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

Abstract

Disclosed is an organic semiconductor composition containing an organic semiconductor material and a thiophene solvent, wherein: the organic semiconductor material contains a compound having a thiophene ring; and the thiophene solvent contains thiophene as a main component. It is preferable that the organic semiconductor material has liquid crystallinity, and it is also preferable that the thiophene solvent is a non-halogen solvent.

Description

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

[0001] The present invention relates to an organic semiconductor composition, a method for manufacturing a transistor, an organic semiconductor thin film, and a transistor. This application claims priority to Japanese Patent Application No. 2023-097654, filed on June 14, 2023, the contents of which are incorporated herein by reference.

[0002] A known method for producing an organic semiconductor thin film involves applying a composition containing an organic semiconductor compound and a solvent to a substrate and then evaporating the solvent to form an organic semiconductor thin film.

[0003] For example, Patent Document 1 discloses a fused 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 production of organic semiconductor thin films, various properties such as high carrier mobility and applicability to low-temperature film-forming processes are required, and further, small variations in the values ​​of these properties are required. "Low-temperature film-forming process" means a process that includes a step in which the film-forming temperature of the organic semiconductor thin film is 60°C or lower.

[0005] Patent No. 4581062

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

[0007] FIG. 1 shows the solubility curve of 2-decyl-7-phenylbenzothieneobenzothiophene in various organic solvents. FIG. 2A shows a polarizing microscope photograph of a crystalline film formed using the organic semiconductor composition of Example 1. FIG. 2B shows a polarizing microscope photograph of a crystalline film formed using the organic semiconductor composition of Comparative Example 1. FIG. 3A shows the results of gas chromatography-mass spectrometry for Substrate 2. FIG. 3B shows the results of gas chromatography-mass spectrometry for Substrate 1. FIG. 3C shows an enlarged view of a portion of the results of gas chromatography-mass spectrometry for Substrate 1. FIG. 4 shows the results of X-ray diffraction measurements for Substrates 3, 4, 11, and 12.

[0008] <Organic Semiconductor Composition> The organic semiconductor composition of this embodiment contains an organic semiconductor material and a thiophene solvent. The thiophene solvent is a solvent containing thiophene as a main component. Here, "containing thiophene as a main component" means that, among the constituent materials of the thiophene solvent, thiophene has the highest content. 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 within a range that does not impair the effects of the present invention.

[0009] In general, from the viewpoint of environmental issues and safety for the human body, it is preferable that the solvent used for coating an organic semiconductor is a non-halogen solvent. A non-halogen solvent means a solvent that does not contain halogen elements such as F, Cl, or Br.

[0010] Thiophene is a material that is not used as an organic solvent. The inventors have found through their investigations that organic semiconductor materials containing compounds having a thiophene ring have high solubility in thiophene.

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

[0012] 1 confirms that the solubility of Ph-BTBT-10 in thiophene is approximately 10 mg / ml in the temperature range of 30 to 40°C. 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. In other words, it can be confirmed that the solubility of Ph-BTBT-10 in thiophene is at least approximately twice as high as that in other organic solvents in the temperature range of 30 to 40°C.

[0013] When forming an organic semiconductor thin film using an organic semiconductor composition, a concentration of at least 5 mg / ml is required. In the temperature range of 30 to 40°C, organic solvents other than thiophene are saturated, and adjusting the concentration to 5 mg / ml results in crystallization, making film formation difficult. On the other hand, thiophene has a large solubility margin, so even when adjusted to a concentration of 5 mg / ml, it does not crystallize and film formation is possible at low temperatures.

[0014] The results in Figure 1 demonstrate that the use of thiophene allows the preparation of highly concentrated organic semiconductor compositions even at temperatures as low as 40°C or lower. One approach to improving the solubility of organic semiconductor compositions is to increase the temperature of the organic solvent, but heating a flammable solvent poses safety concerns. Furthermore, while increasing the temperature of the organic solvent also increases the concentration, it also reduces the viscosity of the organic semiconductor composition, making it difficult to apply.

[0015] The present invention solves this problem by making it possible to prepare highly concentrated organic semiconductor compositions at low temperatures.

[0016] Organic Semiconductor Material The organic semiconductor material used in this embodiment includes a compound having a thiophene ring. Examples of the compound having a thiophene ring include thienoacene derivatives having six or fewer thiophene rings, 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 compound having a thiophene ring is preferably a compound represented by the following formula (1).

[0018]

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

[0020] Although the organic semiconductor material is not limited to a liquid crystal material, it is more preferable that the organic semiconductor material is a material having liquid crystallinity. Examples of thiophene organic semiconductor materials having liquid crystallinity include the following.

[0021]

[0022] In the compound having a thiophene ring, the total number of thioacene rings is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. When the total number of rings is the above upper limit or less, the solubility in a thiophene solvent tends to be increased.

