8 October 2009

… Silver nanoparticles give polymer solar cells boost

Small bits of metal may play a new role in solar power.

Polymer semiconductors that absorb the sun’s energy and generate electricity may make for lighter, cheaper, and more-flexible solar cells. Adding tiny bits of silver to the plastic can boost the materials’ electrical current generation.

A team from Ohio State University measured the amount of light absorbed and the current density—the amount of electrical current generated per square centimeter—generated by an experimental solar cell polymer with and without silver nanoparticles, said Paul Berger, professor of electrical and computer engineering and professor of physics at Ohio State.

Without silver, the material generated 6.2 milli-amps per square centimeter. With silver, it generated 7.0—an increase of almost 12%.

The small silver particles help the polymer capture a wider range of wavelengths of sunlight than would normally be possible, which in turn increases the current output, Berger said.

He added with further work, this technology could go a long way toward making polymer solar cells commercially viable.

“The light absorption of polymer solar cells is inadequate today,” Berger said. “The top-performing materials have an overall efficiency of about 5%. Even with the relatively low production cost of polymers compared to other solar cell materials, you’d still have to boost that efficiency to at least 10% to turn a profit. One way to do that would be to expand the range of wavelengths that they absorb. Current polymers only absorb a small portion of the incident sunlight.”

The new fabrication technique involves encasing each silver particle in an ultra-thin polymer layer, a different polymer than the light-absorbing polymer that makes up the solar cell, before depositing them below the light-absorbing polymer; the coating prevents the silver particles from clumping, but also allows them to self-assemble into a dense and regular mosaic pattern that Berger believes is key to enhancing the light absorption.