solvent used in the electrochemical field having a relatively high dielectric constant is used. For example, dichloromethane, acetonitrile, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, γ-butyrolactone, polyvinylpyrrolidone, a mixed solvent of these solvents, or a mixed solvent of these solvents and water is used. In order to obtain high-quality polycarbazole, dichloromethane, acetonitrile, or a mixed solvent of methanol and water is desirable. In the solvent, a salt necessary for causing an electrochemical reaction is added. However, in order to form a high-quality polycarbazole film , within an electropolymerization potential range (with respect to a saturated calomel reference electrode, an electrolytic potential +0.5 V to (C ₄ H ₉ ) ₄ N ⁺ ClO ₄ can be mentioned as a salt that does not undergo an electrode reaction in the range of +1.8 V.

(Formation of polycarbazole film)
The lower limit of the electrolytic potential at which a polycarbazole film starts to form efficiently varies depending on the substituents R _{1 to} R ₉ , but is about +0.5 V to +1.0 V with respect to the saturated calomel reference electrode, and the potential is + 1.8
When the potential is nobler than V, the nitrogen sites of carbazole are linked to each other, and 9,9′-dicarbazyl having poor durability with respect to electrical conductivity and energization is generated. Further, a potential nobler than +1.8 V is not desirable for electrolytic polymerization of carbazole, because decomposition of the solvent and added salt occurs. In addition, in order to avoid an electrochemical reaction involving oxygen in the air, it is desirable that the electrolytic polymerization operation is performed in a nitrogen atmosphere, that is, nitrogen bubbling is performed in the electrolytic cell containing the solution. However, the polycarbazole film is formed even under normal air. The electrolysis temperature may be about 0 ° C to 30 ° C.

As the anode, a metal that is a conductive material and does not dissolve at a potential of +0.5 V to +1.8 V with respect to the saturated calomel reference electrode, for example, a metal such as Pt, Au, or stainless steel, or a carbon material is desirable. Alternatively, a conductive oxide such as indium tin oxide (ITO) or tin oxide, a conductive plastic, or a conductive semiconductor such as silicon or gallium arsenide may be used. Cathode materials include most metals such as Pt, Au, Cu, Ni, and stainless steel, conductive oxides and conductive plastics such as indium tin oxide (ITO) and tin oxide, and silicon and gallium arsenide. A conductive semiconductor is used.

The film thickness of the polycarbazole film is defined by the amount of electricity applied during the electropolymerization and the structure of carbazole used as a raw material. As an example, when all of the substituents R _{1 to} R ₉ are hydrogen, the anode substrate electrode
When a charge amount of 1 mC is applied to 1 cm ² , the resulting polycarbazole film has a thickness of 16 nm, and the film thickness increases in proportion to the amount of electricity supplied.

(Contact with metal, formation of hybrid film)
Cation radicals and dications are present in the polycarbazole film obtained by the above electropolymerization operation. Then, in order to electrically neutralize the cation radical and dication, anions (ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ^{− and the} like) contained in the electrolytic solution are taken into the film (anion doping). In addition, anion-doped polycarbazole exhibits a clear green color. Then, a state in which cation radicals and dications / metals / adsorbed water coexist is created to cause a galvanic corrosion reaction. One method for creating this state is to deposit a metal on a polycarbazole film. Others, spatter method, plating,
Electrodeposition, electron beam method, etc. are possible.

