CsPbBr3 Perovskite Nanoparticles causes Colitis-Like Symptom via Promoting Intestinal Barrier Damage and Gut Microbiota Dysbiosis.

Lead-based perovskite nanoparticles (Pb-PNPs) with superior optoelectronic properties are promising alternatives for the next generation of photovoltaics materials. This raises a great concern about their potential exposure toxicity in biological systems. However, little is known about their adverse effects on the gastrointestinal tract system so far. Here, the aim is to investigate the biodistribution, biotransformation, potential gastrointestinal tract toxicity, and effect on the gut microbiota after oral exposure to the CsPbBr3 perovskite nanoparticles (CPB PNPs). The advanced synchrotron radiation based microscopic X-ray fluorescence scanning and X-ray absorption near-edge spectroscopy demonstrate that high doses of CPB (CPB-H) PNPs can gradually transform into different lead-based compounds, subsequently accumulating in the gastrointestinal tract, especially the colon. Meanwhile, the pathological changes of stomach, small intestine, and colon reveal that CPB-H PNPs have higher gastrointestinal tract toxicity than Pb(Ac)2 , consequently leading to colitis-like symptoms. More importantly, 16S rRNA gene sequencing analysis discloses that CPB-H PNPs cause more significant alterations in the richness and diversity of the gut microbiota related to inflammation, intestinal barrier, and immune function than Pb(Ac)2 . The findings may contribute to shedding light on understanding the adverse effects on gastrointestinal tract and gut microbiota of Pb-PNPs.

Atomic-Resolution Imaging of Fast Nanoscale Dynamics with Bright Microsecond Electron Pulses.

Atomic-resolution electron microscopy is a crucial tool to elucidate the structure of matter. Recently, fast electron cameras have added the time domain to high-resolution imaging, allowing static images to be acquired as movies from which sample drift can later be removed computationally and enabling real-time observations of atomic-scale dynamics on the millisecond time scale. Even higher time resolution can be achieved with short electron pulses, yet their potential for atomic-resolution imaging remains unexplored. Here, we generate high-brightness microsecond electron pulses from a Schottky emitter whose current we briefly drive to near its limit. We demonstrate that drift-corrected imaging with such pulses can achieve atomic resolution in the presence of much larger amounts of drift than with a continuous electron beam. Moreover, such pulses enable atomic-resolution observations on the microsecond time scale, which we employ to elucidate the crystallization pathways of individual metal nanoparticles as well as the high-temperature transformation of perovskite nanocrystals.

Polymer Zwitterions for Stabilization of CsPbBr3 Perovskite Nanoparticles and Nanocomposite Films.

Functional polymers with sulfobetaine or phosphorylcholine zwitterions as pendent groups are demonstrated as both ligands and host matrices for CsPbBr3 perovskite nanoparticles (PNPs). These polymers produce nanocomposite films with excellent NP dispersion, optical transparency, and impressive resistance to NP degradation upon exposure to water. Multidentate interactions of the zwitterion-containing copolymers with the PNPs induce dispersed or weakly aggregated nanocomposite morphologies, depending on the extent of zwitterionic functionality in the polymer. Incorporating additional functionality into the polymers, such as benzophenone pendent groups, yields lithographically patternable films, while time-resolved photoluminescence measurements provide insight into the electronic impact of PNPs in zwitterionic polymer matrices.

Composition-Controlled Synthesis of Hybrid Perovskite Nanoparticles by Ionic Metathesis: Bandgap Engineering Studies from Experiments and Theoretical Calculations.

Herein a newly discovered non-polar solvent based synthesis of MAPbX3 hybrid perovskite nanoparticles (NPs) is presented, where MA=Methylammonium and X=I, Br and Cl, as well as their mixed halide counterparts. The methodology proposed is simple and uses low-cost commercial precursors. The conventional method of hybrid perovskite preparation requires methylammonium halide precursors and highly polar solvents. Mandatory use of polar solvents and a particular perovskite precursor makes an intermediate compound which then requires a non-polar solvent to recover the NPs. In contrast here, a whole range of mixed halide perovskite NPs is fabricated without using a methylammonium halide precursor and a polar solvent. In this method, a non-polar solvent is used, which provides a better platform for the particle recovery. Organic cations on the nanoparticle surface prevent degradation from water, due to their hydrophobic nature, and hence offer a stable colloidal suspension in toluene for more than three months. Ab-initio calculations within density functional theory (DFT) predict lower formation energies compared to previously reported values, confirming better chemical stability for this synthesis pathway. Through the halide compositional tuning, these NPs exhibit a variety of emission and absorption starting from ultraviolet to near infrared (IR). The absorption spectra of various halide perovskite show a sharp band edge over the visible wavelength with high absorption coefficient. High oscillator strengths due to high excitonic binding energies combined with the simulated finite dipole transition probabilities point towards the observed high absorption. The emission spectra of mixed halide perovskites vary from 400 to 750 nm, which covers the whole range of visible spectra with sharp full-width at half maxima. Different halide perovskite exhibit average recombination lifetime from 5 to 227 ns. Ambient synthesis, chemical robustness and tunability of emission with varying halide compositions make MAPbX3 (X=I, Br and Cl) NPs appealing for the optoelectronic applications.

