JP2019096892A - Thermoelectric conversion material and thermoelectric conversion device - Google Patents

Abstract

To provide a method of producing an organic thermoelectric conversion material exhibiting a significantly higher Seebeck coefficient than conventional organic thermoelectric conversion materials.SOLUTION: In a method of producing an organic thermoelectric conversion material by using a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties and a conductive compound having an alkyl group or a substituent having an alkyl group, a conductive compound whose structural phase transition is specified by DSC at a temperature ranging from -50°C to 200°C is selected.SELECTED DRAWING: None

Description

  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 means for recovering unused thermal energy in the environment as electrical energy.

Conventionally, as a thermoelectric conversion material, inorganic semiconductor materials such as CoSb ₃ have been mainly used and studied because of relatively high thermoelectric conversion efficiency, but such inorganic semiconductor materials contain rare elements and are expensive There is a problem that the processability of the material is poor. For this reason, in recent years, research on organic thermoelectric conversion materials which are inexpensive and excellent in material processability has been actively conducted.

  Conducting 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) as conventional organic thermoelectric conversion materials It has been proposed to consist of a sex polymer.

  However, these conductive polymers do not have sufficient thermoelectric conversion performance, and higher thermoelectric conversion performance is required for practical use. In order to meet the demand for enhancing the thermoelectric conversion efficiency of such thermoelectric conversion materials, conventionally, a dopant is introduced (Patent Documents 2, 3, 4, 5 and 6), and a layer made of a doped conductive polymer And a layer made of a conductive polymer which is not doped (Patent Document 4), dispersed metal particles (Patent Document 1), and specific to the energy level of the molecular orbital of the conductive polymer. It has been proposed to contain a thermal excitation assist agent having a molecular orbital with an energy level difference of (Patent Document 7).

By the way, the thermoelectric conversion efficiency of the thermoelectric conversion material is generally expressed by the following equation [Equation 1] non-dimensional performance index ZT = S ² · σ · T / κ (A)
[Wherein, S (V / K) represents a thermoelectromotive force (Seebeck coefficient), σ (S / m) represents conductivity, κ (W / mK) represents thermal conductivity, and T (K) Represents an absolute temperature, and S ² · σ represents a power factor. ]
The dimensionless performance index (ZT) represented by is used as an index. As can be understood from the above equation, the dimensionless figure of merit (ZT) means that the higher the Seebeck coefficient and the conductivity and the lower the thermal conductivity, the higher the thermoelectric conversion performance. Among the materials that can obtain high ZT, especially for materials with large Seebeck coefficients, flexible thermoelectric conversion elements that use organic thermoelectric conversion materials can be operated by breaking the element thickness or reducing the number of series connections of multiple cells. It is possible to reduce defects.

  In this respect, the introduction of the above-mentioned dopant and the dispersion of the metal particles are intended to improve the thermoelectric conversion efficiency mainly by the increase of the conductivity. According to the conventional thermoelectric theory for non-degenerate semiconductors, the Seebeck coefficient and the conductivity are in a constant trade-off relationship, and the Seebeck coefficient exhibits the maximum value when the carrier density is small, and decreases as the carrier density increases. (Non-patent document 2), in the case of the conventional conductive polymer, the Seebeck coefficient was about several mV / K even at the maximum value.

  On the other hand, the above-described attempts to contain the thermal excitation assist agent improve the thermoelectric conversion efficiency by increasing the thermoelectromotive force (Seebeck coefficient). However, the conductive polymer itself is not improved to increase the thermoelectromotive force (Seebeck coefficient).

  Moreover, shimada et al. Pay attention to the sudden generation of deep traps at low temperatures in organic semiconductors, and predicts that the Seebeck coefficient becomes large at low temperatures due to point defects in pentacene which is a low molecular weight semiconductor (Non-Patent Document 4) . However, the Seebeck coefficient described by shimada et al. Is about 1 mV / K, and does not provide any direct improvement in the Seebeck coefficient due to the thermal motion of the molecule and any teaching for the molecular design therefor.

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

Harada et al., Appl. Phys. Lett. 96, (2010) 253304 Nakamura, Applied Physics 82 (2013) 954 Kim et al., Nat. Mater. 12 (2013) 719 Shimada et al., Appl. Phys. Exp. 4 (2011) 061601 Roichman et al., Appl. Phys. Lett. 80 (2002) 1948

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

  In view of the above problems, the present inventors examined molecular design of a conductive compound that achieves excellent thermoelectric conversion efficiency regardless of the conventional thermoelectric theory. According to the basic skeleton, the plane π conjugated structure In general, when the compound has a structure derived from a polycyclic aromatic compound having a high carrier-transporting ability, and a compound having a side chain thermally moving at a predetermined temperature, it can not be predicted from the conventional thermoelectric theory. Found a high Seebeck coefficient. The present invention is based on such findings.

That is, the present invention provides the following organic thermoelectric conversion material and organic thermoelectric conversion element.
[1] A conductive compound comprising an alkyl group-containing substituent that causes a change in intermolecular distance and molecular packing structure of the basic skeleton by thermal motion to a basic skeleton consisting of polycyclic aromatic rings having carrier transport properties. , Organic thermoelectric conversion material.
[2] An alkyl group or a substituent having an alkyl group is bonded to a basic skeleton consisting of polycyclic aromatic rings 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 as described in [1] which contains the electroconductive compound to be.
[3] The organic thermoelectric conversion material according to [1] or [2], wherein the conductive compound is represented by the following general formula (1).

(Wherein, X represents a polycyclic aromatic ring having a carrier transport property, 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 independently represents an alkyl group or a substituent having an alkyl group, m represents a number equal to or less than the maximum number of R that can be bonded to X, and usually 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).

