Cu(In,Ga)Se₂ (CIGS) is the main photo-absorption layer of thin-film solar cells; however, relative scarcity of In and Ga elements and the selenization using toxic H₂Se gas inhibit its practical usage. Cu₂ZnSnS₄ (CZTS) becomes the promising alternative due to its similar physical properties to CIGS, abundance of Zn and Sn elements in earth and low toxic preparation method. Moreover, the bandgap of CZTS can be modulated by adding selenium (Se) to form the CZTSSe so as to improve the performance of photovoltaic (PV) devices.

This work adopts the CuSe, ZnS and SnS₂ binary alloy powders as the starting ingredients to prepare the single-phase CZTSSe sputtering target. The powders were mixed at the molar ratio of Cu:Zn:Sn = 1.6:1:1, pressured into the pellets form with 6 mm in diameter, sintered in the N₂ ambient at temperatures ranging from 200 to 600°C for 8 hrs. The microstructures and phase constitutions of pellets subjected to various sintering treatments were then characterized in order to identify the sintering condition that may yield the single-phase CZTSSe structure.

The phase evolution in pellets characterized by x-ray diffraction (XRD) revealed that the single-phase kesterite CZTSSe structure can be obtained by the sintering at 600°C and the energy dispersive spectroscopy (EDS) indicated its stoichiometric ratio is Cu_26.18Zn_13.73Sn_12.02S_35.22Se_11.86 which is close to the ideal ratio of 2:1:1:4.

The 2-inch CZTSSe sputtering target was then prepared for CZTSSe layer deposition in accord with the optimized sintering condition. XRD and Raman spectroscopy analyses revealed the deposited CZTSSe layer subjected to the post annealing at 570°C for 1 hr in N₂ ambient also possesses the single-phase kesterite structure. EDS analysis found its stoichiometric ratio is Cu_24.50Zn_14.02Sn_13.92S_38.20Se_9.36 which are close to the ideal ratio of 2:1:1:4 with the Cu-poor/Zn-rich feature. Presently, the CZTSSe layers with desired grain morphologies and compositions are transferred to the preparation of thin-film solar cell and its PV performance is evaluated.