Cesium Lead Halide Perovskite Nanostructures: Tunable Morphology and Halide Composition.

Inorganic halide perovskite (CsPbX3 ) nanostructures have gained considerable interest in recent years owing to their enhanced stability and optoelectronic applications. Recent developments in the synthesis of nanostructures are reviewed. The impact of the precursor and ligand nature, temperature and growth time on the morphology and shape tuning of CsPbX3 nanostructures is described in relation to their optical properties. The presynthetic and postsynthetic anion exchange strategies to retain pre-existing crystal phase and shape are discussed in this minireview.

Lung Toxicity and Molecular Mechanisms of Lead-Based Perovskite Nanoparticles in the Respiratory System.

Lead-based perovskite nanoparticles (Pb-PNPs) have found extensive applications across diverse fields. However, because of poor stability and relatively strong water solubility, the potential toxicity of Pb-PNPs released into the environment during their manufacture, usage, and disposal has attracted significant attention. Inhalation is a primary route through which human exposure to Pb-PNPs occurs. Herein, the toxic effects and underlying molecular mechanisms of Pb-PNPs in the respiratory system are investigated. The in vitro cytotoxicity of CsPbBr3 nanoparticles in BEAS-2B cells is studied using multiple bioassays and electron microscopy. CsPbBr3 nanoparticles of different concentrations induce excessive oxidative stress and cell apoptosis. Furthermore, CsPbBr3 nanoparticles specifically recruit the TGF-ß1, which subsequently induces epithelial-mesenchymal transition. In addition, the biodistribution and lung toxicity of representative CsPbBr3 nanoparticles in ICR mice are investigated following intranasal administration. These findings indicate that CsPbBr3 nanoparticles significantly induce pulmonary inflammation and epithelial-mesenchymal transition and can even lead to pulmonary fibrosis in mouse models. Above findings expose the adverse effects and molecular mechanisms of Pb-PNPs in the lung, which broadens the safety data of Pb-PNPs.

Growth of Hybrid Perovskite Films via Single-Source Perovskite Nanoparticle Evaporation.

Herein, we demonstrate a vacuum-based evaporation approach to fabricate organic-inorganic perovskite thin films by using phase-formed halide perovskite nanoparticles (NPs) as a precursor/source. We are able to consistently obtain MAPbX3 (MA=CH3 NH3 and X=Cl, Br or I) thin films at various substrates (e. g., glass, ITO, or plastic). The perovskite phase formation in thin film form is confirmed by x-ray diffraction (XRD) studies. Small micro-strain (tensile) values of 1.64×10-3 , 1.42×10-3 and 6.85×10-4 obtained for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively from Williamson-Hall equation indicate low structural distortions in perovskite thin films. The absorption spectra of thin films show sharp band edge having direct band gap, which is followed by narrow full width at half maxima (FWHM ∼0.1 eV) of the emission peak. Thin films of MAPbCl3 , MAPbBr3 and MAPbI3 show direct band gap of 3.1 eV, 2.4 eV and 1.6 eV, respectively. Small Urbach energy values of 33 meV, 44 meV and 66 meV for MAPbCl3 , MAPbBr3 and MAPbI3 films respectively indicates low defect density in various perovskite films. Scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDS) shows high surface coverage and uniform chemical composition of MAPbX3 (X=Cl, Br and I) thin films deposited by the present method. We have successfully controlled the film thickness from 250 nm to 1 µm by varying the nanoparticle precursor amount. The perovskite thin films deposited by the present method are highly stable against the degradation under ambient conditions. Systematic XRD studies along with absorption data demonstrate that the MAPbCl3 and MAPbBr3 films stored under ambient conditions remained stable for more than 30 days and MAPbI3 films for more than 7 days.

Extremely Stable Luminescent Crosslinked Perovskite Nanoparticles under Harsh Environments over 1.5 Years.

