Trace Water in Lead Iodide Affecting Perovskite Crystal Nucleation Limits the Performance of Perovskite Solar Cells.

The experimental replicability of highly efficient perovskite solar cells (PSCs) is a persistent challenge faced by laboratories worldwide. Although trace impurities in raw materials can impact the experimental reproducibility of high-performance PSCs, the in situ study of how trace impurities affect perovskite film growth is never investigated. Here, light is shed on the impact of inevitable water contamination in lead iodide (PbI2 ) on the replicability of device performance, mainly depending on the synthesis methods of PbI2 . Through synchrotron-based structure characterization, it is uncovered that even slight additions of water to PbI2 accelerate the crystallization process in the perovskite layer during annealing. However, this accelerated crystallization also results in an imbalance of charge-carrier mobilities, leading to a degradation in device performance and reduced longevity of the solar cells. It is also found that anhydrous PbI2 promotes a homogenous nucleation process and improves perovskite film growth. Finally, the PSCs achieve a remarkable certified power conversion efficiency of 24.3%. This breakthrough demonstrates the significance of understanding and precisely managing the water content in PbI2 to ensure the experimental replicability of high-efficiency PSCs.

Plasmon assisted Ti3C2Tx grafting and surface termination tuning for enhancement of flake stability and humidity sensing performance.

Humidity sensors play a critical role in monitoring human activities, environmental health, food processing and storage, and many other fields. Recently, some 2D materials, particularly MXenes, have been considered as promising candidates for creating humidity sensors because of their high surface area, surface-to-bulk ratio, and excellent conductivity, arising from the high concentration and mobility of free electrons. In this work, we propose the plasmon-assisted surface modification and termination tuning of common MXene (Ti3C2Tx) to enhance their response to humidity and increase their stability against oxidation. Hydrophobic (-C6H4-CF3) and hydrophilic (-C6H4-COOH) chemical moieties were covalently grafted to the Ti3C2Tx surface using plasmon-mediated diazonium chemistry. In situ Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements, performed at different humidity levels indicate that surface modification significantly affects penetration of water molecules in Ti3C2Tx films. As a result, the sensitivity of the flakes to the presence of water molecules was significantly altered. Additionally, proposed surface grafting commonly proceeds on the less stable MXene surface sites, where flake oxidation commonly initiates. As a result of the modification, such "weak" and more chemically active sites were blocked and Ti3C2Tx stability was significantly enhanced.

Tunable Sieving of Ions Using Graphene Oxide: Swelling Peculiarities in Free-Standing and Confined States.

The paper describes a comparative study of swelling processes in free-standing graphene oxide (GO) membranes and GO laminates encapsulated with epoxy glue. For free-standing graphene oxide membranes, a huge variation in d-spacing in the range of 8-12 Å depending on the ambient humidity and from 12 to >30 Å depending on the electrolyte type and its concentration was revealed using direct in situ and in operando XRD studies. Limited swelling at various humidity levels as well as in electrolyte solution with low constriction/expansion of epoxy-encapsulated GO is counterposed to that of free-standing graphene oxides. The swelling suppression was explained by both physical constriction and the intercalation of amines into GO laminates, which was proved by local EDX studies. This results in ion diffusivity variation for over 2 orders of magnitude in free-standing and constrained graphene oxide membranes and provides factual evidence for tunable sieving of ions with confined graphene oxides.

Cross-linking reactions in Langmuir monolayers of specially designed aminolipids - a toolbox for the customized production of amphiphilic nanosheets.

Synthetic amino lipids, already known as highly efficient gene therapy tool, are used in a novel way to create cross-linked stable one-molecule-thin films envisioned for future (bio)-materials applications. The films are prepared as Langmuir monolayers at the air/water interface and cross-linked 'in situ' via dynamic imine chemistry. The cross-linking process and the film characteristics are monitored by various surface-sensitive techniques such as grazing incidence X-ray diffraction, X-ray reflectivity, and infrared reflection-absorption spectroscopy. After transfer onto carbon grids, the cross-linked films are investigated by transmission and scanning electron microscopy. The obtained micrographs display mechanically self-supported nanosheets with area dimensions over several micrometers and, thus, an undeniable visual proof of successful cross-linking. The cross-linking process at the air/water interface allows to obtain Janus-faced sheets with a hydrophobic side characterized by aliphatic alkyl chains and a hydrophilic side characterized by nucleophilic groups like amines, hydroxyl groups and imine.

Investigating the thermal stability of ultra-small Ag, Au and AuAg alloy nanoparticles embedded in a silica matrix.

