JP5472590B2 - Organic semiconductor material and organic thin film transistor using the same - Google Patents

Description

  The present invention provides an organic semiconductor material having a novel structural unit, and further, an organic electronic material having excellent solubility necessary for carrying out a simple liquid film forming process, and an organic thin film transistor using the same About.

In recent years, research and development on organic electronic devices using organic semiconductor materials has been active.
Organic semiconductor materials can be easily formed into thin films by a simple process using a wet process such as a printing method, spin coating method, etc., and the manufacturing process temperature can be lowered as compared with a thin film transistor using a conventional inorganic semiconductor material. There is an advantage.
This enables formation on plastic substrates with generally low heat resistance, which can realize weight reduction and cost reduction of electronic devices such as displays, and various developments such as applications that take advantage of the flexibility of plastic substrates. Can be expected.

So far, as organic semiconductor materials, molecules have a planar structure, so it is possible to take a dense packing form, and relatively high semiconductor characteristics can be obtained, so there are many studies using thiophene molecules as the main skeleton. It is done.
For example, as a polymer material, poly (3-alkylthiophene) into which an alkyl group is introduced has been proposed for the purpose of providing solubility in an organic solvent and driving force for orienting molecules (Non-patent Document 1). reference).
Since this organic semiconductor material has low solubility, it can be thinned by coating or printing without going through a vacuum deposition process. However, this poly (3-alkylthiophene) is easily oxidized, and the organic thin film transistor using this as an active layer has unstable operation in the atmosphere.
In contrast, polythiophenes with improved oxidation stability have also been proposed (see Patent Document 1 and Patent Document 2).
However, in general, high-molecular-weight organic semiconductor materials, including these, are limited in purification methods, and it is very time-consuming to obtain high-purity materials, and there are molecular weights and molecular weight distributions. Has the fundamental problem of lack of stability.

On the other hand, in order to overcome the drawbacks of the polymer system, many organic thiophene skeletons have been studied for oligothiophenes (see, for example, Non-Patent Document 2).
Organic thin-film transistors using oligothiophene as an organic semiconductor layer have been reported to have relatively high mobility, but these materials are not substituted with alkyl groups, so they are extremely soluble in general-purpose solvents. However, when it is thinned as an active layer in an organic thin film transistor, it is necessary to go through a vacuum deposition process. Therefore, it does not meet the expectation for an organic semiconductor material that a thin film can be formed by a simple process such as coating and printing as described above.

In addition, oligothiophenes in which an alkyl group is introduced at the α-position or β-position have been proposed (see, for example, Non-Patent Document 3 and Non-Patent Document 4). It became clear that the solubility in solvents was never satisfactory.
Oligothiophenes based on molecular design guidelines that take solubility into account have also been proposed (see Non-Patent Document 5), but the thin films obtained by film formation do not have continuity and are suitable for device fabrication. The molecular structure is difficult.
Improving solubility and film formability is important from the viewpoint of device fabrication, and further material development is desired.

  The present invention has been made in view of the above-described conventional technology, has very high solubility in general-purpose solvents, can be applied to a low-cost process capable of wet film formation, and easily has high homogeneity. An object is to provide an organic semiconductor material composed of oligothiophenes useful as a material for organic electronics capable of obtaining a thin film, and an organic thin film transistor using the same.

In view of the above problems, as a result of intensive investigations, the present inventors have found that in order to obtain a highly homogeneous thin film, it is important to maintain solubility in a general-purpose solvent and to control the crystallization rate of the thin film after coating. Therefore, the present inventors have found that the above problems can be solved by an organic semiconductor material composed of oligothiophenes containing a specific structural unit and an organic thin film transistor using the same.
That is, this invention is shown by the following (1) to (4).
(1) “An organic semiconductor material represented by the following general formula (I):

