JP2003332638A - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material that exhibits practical- level thermoelectric conversion performance, can be worked easily, and is durable, and to provide a thermoelectric conversion element using the material. <P>SOLUTION: The thermoelectric conversion material is composed of a conductive polymer obtained by doping poly(3-alkyl thiophene) that has a head-to-tail structure and can have a substituting group other than 3-alkyl and having electric conductivity between 10<SP>4</SP>Ω<SP>-1</SP>m<SP>-1</SP>and 10<SP>7</SP>Ω<SP>-1</SP>m<SP>-1</SP>and exhibits practical-level thermoelectric conversion performance. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a thermoelectric conversion element which can be cooled or heated by utilizing the Seebeck effect to generate electric power from a temperature difference or by utilizing the Peltier effect to flow electricity. The present invention relates to a thermoelectric conversion material.

[0002]

2. Description of the Related Art Research and development of thermoelectric conversion materials is mainly conducted in BiTe,
Inorganic semiconductors such as BiPb, FeSi, and NaCoO have been the main focus, but since inorganic semiconductors often contain rare elements, they have a small amount of resources, and may contain harmful substances. There is a problem that it is difficult to process.
Since conductive polymers can overcome these problems,
In addition to inorganic semiconductors, research and development of thermoelectric conversion materials are being conducted for conductive polymers.

JP-A-2000-323758 and JP-A-2001-326393 describe that polyaniline is used as a conductive polymer and the thermoelectric conversion performance is improved by stacking or stretching. Is low and has not reached a practical level.

US Pat. No. 5,472,519 discloses that poly (3-octylthiophene) is used as a conductive polymer and iron chloride is used as a doping agent in a molar ratio of 2: 1. The conductivity is 0.74Ω. ^It is as low as ^-1 · m ^-1, and the thermoelectric conversion performance has not reached the practical level.

In US Pat. No. 5,973,050, high thermoelectric conversion performance is realized by dispersing metal particles in nanofaces without doping the conductive polymer, but the nanoface dispersion processing is not easy.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermoelectric conversion material having thermoelectric conversion performance at a practical level, easy to process and durable.

[0007]

The thermoelectric conversion material according to the present invention is a poly (3-alkylthiophene) which has a head-to-tail structure and may have a substituent other than 3-alkyl. It is characterized in that it is made of a conductive polymer having a conductivity of 10 ⁴ Ω ⁻¹ · m ⁻¹ or more and 10 ⁷ Ω ⁻¹ · m ⁻¹ or less obtained by performing a doping process.

[0008] Head-to-tail structure of a substituted or unsubstituted with a poly (3-alkylthiophene) doping treatment to the conductivity (sigma) of 10 ⁴ Ω ^-1 · m ^-1 or more and 10 ⁷ Omega ^- By adjusting within the range of ¹ · m ⁻¹ or less,
It is possible to improve the physical internal factor (TPF) and the thermoelectric figure of merit (Z), and the obtained thermoelectric conversion material exhibits a practical level of thermoelectric conversion performance.

According to the present invention, the physical intrinsic factor of the conductive polymer obtained by doping is set to 10 ⁻⁵ W · m ^−1.
・ K ⁻² or more, or thermoelectric figure of merit can be 10 ⁻⁴ K ⁻¹ or more.

Further, according to the present invention, by sealing the thermoelectric conversion material according to the present invention so as not to come into direct contact with the atmosphere, a thermoelectric conversion element capable of exhibiting a practical level of thermoelectric conversion performance for a long period of time. Is obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A thermoelectric conversion material according to the present invention has a head-to-tail structure, and 3
-Poly (3- that may have a substituent other than alkyl
It is characterized in that it is made of a conductive polymer having a conductivity of 10 ⁴ Ω ⁻¹ · m ⁻¹ or more and 10 ⁷ Ω ⁻¹ · m ⁻¹ or less, which is obtained by performing a doping treatment on (alkylthiophene).

