How to harness ignored energy through solar cells

Can infrared light be harnessed to improve solar cell efficiency?

In the infrared region of the spectrum, approximately 40 percent of solar energy that touches the earth's surface is largely ignored by typical silicon-based solar cell arrays. Why? Because silicon-based cells are unable to harness light in the spectrum to such extreme degrees.

However, researchers at MIT have come up with an all-carbon based design, which has the possibility of tapping into all of that unused energy. Not only would this drastically improve the output and efficiency of solar cells, but take note -- renewable energy innovation like this is required to meet our modern demands -- which no doubt will continue to increase.

By combining traditional silicon-based cells and the new all-carbon cells, light on all ends of the spectrum could be captured, making use of each cell design's capabilities.

A paper describing the new device was published this week in the journal Advanced Materials.

The new cell design has been created through two forms of carbon, carbon nanotubes and C60. The first all-carbon photovoltaic cell (PV) to be developed, the nanotube carbon has to be extremely pure and uniform -- in this case, single-walled and symmetrical.

Other researchers have created PV cells using carbon nanotubes, but it is only by using a layer of polymer that the tubes can be held in position -- which consequentially adds additional time and expense to production. In air, the cells also require extra coatings to stop degradation -- something the new PV cells do not appear to need.

The carbon-based cell performs best when capturing light in the near-infrared region. As the material is transparent, these cells could in theory be overlaid across traditional PVs, which would result in a dvice with a far higher capacity for capturing solar energy.

However, the design needs further refining and experimentation, as the energy-conversion efficiency is currently only about 0.1 percent.

Strano pointed out that current solar cells generally ignore the near-infrared part of the spectrum, but this unused energy even in low-efficiency cells could be worthwhile to try and grasp -- as long as the cost of producing capable solar-cells is low enough. For those in renewable energy development, being able to create an infrared-absorbing photovoltaic cell without polymer layers is a "dream in the field".

Michael Arnold, an assistant professor of materials science and engineering at the University of Wisconsin at Madison said:

"Carbon nanotubes offer tantalizing possibilities for increasing the efficiency of solar cells and are kind of like photovoltaic polymers on steroids. This work is exciting because it demonstrates photovoltaic power conversion using an active layer that is entirely made from carbon.

This seems like a very promising direction that will eventually allow for nanotubes' promise to be more fully harnessed."

The team hopes that other researchers will join the development, and more ways can be found to improve the efficiency of the system.

(via MIT)

Image credit: Flickr


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