（式中、Ｒ_１およびＲ_２は、互いに異なるアルキル基を表わし、ｘおよびｙは、それぞれ独立に１または２の整数を表わす。）」、
（２）「少なくとも前記第（１）項記載の有機半導体材料と少なくとも１種類の有機溶媒を含むことからなる液体組成物」、
（３）「支持体上に形成され少なくとも前記第（１）項記載の有機半導体材料を含むことを特徴とする有機膜」、
（４）「有機半導体層と、この有機半導体層を通じて電流を流すための対をなす電極を設けてなる構造体と、第三の電極とからなる有機半導体薄膜トランジスタにおいて、有機半導体層が前記第（３）項の有機膜であることを特徴とする有機薄膜トランジスタ」。

(Wherein R ₁ and R ₂ represent different alkyl groups, and x and y each independently represents an integer of 1 or 2) ”
(2) “a liquid composition comprising at least the organic semiconductor material according to item (1) and at least one organic solvent”,
(3) "An organic film formed on a support and containing at least the organic semiconductor material according to item (1)",
(4) “In an organic semiconductor thin film transistor comprising an organic semiconductor layer, a structure having a pair of electrodes for passing a current through the organic semiconductor layer, and a third electrode, the organic semiconductor layer is the first ( An organic thin film transistor characterized by being an organic film according to item 3).

  The organic semiconductor material of the present invention is useful as a material for an active layer of a thin film transistor because it is soluble in various organic solvents, enables low-cost wet film formation, and provides a thin film with high homogeneity. is there.

Schematic of the organic thin film transistor of the present invention Infrared absorption spectrum of the organic semiconductor material of the present invention obtained in Example 1 of the present invention Polarized microscope observation photograph (400 times) of the organic film of Compound 1 formed in Example 2 of the present invention ((a) Open Nicol, (b) Crossed Nicol) Current-Voltage (IV) Characteristic Chart of Organic Thin Film Transistor Produced in Example 3 of the Present Invention

  The organic semiconductor material of the present invention represented by the following general formula (I) is useful as a material for organic electronics such as a charge transporting material for organic thin film transistors.

（式中、Ｒ_１およびＲ_２は、互いに異なるアルキル基を表わし、ｘおよびｙは、それぞれ独立に１または２の整数を表わす。）

(Wherein R ₁ and R ₂ represent different alkyl groups, and x and y each independently represents an integer of 1 or 2)

Specific examples of the alkyl group include methyl group, ethyl group, n-propyl group, i-propyl group, t-butyl group, s-butyl group, n-butyl group, i-butyl group, pentyl group, hexyl group, Heptyl group, octyl group, nonyl group, decyl group, dodecyl group, 3,7-dimethyloctyl group, 2-ethylhexyl group, trifluoromethyl group, 2-cyanoethyl group, benzyl group, 4-chlorobenzyl group, 4-methyl A benzyl group, a cyclopentyl group, a cyclohexyl group, etc. can be mentioned as an example.
As mentioned in the above example, a branched chain may be introduced, but since it may adversely affect the packing of crystals, the introduction of a straight chain is more preferable.

Below, the manufacturing method of the organic-semiconductor material of this invention is demonstrated.
As a method for producing the compound represented by the general formula (I) of the present invention, a method using a Grignard reaction in which an Ar ₁ -Ar ₂ structure is formed from a halide Ar ₁ -X and a Grignard reagent Ar ₂ -MgX, a palladium catalyst is used. A method by Suzuki coupling reaction in which an organic halide having a structure of Ar ₁ -X and a boron compound having a structure of (R ² O) ₂ B—Ar ₂ are cross-coupled to form an Ar ₁ -Ar ₂ structure, Method by Stille coupling reaction in which Ar ₁ -Ar ₂ is formed by cross-coupling of organohalogen compound Ar ₁ -X and organotin compound Ar ₂ -SnR ₃ , Kumada coupling reaction, method by Negishi coupling reaction, Hiyama Coupling reaction method, So Examples of the known method include various coupling reactions represented by a nogashira reaction method, a Heck reaction method, a Wittig reaction method, and the like.
Of these, the Grignard reaction method, the Suzuki coupling reaction or the Stille coupling reaction method is particularly preferable from the viewpoints of reactivity and yield that the intermediate can be easily derivatized.

