Thermoelectric conversion element, thermoelectric conversion module, optical sensor, method for producing thermoelectric conversion material, and method for producing thermoelectric conversion element

Abstract

The thermoelectric conversion element includes a thermoelectric conversion material portion made of a material having a band gap, a first electrode arranged in contact with the thermoelectric conversion material portion, a second electrode arranged in contact with the thermoelectric conversion material portion and spaced apart from the first electrode, and a sealing portion that seals the thermoelectric conversion material portion. The sealing portion maintains the partial pressure of oxygen in the region surrounding the thermoelectric conversion material portion lower than the partial pressure of oxygen in the atmosphere.

Description

Technical Field

[0001] The present disclosure relates to a thermoelectric conversion element, a thermoelectric conversion module, an optical sensor, a method for manufacturing a thermoelectric conversion material, and a method for manufacturing a thermoelectric conversion element. This application claims priority based on Japanese Patent Application No. 2018-164419, filed on September 3, 2018. All the descriptions contained in the Japanese patent application are incorporated herein by reference.

Background Art

[0002] In recent years, renewable energy has attracted attention as clean energy to replace fossil fuels such as oil. Renewable energy includes energy obtained by power generation using sunlight, hydropower, and wind power, as well as energy obtained by thermoelectric conversion using a temperature difference. In thermoelectric conversion, since heat is directly converted into electricity, no extra waste is discharged during the conversion. Thermoelectric conversion has features such as being easy to maintain the device because it does not require a driving part such as a motor.

[0003] The conversion efficiency η of the temperature difference (thermal energy) into electrical energy using a material for thermoelectric conversion (thermoelectric conversion material) is given by the following formula (1).

[0004] η = ΔT / T h ·(M - 1) / (M + T c / T h )···(1) η is the conversion efficiency, ΔT is the difference between T h and T c and T h is the temperature on the high-temperature side, T c is the temperature on the low-temperature side, M is (1 + ZT) 1 / 2 , ZT is α 2 ST / κ, ZT is a dimensionless performance index, α is the Seebeck coefficient, S is the conductivity, and κ is the thermal conductivity. The conversion efficiency is a monotonic increasing function of ZT. Increasing ZT is important in the development of thermoelectric conversion materials.

[0005] A technique has been reported for forming Au nanoparticles in SiGe (silicon germanium) by heat-treating a laminate obtained after stacking Si, Ge, and Au as a thermoelectric conversion material (e.g., Non-Patent Document 1). A technique using Si / GeB as a thermoelectric conversion material has also been reported (e.g., Non-Patent Document 2).

[0006] Patent Document 1 discloses a thermoelectric conversion material that includes nanoparticles containing the base element and a different heterogeneous element within a base material made of a semiconductor material composed of the base element. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Hiroaki Takiguchi et al., “Nano Structural and Thermoelectric Properties of SiGeAu Thin Films”, Japanese Journal of Applied Physics 50 (2011) 041301 [Non-Patent Document 2] Akinari Matoba et al., “Crystallinity and Thermoelectric Properties of Si / GeB Multilayers Prepared with Si Buffer Layer and SiO2 Substrates”, Japanese Journal of Applied Physics 48 (2009) 061201 [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2014 / 196475 [Overview of the project]

[0009] The thermoelectric conversion element according to the present disclosure includes a thermoelectric conversion material portion made of a material having a band gap, a first electrode disposed in contact with the thermoelectric conversion material portion, a second electrode disposed in contact with the thermoelectric conversion material portion and separated from the first electrode, and a sealing portion that seals the thermoelectric conversion material portion. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material portion is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing portion.

Brief Description of Drawings

[0010] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a π-type thermoelectric conversion element (power generation element) which is a thermoelectric conversion element in Embodiment 1. [Figure 2] FIG. 2 is a flowchart showing a typical manufacturing process of the thermoelectric conversion element. [Figure 3] FIG. 3 is a graph showing the relationship between temperature and resistivity in the thermoelectric conversion material portion. [Figure 4] FIG. 4 is a diagram showing an example of the structure of a power generation module in Embodiment 2. [Figure 5] FIG. 5 is a diagram showing an example of the structure of a power generation module in Embodiment 2. [Figure 6] FIG. 6 is a diagram showing an example of the structure of a power generation module in Embodiment 3. [Figure 7] FIG. 7 is a diagram showing an example of the structure of an optical sensor.

Embodiments for Carrying Out the Invention

[0011] [Problems to be Solved by the Present Disclosure] There is a demand for a thermoelectric conversion element using a thermoelectric conversion material having a higher conversion efficiency than the thermoelectric conversion materials disclosed in Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1. Regarding the thermoelectric conversion material provided in the thermoelectric conversion element, if the resistivity, which is the reciprocal of the conductivity, can be maintained low, the efficiency of thermoelectric conversion can be improved.

[0012] Therefore, one of the objectives is to provide a thermoelectric conversion element, a thermoelectric conversion module, a light sensor, a method for manufacturing a thermoelectric conversion material, and a method for manufacturing a thermoelectric conversion element, all of which improve the efficiency of thermoelectric conversion. [Effects of this disclosure] The thermoelectric conversion element of this disclosure can improve the efficiency of thermoelectric conversion.

[0013] [Description of Embodiments in this Disclosure] The embodiments of this disclosure will be listed and described first. The thermoelectric conversion element according to this disclosure comprises a thermoelectric conversion material portion made of a material having a band gap, a first electrode disposed in contact with the thermoelectric conversion material portion, a second electrode disposed in contact with the thermoelectric conversion material portion but separated from the first electrode, and a sealing portion that seals the thermoelectric conversion material portion. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material portion is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing portion.

[0014] The above-described thermoelectric conversion element includes a sealing portion that seals a thermoelectric conversion material portion made of a material having a band gap. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material portion is maintained at a lower level than the partial pressure of oxygen in the atmosphere by the sealing portion. Therefore, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material portion can be suppressed compared to that in the atmosphere. As a result, the increase in the resistivity of the thermoelectric conversion material portion can be suppressed, and the ZT can be maintained at a high level. With such a thermoelectric conversion element, the efficiency of thermoelectric conversion can be improved.

