Transformation of Metal Halides to Facet-Modulated Lead Halide Perovskite Platelet Nanostructures on A-Site Cs-Sublattice Platform

Abstract

The conversion of metal halides to lead halide perovskites with B-site metal ion diffusion has remained a convenient approach for obtaining shape-modulated perovskite nanocrystals. These transformations are typically observed for materials having a common A-site Cs-sublattice platform. However, due to the fast reactions, trapping the interconversion process has been difficult. In an exploration of the tetragonal phase of Cs7Cd3Br13 platelets as the parent material, herein, a slower diffusion of Pb­(II) leading to facet-modulated CsPbBr3 platelets is reported. This was expected due to the presence of Cd­(II) halide octahedra along with Cd­(II) halide tetrahedra in the parent material. This helped in microscopically monitoring their phase transformation via an epitaxially related core/shell intermediate heterostructure. The transformation was also derived and predicted by density functional theory calculations. Further, when the reaction chemistry was tuned, core/shell platelets were transformed to different facet-modulated and hollow CsPbBr3 platelet nanostructures. These platelets having different facets were also explored for catalytic CO2 reduction, and their catalytic rates were compared.

Lead Halide Perovskite Cube Coupled Star Nanocrystal Photocatalysts

“…Hence, understanding facet chemistry and facet dependent anisotropic growth leading to shape modulations could not be largely understood. Literature reports revealed that modifying surfaces and using specific ligands, cubes, multifaceted polyhedrons, platelets, and rods/wires of these nanocrystals could be designed. ,− However, these shapes are limited and need further exploration. Moreover, for the ionic nature and fast formation of these nanocrystals, shape modulation following a classical approach remained indeed difficult.…”

“…These reactions were very fast, and hence, decoupling steps to understand the exact growth process remained indeed difficult. Literature reports revealed that Cd­(II) has been extensively used for the synthesis of different perovskite nanostructures, ,,, but in either case, no such cube coupled star nanocrystals were reported. However, it is also established that the formation of an intermediate heterostructure such as CsPbBr 3 –Cs 2 CdBr 4 and CsPbBr 3 –Cs 7 Cd 3 Br 13 is possible during shape conversion. , This provided the initial impression of heterostructure induced secondary nucleations leading to cube coupled star nanocrystals.…”

Tuning Crystal Plane Orientation in Multijunction and Hexagonal Single Crystalline CsPbBr3 Perovskite Disc Nanocrystals

“…In addition to multijunctions, in most cases, these were observed to be hollow at the center. This was expected due to incomplete ion replacement and the elimination of the host part of the parent nanocrystals at the center during annealing . More representative TEM and HRTEM images of these multijunction CsPbBr 3 disc nanocrystals having more than four junctions are shown in Figures S16–S18.…”

“…In either case, the Cs-sublattice structure remains common, and as Cs is larger in size, the lattice structures are expected to be rigid during this ion exchange process. There are several such reports on Cs-sublattice structures which helped in interconversions between metal halides and lead halide perovskite crystals. ,− Hence, in this case also the Cs-sublattice structure determined the pathways of such unique 2D-shaped nanostructure formation.…”

“…Two-dimensional semiconductor platelet/disc-shaped nanocrystals are important for their 2D quantum confinements and unique self-assembly. − For the recently emerged lead halide perovskite nanocrystals, these 2D structures have also been extensively studied. − Their reaction modulations and formation chemistry have also been largely understood. ,,− Among these, orthorhombic CsPbBr 3 platelets have shown better phase stability and are most widely investigated. − ,,,,− These platelets possess some unique features such as bright blue emission with near-unity photoluminescence quantum yields (PLQY), exclusive self-assembly, and inter-nanocrystal attachments leading to larger nanostructures. − However, from different literature reports, it is revealed that almost all such 2D nanostructures of CsPbBr 3 have a square platelet shape and a vertical [001] axis remaining perpendicular to their basal planes. , These are likely slices of orthorhombic cubes having four {110} and two {002} facets. A recent report on B-site ion placements following a Cs-sublattice platform showed polygonal platelets having other facets, but the vertical direction remained the same as square platelets. This suggests that facet chemistry and crystal orientations leading to more versatile 2D-shaped platelets/discs with changeable axial orientations need deeper investigations and more fundamental understandings.…”