Today's solar cells are relatively expensive because they are made from the computer chip material silicon, which requires relatively expensive manufacturing processes including clean rooms.

It is possible to make solar cells from cheaper, easier-to-work-with materials, including organic, or plastic-based materials. The trick is finding inexpensive materials that are also efficient.

Researchers from the Georgia Institute of Technology have fabricated an inexpensive, plastic-based solar cell that has the potential to be fairly efficient.

Most organic photovoltaic cells are based on amorphous or nearly amorphous organic materials. In contrast, the Georgia researchers are using pentacene, a polycrystalline organic semiconductor. Polycrystalline materials, unlike amorphous materials, consist of crystal grains that have a lattice-like molecular structure. Pentacene is widely used in organic transistor research.

The researchers' device consists of a glass plate, a layer of indium oxide, a layer of pentacene, a layer of carbon buckyball molecules, a layer of bathocuproine, and an aluminum electrode. The pentacene-carbon portion forms a semiconductor junction that separates negative electrons from positive holes to generate electricity. The researchers have measured a power conversion efficiency as high as 3.4 percent for the material.

It will not be difficult to boost the efficiency to 5 percent, according to the researchers. Existing organic solar cells are about 3.5 percent efficient, while state-of-the-art crystal silicon solar cells are about 25 percent efficient.

The method could be used to power radiofrequency ID tags and sensor networks. It could also eventually be used for solar cells that generate residential power, according to the researchers.

The method could be used for powering sensors within two years and for residential solar cells within five years, according to the researchers and. The work appeared in the November 29, 2004 issue of Applied Physics Letters.

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