JP7400396B2 - Thermoelectric conversion materials and thermoelectric conversion elements - Google Patents

Description

The present invention relates to a thermoelectric conversion material and a thermoelectric conversion element using the material.

Thermoelectric conversion materials that can mutually convert thermal energy and electrical energy are used in thermoelectric conversion elements such as thermoelectric generation elements and Peltier elements. A thermoelectric conversion element is an element that converts heat into electric power, and is constructed from a combination of semiconductors and metals. Typical thermoelectric conversion elements are classified into p-type semiconductor alone, n-type semiconductor alone, or a combination of p-type semiconductor and n-type semiconductor. Thermoelectric conversion elements utilize the Seebeck effect, which generates an electromotive force when heat is applied to create a temperature difference between both ends of a semiconductor. In order to obtain a larger potential difference, thermoelectric conversion elements generally use a combination of p-type semiconductor and n-type semiconductor as materials.

Further, the thermoelectric conversion element is used as a thermoelectric module formed by combining a large number of elements into a plate shape or a cylindrical shape. Thermal energy can be directly converted into electricity, and can be used, for example, as a power source for wristwatches powered by body temperature, terrestrial power generation, and satellite power generation. The performance of the thermoelectric conversion element depends on the performance of the thermoelectric conversion material, the durability of the module, and the like.

As described in Non-Patent Document 1, a dimensionless thermoelectric figure of merit (ZT) is used as an index representing the performance of thermoelectric conversion materials. Moreover, a power factor PF (=S ² ·σ) may be used as an index representing the performance of a thermoelectric conversion material.
The dimensionless thermoelectric figure of merit "ZT" is expressed by the following formula (1).
ZT=( ^S2・σ・T)/κ...Formula (1)
Here, S is the Seebeck coefficient (V/K), σ is the electrical conductivity (S·m), T is the absolute temperature (K), and κ is the thermal conductivity (W/(m·K)). The thermal conductivity κ is expressed by the following formula (2).
κ=α・ρ・C...Formula (2)
Here, α is the thermal diffusivity (m ² /s), ρ is the density (kg/m ³ ), and C is the specific heat capacity (J/(kg·K)).
That is, in order to improve thermoelectric conversion performance (hereinafter also referred to as thermoelectric characteristics), it is important to improve the Seebeck coefficient or electrical conductivity, while decreasing the thermal conductivity.

Typical thermoelectric conversion materials include, for example, bismuth/tellurium (Bi-Te) from room temperature to 500K, lead/tellurium (Pb-Te) from room temperature to 800K, and silicon/tellurium (Pb-Te) from room temperature to 1000K. Inorganic materials such as germanium (Si--Ge) are used.

However, thermoelectric conversion materials including these inorganic materials often contain rare elements and are expensive, or may contain harmful substances. Furthermore, since inorganic materials have poor workability, the manufacturing process becomes complicated. Therefore, thermoelectric conversion materials containing inorganic materials require high manufacturing energy and manufacturing costs, making it difficult to generalize them. Furthermore, since inorganic materials are rigid, it is difficult to form flexible thermoelectric conversion elements that can be installed in non-planar shapes.

In response, studies are underway on thermoelectric conversion elements using organic materials instead of conventional inorganic materials. Organic materials have excellent moldability and greater flexibility than inorganic materials, so they are highly versatile within a temperature range in which they do not decompose themselves. Furthermore, since printing technology and the like can be easily utilized, it is more advantageous than inorganic materials in terms of manufacturing energy and manufacturing costs.

In Patent Document 1, a thermoelectric conversion element is created using carbon nanotubes (CNT) and an organic low-molecular compound. However, because the strength of the material is insufficient, cracking or peeling from the base material may occur during fabrication or use, leading to concerns about deterioration in thermoelectric conversion performance and yield.
Patent Document 2 describes a thermoelectric material that has good CNT dispersibility, is suitable for coating methods, and exhibits excellent thermoelectromotive force by bonding an organic dye skeleton to a polymeric dispersant and incorporating it together with carbon nanotubes (CNTs). has been done. However, with this invention, sufficient thermoelectric conversion performance could not be obtained, and further improvements were required.

JP2016-219513 International Publication No. 2015/050113

“Thermoelectric Conversion Technology Handbook (First Edition)” by Takenobu Kajikawa, NTS Publishing, p. 19

The problem to be solved by the present invention is to provide a thermoelectric conversion material that achieves both Seebeck coefficient and conductivity, exhibits a high power factor, and has high strength. Another object of the present invention is to provide a thermoelectric conversion element that exhibits excellent thermoelectric performance using the material.

The present inventors have conducted extensive research to solve the above problems, and as a result, have arrived at the present invention. That is, the present invention contains at least one conductive material (A) selected from the group consisting of a carbon material, a metal material, and a conductive polymer, and an organic polymer compound (B), and the organic polymer compound (B) ) relates to a thermoelectric conversion material which is a non-conjugated polymer, has a repeating unit of a monomer having a pyrrolopyrrole skeleton, and has a mass average molecular weight of 10,000 to 200,000.

The present invention also relates to the thermoelectric conversion material in which the organic polymer compound (B) has a repeating unit represented by the following general formula (1).
General formula (1)

[In general formula (1), X represents a divalent linking group selected from the group consisting of an alkylene group, an oxyalkylene group, a thioalkylene group, and a group in which these groups are bonded together, and Y ₁ and Y ₂ are , each independently represents an oxygen atom, a sulfur atom, or a dicyanomethylene group, and R ₁ and R ₂ each independently represent a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group. ]

The present invention also relates to the thermoelectric conversion material, in which the conductive material (A) includes at least one selected from the group consisting of carbon nanotubes, Ketjenblack, graphene nanoplates, and graphene.

