Optical Sensor

Abstract

To provide an optical sensor with improved thermoelectric conversion efficiency, a method for manufacturing a thermoelectric conversion material, and a method for manufacturing thermoelectric conversion element.SOLUTION: An optical sensor includes a thermoelectric conversion material unit made of a material having a band gap, a first electrode placed in contact with a thermoelectric conversion material, a second electrode that is in contact with the thermoelectric conversion material unit and is located apart from the first electrode, and a sealing unit that seals the thermoelectric conversion material unit, and the partial pressure of oxygen in a region surrounding the thermoelectric conversion material unit is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing unit. By suppressing the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material unit more than in the atmosphere, it is possible to suppress an increase in resistivity of the thermoelectric conversion material unit and improve thermoelectric conversion efficiency.SELECTED DRAWING: Figure 7

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 to Japanese Patent Application No. 2018-164419, filed on September 3, 2018. All contents of the Japanese patent application are incorporated herein by reference. [Background technology]

[0002] In recent years, renewable energy has been attracting attention as a clean energy source to replace fossil fuels such as oil. Renewable energy includes power generation using solar, hydroelectric, and wind power, as well as energy obtained by thermoelectric conversion using temperature differences. In thermoelectric conversion, heat is directly converted into electricity, so no extra waste is generated during the conversion. Thermoelectric conversion does not require a driving unit such as a motor, making it easy to maintain the equipment.

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

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

[0005] As a thermoelectric conversion material, a technology has been reported in which Si, Ge, and Au are laminated, and then the resulting laminate is heat-treated to form Au nanoparticles in SiGe (silicon germanium) (e.g., Non-Patent Document 1). As a thermoelectric conversion material, a technology has been reported in which Si / GeB is used (e.g., Non-Patent Document 2).

[0006] Patent Document 1 discloses a thermoelectric conversion material that includes nanoparticles that contain a matrix element and a heterogeneous element different from the matrix element in a matrix made of a semiconductor material constituted by the matrix 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 Summary of the Invention [Problem to be solved by the invention]

[0009] [Problem that this disclosure aims to solve] 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. If the resistivity, which is the reciprocal of the electrical conductivity, of the thermoelectric conversion material provided in the thermoelectric conversion element can be kept low, the efficiency of thermoelectric conversion can be improved.

[0010] Therefore, one of the objects is to provide 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, which have improved thermoelectric conversion efficiency. [Means for solving the problem]

[0011] A 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 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 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. Effect of the Invention

[0012] [Effects of this disclosure] According to the thermoelectric conversion element of the present disclosure, the efficiency of thermoelectric conversion can be improved. [Brief description of the drawings]

[0013] [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 the first embodiment. [Diagram 2] FIG. 2 is a flowchart showing a typical manufacturing process for a thermoelectric conversion element. [Diagram 3] FIG. 3 is a graph showing the relationship between temperature and resistivity in a thermoelectric conversion material portion. [Figure 4] FIG. 4 is a diagram showing an example of the structure of the power generation module according to the second embodiment. In FIG. [Diagram 5] FIG. 5 is a diagram showing an example of the structure of the power generation module according to the second embodiment. In FIG. [Figure 6] FIG. 6 is a diagram showing an example of the structure of the power generation module according to the third embodiment. In FIG. [Figure 7] FIG. 7 is a diagram illustrating an example of the structure of an optical sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. The thermoelectric conversion element according to the present disclosure includes a thermoelectric conversion material part made of a material having a band gap, a first electrode arranged in contact with the thermoelectric conversion material part, a second electrode arranged in contact with the thermoelectric conversion material part and spaced apart from the first electrode, and a sealing part that seals the thermoelectric conversion material part. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material part is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing part.

[0015] The thermoelectric conversion element includes a sealing portion that seals the 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 lower 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 more than in the atmosphere. As a result, an increase in the resistivity of the thermoelectric conversion material portion can be suppressed, and ZT can be maintained high. With such a thermoelectric conversion element, the efficiency of thermoelectric conversion can be improved.

[0016] In the thermoelectric conversion element, the thermoelectric conversion material portion may be made of a semiconductor material containing an amorphous phase. The semiconductor material has a larger band gap than the conductive material, so that the Seebeck coefficient can be increased. The semiconductor material containing an amorphous phase can reduce the thermal conductivity. 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.

[0017] In the thermoelectric conversion element, the sealing portion may surround the thermoelectric conversion material portion with the region in between. The partial pressure of oxygen in the atmosphere in the region may be less than 2×10 5 The pressure may be less than or equal to 1 Pa. This makes it possible to efficiently suppress the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material section. Therefore, the resistivity of the thermoelectric conversion material section can be maintained low, and high thermoelectric conversion efficiency can be ensured.

[0018] In the thermoelectric conversion element, the pressure in the region is 1×10 -2 The pressure in the region may be 1×10 Pa or less. This reduces the amount of oxygen in the region, and suppresses the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material section. This maintains a low resistivity state in the thermoelectric conversion material section, ensuring high thermoelectric conversion efficiency. The pressure in the region may be 1×10 -7 It is preferable that the pressure is set to Pa or more.

