<p>Advances
in automation and data analytics can aid exploration of the complex chemistry
of nanoparticles. Lead halide perovskite colloidal nanocrystals provide an
interesting proving ground: there are reports of many different phases and
transformations, which has made it hard to form a coherent conceptual framework
for their controlled formation through traditional methods. In this work, we systematically explore the portion of Cs-Pb-Br
synthesis space in which many optically distinguishable species are formed using high-throughput robotic synthesis to understand their formation reactions. We deploy an automated method
that allows us to determine the relative amount of absorbance that can be
attributed to each species in
order to create maps of the synthetic space. These in turn facilitate improved
understanding of the interplay between kinetic and thermodynamic factors that underlie which
combination of species are likely to be prevalent under a given set of
conditions. Based on these
maps, we test potential transformation routes between perovskite nanocrystals
of different shapes and
phases. We find that shape is determined kinetically, but many reactions between different phases show equilibrium behavior. We
demonstrate a dynamic equilibrium between complexes, monolayers and
nanocrystals of lead bromide, with substantial impact on the reaction outcomes.
This allows us to construct a chemical reaction
network that qualitatively explains our results as
well as previous reports and can serve as a guide for those seeking to prepare
a particular composition and shape. </p>
Vibrational study of lead bromide perovskite materials with variable cations based on Raman spectroscopy and density functional theory
