Electrical characterization of PEDOT:PSS beyond humidity saturation

PEDOT:PSS humidity sensor was fabricated using a drop-casting method between thermally evaporated gold electrodes with 30 mu m separation and 300 mu m channel width on a glass substrate. AC, DC resistivity, and AFM techniques were used to characterize the PEDOT: PSS humidity sensor in the same environmental conditions. The change of resistivity was monitored with increasing relative humidity (RH) up to 90%. The resistivity increases linearly up to a maximum value, and then it starts to decrease abruptly above 80% relative humidity (RH) after saturation of water uptake. The decrease in resistivity above 80% RH seems to be due to the water meniscus layer formed on the saturated PEDOT: PSS film. Below 80% RH, the device works like a humidity sensor. (C) 2009 Elsevier B.V. All rights reserved.