Amorphous Ta2O5 films were prepared by sol-gel dip process on different substrates. The dip-coating technique was used to prepare amorphous Ta2O5 films by hydrolysis and condensation of tantalum ethoxide, Ta(OC2H5)(5), precursor. Stable coating solutions were prepared using acetic acid as a chelating ligand and catalyzer. Single layer and multi-layered Ta2O5 films were fabricated at a dipping rate of 107 mm/min. The microstructure, stoichiometry and optical properties of these films were investigated as a function of the film thickness. Room temperature CV measurements clearly revealed a protonic conductor behavior for Ta2O5 films. Optical properties such as refractive index, extinction coefficient and optical band gap value of the Ta2O5 films were calculated from optical transmittance measurements. It was found that the refractive index and extinction coefficient values were affected by the thickness of the coatings. The refractive index at a wavelength of 550 nm increased from 1.70 to 1.72 with increasing film thickness. The optical band gap value (3.75 +/- 0.12 eV) of the coating was unaffected by the film thickness. These results indicate that sol-gel-deposited Ta2O5 films have a promising application as proton conductors in electrochromic devices. (C) 1999 Elsevier Science B.V. All rights reserved.