Publications by authors named "Liberato Manna"

236 Publications

Switchable Anion Exchange in Polymer-Encapsulated APbX Nanocrystals Delivers Stable All-Perovskite White Emitters.

ACS Energy Lett 2021 Aug 22;6(8):2844-2853. Epub 2021 Jul 22.

Nanochemistry, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

We report a one-step synthesis of halide perovskite nanocrystals embedded in amphiphilic polymer (poly(acrylic acid)--poly(styrene), PAA--PS) micelles, based on injecting a dimethylformamide solution of PAA--PS, PbBr, ABr (A = Cs, formamidinium, or both) and "additive" molecules in toluene. These bifunctional or trifunctional short chain organic molecules improve the nanocrystal-polymer compatibility, increasing the nanocrystal stability against polar solvents and high flux irradiation (the nanocrystals retain almost 80% of their photoluminescence after 1 h of 3.2 w/cm irradiation). If the nanocrystals are suspended in toluene, the coil state of the polymer allows the nanocrystals to undergo halide exchange, enabling emission color tunability. If the nanocrystals are suspended in methanol, or dried as powders, the polymer is in the globule state, and they are inert to halide exchange. By mixing three primary colors we could prepare stable, multicolor emissive samples (for example, white emitting powders) and a UV-to-white color converting layer for light-emitting diodes entirely made of perovskite nanocrystals.
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http://dx.doi.org/10.1021/acsenergylett.1c01232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8369489PMC
August 2021

Electrochemical p-Doping of CsPbBr Perovskite Nanocrystals.

ACS Energy Lett 2021 Jul 17;6(7):2519-2525. Epub 2021 Jun 17.

Optoelectronic Materials Section, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629HZ Delft, The Netherlands.

Lead halide perovskite nanocrystals have drawn attention as active light-absorbing or -emitting materials for opto-electronic applications due to their facile synthesis, intrinsic defect tolerance, and color-pure emission ranging over the entire visible spectrum. To optimize their application in, e.g., solar cells and light-emitting diodes, it is desirable to gain control over electronic doping of these materials. However, predominantly due to the intrinsic instability of perovskites, successful electronic doping has remained elusive. Using spectro-electrochemistry and electrochemical transistor measurements, we demonstrate here that CsPbBr nanocrystals can be successfully and reversibly p-doped via electrochemical hole injection. From an applied potential of ∼0.9 V vs NHE, the emission quenches, the band edge absorbance bleaches, and the electronic conductivity quickly increases, demonstrating the successful injection of holes into the valence band of the CsPbBr nanocrystals.
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http://dx.doi.org/10.1021/acsenergylett.1c00970DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294022PMC
July 2021

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

ACS Energy Lett 2021 Jun 27;6(6):2283-2292. Epub 2021 May 27.

Nanochemistry Department Istituto Italiano di Tecnologia, 16163 Genova, Italy.

We synthesize colloidal nanocrystals (NCs) of RbInCl, composed of isolated metal halide octahedra ("0D"), and of CsNaInCl and CsKInCl double perovskites, where all octahedra share corners and are interconnected ("3D"), with the aim to elucidate and compare their optical features once doped with Sb 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" RbInCl NCs exhibit a higher PLQY than Sb-doped "3D" CsNaInCl and CsKInCl 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.
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http://dx.doi.org/10.1021/acsenergylett.1c00789DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294020PMC
June 2021

State of the Art and Prospects for Halide Perovskite Nanocrystals.

ACS Nano 2021 Jul 17;15(7):10775-10981. Epub 2021 Jun 17.

Department of Materials Science and Engineering, and Centre for Functional Photonics (CFP), City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong S.A.R.

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
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http://dx.doi.org/10.1021/acsnano.0c08903DOI Listing
July 2021

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

ACS Energy Lett 2021 Mar 11;6(3):900-907. Epub 2021 Feb 11.

Nanochemistry Department and Electron Microscopy Facility, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

Using mesoporous SiO to encapsulate CsPbBr nanocrystals is one of the best strategies to exploit such materials in devices. However, the CsPbBr/SiO 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 CsPbBr/mesoporous-SiO 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 (KNO-NaNO-KBr) inside silica and the sealing of SiO 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 CsPbBr/mesoporous-SiO 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.
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http://dx.doi.org/10.1021/acsenergylett.1c00052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8025713PMC
March 2021

Why Do We Care about Studying Transformations in Inorganic Nanocrystals?

