Tunable Schottky contact humidity sensor based on S-doped ZnO nanowires on flexible PET substrate with piezotronic effect

A novel, flexible sulfur (S)-doped ZnO (ZnO:S) nanowire relative humidity (RH) sensor with a self-powered piezoelectric nanogenerator is proposed. A sensor based on ZnO NWs was also prepared. With a constant bias applied, the measured current of the sensor increased with increasing RH in the dark and under ultraviolet (UV) exposure. With an operating temperature of 50 °C and a loading weight of 12.5 g/cm2, the RH response of the sensor rapidly increased ∼3 orders of magnitude at 80% RH. The S dopant improved the RH sensing ability of ZnO nanowires. The sensitivity of the RH sensor can be tuned via the Schottky barrier height, which is affected by loading weight compressive strain. The sensor can also generate electrical power, with energy converted from environmental vibration. The ZnO:S nanowire piezoelectric nanogenerator outputs 11.6 and 18.6 nW in the dark and under UV exposure, respectively, under a loading weight of 12.5 g/cm2.