Fourier Transform Infrared Spectroscopy (FTIR) is a fast, accurate, reliable method for studying molecular structure and composition. Both qualitative and quantitative analyses can be performed on a wide variety of materials. The FTIR spectroscopy laboratory has large-area and micro- reflectance and transmittance capabilities, including automated mapping, in the infrared range from 1.3 to 25 mm. We will examine several examples where FTIR is useful for analyzing semiconductor and photovoltaic- related materials. Although not presented here, FT-Raman and FT-Photoluminescence are additional techniques available to study vibrational modes and emitted radiation of electronic transitions in a wavelength range from 0.8 to 2.5 mm.

P-type transparent conductive oxides would have potential applications in photovoltaics, transparent electronics and organic opto-electronics. In this paper we present results on the synthesis of Cu2SrO2, a p-type transparent conducting oxide, by a chemical solution route as well as the conventional pulse laser deposition (PLD) method. For Cu2SrO2 by the chemical solution route, samples were made by spraying deposition on quartz substrates using an aqueous solution of Copper formate and Strontium acetate. Phase pure materials were obtained by an optimum two stage annealing sequence. This initial work led to the development of good quality homogeneous films by a related sol-gel approach. We have also used pulsed laser depostion (PLD) to deposit Cu2SrO2 and CuInO2 thin films on quartz substrates. We have obtained improved conductivities in the CuInO2 thin films over previously published work. We present details on the nature of the relationship of process parameters to the opto-electronic properties of the films.

The World Wide Web provides an incredible resource to genomics researchers in the form of dynamic data sources--e.g. BLAST sequence homology search interfaces. The growth rate of these sources outpaces the speed at which they can be manually classified, meaning that the available data is not being utilized to its full potential. Existing research has not addressed the problems of automatically locating, classifying, and integrating classes of bioinformatics data sources. This paper presents an overview of a system for finding classes of bioinformatics data sources and integrating them behind a unified interface. We examine an approach to classifying these sources automatically that relies on an abstract description format: the service class description. This format allows a domain expert to describe the important features of an entire class of services without tying that description to any particular Web source. We present the features of this description format in the context of BLAST sources to show how the service class description relates to Web sources that are being described. We then show how a service class description can be used to classify an arbitrary Web source to determine if that source is an instance of the described service. To validate the effectiveness …

This paper investigates which reference spectrum should be used to design GaInP/GaAs/Ge triple-junction cells (at 300 K) in order to optimize their performance outdoors (at elevated temperatures). The outdoor performance is simulated using direct spectra from the recently proposed Module Energy Rating Procedure. We find that triple-junction cells designed for AM1.5D, low-AOD and AM1.5G standard spectra at 300 K all work well for maximizing daily energy production at elevated temperatures. AM1.5G cells are the best choice for midday power production, whereas AM1.5D cells are the best choice for power production during the morning and evening. Performance of cells optimized for a newly proposed Low-AOD spectrum is intermediate between these two extremes.

III-V semiconductors grown on silicon substrates are very attractive for lower-cost, high-efficiency multijunction solar cells, but lattice-mismatched alloys that result in high dislocation densities have been unable to achieve satisfactory performance. GaNxP1-x-yAsy is a direct-gap III-V alloy that can be grown lattice-matched to Si when y= 4.7x - 0.1. We have proposed the use of lattice-matched GaNPAs on silicon for high-efficiency multijunction solar cells. We have grown GaNxP1-x-yAsy on GaP (with a similar lattice constant to silicon) by metal-organic chemical vapor phase epitaxy with direct bandgaps in the range of 1.5 to 2.0 eV. We have demonstrated the performance of single-junction GaNxP1-x-yAsy solar cells grown on GaP substrates and shown improvements in material quality by reducing carbon and hydrogen impurities through optimization of growth conditions. We have achieved quantum efficiencies (QE) in these cells as high as 60% and PL lifetimes as high as 3.0 ns.