Acc Chem Res 2021 04;54(7):1543-1544

Pennsylvania State University.

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http://dx.doi.org/10.1021/acs.accounts.1c00123DOI Listing
April 2021

Robustness to High Temperatures of AlO-Coated CsPbBr Nanocrystal Thin Films with High-Photoluminescence Quantum Yield for Light Emission.

ACS Appl Nano Mater 2020 Aug 16;3(8):8167-8175. Epub 2020 Jul 16.

Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

Lead-halide perovskite nanocrystals are a promising material in optical devices due to their high photoluminescence (PL) quantum yield, excellent color purity, and low stimulated emission threshold. However, one problem is the stability of the nanocrystal films under different environmental conditions and under high temperatures. The latter is particularly relevant for device fabrication if further processes that require elevated temperatures are needed after the deposition of the nanocrystal film. In this work, we study the impact of a thin oxide layer of AlO on the light emission properties of thin nanocrystal films. We find that nanocrystals passivated with quaternary ammonium bromide ligands maintain their advantageous optical properties in alumina-coated films and do not suffer from degradation at temperatures up to 100 °C. This is manifested by conservation of the PL peak position and line width, PL decay dynamics, and low threshold for amplified spontaneous emission. The PL remains stable for up to 100 h at a temperature of 80 °C, and the ASE intensity decreases by less than 30% under constant pumping at high fluence for 1 h. Our approach outlines that the combination of tailored surface chemistry with additional protective coating of the nanocrystal film is a feasible approach to obtain stable emission at elevated temperatures and under extended operational time scales.
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http://dx.doi.org/10.1021/acsanm.0c01525DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8009476PMC
August 2020

Metastable [email protected] [email protected] Nanostructures Obtained by Partial Cation Exchange Evolve into Sintered CdTe Films Upon Annealing.

Chem Mater 2020 Apr 12;32(7):2978-2985. Epub 2020 Mar 12.

Nanochemistry Department, Istituto Italiano di Tecnologia (IIT), via Morego 30, 16163 Genova, Italy.

Partial Hg → Cd cation exchange (CE) reactions were exploited to transform colloidal CdTe nanocrystals (NCs, 4-6 nm in size) into [email protected] [email protected] nanostructures. This was achieved by working under a slow CE rate, which limited the exchange to the surface of the CdTe NCs. In such nanostructures, when annealed at mild temperatures (as low as 200 °C), the HgTe shell sublimated or melted and the NCs sintered together, with the concomitant desorption of their surface ligands. At the end of this process, the annealed samples consisted of ligand-free CdTe sintered films containing an amount of Hg that was much lower than that of the starting [email protected] NCs. For example, the [email protected] NCs that initially contained 10% of Hg, after being annealed at 200 °C were transformed to CdTe sintered films containing only traces of Hg (less than 1%). This procedure was then used to fabricate a proof-of-concept CdTe-based photodetector exhibiting a photoresponse of up to 0.5 A/W and a detectivity of ca. 9 × 10 Jones under blue light illumination. Our strategy suggests that CE protocols might be exploited to lower the overall costs of production of CdTe thin films employed in photovoltaic technology, which are currently fabricated at high temperatures (above 350 °C), using post-process ligand-stripping steps.
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http://dx.doi.org/10.1021/acs.chemmater.9b05281DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8016170PMC
April 2020

Bright Blue Emitting Cu-Doped CsZnCl Colloidal Nanocrystals.

Chem Mater 2020 Jul 5;32(13):5897-5903. Epub 2020 Jun 5.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

We report here the synthesis of undoped and Cu-doped CsZnCl nanocrystals (NCs) in which we could tune the concentration of Cu from 0.7 to 7.5%. CsZnCl has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl tetrahedra surrounded by Cs cations. According to our electron paramagnetic resonance analysis, in 0.7 and 2.1% Cu-doped NCs the Cu ions were present in the +1 oxidation state only, while in NCs at higher Cu concentrations we could detect Cu(II) ions (isovalently substituting the Zn(II) ions). The undoped CsZnCl NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at ∼2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (∼55%) for the samples with a low Cu concentration ([Cu] ≤ 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (∼2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped CsZnCl NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.
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http://dx.doi.org/10.1021/acs.chemmater.0c02017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8016065PMC
July 2020

Engineering the Optical Emission and Robustness of Metal-Halide Layered Perovskites through Ligand Accommodation.

