Enhancement of thermoelectric performance of thienoisoindigo based D-A conjugated polymers through the incorporation of 3,4-ethylenedioxythiophene as donor unit

With the good planarity of conjugated backbone and high charge carrier mobilities, thienoisoindigo (TIIG)-based polymers show great potential in organic electronic devices. In this work, two TIIG-based D-A conjugated polymers (PTIIG-3T and PTIIG-2T-EDOT) were designed and synthesized, which exhibit high lying highest occupied molecular orbital (HOMO) energy level and can be facilely doped by FeCl3. Compared with PTIIG-3T, one thiophene unit in the donor building block is replaced by 3,4-ethylenedioxythiophene (EDOT) in PTIIG-2T-EDOT, and PTIIG-2T-EDOT shows a higher HOMO level with slightly higher coplanarity than PTIIG-3T, which induce an enhancement in electrical conductivity after oxidation doping. After proper doping, doped PTIIG-2T-EDOT film achieved a higher TE power factor of 17.9 mu W m(-1) K-2 than that of PTIIG-3T due to its higher conductivity. The results indicate that TIIG unit is a promising building block for future high-performance conjugated polymers for thermoelectric applications, and incorporation of the EDOT unit into D-A conjugated polymers could be an effective way to develop high performance thermoelectric polymers.