Characterization and thermoelectric performance of polymer/inorganic hybrid films using spectroscopic and microscopic techniques

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The main goal of this dissertation was to investigate the thermoelectric performance of films of silver telluride (Ag2Te), bismuth sulfide (Bi2S3) and bismuth telluride (Bi2Te3) nanowires (NWs) dispersed in P(NDI2OD-T2). We hypothesize that the electrical properties of the films made with Ag2Te, Bi2S3, and Bi2Te3 will be n-type and behave like composite materials. Ag2Te was synthesized to make three different lengths of NWs. Powder x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) confirmed that β-Ag2Te was synthesized with the anticipated stoichiometry. Scanning electron microscopy (SEM) of Ag2Te NWs in P(NDI2OD-T2) revealed that the longest Ag2Te NWs produced homogeneous composites whereas the shorter Ag2Te NWs phase-separated. Electrical conductivity and Seebeck coefficients for each composite film were determined and theoretical models were used to investigate charge-transport behavior. Seebeck coefficients confirmed that all composites were n-type. The longest Ag2Te NWs produced the highest electrical conductivities with parallel transport behavior and are promising to the field of thermoelectrics. Bi2S3 and Bi2Te3 NWs were synthesized, and their stoichiometry and structures were confirmed using XRD and EDS. SEM images of the NW/P(NDI2OD-T2) films revealed that both Bi2S3 and Bi2Te3 phase-separated. The electrical conductivity for each composite film was determined and theoretical models were applied. The electrical conductivity of the Bi2S3 and Bi2Te3 composites were slightly higher than pristine P(NDI2OD-T2), further indicating that the NWs phase-separated. Seebeck coefficients for both systems confirmed that the composites were n-type. Despite the various strategies for improving the film morphology, composites made with Bi2Te3 and Bi2S3 NWs did not produce promising results. The spin-dynamics of P(NDI2OD-T2) doped with cobaltocene were studied with continuous-wave electron paramagnetic resonance (EPR). Additionally, the electrical conductivity of cobaltocene doped P(NDI2OD-T2) films increased several orders of magnitude compared to pristine P(NDI2OD-T2). A sputter depth profile in conjunction with x-ray photoelectron spectroscopy was used to analyze how the dopant dispersed in the polymer matrix. Temperature-dependent pulsed EPR of two different doping concentrations suggested two different relaxation rates. Overall, this study investigated the temperature-dependent spin dynamics of cobaltocene doped P(NDI2OD-T2) films and lays the foundation for further investigations on n-doped polymer system.

Electronic Thesis or Dissertation
Analytical chemistry