JP7451932B2 - Thermoelectric conversion materials and thermoelectric conversion elements using the same - Google Patents

Description

The present invention relates to a thermoelectric conversion material and a thermoelectric conversion element using the same.

Thermoelectric conversion materials that can mutually convert thermal energy and electrical energy are used in thermoelectric conversion elements such as thermoelectric generation elements and Peltier elements. A thermoelectric conversion element is an element that converts heat into electric power, and is constructed from a combination of semiconductors and metals. Typical thermoelectric conversion elements are classified into p-type semiconductor alone, n-type semiconductor alone, or a combination of p-type semiconductor and n-type semiconductor. Thermoelectric conversion elements utilize the Seebeck effect, which generates an electromotive force when heat is applied to create a temperature difference between both ends of a semiconductor. In order to obtain a larger potential difference, thermoelectric conversion elements generally use a combination of p-type semiconductor and n-type semiconductor as materials.

Further, the thermoelectric conversion element is used as a thermoelectric module formed by combining a large number of elements into a plate shape or a cylindrical shape. Thermal energy can be directly converted into electricity, and can be used, for example, as a power source for wristwatches powered by body temperature, terrestrial power generation, and satellite power generation. The performance of the thermoelectric conversion element depends on the performance of the thermoelectric conversion material, the durability of the module, and the like.

As described in Non-Patent Document 1, a dimensionless thermoelectric figure of merit (ZT) is used as an index representing the performance of thermoelectric conversion materials. Moreover, a power factor PF (=S ² ·σ) may be used as an index representing the performance of a thermoelectric conversion material.
The dimensionless thermoelectric figure of merit "ZT" is expressed by the following formula (6).
ZT=(S ²・σ・T)/κ Formula (6)
Here, S is the Seebeck coefficient (V/K), σ is the electrical conductivity (S·m), T is the absolute temperature (K), and κ is the thermal conductivity (W/(m·K)). The thermal conductivity κ is expressed by the following formula (7).
κ=α・ρ・C Formula (7)
Here, α is the thermal diffusivity (m ² /s), ρ is the density (kg/m ³ ), and C is the specific heat capacity (J/(kg·K)).
That is, in order to improve thermoelectric conversion performance (hereinafter also referred to as thermoelectric characteristics), it is important to improve the Seebeck coefficient or electrical conductivity while decreasing the thermal conductivity.

Typical thermoelectric conversion materials include, for example, bismuth/tellurium (Bi-Te) from room temperature to 500K, lead/tellurium (Pb-Te) from room temperature to 800K, and silicon/tellurium (Pb-Te) from room temperature to 1000K. Inorganic materials such as germanium (Si--Ge) are known. However, since inorganic materials generally have poor processability, it is difficult to create thermoelectric conversion elements having various shapes and flexibility.

Therefore, in recent years, studies have been progressing on thermoelectric conversion elements made of organic materials. Organic materials have the advantage that they have excellent moldability and can be manufactured using printing techniques and the like. For example, Patent Document 1 discloses a thermoelectric conversion material containing a dispersant containing a repeating unit with a specific structure and carbon nanotubes (hereinafter sometimes abbreviated as "CNT"), and a thermoelectric conversion element using the same. ing. However, in the thermoelectric conversion element disclosed in Patent Document 1, sufficient electromotive force was not obtained as a thermoelectric conversion element.

International Publication No. 2015/050113

Takenobu Kajikawa, "Thermoelectric Conversion Technology Handbook (First Edition)", NTS Publishing, 19 pages (2008).

The problem to be solved by the present invention is to provide a thermoelectric conversion element that can obtain a high electromotive force and a thermoelectric conversion material that can produce such a thermoelectric conversion element.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and have completed the present invention.
That is, the present invention provides a conductive material (A), an organic compound (B) (excluding the conductive material (A)), and an organic compound (C) (excluding the conductive material (A) and the organic compound (B)). ), and relates to a thermoelectric conversion material that satisfies all of the following (1) to (3).
(1) 0<((HOMO of organic compound (B)) - (HOMO of conductive material (A))) x ((HOMO of organic compound (C)) - (HOMO of conductive material (A)))
(2) |(HOMO of organic compound (B)) - (HOMO of conductive material (A)) | < | (HOMO of organic compound (C)) - (HOMO of conductive material (A)) |
(3) The adsorption of the organic compound (B) to the conductive material (A) is greater than the adsorption of the organic compound (C) to the conductive material (A).
(However, HOMO represents the energy level of the highest occupied orbital. Also, when the conductive material (A) is a metal material, the HOMO of the conductive material (A) is the Fermi level of the conductive material (A). represent.)