[0012] Head-to-tail structure of a substituted or unsubstituted with a poly (3-alkylthiophene) doping treatment to the conductivity (sigma) of 10 ⁴ Ω ^-1 · m ^-1 or more and 10 ⁷ Omega ^- By adjusting within the range of ¹ · m ⁻¹ or less,
It is possible to improve a thermoelectric power factor (hereinafter abbreviated as TPF) and a thermoelectric figure of merit (Z), and the obtained thermoelectric conversion material exhibits a practical level of thermoelectric conversion performance.

The conductivity σ (unit: Ω ^-1 · m ^-1 ) is the reciprocal of the volume resistivity and serves as an index relating to the ease of electricity flow. When the conductivity σ of the conductive polymer is lower than 10 ⁴ Ω ⁻¹ · m ⁻¹ , thermocouples composed of two or more thermoelectric conversion materials are usually connected in series to perform thermoelectric conversion. Since the element constitutes an element, the internal resistance of the element increases, so that sufficient power cannot be supplied for power generation applications, and thermal efficiency for supplied power decreases for cooling and heating applications. When this conductivity σ is higher than 10 ⁷ Ω ^-1 m ^-1 , the contribution of electrons involved in heat conduction becomes large, so that the heat conductivity increases and the thermoelectric figure of merit (Z) becomes low. .

In the present invention, the TPF is 10 ⁻⁵ W · m.
^-1 · K ^-2 or more, or thermoelectric figure of merit (Z) is 10 ^-4 K
It is possible to obtain a conductive polymer having a value of ⁻¹ or more, preferably TPF and a thermoelectric figure of merit (Z) both of which are equal to or more than these values.

The TPF is expressed by the following equation TPF = S ² × σ (unit W · m ⁻¹ · K ⁻² ) (where S is the Seebeck coefficient (unit V · K ⁻¹ ), that is, per 1K of absolute temperature. The thermoelectromotive force, σ, is a value defined by the above-mentioned conductivity (unit: Ω ^-1 · m ^-1 ), and serves as an index of the output obtained by the thermoelectric conversion material. Conductive polymer TPF is 10 ^-5 W
When it is lower than m ⁻¹ · K ⁻² , the electric power obtained at a certain temperature difference applied to both ends of the thermoelectric conversion material is low and sufficient thermoelectric conversion performance cannot be exhibited. The conductive polymer TP
If F is 10 ⁻⁵ W · m ⁻¹ · K ⁻² or more, there is no problem in thermoelectric conversion performance, and the upper limit is not particularly limited, but the TPF of the conductive polymer obtained at present is 10 ⁻² W · m. ^-1・ K
^-2 is the maximum.

The thermoelectric figure of merit Z is expressed by the following equation: Z = S ² × σ / κ (unit K ⁻¹ ) (where S is the Seebeck coefficient (unit V · K ⁻¹ ) and σ is the conductivity. Rate (unit: Ω ^-1 · m ^-1 ), κ is a value defined by thermal conductivity (unit: W · m ^-1 · K ^-1 ) and represents the thermoelectric conversion performance of the thermoelectric conversion material. It will be an index. When the thermoelectric figure of merit Z is lower than 10 ^-4 K ^-1 , the electric power obtained at a certain temperature difference applied to both ends of the thermoelectric conversion material is low, or the thermal conductivity is high enough to maintain the temperature difference. Is not low, or both, so sufficient thermoelectric conversion performance cannot be exhibited. If the thermoelectric figure of merit of the conductive polymer is 10 ⁻⁴ K ⁻¹ or more, the thermoelectric conversion performance may be satisfactory, and the upper limit is not particularly limited, but the thermoelectric figure of merit of the conductive polymer obtained at present is 10 ^-1 K ^-1 is the maximum.

