Influence of CuO on the performance of conducting polymer matrix for screen-printed humidity sensing applications

A flexible polyethylene terephthalate (PET) substrate was employed for the fabrication of a resistive-type humidity sensor using screen-printed polypyrrole (PPy)/CuO nanocomposite conductive inks. A series of conducting polymer-metal oxide composite-based sensors with varying compositions was prepared, and their humidity-sensing performances were systematically evaluated. The structural and morphological features of the composites were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The sensing behaviour of the printed devices was investigated over a relative humidity (RH) range 22–97% at room temperature, focusing on parameters such as relative resistance, sensitivity, dynamic response, and hysteresis. Enhanced sensitivity was achieved with the incorporation of CuO into PPy. The superior sensing performance is attributed to the combined structural characteristics and hydrophilic nature of CuO. The PPy/CuO nanocomposite with a 1:1 weight ratio, prepared via mechanical mixing and screen printing, exhibited the highest sensitivity over a broad humidity range (22–97% RH), along with fast response/recovery times (~ 50/60 s) and negligible hysteresis.