A joint research team led by Tae‑Woo Lee, Professor in the Department of Materials Science and Engineering at Seoul National University, and Yury Gogotsi, Professor at Drexel University, has overcome long-standing limitations of next-generation stretchable light-emitting devices by developing the record efficiency fully stretchable organic light-emitting diode (OLED). The study was published in Nature on January 15.
A fully stretchable OLEDs is defined as a devicein which all constituent layers exhibit intrinsic mechanical stretchability. With the rapid growth of the field of wearable electronics, the demand for displays that can be directly laminated onto the skin and visualize physiological signals in real time has increased significantly. However, most previously reported stretchable displays relied on rigid light-emitting devices connected by stretchable interconnects. Such architectures suffer from poor mechanical reliability at junctions under strain, limited skin conformability, and degradation in display resolution.
In contrast, fully stretchable displays deform uniformly underapplied strain, enabling mechanically robust operation while maintaining high resolution in wearable environments. Despite this promise, fully stretchable OLEDs have faced fundamental challenges in both intrinsically stretchable emissive layers and intrinsically stretchable electrodes.
To impart stretchability to emissive layers, soft insulating elastomers are typically added to organic semiconductors. This approach, however, disrupts exciton transport pathways, leading to severe degradation in charge transport, exciton energy transfer, and light-emission efficiency. On the electrode side, conventional metal electrodes such as indium tin oxide cannot be used in fully stretchable OLEDs due to their inherent brittleness. Stretchable electrodes based on metal nanowires embedded in elastomers have thereforebeen explored. Yet these structures often suffer from poor charge transport between exposed nanowires and limited contact area, resulting in inefficient charge injection into overlying organic layers. Consequently, whereas external quantum efficiencies (EQEs) exceeding 30% have been reported for commercial rigid OLEDs,previously reported fully stretchable OLEDs have been limited to EQEs of approximately 6.8%, highlighting a substantial efficiency gap.
To address these limitations, the research team introduced a novel design combining an exciplex-assisted phosphorescent layer (ExciPh) with a MXene-contact stretchable electrode (MCSE). The exciplex cohosts were employed in ExciPh to overcome exciton energy transfer limitations in stretchable emissive layers. While conventional elastomer-containing systems suppress short-range Dexter transfer of triplet excitons, the exciplex cohosts enable the conversion of triplet excitons into singlet excitons, allowing long-range Förster energy transfer. This previously unexplored mechanism enables both high stretchability and high electroluminescent efficiency in the emissive layer, marking the first demonstration of such a structure.
In addition, the team incorporated MXene, a class of two-dimensional transition-metal carbides and nitrides, onto the stretchable electrode to develop MCSE. MXene provides high electrical conductivity, mechanical stretchability, and a wide tunability of work function, significantly enhancing charge-injection efficiency. The MCSE represents the first reported application of MXene in stretchable optoelectronic devices.
As a result, the fully stretchable OLED developed by the team achieved a record-high EQE of 17%, the highest value reported to date for fully stretchable light-emitting devices. Notably, the device maintained stable luminanceand efficiency even under large tensile strains, demonstrating reliable operation under realistic wearable conditions.
Professor Lee commented, "This work presents a materials-level approach that simultaneously addresses the performance degradation inherently associated with imparting stretchability to OLEDs, by innovating both the emissive layer and the electrode. Our results demonstrate that fully stretchable OLEDs can move beyond laboratory demonstrations toward practical applications, significantly accelerating the realization of wearable display technologies."
Meanwhile, this research was conducted as a collaborative project involving a total of ten research institutions, led by Seoul National University and Drexel University.
□ Curriculum Vitae (Prof. Tae-Woo Lee)
1. Personal Information
○ Professor of Department of Materials Science and Engineering,
Seoul National University
