To create its ultra-lightweight solar cells, the first research team-led by Vladimir Bulovic of the Massachusetts Institute of Technology (MIT), USA-focused particularly on slimming down the solar-cell substrate.
At present, the most common substrate for photovoltaics is glass, which-while exceptionally smooth and strong-adds substantial weight and rigidity to the solar cell built on top of it.
As a lighter and more flexible replacement, the scientists zeroed in on a substrate candidate called parylene-C, an organic chemical that is known to form thin, smooth films, and that is already used commercially as a protective coating in biomedical and electronic components.
The key to the ultrathin cells, however, lies, according to Bulovic
, not in the specific material but in the method.
That method begins with spin-coating a glass foundation with a solvent that acts as a "release" layer to allow for removal of the solar cell.
Then, using vapor deposition in vacuum conditions, a base layer of parylene is laid down on the glass, followed by organic solar-cell components, which are finally overtopped by an additional protective coating of parylene.
The ultrathin component is then peeled off of the glass.
The fabrication method allows the entire device to be created in a single room-temperature process, without handling the fragile device or breaking the vacuum, minimizing the risks of damage.
"The innovative step," according to Bulovic
, "is the realization that you can grow the substrate at the same time you grow the device."