Mimicking Natural Antioxidant Systems for Improved Photostability in Wide-Band-Gap Perovskite Solar Cells.

Fostered by the top power conversion efficiencies (PCEs) of lab-scale devices, industrialization of perovskite solar cells is underway. Nevertheless, the intrinsically poor stability of these materials still represents a major concern. Herein, inspired by Nature, the use of ß-carotene in perovskite solar cells is proposed to mimic its role as a protective pigment, as occurs in natural photosynthesis. Laser-mediated photostability (LMPS) assessment, Fourier-transform infrared spectra analysis acquired in attenuate total reflectance (ATR-FTIR), spectroscopy ellipsometry (SE), and time-resolved photoluminescence (TRPL) measurements under stress conditions prove that the inclusion of a thin ß-carotene interlayer promotes a high improvement in the photostability of the perovskite films against photooxidation. Importantly, this is accompanied by an improvement of the solar cell PCE that approaches 20% efficiency with no hysteresis, which is among the highest values reported for a mixed halide (I-Br) perovskite with a band gap of 1.74 eV, relevant for coupling with silicon in tandem cells.

X-ray Investigation of CsPbI3:EuCl3 Infiltrated into Gig-Lox TiO2 Spongy Layers for Perovskite Solar Cells Applications.

In this study, we explore the potential of a blended material comprising CsPbI3:EuCl3 perovskite and Gig-Lox TiO2, a unique transparent spongy material known for its multi-branched porous structure, for application in solar cells. The inclusion of EuCl3 in CsPbI3 serves to stabilize the photoactive γ-phase with a bandgap of 1.75 eV, making it suitable for solar energy conversion in tandem solar cells. Our study applies X-ray-based techniques to investigate the structural properties and interfacial behavior within this blended material, in comparison with a reference perovskite layer deposited on glass. In addition, Spectroscopic ellipsometry is complemented with density functional theory calculations and photoluminescence measurements to elucidate the absorption and radiative emission properties of the blend. Notably, our findings reveal a significant quenching of photoluminescence within the blended material, underscoring the pivotal role of the distributed interfaces in facilitating efficient carrier injection from the CsPbI3:EuCl3 perovskite into the Gig-Lox TiO2 sponge. These findings pave the way for the application of the blend as an Electron Transport Layer (ETL) in semi-transparent perovskite solar cells for tandem and building integrated photovoltaics.

Self-assembled BiFeO3@MIL-101 nanocomposite for antimicrobial applications under natural sunlight.

In this paper, we report on the synthesis of a new hybrid photocatalytic material activated by natural sunlight irradiation. The material consists of multiferroic nanoparticles of bismuth ferrite (BFO) modified through the growth of the Fe-based MIL-101 framework. Material characterization, conducted using various techniques (X-ray diffraction, transmission electron microscopy, FTIR, and X-ray photoelectron spectroscopies), confirmed the growth of the MIL-101 metal-organic framework on the BFO surface. The obtained system possesses the intrinsic photo-degradative properties of BFO nanoparticles significantly enhanced by the presence of MIL-101. The photocatalytic activity of this material was tested in antibacterial experiments conducted under natural sunlight exposure within the nanocomposite concentration range of 100-0.20 µg/ml. The MIL-modified BFO showed a significant decrease in both Minimum Inhibiting Concentration and Minimum Bactericide Concentration values compared to bare nanoparticles. This confirms the photo-activating effect of the MIL-101 modification. In particular, they show an increased antimicrobial activity against the tested Gram-positive species and the ability to begin to inhibit the growth of the four Escherichia coli strains, although at the maximum concentration tested. These results suggest that the new nanocomposite BiFeO3@MOF has been successfully developed and has proven to be an effective antibacterial agent against a wide range of microorganisms and a potential candidate in disinfection processes.

Lead Detection in a Gig-Lox TiO2 Sponge by X-ray Reflectivity.