Further, the present invention relates to the thermoelectric conversion material described above, in which the conductive material (A) contains a carbon material.

The present invention also relates to the thermoelectric conversion material described above, in which the carbon material includes carbon nanotubes.

The present invention also relates to a thermoelectric conversion element having a thermoelectric conversion film containing the above thermoelectric conversion material and an electrode, the thermoelectric conversion film and the electrode being electrically connected to each other.

According to the present invention, it has become possible to produce a thermoelectric conversion element that can obtain a high electromotive force.

(a) represents a top view of a thermoelectric conversion element that is an embodiment of the present invention, and (b) represents a schematic diagram illustrating a method for measuring the electromotive force of the thermoelectric conversion element.

Embodiments of the present invention will be described in detail below.
<Conductive material (A)>
The conductive material (A) refers to a material that conducts electricity. Conductivity can be improved by increasing the content of the conductive material (A) in the thermoelectric conversion material.
The conductive material (A) is not particularly limited as long as it is a material having conductivity (carbon material, metal material, conductive polymer, etc.). For example, carbon materials include graphite, carbon nanotubes, carbon black, and graphene. (including graphene nanoplates), etc. In addition, metal materials include metal powders such as gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, germanium, gallium, and platinum, as well as ZnSe, CdS, InP, Examples include GaN, SiC, SiGe, alloys thereof, and composite powders thereof. Further, fine particles having a nucleus and a substance different from the nucleus substance coated therein, specifically, for example, silver-coated copper powder having a copper nucleus and coating the surface with silver may be mentioned. In addition, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide), Examples include powder whose surface is coated with these metal oxides. Examples of the conductive polymer include PEDOT/PSS (composite of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid), polyaniline, polyacetylene, polypyrrole, polythiophene, polyparaphenylene, and the like.

Examples of flaky graphite include CMX, UP-5, UP-10, UP-20, UP-35N, CSSP, CSPE, CSP, CP, CB-150, CB-100, and ACP manufactured by Nippon Graphite Industries. , ACP-1000, ACB-50, ACB-100, ACB-150, SP-10, SP-20, J-SP, SP-270, HOP, GR-60, LEP, F#1, F#2, F #3, BF-3AK, FBF, BF-15AK, CBR, CPB-6S, CPB-3, 96L, 96L-3, K-3, SC-120, SC-60, HLP, manufactured by Chuetsu Graphite Industries Co., Ltd. Examples include CP-150, SB-1, EC1500, EC1000, EC500, EC300, EC100, EC50 manufactured by Ito Graphite Industries, and 10099M and PB-99 manufactured by Nishimura Graphite Co., Ltd. Examples of the spherical natural graphite include CGC-20, CGC-50, CGB-20, and CGB-50 manufactured by Nippon Graphite Industries. Examples of the earthy graphite include Blue P, AP, AOP, and P#1 manufactured by Nippon Graphite Industries Co., Ltd., and APR, K-5, AP-2000, AP-6, 300F, and 150F manufactured by Chuetsu Graphite Co., Ltd. Examples of artificial graphite include PAG-60, PAG-80, PAG-120, PAG-5, HAG-10W, and HAG-150 manufactured by Nippon Graphite Industries, and G-4AK, G-6S, and G- manufactured by Chuetsu Graphite Co., Ltd. 3G-150, G-30, G-80, G-50, SMF, EMF, SFF, SFF-80B, SS-100, BSP-15AK, BSP-100AK, WF-15C, SGP-100 manufactured by SEC Carbon , SGP-50, SGP-25, SGP-15, SGP-5, SGP-1, SGO-100, SGO-50, SGO-25, SGO-15, SGO-5, SGO-1, SGX-100, SGX -50, SGX-25, SGX-15, SGX-5, SGX-1, etc.

