Search

Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperature. Vacuum-deposited, wide-bandgap solar cells based on mixed-cation and mixed-anion perovskites have been scarcely reported, due to the challenges associated with the multiple-source processing of perovskite thin films. In this work, we describe a four-source vacuum deposition process to prepare wide-bandgap perovskites of the type FA1-n Cs n Pb(I1-x Br x )3 with a tunable bandgap and controlled morphology, using FAI, CsI, PbI2, and PbBr2 as the precursors. The simultaneous sublimation of PbI2 and PbBr2 allows the relative Br/Cs content to be decoupled and controlled, resulting in homogeneous perovskite films with a bandgap in the 1.7-1.8 eV range and no detectable halide segregation. Solar cells based on 1.75 eV bandgap perovskites show efficiency up to 16.8% and promising stability, maintaining 90% of the initial efficiency after 2 weeks of operation.

Herein, the long-term stability of vacuum-deposited methylammonium lead iodide (MAPbI(3)) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low-temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI(3) layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI(3) to be exposed to temperatures as high as 150 degrees C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for approximate to 40 and 37days at 65 and 85 degrees C, respectively. However, room-temperature operation of the solar cells under 1sun illumination leads to a loss of 20% of their initial PCE in 230h. Due to the very thin ALD Al2O3 encapsulation, X-ray diffraction can be performed on the MAPbI(3) films and completed solar cells before and after the different stress conditions. Surprisingly, it is found that the main effect of light soaking and thermal stress is a crystal reorientation with respect to the substrate from (002) to (202) of the perovskite layer, and that this reorientation is accelerated under illumination.

We report herein a simple ligand-assisted reprecipitation method at room temperature to synthesize mixed-cation hybrid organic–inorganic perovskite nanocrystals with low structural dimensionality., We report herein a simple ligand-assisted reprecipitation method at room temperature to synthesize mixed-cation hybrid organic–inorganic perovskite nanocrystals with low structural dimensionality. The emission wavelength of iodide-based perovskites is thus tuned from the near-infrared to the red part of the visible spectrum. While this is mostly achieved in the literature by addition of bromide, we demonstrate here a controllable blueshift of the band gap by varying the chain length of the alkylammonium ligands. Furthermore, an antisolvent washing step was found to be crucial to purify the samples and obtain single-peak photoluminescence with a narrow linewidth. The so-formed nanocrystals exhibit high and stable photoluminescence quantum yields exceeding 90% over 500 hours, making these materials ideal for light-emitting applications.

The surface ligands on colloidal nanocrystals (NCs) play an important role in the performance of NCs based optoelectronic devices such as photovoltaic cells, photodetectors and light emitting diodes (LEDs). On one hand, the NC emission depends critically on the passivation of the surface to minimize trap states that can provide non-radiative recombination channels. On the other hand, the electrical properties of NC films are dominated by the ligands that constitute the barriers for charge transport from one NC to its neighbor. Therefore, surface modifications via ligandexchange have been employed to improve the conductance of NC films. However, in light emitting devices, such surface modifications are more critical due to their possible detrimental effects on the emission properties. In this work, we study the role of surface ligand modifications on the optical and electrical properties of CdSe/CdS dot-in-rods (DiRs) in films, and investigate their performance in all-solution processed LEDs. The DiR films maintain high PLQY, around 40-50%, and their electroluminescence in the LED preserves the excellent color purity of the PL. In the LEDs, the ligand-exchange boosted the luminance, reaching a four-fold increase from 2200 cd/m2 for native surfactants to 8500 cd/m2 for the exchanged aminoethanethiol ligands. Moreover, the efficiency roll-off, operational stability, and shelf life are significantly improved, and the external quantum efficiency is modestly increased from 5.1 % to 5.4 %. We relate these improvements to the increased conductivity of the emissive layer, and to the better charge balance of the electrically injected carriers. In this respect, we performed ultraviolet photoelectron spectroscopy (UPS) to obtain deeper insight in the band alignment of the LED structure., 26 pages, 4 figures

We show that oxygen plasma affects in different ways the structural, chemical, optical, and electrical properties of methylammonium and cesium lead bromide nanocrystals. Hybrid organic–inorganic nanocrystals were severely and quickly degraded by oxygen plasma at 50 W. Their photoluminescence was quenched with almost 100% loss of the initial quantum yield, which is linked to decomposition of the nanocrystals. Inorganic nanocrystals were more resistant to oxygen plasma in the same conditions. Despite a moderate loss of photoluminescence and electrical conductivity, oxygen plasma had a positive impact, removing unbound ligands and resulting in more ohmic behavior of the film. This paves the way for the application of oxygen plasma in the development of perovskite-based optoelectronic devices.