[0015] In the thermoelectric conversion element described above, the thermoelectric conversion material portion may be made of a semiconductor material containing amorphous material. Since semiconductor materials have a larger band gap than conductive materials, the Seebeck coefficient can be increased. The thermal conductivity can be lowered by using a semiconductor material containing amorphous material. Therefore, the dimensionless figure of merit ZT can be increased in the thermoelectric conversion material portion included in the thermoelectric conversion element. As a result, the efficiency of thermoelectric conversion can be improved.

[0016] In the thermoelectric conversion element described above, the sealing portion may surround the thermoelectric conversion material portion with the above region in between. The partial pressure of oxygen in the atmosphere within the above region is 2 × 10 5 The resistivity may be less than Pa. By doing so, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material can be efficiently suppressed. Therefore, it is possible to maintain a low resistivity state in the thermoelectric conversion material and ensure high thermoelectric conversion efficiency.

[0017] In the thermoelectric conversion element described above, the pressure within the above region is 1 × 10⁻⁶ -2 The pressure may be less than or equal to Pa. By doing so, the amount of oxygen in the above region can be reduced, thereby suppressing the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material. Therefore, it is possible to maintain a low resistivity state in the thermoelectric conversion material and ensure high thermoelectric conversion efficiency. The pressure in the above region is 1 × 10⁻⁶ -7 It is preferable that the Pa level be 1 or higher.

[0018] In the thermoelectric conversion element described above, an inert gas may be sealed within the region. By doing so, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material can be more reliably suppressed. Therefore, a low resistivity state can be maintained in the thermoelectric conversion material, ensuring high thermoelectric conversion efficiency. Examples of inert gases include argon gas and nitrogen gas.

[0019] In the thermoelectric conversion element described above, the sealing portion may be composed of a sealing material that fills the region. The sealing material can suppress contact between the thermoelectric conversion material and oxygen molecules. As a result, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material can be suppressed. Therefore, a low resistivity state of the thermoelectric conversion material can be maintained, ensuring high thermoelectric conversion efficiency. Examples of materials for the sealing material include epoxy resin.

[0020] In the thermoelectric conversion element described above, the semiconductor material may have an n-type conductivity and may contain Si, Ge, Fe, and P. With such a thermoelectric conversion element, it is possible to reliably maintain a low resistivity state in the thermoelectric conversion material portion and improve thermoelectric efficiency.

[0021] The thermoelectric conversion module of this disclosure includes a plurality of the above-mentioned thermoelectric conversion elements. According to the thermoelectric conversion module of this disclosure, by including a plurality of the thermoelectric conversion elements of this disclosure which have excellent thermoelectric conversion efficiency, it is possible to obtain a thermoelectric conversion module with improved thermoelectric conversion efficiency.

[0022] The optical sensor of this disclosure comprises an absorber that absorbs light energy, and the thermoelectric conversion element of this disclosure described above, the first electrode of which is connected to the absorber.

[0023] Such optical sensors incorporate improvements in the thermoelectric conversion efficiency of the thermoelectric conversion element. Therefore, they can provide highly sensitive optical sensors.

[0024] The method for manufacturing a thermoelectric conversion material according to the present disclosure includes the steps of: obtaining an amorphous semiconductor material powder by performing mechanical alloying in a reducing atmosphere; and forming a compacted powder by compacting the amorphous powder.

[0025] According to this method for manufacturing thermoelectric materials, since mechanical alloying is performed in a reducing atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder can be suppressed. By using the compacted powder obtained in this way, a thermoelectric material with improved thermoelectric conversion efficiency can be provided.

[0026] In the above method for manufacturing thermoelectric materials, mechanical alloying may be carried out in a mixed gas of hydrogen and nitrogen with a hydrogen content of 4% by volume or less. By doing so, the formation of an oxide film in the process of obtaining the powder can be suppressed.

[0027] The method for manufacturing a thermoelectric conversion element according to the present disclosure includes the steps of: obtaining an amorphous semiconductor material powder by performing mechanical alloying; forming a thermoelectric conversion material part made of compacted powder by compacting the amorphous powder; heating the thermoelectric conversion material part while maintaining a state in which the partial pressure of oxygen in the atmosphere in which the thermoelectric conversion material part is in contact is lower than the partial pressure of oxygen in the atmosphere; and sealing the thermoelectric conversion material part with a sealing part such that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material part is lower than the partial pressure of oxygen in the atmosphere.

[0028] According to the method for manufacturing a thermoelectric conversion element of this disclosure, the thermoelectric conversion material is heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the thermoelectric conversion material is lower than the partial pressure of oxygen in the atmosphere. This allows oxygen atoms from the oxide film on the surface of the particles constituting the compacted powder to diffuse into the interior of the particles, making the oxide film on the surface of the particles thinner. Therefore, the conductivity between the particles constituting the compacted powder is improved, and the resistivity of the thermoelectric conversion material can be lowered. Furthermore, since the thermoelectric conversion material is sealed by the sealing portion such that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material is lower than the partial pressure of oxygen in the atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder is suppressed, and the resistivity of the thermoelectric conversion material can be maintained at a low level. Therefore, according to this method for manufacturing a thermoelectric conversion element, it is possible to manufacture a thermoelectric conversion element that can improve the efficiency of thermoelectric conversion.

[0029] In the above-described method for manufacturing a thermoelectric conversion element, mechanical alloying may be performed in a reducing atmosphere. By doing so, the formation of an oxide film on the surface of the particles constituting the compacted powder can be suppressed in the process of obtaining the amorphous semiconductor material powder. Therefore, a thermoelectric conversion element with a low resistivity in the thermoelectric conversion material portion can be manufactured.

