The performance of sputtered CdS/CdTe solar cells with MoO3-x/Au contacts was examined. The cells were fabricated on Pilkington SnO2:F-coated soda-lime glass with a high resistivity transparent SnO2 buffer layer. The MoO3-x/Au back contact layers were deposited by thermal evaporation. The incorporation of the MoO3-x layer was found to improve the open circuit voltage (V-oc) but reduce the fill factor (FF) of the sputtered CdS/CdTe cells. While V-oc is not sensitive to the thickness of the MoO3 layer, FF is very sensitive. The optimal thickness for the MoO3 layer is found to be 2-5 nm, which yields nearly 12% efficiency. The performance of these CdS/CdTe solar cells was further evaluated under thermal stress at 200 degrees C in controlled environments. We found that the cells degraded significantly under thermal stress in air, due to the increase of series resistance or decrease of FF. Published by Elsevier B.V.