Benzoyl Halides as Alternative Precursors for the Colloidal Synthesis of Lead-Based Halide Perovskite Nanocrystals

Abstract

We propose here a new colloidal approach for the synthesis of both all-inorganic and hybrid organic-inorganic lead halide perovskite nanocrystals (NCs). The main limitation of the protocols that are currently in use, such as the hot injection and the ligand-assisted reprecipitation routes, is that they employ PbX₂ (X = Cl, Br, or I) salts as both lead and halide precursors. This imposes restrictions on being able to precisely tune the amount of reaction species and, consequently, on being able to regulate the composition of the final NCs. In order to overcome this issue, we show here that benzoyl halides can be efficiently used as halide sources to be injected in a solution of metal cations (mainly in the form of metal carboxylates) for the synthesis of APbX₃ NCs (in which A = Cs⁺, CH₃NH₃⁺, or CH(NH₂)₂⁺). In this way, it is possible to independently tune the amount of both cations and halide precursors in the synthesis. The APbX₃ NCs that were prepared with our protocol show excellent optical properties, such as high photoluminescence quantum yields, low amplified spontaneous emission thresholds, and enhanced stability in air. It is noteworthy that CsPbI₃ NCs, which crystallize in the cubic α phase, are stable in air for weeks without any postsynthesis treatment. The improved properties of our CsPbX₃ perovskite NCs can be ascribed to the formation of lead halide terminated surfaces, in which Cs cations are replaced by alkylammonium ions.

Scheme 1. Colloidal Synthesis of Lead Based Halide Perovskite Nanocrystals Using Benzoyl Halides as Halide Precursors

Figure 1

Bright-field TEM images of (a) CsPbCl₃, (b) CsPbBr₃, and (c) CsPbI₃ NCs. Scale bars are 100 nm in all images. XRD patterns of (d) CsPbCl₃, (e) CsPbBr₃, and (f) CsPbI₃ NCs along with the corresponding bulk cubic reference patterns. Absorption and PL spectra of (g) CsPbCl₃, (h) CsPbBr₃, and (i) CsPbI₃ NCs dispersed in toluene.

Figure 2

(a) XRD patterns and (b) UV–vis and PL curves of CsPbI₃ NCs exposed to air up to 20 days.

Figure 3

(a) Evolution of the PL spectra of CsPbBr₃ NCs by the addition of benzoyl chloride or benzoyl iodide. (b) Picture of the different CsPbX₃ NC solutions obtained by anion exchange under a UV lamp.

Figure 4

Bright-field TEM images of (a) MAPbCl₃, (b) MAPbBr₃, and (c) MAPbI₃ NCs. Scale bars are 100 nm in all images. XRD patterns of (d) MAPbCl₃, (e) MAPbBr₃, and (f) MAPbI₃ NCs along with their corresponding bulk cubic reference patterns. In the case of MAPbCl_3, the bulk reflections were calculated using the crystal structure that was reported by Maculan et al.Absorption and PL spectra of (g) MAPbCl₃, (h) MAPbBr₃, and (i) MAPbI₃ NCs dispersed in toluene.

Figure 5

Bright-field TEM images of (a) FAPbCl₃, (b) FAPbBr₃, and (c) FAPbI₃ NCs. Scale bars are 100 nm in all images. XRD patterns of (d) FAPbCl₃, (e) FAPbBr₃, and (f) FAPbI₃ NCs along with the corresponding bulk cubic reference patterns. For FAPbBr₃ and FAPbI₃ NCs, the bulk reflections were calculated using the crystal structure reported by Zhumekenov et al., while the reflections of the FAPbCl₃ NCs were generated using a cubic perovskite structure (Pm-3m) with a = 5.76 Å. Absorption and PL spectra of (g) FAPbCl₃, (h) FAPbBr₃, and (i) FAPbI₃ NCs dispersed in toluene.

Figure 6

ASE dynamics for (a) CsPbBr₃, (b) MAPbBr₃, and (c) FAPbBr₃ together with the ASE threshold calculations (insets).