Basic Research Needs for Solar Energy Utilization - Office of ...

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multi-electron H2O and CO2 activation, but methods are lacking that allow coupling of these components to electron/hole conducting moieties in 3-D frameworks. Molecular-type linkages need to be developed for efficient charge conduction between catalytic sites and photoactive components embedded in the assembly. Integrated Time-resolved Probes Current research on self-assembly has been limited to observation of ordered structures using conventional techniques such as X-ray and electron diffraction, transmission electron microscopy, and atomic force microscopy. Moving self-assembly science forward requires an experimental window that reveals the three-dimensional structural nature, and time scales of the “embryonic nuclei” that trigger self-assembling processes as they cross from the nanoscale to microscopic and macroscopic dimensions. It is equally critical to observe in real time and space the transformations and intermediate states that assemblies go through before reaching their final form. This information is not presently accessible, and requires invention of “integrated” timeresolved probes that record in real time the evolution of the system across length scales. These might be presently unknown hybrids of scanning probe techniques, near-field strategies, confocal microscopy, magnetic resonance imaging, tomographic techniques, vibrational spectroscopies, and others. Opening this spatial and temporal window on self-assembling systems will allow us to direct systems externally (e.g., through solvent, temperature, external fields, and photons) into the desired targets. A grand challenge is to develop such probes for “self-assembly dynamics” that tolerate compositionally controlled atmospheres, liquid phases, variable temperature, and variable pressure. New Computational Approaches New computational approaches are needed to integrate simulations across disparate time and length scales that are important for assembly of solar fuel/energy producing systems (see Figure 65). For example, modeling has traditionally been carried out separately for increments of length scales using quantum mechanics (0.1–10 nm), statistical mechanics (1–1,000 nm), mesoscale (0.1–100 µm), and continuum mechanics (1 mm–10 m). Time scales range from quantum mechanical methods (10 −15 s) to continuum methods (1–10 5 s). There is a critical need for theoretical modeling and simulation (TMS) to span all these length and time scales seamlessly to meet the needs of solar research, to provide insight into the forces and processes that control the organization of functional elements over all length and time scales; to understand quantitatively the kinetics of catalyzed photochemical energy conversion reactions over many length scales in complex, hybrid systems; to identify active sites on nanostructured surfaces, etc. 176 Figure 64 Hierarchical assembly of mesoporous oxide within nanoscopic channels of porous alumina membrane. This example illustrates principles of multiple length ordering.
TMS will be used to discover the design rules for reverse-engineering building blocks capable of self-assembling into target structures. SCIENTIFIC CHALLENGES Presently, there exist many scientific challenges that should be addressed before the ultimate goal can be achieved. Here, inexpensive and simple self-assembly techniques need to be developed for the fabrication of efficient, large-area, low-cost solar cells. The thermodynamic and kinetic principles for integration and self-assembly of different materials should be exploited. The principles of self-assembly to deposit materials (e.g., low-dimensional nanostructures, organic heterostructures, nanocomposites) onto rigid and flexible substrates should be investigated. The science of manipulating interfacial structures and properties, and processing functional materials and structures to optimize optical absorption throughout the solar spectrum, exciton formation and migration towards the proper interface, charge separation, transport, and collection should be established. POTENTIAL IMPACT Ultimately, these efforts would lead to revolutionary multi-functional systems that are capable of light-harvesting, charge separation, molecular transport, fuel production, and chemical separation. This research direction impacts not only the potential efficiency of the solar cell construction, but also the quality. The objective of providing control over morphology and assembly directly impacts a wide range of length scales that can lead to defect-free, high-quality solar photon conversion devices that can be readily produced on a large scale. REFERENCES S. Glotzer, University of Michigan, personal communication. F.X. Redl, K.-S. Cho, C.B. Murray, and S. O'Brien, “Three-dimensional Binary Superlattices of Magnetic Nanocrystals and Semiconductor Quantum Dots,” Nature 423, 968 (2003). S. Stupp, Northwestern University, personal communication. 177 Figure 65 Theoretical simulation for nanorod self-organization into smectic phase (Source: S. Glotzer, University of Michigan, unpublished)
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On the Cover: One route to harvesti
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Revisions, September 2005 p ix, par
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CONTENTS (CONT.) Appendix 4: Additi
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OEC oxygen-evolving complex PCET pr
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viii
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thin films, organic semiconductors,
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genetic sequencing, protein product
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INTRODUCTION The supply and demand
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showing promise to overcome them. T
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GLOBAL ENERGY RESOURCES 7
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energy can be exploited on the need
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BASIC RESEARCH CHALLENGES FOR SOLAR
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CONVERSION OF SUNLIGHT INTO ELECTRI
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PHYSICS OF PHOTOVOLTAIC CELLS Inorg
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Figure 4 Learning curve for PV prod
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Needs of Direct-gap, Thin-film Phot
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Figure 6 Current record efficiencie
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devices. The molecules and material
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Figure 8 Structure for high-efficie
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One critical property of the photoa
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PHOTOELECTROCHEMICAL STORAGE CELLS
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BASIC RESEARCH CHALLENGES FOR SOLAR
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information about the proteins that
