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

Carrier generation, relaxation, and transport can be strongly influenced by the properties of bulk
and interface materials on the atomic scale. Therefore, we will require techniques that are
capable of probing the molecular and electronic structure of materials on an atomic scale at
solid-vacuum, solid-liquid, and buried interfaces, as well as for defects in solids. Scanning probe
techniques will play a central role in elucidating the atomic structure at solid-vacuum and solidliquid
interfaces. Beyond establishing the molecular structure of interfaces, such techniques will
increasingly be used to probe the electronic structure at the atomic level, as well as to determine
chemical composition by inelastic tunneling methods. By combining scanning probe and ultrafast-laser
spectroscopic techniques, scientists may be able to probe the fundamental electron
dynamics at a single-atom or -molecule level. Laser-based nonlinear spectroscopic techniques
will provide vibrational and electronic information about the structure and dynamics at surfaces
and buried interfaces that cannot be determined by using scanning probe methods. In particular,
techniques such as time-resolved photoemission will provide information about the photoinduced
carrier generation, carrier scattering processes that lead to energy relaxation, trapping,
and recombination, as well as carrier transport and localization. Techniques that combine high
spatial and temporal resolution may be of particular value. New methods, such as Z-scan electron
microscopy, will have to be developed for probing atomic-scale buried defects in solids.
Impact
Results from this cross-cutting research have the potential to have a very broad impact on solar
energy conversion. The issues, as indicated above, are central to many distinct approaches to
solar energy utilization. Significant improvements in the efficiency, reliability, and cost of PV
devices can be expected through improved electrical contacts and transparent conductors, as well
as through decreased non-radiative processes. Advances in this cross-cutting research direction
will also improve the operation and design of dye-sensitized PV devices, and they are critical to
the development of photocatalytic approaches to fuel production that exhibit the desired
efficiency and selectivity.
THERMAL STORAGE METHODS
Innovative thermal storage methods must be developed to address the need to provide reliable
electricity supply based on demand. Demand generally does not coincide with the incident
sunlight periods. Achieving this thermal storage capability requires the development of highenergy-density,
high-thermal-conductivity, stable, latent heat materials. One promising approach
is using encapsulated and nanocrystal polymers.
The operating conditions (i.e., temperature and pressure) of the thermal storage system must
match those of the power conversion process and therefore vary from 80–150°C for lowtemperature
systems to 400–1,000°C for high-temperature systems. Solar-derived fuels are the
logical choice for storage at temperatures >1,000°C.
A fundamental understanding of the behavior of phase change storage materials (PCMs) and the
relationship between various (sometime undesirable) chemical processes, phase transition, and
thermal/chemical stability is crucial for the development of thermal storage methods. The PCMs
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