Electricity from plastics
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Solar cells and pocket calculators are
made for one another. The postage
stamp-sized, shiny blue rectangle made
of inexpensive amorphous silicon supplies
the easily satisfied calculator with
electricity and helps prevent embarrassing
homework or examination mistakes.
Then, as nobody needs to do mathematical
exercises in the dark, the device
switches itself off when the protective
cover is slid over it.
While pocket calculators with solar
cells are manufactured by the million,
solar-powered laptops and mobile
phones have not yet advanced beyond
the prototype stage. The main reason is
that most portable electronic devices
consume more electricity than a correspondingly
sized solar cell can supply.
In any case, this would make the device
considerably more expensive. Another
obstacle is that, because they are made
of silicon wafers or produced as ultrathin
cells on glass carriers, present-day
solar cells are rigid and therefore cannot
be shaped to fit the curved contours of
modern-day housings.
Market worth billions:
fl exible plastic solar cells
Yet the dream of a mini solar power
unit on a phone or briefcase has not
yet materialized because the efficiency
of the films – the extent to which they
can convert light energy into electrical
energy – is too low. While cells of
monocrystalline silicon can convert
over 20 percent of the solar energy
into electricity, the best solar films in
the lab manage no more than five to
six percent. And because the efficacy of
these films also begins to decline after
just a few months, the boom has not
yet happened.
Deliberately creating a structure
from nanoparticles
The success of organic photovoltaics,
however, stands and falls with the lightsensitive
layer. It must convert sunlight
as effectively as possible into positive
and negative charge carriers and conduct
them without loss via a network of very
fine nanostructures. What the optimum
structure for a cell that is as efficient as
possible will look like is currently the subject
of much intensive research.
Bayer favors a novel kind of solar
cell technology with inorganic nanoparticles
known as quantum dots, and is
therefore taking a different approach
than most other companies. This is not
because they distrust Bayer’s line of
attack but because there are only very
few companies with a command of this
process. “We can even specifically control
the structure of the nanoparticles,”
says Dr. Frank Rauscher. He and his colleagues
at Bayer Technology Services
are currently developing suitable nanomaterials
and researching the physical
principles of electricity generation in the
plastic/nanoparticle sandwich, which
consists of a network of semi-conductive
plastics.