Electrical Mapping of Silver Nanowire Networks: A Versatile Tool for Imaging Network Homogeneity and Degradation Dynamics during Failure

Abstract

Electrical stability and homogeneity of silver nanowire (AgNW) networks are critical assets for increasing their robustness and reliability when integrated as transparent electrodes in devices. Our ability to distinguish defects, inhomogeneities, or inactive areas at the scale of the entire network is therefore a critical issue. We propose one-probe electrical mapping (1P-mapping) as a specific simple tool to study the electrical distribution in these discrete structures. 1P-mapping has allowed us to show that the tortuosity of the voltage equipotential lines of AgNW networks under bias decreases with increasing network density, leading to a better electrical homogeneity. The impact of the network fabrication technique on the electrical homogeneity of the resulting electrode has also been investigated. Then, by combining 1P-mapping with electrical resistance measurements and IR thermography, we propose a comprehensive analysis of the evolution of the electrical distribution in AgNW networks when subjected to increasing voltage stresses. We show that AgNW networks experience three distinctive stages: optimization, degradation, and breakdown. We also demonstrate that the failure dynamics of AgNW networks at high voltages occurs through a highly correlated and spatially localized mechanism. In particular the in situ formation of cracks could be clearly visualized. It consists of two steps: creation of a crack followed by propagation nearly parallel to the equipotential lines. Finally, we show that current can dynamically redistribute during failure, by following partially damaged secondary pathways through the crack.

Transparent Heaters: A Review

“…Another tool to investigate electrical homogeneity is the one‐probe electrical mapping, which draws up a cartography of voltage distribution. [ 93 ] In addition, terahertz spectroscopy has been used for noncontact measurement of the conductance of AgNW networks. [ 94 ]…”

“…[ 48,117 ] Generally, the relative humidity chosen is over 80%, and the temperature between 45 and 90 °C, which covers most of the harshest use conditions. [ 70,93,118–121 ] Study durations varies strongly, and usually depends on the anticipated stability of the TH and on the expected lifetime of its components. For example, stability studies for copper nanowire (CuNW)/NPs usually last minutes [ 120 ] or hours, [ 118,119 ] while for AgNW the duration of the study can be days [ 70 ] or months.…”

“…Reproduced with permission. [ 93 ] Copyright 2018, American Chemical Society. f) Optical microscopy image of a flexible transparent Au grid electrode with the following geometrical features: grid width: 4.5 µm; grid spacing: 200 µm; Au thickness: ≈90 nm.…”

“…The electrical resistance exhibits a drastic increase associated to the appearance and propagation of a crack, as revealed by the IR image in the inset (the width of the IR image corresponds to 25 mm). [ 93 ] As reported below (Section 4.5.3), the deposition of a thin oxide layer on top of MNW networks drastically enhances their stability or their adhesion. [ 47,48,170 ] These nanocomposites can lead to efficient and stable THs, [ 44,46,47,117,172 ] as discussed further in Section 4.5.…”

“…Furthermore, electrical instability is observed when the networks undergo electrical stress. [ 93,171 ] CuNW networks are interesting [ 30,31 ] since the price of Cu is much lower than Ag. However, Cu is much more prone to oxidation than Ag and thus the chemical stability of CuNWs is a more critical issue.…”