  Photoluminescence intermittency remains one of the biggest challenges to
realizing perovskite quantum dots (QDs) as scalable single photon emitters. We
compare CsPbBr3 QDs capped with different ligands, lecithin, and a combination
of oleic acid and oleylamine, to elucidate the role of surface chemistry on
photoluminescence intermittency. We employ widefield photoluminescence
microscopy, sampling the blinking behavior of hundreds of QDs. Using change
point analysis, we achieve the robust classification of blinking trajectories,
and we analyze representative distributions from large numbers of QDs
(Nlecithin = 1308, Noleic acid/oleylamine =1317). We find that lecithin
suppresses blinking in CsPbBr3 QDs compared to oleic acid/oleylamine. Under
common experimental conditions, lecithin-capped QDs are 7.5 times more likely
to be non-blinking and spend 2.5 times longer in their most emissive state,
despite both QDs having nearly identical solution photoluminescence quantum
yields. We measure photoluminescence as a function of dilution and show that
the differences between lecithin and oleic acid/oleylamine capping emerge at
low concentrations during preparation for single particle experiments. From
experiment and first principles calculations, we attribute the differences in
lecithin and oleic acid/oleylamine performance to differences in their ligand
binding equilibria. Consistent with our experimental data, density functional
theory calculations suggest a stronger binding affinity of lecithin to the QD
surface compared to oleic acid/oleylamine, implying a reduced likelihood of
ligand desorption during dilution. These results suggest that using more
tightly binding ligands is a necessity for surface passivation and
consequently, blinking reduction in perovskite QDs used for single particle and
quantum light experiments.