Metals with a small work function compared to polycarbazole, such as aluminum, indium, zinc, titanium, cadmium, manganese, iron, copper, silver, tin, antimony, lead, sodium, potassium, or calcium are deposited and adsorbed water When held in an existing state (typically in normal air), the difference in work function between polycarbazole and metal becomes a driving force, and electrons move from the deposited metal to polycarbazole. The electrons injected into the polycarbazole combine with cation radicals or dications in the polycarbazole and disappear, or reduce adsorbed water present in the polycarbazole.
On the other hand, the metal that loses electrons and is oxidized becomes a metal ion, which is combined with a negative ion (anionic dopant) paired with a cation radical and a dication in polycarbazole to form a salt, or as described above. It becomes a metal oxide by participating in the water reduction reaction. That is, a galvanic corrosion reaction occurs between the metal and carbazole, and a metal salt and a metal oxide are formed.
Here, if the stoichiometry of the amount of polycarbazole (strictly speaking, the net amount of cations and dications present in polycarbazole) and the amount of metal match, the resulting hybrid film is transparent. It becomes. However, when the amount of the metal is larger than the stoichiometric ratio, unreacted metal remains and does not become transparent. In addition, when the amount of the metal is less than the stoichiometric ratio, the green color resulting from the cation radical and dication of polycarbazole remains, and the white transparency is not achieved.

(application)
In the above method, the organic transparent conductor film is formed on the anode substrate. Use in such an element form, that is, a form integrated with an anode substrate, is applied to an electrode material for an image display panel surface such as a liquid crystal display, an electroluminescent display, an electrochromic display, or an electrode material for a solar cell panel surface. It can be used suitably.

For the purpose of use for a packaging material having transparency, a state where it is not attached to the substrate, that is, a self-supporting form is desirable. Therefore, the insulating polymer resin is coated on the hybrid film obtained above on the anode substrate, and the method of peeling after drying, or the insulating polymer resin is coated on the polycarbazole film obtained on the anode substrate, A self-supporting organic transparent conductive film can be obtained by a method of obtaining a hybrid film by peeling and contacting with a metal.

The insulating polymer used in that case is not particularly limited as long as it is a polymer that does not absorb light in the visible region (transparent) and has excellent film forming properties. For example, a polycarbonate resin, a polyester resin, a polyvinyl alcohol resin, a polymethyl methacrylate resin, a polystyrene resin or the like that is frequently used as a binder resin is preferably used. As an example, a polycarbonate resin manufactured by Teijin Chemicals Limited is dissolved in a mixed solvent of dichloromethane and chloroform to prepare a coating solution. In this case, the weight ratio of polycarbonate resin: dichloromethane: chloroform is 1: 8: 8. The anode substrate on which the hybrid film and the polycarbazole film are formed is immersed in this coating solution, and the hybrid film and the polycarbazole film are covered with a polycarbonate film. If this is dried at 60 ° C. for 3 hours or more and the solvent is evaporated, the film can be easily peeled off from the anode substrate.
Hereinafter, the present invention will be described in more detail with reference to the drawings.

Example 1
An electrolytic solution composed of a dichloromethane solution in which carbazole (5 mM) and tetrabutylammonium perchlorate (0.1 M), which are commercially available, are dissolved is placed in the main chamber of a two-room type electrolytic cell made of heat-resistant glass. Then, a glass electrode coated with an indium tin oxide (ITO) film 170 nm and a platinum plate electrode are immersed in this main chamber. On the other hand, the electrolyte solution is also placed in a subchamber separated by a sintered glass film, and a saturated calomel reference electrode (SCE) is immersed therein. Pass nitrogen gas through the aqueous solution in the main chamber for 40 minutes to eliminate dissolved oxygen. The ITO glass electrode is connected to a constant potential power source (potentiostat) using the working electrode, the platinum plate electrode as a counter electrode, and the SCE as a reference electrode. A potential of +1.2 V was applied to the working electrode relative to the reference electrode. The amount of electricity applied was 70 mC / cm ² , and during the electrolysis, nitrogen gas was allowed to flow above the electrolyte to maintain a nitrogen atmosphere. The electrolysis cell is installed in a thermostat, and the electrolysis temperature is kept constant at 10 ° C.

