Thermoelectric conversion material layer

Abstract

Provided is a thermoelectric conversion material layer composed of a fired body of a thermoelectric semiconductor composition and having high thermoelectric performance and an improved filling ratio of a thermoelectric conversion material in the thermoelectric conversion material layer, the thermoelectric conversion material layer being composed of a fired body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, wherein the metal nanoparticles are particles that are sintered at 450ºC or lower.

Description

[Technical Field]

[0001] This invention relates to a thermoelectric conversion material layer. [Background technology]

[0002] Conventionally, as one means of efficiently utilizing energy, there are devices that directly convert thermal energy and electrical energy into each other using thermoelectric conversion modules that have thermoelectric effects such as the Seebeck effect and the Peltier effect. As the aforementioned thermoelectric conversion module, the use of so-called π-type thermoelectric conversion elements is known. In the π-type, a pair of electrodes spaced apart from each other are provided on a substrate, for example, a P-type thermoelectric element is provided on one electrode and an N-type thermoelectric element is provided on the other electrode, also spaced apart from each other, and the upper surfaces of both thermoelectric materials are connected to the electrodes on the opposing substrate. In addition, the use of so-called in-plane type thermoelectric conversion elements is known. In the in-plane type, P-type thermoelectric elements and N-type thermoelectric elements are provided alternately in the in-plane direction of the substrate, and for example, the lower part of the junction between the two thermoelectric elements is connected in series with an electrode in between. In this context, there is a demand for improved flexibility, thinner design, and enhanced thermoelectric performance of thermoelectric conversion modules. To satisfy these demands, Patent Document 1 discloses, for example, the use of a resin substrate such as polyimide as a substrate for thermoelectric conversion modules from the viewpoint of flexibility. Furthermore, from the viewpoint of flexibility, thin design, and thermoelectric performance, a thermoelectric conversion material layer is disclosed that consists of a thermoelectric semiconductor composition comprising, for example, bismuth telluride-based material (thermoelectric semiconductor particles) formed into particles as a thermoelectric semiconductor material, and a resin that acts as a binder between these particles. Patent Document 2 discloses a thermoelectric conversion material layer comprising a composition for a thermoelectric conversion element, comprising carbon nanotubes on which metal nanoparticles are supported as a thermoelectric semiconductor material, a resin component as a binder, and a solvent, from the viewpoint of excellent processability, flexibility, and thermoelectric performance. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2016 / 104615 [Patent Document 2] International Publication No. 2017 / 122805 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] However, in Patent Document 1, since a resin is used as a binder between thermoelectric semiconductor particles, many voids are included between the thermoelectric semiconductor particles in the formed thermoelectric conversion material layer, and a high electrical conductivity cannot be sufficiently obtained, resulting in insufficient thermoelectric performance. In Patent Document 2, the conductivity of CNT (carbon nanotube) itself is improved by supporting metal nanoparticles on CNT having a defect structure (a portion where a six-membered ring network is not well formed), but it has the same problem as Patent Document 1.

[0005] In view of the above, an object of the present invention is to provide a thermoelectric conversion material layer having high thermoelectric performance with an improved filling rate of a thermoelectric conversion material in a thermoelectric conversion material layer composed of a fired body of a thermoelectric semiconductor composition. [Means for Solving the Problems]

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that by containing metal nanoparticles that sinter at a specific temperature in a thermoelectric semiconductor composition and filling (reducing voids) the voids between thermoelectric semiconductor particles, a thermoelectric conversion material layer with a high filling rate of the thermoelectric conversion material can be obtained, and the thermoelectric conversion material layer has a high electrical conductivity, leading to an improvement in thermoelectric performance, and thus the present invention has been completed. That is, the present invention provides the following (1) to (8). (1) A thermoelectric conversion material layer composed of a fired body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, wherein the metal nanoparticles are particles that sinter at 450°C or lower. (2) The thermoelectric conversion material layer according to (1) above, wherein the average particle size of the metal nanoparticles in the thermoelectric semiconductor composition is 200 nm or less. (3) The thermoelectric conversion material layer according to (1) or (2) above, wherein the metal nanoparticles are particles that are sintered at 300°C or below. (4) The thermoelectric conversion material layer according to any one of (1) to (3) above, wherein the metal nanoparticles are selected from the group consisting of silver, copper, gold, platinum, palladium, aluminum, titanium, nickel, bismuth, tellurium and alloys thereof. (5) The resistivity of the metal nanoparticles is 6.0 × 10 -3 A thermoelectric conversion material layer according to any of (1) to (4) above, having a density of Ω·cm or less. (6) The thermoelectric conversion material layer according to any one of (1) to (5) above, wherein the content of the metal nanoparticles in the thermoelectric semiconductor composition is 0.01 to 15.00% by mass. (7) The thermoelectric conversion material layer according to any one of (1) to (6) above, wherein the thermoelectric conversion material layer is made of a fired body of a coated film of the thermoelectric semiconductor composition. (8) The thermoelectric material layer according to any one of (1) to (7) above, wherein the thermoelectric material layer is composed of a thermoelectric material containing voids, and the filling rate is defined as the ratio of the area of ​​the thermoelectric material to the area of ​​the longitudinal cross-section including the central part of the thermoelectric material layer, and the filling rate is 0.800 or more and less than 1.000. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a thermoelectric conversion material layer with high thermoelectric performance, in which the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer, which is made of a sintered body of a thermoelectric semiconductor composition, is improved. [Brief explanation of the drawing]

[0008] [Figure 1] This figure illustrates the definition of the longitudinal cross-section of the thermoelectric conversion material layer of the present invention. [Figure 2] This is a schematic cross-sectional diagram illustrating the longitudinal section of the thermoelectric conversion material layer of the present invention before and after heating and pressurizing. [Figure 3]This is an explanatory diagram showing one embodiment of the method for manufacturing a thermoelectric conversion material layer according to the present invention, in order of steps. [Modes for carrying out the invention]

