Highly stable and sensitive resistive flexible humidity sensors by means of roll-to-roll printed electrodes and flower-like TiO2 nanostructures

Titanium dioxide (TiO2) nanostructure is synthesized and utilized as a sensing material in flexible resistive humidity sensors. The morphology of TiO2 flower-like nanostructure was optimized to possess high surface area by controlling pH value of precursor solution. The electrode was roll-to-roll gravure printed, and synthesized TiO2 nanoflower and protective layer were drop cast on flexible polyimide substrate. The humidity sensor made of TiO2 nanoflower with highest surface area exhibited highest sensitivity of 485.7 RH%(-1). Furthermore, it showed comparably good repeatability, little hysteresis, and high degree of chemical stability as well as excellent resistance to random mechanical deformation. High sensitivity and stability of sensors based on TiO2 nanoflower hierarchical structure make them suitable for flexible and/or wearable applications.