Organic semiconductor composition, method for manufacturing a transistor, organic semiconductor thin film, and transistor

Abstract

The present invention provides an organic semiconductor composition, a method for manufacturing a transistor, and an organic semiconductor thin film. [Solution] An organic semiconductor composition comprising an organic semiconductor material and a thiophene solvent, wherein the organic semiconductor material comprises a compound having a thiophene ring, and the thiophene solvent is a solvent containing thiophene as a main component. The organic semiconductor material is preferably liquid crystalline, and the thiophene solvent is preferably a non-halogen solvent.

Description

[Technical Field]

[0001] This invention relates to an organic semiconductor composition, a method for manufacturing a transistor, an organic semiconductor thin film, and a transistor. [Background technology]

[0002] One known method for manufacturing organic semiconductor thin films involves coating a substrate with a composition containing an organic semiconductor compound and a solvent, and then evaporating the solvent to form the organic semiconductor thin film.

[0003] For example, Patent Document 1 discloses a condensed polycyclic aromatic compound having a [1]benzothieno[3,2-b][1]benzothiophene skeleton as an organic semiconductor compound exhibiting high carrier mobility.

[0004] In the manufacturing of organic semiconductor thin films, various characteristics such as high carrier mobility and applicability to low-temperature deposition processes are required, and furthermore, it is necessary that the values ​​of these characteristics do not vary. A "low-temperature deposition process" refers to a process that includes steps to deposit organic semiconductor thin films at temperatures of 60°C or lower. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 4581062 [Overview of the project]

[0006] The organic semiconductor composition of the present invention comprises an organic semiconductor material and a thiophene solvent. The organic semiconductor material comprises a compound having a thiophene ring, and the thiophene solvent comprises thiophene as its main component. [Brief explanation of the drawing]

[0007] [Figure 1]Figure 1 shows the solubility curves of 2-decyl-7-phenylbenzothieneobenzothiophene in each organic solvent. [Figure 2A] Figure 2A is a polarized light microscope image of a crystalline film deposited using the organic semiconductor composition of Example 1. [Figure 2B] Figure 2B is a polarized light microscope image of a crystalline film deposited using the organic semiconductor composition of Comparative Example 1. [Figure 3A] Figure 3A shows the results of gas chromatography-mass spectrometry of substrate 2. [Figure 3B] Figure 3B shows the results of gas chromatography-mass spectrometry of substrate 1. [Figure 3C] Figure 3C is an enlarged view of a portion of the results obtained by gas chromatography-mass spectrometry of substrate 1. [Figure 4] Figure 4 shows the results of X-ray diffraction measurements performed on substrates 3, 4, 11, and 12. [Modes for carrying out the invention]

[0008] <Organic semiconductor composition> The organic semiconductor composition of this embodiment comprises an organic semiconductor material and a thiophene solvent. A thiophene solvent is a solvent that contains thiophene as its main component. Here, "contains thiophene as its main component" means that thiophene has the highest content among the constituent materials of the thiophene solvent. The thiophene content relative to the total amount of the thiophene solvent is 50% or more, preferably 70% or more, more preferably 90% or more, and may be 100%. The thiophene solvent may contain other organic compounds as long as they do not impair the effects of the present invention.

[0009] Generally, solvents used for coating organic semiconductors are preferably non-halogen solvents from the standpoint of environmental issues and human safety. A non-halogen solvent means a solvent that does not contain halogen elements such as F, Cl, and Br.

[0010] Thiophene is a material not used as an organic solvent. Through the study by the present inventors, it has been found that an organic semiconductor material containing a compound having a thiophene ring has high solubility in thiophene.

[0011] Figure 1 shows the solubility curve of 2-decyl-7-phenylbenzothieneobenzothiophene (hereinafter referred to as "Ph-BTBT-10") with respect to each organic solvent. Ph-BTBT-10 is an example of an organic semiconductor material containing a compound having a thiophene ring. Figure 1 describes examples using thiophene, o-xylene, p-xylene, and toluene as organic solvents, respectively.

