Thermoelectric conversion element and article having the same

Abstract

The present invention relates to a thermoelectric conversion element and an article having the same. The present invention provides a thermoelectric conversion element having a thermoelectric conversion layer containing a thiophene polymer, wherein the X-ray diffraction spectrum of the thermoelectric conversion layer shows a peak intensity at a diffraction angle (2θ) of 7.9° that is at least five times the peak intensity at a diffraction angle (2θ) of 25.8°.

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion element and an article having the thermoelectric conversion element. Background Art

[0002] Various inorganic materials are used in thermoelectric conversion elements that convert heat energy into electric energy. On the other hand, research on thermoelectric conversion elements using organic materials has been actively conducted in recent years.

[0003] Conductive polymers, among others, exhibit electrical conductivity due to the localized presence of charge within their elements, and consequently exhibit thermoelectric conversion properties, making them promising high-performance materials. Research has been conducted on various conductive polymers, including polyaniline, polyphenylene vinylene, and polythiophenes (e.g., polyethylene dioxythiophene (PEDOT)).

[0004] Specifically, for example, Patent Document 1 discloses “a thermoelectric conversion element using a thermoelectric conversion material containing a polythiophene polymer, carbon nanotubes, and a non-conjugated polymer in a thermoelectric conversion layer.”

[0005] Furthermore, Patent Document 2 discloses “a thermoelectric conversion element using a thermoelectric conversion material containing a conductive polymer, carbon nanotubes, and an onium salt compound and having an electrical conductivity anisotropy of 1.5 to 10”.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 5848284

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-098299 Summary of the Invention

[0010] Technical problem to be solved by the invention

[0011] The technical problem to be solved by the present invention is to provide a thermoelectric conversion element having excellent thermoelectric conversion performance compared to a thermoelectric conversion element having a thermoelectric conversion layer containing a thiophene polymer, in which the peak intensity at a diffraction angle (2θ) of 7.9° in the X-ray diffraction spectrum of the thermoelectric conversion layer is less than 5 times the peak intensity at a diffraction angle (2θ) of 25.8°, or the mirror reflectivity of the thermoelectric conversion layer is less than 10%.

[0012] Means for solving technical problems

[0013] Specific means for solving the above technical problems include the following methods.

[0014] <1>

[0015] A thermoelectric conversion element, wherein:

[0016] having a thermoelectric conversion layer comprising a thiophene polymer,

[0017] In the X-ray diffraction spectrum of the thermoelectric conversion layer, the peak intensity at a diffraction angle (2θ) of 7.9° is 5 times or more the peak intensity at a diffraction angle (2θ) of 25.8°.

[0018] <2>

[0019] like <1> The thermoelectric conversion element described above has a peak intensity at a diffraction angle (2θ) of 7.9° that is at least 7 times the peak intensity at a diffraction angle (2θ) of 25.8°.

[0020] <3>

[0021] A thermoelectric conversion element, wherein:

[0022] having a thermoelectric conversion layer comprising a thiophene polymer,

[0023] The thermoelectric conversion layer has a mirror reflectivity of not less than 10% and not more than 35%.

[0024] <4>

[0025] like <3> In the thermoelectric conversion element, the specular reflectivity of the thermoelectric conversion layer is not less than 15% and not more than 30%.

[0026] <5>

[0027] like <1> ~ <4> The thermoelectric conversion element according to any one of the preceding claims, wherein the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms in the thermoelectric conversion layer is 1500 ppm or less relative to the thiophene polymer.

[0028] <6>

[0029] like <5> In the thermoelectric conversion element, the total content of the Fe atoms, the Cu atoms, the Mn atoms, the Cr atoms, and the Ce atoms is 500 ppm or less relative to the thiophene polymer.

[0030] <7>

[0031] like <6> In the thermoelectric conversion element, the total content of the Fe atoms, the Cu atoms, the Mn atoms, the Cr atoms, and the Ce atoms is 100 ppm or less relative to the thiophene polymer.

[0032] <8>

[0033] like <1> ~ <7> The thermoelectric conversion element according to any one of the preceding claims, wherein the thiophene polymer is a polymer of at least one thiophene selected from the group consisting of alkoxythiophene, aminothiophene, hydroxythiophene, and alkylthiophene.

[0034] <9>

[0035] like <8> In the thermoelectric conversion element, the thiophene polymer is a polymer of at least one thiophene selected from the group consisting of alkoxythiophene and alkylthiophene.

[0036] <10>

[0037] like <8> or <9> In the thermoelectric conversion element, the alkoxy group of the alkoxythiophene has 1 to 6 carbon atoms, and the alkyl group of the alkylthiophene has 2 to 12 carbon atoms.

