Baku, May 7 (AZERTAC). Taking their cue from the humble leaf, researchers have used microscopic folds on the surface of photovoltaic material to significantly increase the power output of flexible, low-cost solar cells.

The team, led by scientists from Princeton University, reported online April 22 in the journal Nature Photonics that the folds resulted in a 47 percent increase in electricity generation. Yueh-Lin (Lynn) Loo, the principal investigator, said the finely calibrated folds on the surface of the panels channel light waves and increase the photovoltaic material`s exposure to light.

"On a flat surface, the light either is absorbed or it bounces back," said Loo, a professor of chemical and biological engineering at Princeton. "By adding these curves, we create a kind of wave guide. And that leads to a greater chance of the light`s being absorbed."

The research team`s work involves photovoltaic systems made of relatively cheap plastic. Current solar panels are typically made of silicon, which is both more brittle and more expensive than plastics. So far, plastic panels have not been practical for widespread use because their energy production has been too low. But researchers have been working to increase that efficiency with the goal of creating a cheap, tough and flexible source of solar power.

If researchers can increase the plastic panels` efficiency, the material could produce power from an array of surfaces from inserts in window panels to overlays on exterior walls or backpacks.

Jong Bok Kim, a postdoctoral researcher in chemical and biological engineering and the paper`s lead author, explained in the Nature Photonics paper that the folds on the surface of the panels channel light waves through the material in much the same way that canals guide water through farmland. By curving the light through the material, the researchers essentially trap the light inside the photovoltaic material for a longer time, which leads to greater absorption of light and generation of energy.

Although the technique results in an overall increase in efficiency, the results were particularly significant at the red side of the light spectrum, which has the longest wavelengths of visible light. The efficiency of conventional solar panels drops off radically as light`s wavelength increases, and almost no light is absorbed as the spectrum approaches the infrared. But the folding technique increased absorption at this end of the spectrum by roughly 600 percent, the researchers found.

The research team created the folded surface in Howard Stone`s laboratory in the mechanical and aerospace engineering department by carefully curing a layer of liquid photographic adhesive with ultraviolet light. By controlling how fast different sections of the adhesive cured, the team was able to introduce stresses in the material and generate ripples in the surface. The shallower ripples were classified as wrinkles and the deeper ones are called folds. The team found that a surface containing a combination of wrinkles and folds produced the best results.