The vision of "skin-like" electronics has long been a staple of science fiction - thin, luminous displays that adhere to our bodies, monitoring our health in real time or providing seamless human-machine interfaces. However, for those of us working in the lab, the reality of fully stretchable organic light-emitting diodes (OLEDs) has been a decade-long struggle against a stubborn ceiling. While rigid OLEDs have already achieved high external quantum efficiency (EQE), and havebeen commercialized, their stretchable counterparts remain in the "efficiency basement," rarely surpassing 10% EQE.
Our recent work, "Exciplex-enabled high-efficiency, fully stretchable OLEDs," published in Nature, is the culmination of our efforts to bridge this gap. It is a story of rethinking molecular interactions and interface engineering to prove that stretchability need not come at the expense of performance.
The Efficiency Paradox
The fundamental challenge for intrinsically stretchable OLEDs lies in the materials. To make a device stretchable, you typically need to incorporate elastomers or use soft, disordered polymers. However, these materials are notorious for poor charge transport and inefficient energy transfer because of their insulating nature. In the past, researchers often settled for "low-performance but stretchable" materials, resulting in devices that were dim, inefficient, and short-lived.
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 can facilitate 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 Breakthrough: The "ExciPh" Strategy
The pivotal turning point in our research was the development of the stretchable exciplex-assisted phosphorescent (ExciPh) system (Figure 1). By carefully blending intrinsically stretchable elastomers with specific organic molecules, we created an emissive layer that maintained stable film morphology under 200% strain without cracking.
Figure 1. A comparison of conventional light-emitting systems with the exciplex-assisted stretchable phosphorescent materials in the presence of insulating polyurethane (PU).
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 EQE exceeding 17% in fully stretchable displays.
Reinventing the Electorde: The MXene Contact
Even with a perfect emissive layer, a device is only as good as its electrodes. This is where we encountered another engineering hurdle. To achieve high efficiency, one needs an electrode that injects charges effectively while remaining conductive and stable under repeated stretching.
Traditionally, researchers have used silver nanowire (AgNW) networks. Although AgNWs offer high conductivity and flexibility, they have a limited contact area and lack work function tunability. This often leads to "hot spots" where current concentrates, causing the device to burn out or perform poorly.
Figure 2. Comparison of pristine AgNW stretchable electrode and MXene contact stretchable electrode (MCSE).
Our solution was the development of MXene Contact Stretchable Electrodes (MCSEs). MXenes are a class of two-dimensional transition metal carbides that are highly conductive, hydrophilic, and mechanically robust. We realized that by "welding" AgNWs with MXenes (specifically Ti₃C₂Tₓ), we could create a synergistic network (Figure 2).
MXene serves as a high-conductivity "glue" and a two-dimensional interlayer. In a standard AgNW network, the charge must hop from one wire to another across high-resistance junctions. In our MCSE, the MXenes fill these gaps, providing a continuous, low-resistance path for electrons. Furthermore, the MXenes have a high work function and surface energy, enabling them to form an exceptionally tight interface with the emissive layer. This MCSE ensured that both electrons and holes were injected uniformly and efficiently across the entire surface, rather than just at the points where a silver nanowire touched the organic film.
Looking Ahead
Breaking the 17.0% EQE barrier for fully stretchable OLEDs is a milestone, but for our team, it’s 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.
We hope this "Behind the Paper" story inspires other researchers to explore hybrid material systems—combining the electronic precision of 2D materials such as MXenes, with the mechanical resilience of polymers. The future of displays isn't just bright; it's elastic. Whether it’s a medical patch that glows to signal a fever or a smartphone you can wrap around your wrist like a bandage, the era of truly comfortable, high-performance technology is finally within reach.