(Wherein, X represents a polycyclic aromatic ring having a carrier transport property, and R each independently represents an alkyl group or a substituent having an alkyl group. M is less than or equal to the maximum number of R 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 the structural phase transition point of the conductive compound by DSC is observed 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 heterocyclic ring.
[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 heterocyclic ring 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 Formula (3), (4) or (5).

(Wherein 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, Aryl group, monocyclic aromatic heterocyclic residue; amino group substituted with alkyl group or aromatic ring residue, alkyloxy group, alkylthioxy group, ester group, carbamoyl group, acetamide, thio group or acyl group And 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 Formulas (4) and (5), W each independently represents N or C-, at least one is C-, and an alkyl group or a substituent containing an alkyl group is bonded, 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 the above [1] to [10], wherein the conductive compound is a compound represented by formula (6), (7), (10), (11), (12) or (13) Organic thermoelectric conversion material described in.






In formulas (6) and (7), X ₁ and X ₂ are the same as Y in the above formula (3), and formulas (6), (7), (10), (11), (12) and ( 13) in which 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 the above formula (1), 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 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].

  INDUSTRIAL APPLICABILITY The present invention can provide an organic thermoelectric conversion material exhibiting a significantly higher Seebeck coefficient than conventional organic thermoelectric conversion materials, and an organic thermoelectric conversion element having a thermoelectric conversion layer including the same.

FIG. 1 is a graph showing the van der Waals volume ratio of C8BTBT, C10DNTT and C12BP. FIG. 2 shows analytical data of differential scanning calorimetry (DSC) of C12H25-H2BP. FIG. 3 is analytical data of differential scanning calorimetry (DSC) of H2BP. FIG. 4 shows analytical data of differential scanning calorimetry (DSC) of C10 DNTT. It is a figure which shows an example of the horizontal thermoelectric conversion element of this invention. The arrows in the figure indicate the direction in which a temperature difference occurs when the device 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 a temperature difference occurs when the device is used. 13 shows the differential scanning calorimetry (DSC) analytical data and relative values of power factors of C12BP of Example 5. FIG.

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

  The conductive compound used in the present invention has a basic π conjugated structure, and generally has a basic skeleton derived from a polycyclic aromatic compound having a high carrier transportability. 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 causing a change in intermolecular distance and molecular packing structure of the basic skeleton by thermal movement at a predetermined temperature is bonded to the polycyclic aromatic ring. Such a substituent has a rotatable bond like an alkyl group or a substituent having an alkyl group, and is thermally moved at a predetermined temperature to change an adjacent intermolecular distance or a molecular packing structure. , Cause a volume change or structural phase transition of the conductive compound. As a result, it is understood that the thermoelectromotive force (Seebeck coefficient) can be enhanced by sensitively detecting the temperature change.

Here, definitions are given for some terms used in the present specification.
The “polycyclic aromatic compound” means a compound having a polycyclic aromatic ring, and the “basic skeleton consisting of the polycyclic aromatic compound” means a substituent part of the entire structure of such a compound. It means the removed structure.
The "van der Waals volume" means the volume of a molecule or its constituent elements when atoms constituting the molecule are approximated by a sphere having a van der Waals radius. The "van der Waals volume ratio" is a ratio of van der Waals volumes of a plurality of constituent elements of the molecule.
The “side chain length” is the length of the atoms constituting the side chain which is the most distant in the stable structure from the central position of the atom to which the side chain is chemically bonded among the atoms constituting the main skeleton. It means the distance to the center position.
The “π conjugated structure” refers to a structure in which multiple bonds are alternately connected to single bonds, and the “planar π conjugated structure” refers to a structure in which atoms forming a π conjugated structure exist in the same plane.
The “thermoelectromotive force (Seebeck coefficient)” is the measurement of the temperature dependence of the steady-state potential difference generated at two different places on a substance having electrical conductivity, and from the gradient, S = −ΔV / ΔT (ΔV is the potential difference , ΔT means a value calculated by temperature difference).
The term "conductivity" refers to the electrical conductance determined from the current-voltage characteristics of the material measured by a source meter or the like, multiplied by the length of the current path and divided by the cross-sectional area.
"Thermal conductivity" means a value obtained by multiplying the specific heat of a material and the density by the thermal diffusivity measured by a thermoreflectance method, a temperature wave analysis method, a steady state heat flow method or the like.
In the present specification, “structural phase transition” refers to a structure (which may be an ordered structure or a disordered structure) that can be regarded as spatially uniform of a substance, converted to a structure in a different state depending on external conditions such as temperature. By "structural phase transition temperature" is meant the temperature at which the change appears. The structural phase transition temperature is, for example, that an endothermic or exothermic peak appears when measured by differential scanning calorimetry (DSC), or that the temperature dependency of the specific heat changes (the gradient of the specific heat differentiated with the temperature changes suddenly) It is measured by In addition, while the temperature dependence of the conductivity in the semiconductor material shows Arrhenius-type thermal activity, it is also measured as a temperature at which the activation energy changes rapidly.

As a conductive compound contained in the organic thermoelectric conversion material of this invention, the compound typically represented by following General formula (1) or (2) is mentioned.


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

  As described above, the polycyclic aromatic ring represented by X, which constitutes the basic skeleton of the conductive compound contained as a thermoelectric conversion material 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 conjugate structure. As a result, the molecules are oriented to easily form a stacking effect between adjacent molecules, facilitating the movement of electrons or holes between molecules, and a high carrier mobility can be easily obtained.

