JP2016001711A - Thermoelectric conversion material and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material indicating a high performance index; to provide a thermoelectric conversion material which flattens the surface roughness of a coating film by adjusting the film formation conditions and improves the electric conductivity; and to provide a thermoelectric conversion material whose film thickness is increased by laminating a conductive polymer and thermal electromotive force is increased by increasing temperature difference in the film thickness direction.SOLUTION: A method of manufacturing a thermoelectric conversion material includes: a preparation step for preparing a mixed solution including a π-conjugated conductive polymer and water; a fine particle forming step for forming fine particles of the mixed solution by atomizing the mixed solution; an attachment step for attaching the fine particles onto a substrate; and a drying step for drying the substrate.

Description

  The present invention relates to a thermoelectric conversion material and a method for producing the same.

  Increasing the concentration of carbon dioxide in the atmosphere is a major cause of global warming, and reducing carbon dioxide emissions has become a long-term challenge on a global scale. On the other hand, as an energy problem, there will be a shortage of power supply in the short term, which will require energy savings and peak cuts in power consumption in the whole society. It is required to secure a mold power supply. For these reasons, unused energy (exhaust heat, snow and ice heat, vibration, electromagnetic waves, etc.) and renewable energy (natural energy such as sunlight and wind power) are used as a means of obtaining energy by suppressing carbon dioxide emissions. As a result, technology for generating electricity from the surrounding environment is eagerly desired.

  Thermoelectric conversion technology has attracted attention as an energy conversion technology that recovers and uses unused energy. This thermoelectric conversion technique is a technique for generating electric power by giving a temperature difference to a thermoelectric conversion element and using the generated thermoelectromotive force. Thermoelectric conversion elements are often configured by connecting a p-type semiconductor having holes as carriers and an n-type semiconductor having electrons as carriers in series in a π-type.

When a temperature difference is given to both ends of the thermoelectric conversion element to form a temperature gradient in the element, hole movement and electron movement occur, a carrier concentration gradient is formed, and an electromotive force is generated. The power generation by the thermoelectric conversion element uses this effect, that is, the Seebeck effect. For this reason, a material having high thermal insulation and high conductivity is suitable for the material of the thermoelectric conversion element. Features of this thermoelectric conversion technology include high reliability because there are no moving parts, maintenance-free and long life, and low efficiency even at a small scale.
Here, the efficiency η of the thermoelectric conversion material is expressed by the following equation.

T _c is a low heat source temperature, and _Th is a high heat source temperature. Further, [Delta] T / T _h is Carnot efficiency, temperature of the high temperature side be fixed to the heat source is determined. Therefore, η is determined by the physical properties of the material, and the second term of the formula (1) is a function of only ZT. ZT is a material parameter called dimensionless figure of merit of thermoelectric conversion materials. Assuming that T _c = 25 ° C. and T _h = 150 ° C., ZT and material efficiency, that is, η are in a monotonically increasing relationship. The dimensionless figure of merit ZT is expressed by the following formula (4).

  Here, S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature.

  From the formula (4), in order to improve the thermoelectric conversion performance, a material having a high Seebeck coefficient S and electrical conductivity σ and a low thermal conductivity κ is a desirable thermoelectric conversion material. However, all three physical property values of S, σ, and κ excluding T are functions of the carrier concentration n, and S and σ have opposite dependence on n, and σ contained in the numerator and κ of the denominator. Is proportional (Widemann-Frantz rule) (see Non-Patent Document 1). For this reason, it is not easy to obtain a large ZT thermoelectric conversion material.

  Conventional thermoelectric conversion materials are composed of inorganic substances such as Bi-Te, Mn-Si, Zn-Sb, TAGS, Pb-Te, skutterudite compounds, La-Te compounds, etc. The thing is known (refer nonpatent literature 2). Among these, Bi—Te, Pb—Te, and Si—Ge compound semiconductors exhibit a high dimensionless figure of merit ZT at low temperatures.

  In recent years, conjugated conductive polymers that have conjugated double bonds in the linear chain of the polymer and electrons move on the π bond have attracted attention as thermoelectric conversion materials due to high electron mobility. (See Non-Patent Document 3). In order to increase carrier mobility, a conjugated conductive polymer is generally used together with a dopant to inject carriers. Among conjugated conductive polymers, polythiophene, polyaniline, polyacetylene, polypyrrole, polycarbazolen vinylene, and poly (3,4-ethylenedioxythiophene) have been shown to exhibit high thermoelectric conversion characteristics (non-patent) Reference 4).