Adv Mater 2021 Apr 1;33(13):e2008004. Epub 2021 Mar 1.

Istituto Italiano di Tecnologia, Via Morego 30, Genova, 16163, Italy.

The unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of organoammonium molecules are exploited to engineer the optical emission and robustness of a new set of Ruddlesden-Popper metal-halide layered perovskites. It is shown that the type of molecule regulates the number of hydrogen bonds that it forms with the edge-sharing [PbBr ] octahedra layers, leading to strong differences in the material emission and tunability of the color coordinates, from deep-blue to pure-white. Also, the emission intensity strongly depends on the length of the molecules, thereby providing an additional parameter to optimize their emission efficiency. The combined experimental and computational study provides a detailed understanding of the impact of lattice distortions, compositional defects, and the anisotropic crystal structure on the emission of such layered materials. It is foreseen that this rational design can be extended to other types of organic linkers, providing a yet unexplored path to tailor the optical and mechanical properties of these materials and to unlock new functionalities.
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http://dx.doi.org/10.1002/adma.202008004DOI Listing
April 2021

Colloidal Bi-Doped CsAg Na InCl Nanocrystals: Undercoordinated Surface Cl Ions Limit their Light Emission Efficiency.

ACS Mater Lett 2020 Nov 28;2(11):1442-1449. Epub 2020 Sep 28.

Nanochemistry Department, Analytical Chemistry Lab, and Functional Nanosystems, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova, Italy.

Understanding and tuning the ligand shell composition in colloidal halide perovskite nanocrystals (NCs) has been done systematically only for Pb-based perovskites, while much less is known on the surface of Pb-free perovskite systems. Here, we reveal the ligand shell architecture of Bi-doped CsAg Na InClNCs via nuclear magnetic resonance analysis. This material, in its bulk form, was found to have a photoluminescence quantum yield (PLQY) as high as 86%, a record value for halide double perovskites. Our results show that both amines and carboxylic acids are present and homogeneously distributed over the surface of the NCs. Notably, even for an optimized surface ligand coating, achieved by combining dodecanoic acid and decylamine, a maximum PLQY value of only 37% is reached, with no further improvements observed when exploiting post-synthesis ligand exchange procedures (involving Cs-oleate, different ammonium halides, thiocyanates and sulfonic acids). Our density functional theory calculations indicate that, even with the best ligands combination, a small fraction of unpassivated surface sites, namely undercoordinated Cl ions, is sufficient to create deep trap states, opposite to the case of Pb-based perovskites that exhibit much higher defect tolerance. This was corroborated by our transient absorption measurements, which showed that an ultrafast trapping of holes (most likely mediated by surface Cl-trap states) competes with their localization at the AgCl octahedra, from where, instead, they can undergo an optically active recombination yielding the observed PL emission. Our results highlight that alternative surface passivation strategies should be devised to further optimize the PLQY of double perovskite NCs, which might include their incorporation inside inorganic shells.
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http://dx.doi.org/10.1021/acsmaterialslett.0c00359DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7901666PMC
November 2020

Mechanical switching of orientation-related photoluminescence in deep-blue 2D layered perovskite ensembles.

Nanoscale 2021 Feb;13(7):3948-3956

Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

The synergy between the organic component of two-dimensional (2D) metal halide layered perovskites and flexible polymers offers an unexplored window to tune their optical properties at low mechanical stress. Thus, there is a significant interest in exploiting their PL anisotropy by controlling their orientation and elucidating their interactions. Here, we apply this principle to platelet structures of micrometre lateral size that are synthesized in situ into free-standing polymer films. We study the photoluminescence of the resulting films under cyclic mechanical stress and observe an enhancement in the emission intensity up to ∼2.5 times along with a switch in the emission profile when stretching the films from 0% to 70% elongation. All the films recovered their initial emission intensity when releasing the stress throughout ca. 15 mechanical cycles. We hypothesize a combined contribution from reduced reabsorption, changes on in-plane and out-of-plane dipole moments that stem from different orientation of the platelets inside the film, and relative sliding of platelets within oriented stacks while stretching the films. Our results reveal how low-mechanical stress affects 2D layered perovskite aggregation and orientation, an open pathway toward the design of strain-controlled emission.
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http://dx.doi.org/10.1039/d0nr08043hDOI Listing
February 2021

Multilayer Diffraction Reveals That Colloidal Superlattices Approach the Structural Perfection of Single Crystals.