[0038] <11>

[0039] An article comprising a thermoelectric conversion element having a thermoelectric conversion layer containing a thiophene polymer, wherein in an X-ray diffraction spectrum of the thermoelectric conversion layer, the peak intensity at a diffraction angle (2θ) of 7.9° is at least five times the peak intensity at a diffraction angle (2θ) of 25.8°.

[0040] Effects of the Invention

[0041] according to <1> or <2> A scheme provides a thermoelectric conversion element, and the thermoelectric conversion element provided by the above scheme has excellent thermoelectric conversion performance compared with a thermoelectric conversion element having a thermoelectric conversion layer containing a thiophene polymer, in which the peak intensity at a diffraction angle (2θ) of 7.9° in the X-ray diffraction spectrum of the thermoelectric conversion layer is less than 5 times the peak intensity at a diffraction angle (2θ) of 25.8°.

[0042] according to <3> or <4> A scheme provides a thermoelectric conversion element, which has excellent thermoelectric conversion performance compared to a thermoelectric conversion element having a conductive substrate and a thermoelectric conversion layer containing a thiophene polymer, in which the mirror reflectivity of the thermoelectric conversion layer is less than 10%.

[0043] according to <5> 、 <6> or <7> A scheme is provided to provide a thermoelectric conversion element, which has excellent thermoelectric conversion performance compared to the case where the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms and Ce atoms in the thermoelectric conversion layer is greater than 1500 ppm relative to the thiophene polymer.

[0044] according to <8> 、 <9> or <10> A scheme provides a thermoelectric conversion element, wherein the thermoelectric conversion layer comprises a polymer of at least one thiophene selected from the group consisting of alkoxythiophene, aminothiophene, hydroxythiophene and alkylthiophene as the thiophene polymer, and the thermoelectric conversion element has excellent thermoelectric conversion performance, compared with a thermoelectric conversion element having a thermoelectric conversion layer comprising a thiophene polymer, wherein the peak intensity at a diffraction angle (2θ) of 7.9° in the X-ray diffraction spectrum of the thermoelectric conversion layer is less than 5 times the peak intensity at a diffraction angle (2θ) of 25.8°, or the mirror reflectivity of the thermoelectric conversion layer is less than 10%.

[0045] according to <11> A scheme provides an article, which has a thermoelectric conversion element with excellent thermoelectric conversion performance compared to a thermoelectric conversion element having a thermoelectric conversion layer containing a thiophene polymer, in which the peak intensity at a diffraction angle (2θ) of 7.9° in the X-ray diffraction spectrum of the thermoelectric conversion layer is less than 5 times the peak intensity at a diffraction angle (2θ) of 25.8°, or the mirror reflectivity of the thermoelectric conversion layer is less than 10%. DETAILED DESCRIPTION

[0046] An embodiment as an example of the present invention will be described in detail below.

[0047] It should be noted that, in the numerical ranges described in stages, the upper limit value or the lower limit value described in a certain numerical range can be replaced by the upper limit value or the lower limit value of another numerical range described in stages.

[0048] In addition, in the numerical range, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the Examples.

[0049] When two or more substances corresponding to each component are present in the composition, the amount of each component in the composition refers to the total amount of the two or more substances present in the composition unless otherwise specified.

[0050] The term "process" does not only refer to an independent process, but also includes processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0051] It should be noted that "ppm" in this article is the abbreviation of parts per million, which is the mass standard.

[0052] [Thermoelectric conversion element]

[0053] The thermoelectric conversion element of this embodiment includes a thermoelectric conversion layer containing a thiophene polymer.

[0054] Furthermore, the thermoelectric conversion element of this embodiment satisfies at least one of the following conditions (1) and (2).

[0055] Condition (1): The peak intensity at a diffraction angle (2θ) of 7.9° in the X-ray diffraction spectrum of the thermoelectric conversion layer is 5 times or more the peak intensity at a diffraction angle (2θ) of 25.8°.

[0056] Condition (2): The specular reflectivity of the thermoelectric conversion layer is 10% or more and 35% or less.

[0057] In thermoelectric conversion elements using thiophene polymers as the conductive polymer, the localization of charge in the thermoelectric conversion layer is strongly affected by the molecular orientation of the thiophene polymer. Therefore, when the molecular orientation of the thiophene polymer is low, the reproducibility of the generated power tends to be insufficient and vary. Consequently, thermoelectric conversion performance of thermoelectric conversion elements using thiophene polymers as the conductive polymer is low.

[0058] On the other hand, in the thermoelectric conversion element of this embodiment, it is known that by ensuring that the thermoelectric conversion layer containing the thiophene polymer satisfies at least one of the above conditions (1) and (2), the thiophene polymer in the thermoelectric conversion layer can be highly oriented. Therefore, it is possible to efficiently localize the charge in the thermoelectric conversion layer, resulting in high reproducibility of power generation and reduced variation.

[0059] Therefore, the thermoelectric conversion element of this embodiment has excellent thermoelectric conversion performance.

