The challenge of making strongly emissive CsPbBr3 perovskite nanocrystals with a robust surface passivation is solved via Cs4PbBr6 → CsPbBr3 transformation triggered by a reaction of oleylamine ligand with poly(maleic anhydride-1-alt-octadecene).
Recent developments in the exploitation of transparent conductive oxide nanocrystals paved the way to the realization of a new class of electrochemical systems capable of selectively shielding the infrared heat loads carried by sunlight and prospected the blooming of a key enabling technology to be implemented in the next generation of "zero-energy" building envelopes. Here we report the fabrication of a set of electrochromic devices embodying an engineered nanostructured electrode made by high aspect-ratio tungsten oxide nanorods, which allow for selectively and dynamically controlling sunlight transmission over the near-infrared to visible range. Varying the intensity of applied voltage makes the spectral response of the device change across three different optical regimes, namely fully transparent, near-infrared only blocking and both visible and near-infrared blocking. It is demonstrated that the degree of reversible modulation of the thermal radiation entering the glazing element can approach a remarkable 85%, accompanied by only a modest reduction in the luminous transmittance.
Nanocrystals
(NCs) of transparent conducting oxides with a localized
surface plasmon resonance (LSPR) in the near-infrared (NIR) spectral
region show promising electrochromic properties for the development
of a new generation of dynamic “smart windows”. In this
regard, we exploit thin films of F, In-codoped CdO (FICO) NCs as active
coatings for electrochromic devices. The control over the dopants
concentration in FICO NCs results in fine tuning of their LSPR across
the NIR region of the electromagnetic spectrum. Highly transparent
mesoporous electrodes were prepared from colloidal FICO NCs by in
situ ligand exchange of the pristine organic capping ligands. This
approach preserves the optical and electrical properties of native
NCs and delivers highly homogeneous, nonscattering films with a good
electronic coupling between the NCs. We achieved a dynamic control
over the LSPR frequency by reversible electrochemical doping, hence
a spectrally selective modulation of the optical transmittance in
the NIR region of the solar spectrum, which carries nearly 50% of
the whole solar heat. Spectroelectrochemical characterization, coloration
efficiency, and switching kinetics results indicate that thin film
based on FICO NCs are potential candidates for plasmonic electrochromic
applications. Moreover, the high electron mobility and wide optical
bandgap of FICO makes NCs of this material suitable for large-area
devices capable of dynamically controlling the heat load coming from
the solar infrared radiation, without affecting the visible light
transmittance.
The encapsulation of colloidal lead halide perovskite nanocrystals within silica (SiO 2 ) is one of the strategies to protect them from polar solvents and other external factors. Here, we demonstrate the overcoating of CsPbBr 3 perovskite nanocrystals with silica by exploiting the anhydride-induced transformation of Cs 4 PbBr 6 nanocrystals. CsPbBr 3 @SiO 2 core−shell nanocrystals are obtained after (i) a reaction between colloidal Cs 4 PbBr 6 nanocrystals and maleic anhydride in toluene that yields CsPbBr 3 nanocrystals and maleamic acid and (ii) a silica-shell growth around CsPbBr 3 nanocrystals via hydrolysis of added alkoxysilanes. The reaction between Cs 4 PbBr 6 nanocrystals and maleic anhydride is necessary to promote shell formation from alkoxysilanes, as demonstrated in control experiments. The best samples of asprepared CsPbBr 3 @SiO 2 nanocrystals consist of ∼10 nm single-crystal CsPbBr 3 cores surrounded by ∼5−7 nm amorphous silica shell. Despite their core−shell structure, such nanostructures are poor emitters and degrade within minutes of exposure to ethanol. The photoluminescence intensity of the core−shell nanocrystals is improved by the treatment with a solution of PbBr 2 and ligands, and their stability in ethanol is extended to several days after applying an additional silica growth step. Overall, the investigated approach outlines a strategy for making colloidal core−shell nanocrystals utilizing the transformative chemistry of metal halides and reveals interesting insights regarding the conditions required for CsPbBr 3 @SiO 2 nanocrystal formation.
Colloidal inorganic nanocrystals (NCs), free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical-chemical properties can be controlled through synthetic tailoring of their compositional, structural, and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/conversion/production, catalysis, and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie NC evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation, and mastering of increasingly complex "colloidal molecules," in which NC modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of allinorganic heterostructured nanocrystals (HNCs) in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in heterodimer, hetero-oligomer, and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic behavior, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described, revisited, and critically interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy.
We implemented a low-temperature approach to fabricate efficient photoanodes for dye-sensitized solar cells, which combines three different nanoarchitectures, namely, a highly conductive and highly transparent AZO film, a thin TiO2-blocking layer, and a mesoporous TiO2 nanorod-based working electrode. All the components were processed at T≤200°C. Both the AZO and the TiO2 blocking layers were deposited by reactive sputtering, whereas the TiO2 nanorods were synthesized by surfactant-assisted wet-chemical routes and processed into photoelectrodes in which the native geometric features assured uniform mesoporous structure with effective nanocrystal interconnectivity suitable to maximize light harvesting and electron diffusion. Because of the optimized structure of the TiO2-blocking/AZO bilayer, and thanks to the good adhesion of the TiO2 nanorods over it, a significant enhancement of the charge recombination resistance was demonstrated, this laying on the basis of the outstanding power conversion efficiency achievable through the use of this photoanode's architecture: a value of 4.6% (N719) was achieved with a 4-μm-thick electrode processed at T=200°C. This value noticeably overcomes the current literature limit got on AZO-based cells (N719), which instead use Nb-doped and thicker blocking layers, and thicker nanostructured photoanodes, which have been even sintered at higher temperatures (450-500°C).
Non-hydrolytic synthesis assisted by long-chain amphiphilic surfactant is exploited to generate dimension-controllable 2D-WS2 nanoflakes in a single-step protocol, where the chemical nature and steric hindrance of the alkylamine are the key points to modulate the lateral size finally achieved.
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