Evaluation of Thermopower of Organic Materials Toward Flexible Thermoelectric Power Generators
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1197-D09-07
Evaluation of Thermopower of Organic Materials toward Flexible Thermoelectric Power Generators Masakazu Nakamura, Atsushi Hoshi, Masatoshi Sakai, and Kazuhiro Kudo Department of Electrical and Electronic Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
ABSTRACT Organic conducting and semiconducting materials are promising as thermoelectric conversion materials in flexible and wearable electronics because they have large Seebeck coefficients and small thermal conductivities. Since there have been only a limited number of studies on the thermoelectricity of organic materials to date, precise evaluation of Seebeck coefficient and electrical conductivity of various organic conducting/semiconducting thin films is important to examine what kind of material is the most effectual. To carry out such experiments, a specially designed instrument for organic thin films has been developed. Its ability to measure Seebeck coefficients of highly resistive materials was confirmed and Seebeck coefficients and power factors of several typical organic functional materials were preliminary evaluated. INTRODUCTION A thin flexible power generator is strongly desired for the wearable electronics that is one of the future images of the printable electronics. The thermoelectric power generator using human-body-originated heat, which is equivalent to a 70-150 W heater, is one of the candidates of the basic power source for such a purpose. In general, the ability of the thermoelectric conversion material is determined by how large the Seebeck coefficient (thermopower) and the electrical conductivity are and how small the thermal conductivity is. Many of organic conducting and semiconducting materials are, in this sense, promising as thermoelectric conversion materials because they have very large Seebeck coefficients, over 1 mV/K for some materials, and small thermal conductivities. However, there are only a limited number of studies on the thermoelectricity of organic materials [1-4] and very few especially on small molecules. Therefore, what is important now are to precisely evaluate the Seebeck coefficients of various organic conducting/semiconducting thin films and to examine what kind of material is the most effectual for thermoelectric conversion. To carry out such experiments, it is necessary to measure the samples in ultra-high vacuum with strictly controlled purity because their electrical characters are greatly influenced by the oxygen and water in the atmosphere. Since there is no commercial instrument that meets such a demand, an original one has been developed in this study to precisely evaluate both the Seebeck coefficient and the electrical conductivity of an organic thin film under strict purity control. In this paper, its ability to measure the Seebeck coefficients of highly resistive materials is shown. Then, Seebeck coefficients and thermoelectric abilities of some typical organic functional materials are presented and discussed.
DEVELOPMENT OF THE SEEBECK-COEFFICIENT-MEASUREMENT
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