Eco‐Friendly and Particle‐Free Copper Ionic Aqueous Precursor for In Situ Low Temperature Photothermal Synthesizing and Patterning of Highly Conductive Copper Microstructures on Flexible Substrate

Abstract

Liquid precursor‐based laser‐induced reductive patterning techniques enable fast and economical fabrication of flexible electronics. Herein, an eco‐friendly and particle‐free copper ionic solution for laser‐induced reductive patterning of copper microlines on a low glass transition temperature and transparent flexible substrate is successfully developed. The solvent used is water and the reducing agent is l‐ascorbic acid. A continuous wave 640 nm laser is used as the heat source to initiate the reductive reaction and to deposit copper microlines on the substrate surface. The resistivity of the copper microlines fabricated with optimized laser parameters is remarkably low at 4.7 μΩ cm. To further improve the electrical conductivity and to enhance mechanical durability, the fabricated microlines are annealed using the same laser after the copper ionic liquid precursor is removed. The microstructures and mechanical robustness of the copper microlines, as well as the adhesion between the copper microlines and the substrate, are investigated by cyclic bending test, pull‐off test and scanning electron microscope analyses. Up to 39% reduction of electrical resistance and up to 77% enhancement of mechanical durability after a 1000 cycle bending test can be achieved by laser postprocessing.