WO2015129877A1 - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

An organic thermoelectric conversion material containing: a basic skeleton that comprises a polycyclic aromatic ring having carrier transport properties; and a conductive compound that bonds to the basic skeleton and includes an alkyl group which causes the intermolecular distance and molecular packing structure of the basic skeleton to change due to thermal motion.

Description

Thermoelectric conversion material and thermoelectric conversion element

The present invention relates to an organic thermoelectric conversion material and a thermoelectric conversion element manufactured using the material.

In recent years, attention has been focused on thermoelectric conversion elements as a means for recovering unused thermal energy in the environment as electrical energy.

Conventionally, as a thermoelectric conversion material, an inorganic semiconductor material such as CoSb ₃ has been mainly used and studied because of its relatively high thermoelectric conversion efficiency. However, such an inorganic semiconductor material contains a rare element and is expensive. In addition, there is a problem that the workability of the material is poor. For this reason, in recent years, research on organic thermoelectric conversion materials that are inexpensive and excellent in workability of materials has been actively conducted.

Conventional organic thermoelectric conversion materials include conductive materials such as polyaniline ( Patent Documents 1, 3, 4, 5 and 7), polyphenylene vinylene (Patent Document 2), polythienylene vinylene (Patent Document 2), and polypyrrole (Patent Document 4). A material composed of a functional polymer has been proposed.

However, these conductive polymers do not have sufficient thermoelectric conversion performance, and higher thermoelectric conversion performance is required for practical use. In response to the demand for increasing the thermoelectric conversion efficiency of such a thermoelectric conversion material, conventionally, a dopant is introduced ( Patent Documents 2, 3, 4, 5 and 6), or a layer made of a doped conductive polymer. And a layer made of an undoped conductive polymer (Patent Document 4), dispersed metal particles (Patent Document 1), specified for the energy level of the molecular orbital of the conductive polymer It has been proposed to include a thermal excitation assisting agent having a molecular orbital of the energy level difference (Patent Document 7).

By the way, the thermoelectric conversion efficiency of the thermoelectric conversion material is generally expressed by the following formula [Equation 1] dimensionless figure of merit ZT = S ² · σ · T / κ (A)
[Wherein, S (V / K) represents the thermoelectromotive force (Seebeck coefficient), σ (S / m) represents the electrical conductivity, κ (W / mK) represents the thermal conductivity, and T (K) Represents an absolute temperature, and S ² · σ represents a power factor. ]
The dimensionless figure of merit (ZT) expressed by As can be understood from the above formula, the dimensionless figure of merit (ZT) means that the higher the Seebeck coefficient and the electrical conductivity, the higher the thermal conductivity, the higher the thermoelectric conversion performance. Among materials that can obtain a high ZT, especially those with a large Seebeck coefficient are flexible thermoelectric conversion elements that use organic thermoelectric conversion materials. Operation by disconnection by reducing the thickness of the element or reducing the number of cells connected in series It is possible to reduce defects.

In this respect, the introduction of the dopant and the dispersion of the metal particles described above are intended to improve the thermoelectric conversion efficiency mainly by increasing the conductivity. According to the conventional thermoelectric theory for non-degenerate semiconductors, the Seebeck coefficient and conductivity are in a certain trade-off relationship, and the Seebeck coefficient shows a maximum value when the carrier density is small, and becomes smaller as the carrier density increases. (Non-Patent Document 2) In the conventional conductive polymer, the Seebeck coefficient was about several mV / K even at the maximum value.

In contrast, an attempt to include the above-described thermal excitation assist agent is to improve thermoelectric conversion efficiency by increasing the thermoelectromotive force (Seebeck coefficient). However, it does not improve the electromotive polymer itself to increase the thermoelectromotive force (Seebeck coefficient).

Furthermore, Shimada et al. Pay attention to the sudden occurrence of deep traps at low temperatures in organic semiconductors, and expect that the Seebeck coefficient will increase at low temperatures due to point defects for pentacene, which is a low molecular semiconductor (Non-Patent Document 4). . However, the Seebeck coefficient shown by Shimada et al. Is about 1 mV / K, and does not give any teaching on the direct improvement of Seebeck coefficient due to the thermal motion of the molecule and the molecular design therefor.

JP 2010-95688 A JP 2009-71131 A JP 2001-326393 A JP 2000-323758 A JP 2002-100815 A JP 2003-332639 A International Publication No. 2013/047730

An object of the present invention is to provide an organic thermoelectric conversion material exhibiting a significantly larger Seebeck coefficient than conventional organic thermoelectric conversion materials.

In view of the above problems, the present inventors examined the molecular design of a conductive compound that achieves excellent thermoelectric conversion efficiency without being bound by the thermoelectric theory in conventional semiconductors. In general, it has a structure derived from a polycyclic aromatic compound having a high carrier transport ability, and on the other hand, it is a compound having a side chain that thermally moves at a predetermined temperature, which is not expected from conventional thermoelectric theory. It has been found that it has a high Seebeck coefficient. The present invention is based on such knowledge.

That is, this invention provides the following organic thermoelectric conversion materials and organic thermoelectric conversion elements.
[1] A conductive compound in which a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties is bonded with a substituent containing an alkyl group that causes a change in the intermolecular distance or molecular packing structure of the basic skeleton by thermal motion. Organic thermoelectric conversion material.
[2] An alkyl group or a substituent having an alkyl group is bonded to a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties, and a structural phase transition (specified by DSC) at a temperature in the range of −50 ° C. to 200 ° C. The organic thermoelectric conversion material according to [1], comprising a conductive compound.
[3] The organic thermoelectric conversion material according to [1] or [2], wherein the conductive compound is represented by the following general formula (1).

(In the formula, X represents a polycyclic aromatic ring having carrier transport properties, and n represents an integer of 1 or more. When n is 2 or more, each X may be a different polycyclic aromatic ring. R represents each independently an alkyl group or a substituent having an alkyl group, and m represents a number equal to or less than the maximum number that R can be bonded to X, and generally represents an integer of 1 to 8.)
[4] The organic thermoelectric conversion material according to any one of [1] to [3], wherein the conductive compound is represented by the following general formula (2).

(In the formula, X represents a polycyclic aromatic ring having carrier transport properties, R represents an alkyl group or a substituent having an alkyl group, and m represents a maximum number of R or less that can be bonded to X. Represents a number, usually an integer from 1 to 8.)
[5] The organic thermoelectric conversion material according to any one of [1] to [4], wherein the van der Waals volume ratio occupied by the substituent in the conductive compound is 5 to 80%.
[6] The organic thermoelectric conversion material according to any one of [1] to [5], wherein a structural phase transition point by DSC of the conductive compound is recognized at a temperature in the range of 0 to 180 ° C.
[7] The organic thermoelectric conversion material according to any one of [1] to [6], wherein the polycyclic aromatic ring is a polycyclic aromatic aromatic hydrocarbon or a polycyclic aromatic heterocycle.
[8] The organic thermoelectric conversion material according to any one of [1] to [7], wherein the polycyclic aromatic heterocycle is heteroacene or polyheteroacene.
[9] The organic thermoelectric conversion material according to [1] to [7], wherein the polycyclic aromatic heterocycle is porphyrin or porphyrazine.
[10] The organic thermoelectric conversion material according to any one of [1] to [9], wherein the polycyclic aromatic heterocycle is a compound represented by the formula (3), (4) or (5).

(In the formula, each Y independently represents S, Se, SO ₂ , O, N (R ₅₁ ) or Si (R ₁ ) (R ₅₂ ), and R ₅₁ and R ₅₂ each independently represent a hydrogen atom, An aryl group, a monocyclic aromatic heterocyclic residue; an amino group, an alkyloxy group, an alkylthioxy group, an ester group, a carbamoyl group, an acetamide, a thio group or an acyl group substituted with an alkyl group or an aromatic ring residue; Y may be different from each other, Z ₁ and Z ₂ each independently represent a hydrogen atom, an aromatic hydrocarbon or an aromatic heterocyclic ring, and Z ₁ and Z ₂ may be the same or different.