[0030] In the above-described method for manufacturing a thermoelectric element, mechanical alloying may be carried out in a mixed gas of hydrogen and nitrogen with a hydrogen content of 4% by volume or less. By doing so, the formation of an oxide film in the process of obtaining the powder can be suppressed. Therefore, a thermoelectric element with improved thermoelectric efficiency can be manufactured.

[0031] [Details of the embodiments of this disclosure] Next, an embodiment of the thermoelectric conversion element of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0032] (Embodiment 1) The configuration of the thermoelectric conversion element according to Embodiment 1 of the present application will now be described. Figure 1 is a schematic diagram showing the structure of a π-type thermoelectric conversion element (power generation element) 21, which is a thermoelectric conversion element in Embodiment 1. Referring to Figure 1, the π-type thermoelectric conversion element 21 comprises thermoelectric conversion material parts 22 and 23 made of a material having a band gap, specifically thermoelectric conversion material parts 22 and 23 made of compacted powder of a semiconductor material containing amorphous material, a high-temperature side electrode 24 as a first electrode positioned in contact with the thermoelectric conversion material parts 22 and 23, a low-temperature side electrode 25 and 26 as a second electrode positioned in contact with the thermoelectric conversion material parts 22 and 23 but separated from the high-temperature side electrode 24, and a sealing part 30 that seals the thermoelectric conversion material parts 22 and 23. In Figure 1, the sealing part 30 is schematically shown by a dashed line. The thermoelectric conversion material part 22 is a p-type thermoelectric conversion material part 22. The thermoelectric conversion material part 23 is an n-type thermoelectric conversion material part 23.

[0033] The thermoelectric conversion material section 22 consists of a thermoelectric conversion material whose component composition has been adjusted, for example, to have a p-type conductivity. The thermoelectric conversion material constituting the thermoelectric conversion material section 22 is doped with p-type impurities that generate p-type carriers (holes), which are majority carriers, thereby making the thermoelectric conversion material section 22 have a p-type conductivity.

[0034] The thermoelectric conversion material section 23 consists of a thermoelectric conversion material whose component composition has been adjusted, for example, to have an n-type conductivity. The thermoelectric conversion material constituting the thermoelectric conversion material section 23 is doped with, for example, n-type impurities that generate n-type carriers (electrons), which are majority carriers, thereby making the conductivity of the thermoelectric conversion material section 23 n-type.

[0035] The thermoelectric material section 22 and the thermoelectric material section 23 are arranged side by side with a gap between them. The high-temperature side electrode 24 is positioned to extend from one end 31 of the thermoelectric material section 22 to one end 32 of the thermoelectric material section 23. The high-temperature side electrode 24 is positioned to contact both one end 31 of the thermoelectric material section 22 and one end 32 of the thermoelectric material section 23. The high-temperature side electrode 24 is positioned to connect one end 31 of the thermoelectric material section 22 and one end 32 of the thermoelectric material section 23. The high-temperature side electrode 24 is made of a conductive material, such as a metal. The high-temperature side electrode 24 is in ohmic contact with the thermoelectric material section 22 and the thermoelectric material section 23.

[0036] The low-temperature electrode 25 is positioned in contact with the other end 33 of the thermoelectric conversion material portion 22. The low-temperature electrode 25 is positioned away from the high-temperature electrode 24. The low-temperature electrode 25 is made of a conductive material, such as a metal. The low-temperature electrode 25 is in ohmic contact with the thermoelectric conversion material portion 22.

[0037] The low-temperature electrode 26 is positioned in contact with the other end 34 of the thermoelectric conversion material portion 23. The low-temperature electrode 26 is positioned away from the high-temperature electrode 24 and the low-temperature electrode 25. The low-temperature electrode 26 is made of a conductive material, such as a metal. The low-temperature electrode 26 is in ohmic contact with the thermoelectric conversion material portion 23.

[0038] The wiring 27 is made of a conductor such as metal. The wiring 27 electrically connects the low-temperature electrode 25 and the low-temperature electrode 26.

[0039] The sealing portion 30 is, for example, a box-shaped member that seals the thermoelectric conversion material portions 22 and 23. The sealing portion 30 surrounds the thermoelectric conversion material portions 22 and 23 with a region 35 in between. The partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material portions 22 and 23 is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing portion 30. In this embodiment, the pressure within region 35 is 1 × 10⁻⁶. -2 It is less than Pa. Specifically, the pressure within region 35 is 1 × 10⁻⁶. -7 Pa or higher and 1 × 10 -2 The pressure is maintained below Pa. The region 35 is essentially a vacuum. For example, silicone resin is selected as the material for the sealing portion 30.

[0040] In the π-type thermoelectric conversion element 21, if a temperature difference is formed such that, for example, one end 31 of the thermoelectric conversion material section 22 and one end 32 of the thermoelectric conversion material section 23 are at a high temperature, and the other end 33 of the thermoelectric conversion material section 22 and the other end 34 of the thermoelectric conversion material section 23 are at a low temperature, then in the thermoelectric conversion material section 22, p-type carriers (holes) move from the one end 31 side to the other end 33 side. At the same time, in the thermoelectric conversion material section 23, n-type carriers (electrons) move from the one end 32 side to the other end 34 side. As a result, current flows in the wiring 27 in the direction of arrow I. In this way, power generation by thermoelectric conversion using the temperature difference is achieved in the π-type thermoelectric conversion element 21. In other words, the π-type thermoelectric conversion element 21 is a power generation element.

[0041] Next, the configuration of the thermoelectric conversion material section 23 will be described. The thermoelectric conversion material section 23 consists of a compacted powder of an amorphous semiconductor material. In this embodiment, the semiconductor material uses Si and Ge as base elements. The semiconductor material contains a first additive element and a second additive element. The semiconductor material contains Fe as the first additive element. Fe forms a first added energy level as a new level within the band gap of SiGe. The semiconductor material contains P as the second additive element. P forms a second added energy level between the first added energy level and the conduction band within the band gap of SiGe. This second added energy level adjusts the Fermi level. That is, in the thermoelectric conversion material section 23 of this embodiment, a donor level can be formed by the second added energy level. As for the manufacturing method of the thermoelectric conversion material section 22, for example, the same method as described above can be used, with the elements used being Si, Ge, Au, and B.