In the case of the Grignard reaction, a halide reagent of thiophene and metal Mg are reacted in an ether solvent such as tetrahydrofuran, diethyl ether, dimethoxyethane or the like to form a Grignard reagent solution, and a monomer solution prepared separately is mixed. An example is a method in which a nickel or palladium catalyst is added while paying attention to excess reaction, and then the reaction is carried out while refluxing at elevated temperature.
The Grignard reagent is used in an equivalent amount or more, preferably 1 to 1.5 equivalents, more preferably 1 to 1.2 equivalents, relative to the monomer. When synthesizing by a method other than these, the reaction can be carried out according to a known method.
In the case of the Suzuki coupling reaction, a method of reacting a thiophene halide with a boronic acid or boronic acid ester of thiophene in the presence of a palladium catalyst and a base is exemplified.
In the case of the Stille coupling reaction, a method of reacting a thiophene halide with a thiophene trialkyltin in the presence of a palladium catalyst is exemplified.

  An example of the organic semiconductor material of the present invention that can be obtained by the synthesis methods listed above is shown below, but is not limited thereto.

The organic semiconductor material obtained as described above is used after removing impurities such as catalysts, inorganic salts, unreacted raw materials, and by-products used in the reaction.
For the purification operation, conventionally known methods such as recrystallization, various chromatographic methods, sublimation purification, reprecipitation, extraction, Soxhlet extraction, ultrafiltration, dialysis and the like can be used.
Since contamination with impurities adversely affects the semiconductor characteristics, it is desirable to make the purity as high as possible.
The material of the present invention having excellent solubility has less restrictions on these purification methods, and as a result, has a positive effect on semiconductor characteristics.

A liquid composition can be prepared by dissolving the organic semiconductor material of the present invention obtained by the above production method in an organic solvent.
Examples of the organic solvent that can be used include dichloromethane, chloroform, carbon tetrachloride, tetrahydrofuran, dioxane, cyclohexanone, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, n-hexane, cyclohexane, n-octane, n-decane, and n-dodecane. , Dimethylformamide, benzene, toluene, cumene, o-xylene, m-xylene, p-xylene, p-cymene, mesitylene, anisole, 2-methylanisole, 3-methylanisole, 4-methylanisole, 2,5-dimethyl Anisole, 3,5-dimethoxytoluene, 2,4-dimethylanisole, phenetol, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, 1,5-dimethyltetralin, n-propylbenzene, n- Tylbenzene, n-pentylbenzene, 1,3,5-triethylbenzene, 1,3-dimethoxybenzene, pyridine, nitrobenzene, aniline, N-methylaniline, N, N-diethylaniline, benzonitrile, N-methylpyrrolidone, dimethyl Sulfoxide, 2-fluorotoluene, 3-fluorotoluene, 2,5-difluorotoluene, 2-fluoroanisole, 3-fluoroanisole, 4-fluoroanisole, 4-fluoro-3-methylanisole, 3-trifluoromethylanisole, Examples include bromobenzene, chlorobenzene, o-dichlorobenzene, trichlorobenzene and the like, but the use is not limited thereto.
The concentration of the organic semiconductor material of the present invention in the prepared liquid composition is preferably 0.01 to 20% by weight, and more preferably 0.1 to 10% by weight.
One kind of organic solvent may be used, but a plurality of kinds of solvents may be mixed and used in order to obtain a desired thin film with high homogeneity.

