Light Management in Organic Photovoltaics Processed in Ambient Conditions Using ZnO Nanowire and Antireflection Layer with Nanocone Array.

Low carrier mobility and lifetime in semiconductor polymers are some of the main challenges facing the field of organic photovoltaics (OPV) in the quest for efficient devices with high current density. Finding novel strategies such as device structure engineering is a key pathway toward addressing this issue. In this work, the light absorption and carrier collection of OPV devices are improved by employment of ZnO nanowire (NW) arrays with an optimum NW length (50 nm) and antireflection (AR) film with nanocone structure. The optical characterization results show that ZnO NW increases the transmittance of the electron transporting layer as well as the absorption of the polymer blend. Moreover, the as-deposited polymer blend on the ZnO NW array shows better charge transfer as compared to the planar sample. By employing PC70BM:PV2000 as a promising air-stable active-layer, power conversion efficiencies of 9.8% and 10.1% are achieved for NW devices without and with an AR film, indicating 22.5% and 26.2% enhancement in PCE as compared to that of planar device. Moreover, it is shown that the AR film enhances the water-repellent ability of the OPV device.

Coherent single-photon emission from colloidal lead halide perovskite quantum dots.

Chemically made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210-picosecond radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Our results present a starting point for the rational design of lead halide perovskite-based quantum emitters that have fast emission, wide spectral tunability, and scalable production and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.

Photochemical Control of Exciton Superradiance in Light-Harvesting Nanotubes.

Photosynthetic antennae and organic electronic materials use topological, structural, and molecular control of delocalized excitons to enhance and direct energy transfer. Interactions between the transition dipoles of individual chromophore units allow for coherent delocalization across multiple molecular sites. This delocalization, for specific geometries, greatly enhances the transition dipole moment of the lowest energy excitonic state relative to the chromophore and increases its radiative rate, a phenomenon known as superradiance. In this study, we show that ordered, self-assembled light-harvesting nanotubes (LHNs) display excitation-induced photobrightening and photodarkening. These changes in quantum yield arise due to changes in energetic disorder, which in turn increases/decreases excitonic superradiance. Through a combination of experiment and modeling, we show that intense illumination induces different types of chemical change in LHNs that reproducibly alter absorption and fluorescence properties, indicating control over excitonic delocalization. We also show that changes in spectral width and shift can be sensitive measures of system dimensionality, illustrating the mixed 1-2D nature of LHN excitons. Our results demonstrate a path forward for mastery of energetic disorder in an excitonic antenna, with implications for fundamental studies of coherent energy transport.

Establishing the overlap of IONP quantification with echo and echoless MR relaxation mapping.

PURPOSE: Iron-oxide nanoparticles (IONPs) have shown tremendous utility for enhancing image contrast and delivering targeted therapies. Quantification of IONPs has been demonstrated at low concentrations with gradient echo (GRE) and spin echo (SE), and at high concentrations with echoless sequences such as swept imaging with Fourier transform (SWIFT). This work examines the overlap of IONP quantification with GRE, SE, and SWIFT. METHODS: The limit of quantification of GRE, SE, inversion-recovery GRE, and SWIFT sequences was assessed using IONPs at a concentration range of 0.02 to 89.29 mM suspended in 1% agarose. Empirically derived limits of quantification were compared with International Union of Pure and Applied Chemistry definitions. Both commercial and experimental IONPs were used. RESULTS: All three IONPs assessed demonstrated an overlap of concentration quantification with GRE, SE, and SWIFT sequences. The largest dynamic range observed was 0.004 to 35.7 mM with Feraheme. CONCLUSIONS: The metrics established allow upper and lower quantitative limitations to be estimated given the relaxivity characteristics of the IONP and the concentration range of the material to be assessed. The methods outlined in this paper are applicable to any pulse sequence, IONP formulation, and field strength. Magn Reson Med 79:1420-1428, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Predictable Heating and Positive MRI Contrast from a Mesoporous Silica-Coated Iron Oxide Nanoparticle.

