Thermoelectric conversion material layer

Abstract

To provide a thermoelectric conversion material layer having high thermoelectric performance and a thermoelectric conversion module including it, the thermoelectric conversion material layer containing thermoelectric conversion material having further improved electric conductivity.SOLUTION: A thermoelectric conversion material layer contains thermoelectric conversion material composed of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, binder resin, and ionic liquid. The average particle diameter of the thermoelectric semiconductor particles is equal to or larger than 8.0 μm and less than 50.0 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, thermoelectric power generation technology, which has a simple system and can be miniaturized, has attracted attention as a power generation technology that can recover unused waste heat energy generated from fossil fuel resources used in buildings, factories, etc. However, thermoelectric power generation generally has low power generation efficiency, and various companies and research institutes are actively conducting research and development to improve power generation efficiency. To improve power generation efficiency, it is essential to improve the efficiency of thermoelectric conversion materials, and to achieve this, it is desirable to develop materials that have high electrical conductivity comparable to that of metals and low thermal conductivity comparable to that of glass.

[0003] The thermoelectric conversion properties of a thermoelectric material are determined by the thermoelectric figure of merit Z (Z=σS 2 / λ), where S is the Seebeck coefficient, σ is the electrical conductivity, and λ is the thermal conductivity. Increasing the value of the thermoelectric figure of merit Z improves power generation efficiency, so in order to improve power generation efficiency, it is important to find a thermoelectric conversion material with a large Seebeck coefficient S and electrical conductivity σ, and a small thermal conductivity λ. As mentioned above, while there is a need to study ways to improve power generation efficiency, currently manufactured thermoelectric conversion elements are not suitable for mass production and the power generation units are expensive, so reducing manufacturing costs is essential for further widespread use in large-area applications such as installation on building walls. In addition, currently manufactured thermoelectric conversion elements have poor flexibility, so there is a demand for thermoelectric conversion elements with excellent flexibility. In this context, Patent Document 1 discusses a thermoelectric conversion material having a thin film made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a heat-resistant resin, and an ionic liquid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 019871 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, an ionic liquid is used as a conductive additive to provide flexibility and effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor particles, thereby improving the overall thermoelectric performance. However, further improvements in thermoelectric performance are required to achieve smaller size, lighter weight, higher integration, etc.

[0006] In view of the above, an object of the present invention is to provide a thermoelectric conversion material layer having high thermoelectric performance, in which the electrical conductivity of the thermoelectric conversion material in the thermoelectric conversion material layer is further improved. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the inventors have found that by forming the thermoelectric conversion material layer into a thin film made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles having a specific average particle size that contributes to a decrease in thermal conductivity and an increase in electrical conductivity, a binder resin that suppresses the formation of voids in the thermoelectric conversion material layer, and an ionic liquid that suppresses the decrease in electrical conductivity in the voids between the particles, the thermoelectric performance of the thermoelectric conversion material layer can be improved compared to the above-mentioned conventional thermoelectric conversion materials, and have completed the present invention. That is, the present invention provides the following [1] to [9]. [1] A thermoelectric conversion material layer comprising a thermoelectric conversion material made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, and an ionic liquid, wherein the average particle size of the thermoelectric semiconductor particles is 8.0 μm or more and less than 50.0 μm. [2] The thermoelectric conversion material layer according to [1] above, wherein the thermoelectric conversion material layer has the thermoelectric conversion material and voids, and the filling rate is defined as the proportion of the area of ​​the thermoelectric conversion material in the area of ​​a vertical cross section including a central portion of the thermoelectric conversion material layer, and the filling rate is 0.900 or more but less than 1.000. [3] The thermoelectric conversion material layer according to the above [1] or [2], which is made of a sintered body of a coating film of a thermoelectric semiconductor composition. [4] The thermoelectric conversion material layer according to [1] above, wherein the binder resin decomposes by 90 mass % or more at the firing temperature of the fired body. [5] The thermoelectric conversion material layer according to the above [1] or [4], wherein the binder resin contains at least one selected from polycarbonate, cellulose derivatives, and polyvinyl polymers. [6] The thermoelectric conversion material layer according to any one of the above [1], [4] and [5], wherein the binder resin decomposes at 90 mass % or more at 400°C. [7] The thermoelectric conversion material layer according to [1] above, wherein the thermoelectric semiconductor particles are made of a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, or a bismuth selenide-based thermoelectric semiconductor material. [8] The thermoelectric conversion material layer according to [1] or [7] above, wherein the thermoelectric semiconductor particles have an average particle size of 8.0 μm or more and less than 40.0 μm. [9] A thermoelectric conversion module comprising the thermoelectric conversion material layer according to any one of [1] to [8] above. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a thermoelectric conversion material layer having high thermoelectric performance in which the electrical conductivity of the thermoelectric conversion material in the thermoelectric conversion material layer is further improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram for explaining the definition of a longitudinal section of a thermoelectric conversion material layer according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view illustrating a longitudinal section of a thermoelectric conversion material layer according to the present invention. [Figure 3] 1A to 1C are explanatory diagrams illustrating an example of a method for producing a thermoelectric conversion material layer according to the present invention. [Figure 4] FIG. 2 is an explanatory diagram illustrating an example of a method for producing a thermoelectric conversion module including a thermoelectric conversion material layer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Thermoelectric conversion material layer] The thermoelectric conversion material layer of the present invention is a thermoelectric conversion material layer containing a thermoelectric conversion material made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, and an ionic liquid, and is characterized in that the average particle size of the thermoelectric semiconductor particles is 8.0 μm or more and less than 50.0 μm. By using a granulated thermoelectric semiconductor material having a specific average particle size as the thermoelectric semiconductor particles that constitute the thermoelectric conversion material layer of the present invention, the interfacial resistance between the thermoelectric semiconductor particles is reduced, making it possible to make the rate of increase in electrical conductivity greater than the rate of increase in thermal conductivity, thereby improving the overall thermoelectric performance of the thermoelectric conversion material layer. Furthermore, by forming the thermoelectric conversion material layer into a thin film made of a thermoelectric semiconductor composition that contains, in addition to the thermoelectric semiconductor particles, a binder resin that suppresses the formation of voids in the thermoelectric conversion material layer, and an ionic liquid that suppresses the decrease in electrical conductivity in the voids between the thermoelectric semiconductor particles, a thermoelectric conversion material layer with higher thermoelectric performance than that of conventional thermoelectric conversion material layers can be obtained. In this specification, the term "thermoelectric conversion material layer" refers to a layer that includes a thermoelectric conversion material and, if voids exist around the thermoelectric conversion material, the voids. In addition, in this specification, the term "thermoelectric conversion material" refers to a product obtained by firing a thermoelectric semiconductor composition (for example, a fired body of a coating film of the thermoelectric semiconductor composition). Even if the thermoelectric semiconductor composition contains a binder resin (described later), if the binder resin is completely decomposed by firing, the thermoelectric conversion material is considered to not contain the binder resin. Furthermore, the thermoelectric conversion material layer after the firing (annealing) treatment may be referred to as a "chip of the thermoelectric conversion material layer" or a "chip of the thermoelectric conversion material."

[0011] The thermoelectric conversion material layer of the present invention contains a thermoelectric conversion material made of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, and an ionic liquid. The thermoelectric conversion material layer of the present invention preferably comprises a sintered body of a coating film of a thermoelectric semiconductor composition. The sintered body is obtained by sintering a coating film of the thermoelectric semiconductor composition at a sintering temperature. The sintering temperature is usually determined depending on the type of thermoelectric semiconductor particles contained in the thermoelectric semiconductor composition, and is usually 260 to 500°C, preferably 400 to 460°C, more preferably 410 to 450°C, and particularly preferably 420 to 450°C. In the examples, the sintering temperature is 430°C.

[0012] <Thermoelectric semiconductor particles> The thermoelectric semiconductor composition includes thermoelectric semiconductor particles. The thermoelectric semiconductor particles used in the present invention are obtained by pulverizing the thermoelectric semiconductor material described below to a predetermined size using a fine grinding device or the like. There are no particular limitations on the method for pulverizing a thermoelectric semiconductor material to obtain thermoelectric semiconductor particles, and the material may be pulverized to a predetermined size using a known fine pulverizing device such as a jet mill, ball mill, bead mill, colloid mill, or roller mill. The average particle size of the thermoelectric semiconductor particles can be obtained by measurement using, for example, a laser diffraction particle size analyzer (Malvern, Mastersizer 3000) or the like, and is taken as the median value of the particle size distribution.

