Beyond Surface Facets and Morphology: Precision Silica Shelling for Enhanced Luminescence and Stability in Halide Perovskite Nanocrystals

Lead halide perovskite nanocrystals are now the workhorse in colloidal optical nanomaterials because of their simpler synthesis and bright emission. Making a robust shell of high-bandgap covalent semiconductor materials on the surface of these ionic nanocrystals still remained challenging, and hence, shelling different organic or soft materials remains the most feasible approach to protect the phase stability and brightness of these nanocrystals. Using three different silane precursors to control the hydrolysis rates in different steps, in this work, the encapsulation of SiO₂ has been performed. The approach remains robust and versatile, where CsPbBr₃ nanocrystals having different surface facets and dimensions and also heterostructures with metal Pt are successfully encapsulated with a shell thickness varying from 5 to 20 nm. In all cases, including year-old samples having a quantum yield of less than 10%, these silica-shelled samples gain near-unity photoluminescence efficiency. The chemistry of using three reagents and the control of thickness, retaining monodispersity, are studied in detail and reported. These core@shell nanocrystals are further explored for low-temperature photoluminescence, and ultrafast spectroscopic study, to explain the mechanism of enhanced brightness as well as biexciton generation. Further, ultrasensitive single-particle spectroscopic measurements are carried out to establish the optical stability of perovskite nanocrystals with versatile morphologies. Importantly, this silica shelling also makes the perovskite nanocrystals nonblinking emitters with a concurrent ON percentage of more than 90% in some cases. Thus, this encapsulation strategy indeed provides a pathway in bringing stability and brightness and also helps in understanding surface involvement for controlling the photophysical processes of ionic halide perovskite nanocrystals.