Improving the Stability of Ball-Milled Lead Halide Perovskites via Ethanol/Water-Induced Phase Transition

Abstract

Recently, lead halide perovskite nanocrystals have been considered as potential light-emitting materials because of their narrow full width at half-maximum (FWHM) and high photoluminescence quantum yield (PLQY). In addition, they have various emission spectra because the bandgap can be easily tuned by changing the size of the nanocrystals and their chemical composition. However, these perovskite materials have poor long-term stability due to their sensitivity to moisture. Thus far, various approaches have been attempted to enhance the stability of the perovskite nanocrystals. However, the required level of stability in the mass production process of perovskite nanocrystals under ambient conditions has not been secured. In this work, we developed a facile two-step ball-milling and ethanol/water-induced phase transition method to synthesize stable CsPbBr₃ perovskite materials. We obtained pure CsPbBr₃ perovskite solutions with stability retention of 86% for 30 days under ambient conditions. Our materials show a high PLQY of 35% in solid films, and excellent thermal stability up to 80 °C. We believe that our new synthetic method could be applicable for the mass production of light-emitting perovskite materials.

Keywords: CsPbBr3 perovskite nanocrystals; ball milling; mass production; phase transition; stability.

Figure 1

Schematic diagram of the phase transition process from Cs₄PbBr₆ MCs to CsPbBr₃ using an ethanol/water treatment: (a) process to obtain Cs₄PbBr₆ MCs via the ball-milling process, (b) photographic image of the Cs₄PbBr₆ and CsPbBr₃ solutions under UV light (365 nm) with an ethanol/water treatment, and (c) crystal structure of the Cs₄PbBr₆ and CsPbBr₃ MCs.

Figure 2

(a) XRD spectra of the synthesized bulk Cs₄PbBr₆ single crystals, Cs₄PbBr₆ MCs obtained through ball milling, and phase-transformed CsPbBr₃ MCs. The standard XRD spectra of rhombohedral Cs₄PbBr₆ and orthorhombic CsPbBr₃ are also indicated. (b) XRD spectra indicating the phase transition of ethanol/water-treated Cs₄PbBr₆ MCs to CsPbBr₃ MCs with differing times.

Figure 3

Comparison of the PL intensity of the CsPbBr₃ MC solutions obtained via the phase transition process with different ratios of ethanol/water.

Figure 4

(a) Absorption and (b) PL spectra of the ball-milled Cs₄PbBr₆ MCs, partially transformed Cs₄PbBr₆–CsPbBr₃ MCs, and fully transformed CsPbBr₃ MCs.

Figure 5

Time-dependent absorption spectra of the CsPbBr₃ MC solutions synthesized using different amounts of PAA: (a) 15 mg, (b) 25 mg, and (c) 35 mg PAA. (d) PL spectra of the CsPbBr₃ MC solutions synthesized with different amounts of PAA obtained via the ethanol/water treatment. Photographic images of the CsPbBr₃ MC solutions (e) under room light and (f) UV light.

Figure 6

Schematic illustration of the phase transition process of Cs₄PbBr₆ MCs obtained via ethanol/water treatment (a) without PAA and (b) with PAA.

Figure 7

SEM images of the Cs₄PbBr₆ MC films before ethanol/water treatment (a) without PAA and (b) with PAA. SEM images of the CsPbBr₃ MC films after ethanol/water treatment (c) without PAA and (d) with PAA.

Figure 8

(a) Time-dependent PL spectra of the CsPbBr₃ MC solution obtained via the ethanol/water treatment and hot-injection method under ambient conditions, and (b) PL spectra of the CsPbBr₃ MC solution obtained via the ethanol/water treatment and high-temperature injection under UV Illumination.

Figure 9

Photographic images of CsPbBr₃ MC thin films under UV light with thermal annealing.