[0009] [Thermoelectric conversion material layer] The thermoelectric conversion material layer of the present invention is a thermoelectric conversion material layer comprising a sintered body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, wherein the metal nanoparticles are particles that are sintered at 450°C or below. By incorporating metal nanoparticles that sinter at temperatures below 450°C into a thermoelectric semiconductor composition, the sintered metal nanoparticles, which sinter at temperatures below the aforementioned temperature, fill the voids between thermoelectric semiconductor particles (reducing the voids). This results in a thermoelectric material layer with a high packing density, which in turn causes the thermoelectric material to exhibit high electrical conductivity, thereby improving thermoelectric performance. In this specification, the "thermoelectric conversion material layer" is composed of a thermoelectric conversion material and voids. In other words, the "thermoelectric conversion material" refers to the portion of the thermoelectric conversion material layer excluding the voids. Furthermore, "sintering at 450°C or below" refers to a state in which, after a thin film made of a thermoelectric semiconductor composition before firing is left to stand for a predetermined time (corresponding to the firing time described later) in an atmosphere with a maximum temperature of 450°C and then returned to room temperature, there are regions where the interface between metal nanoparticles cannot be confirmed, or regions where the interface between metal nanoparticles and thermoelectric semiconductor particles cannot be confirmed. Specifically, the evaluation of "a state in which there is a region where the interface cannot be confirmed" can be performed, for example, by cutting a longitudinal section including the central part of a thermoelectric conversion material layer fired at a temperature below the relevant temperature, and observing the sintered metal nanoparticles and thermoelectric semiconductor particles contained in the longitudinal section using a scanning electron microscope (SEM), according to the following criteria. In an image with an observation field size of 1 μm square (where at least 10 metal nanoparticles are present in the field of view), there is at least one region where the metal nanoparticles form a neck and the interface cannot be visually confirmed. Alternatively, in an image with an observation field size of 10 μm square (where at least one metal nanoparticle and thermoelectric semiconductor particle are present in the field of view), there is at least one region where the interface between the metal nanoparticle and the thermoelectric semiconductor particle cannot be visually confirmed. Furthermore, if a binder resin is present in the thin film made of the thermoelectric semiconductor composition before firing, and the binder resin is completely decomposed by firing, the thermoelectric conversion material layer and the thermoelectric conversion material shall not contain the binder resin.

[0010] The thermoelectric conversion material layer of the present invention consists of a fired body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles. In one preferred embodiment, the fired body consists of a fired body of a coated film of a thermoelectric semiconductor composition. In another preferred embodiment, the fired body consists of a fired body of a thin film formed by known dry film formation methods such as vapor deposition or sputtering of a thermoelectric semiconductor composition.

[0011] The firing temperature is typically 60 to 450°C, preferably 130 to 450°C, more preferably 140 to 450°C, even more preferably 160 to 450°C, and particularly preferably 180 to 450°C, from the viewpoint of obtaining a sintered body of metal nanoparticles. The firing time is not particularly limited, but is typically several minutes to several tens of hours, preferably several minutes to several hours.

[0012] The thickness of the thermoelectric conversion material layer is not particularly limited, but from the viewpoint of flexibility, thermoelectric performance, and film strength, it is preferably 1 nm to 1000 μm, more preferably 3 to 600 μm, and even more preferably 5 to 400 μm.

[0013] <Metal nanoparticles> The thermoelectric semiconductor composition used in the present invention contains metal nanoparticles. In the process of annealing a thin film of a thermoelectric semiconductor composition to form a sintered body (thermoelectric conversion material layer), metal nanoparticles can fill the voids between thermoelectric semiconductor particles by promoting bonding between them through sintering, thereby suppressing the generation of voids. As a result, the packing density of the thermoelectric conversion material in the thermoelectric conversion material layer can be improved. At the same time, similar to the ionic liquid described later, the reduction in electrical conductivity between thermoelectric semiconductor particles can be effectively suppressed.

[0014] Metal nanoparticles are particles that sinter at temperatures below 450°C. Preferably, the particles sinter at 130-450°C, more preferably at 140-450°C, even more preferably at 160-450°C, and particularly preferably at 180-450°C. If the metal nanoparticles sinter within the above range, they can efficiently fill the voids between thermoelectric semiconductor particles in the thin film of the thermoelectric semiconductor composition, which in turn improves the packing density of the thermoelectric material in the thermoelectric material layer and leads to an improvement in the electrical conductivity of the thermoelectric material layer.

[0015] The metal nanoparticles are not particularly limited as long as they can fill the gaps between thermoelectric semiconductor particles and suppress the reduction in electrical conductivity between the thermoelectric semiconductor particles. However, they are preferably selected from the group consisting of silver, copper, gold, platinum, palladium, aluminum, titanium, nickel, bismuth, tellurium, and their alloys. They are more preferably selected from the group consisting of silver, copper, gold, bismuth, tellurium, aluminum, and their alloys. From the viewpoint of low-temperature sinterability and stability, they are even more preferably selected from the group consisting of silver, copper, gold, and alloys of silver and copper, alloys of silver and gold, and alloys of copper and gold.

[0016] The average particle size of the metal nanoparticles in the thermoelectric semiconductor composition is not particularly limited, but from the viewpoint of low-temperature sinterability and efficient filling of narrow voids between thermoelectric semiconductor particles, it is preferably 200 nm or less, more preferably 1 to 200 nm or less, even more preferably 1 to 180 nm, even more preferably 10 to 150 nm, particularly preferably 15 to 120 nm, and most preferably 20 to 100 nm. If the average particle size of the metal nanoparticles is within the above range, the voids between thermoelectric semiconductor particles in the thin film of the thermoelectric semiconductor composition can be efficiently filled. Furthermore, during the process of firing (annealing) the thin film of the thermoelectric semiconductor composition to form a fired body (thermoelectric conversion material layer), the sintering of the metal nanoparticles progresses, further filling of the voids between thermoelectric semiconductor particles. As a result, the packing rate of the thermoelectric conversion material in the thermoelectric conversion material layer is improved, leading to an improvement in the electrical conductivity of the thermoelectric conversion material layer. The average particle size (primary particle) of metal nanoparticles in the thermoelectric semiconductor composition is the arithmetic mean of the average particle sizes of any 20 metal nanoparticles observed by a transmission electron microscope (TEM). Furthermore, it is generally known that metal particles smaller than several tens of nanometers exhibit various physical and chemical properties that differ from those of bulk metals as the particle size decreases. For example, it is known that the melting point of metal particles becomes lower than that of bulk metals as the particle size decreases. Therefore, in this invention, including the point of lowering the sintering temperature, metal particles with small particle sizes are used.

[0017] The resistivity of the metal nanoparticles is preferably 6.0 × 10⁻⁶. -3 It is less than or equal to Ω·cm, and more preferably 8 × 10 -6 It is less than or equal to Ω·cm, and more preferably 8 × 10 -7 It is less than or equal to Ω·cm, and is particularly preferably 8 × 10 -8 It is less than or equal to Ω·cm. If the resistivity of the metal nanoparticles is within the above range, the electrical bonding between thermoelectric semiconductor particles improves, and the electrical resistance of the thermoelectric conversion material layer decreases.

[0018] The content of metal nanoparticles in the thermoelectric semiconductor composition is preferably 0.01 to 15.00% by mass, more preferably 0.50 to 14.00% by mass, still more preferably 1.00 to 12.00% by mass, particularly preferably 2.00 to 11.00% by mass, and most preferably 5.00 to 10.00% by mass. If the content of metal nanoparticles in the thermoelectric semiconductor composition is within the above range, the sintered body of metal nanoparticles during the firing of the thin film made of the thermoelectric semiconductor composition can efficiently fill the gaps between the thermoelectric semiconductor particles. As a result, the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer is improved, leading to an improvement in the electrical conductivity of the thermoelectric conversion material layer.

