Hierarchical copper nanostructures synthesized on microparticles for improved photothermal conversion in photonic sintering of copper-based printed electrodes†

Photonic sintering of Cu-particle-based printed patterns using intense pulsed light (IPL) is a promising route to the large-scale fabrication of printed electronics for commercial applications. Despite the significant advantages of photonic sintering, which include the process being ultrafast, extremely low-cost, and eco-friendly, realizing a high-conductivity Cu-printed electrode remains a major challenge. In particular, low light absorption caused by the low surface plasmon density of Cu particles is the origin of insufficient temperature increase even after IPL irradiation. In this study, hierarchical nanostructured (HN) Cu microparticles (Cu μPs) with improved light absorption ability and lower surface melting point were prepared for the fabrication of high-conductivity Cu electrodes by using IPL sintering. HN-Cu μPs of uniform size were synthesized using a wet chemical hydrothermal method, with Cu(II) nitrate trihydrate, ethylenediamine (EDA), and Cu μPs as the precursor, structure-directing agent, and template, respectively. The morphology of the hierarchical nanostructures could be readily tuned by varying the synthesis time and the amounts of the precursor and EDA. On the basis of ultraviolet-visible spectroscopy, X-ray diffraction, and temperature measurements, the enhanced light absorption in the visible wavelength range was ascribed to the increase in the surface plasmon density of the hierarchical Cu nanostructures. After photonic sintering, the HN-Cu μP-based printed patterns showed highly dense Cu morphologies, which resulted in an extremely low electrical resistivity of 16 μΩ cm for IPL with an energy density of 7 J cm^?2.