Foldable QLED butterfly

Ultrathin QLED can be folded into origami structures

Image credit: Institute for Basic Science

A collaboration between South Korean researchers has created an ultrathin quantum dot LED (QLED) variant that can be folded as freely as paper into various 3D structures such as butterflies, aeroplanes and pyramids.

QLEDs use quantum dots (nanoscale semiconductor particles) for the emission of light. Thanks to their outstanding electroluminescence, they have attracted considerable attention as a candidate for the next generation of display technologies. QLED displays do not require any bulky components such as backlight units, potentially allowing them to be manufactured with ultrathin form factors.

A research team of experts from Seoul National University and the Institute for Basic Science presented a prototype QLED in 2015 that had a thickness of just 3μm. Thanks to its thinness, it had outstanding mechanical flexibility, which allowed it to be applied in wearable devices such as electronic tattoos.

The team has now presented the next stage of this technology - a foldable variant of the ultrathin QLED inspired by origami. Considering the rising popularity of foldable smartphones, the evolution of foldable display technology is becoming more relevant. It is expected that it could provide unprecedented opportunities for next-generation electronics including user-customised form factors with complex structures, as well as allowing for creative and dynamic 3D information displays.

The researchers incorporated foldability into the conventional planar QLED using a new fabrication process that can partially etch the epoxy film deposited on the QLED surface without damaging the underlying structure. Using a power-controllable pulsed laser and the etch-stop layers, the etching depth can be precisely controlled. As the laser-etched part of the device is relatively thin compared with the the surrounding region, it is possible to etch out deformation lines along which the device can be folded like origami paper.

“We were able to build a 3D foldable QLED that can be freely folded just like a paper artwork,” said Professor Kim Dae-Hyeong of Seoul National University. “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.”

Based on this laser-etching technique, the researchers were able to control the radius of curvature down to less than 50μm; under such a tiny radius of curvature, the fold line resembles a shape edge without visible curvature. The researchers minimised the strain loaded on the components using mechanical simulation to carefully engineer the device for folding.

The entire QLED, including the folding line, maintained a stable light-emitting performance after being folded 500 times. Next, the researchers applied the technology to fabricate 3D foldable QLEDs with complex shapes, including butterflies, aeroplanes, and pyramids.

Hyeon Taeghwan, director of the Centre for Nanoparticle Research at Seoul, added: “Through the technology reported in this research, paper-like QLEDs that can be folded into various complex structures have been successfully fabricated. Who knows when the day will come when electronic paper with a display unit can replace real paper?”

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