Carrier Dynamics of CsPbBr ₃ Perovskite Nanocrystals from Ensemble Average to Single-Particle Level for Safeguarding the Dilution-Induced Excited-State Decay Heterogeneity

Photoluminescence blinking remains one of the main challenges for perovskite nanocrystals (PNCs) to be used in single-emitter devices and light-emitting diodes. Besides the persistent surface traps, dilution-induced ligand desorption also affects the blinking. The ligands that can passivate the surface without affecting the charge-transfer efficiency and can resist the dilution-induced desorption will be ideal for having a blinking-free/suppressed PNC for device applications. We used ascorbic acid (AA) and benzoic acid (BA), two short-chain ligands, in the postmodification of oleic acid/oleylamine capped PNC (Un-PNC). The ensemble average transient absorption study reveals that both AA and BA reduced the surface trapping contribution to 12 from 28% in Un-PNC. However, the single-particle photoluminescence analysis reveals AA-PNC to be superior with 84% photoluminescence ON-fraction, 10%, and 23% more compared to BA-PNC and Un-PNC, respectively. A similar trend was observed for AA-PNC in the electron-trapping rate, with a 5-fold and 20-fold reduction than Un-PNCs and BA-PNCs, respectively. AA-PNCs also maintained long-term stability under ambient conditions with a minute decrease in the time-averaged ON-fraction by 9.5% after 4 months, whereas Un-PNCs showed a 36% reduction. Time-resolved photoluminescence and simulation suggest that the dilution-induced ligand detachment due to weaker binding affinity of BA compared to AA with the PNC surface is found to be the origin of disparity in blinking despite having similar photophysics in the bulk spectroscopic analysis. Mitigating the dilution-induced heterogeneity, AA is found to be an effective ligand for synthesizing blinking-suppressed PNCs without compromising charge transfer, opening a pathway for potential application in bioimaging, single-emitter devices, and LEDs.