[0019] In the thermoelectric conversion element, an inert gas may be sealed in the region. This makes it possible to more reliably suppress the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material section. This makes it possible to maintain a low resistivity state of the thermoelectric conversion material section and ensure high thermoelectric conversion efficiency. Examples of the inert gas include argon gas and nitrogen gas.

[0020] In the thermoelectric conversion element, the sealing portion may be made of a sealing material that fills the region. The sealing material can prevent the thermoelectric conversion material portion from coming into contact with oxygen molecules. As a result, the formation of an oxide film on the surface of the material that constitutes the thermoelectric conversion material portion can be prevented. Therefore, the low resistivity of the thermoelectric conversion material portion can be maintained, and high thermoelectric conversion efficiency can be ensured. Examples of materials for the sealing material include epoxy resin.

[0021] In the thermoelectric conversion element, the semiconductor material may have an n-type conductivity and contain Si, Ge, Fe and P. According to such a thermoelectric conversion element, it is possible to reliably maintain a low resistivity state of the thermoelectric conversion material portion and improve the thermoelectric efficiency.

[0022] The thermoelectric conversion module of the present disclosure includes a plurality of the thermoelectric conversion elements. According to the thermoelectric conversion module of the present disclosure, by including a plurality of the thermoelectric conversion elements of the present disclosure, which have excellent thermoelectric conversion efficiency, it is possible to obtain a thermoelectric conversion module with improved thermoelectric conversion efficiency.

[0023] The optical sensor of the present disclosure includes an absorber that absorbs light energy, and the above-described thermoelectric conversion element of the present disclosure, in which a first electrode is connected to the absorber.

[0024] In such an optical sensor, the efficiency of thermoelectric conversion in the thermoelectric conversion element is improved, so that a highly sensitive optical sensor can be provided.

[0025] The method for producing a thermoelectric conversion material according to the present disclosure includes a step of obtaining powder of an amorphous semiconductor material by performing mechanical alloying in a reducing atmosphere, and a step of compressing the amorphous powder to form a green compact.

[0026] According to this method for producing a thermoelectric conversion material, since mechanical alloying is performed in a reducing atmosphere, it is possible to suppress the formation of an oxide film on the surfaces of the grains constituting the powder compact. By using the powder compact thus obtained, it is possible to provide a thermoelectric conversion material with improved thermoelectric conversion efficiency.

[0027] In the method for producing a thermoelectric conversion material, the mechanical alloying may be carried out in a mixed gas of hydrogen and nitrogen, the hydrogen content of which is 4% by volume or less. This makes it possible to suppress the formation of an oxide film in the step of obtaining the powder.

[0028] The manufacturing method of the thermoelectric conversion element disclosed herein includes the steps of performing mechanical alloying to obtain powder of amorphous semiconductor material, compressing the amorphous powder to form a thermoelectric conversion material section consisting of a compact, heating the thermoelectric conversion material section while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the thermoelectric conversion material section is lower than the partial pressure of oxygen in the air, and sealing the thermoelectric conversion material section with a sealing section so that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material section is lower than the partial pressure of oxygen in the air.

[0029] According to the manufacturing method of the thermoelectric conversion element of the present disclosure, the thermoelectric conversion material part is heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the thermoelectric conversion material part is lower than the partial pressure of oxygen in the air, so that the oxygen atoms in the oxide film on the surface of the grains constituting the compact are diffused into the inside of the grains, and the oxide film on the surface of the grains can be made thinner. Therefore, the electrical conductivity between the grains constituting the compact can be improved, and the resistivity of the thermoelectric conversion material part can be reduced. In addition, since the thermoelectric conversion material part is sealed by the sealing part so 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 air, the formation of the oxide film on the surface of the grains constituting the compact can be suppressed, and the resistivity of the thermoelectric conversion material part can be maintained in a low state. Therefore, according to such a manufacturing method of the thermoelectric conversion element, a thermoelectric conversion element capable of improving the efficiency of thermoelectric conversion can be manufactured.

[0030] In the above-mentioned method for producing a thermoelectric conversion element, the mechanical alloying may be performed in a reducing atmosphere. In this way, in the step of obtaining powder of the amorphous semiconductor material, it is possible to suppress the formation of an oxide film on the surface of the grains constituting the compact. Therefore, it is possible to produce a thermoelectric conversion element with a low resistivity of the thermoelectric conversion material portion.

[0031] In the above-mentioned method for producing a thermoelectric conversion element, the mechanical alloying may be performed in a mixed gas of hydrogen and nitrogen, the hydrogen content of which is 4% by volume or less. In this way, it is possible to suppress the formation of an oxide film in the step of obtaining the powder. Therefore, it is possible to produce a thermoelectric conversion element with improved thermoelectric efficiency.

[0032] [Details of the embodiment of the present disclosure] Next, an embodiment of a thermoelectric conversion element according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0033] (Embodiment 1) The configuration of a thermoelectric conversion element according to the first embodiment of the present application will be described. FIG. 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 according to the first embodiment. Referring to FIG. 1, the π-type thermoelectric conversion element 21 includes thermoelectric conversion material parts 22, 23 made of a material having a band gap, specifically, thermoelectric conversion material parts 22, 23 made of a compact of a semiconductor material containing an amorphous phase, a high-temperature side electrode 24 as a first electrode arranged in contact with the thermoelectric conversion material parts 22, 23, low-temperature side electrodes 25, 26 as second electrodes arranged in contact with the thermoelectric conversion material parts 22, 23 and apart from the high-temperature side electrode 24, and a sealing part 30 that seals the thermoelectric conversion material parts 22, 23. In FIG. 1, the sealing part 30 is illustrated generally by a two-dot chain 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.

