Rutgers works on efficient, inexpensive plastic solar cells

Physicists at Rutgers University have discovered new properties in a material that could result in efficient and inexpensive plastic solar cells for pollution-free electricity production.

An organic single-crystal transistor made out of rubrene (red crystal). This is an optoelectronic device similar to those used by Rutgers physicists to measure exciton diffusion

The discovery, posted online and slated for publication in an upcoming issue of the journal Nature Materials, reveals that energy-carrying particles generated by packets of light can travel on the order of a thousand times farther in organic (carbon-based) semiconductors than scientists previously observed. This boosts scientists' hopes that solar cells based on this budding technology may one day overtake silicon solar cells in cost and performance, thereby increasing the practicality of solar-generated electricity as an alternate energy source to fossil fuels.

''Organic semiconductors are promising for solar cells and other uses, such as video displays, because they can be fabricated in large plastic sheets,'' said Vitaly Podzorov, assistant professor of physics at Rutgers. ''But their limited photo-voltaic conversion efficiency has held them back. We expect our discovery to stimulate further development and progress.''

Podzorov and his colleagues observed that excitons – particles that form when semiconducting materials absorb photons, or light particles – can travel a thousand times farther in an extremely pure crystal organic semiconductor called rubrene. Until now, excitons were typically observed to travel less than 20 nanometers – billionths of a meter – in organic semiconductors.

''This is the first time we observed excitons migrating a few microns,'' said Podzorov, noting that they measured diffusion lengths from two to eight microns, or millionths of a meter. This is similar to exciton diffusion in inorganic solar cell materials such as silicon and gallium arsenide.

''Once the exciton diffusion distance becomes comparable to the light absorption length, you can collect most of the sunlight for energy conversion,'' he said.