JP2021040066A - Laminate, thermoelectric conversion element, usage method of thermoelectric conversion element, power generation device, waste heat recovery system, and method - Google Patents

Abstract

To provide a laminate applicable to a thermoelectric conversion element capable of obtaining a current only by irradiating with light such as natural light without heating and/or cooling from the outside.SOLUTION: A laminate 10 includes, in this order, a light emission-spin current generation layer 13 capable of transmitting visible light and near-infrared light, absorbing mid-infrared light, and generating a spin current, a spin-orbit interaction spin-current conversion layer 14 arranged in contact with at least a part of the light emission-spin current generation layer 13, and a light absorption layer 15 that absorbs visible light and near-infrared light.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laminate, a thermoelectric conversion element, a method of using the thermoelectric conversion element, a power generation device, an exhaust heat recovery system, and a method.

Thermoelectric conversion elements having a function of converting heat into electric power are known. As one of the thermoelectric conversion elements, an element utilizing the spin Seebeck effect is known. As such a thermoelectric conversion element, Patent Document 1 includes "a magnetic material (20) and an electromotive force (30) formed on one surface (21) of the magnetic material, which is generated in the magnetic material. A spin thermoelectric conversion element in which an electromotive force is induced in the electromotive force by the spin Seebeck effect generated between the magnetic material and the electromotive force due to a temperature gradient, and the electromotive force is Pt. A spin thermoelectric conversion element composed of an alloy containing Fe and Fe, wherein the electromotive force is configured so that the atomic number concentration of Fe is in the range of 40 at% or more and 60 at% or less. . ”Is described.

Japanese Unexamined Patent Publication No. 2017-045662

Generally, in a conventional thermoelectric conversion element utilizing the Seebeck effect, the direction in which an electromotive force is generated is parallel to the direction of the temperature gradient (heat gradient). On the other hand, in the spin Seebeck element, the electromotive force is generated in the direction perpendicular to the temperature gradient. The thermoelectric power generated by the spin Seebeck element is proportional to the length in the direction perpendicular to the temperature gradient. Therefore, by configuring the element so that the length in the direction perpendicular to the temperature gradient becomes long, an electromotive force proportional to the length can be obtained. Compared with the conventional Seebeck element, the spin Seebeck element has advantages in that a large electromotive force can be obtained even if the thickness of the element is reduced and that the area can be easily increased.

While the spin Seebeck element has excellent performance as a thin thermoelectric conversion element, when the element is made thinner, the temperature on the front and back sides of the element tends to be more uniform, and as a result, the temperature gradient required to obtain electric power can be obtained. There was a problem that it was difficult.
Although the above problem can be solved by heating one surface of the thermoelectric conversion element and cooling the other surface, it is not always sufficient in view of energy efficiency.

Therefore, it is an object of the present invention to provide a laminate applicable to a thermoelectric conversion element capable of obtaining an electric current only by irradiating light such as natural light without heating and / or cooling from the outside. And.
Another object of the present invention is to provide a thermoelectric conversion element, a method of using the thermoelectric conversion element, a power generation device, an exhaust heat recovery system, and a method.

As a result of diligent studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by the following configurations.

[1] A light radiation-spin current generation layer capable of transmitting visible light and near-infrared light, absorbing mid-infrared light, and generating a spin current, and the above-mentioned light radiation-spin current generation layer. A laminate having a spin current-current conversion layer having a spin orbital interaction and a light absorbing layer that absorbs visible light and near-infrared light, which are arranged in contact with at least a part of the above. ..
[2] The laminate according to [1], wherein the light radiation-spin current generation layer is a layer containing a magnetic material having the same magnetization direction.
[3] The laminate according to [2], wherein the magnetic material is a magnetic insulator.
[4] The laminate according to [3], wherein the magnetic insulator contains at least one selected from the group consisting of garnet ferrite and spinel ferrite.
[5] The laminate according to any one of [2] to [4], wherein the magnetic material has a coercive force.
[6] The laminate according to any one of [1] to [5], wherein the spin current-current conversion layer contains a metal.
[7] The laminate according to any one of [1] to [6], wherein the spin current-current conversion layer has a thickness of 1 to 100 nm.
[8] It is used to irradiate light from the side of the light radiation-spin current generation layer to obtain at least one selected from the group consisting of spin current and current [1] to [7]. The laminate according to any one of.
[9] A thermoelectric conversion element having the laminate according to any one of [1] to [8].
[10] A method of using a thermoelectric conversion element, which obtains electric power by irradiating the thermoelectric conversion element according to [9] with light.
[11] A power generation device having the thermoelectric conversion element according to [9].
[12] An exhaust heat recovery system including a heating element and the thermoelectric conversion element according to [9] arranged on the heating element.
[13] A member that transmits visible light and near-infrared light and absorbs mid-infrared light is arranged in contact with one main surface of the thermoelectric conversion element, and at least one of the other main surfaces. In the department,
Members that absorb visible light and near-infrared light are placed in contact with each other to generate a thermal gradient along the thickness direction of the thermoelectric conversion element from the main surface on one side to the main surface on the other side. Method.

