JP6699039B2 - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

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 paid to thermoelectric conversion elements as a means for recovering unused thermal energy in the environment as electric energy.

Conventionally, as a thermoelectric conversion material, an inorganic semiconductor material such as CoSb ₃ has been mainly used and studied because the thermoelectric conversion efficiency is relatively high. 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. Therefore, in recent years, researches on organic thermoelectric conversion materials, which are inexpensive and excellent in workability of materials, have been actively conducted.

  As conventional organic thermoelectric conversion materials, conductive materials such as polyaniline (Patent Documents 1, 3, 4, 5 and 7), polyphenylene vinylene (Patent Document 2), polythienylene vinylene (Patent Document 2), polypyrrole (Patent Document 4) are used. A polymer composed of a volatile polymer has been proposed.

  However, these conductive polymers have insufficient thermoelectric conversion performance, and higher thermoelectric conversion performance is required for practical use. In order to meet the demand for increasing the thermoelectric conversion efficiency of such thermoelectric conversion materials, 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), metal particles dispersed (Patent Document 1), and specified with respect to the energy level of the molecular orbital of the conductive polymer. It has been proposed to include a thermally excited assisting agent having a molecular orbital of the energy level difference (Patent Document 7).

By the way, the thermoelectric conversion efficiency of a thermoelectric conversion material is generally expressed by the following formula [Equation 1] dimensionless figure of merit ZT=S ² ·σ·T/κ (A)
[In the formula, S(V/K) represents a thermoelectromotive force (Seebeck coefficient), σ(S/m) represents electrical conductivity, κ(W/mK) represents thermal conductivity, and T(K) Represents the absolute temperature, and S ² ·σ represents the power factor. ]
The dimensionless figure of merit (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 larger the Seebeck coefficient and the electric conductivity and the lower the thermal conductivity, the higher the value, and the higher the thermoelectric conversion performance. Among the materials that can obtain a high ZT, a material with a particularly large Seebeck coefficient is a flexible thermoelectric conversion element that uses an organic thermoelectric conversion material, and the operation due to disconnection by reducing the thickness of the element or reducing the number of series connection of many cells. It is possible to reduce defects.

  In this respect, the introduction of the dopant and the dispersion of the metal particles 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 the conductivity have a certain trade-off relationship, and the Seebeck coefficient shows the 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.

  On the other hand, the above-mentioned attempt to contain the thermal excitation assisting agent improves the thermoelectric conversion efficiency by increasing the thermoelectromotive force (Seebeck coefficient). However, it does not improve the electromotive force itself (Seebeck coefficient) by improving the conductive polymer itself.

  Also, Shimada et al. focused on the sudden occurrence of deep traps at low temperatures in organic semiconductors and predicted that the point defect of pentacene, which is a small molecule semiconductor, would increase the Seebeck coefficient at low temperatures (Non-Patent Document 4). .. However, the Seebeck coefficient shown by Shimada et al. is about 1 mV/K, and it does not give any teaching on the direct improvement of the Seebeck coefficient by the thermal motion of molecules 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

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 having a Seebeck coefficient which is significantly larger than that of a conventional organic thermoelectric conversion material.

  In view of the above problems, the present inventors have studied the molecular design of a conductive compound that achieves excellent thermoelectric conversion efficiency without being bound by the thermoelectric theory in conventional semiconductors, and for the basic skeleton, a planar π-conjugated structure is used. It has a structure derived from a polycyclic aromatic compound that generally has a high carrier transport ability, and on the other hand, a compound having a side chain that thermally moves at a predetermined temperature, it is not possible to assume from conventional thermoelectric theory. It was found that it has a high Seebeck coefficient. The present invention is based on such knowledge.

That is, the present invention provides the following organic thermoelectric conversion material and organic thermoelectric conversion element.
[1] Containing a conductive compound in which a basic skeleton composed of a polycyclic aromatic ring having carrier-transporting properties is bonded with a substituent containing an alkyl group that causes a change in intermolecular distance or molecular packing structure of the basic skeleton due to thermal motion , Organic thermoelectric conversion materials.
[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-transporting properties, and a structural phase transition (identified by DSC) at a temperature in the range of −50° C. to 200° C. The organic thermoelectric conversion material according to [1], which comprises a conductive compound that
[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 capable of binding 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).

(In the formula, X represents a polycyclic aromatic ring having carrier-transporting properties, R independently 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 of 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 of [1] to [5], wherein the structural phase transition point of the conductive compound by DSC 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 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 formula (3), (4), or (5).

