JP2009033126A - Organic transistor material and organic field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic transistor material which realizes compatibility of high mobility and low threshold voltage of an organic FET element. <P>SOLUTION: An organic transistor material includes a single-wall carbon nanotube and an organic semiconductor material. The ratio (B/A) of an absorbance (B) at a wavelength 1,200 nm with respect to absorbance (A) at a wavelength 1,000 nm which is obtained from a single-wall carbon nanotube contained in an organic transistor material is smaller than 1.0. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic transistor material including a single-walled carbon nanotube and an organic semiconductor material, and a field effect transistor using the same as a semiconductor layer.

  Conventionally, field effect transistor elements (hereinafter referred to as FET elements) use inorganic semiconductors such as silicon and germanium, and in order to form a circuit pattern, a process that requires manufacturing costs such as photolithography and vacuum deposition is performed. It was necessary over many stages. In the semiconductor industry that has adopted such a manufacturing method, there is an increasing demand for a reduction in manufacturing cost and an increase in area of a display device. However, it is difficult to reduce the cost and increase the area of the inorganic semiconductor due to restrictions on the manufacturing apparatus. In addition, since the process of forming an inorganic semiconductor such as silicon is performed at a very high temperature, there is a problem that the types of materials that can be used as a substrate are limited.

  For this reason, an organic field effect transistor element using an organic semiconductor excellent in formability as a semiconductor layer has been proposed. By using an organic semiconductor as an ink, it is becoming possible to form a circuit pattern directly on a substrate by an inkjet technique, a screen printing technique, or the like.

As important indexes indicating the performance of the FET element, there are mobility, on / off ratio, and threshold voltage. The improvement in mobility means that the on-current is increased. On the other hand, improving the on / off ratio means increasing the on-current and decreasing the off-current. Both of these improve the switching characteristics of the FET element. For example, in a liquid crystal display device, high gradation is realized. For example, in the case of a liquid crystal display device, the mobility 0.1cm ² / V · sec or higher, the on-off ratio 10 ⁵ or more is required. The threshold voltage is preferably as close to 0V as possible, and on-off control can be performed with a small gate voltage, so that low-voltage driving is possible.

  As organic semiconductors used in FET elements, organic low-molecular semiconductors such as pentacene, tetracene, and metal phthalocyanine compounds are known, but these often use vacuum processes such as vapor deposition, making it difficult to increase the area and cost. There was a problem of being. Therefore, a thiophene polymer (see, for example, Patent Document 1) is known as a conjugated polymer that is soluble in an organic solvent and can be coated and formed. However, sufficient mobility was not obtained with the polymer alone. On the other hand, a field effect transistor including a carbon nanotube (hereinafter referred to as CNT) and a polythiophene polymer has been disclosed as a field effect transistor capable of achieving sufficient mobility and on / off ratio (for example, Patent Documents). 2-3). However, this method has a problem of increasing the threshold voltage.

  As a method for reducing the threshold voltage of a transistor using an organic semiconductor material, a method of capturing ions present as impurities in the organic semiconductor material (for example, see Patent Documents 4 to 5) is disclosed. Although it has been reduced, high mobility has not been achieved at the same time.

In addition, as a transistor using CNT as a semiconductor layer, a transistor using semiconductor CNT as a channel layer by separating semiconducting CNT and metallic CNT is disclosed (for example, see Patent Document 6). In this transistor, the on / off ratio is improved to about 10 ³ by the separation of semiconducting CNTs, but there is a problem that the threshold voltage is large.
JP-A-6-177380 (Claim 1, Example 1) JP 2007-76998 A (Example 2) JP 2004-266272 A (Claims 1 to 4) Japanese Patent Laying-Open No. 2006-49775 (Example 1, Comparative Example 1) JP 2006-49776 A (Example 1, Comparative Example 1) Japanese Patent Laying-Open No. 2007-31238 (Claims 1, 15, and FIG. 20)

  An object of the present invention is to provide an organic transistor material that can achieve both high mobility and low threshold voltage of an organic FET element.

In order to achieve the above object, the present invention comprises the following constitution.
(1) An organic transistor material comprising a single-walled carbon nanotube and an organic semiconductor material, wherein the ratio of absorbance (B) at a wavelength of 1200 nm to absorbance (A) at a wavelength of 1000 nm of a film obtained from the single-walled carbon nanotube (B / An organic transistor material in which A) is less than 1.0.
(2) The organic transistor material according to (1) above, wherein the single-walled carbon nanotube is treated with hydrogen peroxide.
(3) The organic transistor material according to (1) or (2) above, wherein a conjugated polymer is attached to at least a part of the surface of the single-walled carbon nanotube.
(4) The organic transistor material according to any one of the above (1) to (3), wherein the organic semiconductor material is an organic low-molecular semiconductor having a thiophene skeleton and having a molecular weight of 3000 or less.
(5) The organic transistor material according to any one of the above (1) to (4), comprising 0.01 to 3 parts by weight of single-walled carbon nanotubes with respect to 100 parts by weight of the organic semiconductor material.
(6) An organic field effect transistor having a gate electrode, an insulating layer, a semiconductor layer, a source electrode and a drain electrode, wherein the semiconductor layer uses the organic transistor material according to any one of (1) to (5) above. Organic field effect transistor.

  According to the present invention, it is possible to obtain an organic semiconductor material that can be formed by coating and can achieve both high mobility and low threshold voltage of an organic FET element. By using the organic semiconductor material of the present invention, an organic FET element having high mobility and low threshold voltage can be obtained by a low-cost process such as a coating method.

  The organic transistor material of the present invention includes single-walled CNTs and organic semiconductor materials. Here, the single-walled CNT in which a single carbon film (graphene sheet) is wound in a cylindrical shape, the double-walled CNT in which two graphene sheets are wound concentrically, and a plurality of graphene- There are multi-layer CNTs in which sheets are wound concentrically. The organic transistor material of the present invention contains single-walled CNTs, and may further contain two-walled CNTs or multilayered CNTs. However, the two-walled CNTs or multilayered CNTs are preferably 50% by weight or less of the total CNTs. In particular, since single-walled CNTs have excellent properties, only single-walled CNTs are more preferably used.

  Single-walled CNTs include metallic CNTs and semiconducting CNTs, and an aggregate of single-walled CNTs is a mixture of both. Generally, in the synthesized single-walled CNT aggregate, semiconducting CNTs are present at a ratio of two-thirds and metallic CNTs at a ratio of one-third. In the present invention, an organic semiconductor material capable of reducing the threshold voltage of the organic FET element can be obtained by increasing the ratio of metallic CNT in the single-walled CNT aggregate.

  Considering the role of single-walled CNTs in the present invention, if the ratio of metallic CNTs can be increased, improvement in mobility, reduction in hysteresis, and reduction in threshold voltage are expected. That is, by increasing the ratio of metallic CNT, it is expected that the carrier path between the crystallites of the organic semiconductor becomes smooth and the mobility is improved. In addition, by increasing the ratio of metallic CNT, it is expected that excessive carriers are reduced, and hysteresis and threshold voltage are reduced. In the present invention, it has been found that increasing the ratio of metallic CNT is particularly effective in reducing the threshold voltage while maintaining high mobility.

