Synthesis of Cu2ZnSnS4 films from co-electrodeposited Cu–Zn–Sn precursors and their microstructural and optical properties

The Cu2ZnSnS4 (CZTS) films were successfully prepared using a process of co-electro-deposition of Cu–Sn–Zn precursors by a novel electrolyte formula and optimized parameters on Mo substrates, succeeded by annealing in saturated sulfur atmosphere. The optimized electrolyte formula was achieved as 0.16 M CuSO4·5H2O, 0.33 M ZnSO4, 0.08 M SnCl2·2H2O, 2.25 M NaOH, 1.36 M C6H5Na3O7 and 1.00 M C4H6O6 under a voltage of −1.62 V for 5 min. Cu3Sn, Cu6Sn5 and Cu4Zn alloys were firstly synthesized at temperature lower than 300 °C. At 300 °C, these alloys decomposed in sulfur atmosphere and CuS, SnS and ZnS binary phases were formed. Ternary Cu4SnS6 formed through reaction between CuS and SnS above 350 °C. Finally, the CZTS films were synthesized through reaction among CuS, SnS, ZnS and Cu4SnS6 sulfides. CZTS films synthesized at 550 °C for 1 h had an average atomic ratio of 0.96 and 1.1 for Cu/(Zn + Sn) and Zn/Sn, respectively. The photoluminescence peaking at about 1.55 eV in the prepared samples demonstrated a high quality of the CZTS film.