Impact of Substrate Hydrophobicity on Layer Composition and Work Function of PEDOT:PSS Thin Films

Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) are used to investigate the impact of surface hydrophobicity on the work function of spin-coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films. Although O-2-plasma or UV-ozone treatment of indium tin oxide (ITO) changes the substrate hydrophobicity, the work functions of subsequently spin-coated PEDOT:PSS layers are not affected and stay constant at around 5 eV. ITO modification by a self-assembled monolayer of p-(trifluoromethyl)phenylphosphonic acid leads to a pronounced contact angle of 90 degrees, resulting in a PSS-rich PEDOT:PSS surface (as shown by XPS) and a work function of 5.15 eV (as shown by ultraviolet photoelectron spectroscopy). This can be rationalized by an increased bulk chemical potential of PEDOT:PSS.

Automated summary

UPS and XPS were used to investigate the impact of surface hydrophobicity on the work function of PEDOT:PSS thin films. Treatment of ITO by O2-plasma or UV-ozone did not affect the work function of PEDOT:PSS, while modification with a self-assembled monolayer of p-(trifluoromethyl)phenylphosphonic acid led to an increase in work function due to a PSS-rich surface.