Effect of periodic precursor on sulfurization process of Cu2ZnSnS4 thin film

Abstract

In this study, Cu2ZnSnS4 (CZTS) thin films were fabricated by periodically sequential depositions of metallic precursors by magnetron sputtering followed by sulfurization. The element compositions, crystal structures, and surface morphologies of the single-period precursor (Zn/Sn/Cu) and four-period precursor (Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu/Zn/Sn/Cu) during the sulfurization process were investigated. The experimental results showed that in the initial stage of sulfurization, the single-period precursor had a more efficient reaction with sulfur vapor below 300 °C because of its thicker metal layers. During the process of sulfurization, the CZTS phase first formed in the four-period film at 400 °C, owing to the wide distribution of the internal layer in the periodic thin film. With a further increase in temperature, the crystallinity of CZTS was enhanced and the secondary phases were reduced. A CZTS phase with Cu-poor and Zn-rich composition was confirmed in both thin films after complete sulfurization. The CZTS thin film with a four-period precursor showed a better degree of crystallization, and a single phase of CZTS was obtained more easily than in the single-period thin film. Therefore, using a periodic structure can promote the sulfurization reaction of Cu-Zn-Sn precursors and enhance the properties of CZTS thin films.