Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-Controlled Synthesis

Abstract

The growing demand for perovskite nanocrystals (NCs) for various applications has stimulated the development of facile synthetic methods. Perovskite NCs have often been synthesized by either ligand-assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP affects their stability. Herein, we report on the spontaneous crystallization of perovskite NCs in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without application of any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium⁺ (FA⁺ ) and Cs⁺ ) to divalent (Pb²⁺ ) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and generally applicable for perovskite NCs of different compositions.

Keywords: FAPbX3 nanocubes; FAPbX3 nanoplatelets; ligand-assisted reprecipitation; perovskite nanocrystals; spontaneous crystallization.

Figure 1

a) Schematic illustration of the synthesis of perovskite NCs by addition of a monovalent cation–ligand (e.g. FA–oleate) complex into the PbX₂–ligand solution at ambient conditions. The reaction yields different types and compositions of perovskite NCs depending on the type of A and X. b) Schematic representation of the cubic crystal structure of ABX₃ perovskite NCs. c) UV/Vis absorption (dashed lines) and PL spectra (solid lines) of perovskite NCs obtained by the addition of different amounts of FA–oleate precursor into the PbI₂–ligand solution. The insets show photographs of the colloidal solutions under UV illumination. d,e) HAAD‐STEM image of nanoplatelets and TEM images of FAPbI₃ perovskite nanocubes, respectively; the inset in (e) shows a high‐resolution TEM image of a single nanocube. f) Scaled‐up synthesis of perovskite NCs. Photograph of a FAPbI₃ colloidal nanoplatelet dispersion (scaled up by a factor of 50) under room light (left) and UV light (right, λ=365 nm).

Figure 2

a) Probing the crystallization of perovskite nanocubes in nonpolar organic media by in situ PL measurements. b) Schematic illustration of the possible size distribution of perovskite NCs at different reaction times. c) Schematic illustration showing the transformation of precursor–ligand complexes into either FAPbX₃ nanocubes or nanoplatelets depending on the FA/Pb ratio.

Figure 3

TEM images of a) CsPbBr₃ and b) CsPbI₃ nanoplatelets with their absorption and PL spectra shown in (c) and (d), respectively.