Roberto Simonutti

Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots

Luminescent solar concentrators serving as semitransparent photovoltaic windows could become an important element in net zero energy consumption buildings of the future. Colloidal quantum dots are promising materials for luminescent solar concentrators as they can be engineered to provide the large Stokes shift necessary for suppressing reabsorption losses in large-area devices. Existing Stokes-shift-engineered quantum dots allow for only partial coverage of the solar spectrum, which limits their light-harvesting ability and leads to colouring of the luminescent solar concentrators, complicating their use in architecture. Here, we use quantum dots of ternary I-III-VI2 semiconductors to realize the first large-area quantum dot-luminescent solar concentrators free of toxic elements, with reduced reabsorption and extended coverage of the solar spectrum. By incorporating CuInSexS2-x quantum dots into photo-polymerized poly(lauryl methacrylate), we obtain freestanding, colourless slabs that introduce no distortion to perceived colours and are thus well suited for the realization of photovoltaic windows. Thanks to the suppressed reabsorption and high emission efficiencies of the quantum dots, we achieve an optical power efficiency of 3.2%. Ultrafast spectroscopy studies suggest that the Stokes-shifted emission involves a conduction-band electron and a hole residing in an intragap state associated with a native defect.

Cooperation of multiple CH⋯π interactions to stabilize polymers in aromatic nanochannels as indicated by 2D solid state NMR

Advanced 2D solid state NMR techniques reveal weak intermolecular interactions that cooperatively sustain nanostructures of high molecular mass aliphatic polymers entrapped as guests in channels formed by an aromatic host.

Size-Tunable, Hexagonal Plate-like Cu3P and Janus-like Cu–Cu3P Nanocrystals

We describe two synthesis approaches to colloidal Cu(3)P nanocrystals using trioctylphosphine (TOP) as phosphorus precursor. One approach is based on the homogeneous nucleation of small Cu(3)P nanocrystals with hexagonal plate-like morphology and with sizes that can be tuned from 5 to 50 nm depending on the reaction time. In the other approach, metallic Cu nanocrystals are nucleated first and then they are progressively phosphorized to Cu(3)P. In this case, intermediate Janus-like dimeric nanoparticles can be isolated, which are made of two domains of different materials, Cu and Cu(3)P, sharing a flat epitaxial interface. The Janus-like nanoparticles can be transformed back to single-crystalline copper particles if they are annealed at high temperature under high vacuum conditions, which makes them an interesting source of phosphorus. The features of the Cu-Cu(3)P Janus-like nanoparticles are compared with those of the striped microstructure discovered more than two decades ago in the rapidly quenched Cu-Cu(3)P eutectic of the Cu-P alloy, suggesting that other alloy/eutectic systems that display similar behavior might give origin to nanostructures with flat, epitaxial interface between domains of two diverse materials. Finally, the electrochemical properties of the copper phosphide plates are studied, and they are found to be capable of undergoing lithiation/delithiation through a displacement reaction, while the Janus-like Cu-Cu(3)P particles do not display an electrochemical behavior that would make them suitable for applications in batteries.

13C and 31P MAS NMR investigations of spirocyclotriphosphazene nanotubes

The inclusion compounds (ICs) of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) with several small molecules have been studied, for the first time, by 13C magic angle spinning NMR. The channel-type structure of TPP ICs (about 5 A wide) provides an aromatic environment to trap some molecules such as benzene, tetrahydrofurane and p-xylene. 13C solid state NMR shows that the high symmetry of the adducts is consistent with an hexagonal crystal cell. The dynamic behaviour of the guest and host molecules has been studied by the measurement of 13C Ti relaxation times and compared with structures containing 10 A diameter channels. The release of the guest molecules has been followed by differential scanning calorimetry and by solid state NMR. There exist two crystal structures of the guest-free TPP molecule: the former is monoclinic and the latter retains the channel-type structure and hexagonal packing. 13C CP MAS spectra and relaxation times of guest-free TPP structures demonstrate the existence of empty nanotubes stable up to 150 °C. These structures are easily available for uptaking guest molecules by a phenomenon which is quite unusual for molecular architectures. The peak multiplicity of 31P CP MAS spectra reflect the symmetry of the crystal cells together with residual dipolar coupling with 14N.

