Organic semiconductor materials and their applications

Abstract

To provide an organic semiconductor material which becomes a raw material of an organic semiconductor device (an organic transistor) indicating an excellent carrier mobility, an organic thin film containing the organic semiconductor material, and an organic semiconductor device.SOLUTION: In an organic semiconductor material containing a chemical compound expressed by ( Formula (1), in which R expresses an alkyl group of which the number of carbons is 1 to 4.), an organic thin film containing the organic semiconductor material, and an organic semiconductor device, the alkyl group expressed by the R of Formula (1) is not limited to any of a linear chain shape and a branch chain shape, but has preferably the linear chain shape, and more preferably has a methyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an organic semiconductor material and its use. More specifically, the present invention relates to an organic semiconductor material containing a pyrene derivative having a specific structure, and an organic thin film and an organic semiconductor device containing the material. [Background technology]

[0002] Pyrene derivatives have been investigated for use in organic electroluminescence (EL) applications as luminescent condensed polycyclic aromatic compounds. Recently, their application to organic transistors and organic solar cells has also been investigated. Non-Patent Document 1 summarizes many pyrene derivatives and their mobilities, but most of them have hole transport properties of 10 or less. -6 〜10 -1 This is an order. Non-Patent Document 2 reports that an organic transistor using a compound in which the terminals of an oligothiophene are end-capped with pyrene exhibits a mobility of 3.3, and Non-Patent Document 3 reports that an organic transistor using a 1,6-substituted pyrene compound exhibits a maximum mobility of 2.1. However, there are very few reports that an organic transistor using a compound having a pyrene skeleton exhibits high mobility (transport property).

[0003] On the other hand, Patent Document 1 describes a thiomethylated fused polycyclic aromatic compound as an intermediate of an organic semiconductor material, but there are very few reports on the transport properties of the thiomethylated fused polycyclic aromatic compound itself. For example, Non-Patent Document 4 reports on the transport properties of benzodithiophene compounds, but their hole transport properties are only 10 at most. 0 It was about that extent. Furthermore, Patent Document 2 reports the use of a thiomethylated pyrene compound as a charge transport complex, but does not describe anything about the transport properties of the thiomethylated pyrene compound itself. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2012 / 115236 [Patent Document 2] Japanese Patent Application Publication No. 02-11560 [Non-patent literature]

[0005] [Non-Patent Document 1] Science China Chemistry 2016,12,1623-1631 [Non-patent document 2] Chemical Communications 2016,26,4800-4803 [Non-patent document 3] Applied Materials & Interfaces 2013,5,3855-3860 [Non-patent document 4] Chemistry of Materials 2019,31,6696 -6705 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an organic semiconductor material that can be used as a raw material for an organic semiconductor device (organic transistor) that exhibits excellent carrier mobility, and an organic thin film and an organic semiconductor device that include the organic semiconductor material. [Means for solving the problem]

[0007] As a result of extensive investigations, the present inventors have found that an organic semiconductor material containing a pyrene compound with a specific structure can solve the above problems, and have thus completed the present invention.

[0008] That is, the present invention provides: [1] The following formula (1)

[0009] [ka]

[0010] (wherein R represents an alkyl group having 1 to 4 carbon atoms), [2] The organic semiconductor material according to the above item [1], wherein R is a methyl group. [3] An organic thin film containing the organic semiconductor material according to the preceding item [1] or [2]. [4] An organic semiconductor device comprising the organic semiconductor material according to the preceding item [1] or [2], or the organic thin film according to the preceding item [3]. [5] The organic semiconductor device according to the above item [4], wherein the organic thin film is an active layer; and [6] The organic semiconductor device according to the above item [4] or [5], which is an organic transistor. Regarding. [Effects of the Invention]

[0011] By using an organic thin film containing the organic semiconductor material of the present invention in an active layer, it has been possible to provide a semiconductor device that is superior in carrier mobility and the like to organic semiconductor devices obtained by using known organic semiconductor materials containing pyrene compounds. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a field-effect transistor, which is one of the organic semiconductor devices of the present invention. [Figure 2] FIG. 2 is an example showing the transfer characteristics of the organic thin film transistor of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The organic semiconductor material of the present invention contains a compound represented by the following formula (1). In formula (1), R represents an alkyl group having 1 to 4 carbon atoms.