In the present invention, each of the thermoelectric characteristics is 10
A constant current generator capable of flowing a constant current of ^{-10 -4} mA, an electric furnace capable of controlling temperature from room temperature to 1000 ° C,
Using the precision potentiometer 1 shown in FIG. 1 equipped with a small heater 2 (measurable up to 0.1 μV), the film 3 made of the thermoelectric conversion material obtained by the present invention is set, and the conductivity σ and Seebeck coefficient for each temperature are set. It can be determined by measuring S. More specifically, the part Pt → is a platinum wire, and a current flows in the direction of the arrow. Further, Pt / Pt is formed on the thermoelectric conversion material film obtained by the present invention.
A thermocouple made of —Rh / Pt is provided, the potential is measured between Pt and Pt, and the temperature is measured by the Pt / Pt—Rh thermocouple.

The poly (3-alkylthiophene) has a main chain skeleton in which the structural units represented by the following formula 1 are connected or a main chain skeleton in which the double bond position varies depending on the conjugated system.

[0019]

[Chemical 1]

(In the formula, R represents an alkyl group.) 3-alkyl of poly (3-alkylthiophene) is usually
It is a chain or alicyclic alkyl having 1 to 12 carbon atoms and optionally having a branched or substituent, and among them, butyl, pentyl, hexyl, heptyl, octyl and the like having 4 to 4 carbon atoms.
An alkyl group of 8 is preferred. Poly (3-alkylthiophene) may have a substituent other than 3-alkyl introduced into the constituent unit of the main chain skeleton. The poly (3-alkylthiophene) may be a copolymer containing a constitutional unit other than the 3-alkylthiophene unit as long as the molecular chain has a π-conjugated system. Those containing 50 mol% or more of the chain skeleton are preferable.

Among the poly (3-alkylthiophenes), the head-to-tail structure is a structure represented by the following formula 2, and the head-to-head structure or the formula represented by the formula 3 may be used depending on the polymerization method of the monomer. In some cases, the tail-to-tail structure shown in FIG. Usually, the structures of Formula 2, Formula 3, and Formula 4 coexist in one molecular chain.
Most of them can have a head-to-tail structure by the synthetic method described in m. Chem. Soc., 117, 233-244 (1995).

[0022]

[Chemical 2]

[0023]

[Chemical 3]

[0024]

[Chemical 4]

In the present invention, poly (3-alkylthiophene) having a head-to-tail structure in which 3-alkylthiophene units are connected occupying 80 mol% or more, particularly 90 mol% or more of the main chain skeleton is preferably used. To be

The above head-to-tail structure poly (3
-Alkylthiophene) has a conductivity of 10 ⁴ Ω ^-1 m ^-1 or more, preferably 5 × 10 ⁴ Ω ^-1 m ^-1 by doping.
It is possible to increase the above, and high thermoelectric conversion performance is obtained.

In addition, poly (3-alkylthiophene) having a head-to-tail structure has high solubility in organic solvents such as toluene, xylene, and chloroform among the conductive polymers, and especially before doping, A thin film can be easily formed by dissolving using the above organic solvent and applying casting, spraying, spin coating, or the like, and processing for forming a thermoelectric conversion element is easy.

By subjecting the poly (3-alkylthiophene) thin film to a stretching treatment, the electrical conductivity in the stretching direction can be increased and the thermoelectric conversion performance can be improved. When the stretching treatment is performed, the stretching ratio (%), that is, the ratio of the length in the stretching direction after stretching to the length before stretching is preferably 150% or more, and particularly preferably 200% or more. The higher the draw ratio, the greater the degree of molecular alignment, and thus the greater the effect of increasing the conductivity.

Doping agent (dopant) for doping the above poly (3-alkylthiophene)
, P83 of the book "Conductive Polymer" (edited by Naoya Ogata, published by Kodansha Scientific Publishing, 1990)
~ P90, there are acceptor dopants that accept electrons from π-conjugated polymers and donor dopants that donate electrons. A material having a high electron affinity is used as the acceptor dopant, and a material having a low ionization potential is used as the donor dopant.

