A low-cost printed humidity sensor on cellulose substrate by EHD printing

The use of printing technologies is rapidly increasing in area of electronic devices. Electrohydrodynamic (EHD) jet printing has been a target of research because of its aptness to produce high-resolution patterns for wide range functional materials onto flexible substrates. In this paper, a stable humidity sensor was printed utilizing PEDOT: PSS as sensing layer. Meander-type electrodes using silver nanoparticles ink were fabricated using continuous EHD inkjet printing on flexible paper (cellulose) substrate. The sensing material PEDOT: PSS was dissolved in ethylene glycol and then deposited on silver electrodes. The fabricated sensor exhibited decent response toward change in capacitance above 50% relative humidity. The response and recovery time of the printed sensor for increasing and decreasing humidity levels were approximately 0.58 s and 0.7 s, respectively. This low-cost sensor has potential applications in agriculture, food monitoring, medical and industrial environment as a disposable sensor for humidity detection. Fig. (A): Schematic illustration of EHD printing system, (B): (1) 200 × Optical microscopy images of PEDOT: PSS (a) 50% layer (b) 30% layer (c) 20% layer and (2) AFM images of PEDOT: PSS (a) 50% layer (b) 30% layer (c) 20% layer, (C): Humidity sensor (a) Schematics (b) Printed Ag Electrodes and (c) PEDOT: PSS deposited, and (D): (a) Measured capacitance and (b) Response and Recovery time of 50% PEDOT:PSS sensor and (E): PEDOT:PSS ink preparation.