[0014] [ka]

[0015] The alkyl group represented by R in formula (1) is not limited to either a straight-chain or branched-chain alkyl group, but is preferably a straight-chain alkyl group, and more preferably a methyl group.

[0016] The compound represented by formula (1) can be synthesized based on a known method according to the flow shown in the following reaction scheme: In the following reaction scheme, R has the same meaning as R in formula (1).

[0017] [ka]

[0018] As described above, the compound represented by formula (1), which is an essential component of the organic semiconductor material of the present invention, can be synthesized from raw materials in only one step, and can be produced much more easily than other known compounds with high transportability.

[0019] The method for purifying the compound represented by formula (1) is not particularly limited, and known methods such as recrystallization, column chromatography, and vacuum sublimation purification can be used. These methods can also be combined as necessary.

[0020] Specific examples of the compound represented by formula (1) are shown below, but the present invention is not limited to these.

[0021] [ka]

[0022] The content of the compound represented by formula (1) in the organic semiconductor material of the present invention is not particularly limited as long as it does not adversely affect the properties of an organic semiconductor device obtained using the organic semiconductor material, but is usually 80% by mass or more in the organic semiconductor material, preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass (all of the organic semiconductor material is the compound represented by formula (1)).

[0023] The organic semiconductor material of the present invention is suitably used as a material for organic thin films in organic electronic devices such as organic EL elements, organic solar cell elements, organic photoelectric conversion elements, and organic transistor elements.

[0024] Next, the organic thin film of the present invention will be described. The organic thin film of the present invention is obtained using the organic semiconductor material of the present invention. That is, the organic thin film of the present invention is a thin film containing at least one compound represented by formula (1), and may contain multiple compounds represented by formula (1), or may contain compounds other than the compound represented by formula (1). The thickness of the thin film varies depending on its application, but is usually 1 nm to 1 μm, preferably 5 nm to 500 nm, and more preferably 10 nm to 200 nm.

[0025] The organic thin film can be formed by dry processes such as vapor deposition and sputtering, or by various solution processes, and the method can be appropriately selected depending on the physical properties of the compound represented by formula (1), such as solubility and sublimation. Alternatively, an organic single crystal previously obtained by a dry process or solution process can be used as the organic thin film. Examples of solution processes include spin coating, drop casting, dip coating, spraying, bar coating, die coating, slit coating, pen coating, curtain coating, flexographic printing, letterpress printing, offset printing, dry offset printing, lithographic printing, gravure printing, screen printing, stencil printing, inkjet printing, microcontact printing, and the like, as well as methods combining a plurality of these methods, and spin coating, die coating, slit coating, offset printing, and inkjet printing are preferred. When forming a film by a solution process, it is preferable to apply and print using the above-mentioned method, and then evaporate the solvent to form a thin film. In addition, in order to obtain high transportability, it is preferable to form a thin film using an organic semiconductor material made of a single crystal. The dry process includes a vapor deposition method using resistance heating.

[0026] During the formation of organic thin films, various environmental factors, such as the surface energy and temperature of the substrate, are important for stable thin film formation. These factors can affect the state of the thin film and the characteristics of organic semiconductor devices. For example, inappropriate surface energy can cause defects such as repelling on the substrate surface, preventing the formation of a continuous film. Furthermore, appropriate temperatures during thin film formation, the drying temperature of solvents, and the post-treatment (heat treatment) temperature after thin film formation can alleviate distortions in the film during film formation, reduce pinholes, and control the alignment and orientation of the film, thereby improving and stabilizing the characteristics of organic semiconductor devices. This heat treatment is performed by heating the substrate after the formation of the organic thin film. While there are no particular limitations on the heat treatment temperature, it is typically between room temperature and 200°C. The heat treatment can be performed in air or in an inert atmosphere such as nitrogen or argon. Other methods, such as controlling the film shape using solvent vapor, are also possible.

[0027] Finally, the organic semiconductor device of the present invention will be described. The organic semiconductor device of the present invention is a device that includes an organic thin film containing the organic semiconductor material of the present invention as an organic semiconductor layer, and specific examples thereof include a field-effect transistor, an organic EL element, and a photoelectric conversion element.

