The synthesis and characterization of metal chalcogenide-pedot: pss polymer composites for thermal energy conversion
This dissertation describes the synthesis and characterization of metal chalcogenide/PEDOT:PSS polymer composites as possible thermoelectric materials for thermal energy conversion; specifically, Te, Bi2Te3, Bi2S3, and Ag2Te. The inorganic materials have high Seebeck coefficients while the PEDOT:PSS has high electrical conductivity. This approach allows for optimization of electrical conductivity of the PEDOT while still maintaining the high Seebeck coefficient of the inorganic materials. XRD analysis confirms the crystallinity of the Te, Bi2S3, and Ag2Te synthesized in the presence of PEDOT:PSS. A detailed spectroscopy study revealed several key findings, which may explain the enhanced electrical conductivity seen in Te/PEDOT:PSS composites. XPS revealed loss of the insulating PSS during the purification process but no loss of the conducting PEDOT. XPS also showed the role the polymer plays as a passivating agent as there was minimal oxidation of the nanowires. UV-Vis/NIR and Raman spectroscopy indicated the remaining PEDOT segments on the polymer to be partially reduced with a benzoid-like conformation. Transport measurements showed ohmic and linear I/V curves at room temperature for all films. The temperature dependent electrical conductivity for all systems was measured from 80 – 300 K and Mott’s VRH model was used to qualitatively determine the hopping mechanism. All systems are consistent with three dimensional VRH. The temperature dependent measurements also showed that these systems were all thermally activated.