Sn-deficiency in the electrodeposited ternary Cu_xSn_yS_z thin films by ECALE

Ternary Cu_xSn_yS_z thin films with different Cu/Sn atomic ratios and thicknesses have been electrochemically deposited on the (111) face of a silver single crystal. The surface morphology and chemical composition of these chalcogenides, which have attracted considerable worldwide interest as low cost high conversion efficiency photovoltaic devices, have been characterized by means of SEM, parallel angle resolved (PAR-XPS) and TOF-SIMS depth profiling in order to gain insight into the morphology and element distribution within the layer and their effect on the band gap. This study constitutes the first in-depth chemical study on Cu_xSn_yS_z thin films, providing evidence of notable discrepancies between the expected and real composition, especially regarding the Cu/Sn ratio. The samples were found to be chemically homogeneous through the whole deposit even though strongly tin depleted regardless their thickness or deposition sequence. Finally, the literature band gap data were discussed on the basis of these findings.