25 Years of Light-Emitting Electrochemical Cells: A Flexible and Stretchable Perspective.

Light-emitting electrochemical cells (LECs) are simple electroluminescent devices comprising an emissive material containing mobile ions sandwiched between two electrodes. The operating mechanism of the LEC involves both ionic and electronic transport, distinguishing it from its more well-known cousin, the organic light-emitting diode (OLED). While OLEDs have become a leading player in commercial displays, LECs have flourished in academic research due to the simple device architecture and unique features of its operating mechanism, inviting exploration of new materials and fabrication strategies. These explorations have brought LECs to an exciting frontier in advanced optoelectronics: flexible and stretchable light-emitting devices. Flexible and stretchable LECs are discussed herein, presenting the LEC system as a robust and fault-tolerant development platform. The engineering of emissive composites is highlighted to control mechanical properties, and how the tolerance of LECs to electrode work function and roughness has enabled the incorporation of new electrode materials to achieve flexibility and stretchability. As part of this story, the solution processability of LECs has led to exciting demonstrations of flexible and printed LECs. An outlook is provided for LECs that builds on these strengths, potentially leading to flexible, stretchable, low-cost devices such as illuminated tags, smart packaging, flexible signage, and wearable illumination.

Imine and metal-ligand dynamic bonds in soft polymers for autonomous self-healing capacitive-based pressure sensors.

In this work, a facile and simple yet effective method to generate intrinsic autonomous self-healing polymers was developed, leading to new materials that can be easily fine-tuned both mechanically and chemically. The new materials were designed to incorporate two dynamic and reversible types of chemical bonds, namely dynamic imine and metal-coordinating bonds, to enable autonomous self-healing, controlled degradability and ultra-high tunable stretchability (up to 800% strain) based on the ratio of metal to ligand incorporated. Through an easy condensation reaction, imine bonds are generated at the end-termini of a short siloxane chain. The new dynamic system was characterized by a variety of techniques, including tensile-pull strain testing, atomic force microscopy and UV-Vis spectroscopy, which showed that the highly dynamic imine bonds, combined with coordination with Fe2+ ions, allow for the material to regenerate 88% of its mechanical strength after physical damage. The materials were also controlled to be degraded in mild acidic conditions. Lastly, application in self-healable electronics was demonstrated through the fabrication of a capacitive-based pressure sensor, which shows good sensitivity and dynamic response (∼0.33 kPa-1) before and after healing.