[0034] The thermoelectric conversion material section 22 is made of a thermoelectric conversion material whose composition has been adjusted so that the conductivity type is, for example, p-type. The conductivity type of the thermoelectric conversion material section 22 is p-type by doping the thermoelectric conversion material constituting the thermoelectric conversion material section 22 with p-type impurities that generate p-type carriers (holes), which are majority carriers.

[0035] The thermoelectric conversion material section 23 is made of a thermoelectric conversion material whose composition has been adjusted so that the conductivity type is, for example, n-type. The conductivity type of the thermoelectric conversion material section 23 is n-type by doping the thermoelectric conversion material constituting the thermoelectric conversion material section 23 with n-type impurities that generate n-type carriers (electrons), which are majority carriers.

[0036] The thermoelectric conversion material section 22 and the thermoelectric conversion material section 23 are arranged side by side with a gap therebetween. The high-temperature side electrode 24 is arranged so as to extend from one end 31 of the thermoelectric conversion material section 22 to one end 32 of the thermoelectric conversion material section 23. The high-temperature side electrode 24 is arranged so as to contact both one end 31 of the thermoelectric conversion material section 22 and one end 32 of the thermoelectric conversion material section 23. The high-temperature side electrode 24 is arranged so as to connect one end 31 of the thermoelectric conversion material section 22 and one end 32 of the thermoelectric conversion material section 23. The high-temperature side electrode 24 is made of a conductive material, for example, a metal. The high-temperature side electrode 24 is in ohmic contact with the thermoelectric conversion material section 22 and the thermoelectric conversion material section 23.

[0037] The low-temperature side electrode 25 is disposed in contact with the other end 33 of the thermoelectric conversion material part 22. The low-temperature side electrode 25 is disposed away from the high-temperature side electrode 24. The low-temperature side electrode 25 is made of a conductive material, for example, a metal. The low-temperature side electrode 25 is in ohmic contact with the thermoelectric conversion material part 22.

[0038] The low-temperature side electrode 26 is disposed in contact with the other end 34 of the thermoelectric conversion material part 23. The low-temperature side electrode 26 is disposed away from the high-temperature side electrode 24 and the low-temperature side electrode 25. The low-temperature side electrode 26 is made of a conductive material, for example, a metal. The low-temperature side electrode 26 is in ohmic contact with the thermoelectric conversion material part 23.

[0039] The wiring 27 is made of a conductor such as a metal, etc. The wiring 27 electrically connects the low temperature side electrode 25 and the low temperature side electrode 26.

[0040] The sealing portion 30 is, for example, a box-shaped member, and 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 by the sealing portion 30 to be lower than the partial pressure of oxygen in the atmosphere. In this embodiment, the pressure in the region 35 is 1×10 -2 Specifically, the pressure in the region 35 is 1×10 -7 Pa or more, 1×10 -2 The pressure is maintained at or below Pa. A vacuum is substantially maintained within the region 35. As the material for the sealing portion 30, for example, a silicone resin is selected.

[0041] In the π-type thermoelectric conversion element 21, when a temperature difference is formed such that, for example, one end 31 of the thermoelectric conversion material part 22 and one end 32 of the thermoelectric conversion material part 23 are at high temperature and the other end 33 of the thermoelectric conversion material part 22 and the other end 34 of the thermoelectric conversion material part 23 are at low temperature, p-type carriers (holes) move from one end 31 side to the other end 33 side in the thermoelectric conversion material part 22. At this time, n-type carriers (electrons) move from one end 32 side to the other end 34 side in the thermoelectric conversion material part 23. As a result, a current flows in the wiring 27 in the direction of the arrow I. In this way, in the π-type thermoelectric conversion element 21, power generation is achieved by thermoelectric conversion using the temperature difference. That is, the π-type thermoelectric conversion element 21 is a power generation element.

[0042] Next, the configuration of the thermoelectric conversion material part 23 will be described. The thermoelectric conversion material part 23 is made of a compact of semiconductor material containing amorphous. In this embodiment, the semiconductor material has Si and Ge as base material elements. The semiconductor material includes a first additive element and a second additive element. The semiconductor material includes Fe as the first additive element. Fe forms a first additional level as a new level in the forbidden band (band gap) of SiGe. The semiconductor material includes P as the second additive element. P forms a second additional level between the first additional level and the conduction band in the forbidden band of SiGe. The Fermi level is adjusted by this second additional level. That is, in the thermoelectric conversion material part 23 in this embodiment, a donor level can be formed by the second additional level. The manufacturing method of the thermoelectric conversion material part 22 is performed in the same manner as above, for example, with the elements used being Si, Ge, Au, and B.