Organic-inorganic hybrid perovskite nanoparticles (NPs) are a very strong candidate emitter that can meet the high luminescence efficiency and high color standard of Rec.2020. However, the instability of perovskite NPs is the most critical unsolved problem that limits their practical application. Here, an extremely stable crosslinked perovskite NP (CPN) is reported that maintains high photoluminescence quantum yield for 1.5 years (>600 d) in air and in harsher liquid environments (e.g., in water, acid, or base solutions, and in various polar solvents), and for more than 100 d under 85 °C and 85% relative humidity without additional encapsulation. Unsaturated hydrocarbons in both the acid and base ligands of NPs are chemically crosslinked with a methacrylate-functionalized matrix, which prevents decomposition of the perovskite crystals. Counterintuitively, water vapor permeating through the crosslinked matrix chemically passivates surface defects in the NPs and reduces nonradiative recombination. Green-emitting and white-emitting flexible large-area displays are demonstrated, which are stable for >400 d in air and in water. The high stability of the CPN in water enables biocompatible cell proliferation which is usually impossible when toxic Pb elements are present. The stable materials design strategies provide a breakthrough toward commercialization of perovskite NPs in displays and bio-related applications.

Strong Cathodoluminescence and Fast Photoresponse from Embedded CH3NH3PbBr3 Nanoparticles Exhibiting High Ambient Stability.

This study presents a comprehensive analysis of the strong cathodoluminescence (CL), photoluminescence (PL), and photoresponse characteristics of CH3NH3PbBr3 nanoparticles (NPs) embedded in a mesoporous nanowire (NW) template. Our study revealed a direct correlation between the CL and PL emissions from the perovskite NPs (Per NPs), for the first time. Per NPs are fabricated by a simple spin-coating of a perovskite precursor on the surface of metal-assisted chemically etched mesoporous Si NW arrays. The Per NPs confined in the mesopores show blue-shifted and enhanced CL emission as compared to the bare perovskite film, while the PL intensity of Per NPs is dramatically high compared to that of their bulk counterpart. A systematic analysis of the CL/PL spectra reveals that the quantum confinement effect and ultralow defects in Per NPs are mainly responsible for the enhanced CL and PL emissions. Low-temperature PL and time-resolved PL analysis confirm the high exciton binding energy and radiative recombination in Per NPs. The room temperature PL quantum yield of the Per NP film on the NW template was found to be 40.5%, while that of Per film was 2.8%. The Per NPs show improved ambient air stability than the bare film due to the protection provided by the dense NW array, since a dense NW array can slow down the lateral diffusion of oxygen and water molecules in Per NPs. Interestingly, the Si NW/Per NP junction shows superior visible light photodetection and the prototype photodetector shows a high responsivity (0.223 A/W) with response speeds of 0.32 and 0.28 s of growth and decay in photocurrent, respectively, at 2 V applied bias, which is significantly better than the reported photodetectors based on CH3NH3PbBr3 nanostructures. This work demonstrates a low-cost fabrication of CH3NH3PbBr3 NPs on a novel porous NW template, which shows excellent photophysical and optoelectronic properties with superior ambient stability.

Dual-Band, High-Performance Phototransistors from Hybrid Perovskite and Organic Crystal Array for Secure Communication Applications.

High-performance phototransistors made from organic semiconductor single crystals (OSSCs) have attracted much attention due to the high responsivity and solution-processing capability of OSSCs. However, OSSC-based phototransistors capable of dual-band spectral response remain a difficult challenge to achieve because organic semiconductors usually possess only narrow single-band absorption. Here, we report the fabrication of high-performance, dual-band phototransistors from a hybrid structure of a 2,7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene (C8-BTBT) single-crystal array coated with CH3NH3PbI3 nanoparticles (NPs) synthesized by a simple, one-step solution method. In contrast to C8-BTBT and CH3NH3PbI3 NPs with respective absorption in the ultraviolet (UV) and visible (vis) region, their hybrid structure shows broad absorption covering the entire UV-vis range. The hybrid-based phototransistors exhibit an ultrahigh responsivity of >1.72 × 104 A/W in the 252-780 nm region, which represents the best performance for solution-processing, broadband photodetectors. Moreover, integrated phototransistor circuitries from the hybrid CH3NH3PbI3 NPs/C8-BTBT single-crystal array show applications for high-security communication.

Large exciton binding energy, high photoluminescence quantum yield and improved photostability of organo-metal halide hybrid perovskite quantum dots grown on a mesoporous titanium dioxide template.

Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large exciton binding energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7-5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV-visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size ∼1.7 nm exhibits ∼47 nm blue shift in the PL spectra, ∼43 fold enhancement in PL intensity and ∼25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (∼124 times) PL emission with narrow line width and a PLQY of ∼57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high exciton binding energy (162-272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (≥10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to <67%. Thus, template grown hybrid perovskite QDs exhibiting high photostability and very high PLQY demonstrated here are promising for the next generation optoelectronic applications.

Effect of Ba Content on the Activity of La1-x Ba x MnO3 Towards the Oxygen Reduction Reaction.