[0042] A thermoelectric conversion element 21 equipped with such thermoelectric conversion material parts 22 and 23 is manufactured as follows. Figure 2 is a flowchart showing a typical manufacturing process for a thermoelectric conversion element 21. First, the manufacturing method for the n-type thermoelectric conversion material part 23 will be described. Referring to Figure 2, weighed Si, Ge, Fe, and P are placed in a stainless steel pot. In this case, the content ratio of each element is Si 63 Ge 24 P 10 The mixture is adjusted to become Fe3. The pot is then filled with a foaming gas, a mixture of hydrogen and nitrogen with a hydrogen content of 4% by volume or less, to create a reducing atmosphere. Amorphous powder of SiGe with Fe and P added is then obtained by mechanical alloying. Specifically, the mechanical alloying is performed in a mixture of hydrogen and nitrogen with a hydrogen content of 4% by volume or less. In this way, amorphous semiconductor material powder is obtained by mechanical alloying in a reducing atmosphere (S11).

[0043] Next, with the glove box under a nitrogen gas atmosphere, the obtained powder is filled into a die and a compact is formed by a hot press method. The pressure at this time can be 400 MPa and the temperature 400°C. In this way, the amorphous powder is compressed to form a thermoelectric conversion material part 23 consisting of a compact (S12). In this case, the amorphous powder is compressed while heating. The compact is sintered at this time. Steps S11 and S12 represent an example of a typical step in the method for manufacturing a thermoelectric conversion material of the present invention. That is, the method for manufacturing a thermoelectric conversion material of the present invention includes the step of obtaining amorphous semiconductor material powder by performing mechanical alloying in a reducing atmosphere, and the step of forming a compact by compressing the amorphous powder. For the thermoelectric conversion material part 22, the elements used are Si, Ge, Au, and B, and the content ratio of each element is adjusted, and the process is carried out in the same manner as above.

[0044] Next, the thermoelectric conversion material 23 is heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the obtained thermoelectric conversion material 23 is lower than the partial pressure of oxygen in the atmosphere (S13). In this case, the pressure is 1 × 10⁻⁶. -7 Pa or higher and 1 × 10 -2 The thermoelectric conversion material unit 23 is placed in an atmosphere (vacuum) with a pressure of 1 × 10⁻¹⁰ Pa or less and heated. After that, the pressure is 1 × 10⁻¹⁰ -7 Pa or higher and 1 × 10 -2 Cooling is performed in an atmosphere with a temperature of Pa or less. The same procedure is followed for the thermoelectric conversion material section 22.

[0045] Next, the high-temperature electrode 24, low-temperature electrodes 25, 26, and wiring 27 are attached to the thermoelectric conversion material section 22 and the thermoelectric conversion material section 23, and then sealed with the sealing section 30. Here, the thermoelectric conversion material section 23 is sealed with the sealing section 30 such that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material sections 22 and 23 is lower than the partial pressure of oxygen in the atmosphere (S14). In this case, the pressure is 1 × 10⁻⁶. -7 Pa or higher and 1 × 10 -2In an atmosphere of Pa or less, the thermoelectric conversion material section 22 and thermoelectric conversion material section 23, to which the high-temperature side electrode 24, low-temperature side electrodes 25 and 26, and wiring 27 are attached, are sealed by the sealing section 30. In this way, a thermoelectric conversion element 21 comprising the thermoelectric conversion material sections 22 and 23 is obtained.

[0046] Figure 3 is a graph showing the relationship between temperature and resistivity in the thermoelectric conversion material section 23. In Figure 3, the vertical axis represents resistivity (mΩcm), and the horizontal axis represents temperature (°C). Resistivity was measured using the four-terminal method.

[0047] Refer to Figure 3 and set the pressure to 1 × 10⁻⁶ -7 Pa or more 1×10 -2 When heating from room temperature while maintaining a pressure below Pa, as indicated by arrow 36a and the circle, it can be observed that the resistivity decreases significantly. Specifically, the resistivity, which was 220 mΩcm at room temperature, drops to below 10 mΩcm when the temperature exceeds 700°C. Subsequently, when the pressure is increased to 1 × 10⁻⁶ -7 Pa or more 1×10 -2 Even when cooled to room temperature as indicated by arrow 36b and the square mark while maintaining a state below Pa, the resistivity remains at approximately 10 mΩcm. Furthermore, the low resistivity is maintained even as the temperature decreases. Next, the pressure is set to 1 × 10⁻⁶ -7 Pa or more 1×10 -2 Even when the temperature is raised to 800°C again, as indicated by arrow 36c and the triangle, while maintaining a state below Pa, the resistivity remains below 10 mΩcm. On the other hand, as indicated by the × at room temperature, the pressure is increased to 1 × 10⁻⁶ -7 Pa or more 1×10 -2 After cooling to room temperature while maintaining a pressure below Pa, and then opening to the atmosphere, the resistivity increases to approximately 110 mΩcm. Note that after opening to the atmosphere, the pressure is again increased to 1 × 10⁻⁶. -7 Pa or more 1×10 -2 When the temperature is increased as indicated by arrow 36d and the × mark, the resistivity decreases in a state below Pa.

[0048] Thus, the pressure is 1 × 10 -7 Pa or more 1×10 -2Maintaining a pressure below Pa allows for the maintenance of low resistivity. On the other hand, exposure to the atmosphere increases resistivity. This is thought to be because exposure to the atmosphere causes an oxide film to form on the surface of the particles constituting the compacted powder. The pressure is 1 × 10⁻⁶. -7 The reason it's Pa is because a turbomolecular pump was used; by using an ion pump or cryopump for reduced pressure, it would be 1 × 10⁻¹⁰ -11 The same results were obtained when the experiment was conducted at Pa or higher.