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convert it into H2 and liquid fuels
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charge separation ensures highly ef
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Efficient Photo-initiated Charge Se
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artificial RCs, have proven to be i
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CATALYSTS FOR CO2 REDUCTION Photo-d
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Upon photoexcitation, the electron
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(5) determining the physical and ch
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following challenges must be met: (
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A.F. Heyduk and D.G. Nocera, “Hyd
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J. Seth, V. Palaniappan, R.W. Wagne
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THREE TYPES OF CONCENTRATED SOLAR
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Solar Thermal to Electric Energy Co
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Tm = mean temperature Z = measure o
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control and further diode developme
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An overview of solar thermochemical
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for electron and phonon band struct
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coefficient. The thermal conductivi
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J.J. Greffet, R. Carminati, K. Joul
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CROSS-CUTTING RESEARCH CHALLENGES B
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ange of time and length scales span
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Research Issues Advances in the syn
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Advances across several science fro
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Figure 19 Transparent conductive el
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Carrier generation, relaxation, and
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E. Hutter and J.H. Fendler, “Expl
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PRIORITY RESEARCH DIRECTIONS Revolu
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RESEARCH DIRECTIONS Several paths e
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Multiple Energy Level Solar Cells I
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Strain Relaxation. Growth of layers
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the relevant elastic and inelastic
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A.J. Nozik, “Quantum Dot Solar Ce
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these new organic structures, and t
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Figure 30 Schematic diagram (right)
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carrier injection between the indiv
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108
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Figure 32 One important example of
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interface for charge separation. Fo
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• Light harvesting, • Advanced
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116
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Multicomponent structures are often
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REFERENCES A.J. Bard and M.A. Fox,
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PLANT PRODUCTIVITY AND BIOFUEL PROD
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een made in identifying and charact
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Page 142 and 143: SUMMARY OF RESEARCH DIRECTION The k
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Page 146 and 147: coupling in multi-cofactor-containi
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Page 150 and 151: low toxicity, and processibility. T
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Page 154 and 155: largely unknown are the fundamental
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Page 158 and 159: ealize an efficient artificial phot
Page 160 and 161: Figure 46 Defect-tolerant solar cel
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Page 166 and 167: the sequestration step, these solar
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Page 170 and 171: The continued advances in energy- a
Page 172 and 173: for the detailed understanding and
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Page 176 and 177: A shortcoming of this approach is t
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Page 180 and 181: High-throughput Experimental Screen
Page 182 and 183: Solar Concentrators and Hot Water H
Page 184 and 185: G. Chen, M.S. Dresselhaus, J.-P. Fl
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Page 196 and 197: and quantum dots. Quantum dots are
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Page 202 and 203: Flux (mA/eV.cm2 Flux (mA/eV.cm ) 2
Page 204 and 205: Table 1 Worldwide PV Module Product
Page 206 and 207: Amorphous Silicon. From its discove
Page 208 and 209: Table 2 Are There Enough Materials
Page 210 and 211: passivating window and back-surface
Page 212 and 213: R.R. King, C.M. Fetzer, K.M. Edmond
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Page 216 and 217: Anaerobic Digestion One gasificatio
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Page 228 and 229: periods and extend the system opera
Page 230 and 231: When ηopt < 1, Equation (2) become
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Page 234 and 235: Figure 77 General concept of solar-
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Page 238 and 239: THERMOPHOTOVOLTAICS Thermophotovolt
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N. Benz and Th. Kuckelkorn, “A Ne
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R.A. Sherif, H.L. Cotal, R.R. King,
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Sub-panelists Edmond Amouyal, Centr
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Terry Tritt, Clemson University Joh
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Plenary Closing Session — Wednesd
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Panel 1C (Photoelectrochemistry)
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Agenda for Solar Fuels Breakout Ses
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Tuesday, April 19, 2005, 8:00 a.m.
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Wednesday, April 20, 2005, 8:00 a.m
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Wednesday, April 20, 2005, 8:00 a.m
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250
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R. Corkish, S. Kettemann, and J. Ne
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T. Polivka and V. Sundstrom, “Ult
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microscopy, 81, 85, 101, 155-157, 1
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