Intrinsically Stretchable Polymer Light‐Emitting Devices Using Carbon Nanotube‐Polymer Composite Electrodes

IO N Stretchable electronics are evolving from a conceptual curiosity into an important branch of modern electronics. Such devices can be potentially useful for a wide range of applications including wearable electronics, “smart skins”, and minimally invasive biomedical devices. [ 1–10 ] Conventional inorganic electronic devices are brittle and certain fl exibility may be obtained by using ultrathin layers of the inorganic materials. Buckled device confi gurations have been reported to introduce stretchability in integrated devices consisting of rigid functional components, however they lack intrinsic stretchability. [ 3 , 7 ] Here we report the fabrication of polymer light-emitting devices using single-walled carbon nanotube (SWNT)-polymer composite electrodes as both the electronand hole-injection electrodes. The devices are metal-free and can be linearly stretched up to 45% strain. This represents a proof-of-concept, highly stretchable semiconductor device wherein every part of the device is intrinsically stretchable. Stretchable devices reported so far generally employ a soft rubbery polymer to embed or bond active electronic components that are rigid. [ 1–3 ] Buckled interconnects can be made using prestrained poly(dimethylsiloxane) (PDMS) with evaporated metallic fi lms. [ 11 ] Rogers et al. also reported buckled active devices using prestrained PDMS; [ 12 , 13 ] the buckled interconnects or devices can be elongated until the vertical displacement has all been converted into planar strain, and after that the rigid components prevent further elongation. Someya et al. reported an elastic conductor formed by coating PDMS substrates with a composite consisting of carbon nanotubes, an ionic liquid salt, and a fl uorinated copolymer. [ 14–16 ] These elastic conductors have been used to wire various rigid active devices including organic light-emitting diodes (OLEDs) and sensors. [ 15 , 16 ] The interconnected devices can be made stretchable wherein the deformation occurs essentially at the elastic interconnects. The recent advancement in polymer electronics opens up new opportunities to achieve intrinsically stretchable devices. Compared with their inorganic counterparts, conjugated polymers are much more compliant. When fabricated on fl exible substrates such as polyethylene terephthlate (PET) or metal foils, highly bendable polymer devices have been demonstrated with fl exed radii as small as several millimeters. [ 17–19 ] Nonetheless,