Further, the present invention relates to the thermoelectric conversion material, wherein the conductive material (A) is a carbon nanotube.

The present invention also relates to a thermoelectric conversion element that includes a thermoelectric conversion film made of the thermoelectric conversion material and an electrode, and in which the thermoelectric conversion film and the electrode are electrically connected.

According to the present invention, it is possible to provide a thermoelectric conversion material that achieves both Seebeck coefficient and electrical conductivity and has high material strength. Furthermore, using the material, it is possible to provide a thermoelectric conversion element that exhibits excellent thermoelectric performance.

1 is a schematic diagram showing the structure of an example of a thermoelectric conversion element according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a method for measuring electromotive force of a thermoelectric conversion element according to an embodiment of the present invention.

<Thermoelectric conversion materials>
The thermoelectric conversion material of the present invention includes a conductive material (A) and an organic polymer compound (B), where the organic polymer compound (B) is a non-conjugated polymer and is a repeating monomer having a pyrrolopyrrole skeleton. unit and has a mass average molecular weight of 10,000 to 200,000.
With such a specific combination, it is possible to achieve both a high Seebeck coefficient and conductivity, have high material strength, and exhibit excellent thermoelectric performance. This is because holes (carriers) efficiently move from an organic compound with low thermal excitation energy to a conductive material, and the holes move within the conductive material to achieve a high Seebeck coefficient and conductivity. by.
Embodiments of the present invention will be described in detail below.

<Conductive material (A)>
The conductive material (A) contributes to improving conductivity. Conductivity can be improved by increasing the content of the conductive material (A).
The conductive material (A) is not particularly limited as long as it is a conductive carbon material, metal material, or conductive polymer. For example, carbon materials include graphite, carbon nanotubes, Ketjenblack, graphene nanoplates, and graphene. Examples of metal materials include metal powders such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, germanium, gallium, and platinum, as well as ZnSe and CdS. , InP, GaN, SiC, SiGe, alloys thereof, and composite powders thereof. Further, fine particles having a nucleus covered with a substance different from the above-mentioned nucleus substance, specifically, for example, silver-coated copper powder having a core made of copper and whose surface is coated with silver, etc., can be mentioned. In addition, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide), Examples include powders whose surfaces are coated with these metal oxides, and examples of conductive polymers include PEDOT/PSS, polyaniline, polyacetylene, polypyrrole, polythiophene, polyparaphenylene, and the like. One type of conductive material may be used, or two or more types may be used in combination.

The shape of the conductive material (A) is not particularly limited, and amorphous shapes, aggregate shapes, scale shapes, microcrystal shapes, spherical shapes, flake shapes, wire shapes, etc. can be used as appropriate.

From the viewpoint of achieving both Seebeck coefficient and electrical conductivity, at least one member selected from the group consisting of carbon nanotubes, Ketjenblack, graphene nanoplates, and graphene is preferred, carbon nanotubes are more preferred, and single-walled carbon is particularly preferred. They are nanotubes.

Examples of the conductive material (A) include flaky graphite such as CMX, UP-5, UP-10, UP-20, UP-35N, CSSP, CSPE, CSP, CP, and CB-150 manufactured by Nippon Graphite Industries. , CB-100, ACP, ACP-1000, ACB-50, ACB-100, ACB-150, SP-10, SP-20, J-SP, SP-270, HOP, GR-60, LEP, F#1 , F#2, F#3, BF-3AK, FBF, BF-15AK, CBR, CPB-6S, CPB-3, 96L, 96L-3, K-3, SC-120 manufactured by Chuetsu Graphite Industries Co., Ltd. Examples include SC-60, HLP, CP-150, SB-1, EC1500, EC1000, EC500, EC300, EC100, EC50 manufactured by Ito Graphite Industries, and 10099M and PB-99 manufactured by Nishimura Graphite Co., Ltd. Examples of the spherical natural graphite include CGC-20, CGC-50, CGB-20, and CGB-50 manufactured by Nippon Graphite Industries. Examples of the earthy graphite include Blue P, AP, AOP, and P#1 manufactured by Nippon Graphite Industries Co., Ltd., and APR, K-5, AP-2000, AP-6, 300F, and 150F manufactured by Chuetsu Graphite Co., Ltd. Examples of artificial graphite include PAG-60, PAG-80, PAG-120, PAG-5, HAG-10W, HAG-150 manufactured by Nippon Graphite Industries, and G-4AK, G-6S, G- manufactured by Chuetsu Graphite Co., Ltd. 3G-150, G-30, G-80, G-50, SMF, EMF, SFF, SFF-80B, SS-100, BSP-15AK, BSP-100AK, WF-15C, SGP-100 manufactured by SEC Carbon , SGP-50, SGP-25, SGP-15, SGP-5, SGP-1, SGO-100, SGO-50, SGO-25, SGO-15, SGO-5, SGO-1, SGX-100, SGX -50, SGX-25, SGX-15, SGX-5, and SGX-1. Commercially available carbon blacks include, for example, Toka Black #4300, #4400, #4500, #5500 manufactured by Tokai Carbon, Printex L manufactured by Degussa, Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA manufactured by Columbian, Conductex SC ULTRA, Conductex 975 ULTRA, PUERBLACK100, 115, 205, Mitsubishi Chemical #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, #5 400B, made by Cabot MONARCH1400, 1300, 900, Vulcan Ketjen black such as 600JD, electrochemical Examples include acetylene black such as Denka Black, Denka Black HS-100, and FX-35 manufactured by Kogyo Co., Ltd. Commercially available conductive carbon fibers and carbon nanotubes include vapor grown carbon fibers such as VGCF manufactured by Showa Denko, EC1.5 and EC1.5-P manufactured by Meijo Nano Carbon, TUBALL manufactured by OCSiAl, and Zeon Nano. Examples include single-walled carbon nanotubes such as ZEONANO manufactured by Technology, FloTube9000, FloTube7000, and FloTube2000 manufactured by CNano, NC7000 manufactured by Nanocyl, and 100T and 200P manufactured by Knano. These are not particularly limited, and can be used alone or in combination of two or more.