According to the present invention, it can be applied to a thermoelectric conversion element capable of obtaining an electric current only by irradiating light such as natural light without heating and / or cooling from the outside (hereinafter, "effect of the present invention". Also referred to as "having.") A laminated body can be provided. The present invention can also provide a thermoelectric conversion element, a method of using the thermoelectric conversion element, a power generation device, an exhaust heat recovery system, and a method.

It is a schematic cross-sectional view of the laminated body which concerns on embodiment of this invention. It is a schematic cross-sectional view of the thermoelectric conversion element which concerns on embodiment of this invention. It is a perspective view of the thermoelectric conversion element which concerns on embodiment of this invention. It is a schematic diagram of the power generation apparatus which concerns on embodiment of this invention. It is a schematic diagram of the waste heat recovery system which concerns on embodiment of this invention. It is a schematic diagram of the waste heat recovery system which concerns on embodiment of this invention. It is a schematic diagram of the layer structure of the sample prepared in an Example. It is a photograph of the measuring device used for measuring the electromotive force in the Example. It is a schematic diagram of the measuring apparatus used for measuring the electromotive force in an Example. This is an example of the measurement result of the voltage value when the magnetic field changes from -12 mT to +11 mT according to the applied current. It is a schematic diagram of the arrangement of the sample used for the measurement outdoors. It is the measurement result of the magnitude of the electromotive force in the sunny night and the sunny day when it was measured in the form that the natural light is incident from the GGG substrate side. It is a schematic diagram of the arrangement of the sample used for the measurement outdoors. It is the measurement result of the magnitude of the electromotive force in the sunny night and the sunny day when it was measured in the form in which natural light was incident from the blackbody paint layer side. It is a schematic diagram of the arrangement of the sample used for the measurement indoors. The electromotive force under each condition when the test was performed in different arrangements is shown. It is a schematic diagram of the arrangement of the sample used for the measurement indoors. The electromotive force under each condition when the test was performed in different arrangements is shown.

Hereinafter, the present invention will be described in detail.
The description of the constituent elements described below may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In the present specification, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

[Laminate]
The laminate according to the embodiment of the present invention (hereinafter, also referred to as “the present laminate”) transmits visible light and near-infrared light, absorbs mid-infrared light, and generates a spin current. It has a spin orbital interaction that is arranged such that the possible light radiation-spin flow generation layer is in contact with at least a portion of the light radiation-spin flow generation layer (preferably at 90% or more on an area basis). It is a laminate having a spin current-current conversion layer and a light absorption layer that absorbs visible light and near-infrared light in this order.

FIG. 1 shows a schematic cross-sectional view of this laminated body. The laminate 10 includes a light radiation-spin flow generation layer 13 composed of a light radiation layer 11 and a spin current generation layer 12, a spin flow-current conversion layer 14 arranged in contact with the light radiation-spin flow generation layer 13. It has a light absorbing layer 15.

Next, the thermoelectric power generation function of the laminated body 10 will be described. A case where the laminated body 10 is arranged outdoors and natural light is incident from the light radiating zone 11 side (indicated as “hν” in FIG. 1) will be described.

First, of the natural light incident on the light radiating zone 11, visible light and near-infrared light pass through the light radiating zone 11, and mid-infrared light is absorbed by the light radiating zone 11.
Here, it is generally known that natural light (sunlight observed on the surface of the earth, for example, AM1.5G) contains almost no mid-infrared light. Since the light radiation layer 11 transmits visible light and near-infrared light, which are the main components of natural light, and the natural light contains almost no mid-infrared light, the light radiation layer 11 is irradiated with natural light. It can be considered that there is almost no temperature rise.

On the other hand, since the light radiating zone 11 has a high absorption rate of mid-infrared light, that is, a high emissivity of mid-infrared light, a space having a relatively low temperature from the light radiating zone 11 (in this case, in this case). Heat radiation is likely to occur in space). Therefore, when the light radiating zone 11 is arranged outdoors, it is cooled by the radiative cooling effect. Therefore, the temperature of the light radiation layer 11 tends to be relatively lower than that of the light absorption layer 15 and the like, which will be described later. Therefore, a temperature gradient along the thickness direction of the laminated body (the temperature on the light absorption layer 15 side is high and the temperature on the light radiation layer 11 side is low) is generated between the light absorption layer 15 and the light radiation layer 11. As a result, a large temperature gradient is likely to occur near the interface between the spin current generation layer 12 and the spin current-current conversion layer 14.

The spin current generation layer 12 is a layer that exhibits a spin Seebeck effect that generates electron spins by a heat flow, and generates a spin current according to a temperature gradient (heat gradient) generated by radiative cooling.
This spin current is converted into thermoelectromotive force by the reverse spin Hall effect of the spin current-current conversion layer 14.

The spin current generating layer 12 preferably transmits visible light and near-infrared light in that a laminated body having a more excellent effect of the present invention can be obtained.

The laminated body 10 has a light radiation-spin flow generation layer 13 in which a light radiation layer 11 and a spin current generation layer 12 are laminated, but the configuration of this laminated body is not limited to the above. For example, it may be a light radiation-spin current generating layer composed of one layer that transmits visible and near infrared light, absorbs mid-infrared light, and can generate a spin current.

