Composition controlled preparation of Cu-Zn-Sn precursor films for Cu2ZnSnS4 solar cells using pulsed electrodeposition

A pulsed electrodeposition technique is developed to prepare Cu-Zn-Sn (CZT) precursor films for the Cu2ZnSnS4 (CZTS) solar cells. The CZT precursor films are co-deposited on Mo-coated substrate using a cyanide-free electrolyte containing Zn (II) and Sn (II) salts. During the deposition, CuSO4 solution is supplied at controlled rate using a peristaltic pump to effectively regulate Cu2+ concentration. In addition, C6H5Na3O7 is used as a coordination ligand to further balance activities of the Cu2+, Sn2+ and Zn2+. The CZTS films are then prepared using a sulfurization process to convert the electrodeposited CZT precursors at 580 °C in a sulphur atmosphere. The annealed thin films are characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), EDAX and X-ray photoelectron spectroscopy (XPS) techniques for their structural, morphological, compositional and chemical properties. It is found that the addition rate of Cu (II) has significant effects on the properties of the CZTS thin films. The CZTS film prepared using the optimized copper addition rate (0.15 ml/min) shows pure kesterite phase, Cu-poor and Zn-rich composition, compact morphology and good band gap ∼1.45 eV. Solar cells using the structure glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al achieves a respectable external quantum efficiency and solar cell efficiency.