[0049] According to the manufacturing method of the thermoelectric conversion element 21 of this application, the thermoelectric conversion material parts 22 and 23 are heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in which they come into contact is lower than the partial pressure of oxygen in the atmosphere. This allows oxygen atoms from the oxide film on the surface of the particles constituting the compacted powder to diffuse into the interior of the particles, making the oxide film on the surface of the particles thinner. Therefore, the conductivity between the particles constituting the compacted powder is improved, and the resistivity of the thermoelectric conversion material parts 22 and 23 can be lowered. Furthermore, since the thermoelectric conversion material parts 22 and 23 are sealed by the sealing part 30 such that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material parts 22 and 23 is lower than the partial pressure of oxygen in the atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder is suppressed, and the resistivity of the thermoelectric conversion material parts 22 and 23 can be maintained at a low level. Therefore, according to this manufacturing method of the thermoelectric conversion element 21, it is possible to manufacture a thermoelectric conversion element 21 that can improve the efficiency of thermoelectric conversion.

[0050] Furthermore, since the method for manufacturing thermoelectric materials according to this application involves mechanical alloying in a reducing atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder can be suppressed. By using the compacted powder obtained in this way, a thermoelectric material with improved thermoelectric conversion efficiency can be provided.

[0051] In this embodiment, since mechanical alloying is performed in a reducing atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder can be reduced. By using the compacted powder obtained in this way, a thermoelectric conversion element 21 with improved thermoelectric conversion efficiency can be manufactured.

[0052] In this embodiment, mechanical alloying is carried out in a mixed gas of hydrogen and nitrogen with a hydrogen content of 4% by volume or less. Therefore, the formation of an oxide film in the process of obtaining the powder can be suppressed.

[0053] The method for manufacturing the thermoelectric conversion element 21 may include the steps of: obtaining an amorphous semiconductor material powder by performing mechanical alloying; forming a thermoelectric conversion material part 23 made of compacted powder by compacting the amorphous powder; heating the thermoelectric conversion material part 23 while maintaining a state in which the partial pressure of oxygen in the atmosphere in which the thermoelectric conversion material part 23 is in contact is lower than the partial pressure of oxygen in the atmosphere; and sealing the thermoelectric conversion material part 23 with a sealing part 30 such that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material part 23 is lower than the partial pressure of oxygen in the atmosphere.

[0054] In this method for manufacturing the thermoelectric conversion element 21, the thermoelectric conversion material 23 is heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in which the thermoelectric conversion material 23 comes into contact is lower than the partial pressure of oxygen in the atmosphere. This allows oxygen atoms from the oxide film on the surface of the particles constituting the compacted powder to diffuse into the interior of the particles, making the oxide film on the surface of the particles thinner. Therefore, the conductivity between the particles constituting the compacted powder is improved, and the resistivity of the thermoelectric conversion material 23 can be lowered. Furthermore, since the thermoelectric conversion material 23 is sealed by the sealing part 30 such that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material 23 is lower than the partial pressure of oxygen in the atmosphere, the formation of an oxide film on the surface of the particles constituting the compacted powder is suppressed, and the resistivity of the thermoelectric conversion material 23 can be maintained at a low level. Thus, this method for manufacturing the thermoelectric conversion element 21 makes it possible to manufacture a thermoelectric conversion element 21 that can improve the efficiency of thermoelectric conversion.

[0055] In this embodiment, the thermoelectric conversion element 21 includes a sealing portion 30 that seals the thermoelectric conversion material portions 22 and 23. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material portions 22 and 23 is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing portion 30. Therefore, the formation of an oxide film on the surface of the particles constituting the compacted powder can be suppressed compared to the atmosphere. As a result, the increase in the resistivity of the thermoelectric conversion material portions 22 and 23 can be suppressed, and a high ZT can be maintained. With such a thermoelectric conversion element 21, the efficiency of thermoelectric conversion can be improved.

[0056] In this embodiment, the thermoelectric conversion material sections 22 and 23 are made of an amorphous semiconductor material. Specifically, the thermoelectric conversion material sections 22 and 23 are made of compacted powder of an amorphous semiconductor material. Since semiconductor materials have a larger band gap than conductive materials, the Seebeck coefficient can be increased. The amorphous semiconductor material can lower the thermal conductivity. Therefore, the dimensionless figure of merit ZT can be increased in the thermoelectric conversion material sections 22 and 23 included in the thermoelectric conversion element 21. As a result, the efficiency of thermoelectric conversion can be improved.

[0057] In this embodiment, the pressure within region 35 is 1 × 10 -7 Pa or more 1×10 -2 The pressure is below Pa. Therefore, the amount of oxygen in region 35 can be reduced, suppressing the formation of an oxide film on the surface of the particles constituting the compacted powder. As a result, the low resistivity of the thermoelectric conversion material parts 22 and 23 can be maintained, ensuring high thermoelectric conversion efficiency.

[0058] The semiconductor material constituting the thermoelectric conversion material section 23 has an n-type conductivity and includes Si, Ge, Fe, and P. With such a thermoelectric conversion element 21, it is possible to reliably maintain a low resistivity state of the thermoelectric conversion material section 23 and improve thermoelectric efficiency.

[0059] In the above embodiment, the semiconductor material is said to have Si and Ge as the base elements, but it is not limited to this and may be a SiGe-based material. A SiGe-based material means SiGe and a material in which at least a part of Si and Ge in SiGe is replaced with another element, such as C or Sn. The semiconductor material may also be a MnSi-based material. A MnSi-based material means MnSi and a material in which at least a part of Mn and Si in MnSi is replaced with another element, such as Al or W. Furthermore, the semiconductor material may also be a SnSe-based material. A SnSe-based material means SnSe and a material in which at least a part of Sn and Se in SnSe is replaced with another element. Furthermore, the semiconductor material may also be a Cu2Se-based material. A Cu2Se-based material means Cu2Se and a material in which at least a part of Cu and Se in Cu2Se is replaced with another element. Also, the configuration may not include the first additive element. The configuration may not include the second additive element.