When the laminate has the light radiation layer 11 and the spin current generation layer 12, the spin current generation layer 12 and the spin current-current conversion layer 14 described later are obtained in that a laminate having a better effect of the present invention can be obtained. It is preferable that they are in contact with each other.

The visible and near-infrared light transmitted through the light radiation-spin current generation layer 13 composed of the light radiation layer 11 and the spin current generation layer 12 reaches the spin current-current conversion layer 14 and the light absorption layer 15 and spins. It is absorbed by the flow-current conversion layer 14 and / or the light absorption layer 15. The layer that has absorbed visible and near-infrared light (typically the light absorbing layer 15) absorbs light and the temperature rises (light-heated), and the layer is laminated with the radiant-cooled light radiating zone 11. A larger temperature gradient is generated along the thickness direction of the light, and as a result, a large temperature gradient is likely to be generated near the interface between the spin current generation layer 12 and the spin current-current conversion layer 14.

Up to this point, the case where natural light is irradiated from the light radiating zone 11 side has been described, but the electromotive force having the same reference numeral (polarity) can be obtained from the laminated body 10 even when there is no light irradiation.
When there is no light irradiation (when the light radiating zone 11 is installed facing the space side), as described above, the light radiating zone 11 is cooled by the effect of radiant cooling, and the light absorbing layer 15 to the light radiating zone 11 A temperature gradient (temperature difference / thickness) is generated along the thickness direction toward.
Since this temperature gradient is in the direction in which the temperature decreases along the thickness direction from the light absorption layer 15 to the light radiation layer 11 regardless of the presence or absence of light irradiation, the electromotive force extracted from the spin current-current conversion layer 14 The sign (polarity) is the same.

The above shows that the laminated body 10 can be applied to a thermoelectric conversion element capable of obtaining a direct current having the same code without using a polarity conversion circuit or the like.

Although the case of irradiating light from the light radiating zone 11 side has been described in FIG. 1, even when the light is radiated from the light absorbing layer 15 side, the electromotive force is obtained as shown in Examples described later. Be done.
When irradiating light from the light radiating zone 11 side, the temperature generated along the thickness direction of the laminate between the light radiating zone 11 and the light absorbing layer 15 due to the synergistic action of the effect of radiant cooling and the effect of light heating. The gradient tends to be larger, which is preferable in that a large temperature gradient can be obtained near the interface between the spin current generation layer 12 and the spin current-current conversion layer 14, and as a result, a larger electromotive force can be obtained.
In the following, the configuration of each layer in this laminated body will be described in detail.

[Light radiation-spin current generation layer]
The light radiation-spin current generation layer is a layer that transmits visible light and near-infrared light, absorbs mid-infrared light, and can generate spin current, and is typically visible and. It is preferable that a light absorption layer that transmits near-infrared light and absorbs mid-infrared light and a spin current generation layer capable of generating spin current are laminated. The spin current generation layer is preferably in contact with the spin-current conversion layer described later.

(Light radiation zone)
The light radiation layer is a layer that transmits visible light and near-infrared light and absorbs mid-infrared light.
The material of the light radiation layer is not particularly limited, but for example, an inorganic material such as silica, an organic material containing a polymer such as PDMS (polydimethylsiloxane), each multilayer film, a multilayer film combining the above, and the like. Can be used.

Further, as a material of the light radiation layer, gadolinium gallium garnet (Gd ₃ Ga ₅ O ₁₂ : GGG) may be used. In particular, when YIG is used for the light radiation-spin flow generation layer, it is preferable in that the crystallinity and magnetic characteristics of the light radiation-spin flow generation layer can be improved. At this time, the plane orientation of the gadolinium gallium garnet crystal is not particularly limited, but is preferably (100), (110), or (111).

The thickness of the light radiation layer is not particularly limited, but is generally preferably 1 to 1000 μm.

(Spin current generation layer)
The spin current generating layer means a layer capable of generating a spin current by a heat flow, and is a layer containing a magnetic material having magnetization (hereinafter, "magnetism") in that a laminated body having a more excellent effect of the present invention can be obtained. It is also referred to as "body layer"), and it is preferably made of a magnetic material having magnetization. Above all, it is preferable that the magnetization directions of the magnetic materials are aligned in that a laminated body having a more excellent effect of the present invention can be obtained.
Here, the content of the magnetic material in the magnetic material layer is not particularly limited, but in general, 80% by mass or more is preferable, and 90% by mass or more is more preferable with respect to the total mass of the magnetic material layer.
The magnetic material is not particularly limited, but at least one selected from the group consisting of a ferromagnetic material and a ferrimagnetic material is preferable in that a current may be obtained without applying an external magnetic field. Compared with paramagnetic materials and antiferromagnetic materials, when ferromagnets and / or ferrimagnetic materials are used, there is an advantage that the application of an external magnetic field is unnecessary or less.
In the following, a case where the spin current generation layer is a magnetic material layer will be described.

