WO2022071043A1

WO2022071043A1 - Thermoelectric conversion material layer

Info

Publication number: WO2022071043A1
Application number: PCT/JP2021/034720
Authority: WO
Inventors: 俊弥山▲崎▼; 邦久加藤; 佑太関
Original assignee: リンテック株式会社
Priority date: 2020-09-30
Filing date: 2021-09-22
Publication date: 2022-04-07
Also published as: TW202224219A; JPWO2022071043A1

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

Thermoelectric conversion material layer

The present invention relates to a thermoelectric conversion material layer.

Conventionally, as one of the effective energy utilization means, there is a device in which thermal energy and electric energy are directly converted into each other by a thermoelectric conversion module having a thermoelectric effect such as the Zeebeck effect and the Pelche effect.
As the thermoelectric conversion module, the use of a so-called π-type thermoelectric conversion element is known. In the π type, a pair of electrodes separated from each other are provided on the substrate, for example, a P-type thermoelectric element is provided on one of the electrodes, and an N-type thermoelectric element is provided on the other electrode, also separated from each other. , It is configured by connecting the top surfaces of both thermoelectric materials to the electrodes of the opposing substrates. Further, the use of a so-called in-plane type thermoelectric conversion element is known. In the inplane type, P-type thermoelectric elements and N-type thermoelectric elements are alternately provided in the in-plane direction of the substrate. For example, the lower part of the joint between the two thermoelectric elements is connected in series with an electrode interposed therebetween. It is configured.
Under these circumstances, there are demands for improving the flexibility of the thermoelectric conversion module, making it thinner, and improving the thermoelectric performance. In order to satisfy these requirements, in Patent Document 1, for example, from the viewpoint of flexibility, a resin substrate such as polyimide is used as a substrate used for a thermoelectric conversion module. Further, from the viewpoint of flexibility, thinning, and thermoelectric performance, for example, from a thermoelectric semiconductor composition containing a bismuthellide-based material (thermoelectric semiconductor particles) atomized as a thermoelectric semiconductor material, a resin acting as a binder between the particles, and the like. The thermoelectric conversion material layer is disclosed.
In Patent Document 2, from the viewpoint of excellent processability, flexibility, and thermoelectric performance, a composition for a thermoelectric conversion element containing carbon nanotubes on which metal nanoparticles are supported as a thermoelectric semiconductor material, a resin component as a binder, and a solvent is used. The thermoelectric conversion material layer is disclosed.

International Publication No. 2016/104615 International Publication No. 2017/122805

However, in Patent Document 1, since the resin is used as the binder between the thermoelectric semiconductor particles, many voids are included between the thermoelectric semiconductor particles of the formed thermoelectric conversion material layer, and high electric conductivity is sufficiently achieved. The thermoelectric performance was not sufficient.
In Patent Document 2, the conductivity of the CNT itself is improved by supporting the metal nanoparticles on the CNT (carbon nanotube) having a defect structure (a place where the six-membered ring network is not well formed). It had the same problem as Patent Document 1.

In view of the above, it is an object of the present invention to provide a thermoelectric conversion material layer having high thermoelectric performance, in which the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer made of a fired body of a thermoelectric semiconductor composition is improved. ..

As a result of diligent research to solve the above problems, the present inventors have made the thermoelectric semiconductor composition contain metal nanoparticles that are sintered at a specific temperature, and fill the voids between the thermoelectric semiconductor particles (reduce the voids). The present invention has been completed by finding that a thermoelectric conversion material layer having a high filling rate of a thermoelectric conversion material can be obtained, and that the thermoelectric conversion material layer has a high electric conductivity and leads to improvement of thermoelectric performance.
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, and the metal nanoparticles are particles sintered at 450 ° C. or lower. The thermoelectric conversion material layer.
(2) The thermoelectric conversion material layer according to (1) above, wherein the metal nanoparticles in the thermoelectric semiconductor composition have an average particle size of 200 nm or less.
(3) The thermoelectric conversion material layer according to (1) or (2) above, wherein the metal nanoparticles are particles sintered at 300 ° C. or lower.
(4) Any of the above (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. The thermoelectric conversion material layer described in.
(5) The thermoelectric conversion material layer according to any one of (1) to (4) above, wherein the specific resistance of the metal nanoparticles is 6.0 × 10 ^-3 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 composed of a fired body of a coating film of the thermoelectric semiconductor composition.
(8) 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 vertical cross section including the central portion of the thermoelectric conversion material layer is taken as the filling factor. The thermoelectric conversion material layer according to any one of (1) to (7) above, wherein the filling rate is 0.800 or more and less than 1.000.

According to the present invention, it is possible to provide a thermoelectric conversion material layer having high thermoelectric performance, in which the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer made of a fired body of a thermoelectric semiconductor composition is improved.

It is a figure for demonstrating the definition of the vertical cross section of the thermoelectric conversion material layer of this invention. It is sectional drawing for demonstrating the vertical cross section before and after heating and pressurizing the thermoelectric conversion material layer of this invention. It is explanatory drawing which shows one aspect of the manufacturing method of the thermoelectric conversion material layer of this invention in the order of a process.

[Thermoelectric conversion material layer]
The thermoelectric conversion material layer of the present invention is 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, and the metal nanoparticles are at 450 ° C. It is characterized by being particles to be sintered below.
The thermoelectric semiconductor composition contains metal nanoparticles sintered at 450 ° C. or lower, and the sintered body of the metal nanoparticles having a temperature of 450 ° C. or lower fills the voids between the thermoelectric semiconductor particles (reduces the voids), whereby thermoelectric conversion is performed. A thermoelectric conversion material layer having a high filling rate of the material can be obtained, whereby the thermoelectric conversion material exhibits high electrical conductivity, and thus thermoelectric performance can be improved.
In the present specification, the "thermoelectric conversion material layer" is composed of a thermoelectric conversion material and voids. That is, the "thermoelectric conversion material" means a portion obtained by removing voids from the thermoelectric conversion material layer.
Further, "sintering at 450 ° C or lower" means that a thin film made of a thermoelectric semiconductor composition before firing is allowed to stand in an atmosphere up to 450 ° C for a predetermined time (according to the firing time described later) at room temperature. After returning, there is a region where the interface between the metal nanoparticles cannot be confirmed, or there is a region where the interface between the metal nanoparticles and the thermoelectric semiconductor particles cannot be confirmed.
Specifically, the evaluation relating to "the state where there is a region where the interface cannot be confirmed" is performed by cutting a vertical cross section including the central portion of the thermoelectric conversion material layer fired at the temperature or lower, and firing included in the vertical cross section. The tied metal nanoparticles and thermoelectric semiconductor particles can be carried out according to the following criteria from the images observed by a scanning electron microscope (SEM).
In an image having an observation field size of 1 μm square (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 having an observation field size of 10 μm square (both metal nanoparticles and thermoelectric semiconductor particles are present in the field at least), there is at least one region where the interface between the metal nanoparticles and the thermoelectric semiconductor particles cannot be visually confirmed. be.
Further, when the binder resin is contained in the thin film made of the thermoelectric semiconductor composition before firing, and when the binder resin is completely decomposed by firing, the binder resin is contained in the thermoelectric conversion material layer and the thermoelectric conversion material. Make it not exist.