The importance of lead analysis in environmental matrices becomes increasingly relevant due to the anthropogenic spread of toxic species in nature. Alongside the existing analytical methods to detect lead in a liquid environment, we propose a new dry approach for lead detection and measurement based on its capture from a liquid solution by a solid sponge and subsequent quantification based on X-ray analyses. The detection method exploits the relationship between the electronic density of the solid sponge, which depends on the captured lead, and the critical angle for total reflection of the X-rays. For this purpose, gig-lox TiO2 layers, grown by modified sputtering physical deposition, were implemented for their branched multi-porosity spongy structure that is ideal for capturing lead atoms or other metallic ionic species in a liquid environment. The gig-lox TiO2 layers grown on glass substrates were soaked into aqueous solutions containing different concentrations of Pb, dried after soaking, and finally probed through X-ray reflectivity analyses. It has been found that lead atoms are chemisorbed onto the many available surfaces within the gig-lox TiO2 sponge by establishing stable oxygen bonding. The infiltration of lead into the structure causes an increase in the overall electronic density of the layer and, thus, an increment of its critical angle. Based on the established linear relationship between the amount of lead adsorbed and the augmented critical angle, a standardized quantitative procedure to detect Pb is proposed. The method can be, in principle, applied to other capturing spongy oxides and toxic species.

Perovskite solar cells from the viewpoint of innovation and sustainability.

Innovation is essential around the themes of climate change and sustainability. Commercial photovoltaics (PV) have noticeably contributed to getting to 22.1% share of the gross final energy consumption in Europe from renewable sources in 2020 but a steep further increase is urgent in the near future. Over the last few years, great success has been achieved by perovskites applied to PV, with mixed anions and cations in shared lattices that reached record efficiency values close to those of Si in laboratory-scale solar cells (∼26%). Their use has recently shed light on a medium/long-term compositional instability that arises from the partial miscibility of the species with similar role in the atomic lattice. The chemical route to prepare the materials for Perovskite Solar Cells (PSCs) also needs to be critically reviewed. Material waste and reuse are other concerns to be faced. This perspective paper indeed tackles some aspects for innovation and sustainability on the PSC field for production purposes. Some hints for technologically affordable processes based on in-vacuum deposition of Perovskites are provided in light of their sustainability and for the need to reduce production/maintenance costs. It is also discussed how to make in-vacuum production further competitive by boosting the material quality. Innovation is also projected into the theme of making sustainable choices for device architectures and materials. Carbon-based PSCs are highly focused since they allow avoiding the use of complex, unstable and costly HTLs. From the material side, pros and cons of using fully inorganic CsPbI3 are commented, framed by the current revival of single-cation perovskites. CsPbI3, in particolar, enables recycling and reuse initiatives thanks to the overall mass preservation under degradation. Some closing remarks are provided on the safe use of Pb as its effective sequestration before release from the PSC into the environment is properly engineered. We lastly trust that initiatives bringing together academic and industrial know-how in complementary fields able to take up responsible innovation will contribute to accelerating the ecological transition and will enable the societal transformation to fulfil the 2050 EU agenda for a sustainable future.

Synthesis of MIL-Modified Fe3O4 Magnetic Nanoparticles for Enhancing Uptake and Efficiency of Temozolomide in Glioblastoma Treatment.

A nanometric hybrid system consisting of a Fe3O4 magnetic nanoparticles modified through the growth of Fe-based Metal-organic frameworks of the MIL (Materials Institute Lavoiser) was developed. The obtained system retains both the nanometer dimensions and the magnetic properties of the Fe3O4 nanoparticles and possesses increased the loading capability due to the highly porous Fe-MIL. It was tested to load, carry and release temozolomide (TMZ) for the treatment of glioblastoma multiforme one of the most aggressive and deadly human cancers. The chemical characterization of the hybrid system was performed through various complementary techniques: X-ray-diffraction, thermogravimetric analysis, FT-IR and X-ray photoelectron spectroscopies. The nanomaterial showed low toxicity and an increased adsorption capacity compared to bare Fe3O4 magnetic nanoparticles (MNPs). It can load about 12 mg/g of TMZ and carry the drug into A172 cells without degradation. Our experimental data confirm that, after 48 h of treatment, the TMZ-loaded hybrid nanoparticles (15 and 20 µg/mL) suppressed human glioblastoma cell viability much more effectively than the free drug. Finally, we found that the internalization of the MIL-modified system is more evident than bare MNPs at all the used concentrations both in the cytoplasm and in the nucleus suggesting that it can be capable of overcoming the blood-brain barrier and targeting brain tumors. In conclusion, these results indicate that this combined nanoparticle represents a highly promising drug delivery system for TMZ targeting into cancer cells.