ACS Nano 2021 Apr 22;15(4):6243-6256. Epub 2021 Jan 22.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

Colloidal superlattices are fascinating materials made of ordered nanocrystals, yet they are rarely called "atomically precise". That is unsurprising, given how challenging it is to quantify the degree of structural order in these materials. However, once that order crosses a certain threshold, the constructive interference of X-rays diffracted by the nanocrystals dominates the diffraction pattern, offering a wealth of structural information. By treating nanocrystals as scattering sources forming a self-probing interferometer, we developed a multilayer diffraction method that enabled the accurate determination of the nanocrystal size, interparticle spacing, and their fluctuations for samples of self-assembled CsPbBr and PbS nanomaterials. The multilayer diffraction method requires only a laboratory-grade diffractometer and an open-source fitting algorithm for data analysis. The average nanocrystal displacement of 0.33 to 1.43 Å in the studied superlattices provides a figure of merit for their structural perfection and approaches the atomic displacement parameters found in traditional crystals.
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http://dx.doi.org/10.1021/acsnano.0c08929DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8155329PMC
April 2021

Detection of Pb traces in dispersion of CsPbBr nanocrystals by liquid cell transmission electron microscopy.

Nanoscale 2021 Feb;13(4):2317-2323

Department of Nanochemistry, Italian Institute of Technology, Genova, 16163, Italy.

The Cs4PbBr6 nanocrystals are often used as a starting material for the preparation of green-emitting CsPbBr3 perovskite nanocrystals by means of chemical and physical transformations. Herein, we probe the Cs4PbBr6 nanocrystals dispersed in a solvent by liquid cell transmission electron microscopy (LCTEM). The nanocrystal dispersion in toluene is placed between two electron-transparent membranes separated by a gold spacer in a liquid cell and studied in a high angular annular dark-field scanning TEM mode with a fixed electron dose rate. We observe the spontaneous nucleation and growth of round and dendrite-shaped nanoparticles under electron beam illumination in the areas of solution where no Cs4PbBr6 nanocrystals are seen. These newly-formed nanoparticles show high contrast and contain Pb as the only heavy element, suggesting that they are made from metallic lead and indicating Pb2+-containing species in solution as their precursor. Also, a small amount of Au0 nanoparticles are formed, most likely due to the dissolution of the gold spacer by free Br-containing species in the nanocrystal dispersion and a subsequent reduction of the leached species under the electron beam. The analysis of the UV-Vis absorption spectra of Cs4PbBr6 nanocrystals and the supernatant isolated from the synthesis points to mixed lead(ii) oleate/bromide species as the likely residue, corroborating LCTEM results. The identification of the residual precursors in Cs4PbBr6 nanocrystal samples after the post-synthetic isolation is an important task because the residues may alter the subsequent reactivity of the nanocrystals.
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http://dx.doi.org/10.1039/d0nr08584gDOI Listing
February 2021

Halide Perovskite-Lead Chalcohalide Nanocrystal Heterostructures.

J Am Chem Soc 2021 Jan 13;143(3):1435-1446. Epub 2021 Jan 13.

Department of Nanochemistry, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

We report the synthesis of colloidal CsPbX-PbSBr (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr-PbSBr nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Postsynthesis reaction with either Cl or I ions delivers the corresponding CsPbCl-PbSBr and CsPbI-PbSBr heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable γ phase (or "black" phase) of CsPbI in the CsPbI-PbSBr heterostructure.
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http://dx.doi.org/10.1021/jacs.0c10916DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7844828PMC
January 2021

Metamorphoses of Cesium Lead Halide Nanocrystals.

Acc Chem Res 2021 02 7;54(3):498-508. Epub 2021 Jan 7.

Department of Nanochemistry, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