(In the formula, Y independently represents S, Se, SO ₂ , O, N(R ₅₁ ), or Si(R ₁ )(R ₅₂ ), and R ₅₁ and R ₅₂ are each independently 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, 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 heterocycle. 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 represent 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). The organic thermoelectric conversion material as described in 1.






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

  INDUSTRIAL APPLICABILITY The present invention can provide an organic thermoelectric conversion material having a Seebeck coefficient significantly larger than that of a conventional organic thermoelectric conversion material and an organic thermoelectric conversion element having a thermoelectric conversion layer containing the organic thermoelectric conversion material.

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

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 to the basic skeleton, 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 planar π-conjugated structure and generally has a basic skeleton derived from a polycyclic aromatic compound 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, the conductive compound used in the present invention has a substituent bonded to the polycyclic aromatic ring that causes a change in the intermolecular distance of the basic skeleton and the molecular packing structure due to 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 thermally moves at a predetermined temperature to change the distance between adjacent molecules or the molecular packing structure. , Causing a volume change or a structural phase transition of the conductive compound. As a result, it is understood that the thermoelectromotive force (Seebeck coefficient) is enhanced by sensitively catching the temperature change.

Here, the definitions of some terms used in the present specification will be described.
The “polycyclic aromatic compound” means a compound having a polycyclic aromatic ring, and the “basic skeleton composed of a polycyclic aromatic compound” means a substituent part in the whole structure of such a compound. Means the removed structure.
"Van der Waals volume" means the volume of a molecule or its constituent elements when the atoms constituting the molecule are approximated by a sphere having a van der Waals radius. “Van der Waals volume ratio” is the ratio of van der Waals volumes of a plurality of constituent elements of a molecule.
The "length of the side chain" means the atom that is the most distant in the stable structure among the atoms that form the side chain from the central position of the atom that the side chain chemically bonds among the atoms that form the main skeleton. It means the distance to the center position.
The “π-conjugated structure” means a structure in which multiple bonds are alternately arranged with a single bond, and the “planar π-conjugated structure” means a structure in which atoms forming the π-conjugated structure exist in the same plane.
"Thermo-electromotive force (Seebeck coefficient)" is the temperature dependence of the steady-state potential difference that occurs at two different locations on a substance having electrical conductivity, and from the gradient, S=-ΔV/ΔT (ΔV is the potential difference). , ΔT means a value calculated by the temperature difference).
“Conductivity” means a value obtained by multiplying the electric conductance obtained from the current-voltage characteristics of a material measured by a source meter or the like by the length of the current path and dividing 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. by the specific heat of the material and the density.
In the present specification, “structural phase transition” means that a structure that can be regarded as spatially uniform in a substance (whether an ordered structure or a disordered structure) is transformed into a structure in a different state depending on external conditions such as temperature. The “structural phase transition temperature” means 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), and the temperature dependence of the specific heat changes (the gradient of the specific heat differentiated by temperature changes abruptly). Measured at. Further, while the temperature dependence of the electrical conductivity of the semiconductor material exhibits Arrhenius type thermal activation, it is also measured as the temperature at which the activation energy suddenly changes.

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


In formulas (1) and (2), X represents a polycyclic aromatic ring having carrier transport properties, and R's each independently represent an alkyl group or a substituent having an alkyl group. m is a number that is equal to or less than the maximum number of Rs that can be bonded to X, and represents an integer of, for example, 1 to 8 and typically an integer of 1 to 2, although it varies depending on the basic skeleton. 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 in the organic thermoelectric conversion material of the present invention as a thermoelectric conversion substance, has a structure in which two or more aromatic rings are condensed. And has a plane π-conjugated structure. Therefore, molecules are aligned and a stacking effect between adjacent molecules is easily generated, and electrons or holes between molecules are easily moved, so that high carrier mobility is easily obtained.

  The polycyclic aromatic ring represented by X can be composed of either one or both of an aromatic hydrocarbon and an aromatic heterocycle, 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, naphtoperylene, coronene, ovalen, pyrene, Benzopyrene, hexahelicene, heptahelicene, octahelicene, nonahelicene, decahelicene, undecahelicene, dodecahelicene, etc.; tetraphene, pentaphene, hexaphene, heptaphene, octaphene, nonaphene, decaphene, undecaphene, dodecaphene, C60 fullerene, C70 fullerene, etc. Hydrocarbons; as well as indole, isoindole, purine, quinoline, isoquinoline, quinoxaline, cinnoline, pteridine, benzopyran, acridine, xanthene, benzimidazole, indazole, phenazine, naphthyridine, benzothiadiazole, benzothiazole, dithienosilole, fluorene, thienothiophene, carbazole. , Phenothiazine, phenoxazine, benzothienobenzothiophene, dithienothiophene, benzodithiophene, benzodiselenophene, dinaphthothienothiophene, dianthrathienothiophene, benzobisoxazole, etc. , Phenanthrene, phenanthridine, cyclopentadithiophene, benzo-C-cinnoline, perylene dicarboximide, benzotrifuran, benzotrithiophene, porphyrin, chlorin, choline, phthalocyanine, porphyrazine and other polycyclic aromatic heterocycles Is mentioned.