[0043] The thermoelectric conversion element 21 including such thermoelectric conversion material sections 22, 23 is manufactured as follows. FIG. 2 is a flow chart showing typical manufacturing steps for the thermoelectric conversion element 21. First, a method for manufacturing the n-type thermoelectric conversion material section 23 will be described. With reference to FIG. 2, weighed amounts of Si, Ge, Fe and P are placed in a stainless steel pot. In this case, the content ratio of each element is Si, Ge, Fe and P. 63 Ge 24 P 10 The composition is adjusted to be Fe3. The inside of the pot is filled with forming gas, which is a mixed gas of hydrogen and nitrogen with a hydrogen content of 4 volume % or less, to create a reducing atmosphere. Then, amorphous powder in which Fe and P are added to SiGe is obtained by mechanical alloying. That is, the mechanical alloying is performed in a mixed gas of hydrogen and nitrogen with a hydrogen content of 4 volume % or less. In this way, mechanical alloying is performed in a reducing atmosphere to obtain powder of amorphous semiconductor material (S11).

[0044] Next, in a state where the inside of the glove box is filled with nitrogen gas, the obtained powder is filled into a die, and a powder compact is formed by a hot press method. The pressure at this time can be 400 MPa, and the temperature can be 400°C. In this way, the amorphous powder is compressed to form a thermoelectric conversion material part 23 made of a powder compact (S12). In this case, the amorphous powder is compressed while being heated. Note that the powder compact is a sintered body at this time. The steps S11 and S12 show an example of a typical step in the manufacturing method of the thermoelectric conversion material of the present application. That is, the manufacturing method of the thermoelectric conversion material of the present application includes a step of performing mechanical alloying in a reducing atmosphere to obtain powder of an amorphous semiconductor material, and a step of compressing the amorphous powder to form a powder compact. Note that, 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 same process as above is carried out.

[0045] Next, the thermoelectric conversion material part 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 part 23 is lower than the partial pressure of oxygen in the air (S13). -7 Pa or more, 1×10 -2 The thermoelectric conversion material part 23 is placed in an atmosphere (vacuum) having a pressure of 1×10 Pa or less and heated. -7 Pa or more, 1×10 -2 The thermoelectric conversion material portion 22 is cooled in an atmosphere having a pressure of not more than Pa.

[0046] Next, the high temperature side electrode 24, the low temperature side electrodes 25, 26 and the wiring 27 are attached to the thermoelectric conversion material parts 22 and 23, and are sealed with the sealing part 30. Here, the thermoelectric conversion material part 23 is sealed with the sealing part 30 so that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material parts 22, 23 is lower than the partial pressure of oxygen in the atmosphere (S14). In this case, the pressure is 1×10 -7 Pa or more, 1×10 -2In an atmosphere of 0.1 Pa or less, the thermoelectric conversion material part 22 and the thermoelectric conversion material part 23 to which the high temperature side electrode 24, the low temperature side electrodes 25, 26 and the wiring 27 are attached are sealed by the sealing part 30. In this manner, the thermoelectric conversion element 21 including the thermoelectric conversion material parts 22, 23 is obtained.

[0047] Fig. 3 is a graph showing the relationship between temperature and resistivity in the thermoelectric conversion material portion 23. In Fig. 3, the vertical axis represents resistivity (mΩcm) and the horizontal axis represents temperature (°C). The resistivity was measured by a four-terminal method.

[0048] Referring to Figure 3, the pressure is 1×10 -7 Pa or more 1×10 -2 It can be seen that when the material is heated from room temperature as indicated by the arrow 36a and the circle while maintaining the pressure below 1×10 Pa, the resistivity decreases significantly. Specifically, the resistivity, which was 220 mΩcm at room temperature, decreases to 10 mΩcm or less when the temperature exceeds 700°C. -7 Pa or more 1×10 -2 Even when the material is cooled to room temperature as shown by the arrow 36b and the square mark while maintaining the pressure below 1×10 Pa, the resistivity remains at about 10 mΩ cm. The low resistivity is maintained even while the temperature is decreasing. -7 Pa or more 1×10 -2 Even if the temperature is raised to 800°C again as shown by the arrow 36c and the triangle mark while maintaining the pressure below 1×10 Pa, the resistivity remains below 10 mΩcm. -7 Pa or more 1×10 -2 When the pressure is kept below 1×10 Pa and the sample is cooled to room temperature and then exposed to the atmosphere, the resistivity rises to about 110 mΩ cm. -7 Pa or more 1×10 -2 When the temperature is increased as shown by the arrow 36d and the cross mark in a state of less than Pa, the resistivity decreases.

[0049] In this way, the pressure is 1×10 -7 Pa or more 1×10 -2If the pressure is kept below 1×10 Pa, the resistivity can be kept low. On the other hand, if exposed to the air, the resistivity increases. This is thought to be because an oxide film forms on the surface of the grains that make up the green compact when exposed to the air. -7 The reason why the pressure is 1×10 Pa is because a turbo molecular pump was used. By using an ion pump and a cryopump for pressure reduction, the pressure is 1×10 -11 Experiments at pressures above 100 Pa yielded similar results.

