Reaction pathway for synthesis of Cu₂ZnSn(S/Se)₄ via mechano-chemical route and annealing studies

Reaction pathway for the formation of kesterite Cu₂ZnSn(S/Se)₄ (CZTS/Se) from elemental precursors (Cu, Zn, Sn, S/Se) has been investigated experimentally and is being reported in the current paper. To identify the various stages of reaction pathway and to identify the formation and consumption of secondary phases, X-ray diffraction and Raman spectroscopy tools were employed. A series of experiments for different ballmilling durations (5, 10, 15, 20, 25 and 30 h) were performed and the presence of different phases was recorded for each experiment. In addition to XRD and Raman studies, phase formation has also been confirmed using detailed XPS, TEM and SEM–EDS analysis. In addition, the effect of annealing temperature on composition and band gap of the CZTS/Se material has been discussed. Optical band gap of various samples of CZTS was observed in the range of 1.40–1.60 eV and that of CZTSe was observed in the range of 1.08–1.18 eV. The relatively simple, low cost, easily scalable mechanical alloying process along with understanding of reaction pathway will provide a future scope for bulk production of CZTS/Se absorber material for thin film solar cells.