[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 having a total number of thioacene rings of 6 or less, and the thiophene solvent is a non-halogen solvent containing thiophene as a primary component. It is known that substances with similar chemical structures have high solubility. However, although there are examples in which thiophene derivatives such as chlorothiophene have been used as organic solvents (e.g., JP 2020-167439 A), there have been no examples of thiophene being used as an organic solvent. An aspect of the present invention in which a low-molecular-weight compound having a total number of thiophene rings of 6 or less is used is preferred because it further improves solubility in thiophene solvents.

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

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

[0026] <Method for manufacturing an organic semiconductor thin film> This embodiment relates to a method for manufacturing an organic semiconductor thin film. The method for manufacturing an organic semiconductor thin film of this embodiment includes a step of preparing an organic semiconductor composition containing an organic semiconductor material and a thiophene solvent, a step of applying the organic semiconductor solution to a substrate, and a step of drying the organic semiconductor solution. Each step will be described below.

[0027] [Step of Preparing an Organic Semiconductor Composition] 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] [Coating Step] Next, a liquid film of the organic semiconductor solution is formed on the substrate according to the coating method. In this embodiment, the organic semiconductor composition is preferably coated unidirectionally onto the substrate. As a method for coating the organic semiconductor composition, for example, other known methods may be used as long as they allow unidirectional coating onto the substrate. For example, coating methods such as spin coating, dip coating, die coating, spray coating, roll coating, microgravure coating, lip coating, inkjet coating, applicator coating, and brush coating can be used. Coating may also be performed by a printing method such as flexographic printing or screen printing.

[0029] The thickness of the organic semiconductor film is generally selected depending on the type of device to be fabricated, such as an organic EL element, a photosensor, a solar cell, or a transistor. For example, when fabricating an organic transistor, the film thickness is set to 5 nm or more and 200 nm or less, more preferably 5 nm or more and 100 nm or less, and even more preferably 5 nm or more and 50 nm or less. The film thickness of the fabricated crystal film can also be directly controlled by the thickness of the liquid film applied to the substrate. In addition, the thickness of the formed crystal film 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 Ph-BTBT-10 is used as the organic semiconductor exhibiting liquid crystallinity, it is preferable to adjust the film formation temperature to a range of 40° C. to 150° C. When C8-BTBT is used, it is preferable to adjust the film formation temperature to a range of 30° C. to 120° C.

[0031] [Step of drying the organic semiconductor solution] In the manufacturing method of this embodiment, the 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 evaporates and dries, and a solid film of the organic semiconductor is formed on the surface of the substrate.

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

[0033] The manufacturing method of this embodiment allows film formation by applying a semiconductor solution at a low temperature, so it is not subject to restrictions on the material, size, or shape of the substrate, and can therefore be applied to continuous mass production equipment such as a so-called roll-to-roll process.

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

[0035] <Method for Manufacturing an Electronic Device> This embodiment is a method for manufacturing an electronic device. The method for manufacturing an electronic device of this embodiment includes a step of forming a transistor by the method for manufacturing a transistor of this embodiment.

[0036] <Organic Semiconductor Thin Film> One embodiment of the present invention is an organic semiconductor thin film containing thiophene. Whether or not the organic semiconductor thin film contains thiophene is evaluated by the following method. A substrate having an organic semiconductor thin film is placed in a 100 mL container, sealed, and heated at 120°C for 60 minutes. The gas inside the container is collected with a syringe and analyzed by gas chromatography-mass spectrometry. If a thiophene peak is confirmed, the organic semiconductor thin film is evaluated as "containing thiophene."

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0038] [Evaluation of Carrier Mobility] (Carrier mobility μＡＶ For the organic thin-film transistors, the carrier mobility of all the manufactured samples for carrier mobility measurement was measured. Specifically, a voltage of −50 V was applied between the source electrode and the drain electrode of each organic thin-film transistor element, and the gate voltage was changed in the range of +10 V to −70 V. The carrier mobility μ (cm ) was calculated using the following equation, which represents the drain current Id: ２ The average value of the carrier mobilities of all the samples is calculated, and this is called the carrier mobility μ ＡＶ The carrier mobility μ ＡＶ The higher the value, the more preferable it is.

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

[0040] (Calculation of the Variation Coefficient) For the organic thin film transistor, the above (carrier mobility μ ＡＶ The coefficient of variation was calculated using the following formula for the carrier mobility μ of all samples measured in the test. In the formula below, the standard deviation was calculated using a conventional method, and the average value was calculated using the carrier mobility μ ＡＶ This variation coefficient was used as an index of the variation in carrier mobility and evaluated. Variation coefficient (%) = (standard deviation / average value) x 100

[0041] <Preparation of Organic Semiconductor Composition> Ph-BTBT-10 was synthesized according to a non-patent document (Nature Commun., DOI: 0.1038 / ncomms7828). It was then repeatedly purified 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 mass % Ph-BTBT-10 thiophene solution, which was used as organic semiconductor composition 1.２ The organic semiconductor thin film was produced by spin coating on a Si substrate (300 nm). The spin coating conditions were: the liquid temperature of the organic semiconductor composition 1 was 60°C, the temperature during spin coating was 40°C, and the spin coating was performed at 3000 rpm for 30 seconds. ２ Au was deposited on a (300 nm) / Si substrate using a shadow mask by vacuum deposition to form source and drain electrodes, producing a bottom-gate, top-contact transistor. The channel length and channel width were 100 μm and 500 μm, respectively. Thermal annealing was then performed at 120°C for 5 minutes. The characteristics of the fabricated transistor were examined under atmospheric conditions at room temperature, and the mobility was calculated from the transistor characteristics in the saturation region using the method described above in [Evaluation of carrier mobility]. The average mobility of the transistor was 3.8 cm. ２ / Vs, and the maximum mobility is 4.1 cm ２ / Vs, and the mobility variation was 7%.