The thermoelectric conversion material layer of the present invention comprises a fired body of a thermoelectric semiconductor composition containing thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles.
As a preferred embodiment, the fired body comprises a fired body of a coating film of a thermoelectric semiconductor composition. Further, as another preferred embodiment, it is composed of a fired body of a thin film formed by a known dry film forming method such as a vapor deposition film or a sputter film of a thermoelectric semiconductor composition.

The firing temperature is usually 60 to 450 ° C, preferably 130 to 450 ° C, more preferably 140 to 450 ° C, still more preferably 160 to 450 ° C, and particularly preferably 180 to 180 to obtain a sintered body of metal nanoparticles. It is 450 ° C. The firing time is not particularly limited, but is usually several minutes to several tens of hours, preferably several minutes to several hours.

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

<Metal nanoparticles>
The thermoelectric semiconductor composition used in the present invention contains metal nanoparticles.
Metal nanoparticles are obtained by firing (annealing) a thin film of a thermoelectric semiconductor composition to form a fired body (thermoelectric conversion material layer), and the bonding between the metal nanoparticles progresses due to sintering of the metal nanoparticles. , Voids between thermoelectric semiconductor particles can be filled, and the generation of voids can be suppressed. As a result, the filling factor 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, it is possible to effectively suppress the reduction of the electric conductivity between the thermoelectric semiconductor particles.

Metal nanoparticles are particles that sinter at 450 ° C or lower. The particles are preferably sintered at 130 to 450 ° C, more preferably particles sintered at 140 to 450 ° C, further preferably particles sintered at 160 to 450 ° C, and 180 to 450. It is particularly preferable that the particles are sintered at ° C. If the metal nanoparticles are sintered in the above range, it becomes easy to efficiently fill the voids between the thermoelectric semiconductor particles in the thin film of the thermoelectric semiconductor composition, and as a result, the thermoelectric conversion in the thermoelectric conversion material layer becomes easy. It improves the filling rate of the material and leads to the improvement of the electrical conductivity of the thermoelectric conversion material layer.

The metal nanoparticles are not particularly limited as long as they can fill the voids between the thermoelectric semiconductor particles and suppress the decrease in the electric conductivity between the thermoelectric semiconductor particles, but are not particularly limited, but are silver, copper, gold, platinum, palladium, aluminum, titanium, and nickel. , Bismus, tellurium and alloys thereof are preferably selected, and silver, copper, gold, bismuth, tellurium, aluminum and alloys thereof are more preferably selected, and low temperature sinterability and stability. From the viewpoint of sex, it is more preferable to be selected from the group consisting of silver, copper, gold, an alloy of silver and copper, an alloy of silver and gold, and an alloy of copper and gold.

The average particle size of the metal nanoparticles in the thermoelectric semiconductor composition is not particularly limited, but is preferably 200 nm or less, more preferably 200 nm or less, from the viewpoint of low-temperature sinterability and efficient filling of narrow voids between the thermoelectric semiconductor particles. Is 1 to 200 nm or less, more preferably 1 to 180 nm, still more preferably 10 to 150 nm, particularly preferably 15 to 120 nm, and most preferably 20 to 100 nm. When the average particle size of the metal nanoparticles is within the above range, the voids between the thermoelectric semiconductor particles in the thin film of the thermoelectric semiconductor composition can be efficiently filled, and the thin film of the thermoelectric semiconductor composition is fired (annealed). As the sintering of the metal nanoparticles progresses in the process of forming the fired body (thermoelectric conversion material layer), the voids between the thermoelectric semiconductor particles can be further filled, and as a result, the thermoelectric in the thermoelectric conversion material layer can be filled. It improves the filling rate of the conversion material and leads to the improvement of the electrical conductivity of the thermoelectric conversion material layer.
The average particle size (primary particles) of the metal nanoparticles in the thermoelectric semiconductor composition is an arithmetic average value of the average particle size of any 20 metal nanoparticles observed by a transmission electron microscope (TEM). ..
Further, it is known that metal particles having a diameter of several tens of nm or less generally exhibit various physical and chemical properties different from those of bulk metals as the particle size becomes smaller. For example, it is known that the melting point of metal particles becomes lower than the melting point of bulk metal as the particle size becomes smaller. Therefore, in the present invention, metal particles having a small particle diameter are used, including the point of lowering the sintering temperature.

The specific resistance of the metal nanoparticles is preferably 6.0 × 10 ^-3 Ω · cm or less, more preferably 8 × 10 ^-6 Ω · cm or less, and even more preferably 8 × 10 ^-7 Ω · cm. It is less than or equal to, and particularly preferably 8 × 10 ^-8 Ω · cm or less. When the specific resistance of the metal nanoparticles is within the above range, the electrical bondability between the thermoelectric semiconductor particles is improved, and the electrical resistance value of the thermoelectric conversion material layer is lowered.

The content of the 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, and further 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. When the content of the metal nanoparticles in the thermoelectric semiconductor composition is within the above range, the voids between the thermoelectric semiconductor particles are efficiently filled by the sintered body of the metal nanoparticles at the time of firing the thin film made of the thermoelectric semiconductor composition. As a result, the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer is improved, which leads to the improvement of the electric conductivity of the thermoelectric conversion material layer.

Commercially available products of metal nanoparticles include the following. For example, silver nanoparticles (manufactured by Samsung Belt Co., Ltd., trade name: MDot (registered trademark) CF158, resistivity: 8 × 10 ^-6 Ω · cm, average particle size: 60 nm), silver nanoparticles (manufactured by Daicel Co., Ltd., trade name). : Picosil (registered trademark), resistivity: 1.0 × ^10-5 Ω · cm, average particle size: 60 nm), silver nanoparticles (complex) (manufactured by InkTek, trade name: Tec-PA-010, resistivity) : 8 x ^10-6 Ω · cm, average particle size: 35 nm), copper nanoparticles (manufactured by Taiyo Nisshi Co., Ltd., trade name: copper nanopaste, resistivity: 2.5 x ^10-5 Ω · cm, average Particle size: 120 nm) and the like.