  Among them, acene hydrocarbons such as naphthalene, anthracene, naphthacene, and pentacene, heteroacenes such as benzodithiophene, benzothienobenzothiophene, and dinaphthodithiophene, or porphyrin, phthalocyanine, porphyrazine, etc., in terms of high carrier transport ability. 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 connecting a plurality of polycyclic aromatic rings, the number of polycyclic aromatic rings can be generally 2 to 2000, and preferably 2 to 1000, It is more preferably from 2 to 100, further preferably from 2 to 5. Of course, the basic skeleton may be composed of a single polycyclic aromatic ring. The molecular weight (Mw) of the basic skeleton composed of one or more polycyclic aromatic rings may be 50 to 200,000, preferably 100 to 100,000, more preferably 200 to 50,000 Mw, and particularly preferably. It is 200 to 30,000.

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 the polycyclic aromatic ring has an alkyl group represented by R above. 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 at any temperature in the range of -50°C to 200°C. Such a substituent moves sensitively to heat and causes a volume change or a structural phase transition of the conductive compound. As a result, the carrier transporting ability of the basic skeleton of the polycyclic aromatic compound is modulated, and highly efficient thermoelectric conversion becomes possible. The structural phase transition of the conductive compound due to the thermal motion of the substituent can be confirmed by an endothermic and exothermic peak of differential scanning calorimetry (DSC).

  Substituents are preferably attached to the polycyclic aromatic skeleton by a rotation-free covalent bond in order to generate a thermal motion in response to heat. It is also preferable that the substituent itself has a large number of freely rotatable covalent bonds. From this point of view, the substituent is preferably a substituent having an alkyl group, and a chain alkyl group is used as a main chain. Is more preferable, and a linear alkyl group is still more preferable.

  Further, in order to achieve high thermoelectromotive force (Seebeck coefficient), while maintaining the π-conjugated structure developed by the polycyclic aromatic ring, the thermal motion of the substituent causes a structural phase transition in response to heat. It is considered that it is important to bring them, and from this viewpoint, the van der Waals volume ratio of the side chain to the polycyclic aromatic skeleton is considered to be one of the indicators. The crystallinity and the cohesive force due to the crystal form differ due to the difference in the polycyclic aromatic skeleton, and the bonding force between the molecules differs, but in the conductive compound contained in the thermoelectric conversion material of the present invention, the same compound is generally used. The Van der Waals volume ratio of the substituents therein 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%, particularly preferably 15 to 50%. By designing the van der Waals volume ratio of the side chains to the polycyclic aromatic skeleton, it becomes possible to control the temperature and thermal motion of the structural phase transition. The required temperature (temperature difference) differs depending on the environment in which the element is used, but by utilizing this capability, a suitable element can be designed.

  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, and more preferably 2 to 2 carbon atoms. 18 groups, more preferably 4 to 15 carbon atoms.

  Specifically, the linear alkyl group includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, and a 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 chain 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, and 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 may be mentioned. In addition, examples of the cyclic alkyl group include a cyclopentyl group and a cyclohexyl group.

Examples of the substituent having an alkyl group include groups in which the alkyl group is substituted with the following substituents.
1) Aryl group such as phenyl group, biphenyl group, naphthyl group, etc. 2) Furyl group, thienyl group, thienylene group, tenyl group, pyridyl group, piperidyl group, quinolyl group, isoquinolyl group, imidazolyl group, morpholino group, benzothienyl group, Monocyclic aromatic heterocyclic residue such as benzophenyl group 3) Alkyl group or amino group substituted with aromatic ring residue, alkyloxy group, alkylthioxy group, ester group, carbamoyl group, acetamide, thio group or Acyl group 4) Fluorine atom, chlorine atom, halogen atom such as bromine atom, nitro group, cyano group These substituents may have one or more.