[0019] Examples of commercially available metal nanoparticles include the following. For example, silver nanoparticles (manufactured by Mitsuboshi Belt Co., Ltd., trade name: MDot (registered trademark) CF158, specific resistance: 8×10 -6 Ω·cm, average particle size: 60 nm), silver nanoparticles (manufactured by Daicel Corporation, trade name: Picosil (registered trademark), specific resistance: 1.0×10 -5 Ω·cm, average particle size: 60 nm), silver nanoparticles (complex) (manufactured by InkTec Co., Ltd., trade name: Tec-PA-010, specific resistance: 8×10 -6 Ω·cm, average particle size: 35 nm), copper nanoparticles (manufactured by Taiyo Nippon Sanso Corporation, trade name: Copper Nanopaste, specific resistance: 2.5×10 -5 Ω·cm, average particle size: 120 nm), etc.

[0020] <Thermoelectric semiconductor particles> The thermoelectric semiconductor composition used in the present invention contains thermoelectric semiconductor particles. The thermoelectric semiconductor particles are obtained by pulverizing a thermoelectric semiconductor material described later to a predetermined size using a pulverizer or the like. The thermoelectric semiconductor material is not particularly limited as long as it can generate a thermoelectromotive force by applying a temperature difference. For example, bismuth-tellurium-based thermoelectric semiconductor materials such as P-type bismuth telluride and N-type bismuth telluride; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; antimony-tellurium-based thermoelectric semiconductor materials; ZnSb, Zn3Sb 2、Zinc-antimony-based thermoelectric semiconductor materials such as Zn4Sb3; silicon-germanium-based thermoelectric semiconductor materials such as SiGe; bismuth selenide-based thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73 , silicide-based thermoelectric semiconductor materials such as Mg2Si; oxide-based thermoelectric semiconductor materials; Heusler materials such as FeVAl, FeVAlSi, FeVTiAl; sulfide-based thermoelectric semiconductor materials such as TiS2; etc. are used. These may be used alone or in combination of two or more kinds. Among these, bismuth-telluride-based thermoelectric semiconductor materials, telluride-based thermoelectric semiconductor materials, antimony-telluride-based thermoelectric semiconductor materials, and bismuth selenide-based thermoelectric semiconductor materials are preferred. From the viewpoint of obtaining high thermoelectric performance, bismuth-telluride-based thermoelectric semiconductor materials such as P-type bismuth telluride and N-type bismuth telluride are more preferred.

[0021] P-type bismuth telluride has holes as carriers and a positive value of the Seebeck coefficient. For example, Bi X Te3Sb 2-X represented by is preferably used. In this case, X is preferably 0 < X ≦ 0.8, more preferably 0.4 ≦ X ≦ 0.6. When X is greater than 0 and less than or equal to 0.8, the Seebeck coefficient and electrical conductivity increase, and the characteristics as a P-type thermoelectric element are maintained, which is preferable. Also, N-type bismuth telluride has electrons as carriers and a negative value of the Seebeck coefficient. For example, Bi2Te 3-Y Se Y represented by is preferably used. In this case, Y is preferably 0 ≦ Y ≦ 3 (when Y = 0: Bi2Te3), more preferably 0 < Y ≦ 2.7. When Y is 0 or more and 3 or less, the Seebeck coefficient and electrical conductivity increase, and the characteristics as an N-type thermoelectric element are maintained, which is preferable.

[0022] The content of thermoelectric semiconductor particles in the thermoelectric semiconductor composition is preferably 30 to 99% by mass, more preferably 50 to 96% by mass, and particularly preferably 70 to 95% by mass. When the content of thermoelectric semiconductor particles is within the above range, the Seebeck coefficient (absolute value of the Peltier coefficient) is large, the decrease in electrical conductivity is suppressed, and only the thermal conductivity decreases, resulting in a film that exhibits high thermoelectric performance, as well as sufficient film strength and flexibility, which is preferable.

[0023] The average particle size of the thermoelectric semiconductor particles is preferably 10 nm to 200 μm, more preferably 10 nm to 30 μm, even more preferably 50 nm to 10 μm, and particularly preferably 1 to 6 μm. Within this range, uniform dispersion is easily achieved, and electrical conductivity can be increased. There are no particular limitations on the method for obtaining thermoelectric semiconductor particles by grinding thermoelectric semiconductor materials; they can be ground to a predetermined size using known fine grinding equipment such as jet mills, ball mills, bead mills, colloid mills, and roller mills. The average particle size of the thermoelectric semiconductor particles was obtained by measuring it using a laser diffraction particle size analyzer (Malvern Mastersizer 3000), and was taken as the median value of the particle size distribution.

[0024] Furthermore, it is preferable that the thermoelectric semiconductor particles are pre-heat-treated. Heat treatment improves the crystallinity of the thermoelectric semiconductor particles and removes the surface oxide film of the thermoelectric semiconductor particles, thereby increasing the Seebeck coefficient or Peltier coefficient of the thermoelectric conversion material and further improving the thermoelectric figure of merit. The heat treatment is not particularly limited, but it is preferable to perform it under an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen, or under vacuum conditions with controlled gas flow rates, and more preferably under a mixed gas atmosphere of an inert gas and a reducing gas, before preparing the thermoelectric semiconductor composition, so as not to adversely affect the thermoelectric semiconductor particles. The specific temperature conditions depend on the thermoelectric semiconductor particles used, but it is generally preferable to perform the treatment at a temperature below the melting point of the particles and at 100 to 1500°C for several minutes to several tens of hours.

[0025] <Binder resin> The thermoelectric semiconductor composition used in the present invention includes a binder resin. The binder resin acts as a binder between thermoelectric semiconductor materials (thermoelectric semiconductor particles), improving the flexibility of the thermoelectric conversion module and facilitating the formation of thin films through coating or other methods.

[0026] The binder resin is preferably a resin that decomposes by 90% or more by mass at temperatures above the annealing temperature, more preferably a resin that decomposes by 95% or more by mass, and particularly preferably a resin that decomposes by 99% or more by mass. Furthermore, it is more preferable that the resin maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when thermoelectric semiconductor particles are grown in a coated film (thin film) made of a thermoelectric semiconductor composition by annealing or other treatments. If a resin that decomposes by 90% or more by mass at temperatures above the annealing temperature is used as the binder resin, the binder resin decomposes during firing. This reduces the amount of binder resin, which is an insulating component in the fired body, and promotes the crystal growth of thermoelectric semiconductor particles in the thermoelectric semiconductor composition. As a result, the voids in the thermoelectric conversion material layer can be reduced, and the packing efficiency can be improved. Furthermore, whether or not a resin decomposes by a predetermined amount (for example, 90% by mass) or more above the firing (annealing) temperature is determined by measuring the mass loss rate at the firing (annealing) temperature (the value obtained by dividing the mass after decomposition by the mass before decomposition) using thermogravimetric analysis (TG).

