Scalable Approaches to Copper Nanocrystal Synthesis under Ambient Conditions for Printed Electronics

We demonstrate the synthesis of copper nanocolloids by the thermal decomposition of copper formate in oleylamine under ambient conditions. By progressively increasing the loading of copper formate in the reaction mixture and imposing sufficiently high conversion rates, we demonstrate the formation of nanocrystals that are more than 97% pure copper without using an inert atmosphere. We attribute this result to the excess of copper formate relative to initially dissolved oxygen, and to the suppression of oxygen influx in the reactor. By adjusting the precursor and ligand concentrations, we obtain copper nanocrystals with sizes ranging from 10 to 200 nm. In view of applications, we show that the reaction can be upscaled to a 1 L reaction volume to produce over 50 g of copper nanocrystals. Moreover, we formulate a conductive ink based on the copper nanocolloids obtained here with which we printed copper films exhibiting a resistivity of 23 μΩ cm after thermal sintering under N2. We conclude that the approach presented here constitutes a next step toward the cost-effective production of metallic copper nanocrystals for printed electronics.