A new and straightforward single-step route to decorate melamine foams with silver nanoparticles (ME/Ag) is proposed. Uniform coatings of silver nanoparticles with diameters less than 10 nm are formed in situ directly on the struts surface of the foams, after their dipping in an AgNO3 solution. We prove that the nanoparticles are stably adhered on the foams, and that their amount can be directly controlled by the concentration of the AgNO3 solution and the dipping time. Following this production route, ME/Ag foams can be obtained with silver content ranging between 0.2 and 18.6 wt % and excellent antibacterial performance, making them appropriate for various applications. Herein we explore the possibility to use them as antibacterial filters for water treatment, proving that they are able to remove completely Escherichia coli bacteria from water when filtered at flow rates up to 100 mL/h·cm2 due to the release of less than 1 ppm of Ag+ ions by the foams. No bacterial regrowth was observed after further dilution of the treated water, to arrive below the safety threshold of Ag+ for drinking water (0.1 ppm), demonstrating the excellent bactericide performance of the ME/Ag filters.

New seaweed-based biomaterials have been prepared using a simple method based on the selective dissolution in trifluoroacetic acid (TFA) of specific polymers and bioactive substances from red, green, and brown seaweeds. Depending on the seaweed's origin, the properties were found to be different, especially the mechanical ones. Furthermore, the samples were fully biodegradable in seawater in one month. Moreover, the antioxidant capacity of the biomaterials was highly increased respect to the pristine materials, demonstrating a selective extraction during the process of solubilization. Finally, biocompatibility and anti-inflammatory experiments demonstrated the non-toxicity of the biomaterials prepared from brown seaweed and a similar anti-inflammatory effect to commercial available drugs, confirming the potential application of the prepared biomaterials for the fabrication of biomedical devices.

Perovskite-related Cs4PbBr6 nanocrystals present a “zero-dimensional” crystalline structure where adjacent [PbBr6]4– octahedra do not share any corners. We show in this work that these nanocrystals can be converted into “three-dimensional” CsPbBr3 perovskites by extraction of CsBr. This conversion drastically changes the optoelectronic properties of the nanocrystals that become highly photoluminescent. The extraction of CsBr can be achieved either by thermal annealing (physical approach) or by chemical reaction with Prussian Blue (chemical approach). The former approach can be simply carried out on a dried film without addition of any chemicals but does not yield a full transformation. Instead, reaction with Prussian Blue in solution achieves a full transformation into the perovskite phase. This transformation was also verified on the iodide counterpart (Cs4PbI6).

Superhydrophobic and wear abrasion resistant high impact polystyrene (HIPS)/silica nanocomposite coatings for metal surfaces have been produced by spray. An environmentally friendly perfluorinated acrylic copolymer (PFAC) primer coating layer was applied first, in order to enhance adhesion with the substrate and prolong abrasion resistance. The best nanocomposite composition was found to be 50% silica nanoparticles with respect to HIPS by weight. This coating displayed the lowest friction coefficient compared to other nanocomposites with lower or higher silica concentrations. Tribological experiments on the best performing nanocomposites indicated that wear tracks or marks had no debris, cracks or complete material removal. Furthermore, Taber® abrasion tests confirmed tribological findings and showed that the best nanocomposites resisted superhydrophobic degradation up to 35 continuous linear abrasion cycles (15 kPa). Nanocomposites made with general purpose polystyrene instead of HIPS could only resist up to 15 Taber® abrasion cycles. The reason was attributed to the mechanical energy dissipation capability of rubber domains in HIPS. Thermal annealing of the coatings had a deterministic effect on the durability of the coatings against wear induced loss of superhydrophobicity. Annealed and non-annealed coatings were characterized by Fourier transform infrared and X-ray photoelectron spectroscopy. Due to ease of fabrication, resultant mechanical robustness, use of non-toxic materials, and low-cost industrial scale availability of HIPS, nanoparticles and the primer polymer, these coatings can be effortlessly transformed into larger scale non-wettable protective treatments for metals.

The localized in situ formation of tin dioxide (SnO2 ) nanoparticles embedded in poly(methyl methacrylate) (PMMA) films is presented. This is achieved by the photoinduced conversion of the tin acetate precursor included in polymeric films, through controlled UV or visible pulsed laser irradiation at λ=355 and 532 nm, respectively. The evolution of the formation of nanoparticles is followed by UV/Vis spectroscopy and shows that their growth is affected in different ways by the laser pulses at the two applied wavelengths. This, in combination with electron microscopy analysis, reveals that, depending on the irradiation wavelength, the size of the nanoparticles in the final nanocomposites differs. This difference is attributed to distinct mechanistic pathways that lead to the synthesis of small nanoparticles (from 1.5 to 4.5 nm) at λ=355 nm, whereas bigger ones (from 5 to 16 nm) are formed at λ=532 nm. At the same time, structural studies with both X-ray and electron diffraction measurements demonstrate the crystallinity of SnO2 nanoparticles in both cases, whereas XPS analysis confirms the light-induced oxidation of tin acetate into SnO2 . Taken all together, it is demonstrated that the pulsed laser irradiation at λ=355 and 532 nm leads to the formation of SnO2 nanoparticles with defined features highly dispersed in PMMA solid matrices.