Examples of conductive carbon fibers and carbon nanotubes include vapor grown carbon fibers such as VGCF manufactured by Showa Denko Co., Ltd., EC1.5 and EC1.5-P manufactured by Meijo Nano Carbon Co., Ltd., TUBALL manufactured by Kusumoto Kasei Co., Ltd., and Zeon Nanotechnology. Examples include single-walled carbon nanotubes such as ZEONANO manufactured by CNano, FloTube9000, FloTube7000, FloTube2000 manufactured by CNano, NC7000 manufactured by Nanocyl, and 100T and 200P manufactured by Knano.

Examples of carbon black include Toka Black #4300, #4400, #4500, #5500 manufactured by Tokai Carbon, Printex L manufactured by Degussa, Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, and Conductex SC ULTRA manufactured by Columbian. Conductex 975 ULTRA, PUERBLACK100, 115, 205, Mitsubishi Chemical Corporation #2350, #2400B, #2600B, #3050B, #3030B, #3230B, #3350B, #3400B, #5400B, Cabot Corporation MONARCH14 00, 1300, Furnace black such as 900, Vulcan of Examples include acetylene black such as Denka Black, Denka Black HS-100, and FX-35.

Among the above-mentioned conductive materials (A), it is preferable that the conductive materials (A) contain a carbon material from the viewpoint of achieving both Seebeck coefficient and electrical conductivity. Further, the carbon material preferably contains carbon nanotubes, carbon black, and graphene, and more preferably contains carbon nanotubes. Further, the carbon nanotubes preferably include single-walled carbon nanotubes.

The shape of the conductive material (A) is not particularly limited, and amorphous shapes, aggregate shapes, scale shapes, microcrystal shapes, spherical shapes, flake shapes, wire shapes, etc. can be used as appropriate. Moreover, the number of conductive materials (A) may be one type, or two or more types may be included.

<Organic compounds>
Next, the organic compound (B) and the organic compound (C) will be explained. The organic compound (B) and the organic compound (C) are not determined by their respective physical properties, but are determined by the relative difference in physical properties including the conductive material (A). Specifically, it satisfies the requirements (1) to (3) above. (1) and (2) can be further broadly classified into (4) and (5) below.
(4) When the HOMO of the conductive material (A) is larger than the HOMO of the organic compound (B), and the HOMO of the organic compound (B) is larger than the HOMO of the organic compound (C).
(5) When the HOMO of the conductive material (A) is smaller than the HOMO of the organic compound (B), and the HOMO of the organic compound (B) is smaller than the HOMO of the organic compound (C).

The mechanism of thermoelectric conversion in the present invention is considered as follows. If the organic compound (B) has greater adsorption to the conductive material (A) than the organic compound (C), the organic compound (B) will be more present on the surface of the conductive material (A) than the organic compound (C). It is thought that it is preferentially adsorbed. In order for thermoelectric conversion to occur, carrier movement must occur between the conductive material (A), the organic compound (B), and the organic compound (C). When the HOMO of B) is close to the HOMO of the conductive material (A), carrier movement between the conductive material (A) and the organic compound (B) existing near the surface becomes smooth, and the organic compound (B) and the organic compound ( Since the carrier movement between C) also becomes smooth, carrier movement between the conductive material (A), the organic compound (B), and the organic compound (C) is performed efficiently, and it is considered that the thermoelectric conversion efficiency is increased.

The HOMO of the organic compound (B) and the HOMO of the conductive material (A) are preferably separated by 0.1 to 2.0 eV, more preferably 0.1 to 1.5 eV. Further, the HOMO of the organic compound (C) and the HOMO of the organic compound (B) are preferably separated by 0.1 to 2.0 eV, and more preferably separated by 0.1 to 1.5 eV. For example, when the HOMO of the conductive material (A) is -5.1 eV, the HOMO of the organic compound (B) is -7.1 to -5.2 or -5.0 to -3.0. is preferred. When the HOMO of the conductive material (A) is -5.1 eV and the HOMO of the organic compound (B) is -5.4 eV, the HOMO of the organic compound (C) is -7.5 to -5. Preferably it is 5 eV. When the HOMO of the conductive material (A) is -5.1 eV and the HOMO of the organic compound (B) is -5.0 eV, the HOMO of the organic compound (C) is -4.9 to -2.9 eV. It is preferable that there be.

Further, in order to promote surface adsorption and uniformity to the conductive material (A) and further increase the molecular proportion, the molecular weight of the organic compound (B) is preferably small, and the molecular weight or mass average molecular weight (Mw) is preferably is 5,000 or less, more preferably 3,000 or less. It is preferable that the organic compound (B) and the organic compound (C) are both organic semiconductors.

