Investigation on the properties of Cu 2 ZnSnSe 4 and Cu 2 ZnSn(S,Se) 4 absorber films prepared by magnetron sputtering technique using Zn and ZnS targets in precursor stacks

Abstract

Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 absorber films were grown on soda lime glass and Mo-coated soda lime glass substrates by deposition of the precursor films via RF magnetron sputtering method in the stacking orders of Cu/Sn/Zn/Mo/SLG and Cu/Sn/ZnS/Mo/SLG using metallic Zn or binary sulfide ZnS targets and subsequently carrying out of selenization process. It was aimed to find out the effect of Zn or ZnS target types and the small amount of S originated from ZnS target material used in the deposition of precursor films on the structural, morphological, optical, and electrical characteristics of the films to be selenized. XRD and Raman spectroscopy analysis showed that the kesterite CZTSe structure was predominantly formed in both cases where Zn and ZnS targets were used. According to the EDX analysis, S content in the prepared film using ZnS target was only around 1.79 at%. This indicated that a considerable amount of S in the film was driven out during the selenization process. Scanning electron microscopy analysis revealed that ZnS target material contributed to the achievement of the absorber films with larger grain size. It was also determined that the thickness of the interfacial MoSe2 film between the absorber and Mo films decreased by using ZnS target in the precursor film. This was attributed to ZnS layer with a high melting point acting as a barrier layer over Mo film and retarding the diffusion of Se into the Mo film during the selenization process. In addition, the band gap energy values of the Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 films were found to be 1.18 and 1.28 eV, respectively.