Preparation And Thermoelectric Properties Of Benzodithiophene-based Conjugated Polymers And Their Composites

Thermoelectric material is a functional material which can realize the conversion between thermal energy and electric energy by the movement of carriers in solid.Organic polymer thermoelectric materials have been paid more and more attention by researchers due to their solution processability,mechanical flexibility,low cost and low thermal conductivity.At present,the research on organic polymer thermoelectric materials are mainly focusing on polyaniline,polypyrrole,polyfluorene,polythiophene and their derivatives.Polymers with new structures that show thermoelectric performance are rarely studied,especially the relationship between the structure and thermoelectric properties of polymers are scarecly reported.Based on the above mentioned problems,a series of conjugated polymers based on BDT unit were designed and synthesized in this thesis,and we studied the relationship between their structure and thermoelectric properties systematically.Furthermore,we also prepared composite thermoelectric materials using BDT-based conjugated polymers and SWCNTs,and systematically studied the effects of different mass ratios of polymer to SWCNTs on the thermoelectric properties.The details are as follows:1)We designed and synthesized three BDT-based D-A type conjugated polymers with different side chains.Compared to other polymers,the polymer with the highest conjugated degree of side chains exihibted better thermal stability,narrower band gap and more ordered structure.And after doping with FeCl₃,the polymer with the highest conjugated degree of side chains also showed the largest power factor values among the three polymers.This study clearly exihibited that the enhancement of side chain conjugation is benefit to improve the thermoelectric performance of BDT-based D-A conjugated polymers.2)Secondly,we designed and synthesized two BDT-based conjugated polymers,which contained alkyl side chains or polar side chains,respectively.We systematically investigated the effects of the polymer side chain on the physicochemical properties,especially the thermoelectric performance of the polymers after doping with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone?DDQ?and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane?F4TCNQ?.Compared with the polymer with alkyl side chains,the thermal stability of the polymer containing polar side chains decreased slightly,and the band gap of the polymer containing polar side chains widened slightly.After doping with DDQ and F4TCNQ,the highest power factors of polymer containing polar side chains were over 5-times and 2-times that of the polymer with alkyl side chains,respectively.The results confirmed that polar side chains can effectively enhance the thermoelectric performance of BDT-based conjugated polymers.3)We prepared composite thermoelectric films with SWCNTs and BDT-based conjugated polymer.Strong?-?interfacial interactions are present between the BDT-based polymer and the SWCNTs,and we systematically studied the effects of different mass ratios of BDT-based polymer to SWCNTs on the thermoelectric properties.The maximum electrical conductivity,Seebeck coefficient and power factor of the composite films are 529.3 S cm^-1,68.1?V K^-1,and 80.9?W m^-1 K^-2 at room temperature,respectively.Additionally,the composite film with a BDT-based polymer:SWCNT mass ratio of 1:10 exhibited the highest power factor of 116.7?W m^-1 K^-2 at approximately 95°C.