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SETP Seed Fund, Session: OPV, Sensitized, Seed (Presentation)

Description: This project supports the Solar America Initiative by: (1) Exploring the concept of improving solar cell efficiency by generating and collecting multiple electrons per absorbed photon for h{nu} > 2Eg (Multiple Exciton Generation--MEG); and (2) Developing PV cells based on colloidally-synthesized semiconductor nanocrystals (NCs) which may eventually enable inexpensive and highly-efficient devices (single absorber design can potentially exceed Shockley-Queisser limit).
Date: April 1, 2008
Creator: Ellingson, R.
Partner: UNT Libraries Government Documents Department

Development of Novel Nanocrystal-based Solar Cell to Exploit Multiple Exciton Generation: Cooperative Research and Development Final Report, CRADA Number CRD-07-00227

Description: The purpose of the project was to develop new design and fabrication techniques for NC solar cells with the goal of demonstrating enhanced photocurrent and efficiency by exploiting multiple exciton generation and to investigate multiple exciton generation and charge carrier dynamics in semiconductor NC films used in NC-based solar cells.
Date: August 1, 2010
Creator: Ellingson, R.
Partner: UNT Libraries Government Documents Department

A study of longwave radiation codes for climate studies: Validation with ARM observations and tests in general circulation models

Description: Research by the US Department of Energy (DOE) has shown that cloud radiative feedback is the single most important effect determining the magnitude of possible climatic responses to human activity. However, these effects are still not known at the levels needed for climate prediction. Consequently, DOE has launched a major initiative-- the Atmospheric Radiation Measurements (ARM) Program -- directed at improving the parameterization of the physics governing cloud and radiative processes in general circulation models (GCM's). One specific goal of ARM is to improve the treatment of radiative transfer in GCM's under clear-sky, general overcast and broken cloud conditions. Our approach to developing the radiation model will be to test existing models in an iterative, predictive fashion. We will supply the Clouds and Radiative Testbed (CART) with a set of models to be compared with operationally observed data. The differences we find will lead to the development of new models to be tested with new data. Similarly, our GCM studies will use existing GCM's to study the radiation sensitivity problem. We anticipate that the outcome of this approach will provide both a better longwave radiative forcing algorithm and a better understanding of how longwave radiative forcing influences the equilibrium climate of the atmosphere.
Date: January 1, 1992
Creator: Ellingson, R.G. & Baer, F.
Partner: UNT Libraries Government Documents Department

ICRCCM Phase 2: Verification and calibration of radiation codes in climate models

Description: Following the finding by the InterComparison of Radiation Codes used in Climate Models (ICRCCM) of large differences among fluxes predicted by sophisticated radiation models that could not be sorted out because of the lack of a set of accurate atmospheric spectral radiation data measured simultaneously with the important radiative properties of the atmosphere, our team of scientists proposed to remedy the situation by carrying out a comprehensive program of measurement and analysis called SPECTRE (Spectral Radiance Experiment). SPECTRE will establish an absolute standard against which to compare models, and will aim to remove the hidden variables'' (unknown humidities, aerosols, etc.) which radiation modelers have invoked to excuse disagreements with observation. The data to be collected during SPECTRE will form the test bed for the second phase of ICRCCM, namely verification and calibration of radiation codes used in climate models. This should lead to more accurate radiation models for use in parameterizing climate models, which in turn play a key role in the prediction of trace-gas greenhouse effects.
Date: January 1, 1991
Creator: Ellingson, R.G.; Wiscombe, W.J.; Murcray, D.; Smith, W. & Strauch, R.
Partner: UNT Libraries Government Documents Department

A study of longwave radiation codes for climate studies: Validation with ARM observations and tests in general circulation models. Final report, September 15, 1990--October 31, 1994