<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, which will be described later, to a predetermined size by a fine pulverizer or the like.
The thermoelectric semiconductor material is not particularly limited as long as it is a material capable of generating thermoelectromotive force by applying a temperature difference. For example, a bismuth-tellu system such as P-type bismasterlide and N-type bismasterlide. Thermoelectric semiconductor materials; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; antimon-tellu-based thermoelectric semiconductor materials; zinc-antimon-based thermoelectric semiconductor materials such as ZnSb, Zn ₃ Sb _2, Zn ₄ Sb ₃ ; silicon-germanium such as SiGe. Bismus selenide thermoelectric semiconductor materials such as Bi ₂ Se ₃ ; silicide-based thermoelectric semiconductor materials such as β-FeSi ₂ , CrSi ₂ , MnSi _1.73 , Mg ₂ Si; oxide thermoelectric semiconductor materials; Whistler materials such as FeVAL, FeVALSi, and FeVTiAl; sulfide-based thermoelectric semiconductor materials such as TiS ₂ ; and the like are used. These may be used alone or in combination of two or more.
Among these, bismuth-tellu-based thermoelectric semiconductor material, telluride-based thermoelectric semiconductor material, antimony-tellu-based thermoelectric semiconductor material, and bismuth selenide-based thermoelectric semiconductor material are preferable, and from the viewpoint of obtaining high thermoelectric performance, P-type bismuth sterlide, N. Bismuth-tellu-based thermoelectric semiconductor materials such as type bismuth sterlide are more preferable.

As the P-type bismuth telluride, one having a hole as a carrier and a positive Seebeck coefficient, for example, represented by Bi _X Te ₃ Sb _2-X is preferably used. In this case, X is preferably 0 <X ≦ 0.8, more preferably 0.4 ≦ X ≦ 0.6. When X is larger than 0 and 0.8 or less, the Seebeck coefficient and the electric conductivity become large, and the characteristics as a P-type thermoelectric element are maintained, which is preferable.
Further, as the N-type bismuth telluride, one having an electron carrier and a negative Seebeck coefficient, for example, represented by Bi ₂ Te _3-Y Se _Y is preferably used. In this case, Y is preferably 0 ≦ Y ≦ 3 (when Y = 0: Bi ₂ Te ₃ ), and more preferably 0 <Y ≦ 2.7. When Y is 0 or more and 3 or less, the Seebeck coefficient and the electric conductivity become large, and the characteristics as an N-type thermoelectric element are maintained, which is preferable.

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. When the content of the thermoelectric semiconductor particles is within the above range, the Seebeck coefficient (absolute value of the Perche coefficient) is large, the decrease in the electric conductivity is suppressed, and only the thermal conductivity is decreased, so that high thermoelectric performance is exhibited. At the same time, a film having sufficient film strength and flexibility can be obtained, which is preferable.

The average particle size of the thermoelectric semiconductor particles is preferably 10 nm to 200 μm, more preferably 10 nm to 30 μm, still more preferably 50 nm to 10 μm, and particularly preferably 1 to 6 μm. Within the above range, uniform dispersion can be facilitated and the electrical conductivity can be increased.
The method of pulverizing the thermoelectric semiconductor material to obtain thermoelectric semiconductor particles is not particularly limited, and may be pulverized to a predetermined size by a known fine pulverizer such as a jet mill, a ball mill, a bead mill, a colloid mill, a roller mill or the like. ..
The average particle size of the thermoelectric semiconductor particles was obtained by measuring with a laser diffraction type particle size analyzer (Mastersizer 3000 manufactured by Malvern), and was used as the median value of the particle size distribution.

Further, it is preferable that the thermoelectric semiconductor particles are heat-treated in advance. By performing the heat treatment, the crystallinity of the thermoelectric semiconductor particles is improved, and further, the surface oxide film of the thermoelectric semiconductor particles is removed, so that the Seebeck coefficient or the Perche coefficient of the thermoelectric conversion material is increased, and the thermoelectric performance index is further increased. Can be improved. The heat treatment is not particularly limited, but also under an inert gas atmosphere such as nitrogen and argon in which the gas flow rate is controlled so as not to adversely affect the thermoelectric semiconductor particles before preparing the thermoelectric semiconductor composition. It is preferably performed in a reducing gas atmosphere such as hydrogen or under vacuum conditions, and more preferably in a mixed gas atmosphere of an inert gas and a reducing gas. The specific temperature condition depends on the thermoelectric semiconductor particles used, but it is usually preferable to carry out the process at a temperature equal to or lower than the melting point of the particles and at 100 to 1500 ° C. for several minutes to several tens of hours.

<Binder resin>
The thermoelectric semiconductor composition used in the present invention contains a binder resin.
The binder resin acts as a binder between thermoelectric semiconductor materials (thermoelectric semiconductor particles), can enhance the flexibility of the thermoelectric conversion module, and facilitates the formation of a thin film by coating or the like.

The binder resin is preferably a resin that decomposes by 90% by mass or more at a firing (annealing) temperature or higher, more preferably a resin that decomposes by 95% by mass or more, and a resin that decomposes by 99% by mass or more. Is particularly preferable. Further, when a coating film (thin film) made of a thermoelectric semiconductor composition is subjected to crystal growth such as firing (annealing) treatment, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired. More preferred.
If a resin that decomposes by 90% by mass or more at a firing (annealing) temperature or higher is used as the binder resin, the binder resin is decomposed by firing, so that the content of the binder resin that is an insulating component contained in the fired body is increased. Since the amount is reduced and the crystal growth of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is promoted, the voids in the thermoelectric conversion material layer can be reduced and the filling rate can be improved.
Whether or not the resin decomposes at a predetermined value (for example, 90% by mass) or more at the firing (annealing) temperature or higher is determined by the mass reduction rate (before decomposition) at the firing (annealing) temperature by thermogravimetric analysis (TG). Judgment is made by measuring (the value obtained by dividing the mass after decomposition by the mass).

