Effects of PEDOT:PSS Microstructure on the Charge Transport and Thermoelectric Properties

Conducting polymer-based thermoelectric (TE) device, which can harvest low temperature waste heat, have great potentials as energy sources for operating various low-power electronic devices. Among various conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most attracting candidates owing to its high electrical conductivity, solution processability, flexibility, and air stability. Various post-treatments have been introduced to increase the thermoelectric properties of the PEDOT:PSS films. These methods have been known to change the crystallinity and relative PSS composition of the PEDOT:PSS films, which determines charge transport. However, how both the crystallinity and composition of the PEDOT:PSS films correlated to their charge transport and thermoelectric properties has not been intensively studied. Here, we present the interdependence of the microstructure (i.e. crystallinity and PSS composition), charge transport and TE properties using PEDOT:PSS films post-treated with various methods. The crystallinity and the composition of the PEDOT:PSS films were carefully characterized with both the grazing incidence wide angle spectroscopy (GIWAXS) and X-ray photoelectron spectroscopy (XPS). The charge transport properties of the films were investigated using theoretical models and the temperature-dependent electrical conductivity.