Because the active light-emitting region is situated at the upper tip of the nanowires (a so-called dot-in-wire design), bending or flexing the substrate does not creates stress in this active region, preventing performance degradation in the LEDs.
The researchers published their results under the title “Optically invariant InGaN nanowire light-emitting diodes on flexible substrates under mechanical manipulation“ in Nature‘s Flexible Electronics journal.
What’s more, as well as demonstrating emission invariability under various bending conditions of the substrate, they were able to observe an increase in light intensity when bending the substrate in a concave-up mode, as the tips of the NW LEDs converged to form a spatially denser distribution of emitters.
This was observed experimenting with a 1×1 mm2 array of nanowires, with a turn-on voltage of 2.5V and a forward current of 400μA at 4V. Through finite-element analysis and three-dimensional finite-difference time-domain modelling, the researchers were able to attribute the increase in electroluminescence intensity with constant I–V characteristics to enhanced electromagnetic coupling between the nanowire LEDs as their tips got nearer. The concave bending did not affect the electrical properties nor the peak emission wavelength of the LEDs.
They expect such NW LEDs on flexible substrates to be developed for conformal lighting and wearable bendable displays.