Harnessing Light's Full Spectrum: Scientists Claim Solar Power Breakthrough
By Dan Shapley
Chemists at Ohio State University say they have produced a next-generation material that not only absorbs the full spectrum of sunlight, but also make makes the electrons generated more easy to capture.
The hybrid material -- a combination of electrically conductive plastic and metals like molybdenum and titanium -- is the first of its kind to capture the full solar spectrum, according to Malcolm Chisholm, one of the authors of the paper describing the research, which appears in Proceedings of the National Academy of Sciences. Solar panels in use today capture only a small fraction of the energy contained in sunlight.
The material is years from being made into a commercial product, but is another example of how innovations in the field of solar energy could make vastly more of the sun's energy available for human use. Recent action by Congress to extend industry tax incentives should keep companies investing in new technology research and development. And according to the Department of Energy, "Under the ongoing global financial crisis, a lack of available credit is causing projects to be delayed or canceled, but the clean energy sector is continuing to attract substantial amounts of investment capital."
If coupled with new battery technology, solar energy technology has the potential to revolutionize the way we generate electricity. Millions of homes could be outfitted with their own power sources, and they could store enough electricity -- if efficient enough -- to eliminate the need for power plants in the residential sector.
That's been the promise of solar energy for a long time. Breakthroughs like this one announced by Ohio State brings the vision that much closer to reality.
Here's how the university described the breakthrough:
The material generates electricity just like other solar cell materials do: light energizes the atoms of the material, and some of the electrons in those atoms are knocked loose.
Ideally, the electrons flow out of the device as electrical current, but this is where most solar cells run into trouble. The electrons only stay loose for a tiny fraction of a second before they sink back into the atoms from which they came. The electrons must be captured during the short time they are free, and this task, called charge separation, is difficult.
In the new hybrid material, electrons remain free much longer than ever before.
To design the hybrid material, the chemists explored different molecular configurations on a computer at the Ohio Supercomputer Center. Then, with colleagues at National Taiwan University, they synthesized molecules of the new material in a liquid solution, measured the frequencies of light the molecules absorbed, and also measured the length of time that excited electrons remained free in the molecules.
They saw something very unusual. The molecules didn't just fluoresce as some solar cell materials do. They phosphoresced as well. Both luminous effects are caused by a material absorbing and emitting energy, but phosphorescence lasts much longer.
To their surprise, the chemists found that the new material was emitting electrons in two different energy states -- one called a singlet state, and the other a triplet state. Both energy states are useful for solar cell applications, and the triplet state lasts much longer than the singlet state.
Electrons in the singlet state stayed free for up to 12 picoseconds, or trillionths of a second -- not unusual compared to some solar cell materials. But electrons in the triplet state stayed free 7 million times longer -- up to 83 microseconds, or millionths of a second.
When they deposited the molecules in a thin film, similar to how they might be arranged in an actual solar cell, the triplet states lasted even longer: 200 microseconds.
