Insight into the Degradation Mechanisms of Highly Conductive Poly(3,4-ethylenedioxythiophene) Thin Films

Owing to its high conductivity, good flexibility, low-cost, and ease of processing, poly(3,4-ethylenedioxythiophene) (PEDOT) has become a ubiquitous material, with uses in photovoltaics, energy storage devices, bioelectronics, thin film heaters, and thermoelectric devices. Although PEDOT is generally said to lack stability, very few studies dedicated to its degradation have been reported so far and corresponding mechanisms have not been fully elucidated. In this article, we report on the aging comparison under various conditions of three highly conductive PEDOT-based thin films differing by their counteranions. The effects of specific wavelength ranges (using high-pass optical filters), air and inert gas atmospheres as well as controlled moisture contents were monitored as a function of exposure time. Aging-induced alterations were analyzed by various characterization methods, including UV-vis-NIR spectroscopy, XPS, GIWAXS, and electrical conductivity measurements (down to 3 K). The exposure factors contributing most to degradation were different for each polymer film, indicating that the counteranions play a key role in stability. We highlight the strong impact of UV radiation on altering the structure of the conducting polymers, which in turn degrades electrical performance. Moreover, we propose a straightforward method to enhance stability and slow down the negative effects of aging using encapsulation within polyethylene naphthalate (PEN) thin films.