Cu2ZnSnS4 (CZTS) thin films grown by sulfurization of different precursor layers in sulfur atomsphere

Cu₂ZnSnS₄ (CZTS) thin films have been grown by two step process. Two different precursors; one is stacked layer consists of Cu/ZnSn/Cu and the other one is single layer from an alloy target of Cu-Zn-Sn were deposited onto Mo coated soda lime glass substrates kept at RT by Dc sputtering. The precursor layers were converted into CZTS films by annealing at 560°C for 6 min in sulfur atmosphere. The XRD pattern of the stacked precursor layer consists of Cu₃Sn, CuZn, Cu₆Sn₅, Sn phases suggests that Cu diffuses into the ZnSn during the precursor deposition and forms binary phases. CZTS films grown with stacked precursors were single phase Kesterite with (112) orientation. The films exhibited dense morphology with submicron grain sizes and fine grains at the interface between CZTS and Mo. On the other hand the precursor grown with Cu poor and Zn rich alloy target showed peaks of corresponding to binary metallic phase Cu₆Sn₅. The CZTS films obtained at 560°C for 6 min showed non uniform surface with voids. The cross-sectional morphology of the films shows dense columnar grains. The solar cells fabricated with these films showed no performance due to porous and inhomogeneous surface morphology. We found that the CZTS films grown with stacked precursor layers deposited with Cu and ZnSn targets have shown better properties. Solar cells fabricated with this CZTS absorber showed an efficiency of 4.7% with an open circuit voltage of 632 mV, a short circuit current density of 15.80 mA/cm² and fill factor 47.13% for an area of 0.44 cm².