This New Solar Cell Doesn't Need A Battery

By Roland Piquepaille

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.
The latest version of the sandwich photocapacitor 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).
An earlier version of a dye-sensitived solar cell 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

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