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

As specific examples of the polycyclic aromatic ring represented by X, for example,
Naphthalene, anthracene, tetracene, pentacene, hexacene, heptacene, acenaphthene, naphthacene, azulene, phenalene, benzoanthracene, phenanthrene, phenanthrene, chrysene, anthantrene, pyrantrene, indenoindene, picene, triphenylene, perylene, naphthoperylene, coronene, ovalene, pyrene, Benzopyrene, hexahelicene, heptahelicene, octahelicene, nonahelicene, decahelicene, undecahelicene, dodecahelicene, etc. Hydrocarbons; and indole, isoindole, purine, quinoline, isoquinoli , Quinoxaline, cinnoline, pteridine, benzopyran, acridine, xanthene, benzimidazole, indazole, indazole, phenazine, naphthyridine, benzothiadiazole, benzothiazole, dithienosilole, fluorene, thienothiophene, carbazole, phenothiazine, phenooxazine, benzothienobenzothiophene, dithieno Heteroacenes such as thiophene, benzodithiophene, benzodiselenophene, dinaphthothienothiophene, dianthrathienothiophene, benzobisoxazole, and polyheteroacenes in which a plurality of these are combined, phenanthrene, phenanthridine, cyclopentadithiophene, Benzo-C-cinnoline, perylenedicarboximide, benzotrifuran, benzotrithiophene, porphyri , Chlorine, choline, phthalocyanine, and a polycyclic aromatic heterocyclic rings such as porphyrazine.

  Among them, acene hydrocarbons such as naphthalene, anthracene, naphthacene and pentacene, heteroacenes such as benzodithiophene, benzothienobenzothiophene and dinaphthodithiophene, porphyrin, phthalocyanine, porphyrazine, etc. in view of high carrier transportability. Is preferred.

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





As described above, in the basic skeleton of the conductive compound, two or more polycyclic aromatic rings may be linked by a single bond to form a π-conjugated structure. When the basic skeleton is constituted by linking a plurality of polycyclic aromatic rings, the number of polycyclic aromatic rings can be generally 2 to 2000, preferably 2 to 1000, It is more preferable to set it as 2-100, and it is still more preferable to set it as 2-5. Of course, the basic skeleton may be composed of a single polycyclic aromatic ring. The molecular weight (Mw) of the basic skeleton constituted by one or more 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 30,000.

The conductive compound contained in the organic thermoelectric conversion material of the present invention has the π conjugated structure developed by the above-mentioned polycyclic aromatic ring formed, and the alkyl group represented by R in the above-mentioned polycyclic aromatic ring Or a substituent having an alkyl group is bonded.
Such a substituent has a rotationally free bond and produces thermal motion at a predetermined temperature, preferably any temperature in the range of -50 ° C to 200 ° C. Such substituents move in response to heat in a sensitive manner, causing volume change and structural phase transition of the conductive compound. As a result, it is possible to modulate the carrier transport ability by the basic skeleton or the like of the polycyclic aromatic compound and to enable highly efficient thermoelectric conversion. The structural phase transition of the conductive compound due to the thermal movement of such a substituent can be confirmed by the endothermic peak of differential scanning calorimetry (DSC).

  In order to be responsive to heat and to cause thermal movement, the substituent is preferably attached to the polycyclic aromatic skeleton via a rotatable free covalent bond. In addition, it is preferable that the substituent itself also have a large number of rotational free covalent bonds, and from such a point of view, the substituent is preferably a substituent having an alkyl group, and a chain alkyl group is The substituent is more preferably a linear alkyl group.

  In addition, in order to achieve high thermal electromotive force (Seebeck coefficient), while maintaining the developed π-conjugated structure by the polycyclic aromatic ring, the thermal movement of the substituent responds to the heat sensitively to the structural phase transition. It is considered important to bring about, and in this respect, the van der Waals volume ratio of the side chain to the polycyclic aromatic skeleton is considered to be one of the indexes. Although the cohesion according to crystallinity and crystal form is different due to the difference of the polycyclic aromatic skeleton, and the bonding force between the molecules is different, in general, 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 the inside is preferably 5% to 80%, preferably 25 to 60%, and more preferably 30 to 60%. It is further more preferably 10 to 50%, particularly preferably 15 to 50%. By designing the van der Waals volume ratio of the side chain to the polycyclic aromatic skeleton, it is possible to control the temperature and thermal movement of the structural phase transition. Although the required temperature (temperature difference) varies depending on the environment in which the device is used, it is possible to design a suitable device by utilizing this ability.

  From the same point of view, the alkyl group portion of the alkyl group or the substituent having the alkyl group is a linear or cyclic, preferably linear, group having 1 to 20 carbon atoms, and more preferably 2 to 2 carbon atoms. It is a group of 18 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 And tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl Group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group is preferable, and octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl Groups are more preferred.

  The branched alkyl group is, for example, isopropyl group, isobutyl group, isoamyl group, s-butyl group, t-butyl group, 2-methylbutyl group, 2-methylhexyl group, 2-ethylhexyl group, 2-methyloctyl group, Examples thereof include 2-ethyloctyl group, isobutyl group, isoamyl group, s-butyl group, t-butyl group, 2-methylbutyl group, 2-methylhexyl group, 2-ethylhexyl group, 2-methyloctyl group, 2 -Ethyl octyl group is mentioned. Moreover, a cyclopentyl group, a cyclohexyl group etc. are mentioned as cyclic | annular alkyl group.

