Growth of Cu2ZnSnS4 crystals by the directional freezing method with an induction heater

Copper zinc tin sulfide (Cu2ZnSnS4: CZTS) crystals were prepared from a Sn solution in a vertical induction furnace by a directional freezing method. The CZTS crystal structure and properties were analyzed by using x-ray diffraction (XRD) and Raman shift measurements. The lattice constants of a- and c-axes calculated from XRD analysis were a=5.426±0.010 Å and c=10.847±0.021 Å. From the Raman scattering spectrum, five CZTS-like-phase peaks at 252 cm−1 (E), 287 cm−1 (A), 338 cm−1 (A), 351 cm−1 (E), and 368 cm−1 (B) were observed. Second phase Raman peaks due to SnxSy corresponding to the Sn-rich CZTS crystals were also observed, but no other secondary phase Raman peaks were found. Overtone Raman peaks up to the fourth multi-phonon were measured in the first time. Although our grown CZTS crystals included secondary phases of Sn compounds, CZTS crystal quality was remarkable.