In the world of solar energy, organic
photovoltaic solar cells have a wide range of potential applications, but they
are still considered an upstart. While these carbon-based cells, which use
organic polymers or small molecules as semiconductors, are much thinner and
less expensive to produce than conventional solar cells made with inorganic
silicon wafers, they still lag behind in their ability to efficiently convert
sunlight into electricity.
Now, University
of California, Los
Angeles (UCLA) researchers and their colleagues from China and Japan have shown that by
incorporating gold nanoparticles into these organic photovoltaics—taking
advantage of the plasmonic effect, by which metal helps to enhance the
absorption of sunlight—they can significantly improve the cells’ power
conversion.
In a paper published in ACS Nano,
the team of researchers, led by Yang Yang, a professor of materials science and
engineering at the UCLA Henry Samueli School of Engineering and Applied Science
and director of the Nano Renewable Energy Center at UCLA’s California
NanoSystems Institute, demonstrate how they sandwiched a layer of gold
nanoparticles between two light-absorbing subcells in a tandem polymer solar
cell in order to harvest a greater fraction of the solar spectrum.
They found that by employing the
interconnecting gold-nanoparticle layer, they were able to enhance power conversion
by as much as 20%. The gold nanoparticles create a strong electromagnetic field
inside the thin organic photovoltaic layers by a plasmonic effect, which
concentrates light so that much more of it can be absorbed by the subcells.
The team is the first to report a
plasmonic-enhanced polymer tandem solar cell, having overcome the difficulties
involved in incorporating metal nanostructures into the overall device
structure.
“We have successfully demonstrated a
highly efficient plasmonic polymer tandem solar cell by simply incorporating
gold nanoparticles layer between two subcells,” Yang says. “The
plasmonic effect happening in the middle of the interconnecting layer can
enhance both the top and bottom subcells simultaneously—a ‘sweet spot’—leading
to an improvement in the power conversion efficiency of the tandem solar cell
from 5.22 to 6.24%. The enhancement ratio is as high as 20%.”
The research team included Xing Wang Zhang
from the Key Lab of Semiconductor Materials Science at the Institute of Semiconductors
at Beijing’s Chinese
Academy of Science and Ziruo Hong from
the Graduate School of Science and Engineering at Japan’s
Yamagata University.
Experimental and theoretical results
demonstrate that the enhancement effect was attained from local near-field
enhancement of the gold nanoparticles. The results show that the plasmonic
effect has great potential for the future development of polymer solar cells.
The team’s proposed interlayer structures as an open platform can be applied to
various polymer materials, opening up opportunities for highly efficient,
multi-stacked tandem solar cells.
