Surface modification of halide perovskite using EDTA-complexed SnO2 as electron transport layer in high performance solar cells.

The long-term performance of metal halide perovskite solar cells (PSCs) can be significantly improved by tuning the surface characteristics of the perovskite layers. Herein, low-temperature-processed ethylenediaminetetraacetic acid (EDTA)-complexed SnO2 (E-SnO2) is successfully employed as an electron transport layer (ETL) in PSCs, enhancing the efficiency and stability of the devices. The effects of EDTA treatment on SnO2 are investigated for different concentrations: comparing the solar cells' response with 15%-2.5% SnO2 and E-SnO2 based ETLs, and it was found that 7.5% E-SnO2 provided the best results. The improved surface properties of the perovskite layer on E-SnO2 are attributed to the presence of small amount of PbI2 which contributes to passivate the defects at the grain boundaries and films' surface. However, for the excess PbI2 based devices, photocurrent dropped, which could be attributed to the generation of shallow traps due to excess PbI2. The better alignment between the Fermi level of E-SnO2 and the conduction band of perovskite is another favorable aspect that enables increased open-circuit potential (VOC), from 0.82 V to 1.015 V, yielding a stabilized power conversion efficiency of 15.51%. This complex ETL strategy presented here demonstrates the enormous potential of E-SnO2 as selective contact to enhance the perovskite layer properties and thereby allow stable and high-efficiency PSCs.

MXene-Enhanced Nanoscale Photoconduction in Perovskite Solar Cells Revealed by Conductive Atomic Force Microscopy.

The use of MXene materials in perovskite solar cells (PSCs) has received significant interest due to their distinct features that result from the termination of functional groups and the oxidation of MXene. Herein, we have used photoconductive atomic force microscopy (pcAFM) to map the local (nanoscale) photovoltaic performances of the Ti3C2Tx MXene nanosheet-integrated TiO2 (MXene@TiO2) electron transport layer-based PSCs to determine the influence of the treatment on the microscopic charge flow inside the devices. At different applied voltages, the morphology and current have been simultaneously measured with nanoscale resolution from the top surfaces of the solar cells without back contacts. The PSCs based on MXene@TiO2 exhibit more enhanced current flow across the grains than the only TiO2-based PSCs. At zero applied bias, the average local photocurrent for MXene-integrated PSCs is several times higher than the reference PSCs and decreases gradually when the positive bias is increased until the open circuit voltage. Considerable differences were also observed in the short circuit current among different locations that appear identical in AFM topography. Our findings reveal the potential of MXene-integrated ETLs to enhance the nanoscale photoconduction and inherent characteristics of the active layers, thereby improving the performance of the polycrystalline photovoltaic devices.

Synthesis of Gentamicins C1, C2, and C2a and Antiribosomal and Antibacterial Activity of Gentamicins B1, C1, C1a, C2, C2a, C2b, and X2.

Complementing our earlier syntheses of the gentamicins B1, C1a, C2b, and X2, we describe the synthesis of gentamicins C1, C2, and C2a characterized by methyl substitution at the 6'-position, and so present an alternative access to previous chromatographic methods for accessing these sought-after compounds. We describe the antiribosomal activity of our full set of synthetic gentamicin congeners against bacterial ribosomes and hybrid ribosomes carrying the decoding A site of the human mitochondrial, A1555G mutant mitochondrial, and cytoplasmic ribosomes and establish structure-activity relationships with the substitution pattern around ring I to antiribosomal activity, antibacterial resistance due to the presence of aminoglycoside acetyl transferases acting on the 6'-position in ring I, and literature cochlear toxicity data.

Total Synthesis and Structure Confirmation of Fusaroside.

Recently, we synthesized the proposed structure of the fungal glycolipid fusaroside and suggested corrections in its structure with respect to the positions of the double bonds in the lipid portion. Herein, we report the first total synthesis of the proposed revised structure of fusaroside and thereby confirm its structure. The synthesis involved Julia-Kocienski olefination for the construction of fatty acid and its coupling with trehalose at the O4 position followed by late-stage gem-dimethylation as key steps.

Total Synthesis of a Trehalose-Containing Lipooligosaccharide Analogue from Mycobacterium linda.

A short and efficient methodology has been developed to synthesize an analogue of a lipooligosaccharide from Mycobacterium linda isolated from Crohn's disease. The total synthesis of the tetrasaccharide was achieved via a convergent [2 + 2] glycosylation approach. The key features of the synthesis involve the selective functionalization of a trehalose core via highly regioselective acylations and regioselective glycosylations. The synthesis was completed via a longest linear sequence of 14 steps in a 14.2% overall yield.