The organic film of the present invention can be formed into a thin film by applying a liquid composition containing the organic semiconductor material prepared as described above onto a support.
For example, spin coating method, casting method, dipping method, ink jet method, doctor blade method, screen printing method, offset printing method, letterpress printing method, micro contact printing method, wire bar coating method, spray coating method, dispensing method It is possible to produce a thin film by a known wet film formation method such as. Further, depending on the casting method or the like, it may be in the form of a flat crystal or a thick film state.
These thin films, thick films, or crystals function as charge transporting members for various functional elements such as photoelectric conversion elements, thin film transistors, and light emitting elements.
The organic semiconductor material of the present invention can also be formed by a dry process such as a vacuum deposition method.

Next, the organic thin film transistor of the present invention will be described with reference to a schematic structural diagram in FIG.
The organic semiconductor layer (1) constituting the organic thin film transistor is mainly composed of the compound represented by the general formula (I) of the present invention.

The organic thin film transistor has a first electrode (source electrode) (2) and a second electrode (drain electrode) (3) which are separated and formed through an organic semiconductor layer (1), and is opposed to these. A third electrode (gate electrode) (4) is provided. An insulating film (5) may be provided between the gate electrode (4) and the organic semiconductor layer (1).
In the organic thin film transistor, a current flowing in the organic semiconductor layer (1) between the source electrode (2) and the drain electrode (3) is controlled by applying a voltage to the gate electrode (4).

The organic thin film transistor of the present invention is formed on a predetermined support.
A conventionally known substrate material can be applied as the support, and examples thereof include glass, silicon, and plastic. By using a conductive substrate, the gate electrode (4) can also be used.

In addition, the gate electrode (4) and the conductive substrate may be laminated, but when the organic thin film transistor of the present invention is applied to a device, practical aspects such as flexibility, weight reduction, low cost, impact resistance, etc. In order to improve the above characteristics, it is preferable to use a plastic sheet as the support, and in general, a substrate having a smooth surface is preferably used.
Examples of the plastic sheet include polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate, cellulose triacetate, cellulose acetate propionate, and the like. It is done.

In the organic film and the organic thin film transistor of the present invention, the thickness of the organic semiconductor layer is not particularly limited, but a uniform thin film (that is, there is no gap or hole that adversely affects the carrier transport property of the organic semiconductor layer) is formed. Thickness is selected.
The thickness of the organic semiconductor thin film is generally 1 μm or less, particularly preferably 5 to 200 nm.

Next, components other than the organic semiconductor layer in the organic thin film transistor of FIG. 1 will be described.
The organic semiconductor layer (1) is formed in contact with the first electrode (source electrode), the second electrode (drain electrode), and, if necessary, the insulating film (5).

The insulating film (5) will be described.
The insulating film constituting the organic thin film transistor is formed using various insulating film materials.
For example, silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, titanium oxide, tantalum oxide, tin oxide, vanadium oxide, barium strontium titanate, zirconium barium titanate, lead zirconate titanate, lead lanthanum titanate, titanate Examples thereof include inorganic insulating materials such as strontium, barium titanate, barium magnesium fluoride, bismuth tantalate niobate, and yttrium trioxide.
Also, for example, polymer compounds such as polyimide, polyvinyl alcohol, polyvinylphenol, polyester, polyethylene, polyphenylene sulfide, polystyrene, polymethacrylic acid ester, unsubstituted or halogen atom-substituted polyparaxylylene, polyacrylonitrile, cyanoethyl pullulan, etc. may be used. Can do.
Furthermore, two or more of the above insulating materials may be used in combination. Among these, materials are not particularly limited, but those having a high dielectric constant and a low electrical conductivity are preferable.
As a method for forming the insulating film (5), for example, a dry process such as a CVD method, a plasma CVD method, a plasma polymerization method, a vapor deposition method, a spray coating method, a spin coating method, a dip coating method, an ink jet method, a casting method, a blade Examples thereof include wet processes by coating such as a coating method and a bar coating method.

