Dopant passivation by adsorbed water monomers causes high humidity sensitivity in PEDOT: PSS thin films at ppm-level humidity

Thin layers of hole conducting polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) are widely utilized in the fabrication of organic light emitting devices. More recently, the material has been considered as a platform for humidity sensor fabrication. This is interesting as the conductive component of this composite, PEDOT, is hydrophobic. Moreover, charge transport mechanism in PEDOT:PSS is not yet fully established and understanding the cause of sensitivity to humidity may shed further light on the obscure charge conduction in this conductive polymer composite. Here, we investigate the humidity sensitivity in PEDOT:PSS thin films in a wide relative humidity (RH) range and report the existence of a distinctly higher humidity sensitivity in the RH