[0060] Next, the thermoelectric conversion element of this embodiment will be described in detail.

[0061] <Thermoelectric Conversion Layer>

[0062] (X-ray diffraction spectrum of the thermoelectric conversion layer)

[0063] In the X-ray diffraction spectrum of the thermoelectric conversion layer, the peak intensity at a diffraction angle (2θ) of 7.9° is 5 times or more of the peak intensity at a diffraction angle (2θ) of 25.8°, preferably 6 times or more, more preferably 7 times or more, from the perspective of improving thermoelectric conversion performance.

[0064] In order to make the ratio of the peak intensity at a diffraction angle (2θ) of 7.9° to the peak intensity at a diffraction angle (2θ) of 25.8° fall within the above range, for example, 1) limiting the amount of the metal component (A) described later, 2) forming the thermoelectric conversion layer by a wet method, and 3) selecting the type of coating liquid for the wet method can be mentioned.

[0065] The method for measuring the X-ray diffraction spectrum of the thermoelectric conversion layer is as follows.

[0066] Using a thin film X-ray diffractometer X'Pert MRD (manufactured by Malvern Panalytical), the diffraction spectrum of the thermoelectric conversion layer formed on the substrate was measured by changing the incident angle 2θ / ω of the X-ray to obtain the peak intensity at each diffraction angle.

[0067] Thereafter, the intensity ratio of the peak intensity at a diffraction angle (2θ) of 7.9° to the peak intensity at a diffraction angle (2θ) of 25.8° was determined from the obtained X-ray diffraction spectrum.

[0068] (Mirror reflectivity of thermoelectric conversion layer)

[0069] The specular reflectivity of the thermoelectric conversion layer is 10% to 35%, preferably 12% to 33%, and more preferably 15% to 30% from the viewpoint of improving thermoelectric conversion performance.

[0070] To adjust the mirror reflectance to the above range, for example, 1) limiting the amount of the metal component (A) described below, 2) forming the thermoelectric conversion layer by a wet method, and 3) selecting the type of coating liquid for the wet method can be mentioned.

[0071] The method for measuring the specular reflectance of the thermoelectric conversion layer is as follows.

[0072] An integrating sphere was mounted on an ultraviolet-visible spectrophotometer UV-2600 (manufactured by Shimadzu Corporation), and a specular reflection spectrum was measured using the mirror plate as a standard. The reflectance at 600 nm was determined as the specular reflectance.

[0073] (Composition of Thermoelectric Conversion Layer)

[0074] The thermoelectric conversion layer contains a thiophene polymer. The amount of the thiophene polymer in the thermoelectric conversion layer is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and even more particularly preferably 90% by mass or more, relative to the total mass of the thermoelectric conversion layer.

[0075] Thiophene polymers are polymers formed by bonding two or more thiophenes to each other.

[0076] Thiophene polymers can be prepared by polymerizing a single monomer or two or more monomers.

[0077] Examples of thiophene polymers obtained by polymerizing a single monomer include compounds represented by the following general formula (TP).

[0078]

[0079] In the general formula (TP), R is a substituent and is not limited as long as it can impart thermoelectric conversion performance, and represents an alkoxy group, an alkyl group, an amino group, a hydroxyl group, a hydroxyalkyl group, an aryl group, a cyano group, or a halogen group.

[0080] From the viewpoint of more reliably imparting metallic luster to the film, R is preferably an alkoxy group, an alkyl group, an amino group, or a hydroxyl group, more preferably an alkoxy group, an alkyl group, or an amino group, and even more preferably an alkoxy group or an alkyl group.

[0081] n1 represents an integer of 1 or 2. That is, there may be one or two R on one thiophene ring. When n1 represents an integer of 2, the two R on the thiophene ring may be the same or different.

[0082] n represents an integer of 2 or greater.

[0083] Here, "thiophene" is a heterocyclic compound containing sulfur, and is represented by the following general formula (TP1). In the following general formula (TP1), the definitions of R and n1 are the same as those of the above general formula (TP).

[0084]

[0085] In the general formula (TP1), when R is an alkoxy group, the number of carbon atoms is preferably 1 to 8 (particularly preferably 1 or 2). In this case, specific examples of thiophene include 3-methoxythiophene, 3,4-dimethoxythiophene, 3-ethoxythiophene, 3,4-diethoxythiophene, 3-propoxythiophene, 3-butoxythiophene, 3-hydroxythiophene, 3,4-ethylenedioxythiophene, and 3,4-propylenedioxythiophene.

[0086] In particular, when the number of carbon atoms in the alkoxy group is 1 or 2, the layered orientation structure of the thiophene polymer can be effectively expressed.

