A comparative assessment of surface microstructure and electrical conductivity dependence on co-solvent addition in spin coated and inkjet printed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)

This study focuses on the fabrication of poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) thin films by ink jet printing and investigates the developed surface morphology and electrical conductivity of the printed films as a function of the concentration of dimethyl sulfoxide (DMSO), added as conduction enhancing co-solvent, and Surfynol, added as a surfactant. The printed films are compared with PEDOT:PSS films fabricated by the traditional spin coating technique. Measurements of the surface tension justify including surfactant as a processing additive, where addition of 1% Surfynol results in substantial decrease of the surface tension of the PEDOT:PSS solution, whilst it also increases film surface roughness by an order of magnitude for both fabrication methods. The addition of 5 %wt DMSO is shown to result in a 10 3 decrease in sheet resistance for both spin coated and inkjet printed films with both processing routes demonstrating decrease in surface roughness and coarsening of PEDOT grains as a function of the co-solvent concentration, whilst x-ray photon spectroscopy showed an increase in the surface PEDOT to PSS ratio from 0.4 to 0.5. Ink jet printed films have lower sheet resistance than the corresponding spin coated films, whilst atomic force microscopy reveals a coarser surface morphology for the ink jet printed films. The findings in this work point out at the decrease of sheet resistance due to coarsening of PEDOT grains which is linked to a decrease of surface roughness for small RMS values associated with the PEDOT grains. However, the higher surface roughness generated when Surfynol surfactant was added was not detrimental to the film's in-plane conductivity due to the fact that these higher roughness values were unrelated to the PEDOT grains.