[0013] The thermoelectric semiconductor particles are preferably heat-treated in advance. 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 layer and further improving the thermoelectric figure of merit. The heat treatment is not particularly limited, but is preferably carried out before preparing the thermoelectric semiconductor composition in an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen, or under vacuum conditions with a controlled gas flow rate to avoid adversely affecting the thermoelectric semiconductor particles. Heat treatment is more preferably carried out in a mixed gas atmosphere of an inert gas and a reducing gas. The specific temperature conditions depend on the thermoelectric semiconductor particles used, but are typically carried out at a temperature below the melting point of the particles at 100 to 1500°C for several minutes to several tens of hours.

[0014] As the thermoelectric semiconductor material, there is no particular limitation 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、 Zn4Sb3 and other zinc-antimony-based thermoelectric semiconductor materials; silicon-germanium-based thermoelectric semiconductor materials such as SiGe; bismuth selenide-based thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73 , Mg2Si and other silicide-based thermoelectric semiconductor materials; oxide-based thermoelectric semiconductor materials; Heusler materials such as FeVAl, FeVAlSi, FeVTiAl; sulfide-based thermoelectric semiconductor materials such as TiS2; and the like are used. These may be used alone or in combination of two or more.

[0015] <0​​​​​​​​​​​​​​Those represented by are 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 the electrical conductivity increase, and the characteristics as an N-type thermoelectric element are maintained, which is preferable.

[0017] The average particle size of the thermoelectric semiconductor particles is 8.0 μm or more and less than 50.0 μm. When the average particle size is less than 8.0 μm, the interfacial resistance between the thermoelectric semiconductor particles tends to increase, which easily leads to a decrease in electrical conductivity. When the average particle size is 50.0 μm or more, the interfacial resistance between the thermoelectric semiconductor particles tends to decrease, which easily leads to an increase in electrical conductivity. However, the increase in thermal conductivity becomes more prominent, and the increase in the total thermoelectric performance is suppressed. The average particle size of the thermoelectric semiconductor particles is preferably 8.0 μm or more and less than 45.0 μm, more preferably 8.0 μm or more and less than 42.0 μm, still more preferably 10.0 μm or more and less than 40.0 μm, and particularly preferably 15.0 μm or more and less than 35.0 μm. If the average particle size of the thermoelectric semiconductor particles is within the above range, the interfacial resistance between the thermoelectric semiconductor particles decreases, and it becomes possible to make the increase rate of electrical conductivity larger than the increase rate of thermal conductivity, and the total thermoelectric performance can be improved.

[0018] The content of the 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. If the content of the 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 tends to decrease. Therefore, it exhibits high thermoelectric performance, and a film having sufficient film strength and flexibility is obtained, which is preferable.

[0019] <Binder resin> The thermoelectric semiconductor composition contains a binder resin. The binder resin facilitates peeling of the thermoelectric conversion material layer after baking (annealing) treatment from the substrate described later that was used in producing the chip, and also acts as a binder between the thermoelectric semiconductor particles, thereby increasing the flexibility of the thermoelectric conversion module described later and facilitating the formation of a thin film by coating or the like.

[0020] The binder resin is preferably a resin that decomposes at 90% by mass or more at the baking (annealing) temperature, more preferably a resin that decomposes at 95% by mass or more, and particularly preferably a resin that decomposes at 99% by mass or more. Furthermore, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when a coating film (thin film) made of the thermoelectric semiconductor composition is subjected to a baking (annealing) treatment or the like to cause crystal growth of thermoelectric semiconductor particles is more preferable. When a resin that decomposes at least 90% by mass at the firing (annealing) temperature, i.e., a resin that decomposes at a lower temperature than the heat-resistant resins that have been used conventionally, is used as the binder resin, the binder resin decomposes upon firing, and therefore the content of the binder resin, which serves as an insulating component in the fired body, decreases, and crystal growth of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is promoted, thereby reducing voids in the thermoelectric conversion material layer and improving the filling rate. In one embodiment, the binder resin is preferably such that 90% by mass or more is decomposed at a baking (annealing) temperature of 400°C. Whether or not a resin decomposes to a predetermined extent (e.g., 90% by mass or more) at the baking (annealing) temperature is determined by measuring the mass loss rate (the value obtained by dividing the mass after decomposition by the mass before decomposition) at the baking (annealing) temperature by thermogravimetry (TG).

[0021] Thermoplastic resins and curable resins can be used as such binder 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 ethyl cellulose. 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 resins may be used alone or in combination. Among these, from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, thermoplastic resins are preferred, polycarbonate and cellulose derivatives such as ethyl cellulose are more preferred, and polycarbonate is particularly preferred.

[0022] The binder resin is appropriately selected depending on the temperature of the firing (annealing) treatment of the thermoelectric semiconductor material in the firing (annealing) treatment step (B) described below. From the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, it is preferable to perform the firing (annealing) treatment at a temperature equal to or higher than the final decomposition temperature of the binder resin. In this specification, the term "final decomposition temperature" refers to the temperature at which the mass reduction rate at the firing (annealing) temperature determined by thermogravimetry (TG) is 100% (the mass after decomposition is 0% of the mass before decomposition).

[0023] The final decomposition temperature of the binder resin is usually 150 to 600° C., preferably 200 to 560° C., more preferably 220 to 460° C., and particularly preferably 240 to 360° C. If a binder resin with a final decomposition temperature within this range is used, it functions as a binder for the thermoelectric semiconductor material, making it easier to form a thin film during printing. The binder resin is preferably decomposed and vaporized during hot pressing and / or baking, which will be described later.

[0024] The content of the binder resin in the thermoelectric semiconductor composition is 0.1 to 40 mass%, preferably 0.5 to 20 mass%, more preferably 0.5 to 10 mass%, and particularly preferably 0.5 to 5 mass%. When the content of the binder resin is within the above range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer can be reduced.

[0025] <Ionic liquid> The thermoelectric semiconductor composition includes an ionic liquid. Ionic liquids are molten salts formed by combining cations and anions, and are salts that can exist in liquid form at temperatures ranging from -50°C to less than 400°C. In other words, ionic liquids are ionic compounds with melting points ranging from -50°C to less than 400°C. The melting point of ionic liquids is preferably -25°C to 200°C, more preferably 0°C to 150°C. Ionic liquids have characteristics such as extremely low vapor pressure and nonvolatility, excellent thermal and electrochemical stability, low viscosity, and high ionic conductivity. Therefore, as a conductive additive, they can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor materials. Furthermore, ionic liquids exhibit high polarity due to their aprotic ionic structure and excellent compatibility with binder resins, thereby enabling the electrical conductivity of thermoelectric conversion materials to be uniform.

[0026] The ionic liquid may be a known or commercially available one. For example, a nitrogen-containing cyclic cationic compound such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, or imidazolium, or a derivative thereof; a tetraalkylammonium-based amine-based cation and a derivative thereof; a phosphine-based cation such as phosphonium, trialkylsulfonium, or tetraalkylphosphonium, or a derivative thereof; a lithium cation and a derivative thereof; or a mixture of a cation component and a Cl cation. - , Br - , I -, AlCl4 - , Al2Cl7 - , BF4 - , PF6 - , ClO4 - , 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 - These may be used alone or in combination of two or more.

[0027] Among the above ionic liquids, from the viewpoints of high-temperature stability, compatibility with thermoelectric semiconductor particles and binder resin, and suppression of a decrease in the electrical conductivity of the gaps between thermoelectric semiconductor particles, it is preferred that the cationic component of the ionic liquid contains at least one selected from pyridinium cations and derivatives thereof, and imidazolium cations and derivatives thereof. It is preferred that the anionic component of the ionic liquid contains a halide anion, and Cl - , Br - and I - It is more preferable that the composition contains at least one selected from the following:

[0028] Specific examples of ionic liquids in which the cationic component contains a pyridinium cation and a derivative thereof 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, 1-butyl-4-methylpyridinium iodide, etc. These may be used alone 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.

