NEW SCIENTIFIC OPPORTUNITIES
Development of new defect-tolerant inorganic PV materials will require combined experimental
and theoretical efforts aimed at understanding the factors affecting interactions between a large
variety of possible structural defects and charge carriers. This knowledge could lead to the
design and discovery of new classes of materials satisfying the multiple constraints of high-
volume, low-cost PV systems, including utilizing abundant elements, environmentally benign
chemical components, simplicity of synthesis and processing, and high PV performance
efficiency.
Nanoscale building blocks offer many potential advantages for solar energy research, such as the
low cost of single-crystal synthesis, the above-noted tolerance for lattice mismatch in
heterojunctions, and the ability to control three-dimensional architecture through shape-
controlled growth, microphase separation, and layer-by-layer synthesis. Novel architectures such
as branched nanocrystals, and templated nanowires and nanotubes provide useful building blocks
for coupling of light and photocatalytic components into functioning photocatalytic assemblies.
The challenge is to design these assemblies in order to drive energetically demanding reactions,
such as water-splitting, by using visible and near-infrared light. It is very important to explore
catalysts that are resistant to poisoning.
The challenge of using assembly-disassembly strategies for self-repair is the need to understand
the molecular details of how to prepare modular artificial photosynthetic systems. These systems
must depend on non-covalent interactions for their assembly and disassembly. The disassembly
process must be initiated by recognition of specific damage motifs in the overall artificial
photosynthetic system. This requires a design that identifies and anticipates the structural
consequences of the principal damage motifs. Once these pathways are identified, the overall
molecular recognition properties of each module (which will be based on weak interactions such
as hydrogen-bonding, metal-ligand interactions, and/or π-π stacking of chromophores) must be
optimized so that a particular module will tolerate only a narrow range of conformations to
recognize its partner modules. Deviations from this narrow range of conformations induced by
damage in one or more modules will result in spontaneous disassembly driven by
thermodynamics. Reassembly with intact modules will be driven by having excess intact
modules present in equilibrium with the overall system. This type of approach should work
reasonably well for artificial photosynthetic systems immobilized at surfaces, where they could
be exposed to a “repair solution” containing the modules needed for replacement.
The most challenging and potentially most general approach to self-repair is the design of smart
molecules that will (a) seek out damage sites within a modular artificial photosynthetic system,
(b) recognize the damage site, (c) execute a structural repair, and (d) leave the site to seek other
damage. This approach requires building into molecules the self-autonomous features that are
common in biology, but have not yet been developed for non-living systems.
RELEVANCE AND POTENTIAL IMPACT
Achieving defect-tolerant or active self-repair devices would enable the practical utilization of
many types of solar energy conversion systems that are currently too unstable to last for the