[0050] According to the manufacturing method of the thermoelectric conversion element 21 of the present application, the thermoelectric conversion material parts 22, 23 are heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the thermoelectric conversion material parts 22, 23 is lower than the partial pressure of oxygen in the air, so that the oxygen atoms in the oxide film on the surface of the grains constituting the compact are diffused into the inside of the grains, and the oxide film on the surface of the grains can be made thinner. Therefore, the electrical conductivity between the grains constituting the compact can be improved, and the resistivity of the thermoelectric conversion material parts 22, 23 can be reduced. In addition, since the thermoelectric conversion material parts 22, 23 are sealed by the sealing part 30 so that the partial pressure of oxygen in the region surrounding the thermoelectric conversion material parts 22, 23 is lower than the partial pressure of oxygen in the air, the formation of the oxide film on the surface of the grains constituting the compact can be suppressed, and the low resistivity of the thermoelectric conversion material parts 22, 23 can be maintained. Therefore, according to such a manufacturing method of the thermoelectric conversion element 21, a thermoelectric conversion element 21 that can improve the efficiency of thermoelectric conversion can be manufactured.

[0051] Furthermore, according to the method for producing a thermoelectric conversion material of the present application, since mechanical alloying is performed in a reducing atmosphere, it is possible to suppress the formation of an oxide film on the surfaces of the grains constituting the powder compact. By using the powder compact thus obtained, it is possible to provide a thermoelectric conversion material with improved thermoelectric conversion efficiency.

[0052] In this embodiment, since the mechanical alloying is performed in a reducing atmosphere, it is possible to reduce the formation of an oxide film on the surfaces of the grains constituting the green compact. By using the green compact thus obtained, it is possible to manufacture the thermoelectric conversion element 21 having improved thermoelectric conversion efficiency.

[0053] In this embodiment, the mechanical alloying is carried out in a mixed gas of hydrogen and nitrogen, in which the hydrogen content is 4 volume % or less, and therefore the formation of an oxide film in the process of obtaining the powder can be suppressed.

[0054] The manufacturing method of thermoelectric conversion element 21 may include the steps of: obtaining a powder of amorphous semiconductor material by performing mechanical alloying; compressing the amorphous powder to form a thermoelectric conversion material section 23 consisting of a compact; heating thermoelectric conversion material section 23 while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with thermoelectric conversion material section 23 is lower than the partial pressure of oxygen in the air; and sealing thermoelectric conversion material section 23 with sealing section 30 so that the partial pressure of oxygen in the region surrounding thermoelectric conversion material section 23 is lower than the partial pressure of oxygen in the air.

[0055] According to such a manufacturing method of the thermoelectric conversion element 21, the thermoelectric conversion material part 23 is heated while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the thermoelectric conversion material part 23 is lower than the partial pressure of oxygen in the air, so that the oxygen atoms in the oxide film on the surface of the grains constituting the compact are diffused into the inside of the grains, and the oxide film on the surface of the grains can be thinned. Therefore, the electrical conductivity between the grains constituting the compact can be improved, and the resistivity of the thermoelectric conversion material part can be reduced. In addition, since the thermoelectric conversion material part 23 is sealed by the sealing part 30 so 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 air, the formation of the oxide film on the surface of the grains constituting the compact can be suppressed, and the resistivity of the thermoelectric conversion material part 23 can be maintained at a low state. Therefore, according to such a manufacturing method of the thermoelectric conversion element 21, a thermoelectric conversion element 21 capable of improving the efficiency of thermoelectric conversion can be manufactured.

[0056] In this embodiment, the thermoelectric conversion element 21 includes a sealing portion 30 that seals the thermoelectric conversion material portions 22, 23. The partial pressure of oxygen in the region surrounding the thermoelectric conversion material portions 22, 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 grains constituting the compact can be suppressed more than in the atmosphere. As a result, an increase in the resistivity of the thermoelectric conversion material portions 22, 23 can be suppressed, and a high ZT can be maintained. According to such a thermoelectric conversion element 21, the efficiency of thermoelectric conversion can be improved.

[0057] In this embodiment, the thermoelectric conversion material parts 22 and 23 are made of a semiconductor material containing an amorphous phase. Specifically, the thermoelectric conversion material parts 22 and 23 are made of a compact of a semiconductor material containing an amorphous phase. Since the band gap of the semiconductor material is larger than that of the conductive material, the Seebeck coefficient can be increased. The thermal conductivity can be reduced by the semiconductor material containing an amorphous phase. Therefore, the dimensionless figure of merit ZT can be increased in the thermoelectric conversion material parts 22 and 23 included in the thermoelectric conversion element 21. As a result, the efficiency of thermoelectric conversion can be improved.

[0058] In this embodiment, the pressure in region 35 is 1×10 -7 Pa or more 1×10 -2 Pa or less. Therefore, the amount of oxygen in region 35 can be reduced, and the formation of an oxide film on the surfaces of the grains constituting the powder compact can be suppressed. As a result, the low resistivity state of thermoelectric conversion material portions 22, 23 can be maintained, and high thermoelectric conversion efficiency can be ensured.

[0059] The semiconductor material constituting the thermoelectric conversion material section 23 has an n-type conductivity and contains Si, Ge, Fe and P. According to such a thermoelectric conversion element 21, it is possible to reliably maintain the low resistivity of the thermoelectric conversion material section 23 and improve the thermoelectric efficiency.

