Synthesis and nanostructuration of thin and conductive PEDOT films by liquid-phase polymerization

Conductive polymers (CPs) have represented a key research topic in the field of organic electronic devices, as alternatives to silicon-based technologies. Among them, poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most used and investigated materials because of its good and tailorable electrical properties, transparency to visible light and environmental stability. For all these reasons, PEDOT has found applications in organic solar cells, supercapacitors, organic light-emitting diodes and nanostructured devices. In this project, we studied the synthesis of this polymer using a liquid-phase polymerization process.[1] This process involves the sequential deposition of an oxidant solution (vanadium pentoxide) and a monomer solution (EDOT) onto a glass substrate treated with piranha solution. The resulting film is washed with a solvent to eliminate the excess monomer and then subjected to annealing heat treatment. To enhance the properties of the polymeric film, we varied the deposition time of the oxidizing solution, the rotation speed and the concentration of the oxidizing solution. The analysis showed that the thickness of the polymeric film is primarily influenced by the deposition time of the oxidant solution. Additionally, the concentration of the oxidant slightly affects the polymer thickness due to the varying viscosities of more and less concentrated solutions. We determined the morphology and thickness of the samples using optical profilometry and measured the conductivity of the samples with the Van der Pauw method using a 4-point probe in electrical contact with the polymeric film. A direct current is applied between the outer test leads, while a voltage drop is measured between the inner leads, providing the sheet resistance (Rs, measured in Ω/□). We studied the nanostructuring process of the films using nanosphere lithography. To improve the deposition of nanospheres on the PEDOT layer, a silica one was applied to the film. This layer facilitated the formation of a monolayer of polystyrene particles, which was subsequently reduced using reactive ion etching (RIE).[2] The resulting mask enabled the precise nanostructuring of the PEDOT films. By optimizing this process, we achieved PEDOT nanostructures with a high degree of order.