Oriented Attachment of Perovskite Cesium Lead Bromide Nanocrystals

Abstract

All‐inorganic cesium lead halide (CsPbX3; X=Cl, Br, I) perovskite nanocrystals (NCs) have been appeared as a promising material for various opto‐electronic applications. These perovskite NCs show high absorption co‐efficient, high photoluminescence quantum yield (upto 90%), narrow photoluminescence full width half maxima, color tunable over entire visible range (400‐700 nm) and more stable compared to bulk counterparts. The photo‐physical properties of these NCs strongly depend on the interaction between the outermost atoms and corresponding surface bound organic passivating ligands. Some capping ligands are loosely connected to the perovskite NCs surface and can separate out very easily in presence of polar solvents. Our experimental observations reveal that in present of polar solvents CsPbBr3 NCs agglomerate among themselves via oriented attachment process and create big crystals by an Ostwald ripening process. While highly concentrated spherical CsPbBr3 NCs purified with excess acetonitrile, most of the NCs tends to attach and fuse together in (110) crystal plane to form micrometer sized nanorods. As far as I know, this is the first report on formation of micrometer sized 1‐D CsPbBr3 nanorods from spherical NCs via oriented attachment process at room temperature.

Temperature-Driven Transformation of CsPbBr3 Nanoplatelets into Mosaic Nanotiles in Solution through Self-Assembly

“…Perovskite nanocrystals have the ability to undergo shape and phase transformation by self-assembly, which has been recently exploited to fabricate nanoplates and nanosheets from CsPbBr 3 nanocube superlattices under an external pressure, and to produce nanosheets by applying solvothermal conditions to CsPbX 3 (with X = Cl, Br, and I) nanorods that interact side-to-side . In the building steps of such structures, the oriented attachment between neighboring nanocrystals plays a key role, as it has been also demonstrated for other types of nanocrystals. − Both the transformation and the assembly geometry are affected by the nanocrystal concentration in solution, since the concentration affects the distance between the individual particles. Increasing the particle concentration enhances ligand–ligand interactions, leading to long-range ordered structures; a diluted suspension instead favors ligand destabilization and therefore extended sheets can form via crystallographic oriented attachment .…”

“…26 In the building steps of such structures, the oriented attachment between neighboring nanocrystals plays a key role, as it has been also demonstrated for other types of nanocrystals. [27][28][29] Both the transformation and the assembly geometry are affected by the nanocrystal concentration in solution, since the concentration affects the distance between the individual particles. Increasing the particle concentration enhances strong ligand-ligand interactions, leading to long-range ordered structures; a diluted suspension instead favors ligand destabilization and therefore extended sheets can form via crystallographic oriented attachment.…”

Aging of Self-Assembled Lead Halide Perovskite Nanocrystal Superlattices: Effects on Photoluminescence and Energy Transfer

“…Previously, multiple reports have documented the propensity of CsPbX 3 nanocrystals to coalesce under external stimuli such as light − or heat, − ,, from the destabilizing action of polar solvents, − or spontaneously due to aging in dispersion or on a solid substrate . To gain insight into the transformations of CsPbBr 3 nanocrystals as they age in a vacuum, a series of wide-angle XRD patterns were collected from the sample stored under medium vacuum (∼0.4–0.7 mbar) at room temperature for more than a month.…”

Transformation of Perovskite Nanoplatelets to Large Nanostructures Driven by Solvent Polarity

“…This can be indicative of an Ostwald ripening mechanism, where smaller particles with higher surface energy are sacrificed to form larger particles with lower surface energy. − However, this mechanism would typically be accompanied by a narrowing of the size distribution, whereas we see an increase in both the size and the size distribution of the particles (Figure C–F). Instead, the size distribution analysis indicates that the NPLs are growing due to oriented attachment, in which nanocrystals with identical crystallographic facets “click” together to form larger structures with lower surface energy. , Oriented attachment has been observed in a wide variety of nanomaterials − and has also been observed for both CsPbBr 3 nanocubes and nanoplatelets . For CsPbBr 3 , the attachment process is driven primarily through ligand desorption of the weakly binding oleic acid and oleylamine ligands .…”

“…Instead, the size distribution analysis indicates that the NPLs are growing due to oriented attachment, in which nanocrystals with identical crystallographic facets "click" together to form larger structures with lower surface energy. 59,60 Oriented attachment has been observed in a wide variety of nanomaterials 61−64 and has also been observed for both CsPbBr 3 nanocubes 65 and nanoplatelets. 48 For CsPbBr 3 , the attachment process is driven primarily through ligand desorption of the weakly binding oleic acid and oleylamine ligands.…”