  Changes in the ratio of metallic CNT can be seen by changes in absorbance in the near infrared region. Absorption characteristic of semiconducting CNT is observed at a wavelength of 1200 nm. On the other hand, the absorption near the wavelength of 1000 nm does not depend on the ratio of metallic CNT to semiconducting CNT. Therefore, the ratio (B / A) of the absorbance (B) at a wavelength of 1200 nm to the absorbance (A) at a wavelength of 1000 nm can be used as an index indicating the ratio of metallic CNT and semiconducting CNT.

  Specifically, a single-walled CNT film may be formed and the absorbance may be measured for the film. The single-walled CNT film can be formed, for example, by dispersing the single-walled CNT in a solvent together with a conjugated polymer or a dispersant and applying a dispersion. Since the absorbance near the wavelength of 1000 nm depends only on the film thickness, it is possible to know the absorbance proportional to the film thickness. On the other hand, since the absorption at a wavelength of 1200 nm is characteristic of semiconducting CNT, the ratio (B / A) of the absorbance (B) at a wavelength of 1200 nm to the absorbance (A) at a wavelength of 1000 nm is expressed as a metallic CNT and a semiconducting CNT. It can be used as an index indicating the ratio with CNT. In the present invention, the value of B / A needs to be less than 1.0. When this value is 1.0 or more, the threshold voltage increases to 20 V or more. The value of B / A is preferably as small as possible, more preferably 0.8 or less.

  As described above, generally, in the synthesized single-walled CNT aggregate, semiconducting CNTs are present at a ratio of two-thirds and metallic CNTs at a ratio of one-third. In this case, the value of B / A is 1.0. Therefore, in the present invention, it is preferable to perform a process of increasing the metallic CNT ratio so that the value of B / A is less than 1.0. As a method for increasing the metallic CNT ratio, a method of heat-treating an aggregate of metallic and semiconducting CNTs in hydrogen peroxide water (for example, see JP-A-2006-188380), a semiconductor by irradiating a laser Selective destruction of CNTs (for example, see JP-A-2007-31239), method of selectively removing metallic CNTs using a porphyrin dimer (for example, see JP-A-2006-265178), metal There are methods (for example, see International Publication No. 05/041227 pamphlet) in which strong CNT treatment is performed while electrically protecting CNTs on the electrode, and any of them is preferably used. Among these, the hydrogen peroxide treatment is preferably used because it can be easily and reliably treated. In the hydrogen peroxide treatment, both the semiconducting CNT and the metallic CNT are oxidized little by little by heating and stirring, and disappear as carbon dioxide gas. However, the rate at which the semiconducting CNT is oxidized is faster. As a result, a single-walled CNT aggregate with a high ratio of metallic CNTs can be obtained. By measuring the absorbance of the film obtained from the single-walled CNT aggregate before and after these treatments and examining the change in the B / A value, the increase or decrease in the metal CNT ratio due to the treatment can be known. For example, if the B / A value is decreased by the treatment, the ratio of semiconducting CNTs is decreased, and the ratio of metallic CNTs is increased accordingly.

  In the present invention, the single-walled CNT preferably has a conjugated polymer attached to at least a part of its surface. By attaching the conjugated polymer, the single-walled CNT has improved dispersibility in the organic semiconductor, and the mobility of the organic transistor can be further improved. Moreover, since the dispersibility in a solvent improves, when preparing the coating liquid of the organic-semiconductor material containing single-walled CNT, the coating liquid excellent in uniformity can be obtained. Examples of the conjugated polymer include polythiophene, polythienylene vinylene, polyphenylene vinylene, poly-p-phenylene, polypyrrole, polyaniline, polyacetylene, polydiacetylene, polypyrene, polycarbazole, polyfuran, and polyindole. Among these, polythiophene polymers are preferably used, and poly-3-alkylthiophenes having an amphiphilic side chain are particularly preferably used. As these conjugated polymers, those having a weight average molecular weight of 8000 to 200,000 are preferably used, but even those having a higher molecular weight or oligomers having a molecular weight of 800 to 8000 can be used.

  In the absorption spectrum of the single-walled CNT film to which the conjugated polymer is attached, absorption corresponding to these polymers appears mainly in the visible light region. Even in a polymer having a conjugated system, absorption is observed at a wavelength of 800 nm or less. When the absorbance of the single-walled CNT used in the present invention is measured at 1000 nm or 1200 nm, the absorption of the single-walled CNT and the polymer is absorbed. Since they do not overlap, the absorption of the single-walled CNT with the copolymer attached can be observed as it is.

  The organic transistor material of the present invention preferably contains 0.01 to 3 parts by weight of single-walled CNT with respect to 100 parts by weight of the organic semiconductor material described later. By setting the content of the single-walled CNT to 0.01 parts by weight or more, the mobility can be further improved while maintaining a good on / off ratio as the characteristics of the organic transistor. More preferably, it is 0.1 parts by weight or more. On the other hand, when the content is 3 parts by weight or less, properties as a semiconductor can be maintained, and good mobility and on / off ratio can be obtained. More preferably, it is 1 part by weight or less. By setting it to 1 part by weight or less, the threshold voltage can be further reduced while maintaining good mobility and on / off ratio.

  In the present invention, examples of the organic semiconductor material include conjugated polymers and organic low-molecular semiconductors.

  The conjugated polymer is preferably an organic solvent-soluble one, and a semiconductor layer can be easily formed by applying a solution on a substrate or a film. The type of conjugated polymer is not particularly limited, but polymers such as polythiophene, polythienylene vinylene, polyphenylene vinylene, poly-p-phenylene, polypyrrole, polyaniline, polyacetylene, polydiacetylene, polypyrene, polycarbazole, polyfuran, polyindole, and the like Is mentioned. Among them, it is preferable to use a polythiophene polymer or a copolymer containing a polythiophene unit as a semiconductor having excellent semiconductor characteristics. The polythiophene polymer is a polyalkylthiophene having a structure in which a polymer having a polythiophene structure skeleton is attached to a side chain. Specific examples include poly-3-alkylthiophene such as poly-3-methylthiophene, poly-3-butylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, poly-3-dodecylthiophene, poly ( 3,3 ″ -dialkylterthiophene), poly [5,5′-bis (3-alkyl-2-thienyl-2,2′-dithiophene)], poly [2,5-bis (2-thienyl) -3 , 4-dialkylthiophene] and the like (the carbon number of the alkyl group is not particularly limited, but preferably 1 to 16), poly-3-methoxythiophene, poly-3-ethoxythiophene, poly-3-dodecyloxythiophene, etc. -3-alkoxythiophene (the number of carbon atoms of the alkoxy group is not particularly limited, but preferably 1-12), poly-3-methoxy-4-methyl Poly-3-alkoxy-4-alkylthiophenes such as offene, poly-3-dodecyloxy-4-methylthiophene (the number of carbons of the alkoxy group and alkyl group is not particularly limited, but preferably 1-12), poly-3 -Poly-3-thioalkylthiophene such as thiohexylthiophene and poly-3-thiododecylthiophene (the number of carbons of the alkyl group is not particularly limited, but preferably 1-12), poly-3,4-ethylenedioxythiophene 1 type, or 2 or more types can be used, among which poly-3-alkylthiophene, poly (3,3 ″ -dialkylterthiophene), poly [5,5′-bis (3-alkyl) -2-thienyl-2,2′-dithiophene)], poly-3-alkoxythiophene. A copolymer containing a polythiophene unit includes an arylene unit, a thienylthiazole unit, a fluorene unit, a carbazole unit, a phthalocyanine unit, or a polymer having a derivative of the above unit sandwiched between thiophene units. Any continuous conjugated system can be used. The polymer here refers to a polymer having a molecular weight exceeding 3000, and is usually about 100,000 or less.