Examples of the organic compound (B) and organic compound (C) that satisfy the above conditions include a perylene skeleton, a pyrrolopyrrole skeleton, a phenothiazine skeleton, a thiazolothiazole skeleton, an oxazolothiazole skeleton, an oxazolooxazole skeleton, a benzobisthiazole skeleton, The compound is preferably a compound having any one of a benzobisoxazole skeleton, a thiazolobenzoxazole skeleton, a thioxanthone skeleton, a fluorene skeleton, an oxazole skeleton, and a phthalocyanine skeleton. To give an example of a preferred embodiment, when the conductive material (A) is a carbon nanotube, the organic compound (B) is preferably a compound having a pyrrolopyrrole skeleton or a phenothiazine skeleton, and the organic compound (C) is a compound having a pyrrolopyrrole skeleton or a phenothiazine skeleton. , a thioxanthone skeleton, a fluorene skeleton, or an oxazole skeleton.

Further, the organic compound (B) and the organic compound (C) contribute to improving the Seebeck coefficient in the thermoelectric conversion material. The Seebeck coefficient can be improved by increasing the content of the organic compound (B) and the organic compound (C), but the conductivity decreases. The upper limit of the total amount of B) and the organic compound (C) is preferably 300% by mass or less, more preferably 200% by mass or less, based on the total amount of the conductive material (A). Moreover, the lower limit is preferably 10% by mass or more, more preferably 20% by mass or more.

(solvent)
The solvent is used as a medium when mixing the conductive material (A), the organic compound (B), and the organic compound (C), and makes it possible to improve coating properties by forming an ink. The solvent that can be used is not particularly limited as long as it can dissolve or disperse the conductive material (A), organic compound (B), and organic compound (C) well, and examples include organic solvents and water, and two or more types can be used in combination. It may also be used. However, the organic solvent as used herein refers to something other than the organic compound (B) and the organic compound (C). Examples of organic solvents include methanol, ethanol, propanol, butanol, ethylene glycol methyl ether, diethylene glycol methyl ether, terpineol, dihydroterpineol, 2,4-diethyl-1,5-pentanediol, 1,3-butylene glycol, iso Bornylcyclohexanol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, glycerin, polyethylene glycol, polypropylene glycol, trifluoroethanol, m-cresol, and thiodiglycol, etc. Alcohols, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethers such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, hydrocarbons such as hexane, heptane, octane, benzene, toluene, xylene, cumene It can be appropriately selected from aromatics such as ethyl acetate, esters such as ethyl acetate, butyl acetate, N-methylpyrrolidone, etc., as required.
As the solvent, N-methylpyrrolidone is preferred.

(Inorganic thermoelectric conversion material)
The thermoelectric conversion material of the present invention may contain an inorganic thermoelectric conversion material, if necessary, in order to improve thermoelectric conversion efficiency. Examples of inorganic thermoelectric materials include Bi-(Te, Se) based, Si-Ge based, Mg-Si based, Pb-Te based, GeTe-AgSbTe based, (Co, Ir, Ru)-Sb based, (Ca, Examples include Sr, Bi)Co ₂ O ₅ systems, and the like. More specifically, _{Bi2Te3 , PbTe} , _AgSbTe2 , GeTe, _{Sb2Te3 , NaCo2O4} , _{CaCoO3 , SrTiO3} , ZnO, SiGe, _Mg2Si , _FeSi2 , _Ba8Si46 , At least one selected from the group consisting of MnSi _1.73 , ZnSb, Zn ₄ Sb ₃ , GeFe ₃ CoSb ₁₂ , and LaFe ₃ CoSb ₁₂ can be used. At this time, impurities may be added to the inorganic thermoelectric conversion material to control the polarity (p-type, n-type) and conductivity. When using an inorganic thermoelectric conversion material, the amount used is adjusted within a range that does not affect film formability or film strength.

When producing a dispersion containing a thermoelectric conversion material, for example, it can be obtained by mixing the thermoelectric conversion material, a solvent, and other components as necessary, and then dispersing the mixture using a disperser or ultrasonic waves. .