The magnetic material is not particularly limited, but a material having a smaller thermal conductivity is preferable from the viewpoint of more easily maintaining the generated temperature gradient. In this respect, the magnetic material is more preferably a magnetic insulator. A magnetic insulator is preferable in that heat conduction by electrons is further suppressed.

The magnetic material is not particularly limited, and examples thereof include oxides containing iron (Fe), Co (cobalt), and the like, and garnet ferrite, spinel ferrite, hexagonal ferrite, and the like are preferable, and garnet ferrite or garnet ferrite or , Spinel ferrite is more preferable.
Specific examples of the magnetic material include YIG (yttrium iron garnet) and yttrium gallium iron garnet (Y ₃ Fe _5-x Ga _x O ₁₂ ), which are easily available and have a small dissipation of spin angle momentum, but 0 ≦ x <5. ), And garnet ferrite in which the Y (yttrium) site of YIG is replaced with an atom such as La (lantern) (for example, LaY ₂ Fe ₅ O ₁₂ or the like).

The light emission-spin current generation layer transmits visible light and near-infrared light and absorbs mid-infrared light.
In the present specification, visible light means light having a wavelength of 0.4 to 0.8 μm, and near-infrared light means light having a wavelength exceeding 0.8 μm and 2.5 μm or less. , Mid-infrared light means light having a wavelength of more than 2.5 μm and not more than 15 μm.

Further, in the present specification, transmitting visible light and near-infrared light means that the transmittance of light of 0.4 to 2.5 μm is 60% or more of the incident light. , 70% or more, more preferably 90% or more. The upper limit of the transmittance is not particularly limited.

Further, absorbing mid-infrared light means that the absorption rate of the incident light exceeding 2.5 μm and 15 μm or less is 70% or more, and is preferably 90% or more. More preferably, it is 95% or more.
Of the mid-infrared light, it is preferable that the absorption rate is high only in the wavelength range of 8 to 13 μm, which is called the “window of the atmosphere”.

The light radiation-spin flow generating layer is typically preferably in the form of a film, and in this case, it is preferable that the magnetization directions are aligned in one direction parallel to the film surface. When the magnetic material has a coercive force, it is preferable in that it can operate even after the external magnetic field is removed (under a zero magnetic field) by once applying an external magnetic field to initialize the magnetization direction.

At this time, the method for fixing the magnetization direction is not particularly limited, and for example, a method of applying an external magnetic field using a coil or the like may be used. As described later, since the electromotive force E _Ishe generated by inverse spin Hall effect occurs in the cross product direction of the generated spin current j _S and the spin polarization direction, the magnetic field application direction, a spin current - longitudinal current conversion layer It is preferable that the direction θ = 90 ° perpendicular to the direction.

The method for forming the light radiation-spin current generation layer is not particularly limited, but when yttrium iron garnet or the like is used as the magnetic material, a sputtering method, a pulse laser deposition method, or a MOD method (Metal-Organic Decomposition Method: organic metal coating) is used. It can be formed by a thermal decomposition method), a sol-gel method, a liquid phase epitaxial growth method, an aerosol deposition method, or the like.
Further, the magnetic material may be formed from a single crystal or a polycrystal.

When the MOD method is used, first, a MOD solution having a composition of _{Y 3} Fe ₄ GaO ₁₂ is applied by a spin coating method on a single crystal substrate such as _{GGG (Gd 3} Ga ₅ O _12).
As the conditions for spin coating, for example, after rotating at 500 rpm for 5 seconds, the MOD solution is rotated at 3000 to 4000 rpm for 30 seconds to make the MOD solution uniform so that the film thickness after firing becomes a desired thickness (for example, 100 nm). Apply.

Then, for example, it is dried on a hot plate heated to 150 ° C. for 5 minutes to evaporate the excess organic solvent contained in the MOD solution, and then calcined in an electric furnace, for example, heated at 550 ° C. for 5 minutes. To make an oxide layer.

Next, in the electric furnace, crystallization of the oxide layer is promoted in the main firing of heating at 750 ° C. for 1 to 2 hours to form a YIG layer. Finally, the YIG layer may be cut out to a predetermined size as needed.

When the aerosol deposition method is used, for example _{, 50 mol%, 27 mol%, and 23 mol% aerosol powders having an average particle size of 1 μm, Fe 2} O ₃ , NiO, and ZnO, respectively, are used, and for example, the openings are open. Ar gas, which is a carrier gas, may be flowed by 1000 sccm using a 0.4 mm × 10 mm nozzle, injected onto the substrate, and deposited.

The thickness of the light radiation-spin flow generating layer is not particularly limited, but is preferably 100 to 10000 nm because it is easy to obtain a laminate having a better effect of the present invention, and it can be appropriately adjusted depending on the type of material used. is there.

[Spin current-current conversion layer]
The spin current-current conversion layer is a layer for extracting thermoelectromotive force by the reverse spin Hall effect, and by the action of this layer, the spin current generated in the light radiation-spin current generating layer can generate a spin current. It is converted into a current in the direction perpendicular to the magnetization direction of the layer.

