Near Infrared Light-Emitting Diodes Based on Colloidal InAs/ZnSe Core/Thick-Shell Quantum Dots.

Heavy-metal-free III-V colloidal quantum dots (QDs) exhibit promising attributes for application in optoelectronics. Among them, InAs QDs are demonstrating excellent optical performance with respect to absorption and emission in the near-infrared spectral domain. Recently, InAs QDs attained a substantial improvement in photoluminescence quantum yield, achieving 70% at a wavelength of 900 nm through the strategic overgrowth of a thick ZnSe shell atop the InAs core. In the present study, light-emitting diodes (LEDs) based on this type of InAs/ZnSe QDs are fabricated, reaching an external quantum efficiency (EQE) of 13.3%, a turn-on voltage of 1.5V, and a maximum radiance of 12 Wsr-1m-2. Importantly, the LEDs exhibit an extensive emission dynamic range, characterized by a nearly linear correlation between emission intensity and current density, which can be attributed to the efficient passivation provided by the thick ZnSe shell. The obtained results are comparable to state-of-the-art PbS QD LEDs. Furthermore, it should be stressed not only that the fabricated LEDs are fully RoHS-compliant but also that the emitting InAs QDs are prepared via a synthetic route based on a non-pyrophoric, cheap, and commercially available as precursor, namely tris(dimethylamino)-arsine.

Ru-Cu Nanoheterostructures for Efficient Hydrogen Evolution Reaction in Alkaline Water Electrolyzers.

Combining multiple species working in tandem for different hydrogen evolution reaction (HER) steps is an effective strategy to design HER electrocatalysts. Here, we engineered a hierarchical electrode for the HER composed of amorphous-TiO2/Cu nanorods (NRs) decorated with cost-effective Ru-Cu nanoheterostructures (Ru mass loading = 52 µg/cm2). Such an electrode exhibits a stable, over 250 h, low overpotential of 74 mV at -200 mA/cm2 for the HER in 1 M NaOH. The high activity of the electrode is attributed, by structural analysis, operando X-ray absorption spectroscopy, and first-principles simulations, to synergistic functionalities: (1) mechanically robust, vertically aligned Cu NRs with high electrical conductivity and porosity provide fast charge and gas transfer channels; (2) the Ru electronic structure, regulated by the size of Cu clusters at the surface, facilitates the water dissociation (Volmer step); (3) the Cu clusters grown atop Ru exhibit a close-to-zero Gibbs free energy of the hydrogen adsorption, promoting fast Heyrovsky/Tafel steps. An alkaline electrolyzer (AEL) coupling the proposed cathode and a stainless-steel anode can stably operate in both continuous (1 A/cm2 for over 200 h) and intermittent modes (accelerated stress tests). A techno-economic analysis predicts the minimal overall hydrogen production cost of US$2.12/kg in a 1 MW AEL plant of 30 year lifetime based on our AEL single cell, hitting the worldwide targets (US$2-2.5/kgH2).

Colloidal InAs Tetrapods: Impact of Surfactants on the Shape Control.

We have approached the synthesis of colloidal InAs nanocrystals (NCs) using amino-As and ligands that are different from the commonly employed oleylamine (OA). We found that carboxylic and phosphonic acids led only to oxides, whereas tri-n-octylphosphine, dioctylamine, or trioctylamine (TOA), when employed as the sole ligands, yielded InAs NCs with irregular sizes and a broad size distribution. Instead, various combinations of TOA and OA delivered InAs NCs with good control over the size distribution, and the TOA:OA volume ratio of 4:1 generated InAs tetrapods with arm length of 5-6 nm. Contrary to tetrapods of II-VI materials, which have a zinc-blende core and wurtzite arms, these NCs are entirely zinc-blende, with arms growing along the ⟨111⟩ directions. They feature a narrow excitonic peak at ∼950 nm in absorption and a weak photoluminescence emission at 1050 nm. Our calculations indicated that the bandgap of the InAs tetrapods is mainly governed by the size of their core and not by their arm lengths when these are longer than ∼3 nm. Nuclear magnetic resonance analyses revealed that InAs tetrapods are mostly passivated by OA with only a minor fraction of TOA. Molecular dynamics simulations showed that OA strongly binds to the (111) facets whereas TOA weakly binds to the edges and corners of the NCs and their combined use (at high TOA:OA volume ratios) promotes growth along the ⟨111⟩ directions, eventually forming tetrapods. Our work highlights the use of mixtures of ligands as a means of improving control over InAs NCs size and size distribution.