[0028] As an example of various organic semiconductor devices, we will explain the field-effect transistor. An organic field-effect transistor has two electrodes (a source electrode and a drain electrode) in contact with a semiconductor layer made of an organic thin film, and the current flowing between these electrodes is controlled by the voltage applied to another electrode called the gate electrode.

[0029] Generally, organic transistor devices often use a structure in which the gate electrode is insulated by an insulating film (Metal-Insulator-Semiconductor MIS structure). Those that use a metal oxide film as the insulating film are called MOS structures. There are also structures in which the gate electrode is formed via a Schottky barrier (i.e., MES structures), but the MIS structure is often used for organic transistors.

[0030] Hereinafter, organic transistors will be described in more detail using some exemplary embodiments of the organic transistor device shown in FIG. 1, but the present invention is not limited to these structures.

[0031] In each embodiment shown in Figure 1, 1 represents the source electrode, 2 the semiconductor layer, 3 the drain electrode, 4 the insulator layer, 5 the gate electrode, and 6 the substrate. The arrangement of each layer and electrode can be selected appropriately depending on the device's application. Transistors A to D and F are called horizontal transistors because current flows parallel to the substrate. Transistor A is called a bottom-contact bottom-gate structure, and transistor B is called a top-contact bottom-gate structure. Transistor C has source and drain electrodes and an insulator layer formed on a semiconductor, with a gate electrode further formed on top of that, and is called a top-contact top-gate structure. Transistor D has a structure called a top-and-bottom-contact bottom-gate transistor. Transistor F has a bottom-contact top-gate structure. Transistor E is a schematic diagram of a vertically structured transistor, i.e., a static induction transistor (SIT). This SIT allows for the current flow to spread in a plane, allowing a large number of carriers to move at once. Furthermore, because the source and drain electrodes are arranged vertically, the distance between the electrodes can be reduced, resulting in fast response. Therefore, it is suitable for applications such as large current flow and high-speed switching. Although a substrate is not shown in E in Fig. 1, a substrate is usually provided on the outside of the source or drain electrodes represented by 1 and 3 in Fig. 1E. The organic thin film of the present invention can be used as the semiconductor layer represented by 2 in Fig. 1.

[0032] The organic semiconductor material of the present invention contains the compound represented by formula (1) as an essential component, allowing organic semiconductor devices to be manufactured using a relatively low-temperature process. This allows flexible materials such as plastic plates and films, which cannot be used under high-temperature conditions, to be used as substrates, making it possible to manufacture lightweight, flexible, and durable devices.

[0033] The device of the present invention can be used in the fields of organic transistor devices, diodes, capacitors, thin-film photoelectric conversion devices, color organic EL devices, and the like. [Example]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The structures of the compounds described in the synthesis examples were determined by mass spectrometry (MS) and nuclear magnetic resonance spectrometry (NMR) as necessary. The MS spectra in the examples were obtained using a GCMS-QP2020 (Shimadzu Corporation). 1 1 H NMR spectra were measured using an ECS400 (JEOL).

[0035] Synthesis Example 1 (Synthesis of Compound Represented by Formula (2)) Following a known method, 1,3,6,8-tetrabromopyrene (manufactured by Sigma-Aldrich) and sodium thiomethoxide (manufactured by Sigma-Aldrich) were reacted in an aprotic solvent to obtain the compound represented by formula (2) of the above specific example in a yield of 98%.

[0036] Example 1 (Formation of organic thin film of the present invention) A single crystal thin film was produced by vapor phase growth in a nitrogen atmosphere using the compound obtained in Synthesis Example 1. The obtained thin film was subjected to structural analysis using an X-ray structural analyzer (Rigaku XtaLAB Synergy-S), and it was confirmed that the compound had a π-stacked crystalline structure.

[0037] Example 2 (Fabrication of BGBC-type organic thin-film transistor) A 90 nm thin film was formed on an n-doped silicon wafer with a thermally oxidized SiO2 film by spin coating using CYTOP (Asahi Glass Co., Ltd.), and source and drain electrodes were fabricated by vacuum-depositing Au on the thin film using a shadow mask. The electrodes were then treated with an ethanol solution of pentafluorobenzenethiol (Tokyo Chemical Industry Co., Ltd.) to form a SAM film. A thin film of the compound represented by formula (2) prepared in Example 1 was placed between the source and drain electrodes to fabricate a BGBC-type organic thin-film transistor.