Exploring the Structural Competition between the Black and the Yellow Phase of CsPbI3.

The realization of stable inorganic perovskites is crucial to enable low-cost solution-processed photovoltaics. However, the main candidate material, CsPbI3, suffers from a spontaneous phase transition at room temperature towards a photo-inactive orthorhombic δ-phase (yellow phase). Here we used theoretical and experimental methods to study the structural and electronic features that determine the stability of the CsPbI3 perovskite. We argued that the two physical characteristics that favor the black perovskite phase at low temperatures are the strong spatial confinement in nanocrystalline structures and the level of electron doping in the material. Within this context, we discussed practical procedures for the realization of long-lasting inorganic lead halide perovskites.

Temperature-Dependent Optical Band Gap in CsPbBr3, MAPbBr3, and FAPbBr3 Single Crystals.

Single crystals represent a benchmark for understanding the bulk properties of halide perovskites. We have indeed studied the dielectric function of lead bromide perovskite single crystals (MAPbBr3, CsPbBr3 and for the first time FAPbBr3) by spectroscopic ellipsometry in the range of 1-5 eV while varying the temperature from 183 to 440 K. An extremely low absorption coefficient in the sub-band gap region was found, indicating the high optical quality of all three crystals. We extracted the band gap values through critical point analysis showing that Tauc-based values are systematically underestimated. The two structural phase transitions, i.e., orthorhombic-tetragonal and tetragonal-cubic, show distinct optical behaviors, with the former having a discontinuous character. The cross-correlation of optical data with DFT calculations evidences the role of octahedral tilting in tailoring the value of the band gap at a given temperature, whereas differences in the thermal expansion affect the slope of the band gap trend as a function of temperature.

Local Order and Rotational Dynamics in Mixed A-Cation Lead Iodide Perovskites.

Halide perovskites containing a mixture of formamidinium (FA+), methylammonium (MA+) and cesium (Cs+) cations are the actual standard for obtaining record-efficiency perovskite solar cells. Although the compositional tuning that brings to optimal performance of the devices has been largely established, little is understood on the role of even small quantities of MA+ or Cs+ in stabilizing the black phase of FAPbI3 while boosting its photovoltaic yield. In this paper, we use Car-Parrinello molecular dynamics in large supercells containing different ratios of FA+ and either MA+ or Cs+, in order to study the structural and kinetic features of mixed perovskites at room temperature. Our analysis shows that cation mixing relaxes the rotational disorder of FA+ molecules by preferentially aligning their axis toward ⟨100⟩ cubic directions. The phenomenon stems from the introduction of additional local minima in the energetic landscape, which are absent in pure FAPbI3 crystals. As a result, a higher structural order is achieved, characterized by a pronounced octahedral tilting and a lower vibrational activity for the inorganic framework. We show that both MA+ and Cs+ are qualified for this enhancement, with Cs+ being particularly effective when diluted within the FAPbI3 perovskite.

Chemical Vapor Deposition Growth of Silicon Nanowires with Diameter Smaller Than 5 nm.

Quantum confinement effects in silicon nanowires (SiNWs) are expected when their diameter is less than the size of the free exciton (with a Bohr radius ∼5 nm) in bulk silicon. However, their synthesis represents a considerable technological challenge. The vapor-liquid-solid (VLS) mechanism, mediated by metallic nanoclusters brought to the eutectic liquid state, is most widely used for its simplicity and control on the SiNWs size, shape, orientation, density, and surface smoothness. VLS growth is often performed within high-vacuum physical vapor deposition systems, where the eutectic composition and the pressure conditions define the minimum diameter of the final nanowire usually around 100 nm. In this article, we present and discuss the SiNWs' growth by the VLS method in a plasma-based chemical vapor deposition system, working in the mTorr pressure range. The purpose is to demonstrate that it is possible to obtain nanostructures with sizes well beyond the observed limit by modulating the deposition parameters, like chamber pressure and plasma power, to find the proper thermodynamic conditions for nucleation. The formation of SiNWs with sub-5 nm diameter is demonstrated.

