Nanowires keep white LEDs flexible

Flexible light-emitting diodes allow designers to create wearable displays, flexible screens, and bendable biomedical devices. Today’s best technology for flexible light sources is organic LEDs. But OLEDs have relatively short lifetimes, and bright ones aren’t very energy efficient. Now, researchers have shown the potential to overcome those limitations by building flexible white LEDs out of a more robust, efficient inorganic semiconductor—gallium nitride (ACS Photonics 2016, DOI: 10.1021/acsphotonics.5b00696). Joël Eymery of France’s Alternative Energies & Atomic Energy Commission; Maria Tchernycheva of the University of Paris, Saclay; and colleagues grew GaN nanowires on a sapphire substrate and embedded them in polydimethylsiloxane laced with a commercially available phosphor, yttrium aluminum garnet doped with cerium. The team peeled the material from the substrate and sandwiched it between a silver nanowire mesh and a thin metal foil, which serve as electrodes. The device’s conversion efficiency—the ratio of electrons in to photons out—reached 9.3%. That’s low, but flexible devices’ efficiencies don’t need to be as high as those of general lighting applications, Eymery says. The devices could be bent to a radius of 5 mm without any reduction in performance.