Solar energy production is fast becoming a vital source of renewable energy being
developed as an alternative to traditional fossil fuel-based sources of power. One
of the primary challenges to the full-scale implementation of solar energy
remains the expensive cost associated with the construction of photovoltaic
modules and certain toxic elements in some thin film solar cells. The principal
photovoltaic (PV) material on the market today is silicon, and although silicon-
based solar cells are comprised of a very abundant element, their large-scale
production is hampered by the high cost of processing and refining, which sets
the average electricity cost from a silicon solar cell well above that which comes
from coal- or gas-burning power plants2. Although there are solar cells reported
with very high efficiencies3-5 (>25%), these cells are all constructed on a
laboratory-scale setting, often requiring rare or expensive materials and/or
methods.   If a material is truly to become a marketable option for the
photovoltaic industry, some consideration must be given to the expense of its
synthesis, manufacture, processing, and construction into a device, in addition to
its ultimate PV efficiency.
Generally speaking, materials selection for future photovoltaics should
satisfy several important criteria. The materials should be comprised of abundant
and inexpensive elements. The materials should be environmentally benign to
avoid any issues of potential environmental contamination. And importantly for
any potential PV application, the materials must have an optimal bandgap to
maximize solar absorption such that the resulting solar cell would have a
marketable energy conversion efficiency.

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