Transparent humidity sensor with high sensitivity via a facile and scalable way based on liquid-phase exfoliated MoO_3-x nanosheets

The flourishing of the Internet of Things (IoT) in recent years creates a huge demand for various humidity sensors, since the humidity is closely related to our daily life. Transparent humidity sensors have great application prospects in the fields such as smart furniture and human-machine interface. However, it is difficult for devices made from traditional moisture sensitive materials to have both high optical transparency and sensitive humidity response. Herein, we developed a novel humidity sensor based on 2D MoO_3-x nanosheets, in which the nanosheets were liquid-phase exfoliated from α-MoO₃ powder. With the assistance of ethyl cellulose, a high concentration dispersion of oxygen-deficient MoO_3-x nanosheets can be easily prepared by probe sonicating. The as-prepared humidity sensor shows a transmittance as high as 86% in visible range. Under a constant bias, the current of the sensor increases monotonically over a broad RH range from 11% to 95%. Moreover, the fast response and recovery speed in the subsecond timescale (0.12 s and 0.53 s) enables the transparent humidity sensor to work as a real-time device in the expiration monitoring system. This work demonstrates a promising application of 2D MoO_3-x nanosheets and opens up a new avenue for designing transparent humidity sensors.