As such a binder resin, a thermoplastic resin or a curable resin can be used. Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polymethylpentene; polycarbonate; thermoplastic polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polystyrene, acrylonitrile-styrene copolymer, and polyacetic acid. Examples thereof include polyvinyl polymers such as vinyl, ethylene-vinyl acetate copolymers, vinyl chloride, polyvinylpyridine, polyvinyl alcohol, and polyvinylpyrrolidone; polyurethanes; cellulose derivatives such as ethyl cellulose; and the like. Examples of the curable resin include thermosetting resins and photocurable resins. Examples of the thermosetting resin include epoxy resin and phenol resin. Examples of the photocurable resin include a photocurable acrylic resin, a photocurable urethane resin, and a photocurable epoxy resin. These may be used alone or in combination of two or more.
Among these, from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer, a thermoplastic resin is preferable, a cellulose derivative such as polycarbonate and ethyl cellulose is more preferable, and polycarbonate is particularly preferable.

The binder resin is appropriately selected according to the firing (annealing treatment) temperature of the thermoelectric semiconductor material in the (D) firing (annealing treatment) step described later. It is preferable to bake (anneal) at a temperature equal to or higher than the final decomposition temperature of the binder resin from the viewpoint of the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer.
In the present specification, the "final decomposition temperature" is a temperature at which the mass reduction rate at the firing (annealing) temperature by thermogravimetric analysis (TG) is 100% (the mass after decomposition is 0% of the mass before decomposition). say.

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 having a final decomposition temperature in this range is used, it functions as a binder for the thermoelectric semiconductor material, and it becomes easy to form a thin film at the time of printing.

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%. It is 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.

The content of the binder resin 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. When the content of the binder resin 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.

<Ionic liquid>
The thermoelectric semiconductor composition used in the present invention contains an ionic liquid.
The ionic liquid is a molten salt formed by combining a cation and an anion, and refers to a salt that can exist as a liquid in any temperature range of −50 ° C. or higher and lower than 400 ° C. The ionic liquid has features such as extremely low vapor pressure, non-volatileity, excellent thermal stability and electrochemical stability, low viscosity, and high ionic conductivity. Therefore, as a conductive auxiliary agent, it is possible to effectively suppress the reduction of the electric conductivity between the thermoelectric semiconductor particles. Further, since the ionic liquid exhibits high polarity based on the aprotic ionic structure and has excellent compatibility with the binder resin, the electric conductivity of the chip of the thermoelectric conversion material can be made uniform.

As the ionic liquid, a known or commercially available one can be used. The ionic liquid may be, for example, (1) nitrogen-containing cyclic cation compounds such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, imidazolium and derivatives thereof; amine-based cations of tetraalkylammonium and derivatives thereof; phosphonium, trialkylsulfonium. , Tetraalkylphosphonium and other phosphinic cations and their derivatives; lithium cations and their derivatives; and other cation components, and (2) Cl ⁻ , AlCl _4- ^, Al ₂ Cl _7- ^, ClO _4- ^and other chloride ions. Bromide ions such as Br- ^; iodide ions such as I- ^; fluoride ions such as BF _4- ^, PF _6- ^; halide anions such as F (HF) _n- ^; NO _3- ^, CH ₃ COO- ^, CF ₃ COO- ^, CH ₃ SO _3- ^, CF ₃ SO _3- ^, (FSO ₂ ) ₂ N- ^, (CF ₃ SO ₂ ) ₂ N- ^, (CF ₃ SO ₂ ) ₃ C- ^, AsF _6- ^, SbF _6- ^, NbF _6- ^, TaF _6- ^, F (HF) n- ^, (CN) ₂ N- ^, C ₄ F ₉ SO _3- ^, (C ₂ F ₅ SO ₂ ) ₂ N- ^, C ₃ F ₇ COO ^- , (CF ₃ SO ₂ ) (CF ₃ CO) N- ^; etc., which are composed of anionic components. These may be used alone or in combination of two or more.

Among the above ionic liquids, the cation component of the ionic liquid is pyridinium cation and its It preferably contains at least one selected from derivatives, imidazolium cations and derivatives thereof. The anion component of the ionic liquid preferably contains a halide anion, and more preferably contains at least one selected from Cl ⁻ , Br ⁻ and I ⁻ .

Specific examples of ionic liquids in which the cation component contains a pyridinium cation and its derivatives 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-butylpyridiniumtetrafluoroborate, 4- Methyl-butylpyridinium hexafluorophosphate, 1-butylpyridinium bromide, 1-butyl-4-methylpyridinium bromide, 1-butyl-4-methylpyridinium hexafluorophosphate, 1-butyl-4-methylpyridinium iodide, etc. Be done. 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 preferable.

Further, specific examples of the ionic liquid in which the cation component contains an imidazolium cation and a derivative thereof are [1-butyl-3- (2-hydroxyethyl) imidazolium bromide] and [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, 1-decyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium chloride, 1-Tetradecyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluororobolate, 1-butyl-3-methylimidazolium tetrafuroboroborate, 1-hexyl-3-methylimidazolium tetraflolate Orobolate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-methyl-3-butylimidazolium methylsulfate, 1,3-dibutylimidazolium methyl Sulfate and the like can be mentioned. These 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 preferable.

The electric conductivity of the above ionic liquid is preferably ^10-7 S / cm or more, more preferably ^10-6 S / cm or more. When the electric conductivity is within the above range, the reduction of the electric conductivity between the thermoelectric semiconductor particles can be effectively suppressed as a conductivity auxiliary agent.

Further, the above-mentioned ionic liquid preferably has a decomposition temperature of 300 ° C. or higher. As long as the decomposition temperature is within the above range, the effect as a conductive auxiliary agent can be maintained even when the coating film (thin film) made of the thermoelectric semiconductor composition is fired (annealed) as described later.
As used herein, the "decomposition temperature" means a temperature at which the mass reduction rate at the firing (annealing) temperature by thermogravimetric analysis (TG) is 10%.

Further, in the above ionic liquid, the mass reduction rate at 300 ° C. by thermogravimetric analysis (TG) is preferably 10% or less, more preferably 5% or less, and particularly preferably 1% or less. As long as the mass reduction rate is within the above range, the effect as a conductive auxiliary agent can be maintained even when the coating film (thin film) made of the thermoelectric semiconductor composition is fired (annealed) as described later.

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. When the content of the ionic liquid is within the above range, the decrease in electrical conductivity is effectively suppressed, and a film having high thermoelectric performance can be obtained.

The content of the ionic liquid 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. When the content of the ionic liquid in the thermoelectric conversion material is within the above range, the decrease in electrical conductivity is effectively suppressed, and a film having high thermoelectric performance can be obtained.