[0012] From Figure 1, it can be confirmed that in the temperature range of 30 to 40 °C, the solubility of Ph-BTBT-10 in thiophene is about 10 mg / ml. On the other hand, it can be confirmed that the solubility of Ph-BTBT-10 in organic solvents other than thiophene is less than 5 mg / ml. That is, in the temperature range of 30 to 40 °C, it can be confirmed that the solubility of Ph-BTBT-10 in thiophene is at least about twice that of other organic solvents.

[0013] When forming an organic semiconductor thin film using an organic semiconductor composition, at least 5 mg / ml is required. In the temperature range of 30 to 40 °C, organic solvents other than thiophene are in a saturated state, and if an attempt is made to adjust the concentration to 5 mg / ml, crystallization will occur, making film formation difficult. On the other hand, since thiophene has a margin in solubility, even when adjusted to a concentration of 5 mg / ml, film formation at a low temperature is possible without crystallization.

[0014] From the results of Figure 1, it has been found that when using thiophene, a high-concentration organic semiconductor composition can be prepared even in a low-temperature range of 40 °C or lower. As an approach to improving the solubility of an organic semiconductor composition, there is a method of increasing the temperature of the organic solvent, but heating a flammable solvent has problems from the perspective of safety. Furthermore, while increasing the temperature of the organic solvent increases its concentration, it also leads to a decrease in the viscosity of the organic semiconductor composition, making it difficult to apply.

[0015] This invention solves these problems because it enables the preparation of high-concentration organic semiconductor compositions in a low-temperature range.

[0016] Organic semiconductor materials The organic semiconductor material used in this embodiment includes a compound having a thiophene ring. Examples of compounds containing a thiophene ring include thienoacene derivatives with six or fewer rings containing a thiophene ring, such as thieno[3,2-b]thiophene, dinaphthyl[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), and 2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (BTBT).

[0017] The compounds having a thiophene ring are preferably those represented by the following formula (1).

[0018] [ka]

[0019] In formula (1), R 1 R is an alkyl group having 1 to 16 carbon atoms. 2 This is an alkyl group or aromatic ring having 1 to 16 carbon atoms.

[0020] While not limited to liquid crystal materials, it is even more preferable that the organic semiconductor material is a liquid crystal material. Examples of thiophene organic semiconductor materials with liquid crystalline properties include the following:

[0021] [ka]

[0022] Compounds containing a thiophene ring preferably have a total number of 6 or fewer rings in thioacene, more preferably 5 or fewer, and even more preferably 4 or fewer. When the total number of rings is below the above upper limit, the solubility in thiophene solvent tends to increase.

[0023] One aspect of the present invention is an organic semiconductor composition comprising an organic semiconductor material and a thiophene solvent, wherein the organic semiconductor material comprises a compound with a total number of 6 or fewer thioacene rings, and the thiophene solvent is a non-halogen solvent containing thiophene as a main component. It is known that substances with similar chemical structures have high solubility. However, while there are examples of thiophene derivatives such as chlorothiophene being used as organic solvents (e.g., Japanese Patent Publication No. 2020-167439), there have been no examples of thiophene being used as an organic solvent. One aspect of the present invention, which uses a low molecular weight compound having a thiophene ring and having a total number of rings of 6 or less, is preferable because it further improves solubility in thiophene solvents.

[0024] The organic semiconductor composition may contain a small amount of an insulating polymer, such as polystyrene, to control the morphology of the formed organic semiconductor film. When an insulating polymer is added, the amount can be appropriately adjusted within the range of 0.1% to 10% by mass relative to the total amount of the organic semiconductor composition.

[0025] The organic semiconductor composition preferably has a concentration of organic semiconductor material of 0.2% by mass or more, and more preferably 1.0% by mass or more.

[0026] <Method for manufacturing organic semiconductor thin films> This embodiment relates to a method for manufacturing organic semiconductor thin films. The method for producing an organic semiconductor thin film according to this embodiment comprises the steps of: preparing an organic semiconductor composition containing an organic semiconductor material and a thiophene solvent; applying the organic semiconductor solution to a substrate; and drying the organic semiconductor solution. The following describes each step.

[0027] [Steps for preparing organic semiconductor compositions] First, an organic semiconductor material containing a compound having a thiophene ring is dissolved in a thiophene solvent to prepare an organic semiconductor composition.

