In an advance that could hasten the day when energy-efficient glowing plastic sheets replace traditional lightbulbs, a method for printing microscopic lenses nearly doubles the amount of photons coming out of the materials, called organic light-emitting diodes, or OLEDs.
Stephen Forrest, an electrical engineer and vice president of research at the University of Michigan, says his technology increases the light output of the thin, flexible OLEDs by 70 percent. "They just create local curvature that allows light to pass through," he explains.
Forrest uses microlenses, tiny hemispheres of polymer a few micrometers in diameter that direct the light forward from the OLED. He uses imprint lithography, essentially stamping a hexagonal array of lenses into a liquid polymer. Once it has hardened, the polymer layers making up the OLED can be deposited on top of the lenses. The ones he has made aren't perfect, Forrest says, but can be improved by a company that decides to optimize the manufacturing process.