Tunable optical properties of ternary non‐stoichiometric Cu–In–S nanocrystal emitters

Low toxic, non-stoichiometric colloidal copper–indium–sulphur [Cu–In–S (CIS)] ternary quantum dots with different Cu:In molar ratios by a hot-injection method in octadecene was synthesised. The Cu:In precursor molar ratios were 1/10, 1/20 and 1/40. Varying the fraction of cationic and capping agents, the compositions of CIS nanocrystals were precisely controlled. The photoluminescence (PL) results reveal that, reducing the Cu:In ratio in the CIS is the feasible strategy for bandgap engineering. Tunable PL emissions have been observed. X-ray powder diffraction and high-resolution transmission electron microscopy results indicate that as-prepared CIS nanocrystals are compositional homogeneity. The single-crystal nature of CIS nanocrystals improves the relative PL quantum yield up to 12%, which exhibits substantial enhancement comparing with the stoichiometric CuInS2 and CIS-based semiconductor core QDs. The PL decay curve of CIS has a triexponential feature. The value of τ1, τ2 and τ3 of CIS sample agree well with CuInS2 core QDs. The average PL lifetime of CIS is reduced to 146.9 ns, which can be attributed to the reduction of surface-related trap states.