Stable and Size Tunable CsPbBr<sub>3</sub> Nanocrystals Synthesized with Oleylphosphonic Acid.

Zhang, Baowei; Goldoni, Luca; Lambruschini, Chiara; Moni, Lisa; Imran, Muhammad; Pianetti, Andrea; Pinchetti, Valerio; Brovelli, Sergio et al. · Nano Lett · 2020

basic_science · Level V

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Abstract

We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr<sub>3</sub> 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.