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

In addition, groups in which an alkyl group is bonded to a polycyclic aromatic skeleton via the following chemical structure can be mentioned.
1) Hetero atoms such as oxygen atom, nitrogen atom, sulfur atom, silicon atom and phosphorus atom 2) aryl groups such as phenyl group, biphenyl group and naphthyl group 3) furyl group, thiophene group, thienyl group, thienylene group, tenyl group Aromatic heterocyclic residue 4) carbonyl group, thiocarbonyl group such as pyridyl group, imidazolyl group, morpholino group, benzothienyl group and benzophenyl group

As the substituent having an alkyl group, for example, an alkyl group substituted with a silylethynyl group, an alkyl group substituted with an aryl group (eg, a phenyl group, a biphenyl group, a naphthyl group etc.), an aromatic heterocyclic group (eg, Alkyl group substituted with furyl group, thienyl group, pyridyl group, imidazolyl group etc., alkoxyl group (eg, methoxy group, ethoxy group, propyloxy group, pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group) Group, etc.), cycloalkoxyl group (eg, cyclopentyloxy group, cyclohexyloxy group etc.), alkyl group substituted by aryloxy group (eg, phenoxy group, naphthyloxy group etc.), alkylthio group (eg. Methylthio group, ethylthio group) Group, propylthio group, pentylthio group, hexyl An alkyl group substituted with an aryl group, an octylthio group, a dodecylthio group etc., a cycloalkylthio group (eg, a cyclopentylthio group, a cyclohexylthio group etc.), an arylthio group (eg a phenylthio group, a naphthylthio group etc.), an alkoxycarbonyl group (eg For example, it is substituted with 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-mentioned polycyclic aromatic rings, and usually 1 to 6 per one polycyclic aromatic ring. It may have 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 portion of the above-mentioned 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. It is preferable to occupy%. For example, in a rod-like compound in which one width of the polycyclic aromatic skeleton is as narrow as one benzene ring and the other width is longer, the proportion thereof is more preferably 25 to 60%, and the polycyclic aromatic It is preferable that the width of the skeleton portion is a compound which is broad as two or more benzene rings, and the proportion thereof is 10 to 50%. In addition, it is preferable that a plurality of rotation free bonds exist in the entire substituent. On the other hand, a structure other than an alkyl group may form a π-conjugated structure together with a polycyclic aromatic ring. Optimal characteristics can be obtained by appropriately adjusting the number of alkyl groups, substitution positions, the number of branched chains, and the length.

The temperature causing the structural phase transition of the conductive compound varies depending on the combination of the basic skeleton of the above-mentioned polycyclic aromatic compound and the above-mentioned substituent. Therefore, depending on the temperature at which the conductive compound is expected to be used, it is preferable to appropriately design a preferred molecule. In particular, in the conductive compound of the present invention, it is considered possible to control the temperature of the phase transition of the thermoelectric conversion material and control the thermal motion by controlling the length of the alkyl group of the conductive compound. Therefore, depending on the environment in which the element is used, 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. .
In view of the usual application of the thermoelectric conversion element, it is preferable to design the molecular to generate a structural phase transition at a temperature in the range of -50 ° C to 200 ° C, and to design the molecular phase to generate a structural phase transition at a temperature in the range of It is more preferable that the molecular design be such that a structural phase transition occurs 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 as to cause structural phase transition 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 exhibiting a relative value of a large power factor near the temperature at which a structural phase transition of the conductive compound is observed can be confirmed to be a thermoelectric conversion material most suitable for setting the temperature around that temperature to the use temperature.

  From this point of view, representative examples of preferable conductive compounds are shown below.

(1) Conductive compound having porphyrin skeleton

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

The aromatic hydrocarbon ring constituting Z includes, for example, phenyl, biphenyl, naphthalene, anthracene, tetracene, pentacene, hexacene, heptacene, acenaphthene, naphthacene, azulene, phenalene, benzoanthracene, phenanthrene, chrysene, antanthrene, pyrantrene, Indenoindene, picene, triphenylene, perylene, naphthoperylene, coronene, ovalene, pyrene, benzopyrene, hexahelicene, heptahelene, octahelicene, nonahelicene, decahelicen, undecahelense, dodecahelicene etc .; tetraphen, pentaphen, hexaphen, heptaphen, octaphene, nonaphen , Decaphene, undecaphene, dodecaphene, C60 fullerenes, C70 fullerenes, etc. , Biphenyl, naphthalene is preferable. Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenyl, pyridyl, imidazolyl, morpholino, benzothienyl, benzophenyl and the like. Examples of these aromatic hydrocarbon rings or alkyl groups for optionally substituting aromatic heterocycles or substituents having an alkyl group include the groups described for R in formulas (1) and (2), and carbon The linear alkyl group of several 1-15 is preferable. 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 in one set of opposing positions is a group having a linear alkyl group having 1 to 30 carbon atoms or a linear alkyl group having 1 to 30 carbon atoms, and preferably having 5 to 20 carbon atoms It is more preferable that it is a chain alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms, and is a group having a linear alkyl group having 8 to 15 carbon atoms or a linear alkyl group having 8 to 15 carbon atoms Is more preferred.
The van der Waals volume ratio of the alkyl group or the alkyl moiety to the entire conductive compound is preferably 5 to 60%, more preferably 10 to 50%, still more preferably 15 to 50%. preferable.

As a conductive compound which makes such a porphyrin a basic skeleton, the compound represented by following General formula (10)-(13) is preferable.

In formulas (10), (11), (12) or (13), R _{47 to} R ₅₀ are the same as R in the above 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, the 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 a substituent having an alkyl group can also include the groups described for R in formulas (1) and (2). Preferably, R ₄₇ , R ₄₈ , R ₄₉ or R ₅₀ in one set 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 More preferably, it is a group having a C 4-15 linear alkyl group or a C 4-15 linear alkyl group, and a C 8-13 linear alkyl group or a C 8-13 It is more preferable that it is a group having a linear alkyl group.
Moreover, it is preferable that it is 5 to 60%, and, as for the van der Waals volume ratio with respect to the whole electroconductive compound of an alkyl group or an alkyl part, it is more preferable that it is 10 to 50%. In particular, 15 to 50% is preferable.

