ZnO nanocrystalline films were prepared by the colloidal technique from zinc nitrate. The effect of centrifuge speed on the grain size as well as the crystallinity and the different properties of the resulted powder were studied. The transmission of the as-prepared and annealed films and their optical band gaps are measured and calculated respectively. Artificial and natural dyes are used for ZnO dye-sensitized solar cells. The grain size of the prepared films decreased from 150 to 80 nm by increasing the centrifuge speed. The open circuit voltage of the prepared solar cells ranged from 0.55 to 0.6 V, which indicates good properties of the prepared films using this technique. (C) 2004 Elsevier B.V. All rights reserved.