(In the formulas (4) and (5), W independently represents N or C—, at least one is C—, and an alkyl group or a substituent containing an alkyl group is bonded thereto, and Z is Each independently represents a hydrogen atom, an aromatic hydrocarbon or an aromatic heterocycle, which may be the same or different, and M represents a metal atom.)
[11] Any of [1] to [10], wherein the conductive compound is a compound represented by formula (6), (7), (10), (11), (12) or (13) Organic thermoelectric conversion material according to crab.

In the formulas (6) and (7), X ₁ and X ₂ are the same as Y in the formula (3), and the formulas (6), (7), (10), (11), (12) and ( 13) wherein at least one of R ₁ and R ₂ , typically both, at least one of R _{3 to} R ₁₄ , and R _{47 to} R ₅₀ are the same as R in formula (1) above, m ^{1 to} m ⁴ are the same as m in the above formula (1), R _{47 to} R ₄₉ are bonded to one or more W, and R ₅₀ can be bonded to a bondable position of the basic skeleton. , Preferably bound to one or more W.
[12] An organic thermoelectric conversion element having a thermoelectric conversion layer containing the thermoelectric conversion material according to any one of [1] to [11].
[13] A horizontal or vertical organic thermoelectric conversion element having a thermoelectric conversion layer containing the thermoelectric conversion material according to any one of [1] to [11].

The present invention can provide an organic thermoelectric conversion element having an Seebeck coefficient much higher than that of a conventional organic thermoelectric conversion material and an organic thermoelectric conversion element having a thermoelectric conversion layer including the organic thermoelectric conversion material.

FIG. 1 is a graph showing van der Waals volume ratios of C8BTBT, C10DNTT and C12BP. FIG. 2 shows analytical data of differential scanning calorimetry (DSC) of C12H25-H2BP. FIG. 3 shows analysis data of differential scanning calorimetry (DSC) of H2BP. FIG. 4 is analysis data of differential scanning calorimetry (DSC) of C10DNTT. It is a figure which shows an example of the horizontal type thermoelectric conversion element of this invention. The arrows in the figure indicate the direction in which the temperature difference applied when the element is used. It is a figure which shows an example of the vertical thermoelectric conversion element of this invention. The arrows in the figure indicate the direction in which the temperature difference applied when the element is used. The analytical data of differential scanning calorimetry (DSC) of C12BP of Example 5 and the relative value of a power factor are shown.

Hereinafter, embodiments of the present invention will be described in detail.
The organic thermoelectric conversion material of the present invention has a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties and an alkyl group or a substituent having an alkyl group bonded thereto, and undergoes a structural phase transition at a predetermined temperature. The resulting conductive compound is contained as a thermoelectric conversion substance.

The conductive compound used in the present invention has a basic skeleton derived from a polycyclic aromatic compound having a planar π-conjugated structure and generally having a high carrier transport ability. In such a structure, π-π stacking is expected between adjacent molecules, and the transfer integral between adjacent molecules is so large that band conduction can be expected at room temperature. On the other hand, in the conductive compound used in the present invention, a substituent that causes a change in the intermolecular distance of the basic skeleton or the molecular packing structure is bonded to the polycyclic aromatic ring by thermal motion at a predetermined temperature. Such a substituent has a rotation-free bond like an alkyl group or a substituent having an alkyl group, and changes the distance between adjacent molecules or the molecular packing structure by thermal movement at a predetermined temperature. , Causing volume change and structural phase transition of the conductive compound. As a result, it is understood that the thermoelectromotive force (Seebeck coefficient) can be increased by sensitively detecting the temperature change.

Here, definitions are given for some terms used in this specification.
“Polycyclic aromatic compound” means a compound having a polycyclic aromatic ring, and “basic skeleton composed of a polycyclic aromatic compound” means a substituent moiety in the entire structure of such a compound. It means the structure excluded.
“Van der Waals volume” means the volume of a molecule or its component when the atoms constituting the molecule are approximated by a sphere having a van der Waals radius. The “van der Waals volume ratio” is the ratio of the van der Waals volume of a plurality of components constituting a molecule.
“Length of side chain” means the atom of the atom that is the most distant from the center position of the atom that constitutes the main skeleton and the center position of the atom that is chemically bonded to the side chain in the stable structure. It means the distance to the center position.
“Π-conjugated structure” represents a structure in which multiple bonds are alternately connected to single bonds, and “planar π-conjugated structure” means a structure in which atoms forming a π-conjugated structure exist in the same plane.
“Thermo-electromotive force (Seebeck coefficient)” is the temperature dependence of the steady potential difference occurring at two different locations on a material having electrical conductivity, and S = −ΔV / ΔT (ΔV is the potential difference from the gradient) , ΔT means a value calculated by a temperature difference).
“Conductivity” means a value obtained by multiplying the electrical conductance obtained from the current-voltage characteristics of the material measured by a source meter or the like by the length of the current path and dividing the result by the cross-sectional area.
“Thermal conductivity” means a value obtained by multiplying the thermal diffusivity measured by the thermoreflectance method, the temperature wave analysis method, the steady heat flow method, etc., with the specific heat and density of the material.
In this specification, “structural phase transition” means that a structure (which may be an ordered structure or a disordered structure) that can be regarded as spatially uniform in a substance is transformed into a structure in a different state depending on external conditions such as temperature. “Structural phase transition temperature” means the temperature at which the change appears. When the structural phase transition temperature is measured, for example, by differential scanning calorimetry (DSC), an endothermic or exothermic peak appears, and the temperature dependence of specific heat changes (the gradient obtained by differentiating specific heat with temperature changes suddenly). Measured in Moreover, while the temperature dependence of the electrical conductivity in a semiconductor material shows Arrhenius type thermal activity, it is also measured as the temperature at which the activation energy changes suddenly.

The conductive compound contained in the organic thermoelectric conversion material of the present invention typically includes a compound represented by the following general formula (1) or (2).

In the formulas (1) and (2), X represents a polycyclic aromatic ring having carrier transport properties, and R independently represents an alkyl group or a substituent having an alkyl group. m is a number equal to or less than the maximum number of R that can be bonded to X, and varies depending on the basic skeleton, for example, an integer of 1 to 8, typically an integer of 1 to 2. In formula (1), n is an integer of 1 or more, and when n is 2 or more, X may be a different polycyclic aromatic ring.

As described above, the polycyclic aromatic ring represented by X constituting the basic skeleton of the conductive compound contained as the thermoelectric conversion substance in the organic thermoelectric conversion material of the present invention has a structure in which two or more aromatic rings are condensed. And has a planar π-conjugated structure. For this reason, the molecules are aligned and are likely to cause a stacking effect between adjacent molecules, and movement of electrons or holes between the molecules is facilitated, so that high carrier mobility is easily obtained.

The polycyclic aromatic ring represented by X can be composed of one or both of an aromatic hydrocarbon and an aromatic heterocyclic ring, and it is preferable to select a polycyclic structure having high carrier mobility. .

