Tiny hills and valleys on the surface of leaves have guided a team of Princeton University scientists in the creation of a new kind of solar cell. By wrinkling up a layer of adhesive, the team designed solar cells that can capture more light, even in the infrared region.
“If you look at leaves very closely, they are not smooth,” said Yueh-Lin Loo, Princeton’s principle investigator on the project. “We’d like to mimic this geometric effect in synthetic, man-made light-harvesting systems.”
The research team worked in the Mechanical and Aerospace Engineering Department’s laboratory to design a unique surface by curing a layer of liquid photographic adhesive with ultraviolet light. They produced ripples on the surface by introducing stress to the material and controlling how fast it was cured. Solar cells are then constructed with inexpensive plastic placed over the “folded” material. The best results came when a mixture of shallow ripples (wrinkles) and deep ripples (folds) occupied the surface. It makes sense—if you increase the surface area, you increase the number of places where light can be collected.
The new cells produced 47 percent more electricity than their flat-surfaced counterparts along with a significant increase in the notorious infrared region of the spectrum. Conventional solar cells struggle to capture the long waves of light in the red region, but with the wrinkles and folds, absorption in the region was upped by a whopping 600 percent.