Surface modification strategy improves stability of CsPbBr3 perovskite nanocrystals
Objective In recent years,all-inorganic lead halide perovskite(CsPbX3,X=Cl,Br,I)nanocrystals,a type of nanoscale com-posite material,have attracted significant attention from materials scientists.With a high photoluminescent quantum yield,an extremely narrow full width at half maximum(FWHM),tunable emission across the visible spectrum,and high carrier mobility,CsPbX3 is rapidly becoming one of the most promising materials for optoelectronic devices.However,due to their unique proper-ties,perovskite materials exhibit low stability in aqueous solutions and typically need to be synthesized in non-polar organic sol-vents to prevent decomposition.To enhance stability,it is necessary to modify their surface with hydrophobic groups,which greatly restricts their application in aqueous environments.To overcome these challenges,researchers are exploring green,simple,aqueous-phase synthesis methods to directly synthesize perovskite nanocrystals with specific functions.Traditional syn-thesis methods typically avoid water to prevent adverse effects on the structure and properties of the highly water-sensitive perovskite nanocrystals.Nonetheless,recent research has shown that the presence of water is not always a disadvantage.In this study,the stability and optical properties of CsPbBr3 perovskite nanocrystals were improved by introducing L-aspartate ligands instead of OA ligands.Methods The entire synthesis process was conducted in air without inert gas protection,as shown in Fig.1.CsBr(0.4 mmol)and PbBr2(0.4 mmol)were dissolved in 10 mL of N,N-dimethylacetamide(DMA)solution,heated to 50 ℃,and magnetically stirred for 45 min until completely dissolved.Subsequently,800 μL of OAm was added,during which the solution gradually changed from colorless to white turbid.The precursor was recorded as Cs4PbBr6 NCs.After 15 min of continued stirring,1 mL of the white precursor solution was added into deionized water containing L-aspartate.After 10 s of reaction,the resulting mix-ture was centrifuged for subsequent characterization.The produced sample was recorded as CsPbBr3-L-Asp.Results and Discussion With the gradual addition of aspartic acid from 0.05 mmol to 0.3 mmol in 10 mL of deionized water,the PL intensity of the prepared samples first increased and then decreased,while the emission peak remained stable at 517 nm without significant shifts.The full width at half maximum of 17 nm had a high color purity.The CsPbBr3 NCs synthesized with an optimal addition of 0.15 mmol of aspartic acid exhibited the best PL intensity.Digital photos of CsPbBr3 NCs prepared with different L-aspartate amounts under a 365 nm portable UV lamp were shown in Fig.3(c).Perovskite nanocrystals are prone to degradation in polar environments due to their ionic properties.Fig.6(a)showed the PL spectra of nanocrystals soaked in aque-ous solution for 11 h with changes over time,illustrating that the emission peak maintained its original shape without signifi-cantly shifts during the whole test process.Fig.6(b)showed the fluorescence intensity changes over time,indicating a slow decrease within 1 h,retaining about 95% of the initial value.After 11 h of continuous soaking,the nanocrystals still showed weak green fluorescence under ultraviolet light.Conclusion CsPbBr3-L-Asp perovskite nanocrystals were successfully prepared using water phase synthesis method.CsPbBr3-L-Asp exhibits good crystallization with a maximum emission peak at 517 nm,FHWM of 17 nm,and fluorescence lifetime of 49.45 ns.Surface modification with L-aspartic acid and OAm allows the nanocrystals to emit green light after 11 h soaking in water without significant changes to the emission peak.
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