  The side chain bonding mode of the polythiophene polymer used in the present invention preferably has a regioregular structure, and preferably has a regioregularity of at least 80%. The regioregularity is an index indicating how many side chain directions are regularly aligned in one direction in a plurality of monomer units arranged side by side. The regioregularity can be quantified by a nuclear magnetic resonance spectrometer (NMR), and the higher the regioregular ratio, the better the semiconductor properties. In the present invention, the steric structure of the main chain of the conjugated polymer and the arrangement of the side chain substituents may be controlled as described above.

  As the organic low-molecular semiconductor, any material exhibiting semiconductivity can be used, and a material having a high carrier mobility is particularly preferable. Moreover, an organic solvent soluble thing is preferable. Here, the organic low molecular weight semiconductor in the present invention can be isolated and identified as a single compound having a molecular weight of 3000 or less and no molecular weight distribution. Organic low-molecular semiconductors can be purified by methods such as column purification, recrystallization, and sublimation purification, so they can be highly purified, and can be obtained with a single molecular weight. An organic FET element can be produced. Furthermore, since the conjugated length of the organic semiconductor molecule can be suppressed by setting the molecular weight to 3000 or less, the stability against oxidation can be improved, and a high on / off ratio can be maintained even in the atmosphere. When the molecular weight is 3000 or less, it is possible to easily synthesize a high-purity organic semiconductor material with high yield. The molecular weight can be measured with a mass spectrometer generally used.

  Examples of organic low-molecular semiconductors include polyheteroaryls containing nitrogen-containing aromatic rings such as pyridine, quinoline, phenanthroline, oxazole, and oxadiazole, and condensations such as anthracene, pyrene, naphthacene, pentacene, hexacene, and rubrene. 4,4′-bis (N- (3-methylphenyl), a compound in which four or more polycyclic aromatic compounds, furan, thiophene, benzothiophene, dibenzofuran, pyridine, quinoline, phenanthroline, oxazole, oxadiazole and the like are linked ) -N-phenylamino) biphenyl aromatic amine derivatives, bis (N-allylcarbazole) or bis (N-alkylcarbazole) and other biscarbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds Metal phthalocyanines such as copper phthalocyanine, metal porphyrins such as copper porphyrin, distyrylbenzene derivatives, aminostyryl derivatives, aromatic acetylene derivatives, naphthalene-1,4,5,8-tetracarboxylic acid diimide, perylene-3,4 Examples thereof include condensed ring tetracarboxylic acid diimides such as 1,9,10-tetracarboxylic acid diimide, and organic dyes such as merocyanine, phenoxazine, and rhodamine. Among these, those having a thiophene skeleton are preferable. By having a thiophene skeleton, molecular orientation is improved and mobility is further improved.

As the organic low-molecular semiconductor having a thiophene skeleton, a thiophene compound represented by the following general formula (1) is preferably used.
B ¹ -A ¹ -B ² (1)
In the general formula (1), B ¹ and B ² may be the same or different and each represents a group represented by the following general formula (2). A ¹ represents a divalent linking group represented by any one of the following general formulas (3) to (11).

In the general formula (2), R ^{1 to} R ⁵ may be the same or different and are each hydrogen, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, Alkylthio group, aryl ether group, aryl thioether group, aryl group, heteroaryl group, halogen atom, cyano group, formyl group, alkylcarbonyl group, arylcarbonyl group, carboxyl group, alkoxycarbonyl group, aryloxycarbonyl group, alkylcarbonyloxy It is selected from the group consisting of a group, an arylcarbonyloxy group, a carbamoyl group, an amino group, and a silyl group. R ^{1 to} R ⁵ may form a ring with adjacent substituents. A represents at least one divalent linking group selected from the group listed below. m is an integer of 0-11. When m is 2 or more, each R ¹ and R ² may be the same or different.

R ^{6 to} R ¹⁰ may be the same or different and are each selected from the group consisting of an alkylene group, a cycloalkylene group, a divalent heterocyclic group, a carbonyl group, an oxycarbonyl group, and a carbonyloxy group. Ar ^{1 to} Ar ¹² may be the same or different and are an arylene group or a heteroarylene group. X ^{1 to} X ⁶ may be the same or different and each represents —O—, —S—, —NR ¹¹ — or —SiR ¹² R ¹³ —. Y ^{1 to} Y ⁶ may be the same or different and each represents —CR ¹⁴ — or —N—. R ^{11 to} R ¹⁴ are selected from the same group as R ^{1 to} R ⁵ . a ^{1 to} a ⁶ may be the same or different and are 1 or 2. b ^{1 to} b ⁸ may be the same or different and are integers of 0 to 4. However, when b ³ , b ⁴ , b ⁷ and b ⁸ are 0, Ar ¹ , Ar ³ , Ar ⁹ and Ar ¹¹ are each an arylene group, a heteroarylene group containing at least one nitrogen atom, or a condensed heteroarylene group Indicates a group.

  As the organic low molecular semiconductor represented by the above general formula (1), the following [1] is specifically exemplified as a preferred example.

  The organic transistor material of the present invention may include the above-described plural types of organic semiconductor materials.

  Next, a method for producing the organic transistor material of the present invention will be described.

  Single-walled CNTs used in the present invention are produced by an arc discharge method, a chemical vapor deposition method (hereinafter referred to as a CVD method), a laser ablation method, or the like. It may be obtained.

  When performing the process which increases the ratio of metallic CNT with respect to a single layer CNT aggregate, it is preferable to refine | purify CNT beforehand. If impurities such as metal catalyst and amorphous carbon contained in the single-walled CNT aggregate are 5% by weight or less, it is not necessary to perform purification, but if more impurities are present, the above-mentioned FET characteristics are improved. In addition to reducing the effect, the efficiency of processing to increase the metallic CNT ratio may be reduced. A known method can be used to purify the single-walled CNT, and acid treatment with nitric acid, sulfuric acid, etc., heat treatment in an air atmosphere, or the like is used.