[0027] Examples of such binder resins include thermoplastic resins and curable resins. Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polymethylpentene; polycarbonate; thermoplastic polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyvinyl polymers such as polystyrene, acrylonitrile-styrene copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl chloride, polyvinylpyridine, polyvinyl alcohol, and polyvinylpyrrolidone; polyurethane; and cellulose derivatives such as ethylcellulose. Examples of curable resins include thermosetting resins and photocurable resins. Examples of thermosetting resins include epoxy resins and phenolic resins. Examples of photocurable resins include photocurable acrylic resins, photocurable urethane resins, and photocurable epoxy resins. These may be used individually or in combination of two or more. Among these, from the viewpoint of the electrical resistivity of the thermoelectric material in the thermoelectric material layer, thermoplastic resins are preferred, polycarbonate and cellulose derivatives such as ethyl cellulose are more preferred, and polycarbonate is particularly preferred.

[0028] The binder resin is appropriately selected according to the firing (annealing) temperature for the thermoelectric semiconductor material in the firing (annealing) process described later (D). Firing (annealing) at a temperature above the final decomposition temperature of the binder resin is preferable from the viewpoint of the electrical resistivity of the thermoelectric material in the thermoelectric material layer. In this specification, "final decomposition temperature" refers to the temperature at which the mass reduction rate at the annealing temperature, as determined by thermogravimetric analysis (TG), reaches 100% (the mass after decomposition is 0% of the mass before decomposition).

[0029] The final decomposition temperature of the binder resin is typically 150 to 600°C, preferably 200 to 560°C, more preferably 220 to 460°C, and particularly preferably 240 to 360°C. Using a binder resin with a final decomposition temperature within this range allows it to function as a binder for thermoelectric semiconductor materials, facilitating the formation of thin films during printing.

[0030] The content of the binder resin in the thermoelectric semiconductor composition is 0.1 to 40% by mass, preferably 0.5 to 20% by mass, more preferably 0.5 to 10% by mass, and particularly preferably 0.5 to 5% by mass. When the content of the binder resin is within the above range, the electrical resistivity of the thermoelectric material in the thermoelectric material layer can be reduced.

[0031] The binder resin content in the thermoelectric conversion material is preferably 0 to 10% by mass, more preferably 0 to 5% by mass, and particularly preferably 0 to 1% by mass. If the binder resin content in the thermoelectric conversion material is within the above range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer can be reduced.

[0032] <Ionic Liquid> The thermoelectric semiconductor composition used in the present invention includes an ionic liquid. Ionic liquids are molten salts composed of a combination of cations and anions, and are salts that can exist as liquids in any temperature range between -50°C and 400°C. Ionic liquids have characteristics such as extremely low vapor pressure and non-volatility, excellent thermal and electrochemical stability, low viscosity, and high ionic conductivity, so they can effectively suppress the reduction of electrical conductivity between thermoelectric semiconductor particles when used as a conductivity enhancer. In addition, ionic liquids exhibit high polarity based on their aprotic ionic structure and have excellent compatibility with binder resins, so they can make the electrical conductivity of the thermoelectric conversion material chip uniform.

[0033] Ionic liquids that are known or commercially available can be used. Ionic liquids include, for example, (1) nitrogen-containing cyclic cation compounds such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, and imidazolium and their derivatives; amine cations of tetraalkylammonium and their derivatives; phosphine cations such as phosphonium, trialkylsulfonium, and tetraalkylphosphonium and their derivatives; lithium cations and their derivatives; and (2) Cl - AlCl4 - Al2Cl7 - ClO4 - Chloride ions such as Br - Bromide ions such as; I - Iodide ions such as BF4 - PF6 - Fluoride ions such as F(HF) n - Halide anions such as NO3 - CH3COO - CF3COO - CH3SO3 - CF3SO3 - , (FSO2)2N - , (CF3SO2)2N - (CF3SO2)3C - AsF6 - SbF6 - , NbF6 - TaF6 - F(HF)n - , (CN)2N - , C4F9SO3 - (C2F5SO2)2N - C3F7COO - (CF3SO2)(CF3CO)N - Examples include those composed of anionic components such as ;. These may be used individually or in combination of two or more.

[0034] Among the above ionic liquids, from the viewpoint of high-temperature stability, compatibility with thermoelectric semiconductor particles and binder resin, and suppression of a decrease in electrical conductivity in the gaps between thermoelectric semiconductor particles, it is preferable that the cationic component of the ionic liquid contains at least one selected from pyridinium cations and their derivatives, and imidazolium cations and their derivatives. It is preferable that the anionic component of the ionic liquid contains a halide anion, and Cl - , Br - and I - It is even more preferable to include at least one selected from the following.

[0035] Specific examples of ionic liquids containing pyridinium cations and their derivatives as cationic components include 4-methyl-butylpyridinium chloride, 3-methyl-butylpyridinium chloride, 4-methyl-hexylpyridinium chloride, 3-methyl-hexylpyridinium chloride, 4-methyl-octylpyridinium chloride, 3-methyl-octylpyridinium chloride, 3,4-dimethyl-butylpyridinium chloride, 3,5-dimethyl-butylpyridinium chloride, 4-methyl-butylpyridinium tetrafluoroborate, 4-methyl-butylpyridinium hexafluorophosphate, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate, and 1-butyl-4-methylpyridinium iodide. These may be used individually or in combination of two or more. Among these, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate, and 1-butyl-4-methylpyridinium iodide are preferred.

[0036] Furthermore, specific examples of ionic liquids containing imidazolium cations and their derivatives include [1-butyl-3-(2-hydroxyethyl)imidazolium bromide], [1-butyl-3-(2-hydroxyethyl)imidazolium tetrafluoroborate], 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-decyl-3-methylimidazolium chloride, and 1-decyl-3-methyl Examples include imidazolium bromide, 1-dodecyl-3-methylimidazolium chloride, 1-tetradecyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-methyl-3-butylimidazolium methyl sulfate, and 1,3-dibutylimidazolium methyl sulfate. These may be used individually or in combination of two or more. Among these, [1-butyl-3-(2-hydroxyethyl)imidazolium bromide] and [1-butyl-3-(2-hydroxyethyl)imidazolium tetrafluoroborate] are preferred.

[0037] The electrical conductivity of the above ionic liquid is preferably 10 -7 S / cm or higher, comfortable 10 -6 The conductivity is S / cm or higher. If the electrical conductivity is within the above range, it can effectively suppress the reduction in electrical conductivity between thermoelectric semiconductor particles when used as a conductivity enhancer.

