Optimization of back contacts for CdTe solar cells using sputtered CuxTe

For cadmium telluride solar cells, the back contact material and its properties are still a challenge in terms of increasing and stabilizing the efficiency. This paper discusses RF magnetron sputtering of three different stoichiometries of Cu_xTe (x= 1, 1.4, 2) material for back contacts to sputtered CdTe solar cells. Thin films were grown first on aluminosilicate glass (ASG) to optimize resistivity, carrier concentration, and mobility and to identify the crystallographic phases of Cu_xTe. Films were then deposited on complete cell structures to determine efficiency and other cell performance parameters. Thickness and post-deposition annealing temperature were varied to optimize cell performance. Among the three compositions, the Cu₂Te target produced the best efficiency at 200°C substrate temperature using conditions that yielded Cu_1.4Te as the dominant phase in the sputtered films. This produced cells with efficiency of >;13%.