Next, interface modification between the organic semiconductor layer (1) and the insulating film (5) will be described.
The organic thin film transistor is insulated from the organic semiconductor layer (1) for the purpose of improving the adhesion between the insulating film (5) and the organic semiconductor layer (1) and reducing the driving voltage and the leakage current. A predetermined organic thin film may be provided between the film (5).
The organic thin film is not particularly limited as long as it does not chemically affect the organic semiconductor layer. For example, an organic molecular film or a polymer thin film can be used.
Examples of the organic molecular film include coupling agents such as octadecyltrichlorosilane and hexamethyldisilazane.
As the polymer thin film, the above-described polymer insulating film materials can be used, and these may function as a kind of insulating film.
Further, this organic thin film may be subjected to an anisotropic treatment by rubbing or the like, and the formed organic semiconductor material of the present invention is oriented by the anisotropic treatment and has regularity, so that High transistor performance can be obtained.

The annealing depends on the material of the substrate or the like, but is preferably between room temperature and 300 ° C. More preferably, it is 50 to 300 ° C. When the temperature is 50 ° C. or lower, a general organic solvent cannot be removed. Further, at 300 ° C. or higher, the organic matter may be thermally decomposed.
The annealing atmosphere may be performed in an oxygen atmosphere, a nitrogen atmosphere, an argon atmosphere, or air, or by exposing to an organic solvent atmosphere, for example, a solvent in which the organic semiconductor material can be dissolved, to promote molecular motion of the organic semiconductor material. A preferable organic film can be obtained. The annealing time can be appropriately set according to the aggregation rate of the material.

Next, the electrode which comprises an organic thin-film transistor is demonstrated.
The organic thin film transistor of the present invention includes a pair of a first electrode (source electrode) and a second electrode (drain electrode) separated from each other via an organic semiconductor layer, and a voltage applied to the first thin film transistor. A third electrode (gate electrode) having a function of controlling a current flowing in the organic semiconductor layer between the second electrode and the second electrode is provided.
Since the organic thin film transistor is a switching element, the amount of current flowing between the first electrode (source electrode) and the second electrode (drain electrode) can be greatly modulated by the voltage application state of the third electrode (gate electrode). is important. This means that a large current flows when the transistor is driven, and no current flows when the transistor is not driven.

The gate electrode and the source electrode are not particularly limited as long as they are conductive materials. For example, platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony, lead, tantalum, indium, aluminum, Zinc, magnesium, etc., and their alloys, conductive metal oxides such as indium / tin oxide, or inorganic and organic semiconductors whose conductivity has been improved by doping, such as silicon single crystal, polysilicon, amorphous silicon, Germanium, graphite, polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, polythienylene vinylene, polyparaphenylene vinylene, a complex of polyethylene dioxythiophene and polystyrene sulfonic acid, and the like can be applied.
It is desirable that the source electrode and the drain electrode have a small electric resistance at the contact surface with the semiconductor layer.

As a method for forming the electrode, for example, by applying a known photolithography method or a lift-off method to a conductive thin film formed by using a method such as vapor deposition or sputtering using the electrode forming material as a raw material, The method of making it into a shape is mentioned.
Further, a method of etching on a metal foil such as aluminum or copper by using a resist by thermal transfer, ink jet, or the like can be applied.
Alternatively, a conductive polymer solution or dispersion, or a conductive fine particle dispersion may be directly patterned by inkjet, or may be formed from the coating film by lithography, laser ablation, or the like.
Furthermore, a method of patterning an ink containing a conductive polymer or conductive fine particles, a conductive paste, or the like by a printing method such as relief printing, intaglio printing, planographic printing, or screen printing can also be applied.

The organic thin film transistor of the present invention may be provided with an extraction electrode from each electrode as necessary.
In addition, the organic transistor of the present invention is stably driven even in the atmosphere, but it is necessary for protection from mechanical destruction, protection from moisture and gas, or protection for the convenience of device integration. A protective layer can also be provided.

  The organic thin film transistor of the present invention described above can be suitably used as an element for driving various conventionally known display image elements such as liquid crystal, electroluminescence, electrochromic, electrophoresis, and so on. It is possible to produce a display called “paper”. Further, an IC in which the organic thin film transistor of the present invention is integrated can be used as a device such as an IC tag.