CsPbBr3 nanocrystals passivated with short molecular ligands and deposited on a substrate were annealed from room temperature to 400 °C in inert atmosphere. Chemical, structural, and morphological transformations were monitored in situ and ex situ by different techniques, while optoelectronic properties of the film were also assessed. Annealing at 100 °C resulted in a 1 order of magnitude increase in photocurrent and photoresponse as a result of partial sintering of the NCs and residual solvent evaporation. Beyond 150 °C the original orthorhombic NCs were partially transformed into tetragonal CsPb2Br5 crystals, due to the desorption of weakly bound propionic acid ligands. The photocurrent increased moderately until 300 °C although the photoresponse became slower as a result of the formation of surface trap states. Eventually, annealing beyond 350 °C removed the strongly bound butylamine ligands and reversed the transition to the original orthorhombic phase, with a loss of photocurrent due to the numerous defects induced by the stripping of the passivating butylamine.

Herein we demonstrate the dry synthesis of CsBi3I10 both as a free-standing material and in the form of homogeneous thin films, deposited by thermal vacuum deposition. Chemical and optical characterization shows high thermal stability, phase purity, and photoluminescence centered at 700 nm, corresponding to a bandgap of 1.77 eV. These characteristics make CsBi3I10 a promising low-toxicity material for wide bandgap photovoltaics. Nevertheless, the performance of this material as a semiconductor in solar cells remains rather limited, which can be at least partially ascribed to a low charge carrier mobility, as determined from pulsed-radiolysis time-resolved microwave conductivity. Further developments should focus on understanding and overcoming the current limitations in charge mobility, possibly by compositional tuning through doping and/or alloying, as well as optimizing the thin film morphology which may be another limiting factor. Perovskite Thin-film Photovoltaics (PERTPV) REFERENCIA: 763977 Hetero-structures for Efficient Luminescent Devices (HELD) REFERENCIA: 834431

Fully inorganic cesium lead halide perovskites, such as CsPbI2Br, show enhanced thermal stability compared to hybrid ones and are being widely investigated as wide bandgap absorbers for tandem applications. Despite their simple stoichiometry, the preparation of highly crystalline and stable cesium lead halide thin films is not trivial. In general, high-efficiency solar cells based on solution-processed CsPbI2Br thin films are prepared by hightemperature annealing or the use of chemical additives. In this work, we use solvent-free synthesis to investigate the formation of CsPbI2Br in bulk or in thin films via mechanochemical synthesis and multiple-source vacuum deposition, respectively. We demonstrate the importance of fostering halide alloying in the vacuum processing of inorganic lead halide perovskites, which can be attained either by using mixed halide precursors or by increasing the number of precursors (and hence deposition sources). These strategies lead to highly oriented perovskite films even at room temperature, with improved optoelectronic properties. We obtained promising power conversion efficiencies of 8.3% for solar cells employing asdeposited perovskites (without any annealing) and 10.0% for devices based on CsPbI2Br annealed at low temperatures (150 °C). This study allowed us to highlight the most promising processes and strategies to further optimize the material deposition as well as the solar cell architecture. Hetero-structures for Efficient Luminescent Devices (HELD) REFERENCIA: 834431 PCIN-2019-111829-2

The dual-source vacuum deposition of 2D perovskite films of the type PEA2PbX4, (PEA = phenethylammonium and X = I−, Br−, or a combination of both) is presented. Low-temperature deposited 2D perovskite films showed high crystallinity with the expected trend of bandgap as a function of halide type and concentration. Importantly, we observed an unavoidable halide cross-contamination among different deposition runs, as well as a strong dependence of the material quality on the type of halide precursors used. These findings should be taken into account in the development of vacuum processing for low-dimensional mixed halide perovskites.

Phonons are quantized lattice vibrations that represent a major energy dissipation channel in solid-state systems [1], both at the macro- and at the nano-scale. Although the phonon response of a specific nanomaterial is usually considered as its intrinsic fingerprint, here we show how it can be altered by exploiting the unique properties of terahertz (THz) plasmonic nanocavities [2]. Specifically, we obtained such nanocavities from the end-to-end coupling (30-nm gap size) of few-μm-long plasmonic gold nanoantennas. We fabricated a series of plasmonic arrays featuring different nanoantenna lengths, spanning from 4.75 μm to 6.75 μm, thus tuning their resonances between approximately 7 and 9 THz. We tested our approach on cadmium sulphide (CdS) nanocrystals (NCs), spin-coated over the array surfaces (Fig. 1a), since these NCs feature a dipole-active (Frohlich) phonon mode at 7.85 THz. We performed THz transmission measurements using a Fourier-transform THz microscope coupled to synchrotron light (ELETTRA, Trieste), showing the splitting of the nanoantenna resonance into two new vibro-polariton bands, as shown in Fig. 1b. This anti-crossing behaviour represents a distinctive signature of the strong coupling between the plasmon and phonon modes, the splitting (Rabi) at the crossing point being directly related to the coupling strength. More intriguingly, we also observed the phonon resonance modification without any THz illumination, just exploiting the vacuum electric field of the nanocavities [3] (estimated to be as high as 4.6× 105 V/m). To this end, we performed a series of micro-Raman measurements on individual nanocavity areas, finding evidence of the two new hybrid states (P− and P+ in Fig. 1c) even in THz "dark" conditions. The evidence of phonon mode splitting both in THz and Raman characterizations confirms the possibility of altering the intrinsic phonon response of a nanomaterial using properly tailored plasmonic resonators, which could open new avenues for the manipulation of energy dissipation in nanodevices. Novel cavity geometries that promise to further boost the strong vibrational coupling in these systems will be presented on site.

