Improvement to the thermoelectric properties of PEDOT:PSS

Thermoelectric materials can convert waste heat to electricity without moving parts. Extensive research into improving the efficiency of inorganic thermoelectric materials has allowed some materials such as bismuth tellurides to be commercialized. These materials, however, contain materials in low abundance on earth such as tellurium therefore their use and scaled production would be limited. Organic and hybrid thermoelectric materials can meet the gap for niche markets as well as be synthesized on mass, due to utilization of earth abundant elements such as carbon, sulphur, and nitrogen. The thermoelectric generators require several n and p-type materials connected for optimal efficiency. There are many ways to create inorganic thermoelectric n and p-types. However, for the organic thermoelectric materials the efficiency lags because of their lower electrical conductivity and Seebeck coefficient as well as the lack of effective strategies in the development of n-type materials. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most successful and researched p-type organic thermoelectric material and thus, the thesis will explore effective strategies for decoupling the apparent trade-offs observed when improving either the electrical conductivity or Seebeck coefficient. The first major contribution to knowledge discussed in this study is the utilization of a reducing agent treatment on PEDOT-ionic liquid composites (reader is advised to refer to chapter 5). Another significant finding was the successful development of a novel route to an n-type single walled carbon nanotube, PEDOT:PSS composite (please refer to chapter 6). The final and most significant contribution to knowledge in this research project was the development of a set of novel single walled carbon nanotube, ionic liquid, PEDOT:PSS composites whereby after a post treatment with a guanidinium iodide in ethylene glycol solution allowed for improvement of the electrical conductivity from 3.4 S cm -1 to 3665 S cm-1 and Seebeck coefficient from 12 μV K-1 to 27 μV K-1 thereby leading to an optimised power factor of 236 μW m-1 K-1 at 140 °C (please refer to chapter 7).