This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES) under award number DE-SC0019345. Seung Kyun Ha was partially supported by the Kwanjeong Education Foundation Overseas Doctoral Program Scholarship. This work made use of the MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation under award number DMR-08-19762. We thank Eric Powers for assistance with proofing and editing.

NOTE: Simpler notations of &#8216;n = 1 BX&#8217; and &#8216;n = 2 ABX&#8217; 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 nanopl...

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...

In the past decade, fabrication of lead halide perovskites solar cells1,2,3,4,5,6 has effectively highlighted the excellent properties of this semiconductor material, including long carrier diffusion lengths7,8,9,10, compositional tunability4,5,11 and low-cost synthesis12. In particular, the unique nature of defect tolerance13,14 makes lead halide perovskites fundamentally different from other semiconductors and thus highly promising for next-generation optoelectronic applications.
In addition to solar cells, lead halide perovskites have been shown to make excellent optoelectronic devices such as light-emitting diodes6,15,16,17,18,19,20,21,22, lasers23,24,25, and photodetectors26,27,28. Especially, when prepared in the form of colloidal nanocrystals18,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43, lead halide perovskites may exhibit strong quantum- and dielectric-confinement, large exciton binding energy44,45, and bright luminescence17,19 along with facile solution processability. Various reported geometries including quantum dots29,30,31,32, nanorods33,34 and nanoplatelets18,35,36,37,38,39,40,41,43 further demonstrate the shape tunability of lead halide perovskite nanocrystals.
Among those nanocrystals, colloidal two-dimensional (2D) lead halide perovskites, or &#8220;perovskite nanoplatelets&#8221;, are especially promising for light-emitting applications due to strong confinement of charge carriers, large exciton binding energy reaching up to hundreds of meV44, and spectrally narrow emission from thickness-pure ensembles of nanoplatelets39. Additionally, anisotropic emission reported for 2D perovskite nanocrystals46 and other 2D semiconductors47,48 highlights the potential of maximizing outcoupling efficiency from perovskite nanoplatelet-based light-emitting devices.
Here, we demonstrate a protocol for the simple, universal, room-temperature synthesis of colloidal lead halide perovskite nanoplatelets via a ligand-assisted reprecipitation technique36,38,49. Perovskite nanoplatelets incorporating iodide and/or bromide halide anions, methylammonium or formamidinium organic cations, and variable organic surface ligands are demonstrated. Procedures for controlling the absorption and emission energy and the thickness purity of the colloidal dispersion are discussed.

<table>
	<tbody>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>365nm fiber-coupled LED</td>
			<td>Thorlabs</td>
			<td>M365FP1</td>
			<td>Excitation source (Photoluminescence)</td>
		</tr>
		<tr>
			<td>Avantes fiber-optic spectrometer</td>
			<td>Avantes</td>
			<td>AvaSpec-2048XL</td>
			<td>Photoluminescence detector (Photoluminescence spectra)</td>
		</tr>
		<tr>
			<td>Cary 5000</td>
			<td>Agilent Technologies</td>
			<td></td>
			<td>UV-Vis spectrophotometer (Absorption spectra)</td>
		</tr>
		<tr>
			<td>FEI Tecnai G2 Spirit Twin TEM</td>
			<td>FEI Company</td>
			<td></td>
			<td>Transmission electron microscopy (TEM) operating at 120kV</td>
		</tr>
		<tr>
			<td>PANalytical X&#39;Pert Pro MPD</td>
			<td>Malvern Panalytical</td>
			<td></td>
			<td>X-ray diffraction (XRD) operating at 45 kV and 40 mA with a copper radiation source.</td>
		</tr>
		<tr>
			<td>Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>n-butylammonium bromide (BABr)</td>
			<td>GreatCell Solar</td>
			<td>MS305000-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>n-butylammonium chloride (BACl)</td>
			<td>Fisher Scientific</td>
			<td>B071025G</td>
			<td>butylamine hydrochloride</td>
		</tr>
		<tr>
			<td>n-butylammonium iodide (BAI)</td>
			<td>Sigma-Aldrich</td>
			<td>805874-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>N,N-dimethylforamide (DMF)</td>
			<td>Sigma-Aldrich</td>
			<td>227056-1L</td>
			<td>Anhydrous, 99.8%</td>
		</tr>
		<tr>
			<td>n-dodecylammonium bromide (DDABr)</td>
			<td>GreatCell Solar</td>
			<td>MS300880-05</td>
			<td></td>
		</tr>
		<tr>
			<td>formamidinium bromide (FABr)</td>
			<td>GreatCell Solar</td>
			<td>MS350000-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>formamidinium iodide (FAI)</td>
			<td>GreatCell Solar</td>
			<td>MS150000-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>n-hexylammonium bromide (HABr)</td>
			<td>GreatCell Solar</td>
			<td>MS300860-05</td>
			<td></td>
		</tr>
		<tr>
			<td>lead bromide (PbBr2)</td>
			<td>Sigma-Aldrich</td>
			<td>398853-5G</td>
			<td>.99.999%</td>
		</tr>
		<tr>
			<td>lead chloride (PbCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>268-690-5G</td>
			<td>98%</td>
		</tr>
		<tr>
			<td>lead iodide (PbI2) solution</td>
			<td>Sigma-Aldrich</td>
			<td>795550-10ML</td>
			<td>0.55M in DMF</td>
		</tr>
		<tr>
			<td>methylammonium bromide (MABr)</td>
			<td>GreatCell Solar</td>
			<td>MS301000-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>methylammonium iodide (MAI)</td>
			<td>GreatCell Solar</td>
			<td>MS101000-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>n-octylammonium bromide (OABr)</td>
			<td>GreatCell Solar</td>
			<td>MS305500-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>n-octylammonium chloride (OACl)</td>
			<td>Fisher Scientific</td>
			<td>O04841G</td>
			<td>octylamine hydrochloride</td>
		</tr>
		<tr>
			<td>n-octylammonium iodide (OAI)</td>
			<td>GreatCell Solar</td>
			<td>MS105500-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>iso-pentylammonium bromide (i-PABr)</td>
			<td>GreatCell Solar</td>
			<td>MS300710-05</td>
			<td></td>
		</tr>
		<tr>
			<td>toluene</td>
			<td>Sigma-Aldrich</td>
			<td>244511-1L</td>
			<td>Anhydrous, 99.8%</td>
		</tr>
	</tbody>
</table>