High-performance alkaline water electrolyzers based on Ru-perturbed Cu nanoplatelets cathode.

Alkaline electrolyzers generally produce hydrogen at current densities below 0.5 A/cm2. Here, we design a cost-effective and robust cathode, consisting of electrodeposited Ru nanoparticles (mass loading ~ 53 µg/cm2) on vertically oriented Cu nanoplatelet arrays grown on metallic meshes. Such cathode is coupled with an anode based on stacked stainless steel meshes, which outperform NiFe hydroxide catalysts. Our electrolyzers exhibit current densities as high as 1 A/cm2 at 1.69 V and 3.6 A/cm2 at 2 V, reaching the performances of proton-exchange membrane electrolyzers. Also, our electrolyzers stably operate in continuous (1 A/cm2 for over 300 h) and intermittent modes. A total production cost of US$2.09/kgH2 is foreseen for a 1 MW plant (30-year lifetime) based on the proposed electrode technology, meeting the worldwide targets (US$2-2.5/kgH2). Hence, the use of a small amount of Ru in cathodes (~0.04 gRu per kW) is a promising strategy to solve the dichotomy between the capital and operational expenditures of conventional alkaline electrolyzers for high-throughput operation, while facing the scarcity issues of Pt-group metals.

The Dark Side of Lead-Free Metal Halide Nanocrystals: Substituent-Modulated Photocatalytic Activity in Benzyl Bromide Reduction.

We illustrate here the high photocatalytic activity of sustainable lead-free metal halide nanocrystals (NCs), namely, Cs3Sb2Br9 NCs, in the reduction of p-substituted benzyl bromides in the absence of a cocatalyst. The electronic properties of the benzyl bromide substituents and the substrate affinity to the NC surface determine the selectivity in C-C homocoupling under visible light irradiation. This photocatalyst can be reused for at least three cycles and preserves its good performance with a turnover number of ca. 105,000.

Surface Chemistry of Lead Halide Perovskite Colloidal Nanocrystals.