Supervised by Hiroki Kuwano, “Latest Trends in Energy Harvesting Technology”, CMC Publishing, pp. 147-149, 2010. Edited by the Ceramic Society of Japan / Thermoelectric Society of Japan, “Environmentally Conscious New Material Series Thermoelectric Conversion Materials” P47, P70-72. Supervision by Takenobu Kajikawa, “Thermoelectric Conversion Technology Handbook”, NTS, 312-319, 2008. O. Bubnova et al., "Optimization of the thermoelectric figure of merit in the conducting polymer poly (3,4-ethylenedioxythiophene)", Nature Materials, vol.10, pp.429-433, 2011. Supervision by Takenobu Kajikawa, “Thermoelectric Conversion Technology Handbook”, NTS, 308-309, 2008.

  However, the thermoelectric conversion material described above has the following problems. First, Bi-Te-based, Pb-Te-based, and Zn-Sb-based compound semiconductors contain a large amount of environmental load elements such as Pb, Te, and Sb. In addition, many materials that do not contain environmentally harmful elements are so-called rare metals, and the use of rare metals as a material for thermoelectric conversion elements is a resource risk due to the recent rise in rare metal prices caused by a shortage of rare metals. It is not desirable from the point of view. In addition, since these inorganic materials go through processes such as pulverization, compression, sintering, and molding in manufacturing the element, a lot of energy is required and the manufacturing cost is also high.

  Next, the inorganic thermoelectric conversion material mentioned above has a problem that the output which converts from heat to electricity is small. The conversion efficiency of the inorganic thermoelectric conversion material described above is low, and it has not been put into practical use except for some systems for space use. Therefore, in order to put it into practical use, it is necessary to install a thermoelectric conversion element that can be manufactured at low cost over a large area. However, the above-described inorganic thermoelectric conversion material can be installed flexibly in a heat source having a curved surface. Difficult because of lack of sex.

  In contrast to such an inorganic thermoelectric conversion material, an organic thermoelectric conversion material using a conductive polymer is soluble in water or an organic solvent and can be easily applied to a large area. Moreover, if it is applied to a flexible substrate such as plastic, it can be installed on a curved surface and can be installed in a large area.

  However, thermoelectric conversion materials using conductive polymers are currently difficult to use for thermoelectric conversion elements from the viewpoint of performance as material properties and the viewpoint of mounting. From the viewpoint of material properties, the thermal conductivity κ is lower than that of the inorganic thermoelectric conversion material, but the Seebeck coefficient S and the electrical conductivity σ are low, and the dimensionless figure of merit ZT is Remarkably inferior. From the viewpoint of mounting, technologies for coating large areas, such as spin coating and bar coating, have been established and have been put into practical use as products such as liquid crystal televisions and organic EL televisions. Is that an organic solvent is used. Some use an aqueous solvent, but use it after increasing the solute concentration or increasing the amount of slurry, increasing the viscosity of the solution, and reducing the effects of film thickness unevenness due to surface tension described later. It is common to have. The conductive polymer solution has a low concentration due to poor dispersibility in the solvent, and the method of coating a thick film of 10 μm or more with no film thickness unevenness is realized from the following simple calculation results. It turns out to be difficult.

  As a calculation example, poly (3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (hereinafter, PEDOT / PSS), which are commercially available conductive polymers, are used. For example, the weight concentration is 1.3% by weight (manufactured by H.C. Starck, trade name Clevios RP), the weight concentration is 2.8% by weight (manufactured by Sigma Aldrich, product number: 560596), and the weight concentration is 0.54% by weight. (Manufactured by Sigma Aldrich, product number: 733340).

Of these, a weight concentration of 0.54% by weight (manufactured by Sigma Aldrich, product number: 733340) is used, and the film density is assumed to be 1 g / cm ³ . The volume of the thin film necessary to apply a 50 μm thick PEDOT / PSS film on a 1 cm × 1 cm substrate is as follows:
1 cm × 1 cm × 50 μm = 50 × 10 ⁻⁴ cm ³
In terms of weight,
50 × 10 ⁻⁴ cm ³ × 1 g / cm ³ = 50 × 10 ⁻⁴ g
Since the weight concentration is 0.54% by weight, the weight of the solution required to form this coating film is
50 × 10 ⁻⁴ g / 0.54 wt% = 0.93 g
If the density of the solution is 1 g / cm ³ , the required volume of the solution is
0.93 g / 1 g / cm ³ = 0.93 cm ³
When divided by the substrate area of 1 cm ² , the height of the solution is
0.93cm ³ / ^1cm 2 = 0.93cm

  In other words, in order to form a thin film of conductive polymer of 50 μm, a 0.93 cm thick solution must be uniformly formed on the substrate, which is realized considering the surface tension of water. Impossible.

