Effect of Na₂S₂O₃·5H₂O concentration on the properties of Cu₂ZnSn(S, Se)₄ thin films fabricated by selenization of co-electroplated Cu-Zn-Sn-S precursors

Cu₂ZnSn(S, Se)₄ films were fabricated through post-selenization of Cu-Zn-Sn-S precursors co-electroplated by varied Na₂S₂O₃·5H₂O concentrations. The property of obtained films before and after selenization shows a close dependence on the concentration of Na₂S₂O₃·5H₂O. Only the film grown by 5 mM of Na₂S₂O₃·5H₂O shows a uniform surface with faceted grains, a Zn-poor composition, a single phased Cu₂ZnSn(S, Se)₄ structure and a 1.11 eV band gap evidencing by SEM, EDS, XRD, Raman and transmittance spectra. More than 5 mM of Na₂S₂O₃·5H₂O additive to the electrolyte yielded the films with rougher morphology and the presence of SnSe_x. Less than 5 mM of Na₂S₂O₃·5H₂O additive to the electrolyte resulted in the films with highly Zn-poor content and the primary formation of Cu₂SnSe₃.