[0029] Specific examples of ionic liquids in which the cation component contains an imidazolium cation or a derivative thereof 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-methylimidazolium chloride. Examples of the compound 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, 1,3-dibutylimidazolium methyl sulfate, etc. These compounds may be used alone 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.

[0030] The electrical conductivity of the ionic liquid is preferably 10 -7 S / cm or more, preferably 10 -6 If the electrical conductivity is in the above range, the conductive additive can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor particles.

[0031] The ionic liquid preferably 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 a coating film (thin film) made of the thermoelectric semiconductor composition is subjected to a baking (annealing) treatment, as will be described later. In this specification, the term "decomposition temperature" refers to the temperature at which the mass loss rate at the firing (annealing) temperature determined by thermogravimetry (TG) is 10%.

[0032] Furthermore, the mass loss rate of the above ionic liquid at 300°C as measured by thermogravimetry (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 a coating film (thin film) made of the thermoelectric semiconductor composition is subjected to a firing (annealing) treatment, as will be described later.

[0033] The content of the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and particularly preferably 1.0 to 20 mass%. If the content of the ionic liquid is within the above range, a decrease in electrical conductivity is effectively suppressed, and a film with high thermoelectric performance is obtained.

[0034] <Inorganic ionic compounds> The thermoelectric semiconductor composition may further contain an inorganic ionic compound. Inorganic ionic compounds are compounds composed of at least cations and anions. Inorganic ionic compounds are solid at room temperature, have a melting point somewhere in the temperature range of 400 to 900°C, and have characteristics such as high ionic conductivity, so as a conductive additive they can suppress a decrease in electrical conductivity between thermoelectric semiconductor particles.

[0035] When the thermoelectric semiconductor composition contains an inorganic ionic compound, the content of the inorganic ionic compound in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and particularly preferably 1.0 to 10 mass%. If the content of the inorganic ionic compound is within the above range, a decrease in electrical conductivity can be effectively suppressed, and as a result, a film with improved thermoelectric performance can be obtained. When an inorganic ionic compound and an ionic liquid are used in combination, the total content of the inorganic ionic compound and the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and particularly preferably 1.0 to 10 mass%.

[0036] <Other additives> In addition to the above, the thermoelectric semiconductor composition may further contain, as necessary, other additives such as dispersants, film-forming aids, light stabilizers, antioxidants, tackifiers, plasticizers, colorants, resin stabilizers, fillers, pigments, conductive fillers, conductive polymers, curing agents, etc. These may be used alone or in combination of two or more.

[0037] Since the average particle size of the thermoelectric semiconductor fine particles used in the present invention is 8.0 μm or more and less than 50.0 μm, the thickness of the thermoelectric conversion material layer (thickness of the coating film (thin film) made of the thermoelectric semiconductor composition) is preferably at least 6 times, and more preferably at least 20 times, the average particle size. When the thickness of the thermoelectric conversion material layer is within the above range relative to the average particle size of the thermoelectric semiconductor particles, a decrease in electrical conductivity due to surface roughness of the thermoelectric conversion material layer is suppressed, and high thermoelectric performance can be maintained. The thickness of the thermoelectric conversion material layer is preferably 1000 μm or less, more preferably 600 μm or less, and even more preferably 400 μm or less, from the viewpoints of satisfying the above and also of thermoelectric performance, flexibility, and film strength.

[0038] <Vertical cross section of thermoelectric conversion material layer> The thermoelectric conversion material layer of the present invention has a thermoelectric conversion material and voids, and when the filling rate is defined as the ratio of the area of ​​the thermoelectric conversion material to the area of ​​a vertical cross section including the center of the thermoelectric conversion material layer, the filling rate is preferably 0.900 or more and less than 1.000.

[0039] The definition of "a longitudinal cross section including the central portion of a thermoelectric conversion material layer" in this specification will be explained using drawings. Fig. 1 is a diagram illustrating the definition of the longitudinal cross section of a thermoelectric conversion material layer of the present invention, Fig. 1(a) is a plan view of a thermoelectric conversion material layer 20, which has a length X in the width direction and a length Y in the depth direction, and Fig. 1(b) is a longitudinal cross section of the thermoelectric conversion material layer 20 formed on a substrate 1a, which includes a central portion C in Fig. 1(a) and has a length X and a thickness D when cut between A-A' in the width direction (shown as a rectangle in the figure). Note that voids 30 are included in the thermoelectric conversion material layer 20.

[0040] A longitudinal section of a thermoelectric conversion material layer of the present invention will be described with reference to the drawings. FIG. 2 is a cross-sectional schematic diagram illustrating the longitudinal section of a thermoelectric conversion material layer of the present invention. FIG. 2(a) is an example of a longitudinal section of a thermoelectric conversion material layer 20s formed on a substrate 1a. The thermoelectric conversion material layer 20s has a longitudinal section consisting of a curve with a length X in the width direction and values ​​Dmin and Dmax in the thickness direction. The upper part of the longitudinal section has recesses and protrusions, and voids 30b exist within the longitudinal section. FIG. 2(b) is an example of a longitudinal section of a thermoelectric conversion material layer 20t formed on a substrate 1a. The longitudinal section of the thermoelectric conversion material layer 20t has a length X in the width direction and a thickness D in the thickness direction (when the values ​​Dmin and Dmax in FIG. 2(a) are slightly different). The upper part of the longitudinal section is approximately linear, and voids 40b with reduced void number and volume exist within the longitudinal section. Dmin refers to the minimum thickness in the thickness direction of the longitudinal section, and Dmax refers to the maximum thickness in the thickness direction of the longitudinal section.

[0041] In the thermoelectric conversion material layer of the present invention, the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer, which is defined as the ratio of the area of ​​the thermoelectric conversion material to the area of ​​a vertical cross section including the center of the thermoelectric conversion material layer, is more than 0.900 and less than 1.000, and there are few voids in the thermoelectric conversion material layer. If the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer is 0.900 or less, there will be many voids in the thermoelectric conversion material layer, making it difficult to reduce the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer (making it difficult to obtain excellent electrical conductivity), and high thermoelectric performance will not be obtained. The filling rate is preferably greater than 0.900 and less than 0.999, more preferably 0.920 or more and less than 0.999, even more preferably 0.950 or more and less than 0.999, and particularly preferably 0.970 or more and less than 0.999. If the filling rate is within this range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer will be reduced (making it possible to obtain excellent electrical conductivity), and high thermoelectric performance will be obtained.

[0042] A method for measuring the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer will be described using as an example a test piece (chip) made of the thermoelectric conversion material layer produced in the examples and comparative examples described below. For each test piece (chip) consisting of a thermoelectric conversion material layer obtained in each example and comparative example, a longitudinal section including the center of the thermoelectric conversion material layer was prepared using a polishing machine (manufactured by Refine Tech Co., Ltd., model name: Refine Polisher HV), and the longitudinal section was observed using a scanning electron microscope (SEM) (manufactured by Keyence Corporation). Next, the filling factor, which is 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 (manufactured by the National Institutes of Health, ImageJ ver. 1.44P). To measure the filling rate, a 500x magnification SEM image (longitudinal cross section) was used, and the measurement range was set to an area surrounded by 1280 pixels in the width direction and 220 pixels in the thickness direction at any position on the thermoelectric conversion material layer, and the image was cut out. The cut-out image was binarized by setting the contrast to the maximum value in "Brightness / Contrast," and the dark areas in the binarization process were considered to be voids and the bright areas were considered to be thermoelectric conversion material, and the filling rate of the thermoelectric conversion material was calculated using "Threshold." The filling rate was calculated for three SEM images and the average value was calculated.

[0043] [Thermoelectric conversion module] The thermoelectric conversion material layer of the present invention is preferably applied to a thermoelectric conversion module having a configuration such as a π-type thermoelectric conversion element (FIG. 4(f) to be described later) or an in-plane type thermoelectric conversion element.

