Pure and Zn-doped SnO2 thin films with Zn concentrations ranging from 1 to 5 mol.% were deposited on glass substrates via ultrasonic spray pyrolysis. X-ray diffraction (XRD) confirmed that all films crystallized in the tetragonal rutile structure, while the crystallite size decreased with increasing Zn concentration. Atomic force microscopy (AFM) revealed that moderate Zn doping (1–3%) reduced the surface roughness (Ra, Rq) of Zn–SnO \(_2\) from (93.65 nm, 113.56 nm) to (64.74 nm, 83.42 nm) and improved surface uniformity, whereas higher Zn content (5%) led to grain coalescence and a significant increase in roughness (192.8 nm, 239.64 nm). UV visible spectroscopy showed high optical transparency exceeding 80% in the visible region. The optical band gap (E \(_\text {g}\) ) decreased with increasing Zn, from \(3.92 \pm 0.05\) to \(3.85 \pm 0.03\) eV. Photoluminescence (PL) spectra exhibited both UV and visible emissions with intensities varying with Zn concentration, indicating the presence of various defects including oxygen vacancies (V \(_\text {O}\) ). Photocatalytic activity, evaluated through methylene blue (MB) degradation, reached a maximum values of 74.6% at 3% Zn doping, while higher Zn content (5%) reduced the performance due to structural deterioration. Scavenger test revealed that holes were the dominant reactive species. These results highlight the potential of Zn-doped SnO \(_2\) thin films as efficient materials for environmental remediation.
