Flexible LEDs could be used in applications like rollable displays, wearable intelligent electronics and lighting, to name but three. Most such LEDs today are made from organic materials integrated onto lightweight and flexible substrates. Although these devices have greatly improved over the last few decades, they do suffer from the problem that they wear out quite quickly. What is more, the blue OLEDs made so far are not very bright and have low external quantum efficiency.

Researchers in France, led by Maria Tchernycheva and Xing Dai of the Institut d’Electronique Fondamentale at the University Paris Sud XI, and Joël Eymery and Christophe Durand in the “Nanophysique et Semiconducteurs” group in Grenoble, have now made large-area fully-flexible LEDs based on core/shell indium gallium nitride/gallium nitride nanowires. “The devices emit blue or green light (depending on the amount of indium in the structures), and the two wavelengths can be combined in a multi-layer device with either a broad spectrum or tunable colour emission,” explains Tchernycheva.” The LEDs are also very stable and can be bent and unbent hundreds of times without losing any of their light-emitting properties.

The team made its devices by first encasing the nitride-based nanowires in a layer of polymer polydimethylsiloxane (PDMS) and then detaching them from the substrate. The resulting flexible LEDs, which can be either transparent or semi-transparent, measure several square centimetres across. They are composed of tiny nano-emitters that are hundreds of nanometres in diameter and 20 microns tall.

Once the colour red is added, hybrid structures comprising LEDs that emit both green and blue light could be used to make flexible devices that emit white light. These RGB devices could make for video displays and LED lightbulbs. Other colours could be emitted if the nitride nanowires were replaced with arsenide or phosphide compounds, or by playing with the size of the nanowires, says Tchernycheva. “This technology might also be generalized to other types of optoelectronic devices, such as flexible nanowire-based light sensors or photovoltaic converters,” she tells nanotechweb.org.

Full details of the research are reported in Nano Letters DOI: 10.1021/acs.nanolett.5b02900.