[0044] <Method of manufacturing thermoelectric conversion module> The method for producing a thermoelectric conversion module including a thermoelectric conversion material layer of the present invention includes the following steps (i) to (vii): (i): forming a coating film of a thermoelectric semiconductor composition on a substrate; (ii): A step of annealing the coating film of the thermoelectric semiconductor composition obtained in the step (i) to obtain a thermoelectric conversion material layer (chip) made of the thermoelectric conversion material; (iii): preparing a first layer having a first resin film and a first electrode in this order; (iv): preparing a second A layer having a second resin film and a second electrode in this order, or a second B layer having a second resin film but no electrode; (v): a step of bonding one surface of the thermoelectric conversion material layer (chip) obtained in the step (ii) to the first layer electrode prepared in the step (iii) via a first bonding material layer; (vi): A step of peeling off the other surface of the thermoelectric conversion material layer (chip) from the substrate after the step (v); and (vii): A step of bonding the other surface of the thermoelectric conversion material layer (chip) obtained by peeling in the above step (vi) to the electrode of the 2A layer prepared in the above step (iv) via a second bonding material layer, or a step of bonding to the 2B layer prepared in the above step (iv) via a third bonding material layer.

[0045] <Method for manufacturing thermoelectric conversion material layer (chip)> The thermoelectric conversion material layer (chip) can be manufactured, for example, by the following method: (A) forming a coating film of a thermoelectric semiconductor composition on a substrate; (B) a step of drying the coating film of the thermoelectric semiconductor composition obtained in the step (A); (C) a step of peeling off the dried coating film of the thermoelectric semiconductor composition obtained in (B) from the substrate; (D) a step of subjecting the coating film of the thermoelectric semiconductor composition obtained in (C) to a hot press treatment (heat and pressure treatment); (E) A step of baking (annealing) the coated film of the thermoelectric semiconductor composition after pressing obtained in the step (D) above.

[0046] 3 is an explanatory diagram illustrating an example of a method for producing a thermoelectric conversion material layer (chip) of the present invention. A coating film 12 of a thermoelectric semiconductor composition is formed on a substrate 1, which is then dried, peeled from the substrate 1, hot-pressed (heated and pressurized), and fired (annealed), thereby obtaining a thermoelectric conversion material layer (chip) made of a thermoelectric conversion material as a free-standing film. In the above-described method for manufacturing a thermoelectric conversion material layer (chip), the case where the thermoelectric conversion material layer (chip) is obtained as a free-standing film is described. However, in the above steps (i) to (v), the thermoelectric conversion material layer (chip) is not made into a free-standing film but is formed on a substrate, and in step (vi), the thermoelectric conversion material layer (chip) is peeled off from the substrate to form a free-standing film.

[0047] ((A) Step of forming a coating film of a thermoelectric semiconductor composition) The step of forming a coating film of a thermoelectric semiconductor composition is a step of forming a coating film of a thermoelectric semiconductor composition on a substrate, and for example, in Fig. 3, it is a step of applying coating film 12 made of a thermoelectric semiconductor composition, that is, coating film 12a made of a thermoelectric semiconductor composition containing a P-type thermoelectric semiconductor material and coating film 12b made of a thermoelectric semiconductor composition containing an N-type thermoelectric semiconductor material, on substrate 1. There are no particular restrictions on the arrangement of coating film 12a and coating film 12b, but from the viewpoint of thermoelectric performance, it is preferable that they be formed so as to have a configuration used in a π-type or in-plane type thermoelectric conversion module and be connected by electrodes. Here, when constructing a π-type thermoelectric conversion module, for example, a pair of electrodes (electrodes 5 in FIG. 4 described later) spaced apart from each other are provided on a substrate (resin film 4 in FIG. 4 described later), and a sintered body (P-type chip) of a coating film 12a made of a thermoelectric semiconductor composition containing a P-type thermoelectric semiconductor material is provided on one electrode, and a sintered body (N-type chip) of a coating film 12b made of a thermoelectric semiconductor composition containing an N-type thermoelectric semiconductor material is provided on the other electrode, also spaced apart from each other, with the top surfaces of both chips electrically connected in series to electrodes on the opposing substrates. From the viewpoint of efficiently obtaining high thermoelectric performance, it is preferable to use a plurality of pairs of P-type chips and N-type chips electrically connected in series via the electrodes of the opposing substrates (see FIG. 4(f) described later). Similarly, when configuring an in-plane thermoelectric conversion module, for example, one electrode is provided on a substrate, and a P-type chip and an N-type chip are provided on the surface of the electrode so that the side surfaces of both chips (for example, the surfaces perpendicular to the substrate) are in contact with or spaced apart from each other, and the modules are electrically connected in series via the electrodes in the in-plane direction of the substrate.From the viewpoint of efficiently obtaining high thermoelectric performance, it is preferable that the same number of P-type chips and N-type chips are alternately connected in series via the electrodes in the in-plane direction of the substrate in this configuration.

[0048] -substrate- The material used for the substrate is not particularly limited, and examples thereof include glass, silicon, ceramic, metal, plastic, etc. These may be used alone or in combination of two or more. Among these, glass, silicon, ceramic, and metal are preferred from the viewpoint of firing (annealing) treatment, and glass, silicon, and ceramic are more preferred from the viewpoints of adhesion to the thermoelectric conversion material, material cost, and dimensional stability after heat treatment. The thickness of the substrate may be 100 to 10,000 μm from the viewpoint of process and dimensional stability.

[0049] -Method for preparing thermoelectric semiconductor composition- The method for preparing the thermoelectric semiconductor composition is not particularly limited, and the thermoelectric semiconductor composition may be prepared by mixing and dispersing thermoelectric semiconductor particles, a binder resin, and an ionic liquid, and optionally an inorganic ionic compound, other additives, and a solvent, using a known method such as an ultrasonic homogenizer, a spiral mixer, a planetary mixer, a disperser, or a hybrid mixer. The thermoelectric semiconductor particles, binder resin, ionic liquid, inorganic ionic compound, and other additives are as described above. Examples of solvents include toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, N-methylpyrrolidone, and ethyl cellosolve. These may be used alone or in combination of two or more. The solids concentration of the thermoelectric semiconductor composition is not particularly limited as long as the composition has a viscosity suitable for coating.

[0050] A coating film (thin film) made of a thermoelectric semiconductor composition can be formed by applying the thermoelectric semiconductor composition onto a substrate and drying it.

[0051] The method for applying the thermoelectric semiconductor composition onto a substrate is not particularly limited, and examples thereof include known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, doctor blade, etc. When forming a patterned coating film, screen printing, stencil printing, slot die coating, etc., which allow for easy pattern formation using a screen plate having a desired pattern, are preferably used.

[0052] ((B) Drying process) The drying step is a step in which, after forming a coating film (thin film) of the thermoelectric semiconductor composition on a substrate, the coating film of the thermoelectric semiconductor composition is dried at a predetermined temperature while holding the substrate. The resulting coating film is dried to form a coating film (thin film), and the drying method may be a conventionally known drying method such as hot air drying, hot roll drying, infrared irradiation, etc. The heating temperature is usually 80 to 150°C, and the heating time varies depending on the heating method, but is usually several seconds to several tens of minutes. When a solvent is used in preparing the thermoelectric semiconductor composition, the heating temperature is not particularly limited as long as it is within a temperature range that allows the solvent used to be dried. The thickness of the coating film (thin film) made of the thermoelectric semiconductor composition is as described above.

[0053] ((C) Coating film removal process) The coating film peeling step is a step of peeling off the coating film (thin film) made of the thermoelectric semiconductor composition from the substrate after the drying treatment. The method for peeling off the coating film is not particularly limited as long as it is a method that can peel off the coating film (thin film) from the substrate after drying treatment, and multiple coating films (thin films) may be peeled off from the substrate in the form of individual pieces, or multiple coating films (thin films) may be peeled off together.

[0054] (D) Heat press (heat and pressure) treatment process The hot pressing (heat and pressure) treatment step is a step of performing a hot pressing (heat and pressure) treatment after peeling off the coating film (thin film) of the thermoelectric semiconductor composition from the substrate. This hot pressing (heat and pressure) treatment is a treatment in which, using a device such as a hydraulic press, pressure is applied to the entire upper surface of the coating film (thin film) at a predetermined temperature and in an atmospheric atmosphere at a predetermined pressure for a predetermined time. The temperature for the hot pressing (heating and pressing) treatment is not particularly limited, but is usually 100 to 300°C, and preferably 200 to 300°C. The pressure for the hot pressing (heat and pressure) treatment is not particularly limited, but is usually 20 to 200 MPa, preferably 50 to 150 MPa. The time for the hot pressing (heating and pressing) treatment is not particularly limited, but is usually from several seconds to several tens of minutes, preferably from several tens of seconds to several tens of minutes.

