Engineering of the optochemical properties of (ultra-)thin plasma polymerized polythiophene films

This study presents a comprehensive optochemical characterization of low-pressure plasma polymerized polythiophene films, with a particular focus on the effect of iodine doping on their optical properties. Special attention was given to the use of helium as carrier gas, previously unexplored in polythiophene plasma polymerization. Films deposited using thiophene, either without carrier gas or in the presence of Ar or He were compared by a comprehensive set of techniques. The optical density of the as-deposited polymers was found strongly dependent on plasma energy. Carrier-fed plasmas, in which ion bombardment intensity decreased going from Ar to He, promoted the formation of more compact structures with reduced monomer retention, thereby influencing iodine uptake and doping kinetics. Therefore, beside thickness variation, it was demonstrated that the optical properties can be tuned by doping duration, also providing insights into the iodine out-diffusion kinetics. To this aim, a dedicated case study on 20 nm-thick layers was performed, targeting optoelectronic applications and device integration.