Following the impressive development of bulk lead-based perovskite photovoltaics, the "perovskite fever" did not spare nanochemistry. In just a few years, colloidal cesium lead halide perovskite nanocrystals have conquered researchers worldwide with their easy synthesis and color-pure photoluminescence. These nanomaterials promise cheap solution-processed lasers, scintillators, and light-emitting diodes of record brightness and efficiency. However, that promise is threatened by poor stability and unwanted reactivity issues, throwing down the gauntlet to chemists.More generally, Cs-Pb-X nanocrystals have opened an exciting chapter in the chemistry of colloidal nanocrystals, because their ionic nature and broad diversity have challenged many paradigms established by nanocrystals of long-studied metal chalcogenides, pnictides, and oxides. The chemistry of colloidal Cs-Pb-X nanocrystals is synonymous with change: these materials demonstrate an intricate pattern of shapes and compositions and readily transform under physical stimuli or the action of chemical agents. In this Account, we walk through four types of Cs-Pb-X nanocrystal metamorphoses: change of structure, color, shape, and surface. These transformations are often interconnected; for example, a change in shape may also entail a change of color.The ionic bonding, high anion mobility due to vacancies, and preservation of cationic substructure in the Cs-Pb-X compounds enable fast anion exchange reactions, allowing the precise control of the halide composition of nanocrystals of perovskites and related compounds (e.g., CsPbCl ⇄ CsPbBr ⇄ CsPbI and CsPbCl ⇄ CsPbBr ⇄ CsPbI) and tuning of their absorption edge and bright photoluminescence across the visible spectrum. Ion exchanges, however, are just one aspect of a richer chemistry.Cs-Pb-X nanocrystals are able to capture or release (in short, trade) ions or even neutral species from or to the surrounding environment, causing major changes to their structure and properties. The trade of neutral PbX units allows Cs-Pb-X nanocrystals to cross the boundaries among four different types of compounds: 4CsX + PbX ⇄ CsPbBr + 3PbX ⇄ 4CsPbBr + PbX ⇄ 4CsPbX. These reactions do not occur at random, because the reactant and product nanocrystals are connected by the Cs cation substructure preservation principle, stating that ion trade reactions can transform one compound into another by means of distorting, expanding, or contracting their shared Cs cation substructure.The nanocrystal surface is a boundary between the core and the surrounding environment of Cs-Pb-X nanocrystals. The surface influences nanocrystal stability, optical properties, and shape. For these reasons, the dynamic surface of Cs-Pb-X nanocrystals has been studied in detail, especially in CsPbX perovskites. Two takeaways have emerged from these studies. First, the competition between primary alkylammonium and cesium cations for the surface sites during the CsPbX nanocrystal nucleation and growth governs the cube/plate shape equilibrium. Short-chain acids and branched amines influence that equilibrium and enable shape-shifting synthesis of pure CsPbX cubes, nanoplatelets, nanosheets, or nanowires. Second, quaternary ammonium halides are emerging as superior ligands that extend the shelf life of Cs-Pb-X colloidal nanomaterials, boost their photoluminescence quantum yield, and prevent foreign ions from escaping the nanocrystals. That is accomplished by combining reduced ligand solubility, due to the branched organic ammonium cation, with the surface-healing capabilities of the halide counterions, which are small Lewis bases.
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http://dx.doi.org/10.1021/acs.accounts.0c00710DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7880526PMC
February 2021

Alloy CsCd Pb Br Perovskite Nanocrystals: The Role of Surface Passivation in Preserving Composition and Blue Emission.

Chem Mater 2020 Dec 4;32(24):10641-10652. Epub 2020 Dec 4.

Nanochemistry Department, Photonic Nanomaterials Lab, Analytical Chemistry Lab, Electron Microscopy Facility, Materials Characterization Facility, Istituto Italiano di Tecnologia (IIT), via Morego 30, 16163 Genova, Italy.

Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and composition and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX perovskite NCs composed of two different M cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCd Pb Br NCs, which exhibit a cubic perovskite phase containing Cd-rich domains of Ruddlesden-Popper phases (RP phases). The RP domains spontaneously transform into pure orthorhombic perovskite ones upon NC aging, and the emission color of the NCs shifts from blue to green over days. On the other hand, postsynthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocrystalline NCs with cubic phase, highlighting the metastability of RP domains. When NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd ions are expelled from NCs upon aging, and the NCs phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when NCs are coated with ammonium bromides, the loss of Cd ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in the latter cases is ascribed to the saturation of surface vacancies, which may act as channels for the expulsion of Cd ions from NCs.
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http://dx.doi.org/10.1021/acs.chemmater.0c03825DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7768894PMC
December 2020

Aging of Self-Assembled Lead Halide Perovskite Nanocrystal Superlattices: Effects on Photoluminescence and Energy Transfer.

ACS Nano 2021 Jan 22;15(1):650-664. Epub 2020 Dec 22.

Nanochemistry Department, Italian Institute of Technology, Via Morego 30, Genova 16163, Italy.

