Optimization of CdTe thin‐film solar cell efficiency using a sputtered,oxygenated CdS window layer

A major source of loss in cadmium sulfide/cadmium telluride (CdS/CdTe) solar cells results from light absorbed in the CdS window layer, which is not converted to electrical current. This film can be made more transparent by oxygen incorporation during sputter deposition at ambient temperature. Prior to this work, this material has not produced high‐efficiency devices on tin oxide‐coated soda‐lime‐glass substrates used industrially. Numerous devices were fabricated over a variety of process conditions to produce an optimized device. Although the material does not show a consistent increase in band gap with oxygenation, absorption in this layer can be virtually eliminated over the relevant spectrum, leading to an increase in short‐circuit current. Meanwhile, fill factor is maintained, and open‐circuit voltage increases relative to baseline devices with sublimated CdS. The trend of device parameters with oxygenation and thickness is consistent with an increasing conduction band offset at the window/CdTe interface. Optimization considering both initial efficiency and stability resulted in a National Renewable Energy Laboratory verified 15.2%‐efficient cell on 3.2‐mm soda‐lime glass. This window material was shown to be compatible with SnO₂‐based transparent conducting oxide and high resistance transparent coated substrates using in‐line compatible processes. Copyright © 2015 John Wiley & Sons, Ltd     

Improved estimation of PM2.5 brown carbon contributions to filter light attenuation

Multiwavelength light attenuation measurements have been acquired as part of thermal/optical carbon analysis in the U.S.Chemical Speciation Network(CSN)and the ...     

Dependence of the moduli of random bimodal networks on chain-length distribution

There have now been a number of experimental studies on the preparation and elastomeric properties of random bimodal networks of polydimethylsiloxane. The mole per cent of the short chains and their molecular masses covered a wide range, thus resulting in various polydisperse chain-length distributions. The networks were studied with regard to their stress-strain isotherms in elongation, and values of their moduli in the large-deformation (phantom) limit were found to depend on the chain-length distribution. This Important result is in disagreement with phantom network theory, which assumes the elastic modulus is dependent only on the mean value of chain lengths such that the cycle rank of the network is preserved. The effective functionality of the long chains was found to depend on the number of short chains present. Better agreement with experiment was obtained when account was taken of the connectivity of the very short chains, in what is essentially a bimodal distribution of both network chain lengths and cross-link functionalities. Relevant here is the fact that as the degree of chemical cross-linking Increases, the shear modulus G moves away from the affine limit, toward the phantom limit. This increase toward phantom behavior is presumably due to the fact that the mutual interspersion of chains is less when the chains are shorter, even in the small-strain region.     

Investigation of Metastable Low Dimensional Halometallates

The solvothermal synthesis, structure determination and optical characterization of five new metastable halometallate compounds, [1,10-phenH][Pb_3.5I₈] (1), [1,10-phenH₂][Pb₅I₁₂]·(H₂O) (2), [1,10-phen][Pb₂I₄] (3), [1,10-phen]₂[Pb₅Br₁₀] (4) and [1,10-phenH][SbI₄]·(H₂O) (5), are reported. The materials exhibit rich structural diversity and exhibit structural dimensionalities that include 1D chains, 2D sheets and 3D frameworks. The optical spectra of these materials are consistent with bandgaps ranging from 2.70 to 3.44 eV. We show that the optical behavior depends on the structural dimensionality of the reported materials, which are potential candidates for semiconductor applications.     

