Towards non-blinking perovskite quantum dots

Towards non-blinking perovskite quantum dots | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Towards non-blinking perovskite quantum dots Yitong Dong, Chenjia Mi, Gavin Gee, Chance Lander, Matthew Atteberry, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4214840/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Surface defect-induced photoluminescence blinking is ubiquitous in lead halide perovskite quantum dots (QDs). Despite efforts to passivate the defects on perovskite QDs by chemically engineering ligand binding moieties, blinking accompanied by photodegradation still poses barriers to studying and implementing quantum-confined perovskite QDs in quantum emitters. We posited that the intermolecular interaction between ligands can affect the QD surface passivation. In the solid state, steric repulsions among bulky ligand tails prevent adequate QD surface ligand coverage. Alternatively, attractive π-π stacking between low-steric phenethylammonium (PEA) ligands promotes the formation of a nearly epitaxial surface ligand layer. Here, we demonstrate that single CsPbBr 3 QDs covered by these PEA ligands are nearly non-blinking, with single photon purity reaching 98%. Moreover, these QDs exhibited no spectral shifting and photodegradations, and they remained blinking-free after 12 hours of continuous operation. Free of interferences from blinking and photodegradation, we present size-dependent exciton radiative rates and emission line widths of single CsPbBr 3 QDs ranging from strongly to weakly confined regimes. Physical sciences/Nanoscience and technology/Nanoscale materials/Quantum dots Physical sciences/Chemistry/Theoretical chemistry/Density functional theory Physical sciences/Materials science/Nanoscale materials/Quantum dots Physical sciences/Optics and photonics/Optical physics/Nanophotonics and plasmonics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Photonic-based quantum networks have the potential to paradigmatically change information sciences. 1 One essential element for photonic quantum networks is the quantum light source. CsPbX 3 (X = Cl, Br, I) perovskite quantum dots (QDs) are promising light-emitting materials because of their high photoluminescence (PL) quantum yield (QY) and facile syntheses. 2–4 Recent advances in the precise synthetic control over the size, shape, and composition 5–7 of these perovskite QDs have catalysed the development of highly efficient LEDs 8–10 ,lasers 11 and quantum light sources. 12, 13 Recently, single CsPbX 3 QDs were intensively studied to demonstrate their single photon emissions 14 with high brightness 15 and photocoherence 16 . However, research on exciton dynamics in single CsPbX 3 QDs to date has mainly focused on weakly confined nanocrystals because size-confined CsPbX 3 QDs generally exhibit poor photostability. Particularly, perovskite QDs show severe PL intermittency (“blinking”) and photodegradation when their sizes are smaller than their exciton Bohr diameters. 17–19 This convolutes their exciton properties with defect-related dynamics. 20, 21 Therefore, improving the photostability of strongly confined perovskite QDs is vital to achieving reliable experimental determinations of size-dependent structural-optical relationships in perovskites, including exciton PL lifetime, exciton-lattice coupling, and many-body interactions. This knowledge is crucial to consolidating our current theoretical models of band-edge excitons in perovskites 22–24 and guiding the design of high-fidelity QD-based quantum light emitters. The insufficient photostability of small CsPbX 3 QDs relates to their strong quantum confinement. Since the scales of exciton-surface lattice interactions are inversely proportional to the volume of the QD, the optical properties of small CsPbX 3 QDs are more prone to surface defects. These surface defects can trap photo-generated charge carriers from excitons and leave the QD charged. 25 Subsequently generated excitons in this charged QD will form trions that can undergo fast non-radiative Auger recombination and turn the PL of the QD “OFF”. 26 This defect-induced QD charging is the primary blinking mechanism and relates to structural degradations in perovskite QDs. 19, 27, 28 To improve the photostability of CsPbX 3 QDs, their surface defects need to be well passivated. While coating a wide-bandgap semiconductor shell can suppress blinking and photodarkening in II-VI QDs, such as CdSe, 29 a well-established shelling protocol for highly ionic CsPbX 3 QDs has yet to be discovered. Instead of shelling, a nearly epitaxial ligand coverage is required for a defect-free QD surface. Unfortunately, traditional ligands on CsPbX 3 QDs are under adverse solubilization equilibrium and thus only deliver sufficient surface coverages in concentrated QD colloids. 30, 31 Consequently, when the colloidal QDs are diluted to ensure low QD density for single particle studies, the ligands will be stripped along with ions comprising the QD surfaces, creating surface defects. Ligands with enhanced binding affinities have been developed to mitigate QD surface disintegrations. For example, charge-neutral Zwitter-ionic molecules were applied to weakly confined CsPbBr 3 QDs to mitigate the ionic metathesis during QD dilution. 32–34 Additionally, surface treatments using didodecyldimethylammonium bromide (DDAB) or phosphonic acids can passivate exposed Pb cations and thus improve PLQY of CsPbBr 3 QDs. 35, 36 Nevertheless, small-sized CsPbX 3 QDs still suffer from blinking and photodarkening, 18, 37 suggesting that their surfaces are still under-passivated. While tolerated by weakly confined perovskite QDs, under-passivated surfaces can be detrimental to strongly confined QDs. 9 Incomplete surface ligand coverage in solid-state single QDs The cause of incomplete surface defect passivation lies in the intermolecular interaction in bulky ligands that cohered on QD surfaces in the solid state. 38 These ligands contain long hydrocarbon tails that are required to impart sufficient miscibility of ionic QDs with non-polar solvents. Furthermore, designer ligands often adopt branched or multiple hydrocarbon ligand tails to entropically promote the colloidal stability of QDs. 32, 39 However, the steric effect of bulky tails can negatively affect surface ligand coverage in the solid state. For example, DDA, which has two long-chain tails, is a well-established ligand for colloidal CsPbBr 3 QDs. But fully passivating the (100) facet of CsPbBr 3 using DDA would require an aliphatic chain density of ~ 5.7 chains·nm − 2 , exceeding that of the crystalline aliphatic chain density (4.9 chains·nm − 2 ). 40 Therefore, bulky aliphatic ligands stabilizing QDs in solution are unlikely to accommodate complete surface passivation of single CsPbBr 3 QDs in the solid state. To understand the incomplete surface ligand coverage of perovskite QDs in the solid state, we used density functional theory (DFT) to estimate the surface energies of a DDA (truncated to reduce computation cost) passivated 2×2×1 CsPbBr 3 slab as a function of surface ligand coverages (Supplementary Note 1 and Supplementary Fig. 1–5). Considering that the bulky ligand tails in DDA will lose conformational freedom when being solidified, the intramolecular entropy reduction can significantly increase the surface energy (Supplementary Note 2). As shown in Fig. 1 a and 1 b, the lowest surface energy of the CsPbBr 3 slab was achieved when 7 of the 8 Cs + sites were filled by DDAs, and adding an additional DDA would increase the surface energy. This suggests that the ligand-to-ligand interactions can destabilize the surface passivation (Supplementary Note 3), which is in good agreement with previous studies. 41 To better visualize the effect of intermolecular interactions, we investigated the differential in surface energy regarding the numbers of surface ligands (Fig. 1 b and 1 d) which represents the energy gain/loss of binding the N th (N = 1–8) ligand onto the surface. It is seen that after the 4th DDA (50% surface coverage), additional DDA bindings were less energetically favoured, and the 8th DDA binding was energetically forbidden. Therefore, complete surface passivation is not favoured in solid state QD samples when bulky, entropic ligands are used. Near-epitaxial QD surface passivation This problem can be solved by reducing the size of ligand tails and functionalizing them with moieties featuring attractive intermolecular interactions. To assess the effect of such tail groups, we replaced truncated DDA cations with phenethylammonium (PEA) cations, a small ligand that can feature attractive intermolecular π-π stacking (Fig. 1 c). First, the surface free energy reached the minimum when the surface is fully covered by PEAs (Fig. 1 d). In addition, smaller ligand tails reduced the entropy penalty, and the surface free energy was much lower than that of the DDA-covered surface. Furthermore, the differential surface free energy of the PEA-covered QD slab indicated that increasing PEA coverage would always be favoured. This suggests that intermolecular π-π interaction between PEA cations can drive the near-epitaxial surface passivation of the QD surface, minimizing the probability of defect formations. Our ligand design was then tested using strongly confined CsPbBr 3 QDs synthesized following a previously reported method with modifications (Methods). 5 The QDs have a cubical shape and expose mostly the (100) facets (Fig. 1 e and Supplementary Fig. 6). The π-π interaction between the bound PEA ligands were investigated using nuclear magnetic resonance (NMR) Overhauser effect spectroscopy (NOESY). To prepare PEA-exchanged QD colloids for NMR measurements, a small amount of saturated PEA bromide (PEABr) N , N -dimethylformamide (DMF) solution was added into the QD colloids followed by purification (Methods). The 1 H NMR spectrum showed that both PEA and oleylammonium cations (the original ligands) were bound to the QDs (Supplementary Figs. 7 and 8). The incomplete exchange was expected due to the limited solubility of PEABr in non-polar organic solvents. To investigate the intermolecular interaction between PEAs, the NOESY was used to monitor the coupling of protons on the surface-bound phenyl rings. To distinguish the nOe signals contributed by intermolecular π-π stacking from the intramolecular coupling, half of the PEAs used for the ligand exchange were labelled by a methyl group on the para position of their phenyl rings (MPEA). Figure 1 e shows the expanded region of the NOESY spectrum of the ligand-exchanged CsPbBr 3 QD colloids (full spectrum in Supplementary Fig. 9). Strong cross-peaks at 7.09, 7.13, and 7.32 ppm arose from the intermolecular correlations between the para- , meta- , and ortho -protons on the PEA phenyl rings and the para -methyl protons on the MPEA, respectively. This demonstrates the π-π stacking between the phenyl rings in surface bound PEA and MPEA. An approach to address incomplete surface ligand exchange using solubility-incompatible ligands is solid-state ligand exchange, in which the QDs capped by original ligands were exposed to polar solutions of shorter ligands. 42 To make QD samples for single-particle studies, we performed the solid-state exchange by casting diluted CsPbBr 3 QDs onto a supersaturated PEABr solution in DMF on a spinning substrate (Methods). QD dilutions facilitate the detachment of original ligands, and the low QD concentration also increases the PEA-to-QD ratio, which is critical for thorough ligand exchanges. 