Charge-Carrier Dynamics in 2D Hybrid Metal–Halide Perovskites

Hybrid metal–halide perovskites are promising new materials for use in solar cells; however, their chemical stability in the presence of moisture remains a significant drawback. Quasi two-dimensional (2D) perovskites that incorporate hydrophobic organic interlayers offer improved resistance to degradation by moisture, currently still at the cost of overall cell efficiency. To elucidate the factors affecting the optoelectronic properties of these materials, we have investigated the charge transport properties and crystallographic orientation of mixed methylammonium (MA)–phenylethylammonium (PEA) lead iodide thin films as a function of the MA-to-PEA ratio and, thus, the thickness of the “encapsulated” MA lead–halide layers. We find that monomolecular charge-carrier recombination rates first decrease with increasing PEA fraction, most likely as a result of trap passivation, but then increase significantly as excitonic effects begin to dominate for thin confined layers. Bimolecular and Auger recombination rate constants are found to be sensitive to changes in electronic confinement, which alters the density of states for electronic transitions. We demonstrate that effective charge-carrier mobilities remain remarkably high (near 10 cm2V−1s−1) for intermediate PEA content and are enhanced for preferential orientation of the conducting lead iodide layers along the probing electric field. The trade-off between trap reduction, electronic confinement, and layer orientation leads to calculated charge-carrier diffusion lengths reaching a maximum of 2.5 μm for intermediate PEA content (50%)

Evaluating lithium diffusion mechanisms in the complex spinel Li2NiGe3O8

Lithium-ion diffusion mechanisms in the complex spinel Li2NiGe3O8 have been investigated using solid-state NMR, impedance, and muon spectroscopies. Partial occupancy of migratory interstitial 12d sites is shown to occur at lower temperatures than previously reported. Bulk activation energies for Li+ ion hopping range from 0.43 ± 0.03 eV for powdered samples to 0.53 ± 0.01 eV for samples sintered at 950 °C for 24 h, due to the loss of Li during sintering at elevated temperatures. A lithium diffusion coefficient of 3.89 × 10−12 cm2 s−1 was calculated from muon spectroscopy data for Li2NiGe3O8 at 300 K

Raman Spectrum of the Organic-Inorganic Halide Perovskite CH3NH3PbI3 from First Principles and High-Resolution Low-Temperature Raman Measurements

We investigate the Raman spectrum of the low-temperature orthorhombic phase of the organic-inorganic halide perovskite CH3NH3PbI3, by combining first-principles calculations with high-resolution low-temperature Raman measurements. We find good agreement between theory and experiment, and successfully assign each of the Raman peaks to the underlying vibrational modes. In the low-frequency spectral range (below 60 cm1) we assign the prominent Raman signals at 26, 32, 42 and 49 cm1 to the Pb-I-Pb bending modes with either Ag or B2g symmetry, and the signal at 58 cm1 to the librational mode of the organic cation. Owing to their significant intensity, we propose that these peaks can serve as clear markers of the vibrations of the [PbI3] network and of the CH3NH+ 3 cations in this perovskite, respectively. In particular, the ratios of the intensities of these peaks might be used to monitor possible deviations from the ideal stoichiometry of CH3NH3PbI3

Perovskite-perovskite tandem photovoltaics with optimized bandgaps

We demonstrate four and two-terminal perovskite-perovskite tandem solar cells with ideally matched bandgaps. We develop an infrared absorbing 1.2eV bandgap perovskite, $FA_{0.75}Cs_{0.25}Sn_{0.5}Pb_{0.5}I_3$, that can deliver 14.8 % efficiency. By combining this material with a wider bandgap $FA_{0.83}Cs_{0.17}Pb(I_{0.5}Br_{0.5})_3$ material, we reach monolithic two terminal tandem efficiencies of 17.0 % with over 1.65 volts open-circuit voltage. We also make mechanically stacked four terminal tandem cells and obtain 20.3 % efficiency. Crucially, we find that our infrared absorbing perovskite cells exhibit excellent thermal and atmospheric stability, unprecedented for Sn based perovskites. This device architecture and materials set will enable 'all perovskite' thin film solar cells to reach the highest efficiencies in the long term at the lowest costs

