Wednesday, February 17, 2010

3 Approaches to Nano-Photovoltaics

Using arrays of long, thin silicon wires embedded in a polymer substrate, a team of scientists from the California Institute of Technology (Caltech) has created a new type of flexible solar cell that enhances the absorption of sunlight and efficiently converts its photons into electrons. The solar cell does all this using only a fraction of the expensive semiconductor materials required by conventional solar cells. _ScienceDaily
The Caltech scientists have reportedly exceeded the conventional light-trapping limit of absorptive materials.

Professor Dawn Bonnell the director of the Nano/Bio Interface Center at the University of Pennsylvania and her colleagues have demonstrated the transduction of optical radiation to electrical current in a molecular circuit. The system uses an array of nano-sized molecules of gold that respond to electromagnetic waves by creating surface plasmons to induce and project electrical current across molecules, similar to that of photovoltaic solar cells. _NewEnergyandFuel
This approach is unique in that the hardware acts as an electromagnetic "antenna" for photons. It is worth reading Brian's article in full to understand how this approach is different from traditional photovoltaics. The authors suggest that their approach may eventually lead to a significant price breakthrough in solar electricity.
The cells designed by Solasta are built on a substrate forested with long, thin, vertically arrayed nanopillars. The pillars are coated first with metal, then with a thin layer of semiconducting material such as amorphous silicon, and then with a layer of transparent conductive oxide. Though the silicon layer is thin, a photon still has a relatively long path to travel down the length of the nanopillars, and a good chance of transferring its energy to an electron. Freed electrons then travel perpendicularly over a very short path to the metal at the core of each pillar, and shimmy down this electrical pole off the cell. "Electrons never have to travel through the photovoltaic material," says Zhifeng Ren, professor of physics at Boston College. "As soon as they're generated, they go into the metal." Ren founded Solasta with professors Michael Naughton and Krzysztof Kempa. _TechnologyReview
This approach is traditional photovoltaics, but in 3 dimensions. Increasing the surface area allows for more incident photon absorption.

Al Fin solar specialists prefer solar energy to wind energy, since solar energy is more predictable over huge geographic areas than wind. The energy storage problem is still a significant issue. Even with extremely inexpensive (free) solar cells, the short useful daily time frame for solar energy production will limit applications until large scale, inexpensive energy storage is available.



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