Many indoor sensors are powered by artificial-light-harvesting photovoltaic (PV) cells. The performance evaluation and application of PV devices require irradiance measurement to determine input power. Standard solar irradiance meters provide measurements calibrated to sunlight spectra and do not have the low-light-level capability needed for indoor applications. Light meters, specifically designed for human visible artificial light applications, measure illuminance. This article describes a low-cost method to calculate irradiance from illuminance measurement of artificial light sources. An application example is provided.

Numerous sources provide methods to extract photovoltaic (PV) parameters from PV module datasheet values. The inputs are the number of series cells $\text{N}_{\mathrm {s}}$ , open circuit voltage $\text{V}_{\mathrm {oc}}$ , maximum power voltage $\text{V}_{\mathrm {mp}}$ , maximum power current $\text{I}_{\mathrm {mp}}$ , and short circuit current $\text{I}_{\mathrm {sc}}$ . The 5 Parameter Model solutions outputs are diode ideality factor $\eta $ , series resistance $\text{R}_{\mathrm {s}}$ , parallel resistance $\text{R}_{\mathrm {p}}$ , photon light current $\text{I}_{\mathrm {L}}$ , and diode reverse saturation current $\text{I}_{\mathrm {o}}$ . The parameter solution requires solving three simultaneous transcendental equations for $\eta $ , $\text{R}_{\mathrm {s}}$ , and $\text{R}_{\mathrm {p}}$ and additional calculations for $\text{I}_{\mathrm {L}}$ and $\text{I}_{\mathrm {o}}$ . One of the primary tenants of Systems Engineering, verification, was applied to parameter solution results to check for physical and model fitness. This manuscript provides novel methods to verify parameter results and applies them to available solutions.

We developed and applied an improved theoretical model to optimize characteristics of highly efficient textured solar cells (SCs). The model accounts for all recombination mechanisms, including nonradiative exciton recombination and recombination in the space-charge region (SCR). To compare the theoretical results with an experiment, we proposed empirical formula for the external quantum efficiency (EQE), which describes its experimental spectral dependencies near the absorption edge. The proposed approach allows modeling short-circuit current and photoconversion efficiency in the textured crystalline silicon solar cells. The theoretical results, compared to the experimental measurements, were used to optimize the key parameters of the SCs, such as the base thickness, doping level and others.

The Island Water Association owns and operates a brackish-water reverse osmosis (BWRO) desalination facility with a treated water capacity of 26,477 m3/d. The feedwater for the plant is pumped from two different aquifers via 16 production wells (24,888 m3/d). Both aquifers are semi-confined and they are recharged bottom upwards from the higher leakance lower confining unit, with limited recharge from the low leakage upper confining unit. The aquifer system is density stratified with increasing salinity with depth; the higher salinity water at depth, along with bottom upwards recharge, has led to a slow upward trend in salinity. In operation for nearly 38 y, the facility has increased the quantity of water pumped from the aquifer system. A solute transport model was conducted before the construction of the wellfield in 1982. The model generated a series of curves showing the projected increase in dissolved chloride concentration based on various pumping rates. Projections showed 80 y of increases with pumping and an eventual flattening of the curves. Over the past 20 y, dissolved chloride data collected from the 16 production wells show increase is a range from 0% to 60%. The overall feedwater, a blend of all wells, has shown increases in total dissolved solids from about 2,500 to 2,800 mg/L. These data values are much lower than the original model predicted, with both a lower starting concentration and a lower rate of increase. Based on the collected data, regression analysis, and a 20 y forward projection, the BWRO plant will be able to continue operation without a significant design change in the primary membrane process.

The standard for measuring solar irradiance utilizes the units of watts per meter squared (W/m 2 ). Irradiance meters are both costly and limited in the ability to measure low irradiance values. With a lower cost and higher sensitivity in low light conditions, light meters measure luminous flux per unit area (illuminance) utilizing the units of lumens per meter squared or lux (lx). An effective conversion factor between W/m 2 and lx would enable the use of light meters to evaluate photovoltaic performance under low solar irradiance conditions. A survey of the literature found no definitive and readily available “rule of thumb” conversion standard between solar irradiance and illuminance. Easy-to-find Internet sources contain conflicting and widely varying values ranging from 688449 to 21000 lx for 1000 W/m 2 (1 Sun) of solar irradiance. Peer-reviewed literature contains Luminous Efficacy equivalent values ranging from 21 to 131 lx per W/m 2 . This manuscript explores the relationship and establishes a theoretical and laboratory measurement guide for the conversion between solar irradiance and illuminance. The conversion factor includes standards data, equipment calibration accuracy, and uncertainty estimates. Solar Irradiance of 1 Sun (1000 W/m 2 ) for an LED-based solar simulator is (116 ± 3) klx and (122 ± 1) klx for outdoor sunlight.