Excitonic coupling, electronic coupling, and cooperative interactions in self-assembled lead halide perovskite nanocrystals were reported to give rise to a red-shifted collective emission peak with accelerated dynamics. Here we report that similar spectroscopic features could appear as a result of the nanocrystal reactivity within the self-assembled superlattices. This is demonstrated by studying CsPbBr nanocrystal superlattices over time with room-temperature and cryogenic micro-photoluminescence spectroscopy, X-ray diffraction, and electron microscopy. It is shown that a gradual contraction of the superlattices and subsequent coalescence of the nanocrystals occurs over several days of keeping such structures under vacuum. As a result, a narrow, low-energy emission peak is observed at 4 K with a concomitant shortening of the photoluminescence lifetime due to the energy transfer between nanocrystals. When exposed to air, self-assembled CsPbBr nanocrystals develop bulk-like CsPbBr particles on top of the superlattices. At 4 K, these particles produce a distribution of narrow, low-energy emission peaks with short lifetimes and excitation fluence-dependent, oscillatory decays. Overall, the aging of CsPbBr nanocrystal assemblies dramatically alters their emission properties and that should not be overlooked when studying collective optoelectronic phenomena nor confused with superfluorescence effects.
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http://dx.doi.org/10.1021/acsnano.0c06595DOI Listing
January 2021

Are There Good Alternatives to Lead Halide Perovskite Nanocrystals?

Nano Lett 2021 01 21;21(1):6-9. Epub 2020 Dec 21.

Nanochemistry Department, Istituto Italiano di Tecnologia (IIT), via Morego 30, Genova 16163, Italy.

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http://dx.doi.org/10.1021/acs.nanolett.0c04760DOI Listing
January 2021

Compositional Tuning of Carrier Dynamics in CsNa Ag BiCl Double-Perovskite Nanocrystals.

ACS Energy Lett 2020 Jun 8;5(6):1840-1847. Epub 2020 May 8.

Dipartimento di Scienza dei Materiali, Universitá degli Studi di Milano-Bicocca, via R. Cozzi 55, 20125 Milano, Italy.

We devised a hot-injection synthesis to prepare colloidal double-perovskite CsNaBiCl nanocrystals (NCs). We also examined the effects of replacing Na with Ag cations by preparing and characterizing CsNa Ag BiCl alloy NCs with ranging from 0 to 1. Whereas CsNaBiCl NCs were not emissive, CsNa Ag BiCl 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 CsNaAgBiCl composition. Density functional theory calculations coupled with spectroscopic investigations revealed that CsNa Ag BiCl NCs are characterized by a complex photophysics stemming from the interplay of (i) radiative recombination via trapped excitons localized in spatially connected AgCl-BiCl 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.
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http://dx.doi.org/10.1021/acsenergylett.0c00914DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739488PMC
June 2020

What Defines a Halide Perovskite?

ACS Energy Lett 2020 Feb 28;5(2):604-610. Epub 2020 Jan 28.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

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http://dx.doi.org/10.1021/acsenergylett.0c00039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739487PMC
February 2020

Microwave-Induced Structural Engineering and Pt Trapping in 6R-TaS for the Hydrogen Evolution Reaction.

Small 2020 Dec 23;16(50):e2003372. Epub 2020 Nov 23.

Graphene Labs, Istituto Italiano di Tecnologia, via Morego 30, Genova, 16163, Italy.

The nanoengineering of the structure of transition metal dichalcogenides (TMDs) is widely pursued to develop viable catalysts for the hydrogen evolution reaction (HER) alternative to the precious metallic ones. Metallic group-5 TMDs have been demonstrated to be effective catalysts for the HER in acidic media, making affordable real proton exchange membrane water electrolysers. Their key-plus relies on the fact that both their basal planes and edges are catalytically active for the HER. In this work, the 6R phase of TaS is "rediscovered" and engineered. A liquid-phase microwave treatment is used to modify the structural properties of the 6R-TaS nanoflakes produced by liquid-phase exfoliation. The fragmentation of the nanoflakes and their evolution from monocrystalline to partly polycrystalline structures improve the HER-activity, lowering the overpotential at cathodic current of 10 mA cm from 0.377 to 0.119 V. Furthermore, 6R-TaS nanoflakes act as ideal support to firmly trap Pt species, which achieve a mass activity (MA) up 10 000 A g at overpotential of 50 mV (20 000 A g at overpotentials of 72 mV), representing a 20-fold increase of the MA of Pt measured for the Pt/C reference, and approaching the state-of-the-art of the Pt mass activity.
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http://dx.doi.org/10.1002/smll.202003372DOI Listing
December 2020

Stable and Size Tunable CsPbBr Nanocrystals Synthesized with Oleylphosphonic Acid.

