Wirelessly powered multi-functional wearable humidity sensor based on RGO-WS2 heterojunctions

•Electron transfer was demonstrated by Raman spectroscopy in situ.•Multilayer RGO and WS2 composites formed large area of p-n heterojunction.•The humidity sensor shows excellent sensitivity and fast response/recovery time. High-performance multifunctional sensors that are powered wirelessly could find applications in athlete training, health monitoring, and human-machine interactions. In this paper, a humidity sensor based on a reduced graphene oxide (RGO) and tungsten disulfide (WS2) heterojunction is proposed. The sensor exhibits high performance in regard to humidity sensing. The wireless humidity sensor has a fast response time (0.56 s) and recovery time (2.26 s), which can be attributed to the heterojunction and the synergistic effect. The sensor also has a wide working range between 5%RH to 95 %RH. The flexible humidity sensor can be used to monitor the skin humidity and evaluate the metabolism of the human body. Moreover, in situ Raman spectrum was used to prove the electron transfer between the water molecule and RGO-WS2 (RGWS) at different humidity. Thus, this work could have broad applications in various fields such as personal health, physical training, and psychological state monitoring.