Unveiling the Two-Step Formation Pathway of Cs₄PbBr₆ Nanocrystals

Abstract

All-inorganic cesium lead halide perovskites have received much attention, but the study of the formation pathway is relatively little. We report here a new one-step approach for the synthesis of Cs 4 PbBr 6 nanocrystals (NCs), as well as the exploration of its formation process. Mixing three independent precursors of Cs, Pb, and Br in a cuvette, we monitor the evolution of Cs 4 PbBr 6 NCs by in situ absorption spectroscopy, the formation of which features a sharp absorption peak at 313 nm. Based on this model, we further divide the synthesis process into two stages, in which the two precursors react for a certain period before adding the third precursor to the reaction. We find that the absorption peak exhibits a dramatic change from 358 to 313 nm with the addition of Cs precursor to the reaction mixture of Pb and Br precursors. Accordingly, we propose that there might be a two-step formation pathway for Cs 4 PbBr 6 NCs. The formation of the Pb−Br bond is the first step, and then, a new reaction takes place after the Cs precursor is involved, which eventually results in the formation of Cs 4 PbBr 6 NCs. The present study provides a new approach to synthesize the Cs 4 PbBr 6 NCs and understand their formation pathway.

State of the Art and Prospects for Halide Perovskite Nanocrystals

“…The microemulsion method has been used to obtain other inorganic perovskite NCs with different dimensionalities (CsPbBr 3 and CsPb 2 Br 5 ), as well as the ligand-free highly emissive Cs 4 PbBr 6 NCs . Recently, Hui et al reported a one-step method for the synthesis of Cs 4 PbBr 6 NCs by mixing three independent precursors of Cs, Pb, and Br in a cuvette . They proposed a two-step pathway for forming Cs 4 PbBr 6 NCs.…”

“…418 Recently, Hui et al reported a onestep method for the synthesis of Cs 4 PbBr 6 NCs by mixing three independent precursors of Cs, Pb, and Br in a cuvette. 419 They proposed a two-step pathway for forming Cs 37b). 421 The evolution of the normalized absorbance at these two spectral positions had the inverse dependence on the OLA concentration.…”

Revealing the Aging Effect of Metal-Oleate Precursors on the Preparation of Highly Luminescent CsPbBr3 Nanoplatelets

“…The sample using fresh metal-oleate precursor possesses three absorption peaks which are ascribed to the exciton absorption peaks of CsPbBr 3 , [PbBr 4 ] 2− , and Cs 4 PbBr 6 , respectively. 25 The photoluminescence (PL) peak shows a large full-width-athalf-maximum (fwhm = 29 nm) and low luminescent intensity. After aging the metal-oleate precursors for 4 months, the exciton absorption peaks of [PbBr 4 ] 2− and Cs 4 PbBr 6 disappear and the CsPbBr 3 exciton absorption peak is enhanced, accompanied by a narrower and stronger PL emission peak.…”

Taming the nucleation and growth kinetics of lead halide perovskite quantum dots

“…1). We hypothesized that the conventional approach -referred to as oleylamine -oleic acid (OLAM/OA) path 1 -suffers from the immediate conversion of the PbBr2 into haloplumbate ionic solute (PbBr3 -) upon the action of OLAM/OA 38,39 . The subsequent reaction with injected Cs-ions is thus quantitative and fast, and hence nucleation and growth are not temporally separated.…”

“…Only upon the injection of Cs-DOPA, does the PbBr3appear on the course of 100 ms, evidenced as an additional peak emerging at lower energies (3.85 eV) (Supplementary Fig. 21), owing to the formation of a PbBr3complex 39,49 .Once the accumulation of PbBr3surpasses a nucleation threshold (supersaturation), CsPbBr3 QDs form (on the order of seconds, Fig. 3b).…”