New Synthetic Route for the Growth of α-FeOOH/NH2-Mil-101 Films on Copper Foil for High Surface Area Electrodes.

A novel metal organic framework (MOF)-based composite was synthesized on a Cu substrate via a two-step route. An amorphous iron oxide/hydroxide layer was first deposited on a Cu foil through a sol-gel process; then, Fe-NH2-Mil-101 was grown using both the iron oxide/hydroxide matrix, which provided the Fe3+ centers needed for MOF formation, and 2-aminoterephthalic acid ethanol solution. This innovative synthetic strategy is a convenient approach to grow metal oxide/hydroxide and MOF composite films. Structural, chemical, and morphological characterizations suggest that the obtained composite is made up of both the α-FeOOH goethite and the NH2-Mil-101 phases featuring a hybrid heterostructure. The electrochemical features of the composite structure were investigated using electrochemical impedance spectroscopy. The impedance behavior of the α-FeOOH/NH2-Mil-101 films indicates that they can be used as efficient high surface area metal hydroxide/MOF-based electrodes for applications such as energy storage and sensing.

Bimodal Porosity and Stability of a TiO2 Gig-Lox Sponge Infiltrated with Methyl-Ammonium Lead Iodide Perovskite.

We created a blend between a TiO2 sponge with bimodal porosity and a Methyl-Ammonium Lead Iodide (MAPbI3) perovskite. The interpenetration of the two materials is effective thanks to the peculiar sponge structure. During the early stages of the growth of the TiO2 sponge, the formation of 5-10 nm-large TiO2 auto-seeds is observed which set the micro-porosity (<5 nm) of the layer, maintained during further growth. In a second stage, the auto-seeds aggregate into hundreds-of-nm-large meso-structures by their mutual shadowing of the grazing Ti flux for local oxidation. This process generates meso-pores (10-100 nm) treading across the growing layer, as accessed by tomographic synchrotron radiation coherent X-ray imaging and environmental ellipsometric porosimetry. The distributions of pore size are extracted before (>47% V) and after MAPbI3 loading, and after blend ageing, unfolding a starting pore filling above 80% in volume. The degradation of the perovskite in the blend follows a standard path towards PbI2 accompanied by the concomitant release of volatile species, with an activation energy of 0.87 eV under humid air. The use of dry nitrogen as environmental condition has a positive impact in increasing this energy by ~0.1 eV that extends the half-life of the material to 7 months under continuous operation at 60 °C.

Study on the Physico-Chemical Properties of the Si Nanowires Surface.

Silicon nanowires (Si-NWs) have been extensively studied for their numerous applications in nano-electronics. The most common method for their synthesis is the vapor-liquid-solid growth, using gold as catalyst. After the growth, the metal remains on the Si-NW tip, representing an important issue, because Au creates deep traps in the Si band gap that deteriorate the device performance. The methods proposed so far to remove Au offer low efficiency, strongly oxidize the Si-NW sidewalls, or produce structural damage. A physical and chemical characterization of the as-grown Si-NWs is presented. A thin shell covering the Au tip and acting as a barrier is found. The chemical composition of this layer is investigated through high resolution transmission electron microscopy (TEM) coupled with chemical analysis; its formation mechanism is discussed in terms of atomic interdiffusion phenomena, driven by the heating/cooling processes taking place inside the eutectic-Si-NW system. Based on the knowledge acquired, a new efficient etching procedure is developed. The characterization after the chemical etching is also performed to monitor the removal process and the Si-NWs morphological characteristics, demonstrating the efficiency of the proposed method and the absence of modifications in the nanostructure.

Direct observation of single organic molecules grafted on the surface of a silicon nanowire.

