Optical constants of silver nanowire networks : theory and experiments

Silver nanowire (AgNW) networks are emerging as a leading class of Transparent Conducting Materials (TCMs), offering a unique combination of high optical transparency, excellent electrical conductivity, mechanical flexibility, and scalable, cost-effective production. These properties arise from the interplay between the percolative conductivity of the network and the transparency provided by gaps between nanowires. A deeper understanding of the optical behavior of AgNW networks, particularly through their refractive indices (n, k), is essential for optimizing their use in multilayer systems and advanced device designs. Additionally, the knowledge of the refractive indices not only reveals fundamental optical properties but also enables precise optical simulations of complex structures using the Transfer Matrix Method. This study combines Mie scattering theory and van de Hulst’s mixing model to theoretically determine the refractive indices of AgNW networks without relying on fitting parameters. For the first time, refractive indices across the visible and near-infrared spectrum are calculated and validated against experimental results. Transmittance spectra, derived from numerical solutions of Fresnel’s equations, show strong agreement with measurements, particularly for nanowires with larger diameters and at shorter wavelengths, with a relative error below 10% at λ=550 nm. Crucially, the findings of the present research also highlight for the first time the predominantly metallic optical behavior of AgNW networks. By providing a robust model for the optical properties of AgNW networks, this work enhances their potential for integration into multilayer systems and cutting-edge applications, including energy-efficient smart windows, displays, and sensors. Moreover, it contributes to a deeper theoretical understanding of the fundamental optical properties of silver nanowire networks.