Thermal growth kinetics of embedded bimetallic (AuAg/SiO2) nanoparticles are explored and compared with their monometallic (Au/SiO2 and Ag/SiO2) counterparts, as their practical applicability demands stability and uniformity. The plasmonic properties of these nanoparticles (NPs) significantly improve when their size falls in the ultra-small region (diameter < 10 nm), owing to their large active surface area. Interestingly, the bimetallic NPs exhibit better optical properties and structural stability as compared to their monometallic counterparts. This calls for a thorough understanding of the nucleation and temperature-dependent growth to ensure size stability against thermal coarsening that most bimetallic NPs completely lack. Herein, the atom beam sputtered AuAg NPs are systematically analysed over a wide range of annealing temperatures (ATs), and the results are compared with those of Au and Ag NPs. The X-ray photoelectron spectroscopy spectra and other experimental results confirm the formation of AuAg alloy NPs inside the silica matrix. Furthermore, techniques like transmission electron microscopy and grazing-incidence small-/wide-angle X-ray scattering were used to explore the temperature-dependent structural and morphological stability of the NPs. Our results show that the deposited AuAg NPs retain their spherical shape and remain as an alloy for the entire range of ATs. When the AT increases from 25 °C to 800 °C, the size of the NPs also increases from 3.5 to 4.8 nm; beyond that, their size grows substantially to 13.6 nm at 900 °C. We observed that the NPs remain in the ultra-small size range (∼5 nm) until an AT of 800 °C. Beyond that Ostwald ripening is ascribed to be the major cause of particle growth, resulting in an active surface area loss. Based on the outcomes, a three-step nucleation and growth mechanism is proposed.

Thiol functionalised gold nanoparticles loaded with methotrexate for cancer treatment: From synthesis to in vitro studies on neuroblastoma cell lines.

HYPOTHESIS: Colloidal gold nanoparticles (AuNPs) functionalised with hydrophilic thiols can be used as drug delivery probes, thanks to their small size and hydrophilic character. AuNPs possess unique properties for their use in nanomedicine, especially in cancer treatment, as diagnostics and therapeutic tools. EXPERIMENTS: Thiol functionalised AuNPs were synthesised and loaded with methotrexate (MTX). Spectroscopic and morphostructural characterisations evidenced the stability of the colloids upon interaction with MTX. Solid state (GISAXS, GIWAXS, FESEM, TEM, FTIR-ATR, XPS) and dispersed phase (UV-Vis, DLS, ζ-potential, NMR, SAXS) experiments allowed to understand structure-properties correlations. The nanoconjugate was tested in vitro (MTT assays) against two neuroblastoma cell lines: SNJKP and IMR5 with overexpressed n-Myc. FINDINGS: Molar drug encapsulation efficiency was optimised to be >70%. A non-covalent interaction between the π system and the carboxylate moiety belonging to MTX and the charged aminic group of one of the thiols was found. The MTX loading slightly decreased the structural order of the system and increased the distance between the AuNPs. Free AuNPs showed no cytotoxicity whereas the AuNPs-MTX nanoconjugate had a more potent effect when compared to free MTX. The active role of AuNPs was evidenced by permeation studies: an improvement on penetration of the drug inside cells was evidenced.

Evolution of Structure and Optoelectronic Properties During Halide Perovskite Vapor Deposition.

The efficiency of perovskite-based solar cells has increased dramatically over the past decade to as high as 25%, making them very attractive for commercial use. Vapor deposition is a promising technique that potentially enables fabrication of perovskite solar cells on large areas. However, to implement a large-scale deposition method, understanding and controlling the specific growth mechanisms are essential for the reproducible fabrication of high-quality layers. Here, we study the structural and optoelectronic kinetics of MAPbI3, employing in-situ photoluminescence (PL) spectroscopy and grazing-incidence small/wide-angle X-ray scattering (GI-SAXS/WAXS) simultaneously during perovskite vapor deposition. Such a unique combination of techniques reveals MAPbI3 formation from the early stages and uncovers the morphology, crystallographic structure, and defect density evolution. Furthermore, we show that the nonmonotonous character of PL intensity contrasts with the increasing volume of the perovskite phase during the growth, although bringing valuable information about the presence of defect states.

Oxidized Carbon-Based Spacers for Pressure-Resistant Graphene Oxide Membranes.

In this study, we report the influence of carbon-based spacer-oxidized derivatives of fullerenes (fullerenols) C60(OH)26−32 and graphene oxide nanoribbons on the performance and pressure stability of graphene-oxide-based composite membranes. The impact of the intercalant shape and composition on the permeance of the selective layers for water vapors has been studied under pressure gradients. It is shown that the insertion of ball-shaped fullerenols between graphene oxide nanoflakes allows a suppression in irreversible permeance loss to 2−4.5% and reversible permeance loss to <25% (at 0.1 MPa), while retaining large H2O/N2 selectivities of up to ~30,000. The demonstrated approach opens avenues for the highly effective stabilization of GO membranes at elevated pressures for industrial-scale dehumidification.