Further, a group in which an alkyl group is bonded to a polycyclic aromatic skeleton through the following chemical structure can be mentioned.
1) hetero atom such as oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom 2) aryl group such as phenyl group, biphenyl group, naphthyl group 3) furyl group, thiophene group, thienyl group, thienylene group, tenyl group , Pyridyl group, imidazolyl group, morpholino group, benzothienyl group, benzophenyl group, etc. aromatic heterocyclic residue 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 (eg, phenyl group, biphenyl group, naphthyl group, etc.), an aromatic heterocyclic group (eg, , A furyl group, a thienyl group, a pyridyl group, an imidazolyl group, etc.)-substituted alkyl group, an 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 with an aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio group (eg, methylthio group, ethylthio group) Group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (eg, cyclopentylthio group, cyclohexylthio group, etc.), arylthio group (eg, phenylthio group, naphthylthio group, etc.) Alkyl group, alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, phenyloxycarbonyl group, naphthyl) Oxycarbonyl group, etc.)-substituted alkyl group, alkylsulfamoyl group, alkylcarbonyl group, alkylthiocarbonyl group, alkylcarbonyloxy group, alkylcarbonylamino group, alkylcarbamoyl group, alkylureido group, alkylsulfinyl group, alkylsulfonyl group Group, an arylsulfonyl group substituted with an alkyl group, an alkylamino group, a fluoroalkyl group, a perfluoroalkyl group, an 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 1 per polycyclic aromatic ring. It may have 8 substituents, preferably has 1 to 4 substituents, more preferably has 1 to 3 substituents, and particularly preferably has 2 substituents.

  Further, in the conductive compound which constitutes the present invention, the molecular weight of the alkyl group portion of the above-mentioned substituent (when the substituent is an alkyl group, the alkyl group itself) has a molecular weight of 5 to 80 with respect to the molecular weight of the entire conductive compound. % Is preferable. For example, in a rod-shaped compound in which one width of the polycyclic aromatic skeleton portion is narrow to about one benzene ring and the other width is longer than that, it is more preferable that the proportion occupies 25 to 60%. It is a compound in which the width of the skeleton portion is as wide as two or more benzene rings, and the proportion thereof is preferably 10 to 50%. Further, it is preferable that there are a plurality of rotatable bonds in the entire substituent. On the other hand, the structure other than the alkyl group may form a π-conjugated structure together with the polycyclic aromatic ring. Optimum properties can be obtained by appropriately adjusting the number of alkyl groups, the substitution position, the number of branched chains, and the length.

The temperature at which the structural phase transition of the conductive compound occurs changes depending on the combination of the basic skeleton of the polycyclic aromatic compound and the substituent. Therefore, it is preferable to appropriately design the molecule depending on the temperature at which the conductive compound is expected to be used. Particularly, in the conductive compound of the present invention, it is considered possible to control the temperature of the phase transition and the thermal motion of the thermoelectric conversion material 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 design a molecule that causes a structural phase transition at a temperature in the range of −50° C. to 200° C., and a molecular design that causes a structural phase transition at a temperature in the range of 0 to 180° C. Is more preferable, and it is more preferable that the molecular design is 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 that the structural phase transition occurs in such a temperature range.
The temperature at which the structural phase transition of the conductive compound occurs (structural phase transition point) can be confirmed by the endothermic and exothermic peak of differential scanning calorimetry (DSC). It can be confirmed that the thermoelectric conversion element that exhibits a large relative value of the power factor in the vicinity of the temperature at which the structural phase transition of the conductive compound is observed is the most suitable thermoelectric conversion material in which the temperature around the temperature is used.

  From such a viewpoint, typical 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 independently a hydrogen atom, or an unsubstituted or substituted aromatic hydrocarbon or aromatic heterocycle substituted with an alkyl group or a substituent having an alkyl group, Substituted aromatic hydrocarbons or heterocycles are preferred. A plurality of Z may be the same or different.
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 It represents a substituent having an alkyl group. A pair of W which is preferably opposite represents CR _3, a substituent R ₃ has an alkyl group or an alkyl group, is a set of W to other counter represents N or CR _3, R ₃ is is a hydrogen atom, more preferably represents CR _{3, 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, ovalen, pyrene, benzopyrene, hexahelicene, heptahelicene, octahelicene, nonahelicene, decahelicene, undecahelicene, dodecahelicene, tetraphene, pentaphene, hexaphene, heptaphene, octaphene, nonaphene , Decaphene, undecaphene, dodecaphene, C60 fullerene, C70 fullerene and the like can be mentioned, and phenyl, biphenyl and naphthalene are preferable. Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenyl, pyridyl, imidazolyl, morpholino, benzothienyl and benzophenyl. Examples of the alkyl group or a substituent having an alkyl group which optionally substitutes the aromatic hydrocarbon ring or the aromatic heterocycle include the groups described for R in the formulas (1) and (2), and A straight-chain alkyl group having a number of 1 to 15 is preferable. Further, as the alkyl group or the substituent having an alkyl group which constitutes R ³ , the groups described for R in the formulas (1) and (2) can be mentioned. Preferably, a pair of R ^{3 at} opposite positions is 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 group having 5 to 20 carbon atoms is preferable. A chain 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 8 to 15 carbon atoms or a linear alkyl group having 8 to 15 carbon atoms is preferable. Is more preferable.
The van der Waals volume ratio of the alkyl group or the alkyl moiety 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 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, a plurality of R ₄₇ , R ₄₈ , R ₄₉ or R ₅₀ may be different or the same. Examples of the alkyl group or the substituent having an alkyl group which constitutes R _{47 to} R ₅₀ also include the groups described for R in formulas (1) and (2). Preferably, a pair of R ₄₇ , R ₄₈ , R ₄₉ or R ₅₀ at opposite 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 straight-chain alkyl group having 4 to 15 carbon atoms or a group having a straight-chain alkyl group having 4 to 15 carbon atoms, more preferably a straight-chain alkyl group having 8 to 13 carbon atoms or a straight chain alkyl group having 8 to 13 carbon atoms. A group having a linear alkyl group is more preferable.
Further, the van der Waals volume ratio of the alkyl group or the alkyl portion to the whole conductive compound is preferably 5 to 60%, more preferably 10 to 50%. It is particularly preferably 15 to 50%.