We report the frictional response of few-layer graphene (FLG) flakes obtained by liquid phase exfoliation (LPE) of pristine graphite. To this end, we inkjet print FLG on bare and hexamethyldisilazane-terminated SiO2 substrates, producing micrometric patterns with nanoscopic roughness that are investigated by atomic force microscopy. Normal force spectroscopy and atomically resolved morphologies indicate reduced surface contamination by solvents after a vacuum annealing procedure. Notably, the printed FLG flakes show ultralow friction comparable with micromechanically exfoliated graphene flakes. Lubricity is retained on flakes with lateral size of a few tens of nanometres, and with thickness as small as ~ 2 nm, confirming the high crystalline quality and low defects density in the FLG basal plane. Surface exposed step edges exhibit the highest friction values, representing preferential sites for originating secondary dissipative processes related to edge straining, wear or lateral displacement of the flakes. Our work demonstrates that LPE enables fundamental studies on graphene friction to the single-flake level. The capability to deliver ultralow-friction-graphene over technologically relevant substrates, using a scalable production route and a high-throughput, large-area printing technique, may also open up new opportunities in the lubrication of micro- and nano-electromechanical systems., Comment: 31 pages, 18 figures

Germanium (Ge) nanocrystals combined with multiwalled carbon nanotube (Ge–MWCNT) composites were synthesized via a solvothermal approach and characterized through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning and transmission electron microscopy (SEM and TEM). The electrochemical behaviour during lithium insertion and de-insertion was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge measurements. The as prepared Ge–MWCNT nanocomposite exhibits improved cycling performance with higher capacity retention than pristine Ge. The Ge–MWCNTs exhibit a discharge capacity of ∼1160 mA h g−1 after 60 cycles at a current rate of 0.1C. Furthermore, they showed an excellent rate performance at a current rate of 5C (where 1C is 1600 mA g−1) by delivering a specific capacity of ∼406 mA h g−1 over 400 charge–discharge cycles.

Among the different synthesis approaches to colloidal nanocrystals, a recently developed toolkit is represented by cation exchange reactions, where the use of template nanocrystals gives access to materials that would be hardly attainable via direct synthesis. Besides, postsynthetic treatments, such as thermally activated solid-state reactions, represent a further flourishing route to promote finely controlled cation exchange. Here, we report that, upon in situ heating in a transmission electron microscope, Cu2Se or Cu nanocrystals deposited on an amorphous solid substrate undergo partial loss of Cu atoms, which are then engaged in local cation exchange reactions with Cu “acceptor” phases represented by rod- and wire-shaped CdSe nanocrystals. This thermal treatment slowly transforms the initial CdSe nanocrystals into Cu2–xSe nanocrystals, through the complete sublimation of Cd and the partial sublimation of Se atoms. Both Cu “donor” and “acceptor” particles were not always in direct contact with each othe...

Herein the mechanochemical synthesis of inorganic as well as hybrid organic-inorganic monohalide perovskites with tunable bandgaps is reported. It is shown that the bandgap bowing known for iodide mixed Sn-Pb perovskites is also present in the pure bromide analogous. This results in technologically very interesting materials with bandgaps in the range of 1.7-1.9 eV. Similar bandgap perovskites are typically achieved by mixing two halides that are prone to segregate over time. This limits the achievable open circuit voltage. For monohalide perovskites this problem is eliminated, making these materials especially promising wide bandgap absorbers for tandem solar cells. Perovskite Thin-film Photovoltaics (PERTPV) Hetero-structures for Efficient Luminescent Devices (HELD)

Non-toxic alternatives to lead halide perovskites are highly sought after for applications in optoelectronics. Blue-luminescent materials are especially demanded as they could be used to prepare white light-emitting diodes, with important potential applications in lighting systems. However, wide bandgap blue emitters with high photoluminescence quantum yields (PLQY) are typically more difficult to obtain as compared to green- or red-emitting ones. Here, we prepared two series of inorganic cesium copper halides, with the general formulas Cs3Cu2X5 and CsCu2X3 (X = Cl, Br, I, and mixtures thereof) by dry mechanochemical synthesis at room temperature. X-ray diffraction demonstrates quantitative conversion of binary precursors into the desired ternary structures and good halide mixing in single-phase compounds. We identified Cs3Cu2I5 as the most promising material as it maintains blue luminescence centered at 442 nm with high PLQY (>40%) after several days in air (Cs3Cu2Cl5 shows significantly higher PLQY over 80% but is unstable in air). Based on this, we fabricated homogeneous and pinhole-free Cs3Cu2I5 thin films by thermal single-source vacuum deposition. Crystalline phase and photoluminescence are maintained in the thin films, validating that these low-toxicity materials can be synthesized and processed by fully solvent-free routes for a widespread implementation in optoelectronic devices.