Synthesis of Gentamicin Minor Components: Gentamicin C1a and Gentamicin C2b.

Gentamicin C1a and the minor isomer C2b have been reported to have favorable properties in terms of antibacterial activity and toxicity compared to the commercial mixture from which they have previously been isolated by preparative high-performance liquid chromatography. We report straightforward syntheses of both compounds from readily available sisomicin by selective oxidation of the side chain in ring I, hydrogenation of the double bond in ring I to give the 5'-epi series, inversion of configuration at position 5' under thermodynamic conditions, and installation of the 6'-amino group by reductive amination.

Bandlike Transport in FaPbBr3 Quantum Dot Phototransistor with High Hole Mobility and Ultrahigh Photodetectivity.

Halide perovskites have been widely explored for numerous optoelectronic applications among which phototransistors have appeared as one of the most promising light signal detectors. However, it is still a great challenge to endow halide perovskites with both mobility and high photosensitivity because of their high sensitivity to moisture in ambient atmosphere. Here, we explore an FAPbBr3 perovskite quantum dot (QD) phototransistor with bandlike charge transport and measure a dark hole mobility of 14.2 cm2 V-1 s-1 at ambient atmosphere. Attaining both high mobility and good optical figures of merit, a detectivity of ∼1016 Jones is achieved, which is a record for halide perovskite nanocrystals. Simple A-site salt (FABr) treatments offer a mechanism for connecting between perovskite QDs for better charge transfer in high-quality devices. All of these important properties are superior to most advanced inorganic semiconductor phototransistors, indicating a promising future in optoelectronic applications.

Stacking-Dependent Electrical Transport in a Colloidal CdSe Nanoplatelet Thin-Film Transistor.

Here, we report an exceptional feature of the one-dimensional threadlike assemblies of a four-monolayer colloidal CdSe nanoplatelet (NPL)-based thin-film transistor. A series of different lengths of threads (200-1200 nm) was used as an active n channel in thin-film transistors (TFTs) to understand the change in mobility with the length of the threads. The film with the longest threads shows the highest conductivity of ∼12 S/cm and electron mobility of ∼14.3 cm2 V-1 s-1 for an applied gate voltage of 2 V. The mobility trends with the length seem to be driven mostly by the lower defects in threads, where the loss of electron hopping is less. Furthermore, our results show the mobility trends in stacking-dependent CdSe NPL threads and provide a new insight into fabricating high-mobility TFTs with the use of colloidal CdSe NPLs.

Unusual C-C bond cleavage of an α-trifloxy Sialic acid hemiacetal under Lattrell-Dax conditions.

We describe the novel oxidative fragmentation of methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-5-deoxy-3-O-trifluoromethanesulfonyl-ß-D-erythro-L-gluco-2-nonulopyranos)onate 2 on stirring with sodium nitrite in DMF to give the novel 3-acetamido-2,5,6,7-tetra-O-acetyl-d-glycero-d-galacto-heptono-1,4-lactone 3 in excellent yield. Stirring of the same triflate with sodium carbonate on the other hand affords the novel methyl (5-acetamido-7,8,9-tri-O-acetyl-3,6-anhydro-5-deoxy-d-manno-3-ene-2-nonulos)onate 19 also in excellent yield. Reduction of the heptono lactone with sodium borohydride followed by acetylation gives a peracetylated aminodeoxyheptitol 6 that adopts the zig zag conformation of its carbon backbone.

Total Synthesis and Structure Revision of a Fungal Glycolipid Fusaroside.

Herein, we report a strategy for the total synthesis of a structurally unique fungal glycolipid fusaroside. The first total synthesis of the proposed structure involved construction of the complex, branched lipid chain having a variety of alkenes with E stereochemistry and attachment of the masked α,ß-unsaturated ß-keto acid at the O-4 position of trehalose as key steps. We propose a revision in the structure of fusaroside, particularly the position of olefins in the lipid chain.

Toward Stable Solution-Processed High-Mobility p-Type Thin Film Transistors Based on Halide Perovskites.