The spin current-current conversion layer is preferably a metal layer containing a metal (atom). In the present specification, the metal layer includes both a layer made of a single metal and a layer made of an alloy.
The metal atom contained in the metal layer is not particularly limited, but Au, Pt, Pd, in that a larger spin-orbit interaction can be obtained, and as a result, a laminate having a better effect of the present invention can be obtained. And Ir and the like.
The metal layer may be a layer made of the above-mentioned simple substance or a layer made of an alloy containing the above-mentioned atoms. Further, a material obtained by doping Cu or the like with each of the above metal atoms can also be used.

The thickness of the spin current-current conversion layer is not particularly limited, but is preferably set to be about the same as the spin diffusion length of each metal material.
From the above viewpoint, the thickness of the layer having the spin-orbit interaction is preferably, for example, 1 to 100 nm or less, and can be appropriately adjusted depending on the type of material used.
[Light absorption layer]
The light absorption layer is a layer that absorbs visible light and near-infrared light, and absorbs visible light and near-infrared light that have passed through the light radiation layer (preferably through the light radiation-spin current generation layer). A larger temperature gradient is generated along the thickness direction of the laminate between the light emitting layer, which is heated and relatively cooled, and as a result, the spin current generating layer and the spin current-current conversion layer. It has the function of generating a large temperature gradient near the interface.

The component of the light absorption layer is not particularly limited, but preferably contains a black pigment. The black pigment is not particularly limited, but for example, metal oxides of metals such as chromium (Cr), cobalt (Co), nickel (Ni), iron (Fe), manganese (Mn), and copper (Cu); Activated carbon and carbon pigments such as carbon black; organic pigments such as aniline black; and the like.

The black pigment may be a surface-treated pigment surface-treated with a silicon compound, an aluminum compound, an organic substance, or the like. Examples of the surface treatment include (meth) acrylic silane treatment, alkylation treatment, trimethylsilylation treatment, silicone treatment, and treatment with a coupling agent.

Although not particularly limited, the light absorption layer is preferably a coating film obtained by a black paint containing a black pigment and a resin. The resin contained in the black paint is not particularly limited, and examples thereof include known resins such as (meth) acrylic resin, polyester resin, polyamide resin, vinyl resin, and epoxy resin.
In addition to the above, the black paint may contain a curing agent, a surfactant, a solvent, a pigment, a dye, a filler and the like.

The thickness of the light absorption layer is not particularly limited, but is generally preferably 100 nm to 100 μm.

[Manufacturing method of laminated body]
The method for producing the laminate is not particularly limited, and the laminate can be produced by a known method. For example, if each layer is laminated by liquid phase epitaxial growth (LPE), sputtering method, pulsed laser deposition method (PLD), organometallic deposition method (MOD method), sol-gel method, aerosol deposition method (AD method), or the like. Good. Further, the light absorption layer may be formed by applying a black paint on the spin current-current conversion layer and applying energy (heating or the like) as necessary.

[Use of laminate]
This laminate can be applied to a thermoelectric conversion element that can obtain electric power only by irradiating light such as natural light without heating and / or cooling from the outside.

[Thermoelectric conversion element]
The thermoelectric conversion element according to the embodiment of the present invention is a thermoelectric conversion element having a laminated body as described above. FIG. 2 is a schematic cross-sectional view of the thermoelectric conversion element according to the embodiment of the present invention, and FIG. 3 is a perspective view of the thermoelectric conversion element.
The thermoelectric conversion element 20 is arranged in contact with the light radiation-spin current generation layer 13 composed of the light radiation layer 11 and the spin current generation layer 12 and the light radiation-spin current generation layer 13 (of which the spin current generation layer 12). The spin current-current conversion layer 14 and the light absorption layer 15 are provided in this order, and are arranged so as to face each other along the end of the light absorption layer 15 and are in contact with each other. It has an electrode 21 (a) and an electrode 21 (b).

When the thermoelectric conversion element 20 is irradiated with light (for example, natural light) from the light radiating zone 11, the light radiating zone 11 is affected by the effect of radiating cooling from the light radiating zone 11 and the effect of light heating of the light radiating zone 11. A temperature gradient is generated between the light absorbing layer 15 and the light absorbing layer 15 along the thickness direction of the laminated body, and as a result, a large temperature gradient is generated near the interface between the spin current generating layer 12 and the spin current-current conversion layer 14. Then, a spin current is generated in the light radiation-spin current generation layer 13 (of which the spin current generation layer 12) is generated by the spin Seebeck effect, and an electromotive force is generated by the reverse spin Hall effect of the spin current-current conversion layer 14. It is configured to be taken out via the electrode 21 (a) and the electrode 21 (b).

In this thermoelectric conversion element, when a spin current returning to a temperature gradient in the direction perpendicular to the plane (direction parallel to the Z axis in FIG. 3) is taken out as an electromotive force, the spin current is the magnetization of the light radiation-spin current generation layer 13. Since it is converted into a current (electromotive force) perpendicular to the direction, it is preferable that the magnetization direction of the light radiation-spin flow generation layer 13 is parallel to the Y axis.
By doing so, an electromotive force (current) can be obtained along the in-plane direction (direction parallel to the X-axis in FIG. 3) from the electrodes 21 (a) facing each other toward the electrodes 21 (b). ..

