Silver nanowire networks as transparent electrodes

Transparent electrodes (TEs) are key components of many devices such as solar cells, transparent heaters or touch screens. Indium tin oxide (ITO) has been the most implemented TEs within these devices. However, ITO thin films do not fulfil all the requirements of the next generation of flexible optoelectronics because of its indium scarcity and brittleness. In that context, silver nanowire (AgNW) networks appear as a relevant alternative to ITO thin films. However, their efficient integration for the next generation of flexible TEs is mainly compromised by their nanowire-nanowire junction resistance and, their morphological instability specifically when submitted to stress (i.e. thermal, electrical, humidity).
The main goal of this thesis work is to contribute to a better understanding of both properties and limitations of AgNW networks.

First, conventional thermal annealing and capillary-force-induced cold-welding treatments are compared regarding the optimization of network resistance. Moreover, cold-welding treatment can be performed at a temperature of 100 °C. Both post-deposition treatments exhibit similar efficiency for optimizing electrical resistance, at both the macroscale and nanoscale.

Then, the stability of these networks has been successfully enhanced by protecting them with a thin amorphous tin oxide layer deposited by Atmospheric Pressure Spatial Atomic Layer Deposition, at 200 °C. A physical model is introduced describing the in situ reversible behaviour of AgNW networks when subjected to electrical stress. This simple model enables us to predict the associated Joule heating temperature for any applied voltage and initial network resistance.

In addition, an in-depth investigation of the evolution of both in situ structural and electrical properties of AgNW networks during thermal stress have been carried out thanks to simultaneous in situ measurements of X-ray diffraction and electrical resistance. Finally, the integration of AgNW networks as infrared low-emissivity coating is explored.
We clearly believe that this thesis work significantly contributes to maturing AgNW network science and technology for industrial requirements.

Thesis available on: https://cnrs.hal.science/LGP2/tel-04956979v1