Silicon nanowires inspire since decades a great interest for their fundamental scientific importance and their potential in new technologies. When decorated with organic molecules they form hybrid composites with applications in various fields, from sensors to life science. Specifically the diethyl 1-propylphosphonate/Si combination is considered as a promising alternative to the conventional semiconductor n-type doping methods, thanks to its solution-based processing, which is damage-free and intrinsically conformal. For these characteristics, it is a valid doping process for patterned materials and nanostructures such as the nanowires. Our joined experimental and theoretical study provides insights at atomistic level on the molecular activation, grafting and self-assembling mechanisms during the deposition process. For the first time to the best of our knowledge, by using scanning transmission electron microscopy the direct visualization of the single molecules arranged over the Si nanowire surface is reported. The results demonstrate that the molecules undergo to a sequential decomposition and self-assembling mechanism, finally forming a chemical bond with the silicon atoms. The ability to prepare well-defined molecule decorated Si nanowires opens up new opportunities for fundamental studies and nanodevice applications in diverse fields like physics, chemistry, engineering and life sciences.

Stability and Degradation in Hybrid Perovskites: Is the Glass Half-Empty or Half-Full?

Methylammonium lead iodide (CH3NH3PbI3) is an extensively used perovskite material with a remarkable potential for solar energy conversion. Despite its high photovoltaic efficiency, the material suffers from fast degradation when aging in atmospheric conditions and/or under sunlight. Here we review the principal degradation mechanisms of CH3NH3PbI3, focusing on the thermodynamic, environmental and polymorphic parameters that impact the stability of the material. A critical analysis of the available data indicates that degradation under ambient conditions is a defect-generation process that is highly localized on surfaces and interfaces, while it is further enhanced above the tetragonal-cubic transition at ∼54 °C. Within this context, we discuss the conservative role of N2 and propose strategies for the emergence of industrially viable hybrid photovoltaics.

Multi-Scale-Porosity TiO2 scaffolds grown by innovative sputtering methods for high throughput hybrid photovoltaics.

We propose an up-scalable, reliable, contamination-free, rod-like TiO2 material grown by a new method based on sputtering deposition concepts which offers a multi-scale porosity, namely: an intra-rods nano-porosity (1-5 nm) arising from the Thornton's conditions and an extra-rods meso-porosity (10-50 nm) originating from the spatial separation of the Titanium and Oxygen sources combined with a grazing Ti flux. The procedure is simple, since it does not require any template layer to trigger the nano-structuring, and versatile, since porosity and layer thickness can be easily tuned; it is empowered by the lack of contaminations/solvents and by the structural stability of the material (at least) up to 500 °C. Our material gains porosity, stability and infiltration capability superior if compared to conventionally sputtered TiO2 layers. Its competition level with chemically synthesized reference counterparts is doubly demonstrated: in Dye Sensitized Solar Cells, by the infiltration and chemisorption of N-719 dye (∼1 × 1020 molecules/cm3); and in Perovskite Solar Cells, by the capillary infiltration of solution processed CH3NH3PbI3 which allowed reaching efficiency of 11.7%. Based on the demonstrated attitude of the material to be functionalized, its surface activity could be differently tailored on other molecules or gas species or liquids to enlarge the range of application in different fields.

Influence of the X-ray beam quality on the dose increment in CT with iodinated contrast medium.

