Exploring the conduction mechanism of PEDOT:PSS free-standing thin films doped with SWCNTs: THz and infrared-ultraviolet spectroscopy study

Here, we present an optical conductivity study on poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and PEDOPT:PSS modified with ethylene glycol (EG-PEDOPT:PSS) thin films doped with 0.5, 1, and 2 wt% single-walled carbon nanotubes (SWCNTs) in wide frequency range (0.1-1500 THz). The low frequency part of sigma(omega) spectrum is composed of two components: narrow sigma(LMD1)(omega) and broad sigma(LMD2)(omega) contributions where they mimic conductivity of SWCNTs and PEDOT:PSS or EG-PEDOT:PSS, respectively. At the DC limit, the PEDOT:PSS and EG-PEDOT:PSS do not contribute to the total conductivity sigma(Total)(0) and the sigma(Total)(0) comes from SWCNT' s free electrons. The 0.5 wt% doped samples showed lower conductivities as compared with pure SWCNTs, where the transferred free electrons from the SWCNTs are blocked by reducing the PEDOT:PSS or EG-PEDOT:PSS. For the 1 wt% and 2 wt% composites, there are enough free electrons to reduce the polymer and the rest enhance the total conductivity of the system. The effect of electrons transfer blocking becomes less significant in this case leading to conductivity enhancement.