[0038] Furthermore, it is preferable that the above-mentioned ionic liquid has a decomposition temperature of 300°C or higher. If the decomposition temperature is within the above range, the effect as a conductive additive can be maintained even when the coated film (thin film) made of the thermoelectric semiconductor composition is subjected to firing (annealing) treatment, as will be described later. In this specification, "decomposition temperature" refers to the temperature at which the mass loss rate at the annealing temperature, as determined by thermogravimetric (TG), becomes 10%.

[0039] Furthermore, in the above-mentioned ionic liquid, the mass loss rate at 300°C determined by thermogravimetric analysis (TG) is preferably 10% or less, more preferably 5% or less, and particularly preferably 1% or less. If the mass loss rate is within the above range, the effect as a conductive additive can be maintained even when the coated film (thin film) made of the thermoelectric semiconductor composition is subjected to firing (annealing) treatment, as will be described later.

[0040] The content of the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 20% by mass. If the content of the ionic liquid is within the above range, the decrease in electrical conductivity is effectively suppressed, and a film with high thermoelectric performance can be obtained.

[0041] The ionic liquid content in the thermoelectric conversion material is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 20% by mass. If the ionic liquid content in the thermoelectric conversion material is within the above range, the decrease in electrical conductivity is effectively suppressed, and a film with high thermoelectric performance can be obtained.

[0042] <Inorganic ionic compounds> The thermoelectric semiconductor composition used in the present invention may further contain an inorganic ionic compound. Inorganic ionic compounds are compounds composed of at least a cation and anion. Because inorganic ionic compounds are solid at room temperature, have a melting point in the temperature range of 400-900°C, and possess high ionic conductivity, they can be used as conductive additives to suppress the reduction in electrical conductivity between thermoelectric semiconductor particles.

[0043] The content of inorganic ionic compounds in a thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 10% by mass, when the thermoelectric semiconductor composition contains inorganic ionic compounds. If the content of inorganic ionic compounds is within the above range, the decrease in electrical conductivity can be effectively suppressed, and as a result, a film with improved thermoelectric performance can be obtained. When inorganic ionic compounds and ionic liquids are used in combination, the total amount of inorganic ionic compounds and ionic liquids in the thermoelectric semiconductor composition is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 10% by mass.

[0044] The content of inorganic ionic compounds in the thermoelectric conversion material is preferably 0.01 to 50% by mass, more preferably 0.5 to 30% by mass, and particularly preferably 1.0 to 10% by mass. If the content of inorganic ionic compounds in the thermoelectric conversion material is within the above range, the decrease in electrical conductivity can be effectively suppressed, and as a result, a film with improved thermoelectric performance can be obtained.

[0045] <Other additives> In addition to the above, the thermoelectric semiconductor composition may optionally contain other additives such as dispersants, film-forming aids, light stabilizers, antioxidants, tackifiers, plasticizers, colorants, resin stabilizers, fillers, pigments, conductive fillers, conductive polymers, and curing agents. These may be used individually or in combination of two or more.

[0046] <Cross-sectional view of the thermoelectric conversion material layer> The definition of "longitudinal section including the central part of the thermoelectric conversion material layer" in this specification will be explained with reference to a figure. Figure 1 is a diagram illustrating the definition of the longitudinal section of the thermoelectric conversion material layer of the present invention. Figure 1(a) is a plan view of the thermoelectric conversion material layer 2, which has a length X in the width direction and a length Y in the depth direction. Figure 1(b) is a longitudinal section of the thermoelectric conversion material layer 2 formed on the substrate 1. The longitudinal section includes the central part C in Figure 1(a) and consists of a length X and thickness D obtained when cut between A and A' in the width direction (shown as a rectangle in the figure). The thermoelectric conversion material layer 2 contains voids 3.

[0047] The longitudinal section of the thermoelectric conversion material layer of the present invention will be explained with reference to the figure. Figure 2 is a schematic cross-sectional diagram illustrating the longitudinal sections of the thermoelectric conversion material layer of the present invention before and after heating and pressurizing. Figure 2(a) is an example of a longitudinal section of the thermoelectric conversion material layer 2s formed on a substrate 1a before heating and pressurizing. The thermoelectric conversion material layer 2s has a longitudinal section consisting of a curve with length X in the width direction and Dmin and Dmax values ​​in the thickness direction. The upper part of the longitudinal section has a concave and a convex portion, and a void portion 3a exists within the longitudinal section. Figure 2(b) is an example of a longitudinal section of the thermoelectric conversion material layer 2t formed on a substrate 1a after heating and pressurizing. The longitudinal section of the thermoelectric conversion material layer 2t has length X in the width direction and thickness D in the thickness direction [when the values ​​of Dmin and Dmax in Figure 2(a) are slightly different]. The upper part of the longitudinal section is substantially linear, and a void portion 4a exists within the longitudinal section with a further reduced number and volume of voids. Note that Dmin represents the minimum thickness in the thickness direction of the longitudinal section, and Dmax represents the maximum thickness in the thickness direction of the longitudinal section.

[0048] In the present invention, the packing ratio of the thermoelectric material in the thermoelectric material layer is defined as the ratio of the area of ​​the thermoelectric material to the area of ​​the longitudinal cross-section including the central part of the thermoelectric material layer, and the larger the packing ratio, the fewer voids there are in the thermoelectric material layer. The filling density of the thermoelectric material in the thermoelectric material layer is preferably 0.800 or more and less than 1.000, more preferably 0.900 or more and less than 1.000, even more preferably 0.920 or more and less than 1.000, even more preferably 0.950 or more and less than 1.000, and most preferably 0.970 or more and less than 1.000. When the filling density is within this range, the electrical resistivity of the thermoelectric material in the thermoelectric material layer decreases (electrical conductivity improves), and the thermoelectric performance improves. The filling rate of the thermoelectric material in the thermoelectric material layer was measured by the method described in the examples below.

[0049] The thermoelectric material layer of the present invention exhibits improved thermoelectric performance because its electrical conductivity increases as the filling density of the thermoelectric material increases. Therefore, by applying it as the thermoelectric material layer of a thermoelectric module, a thermoelectric module with high thermoelectric performance can be obtained.

[0050] [Method for manufacturing a thermoelectric conversion material layer] The present invention relates to a method for manufacturing a thermoelectric material layer, comprising a sintered body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, characterized in that the metal nanoparticles are particles that are sintered at 450°C or below. In one embodiment, it is preferable to include the steps of (A) forming a thin film of the thermoelectric material layer, (B) drying the thin film of the thermoelectric material layer obtained in step (A), (C) heating and pressurizing the dried thin film of the thermoelectric material layer obtained in step (B), and (D) firing (annealing) the heated and pressurized thin film of the thermoelectric material layer obtained in step (C). In the method for manufacturing a thermoelectric material layer of the present invention, after forming a thin film of the thermoelectric material layer, it is dried at a predetermined temperature, and then the upper surface of the thermoelectric material layer is heated and pressurized at a predetermined pressure and temperature, and then fired at 450°C or below. This promotes the filling of voids in the thermoelectric material layer due to the inclusion of metal nanoparticles and the progress of their sintering, and reduces the volume of voids in the thermoelectric material within the thermoelectric material layer, thereby obtaining a thermoelectric material layer with improved electrical conductivity. In another embodiment, the manufacturing method may involve simultaneously performing firing at the heating temperature in step (C) after steps (A) and (B), and omitting step (D). Furthermore, in another embodiment, the manufacturing method may include a step (E) after steps (A) and (B), which corresponds to step (D), in which the thin film of the thermoelectric conversion material layer obtained in step (B) after drying is fired (annealed).