  The conductive compound having such a porphyrin structure as a basic skeleton has, for example, an alkyl group or an alkyl moiety as 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 it is expected to be used at 30 to 150° C., the alkyl group or the 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 compound having heteroacene as a basic skeleton

In formula (3), Y represents each independently S, Se, SO ₂ , O, N(R ₅₁ ), Si(R ₅₁ )(R ₅₂ ), and R ₅₁ and R ₅₂ each independently. Represents a hydrogen atom, a substituent, and as a preferable substituent, 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, and 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, and the halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and the like. Y is preferably S or Se, and particularly preferably S.
Z ₁ and Z ₂ each independently represent an alkyl group or a substituent having an alkyl group, or an aromatic hydrocarbon ring or an aromatic heterocycle substituted with 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 aromatic ring or an aromatic hydrocarbon ring in which a plurality of rings are linked or fused. Examples of the monocyclic aromatic hydrocarbon ring include an aromatic hydrocarbon ring having 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms. Further, as the aromatic hydrocarbon ring in which a plurality of rings are linked or condensed, two or more aromatic hydrocarbon rings having 3 to 7 carbon atoms, preferably 4 to 6 carbon atoms (for example, 2 to 7, 2 to 5, Or 2 to 3) linked or condensed structures. Specific examples of the aromatic hydrocarbon ring include, for example, phenyl, biphenyl, naphthyl, anthracene, tetracene, pentacene, phenanthrene, chrysene, triphenylene, tetraphene, pyrene, picene, pentaphene, perylene, helicene, coronene and the like. You can Examples of the aromatic heterocycle include furyl, thiophene, thienyl, thienylene, tenyl, pyridyl, imidazolyl, morpholino, benzothienyl and benzophenyl.
Examples of the alkyl group or the substituent having the alkyl group include the groups described for R in the formulas (1) and (2). 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 preferably a linear alkyl group having 1 to 20 carbon atoms or a linear alkyl group having 1 to 20 carbon atoms. 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.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl portion to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. ..

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

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 , and preferably both, may be the same as the alkyl group or the substituent having the alkyl group, which is described in R in the above formulas (1) and (2). However, the compound of the formula (6) is preferably a linear alkyl group having 1 to 15 carbon atoms or a group having 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.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl portion to the entire conductive compound is preferably 5 to 80%, more preferably 25 to 60%, and further preferably 30 to 60%. ..
The conductive compound having such a structure as a basic skeleton is, for example, a structural phase transition in which an alkyl group or an 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 to 120°C. Therefore, for example, when it is expected to be used at 50°C to 150°C, the alkyl group or the 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 compound of 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) Conductive compound having DNTT or a structure similar thereto as a basic skeleton

In formula (7), X ₁ and X ₂ are the same as Y in formula (3) above, preferably S or Se, and particularly preferably S. R _{3 to} R ₁₄ are hydrogen or a substituent having an alkyl group or an alkyl group described for R in the above formulas (1) and (2), and at least one of R _{3 to} R ₁₄ is the above formula ( It is an alkyl group or a substituent having an alkyl group described for R in 1) and (2). However, in the compound of formula (7), it is preferable that any one of R _{4 to} R ₇ and R _{10 to} R ₁₃ is an alkyl group or a substituent having an alkyl group, and 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 having 4 to 16 carbon atoms. A straight-chain alkyl group or a group having a straight-chain alkyl group having 4 to 16 carbon atoms is more preferable, and a straight-chain alkyl group having 6 to 12 carbon atoms or a straight-chain alkyl group having 6 to 12 carbon atoms is used. More preferably.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl portion to the entire 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 is, for example, a structural phase transition in the case where an alkyl group or an 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 to 140°C. Therefore, for example, when it is expected to be used at 80° C. to 150° C., the alkyl group or the 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 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 structure similar thereto as a basic skeleton