<Inorganic ionic compound>
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 cations and anions. Since the inorganic ionic compound is solid at room temperature, has a melting point in any temperature in the temperature range of 400 to 900 ° C., and has characteristics such as high ionic conductivity, it can be used as a conduction auxiliary agent. It is possible to suppress a decrease in electrical conductivity between thermoelectric semiconductor particles.

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% by mass, more preferably 0.5 to 30% by mass, and particularly preferably. Is 1.0 to 10% by mass. When the content of the inorganic ionic compound is within the above range, the decrease in electrical conductivity can be effectively suppressed, and as a result, a film having improved thermoelectric performance can be obtained.
When the inorganic ionic compound and the 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% by mass, more preferably. Is 0.5 to 30% by mass, particularly preferably 1.0 to 10% by mass.

The content of the inorganic ionic compound 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. When the content of the inorganic ionic compound 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 having improved thermoelectric performance can be obtained.

<Other additives>
In addition to the above, the thermoelectric semiconductor composition may further include a dispersant, a film-forming auxiliary, a photostabilizer, an antioxidant, a tackifier, a plasticizer, a colorant, a resin stabilizer, a filler, and the like. It may contain other additives such as pigments, conductive fillers, conductive polymers and hardeners. These may be used alone or in combination of two or more.

<Vertical section of thermoelectric conversion material layer>
The definition of "longitudinal section including the central portion of the thermoelectric conversion material layer" in the present specification will be described with reference to the drawings.
1A and 1B are views for explaining a definition of a vertical cross section of a thermoelectric conversion material layer of the present invention, FIG. 1A is a plan view of a thermoelectric conversion material layer 2, and FIG. 1A is a plan view of the thermoelectric conversion material layer 2. It has a length X in the width direction and a length Y in the depth direction, and FIG. 1B is a vertical cross section of the thermoelectric conversion material layer 2 formed on the substrate 1, and the vertical cross section is FIG. 1 (a). ), The length X and the thickness D obtained when cutting between A and A'in the width direction are included (the figure is a rectangle). The thermoelectric conversion material layer 2 includes a void portion 3.

The vertical cross section of the thermoelectric conversion material layer of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional view for explaining a vertical cross section of the thermoelectric conversion material layer of the present invention before and after heating and pressurization, and FIG. 2A is a thermoelectric conversion before heating and pressurizing formed on the substrate 1a. It is an example of the vertical cross section of the material layer 2s, and the thermoelectric conversion material layer 2s has a vertical cross section consisting of a curve having a length X in the width direction, Dmin in the thickness direction, and a curve having a value of Dmax. The upper portion is provided with a concave portion and a convex portion, and a gap portion 3a is present in the vertical cross section. Further, FIG. 2B is an example of a vertical cross section of the thermoelectric conversion material layer 2t formed on the substrate 1a after heating and pressurizing the thermoelectric conversion material layer 2s, and the vertical cross section of the thermoelectric conversion material layer 2t has a width. The length is X in the direction and the thickness is D in the thickness direction [when the values of Dmin and Dmax in (a) of FIG. In the plane, there is a void portion 4a in which the number of voids and the volume are further suppressed. Note that Dmin means the minimum value of the thickness in the thickness direction of the vertical cross section, and Dmax means the maximum value of the thickness in the thickness direction of the vertical cross section.

In the present invention, the filling rate of the thermoelectric conversion material in the thermoelectric conversion material layer is defined by the ratio of the area of the thermoelectric conversion material to the area of the longitudinal section including the central portion of the thermoelectric conversion material layer, and the larger the filling rate is, the more the filling rate is defined. , The voids in the thermoelectric conversion material layer are reduced.
The filling factor of the thermoelectric conversion material in the thermoelectric conversion material layer is preferably 0.800 or more and less than 1.000, more preferably 0.900 or more and less than 1.000, and further preferably 0.920 or more and 1. It is less than 000, 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 factor is in this range, the electrical resistivity of the thermoelectric conversion material in the thermoelectric conversion material layer is reduced (improvement of electrical conductivity), and the thermoelectric performance is improved.
The filling factor of the thermoelectric conversion material in the thermoelectric conversion material layer was measured by the method described in Examples described later.

The thermoelectric conversion material layer of the present invention has an increased electric conductivity due to a high filling rate of the thermoelectric conversion material, which leads to an improvement in thermoelectric performance. Therefore, by applying it as a thermoelectric conversion material layer of a thermoelectric conversion module, a thermoelectric conversion module having high thermoelectric performance can be obtained.

[Manufacturing method of thermoelectric conversion material layer]
The method for producing a thermoelectric conversion material layer of the present invention is a method for producing 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. The nanoparticles are characterized by being sintered at 450 ° C. or lower. As one embodiment, (A) a step of forming a thin film of the thermoelectric conversion material layer, (B) a step of drying the thin film of the thermoelectric conversion material layer obtained in the step (A), (C) the step (B). The step of heating and pressurizing the dried thin film of the thermoelectric conversion material layer obtained in the above step, and (D) firing the thin film of the heated and pressurized thermoelectric conversion material layer obtained in the step (C). It is preferable to include a step of annealing).
In the method for producing a thermoelectric conversion material layer of the present invention, a thin film of the thermoelectric conversion material layer is formed, dried at a predetermined temperature, and then the upper surface of the thermoelectric conversion material layer is heated and pressed at a predetermined pressure and a predetermined temperature. After that, by firing at 450 ° C. or lower, the filling of the voids in the thermoelectric conversion material layer is promoted by the inclusion of metal nanoparticles and the progress of sintering thereof, and the volume of the voids in the thermoelectric conversion material layer in the thermoelectric conversion material layer is increased. By reducing the amount, a thermoelectric conversion material layer having improved electric conductivity can be obtained.
Further, as another embodiment, even in a manufacturing method in which firing is simultaneously performed at the heating temperature in the step (C) after the steps (A) and (B), and the step (D) is omitted. good.
Further, as another aspect, after the step (A) and the step (B), the thermoelectric conversion material layer after drying obtained in the step (E) and the step (B) corresponding to the step (D). A manufacturing method including a step of firing (annealing) the thin film of the above may be used.

