Real-Time In Situ Observation of CsPbBr₃ Perovskite Nanoplatelets Transforming into Nanosheets

Abstract

The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr3 perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.

Dynamic Observations on Formation of Coffee-Ring Structures from the Degradation of Cesium Lead Halide Perovskite Nanocrystals

“…This initial decomposition and restructuring behavior is directly responsible for the subsequent formation of coffee-ring structures (see the following text), which can be understood from the following aspects. First and most importantly, as the synthesis of halide perovskite NCs always involves the addition of capping agents (OA/OAm in our situation), the surfaces of NCs are generally covered by these agents (although they are invisible in TEM images). , These long-chain agents themselves, as organic structures, are extremely unstable under electron beam irradiation; furthermore, they have the chance to distort the surface lattices of NCs, − leading to prior degradation of surface Cs 4 PbBr 6 into PbBr 2 before the interior of NCs. Second, it is well-known that the surfaces of NCs are energitically unstable as compared to the internal region .…”

“…In this context, state-of-the-art in situ transmission electron microscopy (TEM) techniques have allowed real-time observations of structural evolution under various stimuli (beam irradiation, heating, biasing, gas or even liquid, etc. ), − which have been adopted in the study of structural instability and degradation mechanisms of perovskite nanomaterials. − Arciniegas et al observed heat-induced transformation of CsPbBr 3 nanoplatelets that underwent morphological changes to form nanosheets and revealed its various merging pathways . Manna et al reported the structural decomposition of inorganic CsPbBr 3 nanocrystals (NCs) with different shapes and sizes, which underwent a radiolysis process and ultimately produced high-contrast particles of Pb .…”

Precise Modulation of Stable 2D/3D Multidimensional (PEA)2PbBr4 Nanosheets via Post Cation Exchange

“…Surface effects such as surface defects and surface energy level adjustments may lead to non-radiative transitions or energy dissipation on the crystal surface, resulting in a decrease in fluorescence lifetime. This has been explained by a slight increase in the thickness of the nanosheets . The real-time monitoring of the exchange process between (PEA) 2 PbBr 4 nanosheets and CsOA is shown in Figure d.…”

“…This has been explained by a slight increase in the thickness of the nanosheets. 39 The real-time monitoring of the exchange process between (PEA) 2 PbBr 4 nanosheets and CsOA is shown in Figure 2d. We observed that the two-dimensional characteristic emission peak at 412 nm remained throughout the entire process while the multi-dimensional (n = 2, 3) peaks corresponding to CsPbBr 3 appeared within 2 min.…”

Dimension and Thickness Control Synthesis of Strongly Confined Cesium Lead Iodide Perovskites with Excellent Two-Photon Absorption Properties

“…We have determined the photoluminescence quantum yield (PLQY) for Cs 4 PbI 6 NCs using eq . − PLQY 0 normalD = N emit N absorb For this purpose, the number of emitted ( N emit ) photons for 0D Cs 4 PbI 6 NCs and absorbed ( N absorb ) photons for 0D Cs 4 PbI 6 NCs were determined using an absolute PLQY spectrometer (Hamamatsu). − Table indicates that the PLQY value for 0D Cs 4 PbI 6 NCs is 49%.…”