In this thermoelectric conversion element, the effect of radiative cooling and the effect of light heating act synergistically, especially when light is incident from the light radiant zone side, and the spin current generation layer 12 and the spin current-current conversion layer 14 Since a larger temperature gradient can be generated near the interface of the above, electric power can be obtained only by irradiating light such as natural light without heating and / or cooling from the outside. Further, in this thermoelectric conversion element, even when it is not irradiated with light such as natural light, electric power can be obtained only by installing it in an environment where radiative cooling is possible (for example, outdoors). According to the usage method in which the light radiating zone side is arranged on the outer (space) side, a direct current having the same code (same polarity) can be obtained regardless of the presence or absence of irradiation with natural light, as shown in Examples described later. ..

[Power generation device]

FIG. 4 is an example of a power generation device according to an embodiment of the present invention. The power generation device 40 has a thermoelectric conversion element 20 and a storage device 41 for storing the electric power generated by the thermoelectric conversion element 20, and the thermoelectric conversion element 20 and the storage device 41 are electrically connected by a lead wire 42. It is connected.

The storage device 41 is not particularly limited, but a lead storage battery, a secondary battery such as an alkaline storage battery; a ceramic capacitor, a capacitor such as a film capacitor; and the like can be used.

[Exhaust heat recovery system]
FIG. 5 is a schematic view of an exhaust heat recovery system according to an embodiment of the present invention. The exhaust heat recovery system 50 includes a heat source 51 and a thermoelectric conversion element 20 arranged on the heat source. The thermoelectric conversion element 20 is arranged in the order of the light absorption layer, the spin current-current conversion layer, and the light radiation-spin current generation layer composed of the spin current generation layer and the light radiation layer from the heat source side. ing.
In the exhaust heat recovery system 50, the light absorption layer is heated by the heat from the heat source 51, and a temperature gradient is generated between the light collection layer and the light radiation layer along the thickness direction of the laminated body, and as a result, a spin current is generated. A large temperature gradient is generated near the interface between the layer and the spin current-current conversion layer. An electromotive force is generated from the spin current generated by this temperature gradient and can be recovered.

This waste heat recovery system is particularly arranged outdoors and can recover a larger amount of electric power even when natural light is irradiated from the light radiating zone side. In a conventional waste heat recovery system using a thermoelectric conversion element, when one surface of the thermoelectric conversion element is heated by heat energy from a heat source and the other surface is light-heated by irradiation with natural light, the thickness direction of the laminate As a result, the temperature gradient near the interface between the spin current generation layer and the spin current-current conversion layer becomes smaller, so that the obtained electromotive force tends to be smaller.

On the other hand, in this exhaust heat recovery system, even under irradiation with light such as natural light, the light radiation layer irradiated with light is radiantly cooled as compared with the light absorption layer whose temperature rises due to light heating. Since it is relatively cooled, not only a stable electromotive force can be obtained regardless of the presence or absence of light irradiation, but also a larger electromotive force can be obtained under light irradiation.

FIG. 6 is a schematic view showing an example of the exhaust heat recovery system according to the embodiment of the present invention. The exhaust heat recovery system 60 has a building 61 as a heat source and a thermoelectric conversion element 20 arranged on the roof of the building 61. The thermoelectric conversion element 20 is arranged in the order of the light absorption layer, the spin current-current conversion layer, and the light radiation-spin current generation layer composed of the spin current generation layer and the light radiation layer from the heat source side. ing.

The heat source in the waste heat recovery system 60 is not particularly limited, and examples thereof include a waste incineration facility (waste incineration plant). Further, the heat source may be other than a building, and may be, for example, a work piece such as a pipe, a tank, and a power generation / substation equipment; a prime mover such as a generator, a turbine, an engine, and an electric motor; Good. Of these, a heat source that can be used outdoors is preferable.

Hereinafter, the present invention will be described in more detail based on Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limiting by the examples shown below.

[Creation of laminate]
First, a platinum (Pt) film was formed on a sample piece on which yttrium iron garnet (YIG) was formed on a gallium gadolinium garnet (GGG) substrate by a sputtering method. The thicknesses of the GGG, YIG, and Pt films were about 400 μm, 2 μm, and 0.005 μm, respectively. Next, a black body spray (black paint) was applied onto the Pt film to form a film, which was used as a sample. Then, two pieces of indium (In) were pressure-bonded to both ends of the sample so as to be in contact with the Pt film to form an electrode. FIG. 7 shows a schematic diagram of the layer structure of the sample in the above test. The term "blackbody paint layer" in the figure means a coating film formed by using a blackbody spray.

[Measurement of electromotive force]
FIG. 8 is a photograph of the measuring device used for measuring the electromotive force, and FIG. 9 is a schematic view thereof. In the measuring device of FIG. 8, a rectangular sample (a portion that looks black) when viewed from above is arranged in the center of the photograph. At this time, the pair of electrodes are arranged so as to face each other along the side of the quadrangle parallel to the Y axis.
Further, the electromagnet (coil-shaped portion) is arranged so that a magnetic field is generated in the Y-axis direction.

