Alternative back contacts for CdTe solar cells:: a photoemission study of the VSe2/CdTe and TiSe2/CdTe interface formation

Low resistance ohmic and stable back contacts are still one of the major issues in improving CdTe based solar cells. According to band alignment arguments chemically inactive and conductive materials of high work functions are most promising for CdTe back contacts. In this study VSe2/CdTe and TiSe2/CdTe interfaces have been prepared by PVD under vacuum conditions and subsequently characterized by photoelectron spectroscopy in order to determine their electronic properties. Despite the high work function of the contact materials (5.7-5.8 eV) no ohmic contacts have been realized. Obviously, a thin Cd interlayer is formed before stoichiometric CdTe growth occurs leading to an interface dipole that compensates the high work function of VSe2 and TiSe2. The resulting band energy diagrams are presented in this study. (C) 2003 Elsevier Science B.V. All rights reserved.