Low-dimensional (quasi-) 2D perovskites are being extensively studied in order to enhance the stability and the open-circuit voltage of perovskite solar cells. Up to now, thin 2D perovskite layers on the surface and/or at the grain boundaries of 3D perovskites have been deposited solely by solution processing, leading to unavoidable intermixing between the two phases. In this work, we report the fabrication of 2D/3D/2D perovskite heterostructures by dual-source vacuum deposition, with the aim of studying the interaction between the 3D and 2D phases as well as the charge transport properties of 2D perovskites in neat 2D/3D interfaces. Unlike what is normally observed in solution-processed 3D/2D systems, we found a reduced charge transport with no direct evidence of surface passivation, in spite of larger open-circuit voltage. This is likely due to a nonfavorable orientation of the 2D perovskite with respect to methylammonium lead iodide and to the formation of 2D phases with very low dimensionality (pure 2D).

It is widely accepted that a long photoluminescence (PL) lifetime in metal halide perovskite films is a crucial and favorable factor, as it ensures a large charge diffusion length leading to a high power conversion efficiency (PCE) in solar cells. It has been recently found that vacuumevaporated CH3NH3PbI3 (eMAPI) films show very short PL lifetimes of several nanoseconds. The corresponding solar cells, however, have high photovoltage (>1.1 V) and PCEs (up to 20%). We rationalize this apparent contradiction and show that eMAPI films are characterized by a very high diffusion coefficient D, estimated from modeling the PL kinetics to exceed 1 cm2/s. Such high D values are favorable for long diffusion length as well as fast transport of carriers to film surfaces, where they recombine nonradiatively with surface recombination velocity S ∼ 104 cm/s. Possible physical origins leading to the high D values are also discussed It is widely accepted that a long photoluminescence (PL) lifetime in metal halide perovskite films is a crucial and favorable factor, as it ensures a large charge diffusion length leading to a high power conversion efficiency (PCE) in solar cells. It has been recently found that vacuumevaporated CH3NH3PbI3 (eMAPI) films show very short PL lifetimes of several nanoseconds. The corresponding solar cells, however, have high photovoltage (>1.1 V) and PCEs (up to 20%). We rationalize this apparent contradiction and show that eMAPI films are characterized by a very high diffusion coefficient D, estimated from modeling the PL kinetics to exceed 1 cm2/s. Such high D values are favorable for long diffusion length as well as fast transport of carriers to film surfaces, where they recombine nonradiatively with surface recombination velocity S ∼ 104 cm/s. Possible physical origins leading to the high D values are also discussed

Methylammonium lead triiodide (MAPI) has emerged as a high-performance photovoltaic material. Common understanding is that at room temperature it adopts a tetragonal phase and it only converts to the perfect cubic phase around 50-60 ºC. Most MAPI films are prepared using a solution-based coating process, yet they can also be obtained by vapor phase deposition methods. Vapor phase processed MAPI films have significantly different characteristics compared to their solvent processed analogous, such as a relatively small crystal grain sizes and short excited state lifetimes. Yet solar cells based on vapor phase processed MAPI films exhibit high power conversion efficiencies. Surprisingly, after detailed characterization we find that our vapor phase processed MAPI films adopt a cubic crystal structure at room temperature that is stable for weeks, even in ambient atmosphere. Furthermore, we demonstrate that by tuning the deposition rates of both precursors during co-deposition it is possible to vary the perovskite phase from cubic to tetragonal at room temperature. Our finding challenges the common belief that MAPI is only stable in tetragonal phase at room temperature. Additionally, these findings can be used to explain the somewhat unexpected high performance of solar cells based on vacuum processed MAPI films with sub 100 nm grain sizes and excited state lifetimes < 100 nanoseconds.

We developed a facile synthesis of nanocomposite powders of CsPbX3 nanocrystals (NCs) embedded in silica. The synthesis starts from colloidal Cs4PbX6 NCs that are mixed with tetraethyl orthosilicate in the presence of nitric acid, which triggers the sol-gel reaction yielding the formation of SiOx and the conversion of starting NCs into CsPbX3 ones. The overall reaction delivers CsPbX3 NCs encased in a silica matrix. The resulting CsPbX3/SiOx nano-composite powders exhibited enhanced moisture and thermal stability in air. Also, when mixing different CsPbX3/SiOx samples having diverse anion compositions, no interparticle anion exchange processes were observed, which is a further indication that the silica matrix acts as a robust barrier surrounding the NCs. Finallly, we used these composites as down-converter phosphors on top of a blue light-emitting diode (LED), delivering nearly ideal white light emission with the Commission Internationale de l'Eclairage (CIE) color coordinates (0.32, 0.33).