[0043] Fig. 2A is a polarizing microscope photograph of a crystalline film formed using the organic semiconductor composition of Example 1. It was confirmed from Fig. 2A that when the organic semiconductor composition of Example 1 was used, there were almost no uneven areas formed by the precipitation of crystal grains due to recrystallization, and a flat film could be formed.

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

[0045] Fig. 2A is a polarizing microscope photograph of a crystalline film formed using the organic semiconductor composition of Example 1. Fig. 2B is a polarizing microscope photograph of a crystalline film formed using the organic semiconductor composition of Comparative Example 1. Fig. 2A confirms that when the organic semiconductor composition of Example 1 was used, there were almost no crystallized portions, and a flat film could be formed. Fig. 2B confirms that when the organic semiconductor composition of Comparative Example 1 was used, crystallized portions were confirmed, and the substrate was exposed in places, i.e., holes were confirmed in the film.

[0046] The results of Example 1 and Comparative Example 1 show that when thiophene is used as a solvent for the organic semiconductor composition, a flat organic semiconductor thin film can be produced at a film formation temperature of 40°C, and the average mobility is 3.8 cm ２ It was confirmed that the mobility was comparable to that of a film formed at a high temperature using p-xylene as the organic solvent.

[0047] In order to check whether or not crystallization occurs during spin coating, out-of-plane XRD measurement was carried out immediately after film formation. o ) was evaluated (Figure 4).

[0048] Ph-BTBT-10 was dissolved in thiophene to prepare a 0.5 mass % Ph-BTBT-10 thiophene solution, and films were formed 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 designated as substrate 3, and the thin film that was thermally annealed at 120°C for 5 minutes was designated as substrate 4.

[0049] In addition, Ph-BTBT-10 was dissolved in p-xylene to prepare a 0.5 mass % p-xylene solution of Ph-BTBT-10. Films were formed 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 FIG. 4, the substrates 11 and 12 have a bilayer crystal peak (001) (2θ=1.7 o) was confirmed. In contrast, no peaks associated with recrystallization were confirmed for Substrate 3. From the results in Figure 4, it was confirmed that when a thiophene solvent is used, a flat thin film can be produced without recrystallization even when the film is formed at 40°C, which is a temperature close to room temperature.

[0051] <Detection Test for Thiophene Solvent> <Test Example 1> A 0.5 mass % Ph-BTBT-10 thiophene solution was prepared in the same manner as in Example 1, and used as organic semiconductor composition 3. Organic semiconductor composition 3 was prepared by adding SiO ２ The organic semiconductor composition 3 was applied to a Si substrate (300 nm) by spin coating. The spin coating conditions were a liquid temperature of 60°C, 3000 rpm, and 30 seconds. The dimensions of the substrate used were 25 mm x 20 mm. After spin coating, the substrate was heat-treated at 120°C for 5 minutes to produce a substrate 1 provided with an organic semiconductor thin film.

[0052] Test Example 2 A substrate 2 provided with an organic semiconductor thin film was produced in the same manner as in Test Example 1, except that the heat treatment after spin coating was not carried out.

[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. Thiophene was used as a standard sample. The measurement conditions for gas chromatography mass spectrometry were as follows: Column used: HP-5 Heating conditions: 40°C for 4 minutes, heated at 10°C per minute to 280°C Injection method: Splitless Injection port temperature: 250°C Carrier gas: Helium Injection amount: 100 μl

[0054] FIG. 3A shows the results for substrate 2, and FIGS. 3B and 3C show the results for substrate 1. FIG. 3C is an enlarged view of a portion of FIG. 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 the thiophene peak. In all of FIGS. 3A, 3B, and 3C, a peak was observed at a retention time of approximately 1.7 minutes. Therefore, it was confirmed that when thiophene is used as a solvent for the organic semiconductor composition, the produced organic semiconductor thin film contains thiophene.

[0055] The results of Test Examples 1 to 3 confirmed that even when a thiophene solvent was used, a transistor with little variation in mobility could be manufactured.

Claims

1. 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 comprises thiophene as a main component.

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

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

4. The organic semiconductor composition according to any one of claims 1 to 3, wherein the compound having a 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 a step of forming an organic semiconductor thin film layer using the organic semiconductor composition according to any one of claims 1 to 5.

7. Thiophene-containing organic semiconductor thin films.

8. A transistor comprising the organic semiconductor thin film according to claim 7.

Images