Researchers from North
Carolina State University have found a way to create
much slimmer thin-film solar cells without sacrificing the cells’ ability to
absorb solar energy. Making the cells thinner should significantly decrease
manufacturing costs for the technology.

“We were able to create solar cells using a ‘nanoscale sandwich’ design with
an ultrathin ‘active’ layer,” says Linyou Cao, PhD, an assistant professor of
materials science and engineering at NC State and co-author of a paper
describing the research. “For example, we created a solar cell with an active
layer of amorphous silicon that is only 70 nm thick. 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.”
The ‘active’ layer in thin-film solar cells is the layer of material that
actually absorbs solar energy for conversion into electricity or chemical fuel.

“The technique we’ve developed is very important because it can be generally
applied to many other solar cell materials, such as cadmium telluride, copper
indium gallium selenide, and organic materials,” Cao adds.

The new technique relies largely on conventional manufacturing processes,
but results in a very different finished product. The first step is to create a
pattern on the substrate using standard lithography techniques. The pattern
outlines structures made of transparent, dielectric material measuring between
200 and 300 nm. The researchers then coat the substrate and the nanostructures
with an extremely thin layer of active material, such as amorphous silicon.
This active layer is then coated with another layer of dielectric material.

Using dielectric nanostructures beneath the active layer creates a thin film
with elevated surfaces evenly spaced all along the film—like crenellations at
the top of a medieval castle.

“One key aspect of this technique is the design of the ‘nanoscale sandwich,’
with the active materials in the middle of two dielectric layers. The
nanostructures act as very efficient optical antennas,” Cao says, “focusing the
solar energy into the active material. This focusing means we can use a thinner
active layer without sacrificing performance. In the conventional thin-film
design, using a thinner active layer would impair the solar cell’s efficiency.”

The paper, “Dielectric Core-shell Optical Antennas for Strong Solar Absorption
Enhancement,” is published online in Nano Letters.

Source: North Carolina State University