42 Furthermore, additional bromide introduced by PEABr can compensate the potential surface bromide loss during QD dilution, and the PEABr surface termination can support the intrinsic electronic structure of CsPbBr 3 , increasing the PLQY. 35, 43 After the exchange, the sample was carefully annealed in a nitrogen glovebox to assist intermolecular stacking (Methods). Accordingly, the PEA-covered QDs were dispersed in a crystalized matrix formed by excess PEABr molecules, as demonstrated in X-ray diffraction patterns (Supplementary Fig. 10). NMR spectra of digested PEA-exchanged QDs show no signal from original ligands, suggesting the high efficiency of the solid-state ligand exchange approach (Supplementary Fig. 11). Also, QDs in the PEABr matrix retained their cubical shape, suggesting the integrity of QDs is preserved during the solid-state ligand exchange (Extended Fig. 1 and Supplementary Fig. 6). Blinking behaviours of single CsPbBr 3 QDs We first studied the blinking behaviours of single CsPbBr 3 QDs (~ 4.5 nm) passivated by long-chain ligands (DDA) and PEA. The OFF-state intensity threshold was determined by the QY of OFF states/trions, which were usually smaller than 20% in CsPbBr 3 QDs. 44, 45 Typically, PL emissions with intensities above the OFF threshold were all considered as the “ON” state. However, PL from this “ON” state cannot properly represent the pure excitonic emissions, since the frequent PL intensity fluctuation in CsPbBr 3 QDs together with photodarkening can convolute PL with dimmer emissive states (e.g., grey states) with the PL from exciton states. 46, 47 To better quantify the ON state fraction, the ON/OFF state threshold was raised to 50% of the maximum PL intensity. As shown in Fig. 2 a and 2 c, the DDA-covered CsPbBr 3 QD exhibited severe PL blinking and was photodarkened only after 120 s of excitation. Typical ON/OFF intensity threshold would result in a 47.0% and 90.2% ON time fraction for measurement duration of 300 s and 60 s, respectively. Instead, our higher threshold yielded 16.5% and 55.4% ON time fraction, which better represented the blinking behaviour of DDA-covered CsPbBr 3 QDs. Despite the aggressive threshold, the PEA-covered QD remained mostly in the ON state without photodarkening over 10 mins (Fig. 2 b). Figure 2 d shows a blinking trace in a 60 s time window. Specifically, the QD exhibited an ON fraction of 94.2% over 10 mins and 98.6% over 60 s, both much higher than that of the DDA-covered QD. To better analyse the PL intensity trajectories of our PEA-covered CsPbBr 3 QD, we also used the Mandel Q parameter to quantify the deviation of the PL intensity distribution from shot-noise limited, Poisson statistics (Supplementary Note 4). 47, 48 The PL intensity distribution of a blinking-free QD should simultaneously have a high ON fraction and a close-to-zero Q parameter. Shown in Fig. 2 c, DDA-covered QDs exhibited a broad and asymmetric PL intensity distribution histogram with a Q parameter of 7.3. In stark contrast, the PEA-covered QD exhibited a narrow PL intensity distribution with a Q parameter of 0.3. The ON time fraction and Mandel Q parameter of the PEA-covered QD remained consistent when a shorter bin time was used (Extended Fig. 2 ). These suggest that the PL emissions from the PEA-covered QD were dominated by exciton radiative recombination and were not influenced by stochastic QD charging or environmental charge redistributions. Another consequence of charging-induced PL blinking is spectral diffusion, which has been frequently reported in long-chain ligands covered CsPbBr 3 QDs. 16, 32 Such PL energy jumping is detrimental to the performance of QDs as quantum emitters. Our PEA-covered QD shows a spectrally stable PL. As shown in Fig. 2 e, no spectral diffusion was detected, which was consistent with the nearly non-blinking behaviour. In comparison, the DDA-covered QD show clear spectral diffusion in the first 10 s of the measurement (Supplementary Fig. 12). The high single photon purity of the PEA-covered QD with a g (2) (0) value of 0.013 was also expected, given its strong size confinement (Fig. 2 f). This is also one of the lowest g (2) (0) values reported for perovskite QDs. This significantly improved single QD optical performance was echoed by the statistics of the ON and OFF durations extracted from blinking traces of 60 PEA-covered CsPbBr 3 QDs, as shown in Fig. 2 g. The probability distributions for the duration ( t ) of the ON and OFF events, P ON/OFF , were fitted to a power law distribution \(P\propto {t}^{-{k}_{\text{O}\text{N}/\text{O}\text{F}\text{F}}}\) , where k ON/OFF were set as the power law exponents that describe the statistics of the ON/OFF events. For instance, a smaller k OFF (a steeper slope in the log-log plot) means long-duration OFF events were less likely to happen. In typical QDs, both k ON and k OFF values are ~ 1.5. 49 Our QDs showed an average k ON of 2.0 and k OFF value of 1.0, comparable to one of the best non-blinking core-shell II-VI and III-V QDs reported. 29, 50 This implies that our CsPbBr 3 QDs are almost defect-free. The nearly complete passivation of PEA-covered QDs benefit from the attractive intermolecular interactions between PEA cations. To demonstrate the necessity of this, we applied another low-steric ligand without π-π stacking effects, iso -propylammonium (IPA) bromide, to cover the same CsPbBr 3 QDs used in Fig. 2 (4.5 nm). IPA-covered QDs still showed suppressed blinking with an ON time fraction of 83% (Extended Fig. 3 ). This was potentially due to the absence of strong intermolecular steric repulsion in IPA compared to DDA. However, a clear OFF fraction distribution was observed, implying the existence of surface defects due to incomplete passivation in IPA-covered QDs. Stability of PEA-covered CsPbBr QDs Similar to PL blinking, rapid photodegradation of CsPbBr 3 QDs has been a long-standing obstacle to investigations of their excitonic properties at the single particle level. Strongly confined CsPbBr 3 QDs are reported to experience spectral blue-shifting due to size shrinking within a short time of laser excitation. 13, 51, 52 According to the DFT modelling, QD surface can be significantly stabilized when it is fully-covered by PEAs. This would be manifested as resistance to photodegradation. Indeed, the single strongly confined CsPbBr 3 QD showed no spectral diffusion and size shrinking-induced blue-shifting during 30 mins of laser irradiation (Fig. 3 a and 3 b), and the PL spectra before and after operation were nearly identical (Fig. 3 c). CsPbBr 3 QDs are notoriously prone to photodarkening. This occurs when light irradiation creates new surface defects on QDs and intensifies their PL blinking. To explore the surface structural stability of strongly confined PEA-covered CsPbBr 3 QDs at an ensemble level, a collection of isolated QDs was illuminated at the same time. Their PL intensity stayed constant over the course of the measurement (> 10 h). In comparison, the PL intensity of the same QDs covered by DDA dispersed in polystyrene decreased since the first minute of laser exposure and became nearly completely dark after ~ 10 min (Fig. 3 d). Notably, the PEA-covered QD remained nearly non-blinking with a 98% ON fraction beyond 12 hours of continuous operation (Fig. 3 e and 3 f). We also tested the PEA-covered single QDs at high excitation rates using a pulsed laser with tuneable laser pulse energy. During the test, QDs remained nearly non-blinking when the excitation density (average number of excitons created per pulse) was increased to 0.21 (Extended Fig. 4 and Supplementary Note 5). In addition, PEA-covered QD stayed blinking-free for about a month of storage at ambient condition (Supplementary Fig. 13). To the best of our knowledge, this is comparable to some of the most photostable non-blinking CdSe QDs with CdS shells. 29 PL performance of CsPbBr QDs with various sizes We then explored our ligand design on single CsPbBr 3 QDs with various sizes. The extent of quantum confinement in QDs increases with decreasing size, making the QD more sensitive to surface defects. Rarely can a surface passivation method work effectively for QDs with different sizes. Figure 4 a – 4 d show blinking traces of four different single CsPbBr 3 QDs covered by PEA with their sizes determined by their PL spectra (Fig. 4 e) with an empirical sizing curve. 6 All CsPbBr 3 QDs were nearly blinking-free with ~ 98% ON fractions and shot noise-limited PL intensity distributions, suggesting that PEA epitaxially passivated CsPbBr 3 QD surfaces (additional single QD measurements are shown in Supplementary Fig. 14). Notably, weakly confined CsPbBr 3 QDs can also benefit from the high surface PEA coverage: a single CsPbBr 3 QD with the size of 9 nm was nearly blinking free and maintained a 94.1% ON time fraction over 30 minutes; no spectral diffusion nor size-shrinking were detected during 1 hour of laser irradiation (Extended Fig. 5 ). These QDs were then examined to study their biexciton dynamics (Fig. 4 f). The fast biexciton Auger recombination of strongly confined CsPbBr 3 QDs was also echoed by a low average g (2) (0) value (0.054) from the statistics built using 60 strongly confined QDs (Extended Fig. 6). We noted that the variations of g (2) (0) values of non-blinking QDs were smaller than QDs exhibiting PL intensity fluctuations (Supplementary Fig. 15). 13 The larger g (2) (0) value variations in blinking QDs can be partially attributed to the attenuated single exciton emissions from other non-radiative channels. Non-blinking QDs are thus particularly useful for studying the biexciton recombination mechanisms since their g (2) (0) values can better represent the biexciton emission QY. 53 Determining the size-dependent exciton properties at the single QD level Size-dependent exciton properties are fundamentally important for unravelling the PL emission mechanism and exciton-lattice interaction in QDs. Experimental determination of PL properties in single QDs exclude the interferences of ensemble inhomogeneity. However, blinking and photodarkening can change exciton dynamics and PL line shapes. The nearly non-blinking CsPbBr 3 QDs with significantly improved photostability are therefore ideal to studying the intrinsic effects of quantum confinement on excitons. 54, 55 Exciton recombination dynamics were then studied using our single CsPbBr 3 QDs. They show mono-exponential PL intensity decay (Fig. 5 a) due to the absence of dimmer emissive states. We extracted the PL lifetimes from 81 QDs with sizes ranging from 3.6 nm to 14 nm (Fig. 5 b). Interestingly, the size-radiative rate correlation was not monotonic: the exciton radiative rate increased with reducing sizes and then decreased when the size was smaller than 4.5 nm. The initial increase of the radiative rates can be attributed to the increase of the optical band gap induced by quantum confinement. 56, 57 When the QD is more confined, thermal mixing of bright and dark exciton states will take over and reduce the radiative rate due to larger exciton fine structure splitting. 55, 56 Not only do our PEA-covered QDs reveal the exciton radiative rates, but they also exhibit intrinsic PL linewidths to help understand the size-dependence on exciton-lattice interaction in QDs. We discovered that the PL spectra were asymmetric for all CsPbBr 3 QDs even without spectral diffusion and shifting (Fig. 5 c). We employed two Voigt functions with a common peak position to fit the single QD PL spectra. The half-width half-maximums (HWHMs) of both functions were extracted for 81 non-blinking QDs (Fig. 5 d). In the weakly confined region, our QDs showed similar or narrower PL peaks compared to reported values from other literature (Supplementary Fig. 16). With decreasing QD size, the PL linewidths increase monotonically, which agreed well with previous studies. 58 However, the low-energy tail of the PL experienced a stronger dependence on the QD size compared to the high-energy part. The low energy tail in PL spectrum of CsPbBr 3 QD ensembles was frequently observed but rarely studied. Bright band tail states were proposed to explain the asymmetric PL. 59 However, this would imply the existence of multiple dimmer emissive states compared to the exciton state and was inconsistent with the mono-exponential PL decay observed in our nearly non-blinking QDs. Asymmetric PL spectra have also been discovered in CsPbBr 3 polycrystalline films and have been attributed to the Cs + relocation. 