Vacuum-assisted low-temperature growth of perovskite nanocrystals reaching near-unity photoluminescence quantum yield

In this work, luminescent perovskite nanocrystals (PNCs) were grown by the modified hot-injection method under reduced pressure at low temperatures. This modified method utilizing the property of reduction of the boiling point of the solvent under reduced pressure. This proposed method facilitates the growth of high-quality nanocrystals (NCs) without a Schlenk line and inert environment. The synthesis temperature of these PNCs using this method is reduced by 30-40 degrees C compared to the conventional hot-injection method. Different PNCs starting from nanoplatelets to nanocubes and nanorods were successfully grown using this method. The morphology, structural and luminescence properties of the NCs which are grown by this modified hot-injection method depend on synthesis temperature. The average lifetime of the charge carriers in PNCs is estimated from the timeresolved photoluminescence (TRPL) measurements is of the order of 25-75ns. The nanocubes synthesized at 120 degrees C reaches nearly 100% photoluminescence quantum yield (PLQY) within the measurement error and also exhibit excellent stability. The aged nanocrystals synthesized at 120 degrees C retain 83% of their initial PLQY when exposed to an ambient atmosphere for one month. Besides, we have investigated the origin of the instability of these PNCs when exposed to an ambient atmosphere. It is evident from the X-ray diffraction (XRD) measurements the degradation of the PNCs via the formation of the Cs-rich by-product Cs4PbBr6. The main reason for the formation of the Cs-rich by-product is due to the limited solubility of PbBr2 at relatively low temperatures, which results in the vacancy formation of Pb and Br during synthesis. Another reason for the formation of Cs-rich byproduct Cs4PbBr6 nanospheres is due to the ligand loss from the surface of the PNC which might cause the Pb and Br defects.

Automated summary

In this study, luminescent perovskite nanocrystals were successfully grown using a modified hot-injection method under reduced pressure at low temperatures, resulting in high-quality NCs with morphological and luminescent properties dependent on synthesis temperature. The average lifetime of charge carriers in PNCs was estimated from TRPL measurements to be 25-75ns, with nanocubes synthesized at 120 degrees C exhibiting nearly 100% PLQY within measurement error and excellent stability. Exposure to an ambient atmosphere led to the formation of Cs-rich by-product Cs4PbBr6, attributed to limited solubility of PbBr2 and ligand loss from the PNC surface during synthesis.