A sputtered Sb-Te modification is identified as a metastable precursor phase of Sb2Te3. The transformation of Sb-Te into monophase Sb2Te3 is characterized by XRD measurements. A simple thermodynamic assessment is introduced for estimating the chemical stability of Ni/Sb2Te3 and Mo/Sb2Te3 double layers. These data and the results of kinetic test reactions for Ni/Sb-Te, Ni/Sb2Te3, Mo/Sb-Te and Mo/Sb2Te3 layers are used to provide a framework for the development of metal/telluride back contact systems for CdTe/CdS thin film solar cells with an improved long-term stability.