There are no particular restrictions on the dispersion machine, and examples include kneaders, attritors, ball mills, sand mills using glass beads or zirconia beads, media dispersion machines such as Scandex, Eiger mills, paint conditioners, paint shakers, colloid mills, etc. can be used.
<Thermoelectric conversion element>
The thermoelectric conversion element of the present invention includes a thermoelectric conversion film containing the thermoelectric conversion material described above and an electrode, and the thermoelectric conversion film and the electrode are electrically connected to each other. Thermoelectric conversion films have excellent heat resistance and flexibility in addition to conductivity and thermoelectric properties. Therefore, a high quality thermoelectric conversion element can be easily manufactured.

The thermoelectric conversion film may be a film obtained by applying a thermoelectric conversion material onto a base material. Since the thermoelectric conversion material has excellent moldability, it is easy to obtain a good film by a coating method. A wet film forming method is mainly used to form a thermoelectric conversion film. Specifically, spin coat method, spray method, roller coat method, gravure coat method, die coat method, comma coat method, roll coat method, curtain coat method, bar coat method, inkjet method, dispenser method, silk screen printing, flexographic method. Examples include methods using various means such as printing. The method can be appropriately selected from the above methods depending on the thickness to be applied, the viscosity of the material, etc.

The thickness of the thermoelectric conversion film is not particularly limited, but as described later, it has a thickness of at least a certain level so that a temperature difference can be generated and transmitted in the thickness direction or surface direction of the thermoelectric conversion film. It is preferable that it be formed as follows. From the viewpoint of thermoelectric properties, the thickness of the thermoelectric conversion film is preferably in the range of 0.1 to 500 μm, preferably in the range of 1 to 300 μm, and more preferably in the range of 1 to 200 μm.

The material for the base material is not particularly limited, but may include nonwoven fabric, paper, plastic films such as polyethylene, polyethylene terephthalate (PET), polyethylene naphthalate, polyether sulfone, polypropylene, polyimide, polycarbonate, cellulose triacetate, or glass. etc. can be used.

Various treatments can be performed on the surface of the base material for the purpose of improving the adhesion between the base material and the thermoelectric conversion film. Specifically, prior to applying the thermoelectric conversion material, UV ozone treatment, corona treatment, plasma treatment, or adhesion promoting treatment may be performed.

The material of the electrode can be selected from metals, alloys, and semiconductors. In one embodiment, metals and alloys are preferable because it is preferable that the conductivity is high and the contact resistance of the thermoelectric conversion film is low. As a specific example, the electrode preferably contains at least one member selected from the group consisting of gold, silver, copper, and aluminum. More preferably, the electrode contains silver.

The electrode can be formed by a method such as a vacuum evaporation method, thermocompression bonding of an electrode material foil or a film having an electrode material film, or application of a paste in which fine particles of the electrode material are dispersed. From the viewpoint of a simple process, a method using thermocompression bonding of an electrode material foil or a film having an electrode material film, or a method using a paste in which the electrode material is dispersed is preferable.

Hereinafter, the present invention will be explained in more detail with reference to experimental examples. In addition, in the examples, "part" means "part by mass" and "%" means "% by mass", respectively. Further, "NMP" refers to N-methylpyrrolidone.

<Method for measuring adsorption>
Adsorption to the conductive material (A) was measured by the following method. 55 parts of NMP and 0.001 part of organic compound (B) (or organic compound (C)) were weighed and mixed and completely dissolved (referred to as "liquid a"). Furthermore, 0.0025 part of the conductive material (A) was added and stirred for 24 hours, and a filtrate was obtained by removing the conductive material (A) with a filter (referred to as "liquid b"). The absorption spectra of each of liquids a and b were measured in the wavelength range of 300 to 800 nm at 25° C. using a spectrophotometer (U-4100 manufactured by Hitachi High-Technologies). The adsorption rate of the organic compound (B) (or organic compound (C)) to the conductive material (A) was calculated according to the following formula, and the adsorptivity was classified as follows.
・Formula: Adsorption rate (%) of organic compound (B) (or organic compound (C)) on conductive material (A) = ((Absorbance at maximum absorption wavelength of liquid a - Absorbance at maximum absorption wavelength of liquid B) ÷ Absorbance at maximum absorption wavelength of liquid a) x 100
AD1: Adsorption rate is 0% or more and less than 25%.
AD2: Adsorption rate is 25% or more and less than 50%.
AD3: Adsorption rate is 50% or more and less than 75%.
AD4: Adsorption rate is 75% or more.
(Measurement condition)
Solvent: NMP
Cell: Quartz cell Optical path length: 10mm

<HOMO, Fermi level measurement method>
To measure the HOMO of the conductive material (A), organic compound (B), and organic compound (C), each single component was fixed on a conductive tape stretched on an ITO glass substrate to form a measurement sample. It was measured by photoelectron spectroscopy (manufactured by Riken Keiki Co., Ltd.: AC-2). The measured values are listed in Table 1.

