Experimental Evaluation of High-Performance Humidity Sensing With Extended Detection Range Using PEDOT:PSS/SnO2/ZnO Double Heterojunction Layers

For the first time, a flower-like tin oxide (SnO₂) nanosheet was integrated onto a tailored zinc oxide (ZnO) nanosheet array, creating SnO₂/ZnO heterostructure films on a Fluorine Tin Oxide (FTO) substrate via a hydrothermal method. A hole-collecting layer of Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) PEDOT:PSS was spin-coated onto the SnO₂ layer, forming a PEDOT:PSS/SnO₂/ZnO double heterostructure. The crystallite sizes of SnO₂ (S-sensor), ZnO (Z-sensor), and SnO₂/ZnO (S/Z-sensor) were measured at 4.08 nm, 20.60 nm, and 22.25 nm, respectively. Structural, morphological, optical, and electrical properties were analyzed using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Ultraviolet–Visible (UV–Vis) Spectroscopy (UV), and photoconductivity studies. The heterostructure formation was confirmed, with a dominant peak at the 101 plane. The bandgap, photoconductivity, and impedance reduction were determined to be 2.36 eV (Electron Volt), 0.45 V (Volt), and 1.51 kΩ, respectively. Humidity sensing experiments at room temperature revealed that the SnO₂/ZnO heterostructure exhibited superior performance, with a sensitivity of 90.8%. The S/Z sensor demonstrated a broad relative humidity (RH) detection range (10–97% RH), low hysteresis (7.1%), fast response (3 seconds), and quick recovery (12 seconds). Additionally, the sensor maintained stability over seven humidity measurement cycles. These findings highlight the potential of the PEDOT: PSS/SnO₂/ZnO double heterostructure for advanced humidity sensing applications.