[0060] Furthermore, in the above embodiment, the thermoelectric conversion material sections 22 and 23 are made of semiconductor materials, specifically, they are made of compacted powder of an amorphous semiconductor material. However, the material constituting the thermoelectric conversion material sections 22 and 23 may be, for example, a conductive material, and any material having a band gap is acceptable. Semiconductor materials containing amorphous material are even more preferable. By doing so, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material sections 22 and 23 can be suppressed compared to air. As a result, the increase in the resistivity of the thermoelectric conversion material sections 22 and 23 can be suppressed, and ZT can be maintained at a high level. With such a thermoelectric conversion element 21, the efficiency of thermoelectric conversion can be improved.

[0061] In the above embodiment, the thermoelectric conversion material parts 22 and 23 are heated (S13) while maintaining a state in which the partial pressure of oxygen in the atmosphere in which they come into contact is lower than the partial pressure of oxygen in the atmosphere. Then, the thermoelectric conversion material parts 22 and 23 are sealed with the sealing part 30 so that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material parts 22 and 23 is lower than the partial pressure of oxygen in the atmosphere (S14). However, steps S13 and S14 may be reversed. That is, the thermoelectric conversion material parts 22 and 23 are sealed with the sealing part 30 so that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material parts 22 and 23 is lower than the partial pressure of oxygen in the atmosphere (S14). Then, the thermoelectric conversion material parts 22 and 23 are heated (S13) while maintaining a state in which the partial pressure of oxygen in the atmosphere in which they come into contact is lower than the partial pressure of oxygen in the atmosphere. In this case, the sealing portion 30 should be made of a material that is durable even when heated to high temperatures. Alternatively, the thermoelectric conversion material portion 23 may be heated (S13) while maintaining a state in which the partial pressure of oxygen in the atmosphere in which the obtained thermoelectric conversion material portion 22, 23 comes into contact is lower than the partial pressure of oxygen in the atmosphere, and the thermoelectric conversion material portion 22, 23 may be sealed (S14) by the sealing portion 30 so that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material portion 22, 23 is lower than the partial pressure of oxygen in the atmosphere. In other words, steps S13 and S14 may be performed in parallel.

[0062] In the above embodiment, the pressure within region 35 is 1 × 10⁻⁶ -7 Pa or more 1×10 -2 Although the limit is set to Pa or less, the partial pressure of oxygen in the atmosphere within region 35 is not limited to this, but is 2 × 10⁻⁶. 5 The Pa value may be less than or equal to Pa. By doing so, the formation of an oxide film on the surface of the particles constituting the compacted powder can be efficiently suppressed. Therefore, the low resistivity of the thermoelectric conversion material parts 22 and 23 can be maintained, and high thermoelectric conversion efficiency can be ensured.

[0063] In the above embodiment, an inert gas may be sealed within the region 35. By doing so, the formation of an oxide film on the surface of the particles constituting the compacted powder can be more reliably suppressed. Therefore, the low resistivity of the thermoelectric conversion material parts 22 and 23 can be maintained, and high thermoelectric conversion efficiency can be ensured. Examples of inert gases include argon gas and nitrogen gas.

[0064] In the above embodiment, a π-type thermoelectric element was described as an example of the thermoelectric element of the present application, but the thermoelectric element of the present application is not limited to this. The thermoelectric element of the present application may be a thermoelectric element having another structure, such as an I-type (unireg-type) thermoelectric element.

[0065] (Embodiment 2) By electrically connecting multiple π-type thermoelectric conversion elements 21 as described above, a power generation module can be obtained as a thermoelectric conversion module. The power generation module 41, which is a thermoelectric conversion module in this embodiment, has a structure in which multiple π-type thermoelectric conversion elements 21 are connected in series.

[0066] Figures 4 and 5 show an example of the structure of the power generation module 41 in Embodiment 2. For ease of understanding, some components are omitted from the illustration in Figure 4, and their shapes are indicated by dashed lines.

[0067] Referring to Figure 4, the power generation module 41 of this embodiment comprises a p-type thermoelectric conversion material section 22, an n-type thermoelectric conversion material section 23, low-temperature side electrodes 25, 26, high-temperature side electrode 24, low-temperature side insulating substrate 29, high-temperature side insulating substrate 28, and a frame 37. The low-temperature side insulating substrate 29 and the high-temperature side insulating substrate 28 are made of ceramic such as alumina. The thermoelectric conversion material sections 22 and 23 are arranged alternately. The low-temperature side electrodes 25, 26 are arranged in contact with the thermoelectric conversion material sections 22 and 23, similar to the π-type thermoelectric conversion element 21 described above. The high-temperature side electrode 24 is arranged in contact with the thermoelectric conversion material sections 22 and 23, similar to the π-type thermoelectric conversion element 21 described above. The thermoelectric conversion material section 22 is connected to an adjacent thermoelectric conversion material section 23 on one side by a common high-temperature side electrode 24. Furthermore, the thermoelectric conversion material section 22 is connected to the adjacent thermoelectric conversion material section 23 on a side different from the one described above by common low-temperature side electrodes 25 and 26. In this way, all thermoelectric conversion material sections 22 and 23 are connected in series.

[0068] The low-temperature side insulating substrate 29 is positioned on the side opposite to the side of the plate-shaped low-temperature side electrodes 25 and 26 that contacts the thermoelectric conversion material portion 22 and thermoelectric conversion material portion 23. One low-temperature side insulating substrate 29 is provided for each of the multiple (all) low-temperature side electrodes 25 and 26. The high-temperature side insulating substrate 28 is positioned on the side opposite to the side of the plate-shaped high-temperature side electrode 24 that contacts the thermoelectric conversion material portion 22 and thermoelectric conversion material portion 23. One high-temperature side insulating substrate 28 is provided for each of the multiple (all) high-temperature side electrodes 24.