  In a conductive compound having such a porphyrin structure as a basic skeleton, for example, when the alkyl group or the alkyl moiety 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 Structural phase transition occurs in the temperature range of 30 to 120 ° C. Therefore, when use at, for example, 30 to 150 ° C. is assumed, the alkyl group or alkyl moiety 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 having heteroacene as a basic skeleton

In formula (3), Y each independently represents S, Se, SO ₂ , O, N (R ₅₁ ), Si (R ₅₁ ) (R ₅₂ ), and R ₅₁ and R ₅₂ each independently represent And a hydrogen atom and a substituent, and preferred examples of the substituent include an aryl group and a monocyclic aromatic heterocyclic residue; an amino group substituted with an alkyl group or an aromatic ring residue, an alkyloxy group and an alkylthioxy group, It is 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 phenyl, biphenyl and naphthyl groups. Examples of the monocyclic aromatic heterocyclic residue include furyl, thienyl, thienylene, tenyl, pyridyl, piperidyl and quinolyl groups. And isoquinolyl group, imidazolyl group, morpholino group, benzothienyl group, benzophenyl group and the like, and as the halogen atom, fluorine atom, chlorine atom, bromine atom and the like can be mentioned. Y is preferably S or Se, particularly preferably S.
Z ₁ and Z ₂ each independently represent an alkyl group or a substituent having an alkyl group, or aromatic hydrocarbon ring or aromatic heterocycle substituted by a substituent having an alkyl group or an alkyl group, Z ₁ And Z ₂ may be the same or different.
As an aromatic hydrocarbon ring, the monocyclic hydrocarbon or the aromatic hydrocarbon ring which several rings connected or condensed can be mentioned, for example. Examples of monocyclic aromatic hydrocarbon rings include aromatic hydrocarbon rings having 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms. In addition, as an aromatic hydrocarbon ring in which a plurality of rings are linked or condensed, an aromatic hydrocarbon ring having 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms, is preferably 2 or more (for example, 2 to 7 or 2 to 5) Or 2-3) linked or condensed structures can be mentioned. Specific examples of the aromatic hydrocarbon ring include, for example, phenyl, biphenyl, naphthyl, anthracene, tetracene, pentacene, phenanthrene, chrysene, triphenylene, tetraphen, pyrene, pyrene, picene, pentacene, perylene, helicene, coronene and the like. Can. Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenyl, pyridyl, imidazolyl, morpholino, benzothienyl, benzophenyl and the like.
As a substituent which has an alkyl group or an alkyl group, the group demonstrated by R of Formula (1) and (2) can be mentioned. Preferably, it is a group having a linear alkyl group having 1 to 30 carbon atoms or a linear alkyl group having 1 to 30 carbon atoms, and a linear alkyl group having 1 to 20 carbon atoms or 1 to 20 carbon atoms It is more preferable that it is a group which has a linear alkyl group, and it is more preferable that it is a group which has a C5-C15 linear alkyl group or a C5-C15 linear alkyl group.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl moiety to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and still more preferably 30 to 60%. .

As the conductive compound having such heteroacene as a basic skeleton, the following compounds are preferable: (2-1) BTBT or a conductive compound having a structure similar thereto is preferable.

In formula (6), X ₁ and X ₂ are the same as Y in formula (3), preferably S or Se, particularly preferably S. At least one of R ₁ and R ₂ , preferably both, may be the same as the alkyl group described for R in the above formulas (1) and (2) or a substituent having an alkyl group. However, in the compound of Formula (6), it is preferable that it is a group which has a C1-C15 linear alkyl group or a C1-C15 linear alkyl group, and a C6-C12 linear alkyl group Or a group having a linear alkyl group having 6 to 12 carbon atoms is more preferable.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl moiety to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and still more preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton is, for example, a structural phase transition when the alkyl group or alkyl moiety is a linear alkyl group having 5 to 12 carbon atoms or a linear alkyl moiety having 5 to 12 carbon atoms. Occurs in the temperature range of 70-120.degree. Therefore, when use at 50 ° C. to 150 ° C., for example, is assumed, the alkyl group or alkyl moiety may be a linear alkyl group having 5 to 12 carbon atoms or a linear alkyl moiety having 5 to 12 carbon atoms preferable.
The compounds of the formula (6) can be produced, for example, by the method described in WO2008 / 047896, the contents of which are incorporated herein by reference.

(2-2) A conductive compound having a basic structure of DNTT or a similar structure thereto

In the formula (7), X ₁ and X ₂ are the same as Y in the above formula (3), preferably S or Se, and particularly preferably S. R _{3 to} R ₁₄ are hydrogen, or the alkyl having the alkyl group or alkyl group described in R of the above formulas (1) and (2), or a substituent having an alkyl group, and at least one of R _{3 to} R ₁₄ has the above formula ( It is a substituent which has the alkyl group or alkyl group demonstrated by R of 1) and (2). 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, in particular R ₆ and R ₁₂ or More preferably, they are located at R ₅ and R ₁₁ . The substituent having an alkyl group or 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. A linear alkyl group or a group having a linear alkyl group having 4 to 16 carbon atoms is more preferable, and a linear alkyl group having 6 to 12 carbon atoms or a group having a linear alkyl group having 6 to 12 carbon atoms It is more preferable that
In addition, the van der Waals volume ratio of the alkyl group or the alkyl moiety to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and still more preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton is, for example, a structural phase transition when the alkyl group or the alkyl moiety is a linear alkyl group having 6 to 12 carbon atoms or a linear alkyl moiety having 6 to 12 carbon atoms. Occurs in the temperature range of 100-140.degree. Therefore, when use at, for example, 80 ° C. to 150 ° C. is assumed, the alkyl group or alkyl moiety may be a linear alkyl group having 6 to 12 carbon atoms or a linear alkyl moiety having 6 to 12 carbon atoms preferable.
The compounds of the 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) A conductive compound having as a basic skeleton a structure similar to that of DATT

