Simultaneous increases in electrical conductivity and work function of ionic liquid treated PEDOT:PSS: In-depth investigation and thermoelectric application

The electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) should be at least comparable to that of transparent conductive oxide electrode for the practical implementation in the electronics industry. In this report, a clever post-treatment method for enhancing both electrical property and work function of the PEDOT:PSS film is studied for application in electronics requiring high work-function organic conducting materials. An ionic liquid that has strong electron-withdrawing group, bis(trifluoromethane)sulfonamide (TFSI), was applied to the PEDOT:PSS film during post-treatment. TFSI molecules were distributed throughout the resulting PEDOT:PSS film, which allowed the film to increase its electrical conductivity and work function, as confirmed by photoemission spectroscopy. The enhancement of the work function after TFSI treatment led to low hole injection barriers at various organic semiconductor/PEDOT:PSS interfaces. Moreover, the TFSI treatment was also found to be effective in changing the electronic properties of a composite of carbon nanotubes and PEDOT:PSS (denoted as MWPE). Finally, the effects of TFSI treatment on the thermoelectronic performance of the PEDOT:PSS and MWPE films were discussed, suggesting potential applicability of TFSI-treated PEDOT:PSS in organic thermoelectrics without inorganic fillers.