3A and 3B are explanatory views showing one aspect of the method for manufacturing a thermoelectric conversion material layer of the present invention in order of steps, and FIG. 3A is a cross-sectional view showing an embodiment in which a thermoelectric conversion material layer 2s is formed on a substrate 1b. The thermoelectric conversion material layer 2s is formed on the substrate 1b as a coating film (including the voids 3b) and dried at a predetermined temperature;
(B) is a cross-sectional view showing an aspect after the heat-pressed portion 5 is opposed to the upper surface of the thermoelectric conversion material layer 2s, and the dried thermoelectric conversion material layer 2s and the heat-pressed portion 5 obtained in (a) are shown. And face each other;
(C) is a cross-sectional view showing an embodiment after the upper surface of the thermoelectric conversion material layer 2s is heated and pressed by the heating press unit 5 and then the heating press unit 5 is released from the thermoelectric conversion material layer 2s.
Then, by performing firing (annealing treatment), the thermoelectric conversion material layer 2t (including the void portion 4b in which the number of voids and the volume are further reduced) of the present invention can be obtained.

(A) Thermoelectric conversion material layer forming step The thermoelectric conversion material layer forming step is a step of forming a thermoelectric conversion material layer on a substrate. For example, in FIG. 3A, a thermoelectric semiconductor composition is formed on a substrate 1b. This is a step of applying and forming the thermoelectric conversion material layer 2s.

(substrate)
The substrate is not particularly limited, and examples thereof include glass, silicon, ceramic, metal, and plastic. When firing (annealing treatment) is performed at a high temperature, glass, silicon, ceramic, and metal are preferable, and glass, silicon, and ceramic are more preferable from the viewpoint of 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.

(Thermoelectric semiconductor composition)
As described above, the thermoelectric semiconductor composition used in the present invention contains thermoelectric semiconductor particles, a binder resin, an ionic liquid, and metal nanoparticles. Further, as described above, it may contain an inorganic ionic compound or may contain other additives. The same applies to preferable materials, contents, etc. of thermoelectric semiconductor particles (thermoelectric semiconductor materials), binder resins, ionic liquids, metal nanoparticles, inorganic ionic compounds, and the like.

(Method for preparing thermoelectric semiconductor composition)
The method for preparing the thermoelectric semiconductor composition used in the present invention is not particularly limited, and as described above, the thermoelectric semiconductor particles can be prepared by a known method such as an ultrasonic homogenizer, a spiral mixer, a planetary mixer, a disperser, or a hybrid mixer. The thermoelectric semiconductor composition may be prepared by adding a binder resin, an ionic liquid, metal nanoparticles, an inorganic ionic compound or other additives as necessary, and a solvent, and mixing and dispersing them.
Examples of the solvent include solvents such as toluene, ethyl acetate, methyl ethyl ketone, alcohol, tetrahydrofuran, methylpyrrolidone, and ethyl cellosolve. One of these solvents may be used alone, or two or more of them may be mixed and used. The solid content concentration of the thermoelectric semiconductor composition is not particularly limited as long as the composition has a viscosity suitable for coating.

As a method of applying the thermoelectric semiconductor composition on a substrate, a screen printing method, a flexographic printing method, a gravure printing method, a spin coating method, a dip coating method, a die coating method, a spray coating method, a bar coating method, a doctor blade method, etc. Known methods such as the applicator method can be mentioned, and the present invention is not particularly limited. When the coating film is formed into a pattern, screen printing, stencil printing, slot die coating, etc., which can easily form a pattern using a screen plate having a desired pattern, are preferably used.

As a preferred embodiment, the thermoelectric conversion material layer may be formed on a substrate in the form of a solid film, and then individualized into a desired chip size. Further, as another preferred embodiment, a coating film may be formed on the substrate in the size of a chip of a thermoelectric conversion material described later. Further, from the viewpoint of shape controllability of the thermoelectric conversion material layer, as a more preferable embodiment, a grid-shaped pattern frame member or the like including separated openings having a chip shape of the thermoelectric conversion material may be used.
The chip size is, for example, about 0.1 to 20 mm on the short side and 0.2 to 25 mm on the long side.

A method for manufacturing a thermoelectric conversion material layer in the case of using a grid-like pattern frame member including separated openings having a chip shape of the thermoelectric conversion material is as follows, for example.
(P) A grid-like pattern frame member including a separated opening having a chip shape of a thermoelectric conversion material is placed on the substrate;
(Q) A coating film of a thermoelectric conversion material layer is formed in the opening of the pattern frame member and dried at a predetermined temperature;
(R) After cooling the dried thermoelectric conversion material layer obtained in (q) to room temperature, the thermoelectric conversion material layer and the heating press unit (corresponding to the heating press unit 5 in FIG. 3) are opposed to each other;
(T) The upper surface of the thermoelectric conversion material layer is pressed by the heating press section to reduce the number and volume of voids in the thermoelectric conversion material layer, the heating press section is released from the thermoelectric conversion material layer, and the pattern frame member is further released;
(U) After that, the chip-shaped thermoelectric conversion material layer of the present invention is obtained by firing (annealing) the thermoelectric conversion material layer reflecting the shape of the opening of the pattern frame member obtained on the substrate. obtain.
The opening is not particularly limited, but may be rectangular, square, or circular as long as it has a shape that is reflected in the shape of the chip of the thermoelectric conversion material after the pattern frame member is released. Is preferable, and it is more preferable that the shape is rectangular or square.
Further, as the pattern frame member, stainless steel, copper or the like can be used from the viewpoint of ease of formation.

(B) Thermoelectric conversion material layer drying step The thermoelectric conversion material layer drying step is a step of drying the thermoelectric conversion material layer obtained in the step (A). For example, in FIG. 3A, on the substrate 1b. This is a step of drying the thermoelectric conversion material layer 2s.
As the drying method, conventionally known drying methods such as a hot air drying method, a hot roll drying method, and an infrared irradiation method can be adopted. The heating temperature is usually 80 to 170 ° C, preferably 100 to 150 ° C, more preferably 110 to 145 ° C, still 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 further preferably 10 minutes to 50 minutes.
When the heating temperature and the heating time are within this range, it is easy to improve the electric conductivity of the thermoelectric conversion material layer after pressurization and firing (annealing treatment).
When a solvent is used in the preparation of the thermoelectric semiconductor composition, the heating temperature may be in a temperature range in which the used solvent can be dried or in a temperature range lower than that.

(C) Thermoelectric conversion material layer heating and pressurizing step The thermoelectric conversion material layer heating and pressurizing step is a step of heating and pressurizing the dried thermoelectric conversion material layer obtained in the step (B), for example, FIG. 3 (B). In b), the upper surface of the thermoelectric conversion material layer 2s is heated and pressed by the heating press unit 5.

