Stability of poly(3,4-ethylenedioxythiophene) thin films prepared by vapor phase polymerization

Sufficient stability of conductive polymers is crucial for allowing widespread application of these materials. Poly(3,4-ethylenedioxythiophene) (PEDOT) has a relatively high conductivity and transparency among conductive polymers. In this study, the stability of PEDOT thin films prepared by vapor phase polymerization was investigated at elevated temperatures in air (100-140 °C) and in argon (140 °C) and at room temperature in various environments. Ultraviolet light, water vapor and vacuum exerted a detrimental effect on the stability of PEDOT films at room temperature. Slow decay of conductivity was unavoidable even under inert gas at room temperature, while decay in air and in inert gas environment was comparable at 140 °C. Characteristic changes in the ultraviolet-visible-near infrared absorbance spectra appeared in all the aged samples. The chemical composition was investigated by using Raman spectroscopy and X-ray photoelectron spectroscopy. The structure of the films was determined by grazing incidence X-ray diffraction. Temperature dependences of resistance were measured for thermally aged and untreated films, demonstrating that during aging a transition occurs from critical to insulating behavior.