Polypyrrole: synthesis, characterization and its potential application for humidity sensor

In this work, polypyrrole (PPy) is synthesized, characterized, and employed as an active sensing material for the fabrication of humidity sensors. An 80 nm thick layer of PPy is spin coated on the pre-patterned thermally deposited silver (Ag) electrodes spaced 50 µm apart to fabricate Ag/PPy/Ag surface-type sensor. Atomic force microscopy analysis revealed granular microstructure morphology in the thin films of PPy. Additionally, X-ray diffraction (XRD), ultraviolet–visible (UV-Vis) and Fourier transformed infrared (FTIR) spectra of PPy are analyzed to study its crystallinity, optical bandgap and bond dynamics to confirm the molecular composition of PPy. The fabricated Ag/PPy/Ag sensor is characterized by varying the humidity levels between a broad range [0–95% relative humidity (RH)] at different frequencies of 120 Hz and 1 kHz. The prepared sensor showed promising sensing features such as higher sensitivity 233 nF/%RH (at 120 Hz), 83 pF/%RH (at 1 kHz), quick response time (5.20 ± 0.2 s) and recovery times (6.43 ± 0.2 s), a wide working range of relative humidity (20–95%RH) and low hysteresis gap (1.57%) with outstanding recyclability. This study reveals the potential of PPy as the best candidate for humidity sensing applications.