Description: DOE has launched a major initiative -- the Atmospheric Radiation Measurements (ARM) Program -- directed at improving the parameterization of the physics governing cloud and radiative processes in general circulation models (GCMs). One specific goal of ARM is to improve the treatment of radiative transfer in GCMs under clear-sky, general overcast and broken cloud conditions. In 1990, the authors proposed to contribute to this goal by attacking major problems connected with one of the dominant radiation components of the problem -- longwave radiation. In particular, their long-term research goals are to: develop an optimum longwave radiation model for use in GCMs that has been calibrated with state-of-the-art observations, assess the impact of the longwave radiative forcing in a GCM, determine the sensitivity of a GCM to the radiative model used in it, and determine how the longwave radiative forcing contributes relatively when compared to shortwave radiative forcing, sensible heating, thermal advection and expansion.
Date: September 1, 1998
Creator: Ellingson, R.G. & Baer, F.
Partner: UNT Libraries Government Documents Department

Short-term Variability of Extinction by Broadband Stellar Photometry

Description: Aerosol optical depth variation over short-term time intervals is determined from broadband observations of stars with a whole sky imager. The main difficulty in such measurements consists of accurately separating the star flux value from the non-stellar diffuse skylight. Using correction method to overcome this difficulty, the monochromatic extinction at the ground due to aerosols is extracted from heterochromatic measurements. A form of closure is achieved by comparison with simultaneous or temporally close measurements with other instruments, and the total error of the method, as a combination of random error of measurements and systematic error of calibration and model, is assessed as being between 2.6 and 3% rms.
Date: March 18, 2005
Creator: Musat, I.C. & Ellingson, R.G.
Partner: UNT Libraries Government Documents Department

Results from the Longwave Effective Cloud Fraction in the Cloudiness Intercomparison Introduction

Description: While it may seem to be a simple quantity, cloud amount is somewhat elusive. Different types of instruments placed next to each other can give different cloud amounts because they use different parts of the spectrum, have different fields of view, sampling rates, etc. Another consideration is that cloud amount depends on the physical scale under consideration. The cloud amount appropriate for comparison to a single pyrgeometer is not likely to be useful for a grid square with 100 km sides.
Date: March 18, 2005
Creator: Takara, E.E. & Ellingson, R.G.
Partner: UNT Libraries Government Documents Department

ICRCCM phase II: Verification and calibration of radiation codes in climate models. Final report, 1 May 1990--30 April 1993

Description: Following the finding by the InterComparison of Radiation Codes used in Climate Models (ICRCCM) of large differences among fluxes predicted by sophisticated radiation models that could not be sorted out because of the lack of a set of accurate atmospheric spectral radiation data measured simultaneously with the important radiative properties of the atmosphere, the team of scientists proposed to remedy the situation by carrying out a comprehensive program of measurement and analysis called SPECTRE (Spectral Radiance Experiment). SPECTRE was to establish an absolute standard against which to compare models, and aimed to remove the hidden variables (unknown humidities, aerosols, etc.) which radiation modelers had invoked to excuse disagreements with observation. The data collected during SPECTRE were to form the test bed for the second phase of ICRCCM, namely verification and calibration of radiation codes used in climate models. This should lead to more accurate radiation models for use in parameterizing climate models, which in turn play a key role in the prediction of trace-gas greenhouse effects. This report summarizes the activities during the project`s Third year to meet stated objectives. The report is divided into three sections entitled: (1) SPECTRE Activities, (2) ICRCCM Activities, and (3) Summary Information. The section on SPECTRE activities summarizes the field portion of the project during 1991, and the data reduction/analysis performed by the various participants. The section on ICRCCM activities summarizes their initial attempts to select data for distribution to ICRCCM participants and at comparison of observations with calculations as will be done by the ICRCCM participants. The Summary Information section lists data concerning publications, presentations, graduate students supported, and post-doctoral appointments during the project.
Date: December 31, 1993
Creator: Ellingson, R.G.; Wiscombe, W.J.; Murcray, D.; Smith, W. & Strauch, R.
Partner: UNT Libraries Government Documents Department

