Enhanced photoresponse of Cu₂ZnSnS₄ absorber thin films fabricated using multi-metallic stacked nanolayers

Cu₂ZnSnS₄ (CZTS) thin films have attracted considerable attention as potential candidates for photovoltaic absorber materials. In a vacuum deposition technique, a sputtering stacked metallic layer followed by a thermal process for sulfur incorporation is used to obtain high-quality CZTS thin films. In this work, for fabricating CZTS thin films, we have done a 3LYS (3 layers), 6LYS, and 9LYS sequential deposition of Sn/ZnS/Cu metal stack (via. metallic stacked nanolayer precursors) onto Mo-coated corning glass substrate via. RF-sputtering. The prepared thin films were sulfurized in a tubular furnace at 550 °C in a gas mixture of 5% H₂S + 95% Ar for 10 min. We further investigated the impact of the Sn/ZnS/Cu metal stacking layers on the quality of the thin film based on its response to light because metal inter-diffusion during sulfurization is unavoidable. The inter-diffusion of precursors is low in a 3-layer stack sample, limiting the fabricated film's performance. CZTS films with 6-layer and 9-layer stacks result in an improved photocurrent density of ∼38 μA cm^-2 and ∼82 μA cm^-2, respectively, compared to a 3-layer sample which has a photocurrent density of ∼19 μA cm^-2. This enhancement can be attributed to the 9-layer approach's superior inter-diffusion of metallic precursors and compact, smooth CZTS microstructure evolution.