CsPbBr₃ Perovskite Nanocrystals: Linking Orthorhombic Structure to Cubic Geometry through Atomic Models and HRTEM Analysis

Abstract

RecommendationsC esium lead halide perovskite nanocrystals have reached one decade since their simpler synthesis method was reported by Kovalenko and co-workers in 2015. 1 Significant research progress has been made in designing and optimizing the reaction chemistry and optical properties of these emerging light-emitting nanocrystals. 2-9However, despite the successes achieved for obtaining several such nanocrystals, CsPbBr 3 remained in the limelight because of its bright green emission and better phase stability. 3,4,7,10,11ven in a reaction flask or centrifuge tube, the eye-catching brightness under UV light 12,13 truly excites researchers, and hence, these remained the representative nanocrystals to explore for investigating properties as well as applications of halide perovskite nanocrystals. 2,14-18Some features of these nanostructures are indeed different, and hence, these occupy some unique positions among all colloidal quantum dots.One such case is their phase-shape relationship.These are largely reported in the orthorhombic phase but mostly in a cube shape. [1][2][3]19,9,20 There is also a report on size-dependent phase variation where smaller size is dominated with cubic phase, but these change to orthorhombic for larger sizes. 21On the other hand, the blue emitting CsPbCl 3 nanocrystals are largely reported in the cubic phase with cubic shapes. 1,3The case of CsPbBr 3 having orthorhombic phase and cube shape indeed puzzles as the orthorhombic phase has different atomic parameters but the cube shape has lengths that are equal along all three directions.These cubes are even so monodisperse that their superlattices [22][23][24] and long-range self-assembly are widely reported. 3,25Hence, from the standard crystallographic point of view, this confuses from first glance, leading to the belief that these are in the orthorhombic phase.This prompted the writing of this Viewpoint as it was realized that detailed information might help newcomers in the field.In nanoscale synthesis, such exceptions are widely seen in shape modulations where the crystal growth follows paths different than as expected in bulk and facets are dominated by surface ligand binding ability.The CsPbBr 3 also remained in such a category of material whose crystal atomic parameters indeed remained unique from their crystal phase to their stability.Keeping this in mind, details of the phase-shape correlation of CsPbBr 3 nanocrystals are interpreted with their atomic models and reported in this Viewpoint.These are further supported with high-resolution transmission electron microscopy

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