| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 101 === This study focuses on investigating the structure of organic conducting polymers ─ poly-3,4-Ethylenedioxythiophene (PEDOT) and compare the resulting figure of merit (ZT) against the PEDOT derivatives, such as PEDOT ─ OCH3, PEDOT ─ CH3, PEDOT ─ Br, and so on. This initiative will provide the opportunity to replace rare and expensive materials. By using PEDOT, the supply of materials can be guaranteed without shortages, a reduction of material costs and the enhancement of the thermoelectric performance is potentially achievable.
Some factors which influence the efficiency of thermoelectric materials include; the electrical conductivity, Seebeck coefficient, and thermal conductivity, among others. All of these properties are dependent on the density of states (DOS) of electrons and phonon dispersion relations. In addition, these properties will also vary with different materials. In this research, we use the method of density functional theory (DFT) with plane wave and periodic boundary condition to build and simulate the PEDOT molecular structures. Following the geometry optimizations, we then proceed to determine the phonon dispersion relations and the phonon density of states from the density functional perturbation theory (DFPT).
After the previously mentioned simulation results have been obtained, these calculated properties are input into the Boltzmann transport equation to obtain key properties such as the of Figure of Merit (ZT). Afterwards, the ZT values obtained from the different PEDOT derivatives are compared. A greater ZT indicates a greater thermoelectric efficiency. From the results, it can be seen that the derivative, PEDOT ─ Br may display a better performance than the PEDOT counterparts and can serve as the design reference for new thermoelectric materials of thermoelectric devices. This thesis initialized the new design method to propose new materials via molecular orbital design.
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