60 However, this effect should not be evident at room temperatures. The strong size dependence of the low energy tail infers that the surface lattices of the QDs may induce the PL asymmetry. Thus, the intrinsic PL asymmetry can be related to the optical phonon sideband 61 or momentarily trapped exciton-polarons formed by exciton-surface lattice interactions, which were also found in 2D perovskite nanoplates. 62 This is supported by the spectrally independent PL decay dynamics of PEA-covered CsPbBr 3 QDs (Supplementary Fig. 17). Our study suggests that even for defect-free QDs, the size can still substantially affect exciton-lattice interactions. Conclusions In conclusion, we have demonstrated that intermolecular interactions can significantly impact the surface ligand coverage of individual CsPbBr 3 QDs in solid states. Although bulky long-chain ligand tails can entropically improve the colloidal stability of perovskite QDs, steric repulsion can lead to uncovered surface sites and ion loss. Considering the packing effect of the ligand tail in the solid state, we employed a low steric ligand, PEA, with attractive intermolecular interactions on QDs, which was confirmed by 2D NOSEY experiment. We demonstrated that the PEA-covered CsPbBr 3 QDs ranging from 3.6 nm to 14 nm were nearly non-blinking, with an average ON time fraction > 90% and single photon emission purity of ~ 95%. Furthermore, the QDs showed no observable spectral diffusion or shifting at room temperature and remained non-blinking after 12 hours of continuous operation. The extraordinary photostability and significantly reduced blinking enabled the determination of size-dependent excitonic properties without the interference of stochastic charging or photodegradation. The exciton radiative recombination rates and PL line shapes were measured as a function of QD size, providing insights on previously uncertain intrinsic exciton fine-structure splitting and exciton-lattice interaction in perovskite QDs. Our study can benefit future fundamental studies on perovskite QDs at the single particle level and potentially realize stable perovskite QD-based quantum emitters. Declarations Acknowledgements This project is supported by the U.S Department of Energy (DE-SC0024441). Financial support for this work was partially provided by the U.S. National Science Foundation (NSF LEAPS-MPS: 231691) and the University of Oklahoma startup funds. This project is also supported by grants from the Research Council and the Dodge Family College of Arts and Science of the University of Oklahoma Norman Campus. We also acknowledge the support of the Vice President for Research and Partnerships of the University of Oklahoma. Y.S. is supported by National Science Foundation via grant CHE-2102071. Use of the TAMU Materials Characterization Facility (RRID: SCR_022202) are acknowledged. We thank Dr. Sisi Xiang for helps on electron microscope image processing. The DFT modelling was performed at the OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma. The authors thank Dr. Robert B. Scafe and Dr. Clara Smith for discussions on manuscript writing. Author information Authors and affiliations Department of Chemistry and Biochemistry, The University of Oklahoma, Norman, OK 73019, USA Chenjia Mi, Gavin C. Gee, Chance W. Lander, Matthew L. Atteberry, Novruz G. Akhmedov, Lamia Hidayatova, Jesse D. DiCenso, Wai Tak Yip, Yihan Shao, Yitong Dong Center for Quantum Research and Technology, The University of Oklahoma, Norman, OK 73019 USA Yihan Shao, Yitong Dong Contributions C.M. and G.C.G. performed the sample preparation, the spectroscopic experiments, and data processing; C.M. and Y.D. performed the data analyses; C.W.L., J.D.D. and Y.S. performed the DFT calculation and provided related discussions; M.L.A., C.M. and L.H. performed the CsPbBr 3 QD syntheses; N.G.A. conducted the NMR and NOESY experiments and helped to perform NMR data analyses; W.T.Y. supported the spectroscopic measurements; All authors contributed to manuscript writing; Y.D. supervised the project. Corresponding author Correspondence to Yitong Dong . Data Availability Data are available from the corresponding authors upon reasonable request. Ethics declarations Competing interests The authors declare no competing interests. References Kimble, H. J., The quantum internet. Nature 453 , 1023-1030 (2008). 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Pulay, P., Convergence acceleration of iterative sequences. the case of scf iteration. Chem. Phys. Lett. 73 , 393-398 (1980). Methods CsPbBr 3 QD syntheses To prepare the Cs-precursor, 900 mg Cs 2 CO 3 , 3.6 mL Oleic Acid (OA) and 9.6 mL 1-Octadecnece (ODE) were added into a 100 mL flask. The mixture was vacuumed on a Schlenk line for 15 min while stirring. The mixture was then heated to 150 °C under vacuum until it turned clear. When the pressure reached ~ 1 Pa, the flask was filled with N 2 . The temperature of the Cs-precursor was maintained at 120 °C for use. The Pb-precursor was prepared by adding 600 mg PbBr 2 , 1400 mg ZnBr 2 , and 200 μL hydrobromic acid (48% w/w aq.) in a 250 mL flask. Then 14 mL OA, 14 mL oleylamine (OAm), and 40 mL ODE were added into the flask. The mixture was stirred vigorously for ~ 3 mins and then vacuumed on a Schlenk line. The flask was then heated to 150 °C under vacuum until all solids were dissolved. The flask was then filled with N 2 , and the solution temperature was adjusted to 80 – 150 °C according to the targeted size of the QDs. When the desired temperature for the Pb-precursor was reached, 5.0 mL of Cs-precursor solution (at ~ 120 °C) was injected to the Pb-precursor. The temperature of the solution was kept constant for 15 – 30 min. The crude product was then cooled to room temperature and transferred to centrifuge tubes for purification. The crude product was first centrifuged at 7800 rpm for 5 min. The precipitate was discarded. The supernatant was transferred to new centrifuge tubes, to which 1:1 volume of acetone was added carefully then shaken vigorously until the mixture turned turbid. This fast mixing was observed to help preserve the PLQY of the purified CsPbBr 3 QDs. The mixture was shaken until it became turbid. QDs were collected by centrifuging the mixture at 7800 rpm for 5 min and discarding the supernatant. The precipitated QDs were redispersed in 5 mL hexanes to yield a stock CsPbBr 3 QD colloid. This stock colloid was further purified 1 – 2 times by reprecipitation with 3:1 volume ratio of methyl acetate and redispersion with hexanes. Larger strongly confined CsPbBr 3 QDs (6 – 7 nm) were synthesized with modified recipes: the amount of ZnBr 2 was increased to 2000 mg, the reaction temperature was increased up to 200 °C and the reaction time was reduced to 1 min. Weakly confined CsPbBr 3 QDs were synthesized using previously reported methods. 2 Solution ligand exchange of CsPbBr 3 QDs for NMR measurements 404 mg PEABr (or 202 mg PEABr + 216 mg MPEABr) was dissolved in 1 mL DMF and filtered through a PTFE syringe filter (VWR, 0.22 μm pore size). 2 mL CsPbBr 3 QD stock colloids (~ 100 μM) were reprecipitated 2 – 3 times with 10 mL methyl acetate and redissolved in 2 mL toluene or chloroform each time. To the purified CsPbBr 3 QD colloids, 40 μL of the PEABr DMF solution was added and vortexed for ~ 5 s. Then the mixture was centrifuged at 7800 rpm for 1 min, and the supernatant was carefully transferred to a new centrifuge tube. To the supernatant, 10 mL of methyl acetate was used to reprecipitate the QDs. This procedure was repeated to promote ligand exchange. After 2 – 3 times of ligand exchange, the precipitate QDs were vacuum-dried for 20 min and then redissolved in 0.8 mL anhydrous CDCl 3 for NMR measurements. NMR measurements The 1 H and NOESY NMR spectra were recorded on a VNMRS 500 MHz spectrometer at 25 °C and 60 °C equipped with a triple-resonance z-axis pulsed field gradient 5-mm probe. Typical parameters for acquiring 1 H NMR spectra were as follows: 8012.8 Hz spectral width, 5.0 s acquisition time, 4.5 μs (45°) pulse width, 1 s relaxation time, and 16 transients. The parameters for the NOESY were as follows: 5506.6 Hz spectral width in both dimensions (F1 and F2), 0.25 s acquisition time, 11.8 μs (90°) pulse width, 1.5 s relaxation time, 500 ms mixing time, 64 transients, with 512 increments along F1 dimension, each in phase sensitive mode. The free induction decays (FIDs) were zero-filled to give a 2k × 2k data matrix, and a Gaussian function was applied in both dimensions (F1 and F2) prior to Fourier transformation. The FIDs of the 1 H and NOESY NMR spectra were processed using MNOVA. The 1 H NMR chemical shifts are assigned relative to the residual proton peaks of CDCl 3 at 7.26 ppm. Solid-state ligand exchange of CsPbBr 3 QDs for single QD sample preparation Glass coverslips (25 mm × 25 mm × 0.17 mm) were cleaned by sonicating in triton-X detergent solution, DI water, acetone, and 2-propanol sequentially (40 min each), and then dried. Before use, the coverslips were cleaned with a UV-ozone cleaner for 40 min and transferred in a nitrogen glovebox. In the glovebox, 200 mg PEABr was dissolved in 1 mL of anhydrous DMF and filtered through a PTFE syringe filter (VWR, 0.22 μm pore size). The stock QD colloid was diluted using anhydrous octane to ~ 200 pM. For the solid-state ligand exchange, 150 μL of the PEABr solution was spin-coated on a clean coverslip at 4000 rpm. After ~ 35 s, 10 μL of the dilute CsPbBr 3 QD colloid was swiftly dropped on the coverslip while spinning. The coverslip was then annealed on a hot plate at 50 – 70 °C for 30 – 120 s. Then the sample coverslip was covered by a glass slide and its edges were sealed using UV-curing optical adhesives (Thorlabs NOA61). Single QD spectroscopy measurements The single QD sample was mounted onto a nano-positioner (Milles Griot Nanomax, with 3-axis manual and close-loop piezoelectric actuators) in a customized wide-field/confocal fluorescence microscope system (Supplementary Fig. 18). A 405 nm diode laser was used to excite the sample (Picoquant LDH-D-C-405, driven by a Picoquant Sepia PDL828 module). The laser was attenuated using a series of neutral density (ND) filters (Thorlabs) and sent into the objective lens (Olympus UPLXAPO100XO, 100× magnification, NA = 1.45) through a single-mode optical fibre (Thorlabs P1-305A-FC-1 with a collimator). The single QD sample was imaged using an EMCCD camera (Andor iXon Ultra 897) under wide-field mode. The QD of interest was moved to the centre of the laser beam focus spot for spectroscopy measurements under confocal mode. PL emissions of a single QD was collected using the same objective and sent through a set of optical filters (a 405 nm notch filter, a 425 nm long-pass filter and optional bandpass filters). The QD PL spectra was measured using a spectrograph (Andor Shamrock 500i equipped with an Andor iXon Ultra 897 EMCCD). The time-tagged, time-resolved single photon counting (to generate the blinking traces, the time-resolved PL decay, and the second-order photon corelation) were recorded using two single-photon avalanche diodes (Hamamatsu C11202-100) connected to a time-correlator (Picoquant HydraHarp 400) in a Hanbury Brown and Twiss configuration. The g (2) (0) values were corrected using a previously reported method. 53 All measurements were performed at room temperature. DFT modelling The ligand binding energies were calculated at the DFT level of theory using the projector augmented plane wave basis as implemented in the VASP 5.4 software package. 63, 64 Structures were optimized using the PBE functional 65 with D3(BJ) 66, 67 dispersion and dampening and an energy cutoff of 400 eV. Coordinates for the CsPbBr 3 surfaces were obtained from the Crystallography Open Database (COD ID: 4510745). 68, 69 Charge neutral 2×2×1 surfaces were constructed with ASE. 70 A 4×4×1 Monkhorst–Pack grid was used for Brillouin zone sampling. All structures were optimized using the RMM-DIIS algorithm 71 with a self-consistent field (SCF) convergence criterion of 1×10 -6 eV and an ionic convergence criterion of 1×10 -3 eV. The coordinates of the perovskite atoms were fixed during optimization. Additional Declarations There is NO Competing Interest. