New solar cell is thinner than spider silk

Film is lighter and more flexible than previous photovoltaic technologies

This photograph shows the only two microns thin solar cell film bent over a 1.5 mm thin tube, it can be extremely deformed without damage. © Martin Kaltenbrunner
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An ultra-thin and highly flexible solar cell could in future drive tiny flying robots and turn even the finest garments into energy suppliers. Because the energy foils developed by an international research team are only two microns thick and thus thinner than a thread spider silk. In addition, they can be crumpled repeatedly like a piece of cling film without being damaged. "These ultra-thin organic solar cells are ten times thinner, lighter, and more flexible than any other solar cell type currently available, " the researchers report in the journal Nature Communications. With an efficiency of 4.2 percent, they are still just as powerful as conventional organic solar cells on glass slides.

Possible applications of the new solar cells are weather balloons, unmanned aerial vehicles or other remote sensing systems where weight is important. "But the same applies to the equipment in the wilderness, where light energy sources are needed, " write Martin Kaltenbrunner of the Johannes Kepler University Linz and his colleagues. Even miniature robots could be powered by it.

Ultrathin and highly flexible solar cell © Martin Kaltenbrunner

Standard materials applied to thin film

The new technology uses standard materials already used for organic solar cells. Nevertheless, the energy foil has only 25 percent of the thickness and 45 percent of the weight of conventional organic solar cells.

As a carrier substrate, the researchers used no coated with indium-tin oxide glass, but only a 1.4 micron thin film of the plastic polyethylene terephthalate (PET). This is the same material that makes many bottles. On top of this film, they applied two different active layers, which together formed the actual organic solar cell.

Ultrathin PET films are already routinely manufactured in the industry. "It will facilitate the future mass production of such cells through roll-to-roll printing, " say the researchers. The optically active layer is continuously applied by large machines, similar to the newspaper printing. display

The new solar cell foil is so thin and flexible at only two micrometers thick that it can even be wound around a human hair - as can be seen here - without breaking. Martin Kaltenbrunner

Solar cell wrapped around a human hair

The new solar cell film is so flexible and thin that it can even wrap around a human hair, the scientists say. The hair was at 35 microns diameter about 16 times thicker than the film. The solar cell foil could also be draped over the tip of a 1.5 mm thin plastic tube without tearing.

In another experiment, the researchers pushed laterally different variants of these solar cell foils and crumpled them. Even when the solar cells were compressed by 80 percent, they still supplied power, as Kaltenbrunner and his colleagues report. If they crumpled and stretched the solar cell foil 20 times in succession, the ultra-thin solar cell would also survive this treatment with only a small reduction in its efficiency. (Nature Communications, 2012; doi: 10.1038 / ncomms1772)

(Nature Communications / dapd, 04.04.2012 - NPO)