Recombination Lifetime of InxGa1-xAs Alloys Used in Thermophotovoltaic Converters

Description: The family of ternary compounds of composition InxGa1-xAs are of considerable interest for thermophotovoltaic energy converters. The recombination lifetimes of the various compositions are critical to the successful application of these materials as efficient converters. Here we will describe experimental results on the composition. In0.53Ga0.47 that is lattice-matched to InP. We will also describe lifetime results on the compositions In0.68Ga0.32As, with bandgap of 0.60 eV to compositions In0.78Ga0.22As with a bandgap of 0.50 eV. Double heterostructure confinement devices have been made over a range of both n- and p-type doping. These results are preliminary, but the goal is to obtain the radiative and Auger recombination coefficients for the alloys in this composition range.
Date: February 16, 1999
Creator: Ahrenkiel, R. K.; Ellingson, R.; Johnston, S.; Webb, J.; Carapella, J. & Wanlass, M.
Partner: UNT Libraries Government Documents Department

ICRCCM (InterComparison of Radiation Codes used in Climate Models) Phase 2: Verification and calibration of radiation codes in climate models

Description: Following the finding by the InterComparison of Radiation Codes used in Climate Models (ICRCCM) of large differences among fluxes predicted by sophisticated radiation models that could not be sorted out because of the lack of a set of accurate atmospheric spectral radiation data measured simultaneously with the important radiative properties of the atmosphere, our team of scientists proposed to remedy the situation by carrying out a comprehensive program of measurement and analysis called SPECTRE (Spectral Radiance Experiment). SPECTRE will establish an absolute standard against which to compare models, and will aim to remove the hidden variables'' (unknown humidities, aerosols, etc.) which radiation modelers have invoked to excuse disagreements with observation. The data to be collected during SPECTRE will form the test bed for the second phase of ICRCCM, namely verification and calibration of radiation codes used to climate models. This should lead to more accurate radiation models for use in parameterizing climate models, which in turn play a key role in the prediction of trace-gas greenhouse effects. Overall, the project is proceeding much as had been anticipated in the original proposal. The most significant accomplishments to date include the completion of the analysis of the original ICRCCM calculations, the completion of the initial sensitivity analysis of the radiation calculations for the effects of uncertainties in the measurement of water vapor and temperature and the acquisition and testing of the inexpensive spectrometers for use in the field experiment. The sensitivity analysis and the spectrometer tests given us much more confidence that the field experiment will yield the quality of data necessary to make a significant tests of and improvements to radiative transfer models used in climate studies.
Date: January 1, 1990
Creator: Ellingson, R.G.; Wiscombe, W.J.; Murcray, D.; Smith, W. & Strauch, R.
Partner: UNT Libraries Government Documents Department

Quantum Dot Solar Cells with Multiple Exciton Generation

Description: We have measured the quantum yield of the multiple exciton generation (MEG) process in quantum dots (QDs) of the lead-salt semiconductor family (PbSe, PbTe, and PbS) using fs pump-probe transient absorption measurements. Very high quantum yields (up to 300%) for charge carrier generation from MEG have been measured in all of the Pb-VI QDs. We have calculated the potential maximum performance of various MEG QD solar cells in the detailed balance limit. We examined a two-cell tandem PV device with singlet fission (SF), QD, and normal dye (N) absorbers in the nine possible series-connected combinations to compare the tandem combinations and identify the combinations with the highest theoretical efficiency. We also calculated the maximum efficiency of an idealized single-gap MEG QD solar cell with M multiplications and its performance under solar concentration.
Date: November 1, 2005
Creator: Hanna, M. C.; Beard, M. C.; Johnson, J. C.; Murphy, J.; Ellingson, R. J. & Nozik, A. J.
Partner: UNT Libraries Government Documents Department

