Syntheses of Cu2SnS3 and Cu2ZnSnS4 nanoparticles with tunable Zn/Sn ratios under multibubble sonoluminescence conditions.

Cu2ZnSnS4 (CZTS) nanoparticles were synthesized by sonochemical reactions under multibubble sonoluminescence (MBSL) conditions. First, Cu2SnS3 (CTS) nanoparticles were synthesized by the sonochemical method with a 91.3% yield. Second, ZnS was coated on Cu2SnS3 nanoparticles by the same method. Then, they were transformed into CZTS nanoparticles of 90-300 nm diameter by heating them at 450 °C for 1 hour. The ratios between Zn and Sn could be controlled from 0.20 to 1.32 by adjusting the relative concentrations of Cu2SnS3 and ZnCl2. With relatively lower Zn : Sn ratios (0.20-0.41), there was a mixture of CTS and CZTS nanoparticles. The prepared nanoparticles show different band gaps from 1.19 to 1.52 eV depending on the zinc to tin ratio. In this sonochemical method without using any toxic or high temperature solvents, the specific stoichiometric element ratios in CZTS were controllable on demand and their experimental results were always reproducible in separate syntheses. The CZTS nanoparticles were investigated by using X-ray diffraction, a UV-Vis spectrophotometer, a scanning electron microscope, Raman spectroscopy, and a high resolution-transmission electron microscope.