Copper Nanoparticles for Printed Electronics: Routes Towards Achieving Oxidation Stability

Abstract

In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices. This paper provides a review on the synthesis of copper nanoparticles, mainly by wet chemistry routes, and their utilization in printed electronics.

Keywords: conductive inks; copper nanoparticles; printed electronics.

Figure 1

(a) Transmission electron microscope (TEM) image of a single copper NP with a thick graphene layer of 3 nm (left) and a corresponding schematic illustration (right); (b) Thermogravimetric analysis (TGA) confirms the thermal stability of these NPs up to 165 °C. Reprinted from reference [16], with permission from IOP Publishing LTD.

Figure 2

Resistivity of the Cu conductive film as a function of heat treatment temperature for various PVP MWs. The ink-jet printed Cu nanoparticulate films were heat-treated at various temperatures between 200 °C and 325 °C under vacuum. Reprinted from [40], Reproduced with permission of copyright Wiley-VCH Verlag GmbH and Co. KGaA.

Figure 3

XRD patterns of (a) uncoated Cu NPs; (b) Cu/SiO₂ NPs; (c) Cu/SiO₂ NPs one month after preparation. (●) Metallic Cu, (▲) Cu₂O. Reprinted from reference [44] with permission from Elsevier.

Figure 4

Schematic illustration of a single Cu NP synthesis and the formation of a silver shell by the transmetalation reaction. The surface copper atoms serve as reducing agents for the silver ions.

Figure 5

(a) TEM and (b) SEM images of the obtained copper-silver core-shell NPs; (c) TGA of the copper-silver core-shell NPs under air atmosphere.

Figure 6

A flexible RFID antenna printed using copper-silver core-shell ink on inkjet photo paper.