Copper-tin-sulphide (CTS) thin films, obtained by a two-electrode electrochemical deposition of metal precursors, followed by soft annealing and sulfurization

Abstract

CTS thin films have been prepared by soft annealing and sulfurization of electrodeposited Cu-Sn precursors. The stacked elemental layer approach was used to deposit the elemental precursors on an ITO substrate using a two-electrode electrochemical cell, with graphite plate as the counter electrode. The stacked metallic layer was then soft annealed in an Argon atmosphere at 350 °C and subsequently, sulfurized at different temperatures of 500 0C and 550 0C for one hour to form CTS films. The films have been characterized by a variety of techniques. From the XRD analysis, the CTS thin films obtained at a sulfurization temperature of 500 oC showed the coexistence of SnS, Cubic-Cu2Sn3S7 and hexagonal-Cu4S16Sn7 phases. The majority phase was clearly identified as cubic-Cu2SnS3, with (111) preferential orientation. For the films sulfurized at 550 oC, the pattern of prominent peaks showed the presence of the Hexagonal-Cu4S16Sn7 phase of CTS with preferred orientation along the (202) plane. There were relatively fewer low intensity peaks assigned to the secondary phases, indicating an improvement in CTS purity at the higher sulfurization temperature. SEM images of the CTS films show a compact, homogenous morphology, with densely packed grains. The films sulfurized at 550 oC, showed better homogeneity. EDAX spectra of the sulfurized alloy precursors were consistent with the formation of CTS. The film obtained at the lower sulfurization temperature had two band gaps as a consequence of the mixture of phases present in the sample. The film obtained at the higher sulfurization temperature had an energy band gap of 1.5 eV, which falls within the range of values reported in literature. The present work provides a new synthesis route for the electrodeposition of CTS thin film for device applications.