  It is difficult to form a water-soluble organic material typified by PEDOT / PSS over a large area without unevenness in film thickness, as well as its poor dispersibility and low solubility, as well as the physical properties of water as a solvent. It is a factor.

  First, unlike ordinary organic solvents, water has a high surface tension because molecules form hydrogen bonds. For this reason, when a water-soluble polymer solution is dropped onto a substrate such as a glass substrate, a force that causes the solution itself to agglomerate acts, and only the central portion of the substrate rises, and the shape of the solution becomes non-uniform. When dried while maintaining this non-uniformity, film thickness unevenness occurs. Therefore, it is difficult to form a coating film with a uniform film thickness by the cast coating method.

  Further, as described above, since water has a hydrogen bond, its boiling point is higher and the film formation rate at room temperature is slower than that of an organic solvent. If an organic solvent typified by xylene or formaldehyde is used as the organic solvent, it will easily evaporate even at room temperature. For example, if a bar coater, dip coater, or spin coater is used, a large area can be formed uniformly. It was easy.

  However, when water is used as the solvent, the dip coating method, in which the substrate is dipped in the polymer solution and then pulled up at a constant rate to coat the film, has a low drying rate. There is a problem that unevenness occurs. In addition, in spin coating in which the coating is dried by rotating the substrate at a constant speed after dropping the solution on the substrate, most of the solution is scattered by centrifugal force during rotation, so forming a thick film Have difficulty.

  In addition, in the case of a polymer using water as a solvent, if there is no treatment such as curing after film formation, the solvent of the solution applied for the second time will dissolve the first thin film at the time of lamination. Lamination was difficult by methods such as coating.

  Since the thermoelectric material generates power when a temperature difference in the material is formed, the thickness of the material is also an important factor. If the thickness of the thermoelectric material is increased, the temperature difference ΔT in the thermoelectric material is improved as shown in Equation (1), which is advantageous in terms of efficiency. A simple calculation procedure is shown below.

  FIG. 16 is an enlarged schematic view of a part of the thermoelectric element. The thermoelectric element has a substrate film (thickness 500 μm, thermal conductivity 0.3 W / m / K), an ITO electrode (thickness 0.1 μm, thermal conductivity 8.2 W / m / K) deposited on the substrate film. ), An organic thermoelectric film (Seebeck coefficient 30 μV / K, thermal conductivity 0.3 W / m / K) formed on the ITO electrode.

  The temperature at the interface between the substrate film and the high temperature heat source is T1, the temperature at the interface between the substrate film and the ITO electrode is T2, the temperature at the interface between the ITO electrode and the organic thermoelectric film is T3, and the temperature at the interface between the organic thermoelectric film and the low temperature heat source is T4.

  The following formula (5) is a basic formula of heat conduction.

  q is the amount of heat transferred per unit time, A is the cross-sectional area, and λ is the thermal conductivity. Assuming that the cross-sectional area of each material is constant, assuming that the thermal conductivity in each layer is λ1, λ2, λ3, the temperature differences are ΔT1, ΔT2, ΔT3, and the film thicknesses are d1, d2, d3, Formula (6) is established.

  Table 1 is a table showing the film thickness dependence of the temperature difference formed in the organic thermoelectric film and the generated thermoelectromotive force, which are obtained by calculation. Table 1 shows the thickness of the organic thermoelectric film, the temperature difference formed in the organic thermoelectric film, and the thermoelectromotive force, assuming that T1 = 50 ° C. and T4 = 35 ° C. using the above material parameters. Yes. From the results of Table 1, as described above, increasing the thickness of the thermoelectric material can improve the temperature difference ΔT in the thermoelectric material, and can be advantageous in terms of efficiency.