We will discuss recent results for the NREL polymer photovoltaics group. The work reported here explores the impact of polymer morphology on the physics and performance of polymer-based photovoltaic devices. By varying both the annealing temperatures and the solvent used for polymer deposition, we can alter the polymer chain morphology, thus shifting the absorption onset and shape and improving the charge transport properties of the resulting devices. The higher degree of order in the films results in increased photovoltaic performance.

Supplemental Environmental Projects (SEPs), an environmental regulatory mechanism available at both State and Federal levels, show promise as a marketing venue for wind developers. SEPs are an alternative available to defendants who have been assessed penalties for environmental non-compliance, allowing them to offset a significant amount of penalties by investing in environmentally beneficial projects. In 1999, the dollar value of Federal SEPs negotiated by the U.S. Environmental Protection Agency (EPA) totaled$277 million. In addition, cumulative state enforcement actions may be settled with SEPs. Aside from some compressed natural gas projects, no clean energy projects have been undertaken with the funds. Wind and other clean energy developers can play a unique role in introducing wind energy projects into the SEP negotiating process.

This paper reviews a testing program conducted at NREL for the past two years that applied voltage, water vapor, and light stresses to thin-film photovoltaic (PV) modules with SnO2:F transparent conducting oxides (TCOs) deposited on soda-lime glass superstrates. Electrochemical corrosion at the glass-TCO interface was observed to result in delamination of the thin-film layers. Experimental testing was directed toward accelerating the corrosion and understanding the nature of the resulting damage.

Surface analysis techniques have been used to investigate tin oxide-coated soda lime glass specimens prior and subsequent to their exposure to DC bias, heat, and humidity. All specimens reported here comprise the following layered structure: tin oxide/silicon oxycarbide/glass. Depth profiling using X-ray photoelectron spectroscopy (XPS) clearly shows the interfacial regions in both control samples and samples exposed to the above-mentioned conditions (stressed). Control samples show distinct and relatively compact interfacial regions as well as an intact silicon oxycarbide diffusion barrier. Stressed films, however, show more diffuse interfacial regions and a physically and chemically altered silicon oxycarbide diffusion barrier. This deterioration of the diffusion barrier is proposed to be a pre-requisite event to enable tin oxide delamination.

We suggest that ultraluminous X-ray sources (ULXs) and some of the variable low latitude EGRET gamma-ray sources may be two different manifestations of the same underlying phenomena: high-mass microquasars with relativistic jets forming a small angle with the line of sight (i.e. microblazars). Microblazars with jets formed by relatively cool plasma (Lorentz factors for the leptons up to a few hundreds) naturally lead to ULXs. If the jet contains very energetic particles (high-energy cutoff above Lorentz factors of several thousands) the result is a relatively strong gamma-ray source. As pointed out by Kaufman Bernads, Romero & Mirabel (2002), a gamma-ray microblazar will always have an X-ray counterpart (although it might be relatively weak), whereas X-ray microblazars might have no gamma-ray counterparts.

High-resolution cathodoluminescence spectroscopic imaging (CLSI) has been employed to study the radiative recombination processes in Cu(In,Ga)Se2 (CIGS) films used in solar cells. Mesoscopic fluctuations of the electrostatic potential explain the observed behavior for the radiative transitions identified in the emission spectrum. We show evidence for passivation of grain boundaries near the surface layers of these films. In addition, our results suggest different point defect physics for the surface layers. These studies have been primarily performed on the CIGS films used in the recently achieved world-record efficiency cell at NREL (19.2%) as a reference to understand differences in performance for the CIGS. However, most of the results are applicable to the standard CIGS deposited by the three-stage process and differences are subtle.

