Basic Research Needs for Solar Energy Utilization

EFFECTS OF LOW DIMENSIONALITY

Reduced dimensionality can be used to control propagation

and interactions of photons, electrons, and phonons.

Photon distributions are controlled in photonic crystals; the plot in

“reciprocal space” shows the limited momentum and spatial

direction that photons can have in controlled geometries.

The energy distribution of possible electronic energy levels is

drastically affected by spatial confinement

A key feature of all nanoscale materials is
the presence of multiple interfaces between
different components. To realize the benefits
of nanoscale patterning, researchers need to
systematically investigate the transport of
charges and molecular species across these
interfaces. This issue has been of particular
concern in the case of electrical contacts.

System Assembly and Defect
Tolerance

To realize the potential of nanoscale-based
solar conversion, the chemistry of molecular
and material synthesis and assembly must
be further elucidated. The synthesis of
complex molecules, macromolecules, and
nanoparticles is an underlying tool that
continues to evolve in important ways. The
key limiting issue now is the merging of
these component building blocks into
functional assemblies and, ultimately, into
complete systems. This capability requires
improved understanding of the organic-
inorganic hard-soft interfaces, as well as the
ability to harness multiple weak interactions
to create designed patterns. This is how
biological materials are organized on length
scales larger than those of individual macromolecules, yet it remains very challenging for
chemists and materials scientists working with artificial components. It is important for
researchers to emulate many features of biological system assembly, chief among them (1) the
ability to create advanced materials despite the presence of disorder and defects and (2) the
ability not only to assemble components, but also to disassemble and reassemble them. These
capabilities are essential for creating advanced solar converters that combine high performance
with low cost.

New Experimental and Theoretical Tools

Progress in the field of solar energy depends critically on the development of new tools for the
characterization of matter and on new theoretical tools. On the experimental front, one major
goal is to create probes that can reveal the structure and composition of nanoscale materials with
atomic resolution. A second goal involves development of tools that can be used to follow the
complete flow of energy through each primary step of the solar conversion processes — from
absorption, to charge transfer, transport, harvesting, and chemical conversion and separation.
Theoretical tools are also needed to aid in the understanding of these elementary steps. The wide