Atomic-level passivation mechanism of ammonium salts enabling highly efficient perovskite solar cells.

The high conversion efficiency has made metal halide perovskite solar cells a real breakthrough in thin film photovoltaic technology in recent years. Here, we introduce a straightforward strategy to reduce the level of electronic defects present at the interface between the perovskite film and the hole transport layer by treating the perovskite surface with different types of ammonium salts, namely ethylammonium, imidazolium and guanidinium iodide. We use a triple cation perovskite formulation containing primarily formamidinium and small amounts of cesium and methylammonium. We find that this treatment boosts the power conversion efficiency from 20.5% for the control to 22.3%, 22.1%, and 21.0% for the devices treated with ethylammonium, imidazolium and guanidinium iodide, respectively. Best performing devices showed a loss in efficiency of only 5% under full sunlight intensity with maximum power tracking for 550 h. We apply 2D- solid-state NMR to unravel the atomic-level mechanism of this passivation effect

Identification and characterization of antibacterial compound(s) of cockroaches (Periplaneta americana)

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. With the worsening trends of drug resistance, there is a need for newer and more powerful antimicrobial agents. We hypothesized that animals living in polluted environments are potential source of antimicrobials. Under polluted milieus, organisms such as cockroaches encounter different types of microbes, including superbugs. Such creatures survive the onslaught of superbugs and are able to ward off disease by producing antimicrobial substances. Here, we characterized antibacterial properties in extracts of various body organs of cockroaches (Periplaneta americana) and showed potent antibacterial activity in crude brain extract against methicillin-resistant Staphylococcus aureus and neuropathogenic E. coli K1. The size-exclusion spin columns revealed that the active compound(s) are less than 10 kDa in molecular mass. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with lysates inhibited bacteria-mediated host cell cytotoxicity. Using spectra obtained with LC-MS on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer, tissues lysates were analyzed. Among hundreds of compounds, only a few homologous compounds were identified that contained isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole containing analogs, sulfonamides, furanones, flavanones, and known to possess broad-spectrum antimicrobial properties, and possess anti-inflammatory, anti-tumour, and analgesic properties. Further identification, characterization and functional studies using individual compounds can act as a breakthrough in developing novel therapeutics against various pathogens including superbugs

Charge Accumulation, Recombination, and Their Associated Time Scale in Efficient (GUA)(x)(MA)(1-x)PbI3-Based Perovskite Solar Cells

Here, we study the influence of guanidinium (GUA) ions on the open-circuit voltage (V-oc) in the (GUA)(x)(MA)(1-x)PbI3 based perovskite solar cells. We demonstrate that incorporation of GUA forms electronic and ionic accumulation regions at the interface of the electron transporting layer and perovskite absorber layer. Our electrochemical impedance spectroscopy results prove that the formed accumulation region is associated with the enhanced surface charge capacitance and photovoltage. Furthermore, we also demonstrate the influence of the GUA ions on the enhanced interfacial and bulk electronic properties due to more efficient charge transfer between the bulk and interfaces and the reduced electronic defect energy levels

Optical and structure properties of CH

Methylammonium lead iodide doped with cesium (MA1–xCsxPbI3, x = 0, 0.03, 0.05, 0.1) thin films were prepared with and without chlorobenzene (CB). X-ray diffraction analysis applying the Rietveld refinement method is carried out, and the effect of Cs and CB on the lattice parameters, crystallite size, lattice microstrain, and dislocation density of the formed films is examined. SEM images with different magnifications are used to investigate the films' morphology and homogeneity. Adding CB reduced the number of pinholes and the grain size in the formed films. The UV-Vis-NIR spectroscopy technique was used to investigate the transmittance, reflectance, and absorbance spectra for Cs doped MAPbI3 with and without CB. In general, for Cs doped films, adding CB increases the film transmittance. The refractive index of 3% Cs doped film has the highest value among the films without CB. The optical bandgap, refractive index, and optical conductivity for films with CB are higher than those without CB for all doping Cs values. The influence of Cs doping and CB addition on the photoluminescence (PL) emitted spectra was studied using a PL set-up with a laser source of 532 nm

SrZnO nanostructures grown on templated <0001> Al2O3 substrates by pulsed laser deposition

The parameters of pulsed laser deposition (PLD) have been optimized to design different nanostructures of Strontium-alloyed zinc oxide (SrZnO). In this work, SrZnO nanostructures are grown on Al2O3 substrates via two-step templating/seeding approach. In the temperature range between 300 - 750 oC and O2 background pressures between 0.01 and 10 Torr, the growth conditions have been tailored to grow unique pointed leaf-like- and pitted olive-like nanostructures. Prior to the growth of the nanostructures, a thin SrZnO layer that serves as seed layer/template is first deposited on the Al2O3 substrates at ∼300oC and background oxygen pressure of 10 mTorr. The optical properties of the nanostructures were examined by UV/Vis spectroscopy and photoluminescence (PL), while the structures/morphologies were examined by SEM, TEM, and XRD. The alloyed SrZnO nanostructures, grown by ablating ZnO targets with 5, 10, 25% SrO contents, have in common a single-crystal hexagonal nanostructure with (0002) preferential orientation and have shown remarkable changes in the morphological and optical properties of the materials. To date, this is the only reported work on optimization of laser ablation parameters to design novel SrZnO nanostructures in the 5-25% alloying range, as most related Sr-doped ZnO studies were done below 7% doping. Although the physical properties of ZnO are modified via Sr doping, the mechanism remains unclear. The PLD-grown SrZnO nanostructures were directly grown onto the Al2O3 substrates; thus making these nanomaterials very promising for potential applications in biosensors, love-wave filters, solar cells, and ultrasonic oscillators

Engineering of Perovskite Materials Based on Formamidinium and Cesium Hybridization for High-Efficiency Solar Cells

Engineering the chemical composition of inorganic-organic hybrid perovskite materials is an effective strategy to boost the performance and operational stability of perovskite solar cells (PSCs). Among the diverse family of ABX(3) perovskites, methylammonium-free mixed A-site cation Cs(x)FA(1-x)PbI(3) perovskites appear as attractive light-absorber materials because of their optimum band gap, superior optoelectronic property, and good thermal stability. Here, we develop a simple and very effective one-step solution method for the preparation of high-quality (Cs)(x)(FA)(1-x)PbI3 perovskite films upon the addition of excess CsCl to the FAPbI(3) precursor solution. It is found that the addition of CsCl as a source of Cs cation instead of relevant addition of CsI to the parent perovskite solution increases effectively the grain size and film quality leading to improved charge mobility, reduced carrier recombination, and long carrier lifetime. The resultant mesoscopic perovskite devices exhibit a maximum efficiency of 20.60% with a stabilized power conversion efficiency of 19.85% and lower hysteresis compared to the reference device. This performance is among the highest reported for PSC devices incorporating mixed cation (Cs)(x)(FA)(1-x)PbI3 perovskites