Journal of Applied Physical Science International

Bio-carbon-doped ZnO thin films were prepared using bio-carbon extracted from pomegranate peels and deposited on glass substrates by spray pyrolysis. The study examined the influence of bio-carbon doping, ranging from 0 to 7.5 wt.%, on the structural, morphological, optical and humidity-sensing properties of the films. X-ray diffraction analysis indicated that all films retained the hexagonal wurtzite structure of ZnO without secondary phases. Increasing bio-carbon content reduced the crystallite size from 29.5 to 25.4 nm and increased microstrain and dislocation density, indicating the introduction of structural defects and lattice distortion. FESEM and AFM analyses showed compact granular surfaces, reduced grain size and increased surface roughness, with roughness increasing from 5.20 to 9.80 nm. FTIR spectra confirmed the presence of Zn-O bonds and carbon-related functional groups, suggesting interaction between bio-carbon components and the ZnO surface. Optical measurements showed enhanced absorbance and a gradual reduction in the optical band gap from 3.28 to 3.09 eV. Humidity-sensing measurements demonstrated improved performance with increasing bio-carbon concentration. The film doped with 7.5 wt.% bio-carbon showed the highest sensitivity of 82% and response/recovery times of 14 s and 18 s over 20–90% relative humidity. The findings indicate that pomegranate-peel-derived bio-carbon can enhance ZnO thin-film properties for low-cost humidity-sensing applications.