A Combinatorial Study Investigating the Growth of Ultrasmall Embedded Silver Nanoparticles upon Thermal Annealing.

Ultrasmall nanoparticles (NPs) with a high active surface area are essential for optoelectronic and photovoltaic applications. However, the structural stability and sustainability of these ultrasmall NPs at higher temperatures remain a critical problem. Here, we have synthesized the nanocomposites (NCs) of Ag NPs inside the silica matrix using the atom beam co-sputtering technique. The post-deposition growth of the embedded Ag NPs is systematically investigated at a wide range of annealing temperatures (ATs). A novel, fast, and effective procedure, correlating the experimental (UV-vis absorption results) and theoretical (quantum mechanical modeling, QMM) results, is used to estimate the size of NPs. The QMM-based simulation, employed for this work, is found to be more accurate in reproducing the absorption spectra over the classical/modified Drude model, which fails to predict the expected shift in the LSPR for ultrasmall NPs. Unlike the classical Drude model, the QMM incorporates the intraband transition of the conduction band electrons to calculate the effective dielectric function of metallic NCs, which is the major contribution of LSPR shifts for ultrasmall NPs. In this framework, a direct comparison is made between experimentally and theoretically observed LSPR peak positions, and it is observed that the size of NPs grows from 3 to 18 nm as AT increases from room temperature to 900 °C. Further, in situ grazing-incidence small- & wide-angle X-ray scattering and transmission electron microscopy measurements are employed to comprehend the growth of Ag NPs and validate the UV + QMM results. We demonstrate that, unlike chemically grown NPs, the embedded Ag NPs ensure greater stability in size and remain in an ultrasmall regime up to 800 °C, and beyond this temperature, the size of NPs increases exponentially due to dominant Ostwald ripening. Finally, a three-stage mechanism is discussed to understand the process of nucleation and growth of the silica-embedded Ag NPs.

The Effects of Cholesterol Oxidation on Erythrocyte Plasma Membranes: A Monolayer Study.

Cholesterol plays a key role in the molecular and mesoscopic organisation of lipid membranes and it is expected that changes in its molecular structure (e.g., through environmental factors such as oxidative stress) may affect adversely membrane properties and function. In this study, we present evidence that oxidation of cholesterol has significant effects on the mechanical properties, molecular and mesoscopic organisation and lipid-sterol interactions in condensed monolayers composed of the main species found in the inner leaflet of the erythrocyte membrane. Using a combination of experimental methods (static area compressibility, surface dilatational rheology, fluorescence microscopy, and surface sensitive X-ray techniques) and atomistic molecular dynamics simulations, we show that oxidation of cholesterol to 7-ketocholesterol leads to stiffening of the monolayer (under both static and dynamic conditions), significant changes in the monolayer microdomain organisation, disruption in the van der Waals, electrostatic and hydrophobic interactions between the sterol and the other lipid species, and the lipid membrane hydration. Surface sensitive X-ray techniques reveal that, whilst the molecular packing mode is not significantly affected by cholesterol oxidation in these condensed phases, there are subtle changes in membrane thickness and a significant decrease in the coherence length in monolayers containing 7-ketocholesterol.

Robust Assembly of Cross-Linked Protein Nanofibrils into Hierarchically Structured Microfibers.

Natural, high-performance fibers generally have hierarchically organized nanosized building blocks. Inspired by this, whey protein nanofibrils (PNFs) are assembled into microfibers, using flow-focusing. By adding genipin as a nontoxic cross-linker to the PNF suspension before spinning, significantly improved mechanical properties of the final fiber are obtained. For curved PNFs, with a low content of cross-linker (2%) the fiber is almost 3 times stronger and 4 times stiffer than the fiber without a cross-linker. At higher content of genipin (10%), the elongation at break increases by a factor of 2 and the energy at break increases by a factor of 5. The cross-linking also enables the spinning of microfibers from long straight PNFs, which has not been achieved before. These microfibers have higher stiffness and strength but lower ductility and toughness than those made from curved PNFs. The fibers spun from the two classes of nanofibrils show clear morphological differences. The study demonstrates the production of protein-based microfibers with mechanical properties similar to natural protein-based fibers and provides insights about the role of the nanostructure in the assembly process.

Percolation of rigid fractal carbon black aggregates.

