Cu₂ZnSnS₄ films synthesized from co-electrodeposited Cu–Zn–Sn metallic alloy films

Cu₂ZnSnS₄ (CZTS) is a promising light absorber photovoltaic material due to its p-type conductivity, optimum direct band gap, high optical absorption coefficient, and the fact that it is composed from the abundant and non toxic elements. Among different preparation techniques, solution based routes are attractive due to their simplicity and low cost aspects. In this work the precursor Cu–Zn–Sn metallic alloy films were co-electrodeposited at the threshold cathode potential of −1.10 V (vs. Ag/AgCl reference electrode) on both molybdenum and ITO-coated glass substrates from the bath solutions containing 20 mM of copper, 10 mM of tin, 500 mM of tri-sodium citrate and different high zinc concentrations in the range of 200–600 mM. This approach of using high zinc concentrations in the bath solution and utilizing the least negative cathode potential in order to minimize the film porousity has not been adopted previously. The precursor films were converted to CZTS by a sulfurization process. We studied the effect of high Zn concentration in the bath solution on the composition, structure, morphology, and optical characteristics of the CZTS films using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, Raman spectroscopy, and optical transmittance spectroscopy. Non-porous and uniform near-stoichiometric and phase-pure stoichiometric CZTS films could be synthesized from the precursor films deposited from the 600-mM Zn-containing solution at 25 and 60 °C, respectively.