xthin films, organic semiconductors, dye sensitization, and quantum dots offer fascinating new
opportunities for cheaper, more efficient, longer-lasting systems. Many of the new approaches
outlined by the workshop participants are enabled by (1) remarkable recent advances in the
fabrication of nanoscale architectures by novel top-down and bottom-up techniques;
(2) advances in nanoscale characterization using electron, neutron, and x-ray scattering and
spectroscopy; and (3) sophisticated computer simulations of electronic and molecular behavior in
nanoscale semiconductor assemblies using density functional theory. Such advances in the basic
science of solar electric conversion, coupled to the new semiconductor materials now available,
could drive a revolution in the way that solar cells are conceived, designed, implemented, and
manufactured.
SOLAR FUELS
The inherent day-night and sunny-cloudy cycles of solar radiation necessitate an effective
method to store the converted solar energy for later dispatch and distribution. The most attractive
and economical method of storage is conversion to chemical fuels. The challenge in solar fuel
technology is to produce chemical fuels directly from sunlight in a robust, cost-efficient fashion.
For millennia, cheap solar fuel production from biomass has been the primary energy source on
the planet. For the last two centuries, however, energy demand has outpaced biomass supply.
The use of existing types of plants requires large land areas to meet a significant portion of
primary energy demand. Almost all of the arable land on Earth would need to be covered with
the fastest-growing known energy crops, such as switchgrass, to produce the amount of energy
currently consumed from fossil fuels annually. Hence, the key research goals are (1) application
of the revolutionary advances in biology and biotechnology to the design of plants and organisms
that are more efficient energy conversion “machines,” and (2) design of highly efficient, all-
artificial, molecular-level energy conversion machines exploiting the principles of natural
photosynthesis. A key element in both approaches is the continued elucidation — by means of
structural biology, genome sequencing, and proteomics — of the structure and dynamics
involved in the biological conversion of solar radiation to sugars and carbohydrates. The
revelation of these long-held secrets of natural solar conversion by means of cutting-edge
experiment and theory will enable a host of exciting new approaches to direct solar fuel
production. Artificial nanoscale assemblies of new organic and inorganic materials and
morphologies, replacing natural plants or algae, can now use sunlight to directly produce H 2 by
splitting water and hydrocarbons via reduction of atmospheric CO 2. While these laboratory
successes demonstrate the appealing promise of direct solar fuel production by artificial
molecular machines, there is an enormous gap between the present state of the art and a
deployable technology. The current laboratory systems are unstable over long time periods, too
expensive, and too inefficient for practical implementation. Basic research is needed to develop
approaches and systems to bridge the gap between the scientific frontier and practical
technology.