ConspectusThe surface chemistry of lead halide perovskite nanocrystals (NCs) plays a major role in dictating their colloidal and structural stability as well as governing their optical properties. A deep understanding of the nature of the ligand shell, ligand-NC, and ligand-solvent interactions is therefore of utmost importance. Our recent studies have revealed that such knowledge can be harnessed following a multidisciplinary approach comprising chemical, structural, and spectroscopic analyses coupled with atomistic modeling. We show that specific surface terminations can be produced only by employing flexible and versatile syntheses that enable to work under desired conditions. In this Account, we first describe our studies aimed at synthesizing CsPbBr3 NCs with various surface terminations. These include CsPbBr3 NCs prepared under Br- and oleylamine-rich conditions, which feature a ligand shell composed of alkylammonium-Br species and a photoluminescence quantum yield (PLQY) of ∼90%. On the other hand, taking advantage of the inability of secondary amines to bind to the perovskite NCs surface, we could prepare cuboidal CsPbBr3 NCs bearing a Cs-oleate surface termination and a PLQY of 70% by employing oleic acid and secondary alkylamines. In the quest to identify ligands that can bind more strongly than oleates or primary alkylammonium ions to the surface of NCs already in the synthesis step, we used phosphonic acids as the sole ligands in the CsPbBr3 NCs synthesis, which yielded NCs with a truncated octahedron shape, high PLQY (∼100%), and a PbBr2-terminated surface passivated by hydrogen phosphonates and phosphonic acid anhydride. The surface chemistry and the stability of perovskite NCs were investigated via ad-hoc postsynthesis treatments. We found, for example, that reacting oleylammonium-Br-terminated NCs with stoichiometric amounts of neutral primary alkylamines (or their conjugated acids) led to a partial replacement of oleylammonium ions with new alkylammonium ions (following a deprotonation/protonation mechanism), which resulted in a boost of the PLQY (up to 100%) and of the NCs' colloidal stability. Similar results in terms of optical properties were achieved by treating Cs-oleate-terminated NCs with alkylammonium-carboxylate or quaternary ammonium-Br (namely, didodecyldimethylammonium-Br, DDA-Br) couples. Interestingly, when the native NCs are ligand exchanged with DDA-Br, the ligand shell is then composed of species not bearing any proton. This, in turn, enabled us to study the interaction of such NCs with a variety of ligands under completely aprotic conditions wherein these DDA-Br-capped NCs were basically inert. The only exceptions were carboxylic, phosphonic, and sulfonic acids that were capable of stripping surface DDA-Br couples. As a note, most studies on CsPbBr3 NCs to date have focused primarily on choosing ligands with specific anchoring groups rather than on tuning the length and type of alkyl chains, as this is time-consuming and requires a large number of syntheses. Our recent developments in the computational chemistry of colloidal NCs are expected to provide a pivotal role in this direction since they can be integrated with machine learning models to investigate with greater details the ligand-NC, ligand-ligand, and ligand-solvent interactions and ultimately find optimal candidates through the prediction of surfactant properties using high-throughput data sets.

Boosting the Photoluminescence Efficiency of InAs Nanocrystals Synthesized with Aminoarsine via a ZnSe Thick-Shell Overgrowth.

InAs-based nanocrystals can enable restriction of hazardous substances (RoHS) compliant optoelectronic devices, but their photoluminescence efficiency needs improvement. We report an optimized synthesis of InAs@ZnSe core@shell nanocrystals allowing to tune the ZnSe shell thickness up to seven mono-layers (ML) and to boost the emission, reaching a quantum yield of ≈70% at ≈900 nm. It is demonstrated that a high quantum yield can be attained when the shell thickness is at least ≈3ML. Notably, the photoluminescence lifetimeshows only a minor variation as a function of shell thickness, whereas the Auger recombination time (a limiting aspect in technological applications when fast) slows down from 11 to 38 ps when increasing the shell thickness from 1.5 to 7MLs. Chemical and structural analyses evidence that InAs@ZnSe nanocrystals do not exhibit any strain at the core-shell interface, likely due to the formation of an InZnSe interlayer. This is supported by atomistic modeling, which indicates the interlayer as being composed of In, Zn, Se and cation vacancies, alike to the In2 ZnSe4 crystal structure. The simulations reveal an electronic structure consistent with that of type-I heterostructures, in which localized trap states can be passivated by a thick shell (>3ML) and excitons are confined in the core.

Colloidal Synthesis of Nickel Arsenide Nanocrystals for Electrochemical Water Splitting.

We report a detailed study on the first colloidal synthesis of NiAs nanocrystals. By optimizing the synthesis parameters, we were able to obtain trioctylphosphine-capped NiAs nanoplatelets with an average diameter of ∼10 nm and a thickness of ca. 4 nm. We then studied the performance of such NiAs nanocrystals as electrocatalysts for electrochemical water splitting reactions, namely, acidic hydrogen evolution reaction (HER) and alkaline oxygen evolution reaction (OER). These nanocrystals were found to be the most HER active ones among the transition metal arsenides reported to date despite exhibiting less than 40 h of stability under benchmark operative conditions (i.e., -10 mA cmgeo -2). When tested as alkaline OER electrocatalysts, our NiAs nanocrystals behaved as a pre-catalyst and transformed superficially into an active Ni-oxy/hydroxide. As a result, NiAs nanocrystals featured an OER activity higher than that of benchmark Ni0 nanocrystals. Noticeably, the OER performance, in terms of , was retained for up to 60 h of continuous operation. The present study highlights how transition metal arsenides, whose structural features could be successfully controlled through a proper tuning of the synthetic parameters, might represent an emerging class of materials for electrocatalytic applications.