[0055] (E) Firing (annealing) process The firing (annealing) treatment step is a step in which a coating film (thin film) of the thermoelectric semiconductor composition is subjected to a hot press (heat and pressure) treatment, and then the coating film of the thermoelectric semiconductor composition is heat-treated at a predetermined temperature. By performing the firing (annealing) treatment, the thermoelectric performance can be stabilized and the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the coating film (thin film) can be grown as crystals, thereby further improving the thermoelectric performance of the thermoelectric conversion material layer.

[0056] The firing (annealing) treatment is not particularly limited, but is usually carried out in an inert gas atmosphere such as nitrogen or argon, in a reducing gas atmosphere, or under vacuum conditions with the gas flow rate controlled. The temperature of the firing (annealing) treatment depends on the thermoelectric semiconductor particles, binder resin, ionic liquid, inorganic ionic compound, etc. used in the thermoelectric semiconductor composition and is adjusted appropriately, but is usually 260 to 600°C, preferably 280 to 550°C. The time for the firing (annealing) treatment is not particularly limited, but is usually from several minutes to several tens of hours, preferably from several minutes to several hours.

[0057] According to the above-described method for producing a thermoelectric conversion module, a thermoelectric conversion material layer (chip) can be produced by a simple method. Furthermore, since the thermoelectric semiconductor composition coating (thin film) and the electrodes are not subjected to a firing (annealing) treatment in a bonded state, problems such as an increase in electrical resistance between the thermoelectric conversion material layer (chip) and the electrodes and a decrease in thermoelectric performance do not occur.

[0058] In the method for producing a thermoelectric conversion module, a thermoelectric conversion module is produced using a thermoelectric conversion material layer (chip) obtained through steps (i) and (ii). Here, step (i) corresponds to step (A) of forming a coating film of a thermoelectric semiconductor composition in the method for producing a thermoelectric conversion material layer (chip), and step (ii) corresponds to step (E) of firing (annealing) in the method for producing a thermoelectric conversion material layer (chip). Furthermore, by performing step (i), for example, an embodiment such as that illustrated in FIG. 3 can be obtained. Furthermore, the substrate and coating film (thin film) of the thermoelectric semiconductor composition used, as well as the preferred materials, thickness, and formation method thereof, are all the same as those described above.

[0059] In the method for manufacturing the thermoelectric conversion module, from the viewpoint of thermoelectric performance, it is preferable that the step (iv) is a step of preparing a second A layer having a second resin film and a second electrode in this order, and the step (vii) is a step of bonding the other surface of the chip of thermoelectric conversion material obtained by peeling in the step (vi) to the second electrode of the second A layer prepared in the step (iv) via a second bonding material layer. The thermoelectric conversion module obtained by the above steps corresponds to the above-mentioned π-type thermoelectric conversion module.

[0060] In another example of the method for manufacturing the thermoelectric conversion module, from the viewpoint of thermoelectric performance, it is preferable that the step (iv) is a step of preparing a second B layer having a second resin film and no electrode, and the step (vii) is a step of bonding the other surface of the chip of thermoelectric conversion material obtained by peeling in the step (vi) to the second B layer prepared in the step (iv) via a third bonding material layer. The thermoelectric conversion module obtained by the above steps corresponds to the in-plane type thermoelectric conversion module described above.

[0061] Hereinafter, a method for manufacturing the thermoelectric conversion module will be described with reference to the drawings. 4A and 4B are explanatory diagrams illustrating an example of a method for producing a thermoelectric conversion module including a thermoelectric conversion material layer of the present invention (a method for producing a π-type thermoelectric conversion module), in which FIG. 4A is a cross-sectional view after a solder-receiving layer, which will be described later, has been formed on one surface (top surface) of a thermoelectric conversion material layer (chip), FIG. 4B is a cross-sectional view after an electrode and a solder material layer have been formed on a resin film, and FIG. 4C is a cross-sectional view after the electrode on the resin film obtained in FIG. 4B has been bonded to one surface (top surface) of the thermoelectric conversion material layer (chip) via the solder material layer and the solder-receiving layer of FIG. 4A. 4(c') is a cross-sectional view after the solder material layer has been bonded by heating and cooling, FIG. 4(d) is a cross-sectional view after the other surface (bottom surface) of the thermoelectric conversion material layer (chip) has been peeled off from the substrate, FIG. 4(e) is a cross-sectional view after a solder-receiving layer has been formed on the other surface (bottom surface) of the thermoelectric conversion material layer (chip) on the resin film obtained in FIG. 4(d), and FIG. 4(f) is a cross-sectional view after the electrode on the resin film obtained in FIG. 4(b) has been attached and bonded to the other surface (bottom surface) of the thermoelectric conversion material layer (chip) via the solder material layer and the solder-receiving layer of FIG. 4(e).

[0062] <<Electrode formation process>> The electrode formation step is a step of forming a first electrode on a first resin film in the step (iii) of preparing a first layer having a first resin film and a first electrode in this order in the method for producing a thermoelectric conversion module. Alternatively, it is a step of forming a second electrode on a second resin film in the step (iv) of preparing a second A layer having a second resin film and a second electrode in this order. In FIG. 4(b), for example, this is a step of forming an electrode 5 by depositing a metal layer on a resin film 4 and processing it into a predetermined pattern.

[0063] (resin film) The first resin film and the second resin film may be resin films made of the same material or different materials. Polyimide films, polyamide films, polyetherimide films, polyaramid films, and polyamideimide films are preferred because they have excellent flexibility, and even when a coating film (thin film) made of a thermoelectric semiconductor composition is baked (annealed), the resin film does not thermally deform, allowing the performance of the thermoelectric element to be maintained, and they have high heat resistance and dimensional stability. Furthermore, polyimide films are particularly preferred because of their versatility.

[0064] From the viewpoints of flexibility, heat resistance, and dimensional stability, the thickness of the first resin film and the second resin film is independently preferably 1 to 1000 μm, more preferably 5 to 500 μm, and particularly preferably 10 to 100 μm. The 5% mass loss temperature of the first resin film and the second resin film measured by thermogravimetric analysis (TG) is preferably 300°C or higher, more preferably 400°C or higher. The thermal dimensional change rate measured at 200°C in accordance with JIS K7133 (1999) is preferably 0.5% or lower, more preferably 0.3% or lower. The linear expansion coefficient in the planar direction measured in accordance with JIS K7197 (2012) is preferably 0.1 to 50 ppm·°C. -1 , more preferably 0.1 to 30 ppm·℃ -1 is.

[0065] (electrode) Examples of metal materials for the first electrode and the second electrode of the thermoelectric conversion module include copper, gold, nickel, aluminum, rhodium, platinum, chromium, palladium, stainless steel, molybdenum, and alloys containing any of these metals. These may be used alone or in combination of two or more. The thickness of the electrode (metal material) layer is preferably 10 nm to 200 μm, more preferably 30 nm to 150 μm, and particularly preferably 50 nm to 120 μm. If the thickness of the electrode (metal material) layer is within the above range, the electrical conductivity is high and the resistance is low, and sufficient strength as an electrode can be obtained.

[0066] The electrodes are formed using the above-mentioned metal materials. Examples of methods for forming electrodes include a method in which an electrode without a pattern is provided on a resin film, and then processed into a predetermined pattern shape by known physical or chemical treatments, mainly photolithography, or a combination of these, or a method in which an electrode pattern is directly formed by screen printing, inkjet printing, or the like. Methods for forming electrodes without patterns include dry processes such as PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, and ion plating, or CVD (chemical vapor deposition) methods such as thermal CVD and atomic layer deposition (ALD); wet processes such as various coating methods and electrodeposition methods such as dip coating, spin coating, spray coating, gravure coating, die coating, and doctor blade methods; silver halide methods; electrolytic plating methods; electroless plating methods; and metal foil lamination; and the like, which are appropriately selected depending on the material of the electrode. Since electrodes are required to have high electrical conductivity and high thermal conductivity in order to maintain thermoelectric performance, it is preferable to use electrodes formed by plating or vacuum film formation. Vacuum film formation methods such as vacuum deposition and sputtering, electrolytic plating, and electroless plating are preferred because they can easily achieve high electrical conductivity and high thermal conductivity. Depending on the dimensions and dimensional accuracy required for the formed pattern, patterns can also be easily formed via a hard mask such as a metal mask.