<Manufacture of thermoelectric conversion materials>
[Example 1]
(Dispersion liquid 1)
Pigment Red 255 (manufactured by Tokyo Kasei Kogyo Co., Ltd.) 0.2 parts, 2-isopropylthioxanthone (manufactured by Tokyo Kasei Kogyo Co., Ltd.) 0.2 parts, SWCNT (manufactured by OCSiAl Co., Ltd.) 0.4 parts, and NMP 79.2 parts were weighed. and mixed to obtain a dispersion liquid 1 of thermoelectric conversion material.

[Examples 2 to 16, Comparative Example 1]
(Dispersions 2 to 17)
Dispersions 2 to 17 of thermoelectric conversion materials were obtained in the same manner as in the method for producing Dispersion 1, except that the types and amounts of the materials were changed as shown in Table 1.

The materials listed in Table 1 are shown below.
Conductive material (A)
GNP: Graphene nanoplatelet “xGNP M5” manufactured by XG Sciences
Graphite: Expanded graphite SMF manufactured by Chuetsu Graphite Industries Co., Ltd.
MWCNT: Multi-wall carbon nanotube “K-nanos-100P” manufactured by KUMHO PETROCHEMICAL
SWCNT: Single-wall carbon nanotube "TUBALL nanotube" manufactured by OCSiAl
Organic compounds (B) and (C)
B1: Pigment Red 255 (manufactured by Tokyo Kasei Kogyo Co., Ltd.)
B2: Methylene green (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
B3: 2,5-bis(2-ethylhexyl)3,6-di(2-thienyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (manufactured by Tokyo Kasei Kogyo Co., Ltd.)
B5: N,N'-bis[4-(diphenylamino)phenyl]-N,N'-diphenylbenzidine (manufactured by Tokyo Chemical Industry Co., Ltd.)
C1: 2-isopropylthioxanthone (manufactured by Tokyo Chemical Industry Co., Ltd.)
C2: 2,2''-bi-9,9'spirobi[9H-fluorene] (manufactured by Aldrich)
C3: 2,5-diphenyl-1,3,4-oxadiazole (manufactured by Tokyo Kasei Kogyo Co., Ltd.)
C4: 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (manufactured by Sigma-Aldrich)
C6: Phloxin B (manufactured by Tokyo Chemical Industry Co., Ltd.)

(Synthesis example: organic compound (B4))
20.0 g of dimethyl succinate, 48.0 g of 4-(dimethylamino)benzonitrile, and 31.6 g of sodium hydride were dissolved in 400 g of amyl alcohol and refluxed for 8 hours. After cooling, the precipitate was filtered and washed with acetic acid and methanol to obtain 11.8 g of a purple solid. Thereafter, 10 g of the obtained solid, 15.6 g of iodomethane, and 10.3 g of sodium butoxide were dissolved in 300 g of dimethylacetamide and refluxed for 8 hours. After cooling, the above mixture was poured into 1000 ml of methanol to precipitate a solid, which was collected by filtration and purified by column chromatography using silica gel to obtain 8.3 g of organic compound (B4).

<Synthesis of organic compounds>
(Synthesis example 1: Organic compound (C5))
5.0 g of 3-aminoperylene, 15.9 g of 3-bromo-9-(m-tolyl)-9H-carbazole, 1.5 g of sodium hydroxide, and 1.0 g of copper oxide were added to 20 ml of nitrobenzene, and the mixture was placed in a nitrogen atmosphere. The mixture was heated and stirred at 200° C. for 50 hours. After cooling, the mixture was diluted with 500 ml of water and extracted with toluene. After concentrating the extract, it was purified by column chromatography using silica gel to obtain 7.2 g of organic compound (C5).

