Colloidal quantum dots (QDs) with versatile solution processability are generating new opportunities in multiple areas including photovoltaics, imaging, solid-state lighting and displays. Predominantly studied cadmium chalcogenides based QDs exhibit high toxicity and hence, in recent years the interest of industry and academia has shifted towards alternate heavy-metal free materials. Majority of the work reported in the literature has focused on QD synthesis using small-scale conventional batch synthesis approach, that limits precise control over reaction conditions – precursor injection, heating rates, temperature, and pressure. As an alternate synthesis approach, continuous flow synthesis offers two-fold advantage: (i) better control over reaction parameters, thus improving the tunability of size, shape, and composition of QDs in a reproducible manner; and (ii) a viable platform for investigating nucleation and growth of QDs.<br/>This presentation will focus on design and implementation of a modular flow reactor setup for synthesis of monodisperse InP QDs. Our unique flow reactor platform allowed the synthesis of InP/ZnSeS core-shell quantum dots exhibiting 67% QY with ability to tune the emission wavelength by simply varying the process parameters (flow rates, temperature and concentration) at different stages. The flow reactor platform also allowed mechanistic investigation of InP QD growth using aminophosphines precursors. Our results show that the presence of excess zinc source shifts equilibrium between two active species involved in the precursor conversion reaction. To further investigate the InP flow chemistry, we developed a dual-stage strategy that enables heating of the precursor streams, first to the nucleation temperature and then a rapid quenching of precursors to the growth temperature (all within 1.5 seconds), thus allowing spatial separation of nucleation and growth. The application of dual-stage reactor platform allowed tuning both the nucleation and growth parameters independent of each other as an additional synthesis knob. A comparison with conventional batch synthesis, and single stage flow synthesis approach further confirms the advantage of spatially-separated nucleation and growth strategy for size-focused growth of InP QDs.

Investigating nucleation and growth kinetics of indium phosphide quantum dots in a continuous flow reactor

2019 Fall National Meeting

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