This heat-pressurizing treatment is performed on the entire upper surface of the coating film (thin film) at a predetermined temperature, in an air atmosphere or under vacuum by using a physical pressurizing means such as a hydraulic press, a vacuum press, or a weight. This is a process of pressurizing at a predetermined pressure for a predetermined time.
The temperature of the heat-pressurizing treatment is not particularly limited, but is usually 100 to 300 ° C, preferably 200 to 300 ° C.
The pressure of the heat-pressurizing treatment is not particularly limited, but is usually 20 to 200 MPa, preferably 50 to 150 MPa.
The time of the heat-pressurizing treatment is not particularly limited, but is usually from several seconds to several tens of minutes, preferably from several tens of seconds to ten and several minutes.
The pressurization may be performed by increasing the pressurization amount to a predetermined amount at once, but the shape stability of the thermoelectric conversion material layer is maintained, the voids in the thermoelectric conversion material layer are reduced more, and the filling rate of the thermoelectric conversion material is reduced. From the viewpoint of improving the pressure, the pressure is adjusted as appropriate, but is usually 0.1 to 50 MPa / min, preferably 0.5 to 30 MPa / min, and more preferably 1.0 to 10 MPa / min to a predetermined pressurization amount. To increase.
When the pressurizing amount and the pressurizing time are within this range, the filling rate is likely to increase, and the electric conductivity of the thermoelectric conversion material layer after firing (annealing treatment) is likely to be improved.

(D) Firing (annealing) step (including step (E))
The firing (annealing treatment) step is, for example, a step of heat-treating the heated and pressurized thermoelectric conversion material layer obtained in the step (C) at a predetermined temperature.
By performing firing (annealing treatment), not only a sintered body of metal nanoparticles can be obtained, but also the thermoelectric performance can be stabilized and the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the thin film can be crystallized. , The thermoelectric performance of the thermoelectric conversion material layer can be further improved.
For example, in FIG. 3C, it is a step of annealing the thermoelectric conversion material layer 2s after heating and pressurizing at a predetermined temperature (after the annealing treatment, the thermoelectric conversion material layer 2t is obtained).

The firing (annealing treatment) is not particularly limited, but is usually carried out under an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere, or a vacuum condition in which the gas flow rate is controlled.
As a firing method, a known method can be used.
The firing (annealing) temperature is as described above.
The firing (annealing treatment) time is not particularly limited, but is usually several minutes to several tens of hours, preferably several minutes to several hours.

The firing (annealing treatment) may be performed in a state where the thermoelectric conversion material layer is pressurized. The amount of pressurization when pressurizing is performed under the same conditions as the above-mentioned heat pressurization treatment step.

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

According to the method for manufacturing a thermoelectric conversion material layer of the present invention, a thermoelectric conversion material layer having improved electrical conductivity can be manufactured by a simple method.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

In the test piece (chip) made of the thermoelectric conversion material produced in Examples and Comparative Examples, the filling rate of the vertical cross section along the thickness direction was measured by the following method.
(Measurement of filling rate of vertical cross section along the thickness direction)
For each test piece (chip) made of the thermoelectric conversion material obtained in each Example and Comparative Example, a longitudinal section including the central portion of the thermoelectric conversion material layer by a polishing device (manufactured by Refine Tech, model name: Refine Polisher HV). Surface emission is performed, and a vertical cross section is observed using a field emission scanning electron microscope (FE-SEM) (manufactured by Hitachi High-Technologies Corporation, model name: S-4700), and then image processing software (National Instruments of Health) is used. The filling rate defined by the ratio of the area of the thermoelectric conversion material to the area of the vertical cross section of the thermoelectric conversion material layer was calculated using ImageJ ver. 1.44P).
In the measurement of the filling factor, an SEM image (longitudinal cross section) having a magnification of 500 times is used, and the measurement range is set to a range surrounded by 1280 pixel in the width direction and 220 pixel in the thickness direction with respect to an arbitrary position of the thermoelectric conversion material layer. , Cut out as an image. The cut out image is binarized from "Brightness / Control" with the maximum contrast, and the dark part in the binarization process is regarded as the void part and the bright part is regarded as the thermoelectric conversion material. The filling rate of was calculated. The filling factor was calculated for three SEM images and used as the average value thereof. The results are shown in Table 1.

(Example 1)
<Making a test piece (chip) made of thermoelectric conversion material>
(1) Preparation of thermoelectric semiconductor composition (preparation of thermoelectric semiconductor particles)
P-type bismuth tellurium Bi _0.4 Te _3.0 Sb _1.6 (manufactured by High Purity Chemical Laboratory, particle size: 20 μm), which is a bismuth-tellurium-based thermoelectric semiconductor material, is used in a planetary ball mill (manufactured by Fritsch Japan, Premium). Thermoelectric semiconductor particles having an average particle size of 2.0 μm were prepared by pulverizing in a nitrogen gas atmosphere using line P-7). The particle size distribution of the thermoelectric semiconductor particles obtained by pulverization was measured by a laser diffraction type particle size analyzer (Mastersizer 3000 manufactured by Malvern).
(Preparation of thermoelectric semiconductor composition (coating liquid))
P-type bismasterlide Bi _0.4 Te _3.0 Sb _1.6 particles (average particle size 2.0 μm) 76.0% by mass obtained above, polyethylene carbonate (final decomposition temperature: 250 ° C.) as a binder resin. Contains polyethylene carbonate solution (EMPOWER MATERIALS, QPAC25, solvent: N-methylpyrrolidone, solid content concentration: 20% by mass) 16.5% by mass (solid content 3.3% by mass), 1-butylpyridinium bromide as an ionic liquid. (IL-P18B, manufactured by Koei Chemical Industry Co., Ltd.) 6.5% by mass, and silver nanoparticles as metal nanoparticles (manufactured by Samsung Belt Co., solvent: N-methylpyrrolidone, solid content concentration: 90% by mass, average particle size 60 nm) ) A coating solution composed of a thermoelectric semiconductor composition in which 1.0% by mass was mixed and dispersed was prepared.
(2) Preparation of test piece (chip) made of thermoelectric conversion material (formation of thermoelectric conversion material layer)
The coating solution prepared in (1) above was printed as a solid film on a glass substrate (blue plate glass, 100 mm × 100 mm, thickness: 0.7 mm) using an applicator, and an argon atmosphere was obtained at a temperature of 120 ° C. for 10 minutes. It was dried underneath to form a thin film [thermoelectric conversion material layer before firing (annealing)].
Next, the dried thermoelectric conversion material layer is cooled to room temperature, and the temperature is raised at a heating rate of 5 K / min in an atmosphere of a mixed gas of hydrogen and argon (hydrogen: argon = 3% by volume: 97% by volume), 430. A thermoelectric conversion material layer (thickness: 55 μm) made of a fired body of the thermoelectric semiconductor composition was prepared by holding at ° C. for 30 minutes and firing the thermoelectric conversion material layer. The obtained thermoelectric conversion material layer was cut into a size of 5 mm × 5 mm and used as a test piece (chip) made of the thermoelectric conversion material.

