Transparent conductors in large-area touch screens, thin-film solar cells, and organic light emitting diodes are currently made from a sputtered film of indium tin oxide (ITO) due to its high transmittance (95%T) at low sheet resistances (50 Ω sq -1). However, the high-conductivity ITO used in these applications is particularly costly due to the slow coating rates involved with sputtering. This high cost, as well as the brittleness of ITO, is promoting the adoption of low-cost, high-performance, and mechanically flexible nanowire-based transparent conducting films (Adv. Mater, 2014).
The Wiley lab was the first to show Cu nanowires could be used as an earth-abundant, solution-coatable alternative to indium tin oxide for transparent conducting films (Adv. Mater. 2010). We subsequently developed syntheses to create longer, thinner nanowires, and were the first lab to achieve Cu nanowire films with properties equivalent to that of ITO (Adv. Mater, 2011; Chem. Commun., 2014). The first synthesis of Ag nanowires that can be used to create films with properties that exceed that of ITO were reported by the Wiley lab (see Figure 1 and Nano Lett., 2015). We worked in collaboration with Karen Winey (Penn, Mat. Sci. & Eng.) to perform the first simulations of the sheet resistance of nanowire films as a function of the nanowire size, size-dispersity, and areal density (ACS Nano 2013). This work clearly demonstrated the importance of nanowire aspect ratio for achieving high transmittance at a low sheet resistance, motivating the field to focus on creating metal nanowires with high aspect ratios.
Figure 1. (A) SEM image of a transparent, conductive film consisting of Ag nanowires with a diameter of 20 nm and an aspect ratio of 2000. (B) Plot of specular transmittance (at λ = 550 nm) vs. sheet resistance for Ag and Cu nanowires produced by the Wiley lab, as well as carbon nanotubes (CNT), indium tin oxide (ITO), and Ag nanowires from a commercial source (Cambrios) for comparison. See the paper for more details
Related Publications:
Rathmell, A. R.; Bergin, S. M.; Hua, Y.-L.; Li, Z.-Y.; Wiley, B. J. The Growth Mechanism of Copper Nanowires and their Properties in Flexible, Transparent Conducting Films. Adv. Mater. 2010, 22, 3558–3563.
Rathmell, A.R., Wiley, B.J. The Synthesis and Coating of Long, Thin Copper Nanowires to make Flexible, Transparent Conducting Films on Plastic Substrates. Adv. Mater. 2011, 23, 4798-4803.
Bergin, S.M.; Rathmell, A.R.; Chen, Y.H; Charbonneau, P.; Li, Z.Y.; Wiley. B.J. The Effect of Nanowire Length and Width on the Properties of Transparent Conducting Films. Nanoscale 2012, 4, 1996-2004.
Mutiso, R. M.; Sherrott, M.C.; Rathmell, A.R.; Wiley, B. J.; Winey K. I. Integrating Simulations and Experiments to Predict Sheet Resistance and Optical Transmittance in Nanowire Films for Transparent Conductors. ACS Nano 2013, 7, 7654-7663.
Ye, S.; Rathmell, A.R.; Chen, Z.; Stewart, I.E.; Wiley, B.J. Metal Nanowire Networks: The Next Generation of Transparent Conductors. Adv. Mater., 2014, 26, 6670-6687.
Borchert, J.W; Stewart, I.E.; Ye, S.; Rathmell, A.R.; Wiley, B.J.; Winey, K.I. Effects of Length Dispersity and Film Fabrication on the Sheet Resistance of Copper Nanowire Transparent Conductors. Nanoscale, 2015, 7, 14496-14504.
Li, B.; Ye, S.; Stewart, I.E.; Wiley, B.J. Synthesis and Purification of Silver Nanowires To Make Conducting Films with a Transmittance of 99%. Nano Lett., 2015, 7, 6722–6726.