Specific examples of the doping agent include Cl ₂ , Br ₂ , I ₂ , and ICl as acceptor dopants.
Halogen such as ICl ₃ , IBr, IF; PF ₅ , As
Lewis acids such as F ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ , and SO ₃ ; HF, HCl, HNO ₃ , H ₂ SO ₄ , HCl
O ₄ , protic acid such as phosphoric acid, organic acid such as 2-naphthalene sulfonic acid, dodecylbenzene sulfonic acid, camphor sulfonic acid; FeCl ₃ , FeOCl, TiCl ₄ , Z
_{rCl 4, HfCl 4, NbF 5} , NbCl 5, TaC
Examples include transition metal compounds such as l ₅ , MoF ₅ and WF ₆ . Further, as a donor dopant, Li, Na, K,
Alkali metals such as Rb and Cs, alkaline earth metals such as Ca, Sr and Ba, lanthanoids such as Eu, and other R
₄ N ⁺ , R ₄ P ⁺ , R ₄ As ⁺ , R ₃ S ⁺ (R: alkyl group),
Acetylcholine and the like can be mentioned.

The conductivity σ is adjusted within the above range by reacting a doping agent such as an acceptor or a donor with a π-conjugated polymer by a known vapor phase method or a liquid phase method to perform chemical doping. It is possible to obtain a conductive polymer having a high TPF and a thermoelectric figure of merit Z. Since the conductivity σ tends to increase as the atmospheric pressure during doping in the vapor phase method decreases and that in the liquid phase method where a doping agent concentration is higher, the conductivity can be changed by changing the conditions of these doping treatments. It is possible to adjust the rate σ to a predetermined value.

In order to produce the thermoelectric conversion material of the present invention, a solution of the above poly (3-alkylthiophene) having a head-to-tail structure is prepared, and a polymer is used to form a thin film. The thin film thus formed may be subjected to doping treatment. As an example of a specific procedure, head-to-
A poly (3-alkylthiophene) having a tail structure is dissolved in an organic solvent such as toluene, xylene, or chloroform to prepare a polymer solution, and the polymer solution is used as a partner material when forming a thermocouple. A thin film of π-conjugated polymer with a predetermined thickness is formed by coating it on a support and drying it, and a doping agent selected appropriately is brought into contact with this film by a vapor phase method or a liquid phase method for chemical doping. By removing the excess doping agent as needed, a thermoelectric conversion material composed of a thin film of a conductive polymer having the conductivity σ, TPF and thermoelectric figure of merit Z in the above ranges is formed.

As another procedure, a polymer solution prepared in the same manner as the above procedure is coated on a temporary support and dried to form a thin film of the poly (3-alkylthiophene) having a predetermined thickness. By peeling this thin film from the support, immersing it in a liquid containing an appropriately selected doping agent to perform liquid phase doping, and washing it as necessary, the conductivity σ, TPF and thermoelectric performance in the above range can be obtained. A thermoelectric conversion material including a thin film of a conductive polymer having an index Z is formed. A thermoelectric conversion element is formed by laminating a thin film of this thermoelectric conversion material on a thin film or any support that is a mating material when constructing a thermocouple after subjecting to a stretching treatment such as uniaxial stretching as necessary. can do.

The thin film of the thermoelectric conversion material made of a conductive polymer is usually about 1 μm to 10 mm thick. If this thickness is too thin, the film resistance will be high, resulting in a loss of power to be taken out. If it is too thick, there is no problem in terms of performance, but the material is wasted, which is disadvantageous in terms of cost.

The thermoelectric conversion material of the present invention thus obtained is sealed so as not to come into direct contact with the atmosphere by a method such as coating the surface of the material with a known sealing agent such as an epoxy type sealing agent. By this, deterioration can be prevented, and thermoelectric properties at a practical level can be maintained for a long time.

Even when the thermoelectric conversion material of the present invention is combined with another thermoelectric conversion material to form a thermocouple and the thermoelectric conversion element is assembled, the thermoelectric conversion material of the present invention is sealed so as not to come into direct contact with the atmosphere. By using it, the thermoelectric conversion performance of a practical level can be exhibited for a long period of time.