Specific examples of the polycyclic aromatic ring represented by X include, for example,
Naphthalene, anthracene, tetracene, pentacene, hexacene, heptacene, acenaphthene, naphthacene, azulene, phenalene, benzoanthracene, phenanthrene, chrysene, anthanthrene, pyranthrene, indenoindene, picene, triphenylene, perylene, naphthoperylene, coronene, obalene, pyrene, Benzopyrene, hexahelicene, heptahelicene, octahelicene, nonahelicene, decahelicene, undecahelicene, dodecahelicene, etc .; polycyclic aromatics such as tetraphen, pentaphen, hexaphene, heptaphene, octaphene, nonaphene, decaphene, undecaphene, dodecaphene, C60 fullerene, C70 fullerene Hydrocarbons; and indole, isoindole, purine, quinoline, isoquinolyl Quinoxaline, cinnoline, pteridine, benzopyran, acridine, xanthene, benzimidazole, indazole, phenazine, naphthyridine, benzothiadiazole, benzothiazole, dithienosilole, fluorene, thienothiophene, carbazole, phenothiazine, phenoxazine, benzothienobenzothiophene, dithieno Heteroacenes such as thiophene, benzodithiophene, benzodiselenophene, dinaphthothienothiophene, dianslathienothiophene, benzobisoxazole, and polyheteroacenes in which these are bonded together, phenanthrene, phenanthridine, cyclopentadithiophene, Benzo-C-cinnoline, perylene dicarboxyimide, benzotrifuran, benzotrithiophene, porphyri , Chlorine, choline, phthalocyanine, and a polycyclic aromatic heterocyclic rings such as porphyrazine.

Among these, acene hydrocarbons such as naphthalene, anthracene, naphthacene, and pentacene, heteroacenes such as benzodithiophene, benzothienobenzothiophene, and dinaphthodithiophene, or porphyrin, phthalocyanine, porphyrazine, etc. Is preferred.

Non-limiting specific examples of the basic skeleton of the polycyclic aromatic compound are shown below.

As described above, the basic skeleton of the conductive compound may form a π-conjugated structure by connecting two or more polycyclic aromatic rings with a single bond. When the basic skeleton is constituted by connecting a plurality of polycyclic aromatic rings, the number of polycyclic aromatic rings is generally 2 to 2000, preferably 2 to 1000, It is more preferably 2 to 100, and further preferably 2 to 5. Of course, the basic skeleton may be composed of a single polycyclic aromatic ring. Further, the molecular weight (Mw) of the basic skeleton constituted by one or a plurality of polycyclic aromatic rings may be 50 to 200,000, preferably 100 to 100,000, more preferably 200 to 50,000 Mw, particularly preferably. 200 to 30000.

The conductive compound contained in the organic thermoelectric conversion material of the present invention has a π-conjugated structure developed by the polycyclic aromatic ring and an alkyl group represented by R on the polycyclic aromatic ring. Alternatively, a substituent having an alkyl group is bonded.
Such a substituent has a rotation-free bond and causes thermal motion at a predetermined temperature, preferably any temperature in the range of −50 ° C. to 200 ° C. Such a substituent moves in response to heat sensitively, and causes a volume change or a structural phase transition of the conductive compound. As a result, the carrier transport ability of the basic skeleton of the polycyclic aromatic compound is modulated to enable highly efficient thermoelectric conversion. Such a structural phase transition of the conductive compound due to the thermal motion of the substituent can be confirmed by an endothermic peak of differential scanning calorimetry (DSC).

In order to generate thermal motion in response to heat sensitivity, it is preferable that the substituent is bonded to the polycyclic aromatic skeleton by a free covalent bond. In addition, the substituent itself preferably has a large number of covalent bonds that are free to rotate. From such a point, the substituent is preferably a substituent having an alkyl group, and a chain-like alkyl group has a main chain. More preferably a linear alkyl group.

In order to achieve a high thermoelectromotive force (Seebeck coefficient), the structural phase transition is performed in response to heat sensitively by the thermal motion of substituents while maintaining the π-conjugated structure developed by the polycyclic aromatic ring. From this point of view, the van der Waals volume ratio of the side chain to the polycyclic aromatic skeleton is considered to be one of the indicators. The cohesive strength depending on the crystallinity and crystal form differs depending on the difference in the polycyclic aromatic skeleton, and the bonding strength between the molecules is different. Generally, in the conductive compound contained in the thermoelectric conversion material of the present invention, the same compound The van der Waals volume ratio occupied by the substituents in it is preferably 5% to 80%, more preferably 25 to 60%, and even more preferably 30 to 60%. Further, it is more preferably 10 to 50%, and particularly preferably 15 to 50%. By designing the van der Waals volume ratio of the side chain to this polycyclic aromatic skeleton, it is possible to control the temperature and thermal motion of the structural phase transition. Although the required temperature (temperature difference) differs depending on the environment in which the element is used, a suitable element can be designed by utilizing this ability.

From the same point, the alkyl group portion of the alkyl group or the substituent having an alkyl group is a chain or cyclic, preferably linear, group having 1 to 20 carbon atoms, more preferably 2 to 2 carbon atoms. 18 groups, and more preferably a group having 4 to 15 carbon atoms.

Specifically, as the linear alkyl group, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group , Tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group Group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group are preferable, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group Groups are more preferred.

Examples of the branched alkyl group include isopropyl group, isobutyl group, isoamyl group, s-butyl group, t-butyl group, 2-methylbutyl group, 2-methylhexyl group, 2-ethylhexyl group, 2-methyloctyl group, 2-ethyloctyl group can be mentioned, such as isobutyl group, isoamyl group, s-butyl group, t-butyl group, 2-methylbutyl group, 2-methylhexyl group, 2-ethylhexyl group, 2-methyloctyl group, 2 -Ethyloctyl group. Examples of the cyclic alkyl group include a cyclopentyl group and a cyclohexyl group.

As a substituent which has an alkyl group, the group by which the alkyl group was substituted by the following substituents is mentioned, for example.
1) Aryl group such as phenyl group, biphenyl group, naphthyl group 2) Furyl group, thienyl group, thienylene group, tenenyl group, pyridyl group, piperidyl group, quinolyl group, isoquinolyl group, imidazolyl group, morpholino group, benzothienyl group, Monocyclic aromatic heterocyclic residues such as benzophenyl groups 3) amino groups, alkyloxy groups, alkylthioxy groups, ester groups, carbamoyl groups, acetamides, thio groups substituted with alkyl groups or aromatic ring residues Acyl group 4) Halogen atom such as fluorine atom, chlorine atom, bromine atom, nitro group, cyano group These substituents may have one or more.

Moreover, the group which the alkyl group has couple | bonded with the polycyclic aromatic skeleton through the following chemical structures is mentioned.
1) Hetero atoms such as oxygen atom, nitrogen atom, sulfur atom, silicon atom and phosphorus atom 2) Aryl group such as phenyl group, biphenyl group and naphthyl group 3) Furyl group, thiophene group, thienyl group, thienylene group and tenenyl group , Pyridyl group, imidazolyl group, morpholino group, benzothienyl group, benzophenyl group, etc. 4) carbonyl group, thiocarbonyl group

Examples of the substituent having an alkyl group include an alkyl group substituted with a silylethynyl group, an alkyl group substituted with an aryl group (for example, a phenyl group, a biphenyl group, a naphthyl group, etc.), an aromatic heterocyclic group (for example, , Furyl group, thienyl group, pyridyl group, imidazolyl group, etc.) substituted alkyl group, alkoxyl group (for example, methoxy group, ethoxy group, propyloxy group, pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group) Group), a cycloalkoxyl group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), an alkyl group substituted with an aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), an alkylthio group (eg, methylthio group, ethylthio). Group, propylthio group, pentylthio group, hexyl O group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (eg, cyclopentylthio group, cyclohexylthio group, etc.), alkylthio group substituted with arylthio group (eg, phenylthio group, naphthylthio group, etc.), alkoxycarbonyl group ( For example, a methyloxycarbonyl group, an ethyloxycarbonyl group, a butyloxycarbonyl group, an octyloxycarbonyl group, a dodecyloxycarbonyl group, etc.), an aryloxycarbonyl group (eg, a phenyloxycarbonyl group, a naphthyloxycarbonyl group, etc.) Alkyl group, alkylsulfamoyl group, alkylcarbonyl group, alkylthiocarbonyl group, alkylcarbonyloxy group, alkylcarbonylamino group, alkylcarbamoyl group, alkylureido group, Ruki Rusuru alkylsulfinyl group, an alkylsulfonyl group, an alkyl group substituted with an arylsulfonyl group, an alkylamino group, fluoroalkyl group, perfluoroalkyl group, alkylsilyl group, and the like.
The conductive compound contained in the conductive material of the present invention may have a plurality of substituents for one of the above-described polycyclic aromatic rings, and usually 1 to 1 per polycyclic aromatic ring. 8 substituents, preferably 1 to 4 substituents, more preferably 1 to 3 substituents, and particularly preferably 2 substituents.

