Single phase polycrystalline Cu2ZnSnS4 grown by vertical gradient freeze technique

We report on the growth of high quality single phase Cu2ZnSnS4 (CZTS) solar absorber material grown by the vertical gradient freeze (VGF) method for the first time. Polycrystalline CZTS ingot was grown in a vacuum sealed quartz ampoule. Structural and compositional analysis of the grown ingot was carried out by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XRD pattern revealed a highly crystalline tetragonal structure with lattice parameters of a=5.429 Å and c=10.847 Å corresponding to kesterite CZTS crystal. Raman spectra confirmed the existence of single phase CZTS without any secondary phases. Energy dispersive X-ray spectroscopy (EDS) and EDS mapping were performed over a large area of the ingot to evaluate the elemental distribution on multiple polycrystals. The grown crystal was nearly stoichiometric with an atomic ratio of Zn/Sn=1.03 and Cu/(Zn+Sn)=0.964. EDS mapping showed a uniform elemental distribution over the polycrystals and a slight Cu-rich and Zn-poor composition at the grain boundaries.