Impact of Cu incorporation on the structural, optical, and electrical properties of SnO 2 thin films deposited by solar spray pneumatic method

Copper-doped SnO 2 thin films, with doping varying from 0 to 7% were successfully deposited on glass substrates using the solar spray pneumatic at 450 ± 15 °C. X-ray diffraction confirmed that all samples are polycrystalline with a tetragonal rutile structure, with a preferential orientation along the (110) plane. A minimum crystallite size of 12.45 nm is observed at a doping concentration of 3%. Optical measurements indicate that the film doped with 7% Cu exhibits the highest transmittance, exceeding 80% in the visible region. However, all samples show a decrease in transmittance with decreasing wavelength, indicating increased photon absorption at higher energies, consistent with the wide band gap nature of SnO 2 . The optical energy narrows from 3.80 eV (0%Cu) to 3.48 eV (1%Cu), which can be attributed to the formation of localized defect states. The electrical resistivity decreases significantly up to 3% Cu doping, slightly increases at 5% Cu, then decreases again at 7% Cu, reaching the lowest value of 4.266 × 10 2 (Ω.cm). The highest figure of merit value of 1,46 × 10 −9 (Ω) − 1 was obtained for the film doped with 7%Cu, indicating the best optoelectronic performance among the prepared samples. These findings confirm that Cu doping is an effective approach for tuning the optoelectronic properties of SnO 2 thin films, thereby enhancing their potential for applications in gas sensing and transparent electrode technologies.