[0028] [Application process] Next, a liquid film of the organic semiconductor solution is formed on the substrate depending on the coating method. In this embodiment, it is preferable that the organic semiconductor composition is applied to the substrate in one direction. As for the method of applying the organic semiconductor composition, other known methods may be used as long as they allow application to the substrate in one direction. For example, application methods such as spin coating, dip coating, die coating, spray coating, roll coating, microgravure, lip coating, inkjet, applicator coating, and brush coating can be used. Alternatively, the composition may be applied by printing methods such as flexographic printing and screen printing.

[0029] The thickness of the organic semiconductor film is generally selected depending on the type of device being fabricated, such as organic EL elements, photosensors, solar cells, and transistors. For example, when fabricating an organic transistor, the film thickness is set to 5 nm to 200 nm, more preferably 5 nm to 100 nm, and even more preferably 5 nm to 50 nm. The thickness of the crystalline film to be fabricated can also be directly controlled by the thickness of the liquid film applied to the substrate. In addition, the thickness of the crystalline film formed can generally be appropriately controlled by the type of solvent used, the concentration of the organic semiconductor, the type of substrate, the temperature of the organic semiconductor solution, and the temperature of the substrate to which it is applied.

[0030] For example, when using Ph-BTBT-10 as the organic semiconductor exhibiting liquid crystalline properties, it is preferable to adjust the film deposition temperature to a range of 40°C to 150°C. Furthermore, when using C8-BTBT, it is preferable to adjust the film deposition temperature to a range of 30°C to 120°C.

[0031] [Process for drying the organic semiconductor solution] In the manufacturing method of this embodiment, an organic semiconductor composition is applied to a substrate, and a liquid layer of the organic semiconductor composition is formed on the substrate. Furthermore, the thiophene solvent contained in the liquid layer dries by evaporation, and a solid film of the organic semiconductor is formed on the surface of the substrate.

[0032] The substrate is not particularly limited and can be glass, quartz glass, silicon wafer, metal plate, or flexible resin sheet. For example, a plastic film can be used as a sheet. Examples of such plastic films include films made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate propionate (CAP), and the like.

[0033] The manufacturing method of this embodiment allows for film formation by coating a semiconductor solution at low temperatures, thus being less constrained by the material, size, and shape of the substrate. For this reason, it can be applied to continuous mass production equipment such as so-called roll-to-roll processes.

[0034] <Transistor manufacturing method> One aspect of the present invention is a method for manufacturing a transistor, comprising the step of forming an organic semiconductor thin film layer using the organic semiconductor composition of this embodiment.

[0035] <Methods for manufacturing electronic devices> This embodiment describes a method for manufacturing an electronic device. The method for manufacturing an electronic device according to this embodiment includes the step of forming a transistor by the method for manufacturing a transistor according to this embodiment.

[0036] <Organic semiconductor thin film> One aspect of the present invention is an organic semiconductor thin film containing thiophene. Whether the organic semiconductor thin film contains thiophene is evaluated by the following method. A substrate with an organic semiconductor thin film is placed in a 100 mL container, sealed, and heated at 120 °C for 60 minutes. The gas in the container is collected with a syringe and analyzed by gas chromatography-mass spectrometry. If the peak of thiophene can be confirmed, it is evaluated as "containing thiophene".

Example

[0037] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples. [[ID=---]]

[0038] [[ID=---]] [Evaluation of carrier mobility] (Measurement of carrier mobility μ AV ) For organic thin film transistors, the carrier mobility of all the specimens manufactured for measuring the carrier mobility was measured. Specifically, a voltage of -50 V is applied between the source electrode and the drain electrode of each organic thin film transistor element, the gate voltage is changed in the range of +10 V to -70 V, and the carrier mobility μ (cm 2 / Vs) is calculated using the following formula representing the drain current Id. The average value of the carrier mobility of all the specimens is obtained and taken as the carrier mobility μ AV . The higher the carrier mobility μ AV , the more preferable.

[0039] I d =(w / 2L)μC i (V g -V th ) 2 In the formula, L represents the channel length, w represents the channel width, μ represents the carrier mobility, C i represents the capacitance per unit area of the gate insulating layer, V g represents the gate voltage, and V th represents the threshold voltage, respectively.

