Impact of Sol aging time on structural, morphological, optical and electrical properties of ZnO coatings

Zinc oxide thin films were spin coated onto glass substrates by a sol gel process. The aging time of the precursor solution was optimized in order to perform a general study on the structural, optical and electrical properties along 72 hours. The increase of the aging time of the precursor solution showed the formation of films with three crystalline orientations (100), (002) and (101) corresponding to a wurtzite phase, and indicating a good crystallization of our films. It was also found that the increase of aging time led to an increase in surface roughness, in addition of that it can also increase the films thickness. From the optical properties results, we revealed a reduction in the optical transmittance of the films while aging the deposition solution, and the optical band gap increases from 3.175 to 3.224 eV. Concerning the electrical properties, the conductivity is limited by the mobility of charge carriers, also a maximum intrinsic conductivity of $3.61 (\Omega\ . \text{cm})^{-1}$ is obtained for films deposited at 24 hours of aging time of the deposition solution.