In formula (8), X ₁ and X ₂ are the same as Y in formula (3) above, preferably S or Se, and particularly preferably S. R _{15 to} R ₃₀ are hydrogen or a substituent having an alkyl group or 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. And an alkyl group or a substituent having an alkyl group. However, in the compound of formula (8), R ₁₈ and R ₂₆ in R _{15 to} R ₃₀ are the alkyl groups or the substituents having an alkyl group described in R of the above formulas (1) and (2), Others are preferably hydrogen. Further, the alkyl group or the substituent having an alkyl group is preferably a group having a linear alkyl group having 1 to 25 carbon atoms or a linear alkyl group having 1 to 25 carbon atoms, and having 5 to 20 carbon atoms. A straight-chain alkyl group or a group having a straight-chain alkyl group having 5 to 20 carbon atoms is more preferable, and a straight-chain alkyl group having 6 to 15 carbon atoms or a straight-chain alkyl group having 6 to 15 carbon atoms is used. More preferably.
In addition, the van der Waals volume ratio of the alkyl group or the alkyl portion to the entire 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 is, for example, a structural phase transition in the case where an alkyl group or an 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 to 140°C. Therefore, for example, when it is expected to be used at 80°C to 150°C, the alkyl group or the 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 compound of 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 compound having DCTT or a structure similar thereto as a basic skeleton

In formula (9), X ₁ and X ₂ are the same as Y in formula (3) above, preferably S or Se, and particularly preferably S. R _{31 to} R ₄₆ 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 _{31 to} R ₄₆ is described for R. And an alkyl group or a substituent having an alkyl group. However, in the compound of the formula (9), R ₃₄ and R ₄₁ in R _{31 to} R ₄₆ are the alkyl groups or the substituents having 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 group having a linear alkyl group having 1 to 25 carbon atoms or a linear alkyl group having 1 to 25 carbon atoms, and having 5 to 20 carbon atoms. A straight-chain alkyl group or a group having a straight-chain alkyl group having 5 to 20 carbon atoms is more preferable, and a straight-chain alkyl group having 6 to 15 carbon atoms or a straight-chain alkyl group having 6 to 15 carbon atoms is used. More preferably.
Further, the van der Waals volume ratio of the alkyl group or the alkyl portion to the whole conductive compound is preferably 5 to 60%, more preferably 10 to 50%. It is particularly 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 and the thermal motion of the thermoelectric conversion material by adjusting the length of the alkyl group or the alkyl portion. It is conceivable that the alkyl group or the alkyl moiety is a straight-chain alkyl group having 6 to 15 carbon atoms or a straight-chain alkyl moiety having 6 to 15 carbon atoms, for example, when it is supposed to be used at 70°C to 150°C. Is preferred.
The compound of 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 include 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 _{6 and} other transition metal compounds, Li, Na, K, Rb, Cs and other alkali metals, Ca, Sr, Ba and other alkaline earth metals, Eu and other lanthanoids, and other 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 the organic thermoelectric conversion material in an amount of 0 to 60% by weight, 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 an organic thermoelectric conversion element. Therefore, the thermoelectric conversion material of the present invention can be effectively used for forming 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 are included. There is also provided a method of thermoelectric conversion by a 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. Other configurations such as relationships are not particularly limited. In the thermoelectric conversion element of the present invention, the thermoelectric conversion layer may be arranged on at least one surface thereof so as to be in contact with the first electrode and the second electrode. A horizontal thermoelectric conversion element (FIG. 5) has a temperature difference in the horizontal direction with respect to the base material, and a vertical thermoelectric conversion element (FIG. 6) has a temperature difference in the vertical direction with respect to the base material. .. The thermoelectric conversion layer in the thermoelectric conversion element of the present invention has only to be arranged so as to be in contact with two electrodes, and an electromotive force is generated by providing a temperature difference between these electrodes.

  As the base material, those capable of holding electrodes and thermoelectric conversion materials such as glass, metal, plastic film, non-woven fabric and paper can be used. It is preferable to use a flexible plastic film or the like in order to give the device flexibility.