[Synthesis of Intermediate 1]
<Synthesis of didodecyl-quaterthiophene>
(Synthesis with reference to synthesis example described in JP-A-2006-8679)

２００ｍｌフラスコに、マグネシウム（フレーク状）２．１５１ｇ（８８．４８ｍｍｏｌ）を入れ、系内をアルゴンガス置換した後、乾燥ＴＨＦ８ｍｌおよび少量のヨウ素を加えた。この分散液に、２−ブロモ−３−ｎ−ドデシルチオフェン１９．８６ｇ（６０ｍｍｏｌ）と乾燥ＴＨＦ５２ｍｌの混合溶液を滴下した後、６時間還流を行ない、室温まで冷却して、３−ｎ−ドデシルチオフェンのグリニャール試薬を調製した。

Magnesium (flakes) 2.151 g (88.48 mmol) was placed in a 200 ml flask, and the system was purged with argon gas. Then, 8 ml of dry THF and a small amount of iodine were added. To this dispersion was added dropwise a mixed solution of 19.86 g (60 mmol) of 2-bromo-3-n-dodecylthiophene and 52 ml of dry THF, followed by refluxing for 6 hours, cooling to room temperature, and 3-n-dodecylthiophene. A Grignard reagent was prepared.

  In a 500 ml flask purged with argon gas, 7.84 g (24.19 mmol) of 5,5′-dibromo-2,2′-bithiophene, [1,2-bis (diphenylphosphino) ethane] dichloronickel (II) 481 g (0.911 mmol) and 105 ml of dry THF were added, and to this solution, the Grignard reagent of 3-n-dodecylthiophene prepared above was transferred to a dropping funnel using a syringe and dropped. Reflux for a period of time.

Thereafter, THF was distilled off, and then toluene was added, followed by quenching with an aqueous hydrochloric acid solution.
This solution was transferred to a separatory funnel, washed with water and saturated brine, and then the organic layer was dehydrated with anhydrous magnesium sulfate. After the desiccant was filtered off, the solvent was distilled off under reduced pressure.
The crude product was purified by silica gel column chromatography (hexane / toluene = 95/5) and then recrystallized from ethanol / toluene to obtain didedecyl-quaterthiophene as yellow needles.
Yield 11.4 g, 71% yield. The melting point was 58.0-59.0 ° C.

[Synthesis of Intermediate 2]
<Synthesis of didodecyl-quaterthiophene dibromo compound>

  A 500 ml flask was charged with 10.56 g (15.83 mmol) of didodecyl-quaterthiophene synthesized in Synthesis Example 1, 5.635 g (31.66 mmol) of N-bromosuccinimide, and 120 ml of chloroform, and 50 ml of acetic acid while stirring at room temperature. It was dripped. Thereafter, refluxing was performed for 1 hour to complete the reaction.

After returning to room temperature, water is added, diluted with chloroform, transferred to a separatory funnel, and the organic layer is washed with 1M potassium hydroxide aqueous solution, water, 0.5% sodium bicarbonate aqueous solution, water, and saturated saline in this order. The organic layer was washed and dried over anhydrous magnesium sulfate.
After the desiccant was filtered off, the solvent was distilled off under reduced pressure.
The crude product was purified by silica gel column chromatography (hexane / toluene = 95/5) and then recrystallized from ethanol / toluene to obtain a dibromo form of didedecyl-quaterthiophene in the form of yellow needles. .
Yield 12.3 g, 95% yield. The melting point was 74.5-75.5 ° C.

  Hereinafter, the present invention will be described with reference to examples.

