JPS6226122B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an organic semiconductor having excellent heat resistance, oxidation resistance, mechanical strength, etc., and a method for manufacturing the same. Organic semiconductors have been studied for a long time, and many substances are known, such as anthracene, pyrene, perylene, tetracyanoquinodimethane, or heat-treated polyacrylonitrile. However, unlike inorganic semiconductors such as silicon and germanium, it is difficult to mold these organic semiconductors into a plate shape, film shape, etc., and many organic semiconductors are in powder form. Furthermore, there is no established technology for converting these organic semiconductors into p-type or n-type semiconductors by doping them with electron-donating or electron-accepting substances such as silicon or germanium, so their uses are limited. However, in recent years, organic semiconductors have been discovered such as polyacetylene that can be relatively easily formed into a film and can also be made into P-type or n-type impurity semiconductors by doping with electron-donating or electron-accepting substances. Research has been conducted on the application of the P-n junction to large-area solar cells. However, these polyacetylenes or substances of this series have low stability because they are highly reactive with oxygen in the air, and have poor heat resistance, so there are many difficulties in actually using them. Furthermore, as can be seen from electron micrographs, polyacetylene film is an aggregate of very thin fibrils, and therefore its bulk density is quite low. For this reason, when a dopant is doped, the entire film is instantly doped, and a P-n junction is formed inside a single sample, such as silicon or germanium, where the front side is P type and the back side is N type. It's difficult to make. That is, since the diffusion rate of the dopant is extremely high, it is extremely difficult to create a bond inside the sample by diffusion control. It has been known for a long time that semiconductors can be made by heat-treating high-molecular polymers; however, these heat-treated products generally lose their shape because the original high-molecular polymer melts or softens during the heat treatment. Not only does it have the disadvantage of not being able to maintain the temperature, but when it melts and softens, it enters a state called meliphaes, which causes crystals of various shapes to form inside the sample. For this reason, the sample is not uniform and has a mixture of crystalline and non-crystalline parts, making it difficult to obtain a homogeneous material. Therefore, it is difficult to control impurities by doping, which poses a problem. It is also known that a relatively homogeneous semiconductor can be obtained by pre-oxidizing polyacrylonitrile to make it difficult to soften and then heat-treating it, but even in this case, polyacrylonitrile is essentially a graphitizable material. Because of this, it is impossible to completely avoid mixing of crystalline and non-crystalline parts. The present inventor completed the present invention as a result of intensive research in view of the above-mentioned problems that existing polymeric organic semiconductors have. The object of the present invention is to be able to be formed into any shape such as a film or a plate, and to have excellent heat resistance, oxidation resistance, mechanical strength, etc., and therefore to have sufficient physical properties for practical use, and not to melt or soften at all during heat treatment. Therefore, the heterogeneous structure of crystalline and amorphous parts does not coexist inside the semiconductor, and it is completely homogeneous down to the molecular level, so dopants can be doped extremely uniformly, and the density of the semiconductor is appropriate. An object of the present invention is to provide an organic semiconductor and a method for manufacturing the same, in which the diffusion rate of a dopant is appropriate and an impurity semiconductor layer can be formed to any depth by diffusion. The above purpose is ^to use a heat-treated product of phenolic resin or furan resin as ^the main component, and to
An organic semiconductor having an electrical resistivity of 1.10 to 1.45 g/cm ³ and a polymer molded body mainly composed of a phenolic resin or a furan resin is heated in a non-oxidizing atmosphere at a temperature of 350 to 700°C. There are no macroscopic continuous pores, the electrical resistivity is 10 ^-1 ~ 10 ¹⁰ Ω・cm, and the density is
This is achieved by a method for producing an organic semiconductor, which is characterized by carrying out a heat treatment to achieve a concentration of 1.10 to 1.45 g/cm ³ . The organic semiconductor according to the present invention must have a density of 1.10 to 1.45 g/cm ³ and must not have macroscopic pores, especially continuous pores, with a minimum diameter of 120 Å or more as measured by a mercury porosimeter. If macroscopic pores exist, the dopant will diffuse abnormally quickly through these pores during doping, resulting in problems such as failure to form a homogeneous doping layer. In this specification, density is a value calculated using the following formula after measuring the volume of a sample using a mercury porosimeter. Density (g/cm ³ ) = (absolute dry weight of sample) / (volume of sample) In the present invention, when a molded article of phenolic resin or furan resin is heat-treated, the temperature increases from 200 to 350°C as the temperature increases. In the temperature range, gases due to decomposition begin to be generated, and as a result, the weight of the sample decreases, but the volume decreases less and the density decreases.
The voids in this case are at the molecular level and extremely small. In the temperature range of 350°C to 700°C, there is a weight loss due to decomposition, but the volume also decreases, so the density increases slightly. When the temperature exceeds 700°C, there is almost no decomposition, the weight remains almost constant, and the volume continues to decrease, so the density continues to increase. The density change during this heat treatment is at the molecular level, and it is most important in the present invention that the dopant enters the voids at the molecular level. In this sense, the density in the present invention is close to the so-called true density. The polymer used in the present invention has a phenolic resin and a furan resin as its main components, and may be a mixture thereof. As will be described later, these resins do not melt or soften at all during heat treatment, and not only can they retain their shape, but also have a homogeneous structure without crystal or amorphous structures when they become semiconductors. It is suitable because it is a material that can be used as a material. Molding of these resins may be carried out as appropriate by conventional methods depending on the type of molded article. For example, to make a film, novolac resin is dissolved in a solvent such as methanol, the solution is cast onto a smooth surface such as a Teflon plate to a uniform thickness, the methanol is evaporated at a relatively low temperature, and then 60 After heat treatment at ~120℃ to eliminate micropores, 60℃ in formalin hydrochloric acid solution.