The electrocatalytic activity of La1-x Ba x MnO3 nanoparticles towards the oxygen reduction reaction (ORR) is investigated as a function of the A-site composition. Phase-pure oxide nanoparticles with a diameter in the range of 40 to 70 nm were prepared by using an ionic liquid route and deposited onto mesoporous carbon films. The structure and surface composition of the nanoparticles are probed by XRD, TEM, EDX, and XPS. Electrochemical studies carried out under alkaline conditions show a strong correlation between the activity of La1-x Ba x MnO3 and the effective number of reducible Mn sites at the catalysts layer. Our analysis demonstrates that, beyond controlling particle size and surface elemental segregation, understanding and controlling Mn coordination at the first atomic layer is crucial for increasing the performance of these materials.

Nonvolatile Perovskite-Based Photomemory with a Multilevel Memory Behavior.

Solution-processable organic-inorganic hybrid perovskite materials with a wealth of exotic semiconducting properties have appeared as the promising front-runners for next-generation electronic devices. Further, regarding its well photoresponsibility, various perovskite-based photosensing devices are prosperously developed in recent years. However, most exploited devices to date only transiently transduce the optical signals into electrical circuits while under illumination, which necessitates using additional converters to further store the output signals for recording the occurrence of light stimulation. Herein, a nonvolatile perovskite-based floating-gate photomemory with a multilevel memory behavior is demonstrated, for which a floating gate comprising a polymer matrix impregnated with perovskite nanoparticles is employed. Owing to the well photoresponsibility introduced by the embedded nanoparticles, the device is enabled to access multiple wavelength response and the functionalities of recording power/time-dependent illumination under no vertical electrical field. Intriguingly, a nonvolatility of photorecording exceeding three months with a high On/Off current ratio over 104 can be achieved.

The Light-Induced Field-Effect Solar Cell Concept - Perovskite Nanoparticle Coating Introduces Polarization Enhancing Silicon Cell Efficiency.

Solar cell generates electrical energy from light one via pulling excited carrier away under built-in asymmetry. Doped semiconductor with antireflection layer is general strategy to achieve this including crystalline silicon (c-Si) solar cell. However, loss of extra energy beyond band gap and light reflection in particular wavelength range is known to hinder the efficiency of c-Si cell. Here, it is found that part of short wavelength sunlight can be converted into polarization electrical field, which strengthens asymmetry in organic-c-Si heterojunction solar cell through molecule alignment process. The light harvested by organometal trihalide perovskite nanoparticles (NPs) induces molecular alignment on a conducting polymer, which generates positive electrical surface field. Furthermore, a "field-effect solar cell" is successfully developed and implemented by combining perovskite NPs with organic/c-Si heterojunction associating with light-induced molecule alignment, which achieves an efficiency of 14.3%. In comparison, the device with the analogous structure without perovskite NPs only exhibits an efficiency of 12.7%. This finding provides a novel concept to design solar cell by sacrificing part of sunlight to provide "extra" asymmetrical field continuously as to drive photogenerated carrier toward respective contacts under direct sunlight. Moreover, it also points out a method to combine promising perovskite material with c-Si solar cell.

Using ferromagnetic nanoparticles with low Curie temperature for magnetic resonance imaging-guided thermoablation.

INTRODUCTION: Magnetic nanoparticles (NPs) represent a tool for use in magnetic resonance imaging (MRI)-guided thermoablation of tumors using an external high-frequency (HF) magnetic field. To avoid local overheating, perovskite NPs with a lower Curie temperature (T c) were proposed for use in thermotherapy. However, deposited power decreases when approaching the Curie temperature and consequently may not be sufficient for effective ablation. The goal of the study was to test this hypothesis. METHODS: Perovskite NPs (T c =66°C-74°C) were characterized and tested both in vitro and in vivo. In vitro, the cells suspended with NPs were exposed to a HF magnetic field together with control samples. In vivo, a NP suspension was injected into a induced tumor in rats. Distribution was checked by MRI and the rats were exposed to a HF field together with control animals. Apoptosis in the tissue was evaluated. RESULTS AND DISCUSSION: In vitro, the high concentration of suspended NPs caused an increase of the temperature in the cell sample, leading to cell death. In vivo, MRI confirmed distribution of the NPs in the tumor. The temperature in the tumor with injected NPs did not increase substantially in comparison with animals without particles during HF exposure. We proved that the deposited power from the NPs is too small and that thermoregulation of the animal is sufficient to conduct the heat away. Histology did not detect substantially higher apoptosis in NP-treated animals after ablation. CONCLUSION: Magnetic particles with low T c can be tracked in vivo by MRI and heated by a HF field. The particles are capable of inducing cell apoptosis in suspensions in vitro at high concentrations only. However, their effect in the case of extracellular deposition in vivo is questionable due to low deposited power and active thermoregulation of the tissue.