Organolead halide perovskites have drawn significant attention from the scientific community as one of the most attractive materials in optoelectronics, especially in the field of photovoltaics. In this study, we focus on using halide perovskites in processing thin film transistors (TFTs). Halide perovskites have high solution processability and excellent carrier transport characteristics, in particular for holes. The present work aims to fill a gap in oxide-based technology. It concerns the process of using high-stable and reliable p-type oxide-based devices to target CMOS technology (complementary metal-oxide-semiconductor). We report on a solution-processed high-performance TFT based on methylammonium lead iodide (CH3NH3PbI3) perovskite semiconductor films, which shows promise for devices that can be simple to manufacture with high reliability, reproducibility, and excellent stability in atmospheric conditions. To achieve a highly stable perovskite semiconductor film, we introduce diethylsulfide in the perovskite precursor. The TFT shows a stable p-type behavior when operated at low voltages (≤-2 V) and has a current modulation of >104, an almost negligible hysteresis, and average saturation mobility of about 18.8 cm2 V-1 s-1, taken over 50 devices tested (the highest one measured was ∼23.2 cm2 V-1 s-1). This is the highest value until now reported in the literature. In addition, we demonstrate that perovskite TFTs can be fabricated at temperatures as low as 150 °C on flexible substrates with a saturation mobility of ∼11.5 cm2 V-1 s-1. The high-performance perovskite TFT with excellent stability is a promising candidate for the next generation of p-type transistors for a plethora of low-cost electronics applications.

Synthesis of trehalose glycolipids.

Trehalose containing glycolipids have been isolated from various species of mycobacteria, fungi and worms. Owing to their versatile biological roles, and heterogenicity of the natural isolates, there is great interest in the synthesis of trehalose glycolipids. In this review we discuss recent developments in the total synthesis of biologically important and structurally complex trehalose glycoconjugates and oligosaccharides.

A Virulence-Associated Glycolipid with Distinct Conformational Attributes: Impact on Lateral Organization of Host Plasma Membrane, Autophagy, and Signaling.

Mycobacterium tuberculosis (Mtb) serves as the epitome of how lipids-next to proteins-are utilized as central effectors in pathogenesis. It synthesizes an arsenal of structurally atypical lipids (C60-C90) to impact various membrane-dependent steps involved in host interactions. There is a growing precedent to support insertion of these exposed lipids into the host membrane as part of their mode of action. However, the vital role of specific virulence-associated lipids in modulating cellular functions by altering the host membrane organization and associated signaling pathways remain unanswered questions. Here, we combined chemical synthesis, biophysics, cell biology, and molecular dynamics simulations to elucidate host membrane structure modifications and modulation of membrane-associated signaling using synthetic Mycobacterium tuberculosis sulfoglycolipids (Mtb SL). We reveal that Mtb SL reorganizes the host cell plasma membrane domains while showing higher preference for fluid membrane regions. This rearrangement is governed by the distinct conformational states sampled by SL acyl chains. Physicochemical assays with SL analogues reveal insights into their structure-function relationships, highlighting specific roles of lipid acyl chains and headgroup, along with effects on autophagy and cytokine profiles. Our findings uncover a mechanism whereby Mtb uses specific chemical moieties on its lipids to fine-tune host lipid interactions and confer control of the downstream functions by modifying the cell membrane structure and function. These findings will inspire development of chemotherapeutics against Mtb by counteracting their effects on the host-cell membrane.

Total Synthesis of Emmyguyacins A and B, Potential Fusion Inhibitors of Influenza Virus.

Fungal glycolipids emmyguyacins A and B inhibit the pH-dependent conformational change of hemaglutinin A during replication of the Influenza virus. Herein, we report the first total synthesis and structure confirmation of emmyguyacins A and B. Our efficient route, which involves regioselective functionalization of trehalose, allows rapid access to adequate amounts of chemically pure emmyguyacin analogues including the desoxylate derivatives for SAR studies.

Imaging the Anomalous Charge Distribution Inside CsPbBr3 Perovskite Quantum Dots Sensitized Solar Cells.

Highly luminescent CsPbBr3 perovskite quantum dots (QDs) have gained huge attention in research due to their various applications in optoelectronics, including as a light absorber in photovoltaic solar cells. To improve the performances of such devices, it requires a deeper knowledge on the charge transport dynamics inside the solar cell, which are related to its power-conversion efficiency. Here, we report the successful fabrication of an all-inorganic CsPbBr3 perovskite QD sensitized solar cell and the imaging of anomalous electrical potential distribution across the layers of the cell under different illuminations using Kelvin probe force microscopy. Carrier generation, separation, and transport capacity inside the cells are dependent on the light illumination. Large differences in surface potential between electron and hole transport layers with unbalanced carrier separation at the junction have been observed under white light (full solar spectrum) illumination. However, under monochromatic light (single wavelength of solar spectrum) illumination, poor charge transport occurred across the junction as a consequence of less difference in surface potential between the active layers. The outcome of this study provides a clear idea on the carrier dynamic processes inside the cells and corresponding surface potential across the layers under the illumination of different wavelengths of light to understand the functioning of the solar cells and ultimately for the improvement of their photovoltaic performances.

