Solar cells can convert solar energy to electricity, but
that's about all they can do. You need batteries to store, and
then release, this electricity. But this extra-step might soon
no longer be necessary. According to PhysicsWeb,
Japanese scientists have developed
a
new type of solar cell which integrates an
electricity storage device. No more batteries or recharger! The
'photocapacitor,' as they call this new device, is also twice
more efficient than a typical silicon-based solar cell when used
on cloudy days. So apparently, you'll soon be able to travel
lighter by leaving your various rechargers for your many
handheld devices at home. Read more...
PhysicsWeb explains us how this 'photocapacitor'
works.
Conventional solar cells need a secondary device, such as a
battery, to store the electrical power generated from light.
The photocapacitor combines the photoelectric and storage
functions in a single structure.
The Japanese device consists of two electrodes -- a
light-absorbing photoelectrode made of semiconducting titanium
dioxide and a counterelectrode made of platinum coated glass
-- separated by a resin film. Both electrodes include a porous
layer of activated carbon that has a large surface area. All
three layers are filled with an ionic solution and form a
capacitor that has a light collection area of 0.64 square
centimetres.
Photons are collected by photoreceptor dye molecules on the
surface of the titanium dioxide layer. When exposed to light,
electrons from the dye molecules are transferred to the
conducting band in the titanium dioxide layer, thus producing
a current. They then transfer to the activated carbon layer at
the counterelectrode via an external circuit.
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Here is a diagram showing the structure of this
sandwich-type multilayered photocapacitor. The dye-adsorbed
titanium dioxide layer on the top is only 10 microns thick
(Credit: Applied Physics Letters). |
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And here is an earlier version of a thin sandwich-structured
plastic dye-sensitived solar cell (DSSC) (Credit: Peccell
Technologies, Inc.). |
The research work has been published by Applied Physics
Letters on October 25, 2004, under the name "The photocapacitor:
An efficient self-charging capacitor for direct storage of solar
energy (Volume 85, Issue 17, pages 3932-3934).
Here is
a link to the abstract.
A light-driven self-charging capacitor was fabricated as an
efficient solar energy storage device. The device, which we
name the photocapacitor, achieves in situ storage of visible
light energy as an electrical power at high quantum conversion
efficiency. The photocapacitor was constructed on a
multilayered photoelectrode comprising dye-sensitized
semiconductor nanoparticles/hole-trapping layer/activated
carbon particles in contact with an organic electrolyte
solution, in which photogenerated charges are stored at the
electric double layer.
But when will see such solar cells on the market? The
scientists, Tsutomu Miyasaka and Takurou N. Murakami, frpm both
the Toin University of Yokohama and
Peccell Technologies, Inc. don't have a definitive
answer.
Miyasaka says that the next goal is to increase the charging
voltage and the charge-discharge capacity to a practically and
industrially useful level for applications.
Sources: Belle Dumé, PhysicsWeb, November 4, 2004; and
various websites |