Ultrafast Photoinduced Interconnection of Metal-Polymer Composites for Fabrication of Transparent and Stretchable Electronic Skins.

The high interest sparked by the foldable smartphones recently released on the market is gradually shifting to the next generation of flexible electronic devices, such as electronic skins in the form of stretchable thin films. To develop such devices, good mechanical flexibility of all components (including the substrate, electrode, and encapsulant) is critical. Various technologies have been developed to enhance the flexibility of these components; however, progress in developing interconnection methods for flexible and stretchable devices has been limited. Here, we developed an ultrafast photoinduced interconnection method that does not require any adhesive or surface treatment. This method is based on heating metal nanostructures using intense pulsed light (IPL) and the reversible cross-linking of polymers. First, we synthesized a stretchable, transparent, and free-standing polymer substrate that can be reversibly cross-linked, and then Ag nanowire (AgNW) networks were formed on its surface. This electrode was irradiated with IPL, which locally heated the AgNWs, followed by decomposition of the polymer via the retro-Diels-Alder reaction and recross-linking. Independently fabricated AgNW/polymer films were layered and irradiated three times with IPL to form a bonded sample with excellent joint quality and no increase in electrical resistance compared to a single electrode. Furthermore, the interconnected electrodes were stretchable and optically transparent. Even when more than 200% strain was applied in a peel test, no breakage at the joint was observed. This allowed us to successfully produce a stretchable, transparent, and bending-insensitive pressure sensor for various applications such as motion detectors or pressure sensor arrays.