Gradual thickness-dependent enhancement of the thermoelectric properties of PEDOT:PSS nanofilms

We have investigated the thickness-dependent change in the thermoelectric properties of nanofilms of the conducting polymer, PEDOT:PSS. Films with varying thickness were prepared by spin coating the polymer solution at different speeds. Because of its relatively facile processing, good electrical conductivity, and environmental stability, PEDOT:PSS is considered to be one of the most promising candidates for application in thermal to electric energy conversion devices. Electrical conductivity is attributed to the enhanced carrier mobility in the ordered chain structures of the polymer. The Seebeck coefficient is influenced by the energy derivative of electronic energy density. This approach can be used to study the dependence of conductivity and the Seebeck coefficient at room temperature with varying film thickness. Both the conductivity and Seebeck coefficient improved with increasing thickness of the polymer nanofilms. This can be attributed to the change in the conformation of PEDOT, which exposes the PEDOT on the surface of the PEDOT:PSS phase. The PEDOT:PSS thin films were characterized by UV-Vis spectroscopy, tapping-mode atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. This study suggests that variation of film thickness is an effective way of improving the thermoelectric properties of PEDOT:PSS.