Friday, February 25, 2011

Quantum Dots - Cheap Solution to Higher Efficiency Solar

Scientists at Stanford University have given the vision of cheap solar power another nudge along the path to reality. They are working with tiny particles called quantum dots, which can be adjusted or “tuned” to absorb different wavelengths of light. Quantum dots are relatively cheap because they can be churned out from chemical reactions, rather than by a fabrication process. The sticking point, as always, is to turn a cheap material into a high efficiency solar energy collector.

The Do-Re-Mi of Quantum Dots
Quantum dots are semiconductors, which are the basic building blocks of modern electronics and a good chunk of solar technology, too. Silicon is one example of a widely used semiconductor. The difference between quantum dots and ordinary semiconductors is a matter of size. Quantum dots are only about one-billionth of a meter – one nanometer – in size, and this gives them a number of unique properties. For the Stanford team’s purposes, the critical difference is that ordinary semiconductors made of one material have a limited ability to absorb energy, but quantum dots can be tailored or “tuned” to accept different wavelengths by adjusting their size, and different sizes can be assembled to form more powerful solar cells.

More Efficient Quantum Dots…Relatively Speaking
As a first step, the Stanford team assembled a solar cell by coating a titanium dioxide semiconductor (titanium dioxide is another promising solar tech material) with a layer of organic molecules. Quantum dots formed at the interface between the semiconductor and the molecules, and the result was a three-fold increase in the efficiency of the solar cell. That sounds like a huge deal but keep in mind that the research is still in the initial stages, and the result was a sort of personal best efficiency of 0.4 percent. The next step is to experiment with more efficient materials for both the quantum dots and the organic molecules, and to improve the design of the solar cell.

A Quantum Leap to Cheap Solar
Solar power is already at or near price parity with natural gas in six states, and the technology is on course to meet overall fossil fuel parity within the ten-year solar and wind energy plan recently laid out by the Department of Energy. Aside from high-tech developments, there are also plenty of effective low-tech energy efficiency solutions at hand. That should be good news, given the generations-long priority this country has placed on washing our hands of dependency on foreign oil.


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