Preliminary design for Arctic atmospheric radiative transfer experiments

Description: If current plans are realized, within the next few years, an extraordinary set of coordinated research efforts focusing on energy flows in the Arctic will be implemented. All are motivated by the prospect of global climate change. SHEBA (Surface Energy Budget of the Arctic Ocean), led by the National Science Foundation (NSF) and the Office of Naval Research (ONR), involves instrumenting an ice camp in the perennial Arctic ice pack, and taking data for 12--18 months. The ARM (Atmospheric Radiation Measurement) North Slope of Alaska and Adjacent Arctic Ocean (NSA/AAO) Cloud and Radiation Testbed (CART) focuses on atmospheric radiative transport, especially in the presence of clouds. The NSA/AAO CART involves instrumenting a sizeable area on the North Slope of Alaska and adjacent waters in the vicinity of Barrow, and acquiring data over a period of about 10 years. FIRE (First ISCCP [International Satellite Cloud Climatology Program] Regional Experiment) Phase 3 is a program led by the National Aeronautics and Space Administration (NASA) which focuses on Arctic clouds, and which is coordinated with SHEBA and ARM. FIRE has historically emphasized data from airborne and satellite platforms. All three program anticipate initiating Arctic data acquisition during spring, 1997. In light of his historic opportunity, the authors discuss a strawman atmospheric radiative transfer experimental plan that identifies which features of the radiative transport models they think should be tested, what experimental data are required for each type of test, the platforms and instrumentation necessary to acquire those data, and in general terms, how the experiments could be conducted. Aspects of the plan are applicable to all three programs.
Date: April 1, 1995
Creator: Zak, B.D.; Church, H.W.; Stamnes, K.; Shaw, G.; Filyushkin, V.; Jin, Z. et al.
Partner: UNT Libraries Government Documents Department

Sub-Picosecond Injection of Electrons from Excited [Ru (2,2'-bipy-4,4'-dicarboxy)2(SCN)2] into TiO2 Using Transient Mid-Infrared Spectroscopy

Description: We have used femtosecond pump-probe spectroscopy to time resolve the injection of electrons into nanocrystalline TiO2 film electrodes under ambient conditions following photoexcitation of the adsorbed dye, [Ru(4,4'-dicarboxy-2,2'-bipyridine)2(NCS)2] (N3). Pumping at one of the metal-to-ligand charge transfer adsorption peaks and probing the absorption of electrons injected into the TiO2 conduction band at 1.52 {micro}m and in the range of 4.1 to 7.0 {micro}m, we have directly observed the arrival of the injected electrons. Our measurements indicate an instrument-limited {approx}50-fs upper limit on the electron injection time under ambient conditions in air. We have compared the infrared transient absorption for noninjecting (blank) systems consisting of N3 in ethanol and N3 adsorbed to films of nanocrystalline Al2O3 and ZrO2, and found no indication of electron injection at probe wavelengths in the mid-IR (4.1 to 7.0 {micro}m). At 1.52 {micro}m interferences exist in the observed transient adsorption signal for the blanks.
Date: May 4, 1999
Creator: Ellingson, R. J.; Asbury, J. B.; Ferrere, S.; Ghosh, H. N.; Sprague, J. R.; Lian, T. et al.
Partner: UNT Libraries Government Documents Department

Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation

Description: Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamic conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. We have observed astoundingly efficient multiple exciton generation (MEG) in QDs of PbSe (bulk Eg = 0.28 eV), ranging in diameter from 3.9 to 5.7nm (Eg = 0.73, 0.82, and 0.91 eV, respectively). The effective masses of electron and holes are about equal in PbSe, and the onset for efficient MEG occurs at about three times the QD HOMO-LUMO transition (its ''bandgap''). The quantum yield rises quickly after the onset and reaches 300% at 4 x Eg (3.64 eV) for the smallest QD; this means that every QD in the sample produces three electron-hole pairs/photon.
Date: January 1, 2005
Creator: Hanna, M. C.; Ellingson, R. J.; Beard, M.; Yu, P.; Micic, O. I.; Nozik, A. J. et al.
Partner: UNT Libraries Government Documents Department

