Solvent effect in the synthesis of Cu–In–S and Cu–In–Se nanocrystals with tunable structure and composition

The role of the solvent in the preparation of ternary CuInX₂ (X = S or Se) nanocrystals was investigated. It was found that the use of oleylamine as a solvent with copper(II) oleate, indium(III) acetate diphenyl diselenide as precursors yields copper-rich, wurtzite-type Cu_2.0In_1.0Se_2.5 (2Cu₂Se–In₂Se₃) nanocrystals which after size sorting exhibit the quantum confinement effect. Changing oleylamine for 1-octadecene, while keeping the same set of precursors and reaction conditions, results in the formation of indium-rich chalcopyrite nanocrystals Cu_1.0In_1.8Se_3.2 (Cu₂Se-1.8 In₂Se₃). The differences in the stoichiometry can be rationalized on the basis of stronger reducing properties of oleylamine which more effectively reduces Cu(II) to Cu(I) in the reaction medium. Stoichiometric chalcopyrite CuInSe₂ nanocrystals can be obtained in the same conditions by exchanging diphenyl diselenide for the Woollins' reagent, never previously applied to the preparation of Cu–In–Se nanocrystals. In the case of Cu–In–S nanocrystals the chemical composition is governed not by the type of the solvent but by the reducing properties of 1-dodecanethiol, the precursor of sulfur. Independently of the solvent copper-rich nanocrystals are obtained of either wurtzite-type Cu_1.6In_1.0S_2.3 (1.6 Cu₂S–In₂S₃) in 1-octadecene or chalcopyrite-type Cu_1.8In_1.0S_2.4 (1.8 Cu₂S–In₂S₃) in oleylamine. - Graphical abstract: Display Omitted - Highlights: • The role of the solvent in the preparation of ternary nanocrystals was investigated. • OLA yields wurtzite-type Cu_2.0In_1.0Se_2.5 and chalcopyrite-type Cu_1.8In_1.0S_2.4. • ODE yields chalcopyrite-type Cu_1.0In_1.8Se_3.2 and wurtzite-type Cu_1.6In_1.0S_2.3