Solar cells that "self assemble" from a liquid have
been developed by scientists at the University of
Cambridge. The breakthrough could make it cheap
and easy to cover large areas, like roofs, with
efficient, ultra-thin solar cell coatings.
"This is potentially very important," says Jenny
Nelson, an expert in solar cells at Imperial College in
London. "If you've got something in solution, you
could, in principle, put down very large areas of
photo-voltaic material very cheaply."
To make the solar cell solution, Lukas
Schmidt-Mende and his colleagues at Cambridge
took two chemicals called perylene and
hexabenzocoronene (HBC) and dissolved them in
chloroform.
They then poured some of the mixture onto a spinning
glass sheet coated with an alloy electrode. As the
chloroform evaporated, they found they were left with
a thin layer of material, just one tenth of a micron thick.
When they examined the layer closely, they found that
the perylene had risen to the top, while the HBC had
crystallised out at the bottom. Inside the layer, though,
needle-like crystals of perylene were mixed closely
with disc-shaped HBC molecules.
High efficiency
To test the material's efficiency as a solar cell, the
scientists evaporated a thin coating of aluminium on
top of the layer and measured the current between
this and the lower alloy electrode while shining a light
on it. "Organic materials normally have low
efficiencies, but we found we
this was high - peaking
at 34 per cent," says Schmidt-Mende. The efficiency
is a measure of the amount of current produced for a
certain illumination.
The material works as a solar cell because as light
photons hit the layer, they knock electrons out of
molecules they co…
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