A magnetic field was generated by applying a current to the electromagnet with a bipolar DC power supply (manufactured by ADCMT, "6240A"). The applied current was swept from −30 mA to + 30 mA. As a result, a magnetic field of -12 mT to + 11 mT was generated.
At this time, half of the difference between the saturated voltage values of the positive and negative currents was used as the electromotive force ( _VISHE : electromotive force generated by the reverse spin Hall effect).
FIG. 10 shows an example of the measurement result of the voltage value when the magnetic field changes from -12 mT to +11 mT according to the applied current. Half the value of dV in FIG. 10 was used as the electromotive force. The electromotive force generated in the sample was measured with a nanovolt meter (“2182A” manufactured by Keithley).

[Measurement outdoors]
The above set of measuring devices including the sample was installed on the roof of a 5-story building on the site of 1-1 Namiki, Tsukuba City, and the current (magnetic field) was swept to measure the electromotive force of the sample. For temperature, humidity, and weather, we used data from the weather station in Tsukuba (1-2 Nagamine, Tsukuba). In addition, the sunlight intensity is an actual measurement value on the roof.

A form in which natural light is incident from the GGG substrate side of the sample (FIG. 11 shows a schematic diagram of the sample arrangement) and a form in which natural light is incident from the blackbody paint layer side (FIG. 13 is a schematic diagram of the sample arrangement). Was shown.).

FIG. 12 shows the magnitude of the electromotive force between the sunny night and the sunny day when measured in the form in which natural light is incident from the GGG substrate side. Table 1 shows the measurement conditions.

From FIG. 12, it was found that the electromotive force of the same code was obtained at night and in the daytime. At night, the temperature of the upper surface (space side) of the thermoelectric conversion layer is relatively lowered by radiative cooling from the GGG substrate, and an electromotive force of a predetermined code is obtained, while during the daytime, the electromotive force is obtained from the GGG layer. In addition to radiative cooling, heating of the blackbody paint layer with visible, near-infrared light results in a greater temperature gradient along the thickness direction between the upper and lower sides of the thermoelectric conversion layer, resulting in a greater temperature gradient. The temperature gradient near the interface between the spin current generation layer and the spin current-current conversion layer became larger, and a larger electromotive force was obtained.

That is, according to the above sample, a direct current having the same code can be obtained regardless of the presence or absence of light irradiation, and the thermoelectric conversion element has a synergistic effect of heating with light and radiative cooling under light irradiation. It was found that a larger electromotive force can be obtained because a larger temperature gradient can be generated on the front and back sides.

In Table 1, "Temp. [DegC]" means "temperature (° C.)", "Humidity [%]" means "humidity (%)", and "Solar irradiance [mW / cm]". ² ] ”indicates“ solar irradiance intensity (mW / cm ² ) ”. The measurement was carried out in May 2019.

FIG. 14 shows the magnitude of the electromotive force in the sunny night and the sunny day when measured in the form in which natural light is incident from the blackbody paint layer side. Table 2 shows the measurement conditions.

From FIG. 14, it was found that although electromotive force was obtained both at night and during the day, the sign (polarity) was different between night and day. At night, due to radiative cooling from the GGG substrate, the temperature of the upper surface (space side) of the thermoelectric conversion layer is relatively lower than that of the lower surface (GGG substrate), and the electromotive force of a predetermined polarity is generated. On the other hand, in the daytime, the blackbody paint layer arranged on the incident side of the light is heated, so that the temperature on the blackbody paint layer side is higher than that on the GGG substrate side, and the voltage of the polarity opposite to that at night. Was found to be obtained.

That is, according to the above sample, direct currents having different polarities can be obtained by irradiating light, and electromotive force can be obtained by the temperature gradient generated by the effect of radiative cooling at night and the effect of heating by light during the day. I understood.

In Table 2, each item has the same meaning as each item in Table 1, and the measurement is also in May 2019.

[Measurement indoors]
The measurement was carried out by arranging the same measuring device used for the outdoor measurement indoors. In order to reproduce the outdoor environment, instead of the low temperature space, a cooling stage (manufactured by Bix, "LVPU-40"), a solar simulator instead of the sun (pseudo solar irradiation device; Peccel, "PEC-L01" ), Was used respectively. The cooling stage was arranged so that the distance from the sample was about 6 cm without contacting the sample, and the stage surface was adjusted to be cooled to 0 degrees Celsius.
The pseudo-sunlight irradiation device was adjusted so that the intensity of the pseudo-sunlight irradiating the sample was about 50 mW / cm ^2. The measurement was performed by sweeping the current in the same manner as the outdoor measurement.

Similar to the outdoor measurement, a form in which natural light is incident from the GGG substrate side of the sample (a schematic diagram of the arrangement of the sample is shown in FIG. 15) and a form in which natural light is incident from the blackbody paint layer side (FIG. 17). A schematic diagram of the sample arrangement is shown in (1).
First, the cooling stage and the pseudo-sunlight irradiation device were operated independently to measure the electromotive force, and further, the cooling stage and the pseudo-sunlight irradiation device were operated at the same time to measure the electromotive force.