  The single-walled CNT used in the present invention is preferably a single-walled CNT shorter than the distance between the device electrodes in order to prevent a short circuit between the electrodes of the organic FET device. Since single-walled CNTs are generally produced in the form of strings, they are cut for use in the form of short fibers, or long-walled CNTs are removed using a filter, and single-walled CNTs shorter than the distance between device electrodes are obtained. Obtainable. In order to cut into short fibers, ultrasonic treatment is effective together with acid treatment with nitric acid, sulfuric acid or the like, and it is more preferable to use separation with a filter in combination for improving purity. In addition, not only the cut single-walled CNT but also a single-walled CNT prepared in a short fiber shape in advance is preferably used according to the present invention. Such short-fiber single-walled CNTs form a catalytic metal such as iron or cobalt on a substrate, and thermally decompose carbon compounds on the surface at 700 to 900 ° C. by CVD to vapor-grow single-walled CNTs. By doing so, it is obtained in a shape oriented in the direction perpendicular to the substrate surface. The short fiber single-walled CNTs thus produced can be taken out by a method such as peeling off from the substrate. In addition, the short fiber-like single-walled CNTs can be obtained by supporting a catalytic metal on a porous support such as porous silicon or an anodic oxide film of alumina and growing the single-walled CNTs on the surface thereof by the CVD method. Even in a method of producing single-walled CNTs on a substrate by using a molecule such as iron phthalocyanine containing a catalytic metal in the molecule and performing CVD in a gas flow of argon / hydrogen, an oriented short fiber-like single layer CNTs can be produced. Furthermore, it is also possible to obtain short fiber single-walled CNTs oriented on the SiC single crystal surface by an epitaxial growth method.

  The single-walled CNT used in the present invention is used by being dispersed in an organic semiconductor material, but it is preferable that the single-walled CNT is uniformly dispersed in a solvent before being added to the organic semiconductor material. Single-walled CNTs usually have a bunch-like structure composed of several tens or more, and a bunch-like structure even after a treatment for increasing the metallic CNT ratio. However, it is preferable to unwind the bundle structure and uniformly disperse it in the solvent, since it is possible to obtain better FET characteristics by unwinding the number of these wires to several. As a method for dispersing single-walled CNTs in a solvent, a method in which single-walled CNTs and a conjugated polymer are mixed in a solvent, and then dispersed by ultrasonic irradiation is preferably used. The ultrasonic irradiation can be performed using an ultrasonic cleaning machine or an ultrasonic homogenizer. An ultrasonic homogenizer is preferably used when dispersing in a short time with high efficiency.

  When the single-walled CNT and the conjugated polymer are mixed in the solvent, the single-walled CNT concentration is preferably in the range of 0.001 to 1 g / l. Moreover, it is preferable that the quantity of the conjugated polymer with respect to single layer CNT is about 0.5 to 10 times. More preferably, it is 1 to 2 times. By being in this range, while maintaining high dispersibility, a state where there is little excess conjugated polymer can be obtained, and a good single-walled CNT dispersion can be obtained.

  The ultrasonic irradiation output is preferably 100 to 500 W in the case of direct irradiation using an ultrasonic homogenizer or the like. 100-500W is preferable, when performing a distributed process by a batch type, 100-300W is more preferable, 200-750W is preferable, and 200-500W is more preferable when performing a distributed process by a continuous flow type. By being in this range, it is possible to obtain a good CNT dispersion while appropriately controlling the rise in liquid temperature due to ultrasonic irradiation of the dispersion. Moreover, the output of the ultrasonic wave in the case of indirect irradiation using an ultrasonic cleaner or the like is preferably 10 to 1000 W. The ultrasonic cleaners that are usually on the market are designed so that the output of the ultrasonic wave and the size of the cleaning tank are approximately proportional, so the output and the size of the cleaning tank are matched to the throughput of the single-walled CNT dispersion. It is preferable to use one having an output of about 100 W / cleaning tank of about 2 liters and an output of about 300 W / cleaning tank of about 10 liters. The frequency of the ultrasonic wave is preferably 20 to 100 kHz. In addition, a conjugated polymer may be added within the range of the above-mentioned blending ratio immediately before the end of the ultrasonic irradiation, thereby suppressing the re-aggregation of the single-walled CNT and improving the dispersion stability. be able to.

  Single-walled CNTs uniformly dispersed in the solvent by the above-described method are composed of a conjugated polymer and a single-walled CNT, but both are not simply a mixture, and the conjugated polymer is at least part of the single-walled CNT, Or it is thought that it is in the state which adhered to all. The reason why the conjugated polymer can adhere to the CNT is presumed to be that the π electron clouds derived from the respective conjugated structures overlap each other to cause an interaction. Whether or not the conjugated polymer is attached to the CNT can be determined by the reflection color of the CNT to which the conjugated polymer is attached approaching the color of the conjugated polymer. Quantitatively, the presence of deposits and the weight ratio of deposits to CNTs can be identified by elemental analysis or X-ray photoelectron spectroscopy (XPS). The conjugated polymer to be attached to the CNTs can be used regardless of the molecular weight, molecular weight distribution, or structure as long as it is a conjugated polymer.

  In the present invention, it is preferable to provide a step of filtering a single-walled CNT dispersion or a solution of an organic semiconductor material containing single-walled CNTs with a filter. By obtaining single-walled CNTs smaller than the filter pore diameter from the filtrate, CNTs shorter than the distance between the source electrode and the drain electrode can be obtained efficiently.

  As long as the filter used for filtration has a pore size smaller than the channel length, any type of filter such as a membrane filter, cellulose filter paper, or glass fiber filter paper can be used. Among them, the membrane filter can be preferably used because it can reduce the amount of CNT adsorbed inside the filter paper, and can recover single-walled CNT from the filtrate with high yield.

  The pore diameter of the filter used for filtration should be smaller than the channel length. For example, when the channel length is 20 μm, a short circuit between the electrodes can be reliably prevented by using a filter having a pore diameter of 10 μm. In practice, a filter having a pore diameter of 0.5 to 10 μm can be preferably used, and can be properly used according to the channel length.

  It is preferable that impurities such as raw materials and by-products used in the synthesis process be removed as much as possible from the organic semiconductor material used in the present invention. The purification method is not particularly limited, and a reprecipitation method, a Soxhlet extraction method, a filtration method, an ion exchange method, a chelate method, and the like can be used. In particular, when removing impurities such as monomers and by-products used during polymerization and dimers deactivated during polymerization, reprecipitation method or Soxhlet extraction method is preferably used. A precipitation method, a chelate method, and an ion exchange method are preferably used. Among these methods, one kind may be used alone, or a plurality may be combined.

