Simple and sustainable synthesis of perovskite-based optoelectronic material: CsPbBr3 nanocrystals via laser ablation in alcohol

Abstract

All-inorganic lead halide perovskite nanocrystals (NCs) have shown great potential as emerging semiconducting materials due to their excellent optoelectronic properties. However, syntheses in solution commonly use high temperatures and toxic solvents, which are obstacles for safety and sustainability of the process. In this work, laser ablation in alcohol is proposed as a simple and sustainable, ligand-free, top-down approach to synthesize CsPbBr₃ nanocrystals in ambient conditions. The effects of different low boiling point commercial alcohols used as solvents on the optical properties of CsPbBr₃ NCs colloidal solutions are investigated. Although in traditional bottom-up synthesis alcohols are usually found to be not appropriate for the synthesis of perovskite NCs, here it is demonstrated that CsPbBr₃ orthorhombic nanocrystals with narrow full width half maximum (FWHM < 18 nm), long photoluminescence lifetimes (up to 17.9 ns) and good photoluminescence quantum yield (PLQY up to 15.5%) can be obtained by selecting the dielectric constant and polarity of the alcohol employed for the synthesis.

Fig. 1. (a) Dielectric constant as a function of relative polarity of most used solvents (red) and antisolvents (blue) for perovskite synthesis. It is noticeable that, contrary to linear chain alcohols (yellow), the use of branched alcohols (green) enables to reach low values of both dielectric constant and polarity. (b) XRD patterns of orthorhombic CsPbBr₃ perovskite NCs synthesized by LASiS in different alcohols. Contributes of non-perovskite phases at low angles are highlighted with red asterisk. Pattern of PbBr₂ NCs obtained by LASiS in alcohol and of CsBr powders are also reported for comparison. The orthorhombic reference spectrum (ICSD 97851) of the CsPbBr₃ orthorhombic phase is taken from ref. .

Fig. 2. Scheme of PbBr₂ nanocrystals synthesis by laser ablation in alcohol and their conversion into CsPbBr₃ colloidal solution by the 2-step protocol. (a) PbBr₂ compressed powder round pellet employed as target. (b) Picture of laser ablation in progress, showing the Nd:YAG laser beam focused on the surface of the target immersed in alcohol. (c) TEM image of PbBr₂ precursor nanocrystals; the inset shows a picture of PbBr₂ NCs solution under visible light. (d) TEM image of CsPbBr₃ perovskite nanocrystals; the inset shows a picture of CsPbBr₃ NCs solution under UV light.

Fig. 3. Comparison of (a) UV-Vis spectra, (b) steady-state PL emissions, and (c) time-resolved PL decays of CsPbBr₃ NCs synthesized by 1-step in situ synthesis in different alcohols (PL profiles are normalized to the intensity of the respective absorption peak). The intensity-averaged lifetimes reported in (c) were calculated by three-exponential fit of the respective PL decays, following previous indications (the reported values are intensity-averaged lifetime values, see Fig. 3a).

Fig. 4. (a) Table summarizing the results of optical characterizations of CsPbBr₃ NCs by laser ablation in alcohols. The excitonic peak positions (Abs_MAX) observed in UV-Vis spectra, the PL emission wavelength (PL_MAX) and FWHM given by SSPL measurements, and the intensity-averaged lifetime values (τ_AVG) calculated by three-exponential fit of the TRPL decays are listed. Data related to CsPbBr₃ NCs by the 2-step conversion protocol are reported with light font. (b) PLQY values measured over time for the CsPbBr₃ NCs by 1-step in situ synthesis method in different alcohols. All samples were kept in ambient conditions during aging.