Use of organic solvent-assisted exfoliated MoS2 for optimizing the thermoelectric performance of flexible PEDOT:PSS thin films

For organic thermoelectric materials, a main challenge is to achieve high electrical conductivity and a large Seebeck coefficient, in order to improve the power factor. Here we suggest a simple way to address this issue through the addition of a small amount of liquid-phase exfoliated MoS2 nanosheets into poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) solutions by direct vacuum filtration. The effects of exfoliated MoS2 nanosheets in common organic solvents on the thermoelectric properties of PEDOT:PSS were investigated. The organic solvent-assisted exfoliated MoS2 nanosheet solution was found to play an important role in improving the thermoelectric performance of the PEDOT:PSS thin film. Common organic solvents effectively removed some of the PSS during the formation of the film, resulting in a significantly enhanced electrical conductivity (1250 S cm−1) for the PEDOT:PSS/MoS2 (PM) thin film. On the other hand, the introduction of MoS2 nanosheets in PEDOT:PSS led to a slight increase of the Seebeck coefficient from 14.5 to 19.5 μV K−1 without a significant reduction of the electrical conductivity of the PM thin film. An optimized power factor of 45.6 μW m−1 K−2 was achieved for the PM thin film with 4 wt% MoS2 exfoliated in an N,N-dimethylformamide (DMF) solution. The exfoliated MoS2 nanosheets in DMF exhibited a better effect on the thermoelectric performance of the PM composites than did those in other organic solvents. The method used here suggests a novel strategy for improving both electrical conductivity and the Seebeck coefficient, and hence optimizing the thermoelectric performance of the PEDOT:PSS thin film.