  The organic transistor material of the present invention can be obtained, for example, by mixing the single-walled CNT and the organic transistor material, preferably in a solvent. More specifically, a method of mixing a single-walled CNT dispersion and an organic semiconductor material, a method of mixing a single-walled CNT dispersion and an organic semiconductor material solution, or the like is preferably used. After mixing these, it is preferable to dissolve and disperse by stirring using a magnetic stirrer or a stirring blade, or by vibration stirring by ultrasonic irradiation.

  Solvents for dissolving single-walled CNTs and organic semiconductor materials, and solvents used for CNT dispersions include methanol, ethanol, butanol, toluene, xylene, o-chlorophenol, acetone, ethyl acetate, ethylene glycol, chloroform, trichloroethane, trichloroethylene. , Chlorobenzene, dichlorobenzene, trichlorobenzene, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, and the like, but not limited thereto, and a solvent can be selected as necessary.

  The dispersibility and shape of the single-walled CNT in the single-walled CNT dispersion, or the dispersibility and shape of the single-walled CNT of the organic transistor material are applied by applying the single-walled CNT dispersion or organic transistor material solution on the substrate. The film can be evaluated by observing the film using an atomic force microscope (AFM). For example, if the single-walled CNT dispersion is applied as it is without being diluted, the dispersibility of the single-walled CNT in the film can be observed. Can be evaluated by observing the thickness and shape of the single-walled CNTs. In the CNT observation by AFM, due to the characteristics of the apparatus, the thickness in the width direction of the single-walled CNT is observed to be larger than the actual single-walled CNT thickness, but the value in the height direction represents the actual numerical value. Can be evaluated as the thickness of the single-walled CNT. In this way, it is possible to evaluate how much the single-walled CNTs have been agglomerated. Specifically, it is preferable that single-walled CNTs are unwound into a bundle of about 1 to 10.

  Next, the organic FET element of the present invention will be described. 1 and 2 are schematic cross-sectional views showing examples of the organic FET element of the present invention. A source electrode 5 and a drain electrode 6 such as gold are formed on a substrate 1 having a gate electrode 2 covered with an insulating layer 3, and then a semiconductor layer 4 is formed in this order. On the other hand, in FIG. 2, after the semiconductor layer 4 is formed on the substrate 1, the source electrode 5 and the drain electrode 6 such as gold are formed. By using the organic transistor material of the present invention for the semiconductor layer 4, an organic FET element having a low threshold voltage can be obtained. Note that the threshold voltage is a gate voltage at which a current flowing between a source and a drain of a transistor rises from off to on. Conventionally, when the semiconductor layer is formed of only an organic semiconductor material, the threshold voltage is 0 to 10 V, whereas in the organic FET element in which mobility is improved by 1 to 2 digits by containing a single layer CNT, There was a problem of being over 20V. However, as described above, by using single-walled CNT having an increased metallic CNT ratio, the threshold voltage can be reduced to 20 V or less, and a high-performance organic FET element that can be driven at a low voltage can be obtained. In the present invention, the semiconductor characteristics are mainly borne by the organic semiconductor material, and the single-walled CNT is responsible for smoothing the carrier path between the crystallites of the organic semiconductor material. Therefore, the higher the ratio of metallic CNT in single-walled CNT, the better.

  Examples of the material used for the substrate 1 include inorganic materials such as silicon wafers, glass and alumina sintered bodies, and organic materials such as polyimide, polyester, polycarbonate, polysulfone, polyethersulfone, polyethylene, polyphenylene sulfide, and polyparaxylene. It is done.

  Examples of the gate electrode 2, the source electrode 5, and the drain electrode 6 include conductive metal oxides such as tin oxide, indium oxide, and indium tin oxide (ITO), or platinum, gold, silver, copper, iron, tin, and zinc. , Aluminum, Indium, Chromium, Lithium, Sodium, Potassium, Cesium, Calcium, Magnesium, Palladium, Molybdenum, Metals such as amorphous silicon and polysilicon and their alloys, Inorganic conductive materials such as copper iodide and copper sulfide, Polythiophene , Polypyrrole, polyaniline, polyethylene dioxythiophene and polystyrene sulfonic acid complex, and conductive polymers whose conductivity is improved by doping with iodine, but are not limited thereto. These electrode materials may be used alone, or a plurality of materials may be laminated or mixed.

  Examples of the method for forming the gate electrode 2, the source electrode 5, and the drain electrode 6 include resistance heating vapor deposition, electron beam, sputtering, plating, CVD, ion plating coating, ink jet, and printing. If it is possible, there is no particular limitation. As a pattern forming method, a pattern can be directly formed by an ink jet technique or a screen printing technique, and a lift-off method using a photoresist, photosensitivity is imparted to an electrode component or a semiconductor layer component, and photolithography is used. Method, pattern etching method of film, method of forming pattern by forming hydrophilic surface and water-repellent surface on substrate surface using photoresist, method of patterning by wiping or scraping the removed portion after coating the entire surface Alternatively, any method such as a method of forming a pattern through a mask having a desired shape at the time of electrode material vapor deposition or sputtering can be used.

  Although it does not specifically limit as a material used for the insulating layer 3 (gate insulating film), Specifically, inorganic materials, such as a silicon oxide and an alumina, a polyimide, polyvinyl alcohol, polyvinyl chloride, a polyethylene terephthalate, a polyvinylidene fluoride, a polymethylmethacrylate, Organic polymer materials such as polystyrene and polyparaxylene, or a mixture of inorganic material powder and organic polymer material can be used. The method for forming the insulating layer is not particularly limited, but resistance heating vapor deposition, electron beam, sputtering, CVD, ion plating, spin coating method, casting method, dip method, bar coater method, dropping method, spray method, A blade coating method, a slit die coating method, a screen printing method, a mold coating method, a printing transfer method, a dip pulling method, an ink jet method, and the like can be mentioned, and they can be used depending on the material.

  The thickness of the insulating layer 3 is not particularly limited, but is generally 50 nm to 3 μm, preferably 100 nm to 1 μm. The insulating layer may be composed of a single layer or a plurality of layers. In the case of a single layer, it may be formed by mixing a plurality of insulating materials. In the case of a plurality of layers, a plurality of insulating materials are laminated. May be formed.

  As a method for forming the semiconductor layer 4, any method such as a spin coating method, a blade coating method, a slit die coating method, a screen printing method, a bar coater method, a mold method, a printing transfer method, a dip pulling method, an ink jet method, a dispensing method, etc. The coating method can be selected according to the properties of the coating film to be obtained, such as coating thickness control and orientation control. For example, when spin coating is performed, a coating film having a thickness of 5 to 200 nm can be obtained when the concentration of the organic semiconductor material solution is 1 to 20 g / l. The formed coating film may be annealed in the air, under reduced pressure, or in an inert gas atmosphere (in a nitrogen or argon atmosphere).