By this operation, a green film of polycarbazole having a thickness of 1100 nm was formed on the ITO glass electrode. The ITO glass electrode substrate on which the green film was formed was taken out from the electrolyte and washed with dichloromethane.
Next, aluminum was deposited on the polycarbazole film to a thickness of 20 nm. FIG. 1 shows a photograph showing how the color of the deposited portion changes with time when aluminum is deposited. The scale bar in the photograph shows a length of 5 mm. The deposited portion of aluminum is the upper half of the sample, and the atmosphere in which the sample is left is a normal atmosphere (about 25 ° C., about 50% humidity). In about 2 minutes after deposition (a in the figure), an aluminum layer having a metallic luster is visible, but 30 minutes (b in the figure), 1 hour (c in the figure), 1 hour 30 minutes (d in the figure), 2 Whenever time (e in the figure), 3 hours (f in the figure), 6 hours (g in the figure) and 24 hours (h in the figure) elapse, the metallic luster caused by aluminum and the polycarbazole are caused. It can be seen that the green color fades and changes to an almost white transparent hybrid film after 24 hours.

Example 2
Polycarbazole was formed on the ITO glass electrode substrate by the same operation as in Example 1. However, since the amount of electricity applied is 28 mC / cm ² , the resulting polycarbazole film has a thickness of 450 nm. And aluminum was vapor-deposited so that a film thickness might be set to 8 nm. Then, by holding the sample in the air for a sufficient time, the fading reaction (hybridization reaction) shown in FIG. 1 was advanced.

FIG. 2 shows a transmission electron micrograph of a cross section of the obtained hybrid membrane. The length of the scale bar below the photo indicates a length of 100 nm. The hybrid film in the center of the photo (the top of the film has a tungsten and carbon layer deposited to protect the film. Underneath the film is a black contrast layer of ITO). Consists of contrast, but by energy dispersive X-ray spectroscopic measurement, the white contrast portion is undoped polycarbazole, and the black contrast portion is undoped polycarbazole + oxidation It was found to be composed of aluminum + aluminum perchlorate. That is, the obtained hybrid film is an organic-inorganic nanohybrid film in which nano-sized regions of aluminum oxide and aluminum perchlorate are uniformly dispersed in a dedope polycarbazole film. It was.

Example 3
Polycarbazole was formed on the ITO glass electrode substrate by the same operation as in Example 1. However, since the amount of electricity applied is 60 mC / cm ² , the resulting polycarbazole film has a thickness of 960 nm. Then, aluminum was deposited by changing the film thickness. Then, by holding the sample in the air for a sufficient time, the fading reaction (hybridization reaction) shown in FIG. 1 was advanced. After the fading reaction converged, the UV-visible absorption spectrum of the sample was measured, and the relationship between the deposited aluminum film thickness and the sample transparency was examined.

FIG. 3 shows the relationship between the absorbance of the sample at 680 nm and the film thickness of the deposited aluminum. Since the green polycarbazole film has light absorption at 680 nm, the degree of progress of the hybridization reaction can be known by monitoring the absorbance at this wavelength. From the results shown in FIG. 3, the absorbance at 680 nm was minimized when the amount of aluminum was 16 nm. This is because when aluminum is deposited in the range of 0 to 16 nm, all of the aluminum is used in the hybrid reaction, and at 16 nm it reacts just with 960 nm thick polycarbazole, ie reacts stoichiometrically. Indicates. On the other hand, when the deposition thickness of aluminum exceeds 16 nm, all of the aluminum does not react and the metallic aluminum remains, so the absorbance increases. From the above results, it was found that the film thickness ratio between polycarbazole and vapor deposited aluminum with the highest transparency was 60: 1. The hybrid film formed with this ratio exhibited a light transmittance of about 83% over the entire visible region.

Example 4
A polycarbazole film was formed under the same conditions as in Example 1 except that the amount of electricity supplied was 50 mC / cm ² (polycarbazole film thickness was 800 nm). Then, aluminum was deposited by changing the film thickness. Then, by holding the sample in the air for a sufficient time, the fading reaction (hybridization reaction) shown in FIG. 1 was advanced. After the fading reaction converged, the electrical conductivity of the sample was measured by the four-probe method, and the relationship between the deposited aluminum film thickness and the electrical conductivity of the sample was examined.