BACKGROUND: In computed tomography (CT), the image contrast is given by the difference in X-ray attenuation in the various tissues of the patient and contrast media are used to enhance image contrast in anatomic regions characterized by similar attenuation coefficients. OBJECTIVE: Aim of the present work is to enlarge the range of applicability of the method previously introduced for organ dosimetry in contrast-enhanced CT, by studying the effects of X-ray beam quality on the parameters of the model. Furthermore, an experimental method for the evaluation of the attenuation properties of iodinated solutions is proposed. METHODS: Monte Carlo simulations of anthropomorphic phantoms were carried out to determine a bi-parametrical (a and b) analytical relationship between iodine concentration and dose increase in organs of interest as a function of the tube kilo-voltage peak potential (kVp) and filtration. Experimental measurements of increments in Hounsfield Units (HU) were conducted in several CT scanners, at all the kVp available, in order to determine the parameter γ which relates the HU increment with the iodine mass fraction. A cylindrical phantom that can be filled with iodine solutions provided with an axial housing for a pencil ionization chamber was designed and assembled in order to measure the attenuation properties of iodine solutions under irradiation of a CT scanner and to obtain a further validation of Monte Carlo simulations. RESULTS: The simulation-derived parameters of the model, a and b, are only slightly dependent upon the tube kilo-voltage peak potential and filtration, while such scanner-dependent features influence mainly the experimentally-derived γ parameter. Relative dose variations registered by the ionization chamber inside the iodine-filled cylindrical phantom decrease when the X-ray mean energy increases, and reaches about 50% for 10 mg/ml of iodine. CONCLUSIONS: The dosimetric method for contrast-enhanced CT can be applied to all CT scanners by adopting average simulative parameters and by carrying out a simple measurement with a series of iodine contrast solutions. The novel experimental methodology introduced can provide a direct measurement of iodine attenuation properties.

Similar Structural Dynamics for the Degradation of CH3 NH3 PbI3 in Air and in Vacuum.

We investigate the degradation path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X-ray diffraction, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2 . We describe how this degradation product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3 NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.

Octahedral faceted Si nanoparticles as optical traps with enormous yield amplification.

We describe a method for the creation of an efficient optical scatter trap by using fully crystalline octahedral Silicon nanoparticles (Si-NPs) of approximately 100 nanometres in size. The light trapping, even when probing an isolated nanoparticle, is revealed by an enormous amplification of the Raman yield of up to 10(8) times that of a similar Si bulk volume. The mechanism conceived and optimised for obtaining such a result was related to the capability of a Si octahedron to trap the light because of its geometrical parameters. Furthermore, Si-NPs act as very efficient light scatterers not only for the direct light beam but also for the trapped light after it escapes the nanoparticle. These two effects are observed, either superimposed or separated, by means of the Raman yield and by photoluminescence enhancements. The inductively coupled plasma synthesis process performed at a temperature of only 50 °C allows for the ubiquitous use of these particles on several substrates for optical and photovoltaic applications.

Effect of pre- and post-treatment α-fetoprotein levels and tumor size on survival of patients with hepatocellular carcinoma treated by resection, transarterial chemoembolization or radiofrequency ablation: a retrospective study.

BACKGROUND: We evaluated treatment modalities and survival in patients with hepatocellular carcinoma (HCC), by pre-treatment and 3-month post-treatment serum alpha-fetoprotein (AFP) levels and pre-treatment tumor diameters. METHODS: We retrospectively reviewed 57 patients treated for HCC in our department from January 2002 to December 2012, including their sex, type of hepatitis, Child class, pre-treatment tumor size, pre-treatment levels of albumin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltransferase (GGT), red blood cells, hemoglobin, and total bilirubin, pre- and 3-month post-treatment serum AFP, and treatment modality (transarterial chemoembolization, resection or radiofrequency ablation). Survival was analyzed at 1, 3, and 5 years after treatment. RESULTS: The 57 patients included 44 men and 13 women, of whom 44 had hepatitis C virus (HCV) infection, 3 had hepatitis B virus (HBV) infection, 3 had both HBV and HCV infection, 1 had both HBV and hepatitis D virus infection, and 3 had alcohol-related liver cirrhosis. Both pre- and post-treatment serum AFP levels significantly correlated with recurrent tumor size (P < 0.05 for both). Pre-treatment tumor size did not correlate with recurrent tumor size. Patients who underwent hepatic resection survived significantly longer than those who underwent transarterial chemoembolization or radiofrequency ablation (P < 0.05). CONCLUSIONS: Serum AFP level is useful in diagnosing tumor recurrence and predicting prognosis in HCC patients treated by hepatic resection, transarterial chemoembolization, and radiofrequency ablation. Hepatic resection remains the treatment of choice for HCC in suitable patients.