  The thickness of the semiconductor layer 4 is preferably 5 nm or more and 100 nm or less. By setting the film thickness within this range, it becomes easy to form a uniform thin film, and further, the source-drain current that cannot be controlled by the gate voltage can be suppressed, and the on / off ratio of the organic FET element can be further increased. The film thickness can usually be measured by an atomic force microscope or an ellipsometry method. The semiconductor layer may be a single layer or a plurality of layers. In the case of a single layer, it may be formed by mixing a plurality of organic semiconductor materials. In the case of a plurality of layers, a plurality of organic semiconductor materials may be stacked. Absent.

  In addition, an orientation layer can be provided between the insulating layer 3 and the semiconductor layer 4. A well-known material, such as a silane compound, a titanium compound, an organic acid, and a hetero organic acid, can be used for the orientation layer, and a silane compound is preferably used. In the silane compound, a part or all of the silane residues react with the surface of the insulating layer and chemically bond to form a thin film. In order to facilitate the reaction, the silane residue preferably has a halogen atom, a hydroxyl group or an alkoxy group. The orientation layer not only improves the wettability of the surface of the insulating layer and improves the film forming ability of the semiconductor layer, but also has the effect of enhancing the orientation of the organic transistor material and further improving the mobility.

  In the organic FET element thus formed, the current flowing between the source electrode and the drain electrode can be controlled by changing the gate voltage. The mobility of the organic FET element can be calculated using the following equation (a).

μ = (δId / δVg) L · D / (W · ε r · ε · Vsd) (a)
Where Id is the source-drain current (A), Vsd is the source-drain voltage (V), Vg is the gate voltage (V), D is the thickness of the insulating layer (m), and L is the channel length (m). , W is the channel width (m), ε _r is the dielectric constant of the insulating layer (here, SiO ₂ 3.9 is used), and ε is the vacuum dielectric constant (8.85 × 10 ⁻¹² F / m). is there.

  Further, the on / off ratio can be obtained from the ratio of the value of Id (on current) at a certain negative gate voltage to the value of Id (off current) at a certain positive gate voltage.

  Furthermore, the threshold voltage can be obtained by extrapolating the drain current Id = 0 from the relationship between the square root of the absolute value of the drain current and the gate voltage.

  Hereinafter, the present invention will be described more specifically based on examples. However, the present invention is not limited to the following examples.

Example 1
First, a process of increasing the metallic CNT ratio by reducing the semiconducting CNT ratio was performed. As the CNT, single-walled carbon nanotubes (HiPco CNT purchased from Science Laboratories, Inc., purity 95%) were used as they were without purification. 5 mg of CNT and 2 ml of 30% hydrogen peroxide solution were placed in a flask and heat-treated in an oil bath at 90 ° C. for 3 hours while stirring. The treated CNTs were collected on a membrane filter having a pore diameter of 0.45 μm using a suction filter, washed with water, and then vacuum-dried to obtain 1.1 mg of oxidized CNTs (22% yield).

  Next, poly-3-hexylthiophene (hereinafter abbreviated as P3HT) (manufactured by Aldrich, regioregular) was purified by a reprecipitation method. Add 5 ml of chloroform to 20 mg of P3HT, dissolve, filter through a membrane filter with a pore size of 0.45 μm, drop the filtrate into a mixture of 15 ml of methanol and 15 ml of 0.1 N hydrochloric acid, and filter the precipitated P3HT. Was collected on a membrane filter having a pore diameter of 0.45 μm, and the solvent was removed by vacuum drying. This procedure was repeated twice for purification.

  Next, a CNT dispersion was prepared using P3HT purified by the above method. Add 1.5 mg of oxidized CNT, 1.5 mg of purified P3HT, and 30 ml of chloroform into a 50 ml sample tube to prepare a CNT mixture, ultrasonic homogenizer (VCX-502, Tokyo Rika Kikai Co., Ltd., output 250 W, direct irradiation) ) Was used for ultrasonic irradiation. The ultrasonic homogenizer uses a titanium alloy probe with a diameter of 13 mm for ultrasonic irradiation, and the surface of the probe is polished in advance with fine sandpaper so that the surface roughness Ra is 1 μm or less. used. When the ultrasonic irradiation was performed for 30 minutes, the irradiation was stopped once, 1.5 mg of purified P3HT was added, and the ultrasonic irradiation was further performed for 1 minute, and the CNT dispersion a (solvent with the conjugated polymer attached to the surface) (solvent CNT concentration to 0.05 g / l and P3HT concentration to solvent 0.1 g / l).

  Here, it was confirmed by the following method that the conjugated polymer adhered to the surface of the CNT in the CNT dispersion a. The CNT dispersion a3 ml was filtered using a membrane filter having a pore diameter of 0.1 μm and a diameter of 13 mm, washed twice with 3 ml of chloroform, and a CNT film was formed on the filter. Next, the CNT film was pressed onto a 3 cm square clean silicon wafer, transferred, and vacuum dried. When the CNT film was analyzed by X-ray electron spectroscopy (XPS), sulfur element contained in P3HT was detected, and it was found that a conjugated polymer was attached to the surface of CNT.

  Subsequently, the CNT dispersion a (CNT concentration 0.05 g / l) was applied onto a 3 cm square glass substrate to form a single-layer CNT film, and wavelengths of 1000 nm and 1200 nm using a spectrophotometer (H3410 manufactured by Hitachi, Ltd.). The absorbance at was measured. The application was repeated 10 times using a spin coater to form a single-wall CNT film having a thickness of 35 nm. The absorbance at a wavelength of 1200 nm at which the intrinsic absorption of semiconducting CNT appears was 0.027. The absorbance at a wavelength of 1000 nm, which depends only on the film thickness, was 0.036. That is, the value of B / A was 0.75.

  Next, a coating solution for the semiconductor layer was prepared. Chloroform is added to the above dispersion a to dilute to 0.02 g / l, and filtration is performed using a membrane filter (pore size 10 μm, diameter 25 mm, Omnipore membrane manufactured by Millipore) to remove CNTs having a length of 10 μm or more. did. The filtrate contained most of the CNTs. The obtained filtrate was designated as CNT dispersion c. CNT dispersion c0.6 ml, chloroform 0.4 ml, and purified P3HT 3 mg are put into a sample tube with a volume of 10 ml, and an ultrasonic cleaner (US-2 manufactured by Inoue Seieido Co., Ltd., output 120 W, indirect irradiation) is used. For 30 minutes, the coating solution for the semiconductor layer (concentration of P3HT with respect to the solvent was 3 g / l, concentration of CNT with respect to the solvent was about 0.012 g / l, and the weight of CNT with respect to 100 parts by weight of P3HT was 0.4 wt. Part).

  Next, an organic field effect transistor was fabricated in the following manner. The structure of this organic FET element is shown in FIG.