Hospitalized cancer patients with severe sepsis: analysis of incidence, mortality, and associated costs of care

INTRODUCTION: Infection is an important complication in cancer patients, which frequently leads to or prolongs hospitalization, and can also lead to acute organ dysfunction (severe sepsis) and eventually death. While cancer patients are known to be at higher risk for infection and subsequent complications, there is no national estimate of the magnitude of this problem. Our objective was to identify cancer patients with severe sepsis and to project these numbers to national levels. METHODS: Data for all 1999 hospitalizations from six states (Florida, Massachusetts, New Jersey, New York, Virginia, and Washington) were merged with US Census data, Centers for Disease Control vital statistics and National Cancer Institute, Surveillance, Epidemiology, and End Results initiative cancer prevalence data. Malignant neoplasms were identified by International Classification of Disease (ninth revision, clinical modification) (ICD-9-CM) codes (140–208), and infection and acute organ failure were identified from ICD-9-CM codes following Angus and colleagues. Cases were identified as a function of age and were projected to national levels. RESULTS: There were 606,176 cancer hospitalizations identified, with severe sepsis present in 29,795 (4.9%). Projecting national estimates for the US population, cancer patients account for 126,209 severe sepsis cases annually, or 16.4 cases per 1000 people with cancer per year. The inhospital mortality for cancer patients with severe sepsis was 37.8%. Compared with the overall population, cancer patients are much more likely to be hospitalized (relative risk, 2.77; 95% confidence interval, 2.77–2.78) and to be hospitalized with severe sepsis (relative risk, 3.96; 95% confidence interval, 3.94–3.99). Overall, severe sepsis is associated with 8.5% (46,729) of all cancer deaths at a cost of $3.4 billion per year. CONCLUSION: Severe sepsis is a common, deadly, and costly complication in cancer patients

Genome-wide analysis of long noncoding RNA stability

Transcriptomic analyses have identified tens of thousands of intergenic, intronic, and cis-antisense long noncoding RNAs (lncRNAs) that are expressed from mammalian genomes. Despite progress in functional characterization, little is known about the post-transcriptional regulation of lncRNAs and their half-lives. Although many are easily detectable by a variety of techniques, it has been assumed that lncRNAs are generally unstable, but this has not been examined genome-wide. Utilizing a custom noncoding RNA array, we determined the half-lives of ∼800 lncRNAs and ∼12,000 mRNAs in the mouse Neuro-2a cell line. We find only a minority of lncRNAs are unstable. LncRNA half-lives vary over a wide range, comparable to, although on average less than, that of mRNAs, suggestive of complex metabolism and widespread functionality. Combining half-lives with comprehensive lncRNA annotations identified hundreds of unstable (half-life 16 h). Analysis of lncRNA features revealed that intergenic and cis-antisense RNAs are more stable than those derived from introns, as are spliced lncRNAs compared to unspliced (single exon) transcripts. Subcellular localization of lncRNAs indicated widespread trafficking to different cellular locations, with nuclear-localized lncRNAs more likely to be unstable. Surprisingly, one of the least stable lncRNAs is the well-characterized paraspeckle RNA Neat1, suggesting Neat1 instability contributes to the dynamic nature of this subnuclear domain. We have created an online interactive resource (http://stability. matticklab.com) that allows easy navigation of lncRNA and mRNA stability profiles and provides a comprehensive annotation of ∼7200 mouse lncRNAs

Risk-based inspection as a cost-effective strategy to reduce human exposure to cysticerci of Taenia saginata in low-prevalence settings

Taenia saginata cysticercus is the larval stage of the zoonotic parasite Taenia saginata, with a life-cycle involving both cattle and humans. The public health impact is considered low. The current surveillance system, based on post-mortem inspection of carcasses has low sensitivity and leads to considerable economic burden. Therefore, in the interests of public health and food production efficiency, this study aims to explore the potential of risk-based and cost-effective meat inspection activities for the detection and control of T. saginata cysticercus in low prevalence settings