In the formula (8), X ₁ and X ₂ are the same as Y in the above formula (3), preferably S or Se, and particularly preferably S. R ₁₅ to _{R 30} is hydrogen, or a substituent having an alkyl group or an alkyl group described for R in the formula (1) and _(2), at least one of _{R 15} to _{R 30} are described in R A substituted alkyl group or a substituent having an alkyl group. However, in the compounds of the formula (8), in R _{15 to} R ₃₀ , R ₁₈ and R ₂₆ are the alkyl group described in R of the above formulas (1) and (2) or a substituent having an alkyl group, The other is preferably hydrogen. In addition, as the substituent having an alkyl group or an alkyl group, a linear alkyl group having 1 to 25 carbon atoms or a group having a linear alkyl group having 1 to 25 carbon atoms is preferable, and 5 to 20 carbon atoms are preferable. A linear alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms is more preferable, and a linear alkyl group having 6 to 15 carbon atoms or a group having a linear alkyl group having 6 to 15 carbon atoms It is more preferable that
In addition, the van der Waals volume ratio of the alkyl group or the alkyl moiety to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and still more preferably 30 to 60%. .
A conductive compound having such a structure as a basic skeleton is, for example, a structural phase transition when the alkyl group or the alkyl moiety is a linear alkyl group having 6 to 15 carbon atoms or a linear alkyl moiety having 6 to 15 carbon atoms. Occurs in the temperature range of 100-140.degree. Therefore, when use at, for example, 80 ° C. to 150 ° C. is assumed, the alkyl group or alkyl moiety may be a linear alkyl group having 6 to 15 carbon atoms or a linear alkyl moiety having 6 to 15 carbon atoms preferable.
The compounds of the formula (8) can be produced, for example, by the method described in WO2008 / 050726, the contents of which are incorporated herein by reference.

(4) Conductive compounds having a basic structure as a structure similar to that of DCTT

In the formula (9), X ₁ and X ₂ are the same as Y in the above formula (3), preferably S or Se, and particularly preferably S. R _{31 to} R _{46 each} represents hydrogen, or the alkyl group or the substituent having the alkyl group described in R of the above formulas (1) and (2), and at least one of R _{31 to} R ₄₆ is described by R A substituted alkyl group 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 alkyl group described in R of the above formulas (1) and (2) or a substituent having an alkyl group, The other is preferably hydrogen. Moreover, as a substituent having an alkyl group or an alkyl group, a linear alkyl group having 1 to 25 carbon atoms or a group having a linear alkyl group having 1 to 25 carbon atoms is preferable, and 5 to 20 carbon atoms are preferable. A linear alkyl group or a group having a linear alkyl group having 5 to 20 carbon atoms is more preferable, and a linear alkyl group having 6 to 15 carbon atoms or a group having a linear alkyl group having 6 to 15 carbon atoms It is more preferable that
Moreover, it is preferable that it is 5 to 60%, and, as for the van der Waals volume ratio with respect to the whole electroconductive compound of an alkyl group or an alkyl part, it is more preferable that it is 10 to 50%. In particular, 15 to 50% is preferable.
As described above, a conductive compound having such a structure as a basic skeleton can control the temperature of structural transition of the thermoelectric conversion material and control the thermal movement by adjusting the length of the alkyl group or the alkyl moiety. For example, when use at 70 ° C. to 150 ° C. is assumed, the alkyl group or alkyl moiety is a linear alkyl group having 6 to 15 carbon atoms or a linear alkyl moiety having 6 to 15 carbon atoms Is preferred.
The compounds of the formula (9) can be produced, for example, by the method described in WO2008 / 050726, the contents of which are incorporated herein by reference.

The organic thermoelectric conversion material of the present invention may optionally contain a dopant. As the dopant, for example, onium salt compounds such as sulfonium salts, iodonium salts, ammonium salts, carbonium salts, phosphonium salts, etc .; camphorsulfonic acid, dodecylbenzenesulfonic acid, 2-naphthalenesulfonic acid, toluenesulfonic acid, 2-naphthalenesulfone Organic acids such as acids; halogens such as Cl ₂ , Br ₂ , I ₂ , ICl, ICl ₃ , IBr, IF etc .; Lewis such as PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ , SO ₃ etc. Acids; Proton acids such as HF, HCl, HNO ₃ , H ₂ SO ₄ , HClO ₄ , phosphoric acid, etc .; 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; Lucal earth metals, lanthanides such as Eu, and others, such as R ₄ N ⁺ , R ₄ P ⁺ , R ₄ As ⁺ , R ₃ S ⁺ (R: alkyl group), acetylcholine and the like can be mentioned.

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

  The thermoelectric conversion material of the present invention has a high thermoelectromotive force, and is useful as a thermoelectric conversion material of an organic thermoelectric conversion element. For this reason, the thermoelectric conversion material of the present invention can be effectively used to form the thermoelectric conversion layer of the 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 containing a thermoelectric conversion material, and a thermoelectric conversion material Also provided is a method of thermoelectric conversion by the thermoelectric conversion layer.

