A new approach to photovoltaic panels

This schematic shows the components of the optical rectenna developed at the Georgia Institute of Technology. Credit: Thomas Bougher, Georgia Tech

A carbon nanotube optical rectenna converts green laser light to electricity in the laboratory of Baratunde Cola at the Georgia Institute of Technology. Credit: Rob Felt, Georgia Tech

Present photovoltaic panels today are made from silicon, exploiting its semiconductor properties to absorb photons and mobilising electrons (a phenomenon that was discovered almost 200 years ago, in 1839 by Bequerel, and explained by Einstein who actually got the Nobel Prize for this, and not for his relativity theory...).

Carbon is also a semiconductor and scientists at the Georgia Institute of Technology have just reported they found a way to use it for converting light into electricity.

They have used carbon nanotubes, billions of them, each one embedding a rectifier (a diode). They work as antennas (rectenna, the name bestowed...). Light is both a beam of particle and a wave, at the same time depending how you decide to look at it (magic on quantum physics). Here we are exploiting the wave characteristics. Waves are captured by billions of rectennas structured into arrays and they induce an oscillation of electrons that through the rectifiers is transformed into a direct current (DC). Each rectifiers switches at petahertz rates (in synch with lightwave "frequency").

So far the efficiency is around 1%, much lower than current silicon based photovoltaic panels, but researchers believe they will be able to perfect this technology. They expect to be able to create solar panels that will dissipate less heat, have higher efficiency and, most crucially, can cost ten times less than current commercial photovoltaic panels.

This just show another application of carbon nanotubes and it is part of the global effort to substitute silicon with carbon. They are both semiconductors, have the same chemical/physical characteristics since they both have 4 electrons and for "holes" in their atomic outer orbit but carbon is less stable, so it is more difficult to control. This is why only in these last few years, with the bettering of technology, researchers feel they will be able to "tame" the carbon in a way that exploits its lower stability, which turns out to be a side effect of the lower level of energy that can affect it. This lower energy both leads to lower stability and less power requirement to use it, which is actually the holy grail being pursued: faster operation at less energy cost.

Author - Roberto Saracco

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