Enhanced thermoelectric performance of PEDOT: PSS films via ionic liquid post-treatment

Thermoelectric (TE) energy harvesting can effectively convert waste heat into electricity, which is a crucial technology to solve energy concerns. As a promising candidate for energy conversion, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has gained significant attention owing to its easy doping, high transparency, and solution processability. However, the TE performance of PEDOT:PSS still needs to be further enhanced. Herein, different approaches have been applied for tuning the TE properties: 1st direct dipping PEDOT:PSS thin films in ionic liquid; 2nd post-treatment of the films with concentrated sulfuric acid (H2SO4), and then dipping in ionic liquid. Besides, the same bis(trifluoromethanesulfonyl)amide (TFSI) anion and different cation salts, including 1-ethyl-3-methylimidazolium (EMIM+) and lithium (Li+), are selected to study the influence of varying cation types on the TE properties of PEDOT:PSS. Further, the Seebeck coefficient and electrical conductivity of the PEDOT:PSS film treated with H2SO4-EMIM:TFSI increase simultaneously, and the resulting maximum power factor is 46.7 μW m-1 K-2, which may be attributed to the ionic liquid facilitating the rearrangement of the molecular chain of PEDOT. The work provides a reference for the development of organic films with high TE properties.