We have synthesized fifteen inorganic and hybrid organic-inorganic non-toxic A3Bi2X9 compounds (A = K+, Rb+, Cs+, CH3NH3+ and HC(NH2)2+; X = I−, Br−, Cl−) through dry mechanochemistry. We demonstrate that this synthetic method is very well suited to prepare compounds from poorly soluble precursors, allowing thus the preparation of so far unreported compounds. X-ray diffraction analysis demonstrates the high crystallinity of the so-formed ternary bismuth halides. Furthermore, we show that, through substitution of the A-cation and X-anion, the bandgap of these compounds can be tuned to absorb throughout the whole visible spectrum. As-prepared powders of Cs3Bi2Br9 and Cs3Bi2I9 without any passivating agents show room-temperature photoluminescence covering the visible spectrum from 450 nm to 800 nm, making them especially promising for white-light emission.

Phase‐pure CsSnI3, FASnI3, Cs(PbSn)I3, FA(PbSn)I3 perovskites (FA = formamidinium = HC(NH2)2+) as well as the analogous so‐called vacancy‐ordered double perovskites Cs2SnI6 and FA2SnI6 are mechanochemically synthesized. The addition of SnF2 is found to be crucial for the synthesis of Cs‐containing perovskites but unnecessary for hybrid ones. All compounds show an absorption onset in the near‐infrared (NIR) region, which makes them especially relevant for photovoltaic applications. The addition of Pb(II) and SnF2 is crucial to improve the electronic properties in 3D Sn(II)‐based perovskites, in particular their charge carriers mobility (≈0.2 cm2 Vs−1) which is enhanced upon reduction of the dark carrier conductivity. Stokes‐shifted photoluminescence is observed on dry powders of Sn(II)‐based perovskites, which makes these materials promising for light‐emitting and sensing applications. Thermal stability of all compounds is examined, revealing no significant degradation up to at least 200 °C. This meets the requirements for standard operation conditions of most optoelectronic devices and is potentially compatible with thermal vacuum deposition of polycrystalline thin films.

Neurodegenerative diseases comprise a large group of disorders characterized by a dramatic synaptic connections loss, occurring as a result of neurodegeneration, which is closely related to the overproduction of reactive oxygen and nitrogen species. Currently, the treatment of neurodegenerative diseases has been limited mainly because of the inability of the synthesized delivery systems to cross the blood-brain barrier and to successfully deliver their therapeutic cargo to the diseased tissue. Taking into consideration the aforementioned limitations, we designed a lipid-based nanotherapeutic vector composed of biomimetic lipids and CeO2nanoparticles (nanoceria, NC). NC have shown to be a promising tool for the treatment of several pathological conditions ranging from cancer to neurological diseases, mainly because of their antioxidant properties, while lipid-based structures have been shown to have an inherent ability to cross the blood-brain barrier. The lipid-based nanotherapeutics were successfully fabricated using a combination of ultrasonication and high-pressure homogenization techniques, and they were fully characterized morphologically and physicochemically. Their antioxidant ability was demonstrated using electron paramagnetic resonance spectroscopy and antioxidant assays. These innovative nanotherapeutics demonstrated a higher colloidal stability with respect to free NC, preserving at the same time their antioxidant properties. Finally, the ability of the lipid carriers to cross a model of the blood-brain barrier and to be internalized by neurons, acting both as neuroprotective and pro-neurogenic agents, was demonstrated using single- and triple-culture systems.

Annealing a film of CsPbBr3 nanocrystals (NCs) leads to the removal of surface ligands and ripening of the NCs below 200 °C. This results in a reduced photoluminescence quantum yield due to the formation of trap states while on the other hand the conductive properties of the films are stabilized, with a significantly stronger photocurrent after annealing.

Films of colloidal CsPbX3 (X = I, Br or Cl) nanocrystals, prepared by solution drop-casting or spin-coating on a silicon substrate, were exposed to a low flux of X-rays from an X-ray photoelectron spectrometer source, causing intermolecular C═C bonding of the organic ligands that coat the surface of the nanocrystals. This transformation of the ligand shell resulted in a greater stability of the film, which translated into the following features: (i) Insolubility of the exposed regions in organic solvents which caused instead complete dissolution of the unexposed regions. This enabled the fabrication of stable and strongly fluorescent patterns over millimeter scale areas. (ii) Inhibition of the irradiated regions toward halide anion exchange reactions, when the films were exposed either to halide anions in solution or to hydrohalic vapors. This feature was exploited to create patterned regions of different CsPbIxBryClz compositions, starting from a film with homogeneous CsPbX3 composition. (iii) Resistance of the films to degradation caused by exposure to air and moisture, which represents one of the major drawbacks for the integration of these materials in devices. (iv) Stability of the film in water and biological buffer, which can open interesting perspectives for applications of halide perovskite nanocrystals in aqueous environments.

Oligo ethylene glycol layers are widely used in biosensor applications, mainly for their anti-fouling abilities. Such surfaces are often characterized by X-ray photoelectron spectroscopy (XPS) as this method allows a precise determination of the surface chemical composition. We show herein that X-rays used during XPS characterization quickly and significantly degrade oligo ethylene glycol immobilized onto silica substrates. It is therefore necessary to introduce a correcting factor to assess the true (i.e. without degradation) corresponding ether contribution in the XPS spectrum of such organic layers. Eventually, fluorescence scans show the loss of anti-fouling properties of the degraded surface, leading to greater amounts of adsorbed (fluorescently labeled) protein. Copyright © 2015 John Wiley & Sons, Ltd.

