Quantum dot LED can be folded like origami paper

South Korean researchers have developed a foldable variant of their ultrathin quantum dot light-emitting diode (QLED), inspired by the ancient art of paper folding known as origami. Their work has been described in the journal Nature Electronics.

The concept of the QLED, which employs quantum dots as a light-emitting material, has attracted significant attention as a promising alternative for next-generation display technologies, owing to its impressive electroluminescence properties. Since it does not require any bulky components such as backlight units, QLED displays can potentially be manufactured into an ultrathin form factor.

A research team from the Center for Nanoparticle Research, within South Korea’s Institute for Basic Science, had previously unveiled a prototype QLED back in 2015. The device had a thickness of only 3 µm, giving it outstanding mechanical flexibility which allowed it to be readily applicable in various wearable devices such as electronic tattoos. Recently, the team further advanced this technology and developed a foldable variant of their ultrathin QLED.

The researchers endowed foldability to the conventional planar QLED via a new fabrication process that can partially etch the epoxy film deposited on the QLED surface without damaging the underlying QLED. Using a power-controllable carbon dioxide pulsed laser and the silver-aluminium alloy-based etch-stop layers, the etching depth can be precisely controlled. As the laser-etched part of the device is relatively thinner than the surrounding region, it is possible to etch out deformation lines along which the device can be folded like origami paper.

Based on the selective laser-etching technique, researchers were able to precisely control the radius of curvature down to less than 50 µm. Under such a small curvature radius, the fold line resembles a sharp edge with no visible curvature. By using mechanical simulation to carefully engineer the device, researchers were able to minimise the strain loaded on the light-emitting components. The entire QLED including the crease region (a fold line) was able to maintain a stable light-emitting performance even when it was repeatedly folded 500 times. The technology was applied to fabricate 3D foldable QLEDs with various complex shapes such as butterflies, aeroplanes and pyramids.

“We were able to build a 3D foldable QLED that can be freely folded just like a paper artwork,” said Professor Dae-Hyeong Kim, Vice-Director of the Center for Nanoparticle Research and co-leader of the research team. “By fabricating the passively driven, 3D foldable QLED arrays composed of 64 individual pixels, we have shown the possibility of developing displays with greater complexity in the future.”

Considering the rising popularity of foldable smartphones, the advancement of foldable display technology is gaining greater importance. It is expected this technology will provide unprecedented opportunities for next-generation electronics with user-customised form factors with complex structures, as well as allowing for dynamic three-dimensional display of visual information.

“Through the technology reported in this research, paper-like QLEDs that can be folded into various complex structures have been successfully fabricated,” said research co-leader Professor Taeghwan Hyeon, Director of the Center for Nanoparticle Research. “Who knows when the day will come when electronic paper with a display unit can replace real paper?”

Image caption: The ultrathin QLED can be sharply folded along the laser-etched line, just like origami paper. The 3D foldable QLED can freely transform between 2D and 3D structures, which allows for a dynamic display of visual information.

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