Chemical surface and interface properties of differently stressed (Au/Cu/)CdTe/CdS thin-film solar cell structures

We have investigated the surface and near-surface bulk chemical properties of differently stressed (Au/Cu/)CdTe/CdS thin-film solar cells. The employed Au/Cu contact design created unique samples in which both the back contact surface/interface and the (back) surface of the CdTe absorber were exposed. X-ray photoelectron spectroscopy and soft x-ray emission spectroscopy were employed to determine the chemical composition of the surface and near-surface bulk of both the exposed CdTe surface and the Au/Cu back contact surface of each sample. Sulfur is observed to have migrated (from the CdS) into the CdTe bulk, forming Au₂S and Cu_2-xS compounds under the back contact. Chlorine is found at the surface and in the near-surface bulk of both the back contact and the exposed CdTe absorber. Under the back contact, Cl is observed to form Cu-Cl bonds only in the samples that were heat stressed under AM 1.5 illumination.