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

We have studied the impact of nanowire alignment and measurement direction at the percolation threshold on the effective resistance (<i>R</i>) 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 (<i>s</i>). These optoelectronic properties are determined for systems with monodisperse and bimodal length distribution (a combination of two fixed lengths of nanowires). The 2D systems 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 that is advantageous in algorithm speed. For a particular disorder parameter<i>s</i>, the conductivity and transmittance increase as the length fraction (<i>LF</i>) 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<i>s</i>(<i>s</i>²). This scaling holds true for the bimodal distribution of nanowires as well. For a particular<i>LF</i>, the electrical anisotropy increases with<i>s</i>. 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<i>LF</i>, we obtained an approximately 50%enhancement in the figure of merit, denoted by<i>φ</i>. Hence, incorporating longer-length wires and increasing the alignment in nanowire networks can increase the conductivity, anisotropy, and figure of merit which may benefit a vast range of applications.