Fig. 2

Dark current (a) and photo-current (b) at various humidity levels under different bias. The insets: corresponding I–V curves of the sensor in the dark (a) and light (b) surrounded by different relative humidity. c Relative humidity dependent moisture responsivity of the sensor in the dark and bright fields, respectively. d Resistance at various relative humidity of the sensor in the dark and bright fields, respectively. e The schematically theoretical diagram of humidity sensing of the sensor