  In addition, the shape of the thin film used for the thermoelectric element should be such that the surface of the produced film is smooth and dense. According to Non-Patent Document 5, poly (thiophene), which is a π-conjugated conductive polymer, is produced by electrolytic polymerization, and the relationship between film density, surface irregularities and electrical conductivity is discussed. According to this, a result is obtained that a film having a higher electric conductivity is denser and has a higher film density and smaller surface irregularities. Furthermore, the same document mentions the conduction mechanism of poly (thiophene) as the cause, and states that the conduction mechanism changes with the densification of the film. Carriers that are responsible for electrical conduction move by hopping between the main chains of poly (thiophene). From the experimental results, low-density poly (thiophene) exhibits variable range hopping advantageous for electric conduction only in a high-temperature region of 200K or higher where the thermal motion of the carrier is intense, but high-density poly (thiophene) has 88K or higher. Variable range hopping is also present in the region. This indicates that the high-density film hops advantageous for electric conduction even in a low temperature region where the thermal motion is not intense, and has high electric conductivity.

  Therefore, as shown in the mathematical formulas (1), (3), and (4), in order to improve the thermoelectric conversion efficiency η, it is necessary to improve the electrical conductivity. There is a need for a method of coating a conductive polymer that is increased and has less surface roughness.

  The present invention has been made to solve the above problems, and an object thereof is to provide a thermoelectric conversion material exhibiting a high performance index. Another object of the present invention is to make it possible to provide a thermoelectric conversion material in which the surface roughness of the coating film is flattened by adjusting the film forming conditions and the electric conductivity is improved. Still another object of the present invention is to provide a thermoelectric conversion material having an increased thermoelectromotive force by increasing the film thickness by laminating conductive polymers and increasing the temperature difference in the film thickness direction. Is to do so.

  An example of means for solving the problems of the present invention includes a preparation step of preparing a mixed solution containing a π-conjugated conductive polymer and water, and fine particles that atomize the mixed solution to form fine particles of the mixed solution A method for producing a thermoelectric conversion material, which includes a forming step, an attaching step for attaching the fine particles to a substrate, and a drying step for drying the substrate.

  Here, it is preferable that the mixed solution further includes a polyhydric alcohol selected from the group consisting of ethylene glycol, glycerol, 1,3-propanediol, and 1,4-pentanediol.

  The mixed solution preferably further contains an organic solvent selected from the group consisting of dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, ethanol, and methanol.

  Furthermore, the amount of the polyhydric alcohol is preferably in the range of 0.1 to 91% by weight with respect to the total amount of the mixed solution.

  Furthermore, it is preferable to repeat the adhesion step and the drying step.

  Another example of means for solving the problems of the present invention is a thermoelectric conversion material containing a π-conjugated conductive polymer, water, and a polyhydric alcohol. In this case, the polyhydric alcohol is preferably selected from the group consisting of ethylene glycol, glycerol, 1,3-propanediol, and 1,4-pentanediol.

  Yet another example of means for solving the problems of the present invention is a thermoelectric conversion material containing a π-conjugated conductive polymer, water, and an organic solvent. In this case, the organic solvent is preferably selected from the group consisting of dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, ethanol, and methanol.

  ADVANTAGE OF THE INVENTION According to this invention, the thermoelectric conversion material which shows a high performance index can be provided. For example, it is possible to provide a thermoelectric conversion material in which the surface roughness of the coating film is flattened by adjusting the film forming conditions and the electric conductivity is improved. Moreover, the thermoelectric conversion material which increased the thermoelectromotive force can be provided by increasing a film thickness suitably by laminating | stacking a conductive polymer, and increasing the temperature difference of a film thickness direction.

2 is a photograph of a coating film using the thermoelectric conversion material of Experimental Example 1. 5 is a photograph of a coating film using the thermoelectric conversion material of Experimental Example 2. It is a characteristic view which shows the film thickness of the thermoelectric conversion material of Experimental example 2. It is an external view after forming a coating film once in Experimental Example 3. The measurement result of the film thickness after forming the coating film once in Experimental Example 3 is shown. It is a photograph of the external view when the coating film is repeatedly applied 20 times in Experimental Example 3. The measurement result of the film thickness when the coating film is repeatedly applied 20 times in Experimental Example 3 is shown. It is a characteristic view which shows the film thickness dependence with respect to the frequency | count of application | coating of the thermoelectric conversion material of Experimental example 3. It is a characteristic view which shows the electrical conductivity dependence with respect to the film thickness of the thermoelectric conversion material of Experimental example 3. FIG. 14 is an external view after a coating film is formed once in Experimental Example 4. In Experimental example 4, the measurement result of the film thickness after forming a coating film once is shown. It is a photograph of the external view when the coating film is repeatedly applied 20 times in Experimental Example 4. In Experimental example 4, the measurement result of the film thickness when the coating film is repeatedly applied 20 times is shown. It is a characteristic view which shows the film thickness dependence with respect to the frequency | count of application | coating of the thermoelectric conversion material of Experimental example 4. It is a characteristic view which shows the electrical conductivity dependence with respect to the film thickness of the thermoelectric conversion material of Experimental example 4. It is a schematic diagram at the time of calculating | requiring the temperature difference formed in an organic thermoelectric film by calculation.

  Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the drawings.

π-Conjugated Conductive Polymer The π-conjugated conductive polymer is typically a conductive polymer having a π-conjugated double bond in the linear chain of the polymer. For example, polythiophene, polyaniline, polyacetylene, polypyrrole, polycarbazolenvinylene, poly (3,4-ethylenedioxythiophene) (hereinafter, PEDOT) can be used as the π-conjugated conductive polymer that exhibits high thermoelectric conversion characteristics. Typically, poly (styrenesulfonic acid) (hereinafter referred to as PSS) is used as a dopant that imparts positive charge to the π-conjugated conductive polymer.

The mixed solution mixed solution contains at least the π-conjugated conductive polymer and water. The amount of water is, for example, 95 to 99.5% by weight with respect to the total amount of the mixed solution. The mixed solution can further contain the following polyhydric alcohol, organic solvent, and additives.

When the polyhydric alcohol atomized mixed solution adheres to the surface of the substrate, polyhydric alcohol can be used in order to lower the polarity of the solvent, lower the surface tension, and reduce surface irregularities. As the polyhydric alcohol, for example, one selected from the group consisting of ethylene glycol, glycerol, 1,3-propanediol, and 1,4-pentanediol can be used.

  The polyhydric alcohol is preferably in the range of 0.1 to 91% by weight with respect to the total amount of the mixed solution, for example, the total amount of the π-conjugated conductive polymer, the dopant, and water. When the weight of the conductive polymer is 1, the weight of the polyhydric alcohol is 10; that is, the polyhydric alcohol weight ratio is 91% by weight or less with respect to the total weight of the mixed solution. It becomes easy to prevent the decrease of the film, and it becomes easy to be independent as a coating film. As a cause of this, when polyhydric alcohol is added exceeding 91% by weight, the main component of the coating film is dominated by the polyhydric alcohol, the distance between the main chains is increased, and the state of the coating film is close to the liquid. It is thought that it became. On the other hand, in order to express the effect of the addition of the polyhydric alcohol, the content of the polyhydric alcohol is preferably 0.1% by weight or more with respect to the total amount of the mixed solution. The polyhydric alcohol content in the finished thermoelectric conversion material is a content (eg, 0.001% by weight) that can be detected by an arbitrary detector (eg, Agilent gas chromatograph, model number H6890). This is because, in the drying process described later, the polyhydric alcohol evaporates with water, but in the finished thermoelectric conversion material, neither water nor polyhydric alcohol has been completely removed, and some of these (the above detection is possible). This is because it remains in the thermoelectric conversion material.

When the organic solvent atomized mixed solution adheres to the surface of the substrate, an organic solvent can be used in order to lower the polarity of the solvent, lower the surface tension, and reduce surface irregularities. As the organic solvent, for example, one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, ethanol, and methanol can be used.

As the additive additive, those used for the purpose of changing the polarity as a solvent can be applied, and a surfactant such as sodium lauryl sulfate or sodium dodecyl sulfate can be used.

As the substrate substrate, glass, quartz glass, silicon wafer, polyethylene naphthalate, polyethylene terephthalate, polyimide, or the like can be used.

Manufacturing Method Next, a manufacturing method of the thermoelectric conversion material according to the present embodiment will be described.

In the preparation step adjustment step, a mixed solution containing a π-conjugated conductive polymer and water is prepared. For example, a mixed solution can be prepared by adding and mixing a polyhydric alcohol to an aqueous solution in which the π-conjugated conductive polymer is dissolved. In the process of preparing the mixed solution, a predetermined amount of polyhydric alcohol is added to the aqueous solution, and the mixture is mixed, for example, by stirring at room temperature (about 23 ° C.) for 30 minutes or more. In addition, the method of mixing is not specifically limited, The solution should just be uniform. For example, there is a method of putting a stirrer chip into a solution in a glass container, rotating the stirrer chip at a speed of 400 rpm using a magnetic stirrer, and stirring the solution in the glass container.

