Femtosecond laser direct writing of highly conductive copper for bendable electrodes with excellent bendability

A bendable electrode is an essential component of flexible electronics. The resistance stability against deformation is highly desired for practice. In this work, a bendable Cu electrode is fabricated by femtosecond laser direct writing (FsLDW), involving photothermal reduction of Cu ions and deposition of Cu on polyethylene terephthalate (PET) substrate. A highly conductive Cu electrode with a sheet resistance of 0.56 Ω·sq⁻¹ is obtained, which is improved by at least one order of magnitude over previous works. It is worth noting that the sheet resistance of the Cu electrode almost remains unchanged after 6000 downward bending cycles at a bending angle of 30° and shows a slight increase after 10 adhesion tests, demonstrating excellent bending stability and adhesive strength. The porous morphology of the deposited Cu may relieve bending stress, resulting in high deformation resistance. The temperature field simulation confirms sufficient heat accumulation during FsLDW for Cu ion reduction and PET surface melting, allowing for Cu embedding on the PET surface and improving adhesion between the Cu electrode and the substrate.