[0087] In the general formula (TP1), when R is an alkyl group, the number of carbon atoms is preferably 2 or more and 12 or less (more preferably 5 or more and 12 or less, further preferably 5 or more and 7 or less, and particularly preferably 4 or more and 7 or less). In this case, specific examples of thiophene include 3-hexylthiophene, 3-heptylthiophene, 3-octylthiophene, 3-nonylthiophene, 3-decylthiophene, 3-undecylthiophene, and 3-dodecylthiophene.

[0088] In particular, when the number of carbon atoms of the alkyl group is 5 or more and 7 or less, the layered orientation structure of the thiophene polymer can be effectively expressed.

[0089] In the general formula (TP1), when R is an amino group, examples of thiophene include 3-aminothiophene, 3,4-diaminothiophene, 3-methylaminothiophene, 3-dimethylaminothiophene, 3-thiophenecarboxamide, and 4-(thiophen-3-yl)aniline. In this case, when R contains carbon, the number of carbon atoms is preferably 1 or 2.

[0090] That is, among these, from the perspective of improving thermoelectric conversion performance, the thiophene polymer is preferably a polymer of at least one thiophene selected from the group consisting of alkoxythiophene, aminothiophene, hydroxythiophene and alkylthiophene, and more preferably a polymer of at least one thiophene selected from the group consisting of alkoxythiophene and alkylthiophene.

[0091] From the same viewpoint, the number of carbon atoms in the alkoxy group of alkoxythiophene is preferably 1 to 6, more preferably 1 to 3. The number of carbon atoms in the alkyl group of alkylthiophene is preferably 2 to 12, more preferably 4 to 7, and even more preferably 5 to 7.

[0092] In particular, the thiophene polymer may be an alkoxythiophene in which the alkoxy group has 1 to 3 carbon atoms.

[0093] From the perspective of improving thermoelectric conversion performance, the thiophene polymer preferably has a weight-average molecular weight distribution peak within the range of 200 to 30,000 (more preferably 500 to 20,000, and even more preferably 10,000). In other words, the thiophene polymer is preferably a so-called oligomer.

[0094] By suppressing the molecular weight of the thiophene polymer to be within the above range, the layered orientation structure of the thiophene polymer can be effectively expressed.

[0095] Here, the weight-average molecular weight is a value obtained by gel permeation chromatography (GPC). Specifically, molecular weight measurement by GPC was performed using a Tosoh Corporation HPLC1100 as the measuring apparatus, using a Tosoh Corporation column TSKgel GMHHR-M + TSKgel GMHHR-M (7.8 mm I.D. × 30 cm), and using chloroform as the solvent. The weight-average molecular weight (Mw) was calculated based on the measurement results using a molecular weight calibration curve prepared using monodisperse polystyrene standard samples.

[0096] The thiophene polymer is obtained, for example, by oxidative polymerization or electrolytic polymerization.

[0097] - Oxidative polymerization method -

[0098] The oxidative polymerization method is a method of polymerizing thiophene in at least one of a liquid phase and a solid phase using an oxidizing agent.

[0099] Examples of the oxidizing agent include iron (III) salts, copper salts, cerium salts, dichromates, permanganates, ammonium persulfate, boron trifluoride, bromates, hydrogen peroxide, chlorine, bromine, and iodine.

[0100] Among these, iron (III) salts are preferred. The iron (III) salts may be hydrates.

[0101] As the counterpart ion of the iron (III) salt, for example, chloride ion, citrate ion, oxalate ion, p-toluenesulfonate ion, perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, etc. can be enumerated. Among these, when at least one of perchlorate ion, hexafluorophosphate ion and tetrafluoroborate ion is used as an ion, a metallic luster similar to gold can be obtained, and these ions are preferred. The reason for being able to obtain a metallic luster similar to gold is speculative, but it is believed that perchlorate ion, hexafluorophosphate ion and tetrafluoroborate ion are incorporated into the thiophene polymer as a dopant during polymerization, and are combined with the cationic site generated in the thiophene polymer to stabilize and contribute to the formation of a regular structure. In fact, when analyzing the film with metallic luster, it has been confirmed that they are stably present.

[0102] The oxidative polymerization method is preferably carried out in a solvent.

[0103] The solvent is preferably one that can sufficiently dissolve the oxidizing agent and thiophene to effectively polymerize thiophene. As the solvent, an organic solvent having high polarity and a certain degree of volatility is preferred.

[0104] Specific examples of the solvent include acetonitrile, nitromethane, γ-butyrolactone, propylene carbonate, nitromethane, 1-methyl-2-pyrrolidone, dimethyl sulfoxide, 2-butanone, tetrahydrofuran, acetone, methanol, anisole, chloroform, ethyl acetate, hexane, trichloroethylene, cyclohexanone, dichloromethane, chloroform, dimethylformamide, ethanol, butanol, pyridine, dioxane, and mixtures thereof.

[0105] Among these, acetonitrile, nitromethane, γ-butyrolactone, and propylene carbonate are preferred as solvents because these solvents can dissolve thiophene polymers and are preferred from the perspective of improving thermoelectric conversion performance.