In the fine particle forming step, it is preferable to reduce the particle size of the atomized solution in order to increase the film density and reduce the surface roughness. As will be described later, if the mixed solution is atomized and the diameter of the fine particles decreases, the surface area value per volume of the fine particles increases, and therefore, it becomes easy to dry. If the atomization is insufficient, the surface becomes very rough and the electrical conductivity is lowered. The mixed solution is atomized into fine particles of, for example, 50 μm or less. In order to form fine particles, for example, a spray coater (rCoater manufactured by Asahi Sunac Co., Ltd.) can be used, but an ink jet method or an electrospray method may be used, and other methods may be used if the solution is atomized. .

In the attaching step , the fine particles are attached to the substrate. The surface temperature of the substrate is preferably maintained at 50 ° C. or higher. As a matter of course, since each function of each constituent material is lost when heated to the decomposition temperature or higher, it is important that the heating temperature does not exceed the decomposition temperature.

Drying step In the drying step, the fine particles of the mixed solution or the substrate is dried to evaporate the solvent. Although the boiling point of water, which is a solvent, is 100 ° C., since the substrate is easily dried in the fine particle formation step, film formation is possible even at a substrate temperature below the boiling point, for example, 50 ° C. or more and 70 ° C. or less. As a matter of course, since each function of each constituent material is lost when heated to the decomposition temperature or higher, it is important that the heating temperature does not exceed the decomposition temperature. In the drying process, water (and possibly polyhydric alcohol) is evaporated, but strictly speaking, water (and possibly polyhydric alcohol) is not completely removed in the finished thermoelectric conversion material. There may be some remaining. However, in the present application, the ratio in the mixed solution before evaporation is more important than the ratio of water (and possibly a polyhydric alcohol) in the thermoelectric conversion material.

  In addition, although it can manufacture by the above drying process by application | coating of a single layer film, the process of repeating the said adhesion process and a drying process is preferable in order to deposit the said (pi) conjugated system conductive polymer on the substrate surface.

[Experiment A]
First, ethylene glycol (manufactured by Kanto Chemical Co., Inc., purity of 99% or more) was added to a mixed aqueous solution of PEDOT / PSS (product number: 483095, polymer ratio: 1.3% by weight) manufactured by Sigma-Aldrich. Was mixed to prepare a mixed solution.

  PEDOT represented by the following chemical formula (1) is a π-conjugated conductive polymer, and PSS represented by the chemical formula (2) is a polymer having a sulfo group serving as a dopant. Further, ethylene glycol represented by the chemical formula (3) is a polyhydric alcohol.

The substrate used was commercially available general-purpose polyethylene terephthalate (thickness: 500 μm), washed with pure water, and then irradiated with a UV / ozone cleaner for 20 minutes to hydrophilize the surface and improve the film formability.
In this experimental example, 0.1 wt% ethylene glycol was added to form a film, but the definition of the ethylene glycol weight ratio is as follows.

  In this experimental example, the film was added at a concentration of 0.1% by weight, but when the ratio of ethylene glycol weight to PEDOT / PSS weight 1 was 10, that is, the ethylene glycol weight ratio exceeded 91% by weight, The mechanical strength of the coating film is reduced and the coating film cannot be self-supporting. The reason for this is considered to be that when 91% by weight or more is added, ethylene glycol is dominant as the main component of the coating film, the distance between the main chains is increased, and the state of the coating film becomes close to a liquid.

  The prepared mixed solution was formed into a film using a spray coater (rCoater manufactured by Asahi Sunac Co., Ltd.). In the spray coater, the atomization conditions of the fine particles applied on the substrate film can be controlled. The nozzle of the spray coater uses AGB-40N, and the nozzle diameter is a circle of 0.8 mm. The discharge amount of the solution was controlled by a syringe pump, the discharge amount was 12 ml / min, and the distance between the spray nozzle tip and the substrate film was fixed at 120 mm. The apparatus can control the atomization pressure of the spray, and increasing the spray atomization pressure can promote atomization of the coating solution.

  According to the equation (8), if the coating solution is atomized and the radius r of the fine particles is decreased, the value of the surface area S per volume V of the fine particles is increased, so that it becomes easy to dry.

