A team of South Korean scientists led by Kim Dae-Hyeong of the Center for Nanoparticle Research within the Institute for Basic Science (IBS) has pioneered a novel approach to stretchable displays. The team announced the first development of intrinsically stretchable quantum dot light-emitting diodes (QLEDs).

In the rapidly evolving world of display techno­logies, the quest for creating intrinsi­cally stretchable displays has been ongoing. Traditional displays, constrained by rigid and inflexible components, have struggled to evolve beyond flexible ones. There has been a clear need for novel materials and device designs that can endure significant stretching while main­taining their functionality, which is essential for appli­cations including wearable and adaptable interfacing techno­logies. The majority of the flexible displays on the market employ organic light-emitting diode (OLED) techno­logy, which employs organic materials as light-emitting components. However, OLED often has drawbacks such as limited brightness and color purity issues. On the other hand, QLED displays offer excellent color reproduction, brightness, and longevity, making them a compelling choice for consumers who prioritize these factors.

However, the intrinsic challenge for developing flexible QLED displays lies in the nature of quantum dots (QDs) themselves; as inorganic nano­particles, they do not possess inherent stretchabi­lity. There have been some attempts to embed QDs within elastic materials to create a light-emitting and elastic composite material. A significant hurdle encountered during this approach was the elastomers' insulating properties, which impede the efficient injection of electrons and holes into the QDs, thereby diminishing the device's electro­luminescent efficiency.

Hence the IBS researchers had to come up with innovations to overcome these limi­tations. Their work showcased the incorpora­tion of a third material in the composite to enhance carrier delivery to the QDs. A p-type semi­conducting polymer (TFB) was employed to enhance both the stretchability of the device and the efficiency of hole injection. Adding TFB also improved the balance between the electron and hole injections. An intriguing aspect of the ternary nano­composite film was the distinctive internal structure exhibiting phase separation, where TFB-rich “islands” are formed at the base and QDs embedded in a matrix lay on top of these islands. This unique structural arrangement minimizes exciton quenching sites and enhances hole injection effi­ciency, resulting in optimal device performance.

After careful selection and engineering of these materials, the researchers achieved QLEDs with high brightness of 15,170 Candela per square meter, which is the highest among the stretchable LEDs, in addition to a low threshold voltage (3.2 V). The device did not suffer damage even when signi­ficant force was applied to stretch the material. Even when stretched up to 1.5 times, there was no significant change in the distance between the quantum dots inside the device. For example, if a 20-inch QLED TV is made with this device, this means that the display performance will remain the same even when pulled to a 30-inch size.

Kim Dong-chan explained, “Our research team has also developed a high-resolution patterning techno­logy that can be applied to stretchable quantum dot light-emitting layers,” adding, “By combining light-emitting materials and patterning techno­logy, we demonstrated the potential of our device for RGB LEDs and complex applications like passive matrix arrays.” This research not only demonstrates the superior performance of QDs in stretchable displays but also sets a new direction for further enhancing device performance. Future research will focus on optimizing carrier injection efficiency and stretcha­bility across all device layers. This finding lays a solid foundation for the next generation is-QLED technology, promising a future where display techno­logies are not just flexible but truly stretchable, allowing new forms of wearable electronics and beyond. (Source: IBS)

Reference: D. C. Kim et al.: Intrinsically stretchable quantum dot light-emitting diodes, Nat. Electron., online 15 April 2024; DOI: 10.1038/s41928-024-01152-w

Link: Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, Republic of Korea