Strategy to Improve the Seebeck Coefficient of PEDOT: Introduction of Chloromethyl Groups on Its Surface

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a prospective thermoelectric polymer owing to high conductivity, low thermal conductivity, and processability. However, the Seebeck coefficient of PEDOT is substantially lower than inorganics, and molecular design strategies to promote this coefficient are yet to be established. Here, the introduction of chloromethyl (-MeCl) on the surface of PEDOT has been established as an effective strategy for elevating its Seebeck coefficient. It was found that the electron-withdrawing effect of -MeCl decreases the highest occupied molecular orbital (HOMO) energy level and increases the oxidation potential of poly(chloromethylated 3,4-ethylenedioxythiophene) (PEDOT-MeCl). The space steric hindrance effect of -MeCl increases the layer spacing of PEDOT-MeCl. Furthermore, -MeCl severely disrupts the localized coplanar structure of PEDOT-MeCl, leading to a more difficult transition of the polariton into a dipolariton. Hence, PEDOT-MeCl is more difficult to be oxidatively doped, and the oxidation level is reduced compared to PEDOT. This ultimately leads to a 22.57% decrease in carrier concentration and a 33.06% increase in Seebeck coefficient for PEDOT-MeCl. This work opens up a new pathway for modulate the Seebeck coefficient of PEDOT.