[0067] <<First electrode bonding process>> The first electrode bonding step is step (v) of the method for manufacturing a thermoelectric conversion module, and is a step of bonding one surface of the thermoelectric conversion material layer (chip) obtained in step (ii) to the first electrode of the first layer prepared in step (iii) via a first bonding material layer. In the first electrode bonding step, for example, as shown in FIG. 4(c), the P-type chip 2a and the N-type chip 2b are bonded to the electrode 5 via the solder material layer 6 on the electrode 5 of the resin film 4 and the solder-receiving layers 3 formed on one surface of the thermoelectric conversion material layer (P-type chip) 2a made of a P-type thermoelectric conversion material and the thermoelectric conversion material layer (N-type chip) 2b made of an N-type thermoelectric conversion material, respectively. The solder material layer 6 is then heated to a predetermined temperature, held for a predetermined time, and then returned to room temperature, thereby bonding the P-type chip 2a and the N-type chip 2b to the electrode 5. The heating temperature, holding time, etc. are described below. Note that FIG. 4(c') shows the state after the solder material layer 6 has been returned to room temperature (the solder material layer 6' solidifies and reduces in thickness by heating and cooling).

[0068] (First bonding material layer formation step) The first electrode bonding step includes a first bonding material layer forming step. The first bonding material layer forming step is a step in the step (v) of the method for producing a thermoelectric conversion module, in which a first bonding material layer is formed on the first electrode obtained in the step (iii). The first bonding material layer forming step is, for example, a step of forming a solder material layer 6 on the electrode 5 in FIG. 4(b). Examples of bonding materials constituting the first bonding material layer include a solder material, a conductive adhesive, and a sintering bonding agent, and these are preferably formed on the electrode as a solder material layer, a conductive adhesive layer, and a sintering bonding agent layer, respectively, in this order. Note that, in this specification, the term "conductive" refers to a material having an electrical resistivity of 1×10 6 This refers to a resistance of less than Ω·m.

[0069] The solder material constituting the solder material layer may be appropriately selected in consideration of electrical conductivity and thermal conductivity, and examples thereof include known materials such as Sn, Sn / Pb alloy, Sn / Ag alloy, Sn / Cu alloy, Sn / Sb alloy, Sn / In alloy, Sn / Zn alloy, Sn / In / Bi alloy, Sn / In / Bi / Zn alloy, Sn / Bi / Pb / Cd alloy, Sn / Bi / Pb alloy, Sn / Bi / Cd alloy, Bi / Pb alloy, Sn / Bi / Zn alloy, Sn / Bi alloy, Sn / Bi / Pb alloy, Sn / Pb / Cd alloy, Sn / Cd alloy, etc. These may be used alone or in combination of two or more. Among these, alloys such as 43Sn / 57Bi alloy, 42Sn / 58Bi alloy, 40Sn / 56Bi / 4Zn alloy, 48Sn / 52In alloy, and 39.8Sn / 52In / 7Bi / 1.2Zn alloy are preferred from the viewpoints of lead-free and / or cadmium-free, melting point, electrical conductivity, and thermal conductivity. Commercially available solder materials include the following: 42Sn / 58Bi alloy (manufactured by Tamura Corporation, product name: SAM10-401-27), 41Sn / 58Bi / Ag alloy (manufactured by Nippon Handa Co., Ltd., product name: PF141-LT7HO), and 96.5Sn3Ag0.5Cu alloy (manufactured by Nippon Handa Co., Ltd., product name: PF305-207BTO).

[0070] The thickness of the solder material layer (after heating and cooling) is preferably 10 to 200 μm, more preferably 20 to 150 μm, even more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm. When the thickness of the solder material layer is within this range, adhesion between the thermoelectric conversion material chip and the electrode can be easily obtained.

[0071] Methods for applying the solder material onto the substrate include known methods such as stencil printing, screen printing, dispensing, etc. Heating conditions vary depending on the solder material, resin film, etc. used, but are usually performed at 150 to 280°C for 3 to 20 minutes.

[0072] When a solder material layer is used, it is preferable to bond it via a solder-receiving layer, which will be described later, in order to improve adhesion between the thermoelectric conversion material and the chip.

[0073] The conductive adhesive constituting the conductive adhesive layer is not particularly limited, and examples thereof include conductive paste, binder, etc. These may be used alone or in combination of two or more. Examples of conductive pastes include copper paste, silver paste, nickel paste, etc. These may be used alone or in combination of two or more. Examples of binders include epoxy resins, acrylic resins, urethane resins, etc. These may be used alone or in combination of two or more. Examples of methods for applying the conductive adhesive onto a resin film include known methods such as screen printing, dispensing, etc. These may be used alone or in combination of two or more.

[0074] The thickness of the conductive adhesive layer is preferably 10 to 200 μm, more preferably 20 to 150 μm, even more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm.

[0075] The sintering bonding agent constituting the sintering bonding agent layer is not particularly limited, and examples thereof include sintering paste. Sintering paste consists of, for example, micron-sized metal powder and nano-sized metal particles, and unlike conductive adhesives, it directly bonds metals by sintering, and may contain resins such as epoxy resin, acrylic resin, and urethane resin. Examples of the sintering paste include silver sintering paste, copper sintering paste, etc. These may be used alone or in combination of two or more. Methods for applying the sintering adhesive layer onto the resin film include known methods such as screen printing, stencil printing, dispensing, etc. These may be used alone or in combination of two or more. The sintering conditions vary depending on the metal material used, but are usually 100 to 300° C. and 30 to 120 minutes. Commercially available sintering bonding agents include, for example, a silver sintering paste (manufactured by Kyocera Corporation, product name: CT2700R7S) and a sintered metal bonding material (manufactured by Nihon Handa Co., Ltd., product name: MAX102).

[0076] The thickness of the sintering bonding agent layer is preferably 10 to 200 μm, more preferably 20 to 150 μm, even more preferably 30 to 130 μm, and particularly preferably 40 to 120 μm.

[0077] <<Solder-receiving layer formation process>> In the method for manufacturing a thermoelectric conversion module, for example, when manufacturing a π-type thermoelectric conversion module or an in-plane type thermoelectric conversion module, it is preferable to further include a step of forming a solder-receiving layer on one surface of the chip of the thermoelectric conversion material after the firing (annealing) treatment obtained in the above step (ii).

[0078] The solder-receiving layer forming process is a process of forming a solder-receiving layer on a thermoelectric conversion material layer (chip) made of a thermoelectric conversion material. For example, in (a) of Figure 4, it is a process of forming a solder-receiving layer 3 on one surface of a thermoelectric conversion material layer (P-type chip) 2a made of a P-type thermoelectric conversion material and a thermoelectric conversion material layer (N-type chip) 2b made of an N-type thermoelectric conversion material.

[0079] The solder-receiving layer preferably contains a metal material. The metal material is preferably at least one selected from gold, silver, aluminum, rhodium, platinum, chromium, palladium, tin, and an alloy containing any of these metal materials. Among these, a two-layer structure of gold, silver, aluminum, or tin and gold is preferred, and silver and aluminum are more preferred from the viewpoints of material cost, high thermal conductivity, and bonding stability. Furthermore, the solder-receiving layer may be formed using a paste material containing a solvent and a resin component in addition to the metal material. When using a paste material, it is preferable to remove the solvent and the resin component by firing or the like, as described below. As the paste material, silver paste and aluminum paste are preferable.

[0080] The thickness of the solder-receiving layer is preferably 10 nm to 50 μm, more preferably 50 nm to 16 μm, even more preferably 200 nm to 4 μm, and particularly preferably 500 nm to 3 μm. When the thickness of the solder-receiving layer is within this range, the adhesion to the surface of the thermoelectric conversion material layer (chip) made of the thermoelectric conversion material and the adhesion to the surface of the solder material layer on the electrode side are excellent, resulting in a highly reliable bond. Furthermore, high thermal conductivity as well as electrical conductivity can be maintained, and as a result, the thermoelectric performance of the thermoelectric conversion module is maintained without any deterioration. The solder-receiving layer may be formed as a single layer using a metal material, or may be formed as a multilayer by laminating two or more metal materials. Alternatively, the metal material may be formed as a composition containing a solvent, resin, or the like. However, in this case, from the viewpoint of maintaining high electrical conductivity and high thermal conductivity (maintaining thermoelectric performance), it is preferable to remove the resin components, including the solvent, by firing or the like, in the final form of the solder-receiving layer.

