Flexible humidity sensors based on aerosol printed green graphene inks

Abstract

In this study, fully flexible graphene-based humidity sensors were developed and investigated. First, three green graphene inks were formulated by direct liquid exfoliation (LPE) of graphite in water bonded biocompatible stabilizers (biopolymer); triton X-100, tween-20, and gelatin. Ultimately, green and eco-friendly graphene inks were formulated, which are clean of Volatile Organic Compounds (VOCs) and harmful compounds. The graphene inks (namely as GGe, GTr, and GTw) were prepared with optimized biopolymer concentrations of 0.1 mg.mL-1 of gelatin, 1 mg.mL-1 triton X-100, and 1.5 mg.mL-1 tween-20, respectively. The aerosol printed graphene films with 500 nm thickness revealed a sheet resistance (Rs) of 2.6 kΩ/□ for GTr, 5 kΩ/□ for GTw, and 14 kΩ/□ for GGe. The low Rs for GTr was assigned to better ink wettability and adhesion properties on top polyethylene terephthalate (PET) substrates. Therefore, it was chosen for the rest of the research to develop green graphene humidity sensors. The GTr ink was later modified with various concentrations of gelatin to improve the sensor's mechanical strength and sensing performance for humidity detection. The final product, 1 mg.mL-1 gelatin-modified GTr ink (1Ge-GTr), was selected for the rest of the research. The 1Ge-GTr ink was printed on top of screen-printed carbon electrodes on PET substrate, resulting in a green and flexible graphene humidity sensor. The 1Ge-GTr showed a decent linear response in the relative humidity (RH) range of 30% RH–90% RH, good sensitivity of 0.55%/RH% at 25°C, ultrafast response time in a second, and good independence from temperature fluctuations ranging from 22°C to 70°C. Moreover, the sensor showed a high practical efficiency toward humidity detection, making the sensor a potential candidate for implementation in real-life Internet of Things (IoT) applications.

Date	23 Mar 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ricardo Izquierdo (Supervisor)