Impact of pre-alloying of sputtered Cu/Sn/Zn precursors for Cu2ZnSnS4 thin films

The Cu2ZnSnS4 (CZTS) films were prepared by sulfurizing the sputtered Cu‒Sn‒Zn precursors. The precursors were fabricated by sequentially sputtering of Cu, Sn and Zn metallic layers onto Mo-coated glass substrate. The effects of alloying before sulfurization on the structural and optical characteristics of the CZTS films were presented. Two independent sulfurization processes were carried out and compared. The sulfurization of the reference was completed in the tube furnace at 550 °C for 2 h. In the two-stage heat treatment approach, the precursor was alloyed at various temperatures before the sulfurization. Experimental results showed that alloying at 170 °C was crucial to improve the CZTS films, yielding uniform and dense grains with single kesterite CZTS phase.