The thermoelectric conversion element of the present invention has a first electrode, a thermoelectric conversion layer and a second electrode on a base material, and the thermoelectric conversion layer contains the thermoelectric conversion material of the present invention.
The thermoelectric conversion element of the present invention only needs to have the first electrode, the thermoelectric conversion layer and the second electrode on the base material, and the positions of the first electrode and the second electrode and the thermoelectric conversion layer There is no particular limitation on the other configuration such as the relationship. 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. When there is a temperature difference in the lateral direction with respect to the substrate, it is a horizontal thermoelectric conversion element (FIG. 5), and when there is a temperature difference in the vertical direction with respect to the substrate, it is a vertical thermoelectric conversion element (FIG. 6) . The thermoelectric conversion layer in the thermoelectric conversion element of the present invention may be disposed in contact with the two electrodes, and an electromotive force is generated by providing a temperature difference between the electrodes.

  As a base material, what can hold electrodes, such as glass, metal, a plastic film, a nonwoven fabric, and paper, and a thermoelectric conversion material can be used. In order to give the device flexibility, it is preferable to use a flexible plastic film or the like.

  Examples of the electrode material 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, etc. Materials with low contact resistance are preferred. Moreover, in order to reduce the contact resistance with the thermoelectric conversion material, it is possible to perform processing such as contact doping.

  The thermoelectric conversion layer of the thermoelectric conversion element of the present invention uses the thermoelectric conversion material 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 It may be an element having a thermoelectric conversion layer formed by using a thermoelectric conversion layer and a thermoelectric conversion layer formed by using a thermoelectric conversion material other than the thermoelectric conversion material of the present invention. Since the thermoelectric conversion material of the present invention can be designed to exert the highest thermoelectromotive force according to the temperature at which the device is used, as described above, the molecular design of the substituent is appropriately selected according to the operating temperature. It can be changed.

The film forming method of the thermoelectric conversion layer and the like in the thermoelectric conversion element of the present invention is not particularly limited, and examples thereof include methods such as a solution process such as printing and a vacuum process. Solution process is preferable in consideration of the device manufacturing cost, 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, and letterpress printing, Examples of the method 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 the high thermoelectric power of the conductive compound itself, and provides a new approach for providing a high-performance organic thermoelectric conversion element . In particular, having a very high Seebeck coefficient facilitates high-voltage device design, making it 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)

  Dipyrromethane (0.30 g, 1.0 mmol) was added to a reaction vessel purged with argon and dissolved in dichloromethane (200 ml). Argon gas was bubbled for 10 minutes here. Then, tridecanal (0.3 ml, 1.1 nnol) and trifluoroacetic acid (TFA) (2 drops) were sequentially added and stirred for 17 hours under light blocking. 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 solution reached half volume, 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 desired 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 in a glass tube oven under vacuum at 200 ° C. for 30 minutes.

  As shown in FIG. 2, by DSC (170-570 K), a sharp peak and a broad peak were observed at 320-360 K, and a peak was observed around 440 K, which indicated 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 (170-570 K).
Synthesis Example 4 Synthesis of C8BTBT (1) Synthesis of 2,7-Di (1-octynyl1) [1] benzothieno [3,2-b] [1] benzothiophene

  Under 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 degassed for 30 minutes. 10 mol% PdCl2 (PPh3) 2 (140 mg), 20 mol% CuI (76 mg), 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 is distilled off under reduced pressure, the residue is purified by column chromatography (silica gel, methylene chloride: hexane = 1: 3, Rf = 0.6), and the target compound represented by the above formula by recrystallization from hexane Colorless plate crystals (yield 710 mg, 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 is distilled off, and the residue is purified by column chromatography (silica gel, hexane, Rf = 0.6) (yield 286 mg, 94% yield) and recrystallized from hexane to give a colorless powder of the target compound. A solid was obtained (yield 250 mg, 82%).

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

Example 1 Production and Evaluation of Thermoelectric Conversion Element Using Compound (C12BP) In this example, an organic thermoelectric conversion element was produced using the compound synthesized in Synthesis Example 1, and the characteristics were evaluated.
The white plate glass to which the shadow mask for electrode preparation was attached was installed in a vacuum evaporation system, and it evacuated until the degree of vacuum in an apparatus became 1.0 * 10 <^-4> Pa or less. Gold was deposited to a thickness of 30 nm at a deposition rate of 0.1 Å / sec by resistance heating deposition to obtain a substrate with an electrode.
Wire a thermocouple and electrodes after attaching a shadow mask to this substrate, install it in the characterization device, and evacuate it until the degree of vacuum in the device is 1.0 x 10 ^-4 Pa or less, A thin film (160 nm) of a compound (C12BP) was formed by resistance heating vapor deposition to obtain a thermoelectric conversion element (distance between electrodes: 10 mm, width of electrodes: 7.6 mm) of the present invention.
The temperature of the obtained thermoelectric conversion element was determined under the condition that the degree of vacuum in the device was 1.0 × 10 ⁻⁵ Pa or less, a voltage was applied, the current value was read, and the conductivity was measured. In addition, a temperature gradient was provided between the electrodes, and the Seebeck coefficient was measured by 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. Further, as shown in FIG. 1, the van der Waals volume ratio of the side chain of C12BP was 50% (Winmostar software was used).

