JP2608865B2 - Method for producing conductive thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive thin film, in particular, a charge transfer complex type thin film of a plasma polymerized thin film of a nitrile group-containing compound.

(Prior Art) Conventionally, synthetic polymer materials such as polyacetylene, poly-p-phenylene, and polyphenylene sulfide are known as organic polymer semiconductor materials. However, they have disadvantages such as difficulty in polymerization, low yield, instability of the product in the air, change over time in electrical conductivity and mechanical properties. Also, semiconductor materials utilizing photochemical energy conversion functions such as natural pigments such as phthalocyanine, merocyanine, and chlorophyll are known. However, when used alone, they have no mechanical strength. And there is a problem in use such as a decrease in film forming efficiency.

Many charge-transfer-type conductors using a combination of an electron-accepting substance / an electron-donating substance such as tetracyanoquinodimethane / tetrathiafulvalene and tetracyanoquinodimethane / tetraselenafulvalene have been proposed. Poor moldability and film-forming body cause practical problems.

(Problems to be solved by the invention) As a result of intensive studies, the present inventors have completed the present invention.

An object of the present invention is to provide an extremely thin, uniform and physically and chemically stable electron-accepting organic compound having a nitrile group without any chemical modification and without using a resin having other moldability. An object of the present invention is to provide a method for producing a stable thin film. Still another object is to provide a method for producing a thin film having excellent conductivity.

(Means for Solving the Problems) The method of the present invention forms a plasma polymerized film on a substrate by vaporizing an electron-accepting organic compound (I) having a nitrile group in a low-temperature gas plasma of a non-polymerizable gas. And then doping with an electron donating substance (II).

The non-polymerizable gas used in the present invention is argon, nitrogen,
Helium, water, hydrogen, carbon dioxide and the like can be used, and among them, argon, nitrogen, helium and hydrogen are preferable.

Low temperature gas plasma refers to so-called non-equilibrium gas plasma and can be generated by any of the known methods for generating such plasma. For example, JR
See Hollahan and AT Bell's "Applied Technologies for Plasma Chemistry", Wiley, NY 1974 and M. Shen's "Polymer Plasma Chemistry", Decker New York, 1976. I have. That is, the monomer can be placed under vacuum between the parallel plate electrodes connected to the high frequency generator, and plasma can be generated using either the parallel plate outside or inside the vacuum chamber. Further, an electric field may be generated by an external induction coil to generate plasma of an ionized gas, or conversely, the plasma may be generated by directly entering a vacuum chamber with an interval between charged electrodes.

Examples of the electron-accepting organic compound (I) (hereinafter also simply referred to as compound (I)) used in the present invention include tetracyanoquinodimethane, tetracyanoethylene, tetracyanothiophene, tetracyanofuran, octacyano-p, p, p−
Triphenylphospholidine, dicyanobenzene, tetracyanobenzene, 2,3-dichloro-5,6-dicyano-P-
There are various derivatives such as benzoquinone and their alkyl or halogen substitution.

In order to activate and polymerize compound (I) in a low-temperature gas plasma, compound (I) must be vaporized. The compound (I) is usually stable even at a normal pressure of 200 ° C. or higher, and cannot be vaporized in a low-temperature gas plasma space of 10 ⁻⁵ to 10 ² torr without heating if necessary. The heating and vaporization of compound (I) is usually performed by heating with a heater,
There are methods such as high-frequency heating, far-infrared heating, laser heating, and electron beam heating, which are appropriately selected.

The vaporization rate of the compound (I), that is, the supply rate of the monomer of the compound (I) in the low-temperature gas plasma, depends on the formation rate of the polymerized film,
This has a significant effect on form and performance. If the vaporization rate of the monomer is high, the ratio between the activated monomer and the inactive monomer is small, and a good polymer film cannot be formed. That is,
The degree of polymerization is not sufficient, and the film cannot take the form of a thin film, or is dissolved in a solvent, and the thin film is broken during use. On the other hand, if the vaporization rate of the monomer is low, the ratio of the active monomer to the inactive monomer is large, the primary structure of the monomer is remarkably destroyed, the crosslinking proceeds extremely, and a polymer film having high surface hardness and high solvent resistance is obtained. However, the primary structure of the monomer is destroyed by that amount, and the conductivity is reduced. The heating sublimation rate of the compound (I) is adjusted by the heating temperature, and the supply time into the plasma is set by opening and closing a shutter provided on the heating vessel.

