Fully stretchable OLEDs are defined as devices in which every constituent layer, including emissive layers and electrodes, possesses intrinsic mechanical stretchability rather than relying on rigid light-emitting islands linked by stretchable interconnects. Previous stretchable display architectures using rigid OLEDs connected by serpentine or elastomeric wiring have suffered from weak mechanical reliability at junctions, reduced conformability to curved or moving surfaces such as human skin, and degraded display resolution when strained.
Uniformly deformable, fully stretchable displays can maintain resolution and mechanical robustness under tensile strain, but such devices have faced fundamental efficiency limitations at both the emissive layer and electrode level. To make emissive layers stretchable, researchers often mix soft insulating elastomers into organic semiconductors, which disrupts exciton transport, hinders charge transport, and suppresses efficient exciton energy transfer pathways, leading to lower light-emission efficiency.
On the electrode side, conventional transparent conducting oxides such as indium tin oxide are too brittle for large tensile strain and crack under deformation. Alternatives using metal nanowires embedded in elastomers can provide mechanical compliance, but tend to exhibit incomplete charge transport between exposed nanowires and limited effective contact area with the overlying organic stack, restricting charge injection efficiency and overall device performance.
As a result of these materials and structural tradeoffs, commercial rigid OLEDs have achieved external quantum efficiencies over 30 percent, while previously reported fully stretchable OLEDs have typically been limited to around 6.8 percent EQE. The new device significantly narrows this performance gap by introducing a combined strategy that re-engineers both the emissive layer and the stretchable electrode.
The team implemented an exciplex-assisted phosphorescent emissive structure, referred to as an ExciPh layer, to overcome exciton energy transfer bottlenecks in elastomer-containing emissive systems. In standard stretchable emissive blends, the presence of elastomer suppresses short-range Dexter transfer of triplet excitons, which is essential for efficient phosphorescent emission and high internal quantum efficiency.
In the ExciPh design, exciplex cohosts facilitate conversion of triplet excitons into singlet excitons, enabling long-range Forster energy transfer that remains effective even in the presence of elastomer. This mechanism allows the emissive layer to retain both high mechanical stretchability and high electroluminescent efficiency, and the researchers report that this is the first demonstration of such an exciplex-enabled structure in a fully stretchable OLED configuration.
To complement the emissive layer innovation, the researchers developed MXene-contact stretchable electrodes, or MCSEs, by integrating MXene materials onto the stretchable electrode surface. MXenes, a family of two-dimensional transition metal carbides and nitrides, provide a combination of high electrical conductivity, intrinsic mechanical stretchability, and tunable work function, making them attractive for use in deformable optoelectronic devices.
By using MXene at the electrode contact, the MCSE structure increases the effective charge-injection area and improves energy-level alignment between the electrode and organic layers. The team reports that this is the first application of MXene-based contacts in stretchable optoelectronics, and that the MCSE architecture markedly enhances charge-injection efficiency compared with conventional nanowire-based stretchable electrodes.
In device testing, the fully stretchable OLED incorporating the ExciPh emissive layer and MCSE electrodes reached an external quantum efficiency of 17 percent, establishing a new record for fully stretchable light-emitting devices. The device maintained stable luminance and efficiency under large tensile strains, including extended operation under strain conditions that mimic realistic wearable scenarios.
Professor Tae-Woo Lee of Seoul National University emphasized the importance of simultaneous materials-level innovation in both the emissive layer and electrode to overcome the performance losses typically associated with imparting stretchability to OLEDs. He noted that the results indicate fully stretchable OLEDs can progress beyond laboratory proofs of concept toward practical wearable display technologies suitable for commercialization.
The study involved a collaboration among ten research institutions, led by Seoul National University and Drexel University, reflecting the multidisciplinary nature of stretchable optoelectronic device development. The research appears in the journal Nature and highlights the potential of exciplex engineering and MXene-based contacts to reshape the design space for high-efficiency, mechanically robust, stretchable displays.
Research Report:Exciplex-enabled high-efficiency, fully stretchable OLEDs
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