Facile Synthesis of Colloidal Lead Halide Perovskite Nanoplatelets via Ligand-Assisted Reprecipitation

Summary

This work demonstrates facile room-temperature synthesis of colloidal quantum-confined lead halide perovskite nanoplatelets by ligand-assisted reprecipitation method. Synthesized nanoplatelets show spectrally narrow optical features and continuous spectral tunability throughout the visible range by varying the composition and thicknesses.

Abstract

In this work, we demonstrate a facile method for colloidal lead halide perovskite nanoplatelet synthesis (Chemical formula: L₂[ABX₃]_n-1BX₄, L: butylammonium and octylammonium, A: methylammonium or formamidinium, B: lead, X: bromide and iodide, n: number of [BX₆]^4- octahedral layers in the direction of nanoplatelet thickness) via ligand-assisted reprecipitation. Individual perovskite precursor solutions are prepared by dissolving each nanoplatelet constituent salt in N,N-dimethylformamide (DMF), which is a polar organic solvent, and then mixing in specific ratios for targeted nanoplatelet thickness and composition. Once the mixed precursor solution is dropped into nonpolar toluene, the abrupt change in the solubility induces the instantaneous crystallization of nanoplatelets with surface-bound alkylammonium halide ligands providing colloidal stability. Photoluminescence and absorption spectra reveal emissive and strongly quantum-confined features. X-ray diffraction and transmission electron microscopy confirm the two-dimensional structure of the nanoplatelets. Furthermore, we demonstrate that the band gap of perovskite nanoplatelets can be continuously tuned in the visible range by varying the stoichiometry of the halide ion(s). Lastly, we demonstrate the flexibility of the ligand-assisted reprecipitation method by introducing multiple species as surface-capping ligands. This methodology represents a simple procedure for preparing dispersions of emissive 2D colloidal semiconductors.

Introduction

In the past decade, fabrication of lead halide perovskites solar cells^1,2,3,4,5,6 has effectively highlighted the excellent properties of this semiconductor material, including long carrier diffusion lengths^7,8,9,10, compositional tunability^4,5,11 and lo....

Protocol

NOTE: Simpler notations of ‘n = 1 BX’ and ‘n = 2 ABX’ will be used from here instead of the complex chemical formula of L₂BX₄ and L₂[ABX₃]BX₄, respectively. For better stability and optical properties of resulting perovskite nanoplatelets, it is recommended to complete the whole procedure under inert conditions⁴⁹ (i.e., a nitrogen glovebox).

1. Preparation of perovskite nanoplatelet precursor solution

1. Prepare ~1 mL of 0.2 M solutions of methylammonium bromide (MABr), formamidinium bromide (FABr), lead bromide ....

Results

Schematic illustration of perovskite nanoplatelets and synthesis procedure gives an overview of the material and synthetic details (Figure 1). Pictures of colloidal perovskite nanoplatelet solutions under ambient light and UV (Figure 2), combined with photoluminescence and absorption spectra (Figure 3) further confirm the emissive and absorptive nature of nanoplatelets. TEM images (Figure 4) and XRD pat.......

Discussion

The product of this synthesis is colloidal lead halide nanoplatelets capped by alkylammonium halide surface ligands (Figure 1a). Figure 1b demonstrates the synthetic procedure of colloidal perovskite nanoplatelets via ligand-assisted reprecipitation. To summarize, constituent precursor salts were dissolved in a polar solvent DMF in specific ratios for desired thickness and composition, and then injected into toluene, which is nonpolar. Due to the abrupt change i.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Equipment
365nm fiber-coupled LED	Thorlabs	M365FP1	Excitation source (Photoluminescence)
Avantes fiber-optic spectrometer	Avantes	AvaSpec-2048XL	Photoluminescence detector (Photoluminescence spectra)
Cary 5000	Agilent Technologies		UV-Vis spectrophotometer (Absorption spectra)
FEI Tecnai G2 Spirit Twin TEM	FEI Company		Transmission electron microscopy (TEM) operating at 120kV
PANalytical X'Pert Pro MPD	Malvern Panalytical		X-ray diffraction (XRD) operating at 45 kV and 40 mA with a copper radiation source.
Materials
n-butylammonium bromide (BABr)	GreatCell Solar	MS305000-50G
n-butylammonium chloride (BACl)	Fisher Scientific	B071025G	butylamine hydrochloride
n-butylammonium iodide (BAI)	Sigma-Aldrich	805874-25G
N,N-dimethylforamide (DMF)	Sigma-Aldrich	227056-1L	Anhydrous, 99.8%
n-dodecylammonium bromide (DDABr)	GreatCell Solar	MS300880-05
formamidinium bromide (FABr)	GreatCell Solar	MS350000-100G
formamidinium iodide (FAI)	GreatCell Solar	MS150000-100G
n-hexylammonium bromide (HABr)	GreatCell Solar	MS300860-05
lead bromide (PbBr2)	Sigma-Aldrich	398853-5G	.99.999%
lead chloride (PbCl2)	Sigma-Aldrich	268-690-5G	98%
lead iodide (PbI2) solution	Sigma-Aldrich	795550-10ML	0.55M in DMF
methylammonium bromide (MABr)	GreatCell Solar	MS301000-100G
methylammonium iodide (MAI)	GreatCell Solar	MS101000-100G
n-octylammonium bromide (OABr)	GreatCell Solar	MS305500-50G
n-octylammonium chloride (OACl)	Fisher Scientific	O04841G	octylamine hydrochloride
n-octylammonium iodide (OAI)	GreatCell Solar	MS105500-50G
iso-pentylammonium bromide (i-PABr)	GreatCell Solar	MS300710-05
toluene	Sigma-Aldrich	244511-1L	Anhydrous, 99.8%