a-SiGe:H Deposited by Hot-Wire CVD Using a Tantalum Filament Operated at Low Temperature

We report the deposition of optimum-quality a-SiGe:H and a-Si:H by the hot-wire chemical vapor deposition (HWCVD) technique using a tantalum filament operating at a low temperature. We gauge the material quality of the a-SiGe:H films by comparing infrared, small-angle x-ray scattering, photocapacitance, and conductivity results to those presented elsewhere

Amorphous Transparent Conducting Oxides (TCOs) Deposited at T 100<= ..deg.. C

The summary of this report is that amorphous InZnO (a-IZO) is a very versatile TCO with: (1) low process temperatures ({approx} 100 C); (2) easy to make by sputtering; (3) excellent optical and electronic properties; (4) very smooth etchable films; and (5) remarkable thermal processing stability

Elucidating the role of ferrous ion cocatalyst in enhancing dilute acid pretreatment of lignocellulosic biomass

<p>Abstract</p> <p>Background</p> <p>Recently developed iron cocatalyst enhancement of dilute acid pretreatment of biomass is a promising approach for enhancing sugar release from recalcitrant lignocellulosic biomass. However, very little is known about the underlying mechanisms of this enhancement. In the current study, our aim was to identify several essential factors that contribute to ferrous ion-enhanced efficiency during dilute acid pretreatment of biomass and to initiate the investigation of the mechanisms that result in this enhancement.</p> <p>Results</p> <p>During dilute acid and ferrous ion cocatalyst pretreatments, we observed concomitant increases in solubilized sugars in the hydrolysate and reducing sugars in the (insoluble) biomass residues. We also observed enhancements in sugar release during subsequent enzymatic saccharification of iron cocatalyst-pretreated biomass. Fourier transform Raman spectroscopy showed that major peaks representing the C-O-C and C-H bonds in cellulose are significantly attenuated by iron cocatalyst pretreatment. Imaging using Prussian blue staining indicated that Fe²⁺ions associate with both cellulose/xylan and lignin in untreated as well as dilute acid/Fe²⁺ion-pretreated corn stover samples. Analyses by scanning electron microscopy and transmission electron microscopy revealed structural details of biomass after dilute acid/Fe²⁺ion pretreatment, in which delamination and fibrillation of the cell wall were observed.</p> <p>Conclusions</p> <p>By using this multimodal approach, we have revealed that (1) acid-ferrous ion-assisted pretreatment increases solubilization and enzymatic digestion of both cellulose and xylan to monomers and (2) this pretreatment likely targets multiple chemistries in plant cell wall polymer networks, including those represented by the C-O-C and C-H bonds in cellulose.</p

Electro-Optical Characterization at NREL

One of the core issues in all of the photovoltaics technologies is relating PV device performance to the methods and materials used to produce them. Due to the nature of PV devices, the electronic and optical properties of the materials are key to device performance. The relationship between materials growth and processing, the resulting electro-optical properties, and device performance can be extremely complex and difficult to determine without direct measurement of these properties. Accurate and timely measurement of the electro-optical properties as a function of device processing provides researchers and manufacturers with the knowledge they need to troubleshoot problems and develop the knowledge base necessary for reducing cost, maximizing efficiency, improving reliability, and enhancing manufacturability. The Electro-optical Characterization Team at NREL provides this support for all internal and external projects funded by the PV Program

Optimization of Conductivity and Transparency in Amorphous In-Zn-O Transparent Conductors: Preprint

Amorphous mixed metal oxide TCOs are of increasing interest due to the excellent opto-electronic properties and smoothness (RRMS < 0.5 nm) obtained for sputtered films deposited at less than 100 ..deg..C. Here, we have investigated the combined materials phase space of oxygen stoichiometry and metals composition (In:Zn ratio) and made two key discoveries

Oxynitride Thin Film Barriers for PV Packaging

Dielectric thin-film barrier and adhesion-promoting layers consisting of silicon oxynitride materials (SiOxNy, with various stoichiometry) were investigated. For process development, films were applied to glass (TCO, conductive SnO2:F; or soda-lime), polymer (PET, polyethylene terephthalate), aluminized soda-lime glass, or PV cell (a-Si, CIGS) substrates. Design strategy employed de-minimus hazard criteria to facilitate industrial adoption and reduce implementation costs for PV manufacturers or suppliers. A restricted process window was explored using dilute compressed gases (3% silane, 14% nitrous oxide, 23% oxygen) in nitrogen (or former mixtures, and 11.45% oxygen mix in helium and/or 99.999% helium dilution) with a worst-case flammable and non-corrosive hazard classification. Method employed low radio frequency (RF) power, less than or equal to 3 milliwatts per cm2, and low substrate temperatures, less than or equal to 100 deg C, over deposition areas less than or equal to 1000 cm2. Select material properties for barrier film thickness (profilometer), composition (XPS/FTIR), optical (refractive index, %T and %R), mechanical peel strength and WVTR barrier performance are presented

Combinatorial Exploration of Novel Transparent Conducting Oxide Materials

High-throughput combinatorial approaches have been used for the discovery and optimization of transparent conducting oxide (TCO) materials for PV applications. We report on current investigations in In-Zn-O, In-Ti-O and In-Mo-O systems. The InZnO system is shown to be amorphous in the best conducting range with a conductivity of ~ 3000 &#937;-cm-1 for 50%-70% In/Zn. The amorphous InZnO films are very smooth (2..ANG.. rms). In-Ti-O is found to be an excellent high-mobility TCO with mobilities of greater than 80 cm2/v-sec and conductivities of more than 6000 &#937;-cm-1 for sputtered thin film materials

Direct patterning of periodic semiconductor nanostructures using single-pulse nanosecond laser interference

We demonstrate an effective method for fabricating large area periodic two-dimensional semiconductor nanostructures by means of single-pulse laser interference. Utilizing a pulsed nanosecond laser with a wavelength of 355 nm, precisely ordered square arrays of nanoholes with a periodicity of 300 nm were successfully obtained on UV photoresist and also directly via a resist-free process onto semiconductor wafers. We show improved uniformity using a beam-shaping system consisting of cylindrical lenses with which we can demonstrate highly regular arrays over hundreds of square micrometers. We propose that our novel observation of direct pattern transfer to GaAs is due to local congruent evaporation and subsequent droplet etching of the surface. The results show that single-pulse interference can provide a rapid and highly efficient route for the realization of wide-area periodic nanostructures on semiconductors and potentially on other engineering materials

Laser structuring of thin-film solar cells on polymers

A permanent growth of the thin-film electronics market stimulates the development of versatile technologies for patterning thin-film materials on flexible substrates. High repetition rate lasers with a short pulse duration offer new possibilities for high efficiency structuring of conducting, semi-conducting and isolating films. Lasers with the picosecond pulse duration were applied in structuring the complex multilayered Cu(InGa)Se2 (CIGS) solar cells deposited on the polyimide substrate. The wavelength of laser radiation was adjusted depending on optical properties both of the film and the substrate. A narrow processing window of laser fluence and pulse overlap was estimated with both 1064 nm and 355 nm irradiation to remove the molybdenum backcontact off the substrate. The selective removal of ITO, ZnO and CIGS layers was achieved with 355 nm irradiation in the multilayer structure of CIGS without significant damage to the underneath layers. Use of the flat-top laser beam profile should prevent inhomogeneity in ablation. The EDS analysis did not show residues of molybdenum projected onto the walls of ablated channel due to melt extrusion. Processing with picosecond lasers should not cause degradation of photo-electrical properties of the solar cells but verification is required