Abstract
We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr3 nanocrystals (NCs). Compared to phosphonic acids with linear alkyl chains, OLPA features a higher solubility in apolar solvents, allowing us to work at lower synthesis temperatures (100 °C), which in turn offer a good control over the NCs size. This can be reduced down to 5.0 nm, giving access to the strong quantum confinement regime. OLPA-based NCs form stable colloidal solutions at very low concentrations (∼1 nM), even when exposed to air. Such stability stems from the high solubility of OLPA in apolar solvents, which enables these molecules to reversibly bind/unbind to/from the NCs, preventing the NCs aggregation/precipitation. Small NCs feature efficient, blue-shifted emission and an ultraslow emission kinetics at cryogenic temperature, in striking difference to the fast decay of larger particles, suggesting that size-related exciton structure and/or trapping-detrapping dynamics determine the thermal equilibrium between coexisting radiative processes.
Highlights
We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr3 nanocrystals (NCs)
In a recent work from our group, we demonstrated that CsPbBr3 NCs, synthesized in the presence of alkyl phosphonic acids as the only ligands in the reaction environment, are very stable against dilution, maintaining ∼100% PLQY even at concentrations as low as ∼1 nM
Letter synthesis approach had two major limitations: (i) the NC dispersions turned out to be unstable in air; (ii) the phosphonic acids employed require high temperatures to solubilize the metal cation precursors and this prevented the synthesis of small NCs.[12]
Summary
We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr3 nanocrystals (NCs). Strong quantum confinement regime (the exciton Bohr diameter of CsPbBr3 is 7 nm).[18,19] OLPA-based CsPbBr3 NCs, which are passivated by hydrogen phosphonates, phosphonic acid anhydrides, and phosphonate species (Scheme 1), exhibit excellent colloidal stability even when exposed to air and at extremely low concentration (∼1 nM), with no need to avoid cleaning procedures or to perform postsynthesis ligand exchange treatments aimed at preventing size evolution, as done in previous works in which small CsPbBr3 NCs were prepared and studied optically.[19,20]
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