[0037]

【Example】

Example 1 A coating liquid having the following composition was prepared. <Composition> ・ Poly (3- (head-to-tail) structure with 98% or more
Hexylthiophene) (manufactured by Aldrich): 1 part by weight / chloroform: 99 parts by weight This coating solution was dropped on a slide glass to form a cast film, and dried under reduced pressure at room temperature (23 ° C.) (2 mmHg (about 266).
N · m ⁻² )) was carried out for 2 hours to obtain a coating film having a thickness of 5 μm.
Then, vapor phase doping (vapor pressure 1 mmHg (about 133 N · m ⁻² )) was performed using iodine as a doping agent to obtain a conductive polymer film. The doping rate was 50% as the molar ratio of I ₃ ^{− to} the monomer unit.

About this conductive polymer film, at room temperature (23
The thermoelectric properties in the in-plane direction at
The results shown in the table were obtained, and it was revealed that the thermoelectric conversion performance was high.

Among the thermoelectric properties in the table, the conductivity σ (unit Ω
⁻¹ · m ⁻¹ ) and Seebeck coefficient S (unit V / K ⁻¹ ) are
Thermoelectric property evaluation device manufactured by ULVAC-RIKO: ZEM-
2 was used, and the thermal conductivity κ (unit: W · m ⁻¹ · K ⁻¹ ) was measured using an optical alternating current method thermal constant measuring device: laser-PIT manufactured by ULVAC-RIKO, Inc. TPF (Unit: W ・ m ^-1・
K ⁻² ) and thermoelectric figure of merit (unit K ⁻¹ ) were calculated from the measured values of conductivity σ, Seebeck coefficient S and thermal conductivity κ.

Further, a one-pack type epoxy sealant (product name 2200, manufactured by ThreeBond Co., Ltd.) is applied to the surface of the conductive polymer film and cured to seal it so as not to come into direct contact with the atmosphere, and the temperature is set to 40 ° C. When the thermoelectric properties were measured in the same manner after storage for 4 days in an environment of 90% RH, all physical properties retained 90% or more of the performance before storage. On the other hand, when the sample is stored without being sealed, it is 30
The value had dropped to below%.

[0041]

[Table 1]

[0042]

The conductivity of the substituted or unsubstituted poly (3-alkylthiophene) having the head-to-tail structure is 10 ⁴ Ω ^-1 m ^-1 or more and 10 ⁷
The conductive polymer obtained by adjusting to within the range of Ω ^-1 · m ^-1 or less exhibits thermoelectric conversion performance of a practical level and is excellent in processability because it is an organic polymer material If it is sealed so that it does not come into contact with it, it has durability and does not deteriorate for a long period of time, and continues to maintain excellent thermoelectric conversion performance, so it can be suitably used as a thermoelectric conversion material.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an apparatus for measuring thermoelectric characteristics.

[Explanation of symbols]

1 ... Measuring device 2 ... Small heater 3 ... Film of thermoelectric conversion material

Claims (4)

[Claims] 1. A head-to-tail structure and 3
-Poly (3- that may have a substituent other than alkyl
A thermoelectric conversion material comprising a conductive polymer having a conductivity of 10 ⁴ Ω ⁻¹ · m ⁻¹ or more and 10 ⁷ Ω ⁻¹ · m ⁻¹ or less, which is obtained by performing a doping treatment on (alkylthiophene). 2. The physical intrinsic factor of the conductive polymer is 1.
The thermoelectric conversion material according to claim 1, which is 0 ^-5 W · m ⁻¹ · K ⁻² or more. 3. The thermoelectric figure of merit of the conductive polymer is 10.
^-4 K ^-1 or more, The thermoelectric conversion material of Claim 1 or 2. 4. A thermoelectric conversion element in which the thermoelectric conversion material according to claim 1 is sealed so as not to come into direct contact with the atmosphere.