[0106] Here, the amounts of thiophene and the oxidizing agent relative to the solvent can be adjusted appropriately without limitation. When the weight of the solvent is 1, the weight of thiophene is preferably 0.00007 to 7, more preferably 0.0007 to 0.7. When the oxidizing agent is iron (III) perchlorate n-hydrate, the weight is preferably 0.0006 to 6, more preferably 0.006 to 0.6.

[0107] The ratio of thiophene to the oxidizing agent is such that, when the weight of thiophene is 1, the weight of the oxidizing agent is preferably 0.1 to 1000, and more preferably 1 to 100.

[0108] Thiophene and the oxidizing agent may be added to the solvent at once, or two solutions, one in which thiophene is added to the solvent and the other in which the oxidizing agent is added to the solvent, may be prepared separately and then combined to carry out the polymerization reaction.

[0109] The thiophene polymer synthesized by the oxidative polymerization method may be used directly in the form of a solution, or may be used in the form of a powdered thiophene polymer (hereinafter referred to as "thiophene polymer powder") by removing the solvent.

[0110] When the oxidant contains the perchlorate ion, hexafluorophosphate ion, tetrafluoroborate ion, or chloride ion, the oxidant remains due to stable bonding with the polymer, and thus the thermoelectric conversion performance can be stably maintained.

[0111] -Electrolytic polymerization-

[0112] Electrolytic polymerization is a method in which a polymer precursor (i.e., a monomer) is dissolved in a solution containing a supporting electrolyte and the monomer is oxidized by electrode to form a solution-insoluble polymer (in other words, a film of the solution-insoluble polymer) on a conductor.

[0113] In the electrolytic polymerization method, a potential sweep method is preferably used when performing anodic oxidation. The potential sweep method is a process in which a pair of electrodes are immersed in a solution containing a supporting electrolyte and the potential is applied while changing at a constant rate.

[0114] The solvent of the electrolytic solution is not particularly limited, and examples thereof include water, alcohol, and solvents described in "Electrochemical Measurement Methods" (Fujishima Akira, Aizawa Masuo, Inoue Toru, published by Gihodo, Vol. 1, pp. 107-114, 1984). A mixed solvent of various solvents is also preferred.

[0115] The supporting electrolyte of the electrolytic solution is an essential component in electrolysis, and examples thereof include electrolytes composed of cations or anions that are sufficiently soluble in a solvent and are not easily electrolyzed.

[0116] Specifically, as the supporting electrolyte, when focusing on cations, for example, lithium salts, sodium salts, potassium salts, calcium salts, and tetraalkylammonium salts are preferred; when focusing on anions, for example, halides, sulfates, nitrates, phosphates, perchlorates, boron trifluoride salts, and hexafluorophosphates are preferred.

[0117] The concentration of the supporting electrolyte is not limited, but is preferably 0.001 M or more and below the solubility, and more preferably 0.01 M or more and 1 M or less.

[0118] The concentration of thiophene as a monomer in the electrolytic solution is not limited, but is preferably 0.1 mM or more and below its solubility, and more specifically, more preferably 1 mM or more and 1 M or less.

[0119] In electrolytic polymerization, a conductor (functioning as a working electrode) can be immersed in an electrolytic container filled with a solution, and a three-electrode system can be used, in which three electrodes, a counter electrode and, if necessary, a reference electrode serving as a potential reference, are used; or a two-electrode system can be used, in which only a conductor and a counter electrode are used.

[0120] Note that a three-electrode system that can strictly define the potential of a conductor relative to a reference electrode serving as a standard is more preferred from the viewpoint of being able to produce a thermoelectric conversion layer containing a thiophene polymer formed by the present method with good reproducibility.

[0121] In either the three-electrode system or the two-electrode system, the conductor serving as the working electrode may be any material that is oxidatively stable against the electrode. For example, as described above, an electrode (transparent glass electrode, metal electrode, glassy carbon electrode, etc.) coated with a conductive film of indium tin oxide (hereinafter referred to as "ITO"), tin oxide, or the like can be suitably used. Furthermore, in addition to the aforementioned electrode materials, metal electrodes such as stainless steel and copper plates can also be suitably used as the counter electrode. Furthermore, a silver-silver chloride electrode (Ag / AgCl electrode) or a saturated calomel electrode can be suitably used as the reference electrode.

[0122] The potential sweep method in the electrolytic polymerization method is preferably performed between a negative potential and a positive potential. In this case, the negative potential is preferably in the range of -1.5V to 0.01V, more preferably in the range of -1.0V to 0.1V, and even more preferably in the range of -0.7V to 0.2V. In addition, the positive potential is preferably in the range of +1.0V to +3.0V, more preferably in the range of +1.0V to +2.0V, and even more preferably in the range of +1.0V to +1.5V.

