Relationship between wire orientation and optical and electrical anisotropy in silver nanowire/polymer composite films

Abstract

Silver nanowire (AgNW)/polymer composite films fabricated by roll-to-roll slot die-coating exhibit optical and electrical anisotropy. To evaluate the dependence of the film’s optical and electrical properties on the AgNW orientation, we quantify their polarized optical extinction and sheet resistance. Applying image analysis tools to microscope images, we show structural anisotropy due to a slightly preferential AgNW orientation. Optical anisotropy due to longitudinal- and transverse-mode surface plasmons resonances is predominantly observed in the lengthwise and crosswise direction of the composite films, respectively. Electrical anisotropy also depends on the measurement direction: sheet resistance is small in the lengthwise direction. These data indicate that the distribution of AgNWs is not fully isotropic, with their long axis preferentially oriented along the lengthwise direction of the composite films. Furthermore, although optical and electrical anisotropies are of comparable magnitude, both are smaller than the structural anisotropy. Optical anisotropy is still observed even when the amount of AgNWs increases, indicating that their orientation remains relatively constant. Electrical anisotropy is also preserved, indicating that junction resistance prevails in such composite films. The relationship between polarized transmittance and sheet resistance at a given measurement angle is consistent with a figure-of-merit equation often used for randomly-oriented AgNWs.