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

Abstract

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 °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 time-resolved photoluminescence (TRPL) measurements is of the order of 25–75ns. The nanocubes synthesized at 120 °C reaches nearly 100% photoluminescence quantum yield (PLQY) within the measurement error and also exhibit excellent stability. The aged nanocrystals synthesized at 120 °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 by-product Cs4PbBr6 nanospheres is due to the ligand loss from the surface of the PNC which might cause the Pb and Br defects.