FIG. 16 shows the electromotive force under each condition when the test was performed in the arrangement of FIG.
In FIG. 16, "only the cooling stage" on the horizontal axis indicates the electromotive force when only the cooling stage is operated, and "only pseudo-sunlight" means that only the pseudo-solar irradiation device is operated. The electromotive force when the cooling stage and the pseudo-solar irradiation device are operated at the same time indicates the electromotive force when the cooling stage and the pseudo-solar irradiation device are operated at the same time. The vertical axis shows the magnitude of the electromotive force and its sign (polarity).

From the results shown in FIG. 16, it was found that the electromotive force having the same code (same polarity) can be obtained under any condition. This is because when the GGG substrate side of FIG. 16 and the blackbody paint layer side are compared, the GGG substrate side has a lower temperature under any condition. That is, in the case of "cooling stage only", the GGG substrate is cooled by radiative cooling to a relatively low temperature compared to the blackbody layer, and in the case of "pseudo-sunlight only", the blackbody is heated by light. It is considered that the coating layer side was heated and the temperature became relatively high as compared with the GGG substrate side.
Comparing the magnitudes of the electromotive force, in the case of "cooling stage and pseudo-sunlight", the electromotive force was larger than other conditions. It is considered that this is because the above-mentioned effect of radiative cooling and the effect of light heating are synergistically expressed.

On the other hand, when the sample arrangement is in the form shown in FIG. 17, as shown in FIG. 18, the results are "pseudo-sunlight only" and "cooling stage and pseudo-sun" as compared with the case of "cooling stage only". In the case of "light", it was found that the code (polarity) of the obtained electromotive force was different.

In the case of “only the cooling stage” in FIG. 18, it is considered that the blackbody paint layer side was cooled by radiative cooling, the temperature became lower than that on the GGG substrate side, and a positive electromotive force was generated. On the other hand, in the case of "pseudo-sunlight only" and "cooling stage and pseudo-sunlight", since the electromotive force is-, it can be seen that the temperature on the blackbody paint layer side is higher than the temperature on the GGG substrate side. .. This indicates that the blackbody paint layer side is light-heated by irradiation with pseudo-sunlight.

The above is also supported by the fact that the absolute value of the electromotive force in the case of "cooling stage and pseudo-sunlight" is smaller than that in the case of "pseudo-sunlight only". That is, under the condition of "cooling stage and pseudo-sunlight", the light heating effect and the radiant cooling effect on the blackbody paint layer compete with each other, and the temperature of the blackbody paint layer is higher than that of "pseudo-sunlight only". The rise was more suppressed (the temperature gradient generated along the thickness direction with the GGG substrate side became smaller, and the temperature gradient near the interface between the spin current generation layer and the spin current-current conversion layer became smaller. ) It is thought that this is the reason.

From the above results, it was found that when light is irradiated from the GGG substrate side, both the effect of radiative cooling and the effect of light heating express electromotive force of the same sign, and more efficient power generation is possible. ..

10: Laminated body 11: Light radiation layer 12: Spin flow generation layer 13: Light radiation-spin flow generation layer 14: Spin flow-current conversion layer 15: Light absorption layer 20: Thermoelectric conversion element 21: Electrode 40: Power generation device 41 : Storage device 42: Lead wires 50, 60: Exhaust heat recovery system 51: Heat source 61: Building

Claims (13)

A light radiation-spin current generation layer that transmits visible light and near-infrared light, absorbs mid-infrared light, and can generate spin current.
A spin-orbit-current conversion layer having a spin-orbit interaction, which is arranged in contact with at least a part of the light radiation-spin current generation layer.
A laminate having a light absorbing layer that absorbs visible light and near infrared light in this order. The laminate according to claim 1, wherein the light radiation-spin flow generation layer is a layer containing a magnetic material having the same magnetization direction. The laminate according to claim 2, wherein the magnetic material is a magnetic insulator. The laminate according to claim 3, wherein the magnetic insulator contains at least one selected from the group consisting of garnet ferrite and spinel ferrite. The laminate according to any one of claims 2 to 4, wherein the magnetic material has a coercive force. The laminate according to any one of claims 1 to 5, wherein the spin current-current conversion layer contains a metal. The laminate according to any one of claims 1 to 6, wherein the spin current-current conversion layer has a thickness of 1 to 100 nm. Any one of claims 1 to 7, which is used to irradiate light from the side of the light radiation-spin current generating layer to obtain at least one selected from the group consisting of spin current and current. The laminate described in. A thermoelectric conversion element having the laminate according to any one of claims 1 to 8. A method of using a thermoelectric conversion element, which obtains electric power by irradiating the thermoelectric conversion element according to claim 9 with light. A power generation device having the thermoelectric conversion element according to claim 9. A waste heat recovery system having a heating element and the thermoelectric conversion element according to claim 9 arranged on the heating element. On one main surface of the thermoelectric conversion element,
Members that transmit visible light and near-infrared light and absorb mid-infrared light are placed in contact with each other.
On at least part of the main surface on the other side,
Members that absorb visible light and near-infrared light are placed in contact with each other.
A method of generating a thermal gradient along the thickness direction of the thermoelectric conversion element from the main surface on one side to the main surface on the other side.