[0123] In the potential scanning method, there is no limitation on the scanning speed as long as a thermoelectric conversion layer containing a thiophene polymer can be produced. It is preferably in the range of 0.1 mV / s to 10 V / s, more preferably in the range of 1 mV / s to 1 V / s, and even more preferably in the range of 2 mV / s to 300 mV / s.

[0124] The electrolytic polymerization time is preferably within the above-mentioned applied voltage range of 1 second to 5 hours, and more preferably within the range of 10 seconds to 1 hour.

[0125] The electrolysis temperature during electrolytic polymerization is preferably within a range of -20°C to 60°C.

[0126] Electrolysis during electrolytic polymerization is a reaction in which the component substances in the atmosphere participate in very little, and is carried out at a relatively low potential, so it can be carried out in the atmosphere. From the perspective of the possibility of the film generated by the oxidation of impurities in the electrolyte being contaminated, it is preferably carried out in a nitrogen or argon atmosphere, and there is almost no worry about pollution. However, in the case of forming electrolytic polymerization, if oxygen is present in a large amount in the solution, it is still possible to affect the electrode reaction, so bubbling based on an inert gas (such as nitrogen, argon) is also useful.

[0127] (Other Compositions of Thermoelectric Conversion Layer)

[0128] In the thermoelectric conversion layer, the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms (hereinafter also referred to as "content of the metal component (A)") is preferably 1500 ppm or less based on the thiophene polymer.

[0129] Here, conventionally, in a thermoelectric conversion layer containing a thiophene polymer, the thiophene polymer is oriented by stacking, thereby exhibiting thermoelectric conversion performance.

[0130] However, if the stacking state collapses due to the influence of impurities, the orientation of the thiophene polymer may be reduced, and the thermoelectric conversion performance may be reduced. The collapse of the stacking state of the thiophene polymer is presumably caused by the insertion of impurities between the molecular chains of the thiophene polymer.

[0131] Furthermore, impurities that cause the stacking state of the thiophene polymer to collapse are the oxidant used in oxidative polymerization and the metal components of the electrolyte used in electrolytic polymerization during the synthesis of the thiophene polymer.

[0132] Therefore, in the thermoelectric conversion layer, the content of the metal component (A) is preferably 1500 ppm or less based on the thiophene polymer.

[0133] Furthermore, when the content of the metal component (A) is within the above range, the orientation of the thiophene polymer is high, and the above conditions (1) and (2) are easily satisfied. As a result, the thermoelectric conversion performance is enhanced.

[0134] The content of the metal component (A) (i.e., the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms) is 1500 ppm or less relative to the thiophene polymer. From the perspective of improving thermoelectric conversion performance, it is preferably 500 ppm or less, and more preferably 100 ppm or less.

[0135] In order to stabilize the doping state, some metal components may be contained. The content of the metal component (A) is preferably 1 ppm or more, more preferably 5 ppm or more.

[0136] In order to adjust the content of the metal component (A) to the above range, the following method can be mentioned.

[0137] 1) A method in which, after synthesizing a thiophene polymer, the obtained thiophene polymer is washed with a solvent that does not dissolve the thiophene polymer (for example, an alcohol such as methanol, ethanol, or isopropanol) under heating.

[0138] 2) After synthesizing a thiophene polymer, the obtained thiophene polymer is dissolved in a good solvent (such as dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran), and the obtained solution is added dropwise to a poor solvent such as alcohol to reprecipitate the thiophene polymer.

[0139] 3) After synthesizing a thiophene polymer, the obtained thiophene polymer is dissolved in a good solvent (dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, etc.), and a poor solvent such as alcohol is added dropwise to the obtained solution to perform reverse reprecipitation of the thiophene polymer.

[0140] The content of the metal component (A) is measured as follows.

[0141] First, when the object to be measured is a solid object, the object to be measured is dissolved in nitric acid to obtain a nitric acid solution.

[0142] Next, the nitric acid solution was subjected to an ashing treatment using microwaves (maximum reaching temperature = 260° C.), and the ashed product was dissolved or dispersed in water to obtain an aqueous solution.

[0143] Thereafter, the metal components in the obtained aqueous solution were quantified using an inductivity coupled plasma optical emission spectrometer (ICP-OES).

[0144] The thermoelectric conversion layer may include, as dopants, onium salt compounds, oxidants (halogens, Lewis acids, proton acids, transition metal compounds, electrolyte anions, etc.), acidic compounds (polyphosphoric acid, hydroxyl compounds, carboxyl compounds, sulfonic acid compounds, etc.), and thermal excitation assist agents (compounds having a LUMO (Lowest Unoccupied Molecular Orbital) energy level lower than the LUMO energy level of the conductive polymer, which is a compound that does not form a doping energy level in the thiophene polymer).

[0145] The thermoelectric conversion layer may contain other components such as known additives such as an antioxidant, a light stabilizer, a heat stabilizer, and a plasticizer.

