Single-wall carbon nanotube coated silicon surface. Imaged with a atomic-force microscope. (via MIT & Rishabh Jain)
Carbon not only provides the foundation for all living things on earth, but it can create some of the most useful materials like carbon fiber and graphene. It can even smell rotting fruit. Now, carbon nanotubes are expanding the range of light rays that can be harvested from the sun. Conventional PV cells harvest photons in the visible spectrum, but researchers at MIT have found out how to manufacture a PV cell exclusively out of carbon nanotubes and C60 (buckyballs) to capture near-infrared energy.
A team led by chemical engineering professor Michael Strano, is working with Italian company Eni, to create the first all-carbon PV cell that does not need polymer layers. Near-infrared photons make up 40% of the solar energy from the sun, and this reserve is what the carbon nanotube cells will collect.
Initial tests have proven the concept of the all-carbon cell but have only provided a 0.1% energy conversion efficiency so far. However, the layer of carbon nanotubes is so thin, the PV cell is transparent and could be used in conjunction with conventional cells to take advantage of a wider photon spectrum. As far as the team can tell, their cell is stable in air, which distinguishes it from previous carbon cells.
The project has already revealed what works, what does not and how the prototype can be improved. They found that a heterogeneous mixture of different types of carbon nanotubes does not work. Instead, researchers hope to improve the efficiency of the cells by experimenting with the exact shape and thickness of the layer of very pure, uniform, single-walled nanotubes.
Because of the nanotube’s exceptionally high light absorption, these all-carbon PV cells require relatively small amounts of carbon and are extremely lightweight. Keeping the cost low, even at a low efficiency, makes these infrared PV cells enticing and worth refining.
The research is supported by the NSF and fellowships from the U.S. DoD.