[0060] In the above embodiment, the semiconductor material is assumed to have Si and Ge as base material elements, but is not limited thereto and may be a SiGe-based material. The SiGe-based material means a material in which at least one of Si and Ge in SiGe and SiGe is partially replaced with another element, for example, C, Sn, etc. The semiconductor material may also be a MnSi-based material. The MnSi-based material means a material in which at least one of Mn and Si in MnSi is partially replaced with another element, for example, Al, W, etc. The semiconductor material may also be a SnSe-based material. The SnSe-based material means a material in which at least one of Sn and Se in SnSe and SnSe is partially replaced with another element. The semiconductor material may also be a Cu2Se-based material. The Cu2Se-based material means a material in which at least one of Cu and Se in Cu2Se and Cu2Se is partially replaced with another element. The semiconductor material may also be a configuration that does not include a first additive element. The semiconductor material may also be a configuration that does not include a second additive element.

[0061] In the above embodiment, the thermoelectric conversion material parts 22, 23 are made of a semiconductor material, specifically, the thermoelectric conversion material parts 22, 23 are made of a compact of a semiconductor material containing an amorphous phase. However, the thermoelectric conversion material parts 22, 23 may be made of a conductive material, for example, as long as the material has a band gap. A semiconductor material containing an amorphous phase is more preferable. This also makes it possible to suppress the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material parts 22, 23 compared to the atmosphere. As a result, the increase in resistivity of the thermoelectric conversion material parts 22, 23 can be suppressed, and ZT can be maintained high. According to such a thermoelectric conversion element 21, it is possible to improve the efficiency of thermoelectric conversion.

[0062] 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 contact with the obtained thermoelectric conversion material parts 22 and 23 is lower than the partial pressure of oxygen in the air, and then the thermoelectric conversion material parts 22 and 23 are sealed by 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 air (S14). However, the steps of S13 and S14 may be reversed. That is, after sealing the thermoelectric conversion material parts 22 and 23 by 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 air (S14), the thermoelectric conversion material parts 22 and 23 may be heated (S13) while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the obtained thermoelectric conversion material parts 23 is lower than the partial pressure of oxygen in the air. In this case, it is preferable to use a material that is durable even when heated to a high temperature for the sealing portion 30. Alternatively, the thermoelectric conversion material portions 22, 23 may be heated (S13) while maintaining a state in which the partial pressure of oxygen in the atmosphere in contact with the obtained thermoelectric conversion material portions 22, 23 is lower than the partial pressure of oxygen in the air, and the thermoelectric conversion material portions 22, 23 may be sealed with the sealing portion 30 (S14) so ​​that the partial pressure of oxygen in the region 35 surrounding the thermoelectric conversion material portions 22, 23 becomes lower than the partial pressure of oxygen in the air. That is, the steps S13 and S14 may be performed in parallel.

[0063] In the above embodiment, the pressure in region 35 is 1×10 -7 Pa or more 1×10 -2 However, the partial pressure of oxygen in the atmosphere in the region 35 is not limited to this, and may be 2×10 5 The pressure may be less than or equal to 1 Pa. This makes it possible to efficiently suppress the formation of an oxide film on the surfaces of the grains constituting the powder compact. As a result, the resistivity of the thermoelectric conversion material parts 22, 23 can be maintained at a low level, and high thermoelectric conversion efficiency can be ensured.

[0064] In the above embodiment, an inert gas may be enclosed within the region 35. In this way, the formation of an oxide film on the surfaces of the grains constituting the compact can be more reliably suppressed. This makes it possible to maintain a low resistivity state of the thermoelectric conversion material parts 22, 23 and ensure high thermoelectric conversion efficiency. Examples of the inert gas include argon gas and nitrogen gas.

[0065] In the above embodiment, a π-type thermoelectric conversion element has been described as an example of the thermoelectric conversion element of the present application, but the thermoelectric conversion element of the present application is not limited to this. The thermoelectric conversion element of the present application may be a thermoelectric conversion element having another structure, such as an I-type (uni-leg type) thermoelectric conversion element.

[0066] (Embodiment 2) A power generation module serving as a thermoelectric conversion module can be obtained by electrically connecting a plurality of the above-described π-type thermoelectric conversion elements 21. The power generation module 41, which is a thermoelectric conversion module of this embodiment, has a structure in which a plurality of π-type thermoelectric conversion elements 21 are connected in series.

[0067] 4 and 5 are diagrams showing an example of the structure of a power generation module 41 in embodiment 2. To facilitate understanding, some components are omitted from illustration in Fig. 4, and their shapes are indicated by two-dot chain lines.

[0068] Referring to FIG. 4, the power generation module 41 of the present embodiment includes a p-type thermoelectric conversion material portion 22, an n-type thermoelectric conversion material portion 23, low-temperature side electrodes 25, 26, a high-temperature side electrode 24, a low-temperature side insulator substrate 29, a high-temperature side insulator substrate 28, and a frame 37. The low-temperature side insulator substrate 29 and the high-temperature side insulator substrate 28 are made of ceramic such as alumina. The thermoelectric conversion material portion 22 and the thermoelectric conversion material portion 23 are arranged alternately. The low-temperature side electrodes 25, 26 are arranged in contact with the thermoelectric conversion material portion 22 and the thermoelectric conversion material portion 23 in the same manner as the above-mentioned π-type thermoelectric conversion element 21. The high-temperature side electrode 24 is arranged in contact with the thermoelectric conversion material portion 22 and the thermoelectric conversion material portion 23 in the same manner as the above-mentioned π-type thermoelectric conversion element 21. The thermoelectric conversion material portion 22 is connected to the thermoelectric conversion material portion 23 adjacent to one side by a common high-temperature side electrode 24. Further, the thermoelectric conversion material section 22 is connected to an adjacent thermoelectric conversion material section 23 on the side other than the one side by common low-temperature side electrodes 25, 26. In this manner, all the thermoelectric conversion material sections 22 and thermoelectric conversion material sections 23 are connected in series.

