The organic light-emitting diode (OLED) technology behind flexible cell phones, curved monitors, and televisions could one day be used to make on-skin sensors that show changes in temperature, blood flow, and pressure in real time. An international collaboration, led by researchers from Seoul National University (SNU) in the Republic of Korea and Drexel University, has developed a flexible and stretchable OLED that could put the technology on track for this use and a range of new applications.
Recently reported in Nature, their work improves on existing technology by integrating a flexible, phosphorescent polymer layer and transparent electrodes made from MXene nanomaterial. The result is an OLED that can be stretched to 1.6 times its original size, while maintaining most of its luminescence.
“This study addresses a longstanding challenge in flexible OLED technology, namely, the durability of its luminescence after repeated mechanical flexion,” said Yury Gogotsi, Ph.D., Distinguished University and Bach Professor in Drexel’s College of Engineering. “While the advances creating flexible light-emitting diodes have been substantial, progress has leveled off in the last decade due to limitations introduced by the transparent conductor layer, limiting their stretchability.”
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Gogotsi.
Tech Briefs: What was the biggest technical challenge you faced while developing the exciplex-assisted phosphorescent (ExciPh) layer?
Gogotsi: The ExciPh layer was developed at Seoul National University by Professor Tae-Woo Lee and his former Ph.D. student Huanyu Zhou (currently a post-doc at Georgia Tech). Here is what Huanyu commented: “We asked ourselves: Why can’t we apply the most advanced physics of rigid OLEDs — specifically exciplex-assisted phosphorescence — to a stretchable format? Exciplex hosts are brilliant because they enable efficient long-range energy transfer to phosphorescent dopants, minimizing energy loss. But translating this to a stretchable system was easier said than done. Most high-performance exciplex hosts are small molecules that crystallize and crack when stretched. We needed a system that maintained its electronic ‘handshake’ even when molecules were pulled apart. The pivotal turning point in our research was the development of the stretchable exciplex-assisted phosphorescent (ExciPh) system. By carefully blending intrinsically stretchable elastomers with specific organic molecules, we created an emissive layer that maintained stable film morphology under 200 percent strain without cracking.”
Tech Briefs: Can you explain in simple terms how it works please?
Gogotsi: The beauty of the ExciPh system lies in its elastomer-tolerant triplet recycling mechanism. In typical stretchable OLEDs, the polymer’s non-conjugated nature leads to exciton loss via nonradiative decay. By using an exciplex host as a bridge, we can recycle these triplets and transfer them directly to a phosphorescent dopant. This strategy overcomes the limitations of stretchable materials, enabling us to achieve an external quantum efficiency (EQE) exceeding 17 percent in fully stretchable displays.
Read more about it here, in our “Behind the Paper: Breaking the Efficiency Barrier for the Future of Wearable Displays” story on Nature Research Communities page .
Tech Briefs: Do you have any set plans for further research/work/etc.? If not, what are your next steps?
Gogotsi: Even with a perfect emissive layer, a device is only as good as its electrodes. To achieve high efficiency, one needs an electrode that injects charges effectively while remaining conductive and stable under repeated stretching. This is where MXene worked extremely well. In our previous publications with Tae-Woo Lee’s group, we showed that Ti3C2Tx MXene, a 2D material discovered at Drexel University, can produce transparent conducting electrodes that replace the brittle indium-tin oxide used in conventional OLEDs, displays, and solar cells.
MXene provided flexibility and improved luminance due to its high and tunable work function. However, to add stretchability, we added silver nanowires that can keep an electrical connection even when the film is stretched by 200 percent. It’s important to mention that this approach can be used to create other flexible and stretchable devices, including solar cells, displays, sensors, and epidermal electronics. The future displays and other devices can become wearable, flexible, and even elastic.
The SNU team also believes that surpassing the 17.0 percent EQE barrier for fully stretchable OLEDs is only a starting point. This research shows that the "efficiency gap" between rigid and stretchable electronics isn’t a law of nature — it’s an engineering challenge that can be solved. Professor Lee’s group will continue efforts in this direction.
Tech Briefs: Is there anything else you’d like to add that I didn’t touch upon?
Gogotsi: MXenes, a chemically and structurally diverse family of 2D transition-metal carbides, nitrides, and carbonitrides, offer an unprecedented variety of compositions and structures. Chemically tunable surfaces are intrinsic to MXenes, and adding surface terminations yields over a thousand stoichiometric compositions. Together with possible mixed terminations and solid solutions on M and X sites — dozens already reported, including high-entropy 2D structures with up to nine transition metals — the permutations are infinite. This chemical and structural richness enables unprecedented property tunability across a wide range of applications. The electrical conductivity of a given MXene composition can be tuned from metallic to semiconducting to superconducting by varying its surface terminations or morphology. Therefore, these materials can enable technologies that were not possible until now. Stretchable electronics is only one example.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Gogotsi: Believe in yourself and never, never give up!
