Sb2Te3 thin films with thickness of 70, 100, 300, and 600nm were co-evaporated by vacuum evaporation. These films were annealed by 423K, 473K, 523K and 573K, respectively, in the protection of N2 ambient. After that, the film structures were investigated by XRD. Composition of the films was surveyed XRF and XPS. Stoichiometric Sb2Te3 thin films were prepared. Then the Sb2Te3 thin films were applied to CdTe thin film solar cells as back contact layer. The influence of Sb2Te3 thin films thickness on the performances of CdS/CdTe thin film solar cells were surveyed by light I-V characteristics and an efficiency of 12.27%, Voc=808.2mV, Jsc=25.1mA/cm2, FF= 0.6051 was obtained.