The Influence of Trifluoroacetic Acid on the Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate)

Abstract

Poly(3,4-ethylenedioxythiophene) :Poly(styrenesulfonate) (PEDOT:PSS) can disperse in the aqueous solution and shows good processability and exhibits very stable, high conductive and transparent characteristics. Therefore, PEDOT:PSS has replaced ITO glass in some electronic devices, such as anode buffer layer of organic solar cells.In this study, we explored how the trifluoroacetic acid (TFA) improves the electrical conductivity of the PEDOT:PSS free standing film which was cast and dried from TFA aqueous solution.To investigate the influence of TFA on the conductivity of the PEDOT:PSS, Raman spectroscope, X-ray photoelectron spectroscope (XPS), and conductive atomic force microscope (C-AFM) were carried out. Besides, the conformation and the phase behaviors of PEDOT:PSS were investigated in this study as well.According to the results, it was proposed that the improvement of the electrical conductivity of PEDOT:PSS film cast from TFA solution was not caused by the higher doping level with TFA., but caused by changing the conformation of PEDOT chain. As TFA is added into the aqueous dispersions of PEDOT:PSS, it can interact with PEDOT and makes PEDOT with more positive charges and more hydrophilic. The conformation of the PEDOT chains is therefore expanded. As a result, the conductive PEDOT domains construct a continuous conductive network and the electrical conductivity of the PEDOT:PSS film is improved.