Welding Mechanisms in Silver Nanowires under Femtosecond Laser Irradiation for Reduced Sheet Resistance Electrode Fabrication

Silver nanowires (AgNWs) have been widely used in flexible transparent electrodes. Femtosecond laser postprocessing is used to reduce the sheet resistance of AgNW electrodes. However, the melting behavior and welding patterns during femtosecond laser welding are not yet clear. In this article, the light field model, electric field model, and temperature field model of AgNW networks under the action of a femtosecond laser are constructed based on finite element software. By changing the energy density and polarization conditions of the femtosecond laser, the electric fields and power density distribution excited by single and multiple AgNWs networks are simulated. The electron temperature field and lattice temperature field reveal the laws of AgNWs melting and welding under the action of a femtosecond laser: A single AgNW cannot achieve electric field enhancement; an increase in the number of AgNWs at the junctions can strengthen the local electric field enhancement effect. AgNWs aligned as parallel as possible to the laser polarization direction are more susceptible to melting. Altering the laser energy density can significantly change the melting behavior of the AgNW network. Whether the AgNW network will melt on a large scale depends on whether the laser can heat the AgNWs above the melting point at a polarization angle theta of 45 degrees. The time required for an AgNW network to undergo one temperature cycle is 1 ns, which is 1/1000th of the interval between femtosecond laser pulses. Each temperature cycle of the AgNW is an independent event that does not accumulate heat.