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4214840","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":294117574,"identity":"1b1056b8-1fc4-4550-8085-76a02afb940f","order_by":0,"name":"Yitong Dong","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5ElEQVRIiWNgGAWjYDACZgjF2AAiEyrAHAMCWpiRtDw4Q4wWBiQtjA/biNBicJz/4OOCXwyy/dLtFxgS59kkNrA3b5PAq+UwM7PxzD4G45lzzhQwJG5LS2zgOVZGSAubNG8PQ+KGGznpPxK3HU5skMgxI1pLAkPiHKAW+TdEaOH5AdKSfoAhsQFkCw9+LZKHmY2NeRskjGfOyAHGy7E04zaetGILfFr4zh98+Jjnj41sv0T6A8YfNUAG++GNN/BpUTgAJBjbQC7hgUQHGz7lICDfACL/gAj2B4QUj4JRMApGwQgFAIUdSJl/fw2iAAAAAElFTkSuQmCC","orcid":"","institution":"University of Oklahoma","correspondingAuthor":true,"prefix":"","firstName":"Yitong","middleName":"","lastName":"Dong","suffix":""},{"id":294117575,"identity":"f3fcea5e-4926-49e4-b648-158781900716","order_by":1,"name":"Chenjia Mi","email":"","orcid":"https://orcid.org/0000-0003-2169-864X","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Chenjia","middleName":"","lastName":"Mi","suffix":""},{"id":294117576,"identity":"3f53a612-d1ea-4cbe-8710-4ec31e7552c9","order_by":2,"name":"Gavin Gee","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Gavin","middleName":"","lastName":"Gee","suffix":""},{"id":294117577,"identity":"0f7f2195-5e79-4d14-90e4-8feaa1792d26","order_by":3,"name":"Chance Lander","email":"","orcid":"https://orcid.org/0000-0002-8819-3905","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Chance","middleName":"","lastName":"Lander","suffix":""},{"id":294117578,"identity":"a757372e-299d-4cfc-aef9-0c501f665341","order_by":4,"name":"Matthew Atteberry","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Matthew","middleName":"","lastName":"Atteberry","suffix":""},{"id":294117579,"identity":"1622796d-8686-4351-ac90-6b42e5302704","order_by":5,"name":"Novruz Akhmedov","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Novruz","middleName":"","lastName":"Akhmedov","suffix":""},{"id":294117581,"identity":"bd31ab36-5cdc-4408-8d76-dd9d8190d5ec","order_by":6,"name":"Lamia Hidayatova","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Lamia","middleName":"","lastName":"Hidayatova","suffix":""},{"id":294117582,"identity":"fbefead8-e234-4236-823d-4ae1bcd3c1c0","order_by":7,"name":"Jesse DiCenso","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Jesse","middleName":"","lastName":"DiCenso","suffix":""},{"id":294117583,"identity":"c1e935c3-0a35-4fb4-8e0a-a242f4330e86","order_by":8,"name":"Wai Tak Yip","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Wai","middleName":"Tak","lastName":"Yip","suffix":""},{"id":294117584,"identity":"bd448be1-892c-405b-adf8-5a03a1807a91","order_by":9,"name":"Yihan Shao","email":"","orcid":"","institution":"The University of Oklahoma","correspondingAuthor":false,"prefix":"","firstName":"Yihan","middleName":"","lastName":"Shao","suffix":""}],"badges":[],"createdAt":"2024-04-03 21:30:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4214840/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4214840/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-024-55619-7","type":"published","date":"2025-01-02T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":55978946,"identity":"e721196f-4211-410d-a3e0-1585694816c9","added_by":"auto","created_at":"2024-05-07 06:12:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":268340,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFree energies of ligand-covered CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e QD surfaces and intermolecular interactions of PEA ligands.\u003c/strong\u003e \u003cstrong\u003ea, c, \u003c/strong\u003eSlabs of CsPbBr\u003csub\u003e3\u003c/sub\u003e fully passivated with \u003cstrong\u003ea,\u003c/strong\u003e DDA (truncated) and \u003cstrong\u003ec,\u003c/strong\u003e PEA used in DFT calculations. The shaded circles in \u003cstrong\u003ea\u003c/strong\u003e indicate the intermolecular steric repulsions, while the dashed arrows in \u003cstrong\u003ec\u003c/strong\u003e indicate the intermolecular π-π stacking interactions. \u003cstrong\u003eb\u003c/strong\u003e, \u003cstrong\u003ed,\u003c/strong\u003e Calculated surface free energies (solid marks) and differential free energies (hollow marks) as a function of the numbers of surface-bound \u003cstrong\u003eb,\u003c/strong\u003e truncated DDA and \u003cstrong\u003ed,\u003c/strong\u003e PEA ligands. \u003cstrong\u003ee,\u003c/strong\u003e STEM image of a strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QD exhibiting cuboidal shape, exposing mostly the (100) facets. \u003cstrong\u003ef,\u003c/strong\u003e Expanded region of the solution NOESY spectrum shows QDs ligand-exchanged with mixed ligands containing PEABr and MPEABr, measured at 60 °C. The intermolecular and intramolecular proton nOe correlations between PEA moieties on the QD surface are schemed and labelled. The peak (partially unshown) marked by “X” is the chloroform solvent residue. The full spectrum is shown in Supplementary Fig. 9.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/a98ce3beddbc25dd3799fb65.png"},{"id":55978945,"identity":"79612bb2-d1d2-4cc4-8351-1ac50ef4dbb3","added_by":"auto","created_at":"2024-05-07 06:12:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":320226,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eNearly non-blinking strongly confined single CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e QD.\u003c/strong\u003e \u003cstrong\u003ea, b,\u003c/strong\u003e PL blinking traces and intensity distribution histograms of two ~ 4.5 nm CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs that are \u003cstrong\u003ea,\u003c/strong\u003e covered by DDA and dispersed in polystyrene measured for 5 min and \u003cstrong\u003eb,\u003c/strong\u003e covered by PEA measured for 10 min. The PL intensity drop in \u003cstrong\u003ea\u003c/strong\u003e is induced by photodarkening. \u003cstrong\u003ec, d,\u003c/strong\u003e A zoomed-in view of the blinking traces with a 1 min window, which is indicated by the vertical dashed lines in \u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003eb\u003c/strong\u003e, respectively. The intensity distribution histograms of \u003cstrong\u003eb\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e are shot noise limited with a \u003cem\u003eQ\u003c/em\u003e parameter of 0.3. The distribution is fit by Poissonian functions (dashed curves). \u003cstrong\u003ee,\u003c/strong\u003e Time-resolved PL spectra of a PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QD. No PL intensity fluctuation and spectral diffusion were observed. \u003cstrong\u003ef,\u003c/strong\u003e Second-order correlation (g\u003csup\u003e(2)\u003c/sup\u003e) function of the QD in \u003cstrong\u003eb\u003c/strong\u003e, fitted (dashed curve) to yield a g\u003csup\u003e(2)\u003c/sup\u003e(0) value of 1.3%. The QDs were excited by a 405 nm laser at \u003cem\u003ecw\u003c/em\u003e mode with an intensity of 120 W cm\u003csup\u003e-2\u003c/sup\u003e for these measurements. \u003cstrong\u003eg,\u003c/strong\u003e Probability distribution of the ON (red)/OFF (blue) durations obtained from blinking traces of 60 CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs, fitted to a power-law distribution (dashed lines).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/52d4adf53f708b2f66138ce2.png"},{"id":55979309,"identity":"4def915f-1093-416e-a99f-d697458d0350","added_by":"auto","created_at":"2024-05-07 06:20:11","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":194213,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpectral stability and resistance to photodarkening of PEA-covered CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e QDs.\u003c/strong\u003e \u003cstrong\u003ea, b,\u003c/strong\u003e Time-resolved PL spectra of a single CsPbBr\u003csub\u003e3\u003c/sub\u003e QD (~ 4.1 nm) \u003cstrong\u003ea\u003c/strong\u003e before and \u003cstrong\u003eb\u003c/strong\u003e after 30 min of continuous laser excitations (\u003cem\u003ecw\u003c/em\u003e mode, 120 W cm\u003csup\u003e-2\u003c/sup\u003e). \u003cstrong\u003ec,\u003c/strong\u003e Integrated PL spectra from \u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003eb\u003c/strong\u003e. The superimposed spectra showed no spectral shifting over 30 min of excitation. \u003cstrong\u003ed,\u003c/strong\u003e Normalized PL intensity of a collection of PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs (red) under 10 h of continuous laser excitation. DDA-covered QDs (blue) were significantly photodarkened in the first 10 minutes of operation. \u003cstrong\u003ee,\u003c/strong\u003e PL blinking trace and \u003cstrong\u003ef,\u003c/strong\u003e intensity distribution histogram of a single PEA-covered QD in \u003cstrong\u003ed\u003c/strong\u003e after 12 h of continuous operation.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/44b6619520cf0a8d5e87e2a0.png"},{"id":55978299,"identity":"6dec1100-ad86-4dc6-8e3f-8537e62d2c8d","added_by":"auto","created_at":"2024-05-07 06:04:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":167369,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eNearly non-blinking PEA-covered CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e QDs with various sizes. a – d,\u003c/strong\u003e Single QD PL blinking traces and intensity distribution histograms of four PEA-covered QDs with different sizes (with 405 nm laser excitation, pulsed mode). The intensity distribution histograms of all QDs were shot noise limited (Poisson fits were superimposed). \u003cstrong\u003ee,\u003c/strong\u003e Their corresponding PL spectra (color-coded). \u003cstrong\u003ef,\u003c/strong\u003e A representative g\u003csup\u003e(2)\u003c/sup\u003e plot of a PEA-covered QD obtained under pulsed excitation, showing a g\u003csup\u003e(2)\u003c/sup\u003e(0) value of 2.1%.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/9e48275d494c311dd2ac5b85.png"},{"id":55978295,"identity":"6c8d5bb2-ca77-46e5-bb7f-5f594304824a","added_by":"auto","created_at":"2024-05-07 06:04:11","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":87813,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSize-dependent exciton properties of CsPbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e QDs. a.\u003c/strong\u003e Representative time-resolved PL intensity traces of two single PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs, exhibiting mono-exponential decay (dashed curves). \u003cstrong\u003eb,\u003c/strong\u003e Statistics of exciton radiative recombination rates of 81 non-blinking QDs with different sizes. Dashed curve is a visual guide. \u003cstrong\u003ec,\u003c/strong\u003e PL spectra of two single PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs (intensity-normalized and peak position-shifted to zero for comparison). Dashed curves were fits, each using two Voigt functions that share a common peak position for the asymmetric spectra. \u003cstrong\u003ed,\u003c/strong\u003e PL linewidths (half-width half-maximum, HWHM) extracted from the high energy side and the low energy side of PL spectra for 81 non-blinking QDs. Dashed lines are visual guides.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/29ed24c03d562fe12c9f3190.png"},{"id":72949914,"identity":"94b3298e-9d27-49b2-8064-ed58d3133b26","added_by":"auto","created_at":"2025-01-04 08:15:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1868665,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/23644256-5699-4ff4-8225-a224ffbca972.pdf"},{"id":55978301,"identity":"47ff4e17-7f57-49a4-8850-89bc66b0ba17","added_by":"auto","created_at":"2024-05-07 06:04:12","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1852949,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/2c04c2a5a993e892701b8df7.docx"},{"id":55978300,"identity":"5443b3ad-ae2d-49fd-a4d3-db1925061f49","added_by":"auto","created_at":"2024-05-07 06:04:12","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":475514,"visible":true,"origin":"","legend":"","description":"","filename":"Extendedfigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-4214840/v1/2e9d32c014fe5b5938868e11.