We report the synthesis of various binary and ternary inorganic and hybrid organic–inorganic iodide nanocrystals (NCs) starting from molecular iodine (I2). The synthesis described herein utilizes a reaction between I2 and oleylamine, which results in oleylammonium iodide, an iodide precursor that can be directly used in the preparation of iodide-based NCs. The generality of the synthesis was demonstrated by synthesizing KI, RbI, CsI, AgI, CsPbI3, FAPbI3, Cs4PbI6, Cs3Bi2I9, FA3Bi2I9, and RbAg4I5 NCs. Furthermore, the syntheses are facile and are carried out in vials heated on a hot plate in air. They exhibit not only narrow size distributions, but also, in the case of lead-based perovskites NCs, 70–80% photoluminescence quantum yields. To further prove the high quality of the CsPbI3 and FAPbI3 perovskite NCs, red and infrared bright light-emitting diodes were fabricated, with external quantum efficiencies (EQEs) exceeding 3%, without following any extensive washing procedures.

Fully inorganic cesium lead halide perovskite thin films were prepared by an easy, fast and dry process based on single-source vacuum deposition. We investigated the structural and optical characteristics of the so-formed films as a function of chemical composition (chloride, bromide and iodide films were formed), post-deposition thermal annealing, as well as previous mechanosynthesis of perovskite powders. We found out that the CsPbX3 perovskite was preferentially formed for the smaller halides and favored by previous ball-milling of CsX and PbX2 precursors. When bigger halides were used and/or CsX and PbX2 precursors were simply mixed without previous mechanosynthesis, PbX2-rich compounds such as CsPb2X5 were preferentially formed in the thin films.

Phonons (quanta of collective vibrations) are a major source of energy dissipation and drive some of the most relevant properties of materials. In nanotechnology, phonons severely affect light emission and charge transport of nanodevices. While the phonon response is conventionally considered an inherent property of a nanomaterial, here we show that the dipole-active phonon resonance of semiconducting (CdS) nanocrystals can be drastically reshaped inside a terahertz plasmonic nanocavity, via the phonon strong coupling with the cavity vacuum electric field. Such quantum zero-point field can indeed reach extreme values in a plasmonic nanocavity, thanks to a mode volume well below λ3/107. Through Raman measurements, we find that the nanocrystals within a nanocavity exhibit two new “hybridized” phonon peaks, whose spectral separation increases with the number of nanocrystals. Our findings open exciting perspectives for engineering the optical phonon response of functional nanomaterials and for implementing a novel platform for nanoscale quantum optomechanics., Here the authors show that the dipole-active phonon resonance of semiconducting nanocrystals can be hybridized by a strongly concentrated terahertz vacuum field of a plasmonic nanocavity, thus achieving strong plasmon–phonon coupling even in the absence of direct terahertz illumination.

Lead halide perovskite semiconductors have recently gained wide interest following their successful embodiment in solid-state photovoltaic devices with impressive power-conversion efficiencies, while offering a relatively simple and low-cost processability. Although the primary optoelectronic properties of these materials have already met the requirement for high-efficiency optoelectronic technologies, industrial scale-up requires more robust processing methods, as well as solvents that are less toxic than the ones that have been commonly used so successfully on the lab-scale. Here we report a fast, room-temperature synthesis of inks based on CsPbBr3 perovskite nanocrystals using short, low-boiling-point ligands and environmentally friendly solvents. Requiring no lengthy post-synthesis treatments, the inks are directly used to fabricate films of high optoelectronic quality, exhibiting photoluminescence quantum yields higher than 30% and an amplified spontaneous emission threshold as low as 1.5 μJ cm−2. Finally, we demonstrate the fabrication of perovskite nanocrystal-based solar cells, with open-circuit voltages as high as 1.5 V. Despite their impressive performance, more efforts are required to develop industrially scalable perovskite solar cells from less toxic solvents. Towards that aim, this study presents the use of colloidal nanoparticle inks for room-temperature fabrication of CsPbBr3 solar cells.

An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb2+ ions to Pb0. Subsequently Pb0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The early stage Pb nanoparticles are epitaxially bound to the parent CsPbBr3 lattice, and evolve into nonepitaxially bound Pb crystals upon further irradiation, leading to local amorphization and consequent dismantling of the CsPbBr3 lattice. The comparison among CsPbBr3 nanocrystals with various shapes and sizes evidences that the damage is particularly pronounced at the corners and edges of the surface, due to a lower diffusion barrier for Pb0 on the surface than inside the crystal and the presence of a larger fraction of under-coordinated atoms.

