Fractal Gold Nanoframework for Highly Stretchable Transparent Strain-Insensitive Conductors

Percolation networks of one-dimensional (1D) building blocks (e.g., metallic nanowires or carbon nanotubes) represent the mainstream strategy to fabricate stretchable conductors. One of the inherent limitations is the control over junction resistance between 1D building blocks in natural and strained states of conductors. Herein, we report highly stretchable transparent strain-insensitive conductors using fractal gold (F-Au) nanoframework based on a one-pot templateless wet chemistry synthesis method. The mono-layered F-Au nanoframework (similar to 20 nm in thickness) can be obtained from the one-pot synthesis without any purification steps involved and can be transferred directly to arbitrary substrates like polyethylene terephthalate, food-wrap, polydimethylsiloxane (PDMS), and ecoflex. The F-Au thin film with no capping agents leads to a highly conductive thin film without any post- treatment and can be stretched up to 110% strain without significantly losing conductivity yet with the optical transparency of 70% at 550 nm. Remarkably, the F-Au thin film shows the strain-insensitive behavior up to 20% stretching strain. This originates from the unique fractal nanomesh-like structure which can absorb external mechanical forces, thus maintaining electron pathways throughout the nanoframework. In addition, a semitransparent bilayered F-Au film on 100% prestrained PDMS could achieve to a high stretchability of 420% strain with negligible resistance changes under low-level strains.