Nano Lett 2020 Dec 17;20(12):8847-8853. Epub 2020 Nov 17.

Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, via R. Cozzi 55, 20125 Milano, Italy.

We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr 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.
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http://dx.doi.org/10.1021/acs.nanolett.0c03833DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7872419PMC
December 2020

Bandgap determination from individual orthorhombic thin cesium lead bromide nanosheets by electron energy-loss spectroscopy.

Nanoscale Horiz 2020 Nov;5(12):1610-1617

CNR - Istituto Nanoscienze, Via Campi 213/A, 41125 Modena, Italy. and IMEM - CNR, Istituto dei Materiali per l'Elettronica e il Magnetismo, Parco Area delle Scienze 37/A, 43124 Parma, Italy.

Inorganic lead halide perovskites are promising candidates for optoelectronic applications, due to their high photoluminescence quantum yield and narrow emission line widths. Particularly attractive is the possibility to vary the bandgap as a function of the halide composition and the size or shape of the crystals at the nanoscale. Here we present an aberration-corrected scanning transmission electron microscopy (STEM) and monochromated electron energy-loss spectroscopy (EELS) study of extended nanosheets of CsPbBr3. We demonstrate their orthorhombic crystal structure and their lateral termination with Cs-Br planes. The bandgaps are measured from individual nanosheets, avoiding the effect of the size distribution which is present in standard optical spectroscopy techniques. We find an increase of the bandgap starting at thicknesses below 10 nm, confirming the less marked effect of 1D confinement in nanosheets compared to the 3D confinement observed in quantum dots, as predicted by density functional theory calculations and optical spectroscopy data from ensemble measurements.
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http://dx.doi.org/10.1039/d0nh00477dDOI Listing
November 2020

Lead-Free Double Perovskite Cs AgInCl.

Angew Chem Int Ed Engl 2021 May 3;60(21):11592-11603. Epub 2021 Feb 3.

The Beijing Municipal Key Laboratory of New Energy Materials and Technologies, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, P. R. China.

Lead-free halide perovskites have drawn wide attention as alternatives to their toxic and poorly stable lead-based counterparts. Among them, double perovskites with Cs AgInCl composition, often doped with various elements, have been in the spotlight owing to their intriguing optical properties, namely, self-trapped exciton (STEs) emission and dopant-induced photoluminescence. This interest has sparked different synthesis approaches towards both crystals and nanocrystals, and the exploration of many alloy compositions with mono- and trivalent cations other than Ag and In . In this Minireview we describe the recent developments on Cs AgInCl bulk crystals and nanocrystals, their synthesis strategies, intrinsic optical properties, and tunable photoluminescence originating from different alloying and doping effects. We also discuss progress on computational studies aimed at understanding the thermodynamic stability, the role of defects, and the origin of photoluminescence in relation to the STEs and the direct band gap character.
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http://dx.doi.org/10.1002/anie.202011833DOI Listing
May 2021

Wide-Angle X-ray Diffraction Evidence of Structural Coherence in CsPbBr Nanocrystal Superlattices.

ACS Mater Lett 2019 Aug 16;1(2):272-276. Epub 2019 Jul 16.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

Films made of colloidal CsPbBr nanocrystals packed in isolated or densely-packed superlattices display a remarkably high degree of structural coherence. The structural coherence is revealed by the presence of satellite peaks accompanying Bragg reflections in wide-angle X-ray diffraction experiments in parallel-beam reflection geometry. The satellite peaks, also called "superlattice reflections", arise from the interference of X-rays diffracted by the atomic planes of the orthorhombic perovskite lattice. The interference is due to the precise spatial periodicity of the nanocrystals separated by organic ligands in the superlattice. The presence of satellite peaks is a fingerprint of the high crystallinity and long-range order of nanocrystals, comparable to those of multilayer superlattices prepared by physical methods. The angular separation between satellite peaks is highly sensitive to changes in the superlattice periodicity. These characteristics of the satellite peaks are exploited to track the superlattice compression under vacuum, as well as to observe the superlattice growth in situ from colloidal solutions by slow solvent evaporation.
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http://dx.doi.org/10.1021/acsmaterialslett.9b00217DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497715PMC
August 2019

Green-Emitting Powders of Zero-Dimensional CsPbBr: Delineating the Intricacies of the Synthesis and the Origin of Photoluminescence.

