Critical concentration of Zinc in amorphous silicon solar cells

Transparent conductive oxide (TCO) contacts based on zinc oxide (ZnO) are often used in thin film silicon solar cells and ZnO has a lower contamination potential compared to Tin Oxide or Indium-Tin Oxide. However, in this paper the adverse effects of zinc contamination on solar cell performance in large area systems when using non-optimal processes are demonstrated. Controlled contamination experiments were performed; optical emission spectroscopy allowed us to study the Zn release dynamic; secondary ions mass spectroscopy measurements allowed us to determine the Zn contamination threshold level in a-Si:H solar cells of 1018 at/cm3. Higher Zn concentrations lead to loss of cell performance in the initial state and increased light induced degradation compared to cells with lower contamination. Additionally, a simple approach for Zn contamination removal is presented.