Chemical stability of Sb2Te3 back contacts to CdS/CdTe solar cells

The chemical stability of back contact materials and metallisations like Sb 2Te3 and Ni:V alloys to CdS/CdTe solar cells was investigated. Ternary and quaternary (Cd-Sb-Te-O, Sb-Ni-Te-O) phase diagrams were calculated using th ermodynamic data. By applying these diagrams to CdTs/Sb2Te3 or Sb2Te3/Ni-V interfaces used as back contacts in CdS/CdTe solar cells, predictions could be made about chemical stability and possible interface reactions. The pha se diagrams and predicted chemical behaviour were proven by some test react ions. Products and reactions were characterised by XRD and DSC. It was foun d that the CdTe/Sb2Te3 interface is in thermodynamic equilibrium and no rea ction occurs. Sb2Te3/Ni and Sb2Te3/V interfaces are not in thermodynamic eq uilibrium and reaction products like NiTe, NiTe2 or V2Te3 are found in test reactions at low temperatures (200 degrees C) after very short times (1 h) , and in the case of V even at room temperature. It is therefore expected t hat chemical reactions at these interfaces will lead to both degradation of the Sb2Te3 and the Ni-V layer and may influence the efficiency of CdS/CdTe solar cells. (C) 2000 Published by Elsevier Science S.A. All rights reserv ed.