Ennaceri, H.; Boujnah, M.; Erfurt, D.; Rappich, J.; Lifei, X.; Khaldoun, A.; Benyoussef, A.; Ennaoui, A.; Taleb, A.: Influence of stress on the photocatalytic properties of sprayed ZnO thin films. Solar Energy Materials and Solar Cells 201 (2019), p. 110058/1-13
10.1016/j.solmat.2019.110058

Abstract:
Zinc oxide (ZnO) thin films grown on glass substrates are prepared by means of the Ion Layer Gas Reaction process. The XRD pattern revealed that the ZnO lattice parameters decrease continuously, with the increasing of the film thickness, indicating a continuous variation in the compressive strain. The influence of the thickness on the optical, morphological and structural properties of deposited ZnO thin films was investigated. The UV–Vis absorption spectra of deposited thin films were shown to exhibit a blue-shift, resulting in an increase in the optical band gap from 3.13 eV to 3.24 eV. Structural parameters such as crystallite size, lattice parameters, Zn–O bond length, and residual stress have been determined, and the compressive strain (tensile stress) is found to increase with the increasing of spray time and in turn deposited thin film thickness. The PL spectra of deposited ZnO films, show stronger PL intensity with increasing deposited thin film thickness, which confirm the influence of deposited film thickness on the recombination process of charge carriers and thus on its optical properties. These results, were confirmed by the photo-electrochemical experiments. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure, which shows that structural defects and surface morphology of deposited thin films were also demonstrated to have a direct impact on deposited films’ optical properties. Furthermore, to further confirm these experimental optical results, theoretical first principle calculations were conducted. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure.