Radio frequency (rf)-sputtered indium tin oxide (ITO) thin films were characterized by studying their structure, electrical and optical properties. Before characterization the ITO films were annealed at different temperatures ranging from 100 to 500 degreesC for a constant time of 15 min in air. The ITO thin films were observed to possess a cubic structure with (110) texture, an electrical resistivity in the range (5-11.5) x 10(-4) Omega cm at different annealing temperatures. The rise in resistivity due to annealing was associated with the filling up of oxygen vacancies, and the fall in resistivity was attributed to the rearrangement and removal of defects as well as improvement in the crystalline nature of these films. The optical bandgap energy was found to be approximate to4.0 eV. The ITO thin films were of comparable quality to those deposited elsewhere for use as window layers in solar cells. (C) 2003 Published by Elsevier B.V.