Chem Mater 2019 Sep 28;31(18):7761-7769. Epub 2019 Aug 28.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

A detailed investigation into the synthesis of green-emitting powders of CsPbBr and CsPbBr materials by antisolvent precipitation from CsBr-PbBr precursor solutions in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is reported. Various solvated lead bromide and polybromide species (PbBr, [PbBr], [PbBr], and possibly [PbBr]or [PbBr]) are detected in the precursor solutions by optical absorbance and emission spectroscopies. The solvodynamic size of the species in solution is strongly solvent-dependent: ~1 nm species were detected in DMSO, while significantly larger species were observed in DMF by dynamic light scattering. The solvodynamic size of the lead bromide species plays a critical role in determining the Cs-Pb-Br composition of the precipitated powders: smaller species favor the precipitation of CsPbBr, while larger species template the formation of CsPbBr under identical experimental conditions. The powders have been characterized by Cs and Pb solid-state nuclear magnetic resonance, and Cs sensitivity toward the different Cs environments within CsPbBr is demonstrated. Finally, the possible origins of green emission in CsPbBr samples are discussed. It is proposed that a two-dimensional CsPbBr inclusion may be responsible for green emission at ~520 nm in addition to the widely acknowledged CsPbBr impurity, although we found no conclusive experimental evidence supporting such claims.
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http://dx.doi.org/10.1021/acs.chemmater.9b02944DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116092PMC
September 2019

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

Chem Sci 2020 Apr 20;11(15):3986-3995. Epub 2020 Mar 20.

Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy.

The preparation of strongly emissive CsPbBr 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 CsPbBr perovskite nanocrystals by reacting oleylammonium/oleate-capped CsPbBr nanocrystals with poly(maleic anhydride--1-octadecene) (PMAO). PMAO contains succinic anhydride units that are reactive towards the oleylamine species present on the CsPbBr nanocrystals' surface and produces polysuccinamic acid, which, in turn, triggers the CsPbBr to CsPbBr conversion. The transformation occurs through the formation of CsPbBr-CsPbBr heterostructures as intermediates, which are captured because of the mild reactivity of PMAO and are investigated by high-resolution electron microscopy. The CsPbBr-CsPbBr heterostructures demonstrate a dual emission at cryogenic temperature with an indication of the energy transfer from CsPbBr to CsPbBr. The fully-transformed CsPbBr 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 CsPbBr NCs opens up a strategy for the chemical modification of metal halide NCs initially passivated with nucleophilic amines.
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http://dx.doi.org/10.1039/D0SC00738BDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116022PMC
April 2020

Cation Exchange Protocols to Radiolabel Aqueous Stabilized ZnS, ZnSe, and CuFeS Nanocrystals with Cu for Dual Radio- and Photo-Thermal Therapy.

Adv Funct Mater 2020 Jul 26;30(28):2002362. Epub 2020 May 26.

Istituto Italiano di Tecnologia (IIT) via Morego 30 Genova 16163 Italy.

Here, cation exchange (CE) reactions are exploited to radiolabel ZnSe, ZnS, and CuFeS metal chalcogenide nanocrystals (NCs) with Cu. The CE protocol requires one simple step, to mix the water-soluble NCs with a Cu solution, in the presence of vitamin C used to reduce Cu(II) to Cu(I). Given the quantitative cation replacement on the NCs, a high radiochemical yield, up to 99%, is reached. Also, provided that there is no free Cu, no purification step is needed, making the protocol easily translatable to the clinic. A unique aspect of the approach is the achievement of an unprecedentedly high specific activity: by exploiting a volumetric CE, the strategy enables to concentrate a large dose of Cu (18.5 MBq) in a small NC dose (0.18 µg), reaching a specific activity of 103 TBq g. Finally, the characteristic dielectric resonance peak, still present for the radiolabeled Cu:CuFeS NCs after the partial-CE reaction, enables the generation of heat under clinical laser exposure (1 W cm). The synergic toxicity of photo-ablation and Cu ionization is here proven on glioblastoma and epidermoid carcinoma tumor cells, while no intrinsic cytotoxicity is seen from the NC dose employed for these dual experiments.
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http://dx.doi.org/10.1002/adfm.202002362DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7357593PMC
July 2020
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