[0069] The low-temperature side insulator substrate 29 is disposed on the side opposite to the side of the plate-shaped low-temperature side electrodes 25, 26 in contact with the thermoelectric conversion material section 22 and the thermoelectric conversion material section 23. One low-temperature side insulator substrate 29 is disposed for each of the plurality (all) of the low-temperature side electrodes 25, 26. The high-temperature side insulator substrate 28 is disposed on the side opposite to the side of the plate-shaped high-temperature side electrode 24 in contact with the thermoelectric conversion material section 22 and the thermoelectric conversion material section 23. One high-temperature side insulator substrate 28 is disposed for each of the plurality (all) of the high-temperature side electrodes 24.

[0070] The frame 37 is made of a frame-shaped member having a certain thickness that conforms to the outer shape of the low-temperature side insulator substrate 29. The frame 37 is in the shape of a rectangular tube. The frame 37 is made of, for example, silicon resin. The frame 37 is attached so as to be sandwiched between the low-temperature side insulator substrate 29 and the high-temperature side insulator substrate 28. In this case, the frame 37 is joined to each of the low-temperature side insulator substrate 29 and the high-temperature side insulator substrate 28. The thermoelectric conversion material parts 22 and 23, the low-temperature side electrodes 25 and 26, and the high-temperature side electrode 24 are arranged in a region 35 surrounded by the low-temperature side insulator substrate 29, the high-temperature side insulator substrate 28, and the frame 37. The sealing part 30 provided in the thermoelectric conversion element 21 in this embodiment is made of the low-temperature side insulator substrate 29, the high-temperature side insulator substrate 28, and the frame 37. The pressure in the region 35 is, for example, 1×10 -7 Pa or more 1×10 -2 Pa or less (vacuum).

[0071] Wiring 42, 43 is connected to high-temperature side electrode 24 or low-temperature side electrodes 25, 26 in contact with thermoelectric conversion material parts 22 or thermoelectric conversion material parts 23 located at both ends of thermoelectric conversion material parts 22 and thermoelectric conversion material parts 23 connected in series. When a temperature difference is created such that the high-temperature side insulator substrate 28 side is high temperature and the low-temperature side insulator substrate 29 side is low temperature, a current flows in the direction of arrow I through thermoelectric conversion material parts 22 and 23 connected in series, similar to the case of the above-mentioned π-type thermoelectric conversion element 21. In this way, power generation is achieved in power generation module 41 by thermoelectric conversion utilizing the temperature difference.

[0072] The power generating module 41 includes a plurality of the above-mentioned thermoelectric conversion elements 21. Here, the power generating module 41 includes a plurality of the thermoelectric conversion elements 21 of the present application, which have excellent thermoelectric conversion efficiency, and thus it is possible to obtain a power generating module as a thermoelectric conversion module with improved thermoelectric conversion efficiency. Note that an inert gas may be sealed in the region 35 shown in FIG. 4 described above.

[0073] (Embodiment 3) Although the sealing portion 30 in the above embodiment is configured to surround the thermoelectric conversion material portions 22, 23 with the region 35 therebetween, the present invention is not limited to this and may be configured as follows. The power generation module 41 in the third embodiment basically has the same configuration as in the second embodiment and achieves the same effects. However, the power generation module 41 in the third embodiment differs from the second embodiment in that the sealing portion 30 is configured from a sealing material 38 that fills the region 35.

[0074] FIG. 6 is a diagram showing an example of the structure of the power generation module in the third embodiment. Referring to FIG. 6, the power generation module includes thermoelectric conversion material parts 22, 23 made of a material having a band gap, a high-temperature side electrode 24 as a first electrode arranged in contact with the thermoelectric conversion material parts 22, 23, a low-temperature side electrode as a second electrode arranged away from the high-temperature side electrode 24 in contact with the thermoelectric conversion material parts 22, 23, and a sealing part 30 that seals the thermoelectric conversion material parts 22, 23. The sealing part 30 is composed of a sealing material 38 that fills the region 35. For example, an epoxy resin is selected as the sealing material 38. For example, the sealing material 38 is composed as follows. That is, a frame 37 is joined onto a low-temperature side insulating substrate 29, and the low-temperature side electrodes 25, 26, the thermoelectric conversion material parts 22, 23, and the high-temperature side electrode 24 are arranged on the low-temperature side insulating substrate 29. Thereafter, the gaps between the low-temperature side electrodes 25, 26, the thermoelectric conversion material parts 22, 23, and the high-temperature side electrode 24 in the region 35 are filled with uncured epoxy resin or the like, and cured. In this manner, a sealant 38 made of cured epoxy resin is formed. In this case, there is no gas around the thermoelectric conversion material parts 22, 23, and no oxygen molecules exist. Therefore, the partial pressure of oxygen in the region surrounding the thermoelectric conversion material parts 22, 23 is zero. That is, in the thermoelectric conversion element 21 according to the present application, the substance disposed in the region 35 surrounding the thermoelectric conversion material parts 22, 23 may be a gas or a solid such as the sealant 38. Such a sealant 38 can prevent the thermoelectric conversion material parts 22, 23 from coming into contact with oxygen molecules. As a result, the formation of an oxide film on the surface of the grains constituting the compact can be suppressed. Therefore, the low resistivity state of the thermoelectric conversion material parts 22, 23 can be maintained, and high thermoelectric conversion efficiency can be ensured.