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Towards non-blinking perovskite quantum dots","fulltext":[{"header":"Main","content":"\u003cp\u003ePhotonic-based quantum networks have the potential to paradigmatically change information sciences.\u003csup\u003e1\u003c/sup\u003e One essential element for photonic quantum networks is the quantum light source. CsPbX\u003csub\u003e3\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;Cl, Br, I) perovskite quantum dots (QDs) are promising light-emitting materials because of their high photoluminescence (PL) quantum yield (QY) and facile syntheses.\u003csup\u003e2\u0026ndash;4\u003c/sup\u003e Recent advances in the precise synthetic control over the size, shape, and composition\u003csup\u003e5\u0026ndash;7\u003c/sup\u003e of these perovskite QDs have catalysed the development of highly efficient LEDs\u003csup\u003e8\u0026ndash;10\u003c/sup\u003e,lasers\u003csup\u003e11\u003c/sup\u003e and quantum light sources.\u003csup\u003e12, 13\u003c/sup\u003e Recently, single CsPbX\u003csub\u003e3\u003c/sub\u003e QDs were intensively studied to demonstrate their single photon emissions\u003csup\u003e14\u003c/sup\u003e with high brightness\u003csup\u003e15\u003c/sup\u003e and photocoherence\u003csup\u003e16\u003c/sup\u003e. However, research on exciton dynamics in single CsPbX\u003csub\u003e3\u003c/sub\u003e QDs to date has mainly focused on weakly confined nanocrystals because size-confined CsPbX\u003csub\u003e3\u003c/sub\u003e QDs generally exhibit poor photostability. Particularly, perovskite QDs show severe PL intermittency (\u0026ldquo;blinking\u0026rdquo;) and photodegradation when their sizes are smaller than their exciton Bohr diameters.\u003csup\u003e17\u0026ndash;19\u003c/sup\u003e This convolutes their exciton properties with defect-related dynamics.\u003csup\u003e20, 21\u003c/sup\u003e Therefore, improving the photostability of strongly confined perovskite QDs is vital to achieving reliable experimental determinations of size-dependent structural-optical relationships in perovskites, including exciton PL lifetime, exciton-lattice coupling, and many-body interactions. This knowledge is crucial to consolidating our current theoretical models of band-edge excitons in perovskites\u003csup\u003e22\u0026ndash;24\u003c/sup\u003e and guiding the design of high-fidelity QD-based quantum light emitters.\u003c/p\u003e \u003cp\u003eThe insufficient photostability of small CsPbX\u003csub\u003e3\u003c/sub\u003e QDs relates to their strong quantum confinement. Since the scales of exciton-surface lattice interactions are inversely proportional to the volume of the QD, the optical properties of small CsPbX\u003csub\u003e3\u003c/sub\u003e QDs are more prone to surface defects. These surface defects can trap photo-generated charge carriers from excitons and leave the QD charged.\u003csup\u003e25\u003c/sup\u003e Subsequently generated excitons in this charged QD will form trions that can undergo fast non-radiative Auger recombination and turn the PL of the QD \u0026ldquo;OFF\u0026rdquo;.\u003csup\u003e26\u003c/sup\u003e This defect-induced QD charging is the primary blinking mechanism and relates to structural degradations in perovskite QDs.\u003csup\u003e19, 27, 28\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTo improve the photostability of CsPbX\u003csub\u003e3\u003c/sub\u003e QDs, their surface defects need to be well passivated. While coating a wide-bandgap semiconductor shell can suppress blinking and photodarkening in II-VI QDs, such as CdSe,\u003csup\u003e29\u003c/sup\u003e a well-established shelling protocol for highly ionic CsPbX\u003csub\u003e3\u003c/sub\u003e QDs has yet to be discovered. Instead of shelling, a nearly epitaxial ligand coverage is required for a defect-free QD surface. Unfortunately, traditional ligands on CsPbX\u003csub\u003e3\u003c/sub\u003e QDs are under adverse solubilization equilibrium and thus only deliver sufficient surface coverages in concentrated QD colloids.\u003csup\u003e30, 31\u003c/sup\u003e Consequently, when the colloidal QDs are diluted to ensure low QD density for single particle studies, the ligands will be stripped along with ions comprising the QD surfaces, creating surface defects. Ligands with enhanced binding affinities have been developed to mitigate QD surface disintegrations. For example, charge-neutral Zwitter-ionic molecules were applied to weakly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs to mitigate the ionic metathesis during QD dilution.\u003csup\u003e32\u0026ndash;34\u003c/sup\u003e Additionally, surface treatments using didodecyldimethylammonium bromide (DDAB) or phosphonic acids can passivate exposed Pb cations and thus improve PLQY of CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs.\u003csup\u003e35, 36\u003c/sup\u003e Nevertheless, small-sized CsPbX\u003csub\u003e3\u003c/sub\u003e QDs still suffer from blinking and photodarkening,\u003csup\u003e18, 37\u003c/sup\u003e suggesting that their surfaces are still under-passivated. While tolerated by weakly confined perovskite QDs, under-passivated surfaces can be detrimental to strongly confined QDs.\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n\u003ch3\u003eIncomplete surface ligand coverage in solid-state single QDs\u003c/h3\u003e\n\u003cp\u003eThe cause of incomplete surface defect passivation lies in the intermolecular interaction in bulky ligands that cohered on QD surfaces in the solid state.\u003csup\u003e38\u003c/sup\u003e These ligands contain long hydrocarbon tails that are required to impart sufficient miscibility of ionic QDs with non-polar solvents. Furthermore, designer ligands often adopt branched or multiple hydrocarbon ligand tails to entropically promote the colloidal stability of QDs.\u003csup\u003e32, 39\u003c/sup\u003e However, the steric effect of bulky tails can negatively affect surface ligand coverage in the solid state. For example, DDA, which has two long-chain tails, is a well-established ligand for colloidal CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs. But fully passivating the (100) facet of CsPbBr\u003csub\u003e3\u003c/sub\u003e using DDA would require an aliphatic chain density of ~\u0026thinsp;5.7 chains\u0026middot;nm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, exceeding that of the crystalline aliphatic chain density (4.9 chains\u0026middot;nm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e).\u003csup\u003e40\u003c/sup\u003e Therefore, bulky aliphatic ligands stabilizing QDs in solution are unlikely to accommodate complete surface passivation of single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs in the solid state.\u003c/p\u003e \u003cp\u003eTo understand the incomplete surface ligand coverage of perovskite QDs in the solid state, we used density functional theory (DFT) to estimate the surface energies of a DDA (truncated to reduce computation cost) passivated 2\u0026times;2\u0026times;1 CsPbBr\u003csub\u003e3\u003c/sub\u003e slab as a function of surface ligand coverages (Supplementary Note 1 and Supplementary Fig.\u0026nbsp;1\u0026ndash;5). Considering that the bulky ligand tails in DDA will lose conformational freedom when being solidified, the intramolecular entropy reduction can significantly increase the surface energy (Supplementary Note 2). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, the lowest surface energy of the CsPbBr\u003csub\u003e3\u003c/sub\u003e slab was achieved when 7 of the 8 Cs\u003csup\u003e+\u003c/sup\u003e sites were filled by DDAs, and adding an additional DDA would increase the surface energy. This suggests that the ligand-to-ligand interactions can destabilize the surface passivation (Supplementary Note 3), which is in good agreement with previous studies.\u003csup\u003e41\u003c/sup\u003e To better visualize the effect of intermolecular interactions, we investigated the differential in surface energy regarding the numbers of surface ligands (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) which represents the energy gain/loss of binding the N\u003csup\u003eth\u003c/sup\u003e (N\u0026thinsp;=\u0026thinsp;1\u0026ndash;8) ligand onto the surface. It is seen that after the 4th DDA (50% surface coverage), additional DDA bindings were less energetically favoured, and the 8th DDA binding was energetically forbidden. Therefore, complete surface passivation is not favoured in solid state QD samples when bulky, entropic ligands are used.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eNear-epitaxial QD surface passivation\u003c/h3\u003e\n\u003cp\u003eThis problem can be solved by reducing the size of ligand tails and functionalizing them with moieties featuring attractive intermolecular interactions. To assess the effect of such tail groups, we replaced truncated DDA cations with phenethylammonium (PEA) cations, a small ligand that can feature attractive intermolecular π-π stacking (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). First, the surface free energy reached the minimum when the surface is fully covered by PEAs (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). In addition, smaller ligand tails reduced the entropy penalty, and the surface free energy was much lower than that of the DDA-covered surface. Furthermore, the differential surface free energy of the PEA-covered QD slab indicated that increasing PEA coverage would always be favoured. This suggests that intermolecular π-π interaction between PEA cations can drive the near-epitaxial surface passivation of the QD surface, minimizing the probability of defect formations.\u003c/p\u003e \u003cp\u003eOur ligand design was then tested using strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs synthesized following a previously reported method with modifications (Methods).\u003csup\u003e5\u003c/sup\u003e The QDs have a cubical shape and expose mostly the (100) facets (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee and Supplementary Fig.\u0026nbsp;6). The π-π interaction between the bound PEA ligands were investigated using nuclear magnetic resonance (NMR) Overhauser effect spectroscopy (NOESY). To prepare PEA-exchanged QD colloids for NMR measurements, a small amount of saturated PEA bromide (PEABr) \u003cem\u003eN\u003c/em\u003e,\u003cem\u003eN\u003c/em\u003e-dimethylformamide (DMF) solution was added into the QD colloids followed by purification (Methods). The \u003csup\u003e1\u003c/sup\u003eH NMR spectrum showed that both PEA and oleylammonium cations (the original ligands) were bound to the QDs (Supplementary Figs.\u0026nbsp;7 and 8). The incomplete exchange was expected due to the limited solubility of PEABr in non-polar organic solvents. To investigate the intermolecular interaction between PEAs, the NOESY was used to monitor the coupling of protons on the surface-bound phenyl rings. To distinguish the nOe signals contributed by intermolecular π-π stacking from the intramolecular coupling, half of the PEAs used for the ligand exchange were labelled by a methyl group on the \u003cem\u003epara\u003c/em\u003e position of their phenyl rings (MPEA). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee shows the expanded region of the NOESY spectrum of the ligand-exchanged CsPbBr\u003csub\u003e3\u003c/sub\u003e QD colloids (full spectrum in Supplementary Fig.\u0026nbsp;9). Strong cross-peaks at 7.09, 7.13, and 7.32 ppm arose from the intermolecular correlations between the \u003cem\u003epara-\u003c/em\u003e, \u003cem\u003emeta-\u003c/em\u003e, and \u003cem\u003eortho\u003c/em\u003e-protons on the PEA phenyl rings and the \u003cem\u003epara\u003c/em\u003e-methyl protons on the MPEA, respectively. This demonstrates the π-π stacking between the phenyl rings in surface bound PEA and MPEA.\u003c/p\u003e \u003cp\u003eAn approach to address incomplete surface ligand exchange using solubility-incompatible ligands is solid-state ligand exchange, in which the QDs capped by original ligands were exposed to polar solutions of shorter ligands.