633 research outputs found
A Simple, Quick, and Precise Procedure for the Determination of Water in Organic Solvents
A procedure for the UV/VIS-spectroscopic determination of water by the use of a solvatochromic pyridiniumphenolate betaine is given. The water content of organic solvents is calculated by a two parameter equation from λmax of the dye. A typical, detection limit is of the order of 1 mg in 1 ml solvent for routine spectrometers. The parameters for the determination of water are given for a number of commonly used solvents
Photoreflectance analysis of a GaInP/GaInAs/Ge multijunction solar cell
We have analyzed the photoreflectance spectra of a GaInP/GaInAs/Ge triple junction solar cell. The spectra reveal signatures from the window layer and middle and top subcells included in the stack. Additional contributions from the multilayer buffer introduced between the mismatched bottom and middle cells have been detected. FranzâKeldysh oscillations (FKOs) dominate the spectra above the fundamental bandgaps of the GaInP and GaInAs absorbers. From the FKO analysis, we have estimated the dominant electric fields within each subcell. In light of these results, photoreflectance is proposed as a useful diagnostic tool for quality assessment of multijunction structures prior to completion of the device or at earlier stages during its processing
Structure-Function Relations in Oxaloacetate Decarboxylase Complex. Fluorescence and Infrared Approaches to Monitor Oxomalonate and Na+ Binding Effect
ions across the membrane, which drives endergonic membrane reactions such as ATP synthesis, transport and motility. OAD is a membrane-bound enzyme composed of α, ÎČ and Îł subunits. The α subunit contains the carboxyltransferase catalytic site. characteristic of a high content of α helix structures. Addition of oxomalonate induced a shift of the amide-I band of OAD toward higher wavenumbers, interpreted as a slight decrease of ÎČ sheet structures and a concomitant increase of α helix structures. Oxomalonate binding to αγand α subunits also provoked secondary structure variations, but these effects were negligible compared to OAD complex. alters the tryptophan environment of the ÎČ subunit, consistent with the function of these subunits within the enzyme complex. Formation of a complex between OAD and its substrates elicits structural changes in the α-helical as well as ÎČ-strand secondary structure elements
Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency
Recent rapid progress in efficiencies for solar water splitting by
photoelectrochemical devices has enhanced its prospects to enable storable
renewable energy. Efficient solar fuel generators all use tandem photoelectrode
structures, and advanced integrated devices incorporate corrosion protection
layers as well as heterogeneous catalysts. Realization of near thermodynamic
limiting performance requires tailoring the energy band structure of the
photoelectrode and also the optical and electronic properties of the surface
layers exposed to the electrolyte. Here, we report a monolithic device
architecture that exhibits reduced surface reflectivity in conjunction with
metallic Rh nanoparticle catalyst layers that minimize parasitic light
absorption. Additionally, the anatase TiO2 protection layer on the photocathode
creates a favorable internal band alignment for hydrogen evolution. An initial
solar-to-hydrogen efficiency of 19.3 % is obtained in acidic electrolyte and an
efficiency of 18.5 % is achieved at neutral pH condition (under simulated
sunlight)
Performance analysis of AlGaAs/GaAs tunnel junctions for ultra-high concentration photovoltaics
An n(++)-GaAs/p(++)-AlGaAs tunnel junction with a peak current density of 10 100Acm(-2) is developed. This device is a tunnel junction for multijunction solar cells, grown lattice-matched on standard GaAs or Ge substrates, with the highest peak current density ever reported. The voltage drop for a current density equivalent to the operation of the multijunction solar cell up to 10 000 suns is below 5 mV. Trap-assisted tunnelling is proposed to be behind this performance, which cannot be justified by simple band-to-band tunnelling. The metal-organic vapour-phase epitaxy growth conditions, which are in the limits of the transport-limited regime, and the heavy tellurium doping levels are the proposed origins of the defects enabling trap-assisted tunnelling. The hypothesis of trap-assisted tunnelling is supported by the observed annealing behaviour of the tunnel junctions, which cannot be explained in terms of dopant diffusion or passivation. For the integration of these tunnel junctions into a triple-junction solar cell, AlGaAs barrier layers are introduced to suppress the formation of parasitic junctions, but this is found to significantly degrade the performance of the tunnel junctions. However, the annealed tunnel junctions with barrier layers still exhibit a peak current density higher than 2500Acm(-2) and a voltage drop at 10 000 suns of around 20 mV, which are excellent properties for tunnel junctions and mean they can serve as low-loss interconnections in multijunction solar cells working at ultra-high concentrations
Rhodium(II)-catalyzed stereocontrolled synthesis of dihydrofuran-3-imines from 1-Tosyl-1,2,3-triazoles
Rhodium(II) acetate catalyzes the denitrogenative transformation of 5-substituted and 4,5-disubstituted 1-sulfonyl-1,2,3-triazoles with pendent allyl and propargyl ether motifs to oxonium ylides that undergo [2,3]-sigmatropic rearrangement to give substituted dihydrofuran-3-imines in high yield and diastereoselectivity
Ein neues, unkompliziertes Verfahren zur Bestimmung der Zusammensetzung binĂ€rer FlĂŒssigkeitsgemische
Ein neues Verfahren zur Bestimmung der Zusammensetzung binĂ€rer FlĂŒssigkeitsgemische mit Hilfe solvatochromer Farbstoffe wird beschrieben. Die Analyse erfolgt durch einfache UV/VIS-Absorptionsmessung und ist unter Verwendung einer Zwei-Parameter-Gleichung ein exakter Schnelltest
On the benchmarking of multi-junction photoelectrochemical fuel generating devices
We discuss benchmarking considerations for multi-junction solar fuel absorbers and investigate the effects of spectral shaping by catalyst nanoparticles on design criteria.MMM acknowledges funding from the fellowship programme of the German National Academy of Sciences Leopoldina, grant LPDS 2015-09
Spectral splitting photovoltaics using perovskite and wideband dye-sensitized solar cells
The extension of the light absorption of photovoltaics into the near-infrared region is important to increase the energy conversion efficiency. Although the progress of the lead halide perovskite solar cells is remarkable, and high conversion efficiency of >20% has been reached, their absorption limit on the long-wavelength side is similar to 800 nm. To further enhance the conversion efficiency of perovskite-based photovoltaics, a hybridized system with near-infrared photovoltaics is a useful approach. Here we report a panchromatic sensitizer, coded DX3, that exhibits a broad response into the near-infrared, up to similar to 1100 nm, and a photocurrent density exceeding 30 mA cm(-2) in simulated air mass 1.5 standard solar radiation. Using the DX3-based dye-sensitized solar cell in conjunction with a perovskite cell that harvests visible light, the hybridized mesoscopic photovoltaics achieved a conversion efficiency of 21.5% using a system of spectral splitting.open0
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