OLEDs stretch two-dimensionally

Researchers from the Korea Advanced Institute of Science and Technology (KAIST) have created stretchable organic light-emitting diodes (OLEDs) that are compliant and maintain their performance under high-strain deformation. Their stress-relief substrates are said to have a unique structure, utilising pillar arrays to reduce the stress on the active areas of devices when strain is applied.

Traditional intrinsically stretchable OLEDs have commercial limitations due to their low efficiency in the electrical conductivity of the electrodes. In addition, previous geometrically stretchable OLEDs laminated to the elastic substrates with thin film devices lead to different pixel emissions of the devices from different peak sizes of the buckles.

To solve these problems, Professor Kyung Cheol Choi and his team designed a stretchable substrate system with surface relief island structures that relieve the stress at the locations of bridges in the devices. Their stretchable OLED devices contained an elastic substrate structure comprising bonded elastic pillars and bridges. A patterned upper substrate with bridges makes the rigid substrate stretchable, while the pillars decentralise the stress on the device.

Although various applications using micropillar arrays have been reported, it has not yet been reported how elastic pillar arrays can affect substrates by relieving the stress applied to those substrates upon stretching. Compared to results using similar layouts with conventional free-standing, flat substrates or island structures, the team’s results with elastic pillar arrays show relatively low stress levels at both the bridges and plates when stretching the devices.

As published in the journal Nano Letters, the team achieved stretchable RGB (red, green, blue) OLEDs and had no difficulties with material selection as practical processes were conducted with stress-relief substrates. Their stretchable OLEDs were mechanically stable and have two-dimensional stretchability — said to be superior to only one-direction stretchable electronics — opening the way for practical applications like wearable electronics and health monitoring systems.

“Our substrate design will impart flexibility into electronics technology development including semiconductor and circuit technologies,” Professor Choi said. “We look forward to this new stretchable OLED lowering the barrier for entering the stretchable display market.”

Image caption: Photographs of the patterned rigid part of the substrate on the finger joint indicating 2D dimensional stretchability and images of stretchable OLEDs on a finger joint emitting green light.

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