Ligand-induced twisting of nanoplatelets and their self-assembly into chiral ribbons.

The emergence of chirality is a central issue in chemistry, materials science, and biology. In nanoparticle assemblies, chirality has been shown to arise through a few different processes, but chiral organizations composed of plate-like nanoparticles, a class of material under scrutiny due to their wide applicative potential, have not yet been reported. We show that ribbons of stacked board-shaped cadmium selenide (CdSe) nanoplatelets (NPLs) twist upon the addition of oleic acid ligand, leading to chiral ribbons that reach several micrometers in length and display a well-defined pitch of ~400 nm. We demonstrate that the chirality originates from surface strain caused by the ligand because isolated NPLs in dilute solution undergo a transition from a flat to a twisted shape as the ligand coverage increases. When the platelets are closely stacked within ribbons, the individual twist propagates over the whole ribbon length. These results show that a ligand-induced mechanical stress can strongly distort thin NPLs and that this stress can be expressed at a larger scale, paving the way to stress engineering in assemblies of nanocrystals. Such a structural change resulting from a simple external stimulus could have broad implications for the design of sensors and other responsive materials.

Chemical Synthesis of Biosurfactant Succinoyl Trehalose Lipids.

Herein, we report, for the first time, a strategy to differentiate O4/O4' positions of 1,1'-α,α-trehalose via regioselective protection or site-selective functionalization and its application in the first chemical synthesis of succinoyl trehalose lipids. The biosurfactant glycolipids were obtained in 11-12 steps starting from trehalose in time span of 8-10 days and 11-12% overall yields.

The preparation of γ-crystalline non-electrically poled photoluminescant ZnO-PVDF nanocomposite film for wearable nanogenerators.

Polyvinylidene fluoride (PVDF) films are filled with various mass fractions (wt%) of zinc oxide nanoparticles (ZnO-NPs) to fabricate the high performance of a wearable polymer composite nanogenerator (PCNG). The ZnO-NPs can induced a fully γ-crystalline phase in PVDF, where traditional electrical poling is not necessary for the generation of piezoelectric properties. The PCNG delivers up to 28 V of open circuit voltage and 450 nA of short circuit current by simple repeated human finger imparting (under a pressure amplitude of 8.43 kPa) that generates sufficient power to turn on at least 48 commercial blue light emitting diodes (LEDs) instantly. Furthermore, it also successfully charged the capacitors, signifying practical applicability as a piezoelectric based nanogenerator for self-powering devices. The applicability of PCNG by wearable means is clarified when it gives rise to a sensible response, say up to 400 mV of output voltage synchronized with the PCNG embedded human finger in a bending and releasing gesture. UV-visible absorption spectral analysis revealed the possibility of estimating a change in the optical band gap value (E g), refractive index (n) and optical activation energy (E a) in different concentrations of ZnO-NP incorporated PVDF nanocomposite films, and it possesses a useful methodology where ZnO-NPs can be used as an optical probe. Near blue light emission is observed from photoluminescence spectra, which are clearly shown from a Commission Internationale de L'Eclairage (CIE) diagram. The piezoelectric charge coefficient of the nanocomposite film is estimated to be -6.4 pC/N, where even electrical poling treatment is not employed. In addition, dielectric properties have been studied to understand the role of molecular kinetic and interfacial polarization occurring in nanocomposite films at different applied frequencies.

CdSe Nanoplatelets: Living Polymers.

Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a "living polymer" character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.

Graphene-Silver-Induced Self-Polarized PVDF-Based Flexible Plasmonic Nanogenerator Toward the Realization for New Class of Self Powered Optical Sensor.

Plasmonic characteristics of graphene-silver (GAg) nanocomposite coupled with piezoelectric property of Poly(vinylidene fluoride) (PVDF) have been utilized to realize a new class of self-powered flexible plasmonic nanogenerator (PNG). A few layer graphene has been prepared in a facile and cost-effective method and GAg doped PVDF hybrid nanocomposite (PVGAg) is synthesized in a one-pot method. The PNG exhibits superior piezoelectric energy conversion efficiency (∼15%) under the dark condition. The plasmonic behavior of GAg nanocomposite makes the PNG highly responsive to the visible light illumination that leads to ∼50% change in piezo-voltage and ∼70% change in piezo-current, leading to enhanced energy conversion efficiency up to ∼46.6%. The piezoelectric throughput of PNG (e.g., capacitor charging performance) has been monitored during the detection of the different wavelengths of visible light illumination and showed maximum selectivity to the green light. The simultaneous mechanical energy harvesting and visible-light detection capabilities of the PNG are attractive for futuristic self-powered optoelectronic smart sensors and devices.