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The scalable synthesis of colloidal organohalide perovskite nanocrystals is essential because of increasing demands for their use in many applications such as photovoltaic and light-emitting devices. However, only subgram quantities of perovskite nanocrystals were produced in the typical precipitation synthesis involving excess amounts of nonsolvent, limiting their high-yield production. In this contribution, ligand-assisted ball milling represents a substantial improvement in the scalability of high quality perovskite nanocrystals as well as the corresponding optoelectronic properties (e.g., PLQYs) by the synergetic effect of chemical fragmentation (i.e., ligand exfoliation) and mechanical shearing force. In particular, the formation of perovskite nanocrystals as well as exfoliated nanoplatelets was preferentially developed in the presence of ligands (n-octylamine or octadecylamine) that protect their surfaces after the reaction of solid precursors. This procedure is facile and robust enough to produce kilogram quantities of perovskite nanocrystals with a controlled crystal size, which allows their usage in practical applications.

Organolead halide perovskite nanocrystals (NCs) have emerged as promising materials for various optoelectronic applications. However, their practical applications have been limited due to low structural integrity and poor luminescence stability associated with fast attachment−detachment dynamics of surface capping molecules during postprocessing. At present, a framework for understanding how the functional additives interact with surface moieties of organolead halide perovskites is not available. Methylammonium lead bromide NCs without surfactants on their surface provide an ideal system to investigate the direct interactions of the perovskite with functional molecules. When the oleic acid is used in a combination with n-octylamine, its contribution to surface passivation is significantly increased by protonating the alkyl amine to the corresponding ammonium ion. Our results demonstrate that the Br vacancies at the nonpassivated surface result in a reduction of Pb 2+ to Pb 0 by trapping electrons generated from the exciton dissociation, which provides a main pathway for exciton trapping.

Organohalide perovskite nanocrystals (NCs) with a variety of nano-scale structures and morphologies have shown promising potential owing to their size- and composition-dependent optoelectronic properties. Despite extensive studies on their size-dependent optical properties, a lack of understanding on their morphological transformation and the relevant stability issues limits a wide range of applications. Herein, we hypothesize a mechanism for the morphological transformation of perovskite NCs, which leads to dissolving NCs and forming microscale rectangular grains, resulting in a reduction of photoluminescence. We found that the morphological transformation from nanocrystal solids to microscale rectangular solids occurs via Ostwald ripening. A surface treatment with a surfactant suppresses the transformation, resulting in nearly monodisperse NCs with a square shape (∼20 nm edge size), and thus improves the stability of NC solution, as well as their photoluminescence performance and quantum yield (PLQY = 82%). Furthermore, we employed similar amine derivatives to investigate the effect of a molecular architecture (i.e. steric hindrance) on perovskite NC stability, which exhibited much enhanced PLQY (93%). These experimental results provide new insights into the fundamental relationship between the physical properties and the structure of perovskite nanocrystals required to understand their diverse optoelectronic properties.