Electricity markets in the United States are evolving. Accurate wind power forecasts are beneficial for wind plant operators, utility operators, and utility customers. An accurate forecast makes it possible for grid operators to schedule the economically efficient generation to meet the demand of electrical customers. In the evolving markets, some form of auction is held for various forward markets, such as hour ahead or day ahead. This paper develops several statistical forecasting models that can be useful in hour-ahead markets that have a similar tariff. Although longer-term forecasting relies on numerical weather models, the statistical models used here focus on the short-term forecasts that can be useful in the hour-ahead markets. We investigate the extent to which time-series analysis can improve on simplistic persistence forecasts. This project applied a class of models known as autoregressive moving average (ARMA) models to both wind speed and wind power output.

Using a band-structure method that includes bandgap correction, we study the chemical trends of the bandgap variation in III-V semiconductors and predict that the bandgap for InN is 0.85 0.1 eV. This result suggests that InN and its III-nitride alloys are suitable for photovoltaic applications. The unusually small bandgap for InN is explained in terms of the atomic energies and the bandgap deformation potentials. The electronic and structural properties of the nitrides and their alloys are also provided.

Research progress on silicon crystal growth processes for photovoltaic applications and defect and impurity effects on PV performance is presented. Growth processes, in addition to thin-film silicon growth, include techniques for silicon-feedstock generation and a method for rapid, replenished Czochralski growth. We have produced research samples of silicon with low and very high dislocation densities for collaborative research with other institutes, and have also made samples with varying amounts of incorporated nitrogen and oxygen, again, for collaborative studies with university researchers, concerning the effects of these impurities on mechanical strength. Transition-metal doping of silicon for understanding metallic impurity effects on lifetime and cell performance is ongoing.

Real-time, in-situ characterization of hot-wire chemical vapor deposition (HWCVD) growth of hydrogenated silicon (Si:H) thin films offers unique insight into the properties of the materials and mechanisms of their growth. We have used in-situ spectroscopic ellipsometry to characterize Si:H crystallinity as a function of film thickness and deposition conditions. We find that the transition from amorphous to microcrystalline growth is a strong function of film thickness and hydrogen dilution, and a weak function of substrate temperature. We have expressed this information in terms of a color-coded phase-space map of the amorphous to microcrystalline transition in HWCVD growth on crystalline Si substrates.

As CdTe photovoltaics reached commercialization, questions have been raised about potential cadmium emissions from CdTe PV modules. Some have attacked the CdTe PV technology as unavoidably polluting the environment, and made comparisons of hypothetical emissions from PV modules to cadmium emissions from coal fired power plants. This paper gives an overview of the technical issues pertinent to these questions and further explores the potential of EHS risks during production, use and decommissioning of CdTe PV modules. The following issues are discussed: (a) The physical and toxicological properties of CdTe, (b) comparisons of Cd use in CdTe PV with its use in other technologies and products, and the (c) the possibility of CdTe releases from PV modules.

In this paper, the charge carrier recombination behavior of grain boundaries(GBs) and intra-grain dislocations in high purity polycrystalline float-zone(FZ) silicon were studied by electron beam induced current (EBIC), laser microwave photoconductance decay (PCD) and preferential etching/Normaski optical microscopy. It was found that the lifetime on a single wafer increased from~10?s to 100?s as the average grain size varied from 100?m to several millimeters, while both dislocations near the surface and grain boundaries produce a strong EBIC contrast at room temperature. Since the near surface dislocation EBIC contrast disappears with increasing space charge probe depth, i.e., diode bias, the electrical activity is not likely to be intrinsic to the grown crystal, but due to contamination introduced during chem-mechanical polishing. However, the 'clean' grain boundaries continue to act as strong recombination centers.