(Example 2)
In Example 1, the test was carried out in the same manner as in Example 1 except that the P-type Bi _0.4 Te _3.0 Sb _1.6 particles were 69.0% by mass and the silver nanoparticles were 8.0% by mass. Pieces (chip size: 5 mm × 5 mm × thickness 58 μm) were prepared.

(Example 3)
In Example 1, the glass substrate was replaced with a polyimide substrate, a coating liquid was printed, and the coating liquid was heated and dried at 120 ° C. for 10 minutes, and then a hydraulic press machine (tabletop test press SA-302 manufactured by Tester Sangyo Co., Ltd.) was used. The entire upper surface of the coating film (thin film) is heat-pressurized at 110 MPa for 10 minutes at 250 ° C. in an air atmosphere to form a thin film [thermoelectric conversion material layer before firing (annealing)]. A test piece (however, chip size: 5 mm × 6 mm × thickness 70 μm) was prepared in the same manner as in Example 1.

(Example 4)
In Example 2, the glass substrate was printed in place of the polyimide substrate, heated and dried at 120 ° C. for 10 minutes, and then the coating film (thin film) was formed at 250 ° C. in an air atmosphere using the hydraulic press machine. A test piece (however, chip size: 5 mm × 6 mm × thickness 70 μm) was prepared in the same manner as in Example 2 except that the entire upper surface was pressurized at 110 MPa for 10 minutes.

(Comparative Example 1)
In Example 1, the test was carried out in the same manner as in Example 1 except that P-type Bi _0.4 Te _3.0 Sb _1.6 particles were 77.0% by mass and silver nanoparticles were not blended (0% by mass). Pieces (chip size: 5 mm × 5 mm × thickness 53 μm) were prepared.

(Comparative Example 2)
In Comparative Example 1, the coating liquid was printed in place of the polyimide substrate instead of the polyimide substrate, and after heating and drying at 120 ° C. for 10 minutes, the coating film (using the hydraulic press machine was used at 250 ° C. in an air atmosphere). The test piece (thin film) was subjected to pressure treatment at 110 MPa for 10 minutes on the entire upper surface of the thin film) to form a thin film [thermoelectric conversion material layer before firing (annealing treatment)] in the same manner as in Comparative Example 1 (thin film). However, a chip size (5 mm × 6 mm × thickness 70 μm) was produced.

The filling rate of the vertical cross section along the thickness direction of the test piece (chip) of the thermoelectric conversion material produced in Examples 1 to 4 and Comparative Examples 1 and 2 was measured. The results are shown in Table 1.

The filling factor of the thermoelectric conversion material in the longitudinal section along the thickness direction of the thermoelectric conversion material layer of Example 1 containing silver nanoparticles is the longitudinal section along the thickness direction of the thermoelectric conversion material layer of Comparative Example 1 not containing silver nanoparticles. It can be seen that the filling rate of the thermoelectric conversion material is increased in comparison with the filling rate of the thermoelectric conversion material. Further, the filling rate of the thermoelectric conversion material in the vertical cross section along the thickness direction of the thermoelectric conversion material layer of Example 3 containing silver nanoparticles and combined with the heat and pressure treatment does not include silver nanoparticles and is combined with the heat and pressure treatment. It can be seen that the filling rate of the thermoelectric conversion material in the vertical cross section along the thickness direction of the thermoelectric conversion material layer of Comparative Example 2 is increased.
From the above, it can be seen that the improvement of the filling rate increases the electric conductivity of the thermoelectric conversion material in the thermoelectric conversion material layer, which leads to the improvement of the thermoelectric performance.

The thermoelectric conversion material layer of the present invention has an increased electric conductivity due to a high filling rate of the thermoelectric conversion material, which leads to an improvement in thermoelectric performance. Therefore, the thermoelectric conversion module using the thermoelectric conversion material layer of the present invention can be used for exhaust heat from various combustion furnaces such as factories, waste combustion furnaces, cement combustion furnaces, automobile combustion gas exhaust heat, and electronic equipment exhaust heat. It is conceivable to apply it to power generation applications that convert electricity into electricity. In the field of electronic equipment, for example, CPUs (Central Processing Units) used in smartphones, various computers, etc., CMOS (Complementary Metal Oxide Sensors), CCDs (Challge Coupled Devices), and other image sensors for cooling applications. , MEMS (Micro Electro Mechanical Systems), and can be applied to temperature control of various sensors such as light receiving elements.

1,1a, 1b:

Substrate

2,2s, 2t: Thermoelectric

conversion material layer

3,3a, 3b, 4a, 4b: Void portion 5: Heat press portion X: Length (width direction)
Y: Length (depth direction)
D: Thickness (thickness direction)
Dmax: Maximum value of thickness in the thickness direction (vertical cross section)
Dmin: Minimum value of thickness in the thickness direction (vertical cross section)
C: Central part of thermoelectric conversion material layer

Claims

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 sintered at 450 ° C. or lower. Thermoelectric conversion material layer.
The thermoelectric conversion material layer according to claim 1, wherein the metal nanoparticles in the thermoelectric semiconductor composition have an average particle size of 200 nm or less.
The thermoelectric conversion material layer according to claim 1 or 2, wherein the metal nanoparticles are particles sintered at 300 ° C. or lower.
The thermoelectric 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. Conversion material layer.
The thermoelectric conversion material layer according to any one of claims 1 to 4, wherein the specific resistance of the metal nanoparticles is 6.0 × 10 -3 Ω · cm or less.
The thermoelectric conversion material layer according to any one of claims 1 to 5, wherein the content of the metal nanoparticles in the thermoelectric semiconductor composition is 0.01 to 15.00% by mass.
The thermoelectric conversion material layer according to any one of claims 1 to 6, wherein the thermoelectric conversion material layer is composed of a fired body of a coating film of the thermoelectric semiconductor composition.
The thermoelectric conversion material layer is composed of a thermoelectric conversion material containing voids, and the filling rate is defined as the ratio of the area of the thermoelectric conversion material to the area of the longitudinal section including the central portion of the thermoelectric conversion material layer. The thermoelectric conversion material layer according to any one of claims 1 to 7, wherein the rate is 0.800 or more and less than 1.000.