[Synthesis of Compound 1]

Magnesium (flaked) 0.757 g (31.14 mmol) was placed in a 100 ml flask, and the system was purged with argon gas. Then, 5 ml of dry THF and a small amount of iodine were added.
To this dispersion was added dropwise a mixed solution of 5.21 g (21.1 mmol) of 2-bromo-3-n-hexylthiophene and 19 ml of dry THF, followed by refluxing for 6 hours, cooling to room temperature, and 3-n -Grignard reagent of hexylthiophene was prepared.

  In a 200 ml flask purged with argon gas, 7 g (8.49 mmol) of the dibromo form of didodecyl-quaterthiophene synthesized in Synthesis Example 2 and 0.169 g of [1,2-bis (diphenylphosphino) ethane] dichloronickel (II) ( 0.320 mmol) and 37 ml of dry THF were added, and to this solution, the Grignard reagent of 3-n-hexylthiophene prepared above was transferred to a dropping funnel using a syringe and dropped, and after the dropping was finished, the mixture was refluxed for 24 hours. Was done. Thereafter, THF was distilled off, and then toluene was added, followed by quenching with an aqueous hydrochloric acid solution.

This solution was transferred to a separatory funnel, washed with water and saturated brine in this order, and then the organic layer was dehydrated with anhydrous magnesium sulfate. After the desiccant was filtered off, the solvent was distilled off under reduced pressure.
This crude product was purified by silica gel column chromatography (hexane / toluene = 9/1), and then recrystallized from ethanol / toluene to obtain orange needle-like compounds.
Yield 4.91 g, 58% yield. The melting point was 57.0-58.0 ° C.
Elemental analysis value (calculated value); C: 72.23% (72.09%), H: 8.50% (8.67%), S: 19.16% (19.24%)
The infrared absorption spectrum (KBr tablet method) is shown in FIG.

  The compound 1 synthesized in Example 1 was examined for solubility in a general-purpose organic solvent and film formability.

[Comparative Example 1]
Similarly, the solubility and film-forming property with respect to a general purpose organic solvent were investigated using the comparative compound 1 of the structural formula shown below. This Comparative Compound 1 is described in Non-Patent Document 3.

[Comparative Example 2]
Similarly, the solubility and film-forming property with respect to a general purpose organic solvent were investigated using the comparative compound 2 of the structural formula shown below. This comparative compound 2 is described in Non-Patent Document 4.

[Comparative Example 3]
Similarly, the solubility and film-forming property with respect to a general purpose organic solvent were investigated using the comparative compound 3 of the structural formula shown below. This comparative compound 3 is a raw material for oligothiophene described in Non-Patent Document 5.

(I) Solubility As a method for examining solubility, a solution having a concentration of 1 mg / ml of each compound was prepared for each solvent, and judgment was made based on the following criteria.
○: Dissolved at room temperature (22 ° C).
Δ: Insoluble at room temperature, but dissolves when heated to 50 ° C., and no solute precipitates when left at room temperature overnight.
X: It does not dissolve even when heated to room temperature and 50 ° C., or dissolves when heated to 50 ° C., but a solute precipitates when left at room temperature overnight.

(Ii) Film-formability First, as a method for producing a support for film formation, an n-type silicon substrate having a thermal oxide film having a thickness of 300 nm is immersed in concentrated sulfuric acid for 24 hours, and then pure water is sufficient. Rinse and then dry to dry.
This cleaned silicon substrate is immersed in a toluene solution (1 mM, 8 mL) of phenyltrichlorosilane, which is a silane coupling agent, for 30 minutes, and then thoroughly washed with pure water and acetone to dry the silicon oxide film surface. A monolayer was constructed.
Next, an organic film is formed by spin-coating a chloroform solution of each of Compound 1, Comparative Compound 1, Comparative Compound 2, and Comparative Compound 3 on a support on a silicon substrate on which this monomolecular film is constructed. I did it. The liquid composition of Comparative Compound 2 on which the solute was precipitated was spin-coated after passing through a PTFE (polytetrafluoroethylene) filter having a pore size of 0.1 μm.
Table 1 shows the results of the solubility and film-formability tests.

