Skin electronics require stretchable conductors that satisfy metallike conductivity, high stretchability, ultrathin thickness, and facile patternability, but achieving these characteristics simultaneously is challenging. We present a float assembly method to fabricate a nanomembrane that meets all these requirements. The method enables a compact assembly of nanomaterials at the water–oil interface and their partial embedment in an ultrathin elastomer membrane, which can distribute the applied strain in the elastomer membrane and thus lead to a high elasticity even with the high loading of the nanomaterials. Furthermore, the structure allows cold welding and bilayer stacking, resulting in high conductivity. These properties are preserved even after high-resolution patterning by using photolithography. A multifunctional epidermal sensor array can be fabricated with the patterned nanomembranes.

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Surface modification of polyimides (PIs) using electrospinning would significantly improve the performance of TENGs because of the larger surface area of the electrospun friction layer. However, PIs generally have high solvent resistance, so it is complicated to convert them into nanofibers using electrospinning process. This study aims to fabricate PI nanofibers via simple, one-step electrospinning and utilize them as a friction layer of TENGs for better performance. PI nanofibers were directly electrospun from PI ink made of polyimide powder without any additional process. The effect of PI concentration on spinnability was investigated. Uniform and continuous nanofibrous structures were successfully produced at concentrations of 15 wt% and 20 wt%. Electrospun PI nanofibers were then utilized as a friction layer for TENGs. A TENG with 20 wt% produced an open circuit voltage of 753 V and a short circuit current of 10.79 μA and showed a power density of 2.61 W m −2 at a 100 MΩ load resistance. During tapping experiment of 10,000 cycles, the TENG could stably harvest electrical energy. The harvested energy from the proposed TENG is sufficient to illuminate more than 55 LEDs and drive small electronic devices, and the TENGs exhibit excellent performance as a wearable energy harvester. The rapid development of flexible electronics has promoted the wide application of various low power consumption electronic devices. Thus, an effective power source of these devices has gained increasing attention. Nanogenerators are good candidates due to their ability to harvest electrical energy sustainably from environmental sources 1-7. Among various types of nanogenerators such as triboelectric, pyroelectric, thermoelectric, and piezoelectric nanogenerators, triboelectric nanogenerators (TENGs) have gained enormous attention over past few years owing to their simple configuration, low weight, and cost-effective fabrication process. TENG's electrical performance is usually assessed by power density (W m −2), including voltage and current. TENG's power density is relatively small compared to other types of nanogenerators because the current generated by TENGs is insufficient. In order to enhance the performance of TENGs, various approaches have been conducted. Selecting materials of the friction layers according to the triboelectric series is an easy, reliable, and straightforward way. The farther two materials on the triboelectric series table, the higher the amount of charges generated. Many synthetic polymers have the nature of being negatively charged while nylon, cotton, and aluminum are generally used as positive friction layers. Polyimide (PI) has been widely used as a negative friction layer for TENGs due to its highly negatively charged nature 8-11. In addition, PI exhibits excellent stability as a friction layer under repetitive external pressure or deformation due to its outstanding mechanical properties. Some researchers have tried to further improve the performance of TENGs by enlarging the surface area of the friction...

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