The substrate of the organic FET element was an antimony-doped silicon wafer (resistivity 0.02 Ωcm or less) with a SiO ₂ film (film thickness 300 nm) formed by thermal oxidation. Here, the silicon wafer is the substrate 1 as well as the gate electrode 2, and the thermal oxide film is the insulating layer 3. Next, a gold source electrode 5 and a drain electrode 6 were formed based on the following procedure. A positive resist solution was dropped onto a silicon wafer with a thermal oxide film, applied using a spinner, and then dried on a hot plate at 90 ° C. to form a resist film. Subsequently, ultraviolet rays were irradiated through a photomask using an exposure machine. Next, the wafer with the resist film was immersed in an alkaline aqueous solution, the ultraviolet irradiation part was removed, and a resist film having a shape in which the comb-shaped electrode was removed was obtained. On the wafer with the resist film, chromium was vacuum-deposited to a thickness of 5 nm, and then gold was vacuum-deposited to a thickness of 45 nm. Next, the gold / chrome on the resist was removed by immersing the wafer with gold / chromium and the resist in acetone and irradiating the wafer with an ultrasonic cleaner. In this manner, gold comb electrodes were formed on the wafer. The width (channel width) of both electrodes was 0.5 cm, the distance (channel length) between both electrodes was 20 μm, and the electrode height was 50 nm.

  Next, 0.05 ml of a coating solution for a semiconductor layer is dropped on the channel formed by the above-described source electrode and drain electrode, and a thin film having a thickness of 25 nm is formed by spin coating (rotation speed: 1000 rpm, 0.3 seconds). Formed. At this time, neither the source electrode nor the drain electrode was eluted or eroded by chloroform contained in the polymer composite solution, and it was confirmed from observation with an optical microscope that the original shape was maintained. After the lead wires were attached to the source and drain electrodes using silver wire and silver paste, they were left in a vacuum dryer at 110 ° C. for 2 hours, slowly cooled to 50 ° C. or lower, and taken out from the dryer. . Thus, an organic FET element was produced.

  The obtained organic FET element was moved to a measurement box, left in a vacuum for 18 hours, and then the current-voltage characteristics were measured to examine the FET characteristics. As a measuring device, a semiconductor characteristic evaluation system 4200-SCS manufactured by Keithley Instruments Inc. was used, and the measurement box kept a reduced pressure state of 1 torr or less.

When the gate-voltage (Vg) of the organic FET element was changed, the source-drain current (Isd) −source-drain voltage (Vsd) were measured to determine the FET characteristics. The mobility was 3.0 × 10 ^{− A} very good value of ² cm ² / V · sec, an on / off ratio of 8.5 × 10 ⁴ , and a threshold voltage of 11 V were obtained.

Example 2
The same operation as in Example 1 was performed except that the hydrogen peroxide treatment of CNT was changed from 3 hours to 1 hour. The yield of CNT after the oxidation treatment was 3 mg (yield 60%). The absorbance of the single-wall CNT film having a thickness of 35 nm was measured at a wavelength of 1000 nm and 1200 nm, which were 0.036 and 0.029, respectively, and the value of B / A was 0.81.

A coating solution for a semiconductor layer was prepared using the CNTs to produce an organic FET element. The FET characteristics were determined by measuring the source-drain current (Isd) -source-drain voltage (Vsd) when the gate voltage (Vg) of the organic FET element was changed, and the mobility was 3.6 × 10 ⁻ Good values of ² cm ² / V · sec, an on / off ratio of 2.2 × 10 ⁴ , and a threshold voltage of 17 V were obtained.

Example 3
The same operation as in Example 1 was performed except that the hydrogen peroxide treatment of CNT was changed from 3 hours to 5 hours. The yield of CNT after the oxidation treatment was 0.3 mg (yield 6%). The absorbance of the single-wall CNT film having a thickness of 35 nm was measured at a wavelength of 1000 nm and 1200 nm, which were 0.036 and 0.022, respectively, and the value of B / A was 0.61.

A coating solution for a semiconductor layer was prepared using the CNTs to produce an organic FET element. When the gate-voltage (Vg) of the organic FET element was changed, the source-drain current (Isd) −source-drain voltage (Vsd) were measured to determine the FET characteristics. The mobility was 2.3 × 10 ⁻ Good values of ² cm ² / V · sec, an on / off ratio of 8.0 × 10 ⁴ , and a threshold voltage of 10 V were obtained.

Example 4
The same operation as in Example 1 was performed except that the CNT treated in Example 1 was used and the weight of CNT with respect to 100 parts by weight of P3HT was changed from 0.4 parts by weight to 0.1 parts by weight. When an organic FET element was produced, the source-drain current (Isd) -source-drain voltage (Vsd) when the gate voltage (Vg) of the organic FET element was changed was measured, and the FET characteristics were obtained. The degree was 1.1 × 10 ⁻² cm ² / V · sec, the on / off ratio was 1.0 × 10 ⁵ , and the threshold voltage was 9 V. Good values were obtained.

Example 5
The same operation as in Example 1 was performed except that the CNT treated in Example 1 was used and the weight of CNT with respect to 100 parts by weight of P3HT was changed from 0.4 part by weight to 1.0 part by weight. When an organic FET element was produced, the source-drain current (Isd) -source-drain voltage (Vsd) when the gate voltage (Vg) of the organic FET element was changed was measured, and the FET characteristics were obtained. The degree was 5.2 × 10 ⁻² cm ² / V · sec, the on / off ratio was 1.1 × 10 ⁴ , and the threshold voltage was 15 V. Good values were obtained.

Example 6
The same operation as in Example 1 was performed except that the CNT treated in Example 1 was used and the weight of CNT relative to 100 parts by weight of P3HT was changed from 0.4 parts by weight to 2.0 parts by weight. When an organic FET element was produced, the source-drain current (Isd) -source-drain voltage (Vsd) when the gate voltage (Vg) of the organic FET element was changed was measured, and the FET characteristics were obtained. The degree was 9.2 × 10 ⁻² cm ² / V · sec, the on / off ratio was 1.1 × 10 ³ , and the threshold voltage was 19V.

Example 7
The following compound [1] was synthesized by the following method as the compound represented by the general formula (1). In addition, ¹ H-NMR for synthetic compound identification was measured with a deuterated chloroform solution using superconducting FT-NMR “EX-270” (manufactured by JEOL Ltd.).

  60 g of 3-n-hexylthiophene was dissolved in 400 ml of dimethylformamide, 50 g of N-bromosuccinimide was added, and the mixture was stirred at room temperature for 4 hours under a nitrogen atmosphere. 200 ml of water and 200 ml of hexane were added to the resulting solution, and the organic layer was separated. After washing with 200 ml of water, it was dried over magnesium sulfate. From the obtained solution, the solvent was distilled off under reduced pressure using a rotary evaporator to obtain 60 g of 2-bromo-3-n-hexylthiophene.

