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5 December 2013 11:26 am ,
Vol. 342 ,
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Catching More Rays
10 November 2003 (All day)
A new semiconductor may lead to improved solar cells that capture a wider range of sunlight's energy--and pump out more electricity.
When sunlight strikes a semiconductor solar cell, energy from the photons knocks loose electrons in the semiconductor, allowing current to flow. But only particular bands of wavelengths have just the right amount of energy to do the trick. Existing silicon solar cells, which have just one such band gap, turn about 15% of light energy into electricity. Combining materials with various band gaps is one way to boost their efficiency. Layering up to three materials can improve the efficiency to about 30%, but that's difficult and expensive to do, limiting the resulting solar cells to high-tech applications such as satellites. Researchers have theorized that a single semiconductor with multiple band gaps would be more efficient, but so far they haven't been able to manufacture one.
Now a group has engineered an alloy of zinc, manganese, and tellurium, with a touch of oxygen, that has two band gaps. One wavelength of light sends electrons into an excited state; another wavelength knocks resting electrons into a second, higher energy excited state. As a bonus, yet a third wavelength can knock electrons from the first excited state to the second, potentially converting even more of the light energy into electricity. In a paper to be published in Physical Review Letters, Kin Man Yu of Lawrence Berkeley National Laboratory and colleagues calculate that in a solar cell, the material would be 45% efficient. And tuning the oxygen content could boost the efficiency above 50%, they suggest.
The concept "is very intriguing," says Paul Sharps, development manager at Emcore Photovoltaics, a solar cell manufacturer in Albuquerque, New Mexico. However, he cautions, "there are many, many issues that have to be addressed before this material can ever be considered for use as a solar cell." For example, he says, charges have trouble moving through semiconductors made of alloys, which could make it hard to extract power from the new material. Nevertheless, the authors have taken an important step by moving from theory to an actual material, says Antonio Marti of the Polytechnic University of Madrid.