[0146] (Other components)

[0147] The thermoelectric conversion element of this embodiment may have a structure other than the thermoelectric conversion layer.

[0148] Specific examples of the thermoelectric conversion element of the present embodiment include the following known embodiments (1) and (2).

[0149] (1) A method comprising a conductive substrate and a thermoelectric conversion layer provided on the conductive substrate

[0150] (2) A method comprising a substrate, a pair of electrodes provided on the substrate, and a thermoelectric conversion layer provided between the pair of electrodes

[0151] Examples of the conductive substrate include a substrate having a conductive layer (specifically, a layer composed of an electrode material described later) formed on the surface.

[0152] Examples of the substrate include glass, transparent ceramics, metals, and plastic films.

[0153] Examples of electrodes include transparent electrodes (electrodes such as ITO and ZnO), metal electrodes (electrodes such as silver, copper, gold, aluminum, chromium, and nickel), electrodes made of carbon materials (electrodes made of CNTs and graphene), and electrodes made of organic materials (electrodes made of PEDOT and PSS). Examples of electrodes include those obtained using a conductive paste containing conductive particles (e.g., a conductive paste containing conductive particles such as silver and carbon dispersed therein), a conductive paste containing metal wires (e.g., a conductive paste containing metal nanowires such as silver, copper, and aluminum), and the like.

[0154] In order to improve the thermoelectric conversion performance, the thickness of the thermoelectric conversion layer is preferably from 0.1 μm to 1000 μm, and more preferably from 1 μm to 100 μm.

[0155] (thing)

[0156] The article of this embodiment is an article including the thermoelectric conversion element of this embodiment.

[0157] Examples of target articles including thermoelectric conversion elements include wearable temperature sensors and power supplies therefor.

[0158] [Example]

[0159] The following examples are given to illustrate the present invention in more detail. However, these examples are not intended to limit the present invention. It should be noted that, unless otherwise stated, "parts" or "%" are by mass.

[0160] (Example 1)

[0161] Thiophene polymer powder (A1) was obtained as follows.

[0162] 11.4 g of 3-methoxythiophene was collected in a three-necked flask, dissolved in 0.5 L of acetonitrile, the system was replaced with nitrogen, and then cooled to 0°C. 101 g of iron (III) perchlorate n-hydrate was dissolved in 0.5 L of acetonitrile, and the resulting reaction solution was added dropwise thereto while being maintained below 5°C. The temperature was then raised to room temperature and stirred at room temperature (specifically 24°C) for 15 hours. 1 L of methanol was then added and stirred for further 1 hour. The main liquid containing the thiophene polymer was subjected to liquid-solid separation using a centrifuge, the solid component was collected, and dried at 60°C under reduced pressure for 16 hours to obtain 10.5 g of thiophene polymer powder (A1).

[0163] Next, the obtained thiophene polymer powder (A1) is subjected to a washing treatment as follows.

[0164] 2.0 g of thiophene polymer powder (A1) was weighed into a beaker, 50 ml of methanol was added, and the mixture was stirred at 45°C for 1 hour. The main liquid was subjected to liquid-solid separation using a centrifuge, and the solid content was collected and transferred to a beaker. 50 ml of methanol was further added, and the mixture was stirred at 45°C for 1 hour. Subsequently, liquid-solid separation was performed using a centrifuge to separate the solid content. The solid content was collected and dried at 60°C under reduced pressure for 16 hours to obtain 1.8 g of thiophene polymer powder (A2).

[0165] Next, 1 part of the obtained thiophene polymer powder (A2) was added to 99 parts by mass of nitromethane, stirred with a stirrer for 1 hour, and then allowed to stand for 22 hours. The obtained solution was used as a coating solution (A).

[0166] Next, the coating liquid (A1) was cast on an ITO glass substrate of 25 mm in length and 10 mm in width, and dried at 25° C. for 45 minutes to form a thermoelectric conversion layer having a thickness of 1.5 μm. A thermoelectric conversion element A was obtained.

[0167] (Example 2)

[0168] A coating liquid (B) was obtained in the same manner as in the coating liquid (A) except that γ-butyrolactone was used instead of nitromethane as a solvent.

[0169] Thereafter, the coating liquid (B) was used and cast, followed by drying at 60° C. for 45 minutes to obtain the thermoelectric conversion element B in the same manner as the thermoelectric conversion element A.

[0170] (Comparative Example 1)

[0171] A coating liquid (C) was obtained in the same manner as in the coating liquid (A) except that the thiophene polymer powder (A1) which had not been subjected to the washing treatment was used instead of the thiophene polymer powder (A2).

[0172] Then, a thermoelectric conversion element C was obtained in the same manner as the thermoelectric conversion element A except that the coating liquid (C) was used.