[0069] The frame 37 is composed of a frame-shaped member having a certain thickness that conforms to the outer shape of the low-temperature side insulating substrate 29. The frame 37 is rectangular in shape. The material of the frame 37 is, for example, silicone resin. The frame 37 is installed so as to be sandwiched between the low-temperature side insulating substrate 29 and the high-temperature side insulating substrate 28. In this case, the frame 37 is joined to the low-temperature side insulating substrate 29 and the high-temperature side insulating substrate 28, respectively. The thermoelectric conversion material parts 22, 23, the low-temperature side electrodes 25, 26, and the high-temperature side electrode 24 are arranged within the region 35 surrounded by the low-temperature side insulating substrate 29, the high-temperature side insulating substrate 28, and the frame 37. The sealing part 30 provided in the thermoelectric conversion element 21 in this embodiment is composed of the low-temperature side insulating substrate 29, the high-temperature side insulating substrate 28, and the frame 37. The pressure within the region 35 is, for example, 1 × 10⁻¹⁰ -7 Pa or more 1×10 -2 It is below Pa (vacuum).

[0070] Wirings 42 and 43 are connected to the high-temperature side electrode 24 or low-temperature side electrode 25, 26 that contact the thermoelectric conversion material section 22 or thermoelectric conversion material section 23 located at both ends of the series-connected thermoelectric conversion material section 22 and thermoelectric conversion material section 23. When a temperature difference is formed such that the high-temperature side insulating substrate 28 is at a high temperature and the low-temperature side insulating substrate 29 is at a low temperature, current flows in the direction of arrow I through the series-connected thermoelectric conversion material section 22 and thermoelectric conversion material section 23, similar to the case of the π-type thermoelectric conversion element 21. In this way, power generation by thermoelectric conversion using the temperature difference is achieved in the power generation module 41.

[0071] The power generation module 41 described above includes a plurality of the thermoelectric conversion elements 21 described above. Here, by including a plurality of the thermoelectric conversion elements 21 of the present invention, which have excellent thermoelectric conversion efficiency, a power generation module can be obtained that has improved thermoelectric conversion efficiency. In addition, an inert gas may be sealed in the region 35 shown in Figure 4 described above.

[0072] (Embodiment 3) In the above embodiment, the sealing portion 30 was configured to surround the thermoelectric conversion material portions 22 and 23 with the region 35 in between, but it is not limited to this and may have the following configurations. The power generation module 41 in Embodiment 3 basically has the same configuration as in Embodiment 2 and produces the same effects. However, the power generation module 41 in Embodiment 3 differs from that in Embodiment 2 in that the sealing portion 30 is composed of a sealing material 38 that fills the region 35.

[0073] Figure 6 shows an example of the structure of a power generation module in Embodiment 3. Referring to Figure 6, the module comprises thermoelectric conversion material sections 22 and 23 made of a material having a band gap, a high-temperature side electrode 24 as a first electrode positioned in contact with the thermoelectric conversion material sections 22 and 23, a low-temperature side electrode as a second electrode positioned in contact with the thermoelectric conversion material sections 22 and 23 but separated from the high-temperature side electrode 24, and a sealing section 30 that seals the thermoelectric conversion material sections 22 and 23. The sealing section 30 is composed of a sealing material 38 that fills a region 35. For example, epoxy resin is selected as the sealing material 38. The sealing material 38 is composed, for example, as follows: a frame 37 is bonded to a low-temperature side insulating substrate 29 and the low-temperature side electrodes 25 and 26, the thermoelectric conversion material sections 22 and 23, and the high-temperature side electrode 24 are placed on the low-temperature side insulating substrate 29. Subsequently, the gaps between the low-temperature electrodes 25, 26, the thermoelectric conversion material parts 22, 23, and the high-temperature electrode 24 within region 35 are filled with uncured epoxy resin or the like, and then cured. In this way, a sealing material 38 made of cured epoxy resin is formed. In this case, there is no gas around the thermoelectric conversion material parts 22, 23, and therefore no oxygen molecules are present. Thus, the partial pressure of oxygen in the region surrounding the thermoelectric conversion material parts 22, 23 is 0. That is, in the thermoelectric conversion element 21 according to the present invention, the substance placed in region 35 surrounding the thermoelectric conversion material parts 22, 23 may be a gas or a solid such as the sealing material 38. Such a sealing material 38 can suppress contact between the thermoelectric conversion material parts 22, 23 and oxygen molecules. As a result, the formation of an oxide film on the surface of the particles constituting the compacted powder can be suppressed. Therefore, it is possible to maintain a low resistivity state of the thermoelectric conversion material parts 22, 23 and ensure high thermoelectric conversion efficiency.

[0074] (Embodiment 4) Next, a light sensor will be described as another embodiment utilizing the power generation module 41 according to Embodiment 2. Figure 7 shows an example of the structure of a light sensor. Referring to Figure 7, the light sensor 44 comprises the power generation module 41 described above, a cap 45 covering the power generation module 41, and a disc-shaped base 46. The power generation module 41 is mounted on one surface 48 of the base 46. The cap 45 includes a cylindrical portion 47a and a lid portion 47b covering an opening on one side of the cylindrical portion 47a. The cap 45 is mounted on one surface 48 of the base 46 so as to cover the power generation module 41. The lid portion 47b is provided with transparent glass 49 that lets in light. Wirings 42 and 43 from the power generation module 41 penetrate the base 46 in the thickness direction, enabling output to the outside. In this embodiment, the power generation module 41 includes an absorber 50 that absorbs light energy. The absorber 50 is positioned in contact with the high-temperature side insulating substrate 28 on the side facing the glass 49. In Figure 7, the absorber 50 is schematically illustrated. The high-temperature side insulating substrate 28 included in the power generation module 41 is connected to the absorber 50. That is, the high-temperature side electrode 24, which is the first electrode included in the power generation module 41, is connected to the absorber 50 via the high-temperature side insulating substrate 28.