Obtained by crosslinking reaction at a temperature of ~100°C. In addition, to make a plate-shaped body, for example, attach resol resin to phenol fiber to create a prepreg, insert it between templates to an appropriate thickness, and heat it at a temperature of 120 to 150°C to produce a prepreg of 10 to 200 kg/cm. ² can be pressurized to form a molded body. Further, even if furan resin is used, it can be molded into a film or a plate by using a suitable catalyst such as hydrochloric acid. For example, if phenol fibers and furan resin are used, it is possible to obtain a molded body made of a mixture of these two types of resins. Further, other shapes such as a rod shape, a pipe shape, etc. can be easily formed by a conventional method. The bulk density of the molded article thus produced before heat treatment is preferably 1.15 g/cm ³ . If the density is too low, macroscopic continuous pores (pores with a minimum diameter of 120 Å or more measured with a mercury porosimeter) are likely to be formed. If there are macroscopic continuous pores in the molded product, if doping is performed when it is subsequently heat-treated to become a semiconductor, the diffusion rate of the dopant will be extremely high, making it difficult to appropriately control the thickness of the impurity semiconductor layer. Become. Further, the content of phenolic resin or furan resin in these molded bodies is preferably 99% by weight or more. This is because if the content of the phenol resin or furan resin is less than 99% by weight, the internal structure becomes non-uniform and the homogeneity decreases when the material is converted into a semiconductor in the subsequent heat treatment step. Next, these molded bodies are heat-treated by a known method, for example in a non-oxidizing atmosphere, until the electrical resistivity is 10 ^-1 ~
10 ¹⁰ Ω·cm and a density of 1.10 to 1.45 g/cm ³ . Although the temperature increase rate and heat treatment temperature at this time vary somewhat depending on the type of molded article to be treated, particularly suitable results can be obtained if they are set as follows. That is, the temperature can be raised relatively quickly from room temperature to 300°C, and a rate of 100°C/hour or less is sufficient. When the temperature is raised to 300°C or higher, gas is generated from the inside due to thermal decomposition of organic matter, so the rate must be sufficiently slow. This heating rate is essentially related to the thickness of the material;
It is preferable to raise the temperature at a rate of 80/h ²⁰ c/hour [h: thickness (mm)] or less. If the temperature is increased faster than this, it becomes difficult to appropriately control the electrical resistivity of the heat-treated semiconductor. Reduce the electrical resistivity of the heat-treated material to 10 ^-1 to ^{10 10} Ω・
cm, and the density is 1.10 to 1.45 g/cm ^{3 ,} it is necessary to set the heat treatment temperature in the range of 350 to 700°C. When the heat treatment temperature is less than 350℃, the electrical resistivity is 10 ¹⁰
The resistance of such semiconductors exceeds Ω·cm, and the electrical resistance of such semiconductors hardly decreases even when doped, making it difficult to use them as impurity semiconductors. On the other hand, when the heat treatment temperature exceeds 700°C, the electrical resistivity becomes less than 10 ^-1 Ω·cm, and even if this sample is doped, the electrical resistance hardly decreases. Furthermore, when the heat treatment temperature exceeds 700℃, the density of the sample decreases.
Since it exceeds 1.45 g/cm ³ , it is difficult for the dopant to penetrate into the material, and if doping is performed forcibly, the sample will be destroyed. The organic semiconductor according to the present invention obtained as described above can have a shape such as a plate or a film, which can be selected as appropriate, and is completely homogeneous and has an appropriate electrical resistance. Furthermore, it not only has excellent heat resistance and oxidation resistance, but also sufficient strength, and can be applied to various uses such as planar thermistors and humidity sensors. In addition, since it has an appropriate density, it is possible to easily form an impurity semiconductor layer inside the semiconductor by doping, and it is possible to create a P-n junction etc. in one sample, making it suitable for applications in diodes and solar cells. is also possible. The present invention will be specifically explained below with reference to Examples. Example 1 Plain weave cloth made of phenolic fibers (Japan Kynor Co., Ltd., trade name Kynor, basis weight 200g/
m ² ) was immersed in a 40% by weight methanol solution of resol resin, the liquid was squeezed using a mangle, the resol resin was applied, and the fibers were dried at room temperature for 24 hours. Phenol fiber/resol resin = 1/1 (weight ratio ) prepreg was created. One sheet of this prepreg is molded to 150Kg/cm ² using a pressure molding machine for laminates heated to 150℃.
Cured under pressure for 30 minutes, thickness 250μ, density 1.23
It was made into a plate of g/cm ³ . This plate was heated to 300℃ under _N2 atmosphere.
The temperature was increased at 70°C/hr up to 20°C/hr and from 300°C to the specified temperature shown in the table below at a rate of 20°C/hr to obtain a molded plate having semiconductivity. The surface and cross section of these plates were examined using an electron microscope.
Although observed up to 25x magnification, no macroscopic pores were found. Table 1 shows the density and electrical resistivity of these plates. The semiconducting molded plate (about 200 μm in thickness) thus obtained was exposed to an I ₂ gas atmosphere at 200° C. and doped with I ₂ from the plate surface for about 60 minutes. After doping, the sample was washed with methanol, air-dried, and then subjected to EMAX (Electron Micro-
Analyzer) analysis was performed to determine the distribution of _I2 within this sample.

