Structure of plastic solar cells impedes their efficiency, researchers find

Oct 05, 2010

(PhysOrg.com) -- A team of researchers from North Carolina State University and the U.K. has found that the low rate of energy conversion in all-polymer solar-cell technology is caused by the structure of the solar cells themselves. They hope that their findings will lead to the creation of more efficient solar cells.

Polymeric are made of thin layers of interpenetrating structures from two different conducting plastics and are increasingly popular because they are both potentially cheaper to make than those currently in use and can be “painted” or printed onto a variety of surfaces, including flexible films made from the same material as most soda bottles. However, these solar cells aren’t yet cost-effective to make because they only have a power conversion rate of about three percent, as opposed to the 15 to 20 percent rate in existing solar technology.

“Solar cells have to be simultaneously thick enough to absorb photons from the sun, but have structures small enough for that captured energy – known as an exciton – to be able to travel to the site of charge separation and conversion into the electricity that we use,” says Dr. Harald Ade, professor of physics and one of the authors of a paper describing the research. “The solar cells capture the photons, but the exciton has too far to travel, the interface between the two different used is too rough for efficient charge separation, and its energy gets lost.”

The researchers’ results appear online in Advanced Functional Materials and Nano Letters.

In order for the solar cell to be most efficient, Ade says, the layer that absorbs the photons should be around 150-200 nanometers thick (a nanometer is thousands of times smaller than the width of a human hair). The resulting exciton, however, should only have to travel a distance of 10 nanometers before . The way that polymeric solar cells are currently structured impedes this process.

Ade continues, “In the all-polymer system investigated, the minimum distance that the exciton must travel is 80 nanometers, the size of the structures formed inside the thin film. Additionally, the way devices are currently manufactured, the interface between the structures isn’t sharply defined, which means that the excitons, or charges, get trapped. New fabrication methods that provide smaller structures and sharper interfaces need to be found.”

Ade and his team plan to look at different types of polymer-based solar cells to see if their low efficiencies are due to this same structural problem. They hope that their data will lead chemists and manufacturers to explore different ways of putting these cells together to increase efficiency.

“Now that we know why the existing technology doesn’t work as well as it could, our next steps will be in looking at physical and chemical processes that will correct for those problems. Once we get a baseline of efficiency, we can redirect research and manufacturing efforts.”

Explore further: Physicists heat freestanding graphene to control curvature of ripples

Related Stories

Hot Electrons Could Double Solar Cell Power Efficiency

Dec 18, 2009

Scientists have experimentally verified a theory suggesting that hot electrons could double the output of solar cells. The researchers, from Boston College, have built solar cells that successfully use hot ...

Substantial improvement in essential cheap solar cell process

Mar 20, 2008

A cheap alternative to silicon solar cells can be found in dye-sensitised solar cells. This type of cell imitates the natural conversion of sunlight into energy by, for instance, plants and light-sensitive bacteria. Annemarie ...

Looking deeply into polymer solar cells

Sep 13, 2009

Researchers from the Eindhoven University of Technology and the University of Ulm have made the first high-resolution 3D images of the inside of a polymer solar cell. This gives them important new insights ...

'Nanocoax' solves solar cell 'thick and thin' dilemma

Jun 07, 2010

A nano-scale solar cell inspired by the coaxial cable offers greater efficiency than any previously designed nanotech thin film solar cell by resolving the "thick and thin" challenge inherent to capturing ...

Solar cells go thin and flimsy

Sep 04, 2006

The next generation of solar cells made out of plastics and microscopic crystals instead of silicon are taking shape at UQ (University of Queensland). UQ Master of Physics student Michael Deceglie is working ...

Recommended for you

Twisted graphene chills out

Sep 17, 2014

(Phys.org) —When two sheets of graphene are stacked in a special way, it is possible to cool down the graphene with a laser instead of heating it up, University of Manchester researchers have shown.

User comments : 0