[0051] Figure 3 is an explanatory diagram showing one embodiment of the method for manufacturing a thermoelectric material layer of the present invention in order of steps, where (a) is a cross-sectional view showing an embodiment in which a thermoelectric material layer 2s is formed on a substrate 1b, and the thermoelectric material layer 2s is formed on the substrate 1b as a coated film (including voids 3b) and dried at a predetermined temperature; (b) is a cross-sectional view showing the configuration after the heating press section 5 is placed facing the upper surface of the thermoelectric conversion material layer 2s, with the dried thermoelectric conversion material layer 2s obtained in (a) facing the heating press section 5; (c) is a cross-sectional view showing the state after the upper surface of the thermoelectric conversion material layer 2s has been heated and pressurized by the heating press unit 5, and then the heating press unit 5 has been released from the thermoelectric conversion material layer 2s. Subsequently, by performing firing (annealing), the thermoelectric conversion material layer 2t of the present invention (including void portions 4b in which the number and volume of voids are further reduced) can be obtained.

[0052] (A) Thermoelectric conversion material layer formation process The thermoelectric conversion material layer formation process is a process of forming a thermoelectric conversion material layer on a substrate. For example, in Figure 3(a), this process involves coating a thermoelectric semiconductor composition onto substrate 1b to form a thermoelectric conversion material layer 2s.

[0053] (substrate) There are no particular restrictions on the substrate material, and examples include glass, silicon, ceramic, metal, or plastic. When firing (annealing) is performed at high temperatures, glass, silicon, ceramic, or metal are preferred, and from the viewpoint of dimensional stability after heat treatment, glass, silicon, or ceramic are more preferable. From the viewpoint of process and dimensional stability, the thickness of the substrate can be between 100 and 10,000 μm.

[0054] (Thermoelectric semiconductor composition) As described above, the thermoelectric semiconductor composition used in the present invention comprises thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles. Furthermore, as described above, it may also contain inorganic ionic compounds and other additives. The same applies to preferred materials and their content for the thermoelectric semiconductor particles (thermoelectric semiconductor material), binder resin, ionic liquid, metal nanoparticles, inorganic ionic compounds, etc.

[0055] (Method for preparing thermoelectric semiconductor compositions) The method for preparing the thermoelectric semiconductor composition used in the present invention is not particularly limited. As described above, thermoelectric semiconductor particles, binder resin, ionic liquid, metal nanoparticles, and optionally inorganic ionic compounds or other additives, as well as a solvent, may be mixed and dispersed using known methods such as ultrasonic homogenizers, spiral mixers, planetary mixers, dispersers, and hybrid mixers to prepare the thermoelectric semiconductor composition. Examples of the aforementioned solvents include toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, methylpyrrolidone, and ethyl cellosolve. These solvents may be used individually or in mixtures of two or more. The solid content concentration of the thermoelectric semiconductor composition is not particularly limited, as long as the composition has a viscosity suitable for coating.

[0056] Methods for coating a thermoelectric semiconductor composition onto a substrate include, but are not limited to, known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, doctor blade coating, and applicator coating. When forming a patterned coating, screen printing, stencil printing, slot die coating, etc., which allow for easy pattern formation using a screen plate with the desired pattern, are preferably used.

[0057] In a preferred embodiment, the thermoelectric conversion material layer may be fabricated as a solid film on a substrate and then fragmented into the desired chip size. In another preferred embodiment, a coating film may be formed on the substrate to the size of the thermoelectric conversion material chips described later. Furthermore, from the viewpoint of shape controllability of the thermoelectric conversion material layer, in a more preferred embodiment, it may be fabricated using a grid-like pattern frame member or the like that includes spaced-out openings having the shape of the thermoelectric conversion material chips. The tip size is, for example, approximately 0.1 to 20 mm on the short side and 0.2 to 25 mm on the long side.

[0058] A method for manufacturing a thermoelectric conversion material layer when using a grid-like pattern frame member that includes spaced-out openings having the chip shape of the thermoelectric conversion material is as follows, for example. (p) A grid-like pattern frame member, which includes spaced-out openings having chip shapes of thermoelectric material, is placed on the substrate; (q) Form a coating film of thermoelectric material layer on the opening of the pattern frame member and dry it at a predetermined temperature; After the dried thermoelectric material layer obtained in (r)(q) is cooled to room temperature, the thermoelectric material layer is placed opposite the heating press section (corresponding to heating press section 5 in Figure 3); (t) The heating press section applies pressure to the upper surface of the thermoelectric material layer, reducing the number of voids and volume of the thermoelectric material layer, releasing the heating press section from the thermoelectric material layer, and then releasing the pattern frame member; (u) Subsequently, the thermoelectric material layer, which reflects the shape of the opening of the pattern frame member obtained on the substrate, is subjected to firing (annealing) to obtain the chip-shaped thermoelectric material layer of the present invention. The opening is not particularly limited, but it should have a shape that is reflected in the shape of the thermoelectric material chip after the pattern frame member is released, and is preferably rectangular, square, or circular, and more preferably rectangular or square. Furthermore, stainless steel, copper, or the like can be used as the pattern frame member from the viewpoint of ease of formation.

[0059] (B) Drying process of thermoelectric material layer The thermoelectric material layer drying process is a process of drying the thermoelectric material layer obtained in process (A). For example, in Figure 3(a), it is a process of drying the thermoelectric material layer 2s on the substrate 1b. Conventional drying methods such as hot air drying, hot roll drying, and infrared irradiation can be used. The heating temperature is usually 80 to 170°C, preferably 100 to 150°C, more preferably 110 to 145°C, and even more preferably 120 to 140°C. The heating time varies depending on the heating method, but is usually 30 seconds to 5 hours, preferably 1 minute to 3 hours, more preferably 5 minutes to 2 hours, and even more preferably 10 minutes to 50 minutes. If the heating temperature and heating time are within this range, it is more likely to lead to an improvement in the electrical conductivity of the thermoelectric conversion material layer after pressurization and firing (annealing). Furthermore, when a solvent is used in the preparation of a thermoelectric semiconductor composition, the heating temperature may be within the temperature range in which the solvent used can be dried, or it may be within a lower temperature range.