Further, in the conductive compound constituting the present invention, the molecular weight of the alkyl group moiety of the above-described substituent (the alkyl group itself when the substituent is an alkyl group) is 5 to 80 with respect to the molecular weight of the entire conductive compound. % Is preferable. For example, in the case of a rod-like compound in which one width of the polycyclic aromatic skeleton is narrow to about one benzene ring and the other width is longer than that, the ratio is more preferably 25 to 60%. It is preferable that the width of the skeleton part is a compound having a width wider than about two benzene rings, and the ratio thereof occupies 10 to 50%. In addition, it is preferable that a plurality of rotationally free bonds exist throughout the substituent. On the other hand, the structure other than the alkyl group may form a π-conjugated structure together with the polycyclic aromatic ring. By appropriately adjusting the number of alkyl groups, the substitution position, the number of branched chains, and the length, it is possible to obtain optimum characteristics.

The temperature causing the structural phase transition of the conductive compound varies depending on the combination of the basic skeleton of the polycyclic aromatic compound and the substituent. Accordingly, it is preferable to appropriately design a molecular according to the temperature at which the conductive compound is expected to be used. In particular, in the conductive compound of the present invention, it is considered that the temperature of the phase transition of the thermoelectric conversion material and the thermal motion can be controlled by controlling the length of the alkyl group of the conductive compound. Therefore, it is considered that an effective thermoelectric conversion element can be obtained by appropriately selecting the combination of the basic skeleton and the substituent, particularly the length of the alkyl group or the van der Waals volume ratio, according to the environment in which the element is used. .
From the normal use of thermoelectric conversion elements, it is preferable to use a molecular design that causes a structural phase transition at a temperature in the range of −50 ° C. to 200 ° C. More preferably, the molecular design causes a structural phase transition at a temperature in the range of 10 to 150 ° C. Therefore, it is preferable to select the combination of the basic skeleton and the substituent, particularly the length of the alkyl group or the van der Waals volume ratio so that the structural phase transition occurs in such a temperature range.
The temperature (structural phase transition point) at which the structural phase transition of the conductive compound occurs can be confirmed by the endothermic peak of differential scanning calorimetry (DSC). A thermoelectric conversion element showing a relative value of a large power factor in the vicinity of the temperature at which the structural phase transition of the conductive compound is observed can be confirmed to be an optimal thermoelectric conversion material for setting the vicinity of the temperature as the use temperature.

From such a viewpoint, typical examples of preferable conductive compounds are shown below.

(1) Conductive compound having a porphyrin skeleton

In formula (5), M represents a metal atom. In the formulas (4) and (5), each Z is independently a hydrogen atom, or an aromatic hydrocarbon or aromatic heterocyclic ring substituted with an unsubstituted or substituted group having an alkyl group or an alkyl group. Substituted aromatic hydrocarbons or aromatic heterocycles are preferred. A plurality of Z may be the same or different.
Each W independently represents N or CR ₃ , at least one W represents CR ₃ , R ₃ represents a hydrogen atom, an alkyl group or a substituent having an alkyl group, and at least one R ₃ represents an alkyl group or A substituent having an alkyl group is represented. Preferably the opposing set of W represents CR ₃ and R ₃ is an alkyl group or a substituent having an alkyl group, the other opposing set of W represents N or CR ₃ and R ₃ is It is a hydrogen atom, more preferably represents CR ₃ , and R ₃ is a hydrogen atom.

Examples of the aromatic hydrocarbon ring constituting Z include phenyl, biphenyl, naphthalene, anthracene, tetracene, pentacene, hexacene, heptacene, acenaphthene, naphthacene, azulene, phenalene, benzoanthracene, phenanthrene, chrysene, anthanthrene, pyranthrene, Indenoindene, picene, triphenylene, perylene, naphthoperylene, coronene, ovarene, pyrene, benzopyrene, hexahelicene, heptahelicene, octahelicene, nonahelicene, decahelicene, undecahelicene, dodecahelicene, etc .; tetraphen, pentaphen, hexaphen, heptaphene, octaphen, nonaphene , Decaphene, undecaphene, dodecaphene, C60 fullerene, C70 fullerene, etc. , Biphenyl, naphthalene is preferable. Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenenyl, pyridyl, imidazolyl, morpholino, benzothienyl, benzophenyl, and the like. Examples of the substituent having an alkyl group or an alkyl group that optionally substitutes these aromatic hydrocarbon rings or aromatic heterocycles include the groups described for R in the formulas (1) and (2), and A linear alkyl group having a number of 1 to 15 is preferred. Moreover, substituents having an alkyl group or an alkyl group representing R ³ can also be a group described by R in formula (1) and (2). Preferably, R ^{3 at} a pair of opposing positions is preferably a linear alkyl group having 1 to 30 carbon atoms or a group having a linear alkyl group having 1 to 30 carbon atoms, and a straight chain having 5 to 20 carbon atoms. It is more preferably a chain alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms, and a group having a linear alkyl group having 8 to 15 carbon atoms or a linear alkyl group having 8 to 15 carbon atoms. It is more preferable.
Further, the van der Waals volume ratio of the alkyl group or alkyl portion to the whole conductive compound is preferably 5 to 60%, more preferably 10 to 50%, and further preferably 15 to 50%. preferable.

As the conductive compound having such a porphyrin as a basic skeleton, compounds represented by the following general formulas (10) to (13) are preferable.

In formula (10), (11), (12) or (13), R _{47 to} R ₅₀ are the same as R in formula (1), and R _{47 to} R ₄₉ are bonded to at least one W. R ₅₀ can be bonded to a bondable position of the basic skeleton, but is preferably bonded to at least one W, and m ^{1 to} m ⁴ are the same as m in the above formula (1). When m ¹ , m ² , m ³ or m ⁴ is 2 or more, a plurality of R ₄₇ , R ₄₈ , R ₄₉ or R ₅₀ may be different or the same. Examples of the alkyl group constituting R _{47 to} R ₅₀ or the substituent having an alkyl group include the groups described for R in formulas (1) and (2). Preferably, R ₄₇ , R ₄₈ , R ₄₉ or R _{50 in} a pair of opposing positions is a linear alkyl group having 1 to 20 carbon atoms or a group having a linear alkyl group having 1 to 20 carbon atoms. A linear alkyl group having 4 to 15 carbon atoms or a group having a linear alkyl group having 4 to 15 carbon atoms is more preferable, and a linear alkyl group having 8 to 13 carbon atoms or a group having 8 to 13 carbon atoms is more preferable. A group having a linear alkyl group is more preferable.
Further, the van der Waals volume ratio of the alkyl group or alkyl portion to the whole conductive compound is preferably 5 to 60%, more preferably 10 to 50%. In particular, it is preferably 15 to 50%.

