Seeing Red: New Solar Energy Material Can Utilize Infrared Spectrum

EM spectrum chart image

EM Spectrum chart via Wikipedia

As I'm sure the vast majority of TreeHugger readers know, the garden variety, conventional solar cell works by absorbing energy from solar radiation as it falls on the earth. However, what you may not have ever given a second thought to is the fact that the solar energy that actually is usable by the solar cell comes from the visible spectrum. The ultraviolet and infrared portions of the spectrum mean nothing in terms of energy production.

63% : New Material's Theoretical Efficiency Limit
A Spanish team of researchers has designed a new solar material which can theoretically harness 63% of the sun's rays. New Scientist explains:

Semiconductor solar cells [TH note: in other words, your ordinary solar cell] produce electricity when photons carrying just the right energy are absorbed by trapped electrons, boosting them into a higher energy level where they can flow freely.

Cells can't make electricity from photons with much more or less energy than the right amount. Cells are tuned to visible light because visible photons vary little in energy, but reach earth in very large numbers. But in 1997 other Spanish researchers came up with a way to increase the spectrum cells could use.

Their idea was to create a kind of energy "stepping stone". Instead of having to jump to the higher energy level in one go, electrons can absorb a low-energy photon and then wait at an intermediate energy level until another arrives to let it complete the trip.

By adding titanium and vanadium into the semiconducting material you can alter the material so that it can use the infrared spectrum of light as well as the visible.

It's because of the utilization of the infrared spectrum that this material has a theoretical absorption limit of 63%, which compares to about 40% for ordinary solar cells.

Real-world Efficiency Will be Lower Than Theoretical Maximum
Researchers are quick to point out, however, that this figure is a theoretical limit. In practice, real-world efficiency of panels using this materials won't reach that theoretical maximum, but "if the [theoretical] limit is higher, you can presume that the real figure that you will be able to reach will also be higher."

Before anyone asks, 'where can I get one?', the answer is 'you can't'. This material has yet to be made into an actual solar cell, though that is a goal for the near future.

via :: New Scientist
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