A novel highly sensitive humidity sensor based on poly(pyrrole-co-formyl pyrrole) copolymer film: AC and DC impedance analysis

A novel humidity sensor of poly(pyrrole-co-formyl pyrrole) (P(Py-co-FPy)) film was successfully prepared via spin coating during chemical polymerization. The chemical structure of the P(Py-co-FPy) film was confirmed using infrared spectroscopy (FT-IR). The distinctly different nanodomain morphology and surface roughness observed for materials produced using different spin-coater rotation speeds were analyzed by field emission scanning microscopy (FE-SEM) and atomic force microscopy (AFM). The electrical humidity response of the sensing film was studied in terms of impedance, capacitance, and complex impedance properties. The impedance properties of the sensing film were highly sensitive to the relative humidity (RH) and the frequency operation. The resistive-type humidity of the P(Py-co-FPy) sensing film was highly sensitive; the impedance changed 5461 times at 100 Hz from RH values of 11 to 97%. The P(Py-co-FPy) sensing film responded rapidly when the RH changed from 30 to 90% within 5 s. The response of sensing films generated a small hysteresis during the adsorption-desorption processes. The experimental data were calculated using an exponential function, revealing an excellent correlation between the impedance parameters and the %RH. Furthermore, the impedance response against humidity can be improved by modulating the speed of spin coating that had effect on regularity properties of the surface film. In addition, the relationships among continuous frequencies (40-200 kHz) of impedance at different humidity (11-97%RH) were discussed in details.