Near-Infrared Light-Emitting Diodes Based on RoHS-Compliant InAs/ZnSe Colloidal Quantum Dots.

We demonstrate efficient, stable, and fully RoHS-compliant near-infrared (NIR) light-emitting diodes (LEDs) based on InAs/ZnSe quantum dots (QDs) synthesized by employing a commercially available amino-As precursor. They have a record external quantum efficiency of 5.5% at 947 nm and an operational lifetime of ∼32 h before reaching 50% of their initial luminance. Our findings offer a new solution for developing RoHS-compliant light-emitting technologies based on Pb-free colloidal QDs.

Indium arsenide quantum dots: an alternative to lead-based infrared emitting nanomaterials.

Colloidal quantum dots (QDs) emitting in the infrared (IR) are promising building blocks for numerous photonic, optoelectronic and biomedical applications owing to their low-cost solution-processability and tunable emission. Among them, lead- and mercury-based QDs are currently the most developed materials. Yet, due to toxicity issues, the scientific community is focusing on safer alternatives. In this regard, indium arsenide (InAs) QDs are one of the best candidates as they can absorb and emit light in the whole near infrared spectral range and they are RoHS-compliant, with recent trends suggesting that there is a renewed interest in this class of materials. This review focuses on colloidal InAs QDs and aims to provide an up-to-date overview spanning from their synthesis and surface chemistry to post-synthesis modifications. We provide a comprehensive overview from initial synthetic methods to the most recent developments on the ability to control the size, size distribution, electronic properties and carrier dynamics. Then, we describe doping and alloying strategies applied to InAs QDs as well as InAs based heterostructures. Furthermore, we present the state-of-the-art applications of InAs QDs, with a particular focus on bioimaging and field effect transistors. Finally, we discuss open challenges and future perspectives.

Cu+ → Mn2+ Energy Transfer in Cu, Mn Coalloyed Cs3ZnCl5 Colloidal Nanocrystals.

In this work, we report the hot-injection synthesis of Cs3ZnCl5 colloidal nanocrystals (NCs) with tunable amounts of Cu+ and Mn2+ substituent cations. All the samples had a rodlike morphology, with a diameter of ∼14 nm and a length of ∼30-100 nm. Alloying did not alter the crystal structure of the host Cs3ZnCl5 NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies. The spectroscopic analysis of unalloyed, Cu-alloyed, Mn-alloyed, and Cu, Mn coalloyed NCs indicated that (i) the Cs3ZnCl5 NCs have a large band gap of ∼5.35 eV; (ii) Cu(I) aliovalent alloying leads to an absorption shoulder/peak at ∼4.8 eV and cyan photoluminescence (PL) peaked at 2.50 eV; (iii) Mn(II) isovalent alloying leads to weak Mn PL, which intensifies remarkably in the coalloyed samples, prompted by an energy transfer (ET) process between the Cu and Mn centers, favored by the overlap between the lowest (6A1 → 4T1) transition for tetrahedrally coordinated Mn2+ and the PL profile from Cu(I) species in the Cs3ZnCl5 NCs. The efficiency of this ET process reaches a value of 61% for the sample with the highest extent of Mn alloying. The PL quantum yield (QY) values in these Cu, Mn coalloyed NCs are lower at higher Mn contents. The analysis of the Mn PL dynamics in these samples indicates that this PL drop stems from inter-Mn exciton migration, which increases the likelihood of trapping in defect sites, in agreement with previous studies.

