Evaluation of Thermopower of Organic Materials Toward Flexible Thermoelectric Power Generators

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.

Estimation of Fermi Level Changes Caused by Changes in Ambient Conditions around Organic Semiconductors by Seebeck Effect Measurement

“…The Seebeck coefficient reported by other authors is slightly fluctuated within the range from several hundred V K À1 to 1.1 mV K À1 . [12][13][14][15] Observed Seebeck coefficient is comparable to that reported by other authors.…”

Giant Seebeck effect over 0.1 V K−1 – is this an intrinsic phenomenon in organic semiconductors?

“…This discovery was made possible using an originally developed apparatus capable of in situ measurement of such a high-purity and high-resistance sample in an ultrahigh vacuum chamber. 10 When impurity-doped C 60 films were measured, the values followed the conventional theory as indicated by a red curve in Fig. 2.…”

“…This discovery was made possible using an originally developed apparatus capable of in situ measurement of such a high-purity and high-resistance sample in an ultrahigh vacuum chamber. 10 When impurity-doped C 60 lms were measured, Fig. 2 Seebeck coefficient and electrical conductivity of pure and doped C 60 thin films measured at room temperature.…”

Potential of Organic Materials for the Application to Thermoelectric Generators

“…The requirements for the measurement are as follows: (i) a thin film of the mixture of host and dopant materials can be deposited in ultrahigh vacuum and the Seebeck coefficient and the electrical conductivity can be measured in-situ, (ii) the base temperature and the thermal gradient of the thin film can be precisely controlled, and (iii) the input impedance of the voltage measurement circuit must be sufficiently high so as to measure the high resistance sample. Figure 1 shows the schematic illustration of our original instrument used in this work [7]. The film deposition and measurement chamber can be evacuated down to 1×10 -6 Pa and two organic materials can be evaporated from two Knudsen cells (K-cells).…”