A facile and low-cost synthesis of promising absorber materials on Cu ₂ZnSn(S _x,Se _1-x) ₄ nanocrystals consisting of earth abundant elements with tunable band gap characteristics

In this paper, we report a facile, low cost synthesis and characterization of kesterite Cu ₂ZnSn(S _x,Se _1-x) ₄ (CZTSSe) nanocrystals (NCs) by a two-step process involving a solution-based precursor and a post-annealing route. The effects of different Se vaporization temperatures, ranging from 350 °C to 550 °C, on the structural, chemical, compositional, and optical properties of CZTSSe NCs were investigated. X-ray diffraction patterns, Raman spectroscopy, and transmission electron microscopy results indicated that the precursor powder showed several broad peaks that could not be assigned to Cu ₂ZnSnS ₄ (CZTS), ZnS, Cu _2-xS, Sn ₂S ₃ and Cu ₂SnS ₃. However, the post-annealed NCs with and without Se vaporization were a single kesterite CZTS phase without a secondary phase. UV-vis spectroscopy results showed that the absorption coefficients of all the post-annealed NCs were over 10 ⁴ cm ^-1 in the visible region, and the optical band gap energy decreased systematically from 1.46 eV to 1.14 eV with increasing Se vaporization temperatures.