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 10(18) at/cm(3). 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. (C) 2015 Elsevier B.V. All rights reserved.