  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, organic conductive materials such as PEDOT:PSS, and the like. Materials with low contact resistance are preferred. Further, 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 material 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 by using and a thermoelectric conversion layer formed by using a thermoelectric conversion material other than the thermoelectric conversion material of the present invention may be used. As described above, the thermoelectric conversion material of the present invention can be designed so as to exhibit the highest thermoelectromotive force depending on the temperature at which the device is used. Can be changed.

The method for forming the thermoelectric conversion layer and 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. Solution process is preferable in consideration of device manufacturing cost, and coating methods such as casting, spin coating, dip coating, blade coating, wire bar coating, and spray coating, printing methods such as inkjet printing, screen printing, offset printing, letterpress printing, and the like, Further, a soft lithography method and the like, and a method combining a plurality of these methods can be mentioned.

  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 to provide 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 becomes 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 in any way.

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

  Dipyrromethane (0.30 g, 1.0 mmol) was added to the reaction vessel replaced with argon and dissolved in dichloromethane (200 ml). Argon gas was bubbled into this for 10 minutes. Then, tridecanal (0.3 ml, 1.1 nol) and trifluoroacetic acid (TFA) (2 drops) were sequentially added, and the mixture was stirred for 17 hours in the dark. 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 became half volume, and alumina column chromatography (chloroform) was performed. The product was further purified by silica gel chromatography (dichloromethane) and GPC, and finally recrystallized (chloroform/methanol) 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

  The porphyrin obtained above was heated in a glass tube oven under vacuum at 200° C. for 30 minutes to obtain benzoporphyrin as a green solid.

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

(Synthesis example 3) 29H,3H-tetrabenzo[b,g,l,q] porphine (BP, LUMO: -2.26eV, HOMO: -4.69eV 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

  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 then degassing was performed 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 the mixture was stirred at room temperature for 8 hours. After completion of stirring, water (30 ml) was added, and the mixture was extracted with chloroform (30 ml×3). The extract was washed with water (100 ml×3) and 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 give the target compound represented by the above formula. Of colorless plate crystals were obtained (amount 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), and the pressure-hydrogen purge with an aspirator was repeated several times, followed by stirring 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, 94%) and recrystallized from hexane to give the target compound as a colorless powder. A solid was obtained (yield amount 250 mg, yield 82%).

(Example)
In each example, an organic thermoelectric conversion element using each compound was prepared and the characteristics were evaluated. As the evaluation device, a homemade ultrahigh resistance sample compatible thermoelectric property evaluation device was used. The characteristic evaluation device comprises: (1) precision vapor deposition of a sublimable material by a Knudsen cell in an ultra-high vacuum chamber; (2) sample resistance measurement using Keithley 6430 source meter up to about 10 ¹⁴ Ω; and (3) It has a function to perform high-precision Seebeck coefficient measurement with a sample resistance of about 10 ¹³ Ω as an upper limit using a homemade high input impedance differential amplifier circuit. (See Non-Patent Document: 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 to evaluate the characteristics.
A white glass plate with a shadow mask for producing electrodes was placed in a vacuum vapor deposition apparatus, and the apparatus was evacuated until the degree of vacuum in the apparatus became 1.0×10 ⁻⁴ Pa or less. Gold was vapor-deposited at a thickness of 30 nm at a vapor deposition rate of 0.1 Å/sec by a resistance heating vapor deposition method to obtain a substrate with electrodes.
After mounting a shadow mask on the substrate, wiring to the thermocouple and the electrodes is performed, the device is installed in the characteristic evaluation device, and the device is evacuated until the degree of vacuum in the device becomes 1.0×10 ⁻⁴ Pa or less, A thin film (160 nm) of the compound (C12BP) was formed by a resistance heating vapor deposition method to obtain a thermoelectric conversion element of the present invention (distance between electrodes: 10 mm, width of electrode: 7.6 mm).
Regarding the obtained thermoelectric conversion element, the temperature was determined under the condition that the degree of vacuum in the apparatus was 1.0×10 ⁻⁵ Pa or less, a voltage was applied, a current value was read, and the conductivity was measured. The Seebeck coefficient was measured by providing a temperature gradient between the electrodes and reading the thermoelectromotive force value.
As a result, the conductivity at 340K 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 Was prepared and evaluated.
A 0.5 wt% C8-BTBT heptane solution was dropped on a white glass substrate, spin-coated (1000 rpm×1 min) to form a film, 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, the shadow mask was placed in a vacuum vapor deposition apparatus, and the apparatus was evacuated until the degree of vacuum in the apparatus became 1.0×10 ⁻⁴ Pa or less. Gold was vapor-deposited by a resistance heating vapor deposition method at a vapor deposition rate of 0.1 Å/sec to a thickness of 30 nm to obtain a thermoelectric conversion element (distance between electrodes: 5 mm, width of electrode: 7.6 mm).
Wiring to the thermocouple and electrodes to this element, installed in the evaluation device, the temperature was determined under the condition that the degree of vacuum in the device was 1.0×10 −5 Pa or less, the voltage was applied, and the current value was read. , The conductivity was measured. The Seebeck coefficient was measured by providing a temperature gradient between the electrodes and reading the thermoelectromotive force value.
As a result, the conductivity at 340K 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 sharp peaks near 380K and a sharp peak at 400K, indicating that structural phase transition occurred.
Further, 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 using the compound (C10DNTT) instead of the compound used in Example 1 and evaluated.
A white glass plate with a shadow mask for producing electrodes was placed in a vacuum vapor deposition apparatus, and the apparatus was evacuated until the degree of vacuum in the apparatus became 1.0×10 ⁻⁴ Pa or less. Gold was vapor-deposited at a thickness of 30 nm at a vapor deposition rate of 0.1 Å/sec by a resistance heating vapor deposition method to obtain a substrate with electrodes.
After attaching a shadow mask to this substrate, wiring to the thermocouple and electrodes, installing in the evaluation device, exhausting until the degree of vacuum in the device is 1.0 × 10 ^-4 Pa or less, resistance heating A thin film (20 nm) of a compound (C10DNTT) is formed by a vapor deposition method at a vapor deposition rate of 0.5 Å/sec to obtain a thermoelectric conversion element of the present invention (distance between electrodes: 5 mm, width of electrode: 7.6 mm). It was
Regarding the obtained thermoelectric conversion element, the temperature was determined under the condition that the degree of vacuum in the apparatus was 1.0×10 ⁻⁵ Pa or less, a voltage was applied, a current value was read, and the conductivity was measured. The 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 chains of C10DNTT was 57%. As shown in FIG. 4, in C10DNTT obtained in Example 1, sharp peaks were observed at 390K, 500K, 570K, and 580K by DSC (170-620K), indicating that structural phase transition occurred. Was done.

