Self-Powered Humidity Sensors Based on SnS₂ Nanosheets

With the advent of the Internet of Things (IoT), the development of self-powered sensors has received much attention. Introducing triboelectric nanogenerators (TENGs) as a power source that converts mechanical movement into electrical signals has been admired recently. Moreover, the monitoring of humidity has become enormously essential in several technological contexts from environment monitoring to biomedical applications, thus joining these two subjects provides a huge benefit in achieving self-powered humidity sensors. Here, in this research, facile, low-priced and self-powered humidity sensors are fabricated utilizing transition-metal dichalcogenides (TMD) nanosheets. Semi-vertical SnS2 nanosheets are synthesized through a modified chemical vapor deposition method at moderate heat treatment (500 °C) utilizing pristine sensor’s substrate and sulfur element on a laser grooved fluorine tin-doped oxide (FTO)/glass. To achieve a self-powered device, the integrated contact-separated (CS) TENG of FTO and Kapton/Al has been coupled with the projected humidity sensor, through the impedance matching circuit. This self-powered SnS2 humidity sensor demonstrated an outstanding response of about 400%, fast response and recovery times (∼4, and 7 s), and long-term stability (at least 5 months). Furthermore, the humidity effect on the electrical performance of the SnS2 layer was studied through first-principle simulations. Based on calculated adsorption energies, charge transfer, electronic band structures, and density of states, H2O molecules physisorbed on the SnS2 nanosheet with a strong adsorption energy of −1.82 eV and 0.0208 e/molecule charges transferred from H2O molecules to the surface. Our density functional theory calculations shed light on the humidity sensing mechanism by illustrating that both Sn and Sulfur atoms could act as adsorption sites. The introduced battery-free and self-powered humidity sensors have great conceivable application in wearable/portable electronics and also smart homes