Wrinkles and deep folds as photonic structures in photovoltaics

Some of the simplest light-harvesting systems in nature rely on the presence of surface structures to increase internal light scattering. We have extended this concept to increase the efficiencies of man-made solar energy harvesting systems. Specifically, we exploit the wrinkles and deep folds that form on polymer surfaces when subjected to mechanical stress to guide and retain light within the photo-active regions of photovoltaics. Devices constructed on such surfaces show substantial improvements in light harvesting efficiencies, particularly in the near-infrared region where light absorption is otherwise minimal. We report a vast increase in the external quantum efficiency of polymer photovoltaics by more than 600% in the near-infrared, where the useful range of solar energy conversion is extended by more than 200 nm. This method of exploiting elastic instabilities of thin, layered materials is straightforward and represents an economical route to patterning photonic structures over large areas to improve the performance of optoelectronics.