Capacitive-resistive measurements of cobalt-phthalocyanine organic humidity sensors

Abstract

In this study, the fabrication and characterization of capacitive humidity sensors using cobalt-phthalocyanine (CoPc) as the active material were presented. Thin films of CoPc were deposited by drop casting on glass substrates with pre-deposited aluminum electrodes to form Al/CoPc/Al surface-type humidity sensors. The effect of humidity on the electrical properties of the CoPc film was investigated by measuring capacitance and resistance of the samples at four different frequencies of the applied voltage. It was observed that the capacitance of the sensor increased while the resistance decreased with raising the relative humidity. It was also found that the values of capacitance and resistance decreased with increasing frequency. The optical absorption spectra and optical band gap energy of CoPc films were measured. The structure of CoPc powder and thin films has been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Results of XRD studies show that the film structure is polycrystalline with the monoclinic structure while thin films have a peak for annealing temperatures with (100) orientation. Also, the surface morphology (grain size and roughness) for CoPc films have been studied by AFM.