Scalable production of CuInS2/ZnS quantum dots in a two-step droplet-based microfluidic platform

We report the scalable formation of CuInS2/ZnS nanocrystals using a two-stage microfluidic reactor integrated with a real-time optical detection system, which is able to monitor reaction parameters prior and subsequent to the addition of the shell material. By injecting a ZnS single source precursor in droplets containing CuInS2 cores and without the need of purification steps, we are able to obtain core-shell nanocrystal populations emitting between 580 and 760 nm with significant narrower size distributions (90-95 nm) than for the same material systems synthesized on the macroscale. In-line monitoring allowed for rapid assessment of optimum reaction parameters (Cu/In, S/(Cu + In), Zn/(Cu + In) molar ratios, temperatures and reaction time) and enabled the formation of CuInS2/ZnS nanocrystals with high photoluminescence quantum yields (similar to 55%) within a few seconds. We believe that this synthetic methodology will be of significant utility in controllable production of ternary and quaternary metal chalcogenides, complex core-shell and doped nanostructures.