Reflections can be a problem for optical technologies, limiting the amount of light absorbed by solar cells or emitted by LEDs. But a new nano coating that virtually eliminates reflections could make such devices more efficient. An LED, say, could emit 40 percent more light, leading to brighter displays. The image at left shows light reflecting from uncoated (top three objects) and coated materials. The second object from the bottom, a piece of semiconductor material used in LEDs, reflects 12 percent of light without the coating. The same semiconductor with the coating (bottom) reflects just 0.1 percent.
Reflectivity is related to the difference between the extent to which two substances, such as air and glass, refract or bend light. Reducing that difference reduces reflection where the materials meet. Researchers at Rensselaer Polytechnic Institute in Troy, NY, and semiconductor maker Crystal IS in Green Island, NY, created a multilayered, porous coating that eases the transition as light moves from the air into a solid material or into the air from a semiconductor in an LED. Each layer is made of nanorods grown at a precise angle. Successive layers bend light more as it moves into a solar cell. Likewise, light emerging from an LED is bent less in each successive layer. Products could be available in three to five years.