[0173] (Comparative Example 2)

[0174] The unwashed thiophene polymer powder (A1) was pressed and stretched on an ITO glass substrate of 25 mm in length and 10 mm in width to form a thermoelectric conversion layer of 0.6 μm in thickness, thereby obtaining a thermoelectric conversion element D.

[0175] (Comparative Example 3)

[0176] A poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) aqueous solution (Sigma-Aldrich: 560596) was prepared as a coating liquid (D).

[0177] Then, a thermoelectric conversion element D was obtained in the same manner as the thermoelectric conversion element A except that the coating liquid (D) was used.

[0178] (Comparative Example 4)

[0179] Dodecylbenzenesulfonic acid (SIGMA-ALDRICH: 522953) was doped into a polyaniline solution (SIGMA-ALDRICH: 530670) to obtain a coating solution (E).

[0180] Then, a thermoelectric conversion element E was obtained in the same manner as the thermoelectric conversion element A except that the coating liquid (E) was used.

[0181] (evaluate)

[0182] -Content of metal component (A)-

[0183] The following various characteristics of the thermoelectric conversion layer of the thermoelectric conversion element of each example were measured by the above-mentioned method.

[0184] Ratio of the peak intensity at a diffraction angle (2θ) of 7.9° to the peak intensity at a diffraction angle (2θ) of 25.8° in the X-ray diffraction spectrum (in the table, "XRD peak intensity ratio" is expressed as 7.9° / 25.8°)

[0185] Specular reflectivity

[0186] ·Content of metal component (A)

[0187] -Thermoelectric conversion performance-

[0188] The surface of one end face of each thermoelectric conversion element was heated to 60° C. using a carbon heater. The potential difference (ie, thermoelectromotive force) generated at both ends of the element by heating was measured using a multimeter (Fluke 179) and evaluated using the following criteria.

[0189] A (◎): Very good power generation performance

[0190] B(○): has good power generation performance

[0191] C(△): has a small power generation performance

[0192] D(×): No power generation

[0193]

[0194] From the above results, it is understood that the thermoelectric conversion performance of the thermoelectric conversion element of this example is higher than that of the thermoelectric conversion element of the comparative example.

Claims

1. A thermoelectric conversion element, wherein: The thermoelectric conversion element has a thermoelectric conversion layer containing a thiophene polymer. In the X-ray diffraction spectrum of the thermoelectric conversion layer, the peak intensity at a diffraction angle (2θ) of 7.9° is at least five times the peak intensity at a diffraction angle (2θ) of 25.8°. In the thermoelectric conversion layer, the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms is 1500 ppm or less relative to the thiophene polymer.

2. The thermoelectric conversion element according to claim 1, wherein The peak intensity at the diffraction angle (2θ) of 7.9° is 7 times or more the peak intensity at the diffraction angle (2θ) of 25.8°.

3. A thermoelectric conversion element, wherein: having a thermoelectric conversion layer comprising a thiophene polymer, The specular reflectivity of the thermoelectric conversion layer is not less than 10% and not more than 35%. In the thermoelectric conversion layer, the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms is 1500 ppm or less relative to the thiophene polymer.

4. The thermoelectric conversion element according to claim 3, wherein The thermoelectric conversion layer has a mirror reflectivity of 15% to 30%.

5. The thermoelectric conversion element according to any one of claims 1 to 4, wherein The total content of the Fe atoms, the Cu atoms, the Mn atoms, the Cr atoms, and the Ce atoms is 500 ppm or less relative to the thiophene polymer. The thermoelectric conversion element according to claim 5 , wherein: The total content of the Fe atoms, the Cu atoms, the Mn atoms, the Cr atoms, and the Ce atoms is 100 ppm or less relative to the thiophene polymer.

7. The thermoelectric conversion element according to any one of claims 1 to 4, wherein The thiophene polymer is a polymer of at least one thiophene selected from the group consisting of alkoxythiophene, aminothiophene, hydroxythiophene, and alkylthiophene.

8. The thermoelectric conversion element according to claim 7, wherein The thiophene polymer is a polymer of at least one thiophene selected from the group consisting of alkoxythiophene and alkylthiophene.

9. The thermoelectric conversion element according to claim 7, wherein The alkoxy group of the alkoxythiophene has 1 to 6 carbon atoms, and the alkyl group of the alkylthiophene has 2 to 12 carbon atoms.

10. An article comprising a thermoelectric conversion element, the thermoelectric conversion element comprising a thermoelectric conversion layer comprising a thiophene polymer, wherein in an X-ray diffraction spectrum of the thermoelectric conversion layer, the peak intensity at a diffraction angle (2θ) of 7.9° is at least five times the peak intensity at a diffraction angle (2θ) of 25.8°. In the thermoelectric conversion layer, the total content of Fe atoms, Cu atoms, Mn atoms, Cr atoms, and Ce atoms is 1500 ppm or less relative to the thiophene polymer.

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