<Organic polymer compound (B)>
The organic polymer compound (B) is a non-conjugated polymer, has a repeating unit of a monomer having a pyrrolopyrrole skeleton, and has a mass average molecular weight of 10,000 to 200,000. In the present invention, a non-conjugated polymer is a polymer that does not have a structure in which carbon-carbon bonds on the main chain of the polymer have alternating single bonds and double bonds spanning between repeating units. refers to

The mechanism of thermoelectric conversion is thought to be as follows. Carriers (holes or electrons) are generated in the thermally excited organic polymer compound (B), and the carriers move to the conductive material (A), creating a potential difference within the conductive material (A) and causing a current to flow. flows. That is, the more efficient carrier movement between the organic polymer compound (B) and the conductive material (A) becomes, the greater the potential difference within the conductive material (A) becomes, and the Seebeck coefficient improves. Although the specific method for making carrier transfer efficient is not clearly understood, it is important to consider the short distance between the organic polymer compound (B) and the conductive material (A) due to the affinity between the organic polymer compound (B) and the conductive material (A). ) and the conductive material (A), the length of the excited state (excitation lifetime) of the organic polymer compound (B), etc. are considered to have an influence. The organic polymer compound (B) of the present invention has a pyrrolopyrrole skeleton, which can reduce the difference in energy level with the conductive material (A) and realize efficient carrier movement. I think so. Further, when a pyrrolopyrrole skeleton is used, it is thought that the carrier becomes a hole. In that case, if the HOMO of the organic polymer compound (B) is deeper than the HOMO of the conductive material (A) (or the Fermi level if the conductive material is a metal), efficient carrier movement will be realized and thermoelectric conversion will be achieved. This is preferable because performance can be improved.

Furthermore, the efficiency of carrier movement in the above mechanism is also influenced by the contact state between the conductive material (A) and the organic polymer compound (B). Studies are known to improve thermoelectric conversion performance such as the Seebeck coefficient by bringing the conductive material (A) into contact with low-molecular compounds such as polycyclic aromatics, but low-molecular compounds such as polycyclic aromatics are crystalline. Many of them have a high value, and there is a possibility that low-molecular-weight compounds may aggregate and crystallize with each other, making it impossible to make efficient contact with the conductive material (A). By using the organic polymer compound (B) of the present invention, a large number of polycyclic aromatic moieties can be provided in the polymer. It is believed that this improves the adsorption force to the conductive material (A), reduces the crystallinity of the polycyclic aromatic moieties, and enables efficient contact with the conductive material (A). Furthermore, since the strength of the film can be improved by using the organic polymer compound (B), cracking and peeling of the device can be suppressed even when changes such as bending occur. Since it becomes difficult to change the contact state with B), changes in thermoelectric conversion characteristics can also be suppressed. By setting the molecular weight of the organic polymer compound (B) to 10,000 or more, it is easy to take an amorphous state under normal solvent drying conditions, and by bringing it into efficient contact with the conductive material (A), the thermoelectric conversion performance is improved. can be expected. Moreover, by setting the molecular weight to 200,000 or less, it is easy to uniformly distribute the organic polymer compound (B) in the coating film, and high performance can be expected.

Furthermore, the organic polymer compound (B) contributes to improving the Seebeck coefficient in the thermoelectric conversion material. The Seebeck coefficient can be improved by increasing the content of the organic polymer compound (B), but increasing the content of the organic polymer compound (B) increases the insulating property and decreases the conductivity. From the viewpoint of achieving both coefficient and conductivity, the content of the organic polymer compound (B) is preferably 400% by mass or less, more preferably 200% by mass or less based on the total amount of the conductive material (A). , more preferably 3 to 120% by weight, particularly preferably 5 to 100% by weight.

It is preferable to have a repeating unit represented by the general formula (1) as the organic polymer compound (B) that satisfies the above conditions.

Here, X, R ₁ and R ₂ in general formula (1) will be explained.

Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, an octylene group, a decylene group, and a dodecylene group. The alkylene group preferably has 2 to 8 carbon atoms.

Examples of the oxyalkylene group include oxymethylene group, oxyethylene group, oxypropylene group, oxybutylene group, and oxyoctylene group. The oxyalkylene group preferably has 2 to 8 carbon atoms.

Examples of the thioalkylene group include a thiomethylene group, a thioethylene group, a thiopropylene group, a thiobutylene group, and a thiooctylene group. The thioalkylene group preferably has 2 to 8 carbon atoms.

Examples of the unsubstituted aryl group include unsubstituted aryl groups such as phenyl group, naphthyl group, anthryl group, phenanthryl group, and pyrenyl group. Preferred examples of the unsubstituted aryl group include phenyl and naphthyl groups.
Substituents in the substituted aryl group include hydrogen atoms, halogen atoms, hydroxyl groups, carboxyl groups, cyano groups, nitro groups, amine groups, aldehyde groups, carboxyl groups, alkyl groups, alkoxy groups, aryloxy groups, alkylthio groups, and arylthio groups. or an aryl group substituted with a heterocyclic group. The substituted aryl group is preferably an alkyl group having 1 to 8 carbon atoms or an arylene group substituted with a halogen atom.