Alloying Bi-Doped Cs2Ag1-xNaxInCl6 Nanocrystals with K+ Cations Modulates Surface Ligands Density and Photoluminescence Efficiency.

We show how, in the synthesis of yellow-emissive Bi-doped Cs2Ag1-xNaxInCl6 double perovskite nanocrystals (NCs), preventing the transient formation of Ag0 particles increases the photoluminescence quantum yield (PLQY) of the NCs from ∼30% to ∼60%. Calculations indicate that the presence of even a single Ag0 species on the surface of a NC introduces deep trap states. The PL efficiency of these NCs is further increased to ∼70% by partial replacement of Na+ with K+ ions, up to a 7% K content, due to a lattice expansion that promotes a more favorable ligands packing on the NC surface, hence better surface passivation. A further increase in K+ lowers the PLQY, due to both the activation of nonradiative quenching channels and a lower oscillator strength of the BiCl6→AgCl6 transition (through which PL emission occurs). The work indicates how a deeper understanding of parameters influencing carrier trapping/relaxation can boost the PLQY of double perovskites NCs.

ZnCl2 Mediated Synthesis of InAs Nanocrystals with Aminoarsine.

The most developed approaches for the synthesis of InAs nanocrystals (NCs) rely on pyrophoric, toxic, and not readily available tris-trimethylsilyl (or tris-trimethylgermil) arsine precursors. Less toxic and commercially available chemicals, such as tris(dimethylamino)arsine, have recently emerged as alternative As precursors. Nevertheless, InAs NCs made with such compounds need to be further optimized in terms of size distribution and optical properties in order to meet the standard reached with tris-trimethylsilyl arsine. To this aim, in this work we investigated the role of ZnCl2 used as an additive in the synthesis of InAs NCs with tris(dimethylamino)arsine and alane N,N-dimethylethylamine as the reducing agent. We discovered that ZnCl2 helps not only to improve the size distribution of InAs NCs but also to passivate their surface acting as a Z-type ligand. The presence of ZnCl2 on the surface of the NCs and the excess of Zn precursor used in the synthesis enable the subsequent in situ growth of a ZnSe shell, which is realized by simply adding the Se precursor to the crude reaction mixture. The resulting InAs@ZnSe core@shell NCs exhibit photoluminescence emission at ∼860 nm with a quantum yield as high as 42±4%, which is a record for such heterostructures, given the relatively high mismatch (6%) between InAs and ZnSe. Such bright emission was ascribed to the formation, under our peculiar reaction conditions, of an In-Zn-Se intermediate layer between the core and the shell, as indicated by X-ray photoelectron spectroscopy and elemental analyses, which helps to release the strain between the two materials.

Stable CsPbBr3 Nanoclusters Feature a Disk-like Shape and a Distorted Orthorhombic Structure.

CsPbBr3 nanoclusters have been synthesized by several groups and mostly employed as single-source precursors for the synthesis of anisotropic perovskite nanostructures or perovskite-based heterostructures. Yet, a detailed characterization of such clusters is still lacking due to their high instability. In this work, we were able to stabilize CsPbBr3 nanoclusters by carefully selecting ad hoc ligands (benzoic acid together with oleylamine) to passivate their surface. The clusters have a narrow absorption peak at 400 nm, a band-edge emission peaked at 410 nm at room temperature, and their composition is identified as CsPbBr2.3. Synchrotron X-ray pair distribution function measurements indicate that the clusters exhibit a disk-like shape with a thickness smaller than 2 nm and a diameter of 13 nm, and their crystal structure is a highly distorted orthorhombic CsPbBr3. Based on small- and wide-angle X-ray scattering analyses, the clusters tend to form a two-dimensional (2D) hexagonal packing with a short-range order and a lamellar packing with a long-range order.

The Reactivity of CsPbBr3 Nanocrystals toward Acid/Base Ligands.

