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Microscopy provides novel insights into the mechanical and electrical failure of flexible silver nanowire electrodes

The paper on “Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes” by Nadine Schrenker and colleagues has been recently published in ACS Nano.

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Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable thin-film optoelectronic devices. Applications range from organic solar cells and organic light-emitting diodes to touch panels and smart clothing. Various coating strategies and testing setups have been developed to further improve the stretchability of AgNWs and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure has been missing so far. Now an interdisciplinary researcher team of the FAU Erlangen led by IMN studied the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks by large-scale scanning electron microscopy straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, three fundamental deformation modes of NWs have been identified, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. By combining high resolution transmission electron microscopy experiments and molecular dynamics simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can pave the way to improve fabrication and design strategies for transparent NW network electrodes in the next generation of optoelectronic devices.

 

This study was made possible by financial support from the German Research Foundation (DFG) through the Research Training Group GRK 1896 “In situ microscopy with electrons, X-rays and scanning probes” and by the European Research Council (ERC) through the project “microKIc” (Grant Agreement No. 725483).