Cu2ZnSnS4 thin films prepared by sulfurization of co-electrodeposited metallic precursors

Abstract

Cu2ZnSnS4 (CZTS) thin films were prepared by thermal sulfurization of co-electrodeposited CuZnSn (CZT) metal precursors. Electrodeposition times between 10 and 40 min were used to study the influence of this parameter on the composition, structure, thickness, and morphology of the sulfurized films. CZT precursors and CZTS films were characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and Raman spectroscopy. The morphologies were evaluated by electronic microscopy. The electrodeposition time was found to influence the chemical composition of the metal precursor, especially the Cu and Sn content. Furthermore, XRD results showed the formation of Cu5Zn8, while Sn seemed to be present in an amorphous state. A cauliflower-like morphology was observed in the precursors, especially at long deposition times, which can be related to an electrodeposition mechanism controlled by mass transfer. A significant increase of the film thickness was observed after sulfurization. The morphology changed to round particles and presented a bi-layered structure with an internal compact layer of nanometer size particles and an external layer formed by micrometer-size particles. Raman spectroscopy, XRD, and EDS measurements confirmed the formation of crystalline CZTS after sulfurization. In addition, a disperse Cu2S secondary phase co-existed in the film. Increasing the precursor deposition time increased the amount of secondary phases in the film after sulfurization. Direct energy gap values close to 1.5 eV were estimated for CZTS films using transmittance spectra in the infrared region. CZTS films obtained with short electrodeposition times are promising as absorbers in kesterite thin films solar cells.