The technological momentum in solar cells right now is aimed largely at pursuing greater efficiency. Most solar cells can convert 15 to 20 percent of the light energy that hits them into electricity, with most advanced hitting 30 percent. But researchers at MIT published a paper a few weeks ago exploring advancements in an alternative direction — instead of pursuing better light-to-electricity conversions, they’re looking into ways to create cells using fewer materials. While the process they’ve laid out would construct solar cells with only 1 or 2 percent efficiency, the cells would also be so incredibly thin that they could produce up to 1,000 times more energy per pound than conventional photovoltaic cells.
According to Jeffrey Grossman — the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, who authored the paper along with Marco Bernardi, a postdoc in MIT’s Department of Materials Science, and Maurizia Palummo, a senior researcher visiting MIT from the University of Rome — the process uses nanotechnology to layer together a one-molecule thick sheet of graphene and a one-molecule-thick sheet of molybdenum disulfide. The resulting two-layer solar cell is only one nanometer, or one billionth of a meter, thick. Bernadi also added that stacking multiple sets of the two-layer cell on top of one another could possibly then boost the otherwise-low conversion efficiency.
For comparison, another ultra-thin solar cell in development right now by Alta Devices — which can hit 30 percent efficiency — is 1,000 time thicker at one micrometer (or micron). The Alta Devices cell is also more expensive to manufacture than traditional photovoltaics. By contrast, the MIT process would reduce costs through far less use of raw materials and by not requiring any use of purified silicon. Half the price of most solar panels today also comes from support structures and installation expenses, which would also be cut down by such thin and light cells. “It’s 20 to 50 times thinner than the thinnest solar cell that can be made today,” Grossman added. “You couldn’t make a solar cell any thinner.”
Surprisingly, the cells should be quite physically robust. Most solar cells have to be protected from the open air by heavy glass, but the MIT cells would be “essentially stable in air, under ultraviolet light, and in moisture,” according to Grossman. Between that and the cells’ incredibly light weight, applications in everything from aviation to the space industries and the military seem especially promising. Furthermore, there’s no inherent reason the process has to be limited to the materials MIT used, meaning there’s a wide range of alternatives and alternative combinations the new layering approach opens up for investigation.
The one (big) downside is that all of this so far exist purely in the realm of computer modeling — the MIT team has yet to produce an actual physical demonstration project. There are also no large scale methods for producing molybdenum disulfide and the other materials used in the process, meaning the ability to put together a practical manufacturing process is still a very long way off. It’s “an essential question,” Grossman admits. “But I think it’s a solvable problem.
(HT: Solar Love)