Colloidal aziridinium lead bromide quantum dots

Abstract

The compositional engineering of lead-halide perovskite nanocrystals (NCs) via the A-site cation represents a lever to fine-tune their structural and electronic properties. However, the presently available chemical space remains minimal since, thus far, only three A-site cations have been reported to favor the formation of stable lead-halide perovskite NCs, i.e., Cs+, formamidinium (FA), and methylammonium (MA). Inspired by recent reports on bulk single crystals with aziridinium (AZ) as the A-site cation, we present a facile colloidal synthesis of AZPbBr3 NCs with narrow size distribution and size tunability down to 4 nm, producing quantum dots (QDs) in the regime of strong quantum confinement. NMR and Raman spectroscopies confirm the stabilization of the AZ cations in the locally distorted cubic structure. AZPbBr3 QDs exhibit bright photoluminescence with quantum efficiencies of up to 80%. Stabilized with cationic and zwitterionic capping ligands, single AZPbBr3 QDs exhibit stable single-photon emission – another essential attribute of QDs. In particular, didodecyldimethylammonium bromide and 2-octyldodecyl-phosphoethanolamine ligands afford AZPbBr3 QDs with high spectral stability at both room and cryogenic temperatures, reduced blinking with a characteristic ON fraction larger than 85%, and high single-photon purity (g(2)(0)=0.1), all comparable to the best-reported values for MAPbBr3 and FAPbBr3 QDs of the same size.

Quantifying Förster Resonance Energy Transfer from Single Perovskite Quantum Dots to Organic Dyes

“…C 8 C 12 -PEA ligands afford significantly improved ligand passivation compared to other ligands, including other zwitterionic ligands. 29,54 Single-particle FRET samples were prepared by mixing highly diluted CsPbBr 3 QD dispersions and a solution of an organic dye, cyanine 3 NHS ester (Cy3), in significantly higher concentration in toluene and spin-coating the resulting solution onto cover glass substrates. This procedure yielded films with a sparse distribution of QDs (<1 QD/μm 2 ) and a high density of Cy3 (see Supporting Information for details on the film preparation).…”

“…For QDs with labile ligands, we have recently found that the electronic passivation of the QD surface is degraded at the high dilution levels required to prepare single-particle samples. 29,54 In contrast, the stronger binding of C 8 C 12 -PEA ligands to the surface of perovskite QDs yields a better surface passivation and a significantly higher resilience to dilution due to a much reduced ligand desorption. 29,54 Nevertheless, sporadic observations of nonresonant ET in single-QD samples at cryogenic temperatures indicate that the permeability of dyes to the QD surface remains finite even for this latest ligand class.…”

“…29,54 In contrast, the stronger binding of C 8 C 12 -PEA ligands to the surface of perovskite QDs yields a better surface passivation and a significantly higher resilience to dilution due to a much reduced ligand desorption. 29,54 Nevertheless, sporadic observations of nonresonant ET in single-QD samples at cryogenic temperatures indicate that the permeability of dyes to the QD surface remains finite even for this latest ligand class. Quantification of FRET Efficiency.…”