Photopatternable and moisture-stable PEDOT:PSS/PEG hybrid thin-film for flexible and wearable humidity sensing

Degradation and delamination have been technically challenging for poly(3,4-ethylenedioxythiophene): polystyrene sulfonate) (PEDOT:PSS) thin-film processing due to environmental humidity. To overcome this problem, we introduced a one-step photolithographic method to both pattern and link a PEDOT:PSS film onto a PEG layer as a hybrid thin-film structure on a flexible substrate, which exhibited excellent long-term moisture stability (10 days) and high lithographic resolution (2 urn). Mechanical characterizations (bending and tensile tests) illustrated strong adhesions between the PEDOT:PSS and PEG layers as well as between the hybrid thin-film and substrate. Moreover, the hybrid moisture-absorbable film showed a quick response of its permittivity to environmental humidity variations, in which patterned PEDOT:PSS layer served as an electrode and the PEG layer as a moisture sensing element. As demonstrations, perspiration tracking over various parts of the body surface as well as breath rate measurement were successfully carried out, which illustrated the potential utility of this stable hybrid thin-film for emerging flexible and wearable humidity sensing applications.