During the fabrication of a thin film photovoltaic device the transparent conducting oxide (TCO), which constitutes an integral part of its basic structure, could be exposed at high temperature processes; in addition, a TCO which could be grown at ambient temperature can be useful in order to minimize possible damages caused to other previously deposited components. Aluminum doped zinc oxide (AZO) is a well known TCO with good properties in terms of light transparency and conductivity, however its electrical properties deteriorate after subsequent high temperature processes in air atmosphere. On the other hand antimony doped tin oxide (ATO) has poorer conductivity than AZO but has good light transparency and better thermal stability. In the present work, ATO layers with a thickness ranging from 30 nm to 210 nm were deposited over a 600 nm thick AZO layer. These AZO/ATO bilayers, which have been developed at ambient temperature by DC magnetron sputtering, were subsequently annealed at high temperatures in order to study their thermal stability. An ATO optimal thickness of 130 nm is found to improve the bilayer thermal stability at temperatures over 350 degrees C in air atmosphere, keeping good optical properties. (C) 2010 Elsevier B.V. All rights reserved.