Self‐organization of conjugated polymer such as poly(3‐hexylthiophene) (P3HT) causes directional anisotropy in the charge carrier mobility. In contrast to an edge‐on orientation formed in thin films of P3HT made by spin coating, in this study electrospray deposition rotates the orientation while producing nanopillar structures as a result of Coulombic fission and significant evaporation of solvent from the droplets. The nanostructured films are investigated by scanning electron microscopy. Due to substantial polymer–air interfaces oriented perpendicular to the substrate, P3HT molecules adopt a face‐on orientation with respect to the substrate plane that is confirmed by grazing incidence X‐ray diffraction. Additionally, enhanced crystallinity (29% increase) is confirmed by a redshift in the UV–vis absorption spectra. Because deposition by electrospray is a scalable nanomanufacturing method, these results inform the design of low‐cost device layers for large‐surface‐area applications such as light emitting diodes and photovoltaics. image

Solution-based chalcogenide glass films, traditionally deposited by spin-coating, are attractive for their potential use in chip-based devices operating in the mid-infrared and for ease of nanostructure incorporation. To overcome limitations of spin-coating such as excessive material waste and difficulty for scale-up, this paper introduces electrospray as a film deposition technique for solution-based chalcogenide glasses. Electrospray is shown to produce Ge23Sb7S70 films with similar surface quality and optical properties as films deposited by spin-coating. The advantages of electrospray deposition for nanoparticle dispersion, scalable and continuous manufacturing with little material waste, and comparable film quality to spin-coating make electrospray a promising deposition method for practical applications of chalcogenide glass films.

Nanostructured grating surfaces with groove widths less than 200 nm impose boundary conditions that frustrate the natural molecular orientational ordering within thin films of blended polymer semiconductor poly(3-hexlythiophene) and phenyl-C-61-butyric acid methyl ester, as revealed by grazing incidence X-ray scattering measurements. Polymer interactions with the grating sidewall strongly inhibit the polymer lamellar alignment parallel to the substrate typically found in planar films, in favor of alignment perpendicular to this orientation, resulting in a preferred equilibrium molecular configuration difficult to achieve by other means. Grating surfaces reduce the relative population of the parallel orientation from 30% to less than 5% in a 400 nm thick film. Analysis of in-plane X-ray scattering with respect to grating orientation shows polymer backbones highly oriented to within 10 degrees of parallel to the groove direction.

Determination of the three-dimensional order in thin nanostructured films remains challenging. Real-space imaging methods, including electron microscopies and scanning-probe methods, have difficulty reconstructing the depth of a film and suffer from limited statistical sampling. X-ray and neutron scattering have emerged as powerful complementary techniques but have substantial data collection and analysis challenges. This article describes a new method, grazing-incidence transmission small-angle X-ray scattering, which allows for fast scattering measurements that are not burdened by the refraction and reflection effects that have to date plagued grazing-incidence X-ray scattering. In particular, by arranging a sample/beam geometry wherein the scattering exits through the edge of the substrate, it is possible to record scattering images that are well described by straightforward (Born approximation) scattering models.

We realize a vertical channel polymer semiconductor field effect transistor architecture by confining the organic material within gratings of interdigitated trenches. The geometric space savings of a perpendicular channel orientation results in devices sourcing areal current densities in excess of 40 mA/cm2, using a one-volt supply voltage, and maintaining near-ideal device operating characteristics. Vertical channel transistors have a similar electronic mobility to that of planar devices using the same polymer semiconductor, consistent with a molecular reorientation within confining trenches we understand through X-ray scattering measurements.

