A highly stretchable metal electrode is developed via the solution-processing of very long (>100 μm) metallic nanowires and subsequent percolation network formation via low-temperature nanowelding. The stretchable metal electrode from very long metal nanowires demonstrated high electrical conductivity (~9 ohm sq(-1) ) and mechanical compliance (strain > 460%) at the same time. This method is expected to overcome the performance limitation of the current stretchable electronics such as graphene, carbon nanotubes, and buckled nanoribbons.

The future electronics will be soft, flexible and even stretchable to be more human friendly in the form of wearable computers. However, conventional electronic materials are usually brittle. Recently, carbon based materials are intensively investigated as a good candidate for flexible electronics but with limited mechanical and electrical performances. Metal is still the best material for electronics with great electrical properties but with poor transparency and mechanical performance. Here we present a simple approach to develop a synthesis method for very long metallic nanowires and apply them as new types of high performance flexible and transparent metal conductors as an alternative to carbon nanotubes, graphene and short nanowire based flexible transparent conductors and indium tin oxide based brittle transparent conductors. We found that very long metallic nanowire network conductors combined with a low temperature laser nano-welding process enabled superior transparent flexible conductors with high transmittance and high electrical conductivity. Further, we demonstrated highly flexible metal conductor LED circuits and transparent touch panels. The highly flexible and transparent metal conductors can be mounted on any non-planar surfaces and applied for various opto-electronics and ultimately for future wearable electronics.

Figure 8 . Demonstration of a bendable touch screen on a non-fl at surface. Letters "ANTS" were written.

As is frequently seen in sci-fi movies, future electronics are expected to ultimately be in the form of wearable electronics. To realize wearable electronics, the electric components should be soft, fl exible, and even stretchable to be human-friendly. An important step is presented toward realization of wearable electronics by developing a hierarchical multiscale hybrid nanocomposite for highly fl exible, stretchable, or transparent conductors. The hybrid nanocomposite combines the enhanced mechanical compliance, electrical conductivity, and optical transparency of small CNTs (d ≈ 1.2 nm) and the enhanced electrical conductivity of relatively bigger Ag nanowire (d ≈ 150 nm) backbone to provide effi cient multiscale electron transport path with Ag nanowire current backbone collector and local CNT percolation network. The highly elastic hybrid nanocomposite conductors and highly transparent fl exible conductors can be mounted on any non-planar or soft surfaces to realize human-friendly electronics interface for future wearable electronics.

cost-effective and large-area energy harvesting without any vacuum process. [27][28][29][30][31][32] Although NCGs have been regarded as a concept of stretchy piezoelectric systems, the authentically operating stretchable NCG has not been yet realized due to the absence of proper stretchable electrodes and robust composite matrix. [33][34][35] While these bendable nanogenerators have been intensively studied using diverse piezoelectric materials and structures, the development of stretchable high-output energy harvesters still requires further investigation to realize self-powered stretchable electronic systems.Several researchers have explored buckling structures with piezoelectric ribbons [36][37][38] or micropatterning-notched structures with polyvinylidenefl oride (PVDF)/graphene. [ 39 ] They reported producing output currents of tens of picoamperes to nanoamperes with the elongating/releasing stretchable energy harvesters. However, the generated output was insuffi cient to operate practical electronic devices, due to the narrow/confi ned piezoactive ribbons or the low piezoelectricity. In addition, the stretchable energy harvesters suffer from defi cient stretchability (below a few tens of percentage) and poor reversibility caused by intrinsic material stiffness and structural dependency, resulting in unstable output signals, incompatible integration, and limited mechanical durability. To achieve ideal stretchable nanogenerators, a new concept is needed for resolving critical issues that incorporate highly elastic piezoelectric components with high-output performance and co-assembly with ultrastretchable electrodes.Herein, we demonstrate a simple and facile route to a highperformance and hyper-stretchable elastic-composite generator (SEG) realized by very long Ag nanowires (VAgNWs) stretchable electrodes. This stretchable energy harvester exhibits over ten times larger stretchability (≈200%) and about seven times higher power output (≈4 V and ≈500 nA), compared to the previous stretchable piezo-nanogenerator. The outstanding performance was achieved by employing a rubber-based piezoelectric elastic composite (PEC) and the very long nanowire percolation (VLNP) electrodes, obviating device structural dependency. The remarkable elongation rate of the reinforced rubbery matrix mechanically stimulates the imbedded piezoelectric particles to effi ciently induce piezopotential throughout the entire PEC. To demonstrate the stable and conformal integration of the SEG with highly stretchable VLNP electrodes, the VAgNWs were successfully transferred onto the surfaces of PEC composed of PMN-PT particles and multiwalled carbon nanotubes (MWCNTs) in a silicone elastomer matrix. The principles of robust stretchability and well-distributed piezopotential generation were also simulated using fi nite element analysis (FEA) to investigate the notable stress relaxation of VLNP over short NWs. Our SEG can directly produce electrical Stretchable electronics that offer elastic characteristics in response to large strain deformatio...