Researchers at MIT have developed a new type of photovoltaic cell made with carbon nanotubes that captures solar energy in the near-infrared region of the spectrum, which conventional silicon solar cells don’t. The new design means solar cell efficiency could be greatly increased, boosting the chances to make solar power a more popular source of energy.

The new solar cell developed at MIT is a consequence of recent advances in the large-scale production of carbon nanotubes. It also features another type of carbon, a fullerene known as C60 (aka Buckminsterfullerene). The nanotubes have to be very pure, single-walled and of the same symmetrical configuration. The material is transparent to visible light and has to be overlaid on conventional silicon cells to form a hybrid cell that could, in theory, capture most of the energy contained in the sunlight it captures.

This is not the first time researchers have used carbon nanotubes to make solar cells, but researcher Michael Strano and his team found that the new all-carbon cells appear to be stable in air, therefore they did not require a layer of polymer to hold the nanotubes together in position. This characteristic eliminates a stage in the production process that hitherto has made it more complex. The cells require relatively small amounts of highly purified carbon, resulting in a lighter end product.

There are several bright, optimistic spots in this research, the scientists say. Although the proof of concept devices have so far achieved an efficiency of only 0.1 percent, the researchers have already identified some of the sources of inefficiency. For instance, they have noticed that homogenous mixtures of carbon nanotubes are more efficient than heterogeneous ones. Mixing single-walled and multiwalled nanotubes is not a good idea, either.

The scientists are positive they are bound to make high-efficiency near-infrared solar cells, and point out that even a low-efficiency cell that works in that region, capturing energy that current cells waste, would be worthwhile provided costs are low. They are now looking into ways to better control the shape and thickness of the layers of the material.

A paper written by Professor Strano describing the all-carbon solar cell in detail was recently published in the journal Advanced Materials.

Source: MIT