Examples of unsubstituted heterocyclic groups include furyl group, thienyl group, pyrrolyl group, pyridyl group, pyrazyl group, oxazolyl group, isoxazolyl group, thiazolyl group, isothiazolyl group, imidazolyl group, pyrazolyl group, quinolyl group, isoquinolyl group, Examples include heterocyclic groups such as a quinoxalinyl group, a benzofuryl group, a benzothienyl group, an indolyl group, a carbazolyl group, and an acridinyl group. The unsubstituted heterocyclic group is preferably an aromatic heterocyclic group, and preferably a 5-membered or 6-membered heterocyclic group.
Examples of the substituent in the substituted heterocyclic group include the same substituents as in the substituted aryl group.

<Other ingredients>
The thermoelectric conversion material of the present invention may contain additional components as necessary from the viewpoint of improving its properties.

(solvent)
The solvent may be used to mix the conductive material (A) and the organic polymer compound (B), making it possible to improve the coating properties by forming it into an ink. The solvent that can be used is not particularly limited as long as it can dissolve or disperse the conductive material (A) and the organic polymer compound (B) well, and examples include organic solvents and water, and two or more types can be used in combination. good.

Examples of organic solvents include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol methyl ether, and diethylene glycol methyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; tetrahydrofuran, dioxane, and ethylene glycol dimethyl ether; Ethers such as diethylene glycol dimethyl ether, hydrocarbons such as hexane, heptane, octane, aromatics such as benzene, toluene, xylene, cumene, esters such as ethyl acetate, butyl acetate, terpineol, dihydroterpineol, 2,4- It can be appropriately selected from diethyl-1,5-pentanediol, 1,3-butylene glycol, isobornylcyclohexanol, N-methylpyrrolidone, etc. as required. N-methylpyrrolidone is particularly preferred as the solvent for dispersing the conductive material (A) and the organic polymer compound (B).

(Auxiliary agent)
The thermoelectric conversion material of the present invention can further improve coatability, conductivity, film strength, film adhesion, weather resistance, heat resistance, and thermoelectric properties by adding, for example, the following auxiliary agents. becomes possible. Usable auxiliaries are not particularly limited, and include, for example, lactams, alcohols, amino alcohols, carboxylic acids, acid anhydrides, and ionic liquids. Specific examples are as follows.
Lactams: pyrrolidone, caprolactam, N-methylcaprolactam, N-octylpyrrolidone, etc.
Alcohols: sucrose, glucose, fructose, lactose, sorbitol, mannitol, xylitol, etc.
Amino alcohols: diethanolamine, triethanolamine, etc. Carboxylic acids: 2-furancarboxylic acid, 3-furancarboxylic acid, dichloroacetic acid, trifluoroacetic acid, etc.
Acid anhydrides: acetic anhydride, propionic anhydride, acrylic anhydride, methacrylic anhydride, benzoic anhydride, succinic anhydride, maleic anhydride, itaconic anhydride, glutaric anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydro Phthalic anhydride (also known as cyclohexane-1,2-dicarboxylic anhydride), trimellitic anhydride, hexahydro trimellitic anhydride, pyromellitic anhydride, himic anhydride, biphenyltetracarboxylic anhydride, 1,2,3 , 4-butanetetracarboxylic anhydride, naphthalenetetracarboxylic anhydride, and 9,9-fluorenylidene bisphthalic anhydride. Copolymers made by copolymerizing maleic anhydride with other vinyl monomers, such as styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, and alkyl vinyl ether-maleic anhydride copolymers.

From the viewpoint of electrical conductivity and thermoelectric properties, it is preferable to use at least one of lactams and alcohols as the auxiliary agent. The content of the auxiliary agent is preferably in the range of 0.1 to 30% by mass, more preferably in the range of 1 to 10% by mass, and even more preferably in the range of 1 to 5% by mass, based on the total mass of the thermoelectric conversion material. . By setting the content of the auxiliary agent to 0.1% by mass or more, the effect of improving conductivity and thermoelectric properties can be easily obtained. Moreover, when the content of the auxiliary agent is 50% by mass or less, deterioration of the film physical properties can be suppressed.

(resin)
The thermoelectric conversion material of the present invention may contain a resin for the purpose of adjusting film formability and film strength, etc., to the extent that it does not affect conductivity and thermoelectric properties.
The resin may be any resin as long as it is compatible with or mixed and dispersed in each component of the thermoelectric conversion material. Either thermosetting resin or thermoplastic resin may be used. Specific examples of usable resins include polyester resin, polyimide resin, polyamide resin, fluororesin, vinyl resin, epoxy resin, xylene resin, aramid resin, polyurethane resin, polyurea resin, melamine resin, phenol resin, polyether resin, and acrylic. Examples include resins, acrylamide resins, acrylonitrile resins, and copolymer resins thereof. Although not particularly limited, in one embodiment, it is preferable to use at least one selected from the group consisting of polyurethane resins, polyether resins, acrylic resins, and acrylamide resins.

(Fine particles made of inorganic thermoelectric material)
The thermoelectric conversion material of the present invention may contain fine particles made of an inorganic thermoelectric material, if necessary, in order to improve thermoelectric conversion performance. Examples of inorganic thermoelectric materials include Bi-(Te, Se) based, Si-Ge based, Mg-Si based, Pb-Te based, GeTe-AgSbTe based, (Co, Ir, Ru)-Sb based, (Ca, Examples include Sr, Bi)Co ₂ O ₅ systems, and the like. More specifically, _{Bi2Te3 , PbTe} , _AgSbTe2 , GeTe, _{Sb2Te3 , NaCo2O4} , _{CaCoO3 , SrTiO3} , ZnO, SiGe, _Mg2Si , _FeSi2 , _Ba8Si46 , At least one selected from the group consisting of MnSi _1.73 , ZnSb, Zn ₄ Sb ₃ , GeFe ₃ CoSb ₁₂ , and LaFe ₃ CoSb ₁₂ can be used. At this time, impurities may be added to the inorganic thermoelectric material to control its polarity (p-type, n-type) and conductivity. When using an inorganic thermoelectric material, the amount used is adjusted within a range that does not affect film formability or film strength.

