Revealing the Aging Effect of Metal-Oleate Precursors on the Preparation of Highly Luminescent CsPbBr₃ Nanoplatelets

Abstract

Due to the ultrafast crystallization process in the triple-source ligand-assisted reprecipitation (TSLARP) technique the [L y PbBr x ] octahedra is easily distorted, resulting in anisotropic two-dimensional nanoplatelets (NPLs) with low photoluminescence quantum yield (PLQY) and poor stability. Unexpectedly, we obtain CsPbBr3 NPLs with PLQY approaching unity and high stability using the TSLARP technique through aging the metal-oleate precursors. We find that the significant enhancement of the PLQY is related to the change of solution chemistry of the Pb-oleate precursor in the aging process. While hybrid CsPbBr3@Cs4PbBr6 NPLs with low PLQY (28%) are formed with fresh Pb-oleate precursor, phase-pure CsPbBr3 NPLs with PLQY of 97.4% are obtained with the aged Pb-oleate precursor. A model that takes into account the transformation of the Pb-oleate in toluene from isolated molecules into clusters after aging is proposed to explain the phenomenon. Our finding highlights the importance of understanding the solution chemistry for the synthesis of the highly luminescent NPLs and provides a new way to break the “blue-wall” in perovskite light-emitting devices.

Slowing Down for Growth Mechanism and Speeding Up for Performance Optimization Based on Single Ligand Passivated CsPbBr3 Nanoplatelets

“…After 240 min, the absorbance peaks of 2ML NPls, PbBr 6 4– and PbBr 4 2– become weakened accompanied by the appearance of 3ML NPls which is proved by the appearance of 462 nm emission. [ 1d,9,11 ] The in situ grown 3ML NPls on the irregular islands after 360 min can be observed from the corresponding TEM image (Figure S3b, Supporting Information), which is consistent with the enhanced emission band at 462 nm and the weakened emission band at 433 nm, indicating the gradual transition from 2ML to thicker 3ML NPls. After stirring for 600 min, only 462 nm emission in the PL spectrum can be observed, accompanied with a new 458 nm absorption bands in the absorption spectra which should be ascribed to 3ML NPls, suggesting almost all 2ML NPls have been consumed for producing 3ML NPls.…”

“…As shown in Figure a, the absorption bands at 428, 398, and 358 nm could be detected once dropping precursor into n‐hexane, which could be ascribed to 2ML NPls, PbBr 6 4– and PbBr 4 2– , respectively. [ 6a,10,11 ] Additionally, an absorption peak at ≈320 nm can be observed, which is generally assigned to Cs 4 PbBr 6 or PbBr 3 – according to previous works. [ 10 ] Then, the additional control group without adding CsBr was conducted (Control group without adding CsBr, see Methods for detail) to assign the peak at 320 nm to PbBr 3 – ionic groups, shown as Figure S2, Supporting Information.…”

“…Inspired by the previously reported Pb‐oleate clusters, [ 11 ] we have further investigated the crude solution of control group but without adding CsBr. Similarly, the cluster morphology can be observed in Figure 1c.…”

“…Intriguingly, these novel clusters in our experiments are obtained in only 10 min (Figure S5), which is more than 50 thousands faster than the formation of Pb‐oleate. [ 11 ] While decreasing the content of OAm below 1500 µL, the obtained PL spectra of products exhibit multiple bands (Figure 1d), indicating the unexpected formation of thicker NPls or nanocubes due to the insufficient PbBr x (OAm) y clusters, which shows the sufficient OAm is critical for the subsequent growth processes.…”

“…revealed the aging effect of metal‐oleate precursor on the preparation of highly luminescent CsPbBr 3 NPls, the PLQY of products is only 28% by using fresh metal‐oleate precursors but reaches 97.4% after aging precursor for 12 months. [ 11 ] Su et al. have slowed down the reaction rate by adding additional Ag + to control the release rate of Br – .…”