We examine network formation and percolation of carbon black by means of Monte Carlo simulations and experiments. In the simulation, we model carbon black by rigid aggregates of impenetrable spheres, which we obtain by diffusion-limited aggregation. To determine the input parameters for the simulation, we experimentally characterize the micro-structure and size distribution of carbon black aggregates. We then simulate suspensions of aggregates and determine the percolation threshold as a function of the aggregate size distribution. We observe a quasi-universal relation between the percolation threshold and a weighted average radius of gyration of the aggregate ensemble. Higher order moments of the size distribution do not have an effect on the percolation threshold. We conclude further that the concentration of large carbon black aggregates has a stronger influence on the percolation threshold than the concentration of small aggregates. In the experiment, we disperse the carbon black in a polymer matrix and measure the conductivity of the composite. We successfully test the hypotheses drawn from simulation by comparing composites prepared with the same type of carbon black before and after ball milling, i.e., on changing only the distribution of aggregate sizes in the composites.

Spray-Deposited Anisotropic Ferromagnetic Hybrid Polymer Films of PS-b-PMMA and Strontium Hexaferrite Magnetic Nanoplatelets.

Spray deposition is a scalable and cost-effective technique for the fabrication of magnetic hybrid films containing diblock copolymers (DBCs) and magnetic nanoparticles. However, it is challenging to obtain spray-deposited anisotropic magnetic hybrid films without using external magnetic fields. In the present work, spray deposition is applied to prepare perpendicular anisotropic magnetic hybrid films by controlling the orientation of strontium hexaferrite nanoplatelets inside ultra-high-molecular-weight DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films. During spray deposition, the evolution of DBC morphology and the orientation of magnetic nanoplatelets are monitored with in situ grazing-incidence small-angle X-ray scattering (GISAXS). For reference, a pure DBC film without nanoplatelets is deposited with the same conditions. Solvent-controlled magnetic properties of the hybrid film are proven with solvent vapor annealing (SVA) applied to the final deposited magnetic films. Obvious changes in the DBC morphology and nanoplatelet localization are observed during SVA. The superconducting quantum interference device data show that ferromagnetic hybrid polymer films with high coercivity can be achieved via spray deposition. The hybrid films show a perpendicular magnetic anisotropy before SVA, which is strongly weakened after SVA. The spray-deposited hybrid films appear highly promising for potential applications in magnetic data storage and sensors.

Hot Hydrocarbon-Solvent Slot-Die Coating Enables High-Efficiency Organic Solar Cells with Temperature-Dependent Aggregation Behavior.

Organic solar cells (OSCs) have made rapid progress in terms of their development as a sustainable energy source. However, record-breaking devices have not shown compatibility with large-scale production via solution processing in particular due to the use of halogenated environment-threatening solvents. Here, slot-die fabrication with processing involving hydrocarbon-based solvents is used to realize highly efficient and environmentally friendly OSCs. Highly compatible slot-die coating with roll-to-roll processing using halogenated (chlorobenzene (CB)) and hydrocarbon solvents (1,2,4-trimethylbenzene (TMB) and ortho-xylene (o-XY)) is used to fabricate photoactive films. Controlled solution and substrate temperatures enable similar aggregation states in the solution and similar kinetics processes during film formation. The optimized blend film nanostructures for different solvents in the highly efficient PM6:Y6 blend is adopted to show a similar morphology, which results in device efficiencies of 15.2%, 15.4%, and 15.6% for CB, TMB, and o-XY solvents. This approach is successfully extended to other donor-acceptor combinations to demonstrate the excellent universality of this method. The results combine a method to optimize the aggregation state and film formation kinetics with the fabrication of OSCs with environmentally friendly solvents by slot-die coating, which is a critical finding for the future development of OSCs in terms of their scalable production and high-performance.

Reorientation of π-conjugated molecules on few-layer MoS2 films.

Small π-conjugated organic molecules have attracted substantial attention in the past decade as they are considered as candidates for future organic-based (opto-)electronic applications. The molecular arrangement in the organic layer is one of the crucial parameters that determine the efficiency of a given device. The desired orientation of the molecules is achieved by a proper choice of the underlying substrate and growth conditions. Typically, one underlying material supports only one inherent molecular orientation at its interface. Here, we report on two different orientations of diindenoperylene (DIP) molecules on the same underlayer, i.e. on a few-layer MoS2 substrate. We show that DIP molecules adopt a lying-down orientation when deposited on few-layer MoS2 with horizontally oriented layers. In contrast, for vertically aligned MoS2 layers, DIP molecules are arranged in a standing-up manner. Employing in situ and real-time grazing-incidence wide-angle X-ray scattering (GIWAXS), we monitored the stress evolution within the thin DIP layer from the early stages of the growth, revealing different substrate-induced phases for the two molecular orientations. Our study opens up new possibilities for the next-generation of flexible electronics, which might benefit from the combination of MoS2 layers with unique optical and electronic properties and an extensive reservoir of small organic molecules.