Controllable Preparation And Characterization Of Cu₄SnS₄ & Cu₂CoSnS₄ Nanocrystals

With the development of human society, the environmental pollution and global warming issues caused by excessive use of non-renewable energy have attracted more and more attention in recently decades. Solar cells, as a method to use the renewable and environment-friendly solar energy, become the research hot these years. Up to now, the main non-silicon-based solar cell absorber materials are CdTe and Cu(In, Ga)Se2 (CIGS). The toxicity of cadmium and scarcity of indium and tellurium limit their widespread application. Therefore, we need to develop some new non-toxic and abundant raw materials for the low-cost and high efficiency thin film solar cells. Cu4SnS4 (CTS) and Cu2CoSnS4 (CCTS) are direct band-gap semiconductor materials with band-gaps around 1.6 eV and high absorption coefficient, showing the potential application in solar cells. Herein, we focus on the preparation, characterization and related optoelectric properties of CTS and CCTS nanocrystals. The mail work is shown as below:(1) We developed a water/oil interface hydrothermal method to synthesize size-controllable CTS nanocrystals. The growth mechanism of the CTS nanocrystals was revealed through the characterization of X-ray diffraction (XRD), Raman, energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The crystallographic orientation of the hexagonal prism nanocrystals was revealed precisely by high-resolution TEM image analysis.(2) The size and size distribution can be controlled through adjusting the ratio of water and oil phases. The UV-Vis-NIR spectrum and Raman spectrum indicate that there is an obvious quantum size effect when the size of CTS nanocrystals reaches the Bohr radius.(3) The improved two-phase hydrothermal method has also been used to synthesis quaternary CCTS nanocrystals. The morphology of the nanocrystals can be well controlled through using different precursors. It is found that the CCTS nanocrystals present a nanosheet morphology when the oleylamine was used as the ligand, and if the oleylamine and 1-Dodecanethiol was used as the ligand, the nanocrystals present a nanorod morphology.