\u003csup\u003e42\u003c/sup\u003e To make QD samples for single-particle studies, we performed the solid-state exchange by casting diluted CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs onto a supersaturated PEABr solution in DMF on a spinning substrate (Methods). QD dilutions facilitate the detachment of original ligands, and the low QD concentration also increases the PEA-to-QD ratio, which is critical for thorough ligand exchanges.\u003csup\u003e42\u003c/sup\u003e Furthermore, additional bromide introduced by PEABr can compensate the potential surface bromide loss during QD dilution, and the PEABr surface termination can support the intrinsic electronic structure of CsPbBr\u003csub\u003e3\u003c/sub\u003e, increasing the PLQY.\u003csup\u003e35, 43\u003c/sup\u003e After the exchange, the sample was carefully annealed in a nitrogen glovebox to assist intermolecular stacking (Methods). Accordingly, the PEA-covered QDs were dispersed in a crystalized matrix formed by excess PEABr molecules, as demonstrated in X-ray diffraction patterns (Supplementary Fig.\u0026nbsp;10). NMR spectra of digested PEA-exchanged QDs show no signal from original ligands, suggesting the high efficiency of the solid-state ligand exchange approach (Supplementary Fig.\u0026nbsp;11). Also, QDs in the PEABr matrix retained their cubical shape, suggesting the integrity of QDs is preserved during the solid-state ligand exchange (Extended Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Supplementary Fig.\u0026nbsp;6).\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eBlinking behaviours of single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe first studied the blinking behaviours of single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs (~\u0026thinsp;4.5 nm) passivated by long-chain ligands (DDA) and PEA. The OFF-state intensity threshold was determined by the QY of OFF states/trions, which were usually smaller than 20% in CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs.\u003csup\u003e44, 45\u003c/sup\u003e Typically, PL emissions with intensities above the OFF threshold were all considered as the \u0026ldquo;ON\u0026rdquo; state. However, PL from this \u0026ldquo;ON\u0026rdquo; state cannot properly represent the pure excitonic emissions, since the frequent PL intensity fluctuation in CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs together with photodarkening can convolute PL with dimmer emissive states (e.g., grey states) with the PL from exciton states.\u003csup\u003e46, 47\u003c/sup\u003e To better quantify the ON state fraction, the ON/OFF state threshold was raised to 50% of the maximum PL intensity. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, the DDA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QD exhibited severe PL blinking and was photodarkened only after 120 s of excitation. Typical ON/OFF intensity threshold would result in a 47.0% and 90.2% ON time fraction for measurement duration of 300 s and 60 s, respectively. Instead, our higher threshold yielded 16.5% and 55.4% ON time fraction, which better represented the blinking behaviour of DDA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs. Despite the aggressive threshold, the PEA-covered QD remained mostly in the ON state without photodarkening over 10 mins (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed shows a blinking trace in a 60 s time window. Specifically, the QD exhibited an ON fraction of 94.2% over 10 mins and 98.6% over 60 s, both much higher than that of the DDA-covered QD.\u003c/p\u003e \u003cp\u003eTo better analyse the PL intensity trajectories of our PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QD, we also used the Mandel \u003cem\u003eQ\u003c/em\u003e parameter to quantify the deviation of the PL intensity distribution from shot-noise limited, Poisson statistics (Supplementary Note 4).\u003csup\u003e47, 48\u003c/sup\u003e The PL intensity distribution of a blinking-free QD should simultaneously have a high ON fraction and a close-to-zero Q parameter. Shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, DDA-covered QDs exhibited a broad and asymmetric PL intensity distribution histogram with a \u003cem\u003eQ\u003c/em\u003e parameter of 7.3. In stark contrast, the PEA-covered QD exhibited a narrow PL intensity distribution with a \u003cem\u003eQ\u003c/em\u003e parameter of 0.3. The ON time fraction and Mandel Q parameter of the PEA-covered QD remained consistent when a shorter bin time was used (Extended Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These suggest that the PL emissions from the PEA-covered QD were dominated by exciton radiative recombination and were not influenced by stochastic QD charging or environmental charge redistributions.\u003c/p\u003e \u003cp\u003eAnother consequence of charging-induced PL blinking is spectral diffusion, which has been frequently reported in long-chain ligands covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs.\u003csup\u003e16, 32\u003c/sup\u003e Such PL energy jumping is detrimental to the performance of QDs as quantum emitters. Our PEA-covered QD shows a spectrally stable PL. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, no spectral diffusion was detected, which was consistent with the nearly non-blinking behaviour. In comparison, the DDA-covered QD show clear spectral diffusion in the first 10 s of the measurement (Supplementary Fig.\u0026nbsp;12). The high single photon purity of the PEA-covered QD with a g\u003csup\u003e(2)\u003c/sup\u003e(0) value of 0.013 was also expected, given its strong size confinement (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). This is also one of the lowest g\u003csup\u003e(2)\u003c/sup\u003e(0) values reported for perovskite QDs.\u003c/p\u003e \u003cp\u003eThis significantly improved single QD optical performance was echoed by the statistics of the ON and OFF durations extracted from blinking traces of 60 PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg. The probability distributions for the duration (\u003cem\u003et\u003c/em\u003e) of the ON and OFF events, \u003cem\u003eP\u003c/em\u003e\u003csub\u003eON/OFF\u003c/sub\u003e, were fitted to a power law distribution \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(P\\propto {t}^{-{k}_{\\text{O}\\text{N}/\\text{O}\\text{F}\\text{F}}}\\)\u003c/span\u003e\u003c/span\u003e, where \u003cem\u003ek\u003c/em\u003e\u003csub\u003eON/OFF\u003c/sub\u003e were set as the power law exponents that describe the statistics of the ON/OFF events. For instance, a smaller \u003cem\u003ek\u003c/em\u003e\u003csub\u003eOFF\u003c/sub\u003e (a steeper slope in the log-log plot) means long-duration OFF events were less likely to happen. In typical QDs, both \u003cem\u003ek\u003c/em\u003e\u003csub\u003eON\u003c/sub\u003e and \u003cem\u003ek\u003c/em\u003e\u003csub\u003eOFF\u003c/sub\u003e values are ~\u0026thinsp;1.5.\u003csup\u003e49\u003c/sup\u003e Our QDs showed an average \u003cem\u003ek\u003c/em\u003e\u003csub\u003eON\u003c/sub\u003e of 2.0 and \u003cem\u003ek\u003c/em\u003e\u003csub\u003eOFF\u003c/sub\u003e value of 1.0, comparable to one of the best non-blinking core-shell II-VI and III-V QDs reported.\u003csup\u003e29, 50\u003c/sup\u003e This implies that our CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs are almost defect-free.\u003c/p\u003e \u003cp\u003eThe nearly complete passivation of PEA-covered QDs benefit from the attractive intermolecular interactions between PEA cations. To demonstrate the necessity of this, we applied another low-steric ligand without π-π stacking effects, \u003cem\u003eiso\u003c/em\u003e-propylammonium (IPA) bromide, to cover the same CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs used in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (4.5 nm). IPA-covered QDs still showed suppressed blinking with an ON time fraction of 83% (Extended Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This was potentially due to the absence of strong intermolecular steric repulsion in IPA compared to DDA. However, a clear OFF fraction distribution was observed, implying the existence of surface defects due to incomplete passivation in IPA-covered QDs.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eStability of PEA-covered CsPbBr QDs\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eSimilar to PL blinking, rapid photodegradation of CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs has been a long-standing obstacle to investigations of their excitonic properties at the single particle level. Strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs are reported to experience spectral blue-shifting due to size shrinking within a short time of laser excitation.\u003csup\u003e13, 51, 52\u003c/sup\u003e According to the DFT modelling, QD surface can be significantly stabilized when it is fully-covered by PEAs. This would be manifested as resistance to photodegradation. Indeed, the single strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QD showed no spectral diffusion and size shrinking-induced blue-shifting during 30 mins of laser irradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb), and the PL spectra before and after operation were nearly identical (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eCsPbBr\u003csub\u003e3\u003c/sub\u003e QDs are notoriously prone to photodarkening. This occurs when light irradiation creates new surface defects on QDs and intensifies their PL blinking. To explore the surface structural stability of strongly confined PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs at an ensemble level, a collection of isolated QDs was illuminated at the same time. Their PL intensity stayed constant over the course of the measurement (\u0026gt;\u0026thinsp;10 h). In comparison, the PL intensity of the same QDs covered by DDA dispersed in polystyrene decreased since the first minute of laser exposure and became nearly completely dark after ~\u0026thinsp;10 min (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Notably, the PEA-covered QD remained nearly non-blinking with a 98% ON fraction beyond 12 hours of continuous operation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). We also tested the PEA-covered single QDs at high excitation rates using a pulsed laser with tuneable laser pulse energy. During the test, QDs remained nearly non-blinking when the excitation density (average number of excitons created per pulse) was increased to 0.21 (Extended Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Supplementary Note 5). In addition, PEA-covered QD stayed blinking-free for about a month of storage at ambient condition (Supplementary Fig.\u0026nbsp;13). To the best of our knowledge, this is comparable to some of the most photostable non-blinking CdSe QDs with CdS shells.\u003csup\u003e29\u003c/sup\u003e\u003c/p\u003e\n\u003ch3\u003ePL performance of CsPbBr QDs with various sizes\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eWe then explored our ligand design on single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs with various sizes. The extent of quantum confinement in QDs increases with decreasing size, making the QD more sensitive to surface defects. Rarely can a surface passivation method work effectively for QDs with different sizes. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea \u0026ndash; \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed show blinking traces of four different single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs covered by PEA with their sizes determined by their PL spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) with an empirical sizing curve.\u003csup\u003e6\u003c/sup\u003e All CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs were nearly blinking-free with ~\u0026thinsp;98% ON fractions and shot noise-limited PL intensity distributions, suggesting that PEA epitaxially passivated CsPbBr\u003csub\u003e3\u003c/sub\u003e QD surfaces (additional single QD measurements are shown in Supplementary Fig.