Example 2 Preparation and Evaluation of Thermoelectric Conversion Device Using Compound (C8-BTBT) Organic Thermoelectric Conversion Device Using Compound (C8-BTBT) Synthesized in Synthesis Example 2 Instead of the Compound Used in Example 1 Were evaluated.
A heptane solution of 0.5 wt% C8-BTBT was dropped onto a white sheet glass substrate, spin-coated (1000 rpm x 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 evaporation system, and evacuated until the degree of vacuum in the system became 1.0 × 10 ⁻⁴ Pa or less. Gold was deposited to a thickness of 30 nm at a deposition rate of 0.1 Å / sec by resistance heating deposition to obtain a thermoelectric conversion element (distance between electrodes: 5 mm, width of electrodes: 7.6 mm).
Wire the thermocouple and electrodes to this element, install in the evaluation device, determine the temperature under the condition that the degree of vacuum in the device is 1.0 x 10 -5 Pa or less, apply the voltage, and read the current value The conductivity was measured. In addition, a temperature gradient was provided between the electrodes, and the Seebeck coefficient was measured by 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, two peaks at around 380 K and a sharp peak at 400 K were observed by DSC (170-570 K), indicating that a structural phase transition occurred.
In addition, 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 Device Using Compound (C10 DNTT) An organic thermoelectric conversion device was produced using compound (C10 DNTT) instead of the compound used in Example 1 and evaluated.
The white plate glass to which the shadow mask for electrode preparation was attached was installed in a vacuum evaporation system, and it evacuated until the degree of vacuum in an apparatus became 1.0 * 10 <^-4> Pa or less. Gold was deposited to a thickness of 30 nm at a deposition rate of 0.1 Å / sec by resistance heating deposition to obtain a substrate with an electrode.
Attach a shadow mask to this substrate, wire to thermocouples and electrodes, install in the evaluation device, evacuate the vacuum in the device to 1.0 × 10 ^-4 Pa or less, and resistance heating A thin film (20 nm) of a compound (C10 DNTT) is formed at a deposition rate of 0.5 Å / sec by vapor deposition to obtain a thermoelectric conversion element (distance between electrodes: 5 mm, width of electrode: 7.6 mm) of the present invention The
The temperature of the obtained thermoelectric conversion element was determined under the condition that the degree of vacuum in the device was 1.0 × 10 ⁻⁵ Pa or less, a voltage was applied, the current value was read, and the conductivity was measured. In addition, a temperature gradient was provided between the electrodes, and the Seebeck coefficient was measured by reading the thermoelectromotive force value.
As a result, the conductivity at 315 K 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 C10 DNTT was 57%. As shown in FIG. 4, in the C10 DNTT obtained in Example 1, sharp peaks were observed at 390 K, 500 K, 570 K and 580 K respectively by DSC (170-620 K), indicating that a structural phase transition occurs. It was done.

Example 4 Preparation and Evaluation of Vertical Thermoelectric Conversion Device Using Compound (C8-BTBT) A vertical organic thermoelectric conversion device was manufactured using the compound (C8-BTBT) synthesized in Synthesis Example 2 and evaluated. .
PEDOT / PSS was spin-coated (7000 rpm × 20 sec) on an ITO glass substrate (manufactured by Asahi Glass Co., Ltd.) and dried to prepare a substrate.
A pair of substrates having a gap of 25 μm was produced by holding high-millan (50 μm, made by Mitsui DuPont Polychemicals) between the two produced substrates and heating at 150 ° C.
The compound (C8BTBT) melted at 130 ° C. was injected into the prepared substrate pair to obtain a thermoelectric conversion device (distance between electrodes: 25 μm, electrode size: 100 mm 2).
Wiring was performed on the ITO surface of the obtained thermoelectric conversion element, and it was confirmed that a thermoelectromotive force was generated by providing a temperature gradient between the electrodes.

(Example 5)
In the thermoelectric conversion element (C12BP) manufactured in Example 1, the temperature (27 to 127 ° C.) was changed, the conductivity and the Seebeck coefficient were measured, and the power factor was calculated. FIG. 7 shows the analysis data of bulk C12BP DSC up to 27-227 ° C. and the relative value (27-127 ° C.) of the power factor 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. From this, it is understood that, by using this thermoelectric conversion element at 70 ° C. to 100 ° C., more preferably at 80 to 90 ° C., efficient thermoelectric conversion can be performed. Therefore, in the thermoelectric conversion element of the present invention, it has been shown that very efficient thermoelectric conversion can be achieved by selecting the optimum use temperature according to each thermoelectric conversion material.

(Comparative example 1)
Similar to Example 3, a compound was produced using DNTT instead of C10 DNTT, to fabricate a similar device. As a result, the conductivity at 360 K was 8.3 × 10 ⁻⁹ Scm ⁻¹ and the Seebeck coefficient was 35 mV / K.
In the DNTT obtained in Comparative Example 1, no peak was observed by DSC (170-570 K).

(Comparative example 2)
A similar device was prepared using pentacene instead of C10 DNTT as in Example 3. 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 for forming a sensor matrix for smart house and smart building, it is useful in reutilization of exhaust heat energy in a house, an office and a car. Moreover, it can also be used as a power supply of a sticker type | mold biological information measuring instrument (a body temperature, a pulse, an electrocardiograph monitor etc.) taking advantage of the flexibility which is the characteristics of the organic thermoelectric conversion material. In particular, having a very high Seebeck coefficient facilitates high-voltage device design, making it possible to provide a characteristic thermoelectric conversion element.

Claims (4)

A method of producing an organic thermoelectric conversion material using a conductive compound having a basic skeleton consisting of a polycyclic aromatic ring having a carrier transport property and an alkyl group or a substituent having an alkyl group,
A method comprising selecting a conductive compound whose structural phase transition is specified by DSC at a temperature ranging from -50 ° C to 200 ° C. A method for improving the Seebeck coefficient of an organic thermoelectric conversion material comprising a conductive compound having a basic skeleton consisting of a polycyclic aromatic ring having carrier transport properties and an alkyl group or a substituent having an alkyl group,
A method comprising selecting the conductive compound whose structural phase transition is specified by DSC at a temperature ranging from -50 ° C to 200 ° C.   The method according to claim 1, wherein the structural phase transition point specified by DSC of the conductive compound is observed at a temperature in the range of 0 to 180 ° C. 4. The method according to any one of claims 1 to 3, wherein a van der Waals volume ratio occupied by the substituent in the conductive compound is 25 to 60%.