(Example 4) Production and evaluation of vertical thermoelectric conversion element using compound (C8-BTBT) Vertical organic thermoelectric conversion element was produced using the compound (C8-BTBT) synthesized in Synthesis Example 2 and evaluated. ..
An ITO glass substrate (manufactured by Asahi Glass) was spin-coated (7000 rpm×20 sec) into a film and dried to prepare a substrate.
Himiran (50 μm manufactured by Mitsui DuPont Polychemical) was sandwiched between the two produced substrates and heated at 150° C. to produce a substrate pair having a gap of 25 μm.
The compound (C8BTBT) melted at 130° C. was injected into the manufactured substrate pair to obtain a thermoelectric conversion element (distance between electrodes: 25 μm, electrode size 100 mm2).
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 electric conductivity and the Seebeck coefficient were measured while changing the temperature (27 to 127° C.), and the power factor was calculated. FIG. 7 shows the DSC analysis data of bulk C12BP up to 27 to 227° C. and the relative value (27 to 127° C.) of the power factor based on 27° C.
From 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 this thermoelectric conversion element can perform efficient thermoelectric conversion by using at 70 to 100°C, more preferably at 80 to 90°C. Therefore, in the thermoelectric conversion element of the present invention, it was shown that extremely efficient thermoelectric conversion can be performed by selecting the optimum use temperature according to each thermoelectric conversion material.

(Comparative Example 1)
Similar to Example 3, a similar device was prepared by using DNTT as the compound 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 due to DSC (170-570K).

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

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

Claims (4)

A method for producing an organic thermoelectric conversion material, using a conductive skeleton having a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties, and an alkyl group or a substituent having an alkyl group,
A method comprising selecting a conductive compound whose structural phase transition is measured by DSC at a temperature in the range of -50°C to 200°C. A method for improving the Seebeck coefficient of an organic thermoelectric conversion material containing a conductive skeleton having a basic skeleton composed of a polycyclic aromatic ring having carrier transport properties, and a substituent having an alkyl group or an alkyl group,
A method, characterized in that the electrically conductive compound is selected whose structural phase transition is measured by DSC at a temperature in the range of -50°C to 200°C. The method according to claim 1 or 2, wherein the structural phase transition point of the conductive compound measured by DSC is observed at a temperature in the range of 0 to 180°C.   The method according to any one of claims 1 to 3, wherein a van der Waals volume ratio of the substituent in the conductive compound is 25 to 60%.