We present the localized in situ formation of Pd and Pt nanoparticles embedded in chitosan solid films. This is achieved by the photo-induced reduction of metallic precursors, previously incorporated in chitosan films, through controlled UV pulsed laser irradiation. Interestingly, at high number of laser pulses, Pd and Pt follow different formation pathways, contrary to their common photoreduction mechanism occurring at low irradiation pulses. Specifically, in the case of the Pd, a photofragmentation process takes place fracturing the previously formed nanoparticles into smaller ones; whereas in the case of Pt, the prolonged irradiation promotes the nanoparticles agglomeration. The combination of both precursors in a binary solid system results in the combined formation of both Pd and Pt nanoparticles in the polymer film upon laser irradiation. The herein reported approach is an efficient and precise tool to generate size- and density-controlled Pd and Pt nanoparticles in desired areas of polymeric films, rendering this method a potential candidate for the fabrication of flexible polymeric devices for gas-sensing or electro-catalysis applications. Graphical Abstract: Schematic representation of Pd, Pt and Pd–Pt combined NPs formation mechanisms under pulsed laser irradiation [Figure not available: see fulltext.]

Surface chemical functionalization is a powerful tool to bridge the gap between top-down and bottom-up nanofabrication methods. By tuning their surface chemistry, we can enable whole sets of different nano-objects to be selectively deposited onto well-defined submicronic anchoring sites on macroscopic substrates. This potentially enables the development of unprecedented systems in different fields such as electronics, photonics or biosensors.

Latex nanoparticles (100 nm and 200 nm diameter) were precisely located onto the gold regions of micro and nanopatterned gold/silica substrates through surface chemical functionalizations. The gold patterns were selectively functionalized with alkylthiols bearing biotin or amine headgroups. This selective functionalization allowed the trapping of streptavidin- or carboxy-functionalized latex nanoparticles onto the gold structures with very little non-specific adsorption onto the surrounding silica. Quantitative data of nanoparticle capture on gold and silica, obtained through SEM image analysis, showed a one to two order of magnitude increase on gold with a similar low coverage on silica (non-specific adsorption) thanks to chemical functionalizations. Single nanoparticles were captured at the gap of dimer gold nanostructures.

In the past couple of decades, colloidal inorganic nanocrystals and, more specifically, semiconductor quantum dots have emerged as crucial materials for the development of nanoscience and nanotechnology, with applications in very diverse areas such as optoelectronics and biotechnology. Films made of inorganic NCs deposited on a substrate can be patterned by e-beam lithography, altering the structure of their capping ligands and thus allowing exposed areas to remain on the substrate while non-exposed areas are redispersed in a solvent, as in a standard lift-off process. This methodology can be described as a direct lithography process, since the exposure is performed directly on the material of interest, in contrast with conventional lithography which uses a polymeric resist as a mask for subsequent material deposition or etching. A few reports from the late 1990 and early 2000 used such direct lithography to fabricate electrical wires from metallic NCs. However, the poor conductivity obtained through this process hindered the widespread use of the technique. In the early 2010, the same method was used to define fluorescent patterns on QD films, allowing for further applications in biosensing. For the past 2 ,3 years, direct lithography on NC films with e-beams and X rays has gone through an important development as it has been demonstrated that it can tune further transformations on the NCs, leading to more complex patternings and opening a whole new set of possible applications., Comment: 21 pages, 8 figures

Cs2AgBiBr6 has been proposed as a promising lead-free and stable double perovskite alternative to hybrid and lead-based perovskites. However, the low solubility of precursors during wet synthesis, or the distinct volatility of components during evaporation, results in complex multistep synthesis approaches, hampering the widespread employment of Cs2AgBiBr6 films. Here, we present pulsed laser deposition of Cs2AgBiBr6 films as a dry, single-step and single-source deposition approach for high-quality film formation. Cs2AgBiBr6 powders were prepared by mechanochemical synthesis and pressed into a solid target maintaining phase purity. Controlled laser ablation of the double perovskite target in vacuum and a substrate temperature of 200 °C results in the formation of highly crystalline Cs2AgBiBr6 films. We discuss the importance of deposition pressure to achieve stoichiometric transfer and of substrate temperature during PLD growth to obtain high-quality Cs2AgBiBr6 films with grain sizes > 200 nm. This work demonstrates the potential of PLD, an established technique in the semiconductor industry, to deposit complex halide perovskite materials while being compatible with optoelectronic device fabrication, such as UV and X-ray detectors.

Potassium halides (KX; X = I, Br, or Cl) were incorporated as partial replacements of CsBr in the mechanosynthesis of CsPbBr3. This led to partial substitution of both monovalent ions forming mixed Cs1−xKxPbBr3−yXy perovskites. Longer photoluminescence lifetimes were also observed, possibly linked to the formation of a non-perovskite KPb2X5 passivating layer.

Methylammonium lead iodide (MAPI) has excellent properties for photovoltaic applications, although it typically shows low photoluminescence quantum yield. Here, we report on vacuum-deposited MAPI perovskites obtained by modifying the methylammonium iodide (MAI) to PbI2 ratio during vacuum deposition. By studying the excitation density dependence of the photoluminescence lifetime, a large concentration of trap states was deduced for the stoichiometric MAPI films. The use of excess MAI during vacuum processing is capable of passivating these traps, resulting in luminescent films which can be used to fabricate planar light-emitting diodes with quantum efficiency approaching 2%.