Solar Cell Efficiency Rises

Plastic solar cell efficiency has been pushed to more than 6 percent via “nanofilaments” within light-absorbing plastic, similar to the veins in tree leaves, enabling the use of thicker absorbing layers in the devices which capture more sunlight.

A paper by researchers at the Wake Forest University Center for Nanotechnology and Molecular Materials, to be published in an upcoming issue of Applied Physics Letters, describes how they have achieved the record efficiency for organic or flexible, plastic solar cells. Efficient plastic solar cells are extremely desirable because they are inexpensive and lightweight, especially in comparison to traditional silicon solar panels. Traditional solar panels are heavy and bulky and convert about 12 percent of the light that hits them to useful electrical power, the researchers said in a university statement.

David Carroll, director of the Wake Forest nanotechnology center (Photo courtesy Wake Forest University)

Scientists have worked for years to create flexible, or “conformal,” organic solar cells that can be wrapped around surfaces, rolled up or even painted onto structures. Three percent was the highest efficiency ever achieved for plastic solar cells until 2005, when David Carroll, director of the Wake Forest nanotechnology center, and his research group announced they had come close to reaching 5 percent efficiency. Now, a little more than a year later, Carroll said his group has surpassed 6 percent.

"Within only two years we have more than doubled the 3 percent mark,” Carroll said. “I fully expect to see higher numbers within the next two years, which may make plastic devices the photovoltaic of choice.” In order to be considered a viable technology for commercial use, solar cells must be able to convert about 8 percent of the energy in sunlight to electricity. Wake Forest researchers hope to reach 10 percent in the next year, said Carroll, who is also associate professor of physics at Wake Forest.

Jiwen Liu, a researcher in the Wake Forest University Center for Nanotechnology and Molecular Materials, tests a new solar cell in the center's laboratory in Winston-Salem, N.C. (Photo courtesy Wake Forest University)

Because they are flexible and easy to work with, plastic solar cells could be used as a replacement for roof tiling or home siding products or incorporated into traditional building facades. These energy-harvesting devices could also be placed on automobiles. Since plastic solar cells are much lighter than the silicon solar panels, structures do not have to be reinforced to support additional weight.

A large part of Carroll’s research is funded by the US Air Force, which is interested in the potential uses of more efficient, lightweight solar cells for satellites and spacecraft. Other members of Carroll’s research team include Jiwen Liu and Manoj Namboothiry, postdoctoral associates at Wake Forest’s nanotechnology center, and Kyungkon Kim, a postdoctoral researcher at the center, who has moved to the Materials Science & Technology Division at the Korea Institute of Science and Technology in Seoul.

Fore more information, visit: wfu.edu