The method for producing a thermoelectric conversion dispersion liquid is not particularly limited as long as a thermoelectric conversion dispersion liquid that satisfies the conditions of the present invention is obtained, and can be appropriately selected. For example, it can be obtained by mixing a thermoelectric conversion material, a dispersion medium, and other components as necessary, and then dispersing the mixture using a disperser or ultrasonic waves.

There are no particular restrictions on the dispersion machine; for example, kneaders, attritors, ball mills, sand mills using glass beads or zirconia beads, media dispersion machines such as Scandex, Eiger mills, paint conditioners, paint shakers, colloid mills, etc. can be used. can do.

<Thermoelectric conversion element>
The thermoelectric conversion element of the present invention is characterized in that it is constructed using the above thermoelectric conversion material. In one embodiment, the thermoelectric conversion element includes a thermoelectric conversion film formed using the thermoelectric conversion material and an electrode, and the thermoelectric conversion film and the electrode are electrically connected to each other. Thermoelectric conversion films have excellent heat resistance and flexibility in addition to conductivity and thermoelectric properties. Therefore, according to this embodiment, a high-quality thermoelectric conversion element can be easily realized.

The thermoelectric conversion film may be a film obtained by applying a thermoelectric conversion material onto a base material. Since the thermoelectric conversion material has excellent moldability, it is easy to obtain a good film by a coating method. A wet film forming method is mainly used to form a thermoelectric conversion film. Specifically, spin coat method, spray method, roller coat method, gravure coat method, die coat method, comma coat method, roll coat method, curtain coat method, bar coat method, inkjet method, dispenser method, silk screen printing, flexographic method. Examples include methods using various means such as printing. The method can be appropriately selected from the above methods depending on the thickness to be applied, the viscosity of the material, etc.

The thickness of the thermoelectric conversion film is not particularly limited, but as described later, it has a thickness of at least a certain level so that a temperature difference can be generated and transmitted in the thickness direction or surface direction of the thermoelectric conversion film. It is preferable that it be formed as follows. In one embodiment, from the viewpoint of thermoelectric properties, the thickness of the thermoelectric conversion film is preferably in the range of 0.1 to 200 μm, preferably in the range of 1 to 100 μm, and more preferably in the range of 1 to 50 μm.

In addition, as a base material to which the thermoelectric conversion material is applied, a plastic film made of materials such as polyethylene, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polypropylene, polyimide, polycarbonate, and cellulose triacetate, or glass, etc. Can be used.

Various treatments can be performed on the surface of the base material for the purpose of improving the adhesion between the base material and the thermoelectric conversion film. Specifically, prior to applying the thermoelectric conversion material, UV ozone treatment, corona treatment, plasma treatment, or adhesion promoting treatment may be performed.

The thermoelectric conversion element according to the embodiment of the present invention can be constructed by applying techniques well known in the art, except that it is constructed using the thermoelectric conversion material described above. Typically, a more specific configuration of the thermoelectric conversion element and its manufacturing method will be described.

In one embodiment, the thermoelectric conversion element includes a thermoelectric conversion film obtained using a thermoelectric conversion material, and a pair of electrodes that are electrically connected to the thermoelectric conversion film. Here, "electrically connected" means that they are connected to each other or that they are in a state where electricity can be passed through other constituent members such as wires.

The material of the electrode can be selected from metals, alloys, and semiconductors. In one embodiment, metals and alloys are preferred because they have high electrical conductivity and low contact resistance with the thermoelectric conversion material according to the present invention constituting the thermoelectric conversion film. As a specific example, the electrode preferably contains at least one member selected from the group consisting of gold, silver, copper, and aluminum. More preferably, the electrode contains silver.

The electrode can be formed by a method such as a vacuum evaporation method, thermocompression bonding of an electrode material foil or a film having an electrode material film, or application of a paste in which fine particles of the electrode material are dispersed. From the viewpoint of a simple process, a method using thermocompression bonding of an electrode material foil or a film having an electrode material film, or a method using a paste in which the electrode material is dispersed is preferable.

Specific examples of the structure of the thermoelectric conversion element include (1) a structure in which electrodes are formed at both ends of the thermoelectric conversion film according to the present invention, and (2) a structure in which electrodes are formed at both ends of the thermoelectric conversion film according to the present invention, based on the positional relationship between the thermoelectric conversion film and a pair of electrodes. It is roughly divided into a structure in which a conversion membrane is sandwiched between two electrodes.
For example, a thermoelectric conversion element having the structure (1) above can be obtained by forming a thermoelectric conversion film on a base material and then applying silver paste to both ends of the film to form first and second electrodes. be able to. In the thermoelectric conversion element in which electrodes are formed at both ends of the thermoelectric conversion film in this way, it is easy to increase the distance between the two electrodes. Therefore, it is easy to generate a large temperature difference between the two electrodes and perform thermoelectric conversion efficiently.

The thermoelectric conversion element having the structure (2) above can be produced, for example, by applying silver paste onto a base material to form a first electrode, forming the thermoelectric conversion film of the present invention on top of that, and then forming a first electrode on top of the first electrode. It can be obtained by coating a silver paste to form the second electrode. In the thermoelectric conversion element in which the thermoelectric conversion film of the present invention is sandwiched between two electrodes as described above, it is difficult to increase the distance between the two electrodes. Therefore, it is difficult to generate a large temperature difference between the two electrodes, but it is possible to increase the temperature difference by increasing the thickness of the thermoelectric conversion film. Further, since the thermoelectric conversion element having such a structure can utilize the temperature difference in the direction perpendicular to the base material, it can be used in a form where it is attached to a heating element. Therefore, it is preferable in that a large area of the heat source can be easily utilized.