[0075] (Embodiment 4) Next, an optical sensor will be described as another embodiment using the power generation module 41 according to the second embodiment. FIG. 7 is a diagram showing an example of the structure of an optical sensor. Referring to FIG. 7, the optical sensor 44 includes the above-mentioned power generation module 41, a cap 45 that covers the power generation module 41, and a disk-shaped base 46. The power generation module 41 is attached to one surface 48 of the base 46. The cap 45 includes a cylindrical portion 47a and a lid portion 47b that covers an opening on one side of the cylindrical portion 47a. The cap 45 is attached to one surface 48 of the base 46 so as to cover the power generation module 41. The lid portion 47b is provided with a transparent glass 49 that takes in light. The wiring 42, 43 from the power generation module 41 penetrates the base 46 in the plate thickness direction to enable output to the outside. In this embodiment, the power generation module 41 includes an absorber 50 that absorbs light energy. The absorber 50 is arranged in contact with the high-temperature side insulator substrate 28 on the surface side facing the glass 49. 7, the absorber 50 is illustrated diagrammatically. 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.

[0076] 7, light passes through glass 49 and enters cylindrical portion 47a, and is irradiated onto absorber 50 in power generation module 41. When absorber 50 in power generation module 41 absorbs light energy due to the incidence of light, a temperature difference occurs between high-temperature side insulator substrate 28 and low-temperature side insulator substrate 29, which are in contact with absorber 50. Thermoelectric conversion material portion 22 and thermoelectric conversion material portion 23, which are connected in series, cause a current to flow in the same direction as in the case of π-type thermoelectric conversion element 21 described above.

[0077] In the optical sensor 44 of the present embodiment, the efficiency of thermoelectric conversion is improved in the thermoelectric conversion element 21. Therefore, it is possible to provide a highly sensitive optical sensor.

[0078] In this embodiment, the optical sensor 44 uses the power generation module 41 shown in Fig. 4 described above, but the present invention is not limited to this and the following configuration may be adopted. That is, for example, the power generation module 41 is configured without the frame body 37, and the power generation module 41 with the thermoelectric conversion material sections 22, 23 not sealed is arranged as shown in Fig. 7. This is then heated by the cap 45 and base 46 until the pressure reaches, for example, 1 x 10 -7 Pa or more 1×10 -2 The sealing is performed with the pressure therein at or below 1 Pa (vacuum). In this case, cap 45 and base 46 form sealing portion 30. That is, thermoelectric conversion element 21 is configured to include cap 45 and base 46 as sealing portion 30. Even in this manner, formation of an oxide film on the surface of the material forming thermoelectric conversion material portions 22, 23 can be suppressed more than in the atmosphere, and a highly sensitive optical sensor 44 can be obtained.

[0079] 1, which includes a pair of p-type and n-type thermoelectric conversion material sections 22, 23, may be used in place of the power generation module 41 shown in FIG. 7. In this case, an absorber 50 that absorbs light energy is provided on the high-temperature side electrode 24. The cap 45 and base 46 are used to reduce the pressure to 1×10 -7 Pa or more 1×10 -2 The thermoelectric conversion element 21 is sealed in a state where the pressure is below 1 Pa (vacuum). That is, in this case as well, the thermoelectric conversion element 21 is configured to include a cap 45 and a base 46 as the sealing portion 30. By doing so, too, the formation of an oxide film on the surface of the material constituting the thermoelectric conversion material portions 22, 23 can be suppressed more than in the atmosphere, and a highly sensitive optical sensor 44 can be obtained.

[0080] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0081] 21 π-type thermoelectric conversion element, 22, 23 thermoelectric conversion material portion, 24 high temperature side electrode, 25, 26 low temperature side electrode, 27, 42, 43 wiring, 28 high temperature side insulator substrate, 29 low temperature side insulator substrate, 30 sealing portion, 31, 32, 33, 34 end portion, 35 area, 36a, 36b, 36c, 36d arrows, 37 frame, 38 sealing material, 41 thermoelectric conversion module, 44 optical sensor, 45 cap, 46 base, 47a cylindrical portion, 47b lid portion, 48 surface, 49 glass, 50 absorber.

Claims

[Claim 1] a thermoelectric conversion element comprising: a thermoelectric conversion material part made of a sintered material having a band gap; a first electrode arranged in contact with the thermoelectric conversion material part; a second electrode arranged in contact with the thermoelectric conversion material part and spaced apart from the first electrode; and a sealing part that seals the thermoelectric conversion material part, wherein a partial pressure of oxygen in a region surrounding the thermoelectric conversion material part is maintained lower than the partial pressure of oxygen in the atmosphere by the sealing part so as to maintain a low resistivity state of the thermoelectric conversion material part; An absorber that absorbs light energy, The first electrode of the thermoelectric conversion element is connected to the absorber.

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