Such a conductive compound having a porphyrin structure as a basic skeleton, for example, when the alkyl group or the alkyl portion is a group having a linear alkyl group having 4 to 15 carbon atoms or a linear alkyl group having 4 to 15 carbon atoms, The structural phase transition occurs in the temperature range of 30 to 120 ° C. Therefore, for example, when use at 30 to 150 ° C. is envisaged, the alkyl group or alkyl portion may be a linear alkyl group having 4 to 15 carbon atoms or a group having a linear alkyl group having 4 to 15 carbon atoms. preferable.

(2) Conductive compounds based on heteroacene

Wherein (3), Y each _{independently} represents _{S, Se, SO 2, O} , N (R 51), Si a _{(R 51) (R 52)} , R 51 and _{R 52} are each independently Represents a hydrogen atom, a substituent, and preferred substituents include an aryl group, a monocyclic aromatic heterocyclic residue; an amino group substituted with an alkyl group or an aromatic ring residue, an alkyloxy group, an alkylthioxy group, An ester group, a carbamoyl group, an acetamide, a thio group or an acyl group; a halogen atom, a nitro group, or a cyano group. Examples of the aryl group include a phenyl group, a biphenyl group, and a naphthyl group. Examples of the monocyclic aromatic heterocyclic residue include a furyl group, a thienyl group, a thienylene group, a tenyl group, a pyridyl group, a piperidyl group, and a quinolyl group. , An isoquinolyl group, an imidazolyl group, a morpholino group, a benzothienyl group, a benzophenyl group, and the like. Examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom. Y is preferably S or Se, particularly preferably S.
Z ₁ and Z ₂ each independently represents an aromatic hydrocarbon ring or an aromatic heterocyclic ring substituted with an alkyl group or a substituent having an alkyl group, or an alkyl group or a substituent having an alkyl group, and Z ₁ And Z ₂ may be the same or different.
Examples of the aromatic hydrocarbon ring include a monocyclic ring or an aromatic hydrocarbon ring in which a plurality of rings are connected or condensed. Examples of monocyclic aromatic hydrocarbon rings include aromatic hydrocarbon rings having 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms. In addition, the aromatic hydrocarbon ring in which a plurality of rings are connected or condensed has 2 or more aromatic hydrocarbon rings having 3 to 7, preferably 4 to 6 carbon atoms (for example, 2 to 7, 2 to 5, (Or 2 to 3) or linked or condensed structures. Specific examples of the aromatic hydrocarbon ring include phenyl, biphenyl, naphthyl, anthracene, tetracene, pentacene, phenanthrene, chrysene, triphenylene, tetraphen, pyrene, picene, pentaphen, perylene, helicene, coronene, and the like. Can do. Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenenyl, pyridyl, imidazolyl, morpholino, benzothienyl, benzophenyl, and the like.
Examples of the alkyl group or the substituent having an alkyl group include the groups described for R in the formulas (1) and (2). A group having a linear alkyl group having 1 to 30 carbon atoms or a linear alkyl group having 1 to 30 carbon atoms is preferable, and a linear alkyl group having 1 to 20 carbon atoms or a group having 1 to 20 carbon atoms is preferable. A group having a linear alkyl group is more preferable, and a group having a linear alkyl group having 5 to 15 carbon atoms or a linear alkyl group having 5 to 15 carbon atoms is more preferable.
Further, the van der Waals volume ratio of the alkyl group or alkyl part to the whole conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. .

As the conductive compound having such a heteroacene as a basic skeleton, the following compounds are preferred: (2-1) Conductive compound having a basic skeleton having a structure similar to BTBT or similar to it

In Formula (6), X ₁ and X ₂ are the same as Y in Formula (3), preferably S or Se, and particularly preferably S. At least one of R ₁ and R ₂ , preferably both, may be the same as the alkyl group or the substituent having an alkyl group described for R in the above formulas (1) and (2). However, the compound of formula (6) is preferably a linear alkyl group having 1 to 15 carbon atoms or a linear alkyl group having 1 to 15 carbon atoms, and a linear alkyl group having 6 to 12 carbon atoms. Alternatively, a group having a linear alkyl group having 6 to 12 carbon atoms is more preferable.
Further, the van der Waals volume ratio of the alkyl group or alkyl part to the whole conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton includes, for example, a structural phase transition when an alkyl group or an alkyl part is a linear alkyl group having 5 to 12 carbon atoms or a linear alkyl part having 5 to 12 carbon atoms. Occurs in the temperature range of 70-120 ° C. Therefore, for example, when use at 50 ° C. to 150 ° C. is envisaged, the alkyl group or alkyl portion may be a linear alkyl group having 5 to 12 carbon atoms or a linear alkyl portion having 5 to 12 carbon atoms. preferable.
In addition, the compound of Formula (6) can be manufactured, for example by the method of WO2008 / 047896, The content is integrated in this-application specification by reference.

(2-2) Conductive compound having DNTT or similar structure as basic skeleton

In the formula (7), X ₁ and X ₂ are the same as Y in the above formula (3), preferably S or Se, particularly preferably S. R _{3 to} R ₁₄ are hydrogen or an alkyl group or a substituent having an alkyl group described in R in the above formulas (1) and (2), and at least one of R _{3 to} R ₁₄ is the above formula ( It is the substituent which has the alkyl group demonstrated by R of 1) and (2), or an alkyl group. However, in the compound of the formula (7), any one of R _{4 to} R ₇ and R _{10 to} R ₁₃ is preferably an alkyl group or a substituent having an alkyl group, particularly R ₆ and R ₁₂ , or More preferably, it is located at R ₅ and R ₁₁ . Further, the alkyl group or the substituent having an alkyl group is preferably a linear alkyl group having 1 to 20 carbon atoms or a group having a linear alkyl group having 1 to 20 carbon atoms, and has 4 to 16 carbon atoms. It is more preferably a linear alkyl group or a group having a linear alkyl group having 4 to 16 carbon atoms, and a group having a linear alkyl group having 6 to 12 carbon atoms or a linear alkyl group having 6 to 12 carbon atoms. More preferably.
Further, the van der Waals volume ratio of the alkyl group or alkyl part to the whole conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton includes, for example, a structural phase transition when an alkyl group or an alkyl portion is a linear alkyl group having 6 to 12 carbon atoms or a linear alkyl portion having 6 to 12 carbon atoms. Occurs in the temperature range of 100-140 ° C. Therefore, for example, when use at 80 ° C. to 150 ° C. is assumed, the alkyl group or the alkyl portion may be a straight alkyl group having 6 to 12 carbon atoms or a straight alkyl portion having 6 to 12 carbon atoms. preferable.
The compound of formula (7) can be produced, for example, by the method described in WO / 2010/098372, the contents of which are incorporated herein by reference.

(4) Conductive compound having DATT or a similar structure as the basic skeleton

In the formula (8), X ₁ and X ₂ are the same as Y in the formula (3), preferably S or Se, and particularly preferably S. R _{15 to} R ₃₀ are hydrogen or an alkyl group or a substituent having an alkyl group described for R in the above formulas (1) and (2), and at least one of R _{15 to} R ₃₀ is described for R. Or a substituent having an alkyl group. However, in the compound of the formula (8), in R _{15 to} R ₃₀ , R ₁₈ and R ₂₆ are substituents having an alkyl group or an alkyl group described in R of the above formulas (1) and (2), The other is preferably hydrogen. Further, the alkyl group or the substituent having an alkyl group is preferably a linear alkyl group having 1 to 25 carbon atoms or a group having a linear alkyl group having 1 to 25 carbon atoms, and has 5 to 20 carbon atoms. It is more preferably a linear alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms, and a group having a linear alkyl group having 6 to 15 carbon atoms or a linear alkyl group having 6 to 15 carbon atoms. More preferably.
Further, the van der Waals volume ratio of the alkyl group or alkyl part to the whole conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton includes, for example, a structural phase transition when an alkyl group or an alkyl portion is a straight-chain alkyl group having 6 to 15 carbon atoms or a straight-chain alkyl portion having 6 to 15 carbon atoms. Occurs in the temperature range of 100-140 ° C. Therefore, for example, when use at 80 ° C. to 150 ° C. is assumed, the alkyl group or the alkyl portion may be a straight alkyl group having 6 to 15 carbon atoms or a straight alkyl portion having 6 to 15 carbon atoms. preferable.
In addition, the compound of Formula (8) can be manufactured, for example by the method of WO2008 / 050726, The content is integrated in this-application specification by reference.

