Preparation and characterization of sphere-like Cu₂SnS₃ nanoparticles and their dropcasted thin films

Ternary sphere-like Cu₂SnS₃(CTS) semiconductor and 2D hexagonal sheets were synthesized via a simple solvothermal method using PVP as the surface ligand at two temperatures of 180 and 220 °C. The structural, morphological, and chemical compositions as well as optical properties of as-synthesized CTS particles were characterized using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectrometry (EDS), field emission scanning electron microscopy (FESEM), and UV–Vis spectroscopy. The size of sphere-like particles and the side length of hexagonal sheets were within the range of 120–140 nm and 500 nm–$2\mu m$, respectively. FESEM, XRD, and EDS were analyzed to investigate the mechanism of the morphological evolution of CTS particles. CTS particles showed proliferation of Sn atomic ratio, which is strongly sensitive to reaction temperature and, highly affects the increase of band gap energy from 1.36 to 1.53 eV due to generation metal defects and formation SnS₂. The optical analysis via the transmittance and reflectance reveals that the band-gap energy of dropcasted CTS thin films decreases after annealing due to grain growth and change of chemical compositions. Photo-responses of CTS nanocrystal thin films indicated a considerable increase in the conductivity of the films under light illumination. All these results showed the potential of these films for solar cell applications. (paper)