Effect of anisotropy and length dispersity on electrical and optical properties ofnanowire network based transparent electrodes: a computational study

Abstract We have studied the impact of nanowire alignment and measurement direction at the percolation
threshold on the effective resistance (R) of two-dimensional (2D) films. This helps us to analyze the
effect of anisotropy on the conductivity and transmittance of the nanowire-based network characterized by the disorder parameter (s). These optoelectronic properties are determined for systems
with monodisperse as well as bimodal distribution of length. The 2D systems that are simulated using our computational approach are assumed to be transparent and conductive in which percolative transport is the primary conduction mechanism.
We obtain our results numerically using a computational and geometrical approach, i.e., a Discrete
(grid) method, advantageous in algorithm speed. For a particular disorder parameter s,
the conductivity and transmittance increase as the length fraction increases for the bimodal
distribution of the length of nanowires in networks. We have observed the maximum conductivity
when the nanowires are highly aligned along the measurement direction of percolation, in contrast
to the isotropic arrangement of nanowires. Significantly, alignment introduced in nanowires leads
to a higher percolation threshold which leads to a decrease in the transmittance of the network. We
show that the resistivity of the monodisperse network in the direction parallel (perpendicular) to the
alignment decreases (increases) with the disorder parameter and scales as s (s2). This scaling holds
true for the bimodal distribution of nanowires as well. For a particular length fraction, the electrical
anisotropy increases with s. The anisotropy is maximum for nearly aligned nanowires in a bimodal
network with the highest proportion of the longest wire considered. For the maximally aligned wires
and highest length fraction, we obtained an approximately 50% enhancement in the figure of merit,
denoted by ϕ. Hence, incorporating longer length wires and increasing the alignment in nanowire
networks increases the conductivity, anisotropy, and figure of merit.