Thermoelectric conversion elements can generate a high voltage by connecting them in series, and can generate a large current by connecting them in parallel. Moreover, the thermoelectric conversion element may be one in which two or more thermoelectric conversion elements are connected. According to the present invention, since the thermoelectric conversion element has excellent flexibility, it is possible to follow and suitably install a heat source having a non-planar shape.

In one embodiment, it is also effective to combine the thermoelectric conversion element of the present invention with a thermoelectric conversion element made of another thermoelectric material. For example, as inorganic thermoelectric materials, Bi-(Te, Se) based, Si-Ge based, Mg-Si based, Pb-Te based, GeTe-AgSbTe based, (Co, Ir, Ru)-Sb based, (Ca, Sr, Bi)Co ₂ O ₅ type, etc. can be mentioned, and specifically, Bi ₂ Te ₃ , PbTe, AgSbTe ₂ , GeTe, Sb ₂ Te ₃ , NaCo ₂ O ₄ , CaCoO ₃ , SrTiO ₃ , ZnO , SiGe, Mg ₂ Si, FeSi ₂ , Ba ₈ Si ₄₆ , MnSi _1.73 , ZnSb, Zn ₄ Sb ₃ , GeFe ₃ CoSb ₁₂ , LaFe ₃ CoSb ₁₂ and the like. I can do it. At this time, impurities may be added to the inorganic thermoelectric material to control its polarity (p-type, n-type) and conductivity. In addition, at least one selected from the group consisting of polythiophene, polyaniline, polyacetylene, fullerene, and derivatives thereof can be used as the organic thermoelectric material. When combining other thermoelectric conversion elements made of these materials, it is preferable to manufacture the other thermoelectric conversion elements within a range that does not impair the flexibility of the element.

When connecting a plurality of thermoelectric conversion elements, they can also be connected and used in a state where they are integrated on one base material. In such an embodiment, a combination of the thermoelectric conversion element according to the present invention and a thermoelectric conversion element made of a thermoelectric material exhibiting n-type polarity is preferable, and it is more preferable to connect these in series. According to this embodiment, it becomes easy to precisely integrate thermoelectric conversion elements.

Hereinafter, the present invention will be explained in more detail with reference to experimental examples. In addition, in the examples, "part" means "part by mass" and "%" means "% by mass", respectively. Furthermore, "NMP" refers to N-methylpyrrolidone.

<Method for measuring mass average molecular weight (Mw)>
For the measurement of Mw, a GPC (gel permeation chromatography) "HPC-8020" manufactured by Tosoh Corporation was used as an apparatus. Two "LF-604" columns (manufactured by Showa Denko Co., Ltd.: GPC column for rapid analysis: 6 mm ID x 150 mm size) were connected in series, the flow rate was 0.6 ml/min, and the column temperature was 40°C. Mw was determined using polystyrene of known molecular weight as a substance.

<Measurement method of HOMO value and Fermi level>
Measurement of the HOMO level (or Fermi level if the conductive material is metal) of the conductive material (A) and the organic polymer compound (B) is carried out using a single conductive material with each component stretched on an ITO glass substrate. After fixing it on a tape to prepare a measurement sample, it was measured by photoelectron spectroscopy (measurement device: AC-3 manufactured by Riken Keiki Co., Ltd.). The measured values are listed in Table 9.

<Synthesis of organic polymer compound (B)>
(Synthesis Example 1: Organic polymer compound (B))
Reaction (1): 125 mmol (18.27 g) of dimethyl succinate, 312.5 mmol (32.23 g) of benzonitrile, and 312.5 mmol (12.49 g) of sodium hydride were dissolved in 300 g of amyl alcohol and refluxed for 8 hours. . After cooling, the precipitate was filtered and washed with acetic acid and methanol to obtain 18.21 g of intermediate pyrrolopyrrole as a reddish brown solid.
Reaction (2): 50 mmol (14.42 g) of the obtained intermediate pyrrolopyrrole, 50 mmol (10.8 g) of 1,4-dibromobutane, and 200 mmol (19.22 g) of sodium tert-butoxide were dissolved in 150 g of dimethylacetamide. It was refluxed for 8 hours. After cooling, the above mixture was poured into 1000 ml of methanol to precipitate a solid, which was collected by filtration to obtain 9.58 g of an organic polymer compound (B) having a structure shown in the synthesis example and having an Mw of 187,000.

(Synthesis examples 2 to 19)
The organic polymers shown in Synthesis Examples 2 to 19 were prepared in the same manner as in Synthesis Example 1, except that the benzonitrile and 1,4-dibromobutane used in Synthesis Example 1 were changed to the raw materials shown in Tables 1 to 4. Molecular compound (B) was synthesized. The blending ratio of the raw materials was the same molar ratio as in Synthesis Example 1. In addition, in the table, "n" represents the number of repeating units corresponding to general formula (1), and "Oc" represents an octyl group.

(Synthesis Example 20: Organic polymer compound (B))
10 g of the organic polymer compound (B) of Synthesis Example 1 and 60 g of Lawson's reagent were added to 200 g of xylene and heated at 120° C. for 8 hours. The reaction solution was dried under reduced pressure, and the obtained solid was purified using a silica gel column to obtain 4.32 g of organic polymer compound (B) of Synthesis Example 20.

(Synthesis Examples 21 to 38)
Each was synthesized by the same method as Synthesis Example 20, except that the organic polymer compound (B) of Synthesis Example 1 used in Synthesis Example 20 was changed to the organic polymer compound (B) of Synthesis Examples 2 to 19. Organic polymer compounds (B) shown in Examples 21 to 38 were synthesized. The blending ratio of the raw materials was the same mass ratio as in Synthesis Example 20.