The interaction of lead bromide perovskite nanocrystals with charged ligands, such as salts, zwitterions, or acid-base pairs, has been extensively documented over the past few years. On the other hand, little is known about the reactivity of perovskite nanocrystals toward neutral ligands. To fill this gap, in this work we study the interaction of CsPbBr3 nanocrystals passivated with didodecyldimethylammonium bromide (DDABr) toward a series of exogenous acid/base ligands using a combined computational and experimental approach. Our analysis indicates that DDABr-capped nanocrystals are inert toward most ligands, except for carboxylic, phosphonic, and sulfonic acids. In agreement with the calculations, our experimental results indicate that the higher the acidity of the ligands employed in the treatment, the more etching is observed. In detail, dodecylbenzenesulfonic acid (pKa = -1.8) is found to etch the nanocrystals, causing their complete degradation. On the other hand, oleic and oleylphosphonic acids (pKa 9.9 and 2, respectively) interact with surface-bound DDA molecules, causing their displacement as DDABr in various amounts, which can be as high as 40% (achieved with oleylphosphonic acid). Despite the stripping of DDA ligands, the optical properties of the nanocrystals, as well as structure and morphology, remain substantially unaffected, empirically demonstrating the defect tolerance characterizing such materials. Our study provides not only a clear overview on the interaction between perovskite nanocrystals and neutral ligands but also presents an effective ligand stripping strategy.

Sb-Doped Metal Halide Nanocrystals: A 0D versus 3D Comparison.

We synthesize colloidal nanocrystals (NCs) of Rb3InCl6, composed of isolated metal halide octahedra ("0D"), and of Cs2NaInCl6 and Cs2KInCl6 double perovskites, where all octahedra share corners and are interconnected ("3D"), with the aim to elucidate and compare their optical features once doped with Sb3+ ions. Our optical and computational analyses evidence that the photoluminescence quantum yield (PLQY) of all these systems is consistently lower than that of the corresponding bulk materials due to the presence of deep surface traps from under-coordinated halide ions. Also, Sb-doped "0D" Rb3InCl6 NCs exhibit a higher PLQY than Sb-doped "3D" Cs2NaInCl6 and Cs2KInCl6 NCs, most likely because excitons responsible for the PL emission migrate to the surface faster in 3D NCs than in 0D NCs. We also observe that all these systems feature a large Stokes shift (varying from system to system), a feature that should be of interest for applications in photon management and scintillation technologies. Scintillation properties are evaluated via radioluminescence experiments, and re-absorption-free waveguiding performance in large-area plastic scintillators is assessed using Monte Carlo ray-tracing simulations.

Low-Temperature Molten Salts Synthesis: CsPbBr3 Nanocrystals with High Photoluminescence Emission Buried in Mesoporous SiO2.

Using mesoporous SiO2 to encapsulate CsPbBr3 nanocrystals is one of the best strategies to exploit such materials in devices. However, the CsPbBr3/SiO2 composites produced so far do not exhibit strong photoluminescence emission and, simultaneously, high stability against heat and water. We demonstrate a molten-salts-based approach delivering CsPbBr3/mesoporous-SiO2 composites with high PLQY (89 ± 10%) and high stability against heat, water, and aqua regia. The molten salts enable the formation of perovskite nanocrystals and other inorganic salts (KNO3-NaNO3-KBr) inside silica and the sealing of SiO2 pores at temperatures as low as 350 °C, representing an important technological advancement (analogous sealing was observed only above 700 °C in previous reports). Our CsPbBr3/mesoporous-SiO2 composites are attractive for different applications: as a proof-of-concept, we prepared a white-light emitting diode exhibiting a correlated color temperature of 7692K. Our composites are also stable after immersion in saline water at high temperatures (a typical underground environment of oil wells), therefore holding promise as oil tracers.

