Stable, High-Sensitivity, and Rapid-Response Humidity Sensor Based on Ultrathin Graphene Oxide Film after Vacuum Annealing

Graphene oxide (GO) contains a significant number of hydrophilic oxygen-containing functional groups (OCGs) within its molecular structure, which can facilitate the adsorption of water molecules. Therefore, GO is considered to be an effective moisture-sensitive material. However, GO is inherently unstable and highly susceptible to temperature variations. Herein, we report a high-performance resistive humidity sensor utilizing an ultrathin GO film, prepared by drop-casting a single-layer GO aqueous dispersion and subsequently vacuum annealing at 120 °C. The sensor demonstrates excellent temperature stability for the ambient temperature range of 20–80 °C. Additionally, it exhibits high sensitivity and rapid-response humidity sensing capabilities within a humidity range of 20–90% relative humidity (RH). The sensitivity of the sensor reaches 4.29 MΩ/%RH, which is 3 orders of magnitude higher than that of similar sensors operating on the same principles. The response time and recovery time are about 0.32 and 0.42 s, respectively, among the rapidest GO-based resistive humidity sensors reported to date. Due to the rapid response and high sensitivity, the sensor enables noncontact monitoring of human breath as well as monitoring the distance between human fingers and the sensor. Furthermore, we fabricated flexible GO humidity sensors, which demonstrate great potential for applications in wearable devices for monitoring vital signs related to humidity.