Atmospheric radiation measurement: A program for improving radiative forcing and feedback in general circulation models

Description: The Atmospheric Radiation Measurement (ARM) Program is a key element of the Department of Energy's (DOE's) global change research strategy. ARM represents a long-term commitment to conduct comprehensive studies of the spectral atmospheric radiative energy balance profile for a wide range of cloud conditions and surface types, and to develop the knowledge necessary to improve parameterizations of radiative processes under various cloud regimes for use in general circulation models (GCMs) and related models. The importance of the ARM program is a apparent from the results of model assessments of the impact on global climate change. Recent studies suggest that radiatively active trace gas emissions caused by human activity can lead to a global warming of 1.5 to 4.5 degrees Celsius and to important changes in water availability during the next century (Cess, et al. 1989). These broad-scale changes can be even more significant at regional levels, where large shifts in temperature and precipitation patterns are shown to occur. However, these analyses also indicate that considerable uncertainty exists in these estimates, with the manner in which cloud radiative processes are parameterized among the most significant uncertainty. Thus, although the findings have significant policy implications in assessment of global and regional climate change, their uncertainties greatly influence the policy debate. ARM's highly focused observational and analytical research is intended to accelerate improvements and reduce key uncertainties associated with the way in which GCMs treat cloud cover and cloud characteristics and the resulting radiative forcing. This paper summarizes the scientific context for ARM, ARM's experimental approach, and recent activities within the ARM program.
Date: January 1, 1991
Creator: Patrinos, A.A. (USDOE, Washington, DC (United States)); Renne, D.S.; Stokes, G.M. (Pacific Northwest Lab., Richland, WA (United States)) & Ellingson, R.G. (Maryland Univ., College Park, MD (United States))
Partner: UNT Libraries Government Documents Department

Basic Research Needs for Solar Energy Utilization. Report of the Basic Energy Sciences Workshop on Solar Energy Utilization, April 18-21, 2005

Description: World demand for energy is projected to more than double by 2050 and to more than triple by the end of the century. Incremental improvements in existing energy networks will not be adequate to supply this demand in a sustainable way. Finding sufficient supplies of clean energy for the future is one of society?s most daunting challenges. Sunlight provides by far the largest of all carbon-neutral energy sources. More energy from sunlight strikes the Earth in one hour (4.3 ? 1020 J) than all the energy consumed on the planet in a year (4.1 ? 1020 J). We currently exploit this solar resource through solar electricity ? a $7.5 billion industry growing at a rate of 35?40% per annum ? and solar-derived fuel from biomass, which provides the primary energy source for over a billion people. Yet, in 2001, solar electricity provided less than 0.1% of the world's electricity, and solar fuel from modern (sustainable) biomass provided less than 1.5% of the world's energy. The huge gap between our present use of solar energy and its enormous undeveloped potential defines a grand challenge in energy research. Sunlight is a compelling solution to our need for clean, abundant sources of energy in the future. It is readily available, secure from geopolitical tension, and poses no threat to our environment through pollution or to our climate through greenhouse gases. This report of the Basic Energy Sciences Workshop on Solar Energy Utilization identifies the key scientific challenges and research directions that will enable efficient and economic use of the solar resource to provide a significant fraction of global primary energy by the mid 21st century. The report reflects the collective output of the workshop attendees, which included 200 scientists representing academia, national laboratories, and industry in the United States and abroad, and the ...
Date: April 21, 2005
Creator: Lewis, N. S.; Crabtree, G.; Nozik, A. J.; Wasielewski, M. R.; Alivisatos, P.; Kung, H. et al.
Partner: UNT Libraries Government Documents Department