facile synthesis of colloidal lead halide perovskite nanoplatelets via ligand-assisted reprecipitation

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.

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...

Watch this Scientific Journal Video about Facile Synthesis of Colloidal Lead Halide Perovskite Nanoplatelets via Ligand-Assisted Reprecipitation at JoVE.com

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

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.

In this work, we demonstrate a facile method for colloidal lead halide perovskite nanoplatelet synthesis (Chemical formula: L2[ABX3]n-1BX4, L: ...

This protocol demonstrates the room temperature synthesis of colloidal perovskite nanoplatelets for future optoelectronic applications. The main advantage of this approach is the compositional flexibility it provides. By making straightforward changes to the precursor mixtures, different perovskite nanoplatelets can be easily obtained.Lead halide perovskites are uniquely suited to the ligand-assisted reprecipitation method. Unlike traditional semiconductors, the bonds within the perovskite crystal lattice can be easily broken and reformed at room temperature. To synthesize and equals to methylammonium lead bromide nanoplatelets, mix individual one milliliter volumes of the indicated 0.2 molar precursor solutions according to the table.To synthesize and equals to methylammonium lead iodide nanoplatelets, mix individual one milliliter volumes of the indicated 0.2 molar precursor solutions according to the table. To synthesize nanoplatelets with mixed halide compositions, combine bromide only and iodide only perovskite nanoplatelet precursor solutions of the same thickness at the desired volumetric ratio for the target composition. For perovskite nanoplatelet synthesis, inject 10 microliters of each mixed precursor solution into individual 10 milliliter aliquots of toluene under vigorous stirring.Leave the solutions under stirring for 10 minutes until no further color changes are observed to ensure a complete crystallization of each of the perovskite nanoplatelets. For general purification of the perovskite nanoplatelets, centrifuge the solutions at 2, 050 times g for 10 minutes and discard the supernatants. Then, re-disburse the nanoplatelets in an appropriate volume of solvent according to the planned downstream analysis with vortexing.Pictures of colloidal perovskite nanoplatelet solutions under ambient and ultraviolet light combined with photoluminescence and absorption spectra further confirm the emissive and absorptive nature of the nanoplatelets. Transmission electron microscopy images and X-ray defraction patterns can be used to estimate the lateral dimensions and stacking spacings of the nanoplatelets, respectively, while also confirming their two-dimensional structures. Absorption spectra of perovskite nanoplatelet solutions with mixed halides demonstrate the tunability of the band gap.Identical photoluminescence spectra from perovskite nanoplatelets with different ligands demonstrate the compositional flexibility of the organic surface capping species. It must be noted that the precise control of the ratios between individual precursors determines the thickness of the resulting nanoplatelets and ensures their thickness homogeneity. Following the synthesis and purification of the nanoplatelets, post-synthesis processes, such as thin film deposition, polymer encapsulation, and optoelectronic device fabrication can be performed depending on the planned usage.One exciting feature of this synthetic method is its suitability for automated and high through-put experimentation, which can be used to quickly generate large data sets to train predictive computer models. Lead halides are believed to be carcinogenic and the inhalation of organic solvents and nanoparticles can be dangerous. Handle all of the chemicals in a well contained environment.

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12.7K visualizações.  Massachusetts Institute of Technology. Este protocolo demonstra a síntese de temperatura ambiente de nanoplatos perovskite coloidais para futuras aplicações optoeletrônicas. A principal vantagem dessa abordagem é a flexibilidade composicional que proporciona. Ao fazer alterações simples nas misturas precursoras, diferentes nanoplatas perovskite podem ser facilmente obtidas.Perovskites de halide de chumbo são exclusivamente adequados ao método de reprecipitação assistido por ligante. Ao contrário dos semicondutor...