[0060] (C) Heating and pressurizing process of thermoelectric conversion material layer The thermoelectric conversion material layer heating and pressurizing process is a process of heating and pressurizing the dried thermoelectric conversion material layer obtained in process (B). For example, in Figure 3(b), this is a process of heating and pressurizing the upper surface of the thermoelectric conversion material layer 2s with the heating press section 5.

[0061] This heating and pressurizing process involves applying a predetermined pressure to the entire upper surface of a coated film (thin film) at a predetermined temperature, in an atmospheric or vacuum environment, for a predetermined time, using physical pressurizing means such as a hydraulic press, vacuum press, or weight. There are no particular restrictions on the temperature of the heating and pressurizing treatment, but it is usually 100 to 300°C, preferably 200 to 300°C. There are no particular restrictions on the pressure used for the heating and pressurizing process, but it is usually 20 to 200 MPa, preferably 50 to 150 MPa. There are no particular restrictions on the duration of the heating and pressurizing treatment, but it is usually from a few seconds to several tens of minutes, preferably from several tens of seconds to over ten minutes. The pressurization may be increased rapidly to a predetermined pressure level, but from the viewpoint of maintaining the shape stability of the thermoelectric conversion material layer and reducing the amount of voids within the thermoelectric conversion material layer to improve the filling rate of the thermoelectric conversion material, the pressurization is adjusted as appropriate, but is usually increased at a rate of 0.1 to 50 MPa / min, preferably 0.5 to 30 MPa / min, and more preferably 1.0 to 10 MPa / min until the predetermined pressure level is reached. If the amount and duration of pressurization are within this range, the filling density tends to increase, and the electrical conductivity of the thermoelectric conversion material layer after firing (annealing) tends to improve.

[0062] (D) Firing (annealing) process (including process (E)) The firing (annealing) process is, for example, a process of heat-treating the heated and pressurized thermoelectric conversion material layer obtained in step (C) at a predetermined temperature. By performing sintering (annealing), not only can a sintered body of metal nanoparticles be obtained, but the thermoelectric performance can also be stabilized, and the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the thin film can be grown crystallly, thereby further improving the thermoelectric performance of the thermoelectric conversion material layer. For example, in Figure 3(c), the thermoelectric conversion material layer 2s after heating and pressurizing is annealed at a predetermined temperature (after the annealing treatment, a thermoelectric conversion material layer 2t is obtained).

[0063] While there are no particular restrictions on annealing, it is usually carried out under controlled gas flow conditions, such as inert gases like nitrogen or argon, reducing gases, or vacuum. The firing method can be carried out by known methods. The firing (annealing) temperature is as described above. There are no particular restrictions on the annealing time, but it is usually several minutes to several tens of hours, preferably several minutes to several hours.

[0064] The firing (annealing) process may be carried out under pressure on the thermoelectric material layer. If pressurization is performed, the amount of pressurization shall be the same as that used in the heating and pressurizing process described above.

[0065] The thickness of the thermoelectric conversion material layer is not particularly limited as long as its shape stability and thermoelectric performance are not impaired by pressurization, as described above.

[0066] According to the method for manufacturing a thermoelectric material layer of the present invention, a thermoelectric material layer with improved electrical conductivity can be manufactured by a simple method. [Examples]

[0067] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples.

[0068] The filling density in the longitudinal section along the thickness direction of the test specimens (chips) made of thermoelectric conversion materials prepared in the examples and comparative examples was measured by the following method. (Measurement of filling density in the longitudinal section along the thickness direction) For each test piece (chip) made of thermoelectric conversion material obtained in each example and comparative example, a longitudinal section including the central part of the thermoelectric conversion material layer was prepared using a polishing device (RefineTech, model: Refine Polisher HV), and the longitudinal section was observed using a field emission scanning electron microscope (FE-SEM) (Hitachi High-Technologies, model: S-4700). Then, the packing efficiency, defined as the ratio of the area of ​​the thermoelectric conversion material to the area of ​​the longitudinal section of the thermoelectric conversion material layer, was calculated using image processing software (National Institutes of Health, ImageJ ver.1.44P). For measuring the filling density, a 500x magnification SEM image (longitudinal section) was used. The measurement range was defined as an area enclosed by 1280 pixels in the width direction and 220 pixels in the thickness direction at an arbitrary position in the thermoelectric conversion material layer, and this area was extracted as an image. The extracted image was binarized by setting the contrast to the maximum value using "Brightness / Contrast". In the binarized image, the dark areas were considered voids and the bright areas were considered thermoelectric conversion material, and the filling density of the thermoelectric conversion material was calculated using "Threshold". The filling density was calculated for three SEM images, and the average value was used. The results are shown in Table 1.

[0069] (Example 1) <Preparation of test specimens (chips) made from thermoelectric conversion materials> (1) Preparation of thermoelectric semiconductor composition (Preparation of thermoelectric semiconductor particles) P-type bismuth telluride Bi is a bismuth-tellurium-based thermoelectric semiconductor material. 0.4 Te 3.0 S 1.6 Thermoelectric semiconductor particles with an average particle size of 2.0 μm were prepared by grinding (manufactured by Kojun Chemical Laboratory, particle size: 20 μm) using a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7) under a nitrogen gas atmosphere. The particle size distribution of the obtained thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000). (Preparation of thermoelectric semiconductor composition (coating solution)) The P-type bismuth telluride Bi obtained above 0.4 Te 3.0 S 1.6A coating solution was prepared consisting of a thermoelectric semiconductor composition comprising 76.0% by mass of particles (average particle size 2.0 μm), 16.5% by mass (solid content 3.3% by mass) of a polyethylene carbonate solution (manufactured by EMPOWER MATERIALS, QPAC25, solvent: N-methylpyrrolidone, solid content concentration: 20% by mass) containing polyethylene carbonate (final decomposition temperature: 250°C) as a binder resin, 6.5% by mass of 1-butylpyridinium bromide (manufactured by Koei Chemical Industry Co., Ltd., IL-P18B) as an ionic liquid, and 1.0% by mass of silver nanoparticles (manufactured by Mitsuboshi Belting Co., Ltd., solvent: N-methylpyrrolidone, solid content concentration: 90% by mass, average particle size 60 nm) as metal nanoparticles. (2) Preparation of test specimens (chips) made of thermoelectric conversion material (formation of thermoelectric conversion material layer) The coating solution prepared in (1) above was printed as a solid film onto a glass substrate (blue glass plate, 100 mm x 100 mm, thickness: 0.7 mm) using an applicator, and dried at 120°C for 10 minutes in an argon atmosphere to form a thin film [thermoelectric conversion material layer before firing (annealing)]. Next, the dried thermoelectric material layer was cooled to room temperature, and then heated at a rate of 5 K / min in a hydrogen and argon mixed gas atmosphere (hydrogen:argon = 3 vol%:97 vol%), held at 430°C for 30 minutes, and fired to produce a thermoelectric material layer (thickness: 55 μm) made of a fired thermoelectric semiconductor composition. The obtained thermoelectric material layer was cut into 5 mm × 5 mm pieces to form test pieces (chips) made of the thermoelectric material.