Iron oxide nanoparticles have great potential as diagnostic and therapeutic agents in cancer and other diseases; however, biological aggregation severely limits their function in vivo. Aggregates can cause poor biodistribution, reduced heating capability, and can confound their visualization and quantification by magnetic resonance imaging (MRI). Herein, we demonstrate that the incorporation of a functionalized mesoporous silica shell can prevent aggregation and enable the practical use of high-heating, high-contrast iron oxide nanoparticles in vitro and in vivo. Unmodified and mesoporous silica-coated iron oxide nanoparticles were characterized in biologically relevant environments including phosphate buffered saline, simulated body fluid, whole mouse blood, lymph node carcinoma of prostate (LNCaP) cells, and after direct injection into LNCaP prostate cancer tumors in nude mice. Once coated, iron oxide nanoparticles maintained colloidal stability along with high heating and relaxivity behaviors (SARFe = 204 W/g Fe at 190 kHz and 20 kA/m and r1 = 6.9 mM(-1) s(-1) at 1.4 T). Colloidal stability and minimal nonspecific cell uptake allowed for effective heating in salt and agarose suspensions and strong signal enhancement in MR imaging in vivo. These results show that (1) aggregation can lower the heating and imaging performance of magnetic nanoparticles and (2) a coating of functionalized mesoporous silica can mitigate this issue, potentially improving clinical planning and practical use.

Characterization of Magnetic Nanoparticles in Biological Matrices.

This Feature describes several methods for the characterization of magnetic nanoparticles in biological matrices such as cells and tissues. The Feature focuses on sample preparation and includes several case studies where multiple techniques were used in conjunction.

Dark field transmission electron microscopy as a tool for identifying inorganic nanoparticles in biological matrices.

Dark field transmission electron microscopy has been applied herein to visualize the interactions of inorganic nanomaterials with biological systems. This new application of a known technique addresses a deficiency in status quo visualization techniques. High resolution and low noise images can be acquired to locate and identify crystalline nanoparticles in complex biological matrices. Moreover, through the composition of multiple images taken at different angular beam tilts, it is possible to image a majority of nanoparticles present at a site in dark field mode. This facilitates clarity regarding the internalization of nanomaterials in cellular systems. In addition, comparing dark field images recorded at different angular tilts yields insight into the character of nanoparticle faceting.

Crystal structure of (1S,2R,6R,7R,8S,12S)-4,10,17-triphenyl-15-thia-4,10-diaza-penta-cyclo[5.5.5.0(1,16).0(2,6).0(8,12)]hepta-deca-13,16-diene-3,5,9,11-tetrone p-xylene hemisolvate.

The title tetrone compound, C32H22N2O4S· 0.5C8H10, is the major product (50% yield) of an attempted Diels-Alder reaction of 2-(α-styr-yl)thio-phene with N-phenyl-male-imide (2 equivalents) in toluene. Recrystallization of the resulting powder from p-xylene gave the title hemisolvate; the p-xylene mol-ecule is located about an inversion center. In the crystal, the primary tetrone contacts are between a carbonyl O atom and the four flagpole H atoms of the bi-cyclo-[2.2.2]octene core, forming chains along [001].

Simulator sickness during driving simulation studies.

While driving simulators are a valuable tool for assessing multiple dimensions of driving performance under relatively safe conditions, researchers and practitioners must be prepared for participants that suffer from simulator sickness. This paper describes multiple theories of motion sickness and presents a method for assessing and reacting to simulator sickness symptoms. Results showed that this method identified individuals who were unable to complete a driving simulator study due to simulator sickness with greater than 90% accuracy and that older participants had a greater likelihood of simulator sickness than younger participants. Possible explanations for increased symptoms experienced by older participants are discussed as well as implications for research ethics and simulator sickness prevention.