The degree of vacuum when generating low-temperature gas plasma is usually 10 ^-3
~ 10 ² torr, preferably 10 ^-2 to 10 ¹ torr, more preferably
Carried out in 10 ^-1 ~10 ⁰ torr. Vacuum degree less than 10 ^-3 torr or 1
0 The ² torr or more, and or unstable plasma generation is insufficient, undesirably. The pressure is controlled by introducing an inert gas such as argon, nitrogen or helium from the outside.

The plasma output is, for example, at most 200 W or less, preferably 2 to 150 W or less, more preferably 10 to 100 W in a parallel plate electrode having a diameter of 10 cm. When the output is higher than 200 W, the destruction of the monomer of the organic compound (I) proceeds excessively, and the conductivity and photoelectric conversion ability of the plasma polymerized film are not sufficient. on the other hand
When the output is as low as 2 W or less, the strength, surface hardness, or solvent solubility of the plasma polymerized film is slightly small.

Plasma polymerization time is usually 10 minutes or less, preferably 2 to
8 minutes. When the plasma polymerization time is longer than 10 minutes,
Deterioration and destruction of the generated plasma-polymerized film proceed, and if the polymerization time is short, the film strength and hardness of the plasma-polymerized film decrease, and the subsequent doping treatment and handling become somewhat difficult.

The plasma polymerized film obtained by the method of the present invention is transparent or light brown, has a gloss, is very thin, and has a thickness of 0.01 μm to 5 μm.
Since m is used, it is rarely used alone. In many cases, a plasma polymerized film is formed on a substrate. As the substrate, for example, granular (spherical) or film-like, film-like,
A sheet-like thing is mentioned. The plasma polymerized film obtained here has a conductivity of at least 10 ^-9 S / cm, and the presence of the double bond of compound (I) in the plasma polymerized film.
Estimate the existence of stacking structures.

Next, in order to further improve the conductivity of the thin film, an electron donating substance (II) (hereinafter, also simply referred to as substance (II)) is doped. The substance (II) is not particularly limited as long as it has an electron donating property to the compound (I). For example, tetrathiafulvalene and its derivatives, tetraselenafulvalene and its derivatives, diselenadithiafulvalene and its derivatives, iodine , Bromine, chlorine, fluorine and other halogen elements,
Amines such as trimethylamine and triethylamine, N
-Vinyl carbazole, pyridine, morpholine dimethyl aniline, 1,5-diaminonaphthalene, phenothiazine,
Benzene, knife tarene, pyrene, 1-6 diaminopyrene and the like can be mentioned.

The doping can be easily achieved by exposing the plasma polymerized film of the compound (I) to the vapor of the substance (II) or dipping the film in the solution of the substance (II). Alternatively, the substance (II), for example, iodine can be vaporized simultaneously with the plasma polymerization, and can be doped into the plasma polymerization film. In this method, since the vapor pressure of iodine is low at the time of doping, a substrate such as aluminum or ITO glass is damaged as in the case of normal doping,
It is preferable because it does not corrode. Further, it is also possible to extract iodine doped in the plasma polymerized film with alcohol or the like to form predetermined fine holes in the plasma polymerized film. Next, the plasma polymerized film having the pores can be subjected to doping treatment with another electron donating substance. The conductivity of the thin film after doping is at least 10 times that of before doping, and in most cases 100 times or more, indicating that the thin film has a charge-transfer complex formed.

The conductive thin film of the present invention not only has conductivity, but also forms a sandwich cell sandwiched between a metal forming an ohmic junction with the thin film and a metal forming a potential barrier, and is irradiated with sunlight or artificial light. As a result, a potential is generated at both ends of the cell, and the cell functions as a solar cell. That is, a Schottky junction is formed between the conductive thin film and the metal or metal compound, and the generated potential can be taken out. A metal or metal compound for forming a bond is brought into contact with the conductive thin film by contacting a metal foil, vapor deposition or sputtering. In order to reduce the contact resistance, it is preferable to use evaporation or sputtering. Metals that form an ohmic junction include gold, platinum, copper, indium tin oxide, and the like, and metals that form a potential barrier include aluminum or indium.

