Enhanced thermoelectric properties of PEDOT:PSS films via a novel two-step treatment

Post-treatment of PEDOT:PSS films to fabricate high performance thermoelectric (TE) materials has been widely studied. The depletion of PSS and tuning the redox level of PEDOT have been considered important. The effective control of these two issues is crucial, yet has not been systematically investigated. Herein, HI and DMSO are used to post-treat PEDOT:PSS films, issues including using these solvents in a step-wise fashion, using solvent or vapour and treatment time are studied. HI is found to have both a physical doping and reducing effect on PEDOT:PSS simultaneously. However, HI solution or vapour could not remove most of the excess PSS to obtain high electrical conductivity. Therefore, DMSO is used to achieve this. Subsequently, HI vapour was used to alter the redox level. Through this method, the power factor reaches as high as 45.02 mu W mK(-2), which is over 5000 times higher than the as spun film. These films are characterized by different methods, including: AFM, XPS, UV, SEM and Raman spectroscopy. It is concluded that such enhancement in TE properties is caused by two issues: the depleting effect of PSS by DMSO and oxidation level change of PEDOT by HI vapour. The former leads to enhanced electrical conductivity and the latter leads to reduced charge carrier concentration, thus, enhanced Seebeck coefficient. It is thought that such a two-step solvent post-treatment method could offer a novel route to optimize the TE properties of PEDOT:PSS based materials.