Compositional Tuning of Carrier Dynamics in Cs2Na1-x Ag x BiCl6 Double-Perovskite Nanocrystals.

We devised a hot-injection synthesis to prepare colloidal double-perovskite Cs2NaBiCl6 nanocrystals (NCs). We also examined the effects of replacing Na+ with Ag+ cations by preparing and characterizing Cs2Na1-x Ag x BiCl6 alloy NCs with x ranging from 0 to 1. Whereas Cs2NaBiCl6 NCs were not emissive, Cs2Na1-x Ag x BiCl6 NCs featured a broad photoluminescence band at ∼690 nm, Stokes-shifted from the respective absorption by ≥1.5 eV. The emission efficiency was maximized for low Ag+ amounts, reaching ∼3% for the Cs2Na0.95Ag0.05BiCl6 composition. Density functional theory calculations coupled with spectroscopic investigations revealed that Cs2Na1-x Ag x BiCl6 NCs are characterized by a complex photophysics stemming from the interplay of (i) radiative recombination via trapped excitons localized in spatially connected AgCl6-BiCl6 octahedra; (ii) surface traps, located on undercoordinated surface Bi centers, behaving as phonon-assisted nonradiative decay channels; and (iii) a thermal equilibrium between trapping and detrapping processes. These results offer insights into developing double-perovskite NCs with enhanced optoelectronic efficiency.

Stable and Size Tunable CsPbBr3 Nanocrystals Synthesized with Oleylphosphonic Acid.

We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr3 nanocrystals (NCs). Compared to phosphonic acids with linear alkyl chains, OLPA features a higher solubility in apolar solvents, allowing us to work at lower synthesis temperatures (100 °C), which in turn offer a good control over the NCs size. This can be reduced down to 5.0 nm, giving access to the strong quantum confinement regime. OLPA-based NCs form stable colloidal solutions at very low concentrations (∼1 nM), even when exposed to air. Such stability stems from the high solubility of OLPA in apolar solvents, which enables these molecules to reversibly bind/unbind to/from the NCs, preventing the NCs aggregation/precipitation. Small NCs feature efficient, blue-shifted emission and an ultraslow emission kinetics at cryogenic temperature, in striking difference to the fast decay of larger particles, suggesting that size-related exciton structure and/or trapping-detrapping dynamics determine the thermal equilibrium between coexisting radiative processes.

Transforming colloidal Cs4PbBr6 nanocrystals with poly(maleic anhydride-alt-1-octadecene) into stable CsPbBr3 perovskite emitters through intermediate heterostructures.

The preparation of strongly emissive CsPbBr3 perovskite nanocrystals with robust surface passivation is a challenge in the field of lead halide perovskite nanomaterials. We report an approach to prepare polymer-capped CsPbBr3 perovskite nanocrystals by reacting oleylammonium/oleate-capped Cs4PbBr6 nanocrystals with poly(maleic anhydride-alt-1-octadecene) (PMAO). PMAO contains succinic anhydride units that are reactive towards the oleylamine species present on the Cs4PbBr6 nanocrystals' surface and produces polysuccinamic acid, which, in turn, triggers the Cs4PbBr6 to CsPbBr3 conversion. The transformation occurs through the formation of Cs4PbBr6-CsPbBr3 heterostructures as intermediates, which are captured because of the mild reactivity of PMAO and are investigated by high-resolution electron microscopy. The Cs4PbBr6-CsPbBr3 heterostructures demonstrate a dual emission at cryogenic temperature with an indication of the energy transfer from Cs4PbBr6 to CsPbBr3. The fully-transformed CsPbBr3 NCs have high photoluminescence quantum yield and enhanced colloidal stability, which we attribute to the adhesion of polysuccinamic acid to the NC surface through its multiple functional groups in place of oleate and alkylammonium ligands. The PMAO-induced transformation of Cs4PbBr6 NCs opens up a strategy for the chemical modification of metal halide NCs initially passivated with nucleophilic amines.