Two-step surface treatment of femtosecond laser irradiation and ionic liquid to enhance thermoelectric properties of PEDOT:PSS films

Abstract

Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has garnered significant considerable interest in the field of flexible thermoelectric films owing to its very low thermal conductivity, highly adjustable electrical conductivity (σ) and Seebeck coefficient (S). However, improving the σ and S of PEDOT:PSS simultaneously remains challenging for achieving efficient thermoelectrics. In this paper, we proposed a two-step process involving femtosecond laser irradiation and ionic liquid (IL) 1-Ethyl-3-MethylImidazolium DiCyAmide treatment to enhance the thermoelectric properties of PEDOT: PSS thin films. This finding revealed that the increase in PEDOT: PSS conductivity was attributed to both laser irradiation and the post-treatment with IL, in which the former enabled the efficient elimination of insulating PSS from the surface of the conductive polymer, the latter further contributed to the decoupling of PEDOT and PSS. The enhanced Seebeck coefficient was due to the ion exchange resulting from IL post-processing, which regulated the PEDOT doping level. By employing laser irradiation and surface treatment with IL, the modified PEDOT:PSS films showed a S of 20.63 μV·K−1, a σ of 960.7 S·cm−1, and a power factor (PF) of 40.89 μW·m−1·K−2. Furthermore, a thermoelectric device was developed which can generate a voltage of 0.8 mV at a temperature difference of 11.7 K.