  The thickness of the formed coating film was calculated by measuring the level difference between the film substrate and the organic thermoelectric film using a stylus shape measuring instrument (Dektak 150 manufactured by ULVAC). This measurement result was used for measurement (calculation) of electric conductivity described later.

Measurement of Seebeck coefficient Seebeck coefficient S was measured using ZERU-3 manufactured by ULVAC-RIKO. A temperature gradient was formed above and below the organic thermoelectric film, and the generated thermoelectromotive force was measured.

Measurement of electric conductivity The electric conductivity σ was measured by a four-end needle method using an electric resistance measuring instrument (Lorestar GP manufactured by Mitsubishi Chemical Analytech).

  By measuring the thermal conductivity separately from the result of this measurement, the dimensionless performance index ZT, which is an index for evaluating the thermoelectric conversion performance, can be calculated using Equation (4).

Experimental example 1
Here, an experimental example is shown in the case where a uniform coating film cannot be formed because the substrate temperature is insufficient. In this experimental example, the means used in experimental example A were adopted except for the matters specifically described below.

  As described above, since the boiling point of the water solvent is high in the conventional coating method, the evaporation rate of the water solvent is slow in the spin coating method, the dip coating method, the casting method, the bar coating method, etc., in which the coating time is short. A uniform thick film could not be formed due to the surface tension of water. A general solution is to mix a large amount of slurry to increase the proportion of solute in the solvent. However, when a large amount of slurry is mixed with the material of this experimental example, the slurry becomes a π-conjugated conductive polymer. This hinders intermolecular hopping and significantly deteriorates performance.

  Therefore, the atomizing air pressure was set as 0.25 MPa using the spray coating apparatus. A substrate film is set on a hot plate heated to 30 ° C., and an external view (FIG. 1) after the film is formed once on the substrate film is shown. Due to the low substrate temperature, the surface did not dry immediately after application to the substrate.

  From the external view (FIG. 1), the concentration in the peripheral part (center part of FIG. 1) of the glass substrate is high, while the density in the central part (upper part of FIG. 1) is low, resulting in uneven density. It is clear. Further, the uneven formation of the density unevenness indicates that it is difficult to form a coating film uniformly.

Experimental example 2
Although the substrate temperature is sufficient, the atomizing air pressure is insufficient, and the atomization of the spray fine particles is insufficient. In this experimental example, the means used in experimental example A were adopted except for the matters specifically described below.

  The atomization air pressure was set as 0.025 MPa. An external view (FIG. 2) and a film thickness measurement result (FIG. 3) after a substrate film is placed on a hot plate heated to 70 ° C. and formed once on the substrate film are shown.

  Although the surface roughness of this coating film can be confirmed by visual observation, thermoelectric properties as a thermoelectric film have been developed. Table 2 summarizes the electrical conductivity and Seebeck coefficient in the thermoelectric conversion materials in Experimental Examples 2, 3, and 4. In Table 2, measurement results of electrical conductivity and Seebeck coefficient are shown.

  As shown in Non-Patent Document 5, the conductive polymer material is mainly hopping conduction. In this document, there is a report that, when the polymer particle size is large, electric conduction is hindered. Therefore, when the conditions for electric field polymerization are adjusted, a flat coating film is formed and the electric conductivity is improved. As described above, in order to improve thermoelectric properties as a coating film, it is necessary to increase electrical conductivity. Therefore, the flattening of the coating film is suitable as a means for improving the thermoelectric performance.

Experimental example 3
Based on Experimental Example 1 and Experimental Example 2, an experimental example in which the substrate heating temperature and the atomizing air pressure are adjusted to adjust the coating film conditions is shown. In this experimental example, the means used in Experimental Example A were adopted except for the matters specifically described below.

  The substrate heating temperature was set to 70 ° C., and the atomizing air pressure was set to 0.25 MPa. An external view (FIG. 4) and a film thickness measurement result (FIG. 5) after the substrate film is placed on a hot plate heated to 70 ° C. and formed once on the substrate film are shown.

  Compared with Experimental Example 2, the flatness was improved. The measurement results of electrical conductivity and Seebeck coefficient are shown in Table 2. Compared with the result of Experimental Example 2, the Seebeck coefficient was not significantly changed, but the electrical conductivity was improved.

