Structure-property relationships of printed bismuth telluride thermoelectrics

Thermoelectric devices are designed to either produce useful power from a thermal gradient or produce a thermal gradient from an applied voltage. The design of such devices requires the production of advanced materials with a maximum thermoelectric figure of merit, ZT. The performance of these materials must also meet device-level requirements such as performance at a given operating temperature and the ability to tolerate external forces while maintaining overall device functionality. ☐ The motivation for this work is based on applications that require mechanical flexibility while also providing surface cooling relative to room temperature conditions, such as flexible automotive seat coolers. With that targeted application in mind, this work focuses on developing a straightforward way to produce these materials and model the relationship between the microstructure and mechanical properties of these materials. This work studied the classic room temperature thermoelectric material, bismuth telluride, in the form of a simple thermoelectric paste consisting of bismuth telluride powder, ethyl cellulose polymer, and Texanol TM solvent. This paste lends itself to be used in standard flexible electronics industry fabrication techniques such as screen-printing and belt-furnace thermal processing. ☐ This research is instructive in that it provides a method for the production of a screen-printable thermoelectric paste, defines the processing conditions that vary the mechanical properties of the sintered thermoelectric prints, and develops a straight forward process of measuring the porosity of those prints using SEM and image processing techniques. The output of this research is a model of the relationship between porosity and elastic modulus of a sintered bismuth telluride film system. This approach can be used to model the relationship of any printed and sintered thermoelectric materials system.