We improve narrow-bandgap (1.2< ETauc< 1.3 eV) amorphous silicon germanium (a-Si1-xGex:H) alloys grown by hot-wire chemical vapor deposition (HWCVD) by lowering both substrate and filament temperatures. We grew two series of films using a tungsten filament. First we systematically varied the filament temperature (Tf) from our standard temperature of 2150ýC down to 1750ýC, while fixing all other deposition parameters. Secondly we systematically varied the substrate temperature (Ts) from our previous optimized temperature of 350ýC down to 125ýC, while fixing all other deposition parameters including Tf= 1800ýC. Films with the best properties are grown with Tf< 1880ýC and Ts between 200ý-250ýC. Improvement of the material properties are characterized by improvements in the H-bonding, reduced microvoid density, and good photoresponse (for a given ETauc). There are about 15% more Ge-H bonds-passivating Ge-dangling bonds-relative to our previous work. The films are more compact due to microvoid reduction as measured by small-angle X-ray scattering (SAXS). We also fabricated solar cells with these optimized materials and obtained~3.58%-efficient devices without doing bandgap profiling yet. Due to the high optical absorption of these a-Si1-xGex:H (~1.25 eV bandgap) alloys, we need an i-layer that is only~1200ý thick to obtain a Jsc of~20 mAcm2. Additionally, we increased the GeH4 …

Recently, efficiencies in the 29-34% range have been demonstrated for GaInP/GaAs/Ge ("3J") cells under various spectral and concentration conditions. There is still room for some further improvement in these cell efficiencies, especially in the front grid metallization, optimization of which is especially important for high-concentration operation. Here, we make an estimate of the maximum efficiency which is realistically achievable for the 3J cell under concentration, assuming that all parts of the device, including the front grids, are to be optimized as well as is practically possible. We make this estimate semi-empirically, by starting from the performance which has been demonstrated for the best 3J cells under one-sun conditions. We then extrapolate to concentrator operation assuming optimized front grids. A standard operating temperature of 300K is used throughout.

A major objective of our research is to define and solve the problems that limit the efficiency and commercial viability of solar cells based on dye-sensitized nanocrystalline TiO2. Toward this end, we are currently elucidating the factors that govern charge transport and the loss mechanisms in mesoporous nanoparticle films of TiO2. In this paper, we describe the first experimental evidence that the network geometry strongly influences electron transport and the first application of percolation theory to dye-sensitized solar cells.

'Theoretical investigations of doping of several wide-gap materials suggest a number of rather general, practical"doping principles" that may help guide experimental strategies of overcoming doping bottlenecks. This paper will be published as a journal article in the future.

A hybrid divide and conquer algorithm is one that switches from a divide and conquer to an iterative strategy at a specified problem size. Such algorithms can provide significant performance improvements relative to alternatives that use a single strategy. However, the identification of the optimal problem size at which to switch for a particular algorithm and platform can be challenging. We describe an automated approach to this problem that first conducts experiments to explore the performance space on a particular platform and then uses the resulting performance data to construct an optimal hybrid algorithm on that platform. We implement this technique in a tool, ''Ouroboros'', that automatically constructs a high-performance hybrid algorithm from a set of registered algorithms. We present results obtained with this tool for several classical divide and conquer algorithms, including matrix multiply and sorting, and report speedups of up to six times achieved over non-hybrid algorithms.

We describe a final version of revisions to current ASTM reference standard spectral distributions used to evaluate photovoltaic device performance. An NREL-developed graphical user interface for working with the SMARTS2 spectral model has been developed and is being tested. A proposed ASTM reference Ultraviolet (UV) spectra for materials durability is presented. Improvements in broadband outdoor radiometer calibration, characterization, and reporting software reduce uncertainties in broadband radiometer calibrations.

This paper describes nondestructive characterization techniques for module reliability. These techniques include light and dark current versus voltage and related analysis such as resistance, diode quality factor, and dark current. The use of the NREL laser scanner at zero volts and forward bias is also described as a technique to uncover cracks, shunts, and open-circuit regions in a module. Quantum-efficiency measurements of isolated cells or regions in a module are also possible. The interpretation of laser-scanning data is enhanced by hot-spot testing with an infrared camera or thermographic paper. Specialized nondestructive techniques have also been developed to determine the shunt resistance of individual cells in a module by selective shading of cells under sunlight. Ultraviolet fluorescence and reflectivity measurements at NREL have proven useful in evaluating encapsulant stability.