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A1: Low temperature materials

Study on the thermoelectric properties of conducting polymer having a thick film-thickness with the aim of manufacture of flexible organic thermoelectric module

Sunbin Hwang1,2, William J. Potscavage2,3, Ryosuke Nakamichi1,2 and Chihaya Adachi1,2,3
Department of Chemistry and Bio Chemistry, Univ. of Kyushu1, Center for Organic Photonics and Electronics Research (OPERA)2, International Institute for Carbon Neutral Energy Research (WPI-I2CNER)3

    Recent progress in polymer-based organic thermoelectric (OTE) devices has yielded remarkably high performance. These achievements, with performance that can be comparable to inorganic materials, are the result of high Seebeck coefficient, high conductivity, and low thermal conductivity obtained by chemically controlling the material’s oxidation level. Although, increasing of inherent properties of thermoelectric elements is required in order to obtain a high efficiency, it is also necessary to modularize many thermocouples, connected electrically in series and thermally in parallel such as π-leg type module, to get huge thermoelectric voltage. Especially, the flexible OTE modules are targeted for use covering large heat exchanger surfaces and for driving below 200 °C, so having the longest thermal and electrical conduction paths (i.e., thickest active layer) possible while maintaining flexibility is very important. Organic thin films usually have thicknesses on the nanometer scale (nano-films). However, films with micrometer-scale thicknesses (micro-films) provide a longer thermal conduction path that makes realizing high thermoelectric voltages in modules easier because of the resulting larger temperature gradient from the same heat source. Furthermore, doping treatment in nano-films could behave differently and yield different electrical properties in micro-films. Therefore, differences in doping processes between micro-films and the more commonly studied nano-films should also be investigated.

    In this study, the effectiveness of two different dopants and differences in the doping properties of nano- and micro-films fabricated by solution processing are studied using the Poly(3-hexylthiophene-2,5-diyl) and the dopants tetrafluorotetracyanoquinodimethane and iron(III) p-toluenesulfonate hexahydrate. In addition, all-solution module fabrication process using photo-etching technique for patterning of micrometer-thick active layers that is not necessary alignment and assembly of individual element such as inorganic process was introduced. Such solution processing methods may be applicable for roll-to-roll mass production and may be able to significantly reduce the production costs of thermoelectric modules compared to conventional processes.