\u0026nbsp;14). Notably, weakly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs can also benefit from the high surface PEA coverage: a single CsPbBr\u003csub\u003e3\u003c/sub\u003e QD with the size of 9 nm was nearly blinking free and maintained a 94.1% ON time fraction over 30 minutes; no spectral diffusion nor size-shrinking were detected during 1 hour of laser irradiation (Extended Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThese QDs were then examined to study their biexciton dynamics (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). The fast biexciton Auger recombination of strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs was also echoed by a low average g\u003csup\u003e(2)\u003c/sup\u003e(0) value (0.054) from the statistics built using 60 strongly confined QDs (Extended Fig.\u0026nbsp;6). We noted that the variations of g\u003csup\u003e(2)\u003c/sup\u003e(0) values of non-blinking QDs were smaller than QDs exhibiting PL intensity fluctuations (Supplementary Fig.\u0026nbsp;15).\u003csup\u003e13\u003c/sup\u003e The larger g\u003csup\u003e(2)\u003c/sup\u003e(0) value variations in blinking QDs can be partially attributed to the attenuated single exciton emissions from other non-radiative channels. Non-blinking QDs are thus particularly useful for studying the biexciton recombination mechanisms since their g\u003csup\u003e(2)\u003c/sup\u003e(0) values can better represent the biexciton emission QY.\u003csup\u003e53\u003c/sup\u003e\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDetermining the size-dependent exciton properties at the single QD level\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSize-dependent exciton properties are fundamentally important for unravelling the PL emission mechanism and exciton-lattice interaction in QDs. Experimental determination of PL properties in single QDs exclude the interferences of ensemble inhomogeneity. However, blinking and photodarkening can change exciton dynamics and PL line shapes. The nearly non-blinking CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs with significantly improved photostability are therefore ideal to studying the intrinsic effects of quantum confinement on excitons.\u003csup\u003e54, 55\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eExciton recombination dynamics were then studied using our single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs. They show mono-exponential PL intensity decay (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) due to the absence of dimmer emissive states. We extracted the PL lifetimes from 81 QDs with sizes ranging from 3.6 nm to 14 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). Interestingly, the size-radiative rate correlation was not monotonic: the exciton radiative rate increased with reducing sizes and then decreased when the size was smaller than 4.5 nm. The initial increase of the radiative rates can be attributed to the increase of the optical band gap induced by quantum confinement.\u003csup\u003e56, 57\u003c/sup\u003e When the QD is more confined, thermal mixing of bright and dark exciton states will take over and reduce the radiative rate due to larger exciton fine structure splitting.\u003csup\u003e55, 56\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eNot only do our PEA-covered QDs reveal the exciton radiative rates, but they also exhibit intrinsic PL linewidths to help understand the size-dependence on exciton-lattice interaction in QDs. We discovered that the PL spectra were asymmetric for all CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs even without spectral diffusion and shifting (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). We employed two Voigt functions with a common peak position to fit the single QD PL spectra. The half-width half-maximums (HWHMs) of both functions were extracted for 81 non-blinking QDs (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). In the weakly confined region, our QDs showed similar or narrower PL peaks compared to reported values from other literature (Supplementary Fig.\u0026nbsp;16). With decreasing QD size, the PL linewidths increase monotonically, which agreed well with previous studies.\u003csup\u003e58\u003c/sup\u003e However, the low-energy tail of the PL experienced a stronger dependence on the QD size compared to the high-energy part.\u003c/p\u003e \u003cp\u003eThe low energy tail in PL spectrum of CsPbBr\u003csub\u003e3\u003c/sub\u003e QD ensembles was frequently observed but rarely studied. Bright band tail states were proposed to explain the asymmetric PL.\u003csup\u003e59\u003c/sup\u003e However, this would imply the existence of multiple dimmer emissive states compared to the exciton state and was inconsistent with the mono-exponential PL decay observed in our nearly non-blinking QDs. Asymmetric PL spectra have also been discovered in CsPbBr\u003csub\u003e3\u003c/sub\u003e polycrystalline films and have been attributed to the Cs\u003csup\u003e+\u003c/sup\u003e relocation.\u003csup\u003e60\u003c/sup\u003e However, this effect should not be evident at room temperatures. The strong size dependence of the low energy tail infers that the surface lattices of the QDs may induce the PL asymmetry. Thus, the intrinsic PL asymmetry can be related to the optical phonon sideband\u003csup\u003e61\u003c/sup\u003e or momentarily trapped exciton-polarons formed by exciton-surface lattice interactions, which were also found in 2D perovskite nanoplates.\u003csup\u003e62\u003c/sup\u003e This is supported by the spectrally independent PL decay dynamics of PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs (Supplementary Fig.\u0026nbsp;17). Our study suggests that even for defect-free QDs, the size can still substantially affect exciton-lattice interactions.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn conclusion, we have demonstrated that intermolecular interactions can significantly impact the surface ligand coverage of individual CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs in solid states. Although bulky long-chain ligand tails can entropically improve the colloidal stability of perovskite QDs, steric repulsion can lead to uncovered surface sites and ion loss. Considering the packing effect of the ligand tail in the solid state, we employed a low steric ligand, PEA, with attractive intermolecular interactions on QDs, which was confirmed by 2D NOSEY experiment. We demonstrated that the PEA-covered CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs ranging from 3.6 nm to 14 nm were nearly non-blinking, with an average ON time fraction\u0026thinsp;\u0026gt;\u0026thinsp;90% and single photon emission purity of ~\u0026thinsp;95%. Furthermore, the QDs showed no observable spectral diffusion or shifting at room temperature and remained non-blinking after 12 hours of continuous operation. The extraordinary photostability and significantly reduced blinking enabled the determination of size-dependent excitonic properties without the interference of stochastic charging or photodegradation. The exciton radiative recombination rates and PL line shapes were measured as a function of QD size, providing insights on previously uncertain intrinsic exciton fine-structure splitting and exciton-lattice interaction in perovskite QDs. Our study can benefit future fundamental studies on perovskite QDs at the single particle level and potentially realize stable perovskite QD-based quantum emitters.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis project is supported by the U.S Department of Energy (DE-SC0024441). Financial support for this work was partially provided by the U.S. National Science Foundation (NSF LEAPS-MPS: 231691) and the University of Oklahoma startup funds. This project is also supported by grants from the Research Council and the Dodge Family College of Arts and Science of the University of Oklahoma Norman Campus. We also acknowledge the support of the Vice President for Research and Partnerships of the University of Oklahoma. Y.S. is supported by National Science Foundation via grant CHE-2102071. Use of the TAMU Materials Characterization Facility (RRID: SCR_022202) are acknowledged. We thank Dr. Sisi Xiang for helps on electron microscope image processing. The DFT modelling was performed at the OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma.\u0026nbsp;The authors thank Dr. Robert B. Scafe and Dr. Clara Smith for discussions on manuscript writing.\u003c/p\u003e\n\u003cp\u003eAuthor information\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAuthors and affiliations\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Chemistry and Biochemistry, The University of Oklahoma, Norman, OK 73019, USA\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eChenjia Mi, Gavin C. Gee, Chance W. Lander, Matthew L. Atteberry, Novruz G. Akhmedov, Lamia Hidayatova, Jesse D. DiCenso, Wai Tak Yip, Yihan Shao, Yitong Dong\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCenter for Quantum Research and Technology, The University of Oklahoma, Norman, OK 73019 USA\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYihan Shao, Yitong Dong\u003c/p\u003e\n\u003cp\u003eContributions\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eC.M. and G.C.G. performed the sample preparation, the spectroscopic experiments, and data processing; C.M. and Y.D. performed the data analyses; C.W.L., J.D.D. and Y.S. performed the DFT calculation and provided related discussions; M.L.A., C.M. and L.H. performed the CsPbBr\u003csub\u003e3\u003c/sub\u003e QD syntheses; N.G.A. conducted the NMR and NOESY experiments and helped to perform NMR data analyses; W.T.Y. supported the spectroscopic measurements; All authors contributed to manuscript writing; Y.D. supervised the project.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCorresponding author\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCorrespondence to \u003cu\u003eYitong Dong\u003c/u\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData Availability\u003c/p\u003e\n\u003cp\u003eData are available from the corresponding authors upon reasonable request.\u003c/p\u003e\n\u003cp\u003eEthics declarations\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompeting interests\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests. \u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eKimble, H. 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Phys.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e132\u003c/strong\u003e, (2010).\u003c/li\u003e\n \u003cli\u003eGrimme, S.; Ehrlich, S.; Goerigk, L., Effect of the damping function in dispersion corrected density functional theory. \u003cem\u003eJ. Comput. Chem.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e32\u003c/strong\u003e, 1456-1465 (2011).\u003c/li\u003e\n \u003cli\u003eGrazulis, S., et al., Crystallography Open Database - an open-access collection of crystal structures. \u003cem\u003eJ. Appl. Crystallogr.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e42\u003c/strong\u003e, 726-729 (2009).\u003c/li\u003e\n \u003cli\u003eStoumpos, C. C., et al., Crystal Growth of the Perovskite Semiconductor CsPbBr\u003csub\u003e3\u003c/sub\u003e: A New Material for High-Energy Radiation Detection. \u003cem\u003eCryst. Growth Des.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e13\u003c/strong\u003e, 2722-2727 (2013).\u003c/li\u003e\n \u003cli\u003eHjorth Larsen, A., et al., The atomic simulation environment\u0026mdash;a Python library for working with atoms. \u003cem\u003eJ. Condens. Matter Phys.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e29\u003c/strong\u003e, 273002 (2017).\u003c/li\u003e\n \u003cli\u003ePulay, P., Convergence acceleration of iterative sequences. the case of scf iteration. \u003cem\u003eChem. Phys. Lett.\u0026nbsp;\u003c/em\u003e\u003cstrong\u003e73\u003c/strong\u003e, 393-398 (1980).