Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, like handheld calculators or wrist watches, remote radiotelephones and water pumping applications. More recently, they are starting to be used in assemblies of solar modules (photovoltaic arrays) connected to the electricity grid through an inverter, often in combination with a net metering arrangement.

Solar cells are regarded as one of the key technologies towards a sustainable energy supply.

Heating plastic solar cells can alter their structure in a way that boosts efficiency, new research shows. The US and Korean scientists behind the discovery say it could ultimately allow flexible, lightweight plastic cells to replace rigid traditional cells.

Solar cells are usually made from silicon, which is inflexible and relatively heavy. By contrast, plastic solar cells could be more easily supported and wrapped around surfaces. It might even be possible to spray light-collecting plastic onto a surface.

Plastic cells lag behind silicon in terms of efficiency, however, at best converting just 5% of solar energy into electricity compared with up to 40% for conventional cells. "To make plastic cells commercially viable, you need to reach about 8%," says David Carroll of Wake Forest University in Winston-Salem, US. "That matches some silicon products already on the market."

The best plastic solar cells are made from a light-absorbing polymer containing soccer ball-shaped carbon molecules called fullerenes. The fullerenes provide stepping stones in the plastic film for charge to hop across.

Three percent was the highest efficiency ever achieved by plastic solar cells until 2005 when David Carroll, 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 the 6 percent mark.

"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 applications, solar cells must be able to convert about 8 percent of the energy in sunlight into electricity, but the researchers hope to achieve a 10% standard in a few years.

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, the latter do not have to be reinforced to support additional weight.