"Nanoscale sandwich" technique could mean thinner, cheaper solar cells
By Ben Coxworth
June 25, 2012
We certainly hear a lot about solar cells that are able to convert larger and larger percentages of the sun’s energy into electricity. That’s all very well and good, but if those more-efficient solar cells are too expensive, they will still ultimately prove impractical for everyday use. Researchers from North Carolina State University, however, have found a way of creating “ultra-thin” solar cells that should create just as much electricity as their thicker siblings, but at a lower cost.
The new cells are made using what is called a “nanoscale sandwich” design. The process starts with a pattern being laid down on a transparent dielectric substrate, using regular lithography techniques. That pattern forms the substrate into tiny structures measuring between 200 and 300 nanometers in height – when viewed in cross-section, they resemble the crenelations along the top of a medieval castle.
Next, a very thin layer of the active material is deposited onto the altered substrate. This “active layer” is what actually converts the solar energy into electricity. Finally, on top of that layer, another layer of the dielectric material is deposited. This results in a dielectric/active material/dielectric sandwich.
The crenelated shape of this sandwich allows the two dielectric layers to serve as highly-efficient optical antennas, focusing the solar energy onto the layer of active material – this means that less of that material can be used, without a loss in performance.
“We created a solar cell with an active layer of amorphous silicon that is only 70 nanometers (nm) thick,” said Dr. Linyou Cao, co-author of a paper on the research. “This is a significant improvement, because typical thin-film solar cells currently on the market that also use amorphous silicon have active layers between 300 and 500 nm thick.”
He added that the same technique could be used to create solar cells incorporating other active materials, such as cadmium telluride, copper indium gallium selenide, and organic materials.
His paper was recently published in the journal Nano Letters.
Source: North Carolina State University