Quantum Crystals: The Secret to Inexpensive & Efficient Green Energy?

If we can truly harness the power of the sun—in an efficient and cost effective manor—clean energy may become a widespread reality. Climate change experts say that humankind must find ways to turn to cleaner energy if we want to mitigate the potential devastating consequences of global warming.

Those concerned about Earth’s future will be encouraged to hear about the recent announcement by scientists at the U.S. Department of Energy. They have reported the discovery of a unique quantum physics effect in silicon nanocrystals, which should eventually help humankind come much closer to the goal of leaving “dirty” energy behind.

The researchers at the National Renewable Energy Laboratory, in collaboration with scientists at Innovalight Inc., discovered a new effect called Multiple Exciton Generation (MEG).

The effect occurs efficiently in silicon nanocrystals, resulting in the formation of more than one electron per absorbed photon, the scientists reported.

Until the new discovery, MEG had been reported during the past two years to occur only in nanocrystals (also called quantum dots) semiconductor materials that are not presently used in commercial solar cells, and which contained environmentally harmful materials such as lead. This new finding is of particular importance because silicon is already widely used in the industry, is readily available and plentiful within the Earth's crust, and poses no significant environmental problems regarding toxicity.

Quantum dots are particularly significant for optical applications due to their theoretically high quantum yield. In electronic applications they have been proven to operate like a single-electron transistor. Quantum dots have also been suggested as implementations of qubits for quantum information processing.

When today’s photovoltaic solar cells absorb a photon of sunlight, about 50 percent of the incident energy is lost as heat. MEG provides a way to convert energy lost as heat into additional electricity.

The new finding might lead to the application of MEG for greatly enhancing the conversion efficiency of solar cells based on silicon. That would represent a key step toward making solar energy more cost-competitive with conventional power sources. Innovalight is already planning to make flexible solar panels available at a cost that could be as much as ten times cheaper than the current solar cell technology.

* This research is detailed in the on-line version of the American Chemical Society's Nano Letters Journal.

Posted by Rebecca Sato