(4) Conductive compound having DCTT or a similar structure as a basic skeleton

In the formula (9), X ₁ and X ₂ are the same as Y in the above formula (3), preferably S or Se, particularly preferably S. R _{31 to} R ₄₆ are hydrogen or an alkyl group or a substituent having an alkyl group described in R in the above formulas (1) and (2), and at least one of R _{31 to} R ₄₆ is described as R. Or a substituent having an alkyl group. However, in the compound of the formula (9), in R _{31 to} R ₄₆ , R ₃₄ and R ₄₁ are the substituents having the alkyl group or the alkyl group described in R of the above formulas (1) and (2), The other is preferably hydrogen. Further, the alkyl group or the substituent having an alkyl group is preferably a linear alkyl group having 1 to 25 carbon atoms or a group having a linear alkyl group having 1 to 25 carbon atoms, and has 5 to 20 carbon atoms. It is more preferably a linear alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms, and a group having a linear alkyl group having 6 to 15 carbon atoms or a linear alkyl group having 6 to 15 carbon atoms. More preferably.
Further, the van der Waals volume ratio of the alkyl group or alkyl portion to the whole conductive compound is preferably 5 to 60%, more preferably 10 to 50%. In particular, it is preferably 15 to 50%.
As described above, the conductive compound having such a structure as a basic skeleton can control the temperature of the structural transition of the thermoelectric conversion material and the thermal motion by adjusting the length of the alkyl group or the alkyl portion. For example, when use at 70 ° C. to 150 ° C. is envisaged, the alkyl group or alkyl portion should be a straight chain alkyl group having 6 to 15 carbon atoms or a straight chain alkyl portion having 6 to 15 carbon atoms. Is preferred.
In addition, the compound of Formula (9) can be manufactured by the method of WO2008 / 050726, for example, The content is integrated in this-application specification by reference.

The organic thermoelectric conversion material of the present invention may optionally contain a dopant. Examples of the dopant include onium salt compounds such as sulfonium salts, iodonium salts, ammonium salts, carbonium salts, and phosphonium salts; camphorsulfonic acid, dodecylbenzenesulfonic acid, 2-naphthalenesulfonic acid, toluenesulfonic acid, and 2-naphthalenesulfone. Organic acids such as acids; halogens such as Cl ₂ , Br ₂ , I ₂ , ICl, ICl ₃ , IBr and IF; Lewis such as PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ and SO ₃ Acid; Protonic acid such as HF, HCl, HNO ₃ , H ₂ SO ₄ , HClO ₄ , phosphoric acid; FeCl ₃ , FeOCl, TiCl ₄ , ZrCl ₄ , HfCl ₄ , NbF ₅ , NbCl ₅ , TaCl ₅ , MoF ₅ , WF Transition metal compounds such as ₆ ; alkali metals such as Li, Na, K, Rb, and Cs; and alloys such as Ca, Sr, and Ba Examples thereof include lucan earth metal, lanthanoids such as Eu, R ₄ N ⁺ , R ₄ P ⁺ , R ₄ As ⁺ , R ₃ S ⁺ (R: alkyl group), and acetylcholine.

In the present invention, the dopant is not an essential component but is preferably contained in the organic thermoelectric conversion material in an amount of 0 to 60% by weight, and more preferably 0 to 20% by weight.

The thermoelectric conversion material of the present invention has a high thermoelectromotive force and is useful as a thermoelectric conversion material for organic thermoelectric conversion elements. For this reason, the thermoelectric conversion material of this invention can be used effectively in order to form the thermoelectric conversion layer of an organic thermoelectric conversion element. Therefore, according to another embodiment of the present invention, the use of the thermoelectric conversion material of the present invention for forming a thermoelectric conversion layer, a thermoelectric conversion element having a thermoelectric conversion layer including a thermoelectric conversion material, and a thermoelectric conversion material are included. A method for thermoelectric conversion by the thermoelectric conversion layer is also provided.

The thermoelectric conversion element of the present invention has a first electrode, a thermoelectric conversion layer, and a second electrode on a substrate, and the thermoelectric conversion layer contains the thermoelectric conversion material of the present invention.
The thermoelectric conversion element of this invention should just have a 1st electrode, a thermoelectric conversion layer, and a 2nd electrode on a base material, The position of a 1st electrode, a 2nd electrode, and a thermoelectric conversion layer There are no particular limitations on other configurations such as relationships. In the thermoelectric conversion element of the present invention, the thermoelectric conversion layer may be disposed on at least one surface thereof so as to be in contact with the first electrode and the second electrode. The case where there is a temperature difference in the horizontal direction with respect to the base material is a horizontal thermoelectric conversion element (FIG. 5), and the case where there is a temperature difference in the vertical direction with respect to the base material is a vertical thermoelectric conversion element (FIG. 6) . The thermoelectric conversion layer in the thermoelectric conversion element of this invention should just be arrange | positioned so that two electrodes may be contacted, and an electromotive force is generated by providing a temperature difference between these electrodes.

As the base material, glass, metal, plastic film, non-woven fabric, paper and other electrodes and materials that can hold thermoelectric conversion materials can be used. In order to give the device flexibility, it is preferable to use a flexible plastic film or the like.

Examples of electrode materials include transparent electrodes such as ITO, metal electrodes such as gold, silver, copper, and aluminum, carbon electrodes such as carbon nanotubes and graphene, and organic conductive materials such as PEDOT: PSS. A material with low contact resistance is preferred. Further, in order to reduce the contact resistance with the thermoelectric conversion material, it is possible to perform a treatment such as contact doping.

The thermoelectric conversion layer of the present invention is used for the thermoelectric conversion layer of the thermoelectric conversion element of the present invention. The thermoelectric conversion layer may be a single layer or a plurality of layers. When the thermoelectric conversion element of the present invention has a plurality of thermoelectric conversion layers, it may be an element having only a plurality of thermoelectric conversion layers formed using the thermoelectric conversion material of the present invention, or the thermoelectric conversion material of the present invention. An element having a thermoelectric conversion layer formed using a thermoelectric conversion layer formed using a thermoelectric conversion material other than the thermoelectric conversion material of the present invention may be used. Since the thermoelectric conversion material of the present invention can be designed so as to exhibit the highest thermoelectromotive force according to the temperature at which the element is used as described above, the molecular design of the substituent is appropriately determined according to the operating temperature. Can be changed.

A method for forming a thermoelectric conversion layer or the like in the thermoelectric conversion element of the present invention is not particularly limited, and examples thereof include a solution process such as printing and a vacuum process. In consideration of device manufacturing costs, solution processes are preferable, and coating methods such as casting, spin coating, dip coating, blade coating, wire bar coating, spray coating, and printing methods such as inkjet printing, screen printing, offset printing, letterpress printing, Examples thereof include a soft lithography method and a method in which a plurality of these methods are combined.

As described above, the thermoelectric conversion element of the present invention can achieve high thermoelectric conversion efficiency through high thermoelectromotive force of the conductive compound itself, and provides a new approach for providing a high-performance organic thermoelectric conversion element. . In particular, since it has a very high Seebeck coefficient, it becomes easy to design a high-voltage device, and it is possible to provide a characteristic thermoelectric conversion element.

Hereinafter, the present invention will be described in more detail based on examples. However, the following examples do not limit the technical scope of the present invention.

