from the lab Game-changing technology on the Horizon
portance for space missions is the IMM cell’s
reduced weight. Removing the substrate and
replacing it with a lightweight handle increases
the IMM cell’s power-to-weight ratio tenfold.
Yet the IMM cell may have its biggest impact in the terrestrial concentrating photovoltaic (CPV) power market. The primary
application of CPV systems is for utility-scale
power from control stations in regions such
as the U.S. desert Southwest, where utilities
will be able to generate electricity in the range
of hundreds of megawatts to gigawatts. (For
context, a large electric power plant might
produce 1,000 MW.) CPV systems based on
high-efficiency cells are just starting to be built
for utility-scale electrical generation, and they
promise to be cost-competitive.
the hybrid CiGS manufacturing approach
could, at relatively low cost, create enough of
the flexible PV film to integrate it with windows,
roofing, façades and other structural components. it may help bring installations like this
solar electricity-generating façade, which uses
144 custom PV modules (rather than CiGS film),
into common use. Solar technology company
GeG aG completed the façade at a German
manufacturer’s headquarters in January.
engineered to fit the application. In so doing, it
raises the bar for PV several levels in terms of
performance, adaptability and cost reduction.
The IMM cell’s first major innovation is
that the cell layers are grown or deposited
in an inverted sequence, from top to bottom
— reversing the “normal” order. The second
innovation is the use of a transparent transition layer to allow the growth of one subcell
layer on another, even though the lattices do
not match (i.e., their crystal structures have
different atomic spacing). The primary benefit
of using these innovative techniques is to enable the inclusion of a “bottom” subcell with
an ideal range of solar energy response, which
is 1 electron volt.
Because the IMM cell is grown in reverse
order, one must remove the substrate on
which it was grown and mount the cell on a
“handle” (a supporting carrier). This opens up
a world of opportunities. One can choose the
handle from a range of materials according to
the qualities desired. For space applications,
the handle will be ultra-thin and ultra-light,
conferring a heretofore-impossible degree of
flexibility on the solar cells. But of greatest im-
In CPV applications, there is a major performance advantage for heat-conducting cells
that dissipate waste heat efficiently. With
IMM cell technology, one can optimize thermal management because thick parent substrates (the materials on which the solar cell
is grown) with low thermal conductivity are
eliminated; the ultra-thin cell structures are in
intimate contact with the supporting handle,
which can have a high thermal conductivity.
Robust handle materials will also create robust cells, thus improving processing yields
and reducing costs.
The potential for additional cost savings
is another rationale for perfecting the IMM
cell. The parent substrate can be an impure,
low-cost material, because its only function is
that of a template, which serves as a pattern
for the cell’s growth and is later removed. It is
also possible to reuse and/or reclaim the parent substrate.
The IMM cell is a revolutionary advance, because it allows
The IMM cell’s attributes were so compelling that they attracted the interest of PV technology developer and manufacturer Emcore
Corp. ( emcore.com). Through a Cooperative Research and Development Agreement
with NREL and funding from the Air Force
Research Laboratories Space Vehicles Directorate, Emcore raised the manufacturability
and performance of the IMM cell technology
the cell’s attributes to be engineered to fit the application.
In so doing, it raises the bar for PV several levels in terms
of performance, adaptability and cost reduction.
According to Fred Newman, Ph.D., Emcore’s manager of terrestrial concentrator
device development, one of the keys to the
success of the IMM approach in the CPV market is increasing its efficiency to a point that