[0075] Light enters the cylindrical portion 47a through the glass 49 from the direction indicated by the arrow in Figure 7, and the absorber 50 in the power generation module 41 is irradiated with light. When the absorber 50 in the power generation module 41 absorbs light energy due to the incidence of light, a temperature difference is generated between the high-temperature side insulating substrate 28 and the low-temperature side insulating substrate 29 that are in contact with the absorber 50. Due to the thermoelectric conversion material section 22 and thermoelectric conversion material section 23 connected in series, current flows in the same direction as in the case of the π-type thermoelectric conversion element 21.

[0076] In the optical sensor 44 of this embodiment, the efficiency of thermoelectric conversion is improved in the thermoelectric conversion element 21. Therefore, a highly sensitive optical sensor can be provided.

[0077] In this embodiment, the optical sensor 44 utilizes the power generation module 41 shown in Figure 4 above, but it is not limited to this, and the following configuration may also be adopted. That is, for example, the power generation module 41 may be configured without a frame 37, and the power generation module 41 with the thermoelectric conversion material parts 22 and 23 not sealed may be arranged as shown in Figure 7. This is then sealed by the cap 45 and base 46, for example, when the pressure is 1 × 10 -7 Pa or more 1×10 -2 The thermoelectric element is sealed under conditions of Pa or less (vacuum). In this case, the cap 45 and base 46 constitute the sealing portion 30. That is, the thermoelectric element 21 is configured to include a cap 45 and a base 46 as the sealing portion 30. By doing so, the formation of an oxide film on the surface of the materials constituting the thermoelectric material portions 22 and 23 is suppressed more than in air, and a highly sensitive optical sensor 44 can be obtained.

[0078] Furthermore, the light sensor 44 may also use a thermoelectric conversion element 21, as shown in Figure 1, which comprises a pair of p-type and n-type thermoelectric conversion material sections 22 and 23, instead of the power generation module 41 shown in Figure 7. In this case, an absorber 50 that absorbs light energy is provided on the high-temperature side electrode 24. Then, the cap 45 and base 46 reduce the pressure to 1 × 10⁻⁶ -7 Pa or more 1×10 -2 The thermoelectric element is sealed in a state of Pa or less (vacuum). In this case as well, the thermoelectric element 21 is configured to include a cap 45 and a base 46 as the sealing part 30. By doing so, the formation of an oxide film on the surface of the materials constituting the thermoelectric material parts 22 and 23 is suppressed more than in air, and a highly sensitive optical sensor 44 can be obtained.

[0079] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0080] 21 π-type thermoelectric element, 22,23 thermoelectric material section, 24 high-temperature side electrode, 25,26 low-temperature side electrode, 27,42,43 wiring, 28 high-temperature side insulating substrate, 29 low-temperature side insulating substrate, 30 sealing section, 31,32,33,34 end section, 35 region, 36a,36b,36c,36d arrows, 37 frame, 38 sealing material, 41 thermoelectric module, 44 light sensor, 45 cap, 46 base, 47a cylindrical section, 47b lid section, 48 surface, 49 glass, 50 absorber.

Claims

1. a thermoelectric conversion material portion made of a material having a band gap; a first electrode disposed in contact with the thermoelectric conversion material portion; a second electrode in contact with the thermoelectric conversion material portion and spaced apart from the first electrode; a sealing portion that seals the thermoelectric conversion material portion, A thermoelectric conversion element, wherein the partial pressure of oxygen in the region surrounding the thermoelectric conversion material portion is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing portion.

2. 2. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material portion is made of a semiconductor material containing an amorphous phase.

3. 3. The thermoelectric conversion element according to claim 2, wherein the semiconductor material has n-type conductivity and contains Si, Ge, Fe, and P.

4. the sealing portion surrounds the thermoelectric conversion material portion with the region interposed therebetween, The partial pressure of oxygen in the atmosphere in the region is 2×10 5 4. The thermoelectric conversion element according to claim 1, wherein the thermal conductivity is 0.05 Pa or less.

5. The pressure in the region is 1×10 -2 4. The thermoelectric conversion element according to claim 1, wherein the thermal conductivity is 0.05 Pa or less.

6. 6. The thermoelectric conversion element according to claim 4, wherein an inert gas is sealed in the region.

7. 4. The thermoelectric conversion element according to claim 1, wherein the sealing portion is made of a sealing material that fills the region.

8. 8. A thermoelectric conversion module comprising a plurality of thermoelectric conversion elements according to claim 1.

9. an absorber that absorbs light energy; 8. An optical sensor comprising: the thermoelectric conversion element according to claim 1, wherein the first electrode is connected to the absorber.

10. performing mechanical alloying in a reducing atmosphere to obtain powder of an amorphous semiconductor material; and compressing the powder to form a green compact.

11. 11. The method for producing a thermoelectric conversion material according to claim 10, wherein the mechanical alloying is carried out in a mixed gas of hydrogen and nitrogen, the hydrogen content of which is 4% by volume or less.

12. performing mechanical alloying to obtain a powder of an amorphous semiconductor material; a step of compressing the powder to form a thermoelectric conversion material part made of a powder compact; heating the thermoelectric conversion material part while maintaining a state in which the partial pressure of oxygen in an atmosphere in contact with the thermoelectric conversion material part is lower than the partial pressure of oxygen in the air; and sealing the thermoelectric conversion material portion with a sealing portion so that the partial pressure of oxygen in a region surrounding the thermoelectric conversion material portion is lower than the partial pressure of oxygen in the atmosphere.

13. 13. The method for producing a thermoelectric conversion element according to claim 12, wherein the mechanical alloying is carried out in a reducing atmosphere.

14. 14. The method for producing a thermoelectric conversion element according to claim 12, wherein the mechanical alloying is carried out in a mixed gas of hydrogen and nitrogen, the hydrogen content of which is 4% by volume or less.

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