Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
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A key feature <strong>of</strong> all nanoscale materials is<br />
the presence <strong>of</strong> multiple interfaces between<br />
different components. To realize the benefits<br />
<strong>of</strong> nanoscale patterning, researchers need to<br />
systematically investigate the transport <strong>of</strong><br />
charges and molecular species across these<br />
interfaces. This issue has been <strong>of</strong> particular<br />
concern in the case <strong>of</strong> electrical contacts.<br />
System Assembly and Defect<br />
Tolerance<br />
To realize the potential <strong>of</strong> nanoscale-based<br />
solar conversion, the chemistry <strong>of</strong> molecular<br />
and material synthesis and assembly must<br />
be further elucidated. The synthesis <strong>of</strong><br />
complex molecules, macromolecules, and<br />
nanoparticles is an underlying tool that<br />
continues to evolve in important ways. The<br />
key limiting issue now is the merging <strong>of</strong><br />
these component building blocks into<br />
functional assemblies and, ultimately, into<br />
complete systems. This capability requires<br />
improved understanding <strong>of</strong> the organicinorganic<br />
hard-s<strong>of</strong>t interfaces, as well as the<br />
ability to harness multiple weak interactions<br />
to create designed patterns. This is how<br />
biological materials are organized on length<br />
76<br />
EFFECTS OF LOW DIMENSIONALITY<br />
Reduced dimensionality can be used to control propagation<br />
and interactions <strong>of</strong> photons, electrons, and phonons.<br />
Photon distributions are controlled in photonic crystals; the plot in<br />
“reciprocal space” shows the limited momentum and spatial<br />
direction that photons can have in controlled geometries.<br />
The energy distribution <strong>of</strong> possible electronic energy levels is<br />
drastically affected by spatial confinement<br />
scales larger than those <strong>of</strong> individual macromolecules, yet it remains very challenging <strong>for</strong><br />
chemists and materials scientists working with artificial components. It is important <strong>for</strong><br />
researchers to emulate many features <strong>of</strong> biological system assembly, chief among them (1) the<br />
ability to create advanced materials despite the presence <strong>of</strong> disorder and defects and (2) the<br />
ability not only to assemble components, but also to disassemble and reassemble them. These<br />
capabilities are essential <strong>for</strong> creating advanced solar converters that combine high per<strong>for</strong>mance<br />
with low cost.<br />
New Experimental and Theoretical Tools<br />
Progress in the field <strong>of</strong> solar energy depends critically on the development <strong>of</strong> new tools <strong>for</strong> the<br />
characterization <strong>of</strong> matter and on new theoretical tools. On the experimental front, one major<br />
goal is to create probes that can reveal the structure and composition <strong>of</strong> nanoscale materials with<br />
atomic resolution. A second goal involves development <strong>of</strong> tools that can be used to follow the<br />
complete flow <strong>of</strong> energy through each primary step <strong>of</strong> the solar conversion processes — from<br />
absorption, to charge transfer, transport, harvesting, and chemical conversion and separation.<br />
Theoretical tools are also needed to aid in the understanding <strong>of</strong> these elementary steps. The wide