(Synthesis Example 1) (6,20-Didodecyl-29H, 3H-tetrabenzo [b, g, l, q] porphyrin)

Dipyromethane (0.30 g, 1.0 mmol) was added to a reaction vessel purged with argon and dissolved in dichloromethane (200 ml). Here, argon gas was bubbled for 10 minutes. Subsequently, tridecanal (0.3 ml, 1.1 nanol) and trifluoroacetic acid (TFA) (2 drops) were sequentially added, and the mixture was stirred for 17 hours under light shielding. 2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ) (0.35 g) was added thereto, and the mixture was further stirred for 2 hours. After completion of the reaction, the solvent was removed until the amount of the solution became half, and alumina column chromatography (chloroform) was performed. Further purification was performed using silica gel chromatography (dichloromethane) and GPC, and finally recrystallization (chloroform / methanol) was performed to obtain the target product as a reddish brown solid. Yield: 80% (389 mg, 0.405 mmol)

(Synthesis Example 2) C ₁₂ H ₂₅ -H ₂ BP

Benzoporphyrin was obtained as a green solid by heating the porphyrin obtained above at 200 ° C. for 30 minutes under vacuum in a glass tube oven.

As shown in FIG. 2, DSC (170-570K) showed a sharp peak and a broad peak at 320-360K, and a peak around 440K, indicating that a structural phase transition occurred.

Synthesis Example 3 29H, 3H-tetrabenzo [b, g, l, q] porphine (BP, LUMO: -2.26 eV, HOMO: -4.69 eV manufactured by ALDRICH).
As shown in FIG. 3, no clear peak was observed in DSC (170-570K).
(Synthesis Example 4) Synthesis of C8BTBT (1) Synthesis of 2,7-Di (1-octynyl1) [1] benzothieno [3,2-b] [1] benzothiophene

In a nitrogen atmosphere, 2,7-diiodobenzothienobenzothiophene (1.0 g, 2.0 mmol) was dissolved in anhydrous diisopropylamine (15 ml) and anhydrous benzene (15 ml), and then degassed for 30 minutes. 10 mol% PdCl2 (PPh3) 2 (140 mg), 20 mol% CuI (76 mg) and 1-octyne (0.81 ml, 5.5 mmol) were added and stirred at room temperature for 8 hours. After completion of the stirring, water (30 ml) was added and extracted with chloroform (30 ml × 3). The extract was washed with water (100 ml × 3) and then dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, purified by column chromatography (silica gel, methylene chloride: hexane = 1: 3, Rf = 0.6), and recrystallized from hexane to obtain the target compound represented by the above formula. Of colorless plate crystals were obtained (yield 710 mg, yield 77%).

(2) Synthesis of 2,7-Dioctyl [1] benzothieno [3,2-b] [1] benzothiophene

The obtained compound (300 mg, 0.66 mmol) and Pd / C (70 mg) were added to anhydrous toluene (10 mL), vacuum-hydrogen purge with an aspirator was repeated several times, and the mixture was stirred for 8 hours. After completion of the reaction, the solvent was distilled off and the residue was purified by column chromatography (silica gel, hexane, Rf = 0.6) (yield 286 mg, yield 94%) and recrystallized from hexane to give a colorless powder of the target compound. A solid was obtained (yield 250 mg, 82% yield).

(Example)
In each Example, the organic thermoelectric conversion element using each compound was produced, and the characteristic was evaluated. As an evaluation device, a thermoelectric property evaluation device for homemade ultra-high resistance samples was used. In the ultra-high vacuum chamber, the characteristic evaluation apparatus includes (1) precise deposition of sublimable material using a Knudsen cell, (2) sample resistance measurement using a Keithley 6430 source meter up to about 10 ¹⁴ Ω, and (3) It has a function of performing high-precision Seebeck coefficient measurement using a home-made high input impedance differential amplifier circuit with a sample resistance of about 10 ¹³ Ω as an upper limit. (See Non-Patent Literature: Nakamura, Applied Physics 82 (2013) 954)

Example 1 Production / Evaluation of Thermoelectric Conversion Element Using Compound (C12BP) In this example, an organic thermoelectric conversion element using the compound synthesized in Synthesis Example 1 was produced, and the characteristics were evaluated.
White plate glass to which a shadow mask for electrode preparation was attached was placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus was 1.0 × 10 ⁻⁴ Pa or less. By resistance heating vapor deposition, gold was vapor-deposited to a thickness of 30 nm at a vapor deposition rate of 0.1 kg / sec to obtain a substrate with electrodes.
After attaching a shadow mask to the substrate, wiring to the thermocouple and the electrode, installing in the characteristic evaluation apparatus, exhausting until the degree of vacuum in the apparatus is 1.0 × 10 ⁻⁴ Pa or less, A thin film (160 nm) of the compound (C12BP) was formed by resistance heating vapor deposition to obtain the thermoelectric conversion element of the present invention (distance between electrodes: 10 mm, electrode width: 7.6 mm).
The obtained thermoelectric conversion element determined the temperature under the condition that the degree of vacuum in the apparatus was 1.0 × 10 ⁻⁵ Pa or less, applied a voltage, read the current value, and measured the conductivity. Further, a Seebeck coefficient was measured by providing a temperature gradient between the electrodes and reading the thermoelectromotive force value.
As a result, the conductivity at 340 K was 3.0 × 10 ⁻⁸ Scm ⁻¹ and the Seebeck coefficient was 123 mV / K. In addition, as shown in FIG. 1, the van der Waals volume ratio of the side chain of C12BP was 50% (using Winmostar software).

Example 2 Production and Evaluation of Thermoelectric Conversion Element Using Compound (C8-BTBT) Organic thermoelectric conversion element using Compound (C8-BTBT) synthesized in Synthesis Example 2 instead of the compound used in Example 1 Were made and evaluated.
A 0.5 wt% C8-BTBT heptane solution was dropped onto a white glass substrate, a spin coat (1000 rpm × 1 min) was formed, and dried to obtain an organic thin film (30 nm) substrate. A shadow mask for electrode formation was attached to the organic thin film substrate, placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus became 1.0 × 10 ⁻⁴ Pa or less. Gold was vapor-deposited to a thickness of 30 nm at a deposition rate of 0.1 Å / sec by a resistance heating vapor deposition method to obtain a thermoelectric conversion element (distance between electrodes: 5 mm, electrode width: 7.6 mm).
This element is wired to the thermocouple and electrode, installed in the evaluation device, the voltage is applied under the condition that the degree of vacuum in the device is 1.0 × 10-5 Pa or less, the voltage is applied, and the current value is read. The conductivity was measured. Further, a Seebeck coefficient was measured by providing a temperature gradient between the electrodes and reading the thermoelectromotive force value.
As a result, the conductivity at 340 K was 2.1 × 10 ⁻⁸ Scm−1, and the Seebeck coefficient was 190 mV / K.

In (C8-BTBT) obtained in Example 2, DSC (170-570K) showed two peaks in the vicinity of 380K and a sharp peak at 400K, indicating that a structural phase transition occurred.
Moreover, as shown in FIG. 1, the van der Waals volume ratio of the side chain of C8BTBT was 60%.