Short circuit current (Jsc) of a cell using the conductive thin film of the present invention
Usually 1 nA / cm ² or more, preferably 10 nA / cm ² or more, more preferably 100 nA / cm ² or more. Open circuit voltage (Voc)
Is usually 0.1 V or more, preferably 0.2 V or more, more preferably
0.5 V or more, and the photoelectric conversion ability η (%) is usually 1 × 10 ⁻⁷ %
Or more, preferably 1 × 10 ⁻⁶ % or more, more preferably 1 × 10 ⁻⁶ % or more.
10 ^-5 % or more.

(Effects of the Invention) According to the method of the present invention, a polymerized thin film that is chemically and physically stable and has excellent conductivity can be used without using other materials and additives, and can be polymerized into a raw material. It can be easily obtained without the need for complicated and expensive steps such as introduction of groups and mixing with other polymers after pulverization into fine particles, and is industrially extremely useful.

(Example) Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 A glass plate having an ITO thin film (indium tin oxide) was placed as a substrate on the upper electrode of the plasma reactor shown in FIG. 1, and the inside of the reactor was degassed at 10 ^-3 torr for 30 minutes, and then argon was applied.
The pressure was adjusted to 0.1 torr.

Next, a high frequency of 13.56 MHz was applied between the two electrodes at an output of 100 W to generate low-temperature gas plasma for 3 minutes, and then the tetracyanoethylene contained in the heating vessel in the reactor was heated.
Sublimated. Heating and sublimation were performed for 3 minutes. A glossy brown thin film was formed on the substrate.

This thin film was insoluble in the solvent of tetracyanoethylene and insoluble in general-purpose solvents such as methanol, ethanol, acetone, and THF.

Next, the doping solutions shown in Table 1 were heated to 40 ° C. and immersed, and the plasma polymerized thin films were subjected to doping treatment.

The electric conductivity was measured by forming a gold vapor deposition film on a plasma polymerized thin film or a doped thin film to form an electrode.
The results are shown in Table 1.

Example 2 As in Example 1, a glass plate having an ITO thin film on an upper electrode was used as a substrate, and the inside of the reactor was degassed at 10 ⁻³ torr for about 30 minutes, and the pressure was adjusted to 0.1 torr with argon.

Next, a high frequency of 13.56 MHz is applied between the electrodes at an output of 50 W to generate low-temperature gas plasma. Three minutes later, tetracyanoethylene and iodine contained in separate heating vessels provided in the reactor were heated and sublimated. Heat sublimation was performed for about 3 minutes. The ratio (weight ratio) of sublimed tetocyanoethylene to iodine was 95: 5. A glossy but brownish thin film was formed on the substrate.

The brown color is due to the effect of iodine, iodine is dispersed in the form of molecular to extremely fine particles in the plasma-polymerized film, and is substantially doped with tetracyanoethylene. The conductivity of the plasma polymerized thin film was 6.5 × 10 ⁻⁷ S / cm.

Aluminum is deposited on this plasma polymerized film, and MS
When an M-type cell was formed and a 500 W tungsten lamp was irradiated from the aluminum electrode side, a potential was generated between the electrodes, indicating that the cell had a photoelectric conversion function. Open circuit voltage Vo
c is 0.9 V, short-circuit current Jsc is 54 nA / cm ² , and fill factor (FF) is
0.19, and the photoelectric conversion efficiency η was 7.5 × 10 ⁻⁶ %.

[Brief description of the drawings]

FIG. 1 shows an example of a plasma reactor that can be used in the present invention. A parallel plate electrode (3, 9), a heating filament (4) on which a monomer disk (6) is placed, and a polymer film adhered to the electrode are shown. It comprises a substrate (8) to be formed, a shutter (10) for controlling the supply of monomers, a pressure-resistant plasma reactor (2), a high-frequency power supply (1), and a vacuum exhaust system (5).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01L 31/04 H01L 31/04 D

Claims (5)

(57) [Claims] An electron-accepting organic compound having a nitrile group is vaporized in a non-polymerizable low-temperature gas plasma to form a plasma-polymerized film on a substrate. A method for producing a conductive organic thin film, characterized by doping. 2. The method according to claim 1, wherein the non-polymerizable cryogenic gas plasma is a cryogenic gas plasma of nitrogen, argon, helium, and hydrogen. 3. The method according to claim 1, wherein the organic compound (I) is tetracyanoethylene, tetracyanoquinodimethane, or tetracyanothiophene. 4. The method of claim 1, wherein the plasma polymerized film has a conductivity of at least 10 ^-9 S / cm. 5. The conductivity after doping is at least 10 ⁻⁷ S /
2. The method of claim 1, wherein the distance is cm.