  Inkjet-printed wearable electronic textiles (e-textiles) are considered to be
very promising due to excellent processing and environmental benefits offered
by digital fabrication technique. Inkjet-printing of conductive metallic inks
such as silver (Ag) nanoparticles (NPs) are well-established and that of
graphene-based inks is of great interest due to multi-functional properties of
graphene-based materials. However, poor ink stability at higher graphene
concentration and the cost associated with the higher Ag loading in metal inks
have limited their wider use. Moreover, graphene-based e-textiles reported so
far are mainly based on graphene derivatives such as graphene oxide (GO) or
reduced graphene oxide (rGO), which suffers from poor electrical conductivity.
Here we report inkjet printing of highly conductive and cost-effective
graphene/Ag composite inks for wearable e-textiles applications. The composite
inks were formulated, characterised and inkjet-printed onto PEL paper first and
then sintered at 150 C for 1 hr. The sheet resistance of the printed patterns
is found to be in the range of ~0.08 - 4.74 ohm/sq depending on the number of
print layers and the graphene/Ag ratio in the formulation. The optimised
composite ink was then successfully printed onto surface pre-treated (by inkjet
printing) cotton fabrics in order to produce all-inkjet-printed highly
conductive and cost-effective electronic textiles.
