Liquid organic semiconductor material
|発明の名称 （英語）||Liquid organic semiconductor material|
|発明の概要（英語）||An organic material having at least one aromatic conjugated π-electron system is selected. The purity of the organic material is improved by purification, and a conduction mechanism of the organic material is confirmed by a time-of-flight method, whereby a liquid phase of the organic material is usable as an organic semiconductor. A method that enables the usage of a liquid phase of an organic material as an organic semiconductor is provided. The method involves confirming the electronic conduction of the organic material having at least one aromatic conjugated π-electron system by evaluation of a charge transport property using a time-of-flight method, and by evaluation of a dilution effect caused by addition of a diluent.|
An organic semiconductor material is a material which can be used for an optical sensor, an organic photoreceptor, an organic EL element, an organic transistor, an organic solar cell, an organic semiconductor memory, and the like. Specific examples of the organic semiconductor material which have heretofore been used may include: for example, an amorphous thin film or polycrystalline thin film which has been formed on a by using vacuum deposition of an organic semiconductor substance, or by applying a solution containing an organic semiconductor substance onto a substrate. The organic semiconductor material may be, for example, a thin film material formed by dispersing the organic semiconductor substance into a polymer material or the like and applying the dispersed semiconductor substance onto a substrate; or a single-crystal material of the organic semiconductor material (that is, a semiconductor material which is a solid in a temperature range wherein a device using the semiconductor material can be driven). This is because, in order to produce an organic electronic device, the function of such a device should be achieved by utilizing the electronic conductivity exhibited by the organic semiconductor. From this point, it has been considered that it is necessary to use an amorphous material, a polycrystalline material, a single-crystal material or the like, which has been hitherto considered as the material which can achieve the electronic conduction.
On the other hand, in recent years, it has been found that a liquid crystal material capable of providing a molecular orientation having a higher viscosity, compared to that of a general liquid material, can also exhibit the electronic conduction in the nematic phase, in the smectic phase, in the columnar phase thereof, or the like. It has also been found that such a liquid crystal material which can be used as the organic semiconductor material, and accordingly, the applications of the liquid crystal material to organic electronic devices have also been studied.
The conduction of a low-molecular-weight non-liquid crystal organic compound in an isotropic phase (i.e., liquid phase) is considered to show the ion conduction, because its viscosity is generally low. An example in which the electronic conduction in such a material is recognized, has been reported only in a extremely specific system. An example thereof is such that high-energy electrons are generated by the application of a high-energy electron beam, an X ray, or a short-wavelength light to a hydrocarbon, such as methane or ethane, and the conduction of the high-energy electrons is confirmed by using a time-of-flight method or the like (IEEE Transaction on Electrical Insulation vol. EI-19, No. 5, 390-418).
It is considered that the conduction of high-energy electrons, which have been generated in the above manner, is similar to the conduction of free electrons which are weakly bound to a molecule. Further, it has also been found that the mobility of the high-energy electron in the above-mentioned organic compound is much more than that in a general organic solid, and that some high-energy electrons show a mobility exceeding several tens cm2/Vs. Among the liquid crystal substances, a phthalocyanine liquid crystal in an isotropic phase, which is one of discotic liquid crystals with a high viscosity, shows an electronic conduction, which has been confirmed by using the time-of-flight method (Extended Abstract of the 54th Meeting of The Japan Society of Applied Physics and Related Societies, 2007, p 1333). However, at present, it is considered that the conduction in a rod-like non-polymeric liquid crystal substance or the conduction in a liquid phase (isotropic phase) of a non-liquid crystal substance is the ionic conduction, and there has been no example wherein an electronic conduction of such a substance is experimentally confirmed. Accordingly, the electronic conduction of such a substance has never been confirmed.
In general, it has been considered that the conduction of the so-called liquid (i.e., the liquid state in an isotropic phase) is the ionic conduction. That is, it has been considered that the organic material in the liquid state cannot achieve any organic electronic device using the electronic conduction. In other words, in the prior art, in order to achieve the function of the device using the electronic conduction, the organic semiconductor material to be used for the organic electronic device is required to be an amorphous solid or crystal, or a liquid crystal phase of a liquid crystal material, the electronic conduction of which has already been confirmed, in a temperature range wherein the device can be driven.
1. A method for measuring characteristics of an organic substance, comprising:
(a) disposing the organic substance to be measured between a pair of electrodes;
(b) injecting charges into the organic substance and measuring a transient current in an isotropic liquid phase of the organic substance using a time-of-flight method;
(c) separating the transient current into a current by electronic conduction and a current by ionic conduction; and
(d) measuring a charge amount corresponding to each separated current,
wherein purity of the organic substance is evaluated based on the charge amount corresponding to each separated current.
2. The method according to claim 1, wherein the charge injection into the organic substance is conducted by applying a pulse voltage or a pulse light to the organic substance.
3. The method according to claim 1, wherein the organic substance is purified to the extent that the organic substance exhibits electron conduction and/or hole conduction.
4. The method according to claim 1, wherein the organic substance is an organic semiconductor material, and a semiconductor property of the organic semiconductor material is evaluated based on the charge amount corresponding to each separated current.
5. The method according to claim 4, wherein the semiconductor property is purity of the organic semiconductor material as an electronic material, wherein the purity of the organic semiconductor material as an electronic material is relative concentration of a substance serving as an electronic trap.
6. The method according to claim 4, wherein the semiconductor property is mobility, and whether the conduction mechanism, in the organic semiconductor material, is electronic conduction or ionic conduction is determined based on a value of mobility measured.
7. The method according to claim 6, wherein when the mobility measured ismobility of 10－3 cm2/Vs, the conduction in the organic semiconductor material is evaluated as electronic conduction.
8. The method according to claim 6 or 7, wherein whether the conduction mechanism is electronic conduction or ionic conduction is determined based on a change in the mobility due to a change in viscosity of the organic substance or a change in an intermolecular distance of the organic substance between before and after adding a diluent.
9. The method according to claim 8, wherein the diluent is a substance having HOMO and LUMO levels, the HOMO and LUMO levels being not providing an electronic trap level with respect to HOMO and LUMO levels of the organic substance.
10. The method according to claim 1, wherein the organic substance is a mixture.
11. The method according to claim 10, wherein the organic substance is in the form of solution.
12. The method according to claim 1, wherein the pair of electrodes are respectively disposed on a pair of substrates, and a charge injection means for injecting charges into the organic substance is provided.
13. The method according to claim 12, wherein the pair of substrates, the pair of electrodes and the charge injection means form a cell for measuring electronic conduction and/or ionic conduction.
|参考情報 （研究プロジェクト等）||CREST Establishment of Innovative Manufacturing Technology Based on Nanoscience AREA|
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