Chemical Availability of Bromide Dictates CsPbBr₃ Nanocrystal Growth

Abstract

Lack of detailed understanding of the growth mechanism of CsPbBr 3 nanocrystals has hindered sophisticated morphological and chemical control of this important emerging optoelectronic material. Here, we have elucidated the growth mechanism by slowing the reaction kinetics. When 1bromohexane is used as an alternative halide source, bromide is slowly released into the reaction mixture, extending the reaction time from ∼3 s to greater than 20 min. This enables us to monitor the phase evolution of products over the course of reaction, revealing that CsBr is the initial species formed, followed by Cs 4 PbBr 6 , and finally CsPbBr 3 . Furthermore, formation of monodisperse CsBr nanocrystals is demonstrated in a bromide-deficient and lead-abundant solution. The CsBr can be transformed only into CsPbBr 3 nanocubes if additional bromide is added. Our results indicate a fundamentally different growth mechanism for CsPbBr 3 in comparison with more established semiconductor nanocrystal systems and reveal the critical role of the chemical availability of bromide for the growth reactions.

One‐Step Polymeric Melt Encapsulation Method to Prepare CsPbBr3 Perovskite Quantum Dots/Polymethyl Methacrylate Composite with High Performance

“…In addition, different Cs + or Pb 2+ sources react to form CsPbBr 3 PQDs at different rates. [ 32 ] Figure S1b,c in the Supporting Information shows the PL spectra of composites with different Cs + or Pb 2+ sources. As seen in both figures, the use of CH 3 (CH 2 ) 16 COOCs, [CH 3 (CH 2 ) 16 COO] 2 Pb, and KBr in the 1:1:3 molar ratio (hereafter abbreviated as CCK) as the raw materials of the perovskites results in the strongest emission of the composites.…”

Equilibriums in Formation of Lead Halide Perovskite Nanocrystals

“…Unlike cationic components, there are few reports on anionic component (halide) induced phase change of Cs–Pb–X which also helped to tune the phase and morphology of the perovskite nanocrystals. A Br-deficient environment might also lead to the formation of CsPbBr 3 through CsBr and Cs 4 PbBr 6 intermediates, suggesting that bromine might also induce transformation from Cs 4 PbBr 6 to CsPbBr 3 …”

“…A Br-deficient environment might also lead to the formation of CsPbBr 3 through CsBr and Cs 4 PbBr 6 intermediates, suggesting that bromine might also induce transformation from Cs 4 PbBr 6 to CsPbBr 3 . 54 Moreover, fast nucleation of ionic halide perovskites and the competition between coordinated solvent molecules or ligands and halide ions to form distorted octahedrons with Pb(II) ions in solution ion equilibrium resulted in the formation of V Br − defects, as shown in Figure 6a. 55 Hence, more halide ions in octahedrons during nucleation led to fewer V Br − defects, resulting in higher PLQY in several cases.…”

Growth mechanistic insights into perovskite nanocrystals: dimensional growth

“…However, upon washing this is not observable. The transition between these two phases is extremely facile for this phase, particularly for the sample synthesized at 100 C. Wen et al 31 showed a phase evolution occurring within a short period of 2 hours. Further repeated measurements of this sample show varying intensity ratios for the two phases suggesting the role of the environment in an extremely long measurement timescale ($4 hours).…”