A single-crystal imprints macroscopic orientation on xenon atoms

A porous single-crystal collects xenon atoms from the gas phase and orients them macroscopically, as highlighted by hyperpolarized xenon NMR.

Structural and Thermal Behavior of Poly (3‐octylthiophene): a DSC, 13C MAS NMR, XRD, Photoluminescence, and Raman Scattering Study

This work tries to give an answer to questions persisting over a decade in literature, concerning poly(3-alkylthiophene)s : polymorphism and phase stability related to the molecular masses, their distribution, the degree of regioregularity, the length of the side chain, and its nature. In fact we have studied, by means of five different techniques, the structural and thermal behavior of poly(3-octylhiophene) prepared by Ni catalyzed polymerization. A different thermal behavior for the rod-like conjugated backbone and for the side chains has been found having a strong influence both on the structural arrangement and the photoluminescence properties of the polymer. A thermal transition occuring at 84°C was found to correspond to the trans to gauche transition in the side chain conformations without a relevant change in the conjugated backbone planarity.

NIR emitting ytterbium chelates for colourless luminescent solar concentrators

A new oxyiminopyrazole-based ytterbium chelate enables NIR emission upon UV excitation in colorless single layer luminescent solar concentrators for building integrated photovoltaics.

High dielectric constant rutile–polystyrene composite with enhanced percolative threshold

TiO2 (rutile) nanocrystals, obtained by hydrothermal synthesis, are coated with polystyrene, grown by RAFT polymerization, and are dispersed into a polystyrene matrix at various concentrations. The morphology of both the polystyrene coating shell and TiO2 filler particles dispersed in the polymeric matrix is investigated. The polymer molecules attached to the surfaces of TiO2 nanoparticles exist in a “brush” regime; rutile nanoparticles self-assemble in chestnut-burr aggregates whose number increases with the filler amount. By increasing the filler concentration, the composites display a high dielectric constant, which is ascribed to the self-assembling of rutile nanoparticles in chestnut-burr aggregates, where a number of rutile crystals share the lateral faces and form capacitive microstructures. The crystals in these aggregates are separated by a polymer thin layer and allow a high percolative threshold, 41% v/v of filler amount, before the formation of a continuous network responsible for the sudden change of the dielectric characteristics. Despite the high content of inorganic filler, the dissipation factor remains low, even approaching the lower frequencies. The material is easily processable because of its polymeric nature and good reproducibility, thanks to the morphology control of the filler particles and their aggregates.

Cage-Like Local Structure of Ionic Liquids Revealed by a 129Xe Chemical Shift

The chemical shift of xenon (at natural abundance) dissolved in a variety of 1-butyl-3-methylimidazolium-based ionic liquids (ILs) has been measured with (129)Xe NMR spectroscopy. The large chemical shift differences observed are mainly related to the type of anion; the strongest deshielding effect is observed ILs with I(-), Br(-), and Cl(-) anions, and the strongest shielding is found for the bis(trifluoromethanesulfonyl)imide ([Tf2N](-))-based IL. The measured (129)Xe chemical shift variations correlate well with the IL structure organization imposed by the anions and with the size of the empty voids due to charge alternation patterns. Descriptors taken from literature data on X-ray and neutron scattering, as well as single-crystal structures where available, support this interpretation. The proposed methodology adds a new investigating tool to the elucidation of the short-range order in ILs. The observed chemical shift trend provides information about how these solvents are organized.

Direct 3D Visualization of the Phase-Separated Morphology in Chlorinated Polyethylene/Nylon Terpolyamide Based Thermoplastic Elastomers

Blends of chlorinated polyethylene and nylon-6/-6,6/-12 terpolyamide were prepared. The ratio of the two components was systematically varied within the blends. The mechanical behavior of the samples was analyzed with tensile tests and dynamical mechanical analysis showing that, for several ratios, materials with improved mechanical properties typical of thermoplastic elastomers were obtained. In such a mechanical regime, a co-continuous phase-separated morphology was clearly evidenced at the microscopic scale by 3D laser scanning confocal fluorescent microscopy (LSCFM). At blend compositions where plastic tensile behavior is observed, LSCFM reveals dispersed spheres of one component in the other.