3 years ago

Microfluidic Reactors Provide Preparative and Mechanistic Insights into the Synthesis of Formamidinium Lead Halide Perovskite Nanocrystals

Microfluidic Reactors Provide Preparative and Mechanistic Insights into the Synthesis of Formamidinium Lead Halide Perovskite Nanocrystals
Loredana Protesescu, Ioannis Lignos, Andrew J. deMello, Maksym V. Kovalenko, Kim Dümbgen, Richard M. Maceiczyk
Formamidinium lead bromide and iodide (FAPbX3, X = Br, I) in the form of colloidal nanocrystals (NCs) exhibit outstanding photoluminescence properties in the green and infrared regions of the electromagnetic spectrum, characterized by narrow emission line widths (below 90 meV) and high quantum yields (above 90%). The controlled formation of Br-I mixed halide NCs is a facile strategy for tuning band-gap energies, in particular between 700 and 800 nm, not accessible with CsPbX3 NCs. Herein, we report a mechanistic and high-throughput parametric screening study of the synthesis of such NCs using droplet-based microfluidic platforms, equipped with in situ optical characterization. We establish the growth conditions that fully suppress the formation of nanoplatelet impurities in the final colloid and demonstrate that the formation mechanism of FAPbBr3 NCs proceeds via the formation of nanoplatelets as transient species, whereas FAPbI3 forms directly as cubic-shaped NCs. In contrast to CsPb(Br/I)3 NCs, the stability of FAPb(Br/I)3 NCs increases with iodine content. Such NCs form by first nucleating pure FAPbI3 NCs, followed by incorporation of bromide ions.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b02998

DOI: 10.1021/acs.chemmater.7b02998

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