Postsynthesis Transformation of Insulating Cs₄PbBr₆ Nanocrystals into Bright Perovskite CsPbBr₃ through Physical and Chemical Extraction of CsBr

Abstract

Perovskite-related Cs4PbBr6 nanocrystals present a “zero-dimensional” crystalline structure where adjacent [PbBr6]4– octahedra do not share any corners. We show in this work that these nanocrystals can be converted into “three-dimensional” CsPbBr3 perovskites by extraction of CsBr. This conversion drastically changes the optoelectronic properties of the nanocrystals that become highly photoluminescent. The extraction of CsBr can be achieved either by thermal annealing (physical approach) or by chemical reaction with Prussian Blue (chemical approach). The former approach can be simply carried out on a dried film without addition of any chemicals but does not yield a full transformation. Instead, reaction with Prussian Blue in solution achieves a full transformation into the perovskite phase. This transformation was also verified on the iodide counterpart (Cs4PbI6).

Single‐Solvent, Ligand‐Free, Gram‐Scale Synthesis of Cs4PbBr6 Perovskite Solids with Robust Green Photoluminescence

“…The PL spectrum shown in Figure d indicates that the product exhibits a narrow and intense emission band at 517 nm with a full width at half maximum (FWHM) of 24 nm and a 71% absolute PLQY. Obviously, the optical properties of our products are distinct from those well‐crystalline Cs 4 PbBr 6 NCs obtained by the hot‐injection methods . They generally exhibit only a sharp absorption peak at 314 nm and no luminescence under UV light.…”

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

“…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).…”

Photoluminescence Mechanisms of All‐Inorganic Cesium Lead Bromide Perovskites Revealed by Single Particle Spectroscopy

“…Palazon et al. have prepared pure Cs 4 PbBr 6 NCs that displayed no PL . The diffractogram of the pristine NCs at room temperature (Figure a, bottom) matched that of bulk Cs 4 PbBr 6 .…”

“… (a) XRD spectra of Cs 4 PbBr 6 NCs upon annealing in vacuum, (b) PL spectra and photographs under a UV lamp (inset) of the original sample and sample annealed at 200 °C . Copyright 2017, American Chemical Society.…”