Phase transition in Cu2+xSnS3+y (0 ≤ x ≤ 2; 0 ≤ y ≤ 1) ternary systems synthesized from complexes of coumarin derived thiocarbamate motifs: optical and morphological properties

Abstract

Tetragonal Cu₂SnS₃ and orthorhombic Cu₄SnS₄ nanocubes were synthesized by a heat up procedure with oleylamine (OLA) and dodecanethiol (DT) acting as both solvent and capping ligands. Both mohite–anorthic and monoclinic phases were obtained from the same variant of precursors mixture, by hot injection synthesis, at 200 and 250 °C. Changing the reaction conditions also leads to the formation of different morphologies. When OLA was used as a solvent, nanosheets or nanocubes were obtained, while the reaction with DT resulted in the formation of particles in the form of nanohexagons. The growth process of copper tin sulphide starts with the formation of Cu⁺ seeds, followed by the oxidation of Sn²⁺ to Sn⁴⁺. Dodecanethiol was an additional source of sulphur. The overall reaction leads to the formation of either phase pure Cu₂SnS₃ or Cu₄SnS₄, depending on the reaction conditions, with band-gap energies of 1.05–1.45 eV, which are in the optimum range for photovoltaic applications.