Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity

Over the past several decades with increasing of global energy demand, thermoelectric materials have gained considerable attention due to their unique ability to directly convert heat to electricity. In addition to inorganic semiconductors, polymers are potential candidates for high-performance thermoelectric applications due to their intrinsic advantages such as low thermal conductivity, solution processability, and roll-to-roll production, lightweight, and flexible thermoelectric modules. This thesis provides an insight into the emerging field of organic thermoelectrics, more specifically, thermoelectric power generation based on the composites of conducting polymers (MEH-PPV, P3HT and PEDOT:PSS) and carbon nanotubes (SWNT, SWNT-COOH, SWNT-OH and MWNT). A substantial portion of my work at the graduate level has involved the composite materials of conductive polymers and carbon nanotubes (CNTs) for use in organic thermoelectrics (TE). This work comprised multiple iterations to test effects of chain length (molecular weight) and regioregularity, amount and type of CNT added, sample fabrication solvent, and doping duration led to substantial optimization of the TE power factors. A power factor of 148 μW m-1 K-2 was obtained in the optimized sample preparation with rr-P3HT-Rieke/50%SWnNT which is quite competitive with the PFs mentioned in section 2.3. Besides polymers, I also investigated TE properties of cross-linked network structures established from UV curable small molecules with CNTs. A variety of distinct morphological architectures -- consistent with differences in TE performances -- have been observed. I described the synthesis of new pyridinium and extended viologen molecules capturing light in the visible portion of the solar spectrum with high molar extinction coefficient (~22,000 to 278,000 M-1 cm-1) by means of intramolecular charge transfer (ICT), using electron-donor and electron-accepter groups linked through π-conjugation. Also, these compounds exhibited solvatochromic properties in absorption and emission spectra with respect to the ICT band