Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol-gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 degrees C and 500 degrees C for 1 h. The coatings have been characterized by X-ray diffraction, UV-Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (similar to 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 degrees C to 500 degrees C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 degrees C, 780 nm film thickness. (C) 2007 Elsevier B.V. All rights reserved.