(Synthesis Example 39: Organic polymer compound (B))
10 g of the organic polymer compound (B) of Synthesis Example 1, 5 g of malononitrile, and 30 g of aluminum oxide were added to 200 g of chloroform and stirred for 4 hours. The reaction solution was dried under reduced pressure and the obtained solid was purified using a silica gel column to obtain 6.31 g of organic polymer compound (B) of Synthesis Example 39.

(Synthesis Examples 40 to 57)
Each was synthesized by the same method as Synthesis Example 39, except that the organic polymer compound (B) of Synthesis Example 1 used in Synthesis Example 39 was changed to the organic polymer compound (B) of Synthesis Examples 2 to 19. Organic polymer compounds (B) shown in Examples 40 to 57 were synthesized. The blending ratio of the raw materials was the same mass ratio as in Synthesis Example 39.

(Synthesis Example 58: Organic polymer compound (B))
Reaction (2) used in Synthesis Example 1: 50 mmol (10.8 g) of 1,4-dibromobutane was changed to 50 mmol (10.8 g) of 1,4-dibromobutane and 0.16 mmol (23.6 mg) of iodomethane. Except for this, an organic polymer compound (B) having the structure shown in Synthesis Example 1 and having an Mw of 151,000 was synthesized by the same method as in Synthesis Example 1.

(Synthesis Example 59: Organic polymer compound (B))
Reaction (2) used in Synthesis Example 1: 50 mmol (10.8 g) of 1,4-dibromobutane was changed to 50 mmol (10.8 g) of 1,4-dibromobutane and 0.25 mmol (35.5 mg) of iodomethane. Except for this, an organic polymer compound (B) having the structure shown in Synthesis Example 1 and having an Mw of 125,000 was synthesized by the same method as in Synthesis Example 1.

(Synthesis Example 60: Organic polymer compound (B))
Reaction (2) used in Synthesis Example 1: 50 mmol (10.8 g) of 1,4-dibromobutane was changed to 50 mmol (10.8 g) of 1,4-dibromobutane and 0.33 mmol (47.3 mg) of iodomethane. Except for this, an organic polymer compound (B) having the structure shown in Synthesis Example 1 and having an Mw of 89,000 was synthesized by the same method as in Synthesis Example 1.

(Synthesis Example 61: Organic polymer compound (B))
Reaction (2) used in Synthesis Example 1: 50 mmol (10.8 g) of 1,4-dibromobutane was changed to 50 mmol (10.8 g) of 1,4-dibromobutane and 2.0 mmol (283.9 mg) of iodomethane. Except for this, an organic polymer compound (B) having the structure shown in Synthesis Example 1 and having an Mw of 21,000 was synthesized by the same method as in Synthesis Example 1.

(Synthesis example 62)
With reference to paragraphs 0074 and 0075 of International Publication No. 2015/050113, an acrylic polymer in which a perylene carbodiimide skeleton was introduced into the side chain having a mass average molecular weight (Mw) of about 21,000 and represented by the following structure was obtained.

<Manufacture of thermoelectric conversion materials>
[Example 1]
(Thermoelectric conversion material dispersion 1)
0.4 parts of TUBALL (single-walled carbon nanotubes manufactured by Kusumoto Kasei Co., Ltd.), 0.4 parts of the organic polymer compound of Synthesis Example 1, and 79.2 parts of NMP were each weighed and mixed. Furthermore, 140 parts of zirconia beads (φ1.25 mm) were added, and after shaking with Scandex for 2 hours, the zirconia beads were removed by filtration to obtain dispersion liquid 1 of thermoelectric conversion material.

.
[Examples 2 to 68 and Comparative Examples 1 to 2]
(Dispersion 2-70)
Dispersions 2 to 70 of thermoelectric conversion materials were obtained in the same manner as Dispersion 1, except that the types and amounts of materials constituting the dispersions were changed to those shown in Table 9.

<Evaluation of thermoelectric conversion materials>
The obtained dispersions 1 to 70 were applied onto a polyimide film with a thickness of 50 μm as a sheet-like base material using an applicator, and then heated and dried at 130° C. for 30 minutes to form a film with a thickness of 5 μm on the polyimide film. A laminate having a thermoelectric conversion film was obtained.
The conductivity, Seebeck coefficient, power factor (PF), and bending resistance of the obtained laminate having the thermoelectric conversion film (hereinafter also referred to as coating film) were evaluated as follows. The results are shown in Table 9.

(conductivity)
The obtained laminate was cut into a size of 2.5 cm x 5 cm, and its conductivity was measured using a four-probe method using Loresta GX MCP-T700 (manufactured by Mitsubishi Chemical Analytech) in accordance with JIS-K7194.

(Seebeck coefficient)
The obtained laminate was cut into a size of 3 mm x 10 mm, and the Seebeck coefficient (μW/K) at 80° C. was measured using ZEM-3LW manufactured by Advance Riko Co., Ltd.

(Power factor (PF))
Using the obtained conductivity and Seebeck coefficient, PF (=S ² ·σ) at 80° C. was calculated and evaluated according to the following criteria.
◎: PF is 20 μW/(mK ² ) or more (very good)
○: PF is 10 μW/(mK ² ) or more and less than 20 μW/(mK ² ) (good)
△: PF is 2.5 μW/(mK ² ) or more and less than 10 μW/(mK ² ) (practical)
×: PF is less than 2.5 μW/(mK ² ) (not practical)

<Flexibility test>
Flexibility tests were conducted to evaluate the strength and process suitability of the coating film of thermoelectric conversion materials. By evaluating the conductivity before and after bending, it is possible to evaluate the strength of the material in terms of resistance to peeling and cracking due to bending, changes in the adsorption state of the conductive material (A) and the organic polymer compound (B), etc. can.
The bendability test was conducted using a bendability tester (manufactured by Coating Tester Co., Ltd., cylindrical mandrel method) using a mandrel with a diameter of 20 mm. The polyimide film was set in the apparatus so as to face downward, and the film was bent 5 times at a rate of 1 time/10 seconds. The conductivity of the laminate before the test of the conductive pattern portion and after being bent five times was measured, and the rate of change was calculated. The rate of change was calculated using the following formula.
Rate of change = (Conductivity before bending - Conductivity after bending) / Conductivity before bending x 100
・Evaluation criteria ◎: Change rate less than 10% (excellent)
○: Rate of change is 10% or more and less than 20% (good)
△: Rate of change is 20% or more and less than 25% (no problem in practice)
×: Rate of change is 25% or more (not practical)

The abbreviations in Table 1 are as follows.
SWCNT: Single-walled carbon nanotube “TUBALL” manufactured by OCSiAl
GNP: Graphene nanoplatelet “xGNP-M-5” manufactured by XG Sciences
KB: Lion Corporation Ketjen Black “EC-300J”
Graphite: Graphite "CPB" manufactured by Nippon Graphite Co., Ltd.
MWCNT: Multi-walled carbon nanotube “100P” manufactured by Knano
PEDOT/PSS: “Clevios PH1000” manufactured by Heraeus

As shown in Table 9, the thermoelectric conversion element of the present invention exhibits superior thermoelectric properties and excellent flexibility compared to Comparative Examples 1 and 2, and has excellent process suitability as a thermoelectric conversion element. Shown.

<Manufacture of thermoelectric conversion elements>
[Example]
(Thermoelectric conversion element 1)
Dispersion 1 of the thermoelectric conversion material prepared in Example 1 was applied onto a 50 μm polyimide film to produce five thermoelectric conversion films each having a shape of 5 mm x 30 mm, spaced apart by 10 mm (reference numeral 2 in FIG. 1). ). Next, four silver circuits each having a shape of 5 mm x 33 mm were fabricated using silver paste so that each thermoelectric conversion film was connected in series (see reference numeral 3 in FIG. 1), and the thermoelectric conversion element 1 I got it. As the silver paste, REXALPHA RA FS 074 manufactured by Toyochem Co., Ltd. was used.

[Example 69 to Example 136, Comparative Examples 3 to 4]
(Thermoelectric conversion elements 2 to 70)
Thermoelectric conversion elements 2 to 70 were obtained in the same manner as thermoelectric conversion element 1, except that the dispersion of the thermoelectric conversion material used in thermoelectric conversion element 1 was changed to the dispersion shown in Table 10.

<Evaluation of thermoelectric conversion element>
The electromotive force of the obtained thermoelectric conversion element was evaluated as follows. The results are shown in Table 2.

(Measurement of electromotive force)
Bend each thermoelectric conversion element so that the thermoelectric conversion film and silver circuit are on the inside (along line AA' shown in Figure 2), and place it in that state on a hot plate heated to 100°C. did. The degree of bending was adjusted so that the distance between BB' in FIG. 2 was 10 mm. The sample bent as described above was placed on a hot plate, and the electromotive force between the coating films was measured using a voltmeter 10 minutes later. The measurements were carried out at room temperature (20°C). The thermoelectric properties were evaluated from the measured values according to the following criteria.
◎: Electromotive force is 1 mV or more (good)
〇: Electromotive force is 500μV or more and less than 1mV (practical possible)
×: Electromotive force is less than 500 μV (defective)

As shown in Table 10, the thermoelectric conversion element of the present invention had superior thermoelectric properties compared to Comparative Examples 3 and 4. From the above, according to the embodiments of the present invention, it is possible to realize a thermoelectric conversion material having excellent Seebeck coefficient and conductivity, and exhibiting a high PF and excellent thermoelectric properties, and a highly efficient thermoelectric conversion element can be realized. I know it can be achieved.

Since the conductive composition according to the embodiment of the present invention has both conductivity and Seebeck coefficient, and also has excellent thermoelectric properties, it is possible to provide a high-performance thermoelectric conversion element using the above-mentioned material.

1: Base material 2: Thermoelectric conversion film 3: Circuit 10: Thermoelectric conversion element test sample 20: Hot plate

Claims (4)

Containing at least one conductive material (A) selected from the group consisting of carbon materials, metal materials, and conductive polymers and an organic polymer compound (B),
The organic polymer compound (B) is a non-conjugated polymer, has a repeating unit of a monomer having a pyrrolopyrrole skeleton, and has a mass average molecular weight of 10,000 to 200,000,
A thermoelectric conversion material , wherein the repeating unit of the monomer having a pyrrolopyrrole skeleton has a repeating unit represented by the following general formula (1) . (However, the conductive material (A) excludes the organic polymer compound (B))
General formula (1)
[In general formula (1), X represents a divalent linking group selected from the group consisting of an alkylene group, an oxyalkylene group, a thioalkylene group, and a group in which these groups are bonded together, and Y 1 _and Y ₂ are , each independently represents an oxygen atom, a sulfur atom, or a dicyanomethylene group, and R ₁ and
R ₂ is each independently a substituted or unsubstituted aryl group, or a substituted or unsubstituted aryl group, or a substituted or unsubstituted aryl group;
Represents a heterocyclic group. ] The thermoelectric conversion material according to claim 1 , wherein the conductive material (A) contains at least one selected from the group consisting of carbon nanotubes, Ketjenblack, graphene nanoplates, and graphene. The thermoelectric conversion material according to claim 2 , wherein the conductive material (A) is a carbon nanotube. A thermoelectric conversion element comprising a thermoelectric conversion film made of the thermoelectric conversion material according to any one of claims 1 to 3 and an electrode, the thermoelectric conversion film and the electrode being electrically connected.

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