【table】

[Table] From the above table, when the heat treatment temperature is lower than 350°C, the density of the sample is less than 1.10 g/cm ² , and when I ₂ is doped, the diffusion rate of I ₂ is high, so the entire sample is doped, and I ₂ is inside the sample. It can be seen that cracks occur in the sample when doped with I ₂ because an impregnated layer cannot be created and the density of the sample exceeds 1.45 g/cm ³ when the heat treatment temperature exceeds 750°C. Furthermore, when the molded body made of the semiconductor of the present invention was doped with I ₂ , it was possible to form an impurity semiconductor layer inside the sample because the dopant diffusion rate was appropriate. Example 2 Resol resin and furan resin (manufactured by Hitachi Chemical Co., Ltd., trade name Hitafuran 302) were dissolved in acetone at a weight ratio of 1:1, the plain weave cloth used in Example 1 was immersed in this solution, and air-dried. Phenol fiber/
A prepreg with resin = 2/1 was created. This prepreg was heated and pressure molded in the same manner as in Example 1 except that the molding pressure was varied to produce molded plates of various bulk densities. Bulk density of polymer molded plate
At 1.23 g/cm ³ and 1.27 g/cm ³ , there were no macroscopic pores observed by electron microscopy, but at 1.05 g/cm ³ macroscopic pores were present. This plate was heated to the predetermined temperature shown in the table below under the same heating conditions as in Example 1 and heat-treated. The thickness of these semiconductor plates was about 200μ. Next, these plates were doped with I ₂ at 150℃ for about 5 minutes to determine the thickness of the I ₂ doped layer.
Obtained by EMAX analysis. The results are shown in Table 2.

[Table] If the density of the polymer molded body is less than 1.15g/ ^cm3 ,
Even if heat treatment was performed at a temperature of 350 to 700°C, it was not possible to form an I ₂ doped layer inside the semiconductor because macroscopic continuous pores existed and the diffusion rate of the dopant was high. Also, the density of heat-treated semiconductor is 1.45
When the amount exceeds g/cm ³ , it is difficult to dope I ₂ and cracks appear on the surface. In the molded plate made of the semiconductor of the present invention, an impurity semiconductor (P-type semiconductor in this case) layer made of an I ₂ doped layer is formed inside the plate, and the electrical resistance of this layer is greatly reduced compared to before doping. Was.

Claims (1)

[Scope of Claims] 1. An organic semiconductor whose main component is a heat-treated product of phenolic resin or furan resin, and which has an electrical resistivity of 10 ^-1 to ¹⁰ Ω·cm and a density of 1.10 to 1.45 g/cm ³ . 2. Polymer molded product mainly composed of phenolic resin or furan resin is heated to 350~350°C in a non-oxidizing atmosphere.
At a temperature of 700℃, there are no macroscopic continuous pores,
Electrical specific resistance is 10 ^-1 ~ 10 ¹⁰ Ω・cm, density is 1.10 ~
A method for producing an organic semiconductor, characterized by heat-treating it so that it becomes 1.45 g/cm ³ . 3. The method for producing an organic semiconductor according to claim 2, wherein the polymer molded product contains 99% by weight or more of a phenolic resin or a furan resin.