Controllable colloidal synthesis of anisotropic tin dichalcogenide nanocrystals for thin film thermoelectrics

Tin chalcogenides have shown promise in applications including energy storage, optoelectronics, photovoltaics, and thermoelectrics. Here, we present a colloidal synthesis strategy to produce tin dichalcogenide nanocrystals (NCs) with controllable stoichiometry, vacancies, shape, and crystal structure. Compared with previously reported methods, we use less expensive precursors, such as tin(iv) chloride and sulfur or selenium powder, to produce tin(iv) chalcogenide NCs. SnS₂ and SnSe₂ NCs with novel NC morphologies including SnS₂ nanoflowers/nanoflakes, SnSe₂ nanosheets with circular and hexagonal shapes, as well as mixtures of nanospheres and nanoflakes were prepared by varying the solvents and anion precursors. We were also able to reduce tin(iv) to tin(ii) to produce tin(ii) chalcogenide NCs. The corresponding thin films were prepared by spin-coating, followed by post-treatment to study their thermoelectric properties. Room temperature Seebeck coefficients of -150 μV K^-1 and -126 μV K^-1 were measured for SnS₂ and SnSe₂ films, demonstrating their promise as thin film thermoelectric materials.