Abstract

Colloidal semiconductor nanocrystals or quantum dots (QDs) attract extensive interest in nowadays science. For the characterization of their materials properties and their use in applications, the synthesis of QDs with sharp size distributions at a desired mean size is of fundamental importance. In widely used colloidal synthetic strategies based on hot injection, size control is achieved by adjusting the reaction time. Although highly successful, these procedures have an intrinsic drawback: sizes below the size reached at the end of the reaction driven growth regime (post-focused size) are only obtained at the expense of a reduced reaction yield. Here, we propose two strategies for controlling the post-focused size, either by adjusting the initial nucleation rate or the solubility of the reactive monomer. We first explore these concepts by means of a QD synthesis model that is based on the assumption that nucleation and growth of QDs involves a monomer species, formed at a specific rate from the initial precursors. Next, the modeling predictions are verified using a synthesis for CdSe QDs. This involves the confirmation of the basic model assumption, i.e., the formation of a monomer species, and the demonstration of size tuning at full yield from diameters of 2.8 to 4.1 nm. Our strategy thus makes it possible to prepare monodisperse batches of different sized QDs at high yield, which is a key result for synthesis reproducibility and efficient reaction upscaling.

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