From Nonluminescent Cs₄PbX₆ (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX₃ Nanocrystals: Water-Triggered Transformation through a CsX-Stripping Mechanism

Abstract

We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent CsPbX (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX NCs. During the transformation, CsPbX NCs dispersed in a nonpolar solvent are converted into CsPbX NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of CsPbX NCs, and produces monodisperse and air-stable CsPbX NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as CsPbX NCs are converted into CsPbX NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals.

Pressure-induced emission of cesium lead halide perovskite nanocrystals

“…The cesium lead halide perovskite of Cs 4 PbBr 6 is a typical zero-dimensional (0D) inorganic MHP, in which the octahedra are completely isolated by cation bridges and charge carriers are localized within the ordered metal halide component 7–10 . The electronic structure and optical properties of these materials are expected to show a significant dependence on pressure 11–16 .…”

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…16 The proposed origin of the green PL is either intrinsic to Cs 4 PbBr 6 (due to the presence of defects) 11,12,14,17−26 or from contamination by CsPbBr 3 NC-like impurities. 13,27−42 …”

“…13,27 This can be done via the insertion of PbBr 2 , the extraction of CsBr with water or with Prussian Blue, or the extraction of Pb 2+ with amines. 13,27,28,33,37 Several groups have reported that the size and shape of the starting Cs 4 PbBr 6 NCs can be used to tune the size of the final CsPbBr 3 NCs (Figure 5b).…”

“…13,27 This can be done via the insertion of PbBr 2 , the extraction of CsBr with water or with Prussian Blue, or the extraction of Pb 2+ with amines. 13,27,28,33,37 Several groups have reported that the size and shape of the starting Cs 4 PbBr 6 NCs can be used to tune the size of the final CsPbBr 3 NCs (Figure 5b). 13,27,28,33,37 The transformed CsPbBr 3 NCs exhibit a strong green PL, similar to the PL of directly synthesized CsPbBr 3 NCs, and they show no excitonic absorption in the UV from their parent Cs 4 PbBr 6 NCs (Figure 5c).…”

Lead‐Free Halide Perovskite Nanocrystals: Crystal Structures, Synthesis, Stabilities, and Optical Properties

“…First discovered in 2014, LHP NCs are of great interest because the bright, narrow-band photoluminescence (PL) of this new class of nanomaterials can be readily tuned from ultraviolet to near-infrared wavelengths simply by tailoring either the halide composition or size of NCs. [27][28][29][30][31][32][33] An otable advantage of LHP NCs over conventional semiconductor NCs (such as CdSe and InP) is their defect tolerance (i.e., the apparently benign nature of structural defects with respect to optical and electronic properties). [34][35][36] Great effort has been devoted to synthesizing various LHP NCs,investigating their photophysical properties,a nd exploiting them for use in optoelectronic or photovoltaic devices.…”