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Methods","content":"\u003ch2\u003eCsPbBr\u003csub\u003e3\u003c/sub\u003e QD syntheses\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eTo prepare the Cs-precursor, 900 mg Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, 3.6 mL Oleic Acid (OA) and 9.6 mL 1-Octadecnece (ODE) were added into a 100 mL flask. The mixture was vacuumed on a Schlenk line for 15 min while stirring. The mixture was then heated to 150 °C under vacuum until it turned clear. When the pressure reached ~ 1 Pa, the flask was filled with N\u003csub\u003e2\u003c/sub\u003e. The temperature of the Cs-precursor was maintained at 120 °C for use.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Pb-precursor was prepared by adding 600 mg PbBr\u003csub\u003e2\u003c/sub\u003e, 1400 mg ZnBr\u003csub\u003e2\u003c/sub\u003e, and 200 μL hydrobromic acid (48% w/w aq.) in a 250 mL flask. Then 14 mL OA, 14 mL oleylamine (OAm), and 40 mL ODE were added into the flask. The mixture was stirred vigorously for ~ 3 mins and then vacuumed on a Schlenk line. The flask was then heated to 150 °C under vacuum until all solids were dissolved. The flask was then filled with N\u003csub\u003e2\u003c/sub\u003e, and the solution temperature was adjusted to 80 – 150 °C according to the targeted size of the QDs. When the desired temperature for the Pb-precursor was reached, 5.0 mL of Cs-precursor solution (at ~ 120 °C) was injected to the Pb-precursor. The temperature of the solution was kept constant for 15 – 30 min. The crude product was then cooled to room temperature and transferred to centrifuge tubes for purification.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe crude product was first centrifuged at 7800 rpm for 5 min. The precipitate was discarded. The supernatant was transferred to new centrifuge tubes, to which 1:1 volume of acetone was added carefully then shaken vigorously until the mixture turned turbid. This fast mixing was observed to help preserve the PLQY of the purified CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs. The mixture was shaken until it became turbid. QDs were collected by centrifuging the mixture at 7800 rpm for 5 min and discarding the supernatant. The precipitated QDs were redispersed in 5 mL hexanes to yield a stock CsPbBr\u003csub\u003e3\u003c/sub\u003e QD colloid. This stock colloid was further purified 1 – 2 times by reprecipitation with 3:1 volume ratio of methyl acetate and redispersion with hexanes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLarger strongly confined CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs (6 – 7 nm) were synthesized with modified recipes: the amount of ZnBr\u003csub\u003e2\u003c/sub\u003e was increased to 2000 mg, the reaction temperature was increased up to 200 °C and the reaction time was reduced to 1 min.\u0026nbsp;Weakly confined\u0026nbsp;CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs were synthesized using previously reported methods.\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n\u003ch2\u003eSolution ligand exchange of CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs for\u0026nbsp;NMR\u0026nbsp;measurements\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003e404 mg PEABr (or 202 mg PEABr + 216 mg MPEABr) was dissolved in 1 mL DMF and filtered through a PTFE syringe filter (VWR, 0.22 μm pore size). 2 mL CsPbBr\u003csub\u003e3\u003c/sub\u003e QD stock colloids (~ 100 μM) were reprecipitated 2 – 3 times with 10 mL methyl acetate and redissolved in 2 mL toluene or chloroform each time. To the purified CsPbBr\u003csub\u003e3\u003c/sub\u003e QD colloids, 40 μL of the PEABr DMF solution was added and vortexed for ~ 5 s. Then the mixture was centrifuged at 7800 rpm for 1 min, and the supernatant was carefully transferred to a new centrifuge tube. To the supernatant, 10 mL of methyl acetate was used to reprecipitate the QDs. This procedure was repeated to promote ligand exchange. After 2 – 3 times of ligand exchange, the precipitate QDs were vacuum-dried for 20 min and then redissolved in 0.8 mL anhydrous CDCl\u003csub\u003e3\u003c/sub\u003e for NMR measurements.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eNMR measurements\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH and NOESY NMR spectra were recorded on a VNMRS 500 MHz spectrometer at 25 °C and 60 °C equipped with a triple-resonance z-axis pulsed field gradient 5-mm probe. Typical parameters for acquiring \u003csup\u003e1\u003c/sup\u003eH NMR spectra were as follows: 8012.8 Hz spectral width, 5.0 s acquisition time, 4.5 μs (45°) pulse width, 1 s relaxation time, and 16 transients. The parameters for the NOESY were as follows: 5506.6 Hz spectral width in both dimensions (F1 and F2), 0.25 s acquisition time, 11.8 μs (90°) pulse width, 1.5 s relaxation time, 500 ms mixing time, 64 transients, with 512 increments along F1 dimension, each in phase sensitive mode. The free induction decays (FIDs) were zero-filled to give a 2k × 2k data matrix, and a Gaussian function was applied in both dimensions (F1 and F2) prior to Fourier transformation. The FIDs of the \u003csup\u003e1\u003c/sup\u003eH and NOESY NMR spectra were processed using MNOVA. The \u003csup\u003e1\u003c/sup\u003eH NMR chemical shifts are assigned relative to the residual proton peaks of CDCl\u003csub\u003e3\u003c/sub\u003e at 7.26 ppm.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eSolid-state ligand exchange of CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs for single QD sample preparation\u003c/h2\u003e\n\u003cp\u003eGlass coverslips (25 mm × 25 mm × 0.17 mm) were cleaned by sonicating in triton-X detergent solution, DI water, acetone, and 2-propanol sequentially (40 min each), and then dried. Before use, the coverslips were cleaned with a UV-ozone cleaner for 40 min and transferred in a nitrogen glovebox. In the glovebox, 200 mg PEABr was dissolved in 1 mL of anhydrous DMF and filtered through a PTFE syringe filter (VWR, 0.22 μm pore size). The stock QD colloid was diluted using anhydrous octane to ~ 200 pM. For the solid-state ligand exchange, 150 μL of the PEABr solution was spin-coated on a clean coverslip at 4000 rpm. After ~ 35 s, 10 μL of the dilute CsPbBr\u003csub\u003e3\u003c/sub\u003e QD colloid was swiftly dropped on the coverslip while spinning. The coverslip was then annealed on a hot plate at 50 – 70 °C for 30 – 120 s. Then the sample coverslip was covered by a glass slide and its edges were sealed using UV-curing optical adhesives (Thorlabs NOA61).\u003c/p\u003e\n\u003ch2\u003eSingle QD\u0026nbsp;spectroscopy\u0026nbsp;measurements\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe single QD sample was mounted onto a nano-positioner (Milles Griot Nanomax, with 3-axis manual and close-loop piezoelectric actuators) in a\u0026nbsp;customized wide-field/confocal fluorescence\u0026nbsp;microscope system\u0026nbsp;(Supplementary Fig. 18). A 405 nm diode laser was used to excite the sample (Picoquant LDH-D-C-405, driven by a Picoquant Sepia PDL828 module). The laser was attenuated using a series of neutral density (ND) filters (Thorlabs) and sent into the objective lens (Olympus UPLXAPO100XO, 100× magnification, NA = 1.45) through a single-mode optical fibre (Thorlabs P1-305A-FC-1 with a collimator). The single QD sample was imaged using an EMCCD camera (Andor iXon Ultra 897) under wide-field mode. The QD of interest was moved to the centre of the laser beam focus spot for spectroscopy measurements under confocal mode. PL emissions of a single QD was collected using the same objective and sent through a set of optical filters (a 405 nm notch filter, a 425 nm long-pass filter and optional bandpass filters). The QD PL spectra was measured using a spectrograph (Andor Shamrock 500i equipped with an Andor iXon Ultra 897 EMCCD). The time-tagged, time-resolved single photon counting (to generate the blinking traces, the time-resolved PL decay, and the second-order photon corelation) were recorded using two single-photon avalanche diodes (Hamamatsu C11202-100) connected to a time-correlator (Picoquant HydraHarp 400) in a Hanbury Brown and Twiss configuration.\u0026nbsp;The g\u003csup\u003e(2)\u003c/sup\u003e(0) values were corrected using a previously reported method.\u003csup\u003e53\u003c/sup\u003e \u0026nbsp;All measurements were performed at room temperature.\u003c/p\u003e\n\u003ch2\u003eDFT modelling\u003c/h2\u003e\n\u003cp\u003eThe ligand binding energies were calculated at the DFT level of theory using the projector augmented plane wave basis as implemented in the VASP 5.4 software package.\u003csup\u003e63, 64\u003c/sup\u003e Structures were optimized using the PBE functional\u003csup\u003e65\u003c/sup\u003e with D3(BJ)\u003csup\u003e66, 67\u003c/sup\u003e dispersion and dampening and an energy cutoff of 400 eV. Coordinates for the CsPbBr\u003csub\u003e3\u003c/sub\u003e surfaces were obtained from the Crystallography Open Database (COD ID: 4510745).\u003csup\u003e68, 69\u003c/sup\u003e Charge neutral 2×2×1 surfaces were constructed with ASE.\u003csup\u003e70\u003c/sup\u003e A 4×4×1 Monkhorst–Pack grid was used for Brillouin zone sampling. All structures were optimized using the RMM-DIIS algorithm\u003csup\u003e71\u003c/sup\u003e with a self-consistent field (SCF) convergence criterion of 1×10\u003csup\u003e-6\u003c/sup\u003e eV and an ionic convergence criterion of 1×10\u003csup\u003e-3\u003c/sup\u003e eV. The coordinates of the perovskite atoms were fixed during optimization.\u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4214840/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4214840/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSurface defect-induced photoluminescence blinking is ubiquitous in lead halide perovskite quantum dots (QDs). Despite efforts to passivate the defects on perovskite QDs by chemically engineering ligand binding moieties, blinking accompanied by photodegradation still poses barriers to studying and implementing quantum-confined perovskite QDs in quantum emitters. We posited that the intermolecular interaction between ligands can affect the QD surface passivation. In the solid state, steric repulsions among bulky ligand tails prevent adequate QD surface ligand coverage. Alternatively, attractive π-π stacking between low-steric phenethylammonium (PEA) ligands promotes the formation of a nearly epitaxial surface ligand layer. Here, we demonstrate that single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs covered by these PEA ligands are nearly non-blinking, with single photon purity reaching 98%. Moreover, these QDs exhibited no spectral shifting and photodegradations, and they remained blinking-free after 12 hours of continuous operation. Free of interferences from blinking and photodegradation, we present size-dependent exciton radiative rates and emission line widths of single CsPbBr\u003csub\u003e3\u003c/sub\u003e QDs ranging from strongly to weakly confined regimes.\u003c/p\u003e","manuscriptTitle":"Towards non-blinking perovskite quantum dots","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-07 06:04:06","doi":"10.21203/rs.3.rs-4214840/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8f08d0a2-0f28-4294-b8a1-6802c8e938c0","owner":[],"postedDate":"May 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":31001707,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Quantum dots"},{"id":31001708,"name":"Physical sciences/Chemistry/Theoretical chemistry/Density functional theory"},{"id":31001709,"name":"Physical sciences/Materials science/Nanoscale materials/Quantum dots"},{"id":31001710,"name":"Physical sciences/Optics and photonics/Optical physics/Nanophotonics and plasmonics"}],"tags":[],"updatedAt":"2025-01-04T08:15:52+00:00","versionOfRecord":{"articleIdentity":"rs-4214840","link":"https://doi.org/10.1038/s41467-024-55619-7","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-01-02 05:00:00","publishedOnDateReadable":"January 2nd, 2025"},"versionCreatedAt":"2024-05-07 06:04:06","video":"","vorDoi":"10.1038/s41467-024-55619-7","vorDoiUrl":"https://doi.org/10.1038/s41467-024-55619-7","workflowStages":[]},"version":"v1","identity":"rs-4214840","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4214840","identity":"rs-4214840","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}