[0070] (Example 2) In Example 1, P-type Bi 0.4 Te 3.0 S 1.6 A test specimen (chip size: 5 mm × 5 mm × thickness 58 μm) was prepared in the same manner as in Example 1, except that the particles made up 69.0 mass% and the silver nanoparticles made up 8.0 mass%.

[0071] (Example 3) In Example 1, a glass substrate was replaced with a polyimide substrate, the coating solution was printed onto it, and it was heated and dried at 120°C for 10 minutes. Then, using a hydraulic press (Tester Industries Co., Ltd., Tabletop Test Press SA-302), the entire upper surface of the coated film (thin film) was heated and pressurized at 250°C in an air atmosphere at 110 MPa for 10 minutes to form a thin film [thermoelectric conversion material layer before firing (annealing)]. Except for these differences, a test piece (chip size: 5 mm × 6 mm × thickness 70 μm) was prepared in the same manner as in Example 1.

[0072] (Example 4) In Example 2, a test specimen (chip size: 5 mm × 6 mm × thickness 70 μm) was prepared in the same manner as in Example 2, except that the glass substrate was replaced with a polyimide substrate for printing, heated and dried at 120°C for 10 minutes, and then subjected to a pressurizing treatment at 110 MPa for 10 minutes on the entire upper surface of the coated film (thin film) at 250°C in an air atmosphere using the hydraulic press.

[0073] (Comparative Example 1) In Example 1, P-type Bi 0.4 Te 3.0 S 1.6 A test specimen (chip size: 5 mm × 5 mm × thickness 53 μm) was prepared in the same manner as in Example 1, except that the particle content was 77.0 mass% and no silver nanoparticles were added (0 mass%).

[0074] (Comparative Example 2) In Comparative Example 1, the glass substrate was replaced with a polyimide substrate, the coating solution was printed, and after heating and drying at 120°C for 10 minutes, the entire upper surface of the coated film (thin film) was pressurized at 110 MPa for 10 minutes at 250°C in an air atmosphere using the hydraulic press to form a thin film [thermoelectric conversion material layer before firing (annealing)]. Except for these differences, a test specimen (chip size: 5 mm × 6 mm × thickness 70 μm) was prepared in the same manner as in Comparative Example 1.

[0075] The packing density in the longitudinal section along the thickness direction of the thermoelectric conversion material test specimens (chips) prepared in Examples 1-4 and Comparative Examples 1 and 2 was measured. The results are shown in Table 1.

[0076] [Table 1]

[0077] It can be seen that the packing density of the thermoelectric material in the longitudinal section along the thickness direction of the thermoelectric material layer in Example 1, which contains silver nanoparticles, is increased compared to the packing density of the thermoelectric material in the longitudinal section along the thickness direction of the thermoelectric material layer in Comparative Example 1, which does not contain silver nanoparticles. Furthermore, it can be seen that the packing density of the thermoelectric material in the longitudinal section along the thickness direction of the thermoelectric material layer in Example 3, which contains silver nanoparticles and is subjected to a heat and pressure treatment, is increased compared to the packing density of the thermoelectric material in the longitudinal section along the thickness direction of the thermoelectric material layer in Comparative Example 2, which does not contain silver nanoparticles and is subjected to a heat and pressure treatment. From the above, it can be seen that improving the packing density increases the electrical conductivity of the thermoelectric material in the thermoelectric material layer, leading to an improvement in thermoelectric performance. [Industrial applicability]

[0078] The thermoelectric material layer of the present invention exhibits improved thermoelectric performance because its electrical conductivity increases with higher filling density of the thermoelectric material. Therefore, thermoelectric modules using the thermoelectric material layer of the present invention can be applied to power generation applications that convert waste heat from various combustion furnaces such as factories, waste incinerators, and cement incinerators, as well as exhaust heat from combustion gases of automobiles and waste heat from electronic equipment into electricity. For cooling applications, it can be applied to temperature control of various sensors in the field of electronic equipment, such as CPUs (Central Processing Units) used in smartphones and various computers, as well as image sensors such as CMOS (Complementary Metal Oxide Semiconductor) and CCD (Charge Coupled Device), and MEMS (Micro Electro Mechanical Systems) and photodetectors. [Explanation of symbols]

[0079] 1,1a,1b: Circuit board 2,2s,2t: Thermoelectric conversion material layer 3,3a,3b,4a,4b:Void part 5: Heating press section X: Length (width direction) Y: Length (depth direction) D: Thickness (in the thickness direction) Dmax: Maximum thickness in the thickness direction (longitudinal section) Dmin: Minimum thickness in the thickness direction (longitudinal section) C: Central part of the thermoelectric conversion material layer

Claims

1. A method for producing a thermoelectric conversion material layer comprising a thermoelectric semiconductor composition comprising thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles, wherein the metal nanoparticles are particles sintered at a temperature of 130°C to 450°C. The binder resin has a final decomposition temperature of 150 to 360°C, and is a resin that decomposes by 90% or more by mass at a firing temperature above the firing temperature at which the fired body is obtained. The firing temperature at which the aforementioned fired body is obtained is 180 to 450°C. A method for manufacturing a thermoelectric conversion material layer.

2. A method for producing a thermoelectric conversion material layer according to claim 1, wherein the average particle size of the metal nanoparticles in the thermoelectric semiconductor composition is 1 nm or more and 200 nm or less.

3. The method for producing a thermoelectric conversion material layer according to claim 1 or 2, wherein the metal nanoparticles are particles that are sintered at a temperature of 130°C or higher and 300°C or lower.

4. A method for producing a thermoelectric conversion material layer according to any one of claims 1 to 3, wherein the metal nanoparticles are selected from the group consisting of silver, copper, gold, platinum, palladium, aluminum, titanium, nickel, bismuth, tellurium, and alloys thereof.

5. A method for producing a thermoelectric conversion material layer according to any one of claims 1 to 4, wherein the content of the metal nanoparticles in the thermoelectric semiconductor composition is 0.01 to 15.00% by mass.

6. A method for manufacturing a thermoelectric conversion material layer according to any one of claims 1 to 5, wherein the thermoelectric conversion material layer is made of a fired body of a coated film of the thermoelectric semiconductor composition.

7. A method for manufacturing a thermoelectric conversion material layer according to any one of claims 1 to 6, wherein the thermoelectric conversion material layer is composed of a thermoelectric conversion material containing voids, and when the ratio of the area of ​​the thermoelectric conversion material to the area of ​​the longitudinal cross-section including the central part of the thermoelectric conversion material layer is defined as the filling rate, the filling rate is 0.800 or more and less than 1.000.

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