[0040] (Calculation of coefficient of variation) For organic thin film transistors, regarding the above (carrier mobility μAV For the carrier mobility μ of all samples measured in the (measurement) test, the mutation coefficient was calculated using the following formula. In the formula below, the standard deviation is calculated by the standard method, and the mean is the carrier mobility μ mentioned above. AV This coefficient of variation was used and evaluated as an indicator of the variability in carrier mobility. Coefficient of variation (%) = (Standard deviation / Mean) × 100

[0041] <Preparation of Organic Semiconductor Compositions> Ph-BTBT-10 was synthesized according to a non-patent document (Nature Commun., DOI: 0.1038 / ncomms7828). It was then purified repeatedly by silica column chromatography and recrystallization to improve its purity before use.

[0042] <Example 1> Ph-BTBT-10 was dissolved in thiophene to prepare a 0.4% by mass Ph-BTBT-10 thiophene solution, which was used as organic semiconductor composition 1. An organic semiconductor thin film was fabricated by applying organic semiconductor composition 1 to an SiO2 (300 nm) / Si substrate using a spin coating method. The spin coating conditions were as follows: the liquid temperature of organic semiconductor composition 1 was 60°C, and the spin coating temperature was 40°C at 3000 rpm for 30 seconds. For the fabrication of the transistors, Au was deposited onto an SiO2 (300 nm) / Si substrate using a vacuum deposition method with a shadow mask to form source and drain electrodes, creating a bottom-gate, top-contact type transistor. The channel length and channel width were set to 100 μm and 500 μm, respectively. Subsequently, thermal annealing was performed at 120°C for 5 minutes. The characteristics of the fabricated transistors were investigated under atmospheric conditions at room temperature, and the mobility was calculated from the transistor characteristics in the saturation region using the method described in [Evaluation of Carrier Mobility] above. The average mobility of a transistor is 3.8 cm. 2 The value is / Vs, and the maximum mobility is 4.1cm. 2 The ratio was / Vs, and the variability in mobility was 7%.

[0043] Figure 2A is a polarized light microscope image of a crystalline film deposited using the organic semiconductor composition of Example 1. Figure 2A shows that when the organic semiconductor composition of Example 1 is used, there are almost no non-uniform areas formed by the precipitation of crystal grains due to recrystallization, and a flat film can be formed.

[0044] <Comparative Example 1> Ph-BTBT-10 was dissolved in p-xylene to prepare a 0.6% by mass Ph-BTBT-10p-xylene solution, which was used as organic semiconductor composition 2. An organic semiconductor thin film was manufactured and a transistor was produced in the same manner as in Example 1, except that organic semiconductor composition 2 was used. The average mobility of the transistor measured by the method described in [Evaluation of Carrier Mobility] above was 1.4 cm². 2 The value is / Vs, and the maximum mobility is 1.8cm. 2 The ratio was / Vs, and the variability in mobility was 26%.

[0045] Figure 2A is a polarized light microscope image of a crystalline film deposited using the organic semiconductor composition of Example 1. Figure 2B is a polarized light microscope image of a crystalline film deposited using the organic semiconductor composition of Comparative Example 1. Figure 2A shows that when the organic semiconductor composition of Example 1 is used, it can be confirmed that there are almost no crystalline areas and a flat film can be formed. Figure 2B shows that when the organic semiconductor composition of Comparative Example 1 was used, areas of crystallization were observed, and the substrate was exposed in some places, i.e., holes were observed in the film.

[0046] The results from Example 1 and Comparative Example 1 show that when thiophene is used as a solvent for an organic semiconductor composition, a flat organic semiconductor thin film can be produced at a deposition temperature of 40°C, with an average mobility of 3.8 cm². 2 It was confirmed that the film had a mobility of approximately the same level as that obtained when film formation was carried out at high temperature using p-xylene as the organic solvent, as indicated by / Vs.

[0047] To investigate whether or not crystallization occurs during spin-coating, out-of-plane XRD measurements were performed immediately after deposition, and bilayer crystals (2θ=1.7) that appear during crystallization were identified. o The presence or absence of ) was evaluated (Figure 4).