[0081] The solder-receiving layer is preferably formed using the above-mentioned metal material. Methods for forming the solder-receiving layer include a method in which an unpatterned solder-receiving layer is provided on the thermoelectric conversion material layer (chip), and then processed into a predetermined pattern shape by known physical or chemical treatments, primarily photolithography, or a combination of these, or a method in which a pattern of the solder-receiving layer is directly formed by screen printing, stencil printing, inkjet printing, or the like. Methods for forming a solder-receiving layer without a pattern include PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, and ion plating; CVD (chemical vapor deposition) methods such as thermal CVD and atomic layer deposition (ALD); various coating methods such as dip coating, spin coating, spray coating, gravure coating, die coating, and doctor blade; wet processes such as electrodeposition; silver halide methods; electrolytic plating; electroless plating; and metal foil lamination; and the method is selected appropriately depending on the material of the solder-receiving layer. The solder-receiving layer is required to have high electrical conductivity and high thermal conductivity in order to maintain thermoelectric performance, and therefore it is preferable to use a solder-receiving layer formed by screen printing, stencil printing, electrolytic plating, electroless plating, or vacuum film formation.

[0082] <<Chip Batch Peeling Process>> The chip collective peeling step is the above-mentioned step (vi) in the method for producing a thermoelectric conversion module, and is a step of peeling off the other surface of the thermoelectric conversion material layer (chip) from the substrate after the above-mentioned step (v). The chip bulk peeling process is, for example, in (d) of Figure 4, a process of peeling off the other surfaces of the thermoelectric conversion material layer (P-type chip) 2a made of a P-type thermoelectric conversion material and the thermoelectric conversion material layer (N-type chip) 2b made of an N-type thermoelectric conversion material from the substrate 1 at the same time. The method for peeling off the thermoelectric conversion material layers is not particularly limited as long as it is a method that can peel off the entire thermoelectric conversion material layer (chip) from the substrate all at once.

[0083] <<Second electrode bonding process>> The second electrode bonding step is included in the above step (vii) of the method for manufacturing a thermoelectric conversion module, and is a step of bonding the other surface of the thermoelectric conversion material layer (chip) obtained by peeling in the above step (vi) to the second electrode of the second A layer prepared in step (iv) via a second bonding material layer. The second electrode bonding process is, for example, a process of bonding the other surfaces of the thermoelectric conversion material layer (P-type chip) 2a made of a P-type thermoelectric conversion material and the thermoelectric conversion material layer (N-type chip) 2b made of an N-type thermoelectric conversion material to an electrode 5 on a resin film 4 via a solder-receiving layer 3 and a solder material layer 6, as shown in FIG. 4(f). The materials for both the second electrode and the second resin film of the 2A layer can be the same as those described in the first electrode bonding step, and the bonding method is also the same. The bonding to the electrode is preferably performed via the above-mentioned solder material layer, conductive adhesive layer, or sintered adhesive layer.

[0084] (Second bonding material layer formation process) The second electrode bonding step includes a second bonding material layer forming step. The second bonding material layer forming step is a step of forming a second bonding material layer on the second electrode of the second A layer prepared in the step (iv) in the step (vii) of the method for manufacturing a thermoelectric conversion module. The second bonding material layer can be made of the same material as the first bonding material layer described above, and the forming method, thickness, etc. are all the same.

[0085] Furthermore, for example, when a solder material layer is used in manufacturing a π-type thermoelectric conversion module, it is preferable to further include a step of forming a solder-receiving layer on the other surface of the thermoelectric conversion material layer (chip) obtained by peeling in the above step (vi). For example, (e) in Figure 4 shows a process of forming a solder-receiving layer 3 on the other surface of a thermoelectric conversion material layer (P-type chip) 2a made of a P-type thermoelectric conversion material and a thermoelectric conversion material layer (N-type chip) 2b made of an N-type thermoelectric conversion material.

[0086] The combination of bonding material layers used for the electrodes on a pair of resin films in a thermoelectric conversion module (except when no electrode is present on one of the pair of resin films) is not particularly limited, but from the viewpoint of preventing mechanical deformation of the thermoelectric conversion module and suppressing deterioration of thermoelectric performance, it is preferable to combine solder material layers, conductive adhesive layers, or sintered bonding agent layers.

[0087] <<Resin film bonding process>> The resin film bonding step is included in the step (vii) of the method for manufacturing a thermoelectric conversion module, and is a step of bonding the other surface of the thermoelectric conversion material layer (chip) obtained by peeling in the step (vi) to the second B layer having the second resin film and no electrode prepared in the step (iv) via a third bonding material layer. The second resin film is as described above. The third bonding material layer is used to bond the second B layer having the second resin film and no electrode.

[0088] The bonding material constituting the third bonding material layer is preferably a resin material, and is formed as a resin material layer on the resin film. The resin material preferably contains a polyolefin resin, an epoxy resin, or an acrylic resin. Furthermore, the resin material preferably has adhesive properties and low water vapor permeability. In this specification, having adhesive properties means that the resin material has pressure-sensitive adhesive properties that allow it to adhere by pressure in the initial stage of application. The resin material layer can be formed by a known method.

[0089] The thickness of the resin material layer is preferably 1 to 100 μm, more preferably 3 to 50 μm, and particularly preferably 5 to 30 μm.

[0090] (Another manufacturing method for thermoelectric conversion module) Another example of a method for producing the thermoelectric conversion module is as follows. Specifically, this method forms a thermoelectric conversion module by peeling off multiple chips one by one from the above-mentioned substrate to obtain multiple chips, and then placing the multiple chips one by one on designated electrodes on a resin film. A method for arranging a plurality of chips on the electrode can be a known method, such as handling each chip by a robot or the like, aligning the chips with a microscope or the like, and arranging them.

[0091] According to the above-described method for manufacturing a thermoelectric conversion module, chips can be formed by a simple method, and in a thermoelectric conversion module in which multiple chips are combined, it is possible to prevent a decrease in thermoelectric performance resulting from the formation of an alloy layer due to diffusion between the thermoelectric semiconductor composition and the electrodes in the conventional firing (annealing) treatment step. [Example]

[0092] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0093] The thermoelectric performance of the test pieces (chips) obtained by dicing the thermoelectric conversion material layers produced in the examples and comparative examples was evaluated by calculating the electrical conductivity, Seebeck coefficient, and thermal conductivity using the following methods. <Thermoelectric performance evaluation> (a) Electrical conductivity For each test piece (chip) obtained by dicing the thermoelectric conversion material layer obtained in the examples and comparative examples, the electrical resistance value (Ω) was measured by four-terminal measurement using a low resistance meter (manufactured by Hioki E.E. Corporation, RM3545), and the thickness (cm) and area (a plane perpendicular to the thickness direction of the test piece; cm) of the test piece were recorded. 2 ) and the electrical conductivity σ (S / cm) was calculated using the following formula. Electrical conductivity σ = (electrical resistance value × thickness of test piece) / area of ​​test piece (b) Seebeck coefficient The thermoelectric conversion material layers prepared in the examples and comparative examples were diced to obtain test pieces (chips) and the thermoelectromotive force was measured in accordance with JIS C 2527:1994, and the Seebeck coefficient S was calculated. The thermoelectromotive force was measured by heating one end of the prepared thermoelectric conversion material, measuring the temperature difference between both ends of the thermoelectric conversion material using a chromel-alumel thermocouple, and then measuring the potential between the electrodes adjacent to the thermocouple installation position. Specifically, the distance between both ends of the sample for measuring the temperature difference and electromotive force was 25 mm, and one end was kept at 20°C while the other end was heated from 25°C to 50°C in 1°C increments. The thermoelectromotive force was measured during this heating, and the Seebeck coefficient S (μV / K) was calculated from the slope. The thermocouple and electrode were installed symmetrically with respect to the center line of the thin film, and the distance between the thermocouple and the electrode was 1 mm. (c) Thermal conductivity The thermal conductivity was measured using the 3ω method, and the thermal conductivity λ (W / (m·K)) was calculated. From the obtained electrical conductivity σ, Seebeck coefficient S, and thermal conductivity λ, the thermoelectric figure of merit Z (Z = σS 2 / λ) was calculated, and the dimensionless thermoelectric figure of merit ZT (T=300K) was calculated. However, the thermoelectric figure of merit Z was calculated using the electrical conductivity σ (S / m) and the Seebeck coefficient S (V / K).

