Thermoelectric plastics: Structure-property relationships of P3HT

Licentiate thesis, 2018

The advancing development of inter-connected small devices, so-called Internet of Things is increasing the demand for independent power sources. Heat is an abundant and often wasted source of energy, thermoelectric generators could be used to harvest this waste energy. Small devices such as heart-rate monitors or gas sensors etc. could potentially be powered by the heat dissipated from the human body using flexible plastic thermoelectric generators. This thesis discusses thermoelectric plastics and in particular the semiconducting polymer P3HT. P3HT is a model conjugated polymer that is commercially available and has become an important reference material for the study of optoelectronic processes in organic semiconductors. At first, we investigated doping from the vapor phase, which permits us to disentangle the influence of polymer processing and doping. We demonstrate that improving the degree of solid-state order of P3HT strongly increased the electrical conductivity. Secondly we studied how the increased solid-state order of P3HT influenced the Seebeck coefficient and the power factor of vapor doped P3HT. Overall, the Seebeck coefficient did not vary to a larger extent whilst the power factor increased by one order of magnitude, to a value of about 3 µW m-1 K-2. This increase was attributed to the improved mobility of charge carriers in the more ordered P3HT.