[0048] A 0.5% by mass Ph-BTBT-10 thiophene solution was prepared by dissolving Ph-BTBT-10 in thiophene, and a film was deposited in the same manner as in Example 1, except that organic semiconductor composition 1 was used. The thin film that was not thermally annealed was used as substrate 3, and the thin film that was thermally annealed at 120°C for 5 minutes was used as substrate 4.

[0049] Furthermore, a 0.5% by mass Ph-BTBT-10 p-xylene solution was prepared by dissolving Ph-BTBT-10 in p-xylene, and a film was deposited in the same manner as in Comparative Example 1, except that organic semiconductor composition 2 was used. The thin film that was not thermally annealed was used as substrate 11, and the thin film that was thermally annealed at 120°C for 5 minutes was used as substrate 12.

[0050] As shown in Figure 4, substrates 11 and 12 exhibit bilayer crystal peaks (001) (2θ=1.7) associated with recrystallization. o ) was confirmed. In contrast, no peaks associated with recrystallization were observed in substrate 3. The results shown in Figure 4 confirm that using a thiophene solvent allows for the production of flat thin films without recrystallization, even when deposited at a temperature of 40°C, which is close to room temperature.

[0051] <Detection test of thiophene solvent> ≪Test Example 1≫ A 0.5% by mass solution of Ph-BTBT-10 thiophene was prepared by the same method as in Example 1, and this was designated as organic semiconductor composition 3. Organic semiconductor composition 3 was applied to an SiO2 (300 nm) / Si substrate by spin coating. The spin coating conditions were a liquid temperature of 60°C for organic semiconductor composition 3 and a spinning speed of 3000 rpm for 30 seconds. The dimensions of the substrate used were 25 mm × 20 mm. After spin coating, heat treatment was performed at 120°C for 5 minutes to produce a substrate 1 with an organic semiconductor thin film.

[0052] ≪Test Example 2≫ A substrate 2 containing an organic semiconductor thin film was manufactured using the same method as in Test Example 1, except that heat treatment was not performed after spin coating.

[0053] The obtained substrates were each placed in a 50 mL container and heated at 120°C for 60 minutes. The gas inside the container was collected with a syringe and analyzed by gas chromatography-mass spectrometry. Thiofen was used as a standard sample. The measurement conditions for gas chromatography-mass spectrometry were as follows: • Column used: HP-5 • Heating conditions: Heat at 40°C for 4 minutes, increasing the temperature by 10°C per minute until it reaches 280°C. • Injection method: Splitless ·Inlet temperature: 250℃ • Carrier gas: Helium ·Injection volume: 100μl

[0054] Figure 3A shows the results for substrate 2, and Figures 3B and 3C show the results for substrate 1. Figure 3C is an enlarged view of a portion of Figure 3B. When only thiophene was used as the standard sample, a peak was observed at a retention time of approximately 1.7 minutes. Therefore, the peak at approximately 1.7 minutes is considered to be the peak for thiophene. In Figures 3A, 3B, and 3C, a peak was observed around a retention time of 1.7 minutes. Therefore, it was confirmed that when thiophene is used as a solvent for the organic semiconductor composition, the resulting organic semiconductor thin film contains thiophene.

[0055] The results from Test Examples 1-3 confirmed that transistors with minimal mobility variation can be manufactured even when using thiophene solvents.

Claims

1. An organic semiconductor composition comprising an organic semiconductor material and a thiophene solvent, The aforementioned organic semiconductor material includes a compound having a thiophene ring, The thiophene solvent is an organic semiconductor composition containing thiophene as its main component.

2. The organic semiconductor composition according to claim 1, wherein the organic semiconductor material has liquid crystalline properties.

3. The organic semiconductor composition according to claim 1 or 2, wherein the thiophene solvent is a non-halogen solvent.

4. The organic semiconductor composition according to any one of claims 1 to 3, wherein the compound having the thiophene ring has a total number of rings of 6 or less.

5. The organic semiconductor composition according to any one of claims 1 to 4, wherein the organic semiconductor material is 2-decyl-7-phenylbenzothieneobenzothiophene.

6. A method for manufacturing a transistor, comprising the step of forming an organic semiconductor thin film layer using an organic semiconductor composition according to any one of claims 1 to 5.

7. A thin film of organic semiconductor containing thiophene.

8. A transistor comprising an organic semiconductor thin film as described in claim 7.

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