[0094] Example 1 <Preparation of test pieces (chips) made of thermoelectric conversion materials> (1) Preparation of thermoelectric semiconductor particles As thermoelectric semiconductor particles, p-type bismuth telluride Bi, a bismuth-tellurium-based thermoelectric semiconductor material, was used. 0.4 Te 3.0 Sb 1.6 (manufactured by Kojundo Chemical Laboratory, particle size: 16.0 μm) was used. Furthermore, the particle size distribution of the thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000). (2) Preparation of thermoelectric semiconductor composition As shown in Example 1 of Table 1, P-type bismuth telluride Bi 0.4 Te 3.0 Sb 1.6A coating liquid was prepared comprising a thermoelectric semiconductor composition in which 78.5 mass% of particles (average particle size 16.0 μm), 20.7 mass% (solid content 6.7 mass%) of a polyethylene carbonate solution (manufactured by EMPOWER MATERIALS, QPAC25, solvent: N-methylpyrrolidone, solid content concentration: 25 mass%) containing polyethylene carbonate as a binder resin (final decomposition temperature: 250°C) and 0.8 mass% of 1-butylpyridinium bromide (manufactured by Koei Chemical Industry Co., Ltd., IL-P18B) as an ionic liquid were mixed and dispersed. (3) Preparation of test pieces (chips) made of thermoelectric conversion material layers (formation of thermoelectric conversion material layers) The coating solution prepared in (2) was applied to a polyimide film (Ube Industries, Ltd., product name "Kapton 500H", thickness 125 μm) using an applicator and dried by heating at 110 °C for 20 minutes to form a 600 μm-thick thin film. The resulting thin film was then heated and pressed at 250 °C and 50 MPa for 30 minutes to produce a wafer with a 250 μm-thick thermoelectric semiconductor material layer on the polyimide film. The wafer was then heated at a heating rate of 5 K / min in an atmosphere of a hydrogen and argon gas mixture (hydrogen:argon = 3 vol%:97 vol%) and annealed at 430 °C for 30 minutes. The wafer was then diced to obtain 1.0 × 1.0 mm square test pieces (chips).

[0095] Example 2 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that the average particle size of the thermoelectric semiconductor particles was changed from 16.0 μm to 8.0 μm. The thermoelectric semiconductor particles with an average particle size of 8.0 μm are P-type bismuth telluride Bi 0.4 Te 3.0 Sb 1.6 (manufactured by Kojundo Chemical Laboratory, particle size: 16.0 μm) was pulverized in a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7) under a nitrogen gas atmosphere to prepare the thermoelectric semiconductor particles. The particle size distribution of the pulverized thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000).

[0096] Example 3 A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that the average particle size of the thermoelectric semiconductor particles was 35.0 μm (manufactured by Kojundo Chemical Laboratory).

[0097] (Comparative Example 1) A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that the average particle size of the thermoelectric semiconductor particles was changed from 16.0 μm to 2.0 μm. The thermoelectric semiconductor particles with an average particle size of 2.0 μm are P-type bismuth telluride Bi 0.4 Te 3.0 Sb 1.6 (manufactured by Kojundo Chemical Laboratory, particle size: 16.0 μm) was pulverized in a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7) under a nitrogen gas atmosphere to prepare the thermoelectric semiconductor particles. The particle size distribution of the pulverized thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000).

[0098] (Comparative Example 2) A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that the average particle size of the thermoelectric semiconductor particles was 50.0 μm (manufactured by Kojundo Chemical Laboratory).

[0099] (Comparative Example 3) A thermoelectric conversion material layer was produced in the same manner as in Example 1, except that the average particle size of the thermoelectric semiconductor particles was changed from 16.0 μm to 5.0 μm. The thermoelectric semiconductor particles with an average particle size of 5.0 μm are P-type bismuth telluride Bi 0.4 Te 3.0 Sb 1.6 (manufactured by Kojundo Chemical Laboratory, particle size: 16.0 μm) was pulverized in a planetary ball mill (manufactured by Fritsch Japan, Premium line P-7) under a nitrogen gas atmosphere to prepare the thermoelectric semiconductor particles. The particle size distribution of the pulverized thermoelectric semiconductor particles was measured using a laser diffraction particle size analyzer (manufactured by Malvern, Mastersizer 3000).

[0100] [Table 1]

[0101] Table 2 shows the evaluation results of the thermoelectric performance of the test pieces (chips) of the thermoelectric conversion material layers obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

[0102] [Table 2]

[0103] It can be seen that the thermoelectric performance (dimensionless thermoelectric figure of merit ZT) of the thermoelectric conversion material layers of Examples 1 to 3, in which the range of the average particle size of the thermoelectric semiconductor particles satisfies the specification of the present invention, is superior to the thermoelectric performance of the thermoelectric conversion material layers of Comparative Examples 1 to 3, in which the range of the average particle size of the thermoelectric semiconductor particles does not satisfy the specification of the present invention. [Industrial Applicability]

[0104] The thermoelectric conversion material layer of the present invention, when used as a thermoelectric conversion element layer of a thermoelectric conversion module, can be used for power generation applications, such as converting exhaust heat from various combustion furnaces, such as factories, waste incineration furnaces, and cement combustion furnaces, exhaust heat from automobile combustion gases, and exhaust heat from electronic devices into electricity. Cooling applications in the field of electronics include temperature control of central processing units (CPUs) used in smartphones and various computers, image sensors such as complementary metal oxide semiconductors (CMOSs) and charge coupled devices (CCDs), and various sensors, such as microelectromechanical systems (MEMSs) and light-receiving elements. [Explanation of symbols]

[0105] 1, 1a: Substrate 2a: Thermoelectric conversion material layer made of P-type thermoelectric conversion material (P-type chip) 2b: Thermoelectric conversion material layer made of N-type thermoelectric conversion material (N-type chip) 3: Solder acceptance layer 4: Resin film 5: Electrode 6: Solder material layer (when formed) 6': Solder material layer (after bonding) 12: Thermoelectric semiconductor composition coating film 12a: Coating film 12b: Coating film 20, 20s, 20t: Thermoelectric conversion material layer 30:Void part 30b:Void part 40b:Void part X: Length (width) Y: Length (depth direction) D: Thickness (thickness direction) Dmax: Maximum thickness in the thickness direction (longitudinal cross section) Dmin: Minimum thickness in the thickness direction (longitudinal section) C: Center of the thermoelectric conversion material layer

Claims

1. A thermoelectric conversion material layer including a thermoelectric conversion material made of a thermoelectric semiconductor composition including thermoelectric semiconductor particles, a binder resin, and an ionic liquid, wherein the thermoelectric semiconductor particles have an average particle size of 10.0 μm or more and less than 50.0 μm; The thermoelectric conversion material layer has a thickness that is 6 times or more the average particle size of the thermoelectric semiconductor particles and 1000 μm or less.

2. The thermoelectric conversion material layer according to claim 1 , wherein the thermoelectric conversion material layer is made of a sintered body of a coating film of a thermoelectric semiconductor composition.

3. The thermoelectric conversion material layer according to claim 2 , wherein the binder resin decomposes by 90 mass % or more at a firing temperature of the fired body.

4. 4. The thermoelectric conversion material layer according to claim 1, wherein the binder resin comprises at least one selected from the group consisting of polycarbonate, a cellulose derivative, and a polyvinyl polymer.

5. The thermoelectric conversion material layer according to any one of claims 1 to 4, wherein the binder resin decomposes at 90 mass % or more at 400°C.

6. 6. The thermoelectric conversion material layer according to claim 1, wherein the thermoelectric semiconductor particles are made of a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, or a bismuth selenide-based thermoelectric semiconductor material.

7. 7. The thermoelectric conversion material layer according to claim 1, wherein the thermoelectric semiconductor particles have an average particle size of 10.0 μm or more and less than 40.0 μm.

8. A thermoelectric conversion module comprising the thermoelectric conversion material layer according to any one of claims 1 to 7.

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