posted on 2021-09-28, 17:14authored byRazi Ahmad, Lukáš Zdražil, Sergii Kalytchuk, Alberto Naldoni, Andrey L. Rogach, Patrik Schmuki, Radek Zboril, Štěpán Kment
Doping and compositional
tuning of Cs2AInCl6 (A = Ag, Na) double perovskite
nanocrystals (PNCs) is considered
a promising strategy toward the development of light-emitting sources
for applications in solution-processed optoelectronic devices. Oleic
acid and oleylamine are by far the most often used surface capping
ligands for PNCs. However, the undesirable desorption of these ligands
due to proton-exchange reaction during isolation and purification
processing results in colloidal and structural instabilities. Thus,
the improvement of colloidal and optical stability of PNCs represents
one of the greatest challenges in the field. Here, we report a trioctylphosphine-mediated
synthesis and purification method toward Sb-alloyed Cs2NaInCl6 PNCs with excellent stability and optical features.
Nuclear magnetic resonance spectroscopy enabled one to explain the
role of trioctylphosphine and to reveal the reaction mechanism during
crystal nucleation and growth. Under the optimized reaction conditions, in situ-generated trioctylphosphonium chloride and benzoyl
trioctylphosphonium chloride serve as highly reactive halide sources,
while benzoyl trioctylphosphonium and oleylammonium cations together
with the oleate anion serve as surface capping ligands, which are
bound strongly to the PNC surface. The tightly bound ionic pair of
oleylammonium oleate and benzoyl trioctylphosphonium chloride/oleate
ligands allows one to obtain monodispersed bright-blue-emitting PNCs
with high photoluminescence quantum yields exceeding 50% at an optimum
Sb content (0.5%), which also exhibit long-term colloidal stability.
The approach based on dual cationic ligand passivation of double PNCs
opens the doors for applications in other systems with a potential
to achieve higher stability along with superior optical properties.