In FIG. 4, the relationship between the electrical conductivity of a sample and the film thickness of vapor deposition aluminum is shown. When the film thickness of the deposited aluminum is in the range of 0 to 15 nm, the hybridization reaction including the polycarbazole de-doping reaction proceeds, so the electrical conductivity decreased. On the other hand, when the deposition thickness of aluminum exceeded 15 nm, all of the aluminum did not react and the metal aluminum remained disappeared, increasing the electrical conductivity. In addition, a hybrid film with high white transparency was obtained when the film thickness of the aluminum deposited film was around 15 nm. When aluminum was not vapor-deposited (when the vapor-deposited aluminum film thickness was 0 in FIG. 4), that is, the polycarbazole film exhibited an electrical conductivity of 5.4 × 10 ⁻³ S / cm. On the other hand, the hybrid film with high white transparency (when the deposited film thickness of aluminum was 15 nm) also showed an electric conductivity of 1.6 × 10 ⁻⁴ S / cm. Usually, the electric conductivity of the conductive polymer film decreases by several orders of magnitude due to the dedoping reaction, but in the case of the above example, the electric conductivity value is at most 1 in spite of including the dedoping reaction in the hybridization reaction. Note that only an order of magnitude declined.

Example 5
A polycarbazole film was formed under the same conditions as in Example 1 except that the amount of electricity supplied was 54 mC / cm ² (polycarbazole film thickness was 860 nm). Then, an aluminum film having a thickness of 15 nm was vapor-deposited on the obtained polycarbazole film and kept in air for a sufficient time to form a hybrid film having high white transparency. Next, the ITO substrate on which this hybrid film was formed was immersed in an electrolyte solution consisting of a dichloromethane solution in which tetrabutylammonium perchlorate (0.1 M) was dissolved, and cyclic voltammetry (the potential applied to the working electrode at a constant rate). The hybrid film was subjected to an oxidation-reduction repeated durability test by measuring the current flowing at that time and measuring the current-potential relationship. The counter electrode at this time was a platinum plate, and a saturated calomel electrode (SCE) was used as the reference electrode. During cyclic voltammetry measurement, nitrogen gas was allowed to flow above the electrolyte to maintain a nitrogen atmosphere.

FIG. 5 shows current-potential characteristics (cyclic voltammogram) obtained by cyclic voltammetry measurement. A positive current flows due to the potential sweep in the positive direction, which is a response to the oxidation (injection of holes) of the hybrid film. On the other hand, a negative current flows due to a potential sweep in the negative direction, which is a response to the reduction (injection of electrons) of the hybrid film. When the potential sweep is repeated, a steady current flows from the fifth time onward, indicating that the oxidation-reduction durability of the hybrid membrane is extremely good.

Comparative Example 1
A polycarbazole film was formed under the same conditions as in Example 4 except that the amount of electricity supplied was 62 mC / cm ² (polycarbazole film thickness was 990 nm). Then, the ITO substrate on which the polycarbazole film was formed without depositing aluminum was immersed in an electrolytic solution consisting of a dichloromethane solution in which tetrabutylammonium perchlorate (0.1 M) was dissolved, and cyclic voltammetry (constant) The oxidation-reduction repeated durability test of the hybrid film was performed by changing the potential applied to the working electrode at a speed of 5 and measuring the current flowing at that time to measure the current-potential relationship. The counter electrode at this time was a platinum plate, and a saturated calomel electrode (SCE) was used as the reference electrode. During cyclic voltammetry measurement, nitrogen gas was allowed to flow above the electrolyte to maintain a nitrogen atmosphere.

FIG. 6 shows a cyclic voltammogram obtained by cyclic voltammetry measurement. In this case where aluminum is not deposited and hybridized, the polycarbazole film expands, contracts, and dissolves. In the initial stage of potential application, a large current flows due to structural changes such as film peeling. The phenomenon of electric current due to the decrease of reactants due to dissolution of the film was observed. A non-stationary current that changes every time the potential sweep is repeated flows, and it can be seen that the oxidation-reduction durability is extremely poor only with the polycarbazole film.

