Controlling the nucleation and growth kinetics of lead halide perovskite quantum dots

Abstract

Colloidal lead halide perovskite (LHP) nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable spheroidal APbBr 3 QDs (A=Cs, formamidinium, methylammonium) that are size-tunable from 3 to over 13 nanometers. The kinetics of both nucleation and growth are temporally separated and drastically slowed down by the intricate equilibrium between the precursor (PbBr 2 ) and the A[PbBr 3 ] solute, with the latter serving as a monomer. QDs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.

Confined Excitons in Spherical-Like Halide Perovskite Quantum Dots

“…Recent advancements on the synthesis of monodisperse CsPbBr 3 QDs in the range of 4–14 nm show a series of well-defined absorption lines and thus are ideal candidates for studying confinement effects. − In this paper, we have investigated center-of-mass motion confined excitons by studying excitonic and biexcitonic transitions in spherical-like CsPbBr 3 QDs. In a simplified analysis within the envelope function approximation, we show that the observed series of absorption resonances can be modeled by assuming excitons being confined with respect to their center-of-mass motion within an infinitely high spherical potential.…”

“…The spherical-like CsPbBr 3 QDs in this work were synthesized via a recently reported slow growth reaction approach utilizing weakly binding ligands (see Supporting Information (SI) for details) Figure A and Figure S1 show the corresponding high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images revealing the highly monodisperse and spherical-like nature of the QDs with ∼7 nm in diameter.…”

“…The linear optical absorption spectrum of the QDs in Figure B (and Figure S2 for a few different QD sizes) reveals several distinct absorption resonances, in contrast to typical >10 nm cuboidal CsPbBr 3 NCs (Figure S3), pointing toward a high sample quality and monodispersity. Spherical-like QDs are expected to have more distinct absorption peaks due to their higher symmetry as well as less oblate shape compared to their cuboidal counterparts . This should result into distinct signals in the TA spectra of such spherical-like CsPbBr 3 QDs.…”

“…The spherical-like CsPbBr 3 QDs in this work were synthesized via a recently reported slow growth reaction approach utilizing weakly binding ligands (see Supporting Information (SI) for details). 45 Figure 2A and Figure S1 show the corresponding high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images revealing the highly monodisperse and spherical-like nature of the QDs with ∼7 nm in diameter. The linear optical absorption spectrum of the QDs in Figure 2B (and Figure S2 for a few different QD sizes) reveals several distinct absorption resonances, in contrast to typical >10 nm cuboidal CsPbBr 3 NCs (Figure S3), pointing toward a high sample quality and monodispersity.…”

“…Spherical-like QDs are expected to have more distinct absorption peaks due to their higher symmetry as well as less oblate shape compared to their cuboidal counterparts. 45 This should result into distinct signals in the TA spectra of such spherical-like CsPbBr 3 QDs. To understand which quasiparticles, either individually confined electrons and holes (with Coulomb interaction) or confined Wannier excitons best describe the observed distinct absorption resonances, we calculated the individual absorption peaks within the strong and weak confinement model, respectively, for several QD sizes in the range between 4.5 and 12 nm (the detailed procedure can be found in the SI).…”