  Since a flat thin film could be formed in the first film formation, overcoating was performed twice, 10 times, and 20 times. An external view (FIG. 6) and a film thickness measurement result (FIG. 7) when it is overcoated 20 times are shown. Also, FIG. 8 shows the film thickness dependency when the layers are laminated once, twice, 10 times, and 20 times, and FIG. 9 shows the electric conductivity dependency. As the number of overcoats increased, the film thickness increased almost linearly and the electrical conductivity increased.

Experimental Example 4
Based on the results of Experimental Example 1 and Experimental Example 3, it is thought that the electrical conductivity can be improved by further reducing the surface roughness of the coating film, and when PEDOT / PSS is added with a polyhydric alcohol, ethylene glycol. An experimental example is shown. In this experimental example, by adding ethylene glycol, the surface roughness is reduced and the electrical conductivity is improved. In this experimental example, the means used in experimental example A were adopted except for the matters specifically described below.

  The material was a mixture of 0.1% by weight of ethylene glycol in a PEDOT / PSS aqueous solution, the substrate heating temperature was set to 70 ° C., and the atomizing air pressure was set to 0.25 MPa. In this case, the ratio of the total amount of PEDOT and PSS is 1.3% by weight, the ratio of water is 98.7% by weight, and the ratio of ethylene glycol is 0.1% by weight (the total exceeds 100% by weight) Based on the error). An external view (FIG. 10) and a film thickness measurement result (FIG. 11) after the substrate film is placed on a hot plate heated to 70 ° C. and formed once on the substrate film are shown.

  Compared with Experimental Example 3, the flatness was improved. The measurement results of electrical conductivity and Seebeck coefficient are shown in Table 2. Compared with the result of Experimental Example 3, the Seebeck coefficient was not significantly changed, but the electrical conductivity was improved.

  Since a flat thin film could be formed in the first film formation, overcoating was performed twice, 10 times, and 20 times. An external view (FIG. 12) and a measurement result (FIG. 13) of the film thickness when it is overcoated 20 times are shown. Further, FIG. 14 shows the film thickness dependency when the layers are laminated once, twice, 10 times, and 20 times, and FIG. 15 shows the electric conductivity dependency. As the number of overcoats increased, the film thickness increased almost linearly and the electrical conductivity increased.

  As described above, in the present invention, a thermoelectric conversion material exhibiting a high performance index can be configured. Preferably, the surface roughness of the water-soluble conductive polymer thin film can be reduced. More preferably, by laminating the polymer thin film, an excellent effect of improving the output of thermoelectric conversion by increasing the temperature difference in the film thickness direction can be obtained.

  Note that the present invention is not limited to the embodiment and experimental examples described above. Many variations and combinations can be employed by persons having ordinary knowledge in the art within the technical idea of the present invention.

T1 Temperature at the interface between the substrate film and the high temperature heat source T2 Temperature at the interface between the substrate film and the ITO electrode T3 Temperature at the interface between the ITO electrode and the organic thermoelectric film T4 Temperature at the interface between the organic thermoelectric film and the low temperature heat source

Claims (9)

a preparation step of preparing a mixed solution containing a π-conjugated conductive polymer and water;
A fine particle forming step of atomizing the mixed solution to form fine particles of the mixed solution;
An attaching step for attaching the fine particles to the substrate;
A drying step of drying the substrate;
The manufacturing method of the thermoelectric conversion material containing this.   The method according to claim 1, wherein the mixed solution further contains a polyhydric alcohol selected from the group consisting of ethylene glycol, glycerol, 1,3-propanediol, and 1,4-pentanediol. .   The production method according to claim 1 or 2, wherein the mixed solution further contains an organic solvent selected from the group consisting of dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, ethanol, and methanol.   The method according to claim 2 or 3, wherein the amount of the polyhydric alcohol is in the range of 0.1 to 91% by weight with respect to the total amount of the mixed solution.   The manufacturing method according to claim 1, wherein the attaching step and the drying step are further repeated.   A thermoelectric conversion material containing a π-conjugated conductive polymer, water, and a polyhydric alcohol.   The thermoelectric conversion material according to claim 6, wherein the polyhydric alcohol is selected from the group consisting of ethylene glycol, glycerol, 1,3-propanediol, and 1,4-pentanediol.   A thermoelectric conversion material containing a π-conjugated conductive polymer, water, and an organic solvent.   The thermoelectric conversion material according to claim 8, wherein the organic solvent is selected from the group consisting of dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, ethanol, and methanol.