[0038] Example 3 (Fabrication of BGTC-type organic thin-film transistor) A 90 nm thin film was formed on an n-doped silicon wafer with a thermally oxidized SiO2 film by spin coating using CYTOP (Asahi Glass Co., Ltd.). A thin film of the compound represented by formula (2) prepared in Example 1 was then placed on the thin film. A source electrode and a drain electrode were formed on the thin film by vacuum deposition of 15 nm of molybdenum oxide and 30 nm of Au using a shadow mask, thereby producing a BGTC-type organic thin film transistor.

[0039] Example 4 (Fabrication of an organic thin film transistor using graphite electrodes) A BGTC-type organic thin-film transistor using graphite electrodes was fabricated in the same manner as in Example 3, except that the method for forming the source and drain electrodes was changed from the vacuum deposition method of molybdenum oxide 15 nm and Au 30 nm using a shadow mask to a method of drop-casting colloidal graphite and then drying it.

[0040] Example 5 (Evaluation of organic thin film transistor characteristics) The performance of an organic thin-film transistor device depends on the amount of current that flows when a potential is applied between the source and drain while a potential is applied to the gate. Measuring this current value allows us to determine the mobility, a characteristic of the transistor. Mobility can be calculated using the following formula (a), which expresses the electrical properties of the carrier species generated in the organic semiconductor layer as a result of applying a gate electric field to SiO2, an insulator. Id = ZμCi(Vg-Vt) 2 / 2L (a) where Id is the saturated source-drain current, Z is the channel width, Ci is the capacitance of the insulator, Vg is the gate potential, Vt is the threshold potential, L is the channel length, and μ is the mobility (cm 2 / Vs). Ci is the dielectric constant of the SiO2 insulating film used, Z and L are determined by the device structure of the organic transistor device, Id and Vg are determined when measuring the current value of the organic transistor device, and Vt can be calculated from Id and Vg. By substituting each value into equation (a), the mobility at each gate potential can be calculated. The transistor characteristics were evaluated using a Keithley 4200 semiconductor parameter analyzer.

[0041] The characteristics of the organic thin-film transistors obtained in Examples 2 to 4 were evaluated. Figure 2 shows the transfer characteristics of the transistor obtained in Example 4, and Table 1 shows the results of the transistor characteristics. All of the multiple devices fabricated maintained a mobility that was 10 or higher and a low threshold voltage. Furthermore, 25 transistors fabricated in Example 4 showed an average mobility of over 31 with very low variation, demonstrating high reproducibility.

[0042] [Table 1]

[0043] From the above, it has been found that organic semiconductor devices using organic thin films containing the organic semiconductor material of the present invention have very excellent properties. According to the present invention, it has become possible to fabricate high-performance organic semiconductor devices, which have great industrial value, as they can be used in a wider range of processes and applications. [Industrial Applicability]

[0044] The organic semiconductor material of the present invention can be easily synthesized and also exhibits extremely high hole transport properties. Therefore, thin films containing the material have excellent transistor properties and photoelectric conversion properties. The material is expected to be applied to digital devices such as memory circuit devices, signal driver circuit devices, and signal processing circuit devices as organic transistors, and to devices such as organic solar cells, organic image sensors, photosensors, and photon counters as photoelectric conversion elements, as well as to fields such as solar cells, cameras, video cameras, and infrared cameras that utilize the same. [Explanation of symbols]

[0045] Figure 1 1. Source electrode 2. Semiconductor layer 3 Drain electrode 4 Insulator Layer 5. Gate electrode 6 PCB 7 Protective layer

Claims

1. The following formula (1) 【Chemical 1】 (In formula (1), R represents an alkyl group having 1 to 4 carbon atoms.) An organic semiconductor device comprising a compound represented by the formula:

2. The organic semiconductor device according to claim 1, wherein R in formula (1) is a methyl group.

3. An organic semiconductor device containing the compound represented by formula (1) as an organic thin film.

4. An organic semiconductor device as described in claim 3, wherein the organic thin film is an active layer.

5. 5. The organic semiconductor device according to claim 1, which is an organic transistor.

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