Self-assembled block copolymer patterns may render more robust masks for plasma etch transfer through block-selective infiltration with metal oxides, affording opportunities for improved high contrast, high fidelity pattern transfer for sub-15 nm lithography in wafer-scale processes. However, block selective infiltration alters the self-assembled block copolymer latent image by changing feature size, duty cycle, and sidewall profile. The authors systematically investigate the effects of aluminum oxide infiltration of 27 and 41 nm pitch line/space patterns formed using polystyrene-b-poly(methyl methacrylate) block copolymers and evaluate the process compatibility with directed self assembly. The degree of image distortion depends on the amount of infiltrated material, with smaller amounts resulting in complete mask hardening and larger amounts shifting and collapsing pattern features. An attractive feature of the resulting oxide mask is the relatively smooth line edge roughness of the final transferred features into Si with a 3σ = 2.9 nm line edge roughness.

Self-organizing block copolymer thin films hold promise as a photolithography enhancement material for the 22-nm microelectronics technology generation and beyond, primarily because of their ability to form highly uniform patterns at the relevant nanometer-scale dimensions. Importantly, the materials are chemically similar to photoresists and can be implemented in synergy with photolithography. Beyond the challenges of achieving sufficient control of self-assembled pattern defectivity and feature roughness, block copolymer-based patterning requires creation of robust processes for transferring the polymer patterns into underlying electronic materials. Here, we describe research efforts in hardening block copolymer resist patterns using inorganic materials and high aspect ratio plasma etch transfer of self-assembled patterns to silicon using fluorine-based etch chemistries.

The photoconductivity of samples including both individual nanorods and bundles self-assembled from mesotetra(4-sulfonato-phenyl)porphine grows over several days of illumination by more than a factor of 15. It also shows a transition from an initially nonpersistent response (in which the conductivity goes to zero when illumination is removed) to a primarily persistent response (in which the conductivity decays slowly when illumination is removed). Application of a gate voltage results in an initial n-type response, most of which decays away slowly, even though the gate voltage is held constant. The addition of O-2 to the inert atmosphere surrounding the samples drastically reduces the persistent photoconductivity. When Xe is used instead of O-2, there is at most a slight reduction of conductivity. A qualitative model is presented, in which the conductivity changes are attributed to light-induced and gate-voltage-induced adsorption and desorption of O-2.

Submitted for the MAR09 Meeting of The American Physical Society Exploration of conductance peak splitting in carbon nanotube field effect transistors at critical field strengths JEFFREY D. STEPHENS, JEROME C. LICINI, Lehigh University , A.T. CHARLIE JOHNSON , DOUG R. STRACHAN , DANVERS E. JOHNSTON , SAM KHAMIS, University of Pennsylvania — Carbon nanotube field effect transistors were produced by chemical vapor deposition growth of nanotubes on oxidized silicon substrate. Samples were back gated on doped silicon and contacted with gold/chrome contacts. Conductance measurements were performed at low temperature and high magnetic field using a dilution refrigerator and a superconducting magnet. Data was taken at 0.5 Tesla increments from 0-11Tesla. The differential conductance (dI/dV) shows an interesting asymmetry with bias voltage as well as a near zero bias conductance peak. The near zero bias conductance peak demonstrates splitting at two critical magnetic field strengths on the 0.5T scale. These two critical regimes are further explored on a finer magnetic field scale. Jeff Stephens Lehigh University Date submitted: 25 Nov 2008 Electronic form version 1.4

meso-Tri(4-sulfonatophenyl)monophenylporphine (TPPS(3)) has one fewer sulfonate group than. meso-tetra(4-sulfonatophenyl)porphine (TPPS(4)), which has been shown to form well-defined, photoelectronically active nanorods. TPPS(3), when deposited via immersion and spin-drying, forms tapelike aggregates of two distinct heights. The larger width of these nanotapes (compared to TPPS(4) nanorods) is expected from the smaller charge of the monomer when it is dissolved in acidic solution. The deposition of nanotapes onto a substrate can be patterned to a limited extent by scratching the substrate prior to aggregation. The nanotapes exhibit photoconductive properties very similar to those of TPPS(4) nanorods, including growth of photoconductivity over hundreds of seconds, as well as photovoltaic activity with trainable polarity. However, they show a stronger memory of the slow growth of photoconductivity. The quantum efficiency of photoconductivity is approximately 10 times lower than that for TPPS(4) nanorods.

We present real-time transmission electron microscopy of nanogap formation by feedback controlled electromigration that reveals a remarkable degree of crystalline order. Crystal facets appear during feedback controlled electromigration indicating a layer-by-layer, highly reproducible electromigration process avoiding thermal runaway and melting. These measurements provide insight into the electromigration induced failure mechanism in sub-20 nm size interconnects, indicating that the current density at failure increases as the width decreases to approximately 1 nm.