Example 3 Production and Evaluation of Thermoelectric Conversion Element Using Compound (C10DNTT) An organic thermoelectric conversion element was produced and evaluated using the compound (C10DNTT) instead of the compound used in Example 1.
White plate glass to which a shadow mask for electrode preparation was attached was placed in a vacuum deposition apparatus, and evacuated until the degree of vacuum in the apparatus was 1.0 × 10 ⁻⁴ Pa or less. By resistance heating vapor deposition, gold was vapor-deposited to a thickness of 30 nm at a vapor deposition rate of 0.1 kg / sec to obtain a substrate with electrodes.
A shadow mask is attached to the substrate, wiring is made to the thermocouple and the electrode, and is installed in the evaluation apparatus. The vacuum in the apparatus is exhausted to 1.0 × 10 ⁻⁴ Pa or less, and resistance heating is performed. A thin film (20 nm) of the compound (C10DNTT) is formed by a vapor deposition method at a deposition rate of 0.5 Å / sec, and the thermoelectric conversion element of the present invention (distance between electrodes: 5 mm, electrode width: 7.6 mm) is obtained. It was.
The obtained thermoelectric conversion element determined the temperature under the condition that the degree of vacuum in the apparatus was 1.0 × 10 ⁻⁵ Pa or less, applied a voltage, read the current value, and measured the conductivity. Further, a Seebeck coefficient was measured by providing a temperature gradient between the electrodes and reading the thermoelectromotive force value.
As a result, the conductivity at 315K was 1.1 × 10 ⁻⁷ Scm ⁻¹ and the Seebeck coefficient was 128 mV / K.
Moreover, as shown in FIG. 1, the van der Waals volume ratio of the side chain of C10DNTT was 57%. As shown in FIG. 4, in C10DNTT obtained in Example 1, DSC (170-620K) showed sharp peaks at 390K, 500K, 570K and 580K, respectively, indicating that structural phase transition occurred. It was done.

Example 4 Production and Evaluation of Vertical Thermoelectric Conversion Element Using Compound (C8-BTBT) A vertical organic thermoelectric conversion element was produced and evaluated using the compound (C8-BTBT) synthesized in Synthesis Example 2. .
A PEDOT / PSS film was formed on an ITO glass substrate (Asahi Glass) by spin coating (7000 rpm × 20 sec) and dried to prepare a substrate.
A pair of substrates having a gap of 25 μm was produced by sandwiching high Milan (50 μm, made by Mitsui DuPont Polychemical) between the two produced substrates and heating at 150 ° C.
A compound (C8BTBT) melted at 130 ° C. was injected into the produced substrate pair to obtain a thermoelectric conversion element (distance between electrodes: 25 μm, electrode size 100 mm 2).
It was confirmed that thermoelectromotive force was generated by wiring the ITO surface of the obtained thermoelectric conversion element and providing a temperature gradient between the electrodes.

(Example 5)
In the thermoelectric conversion element (C12BP) produced in Example 1, the electrical conductivity and Seebeck coefficient were measured at different temperatures (27 to 127 ° C.), and the power factor was calculated. FIG. 7 shows DSC analysis data of bulk C12BP up to 27-227 ° C. and relative power factor values (27-127 ° C.) based on 27 ° C.
According to this result, it can be confirmed that a large power factor is shown in the vicinity of the temperature (80 to 90 ° C.) at which the structural phase transition of the material is observed. This shows that the thermoelectric conversion element can perform efficient thermoelectric conversion when used at 70 to 100 ° C., more preferably 80 to 90 ° C. Therefore, in the thermoelectric conversion element of the present invention, it was shown that very efficient thermoelectric conversion can be performed by selecting an optimum use temperature according to each thermoelectric conversion material.

(Comparative Example 1)
Similar to Example 3, a similar device was prepared using DNTT instead of C10DNTT. As a result, the conductivity at 360 K was 8.3 × 10 ⁻⁹ Scm ⁻¹ and the Seebeck coefficient was 35 mV / K.
In DNTT obtained in Comparative Example 1, no peak was observed by DSC (170-570K).

(Comparative Example 2)
Similar to Example 3, a similar device was produced using pentacene instead of C10DNTT as the compound. As a result, the conductivity at 300 K was 1.3 × 10 ⁻⁶ Scm ⁻¹ and the Seebeck coefficient was 2.4 mV / K.

As a distributed power source and energy harvesting element to form a sensor matrix for smart houses and smart buildings, it is useful in the reuse of exhaust heat energy in homes, offices and automobiles. In addition, it can be used as a power source for sticker-type biological information measuring instruments (body temperature, pulse, electrocardiogram monitor, etc.) by taking advantage of the flexibility characteristic of organic thermoelectric conversion materials. In particular, since it has a very high Seebeck coefficient, it becomes easy to design a high-voltage device, and it is possible to provide a characteristic thermoelectric conversion element.

Claims (11)

1. Conductive compound comprising a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties and a substituent containing an alkyl group that causes a change in intermolecular distance or molecular packing structure of the basic skeleton by thermal motion Organic thermoelectric conversion materials including
2. A basic skeleton composed of a polycyclic aromatic ring having carrier transport properties and an alkyl group or a substituent having an alkyl group are bonded to each other, and a structural phase transition (specified by DSC) at a temperature in the range of −50 ° C. to 200 ° C. The organic thermoelectric conversion material according to claim 1, comprising a conductive compound.
3. The organic thermoelectric conversion material according to claim 1, wherein the conductive compound is represented by the following general formula (1).
   

   

   
   (In the formula, X represents a polycyclic aromatic ring having carrier transport properties. However, when n is 2 or more, they may be different polycyclic aromatic rings. R is independently alkyl. Represents a substituent having a group or an alkyl group, m represents an integer of 1 to 8, and n represents an integer.)
4. The organic thermoelectric conversion material according to any one of claims 1 to 3, wherein the conductive compound is represented by the following general formula (2).
   

   

   
   (In the formula, X represents a polycyclic aromatic ring having carrier transport properties. R independently represents an alkyl group or a substituent having an alkyl group. M represents an integer of 1 to 8.)
5. The organic thermoelectric conversion material according to any one of claims 1 to 4, wherein a van der Waals volume ratio occupied by the substituent in the conductive compound is 10 to 80%.
6. The organic thermoelectric conversion material according to any one of claims 1 to 5, wherein a structural phase transition point by DSC of the conductive compound is recognized at a temperature in the range of 0 to 180 ° C.
7. The organic thermoelectric conversion material according to any one of claims 1 to 6, wherein the polycyclic aromatic ring is a polycyclic aromatic hydrocarbon or a polycyclic aromatic heterocycle.
8. The organic thermoelectric conversion material according to any one of claims 1 to 7, wherein the polycyclic aromatic heterocycle is heteroacene or polyheteroacene.
9. The organic thermoelectric conversion material according to claim 1, wherein the polycyclic aromatic heterocycle is porphyrin or porphyrazine.
10. The organic thermoelectric conversion material according to any one of claims 1 to 9, wherein the polycyclic aromatic heterocycle is a compound represented by the formula (3), (4) or (5).
    

    

    
    (In the formula, each Y independently represents S, Se, SO ₂ , O, N (R ¹ ) or Si (R ¹ ) (R ² ), and R ¹ and R ² each independently represent a hydrogen atom, An aryl group, a monocyclic aromatic heterocyclic residue; or an amino group, an alkyloxy group, an alkylthioxy group, an ester group, a carbamoyl group, an acetamide, a thio group or an acyl group substituted with an aromatic ring residue; Y may be different from each other, each Z independently represents a hydrogen atom, an aromatic hydrocarbon or an aromatic heterocycle, and l represents an integer of 0 to 10. When Z is plural, May be different.)
    

    

    
    (In the formulas (4) and (5), W independently represents N or CR ³ , and R ³ represents a hydrogen atom, an aryl group, a monocyclic aromatic heterocyclic residue; or an aromatic ring residue. Represents an amino group, an alkyloxy group, an alkylthioxy group, an ester group, a carbamoyl group, an acetamido, a thio group, or an acyl group, each independently substituted with a hydrogen atom, an aromatic hydrocarbon, or an aromatic heterocyclic ring. And a plurality of Z may be the same or different, and M represents a metal atom.)
11. An organic thermoelectric conversion element produced using the thermoelectric conversion material according to any one of claims 1 to 10.
    

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