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

“bottom-up” construction of inorganic PV materials that are organized on length scales ranging
from angstroms (crystal structure) to microns (e.g., superlattice of quantum structures) (see
Figure 61). Such assemblies could allow for the simultaneous control of band gap, relative
donor-acceptor conduction band energy levels, and the photonic band gap of the material. On
even longer length scales, it is anticipated that self-assembly methods could be used to assemble
microscale cells into larger solar cell “modules” allowing for easy fabrication of large-area solar
arrays that incorporate many miniature multijunction cells.
Figure 61 Superlattice formation via self-assembly of inorganic
nanocrystals (Source: Redl et al. 2003)
There is also a strong correlation between the structure and morphology of thin-film materials
and the nature of the underlying substrate. Issues such as surface crystal morphology, wettability,
and surface energy patterning can have a strong influence on the nano- and mesoscale
morphology of the deposited film. Fundamental scientific studies need to be carried out to
understand how surfaces can be used to gain control over the structure of the PV active layer.
Nano- and microscale patterning of a surface can be used to aid self-assembly of cell elements
and interconnects.
While some methods have already been developed to allow structural control on the nanoscale of
the active materials of organic, hybrid, and inorganic solar cells, considerable new research is
needed to develop entirely new approaches. This work will require fundamental scientific studies
ranging from a focus on the thermodynamics and kinetics of self-assembly to the development of
novel approaches to correlate material structure with macroscale performance in active solar
cells. The latter concept will be particularly important in guiding the development of new
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