(Measurement of electromotive force)
The obtained dispersions 1 to 17 were each applied onto a 50 μm thick polyimide film as a sheet-like base material using an applicator, and then heated and dried at 120° C. for 30 minutes to form a coating on the polyimide base material. A laminate having a thermoelectric conversion film with a thickness of 3 μm was obtained. The obtained laminate was cut into a size of 1 cm x 5 cm, and electrodes having a thickness of 10 μm and a shape of 1 cm x 1 cm were made using silver paste so as to be electrically connected to both ends of the laminate. A thermoelectric conversion element was obtained. For each thermoelectric conversion element, bend it so that the thermoelectric conversion film and silver circuit are on the inside (along the line AA' shown in Figure 1), and place it in that state on a hot plate heated to 80°C. did. The degree of bending was adjusted so that the distance between BB' in FIG. 1 was 10 mm. The sample bent as described above was placed on a hot plate, and after 5 minutes, the electromotive force (mV) between the coating films was measured using an electromotive force meter (KEITHLEY 2400 manufactured by Tektronix). Measurements were carried out at 20°C. When the absolute value of the electromotive force in Comparative Example 1 is set to 1, Table 1 shows the relative values to the absolute value of the electromotive force in each example.

As shown in Table 1, the thermoelectric conversion element of the present invention exhibited high electromotive force. The mechanism of thermoelectric conversion in the present invention is considered as follows. If the organic compound (B) has greater adsorption to the conductive material (A) than the organic compound (C), the organic compound (B) will be more present on the surface of the conductive material (A) than the organic compound (C). It is thought that it is preferentially adsorbed. In order for thermoelectric conversion to occur, carrier movement must occur between the conductive material (A), the organic compound (B), and the organic compound (C). When the HOMO value of (B) is close to the HOMO value of the conductive material (A), carrier movement between the conductive material (A) and the organic compound (B) existing near the surface becomes smooth, and the organic compound (B) Since the carrier movement between the organic compounds (C) also becomes smooth, the carrier movement between the conductive material (A), the organic compound (B), and the organic compound (C) is performed efficiently, and the thermoelectric conversion efficiency is increased. Conceivable. On the other hand, in Comparative Example 1, the adsorption of the organic compound (B) to the conductive material (A) was greater than the adsorption of the organic compound (C) to the conductive material (A), and the HOMO of the organic compound (C) The HOMO value of the organic compound (B) is further away from the HOMO value of the conductive material (A) than the value. As a result, although requirements (1) and (2) above are met, requirement (3) is not met, and the transfer efficiency of carriers (electrons or holes) between organic compounds (C) is This is thought to indicate a low electromotive force.

Since the thermoelectric conversion material according to the embodiment of the present invention can obtain a high electromotive force, the above material can be used to provide a high-performance thermoelectric conversion element.

10: Test sample of thermoelectric conversion element 101: Thermoelectric conversion film 102: Electrode 20: Hot plate

Claims (4)

Contains a conductive material (A), an organic compound (B) (excluding the conductive material (A)), and an organic compound (C) (excluding the conductive material (A) and the organic compound (B)). , satisfies all of the following (1) to (3), and the difference between the HOMO of the organic compound (B) and the HOMO of the conductive material (A) is 0.1 to 2.0 eV, and the organic compound (C) A p-type thermoelectric conversion material in which the difference between the HOMO of and the HOMO of the organic compound (B) is 0.1 to 2.0 eV .
(1) 0<((HOMO of organic compound (B)) - (HOMO of conductive material (A))) x ((HOMO of organic compound (C)) - (HOMO of conductive material (A)))
(2) |(HOMO of organic compound (B)) - (HOMO of conductive material (A)) | < | (HOMO of organic compound (C)) - (HOMO of conductive material (A)) |
(3) The adsorption of the organic compound (B) to the conductive material (A) is greater than the adsorption of the organic compound (C) to the conductive material (A).
(However, HOMO represents the energy level of the highest occupied orbital. Also, when the conductive material (A) is a metal material, the HOMO of the conductive material (A) is the Fermi level of the conductive material (A). represent.) The p-type thermoelectric conversion material according to claim 1, wherein the conductive material (A) contains a carbon material. The p-type thermoelectric conversion material according to claim 2, wherein the carbon material includes carbon nanotubes. A thermoelectric conversion element comprising a thermoelectric conversion film comprising the p-type thermoelectric conversion material according to any one of claims 1 to 3 and an electrode, the thermoelectric conversion film and the electrode being electrically connected to each other.

Images