Hot-injection technique approaches are convenient and fast one-pot processes, which are capable of providing colloidal nanocrystals with ultra-narrow size distributions. Effective time separation between nucleation and growth processes is facilitated by fast addition (i.e., injection) of an elemental precursor or reducing agent to the hot reaction mixture. However, it is this fast addition of large volumes that presents a serious challenge for upscaling hot-injection protocols.
Here we focus on the possibility to upscale injection-based syntheses of colloidal nanocrystals without modifying the original protocol or using specially designed jet equipment. This work presents an easy and universal solution for linear upscaling of hot-injection synthesis (Fig. 1). [1] Applying a mild vacuum to the reaction mixture prior the injection enables an injection rate of 100-150 mL·s^-1 such that large volumes of 200-500 mL can be introduced into the reaction flask within few seconds. We apply this underpressure-assisted approach to successfully upscale synthetic protocols for metallic (Sn) and semiconductor (PbS, CsPbBr₃ and Cu₃In₅Se₉) nanocrystals by one-to-two orders of magnitude to obtain tens of grams of nanocrystals per synthesis. We provide the technical details of how to carry out underpressure-assisted upscaling and demonstrate that nanocrystal quality is maintained for the large-batch syntheses by characterizing the size, size distribution, composition, optical properties, and ligand coverage of the nanocrystals for both small- and large-scale syntheses.
This work shows that fast addition of large injection volumes does not intrinsically limit upscaling of hot injection-based colloidal syntheses. An underpressure-governed hot-injection method enables a systematic optimization of nanocrystals and nanocrystal-based devices from a single source batch for research and development purposes and reinforce the commercial viability of electronic, photonic, and electrochemical devices that use large numbers of colloidal nanocrystals (e.g., solar cells, lithium-ion batteries, thermoelectrics, phase-change memories, etc.).

Fig. 1. Schematic illustration of underpressure-governed hot-injection set-up and various colloidal nanocrystals, obtained from single-batch large-scale syntheses

[1] Maksym Yarema, Olesya Yarema, Weyde M. M. Lin, Sebastian Volk, Nuri Yazdani, Deniz Bozyigit, and Vanessa Wood. Chemistry of Materials, 2017, 29, 796-803.