When the formed organic films were visually observed, the organic films of Comparative Compound 1, Comparative Compound 2 and Comparative Compound 3 were all discontinuous films, but the organic film of Compound 1 was a uniform continuous film. It was confirmed that a film was formed.
Further, the organic film of Compound 1 was observed with a polarizing microscope. The result is shown in FIG.
From this, it became clear that the organic film of Compound 1 was uniformly formed on the support and was oriented in a relatively large domain.

<Production of organic thin film transistor element and evaluation of static characteristics>
100 nm of Au serving as a source / drain electrode is deposited on the organic film of Compound 1 formed on the silicon substrate obtained in Example 2 through a metal mask so that the channel length is 50 μm and the channel width is 2000 μm. Thus, a field effect transistor having the structure of FIG.
Next, the organic semiconductor layer and the silicon oxide film at portions different from the source / drain electrodes of the substrate were scraped off, and a conductive paste (manufactured by Fujikura Kasei Co., Ltd.) was applied to the portions, and the solvent was dried. This portion was used as a gate electrode, and a voltage was applied to the silicon substrate.
As a result of evaluating the electrical characteristics of the FET element thus obtained using a semiconductor parameter analyzer 4156C manufactured by Agilent, the characteristics as a p-type transistor element were shown. FIG. 4 shows the current-voltage (IV) characteristics of the organic thin film transistor.
From this saturation region, field effect mobility was determined.
In addition, the following formula | equation was used for calculation of the field effect mobility of an organic thin-film transistor.
I _ds = μC _in W (V _g −V _th ) 2 / 2L
(Where C _in is the capacitance per unit area of the gate insulating film, W is the channel width, L is the channel length, V _g is the gate voltage, I _ds is the source-drain current, μ is the mobility, and V _th is the channel. (This is the threshold voltage of the gate that begins to form.)

The mobility of the produced organic thin film transistor element was 4.4 × 10 ⁻² cm ² / Vsec.
The on-off ratio _(V ds = _-20V, and _{I ds} in _{V g = -40V, V ds =} -20V, the ratio of V g = + 20~-40V minimum _{I ds} observed within the) 2. The threshold voltage was −10.0 V at 9 × 10 ⁷ .

The organic thin film transistor element produced in Example 3 was placed on a hot plate, heated at 50 ° C. for 30 minutes, and then the hot plate was turned off and allowed to cool overnight to anneal the organic semiconductor film. Thereafter, the mobility of the element was evaluated in the same manner as in Example 3. As a result, the mobility was 6.8 × 10 ⁻² cm ² / Vsec, the on / off ratio was 1.1 × 10 ⁶ , and the threshold value was The voltage was -11.0V.
It can be seen that the annealing density of the fabricated organic thin film transistor element increased the orientation density of the organic semiconductor film, and the performance of the element was improved.

1 Organic Semiconductor Layer 2 Source Electrode 3 Drain Electrode 4 Gate Electrode 5 Gate Insulating Film

JP 2003-221434 A JP 2003-268083 A

Appl. Phys. Lett., 69 (26), 4108 (1996). Adv.Mat., 12, 1046 (2000). Syn.Met., 67, 47 (1994). J. Appl. Phys., 93 (5), 2977 (2003). Chem. Lett., 35 (8), 942 (2006) (closest prior art)

Claims (4)

An organic semiconductor material represented by the following general formula (I):

(Wherein R ₁ and R ₂ represent different alkyl groups, and x and y each independently represents an integer of 1 or 2)   A liquid composition comprising at least the organic semiconductor material according to claim 1 and at least one organic solvent.   An organic film formed on a support and comprising at least the organic semiconductor material according to claim 1.   An organic semiconductor thin film transistor comprising an organic semiconductor layer, a structure in which a pair of electrodes for allowing a current to flow through the organic semiconductor layer is provided, and a third electrode, wherein the organic semiconductor layer is an organic film according to claim 3. An organic thin film transistor characterized in that:

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