According to the method of the present invention, as an alternative to an expensive transparent conductive inorganic oxide thin film, an organic conductive film having a high white transparency that has hardly been produced so far can be formed, and a display element using an organic electronic material ( A liquid crystal display, an organic electroluminescent element, etc.) and an energy conversion element (organic solar cell) charge injection electrode can be provided. In addition, since it is an organic substance, it is flexible, and a material for a touch panel that is a two-dimensional information input device requiring flexibility and a packaging material having transparency can be provided.

FIG. 1 is a drawing-substituting photograph showing the progress of the hybridization reaction described in Example 1. FIG. 2 is a transmission electron microscope (TEM) photograph instead of a drawing showing a cross-sectional nanostructure of the hybrid film obtained by the solid reaction of FIG. FIG. 3 is an explanatory diagram showing the relationship between the absorbance at 680 nm of the obtained hybrid film and the film thickness of the deposited aluminum by performing the solid reaction shown in Example 1 with various film thicknesses of the deposited aluminum. is there. FIG. 4 is an explanatory diagram showing the relationship between the electrical conductivity of the obtained hybrid film and the film thickness of the evaporated aluminum obtained by performing the solid reaction shown in Example 1 with various film thicknesses of the evaporated aluminum. FIG. 5 shows a solid reaction between the polycarbazole film and the aluminum deposited film as shown in Example 1 in a stoichiometric ratio, and is obtained by cyclic voltammetry of the obtained hybrid film with high white transparency. It is explanatory drawing which shows an electric current-potential characteristic (cyclic voltammogram). FIG. 6 is an explanatory diagram showing current-potential characteristics (cyclic voltammogram) obtained by cyclic voltammetry of a polycarbazole film.

Claims (6)

A solution in which a supporting electrolyte composed of carbazole or a derivative thereof and tetrabutylammonium perchlorate is dissolved is electrolyzed with respect to a saturated calomel reference electrode in the range of electrolytic potential +0.5 V to 1.8 V, and a supporting electrolyte anion is formed on the anode. After forming a doped polycarbazole film with a thickness of 1100 nm or less, an aluminum film with a thickness of 20 nm or less is formed, and the polycarbazole film and the aluminum film are made transparent by bringing the polycarbazole film and the aluminum film into contact with each other. To obtain a transparent conductor film. After forming the aluminum film, a transparent polymer film is coated, and the transparent polymer film, the polycarbazole film, and the aluminum film are peeled off from the anode to form a self-standing (free standing) transparent conductor film. The method of obtaining the transparent conductor film of Claim 1 obtained. A solution in which a supporting electrolyte composed of carbazole or a derivative thereof and tetrabutylammonium perchlorate is dissolved is electrolyzed with respect to a saturated calomel reference electrode in the range of electrolytic potential +0.5 V to 1.8 V, and a supporting electrolyte anion is formed on the anode. A self-supporting polycarbazole film is formed by forming a doped polycarbazole film with a thickness of 1100 nm or less, coating a transparent polymer film, and peeling the polycarbazole film together with the transparent polymer film. Thereafter, an aluminum film having a thickness of 20 nm or less is formed, and the polycarbazole film and the aluminum film are made transparent by bringing the polycarbazole film and the aluminum film into contact with each other, thereby obtaining a transparent conductor film. 4. The method for obtaining a transparent conductor film according to claim 1, wherein the stoichiometry of the substance amount of polycarbazole and the substance amount of metal are matched. 4. The method for obtaining a transparent conductor film according to claim 1, wherein the aluminum film is formed by vapor deposition . 4. The method for obtaining a transparent conductor film according to claim 1, wherein the film thickness of the polycarbazole is 53 or more and less than 75 when the film thickness of the aluminum film is 1. 5 .