Chemical and electronic properties of CdTe/Sb/sub 2/Te/sub 3//metal contacts for CdTe thin film solar cells studied by photoelectron spectroscopy

Formation of low resistance back contacts in CdTe thin film solar cells has been a research issue for many years. Ohmic contacts to the absorber layer are typically prepared using the diffusion of dopant atoms from the back contact material into the CdTe forming a thin space charge layer that can easily be tunnelled. Stable CdTe solar cells with reasonable back contact characteristics have been prepared using metal/Sb/sub 2/Te/sub 3/ layer sequences. In this study the chemical and electronic properties of such layer systems have been investigated using photoelectron spectroscopy. The vacuum deposited Sb/sub 2/Te/sub 3/ layers do not react with the CdTe substrate. Band alignment does not indicate the formation of a good back contact. By subsequent deposition of metals a chemical reaction is induced forming metal-tellurides, a metal/Sb-alloy and elemental Sb. Although an Sb diffusion into the CdTe absorber is observed, no increase of p-doping in the surface region is evident.