Slowing Down for Growth Mechanism and Speeding Up for Performance Optimization Based on Single Ligand Passivated CsPbBr₃ Nanoplatelets

Abstract

green and red LED devices reached more than 20% in recent years, while the EQE of pure blue (460-470 nm) is still lower than 10%, [1b,3] which has greatly hindered the development of trichromatic display fields. Besides the structural optimizing of devices, designing stable and bright pure blue emissive MHPs via a simple and effective method is still a key part for improving the final EQE values.Three typical strategies for pure blue emissive perovskites are available: composition engineering (e.g., Br-Cl hybridization), quantum confinement strategy (e.g., synthesis of small size Br-based quantum dots), and dimensional engineering (e.g., quasi-two dimension Br-based nanoplatelets (NPls)). [4] Among them, composition engineering through Br-Cl hybridization may cause unavoidable phase segregation under photo-excitation or electrical bias, leading to redshift or multiple emissions in photoluminescence emission (PL) spectrum. [5] Quantum confinement strategy for Br-based perovskites nanocrystals is widely accepted for blue emitters because of its higher defect tolerance compared with Cl-or Br/ Cl-based MHPs. [1a] However, ultrasmall CsPbBr 3 quantum dots (<5 nm) with uniform size are relatively difficult to achieve due to the ultrafast reaction rate, which easily leads to a broad emission band (FWHM > 30 nm). [1b] For quasi-2D NPls, the emission peak position mainly depends on their thickness, which exhibits a quantum confinement effect when it is smaller than Quasi 2D metal halide perovskite nanoplatelets (NPls), as a kind of important materials to achieve pure blue emission, attract significant attention in pursuit of high gamut trichromatic display. However, in-depth study on the specific growth processes of NPls is still lacking due to the ultrafast reaction rate. Here, a single ligand passivation strategy to investigate the concrete growth mechanism of NPls is proposed, in which the PbBr x (OAm) y clusters play a pivotal template role in guiding the growth of crystals, and the final products with 3-monolayer (3ML) are grown from the intermediate 2ML NPls instead of being synthesized directly. Based on the new discovery about growth mechanism of NPls, the reaction time has been shortened from hours to seconds by introducing hydrobromic acid and ethanol. The ethanol used here is considered as an accelerator for the transition from 2ML to 3ML NPls rather than an initiator for nucleation of products, which is different from the generally accepted viewpoints. With further passivation of hydrobromic acid, the synthesized 3ML NPls show 462 nm emission with quantum yield of 97.04% and great photostability. The novel growth model proposed in this work will provide a paradigm for future design and optimization of new synthesis schemes.

A universal hydrochloric acid-assistant powder-to-powder strategy for quick and mass preparation of lead-free perovskite microcrystals

“…Meanwhile, poorly passivated surface halogen vacancies increase the ratio of non-radiation transition, resulting in a gradual decrease in the lifetime from 14.40 to 12.87 μs while diluting HCl solution from 35 wt% to 20 wt% (Fig. 5b ) 47 , 48 . Concentrated HCl solution is proved again as an ideal solvent for synthesis of products (Supplementary Fig.…”

Thickness-Dependent Photoluminescence Properties of Mn-Doped CsPbBr3 Perovskite Nanoplatelets Synthesized at Room Temperature

“…The absorption band edge shift to about 463 nm and become smoother. The absorption peak at 395 nm is generated from [PbBr 6 ] 4– or the monolayer of perovskite. , The PL spectra of the sample with a higher Mn/Pb molar ratio of 6/1 and 8/1 are shown in Figure S2. The higher Mn/Pb molar ratios result in the red-shift of the Mn 2+ PL peak (607 nm for 6/1 and 609 nm for 8/1) and the reduction of PL QY (66.8% for 6/1and 48.5% for 8/1).…”

Suppressing Growth Strategy on Synthesizing Stable and High-Quality Blue-Emitting CsPbBr3 Quantum Dots

“…25,26 Unfortunately, obtaining small-sized CsPbBr 3 QDs is challenging due to ultrafast nucleation and growth rates. 27 Suppressing the nucleation and growth rate is an effective method to obtain strongly confined CsPbBr 3 QDs with blue emission. 28,29 Kovalenko et al extended the use of the hot-injection method for the synthesis of perovskite nanocrystals for the first time.…”