A new way to harvest more light to make solar cells more efficient

Researchers at MIT have figured out a new technique to make a traditional silicon solar cell — the kind that makes up most solar panels on rooftops — more efficient. The scientists published the findings in Nature Nanotechnology this week.

The innovation embeds a two-layer device made of carbon nanotubes and photonic crystals between the solar cell and the sun’s light. The device absorbs the sun light, heats up, and emits light that has a specific wavelength that can be used efficiently by the adjacent solar cell. A typical silicon solar cell doesn’t use all of the wavelengths of sun light, and many go to waste.

Austin's 's Pecan Street Project. Photo courtesy of Pecan Street Inc.

Austin’s ‘s Pecan Street Project. Photo courtesy of Pecan Street Inc.

The MIT researchers say that with these types of designs, which use heat to boost efficiency, some solar cells in theory could one day produce an efficiency of over 80 percent. In comparison some of the highest efficient solar cells in mass production currently are in the low 20 percent range from SunPower. Alta Devices claims a solar cell that delivers 30 percent efficiency.

The innovation is currently just in the lab (and only developed at a 3.2 percent efficiency) and as we all know many things change in the journey from the lab to the factory. But the MIT researchers think they can push their tech to reach a 20 percent efficiency, which could deliver a commercial product.

Efficiency is very important for solar manufacturers because it’s one of the best ways for these companies to differentiate and sell a higher end product — the cells can convert more light, and more power is created with the same amount of panels. SunPower can sell its panels for more money than the lower commodity 10 percent conversion panels.

Other innovations that can boost efficiency for solar cells include tiny super conducting dots, photon recycling and epitaxial lift-off, and using optics to split spectrum.