Conductive copper complex ink with self-reduction mechanism for flexible substrates

Flexible electronics have attracted significant attention because of their wide application in the fields of thin-film solar cells, biomedical devices, antennas, soft robotics and in general, Internet of things (IoT) applications. One approach to form electrical circuits is by direct printing of conductive ink, mainly based on silver dispersions. However, the high cost of silver poses a barrier to the fabrication of cost-effective devices. The best alternative to silver is copper, which is about a hundred times cheaper and only 5% less conductive. However, copper tends to undergo oxidation at ambient conditions and therefore loses its metallic conductivity. Therefore, there is an unmet need for copper inks that are stable to oxidation and can be processed at low temperatures, which are suitable for common plastics.

To overcome these challenges, here we describe the formation and utilization of a metal ink based on soluble copper complexes which are thermodynamically stable. This ink can undergo decomposition and self-reduction to yield copper nanoparticles, either by post-printing heating (below 180°C), or by plasma treatment at temperatures below 70°C. The later induces self-reduction of the ink, regardless of the decomposition temperature of the complex, and therefore opens new opportunities in utilization with a wide variety of plastic substrates.