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

Abstract

Colloidal lead halide perovskite (LHP) nanocrystals (NCs, with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are the latest generation of semiconductor quantum dots (QDs) of immense interest as classical and quantum light sources. LHP NCs form by sub-second fast and hence hard-to-control ionic metathesis reactions, which severely limits the access to size-uniform and shape-regular NCs in the sub-10 nm range. We posit that a synthesis path comprising an intricate equilibrium between the precursor (PbBr2) and the Cs[PbBr3] solute for the QD nucleation may circumvent this challenge. Here, we report a room-temperature synthesis of monodisperse, isolable spheroidal CsPbBr3 QDs, size-tunable in the 3-13 nm range. The kinetics of both nucleation and therefrom temporally separated growth are drastically slowed down by the formation of transient Cs[PbBr3], resulting in total reaction times of up to 30 minutes. The methodology is then extended to FAPbBr3 (FA = formamidinium) and MAPbBr3 (MA = methylammonium), allowing for thorough experimental comparison and modeling of their physical properties under intermediate quantum confinement. In particular, 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.

Precision Synthesis and Atomistic Analysis of Deep-Blue Cubic Quantum Dots Made via Self-Organization

“…Ideally, they are to be made with a high quantum yield and sufficient size uniformity for any applications, and with precise shape control for mimicking valency and bond directionality to be used as material voxels − or artificial nanocrystal molecules . However, this stringent requirement has been more difficult to meet as the QDs become smaller, , previous literature being unable to synthesize small, high quality, deep-blue emitting perovskite QDs with reasonable purity. − This is because their synthesis has been modeled after colloid synthesis relying on hot injection methods under nitrogen: , high temperatures promote rapid nucleation growth kinetics, making the synthesis harder to control when the materials become smaller. In addition, the conventional metrics of purity assessment such as photoluminescence quantum yield (PLQY) and full width at half maximum (FWHM) are unsuitable for atomic precision analysis of individual QD particles.…”