Design Synthesis And Thermoelectric Properties Of Thiazole-based DA-type Conjugated Polymers

Thermoelectric materials that can convert heat into electricity have been considered as a promising source of sustainable energy.To date,organic thermoelectric materials have become the promising materials for thermoelectric applications with the advantages of good flexibility,processability,light-weight,low toxicity,high Seebeck coefficient,and low thermal conductivity.Based on the novel D-A structure with strong acceptor-benzothiadiazole unit,we explored the relationships between the structure?alkyl side chain and polymer backbone?and thermoelectric properties of benzothiadiazole based polymers.We selected F8 BT which has high Seebeck coefficient among the studied polymers,to form composites with SWCNT,the thermoelectric properties of the composites were studied.We concluded that the thermoelectric properties of the benzothiadiazole based copolymer can be improved by reducing the length of the alkyl side chain,lowing theband gap,exchanging a donor with good electric property,and combining with carbon nanotubes.The details are as follows:1.In chapter 3,we studied a series of fluorene-benzothiadiazole copolymers?F6BT,F8 BT,and F12BT?with D-A structure,without changing the band gap of these polymers,we studied the influence of alkyl side chain on thermoelectric properties of those polymers.The results showed that short alky chain with intense molecular packing had better conductivity.Therefore,F6 BT showed the best thermoelectric performance,with the conductivity up to 1.52 S/cm?22 °C?and power factor was about 1.65 ?W m^-1 K^-2.By increasing the temperature,molecular arrangement of the polymers was influenced,and the carrier mobility was decreased,causing an enhanced Seebeck coefficient and decreased electric conductivity.2.Based on the results in Chapter 3,we added thiophene unit into the polymer backbone to tune the band gap.And study the relationship between the polymer backbone and thermoelectric properties.We found that polymers with narrow band gap showed increased conductivity and realatively lower Seebeck coefficient.Without changing the band gap of the polymer backbone,the donor was changed from fluorene into carbazole which has better electric property.We found that the introduction of carbazole unit further improved the conductivity of the material,but had little effect on Seebeck coefficient.At the temperature of 90 °C,we found that the Seebeck coefficient could be up to 335 ?V/K,and the PF value could be up to 13 ?W m^-1 K^-2.3.Based on the results in Chapter 3 and 4,we selected the F8 BT with high Seebeck coefficient and SWCNT with high conductivity to thermoelectric composites.We found that with the ratio of SWCNT increased,the electrical conductivity increased first and then decreased,but the ratio of SWCNT had little effect on the Seebeck coefficient.When the weight ratio of SWCNTs was added to 50%,the conductivity of F8BT-FeCl3/SWCNT composites was up to 1625 S/cm,and the PF value was 33.4 ?W m^-1 K^-2.It was shown that the thermoelectric properties of F8 BT can be enhanced by combinding the F8 BT with carbon nanotubes.