Flexible electronics: ‘liquid’ metal

A silver nanoparticle ink that can be applied without heat treatment could lead to the large-scale production of flexible electronics. Low-cost, lightweight, flexible electronics are now

used in a wide range of applications, from radiofrequency identification tags found in items such as public transit smart cards, to the latest flexible displays. As the plastic substrates

used for flexible electronics are not compatible with the high temperatures needed for forming metal circuits, researchers have turned to polymers and even carbon-based materials as the

conduction medium. Nothing yet, however, compares to the high conductivity provided by metal. Now, Qing-Hua Xu and co-workers from the National University of Singapore1 have prepared silver

films for flexible electronics at mild fabrication temperatures. “We wanted to design a process that could be used to produce conductive films on heat-sensitive plastics,” explains Xu.

Patterning metal-based electronic circuits using techniques such as inkjet printing could lead to the cheap, large-area mass-production of high-performance flexible electronics. However,

developing the printed nanoparticle inks used in the inkjet process into conductive circuit tracks requires high-temperature annealing, which can damage plastic substrates. To print metal

nanoparticles using an inkjet process, the particles must first be coated with an insulating organic stabilizer. Once deposited, however, this stabilizer prevents contact between the metal

particles and so blocks the conduction of electrons. To solve this problem, Xu and his co-workers stabilized their silver nanoparticles with poly(vinylpyrrolidone). This alternative

treatment still allows the nanoparticles to be printed, but it also lets the particles self-aggregate on the substrate simply by evaporating away the printing solvent under low heat. Fig. 1:

A flexible silver film produced by evaporation of a solvent from silver nanoparticle ink The researchers have used their technique to prepare silver films (pictured) for use as metal

electrodes in a solar cell, with performance comparable to that for conventional aluminum electrodes produced by vacuum evaporation. In the future, the method could be used to fabricate

metal contacts in other devices such as field-effect transistors and light-emitting diodes. “The stabilizer we use is ideal for producing silver nanoparticles,” explains Xu, “but if we use

it to produce gold or alloy nanoparticles, the resulting nanoparticle inks are not very stable. We are now investigating other stabilizers that could prove suitable for producing

nanoparticle inks of gold and other metal alloys.” REFERENCES * Polavarapu, L., Manga, K. K., Cao, H. D., Loh, K. P. Xu, Q.-H. Preparation of conductive silver films at mild temperatures for

printable organic electronics. _Chemistry of Materials_ 23, 3273–3276 (2011). Article  CAS  Google Scholar  Download references ADDITIONAL INFORMATION This research highlight has been

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CITE THIS ARTICLE Flexible electronics: ‘Liquid’ metal. _NPG Asia Mater_ (2011). https://doi.org/10.1038/asiamat.2011.159 Download citation * Published: 17 October 2011 * DOI:

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