Stereoelectronic Features of a Complex Ketene Dimerization Reaction

The amidation reaction of a tetrahydroisoquinolin-1-one-4-carboxylic acid is a key step in the multi-kilogram-scale preparation of the antimalarial drug SJ733, now in phase 2 clinical trials. In the course of investigating THIQ carboxamidations, we found that propanephosphonic acid anhydride (T3P) is an effective reagent, although the yield and byproducts vary with the nature and quantity of the base. As a control, the T3P reaction of a 3-(2-thienyl) THIQ was performed in the absence of the amine, and the products were characterized: among them are three dimeric allenes and two dimeric lactones. A nucleophile-promoted ketene dimerization process subject to subtle steric and stereoelectronic effects accounts for their formation. Two novel monomeric products, a decarboxylated isoquinolone and a purple, fused aryl ketone, were also isolated, and mechanisms for their formation from the ketene intermediate are proposed.     

NMR imaging of solid polymers: Strategies for chemical-shift selectivity

One reason that the solid-state imaging field is exciting is because of its potential to provide spatially resolved chemical information from deep inside a solid sample. To achieve this goal, methods are needed which exploit the many NMR parameters to generate image contrast. We describe two strategies for employing the chemical-shift anisotropy as a contrast mechanism in images of abundant nuclei in solid polymers. We illustrate these approaches with images which map spatial variations of molecular orientation in samples of polytetrafluoroethylene.     

The zeolate ligand; zeolite encapsulated semiconductor nanomaterials

Consolidation of the results of structural, spectroscopic and kinetic studies of a range of intrazeolite guests and their reactions have led to the development of the “crown ether-zeolite ligand analogy” and the concept of the “zeolate” as a macrospheroidal or macrocylindrical multidentate anionic ligand. This view of a zeolite cavity or channel as a collection of interconnected aluminosilicate crown ether-like building blocks, permits a coordination chemistry approach to the understanding of metal-ligand bonding (capping, anchoring, complexing, stabilizing and structure-directing phenomena) in a variety of zeolite guest-host inclusion systems. In this paper we focus attention on the role that the zeolate ligand plays in the organization of semiconductor precursors and their assembly to semiconductor nanoclusters with particular reference to II-VI nanomaterials.     

Influence of connectivity and porosity on ligand-based luminescence in zinc metal-organic frameworks

Applications of metal-organic frameworks (MOFs) require close correlation between their structure and function. We describe the preparation and characterization of two zinc MOFs based on a flexible and emissive linker molecule, stilbene, which retains its luminescence within these solid materials. Reaction of trans-4,4'-stilbene dicarboxylic acid and zinc nitrate in N,N-dimethylformamide (DMF) yielded a dense 2-D network, 1, featuring zinc in both octahedral and tetrahedral coordination environments connected by trans-stilbene links. Similar reaction in N,N-diethylformamide (DEF) at higher temperatures resulted in a porous, 3-D framework structure, 2. This framework consists of two interpenetrating cubic lattices, each featuring basic zinc carboxylate vertices joined by trans-stilbene, analogous to the isoreticular MOF (IRMOF) series. We demonstrate that the optical properties of both 1 and 2 correlate with the local ligand environments observed in the crystal structures. Steady-state and time-resolved spectroscopic measurements reveal that the stilbene linkers in the dense structure 1 exhibit a small degree of interchromophore coupling. In contrast, the stilbenoid units in 2 display very little interaction in this low-density 3-D framework, with excitation and emission spectra characteristic of monomeric stilbenes, similar to the dicarboxylic acid in dilute solution. In both cases, the rigidity of the stilbene linker increases upon coordination to the inorganic units through inhibition of torsion about the central ethylene bond, resulting in luminescent crystals with increased emission lifetimes compared to solutions of trans-stilbene. The emission spectrum of 2 is found to depend on the nature of the incorporated solvent molecules, suggesting use of this or related materials in sensor applications.     

Rh(I)-catalyzed carbonylative ring opening of diazabicycles with acyl anion equivalents

A catalytic desymmetrization of strained alkenes by ring-opening of meso-diazabicycles with acyl anion nucleophiles is reported. Densely functionalized trans-1,2-hydrazinoacyl cyclopentene building blocks are obtained stereoselectively. The acyl anion equivalent is generated in situ under very mild conditions from readily available organoboron precursors.