Integrating Simulations and Experiments To Predict Sheet Resistance and Optical Transmittance in Nanowire Films for Transparent Conductors

Abstract

Metal nanowire films are among the most promising alternatives for next-generation flexible, solution-processed transparent conductors. Breakthroughs in nanowire synthesis and processing have reported low sheet resistance (Rs ≤ 100 Ω/sq) and high optical transparency (%T > 90%). Comparing the merits of the various nanowires and fabrication methods is inexact, because Rs and %T depend on a variety of independent parameters including nanowire length, nanowire diameter, areal density of the nanowires and contact resistance between nanowires. In an effort to account for these fundamental parameters of nanowire thin films, this paper integrates simulations and experimental results to build a quantitatively predictive model. First, by fitting the results from simulations of quasi-2D rod networks to experimental data from well-defined nanowire films, we obtain an effective average contact resistance, which is indicative of the nanowire chemistry and processing methods. Second, this effective contact resistance is used to simulate how the sheet resistance depends on the aspect ratio (L/D) and areal density of monodisperse rods, as well as the effect of mixtures of short and long nanowires on the sheet resistance. Third, by combining our simulations of sheet resistance and an empirical diameter-dependent expression for the optical transmittance, we produced a fully calculated plot of optical transmittance versus sheet resistance. Our predictions for silver nanowires are validated by experimental results for silver nanowire films, where nanowires of L/D > 400 are required for high performance transparent conductors. In contrast to a widely used approach that employs a single percolative figure of merit, our method integrates simulation and experimental results to enable researchers to independently explore the importance of contact resistance between nanowires, as well as nanowire area fraction and arbitrary distributions in nanowire sizes. To become competitive, metal nanowire systems require a predictive tool to accelerate their design and adoption for specific applications.

Effective Electrode Length Enhances Electrical Activation of Nanowire Networks: Experiment and Simulation

“…Furthermore, we visualize these changes in the network, both experimentally using passive voltage contrast electron microscopy techniques, 20 and in simulations of nanowires as line segments connected in a two-dimensional plane by junctions that can either be capacitive before activation or resistive after activation. 9,19,[21][22][23][24] We compare devices of different electrode geometry: two flat electrodes, one serrated and one flat electrode, two serrated electrodes, and one pointed and one flat electrode. By extending our previously developed model of connectivity in these networks, 2 we can predict the effects of microstructuring electrodes on the activation voltage and sheet resistance of networks, confirmed here through experimental data.…”

From stretchable to reconfigurable inorganic electronics

“…Winey et al found that low sheet resistance (Rs ≤ 100 Ω/sq) correlates with high optical transparency (%T > 90%) [130] (Figure 6c).They conclude that achieving lower contact resistance reduces the sheet resistance with the same number of NWs [130] . Their study demonstrates that modulating junction resistance is central to adjusting the surface roughness, electrical properties and optical properties of composite electrodes.…”

“…Low sheet resistance and high optical transparency can be achieved for a higher length to diameter ratio. Reprinted with permission from [130] .…”

Nanomaterial-based stretchable and transparent electrodes

“…According to a previous report, the stretchable and transparent electrode can obtain lower sheet resistance in the same area fraction as the increase in the length of the nanowire [26,53]. A very long metal nanowire has a much higher aspect ratio compared to the conventional metal nanowires, and can reduce the number of junction points in the current path by decreasing the percolation threshold, which are the disadvantages of short metal nanowires.…”