  Next, 4.3 g of magnesium powder and 10 mg of iodine were added to 100 ml of tetrahydrofuran and stirred for 30 minutes under a nitrogen atmosphere. A mixed solution of 42 g of 2-bromo-3-n-hexylthiophene and 100 ml of tetrahydrofuran was added dropwise thereto, and the mixture was heated to reflux for 1 hour. After cooling to room temperature, a mixed solution of 20 g of 5,5′-dibromo-2,2′-bithiophene and 200 ml of tetrahydrofuran was added, and 0.48 g of diphenylphosphinopropanenickel (II) dichloride was added little by little, and under a nitrogen atmosphere. Heated to reflux for 3 hours. To the obtained solution, 800 ml of 1N aqueous ammonium chloride solution and 600 ml of hexane were added, and the organic layer was separated. The extract was washed with 200 ml of a saturated aqueous sodium hydrogen carbonate solution and 200 ml of water, and then dried over magnesium sulfate. The resulting solution was concentrated by a rotary evaporator and purified by column chromatography (filler: silica gel, eluent: hexane) to obtain 28 g of 4T represented by the following formula.

  After cooling a mixed solution of 16.3 g of the above 4T and 20 ml of tetrahydrofuran to −30 ° C., 21 ml of n-butyllithium solution (1.6 mol / l hexane solution) was added dropwise and stirred at room temperature for 1 hour. The mixed solution was cooled to −10 ° C., 5.7 g of 2-isoporopoxy-4,4,5,5-tetramethyl- [1,3,2] dioxaborolane was added, and the mixture was stirred at room temperature for 3 hours. To the obtained solution, 33 ml of 1N hydrochloric acid aqueous solution, 200 ml of water and 200 ml of dichloromethane were added, and the organic layer was separated. After washing with 100 ml of water, it was dried over magnesium sulfate. The resulting solution was concentrated by a rotary evaporator and then purified by column chromatography (filler: silica gel, eluent: hexane / dichloromethane) to obtain 11 g of 4T-BPin represented by the following formula.

To a mixed solution of 1.6 g of the above 4T-BPin, 0.34 g of 4,4′-dibromostilbene and 50 ml of toluene, 10 ml of ethanol, 15 ml of 2N sodium carbonate aqueous solution and 31 mg of tetrakis (triphenylphosphine) palladium (0) The mixture was refluxed at 110 ° C. for 9 hours under a nitrogen stream. The solid precipitated in the resulting solution was collected by filtration, washed with 20 ml of water, 20 ml of ethanol, and 20 ml of toluene, and then recrystallized from toluene. After vacuum drying, 0.90 g of orange powder was obtained. The results of ¹ H-NMR analysis of the obtained powder are as follows and confirmed to be compound [1].
¹ H-NMR (CDCl ₃ (d = ppm)): 0.89-0.93 (t, 12H), 1.26-1.42 (m, 24H), 1.57-1.68 (m, 8H), 2.74-2.82 (m, 8H), 6.93-6.96 (m, 6H), 7.02 (d, 2H), 7.06 (d, 2H), 7.13-7.24 (m, 8H), 7.52-7.63 (dd, 8H)
A coating solution for the semiconductor layer was prepared in the same manner as in Example 3 except that the semiconductor layer was changed from P3HT to compound [1] to prepare an organic FET element. The CNT was treated with hydrogen peroxide for 5 hours. The absorbance of the single-walled CNT film having a thickness of 35 nm at a wavelength of 1000 nm and 1200 nm was 0.036 and 0.022, respectively, and the B / A value was 0.61. The thing of was used. When the gate-voltage (Vg) of the organic FET element was changed, the source-drain current (Isd) -source-drain voltage (Vsd) was measured to determine the FET characteristics. The mobility was 4.7 × 10 ⁻ Good values of ² cm ² / V · sec, an on / off ratio of 8.5 × 10 ⁴ , and a threshold voltage of 11 V were obtained.

Comparative Example 1
The same operation as in Example 1 was performed except that CNT was not subjected to hydrogen peroxide treatment. A single-walled CNT film having a thickness of 35 nm was obtained by applying CNT dispersion b (CNT concentration 0.05 g / l) prepared by the above-described dispersion method onto a glass substrate using CNT that had not been subjected to hydrogen peroxide treatment. When the absorbance was measured at wavelengths of 1200 nm and 1000 nm, it was 0.037 and 0.037, respectively, and the value of B / A was 1.0.

A coating solution for a semiconductor layer was prepared using the CNTs to produce an organic FET element. When the gate-voltage (Vg) of the organic FET element was changed, the source-drain current (Isd) −source-drain voltage (Vsd) were measured to determine the FET characteristics. The mobility was 4.3 × 10 ^{− 2} cm ² / V · sec and the on / off ratio were as good as 3.0 × 10 ⁴ , but the threshold voltage was as large as 25V.

Comparative Example 2
A coating solution for the semiconductor layer was prepared in the same manner as in Comparative Example 1 except that the semiconductor layer was changed from P3HT to compound [1] to prepare an organic FET element. CNTs that had not been subjected to hydrogen peroxide treatment were used. Absorbance at a wavelength of 1200 nm and 1000 nm of a CNT film having a thickness of 35 nm was 0.037 and 0.037, respectively, and a B / A value was 1.0. Using. When the gate-voltage (Vg) of the organic FET element was changed, the source-drain current (Isd) −source-drain voltage (Vsd) were measured to determine the FET characteristics. The mobility was 6.5 × 10 ^{− 2} cm ² / V · sec and the on / off ratio were 4.0 × 10 ⁴ and good values, but the threshold voltage was as high as 27V.

  Table 1 shows the evaluation results of the examples and comparative examples.

  The organic FET element of the present invention can be produced by using a low-cost process such as a coating method, and has excellent characteristics such as high mobility and low threshold voltage. Therefore, a liquid crystal display, an electroluminescence (EL) display, an electronic paper display, etc. Used for thin film transistors. It is also used in smart cards and security tag transistors.

Schematic sectional view showing an organic FET element which is one embodiment of the present invention Schematic sectional view showing an organic FET element which is another embodiment of the present invention

Explanation of symbols

1 Substrate 2 Gate electrode 3 Insulating layer 4 Semiconductor layer 5 Source electrode 6 Drain electrode

Claims (6)

An organic transistor material including a single-walled carbon nanotube and an organic semiconductor material, wherein a ratio (B / A) of absorbance (B) at a wavelength of 1200 nm to absorbance (A) at a wavelength of 1000 nm of a film obtained from the single-walled carbon nanotube Organic transistor material that is less than 1.0. The organic transistor material according to claim 1, wherein the single-walled carbon nanotube is treated with hydrogen peroxide. The organic transistor material according to claim 1 or 2, wherein a conjugated polymer is attached to at least a part of the surface of the single-walled carbon nanotube. The organic transistor material according to claim 1, wherein the organic semiconductor material is an organic low molecular weight semiconductor having a molecular weight of 3000 or less containing a thiophene skeleton. The organic transistor material according to claim 1, comprising 0.01 to 3 parts by weight of single-walled carbon nanotubes with respect to 100 parts by weight of the organic semiconductor material. An organic field effect transistor having a gate electrode, an insulating layer, a semiconductor layer, a source electrode, and a drain electrode, wherein the semiconductor layer uses the organic transistor material according to any one of claims 1 to 5. Transistor.

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