UC Riverside

Transparent conductive electrodes are essential components in many optoelectronic devices such as solar cells, touch panels, and organic light-emitting diodes (OLEDs), all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO, which alone accounts for 93% of the entire market of the transparent conductor. However, there are several attributes of ITO that are undesirable. (1), ITO is a ceramic material that is brittle and prone to cracking. (2), The abundance of indium in the earth’s crust is low (0.05 ppm), and its cost is correspondingly high, approximately $700 kg-1. (3), ITO is produced by a slow vapor phase sputtering process, leading to high fabrication cost that dominates the cost of ITO (Indium costs only ~2% for 100 nm thick ITO). In addition, the rate of film throughput decreases with increasing film thickness, making thicker, high-conductivity ITO (~$26/m2 for 10 Ω sq-1) more expensive than thinner, low-conductivity ITO (~$5.5/m2 for 150 Ω sq-1), which is especially problematic for OLEDs and solar cells due to their need to carry higher currents, and thus use relatively expensive ITO with a low sheet resistance. In these devices, ITO can account for over 50% of the material cost.

This proposal will focus on developing scalable and cost-efficient methods to fabricate air-stable metal nanowire networks for transparent flexible electronics, targeting at a sheet resistance (Rs) of <10Ωsq-1 at 90% transmittance (T) and low cost at <$5/m2. This overall objective will be realized through two thrusts: (1), developing air-stable, highly-oriented epitaxial Ag@Au core-shell nanowire networks, aiming for large-scale roll-to-roll solution-phase fabrication of high-performance transparent conducting films for flexible optoelectronics; (2), developing air-stable super-stretchable Cu@rGO core-shell nanowire networks, aiming at cost-efficient foldable and wearable electronics.